FRAGMENTS OF SCIENCE:

A Series of Detached

ESSAYS, ADDRESSES, AND REVIEWS. 

BY

JOHN TYNDALL, F. R. S. 

Printed By Spottiswoode AND CO. 

NEW-STREET SQUARE

PARLIAMENT STREET

SIXTH EDITION, VOL. 1. 

LONDON: LONGMANS, GREEN, AND CO. 

1879. 

All rights reserved. 

PREFACE TO THE SIXTH EDITION. 

VOL. I. INORGANIC NATURE. 

I. THE CONSTITUTION OF NATURE. 

II. RADIATION. 

 1. Visible and Invisible Radiation. 

 2. Origin and Character of Radiation. The Aether. 

 3. The Atomic Theory in reference to the Aether. 

 4. Absorption of Radiant Heat by Gases. 

 5. Formation of Invisible Foci. 

 6. Visible and Invisible Rays of the Electric Light. 

 Figure 1 Spectrum of Electric Light. 

 7. Combustion by Invisible Rays. 

 8. Transmutation of Rays: Calorescence. 

 9. Deadness of the Optic Nerve to the Calorific Rays. 

 10. Persistence of Rays. 

 11. Absorption of Radiant Heat by Vapours and Odours. 

 12. Aqueous Vapour in relation to the Terrestrial Temperatures. 

 13. Liquids and their Vapours in relation to Radiant Heat. 

 14. Reciprocity of Radiation and Absorption. 

 15. Influence of Vibrating Period and Molecular Form. 

 Physical Analysis of the Human Breath. 

 16. Summary and Conclusion. 

III. ON RADIANT HEAT IN RELATION TO THE COLOUR ANDCHEMICAL CONSTITUTION OF BODIES. 

IV. NEW CHEMICAL REACTIONS PRODUCED BY LIGHT. 

 1. DECOMPOSITION BY LIGHT. 

 Physical Considerations. 

 Production of Sky-blue by the Decomposition of Nitrite of Amyl. 

 2. ON THE BLUE COLOUR OF THE SKY, & THE POLARISATION OF SKYLIGHT. 

 3. THE SKY OF THE ALPS. 

V. ON DUST AND DISEASE. 

 Experiments on Dusty Air. 

 The Germ Theory of Contagious Disease. 

 Parasitic Diseases of Silkworms. Pasteur's Researches. 

 Origin and Propagation of Contagious Matter. 

 The Germ Theory applied to Surgery. 

 The Luminous beam as a means of Research. 

 The Floating Matter of the Air. 

 Dr. Bennett's Experiments. 

 Application of Luminous beams to Water. 

 Chalk-water. Clark's Softening Process. 

 Cotton-wool Respirator. 

 Fireman's Respirator. 

 Helmholtz on Hay Fever. 

VI. VOYAGE TO ALGERIA TO OBSERVE THE ECLIPSE. 

VII. NIAGARA. 

VIII THE PARALLEL ROADS OF GLEN ROY. 

IX. ALPINE SCULPTURE. 

X. RECENT EXPERIMENTS ON FOG-SIGNALS. 

XI. ON THE STUDY OF PHYSICS. 

XII. ON CRYSTALLINE AND SLATY CLEAVAGE. 

XIII. ON PARAMAGNETIC AND DIAMAGNETIC FORCES. 

XIV. PHYSICAL BASIS OF SOLAR CHEMISTRY. 

XV. ELEMENTARY MAGNETISM. 

XVI. ON FORCE. 

XVII. CONTRIBUTIONS TO MOLECULAR PHYSICS. 

XVIII. LIFE, AND LETTERS OF FARADAY. 

XIX. THE COPLEY MEDALIST OF 1870. 

XX. THE COPLEY MEDALIST OF 1871. 

XXI. DEATH BY LIGHTNING. 

XXII. SCIENCE AND THE 'SPIRITS'. 

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VOL. II. 

I. REFLECTIONS ON PRAYER AND NATURAL LAW. 

II MIRACLES AND SPECIAL PROVIDENCES. 

 ADDITIONAL REMARKS ON MIRACLES. 

III ON PRAYER AS A FORM OF PHYSICAL ENERGY. 

IV. VITALITY. 

V. MATTER AND FORCE. 

VI. SCIENTIFIC MATERIALISM. 

VII. AN ADDRESS TO STUDENTS. 

VIII. SCIENTIFIC USE OF THE IMAGINATION. 

IX. THE BELFAST ADDRESS. 

X. APOLOGY FOR THE BELFAST ADDRESS. 

XI. THE REV. JAMES MARTINEAU AND THE BELFAST ADDRESS. 

XII. FERMENTATION, & ITS BEARINGS ON SURGERY & MEDICINE. 

XIII. SPONTANEOUS GENERATION. 

XIV. SCIENCE AND MAN. 

XV. PROFESSOR VIRCHOW AND EVOLUTION. 

XVI. THE ELECTRIC LIGHT. 

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PREFACE TO THE SIXTH EDITION. 

TO AVOID unwieldiness of bulk this edition of the 'Fragments' ispublished in two volumes, instead of, as heretofore, in one. 

The first volume deals almost exclusively with the laws and phenomenaof matter. The second trenches upon questions in which the phenomenaof matter interlace more or less with those of mind. 

New Essays have been added, while old ones have been revised, and inpart recast. To be clear, without being superficial, has been my aimthroughout. 

In neither volume have I aspired to sit in the seat of the scornful, but rather to treat the questions touched upon with a tolerance, ifnot a reverence, befitting their difficulty and weight. 

Holding, as I do, the nebular hypothesis, I am logically bound todeduce the life of the world from forces inherent in the nebula. Withthis view, which is set forth in the second volume, it seemed but fairto associate the reasons which cause me to conclude that every attemptmade in our day to generate life independently of antecedent life hasutterly broken down. 

A discourse on the Electric Light winds up the Second volume. Theincongruity of its position is to be referred to the lateness of itsdelivery. 

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VOL. I. INORGANIC NATURE. 

I. THE CONSTITUTION OF NATURE. 

[Footnote: 'Fortnightly Review, ' 1865, vol. Iii. P. 129. ]

WE cannot think of space as finite, for wherever in imagination weerect a boundary, we are compelled to think of space as existingbeyond it. Thus by the incessant dissolution of limits we arrive at amore or less adequate idea of the infinity of space. But, thoughcompelled to think of space as unbounded, there is no mental necessitycompelling us to think of it either as filled or empty; whether it isso or not must be decided by experiment and observation. That it isnot entirely void, the starry heavens declare; but the question stillremains, Are the stars themselves hung in vacuo? Are the vastregions which surround them, and across which their light ispropagated, absolutely empty? A century ago the answer to thisquestion, founded on the Newtonian theory, would have been, 'No, forparticles of light are incessantly shot through space. ' The reply ofmodern science is also negative, but on different grounds. It has thebest possible reasons for rejecting the idea of luminiferousparticles; but, in support of the conclusion that the celestial spacesare occupied by matter, it is able to offer proofs almost as cogent asthose which can be adduced of the existence of an atmosphere round theearth. Men's minds, indeed, rose to a conception of the celestial anduniversal atmosphere through the study of the terrestrial and localone. From the phenomena of sound, as displayed in the air, theyascended to the phenomena of light, as displayed in the _aether_; whichis the name given to the interstellar medium. 

The notion of this medium must not be considered as a vague orfanciful conception on the part of scientific men. Of its realitymost of them are as convinced as they are of the existence of the sunand moon. The luminiferous aether has definite mechanical properties. It is almost infinitely more attenuated than any known gas, but itsproperties are those of a solid rather than of a gas. It resemblesjelly rather than air. This was not the first conception of theaether, but it is that forced upon us by a more complete knowledge ofits phenomena. A body thus constituted may have its boundaries; but, although the aether may not be co-extensive with space, it must at allevents extend as far as the most distant visible stars. In fact it isthe vehicle of their light, and without it they could not be seen. This all-pervading substance takes up their molecular tremors, andconveys them with inconceivable rapidity to our organs of vision. Itis the transported shiver of bodies countless millions of milesdistant, which translates itself in human consciousness into thesplendour of the firmament at night. 

If the aether have a boundary, masses of ponderable matter might beconceived to exist beyond it, but they could emit no light. Beyondthe aether dark suns might burn; there, under proper conditions, combustion might be carried on; fuel might consume unseen, and metalsbe fused in invisible fires. A body, moreover, once heated there, would continue for ever heated; a sun or planet once molten, wouldcontinue for ever molten. For, the loss of heat being simply theabstraction of molecular motion by the aether, where this medium isabsent no cooling could occur. A sentient being on approaching aheated body in this region, would be conscious of no augmentation oftemperature. The gradations of warmth dependent on the laws ofradiation would not exist, and actual contact would first reveal theheat of an extra ethereal sun. 

Imagine a paddle-wheel placed in water and caused to rotate. From it, as a centre, waves would issue in all directions, and a wader as heapproached the place of disturbance would be met by stronger andstronger waves. This gradual augmentation of the impression made uponthe wader is exactly analogous to the augmentation of light when weapproach a luminous source. In the one case, however, the coarsecommon nerves of the body suffice; for the other we must have thefiner optic nerve. But suppose the water withdrawn; the action at adistance would then cease, and, as far as the sense of touch isconcerned, the wader would be first rendered conscious of the motionof the wheel by the blow of the paddles. The transference of motionfrom the paddles to the water is mechanically similar to thetransference of molecular motion from the heated body to the aether;and the propagation of waves through the liquid is mechanicallysimilar to the propagation of light and radiant heat. 

As far as our knowledge of space extends, we are to conceive it as theholder of the luminiferous aether, through which are interspersed, atenormous distances apart, the ponderous nuclei of the stars. Associated with the star that most concerns us we have a group of darkplanetary masses revolving at various distances round it, each againrotating on its own axis; and, finally, associated with some of theseplanets we have dark bodies of minor note--the moons. Whether theother fixed stars have similar planetary companions or not is to us amatter of pure conjecture, which may or may not enter into ourconception of the universe. But probably every thoughtful personbelieves, with regard to those distant suns, that there is, in space, something besides our system on which they shine. 

From this general view of the present condition of space, and of thebodies contained in it, we pass to the enquiry whether things were socreated at the beginning. Was space furnished at once, by the fiat ofOmnipotence, with these burning orbs? In presence of the revelationsof science this view is fading more and more. Behind the orbs, we nowdiscern the nebulae from which they have been condensed. And withoutgoing so far back as the nebulae, the man of science can prove thatout of common non-luminous matter this whole pomp of stars might havebeen evolved. 

The law of gravitation enunciated by Newton is, that every particle ofmatter in the universe attracts every other particle with a forcewhich diminishes as the square of the distance increases. Thus thesun and the earth mutually pull each other; thus the earth and themoon are kept in company, the force which holds every respective pairof masses together being the integrated force of their componentparts. Under the operation of this force a stone falls to the groundand is warmed by the shock; under its operation meteors plunge intoour atmosphere mid rise to incandescence. Showers of such meteorsdoubtless fall incessantly upon the sun. Acted on by this force, theearth, were it stopped in its orbit to-morrow, would rush towards, andfinally combine with, the sun. Heat would also be developed by thiscollision. Mayer first, and Helmholtz and Thomson afterwards, havecalculated its amount. It would equal that produced by the combustionof more than 5, 000 worlds of solid coal, all this heat being generatedat the instant of collision. In the attraction of gravity, therefore, acting upon non-luminous matter, we have a source of heat morepowerful than could be derived from any terrestrial combustion. Andwere the matter of the universe thrown in cold detached fragments intospace, and there abandoned to the mutual gravitation of its own parts, the collision of the fragments would in the end produce the fires ofthe stars. 

The action of gravity upon matter originally cold may, in fact, be theorigin of all light and heat, and also the proximate source of suchother powers as are generated by light and heat. But we have now toenquire what is the light and what is the heat thus produced? Thisquestion has already been answered in a general way. Both light andheat are modes of motion. Two planets clash and come to rest; theirmotion, considered as that of masses, is destroyed, but it is in greatpart continued as a motion of their ultimate particles. It is thislatter motion, taken up by the rather, and propagated through it witha velocity of 186, 000 miles a second, that comes to its as the lightand heat of suns and stars. The atoms of a hot body swing withinconceivable rapidity--billions of times in a second--but this powerof vibration necessarily implies the operation of forces between theatoms themselves. It reveals to us that while they are held togetherby one force, they are kept asunder by another, their position at anymoment depending on the equilibrium of attraction and repulsion. Theatoms behave as if connected by elastic springs, which oppose at thesame time their approach and their retreat, but which tolerate thevibration called heat. The molecular vibration once set up isinstantly shared with the aether, and diffused by it throughout space. 

We on the earth's surface live night and day in the midst of aetherealcommotion. The medium is never still. The cloud canopy above us maybe thick enough to shut out the light of the stars; but this canopy isitself a warm body, which radiates its thermal motion through theaether. The earth also is warm, and sends its heat-pulses incessantlyforth. It is the waste of its molecular motion in space that chillsthe earth upon a clear night; it is the return of thermal motion fromthe clouds which prevents the earth's temperature, on a cloudy night, from falling so low. To the conception of space being filled, we musttherefore add the conception of its being in a state of incessanttremor. 

The sources of this vibration are the ponderable masses of theuniverse. Let us take a sample of these and examine it in detail. When we look to our planet, we find it to be an aggregate of solids, liquids, and gases. Subjected to a sufficiently low temperature, thetwo last, would also assume the solid form. When we look at any oneof these, we generally find it composed of still more elementaryparts. We learn, for example, that the water of our rivers is formedby the union, in definite proportions, of two gases, oxygen andhydrogen. We know how to bring these constituents together, so as toform water: we also know how to analyse the water, and recover from itits two constituents. So, likewise, as regards the solid portions ofthe earth. Our chalk hills, for example, are formed by a combinationof carbon, oxygen, and calcium. These are the so-called elements theunion of which, in definite proportions, has resulted in the formationof chalk. The flints within the chalk we know to be a compound ofoxygen and silicium, called silica; and our ordinary clay is, for themost part, formed by the union of silicium, oxygen, and the well-knownlight metal, aluminium. By far the greater portion of the earth'scrust is compounded of the elementary substances mentioned in thesefew lines. 

The principle of gravitation has been already described as anattraction which every particle of matter, however small, exerts onevery other particle. With gravity there is no selection; noparticular atoms choose, by preference, other particular atoms asobjects of attraction; the attraction of gravitation is proportionalsimply to the quantity of the attracting matter, regardless of itsquality. But in the molecular world which we have now entered mattersare otherwise arranged. Here we have atoms between which a strongattraction is exercised, and also atoms between which a weakattraction is exercised. One atom can jostle another out of its placein virtue of a superior force of attraction. But, though the amountof force exerted varies thus from atom to atom, it is still anattraction of the same mechanical quality, if I may use the term, asthat of gravity itself. Its intensity might be measured in the sameway, namely by the amount of motion which it can generate in a certaintime. Thus the attraction of gravity at the earth's surface isexpressed by the number 32; because, when acting freely on a body fora second of time, gravity imparts to the body a velocity of thirty-twofeet a second. In like manner the mutual attraction of oxygen andhydrogen might be measured by the velocity imparted to the atoms intheir rushing together. Of course such a unit of time as a second isnot here to be thought of, the whole interval required by the atoms tocross the minute spaces which separate them amounting only to aninconceivably small fraction of a second. 

It has been stated that when a body falls to the earth it is warmed bythe shock. Here, to use the terminology of Mayer, we have a_mechanical_ combination of the earth and the body. Let us suffer thefalling body and the earth to dwindle in imagination to the size ofatoms, and for the attraction of gravity let us substitute that ofchemical affinity; we have then what is called a chemical combination. The effect of the union in this case also is the development of heat, and from the amount of heat generated we can infer the intensity ofthe atomic pull. Measured by ordinary mechanical standards, this isenormous. Mix eight pounds of oxygen with one of hydrogen, and pass aspark through the mixture; the gases instantly combine, their atomsrushing over the little distances which separate them. Take a weightof 47, 000 pounds to an elevation of 1, 000 feet above the earth'ssurface, and let it fall; the energy with which it will strike theearth will not exceed that of the eight pounds of oxygen atoms, asthey dash against one pound of hydrogen atoms to form water. 

It is sometimes stated that gravity is distinguished from all otherforces by the fact of its resisting conversion into other forms offorce. Chemical affinity, it is said, can be converted into heat andlight, and these again into magnetism and electricity: but gravityrefuses to be so converted; being a force maintaining itself under allcircumstances, and not capable of disappearing to give place toanother. The statement arises from vagueness of thought. If by it bemeant that a particle of matter can never be deprived of its weight, the assertion is correct; but the law which affirms the convertibilityof natural forces was never intended, in the minds of those whounderstood it, to affirm that such a conversion as that here impliedoccurs in any case whatever. As regards convertibility into heat, gravity and chemical affinity stand on precisely the same footing. The attraction in the one case is as indestructible as in the other. Nobody affirms that when a stone rests upon the surface of the earth, the mutual attraction of the earth and stone is abolished; nobodymeans to affirm that the mutual attraction of oxygen for hydrogenceases, after the atoms have combined to form water. What is meant, in the case of chemical affinity, is, that the pull of that affinity, acting through a certain space, imparts a motion of translation of theone atom towards the other. This motion is not heat, nor is the forcethat produces it heat. But when the atoms strike and recoil, themotion of translation is converted into a motion of vibration, whichis heat. The vibration, however, so far from causing the extinctionof the original attraction, is in part carried on by that attraction. The atoms recoil, in virtue of the elastic force which opposes actualcontact, and in the recoil they are driven too far back. The originalattraction then triumphs over the force of recoil, and urges the atomsonce more together. Thus, like a pendulum, they oscillate, untiltheir motion is imparted to the surrounding aether; or, in otherwords, until their heat becomes radiant heat. 

In this sense, and in this sense only, is chemical affinity convertedinto heat. There is, first of all, the attraction between the atoms;there is, secondly, space between them. Across this space theattraction urges them. They collide, they recoil, they oscillate. There is here a change in the form of the motion, but there is no realloss. It is so with the attraction of gravity. To produce motion bygravity space must also intervene between the attracting bodies. Whenthey strike together motion is apparently destroyed, but in realitythere is no destruction. Their atoms are suddenly urged together bythe shock; by their own perfect elasticity these atoms recoil; andthus is set up the molecular oscillation which, when communicated tothe proper nerves, announces itself as heat. 

It was formerly universally supposed that by the collision ofunelastic bodies force was destroyed. Men saw, for example, that whentwo spheres of clay, painter's putty, or lead for example, were urgedtogether, the motion possessed by the masses, prior to impact, wasmore or less annihilated. They believed in an absolute destruction ofthe force of impact. Until recent times, indeed, no difficulty wasexperienced in believing this, whereas, at present, the ideas of forceand its destruction refuse to be united in most philosophic minds. Inthe collision of elastic bodies, on the contrary, it was observed thatthe motion with which they clashed together was in great part restoredby the resiliency of the masses, the more perfect the elasticity themore complete being the restitution. This led to the idea ofperfectly elastic bodies--bodies competent to restore by their recoilthe whole of the motion which they possessed before impact--and thisagain to the idea of the _conservation_ of force, as opposed to thatdestruction of force which was supposed to occur when unelastic bodiesmet in collision. 

We now know that the principle of conservation holds equally good withelastic and unelastic bodies. Perfectly elastic bodies would developno heat on collision. They would retain their motion afterwards, though its direction might be changed; and it is only when sensiblemotion is wholly or partly destroyed, that heat is generated. Thisalways occurs in unelastic collision, the heat developed being theexact equivalent of the sensible motion extinguished. This heatvirtually declares that the property of elasticity, denied to themasses, exists among their atoms; by the recoil and oscillation ofwhich the principle of conservation is vindicated. 

But ambiguity in the use of the term 'force' makes itself more andmore felt as we proceed. We have called the attraction of gravity aforce, without any reference to motion. A body resting on a shelf isas much pulled by gravity as when, after having been pushed off theshelf, it falls towards the earth. We applied the term force also tothat molecular attraction which we called chemical affinity. When, however, we spoke of the conservation of force, in the case of elasticcollision, we meant neither a pull nor a push, which, as justindicated, might be exerted upon inert matter, but we meant forceinvested in motion--the _vis viva_, as it is called, of the collidingmasses. 

Force in this form has a definite mechanical measure, in the amount ofwork that it can perform. The simplest form of work is the raising ofa weight. A man walking up-hill, or up-stairs, with a pound weight inhis hand, to an elevation say of sixteen feet, performs a certainamount of work, over and above the lifting of his own body. If hecarries the pound to a height of thirty-two feet, he does twice thework; if to a height of forty-eight feet, he does three times thework; if to sixty-four feet, he does four times the work, and so on. If, moreover, he carries up two pounds instead of one, other thingsbeing equal, he does twice the work; if three, four, or five pounds, he does three, four, or five times the work. In fact, it is plainthat the work performed depends on two factors, the weight raised andthe height to which it is raised. It is expressed by the product ofthese two factors. 

But a body may be caused to reach a certain elevation in opposition tothe force of gravity, without being actually carried up. If a hodman, for example, wished to land a brick at an elevation of sixteen feetabove the place where he stood, he would probably pitch it up to thebricklayer. He would thus impart, by a sudden effort, a velocity tothe brick sufficient to raise it to the required height; the workaccomplished by that effort being precisely the same as if he hadslowly carried up the brick. The initial velocity to be imparted, inthis case, is well known. To reach a height of sixteen feet, thebrick must quit the man's hand with a velocity of thirty-two feet asecond. It is needless to say, that a body starting with anyvelocity, would, if wholly unopposed or unaided, continue to move forever with the same velocity. But when, as in the case before us, thebody is thrown upwards, it moves in opposition to gravity, whichincessantly retards its motion, and finally brings it to rest at anelevation of sixteen feet. If not here caught by the bricklayer, itwould return to the hodman with an accelerated motion, and reach hishand with the precise velocity it possessed on quitting it. 

An important relation between velocity and work is here to be pointedout. Supposing the hodman competent to impart to the brick, atstarting, a velocity of sixty-four feet a second, or twice its formervelocity, would the amount of work performed be twice what it was inthe first instance? No; it would be four times that quantity; for abody starting with twice the velocity of another, will rise to fourtimes the height. In like manner, a three-fold velocity will give anine-fold elevation, a four-fold velocity will give a sixteen-foldelevation, and so on. The height attained, then, is not proportionalto the initial velocity, but to the square of the velocity. Asbefore, the work is also proportional to the weight elevated. Hencethe work which any moving mass whatever is competent to perform, invirtue of the motion which it at any moment possesses, is jointlyproportional to its weight and the square of its velocity. Here, then, we have a second measure of work-, in which we simply translatethe idea of height into its equivalent idea of motion. 

In mechanics, the product of the mass of a moving body into the squareof its velocity, expresses what is called the _vis viva_, or livingforce. It is also sometimes called the 'mechanical effect. ' If, forexample, a cannon pointed to the zenith urge a ball upwards with twicethe velocity imparted to a second ball, the former will rise to fourtimes the height attained by the latter. If directed against atarget, it will also do four times the execution. Hence theimportance of imparting a high velocity to projectiles in war. Havingthus cleared our way to a perfectly definite conception of the _visviva_ of moving masses, we are prepared for the announcement that theheat generated by the shock of a falling body against the earth isproportional to the _vis viva_ annihilated. The heat is proportional tothe square of the velocity. In the case, therefore, of twocannon-balls of equal weight, if one strike a target with twice thevelocity of the other, it will generate four times the heat, if withthree times the velocity, it will generate nine times the heat, and soon. 

Mr. Joule has shown that a pound weight falling from a height of 772feet, or 772 pounds falling through one foot, will generate by itscollision with the earth an amount of heat sufficient to raise a poundof water one degree Fahrenheit in temperature. 772 "foot-pounds"constitute the mechanical equivalent of heat. Now, a body fallingfrom a height of 772 feet, has, upon striking the earth, a velocity of223 feet a second; and if this velocity were imparted to the body, byany other means, the quantity of heat generated by the stoppage of itsmotion would be that stated above. Six times that velocity, or 1, 338feet, would not be an inordinate one for a cannon-ball as it quits thegun. Hence, a cannon-ball moving with a velocity of 1, 338 feet asecond, would, by collision, generate an amount of heat competent toraise its own weight of water 36 degrees Fahrenheit in temperature. Ifcomposed of iron, and if all the heat generated were concentrated inthe ball itself, its temperature would be raised about 360 degreesFahrenheit; because one degree in the case of water is equivalent toabout ten degrees in the case of iron. In artillery practice, theheat generated is usually concentrated upon the front of the bolt, andon the portion of the target first struck. By this concentration theheat developed becomes sufficiently intense to raise the dust of themetal to incandescence, a flash of light often accompanying collisionwith the target. 

Let us now fix our attention for a moment on the gunpowder which urgesthe cannon-ball. This is composed of combustible matter, which ifburnt in the open air would yield a certain amount of heat. It willnot yield this amount if it perform the work of urging a ball. Theheat then generated by the gunpowder will fall short of that producedin the open air, by an amount equivalent to the _vis viva_ of the ball;and this exact amount is restored by the ball on its collision withthe target. In this perfect way are heat and mechanical motionconnected. 

Broadly enunciated, the principle of the conservation of forceasserts, that the quantity of force in the universe is as unalterableas the quantity of matter; that it is alike impossible to create forceand to annihilate it. But in what sense are we to understand thisassertion? It would be manifestly inapplicable to the force ofgravity as defined by Newton; for this is a force varying inversely asthe square of the distance; and to affirm the constancy of a varyingforce would be self-contradictory. Yet, when the question is properlyunderstood, gravity forms no exception to the law of conservation. Following the method pursued by Helmholtz, I will here attempt anelementary exposition of this law. Though destined in itsapplications to produce momentous changes in human thought, it is notdifficult of comprehension. 

For the sake of simplicity we will consider a particle of matter, which we may call F, to be perfectly fixed, and a second movableparticle, D, placed at a distance from F. We will assume that thesetwo particles attract each other according to the Newtonian law. At acertain distance, the attraction is of a certain definite amount, which might be determined by means of a spring balance. At half thisdistance the attraction would be augmented four times; at a third ofthe distance, nine times; at one-fourth of the distance, sixteentimes, and so on. In every case, the attraction might be measured bydetermining, with the spring balance, the amount of tension justsufficient to prevent D from moving towards F. Thus far we havenothing whatever to do with motion; we deal with statics, not withdynamics. We simply take into account the _distance_ of D from F, andthe _pull_ exerted by gravity at that distance. 

It is customary in mechanics to represent the magnitude of a force bya line of a certain length, a force of double magnitude beingrepresented by a line of double length, and so on. Placing then theparticle D at a distance from F, we can, in imagination, draw astraight line from D to F, and at D erect a perpendicular to thisline, which shall represent the amount of the attraction exerted on D. If D be at a very great distance from F, the attraction will be verysmall, and the perpendicular consequently very short. If the distancebe practically infinite, the attraction is practically _nil_. Let usnow suppose at every point in the line joining F and D a perpendicularto be erected, proportional in length to the attraction exerted atthat point; we thus obtain an infinite number of perpendiculars, ofgradually increasing length, as D approaches F. Uniting the ends ofall these perpendiculars, we obtain a curve, and between this curveand the straight line joining F and D we have an area containing allthe perpendiculars placed side by side. Each one of this infiniteseries of perpendiculars representing an attraction, or tension, as itis sometimes called, the area just referred to represents the sum ofthe tensions exerted upon the particle D, during its passage from itsfirst position to F. 

Up to the present point we have been dealing with tensions, not withmotion. Thus far _vis viva_ has been entirely foreign to ourcontemplation of D and F. Let us now suppose D placed at apractically infinite distance from F; here, as stated, the pull ofgravity would be infinitely small, and the perpendicular representingit would dwindle almost to a point. In this position the sum of thetensions capable of being exerted on D would be a maximum. Let D nowbegin to move in obedience to the infinitesimal attraction exertedupon it. Motion being once set up, the idea of _vis viva_ arises. Inmoving towards F the particle D consumes, as it were, the tensions. Let us fix our attention on D, at any point of the path over which itis moving. Between that point and F there is a quantity of unusedtensions; beyond that point the tensions have been all consumed, butwe have in their place an equivalent quantity of _vis viva_. After Dhas passed any point, the tension previously in store at that pointdisappears, but not without having added, during the infinitely smallduration of its action, a due amount of motion to that previouslypossessed by D. The nearer D approaches to F, the smaller is the sumof the tensions remaining, but the greater is the _vis viva_; thefarther D is from F, the greater is the sum of the unconsumedtensions, and the less is the living force. Now the principle ofconservation affirms _not_ the constancy of the value of the tensions ofgravity, nor yet the constancy of the _vis viva_, taken separately, butthe absolute constancy of the value of both taken together. At thebeginning the _vis viva_ was zero, and the tension area was a maximum;close to F the _vis viva_ is a maximum, while the tension area is zero. At every other point, the work-producing power of the particle Dconsists in part of _vis viva_, and in part of tensions. 

If gravity, instead of being attraction, were repulsion, then, withthe particles in contact, the sum of the tensions between D and Fwould be a maximum, and the _vis viva_ zero. If, in obedience to therepulsion, D moved away from F, _vis viva_ would be generated; and thefarther D retreated from F the greater would be its _vis viva_, and theless the amount of tension still available for producing motion. Taking repulsion as well as attraction into account, the principle ofthe conservation of force affirms that the mechanical value of the_tensions_ and _vires vivae_ of the material universe, so far as we knowit, is a constant quantity. The universe, in short, possesses twokinds of property which are mutually convertible. The diminution ofeither carries with it the enhancement of the other, the total valueof the property remaining unchanged. 

The considerations here applied to gravity apply equally to chemicalaffinity. Ina mixture of oxygen and hydrogen the atoms exist apart, but by the application of proper means they may be caused to rushtogether across that space that separates them. While this spaceexists, and as long as the atoms have not begun to move towards eachother, we have tensions and nothing else. During their motion towardseach other the tensions, as in the case of gravity, are converted into_vis viva_. After they clash we have still _vis viva_, but in anotherform. It _was_ translation, it _is_ vibration. It _was_ moleculartransfer, it _is_ heat. 

It is possible to reverse these processes, to unlock the combinedatoms and replace them in their first positions. But, to accomplishthis, as much heat would be required as was generated by their union. Such reversals occur daily and hourly in nature. By the solar waves, the oxygen of water is divorced from its hydrogen in the leaves ofplants. As molecular _vis viva_ the waves disappear, but in so doingthey re-endow the atoms of oxygen and hydrogen with tension. Theatoms are thus enabled to recombine, and when they do so they restorethe precise amount of heat consumed in their separation. The sameremarks apply to the compound of carbon and oxygen, called carbonicacid, which is exhaled from our lungs, produced by our fires, andfound sparingly diffused everywhere throughout the air. In the leavesof plants the sunbeams also wrench the atoms of carbonic acid asunder, and sacrifice themselves in the act; but when the plants are burnt, the amount of heat consumed in their production is restored. 

This, then, is the rhythmic play of Nature as regards her forces. Throughout all her regions she oscillates from tension to _vis viva_, from _vis viva_ to tension. We have the same play in the planetarysystem. The earth's orbit is an ellipse, one of the foci of which isoccupied by the sun. Imagine the earth at the most distant part ofthe orbit. Her motion, and consequently her _vis viva_, is then aminimum. The planet rounds the curve, and begins its approach to thesun. In front it has a store of tensions, which are graduallyconsumed, an equivalent amount of _vis viva_ being generated. Whennearest to the sun the motion, and consequently the _vis viva_, reach amaximum. But here the available tensions have been used up. Theearth rounds this portion of the curve and retreats from the sun. Tensions are now stored up, but _vis viva_ is lost, to be again restoredat the expense of the complementary force on the opposite side of thecurve. Thus beats the heart of the universe, but without increase ordiminution of its total stock of force. 

I have thus far tried to steer clear amid confusion, by fixing themind of the reader upon things rather than upon names. But good namesare essential; and here, as yet, we are not provided with such. Wehave had the force of gravity and living force--two utterly distinctthings. We have had pulls and tensions; and we might have had theforce of heat, the force of light, the force of magnetism, or theforce of electricity--all of which terms have been employed more orless loosely by writers on physics. This confusion is happily avoidedby the introduction of the term 'energy, ' which embraces both _tension_and _vis viva_. Energy is possessed by bodies already in motion; it isthen actual, and we agree to call it actual or dynamic energy. It isour old _vis viva_. On the other hand, energy is possible to bodies notin motion, but which, in virtue of attraction or repulsion, possess apower of motion which would realise itself if all hindrances wereremoved. Looking, for example, at gravity; a body on the earth'ssurface in a position from which it cannot fall to a lower onepossesses no energy. It has neither motion nor power of motion. Butthe same body suspended at a height above the earth has a power ofmotion, though it may not have exercised it. Energy is possible tosuch a body, and we agree to call this potential energy. It consistsof our old tensions. We, moreover, speak of the conservation ofenergy, instead of the conservation of force; and say that the sum ofthe potential and dynamic energies of the material universe is aconstant quantity. 

A body cast upwards consumes the actual energy of projection, and laysup potential energy. When it reaches its utmost height all its actualenergy is consumed, its potential energy being then a maximum. Whenit returns, there is a reconversion of the potential into the actual. A pendulum at the limit of its swing possesses potential energy; atthe lowest point of its arc its energy is all actual. A patch of snowresting on a mountain slope has potential energy; loosened, andshooting down as an avalanche, it possesses dynamic energy. Thepine-trees growing on the Alps have potential energy; but rushing downthe _Holzrinne_ of the woodcutters they possess actual energy. The sameis true of the mountains themselves. As long as the rocks whichcompose them can fall to a lower level, they possess potential energy, which is converted into actual when the frost ruptures their cohesionand hands them over to the action of gravity. The stone avalanches ofthe Matterhorn and Weisshorn are illustrations in point. The hammerof the great bell of Westminster, when raised before striking, possesses potential energy; when it falls, the energy becomes dynamic;and after the stroke, we have the rhythmic play of potential anddynamic in the vibrations of the bell. The same holds good for themolecular oscillations of a heated body. An atom is driven againstits neighbour, and recoils. The ultimate amplitude of the recoilbeing attained, the motion of the atom in that direction is checked, and for an instant its energy is all potential. It is then drawntowards its neighbour with accelerated speed; thus, by attraction, converting its potential into dynamic energy. Its motion in thisdirection is also finally checked, and again, for an instant, itsenergy is all potential. It once more retreats, converting, byrepulsion, its potential into dynamic energy, till the latter attainsa maximum, after which it is again changed into potential energy. Thus, what is true of the earth, as she swings to and fro in heryearly journey round the sun, is also true of her minutest atom. Wehave wheels within wheels, and rhythm within rhythm. 

When a body is heated, a change of molecular arrangement alwaysoccurs, and to produce this change heat is consumed. Hence, a portiononly of the heat communicated to the body remains as dynamic energy. Looking back on some of the statements made at the beginning of thisarticle, now that our knowledge is more extensive, we see thenecessity of qualifying them. When, for example, two bodies clash, heat is generated; but the heat, or molecular dynamic energy, developed at the moment of collision, is not the exact equivalent ofthe sensible dynamic energy destroyed. The true equivalent is thisheat, plus the potential energy conferred upon the molecules by theplacing of greater distances between them. This molecular potentialenergy is afterwards, on the cooling of the body, converted into heat. 

Wherever two atoms capable of uniting together by their mutualattractions exist separately, they form a store of potential energy. Thus our woods, forests, and coal-fields on the one hand, and ouratmospheric oxygen on the other, constitute a vast store of energy ofthis kind--vast, but far from infinite. We have, besides ourcoal-fields, metallic bodies more or less sparsely distributed throughthe earth's crust. These bodies can be oxydised; and hence they are, so far as they go, stores of energy. But the attractions of the greatmass of the earth's crust are already satisfied, and from them nofurther energy can possibly be obtained. Ages ago the elementaryconstituents of our rocks clashed together and produced the motion ofheat, which was taken up by the aether and carried away throughstellar space. It is lost for ever as far as we are concerned. Inthose ages the hot conflict of carbon, oxygen, and calcium producedthe chalk and limestone bills which are now cold; and from thiscarbon, oxygen, and calcium no further energy can be derived. So itis with almost all the other constituents of the earth's crust. Theytook their present form in obedience to molecular force; they turnedtheir potential energy into dynamic, and yielded it as radiant heat tothe universe, ages before man appeared upon this planet. For him aresidue of potential energy remains, vast, truly, in relation to thelife and wants of an individual, but exceedingly minute in comparisonwith the earth's primitive store. 

To sum up. The whole stock of energy or working-power in the worldconsists of attractions, repulsions, and motions. If the attractionsand repulsions be so circumstanced as to be able to produce motion, they are sources of working-power, but not otherwise. As stated amoment ago, the attraction exerted between the earth and a body at adistance from the earth's surface, is a source of working-power;because the body can be moved by the attraction, and in falling canperform work. When it rests at its lowest level it is not a source ofpower or energy, because it can fall no farther. But though it hasceased to be a source of _energy_, the attraction of gravity still actsas a _force_, which holds the earth and weight together. 

The same remarks apply to attracting atoms and molecules. As long asdistance separates them, they can move across it in obedience to theattraction; and the motion thus produced may, by proper appliances, becaused to perform mechanical work. When, for example, two atoms ofhydrogen unite with one of oxygen, to form water, the atoms are firstdrawn towards each other--they move, they clash, and then by virtue oftheir resiliency, they recoil and quiver. To this quivering motion wegive the name of heat. This atomic vibration is merely theredistribution of the motion produced by the chemical affinity; andthis is the only sense in which chemical affinity can be said to beconverted into heat. We must not imagine the chemical attractiondestroyed, or converted into anything else. For the atoms, whenmutually clasped to form a molecule of water, are held together by thevery attraction which first drew them towards each other. That whichhas really been expended is the _pull_ exerted through the space bywhich the distance between the atoms has been diminished. 

If this be understood, it will be at once seen that gravity, as beforeinsisted on, may, in this sense, be said to be convertible into heat;that it is in reality no more an outstanding and inconvertible agent, as it is sometimes stated to be, than is chemical affinity. By theexertion of a certain pull through a certain space, a body is causedto clash with a certain definite velocity against the earth. Heat isthereby developed, and this is the only sense in which gravity can besaid to be converted into heat. In no case is the _force_, whichproduces the motion annihilated or changed into anything else. Themutual attraction of the earth and weight exists when they are incontact, as when they were separate but the ability of that attractionto employ itself in the production of motion does not exist. 

The transformation, in this case, is easily followed by the mind'seye. First, the weight as a whole is set in motion by the attractionof gravity. This motion of the mass is arrested by collision with theearth, being broken up into molecular tremors, to which we give thename of heat. 

And when we reverse the process, and employ those tremors of heat toraise a weight--which is done through the intermediation of an elasticfluid in the steam-engine--a certain definite portion of the molecularmotion is consumed. In this sense, and in this sense only, can theheat be said to be converted into gravity; or, more correctly, intopotential energy of gravity. Here the destruction of the heat hascreated no new attraction; but the old attraction has conferred uponit a power of exerting a certain definite pull, between thestarting-point of the falling weight and the earth. 

When, therefore, writers on the conservation of energy speak oftensions being 'consumed' and 'generated, ' they do not mean therebythat old attractions have been annihilated, and new ones brought intoexistence, but that, in the one case, the power of the attraction toproduce motion has been diminished by the shortening of the distancebetween the attracting bodies, while, in the other case, the power ofproducing motion has been augmented by the increase of the distance. These remarks apply to all bodies, whether they be sensible masses ormolecules. 

Of the inner quality that enables matter to attract matter we knownothing; and the law of conservation makes no statement regarding thatquality. It takes the facts of attraction as they stand, and affirmsonly the constancy of working-power. That power may exist in the formof MOTION; or it may exist in the form of FORCE, _with distance to actthrough_. The former is dynamic energy, the latter is potentialenergy, the constancy of the sum of both being affirmed by the law ofconservation. The convertibility of natural forces consists solely intransformations of dynamic into potential, and of potential intodynamic energy. In no other sense has the convertibility of force anyscientific meaning. 

Grave errors have been entertained as to what is really intended to beconserved by the doctrine of conservation. This exposition I hopewill tend to remove them. 

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II. RADIATION. 

[Footnote: The Rede Lecture delivered in the Senate House before theUniversity of Cambridge, May 16, 1865. ]

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1. Visible and Invisible Radiation. 

BETWEEN the mind of man and the outer world are interposed the nervesof the human body, which translate, or enable the mind to translate, the impressions of that world into facts of consciousness and thought. 

Different nerves are suited to the perception of differentimpressions. We do not see with the ear, nor hear with the eye, norare we rendered sensible of sound by the nerves of the tongue. Out ofthe general assemblage of physical actions, each nerve, or group ofnerves, selects and responds to those for the perception of which itis specially organised. 

The optic nerve passes from the brain to the back of the eyeball andthere spreads out, to form the retina, a web of nerve filaments, onwhich the images of external objects are projected by the opticalportion of the eye. This nerve is limited to the apprehension of thephenomena of radiation, and, notwithstanding its marvelloussensibility to certain impressions of this class, it is singularlyobtuse to other impressions. 

Nor does the optic nerve embrace the entire range even of radiation. Some rays, when they reach it, are incompetent to evoke its power, while others never reach it at all, being absorbed by the humours ofthe eye. To all rays which, whether they reach the retina or not, fail to excite vision, we give the name of invisible or obscure rays. All non-luminous bodies emit such rays. There is no body in natureabsolutely cold, and every body not absolutely cold emits rays ofheat. But to render radiant heat fit to affect the optic nerve acertain temperature is necessary. A cool poker thrust into a fireremains dark for a time, but when its temperature has become equal tothat of the surrounding coals, it glows like them. In like manner, ifa current of electricity, of gradually increasing strength, be sentthrough a wire of the refractory metal platinum, the wire firstbecomes sensibly warm to the touch; for a time its heat augments, still however remaining obscure; at length we can no longer touch themetal with impunity; and at a certain definite temperature it emits afeeble red light. As the current augments in power the light augmentsin brilliancy, until finally the wire appears of a dazzling white. Thelight which it now emits is similar to that of the sun. 

By means of a prism Sir Isaac Newton unravelled the texture of solarlight, and by the same simple instrument we can investigate theluminous changes of our platinum wire. In passing through the prismall its rays (and they are infinite in variety) are bent or refractedfrom their straight course; and, as different rays are differentlyrefracted by the prism, we are by it enabled to separate one class ofrays from another. By such prismatic analysis Dr. Draper has shown, that when the platinum wire first begins to glow, the light emitted issensibly red. As the glow augments the red becomes more brilliant, but at the same time orange rays are added to the emission. Augmentingthe temperature still further, yellow rays appear beside the orange;after the yellow, green rays are emitted; and after the green come, insuccession, blue, indigo, and violet rays. To display all thesecolours at the same time the platinum wire must be _white-hot_: theimpression of whiteness being in fact produced by the simultaneousaction of all these colours on the optic nerve. 

In the experiment just described we began with a platinum wire at anordinary temperature, and gradually raised it to a white heat. At thebeginning, and even before the electric current had acted at all uponthe wire, it emitted invisible rays. For some time after the actionof the current had commenced, and even for a time after the wire hadbecome intolerable to the touch, its radiation was still invisible. The question now arises, What becomes of these invisible rays when thevisible ones make their appearance? It will be proved in the sequelthat they maintain themselves in the radiation; that a ray onceemitted continues to be emitted when the temperature is increased, andhence the emission from our platinum wire, even when it has attainedits maximum brilliancy, consists of a mixture of visible and invisiblerays. If, instead of the platinum wire, the earth itself were raisedto incandescence, the obscure radiation which it now emits wouldcontinue to be emitted. To reach incandescence the planet would haveto pass through all the stages of non-luminous radiation, and thefinal emission would embrace the rays of all these stages. There canhardly be a doubt that from the sun itself, rays proceed similar inkind to those which the dark earth pours nightly into space. In fact, the various kind of obscure rays emitted by all the planets of oursystem are included in the present radiation of the sun. 

The great pioneer in this domain of science was Sir William Herschel. Causing a beam of solar light to pass through a prism, he resolved itinto its coloured constituents; he formed what is technically calledthe solar spectrum. Exposing thermometers to the successive colourshe determined their heating power, and found it to augment from theviolet or most refracted end, to the red or least refracted end of thespectrum. But he did not stop here. Pushing his thermometers intothe dark space beyond the red he found that, though the light haddisappeared, the radiant heat falling on the instruments was moreintense than that at any visible part of the spectrum. In fact, SirWilliam Herschel showed, and his results have been verified by variousphilosophers since his time, that, besides its luminous rays, the sunpours forth a multitude of other rays, more powerfully calorific thanthe luminous ones, but entirely unsuited to the purposes of vision. 

At the less refrangible end of the solar spectrum, then, the range ofthe sun's radiation is not limited by that of the eye. The samestatement applies to the more refrangible end. Ritter discovered theextension of the spectrum into the invisible region beyond the violet;and, in recent times, this ultra-violet emission has had peculiarinterest conferred upon it by the admirable researches of ProfessorStokes. The complete spectrum of the sun consists, therefore, ofthree distinct parts: first, of ultra-red rays of high heating power, but unsuited to the purposes of vision; secondly, of luminous rayswhich display the succession of colours, red, orange, yellow, green, blue, indigo, violet; thirdly, of ultra-violet rays which, like theultra-red ones, are incompetent to excite vision, but which, unlikethe ultra-red rays, possess a very feeble heating power. Inconsequence, however, of their chemical energy these ultra-violet raysare of the utmost importance to the organic world. 

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2. Origin and Character of Radiation. The Aether. 

When we see a platinum wire raised gradually to a white heat, andemitting in succession all the colours of the spectrum, we are simplyconscious of a series of changes in the condition of our own eyes. Wedo not see the actions in which these successive colours originate, but the mind irresistibly infers that the appearance of the colourscorresponds to certain contemporaneous changes in the wire. What isthe nature of these changes? In virtue of what condition does thewire radiate at all? We must now look from the wire, as a whole, toits constituent atoms. Could we see those atoms, even before theelectric current has begun to act upon them, we should find them in astate of vibration. In this vibration, indeed, consists such warmthas the wire then possesses. Locke enunciated this idea with greatprecision, and it has been placed beyond the pale of doubt by theexcellent quantitative researches of Mr. Joule. 'Heat, ' says Locke, 'is a very brisk agitation of the insensible parts of the object, which produce in us that sensation from which we denominate the objecthot: so what in our sensations is _heat_ in the object is nothing but_motion_. ' When the electric current, still feeble, begins to passthrough the wire, its first act is to intensify the vibrations alreadyexisting, by causing the atoms to swing through wider ranges. Technically speaking, the _amplitudes_ of the oscillations areincreased. The current does this, however, without altering theperiods of the old vibrations, or the times in which they wereexecuted. But besides intensifying the old vibrations the currentgenerates new and more rapid ones, and when a certain definiterapidity has been attained, the wire begins to glow. The colour firstexhibited is red, which corresponds to the lowest rate of vibration ofwhich the eye is able to take cognisance. By augmenting the strengthof the electric current more rapid vibrations are introduced, andorange rays appear. A quicker rate of vibration produces yellow, astill quicker green; and by further augmenting the rapidity, we passthrough blue, indigo, and violet, to the extreme ultra-violet rays. 

Such are the changes recognised by the mind in the wire itself, asconcurrent with the visual changes taking place in the eye. But whatconnects the wire with this organ By what means does it send suchintelligence of its varying condition to the optic nerve? Heat beingas defined by Locke, 'a very brisk agitation of the insensible partsof an object, ' it is readily conceivable that on touching a heatedbody the agitation may communicate itself to the adjacent nerves, andannounce itself to them as light or heat. But the optic nerve doesnot touch the hot platinum, and hence the pertinence of the question, By what agency are the vibrations of the wire transmitted to the eye?

The answer to this question involves one of the most importantphysical conceptions that the mind of man has yet achieved: theconception of a medium filling space and fitted mechanically for thetransmission of the vibrations of light and heat, as air is fitted forthe transmission of sound. This medium is called the _luminiferousaether_. Every vibration of every atom of our platinum wire raises inthis aether a wave, which speeds through it at the rate of 186, 000miles a second. 

The aether suffers no rupture of continuity at the surface of the eye, the inter-molecular spaces of the various humours are filled with it;hence the waves generated by the glowing platinum can cross thesehumours and impinge on the optic nerve at the back of the eye. [Footnote: The action here described is analogous to the passage ofsound-waves through thick felt whose interstices are occupied by air. ]Thus the sensation of light reduces itself to the acceptance ofmotion. Up to this point we deal with pure mechanics; but thesubsequent translation of the shock of the aethereal waves intoconsciousness eludes mechanical science. As an oar dipping into theCam generates systems of waves, which, speeding from the centre ofdisturbance, finally stir the sedges on the river's bank, so do thevibrating atoms generate in the surrounding aether undulations, whichfinally stir the filaments of the retina. The motion thus imparted istransmitted with measurable, and not very great velocity to the brain, where, by a process which the science of mechanics does not even tendto unravel, the tremor of the nervous matter is converted into theconscious impression of light. 

Darkness might then be defined as aether at rest; light as aether inmotion. But in reality the aether is never at rest, for in theabsence of light-waves we have heat-waves always speeding through it. In the spaces of the universe both classes of undulations incessantlycommingle. Here the waves issuing from uncounted centres cross, coincide, oppose, and pass through each other, without confusion orultimate extinction. Every star is seen across the entanglement ofwave-motions produced by all other stars. It is the ceaseless thrillcaused by those distant orbs collectively in the aether, thatconstitutes what we call the 'temperature of space. ' As the air of aroom accommodates itself to the requirements of an orchestra, transmitting each vibration of every pipe and string, so does theinter-stellar aether accommodate itself to the requirements of lightand heat. Its waves mingle in space without disorder, each beingendowed with an individuality as indestructible as if it alone haddisturbed the universal repose. 

All vagueness with regard to the use of the terms 'radiation' and'absorption' will now disappear. Radiation is the communication ofvibratory motion to the aether; and when a body is said to be chilledby radiation, as for example the grass of a meadow on a starlightnight, the meaning is, that the molecules of the grass have lost aportion of their motion, by imparting it to the medium in which theyvibrate. On the other hand, the waves of aether may so strike againstthe molecules of a body exposed to their action as to yield up theirmotion to the latter; and in this transfer of the motion from theaether to the molecules consists the absorption of radiant heat. Allthe phenomena of heat are in this way reducible to interchanges ofmotion; and it is purely as the recipients or the donors of thismotion, that we ourselves become conscious of the action of heat andcold. 

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3. The Atomic Theory in reference to the Aether. 

The word 'atoms' has been more than once employed in this discourse. Chemists have taught us that all matter is reducible to certainelementary forms to which they give this name. These atoms areendowed with powers of mutual attraction, and under suitablecircumstances they coalesce to form compounds. Thus oxygen andhydrogen are elements when separate, or merely _mixed_, but they may bemade to _combine_ so as to form molecules, each consisting of two atomsof hydrogen and one of oxygen. In this condition they constitutewater. So also chlorine and sodium are elements, the former a pungentgas, the latter a soft metal; and they unite together to form chlorideof sodium or common salt. In the same way the element nitrogencombines with hydrogen, in the proportion of one atom of the former tothree of the latter, to form ammonia. Picturing in imagination theatoms of elementary bodies as little spheres, the molecules ofcompound bodies must be pictured as groups of such spheres. This isthe atomic theory as Dalton conceived it. Now if this theory have anyfoundation in fact, and if the theory of an aether pervading space, and constituting the vehicle of atomic motion, be founded in fact, itis surely of interest to examine whether the vibrations of elementarybodies are modified by the act of combination--whether as regardsradiation and absorption, or, in other words, whether as regards thecommunication of motion to the aether, and the acceptance of motionfrom it, the deportment of the uncombined atoms will be different fromthat of the combined. 

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4. Absorption of Radiant Heat by Gases. 

We have now to submit these considerations to the only test by whichthey can be tried, namely, that of experiment. An experiment is welldefined as a question put to Nature; but, to avoid the risk of askingamiss, we ought to purify the question from all adjuncts which do notnecessarily belong to it. Matter has been shown to be composed ofelementary constituents, by the compounding of which all its varietiesare produced. But, besides the chemical unions which they form, bothelementary and compound bodies can unite in another and less intimateway. Gases and vapours aggregate to liquids and solids, without anychange of their chemical nature. We do not yet know how thetransmission of radiant heat may be affected by the entanglement dueto cohesion; and, as our object now is to examine the influence ofchemical union alone, we shall render our experiments more pure byliberating the atoms and molecules entirely from the bonds ofcohesion, and employing them in the gaseous or vaporous form. 

Let us endeavour to obtain a perfectly clear mental image of theproblem now before us. Limiting in the first place our enquiries tothe phenomena of absorption, we have to picture a succession of wavesissuing from a radiant source and passing through a gas; some of themstriking against the gaseous molecules and yielding up their motion tothe latter; others gliding round the molecules, or passing through theintermolecular spaces without apparent hindrance. The problem beforeus is to determine whether such free molecules have any power whateverto stop the waves of heat; and if so, whether different moleculespossess this power in different degrees. 

In examining the problem let us fall back upon an actual piece ofwork, choosing as the source of our heat-waves a plate of copper, against the back of which a steady sheet of flame is permitted toplay. On emerging from the copper, the waves, in the first instance, pass through a space devoid of air, and then enter a hollow glasscylinder, three feet long and three inches wide. The two ends of thiscylinder are stopped by two plates of rock-salt, a solid substancewhich offers a scarcely sensible obstacle to the passage of thecalorific waves. After passing through the tube, the radiant heatfalls upon the anterior face of a thermo-electric pile, [Footnote: Inthe Appendix to the first chapter of 'Heat as a Mode of 'Motion, ' theconstruction of the thermo-electric pile is fully explained. ] whichinstantly converts the heat into an electric current. This currentconducted round a magnetic needle deflects it, and the magnitude ofthe deflection is a measure of the heat falling upon the pile. Thisfamous instrument, and not an ordinary thermometer, is what we shalluse in these enquiries, but we shall use it in a somewhat novel way. As long as the two opposite faces of the thermo-electric pile are keptat the same temperature, no matter how high that may be, there is nocurrent generated. The current is a consequence of a difference oftemperature between the two opposite faces of the pile. Hence, ifafter the anterior face has received the heat from our radiatingsource, a second source, which we may call the compensating source, bepermitted to radiate against the posterior face, this latter radiationwill tend to neutralise the former. When the neutralisation isperfect, the magnetic needle connected with the pile is no longerdeflected, but points to the zero of the graduated circle over whichit hangs. 

And now let us suppose the glass tube, through which the waves fromthe heated plate of copper are passing, to be exhausted by anair-pump, the two sources of heat acting at the same time on the twoopposite faces of the pile. When by means of an adjusting screen, perfectly equal quantities of heat are imparted to the two faces, theneedle points to zero. Let any gas be now permitted to enter theexhausted tube; if its molecules possess any power of intercepting thecalorific waves, the equilibrium previously existing will bedestroyed, the compensating source will triumph, and a deflection ofthe magnetic needle will be the immediate consequence. From thedeflections thus produced by different gases, we can readily deducethe relative amounts of wave-motion which their molecules intercept. 

In this way the substances mentioned in the following table wereexamined, a small portion only of each being admitted into the glasstube. The quantity admitted in each case was just sufficient todepress a column of mercury associated with the tube one inch: inother words, the gases were examined at a pressure of one-thirtieth ofan atmosphere. The numbers in the table express the relative amountsof wave-motion absorbed by the respective gases, the quantityintercepted by air being taken as unity. 

Radiation through Gases. 

Name of gas Relative absorption

Air 1

Oxygen 1

Nitrogen 1

Hydrogen 1

Carbonic oxide 750

Carbonic acid 972

Hydrochloric acid. 1, 005

Nitric oxide 1, 590

Nitrous oxide 1, 860

Sulphide of hydrogen 2, 100

Ammonia 5, 460

Olefiant gas 6, 030

Sulphurous acid 6, 480

Every gas in this table is perfectly transparent to light, that is tosay, all waves within the limits of the visible spectrum pass throughit without obstruction; but for the waves of slower period, emanatingfrom our heated plate of copper, enormous differences of absorptivepower are manifested. These differences illustrate in the mostunexpected manner the influence of chemical combination. Thus theelementary gases, oxygen, hydrogen, and nitrogen, and the mixtureatmospheric air, prove to be practical vacua to the rays of heat; forevery ray, or, more strictly speaking, for every unit of wave-motion, which any one of them intercepts, perfectly transparent ammoniaintercepts 5, 460 units, olefiant gas 6, 030 units, while sulphurousacid gas absorbs 6, 480 units. What, becomes of the wave-motion thusintercepted? It is applied to the heating of the absorbing gas. Through air, oxygen, hydrogen, and nitrogen, the waves of aether passwithout absorption, and these gases are not sensibly changed intemperature by the most powerful calorific rays. The position ofnitrous oxide in the foregoing table is worthy of particular notice. In this gas we have the same atoms in a state of chemical union, thatexist uncombined in the atmosphere; but the absorption of the compoundis 1, 800 times that of air. 

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5. Formation of Invisible Foci. 

This extraordinary deportment of the elementary gases naturallydirected attention to elementary bodies 'in other states ofaggregation. Some of Melloni's results now attained a newsignificance. This celebrated experimenter had found crystals ofsulphur to be highly pervious to radiant heat; he had also proved thatlamp-black, and black glass, (which owes its blackness to the elementcarbon) were to a considerable extent transparent to calorific rays oflow refrangibility. These facts, harmonising so strikingly with thedeportment of the simple gases, suggested further enquiry. Sulphurdissolved in bisulphide of carbon was found almost perfectlydiathermic. The dense and deeply-coloured element bromine wasexamined, and found competent to cut off the light of our mostbrilliant flames, while it transmitted the invisible calorific rayswith extreme freedom. Iodine, the companion element of bromine, wasnext thought of, but it was found impracticable to examine thesubstance in its usual solid condition. It however dissolves freelyin bisulphide of carbon. There is no chemical union between theliquid and the iodine; it is simply a case of solution, in which theuncombined atoms of the element can act upon the radiant heat. Whenpermitted to do so, it was found that a layer of dissolved iodine, sufficiently opaque to cut off the light of the midday sun, was almostabsolutely transparent to the invisible calorific rays. [Footnote:Professor Dewar has recently succeeded in producing a medium highlyopaque to light, and highly transparent to obscure heat, by fusingtogether sulphur and iodine. ]

By prismatic analysis Sir William Herschel separate the luminous fromthe non-luminous rays of the sun, and he also sought to render theobscure rays visible by concentration. Intercepting the luminousportion of his spectrum he brought, by a converging lens, theultra-red rays to a focus, but by this condensation he obtained nolight. The solution of iodine offers a means of filtering the solarbeam, or failing it, the beam of the electric lamp, which rendersattainable far more powerful foci of invisible rays than couldpossibly be obtained by the method of Sir William Herschel. For toform his spectrum he was obliged to operate upon solar light which hadpassed through a narrow slit or through a small aperture, the amountof the obscure heat being limited by this circumstance. But with ouropaque solution we may employ the entire surface of the largest lens, and having thus converged the rays, luminous and non-luminous, we canintercept the former by the iodine, and do what we please with thelatter. Experiments of this character, not only with the iodinesolution, but also with black glass and layers of lampblack, werepublicly performed at the Royal Institution in the early part of 1862, and the effects at the foci of invisible rays, then obtained, weresuch as had never been witnessed previously. 

In the experiments here referred to, glass lenses were employed toconcentrate the rays. But glass, though highly transparent to theluminous, is in a high degree opaque to the invisible, heat-rays ofthe electric lamp, and hence a large portion of those rays wasintercepted by the glass. The obvious remedy here is to employrock-salt lenses instead of glass ones, or to abandon the use oflenses wholly, and to concentrate the rays by a metallic mirror. Bothof these improvements have been introduced, and, as anticipated, theinvisible foci have been thereby rendered more intense. The mode ofoperating remains however the same, in principle, as that made knownin 1862. It was then found that an instant's exposure of the face ofthe thermoelectric pile to the focus of invisible rays, dashed theneedles of a coarse galvanometer violently aside. It is now foundthat on substituting for the face of the thermo-electric pile acombustible body, the invisible rays are competent to set that body onfire. 

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6. Visible and Invisible Rays of the Electric Light. 

We have next to examine what proportion the non-luminous rays of theelectric light bear to the luminous ones. This the opaque solution ofiodine enables us to do with an extremely close approximation to thetruth. 

The pure bisulphide of carbon, which is the solvent of the iodine, isperfectly transparent to the luminous, and almost perfectlytransparent to the dark, rays of the electric lamp. Supposing thetotal radiation of the lamp to pass through the transparentbisulphide, while through the solution of iodine only the dark raysare transmitted. If we determine, by means of a thermoelectric pile, the total radiation, and deduct from it the purely obscure, we obtainthe value of the purely luminous emission. Experiments, performed inthis way, prove that if all the visible rays of the electric lightwere converged to a focus of dazzling brilliancy, its heat would onlybe one-eighth of that produced at the unseen focus of the invisiblerays. 

Exposing his thermometers to the successive colours of the solarspectrum, Sir William Herschel determined the heating power of each, and also that of the region beyond the extreme red. Then drawing astraight line to represent the length of the spectrum, he erected, atvarious points, perpendiculars to represent the calorific intensityexisting at those points. Uniting the ends of all his perpendiculars, he obtained a curve which showed at a glance the manner in which theheat was distributed in the solar spectrum. Professor Müller ofFreiburg, with improved instruments, afterwards made similarexperiments, and constructed a more accurate diagram of the same kind. We have now to examine the distribution of heat in the spectrum of theelectric light; and for this purpose we shall employ a particular formof the thermo-electric pile, devised by Melloni. Its face is arectangle, which by means of movable side-pieces can be rendered asnarrow as desired. We can, for example, have the face of the pile thetenth, the hundredth, or even the thousandth of an inch in breadth. Bymeans of an endless screw, this linear thermo-electric pile may bemoved through the entire spectrum, from the violet to the red, theamount of heat falling upon the pile at every point of its march, being declared by a magnetic needle associated with the pile. 

When this instrument is brought up to the violet end of the spectrumof the electric light, the heat is found to be insensible. As thepile is gradually moved from the violet end towards the red, heat soonmanifests itself, augmenting as we approach the red. Of all thecolours of the visible spectrum the red possesses the highest heatingpower. On pushing the pile into the dark region beyond the red, theheat, instead of vanishing, rises suddenly and enormously inintensity, until at some distance beyond the red it attains a maximum. Moving the pile still forward, the thermal power falls, somewhat morerapidly than it rose. It then gradually shades away, but, for adistance beyond the red greater than the length of the whole visiblespectrum, signs of heat may be detected. 

Drawing a datum line, and erecting along it perpendiculars, proportional in length to the thermal intensity at the respectivepoints, we obtain the extraordinary curve, shown on the opposite page, which exhibits the distribution of heat in the spectrum of theelectric light. In the region of dark rays, beyond the red, the curveshoots up to B, in a steep and massive peak--a kind of Matterhorn ofheat, which dwarfs the portion of the diagram C D E, representing theluminous radiation. Indeed the idea forced upon the mind by thisdiagram is that the light rays are a mere insignificant appendage tothe heat-rays represented by the area A B C D, thrown in as it were bynature for the purpose of vision. 

Figure 1. Spectrum of Electric Light

The diagram drawn by Professor Müller to represent the distribution ofheat in the solar spectrum is not by any means so striking as thatjust described, and the reason, doubtless, is that prior to reachingthe earth the solar rays have to traverse our atmosphere. By theaqueous vapour there diffused, the summit of the peak representing thesun's invisible radiation is cut off. A similar lowering of themountain of invisible heat is observed when the rays from the electriclight are permitted to pass through a film of water, which acts uponthem as the atmospheric vapour acts upon the rays of the sun. 

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7. Combustion by Invisible Rays. 

The sun's invisible rays far transcend the visible ones in heatingpower, so that if the alleged performances of Archimedes during thesiege of Syracuse had any foundation in fact, the dark solar rayswould have been the philosopher's chief agents of combustion. On asmall scale we can readily produce, with the purely invisible rays ofthe electric light, all that Archimedes is said to have performed withthe sun's total radiation. Placing behind the electric light a smallconcave mirror, the rays are converged, the cone of reflected rays andtheir point of convergence being rendered clearly visible by the dustalways floating in the air. Placing between the luminous focus andthe source of rays our solution of iodine, the light of the cone isentirely cut away; but the intolerable heat experienced when the bandis placed, even for a moment, at the dark focus, shows that thecalorific rays pass unimpeded through the opaque solution. 

Almost anything that ordinary fire can effect may be accomplished atthe focus of invisible rays; the air at the focus remaining at thesame time perfectly cold, on account of its transparency to theheat-rays. An air thermometer, with a hollow rack-salt bulb, would beunaffected by the heat of the focus: there would be no expansion, andin the open air there is no convection. The aether at the focus, andnot the air, is the substance in which the heat is embodied. A blockof wood, placed at the focus, absorbs the heat, and dense volumes ofsmoke rise swiftly upwards, showing the manner in which the air itselfwould rise, if the invisible rays were competent to heat it. At theperfectly dark focus dry paper is instantly inflamed: chips of woodare speedily burnt up: lead, tin, and zinc are fused: and disks ofcharred paper are raised to vivid incandescence. It might be supposedthat the obscure rays would show no preference for black over white;but they do show a preference, and to obtain rapid combustion, thebody, if not already black, ought to be blackened. When metals are tobe burned, it is necessary to blacken or otherwise tarnish them, so asto diminish their reflective power. Blackened zinc foil, when broughtinto the focus of invisible rays, is instantly caused to blaze, andburns with its peculiar purple light. Magnesium wire flattened, ortarnished magnesium ribbon, also bursts into flame. Pieces ofcharcoal suspended in a receiver full of oxygen are also set on firewhen the invisible focus falls upon them; the dark rays after havingpassed through the receiver, still possessing sufficient power toignite the charcoal, and thus initiate the attack of the oxygen. If, instead of being plunged in oxygen, the charcoal be suspended invacuo, it immediately glows at the place where the focus falls. 

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8. Transmutation of Rays: Calorescence. 

[Footnote: I borrow this term from Professor Challis, 'PhilosophicalMagazine, ' vol. Xii. P. 521]

Eminent experimenters were long occupied in demonstrating thesubstantial identity of light and radiant heat, and we have now themeans of offering a new and striking proof of this identity. Aconcave mirror produces, beyond the object which it reflects, aninverted and magnified image of the object. Withdrawing, for example, our iodine solution, an intensely luminous inverted image of thecarbon points of the electric light is formed at the focus of themirror employed in the foregoing experiments. When the solution isinterposed, and the light is cut away, what becomes of this image? Itdisappears from sight; but an invisible thermograph remains, and it isonly the peculiar constitution of our eyes that disqualifies us fromseeing the picture formed by the calorific rays. Falling on whitepaper, the image chars itself out: falling on black paper, two holesare pierced in it, corresponding to the images of the two coke points:but falling on a thin plate of carbon in vacuo, or upon a thin sheetof platinised platinum, either in vacuo or in air, radiant heat isconverted into light, and the image stamps itself in vividincandescence upon both the carbon and the metal. Results similar tothose obtained with the electric light have also been obtained withthe invisible rays of the lime-light and of the sun. 

Before a Cambridge audience it is hardly necessary to refer to theexcellent researches of Professor Stokes at the opposite end of thespectrum. The above results constitute a kind of complement to hisdiscoveries. Professor Stokes named the phenomena which he hasdiscovered and investigated _Fluorescence_; for the new phenomena heredescribed I have proposed the term _Calorescence_. He, by theinterposition of a proper medium, so lowered the refrangibility of theultraviolet rays of the spectrum as to render them visible. Here, bythe interposition of the platinum foil, the refrangibility of theultra-red rays is so exalted as to render them visible. Lookingthrough a prism at the incandescent image of the carbon points, thelight of the image is decomposed, and a complete spectrum is obtained. The invisible rays of the electric light, remoulded by the atoms ofthe platinum, shine thus visibly forth; ultra-red rays being convertedinto red, orange, yellow, green, blue, indigo, violet, and ultravioletones. Could we, moreover, raise the original source of rays to asufficiently high temperature, we might not only obtain from the darkrays of such a source a single incandescent image, but from the darkrays of this image we might obtain a second one, from the dark rays ofthe second a third, and so on--a series of complete images and spectrabeing thus extracted from the invisible emission of the primitivesource. [Footnote: On investigating the calorescence produced by raystransmitted through glasses of various colours, it was found that inthe case of certain specimens of blue glass, the platinum foil glowedwith a pink or purplish light. The effect was not subjective, andconsiderations of obvious interest are suggested by it. Differentkinds of black glass differ notably as to their power of transmittingradiant heat. When thin, some descriptions tint the sun with agreenish hue: others make it appear a glowing red without any trace ofgreen. The latter are far more diathermic than the former. In fact, carbon when perfectly dissolved and incorporated with a good whiteglass, is highly transparent to the calorific rays, and by employingit as an absorbent the phenomena of 'calorescence' may be obtained, though in a less striking form than with the iodine. The black glasschosen for thermometers, and intended to absorb completely the solarheat, may entirely fail in this object, if the glass in which thecarbon is incorporated be colourless. To render the bulb of athermometer a perfect absorbent, the glass ought in the first instanceto be green. Soon after the discovery of fluorescence the late Dr. William Allen Miller pointed to the lime-light as an illustration ofexalted refrangibility. Direct experiments have since entirelyconfirmed the view expressed at page 210 of his work on 'Chemistry, 'published in 1855. ]

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9. Deadness of the Optic Nerve to the Calorific Rays. 

The layer of iodine used in the foregoing experiments intercepted therays of the noonday sun. No trace of light from the electric lamp wasvisible in the darkest room, even when a white screen was placed atthe focus of the mirror employed to concentrate the light. It wasthought, however, that if the retina itself were brought into thefocus the sensation of light might be experienced. The danger of thisexperiment was twofold. If the dark rays were absorbed in a highdegree by the humours of the eye the albumen of the humours mightcoagulate along the line of the rays. If, on the contrary, no suchhigh absorption took place, the rays might reach the retina with aforce sufficient to destroy it. To test the likelihood of theseresults, experiments were made on water and on a solution of alum, andthey showed it to be very improbable that in the brief time requisitefor an experiment any serious damage could be done. The eye wastherefore caused to approach the dark focus, no defence, in the firstinstance, being provided; but the heat, acting upon the partssurrounding the pupil, could not be borne. An aperture was thereforepierced in a plate of metal, and the eye, placed behind the aperture, was caused to approach the point of convergence of invisible rays. Thefocus was attained, first by the pupil and afterwards by the retina. Removing the eye, but permitting the plate of metal to remain, a sheetof platinum foil was placed in the position occupied by the retina amoment before. The platinum became red-hot. No sensible damage wasdone to the eye by this experiment; no impression of light wasproduced; the optic nerve was not even conscious of heat. 

But the humours of the eye are known to be highly impervious to theinvisible calorific rays, and the question therefore arises, 'Did theradiation in the foregoing experiment reach the retina at all?' Theanswer is, that the rays were in part transmitted to the retina, andin part absorbed by the humours. Experiments on the eye of an oxshowed that the proportion of obscure rays which reached the retinaamounted to 18 per cent. Of the total radiation; while the luminousemission from the electric light amounts to no more than 10 per cent. Of the same total. Were the purely luminous rays of the electric lampconverged by our mirror to a focus, there can be no doubt as to thefate of a retina placed there. Its ruin would be inevitable; and yetthis would be accomplished by an amount of wave-motion but little morethan half of that which the retina, without exciting consciousness, bears at the focus of invisible rays. 

This subject will repay a moment's further attention. At a commondistance of a foot the visible radiation of the electric lightemployed in these experiments is 800 times the light of a candle. Atthe same distance, the portion of the radiation of the electric lightwhich reaches the retina, but fails to excite vision, is about 1, 500times the luminous radiation of the candle. ' [Footnote: It will beborne in mind that the heat which any ray, luminous or non-luminous, is competent to generate is the true measure of the energy of theray. ] But a candle on a clear night can readily be seen at a distanceof a mile, its light at this distance being less than 1/20, 000, 000 ofits light at the distance of a foot. 

Hence, to make the candle-light a mile off equal in power to thenon-luminous radiation received from the electric light at a footdistance, its intensity would have to be multiplied by 1, 500 x20, 000, 000, or by thirty thousand millions. Thus the thirty thousandmillionth part of the invisible radiation from the electric light, received by the retina at the distance of a foot, would, if slightlychanged in character, be amply sufficient to provoke vision. Nothingcould more forcibly illustrate that special relationship supposed byMelloni and others to subsist between the optic nerve and theoscillating periods of luminous bodies. The optic nerve responds, asit were, to the waves with which it is in consonance, while it refusesto be excited by others of almost infinitely greater energy, whoseperiods of recurrence are not in unison with its own. 

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10. Persistence of Rays. 

At an early part of this lecture it was affirmed, that when a platinumwire was, gradually raised to a state of high incandescence, new rayswere constantly added, while the intensity of the old ones wasincreased. Thus, in Dr. Draper's experiments, the rise of temperaturethat generated the orange, yellow, green, and blue augmented theintensity of the red. What is true of the red is true of every otherray of the spectrum, visible and invisible. We cannot indeed see theaugmentation of intensity in the region beyond the red, but we canmeasure it and express it numerically. With this view the followingexperiment was performed: A spiral of platinum wire was surrounded bya small glass globe to protect it from currents of air; through anorifice in the globe the rays could pass from the spiral and fallafterwards upon a thermo-electric pile. Placing in front of theorifice an opaque solution of iodine, the platinum was graduallyraised from a low dark heat to the fullest incandescence, with thefollowing results:

Appearance of spiral Energy of obscure radiation

Dark 1

Dark, but hotter 3

Dark, but still hotter 5

Dark, but still hotter 10

Feeble red 19

Dull red 25

Red 37

Full red. 62

Orange 89

Bright orange 144

Yellow 202

White 276

Intense white 440

Thus the augmentation of the electric current, which raises the wirefrom its primitive dark condition to an intense white heat, exalts atthe same time the energy of the obscure radiation, until at the end itis fully 440 times what it was at the beginning. 

What has been here proved true of the totality of the ultra-red raysis true for each of them singly. Placing our linear thermo-electricpile in any part of the ultra-red spectrum, it may be proved that aray once emitted continues to be emitted with increased energy as thetemperature is augmented. The platinum spiral, so often referred to, being raised to whiteness by an electric current, a brilliant spectrumwas formed from its light. A linear thermo-electric pile was placedin the region of obscure rays beyond the red, and by diminishing thecurrent the spiral was reduced to a low temperature. It was thencaused to pass through various degrees of darkness and incandescence, with the following results:

Appearance of spiral Energy of obscure rays

Dark 1

Dark 6

Faint red 10

Dull red 13

Red 18

Full red. 27

Orange 60

Yellow 93

White 122

Here, as in the former case, the dark and bright radiations reachedtheir maximum together; as the one augmented, the other augmented, until at last the energy of the obscure rays of the particularrefrangibility here chosen, became 122 times what it was at first. Toreach a white heat the wire has to pass through all the stages ofinvisible radiation, but in its most brilliant condition it embraces, in an intensified form, the rays of all those stages. 

And thus it is with all other kinds of matter, as far as they havehitherto been examined. Coke, whether brought to a white heat by theelectric current, or by the oxyhydrogen jet, pours out invisible rayswith augmented energy, as its light is increased. The same is true oflime, bricks, and 'other substances. It is true of all metals whichare capable of being heated to incandescence. It also holds good forphosphorus burning in oxygen. Every gush of dazzling light hasassociated with it a gush of invisible radiant heat, which fartranscends the light in energy. This condition of things applies toall bodies capable of being raised to a white heat, either in thesolid or the molten condition. It would doubtless also apply to theluminous fogs formed by the condensation of incandescent vapours. Insuch cases when the curve representing the radiant energy of the bodyis constructed, the obscure radiation towers upwards like a mountain, the luminous radiation resembling a mere 'spur' at its base. From thevery brightness of the light of some of the fixed stars we may inferthe intensity of that dark radiation, which is the precursor andinseparable associate of their luminous rays. 

We thus find the luminous radiation appearing when the radiant bodyhas attained a certain temperature; or, in other words, when thevibrating atoms of the body have attained a certain width of swing. Insolid and molten bodies a certain amplitude cannot be surpassedwithout the introduction of periods of vibration, which provoke thesense of vision. How are we to figure this? If permitted tospeculate, we might ask, are not these more rapid vibrations theprogeny of the slower? Is it not really the mutual action of theatoms, when they swing through very wide spaces, and thus encroachupon each other, that causes them to tremble in quicker periods? Ifso, whatever be the agency by which the large swinging space isobtained, we shall have light-giving vibrations associated with it. Itmatters not whether the large amplitudes be produced by the strokes ofa hammer, or by the blows of the molecules of a non-luminous gas, likeair at some height above a gas-flame; or by the shock of the aetherparticles when transmitting radiant heat. The result in all caseswill be incandescence. Thus, the invisible waves of our filteredelectric beam may be regarded as generating synchronous vibrationsamong the atoms of the platinum on which they impinge; but, once thesevibrations have attained a certain amplitude, the mutual jostling ofthe atoms produces quicker tremors, and the light-giving waves followas the necessary product of the heat-giving ones. 

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11. Absorption of Radiant Heat by Vapours and Odours. 

We commenced the demonstrations brought forward in this lecture byexperiments on permanent gases, and we have now to turn our attentionto the vapours of volatile liquids. Here, as in the case of thegases, vast differences have been proved to exist between variouskinds of molecules, as regards their power of intercepting thecalorific waves. While some vapours allow the waves a comparativelyfree passage, the faintest mixture of other vapours causes adeflection of the magnetic needle. Assuming the absorption effectedby air, at a pressure of one atmosphere, to be unity, the followingare the absorptions effected by a series of vapours at a pressure of1/60th of an atmosphere:

Name of vapour Absorption

Bisulphide of carbon 47

Iodide of methyl 115

Benzol 136

Amylene 321

Sulphuric ether 440

Formic ether 548

Acetic ether 612

Bisulphide of carbon is the most transparent vapour in this list; andacetic ether the most opaque; 1/60th of an atmosphere of the former, however, produces 47 times the effect of a whole atmosphere of air, while 1/60th of an atmosphere of the latter produces 612 times theeffect of a whole atmosphere of air. Reducing dry air to the pressureof the acetic ether here employed, and comparing them then together, the quantity of wave-motion intercepted by the ether would be manythousand times that intercepted by the air. 

Any one of these vapours discharged into the free atmosphere, in frontof a body emitting obscure rays, intercepts more or less of theradiation. A similar effect is produced by perfumes diffused in theair, though their attenuation is known to be almost infinite. Carrying, for example, a current of dry air over bibulous paper, moistened by patchouli, the scent taken up by the current absorbs 30times the quantity of heat intercepted by the air which carries it;and yet patchouli acts more feebly on radiant heat than any otherperfume yet examined. 

Here follow the results obtained with various essential oils, theodour, in each case, being carried by a current of dry air into the bealready employed for gases and vapours:

Name of perfume Absorption

Patchouli 30

Sandal wood 32

Geranium 33

Oil of cloves 34

Otto of roses 37

Bergamot 44

Neroli 47

Lavender 60

Lemon 65

Portugal 67

Thyme 68

Rosemary 74

Oil of laurel 80

Camomile flowers 87

Cassia 109

Spikenard 355

Aniseed 372

Thus the absorption by a tube full of dry air being 1, that of theodour of patchouli diffused in it is 30, at of lavender 60, that ofrosemary 74, whilst that of aniseed amounts to 372. It would be idleto speculate the quantities of matter concerned in these actions. 

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12. Aqueous Vapour in relation to the Terrestrial Temperatures. 

We are now fully prepared for a result which, without suchpreparation, might appear incredible. Water is, to some extent, avolatile body, and our atmosphere, resting as it does upon the surfaceof the ocean, receives from it a continual supply of aqueous vapour. It would be an error to confound clouds or fog or any visible mistwith the vapour of water, which is a perfectly impalpable gas, diffused, even on the clearest days, throughout the atmosphere. Compared with the great body of the air, the aqueous vapour itcontains is of almost infinitesimal amount, 99. 5 out of every 100parts of the atmosphere being composed of oxygen and nitrogen. In theabsence of experiment, we should never think of ascribing to thisscant and varying constituent any important influence on terrestrialradiation; and yet its influence is far more potent than that of thegreat body of the air. To say that on a day of average humidity inEngland, the atmospheric vapour exerts 100 times the action of the airitself, would certainly be an understatement of the fact. Comparing asingle molecule of aqueous vapour with an atom of either of the mainconstituents of our atmosphere, I am not prepared to say how manythousand times the action of the former exceeds that of the latter. 

But it must be borne in mind that these large numbers depend, in part, on the extreme feebleness of the air; the power of aqueous vapourseems vast, because that of the air with which it is compared isinfinitesimal. Absolutely considered, however, this substance, notwithstanding its small specific gravity, exercises a very potentaction. Probably from 10 to 15 per cent. Of the heat radiated fromthe earth is absorbed within 10 or 20 feet of the earth's surface. This must evidently be of the utmost consequence to the life of theworld. Imagine the superficial molecules of the earth agitated withthe motion of heat, and imparting it to the surrounding aether; thismotion would be carried rapidly away, and lost for ever to our planet, if the waves of aether had nothing but the air to contend with intheir outward course. But the aqueous vapour takes up the motion, andbecomes hereby heated, thus wrapping the earth like a warm garment, and protecting its surface from the deadly chill which it wouldotherwise sustain. Various philosophers have speculated on theinfluence of an atmospheric envelope. De Saussure, Fourier, M. Pouillet, and Mr. Hopkins have, one and all, enriched scientificliterature with contributions on this subject, but the considerationswhich these eminent men have applied to atmospheric air, have, if myexperiments be correct, to be transferred to the aqueous vapour. 

The observations of meteorologists furnish important, though hithertounconscious evidence of the influence of this agent. Wherever the airis dry we are liable to daily extremes of temperature. By day, suchplaces, the sun's heat reaches the earth unimpeded, and renders themaximum high; by night, on the other hand, the earth's heat escapesunhindered to space, and renders the minimum low. Hence thedifference between the maximum and minimum is greatest where the airis driest. In the plains of India, the heights of the Himalaya, incentral Asia, in Australia--wherever drought reigns, we have the heatof day forcibly contrasted with the chill of night. In the Saharaitself, when the sun's rays cease to impinge on the burning soil, thetemperature runs rapidly down to freezing, because there is no vapouroverhead to check the calorific drain. And here another instancemight be added to the numbers already known, in which nature tends asit were to check her own excess. By nocturnal refrigeration, theaqueous vapour of the air is condensed to water on the surface of theearth; and, as only the superficial portions radiate, the act ofcondensation makes water the radiating body. Now experiment provesthat to the rays emitted by water, aqueous vapour is especiallyopaque. Hence the very act of condensation, consequent on terrestrialcooling, becomes a safeguard to the earth, imparting to its radiationthat particular character which renders it most liable to be preventedfrom escaping into space. 

It might however be urged that, inasmuch as we derive all our heatfrom the sun, the selfsame covering which protects the earth fromchill must also shut out the solar radiation. This is partially true, but only partially; the sun's rays are different in quality from theearth's rays, and it does not at all follow that the substance whichabsorbs the one must necessarily absorb the other. Through a layer ofwater, for example, one tenth of an inch in thickness, the sun's raysare transmitted with comparative freedom; but through a layer halfthis thickness, as Melloni has proved, no single ray from the warmedearth could pass. In like manner, the sun's rays pass withcomparative freedom through the aqueous vapour of the air: theabsorbing power of this substance being mainly exerted upon theinvisible heat that endeavours to escape from the earth. Inconsequence of this differential action upon solar and terrestrialheat, the mean temperature of our planet is higher than is due to itsdistance from the sun. 

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13. Liquids and their Vapours in relation to Radiant Heat. 

The deportment here assigned to atmospheric vapour has beenestablished by direct experiments on it taken from the streets andparks of London, from the downs of Epsom, from the hills and sea-beachof the Isle of Wight, and also by experiments on air in the firstinstance dried, and afterwards rendered artificially humid by puredistilled water. It has also en established in the following way: Tenvolatile quids were taken at random and the power of these quids, at acommon thickness, to intercept the waves f heat, was carefullydetermined. The vapours of the quids were next taken, in quantitiesproportional to e quantities of liquid, and the power of the vapoursintercept the waves of heat was also determined. 

Commencing with the substance which exerted the least absorptivepower, and proceeding onwards to the most energetic, the followingorder of absorption was observed:

Liquids Vapours

Bisulphide of carbon. Bisulphide of carbon. 

Chloroform. Chloroform. 

Iodide of methyl. Iodide of methyl. 

Iodide of ethyl. Iodide of ethyl. 

Benzol. Benzol. 

Amylene. Amylene. 

Sulphuric aether. Sulphuric aether. 

Acetic aether. Acetic aether. 

Formic aether. Formic aether. 

Alcohol. Alcohol. 

Water. 

We here find the order of absorption in both cases be the same. Wehave liberated the molecules from the bonds which trammel them more orless in a liquid condition; but this change in their state ofaggregation does not change their relative powers of absorption. Nothing could more clearly prove that the act of absorption dependsupon the individual molecule, which equally asserts its power in theliquid and the gaseous state. We may safely conclude from the abovetable that the position of a vapour is determined by that of itsliquid. Now at the very foot of the list of liquids stands _water_, signalising itself above all others by its enormous power ofabsorption. And from this fact, even if no direct experiment on thevapour of water had ever been made, we should be entitled to rank thatvapour as our most powerful absorber of radiant heat. Itsattenuation, however, diminishes its action. I have proved that ashell of air two inches in thickness surrounding our planet, andsaturated with the vapour of sulphuric aether, would intercept 35 percent. Of the earth's radiation. And though the quantity of aqueousvapour necessary to saturate air is much less than the amount ofsulphuric aether vapour which it can sustain, it is still extremelyprobable that the estimate already made of the action of atmosphericvapour within 10 feet of the earth's surface, is under the mark; andthat we are indebted to this wonderful substance, to an extent notaccurately determined, but certainly far beyond what has hitherto beenimagined, for the temperature now existing at the surface of theglobe. 

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14. Reciprocity of Radiation and Absorption. 

Throughout the reflections which have hitherto occupied us, the imagebefore the mind has been that of a radiant source sending forthcalorific waves, which on passing among the molecules of a gas orvapour were intercepted by those molecules in various degrees. In allcases it was the transference of motion from the aether to thecomparatively quiescent molecules of the gas or vapour that occupiedour thoughts. We have now to change the form of our conception, andto figure these molecules not as absorbers but as radiators, not asthe recipients but as the originators of wave-motion. That is to say, we must figure them vibrating, and generating in the surroundingaether undulations which speed through it with the velocity of light. Our object now is to enquire whether the act of chemical combination, which proves so potent as regards the phenomena of absorption, doesnot also manifest its power in the phenomena of radiation. For theexamination of this question it is necessary, in the first place, toheat our gases and vapours to the same temperature, and then examinetheir power of discharging the motion thus imparted to them upon theaether in which they swing. 

A heated copper ball was placed above a ring gas-burner possessing agreat number of small apertures, the burner being connected by a tubewith vessels containing the various gases to be examined. By gentlepressure the gases were forced through the orifices of the burneragainst the copper ball, where each of them, being heated, rose in anascending column. A thermoelectric pile, entirely screened from thehot ball, was exposed to the radiation of the warm gas, while thedeflection of a magnetic needle connected with the pile declared theenergy of the radiation. 

By this mode of experiment it was proved that the selfsame moleculararrangement which renders a gas a powerful absorber, renders it apowerful radiator--that the atom or molecule which is competent tointercept the calorific waves is, in the same degree, competent tosend them forth. Thus, while the atoms of elementary gases provedthemselves unable to emit any sensible amount of radiant heat, themolecules of compound gases were shown to be capable of powerfullydisturbing the surrounding aether. By special modes of experiment thesame was proved to hold good for the vapours of volatile liquids, theradiative power of every vapour being found proportional to itsabsorptive power. 

The method of experiment here pursued, though not of the simplestcharacter, is still easy to grasp. When air is permitted to rush intoan exhausted tube, the temperature of the air is raised to a degreeequivalent to the _vis viva_ extinguished. [Footnote: See above for adefinition of _vis viva_. ] Such air is said to be dynamically heated, and, if pure, it shows itself incompetent to radiate, even when arock-salt window is provided for the passage of its rays. But ifinstead of being empty the tube contain a small quantity of vapour, the warmed air communicates its heat by contact to the vapour, themolecules of which convert into the radiant form the heat imparted tothem by the atoms of the air. By this process also, which I havecalled Dynamic Radiation, the reciprocity of radiation and absorptionhas been conclusively proved. [Footnote: When heated air imparts itsmotion to another gas or vapour, the transference of heat isaccompanied by a change of vibrating period. The Dynamic Radiation ofvapours is rendered possible by this transmutation of vibrations. ]

In the excellent researches of Leslie, De la Provostaye and Detains, and Balfour Stewart, the same reciprocity, as regards solid bodies, has been variously illustrated; while the labours, theoretical andexperimental, of Kirchhoff have given this subject a wonderfulexpansion, and enriched it by applications of the highest kind. Totheir results are now to be added the foregoing, whereby gases andvapours, which have been hitherto thought inaccessible to experimentswith the thermo-electric pile, are proved by it to exhibit theindissoluble duality of radiation and absorption, the influence ofchemical combination on both being exhibited in the most decisive andextraordinary way. 

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15. Influence of Vibrating Period and Molecular Form. PhysicalAnalysis of the Human Breath. 

In the foregoing experiments with gases and vapours have employedthroughout invisible rays, and found e of these bodies so imperviousto radiant heat, that lengths of a few feet they intercept every rayas actually as a layer of pitch. The substances, however, which showthemselves thus opaque to radiant heat perfectly transparent to light. Now the rays of light differ from those of invisible heat merely inpoint period, the former failing to affect the retina because theirperiods of recurrence are too slow. Hence, in one way or other, thetransparency of our gases and vapours depends upon the periods of thewaves which impinge upon them. What is the nature of this dependence?The admirable researches of Kirchhoff help us an answer. The atomsand molecules of every gas e certain definite rates of oscillation, and those waves aether are most copiously absorbed whose periodsrecurrence synchronise with those of the atomic ups amongst which theypass. Thus, when we find invisible rays absorbed and the visible onestransmitted by a layer of gas, we conclude that the oscillatingperiods of the atoms constituting the gaseous molecules coincide withthose of the invisible, and not with those of the visible spectrum. 

It requires some discipline of the imagination to form a clear pictureof this process. Such a picture is, however, possible, and ought tobe obtained. When the waves of aether impinge upon molecules whoseperiods of vibration coincide with the recurrence of the undulations, the timed strokes of the waves augment the vibration of the molecules, as a heavy pendulum is set in motion by well-timed puffs of breath. Millions of millions of shocks are received every second from thecalorific waves; and it is not difficult to see that as every wavearrives just in time to repeat the action of its predecessor, themolecules must finally be caused to swing through wider spaces than ifthe arrivals were not so timed. In fact, it is not difficult to seethat an assemblage of molecules, operated upon by contending waves, might remain practically quiescent. This is actually the case whenthe waves of the visible spectrum pass through a transparent gas orvapour. There is here no sensible transference of motion from theaether to the molecules; in other words, there is no sensibleabsorption of heat. 

One striking example of the influence of period may be here recorded. Carbonic acid gas is one of the feeblest absorbers of the radiant heatemitted by solid bodies. It is, for example, to a great extenttransparent to the rays emitted by the heated copper plate alreadyreferred to. There are, however, certain rays, comparatively few innumber, emitted by the copper, to which the carbonic acid isimpervious; and could we obtain a source of heat emitting such raysonly, we should find carbonic acid more opaque to the radiation fromthat source, than any other gas. Such a source is actually found inthe flame of carbonic oxide, where hot carbonic acid constitutes themain radiating body. Of the rays emitted by our heated plate ofcopper, olefiant gas absorbs ten times the quantity absorbed bycarbonic acid. Of the rays emitted by a carbonic oxide flame, carbonic acid absorbs twice as much as olefiant gas. This wonderfulchange in the power of the former, as an absorber, is simply due tothe fact, that the periods of the hot and cold carbonic acid areidentical, and that the waves from the flame freely transfer theirmotion to the molecules which synchronise with them. Thus it is thatthe tenth an atmosphere of carbonic acid, enclosed in a tube four feetlong, absorbs 60 per cent. Of the radiation from carbonic oxideflame, while one-thirtieth of an atmosphere absorbs 48 per cent. Ofthe heat from the same source. 

In fact, the presence of the minutest quantity of carbonic acid may bedetected by its action on the rays from the carbonic oxide flame. Carrying, for example, the dried human breath into a tube four feetlong, the absorption there effected by the carbonic acid of the breathamounts to 50 per cent. Of the entire radiation. Radiant heat mayindeed be employed as a means of determining practically the amount ofcarbonic acid expired from the lungs. My late assistant, Mr. Barrett, while under my direction, made this determination. The absorptionproduced by the breath freed from its moisture, but retaining itscarbonic acid, was first determined. Carbonic acid, artificiallyprepared, was then mixed with dry air in such proportions that theaction of the mixture upon the rays of heat was the same as that ofthe dried breath. The percentage of the former being known, immediately gave that of the latter. The same breath, analysedchemically by Dr. Frankland, and physically by Mr. Barrett, gave thefollowing results:

Percentage of Carbonic Acid in the Human Breath. 

Chemical analysis Physical analysis

4. 66 4. 56

5. 33 5. 22

It is thus proved that in the quantity of aethereal motion which it iscompetent to take up, we have a practical measure of the carbonic acidof the breath, and hence of the combustion going on in the humanlungs. 

Still this question of period, though of the utmost importance, is notcompetent to account for the whole of the observed facts. The aether, as far as we know, accepts vibrations of all periods with the samereadiness. To it the oscillations of an atom of free oxygen are justas acceptable as those of the atoms in a molecule of olefiant gas;that the vibrating oxygen then stands so far below the olefiant gas inradiant power must be referred not to period, but to some otherpeculiarity. The atomic group which constitutes the molecule ofolefiant gas, produces many thousand times the disturbance caused bythe oxygen, it may be because the group is able to lay a vastly morepowerful hold upon the aether than single atoms can. Another, andprobably very potent cause of the difference may be, that thevibrations, being those of the constituent atoms of the molecule, [Footnote: See 'Physical Considerations, ' Art. Iv. ] are generatedin highly condensed aether, which acts like: condensed air upon sound. But whatever may be the fate of these attempts to visualise the physicsof the process, it will still remain true, that to account for thephenomena of radiation and absorption we must take into considerationthe shape, size, and condition of the aether within the molecules, bywhich the external aether is disturbed. 

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16. Summary and Conclusion. 

Let us now cast a momentary glance over the ground that we have leftbehind. The general nature of light and heat was first brieflydescribed: the compounding of matter from elementary atoms, and theinfluence of the act of combination on radiation and absorption, wereconsidered and experimentally illustrated. Through the transparentelementary gases radiant heat was found to pass as through a vacuum, while many of the compound gases presented almost impassable obstaclesto the calorific-waves. This deportment of the simple gases directedour attention to other elementary bodies, the examination of which ledto the discovery that the element iodine, dissolved in bisulphide ofcarbon, possesses the power detaching, with extraordinary sharpness, the light of the spectrum from its heat, intercepting all luminousrays up to the extreme red, and permitting the calorific rays beyondthe red to pass freely through it. This substance was then employedto filter the beams of the electric light, and to form foci ofinvisible rays so intense as to produce almost all the effectsobtainable in ordinary fire. Combustible bodies were burnt, andrefractory ones were raised to a white heat, by the concentratedinvisible rays. Thus, by exalting their refrangibility, the invisiblerays of the electric light were rendered visible, and all the coloursof the solar spectrum were extracted from utter darkness. The extremerichness of the electric light in invisible rays of low refrangibilitywas demonstrated, one-eighth only of its radiation consisting ofluminous rays. The deadness of the optic nerve to those invisiblerays was proved, and experiments were then added to show that thebright and the dark rays of a solid body, raised gradually toincandescence, are strengthened together; intense dark heat being aninvariable accompaniment of intense white heat. A sun could not beformed, or a meteorite rendered luminous, on any other condition. Thelight-giving rays constituting only a small fraction of the totalradiation, their unspeakable importance to us is due to the fact, thattheir periods are attuned to the special requirements of the eye. 

Among the vapours of volatile liquids vast differences were also foundto exist, as regards their powers of absorption. We followed variousmolecules from a state of liquid to a state of gas, and found, in bothstates of aggregation, the power of the individual molecules equallyasserted. The position of a vapour as an absorber of radiant heat wasshown to be determined by that of the liquid from which it is derived. Reversing our conceptions, and regarding the molecules of gases andvapours not as the recipients but as the originators of wave-motion;not as absorbers but as radiators; it was proved that the powers ofabsorption and radiation went hand in hand, the self-same chemical actwhich rendered a body competent to intercept the waves of aether, rendering it competent, in the same degree, to generate them. Perfumeswere next subjected to examination, and, notwithstanding theirextraordinary tenuity, they were found vastly superior, in point ofabsorptive power, to the body of the air in which they were diffused. We were led thus slowly up to the examination of the most widelydiffused and most important of all vapours--the aqueous vapour of ouratmosphere, and we found in it a potent absorber of the purelycalorific rays. The power of this substance to influence climate, andits general influence on the temperature of the earth, were thenbriefly dwelt upon. A cobweb spread above a blossom is sufficient toprotect it from nightly chill; and thus the aqueous vapour of ourair, attenuated as it is, checks the drain of terrestrial heat, andsaves the surface of our planet from the refrigeration which wouldassuredly accrue, were no such substance interposed between it and thevoids of space. We considered the influence of vibrating period, andmolecular form, on absorption and radiation, and finally deduced, fromits action upon radiant heat, the exact amount of carbonic acidexpired by the human lungs. 

Thus, in brief outline, were placed before you some ofthe results ofrecent enquiries in the domain of Radiation, and my aim throughout hasbeen to raise in your minds distinct physical images of the variousprocesses involved in our researches. It is thought by some thatnatural science has a deadening influence on the imagination, and adoubt might fairly be raised as to the value of any study which wouldnecessarily have this effect. But the experience of the last hourmust, I think, have convinced you, that the study of natural sciencegoes hand in hand with the culture of the imagination. Throughout thegreater part of this discourse we have been sustained by this faculty. We have been picturing atoms, and molecules, and vibrations, andwaves, which eye has never seen nor ear heard, and which can only bediscerned by the exercise of imagination. This, in fact, is thefaculty which enables us transcend the boundaries of sense, andconnect the phenomena of our visible world with those of an invisibleone. Without imagination we never could have risen to the conceptionswhich have occupied us here today; and in proportion to your power ofexercising this faculty aright, and of associating definite mentalimages with the terms employed, will be the pleasure and the profitwhich you will derive from this lecture. 

The outward facts of nature are insufficient to satisfy the mind. Wecannot be content with knowing that the light and heat of the sunilluminate and warm the world. We are led irresistibly to enquire, 'What is light, and what is heat?' and this question leads us at onceout of the region of sense into that of imagination. [Footnote: Thisline of thought was pursued further five years subsequently. See'Scientific Use of the Imagination' in Vol. II. ]

Thus pondering, and questioning, and striving to supplement that whichis felt and seen, but which is incomplete, by something unfelt andunseen which is necessary to its completeness, men of genius have inpart discerned, not only the nature of light and heat, but also, through them, the general relationship of natural phenomena. Theworking power of Nature consists of actual or potential motion, ofwhich all its phenomena are but special forms. This motion manifestsitself in tangible and in intangible matter, being incessantlytransferred from the one to the other, and incessantly transformed bythe change. It is as real in the waves of the aether as in the wavesof the sea; the latter--derived as they are from winds, which in theirturn are derived from the sun--are, indeed, nothing more than theheaped-up motion of the aether waves. It is the calorific wavesemitted by the sun which heat our air, produce our winds, and henceagitate our ocean. And whether they break in foam upon the shore, orrub silently against the ocean's bed, or subside by the mutualfriction of their own parts, the sea waves, which cannot subsidewithout producing heat, finally resolve themselves into waves ofaether, thus regenerating the motion from which their temporaryexistence was derived. This connection is typical. Nature is not anaggregate of independent parts, but an organic whole. If you open apiano and sing into it, a certain string will respond. Change thepitch of our voice; the first string ceases to vibrate, but anotherreplies. Change again the pitch; the first two strings are silent, while another resounds. Thus is sentient man acted on by Nature, theoptic, the auditory, and other nerves of the human body being so manystrings differently tuned, and responsive to different forms of theuniversal power. 

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III ON RADIANT HEAT IN RELATION TO THE COLOUR AND CHEMICALCONSTITUTION OF BODIES. 

[Footnote: A discourse delivered in the Royal Institution of GreatBritain, Jan. 19, 1866. ]

ONE of the most important functions of physical science, considered asa discipline of the mind, is to enable us by means of the sensibleprocesses of Nature to apprehend the insensible. The sensibleprocesses give direction to the line of thought; but this once given, the length of the line is not limited by the boundaries of the senses. Indeed, the domain of the senses, in Nature, is almost infinitelysmall in comparison with the vast region accessible to thought whichlies beyond them. From a few observations of a comet, when it comeswithin the range of his telescope, an astronomer can calculate itspath in regions which no telescope can reach: and in like manner, bymeans of data furnished in the narrow world of the senses, we makeourselves at home in other and wider worlds, which are traversed bythe intellect alone. 

From the earliest ages the questions, 'What is light?' and 'What isheat?' have occurred to the minds of men; but these questions neverwould have been answered had they not been preceded by the question, 'What is sound?' Amid the grosser phenomena of acoustics the mind wasfirst disciplined, conceptions being thus obtained from directobservation, which were afterwards applied to phenomena of a characterfar too subtle to be observed directly. Sound we know to be due tovibratory motion. A vibrating tuning-fork, for example, moulds theair around it into undulations or waves, which speed away on all sideswith a certain measured velocity, impinge upon the drum of the ear, shake the auditory nerve, and awake in the brain the sensation ofsound. When sufficiently near a sounding body we can feel thevibrations of the air. A deaf man, for example, plunging his handinto a bell when it is sounded, feels through the common nerves of hisbody those tremors which, when imparted to the nerves of healthy ears, are translated into sound. There are various ways of rendering thosesonorous vibrations not only tangible but visible; and it was notuntil numberless experiments of this kind had been executed, that thescientific investigator abandoned himself wholly, and without a shadowof misgiving, to the conviction that what is sound within us is, outside of us, a motion of the air. 

But once having established this fact--once having proved beyond alldoubt that the sensation of sound is produced by an agitation of theauditory nerve--the thought soon suggested itself that light might bedue to an agitation of the optic nerve. This was a great step inadvance of that ancient notion which regarded light as somethingemitted by the eye, and not as anything imparted to it. But if lightbe produced by an agitation of the retina, what is it that producesthe agitation? Newton, you know, supposed minute particles to be shotthrough the humours of the eye against the retina, which he supposedto hang like a target at the back of the eye. The impact of theseparticles against the target, Newton believed to be the cause oflight. But Newton's notion has not held its ground, being entirelydriven from the field by the more wonderful and far more philosophicalnotion that light, like sound, is a product of wave-motion. 

The domain in which this motion of light is carried on lies entirelybeyond the reach of our senses. The waves of light require a mediumfor their formation and propagation; but we cannot see, or feel, ortaste, or smell this medium. How, then, has its existence beenestablished? By showing, that by the assumption of this wonderfulintangible aether, all the phenomena of optics are accounted for, witha fulness, and clearness, and conclusiveness, which leave no desire ofthe intellect unsatisfied. When the law of gravitation firstsuggested itself to the mind of Newton, what did he do? He sethimself to examine whether it accounted for all the facts. Hedetermined the courses of the planets; he calculated the rapidity ofthe moon's fall towards the earth; he considered the precession of theequinoxes, the ebb and flow of the tides, and found all explained bythe law of gravitation. He therefore regarded this law asestablished, and the verdict of science subsequently confirmed hisconclusion. On similar, and, if possible, on stronger grounds, wefound our belief in the existence of the universal aether. Itexplains facts far more various and complicated than those on whichNewton based his law. If a single phenomenon could be pointed outwhich the aether is proved incompetent to explain, we should have togive it up; but no such phenomenon has ever been pointed out. It is, therefore, at least as certain that space is filled with a medium, bymeans of which suns and stars diffuse their radiant power, as that itis traversed by that force which holds in its grasp, not only ourplanetary system, but the immeasurable heavens themselves. 

There is no more wonderful instance than this of the production of aline of thought, from the world of the senses into the region of pureimagination. I mean by imagination here, not that play of fancy whichcan give to airy nothings a local habitation and a name, but thatpower which enables the mind to conceive realities which lie beyondthe range of the senses--to present to itself distinct images ofprocesses which, though mighty in the aggregate beyond all conception, are so minute individually as to elude all observation. It is thewaves of air excited by a tuning-fork which render its vibrationsaudible. It is the waves of aether sent forth from those lampsoverhead which render them luminous to us; but so minute are thesewaves, that it would take from 30, 000 to 60, 000 of them placed end toend to cover a single inch. Their number, however, compensates fortheir minuteness. Trillions of them have entered your eyes, and hitthe retina at the backs of your eyes, in the time consumed in theutterance of the shortest sentence of this discourse. This is thesteadfast result of modern research; but we never could have reachedit without previous discipline. We never could have measured thewaves of light, nor even imagined them to exist, had we not previouslyexercised ourselves among the waves of sound. Sound and light are nowmutually helpful, the conceptions of each being expanded, strengthened, and defined by the conceptions of the other. 

The aether which conveys the pulses of light and heat not only fillscelestial space, swathing suns, and planets, and moons, but it alsoencircles the atoms of which these bodies are composed. It is themotion of these atoms, and not that of any sensible parts of bodies, that the aether conveys. This motion is the objective cause of what, in our sensations, are light and heat. An atom, then, sending itspulses through the aether, resembles a tuning-fork sending its pulsesthrough the air. Let us look for a moment at this thrilling medium, and briefly consider its relation to the bodies whose vibrations itconveys. Different bodies, when heated to the same temperature, possess very different powers of agitating the aether: some are goodradiators, others are bad radiators; which means that some are soconstituted as to communicate their atomic motion freely to theaether, producing therein powerful undulations; while the atoms ofothers are unable thus to communicate their motions, but glide throughthe medium without materially disturbing its repose. Recentexperiments have proved that elementary bodies, except under certainanomalous conditions, belong to the class of bad radiators. An atom, vibrating in the aether, resembles a naked tuning-fork vibrating inthe air. The amount of motion communicated to the air by the thinprongs is too small to evoke at any distance the sensation of sound. But if we permit the atoms to combine chemically and form molecules, the result, in many cases, is an enormous change in the power ofradiation. The amount of aethereal disturbance, produced by thecombined atoms of a body, may be many thousand times that produced bythe same atoms when uncombined. 

The pitch of a musical note depends upon the rapidity of itsvibrations, or, in other words, on the length of its waves. Now, thepitch of a note answers to the colour of light. Taking a slice ofwhite light from the sun, or from an electric lamp, and causing thelight to pass through an arrangement of prisms, it is decomposed. Wehave the effect obtained by Newton, who first unrolled the solar beaminto the splendours of the solar spectrum. At one end of thisspectrum we have red light, at the other, violet; and between thoseextremes lie the other prismatic colours. As we advance along thespectrum from the red to the violet, the pitch of the light--if I mayuse the expression--heightens, the sensation of violet being producedby a more rapid succession of impulses than that which produces theimpression of red. The vibrations of the violet are about twice asrapid as those of the red; in other words, the range of the visiblespectrum is about an octave. 

There is no solution of continuity in this spectrum one colour changesinto another by insensible gradations. It is as if an infinite numberof tuning-forks, of gradually augmenting pitch, were vibrating at thesame time. But turning to another spectrum--that, namely, obtainedfrom the incandescent vapour of silver--you observe that it consistsof two narrow and intensely luminous green bands. Here it is as iftwo forks only, of slightly different pitch, were vibrating. Thelength of the waves which produce this first band is such that 47, 460of them, placed end to end, would fill an inch. The waves whichproduce the second band are a little shorter; it would take of these47, 920 to fill an inch. In the case of the first band, the number ofimpulses imparted, in one second, to every eye which sees it, is 677millions of millions; while the number of impulses imparted, in thesame time, by the second band is 600 millions of millions. We mayproject upon a white screen the beautiful stream of green light fromwhich these bands were derived. This luminous stream is theincandescent vapour of silver. The rates of vibration of the atoms ofthat vapour are as rigidly fixed as those of two tuning-forks; and towhatever height the temperature of the vapour may be raised, therapidity of its vibrations, and consequently its colour, which whollydepends upon that rapidity, remain unchanged. 

The vapour of water, as well as the vapour of silver, has its definiteperiods of vibration, and these are such as to disqualify the vapour, when acting freely as such, from being raised to a white heat. Theoxyhydrogen flame, for example, consists of hot aqueous vapour. It isscarcely visible in the air of this room, and it would be still lessvisible if we could burn the gas in a clean atmosphere. But theatmosphere, even at the summit of Mont Blanc, is dirty; in London itis more than dirty; and the burning dirt gives to this flame thegreater portion of its present light. But the heat of the flame isenormous. Cast iron fuses at a temperature of 2, 000° Fahr; while thetemperature of the oxyhydrogen flame is 6, 000° Fahr. A piece ofplatinum is heated to vivid redness, at a distance of two inchesbeyond the visible termination of the flame. The vapour whichproduces incandescence is here absolutely dark. In the flame itselfthe platinum is raised to dazzling whiteness, and is even pierced bythe flame. When this flame impinges on a piece of lime, we have thedazzling Drummond light. But the light is here due to the fact thatwhen it impinges upon the solid body, the vibrations excited in thatbody by the flame are of periods different from its own. 

Thus far we have fixed our attention on atoms and molecules in a stateof vibration, and surrounded by a medium which accepts theirvibrations, and transmits them through space. But suppose the wavesgenerated by one system of molecules to impinge upon another system, how will the waves be affected? Will they be stopped, or will they bepermitted to pass? Will they transfer their motion to the moleculeson which they impinge, or will they glide round the molecules, throughthe intermolecular spaces, and thus escape?

The answer to this question depends upon a condition which may bebeautifully exemplified by an experiment on sound. These twotuning-forks are tuned absolutely alike. They vibrate with the samerapidity, and, mounted thus upon their resonant cases, you hear themloudly sounding the same musical note. Stopping one of the forks, Ithrow the other into strong vibration, and bring that other near thesilent fork, but not into contact with it. Allowing them to continuein this position for four or five seconds, and then stopping thevibrating fork, the sound does not cease. The second fork has takenup the vibrations of its neighbour, and is now sounding in its turn. Dismounting one of the forks, and permitting the other to remain uponits stand, I throw the dismounted fork into strong vibration. Youcannot hear it sound. Detached from its case, the amount of motionwhich it can communicate to the air is too small to be sensible at anydistance. When the dismounted fork is brought close to the mountedone, but not into actual contact with it, out of the silence rises amellow sound. Whence comes it? From the vibrations which have beentransferred from the dismounted fork to the mounted one. 

That the motion should thus transfer itself through the air it isnecessary that the two forks should be in perfect unison. If a morselof wax not larger than a pea be placed on one of the forks, it isrendered thereby powerless to affect, or to be affected by, the other. It is easy to understand this experiment. The pulses of the one forkcan affect the other, because they are _perfectly timed_. A singlepulse causes the prong of the silent fork to vibrate through aninfinitesimal space. But just as it has completed this smallvibration another pulse is ready to strike it. Thus, the impulses addthemselves together. In the five seconds during which the forks wereheld near each other, the vibrating fork sent 1, 280 waves against itsneighbour and those 1, 280 shocks, all delivered at the proper moment, all, as I have said, perfectly timed, have given such strength to thevibrations of the mounted fork as to render them audible to all. 

Another curious illustration of the influence of synchronism onmusical vibrations, is this: Three small gas-flames are inserted intothree glass tubes of different lengths. Each of these flames can becaused to emit a musical note, the pitch of which is determined by thelength of the tube surrounding the flame. The shorter the tube thehigher is the pitch. The flames are now silent within theirrespective tubes, but each of them can be caused to respond to aproper note sounded anywhere in this room. With an instrument calleda syren, a powerful musical note, of gradually increasing pitch, canbe produced. Beginning with a low note, and ascending gradually to ahigher one, we finally attain the pitch of the flame in the longesttube. The moment it is reached, the flame bursts into song. Theother flames are still silent within their tubes. But by urging theinstrument on to higher notes, the second flame is started, and thethird alone remains. A still higher note starts it also. Thus, asthe sound of the syren rises gradually in pitch, it awakens everyflame in passing, by striking it with a series of waves whose periodsof recurrence are similar to its own. 

Now the wave-motion from the syren is in part taken up by the flamewhich synchronises with the waves; and were these waves to impingeupon a multitude of flames, instead of upon one flame only, thetransference might be so great as to absorb the whole of the originalwave motion. Let us apply these facts to radiant heat. This blueflame is the flame of carbonic oxide; this transparent gas is carbonicacid gas. In the blue flame we have carbonic acid intensely heated, or, in other words, in a state of intense vibration. It thusresembles the sounding fork, while this cold carbonic acid resemblesthe silent one. What is the consequence? Through the synchronism ofthe hot and cold gas, the waves emitted by the former are interceptedby the latter, the transmission of the radiant heat being thusprevented. The cold gas is intensely opaque to the radiation fromthis particular flame, though highly transparent to heat of everyother kind. We are here manifestly dealing with that great principlewhich lies at the basis of spectrum analysis, and which has enabledscientific men to determine the substances of which the sun, thestars, and even the nebulae are composed; the principle, namely, thata body which is competent to emit any ray, whether of heat or light, is competent in the same degree to absorb that ray. The absorptiondepends on the synchronism existing between the vibrations of the tomsfrom which the rays, or more correctly the waves, sue, and those ofthe atoms on which they impinge. 

To its almost total incompetence to emit white light, aqueous vapouradds a similar incompetence to absorb bite light. It cannot, forexample, absorb the luminous rays of the sun, though it can absorb thenon-luminous rays of the earth. This incompetence of the vapour toabsorb luminous rays is shared by water and ice--in fact, by allreally transparent substances. Their transparency is due to theirinability to absorb luminous rays. The molecules of such substancesare in dissonance with luminous waves; and hence such waves passthrough transparent bodies without disturbing the molecular rest. Apurely luminous beam, however intense may be its heat, is sensiblyincompetent to melt ice. We can, for example, converge a powerfulluminous beam upon a surface covered with hoar frost, without meltinga single spicula of the crystals. How then, it may be asked, are thesnows of the Alps swept away by the sunshine of summer? I answer, they are not swept away by sunshine at all, but by rays which have nosunshine whatever in them. The luminous rays of the sun fall upon thesnow-fields and are flashed in echoes from crystal to crystal, butthey find next to no lodgment within the crystals. They are hardly atall absorbed, and hence they cannot produce fusion. But a body ofpowerful dark rays is emitted by the sun; and it is these that causethe glaciers to shrink and the snows to disappear; it is they thatfill the banks of the Arve and Arveyron, and liberate from theirfrozen captivity the Rhone and the Rhine. 

Placing a concave silvered mirror behind the electric light its raysare converged to a focus of dazzling brilliancy. Placing in the pathof the rays, between the light and the focus, a vessel of water, andintroducing at the focus a piece of ice, the ice is not melted by theconcentrated beam. Matches, at the same place, are ignited, and woodis set on fire. The powerful heat, then, of this luminous beam isincompetent to melt the ice. On withdrawing the cell of water, theice immediately liquefies, and the water trickles from it in drops. Reintroducing the cell of water, the fusion is arrested, and the dropscease to fall. The transparent water of the cell exerts no sensibleabsorption on the luminous rays, still it withdraws something from thebeam, which, when permitted to act, is competent to melt the ice. Thissomething is the dark radiation of the electric light. Again, I placea slab of pure ice in front of the electric lamp; send a luminous beamfirst through our cell of water and then through the ice. By means ofa lens an image of the slab is cast upon a white screen. The beam, sifted by the water, has little power upon the ice. But observe whatoccurs when the water is removed; we have here a star and there astar, each star resembling a flower of six petals, and growing visiblylarger before our eyes. As the leaves enlarge, their edges becomeserrated, but there is no deviation from the six-rayed type. We havehere, in fact, the crystallisation of the ice reversed by theinvisible rays of the electric beam. They take the molecules down inthis wonderful way, and reveal to us the exquisite atomic structure ofthe substance with which Nature every winter roofs our ponds andlakes. 

Numberless effects, apparently anomalous, might be adduced inillustration of the action of these lightless rays. These twopowders, for example, are both white, and undistinguishable from eachother by the eye. The luminous rays of the sun are unabsorbed byboth--from such rays these powders acquire no heat; still one of them, sugar, is heated so highly by the concentrated beam of the electriclamp, that it first smokes and then violently inflames, while theother substance, salt, is barely warmed at the focus. Placing twoperfectly transparent liquids in test-tubes at the focus, one of themboils in a couple of seconds, while the other, in a similar position, is hardly warmed. The boiling-point of the first liquid is 78°C, which is speedily reached; that of the second liquid is only 48°C, which is never reached at all. These anomalies are entirely due tothe unseen element which mingles with the luminous rays of theelectric beam, and indeed constitutes 90 per cent. Of its calorificpower. 

A substance, as many of you know, has been discovered, by which thesedark rays may be detached from the total emission of the electriclamp. This ray-filter is a liquid, black as pitch to the luminous, but bright as a diamond to the non-luminous, radiation. Itmercilessly cuts off the former, but allows the latter freetransmission. When these invisible rays are brought to a focus, at adistance of several feet from the electric lamp, the dark rays form aninvisible image of their source. By proper means, this image may betransformed into a visible one of dazzling brightness. It might, moreover, be shown, if time permitted, how, out of those perfectlydark rays, could be extracted, by a process of transmutation, all thecolours of the solar spectrum. It might also be proved that thoserays, powerful as they are, and sufficient to fuse many metals, can bepermitted to enter the eye, and to break upon the retina, withoutproducing the least luminous impression. 

The dark rays being thus collected, you see nothing at their place ofconvergence. With a proper thermometer it could be proved that eventhe air at the focus is just as cold as the surrounding air. And markthe conclusion to which this leads. It proves the aether at the focusto be practically detached from the air, --that the most violentaethereal motion may there exist, without the least aerial motion. But, though you see it not, there is sufficient heat at that focus toset London on fire. The heat there is competent to raise iron to atemperature at which it throws off brilliant scintillations. It canheat platinum to whiteness, and almost fuse that refractory metal. Itactually can fuse gold, silver, copper, and aluminium. The moment, moreover, that wood is placed at the focus it bursts into a blaze. 

It has been already affirmed that, whether as regards radiation orabsorption, the elementary atoms possess but little power. This mightbe illustrated by a long array of facts; and one of the most singularof these is furnished by the deportment of that extremely combustiblesubstance, phosphorus, when placed at the dark focus. It isimpossible to ignite there a fragment of amorphous phosphorus. Butordinary phosphorus is a far quicker combustible, and its deportmenttowards radiant heat is still more impressive. It may be exposed tothe intense radiation of an ordinary fire without bursting into flame. It may also be exposed for twenty or thirty seconds at an obscurefocus, of sufficient power to raise platinum to a red heat, withoutignition. Notwithstanding the energy of the aethereal waves hereconcentrated, notwithstanding the extremely inflammable character ofthe elementary body exposed to their action, the atoms of that bodyrefuse to partake of the motion of the powerful waves of lowrefrangibility, and consequently cannot be affected by their heat. 

The knowledge we now possess will enable us to analyse with profit apractical question. White dresses are worn in summer, because theyare found to be cooler than dark ones. The celebrated BenjaminFranklin placed bits of cloth of various colours upon snow, exposedthem to direct sunshine, and found that they sank to different depthsin the snow. The black cloth sank deepest, the white did not sink atall. Franklin inferred from this experiment that black-bodies are thebest absorbers, and white ones the worst absorbers, of radiant heat. Let us test the generality of this conclusion. One of these two cardsis coated with a very dark powder, and the other with a perfectlywhite one. I place the powdered surfaces before a fire, and leavethem there until they have acquired as high a temperature as they canattain in this position. Which of the cards is then most highlyheated? It requires no thermometer to answer this question. Simplypressing the back of the card, on which the white powder is strewn, against the cheek or forehead, it is found intolerably hot. Placingthe dark card in the same position, it is found cool. The whitepowder has absorbed far more heat than the dark one. This simpleresult abolishes a hundred conclusions which have been hastily drawnfrom the experiments of Franklin. Again, here are suspended twodelicate mercurial thermometers at the same distance from a gas-flame. The bulb of one of them is covered by a dark substance, the bulb ofthe other by a white one. Both bulbs have received the radiation fromthe flame, but the white bulb has absorbed most, and its mercurystands much higher than that of the other thermometer. Thisexperiment might be varied in a hundred ways: it proves that from thedarkness of a body you can draw no certain conclusion regarding itspower of absorption. 

The reason of this simply is, that colour gives us intelligence ofonly one portion, and that the smallest one, of the rays impinging onthe coloured body. Were the rays all luminous, we might withcertainty infer from the colour of a body its power of absorption; butthe great mass of the radiation from our fire, our gas-flame, and evenfrom the sun itself, consists of invisible calorific rays, regardingwhich colour teaches us nothing. A body may be highly transparent tothe one class of rays, and highly opaque to the other. Thus the whitepowder, which has shown itself so powerful an absorber, has beenspecially selected on account of its extreme perviousness to thevisible rays, and its extreme imperviousness to the invisible ones;while the dark powder was chosen on account of its extremetransparency to the invisible, and its extreme opacity to the visible, rays. In the case of the radiation from our fire, about 98 per centof the whole emission consists of invisible rays; the body, therefore, which was most opaque to these triumphed as an absorber, though thatbody was a white one. 

And here it is worth while to consider the manner in which we obtainfrom natural facts what may be called their intellectual value. Throughout the processes of Nature we have interdependence andharmony; and the main value of physics, considered as a mentaldiscipline, consists in the tracing out of this interdependence, andthe demonstration of this harmony. The outward and visible phenomenaare the counters of the intellect; and our science would not be worthyof its name and fame if it halted at facts, however practicallyuseful, and neglected the laws which accompany and rule the phenomena. Let us endeavour, then, to extract from the experiment of Franklin allthat it can yield, calling to our aid the knowledge which ourpredecessors have already stored. Let us imagine two pieces of clothof the same texture, the one black and the other white, placed uponsunned snow. Fixing our attention on the white piece, let us enquirewhether there is any reason to expect that it will sink in the snow atall. There is knowledge at hand which enables us to reply at once inthe negative. There is, on the contrary, reason to expect that, aftera sufficient exposure, the bit of cloth will be found on an eminenceinstead of in a hollow; that instead of a depression, we shall have arelative elevation of the bit of cloth. For, as regards the luminousrays of the sun, the cloth and the snow are alike powerless; the onecannot be warmed, nor the other melted, by such rays. The cloth iswhite and the snow is white, because their confusedly mingled fibresand particles are incompetent to absorb the luminous rays. Whether, then, the cloth will sink or not depends entirely upon the dark raysof the sun. Now the substance which absorbs these dark rays with thegreatest avidity is ice, --or snow, which is merely ice in powder. Hence, a less amounts of heat will be lodged in the cloth than in thesurrounding snow. The cloth must therefore act as a shield to thesnow on which it rests; and, in consequence of the more rapid fusionof the exposed snow, its shield must, in due time, be left behind, perched upon an eminence like a glacier-table. 

But though the snow transcends the cloth, both as a radiator andabsorber, it does not much transcend it. Cloth is very powerful inboth these respects. Let us now turn our attention to the piece ofblack cloth, the texture and fabric of which I assume to be the sameas that of the white. For our object being to compare the effects ofcolour, we must, in order to study this effect in its purity, preserveall the other conditions constant. Let us then suppose the blackcloth to be obtained from the dyeing of the white. The cloth itself, without reference to the dye, is nearly as good an absorber of heat asthe snow around it. But to the absorption of the dark solar rays bythe undyed cloth, is now added the absorption of the whole of theluminous rays, and this great additional influx of heat is far morethan sufficient to turn the balance in favour of the black cloth. Thesum of its actions on the dark and luminous rays, exceeds the actionof the snow on the dark rays alone. Hence the cloth will sink in thesnow, and this is the complete analysis of Franklin's experiments. 

Throughout this discourse the main stress has been laid on chemicalconstitution, as influencing most powerfully the phenomena ofradiation and absorption. 

With regard to gases and vapours, and to the liquids from which thesevapours are derived, it has been proved by the most varied andconclusive experiments that the acts of radiation and absorption aremolecular--that they depend upon chemical, and not upon mechanical, condition. In attempting to extend this principle to solids I was metby a multitude of facts, obtained by celebrated experimenters, whichseemed flatly to forbid such an extension. Mellon, for example, hadfound the same radiant and absorbent power for chalk and lamp-black. MM. Masson and Courtépée had performed a most elaborate series ofexperiments on chemical precipitates of various kinds, and found thatthey one and all manifested the same power of radiation. Theyconcluded from their researches, that when bodies are reduced to anextremely fine state of division, the influence of this state is sopowerful as entirely to mask and override whatever influence may bedue to chemical constitution. 

But it appears to me that through the whole of these researches anoversight has run, the mere mention of which will show what caution isessential in the operations of experimental philosophy; while anexperiments or two will make clear wherein the oversight consists. Filling a brightly polished metal cube with boiling water, I determinethe quantity of heat emitted by two of the bright surfaces. As aradiator of heat one of them far transcends the other. Both surfacesappear to be metallic; what, then, is the cause of the observeddifference in their radiative power? Simply this: one of the surfacesis coated with transparent gum, through which, of course, is seen themetallic lustre behind; and this varnish, though so perfectlytransparent to luminous rays, is as opaque as pitch, or lamp-black, tonon-luminous ones. It is a powerful emitter of dark rays; it is alsoa powerful absorber. While, therefore, at the present moment, it iscopiously pouring forth radiant heat itself, it does not allow asingle ray from the metal behind to pass through it. The varnishthen, and not the metal, is the real radiator. 

Now Melloni, and Masson, and Courtépée experimented thus: they mixedtheir powders and precipitates with gum-water, and laid them, by meansof a brush, upon the surfaces of a cube like this. True, they sawtheir red powders red, their white ones white, and their black onesblack, but they saw these colours _through the coat of varnish whichsurrounded every particle_. When, therefore, it was concluded thatcolour had no influence on radiation, no chance had been given to itof asserting its influence; when it was found that all chemicalprecipitates radiated alike, it was the radiation from a varnish, common to them all, which showed the observed constancy. Hundreds, perhaps thousands, of experiments on' radiant heat have been performedin this way, by various enquirers, but the work will, I fear, have tobe done over again. I am not, indeed, acquainted with an instance inwhich an oversight of so trivial a character has been committed by somany able men in succession, vitiating so large an amounts ofotherwise excellent work. Basing our reasonings thus on demonstratedfacts, we arrive at the extremely probable conclusion that theenvelope of the particles, and not the particles themselves, was thereal radiator in the experiments just referred to. To reason thus, and deduce their more or less probable consequences from experimentalfacts, is an incessant exercise of the student of physical science. But having thus followed, for a time, the light of reason alonethrough a series of phenomena, and emerged from them with a purelyintellectual conclusion, our duty is to bring that conclusion to anexperimental test. In this way we fortify our science. 

For the purpose of testing our conclusion regarding the influence ofthe gum, I take two powders presenting the same physical appearance;one of them is a compound of mercury, and the other a compound oflead. On two surfaces of a cube are spread these bright red powders, without varnish of any kind. Filling the cube with boiling water, anddetermining the radiation from the' two surfaces, one of them is foundto emit thirty-nine units of heat, while the other emits seventy-four. This, surely, is a great difference. Here, however, is a second cube, having two of its surfaces coated with the same powders, the onlydifference being that the powders are laid on by means of atransparent gum. Both surfaces are now absolutely alike in radiativepower. Both of them emit somewhat more than was emitted by either ofthe unvarnished powders, simply because the gum employed is a betterradiator than either of them. Excluding all varnish, and comparingwhite with white, vast differences are found; comparing black withblack, they are also different; and when black and white are compared, in some cases the black radiates far more than the white, while inother cases the white radiates far more than the black. Determining, moreover, the absorptive power of those powders, it is found to gohand-in-hand with their radiative power. The good radiator is a goodabsorber, and the bad radiator is a bad absorber. From all this it isevident that as regards the radiation and absorption of non-luminousheat, colour teaches us nothing; and that even as regards theradiation of the sun, consisting as it does mainly of non-luminousrays, conclusions as to the influence of colour may be altogetherdelusive. This is the strict scientific upshot of our researches. Butit is not the less true that in the case of wearing apparel--and thisfor reasons which I have given in analysing the experiments ofFranklin--black dresses are more potent than white ones as absorbersof solar heat. 

Thus, in brief outline, have been brought before you a few of theresults of recent enquiry. If you ask me what is the use of them, Ican hardly answer you, unless you define the term use. If you meantto ask whether those dark rays which clear away the Alpine snows, willever be applied to the roasting of turkeys, or the driving ofsteam-engines--while affirming their power to do both, I would franklyconfess that they are not at present capable of competing profitablywith coal in these particulars. Still they may have great usesunknown to me; and when our coal-fields are exhausted, it is possiblethat a more aethereal race than we are may cook their victuals, andperform their work, in this transcendental way. But is it necessarythat the student of science should have his labours tested by theirpossible practical applications? What is the practical value ofHomer's Iliad? You smile, and possibly think that Homer's Iliad isgood as a means of culture. There's the rub. The people who demandof science practical uses, forget, or do not know, that it also isgreat as a means of culture--that the knowledge of this wonderfuluniverse is a thing profitable in itself, and requiring no practicalapplication to justify its pursuit. 

But while the student of Nature distinctly refuses to have his laboursjudged by their practical issues, unless the term practical be made toinclude mental as well as material good, he knows full well that thegreatest practical triumphs have been episodes in the search afterpure natural truth. The electric telegraph is the standing wonder ofthis age, and the men whose scientific knowledge, and mechanicalskill, have made the telegraph what it is, are deserving of allhonour. In fact, they have had their reward, both in reputation andin those more substantial benefits which the direct service of thepublic always carries in its train. But who, I would ask, put thesoul into this telegraphic body? Who snatched from heaven the firethat flashes along the line? This, I am bound to say, was done by twomen, the one a dweller in Italy, [Footnote: Volta] the other adweller in England, [Footnote: Faraday] who never in their enquiriesconsciously set a practical object before them--whose only stimuluswas the fascination which draws the climber to a never-trodden peak, and would have made Caesar quit his victories for the sources of theNile. That the knowledge brought to us by those prophets, priests, and kings of science is what the world calls 'useful knowledge, ' thetriumphant application of their discoveries proves. But science hasanother function to fulfil, in the storing and the training of thehuman mind; and I would base my appeal to you on the specimen whichhas this evening been brought before you, whether any system ofeducation at the present day can be deemed even approximatelycomplete, in which the knowledge of Nature is neglected or ignored. 

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IV. NEW CHEMICAL REACTIONS PRODUCED BY LIGHT. 

1868-69. 

1 DECOMPOSITION BY LIGHT. 

MEASURED by their power, not to excite vision, but to produce heat--inother words, measured by their absolute energy--the ultra-red waves ofthe sun and of the electric light, as shown in the preceding articles, far transcend the visible. In the domain of chemistry, however, thereare numerous cases in which the more powerful waves are ineffectual, while the more minute waves, through what may be called theirtimeliness of application, are able to produce great effects. Aseries of these, of a novel and beautiful character, discovered in1868, and further illustrated in subsequent years, may be exhibited bysubjecting the vapours of volatile liquids to the action ofconcentrated sunlight, or to the concentrated beam of the electriclight. Their investigation led up to the discourse on 'Dust andDisease' which follows in this volume; and for this reason someaccount of them is introduced here. 

*****

A glass tube 3 feet long and 3 inches wide, which had been frequentlyemployed in my researches on radiant heat, was supported horizontallyon two stands. At one end of the tube was placed an electric lamp, the height and position of both being so arranged, that the axis ofthe tube, and that of the beam issuing from the lamp, were coincident. In the first experiments the two ends of the tube were closed byplates of rock-salt, and subsequently by plates of glass. For thesake of distinction, I call this tube the experimental tube. It wasconnected with an air-pump, and also with a series of drying and othertubes used for the purification of the air. 

A number of test-tubes, like F, fig. 2 (I have used at least fifty ofthem), were converted into Woulf's flasks. Each of them was stoppedby a cork, through which passed two glass tubes: one of these tubes(a) ended immediately below the cork, while the other (b) descended tothe bottom of the flask, being drawn out at its lower end to anorifice about 0. 03 of an inch in diameter. It was found necessary tocoat the cork carefully with cement. In the later experiments corksof vulcanised India-rubber were invariably employed. 

The little flask, thus formed, being partially filled with the liquidwhose vapour was to be examined, was introduced into the path of thepurified current Of air. The experimental tube being exhausted, andthe cock hick cut off the supply of purified air being cautiouslyturned on, the air entered the flask through the tube b, and escapedby the small orifice at the lower end of into the liquid. Throughthis it bubbled, loading itself with vapour, after which the mixed airand vapour, passing from the flask by the tube a, entered theexperimental tube, where they were subjected to the action of light. 

The whole arrangement is shown in fig. 3, where L represents theelectric lamp, ss' the experimental tube, pp' the pipe leading to theair-pump, and F the test-tube containing the volatile liquid. Thetube tt' is plugged with cotton-wool intended to intercept thefloating matter of the air; the bent tube T' contains caustic potash, the tube T sulphuric acid, the one intended to remove the carbonicacid and the other the aqueous vapour of the air. 

The power of the electric beam to reveal the existence of anythingwithin the experimental tube, or the impurities of the tube itself, isextraordinary. When the experiments is made in a darkened room, atube which in ordinary daylight appears absolutely clean, is oftenshown by the present mode of examination to be exceedingly filthy. 

The following are some of the results obtained with this arrangement:

Nitrite of amyl. The vapour of this liquid was in the first instancepermitted to enter the experimental tube, while the beam from theelectric lamp was passing through it. Curious clouds, the cause ofwhich was then unknown, were observed to form near the place of entry, being afterwards whirled through the tube. 

The tube being again exhausted, the mixed air and vapour were allowedto enter it in the dark. The slightly convergent beam of the electriclight was then sent through the mixture. For a moment the tube was_optically empty_, nothing whatever being seen within it; but before asecond had elapsed a shower of particles was precipitated on the beam. The cloud thus generated became denser as the light continued to act, slowing at some places vivid iridescence. 

The lens of the electric lamp was now placed so as to form within thetube a strongly convergent cone of rays. The tube was cleansed andagain filled in darkness. When the light was sent through it, theprecipitation upon the beam was so rapid and intense that the cone, which a moment before was invisible, flashed suddenly forth like asolid luminous spear. The effect was the same when the air and vapourwere allowed to enter the tube in diffuse daylight. The cloud, however, which shone with such extraordinary radiance under theelectric beam, was invisible in the ordinary light of the laboratory. 

The quantity of mixed air and vapour within the experimental tubecould of course be regulated at pleasure. The rapidity of the actiondiminished with the attenuation of the vapour. When, for example, themercurial column associated with the experimental tube was depressedonly five inches, the action was not nearly so rapid as when the tubewas full. In such cases, however, it was exceedingly interesting toobserve, after some seconds of waiting, a thin streamer of delicatebluish-white cloud slowly forming along the axis of the tube, andfinally swelling so as to fill it. 

Fig. 2. 

Fig. 3. 

When dry oxygen was employed to carry in the vapour the effect was thesame as that obtained with air. 

When dry hydrogen was used as a vehicle, the effect was also the same. 

The effect, therefore, is not due to any interaction between thevapour of the nitrite and its vehicle. 

This was further demonstrated by the deportment of the vapour itself. When it was permitted to enter the experimental tube unmixed with airor any other gas, the effect was substantially the same. Hence theseat of the observed action is the vapour. 

This action is not to be ascribed to heat. As regards the glass ofthe experimental tube, and the air within the tube, the beam employedin these experiments was perfectly cold. It had been sifted bypassing it through a solution of alum, and through the thickdouble-convex lens of the lamp. When the unsifted beam of the lampwas employed, the effect was still the same; the obscure calorificrays did not appear to interfere with the result. 

My object here being simply to point out to chemists a method ofexperiments which reveals a new and beautiful series of reactions, Ileft to them the examination of the products of decomposition. Thegroup of atoms forming the molecule of nitrite of amyl is obviouslyshaken asunder by certain specific waves of the electric beam, nitricoxide and other products, of which the _nitrate_ of amyl is probablyone, being the result of the decomposition. The brown fumes ofnitrous acid were seen mingling with the cloud within the experimentaltube. The nitrate of amyl, being less volatile than the nitrite, andnot being able to maintain itself in the condition of vapour, would beprecipitated as a visible cloud along the track of the beam. 

In the anterior portions of the tube a powerful sifting of the beam bythe vapour occurs, which diminishes the chemical action in theposterior portions. In some experiments the precipitated cloud onlyextended halfway down the tube. When, under these circumstances, thelamp was shifted so as to send the beam through the other end of thetube, copious precipitation occurred there also. 

Solar light also effects the decomposition of the nitrite-of-amylvapour. On October 10, 1868, I partially darkened a small room in theRoyal Institution, into which the sun shone, permitting the light toenter through an open portion of the window-shutter. In the track ofthe beam was placed a large plano-convex lens, which formed a fineconvergent cone in the dust of the room behind it. The experimentaltube was filled in the laboratory, covered with a black cloth, andcarried into the partially darkened room. On thrusting one end of thetube into the cone of rays behind the lens, precipitation within thecone was copious and immediate. The vapour at the distant end of thetube was in part shielded by that in front, and was also more feeblyacted on through the divergence of the rays. On reversing the tube, asecond and similar cone was precipitated. 

Physical Considerations. 

I sought to determine the particular portion of the light whichproduced the foregoing effects. When, previous to entering theexperimental tube, the beam was caused to pass through a red glass, the effect was greatly weakened, but not extinguished. This was alsothe case with various samples of yellow glass. A blue glass beingintroduced before the removal of the yellow or the red, on taking thelatter away prompt precipitation occurred along the track of the bluebeam. Hence, in this case, the more refrangible rays are the mostchemically active. The colour of the liquid nitrite of amyl indicatesthat this must be the case; it is a feeble but distinct yellow: inother words, the yellow portion of the beam is most freelytransmitted. It is not, however, the transmitted portion of any beamwhich produces chemical action, but the absorbed portion. Blue, asthe complementary colour to yellow, is here absorbed, and hence themore energetic action of the blue rays. 

This reasoning, however, assumes that the same rays are absorbed bythe liquid and its vapour. The assumption is worth testing. Asolution of the yellow chromate of potash, the colour of which may bemade almost, if not altogether, identical with that of the liquidnitrite of amyl, was found far more effective in stopping the chemicalrays than either the red or the yellow glass. But of all substancesthe liquid nitrite itself is most potent in arresting the rays whichact upon its vapour. A layer one-eighth of an inch in thickness, which scarcely perceptibly affected the luminous intensity, absorbedthe entire chemical energy of the concentrated beam of the electriclight. 

The close relation subsisting between a liquid and its vapour, asregards their action upon radiant heat, has been already amplydemonstrated. [Footnote: 'Phil. Trans. ' 1864; 'Heat, a Mode ofMotion, ' chap, xii; and P. 61 of this volume. ] As regards the nitriteof amyl, this relation is more specific than in the cases hithertoadduced; for here the special constituent of the beam, which provokesthe decomposition of the vapour, is shown to be arrested by theliquid. 

A question of extreme importance in molecular physics here arises:What is the real mechanism of this absorption, and where is its seat?[Footnote: My attention was very forcibly directed to this subjectsome years ago by a conversation with my excellent friend ProfessorClausius. ]

I figure, as others do, a molecule as a group of atoms, held togetherby their mutual forces, but still capable of motion among themselves. The vapour of the nitrite of amyl is to be regarded as an assemblageof such molecules. The question now before us is this: In the act ofabsorption, is it the molecules that are effective, or is it theirconstituent atoms? Is the _vis viva_ of the intercepted light-wavestransferred to the molecule as a whole, or to its constituent parts?

The molecule, as a whole, can only vibrate in virtue of the forcesexerted between it and its neighbour molecules. The intensity ofthese forces, and consequently the rate of vibration, would, in thiscase, be a Junction of the distance between the molecules. Now theidentical absorption of the liquid and of the vaporous nitrite of amylindicates an identical vibrating period on the part of liquid andvapour, and this, to my mind, amounts to an experimental proof thatthe absorption occurs in the main _within_ the molecule. For it canhardly be supposed, if the absorption were the act of the molecule asa whole, that it could continue to affect waves of the same periodafter the substance had passed from the vaporous to the liquid state. 

In point of fact, the decomposition of the nitrite of amyl is itselfto some extent an illustration of this internal molecular absorption;for were the absorption the act of the molecule as a whole, therelative motions of its constituent atoms would remain unchanged, andthere would be no mechanical cause for their separation. It isprobably the synchronism of the vibrations of one portion of themolecule with the incident waves, that enables the amplitude of thosevibrations to augment, until the chain which binds the parts of themolecule together is snapped asunder. 

I anticipate wide, if not entire, generality for the fact that aliquid and its vapour absorb the same rays. A cell of liquid chlorinewould, I imagine, deprive light more effectually of its power ofcausing chlorine and hydrogen to combine than any other filter of theluminous rays. The rays which give chlorine its colour have nothingto do with this combination, those that are absorbed by the chlorinebeing really effective rays. A highly sensitive bulb, containingchlorine and hydrogen, in the exact proportions necessary for theformation of hydrochloric acid, was placed at one end of anexperimental tube, the beam of the electric lamp being sent through itfrom the other. The bulb did not explode when the tube was filledwith chlorine, while the explosion was violent and immediate when thetube was filled with air. I anticipate for the liquid chlorine anaction similar to, but still more energetic than, that exhibited bythe gas. If this should prove to be the case, it will favour the viewthat chlorine itself is _molecular_ and not _monatomic_. 

Production of Sky-blue by the Decomposition of Nitrite of Amyl. 

When the quantity of nitrite vapour is considerable, and the lightintense, the chemical action is exceedingly rapid, the particlesprecipitated being so large as to whiten the luminous beam. Not so, however, when a well-mixed and highly attenuated vapour fills theexperimental tube. The effect now to be described was first obtainedwhen the vapour of the nitrite was derived from a portion of itsliquid which had been accidentally introduced into the passage throughwhich the dry air flowed into the experimental tube. 

In this case, the electric beam traversed the tube for several secondsbefore any action was visible. Decomposition then visibly commenced, and advanced slowly. When the light was very strong, the cloudappeared of a milky blue. When, on the contrary, the intensity wasmoderate, the blue was pure and deep. In Brücke's importantexperiments on the blue of the sky and the morning and evening red, pure mastic is dissolved in alcohol, and then dropped into water wellstirred. When the proportion of mastic to alcohol is correct, theresin is precipitated so finely as to elude the highest microscopicpower. By reflected light, such a medium appears bluish, bytransmitted light yellowish, which latter colour, by augmenting thequantity of the precipitate, can be caused to pass into orange or red. 

But the development of colour in the attenuated nitrite-of-amyl vapouris doubtless more similar to what takes place in our atmosphere. Theblue, moreover, is far purer and more sky-like than that obtained fromBruecke's turbid medium. Never, even in the skies of the Alps, have Iseen a richer or a purer blue than that attainable by a suitabledisposition of the light falling upon the precipitated vapour. 

Iodide of Allyl. --Among the liquids hitherto subjected to theconcentrated electric light, iodide of allyl, in point of rapidity andintensity of action, comes next to the nitrite of amyl. With theiodide I have employed both oxygen and hydrogen, as well as air, as avehicle, and found the effect in all cases substantially the same. Thecloud-column here was exquisitely beautiful. It revolved round theaxis of the decomposing beam; it was nipped at certain places like anhour-glass, and round the two bells of the glass delicatecloud-filaments twisted themselves in spirals. It also folded itselfinto convolutions resembling those of shells. In certain conditionsof the atmosphere in the Alps I have often observed clouds of aspecial pearly lustre; when hydrogen was made the vehicle of theiodide-of allyl vapour a similar lustre was most exquisitely shown. With a suitable disposition of the light, the purple hue ofiodine-vapour came out very strongly in the tube. 

The remark already made, as to the bearing of the decomposition ofnitrite of amyl by light on the question of molecular absorption, applies here also; for were the absorption the work of the molecule asa whole, the iodine would not be dislodged from the allyl with whichit is combined. The non-synchronism of iodine with the waves ofobscure heat is illustrated by its marvellous transparency to suchheat. May not its synchronism with the waves of light in the presentinstance be the cause of its divorce from the allyl?

Iodide of Isopropyl. --The action of light upon the vapour of thisliquid is, at first, more languid than upon iodide of allyl; indeedmany beautiful reactions may be overlooked, in consequence of thislanguor at the commencement. After some minutes' exposure, however, clouds begin to form, which grow in density and in beauty as the lightcontinues to act. In every experiments hitherto made with thissubstance the column of cloud filling the experimental tube, wasdivided into two distinct parts near the middle of the tube. In oneexperiments a globe of cloud formed at the centre, from which, rightand left, issued an axis uniting the globe with two adjacentcylinders. Both globe and cylinders were animated by a common motionof rotation. As the action continued, paroxysms of motion weremanifested; the various parts of the cloud would rush through eachother with sudden violence. During these motions beautiful andgrotesque cloud-forms were developed. At some places the nebulousmass would become ribbed so as to resemble the graining of wood; alongitudinal motion would at times generate in it a series of curved, transverse bands, the retarding influence of the sides the tubecausing an appearance resembling, on a small scale, the dirt-bands ofthe Mer de Glace. In the anterior portion of the tube those suddencommotion were most intense; here buds of cloud would sprout forth, and grow in a few seconds into perfect flower-like forms. The cloudof iodide of isopropyl had a character Of its own, and differedmaterially from all others that I had seen. A gorgeous mauve colourwas observed in the last twelve inches of the tube; the vapour ofiodine was present, and it may have been the sky-blue scattered by theprecipitated particles which, mingling with the purple of the iodine, produced the mauve. As in all other cases here adduced, the effectswere proved to be due to the light; they never occurred in darkness. 

The forms assumed by some of those actinic clouds, as I propose tocall them, in consequence of rotations and other motions, due todifferences of temperature, are perfectly astounding. I contentmyself here with a meagre description of one more of them. 

The tube being filled with the sensitive mixture, the beam was sentthrough it, the lens at the same time being so placed as to produce acone of very intense light. Two minutes elapsed before anything wasvisible; but at the end of this time a faint bluish cloud appeared tohang itself on the most concentrated portion of the beam. 

Soon afterwards a second cloud was formed five inches farther down theexperimental tube. Both clouds were united by a slender cord of thesame bluish tint as themselves. 

As the action of the light continued, the first cloud graduallyresolved itself into a series of parallel disks of exquisite delicacy, which rotated round an axis perpendicular to their surfaces, andfinally blended to a screw surface with an inclined generatrix. Thisgradually changed into a filmy funnel, from the narrow end of whichthe 'cord' extended to the cloud in advance. 

The latter also underwent slow but incessant modification. It firstresolved itself into a series of strata resembling those of theelectric discharge. After a little time, and through changes which itwas difficult to follow, both clouds presented the appearance of aseries of concentric funnels set one within the other, the interiorones being seen through the outer ones. Those of the distant cloudresembled claret-glasses in shape. As many as six funnels were thusconcentrically set together, the two series being united by thedelicate cord of cloud already referred to. Other cords and Blendertubes were afterwards formed, which coiled themselves in delicatespirals around the funnels. 

Rendering the light along the connecting-cord more intense, itdiminished in thickness and became whiter; this was a consequence ofthe enlargement of its particles. The cord finally disappeared, whilethe funnels melted into two ghost-like films, shaped like parasols. They were barely visible, being of an exceedingly delicate blue tint. They seemed woven of blue air. To compare them with cobweb or withgauze would be to liken them to something infinitely grosser thanthemselves. 

In all cases a distant candle-flame, when looked at through the cloud, was sensibly undimmed. 

2. ON THE BLUE COLOUR OF THE SKY, AND THE POLARISATION OF SKYLIGHT. 

[Footnote: In my 'Lectures on Light' (Longman), the polarisation oflight will be found briefly, but, I trust, clearly explained. ]

1869. 

After the communication to the Royal Society of the foregoing briefaccount of a new Series of Chemical Reactions produced by Light, theexperiments upon this subject were continued, the number of substancesthus acted on being considerably increased. 

I now, however, beg to direct attention to two questions glanced atincidentally in the preceding pages--the blue colour of the sky, andthe polarisation of skylight. Reserving the historic treatment of thesubject for a more fitting occasion, I would merely mention now thatthese questions constitute, in the opinion of our most eminentauthorities, the two great standing enigmas of meteorology. Indeed itwas the interest manifested in them by Sir John Herschel, in a letterof singular speculative power, addressed to myself, that caused me toenter upon the consideration of these questions so soon. 

The apparatus with which I work consists, as already stated, of aglass tube about a yard in length, and from 2. 5 to 3 inches internaldiameter. The vapour to be examined is introduced into this tube inthe manner already described, and upon it the condensed beam of theelectric lamp is permitted to act, until the neutrality or theactivity of the substance has been declared. 

It has hitherto been my aim to render the chemical action of lightupon vapours visible. For this purpose substances have been chosen, one at least of whose products of decomposition under light shall havea boiling-point so high, that as soon as the substance is formed itshall be precipitated. By graduating the quantity of the vapour, thisprecipitation may be rendered of any degree of fineness, formingparticles distinguishable by the naked eye, or far beyond the reach ofour highest microscopic powers. I have no reason to doubt thatparticles may be thus obtained, whose diameters constitute but a smallfraction of the length of a wave of violet light. 

In all cases when the vapours of the liquids employed are sufficientlyattenuated, no matter what the liquid may be, the visible actioncommences with the formation of a _blue cloud_. But here I must guardmyself against all misconception as to the use of this term. The'cloud' here referred to is totally invisible in ordinary daylight. Tobe seen, it requires to be surrounded by darkness, _it only_ beingilluminated by a powerful beam of light. This blue cloud differs inmany important particulars from the finest ordinary clouds, and mightjustly have assigned to it an intermediate position between suchclouds and true vapour. With this explanation, the term 'cloud, ' or'incipient cloud, ' or 'actinic cloud, ' as I propose to employ it, cannot, I think, be misunderstood. 

I had been endeavouring to decompose carbonic acid gas by light. Afaint bluish cloud, due it may be, or it may not be, to the residue ofsome vapour previously employed, was formed in the experimental tube. On looking across this cloud through a Nicol's prism, the line ofvision being horizontal, it was found that when the short diagonal ofthe prism was vertical, the quantity of light reaching the eye wasgreater than when the long diagonal was vertical. When a plate oftourmaline was held between the eye and the bluish cloud, the quantityof light reaching the eye when the axis of the prism was perpendicularto the axis of the illuminating beam, was greater than when the axesof the crystal and of the beam were parallel to each other. 

This was the result all round the experimental tube. Causing thecrystal of tourmaline to revolve round the tube, with its axisperpendicular to the illuminating beam, the quantity of light thatreached the eye was in all its positions a maximum. When thecrystallographic axis was parallel to the axis of the beam, thequantity of light transmitted by the crystal was a minimum. 

From the illuminated bluish cloud, therefore, polarised light wasdischarged, the direction of maximum polarisation being at rightangles to the illuminating beam; the plane of vibration of thepolarised light was perpendicular to the beam. [Footnote: This isstill an undecided point; but the probabilities are so much in itsfavour, and it is in my opinion so much preferable to have a physicalimage on which the mind can rest, that I do not hesitate to employ thephraseology in the text. ]

Thin plates of selenite or of quartz, placed between the Nicol and theactinic cloud, displayed the colours of polarised light, these coloursbeing most vivid when the line of vision was at right angles to theexperimental tube. The plate of selenite usually employed was acircle, thinnest at the centre, and augmenting uniformly in thicknessfrom the centre outwards. When placed in its proper position betweenthe Nicol and the cloud, it exhibited a system of splendidly-colouredrings. 

The cloud here referred to was the first operated upon in the mannerdescribed. It may, however, be greatly improved upon by the choice ofproper substances, and by the application, in proper quantities, ofthe substances chosen. Benzol, bisulphide of carbon, nitrite of amyl, nitrite of butyl, iodide of allyl, iodide of isopropyl, and many othersubstances may be employed. I will take the nitrite of butyl asillustrative of the means adopted to secure the best result, withreference to the present question. 

And here it may be mentioned that a vapour, which when alone, or mixedwith air in the experimental tube, resists the action of light, orshows but a feeble result of this action, may, when placed inproximity with another gas or vapour, exhibit vigorous, if not violentaction. The case is similar to that of carbonic acid gas, which, diffused in the atmosphere, resists the decomposing action of solarlight, but when placed in contiguity with chlorophyl in the leaves ofplants, has its molecules shaken asunder. 

Dry air was permitted to bubble through the liquid nitrite of butyl, until the experimental tube, which had been previously exhausted, wasfilled with the mixed air and vapour. The visible action of lightupon the mixture after fifteen minutes' exposure was slight. The tubewas afterwards filled with half an atmosphere of the mixed air andvapour, and a second half-atmosphere of air which had been permittedto bubble through fresh commercial hydrochloric acid. On sending thebeam through this mixture, the tube, for a moment, was opticallyempty. But the pause amounted only to a small fraction of a second, adense cloud being immediately precipitated upon the beam. 

This cloud began blue, but the advance to whiteness was so rapid asalmost to justify the application of the term instantaneous. Thedense cloud, looked at perpendicularly to its axis, showed scarcelyany signs of polarisation. Looked at obliquely the polarisation wasstrong. 

The experimental tube being again cleansed and exhausted, the mixedair and nitrite-of-butyl vapour was permitted to enter it until theassociated mercury column was depressed 1/10 of an inch. In otherwords, the air and vapour, united, exercised a pressure not exceeding1/300th of an atmosphere. Air, passed through a solution ofhydrochloric acid, was then added, till the mercury column wasdepressed three inches. The condensed beam of the electric light waspassed for some time through this mixture without revealing anythingwithin the tube competent to scatter the light. Soon, however, asuperbly blue cloud was formed along, the track of the beam, and itcontinued blue sufficiently long to permit of its thoroughexamination. The light discharged from the cloud, at right angles toits own length, was at first perfectly polarised. It could be totallyquenched by the Nicol. By degrees the cloud became of whitish blue, and for a time the selenite colours, obtained by looking at itnormally, were exceedingly brilliant. The direction of maximumpolarisation was distinctly at right angles to the illuminating beam. This continued to be the case as long as the cloud maintained adecided blue colour, and even for some time after the blue had changedto whitish blue. But, as the light continued to act, the cloud becamecoarser and whiter, particularly at its centre, where it at lengthceased to discharge polarised light in the direction of theperpendicular, while it continued to do so at both ends. 

But the cloud which had thus ceased to polarise the light emittednormally, showed vivid selenite colours when looked at obliquely, proving that the direction of maximum polarisation changed with thetexture of the cloud. This point shall receive further illustrationsubsequently. 

A blue, equally rich and more durable, was obtained by employing thenitrite-of-butyl vapour in a still more attenuated condition. Theinstance here cited is representative. In all cases, and with allsubstances, the cloud formed at the commencement, when theprecipitated particles are sufficiently fine, is _blue_, and it can bemade to display a colour rivalling that of the purest Italian sky. Inall cases, moreover, this fine blue cloud polarises _perfectly_ the beamwhich illuminates it, the direction of polarisation enclosing an angleof 90° with the axis of the illuminating beam. 

It is exceedingly interesting to observe both the perfection and thedecay of this polarisation. For ten or fifteen minutes after itsfirst appearance the light from a vividly illuminated actinic cloud, looked at perpendicularly, is absolutely quenched by a Nicol's prismwith its longer diagonal vertical. But as the sky-blue is graduallyrendered impure by the growth of the particles--in other words, asreal clouds begin to be formed--the polarisation begins to decay, aportion of the light passing through the prism in all its positions. It is worthy of note, that for some time after the cessation ofperfect polarisation, the residual light which passes, when the Nicolis in its position of minimum transmission, is of a gorgeous blue, thewhiter light of the cloud being extinguished. [Footnote: This showsthat particles too large to polarise the blue, polarise perfectlylight of lower refrangibility. ] When the cloud texture has becomesufficiently coarse to approximate to that of ordinary clouds, therotation of the Nicol ceases to have any sensible effect on thequantity of light discharged normally. 

The perfection of the polarisation, in a direction perpendicular tothe illuminating beam, is also illustrated by the followingexperiments: A Nicol's prism, large enough to embrace the entire beamof the electric lamp, was placed between the lamp and the experimentaltube. A few bubbles of air, carried through the liquid nitrite ofbutyl, were introduced into the tube, and they were followed by aboutthree inches (measured by the mercurial gauge) of air which had passedthrough aqueous hydrochloric acid. Sending the polarised beam throughthe tube, I placed myself in front of it, my eye being on a level withits axis, my assistant occupying a similar position behind the tube. The short diagonal of the large Nicol was in the first instancevertical, the plane of vibration of the emergent beam being thereforealso vertical. As the light continued to act, a superb blue cloud, visible to both my assistant and myself, was slowly formed. But thiscloud, so deep and rich when looked at from the positions mentioned, _utterly disappeared when looked at vertically downwards, or verticallyupwards_. Reflection from the cloud was not possible in thesedirections. When the large Nicol was slowly turned round its axis, the eye of the observer being on the level of the beam, and the lineof vision perpendicular to it, entire extinction of the light emittedhorizontally occurred when the longer diagonal of the large Nicol wasvertical. But now a vivid blue cloud was seen when looked atdownwards or upwards. This truly fine experiments, which Icontemplated making on my own account, was first definitely suggestedby a remark in a letter addressed to me by Professor Stokes. 

As regards the polarisation of skylight, the greatest stumbling-blockhas hitherto been, that, in accordance with the law of Brewster, whichmakes the index of refraction the tangent of the polarising angle, thereflection which produces perfect polarisation would require to bemade in air upon air; and indeed this led many of our most eminentmen, Brewster himself among the number, to entertain the idea ofaerial molecular reflection. [Footnote: 'The cause of thepolarisation is evidently a reflection of the sun's light uponsomething. The question is on what? Were the angle of maximumpolarisation 76°, we should look to water or ice as the reflectingbody, however inconceivable the existence in a cloudless atmosphereand a hot summer's day of unevaporated molecules (particles?) ofwater. But though we were once of this opinion, careful observationhas satisfied us that 90°, or thereabouts, is the correct angle, andthat therefore whatever be the body on which the light has beenreflected, if polarised by a single reflection, the polarising anglemust be 45°, and the index of refraction, which is the tangent of thatangle, unity; in other words, the reflection would require to be madein air upon air!' (Sir John Herschel, 'Meteorology, ' par. 233. )

Any particles, if small enough, will produce both the colour and thepolarisation of the sky. But is the existence of smallwater-particles on a hot summer's day in the higher regions of ouratmosphere inconceivable? It is to be remembered that the oxygen andnitrogen of the air behave as a vacuum to radiant heat, theexceedingly attenuated vapour of the higher atmosphere being thereforein practical contact with the cold of space. ]

I have, however, operated upon substances of widely differentrefractive indices, and therefore of very different polarising anglesas ordinarily defined, but the polarisation of the beam, by theincipient cloud, has thus far proved itself to be absolutelyindependent of the polarising angle. The law of Brewster does notapply to matter in this condition, and it rests with the undulatorytheory to explain why. Whenever the precipitated particles aresufficiently fine, no matter what the substance forming the particlesmay be, the direction of maximum polarisation is at right angles tothe illuminating beam, the polarising angle for matter in thiscondition being invariably 45°. 

Suppose our atmosphere surrounded by an envelope impervious to light, but with an aperture on the sunward side through which a parallel beamof solar light could enter and traverse the atmosphere. Surrounded byair not directly illuminated, the track of such a beam would resemblethat of the parallel beam of the electric lamp through an incipientcloud. The sunbeam would be blue, and it would discharge laterallylight in precisely the same condition as that discharged by theincipient cloud. In fact, the azure revealed by such a beam would beto all intents and purposes that which I have called a 'blue cloud. 'Conversely our 'blue cloud' is, to all intents and purposes, an_artificial sky_. ' [Footnote: The opinion of Sir John Herschel, connecting the polarisation and the blue colour of the sky, isverified by the foregoing results. 'The more the subject [thepolarisation of skylight] is considered, ' writes this eminentphilosopher, 'the more it will be found beset with difficulties, andits explanation when arrived at will probably be found to carry withit that of the blue colour of the sky itself, and of the greatquantity of light it actually does send down to us. ' 'We may observe, too, ' he adds, 'that it is only where the purity of the sky is mostabsolute that the polarisation is developed in its highest degree, andthat where there is the slightest perceptible tendency to cirrus it ismaterially impaired. ' This applies word for word to our 'incipientclouds. ']

But, as regards the polarisation of the sky, we know that not only isthe direction of maximum polarisation at right angles to the track ofthe solar beams, but that at certain angular distances, probablyvariable ones, from the sun, 'neutral points, ' or points of nopolarisation, exist, on both sides of which the planes of atmosphericpolarisation are at right angles to each other. I have made variousobservations upon this subject which are reserved for the present;but, pending the more complete examination of the question, thefollowing facts bearing upon it may be submitted. 

The parallel beam employed in these experiments tracked its waythrough the laboratory air, exactly as sunbeams are seen to do in thedusty air of London. I have reason to believe that a great portion ofthe matter thus floating in the laboratory air consists of organicparticles, which are capable of imparting a perceptibly bluish tint tothe air. These also showed, though far less vividly, all the effectsof polarisation obtained with the incipient clouds. The lightdischarged laterally from the track of the illuminating beam waspolarised, though not perfectly, the direction of maximum polarisationbeing at right angles to the beam. At all points of the beam, moreover, throughout its entire length, the light emitted normally wasin the same state of polarisation. Keeping the positions of the Nicoland the selenite constant, the same colours were observed throughoutthe entire beam, when the line of vision was perpendicular to itslength. 

The horizontal column of air, thus illuminated, was 18 feet long, andcould therefore be looked at very obliquely. I placed myself near theend of the beam, as it issued from the electric lamp, and, lookingthrough the Nicol and selenite more and more obliquely at the beam, observed the colours fading until they disappeared. Augmenting theobliquity the colours appeared once more, but they were nowcomplementary to the former ones. 

Hence this beam, like the sky, exhibited a neutral point, on oppositesides of which the light was polarised in planes at right angles toeach other. 

Thinking that the action observed in the laboratory might be caused, in some way, by the vaporous fumes diffused in its air, I had thelight removed to a room at the top of the Royal Institution. Thetrack of the beam was seen very finely in the air of this room, alength of 14 or 15 feet being attainable. This beam exhibited all theeffects observed with the beam in the laboratory. Even theuncondensed electric light falling on the floating matter showed, though faintly, the effects of polarisation. 

When the air was so sifted as to entirely remove the visible floatingmatter, it no longer exerted any sensible action upon the light, butbehaved like a vacuum. The light is scattered and polarised by_particles_, not by molecules or atoms. 

By operating upon the fumes of chloride of ammonium, the smoke ofbrown paper, and tobacco-smoke, I had varied and confirmed in manyways those experiments on neutral points, when my attention was drawnby Sir Charles Wheatstone to an important observation communicated tothe Paris Academy in 1860 by Professor Govi, of Turin. [Footnote:Comptes Rendus, ' tome li, pp. 360 and 669. ] M. Govi had been led toexamine a beam of light sent through a room in which were successivelydiffused the smoke of incense, and tobacco-smoke. His first briefcommunication stated the fact of polarisation by such smoke; but inhis second communication he announced the discovery of a neutral pointin the beam, at the opposite sides of which the light was polarised inplanes at right angles to each other. 

But unlike my observations on the laboratory air, and unlike theaction of the sky, the direction of maximum polarisation in M. Govi'sexperiments enclosed a very small angle with the axis of theilluminating beam. The question was left in this condition, and I amnot aware that M. Govi or any other investigator has pursued itfurther. 

I had noticed, as before stated, that as the clouds formed in theexperimental tube became denser, the polarisation of the lightdischarged at right angles to the beam became weaker, the direction ofmaximum polarisation becoming oblique to the beam. Experiments on thefumes of chloride of ammonium gave me also reason to suspect that theposition of the neutral point was not constant, but that it variedwith the density of the illuminated fumes. 

The examination of these questions led to the following new andremarkable results: The laboratory being well filled with the fumes ofincense, and sufficient time being allowed for their uniformdiffusion, the electric beam was sent through the smoke. From thetrack of the beam polarised light was discharged; but the direction ofmaximum polarisation, instead of being perpendicular, now enclosed anangle of only 12° or 13° with the axis of the beam. 

A neutral point, with complementary effects at opposite sides of it, was also exhibited by the beam. The angle enclosed by the axis of thebeam, and a line drawn from the neutral point to the observer's eye, measured in the first instance 66°. 

The windows of the laboratory were now opened for some minutes, aportion of the incense-smoke being permitted to escape. On againdarkening the room and turning on the light, the line of vision to theneutral point was found to enclose, with the axis of the beam, anangle of 63°. 

The windows were again opened for a few minutes, more of the smokebeing permitted to escape. Measured as before, the angle referred towas found to be 54°. 

This process was repeated three additional times the neutral point wasfound to recede lower and lower down the beam, the angle between aline drawn from the eye to the neutral point and the axis of the beamfalling successively from 54° to 49°, 43° and 33°. 

The distances, roughly measured, of the neutral point from the lamp, corresponding to the foregoing series of observations, were these:

1st observation 2 feet 2 inches. 

2nd observation 2 feet 6 inches. 

3rd observation 2 feet 10 inches. 

4th observation 3 feet 2 inches. 

5th observation 3 feet 7 inches. 

6th observation 4 feet 6 inches. 

At the end of this series of experiments the direction of maximumpolarisation had again become normal to the beam. 

The laboratory was next filled with the fumes of gunpowder. In fivesuccessive experiments, corresponding to five different densities ofthe gunpowder-smoke, the angles enclosed between the line of vision tothe neutral point and the axis of the beam, were 63 degrees, 50°, 47°, 42°, and 38° respectively. 

After the clouds of gunpowder had cleared away, the laboratory wasfilled with the fumes of common resin, rendered so dense as to be veryirritating to the lungs. The direction of maximum polarisationenclosed, in this case, an angle of 12°, or thereabouts, with the axisof the beam. Looked at, as in the former instances, from a positionnear the electric lamp, no neutral point was observed throughout theentire extent of the beam. 

When this beam was looked at normally through the selenite and Nicol, the ring-system, though not brilliant, was distinct. Keeping the eyeupon the plate of selenite, and the line of vision perpendicular, thewindows were opened, the blinds remaining undrawn. The resinous fumesslowly diminished, and as they did so the ring-system became paler. Itfinally disappeared. Continuing to look in the same direction, therings revived, but now the colours were complementary to the formerones. _The neutral point had passed me in its motion down the beam, consequent upon the attenuation of the fumes of resin_. 

With the fumes of chloride of ammonium substantially the same resultswere obtained. Sufficient, however, has been here stated toillustrate the variability of the position of the neutralpoint. [Footnote: Brewster has proved the variability of the positionof the neutral point for skylight with the sun's altitude, a resultobviously connected with the foregoing experiments. ]

By a puff of tobacco-smoke, or of condensed steam, blown into theilluminated beam, the brilliancy of the selenite colours may begreatly enhanced. But with different clouds two different effects areproduced. Let the ring-system observed in the common air be broughtto its maximum strength, and then let an attenuated cloud of chlorideof ammonium be thrown into the beam at the point looked at; the ringsystem flashes out with augmented brilliancy, but the character of thepolarisation remains unchanged. This is also the case whenphosphorus, or sulphur, is burned underneath the beam, so as to causethe fine particles of phosphorus or of sulphur to rise into the light. With the sulphur-fumes the brilliancy of the colours is exceedinglyintensified; but in none of these cases is there any change in thecharacter of the polarisation. 

But when a puff of the fumes of hydrochloric acid, hydriodic acid, ornitric acid is thrown into the beam, there is a complete reversal ofthe selenite tints. Each of these clouds twists the plane ofpolarisation 90°, causing the centre of the ring-system to change fromblack to white, and the rings themselves to emit their complementarycolours. [Footnote: Sir John Herschel suggested to me that thischange of the polarisation from positive to negative may indicate achange from polarisation by reflection to polarisation by refraction. This thought repeatedly occurred to me while looking at the effects;but it will require much following up before it emerges intoclearness. ]

Almost all liquids have motes in them sufficiently numerous topolarise sensibly the light, and very beautiful effects may beobtained by simple artificial devices. When, for example, a cell ofdistilled water is placed in front of the electric lamp, and a thinslice of the beam is permitted to pass through it, scarcely anypolarised light is discharged, and scarcely any colour produced with aplate of selenite. But if a bit of soap be agitated in the water abovethe beam, the moment the infinitesimal particles reach the light theliquid sends forth laterally almost perfectly polarised light; and ifthe selenite be employed, vivid colours flash into existence. A stillmore brilliant result is obtained with mastic dissolved in a greatexcess of alcohol. 

The selenite rings, in fact, constitute an extremely delicate test asto the collective quantity of individually invisible particles in aliquid. Commencing with distilled water, for example, a thick sliceof light is necessary to make the polarisation of its suspendedparticles sensible. A much thinner slice suffices for common water;while, with Bruecke's precipitated mastic, a slice too thin to produceany sensible effect with most other liquids, suffices to bring outvividly the selenite colours. 

3. THE SKY OF THE ALPS. 

The vision of an object always implies a differential action on theretina of the observer. The object is distinguished from surroundingspace by its excess or defect of light in relation to that space. Byaltering the illumination, either of the object itself or of itsenvironment, we alter the appearance of the object. Take the case ofclouds floating in the atmosphere with patches of blue between them. Anything that changes the illumination of either alters the appearanceof both, that appearance depending, as stated, upon differentialaction. 

Now the light of the sky, being polarised, may, as the reader of theforegoing pages knows, be in great part quenched by a Nicol's prism, while the light of a common cloud, being unpolarised, cannot be thusextinguished. Hence the possibility of very remarkable variations, not only in the aspect of the firmament, which is really changed, butalso in the aspect of the clouds, which have that firmament as abackground. It is possible, for example, to choose clouds of such adepth of shade that when the Nicol quenches the light behind them, they shall vanish, being undistinguishable from the residual dull tintwhich outlives the extinction of the brilliancy of the sky. A cloudless deeply shaded, but still deep enough, when viewed with the nakedeye, to appear dark on a bright ground, is suddenly changed to a whitecloud on a dark ground by the quenching of the light behind it. Whena reddish cloud at sunset chances to float in the region of maximumpolarisation, the quenching of the surrounding light causes it toflash with a brighter crimson. Last Easter eve the Dartmoor sky, whichhad just been cleansed by a snow-storm, wore a very wild appearance. Round the horizon it was of steely brilliancy, while reddish cumuliand cirri floated southwards. When the sky was quenched behind themthese floating masses seemed like dull embers suddenly blown upon;they brightened like a fire. 

In the Alps we have the most magnificent examples of crimson cloudsand snows, so that the effects just referred to may be here studiedunder the best possible conditions. On August 23, 1869, the eveningAlpenglow was very fine, though it did not reach its maximum depth andsplendour. The side of the Weisshorn seen from the Bel Alp, beingturned from the sun, was tinted mauve; but I wished to observe one ofthe rose-coloured buttresses of the mountain. Such a one was visiblefrom a point a few hundred feet above the hotel. The Matterhorn also, though for the most part in shade, had a crimson projection, while adeep ruddy red lingered along its western shoulder. Four distinctpeaks and buttresses of the Dom, in addition to its dominant head--allcovered with pure snow--were reddened by the light of sunset. Theshoulder of the Alphubel was similarly coloured, while the great massof the Fletschorn was all a-glow, and so was the snowy spine of theMonte Leone. 

Looking at the Weisshorn through the Nicol, the glow of itsprotuberance was strong or weak according to the position of theprism. The summit also underwent striking changes. In one positionof the prism it exhibited a pale white against a dark background; inthe rectangular position it was a dark mauve against a lightbackground. The red of the Matterhorn changed in a similar manner;but the whole mountain also passed through wonderful changes ofdefinition. The air at the time was filled with a silvery haze, inwhich the Matterhorn almost disappeared. This could be whollyquenched by the Nicol, and then the mountain sprang forth withastonishing solidity and detachment from the surrounding air. Thechanges of the Dom were still more wonderful. A vast amounts of lightcould be removed from the sky behind it, for it occupied the positionof maximum polarisation. By a little practice with the Nicol it waseasy to render the extinction of the light, or its restoration, almostinstantaneous. When the sky was quenched, the four minor peaks andbuttresses, and the summit of the Dom, together with the shoulder ofthe Alphubel, glowed as if set suddenly on fire. This was immediatelydimmed by turning the Nicol through an angle of 90°. It was not thestoppage of the light of the sky behind the mountains alone whichproduced this startling effect; the air between them and me was highlyopalescent, and the quenching of this intermediate glare augmentedremarkably the distinctness of the mountains. 

On the morning of August 24 similar effects were finely shown. At 10A. M. All three mountains, the Dom, the Matterhorn, and the Weisshorn, were powerfully affected by the Nicol. But in this instance also, theline drawn to the Dom being very nearly perpendicular to the solarbeams, the effects on this mountain were most striking. The greysummit of the Matterhorn, at the same time, could scarcely bedistinguished from the opalescent haze around it; but when the Nicolquenched the haze, the summit became instantly isolated, and stood outin bold definition. It is to be remembered that in the production ofthese effects the only things changed are the sky behind, and theluminous haze in front of the mountains; that these are changedbecause the light emitted from the sky and from the haze is planepolarised light, and that the light from the snows and from themountains, being sensibly unpolarised, is not directly affected by theNicol. It will also be understood that it is not the interposition ofthe haze _as an opaque body_ that renders the mountains indistinct, butthat it is the _light_ of the haze which dims and bewilders the eye, andthus weakens the definition of objects seen through it. 

These results have a direct bearing upon what artists call 'aerialperspective. ' As we look from the summit of Mont Blanc, or from alower elevation, at the serried crowd of peaks, especially if themountains be darkly coloured--covered with pines, for example--everypeak and ridge is separated from the mountains behind it by a thinblue haze which renders the relations of the mountains as to distanceunmistakable. When this haze is regarded through the Nicolperpendicular to the sun's rays, it is in many cases wholly quenched, because the light which it emits in this direction is whollypolarised. When this happens, aerial perspective is abolished, andmountains very differently distant appear to rise in the same verticalplane. Close to the Bel Alp for instance, is the gorge of the Massa, and beyond the gorge is a high ridge darkened by pines. This ridgemay be projected upon the dark slopes at the opposite side of theRhone valley, and between both we have the blue haze referred to, throwing the distant mountains far away. But at certain hours of theday the haze may be quenched, and then the Massa ridge and themountains beyond the Rhone seem almost equally distant from the eye. The one appears, as it were, a vertical continuation of the other. Thehaze varies with the temperature and humidity of the atmosphere. Atcertain times and places it is almost as blue as the sky itself; butto see its colour, the attention must be withdrawn from the mountainsand from the trees which cover them. In point of fact, the haze is apiece of more or less perfect sky; it is produced in the same manner, and is subject to the same laws, as the firmament itself. We live _in_the sky, not _under_ it. 

These points were further elucidated by the deportment of theselenite, plate, with which the readers of the foregoing pagesare so well acquainted. On some of the sunny days of August thehaze in the valley of the Rhone, as looked at from the Bel Alp, was very remarkable. Towards evening the sky above the mountainsopposite to my place of observation yielded a series of the mostsplendidly-coloured iris-rings; but on lowering the selenite until ithad the darkness of the pines at the opposite side of the Rhone'valley, instead of the darkness of space, as a background, thecolours were not much diminished in brilliancy. I should estimate thedistance across the valley, as the crow flies, to the oppositemountain, at nine miles; so that a body of air of this thickness can, under favourable circumstances, produce chromatic effects ofpolarisation almost as vivid as those produced by the sky itself. 

Again: the light of a landscape, as of most other things, consists oftwo parts; the one, coming purely from superficial reflection, isalways of the same colour as the light which falls upon the landscape;the other part reaches us from a certain depth within the objectswhich compose the landscape, and it is this portion of the total lightwhich gives these objects their distinctive colours. The white lightof the sun enters all substances to a certain depth, and is partlyejected by internal reflection; each distinct substance absorbing andreflecting the light, in accordance with the laws of its own molecularconstitution. Thus the solar light is _sifted_ by the landscape, whichappears in such colours and variations of colour as, after the siftingprocess, reach the observer's eye. Thus the bright green of grass, orthe darker colour of the pine, never comes to us alone, but is alwaysmingled with an amounts of light derived from superficial reflection. A certain hard brilliancy is conferred upon the woods and meadows bythis superficially-reflected light. Under certain circumstances, itmay be quenched by a Nicol's prism, and we then obtain the true colourof the grass and foliage. Trees and meadows, thus regarded, exhibit arichness and softness of tint which they never show as long as thesuperficial light is permitted to mingle with the true interioremission. The needles of the pines show this effect very well, large-leaved trees still better; while a glimmering field of maizeexhibits the most extraordinary variations when looked at through therotating Nicol. 

Thoughts and questions like those here referred to took me, in August1869, to the top of the Aletschhorn. The effects described in theforegoing paragraphs were for the most part reproduced on the summitof the mountain. I scanned the whole of the sky with my Nicol. Bothalone, and in conjunction with the selenite, it pronounced theperpendicular to the solar beams to be the direction of maximumpolarisation. 

But at no portion of the firmament was the polarisation complete. Theartificial sky produced in the experiments recorded in the precedingpages could, in this respect, be rendered far more perfect than thenatural one; while the gorgeous 'residual blue' which makes itsappearance when the polarisation of the artificial sky ceases to beperfect, was strongly contrasted with the lack-lustre hue which, inthe case of the firmament, outlived the extinction of the brilliancy. With certain substances, however, artificially treated, this dullresidue may also be obtained. 

All along the arc from the Matterhorn to Mont Blanc the light of thesky immediately above the mountains was powerfully acted upon by theNicol. In some cases the variations of intensity were astonishing. Ihave already said that a little practice enables the observer to shiftthe Nicol from one position to another so rapidly as to render thealternative extinction and restoration of the light immediate. Whenthis was done along the arc to which I have referred, the alternationsof light and darkness resembled the play of sheet lightning behind themountains. There was an element of awe connected with the suddennesswith which the mighty masses, ranged along the line referred to, changed their aspect and definition under the operation of the prism. 

*****

The physical reason of the blueness of both natural and artificialskies is, I trust, correctly given in the essay on the Scientific useof the Imagination published in the second volume of these Fragments. 

********************

V. ON DUST AND DISEASE. 

[Footnote: A discourse delivered before the Royal Institution of GreatBritain, January 21, 1870. ]

Experiments on Dusty Air. 

SOLAR light, in passing through a dark room, reveals its track byilluminating the dust floating in the air. 'The sun, ' says DanielCulverwell, 'discovers atomes, though they be invisible bycandle-light, and makes them dance naked in his beams. '

In my researches on the decomposition of vapours by light, I wascompelled to remove these 'atoms' and this dust. It was essential thatthe space containing the vapours should embrace no visible thing--thatno substance capable of scattering light in the slightest sensibledegree should, at the outset of an experiments, be found in the wide'experimental tube' in which the vapour was enclosed. 

For a long time I was troubled by the appearance there of floatingmatter, which, though invisible in diffuse daylight, was at oncerevealed by a powerfully condensed beam. Two U-tubes were placed insuccession in the path of the air, before it entered the liquid whosevapour was to be carried into the experimental tube. One of theU-tubes contained fragments of marble wetted with a strong solution ofcaustic potash; the other, fragments of glass wetted with concentratedsulphuric acid which, while yielding no vapour of its own, powerfullyabsorbs the aqueous vapour of the air. [Footnote: The apparatus isfigured in Fig. 3. ] To my astonishment, the air of the RoyalInstitution, sent through these tubes at a rate sufficiently slow todry it, and to remove its carbonic acid, carried into the experimentaltube a considerable amounts of mechanically suspended matter, whichwas illuminated when the beam passed through the tube. The effect wassubstantially the same when the air was permitted to bubble throughthe liquid acid, and through the solution of potash. 

I tried to intercept this floating matter in various ways; and onOctober 5, 1868, prior to sending the air through the dryingapparatus, it was carefully permitted to pass over the tip of aspirit-lamp flame. The floating matter no longer appeared, havingbeen burnt up by the flame. It was therefore _organic matter_. I wasby no means prepared for this result; having previously thought thatthe dust of our air was, in great part, inorganic and non-combustible. [Footnote: According to an analysis kindly furnished to me by Dr. Percy, the dust collected _from the walls_ of the British Museumcontains fully 50 per cent. Of inorganic matter. I have everyconfidence in the results of this distinguished chemist; they showthat the _floating_ dust of our rooms is, as it were, winnowed from theheavier matter. As bearing directly upon this point I may quote thefollowing passage from Pasteur: 'Mais ici se présente une remarque: lapoussière que Pon trouve à la surface de tous les corps est soumiseconstamment à des courants d'air, qui doivent soulever des particulesles plus légères, au nombre desquelles se trouvent, sans doute, depréférence les corpuscules organisés, oeufs ou spores, moins lourdsgénéralement que les particules minérales. ']

I had constructed a small gas-furnace, now much employed by chemists, containing a platinum tube, which could be heated to vivid redness. [Footnote: Pasteur was, I believe, the first to employ such a tube. ]The tube contained a roll of platinum gauze, which, while it permittedthe air to pass through it, ensured the practical contact of the dustwith the incandescent metal. The air of the laboratory was permittedto enter the experimental tube, sometimes through the cold, andsometimes through the heated, tube of platinum. In the first columnof the following fragment of a long table the quantity of air operatedon is expressed by the depression of the mercury gauge of theair-pump. In the second column the condition of the platinum tube ismentioned, and in the third the state of the air in the experimentaltube. 

Quantity of air State of platinum tube State of experimental tube

15 inches Cold Full of particles. 

30 inches Red-hot Optically empty. 

The phrase 'optically empty' shows that when the conditions of perfectcombustion were present, the floating matter totally disappeared. 

*****

In a cylindrical beam, which strongly illuminated the dust of thelaboratory, I placed an ignited spirit-lamp. Mingling with the flame, and round its rim, were seen curious wreaths of darkness resembling anintensely black smoke. On placing the flame at some distance belowthe beam, the same dark masses stormed upwards. They were blackerthan the blackest smoke ever seen issuing from the funnel of asteamer; and their resemblance to smoke was so perfect as to lead themost practised observer to conclude that the apparently pure flame ofthe alcohol lamp required but a beam of sufficient intensity to revealits clouds of liberated carbon. But is the blackness smoke? Thisquestion presented itself in a moment and was thus answered: A red-hotpoker was placed underneath the beam: from it the black wreaths alsoascended. A large hydrogen flame was next employed, and it producedthose whirling masses of darkness, far more copiously than either thespirit-flame or poker. Smoke was therefore out of the question. [Footnote: In none of the public rooms of the United States where Ihad the honour to lecture was this experiment made. The organic dustwas too scanty. Certain rooms in England--the Brighton Pavilion, forexample--also lack the necessary conditions. ]

What, then, was the blackness? It was simply that of stellar space;that is to say, blackness resulting from the absence from the track ofthe beam of all matter competent to scatter its light. When the flamewas placed below the beam the floating matter was destroyed _in situ_;and the air, freed from this matter, rose into the beam, jostled asidethe illuminated particles, and substituted for their light thedarkness due to its own perfect transparency. Nothing could moreforcibly illustrate the invisibility of the agent which renders allthings visible. The beam crossed, unseen, the black chasm formed bythe transparent air, while, at both sides of the gap, the thick-strewnparticles shone out like a luminous solid under the powerfulillumination. 

It is not, however, necessary to burn the particles to produce astream of darkness. Without actual combustion, currents may begenerated which shall displace the floating matter, and appear darkamid the surrounding brightness. I noticed this effect first onplacing a red-hot copper ball below the beam, and permitting it toremain there until its temperature had fallen below that of boilingwater. The dark currents, though much enfeebled, were still produced. They may also be produced by a flask filled with hot water. 

To study this effect a platinum wire was stretched across the beam, the two ends of the wire being connected with the two poles of avoltaic battery. To regulate the strength of the current a rheostatwas placed in the circuit. Beginning with a feeble current thetemperature of the wire was gradually augmented; but long before itreached the heat of ignition, a flat stream of air rose from it, whichwhen looked at edgeways appeared darker and sharper than one of theblackest lines of Fraunhofer in the purified spectrum. Right and leftof this dark vertical band the floating matter rose upwards, boundingdefinitely the non-luminous stream of air. What is the explanation?Simply this: The hot wire rarefied the air in contact with it, but itdid not equally lighten the floating matter. The convection currentof pure air therefore passed upwards among the inert particles, dragging them after it right and left, but forming between them animpassable black partition. This elementary experiments enables us torender an account of the dark currents produced by bodies at atemperature below that of combustion. 

But when the platinum wire is intensely heated, the floating matter isnot only displaced, but destroyed. I stretched a wire about 4 incheslong through the air of an ordinary glass shade resting oncotton-wool, which also surrounded the rim. The wire being raised toa white heat by an electric current, the air expanded, and some of itwas forced through the cotton-wool. When the current was interrupted, and the air within the shade cooled, the returning air did not carrymotes along with it, being filtered by the wool. At the beginning ofthis experiments the shade was charged with floating matter; at theend of half an hour it was optically empty. 

On the wooden base of a cubical glass shade, a cubic foot in volume, upright supports were fixed, and from one support to the other 38inches of platinum wire were stretched in four parallel lines. Theends of the platinum wire were soldered to two stout copper wireswhich passed through the base of the shade and could be connected witha battery. As in the last experiments the shade rested uponcotton-wool. A beam sent through the shade revealed the suspendedmatter. The platinum wire was then raised to whiteness. In fiveminutes there was a sensible diminution of the matter, and in tenminutes it was totally consumed. 

Oxygen, hydrogen, nitrogen, carbonic acid, so prepared as to excludeall floating particles, produce, when poured or blown into the beam, the darkness of stellar space. Coal-gas does the same. An ordinaryglass shade, placed in the air with its mouth downwards, permits thetrack of the beam to be seen crossing it. When coal-gas or hydrogenis allowed to enter the shade by a tube reaching to its top, the gasgradually fills the shade from above downwards. As soon as itoccupies the space crossed by the beam, the luminous track isabolished. Lifting the shade so as to bring the common boundary ofgas and air above the beam, the track flashes forth. After the shadeis full, if it be inverted, the pure gas passes upwards like a blacksmoke among the illuminated particles. 

The Germ Theory of Contagious Disease. 

There is no respite to our contact with the floating matter of theair; and the wonder is, not that we should suffer occasionally fromits presence, but that so small a portion of it, and even that butrarely diffused over large areas, should appear to be deadly to man. And what is this portion? It was some time ago the current beliefthat epidemic diseases generally were propagated by a kind of malaria, which consisted of organic matter in a state of motor-decay; that whensuch matter was taken into the body through the lungs, skin, orstomach, it had the power of spreading there the destroying process bywhich itself had been assailed. Such a power was visibly exerted inthe case of yeast. A little leaven was seen to leaven the wholelump--a mere speck of matter, in this supposed state of decomposition, being apparently competent to propagate indefinitely its own decay. Why should not a bit of rotten malaria act in a similar manner withinthe human frame? In 1836 a very wonderful reply was given to thisquestion. In that year Cagniard de la Tour discovered theyeast-plant--a living organism, which when placed in a proper mediumfeeds, grows, and reproduces itself, and in this way carries on theprocess which we name fermentation. By this striking discoveryfermentation was connected with organic growth. 

Schwann, of Berlin, discovered the yeast-plant independently about thesame time; and in February, 1837, he also announced the importantresult, that when a decoction of meat is effectually screened fromordinary air, and supplied solely with calcined air, putrefactionnever sets in. Putrefaction, therefore, he affirmed to be caused, notby the air, but by something which could be destroyed by asufficiently high temperature. The results of Schwann were confirmedby the independent experiments of Helmholtz, Ure, and Pasteur, whileother methods, pursued by Schultze, and by Schroeder and Dusch, led tothe same result. 

But as regards fermentation, the minds of chemists, influencedprobably by the great authority of Gay-Lussac, fell back upon the oldnotion of matter in a state of decay. It was not the livingyeast-plant, but the dead or dying parts of it, which, assailed byoxygen, produced the fermentation. Pasteur, however, proved the real'ferments, ' mediate or immediate, to be organised beings which find inthe reputed ferments their necessary food. 

Side by side with these researches and discoveries, and fortified bythem and others, has run the germ theory of epidemic disease. Thenotion was expressed by Kircher, and favoured by Linnaeus, thatepidemic diseases may be due to germs which float in the atmosphere, enter the body, and produce disturbance by the development within thebody of parasitic life. The strength of this theory consists in theperfect parallelism of the phenomena of contagious disease with thoseof life. As a planted acorn gives birth to an oak, competent toproduce a whole crop of acorns, each gifted with the power ofreproducing its parent tree; and as thus from a single seedling awhole forest may spring; so, it is contended, these epidemic diseasesliterally plant their seeds, grow, and shake abroad new germs, which, meeting in the human body their proper food and temperature, finallytake possession of whole populations. There is nothing to myknowledge in pure chemistry which resembles the power of propagationand self-multiplication possessed by the matter which producesepidemic disease. If you sow wheat you do not get barley; if you sowsmall-pox you do not get scarlet-fever, but small-pox indefinitelymultiplied, and nothing else. The matter of each contagious diseasereproduces itself as rigidly as if it were (as Miss Nightingale putsit) dog or cat. 

Parasitic Diseases of Silkworms. Pasteur's Researches. 

It is admitted on all hands that some diseases are the product ofparasitic growth. Both in man and in lower creatures, the existenceof such diseases has been demonstrated. I am enabled to lay beforeyou an account of an epidemic of this kind, thoroughly investigatedand successfully combated by M. Pasteur. For fifteen years a plaguehad raged among the silkworms of France. They had sickened and diedin multitudes, while those that succeeded in spinning their cocoonsfurnished only a fraction of the normal quantity of silk. In 1853 thesilk culture of France produced a revenue of one hundred and thirtymillions of francs. During the twenty previous years the revenue haddoubled itself, and no doubt was entertained as to its furtheraugmentation. The weight of the cocoons produced in 1853 was26, 000, 000 kilogrammes; in 1865 it had fallen to 4, 000, 000, the fallentailing, in a single year, a loss of 100, 000, 000 francs. 

The country chiefly smitten by this calamity happened to be that ofthe celebrated chemist Dumas, now perpetual secretary of the FrenchAcademy of Sciences. He turned to his friend, colleague, and pupil, Pasteur, and besought him, with an earnestness which the circumstancesrendered almost personal, to undertake the investigation of themalady. Pasteur at this time had never seen a silkworm, and he urgedhis inexperience in reply to his friend. But Dumas knew too well thequalities needed for such an enquiry to accept Pasteur's reason fordeclining it. 'Je mets, ' said he, 'un prix extréme à voir votreattention fixée sur la question qui intéresse mon pauvre pays; lamisére surpasse tout ce que vous pouvez imaginer. ' Pamphlets about theplague had been showered upon the public, the monotony of waste paperbeing broken, at rare intervals, by a more or less useful publication. 'The Pharmacopoeia of the Silkworm, ' wrote M. Cornalia in 1860, 'isnow as complicated as that of man. Gases, liquids, and solids havebeen laid under contribution. From chlorine to sulphurous acid, fromnitric acid to rum, from sugar to sulphate of quinine, --all has beeninvoked in behalf of this unhappy insect. ' The helpless cultivators, moreover, welcomed with ready trustfulness every new remedy, if onlypressed upon them with sufficient hardihood. It seemed impossible todiminish their blind confidence in their blind guides. In 1863 theFrench Minister of Agriculture signed an agreement to pay 500, 000francs for the use of a remedy, which its promoter declared to beinfallible. It was tried in twelve different departments of France, and found perfectly useless. In no single instance was it successful. It was under these circumstances that M. Pasteur, yielding to theentreaties of his friend, betook himself to Alais in the beginning ofJune, 1865. As regards silk husbandry, this was the most importantdepartment in France, and it was the most sorely smitten by theplague. 

The silkworm had been previously attacked by muscardine, a diseaseproved by Bassi to be caused by a vegetable parasite. This malady waspropagated annually by the parasitic spores. Wafted by winds theyoften sowed the disease in places far removed from the centre ofinfection. Muscardine is now said to be very rare, a deadlier maladyhaving taken its place. This new disease is characterised by theblack spots which cover the silkworms; hence the name _pébrine_, firstapplied to the plague by M. De Quatrefages, and adopted by Pasteur. _pébrine_ declares itself in the stunted and unequal growth of theworms, in the languor of their movements, in their fastidiousness asregards food, and in their premature death. The course of discoveryas regards the epidemic is this: In 1849 Guérin Méneville noticed inthe blood of silkworms vibratory corpuscles, which he supposed fromtheir motions to be endowed with independent life. Filippi, however, showed that the motion of the corpuscles was the well-known Brownianmotion; but he committed the error of supposing the corpuscles to benormal to the life of the insect. Possessing the power of indefiniteself-multiplication, they are really the cause of its mortality--theform and substance of its disease. This was well described byCornalia; while Lebert and Frey subsequently found the corpuscles notonly in the blood, but in all the tissues of the insect. Osimo, in1857, discovered them in the eggs; and on this observation Vittadianifounded, in 1859, a practical method of distinguishing healthy fromdiseased eggs. The test often proved fallacious, and it was neverextensively applied. 

These living corpuscles take possession of the intestinal canal, andspread thence throughout the body of the worm. They fill the silkcavities, the stricken insect often going automatically through themotions of spinning, without any material to work upon. Its organs, instead of being filled with the clear viscous liquid of the silk, arepacked to distension by the corpuscles. On this feature of the plaguePasteur fixed his entire attention. The cycle of the silkworm's lifeis briefly this: From the fertile egg comes the little worm, whichgrows, and casts its skin. This process of moulting is repeated twoor three times at intervals during the life of the insect. After thelast moulting the worm climbs the brambles placed to receive it, andspins among them its cocoon. It passes thus into a chrysalis; thechrysalis becomes a moth, and the moth, when liberated, lays the eggswhich form the starting-point of a new cycle. Now Pasteur proved thatthe plague-corpuscles might be incipient in the egg, and escapedetection; they might also be germinal in the worm, and still bafflethe microscope. But as the worm grows, the corpuscles grow also, becoming larger and more defined. In the aged chrysalis they are morepronounced than in the worm; while in the moth, if either the egg orthe worm from which it comes should have been at all stricken, thecorpuscles infallibly appear, offering no difficulty of detection. This was the first great point made out in 1865 by Pasteur. TheItalian naturalists, as aforesaid, recommended the examination of theeggs before risking their incubation. Pasteur showed that both eggsand worms might be smitten, and still pass muster, the culture of sucheggs or such worms being sure to entail disaster. He made the mothhis starting-point in seeking to regenerate the race. 

Pasteur made his first communication on this subject to the Academy ofSciences in September, 1865. It raised a cloud of criticism. Here, forsooth, was a chemist rashly quitting his proper _métier_ andpresuming to lay down the law for the physician and biologist on asubject which was eminently theirs. 'On trouva étrange que je fussesi peu au courant de la question; on m'opposa des travaux qui avaientparu depuis longtemps en Italie, dont les résultats montraientl'inutilité de mes efforts, et l'impossibilité d'arriver à un résultatpratique dans la direction que je m'étais engagé. Que mon ignorancefut grande au sujet des recherches sans nombre qui avaient paru depuisquinze années. ' Pasteur heard the buzz, but he continued his work. Inchoosing the eggs intended for incubation, the cultivators selectedthose produced in the successful 'educations' of the year. But theycould not understand the frequent and often disastrous failures oftheir selected eggs; for they did not know, and nobody prior toPasteur was competent to tell them, that the finest cocoons mayenvelope doomed corpusculous moths. It was not, however, easy to makethe cultivators accept new guidance. To strike their imagination, andif possible determine their practice, Pasteur hit upon the expedientof prophecy. In 1866 he inspected, at St. Hippolyte-du-Fort, fourteendifferent parcels of eggs intended for incubation. Having examined asufficient number of the moths which produced these eggs, he wrote outthe prediction of what would occur in 1867, and placed the prophecy asa sealed letter in the hands of the Mayor of St. Hippolyte. 

In 1867 the cultivators communicated to the mayor their results. Theletter of Pasteur was then opened and read, and it was found that intwelve out of fourteen cases there was absolute conformity between hisprediction and the observed facts. Many of the groups had perishedtotally; the others had perished almost totally; and this was theprediction of Pasteur. In two out of the fourteen cases, instead ofthe prophesied destruction, half an average crop was obtained. Now, the parcels of eggs here referred to were considered healthy by theirowners. They had been hatched and tended in the firm hope that thelabour expended on them would prove remunerative. The application ofthe moth-test for a few minutes in 1866, would have saved the labourand averted the disappointment. Two additional parcels of eggs wereat the same time submitted to Pasteur. He pronounced them healthy;and his words were verified by the production of an excellent crop. Other cases of prophecy still more remarkable, because morecircumstantial, are recorded in Pasteur's work. 

Pasteur subjected the development of the corpuscles to a searchinginvestigation, and followed out with admirable skill and completenessthe various modes by which the plague was propagated. From mothsperfectly free from corpuscles he obtained healthy worms, andselecting 10, 20, 30, 50, as the case might be, he introduced into theworms the corpusculous matter. It was first permitted to accompany thefood. Let its take a single example out of many. Rubbing up a smallcorpusculous worm in water, he smeared the mixture over themulberry-leaves. Assuring himself that the leaves had been eaten, hewatched the consequences from day to day. Side by side with theinfected worms he reared their fellows, keeping them as much aspossible out of the way of infection. These constituted his 'lottémoin, '--his standard of comparison. On April 16, 1868, he thusinfected thirty worms. Up to the 23rd they remained quite well. On the25th they seemed well, but on that day corpuscles were found in theintestines of two of them. On the 27th, or eleven days after theinfected repast, two fresh worms were examined, and not only was theintestinal canal found in each case invaded, but the silk organ itselfwas charged with corpuscles. On the 28th the twenty-six remainingworms were covered by the black spots of _pébrine_. On the 30th thedifference of size between the infected and non-infected worms wasvery striking, the sick worms being not more than two-thirds of thebulk of the healthy ones. On May 2 a worm which had just finished itsfourth moulting was examined. Its whole body was so filled with theparasite as to excite astonishment that it could live. 

The disease advanced, the worms died and were examined, and on May 11only six out of the thirty remained. They were the strongest of thelot, but on being searched they also were found charged withcorpuscles. Not one of the thirty worms had escaped; a single meal hadpoisoned them all. The standard lot, on the contrary, spun their finecocoons, two only of their moths being proved to contain any trace ofthe parasite, which had doubtless been introduced during the rearingof the worms. 

As his acquaintance with the subject increased, Pasteur's desire forprecision augmented, and he finally counted the growing number ofcorpuscles seen in the field of his microscope from day to day. Aftera contagious repast the number of worms containing the parasitegradually augmented until finally it became cent. Per cent. The numberof corpuscles would at the same time rise from 0 to 1, to 10, to 100, and sometimes even to 1, 000 or 1, 500 in the field of his microscope. He then varied the mode of infection. He inoculated healthy worms withthe corpusculous matter, and watched the consequent growth of thedisease. He proved that the worms inoculate each other by theinfliction of visible wounds with their claws. In various cases hewashed the claws, and found corpuscles in the water. He demonstratedthe spread of infection by the simple association of healthy anddiseased worms. By their claws and their dejections, the diseasedworms spread infection. It was no hypothetical infected medium--noproblematical pythogenic gas--that killed the worms, but a definiteorganism. The question of infection at a distance was also examined, and its existence demonstrated. As might be expected from Pasteur'santecedents, the investigation was exhaustive, the skill and beauty ofhis manipulation finding fitting correlatives in the strength andclearness of his thought. 

The following quotation from Pasteur's work clearly shows the relationin which his researches stand to the important question on which hewas engaged:

*****

Place (he says) the most skilful educator, even the most expertmicroscopist, in presence of large educations which present thesymptoms described in our experiments; his judgment will necessarilybe erroneous if he confines himself to the knowledge which preceded myresearches. The worms will not present to him the slightest spot of_pébrine_; the microscope will not reveal the existence of corpuscles;the mortality of the worms will be null or insignificant; and thecocoons leave nothing to be desired. Our observer would, therefore, conclude without hesitation that the eggs produced will be good forincubation. The truth is, on the contrary, that all the worms ofthese fine crops have been poisoned; that from the beginning theycarried in them the germ of the malady; ready to multiply itselfbeyond measure in the chrysalides and the moths, thence to pass intothe eggs and smite with sterility the next generation. And what isthe first cause of the evil concealed under so deceitful an exterior?In our experiments we can, so to speak, touch it with our fingers. Itis entirely the effect of a single corpusculous repast; an effect moreor less prompt according to the epoch of life of the worm that haseaten the poisoned food. 

*****

Pasteur describes in detail his method of securing healthy eggs. Itis nothing less than a mode of restoring to France her ancient silkhusbandry. The justification of his work is to be found in thereports which reached him of the application and the unparalleledsuccess of his method, while editing his researches for finalpublication. In both France and Italy his method has been pursuedwith the most surprising results. But it was an up-hill fight whichled to this triumph. 

'Ever, ' he says, 'since the commencement of these researches, I havebeen exposed to the most obstinate and unjust contradictions; but Ihave made it a duty to leave no trace of these conflicts in thisbook. ' And in reference to parasitic diseases, generally, he uses thefollowing weighty words: 'Il est au pouvoir de l'homme de fairedisparaitre de la surface du globe les maladies parasitaires, si, comme c'est ma conviction, la doctrine des générations spontanées estune chimère. '

Pasteur dwells upon the ease with which an island like Corsica mightbe absolutely isolated from the silkworm epidemic. And with regard toother epidemics, Mr. Simon describes an extraordinary case of insularexemption, for the ten years extending from 1851 to 1860. Of the 627registration districts of England, one only had an entire escape fromdiseases which, in whole or in part, were prevalent in all the others:'In all the ten years it had not a single death by measles, nor asingle death by small-pox, nor a single death by scarlet-fever. Andwhy? Not because of its general sanitary merits, for it had anaverage amounts of other evidence of unhealthiness. Doubtless, thereason of its escape was that it was insular. It was the district ofthe Scilly Isles; to which it was most improbable that any febrilecontagion should come from without. And its escape is anapproximative proof that, at least for those ten years, no _contagium_of measles, nor any _contagium_ of scarlet-fever, nor any _contagium_ ofsmallpox had arisen spontaneously within its limits. ' It may be addedthat there were only seven districts in England in which no death fromdiphtheria occurred, and that, of those seven districts, the districtof the Scilly Isles was one. 

A second parasitic disease of silkworms, called in France _laFlacherie_, co-existent with _pébrine_, but quite distinct from it, hasalso been investigated by Pasteur. Enough, however, has been said tosend the reader interested in these questions to the original volumesfor further information. To one important practical point M. Pasteur, in a letter to myself, directs attention:

*****

Permettez-moi de terminer ces quelques lignes que je dois dicter, vaincu que je suis par la maladie, en vous faisant observer que vousrendriez service aux Colonies de la Grande-Bretagne en répandant laconnaissance de ce livre, et des principes que j'établis touchant lamaladie des vers à soie. Beaucoup de ces colonies pourraient cultiverle mûrier avec succés, et, en jetant les yeux sur mon ouvrage, vousvous convaincrez aisement qu'il est facile aujourd'hui, nonseulementd'éloigner la maladie régnante, mais en outre de donner aux récoltesde la soie une prospérité qu'elles n'ont jamais eue. 

Origin and Propagation of Contagious Matter. 

Prior to Pasteur, the most diverse and contradictory opinions wereentertained as to the contagious character of _pébrine_; some stoutlyaffirmed it, others as stoutly denied it. But on one point all wereagreed. I They believed in the existence of a deleterious medium, rendered epidemic by some occult and mysterious influence, to whichwas attributed the cause of the disease. ' Those acquainted with ourmedical literature will not fail to observe an instructive analogyhere. We have on the one side accomplished writers ascribing epidemicdiseases to 'deleterious media' which arise spontaneously in crowdedhospitals and ill-smelling drains. According to them, the _contagia_ ofepidemic disease are formed _de novo_ in a putrescent atmosphere. Onthe other side we have writers, clear, vigorous, with well-definedideas and methods of research, contending that the matter whichproduces epidemic disease comes always from a parent stock. Itbehaves as germinal matter, and they do not hesitate to regard it assuch. They no more believe in the spontaneous generation of suchdiseases, than they do in the spontaneous generation of mice. Pasteur, for example, found that _pébrine_ had been known for an indefinite timeas a disease among silkworms. The development of it which he combatedwas merely the expansion of an already existing power--the burstinginto open conflagration of a previously smouldering fire. There isnothing surprising in this. For though epidemic disease requires aspecial _contagium_ to produce it, surrounding conditions must have apotent influence on its development. Common seeds may be duly sown, but the conditions of temperature and moisture may be such as torestrict, or altogether prevent, the subsequent growth. Looked at, therefore, from the point of view of the germ theory, the exceptionalenergy which epidemic disease from time to time exhibits, is inharmony with the method of Nature. We sometimes hear diphtheriaspoken of as if it were a new disease of the last twenty years; butMr. Simon tells me that about three centuries ago tremendous epidemicsof it began to rage in Spain (where it was named _Garrotillo_), and soonafterwards in Italy; and that since that time the disease has beenwell known to all successive generations of doctors. In or about1758, for instance, Dr. Starr, of Liskeard, in a communication to theRoyal Society, particularly described the disease, with all thecharacters which have recently again become familiar, but under thename of _morbus strangulatorius_, as then severely epidemic in Cornwall. This fact is the more interesting, as diphtheria, in its more modernreappearance, again showed predilection for that remote county. Manyalso believe that the Black Death, of five centuries ago, hasdisappeared as mysteriously as it came; but Mr. Simon finds that it isbelieved to be prevalent at this hour in some of the north-westernparts of India. 

Let me here state an item of my own experience. When I was at the BelAlp in 1869, the English chaplain received letters informing him ofthe breaking out of scarlet-fever among his children. He lived, if Iremember rightly, on the healthful eminence of Dartmoor, and it wasdifficult to imagine how scarlet-fever could have been wafted to theplace. A drain ran close to his house, and on it his suspicions weremanifestly fixed. Some of our medical writers would fortify him inthis notion, and thus deflect him from the truth, while those ofanother, and, in my opinion, a wiser school, would deny to a drain, however foul, the power of generating _de novo_ a specific disease. After close enquiry he recollected that a hobby-horse had been usedboth by his boy and another, who, a short time previously, had passedthrough scarlet-fever. 

Drains and cesspools, indeed, are by no means in such evil odour asthey used to be. A fetid Thames and a low death-rate occur from timeto time together in London. For, if the special matter or germs ofepidemic disorder be not present, a corrupt atmosphere, howeverobnoxious otherwise, will not produce the disorder. But, if the germsbe present, defective drains and cesspools become the potentdistributors of disease and death. Corrupted air may promote anepidemic, but cannot produce it. On the other hand, through thetransport of the special germ or virus, disease may develop itself inregions where the drainage is good and the atmosphere pure. 

If you see a new thistle growing in your field, you feel sure that itsseed has been wafted thither. Just as sure does it seem that thecontagious matter of epidemic disease has been transplanted to theplace where it newly appears. With a clearness and conclusiveness snot to be surpassed, Dr. William Budd has traced such diseases fromplace to place; showing how they plant themselves, at distinct foci, among populations subjected to the same atmospheric influences, justas grains of corn might be carried in the pocket and sown. Hildebrand, to whose remarkable work, 'Du Typhus contagieux, ' Dr. De Mussy hasdirected my attention, gives the following striking case, both of thedurability and the transport of the virus of scarlatina: 'Un habitnoir que j'avais en visitant une malade attaquée de scarlatina, et queje portai de Vienne en Podolie, sans l'avoir mis depuis plus d'un anet demi, me communiqua, dès que je fus arrivé, cette maladiecontagieuse, que je répandis ensuite dans cette province, où elleétait jusqu'alors presque inconnue. ' Some years ago Dr. De Mussyhimself was summoned to a country house in Surrey, to see a young ladywho was suffering from a dropsy, evidently the consequence ofscarlatina. The original disease, being of a very mild character, hadbeen quite overlooked; but circumstances were recorded which couldleave no doubt upon the mind as to the nature and cause of thecomplaint. But then the question arose, How did the young lady catchthe scarlatina? She had come there on a visit two months previously, and it was only after she had been a month in the house that she wastaken ill. The housekeeper at length cleared up the mystery. Theyoung lady, on her arrival, had expressed a wish to occupy a room inan isolated tower. Her desire was granted; and in that room, sixmonths previously, a visitor had been confined with an attack ofscarlatina. The room had been swept and whitewashed, but the carpetshad been permitted to remain. 

Thousands of cases could probably be cited in which the disease hasshown itself in this mysterious way, but where a strict examinationhas revealed its true parentage and extraction. Is it, then, philosophical to take refuge in the fortuitous concourse of atoms as acause of specific disease, merely because in special cases theparentage may be indistinct? Those best acquainted with atomicnature, and who are most ready to admit, as regards even higher thingsthan this, the potentialities of matter, will be the last to acceptthese rash hypotheses. 

The Germ Theory applied to Surgery. 

Not only medical but still more especially surgical science is nowseeking light and guidance from this germ theory. Upon it theantiseptic system of Professor Lister of Edinburgh is founded. Asalready stated, the germ theory of putrefaction was started bySchwann; but the illustrations of this theory adduced by ProfessorLister are of such public moment as not only to justify, but to renderimperative, their introduction here. 

Schwann's observations (says Professor Lister) did not receive theattention which they appeared to me to have deserved. Thefermentation of sugar was generally allowed to be occasioned by the_Torula cerevisiae_; but it was not admitted that putrefaction was dueto an analogous agency. And yet the two cases present a very strikingparallel. In each a stable chemical compound, sugar in the one case, albumen in the other, undergoes extraordinary chemical changes underthe influence of an excessively minute quantity of a substance which, regarded chemically, we should suppose inert. As an example of thisin the case of putrefaction, let us take a circumstance oftenwitnessed in the treatment of large chronic abscesses. In order toguard against the access of atmospheric air, we used to draw off thematter by means of a canula and trocar, such as you see here, consisting of a silver tube with a sharp-pointed steel rod fitted intoit, and projecting beyond it. The instrument, dipped in oil, wasthrust into the cavity of the abscess, the trocar was withdrawn, andthe pus flowed out through the canula, care being taken by gentlepressure over the part to prevent the possibility of regurgitation. The canula was then drawn out with due precaution against the refluxof air. This method was frequently successful as to its immediateobject, the patient being relieved from the mass of the accumulatedfluid, and experiencing no inconvenience from the operation. But thepus was pretty certain to reaccumulate in course of time, and itbecame necessary again and again to repeat the process. And unhappilythere was no absolute security of immunity from bad consequences. However carefully the procedure was conducted, it sometimes happened, even though the puncture seemed healing by first intention, thatfeverish symptoms declared themselves in the course of the first orsecond day, and, on inspecting the seat of the abscess, the skin wasperhaps seen to be red, implying the presence of some cause ofirritation, while a rapid reaccumulation of the fluid was found tohave occurred. Under these circumstances, it became necessary to openthe abscess by free incision, when a quantity, large in proportion tothe size of the abscess, say, for example, a quart, of pus escaped, fetid from putrefaction. Now, how had this change been brought about?Without the germ theory, I venture to say, no rational explanation ofit could have been given. It must have been caused by theintroduction of something from without. Inflammation of the puncturedwound, even supposing it to have occurred, would not explain thephenomenon. For mere inflammation, whether acute or chronic, thoughit occasions the formation of pus, does not induce Putrefaction. Thepus originally evacuated was perfectly sweet, and we know of nothingto account for the alteration in its quality but the influence ofsomething derived from the external world. And what could thatsomething be? The dipping of the instrument in oil, and thesubsequent precautions, prevented the entrance of oxygen. Or even ifyou allowed that a few atoms of the gas did enter, it would be anextraordinary assumption to make that these could in so short a timeeffect such changes in so large a mass of albuminous material. Besides, the pyogenic membrane is abundantly supplied with capillaryvessels, through which arterial blood, rich in oxygen, is perpetuallyflowing; and there can be little doubt that the pus, before it wasevacuated at all, was liable to any action which the element might bedisposed to exert upon it. 

On the oxygen theory, then, the occurrence of putrefaction under thesecircumstances is quite inexplicable. But if you admit the germtheory, the difficulty vanishes at once. The canula and trocar havingbeen lying exposed to the air, dust will have been deposited uponthem, and will be present in the angle between the trocar and thesilver tube, and in that protected situation will fail to be wiped offwhen the instrument is thrust through the tissues. Then when thetrocar is withdrawn, some portions of this dust will naturally remainupon the margin of the canula, which is left projecting into theabscess, and nothing is more likely than that some particles may failto be washed off by the stream of out-flowing pus, but may bedislodged when the tube is taken out, and left behind in the cavity. The germ theory tells us that these particles of dust will be prettysure to contain the germs of putrefactive organisms, and if one suchis left in the albuminous liquid, it will rapidly develop at the hightemperature of the body, and account for all the phenomena. 

But striking as is the parallel between putrefaction in this instanceand the vinous fermentation, as regards the greatness of the effectproduced, compared with the minuteness and the inertness, chemicallyspeaking, of the cause, you will naturally desire further evidence ofthe similarity of the two processes. You can see with the microscopethe Torula of fermenting must or beer. Is there, you may ask, anyorganism to be detected in the putrefying pus? Yes, gentlemen, thereis. If any drop of the putrid matter is examined with a good glass, it is found to be teeming with myriads of minute jointed bodies, called vibrios, which indubitably proclaim their vitality by theenergy of their movements. It is not an affair of probability, but afact, that the entire mass of that quart of pus has become peopledwith living organisms as the result of the introduction of the canulaand trocar; for the matter first let out was as free from vibrios asit was from putrefaction. If this be so, the greatness of thechemical changes that have taken place in the pus ceases to besurprising. We know that it is one of the chief peculiarities ofliving structures that they possess extraordinary powers of effectingchemical changes in materials in their vicinity, out of all proportionto their energy as mere chemical compounds. And we can hardly doubtthat the animalcules which have been developed in the albuminousliquid, and have grown at its expense, must have altered itsconstitution, just as we ourselves alter that of the materials onwhich we feed. [Footnote: 'Introductory Lecture before the Universityof Edinburgh. ']

In the operations of Professor Lister care is taken that every portionof tissue laid bare by the knife shall be defended from germs; that ifthey fall upon the wound they should be killed as they fall. Withthis in view he showers upon his exposed surfaces the spray of dilutecarbolic acid, which is particularly deadly to the germs, and hesurrounds the wound in the most careful manner with antisepticbandages. To those accustomed to strict experiment it is manifestthat we have a strict experimenter here--a man with a perfectlydistinct object in view, which he pursues with never-tiring patienceand unwavering faith. And the result, in his hospital practice, asdescribed by himself, has been, that even in the midst of abominationstoo shocking to be mentioned here, and in the neighbourhood of wardswhere death was rampant from pyaemia, erysipelas, and hospitalgangrene, he was able to keep his patients absolutely free from theseterrible scourges. Let me here recommend to your attention ProfessorLister's 'Introductory Lecture before the University of Edinburgh, 'which I have already quoted; his paper on The Effect of the AntisepticSystem of Treatment on the Salubrity of a Surgical Hospital;' and thearticle in the 'British Medical Journal' of January 14, 1871. 

If, instead of using carbolic acid spray, he could surround his woundswith properly filtered air, the result would, he contends, be thesame. In a room where the germs not only float but cling to clothesand walls, this would be difficult, if not impossible. But surgery isacquainted with a class of wounds in which the blood is freely mixedwith air that has passed through the lungs, and it is a mostremarkable fact that such air does not produce putrefaction. ProfessorLister, as far as I know, was the first to give a philosophicalinterpretation of this fact, which he describes and comments uponthus:

I have explained to my own mind the remarkable fact that in simplefracture of the ribs, if the lung be punctured by a fragment, theblood effused into the pleural cavity, though freely mixed with air, undergoes no decomposition. The air is sometimes pumped into thepleural cavity in such abundance that, making its way through thewound in the pleura costalis, it inflates the cellular tissue of thewhole body. Yet this occasions no alarm to the surgeon (although ifthe blood in the pleura were to putrefy, it would infallibly occasiondangerous suppurative pleurisy). Why air introduced into the pleuralcavity through a wounded lung, should have such wholly differenteffects from that entering directly through a wound in the chest, wasto me a complete mystery until I heard of the germ theory ofputrefaction, when it at once occurred to me that it was only naturalthat air should be filtered of germs by the air-passages, one of whoseoffices is to arrest inhaled particles of dust, and prevent them fromentering the air-cells. 

*****

I shall have occasion to refer to this remarkable hypothesis fartheron. 

The advocates of the germ theory, both of putrefaction and epidemicdisease, hold that both arise, not from the air, but from somethingcontained in the air. They hold, moreover, that this 'something' isnot a vapour nor a gas, nor indeed a molecule of any kind, but a_particle_. [Footnote: As regards size, there is probably no sharp lineof division between molecules and particles; the one gradually shadesinto the other. But the distinction that I would draw is this: theatom or the molecule, if free, is always part of a gas, the particleis never so. A particle is a bit of liquid or solid matter, formed bythe Aggregation of atoms or molecules. ] The term 'particulate 'hasbeen used in the Reports of the Medical Department of the PrivyCouncil to describe this supposed constitution of contagious matter;and Dr. Sanderson's experiments render it in the highest degreeprobable, if they do not actually demonstrate, that the virus ofsmall-pox is 'particulate. ' Definite knowledge upon this point is ofexceeding importance, because in the treatment of _particles_ methodsare available which it would be futile to apply to _molecules_. 

The Luminous beam as a means of Research. 

My own interference with this great question, while sanctioned byeminent names, has been also an object of varied and ingenious attack. On this point I will only say that when angry feeling escapes frombehind the intellect, where it may be useful as an urging force, andplaces itself athwart the intellect, it is liable to produce allmanner of delusions. Thus my censors, for the most part, havelevelled their remarks against positions which were never assumed, andagainst claims which were never made. The simple history of thematter is this: During the autumn of 1868 I was much occupied with theobservations referred to at the beginning of this discourse, and inpart described in the preceding article. For fifteen years it hadbeen my habit to make use of floating dust to reveal the paths ofluminous beams through the air; but until 1868 I did not intentionallyreverse the process, and employ a luminous beam to reveal and examinethe dust. In a paper presented to the Royal Society in December, 1869, the observations which induced me to give more special attention tothe question of spontaneous generation, and the germ theory ofepidemic disease, are thus described:

The Floating Matter of the Air. 

Prior to the discovery of the foregoing action (the chemical action oflight upon vapours, Fragment IV. ), and also during the experimentsjust referred to, the nature of my work compelled me to aim atobtaining experimental tubes absolutely clean upon the surface, andabsolutely free within from suspended matter. Neither condition is, however, easily attained. 

For however well the tubes might be washed and polished, and howeverbright and pure they might appear in ordinary daylight, the electricbeam infallibly revealed signs and tokens of dirt. The air was alwayspresent, and it was sure to deposit some impurity. All chemicalprocesses, not conducted in a vacuum, are open to this disturbance. When the experimental tube was exhausted, it exhibited no trace offloating matter, but on admitting the air through the U-tubes(containing caustic potash and sulphuric acid), a _dust-cone_ more orless distinct was always revealed by the powerfully condensed electricbeam. 

The floating motes resembled minute particles of liquid which had beencarried mechanically from the U-tubes into the experimental tube. Precautions were therefore taken to prevent any such transfer. Theyproduced little or no mitigation. I did not imagine, at the time, that the dust of the external air could find such free passage throughthe caustic potash and sulphuric acid. This, however, was the case;the motes really came from without. They also passed with freedomthrough a variety of aethers and alcohols. In fact, it requireslong-continued action on the part of an acid first to wet the motesand afterwards to destroy them. By carefully passing the air throughthe flame of a spirit lamp, or through a platinum tube heated tobright redness, the floating matter was sensibly destroyed. It wastherefore combustible, in other words, organic, matter. I tried tointercept it by a large respirator of cotton-wool. Close pressure wasnecessary to render the wool effective. A plug of the wool, rammedpretty tightly into the tube through which the air passed, was finallyfound competent to hold back the motes. They appeared from time totime afterwards, and gave me much trouble; but they were invariablytraced in the end to some defect in the purifying apparatus--to somecrack or flaw in the sealing-wax employed to render the tubesair-tight. Thus through proper care, but not without a great deal ofsearching out of disturbances, the experimental tube, even when filledwith air or vapour, contains nothing competent to scatter the light. The space within it has the aspect of an absolute vacuum. 

An experimental tube in this condition I call _optically empty_. 

The simple apparatus employed in these experiments will be at onceunderstood by reference to a figure printed in the last article (Fig. 3. ) s s' is the glass experimental tube, which has varied in lengthfrom 1 to 5 feet, and which may be from 2 to 3 inches in diameter. From the end s, the pipe pp' passes to an air-pump. Connected withthe other end s' we have the flask F, containing the liquid whosevapour is to be examined; then follows a U-tube, T, filled withfragments of clean glass, wetted with sulphuric acid; then a secondU-tube, T, containing fragments of marble, wetted with caustic potash;and finally a narrow straight tube t t', containing a tolerablytightly fitting plug of cotton-wool. To save the air-pump gauge fromthe attack of such vapours as act on mercury, as also to facilitateobservation, a separate barometer tube was employed. 

Through the cork which stops the flask F two glass tubes, a and b, pass air-tight. The tube a ends immediately under the cork; the tubeb, on the contrary, descends to the bottom of the flask and dips intothe liquid. The end of the tube b is drawn out so as to render verysmall the orifice through which the air escapes into the liquid. 

The experimental tube s s' being exhausted, a cock at the end s' isturned carefully on. The air passes slowly through the cotton-wool, the caustic potash, and the sulphuric acid in succession. Thuspurified, it enters the flask F and bubbles through the liquid. Charged with vapour, it finally passes into the experimental tube, where it is submitted to examination. The electric lamp L placed atthe end of the experimental tube furnishes the necessary beam. 

*****

The facts here forced upon my attention had a bearing too evident tobe overlooked. The inability of air which had been filtered throughcotton-wool to generate animalcular life, had been demonstrated bySchroeder and Pasteur: here the cause of its impotence was renderedevident to the eye. The experiment proved that no sensible amount oflight was scattered by the molecules of the air; that the scatteredlight always arose from suspended particles; and the fact that theremoval of these abolished simultaneously the power of scatteringlight and of originating life, obviously detached the life-originatingpower from the air, and fixed it on something suspended in the air. Gases of all kinds passed with freedom through the plug ofcotton-wool; hence the thing whose removal by the cotton-wool renderedthe gas impotent, could not itself have been matter in the gaseouscondition. It at once occurred to me that the retina, protected as itwas, in these experiments, from all extraneous light, might beconverted into a new and powerful instrument of demonstration inrelation to the germ theory. 

But the observations also revealed the danger incurred in experimentsof this nature; showing that without an amount of care far beyond thathitherto bestowed upon them, such experiments left the door open toerrors of the gravest description. It was especially manifest thatthe chemical method employed by Schultze in his experiments, and sooften resorted to since, might lead to the most erroneousconsequences; that neither acids nor alkalies had the power of rapiddestruction hitherto ascribed to them. In short, the employment ofthe luminous beam rendered evident the cause of success in experimentsrigidly conducted like those of Pasteur; while it made equally evidentthe certainty of failure in experiments less severely carried out. 

Dr. Bennett's Experiments. 

But I do not wish to leave an assertion of this kind withoutillustration. Take, then', the well-conceived experiments of Dr. Hughes Bennett, described before the Royal Society of Surgeons inEdinburgh on January 17, 1868. [Footnote: 'British Medical Journal, '13, pt. Ii. 1868. ] Into flasks containing decoctions ofliquorice-root, hay, or tea, Dr. Bennett, by an ingenious method, forced air. The air was driven through two U-tubes, the onecontaining a solution of caustic potash, the other sulphuric acid. 'All the bent tubes were filled with fragments of pumice-stone tobreak up the air, so as to prevent the possibility of any germspassing through in the centre of bubbles. ' The air also passedthrough a Liebig's bulb containing sulphuric acid, and also through abulb containing gun-cotton. 

It was only natural for Dr. Bennett to believe that his 'bent tubes'entirely cut off the germs. Previous to the observations justreferred to, I also believed in their efficacy. But theseobservations destroy any such notion. The gun-cotton, moreover, willfail to arrest the whole of the floating matter, unless it is tightlypacked, and there is no indication in Dr. Bennett's memoir that it wasso packed. On the whole, I should infer, from the mere inspection ofDr. Bennett's apparatus, the very results which he has described--aretardation of the development of life, a total absence of it in somecases, and its presence in others. 

In his first series of experiments, eight flasks were fed with siftedair, and five with common air. In ten or twelve days all the five hadfungi in them; whilst it required from four to nine months to developfungi in the others. In one of the eight, moreover, even after thisinterval no fungi appeared. In a second series of experiments therewas a similar exception. In a third series the cork stoppers used inthe first and second series were abandoned, and glass stoppersemployed. Flasks containing decoctions of tea, beef, and hay werefilled with common air, and other flasks with sifted air. In everyone of the former fungi appeared and in not one of the latter. Theseexperiments simply ruin the doctrine that Dr. Bennett finallyespouses. 

In all these negative cases, the prepared air was forced into theinfusion when it was boiling hot. Dr. Bennett made a fourth series ofexperiments, in which, previous to forcing in the air, he permittedthe flasks to cool. Into four bottles thus treated he forced preparedair, and after a time found fungi in all of them. What is hisconclusion? Not that the boiling hot liquid, employed in his firstexperiments, had destroyed such germs as had run the gauntlet of hisapparatus; but that air which, previous to being sealed up, had beenexposed to a temperature of 212°, _is too rare to support life_. Thisconclusion is so remarkable that it ought to be stated in Dr. Bennett's own words. 'It may be easily conceived that air subjectedto a boiling temperature is so expanded as scarcely to merit the nameof air, and that it is more or less unfit for the purpose ofsustaining animal or vegetable life. '

Now numerical data are attainable here, and as a matter of fact I liveand flourish for a considerable portion of each year in a medium ofless density than that which Dr. Bennett describes as scarcelymeriting the name of air. The inhabitants of the higher Alpinechalets, with their flocks and herds, and the grasses which supportthese, do the same; while the chamois rears its kids in air rarerstill. Insect life, moreover, is sometimes exhibited with monstrousprodigality at Alpine heights. 

In a fifth series of experiments sixteen bottles were filled withinfusions. Into four of them, while cold, ordinary unheated andunsifted air was pumped. In these four bottles fungi were developed. Into four other bottles, containing a boiling infusion, ordinary airwas also pumped--no fungi were here developed. Into four otherbottles containing an infusion which had been boiled and permitted tocool, sifted air was pumped--no fungi were developed. Finally, intofour bottles containing a boiling infusion sifted air was pumped nofungi were developed. Only, therefore, in the four cases where theinfusions were cold infusions, and the air ordinary air, did fungiappear. 

Dr. Bennett does not draw from his experiments the conclusion to whichthey so obviously point. On them, on the contrary, he founds adefence of the doctrine of spontaneous generation, and a generaltheory of spontaneous development. So strongly was he impressed withthe idea that the germs could not possibly pass through his potash andsulphuric acid tubes, that the appearance of fungi, even in a smallminority of cases, where the air had been sent through these tubes, was to him conclusive evidence of the spontaneous origin of suchfungi. And he accounts for the absence of life in many of hisexperiments by an hypothesis which will not bear a moment'sexamination. But, knowing that organic particles may pass unscathedthrough alkalies and acids, the results of Dr. Bennett are preciselywhat ought wider the circumstances to be expected. Indeed, theirharmony with the conditions now revealed is a proof of the honesty andaccuracy with which they were executed. 

The caution exercised by Pasteur both in the execution of hisexperiments, and in the reasoning based upon them, is perfectlyevident to those who, through the practice of severe experimentalenquiry, have rendered themselves competent to judge of goodexperimental work. He found germs in the mercury used to isolate hisair. He was never sure that they did not cling to the instruments heemployed, or to his own person. Thus when he opened his hermeticallysealed flasks upon the Mer de Glace, he had his eye upon the file usedto detach the drawn-out necks of his bottles; and he was careful tostand to leeward when each flask was opened. Using these precautions, he found the glacier air incompetent, in nineteen cases out of twenty, to generate life; while similar flasks, opened amid the vegetation ofthe lowlands, were soon crowded with living things. M. Pouchetrepeated Pasteur's experiments in the Pyrenees, adopting theprecaution of holding his flasks above his head, and obtaining adifferent result. Now great care would be needed to render thisprocedure a real precaution. The luminous beam at once shows us itspossible effect. Let smoking brown paper be placed at the open mouthof a glass shade, so that the smoke shall ascend and fill the shade. Abeam sent through the shade forms a bright track through the smoke. When the closed fist is placed underneath the shade, a vertical windof surprising violence, considering the small elevation oftemperature, rises from the band, displacing by comparatively dark airthe illuminated smoke. Unless special care were taken such a windwould rise from M. Pouchet's body as he held his flasks above hishead, and thus the precaution of Pasteur, of not coming between thewind and the flask, would be annulled. 

Let me now direct attention to another result of Pasteur, the causeand significance of which are at once revealed by the luminous beam. He prepared twenty one flasks, each containing a decoction of yeast, filtered and clear. He boiled the decoction so as to destroy whatevergerms it might contain, and, while the space above the liquid wasfilled with pure steam, he sealed his flasks with a blow-pipe. Heopened ten of them in the deep, damp caves of the Paris Observatory, and eleven of them in the courtyard of the establishment. Of theformer, one only showed signs of life subsequently. In nine out ofthe ten flasks no organisms of any kind were developed. In all theothers organisms speedily appeared. 

Now here is an experiment conducted in Paris, on which we can throwobvious light in London. Causing our luminous beam to pass through alarge flask filled with the air of this room, and charged with itsgerms and its dust, the beam is seen crossing the flask from side toside. But here is another similar flask, which cuts a clear gap outof the beam. It is filled with _unfiltered_ air, and still no trace ofthe beam is visible. Why? By pure accident I stumbled on this flaskin our apparatus room, where it had remained quiet for some time. Acting upon this obvious suggestion I set aside three other flasks, filled, in the first instance, with mote-laden air. They are nowoptically empty. Our former experiments proved that thelife-producing particles attach themselves to the fibres ofcotton-wool. In the present experiment the motes have been brought bygentle air-currents, established by slight differences of temperaturewithin our closed vessels, into contact with the interior surface, towhich they adhere. The air of these flasks has deposited its dust, germs and all, and is practically free from suspended matter. 

I had a chamber erected, the lower half of which is of wood, its upperhalf being enclosed by four glazed window-frames. It tapers to atruncated cone at the top. It measures in plan 3 ft. By 2 ft. 6 in, and its height is 5 ft. 10 in. On February 6 it was closed, everycrevice that could admit dust, or cause displacement of the air, beingcarefully pasted over with paper. The electric beam at first revealedthe dust within the chamber as it did in the air of the laboratory. The chamber was examined almost daily; a perceptible diminution of thefloating matter being noticed as time advanced. At the end of a weekthe chamber was optically empty, exhibiting no trace of mattercompetent to scatter the light. Such must have been the case in thestagnant caves of the Paris Observatory. Were our electric beam sentthrough the air of these caves its track would be invisible; thusshowing the indissoluble association of the scattering of light by airand its power to generate life. 

I will now turn to what seems to me a more interesting application ofthe luminous beam than any hitherto described. My reference toProfessor Lister's interpretation of the fact, that air which haspassed through the lungs cannot produce putrefaction, is fresh in yourmemories. 'Why air, ' said he, 'introduced into the pleural cavity, through a wounded lung, should have such wholly different effects fromthat entering through a permanently open wound, penetrating fromwithout, was to me a complete mystery, till I heard of the germtheory of putrefaction, when it at once occurred to me that it wasonly natural that the air should be filtered of germs by the airpassages, one of whose offices is to arrest inhaled particles ofdust, and prevent them from entering the air-cells. '

Here is a surmise which bears the stamp of genius, but which needsverification. If, for the words 'it is only natural' we wereauthorised to write 'it is perfectly certain, ' the demonstration wouldbe complete. Such demonstration is furnished by experiments with abeam of light. One evening, towards the close of 1869, while pouringvarious pure gases across the dusty track of a luminous beam, thethought occurred to me of using my breath instead of the gases. Ithen noticed, for the first time, the extraordinary darkness producedby the expired air, _towards the end of the expiration_. Permit me torepeat the experiment in your presence. I fill my lungs with ordinaryair and breathe through a glass tube across the beam. Thecondensation of the aqueous vapour of the breath is shown by theformation of a luminous white cloud of delicate texture. We abolishthis cloud by drying the breath previous to its entering the beam; or, still more simply, by warming the glass tube. The luminous track ofthe beam is for a time uninterrupted by the breath, because the dustreturning from the lungs makes good, in great part, the particlesdisplaced. After a time, however, an obscure disk appears in thebeam, the darkness of which increases, until finally, towards the endof the expiration, the beam is, as it were, pierced by an intenselyblack hole, in which no particles whatever can be discerned. Thedeeper air of the lungs is thus proved to be absolutely free fromsuspended matter. It is therefore in the precise condition requiredby Professor Lister's explanation. This experiment may be repeatedany number of times with the same result. I think it must be regardedas a crowning piece of evidence both of the correctness of ProfessorLister's views and of the impotence, as regards vital development, ofoptically pure air. [Footnote: Dr. Burden Sanderson draws attention tothe important observation of Brauell, which shows that the _contagium_of a pregnant animal, suffering from splenic fever, is not found inthe blood of the foetus; the placental apparatus acting as a filter, and holding back the infective particles. ]

Application of Luminous beams to Water. 

The method of examination here pursued is also applicable to water. Itis in some sense complementary to that of the microscope, and may, Ithink, materially aid enquiries conducted with that instrument. Inmicroscopic examination attention is directed to a small portion ofthe liquid, and the aim is to detect the individual particles. By thepresent method a large portion of the liquid is illuminated, thecollective action of the particles being revealed, by the scatteredlight. Care is taken to defend the eye from the access of all otherlight, and, thus defended, it becomes an organ of inconceivabledelicacy. Indeed, an amount of impurity so infinitesimal as to bescarcely expressible in numbers, and the individual particles of whichare so small as wholly to elude the microscope, may, when examined bythe method alluded to, produce not only sensible, but striking, effects upon the eye. 

We will apply the method, in the first place, to an experiment of M. Pouchet intended to prove conclusively that animalcular life isdeveloped in cases where no antecedent germs could possibly exist. Heproduced water from the combustion of hydrogen in air, justly arguingthat no germ could survive the heat of a hydrogen flame. But heoverlooked the fact that his aqueous vapour was condensed in the air, and was allowed as water to trickle through the air. Indeed theexperiment is one of a number by which workers like M. Pouchet aredifferentiated from workers like Pasteur. I will show you some water, produced by allowing a hydrogen flame to play upon a polished silvercondenser, formed by the bottom of a silver basin, containing ice. Thecollected liquid is pellucid in the common light; but in the condensedelectric beam it is seen to be laden with particles, so thick-strewnand minute as to produce a continuous luminous cone. In passingthrough the air the water loaded itself with this matter; and thedeportment of such water could obviously have no influence in decidingthis great question. 

We are invaded with dirt not only in the air we breathe, but in thewater we drink. To prove this I take the bottle of water intended toquench your lecturer's thirst; which, in the track of the beam, simplyreveals itself as dirty water. And this water is no worse than theother London waters. Thanks to the kindness of Professor Frankland, Ihave been furnished with specimens of the water of eight Londoncompanies. They are all laden with impurities mechanically suspended. But you will ask whether filtering will not remove the suspendedmatter? The grosser matter, undoubtedly, but not the more finelydivided matter. Water may be passed any number of times throughbibulous paper, it will continue laden with fine matter. Water passedthrough Lipscomb's charcoal filter, or through the filters of theSilicated Carbon Company, has its grosser matter removed, but it isthick with fine matter. Nine-tenths of the light scattered by thesesuspended particles is perfectly polarised in a direction at rightangles to the beam, and this release of the particles from theordinary law of polarisation is a demonstration of their smallness. Ishould say by far the greater number of the particles concerned inthis scattering are wholly beyond the range of the microscope, and noordinary filter can intercept such particles. It is next toimpossible, by artificial means, to produce a pure water. Mr. Hartley, for example, some time ago distilled water while surroundedby hydrogen, but the water was not free from floating matter. It isso hard to be clean in the midst of dirt. In water from the Lake ofGeneva, which has remained long without being stirred, we have anapproach to the pure liquid. I have a bottle of it here, which wascarefully filled for me by my distinguished friend Soret. The trackof the beam through it is of a delicate sky-blue; there is scarcely atrace of grosser matter. 

The purest water that I have seen--probably the purest which has beenseen hitherto--has been obtained from the fusion of selected specimensof ice. But extraordinary precautions are required to obtain thisdegree of purity. The following apparatus has been constructed forthis purpose: Through the plate of an air-pump passes the shank of alarge funnel, attached to which below the plate is a clean glass bulb. In the funnel is placed a block of the most transparent ice, and overthe funnel a glass receiver. This is first exhausted and refilledseveral times with air, filtered by its passage through cotton-wool, the ice being thus surrounded by pure moteless air. But the ice haspreviously been in contact with mote-filled air; it is thereforenecessary to let it wash its own surface, and also to wash the bulbwhich is to receive the water of liquefaction. The ice is permittedto melt, the bulb is filled and emptied several times, until finallythe large block dwindles to a small one. We may be sure that allimpurity has been thus removed from the surface of the ice. The waterobtained in this way is the purest hitherto obtained. Still I shouldhesitate to call it absolutely pure. When condensed light is sentthrough it, the track of the beam is not invisible, but of the mostexquisitely delicate blue. This blue is purer than that of the sky, so that the matter which produces it must be finer than that of thesky. It may be and indeed has been, contended that this blue isscattered by the very molecules of the water, and not by mattersuspended in the water. But when we remember that this perfection ofblue is approached gradually through stages of less perfect blue; andwhen we consider that a blue in all respects similar is demonstrablyobtainable from particles mechanically suspended, we should hesitate, I think, to conclude that we have arrived here at the last stage ofpurification. The evidence, I think, points distinctly to theconclusion that, could we push the process of purification stillfarther, even this last delicate trace of blue would disappear. 

Chalk-water. Clark's Softening Process. 

But is it not possible to match the water of the Lake of Geneva herein England? Undoubtedly it is. We have in England a kind of rockwhich constitutes at once an exceedingly clean recipient and a naturalfilter, and from which we can obtain water extremely free frommechanical impurities. I refer to the chalk formation, in which largequantities of water are held in store. Our chalk hills are in mostcases covered with thin layers of soil, and with very scantyvegetation. Neither opposes much obstacle to the entry of the raininto the chalk, where any organic impurity which the water may carryin is soon oxidised and rendered harmless. Those who have scamperedlike myself over the downs of Hants and Wilts will remember thescarcity of water in these regions. In fact, the rainfall, instead ofwashing the surface and collecting in streams, sinks into the fissuredchalk and percolates through it. When this formation is suitablytapped, we obtain water of exceeding briskness and purity. A largeglass globe, filled with the water of a well near Tring, shows itselfto be wonderfully free from mechanical impurity. Indeed, it stands toreason that water wholly withdrawn from surface contamination, andpercolating through so clean a substance, should be pure. It has beena subject much debated, whether the supply of excellent water whichthe chalk holds in store could not be rendered available for London. Many of the most eminent engineers and chemists have ardentlyrecommended this source, and have sought to show, not only that itspurity is unrivalled, but that its quantity is practicallyinexhaustible. Data sufficient to test this are now, I believe, inexistence; the number of wells sunk in the chalk being soconsiderable, and the quantity of water which they yield so wellknown. 

But this water, so admirable as regards freedom from mechanicalimpurity, labours under the disadvantage of being rendered very hardby the carbonate of lime which it holds in solution. The chalk-waterin the neighbourhood of Watford contains about seventeen grains ofcarbonate of lime per gallon. This, in the old terminology, used tobe called seventeen degrees of hardness. This hard water is bad fortea, bad for washing, and it furs our boilers, because the lime heldin solution is precipitated by boiling. If the water be used cold, its hardness must be neutralised at the expense of soap, before itwill give a lather. These are serious objections to the use ofchalk-water in London. But they are successfully met by the fact thatsuch water can be softened inexpensively, and on a grand scale. I hadlong known the method of softening water called Clark's process, butnot until recently, under the guidance of Mr. Homersham, did I seeproof of its larger applications. The chalk-water is softened for thesupply of the city of Canterbury; and at the Chiltern Hills it issoftened for the supply of Tring and Aylesbury. Caterham also enjoysthe luxury. 

I have visited all these places, and made myself acquainted with theworks. At Canterbury there are three reservoirs covered in andprotected, by a concrete roof and layers of pebbles, both from thesummer's heat and the winter's cold. Each reservoir holds 120, 000gallons of water. Adjacent to these reservoirs are others containingpure slaked lime--the so-called 'cream of lime. ' These being filledwith water, the lime and water are thoroughly mixed by air forced byan engine through apertures in the bottom of the reservoir. The watersoon dissolves all the lime it is capable of dissolving. Themechanically suspended lime is then allowed to subside to the bottom, leaving a perfectly transparent lime-water behind. 

The softening process is this: Into one of the empty reservoirs isintroduced a certain quantity of the clear lime-water, and after thisabout nine times the quantity of the chalk-water. The transparencyimmediately disappears--the mixture of the two clear liquids becomingthickly turbid, through the precipitation of carbonate of lime. Theprecipitate is crystalline and heavy, and in about twelve hours alayer of pure white carbonate of lime is formed at the bottom of thereservoir, with a water of extraordinary beauty and purity overhead. Afew days ago I pitched some halfpence into a reservoir sixteen feetdeep at the Chiltern Hills. This depth hardly dimmed the coin. Had Icast in a pin, it could have been seen at the bottom. By this processof softening, the water is reduced from about seventeen degrees ofhardness, to three degrees of hardness. It yields a latherimmediately. Its temperature is constant throughout the year. In thehottest summer it is cool, its temperature being twenty degrees abovethe freezing point; and it does not freeze in winter if conveyed inproper pipes. The reservoirs are covered; a leaf cannot blow intothem, and no surface contamination can reach the water. It passesdirect from the main into the house tap; no cisterns are employed, andthe supply is always fresh and pure. This is the kind of water whichis supplied to the fortunate people of Tring, Caterham, andCanterbury. 

*****

The foregoing article, as far as it relates to the theory whichascribes epidemic disease to the development of low parasitic lifewithin the human life, was embodied in a discourse delivered beforethe Royal Institution in January 1870. In June 1871, after a briefreference to the polarisation of light by cloudy matter, I ventured torecur to the subject in these terms: What is the practical use ofthese curiosities? If we exclude the interest attached to theobservation of new facts, and the enhancement of that interest throughthe knowledge that facts often become the exponents of laws, thesecuriosities are in themselves worth little. They will not enable usto add to our stock of food, or drink, or clothes, or jewellery. Butthough thus shorn of all usefulness in themselves, they may, bycarrying thought into places which it would not otherwise haveentered, become the antecedents of practical consequences. Inlooking, for example, at our illuminated dust, we may ask ourselveswhat it is. How does it act, not upon a beam of light, but upon ourown bodies? The question then assumes a practical character. We findon examination that this dust is mainly organic matter--in partliving, in part dead. There are among it particles of ground straw, torn rags, smoke, the pollen of flowers, the spores of fungi, and thegerms of other things. But what have they to do with the animaleconomy? Let me give you an illustration to which my attention hasbeen lately drawn by Mr. George Henry Lewes, who writes to me thus:

'I wish to direct your attention to the experiments of vonRecklingshausen should you happen not to know them. They are strikingconfirmations of what you say of dust and disease. Last spring, whenI was at his laboratory in Wuerzburg, I examined with him blood thathad been three weeks, a month, and five weeks, out of the body, preserved in little porcelain cups under glass shades. This blood wasliving and growing. Not only were the Amoeba-like movements of thewhite corpuscles present, but there were abundant evidences of thegrowth and development of the corpuscles. (I also saw a frog's heartstill pulsating which had been removed from the body I forget how manydays, but certainly more than a week). There were other examples ofthe same persistent vitality, or absence of putrefaction. VonRecklingshausen did not attribute this to the absence of germs--germswere not mentioned by him; but when I asked him how he represented thething to himself, he said the whole mystery of his operation consistedin keeping the blood _free from dirt_. The instruments employed wereraised to a red heat just before use; the thread was silver thread andwas similarly treated; and the porcelain cups, though not kept freefrom air, were kept free from currents. He said he often hadfailures, and these he attributed to particles of dust having escapedhis precautions. '

Professor Lister, who has founded upon the removal or destruction ofthis 'dirt' momentous improvements in surgery, tells us the effect ofits introduction into the blood of wounds. The blood would putrefyand become fetid; and when you examine more closely what putrefactionmeans, you find the putrefying substance swarming with infusoriallife, the germs of which have been derived from the atmospheric dust. 

We are now assuredly in the midst of practical matters; and with yourpermission I will refer once more to a question which has recentlyoccupied a good deal of public attention. As regards the lowest formsof life, the world is divided, and has for a long time been divided, into two parties, the one affirming that we have only to submitabsolutely dead matter to certain physical conditions, to evolve fromit living things; the other (without wishing to set bounds to thepower of matter) affirming that, in our day, life has never been foundto arise independently of pre-existing life. I belong to the partywhich claims life as a derivative of life. The question has twofactors--the evidence, and the mind that judges of the evidence; andit may be purely a mental set or bias on my part that causes methroughout this long discussion, to see, on the one side, dubiousfacts and defective logic, and on the other side firm reasoning and aknowledge of what rigid experimental enquiry demands. But, judged ofpractically, what, again, has the question of Spontaneous Generationto do with us? Let us see. There are numerous diseases of men andanimals that are demonstrably the products of parasitic life, and suchdiseases may take the most terrible epidemic forms, as in the case ofthe silkworms of France, referred to at an earlier part of thisarticle. Now it is in the highest degree important to know whetherthe parasites in question are spontaneously developed, or whether theyhave been wafted from without to those afflicted with the disease. Themeans of prevention, if not of cure, would be widely different in thetwo cases. 

But this is not all. Besides these universally admitted cases, thereis the broad theory, now broached and daily growing in strength andclearness--daily, indeed, gaining more and more of assent from themost successful workers and profound thinkers of the medicalprofession itself--the theory, namely, that contagious disease, generally, is of this parasitic character. Had I any cause to regrethaving introduced this theory to your notice more than a year ago, that regret should now be expressed. I would certainly renounce inyour presence whatever leaning towards the germ theory my words mightthen have betrayed. But since the time referred to nothing hasoccurred to shake my conviction of the truth of the theory. Let mebriefly state the grounds on which its supporters rely. From theirrespective viruses you may plant typhoid fever, scarlatina, orsmall-pox. What is the crop that arises from this husbandry? Assurely as a thistle rises from a thistle seed, as surely as the figcomes from the fig, the grape from the grape, the thorn from thethorn, so surely does the typhoid virus increase and multiply intotyphoid fever, the scarlatina virus into scarlatina, the small-poxvirus into small-pox. What is the conclusion that suggests itselfhere? It is this: That the thing which we vaguely call a virus is toall intents and purposes a seed. Excluding the notion of vitality, inthe whole range of chemical science you cannot point to an actionwhich illustrates this perfect parallelism with the phenomena oflife--this demonstrated power of self-multiplication and reproduction. The germ theory alone accounts for the phenomena. 

In cases of epidemic disease, it is not on bad air or foul drains thatthe attention of the physician of the future will primarily be fixed, but upon disease germs, which no bad air or foul drains can create, but which may be pushed by foul air into virulent energy ofreproduction. You may think I am treading on dangerous ground, that Iam putting forth views that may interfere with salutary practice. Nosuch thing. If you wish to learn the impotence of medical practice indealing with contagious diseases, you have only to refer to theHarveian oration for 1871, by Sir William Gull. Such diseases defythe physician. They must run their course, and the utmost that can bedone for them is careful nursing. And this, though I do not speciallyinsist upon it, would favour the idea of their vital origin. For ifthe seeds of contagious disease be themselves living things, it may bedifficult to destroy either them or their progeny, without involvingtheir living habitat in the same destruction. 

It has been said, and it is sure to be repeated, that I am quitting myown métier, in speaking of these things. Not so. I am dealing witha question on which minds accustomed to weigh the value ofexperimental evidence are alone competent to decide, and regardingwhich, in its present condition, minds so trained are as capable offorming an opinion as regarding the phenomena of magnetism or radiantheat. 'The germ theory of disease, ' it has been said, 'appertains tothe biologist and the physician. ' Where, I would ask in reply, is thebiologist or physician, whose researches, in connection with thissubject, could for one instant be compared to those of the chemistPasteur? It is not the philosophic members of the medical professionwho are dull to the reception of truth not originated within the paleof the profession itself. I cannot better conclude this portion of mystory than by reading to you an extract from a letter addressed to mesome time ago by Dr. William Budd, of Clifton, to whose insight andenergy the town of Bristol owes so much in the way of sanitaryimprovement. 

'As to the germ theory itself, ' writes Dr. Budd, that is a matter onwhich I have long since made up my mind. From the day when I firstbegan to think of these subjects I have never had a doubt that thespecific cause of contagious fevers must be living organisms. 

'It is impossible, in fact, to make any statement bearing upon theessence or distinctive characters of these fevers, without using termswhich are of all others _the most distinctive of life_. Take up thewritings of the most violent opponent of the germ theory, and, ten toone, you will find them full of such terms as "propagation, ""self-propagation, " "reproduction, " "self-multiplication, " and so on. Try as he may--if he has anything to say of those diseases which ischaracteristic of them--he cannot evade the use of these terms, or theexact equivalents to them. While perfectly applicable to livingthings, these terms express qualities which are not only inapplicableto common chemical agents, but, as far as I can see, actuallyinconceivable of them. '

Cotton-wool Respirator. 

Once, then, established within the body, this evil form of life, ifyou will allow me to call it so, must run its course. Medicine as yetis powerless to arrest its progress, and the great point to be aimedat is to prevent its access to the body. It was with this thought inmy mind that I ventured to recommend, more than a year ago, the use ofcotton-wool respirators in infectious places. I would here repeat mybelief in their efficacy if properly constructed. But I do not wishto prejudice the use of these respirators, by connecting themindissolubly with the germ theory. There are too many trades inEngland where life is shortened and rendered miserable by theintroduction of matters into the lungs which might be kept out ofthem. Dr. Greenhow has shown the stony grit deposited in the lungs ofstonecutters. The black lungs of colliers is another case in point. In fact, a hundred obvious cases might be cited, and others that arenot obvious might be added to them. We should not, for example, thinkthat printing implied labour where the use of cotton-wool respiratorsmight come into play; but the fact is that the dust arising from thesorting of the type is very destructive of health. I went some timeago into a manufactory in one of our large towns, where iron vesselsare enamelled by coating them with a mineral powder, and subjectingthem to a heat sufficient to fuse the powder. The organisation of theestablishment was excellent, and one thing only was needed to make itfaultless. In a large room a number of women were engaged coveringthe vessels. The air was laden with the fine dust, and their facesappeared as white and bloodless as the powder with which they worked. By the use of cotton-wool respirators these women might be caused tobreathe air as free from suspended matter as that of the open street. Over a year ago a Lancashire seedsman wrote to me, stating that duringthe seed season his men suffered horribly from irritation and fever, so that many of them left his service. He asked for help, and I gavehim my advice. At the conclusion of the season, this year, he wroteto inform me that he had folded a little cotton-wool in muslin, andtied it in front of the mouth; and that with this simple defence hehad passed through the season in comfort, and without a singlecomplaint from his men. 

Against the use of such a respirator the obvious objection arises, that it becomes wet and heated by the breath. While casting about fora remedy for this, a friend forwarded to me from Newcastle a form ofrespirator invented by Mr. Carrick, a hotel-keeper at Glasgow, which, by a slight modification, may be caused to meet the case perfectly. The respirator, with its back in part removed, is shown in fig. 4. Under the partition of wire-gauze q r, is a space intended by Mr. Carrick for 'medicated substances, ' and which may be filled withcotton-wool. The mouth is placed against the aperture o, which fitsclosely round the lips, and the filtered air enters the mouth througha light valve v, which is lifted by the act of inhalation. 

During exhalation this valve closes; the breath escapes by a secondvalve, v', into the open air. The wool is thus kept dry and cool; theair in passing through it being filtered of everything it holds insuspension. The respirator has since taken other forms. 

FIG. 4. 

*****

Fireman's Respirator. 

We have thus been led by our first unpractical experiments into athicket of practical considerations. But another step is possible. Admiring, as I do, the bravery of our firemen, and hearing that smokewas a more serious enemy than flame itself, I thought of devising afireman's respirator. 

Our fire-escapes are each in charge of a single man, and it would beof obvious importance to place it in the power of each of those men topenetrate through the densest smoke, into the recesses of a house, andthere to rescue those who would otherwise be suffocated or burnt. Cotton-wool, which so effectually arrested dust, was first tried; but, though found soothing in certain gentle kinds of smoke, it was nomatch for the pungent fumes of a resinous fire. For the purpose ofcatching the atmospheric germs, M. Pouchet spread a film of glycerineon a plate of glass, urged air against the film, and examined the dustwhich stuck to it. The moistening of the cotton-wool with glycerinewas a decided improvement; still the respirator only enabled us toremain in dense smoke for three or four minutes, after which theirritation became unendurable. Reflection suggested that, besides thesmoke, there must be numerous hydrocarbons produced, which, being in astate of vapour, would be very imperfectly arrested by thecotton-wool. These, in all probability, were the cause of theresidual irritation; and if these could be removed, a practicallyperfect respirator might possibly be obtained. 

I state the reasoning exactly as it occurred to my mind. Its resultwill be anticipated by many present. All bodies possess the power ofcondensing, in a greater or less degree, gases and vapours upon theirsurfaces, and when the condensing body is very porous, or in a finestate of division, the force of condensation may produce veryremarkable effects. Thus, a clean piece of platinum-foil placed in amixture of oxygen and hydrogen so squeezes the gases together as tocause them to combine; and if the experiment be made with care, theheat of combination may raise the platinum to bright redness. Thepromptness of this action is greatly augmented by reducing theplatinum to a state of fine division. A pellet of 'spongy platinum, 'for instance, plunged into a mixture of oxygen and hydrogen, causesthe gases to explode instantly. In virtue of its extreme porosity, asimilar power is possessed by charcoal. It is not strong enough tocause the oxygen and hydrogen to combine like the spongy platinum, butit so squeezes the more condensable vapours, and acts with suchcondensing power upon the oxygen of the air, as to bring both withinthe combining distance, thus enabling the oxygen to attack and destroythe vapours in the pores of the charcoal. In this way, effluvia ofall kinds may be virtually burnt up; and this is the principle of theexcellent charcoal respirators invented by Dr. Stenhouse. Armed withone of these, you may go into the foulest-smelling places withouthaving your nose offended. 

But, while powerful to arrest vapours, the charcoal respirator isineffectual as regards smoke. The smoke-particles get freely throughthe respirator. With a number of such respirators, tested in a properroom, from half a minute to a minute was the limit of endurance. Thismight be exceeded by Faraday's simple method of emptying the lungscompletely, and then filling them before going into a smokyatmosphere. In fact, each solid smoke particle is itself a bit ofcharcoal, and carries on it, and in it, its little load of irritatingvapour. It is this, far more than the particles of carbon themselves, that produces the irritation. Hence two causes of offence are to beremoved: the carbon particles which convey the irritant by adhesionand condensation, and the free vapour which accompanies the particles. The cotton-wool moistened with glycerine I knew would arrest thefirst; fragments of charcoal I hoped would stop the second. In thefirst fireman's respirator, Mr. Carrick's arrangement of two valves, the one for inhalation, the other for exhalation, was preserved. Butthe portion of the respirator which holds the filtering and absorbentsubstances, was prolonged to a depth of four or five inches (see fig. 5). Under the partition of wire-gauze q r at the bottom of the spacewhich fronts the mouth was placed a layer of cotton-wool, c, moistenedwith glycerine; then a thin layer of dry wool, c'; then a layer ofcharcoal fragments; and finally a second thin layer of drycotton-wool. The succession of the layers may be changed withoutprejudice to the action. A wire-gauze cover, shown in plan under fig. 5, keeps the substances from falling out of the respirator. A layerof caustic lime may be added for the absorption of carbonic acid; butin the densest smoke that we have hitherto employed, it has not beenfound necessary, nor is it shown in the figure. In a flamingbuilding, indeed, the mixture of air with the smoke never permits thecarbonic acid to become so dense as to be irrespirable; but in a placewhere the gas is present in undue quantity, the fragments of limewould materially mitigate its action. 

In a small cellar-like chamber with a stone flooring and stone walls, the first experiments were made. We Placed there furnaces containingresinous pine-wood, lighted the wood, and, placing over it a lid whichprevented too brisk a circulation of the air, generated dense volumesof smoke. With our eyes protected by suitable glasses, my assistantand I have remained for half an hour and more in smoke so dense andpungent that a single inhalation, through the undefended mouth, wouldbe perfectly unendurable. We might have prolonged our stay for hours. 

FIG. 5. 

Having thus far perfected the instrument, I wrote to the chief officerof the Metropolitan Fire Brigade, asking him whether such a respiratorwould be of use to him. His reply was prompt; it would be mostvaluable. He had, however, made himself acquainted with everycontrivance of the kind in this and other countries, and had foundnone of them of any practical use. He offered to come and test ithere, or to place a room at my disposal in the City. At my request hecame here, accompanied by three of his men. Our small room was filledwith smoke to their entire satisfaction. The three men wentsuccessively into it, and remained there as long as Captain Shawwished them. On coming out they said that they had not suffered theslightest inconvenience; that they could have remained all day in thesmoke. Captain Shaw then tested the respirator with the same result, and he afterwards took great interest in the perfecting of theinstrument. 

*****

Various ameliorations and improvements have recently been introducedinto the smoke respirator. The hood of Captain Shaw has been improvedupon by the simple and less expensive mouthpiece of Mr. Sinclair; andthis, in its turn, has been simplified and improved by my assistantMr. John Cottrell. The respirator is now in considerable demand, andit has already done good practical service. Care is, however, necessary, in moistening the wool with glycerine. It must becarefully teazed, so that the individual fibres may be moistened, and_clots_ must be avoided. I cannot recommend the layers of moistenedflannel which, in some cases, have been used instead of cotton-wool:nothing equals the wool, when carefully treated. 

An experiment made last year brought out very conspicuously thenecessity of careful packing, and the enormous comparative power ofresisting smoke irritation possessed by our firemen, and the ableofficer who commands them. Having heard from Captain Shaw that, insome recent very trying experiments, he had obtained the best effectsfrom dry cotton-wool, and thinking that I could not have been mistakenin my first results, which proved the dry so much inferior to themoistened wool and its associated charcoal, I proposed to Captain Shawto bring the matter to a test at his workshops in the City. He wasgood enough to accept my proposal, and thither I went on May 7, 1874. The smoke was generated in a confined space from wet straw, and it wascertainly very diabolical. 

At this season of the year I am usually somewhat shorn of vigour, andtherefore not in the best condition for severe experiments; still Iwished to test the matter in my own person. With a respirator whichhad been in use some days previously, and which was not carefullypacked, I followed a fireman into the smoke, he being provided with adry-wool respirator. I was compelled to quit the place in about threeminutes, while the fireman remained there for six or seven minutes. 

I then tried his respirator upon myself, and found that with it Icould not remain more than a minute in the smoke; in fact the firstinhalation provoked coughing. 

Thinking that Captain Shaw himself might have lungs more like minethan those of his fireman, I proposed that we should try therespirators together; but he informed me that his lungs were verystrong. He was, however, good enough to accede to my request. Beforeentering the den a second time I repacked my respirator, with duecare, and entered the smoke in company with Captain Shaw. I couldhear him breathe long slow inhalations; his labour was certainlygreater than mine, and after the lapse of seven minutes I heard himcough. In seven and a half minutes he had to quit the place, thusproving that his lungs were able to endure the irritation seven timesas long as mine could bear it. I continued in the smoke, with hardlyany discomfort, for sixteen minutes, and certainly could have remainedin it much longer. The advantage arising from the glycerine was thusplaced beyond question. 

During this time I was in a condition to render very materialassistance to a person in danger of suffocation. 

Helmholtz on Hay Fever. 

In my lecture on Dust and Disease in 1870, I referred to an experimentmade by Helmholtz upon himself which strikingly connected hay feverwith animalcular life. About a year ago I received from ProfessorBinz of Bonn a short, but important paper, embracing Helmholtz'saccount of his observation, to which Professor Binz has added someremarks of his own. The paper, being mainly intended for Englishmedical men, was published in English, and though here and there itsstyle might be amended, I think it better to publish it unaltered. 

From what I have observed (says Professor Binz) of recent Englishpublications on the subject of hay fever, I am led to suppose thatEnglish authorities are inaccurately acquainted with the discovery ofProfessor Helmholtz, as far back as 1868, of the existence of uncommonlow organisms in the nasal secretions in this complaint, and of thepossibility of arresting their action by the local employment ofquinine. I therefore purpose to republish the letter in which heoriginally announced these facts to myself, and to add some furtherobservations on this topic. The letter is as follows: [Footnote:Cf. Virchow's 'Archiv. ' vol. Xlvi. ]

'I have suffered, as well as I can remember, since the year 1847, fromthe peculiar catarrh called by the English "hay fever, " the specialityof which consists in its attacking its victims regularly in the hayseason (myself-between May 20 and the end of June), that it ceases inthe cooler weather, but on the other hand quickly reaches a greatintensity if the patients expose themselves to heat and sunshine. Anextraordinary violent sneezing then sets in, and a strongly corrosivethin discharge, with which much epithelium is thrown off. Thisincreases, after a few hours, to a painful inflammation of the mucousmembrane and of the outside of the nose, and excites fever with severeheadache and great depression, if the patient cannot withdraw himselffrom the heat and the sunshine. In a cool room, however, thesesymptoms vanish as quickly as they come on, and there then onlyremains for a few days a lessened discharge and soreness, as if causedby the loss of epithelium. I remark, by the way, that in all my otheryears I had very little tendency to catarrh or catching cold, whilethe hay fever has never failed during the twenty-one years of which Ihave spoken, and has never attacked me earlier or later in the yearthan the times named. The condition is extremely troublesome, andincreases, if one is obliged to be much exposed to the sun, to anexcessively severe malady. 

'The curious dependence of the disease on the season of the yearsuggested to me the thought that organisms might be the origin of themischief. In examining the secretion I regularly found, in the lastfive years, certain vibrio-like bodies in it, which _at other times Icould not observe_ in my nasal secretion... They are verysmall, and can only be recognised with the immersion-lens of a verygood Hartnack's microscope. It is characteristic of the commonisolated single joints that they contain four nuclei in a row, ofwhich two pairs are more closely united. The length of the joints is0. 004 millimetre. Upon the warm objective-stage they move withmoderate activity, partly in, mere vibration, partly shootingbackwards and forwards in the direction of their long axis; in lowertemperatures they are very inactive. Occasionally one finds themarranged in rows upon each other, or in branching series. Observedsome days in the moist chamber, they vegetated again, and appearedsomewhat larger and more conspicuous than immediately after theirexcretion. It is to be noticed that only that kind of secretioncontains them which is expelled by violent sneezings; that which dropsslowly does not contain any. They stick tenaciously enough in thelower cavities and recesses of the nose. 

'When I saw your first notice respecting the poisonous action ofquinine upon infusoria, I determined at once to make an experimentwith that substance, thinking that these vibrionic bodies, even ifthey did not cause the whole illness, still could render it much moreunpleasant through their movements and the decompositions caused bythem. For that reason I made a neutral solution of sulphate ofquinine, which did not contain much of the salt (1·800), but still waseffective enough, and caused moderate irritation on the mucusmembrane of the nose. I then lay flat on my back, keeping my headvery low, and poured with a pipette about four cubic centimetres intoboth nostrils. Then I turned my head about in order to let the liquidflow in all directions. 

'The desired effect was obtained immediately, and remained for somehours; I could expose myself to the sun without fits of sneezing andthe other disagreeable symptoms coming on. It was sufficient torepeat the treatment three times a day, even under the mostunfavourable circumstances, in order to keep myself quite free. [Footnote: There is no foundation for the objection that syringing thenose could not cure the asthma which accompanies hay fever; for thisasthma is only the reflex effect arising from the irritation of thenose. --B. ] There were then no such vibrios in the secretion. If Ionly go out in the evening, it suffices to inject the quinine once aday, just before going. After continuing this treatment for some daysthe symptoms disappear completely, but if I leave off they return tilltowards the end of June. 

'My first experiments with quinine date from the summer of 1867; thisyear (1868) I began at once as soon as the first traces of the illnessappeared, and I have thus been able to stop its developmentcompletely. 

'I have hesitated as yet in publishing the matter, because I havefound no other patient [Footnote: Helmholtz, now Professor ofPhysics at the University of Berlin, is, although M. D. , no medicalpractitioner. --B. ] on whom I could try the experiment. There is, itseems to me, no doubt, considering the extraordinary regularity in therecurrence and course of the illness, that quinine had here a mostquick and decided effect. And this again makes my hypothesis veryprobable, that the vibrios, although of no specific form but a veryfrequent one, are at least the cause of the rapid increase of thesymptoms in warm air, as heat excites them to lively action. 

I should be very glad if the above lines would induce medical men inEngland--the haunt of hay fever--to test the observation of Helmholtz. To most patients the application with the pipette may be too difficultor impossible; I have therefore already suggested the use of Weber'svery simple but effective nose-douche. Also it will be advisable toapply the solution of quinine _tepid_. It can, further, not be repeatedoften enough that quinine is frequently adulterated, especially withcinchona, the action of which is much less to be depended upon. 

Dr. Frickhoefer, of Schwalbach, has communicated to me a second casein which hay fever was cured by local application of quinine. [Footnote: Cf. Virchow's 'Archiv. ' (1870), vol. Li. P. 176. ]Professor Busch, of Bonn, authorises me to say that he succeeded intwo cases of 'catarrhus aestivus' by the same method: a third patientwas obliged to abstain from the use of quinine, as it produced anunbearable irritation of the sensible nerves of the nose. In theautumn of 1872 Helmholtz told me that his fever was quite cured, andthat in the meantime two other patients had, by his advice, tried thismethod, and with the same success. [Footnote: Prof. Helmholtz, whom Ihad the pleasure of meeting in Switzerland last year, then told methat he was quite convinced that hay fever was produced by the pollenafloat in early summer in the atmosphere. ]

********************

VI. VOYAGE TO ALGERIA TO OBSERVE THE ECLIPSE. 

1870. 

THE opening of the Eclipse Expedition was not propitious. Portsmouth, on Monday, December 5, 1870, was swathed by fog, which was intensifiedby smoke, and traversed by a drizzle of fine rain. At six P. M. I wason board the "Urgent. " On Tuesday morning the weather was too thick topermit of the ship's being swung and her compasses calibrated. TheAdmiral of the port, a man of very noble presence, came on board. Under his stimulus the energy which the weather had damped appeared tobecome more active, and soon after his departure we steamed down toSpithead. Here the fog had so far lightened as to enable the officersto swing the ship. 

At three P. M. On Tuesday, December 6, we got away, glidingsuccessively past Whitecliff Bay, Bembridge, Sandown, Shanklin, Ventnor, and St. Catherine's Lighthouse. On Wednesday morning wesighted the Isle of Ushant, on the French side of the Channel. Thenorthern end of the island has been fretted by the waves into detachedtower-like masses of rock of very remarkable appearance. In theChannel the sea was green, and opposite Ushant it was a brightergreen. On Wednesday evening we committed ourselves to the Bay ofBiscay. The roll of the Atlantic was full, but not violent. Therehad been scarcely a gleam of sunshine throughout the day, but thecloud-forms were fine, and their apparent solidity impressive. OnThursday morning the green of the sea was displaced by a deep indigoblue. The whole of Thursday we steamed across the bay. We had littleblue sky, but the clouds were again grand and varied--cirrus, stratus, cumulus, and nimbus, we had them all. Dusky hair-like trails weresometimes dropped from the distant clouds to the sea. 

These were falling showers, and they sometimes occupied the wholehorizon, while we steamed across the rainless circle which was thussurrounded. Sometimes we plunged into the rain, and once or twice, byslightly changing our course, avoided a heavy shower. From time totime perfect rainbows spanned the heavens from side to side. At timesa bow would appear in fragments, showing the keystone of the archmidway in air, and its two buttresses on the horizon. In all casesthe light of the bow could be quenched by a Nicol's prism, with itslong diagonal tangent to the arc. Sometimes gleaming patches of thefirmament were seen amid the clouds. When viewed in the properdirection, the gleam could be quenched by a Nicol's prism, a darkaperture being thus opened into stellar space. 

At sunset on Thursday the denser clouds were fiercely fringed, whilethrough the lighter ones seemed to issue the glow of a conflagration. On Friday morning we sighted Cape Finisterre--the extreme end of thearc which sweeps from Ushant round the Bay of Biscay. Calm spaces ofblue, in which floated quietly scraps of cumuli, were behind us, butin front of us was a horizon of portentous darkness. It continuedthus threatening throughout the day. Towards evening the windstrengthened to a gale, and at dinner it was difficult to preserve theplates and dishes from destruction. Our thinned company hinted thatthe rolling had other consequences. It was very wild when we went tobed. I slumbered and slept, but after some time was renderedanxiously conscious that my body had become a kind of projectile, withthe ship's side for a target. I gripped the edge of my berth to savemyself from being thrown out. Outside, I could hear somebody say thathe had been thrown from his berth, and sent spinning to the other sideof the saloon. The screw laboured violently amid the lurching; itincessantly quitted the water, and, twirling in the air, rattledagainst its bearings, causing the ship to shudder from stem to stern. At times the waves struck us, not with the soft impact which might beexpected from a liquid, but with the sudden solid shock ofbattering-rams. 'No man knows the force of water, ' said one of theofficers, ' until he has experienced a storm at sea. ' These blowsfollowed each other at quicker intervals, the screw rattling aftereach of them, until, finally, the delivery of a heavier stroke thanordinary seemed to reduce the saloon to chaos. Furniture crashed, glasses rang, and alarmed enquiries immediately followed. Amid thenoises I heard one note of forced laughter; it sounded very ghastly. Men tramped through the saloon, and busy voices were heard aft, as ifsomething there had gone wrong. 

I rose, and not without difficulty got into my clothes. In theafter-cabin, under the superintendence of the able and energeticnavigating lieutenant, Mr. Brown, a group of blue-jackets were workingat the tiller-ropes. These had become loose, and the helm refused toanswer the wheel. High moral lessons might be gained on shipboard, byobserving what steadfast adherence to an object can accomplish, andwhat large effects are heaped up by the addition of infinitesimals. The tiller-rope, as the blue-jackets strained in concert, seemedhardly to move; still it did move a little, until finally, by timingthe pull to the lurching of the ship, the mastery of the rudder wasobtained. I had previously gone on deck. Round the saloon-door werea few members of the eclipse party, who seemed in no mood forscientific observation. Nor did I; but I wished to see the storm. Iclimbed the steps to the poop, exchanged a word with Captain Toynbee, the only member of the party to be seen on the poop, and by hisdirection made towards a cleat not far from the wheel. [Footnote: Thecleat is a T-shaped mass of metal employed for the fastening ofropes. ] Round it I coiled my arms. With the exception of the men atthe wheel, who stood as silent as corpses, I was alone. 

I had seen grandeur elsewhere, but this was a new form of grandeur tome. The "Urgent" is long and narrow, and during our expedition shelacked the steadying influence of sufficient ballast. She was for atime practically rudderless, and lay in the trough of the sea. Icould see the long ridges, with some hundreds of feet between theircrests, rolling upon the ship perfectly parallel to her sides. Asthey approached, they so grew upon the eye as to render the expression'mountains high' intelligible. At all events, there was no mistakingtheir mechanical might, as they took the ship upon their shoulders, and swung her like a pendulum. The deck sloped sometimes at an anglewhich I estimated at over forty-five degrees; wanting my previousAlpine practice, I should have felt less confidence in my grip of thecleat. Here and there the long rollers were tossed by interferenceinto heaps of greater height. The wind caught their crests, andscattered them over the sea, the whole surface of which was seethingwhite. The aspect of the clouds was a fit accompaniment to the furyof the ocean. The moon was almost full--at times concealed, at timesrevealed, as the scud flew wildly over it. These things appealed tothe eye, while the ear was filled by the groaning of the screw and thewhistle and boom of the storm. 

Nor was the outward agitation the only object of interest to me. Iwas at once subject and object to myself, and watched with intenseinterest the workings of my own mind. The "Urgent" is an elderlyship. She had been built, I was told, by a contracting firm for someforeign Government, and had been diverted from her first purpose whenconverted into a troop-ship. She had been for some time out of work, and I had heard that one of her boilers, at least, needed repair. Ourscanty but excellent crew, moreover, did not belong to the "Urgent, "but had been gathered from other ships. Our three lieutenants werealso volunteers. All this passed swiftly through my mind as thesteamer shook under the blows of the waves, and I thought thatprobably no one on board could say how much of this thumping andstraining the "Urgent" would be able to bear. This uncertainty causedme to look steadily at the worst, and I tried to strengthen myself inthe face of it. 

But at length the helm laid hold of the water, and the ship was gotgradually round to face the waves. The rolling diminished, a certainamount of pitching taking its place. Our speed had fallen from elevenknots to two. I went again to bed. After a space of calm, when weseemed crossing the vortex of a storm, heavy tossing recommenced. Iwas afraid to allow myself to fall asleep, as my berth was high, andto be pitched out of it might be attended with bruises, if not withfractures. From Friday at noon to Saturday at noon we accomplishedsixty-six miles, or an average of less than three miles an hour. Ioverheard the sailors talking about this storm. The "Urgent, "according to those that knew her, had never previously experiencedanything like it. [Footnote: 'There is, it will be seen, a fairagreement between these impressions and those so vigorously describedby a scientific correspondent of the 'Times. ']

All through Saturday the wind, though somewhat sobered, blew deadagainst us. The atmospheric effects were exceedingly fine. Thecumuli resembled mountains in shape, and their peaked summitsshone as white as Alpine snows. At one place this resemblance wasgreatly strengthened by a vast area of cloud, uniformly illuminated, and lying like a _névé_ below the peaks. From it fell a kind ofcloud-river strikingly like a glacier. The horizon at sunset wasremarkable--spaces of brilliant green between clouds of fiery red. Rainbows had been frequent throughout the day, and at night aperfectly continuous lunar bow spanned the heavens from side to side. Its colours were feeble; but, contrasted with the black ground againstwhich it rested, its luminousness was extraordinary. 

Sunday morning found us opposite to Lisbon, and at midnight we roundedCape St. Vincent, where the lurching seemed disposed to recommence. Through the kindness of Lieutenant Walton, a cot had been slung forme. It hung between a tiller-wheel and a flue, and at one A. M. I wasroused by the banging of the cot against its boundaries. But the windwas now behind us, and we went along at a speed of eleven knots. Wefelt certain of reaching Cadiz by three. But a new lighthouse came insight, which some affirmed to be Cadiz Lighthouse, while thesurrounding houses were declared to be those of Cadiz itself. Out ofdeference to these statements, the navigating lieutenant changed hiscourse, and steered for the place. A pilot came on board, and heinformed us that we were before the mouth of the Guadalquivir, andthat the lighthouse was that of Cipiòna. Cadiz was still someeighteen miles distant. 

We steered towards the city, hoping to get into the harbour beforedark. But the pilot who would have guided us had been snapped up byanother vessel, and we did not get in. We beat about during thenight, and in the morning found ourselves about fifteen miles fromCadiz. The sun rose behind the city, and we steered straight into thelight. The three-towered cathedral stood in the midst, round whichswarmed apparently a multitude of chimney-stacks. A nearer approachshowed the chimneys to be small turrets. A pilot was taken on board;for there is a dangerous shoal in the harbour. The appearance of thetown as the sun shone upon its white and lofty walls was singularlybeautiful. We cast anchor; some officials arrived and demanded aclean bill of health. We had none. They would have nothing to dowith us; so the yellow quarantine flag was hoisted, and we waited forpermission to land the Cadiz party. After some hours' delay theEnglish consul and vice-consul came on board, and with them a Spanishofficer ablaze with gold lace and decorations. Under slight pressurethe requisite permission had been granted. We landed our party, andin the afternoon weighed anchor. Thanks to the kindness of ourexcellent paymaster, I was here transferred to a more roomy berth. 

Cadiz soon sank beneath the sea, and we sighted in succession CapeTrafalgar, Tarifa, and the revolving light of Ceuta. The water wasvery calm, and the moon rose in a quiet heaven. She swung with herconvex surface downwards, the common boundary between light and shadowbeing almost horizontal. A pillar of reflected light shimmered up tous from the slightly rippled sea. I had previously noticed thephosphorescence of the water, but tonight it was stronger than usual, especially among the foam at the bows. A bucket let down into the seabrought up a number of the little sparkling organisms which caused thephosphorescence. I caught some of them in my hand. And here anappearance was observed which was new to most of us, and strikinglybeautiful to all. Standing at the bow and looking forwards, at adistance of forty or fifty yards from the ship, a number of luminousstreamers were seen rushing towards us. On nearing the vessel theyrapidly turned, like a comet round its perihelion, placed themselvesside by side, and, in parallel trails of light, kept up with the ship. One of them placed itself right in front of the bow as a pioneer. These comets of the sea were joined at intervals by others. Sometimesas many as six at a time would rush at us, bend with extraordinaryrapidity round a sharp curve, and afterwards keep us company. Ileaned over the bow, and scanned the streamers closely. The frontalportion of each of them revealed the outline of a porpoise. The rushof the creatures through the water had started the phosphorescence, every spark of which was converted by the motion of the retina into aline of light. Each porpoise was thus wrapped in a luminous sheath. The phosphorescence did not cease at the creature's tail, but wascarried many porpoise-lengths behind it. 

To our right we had the African hills, illuminated by the moon. Gibraltar Rock at length became visible, but the town remained longhidden by a belt of haze, through which at length the brighter lampsstruggled. It was like the gradual resolution of a nebula into stars. As the intervening depth became gradually less, the mist vanished moreand more, and finally all the lamps shone through it They formed abright foil to the sombre mass of rock above them. The sea was socalm and the scene so lovely that Mr. Huggins and myself stayed ondeck till near midnight, when the ship was moored. During our walkingto and fro a striking enlargement of the disk of Jupiter wasobserved, whenever the heated air of the funnel came between us andthe planet. On passing away from the heated air, the flat dim diskwould immediately shrink to a luminous point. The effect was one ofvisual persistence. The retinal image of the planet was set quiveringin all azimuths by the streams of heated air, describing in quicksuccession minute lines of light, which summed themselves to a disk ofsensible area. 

At six o'clock next morning, the gun at the Signal Station on thesummit of the rock, boomed. At eight the band on board the'Trafalgar' training-ship, which was in the harbour, struck up thenational anthem; and immediately afterwards a crowd of mite-likecadets swarmed up the rigging. After the removal of the apparatusbelonging to the Gibraltar party we went on shore. Winter was inEngland when we left, but here we had the warmth of summer. Thevegetation was luxuriant--palm-trees, cactuses, and aloes, all ablazewith scarlet flowers. A visit to the Governor was proposed, as an actof necessary courtesy, and I accompanied Admiral Ommaney and Mr. Huggins to 'the Convent, ' or Government House. We sent in our cards, waited for a time, and were then conducted by an orderly to hisExcellency. He is a fine old man, over six feet high, and of frankmilitary bearing. He received us and conversed with us in a verygenial manner. He took us to see his garden, his palms, his shadedpromenades, and his orange-trees loaded with fruit, in all of which hetook manifest delight. Evidently 'the hero of Kars' had fallen uponquarters after his own heart. He appeared full of good nature, andengaged us on the spot to dine with him that day. 

We sought the town-major for a pass to visit the lines. Whileawaiting his arrival I purchased a stock of white glass bottles, witha view to experiments on the colour of the sea. Mr. Huggins andmyself, who wished to see the rock, were taken by Captain Salmond tothe library, where a model of Gibraltar is kept, and where we had auseful preliminary lesson. At the library we met Colonel Maberly, acourteous and kindly man, who gave us good advice regarding ourexcursion. He sent an orderly with us to the entrance of the lines. The orderly handed us over to an intelligent Irishman, who wasdirected to show us everything that we desired to see, and to hidenothing from us. We took the 'upper line, ' traversed the gallerieshewn through the limestone; looked through the embrasures, whichopened like doors in the precipice, towards the hills of Spain;reached St. George's hall, and went still higher, emerging on thesummit of one of the noblest cliffs I have ever seen. 

Beyond were the Spanish lines, marked by a line of white sentry-boxes;nearer were the English lines, less conspicuously indicated; andbetween both was the neutral ground. Behind the Spanish lines rosethe conical hill called the Queen of Spain's Chair. The generalaspect of the mainland from the rock is bold and rugged. Doublingback from the galleries, we struck upwards towards the crest, reachedthe Signal Station, where we indulged in 'shandy-gaff' and bread andcheese. Thence to O'Hara's Tower, the highest point of the rock. Itwas built by a former Governor, who, forgetful of the laws ofterrestrial curvature, thought he might look from the tower into-theport of Cadiz. The tower is riven, and it may be climbed along theedges of the crack. We got to the top of it; thence descended thecurious Mediterranean Stair--a zigzag, mostly of steps down a steeplyfalling slope, amid palmetto brush, aloes, and prickly pear. 

Passing over the Windmill Hill, we were joined at the 'Governor'sCottage' by a car, and drove afterwards to the lighthouse at EuropaPoint. The tower was built, I believe, by Queen Adelaide, and itcontains a fine dioptric apparatus of the first order, constructed byMessrs. Chance, of Birmingham. At the appointed hour we were at theConvent. During dinner the same genial traits which appeared in themorning were still more conspicuous. The freshness of the Governor'snature showed itself best when he spoke of his old antagonist in arms, Mouravieff. Chivalry in war is consistent with its stern prosecution. These two men were chivalrous, and after striking the last blow becamefriends for ever. Our kind and courteous reception at Gibraltar is athing to be remembered with pleasure. 

On December 15 we committed ourselves to the Mediterranean. The viewsof Gibraltar with which we are most acquainted represent it as a hugeridge; but its aspect, end on, both from the Spanish lines and fromthe other side, is truly noble. There is a sloping bank of sand atthe back of the rock, which I was disposed to regard simply as the_débris_ of the limestone. I wished to let myself down upon it, but hadnot the time. My friend Mr. Busk, however, assures me that it issilica, and that the same sand constitutes the adjacent neutralground. There are theories afloat as to its having been blown fromSahara. The Mediterranean throughout this first day, and indeedthroughout the entire voyage to Oran, was of a less deep blue than theAtlantic. Possibly the quantity of organisms may have modified thecolour. At night the phosphorescence was startling, breaking suddenlyout along the crests of the waves formed by the port and starboardbows. Its strength was not uniform. Having flashed brilliantly for atime, it would in part subside, and afterwards regain its vigour. Several large phosphorescent masses of weird appearance also floatedpast. 

On the morning of the 16th we sighted the fort and lighthouse of Marsael Kibir, and beyond them the white walls of Oran lying in the bightof a bay, sheltered by dominant hills. The sun was shining brightly;during our whole voyage we had not had so fine a day. The wisdomwhich had led us to choose Oran as our place of observation seemeddemonstrated. A rather excitable pilot came on board, and he guidedus in behind the Mole, which had suffered much damage the previousyear from an unexplained outburst of waves from the Mediterranean. Both port and bow anchors were cast in deep water. With three hugehawsers the ship's stem was made fast to three gun-pillars fixed inthe Mole; and here for a time the "Urgent" rested from her labours. 

M. Janssen, who had rendered his name celebrated by his observationsof the eclipse in India in 1868, when he showed the solar flames to beeruptions of incandescent hydrogen, was already encamped in the opencountry about eight miles from Oran. On December 2 he had quittedParis in a balloon, with a strong young sailor as his assistant, haddescended near the mouth of the Loire, seen M. Gambetta, and receivedfrom him encouragement and aid. On the day of our arrival hisencampment was visited by Mr. Huggins, and the kind and courteousEngineer of the Port drove me subsequently, in his own phaeton, to theplace. It bore the best repute as regards freedom from haze and fog, and commanded an open outlook; but it was inconvenient for us onaccount of its distance from the ship. The place next in repute wasthe railway station, between two and three miles distant from theMole. It was inspected, but, being enclosed, was abandoned for aneminence in an adjacent garden, the property of Mr. Hinshelwood, aScotchman who had settled some years previously as an Esparto merchantin Oran. [Footnote: Esparto is a kind of grass now much used in themanufacture of paper. ] He, in the most liberal manner, placed hisground at the disposition of the party. Here the tents were pitched, on the Saturday, by Captain Salmond and his intelligent corps ofsappers, the instruments being erected on the Monday under cover ofthe tents. 

Close to the railway station runs a new loopholed wall of defence, through which the highway passes into the open country. Standing onthe highway, and looking southwards, about twenty yards to the rightis a small bastionet, intended to carry a gun or two. Its roof Ithought would form an admirable basis for my telescope, while the viewof the surrounding country was unimpeded in all directions. Theauthorities kindly allowed me the use of this bastionet. Two men, onea blue-jacket named Elliot, and the other a marine named Hill, wereplaced at my disposal by Lieutenant Walton; and, thus aided, on Mondaymorning I mounted my telescope. The instrument was new to me, andsome hours of discipline were spent in mastering all the details ofits manipulation. 

Mr. Huggins joined me, and we visited together the Arab quarter ofOran. The flat-roofed houses appeared very clean and white. Thestreet was filled with loiterers, and the thresholds were occupied bypicturesque groups. Some of the men were very fine. We saw manystraight, manly fellows who must have been six feet four in height. They passed us with perfect indifference, evincing no anger, suspicion, or curiosity, hardly caring in fact to glance at us as wepassed. In one instance only during my stay at Oran was I spoken toby an Arab. He was a tall, good-humoured fellow, who came smiling upto me, and muttered something about 'les Anglais. ' The mixedpopulation of Oran is picturesque in the highest degree: the Jews, rich and poor, varying in their costumes as their wealth varies; theArabs more picturesque still, and of all shades of complexion--thenegroes, the Spaniards, the French, all grouped together, each racepreserving its own individuality, formed a picture intenselyinteresting to me. 

On Tuesday, the 20th, I was early at the bastionet. The night hadbeen very squally. The sergeant of the sappers had taken charge ofour key, and on Tuesday morning Elliot went for it. He brought backthe intelligence that the tents had been blown down, and theinstruments overturned. Among these was a large and valuableequatorial from the Royal Observatory, Greenwich. It seemed hardlypossible that this instrument, with its wheels and verniers anddelicate adjustments, could have escaped uninjured from such a fall. This, however, was the case; and during the day all the overturnedinstruments were restored to their places, and found to be inpractical working order. This and the following day were devoted toincessant schooling. I had come out as a general stargazer, and notwith the intention of devoting myself to the observation of anyparticular phenomenon. I wished to see the whole--the first contact, the advance of the moon, the successive swallowing up of the solarspots, the breaking of the last line of crescent by the lunarmountains into Bailey's beads, the advance of the shadow through theair, the appearance of the corona and prominences at the moment oftotality, the radiant streamer; of the corona, the internal structureof the flames, a glance through a polariscope, a sweep round thelandscape with the naked eye, the reappearance of the soar limbthrough Bailey's beads, and, finally, the retreat of the lunar shadowthrough the air. 

I was provided with a telescope of admirable definition, mounted, adjusted, packed, and most liberally placed at my disposal by Mr. Warren De La Rue. The telescope grasped the whole of the sun, and aconsiderable portion of the space surrounding it. But it would nottake in the extreme limits of the corona. For this I had lashed on tothe large telescope a light but powerful instrument, constructed byRoss, and lent to me by Mr. Huggins. I was also furnished with anexcellent binocular by Mr. Dallmeyer. In fact, no man could have beenmore efficiently supported. 

It required a strict parcelling out of the interval of totality toembrace in it the entire series of observations. These, while the sunremained visible, were to be made with an unsilvered diagonaleye-piece, which reflected but a small fraction of the sun's light, this fraction, being still further toned down by a dark glass. At themoment of totality the dark glass was to be removed, and a silverreflector pushed in, so as to get the maximum of light from the coronaand prominences The time of totality was distributed as follows:

1. Observe approach of shadow through the air: totality. 

2. Telescope 30 seconds. 

3. Finder 30 seconds. 

4. Double image prism 15 seconds. 

5. Naked eye 10 seconds. 

6. Finder or binocular 20 seconds. 

7. Telescope 20 seconds. 

8. Observe retreat of shadow. 

In our rehearsals Elliot stood beside me, watch in hand, andfurnished with a lantern. He called out at the end of each interval, while I moved from telescope to finder, from finder to polariscope, from polariscope to naked eye, from naked eye back to finder, fromfinder to telescope, abandoning the instrument finally to observe theretreating shadow. All this we went over twenty times, while lookingat the actual sun, and keeping him in the middle of the field. It wasmy object to render the repetition of the lesson so mechanical as toleave no room for flurry, forgetfulness, or excitement. Volition wasnot to be called upon, nor judgment exercised, but a well-beaten pathof routine was to be followed. Had the opportunity occurred, I thinkthe programme would have been strictly carried out. 

But the opportunity did not occur. For several days the weather hadbeen ill-natured. We had wind so strong As to render the hawsers atthe stern of the "Urgent" as rigid as iron, and to destroy thenavigating lieutenant's sleep. We had clouds, a thunder-storm, andsome rain. Still the hope was held out that the atmosphere wouldcleanse itself, and if it did we were promised air of extraordinarylimpidity. Early on the 22nd we were all at our posts. Spaces ofblue in the early morning gave us some encouragement, but all dependedon the relation of these spaces to the surrounding clouds. Which ofthem were to grow as the day advanced? The wind was high, and tosecure the steadiness of my instrument I was forced to retreat behinda projection of the bastionet, place stones upon its stand, and, further, to avail myself of the shelter of a sail. My practised menfastened the sail at the top, and loaded it with boulders at thebottom. It was tried severely, but it stood firm. 

The clouds and blue spaces fought for a time with varying success. Thesun was bidden and revealed at intervals, hope oscillating insynchronism with the changes of the sky. At the moment of firstcontact a dense cloud intervened; but a minute or two afterwards thecloud had passed, and the encroachment of the black body of the moonwas evident upon the solar disk. The moon marched onward, and I sawit at frequent intervals; a large group of spots were approached andswallowed up. Subsequently I caught sight of the lunar limb as it cutthrough the middle of a large spot. The spot was not to bedistinguished from the moon, but rose like a mountain above it. Theclouds, when thin, could be seen as grey scud drifting across theblack surface of the moon; but they thickened more and more, and madethe intervals of clearness scantier. During these moments I watchedwith an interest bordering upon fascination the march of the silversickle of the sun across the field of the telescope. It was so sharpand so beautiful. No trace of the lunar limb could be observed beyondthe sun's boundary. Here, indeed, it could only be relieved by thecorona, which was utterly cut off by the dark glass. The blackness ofthe moon beyond the sun was, in fact, confounded with the blackness ofspace. 

Beside me was Elliot with the watch and lantern, while LieutenantArcher, of the Royal Engineers, had the kindness to take charge of mynote-book. I mentioned, and he wrote rapidly down, such things asseemed worthy of remembrance. Thus my hands and mind were entirelyfree; but it was all to no purpose. A patch of sunlight fell andrested upon the landscape some miles away. It was the onlyilluminated spot within view. But to the north-west there was still aspace of blue which might reach us in time. Within seven minutes oftotality another space towards the zenith became very dark. Theatmosphere was, as it were, on the brink of a precipice, being chargedwith humidity, which required but a slight chill to bring it down inclouds. This was furnished by the withdrawal of the solar beams: theclouds did come down, covering up the space of blue on which our hopeshad so long rested. I abandoned the telescope and walked to and froin despair. As the moment of totality approached, the descent towardsdarkness was as obvious as a falling stone. I looked towards adistant ridge, where the darkness would first appear. At the moment afan of beams, issuing from the hidden sun, was spread out over thesouthern heavens. These beams are bars of alternate light and shade, produced in illuminated haze by the shadows of floating cloudlets ofvarying density. The beams are practically parallel, but by an effectof perspective they appear divergent, having the sun, in fact, fortheir point of convergence. The darkness took possession of the ridgereferred to, lowered upon M. Janssen's observatory, passed over thesouthern heavens, blotting out the beams as if a sponge had been drawnacross them. It then took successive possession of three spaces ofblue sky in the south-eastern atmosphere. I again looked towards theridge. A glimmer as of day-dawn was behind it, and immediatelyafterwards the fan of beams, which had been for more than two minutesabsent, revived. The eclipse of 1870 had ended, and, as far as thecorona and flames were concerned, we had been defeated. 

Even in the heart of the eclipse the darkness was by no means perfect. Small print could be read. In fact, the clouds which rendered the daya dark one, by scattering light into the shadow, rendered the darknessless intense than it would have been had the atmosphere been withoutcloud. In the more open spaces I sought for stars, but could findnone. There was a lull in the wind before and after totality, butduring the totality the wind was strong. I waited for some time onthe bastionet, hoping to get a glimpse of the moon on the oppositeborder of the sun, but in vain. The clouds continued, and some rainfell. The day brightened somewhat afterwards, and, having packed allup, in the sober twilight Mr. Crookes and myself climbed the heightsabove the fort of Vera Cruz. From this eminence we had a very nobleview over the Mediterranean and the flanking African hills. Thesunset was remarkable, and the whole outlook exceedingly fine. 

The able and well-instructed medical officer of the "Urgent, " Mr. Goodman, observed the following temperatures during the progress ofthe eclipse:

Hour Deg. 

11. 45 56

11. 55 55

12. 10 54

12. 37 53

12. 39 52

12. 43 51

 1. 5 52

 1. 27 53

 1. 44 56

 2. 10 57

The minimum temperature occurred some minutes after totality, when aslight rain fell. 

The wind was so strong on the 23rd that Captain Henderson would notventure out. Guided by Mr. Goodman, I visited a cave in a remarkablestratum of shell-breccia, and, thanks to my guide, secured specimens. Mr. Busk informs me that a precisely similar breccia, is found atGibraltar, at approximately the same level. During the afternoon, Admiral Ommaney and myself drove to the fort of Marsa el Kibir. Thefortification is of ancient origin, the Moorish arches being stillthere in decay, but the fort is now very strong. About four or fivehundred fine-looking dragoons were looking after their horses, waitingfor a lull to enable them to embark for France. One of their officerswas wandering in a very solitary fashion over the fort. We had someconversation with him. He had been at Sedan, had been taken prisoner, but had effected his escape. He shook his head when we spoke of thetermination of the war, and predicted its long continuance. There wasbitterness in his tone as he spoke of the charges of treason solightly levelled against French commanders. 

The green waves raved round the promontory on which the fort stands, smiting the rocks, breaking into foam, and jumping, after impact, to aheight of a hundred feet and more into the air. As we returned ourvehicle broke down through the loss of a wheel. The Admiral went onboard, while I remained long watching the agitated sea. The littlehorses of Oran well merit a passing word. Their speed and endurance, both of which are heavily drawn upon by their drivers, areextraordinary. 

The wind sinking, we lifted anchor on the 24th. For some hours wewent pleasantly along; but during the afternoon the storm revived, andit blew heavily against us all the night. When we came opposite theBay of Almeria, on the 25th, the captain turned the ship, and steeredinto the bay, where, under the shadow of the Sierra Nevada, we passedChristmas night in peace. Next morning 'a rose of dawn' rested on thesnows of the adjacent mountains, while a purple haze was spread overthe lower hills. I had no notion that Spain possessed so fine a rangeof mountains as the Sierra Nevada. The height is considerable, butthe form also is such as to get the maximum of grandeur out of theheight. We weighed anchor at eight A. M. , passing for a time throughshoal water, the bottom having been evidently stirred up. Theadjacent land seemed eroded in a remarkable manner. It has itsfloods, which excavate these valleys and ravines, and leave thosesingular ridges behind. Towards evening I climbed the mainmast, and, standing on the cross-trees, saw the sun set amid a blaze of fieryclouds. The wind was strong and bitterly cold, and I was glad toslide back to the deck along a rope, which stretched from themast-head to the ship's side. That night we cast anchor beside theMole of Gibraltar. 

On the morning of the 27th, in company with two friends, I drove tothe Spanish lines, with the view of seeing the rock from that side. Itis an exceedingly noble mass. The Peninsular and Oriental mail-boathad been signalled and had come. Heavy duties called me homeward, andby transferring myself from the "Urgent" to the mail-steamer I shouldgain three days. I hired a boat, rowed to the steamer, learned thatshe was to start at one, and returned with all speed to the "Urgent. "Making known to Captain Henderson my wish to get away, he expresseddoubts as to the possibility of reaching the mail-steamer in time. With his accustomed kindness, he however placed a boat at my disposal. Four hardy fellows and one of the ship's officers jumped into it; myluggage, hastily thrown together, was tumbled in, and we wereimmediately on our way. We had nearly four miles to row in abouttwenty minutes; but we hoped the mail-boat might not be punctual. Fora time we watched her anxiously; there was no motion; we came nearer, but the flags were not yet hauled in. The men put forth all theirstrength, animated by the exhortations of the officer at the helm. The roughness of the sea rendered their efforts to some extentnugatory: still we were rapidly approaching the steamer. At lengthshe moved, punctual almost to the minute, at first slowly, but soonwith quickened pace. 

We turned to the left, so as to cut across her bows. Five minutes'pull would have brought us up to her. The officer waved his cap and Imy hat. 'If they could only see us, they might back to us in amoment. ' But they did not see us, or if they did, they paid us noattention. I returned to the "Urgent, " discomfited, but grateful tothe fine fellows who had wrought so hard to carry out my wishes. 

Glad of the quiet, in the sober afternoon I took a walk towards EuropaPoint. The sky darkened and heavy squalls passed at intervals. Private theatricals were at the Convent, and the kind and courteousGovernor had sent cards to the eclipse party. I failed in my duty innot going. St. Michael's Cave is said to rival, if it does notoutrival, the Mammoth Cave of Kentucky. On the 28th Mr. Crookes, Mr. Carpenter, and myself, guided by a military policeman who understoodhis work, explored the cavern. The mouth is about 1, 100 feet abovethe sea. We zigzagged up to it, and first were led into an aperturein the rock, at some height above the true entrance of the cave. Inthis upper cavern we saw some tall and beautiful stalactite pillars. 

The water drips from the roof charged with bicarbonate of lime. Exposed to the air, the carbonic acid partially escapes, and thesimple carbonate of lime, which is hardly at all soluble in water, deposits itself as a solid, forming stalactites and stalagmites. Eventhe exposure of chalk or limestone water to the open air partiallysoftens it. A specimen of the Redbourne water exposed by ProfessorsGraham, Miller, and Hofmann, in a shallow basin, fell from eighteendegrees to nine degrees of hardness. The softening process of Clarkis virtually a hastening of the natural process. Here, however, instead of being permitted to evaporate, half the carbonic acid isappropriated by lime, the half thus taken up, as well as the remaininghalf, being precipitated. The solid precipitate is permitted to sink, and the clear supernatant liquid is limpid soft water. 

We returned to the real mouth of St. Michael's Cave, which is enteredby a wicket. The floor was somewhat muddy, and the roof and wallswere wet. We soon found ourselves in the midst of a natural temple, where tall columns sprang complete from floor to roof, while incipientcolumns were growing to meet each other, upwards and downwards. Thewater which trickles from the stalactite, after having in part yieldedup its carbonate of lime, falls upon the floor vertically underneath, and there builds the stalagmite. Consequently, the pillars grow fromabove and below simultaneously, along the same vertical. It is easyto distinguish the stalagmitic from the stalactitic portion of thepillars. The former is always divided into short segments byprotuberant rings, as if deposited periodically, while the latterpresents a uniform surface. In some cases the points of invertedcones of stalactite rested on the centres of pillars of stalagmite. The process of solidification and the consequent architecture werealike beautiful. 

We followed our guide through various branches and arms of the cave, climbed and descended steps, halted at the edges of dark shafts andapertures, and squeezed ourselves through narrow passages. From timeto time we halted, while Mr. Crookes illuminated with ignitedmagnesium wire, the roof, columns, dependent spears, and gracefuldrapery of the stalactites. Once, coming to a magnificent cluster oficicle-like spears, we helped ourselves to specimens. There was somedifficulty in detaching the more delicate ones, their fragility was sogreat. A consciousness of vandalism, which smote me at the time, haunts me still; for, though our requisitions were moderate, thisbeauty ought not to be at all invaded. Pendent from the roof, intheir natural habitat, nothing can exceed their delicate beauty; they_live_, as it were, surrounded by organic connections. In London theyare curious, but not beautiful. Of gathered shells Emerson writes:

 I wiped away the weeds and foam, And brought my sea-born treasures home But the poor, unsightly, noisome things Had left their beauty on the shore, With the sun, and the sand, and the wild uproar. 

The promontory of Gibraltar is so burrowed with caverns that it hasbeen called the Hill of Caves. They are apparently related to thegeologic disturbances which the rock has undergone. The earliest ofthese is the tilting of the once horizontal strata. Suppose a forceof torsion to act upon the promontory at its southern extremity nearEuropa Point, and suppose the rock to be of a partially yieldingcharacter; such a force would twist the strata into screw-surfaces, the greatest amount of twisting being endured near the point ofapplication of the force. Such a twisting the rock appears to havesuffered; but instead of the twist fading gradually and uniformly off, in passing from south to north, the want of uniformity in the materialhas produced lines of dislocation where there are abrupt changes inthe amount of twist. Thus, at the northern end of the rock the dip tothe west is nineteen degrees; in the Middle Hill, it is thirty-eightdegrees; in the centre of the South hill, or Sugar Loaf, it isfifty-seven degrees. At the southern extremity of the Sugar Loafstrata are vertical, while farther to the south they actually turnover and dip to the east. 

The rock is thus divided into three sections, separated from eachother by places of dislocation, where the strata are much wrenched andbroken. These are called the Northern and Southern Quebrada, from theSpanish 'Tierra Quebrada, ' or broken ground. It is at these placesthat the inland caves of Gibraltar are almost exclusively found. Basedon the observations of Dr. Falconer and himself, an excellent and mostinteresting account of these 'caves, and of the human remains andworks of art which they contain, was communicated by Mr. Busk to themeeting of the Congress of Prehistoric Archaeology at Norwich, andafterwards printed in the 'Transactions' of the Congress. [Footnote:In this essay Mr. Busk refers to the previous labours of Mr. Smith, ofJordan Hill, to whom we owe most of our knowledge of the geology ofthe rock. ] Long subsequent to the operation of the twisting forcejust referred to, the promontory underwent various changes of level. There are sea-terraces and layers of shell-breccia along its flanks, and numerous caves which, unlike the inland ones, are the product ofmarine erosion. The Ape's Hill, on the African side of the strait, Mr. Busk informs me has undergone similar disturbances. [Footnote: Noone can rise from the perusal of Mr. Busk's paper without a feeling ofadmiration for the principal discoverer and indefatigable explorer ofthe Gibraltar caves, the late Captain Frederick Brome. ]

*****

In the harbour of Gibraltar, on the morning of our departure, Iresumed a series of observations on the colour of the sea. On the wayout a number of specimens had been collected, with a view tosubsequent examination. But the bottles were claret bottles, ofdoubtful purity. At Gibraltar, therefore, I purchased fifteen whiteglass bottles, with ground glass stoppers, and at Cadiz, thanks to thefriendly guidance of Mr. Cameron, I secured a dozen more. Theseseven-and-twenty bottles were filled with water, taken at differentplaces between Oran and Spithead. 

And here let me express my warmest acknowledgments to CaptainHenderson, the commander of H. M. S. "Urgent, " who aided me in myobservations in every possible way. Indeed, my thanks are due to allthe officers for their unfailing courtesy and help. The captainplaced at my disposal his own coxswain, an intelligent fellow namedThorogood, who skilfully attached a cord to each bottle, weighted itwith lead, cast it into the sea, and, after three successive rinsings, filled it under my own eyes. The contact of jugs, buckets, or othervessels was thus avoided; and even the necessity of pouring out thewater, afterwards, through the dirty London air. 

The mode of examination applied to these bottles has been alreadydescribed. [Footnote: On Dust and Disease, p. 168. ] The liquid isilluminated by a powerfully condensed beam, its condition beingrevealed through the light scattered by its suspended particles. 'Careis taken to defend the eye from the access of all other light, and, thus defended, it becomes an organ of inconceivable delicacy. ' Werewater of uniform density perfectly free from suspended matter, itwould, in my opinion, scatter no light at all. The track of aluminous beam could not be seen in such water. But 'an amount ofimpurity so infinitesimal as to be scarcely expressible in numbers, and the individual particles of which are so small as wholly to eludethe microscope, may, when examined by the method alluded to, producenot only sensible, but striking, effects upon the eye. '

The results of the examination of nineteen bottles filled at variousplaces between Gibraltar and Spithead, are here tabulated:

No. Locality Colour of Sea Appearance in Luminous beam

1 Gibraltar Harbour Green Thick with fine particles

2 Two miles Clearer green Thick with very from Gibraltar fine particles

3 Off Cabreta Point Bright green Still thick, but less so

4 Off Cabreta Point Black-indigo Much less thick, very pure

5 Off Tarifa Undecided Thicker than No. 4

6 Beyond Tarifa Cobalt-blue Much purer than No. 5

7 Twelve miles Yellow-green Very thick from Cadiz

8 Cadiz Harbour Yellow-green Exceedingly thick

9 Fourteen miles Yellow-green Thick, but less so from Cadiz

10 Fourteen miles Bright green Much less thick from Cadiz

11 Between Capes Deep Indigo Very little matter, St. Mary and Vincent very pure

12 Off the Burlings. Strong green Thick, with fine matter

13 Beyond the Burlings Indigo Very little matter, pure

14 Off Cape Finisterre Undecided Less pure

15 Bay of Biscay Black-indigo Very little matter, very pure

16 Bay of Biscay Indigo Very fine matter. Iridescent

17 Off Ushant Dark green A good deal of matter

18 Off St. Catherine's Yellow-green Exceedingly thick

19 Spithead Green Exceedingly thick

Here we have three specimens of water, described as green, a clearergreen, and bright green, taken in Gibraltar Harbour, at a point twomiles from the harbour, and off Cabreta Point. The home examinationshowed the first to be thick with suspended matter, the second lessthick, and the third still less thick. Thus the green brightened asthe suspended matter diminished in amount. 

Previous to the fourth observation our excellent navigatinglieutenant, Mr. Brown, steered along the coast, thus avoiding theadverse current which sets in, through the Strait, from the Atlanticto the Mediterranean. He was at length forced to cross the boundaryof the Atlantic current, which was defined with extraordinarysharpness. On the one side of it the water was a vivid green, on theother a deep blue. Standing at the bow of the ship, a bottle could befilled with blue water, while at the same moment a bottle cast fromthe stern could be filled with green water. Two bottles were secured, one on each side of this remarkable boundary. In the distance theAtlantic had the hue called ultra-marine; but looked fairly down upon, it was of almost inky blackness--black qualified by a trace ofindigo. 

What change does the home examination here reveal? In passing toindigo, the water becomes suddenly augmented in purity, the suspendedmatter becoming suddenly less. Off Tarifa, the deep indigodisappears, and the sea is undecided in colour. Accompanying thischange, we have a rise in the quantity of suspended matter. BeyondTarifa, we change to cobalt-blue, the suspended matter falling at thesame time in quantity. This water is distinctly purer than the green. We approach Cadiz, and at twelve miles from the city get intoyellow-green water; this the London examination shows to be thick withsuspended matter. The same is true of Cadiz harbour, and also of apoint fourteen miles from Cadiz in the homeward direction. Here thereis a sudden change from yellow-green to a bright emerald-green, andaccompanying the change a sudden fall in the quantity of suspendedmatter. Between Cape St. Mary and Cape St: Vincent the water changesto the deepest indigo, a further diminution of the suspended matterbeing the concomitant phenomenon. 

We now reach the remarkable group of rocks called the Burlings, andfind the water between the shore and the rocks a strong green; thehome examination shows it to be thick with fine matter. Fifteen ortwenty miles beyond the Burlings we come again into indigo water, fromwhich the suspended matter has in great part disappeared. Off CapeFinisterre, about the place where the 'Captain' went down, the waterbecomes green, and the home examination pronounces it to be thicker. Then we enter the Bay of Biscay, where the indigo resumes its power, and where the home examination shows the greatly augmented purity ofthe water. A second specimen of water, taken from the Bay of Biscay, held in suspension fine particles of a peculiar kind; the size of themwas such as to render the water richly iridescent. It showed itselfgreen, blue, or salmon-coloured, according to the direction of theline of vision. Finally, we come to our last two bottles, the onetaken opposite St. Catherine's lighthouse, in the Isle of Wight, theother at Spithead. The sea at both these places was green, and bothspecimens, as might be expected, were pronounced by the homeexamination to be thick with suspended matter. 

Two distinct series of observations are here referred to--the oneconsisting of direct observations of the colour of the sea, conductedduring the voyage from Gibraltar to Portsmouth: the other carried outin the laboratory of the Royal Institution. And here it is to benoted that in the home examination I never knew what water was placedin my hands. The labels, with the names of the localities writtenupon them, had been tied up, all information regarding the source ofthe water being thus held back. The bottles were simply numbered, andnot till all of them had been examined, and described, were the labelsopened, and the locality and sea-colour corresponding to the variousspecimens ascertained. The home observations, therefore, must havebeen perfectly unbiassed, and they clearly establish the associationof the green colour with fine suspended matter, and of the ultramarinecolour, and more especially of the black-indigo hue of the Atlantic, with the comparative absence of such matter. 

So much for mere observation; but what is the cause of the dark hue ofthe deep ocean? [Footnote: A note, written to me on October 22, by myfriend Canon Kingsley, contains the following reference to this point:'I have never seen the Lake of Geneva, but I thought of the brilliantdazzling dark blue of the mid-Atlantic under the sunlight, and itsblack-blue under cloud, both so solid that one might leap off thesponson on to it without fear; this was to me the most wonderful thingwhich I saw on my voyages to and from the West Indies. ']

A preliminary remark or two will clear our way towards an explanation. Colour resides in white light, appearing when any constituent of thewhite light is withdrawn. The hue of a purple liquid, for example, isimmediately accounted for by its action on a spectrum. It cuts outthe yellow and green, and allows the red and blue to pass through. Theblending of these two colours produces the purple. But while such aliquid attacks with special energy the yellow and green, it enfeeblesthe whole spectrum. By increasing the thickness of the stratum we mayabsorb the whole of the light. The colour of a blue liquid issimilarly accounted for. It first extinguishes the red; then, as thethickness augments, it attacks the orange, yellow, and green insuccession; the blue alone finally remaining. But even it might beextinguished by a sufficient depth of 'the liquid. 

And now we are prepared for a brief, but tolerably complete, statementof that action of sea-water upon light, to which it owes its darkness. The spectrum embraces three classes of rays--the thermal, the visual, and the chemical. These divisions overlap each other; the thermalrays are in part visual, the visual rays in part chemical, and viceversa. The vast body of thermal rays lie beyond the red, beinginvisible. These rays are attacked with exceeding energy by water. They are absorbed close to the surface of the sea, and are the greatagents in evaporation. At the same time the whole spectrum suffersenfeeblement; water attacks all its rays, but with different degreesof energy. Of the visual rays, the red are first extinguished. Asthe solar beam plunges deeper into the sea, orange follows red, yellowfollows orange, green follows yellow, and the various shades of blue, where the water is deep enough, follow green. Absolute extinction ofthe solar beam would be the consequence if the water were deep anduniform. If it contained no suspended matter, such water would be asblack as ink. A reflected glimmer of ordinary light would reach usfrom its surface, as it would from the surface of actual ink; but nolight, hence no colour, would reach us from the body of the water. 

In very clear and deep sea-water this condition is approximatelyfulfilled, and hence the extraordinary darkness of such water. Theindigo, already referred to, is, I believe, to be ascribed in part tothe suspended matter, which is never absent, even in the purestnatural water; and in part to the slight reflection of the light fromthe limiting surfaces of strata of different densities. A modicum oflight is thus thrown back to the eye, before the depth necessary toabsolute extinction has been attained. An effect precisely similaroccurs under the moraines of glaciers. The ice here is exceptionallycompact, and, owing to the absence of the internal scattering commonin bubbled ice, the light plunges into the mass, where it isextinguished, the perfectly clear ice presenting an appearance ofpitchy blackness. [Footnote: I learn from a correspondent that certainWelsh tarns, which are reputed bottomless, have this inky hue. ]

The green colour of the sea has now to be accounted for; and here, again, let us fall back upon the sure basis of experiment. A strongwhite dinner-plate had a lead weight securely fastened to it. Fiftyor sixty yards of strong hempen line were attached to the plate. 

My assistant, Thorogood, occupied a boat, fastened as usual to thedavits of the "Urgent, " while I occupied a second boat nearer thestern of the ship. He cast the plate as a mariner heaves the lead, and by the time it reached me it had sunk a considerable depth in thewater. In all cases the hue of this plate was green. Even when thesea was of the darkest indigo, the green, was vivid and pronounced. Icould notice the gradual deepening of the colour as the plate sank, but at its greatest depth, even in indigo water, the colour was stilla blue-green. [Footnote: In no case, of course, is the green pure, buta mixture of green and blue. ]

Other observations confirmed this one. The "Urgent" is a screwsteamer, and right over the blades of the screw was an orifice calledthe screw-well, through which one could look from the poop down uponthe screw. The surface-glimmer, which so pesters the eye, was here ina great measure removed. Midway down, a plank crossed the screw-wellfrom side to side; on this I placed myself and observed the action ofthe screw underneath. The eye was rendered sensitive by themoderation of the light; and, to remove still further all disturbingcauses, Lieutenant Walton had a sail and tarpaulin thrown over themouth of the well. Underneath this I perched myself on the plank andwatched the screw. In an indigo sea the play of colour wasindescribably beautiful, and the contrast between the water, which hadthe screw-blades, and that which had the bottom of the ocean, as abackground, was extraordinary. The one was of the most brilliantgreen, the other of the deepest ultramarine. The surface of the waterabove the screw-blade was always ruffled. Liquid lenses were thusformed, by which the coloured light was withdrawn from some places andconcentrated upon others, the water flashing with metallic lustre. Thescrew-blades in this case played the part of the dinner-plate in theformer case, and there were other instances of a similar kind. Thewhite bellies of porpoises showed the green hue, varying in intensityas the creatures swung to and fro between the surface and the deeperwater. Foam, at a certain depth below the surface, was also green. In a rough sea the light which penetrated the summit of a wavesometimes reached the eye, a beautiful green cap being thus placedupon the wave, even in indigo water. 

But how is this colour to be connected with the suspended particles?Thus. Take the dinner-plate which showed so brilliant a green whenthrown into indigo water. Suppose it to diminish in size, until itreaches an almost microscopic magnitude. It would still behavesubstantially as the larger plate, sending to the eye its modicum ofgreen light. If the plate, instead of being a large coherent mass, were ground to a powder sufficiently fine, and in this conditiondiffused through the clear sea-water, it would also send green lightto the eye. In fact, the suspended particles which the homeexamination reveals, act in all essential particulars like the plate, or like the screw-blades, or like the foam, or like the bellies of theporpoises. Thus I think the greenness of the sea is physicallyconnected with the matter which it holds in suspension. 

We reached Portsmouth on January 5, 1871. Then ended a voyage which, though its main object was not realised, has left behind it pleasantmemories, both of the aspects of nature and the kindliness of men. 

********************

VII. NIAGARA. 

[Footnote: A Discourse delivered at the Royal Institution of GreatBritain, April 4, 1873. ]

It is one of the disadvantages of reading books about natural scenerythat they fill the mind with pictures, often exaggerated, oftendistorted, often blurred, and, even when well drawn, injurious to thefreshness of first impressions. Such has been the fate of most of uswith regard to the Falls of Niagara. There was little accuracy in theestimates of the first observers of the cataract. Startled by anexhibition of power so novel and so grand, emotion leaped beyond thecontrol of the judgment, and gave currency to notions which have oftenled to disappointment. 

A record of a voyage in 1535 by a French mariner named JacquesCartier, contains, it is said, the first printed allusion to Niagara. In 1603 the first map of the district was constructed by a Frenchmannamed Champlain. In 1648 the Jesuit Rageneau, in a letter to hissuperior at Paris, mentions Niagara as 'a cataract of frightfulheight. ' [Footnote: From an interesting little book presented to me atBrooklyn by its author, Mr. Holly, some of these data are derived:Hennepin, Kalm, Bakewell, Lyell, Hall, and others I have myselfconsulted. ] In the winter of 1678 and 1679 the cataract was visitedby Father Hennepin, and described in a book dedicated 'to the King ofGreat Britain. ' He gives a drawing of the waterfall, which shows thatserious changes have taken place since his time. He describes it as'a great and prodigious cadence of water, to which the universe doesnot offer a parallel. ' The height of the fall, according to Hennepin, was more than 600 feet. 'The waters, ' he says, 'which fall from thisgreat precipice do foam and boil in the most astonishing manner, making a noise more terrible than that of thunder. When the windblows to the south its frightful roaring may be heard for more thanfifteen leagues. ' The Baron la Hontan, who visited Niagara in 1687, makes the height 800 feet. In 1721 Charlevois, in a letter to Madamede Maintenon, after referring to the exaggerations of hispredecessors, thus states the result of his own observations: 'For mypart, after examining it on all sides, I am inclined to think that wecannot allow it less than 140 or 150 feet, '--a remarkably closeestimate. At that time, viz. A hundred and fifty years ago, it hadthe shape of a horseshoe, and reasons will subsequently be given forholding that this has been always the form of the cataract, from itsorigin to its present site. 

As regards the noise of the fall, Charlevois declares the accounts ofhis predecessors, which, I may say, are repeated to the present hour, to be altogether extravagant. He is perfectly right. The thunders ofNiagara are formidable enough to those who really seek them at thebase of the Horseshoe Fall; but on the banks of the river, andparticularly above the fall, its silence, rather than its noise, issurprising. This arises, in part, from the lack of resonance; thesurrounding country being flat, and therefore furnishing no echoingsurfaces to reinforce the shock of the water. The resonance from thesurrounding rocks causes the Swiss Reuss at the Devil's Bridge, whenfull, to thunder more loudly than the Niagara. 

On Friday, November 1, 1872, just before reaching the village ofNiagara Falls, I caught, from the railway train, my first glimpse ofthe smoke of the cataract. Immediately after my arrival I went with afriend to the northern end of the American Fall. It may be that mymood at the time toned down the impression produced by the firstaspect of this grand cascade; but I felt nothing like disappointment, knowing, from old experience, that time and close acquaintanceship, the gradual interweaving of mind and nature, must powerfully influencemy final estimate of the scene. After dinner we crossed to GoatIsland, and, turning to the right, reached the southern end of theAmerican Fall. The river is here studded with small islands. Crossinga wooden bridge to Luna Island, and clasping a tree which grows nearits edge, I looked long at the cataract, which here shoots down theprecipice like an avalanche of foam. It grew in power and beauty. The channel spanned by the wooden bridge was deep, and the river theredoubled over the edge of the precipice, like the swell of a muscle, unbroken. The ledge here overhangs, the water being poured out farbeyond the base of the precipice. A space, called the Cave of theWinds, is thus enclosed between the wall of rock and the fallingwater. 

Goat Island ends in a sheer dry precipice, which connects the Americanand Horseshoe Falls. Midway between both is a wooden hut, theresidence of the guide to the Cave of the Winds, and from the hut awinding staircase, called Biddle's Stair, descends to the base of theprecipice. On the evening of my arrival I went down this stair, andwandered along the bottom of the cliff. One well-known factor in theformation and retreat of the cataract was immediately observed. Athick layer of limestone formed the upper portion of the cliff. Thisrested upon a bed of soft shale, which extended round the base of thecataract. The violent recoil of the water against this yieldingsubstance crumbles it away, undermining the ledge above, which, unsupported, eventually breaks off, and produces the observedrecession. 

At the southern extremity of the Horseshoe is a promontory, formed bythe doubling back of the gorge excavated by the cataract, and intowhich it plunges. On the promontory stands a stone building, calledthe Terrapin Tower, the door of which had been nailed up because ofthe decay of the staircase within it. Through the kindness of Mr. Townsend, the superintendent of Goat Island, the door was opened forme. From this tower, at all hours of the day, and at some hours ofthe night, I watched and listened to the Horseshoe Fall. The riverhere is evidently much deeper than the American branch; and instead ofbursting into foam where it quits the ledge, it bends solidly over, and falls in a continuous layer of the most vivid green. The tint isnot uniform; long stripes of deeper hue alternating with bands ofbrighter colour. Close to the ledge over which the water rolls, foamis generated, the light falling upon which, and flashing back from it, is sifted in its passage to and fro, and changed from white toemerald-green. Heaps of superficial foam are also formed at intervalsalong the ledge, and are immediately drawn into long white striae. [Footnote: The direction of the wind with reference to the course of aship may be inferred with accuracy from the foam-streaks on thesurface of the sea. ] Lower down, the surface, shaken by the reactionfrom below, incessantly rustles into whiteness. The descent finallyresolves itself into a rhythm, the water reaching the bottom of thefall in periodic gushes. Nor is the spray uniformly diffused throughthe air, but is wafted through it in successive veils of gauze-liketexture. From all this it is evident that beauty is not absent fromthe Horseshoe Fall, but majesty is its chief attribute. The plunge ofthe water is not wild, but deliberate, vast, and fascinating. Fromthe Terrapin Tower, the adjacent arm of the Horseshoe is seenprojected against the opposite one, midway down; to the imagination, therefore, is left the picturing of the gulf into which the cataractplunges. 

The delight which natural scenery produces in some minds is difficultto explain, and the conduct which it prompts can hardly be fairlycriticised by those who have never experienced it. It seems to me adeduction from the completeness of the celebrated Thomas Young, thathe was unable to appreciate natural scenery. 'He had really, ' saysDean Peacock, 'no taste for life in the country; he was one of thosewho thought that no one who was able to live in London would becontent to 'live elsewhere. ' Well, Dr. Young, like Dr. Johnson, had aright to his delights; but I can understand a hesitation to acceptthem, high as they were, to the exclusion of

 That o'erflowing joy which Nature yields To her true lovers. 

To all who are of this mind, the strengthening of desire on my part tosee and know Niagara Falls, as far as it is possible for them to beseen and known, will be intelligible. 

On the first evening of my visit, I met, at the head of Biddle'sStair, the guide to the Cave of the Winds. He was in the prime ofmanhood--large, well built, firm and pleasant in mouth and eye. Myinterest in the scene stirred up his, and made him communicative. 

Turning to a photograph, he described, by reference to it, a featwhich he had accomplished some time previously, and which had broughthim almost under the green water of the Horseshoe Fall. 'Can you leadme there to-morrow?' I asked. He eyed me enquiringly, weighing, perhaps, the chances of a man of light build, and with grey in hiswhiskers, in such an undertaking. 'I wish, ' I added, 'to see as muchof the fall as can be seen, and where you lead I will endeavour tofollow. ' His scrutiny relaxed into a smile, and he said, 'Very well;I shall be ready for you to-morrow. '

On the morrow, accordingly, I came. In the hut at the head ofBiddle's Stair I stripped wholly, and re-dressed according toinstructions, --drawing on two pairs of woollen pantaloons, threewoollen jackets, two pairs of socks, and a pair of felt shoes. Evenif wet, my guide assured me that the clothes would keep me from beingchilled; and he was right. A suit and hood of yellow oilcloth coveredall. Most laudable precautions were taken by the young assistant whohelped to dress me to keep the water out; but his devices broke downimmediately when severely tested. 

We descended the stair; the handle of a pitchfork doing, in my case, the duty of an alpenstock. At the bottom, the guide enquired whetherwe should go first to the Cave of the Winds, or to the Horseshoe, remarking that the latter would try us most. I decided on getting theroughest done first, and he turned to the left over the stones. Theywere sharp and trying. The base of the first portion of the cataractis covered with huge boulders, obviously the ruins of the limestoneledge above. The water does not distribute itself uniformly amongthese, but seeks out channels through which it pours torrentially. Wepassed some of these with wetted feet, but without difficulty. Atlength we came to the side of a more formidable current. My guidewalked along its edge until he reached its least turbulent portion. Halting, he said, 'This is our greatest difficulty; if we can crosshere, we shall get far towards the Horseshoe. '

He waded in. It evidently required all his strength to steady him. The water rose above his loins, and it foamed still higher. He had tosearch for footing, amid unseen boulders, against which the torrentrose violently. He struggled and swayed, but he struggledsuccessfully, and finally reached the shallower water at the otherside. Stretching out his arm, he said to me, 'Now come on. ' I lookeddown the torrent, as it' rushed to the river below, which was seethingwith the tumult of the cataract. De Saussure recommended theinspection of Alpine dangers, with the view of making them familiar tothe eye before they are encountered; and it is a wholesome custom inplaces of difficulty to put the possibility of an accident clearlybefore the mind, and to decide beforehand what ought to be done shouldthe accident occur. Thus wound up in the present instance, I enteredthe water. Even where it was not more than knee-deep, its power wasmanifest. As it rose around me, I sought to split the torrent bypresenting a side to it; but the insecurity of the footing enabled itto grasp my loins, twist me fairly round, and bring its impetus tobear upon my back. Further struggle was impossible; and feeling mybalance hopelessly gone, I turned, flung myself towards the bank justquitted, and was instantly, as expected, swept into shallower water. 

The oilcloth covering was a great incumbrance; it had been made for amuch stouter man, and, standing upright after my submersion, my legsoccupied the centre of two bags of water. My guide exhorted me to tryagain. Prudence was at my elbow, whispering dissuasion; but, takingeverything into account, it appeared more immoral to retreat than toproceed. Instructed by the first misadventure, I once more enteredthe stream. Had the alpenstock been of iron it might have helped me;but, as it was, the tendency of the water to sweep it out of my handsrendered it worse than useless. I, however, clung to it by habit. Again the torrent rose, and again I wavered; but, by keeping the lefthip well against it, I remained upright, and at length grasped thehand of my leader at the other side. He laughed pleasantly. Thefirst victory was gained, and he enjoyed it. 'No traveller, ' he said, 'was ever here before. ' Soon afterwards, by trusting to a piece ofdrift-wood which seemed firm, I was again taken off my feet, but wasimmediately caught by a protruding rock. 

We clambered over the boulders towards the thickest spray, which soonbecame so weighty as to cause us to stagger under its shock. For themost part nothing could be seen; we were in the midst of bewilderingtumult, lashed by the water, which sounded at times like the crackingof innumerable whips. Underneath this was the deep resonant roar ofthe cataract. I tried to shield my eyes with my hands, and lookupwards; but the defence was useless. The guide continued to move on, but at a certain place he halted, desiring me to take shelter in hislee, and observe the cataract. The spray did not come so much fromthe upper ledge, as from the rebound of the shattered water when itstruck the bottom. Hence the eyes could be protected from theblinding shock of the spray, while the line of vision to the upperledges remained to some extent clear. On looking upwards over theguide's shoulder I could see the water bending over the ledge, whilethe Terrapin Tower loomed fitfully through the intermittentspray-gusts. We were right under the tower. A little farther on thecataract, after its first plunge, hit a protuberance some way down, and flew from it in a prodigious burst of spray; through this westaggered. We rounded the promontory on which the Terrapin Towerstands, and moved, amid the wildest commotion, along the arm of theHorse-hoe, until the boulders failed us, and the cataract fell intothe profound gorge of the Niagara River. 

Here the guide sheltered me again, and desired me to look up; I didso, and could see, as before, the green gleam of the mighty curvesweeping over the uipper ledge, and the fitful plunge of the water, asthe spray between us and it alternately gathered and disappeared. Aneminent friend of mine often speaks of the mistake of those physicianswho regard man's ailments as purely chemical, to be met by chemicalremedies only. He contends for the psychological element of cure. Byagreeable emotions, he says, nervous currents are liberated whichstimulate blood, brain, and viscera. The influence rained fromladies' eyes enables my friend to thrive on dishes which would killhim if eaten alone. A sanative effect of the same order I experiencedamid the spray and thunder of Niagara. Quickened by the emotionsthere aroused, the blood sped exultingly through the arteries, abolishing introspection, clearing the heart of all bitterness, andenabling one to think with tolerance, if not with tenderness, on themost relentless and unreasonable foe. Apart from its scientificvalue, and purely as a moral agent, the play was worth the candle. Mycompanion knew no more of me than that I enjoyed the wildness of thescene; but as I bent in the shelter of his large frame he said, 'Ishould like to see you attempting to describe all this. ' He rightlythought it indescribable. The name of this gallant fellow was ThomasConroy. 

We returned, clambering at intervals up and down, so as to catchglimpses of the most impressive portions of the cataract. We passedunder ledges formed by tabular masses of limestone, and through somecurious openings formed by the falling together of the summits of therocks. At length we found ourselves beside our enemy of the morning. Conroy halted for a minute or two, scanning the torrent thoughtfully. I said that, as a guide, he ought to have a rope in such a place; buthe retorted that, as no traveller had ever thought of coming there, hedid not see the necessity of keeping a rope. He waded in. Thestruggle to keep himself erect was evident enough; he swayed, butrecovered himself again and again. At length he slipped, gave way, did as I had done, threw himself towards the bank, and was swept intothe shallows. Standing in the stream near its edge, he stretched hisarm towards me. I retained the pitchfork handle, for it had beenuseful among the boulders. By wading some way in, the staff could bemade to reach him, and I proposed his seizing it. 'If you are sure, 'he replied, 'that, in case of giving way, you can maintain your grasp, then I will certainly hold you. ' Remarking that he might count onthis, I waded in, and stretched the staff to my companion. It wasfirmly grasped by both of us. Thus helped, though its onset wasstrong, I moved safely across the torrent. All danger ended here. Weafterwards roamed sociably among the torrents and boulders below theCave of the Winds. The rocks were covered with organic slime, whichcould not have been walked over with bare feet, but the felt shoeseffectually prevented slipping. We reached the cave and entered it, first by a wooden way carried over the boulders, and then along anarrow ledge, to the point eaten deepest into the shale. When thewind is from the south, the falling water, I am told, can be seentranquilly from this spot; but when we were there, a blindinghurricane of spray was whirled against us. On the evening of the sameday, I went behind the water on the Canada side, which, after theexperiences of the morning, struck me as an imposture. 

Still even this latter is exciting to some nerves. Its effect uponhimself is thus vividly described by Bakewell, jun: 'On turning asharp angle of the rock, a sudden gust of wind met us, coming fromthe hollow between the fall and the rock, which drove the spraydirectly in our faces, with such force that in an instant we were wetthrough. When in the midst of this shower-bath the shock took away mybreath: I turned back and scrambled over the loose stones to escapethe conflict. The guide soon followed, and told me that I had passedthe worst part. With that assurance I made a second attempt; but sowild and disordered was my imagination that when I had reached halfway I could bear it no longer. ' [Footnote: 'Mag. Of Nat. Hist, ' 1830, pp. 121, 122. ]

To complete my knowledge I desired to see the fall from the riverbelow it, and long negotiations were necessary to secure the means ofdoing so. The only boat fit for the undertaking had been laid up forthe winter; but this difficulty, through the kind intervention of Mr. Townsend, was overcome. The main one was to secure oarsmensufficiently strong and skilful to urge the boat where I wished it tobe taken. The son of the owner of the boat, a finely-built youngfellow, but only twenty, and therefore not sufficiently hardened, waswilling to go; and up the river, it was stated, there lived anotherman who could do anything with the boat which strength and daringcould accomplish. He came. His figure and expression of facecertainly indicated extraordinary firmness and power. On Tuesday, November 5, we started, each of us being clad in oilcloth. The elderoarsman at once assumed a tone of authority over his companion, andstruck immediately in amid the breakers below the American Fall. Hehugged the cross freshets instead of striking out into the smootherwater. I asked him why he did so, and he replied that they weredirected outwards, not downwards. The struggle, however, to preventthe bow of the boat from being turned by them, was often very severe. 

The spray was in general blinding, but at times it disappeared andyielded noble views of the fall. The edge of the cataract is crimpedby indentations which exalt its beauty. Here and there, a littlebelow the highest ledge, a secondary one juts out; the water strikesit and bursts from it in huge protuberant masses of foam and spray. Wepassed Goat Island, came to the Horseshoe, and worked for a time alongits base, the boulders over which Conroy and myself had scrambled afew days previously lying between us and the cataract. A rock wasbefore us, concealed and revealed at intervals, as the waves passedover it. Our leader tried to get above this rock, first on theoutside of it. The water, however, was here in violent motion. Themen struggled fiercely, the older one ringing out an incessant peal ofcommand and exhortation to the younger. As we were just clearing therock, the bow came obliquely to the surge; the boat was turnedsuddenly round and shot with astonishing rapidity down the river. Themen returned to the charge, now trying to get up between thehalf-concealed rock and the boulders to the left. But the torrent setin strongly through this channel. The tugging was quick and violent, but we made little way. At length, seizing a rope, the principaloarsman made a desperate attempt to get upon one of the boulders, hoping to be able to drag the boat through the channel; but it bumpedso violently against the rock, that the man flung himself back andrelinquished the attempt. 

We returned along the base of the American Fall, running in and outamong the currents which rushed, from it laterally into the river. Seen from below the American Fall is certainly exquisitely beautiful, but it is a mere frill of adornment to its nobler neighbour theHorseshoe. At times we took to the river, from the centre of whichthe Horseshoe Fall appeared especially magnificent. A streak of cloudacross the neck of Mont Blanc can double its apparent height, so herethe green summit of the cataract shining above the smoke of sprayappeared lifted to an extraordinary elevation. Had Hennepin and LaHontan seen the fall from this position, their estimates of the heightwould have been perfectly excusable. 

*****

From a point a little way below the American Fall, a ferry crossesthe river, in summer, to the Canadian side. Below the ferry is asuspension bridge for carriages and foot-passengers, and a mile or twolower down is the railway suspension bridge. Between ferry and bridgethe river Niagara flows unruffled; but at the suspension bridge thebed steepens and the river quickens its motion. Lower down the gorgenarrows, and the rapidity and turbulence increase. At the placecalled the' Whirlpool Rapids' I estimated the width of the river at300 feet, an estimate confirmed by the dwellers on the spot. When itis remembered that the drainage of nearly half a continent iscompressed into this space, the impetuosity of the river's rush may beimagined. Had it not been for Mr. Bierstädt, the distinguishedphotographer of Niagara, I should have quitted the place withoutseeing these rapids; for this, and for his agreeable company to thespot, I have to thank him. From the edge of the cliff above therapids, we descended, a little, I confess, to a climber's disgust, inan 'elevator, ' because the effects are best seen from the water level. 

Two kinds of motion are here obviously active, a motion of translationand a motion of undulation--the race of the river through its gorge, and the great waves generated by its collision with, and rebound from, the obstacles in its way. In the middle of the river the rush andtossing are most violent; at all events, the impetuous force of theindividual waves is here most strikingly displayed. Vast pyramidalheaps leap incessantly from the river, some of them with such energyas to jerk their summits into the air, where they hang momentarilysuspended in crowds of liquid spherules. The sun shone for a fewminutes. At times the wind, coming up the river, searched and siftedthe spray, carrying away the lighter drops, and leaving the heavierones behind. Wafted in the proper direction, rainbows appeared anddisappeared fitfully in the lighter mist. In other directions thecommon gleam of the sunshine from the waves and their shattered crestswas exquisitely beautiful. The complexity of the action was stillfurther illustrated by the fact, that in some cases, as if by theexercise of a local explosive force, the drops were shot radially froma particular centre, forming around it a kind of halo. 

The first impression, and, indeed, the current explanation of theserapids is, that the central bed of the river is cumbered with largeboulders, and that the jostling, tossing, and wild leaping of thewater there, are due to its impact against these obstacles. I doubtthis explanation. At all events, there is another sufficient reasonto be taken into account. Boulders derived from the adjacent cliffsvisibly cumber the sides of the river. Against these the water risesand sinks rhythmically but violently, large waves being thus produced. On the generation of each wave, there is an immediate compounding ofthe wave-motion with he river-motion. The ridges, which in stillwater would proceed in circular curves round the centre ofdisturbance, cross the river obliquely, and the result is that at thecentre waves commingle, which have really been generated at the sides. In the first instance, we had a composition of wave-motion withriver-motion; here we have the coalescence of waves with waves. Wherecrest and furrow cross each other, the motion is annulled; wherefurrow and furrow cross, the river is ploughed to a greater depth; andwhere crest and crest aid each other, we have that astonishing leap ofthe water which breaks the cohesion of the crests, and tosses themshattered into the air. From the water level the cause of the actionis not so easily seen; but from the summit of the cliff the lateralgeneration of the waves, and their propagation to the perfectlyobvious. If this explanation be correct, the phenomena observed atthe Whirlpool Rapids form one of the grandest illustrations of theprinciple of _interference_. The Nile 'cataract, ' Mr. Huxley informsme, offers more moderate examples of the same action. 

At some distance below the Whirlpool Rapids we have the celebratedwhirlpool itself. Here the river makes a sudden bend to thenorth-east, forming nearly a right angle with its previous direction. The water strikes the concave bank with great force, and scoops itincessantly away. A vast basin has been thus formed, in which thesweep of the river prolongs itself in gyratory currents. Bodies andtrees which have come over the falls, are stated to circulate here fordays without finding the outlet. From various points of the cliffsabove, this is curiously hidden. The rush of the river into thewhirlpool is obvious enough; and though you imagine the outlet must bevisible, if one existed, you cannot find it. Turning, however, roundthe bend of the precipice to the north-east, the outlet comes intoview. 

The Niagara season was over; the chatter of sightseers had ceased, andthe scene presented itself as one of holy seclusion and beauty. Iwent down to the river's edge, where the weird loneliness seemed toincrease. The basin is enclosed by high and almost precipitousbanks--covered, at the time, with russet woods. A kind of mysteryattaches itself to gyrating water, due perhaps to the fact that we areto some extent ignorant of the direction of its force. It is saidthat at certain points of the whirlpool, pine-trees are sucked down, to be ejected mysteriously elsewhere. The 'water is of the brightestemerald-green. The gorge through which it escapes is narrow, and themotion of the river swift though silent. The surface is steeplyinclined, but it is perfectly unbroken. There are no lateral waves, no ripples with their breaking bubbles to raise a murmur; while thedepth is here too great to allow the inequality of the bed to rufflethe surface. Nothing can be more beautiful than this sloping liquidmirror formed by the Niagara, in sliding from the whirlpool. 

The green colour is, I think, correctly accounted for in the lastFragment. While crossing the Atlantic in 1872-73 I had frequentopportunities of testing the explanation there given. Looked properlydown upon, there are portions of the ocean to which we should hardlyascribe a trace of blue; at the most, a mere hint of indigo reachesthe eye. The water, indeed, is practically black, and this is anindication both of its depth and of its freedom from mechanicallysuspended matter. In small thicknesses water is sensibly transparentto all kinds of light; but, as the thickness increases, the rays oflow refrangibility are first absorbed, and after them the other rays. Where, therefore, the water is very deep and very pure, all thecolours are absorbed, and such water ought to appear black, as nolight is sent from its interior to the eye. The approximation of theAtlantic Ocean to this condition is an indication of its extremepurity. 

Throw a white pebble into such water; as it sinks it becomes greenerand greener, and, before it disappears, it reaches a vivid blue-green. Break such a pebble into fragments, each of these will behave like theunbroken mass; grind the pebble to powder, every particle will yieldits modicum of green; and if the particles be so fine as to remainsuspended in the water, the scattered light will be a uniform green. Hence the greenness of shoal water. You go to bed with the blackAtlantic around you. You rise in the morning, find it a vivid green, and correctly infer that you are crossing the bank of Newfoundland. Such water is found charged with fine matter in a state of mechanicalsuspension. The light from the bottom may sometimes come into play, but it is not necessary. A storm can render the water muddy, byrendering the particles too numerous and gross. Such a case occurredtowards the close of my visit to Niagara. There had been rain andstorm in the upper lake-regions, and the quantity of suspended matterbrought down quite extinguished the fascinating green of theHorseshoe. 

Nothing can be more superb than the green of the Atlantic waves, whenthe circumstances are favourable to the exhibition of the colour. Aslong as a wave remains unbroken no colour appears; but when the foamjust doubles over the crest, like an Alpine snow-cornice, under thecornice we often see a display of the most exquisite green. It ismetallic in its brilliancy. But the foam is necessary to itsproduction. The foam is first illuminated, and it scatters the lightin all directions; the light which passes through the higher portionof the wave alone reaches the eye, and gives to that portion itsmatchless colour. The folding of the wave, producing as it does, aseries of longitudinal protuberances and furrows which act likecylindrical lenses, introduces variations in the intensity of thelight, and materially enhances its beauty. 

*****

We have now to consider the genesis and proximate destiny of the Fallsof Niagara. We may open our way to this subject by a few preliminaryremarks upon erosion. Time and intensity are the main factors ofgeologic change, and they are in a certain sense convertible. Afeeble force acting through long periods, and an intense force actingthrough short ones, may produce approximately the same results. ToDr. Hooker I have been indebted for some specimens of stones, thefirst examples of which were picked up by Mr. Hackworth on the shoresof Lyell's Bay, near Wellington, in New Zealand. They were describedby Mr. Travers in the 'Transactions of the New Zealand Institute. 'Unacquainted with their origin, you would certainly ascribe theirforms to human workmanship. They resemble knives and spear-heads, being apparently chiselled off into facets, with as much attention tosymmetry as if a tool, guided by human intelligence, had passed overthem. But no human instrument has been brought to bear upon thesestones. They have been wrought into their present shape by thewind-blown sand of Lyell's Bay. Two winds are, dominant here, andthey in succession urged the sand against opposite sides of the stone;every little particle of sand chipped away its infinitesimal bit ofstone, and in the end sculptured these singular forms. [Footnote:'These stones, which have a strong resemblance to works of human art, occur in great abundance, and of various sizes, from half-an-inch toseveral inches in length. A large number were exhibited showing thevarious forms, which are those of wedges, knives, arrow-heads, &c, andall with sharp cutting edges. 

'Mr. Travers explained that, notwithstanding their artificialappearance, these stones were formed by the cutting action of thewind-driven sand, as it passed to and fro over an exposedboulder-bank. He gave a minute account of the manner in which thevarieties of form are produced, and referred to the effect which theerosive action thus indicated would have on railway and other worksexecuted on sandy tracts. 

'Dr. Hector stated that although, as a group, the specimens on thetable could not well be mistaken for artificial productions, still theforms are so peculiar, and the edges, in a few of them, so perfect, that if they were discovered associated with human works, there is nodoubt that they would have been referred to the so-called "stoneperiod. "'--Extracted from the Minutes of the Wellington PhilosophicalSociety, February 9, 1869. ]

The Sphynx of Egypt is nearly covered up by the sand of the desert. The neck of the Sphynx is partly cut across, not, as I am assured byMr. Huxley, by ordinary weathering, but by the eroding action of thefine sand blown against it. In these cases Nature furnishes us withhints which may be taken advantage of in art; and this action of sandhas been recently turned to extraordinary account in the UnitedStates. When in Boston, I was taken by my courteous and helpfulfriend, Mr. Josiah Quincey, to see the action of the sand-blast. Akind of hopper containing fine silicious sand was connected with areservoir of compressed air, the pressure being variable at pleasure. The hopper ended in a long slit, from which the sand was blown. Aplate of glass was placed beneath this slit, and caused to pass slowlyunder it; it came out perfectly depolished, with a bright opalescentglimmer, such as could only be produced by the most careful grinding. Every little particle of sand urged against the glass, having all itsenergy concentrated on the point of impact, formed there a little pit, the depolished surface consisting of innumerable hollows of thisdescription. 

But this was not all. By protecting certain portions of the surface, and exposing others, figures and tracery of any required form could beetched upon the glass. The figures of open iron-work could be thuscopied; while wire-gauze placed over the glass produced a reticulatedpattern. But it required no such resisting substance as iron toshelter the glass. The patterns of the finest lace could be thusreproduced; the delicate filaments of the lace itself offering asufficient protection. All these effects have been obtained with asimple model of the sand-blast devised by my assistant. A fraction ofa minute suffices to etch upon glass a rich and beautiful lacepattern. Any yielding substance may be employed to protect the glass. By diffusing the shock of the particle, such substances practicallydestroy the local erosive power. The hand can bear, withoutinconvenience, a sand-shower which would pulverise glass. Etchingsexecuted on glass with suitable kinds of ink are accurately worked outby the sandblast. In fact, within certain limits, the harder thesurface, the greater is the concentration of the shock, and the moreeffectual is the erosion. It is not necessary that the sand should bethe harder substance of the two; corundum, for example, is much harderthan quartz; still, quartz-sand can not only depolish, but actuallyblow a hole through a plate of corundum. Nay, glass may be depolishedby the impact of fine shot; the grains in this case bruising theglass, before they have time to flatten and turn their energy intoheat. 

And here, in passing, we may tie together one or two apparentlyunrelated facts. Supposing you turn on, at the lower part of a house, a cock which is fed by a pipe from a cistern at the top of the house, the column of water, from the cistern downwards, is set in motion. Byturning off the cock, this motion is stopped; and, when the turningoff is very sudden, the pipe, if not strong, may be burst by theinternal impact of the water. By distributing the turning of the cockover half a second of time, the shock and danger of rupture may beentirely avoided. We have here an example of the concentration ofenergy in time. The sand-blast illustrates the concentration ofenergy in space. The action of flint and steel is an illustration ofthe same principle. The heat required to generate the spark isintense; and the mechanical action, being moderate, must, to producefire, be in the highest degree concentrated. This concentration issecured by the collision of hard substances. Calc-spar will notsupply the place of flint, nor lead the place of steel, in theproduction of fire by collision. With the softer substances, thetotal heat produced may be greater than with the hard ones, but, toproduce the spark, the heat must be intensely localised. 

We can, however, go far beyond the mere depolishing of glass; indeed Ihave already said that quartz-sand can wear a hole through corundum. This leads me to express my acknowledgments to General Tilghman, whois the inventor of the sand-Blast. [Footnote: The absorbent power, if I may use the phrase, exerted by the industrial arts in the UnitedStates, is forcibly illustrated by the rapid transfer of men likeMr. Tilghman from the life of the soldier to that of the civilian. General McClellan, now a civil engineer, whom I had the honour offrequently meeting in New York, is a most eminent example of the samekind. At the end of the war, indeed, a million and a half of men werethus drawn, in an astonishingly short time, from military to civillife. ] To his spontaneous kindness I am indebted for some beautifulillustrations of his process. In one thick plate of glass a figurehas been worked out to a depth of three eighths of an inch. A secondplate, seven eighths of an inch thick, is entirely perforated. In acircular plate of marble, nearly half an inch thick, open work of mostintricate and elaborate description has been executed. It wouldprobably take many days to perform this work by any ordinary process;with the sand-blast it was accomplished in an hour. So much for thestrength of the blast; its delicacy is illustrated by this beautifulexample of line engraving, etched on glass by means of the Blast. 

This power of erosion, so strikingly displayed when sand is urged byair, renders us better able to conceive its action when urged bywater. The erosive power of a river is vastly augmented by the solidmatter carried along with it. Sand or pebbles, caught in a rivervortex, can wear away the hardest rock potholes' and deep cylindricalshafts being thus produced. An extraordinary instance of this kind oferosion is to be seen in the Val Tournanche, above the village of thisname. The gorge at Handeck has been thus cut out. Such waterfallswere once frequent in the valleys of Switzerland; for hardly anyvalley is without one or more transverse barriers of resistingmaterial, over which the river flowing through the valley once fell asa cataract. Near Pontresina, in the Engadin, there is such a case; ahard gneiss being there worn away to form a gorge, through which theriver from the Morteratsch glacier rushes. The barrier of the Kirchetabove Meyringen is also a case in point. Behind it was a lake, derived from the glacier of the Aar, and over the barrier the lakepoured its excess of water. Here the rock, being limestone, was inpart dissolved; but added to this we had the action of the sand andgravel carried along by the water, which, on striking the rock, chipped it away like the particles of the sand-Blast. Thus, bysolution and mechanical erosion, the great chasm of theFinsteraarschlucht was formed. It is demonstrable that the waterwhich flows at the bottoms of such deep fissures once flowed at thelevel of their present edges, and tumbled down the lower faces of thebarriers. Almost every valley in Switzerland furnishes examples ofthis kind; the untenable hypothesis of earthquakes, once so readilyresorted to in accounting for these gorges, being now for the mostpart abandoned. To produce the Canons of Western America, no othercause is needed than the integration of effects individuallyinfinitesimal. 

And now we come to Niagara. Soon after Europeans had taken possessionof the country, the conviction appears to have arisen that the deepchannel of the river Niagara below the falls had been excavated by thecataract. In Mr. Bakewell's 'Introduction to Geology, ' the prevalenceof this belief has been referred to. It is expressed thus byProfessor Joseph Henry in the 'Transactions of the Albany Institute:'[Footnote: Quoted by Bakewell. ] 'In viewing the position of thefalls, and the features of the country round, it is impossible not tobe impressed with the idea that this great natural raceway has beenformed by the continued action of the irresistible Niagara, and thatthe falls, beginning at Lewiston, have, in the course of ages, wornback the rocky strata to their present site. ' The same view isadvocated by Sir Charles Lyell, by Mr. Hall, by M. Agassiz, byProfessor Ramsay, indeed by most of those who have inspected theplace. 

A connected image of the origin and progress of the cataract is easilyobtained. Walking northward from the village of Niagara Falls by theside of the river, we have to our left the deep and comparativelynarrow gorge, through which the Niagara flows. The bounding cliffs ofthis gorge are from 300 to 350 feet high. We reach the whirlpool, trend to the north-east, and after a little time gradually resume ournorthward course. Finally, at about seven miles from the presentfalls, we come to the edge of a declivity, which informs us that wehave been hitherto walking on table-land. At some hundreds of feetbelow us is a comparatively level plain, which stretches to LakeOntario. The declivity marks the end of the precipitous gorge of theNiagara. Here the river escapes from its steep mural boundaries, andin a widened bed pursues its way to the lake which finally receivesits waters. 

The fact that in historic times, even within the memory of man, thefall has sensibly receded, prompts the question, How far has thisrecession gone? At what point did the ledge which thus continuallycreeps backwards begin its retrograde course? To minds disciplined insuch researches the answer has been, and will be--At the precipitousdeclivity which crossed the Niagara from Lewiston on the American toQueenston on the Canadian side. Over this transverse barrier theunited affluents of all the upper lakes once poured their waters, andhere the work of erosion began. The dam, moreover, was demonstrablyof sufficient height to cause the river above it to submerge GoatIsland; and this would perfectly account for the finding by SirCharles Lyell, Mr. Hall, and others, in the sand and gravel of theisland, the same fluviatile shells as are now found in the NiagaraRiver higher up. It would also account for those deposits along thesides of the river, the discovery of which enabled Lyell, Hall, andRamsay to reduce to demonstration the popular belief that the Niagaraonce flowed through a shallow valley. 

The physics of the problem of excavation, which I made clear to mymind before quitting Niagara, are revealed by a close inspection ofthe present Horseshoe Fall. We see evidently that the greatest weightof water bends over the very apex of the Horseshoe. In a passage inhis excellent chapter on Niagara Falls, Mr. Hall alludes to this fact. Here we have the most copious and the most violent whirling of theshattered liquid; here the most powerful eddies recoil against theshale. From this portion of the fall, indeed, the spray sometimesrises without solution of continuity to the region of clouds, becominggradually more attenuated, and passing finally through the conditionof true cloud into invisible vapour, which is sometimes reprecipitatedhigher up. All the phenomena point distinctly to the centre of theriver as the place of greatest mechanical energy, and from the centrethe vigour of the fall gradually dies away towards the sides. TheHorseshoe form, with the concavity facing downwards, is an obvious andnecessary consequence of this action. Right along the middle of theriver the apex of the curve pushes its way backwards, cutting alongthe centre a deep and comparatively narrow groove, and draining thesides as it passes them. [Footnote: In the discourse the excavation ofthe centre and drainage of the sides action was illustrated by a modeldevised by my assistant, Mr. John Cottrell. ] Hence the remarkablediscrepancy between the widths of the Niagara above and below theHorseshoe. All along its course, from Lewiston Heights to its presentposition, the form of the fall was probably that of a horseshoe; forthis is merely the expression of the greater depth, and consequentlygreater excavating power, of the centre of the river. The gorge, moreover, varies in width, as the depth of the centre of the ancientriver varied, being narrowest where that depth was greatest. 

The vast comparative erosive energy of the Horseshoe Fall comesstrikingly into view when it and the American Fall are comparedtogether. The American branch of the river is cut at a right angle bythe gorge of the Niagara. Here the Horseshoe Fall was the realexcavator. It cut the rock, and formed the precipice, over which theAmerican Fall tumbles. But since its formation, the erosive action ofthe American Fall has been almost nil, while the Horseshoe has cut itsway for 600 yards across the end of Goat Island, and is now doublingback to excavate its channel parallel to the length of the island. This point, which impressed me forcibly, has not, I have just learned, escaped the acute observation of Professor Ramsay. [Footnote: Hiswords are: 'Where the body of water is small in the American Fall, theedge has only receded a few yards (where most eroded) during the timethat the Canadian Fall has receded from the north corner of GoatIsland to the innermost curve of the Horseshoe Fall. '--QuarterlyJournal of Geological Society, May 1859. ] The river bends; theHorseshoe immediately accommodates itself to the bending, and willfollow implicitly the direction of the deepest water in the upperstream. The flexures of the gorge are determined by those of theriver channel above it. Were the Niagara centre above the fallsinuous, the gorge would obediently follow its sinuosities. Oncesuggested, no doubt geographers will be able to point out manyexamples of this action. The Zambesi is thought to present a greatdifficulty to the erosion theory, because of the sinuosity of thechasm below the Victoria Falls. But, assuming the basalt to be oftolerably uniform texture, had the river been examined before theformation of this sinuous channel, the present zigzag course of thegorge below the fall could, I am persuaded, have been predicted, whilethe sounding of the present river would enable us to predict thecourse to be pursued by the erosion in the future. 

But not only has the Niagara River cut the gorge; it has carried awaythe chips of its own workshop. The shale, being probably crumbled, iseasily carried away. But at the base of the fall we find the hugeboulders already described, and by some means or other these areremoved down the river. The ice which fills the gorge in winter, andwhich grapples with the boulders, has been regarded as thetransporting agent. Probably it is so to some extent. But erosionacts without ceasing on the abutting points of the boulders, thuswithdrawing their support and urging them gradually down the river. Solution also does its portion of the work. That solid matter iscarried down is proved by the difference of depth between the NiagaraRiver and Lake Ontario, where the river enters it. The depth fallsfrom 72 feet to 20 feet, in consequence of the deposition of solidmatter caused by the diminished motion of the river. [Footnote: Nearthe mouth of the gorge at Queenston, the depth, according to theAdmiralty Chart, is 180 feet; well within the gorge it is 132 feet. ]

The annexed highly instructive map has been reduced from one publishedin Mr. Hall's 'Geology of New York. ' It is based on surveys executedin 1842, by Messrs. Gibson and Evershed. The ragged edge of theAmerican Fall north of Goat Island marks the amount of erosion whichit has been able to accomplish, while the Horseshoe Fall was cuttingits way southward across the end of Goat Island to its presentposition. The American Fall is 168 feet high, a precipice cut down, not by itself, but by the Horseshoe Fall. The latter in 1842 was 159feet high, and, as shown by the map, is already turning eastward, toexcavate its gorge along the centre of the upper river. P is the apexof the Horseshoe, and T marks the site of the Terrapin Tower, with thepromontory adjacent, round which I was conducted by Conroy. Probablysince 1842 the Horseshoe has worked back beyond the position hereassigned to it. 

In conclusion, we may say a word regarding the proximate future ofNiagara. At the rate of excavation assigned to it by Sir CharlesLyell, namely, a foot a year, five thousand years or so will carry theHorseshoe Fall far higher than Goat Island. As the gorge recedes itwill drain, as it has hitherto done, the banks right and left of it, thus leaving a nearly level terrace between Goat Island and the edgeof the gorge. Higher up it will totally drain the American branch ofthe river; the channel of which in due time will become cultivableland. The American Fall will then be transformed into a dryprecipice, forming a simple continuation of the cliffy boundary of theNiagara gorge. At the place occupied by the fall at this moment weshall have the gorge enclosing a right angle, a second whirlpool beingthe consequence. To those who visit Niagara a few millenniums hence Ileave the verification of this prediction. All that can be said is, that if the causes now in action continue to act, it will prove itselfliterally true. 

*****

Fig. 6. 

POSTSCRIPT. 

A year or so after I had quitted the United States, a man sixty yearsof age, while engaged in painting one of the bridges which connectGoat Island with the Three Sisters, slipped through the rails of thebridge into the rapids, and was carried impetuously towards theHorseshoe Fall. He was urged against a rock which rose above thewater, and with the grasp of desperation he clung to it. Thepopulation of the village of Niagara Falls was soon upon the island, and ropes were brought, but there was none to use them. In the midstof the excitement, a tall powerful young fellow was observed makinghis way silently through the crowd. He reached a rope; selected fromthe bystanders a number of men, and placed one end of the rope intheir hands. The other end he fastened round himself, and choosing apoint considerably above that to which the man clung, he plunged intothe rapids. He was carried violently downwards, but he caught therock, secured the old painter and saved him. Newspapers from allparts of the Union poured in upon me, describing this gallant act ofmy guide Conroy. 

********************

VIII. THE PARALLEL ROADS OF GLEN ROY. 

[Footnote: A discourse delivered at the Royal Institution of GreatBritain on June 9, 1876. ]

THE first published allusion to the Parallel Roads of Glen Roy occursin the appendix to the third volume of Pennant's 'Tour in Scotland, ' awork published in 1776. 'In the face of these hills, ' says thiswriter, 'both sides of the glen, there are three roads at smalldistances from each other and directly opposite on each side. Theseroads have been measured in the complete parts of them, and found tobe 26 paces of a man 5 feet 10 inches high. The two highest arepretty near each other, about 50 yards, and the lowest double thatdistance from the nearest to it. They are carried along the sides ofthe glen with the utmost regularity, nearly as exact as drawn with aline of rule and compass. '

The correct heights of the three roads of Glen Roy are respectively1150, 1070, and 860 feet above the sea. Hence a vertical distance of80 feet separates the two highest, while the lowest road is 210 feetbelow the middle one. 

These 'roads' are usually shelves or terraces formed in the yieldingdrift which here covers the slopes of the mountains. They are allsensibly horizontal and therefore parallel. Pennant accepted asreasonable the explanation of them given by the country people in histime. They thought that the roads 'were designed for the chase, andthat the terraces were made after the spots were cleared in lines fromwood, in order to tempt the animals into the open paths after theywere rouzed, in order that they might come within reach of the bowmenwho might conceal themselves in the woods above and below. '

In these attempts of 'the country people' we have an illustration ofthat impulse to which all scientific knowledge is due--the desire toknow the causes of things; and it is a matter of surprise that in thecase of the parallel roads, with their weird appearance challengingenquiry, this impulse did not make itself more rapidly andenergetically felt. Their remoteness may perhaps account for the factthat until the year 1817 no systematic description of them, and noscientific attempt at an explanation of them, appeared. In that yearDr. MacCulloch, who was then President of the Geological Society, presented to that Society a memoir, in which the roads were discussed, and pronounced to be the margins of lakes once embosomed in Glen Roy. Why there should be three roads, or why the lakes should stand atthese particular levels, was left unexplained. 

To Dr. MacCulloch succeeded a man, possibly not so learned as ageologist, but obviously fitted by nature to grapple with her factsand to put them in their proper setting. I refer to Sir ThomasDick-Lauder, who presented to the Royal Society of Edinburgh, on the2nd of March, 1818, his paper on the Parallel Roads of Glen. Roy. Inlooking over the literature of this subject, which is now copious, itis interesting to observe the differentiation of minds, and to singleout those who went by a kind of instinct to the core of the question, from those who erred in it, or who learnedly occupied themselves withits analogies, adjuncts, and details. There is no man, in my opinion, connected with the history of the subject, who has shown, in relationto it, this spirit of penetration, this force of scientific insight, more conspicuously than Sir Thomas Dick-Lauder. Two distinct mentalprocesses are involved in the treatment of such a question. Firstly, the faithful and sufficient observation of the data; and secondly, that higher mental process in which the constructive imagination comesinto play, connecting the separate facts of observation with theircommon cause, and weaving them into an organic whole. In neither ofthese requirements did Sir Thomas Dick-Lauder fail. 

Adjacent to Glen Roy is a valley called Glen Gluoy, along the sides ofwhich ran a single shelf, or terrace, formed obviously in the samemanner as the parallel roads of Glen Roy. The two shelves on theopposing sides of the glen were at precisely the same level, andDick-Lauder wished to see whether, and how, they became united at thehead of the glen. He followed the shelves into the recesses of themountains. The bottom of the valley, as it rose, came ever nearer tothem, until finally, at the head of Glen Gluoy, he reached a col, orwatershed, of precisely the same elevation as the road which sweptround the glen. 

The correct height of this col is 1170 feet above the sea; that is tosay, 20 feet above the highest road in Glen Roy. 

From this col a lateral branch-valley--Glen Turrit--led down to GlenRoy. Our explorer descended from the col to the highest road of thelatter glen, and pursued it exactly as he had pursued the road in GlenGluoy. For a time it belted the mountain sides at a considerableheight above the bottom of the valley; but this rose as he proceeded, coming ever nearer to the highest shelf, until finally he reached acol, or watershed, looking into Glen Spey, and of precisely the sameelevation as the highest road of Glen Roy. 

He then dropped down to the lowest of these roads, and followed ittowards the mouth of the glen. Its elevation above the bottom of thevalley gradually increased; not because the shelf rose, but because itremained level while the valley sloped downwards. He found thislowest road doubling round the hills at the mouth of Glen Roy, andrunning along the sides of the mountains which flank Glen Spean. Hefollowed it eastwards. 

PARALLEL ROADS OF GLEN ROY. 

After a Sketch by Sir Thomas Dick-Lauder. 

The bottom of the Spean Valley, like the others, gradually rose, andtherefore gradually approached the road on the adjacent mountain-side. He came to Loch Laggan, the surface of which rose almost to the levelof the road, and beyond the head of this lake he found, as in theother two cases, a col, or watershed, at Makul, of exactly the samelevel as the single road in Glen Spean, which, it will be remembered, is a continuation of the lowest road in Glen Roy. 

Here we have a series of facts of obvious significance as regards thesolution of this problem. The effort of the mind to form a coherentimage from such facts may be compared with the effort of the eyes tocause the pictures of a stereoscope to coalesce. For a time weexercise a certain strain, the object remaining vague and indistinct. Suddenly its various parts seem to run together, the object startingforth in clear and definite relief. Such, I take it, was the effectof his ponderings upon the mind of Sir Thomas Dick-Lauder. Hissolution was this: Taking all their features into account, he wasconvinced that water only could have produced the terraces. But howhad the water been collected? He saw clearly that, supposing themouth of Glen Gluoy to be stopped by a barrier sufficiently high, ifthe waters from the mountains flanking the glen were allowed tocollect, they would form behind the barrier a lake, the surface ofwhich would gradually rise until it reached the level of the col atthe head of the glen. The rising would then cease; the superfluouswater of Glen Gluoy discharging itself over the col into Glen Roy. Aslong as the barrier stopping the mouth of Glen Gluoy continued highenough, we should have in that glen a lake at the precise level of itsshelf, which lake, acting upon the loose drift of the flankingmountains, would form the shelf revealed by observation. 

So much for Glen Gluoy. But suppose the mouth of Glen Roy alsostopped by a similar barrier. Behind it also the water from theadjacent mountains would collect. The surface of the lake thus formedwould gradually rise, until it had reached the level of the col whichdivides Glen Roy from Glen Spey. Here the rising of the lake wouldcease; its superabundant water being poured over the col into thevalley of the Spey. This state of things would continue as long as asufficiently high barrier remained at the mouth of Glen Roy. The lakethus dammed in, with its surface at the level of the highest parallelroad, would act, as in Glen Gluoy, upon the friable driftoverspreading the mountains, and would form the highest road orterrace of Glen Roy. 

And now let us suppose the barrier to be so far removed from the mouthof Glen Roy as to establish a connection between it and the upper partof Glen Spean, while the lower part of the latter glen still continuedto be blocked up. Upper Glen Spean and Glen Roy would then beoccupied by a continuous lake, the level of which would obviously bedetermined by the col at the head of Loch Laggan. The water in GlenRoy would sink from the level it had previously maintained, to thelevel of its new place of escape. This new lake-surface wouldcorrespond exactly with the lowest parallel road, and it would formthat road by its action upon the drift of the adjacent mountains. 

In presence of the observed facts, this solution commends itselfstrongly to the scientific mind. The question next occurs, What wasthe character of the assumed barrier which stopped the glens? Thereare at the present moment vast masses of detritus in certain portionsof Glen Spean, and of such detritus Sir Thomas Dick-Lauder imaginedhis barriers to have been formed. By some unknown convulsion, thisdetritus had been heaped up. But, once given, and once granted thatit was subsequently removed in the manner indicated, the single roadof Glen Gluoy and the highest and lowest roads of Glen Roy would beexplained in a satisfactory manner. 

To account for the second or middle road of Glen Roy, Sir ThomasDick-Lauder invoked a new agency. He supposed that at a certain pointin the breaking down or waste of his dam, a halt occurred, the barrierholding its ground at a particular level sufficiently long to dam alake rising to the height of, and forming the second road. This pointof weakness was at once detected by Mr. Darwin, and adduced by him asproving that the levels of the cols did not constitute an essentialfeature in the phenomena of the parallel roads. Though not destroyed, Sir Thomas Dick-Lauder's theory was seriously shaken by this argument, and it became a point of capital importance, if the facts permitted, to remove such source of weakness. This was done in 1847 by Mr. DavidMilne, now Mr. Milne-Home. On walking up Glen Roy from Roy Bridge, wepass the mouth of a lateral glen, called Glen Glaster, runningeastward from Glen Roy. There is nothing in this lateral glen toattract attention, or to suggest that it could have any conspicuousinfluence in the production of the parallel roads. Hence, probably, the failure of Sir Thomas Dick-Lauder to notice it. But Mr. Milne-Home entered this glen, on the northern side of which the middleand lowest roads are fairly shown. The principal stream runningthrough the glen turns at a certain point northwards and loses itselfamong hills too high to offer any outlet. But another branch of theglen turns to the south-east; and, following up this branch, Mr. Milne-Home reached a col, or watershed, of the precise level of thesecond Glen Roy road. When the barrier blocking the glens had been sofar removed as to open this col, the water in Glen Roy would sink tothe level of the second road. A new lake of diminished depth would bethus formed, the surplus water of which would escape over the GlenGlaster col into Glen Spean. The margin of this new lake, acting uponthe detrital matter, would form the second road. The theory of SirThomas Dick-Lauder, as regards the part played by the cols, wasre-riveted by this new and unexpected discovery. 

I have referred to Mr. Darwin, whose powerful mind swayed for a timethe convictions of the scientific world in relation to this question. His notion was--and it is a notion which very naturally presentsitself--that the parallel roads were formed by the sea; that thiswhole region was once submerged and subsequently upheaved; that therewere pauses in the process of upheaval, during which these glensconstituted so many fiords, on the sides of which the parallelterraces were formed. This theory will not bear close criticism; noris it now maintained by Mr. Darwin himself. It would not account forthe sea being 20 feet higher in Glen Gluoy than in Glen Roy. It wouldnot account for the absence of the second and third Glen Roy roadsfrom Glen Gluoy, where the mountain flanks are quite as impressionableas in Glen Roy. It would not account for the absence of the shelvesfrom the other mountains in the neighbourhood, all of which 'wouldhave been clasped by the sea had the sea been there. Here then, andno doubt elsewhere, Mr. Darwin has shown himself to be fallible; buthere, as elsewhere, he has shown himself equal to that discipline ofsurrender to evidence which girds his intellect with such unassailablemoral strength. 

But, granting the significance of Sir Thomas Dick-Lauder's facts, andthe reasonableness, on the whole, of the views which he has founded onthem, they will not bear examination in detail. No such barriers ofdetritus as he assumed could have existed without leaving tracesbehind them; but there is no trace left. There is detritus enough inGlen Spean, but not where it is wanted. The two highest parallelroads stop abruptly at different points near the mouth of Glen Roy, but no remnant of the barrier against which they abutted is to beseen. It might be urged that the subsequent invasion of the valley byglaciers has swept the detritus away; but there have been no glaciersin these valleys since the disappearance of the lakes. ProfessorGeikie has favoured me with a drawing of the Glen Spean 'road' nearthe entrance to Glen Trieg. The road forms a shelf round a greatmound of detritus which, had a glacier followed the formation of theshelf, must have been cleared away. Taking all the circumstances intoaccount, you may, I think, with safety dismiss the detrital barrier asincompetent to account for the present condition of Glen Gluoy andGlen Roy. 

Hypotheses in science, though apparently transcending experience, arein reality experience modified by scientific thought and pushed intoan ultra experiential region. At the time that he wrote, Sir ThomasDick-Lauder could not possibly have discerned the cause subsequentlyassigned for the blockage of these glens. A knowledge of the actionof ancient glaciers was the necessary antecedent to the newexplanation, and experience of this nature was not possessed by thedistinguished writer just mentioned. The extension of Swiss glaciersfar beyond their present limits, was first made known by a Swissengineer named Venetz, who established, by the marks they had leftbehind them, their former existence in places which they had longforsaken. The subject of glacier extension was subsequently followedup with distinguished success by Charpentier, Studer, and others. Withcharacteristic vigour Agassiz grappled with it, extending hisobservations far beyond the domain of Switzerland. He came to thiscountry in 1840, and found in various places indubitable marks ofancient glacier action. England, Scotland, Wales, and Ireland heproved to have once given birth to glaciers. He visited Glen Roy, surveyed the surrounding neighbourhood, and pronounced, as aconsequence of his investigation, the barriers which stopped the glensand produced the parallel roads to have been barriers of ice. To Mr. Jamieson, above all others, we are indebted for the thorough testingand confirmation of this theory. 

And let me here say that Agassiz is only too likely to be misrated andmisjudged by those who, though accurate within a limited sphere, failto grasp in their totality the motive powers invoked in scientificinvestigation. True he lacked mechanical precision, but he aboundedin that force and freshness of the scientific imagination which insome sciences, and probably in some stages of all sciences, areessential to the creator of knowledge. To Agassiz was given, not theart of the refiner, but the instinct of the discoverer, and thestrength of the delver who brings ore from the recesses of the mine. That ore may contain its share of dross, but it also contains theprecious metal which gives employment to the refiner, and withoutwhich his occupation would depart. 

Let us dwell for a moment upon this subject of ancient glaciers. Undera flask containing water, in which a thermometer is immersed, isplaced a Bunsen's lamp. The water is heated, reaches a temperature of212°, and then begins to boil. The rise of the thermometer thenceases, although heat continues to be poured by the lamp into thewater. What becomes of that heat? We know that it is consumed in themolecular work of vaporization. In the experiment here arranged, thesteam passes from the flask through a tube into a second vessel keptat a low temperature. Here it is condensed, and indeed congealed toice, the second vessel being plunged in a mixture cold enough tofreeze the water. As a result of the process we obtain a mass of ice. That ice has an origin very antithetical to its own character. Thoughcold, it is the child of heat. If we removed the lamp, there would beno steam, and if there were no steam there would be no ice. The merecold of the mixture surrounding the second vessel would not produceice. The cold must have the proper material to work upon; and thismaterial--aqueous vapour--is, as we here see, the direct product ofheat. 

It is now, I suppose, fifteen or sixteen years since I found myselfconversing with an illustrious philosopher regarding that glacialepoch which the researches of Agassiz and others had revealed. Thisprofoundly thoughtful man maintained the fixed opinion that, at acertain stage in the history of the solar system, the sun's radiationhad suffered diminution, the glacial epoch being a consequence of thissolar chill. The celebrated French mathematician Poisson had anothertheory. Astronomers have shown that the solar system moves throughspace, and 'the temperature of space' is a familiar expression withscientific men. It was considered probable by Poisson that oursystem, during its motion, had traversed portions of space ofdifferent temperatures; and that, during its passage through one ofthe colder regions of the universe, the glacial epoch occurred. Notions such as these were more or less current everywhere not manyyears ago, and I therefore thought it worth while to show howincomplete they were. Suppose the temperature of our planet to bereduced, by the subsidence of solar heat, the cold of space, or anyother cause, say one hundred degrees. Four-and-twenty hours of such achill would bring down as, snow nearly all the moisture of ouratmosphere. But this would not produce a glacial epoch. Such anepoch would require the long-continued generation of the material fromwhich the ice of glaciers is derived. Mountain snow, the nutriment ofglaciers, is derived from aqueous vapour raised mainly from thetropical ocean by the sun. The solar fire is as necessary a factor inthe process as our lamp in the experiment referred to a moment ago. Nothing is easier than to calculate the exact amount of heat expendedby the sun in the production of a glacier. It would, as I haveelsewhere shown, [Footnote: 'Heat a Mode of Motion, ' fifth edition, chap. Vi: Forms of Water, sections 55 and 56. ] raise a quantity ofcast iron five times the weight of the glacier not only to a whiteheat, but to its point of fusion. If, as I have already urged, instead of being filled with ice, the valleys of the Alps were filledwith white-hot metal, of quintuple the mass of the present glaciers, it is the heat, and not the cold, that would arrest our attention andsolicit our explanation. The process of glacier making is obviouslyone of distillation, in which the fire of the sun, which generates thevapour, plays as essential a part as the cold of the mountains whichcondenses it. [Footnote: In Lyell's excellent 'Principles of Geology, 'the remark occurs that 'several writers have fallen into the strangeerror of supposing that the glacial period must have been one ofhigher mean temperature than usual. ' The really strange error was theforgetfulness of the fact that without the heat the substancenecessary to the production of glaciers would be wanting. ]

It was their ascription to glacier action that first gave the parallelroads of Glen Roy an interest in my eyes; and in 1867, with a view toself-instruction, I made a solitary pilgrimage to the place, andexplored pretty thoroughly the roads of the principal glen. I tracedthe highest road to the col dividing Glen Roy from Glen Spey, and, thanks to the civility of an Ordnance surveyor, I was enabled toinspect some of the roads with a theodolite, and to satisfy myselfregarding the common level of the shelves at opposite sides of thevalley. As stated by Pennant, the width of the roads amountssometimes to more than twenty yards; but near the head of Glen Roy thehighest road ceases to have any width, for it runs along the face of arock, the effect of the lapping of the water on the more friableportions of the rock being perfectly distinct to this hour. Myknowledge of the region was, however, far from complete, and nineyears had dimmed the memory even of the portion which had beenthoroughly examined. Hence my desire to see the roads once morebefore venturing to talk to you about them. The Easter holidays of1876 were to be devoted to this purpose; but at the last moment atelegram from Roy Bridge informed me that the roads were snowed up. Finding books and memories poor substitutes for the flavour of facts, I resolved subsequently to make another effort to see the roads. Accordingly last Thursday fortnight, after lecturing here, I packedup, and started (not this time alone) for the North. Next day at noonmy wife and I found ourselves at Dalwhinnie, whence a drive of somefive-and-thirty miles brought us to the excellent hostelry of Mr. Macintosh, at the mouth of Glen Roy. 

We might have found the hills covered with mist, which would havewholly defeated us; but Nature was good-natured, and we had twosuccessful working days among the hills. Guided by the excellentordnance map of the region, on the Saturday morning we went up theglen, and on reaching the stream called Allt Bhreac Achaidh faced thehills to the west. At the watershed between Glen Roy and Glen Fintaigwe bore northwards, struck the ridge above Glen Gluoy, came in view ofits road, which we persistently followed as long as it continuedvisible. It is a feature of all the roads that they vanish beforereaching the cola over which fell the waters of the lakes which formedthem. One reason doubtless is that at their upper ends the lakes wereshallow, and incompetent on this account to raise wavelets of anystrength to act upon the mountain drift. A second reason is that theywere land-locked in the higher portions and protected from thesouth-westerly winds, the stillness of their waters causing them toproduce but a feeble impression upon the mountain sides. From GlenGluoy we passed down Glen Turrit to Glen Roy, and through ithomewards, thus accomplishing two or three and twenty miles of roughand honest work. 

Next day we thoroughly explored Glen Glaster, following its two roadsas far as they were visible. We reached the col discovered by Mr. Milne-Home, which stands at the level of the middle road of Glen Roy. Thence we crossed southwards over the mountain _Creag Dhubh_, andexamined the erratic blocks upon its sides, and the ridges and moundsof moraine matter which cumber the lower flanks of the mountain. Theobservations of Mr. Jamieson upon this region, including the mouth ofGlen Trieg, are in the highest degree interesting. We entered GlenSpean, and continued a search begun on the evening of our arrival atRoy Bridge--the search, namely, for glacier polishings and markings. We did not find them copious, but they are indubitable. 

One of the proofs most convenient for reference, is a great roundedrock by the roadside, 1, 000 yards east of the milestone markedthree-quarters of a mile from Roy Bridge. Farther east other casesoccur, and they leave no doubt upon the mind that Glen Spean was atone time filled by a great glacier. To the disciplined eye the aspectof the mountains is perfectly conclusive on this point; and in noposition can the observer more readily and thoroughly convince himselfof this than at the head of Glen Glaster. The dominant hills here areall intensely glaciated. 

But the great collecting ground of the glaciers which dammed the glensand produced the parallel roads, were the mountains south and west ofGlen Spean. The monarch of these is Ben Nevis, 4, 370 feet high. Theposition of Ben Nevis and his colleagues, in reference to thevapour-laden winds of the Atlantic, is a point of the firstimportance. It is exactly similar to that of Carrantual and theMacgillicuddy Reeks in the south-west of Ireland. These mountainsare, and were, the first to encounter the south-western Atlanticwinds, and the precipitation, even at present, in the neighbourhood ofKillarney, is enormous. The winds, robbed of their vapour, andcharged with the heat set free by its precipitation, pursue theirdirection obliquely across Ireland; and the effect of the dryingprocess may be understood by comparing the rainfall at Cahirciveenwith that at Portarlington. As found by Dr. Lloyd, the ratio is as 59to 21--fifty-nine inches annually at Cahirciveen to twenty-one atPortarlington. During the glacial epoch this vapour fell as snow, andthe consequence was a system of glaciers which have left traces andevidences of the most impressive character in the region of theKillarney Lakes. I have referred in other places to the great glacierwhich, descending from the Reeks, moved through the Black Valley, tookpossession of the lake-basins, and left its traces on every rock andisland emergent from the waters of the upper lake. They are allconspicuously glaciated. Not in Switzerland itself do we find clearertraces of ancient glacier action. 

What the Macgillicuddy Reeks did in Ireland, Ben Nevis and theadjacent mountains did, and continue to do, in Scotland. We had anexample of this on the morning we quitted Roy Bridge. From the bridgewestward rain fell copiously, and the roads were wet; but theprecipitation ceased near Loch Laggan, whence eastward the roads weredry. Measured by the gauge, the rainfall Fort William is 86 inches, while at Laggan it is only 46 inches annually. The difference betweenwest and east is forcibly brought out by observations at the two endsof the Caledonian Canal. Fort William at the south-western end has, as just stated, 86 inches, while Culloden, at its north-eastern end, has only 24. To the researches of that able and accomplishedmeteorologist, Mr. Buchan, we are indebted for these and other data ofthe most interesting and valuable kind. 

Adhering to the facts now presented to us, it is not difficult torestore in idea the process by which the glaciers of Lochaber wereproduced and the glens dammed by ice. When the cold of the glacialepoch began to invade the Scottish hills, the sun at the same timeacting with sufficient power upon the tropical ocean, the vapoursraised and drifted on to these 'northern mountains were more and moreconverted into snow. This slid down the slopes, and from everyvalley, strath, and corry, south of Glen Spean, glaciers were pouredinto that glen. The two great factors here brought into play are thenutrition of the glaciers by the frozen material above, and theirconsumption in the milder air below. For a period supply exceededconsumption, and the ice extended, filling Glen Spean to anever-increasing height, and abutting against the mountains to thenorth of that glen. But why, it may be asked, should the valleyssouth of Glen Spean be receptacles of ice at a time when those northof it were receptacles of water? The answer is to be found in theposition and the greater elevation of the mountains south of GlenSpean. They first received the loads of moisture carried by theAtlantic winds, and not until they had been in part dried, and alsowarmed by the liberation of their latent heat, did these winds touchthe hills north of the Glen. 

An instructive observation bearing upon this point is here to benoted. Had our visit been in the winter we should have found all themountains covered; had it been in the summer we should have found thesnow all gone. But happily it was at a season when the aspect of themountains north and south of Glen Spean exhibited their relativepowers as snow collectors. Scanning the former hills from many pointsof view, we were hardly able to detect a fleck of snow, while heavyswaths and patches loaded the latter. Were the glacial epoch toreturn, the relation indicated by this observation would cause GlenSpean to be filled with glaciers from the south, while the hills andvalleys on the north, visited by warmer and drier winds, would remaincomparatively free from ice. This flow from the south would bereinforced from the west, and as long as the supply was in excess ofthe consumption the glaciers would extend, the dams which closed theglens increasing in height. By-and-by supply and consumption becomingapproximately equal, the height of the glacier barriers would remainconstant. Then, as milder weather set in, consumption would be inexcess, a lowering of the barriers and a retreat of the ice being theconsequence. But for a long time the conflict between supply andconsumption would continue, retarding indefinitely the disappearanceof the barriers, and keeping the imprisoned lakes in the northernglens. But however slow its retreat, the ice in the long run would beforced to yield. The dam at the mouth of Glen Roy, which probablyentered the glen sufficiently far to block up Glen Glaster, wouldgradually retreat. Glen Glaster and its col being opened, thesubsidence of the lake eighty feet, from the level of the highest tothat of the second parallel road, would follow as a consequence. Ithink this the most probable course of things, but it is also possiblethat Glen Glaster may have been blocked by a glacier from Glen Trieg. The ice dam continuing to retreat, at length permitted Glen Roy toconnect itself with upper Glen Spean. A continuous lake then filledboth glens, the level of which, as already explained, was determinedby the col at Makul, above the head of Loch Laggan. The last to yieldwas the portion of the glacier which derived nutrition from Ben Nevis, and probably also from the mountains north and south of Loch Arkaig. But it at length yielded, and the waters in the glens resumed thecourses which they pursue to-day. 

For the removal of the ice barriers no cataclysm is to be invoked; thegradual melting of the dam would produce the entire series ofphenomena. In sinking from col to col the water would flow over agradually melting barrier, the surface of the imprisoned lake notremaining sufficiently long at any particular level to produce a shelfcomparable to the parallel roads. By temporary halts in the processof melting due to atmospheric conditions or to the character of thedam itself, or through local softness in the drift, smallpseudo-terraces would be formed, which, to the perplexity of someobservers, are seen upon the flanks of the glens to-day. 

In presence then of the fact that the barriers which stopped theseglens to a height, it may be, of 1, 500 feet above the bottom of GlenSpean, have dissolved and left not a wreck behind; in presence of thefact, insisted on by Professor Geikie, that barriers of detritus wouldundoubtedly have been able to maintain themselves had they ever beenthere; in presence of the fact that great glaciers once most certainlyfilled these valleys--that the whole region, as proved by Mr. Jamieson, is filled with the traces of their action; the theory whichascribes the parallel roads to lakes dammed by barriers of ice has, inmy opinion, a degree of probability on its side which amounts to apractical demonstration of its truth. 

Into the details of the terrace formation I do not enter. Mr. Darwinand Mr. Jamieson on the one side, and Sir John Lubbock on the other, deal with true causes. The terraces, no doubt, are due in part to thedescending drift arrested by the water, and in part to the fretting ofthe wavelets, and the rearrangement of the stirred detritus, along thebelts of contact of lake and bill. The descent of matter must havebeen frequent when the drift was unbound by the rootlets which hold ittogether now. In some cases, it may be remarked, the visibility ofthe roads is materially augmented by differences of vegetation. Thegrass upon the terraces is not always of the same character as thatabove and below them, while on heather-covered hills the absence ofthe dark shrub from the roads greatly enhances their conspicuousness. 

The annexed sketch of a model will enable the reader to grasp theessential features of the problem and its solution. Glen Gluoy andGlen Roy are lateral valleys which open into Glen Spean. Let ussuppose Glen Spean filled from v to w with ice of a uniform elevationof 1, 500 feet above the sea, the ice not filling the upper part ofthat glen. The ice would thrust itself for some distance up thelateral valleys, closing all their mouths. The streams from themountains right and left of Glen Gluoy would pour their waters intothat glen, forming a lake, the level of which would be determined bythe height of the col at A, 1170 feet above the sea. Over this colthe water would flow into Glen Roy. But in Glen Roy it could not risehigher than 1150 feet, the height of the col at B, over which it wouldflow into Glen Spey. 

The water halting at these levels for a sufficient time, would formthe single road in Glen Gluoy and the highest road in Glen Roy. Thisstate of things would continue as long as the ice dam was sufficientlyhigh to dominate the cols at A and B; but when through change ofclimate the gradually sinking dam reached, in succession, the levelsof these cols, the water would then begin to flow over the dam insteadof over the cols. Let us suppose the wasting of the ice to continueuntil a connection was established between Glen Roy and Glen Glaster, a common lake would then fill both these glens, the level of whichwould be determined by that of the col c, over which the water wouldpour for an indefinite period into Glen Spean. During this period thesecond Glen Roy road and the highest road of Glen Glaster would beformed. The ice subsiding still further, a connection wouldeventually be established between Glen Roy, Glen Glaster, and theupper part of Glen Spean. A common lake would fill all three glens, the level of which would be that of the col D, over which for anindefinite period the lake would pour its water. During this periodthe lowest Glen Roy road, which is common also to Glen Glaster andGlen Spean, would be formed. Finally, on the disappearance of the icefrom the lower part of Glen Spean the waters would flow down theirrespective valleys as they do to-day. 

Fig. 7

Reviewing our work, we find three considerable steps to have markedthe solution of the problem of the Parallel Roads of Glen Roy. Thefirst of these was taken by Sir Thomas Dick-Lauder, the second was thepregnant conception of Agassiz regarding glacier action, and the thirdwas the testing and verification of this conception by the verythorough researches of Mr. Jamieson. No circumstance or incidentconnected with this discourse gives me greater pleasure than therecognition of the value of these researches. They are markedthroughout by unflagging industry, by novelty and acuteness ofobservation, and by reasoning power of a high and varied kind. Thesepages had been returned 'for press' when I learned that the relationof Ben Nevis and his colleagues to the vapour-laden winds of theAtlantic had not escaped Mr. Jamieson. To him obviously theexploration of Lochaber, and the development of the theory of theParallel Roads, has been a labour of love. 

Thus ends our rapid survey of this brief episode in the physicalhistory of the Scottish hills, --brief, that is to say, in comparisonwith the immeasurable lapses of time through which, to produce itsvaried structure and appearances, our planet must have passed. In thesurvey of such a field two things are specially worthy to be takeninto account--the widening of the intellectual horizon and thereaction of expanding knowledge upon the intellectual organ itself. 

At first, as in the case of ancient glaciers, through sheer want ofcapacity, the mind refuses to take in revealed facts. But by degreesthe steady contemplation of these facts so strengthens and expands theintellectual powers, that where truth once could not find an entranceit eventually finds a home. [Footnote: The formation, connection, successive subsidence, and final disappearance of the glacial lakes ofLochaber were illustrated in the discourse here reported by the modeljust described, constructed under the supervision of my assistant, Mr. John Cottrell. Glen Gluoy with its lake and road and the cataractover its col; Glen Roy and its three roads with their respectivecataracts at the head of Glen Spey, Glen Glaster, and Glen Spean, wereall represented. The successive shiftings of the barriers, which wereformed of plate glass, brought each successive lake and itscorresponding road into view, while the entire removal of the barrierscaused the streams to flow down the glens of the model as they flowdown the real glens of to-day. ]

A map of the district, with the parallel roads shown in red, isannexed. 

LITERATURE OF THE SUBJECT. 

THOMAS PENNANT. --A Tour in Scotland. Vol. Iii. 1776, p. 394. JOHNMACCULLOCH. --On the Parallel Roads of Glen Roy. Geol. Soc. Trans. Vol. Iv. 1817, p. 314. 

THOMAS LAUDER DICK (afterwards SIR THOMAS DICK-LAUDER, Bart. )--On theParallel Roads of Lochaber. Edin. Roy. Soc. Trans. 1818, vol. Ix. P. 1. 

CHARLES DARWIN. --Observations on the Parallel Roads of Glen Roy, andof the other parts of Lochaber in Scotland, with an attempt to provethat they are of marine origin. Phil. Trans. 1839, vol. Cxxix. P. 39. 

SIR CHARLES LYELL. --Elements of Geology. Second edition, 1841. 

Louis AGASSIZ. --The Glacial Theory and its Recent Progress--ParallelTerraces. Edin. New Phil. Journal, 1842, vol. Xxxiii. P. 236. 

DAVID MILNE (afterwards DAVID MILNE-HOME). --On the Parallel Roads ofLochaber; with Remarks on the Change of Relative Levels of Sea andLand in Scotland, and on the Detrital Deposits in that Country. Edin. Roy. Soc. Trans. 1847, vol. Xvi. P. 395. 

ROBERT CHAMBERS. --Ancient Sea Margins. Edinburgh, 1848. 

H. D. ROGERS. --On the Parallel Roads of Glen Roy. Royal Inst. Proceedings, 1861, vol. Iii. P. 341. 

THOMAS F. JAMIESON. --On the Parallel Roads of Glen Roy, and theirPlace in the History of the Glacial Period. Quart. Journal Geol. Soc. 1863, vol. Xix. P. 235. 

SIR CHARLES LYELL. --Antiquity of Man. 1863, p. 253. 

REV. R. B. WATSON. --On the Marine Origin of the Parallel Roads of GlenRoy. Quart. Journ. Geol. Soc. 1865, vol. Xxii. P. 9. 

SIR JOHN LUBBOCK. --On the Parallel Roads of Glen Roy. Quart. Journ. Geol. Soc. 1867, vol. Xxiv. P. 83. 

CHARLES BABBAGE. --Observations on the Parallel Roads of Glen Roy. Quart. Journ. Geol. Soc. 1868, vol. Xxiv. P. 273. 

JAMES NICOL. --On the Origin of the Parallel Roads of Glen Roy. 1869. Geol. Soc. Journal, vol. Xxv. P. 282. 

JAMES NICOL. --How the Parallel Roads of Glen Roy were formed. 1872. Geol. Soc. Journal, vol. Xxviii. P. 237. 

MAJOR-GENERAL SIR HENRY JAMES, R. E. --Notes on the Parallel Roads ofLochaber. 4to. 1874. 

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IX. ALPINE SCULPTURE. 

1864. 

TO account for the conformation of the Alps, two hypotheses have beenadvanced, which may be respectively named the hypothesis of fractureand the hypothesis of erosion. The former assumes that the forces bywhich the mountains were elevated produced fissures in the earth'scrust, and that the valleys of the Alps are the tracks of thesefissures; while the latter maintains that the valleys have been cutout by the action of ice and water, the mountains themselves being theresidual forms of this grand sculpture. I had heard the Via Malacited as a conspicuous illustration of the fissure theory--theprofound chasm thus named, and through which the Hinter-Rhein nowflows, could, it was alleged, be nothing else than a crack in theearth's crust. To the Via Mala I therefore went in 1864 to instructmyself upon the point in question. 

The gorge commences about a quarter of an hour above Tusis; and, onentering it, the first impression certainly is that it must be afissure. This conclusion in my case was modified as I advanced. Somedistance up the gorge I found upon the slopes to my right quantitiesof rolled stones, evidently rounded by water-action. Still furtherup, and just before reaching the first bridge which spans the chasm, Ifound more rolled stones, associated with sand and gravel. Throughthis mass of detritus, fortunately, a vertical cutting had been made, which exhibited a section showing perfect stratification. There wasno agency in the place to roll these stones, and to deposit thesealternating layers of sand and pebbles, but the river which now rushessome hundreds of feet below them. At one period of the Via Mala'shistory the river must have run at this high level. Other evidencesof water-action soon revealed themselves. From the parapet of thefirst bridge I could see the solid rock 200 feet above the bed of theriver scooped and eroded. 

It is stated in the guide-books that the river, which usually runsalong the bottom of the gorge, has been known almost to fill it duringviolent thunder-storms; and it may be urged that the marks of erosionwhich the sides of the chasm exhibit are due to those occasionalfloods. In reply to this, it may be stated that even the existence ofsuch floods is not well authenticated, and that if the suppositionwere true, it would be an additional argument in favour of the cuttingpower of the river. For if floods operating at rare intervals couldthus erode the rock, the same agency, acting without ceasing upon theriver's bed, must certainly be competent to excavate it. 

I proceeded upwards, and from a point near another bridge (which ofthem I did not note) had a fine view of a portion of the gorge. Theriver here runs at the bottom of a cleft of profound depth, but sonarrow that it might be leaped across. That this cleft must be acrack is the impression first produced; but a brief inspectionsuffices to prove that it has been cut by the river. From top tobottom we have the unmistakable marks of erosion. This cleft was bestseen on looking downwards from a point near the bridge; but lookingupwards from the bridge itself, the evidence of aqueous erosion wasequally convincing. 

The character of the erosion depends upon the rock as well as upon theriver. The action of water upon some rocks is almost purelymechanical; they are simply ground away or detached in sensiblemasses. Water, however, in passing over limestone, charges itselfwith carbonate of lime without damage to its transparency; the rock isdissolved in the water; and the gorges cut by water in such rocksoften resemble those cut in the ice of glaciers by glacier streams. Tothe solubility of limestone is probably to be ascribed the fantasticforms which peaks of this rock usually assume, and also the grottosand caverns which interpenetrate limestone formations. A rock capableof being thus dissolved will expose a smooth surface after the waterhas quitted it; and in the case of the Via Mala it is the polish ofthe surfaces and the curved hollows scooped in the sides of the gorge, which assure us that the chasm has been the work of the river. 

About four miles from Tusis, and not far from the little village ofZillis, the Via Mala opens into a plain bounded by high terraces. Itoccurred to me the moment I saw it that the plain had been the bed ofan ancient lake; and a farmer, who was my temporary companion, immediately informed me that such was the tradition of theneighbourhood. This man conversed with intelligence, and as I drewhis attention to the rolled stones, which rest not only above theriver, but above the road, and inferred that the river must once havebeen there to have rolled those stones, he saw the force of theevidence perfectly. In fact, in former times, and subsequent to theretreat of the great glaciers, a rocky barrier crossed the valley atthis place, damming the river which came from the mountains higher up. A lake was thus formed which poured its waters over the barrier. Twoactions were here at work, both tending to obliterate the lake--theraising of its bed by the deposition of detritus, and the cutting ofits dam by the river. In process of time the cut deepened into theVia Mala; the lake was drained, and the river now flows in a definitechannel through the plain which its waters once totally covered. 

From Tusis I crossed to Tiefenkasten by the Schien Pass, and thenceover the Julier Pass to Pontresina. There are three or four ancientlake-beds between Tiefenkasten and the summit of the Julier. They areall of the same type--a more or less broad and level valley-bottom, with a barrier in front through which the river has cut a passage, thedrainage of the lake being the consequence. These lakes weresometimes dammed by barriers of rock, sometimes by the moraines ofancient glaciers. 

An example of this latter kind occurs in the Rosegg valley, abouttwenty minutes below the end of the Rosegg glacier, and about an hourfrom Pontresina. The valley here is crossed by a pine-covered moraineof the noblest dimensions; in the neighbourhood of London it might becalled a mountain. That it is a moraine, the inspection of it from apoint on the Surlei slopes above it will convince any personpossessing an educated eye. Where, moreover, the interior of themound is exposed, it exhibits moraine-matter--detritus pulverised bythe ice, with boulders entangled in it. It stretched quite across thevalley, and at one time dammed the river up. But now the barrier iscut through, the stream having about one-fourth of the moraine to itsright, and the remaining three-fourths to its left. Other moraines ofa more resisting character hold their ground as barriers to thepresent day. 

In the Val di Campo, for example, about three-quarters of an hour fromPisciadello, there is a moraine composed of large boulders, whichinterrupt the course of a river and compel the water to fall over themin cascades. They have in great part resisted its action since theretreat of the ancient glacier which formed the moraine. Behind themoraine is a lake-bed, now converted into a level meadow, which restson a deep layer of mould. 

At Pontresina a very fine and instructive gorge is to be seen. Theriver from the Morteratsch glacier rushes through a deep and narrowchasm which is spanned at one place by a stone bridge. The rock isnot of a character to preserve smooth polishing; but the largerfeatures of water-action are perfectly evident from top to bottom. Those features are in part visible from the bridge, but still betterfrom a point a little distance from the bridge in the direction of theupper village of Pontresina. The hollowing out of the rock by theeddies of the water is here quite manifest. A few minutes' walkupwards brings us to the end of the gorge; and behind it we have theusual indications of an ancient lake, and terraces of distinct waterorigin. From this position indeed the genesis of the gorge is clearlyrevealed. After the retreat of the ancient glacier, a transverseridge of comparatively resisting material crossed the valley at thisplace. Over the lowest part of this ridge the river flowed, rushingsteeply down to join at the bottom of the slope the stream whichissued from the Rosegg glacier. On this incline the water became apowerful eroding agent, and finally cut the channel to its presentdepth. 

Geological writers of reputation assume at this place the existence ofa fissure, the 'washing out' of which resulted in the formation of thegorge. Now no examination of the bed of the river ever proved theexistence of this fissure; and it is certain that water, particularlywhen charged with solid matter in suspension, can cut a channelthrough unfissured rock. Cases of deep cutting can be pointed outwhere the clean bed of the stream is exposed, the rock which forms thefloor of the river not exhibiting a trace of fissure. An example ofthis kind on a small scale occurs near the Bernina Gasthaus, about twohours from Pontresina. A little way below the junction of the twostreams from the Bernina Pass and the Heuthal the river flows througha channel cut by itself, and 20 or 30 feet in depth. At some placesthe river-bed is covered with rolled stones; at other places it isbare, but shows no trace of fissure. The abstract power of water, ifI may use the term, to cut through rock is demonstrated by suchinstances. But if water be competent to form a gorge without the aidof a fissure, why assume the existence of such fissures in cases likethat at Pontresina? It seems far more philosophical to accept thesimple and impressive history written on the walls of those gorges bythe agent which produced them. 

Numerous cases might be pointed out, varying in magnitude, but allidentical in kind, of barriers which crossed valleys and formed lakeshaving been cut through by rivers, narrow gorges being theconsequence. One of the most famous examples of this kind is theFinsteraarschlucht in the valley of Hash. Here the ridge called theKirchet seems split across, and the river Aar rushes through thefissure. Behind the barrier we have the meadows and pastures of Imhofresting on the sediment of an ancient lake. Were this an isolatedcase, one might with an apparent show of reason conclude that theFinsteraarschlucht was produced by an earthquake, as some suppose itto have been; but when we find it to be a single sample of actionswhich are frequent in the Alps--when probably a hundred cases of thesame kind, though different in magnitude, can be pointed out--it seemsquite unphilosophical to assume that in each particular case anearthquake was at hand to form a channel for the river. As in the caseof the barrier at Pontresina, the Kirchet, after the retreat of theAar glacier, dammed the waters flowing from it, thus forming a lake, on the bed of which now stands the village of Imhof. Over thisbarrier the Aar tumbled towards Meyringen, cutting, as the centuriespassed, its bed ever deeper, until finally it became deep enough todrain the lake, leaving in its place the alluvial plain, through whichthe river now flows in a definite channel. 

In 1866 I subjected the Finsteraarschlucht to a close examination. Theearthquake theory already adverted to was then prevalent regarding it, and I wished to see whether any evidences existed of aqueous erosion. Near the summit of the Kirchet is a signboard inviting the travellerto visit the Aarenschlucht, a narrow lateral gorge which runs down tothe very bottom of the principal one. The aspect of this smallerchasm from bottom to top proves to demonstration that water had informer ages been there at work. It is scooped, rounded, and polished, so as to render palpable to the most careless eye that it is a gorgeof erosion. But it was regarding the sides of the great chasm thatinstruction was needed, and from its edge nothing to satisfy me couldbe seen. I therefore stripped and waded into the river until a pointwas reached which commanded an excellent view of both sides of thegorge. The water was cutting cold, but I was repaid. Below me on theleft-hand side was a jutting cliff which bore the thrust of the riverand caused the Aar to swerve from its direct course. From top tobottom this cliff was polished, rounded, and scooped. There was noroom for doubt. The river which now runs so deeply down had once beenabove. It has been the delver of its own channel through the barrierof the Kirchet. 

But the broad view taken by the advocates of the fracture theory is, that the valleys themselves follow the tracks of primeval fissuresproduced by the upheaval of the land, the cracks across the barriersreferred to being in reality portions of the great cracks which formedthe valleys. Such an argument, however, would virtually concede thetheory of erosion as applied to the valleys of the Alps. The narrowgorges, often not more than twenty or thirty feet across, sometimeseven narrower, frequently occur at the bottom of broad valleys. Suchfissures might enter into the list of accidents which gave directionto the real erosive agents which scooped the valley out; but theformation of the valley, as it now exists, could no more be ascribedto such cracks than the motion of a railway train could be ascribed tothe finger of the engineer which turns on the steam. 

These deep gorges occur, I believe, for the most part in limestonestrata; and the effects which the merest driblet of water can produceon limestone are quite astonishing. It is not uncommon to meet chasmsof considerable depth produced by small streams the beds of which aredry for a large portion of the year. Right and left of the largergorges such secondary chasms are often found. The idea of time must, I think, be more and more included in our reasonings on thesephenomena. Happily, the marks which the rivers have, in most cases, left behind them, and which refer, geologically considered, to actionsof yesterday, give us ground and courage to conceive what may beeffected in geologic periods. Thus the modern portion of the Via Malathrows light upon the whole. Near Bergün, in the valley of theAlbula, there is also a little Via Mala, which is not less significantthan the great one. The river flows here through a profound limestonegorge, and to the very edges of the gorge we have the evidences oferosion. But the most striking illustration of water-action uponlimestone rock that I have ever seen is the gorge at Pfaeffers. Herethe traveller passes along the side of the chasm midway between topand bottom. Whichever way he looks, backwards or forwards, upwards ordownwards, towards the sky or towards the river, he meets everywherethe irresistible and impressive evidence that this wonderful fissurehas been sawn through the mountain by the waters of the Tamina. 

I have thus far confined myself to the consideration of the gorgesformed by the cutting through of the rock-barriers which frequentlycross the valleys of the Alps; as far as they have been examined by methey are the work of erosion. But the larger question still remains, To what action are we to ascribe the formation of the valleysthemselves? This question includes that of the formation of themountain-ridges, for were the valleys wholly filled, the ridges woulddisappear. Possibly no answer can be given to this question which isnot beset with more or less of difficulty. Special localities mightbe found which would seem to contradict every solution which, refersthe conformation of the Alps to the operation of a single cause. 

Still the Alps present features of a character sufficiently definiteto bring the question of their origin within the sphere of closereasoning. That they were in whole or in part once beneath the seawill not be disputed; for they are in great part composed ofsedimentary rocks which required a sea to form them. Their presentelevation above the sea is due to one of those local changes in theshape of the earth which have been of frequent occurrence throughoutgeologic time, in some cases depressing the land, and in otherscausing the sea-bottom to protrude beyond its surface. Consideringthe inelastic character of its materials, the protuberance of the Alpscould hardly have been pushed out without dislocation and fracture;and this conclusion gains in probability when we consider thefoldings, contortions, and even reversals in position of the strata inmany parts of the Alps. Such changes in the position of beds whichwere once horizontal could not have been effected without dislocation. Fissures would be produced by these changes; and such fissures, theadvocates of the fracture theory contend, mark the positions of thevalleys of the Alps. 

Imagination is necessary to the man of science, and we could notreason on our present subject without the power of presenting mentallya picture of the earth's crust cracked and fissured by the forceswhich produced its upheaval. Imagination, however, must be strictlychecked by reason and by observation. That fractures occurred cannot, I think, be doubted, but that the valleys of the Alps are thus formedis a conclusion not at all involved in the admission of dislocations. I never met with a precise statement of the manner in which theadvocates of the fissure theory suppose the forces to haveacted--whether they assume a general elevation of the region, or alocal elevation of distinct ridges; or whether they assume localsubsidences after a general elevation, or whether they would superposeupon the general upheaval minor and local upheavals. 

In the absence of any distinct statement, I will assume the elevationto be general--that a swelling out of the earth's crust occurred here, sufficient to place the most prominent portions of the protuberancethree miles above the sea-level. To fix the ideas, let us consider acircular portion of the crust, say one hundred miles in diameter, andlet us suppose, in the first instance, the circumference of thiscircle to remain fixed, and that the elevation was confined to thespace within it. The upheaval would throw the crust into a state ofstrain; and, if it were inflexible, the strain must be relieved byfracture. Crevasses would thus intersect the crust. Let us nowenquire what proportion the area of these open fissures is likely tobear to the area of the unfissured crust. An approximate answer is allthat is here required; for the problem is of such a character as torender minute precision unnecessary. 

No one, I think, would affirm that the area of the fissures would beone-hundredth the area of the land. For let us consider the strainupon a single line drawn over the summit of the protuberance from apoint on its rim to a point opposite. Regarding the protuberance as aspherical swelling, the length of the arc corresponding to a chord of100 miles and a versed sine of 3 miles is 100. 24 miles; consequentlythe surface to reach its new position must stretch 0. 24 of a mile, orbe broken. A fissure or a number of cracks with this total widthwould relieve the strain; that is to say, the sum of the widths of allthe cracks over the length of 100 miles would be 420 yards. If, instead of comparing the width of the fissures with the length of thelines of tension, we compared their areas with the area of theunfissured land, we should of course find the proportion much less. These considerations will help the imagination to realise what a smallratio the area of the open fissures must bear to the unfissured crust. They enable us to say, for example, that to assume the area of thefissures to be one-tenth of the area of the land would be quiteabsurd, while that the area of the fissures could be one-half or morethan one-half that of the land would be in a proportionate degreeunthinkable. If we suppose the elevation to be due to the shrinkingor subsidence of the land all round our assumed circle, we arriveequally at the conclusion that the area of the open fissures would bealtogether insignificant as compared with that of the unfissuredcrust. 

To those who have seen them from a commanding elevation, it isneedless to say that the Alps themselves bear no sort of resemblanceto the picture which this theory presents to us. Instead of deepcracks with approximately vertical walls, we have ridges running intopeaks, and gradually sloping to form valleys. Instead of a fissuredcrust, we have a state of things closely resembling the surface of theocean when agitated by a storm. The valleys, instead of being muchnarrower than the ridges, occupy the greater space. A plaster cast ofthe Alps turned upside down, so as to invert the elevations anddepressions, would exhibit blunter and broader mountains, withnarrower valleys between them, than the present ones. The valleysthat exist cannot, I think, with any correctness of language be calledfissures. It may be urged that they originated in fissures: but eventhis is unproved, and, were it proved, the fissures would still playthe subordinate part of giving direction to the agents which are to beregarded as the real sculptors of the Alps. 

The fracture theory, then, if it regards the elevation of the Alps asdue to the operation of a force acting throughout the entire region, is, in my opinion, utterly incompetent to account for the conformationof the country. If, on the other hand, we are compelled to resort tolocal disturbances, the manipulation of the earth's crust necessary toobtain the valleys and the mountains will, I imagine, bring thedifficulties of the theory into very strong relief. Indeed anexamination of the region from many of the more accessibleeminences--from the Galenstock, the Grauhaupt, the Pitz Languard, theMonte Confinale--or, better still, from Mont Blanc, Monte Rosa, theJungfrau, the Finsteraarhorn, the Weisshorn, or the Matterhorn, wherelocal peculiarities are toned down, and the operations of the powerswhich really made this region what it is are alone brought intoprominence--must, I imagine, convince every physical geologist of theinability of any fracture theory to account for the presentconformation of the Alps. 

A correct model of the mountains, with an unexaggerated verticalscale, produces the same effect upon the mind as the prospect from oneof the highest peaks. We are apt to be influenced by local phenomenawhich, though insignificant in view of the general question of Alpineconformation, are, with reference to our customary standards, vast andimpressive. In a true model those local peculiarities disappear; foron the scale of a model they are too small to be visible; while theessential facts and forms are presented to the undistracted attention. 

A minute analysis of the phenomena strengthens the conviction whichthe general aspect of the Alps fixes in the mind. We find, forexample, numerous valleys which the most ardent plutonist would notthink of ascribing to any other agency than erosion. That such istheir genesis and history is as certain as that erosion produced theChines in the Isle of Wight. From these indubitable cases oferosion--commencing, if necessary, with the small ravines which rundown the flanks of the ridges, with their little working navigators attheir bottoms--we can proceed, by almost insensible gradations, to thelargest valleys of the Alps; and it would perplex the plutonist to fixupon the point at which fracture begins to play a material part. 

In ascending one of the larger valleys, we enter it where it is wideand where the eminences are gentle on either side. The flankingmountains become higher and more abrupt as we ascend, and at length wereach a place where the depth of the valley is a maximum. Continuingour walk upwards, we find ourselves flanked by gentler slopes, andfinally emerge from the valley and reach the summit of an open col, ordepression in the chain of mountains. This is the common character ofthe large valleys. Crossing the col, we descend along the oppositeslope of the chain, and through the same series of appearances in thereverse order. If the valleys on both sides of the col were producedby fissures, what prevents the fissure from prolonging itself acrossthe col? The case here cited is representative; and I am notacquainted with a single instance in the Alps where the chain has beencracked in the manner indicated. The cols are simply depressions; inmany of which the unfissured rock can be traced from side to side. 

The typical instance just sketched follows as a natural consequencefrom the theory of erosion. Before either ice or water can exertgreat power as an erosive agent, it must collect in sufficient mass. On the higher slopes and plateaus--in the region of cols--the power isnot fully developed; but lower down tributaries unite, erosion iscarried on with increased vigour, and the excavation gradually reachesa maximum. Lower still the elevations diminish and the slopes becomemore gentle; the cutting power gradually relaxes, until finally theeroding agent quits the mountains altogether, and the grand effectswhich it produced in the earlier portions of its course entirelydisappear. 

I have hitherto confined myself to the consideration of the broadquestion of the erosion theory as compared with the fracture theory;and all that I have been able to observe and think with reference tothe subject leads me to adopt the former. Under the term erosion Iinclude the action of water, of ice, and of the atmosphere, includingfrost and rain. Water and ice, however, are the principal agents, andwhich of these two has produced the greatest effect it is perhapsimpossible to say. Two years ago I wrote a brief note 'On theConformation of the Alps, ' [Footnote: Phil. Mag. Vol. Xxiv. P. 169]in which I ascribed the paramount influence to glaciers. The facts onwhich that opinion was founded are, I think, unassailable; but whetherthe conclusion then announced fairly follows from the facts is, Iconfess, an open question. 

The arguments which have been thus far urged against the conclusionare not convincing. Indeed, the idea of glacier erosion appears sodaring to some minds that its boldness alone is deemed its sufficientrefutation. It is, however, to be remembered that a precisely similarposition was taken up by many excellent workers when the question ofancient glacier extension was first mooted. The idea was consideredtoo hardy to be entertained; and the evidences of glacial action weresought to be explained by reference to almost any process rather thanthe true one. Let those who so wisely took the side of 'boldness' inthat discussion beware lest they place themselves, with reference tothe question of glacier erosion, in the position formerly occupied bytheir opponents. 

Looking at the little glaciers of the present day--mere pigmies ascompared to the giants of the glacial epoch--we find that from everyone of them issues a river more or less voluminous, charged with thematter which the ice has rubbed from the rocks. Where the rocks aresoft, the amount of this finely pulverised matter suspended in thewater is very great. The water, for example, of the river which flowsfrom Santa Catarina to Bormio is thick with it. The Rhine is chargedwith this matter, and by it has so silted up the Lake of Constance asto abolish it for a large fraction of its length. The Rhone ischarged with it, and tens of thousands of acres of cultivable land areformed by the silt above the Lake of Geneva. 

In the case of every glacier we have two agents at work--the iceexerting a crushing force on every point of its bed which bears itsweight, and either rasping this point into powder or tearing it bodilyfrom the rock to which it belongs; while the water which everywherecirculates upon the bed of the glacier continually washes the detritusaway and leaves the rock clean for further abrasion. Confining theaction of glaciers to the simple rubbing away of the rocks, andallowing them sufficient time to act, it is not a matter of opinion, but a physical certainty, that they will scoop out valleys. But theglacier does more than abrade. Rocks are not homogeneous; they areintersected by joints and places of weakness, which divide them intovirtually detached masses. A glacier is undoubtedly competent to rootsuch masses bodily away. Indeed the mere _à priori_ consideration ofthe subject proves the competence of a glacier to deepen its bed. Taking the case of a glacier 1, 000 feet deep (and some of the olderones were probably three times this depth), and allowing 40 feet ofice to an atmosphere, we find that on every square inch of its bedsuch a glacier presses with a weight of 375 lbs, and on every squareyard of its bed with a weight of 486, 000 lbs. With a vertical pressureof this amount the glacier is urged down its valley by the pressurefrom behind. We can hardly, I think, deny to such a tool a power ofexcavation. 

The retardation of a glacier by its bed has been referred to asproving its impotence as an erosive agent; but this very retardationis in some measure an expression of the magnitude of the erosiveenergy. Either the bed must give way, or the ice must slide overitself. We get indeed some idea of the crushing pressure which themoving glacier exercises against its bed-from the fact that theresistance, and the effort to overcome it, are such as to make theupper layers of a glacier move bodily over the lower ones--a portiononly of the total motion being due to the progress of the entire massof the glacier down its valley. 

The sudden bend in the valley of the Rhone at Martigny has also beenregarded as conclusive evidence against the theory of erosion. 'Why, 'it has been asked, I did not the glacier of the Rhone go straightforward instead of making this awkward bend?' But if the valley be acrack, why did the crack make this bend? The crack, I submit, had atleast as much reason to prolong itself in a straight line as theglacier had. A statement of Sir John Herschel with reference toanother matter is perfectly applicable here: 'A crack once producedhas a tendency to run--for this plain reason, that at its momentarylimit, at the point at which it has just arrived, the divellent forceon the molecules there situated is counteracted only by half of thecohesive force which acted when there was no crack, viz. The cohesionof the uncracked portion alone' ('Proc. Roy. Soc. ' vol. Xii. P. 678). To account, then, for the bend, the adherent of the fracturetheory must assume the existence of some accident which turned thecrack at right angles to itself; and he surely will permit theadherent of the erosion theory to make a similar assumption. 

The influence of small accidents on the direction of rivers isbeautifully illustrated in glacier streams, which are made to cuteither straight or sinuous channels by causes apparently of the mosttrivial character. In his interesting paper 'On the Lakes ofSwitzerland, ' M. Studer also refers to the bend of the Rhine atSargans in proof that the river must there follow a pre-existingfissure. I made a special expedition to the place in 1864; and thoughit was plain that M. Studer had good grounds for the selection of thisspot, I was unable to arrive at his conclusion as to the necessity ofa fissure. 

Again, in the interesting volume recently published by the SwissAlpine Club, M. Desor informs us that the Swiss naturalists who metlast year at Samaden visited the end of the Morteratsch glacier, andthere convinced themselves that a glacier had no tendency whatever toimbed itself in the soil. I scarcely think that the question ofglacier erosion, as applied either to lakes or valleys, is to bedisposed of so easily. Let me record here my experience of theMorteratsch glacier. 

I took with me in 1864 a theodolite to Pontresina, and while there hadto congratulate myself on the aid of my friend Mr. Hirst, who in 1857did such good service upon the Mer de Glace and its tributaries. Weset out three lines across the Morteratsch glacier, one of whichcrossed the ice-stream near the well-known hut of the painter Georgei, while the two others were staked out, the one above the hut and theother below it. Calling the highest line A, the line which crossedthe glacier at the hut B, and the lowest line C, the following are themean hourly motions of the three lines, deduced from observationswhich extended over several days. On each line eleven stakes werefixed, which are designated by the figures 1, 2, 3, &c. In theTables. 

Morteratsch Glacier, Line A. 

No. Of Stake. Hourly Motion. 

1 0. 35 inch. 

2 0. 49 inch. 

3 0. 53 inch. 

4 0. 54 inch. 

5 0. 56 inch. 

6 0. 54 inch. 

7 0. 52 inch. 

8 0. 49 inch. 

9 0. 40 inch. 

10 0. 29 inch. 

11 0. 20 inch. 

As in all other measurements of this kind, the retarding influence ofthe sides of the glacier is manifest: the centre moves with thegreatest velocity. 

Morteratsch Glacier, Line B. 

No. Of Stake. Hourly Motion. 

1 0. 05 inch. 

2 0. 14 inch. 

3 0. 24 inch. 

4 0. 32 inch. 

5 0-41 inch. 

6 0. 44 inch. 

7 0. 44 inch. 

8 0. 45 inch. 

9 0. 43 inch. 

10 0. 44 inch. 

11 0. 44 inch. 

The first stake of this line was quite close to the edge of theglacier, and the ice was thin at the place, hence its slow motion. Crevasses prevented us from carrying the line sufficiently far acrossto render the retardation of the further side of the glacier fullyevident. 

Morteratsch Glacier, Line C. 

No. Of Stake Hourly Motion. 

1 0. 05 inch. 

2 0. 09 inch. 

3 0. 18 inch. 

4 0. 20 inch. 

5 0. 25 inch. 

6 0. 27 inch. 

7 0. 27 inch. 

8 0. 30 inch. 

9 0. 21 inch. 

10 0. 20 inch. 

11 0. 16 inch. 

Comparing the three lines together, it will be observed that thevelocity diminishes as we descend the glacier. In 100 hours themaximum motion of three lines respectively is as follows:

Maximum Motion in 100 hours. 

Line A 56 inches

Line B 45 inches. 

Line C 30 inches. 

This deportment explains an appearance which must strike everyobserver who looks upon the Morteratsch from the Piz Languard, or fromthe new Bernina Road. A medial moraine runs along the glacier, commencing as a narrow streak, but towards the end the moraineextending in width, until finally it quite covers the terminal portionof the glacier. The cause of this is revealed by the foregoingmeasurements, which prove that a stone on the moraine where it iscrossed by the line A approaches a second stone on the moraine whereit is crossed by the line C with a velocity of twenty-six inches perone hundred hours. The moraine is in a state of longitudinalcompression. Its materials are more and more squeezed together, andthey must consequently move laterally and render the moraine at theterminal portion of the glacier wider than above. 

The motion of the Morteratsch glacier, then, diminishes as we descend. The maximum motion of the third line is thirty inches in one hundredhours, or seven inches a day--a very slow motion; and had we run aline nearer to the end of the glacier, the motion would have beenslower still. At the end itself it is nearly insensible. [Footnote:The snout of the Aletsch Glacier has a diurnal motion of less than twoinches, while a mile or so above the snout the velocity is eighteeninches. The spreading out of the moraine is here very striking. ] NowI submit that this is not the Place to seek for the scooping power ofa glacier. The opinion appears to be prevalent that it is the snoutof a glacier that must act the part of ploughshare; and it iscertainly an erroneous opinion. The scooping power will exert itselfmost where the weight and the motion are greatest. A glacier's snoutoften rests upon matter which has been scooped from the glacier's bedhigher up. I therefore do not think that the inspection of what theend of a glacier does or does not accomplish can decide this question. 

The snout of a glacier is potent to remove anything against which itcan fairly abut; and this power, notwithstanding the slowness of themotion, manifests itself at the end of the Morteratsch glacier. Ahillock, bearing pine-trees, was in front of the glacier when Mr. Hirst and myself inspected its end; and this hillock is being bodilyremoved by the thrust of the ice. Several of the trees areoverturned; and in a few years, if the glacier continues its reputedadvance, the mound will certainly be ploughed away. 

The question of Alpine conformation stands, I think, thus: We have, in the first place, great valleys, such as those of the Rhine and theRhone, which we might conveniently call valleys of the first order. The mountains which flank these main valleys are also cut by lateralvalleys running into the main ones, and which may be called valleys ofthe second order. When these latter are examined, smaller valleys arefound running into them, which may be called valleys of the thirdorder. Smaller ravines and depressions, again, join the latter, whichmay be called valleys of the fourth order, and so on until we reachstreaks and cuttings so minute as not to merit the name of valleys atall. At the bottom of every valley we have a stream, diminishing inmagnitude as the order of the valley ascends, carving the earth andcarrying its materials to lower levels. We find that the largervalleys have been filled for untold ages by glaciers of enormousdimensions, always moving, grinding down and tearing away the rocksover which they passed. We have, moreover, on the plains at the feetof the mountains, and in enormous quantities, the very matter derivedfrom the sculpture of the mountains themselves. 

The plains of Italy and Switzerland are cumbered by the _débris_ of theAlps. The lower, wider, and more level valleys are also filled tounknown depths with the materials derived from the higher ones. Inthe vast quantities of moraine-matter which cumber many even of thehigher valleys we have also suggestions as to the magnitude of theerosion which has taken place. This moraine-matter, moreover, canonly in small part have been derived from the falling of rocks uponthe ancient glacier; it is in great part derived from the grinding andthe ploughing-out of the glacier itself. This accounts for themagnitude of many of the ancient moraines, which date from a periodwhen almost all the mountains were covered with ice and snow, andwhen, consequently, the quantity of moraine-matter derived from thenaked crests cannot have been considerable. 

The erosion theory ascribes the formation of Alpine valleys to theagencies here briefly referred to. It invokes nothing but truecauses. Its artificers are still there, though, it may be, indiminished strength; and if they are granted sufficient time, it isdemonstrable that they are competent to produce the effects ascribedto them. And what does the fracture theory offer in comparison? Fromno possible application of this theory, pure and simple, can we obtainthe slopes and forms of the mountains. Erosion must in the long runbe invoked, and its power therefore conceded. The fracture theoryinfers from the disturbances of the Alps the existence of fissures;and this is a probable inference. But that they were of a magnitudesufficient to produce the conformation of the Alps, and that theyfollowed, as the Alpine valleys do, the lines of natural drainage ofthe country, are assumptions which do not appear to me to be justifiedeither by reason or by observation. 

There is a grandeur in the secular integration of small effectsimplied by the theory of erosion almost superior to that involved inthe idea of a cataclysm. Think of the ages which must have beenconsumed in the execution of this colossal sculpture. The questionmay, of course, be pushed further. Think of the ages which the moltenearth required for its consolidation. But these vaster epochs lacksublimity through our inability to grasp them. They bewilder us, butthey fail to make a solemn impression. The genesis of the mountainscomes more within the scope of the intellect, and the majesty of theoperation is enhanced by our partial ability to conceive it. In thefalling of a rock from a mountain-head, in the shoot of an avalanche, in the plunge of a cataract, we often see more impressiveillustrations of the power of gravity than in the motions of thestars. When the intellect has to intervene, and calculation isnecessary to the building up of the conception, the expansion of thefeelings ceases to be proportional to the magnitude of the phenomena. 

*****

I will here record a few other measurements executed on the Roseggglacier: the line was staked out across the trunk formed by thejunction of the Rosegg proper with the Tschierva glacier, a shortdistance below the rocky promontory called Agaliogs. 

Rosegg Glacier. 

No. Of Stake. Hourly Motion. 

1 0. 01 inch. 

2 0. 05

3 0. 07

4 0. 10

5 0. 11

6 0. 13

7 0. 14

8 0. 18

9 0. 24

10 0. 23

11 0. 24

This is an extremely slowly moving glacier; the maximum motion hardlyamounts to seven inches a day. Crevasses prevented us from continuingthe line quite across the glacier. 

********************

X. RECENT EXPERIMENTS ON FOG-SIGNALS. 

[Footnote: A discourse delivered in the Royal Institution, March 22, 1878. ]

The care of its sailors is one of the first duties of a maritimepeople, and one of the sailor's greatest dangers is his proximity tothe coast at night. Hence, the idea of warning him of such proximityby beacon-fires placed sometimes on natural eminences and sometimes ontowers built expressly for the purpose. Close to Dover Castle, forexample, stands an ancient Pharos of this description. 

As our marine increased greater skill was invoked, and lampsreinforced by parabolic reflectors poured their light upon the sea. Several of these lamps were sometimes grouped together so as tointensify the light, which at a little distance appeared as if itemanated from a single source. This 'catoptric' form of apparatus isstill to some extent employed in our lighthouse-service, but for along time past it has been more and more displaced by the great lensesdevised by the illustrious Frenchman, Fresnel. 

In a first-class 'dioptric' apparatus the light emanates from a lampwith several concentric wicks, the flame of which, being kindled by avery active draught, attains to great intensity. In fixed lights thelenses refract the rays issuing from the lamp so as to cause them toform a luminous sheet which grazes the sea-horizon. In revolvinglights the lenses gather up the rays into distinct beams, resemblingthe spokes of a wheel, which sweep over the sea and strike the eye ofthe mariner in succession. 

It is not for clear weather that the greatest strengthening of thelight is intended, for here it is not needed. Nor is it for denselyfoggy weather, for here it is ineffectual. But it is for theintermediate stages of hazy, snowy, or rainy weather, in which apowerful light can assert itself, while a feeble one is extinguished. The usual first-order lamp is one of four wicks, but Mr. Douglass, theable and indefatigable engineer of the Trinity House, has recentlyraised the number of the wicks to six, which produce a very nobleflame. To Mr. Wigham, of Dublin, we are indebted for the successfulapplication of gas to lighthouse illumination. In some lighthouseshis power varies from 28 jets to 108 jets, while in the lighthouse ofGalley Head three burners of the largest size can be employed, themaximum number of jets being 324. These larger powers are invokedonly in case of fog, the 28-jet burner being amply sufficient forclear weather. The passage from the small burner to the large, andfrom the large burner to the small, is made with ease, rapidity, andcertainty. This employment of gas is indigenous to Ireland, and theBoard of Trade has exercised a wise liberality in allowing everyfacility to Mr. Wigham for the development of his invention. 

The last great agent employed in lighthouse illumination iselectricity. It was in this Institution, beginning in 1831, thatFaraday proved the existence and illustrated the laws of those inducedcurrents which in our day have received such astounding development. In relation to this subject Faraday's words have a prophetic ring. 'Ihave rather, ' he writes in 1831, 'been desirous of discovering newfacts and new relations dependent on magneto-electric induction thanof exalting the force of those already obtained, being assured thatthe latter would find their full development hereafter. ' The laboursof Holmes, of the Paris Alliance Company, of Wilde, and of Gramme, constitute a brilliant fulfilment of this prediction. 

But, as regards the augmentation of power, the greatest step hithertomade was independently taken a few years ago by Dr. Werner Siemens andSir Charles Wheatstone. Through the application of their discovery amachine endowed with an infinitesimal charge of magnetism may, by aprocess of accumulation at compound interest, be caused so to enrichitself magnetically as to cast by its performance all the oldermachines into the shade. The light now before you is that of a smallmachine placed downstairs, and worked there by a minute steam-engine. It is a light of about 1000 candles; and for it, and for thesteam-engine that 'works it, our members are indebted to theliberality of Dr. William Siemens, who in the most generous manner haspresented the machine to this Institution. After an exhaustive trialat the South Foreland, machines on the principle of Siemens, but offar greater power than this one, have been recently chosen by theElder Brethren of the Trinity House for the two light-houses at theLizard Point. 

Our most intense lights, including the six-wick lamp, the Wighamgas-light, and the electric light, being intended to aid the marinerin heavy weather, may be regarded, in a certain sense, as fog-signals. But fog, when thick, is intractable to light. The sun cannotpenetrate it, much less any terrestrial source of illumination. Hencethe necessity of employing sound-signals in dense fogs. Bells, gongs, horns, whistles, guns, and syrens have been used for this purpose; butit is mainly, if not wholly, with explosive signals that we have nowto deal. The gun has been employed with useful effect at the NorthStack, near Holyhead, on the Kish Bank near Dublin, at Lundy Island, and at other points on our coasts. During the long, laborious, and Iventure to think memorable series of observations conducted under theauspices of the Elder Brethren of the Trinity House at the SouthForeland in 1872 and 1873, it was proved that a short 5. 5-inchhowitzer, firing 3 lbs. Of powder, yielded a louder report than a long18-pounder firing the same charge. Here was a hint to be acted on bythe Elder Brethren. The effectiveness of the sound depended on theshape of the gun, and as it could not be assumed that in the howitzerwe had hit accidentally upon the best possible shape, arrangementswere made with the War Office for the construction of a gun speciallycalculated to produce the loudest sound attainable from the combustionof 3 lbs. Of powder. To prevent the unnecessary landward waste of thesound, the gun was furnished with a parabolic muzzle, intended toproject the sound over the sea, where it was most needed. Theconstruction of this gun was based on a searching series ofexperiments executed at Woolwich with small models, provided withmuzzles of various kinds. A drawing of the gun is annexed (p. 309). It was constructed on the principle of the revolver, its variouschambers being loaded and brought in rapid succession into the firingposition. The performance of the gun proved the correctness of theprinciples on which its construction was based. 

An incidental point of some interest was decided by the earliestWoolwich experiments. It had been a widely spread opinion amongartillerists, that a bronze gun produces a specially loud report. Idoubted from the outset whether this would help us; and in a letterdated 22nd April, 1874, I ventured to express myself thus: 'Thereport of a gun, as affecting an observer close at hand, is made up oftwo factors--the sound due to the shock of the air by the violentlyexpanding gas, and the sound derived from the vibrations of the gun, which, to some extent, rings like a bell. This latter, I apprehend, will disappear at considerable distances. '

FIG. 8. Breech-loading Fog-signal Gun, with Bell Mouth, proposed byMajor Maitland, R. A. Assistant Superintendent. [Footnote: The carriageof this gun has been modified in construction since this drawing wasmade. ]

The result of subsequent trial, as reported by General Campbell, is, 'that the sonorous qualities of bronze are greatly superior to thoseof cast iron at short distances, but that the advantage lies with thebaser metal at long ranges. ' [Footnote: General Campbell assigns atrue cause for this difference. The ring of the bronze gun representsso much energy withdrawn from the explosive force of the gunpowder. Further experiments would, however, be needed to place the superiorityof the cast-iron gun at a distance beyond question. ]

Coincident with these trials of guns at Woolwich, gun-cotton wasthought of as a probably effective sound-producer. From the first, indeed, theoretic considerations caused me to fix my attentionpersistently on this substance; for the remarkable experiments of Mr. Abel, whereby its rapidity of combustion and violently explosiveenergy are demonstrated, seemed to single it out as a substanceeminently calculated to fulfil the conditions necessary to theproduction of an intense wave of sound. What those conditions are weshall now more particularly enquire, calling to our aid a brief butvery remarkable paper, published by Professor Stokes in the'Philosophical Magazine' for 1868. 

The explosive force of gunpowder is known to depend on the suddenconversion of a solid body into an intensely heated gas. Now the workwhich the artillerist requires the expanding gas to perform is thedisplacement of the projectile, besides which it has to displace theair in front of the projectile, which is backed by the whole pressureof the atmosphere. Such, however, is not the work that we want ourgunpowder to perform. We wish to transmute its energy not into themere mechanical translation of either shot or air, but into vibratorymotion. We want _pulses_ to be formed which shall propagate themselvesto vast distances through the atmosphere, and this requires a certainchoice and management of the explosive material. 

A sound-wave consists essentially of two parts--a condensation and ararefaction. Now air is a very mobile fluid, and if the shockimparted to it lack due promptness, the wave is not produced. Considerthe case of a common clock pendulum, which oscillates to and fro, andwhich might be expected to generate corresponding pulses in the air. When, for example, the bob moves to the right, the air to the right ofit might be supposed to be condensed, while a partial vacuum might besupposed to follow the bob. As a matter of fact, we have nothing ofthe kind. The air particles in front of the bob retreat so rapidly, and those behind it close so rapidly in, that no sound-pulse isformed. The mobility of hydrogen, moreover, being far greater thanthat of air, a prompter action is essential to the formation ofsonorous waves in hydrogen than in air. It is to this rapid power ofreadjustment, this refusal, so to speak, to allow its atoms to becrowded together or to be drawn apart, that Professor Stokes, withadmirable penetration, refers the damping power, first described bySir John Leslie, of hydrogen upon sound. 

A tuning-fork which executes 256 complete vibrations in a second, ifstruck gently on a pad and held in free air, emits a scarcely audiblenote. It behaves to some extent like the pendulum bob just referredto. This feebleness is due to the prompt 'reciprocating flow' of theair between the incipient condensations and rarefactions, whereby theformation of sound-pulses is forestalled. Stokes, however, has taughtus that this flow may be intercepted by placing the edge of a card inclose proximity to one of the corners of the fork. An immediateaugmentation of the sound of the fork is the consequence. 

The more rapid the shock imparted to the air, the greater is thefractional part of the energy of the shock converted into wave motion. And as different kinds of gunpowder vary considerably in theirrapidity of combustion, it may be expected that they will also vary asproducers of sound. This theoretic inference is completely verifiedby experiment. In a series of preliminary trials conducted atWoolwich on the 4th of June, 1875, the sound-producing powers of fourdifferent kinds of powder were determined. In the order of the sizeof their grains they bear the names respectively of Fine-grain(F. G. ), Large-grain (L. G. ), Rifle Large-grain (R. L. G. ), andPebble-powder (P. ) (See annexed figures. ) The charge in each caseamounted to 4. 5 lbs. Four 24-lb. Howitzers being employed to fire therespective charges. 

FIG. 9. 

There were eleven observers, all of whom, without a singledissentient, pronounced the sound of the fine-grain powder loudest ofall. In the opinion of seven of the eleven the large-grain powdercame next; seven also of the eleven placed the rifle large-grain thirdon the list; while they were again unanimous in pronouncing thepebble-powder the worst sound-producer. These differences areentirely due to differences in the rapidity of combustion. All whohave witnessed the performance of the 80-ton gun must have beensurprised at the mildness of its thunder. To avoid the strainresulting from quick combustion, the powder employed is composed oflumps far larger than those of the pebble-powder above referred to. Inthe long tube of the gun these lumps of solid matter gradually resolvethemselves into gas, which on issuing from muzzle imparts a kind ofpush to the air, instead of the sharp shock necessary to form thecondensation of an intensely sonorous wave. 

These are some of the physical reasons why guncotton might be regardedas a promising fog-signal. Firing it as we have been taught to do byMr. Abel, its explosion is more rapid than that of gunpowder. In itscase the air particles, alert as they are, will not, it might bepresumed, be able to slip from condensation to rarefaction with arapidity sufficient to forestall the formation of the wave. On _àpriori_ grounds then, we are entitled to infer the effectiveness ofgun-cotton, while in a great number of comparative experiments, stretching from 1874 to the present time, this inference has beenverified in the most conclusive manner. 

As regards explosive material, and zealous and accomplished help inthe use of it, the resources of Woolwich Arsenal have been freelyplaced at the disposal of the Elder Brethren. General Campbell, General Younghusband, Colonel Fraser, Colonel Maitland, and otherofficers, have taken an active personal part in the investigation, andin most cases have incurred the labour of reducing and reporting onthe observations. Guns of various forms and sizes have been invokedfor gunpowder, while gun-cotton has been fired in free air and in thefoci of parabolic reflectors. 

On the 22nd of February, 1875, a number of small guns, cast speciallyfor the purpose--some with plain, some with conical, and some withparabolic muzzles--firing 4 oz. Of fine-grain powder, were pittedagainst 4 oz. Of gun-cotton detonated both in the open, and in thefocus of a parabolic reflector. [Footnote: For charges of thisweight the reflector is of moderate size, and may be employed withoutfear of fracture. ]

The sound produced by the gun-cotton, reinforced by the reflector, wasunanimously pronounced loudest of all. With equal unanimity, thegun-cotton detonated in free air was placed second in intensity. Though the same charge was used throughout, the guns differed notablyamong themselves, but none of them came up to the gun-cotton, eitherwith or without the reflector. A second series, observed from adifferent distance on the same day, confirmed to the letter theforegoing result. 

As a practical point, however, the comparative cost of gun-cotton andgunpowder has to be taken into account, though considerations of costought not to be stretched too far in cases involving the safety ofhuman life. In the earlier experiments, where quantities of equalprice were pitted against each other, the results were somewhatfluctuating. Indeed, the perfect manipulation of the gun-cottonrequired some preliminary discipline--promptness, certainty, andeffectiveness of firing, augmenting as experience increased. As 1 lb. Of gun-cotton costs as much as 3 lbs. Of gunpowder, these quantitieswere compared together on the 22nd of February. The guns employed todischarge the gunpowder were a 12-lb. Brass howitzer, a 24-lb. Cast-iron howitzer, and the long 18-pounder employed at the SouthForeland. The result was, that the 24-lb. Howitzer, firing 3 lbs. Ofgunpowder, had a slight advantage over 1 lb. Of gun-cotton detonatedin the open; while the 12-lb. Howitzer and the 18-pounder were bothbeaten by the gun-cotton. On the end of May, on the other hand, thegun-cotton is reported as having been beaten by all the guns. 

Meanwhile, the parabolic-muzzle gun, expressly intended forfog-signalling, was pushed rapidly forward, and on March 22 and 23, 1876, its power was tested at Shoeburyness. Pitted against it were a16-pounder, a 5. 5-inch howitzer, 1. 5 lb. Of gun-cotton detonated inthe focus of a reflector (see annexed figure), and 1. 5 lb. Ofgun-cotton detonated in free air. On this occasion nineteen differentseries of experiments were made, when the new experimental gun, firinga 3-lb. Charge, demonstrated its superiority over all guns previouslyemployed to fire the same charge. As regards the comparative meritsof the gun-cotton fired in the open, and the gunpowder fired from thenew gun, the mean values of their sounds were the same. Fired in thefocus of the reflector, the gun-cotton clearly dominated over all theother sound-producers. [Footnote: The reflector was fractured by theexplosion, but it did good service afterwards. ]

FIG. 10. 

Gun-cotton Slab (1. 5 lb. ) Detonated in the Focus of a Cast-ironReflector. 

The whole of the observations here referred to were embraced by anangle of about 70°, of which 50' lay on the one side and 20° on theother side of the line of fire. The shots were heard by elevenobservers on board the 'Galatea, ' which took up positions varying from2 miles to 13. 5 miles from the firing-point. In all theseobservations, the reinforcing action of the reflector, and of theparabolic muzzle of the gun, came into play. But the reinforcement ofthe sound in one direction implies its withdrawal from some otherdirection, and accordingly it was found that at a distance of 5. 25miles from the firing-point, and on a line including nearly an angleof 90° with the line of fire, the gun-cotton in the open beat the newgun; while behind the station, at distances of 8. 5 miles and 13. 5miles respectively, the gun-cotton in the open beat both the gun andthe gun-cotton in the reflector. This result is rendered moreimportant by the fact that the sound reached the Mucking Light, adistance of 13. 5 miles, against a light wind which was blowing at thetime. 

Most, if not all, of our ordinary sound-producers send forth waveswhich are not of uniform intensity throughout. A trumpet is loudestin the direction of its axis. The same is true of a gun. A bell, with its mouth pointed upwards or downwards, sends forth waves whichare far denser in the horizontal plane passing through the bell thanat an angular distance of 90° from that plane. The oldest bellbangersmust have been aware of the fact that the sides of the bell, and notits mouth, emitted the strongest sound, their practice being probablydetermined by this knowledge. Our slabs of gun-cotton also emit wavesof different densities in different parts. It has occurred in theexperiments at Shoeburyness that when the broad side of a slab wasturned towards the suspending wire of a second slab six feet distant, the wire was cut by the explosion, while when the edge of the slab wasturned to the wire this never occurred. 

To the circumstance that the broadsides of the slabs faced the sea isprobably to be ascribed the remarkable fact observed on March 23, thatin two directions, not far removed from the line of fire, thegun-cotton detonated in the open had a slight advantage over the newgun. 

Theoretic considerations rendered it probable that the shape and sizeof the exploding mass would affect the constitution of the wave ofsound. I did not think large rectangular slabs the most favourableshape, and accordingly proposed cutting a large slab into fragments ofdifferent sizes, and pitting them against each other The differencesbetween the sounds were by no means so great as the differences in thequantities of explosive material might lead one to expect. The meanvalues of eighteen series of observations made on board the 'Galatea, 'at distances varying from 1. 75 mile to 4. 8 miles, were as follows:

Weights 4 oz. 6 oz. 9 oz. 12 oz. 

Value of sound 3. 12 3. 34 4. 0 4. 03

These charges were cut from a slab of dry gun-cotton about 1. 75 inchthick: they were squares and rectangles of the following dimensions:

4 oz, 2 inches by 2 inches;

6 oz, 2 inches by 3 inches;

9 oz, 3 inches by 3 inches;

12 oz, 2 inches by 6 inches. 

The numbers under the respective weights express the recorded value ofthe sounds. They must be simply taken as a ready means of expressingthe approximate relative intensity of the sounds as estimated by theear. When we find a 9-oz. Charge marked 4, and a 12-oz. Charge marked4. 03, the two sounds may be regarded as practically equal inintensity, thus proving that an addition of 30 per cent. In thelarger charges produces no sensible difference in the sound. Were thesounds estimated by some physical means, instead of by the ear, thevalues of the sounds at the distances recorded would not, in myopinion, show a greater advance with the increase of material thanthat indicated by the foregoing numbers. Subsequent experimentsrendered still more certain the effectiveness, as well as the economy, of the smaller charges of gun-cotton. 

It is an obvious corollary from the foregoing experiments that on our'nesses' and promontories, where the land is clasped on both sides fora considerable distance by the sea--where, therefore, the sound has topropagate itself rearward as well as forward--the use of the parabolicgun, or of the parabolic reflector, might be a disadvantage ratherthan an advantage. Here guncotton, exploded in the open, forms themost appropriate source of sound. This remark is especiallyapplicable to such lightships as are intended to spread the sound allround them as from central foci. 

As a signal in rock lighthouses, where neither syren, steam-whistle, nor gun could be mounted; and as a handy fleet-signal, dispensing withthe lumber of special signal-guns, the gun-cotton will proveinvaluable. But in most of these cases we have the drawback thatlocal damage may be done by the explosion. The lantern of the rocklighthouse might suffer from concussion near at hand, and thoughmechanical arrangements might be devised, both in the case of thelighthouse and of the ship's deck, to place the firing-point of thegun-cotton at a safe distance, no such arrangement could compete, asregards simplicity and effectiveness, with the expedient of agun-cotton rocket. Had such a means of signalling existed at theBishop's Rock lighthouse, the ill-fated 'Schiller' might have beenwarned of her approach to danger ten, or it may be twenty, milesbefore she reached the rock which wrecked her. Had the fleetpossessed such a signal, instead of the ubiquitous but ineffectualwhistle, the 'Iron Duke' and 'Vanguard' need never have come intocollision. 

It was the necessity of providing a suitable signal for rocklighthouses, and of clearing obstacles which cast an acoustic shadow, that suggested the idea of the gun-cotton rocket to Sir RichardCollinson, Deputy Master of the Trinity House. His idea was to placea disk or short cylinder of gun-cotton in the head of a rocket, theascensional force of which should be employed to carry the disk to anelevation of 1000 feet or thereabouts, where by the ignition of a fuseassociated with a detonator, the gun-cotton should be fired, sendingits sound in all directions vertically and obliquely down upon earthand sea. The first attempt to realise this idea was made on July 18, 1876, at the firework manufactory of the Messrs. Brock, at Nunhead. Eight rockets were then fired, four being charged with 5 oz. And fourwith 7. 5 oz. Of gun-cotton. They ascended to a great height, andexploded with a very loud report in the air. On July 27, the rocketswere tried at Shoeburyness. 

The most noteworthy result on this occasion was the hearing of thesounds at the Mouse Lighthouse, 8. 5 miles E. By S, and at the ChapmanLighthouse, 8. 5 miles W. By N; that is to say, at opposite sides ofthe firing-point. It is worthy of remark that, in the case of theChapman Lighthouse, land and trees intervened between the firing-pointand the place of observation. This, ' as General Younghusband justlyremarked at the time, 'may prove to be a valuable consideration if itshould be found necessary to place a signal station in a positionwhence the sea could not be freely observed. ' Indeed, the clearing ofsuch obstacles was one of the objects which the inventor of the rockethad in view. 

With reference to the action of the wind, it was thought desirable tocompare the range of explosions produced near the surface of the earthwith others produced at the elevation attainable by the gun-cottonrockets. Wind and weather, however, are not at our command; and henceone of the objects of a series of experiments conducted on December13, 1876, was not fulfilled. It is worthy, however, of note that onthis day, with smooth water and a calm atmosphere, the rockets weredistinctly heard at a distance of 11. 2 miles from the firing-point. The quantity of gun-cotton employed was 7. 5 oz. On Thursday, March 8, 1877, these comparative experiments of firing at high and lowelevations were pushed still further. The gun-cotton near the groundconsisted of 0. 5-lb. Disks, suspended from a horizontal iron bar about4. 5 feet above the ground. 

The rockets carried the same quantity of gun-cotton in their heads, and the height to which they attained, as determined by a theodolite, was from 800 to 900 feet. The day was cold, with occasional squallsof snow and hail, the direction of the sound being at right angles tothat of the wind. Five series of observations were made on board the'Vestal, ' at distances varying from 3 to 6 miles. The mean value ofthe explosions in the air exceeded that of the explosions near theground by a small but sensible quantity. At Windmill Hill, Gravesend, however, which was nearly to leeward, and 5. 5 miles from thefiring-point, in nineteen cases out of twenty-four the disk fired nearthe ground was loudest; while in the remaining five the rocket had theadvantage. 

Towards the close of the day the atmosphere became very serene. A fewdistant cumuli sailed near the horizon, but the zenith and a vastangular space all round it were absolutely free from cloud. From thedeck of the 'Galatea' a rocket was discharged, which reached a greatelevation, and exploded with a loud report. Following this solidnucleus of sound was a continuous train of echoes, which retreated toa continually greater distance, dying gradually off into silence afterseven seconds' duration. These echoes were of the same character asthose so frequently noticed at the South Foreland in 1872-73, andcalled by me 'aerial echoes. '

On the 23rd of March the experiments were resumed, the most noteworthyresults of that day's observations being that the sounds were heard atTillingham, 10 miles to the N. E. ; at West Mersea, 15. 75 miles to theN. E. By E; at Brightlingsea, 17. 5 miles to the N. E. ; and at ClactonWash, 20. 5 miles to the N. E. By 1/2 E. The wind was blowing at thetime from the S. E. Some of these sounds were produced by rockets, some by a 24-lb. Howitzer, and some by an 8-inch Maroon. 

In December, 1876, Mr. Gardiner, the managing director of theCotton-powder Company, had proposed a trial of this material againstthe gun-cotton. The density of the cotton he urged was only 1. 03, while that of the powder was 1. 70. A greater quantity of explosivematerial being thus compressed into the same volume, Mr. Gardinerthought that a greater sonorous effect must be produced by the powder. At the instance of Mr. Mackie, who had previously gone verythoroughly into the subject, a Committee of the Elder Brethren visitedthe cotton-powder manufactory, on the banks of the Swale, nearFaversham, on the 16th of June, 1877. The weights of cotton-powderemployed were 2 oz, 8 oz, 1 lb, and 2 lbs, in the form of rockets andof signals fired a few feet above the ground. The experimentsthroughout were arranged and conducted by Mr. Mackie. Our desire onthis occasion was to get 'as near to windward as possible, but theSwale and other obstacles limited our distance to 1. 5 mile. We stoodhere E. S. E. From the firing-point while the wind blew fresh from theN. E. 

The cotton-powder yielded a very effective report. The rockets ingeneral had a slight advantage over the same quantities of materialfired near the ground. The loudness of the sound was by no meansproportional to the quantity of the material exploded, 8 oz. Yieldingvery nearly as loud a report as 1 lb. The 'aerial echoes, ' whichinvariably followed the explosion of the rockets, were loud andlong-continued. 

On the 17th of October, 1877, another series of experiments withhowitzers and rockets was carried out at Shoeburyness. The charge ofthe howitzer was 3 lbs. Of L. G. Powder. The charges of the rocketswere 12 oz, 8 oz, 4 oz, and 2 oz. Of gun-cotton respectively. The gunand the four rockets constituted a series, and eight series were firedduring the afternoon of the 17th. The observations were made from the'Vestal' and the 'Galatea, ' positions being successively assumed whichpermitted the sound to reach the observers with the Wind, against thewind, and across the wind. The distance of the 'Galatea' varied from3 to 7 miles, that of the 'Vestal, ' which was more restricted in hermovements, being 2 to 3 miles. Briefly summed up, the result is thatthe howitzer, firing a 3-lb. Charge, which it will be remembered wasour best gun at 'the South Foreland, was beaten by the 12-oz. Rocket, by the 8-oz. Rocket, and by the 4-oz. Rocket. The 2-oz. Rocket alonefell behind the howitzer. 

It is worth while recording the distances at which some of the soundswere heard on the day now referred to:

1. Leigh 6. 5 miles W. N. W. 24 out of 40 sounds heard. 

2. Girdler 12 miles S. E. By E. 5 out of 40 sounds heard. Light-vessel

3. Reculvers 171 miles S. E. By S. 18 out of 40 sounds heard. 

4. St. Nicholas 20 miles S. E. 3 out of 40 sounds heard. 

5. Epple Bay 22 miles S. E. By E. 19 out of 40 sounds heard. 

6. Westgate 23 miles S. E. By E. 9 out of 40 sounds heard. 

7. Kingsgate 25 miles S. E. By E. 8 out of 40 sounds heard. 

The day was cloudy, with occasional showers of drizzling rain; thewind about N. W. By N. All day; at times squally, rising to a force of6 or 7 and sometimes dropping to a force of 2 or 3. The station atLeigh excepted, all these places were to leeward of Shoeburyness. Atfour other stations to leeward, varying in distance from 15. 5 to 24. 5miles, nothing was heard, while at eleven stations to windward, varying from 8 to 26 miles, the sounds were also inaudible. It wasfound, indeed, that the sounds proceeding directly against the winddid not penetrate much beyond 3 miles. 

On the following day, viz. The 18th October, we proceeded to Dungenesswith the view of making a series of strict comparative experimentswith gun-cotton and cotton-powder. Rockets containing 8 oz, 4 oz, and2 oz. Of gun-cotton had been prepared at the Royal Arsenal; whileothers, containing similar quantities of cotton-powder, had beensupplied by the Cotton-powder Company at Faversham. With these werecompared the ordinary 18-pounder gun, which happened to be mounted atDungeness, firing the usual charge of 3 lbs. Of powder, and a syren. 

From these experiments it appeared that the guncotton andcotton-powder were practically equal as producers of sound. 

The effectiveness of small charges was illustrated in a very strikingmanner, only a single unit separating the numerical value of the 8-oz. Rocket from that of the 2-oz. Rocket. The former was recorded as 6. 9and the latter as 5. 9, the value of the 4-oz. Rocket beingintermediate between them. These results were recorded by a number ofvery practised observers on board the 'Galatea. ' They were completelyborne out by the observations of the Coastguard, who marked the valueof the 8-oz rocket 6-1, and that of the 2-oz. Rocket 5. 2. The18-pounder gun fell far behind all the rockets, a result, possibly, tobe in part ascribed to the imperfection of the powder. Theperformance of the syren was, on the whole, less satisfactory thanthat of the rocket. The instrument was worked, not by steam of 70lbs. Pressure, as at the South Foreland, but by compressed air, beginning with 40 lbs. And ending with 30 lbs. Pressure. The trumpetwas pointed to windward, and in the axis of the instrument the soundwas about as effective as that of the 8-oz. Rocket. But in adirection at right angles to the axis, and still more in the rear ofthis direction, the syren fell very sensibly behind even the 2-oz. Rocket. 

These are the principal comparative trials made between the gun-cottonrocket and other fog-signals; but they are not the only ones. On the2nd of August, 1877, for example, experiments were made at LundyIsland with the following results. At 2 miles distant from thefiring-point, with land intervening, the 18-pounder, firing a 3-lb. Charge, was quite unheard. Both the 4-oz. Rocket and the 8-oz. Rocket, however, reached an elevation which commanded the acousticshadow, and yielded loud reports. When both were in view the rocketswere still superior to the gun. On the 6th of August, at St. Ann's, the 4-oz. And 8-oz. Rockets proved superior to the syren. On theShambles Light-vessel, when a pressure of 13 lbs. Was employed tosound the syren, the rockets proved greatly superior to thatinstrument. Proceeding along the sea margin at Flamboro' Head, Mr. Edwards states that at a distance of 1. 25 mile, with the 18-pounderpreviously used as a fog-signal hidden behind the cliffs, its reportwas quite unheard, while the 4-oz. Rocket, rising to an elevationwhich brought it clearly into view, yielded a powerful sound in theface of an opposing wind. 

On the evening of February 9th, 1877, a remarkable series ofexperiments were made by Mr. Prentice at Stowmarket with thegun-cotton rocket. From the report with which he has kindly furnishedme I extract the following particulars. The first column in theannexed statement contains the name of the place of observation, thesecond its distance from the firing-point, and the third the resultobserved:

Stoke Hill, Ipswich 10 miles Rockets clearly seen and soundsdistinctly heard 53 seconds after the flash. 

Melton 15 miles Signals distinctly heard. Thought at first that sounds were reverberated from the sea. 

Framlingham 18 miles Signals very distinctly heard, both in the open air and in a closed room. Wind in favour of sound. 

Stratford. 19 miles St. Andrews Reports loud; startled pheasants in a cover close by. 

Tuddenham. 10 miles St. Martin Reports very loud; rolled away like thunder. 

Christ Church Park. 11 miles Report arrived a little more than a minute after flash. 

Nettlestead Hall 6 miles Distinct in every part of observer's house. Very loud in the open air. 

Bildestone 6 miles Explosion very loud, wind against sound. 

Nacton 14 miles Reports quite distinct--mistaken by inhabitants for claps of thunder. 

Aldboro' 25 miles Rockets seen through a very hazy atmosphere; a rumbling detonation heard. 

Capel Mills 11 miles Reports heard within and without the observer's house. Wind opposed to sound. 

Lawford 15. 5 miles Reports distinct: attributed to distant thunder. 

In the great majority of these cases, the direction of the soundenclosed a large angle with the direction of the wind. In some cases, indeed, the two directions were at right angles to each other. It isneedless to dwell for a moment on the advantage of possessing a signalcommanding ranges such as these. 

The explosion of substances in the air, after having been carried to aconsiderable elevation by rockets, is a familiar performance. In1873, moreover, the Board of Trade proposed a light-and-sound rocketas a signal of distress, which proposal was subsequently realized, butin a form too elaborate and expensive for practical use. The idea ofa gun-cotton rocket fit for signalling in fogs is, I believe, whollydue to Sir Richard Collinson, the Deputy Master of the Trinity House. Thanks to the skilful aid given by the authorities of Woolwich, by Mr. Prentice, and Mr. Brock, that idea is now an accomplished fact; asignal of great power, handiness, and economy, being thus placed atthe service of our mariners. Not only may the rocket be applied inassociation with lighthouses and lightships, but in the Navy also itmay be turned to important account. Soon after the loss of the'Vanguard' I ventured to urge upon an eminent naval officer thedesirability of having an organized code of fog-signals for the fleet. He shook his head doubtingly, and referred to the difficulty offinding room for signal guns. The gun-cotton rocket completelysurmounts this difficulty, It is manipulated with ease and rapidity, while its discharges may be so grouped and combined as to give a mostimportant extension to the voice of the admiral in command. It isneedless to add that at any point upon our coasts, or upon any othercoast, where its establishment might be desirable, a fog-signalstation might be extemporised without difficulty. 

*****

I have referred more than once to the train of echoes whichaccompanied the explosion of gun-cotton in free air, speaking of themas similar in all respects to those which were described for the firsttime in my Report on Fog-signals, addressed to the Corporation ofTrinity House in 1874. [Footnote: See also 'PhilosophicalTransactions' for 1874, p. 183. ] To these echoes I attached afundamental significance. There was no visible reflecting surfacefrom which they could come. On some days, with hardly a cloud in theair and hardly a ripple on the sea, they reached a magical intensity. As far as the sense of hearing could judge, they came from the body ofthe air in front of the great trumpet which produced them. Thetrumpet blasts were five seconds in duration, but long before theblast had ceased the echoes struck in, adding their strength to theprimitive note of the trumpet. After the blast had ended the echoescontinued, retreating further and further from the point ofobservation, and finally dying away at great distances. The echoeswere perfectly continuous as long as the sea was clear of ships, 'tapering' by imperceptible gradations into absolute silence. Butwhen a ship happened to throw itself athwart the course of the sound, the echo from the broadside of the vessel was returned as a shockwhich rudely interrupted the continuity of the dying atmosphericmusic. 

These echoes have been ascribed to reflection from the crests of thesea-waves. But this hypothesis is negatived by the fact, that theechoes were produced in great intensity and duration when no wavesexisted--when the sea, in fact, was of glassy smoothness. It has beenalso shown that the direction of the echoes depended not on that ofwaves, real or assumed, but on the direction of the axis of thetrumpet. Causing that axis to traverse an arc of 210°, and thetrumpet to sound at various points of the arc, the echoes were always, at all events in calm weather, returned from that portion of theatmosphere towards which the trumpet was directed. They could not, under the circumstances, come from the glassy sea; while both theirvariation of direction and their perfectly continuous fall intosilence, are irreconcilable with the notion that they came from fixedobjects on the land. They came from that portion of the atmosphereinto which the trumpet poured its maximum sound, and fell in intensityas the direct sound penetrated to greater atmospheric distances. 

The day on which our latest observations were made was particularlyfine. Before reaching Dungeness, the smoothness of the sea and theserenity of the air caused me to test the echoing power of theatmosphere. A single ship lay about half a mile distant between usand the land. The result of the proposed experiment was clearlyforeseen. It was this. The rocket being sent up, it exploded at agreat height; the echoes retreated in their usual fashion, becomingless and less intense as the distances of the invisible surfaces ofreflection from the observers increased. About five seconds after theexplosion, a single loud shock was sent back to us from the side ofthe vessel lying between us and the land. Obliterated for a moment bythis more intense echo the aerial reverberation continued its retreat, dying away into silence in two or three seconds afterwards. [Footnote:The echoes of the gun fired on shore this day were very brief; thoseof the 12-oz. Gun-cotton rocket were 12" and those of the 8-oz. Cotton-powder rocket 11" in duration. ]

I have referred to the firing of an 8-oz. Rocket from the deck of the'Galatea' on March 8, 1877, stating the duration of its echoes to beseven seconds. Mr. Prentice, who was present at the time, assured methat in his experiments similar echoes had been frequently heard ofmore than twice this duration. The ranges of his sounds alone wouldrender this result in the highest degree probable. 

To attempt to interpret an experiment which I have not had anopportunity of repeating, is an operation of some risk; and it is notwithout a consciousness of this that I refer here to a resultannounced by Professor Joseph Henry, which he considers adverse to thenotion of aerial echoes. He took the trouble to point the trumpet ofa syren towards the zenith, and found that when the syren was soundedno echo was returned. Now the reflecting surfaces which give rise tothese echoes are for the most part due to differences of temperaturebetween sea and air. If, through any cause, the air above be chilled, we have descending streams--if the air below be warmed, we haveascending streams as the initial cause of atmospheric flocculence. Asound proceeding vertically does not cross the streams, nor impingeupon the reflecting surfaces, as does a sound proceeding horizontallyacross them. Aerial echoes, therefore, will not accompany thevertical sound as they accompany the horizontal one. The experiment, as I interpret it, is not opposed to the theory of these echoes whichI have ventured to enunciate. But, as I have indicated, not only tosee but to vary such an experiment is a necessary prelude to graspingits full significance. 

In a paper published in the 'Philosophical Transactions' for 1876, Professor Osborne Reynolds refers to these echoes in the followingterms Without attempting to explain the reverberations and echoeswhich have been observed, I will merely call attention to the factthat in no case have I heard any attending the reports of the rockets, [Footnote: These carried 12 oz. Of gunpowder, which has been found byCol. Fraser to require an iron case to produce an effectiveexplosion. ] although they seem to have been invariable with the gunsand pistols. These facts suggest that the echoes are in some wayconnected with the direction given to the sound. They are caused bythe voice, trumpets, and the syren, all of which give direction to thesound; but I am not aware that they have ever been observed in thecase of a sound which has no direction of greatest intensity. ' Thereference to the voice, and other references in his paper, cause me tothink that, in speaking of echoes, Professor Osborne Reynolds andmyself are dealing with different phenomena. Be that as it may, theforegoing observations render it perfectly certain that the conditionas to direction here laid down is not necessary to the production ofthe echoes. 

There is not a feature connected with the aerial echoes which cannotbe brought out by experiments in the air of the laboratory. I haverecently made the following experiment: A rectangle, x Y (p. 331), 22 inches by 12, was crossed by twenty-three brass tubes (half thenumber would suffice and only eleven are shown in the figure), eachhaving a slit along it from which gas can issue. In this waytwenty-three low flat flames were obtained. A sounding reed a fixedin a short tube was placed at one end of the rectangle, and a'sensitive flame, ' [Footnote: Fully described in my 'Lectures onSound, ' 3rd edition, p. 227. ] f, at some distance beyond the otherend. When the reed sounded, the flame in front of it was violentlyagitated, and roared boisterously. Turning on the gas, and lightingit as it issued from the slits, the air above the flames became soheterogeneous that the sensitive flame was instantly stilled, risingfrom a height of 6 inches to a height of 18 inches. Here we had theacoustic opacity of the air in front of the South Foreland strikinglyimitated. [Footnote: Lectures on Sound, 3rd ed, p. 268. ] Turning offthe gas, and removing the sensitive flame to f, some distance behindthe reed, it burned there tranquilly, though the reed was sounding. Again lighting the gas as it issued from the brass tubes, the soundreflected from the heterogeneous air threw the sensitive flame intoviolent agitation. Here we had imitated the aerial echoes heard whenstanding behind the syren-trumpet at the South Foreland. Theexperiment is extremely simple, and in the highest degree impressive. 

Fig. 11. 

*****

The explosive rapidity of dynamite marks it as a substance speciallysuitable for the production of sound. At the suggestion of ProfessorDewar, Mr. McRoberts has carried out a series of experiments ondynamite, with extremely promising results. Immediately after thedelivery of the foregoing lecture I was informed that Mr. Brockproposed the employment of dynamite in the Collinson rocket. 

********************

XI. ON THE STUDY OF PHYSICS. 

[Footnote: From a lecture delivered in the Royal Institution of GreatBritain in the Spring of 1854. ]

I HOLD in my hand an uncorrected proof of the syllabus of this courseof lectures, and the title of the present lecture A there stated to be'On the Importance of the Study of Physics as a Means of Education. 'The corrected proof, however, contains the title: 'On the Importanceof the Study of Physics as a Branch of Education. ' Small as thiseditorial alteration may seem, the two words suggest two radicallydistinct modes of viewing the subject before us. The term Educationis sometimes applied to a single faculty or organ, and if we knowwherein the education of a single faculty consists, this will help usto clearer notions regarding the education of the sum of all thefaculties, or of the mind. When, for example, we speak of theeducation of the voice, what do we mean? There are certain membranesat the top of the windpipe which throw into vibration the air forcedbetween them from the lungs, thus producing musical sounds. Thesemembranes are, to some extent, under the control of the will, and itis found that they can be so modified by exercise as to produce notesof a clearer and more melodious character. This exercise we call theeducation of the voice. We may choose for our exercise songs new orold, festive or solemn; the education of the voice being the objectaimed at, the songs may be regarded as the means by which thiseducation is accomplished. I think this expresses the state of thecase more clearly than if we were to call the songs a branch ofeducation. Regarding also the education of the human mind as theimprovement and development of the mental faculties, I shall considerthe study of Physics as a means towards the attainment of this end. From this point of view, I degrade Physics into an implement ofculture, and this is my deliberate design. 

The term Physics, as made use of in the present Lecture, refers tothat portion of natural science which lies midway between astronomyand chemistry. The former, indeed, is Physics applied to 'masses ofenormous weight, ' while the latter is Physics applied to atoms andmolecules. The subjects of Physics proper are therefore those whichlie nearest to human perception: light and heat, colour, sound, motion, the loadstone, electrical attractions and repulsions, thunderand lightning, rain, snow, dew, and so forth. Our senses standbetween these phenomena and the reasoning mind. We observe the fact, but are not satisfied with the mere act of observation: the fact mustbe accounted for--fitted into its position in the line of cause andeffect. Taking our facts from Nature we transfer them to the domainof thought: look at them, compare them, observe their mutual relationsand connexions, and bringing them ever clearer before the mental eye, finally alight upon the cause which unites them. This is the last actof the mind, in this centripetal direction--in its progress from themultiplicity of facts to the central cause on which they depend. But, having guessed the cause, we are not yet contented. We set out fromthe centre and travel in the other direction. If the guess be true, certain consequences must follow from it, and we appeal to the law andtestimony of experiment whether the thing is so. Thus is the circuitof thought completed, --from without inward, from multiplicity tounity, and from within outward, from unity to multiplicity. In thustraversing both ways the line between cause and effect, all ourreasoning powers are called into play. The mental effort involved inthese processes may be compared to those exercises of the body whichinvoke the co-operation of every muscle, and thus confer upon thewhole frame the benefits of healthy action. 

The first experiment a child makes is a physical experiment: thesuction-pump is but an imitation of the first act of every new-borninfant. Nor do I think it calculated to lessen that infant'sreverence, or to make him a worse citizen, when his riper experienceshows him that the atmosphere was his helper in extracting the firstdraught from his mother's breast. The child grows, but is still anexperimenter: he grasps at the moon, and his failure teaches him torespect distance. At length his little fingers acquire sufficientmechanical tact to lay hold of a spoon. He thrusts the instrumentinto his mouth, hurts his gums, and thus learns the impenetrability ofmatter. He lets the spoon fall, and jumps with delight to hear itrattle against the table. The experiment made by accident is repeatedwith intention, and thus the young student receives his first lessonsupon sound and gravitation. There are pains and penalties, however, in the path of the enquirer: he is sure to go wrong, and Nature isjust as sure to inform him of the fact. He falls downstairs, burnshis fingers, cuts his hand, scalds his tongue, and in this way learnsthe conditions of his physical well being. This is Nature's way ofproceeding, and it is wonderful what progress her pupil makes. Hisenjoyments for a time are physical, and the confectioner's shopoccupies the foreground of human happiness; but the blossoms of afiner life are already beginning to unfold themselves, and therelation of cause and effect dawns upon the boy. He begins to seethat the present condition of things is not final, but depends uponone that has gone before, and will be succeeded by another. Hebecomes a puzzle to himself; and to satisfy his newly-awakenedcuriosity, asks all manner of inconvenient questions. The needs andtendencies of human nature express themselves through these earlyyearnings of the child. As thought ripens, he desires to know thecharacter and causes of the phenomena presented to his observation;and unless this desire has been granted for the express purpose ofhaving it repressed, unless the attractions of natural phenomena belike the blush of the forbidden fruit, conferred merely for thepurpose of exercising our self-denial in letting them alone; we mayfairly claim for the study of Physics the recognition that it answersto an impulse implanted by nature in the constitution of man. 

A few days ago, a Master of Arts, who is still a young man, andtherefore the recipient of a modern education, stated to me that untilhe had reached the age of twenty years he had never been taughtanything whatever regarding natural phenomena, or natural law. Twelveyears of his life previously had been spent exclusively among theancients. The case, I regret to say, is typical. Now, we cannot, without prejudice to humanity, separate the present from the past. Thenineteenth century strikes its roots into the centuries gone by, anddraws nutriment from them. The world cannot afford to lose the recordof any great deed or utterance; for such are prolific throughout alltime. We cannot yield the companionship of our loftier brothers ofantiquity, --of our Socrates and Cato, --whose lives provoke us tosympathetic greatness across the interval of two thousand years. Aslong as the ancient languages are the means of access to the ancientmind, they must ever be of priceless value to humanity; but surelythese avenues might be kept open without making such sacrifices asthat above referred to, universal. We have conquered and possessedourselves of continents of land, concerning which antiquity knewnothing; and if new continents of thought reveal themselves to theexploring human spirit, shall we not possess them also? In theselatter days, the study of Physics has given us glimpses of the methodsof Nature which were quite hidden from the ancients, and we should befalse to the trust committed to us, if we were to sacrifice the hopesand aspirations of the Present out of deference to the Past. 

The bias of my own education probably manifests itself in a desire Ialways feel to seize upon every possible opportunity of checking myassumptions and conclusions by experience. In the present case, it istrue, your own consciousness might be appealed to in proof of thetendency of the human mind to inquire into the phenomena presented toit by the senses; but I trust you will excuse me if, instead of doingthis, I take advantage of the facts which have fallen in my waythrough life, referring to your judgment to decide whether such factsare truly representative and general, and not merely individual andlocal. 

At an agricultural college in Hampshire, with which I was connectedfor some time, and which is now converted into a school for thegeneral education of youth, a Society was formed among the boys, whomet weekly for the purpose of reading reports and papers upon varioussubjects. The Society had its president and treasurer; and abstractsof its proceedings were published in a little monthly periodicalissuing from the school press. One of the most remarkable features ofthese weekly meetings was, that after the general business had beenconcluded, each member enjoyed the right of asking questions on anysubject on which he desired information. The questions were eitherwritten out previously in a book, or, if a question happened tosuggest itself during the meeting, it was written upon a slip of paperand handed in to the Secretary, who afterwards read all the questionsaloud. A number of teachers were usually present, and they and theboys made a common stock of their wisdom in furnishing replies. Asmight be expected from an assemblage of eighty or ninety boys, varyingfrom eighteen to eight years old, many odd questions were proposed. Tothe mind which loves to detect in the tendencies of the young theinstincts of humanity generally, such questions are not without acertain philosophic interest, and I have therefore thought it notderogatory to the present course of Lectures to copy a few of them, and to introduce them here. They run as follows:

What are the duties of the Astronomer Royal?

What is frost?

Why are thunder and lightning more frequent in summer than in winter?

What occasions falling stars?

What is the cause of the sensation called 'pins and needles '?

What is the cause of waterspouts?

What is the cause of hiccup?

If a towel be wetted with water, why does the wet portion becomedarker than before?

What is meant by Lancashire witches?

Does the dew rise or fall?

What is the principle of the hydraulic press?

Is there more oxygen in the air in summer than in winter?

What are those rings which we see round the gas and sun?

What is thunder?

How is it that a black hat can be moved by forming round it a magneticcircle, while a white hat remains stationary?

What is the cause of perspiration?

Is it true that men were once monkeys?

What is the difference between the soul and the mind?

Is it contrary to the rules of Vegetarianism to eat eggs?

In looking over these questions, which were wholly unprompted, andhave been copied almost at random from the book alluded to, we seethat many of them are suggested directly by natural objects, and arenot such as had an interest conferred on them' by previous culture. Now the fact is beyond the boy's control, and so certainly is thedesire to know its cause. The sole question then is, whether thisdesire is to be gratified or not. Who created the fact? Whoimplanted the desire? Certainly not man. Who then will undertake toplace himself between the desire and its fulfilment, and proclaim adivorce between them? Take, for example, the case of the wettedtowel, which at first sight appears to be one of the most unpromisingquestions in the list. Shall we tell the proposer to repress hiscuriosity, as the subject is improper for him to know, and thusinterpose our wisdom to rescue the boy from the consequences of a wishwhich acts to his prejudice? Or, recognising the propriety of thequestion, how shall we answer it? It is impossible to answer itwithout reference to the laws of optics--without making the boy tosome extent a natural philosopher. You may say that the effect is dueto the reflection of light at the common surface of two media ofdifferent refractive indices. But this answer presupposes on the partof the boy a knowledge of what reflection and refraction are, orreduces you to the necessity of explaining them. 

On looking more closely into the matter, we find that our wet towelbelongs to a class of phenomena which have long excited the interestof philosophers. The towel is white for the same reason that snow iswhite, that foam is white, that pounded granite or glass is white, andthat the salt we use at table is white. On quitting one medium andentering another, a portion of light is always reflected, but on thiscondition--the media must possess different refractive indices. Thus, when we immerse a bit of glass in water, light is reflected from thecommon surface of both, and it is this light which enables us to seethe glass. But when a transparent solid is immersed in a liquid ofthe same refractive index as itself, it immediately disappears. Iremember once dropping the eyeball of an ox into water; it vanished asif by magic, with the exception of the crystalline lens, and thesurprise was so great as to cause a bystander to suppose that thevitreous humour had been instantly dissolved. This, however, was notthe case, and a comparison of the refractive index of the humour withthat of water cleared up the whole matter. The indices wereidentical, and hence the light pursued its way through both as if theyformed one continuous mass. 

In the case of snow, powdered quartz, or salt, we have a transparentsolid mixed with air. At every transition from solid to air, orfrom air to solid, a portion of light is reflected, and this takesplace so often that the light is wholly intercepted. Thus from themixture of two transparent bodies we obtain an opaque one. Now thecase of the towel is precisely similar. The tissue is composed ofsemi-transparent vegetable fibres, with the interstices between themfilled with air; repeated reflection takes place at the limitingsurfaces of air and fibre, and hence the towel becomes opaque likesnow or salt. But if we fill the interstices with water, we diminishthe reflection; a portion of the light is transmitted, and thedarkness of the towel is due to its increased transparency. Thus thedeportment of various minerals, such as hydrophane and tabasheer, thetransparency of tracing paper used by engineers, and many otherconsiderations of the highest scientific interest, are involved in thesimple enquiry of this unsuspecting little boy. 

Again, take the question regarding the rising or falling of the dew--aquestion long agitated, and finally set at rest by the beautifulresearches of Wells. I do not think that any boy of averageintelligence will be satisfied with the simple answer that the dewfalls. He will wish to learn how you know that it falls, and, ifacquainted with the notions of the middle ages, he may refer to theopinion of Father Laurus, that a goose egg filled in the morning withdew and exposed to the sun, will rise like a balloon--a swan's eggbeing better for the experiment than a goose egg. It is impossible togive the boy a clear notion of the beautiful phenomenon to which hisquestion refers, without first making him acquainted with theradiation and conduction of heat. Take, for example, a blade ofgrass, from which one of these orient pearls is depending. 

During the day the grass, and the earth beneath it, possess a certainamount of warmth imparted by the sun; during a serene night, heat isradiated from the surface of the grass into space, and to supply theloss, there is a flow of heat from the earth to the blade. Thus theblade loses heat by radiation, and gains heat by conduction. Now, inthe case before us, the power of radiation is great, whereas the powerof conduction is small; the consequence is that the blade loses morethan it gains, and hence becomes more and more refrigerated. Thelight vapour floating around the surface so cooled is condensed uponit, and there accumulates to form the little pearly globe which wecall a dew-drop. 

Thus the boy finds the simple and homely fact which addressed hissenses to be the outcome and flower of the deepest laws. The factbecomes, in a measure, sanctified as an object of thought, andinvested for him with a beauty for evermore. He thus learns thatthings which, at first sight, seem to stand isolated and withoutapparent brotherhood in Nature are organically united, and finds thedetection of such analogies a source of perpetual delight. To enlistpleasure on the side of intellectual performance is a point of theutmost importance; for the exercise of the mind, like that of thebody, depends for its value upon the spirit in which it isaccomplished. Every physician knows that something more than meremechanical motion is comprehended under the idea of healthfulexercise--that, indeed, being most healthful which makes us forget allulterior ends in the mere enjoyment of it. What, for example, couldbe substituted for the action of the playground, where the boy playsfor the mere love of playing, and without reference to physiologicallaws; while kindly Nature accomplishes her ends unconsciously, andmakes his very indifference beneficial to him. You may have moresystematic motions, you may devise means for the more perfect tractionof each particular muscle, but you cannot create the joy and gladnessof the game, and where these are absent, the charm and the health ofthe exercise are gone. The case is similar with the education of themind. 

The study of Physics, as already intimated, consists of two processes, which are complementary to each other--the tracing of facts to theircauses, and the logical advance from the cause to the fact. In theformer process, called _induction_, certain moral qualities come intoplay. The first condition of success is patient industry, an honestreceptivity, and a willingness to abandon all preconceived notions, however cherished, if they be found to contradict the truth. Believeme, a self-renunciation which has something lofty in it, and of whichthe world never hears, is often enacted in the private experience ofthe true votary of science. And if a man be not capable of thisself-renunciation--this loyal surrender of himself to Nature and tofact, he lacks, in my opinion, the first mark of a true philosopher. 

Thus the earnest prosecutor of science, who does not work with theidea of producing a sensation in the world, who loves the truth betterthan the transitory blaze of to-day's fame, who comes to his task witha single eye, finds in that task an indirect means of the highestmoral culture. And although the virtue of the act depends upon itsprivacy, this sacrifice of self, this upright determination to acceptthe truth, no matter how it may present itself--even at the hands of ascientific foe, if necessary--carries with it its own reward. Whenprejudice is put under foot and the stains of personal bias have beenwashed away--when a man consents to lay aside his vanity and to becomeNature's organ--his elevation is the instant consequence of hishumility. 

I should not wonder if my remarks provoked a smile, for they seem toindicate that I regard the man of science as a heroic, if not indeedan angelic, character; and cases may occur to you which indicate thereverse. You may point to the quarrels of scientific men, to theirstruggles for priority, to that unpleasant egotism which screamsaround its little property of discovery like a scared plover about itsyoung. I will not deny all this; but let it be set down to its properaccount, to the weakness--or, if you will--to the selfishness of Man, but not to the charge of Physical Science. 

The second process in physical investigation is _deduction_, or theadvance of the mind from fixed principles to the conclusions whichflow from them. The rules of logic are the formal statement of thisprocess, which, however, was practised by every healthy mind beforeever such rules were written. In the study of Physics, induction anddeduction are perpetually wedded to each other. The man observes, strips facts of their peculiarities of form, and tries to unite themby their essences; having effected this, he at once deduces, and thuschecks his induction. 

Here the grand difference between the methods at present followed, andthose of the ancients, becomes manifest. They were one-sided in thesematters: they omitted the process of induction, and substitutedconjecture for observation. They could never, therefore, fulfil themission of Man to 'replenish the earth, and subdue it. ' Thesubjugation of Nature is only to be accomplished by the penetration ofher secrets and the patient mastery of her laws. This not onlyenables us to protect ourselves from the hostile action of naturalforces, but makes them our slaves. By the study of Physics we haveindeed opened to us treasuries of power of which antiquity neverdreamed. But while we lord it over Matter, we have thereby becomebetter acquainted with the laws of Mind; for to the mental philosopherthe study of Physics furnishes a screen against which the human spiritprojects its own image, and thus becomes capable of self-inspection. 

Thus, then, as a means of intellectual culture, the study of Physicsexercises and sharpens observation: it brings the most exhaustivelogic into play: it compares, abstracts, and generalizes, and providesa mental scenery appropriate to these processes. The strictestprecision of thought is everywhere enforced, and prudence, foresight, and sagacity are demanded. By its appeals to experiment, itcontinually checks itself, and thus walks on a foundation of facts. Hence the exercise it invokes does not end in a mere game ofintellectual gymnastics, such as the ancients delighted in, but tendsto the mastery of Nature. This gradual conquest of the externalworld, and the consciousness of augmented strength which accompaniesit, render the study of Physics as delightful as it is important. 

With regard to the effect on the imagination, certain it is that thecool results of physical induction furnish conceptions which transcendthe most daring flights of that faculty. Take for example the idea ofan all-pervading aether which transmits a tingle, so to speak, to thefinger ends of the universe every time a street lamp is lighted. Theinvisible billows of this aether can be measured with the same easeand certainty as that with which an engineer measures a base and twoangles, and from these finds the distance across the Thames. Now itis to be confessed that there may be just as little poetry in themeasurement of an aethereal undulation as in that of the river; forthe intellect, during the acts of measurement and calculation, destroys those notions of size which appeal to the poetic sense. Itis a mistake to suppose, with Dr. Young, that

 An undevout astronomer is mad;

there being no necessary connexion between a devout state of mind andthe observations and calculations of a practical astronomer. It isnot until the man withdraws from his calculation, as a painter fromhis work, and thus realizes the great idea on which he has beenengaged, that imagination and wonder are excited. There is, I admit, a possible danger here. If the arithmetical processes of science betoo exclusively pursued, they may impair the imagination, and thus thestudy of Physics is open to the same objection as philological, theological, or political studies, when carried to excess. But evenin this case, the injury done is to the investigator himself: it doesnot reach the mass of mankind. Indeed, the conceptions furnished byhis cold unimaginative reckonings may furnish themes for the poet, andexcite in the highest degree that sentiment of wonder which, notwithstanding all its foolish vagaries, table-turning included, I, for my part, should be sorry to see banished from the world. 

I have thus far dwelt upon the study of Physics as an agent ofintellectual culture; but like other things in Nature, this studysubserves more than a single end. The colours of the clouds delightthe eye, and, no doubt, accomplish moral purposes also, but theselfsame clouds hold within their fleeces the moisture by which ourfields are rendered fruitful. The sunbeams excite our interest andinvite our investigation; but they also extend their beneficentinfluences to our fruits and corn, and thus accomplish, not onlyintellectual ends, but minister, at the same time, to our materialnecessities. And so it is with scientific research. 

While the love of science is a sufficient incentive to the pursuit ofscience, and the investigator, in the prosecution of his enquiries, israised above all material considerations, the results of his laboursmay exercise a potent influence upon the physical condition of thecommunity. This is the arrangement of Nature, and not that of thescientific investigator himself; for he usually pursues his objectwithout regard to its practical applications. 

And let him who is dazzled by such applications--who sees in thesteam-engine and the electric telegraph the highest embodiment ofhuman genius and the only legitimate object of scientific research, beware of prescribing conditions to the investigator. Let him bewareof attempting to substitute for that simple love with which the votaryof science pursues his task, the calculations of what he is pleased tocall utility. The professed utilitarian is unfortunately, in mostcases, the very last man to see the occult sources from which usefulresults are derived. He admires the flower, but is ignorant of theconditions of its growth. The scientific man must approach Nature inhis own way; for if you invade his freedom by your so-called practicalconsiderations, it may be at the expense of those qualities on whichhis success as a discoverer depends. Let the self-styled practicalman look to those from the fecundity of whose thought be, andthousands like him, have sprung into existence. Were they inspired intheir first enquiries by the calculations of utility? Not one ofthem. They were often forced to live low and lie hard, and to seekcompensation for their penury in the delight which their favouritepursuits afforded them. 

In the words of one well qualified to speak upon this subject, 'I saynot merely look at the pittance of men like John Dalton, or thevoluntary starvation of the late Graff; but compare what is consideredas competency or affluence by your Faradays, Liebigs, and Herschels, with the expected results of a life of successful commercialenterprise: then compare the amount of mind put forth, the work donefor society in either case, and you will be constrained to allow thatthe former belong to a class of workers who, properly speaking, arenot paid, and cannot be paid for their work, as indeed it is of a sortto which no payment could stimulate. '

But while the scientific investigator, standing upon the frontiers ofhuman knowledge, and aiming at the conquest of fresh soil from thesurrounding region of the unknown, makes the discovery of truth hisexclusive object for the time, he cannot but feel the deepest interestin the practical application of the truth discovered. There issomething ennobling in the triumph of Mind over Matter. Apart evenfrom its uses to society, there is something elevating in the idea ofMan having tamed that wild force which flashes through the telegraphicwire, and made it the minister of his will. Our attainments in thesedirections appear to be commensurate with our needs. We had alreadysubdued horse and mule, and obtained from them all the service whichit was in their power to render: we must either stand still, or findmore potent agents to execute our purposes. At this point thesteam-engine appears. These are still new things; it is not longsince we struck into the scientific methods which have produced theseresults. We cannot for an instant regard them as the finalachievements of Science, but rather as an earnest of what she is yetto do. They mark our first great advances upon the dominion ofNature. Animal strength fails, but here are the forces which hold theworld together, and the instincts and successes of Man assure him thatthese forces are his when he is wise enough to command them. 

As an instrument of intellectual culture, the study of Physics isprofitable to all: as bearing upon special functions, its value, though not so great, is still more tangible. Why, for example, shouldMembers of Parliament be ignorant of the subjects concerning whichthey are called upon to legislate? In this land of practical physics, why should they be unable to form an independent opinion upon aphysical question? Why should the member of a parliamentary committeebe left at the mercy of interested disputants when a scientificquestion is discussed, until he deems the nap a blessing which rescueshim from the bewilderments of the committee-room? The education whichdoes not supply the want here referred to, fails in its duty toEngland. With regard to our working people, in the ordinary sense ofthe term working, the study of Physics would, I imagine, beprofitable, not only as a means of intellectual culture, but also as amoral influence to woo them from pursuits which now degrade them. Aman's reformation oftener depends upon the indirect, than upon thedirect action of the will. The will must be exerted in the choice ofemployment which shall break the force of temptation by erecting abarrier against it. The drunkard, for example, is in a perilouscondition if he content himself merely with saying, or swearing, thathe will avoid strong drink. His thoughts, if not attracted by anotherforce, will revert to the public-house, and to rescue him permanentlyfrom this, you must give him an equivalent. 

By investing the objects of hourly intercourse with an interest whichprompts reflection, new enjoyments would be opened to the working man, and every one of these would be a point of force to protect himagainst temptation. Besides this, our factories and our foundriespresent an extensive field of observation, and were those who work inthem rendered capable, by previous culture, of _observing_ what theysee, the results might be incalculable. Who can say what intellectualSamsons are at the present moment toiling with closed eyes in themills and forges of Manchester and Birmingham? Grant these Samsonssight, and you multiply the chances of discovery, and with them theprospects of national advancement. In our multitudinous technicaloperations we are constantly playing with forces our ignorance ofwhich is often the cause of our destruction. There are agencies atwork in a locomotive of which the maker of it probably never dreamed, but which nevertheless may be sufficient to convert it into an engineof death. When we reflect on the intellectual condition of the peoplewho work in our coal mines, those terrific explosions which occur fromtime to time need not astonish us. If these men possessed sufficientphysical knowledge, from the operatives themselves would probablyemanate a system by which these shocking accidents might be avoided. Possessed of the knowledge, their personal interests would furnish thenecessary stimulus to its practical application, and thus two endswould be served at the same time the elevation of the men and thediminution of the calamity. 

Before the present Course of Lectures was publicly announced, I hadmany misgivings as to the propriety of my taking a part in them, thinking that my place might be better filled by an older and moreexperienced man. To my experience, however, such as it was, Iresolved to adhere, and I have therefore described things as theyrevealed themselves to my own eyes, and have been enacted in my ownlimited practice. There is one mind common to us all; and the trueexpression of this mind, even in small particulars, will attest itselfby the response which it calls forth in the convictions of my hearers. I ask your permission to proceed a little further in this fashion, andto refer to a fact or two in addition to those already cited, whichpresented themselves to my notice during my brief career as a teacherin the college already alluded to. The facts, though extremelyhumble, and deviating in some slight degree from the strict subject ofthe present discourse, may yet serve to illustrate an educationalprinciple. 

One of the duties which fell to my share was the instruction of aclass in mathematics, and I usually found that Euclid and the ancientgeometry generally, when properly and sympathetically addressed to theunderstanding, formed a most attractive study for youth. But it wasmy habitual practice to withdraw the boys from the routine of thebook, and to appeal to their self-power in the treatment of questionsnot comprehended in that routine. At first, the change from thebeaten track usually excited aversion: the youth felt like a childamid strangers; but in no single instance did this feeling continue. When utterly disheartened, I have encouraged the boy by the anecdoteof Newton, where he attributes the difference between him and othermen, mainly to his own patience; or of Mirabeau, when he ordered hisservant, who had stated something to be impossible, never again to usethat blockhead of a word. Thus cheered, the boy has returned to histask with a smile, which perhaps had something of doubt in it, butwhich, nevertheless, evinced a resolution to try again. I have seenhis eye brighten, and, at length, with a pleasure of which the ecstasyof Archimedes was but a simple expansion, heard him exclaim, 'I haveit, sir. ' The consciousness of self-power, thus awakened, was ofimmense value; and, animated by it, the progress of the class wasastonishing. It was often my custom to give the boys the choice ofpursuing their propositions in the book, or of trying their strengthat others not to be found there. Never in a single instance was thebook chosen. I was ever ready to assist when help was needful, but myoffers of assistance were habitually declined. The boys had tastedthe sweets of intellectual conquest and demanded victories of theirown. Their diagrams were scratched on the walls, cut into the beamsupon the playground, and numberless other illustrations were affordedof the living interest they took in the subject. For my own part, asfar as experience in teaching goes, I was a mere fledgling--knowingnothing of the rules of pedagogics, as the Germans name it; butadhering to the spirit indicated at the commencement of thisdiscourse, and endeavouring to make geometry a means rather than abranch of education. The experiment was successful, and some of themost delightful hours of my existence have been spent in marking thevigorous and cheerful expansion of mental power, when appealed to inthe manner here described. 

Our pleasure was enhanced when we applied our mathematical knowledgeto the solution of physical problems. Many objects of hourly contacthad thus a new interest and significance imparted to them. The swing, the see-saw, the tension of the giant-stride ropes, the fall andrebound of the football, the advantage of a small boy over a large onewhen turning short, particularly in slippy weather; all becamesubjects of investigation. A lady stands before a looking-glass, ofher own height; it was required to know how much of the glass wasreally useful to her? We learned with pleasure the economic fact thatshe might dispense with the lower half and see her whole figurenotwithstanding. It was also pleasant to prove by mathematics, andverify by experiment, that the angular velocity of a reflected beam istwice that of the mirror which reflects it. From the hum of a bee wewere able to determine the number of times the insect flaps its wingsin a second. Following up our researches upon the pendulum, welearned how Colonel Sabine had made it the means of determining thefigure of the earth; and we were also startled by the inference whichthe pendulum enabled us to draw, that if the diurnal velocity of theearth were seventeen times its present amount, the centrifugal forceat the equator would be precisely equal to the force of gravitation, so that an inhabitant of those regions would then have the sametendency to fall upwards as downwards. All these things were sourcesof wonder and delight to us: and when we remembered that we weregifted with the powers which had reached such results, and that thesame great field was ours to work in, our hopes arose that at somefuture day we might possibly push the subject a little further, andadd our own victories to the conquests already won. 

I ought to apologise to you for dwelling so long upon this subject;but the days spent among these young philosophers made a deepimpression on me. I learned among them something of myself and ofhuman nature, and obtained some notion of a teacher's vocation. Ifthere be one profession in England of paramount importance, I believeit to be that of the schoolmaster; and if there be a position whereselfishness and incompetence do most serious mischief, by lowering themoral tone and exciting irreverence and cunning where reverence andnoble truthfulness ought to be the feelings evoked, it is that of theprincipal of a school. When a man of enlarged heart and mind comesamong boys, when he allows his spirit to stream through them, andobserves the operation of his own character evidenced in the elevationof theirs, --it would be idle to talk of the position of such a manbeing honourable. It is a blessed position. The man is a blessing tohimself and to all around him. Such men, I believe, are to be foundin England, and it behoves those who busy themselves with themechanics of education at the present day, to seek them out. For nomatter what means of culture may be chosen, whether physical orphilological, success must ever mainly depend upon the amount of life, love, and earnestness, which the teacher himself brings with him tohis vocation. 

Let me again, and finally, remind you that the claims of that sciencewhich finds in me to-day its unripened advocate, are those of thelogic of Nature upon the reason of her child--that its disciplines, asan agent of culture, are based upon the natural relations subsistingbetween Man and the universe of which he forms a part. On the oneside, we have the apparently lawless shifting of phenomena; on theother side, mind, which requires law for its equilibrium, and throughits own indestructible instincts, as well as through the teachings ofexperience, knows that these phenomena are reducible to law. Tochasten this apparent chaos is a problem which man has set before him. The world was built in order: and to us are trusted the will and powerto discern its harmonies, and to make them the lessons of our lives. From the cradle to the grave we are surrounded with objects whichprovoke inquiry. Descending for a moment from this high plea toconsiderations which lie closer to us as a nation--as a land of gasand furnaces, of steam and electricity: as a land which science, practically applied, has made great in peace and mighty in war: I askyou whether this 'land of old and just renown' has not a right toexpect from her institutions a culture more in accordance with herpresent needs than that supplied by declension and conjugation? Andif the tendency should be to lower the estimate of science, byregarding it exclusively as the instrument of material prosperity, letit be the high mission of our universities to furnish the propercounterpoise by pointing out its nobler uses--lifting the nationalmind to the contemplation of it as the last development of that'increasing purpose' which runs through the ages and widens thethoughts of men. 

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XII. ON CRYSTALLINE AND SLATY CLEAVAGE. 

[Footnote: From a discourse delivered in the Royal Institution ofGreat Britain, June 6, 1856. ]

WHEN the student of physical science has to investigate the characterof any natural force, his first care must be to purify it from themixture of other forces, and thus study its simple action. If, forexample, he wishes to know how a mass of liquid would shape itself ifat liberty to follow the bent of its own molecular forces, he must seethat these forces have free and undisturbed exercise. We mightperhaps refer him to the dewdrop for a solution of the question; buthere we have to do, not only with the action of the molecules of theliquid upon each other, but also with the action of gravity upon themass, which pulls the drop downwards and elongates it. If he wouldexamine the problem in its purity, he must do as Plateau has done, detach the liquid mass from the action of gravity; he would then findthe shape to be a perfect sphere. Natural processes come to us in amixed manner, and to the uninstructed mind are a mass ofunintelligible confusion. Suppose half-a-dozen of the best musicalperformers to be placed in the same room, each playing his owninstrument to perfection, but no two playing the same tune; thougheach individual instrument might be a source of perfect music, stillthe mixture of all would produce mere noise. 

Thus it is with the processes of nature, where mechanical andmolecular laws intermingle and create apparent confusion. Theirmixture constitutes what may be called the _noise_ of natural laws, andit is the vocation of the man of science to resolve this noise intoits components, and thus to detect the underlying music. 

The necessity of this detachment of one force from all other forces isnowhere more strikingly exhibited than in the phenomena ofcrystallisation. Here, for example, is a solution of common sulphateof soda or Glauber salt. Looking into it mentally, we see themolecules of that liquid, like disciplined squadrons under a governingeye, arranging themselves into battalions, gathering round distinctcentres, and forming themselves into solid masses, which after a timeassume the visible shape of the crystal now held in my hand. I may, like an ignorant meddler wishing to hasten matters, introduceconfusion into this order. This may be done by plunging a glass rodinto the vessel; the consequent action is not the pure expression ofthe crystalline forces; the molecules rush together with the confusionof an unorganised mob, and not with the steady accuracy of adisciplined host. In this mass of bismuth also we have an example ofconfused crystallisation; but in the crucible behind me a slowerprocess is going on: here there is an architect at work 'who makes nochips, no din, ' and who is now building the particles into crystals, similar in shape and structure to those beautiful masses which we seeupon the table. By permitting alum to crystallise in this slow way, we obtain these perfect octahedrons; by allowing carbonate of lime tocrystallise, nature produces these beautiful rhomboids; when silicacrystallises, we have formed these hexagonal prisms capped at the endsby pyramids; by allowing saltpetre to crystallise we have theseprismatic masses, and when carbon crystallises, we have the diamond. If we wish to obtain a perfect crystal we must allow the molecularforces free play; if the crystallising mass be permitted to rest upona surface it will be flattened, and to prevent this a small crystalmust be so suspended as to be surrounded on all sides by the liquid, or, if it rest upon the surface, it must be turned daily so as topresent all its faces in succession to the working builder. 

In building up crystals these little atomic bricks often arrangethemselves into layers which are perfectly parallel to each other, andwhich can be separated by mechanical means; this is called thecleavage of the crystal. The crystal of sugar I hold in my hand hasthus far escaped the solvent and abrading forces which sooner or laterdetermine the fate of sugar-candy. I readily discover that it cleaveswith peculiar facility in one direction. Again I lay my knife uponthis piece of rocksalt, and with a blow cleave it in one direction. Laying the knife at right angles to its former position, the crystalcleaves again; and finally placing the knife at right angles to thetwo former positions, we find a third cleavage. Rocksalt cleaves inthree directions, and the resulting solid is this perfect cube, whichmay be broken up into any number of smaller cubes. Iceland spar alsocleaves in three directions, not at right angles, but oblique to eachother, the resulting solid being a rhomboid. In each of these casesthe mass cleaves with equal facility in all three directions. For thesake of completeness I may say that many crystals cleave with unequalfacility in different directions: heavy spar presents an example ofthis kind of cleavage. 

Turn we now to the consideration of some other phenomena to which theterm cleavage may be applied. Beech, deal, and other woods cleavewith facility along the fibre, and this cleavage is most perfect whenthe edge of the axe is laid across the rings which mark the growth ofthe tree. If you look at this bundle of hay severed from a rick, youwill see a sort of cleavage in it also; the stalks lie in horizontalplanes, and only a small force is required to separate them laterally. But we cannot regard the cleavage of the tree as the same in characteras that of the hayrick. In the one case it is the molecules arrangingthemselves according to organic laws which produce a cleavablestructure, in the other case the easy separation in one direction isdue to the mechanical arrangement of the coarse sensible stalks ofhay. 

This sandstone rock was once a powder held in mechanical suspension bywater. The powder was composed of two distinct parts, fine grains ofsand and small plates of mica. Imagine a wide strand covered by atide, or an estuary with water which holds such powder in suspension:how will it sink? The rounded grains of sand will reach the bottomfirst, because they encounter least resistance, the mica afterwards, and when the tide recedes we have the little plates shining likespangles upon the surface of the sand. Each successive tide bringsits charge of mixed powder, deposits its duplex layer day after day, and finally masses of immense thickness are piled up, which bypreserving the alternations of sand and mica tell the tale of theirformation. Take the sand and mica, mix them together in water, andallow them to subside; they will arrange themselves in the mannerindicated, and by repeating the process you can actually build up amass which shall be the exact counterpart of that presented by nature. Now this structure cleaves with readiness along the planes in whichthe particles of mica are strewn. Specimens of such a rock sent to mefrom Halifax, and other masses from the quarries of Over Darwen inLancashire, are here before you. With a hammer and chisel I cancleave them into flags; indeed these flags are employed for roofingpurposes in the districts from which the specimens have come, andreceive the name of 'slatestone. ' But you will discern without a wordfrom me, that this cleavage is not a crystalline cleavage any morethan that of a hayrick is. It is molar, not molecular. 

This, so far as I am aware of, has never been imagined, and it hasbeen agreed among geologists not to call such splitting as thiscleavage at all, but to restrict the term to a phenomenon of a totallydifferent character. 

Those who have visited the slate quarries of Cumberland and NorthWales will have witnessed the phenomenon to which I refer. We havelong drawn our supply of roofing-slates from such quarries;school-boys ciphered on these slates, they were used for tombstones inchurchyards, and for billiard-tables in the metropolis; but not untila comparatively late period did men begin to enquire how theirwonderful structure was produced. What is the agency which enables usto split Honister Crag, or the cliffs of Snowdon, into laminae fromcrown to base? This question is at the present moment one of thegreat difficulties of geologists, and occupies their attention perhapsmore than any other. You may wonder at this. Looking into the quarryof Penrhyn, you may be disposed to offer the explanation I heard giventwo years ago. 'These planes of cleavage, ' said a friend who stoodbeside me on the quarry's edge, 'are the planes of stratificationwhich have been lifted by some convulsion into an almost verticalposition. ' But this was a mistake, and indeed here lies the granddifficulty of the problem. The planes of cleavage stand in most casesat a high angle to the bedding. Thanks to Sir Roderick Murchison, Iam able to place the proof of this before you. Here is a specimen ofslate in which both the planes of cleavage and of bedding aredistinctly marked, one of them making a large angle with the other. This is common. The cleavage of slates then is not a question ofstratification; what then is its cause?

In an able and elaborate essay published in 1835, Prof. Sedgwickproposed the theory that cleavage is due to the action of crystallineor polar forces subsequent to the consolidation of the rock. 'We mayaffirm, ' he says, 'that no retreat of the parts, no contraction ofdimensions in passing to a solid state, can explain such phenomena. They appear to me only resolvable on the supposition that crystallineor polar forces acted upon the whole mass simultaneously in onedirection and with adequate force. ' And again, in another place:'Crystalline forces have re-arranged whole mountain masses, producinga beautiful crystalline cleavage, passing alike through all thestrata. ' [Footnote: Transactions of the Geological Society, ser. Ii, vol. Iii. P. 477. ]

The utterance of such a man struck deep, as it ought to do, into theminds of geologists, and at the present day there are few who do notentertain this view either in whole or in part. [Footnote: In a letterto Sir Charles Lyell, dated from the Cape of Good Hope February 20, 1836, Sir John Herschel writes as follows: 'If rocks have been soheated as to allow of a commencement of crystallisation, that is tosay, if they have been heated to a point at which the particles canbegin to move amongst themselves, or at least on their own axes, somegeneral law must then determine the position in which these particleswill rest on cooling. Probably that position will have some relationto the direction in which the heat escapes. Now when all or amajority of particles of the same nature have a general tendency toone position, that must of course determine a cleavage plane. '] Theboldness of the theory, indeed, has, in some cases, caused speculationto run riot, and we have books published on the action of polar forcesand geologic magnetism, which rather astonish those who know somethingabout the subject. According to this theory whole districts of NorthWales and Cumberland, mountains included, are neither more nor lessthan the parts of a gigantic crystal. These masses of slate wereoriginally fine mud, composed of the broken and abraded particles ofolder rocks. They contain silica, alumina, potash, soda, and micamixed mechanically together. In the course of ages the mixture becameconsolidated, and the theory before us assumes that a process ofcrystallisation afterwards rearranged the particles and developed init a single plane of cleavage. Though a bold, and I thinkinadmissible, stretch of analogies, this hypothesis has done goodservice. Right or wrong, a thoughtfully uttered theory has a dynamicpower which operates against intellectual stagnation; and even byprovoking opposition is eventually of service to the cause of truth. It would, however, have been remarkable if, among the ranks ofgeologists themselves, men were not found to seek an explanation ofslate-cleavage involving a less hardy assumption. 

The first step in an enquiry of this kind is to seek facts. This hasbeen done, and the labours of Daniel Sharpe (the late President of theGeological Society, who, to the loss of science and the sorrow of allwho knew him, has so suddenly been taken away from us), Mr. HenryClifton Sorby, and others, have furnished us with a body of factsassociated with slaty cleavage, and having a most important bearingupon the question. 

Fossil shells are found in these slate-rocks. I have here severalspecimens of such shells in the actual rock, and occupying variouspositions in regard to the cleavage planes. They are squeezed, distorted, and crushed; in all cases the distortion leads to theinference that the rock which contains these shells has been subjectedto enormous pressure in a direction at right angles to the planes ofcleavage. The shells are all flattened and spread out in theseplanes. Compare this fossil trilobite of normal proportions withthese others which have suffered distortion. Some have lain across, some along, and some oblique to the cleavage of the slate in whichthey are found; but in all cases the distortion is such, as requiredfor its production a compressing force acting, at right angles to theplanes of cleavage. As the trilobites lay in the mud, the jaws of agigantic vice appear to have closed upon them and squeezed them intothe shapes you see. 

We sometimes find a thin layer of coarse gritty material, between twolayers of finer rock, through which and across the gritty layer passthe planes of lamination. The coarse layer is found bent by thepressure into sinuosities like a contorted ribbon. Mr. Sorby hasdescribed a striking case of this kind. This crumpling can beexperimentally imitated; the amount of compression might, moreover, beroughly estimated by supposing the contorted bed to be stretched out, its length measured and compared with the shorter distance into whichit has been squeezed. We find in this way that the yielding of themass has been considerable. 

Let me now direct your attention to another proof of pressure; you seethe varying colours which indicate the bedding on this mass of slate. The dark portion is gritty, being composed of comparatively coarseparticles, which, owing to their size, shape and gravity, sink firstand constitute the bottom of each layer. Gradually, from bottom totop the coarseness diminishes, and near the upper surface we have alayer of exceedingly fine grain. It is the fine mud thus consolidatedfrom which are derived the German razor-stones, so much prized for thesharpening of surgical instruments. 

When a bed is thin, the fine-grain slate is permitted to rest upon aslab of the coarse slate in contact with it; when the fine bed isthick, it is cut into slices which are cemented to pieces of ordinaryslate, and thus rendered stronger. The mud thus deposited is, asmight be expected, often rolled up into nodular masses, carriedforward, and deposited among coarser material by the rivers from whichthe slate-mud has subsided. Here are such nodules enclosed insandstone. Everybody, moreover, who has ciphered upon a school-slatemust remember the whitish-green spots which sometimes dotted thesurface of the slate, and over which the pencil usually slid as if thespots were greasy. Now these spots are composed of the finer mud, andthey could not, on account of their fineness, bite the pencil like thesurrounding gritty portions of the slate. Here is a beautiful exampleof these spots: you observe them, on the cleavage surface, in broadround patches. But turn the slate edgeways and the section of eachnodule is seen to be a sharp oval with its longer axis parallel to thecleavage. This instructive fact has been adduced by Mr. Sorby. Ihave made excursions to the quarries of Wales and Cumberland, and tomany of the slate yards of London, and found the fact general. Thuswe elevate a common experience of our boyhood into evidence of thehighest significance as regards a most important geological problem. From the magnetic deportment of these slates, I was led to infer thatthese spots contain a less amount of iron than the surrounding darkslate. An analysis was made for me by Mr. Hambly in the laboratory ofDr. Percy at the School of Mines with the following result:

ANALYSIS OF SLATE. 

Dark Slate, two analyses. 

1. Percentage of iron 5. 85

2. Percentage of iron 6. 13

 Mean 5. 99

Whitish Green Slate. 

1. Percentage of iron 3. 24

2. Percentage of iron 3. 12

 Mean 3. 18

According to these analyses the quantity of iron in the dark slateimmediately adjacent to the greenish spot is nearly double thequantity contained in the spot itself. This is about the proportionwhich the magnetic experiments suggested. 

Let me now remind you that the facts brought before you aretypical--each is the representative of a class. We have seen shellscrushed; the trilobites squeezed, beds contorted, nodules of greenishmarl flattened; and all these sources of independent testimony pointto one and the same conclusion, namely, that slate-rocks have beensubjected to enormous pressure in a direction at right angles to thePlanes of cleavage. 

In reference to Mr. Sorby's contorted bed, I have said that bysupposing it to be stretched out and its length measured, it wouldgive us an idea of the amount of yielding of the mass above and belowthe bed. Such a measurement, however, would not give the exact amountof yielding. I hold in my hand a specimen of slate with its beddingmarked upon it; the lower portions of each layer being composed of acomparatively coarse gritty material something like what you maysuppose the contorted bed to be composed of. Now in crossing thesegritty portions, the cleavage turns, as if tending to cross thebedding at another angle. When the pressure began to act, theintermediate bed, which is not entirely unyielding, sufferedlongitudinal pressure; as it bent, the pressure became gradually moretransverse, and the direction of its cleavage is exactly such as youwould infer from an action of this kind--it is neither quite acrossthe bed, nor yet in the same direction as the cleavage of the slateabove and below it, but intermediate between both. Supposing thecleavage to be at right angles to the pressure, this is the directionwhich it ought to take across these more unyielding strata. 

Thus we have established the concurrence of the phenomena of cleavageand pressure--that they accompany each other; but the question stillremains, Is the pressure sufficient to account for the cleavage? Asingle geologist, as far as I am aware, answers boldly in theaffirmative. This geologist is Sorby, who has attacked the questionin the true spirit of a physical investigator. Call to mind thecleavage of the flags of Halifax and Over Darwen, which is caused bythe interposition of layers of mica between the gritty strata. Mr. Sorby finds plates of mica to be also a constituent of slate-rock. Heasks himself, what will be the effect of pressure upon a masscontaining such plates confusedly mixed up in it? It will be, heargues, and he argues rightly, to place the plates with their flatsurfaces more or less perpendicular to the direction in which thepressure is exerted. He takes scales of the oxide of iron, mixes themwith a fine powder, and on squeezing the mass finds that the tendencyof the scales is to set themselves at right angles to the line ofpressure. Along the planes of weakness produced by the scales themass cleaves. 

By tests of a different character from those applied by Mr. Sorby, itmight be shown how true his conclusion is--that the effect of pressureon elongated particles, or plates, will be such as he describes it. But while the scales must be regarded as a true cause, I should notascribe to them a large share in the production of the cleavage. Ibelieve that even if the plates of mica were wholly absent, thecleavage of slate-rocks would be much the same as it is at present. 

Here is a mass of pure white wax: it contains no mica particles, noscales of iron, or anything analogous to them. Here is the selfsamesubstance submitted to pressure. I would invite the attention of theeminent geologists now before me to the structure of this wax. Noslate ever exhibited so clean a cleavage; it splits into laminae ofsurpassing tenuity, and proves at a single stroke that pressure issufficient to produce cleavage, and that this cleavage is independentof intermixed plates or scales. I have purposely mixed this wax withelongated particles, and am unable to say at the present moment thatthe cleavage is sensibly affected by their presence--if anything, Ishould say they rather impair its fineness and clearness than promoteit. 

The finer the slate is the more perfect will be the resemblance of itscleavage to that of the wax. Compare the surface of the wax with thesurface of this slate from Borrodale in Cumberland. You haveprecisely the same features in both: you see flakes clinging to thesurfaces of each, which have been partially torn away in cleaving. Letany close observer compare these two effects, he will, I am persuaded, be led to the conclusion that they are the product of a common cause. [Footnote: I have usually softened the wax by warming it, kneaded itwith the fingers, and pressed it between thick plates of glasspreviously wetted. At the ordinary summer temperature the pressed waxis soft, and tears rather than cleaves; on this account I cool mycompressed specimens in a mixture of pounded ice and salt, and whenthus cooled they split cleanly. ]

But you will ask me how, according to my view, does pressure producethis remarkable result? This may be stated in a very few words. 

There is no such thing in nature as a body of perfectly homogeneousstructure. I break this clay which seems so uniform, and find thatthe fracture presents to my eyes innumerable surfaces along which ithas given way, and it has yielded along those surfaces because in themthe cohesion of the mass is less than elsewhere. I break this marble, and even this wax, and observe the same result; look at the mud at thebottom of a dried pond; look at some of the ungravelled walks inKensington Gardens on drying after rain, --they are cracked and split, and other circumstances being equal, they crack and split where thecohesion is a minimum. Take then a mass of partially consolidatedmud. Such a mass is divided and subdivided by interior surfaces alongwhich the cohesion is comparatively small. Penetrate the mass inidea, and you will see it composed of numberless irregular polyhedrabounded by surfaces of weak cohesion. Imagine such a mass subjectedto pressure, --it yields and spreads out in the direction of leastresistance; the little polyhedra become converted into laminae, separated from each other by surfaces of weak cohesion, and theinfallible result will be a tendency to cleave at right angles to theline of pressure. [Footnote: It is scarcely necessary to say that if themass were squeezed equally in all directions no laminated structurecould be produced; it must have room to yield in a lateral direction. Mr. Warren De la Rue informs me that he once wished to obtainwhite-lead in a fine granular state, and to accomplish this he firstcompressed it. The mould was conical, and permitted the lead tospread out a little laterally. The lamination was as perfect as thatof slate, and it quite defeated him in his effort to obtain a granularpowder. ]

Further, a mass of dried mud is full of cavities and fissures. If youbreak dried pipe-clay you see them in great numbers, and there aremultitudes of them so small that you cannot see them. A flattening ofthese cavities must take place in squeezed mud, and this must to someextent facilitate the cleavage of the mass in the direction indicated. 

Although the time at my disposal has not permitted me duly to developethese thoughts, yet for the last twelve months the subject haspresented itself to me almost daily under one aspect or another. Ihave never eaten a biscuit during this period without remarking thecleavage developed by the rolling-pin. You have only to break abiscuit across, and to look at the fracture, to see the laminatedstructure. We have here the means of pushing the analogy further. Iinvite you to compare the structure of this slate, which was subjectedto a high temperature during the conflagration of Mr. Scott Russell'spremises, with that of a biscuit. Air or vapour within the slate hascaused it to swell, and the mechanical structure it reveals isprecisely that of a biscuit. During these enquiries I have receivedmuch instruction in the manufacture of puff-paste. Here is some suchpaste baked under my own superintendence. The cleavage of our hillsis accidental cleavage, but this is cleavage with intention. Thevolition of the pastrycook has entered into its formation. It hasbeen his aim to preserve a series of surfaces of structural weakness, along which the dough divides into layers. Puff-paste in preparationmust not be handled too much; it ought, moreover, to be rolled on acold slab, to prevent the butter from melting, and diffusing itself, thus rendering the paste more homogeneous and less liable to split. Puff-paste is, then, simply an exaggerated case of slaty cleavage. 

The principle here enunciated is so simple as to be almost trivial;nevertheless, it embraces not only the cases mentioned, but, if timepermitted, it might be shown you that the principle has a much widerrange of application. When iron is taken from the puddling furnace itis more or less spongy, an aggregate in fact of small nodules: it isat a welding heat, and at this temperature is submitted to the processof rolling. Bright smooth bars are the result. But notwithstandingthe high heat the nodules do not perfectly blend together. Theprocess of rolling draws them into fibres. Here is a mass acted uponby dilute sulphuric acid, which exhibits in a striking manner thisfibrous structure. The experiment was made by my friend Dr. Percy, without any reference to the question of cleavage. 

Break a piece of ordinary iron and you have a granular fracture; heatthe iron, you elongate these granules, and finally render the massfibrous. Here are pieces of rails along which the wheels oflocomotives have slid-den; the granules have yielded and becomeplates. They exfoliate or come off in leaves; all these effectsbelong, I believe, to the great class of phenomena of which slatycleavage forms the most prominent example. [Footnote: For some furtherobservations on this subject by Mr. Sorby and myself, seePhilosophical Magazine for August, 1856. ]

We have now reached the termination of our task. You have witnessedthe phenomena of crystallisation, and have had placed before you thefacts which are found associated with the cleavage of slate rocks. Such facts, as expressed by Helmholtz, are so many telescopes to ourspiritual vision, by which we can see backward through the night ofantiquity, and discern the forces which have been in operation uponthe earth's surface

 Ere the lion roared, Or the eagle soared. 

From evidence of the most independent and trustworthy character, wecome to the conclusion that these slaty masses have been subjected toenormous pressure, and by the sure method of experiment we haveshown--and this is the only really new point which has been broughtbefore you--how the pressure is sufficient to produce the cleavage. Expanding our field of view, we find the self-same law, whosefootsteps we trace amid the crags of Wales and Cumberland, extendinginto the domain of the pastrycook and ironfounder; nay, a wheel cannotroll over the half-dried mud of our streets without revealing to usmore or less of the features of this law. Let me say, in conclusion, that the spirit in which this problem has been attacked by geologists, indicates the dawning of a new day for their science. The greatintellects who have laboured at geology, and who have raised it to itspresent pitch of grandeur, were compelled to deal with the subject inmass; they had no time to look after details. But the desire for moreexact knowledge is increasing; facts are flowing in which, while theyleave untouched the intrinsic wonders of geology, are graduallysupplanting by solid truths the uncertain speculations which beset thesubject in its infancy. Geologists now aim to imitate, as far aspossible, the conditions of nature, and to produce her results; theyare approaching more and more to the domain of physics, and I trustthe day will soon come when we shall interlace our friendly armsacross the common boundary of our sciences, and pursue our respectivetasks in a spirit of mutual helpfulness, encouragement and goodwill. 

[I would now lay more stress on the lateral yielding, referred to inthe footnote concerning Mr. Warren De la Rue's attempt to producefinely granular white-lead, accompanied as it is by tangentialsliding, than I was prepared to do when this lecture was given. Thissliding is, I think, the principal cause of the planes of weakness, both in pressed wax and slate rock. J. T. 1871. ]

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XIII. ON PARAMAGNETIC AND DIAMAGNETIC FORCES

[Footnote: Abstract of a discourse delivered in the Royal Institution, February 1, 1856. ]

THE notion of an attractive force, which draws bodies towards thecentre of the earth, was entertained by Anaxagoras and his pupils, byDemocritus, Pythagoras, and Epicurus; and the conjectures of theseancients were renewed by Galileo, Huyghens, and others, who statedthat bodies attract each other as a magnet attracts iron. Keplerapplied the notion to bodies beyond the surface of the earth, andaffirmed the extension of this force to the most distant stars. Thusit would appear, that in the attraction of iron by a magnet originatedthe conception of the force of gravitation. Nevertheless, if we lookclosely at the matter, it will be seen that the magnetic forcepossesses characters strikingly distinct from those of the force whichholds the universe together. The theory of gravitation is, that everyparticle of matter attracts every other particle; in magnetism also wehave attraction, but we have always, at the same time, repulsion, thefinal effect being due to the difference of these two forces. A bodymay be intensely acted on by a magnet, and still no motion oftranslation will follow, if the repulsion be equal to the attraction. Previous to magnetization, a dipping needle, when its centre ofgravity is supported, stands accurately level; but, aftermagnetization, one end of it, in our latitude, is pulled towards thenorth pole of the earth. The needle, however, being suspended fromthe arm of a fine balance, its weight is found unaltered by itsmagnetization. In like manner, when the needle is permitted to floatupon a liquid, and thus to follow the attraction of the north magneticpole of the earth, there is no motion of the mass towards that pole. The reason is known to be, that although the marked end of the needleis attracted by the north pole, the unmarked end is repelled by anequal force, the two equal and opposite forces neutralizing eachother. 

When the pole of an ordinary magnet is brought to act upon theswimming needle, the latter is attracted, --the reason being that theattracted end of the needle being nearer to the pole of the magnetthan the repelled end, the force of attraction is the more powerful ofthe two. In the case of the earth, its pole is so distant that thelength of the needle is practically zero. In like manner, when apiece of iron is presented to a magnet, the nearer parts areattracted, while the more distant parts are repelled; and because theattracted portions are nearer to the magnet than the repelled ones, wehave a balance in favour of attraction. Here then is the specialcharacteristic of the magnetic force, which distinguishes it from thatof gravitation. The latter is a simple unpolar force, while theformer is duplex or polar. Were gravitation like magnetism, a stonewould no more fall to the ground than a piece of iron towards thenorth magnetic pole: and thus, however rich in consequences thesupposition of Kepler and others may have been, it is clear that aforce like that of magnetism would not be able to transact thebusiness of the universe. 

The object of this discourse is to enquire whether the force ofdiamagnetism, which manifests itself as a repulsion of certain bodiesby the poles of a magnet, is to be ranged as a polar force, besidethat of magnetism; or as an unpolar force, beside that of gravitation. When a cylinder of soft iron is placed within a wire helix, andsurrounded by an electric current, the antithesis of its two ends, or, in other words, its polar excitation, is at once manifested by itsaction upon a magnetic needle; and it may be asked why a cylinder ofbismuth may not be substituted for the cylinder of iron, and its statesimilarly examined. The reason is, that the excitement of the bismuthis so feeble, that it would be quite masked by that of the helix inwhich it is enclosed; and the problem that now meets us is, so toexcite a diamagnetic body that the pure action of the body upon amagnetic needle may be observed, unmixed with the action of the bodyused to excite the diamagnetic. 

How this has been effected may be illustrated in the followingmanner:

When through an upright helix of covered copper wire, a voltaiccurrent is sent, the top of the helix attracts, while its bottomrepels, the same pole of a magnetic needle; its central point, on thecontrary, is neutral, and exhibits neither attraction nor repulsion. Such a helix is caused to stand between the two poles N'S' of anastatic system. [Footnote: The reversal of the poles of the twomagnets, which were of the same strength, completely annulled theaction of the earth as a magnet. ] The two magnets S N' and S'N areunited by a rigid cross piece at their centres, and are suspended fromthe point a, so that both magnets swing in the same horizontal plane. It is so arranged that the poles N' s' are opposite to the central orneutral point of the helix, so that when a current is sent through thelatter, the magnets, as before explained, are unaffected. Here thenwe have an excited helix which itself has no action upon the magnets, and we are thus enabled to examine the action of a body placed withinthe helix and excited by it, undisturbed by the influence of thelatter. The helix being 12 inches high, a cylinder of soft iron 6inches long, suspended from a string and passing over a pulley, can beraised or lowered within the helix. When it is so far sunk that itslower end rests upon the table, the upper end finds itself between thepoles N´S´ of the astatic system. The iron cylinder is thus convertedinto a strong magnet, attracting one of the poles, and repelling theother, and consequently deflecting the entire astatic system. Whenthe cylinder is raised so that the upper end is at the level of thetop of the helix, its lower end comes between the poles N´S´; and adeflection opposed in direction to the former one is the immediateconsequence. To render these deflections more easily visible, amirror m is attached to the system of magnets; a beam of light thrownupon the mirror being reflected and projected as a bright disk againstthe wall. The distance of this image from the mirror beingconsiderable, and its angular motion double that of the latter, a veryslight motion of the magnet is sufficient to produce a displacement ofthe image through several yards. 

This then is the principle of the beautiful apparatus [Footnote:Devised by Prof. W. Weber, and constructed by M. Leyser, of Leipzig. ]by which the investigation was conducted. It is manifest that if asecond helix be placed between the poles SN with a cylinder withinit, the action upon the astatic magnet may be exalted. This was thearrangement made use of in the actual enquiry. Thus to intensify thefeeble action, which it is here our object to seek, we have in thefirst place neutralized the action of the earth upon the magnets, byplacing them astatically. Secondly, by making use of two cylinders, and permitting them to act simultaneously on the four poles of themagnets, we have rendered the deflecting force four times what itwould be, if only a single pole were used. Finally, the wholeapparatus was enclosed in a suitable case which protected the magnetsfrom air-currents, and the deflections were read off through a glassplate in the case, by means of a telescope and scale placed at aconsiderable distance from the instrument. 

A pair of bismuth cylinders was first examined. Sending a currentthrough the helices, and observing that the magnets swung perfectlyfree, it was first arranged that the bismuth cylinders within thehelices had their central or neutral points opposite to the poles ofthe magnets. All being at rest the number on the scale marked by thecross wire of the telescope was 572. The cylinders were then moved, one up the other down, so that two of their ends were brought to bearsimultaneously upon the magnetic poles: the magnet moved promptly, andafter some oscillations [Footnote: To lessen these a copper damper wasmade use of. ] came to rest at the number 612; thus moving from asmaller to a larger number. The other two ends of the bars were nextbrought to bear upon the magnet: a prompt deflection was theconsequence, and the final position of equilibrium was 526; themovement being from a larger to a smaller number. We thus observe amanifest polar action of the bismuth cylinders upon the magnet; onepair of ends deflecting it in one direction, and the other pairdeflecting it in the opposite direction. 

Substituting for the cylinders of bismuth thin cylinders of iron, ofmagnetic slate, of sulphate of iron, carbonate of iron, protochlorideof iron, red ferrocyanide of potassium, and other magnetic bodies, itwas found that when the position of the magnetic cylinders was thesame as that of the cylinders of bismuth, the deflection produced bythe former was always opposed in direction to that produced by thelatter; and hence the disposition of the force in the diamagnetic bodymust have been precisely antithetical to its disposition in themagnetic ones. 

But it will be urged, and indeed has been urged against thisinference, that the deflection produced by the bismuth cylinders maybe due to induced currents excited in the metal by its motion withinthe helices. In reply to this objection, it may be stated, in thefirst place, that the deflection is permanent, and cannot therefore bedue to induced currents, which are only of momentary duration. It hasalso been urged that such experiments ought to be made with othermetals, and with better conductors than bismuth; for if due tocurrents of induction, the better the conductor the more exalted willbe the effect. This requirement was complied with. 

Cylinders of antimony were substituted for those of bismuth. Thismetal is a better conductor of electricity, but less stronglydiamagnetic than bismuth. If therefore the action referred to be dueto induced currents we ought to have it greater in the case ofantimony than with bismuth; but if it springs from a true diamagneticpolarity, the action of the bismuth ought to exceed that of theantimony. Experiment proves this to be the case. Hence thedeflection produced by these metals is due to their diamagnetic, andnot to their conductive capacity. Copper cylinders were nextexamined: here we have a metal which conducts electricity fifty timesbetter than bismuth, but its diamagnetic power is nearly null; if theeffects be due to induced currents we ought to have them here in anenormously exaggerated degree, but no sensible deflection was producedby the two cylinders of copper. 

It has also been proposed by the opponents of diamagnetic polarity tocoat fragments of bismuth with some insulating substance, so as torender the formation of induced currents impossible, and to test thequestion with cylinders of these fragments. This requirement was alsofulfilled. It is only necessary to reduce the bismuth to powder andexpose it for a short time to the air to cause the particles to becomeso far oxidised as to render them perfectly insulating. Theinsulating power of the powder was exhibited experimentally;nevertheless, this powder, enclosed in glass tubes, exhibited anaction scarcely less powerful than that of the massive bismuthcylinders. 

But the most rigid proof, a proof admitted to be conclusive by thosewho have denied the antithesis of magnetism and diamagnetism, remainsto be stated. Prisms of the same heavy glass as that with which thediamagnetic force was discovered, were substituted for the metalliccylinders, and their action upon the magnet was proved to be preciselythe same in kind as that of the cylinders of bismuth. The enquiry wasalso extended to other insulators: to phosphorus, sulphur, nitre, calcareous spar, statuary marble, with the same invariable result:each of these substances was proved to be polar, the disposition ofthe force being the same as that of bismuth and the reverse of that ofiron. When a bar of iron is set erect, its lower end is known to be anorth pole, and its upper end a south pole, in virtue of the earth'sinduction. A marble statue, on the contrary, has its feet a southpole, and its head a north pole, and there is no doubt that the sameremark applies to its living archetype; each man walking over theearth's surface is a true diamagnet, with its poles the reverse ofthose of a mass of magnetic matter of the same shape and position. 

An experiment of practical value, as affording a ready estimate of thedifferent conductive powers of two metals for electricity, wasexhibited in the lecture, for the purpose of proving experimentallysome of the statements made in reference to this subject. A cube ofbismuth was suspended by a twisted string between the two poles of anelectro-magnet. The cube was attached by a short copper wire to alittle square pyramid, the base of which was horizontal, and its sidesformed of four small triangular pieces of looking-glass. A beam oflight was suffered to fall upon this reflector, and as the reflectorfollowed the motion of the cube the images cast from its sidesfollowed each other in succession, each describing a circle aboutthirty feet in diameter. As the velocity of rotation augmented, theseimages blended into a continuous ring of light. At a particularinstant the electro-magnet was excited, currents were evolved in therotating cube, and the strength of these currents, which increaseswith the conductivity of the cube for electricity, was practicallyestimated by the time required to bring the cube and its associatedmirrors to a state of rest. With bismuth this time amounted to a scoreof seconds or more: a cube of copper, on the contrary, was struckalmost instantly motionless when the circuit was established. 

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XIV. PHYSICAL BASIS OF SOLAR CHEMISTRY. 

[Footnote: From a discourse delivered at the Royal Institution ofGreat Britain, June 7, 1861. ]

OMITTING all preface, attention was first drawn to an experimentalarrangement intended to prove that gaseous bodies radiate heat indifferent degrees. Near a double screen of polished tin was placed anordinary ring gas-burner, and on this was placed a hot copper ball, from which a column of heated air ascended. Behind the screen, but sosituated that no ray from the ball could reach the instrument, was anexcellent Thermo-electric pile, connected by wires with a verydelicate galvanometer. The pile was known to be an instrument wherebyheat is applied to the generation of electric currents; the strengthof the current being an accurate measure of the quantity of the heat. As long as both faces of the pile are at the same temperature, nocurrent is produced; but the slightest difference in the temperatureof the two faces at once declares itself by the production of acurrent, which, when carried through the galvanometer, indicates bythe deflection of the needle both its strength and its direction. 

The two faces of the pile were in the first instance brought to thesame temperature; the equilibrium being shown by the needle of thegalvanometer standing at zero. The rays emitted by the current of hotair already referred to were permitted to fall upon one of the facesof the pile; and an extremely slight movement of the needle showedthat the radiation from the hot air, though sensible, was extremelyfeeble. Connected with the ring-burner was a holder containing oxygengas; and by turning a cock, a stream of this gas was permitted toissue from the burner, strike the copper ball, and ascend in a heatedcolumn in front of the pile. The result was, that oxygen showeditself, as a radiator of heat, to be quite as feeble as atmosphericair. 

A second holder containing olefiant gas was then connected with thering-burner. Oxygen and air had already flowed over the ball andcooled it in some degree. Hence the olefiant gas laboured under adisadvantage. But on permitting the gas to rise from the ball, itcasts an amount of heat against the adjacent face of the pilesufficient to impel the needle of the galvanometer almost to 90°. Thisexperiment proved the vast difference between two equally invisiblegases with regard to their power of emitting radiant heat. 

The converse experiment was now performed. The thermo-electric pilewas removed and placed between two cubes filled with water kept in astate of constant ebullition; and it was so arranged that thequantities of heat falling from the cubes on the opposite faces of thepile were exactly equal, thus neutralising each other. The needle ofthe galvanometer being at zero, a sheet of oxygen gas was caused toissue from a slit between one of the cubes and the adjacent face ofthe pile. If this sheet of gas possessed any sensible power ofintercepting the thermal rays from the cube, one face of the pilebeing deprived of the heat thus intercepted, a difference oftemperature between its two faces would instantly set in, and theresult would be declared by the galvanometer. The quantity absorbedby the oxygen under those circumstances was too feeble to affect thegalvanometer; the gas, in fact, proved perfectly transparent to therays of heat. It had but a feeble power of radiation: it had anequally feeble power of absorption. 

The pile remaining in its position, a sheet of olefiant gas was causedto issue from the same slit as that through which the oxygen hadpassed. No one present could see the gas; it was quite invisible, thelight went through it as freely as through oxygen or air; but itseffect upon the thermal rays emanating from the cube was what might beexpected from a sheet of metal. A quantity so large was cut off, thatthe needle of the galvanometer, promptly quitting the zero line, movedwith energy to its stops. Thus the olefiant gas, so light and clearand pervious to luminous rays, was proved to be a most potentdestroyer of the rays emanating from an obscure source. Thereciprocity of action established in the case of oxygen comes outhere; the good radiator is found by this experiment to be the goodabsorber. 

This result, now exhibited before a public audience for the firsttime, was typical of what had been obtained with gases generally. Going through the entire list of gases and vapours in this way, wefind radiation and absorption to be as rigidly associated as positiveand negative in electricity, or as north and south polarity inmagnetism. So that if we make the number which expresses theabsorptive power the numerator of a fraction, and that which expressesits radiative power the denominator, the result would be, that onaccount of the numerator and denominator varying in the same, proportion, the value of that fraction would always remain the same, whatever might be the gas or vapour experimented with. 

But why should this reciprocity exist? What is the meaning ofabsorption? what is the meaning of radiation? When you cast a stoneinto still water, rings of waves surround the place where it falls;motion is radiated on all sides from the centre of disturbance. Whena hammer strikes a bell, the latter vibrates; and sound, which isnothing more than an undulatory motion of the air, is radiated in alldirections. Modern philosophy reduces light and heat to the samemechanical category. A luminous body is one with its atoms in a stateof vibration; a hot body is one with its atoms also vibrating, but ata rate which is incompetent to excite the sense of vision; and, as asounding body has the air around it, through which it propagates itsvibrations, so also the luminous or heated body has a medium, calledaether, which accepts its motions and carries them forward withinconceivable velocity. Radiation, then, as regards both light andheat, is the transference of motion from the vibrating body to theaether in which it swings: and, as in the case of sound, the motionimparted to the air is soon transferred to surrounding objects, against which the aerial undulations strike, the sound being, intechnical language, absorbed; so also with regard to light and heat, absorption consists in the transference of motion from the agitatedaether to the molecules of the absorbing body. 

The simple atoms are found to be bad radiators; the compound atomsgood ones: and the higher the degree of complexity in the atomicgrouping, the more potent, as a general rule, is the radiation andabsorption. Let us get definite ideas here, however gross, and purifythem afterwards by the process of abstraction. Imagine our simpleatoms swinging like single spheres in the aether; they cannot createthe swell which a group of them united to form a system can produce. An oar runs freely edgeways through the water, and imparts far less ofits motion to the water than when its broad flat side is brought tobear upon it. In our present language the oar, broad side vertical, is a good radiator; broad side horizontal, it is a bad radiator. Conversely the waves of water, impinging upon the flat face of theoar-blade, will impart a greater amount of motion to it than whenimpinging upon the edge. In the position in which the oar radiateswell, it also absorbs well. Simple atoms glide through the aetherwithout much resistance; compound ones encounter resistance, and henceyield up more speedily their motion to the aether. Mix oxygen andnitrogen mechanically, they absorb and radiate a certain amount ofheat. Cause these gases to combine chemically and form nitrous oxide, both the absorption and radiation are thereby augmented hundreds oftimes!

In this way we look with the telescope of the intellect into atomicsystems, and obtain a conception of processes which the eye of sensecan never reach. But gases and vapours possess a power of choice asto the rays which they absorb. They single out certain groups of raysfor destruction, and allow other groups to pass unharmed. This isbest illustrated by a famous experiment of Sir David Brewster's, modified to suit present requirements. Into a glass cylinder, withits ends stopped by discs of plate-glass, a small quantity of nitrousacid gas is introduced; the presence of the gas being indicated by itsrich brown colour. The beam from an electric lamp being sent throughtwo prisms of bisulphide of carbon, a spectrum seven feet long andeighteen inches wide is cast upon the screen. Introducing thecylinder containing the nitrous acid into the path of the beam as itissues from the lamp, the splendid and continuous spectrum becomesinstantly furrowed by numerous dark bands, the rays answering to whichare intercepted by the nitric gas, while the light which falls uponthe intervening spaces is permitted to pass with comparative impunity. 

Here also the principle of reciprocity, as regards radiation andabsorption, holds good; and could we, without otherwise altering itsphysical character, render that nitrous gas luminous, we should findthat the very rays which it absorbs are precisely those which it wouldemit. When atmospheric air and other gases are brought to a state ofintense incandescence by the passage of an electric spark, the spectrawhich we obtain from them consist of a series of bright bands. Butsuch spectra are produced with the greatest brilliancy when, insteadof ordinary gases, we make use of metals heated so highly as tovolatilise them. This is easily done by the voltaic current. Acapsule of carbon filled with mercury, which formed the positiveelectrode of the electric lamp, has a carbon point brought down uponit. On separating the one from the other, a brilliant arc containingthe mercury in a volatilised condition passes between them. Thespectrum of this arc is not continuous like that of the solid carbonpoints, but consists of a series of vivid bands, each corresponding incolour to that particular portion of the spectrum to which its raysbelong. Copper gives its system of bands; zinc gives its system; andbrass, which is an alloy of copper and zinc, gives a spectrum made upof the bands belonging to both metals. 

Not only, however, when metals are united like zinc and copper to forman alloy, is it possible to obtain the bands which belong to them. Nomatter how we may disguise the metal--allowing it to unite with oxygento form an oxide, and this again with an acid to form a salt; if theheat applied be sufficiently intense, the bands belonging to the metalreveal themselves with perfect definition. Into holes drilled in acylinder of retort carbon, pure culinary salt is introduced. When thecarbon is made the positive electrode of the lamp, the resultantspectrum shows the brilliant yellow lines of the metal sodium. Similar experiments made with the chlorides of strontium, calcium, lithium, [Footnote: The vividness of the colours of the lithiumspectrum is extraordinary; the spectrum, moreover, contained a blueband of indescribable splendour. It was thought by many, during thediscourse, that I had mistaken strontium for lithium, as this blueband had never before been seen. I have obtained it many times since;and my friend Dr. Miller, having kindly analysed the substance madeuse of, pronounces it pure chloride of lithium. --J. T. ] and othermetals, give the bands due to the respective metals. When differentsalts are mixed together, and rammed into holes in the carbon; aspectrum is obtained which contains the bands of them all. 

The position of these bright bands never varies, and each metal hasits own system. Hence the competent observer can infer from the bandsof the spectrum the metals which produce it. It is a languageaddressed to the eye instead of the ear; and the certainty would notbe augmented if each metal possessed the power of audibly calling out, 'I am here!' Nor is this language affected by distance. If we findthat the sun or the stars give us the bands of our terrestrial metals, it is a declaration on the part of these orbs that such metals enterinto their composition. Does the sun give us any such intimation?Does the solar spectrum exhibit bright lines which we might comparewith those produced by our terrestrial metals, and prove either theiridentity or difference? No. The solar spectrum, when closelyexamined, gives us a multitude of fine dark lines instead of brightones. They were first noticed by Dr. Wollaston, but were multipliedand investigated with profound skill by Fraunhofer, and named afterhim Fraunhofer's lines. They had been long a standing puzzle tophilosophers. The bright lines yielded by metallic vapours had beenalso known to us for years; but the connection between both classes ofphenomena was wholly unknown, until Kirchhoff, with admirableacuteness, revealed the secret, and placed it at the same time in ourpower to chemically analyse the sun. 

We have now some difficult work before us. Hitherto we have beendelighted by objects which addressed themselves as much to ouraesthetic taste as to our scientific faculty; we have riddenpleasantly to the base of the final cone of Etna, and must nowdismount and march through ashes and lava, if we would enjoy theprospect from the summit. Our problem is to connect the dark lines ofFraunhofer with the bright ones of the metals. The white beam of thelamp is refracted in passing through our two prisms, but its differentcomponents are refracted in different degrees, and thus its coloursare drawn apart. 

Now the colour depends solely upon the rate of oscillation of theatoms of the luminous body; red light being produced by one rate, bluelight by a much quicker rate, and the colours between red and blue bythe intermediate rates. The solid incandescent coal-points give us acontinuous spectrum; or in other words they emit rays of all possibleperiods between the two extremes of the spectrum. Colour, as many ofyou know, is to light what _pitch_ is to sound. When a violin-playerpresses his finger on a string he makes it shorter and tighter, andthus, causing it to vibrate more speedily, heightens the pitch. Imagine such a player to move his fingers slowly along the string, shortening it gradually as he draws his bow, the note would rise inpitch by a regular gradation; there would be no gap interveningbetween note and note. Here we have the analogue to the continuousspectrum, whose colours insensibly blend together without gap orinterruption, from the red of the lowest pitch to the violet of thehighest. But suppose the player, instead of gradually shortening hisstring, to press his finger on a certain point, and to sound thecorresponding note; then to pass on to another point more or lessdistant, and sound its note; then to another, and so on, thus soundingparticular notes separated from each other by gaps which correspond tothe intervals of the string passed over; we should then have the exactanalogue of a spectrum composed of separate bright bands withintervals of darkness between them. But this, though a perfectly trueand intelligible analogy, is not sufficient for our purpose; we mustlook with the mind's eye at the oscillating atoms of the volatilisedmetal. 

Figure these atoms as connected together by springs of a certaintension, which, if the atoms are squeezed together, push them againasunder, and if the atoms are drawn apart, pull them again together, causing them, before coming to rest, to quiver for a certain time at acertain definite rate determined by the strength of the spring. Nowthe volatilised metal which gives us one bright band is to be figuredas having its atoms united by springs all of the same tension, itsvibrations are all of one kind. The metal which gives us two bandsmay be figured as having some of its atoms united by springs of onetension, and others by springs of a different tension. Its vibrationsare of two distinct kinds; so also when we have three or more bands weare to figure as many distinct sets of springs, each capable ofvibrating in its own particular time and at a different rate from theothers. If we seize this idea definitely, we shall have no difficultyin dropping the metaphor of springs, and substituting for it mentallythe forces by which the atoms act upon each other. Having thus farcleared our way, let us make another effort to advance. 

A heavy ivory ball is here suspended from a string. I blow againstthis ball; a single puff of my breath moves it a little way from itsposition of rest; it swings back towards me, and when it reaches thelimit of its swing I puff again. It now swings further; and thus bytiming the puffs I can so accumulate their action as to produceoscillations of large amplitude. The ivory ball here has absorbed themotion which my breath communicated to the air. I now bring the ballto rest. Suppose, instead of the breath, a wave of air to strikeagainst it, and that this wave is followed by a series of others whichsucceed each other exactly in the same intervals as my puffs; it isobvious that these waves would communicate their motion to the balland cause it to swing as the puffs did. And it is equally manifestthat this would not be the case if the impulses of the waves were notproperly timed; for then the motion imparted to the pendulum by onewave would be neutralised by another, and there could not be theaccumulation of effect obtained when the periods of the wavescorrespond with the periods of the pendulum. So much for theparticular impulses absorbed by the pendulum. But if such a pendulumset oscillating in air could produce waves in the air, it is evidentthat the waves it would produce would be of the same period as thosewhose motions it would take up or absorb most completely, if theystruck against it. Perhaps the most curious effect of these timedimpulses ever described was that observed by a watchmaker, namedEllicott, in the year 1741. He left two clocks leaning against thesame rail; one of them, which we may call A, was set going; the other, B, not. Some time afterwards he found, to his surprise, that B wasticking also. The pendulums being of the same length, the shocksimparted by the ticking of A to the rail against which both clocksrested were propagated to B, and were so timed as to set B going. Other curious effects were at the same time observed. When, thependulums differed from each other a certain amount, set B going, butthe reaction of B stopped A. Then B set A going, and the re-action ofA stopped B. When the periods of oscillation were close to eachother, but still not quite alike, the clocks mutually controlled eachother, and by a kind of compromise they ticked in perfect unison. 

But what has all this to do with our present subject? The variedactions of the universe are all modes of motion; and the vibration ofa ray claims strict brotherhood with the vibrations of our pendulum. Suppose aethereal waves striking upon atoms which oscillate in thesame periods as the waves, the motion of the waves will be absorbed bythe atoms; suppose we send our beam of white light through a sodiumflame, the atoms of that flame will be chiefly affected by thoseundulations which are synchronous with their own periods of vibration. There will be on the part of those particular rays a transference ofmotion from the agitated aether to the atoms of the volatilised metal, which, as already defined, is absorption. 

The experiment justifying this conclusion is now for the first time tobe made before a public audience. I pass a beam through our twoprisms, and the spectrum spreads its colours upon the screen. Betweenthe lamp and the prism I interpose a snapdragon light. Alcohol andwater are here mixed with common salt, and the metal dish that holdsthem is heated by a spirit-lamp. The vapour from the mixture ignitesand we have a monochromatic flame. Through this flame the beam fromthe lamp is now passing; and observe the result upon the spectrum. Yousee a shady band cut out of the yellow, --not very dark, butsufficiently so to be seen by everybody present. 

But let me exalt this effect. Placing in front of the electric lampthe intense flame of a large Bunsen's burner, a platinum capsulecontaining a bit of sodium less than a pea in magnitude is plungedinto the flame. The sodium soon volatilises and burns with brilliantincandescence. The beam crosses the flame, and at the same time theyellow band of the spectrum is clearly and sharply cut out, a band ofintense darkness occupying its place. On withdrawing the sodium, thebrilliant yellow of the spectrum takes its proper place, while thereintroduction of the flame causes the band to reappear. 

Let me be more precise: The yellow colour of the spectrum extendsover a sensible space, blending on one side with the orange and on theother with the green. The term 'yellow band' is therefore somewhatindefinite. This vagueness may be entirely removed. By dipping thecarbon-point used for the positive electrode into a solution of commonsalt, and replacing it in the lamp, the bright yellow band produced bythe sodium vapour stands out from the spectrum. When the sodium flameis caused to act upon the beam it is that particular yellow band thatis obliterated, an intensely black streak occupying its place. 

An additional step of reasoning leads to the conclusion that if, instead of the flame of sodium alone, we were to introduce into thepath of the beam a flame in which lithium, strontium, magnesium, calcium, &c, are in a state of volatilisation, each metallic vapourwould cut out a system of bands, corresponding exactly in positionwith the bright bands of the same metallic vapour. The light of ourelectric lamp shining through such a composite flame would give us aspectrum cut up by dark lines, exactly as the solar spectrum is cut upby the lines of Fraunhofer. 

Thus by the combination of the strictest reasoning with the mostconclusive experiment, we reach the solution of one of the grandest ofscientific problems--the constitution of the sun. The sun consists ofa nucleus surrounded by a flaming atmosphere. The light of thenucleus would give us a continuous spectrum, like that of our commoncarbon-points; but having to pass through the photosphere, as our beamhad to pass through the flame, those rays of the nucleus which thephotosphere can itself emit are absorbed, and shaded spaces, corresponding to the particular rays absorbed, occur in the spectrum. Abolish the solar nucleus, and we should have a spectrum showing abright line in the place of every dark line of Fraunhofer. Theselines are therefore not absolutely dark, but dark by an amountcorresponding to the difference between the light of the nucleusintercepted by the photosphere, and the light which issues from thelatter. 

The man to whom we owe this noble generalisation is Kirchhoff, Professor of Natural Philosophy in the University of Heidelberg;[Footnote: Now Professor in the University of Berlin. ] but, likeevery other great discovery, it is compounded of various elements. Mr. Talbot observed the bright lines in the spectra of coloured flames. Sixteen years ago Dr. Miller gave drawings and descriptions of thespectra of various coloured flames. Wheatstone, with his accustomedingenuity, analysed the light of the electric spark, and showed thatthe metals between which the spark passed determined the bright bandsin the spectrum of the spark. Masson published a prize essay on thesebands; Van der Willigen, and more recently Plucker, have given usbeautiful drawings of the spectra, obtained from the discharge ofRuhmkorff's coil. But none of these distinguished men betrayed theleast knowledge of the connection between the bright bands of themetals and the dark lines of the solar spectrum. The man who camenearest to the philosophy of the subject was Angstrom. In a papertranslated from Poggendorff's 'Annalen' by myself, and published inthe 'Philosophical Magazine' for 1855, he indicates that the rayswhich a body absorbs are precisely those which it can emit whenrendered luminous. In another place, he speaks of one of his spectragiving the general impression of a reversal of the solar spectrum. Foucault, Stokes, and Thomson, have all been very close to thediscovery; and, for my own part, the examination of the radiation andabsorption of heat by gases and vapours, some of the results of whichI placed before you at the commencement of this discourse, would haveled me in 1859 to the law on which all Kirchhoff's speculations arefounded, had not an accident withdrawn me from the investigation. ButKirchhoff's claims are unaffected by these circumstances. True, muchthat I have referred to formed the necessary basis of his discovery;so did the laws of Kepler furnish to Newton the basis of the theory ofgravitation. But what Kirchhoff has done carries us far beyond allthat had before been accomplished. He has introduced the order of lawamid a vast assemblage of empirical observations, and has ennobled ourprevious knowledge by showing its relationship to some of the mostsublime of natural phenomena. 

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XV. ELEMENTARY MAGNETISM. 

A LECTURE TO SCHOOLMASTERS. 

WE have no reason to believe that the sheep or the dog, or indeed anyof the lower animals, feel an interest in the laws by which naturalphenomena are regulated. A herd may be terrified by a thunderstorm;birds may go to roost, and cattle return to their stalls, during asolar eclipse; but neither birds nor cattle, as far as we know, everthink of enquiring into the causes of these things. It is otherwisewith Man. The presence of natural objects, the occurrence of naturalevents, the varied appearances of the universe in which he dwellspenetrate beyond his organs of sense, and appeal to an inner power ofwhich the senses are the mere instruments and excitants. No fact isto him either original or final. He cannot limit himself to thecontemplation of it alone, but endeavours to ascertain its position ina series to which uniform experience assures him it must belong. Heregards all that he witnesses in the present as the efflux andsequence of something that has gone before, and as the source of asystem of events which is to follow. The notion of spontaneity, bywhich in his ruder state he accounted for natural events, isabandoned; the idea that nature is an aggregate of independent partsalso disappears, as the connection and mutual dependence of physicalpowers become more and more manifest: until he is finally led toregard Nature as an organic whole--as a body each of whose memberssympathises with the rest, changing, it is true, from age to age, butchanging without break of continuity in the relation of cause andeffect. 

The system of things which we call Nature is, however, too vast andvarious to be studied first-hand by any single mind. As knowledgeextends there is always a tendency to subdivide the field ofinvestigation. Its various parts are taken up by different minds, andthus receive a greater amount of attention than could possibly bebestowed on them if each investigator aimed at the mastery of thewhole. The centrifugal form in which knowledge, as a whole, advances, spreading ever wider on all sides, is due in reality to the exertionsof individuals, each of whom directs his efforts, more or less, alonga single line. Accepting, in many respects, his culture from hisfellow-men--taking it from spoken words or from written books--in someone direction, the student of Nature ought actually to touch his work. He may otherwise be a distributor of knowledge, but not a creator, andhe fails to attain that vitality of thought, and correctness ofjudgment, which direct and habitual contact with natural truth canalone impart. 

One large department of the system of Nature which forms the chiefsubject of my own studies, and to which it is my duty to call yourattention this evening, is that of physics, or natural philosophy. This term is large enough to cover the study of Nature generally, butit is usually restricted to a department which, perhaps, lies closerto our perceptions than any other. It deals with the phenomena andlaws of light and heat--with the phenomena and laws of magnetism andelectricity--with those of sound--with the pressures and motions ofliquids and gases, whether at rest or in a state of translation or ofundulation. The science of mechanics is a portion of naturalphilosophy, though at present so large as to need the exclusiveattention of him who would cultivate it profoundly. Astronomy is theapplication of physics to the motions of the heavenly bodies, thevastness of the field causing it, however, to bed regarded as adepartment in itself. In chemistry physical agents play importantparts. By heat and light we cause atoms and molecules to unite or tofall asunder. Electricity exerts a similar power. Through theirability to separate nutritive compounds into their constituents, thesolar beams build up the whole vegetable world, and by it the animalworld. The touch of the self-same beams causes hydrogen and chlorineto; unite with sudden explosion, and to form by their combination apowerful acid. Thus physics and chemistry intermingle. Physicalagents are, however, employed by the chemist as a means to an end;while in physics proper the laws and phenomena of the agentsthemselves, both qualitative and quantitative, are the primary objectsof attention. 

My duty here to-night is to spend an hour in telling how this subjectis to be studied, and how a knowledge of it is to be imparted toothers. From the domain of physics, which would be unmanageable as awhole, I select as a sample the subject of magnetism. I might readilyentertain you on the present occasion with an account of what naturalphilosophy has accomplished. I might point to those applications ofscience of which we hear so much in the newspapers, and which are sooften mistaken for science itself. I might, of course, ring changeson the steam-engine and the telegraph, the electrotype and thephotograph, the medical applications of physics, and the various otherinlets by which scientific thought filters into practical life. Thatwould be easy compared with the task of informing you how you are tomake the study of physics the instrument of your pupil's culture; howyou are to possess its facts and make them living seeds which shalltake root and grow in the mind, and not lie like dead lumber in thestorehouse of memory. This is a task much heavier than the mererecounting of scientific achievements; and it is one which, feeling myown want of time to execute it aright, I might well hesitate toaccept. 

But let me sink excuses, and attack the work before me. First andforemost, then, I would advise you to get a knowledge of facts fromactual observation. Facts looked at directly are vital; when theypass into words half the sap is taken out of them. You wish, forexample, to get a knowledge of magnetism; well, provide yourself witha good book on the subject, if you can, but do not be content withwhat the book tells you; do not be satisfied with its descriptivewoodcuts; see the operations of the force yourself. Half of our bookwriters describe experiments which they never made, and theirdescriptions often lack both force and truth; but, no matter howclever or conscientious they may be, their written words cannot supplythe place of actual observation. Every fact has numerous radiations, which are shorn off by the man who describes it. 

Go, then, to a philosophical instrument maker, and give a shilling orhalf a crown for a straight bar-magnet, or, if you can afford it, purchase a pair of them; or get a smith to cut a length of ten inchesfrom a bar of steel an inch wide and half an inch thick; file its endssmoothly, harden it, and get somebody like myself to magnetise it. Procure some darning needles, and also a little unspun silk, whichwill give you a suspending fibre void of torsion. Make little loopof paper, or of wire, and attach your fibre to it. Do it neatly. Inthe loop place a darning-needle, and bring the two ends or poles, asthey are called, of your bar-magnet successively up to the ends of theneedle. Both the poles, you find, attract both ends of the needle. Replace the needle by a bit of annealed iron wire; the same effectsensue. Suspend successively little rods of lead, copper, silver, brass, wood, glass, ivory, or whalebone; the magnet produces nosensible effect upon any of the substances. You thence infer aspecial property in the case of steel and iron. Multiply yourexperiments, However, and you will find that some other substances, besides iron and steel, are acted upon by your magnet. A rod of themetal nickel, or of the metal cobalt, from which the blue colour usedby painters is derived, exhibits powers similar to those observed withthe iron and steel. 

In studying the character of the force you may, however, confineyourself to iron and steel, which are always at hand. Make yourexperiments with the darning-needle over and over again; operate onboth ends of the needle; try both ends of the magnet. Do not thinkthe work dull; you are conversing with Nature, and must acquire overher language a certain grace and mastery, which practice can aloneimpart. Let every movement be made with care, and avoid slovenliness, from the outset. Experiment, as I have said, is the language by whichwe address Nature, and through which she sends her replies; in the useof this language a lack of straightforwardness is as possible, and asprejudicial, as in the spoken language of the tongue. If, therefore, you wish to become acquainted with the truth of Nature, you must fromthe first resolve to deal with her sincerely. 

Now remove your needle from its loop, and draw it from eye to pointalong one of the ends of the magnet; resuspend it, and repeat yourformer experiment. You now find that each extremity of the magnetattracts one end of the needle, and repels the other. The simpleattraction observed in the first instance, is now replaced by a _dual_force. Repeat the experiment till you have thoroughly observed theends which attract and those which repel each other. 

Withdraw the magnet entirely from the vicinity of your needle, andleave the latter freely suspended by its fibre. Shelter it as well asyou can from currents of air, and if you have iron buttons on yourcoat, or a steel penknife in your pocket, beware of their action. Ifyou work at night, beware of iron candlesticks, or of brass ones withiron rods inside. Freed from such disturbances, the needle takes up acertain determinate position. It sets its length nearly north andsouth. Draw it aside and let it go. After several oscillations itwill again come to the same position. If you have obtained yourmagnet from a philosophical instrument maker, you will see a mark onone of its ends. Supposing, then, that you drew your needle along theend thus marked, and that the point of your needle was the last toquit the magnet, you will find that the point turns to the south, theeye of the needle turning towards the north. Make sure of this, anddo not take the statement on my authority. 

Now take a second darning-needle like the first, and magnetise it inprecisely the same manner: freely suspended it also will turn its eyeto the north and its point to the south. Your next step is to examinethe action of the two needles which you have thus magnetised upon eachother. 

Take one of them in your hand, and leave the other suspended; bringthe eye-end of the former near the eye-end of the latter; thesuspended needle retreats: it is repelled. Make the same experimentwith the two points; you obtain the same result, the suspended needleis repelled. Now cause the dissimilar ends to act on each other--youhave attraction--point attracts eye, and eye attracts point. Provethe reciprocity of this action by removing the suspended needle, andputting the other in its place. You obtain the same result. Theattraction, then, is mutual, and the repulsion U mutual. You havethus demonstrated in the clearest manner the fundamental law ofmagnetism, that like poles repel, and that unlike poles attract, eachother. You may say that this is all easily understood without doing;but _do it_, and your knowledge will not be confined to what I haveuttered here. 

I have said that one end of your bar magnet has a mark upon it; layseveral silk fibres together, so as to get sufficient strength, oremploy a thin silk ribbon, and form a loop large enough to hold yourmagnet. Suspend it; it turns its marked end towards the north. Thismarked end is that which in England is called the north pole. If acommon smith has made your magnet, it will be convenient to determineits north pole yourself, and to mark it with a file. Vary yourexperiments by causing your magnetised darning-needle to attract andrepel your large magnet; it is quite competent to do so. Inmagnetising the needle, I have supposed the point to be the last toquit the marked end of the magnet; the point of the needle is a southpole. The end which last quits the magnet is always opposed inpolarity to the end of the magnet with which it, has been last incontact. 

You may perhaps learn all this in a single hour; but spend several atit, if necessary; and remember, understanding it is not sufficient:you must obtain a manual aptitude in addressing Nature. If you speakto your fellow-man you are not entitled to use jargon. Badexperiments are jargon addressed to Nature, and just as much to bedeprecated. Manual dexterity in illustrating the interaction ofmagnetic poles is of the utmost importance at this stage of yourprogress; and you must not neglect attaining this power over yourimplements. As you proceed, moreover, you will be tempted to do morethan I can possibly suggest. Thoughts will occur to you which you willendeavour to follow out: questions will arise which you will try toanswer. The same experiment may be twenty different things to twentypeople. Having witnessed the action of pole on pole, through the air, you will perhaps try whether the magnetic power is not to be screenedoff. You use plates of glass, wood, slate, pasteboard, orgutta-percha, but find them all pervious to this wondrous force. Onemagnetic pole acts upon another through these bodies as if they werenot present. Should you ever become a patentee for the regulation ofships' compasses, you will not fall, as some projectors have done, into the error of screening off the magnetism of the ship by theinterposition of such substances. 

If you wish to teach a class you must contrive that the effects whichyou have thus far witnessed for yourself shall be witnessed by twentyor thirty pupils. And here your private ingenuity must come intoplay. You will attach bits of paper to your needles, so as to rendertheir movements visible at a distance, denoting the north and southpoles by different colours, say green and red. You may also improveupon your darning-needle. Take a strip of sheet steel, heat it tovivid redness and plunge it into cold water. It is thereby hardened;rendered, in fact, almost as brittle as glass. Six inches of this, magnetised in the manner of the darning-needle, will be better able tocarry your paper indexes. Having secured such a strip, you proceedthus:

Magnetise a small sewing-needle and determine its poles; or, breakhalf an inch, or an inch, off your magnetised darning-needle andsuspend it by a fine silk fibre. The sewing-needle, or the fragmentof the darning needle, is now to be used as a test-needle, to examinethe distribution of the magnetism in your strip of steel. Hold thestrip upright in your left hand, and cause the test-needle to approachthe lower end of your strip; one end of the test-needle is attracted, the other is repelled. Raise your needle along the strip; itsoscillations, which at first were quick, become slower; opposite themiddle of the strip they cease entirely; neither end of the needle isattracted; above the middle the test-needle turns suddenly round, itsother end being now attracted. Go through the experiment thoroughly:you thus learn that the entire lower half of the strip attracts oneend of the needle, while the entire upper half attracts the oppositeend. Supposing the north end of your little needle to be thatattracted below, you infer that the entire lower half of yourmagnetised strip exhibits south magnetism, while the entire upper halfexhibits north magnetism. So far, then, you have determined thedistribution of magnetism in your strip of steel. 

You look at this fact, you think of it; in its suggestiveness thevalue of an experiment chiefly consists. The thought naturallyarises: 'What will occur if I break my strip of steel across in themiddle? Shall I obtain two magnets each possessing a single pole?'Try the experiment; break your strip of steel, and test each half asyou tested the whole. The mere presentation of its two ends insuccession to your test-needle, suffices to show that you have _not_ amagnet with a single pole--that each half possesses two poles with aneutral point between them. And if you again break the half into twoother halves, you will find that each quarter of the original stripexhibits precisely the same magnetic distribution as the whole strip. You may continue the breaking process: no matter how small yourfragment may be, it still possesses two opposite poles and a neutralpoint between them. Well, your hand ceases to break where breakingbecomes a mechanical impossibility; but does the mind stop there? No:you follow the breaking process in idea when you can no longer realiseit in fact; your thoughts wander amid the very atoms of your steel, and you conclude that each atom is a magnet, and that the forceexerted by the strip of steel is the mere summation, or resultant, ofthe forces of its ultimate particles. 

Here, then, is an exhibition of power which we can call forth atpleasure or cause to disappear. We magnetise our strip, of steel bydrawing it along the pole of a magnet; we can demagnetise it, orreverse its magnetism, by properly drawing it along the same pole inthe opposite direction. What, then, is the real nature of thiswondrous change? What is it that takes place among the atoms of thesteel when the substance is magnetised? The question leads us beyondthe region of sense, and into that of imagination. This faculty, indeed, is the divining-rod of the man of science. Not, however, animagination which catches its creations from the air, but one informedand inspired by facts; capable of seizing firmly on a physical imageas a principle, of discerning its consequences, and of devising meanswhereby these forecasts of thought may be brought to an experimentaltest. If such a principle be adequate to account for all thephenomena--if from an assumed cause the observed acts necessarilyfollow, we call the assumption a theory, and, once possessing it, wecan not only revive at pleasure facts already known, but we canpredict others which we have never seen. Thus, then, in theprosecution of physical science, our powers of observation, memory, imagination, and inference, are all drawn upon. We observe facts andstore them up; the constructive imagination broods upon thesememories, tries to discern their interdependence and weave them to anorganic whole. The theoretic principle flashes or slowly dawns uponthe mind; and then the deductive faculty interposes to carry out theprinciple to its logical consequences. A perfect theory givesdominion over natural facts; and even an assumption which can onlypartially stand the test of a comparison with facts, may be of eminentuse in enabling us to connect and classify groups of phenomena. Thetheory of magnetic fluids is of this latter character, and with it wemust now make ourselves familiar. 

With the view of stamping the thing more firmly on your minds, I willmake use of a strong and vivid image. In optics, red and green arecalled complementary colours; their mixture produces white. Now I askyou to imagine each of these colours to possess a self-repulsivepower; that red repels red, that green repels green; but that redattracts green and green attracts red, the attraction of thedissimilar colours being equal to the repulsion of the similar ones. Imagine the two colours mixed so as to produce white, and suppose twostrips of wood painted with this white-; what will be their actionupon each other? Suspend one of them freely as we suspended ourdarning-needle, and bring the other near it; what will occur? The redcomponent of the strip you hold in your hand will repel the redcomponent of your suspended strip; but then it will attract the green, and, the forces being equal, they neutralise each other. In fact, theleast reflection shows you that the strips will be as indifferent toeach other as two unmagnetised darning-needles would be under the samecircumstances. 

But suppose, instead of mixing the colours, we painted one half ofeach strip from centre to end red, and the other half green, it isperfectly manifest that the two strips would now behave towards eachother exactly as our two magnetised darning-needles--the red end wouldrepel the red and attract the green, the green would repel the greenand attract the red; so that, assuming two colours thus related toeach other, we could by their mixture produce the neutrality of anunmagnetised body, while by their separation we could produce theduality of action of magnetised bodies. 

But you have already anticipated a defect in my conception; for if webreak one of our strips of wood in the middle we have one halfentirely red, and the other entirely green, and with these it would beimpossible to imitate the action of our broken magnet. How, then, must we modify our conception? We must evidently suppose _eachmolecule of the wood_ painted green on one face and red on the oppositeone. The resultant action of all the atoms would then exactlyresemble the action of a magnet. Here also, if the two oppositecolours of each atom could be caused to mix so as to produce white, weshould have, as before, perfect neutrality. 

For these two self-repellent and mutually attractive colours, substitute in your minds two invisible self-repellent and mutuallyattractive fluids, which in ordinary steel are mixed to form a neutralcompound, but which the act of magnetisation separates from eachother, placing the opposite fluids on the opposite face of eachmolecule. You have then a perfectly distinct conception of thecelebrated theory of magnetic fluids. The strength of the magnetismexcited is supposed to be proportional to the quantity of neutralfluid decomposed. According to this theory nothing is actuallytransferred from the exciting magnet to the excited steel. The act ofmagnetisation consists in the forcible separation of two fluids whichexisted in the steel before it was magnetised, but which thenneutralised each other by their coalescence. And if you test yourmagnet, after it has excited a hundred pieces of steel, you will findthat it has lost no force--no more, indeed, than I should lose, had mywords such a magnetic influence on your minds as to excite in them astrong resolve to study natural philosophy. I should rather be thegainer by my own utterance, and by the reaction of your fervour. Themagnet also is the gainer by the reaction of the body which itmagnetises. 

Look now to your excited piece of steel; figure each molecule with itsopposed fluids spread over its opposite faces. How can this state ofthings be permanent? The fluids, by hypothesis, attract each other;what, then, keeps them apart? Why do they not instantly rush togetheracross the equator of the atom, and thus neutralise each other? Tomeet this question philosophers have been obliged to infer theexistence of a special force, which holds the fluids asunder. Theycall it _coercive force_; and it is found that those kinds of steelwhich offer most resistance to being magnetised--which require thegreatest amount of 'coercion' to tear their fluids asunder--are thevery ones which offer the greatest resistance to the reunion of thefluids, after they have been once separated. Such kinds of steel aremost suited to the formation of _permanent_ magnets. It is manifest, indeed, that without coercive force a permanent magnet would not be atall possible. 

Probably long before this you will have dipped the end of your magnetamong iron filings, and observed how they cling to it; or into anail-box, and found how it drags the nails after it. I know very wellthat if you are not the slaves of routine, you will have by this timedone many things that I have not told you to do, and thus multipliedyour experience beyond what I have indicated. You are almost sure tohave caused a bit of iron to hang from the end of your magnet, and youhave probably succeeded in causing a second bit to attach itself tothe first, a third to the second; until finally the force has becometoo feeble to bear the weight of more. If you have operated withnails, you may have observed that the points and edges hold togetherwith the greatest tenacity; and that a bit of iron clings more firmlyto the corner of your magnet than to one of its flat surfaces. Inshort, you will in all likelihood have enriched your experience inmany ways without any special direction from me. 

Well, the magnet attracts the nail, and the nail attracts a secondone. This proves that the nail in contact with the magnet has had themagnetic quality developed in it by that contact. If it be withdrawnfrom the magnet its power to attract its fellow nail ceases. Contact, however, is not necessary. A sheet of glass or paper, or a space ofair, may exist between the magnet and the nail; the latter is stillmagnetised, though not so forcibly as when in actual contact. Thenail thus presented to the magnet is itself a temporary magnet. Thatend which is turned towards the magnetic pole has the oppositemagnetism of the pole which excites it; the end most remote from thepole has the same magnetism as the pole itself, and between the twopoles the nail, like the magnet, possesses a magnetic equator. 

Conversant as you now are with the theory of magnetic fluids, you havealready, I doubt not, anticipated me in imagining the exact conditionof an iron nail under the influence of the magnet. You picture theiron as possessing the neutral fluid in abundance; you picture themagnetic pole, when brought near, decomposing the fluid; repelling thefluid of a like kind with itself, and attracting the unlike fluid;thus exciting in the parts of the iron nearest to itself the oppositepolarity. But the iron is incapable of becoming a permanent magnet. It only shows its virtue as long as the magnet acts upon it. What, then, does the iron lack which the steel possesses? It lacks coerciveforce. Its fluids are separated with ease; but, once the separatingcause is removed, they flow together again, and neutrality isrestored. Imagination must be quite nimble in picturing thesechanges--able to see the fluids dividing and reuniting, according asthe magnet is brought near or withdrawn. Fixing a definite pole inyour mind, you must picture the precise arrangement of the two fluidswith reference to this pole, and be able to arouse similar pictures inthe minds of your pupils. You will cause them to place magnets andiron in various positions, and describe the exact magnetic state ofthe iron in each particular case. The mere facts of magnetism willhave their interest immensely augmented by an acquaintance with theprinciples whereon the facts depend. Still, while you use this theoryof magnetic fluids to track out the phenomena and link them together, you will not forget to tell your pupils that it is to be regarded as asymbol merely, --a symbol, moreover, which is incompetent to cover allthe facts, but which does good practical service whilst we are waitingfor the actual truth. [Footnote: This theory breaks down when appliedto diamagnetic bodies which are repelled by magnets. Like soft iron, such bodies are thrown into a state of temporary excitement, in virtueof which they are repelled; but any attempt to explain such arepulsion by the decomposition of a fluid will demonstrate its ownfutility. ]

The state of excitement into which iron is thrown by the influence, ofa magnet, is sometimes called 'magnetisation by influence. ' Morecommonly, however, the magnetism is said to be 'induced' in the iron, and hence this mode of magnetising is called 'magnetic induction. 'Now, there is nothing theoretically perfect in Nature: there is noiron so soft as not to possess a certain amount of coercive force, andno steel so hard as not to be capable, in some degree, of magneticinduction. The quality of steel is in some measure possessed by iron, and the quality of iron is shared in some degree by steel. It is invirtue of this latter fact that the unmagnetised darning-needle wasattracted in your first experiment; and from this you may at oncededuce the consequence that, after the steel has been magnetised, therepulsive action of a magnet must be always less than its attractiveaction. For the repulsion is opposed by the inductive action of themagnet on the steel, while the attraction is assisted by the sameinductive action. Make this clear to your minds, and verify it byyour experiments. In some cases you can actually make the attractiondue to the temporary magnetism overbalance the repulsion due to thepermanent magnetism, and thus cause two poles of the same kindapparently to attract each other. When, however, good hard magnetsact on each other from a sufficient distance, the inductive actionpractically vanishes, and the repulsion of like poles is sensiblyequal to the attraction of unlike ones. 

I dwell thus long on elementary principles, because they are of thefirst importance, and it is the temptation of this age of unhealthycramming to neglect them. Now follow me a little farther. Inexamining the distribution of magnetism in your strip of steel youraised the needle slowly from bottom to top, and found what we calleda neutral point at the centre. 

Now does the magnet really exert no influence on the pole presented toits centre? Let us see. 

Let SN, fig. 13, be our magnet, and let n represent a particle ofnorth magnetism placed exactly opposite the middle of the magnet. Ofcourse this is an imaginary case, as you can never in reality thusdetach your north magnetism from its neighbour. But supposing us tohave done so, what would be the action of the two poles of the magneton n? Your reply will of course be that the pole S attracts n whilethe pole N repels it. Let the magnitude and direction of theattraction be expressed by the line n m, and the magnitude anddirection of the repulsion by the line n o. Now, the particle n beingequally distant from s and N, the line n o, expressing the repulsion, will be equal to m n, which expresses the attraction. Acted upon bytwo such forces, the particle n must evidently move in the direction np, exactly midway between m n and n o. Hence you see that, althoughthere is no tendency of the particle n to move towards the magneticequator, there is a tendency on its part to move parallel to themagnet. If, instead of a particle of north magnetism, we placed aparticle of south magnetism opposite to the magnetic equator, it wouldevidently be urged along the line n q; and if, instead of two separateparticles of magnetism, we place a little magnetic needle, containingboth north and south magnetism, opposite the magnetic equator, itssouth pole being urged along n q, and its north along n p, the littleneedle will be compelled to set itself parallel to the magnet s N. Make the experiment, and satisfy yourselves that this is a truededuction. 

Substitute for your magnetic needle a bit of iron wire, devoid ofpermanent magnetism, and it will set itself exactly as the needledoes. Acted upon by the magnet, the wire, as you know, becomes amagnet and behaves as such; it will turn its north pole towards p, andsouth pole towards q, just like the needle. 

But supposing you shift the position of your particle of northmagnetism, and bring it nearer to one end of your magnet than to theother; the forces acting on the particle are no longer equal; thenearest pole of the magnet will act more powerfully on the particlethan the more distant one. Let SN, fig. 14, be the magnet, and n theparticle of north magnetism, in its new position. It is repelled byN, and attracted by S. Let the repulsion be represented in magnitudeand direction by the line n o, and the attraction by the shorter linen M. The resultant of these two forces will be found by completing theparallelogram m n o p, and drawing its diagonal n p. Along n p, then, a particle of north magnetism would be urged by the simultaneousaction of S and N. Substituting a particle of south magnetism for n, the same reasoning would lead to the conclusion that the particlewould be urged along it q. If we place at n a short magnetic needle, its north pole will be urged along n p, its south pole along n q, theonly position possible to the needle, thus acted on, being along theline p q, which is no longer parallel to the magnet. Verify thisdeduction by actual experiment. 

In this way we might go round the entire magnet; and, considering itstwo poles as two centres from which the force emanates, we could, inaccordance with ordinary mechanical principles, assign a definitedirection to the magnetic needle at every particular place. Andsubstituting, as before, a bit of iron wire for the magnetic needle, the positions of both will be the same. 

Now, I think, without further preface, you will be able' to comprehendfor yourselves, and explain to others, one of the most interestingeffects in the whole domain of magnetism. Iron filings you know areparticles of iron, irregular in shape, being longer in some directionsthan in others. For the present experiment, moreover, instead of theiron filings, very small scraps of thin iron wire might be employed. Iplace a sheet of paper over the magnet; it is all the better if thepaper be stretched on a wooden frame as this enables us to keep itquite level. I scatter the filings, or the scraps of wire, from asieve upon the paper, and tap the latter gently, so as to liberate theparticles for a moment from its friction. The magnet acts on thefilings through the paper, and see how it arranges them! Theyembrace the magnet in a series of beautiful curves, which aretechnically called 'magnetic curves, ' or 'lines of magnetic force. 'Does the meaning of these lines yet flash upon you? Set your magneticneedle, or your suspended bit of wire, at any point of one of thecurves, and you will find the direction of the needle, or of the wire, to be exactly that of the particle of iron, or of the magnetic curve, at that point. Go round and round the magnet; the direction of yourneedle always coincides with the direction of the curve on which it isplaced. These, then, are the lines along which a particle of southmagnetism, if you could detach it, would move to the north pole, and abit of north magnetism to the south pole. They are the lines alongwhich the decomposition of the neutral fluid takes place. In the caseof the magnetic needle, one of its poles being urged in one direction, and the other pole in the opposite direction, the needle mustnecessarily set itself as a _tangent_ to the curve. I will not seek tosimplify this subject further. If there be anything obscure orconfused or incomplete in my statement, you ought now, by patientthought, to be able to clear away the obscurity, to reduce theconfusion to order, and to supply what is needed to render theexplanation complete. Do not quit the subject until you thoroughlyunderstand it; and if you are then able to look with your mind's eyeat the play of forces around a magnet, and see distinctly theoperation of those forces in the production of the magnetic curves, the time which we have spent together will not have been spent invain. 

FIG. 15. 

In this thorough manner we must master our materials, reason uponthem, and, by determined study, attain to clearness of conception. Facts thus dealt with exercise an expansive force upon the intellect;they widen the mind to generalisation. We soon recognise abrotherhood between the larger phenomena of Nature and the minuteeffects which we have observed in our private chambers. Why, weenquire, does the magnetic needle set north and south? Evidently itis compelled to do so by the earth; the great globe which we inheritis itself a magnet. Let us learn a little more about it. By means ofa bit of wax, or otherwise, attach the end of your silk fibre to themiddle point of your magnetic needle; the needle will thus beuninterfered with by the paper loop, and will enjoy to some extent apower of dipping' its point, or its eye, below the horizon. Lay yourbar magnet on a table, and hold the needle over the equator of themagnet. The needle sets horizontal. Move it towards the north end ofthe magnet; the south end of the needle dips, the dip augmenting asyou approach the north pole, over which the needle, if free to move, will set itself exactly vertical. Move it back to the centre, itresumes its horizontality; pass it on towards the south pole, itsnorth end now dips, and directly over the south pole the needlebecomes vertical, its north end being now turned downwards. Thus welearn that on the one side of the magnetic equator the north end ofthe needle dips; on the other side the south end dips, the dip varyingfrom nothing to 90°. If we go to the equatorial regions of the earthwith a suitably suspended needle we shall find there the position ofthe needle horizontal. If we sail north one end of the needle dips;if we sail south the opposite end dips; and over the north or southterrestrial magnetic pole the needle sets vertical. The southmagnetic pole has not yet been found, but Sir James Ross discoveredthe north magnetic pole on June 1, 1831. In this manner we establisha complete parallelism between the action of the earth and that of anordinary magnet. 

The terrestrial magnetic poles do not coincide with the geographicalones; nor does the earth's magnetic equator quite coincide with thegeographical equator. The direction of the magnetic needle in London, which is called the magnetic meridian, encloses an angle of 24° withthe astronomical meridian, this angle being called the Declination ofthe needle for London. The north, pole of the needle now lies to thewest of the true meridian; the declination is westerly. In the year1660, however, the declination was nothing, while before that time itwas easterly. All this proves that the earth's magnetic constituentsare gradually changing their distribution. This change is very slow:it is therefore called the secular change, and the observation of ithas not yet extended over a sufficient period to enable us to guess, even approximately, at its laws. 

Having thus discovered, to some extent, the secret of the earth'smagnetic power, we can turn it to account. In the line of 'dip' Ihold a poker formed of good soft iron. The earth, acting as a magnet, is at this moment constraining the two fluids of the poker toseparate, making the lower end of the poker a north pole, and theupper end a south pole. Mark the experiment: When the knob isuppermost, it attracts the north end of a magnetic needle; whenundermost it attracts the south end of a magnetic needle. With such apoker repeat this experiment and satisfy yourselves that the fluidsshift their position according to the manner in which the poker ispresented to the earth. It has already been stated that the softestiron possesses a certain amount of coercive force. The earth, at thismoment, finds in this force an antagonist which opposes thedecomposition of the neutral fluid, The component fluids may befigured as meeting an amount of friction, or possessing an amount ofadhesion, which prevents them from gliding over the molecules of thepoker. Can we assist the earth in this case? If we wish to removethe residue of a powder from the interior surface of a glass to whichthe powder clings, we invert the glass, tap it, loosen the hold of thepowder, and thus enable the force of gravity to pull it down. So alsoby tapping the end of the poker we 'loosen the adhesion of themagnetic fluids to the molecules and enable the earth to pull themapart. But, what is the consequence? The portion of fluid which hasbeen thus forcibly dragged over the molecules refuses to return whenthe poker has been removed from the line of dip; the iron, as you see, has become a permanent magnet. By reversing its position and tappingit again we reverse its magnetism. A thoughtful and competent teacherwill know how to place these remarkable facts before his pupils in amanner which will excite their interest. By the use of sensibleimages, more or less gross, he will first give those whom he teachesdefinite conceptions, purifying these conceptions afterwards, as theminds of his pupils become more capable of abstraction. By thusgiving them a distinct substratum for their reasonings, he will conferupon his pupils a profit and a joy which the mere exhibition of factswithout principles, or the appeal to the bodily senses and the powerof memory alone, could never inspire. 

*****

As an expansion of the note on magnetic fluids, the following extractmay find a place here: 'It is well known that a voltaic currentexerts an attractive force upon a second current, flowing in the samedirection; and that when the directions are opposed to each other theforce exerted is a repulsive one. By coiling wires into spirals, Ampère was enabled to make them produce all the phenomena ofattraction and repulsion exhibited by magnets, and from this it wasbut a step to his celebrated theory of molecular currents. Hesupposed the molecules of a magnetic body to be surrounded by suchcurrents, which, however, in the natural state of the body mutuallyneutralised each other, on account of their confused grouping. Theact of magnetisation he supposed to consist in setting these molecularcurrents parallel to each other; and, starting from this principle, hereduced all the phenomena of magnetism to the mutual action ofelectric currents. 

'If we reflect upon the experiments recorded in the foregoing pagesfrom first to last, we can hardly fail to be convinced thatdiamagnetic bodies operated on by magnetic forces possess a polarity"the same in kind as, but the reverse in direction of, that acquiredby magnetic bodies. " But if this be the case, how are we to conceivethe _physical mechanism_ of this polarity? According to Coulomb's andPoisson's theory, the act of magnetisation consists in thedecomposition of a neutral magnetic fluid; the north pole of a magnet, for example, possesses an attraction for the south fluid of a piece ofsoft iron submitted to its influence, draws the said fluid towards it, and with it the material particles with which the fluid is associated. To account for diamagnetic phenomena this theory seems to failaltogether; according to it, indeed, the oft-used phrase, "a northpole exciting a north pole, and a south pole a south pole, " involves acontradiction. For if the north fluid be supposed to be _attracted_towards the influencing north pole, it is absurd to suppose that itspresence there could produce _repulsion_. The theory of Ampère isequally at a loss to explain diamagnetic action; for if we suppose theparticles of bismuth surrounded by molecular currents, then, accordingto all that is known of electrodynamic laws, these currents would setthemselves parallel to, and in the same direction as, those of themagnet, and hence attraction, and not repulsion, would be the result. The fact, however, of this not being the case, proves that thesemolecular currents are not the mechanism by which diamagneticinduction is effected. The consciousness of this, I doubt not, droveM. Weber to the assumption that the phenomena of diamagnetism areproduced by molecular currents, not _directed_, but actually _excited_ inthe bismuth by the magnet. Such induced currents would, according toknown laws, have a direction opposed to those of the inducing magnet, and hence would produce the phenomena of repulsion. To carry out theassumption here made, M. Weber is obliged to suppose that themolecules of diamagnetic bodies are surrounded by channels, in whichthe induced molecular currents, once excited, continue to flow withoutresistance. ' [Footnote: In assuming these non-resisting channels M. Weber, it must be admitted, did not go beyond the assumptions ofAmpère. ]--Diamagnetism and Magne-crystallic Action, p. 136-7. 

********************

XVI. ON FORCE. 

[Footnote: A discourse delivered in the Royal Institution, June 6, 1862. ]

A SPHERE of lead was suspended at a height of 16 feet above thetheatre floor of the Royal Institution. It was liberated, and fell bygravity. That weight required a second to fall to the floor from thatelevation; and the instant before it touched the floor, it had avelocity of 32 feet a second. That is to say, if at that instant theearth were annihilated, and its attraction annulled, the weight wouldproceed through space at the uniform velocity of 32 feet a second. 

If instead of being pulled downward by gravity, the weight be castupward in opposition to gravity, then, to reach a height of 16 feet itmust start with a velocity of 32 feet a second. This velocityimparted to the weight by the human hand, or by any other mechanicalmeans, would carry it to the precise height from which we saw it fall. 

Now the lifting of the weight may be regarded as so much mechanicalwork performed. By means of a ladder placed against the wall, theweight might be carried up to a height of 16 feet; or it might bedrawn up to this height by means of a string and pulley, or it mightbe suddenly jerked up to a height of 16 feet. The amount of work donein all these cases, as far as the raising of the weight is concerned, would be absolutely the same. The work done at one and the sameplace, and neglecting the small change of gravity with the height, depends solely upon two things; on the quantity of matter lifted, andon the height to which it is lifted. If we call the quantity or massof matter m, and the height through which it is lifted h, then theproduct of m into h, or mh, expresses, or is proportional to, theamount of work done. 

Supposing, instead of imparting a velocity of 32 feet a second weimpart at starting twice this velocity. To what height will theweight rise? You might be disposed to answer, 'To twice the height;'but this would be quite incorrect. Instead of twice 16, or 32 feet, it would reach a height of four times 16, or 64 feet. So also, if wetreble the starting velocity, the weight would reach nine times theheight; if we quadruple the speed at starting, we attain sixteen timesthe height. Thus, with a four-fold velocity of 128 feet a second atstarting, the weight would attain an elevation of 256 feet. With aseven-fold velocity at starting, the weight would rise to 49 times theheight, or to an elevation of 784 feet. 

Now the work done--or, as it is sometimes called, the _mechanicaleffect_--other things being constant, is, as before explained, proportional to the height, and as a double velocity gives four timesthe height, a treble velocity nine times the height, and so on, it isperfectly plain that the mechanical effect increases as the square ofthe velocity. If the mass of the body be represented by the letter m, and its velocity by v, the mechanical effect would be proportional toor represented by m v2. In the case considered, I have supposed theweight to be cast upward, being opposed in its flight by theresistance of gravity; but the same holds true if the projectile besent into water, mud, earth, timber, or other resisting material. If, for example, we double the velocity of a cannon-ball, we quadruple itsmechanical effect. Hence the importance of augmenting the velocity ofa projectile, and hence the philosophy of Sir William Armstrong inusing a large charge of powder in his recent striking experiments. 

The measure then of mechanical effect is the mass of the bodymultiplied by the square of its velocity. 

Now in firing a ball against a target the projectile, after collision, is often found hot. Mr. Fairbairn informs me that in the experimentsat Shoeburyness it is a common thing to see a flash, even in broaddaylight, when the ball strikes the target. And if our lead weight beexamined after it has fallen from a height it is also found heated. Now here experiment and reasoning lead us to the remarkable law that, like the mechanical effect, the amount of heat generated isproportional to the product of the mass into the square of thevelocity. Double your mass, other things being equal, and you doubleyour amount of heat; double your velocity, other things remainingequal, and you quadruple your amount of heat. Here then we havecommon mechanical motion destroyed and heat produced. When a violinbow is drawn across a string, the sound produced is due to motionimparted to the air, and to produce that motion muscular force hasbeen expended. We may here correctly say, that the mechanical forceof the arm is converted into music. In a similar way we say that thearrested motion of our descending weight, or of the cannon-ball, isconverted into heat. The mode of motion changes, but motion stillcontinues; the motion of the mass is converted into a motion of theatoms of the mass; and these small motions, communicated to thenerves, produce the sensation we call heat. 

We know the amount of heat which a given amount of mechanical forcecan develope. Our lead ball, for example, in falling to the earthgenerated a quantity of heat sufficient to raise its own temperaturethree-fifths of a Fahrenheit degree. It reached the earth with avelocity of 32 feet a second, and forty times this velocity would besmall for a rifle bullet; multiplying 0. 6 by the square of 40, we findthat the amount of heat developed by collision with the target would, if wholly concentrated in the lead, raise its temperature 960 degrees. This would be more than sufficient to fuse the lead. In reality, however, the heat developed is divided between the lead and the bodyagainst which it strikes; nevertheless, it would be worth while to payattention to this point, and to ascertain whether rifle bullets donot, under some circumstances, show signs of fusion. [Footnote: Eightyears subsequently this surmise was proved correct. In theFranco-German War signs of fusion were observed in the case of bulletsimpinging on bones. ]

From the motion of sensible masses, by gravity and other means, we nowpass to the motion of atoms towards each other by chemical affinity. Acollodion balloon filled with a mixture of chlorine and hydrogen beinghung in the focus of a parabolic mirror, in the focus of a secondmirror 20 feet distant a strong electric light was suddenly generated;the instant the concentrated light fell upon the balloon, the gaseswithin it exploded, hydrochloric acid being the result. Here the atomsvirtually fell together, the amount of heat produced showing theenormous force of the collision. The burning of charcoal in oxygen isan old experiment, but it has now a significance beyond what it usedto have; we now regard the act of combination on the part of the atomsof oxygen and coal as we regard the clashing of a falling weightagainst the earth. The heat produced in both cases is referable to acommon cause. A diamond, which burns in oxygen as a star of whitelight, glows and burns in consequence of the falling of the atoms ofoxygen against it. And could we measure the velocity of the atomswhen they clash, and could we find their number and weights, multiplying the weight of each atom by the square of its velocity, andadding all together, we should get a number representing the exactamount of heat developed by the union of the oxygen and carbon. 

Thus far we have regarded the heat developed by the clashing ofsensible masses and of atoms. Work is expended in giving motion tothese atoms or masses, and heat is developed. But we reverse thisprocess daily, and by the expenditure of heat execute work. We canraise a weight by heat; and in this agent we possess an enormous storeof mechanical power. A pound of coal produces by its combination withoxygen an amount of heat which, if mechanically applied, would sufficeto raise a weight of 100 lbs. To a height of 20 miles above theearth's surface. Conversely, 100 lbs. Falling from a height of 20miles, and striking against 'the earth, would generate an amount ofheat equal to that developed by the combustion of a pound of coal. Wherever work is done by heat, heat disappears. A gun which fires aball is less heated than one which fires blank cartridge. Thequantity of heat communicated to the boiler of a working steam-engineis greater than that which could be obtained from the re-condensationof the steam, after it had done its work; and the amount of workperformed is the exact equivalent of the amount of heat lost. Mr. Smyth informed us in his interesting discourse, that we dig annually84 millions of tons of coal from our pits. The amount of mechanicalforce represented by this quantity of coal seems perfectly fabulous. The combustion of a single pound of coal, supposing it to take placein a minute, would be equivalent to the work of 300 horses; and if wesuppose 108 millions of horses working day and night with unimpairedstrength, for a year, their united energies would enable them toperform an amount of work just equivalent to that which the annualproduce of our coal-fields would be able to accomplish. 

Comparing with ordinary gravity the force with which oxygen and carbonunite together, chemical affinity seems almost infinite. But let usgive gravity fair play by permitting it to act throughout its entirerange. Place a body at such a distance from the earth that theattraction of our planet is barely sensible, and let it fall to theearth from this distance. It would reach the earth with a finalvelocity of 36, 747 feet a second; and on collision with the earth thebody would generate about twice the amount of heat generated by thecombustion of an equal weight of coal. We have stated that by fallingthrough a space of 16 feet our lead bullet would be heatedthree-fifths of a degree; but a body falling from an infinite distancehas already used up 1, 299, 999 parts out of 1, 300, 000 of the earth'spulling power, when it has arrived within 16 feet of the surface; onthis space only 1/1, 300, 000 of the whole force is exerted. 

Let us now turn our thoughts for a moment from the earth to the sun. The researches of Sir John Herschel and M. Pouillet have informed usof the annual expenditure of the sun as regards heat; and by an easycalculation we ascertain the precise amount of the expenditure whichfalls to the share of our planet. Out of 2300 million parts of lightand heat the earth receives one. The whole heat emitted by the sun ina minute would be competent to boil 12, 000 millions of cubic miles ofice-cold water. How is this enormous loss made good--whence is thesun's heat derived, and by what means is it maintained? Nocombustion--no chemical affinity with which we are acquainted, wouldbe competent to produce the temperature of the sun's surface. Besides, were the sun a burning body merely, its light and heat wouldspeedily come to an end. Supposing it to be a solid globe of coal, its combustion would only cover 4600 years of expenditure. In thisshort time it would burn itself out. What agency then can produce thetemperature and maintain the outlay? We have already regarded thecase of a body falling from a great distance towards the earth, andfound that the heat generated by its collision would be twice thatproduced by the combustion of an equal weight of coal. How muchgreater must be the heat developed by a body falling against the sun!The maximum velocity with which a body can strike the earth is about 7miles in a second; the maximum velocity with which it can strike thesun is 390 miles in a second. And as the heat developed by thecollision is proportional to the square of the velocity destroyed, anasteroid falling into the sun with the above velocity would generateabout 10, 000 times the quantity of heat produced by the combustion ofan asteroid of coal of the same weight. 

Have we any reason to believe that such bodies exist in space, andthat they may be raining down upon the sun? The meteorites flashingthrough the air are small planetary bodies, drawn by the earth'sattraction. They enter our atmosphere with planetary velocity, and byfriction against the air they are raised to incandescence and causedto emit light and heat. At certain seasons of the year they showerdown upon us in great numbers. In Boston 240, 000 of them wereobserved in nine hours. There is no reason to suppose that theplanetary system is limited to 'vast masses of enormous weight;' thereis, on the contrary, reason to believe that space is stocked withsmaller masses, which obey the same laws as the larger ones. Thatlenticular envelope which surrounds the sun, and which is known toastronomers as the Zodiacal light, is probably a crowd of meteors; andmoving as they do in a resisting medium, they must continuallyapproach the sun. Falling into it, they would produce enormous heat, and this would constitute a source from which the annual loss of heatmight be made good. The sun, according to this hypothesis, wouldcontinually grow larger; but how much larger? Were our moon to fallinto the sun, it would develope an amount of heat sufficient to coverone or two years' loss; and were our earth to fall into the sun acentury's loss would be made good. Still, our moon and our earth, ifdistributed over the surface of the sun, would utterly vanish fromperception. Indeed, the quantity of matter competent to produce therequired effect would, during the range of history, cause noappreciable augmentation in the sun's magnitude. The augmentation ofthe sun's attractive force would be more sensible. However thishypothesis may fare as a representant of what is going on in nature, it certainly shows how a sun _might_ be formed and maintained on knownthermo-dynamic principles. 

Our earth moves in its orbit with a velocity of 68, 040 miles an hour. Were this motion stopped, an amount of heat would be developedsufficient to raise the temperature of a globe of lead of the samesize as the earth 384, 000 degrees of the centigrade thermometer. Ithas been prophesied that 'the elements shall melt with fervent heat. 'The earth's own motion embraces the conditions of fulfilment; stopthat motion, and the greater part, if not the whole, of our planetwould be reduced to vapour. If the earth fell into the sun, theamount of heat developed by the shock would be equal to that developedby the combustion of a mass of solid coal 6435 times the earth insize. 

There is one other consideration connected with the permanence of ourpresent terrestrial conditions, which is well worthy of our attention. Standing upon one of, the London bridges, we observe the current ofthe Thames reversed, and the water poured upward twice a-day. Thewater thus moved rubs against the river's bed, and heat is theconsequence of this friction. The heat thus generated is in partradiated into space and lost, as far as the earth is concerned. Whatsupplies this incessant loss? The earth's rotation. Let us look alittle more closely at the matter. Imagine the moon fixed, and theearth turning like a wheel from west to east in its diurnal rotation. Suppose a high mountain on the earth's surface approaching the earth'smeridian; that mountain is, as it were, laid hold of by the moon; itforms a kind of handle by which the earth is pulled more quicklyround. But when the meridian is passed the pull of the moon on themountain would be in the opposite direction, it would tend to diminishthe velocity of rotation as much as it previously augmented it; thusthe action of all fixed bodies on the earth's surface is neutralised. But suppose the mountain to lie always to the east of the moon'smeridian, the pull then would be always exerted against the earth'srotation, the velocity of which would be diminished in a degreecorresponding to the strength of the pull. _The tidal wave occupiesthis position_--it lies always to the east of the moon's meridian. Thewaters of the ocean are in part dragged as a brake along the surfaceof the earth; and as a brake they must diminish the velocity of theearth's rotation. [Footnote: Kant surmised an action of this kind. ]Supposing then that we turn a mill by the action of the tide, andproduce heat by the friction of the millstones; that heat has anorigin totally different from the heat produced by another mill whichis turned by a mountain stream. The former is produced at the expenseof the earth's rotation, the latter at the expense of the sun'sradiation. 

The sun, by the act of vaporisation, lifts mechanically all themoisture of our air, which when it condenses falls in the form ofrain, and when it freezes falls as snow. In this solid form it ispiled upon the Alpine heights, and furnishes materials for glaciers. But the sun again interposes, liberates the solidified liquid, andpermits it to roll by gravity to the sea. The mechanical force ofevery river in the world as it rolls towards the ocean, is drawn fromthe heat of the sun. No streamlet glides to a lower level withouthaving been first lifted to the elevation from which it springs by thepower of the sun. The energy of winds is also due entirely to thesame power. 

But there is still another work which the sun performs, and itsconnection with which is not so obvious. Trees and vegetables growupon the earth, and when burned they give rise to heat, and hence tomechanical energy. Whence is this power derived? You see this oxideof iron, produced by the falling together of the atoms of iron andoxygen; you cannot see this transparent carbonic acid gas, formed bythe falling together of carbon and oxygen. The atoms thus in closeunion resemble our lead weight while resting on the earth; but we canwind up the weight and prepare it for another fall, and so these atomscan be wound up and thus enabled to repeat the process of combination. In the building of plants carbonic acid is the material from which thecarbon of the plant is derived; and the solar beam is the agent whichtears the atoms asunder, setting the oxygen free, and allowing thecarbon to aggregate in woody fibre. Let the solar rays fall upon asurface of sand; the sand is heated, and finally radiates away as muchheat as it receives; let the same beams fall upon a forest, thequantity of heat given back is less than the forest receives; for theenergy of a portion of the sunbeams is invested in building the trees. Without the sun the reduction of the carbonic acid cannot be effected, and an amount of sunlight is consumed exactly equivalent to themolecular work done. Thus trees are formed; thus the cotton on whichMr. Bazley discoursed last Friday is produced. I ignite this cotton, and it flames; the oxygen again unites with the carbon; but an amountof heat equal to that produced by its combustion was sacrificed by thesun to form that bit of cotton. 

We cannot, however, stop at vegetable life, for it is the source, mediate or immediate, of all animal life. The sun severs the carbonfrom its oxygen and builds the vegetable; the animal consumes thevegetable thus formed, a reunion of the severed elements takes place, producing animal heat. The process of building a vegetable is one ofwinding up; the process of building an animal is one of running down. The warmth of our bodies, and every mechanical energy which we exert, trace their lineage directly to the sun. 

The fight of a pair of pugilists, the motion of an army, or thelifting of his own body by an Alpine climber up a mountain slope, areall cases of mechanical energy drawn from the sun. A man weighing 150pounds has 64 pounds of muscle; but these, when dried, reducethemselves to 15 pounds. Doing an ordinary day's work, for eightydays, this mass of muscle would be wholly oxidised. Special organswhich do more work would be more quickly consumed: the heart, forexample, if entirely unsustained, would be oxidised in about a week. Take the amount of heat due to the direct oxidation of a given weightof food; less heat is developed by the oxidation of the same amount offood in the working animal frame, and the missing quantity is theequivalent of the mechanical work accomplished by the muscles. 

I might extend these considerations; the work, indeed, is done to myhand--but I am warned that you have been already kept too long. Towhom then are we indebted for the most striking generalisations ofthis evening's discourse? They are the work of a man of whom you havescarcely ever heard--the published labours of a German doctor, namedMayer. Without external stimulus, and pursuing his profession as townphysician in Heilbronn, this man was the first to raise the conceptionof the interaction of heat and other natural forces to clearness inhis own mind. And yet he is scarcely ever heard of, and even toscientific men his merits are but partially known. Led by his ownbeautiful researches, and quite independent of Mayer, Mr. Joulepublished in 1843 his first paper on the 'Mechanical Value of Heat;'but in 1842 Mayer had actually calculated the mechanical equivalent ofheat from data which only a man of the rarest penetration could turnto account. 

In 1845 he published his memoir on 'Organic Motion, ' and applied themechanical theory of heat in the most fearless and precise manner tovital processes. He also embraced the other natural agents in hischain of conservation. In 1853 Mr. Waterston proposed, independently, the meteoric theory of the sun's heat, and in 1854 Professor WilliamThomson applied his admirable mathematical powers to the developmentof the theory; but six years previously the subject had been handledin a masterly manner by Mayer, and all that I have said about it hasbeen derived from him. When we consider the circumstances of Mayer'slife, and the period at which he wrote, we cannot fail to be struckwith astonishment at what he has accomplished. Here was a man ofgenius working in silence, animated solely by a love of his subject, and arriving at the most important results in advance of those whoselives were entirely devoted to Natural Philosophy. It was theaccident of bleeding a feverish patient at Java in 1840 that led Mayerto speculate on these subjects. He noticed that the venous blood inthe tropics was of a brighter red than in colder latitudes, and hisreasoning on this fact led him into the laboratory of natural forces, where he has worked with such signal ability and success. Well, youwill desire to know what has become of this man. His mind, it isalleged, gave way; it is said he became insane, and he was certainlysent to a lunatic asylum. In a biographical dictionary of his countryit is stated that he died there, but this is incorrect. He recovered;and, I believe, is at this moment a cultivator of vineyards inHeilbronn. 

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June 20, 1862. 

While preparing for publication my last course of lectures on Heat, Iwished to make myself acquainted with all that Dr. Mayer had done inconnection with this subject. I accordingly wrote to two gentlemenwho above all others seemed likely to give me the information which Ineeded. [Footnote: Helmholtz and Clausius. ] Both of them are Germans, and both particularly distinguished in connection with the DynamicalTheory of Heat. Each of them kindly furnished me with the list ofMayer's publications, and one of them [Clausius] was so friendly as toorder them from a bookseller, and to send them to me. This friend, inhis reply to my first letter regarding Mayer, stated his belief that Ishould not find anything very important in Mayer's writings; butbefore forwarding the memoirs to me he read them himself. His letteraccompanying them contains the following words: 'I must here retractthe statement in my last letter, that you would not find much matterof importance in Mayer's writings: I am astonished at the multitude ofbeautiful and correct thoughts which they contain;' and he goes on topoint out various important subjects, in the treatment of which Mayerhad anticipated other eminent writers. My other friend, in whose ownpublications the name of Mayer repeatedly occurs, and whose paperscontaining these references were translated some years ago by myself, was, on the 10th of last month, unacquainted with the thoughtful andbeautiful essay of Mayer's, entitled 'Beitraege zur Dynamik desHimmels, ' and in 1854, when Professor William Thomson developed in sostriking a manner the meteoric theory of the sun's heat, he wascertainly not aware of the existence of that essay, though from arecent article in 'Macmillan's Magazine' I infer that he is now awareof it. Mayer's physiological writings have been referred to byphysiologists--by Dr. Carpenter, for example--in terms of honouringrecognition. We have hitherto, indeed, obtained fragmentary glimpsesof the man, partly from physicists and partly from physiologists; buthis total merit has never yet been recognised as it assuredly wouldhave been had he chosen a happier mode of publication. I do not thinka greater disservice could be done to a man of science, than tooverstate his claims: such overstatement is sure to recoil to thedisadvantage of him in whose interest it is made. But when Mayer'sopportunities, achievements, and fate are taken into account, I do notthink that I shall be deeply blamed for attempting to place him inthat honourable position, which I believe to be his due. 

Here, however, are the titles of Mayer's papers, the perusal of whichwill correct any error of judgment into which I may have fallenregarding their author. 'Bemerkungen ueber die Kraefte der unbelebtenNatur, ' Liebig's 'Annalen, ' 1842, Vol. 42, p. 231; 'Die OrganischeBewegung in ihrem Zusammenhange mit dem Stoffwechsel, ' Heilbronn, 1845; 'Beitraege zur Dynamik des Himmels, ' Heilbronn, 1848;'Bemerkungen ueber das Mechanische Equivalent der Waerme, ' Heilbronn, 1851. 

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IN MEMORIAM. --Dr. Julius Robert Mayer died at Heilbronn on March 20, 1878, aged 63 years. It gives me pleasure to reflect that the greatpositionwhich he will for ever occupy in the annals of science wasfirst virtually assigned to him in the foregoing discourse. He wassubsequently hosen by acclamation a member of the French Academy ofSciences; and he received from the Royal Society the Copley medal-itsHighest reward. [Footnote: See 'The Copley Medalist for 1871, ' p. 479. ]

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November 1878. 

At the meeting of the British Association at Glasgow in 1876--that isto say, more than fourteen years after its delivery andpublication--the foregoing lecture was made the cloak for an unseemlypersonal attack by Professor Tait. The anger which found thisuncourteous vent dates from 1863, when it fell to my lot to maintain, in opposition to him and a more eminent colleague, the position whichin 1862 I had assigned to Dr. Mayer. [Footnote: See 'PhilosophicalMagazine' for this and the succeeding years. ] In those days ProfessorTait denied to Mayer all originality, and he has since, I regret to say, never missed an opportunity, however small, of carping at Mayer'sclaims. The action of the Academy of Sciences and of the Royal Societysummarily disposes of this detraction, to which its object, during hislifetime, never vouchsafed either remonstrance or reply. 

Some time ago Professor Tait published a volume of lectures entitled'Recent Advances in Physical Science, ' which I have reason to know hasevoked an amount of censure far beyond that hitherto publiclyexpressed. Many of the best heads on the continent of Europe agree intheir rejection and condemnation of the historic portions of thisbook. In March last it was subjected to a brief but pungent critiqueby Du Bois-Reymond, the celebrated Perpetual Secretary of the Academyof Sciences in Berlin. Du Bois-Reymond's address was on 'NationalFeeling, ' and his critique is thus wound up: 'The author of the"Lectures" is not, perhaps, sufficiently well acquainted with thehistory on which he professes to throw light, and on the later phasesof which he passes so unreserved (schroff) a judgment. He thusexposes himself to the suspicion--which, unhappily, is not weakened byhis other writings--that the fiery Celtic blood of his countryoccasionally runs away with him, converting him for the time into ascientific Chauvin. Scientific Chauvinism, ' adds the learnedsecretary, 'from which German investigators have hitherto kept free, is more reprehensible (gehaessig) than political Chauvinism, inasmuchas self-control (_sittliche Haltung_) is more to be expected from men ofscience, than from the politically excited mass. ' [Footnote: Festrede, delivered before the Academy of Sciences of Berlin, in celebration ofthe birthday of the Emperor and King, March 28, 1878. ]

In the case before this 'expectation' would, I fear, be doomed todisappointment. But Du Bois-Reymond and his countrymen must notaccept the writings of Professor Tait as representative of the thoughtof England. Surely no nation in the world has more effectually shakenitself free from scientific Chauvinism. From the day that Davy, onpresenting the Copley medal to Arago, scornfully brushed aside thatspurious patriotism which would run national boundaries through thefree domain of science, chivalry towards foreigners has been a guidingprinciple with the Royal Society. 

On the more private amenities indulged in by Professor Tait, I do notconsider it necessary to say a word. 

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XVII. CONTRIBUTIONS TO MOLECULAR PHYSICS. 

[Footnote: A discourse delivered at the Royal Institution, March 18, 1864--supplementing, though of prior date, the Rede Lecture onRadiation. ]

HAVING on previous occasions dwelt upon the enormous differences whichexist among gaseous bodies both as regards their power of absorbingand emitting radiant heat, I have now to consider the effect of achange of aggregation. When a gas is condensed to a liquid, or aliquid congealed to a solid, the molecules coalesce, and grapple witheach other by forces which are insensible as long as the gaseous stateis maintained. But, even in the solid and liquid conditions, theluminiferous aether still surrounds the molecules: hence, if the actsof radiation and absorption depend on them individually, regardless oftheir state of aggregation, the change from the gaseous to the liquidstate ought not materially to affect the radiant and absorbent power. If, on the contrary, the mutual entanglement of the molecular by theforce of cohesion be of paramount influence, then we may expect thatliquids will exhibit a deportment towards radiant heat altogetherdifferent from that of the vapours from which they are derived. 

The first part of an enquiry conducted in 1863-64 was devoted to anexhaustive examination of this question. Twelve different liquidswere employed, and five different layers of each, varying in thicknessfrom 0. 02 of an inch to 0. 27 of an inch. The liquids were enclosed, not in glass vessels, which would have materially modified theincident heat, but between plates of transparent rock-salt, which onlyslightly affected the radiation. The source of heat throughout thesecomparative experiments consisted of a platinum wire, raised toincandescence by an electric current of unvarying strength. Thequantities of radiant heat absorbed and transmitted by each of theliquids at the respective thicknesses were first determined. Thevapours of these liquids were subsequently examined, the quantities ofvapour employed being rendered proportional to the quantities ofliquid previously traversed by the radiant heat. The result was that, for heat from the same source, the order of absorption of liquids andof their vapours proved absolutely the same. There is no knownexception to this law; so that, to determine the position of a vapouras an absorber or a radiator, it is only necessary to determine theposition of its liquid. 

This result proves that the state of aggregation, as far at all eventsas the liquid stage is concerned, is of altogether subordinatemoment--a conclusion which will probably prove to be of cardinalimportance in molecular physics. On one important and contested pointit has a special bearing. If the position of a liquid as an absorberand radiator determine that of its vapour, the position of water fixesthat of aqueous vapour. Water has been compared with other liquids ina multitude of experiments, and it has been found, both as a radiantand as an absorbent, to transcend them all. Thus, for example, alayer of bisulphide of carbon 0. 02 of an inch in thickness absorbs 6per cent, and allows 94 per cent of the radiation from the red-hotplatinum spiral to pass through it; benzol absorbs 43 and transmits 57per cent. Of the same radiation; alcohol absorbs 67 and transmits 33per cent, and alcohol, as an absorber of radiant heat, stands at thehead of all liquids except one. The exception is water. A layer ofthis substance, of the thickness above given, absorbs 81 per cent, andpermits only 19 per cent. Of the radiation to pass through it. Had nosingle experiment ever been made upon the vapour of water, itsvigorous action upon radiant heat might be inferred from thedeportment of the liquid. 

The relation of absorption and radiation to the chemical constitutionof the radiating and absorbing substances was next briefly considered. For the first six substances in the list of liquids examined, theradiant and absorbent powers augment as the number of atoms in thecompound molecule augments. Thus, bisulphide of carbon has 3 atoms, chloroform 5, iodide of ethyl 8, benzol 12, and amylene 15 atoms intheir respective molecules. The order of their power as radiants andabsorbents is that here indicated, bisulphide of carbon being thefeeblest, and amylene the strongest of the six. Alcohol, however, excels benzol as an absorber, though it has but 9 atoms in itsmolecule; but, on the other hand, its molecule is rendered morecomplex by the introduction of a new element. Benzol contains carbonand hydrogen, while alcohol contains carbon, hydrogen and oxygen. Thus, not only does atomic _multitude_ come into play in absorption andradiation--atomic _complexity_ must also be taken into account. I wouldrecommend to the particular attention of chemists the molecule ofwater; the deportment of this substance towards radiant heat beingperfectly anomalous, if the chemical formula at present ascribed to itbe correct. 

Sir William Herschel made the important discovery that, beyond thelimits of the red end of the solar spectrum, rays of high heatingpower exist which are incompetent to excite vision. The discovery iscapable of extension. Dissolving iodine in the bisulphide of carbon, a solution is obtained which entirely intercepts the light of the mostbrilliant flames, while to the ultra-red rays of such flames the sameiodine is found to be perfectly diathermic. The transparentbisulphide, which is highly pervious to invisible heat, exercises onit the same absorption as the perfectly opaque solution. A hollowprism filled with the opaque liquid being placed in the path of thebeam from an electric lamp, the light-spectrum is completelyintercepted, but the heat spectrum may be received upon a screen andthere examined. Falling upon a thermo-electric pile, its invisiblepresence is shown by the prompt deflection of even a coarsegalvanometer. 

What, then, is the physical meaning of opacity and transparency asregards light and radiant heat? The visible rays of the spectrumdiffer from the invisible ones simply in period. The sensation oflight is excited by waves of aether shorter and more quickly recurrentthan the non-visual waves which fall beyond 'the extreme red. But whyshould iodine stop the former and allow the latter to pass? Theanswer to this question no doubt is, that the intercepted waves arethose whose periods of recurrence coincide with the periods ofoscillation possible to the atoms of the dissolved iodine. Theelastic forces which keep these atoms apart compel them to vibrate indefinite periods, and, when these periods synchronise with those ofthe aethereal waves, the latter are absorbed. Briefly defined, then, transparency in liquids, as well as in gases, is synonymous withdiscord, while opacity is synonymous with accord, between the periodsof the waves of aether and those of the molecules on which theyimpinge. 

According to this view transparent and colourless substances owe theirtransparency to the dissonance existing between the oscillatingperiods of their atoms and those of the waves of the whole visiblespectrum. From the prevalence of transparency in compound bodies, thegeneral discord of the vibrating periods of their atoms with thelight-giving waves of the spectrum, may be inferred; while theirsynchronism with the ultra-red periods is to be inferred from theiropacity to the ultra-red rays. Water illustrates this in a moststriking manner. It is highly transparent to the luminous rays, whichproves that its atoms do not readily oscillate in the periods whichexcite vision. It is highly opaque to the ultra-red undulations, which proves the synchronism of its vibrating periods with those ofthe longer waves. 

If, then, to the radiation from any source water shows itselfeminently or perfectly opaque, we may infer that the atoms whence theradiation emanates oscillate in ultra-red periods. Let us apply thistest to the radiation from a flame of hydrogen. This flame consistsmainly of incandescent aqueous vapour, the temperature of which, ascalculated by Bunsen, is 3259°C, so that, if the penetrative power ofradiant heat, as generally supposed, augment with the temperature ofits source, we may expect the radiation from this flame to becopiously transmitted by water. While, however, a layer of thebisulphide of carbon 0. 07 of an inch in thickness transmits 72 percent. Of the incident radiation, and while every other liquidexamined transmits more or less of the heat, a layer of water of theabove thickness is entirely opaque to the radiation from the hydrogenflame. Thus we establish accord between the periods of the atoms ofcold water and those of aqueous vapour at a temperature of 3259°C. Butthe periods of water have already been proved to be ultra red--hencethose of the hydrogen flame must be sensibly ultra-red also. Theabsorption by dry air of the heat emitted by a platinum spiral raisedto incandescence by electricity is insensible, while that by theordinary undried air is 6 per cent. Substituting for the platinumspiral a hydrogen flame, the absorption by dry air still remainsinsensible, while that of the undried air rises to 20 per cent. Ofthe entire radiation. The temperature of the hydrogen flame is, asstated, 3259°C; that of the aqueous vapour of the air 20°C. Suppose, then, the temperature of aqueous vapour to rise from 20°C. To 3259°C, we must conclude that the augmentation of temperature is applied to anincrease of amplitude or width of swing, and not to the introductionof quicker periods into the radiation. 

The part played by aqueous vapour in the economy of nature is far morewonderful than has been hitherto supposed. To nourish the vegetationof the earth the actinic and luminous rays of the sun must penetrateour atmosphere; and to such rays aqueous vapour is eminentlytransparent. The violet and the ultra-violet rays pass through itwith freedom. To protect vegetation from destructive chills theterrestrial rays must be checked in their transit towards stellarspace; and this is accomplished by the aqueous vapour diffused throughthe air. This substance is the great moderator of the earth'stemperature, bringing its extremes into proximity, and obviatingcontrasts between day and night which would render life insupportable. But we can advance beyond this general statement, now that we know theradiation from aqueous vapour is intercepted, in a special degree, bywater, and, reciprocally, the radiation from water by aqueous vapour;for it follows from this that the very act of nocturnal refrigerationwhich produces the condensation of aqueous vapour at the surface ofthe earth--giving, as it were, a varnish of water to thatsurface--imparts to terrestrial radiation that particular characterwhich disqualifies it from passing through the earth's atmosphere andlosing itself in space. 

And here we come to a question in molecular physics which at thepresent moment occupies attention. By allowing the violet andultra-violet rays of the spectrum to fall upon sulphate of quinine andother substances Professor Stokes has changed the periods of thoserays. Attempts have been made to produce a similar result at theother end of the spectrum--to convert the ultra-red periods intoperiods competent to excite vision--but hitherto without success. Sucha change of period, I agree with Dr. Miller in believing, occurs whenthe limelight is produced by an oxy-hydrogen flame. In this commonexperiment there is an actual breaking up of long periods into shortones--a true rendering of unvisual periods visual. The change ofrefrangibility here effected differs from that of Professor Stokes;firstly, by its being in the opposite direction--that is, from a lowerrefrangibility to a higher; and, secondly, in the circumstance thatthe lime is heated by the collision of the molecules of aqueousvapour, before their heat has assumed the radiant form. But it cannotbe doubted that the same effect would be produced by radiant heat ofthe same periods, provided the motion of the aether could be renderedsufficiently intense. [Footnote: This was soon afterwardsaccomplished. See the section on 'Transmutation of Rays'. ] Theeffect in principle is the same, whether we consider the lime to bestruck by a particle of aqueous vapour oscillating at a certain rate, or by a particle of aether oscillating at the same rate. 

By plunging a platinum wire into a hydrogen flame we cause it to glow, and thus introduce shorter periods into the radiation. These, asalready stated, are in discord with the atomic vibrations of water;hence we may infer that the transmission through water will berendered more copious by the introduction of the wire into the flame. Experiment proves this conclusion to be true. Water, from beingopaque, opens a passage to 6 per cent. Of the radiation from thespiral. A thin plate of colourless glass, moreover, transmits 68 percent. Of the radiation from the hydrogen flame; but when the flameand spiral are employed, 78 per cent. Of the heat is transmitted. 

For an alcohol flame Knoblauch and Melloni found glass to be lesstransparent than for the same flame with a platinum spiral immersed init; but Melloni afterwards showed that the result was notgeneral--that black glass and black mica were decidedly morediathermic to the radiation from the pure alcohol flame. Melloni didnot explain this, but the reason is now obvious. The mica and glassowe their blackness to the carbon diffused through them. This carbon, as first proved by Melloni, is in some measure transparent to theultra-red rays, and I have myself succeeded in transmitting between 40and 50 per cent. Of the radiation from a hydrogen flame through alayer of carbon which intercepted the light of an intensely brilliantflame. The products of combustion of alcohol are carbonic acid andaqueous vapour, the heat of which is almost wholly ultra-red. Forthis radiation, then, the carbon is in a considerable degreetransparent, while for the radiation from the platinum spiral, it isin a great measure opaque. The platinum wire, therefore, whichaugmented the radiation through the pure glass, augmented theabsorption of the black glass and mica. 

No more striking or instructive illustration of the influence ofcoincidence could be adduced than that furnished by the radiation froma carbonic oxide flame. Here the product of combustion is carbonicacid; and on the radiation from this flame even the ordinary carbonicacid of the atmosphere exerts a powerful effect. A quantity of thegas, only one-thirtieth of an atmosphere in density, contained in apolished brass tube four feet long, intercepts 50 per cent. Of theradiation from the carbonic oxide flame. For the heat emitted bylampblack, olefiant gas is a far more powerful absorber than carbonicacid; in fact, for such heat, with one exception, carbonic acid is themost feeble absorber to be found among the compound gases. Moreover, for the radiation from a hydrogen flame olefiant gas possesses twicethe absorbent power of carbonic acid, while for the radiation from thecarbonic oxide flame, at a common pressure of one inch of mercury, theabsorption by carbonic acid is more than twice that of olefiant gas. Thus we establish the coincidence of period between carbonic acid at atemperature of 20°C. And carbonic acid at a temperature of over3000°C, the periods of oscillation of both the incandescent and thecold gas belonging to the ultra-red portion of the spectrum. 

It will be seen from the foregoing remarks and experiments howimpossible it is to determine the effect of temperature pure andsimple on the transmission of radiant heat if different sources ofheat be employed. Throughout such an examination the same oscillatingatoms ought to be retained. This is done by beating a platinum spiralby an electric current, the temperature meanwhile varying between thewidest possible limits. Their comparative opacity to the ultra-redrays shows the general accord of the oscillating periods of thevapours referred to at the commencement of this lecture with those ofthe ultra-red undulations. Hence, by gradually heating a platinum wirefrom darkness up to whiteness, we ought gradually to augment thediscord between it and these vapours, and thus augment thetransmission. Experiment entirely confirms this conclusion. Formicnether, for example, absorbs 45 per cent. Of the radiation from aplatinum spiral heated to barely visible redness; 32 per cent. Of theradiation from the same spiral at a red heat; 26 per cent. Of theradiation from a white-hot spiral, and only 21 per cent. When thespiral is brought near its point of fusion. Remarkable cases ofinversion as to transparency also occur. For barely visible rednessformic aether is more opaque than sulphuric; for a bright red heatboth are equally transparent; while, for a white heat, and still morefor a higher temperature, sulphuric aether is more opaque than formic. This result gives us a clear view of the relationship of the twosubstances to the luminiferous aether. As we introduce waves ofshorter period the sulphuric aether augments most rapidly in opacity;that is to say, its accord with the shorter waves is greater than thatof the formic. Hence we may infer that the atoms of formic aetheroscillate, on the whole, more slowly than those of sulphuric aether. 

When the source of heat is a Leslie's cube coated with lampblack andfilled with boiling water, the opacity of formic aether in comparisonwith sulphuric is very decided. With this source also the positions ofchloroform and iodide of methyl are inverted. For a white-hot spiral, the absorption of chloroform vapour being 10 per cent, that of iodideof methyl is 16; with the blackened cube as source, the absorption bychloroform is 22 per cent, while that by the iodide of methyl is only19. This inversion is not the result of temperature merely; for whena platinum wire, heated to the temperature of boiling water, isemployed as a source, the iodide continues to be the most powerfulabsorber. All the experiments hitherto made go to prove that fromheated lampblack an emission takes place which synchronises in anespecial manner with chloroform. For the cube at 100' C, coated withlampblack, the absorption by chloroform is more than three times thatby bisulphide of carbon; for the radiation from the most luminousportion of a gas-flame the absorption by chloroform is alsoconsiderably in excess of that by bisulphide of carbon; while, for theflame of a Bunsen's burner, from which the incandescent carbonparticles are removed by the free admixture of air, the absorption bybisulphide of carbon is nearly twice that by chloroform. _The removalof the carbon particles more than doubles the relative transparency ofthe chloroform_. Testing, moreover, the radiation from various partsof the same flame, it was found that for the blue base of the flamethe bisulphide of carbon was most opaque, while for all other parts ofthe flame the chloroform was most opaque. For the radiation from avery small gas flame, consisting of a blue base and a small white tip, the bisulphide was also most opaque, and its opacity very decidedlyexceeded that of the chloroform when the source of heat was the flameof bisulphide of carbon. Comparing the radiation from a Leslie's cubecoated with isinglass with that from a similar cube coated withlampblack, at the common temperature of 100°C, it was found that, outof eleven vapours, all but one absorbed the radiation from theisinglass most powerfully; the single exception was chloroform. 

It is worthy of remark that whenever, through a change of source, theposition of a vapour as an absorber of radiant heat was altered, theposition of the liquid from which the vapour was derived underwent asimilar change. 

It is still a point of difference between eminent investigatorswhether radiant heat, up to a temperature of 100°C, is monochromaticor not. Some affirm this; some deny it. A long series of experimentsenables me to state that probably no two substances at a temperatureof 100°C. Emit heat of the same quality. The heat emitted byisinglass, for example, is different from that emitted by lampblack, and the heat emitted by cloth, or paper, differs from both. It isalso a subject of discussion whether rock-salt is equally diathermicto all kinds of calorific rays; the differences affirmed to exist bysome investigators being ascribed by others to differences ofincidence from the various sources employed. MM. De la Provostayeand Desains maintain the former view, Melloni and M. Knoblauchmaintain the latter. I tested this point without changing anythingbut the temperature of the source; its size, distance, andsurroundings remaining the same. The experiments proved rock-salt tobe coloured thermally. It is more opaque, for example, to theradiation from a barely visible spiral than to that from a white-hotone. 

In regard to the relation of radiation to conduction, if we defineradiation, internal as well as external, as the communication ofmotion from the vibrating atoms to the aether, we may, I think, byfair theoretic reasoning, reach the conclusion that the best radiatorsought to prove the worst conductors. A broad consideration of thesubject shows at once the general harmony of this conclusion withobserved facts. Organic substances are all excellent radiators; theyare also extremely bad conductors. The moment we pass from the metalsto their compounds we pass from good conductors to bad ones, and frombad radiators to good ones. Water, among liquids, is probably theworst conductor; it is the best radiator. Silver, among solids, isthe best conductor; it is the worst radiator. The excellentresearches of MM. De la Provostaye and Desains furnish a strikingillustration of what I am inclined to regard as a natural law--thatthose atoms which transfer the greatest amount of motion to theaether, or, in other words, radiate most powerfully, are the leastcompetent to communicate motion to each other, or, in other words, topropagate by conduction readily. 

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XVIII. LIFE, AND LETTERS OF FARADAY. 

1870. 

UNDERTAKEN and executed in a reverent and loving spirit, the work ofDr. Bence Jones makes Faraday the virtual writer of his own life. Everybody now knows the story of the philosopher's birth; that hisfather was a smith; that he was born at Newington Butts in 1791; thathe ran along the London pavements, a bright-eyed errand boy, with aload of brown curls upon his head and a packet of newspapers under hisarm; that the lad's master was a bookseller and bookbinder--a kindlyman, who became attached to the little fellow, and in due time madehim his apprentice without fee; that during his apprenticeship hefound his appetite for knowledge provoked and strengthened by thebooks he stitched and covered. Thus he grew in wisdom and stature tohis year of legal manhood, when he appears in the volumes before us asa writer of letters, which reveal his occupation, acquirements, andtone of mind. His correspondent was Mr. Abbott, a member of theSociety of Friends, who, with a forecast of his correspondent'sgreatness, preserved his letters and produced them at the proper time. 

In later years Faraday always carried in his pocket a blank card, onwhich he jotted down in pencil his thoughts and memoranda. He madehis notes in the laboratory, in the theatre, and in the streets. Thisdistrust of his memory reveals itself in his first letter to Abbot. Toa proposition that no new enquiry should be started between thembefore the old one had been exhaustively discussed, Faraday objects. 'Your notion, ' he says, 'I can hardly allow, for the followingreason: ideas and thoughts spring up in my mind which are irrevocablylost for want of noting at the time. ' Gentle as he seemed, he wishedto have his own way, and he had it throughout his life. Differencesof opinion sometimes arose between the two friends, and then theyresolutely faced each other. 'I accept your offer to fight it outwith joy, and shall in the battle of experience cause not pain, but, Ihope, pleasure. ' Faraday notes his own impetuosity, and incessantlychecks it. There is at times something almost mechanical in hisself-restraint. In another nature it would have hardened into mere'correctness' of conduct; but his overflowing affections preventedthis in his case. The habit of self control became a second nature tohim at last, and lent serenity to his later years. 

In October 1812 he was engaged by a Mr. De la Roche as a journeymanbookbinder; but the situation did not suit him. His master appears tohave been an austere and passionate man, and Faraday was to the lastdegree sensitive. All his life he continued so. He suffered at timesfrom dejection; and a certain grimness, too, pervaded his moods. 'Atpresent, ' he writes to Abbott, 'I am as serious as you can be, andwould not scruple to speak a truth to any human being, whateverrepugnance it might give rise to. Being in this state of mind, Ishould have refrained from writing to you, did I not conceive from thegeneral tenor of your letters that your mind is, at proper times, occupied upon serious subjects to the exclusion of those that arefrivolous. ' Plainly he had fallen into that stern Puritan mood, whichnot only crucifies the affections and lusts of him who harbours it, but is often a cause of disturbed digestion to his friends. 

About three months after his engagement with De la Roche, Faradayquitted him and bookbinding together. He had heard Davy, copied hislectures, and written to him, entreating to be released from Trade, which he hated, and enabled to pursue Science. Davy recognised themerit of his correspondent, kept his eye upon him, and, when occasionoffered, drove to his door and sent in a letter, offering him the postof assistant in the laboratory of the Royal Institution. He wasengaged March 1, 1813, and on the 8th we find him extracting the sugarfrom beet-root. He joined the City Philosophical Society which hadbeen founded by Mr. Tatum in 1808. 'The discipline was very sturdy, the remarks very plain, and the results most valuable. ' Faradayderived great profit from this little association. In the laboratoryhe had a discipline sturdier still. Both Davy and himself were atthis time frequently cut and bruised by explosions of chloride ofnitrogen. One explosion was so rapid 'as to blow my hand open, tearaway a part of one nail, and make my fingers so sore that I cannot usethem easily. ' In another experiment 'the tube and receiver were blownto pieces, I got a cut on the head, and Sir Humphry a bruise on hishand. ' And again speaking of the same substance, he says, 'when put inthe pump and exhausted, it stood for a moment, and then exploded witha fearful noise. Both Sir H. And I had masks on, but I escaped thistime the best. Sir H. Had his face cut in two places about the chin, and a violent blow on the forehead struck through a considerablethickness of silk and leather. ' It was this same substance that blewout the eye of Dulong. 

Over and over again, even at this early date, we can discern thequality which, compounded with his rare intellectual power, madeFaraday a great experimental philosopher. This was his desire to seefacts, and not to rest contented with the descriptions of them. Hefrequently pits the eye against the ear, and affirms the enormoussuperiority of the organ of vision. Late in life I have heard him saythat he could never fully understand an experiment until he had seenit. But he did not confine himself to experiment. He aspired to be ateacher, and reflected and wrote upon the method of scientificexposition. 'A lecturer, ' he observes, 'should appear easy andcollected, undaunted and unconcerned:' still 'his whole behaviourshould evince respect for his audience. ' These recommendations wereafterwards in great part embodied by himself. I doubt his'unconcern, ' but his fearlessness was often manifested. It used torise within him as a wave, which carried both him and his audiencealong with it. On rare occasions also, when he felt himself and hissubject hopelessly unintelligible, he suddenly evoked a certainrecklessness of thought, and, without halting to extricate hisbewildered followers, he would dash alone through the jungle intowhich he had unwittingly led them; thus saving them from ennui by theexhibition of a vigour which, for the time being, they could neithershare nor comprehend. 

In October 1813 he quitted England with Sir Humphry and Lady Davy. During his absence he kept a journal, from which copious andinteresting extracts have been made by Dr. Bence Jones. Davy wasconsiderate, preferring at times to be his own servant rather thanimpose on Faraday duties which he disliked. But Lady Davy was thereverse. She treated him as an underling; he chafed under thetreatment, and was often on the point of returning home. They haltedat Geneva. De la Rive, the elder, had known Davy in 1799, and, by hiswritings in the 'Bibliothéque Britannique, ' had been the first to makethe English chemist's labours known abroad. He welcomed Davy to hiscountry residence in 1814. Both were sportsmen, and they often wentout shooting together. On these occasions Faraday charged Davy's gunwhile De la Rive charged his own. Once the Genevese philosopher foundhimself by the side of Faraday, and in his frank and genial wayentered into conversation with the young man. It was evident that aperson possessing such a charm of manner and such high intelligencecould be no mere servant. On enquiry De la Rive was somewhat shockedto find that the _soi-disant domestique_ was really _préparateur_ in thelaboratory of the Royal Institution; and he immediately proposed thatFaraday thenceforth should join the masters instead of the servants attheir meals. To this Davy, probably out of weak deference to hiswife, objected; but an arrangement was come to that Faradaythenceforward should have his food in his own room. Rumour statesthat a dinner in honour of Faraday was given by De la Rive. This is adelusion; there was no such banquet; but Faraday never forgot thekindness of the friend who saw his merit when he was a mere _garcon delaboratoire_. [Footnote: While confined last autumn at Geneva by theeffects of a fall in the Alps, my friends, with a kindness I can neverforget, did all that friendship could suggest to render my captivitypleasant to me. M. De la Rive then wrote out for me the full account, of which the foregoing is a condensed abstract. It was at the desireof Dr. Bence Jones that I asked him to do so. The rumour of a banquetat Geneva illustrates the tendency to substitute for the youth of 1814the Faraday of later years. ]

He returned in 1815 to the Royal Institution. Here he helped Davy foryears; he worked also for himself, and lectured frequently at the CityPhilosophical Society. He took lessons in elocution, happily withoutdamage to his natural force, earnestness, and grace of delivery. Hewas never pledged to theory, and he changed in opinion as knowledgeadvanced. With him life was growth. In those early lectures we hearhim say, 'In knowledge, that man only is to be contemned and despisedwho is not in a state of transition. ' And again: 'Nothing is moredifficult and requires more caution than philosophical deduction, noris there anything more adverse to its accuracy than fixity ofopinion. ' Not that he was wafted about by every wind of doctrine; butthat he united flexibility with his strength. In striking contrastwith this intellectual expansiveness was his fixity in religion, butthis is a subject which cannot be discussed here. 

Of all the letters published in these volumes none possess a greatercharm than those of Faraday to his wife. Here, as Dr. Bence Jonestruly remarks, 'he laid open all his mind and the whole of hischaracter, and what can be made known can scarcely fail to charm everyone by its loveliness, its truthfulness, and its earnestness. ' Abbottand he sometimes swerved into wordplay about love; but up to 1820, orthereabouts, the passion was potential merely. Faraday's journalindeed contains entries which show that he took pleasure in theassertion of his contempt for love; but these very entries becamelinks in his destiny. It was through them that he became acquaintedwith one who inspired him with a feeling which only ended with hislife. His biographer has given us the means of tracing the varyingmoods which preceded his acceptance. They reveal more than the commonalternations of light and gloom; at one moment he wishes that hisflesh might melt and that he might become nothing; at another he isintoxicated with hope. The impetuosity of his character was thenunchastened by the discipline to which it was subjected in afteryears. The very strength of his passion proved for a time a bar toits advance, suggesting, as it did, to the conscientious mind of MissBarnard, doubts of her capability to return it with adequate force. But they met again and again, and at each successive meeting he foundhis heaven clearer, until at length he was able to say, 'Not amoment's alloy of this evening's happiness occurred. Everything wasdelightful to the last moment of my stay with my companion, becauseshe was so. ' The turbulence of doubt subsided, and a calm andelevating confidence took its place. 'What can I call myself, ' hewrites to her in a subsequent letter, 'to convey most perfectly myaffection and love for you? Can I or can truth say more than that forthis world I am yours? Assuredly he made his profession good, and nofairer light falls upon his character than that which reveals hisrelations to his wife. Never, I believe, existed a manlier, purer, steadier love. Like a burning diamond, it continued to shed, forsix-and-forty years, its white and smokeless glow. 

Faraday was married on June 12, 1821; and up to this date Davy appearsthroughout as his friend. Soon afterwards, however, disunion occurredbetween them, which, while it lasted, must have given Faraday intensepain. It is impossible to doubt the honesty of conviction with whichthis subject has been treated by Dr. Bence Jones, and there may befacts known to him, but not appearing in these volumes, which justifyhis opinion that Davy in those days had become jealous of Faraday. This, which is the prevalent belief, is also reproduced in anexcellent article in the March number of 'Framer's Magazine. ' But thebest analysis I can make of the data fails to present Davy in thislight to me. The facts, as I regard them, are briefly these. 

In 1820, Oersted of Copenhagen made the celebrated discovery whichconnects electricity with magnetism, and immediately afterwards theacute mind of Wollaston perceived that a wire carrying a current oughtto rotate round its own axis under the influence of a magnetic pole. In 1821 'he tried, but failed, to realise this result in thelaboratory of the Royal Institution. Faraday was not present at themoment, but he came in immediately afterwards and heard theconversation of Wollaston and Davy about the experiment. He had alsoheard a rumour of a wager that Dr. Wollaston would eventually succeed. 

This was in April. In the autumn of the same year Faraday wrote ahistory of electro-magnetism, and repeated for himself the experimentswhich he described. It was while thus instructing himself that hesucceeded in causing a wire, carrying an electric current, to rotateround a magnetic pole. This was not the result sought by Wollaston, but it was closely related to that result. 

The strong tendency of Faraday's mind to look upon the reciprocalactions of natural forces gave birth to his greatest discoveries; andwe, who know this, should be justified in concluding that, even hadWollaston not preceded him, the result would have been the same. Butin judging Davy we ought to transport ourselves to his time, andcarefully exclude from our thoughts and feelings that noble subsequentlife, which would render simply impossible the ascription to Faradayof anything unfair. It would be unjust to Davy to put our knowledgein the place of his, or to credit him with data which he could nothave possessed. Rumour and fact had connected the name of Wollastonwith these supposed interactions between magnets and currents. When, therefore, Faraday in October published his successful experiment, without any allusion to Wollaston, general, though really ungrounded, criticism followed. I say ungrounded because, firstly, Faraday'sexperiment was not that of Wollaston, and secondly, Faraday, before hepublished it, had actually called upon Wollaston, and not finding himat home, did not feel himself authorised to mention his name. 

In December, Faraday published a second paper on the same subject, from which, through a misapprehension, the name of Wollaston was alsoomitted. Warburton and others thereupon affirmed that Wollaston'sideas had been appropriated without acknowledgment, and it is plainthat Wollaston himself, though cautious in his utterance, was alsohurt. Censure grew till it became intolerable. 'I hear, ' writesFaraday to his friend Stodart, 'every day more and more of thesesounds, which, though only whispers to me, are, I suspect, spokenaloud among scientific men. ' He might have written explanations anddefences, but he went straighter to the point. He wished to see theprincipals face to face--to plead his cause before them personally. There was a certain vehemence in his desire to do this. He sawWollaston, he saw Davy, he saw Warburton; and I am inclined to thinkthat it was the irresistible candour and truth of character whichthese viva voce defences revealed, as much as the defences themselves, that disarmed resentment at the time. 

As regards Davy, another cause of dissension arose in 1823. In thespring of that year Faraday analysed the hydrate of chlorine, asubstance once believed to be the element chlorine, but proved by Davyto be a compound of that element and water. The analysis was lookedover by Davy, who then and there suggested to Faraday to heat thehydrate in a closed glass tube. This was done, the substance wasdecomposed, and one of the products of decomposition was proved byFaraday to be chlorine liquefied by its own pressure. On the day ofits discovery he communicated this result to Dr. Paris. Davy, onbeing informed of it, instantly liquefied another gas in the same way. Having struck thus into Faraday's enquiry, ought he not to have leftthe matter in Faraday's hands? I think he ought. But, consideringhis relation to both Faraday and the hydrate of chlorine, Davy, Isubmit, may be excused for thinking differently. A father is notalways wise enough to see that his son has ceased to be a boy, andestrangement on this account is not rare; nor was Davy wise enough todiscern that Faraday had passed the mere assistant stage, and become adiscoverer. It is now hard to avoid magnifying this error. But hadFaraday died or ceased to work at this time, or had his subsequentlife been devoted to money-getting, instead of to research, wouldanybody now dream of ascribing jealousy to Davy? Assuredly not. Whyshould he be jealous? His reputation at this time was almost withouta parallel: his glory was without a cloud. He had added to his otherdiscoveries that of Faraday, and after having been his teacher forseven years, his language to him was this: 'It gives me great pleasureto hear that you are comfortable at the Royal Institution, and I trustthat you will not only do something good and honourable for yourself, but also for science. ' This is not the language of jealousy, potentialor actual. But the chlorine business introduced irritation and anger, to which, and not to any ignobler motive, Davy's opposition to theelection of Faraday to the Royal Society is, I am persuaded, to beascribed. 

These matters are touched upon with perfect candour, and becomingconsideration, in the volumes of Dr. Bence Jones; but in 'society'they are not always so handled. Here a name of noble intellectualassociations is surrounded by injurious rumours which I wouldwillingly scatter for ever. The pupil's magnitude, and the splendourof his position, are too great and absolute to need as a foil thehumiliation of his master. Brothers in intellect, Davy and Faraday, however, could never have become brothers in feeling; their characterswere too unlike. Davy loved the pomp and circumstance of fame;Faraday the inner consciousness that he had fairly won renown. Theywere both proud men. But with Davy pride projected itself into theouter world; while with Faraday it became a steadying and dignifyinginward force. In one great particular they agreed. Each of themcould have turned his science to immense commercial profit, butneither of them did so. The noble excitement of research, and thedelight of discovery, constituted their reward. I commend them to thereverence which great gifts greatly exercised ought to inspire. Theywere both ours; and through the coming centuries England will be ableto point with just pride to the possession of such men. 

====================

The first volume of the 'Life and Letters' reveals to us the youth whowas to be father to the man. Skilful, aspiring, resolute, he grewsteadily in knowledge and in power. Consciously or unconsciously, therelation of Action to Reaction was ever present to Faraday's mind. Ithad been fostered by his discovery of Magnetic Rotations, and itplanted in him more daring ideas of a similar kind. Magnetism he knewcould be evoked by electricity, and he thought that electricity, inits turn, ought to be capable of evolution by magnetism. On August29, 1831, his experiments on this subject began. He had beenfortified by previous trials, which, though failures, had begotteninstincts directing him towards the truth. He, like every strongworker, might at times miss the outward object, but he always gainedthe inner light, education, and expansion. Of this Faraday's life wasa constant illustration. By November he had discovered and colligateda multitude of the most wonderful and unexpected phenomena. He hadgenerated currents by currents; currents by magnets, permanent andtransitory; and he afterwards generated currents by the earth itself. Arago's 'Magnetism of Rotation, ' which had for years offered itselfas a challenge to the best scientific intellects of Europe, now fellinto his hands. It proved to be a beautiful, but still special, illustration of the great principle of Magneto-electric Induction. Nothing equal to this latter, in the way of pure experimental enquiry, had previously been achieved. 

Electricities from various sources were next examined, and theirdifferences and resemblances revealed. He thus assured himself oftheir substantial identity. He then took up Conduction, and gave manystriking illustrations of the influence of Fusion on Conducting Power. Renouncing professional work, from which at this time he might havederived an income of many thousands a year, he poured his wholemomentum into his researches. He was long entangled inElectrochemistry. The light of law was for a time obscured by thethick umbrage of novel facts; but he finally emerged from hisresearches with the great principle of Definite Electro-chemicalDecomposition in his hands. If his discovery of Magneto-electricitymay be ranked with that of the pile by Volta, this new discovery, mayalmost stand beside that of Definite Combining Proportions inChemistry. He passed on to Static Electricity--its Conduction, Induction, and Mode of Propagation. He discovered and illustrated theprinciple of Inductive Capacity; and, turning to theory, he askedhimself how electrical attractions and repulsions are transmitted. Arethey, like gravity, actions at a distance, or do they require amedium? If the former, then, like gravity, they will act in straightlines; if the latter, then, like sound or light, they may turn acorner. Faraday held--and his views are gaining ground--that hisexperiments proved the fact of curvilinear propagation, and hence theoperation of a medium. Others denied this; but none can deny theprofound and philosophic character of his leading thought. [Footnote:In a very remarkable paper published in Poggendorff's 'Annalen' for1857, Werner Siemens accepts and develops Faraday's theory ofMolecular Induction. ] The first volume of the Researches contains allthe papers here referred to. 

Faraday had heard it stated that henceforth physical discoveries wouldbe made solely by the aid of mathematics; that we had our data, andneeded only to work deductively. Statements of a similar charactercrop out from time to time in our day. They arise from an imperfectacquaintance with the nature, present condition, and prospectivevastness of the field of physical enquiry. The tendency of naturalscience doubtless is to bring all physical phenomena under thedominion of mechanical laws; to give them, in other words, mathematical expression. But our approach to this result isasymptotic; and for ages to come--possibly for all the ages of thehuman race--Nature will find room for both the philosophicalexperimenter and the mathematician. Faraday entered his protestagainst the foregoing statement by labelling his investigations'Experimental Researches in Electricity. ' They were completed in 1854, and three volumes of them have been published. For the sake ofreference, he numbered every paragraph, the last number being 3362. In1859 he collected and published a fourth volume of papers, under thetitle, 'Experimental Researches in Chemistry and Physics. ' Thus didthis apostle of experiment illustrate its power, and magnify hisoffice. 

The second volume of the Researches embraces memoirs on theElectricity of the Gymnotus; on the Source of Power in the VoltaicPile; on the Electricity evolved by the Friction of Water and Steam, in which the phenomena and principles of Sir William Armstrong'sHydro-electric machine are described and developed; a paper onMagnetic Rotations, and Faraday's letters in relation to thecontroversy it aroused. The contribution of most permanent valuehere, is that on the Source of Power in the Voltaic Pile. By it theContact Theory, pure and simple, was totally overthrown, and thenecessity of chemical action to the maintenance of the currentdemonstrated. 

The third volume of the Researches opens with a memoir entitled 'TheMagnetisation of Light, ' and the Illumination of Magnetic Lines ofForce. ' It is difficult even now to affix a definite meaning to thistitle; but the discovery of the rotation of the plane of polarisation, which it announced, seems pregnant with great results. The writingsof William Thomson on the theoretic aspects of the discovery; theexcellent electrodynamic measurements of Wilhelm Weber, which aremodels of experimental completeness and skill; Weber's labours inconjunction with his lamented friend Kohlrausch--above all, theresearches of Clerk Maxwell on the Electro-magnetic Theory ofLight--point to that wonderful and mysterious medium, which is thevehicle of light and radiant heat, as the probable basis also ofmagnetic and electric phenomena. The hope of such a connection wasfirst raised by the discovery here referred to. [Footnote: A letteraddressed to me by Professor Weber on March 18 last contains thefollowing reference to the connection here mentioned: 'Die Hoffnungeiner solchen Combination ist durch Faraday's Entdeckung derDrehung er Polarisationsebene durch magnetische Directionskraftzuerst, und sodann durch die Uebereinstimmung derjenigenGeschwindigkeit, welche das Verhaeltniss der electro-dynamischenEinheit zur lectro-statischen ausdrueckt, mit der Geschwindigkeitdes Lichts angeregt worden; und mir scheint von allen Versuchen, welche zur erwirklichung dieser Hoffnung gemacht worden sind, das vonHerrn Maxwell gemachte am erfolgreichsten. '] Faraday himself seemed tocling with particular affection to this discovery. He felt that therewas more in it than he was able to unfold. He predicted that it wouldgrow in meaning with the growth of science. This it has done; this itis doing now. Its right interpretation will probably mark an epoch inscientific history. 

Rapidly following it is the discovery of Diamagnetism, or therepulsion of matter by a magnet. Brugmans had shown that bismuthrepelled a magnetic needle. Here he stopped. Le Bailliff proved thatantimony did the same. Here he stopped. Seebeck, Becquerel, andothers, also touched the discovery. These fragmentary gleams exciteda momentary curiosity and were almost forgotten, when Faradayindependently alighted on the same facts; and, instead of stopping, made them the inlets to a new and vast region of research. The valueof a discovery is to be measured by the intellectual action it callsforth; and it was Faraday's good fortune to strike such lodes ofscientific truth as give occupation to some of the best intellects ofour age. 

The salient quality of Faraday's scientific character reveals itselffrom beginning to end of these volumes; a union of ardour andpatience--the one prompting the attack, the other holding him on toit, till defeat was final or victory assured. Certainty in one senseor the other was necessary to his peace of mind. The right method ofinvestigation is perhaps incommunicable; it depends on the individualrather than on the system, and the mark is missed when Faraday'sresearches are pointed to as merely illustrative of the power of theinductive philosophy. The brain may be filled with that philosophy;but without the energy and insight which this man possessed, and whichwith him were personal and distinctive, we should never rise to thelevel of his achievements. His power is that of individual genius, rather than of philosophic method; the energy of a strong soulexpressing itself after its own fashion, and acknowledging no mediatorbetween it and Nature. 

The second volume of the 'Life and Letters, ' like the first, is ahistoric treasury as regards Faraday's work and character, and hisscientific and social relations. It contains letters from Humboldt, Herschel, Hachette, De la Rive, Dumas, Liebig, Melloni, Becquerel, Oersted, Plucker, Du Bois Reymond, Lord Melbourne, Prince LouisNapoleon, and many other distinguished men. I notice with particularpleasure a letter from Sir John Herschel, in reply to a sealed packetaddressed to him by Faraday, but which he had permission to open if hepleased. The packet referred to one of the many unfulfilled hopeswhich spring up in the minds of fertile investigators:

'Go on and prosper, "from strength to strength, " like a victormarching with assured step to further conquests; and be certain thatno voice will join more heartily in the peans that already begin torise, and will speedily swell into a shout of triumph, astounding evento yourself, than that of J. F. W. Herschel. '

Faraday's behaviour to Melloni in 1835 merits a word of notice. Theyoung man was a political exile in Paris. He had newly fashioned andapplied the thermo-electric pile, and had obtained with it results ofthe greatest importance. But they were not appreciated. With thesickness of disappointed hope Melloni waited for the report of theCommissioners, appointed by the Academy of Sciences to examine thePrimier. At length he published his researches in the 'Annales deChimie. ' They thus fell into the hands of Faraday, who, discerning atonce their extraordinary merit, obtained for their author the RumfordMedal of the Royal Society. A sum of money always accompanies thismedal; and the pecuniary help was, at this time, even more essentialthan the mark of honour to the young refugee. Melloni's gratitude wasboundless:

'Et vous, monsieur, ' he writes to Faraday, 'qui appartenez à unesociété à laquelle je n'avais rien offert, vous qui me connaissiez àpeine de nom; vous n'avez pas demandé si j'avais des ennemis faiblesou puissants, ni calculé quel en était le nombre; mais vous avez parlépour l'opprimé étranger, pour celui qui n'avait pas le moindre droit àtant de bienveillance, et vos paroles ont été accueilliesfavorablement par des collègues consciencieux! Je reconnais bien làdes hommes dignes de leur noble mission, les véritable représentantsde la science d'un pays libre et généreux. '

Within the prescribed limits of this article it would be impossible togive even the slenderest summary of Faraday's correspondence, or tocarve from it more than the merest fragments of his character. Hisletters, written to Lord Melbourne and others in 1836, regarding hispension, illustrate his uncompromising independence. The PrimeMinister had offended him, but assuredly the apology demanded andgiven was complete. I think 'it certain that, notwithstanding thevery full account of this transaction given by Dr. Bence Jones, motives and influences were at work which even now are not entirelyrevealed. The minister was bitterly attacked, but he bore the censureof the press with great dignity. Faraday, while he disavowed havingeither directly or indirectly furnished the matter of those attacks, did not publicly exonerate the Premier. The Hon. Caroline Fox hadproved herself Faraday's ardent friend, and it was she who had healedthe breach between the philosopher and the minister. She manifestlythought that Faraday ought to have come forward in Lord Melbourne'sdefence, and there is a flavour of resentment in one of her letters tohim on the subject. No doubt Faraday had good grounds for hisreticence, but they are to me unknown. 

In 1841 his health broke down utterly, and he went to Switzerland withhis wife and brother-in-law. His bodily vigour soon revived, and heaccomplished feats of walking respectable even for a trainedmountaineer. The published extracts from his Swiss journal containmany beautiful and touching allusions. Amid references to the tintsof the Jungfrau, the blue rifts of the glaciers, and the noble Niesentowering over the Lake of Thun, we come upon the charming little scrapwhich I have elsewhere quoted: 'Clout-nail making goes on here ratherconsiderably, and is a very neat and pretty operation to observe. Ilove a smith's shop and anything relating to smithery. My father wasa smith. ' This is from his journal; but he is unconsciously speakingto somebody--perhaps to the world. 

His description of the Staubbach, Giessbach, and of the scenic effectsof sky and mountain, are all fine and sympathetic. But amid it all, and in reference to it all, he tells his sister that 'true enjoymentis from within, not from without. ' In those days Agassiz was livingunder a slab of gneiss on the glacier of the Aar. Faraday met Forbesat the Grimsel, and arranged with him an excursion to the 'Hôtel desNeufchâtelois'; but indisposition put the project out. 

From the Fort of Ham, in 1843, Faraday received a letter addressed tohim by Prince Louis Napoleon Bonaparte. He read this letter to memany years ago, and the desire, shown in various ways by the FrenchEmperor, to turn modern science to account, has often reminded me ofit since. At the age of thirty-five the prisoner of Ham speaks of'rendering his captivity less sad by studying the great discoveries'which science owes to Faraday; and he asks a question which revealshis cast of thought at the time: 'What is the most simple combinationto give to a voltaic battery, in order to produce a spark capable ofsetting fire to powder under water or under ground?' Should thenecessity arise, the French Emperor will not lack at the outset thebest appliances of modern science; while we, I fear, shall have tolearn the magnitude of the resources we are now neglecting amid thepangs of actual war. ' [Footnote: The 'science' has since been applied, with astonishing effect, by those who had studied it far morethoroughly than the Emperor of the French. We also, I am happy tothink, have improved the time since the above words were written[1878]. ]

One turns with renewed pleasure to Faraday's letters to his wife, published in the second volume. Here surely the loving essence of theman appears more distinctly than anywhere else. From the house of Dr. Percy, in Birmingham, he writes thus:

'Here--even here the moment I leave the table, I wish I were with youIN QUIET. Oh, what happiness is ours! My runs into the world in thisway only serve to make me esteem that happiness the more. '

And again:

'We have been to a grand conversazione in the town-hall, and I havenow returned to my room to talk with you, as the pleasantest andhappiest thing that I can do. Nothing rests me so much as communionwith you. I feel it even now as I write, and catch myself saying thewords aloud as I write them. '

Take this, moreover, as indicative of his love for Nature:

'After writing, I walk out in the evening hand in hand with my dearwife to enjoy the sunset; for to me who love scenery, of all that Ihave seen or can see, there is none surpasses that of heaven. Aglorious sunset brings with it a thousand thoughts that delight me. '

Of the numberless lights thrown upon him by the Life and Letters, 'some fall upon his religion. In a letter to Lady Lovelace, hedescribes himself as belonging to 'a very small and despised sect ofChristians, known, if known at all, as _Sandemanians_, and our hope isfounded on the faith that is in Christ. ' He adds: 'I do not think itat all necessary to tie the study of the natural sciences and religiontogether, and in my intercourse with my fellow-creatures, that whichis religious, and that which is philosophical, have ever been twodistinct things. ' He saw clearly the danger of quitting his moorings, and his science acted indirectly as the safeguard of his faith. Forhis investigations so filled his mind as to leave no room forsceptical questionings, thus shielding from the assaults ofphilosophy, the creed of his youth. His religion was constitutionaland hereditary. It was implied in the eddies of his blood and in thetremors of his brain; and, however its outward and visible form mighthave changed, Faraday would still have possessed its elementalconstituents--awe, reverence, truth, and love. 

It is worth enquiring how so profoundly religious a mind, and so greata teacher, would be likely to regard our present discussions on thesubject of education. Faraday would be a 'secularist' were he nowalive. He had no sympathy with those who contemn knowledge unless itbe accompanied by dogma. A lecture delivered before the CityPhilosophical Society in 1818, when he was twenty-six years of age, expresses the views regarding education which he entertained to theend of his life. 'First, then, ' he says, 'all theologicalconsiderations are banished from the society, and of course from myremarks; and whatever I may say has no reference to a future state, orto the means which are to be adopted in this world in anticipation ofit. Next, I have no intention of substituting anything for religion, but I wish to take that part of human nature which is independent ofit. Morality, philosophy, commerce, the various institutions andhabits of society, are independent of religion, and may exist eitherwith or without it. They are always the same, and can dwell alike inthe breasts of those who, from opinion, are entirely opposed in theset of principles they include in the term religion, or in those whohave none. 

'To discriminate more closely, if possible, I will observe that wehave no right to judge religious opinions; but the human nature ofthis evening is that part of man which we have a right to judge. AndI think it will be found on examination, that this humanity--as it mayperhaps be called--will accord with what I have before described asbeing in our own hands so improvable and perfectible. '

In an old journal I find the following remarks on one of my earliestdinners with Faraday: 'At two o'clock he came down for me. He, hisniece, and myself, formed the party, "I never give dinners, " he said. "I don't know how to give dinners, and I never dine out. But I shouldnot like my friends to attribute this to a wrong cause. I act thusfor the sake of securing time for work, and not through religiousmotives, as some imagine. " He said grace. I am almost ashamed tocall his prayer a "saying Of grace. " In the language of Scripture, itmight be described as the petition of a son, into whose heart God hadsent the Spirit of His Son, and who with absolute trust asked ablessing from his father. We dined on roast beef, Yorkshire pudding, and potatoes; drank sherry, talked of research and its requirements, and of his habit of keeping himself free from the distractions ofsociety. He was bright and joyful--boy-like, in fact, though he isnow sixty-two. His work excites admiration, but contact with himwarms and elevates the heart. Here, surely, is a strong man. I lovestrength; but let me not forget the example of its union with modesty, tenderness, and sweetness, in the character of Faraday. '

Faraday's progress in discovery, and the salient points of hischaracter, are well brought out by the wise choice of letters andextracts published in the volumes before us. I will not call thelabours of the biographer final. So great a character will challengereconstruction. In the coming time some sympathetic spirit, with therequisite strength, knowledge, and solvent power, will, I doubt not, render these materials plastic, give them more perfect organic form, and send through them, with less of interruption, the currents ofFaraday's life. 'He was too good a man, ' writes his presentbiographer, 'for me to estimate rightly, and too great a philosopherfor me to understand thoroughly. ' That may be: but the reverentaffection to which we owe the discovery, selection, and arrangement ofthe materials here placed before us, is probably a surer guide thanmere literary skill. The task of the artist who may wish in futuretimes to reproduce the real though unobtrusive grandeur, the purity, beauty, and childlike simplicity of him whom we have lost, will findhis chief treasury already provided for him by Dr. Bence Jones'slabour of love. 

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XIX. THE COPLEY MEDALIST OF 1870. 

THIRTY years ago Electro-magnetism was looked to as a motive power, which might possibly compete with steam. In centres of industry, suchas Manchester, attempts to investigate and apply this power werenumerous. This is shown by the scientific literature of the time. Among others Mr. James Prescot Joule, a resident of Manchester, tookup the subject, and, in a series of papers published in Sturgeon's'Annals of Electricity' between 1839 and 1841, described variousattempts at the construction and perfection of electro-magneticengines. The spirit in which Mr. Joule pursued these enquiries isrevealed in the following extract: 'I am particularly anxious, ' hesays, 'to communicate any new arrangement in order, if possible, toforestall the monopolising designs of those who seem to regard thismost interesting subject merely in the light of pecuniaryspeculation. ' He was naturally led to investigate the laws ofelectro-magnetic attractions, and in 1840 he announced the importantprinciple that the attractive force exerted by two electromagnets, orby an electro-magnet and a mass of annealed iron, is directlyproportional to the square of the strength of the magnetising current;while the attraction exerted between, an electro-magnet and the poleof a permanent steel magnet, varies simply as the strength of thecurrent. These investigations were conducted independently of, thougha little subsequently to, the celebrated enquiries of Henry, Jacobi, and Lenz and Jacobi, on the same subject. 

On December 17, 1840, Mr. Joule communicated to the Royal Society apaper on the production of heat by Voltaic electricity. In it heannounced the law that the calorific effects of equal quantities oftransmitted electricity are proportional to the resistance overcome bythe current, whatever may be the length, thickness, shape, orcharacter of the metal which closes the circuit; and also proportionalto the square of the quantity of transmitted electricity. This is alaw of primary importance. In another paper, presented to, butdeclined by, the Royal Society, he confirmed this law by newexperiments, and materially extended it. He also executed experimentson the heat consequent on the passage of Voltaic electricity throughelectrolytes, and found, in all cases, that the heat evolved by theproper action of any Voltaic current is proportional to the square ofthe intensity of that current, multiplied by the resistance toconduction which it experiences. From this law he deduced a number ofconclusions of the highest importance to electrochemistry. 

It was during these enquiries, which are marked throughout by raresagacity and originality, that the great idea of establishingquantitative relations between Mechanical Energy and Heat arose andassumed definite form in his mind. In 1843 Mr. Joule read before themeeting of the British Association at Cork a. Paper' On the CalorificEffects of Magneto-Electricity, and on the Mechanical Value of Heat. 'Even at the present day this memoir is tough reading, and at the timeit was written it must have appeared hopelessly entangled. This, Ishould think, was the reason why Faraday advised Mr. Joule not tosubmit the paper to the Royal Society. But its drift and results aresummed up in these memorable words by its author, written some timesubsequently: 'In that paper it was demonstrated experimentally, thatthe mechanical power exerted in turning a magneto-electric machine isconverted into the heat evolved by the passage of the currents ofinduction through its coils; and, on the other hand, that the motivepower of the electromagnetic engine is obtained at the expense of theheat due to the chemical reaction of the battery by which it isworked. ' [Footnote: Phil. Mag. May, 1845. ] It is needless to dwellupon the weight and importance of this statement. 

Considering the imperfections incidental to a first determination, itis not surprising that the 'mechanical values of heat, ' deduced fromthe different series of experiments published in 1843, varied widelyfrom each other. The lowest limit was 587, and the highest 1, 026foot-pounds, for 1 degree Fahr. Of temperature. 

One noteworthy result of his enquiries, which was pointed out at thetime by Mr. Joule, had reference to the exceedingly small fraction ofthe heat actually converted into useful effect in the steam-engine. The thoughts of the celebrated Julius Robert Mayer, who was thenengaged in Germany upon the same question, had moved independently inthe same groove; but to his labours due reference will be made on afuture occasion. [Footnote: See the next Fragment. ] In the memoir nowreferred to, Mr. Joule also announced that he had proved heat to beevolved during the passage of water through narrow tubes; and hededuced from these experiments an equivalent of 770 foot-pounds, afigure remarkably near the one now accepted. A detached statementregarding the origin and convertibility of animal heat strikinglyillustrates the penetration of Mr. Joule, and his mastery ofprinciples, at the period now referred to. A friend had mentioned tohim Haller's hypothesis, that animal heat might arise from thefriction of the blood in the veins and arteries. 'It isunquestionable, ' writes Mr. Joule, ' that heat is produced by suchfriction; but it must be understood that the mechanical force expendedin the friction is a part of the force of affinity which causes thevenous blood to unite with oxygen, so that the whole heat of thesystem must still be referred to the chemical changes. But if theanimal were engaged in turning a piece of machinery, or in ascending amountain, I apprehend that in proportion to the muscular effort putforth for the purpose, a _diminution_ of the heat evolved in the systemby a given chemical action would be experienced. ' The italics in thismemorable passage, written, it is to be remembered, in 1843, are Mr. Joule's own. 

The concluding paragraph of this British Association paper equallyillustrates his insight and precision, regarding the nature ofchemical and latent heat. 'I had, ' he writes, 'endeavoured to provethat when two atoms combine together, the heat evolved is exactly thatwhich would have been evolved by the electrical current due to thechemical action taking place, and is therefore proportional to theintensity of the chemical force causing the atoms to combine. I nowventure to state more explicitly, that it is not precisely theattraction of affinity, but rather the mechanical force expended bythe atoms in falling towards one another, which determines theintensity of the current, and, consequently, the quantity of heatevolved; so that we have a simple hypothesis by which we may explainwhy heat is evolved so freely in the combination of gases, and bywhich indeed we may account "latent heat" as a mechanical power, prepared for action, as a watch-spring is when wound up. Suppose, forthe sake of illustration, that 8 lbs. Of oxygen and 1 lb. Of hydrogenwere presented to one another in the gaseous state, and then exploded;the heat evolved would be about 1 degree Fahr. In 60, 000 lbs. Ofwater, indicating a mechanical force, expended in the combination, equal to a weight of about 50, 000, 000 lbs. Raised to the height of onefoot. Now if the oxygen and hydrogen could be presented to each otherin a liquid state, the heat of combination would be less than before, because the atoms in combining would fall through less space. ' Nowords of mine are needed to point out the commanding grasp ofmolecular physics, in their relation to the mechanical theory of heat, implied by this statement. 

Perfectly assured of the importance of the principle which hisexperiments aimed at establishing, Mr. Joule did not rest content withresults presenting such discrepancies as those above referred to. Heresorted in 1844 to entirely new methods, and made elaborateexperiments on the thermal changes produced in air during itsexpansion: firstly, against a pressure, and therefore performing work;secondly, against no pressure, and therefore performing no work. Hethus established anew the relation between the heat consumed and thework done. From five different series of experiments he deduced fivedifferent mechanical equivalents, the agreement between them being fargreater than that attained in his first experiments. The mean of themwas 802 foot-pounds. From experiments with water agitated by apaddle-wheel, he deduced, in 1845, an equivalent of 890 foot-pounds. In 1847 he again operated upon water and sperm-oil, agitated them by apaddle-wheel, determined their elevation of temperature, and themechanical power which produced it. From the one he derived anequivalent of 781. 6 foot-pounds; from the other an equivalent of 782. 1foot-pounds. The mean of these two very close determinations is 781. 8foot-pounds. 

By this time the labours of the previous ten years had made Mr. Joulecompletely master of the conditions essential to accuracy and success. Bringing his ripened experience to bear upon the subject, he executedin 1849 a series of 40 experiments on the friction of water, 50experiments on the friction of mercury, and 20 experiments on thefriction of plates of cast-iron. He deduced from these experimentsour present mechanical equivalent of heat, justly recognised all overthe world as 'Joule's equivalent. '

There are labours so great and so pregnant in consequences, that theyare most highly praised when they are most simply stated. Such arethe labours of Mr. Joule. They constitute the experimental foundationof a principle of incalculable moment, not only to the practice, butstill more to the philosophy of Science. Since the days of Newton, nothing more important than the theory, of which Mr. Joule is theexperimental demonstrator, has been enunciated. 

I have omitted all reference to the numerous minor papers with whichMr. Joule has enriched scientific literature. Nor have I alluded tothe important investigations which he has conducted jointly with SirWilliam Thomson. But sufficient, I think, has been here said to showthat, in conferring upon Mr. Joule the highest honour of the RoyalSociety, the Council paid to genius not only a well-won tribute, butone which had been fairly earned twenty years previously. [Footnote:Lord Beaconsfield has recently honoured himself and England bybestowing an annual pension of 200 pounds on Dr. Joule. ]

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XX. THE COPLEY MEDALIST OF 1871. 

DR. JULIUS ROBERT MAYER was educated for D the medical profession. Inthe summer of 1840, as he himself informs us, he was at Java, andthere observed that the venous blood of some of his patients had asingularly bright red colour. The observation riveted his attention;he reasoned upon it, and came to the conclusion that the brightness ofthe colour was due to the fact that a less amount of oxidationsufficed to keep up the temperature of the body in a hot climate thanin a cold one. The darkness of the venous blood he regarded as thevisible sign of the energy of the oxidation. 

It would be trivial to remark that accidents such as this, appealingto minds prepared for them, have often led to great discoveries. Mayer's attention was thereby drawn to the whole question of animalheat. Lavoisier had ascribed this heat to the oxidation of the food. 'One great principle, ' says Mayer, 'of the physiological theory ofcombustion, is that under all circumstances the same amount of fuelyields, by its perfect combustion, the same amount of heat; that thislaw holds good even for vital processes; and that hence the livingbody, notwithstanding all its enigmas and wonders, is incompetent togenerate heat out of nothing. '

But beyond the power of generating internal heat, the animal organismcan also generate heat outside of itself. A blacksmith, for example, by hammering can heat a nail, and a savage by friction can warm woodto its point of ignition. Now, unless we give up the physiologicalaxiom that the living body cannot create heat out of nothing, 'we aredriven, ' says Mayer, 'to the conclusion that it is the total heatgenerated within and without that is to be regarded as the truecalorific effect of the matter oxidised in the body. '

From this, again, he inferred that the heat generated externally muststand in a fixed relation to the work expended in its production. For, supposing the organic processes to remain the same; if it werepossible, by the mere alteration of the apparatus, to generatedifferent amounts of heat by the same amount of work, it would followthat the oxidation of the same amount of material would sometimesyield a less, sometimes a greater, quantity of heat. 'Hence, ' saysMayer, 'that a fixed relation subsists between heat and work, is apostulate of the physiological theory of combustion. '

This is the simple and natural account, given subsequently by Mayerhimself, of the course of thought started by his observation in Java. But the conviction once formed, that an unalterable relation subsistsbetween work and heat, it was: inevitable that Mayer should seek toexpress it numerically. It was also inevitable that a mind like his, having raised itself to clearness on this important point, should pushforward to consider the relationship of natural forces generally. Atthe beginning of 1842 his work had made considerable progress; but hehad become physician to the town of Heilbronn, and the duties of hisprofession limited the time which he could devote to purely scientificenquiry. He thought it wise, therefore, to secure himself againstaccident, and in the spring of 1842 wrote to Liebig, asking him topublish in his 'Annalen' a brief preliminary notice of the work thenaccomplished. Liebig did so, and Dr. Mayer's first paper is containedin the May number of the 'Annalen' for 1842. 

Mayer had reached his conclusions by reflecting on the complexprocesses of the living body; but his first step in public was tostate definitely the physical principles on which his physiologicaldeductions were to rest. He begins, therefore, with the forces ofinorganic nature. He finds in the universe two systems of causeswhich are not mutually convertible;--the different kinds of matter andthe different forms of force. The first quality of both he affirms tobe indestructibility. A force cannot become nothing, nor can it arisefrom nothing. Forces are convertible but not destructible. In theterminology of his time, he then gives clear expression to the ideasof potential and dynamic energy, illustrating his point by a weightresting upon the earth, suspended at a height above the earth, andactually falling to the earth. He next fixes his attention on caseswhere motion is apparently destroyed, without producing other motion;on the shock of inelastic bodies, for example. Under what form doesthe vanished motion maintain itself? Experiment alone, says Mayer, can help us here. He warms water by stirring it; he refers to theforce expended in overcoming friction. Motion in both casesdisappears; but heat is generated, and the quantity generated is theequivalent of the motion destroyed. 'Our locomotives, ' he observeswith extraordinary sagacity, 'may be compared to distilling apparatus:the heat beneath the boiler passes into the motion of the train, andis again deposited as heat in the axles and wheels. 

A numerical solution of the relation between heat and work was whatMayer aimed at, and towards the end of his first paper he makes theattempt. It was known that a definite amount of air, in rising onedegree in temperature, can take up two different amounts of heat. Ifits volume be kept constant, it takes up one amount: if its pressurebe kept constant it takes up a different amount. These two amountsare called the specific heat under constant volume and under constantpressure. The ratio of the first to the second is as 1: 1. 421. Noman, to my knowledge, prior to Dr. Mayer, penetrated the significanceof these two numbers. He first saw that the excess 0. 421 was not, asthen universally supposed, heat actually lodged in the gas, but heatwhich had been actually consumed by the gas in expanding againstpressure. The amount of work here performed was accurately known, theamount of heat consumed was also accurately known, and from these dataMayer determined the mechanical equivalent of heat. Even in thisfirst paper he is able to direct attention to the enormous discrepancybetween the theoretic power of the fuel consumed in steam-engines, andtheir useful effect. 

Though this paper contains but the germ of his further labours, Ithink it may be safely assumed that, as regards the mechanical theoryof heat, this obscure Heilbronn physician, in the year 1842, was inadvance of all the scientific men of the time. 

Having, by the publication of this paper, secured himself against whathe calls 'Eventualitaeten, ' he devoted every hour of his spare timeto his studies, and in 1845 published a memoir which far transcendshis first one in weight and fulness, and, indeed, marks an epoch inthe history of science. The title of Mayer's first paper was, 'Remarks on the Forces of Inorganic Nature. ' The title of his secondgreat essay was, 'Organic Motion in its Connection with Nutrition. ' Init he expands and illustrates the physical principles laid down in hisfirst brief paper. 

He goes fully through the calculation of the mechanical equivalent ofheat. He calculates the performances of steam-engines, and finds that100 lbs. Of coal, in a good working engine, produce only the sameamount of heat as 95 lbs. In an unworking one; the 5 missing lbs. Having been converted into work. He determines the useful effect ofgunpowder, and finds nine per cent. Of the force of the consumedcharcoal invested on the moving ball. He records observations on theheat generated in water agitated by the pulping engine of a papermanufactory, and calculates the equivalent of that heat inhorse-power. He compares chemical combination with mechanicalcombination--the union of atoms with the union of falling bodies withthe earth. He calculates the velocity with which a body starting atan infinite distance would strike the earth's surface, and finds thatthe heat generated by its collision would raise an equal weight ofwater 17, 356' C. In temperature. He then determines the thermaleffect which would be produced by the earth itself falling into thesun. So that here, in 1845, we have the germ of that meteoric theoryof the sun's heat which Mayer developed with such extraordinaryability three years afterwards. He also points to the almostexclusive efficacy of the sun's heat in producing mechanical motionsupon the earth, winding up with the profound remark, that the heatdeveloped by friction in the wheels of our wind and water mills comesfrom the sun in the form of vibratory motion; while the heat producedby mills driven by tidal action is generated at the expense of theearth's axial rotation. 

Having thus, with firm step, passed through the powers of inorganicnature, his next object is to bring his principles to bear upon thephenomena of vegetable and animal life. Wood and coal can burn;whence come their heat, and the work producible by that heat? Fromthe immeasurable reservoir of the sun. Nature has proposed to herselfthe task of storing up the light which streams earthward from the sun, and of casting into a permanent form the most fugitive of all powers. To this end she has overspread the earth with organisms which, whileliving, take in the solar light, and by its consumption generateforces of another kind. These organisms are plants. The vegetableworld, indeed, constitutes the instrument whereby the wave-motion ofthe sun is changed into the rigid form of chemical tension, and thusprepared for future use. With this prevision, as shall subsequentlybe shown, the existence of the human race itself is inseparablyconnected. It is to be observed that Mayer's utterances are far frombeing anticipated by vague statements regarding the 'stimulus' oflight, or regarding coal as 'bottled sunlight. ' He first saw the fullmeaning of De Saussure's observation as to the reducing power of thesolar rays, and gave that observation its proper place in the doctrineof conservation. In the leaves of a tree, the carbon and oxygen ofcarbonic acid, and the hydrogen and oxygen of water, are forcedasunder at the expense of the sun, and the amount of power thussacrificed is accurately restored by the combustion of the tree. Theheat and work potential in our coal strata are so much strengthwithdrawn from the sun of former ages. Mayer lays the axe to the rootof the notions regarding 'vital force' which were prevalent when hewrote. With the plain fact before us that in the absence of the solarrays plants cannot perform the work of reduction, or generate chemicaltensions, it is, he contends, incredible that these tensions should becaused by the mystic play of the vital force. Such an hypothesiswould cut off all investigation; it would land us in a chaos ofunbridled phantasy. 

'I count, ' he says, 'therefore, upon your agreement with me when Istate, as an axiomatic truth, that during vital processes theconversion only, and never the creation of matter or force occurs. '

Having cleared his way through the vegetable world, as he hadpreviously done through inorganic nature, Mayer passes on to the otherorganic kingdom. The physical forces collected by plants become theproperty of animals. Animals consume vegetables, and cause them toreunite with the atmospheric oxygen. Animal heat is thus produced;and not only animal heat, but animal motion. There is noindistinctness about Mayer here; he grasps his subject in all itsdetails, and reduces to figures the concomitants of muscular action. Abowler who imparts to an 8-lb. Ball a velocity of 30 feet, consumesin the act one tenth of a grain of carbon. A man weighing 150 lbs, who lifts his own body to a height of 8 feet, consumes in the act 1grain of carbon. In climbing a mountain 10, 000 feet high, theconsumption of the same man would be 2 oz. 4 drs. 50 grs. Of carbon. Boussingault had determined experimentally the addition to be made tothe food of horses when actively working, and Liebig had determinedthe addition to be made to the food of men. Employing the mechanicalequivalent of heat, which he had previously calculated, Mayer provesthe additional food to be amply sufficient to cover the increasedoxidation. 

But he does not content himself with showing, in a general way, thatthe human body burns according to definite laws, when it performsmechanical work. He seeks to determine the particular portion of thebody consumed, and in doing so executes some noteworthy calculations. The muscles of a labourer 150 lbs. In weight weigh 64 lbs; but whenperfectly desiccated they fall to 15 lbs. Were the oxidationcorresponding to that labourer's work exerted on the muscles alone, they would be utterly consumed in 80 days. The heart furnishes astill more striking example. Were the oxidation necessary to sustainthe heart's action exerted upon its own tissue, it would be utterlyconsumed in 8 days. And if we confine our attention to the twoventricles, their action would be sufficient to consume the associatedmuscular tissue in 3. 5 days. Here, in his own words, emphasised inhis own way, is Mayer's pregnant conclusion from these calculations:'The muscle is only the apparatus by means of which the conversion ofthe force is effected; but it is not the substance consumed in theproduction of the mechanical effect. ' He calls the blood 'the oil ofthe lamp of life;' it is the slow-burning fluid whose chemical force, in the furnace of the capillaries, is sacrificed to produce animalmotion. This was Mayer's conclusion twenty-six years ago. It was incomplete opposition to the scientific conclusions of his time; buteminent investigators have since amply verified it. 

Thus, in baldest outline, I have sought to give some notion of thefirst half of this marvellous essay. The second half is soexclusively physiological that I do not wish to meddle with it. Iwill only add the illustration employed by Mayer to explain the actionof the nerves upon the muscles. As an engineer, by the motion of hisfinger in opening a valve or loosing a detent, can liberate an amountof mechanical motion almost infinite compared with its exciting cause, so the nerves, acting upon the muscles, can unlock an amount ofactivity, wholly out of proportion to the work done by the nervesthemselves. 

As regards these questions of weightiest import to the science ofphysiology, Dr. Mayer, in 1845, was assuredly far in advance of allliving men. 

Mayer grasped the mechanical theory of heat with commanding power, illustrating it and applying it in the most diverse domains. He began, as we have seen, with physical principles; he determined the numericalrelation between heat and work; he revealed the source of the energiesof the vegetable world, and showed the relationship of the heat of ourfires to solar heat. He followed the energies which were potential inthe vegetable, up to their local exhaustion in the animal. But in1845 a new thought was forced upon him by his calculations. He then, for the first time, drew attention to the astounding amount of heatgenerated by gravity where the force has sufficient distance to actthrough. He proved, as I have before stated, the heat of collision ofa body falling from an infinite distance to the earth, to besufficient to raise the temperature of a quantity of water, equal tothe falling body in weight, 17, 356°C. He also found, in 1845, thatthe gravitating force between the earth and sun was competent togenerate an amount of heat equal to that obtainable from thecombustion of 6, 000 times the weight of the earth of solid coal. Withthe quickness of genius he saw that we had here a power sufficient toproduce the enormous temperature of the sun, and also to account forthe primal molten condition of our own planet. Mayer shows the utterinadequacy of chemical forces, as we know them, to produce or maintainthe solar temperature. He shows that were the sun a lump of coal itwould be utterly consumed in 5, 000 years. He shows the difficultiesattending the assumption that the sun is a cooling body; for, supposing it to possess even the high specific heat of water, itstemperature would fall 15, 000' in 5, 000 years. He finally concludesthat the light and heat of the sun are maintained by the constantimpact of meteoric matter. I never ventured an opinion as to thetruth of this theory; that is a question which may still have to befought out. But I refer to it as an illustration of the force ofgenius with which Mayer followed the mechanical theory of heat throughall its applications. Whether the meteoric theory be a matter of factor not, with him abides the honour of proving to demonstration thatthe light and heat of suns and stars may be originated and maintainedby the collisions of cold planetary matter. 

It is the man who with the scantiest data could accomplish all this insix short years, and in, the hours snatched from the duties of anarduous profession, that the Royal Society, in 1871, crowned with itshighest honour. 

Comparing this brief history with that of the Copley Medalist of 1870, the differentiating influence of 'environment, ' on two minds ofsimilar natural cast and endowment, comes out in an instructivemanner. Withdrawn from mechanical appliances, Mayer fell back uponreflection, selecting with marvellous sagacity, from existing physicaldata, the single result on which could be founded a calculation of themechanical equivalent of heat. In the midst of mechanical appliances, Joule resorted to experiment, and laid the broad and firm foundationwhich has secured for the mechanical theory the acceptance it nowenjoys. A great portion of Joule's time was occupied in actualmanipulation; freed from this, Mayer had time to follow the theoryinto its most abstruse and impressive applications. With their placesreversed, however, Joule might have become Mayer, and Mayer might havebecome Joule. 

It does not lie within the scope of these brief articles to enter uponthe developments of the Dynamical Theory accomplished since Joule andMayer executed their memorable labours. 

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XXI. DEATH BY LIGHTNING. 

PEOPLE in general imagine, when they think at all about the matter, that an impression upon the nerves--a blow, for example, or the prickof a pin--is felt at the moment it is inflicted. But this is not thecase. The seat of sensation being the brain, to it the intelligenceof any impression made upon the nerves has to be transmitted beforethis impression can become manifest as consciousness. Thetransmission, moreover, requires time, and the consequence is, that awound inflicted on a portion of the body distant from the brain ismore tardily appreciated than one inflicted adjacent to the brain. Byan extremely ingenious experimental arrangement, Helmholtz hasdetermined the velocity of this nervous transmission, and finds it tobe about eighty feet a second, or less than one-thirteenth of thevelocity of sound in air. If therefore, a whale forty feet long werewounded in the tail, it would not be conscious of the injury till halfa second after the wound had been inflicted. [Footnote: A mostadmirable lecture on the velocity of nervous transmission has beenpublished by Dr. Du Bois Reymond in the 'Proceedings of the RoyalInstitution' for 1866, vol. Iv. P. 575. ] But this is not the onlyingredient in the delay. There can scarcely be a doubt that to everyact of consciousness belongs a determinate molecular arrangement ofthe brain--that every thought or feeling has its physical correlativein that organ; and nothing can be more certain than that everyphysical change, whether molecular or mechanical, requires time forits accomplishment. So that, besides the interval of transmission, astill further time is necessary for the brain to put itself inorder--for its molecules to take up the motions or positions necessaryto the completion of consciousness. Helmholtz considers thatone-tenth of a second is demanded for this purpose. Thus, in the caseof the whale above supposed, we have first half a second consumed inthe transmission of the intelligence through the sensor nerves to thehead, one-tenth of a second consumed by the brain in completing thearrangements necessary to consciousness, and, if the velocity oftransmission through the motor be the same as that through the sensornerves, half a second in sending a command to the tail to defenditself. Thus one second and a tenth would elapse before an impressionmade upon its caudal nerves could be responded to by a whale fortyfeet long. 

Now, it is quite conceivable that an injury might be inflicted sorapidly that within the time required by the brain to complete thearrangements necessary to consciousness, its power of arrangementmight be destroyed. In such a case, though the injury might be of anature to cause death, this would occur without pain, Death in thiscase would be simply the sudden negation of life, without anyintervention of consciousness whatever. 

The time required for a rifle-bullet to pass clean through a man'shead may be roughly estimated at a thousandth of a second. Here, therefore, we should have no room for sensation, and death would bepainless. But there are other actions which far transcend in rapiditythat of the rifle-bullet. A flash of lightning cleaves a cloud, appearing and disappearing in less than a hundred-thousandth of asecond, and the velocity of electricity is such as would carry it in asingle second over a distance almost equal to that which separates theearth and moon. It is well known that a luminous impression once madeupon the retina endures for about one-sixth of a second, and that thisis the reason why we see a continuous band of light when a glowingcoal is caused to pass rapidly through the air. A body illuminated byan instantaneous flash continues to be seen for the sixth of a secondafter the flash has become extinct; and if the body thus illuminatedbe in motion, it appears at rest at the place where the flash fallsupon it. When a colour-top with differently-coloured sectors iscaused to spin rapidly the colours blend together. Such a top, rotating in a dark room and illuminated by an electric spark, appearsmotionless, each distinct colour being clearly seen. Professor Dovehas found that a flash of lightning produces the same effect. Duringa thunderstorm he put a colour-top in exceedingly rapid motion, andfound that every flash revealed the top as a motionless object withits colours distinct. If illuminated solely by a flash of lightning, the motion of all bodies on the earth's surface would, as Dove hasremarked, appear suspended. A cannon-ball, for example, would haveits flight apparently arrested, and would seem to hang motionless inspace as long as the luminous impression which revealed the ballremained upon the eye. 

If, then, a rifle-bullet move with sufficient rapidity to destroy lifewithout the interposition of sensation, much more is a flash oflightning competent to produce this effect. Accordingly, we havewell-authenticated cases of people being struck senseless by lightningwho, on recovery, had no memory of pain. The following circumstantialcase is described by Hemmer:

On June 30, 1788, a soldier in the neighbourhood of Mannheim, beingovertaken by rain, placed himself under a tree, beneath which a womanhad previously taken shelter. He looked upwards to see whether thebranches were thick enough to afford the required protection, and, indoing so, was struck by lightning, and fell senseless to the earth. The woman at his side experienced the shock in her foot, but was notstruck down. Some hours afterwards the man revived, but rememberednothing about what had occurred, save the fact of his looking up atthe branches. This was his last act of consciousness, and he passedfrom the conscious to the unconscious condition without pain. Thevisible marks of a lightning stroke are usually insignificant: thehair is sometimes burnt; slight wounds are observed; while, in someinstances, a red streak marks the track of the discharge over theskin. 

Under ordinary circumstances, the discharge from a small Leyden jar isexceedingly unpleasant to me. Some time ago I happened to stand inthe presence of a numerous audience, with a battery of fifteen largeLeyden jars charged beside me. Through some awkwardness on my part, Itouched a wire leading from the battery, and the discharge wentthrough my body. Life was absolutely blotted out for a very sensibleinterval, without a trace of pain. Ina second or so consciousnessreturned; I vaguely discerned the audience and apparatus, and, by thehelp of these external appearances, immediately concluded that I hadreceived the battery discharge. The intellectual consciousness of myposition was restored with exceeding rapidity, but not so the opticalconsciousness. To prevent the audience from being alarmed, I observedthat it had often been my desire to receive accidentally such a shock, and that my wish had at length been fulfilled. But, while making thisremark, the appearance which my body presented to my eyes was that ofa number of separate pieces. The arms, for example, were detachedfrom the trunk, and seemed suspended in the air. In fact, memory andthe power of reasoning appeared to be complete long before the opticnerve was restored to healthy action. But what I wish chiefly todwell upon here is, the absolute painlessness of the shock; and therecannot, I think, be a doubt that, to a person struck dead bylightning, the passage from life to death occurs without consciousnessbeing in the least degree implicated. It is an abrupt stoppage ofsensation, unaccompanied by a pang. 

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XXII. SCIENCE AND THE 'SPIRITS. '

THEIR refusal to investigate 'spiritual phenomena' is often urged as areproach against scientific men. I here propose to give a sketch ofan attempt to apply to the 'phenomena' those methods of enquiry whichare found available in dealing with natural truth. 

Some years ago, when the spirits were particularly active in thiscountry, Faraday was invited, or rather entreated, by one of hisfriends to meet and question them. He had, however, already madetheir acquaintance, and did not wish to renew it. I had not been soprivileged, and he therefore kindly arranged a transfer of theinvitation to me. The spirits themselves named the time of meeting, and I was conducted to the place at the day and hour appointed. 

Absolute unbelief in the facts was by no means my condition of mind. On the contrary, I thought it probable that some physical principle, not evident to the spiritualists themselves, might underlie theirmanifestations. Extraordinary effects are produced by theaccumulation of small impulses. Galileo set a heavy pendulum inmotion by the well-timed puffs of his breath. Ellicot set one clockgoing by the ticks of another, even when the two clocks were separatedby a wall. Preconceived notions, can, moreover, vitiate, to anextraordinary degree, the testimony of even veracious persons. Hencemy desire to witness those extraordinary phenomena, the existence ofwhich seemed placed beyond a doubt by the known veracity of those whohad witnessed and described them. The meeting took place at a privateresidence in the neighbourhood of London. My host, his intelligentwife, and a gentleman who may be called X, were in the house when Iarrived. I was informed that the 'medium' had not yet made herappearance; that she was sensitive, and might resent suspicion. Itwas therefore requested that the tables and chairs should be examinedbefore her arrival, in order to be assured that there was no trickeryin the furniture. This was done; and I then first learned that myhospitable host had arranged that the séance should be a dinner-party. This was to me an unusual form of investigation; but I accepted it, asone of the accidents of the occasion. 

The 'medium' arrived--a delicate-looking young lady, who appeared tohave suffered much from ill health. I took her to dinner and satclose beside her. Facts were absent for a considerable time, a seriesof very wonderful narratives supplying their place. The duty ofbelief on the testimony of witnesses was frequently insisted on. X. Appeared to be a chosen spiritual agent, and told us many surprisingthings. He affirmed that, when he took a pen in his hand, aninfluence ran from his shoulder downwards, and impelled him to writeoracular sentences. I listened for a time, offering no observation. 'And now, ' continued X, 'this power has so risen as to reveal to methe thoughts of others. Only this morning I told a friend what he wasthinking of, and what he intended to do during the day. ' Here, Ithought, is something that can be at once tested. I said immediatelyto X: 'If you wish to win to your cause an apostle, who will proclaimyour principles to the world from the housetop, tell me what I am nowthinking of. ' X. Reddened, and did not tell me my thought. 

Some time previously I had visited Baron Reichenbach, in Vienna, and Inow asked the young lady who sat beside me, whether she could see anyof the curious things which he describes--the light emitted bycrystals, for example? Here is the conversation which followed, asextracted from my notes, written on the day following the séance. 

Medium. --'Oh, yes; but I see light around all bodies. '

I--'Even in perfect darkness?'

Medium. --'Yes; I see luminous atmospheres round all people. Theatmosphere which surrounds Mr. R. C. Would fill this room withlight. '

I. --'You are aware of the effects ascribed by Baron Reichenbach tomagnets?'

Medium. --'Yes; but a magnet makes me terribly ill. '

I. --'Am I to understand that, if this room were perfectly dark, youcould tell whether it contained a magnet, without being informed ofthe fact?'

Medium. --'I should know of its presence on entering the room. '

I. --'How?'

Medium. --'I should be rendered instantly ill. '

I. --'How do you feel to-day?'

Medium. --'Particularly well; I have not been so well for months. '

I. --'Then, may I ask you whether there is, at the present moment, amagnet in my possession?'

The young lady looked at me, blushed, and stammered, 'No; I am not enrapport with you. '

I sat at her right hand, and a left-hand pocket, within six inches ofher person, contained a magnet. 

Our host here deprecated discussion, as it 'exhausted the medium. ' Thewonderful narratives were resumed; but I had narratives of my ownquite as wonderful. These spirits, indeed, seemed clumsy creations, compared with those with which my own work had made me familiar. Itherefore began to match the wonders related to me by other wonders. Alady present discoursed on spiritual atmospheres, which she could seeas beautiful colours when she closed her eyes. I professed myselfable to see similar colours, and, more than that, to be able to seethe interior of my own eyes. The medium affirmed that she could seeactual waves of light coming from the sun. I retorted that men ofscience could tell the exact number of waves emitted in a second, andalso their exact length. The medium spoke of the performances of thespirits on musical instruments. I said that such performance wasgross, in comparison with a kind of music which had been discoveredsome time previously by a scientific man. Standing at a distance oftwenty feet from a jet of gas, he could command the flame to emit amelodious note; it would obey, and continue its song for hours. Soloud was the music emitted by the gas-flame, that it might be heard byan assembly of a thousand people. These were acknowledged to be asgreat marvels as any of those of spiritdom. The spirits were thenconsulted, and I was pronounced to be a first-class medium. 

During this conversation a low knocking was heard from time to timeunder the table. These, I was told, were the spirits' knocks. I wasinformed that one knock, in answer to a question, meant 'No;' that twoknocks meant 'Not yet;' and that three knocks meant 'Yes. '

In answer to a question whether I was a medium, the response was threebrisk and vigorous knocks. I noticed that the knocks issued from aparticular locality, and therefore requested the spirits to be goodenough to answer from another corner of the table. They did notcomply; but I was assured that they would do it, and much more, by-and-by. The knocks continuing, I turned a wine-glass upside down, and placed my ear upon it, as upon a stethoscope. The spirits seemeddisconcerted by the act; they lost their playfulness, and did notrecover it for a considerable time. 

Somewhat weary of the proceedings, I once threw myself back against mychair and gazed listlessly out of the window. While thus engaged, thetable was rudely pushed. Attention was drawn to the wine, stilloscillating in the glasses, and I was asked whether that was notconvincing. I readily granted the fact of motion, and began to feelthe delicacy of my position. There were several pairs of arms uponthe table, and several pairs of legs under it; but how was I, withoutoffence, to express the conviction which I really entertained? Toward off the difficulty, I again turned a wine-glass upside down andrested my ear upon it. The rim of the glass was not level, and myhair, on touching it, caused it to vibrate, and produce a peculiarbuzzing sound. A perfectly candid and warm-hearted old gentleman atthe opposite side of the table, whom I may call A, drew attention tothe sound, and expressed his entire belief that it was spiritual. I, however, informed him that it was the moving hair acting on the glass. The explanation was not well received; and X, in a tone of severepleasantry, demanded whether it was the hair that had moved the table. The promptness of my negative probably satisfied him that my notionwas a very different one. 

The superhuman power of the spirits was next dwelt upon. The strengthof man, it was stated, was unavailing in opposition to theirs. Nohuman power could prevent the table from moving when they pulled it. During the evening this pulling of the table occurred, or rather wasattempted, three times. Twice the table moved when my attention waswithdrawn from it; on a third occasion, I tried whether the act couldbe provoked by an assumed air of inattention. Grasping the tablefirmly between my knees, I threw myself back in the chair, and waited, with eyes fixed on vacancy, for the pull. It came. For some secondsit was pull spirit, hold muscle; the muscle, however, prevailed, andthe table remained at rest. Up to the present moment, this interestingfact is known only to the particular spirit in question and myself. 

A species of mental scene-painting, with which my own pursuits hadlong rendered me familiar, was employed to figure the changes anddistribution of spiritual power. The spirits, it was alleged, wereprovided with atmospheres, which combined with and interpenetratedeach other, and considerable ingenuity was shown in demonstrating thenecessity of time in effecting the adjustment of the atmospheres. Arearrangement of our positions was proposed and carried out; and soonafterwards my attention was drawn to a scarcely sensible vibration onthe part of the table. Several persons were leaning on the table atthe time, and I asked permission to touch the medium's hand. 'Oh! Iknow I tremble, ' was her reply. Throwing one leg across the other, Iaccidentally nipped a muscle, and produced thereby an involuntaryvibration of the free leg. This vibration, I knew, must becommunicated to the floor, and thence to the chairs of all present. Itherefore intentionally promoted it. My attention was promptly drawnto the motion; and a gentleman beside me, whose value as a witness Iwas particularly desirous to test, expressed his belief that it wasout of the compass of human power to produce so strange a tremor. 'Ibelieve, ' he added, earnestly, 'that it is entirely the spirits'work. ' 'So do I, ' added, with heat, the candid and warmhearted oldgentleman A. 'Why, sir, ' he continued, 'I feel them at this momentshaking my chair. ' I stopped the motion of the leg. 'Now, sir, ' A. Exclaimed, 'they are gone. ' I began again, and A. Once more affirmedtheir presence. I could, however, notice that there were doubterspresent, who did not quite know what to think of the manifestations. Isaw their perplexity; and, as there was sufficient reason to believethat the disclosure of the secret would simply provoke anger, I keptit to myself. 

Again a period of conversation intervened, during which the spiritsbecame animated. The evening was confessedly a dull one, but mattersappeared to brighten towards its close. The spirits were requested tospell the name by which I was known in the heavenly world. Our hostcommenced repeating the alphabet, and when he reached the letter 'P' aknock was heard. He began again, and the spirits knocked at theletter 'O. ' I was puzzled, but waited for the end. The next letterknocked down was 'E. ' I laughed, and remarked that the spirits weregoing to make a poet of me. Admonished for my levity, I was informedthat the frame of mind proper for the occasion ought to have beensuperinduced by a perusal of the Bible immediately before the séance. The spelling, however, went on, and sure enough I came out a poet. Butmatters did not end here. Our host continued his repetition of thealphabet, and the next letter of the name proved to be '0. ' Here wasmanifestly an unfinished word; and the spirits were apparently intheir most communicative mood. The knocks came from under the table, but no person present evinced the slightest desire to look under it. Iasked whether I might go underneath; the permission was granted; so Icrept under the table. Some tittered; but the candid old A. Exclaimed, 'He has a right to look into the very dregs of it, toconvince himself. ' Having pretty well assured myself that no soundcould be produced under the table without its origin being revealed, Irequested our host to continued his questions. He did so, but invain. He adopted a tone of tender entreaty; but the 'dear spirits'had become dumb dogs, and refused to be entreated. I continued underthat table for at least a quarter of an hour, after which, with afeeling of despair as regards the prospects of humanity never beforeexperienced, I regained my chair. Once there, the spirits resumedtheir loquacity, and dubbed me 'Poet of Science. '

This, then, is the result of an attempt made by a scientific man tolook into these spiritual phenomena. It is not encouraging; and forthis reason. The present promoters of spiritual phenomena dividethemselves into two classes, one of which needs no demonstration, while the other is beyond the reach of proof. The victims like tobelieve, and they do not like to be undeceived. Science is perfectlypowerless in the presence of this frame of mind. It is, moreover, astate perfectly compatible with extreme intellectual subtlety and acapacity for devising hypotheses which only require the hardihoodengendered by strong conviction, or by callous mendacity, to renderthem impregnable. The logical feebleness of science is notsufficiently borne in mind. It keeps down the weed of superstition, not by logic but by, slowly rendering the mental soil unfit for itscultivation. When science appeals to uniform experience, thespiritualist will retort, 'How do you know that a uniform experiencewill continue uniform? You tell me that the sun has risen for sixthousand years: that is no proof that it will rise tomorrow; withinthe next twelve hours it may be puffed out by the Almighty. ' Takingthis ground, a man may maintain the story of 'Jack and the Beanstalk'in the face of all the science in the world. You urge, in vain, thatscience has given us all the knowledge of the universe which we nowpossess, while spiritualism has added nothing to that knowledge. Thedrugged soul is beyond the reach of reason. It is in vain thatimpostors are exposed, and the special demon cast out. He has butslightly to change his shape, return to his house, and find it 'empty, swept, and garnished. '

*****

Since the time when the foregoing remarks were written I have beenmore than once among the spirits, at their own invitation. They donot improve on acquaintance. Surely no baser delusion ever obtaineddominance over the weak mind of man. 

END OF THE FIRST VOLUME. 

LONDON: PRINTED BY

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FRAGMENTS OF SCIENCE:

A SERIES OF DETACHED ESSAYS, ADDRESSES, AND REVIEWS. 

BY

JOHN TYNDALL, F. R. S. 

LONDON: PRINTED BY

SPOTTISWOODE AND CO, NEW-STREET SQUARE

AND PARLIAMENT STREET

SIXTH EDITION. 

VOL. II. 

LONDON:

LONGMANS, GREEN, AND CO. 

1879. 

All rights reserved. 

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In the bright sky they perceived an illuminator;in the all-encircling firmament an embracer;in the roar of thunder and in the violence ofthe storm they felt the presence of a shouter and of furious strikers;and out of the rain they created an Indra, or giver of rain. --MAX MULLER. 

*****

I. REFLECTIONS ON PRAYER AND NATURAL LAW. 

1861. 

AMID the apparent confusion and caprice of natural phenomena, whichroused emotions hostile to calm investigation, it must for ages haveseemed hopeless to seek for law or orderly relation; and before thethought of law dawned upon the unfolding human mind these otherwiseinexplicable effects were referred to personal agency. In the fall ofa cataract the savage saw the leap of a spirit, and the echoedthunder-peal was to him the hammer-clang of an exasperated god. Propitiation of these terrible powers was the consequence, andsacrifice was offered to the demons of earth and air. 

But observation tends to chasten the emotions and to check thosestructural efforts of the intellect which have emotion for their base. One by one natural phenomena came to be associated with theirproximate causes; the idea of direct personal volition mixing itselfwith the economy of nature retreating more and more. Many of us fearthis change. Our religious feelings are dear to us, and we look withsuspicion and dislike on any philosophy, the apparent tendency ofwhich is to dry them up. Probably every change from ancient savageryto our present enlightenment has excited, in a greater or less degree, fears of this kind. But the fact is, that we have not yet determinedwhether its present form is necessary to the life and warmth ofreligious feeling. We may err in linking the imperishable with thetransitory, and confound the living plant with the decaying pole towhich it clings. My object, however, at present is not to argue, butto mark a tendency. We have ceased to propitiate the powers ofnature--ceased even to pray for things in manifest contradiction tonatural laws. In Protestant countries, at least, I think it isconceded that the age of miracles is past. 

At an auberge near the foot of the Rhone glacier, I met, in the summerof 1858, an athletic young priest, who, after a solid breakfast, including a bottle of wine, informed me that he had come up to 'blessthe mountains. ' This was the annual custom of the place. Year by yearthe Highest was entreated, by official intercessors, to make suchmeteorological arrangements as should ensure food and shelter for theflocks and herds of the Valaisians. A diversion of the Rhone, or adeepening of the river's bed, would, at the time I now mention, havebeen of incalculable benefit to the inhabitants of the valley. Butthe priest would have shrunk from the idea of asking the Omnipotent toopen a new channel for the river, or to cause a portion of it to flowover the Grimsel pass, and down the valley of Oberhasli to Brientz. This he would have deemed a miracle, and he did not come to ask theCreator to perform miracles, but to do something which he manifestlythought lay quite within the bounds of the natural and non-miraculous. A Protestant gentleman who was present at the time smiled at thisrecital. He had no faith in the priest's blessing; still, he deemedhis prayer different in kind from a request to open a new river-cut, or to cause the water to flow up-hill. 

In a similar manner the same Protestant gentleman would doubtlesssmile at the honest Tyrolese priest, who, when he feared the burstingof a glacier dam, offered the sacrifice of the Mass upon the ice as ameans of averting the calamity. That poor man did not expect toconvert the ice into adamant, or to strengthen its texture, so as toenable it to withstand the pressure of the water; nor did he expectthat his sacrifice would cause the stream to roll back upon its sourceand relieve him, by a miracle, of its presence. But beyond theboundaries of his knowledge lay a region where rain was generated, heknew not how. He was not so presumptuous as to expect a miracle, buthe firmly believed that in yonder cloud-land matters could be soarranged, without trespass on the miraculous, that the stream whichthreatened him and his people should be caused to shrink within itsproper bounds. 

Both these priests fashioned that which they did not understand totheir respective wants and wishes. In their case imagination cameinto play, uncontrolled by a knowledge of law. A similar state ofmind was long prevalent among mechanicians. Many of these, among whomwere to be reckoned men of consummate skill, were occupied a centuryago with the question of perpetual motion. They aimed at constructinga machine which should execute work without the expenditure of power;and some of them went mad in the pursuit of this object. The faith insuch a consummation, involving, as it did, immense personal profit tothe inventor, was extremely exciting, and every attempt to destroythis faith was met by bitter resentment on the part of those who heldit. Gradually, however, as men became more and more acquainted withthe true functions of machinery, the dream dissolved. The hope ofgetting work out of mere mechanical combinations disappeared: butstill there remained for the speculator a cloud-land denser than thatwhich filled the imagination of the Tyrolese priest, and out of whichhe still hoped to evolve perpetual motion. There was the mystic storeof chemic force, which nobody understood; there were heat and light, electricity and magnetism, all competent to produce mechanical motion. [Footnote: See Helmholtz: 'Wechselwirkung der Naturkräfte. '] Here, then, was the mine in which our gem must be sought. A modified andmore refined form of the ancient faith revived; and, for aught I know, a remnant of sanguine designers may at the present moment be engagedon the problem which like-minded men in former ages left unsolved. 

And why should a perpetual motion, even under modern conditions, beimpossible? The answer to this question is the statement of thatgreat generalisation of modern science, which is known under the nameof the Conservation of Energy. This principle asserts that no powercan make its appearance in nature without an equivalent expenditure ofsome other power; that natural agents are so related to each other asto be mutually convertible, but that no new agency is created. Lightruns into heat; heat into electricity; electricity into magnetism;magnetism into mechanical force; and mechanical force again into lightand heat. The Proteus changes, but he is ever the same; and hischanges in nature, supposing no miracle to supervene, are theexpression, not of spontaneity, but of physical necessity. Aperpetual motion, then, is deemed impossible, because it demands thecreation of energy, whereas the principle of Conservation is--nocreation, but infinite conversion. 

It is an old remark that the law which moulds a tear also rounds aplanet. In the application of law in nature the terms great and smallare unknown. Thus the principle referred to teaches us that theItalian wind, gliding over the crest of the Matterhorn, is as firmlyruled as the earth in its orbital revolution round the sun; and thatthe fall of its vapour into clouds is exactly as much a matter ofnecessity as the return of the seasons. The dispersion, therefore, ofthe slightest mist by the special volition of the Eternal, would be asmuch a miracle as the rolling of the Rhone over the Grimselprecipices, down the valley of Hash to Meyringen and Brientz. 

It seems to me quite beyond the present power of science todemonstrate that the Tyrolese priest, or his colleague of the Rhonevalley, asked for an 'impossibility' in praying for good weather; butScience can demonstrate the incompleteness of the knowledge of naturewhich limited their prayers to this narrow ground; and she may lessenthe number of instances in which we 'ask amiss, ' by showing that wesometimes pray for the performance of a miracle when we do not intendit. She does assert, for example, that without a disturbance ofnatural law, quite as serious as the stoppage of an eclipse, or therolling of the river Niagara up the Falls, no act of humiliation, individual or national, could call one shower from heaven, or deflecttowards us a single beam of the sun. 

Those, therefore, who believe that the miraculous is still active innature, may, with perfect consistency, join in our periodic prayersfor fair weather and for rain: while those who hold that the age ofmiracles is past, will, if they be consistent, refuse to join in thesepetitions. And these latter, if they wish to fall back upon such ajustification, may fairly urge that the latest conclusions of scienceare in perfect accordance with the doctrine of the Master himself, which manifestly was that the distribution of natural phenomena is notaffected by moral or religious causes. 'He maketh His sun to rise onthe evil and on the good, and sendeth rain on the just and on theunjust. ' Granting 'the power of Free Will in man, ' so strongly claimedby Professor Mansel in his admirable defence of the belief inmiracles, and assuming the efficacy of free prayer to produce changesin external nature, it necessarily follows that natural laws are moreor less at the mercy of man's volition, and no conclusion founded onthe assumed permanence of those laws would be worthy of confidence. 

It is a wholesome sign for England that she numbers among her clergymen wise enough to understand all this, and courageous enough to actup to their knowledge. Such men do service to public character, byencouraging a manly and intelligent conflict with the real causes ofdisease and scarcity, instead of a delusive reliance on supernaturalaid. But they have also a value beyond this local and temporary one. They prepare the public mind for changes, which though inevitable, could hardly, without such preparation, be wrought without violence. Iron is strong; still, water in crystallising will shiver an ironenvelope, and the more unyielding the metal is, the worse for itssafety. There are in the world men who would encompass philosophicspeculation by a rigid envelope, hoping thereby to restrain it, but inreality giving it explosive force. In England, thanks to men of thestamp to which I have alluded, scope is gradually given to thought forchanges of aggregation, and the envelope slowly alters its form, inaccordance with the necessities of the time. 

*****

The proximate origin of the foregoing slight article, and probably theremoter origin of the next following one, was this. Some years ago, aday of prayer and humiliation, on account of a bad harvest, wasappointed by the proper religious authorities; but certain clergymenof the Church of England, doubting the wisdom of the demonstration, declined to join in the services of the day. For this act ofnonconformity they were severely censured by some of their brethren. Rightly or wrongly, my sympathies were on the side of these men; and, to lend them a helping hand in their struggle against odds, I insertedthe foregoing chapter in a little book entitled 'Mountaineering in1861. ' Some time subsequently I received from a gentleman of greatweight and distinction in the scientific world, and, I believe, ofperfect orthodoxy in the religious one, a note directing my attentionto an exceedingly thoughtful article on Prayer and Cholera in the'Pall Mall Gazette. ' My eminent correspondent deemed the article afair answer to the remarks made by me in 1861. I, also, was struck bythe temper and ability of the article, but I could not deem itsarguments satisfactory, and in a short note to the editor of the 'PallMall Gazette' I ventured to state so much. This letter elicited somevery able replies, and a second leading article was also devoted tothe subject. In answer to all, I risked the publication of a secondletter, and soon afterwards, by an extremely courteous note from theeditor, the discussion was closed. 

Though thus stopped locally, the discussion flowed in otherdirections. Sermons were preached, essays were published, articleswere written, while a copious correspondence occupied the pages ofsome of the religious newspapers. It gave me sincere pleasure tonotice that the discussion, save in a few cases where naturalcoarseness had the upper hand, was conducted with a minimum ofvituperation. The severity shown was hardly more than sufficient todemonstrate earnestness, while gentlemanly feeling was too predominantto permit that earnestness to contract itself to bigotry or to clotheitself in abuse. It was probably the memory of this discussion whichcaused another excellent friend of mine to recommend to my perusal theexceedingly able work which in the next article I have endeavoured toreview. 

Mr. Mozley's book belongs to that class of writing of which Butler maybe taken as the type. It is strong, genuine argument about difficultmatters, fairly tracing what is difficult, fairly trying to grapple, not with what appears the gist and strong point of a question, butwith what really at bottom is the knot of it. It is a book thereasoning of which may not satisfy everyone... But we think it is abook for people who wish to see a great subject handled on a scalewhich befits it, and with a perception of its real elements. It is abook which will have attractions for those who like to see a powerfulmind applying itself, without shrinking or holding back, without trickor reserve or show of any kind, as a wrestler closes body to body withhis antagonist, to the strength of an adverse and powerfulargument. --Times, Tuesday, June 5, 1866. 

We should add, that the faults of the work are wholly on the surfaceand in the arrangement; that the matter is as solid and as logical asthat of any book within recent memory, and that it abounds in strikingpassages, of which we have scarcely been able even to give a sample. No future arguer against miracles can afford to pass itover. --SATURDAY REVIEW, September 15, 1866. 

********************

II MIRACLES AND SPECIAL PROVIDENCES. 

[Footnote: Fortnightly Review, New Series, vol. I. P. 645. ]

1867. 

IT is my privilege to enjoy the friendship of a select number ofreligious men, with whom I converse frankly upon theological subjects, expressing without disguise the notions and opinions I entertainregarding their tenets, and hearing in return these notions andopinions subjected to criticism. I have thus far found them liberaland loving men, patient in hearing, tolerant in reply, who know how toreconcile the duties of courtesy with the earnestness of debate. Fromone of these, nearly a year ago, I received a note, recommendingstrongly to my attention the volume of 'Bampton Lectures' for 1865, inwhich the question of miracles is treated by Mr. Mozley. Previous toreceiving this note, I had in part made the acquaintance of the workthrough an able and elaborate review of it in the 'Times. ' Thecombined effect of the letter and the review was to make the book thecompanion of my summer tour in the Alps. There, during the wet andsnowy days which were only too prevalent in 1866, and during the daysof rest interpolated between days of toil, I made myself morethoroughly conversant with Mr. Mozley's volume. I found it clear andstrong--an intellectual tonic, as bracing and pleasant to my mind asthe keen air of the mountains was to my body. From time to time Ijotted down thoughts regarding it, intending afterwards to work themup into a coherent whole. Other duties, however, interfered with thecomplete carrying out of this intention, and what I wrote last summerI now publish, not hoping to be able, within any reasonable time, torender my defence of scientific method more complete. 

Mr. Mozley refers at the outset of his task to the movement againstmiracles which of late years has taken place, and which determined hischoice of a subject. He acquits modern science of having had anygreat share in the production of this movement. The objection againstmiracles, he says, does not arise from any minute knowledge of thelaws of nature, but simply because they are opposed to that plain andobvious order of nature which everybody sees. The present movementis, he thinks, to be ascribed to the greater earnestness andpenetration of the present age. Formerly miracles were acceptedwithout question, because without reflection; but the exercise of the'historic imagination' is a characteristic of our own time. Men arenow accustomed to place before themselves vivid images of historicfacts; and when a miracle rises to view, they halt before theastounding occurrence, and, realising it with the same clearness as ifit were now passing before their eyes, they ask themselves, 'Can thishave taken place?' In some instances the effort to answer thisquestion has led to a disbelief in miracles, in others to astrengthening of belief. The aim of Mr. Mozley's lectures is to showthat the strengthening of belief is the logical result which ought tofollow from the examination of the facts. 

Attempts have been made by religious men to bring the Scripturemiracles within the scope of the order of nature, but all suchattempts are rejected by Mr. Mozley as utterly futile and wide of themark. Regarding miracles as a necessary accompaniment of a revelation, their evidential value in his eyes depends entirely upon theirdeviation from the order of nature. Thus deviating, they suggest andillustrate a power higher than nature, a 'personal will;' and theycommend the person in whom this power is vested as a messenger from onhigh. Without these credentials such a messenger would have no rightto demand belief, even were his assertions regarding his Divinemission backed by a holy life. Nor is it by miracles alone that theorder of nature is, or may be, disturbed. The material universe isalso the arena of 'special providences. ' Under these two heads Mr. Mozley distributes the total preternatural. One form of thepreternatural may shade into the other, as one colour passes intoanother in the rainbow; but, while the line which divides thespecially providential from the miraculous cannot be sharply drawn, their distinction broadly expressed is this: that, while a specialprovidence can only excite surmise more or less probable, it is 'thenature of a miracle to give proof, as distinguished from surmise, ofDivine design. '

Mr. Mozley adduces various illustrations of what he regards to bespecial providences, as distinguished from miracles. 'The death ofArius, ' he says, 'was not miraculous, because the coincidence of thedeath of a heresiarch taking place when it was peculiarly advantageousto the orthodox faith ... Was not such as to compel the inferenceof extraordinary Divine agency; but it was a special providence, because it carried a reasonable appearance of it. The miracle of theThundering Legion was a special providence, but not a miracle, forthe same reason, because the coincidence of an instantaneous fall ofrain, in answer to prayer, carried some appearance, but not proof, ofpreternatural agency. '

The eminent lecturer's remarks on this head brought to my recollectioncertain narratives published in Methodist magazines, which I used toread with avidity when a boy. The general title of these excitingstories, if I remember right, was 'The Providence of God asserted, 'and in them the most extraordinary escapes from peril were recountedand ascribed to prayer, while equally wonderful instances of calamitywere adduced as illustrations of Divine retribution. In suchmagazines, or elsewhere, I found recorded the case of the celebratedSamuel Hick, which, as it illustrates a whole class of specialprovidences approaching in conclusiveness to miracles, is worthy ofmention here. It is related of this holy man that, on one occasion, flour was lacking to make the sacramental bread. Grain was present, and a windmill was present, but there was no wind to grind the corn. With faith undoubting, Samuel Hick prayed to the Lord of the winds:the sails turned, the corn was ground, after which the wind ceased. According to the canon of the Bampton Lecturer, this, though carryinga strong appearance of an immediate exertion of Divine energy, lacksby a hair's-breadth the quality of a miracle. For the wind _might_ havearisen, and _might_ have ceased, in the ordinary course of nature. Hencethe occurrence did not 'compel the inference of extraordinary Divineagency. ' In like manner Mr. Mozley considers that 'the appearance ofthe cross to Constantine was a miracle, or a special providence, according to what account of it we adopt. As only a meteoricappearance in the shape of a cross it gave some token of preternaturalagency, but not full evidence. '

In the Catholic canton of Switzerland where I now write, and stillmore among the pious Tyrolese, the mountains are dotted with shrines, containing offerings of all kinds, in acknowledgment of specialmercies--legs, feet, arms, and hands--of gold, silver, brass, andwood, according as worldly possessions enabled the grateful heart toexpress its indebtedness. Most of these offerings are made to theVirgin Mary. They are recognitions of 'special providences, ' wroughtthrough the instrumentality of the Mother of God. Mr. Mozley'sbelief, that of the Methodist chronicler, and that of the Tyrolesepeasant, are substantially the same. Each of them assumes thatnature, instead of flowing ever onward in the uninterrupted rhythm ofcause and effect, is mediately ruled by the free human will. Asregards _direct_ action upon natural phenomena, man's wish and will, asexpressed in prayer, are confessedly powerless; but prayer is thetrigger which liberates the Divine power, and to this extent, if thewill be free, man, of course, commands nature. 

Did the existence of this belief depend solely upon the materialbenefits derived from it, it could not, in my opinion, last a decade. As a purely objective fact, we should soon see that the distributionof natural phenomena is unaffected by the merits or the demerits ofmen; that the law of gravitation crushes the simple worshippers ofOttery St. Mary, while singing their hymns, just as surely as if theywere engaged in a midnight brawl. The hold of this belief upon thehuman mind is not due to outward verification, but to the innerwarmth, force, and elevation with which it is commonly associated. Itis plain, however, that these feelings may exist under the mostvarious forms. They are not limited to Church of EnglandProtestantism--they are not even limited to Christianity. Though lessrefined, they are certainly not less strong in the heart of theMethodist and the Tyrolese peasant than in the heart of Mr. Mozley. Indeed, those feelings belong to the primal powers of man's nature. A'sceptic' may have them. They find vent in the battle-cry of theMoslem. They take hue and form in the hunting-grounds of the RedIndian; and raise all of them, as they raise the Christian, upon awave of victory, above the terrors of the grave. 

The character, then, of a miracle, as distinguished from a specialprovidence, is that the former furnishes _proof_, while in the case ofthe latter we have only surmise. Dissolve the element of doubt, andthe alleged fact passes from the one class of 'the preternatural intothe other. In other words, if a special providence could be proved tobe a special providence, it would cease to be a special providence andbecome a miracle. There is not the least cloudiness about Mr. Mozley's meaning here. A special providence is a doubtful miracle. Why, then, not call it so? The term employed by Mr. Mozley conveys nonegative suggestion, whereas the negation of certainty is the peculiarcharacteristic of the thing intended to be expressed. There is anapparent unwillingness on the part of the lecturer to call a specialprovidence what his own definition makes it to be. Instead ofspeaking of it as a doubtful miracle, he calls it 'an invisiblemiracle. ' He speaks of the point of contact of supernatural power withthe chain of causation being so high up as to be wholly, or in part, out of sight, whereas the essence of a special providence is theuncertainty whether there is any contact at all, either high or low. By the use of an incorrect term, however, a grave danger is avoided. For the idea of doubt, if kept systematically before the mind, wouldsoon be fatal to the special providence, considered as a means ofedification. The term employed, on the contrary, invites andencourages the trust which is necessary to supplement the evidence. 

This inner trust, though at first rejected by Mr. Mozley in favour ofexternal proof, is subsequently called upon to do momentous duty inregard to miracles. Whenever the evidence of the miraculous seemsincommensurate with the fact which it has to establish, or ratherwhen the fact is so amazing that hardly any evidence is sufficient toestablish it, Mr. Mozley invokes 'the affections. ' They must urge thereason to accept the conclusion, from which unaided it recoils. Theaffections and emotions are eminently the court of appeal in mattersof real religion, which is an affair of the heart; but they are not, Isubmit, the court in which to weigh allegations regarding thecredibility of physical facts. These must be judged by the dry lightof the intellect alone, appeals to the affections being reserved forcases where moral elevation, and not historic conviction, is the aim. It is, moreover, because the result, in the case under consideration, is deemed desirable that the affections are called upon to back it. Ifundesirable, they would, with equal right, be called upon to act theother way. Even to the disciplined scientific mind this would be adangerous doctrine. A favourite theory--the desire to establish oravoid a certain n result--can so warp the mind as to destroy itspowers of estimating facts. I have known men to work for years undera fascination of this kind, unable to extricate themselves from itsfatal influence. They had certain data, but not, as it happened, enough. By a process exactly analogous to that invoked by Mr. Mozley, they supplemented the data, and went wrong. From that hour theirintellects were so blinded to the perception of adverse phenomena thatthey never reached truth. If, then, to the disciplined scientificmind, this incongruous mixture of proof and trust be fraught withdanger, what must it be to the indiscriminate audience which. Mr. Mozley addresses? In calling upon this agency he acts the part ofFrankenstein. It is a monster thus evoked that we see stalkingabroad, in the degrading spiritualistic phenomena of the present day. Again, I say, where the aim is to elevate the mind, to quicken themoral sense, to kindle the fire of religion in the soul, let theaffections by all means be invoked; but they must not be permitted tocolour our reports, or to influence our acceptance of reports ofoccurrences in external nature. Testimony as to natural facts isworthless when wrapped in this atmosphere of the affections; the mostearnest subjective truth being thus rendered perfectly compatible withthe most astounding objective error. 

There are questions in judging of which the affections or sympathiesare often our best guides, the estimation of moral goodness being oneof these. But at this precise point, where they are really of use, Mr. Mozley excludes the affections and demands a miracle as acertificate of character. He will not accept any other evidence ofthe perfect goodness of Christ. 'No outward life and conduct, ' hesays, 'however irreproachable, could prove His perfect sinlessness, because goodness depends upon the inward motive, and the perfection ofthe inward motive is not proved by the outward act. ' But surely themiracle is an outward act, and to pass from it to the inner motiveimposes a greater strain upon logic than that involved in ourordinary methods of estimating men. There is, at least, moralcongruity between the outward goodness and the inner life, but thereis no such congruity between the miracle and the life within. Thetest of moral goodness laid down by Mr. Mozley is not the test ofJohn, who says, 'He that doeth righteousness is righteous; 'nor is itthe test of Jesus: 'By their fruits ye shall know them: do men gathergrapes of thorns, or figs of thistles?' But it is the test ofanother: 'If thou be the Son of God, command that these stones bemade bread. ' For my own part, I prefer the attitude of Fichte to thatof Mr. Mozley. The Jesus of John, ' says this noble and mightythinker, knows no other God than the True God, in whom we all are, andlive, and may be blessed, and out of whom there is only Death andNothingness. And, ' continues Fichte, 'he appeals, and rightlyappeals, in support of this truth, not to reasoning, but to the inwardpractical sense of truth in man, not even knowing any other proof thanthis inward testimony, "If any man will do the will of Him who sentMe, he shall know of the doe-trine whether it be of God. "'

Accepting Mr. Mozley's test, with which alone I am now dealing, it isevident that, in the demonstration of moral goodness, the _quantity_ ofthe miraculous comes into play. Had Christ, for example, limitedhimself to the conversion of water into wine, He would have fallenshort of the performance of Jannes and Jambres; for it is a smallerthing to convert one liquid into another than to convert a dead rodinto a living serpent. But Jannes and Jambres, we are informed, werenot good. Hence, if Mr. Mozley's test be a true one, a point mustexist, on the one side of which miraculous power demonstratesgoodness, while on the other side it does not. How is this 'point ofcontrary flexure' to be determined? It must lie somewhere between themagicians and Moses, for within this space the power passed from thediabolical to the Divine. But how to mark the point of passage--how, out of a purely _quantitative_ difference in the visible manifestationof power, we are to infer a total inversion of quality--it isextremely difficult to see. Moses, we are informed, produced a largereptile; Jannes and Jambres produced a small one. I do not possessthe intellectual faculty which would enable me to infer, from thosedata, either the goodness of the one or the badness of the other; andin the highest recorded manifestations of the miraculous I am equallyat a loss. Let us not play fast and loose with the miraculous; eitherit is a demonstration of goodness in all cases or in none. If Mr. Mozley accepts Christ's goodness as transcendent, because He did suchworks as no other man did, he ought, logically speaking, to accept theworks of those who, in His name, had cast out devils, as demonstratinga proportionate goodness on their part. But it is people of thisclass who are consigned to ever-lasting fire prepared for the deviland his angels. Such zeal as that of Mr. Mozley for miracles tends, Ifear, to eat his religion up. The logical threatens to stifles thespiritual. The truly religious soul needs no miraculous proof of thegoodness of Christ. The words addressed to Matthew at the receipt ofcustom required no miracle to produce obedience. It was by no strokeof the supernatural that Jesus caused those sent to seize Him to gobackward and fall to the ground. It was the sublime and holyeffluence from within, which needed no prodigy to commend it to thereverence even of his foes. 

As regards the function of miracles in the founding of a religion, Mr. Mozley institutes a comparison between the religion of Christ and thatof Mahomet; and he derides the latter as 'irrational' because it doesnot profess to adduce miracles in proof of its supernatural origin. But the religion of Mahomet, notwithstanding this drawback, hasthriven in the world, and at one time it held sway over largerpopulations than Christianity itself. The spread and influence ofChristianity are, however, brought forward by Mr. Mozley as 'apermanent, enormous, and incalculable practical result' of Christianmiracles; and he makes use of this result to strengthen his plea forthe miraculous. His logical warrant for this proceeding is not clear. It is the method of science, when a phenomenon presents itself, towards the production of which several elements may contribute, toexclude them one by one, so as to arrive at length at the trulyeffective cause. Heat, for example, is associated with a phenomenon;we exclude heat, but the phenomenon remains: hence, heat is not itscause. Magnetism is associated with a phenomenon; we excludemagnetism, but the phenomenon remains: hence, magnetism is not itscause. Thus, also, when we seek the cause of a diffusion of areligion--whether it be due to miracles, or to the spiritual force ofits founders--we exclude the miracles, and, finding the resultunchanged, we infer that miracles are not the effective cause. Thisimportant experiment Mahometanism has made for us. It has lived andspread without miracles; and to assert, in the face of this, thatChristianity has spread _because_ of miracles, is, I submit, opposedboth to the spirit of science and the common sense of mankind. 

The incongruity of inferring moral goodness from miraculous power hasbeen dwelt upon above; in another particular also the strain put byMr. Mozley upon miracles is, I think, more than they can bear. Inconsistency with his principles, it is difficult to see how he is todraw from the miracles of Christ any certain conclusion as to HisDivine nature. He dwells very forcibly on what he calls 'theargument from experience, ' in the demolition of which he takes obviousdelight. He destroys the argument, and repeats it, for the merePleasure of again and again knocking the breath out of it. Experience, he urges, can only deal with the past; and the moment we attempt toproject experience a hair's-breadth beyond the point it has at anymoment reached, we are condemned by reason. It appears to me thatwhen he infers from Christ's miracles a Divine and altogethersuperhuman energy, Mr. Mozley places himself precisely under thiscondemnation. For what is his logical ground for concluding that themiracles of the New Testament illustrate Divine power? May they notbe the result of expanded human power? A miracle he defines assomething impossible to man. But how does he know that the miraclesof the New Testament are impossible to man? Seek as he may, he hasabsolutely no reason to adduce save this--that man has never hithertoaccomplished such things. But does the fact that man _has_ never raisedthe dead prove that he _can_ never raise the dead? 'Assuredly not, 'must be Mr. Mozley's reply; 'for this would be pushing experiencebeyond the limit it has now reached--which I pronounce unlawful. ' Thena period may come when man will be able to raise the dead. If this beconceded--and I do not see how Mr. Mozley can avoid the concession--itdestroys the necessity of inferring Christ's Divinity from Hismiracles. He, it may be contended, antedated the humanity of thefuture; as a mighty tidal wave leaves high upon the beach a mark whichby-and-by becomes the general level of the ocean. Turn the matter asyou will, no other warrant will be found for the all-importantconclusion that Christ's miracles demonstrate Divine power, than anargument which has been stigmatised by Mr. Mozley as a 'rope ofsand'--the argument from experience. 

The learned Bampton Lecturer would be in this position, even had heseen with his own eyes every miracle recorded in the New Testament. But he has, not seen these miracles; and his intellectual plight istherefore worse. He accepts these miracles on testimony. Why does hebelieve that testimony? How does he know that it is not delusion; howis he sure that it is not even fraud? He will answer, that thewriting bears the marks of sobriety and truth; and that in many casesthe bearers of this message to mankind sealed it with their blood. Granted with all my heart; but whence the value of all this? Is itnot solely derived from the fact that men, _as we know them_, do notsacrifice their lives in the attestation of that which they know to beuntrue? Does not the entire value of the testimony of the Apostlesdepend ultimately upon our experience of human nature? It appears, then, that those said to have seen the miracles, based theirinferences from what they saw on the argument from experience; andthat Mr. Mozley bases his belief in their testimony on the sameargument. The weakness of his conclusion is quadrupled by this doubleinsertion of a principle of belief, to which he flatly deniesrationality. His reasoning, in fact, cuts two ways--if it destroysour trust in the order of nature, it far more effectually abolishesthe basis on which Mr. Mozley seeks to found the Christian religion. 

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Over this argument from experience, which at bottom is _his_ argument, Mr. Mozley rides rough-shod. There is a dash of scorn in the energywith which he tramples on it. Probably some previous writer had madetoo much of it, and thus invited his powerful assault. Finding thedifficulty of belief in miracles to rise from their being incontradiction to the order of nature, he sets himself to examine thegrounds of our belief in that order. With a vigour of logic rarelyequalled, and with a confidence in its conclusions never surpassed, hedisposes of this belief in a manner calculated to startle those who, without due examination, had come to the conclusion that the order ofnature was secure. What we mean, he says, by our belief in the orderof nature, is the belief that the future will be like the past. Thereis not, according to Mr. Mozley, the slightest rational basis for thisbelief. 

That any cause in nature is more permanent than its existing and knowneffects, extending further, and about to produce other and moreinstances besides what it has produced already, we have no evidence. Let us imagine, ' he continues, 'the occurrence of a particularphysical phenomenon for the first time. Upon that single occurrencewe should have but the very faintest expectation of another. If itdid occur again, once or twice, so far from counting on anotheroccurrence, a cessation would occur as the most natural event to us. But let it continue one hundred times, and we should find nohesitation in inviting persons from a distance to see it; and if itoccurred every day for years, its occurrence would be a certainty tous, its cessation a marvel... What ground of reason can we assign foran expectation that any part of the course of nature will be the nextmoment what it has been up to this moment, i. E. For our belief in theuniformity of nature? None. No demonstrative reason can be given, for the contrary to the recurrence of a fact of nature is nocontradiction. No probable reason can be given; for all probablereasoning respecting the course of nature is founded _upon_ thispresumption of likeness, and therefore cannot be the foundation of it. No reason can be given for this belief. It is without a reason. Itrests upon no rational grounds, and can be traced to no rationalprinciple. '

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'Everything, ' Mr. Mozley, however, adds, 'depends upon this belief, every provision we make for the future, every safeguard and caution weemploy against it, all calculation, all adjustment of means to ends, supposes this belief; and yet this belief has no more produciblereason for it than a speculation of fancy. It is necessary, all-important for the purposes of life, but solely practical, andpossesses no intellectual character. 

'... The proper function, ' continues Mr. Mozley, 'of the inductiveprinciple, the argument from experience, the belief in the order ofnature--by whatever phrase we designate the same instinct--is tooperate as a practical basis for the affairs of life and the carryingon of human society. ' To sum up, the belief in the order of nature isgeneral, but it is 'an unintelligent impulse, of which we can give norational account. ' It is inserted into our constitution solely toinduce us to till our fields, to raise our winter fuel, and thus tomeet the future on the perfectly gratuitous supposition that it willbe like the past. 

'Thus, step by step, ' says Mr. Mozley, with the emphasis of a man whofeels his position to be a strong one, 'has philosophy loosened theconnection of the order of nature with the ground of reason, befriending in exact proportion as it has done this the principle ofmiracles. ' For 'this belief not having itself a foundation in reason, the ground is gone upon which it could be maintained that miracles, asopposed to the order of nature, are opposed to reason. ' When we regardthis belief in connection with science, 'in which connection itreceives a more imposing name, and is called the inductive principle, 'the result is the same. 'The inductive principle is only thisunreasoning impulse applied to a scientifically ascertained fact... Science has led up to the fact; but there it stops, and for convertingthis fact into a law, a totally unscientific principle comes intoplay, the same as that which generalises the commonest observation ofnature. '

The eloquent pleader of the cause of miracles passes over without aword the _results_ of scientific investigation, as proving anythingrational regarding the principles or method by which such results havebeen achieved. Here, as elsewhere, he declines the test, 'By theirfruits shall ye know them. ' Perhaps our best way of proceeding will beto give one or two examples of the mode in which men of science applythe unintelligent impulse with which Mr. Mozley credits them, andwhich shall show, by illustration, the surreptitious method wherebythey climb from the region of facts to that of laws. 

Before the sixteenth century it was known that water rises in a pump;the effect being then explained by the maxim that 'Nature abhors avacuum. ' It was not known that there was any limit to the height towhich the water would ascend, until, on one occasion, the gardeners ofFlorence, while attempting to raise water to a very great elevation, found that the column ceased at a height of thirty-two feet. Beyondthis all the skill of the pump-maker could not get it to rise. Thefact was brought to the notice of Galileo, and he, soured by a worldwhich had not treated his science over kindly, is said to have twittedthe philosophy of the time by remarking that nature evidently abhorreda vacuum only to a height of thirty-two feet. Galileo, however, didnot solve the problem. It was taken up by his pupil Torricelli, towhom, after due pondering, the thought occurred, that the water mightbe forced into the tube by a pressure applied to the surface of theliquid outside. But where, under the actual circumstances, was such apressure to be found? After much reflection, it flashed uponTorricelli that the atmosphere might possibly exert this pressure;that the impalpable air might possess weight, and that a column ofwater thirty-two feet high might be of the exact weight necessary tohold the pressure of the atmosphere in equilibrium. 

There is much in this process of pondering and its results which it isimpossible to analyse. It is by a kind of inspiration that we risefrom the wise and sedulous contemplation of facts to the principles onwhich they depend. The mind is, as it were, a photographic plate, which is gradually cleansed by the effort to think rightly, and which, when so cleansed, and not before, receives impressions from the lightof truth. This passage from 'facts to principles is called induction;and induction, in its highest form, is, as I have just stated, a kindof inspiration. But, to make it sure, the inward sight must be shownto be in accordance with outward fact. To prove or disprove theinduction, we must resort to deduction and experiment. 

Torricelli reasoned thus: If a column of water thirty-two feet highholds the pressure of the atmosphere in equilibrium, a shorter columnof a heavier liquid ought to do the same. Now, mercury is thirteentimes heavier than water; hence, if my induction be correct, theatmosphere ought to be able to sustain only thirty inches of mercury. Here, then, is a deduction which can be immediately submitted toexperiment. Torricelli took a glass tube a yard or so in length, closed at one end and open at the other, and filling it with mercury, he stopped the open end with his thumb, and inverted it into a basinfilled with the liquid metal. One can imagine the feeling with whichTorricelli removed his thumb, and the delight he experienced onfinding that his thought had forestalled a fact never before revealedto human eyes. The column sank, but it ceased to sink at a height ofthirty inches, leaving the Torricellian vacuum over-head. From thathour the theory of the pump was established. 

The celebrated Pascal followed Torricelli with another deduction. Hereasoned thus: If the mercurial column be supported by the atmosphere, the higher we ascend in the air, the lower the column ought to sink, for the less will be the weight of the air overhead. He caused afriend to ascend the Puy de Dôme, carrying with him a barometriccolumn; and it was found that during the ascent the column sank, andthat during the subsequent descent the column rose. 

Between the time here referred to and the present, millions ofexperiments have been made upon this subject. Every village pump isan apparatus for such experiments. In thousands of instances, moreover, pumps have refused to work; but on examination it hasinfallibly been found that the well was dry, that the pump requiredpriming, or that some other defect in the apparatus accounted for theanomalous action. In every case of the kind the skill of thepump-maker has been found to be the true remedy. In no case has thepressure of the atmosphere ceased; constancy, as regards the liftingof pump-water, has been hitherto the demonstrated rule of nature. Soalso as regards Pascal's experiment. His experience has been theuniversal experience ever since. Men have climbed mountains, and goneup in balloons; but no deviation from Pascal's result has ever beenobserved. Barometers, like pumps, have refused to act; but instead ofindicating any suspension of the operations of nature, or anyinterference on the part of its Author with atmospheric pressure, examination has in every instance fixed the anomaly upon theinstruments themselves. It is this welding, then, of rigid logic toverifying fact that Mr. Mozley refers to an 'unreasoning impulse. '

Let us now briefly consider the case of Newton. Before his time menhad occupied themselves with the problem of the solar system. Keplerhad deduced, from a vast mass of observations, those generalexpressions of planetary motion known as 'Kepler's laws. ' It had beenobserved that a magnet attracts iron; and by one of those flashes ofinspiration which reveal to the human mind the vast in the minute, thegeneral in the particular, it had been inferred, that the force bywhich bodies fall to the earth might also be an attraction. Newtonpondered all these things. He looked, as was his wont, into thedarkness until it became entirely luminous. How this light arises wecannot explain; but, as a matter of fact, it does arise. Let meremark here, that this kind of pondering is a process with which theancients could have been but imperfectly acquainted. They, for themost part, found the exercise of fantasy more pleasant than carefulobservation, and subsequent brooding over facts. Hence it is, thatwhen those whose education has been derived from the ancients speak of'the reason of man, ' they are apt to omit from their conception ofreason one of its most important factors. 

Well, Newton slowly marshalled his thoughts, or rather they came tohim while he 'intended his mind, ' rising like a series ofintellectual births out of chaos. He made this idea of attraction hisown. But, to apply the idea to the solar system, it was necessary toknow the magnitude of the attraction, and the law of its variationwith the distance. His conceptions first of all passed from theaction of the earth as a whole, to that of its constituent particles. And persistent thought brought more and more clearly out the finalconclusion, that every particle of matter attracts every otherparticle with a force varying inversely as the square of the distancebetween the particles. 

Here we have the flower and outcome of Newton's induction; and how toverify it, or to disprove it, was the next question. The first stepof the philosopher in this direction was to prove, mathematically, that if this law of attraction be the true one; if the earth beconstituted of particles which obey this law; then the action of asphere equal to the earth in size on a body outside of it, is the sameas that which would be exerted if the whole mass of the sphere werecontracted to a point at its centre. Practically speaking, then, thecentre of the earth is the point from which distances must be measuredto bodies attracted by the earth. 

From experiments executed before his time, Newton knew the amount ofthe earth's attraction at the earth's surface, or at a distance of4, 000 miles from its centre. His object now was to measure theattraction at a greater distance, and thus to determine the law of itsdiminution. But how was he to find a body at a sufficient distance?He had no balloon? and even if he had, he knew that any height towhich he could attain would be too small to enable him to solve hisproblem. What did he do? He fixed his thoughts upon the moon;--abody 240, 000 miles, or sixty times the earth's radius, from theearth's centre. He virtually weighed the moon, and found that weightto be 1/3600th of what it would be at the earth's surface. This isexactly what his theory required. I will not dwell here upon thepause of Newton after his first calculations, or speak of hisself-denial in withholding them because they did not quite agree withthe observations then at his command. Newton's action in this matteris the normal action of the scientific mind. If it were otherwise--ifscientific men were not accustomed to demand verification--if theywere satisfied with the imperfect while the perfect is attainable, their science, instead of being, as it is, a fortress of adamant, would be a house of clay, ill-fitted to bear the buffetings of thetheologic storms to which it is periodically exposed. 

Thus we see that Newton, like Torricelli, first pondered his facts, illuminated them with persistent thought, and finally divined thecharacter of the force of gravitation. But, having thus travelledinward to the principle, he reversed his steps, carried the principleoutwards, and justified it by demonstrating its fitness to externalnature. 

And here, in passing, I would notice a point which is well worthy ofattention. Kepler had deduced his laws from observation. As far backas those observations extended, the planetary motions had obeyed theselaws; and neither Kepler nor Newton entertained a doubt as to theircontinuing to obey them. Year after year, as the ages rolled, theybelieved that those laws would continue to illustrate themselves inthe heavens. But this was not sufficient. The scientific mind canfind no repose in the mere registration of sequence in nature. Thefurther question intrudes itself with resistless might, Whence comesthe sequence? What is it that binds the consequent to its antecedentin nature? The truly scientific intellect never can attain rest untilit reaches the _forces_ by which the observed succession is produced. Itwas thus with Torricelli; it was thus with Newton; it is thuspre-eminently with the scientific man of to-day. In common with themost ignorant, he shares the belief that spring will succeed winter, that summer will succeed spring, that autumn will succeed summer, andthat winter will succeed autumn. But he knows still further--and thisknowledge is essential to his intellectual repose--that thissuccession, besides being permanent, is, under the circumstances, _necessary_; that the gravitating force exerted between the sun and arevolving sphere with an axis inclined to the plane of its orbit, mustproduce the observed succession of the seasons. Not until thisrelation between forces and phenomena has been established, is the lawof reason rendered concentric with the law of nature; and not untilthis is effected does the mind of the scientific philosopher rest inpeace. 

The expectation of likeness, then, in the procession of phenomena, isnot that on which the scientific mind founds its belief in the orderof nature. If the force be _permanent_ the phenomena are _necessary_, whether they resemble or do not resemble anything that has gonebefore. Hence, in judging of the order of nature, our enquirieseventually relate to the permanence of force. From Galileo to Newton, from Newton to our own time, eager eyes have been scanning theheavens, and clear heads have been pondering the phenomena of thesolar system. The same eyes and minds have been also observing, experimenting, and reflecting on the action of gravity at the surfaceof the earth. Nothing has occurred to indicate that the operation ofthe law has for a moment been suspended; nothing has ever intimatedthat nature has been crossed by spontaneous action, or that a state ofthings at any time existed which could not be rigorously deduced fromthe preceding state. 

Given the distribution of matter, and the forces in operation, in thetime of Galileo, the competent mathematician of that day could predictwhat is now occurring in our own. We calculate eclipses in advance, and find our calculations true to the second. We determine the datesof those that have occurred in the early times of history, and findcalculation and history in harmony. Anomalies and perturbations inthe planets have been over and over again observed; but these, insteadof demonstrating any inconstancy on the part of natural law, haveinvariably been reduced to consequences of that law. Instead ofreferring the perturbations of Uranus to any interference on the partof the Author of nature with the law of gravitation, the questionwhich the astronomer proposed to himself was, 'How, in accordance withthis law, can the perturbation be produced?' Guided by a principle, hewas enabled to fix the point of space in which, if a mass of matterwere placed, the observed perturbations would follow. We know theresult. The practical astronomer turned his telescope towards theregion which the intellect of the theoretic astronomer had alreadyexplored, and the Planet now named Neptune was found in its predictedPlace. A very respectable outcome, it will be admitted, of an impulsewhich 'rests upon no rational grounds, and can be traced to norational principle;' which possesses 'no intellectual character;'which 'philosophy' has uprooted from 'the ground of reason, ' and fixedin that 'large irrational department' discovered for it, by Mr. Mozley, in the hitherto unexplored wilderness of the human mind. 

The proper function of the inductive principle, or the belief in theorder of nature, says Mr. Mozley, is 'to act as a practical basis forthe affairs of life, and the carrying on of human society. ' But what, it may be asked, has the planet Neptune, or the belts of Jupiter, orthe whiteness about the poles of Mars, to do with the affairs ofsociety? How is society affected by the fact that the sun'satmosphere contains sodium, or that the nebula of Orion containshydrogen gas? Nineteen-twentieths of the force employed in theexercise of the inductive principle, which, reiterates Mr. Mozley, is'purely practical, ' have been expended upon subjects as unpractical asthese. What practical interest has society in the fact that the spotson the sun have a decennial period, and that when a magnet is closelywatched for half a century, it is found to perform small motions whichsynchronise with the appearance and disappearance of the solar spots?And yet, I doubt not, Sir Edward Sabine would deem a life ofintellectual toil amply rewarded by being privileged to solve, at itsclose, these infinitesimal motions. The inductive principle isfounded in man's desire to know--a desire arising from his positionamong phenomena which are reducible to order by his intellect: Thematerial universe is the complement of the intellect; and, without thestudy of its laws, reason could never have awakened to the higherforms of self-consciousness at all. It is the Non-ego through and bywhich the Ego is endowed with self-discernment. We hold it to be anexercise of reason to explore the meaning of a universe to which westand in this relation, and the work we have accomplished is theproper commentary on the methods we have pursued. 

Before these methods were adopted the unbridled imagination roamedthrough nature, putting in the place of law the figments ofsuperstitious dread. For thousands of years witchcraft, and magic, and miracles, and special providences, and Mr. Mozley's 'distinctivereason of man, ' had the world to themselves. They made worse thannothing of it--_worse_, I say, because they let and hindered those whomight have made something of it. Hence it is, that during a singlelifetime of this era of 'unintelligent impulse, ' the progress inknowledge is all but infinite as compared with that of the ages whichpreceded ours. 

The believers in magic and miracles of a couple of centuries ago hadall the strength of Mr. Mozley's present logic on their side. Theyhad done for themselves what he rejoices in having so effectually donefor us--cleared the ground of the belief in the order of nature, anddeclared magic, miracles, and witchcraft to be matters for 'ordinaryevidence' to decide. 'The principle of miracles' thus 'befriended'had free scope, and we know the result. Lacking that rock-barrier ofnatural knowledge which we now possess, keen jurists and cultivatedmen were hurried on to deeds, the bare recital of which makes theblood run cold. Skilled in all the rules of human evidence, andversed in all the arts of cross-examination, these men, nevertheless, went systematically astray, and committed the deadliest wrongs againsthumanity. And why? Because they could not put Nature into thewitness-box, and question her--of her voiceless 'testimony' they knewnothing. In all cases between man and man, their judgment was to berelied on; but in all cases between man and nature, they were blindleaders of the blind. [Footnote: 'In 1664 two women were hung inSuffolk, under a sentence of Sir Matthew Hale, who took theopportunity of declaring that the reality of witchcraft wasunquestionable; "for first, the Scriptures had affirmed so much; andsecondly, the wisdom of all nations had provided laws against suchpersons, which is an argument of their confidence of such a crime. "Sir Thomas Browne, who was a great physician as well as a greatwriter, was called as a witness, and swore "that he was clearly ofopinion that the persons were bewitched. "--Lecky's History ofRationalism, vol. I. P. 120. ]

Mr. Mozley concedes that it would be no great result if miracles wereonly accepted by the ignorant and superstitious, 'because it is easyto satisfy those who do not enquire. ' But he does consider it 'agreat result' that they have been accepted by the educated. In whatsense educated? Like those statesmen, jurists, and church dignitarieswhose education was unable to save them from the frightful errorsglanced at above? Not even in this sense; for the great mass of Mr. Mozley's educated people had no legal training, and must have beenabsolutely defenceless against delusions which could set even thattraining at naught. Like nine-tenths of our clergy at the presentday, they were versed in the literature of Greece, Rome, and Judea;but as regards a knowledge of nature, which is here the one thingneedful, they were 'noble savages, ' and nothing more. In the case ofmiracles, then, it behoves us to understand the weight of thenegative, before we assign a value to the positive; to comprehend thedepositions of nature, before we attempt to measure, with them, theevidence of men. We have only to open our eyes to see what honest andeven intellectual men and women are capable of, as to judgingevidence, in this nineteenth century of the Christian era, and inlatitude fifty-two degrees north. The experience thus gained ought, Iimagine, to influence our opinion regarding the testimony of peopleinhabiting a sunnier clime, with a richer imagination, and without aparticle of that restraint which the discoveries of physical sciencehave imposed upon mankind. 

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Having thus submitted Mr. Mozley's views to the examination which theychallenged at the hands of a student of nature, I am unwilling to quithis book without expressing my admiration of his genius, and myrespect for his character. Though barely known to him personally, hisrecent death affected me as that of a friend. With regard to thestyle of his book, I heartily subscribe to the description with whichthe 'Times' winds up its able and appreciative review. It is markedthroughout with the most serious and earnest conviction, but iswithout a single word from first to last of asperity or insinuationagainst opponents; and this not from any deficiency of feeling as tothe importance of the issue, but from a deliberate and resolutelymaintained self-control, and from an over-ruling, ever-present senseof the duty, on themes like these, of a more than judicial calmness. '

[To the argument regarding the quantity of the miraculous, introducedat page 17, Mr. Mozley has done me the honour of publishing a Reply inthe seventh volume of the 'Contemporary Review. '--J. T. ]

ADDITIONAL REMARKS ON MIRACLES. 

AMONG the scraps of manuscript, written at the time when Mr. Mozley'swork occupied my attention, I find the following reflections:

With regard to the influence of modern science which Mr. Mozley ratesso low, one obvious effect of it is to enhance the magnitude of manyof the recorded miracles, and to increase proportionably thedifficulties of belief. The ancients knew but little of the vastnessof the universe. The Rev. Mr. Kirkman, for example, has shown whatinadequate notions the Jews entertained regarding the 'firmament ofheaven;' and Sir George Airy refers to the case of a Greek philosopherwho was persecuted for hazarding the assertion, then deemed monstrous, that the sun might be as large as the whole country of Greece. Theconcerns of a universe, regarded from this point of view, were muchmore commensurate with man and his concerns than those of the universewhich science now reveals to us; and hence that to suit man'spurposes, or that in compliance with his prayers, changes should occurin the order of the universe, was more easy of belief in the ancientworld than it can be now. In the very magnitude which it assigns tonatural phenomena, science has augmented the distance between them andman, and increased the popular belief in their orderly progression. 

As a natural consequence the demand for evidence is more exacting thanit used to be, whenever it is affirmed that the order of nature hasbeen disturbed. Let us take as an illustration the miracle by whichthe victory of Joshua over the Amorites was rendered complete. Inthis case the sun is reported to have stood still for 'about a wholeday' upon Gibeon, and the moon in the valley of Ajalon. An Englishmanof average education at the present day would naturally demand agreater amount of evidence to prove that this occurrence took place, than would have satisfied an Israelite in the age succeeding that ofJoshua. For to the one, the miracle probably consisted in thestoppage of a fiery ball less than a yard in diameter, while to theother it would be the stoppage of an orb fourteen hundred thousandtimes the earth in size. And even accepting the interpretation thatJoshua dealt with what was apparent merely, but that what reallyoccurred was the suspension of the earth's rotation, I think the rightto exercise a greater reserve in accepting the miracle, and to demandstronger evidence in support of it than that which would havesatisfied an ancient Israelite, will still be conceded to a man ofscience. 

There is a scientific as well as an historic imagination; and when, bythe exercise of the former, the stoppage of the earth's rotation isclearly realised, the event assumes proportions so vast, in comparisonwith the result to be obtained by it, that belief reels under thereflection. The energy here involved is equal to that of sixtrillions of horses working for the whole of the time employed byJoshua in the destruction of his foes. The amount of power thusexpended would be sufficient to supply every individual of an army athousand times the strength of that of Joshua, with a thousand timesthe fighting power of each of Joshua's soldiers, not for the few hoursnecessary to the extinction of a handful of Amorites, but for millionsof years. All this wonder is silently passed over by the sacredhistorian, manifestly because he knew nothing about it. Whether, therefore, we consider the miracle as purely evidential, or as apractical means of vengeance, the same lavish squandering of energystares us in the face. If evidential, the energy was wasted, becausethe Israelites knew nothing of its amount; if simply destructive, thenthe ratio of the quantity lost to the quantity employed, may beinferred from the foregoing figures. 

To other miracles similar remarks apply. Transferring our thoughtsfrom this little sand-grain of an earth to the immeasurable heavens, where countless worlds with freights of life probably revolve unseen, the very suns which warm them being barely visible across abysmalspace; reflecting that beyond these sparks of solar fire, sunsinnumerable may burn, whose light can never stir the optic nerve atall; and bringing these reflections face to face with the idea of theBuilder and Sustainer of it all showing Himself in a burning bush, exhibiting His hinder parts, or behaving in other familiar waysascribed to Him in the Jewish Scriptures, the incongruity must appear. Did this credulous prattle of the ancients about miracles stand alone;were it not associated with words of imperishable wisdom, and withexamples of moral grandeur unmatched elsewhere in the history of thehuman race, both the miracles and their 'evidences' would have longsince ceased to be the transmitted inheritance of intelligent men. Influenced by the thoughts which this universe inspires, well may weexclaim in David's spirit, if not in David's words: 'When I considerthe heavens, the work of thy fingers, the moon, and the stars, whichthou hast ordained; what is man that thou shouldst be mindful of him, or the son of man that thou shouldst so regard him?'

If you ask me who is to limit the outgoings of Almighty power, myanswer is, Not I. If you should urge that if the Builder and Maker ofthis universe chose to stop the rotation of the earth, or to take theform of a burning bush, there is nothing to prevent Him from doing so, I am not prepared to contradict you. I neither agree with you nordiffer from you, for it is a subject of which I know nothing. But Iobserve that in such questions regarding Almighty power, yourenquiries relate, not to that power as it is actually displayed in theuniverse, but to the power of your own imagination. Your question is, not has the Omnipotent done so and so? or is it in the least degreelikely that the Omnipotent should do so and so? but, is myimagination competent to picture a Being able and willing to do so andso? I am not prepared to deny your competence. To the human mindbelongs the faculty of enlarging and diminishing, of distorting andcombining, indefinitely the objects revealed by the senses. It canimagine a mouse as large as an elephant, an elephant as large as amountain, and a mountain as high as the stars. It can separatecongruities and unite incongruities. We see a fish and we see a womanwe can drop one half of each, and unite in idea the other two halvesto a mermaid. We see a horse and we see a man; we are able to dropone half of each, and unite the other two halves to a centaur. Thusalso the pictorial representations of the Deity, the bodies and wingsof cherubs and seraphs, the hoofs, horns, and tail of the Evil One, the joys of the blessed, and the torments of the damned, have beenelaborated from materials furnished to the imagination by the senses. It behoves you and me to take care that our notions of the Power whichrules the universe are not mere fanciful or ignorant enlargements ofhuman power. The capabilities of what you call your reason are notdenied. By the exercise of the faculty here adverted to, you canpicture to yourself a Being able and willing to do any and everyconceivable thing. You are right in saying that in opposition to thisPower science is of no avail--that it is 'a weapon of air. ' The man ofscience, however, while accepting the figure, would probably reverseits application, thinking it is not science which is here the thing ofair, but that unsubstantial pageant of the imagination to which thesolidity of science is opposed. 

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 Prayer as a means to effect a private end is theft and meanness. --EMERSON. 

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III ON PRAYER AS A FORM OF PHYSICAL ENERGY. 

THE Editor of the 'Contemporary Review' is liberal enough to grant mespace for some remarks upon a subject, which, though my relation to itwas simply that of a vehicle of transmission, has brought down upon mea considerable amount of animadversion. 

It may be interesting to some of my readers if I glance at a few casesillustrative of the history of the human mind, in relation to this andkindred questions. In the fourth century the belief in Antipodes wasdeemed unscriptural and heretical. The pious Lactantius was as angrywith the people who held this notion as my censors are now with me, and quite as unsparing in his denunciations of their 'Monstrosities. 'Lactantius was irritated because, in his mind, by education and habit, cosmogony and religion were indissolubly associated, and, therefore, simultaneously disturbed. In the early part of the seventeenthcentury the notion that the earth was fixed, and that the sun andstars revolved round it daily, was interwoven with religious feeling, the separation then attempted by Galileo rousing the animosity andkindling the persecution of the Church. Men still living can rememberthe indignation excited by the first revelations of geology regardingthe age of the earth, the association between chronology and religionbeing for the time indissoluble. In our day, however, thebest-informed theologians are prepared to admit that our views of theUniverse and its Author are not impaired, but improved, by theabandonment of the Mosaic account of the Creation. Look, finally, atthe excitement caused by the publication of the 'Origin of Species;'and compare it with the calm attendant on the appearance of the farmore outspoken, and, from the old point of view, more impious, 'Descent of Man. '

Thus religion survives-after the removal of what had been longconsidered essential to it. In our day the Antipodes are accepted;the fixity of the earth is given up; the period of Creation and thereputed age of the world are alike dissipated; Evolution is lookedupon without terror; and other changes have occurred in the samedirection too numerous to be dwelt upon here. In fact, from theearliest times to the present, religion has been undergoing a processof purification, freeing itself slowly and painfully from the physicalerrors which the active but uninformed intellect mingled with theaspirations of the soul. Some of us think that a final act ofpurification is needed, while others oppose this notion with theconfidence and the warmth of ancient times. The bone of contention atpresent is _the physical value of prayer_. It is not my wish to excitesurprise, much less to draw forth protest, by the employment of thisphrase. I would simply ask any intelligent person to look the problemhonestly in the face, and then to say whether, in the estimation ofthe great body of those who sincerely resort to it, prayer does not, at all events upon special occasions, invoke a Power which checks andaugments the descent of rain, which changes the force and direction ofwinds, which affects the growth of corn and the health of men andcattle a Power, in short, which, when appealed to under pressingcircumstances, produces the precise effects caused by physical energyin the ordinary course of things. To any person who deals sincerelywith the subject, and refuses to blur his moral vision by intellectualsubtleties, this, I think, will appear a true statement of the case. 

It is under this aspect alone that the scientific student, so far as Irepresent him, has any wish to meddle with prayer. Forced upon hisattention as a form of physical energy, or as the equivalent of suchenergy, he claims the right of subjecting it to those methods ofexamination from which all our present knowledge of the physicaluniverse is derived. And if his researches lead him to a conclusionadverse to its claims--if his enquiries rivet him still closer to thephilosophy implied in the words, 'He maketh His sun to shine on theevil and on the good, and sendeth rain upon the just and upon theunjust'--he contends only for the displacement of prayer, not for itsextinction. He simply says, physical nature is not its legitimatedomain. 

This conclusion, moreover, must be based on pure physical evidence, and not on any inherent, unreasonableness in the act of prayer. Thetheory that the system of nature is under the control of a Being whochanges phenomena in compliance with the prayers of men, is, in myopinion, a perfectly legitimate one. It may of course be renderedfutile by being associated `with conceptions which contradict it; butsuch conceptions form no necessary part of the theory. It is a matterof experience that an earthly father, who is at the same time bothwise and tender, listens to the requests of his children, and, if theydo not ask amiss, takes pleasure in granting their requests. We knowalso that this compliance extends to the alteration, within certainlimits, of the current of events on earth. With this suggestionoffered by experience, it is no departure from scientific method toplace behind natural phenomena a Universal Father, who, in answer tothe prayers of His children, alters the currents of those phenomena. Thus far Theology and Science go hand in hand. The conception of anaether, for example, trembling with the waves of light, is suggestedby the ordinary phenomena of wave-motion in water and in air; and inlike manner the conception of personal volition in nature is suggestedby the ordinary action of man upon earth. I therefore urge no_impossibilities_, though I am constantly charged with doing so. I donot even urge inconsistency, but, on the contrary, frankly admit thatthe theologian has as good a right to place his conception at the rootof phenomena as I have to place mine. 

But without _verification_ a theoretic conception is a mere figment ofthe intellect, and I am sorry to find us parting company at thispoint. The region of theory, both in science and theology, liesbehind the world of the senses, but the verification of theory occursin the sensible world. To check the theory we have simply to comparethe deductions from it with the facts of observation. If thedeductions be in accordance with the facts, we accept the theory: ifin opposition, the theory is given up. A single experiment isfrequently devised, by which the theory must stand or fall. Of thischaracter was the determination of the velocity of light in liquids, as a crucial test of the Emission Theory. According to it, lighttravelled faster in water than in air; according to the UndulatoryTheory, it travelled faster in air than in water. An experimentsuggested by Arago, and executed by Fizeau and Foucault, wasconclusive against Newton's theory. 

But while science cheerfully submits to this ordeal, it seemsimpossible to devise a mode of verification of their theories whichdoes not rouse resentment in theological minds. Is it that, while thepleasure of the scientific man culminates in the demonstrated harmonybetween theory and fact, the highest pleasure of the religious man hasbeen already tasted in the very act of praying, prior to verification, any further effort in this direction being a mere disturbance of hispeace? Or is it that we have before us a residue of that mysticism ofthe middle ages, so admirably described by Whewell--that 'practice ofreferring things and events not to clear and distinct notions, not togeneral rules capable of direct verification, but to notions vague, distant, and vast, which we cannot bring into contact with facts; aswhen we connect natural events with moral and historic causes. ''Thus, ' he continues, 'the character of mysticism is that it refersparticulars, not to generalisations, homogeneous and immediate, but tosuch as are heterogeneous and remote; to which we must add, that theprocess of this reference is not a calm act of the intellect, but isaccompanied with a glow of enthusiastic feeling. '

Every feature here depicted, and some more questionable ones, haveshown themselves of late; most conspicuously, I regret to say, in theleaders' of a weekly journal of considerable influence, and one, onmany grounds, entitled to the respect of thoughtful men. In thecorrespondence, however, published by the same journal, are to befound two or three letters well calculated to correct the temporaryflightiness of the journal itself. 

It is not my habit of mind to think otherwise than solemnly of thefeeling which prompts prayer. It is a power which I should like tosee guided, not extinguished--devoted to practicable objects insteadof wasted upon air. In some form or other, not yet evident, it may, as alleged, be necessary to man's highest culture. Certain it isthat, while I rank many persons who resort to prayer low in the scaleof being--natural foolishness, bigotry, and intolerance being in theircase intensified by the notion that they have access to the ear ofGod--I regard others who employ it, as forming part of the very creamof the earth. The faith that adds to the folly and ferocity of theone is turned to enduring sweetness, holiness, abounding charity, andself-sacrifice by the other. Religion, in fact, varies with thenature upon which it falls. Often unreasonable, if not contemptible, prayer, in its purer forms, hints at disciplines which few of us canneglect without moral loss. But no good can come of giving it adelusive value, by claiming for it a power in physical nature. It maystrengthen the heart to meet life's losses, and thus indirectlypromote physical well-being, as the digging of Aesop's orchard broughta treasure of fertility greater than the golden treasure sought. Suchindirect issues we all admit; but it would be simply dishonest toaffirm that it is such issues that are always in view. Here, for thepresent, I must end. I ask no space to reply to those railers whomake such free use of the terms insolence, outrage, profanity, andblasphemy. They obviously lack the sobriety of mind necessary to giveaccuracy to their statements, or to render their charges worthy ofserious refutation. 

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IV. VITALITY. 

THE origin, growth, and energies of living things are subjects whichhave always engaged the attention of thinking men. To account forthem it was usual to assume a special agent, free to a great extentfrom the limitations observed among the powers of inorganic nature. This agent was called _vital force_; and, under its influence, plantsand animals were supposed to collect their materials and to assumedeterminate forms. Within the last few years, however, our ideas ofvital processes have undergone profound modifications; and theinterest, and even disquietude, which the change has excited are amplyevidenced by the discussions and protests which are now common, regarding the phenomena of vitality. In tracing these phenomenathrough all their modifications, the most advanced philosophers of thepresent day declare that they ultimately arrive at a single source ofpower, from which all vital energy is derived; and the disquietingcircumstance is that this source is not the direct fiat of asupernatural agent, but a reservoir of what, if we do not accept thecreed of Zoroaster, must be regarded as inorganic force. In short, itis considered as proved that all the energy which we derive fromplants and animals is drawn from the sun. 

A few years ago, when the sun was affirmed to be the source of life, nine out of ten of those who are alarmed by the form which thisassertion has latterly assumed would have assented, in a general way, to its correctness. Their assent, however, was more poetic thanscientific, and they were by no means prepared to see a rigidmechanical signification attached to their words. This, however, isthe peculiarity of modern conclusions: that there is no creativeenergy whatever in the vegetable or animal organism, but that all thepower which we obtain from the muscles of man and animals, as much asthat which we develop by the combustion of wood or coal, has beenproduced at the sun's expense. The sun is so much the colder that wemay have our fires; he is also so much the colder that we may have ourhorse-racing and Alpine climbing. It is, for example, certain thatthe sun has been chilled to an extent capable of being accuratelyexpressed in numbers, in order to furnish the power which lifted thisyear a certain number of tourists from the vale of Chamouni to thesummit of Mont Blanc. 

To most minds, however, the energy of light and heat presents itselfas a thing totally distinct from ordinary mechanical energy. Eitherof them can nevertheless be derived from the other. Wood can beraised by friction to the temperature of ignition; while by properlystriking a piece of iron a skilful blacksmith can cause it to glow. Thus, by the rude agency of his hammer, he generates light and heat. This action, if carried far enough, would produce the light and heatof the sun. In fact, the sun's light and heat have actually beenreferred to the fall of meteoric matter upon his surface; and whetherthe sun is thus supported or not, it is perfectly certain that hemight be thus supported. Whether, moreover, the whilom moltencondition of our planet was, as supposed by eminent men, due to thecollision of cosmic masses or not, it is perfectly certain that themolten condition might be thus brought about. 

If, then, solar light and heat can be produced by the impact of deadmatter, and if from the light and heat thus produced we can derive theenergies which we have been accustomed to call _vital_, it indubitablyfollows that vital energy may have a proximately mechanical origin. 

In what sense, then, is the sun to be regarded as the origin of theenergy derivable from plants and animals? Let us try to give anintelligible answer to this question. Water may be raised from thesea-level to a high elevation, and then permitted to descend. Indescending it may be made to assume various forms--to fall incascades, to spurt in fountains, to boil in eddies, or to flowtranquilly along a uniform bed. It may, moreover, be caused to setcomplex machinery in motion, to turn millstones, throw shuttles, worksaws and hammers, and drive piles. But every form of power hereindicated would be derived from the original power expended in raisingthe water to the height from which it fell. There is no energy_generated_ by the machinery: the work performed by the water indescending is merely the parcelling out and distribution of the workexpended in raising it. In precisely this sense is all the energy ofplants and animals the parcelling out and distribution of a poweroriginally exerted by the sun. In the case of the water, the sourceof the power consists in the forcible separation of a quantity of theliquid from a low level of the earth's surface, and its elevation to ahigher position, the power thus expended being returned by the waterin its descent. In the case of vital phenomena, the source of powerconsists in the forcible separation of the atoms of compoundsubstances by the sun. We name the force which draws the waterearthward 'gravity, ' and that which draws atoms together 'chemicalaffinity'; but these different names must not mislead us regarding thequalitative identity of the two forces. They are both _attractions_;and, to the intellect, the falling of carbon atoms against oxygenatoms is not more difficult of conception than the falling of water tothe earth. 

The building up of the vegetable, then, is effected by the sun, through the reduction of chemical compounds. The phenomena of animallife are more or less complicated reversals of these processes ofreduction. We eat the vegetable, and we breathe the oxygen of theair; and in our bodies the oxygen, which had been lifted from thecarbon and hydrogen by the action of the sun, again falls towardsthem, producing animal heat and developing animal forms. Through themost complicated phenomena of vitality this law runs: the vegetableis produced while a weight rises, the animal is produced while aweight falls. But the question is not exhausted here. The wateremployed in our first illustration generates all the motion displayedin its descent, but the _form_ of the motion depends on the character ofthe machinery interposed in the path of the water. In a similar way, the primary action of the sun's rays is qualified by the atoms andmolecules among which their energy is distributed. Molecular forcesdetermine the form which the solar energy will assume. In theseparation of the carbon and oxygen this energy may be so conditionedas to result in one case in the formation of a cabbage, and in anothercase in the formation of an oak. So also, as regards the reunion ofthe carbon and the oxygen, the molecular machinery through which thecombining energy acts may, in one case, weave the texture of a frog, while in another it may weave the texture of a man. 

The matter of the animal body is that of inorganic nature. There isno substance in the animal tissues which is not primarily derived fromthe rocks, the water, and the air. Are the forces of organic matter, then, different in kind from those of inorganic matter? Thephilosophy of the present day negatives the question. It is thecompounding, in the organic world, of forces belonging equally to theinorganic, that constitutes the mystery and the miracle of vitality. Every portion of every animal body may be reduced to purely inorganicmatter. A perfect reversal of this process of reduction would carryus from the inorganic to the organic; and such a reversal is at leastconceivable. The tendency, indeed, of modern science is to break downthe wall of partition between organic and inorganic, and to reduceboth to the operation of forces which are the same in kind, but whichare differently compounded. 

Consider the question of personal identity, in relation to that ofmolecular form. Thirty-four years ago, Mayer of Heilbronn, with thatpower of genius which breathes large meanings into scanty facts, pointed out that the blood was 6 the oil of the lamp of life, ' thecombustion of which sustains muscular action. The muscles are themachinery by which the dynamic power of the blood is brought intoplay. Thus the blood is consumed. But the whole body, though moreslowly than the blood, wastes also, so that after a certain number ofyears it is entirely renewed. How is the sense of personal identitymaintained across this flight of molecules? To man, as we know him, matter is necessary to consciousness; but the matter of any period maybe all changed, while consciousness exhibits no solution ofcontinuity. Like changing sentinels, the oxygen, hydrogen, and carbonthat depart, seem to whisper their secret to their comrades thatarrive, and thus, while the Non-ego shifts, the Ego remains the same. Constancy of form in the grouping of the molecules, and not constancyof the molecules themselves, is the correlative of this constancy ofperception. Life is a wave which in no two consecutive moments of itsexistence is composed of the same particles. 

Supposing, then, the molecules of the human body, instead of replacingothers, and thus renewing a pre-existing form, to be gathered firsthand from nature and put together in the same relative positions asthose which they occupy in the body. Supposing them to have theselfsame forces and distribution of forces, the selfsame motions anddistribution of motions--would this organised concourse of moleculesstand before us as a sentient thinking being? There seems no validreason to believe that it would not. Or, supposing a planet carvedfrom the sun, set spinning round an axis, and revolving round the sunat a distance from him equal to that of our earth, would one of theconsequences of its refrigeration be the development of organic forms?I lean to the affirmative. _Structural_ forces are certainly in themass, whether or not those forces reach to the extent of forming aplant or an animal. In an amorphous drop of water lie latent all themarvels of crystalline force; and who will set limits to the possibleplay of molecules in a cooling planet? If these statements startle, it is because matter has been defined and maligned by philosophers andtheologians, who were equally unaware that it is, at bottom, essentially mystical and transcendental. 

Questions such as these derive their present interest in great partfrom their audacity, which is sure, in due time, to disappear. Andthe sooner the public dread is abolished with reference to suchquestions the better for the cause of truth. As regards knowledge, physical science is polar. In one sense it knows, or is destined toknow, everything. In another sense it knows nothing. Scienceunderstands much of this intermediate phase of things that we callnature, of which it is the product; but science knows nothing of theorigin or destiny of nature. Who or what made the sun, and gave hisrays their alleged power? Who or what made and bestowed upon theultimate particles of matter their wondrous power of variedinteraction? Science does not know: the mystery, though pushed back, remains unaltered. To many of us who feel that there are more thingsin heaven and earth than are dreamt of in the present philosophy ofscience, but who have been also taught, by baffled efforts, how vainis the attempt to grapple with the Inscrutable, the ultimate frame ofmind is that of Goethe:

 Who dares to name His name, Or belief in Him proclaim, Veiled in mystery as He is, the All-enfolder? Gleams across the mind His light, Feels the lifted soul His might, Dare it then deny His reign, the All-upholder?

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 As I rode through the Schwarzwald, I said to myself: That little fire which glows star-like across the dark-growing moor, where the sooty smith bends over his anvil, and thou hopest to replace thy lost horse-shoe, --is it a detached, separated speck, cut off from the whole Universe; or indissolubly joined to the whole? Thou fool, that smithy-fire was primarily kindled at the Sun; is fed by air that circulates from before Noah's Deluge, from beyond the Dogstar; therein, with Iron Force, and Coal Force, and the far stranger Force of Man, are cunning affinities and battles and victories of Force brought about; it is a little ganglion, or nervous centre, in the great vital system of Immensity. Call it, if thou wilt, an unconscious Altar, kindled on the bosom of the All... Detached, separated! I say there is no such separation: nothing hitherto was ever stranded, cast aside; but all, were it only a withered leaf, works together with all; is borne forward on the bottomless, shoreless flood of action, and lives through perpetual metamorphoses. --CARLYLE. 

*****

V. MATTER AND FORCE. 

[Footnote: A Lecture delivered to the working men of Dundee, September5, 1867, with additions. ]

It is the custom of the Professors in the Royal School of Mines inLondon to give courses of evening lectures every year to working men. The lecture-room holds 600 people; and tickets to this amount aredisposed of as quickly as they can be handed to those who apply forthem. So desirous are the working men of London to attend theselectures, that the persons who fail to obtain tickets always bear alarge proportion to those who succeed. Indeed, if the lecture-roomcould hold 2, 000 instead of 600, I do not doubt that every one of itsbenches would be occupied on these occasions. It is, moreover, worthyof remark that the lectures are but rarely of a character which couldhelp the working man in his daily pursuits. The information acquiredis hardly ever of a nature which admits of being turned into money. Itis, therefore, a pure desire for knowledge, as a thing good in itself, and without regard to its practical application, which animates thehearers of these lectures. 

It is also my privilege to lecture to another audience in London, composed in part of the aristocracy of rank, while the audience justreferred to is composed wholly of the aristocracy of labour. Asregards attention and courtesy to the lecturer, neither of theseaudiences has anything to learn of the other; neither can claimsuperiority over the other. It would not, perhaps, be quite correctto take those persons who flock to the School of Mines as averagesamples of their class; they are probably picked men--the aristocracyof labour, as I have just called them. At all events, their conductdemonstrates that the essential qualities of what we in Englandunderstand by a gentleman are confined to no class; and they haveoften raised in my mind the wish that the gentlemen of all classes, artisans as well as lords, could, by some process of selection, besifted from the general mass of the community, and caused to know eachother better. 

When pressed some months ago by the Council of the British Associationto give an evening lecture to the working men of Dundee, my experienceof the working men of London naturally rose to my mind; and, thoughheavily weighted with other duties, I could not bring myself todecline the request of the Council. Hitherto, the evening discoursesof the Association have been delivered before its members andassociates alone. But after the meeting at Nottingham, last year, where the working men, at their own request, were addressed by ourlate President, Mr. Grove, and by my excellent friend, ProfessorHuxley, the idea arose of incorporating with all subsequent meetingsof the Association an address to the working men of the town in whichthe meeting is held. A resolution to that effect was sent to theCommittee of Recommendations; the Committee supported the resolution;the Council of the Association ratified the decision of the Committee;and here I am to carry out to the best of my ability their unitedwishes. 

*****

Whether it be a consequence of long-continued development, or anendowment conferred once for all on man at his creation, we find himhere gifted with a mind curious to know the causes of things, andsurrounded by objects which excite its questionings, and raise thedesire for an explanation. It is related of a young Prince of one ofthe Pacific Islands, that when he first saw himself in alooking-glass, he ran round the glass to see who was standing at theback. And thus it is with the general human intellect, as regards thephenomena of the external world. It wishes to get behind and learnthe causes and connections of these phenomena. What is the sun, whatis the earth, what should we see if we came to the edge of the earthand looked over? What is the meaning of thunder and lightning, ofhail, rain, storm, and snow? Such questions presented themselves toearly men, and by and by it was discovered that this desire forknowledge was not implanted in vain. After many trials it becameevident that man's capacities were, so to speak, the complement ofnature's facts, and that, within certain limits, the secret of theuniverse was open to the human understanding. It was found that themind of man had the power of penetrating far beyond the boundaries ofhis five senses; that the things which are seen in the material worlddepend for their action upon things unseen; in short, that besides thephenomena which address the senses, there are laws and principles andprocesses which do not address the senses at all, but which must be, and can be, spiritually discerned. 

To the subjects which require this discernment belong the phenomena ofmolecular force. But to trace the genesis of the notions nowentertained upon this subject, we have to go a long way back. In thedrawing of a bow, the darting of a javelin, the throwing of astone--in the lifting of burdens, and in personal combats, even savageman became acquainted with the operation of _force_. Ages ofdiscipline, moreover, taught him foresight. He laid by at the properseason stores of food, thus obtaining time to look about him, and tobecome an observer and enquirer. Two things which he noticed musthave profoundly stirred his curiosity. He found that a kind of resindropped from a certain tree possessed, when rubbed, the power ofdrawing light bodies to itself, and of causing them to cling to it;and he also found that a particular stone exerted a similar power overa particular kind of metal. I allude, of course, to electrifiedamber, and to the load-stone, or natural magnet, and its power toattract particles of iron. Previous experience of his own muscles hadenabled our early enquirer to distinguish between a push and a pull. Augmented experience showed him that in the case of the magnet and theamber, pulls and pushes--attractions and repulsions--were alsoexerted; and, by a kind of poetic transfer, be applied to thingsexternal to himself, conceptions derived from himself. The magnet andthe rubbed amber were credited with pushing and pulling, or, in otherwords, with exerting force. 

In the time of the great Lord Bacon the margin of these pushes andpulls was vastly extended by Dr. Gilbert, a man probably of firmerscientific fibre, and of finer insight, than Bacon himself. Gilbertproved that a multitude of other bodies, when rubbed, exerted thepower which, thousands of years previously, had been observed inamber. In this way the notion of attraction and repulsion in externalnature was rendered familiar. It was a matter of experience thatbodies, between which no visible link or connection existed, possessedthe power of acting upon each other; and the action came to betechnically called 'action at a distance. '

But out of experience in science there grows something finer than mereexperience. Experience furnishes the soil for plants of highergrowth; and this observation of action at a distance provided materialfor speculation upon the largest of problems. Bodies were observed tofall to the earth. Why should they do so? The earth was proved torevolve round the sun; and the moon to revolve round the earth. Whyshould they do so? What prevents them from flying straight off intospace? Supposing it were ascertained that from a part of the earth'srocky crust a firmly fixed and tightly stretched chain started towardsthe sun, we might be inclined to conclude that the earth is held inits orbit by the chain--that the sun twirls the earth around him, as aboy twirls round his head a bullet at the end of a string. But whyshould the chain be needed? It is a fact of experience that bodiescan attract each other at a distance, without the intervention of anychain. Why should not the sun and earth so attract each other? andwhy should not the fall of bodies from a height be the result of theirattraction by the earth? Here then we reach one of those higherspeculations which grow out of the fruitful soil of observation. Having started with the savage, and his sensations of muscular force, we pass on to the observation of force exerted between a magnet andrubbed amber and the bodies which they attract, rising, by an unbrokengrowth of ideas, to a conception of the force by which sun and planetsare held together. 

This idea of attraction between sun and planets had become familiar inthe time of Newton. He set himself to examine the attraction; andhere, as elsewhere, we find the speculative mind falling back for itsmaterials upon experience. It had been observed, in the case ofmagnetic and electric bodies, that the nearer they were broughttogether the stronger was the force exerted between them; while, byincreasing the distance, the force diminished until it becameinsensible. Hence the inference that the assumed pull between theearth and the sun would be influenced by their distance asunder. Guesses had been made as to the exact manner in which the force variedwith the distance; but Newton supplemented the guess by the severetest of experiment and calculation. Comparing the pull of the earthupon a body close to its surface, with its pull upon the moon, 240, 000miles away, Newton rigidly established the law of variation with thedistance. But on his way to this result Newton found room for otherconceptions, some of which, indeed, constituted the necessarystepping-stones to his result. The one which here concerns us is, that not only does the sun attract the earth, and the earth attractthe sun, as wholes, but every particle of the sun attracts everyparticle of the earth, and the reverse. His conclusion was, that theattraction of the masses was simply the sum of the attractions oftheir constituent particles. 

This result seems so obvious that you will perhaps wonder at mydwelling upon it; but it really marks a turning point in our notionsof force. You have probably heard of certain philosophers of theancient world named Democritus, Epicurus, and Lucretius. These menadopted, developed, and diffused the doctrine of atoms and molecules, which found its consummation at the hands of the illustrious JohnDalton. But the Greek and Roman philosophers I have named, and theirfollowers, up to the time of Newton, pictured their atoms as fallingand flying through space, hitting each other, and clinging together byimaginary hooks and claws. They missed the central idea that atomsand molecules could come together, not by being fortuitously knockedAgainst each other, but by their own mutual attractions. This is oneof the great steps taken by Newton. He familiarised the world withthe conception of _molecular force_. 

Newton, you know, was preceded by a grand fellow named John Kepler--atrue working man--who, by analysing the astronomical observations ofhis master, Tycho Brahe, had actually found that the planets moved asthey are now known to move. Kepler knew as much about the motion ofthe planets as Newton did; in fact, Kepler taught Newton and the worldgenerally the facts of planetary motion. But this was not enough. Thequestion arose--Why should the facts be so? This was the greatquestion for Newton, and it was the solution of it which renders hisname and fame immortal. Starting from the principle that everyparticle of matter in the solar system attracts every other particleby a force which varies as the inverse square of the distance betweenthe particles, he proved that the Planetary motions must be whatobservation makes them to be. He showed that the moon fell towardsthe earth, and that the planets fell towards the sun, through theoperation of the same force that pulls an apple from its tree. Thisall-pervading force, which forms the solder of the material universe, and the conception of which was necessary to Newton's intellectualpeace, is called the force of gravitation. 

Gravitation is a purely attractive force, but in electricity andmagnetism, repulsion had been always seen to accompany attraction. Electricity and magnetism are double or _polar forces_. In the case ofmagnetism, experience soon pushed the mind beyond the bounds ofexperience, compelling it to conclude that the polarity of the magnetwas resident in its molecules. I hold a magnetised strip of steel byits centre, and find that one half of the strip attracts, and theother half repels, the north end of a magnetic needle. I break thestrip in the middle, find that this half, which a moment ago attractedthroughout its entire length the north pole of a magnetic needle, isnow divided into two new halves, one of which wholly attracts, and theother of which wholly repels, the north pole of the needle. The halfproves to be as perfect a magnet as the whole. You may break thishalf and go on till further breaking becomes impossible through thevery smallness of the fragments; the smallest fragment is foundendowed with two poles, and is, therefore, a perfect magnet. But youcannot stop here: you _imagine_ where you cannot _experiment_; and reachthe conclusion entertained by all scientific men, that the magnetwhich you see and feel is an assemblage of molecular magnets which youcannot see and feel, but which, as before stated, must beintellectually discerned. 

Magnetism then is a polar force; and experience hints that a force ofthis kind may exert a certain structural power. It is known, forexample, that iron filings strewn round a magnet arrange themselves indefinite lines, called, by some, 'magnetic curves, ' and, by others, 'lines of magnetic force. ' Over two magnets now before me is spread asheet of paper. Scattering iron filings over the paper, polar forcecomes into play, and every particle of the iron responds to thatforce. We have a kind of architectural effort--if I may use theterm--exerted on the part of the iron filings. Here then is a fact ofexperience which, as you will see immediately, furnishes furthermaterial for the mind to operate upon, rendering it possible to attainintellectual clearness and repose, while speculating upon apparentlyremote phenomena. 

The magnetic force has here acted upon particles visible to the eye. But, as already stated, there are numerous processes in nature whichentirely elude the eye of the body, and must be figured by the eye ofthe mind. The processes of chemistry are examples of these. Longthinking and experimenting has led philosophers to conclude thatmatter is composed of atoms from which, whether separate or incombination, the whole material world is built up. The air webreathe, for example, as mainly a mechanical mixture of the atoms ofoxygen and nitrogen. The water we drink is also composed of oxygenand hydrogen. But it differs from the air in this particular, that inwater the oxygen and hydrogen are not mechanically mixed, butchemically combined. The atoms of oxygen and those of hydrogen exertenormous attractions on each other, so that when brought intosufficient proximity they rush together with an almost incredibleforce to form a chemical compound. But powerful as is the force withwhich these atoms lock themselves together, we have the means oftearing them asunder, and the agent by which we accomplish this mayhere receive a few moments' attention. 

Into a vessel containing acidulated water I dip two strips of metal, the one being zinc and the other platinum, not permitting them totouch each other in the liquid. I connect the two upper ends of thestrips by a piece of copper wire. The wire is now the channel ofwhat, for want of a better name, we call an 6 electric current. ' Whatthe inner change of the wire is we do not know, but we do know that achange has occurred, by the external effects produced by the wire. Letme show you one or two of these effects. Before you is a series often vessels, each with its pair of metals, and I wish to get the addedforce of all ten. The arrangement is called a voltaic battery. Iplunge a piece of copper wire among these iron filings; they refuse tocling to it. I employ the selfsame wire to connect the two ends ofthe battery, and subject it to the same test. The iron filings nowcrowd round the wire and cling to it. I interrupt the current, andthe filings immediately fall; the power of attraction continues onlyso long as the wire connects the two ends of the battery. 

Here is a piece of similar wire, overspun with cotton, to prevent thecontact of its various parts, and formed into a coil. I make the coilpart of the wire which connects the two ends of the voltaic battery. By the attractive force with which it has become suddenly endowed, itnow empties this tool-box of its iron nails. I twist a covered copperwire round this common poker; connecting the wire with the two ends ofthe voltaic battery, the poker is instantly transformed into a strongmagnet. Two flat spirals are here suspended facing each other, aboutsix inches apart. Sending a current through both spirals, they clashsuddenly together; reversing what is called the direction of thecurrent in one of the spirals, they fly asunder. All these effectsare due to the power which we name an electric current, and which wefigure as flowing through the wire when the voltaic circuit iscomplete. 

By the same agent we tear asunder the locked atoms of a chemicalcompound. Into this small cell, containing water, dip two thin wires. A magnified image of the cell is thrown upon the screen before you, and you see plainly the images of the wires. From a small battery Isend an electric current from wire to wire. Bubbles of gas riseimmediately from each of them, and these are the two gases of whichthe water is composed. The oxygen is always liberated on the onewire, the hydrogen on the other. The gases may be collected eitherseparately or mixed. I place upon my hand a soap bubble filled withthe mixture of both gases. Applying a taper to the bubble, a loudexplosion is heard. The atoms have rushed together with detonation, and without injury to my hand, and the water from which they wereextracted is the result of their re-union. 

*****

One consequence of the rushing together of the atoms is thedevelopment of heat. What is this heat? Here are two ivory ballssuspended from the same point of support by two short strings. I drawthem thus apart and then liberate them. They clash together, but, byvirtue of their elasticity, they quickly recoil, and a sharp vibratoryrattle succeeds their collision. This experiment will enable you tofigure to your mind a pair of clashing atoms. We have in the firstplace, a motion of the one atom towards the other--a motion oftranslation, as it is usually called--then a recoil, and afterwards amotion of vibration. To this vibratory motion we give the name ofheat. Thus, three things are to be kept before the mind--first, theatoms themselves; secondly, the force with which they attract eachother; and thirdly, the motion consequent upon the exertion of thatforce. This motion must be figured first as a motion of translation, and then as a motion of vibration, to which latter we give the name ofheat. For some time after the act of combination this motion is soviolent as to prevent the molecules from coming together, the waterbeing maintained in a state of vapour. But as the vapour cools, or inother words loses its motion, the molecules coalesce to form a liquid. 

And now we approach a new and wonderful display of force. As long asthe substance remains in a liquid or vaporous condition, the play ofthis force is altogether masked and bidden. But as the heat isgradually withdrawn, the molecules prepare for new arrangements andcombinations. Solid crystals of water are at length formed, to whichwe give the familiar name of ice. Looking at these beautiful edificesand their internal structure, the pondering mind has forced upon itthe question, How are they built up? We have obtained clearconceptions of polar force; and we infer from our broken magnet thatpolar force may be resident in the molecules or smallest particles ofmatter, and that by the play of this force structural arrangement ispossible. What, in relation to our present question, is the naturalaction of a mind furnished with this knowledge? It is compelled totranscend experience, and endow the atoms and molecules of whichcrystals are built with definite poles whence issue attractions andrepulsions. In virtue of these forces some poles are drawn together, while some retreat from each other; atom is added to atom, andmolecule to molecule, not boisterously or fortuitously, but silentlyand symmetrically, and in accordance with laws more rigid than thosewhich guide a human builder when he places his materials together. Imagine the bricks and stones of this town of Dundee endowed withstructural power. 

Imagine them attracting and repelling, and arranging themselves intostreets and houses and Kinnaird Halls--would not that be wonderful?Hardly less wonderful is the play of force by which the molecules ofwater build themselves into the sheets of ice which every winter roofyour ponds and lakes. 

If I could show you the actual progress of this moleculararchitecture, its beauty would delight and astonish you. A reversalof the process of crystallisation may be actually shown. Themolecules of a piece of ice may be taken asunder before your eyes; andfrom the manner in which they separate, you may to some extent inferthe manner in which they go together. When a beam is sent from ourelectric lamp through a plate of glass, a portion of the beam isintercepted, and the glass is warmed by the portion thus retainedwithin it. When the beam is sent through a plate of ice, a portion ofthe beam is also absorbed; but instead of warming the ice, theintercepted heat melts it internally. It is to the delicate silentaction of this beam within the ice that I now wish to direct yourattention. Upon the screen is thrown a magnified image of the slab ofice: the light of the beam passes freely through the ice withoutmelting it, and enables us to form the image; but the heat is in greatpart intercepted, and that heat now applies itself to the work ofinternal liquefaction. Selecting certain points for attack, roundabout those points the beam works silently, undoing the crystallinearchitecture, and reducing to the freedom of liquidity molecules whichhad been previously locked in a solid embrace. The liquefied spacesare rendered visible by strong illumination. Observe thosesix-petaled flowers breaking out over the white surface, and expandingin size as the action of the beam continues. These flowers areliquefied ice. Under the action of the heat the molecules of thecrystals fall asunder, so as to leave behind them these exquisiteforms. We have here a process of demolition which clearly reveals thereverse process of construction. In this fashion, and in strictaccordance with this hexangular type, every ice molecule takes itsplace upon our ponds and lakes during the frosts of winter. To usethe language of an American poet, 'the atoms march in tune, ' moving tothe music of law, which thus renders the commonest substance in naturea miracle of beauty. 

It is the function of science, not as some think to divest thisuniverse of its wonder and mystery, but, as in the case before us, topoint out the wonder and the mystery of common things. Thosefern-like forms, which on a frosty morning overspread yourwindowpanes, illustrate the action of the same force. Breathe uponsuch a pane before the fires are lighted, and reduce the solidcrystalline film to the liquid condition; then watch its subsequentresolidification. You will see it all the better if you look at itthrough a common magnifying glass. After you have ceased breathing, the film, abandoned to the action of its own forces, appears for amoment to be alive. Lines of motion run through it; molecule closeswith molecule, until finally the whole film passes from the state ofliquidity, through this state of motion, to its final crystallinerepose. 

I can show you something similar. Over a piece of perfectly cleanglass I pour a little water in which certain crystals have beendissolved. A film of the solution clings to the glass. By means of amicroscope and a lamp, an image of the plate of glass is thrown uponthe screen. The beam of the lamp, besides illuminating the glass, also heats it; evaporation sets in, and at a certain moment, when thesolution has become supersaturated, splendid branches of crystal shootout over the screen. A dozen square feet of surface are now coveredby those beautiful forms. With another solution we obtain crystallinespears, feathered right and left by other spears. From distant nucleiin the middle of the field of view the spears shoot with magicalrapidity in all directions. The film of water on a window-pane on afrosty morning exhibits effects quite as wonderful as these. Latentin these formless solutions, latent in every drop of water, lies thismarvellous structural power, which only requires the withdrawal ofopposing forces to bring it into action. 

The clear liquid now held up before you is a solution of nitrate ofsilver--a compound of silver and nitric acid. When an electriccurrent is sent through this liquid the silver is severed from theacid, as the hydrogen was separated from the oxygen in a formerexperiment; and I would ask you to observe how the metal behaves whenits molecules are thus successively set free. The image of the cell, and of the two wires which dip into the liquid of the cell, are nowclearly shown upon the screen. Let us close the circuit, and send thecurrent through the liquid. From one of the wires a beautiful silvertree commences immediately to sprout. Branches of the metal arethrown out, and umbrageous foliage loads the branches. You have herea growth, apparently as wonderful as that of any vegetable, perfectedin a minute before your eyes. Substituting for the nitrate of silveracetate of lead, which is a compound of lead and acetic acid, theelectric current severs the lead from the acid, and you see the metalslowly branching into exquisite metallic ferns, the fronds of which, as they become too heavy, break from their roots and fall to thebottom of the cell. 

These experiments show that the common matter of our earth--'brutematter, ' as Dr. Young, in his _Night Thoughts_, is pleased to callit--when its atoms and molecules are permitted to bring their forcesinto free play, arranges itself, under the operation of these forces, into forms which rival in beauty those of the vegetable world. Andwhat is the vegetable world itself, but the result of the complex playof these molecular forces? Here, as elsewhere throughout nature, ifmatter moves it is force that moves it, and if a certain structure, vegetable or mineral, is produced, it is through the operation of theforces exerted between the atoms and molecules. 

The solid matter of which our lead and silver trees were formed was, in the first instance, disguised in a transparent liquid; the solidmatter of which our woods and forests are composed is also, for themost part disguised in a transparent gas, which is mixed in smallquantities with the air of our atmosphere. This gas is formed by theunion of carbon and oxygen, and is called carbonic acid gas. Thecarbonic acid of the air being subjected to an action somewhatanalogous to that of the electric current in the case of our lead andsilver solutions, has its carbon liberated and deposited as woodyfibre. The watery vapour of the air is subjected to similar action;its hydrogen is liberated from its oxygen, and lies down side by sidewith the carbon in the tissues of the tree. The oxygen in both casesis permitted to wander away into the atmosphere. But what is it innature that plays the part of the electric current in our experiments, tearing asunder the locked atoms of carbon, oxygen, and hydrogen? Therays of the sun. The leaves of plants which absorb both the carbonicacid and the aqueous vapour of the air, answer to the cells in whichour decompositions took place. And just as the molecular attractionsof the silver and the lead found expression in those beautifulbranching forms seen in our experiments, so do the molecularattractions of the liberated carbon and hydrogen find expression inthe architecture of grasses, plants, and trees. 

In the fall of a cataract and the rush of the wind we have examples ofmechanical power. In the combinations of chemistry and in theformation of crystals and vegetables we have examples of molecularpower. You have learned how the atoms of oxygen and hydrogen rushtogether to form water. I have not thought it necessary to dwell uponthe mighty mechanical energy of their act of combination; but it maybe said, in passing, that the clashing together of 1 lb. Of hydrogenand 8 lbs. Of oxygen to form 9 lbs. Of aqueous vapour, is greater thanthe shock of a weight of 1, 000 tons falling from a height of 20 feetagainst the earth. Now, in order that the atoms of oxygen andhydrogen should rise by their mutual attractions to the velocitycorresponding to this enormous mechanical effect, a certain distancemust exist between the particles. It is in rushing over this that thevelocity is attained. 

*****

This idea of distance between the attracting atoms is of the highestimportance in our conception of the system of the world. For thematter of the world may be classified under two distinct heads: atomsand molecules which have already combined and thus satisfied theirmutual attractions, and atoms and molecules which have not yetcombined, and whose mutual attractions are, therefore, unsatisfied. Now, as regards motive power, we are entirely dependent on atoms andmolecules of the latter kind. Their attractions can produce motion, because sufficient distance intervenes between the attracting atoms, and it is this atomic motion that we utilise in our machines. Thus wecan get power out of oxygen and hydrogen by the act of their union;but once they are combined, and once the vibratory motion consequenton their combination has been expended, no further power can be gotout of their mutual attraction. As dynamic agents they are dead. Thematerials of the earth's crust consist for the most part of substanceswhose atoms have already closed in chemical union--whose mutualattractions are satisfied. Granite, for instance, is a widelydiffused substance; but granite consists, in great part, of silicon, oxygen, potassium, calcium, and aluminum, whose atoms united long ago, and are therefore dead. Limestone is composed of carbon, oxygen, anda metal called calcium, the atoms of which have already closed inchemical union, and are therefore finally at rest. In this way wemight go over nearly the whole of the materials of the earth's crust, and satisfy ourselves that though they were sources of power in agespast, and long before any creature appeared on the earth capable ofturning their power to account, they are sources of power no longer. And here we might halt for a moment to remark on that tendency, soprevalent in the world, to regard everything as made for human use. Those who entertain this notion, hold, I think, an overweening opinionof their own importance in the system of nature. Flowers bloomedbefore men saw them, and the quantity of power wasted before man couldutilise it is all but infinite compared with what now remains. We aretruly heirs of all the ages; but as honest men it behoves us to learnthe extent of our inheritance, and as brave ones not to whimper if itshould prove less than we had supposed. The healthy attitude of mindwith reference to this subject is that of the poet, who, when askedwhence came the rhodora, joyfully acknowledged his brotherhood withthe flower:

 Why thou wert there, O rival of the rose! I never thought to ask, I never knew, But in my simple ignorance supposed The self-same power that brought me there brought you. 

 Emerson. 

A few exceptions to the general state of union of the molecules of theearth's crust--vast in relation to us, but trivial in comparison tothe total store of which they are the residue--still remain. Theyconstitute our main sources of motive power. By far the mostimportant of these are our beds of coal. Distance still intervenesbetween the atoms of carbon and those of atmospheric oxygen, acrosswhich the atoms may be urged by their mutual attractions; and we canutilise the motion thus produced. Once the carbon and the oxygen haverushed together, so as to form carbonic acid, their mutual attractionsare satisfied; and, while they continue in this condition, as dynamicagents they are dead. Our woods and forests are also sources ofmechanical energy, because they have the power of uniting with theatmospheric oxygen. Passing from plants to animals, we find that thesource of motive power just referred to is also the source of muscularpower. A horse can perform work, and so can a man; but this work isat bottom the molecular work of the transmuted food and the oxygen ofthe air. We inhale this vital gas, and bring it into sufficientlyclose proximity with the carbon and the hydrogen of the body. Theseunite in obedience to their mutual, attractions; and their motiontowards each other, properly turned to account by the wonderfulmechanism of the body, becomes muscular motion. 

One fundamental thought pervades all these statements: there is onetap root from which they all spring. This is the ancient maxim thatout of nothing nothing comes; that neither in the organic world nor inthe inorganic is power produced without the expenditure of power; thatneither in the plant nor in the animal is there a creation of force ormotion. Trees grow, and so do men and horses; and here we have newpower incessantly introduced upon the earth. But its source, as Ihave already stated, is the sun. It is the sun that separates thecarbon from the oxygen of the carbonic acid, and thus enables them torecombine. Whether they recombine in the furnace of the steam-engineor in the animal body, the origin of the power they produce is thesame. In this sense we are all 'souls of fire and children of thesun. ' But, as remarked by Helmholtz, we must be content to share ourcelestial pedigree with the meanest of living things. 

Some estimable persons, here present, very possibly shrink fromaccepting these statements; they may be frightened by their apparenttendency towards what is called materialism--a word which, to manyminds, expresses something very dreadful. But it ought to be knownand avowed that the physical philosopher, as such, must be a purematerialist. His enquiries deal with matter and force, and with themalone. And whatever be the forms which matter and force assume, whether in the organic world or the inorganic, whether in thecoal-beds and forests of the earth, or in the brains and muscles ofmen, the physical philosopher will make good his right to investigatethem. It is perfectly vain to attempt to stop enquiry in thisdirection. Depend upon it, if a chemist by bringing the propermaterials together, in a retort or crucible, could make a baby, hewould do it. There is no law, moral or physical, forbidding him to doit. At the present moment there are, no doubt, persons experimentingon the possibility of producing what we call life out of inorganicmaterials. Let them pursue their studies in peace; it is only by suchtrials that they will learn the limits of their own powers and theoperation of the laws of matter and force. 

But while thus making the largest demand for freedom ofinvestigation--while I consider science to be alike powerful as aninstrument of intellectual culture and as a ministrant to the materialwants of men; if you ask me whether it has solved, or is likely in ourday to solve, the problem of this universe, I must shake my head indoubt. You remember the first Napoleon's question, when the savantswho accompanied him to Egypt discussed in his presence the origin ofthe universe, and solved it to their own apparent satisfaction. Helooked aloft to the starry heavens, and said, 'It is all very well, gentlemen; but who made these?' That question still remainsunanswered, and science makes no attempt to answer it. As far as Ican see, there is no quality in the human intellect which is fit to beapplied to the solution of the problem. It entirely transcends us. The mind of man may be compared to a musical instrument with a certainrange of notes, beyond which in both directions we have an infinitudeof silence. The phenomena of matter and force lie within ourintellectual range, and as far as they reach we will at all hazardspush our enquiries. But behind, and above, and around all, the realmystery of this universe lies unsolved, and, as far as we areconcerned, is incapable of solution. Fashion this mystery as youwill, with that I have nothing to do. But let your conception of itnot be an unworthy one. Invest that conception with your highest andholiest thought, but be careful of pretending to know more about itthan is given to man to know. Be careful, above all things, ofprofessing to see in the phenomena of the material world the evidencesof Divine pleasure or displeasure. Doubt those who would deduce fromthe fall of the tower of Siloam the anger of the Lord against thosewho were crushed. Doubt equally those who pretend to see in cholera, cattle-plague, and bad harvests, evidences of Divine anger. Doubtthose spiritual guides who in Scotland have lately propounded themonstrous theory that the depreciation of railway scrip is aconsequence of railway travelling on Sundays. Let them not, as far asyou are concerned, libel the system of nature with their ignoranthypotheses. Looking from the solitudes of thought into this highestof questions, and seeing the puerile attempts often made to solve it, well might the mightiest of living Scotchmen--that strong and earnestsoul, who has made every soul of like nature in these islands hisdebtor--well, I say, might your noble old Carlyle scornfully retort onsuch interpreters of the ways of God to men:

 The Builder of this universe was wise, He formed all souls, all systems, planets, particles; The plan he formed his worlds and Aeons by, Was--Heavens!--was thy small nine-and-thirty articles!

********************

 Here, indeed, we arrive at the barrier which needs to be perpetually pointed out; alike to those who seek materialistic explanations of mental phenomena, and to those who are alarmed lest such explanations may be found. The last class prove by their fear almost as much as the first prove by their hope, that they believe Mind may possibly be interpreted in terms of Matter; whereas many whom they vituperate as materialists are profoundly convinced that there is not the remotest possibility of so interpreting them. 

 HERBERT SPENCER. 

====================

VI. SCIENTIFIC MATERIALISM. 

[Footnote: President's Address to the Mathematical and PhysicalSection of the British Association at Norwich. ]

1868. 

THE celebrated Fichte, in his lectures on the 'Vocation of theScholar, ' insisted on a culture which should be not one-sided, butall-sided. The scholar's intellect was to expand spherically, and notin a single direction only. In one direction, however, Fichterequired that the scholar should apply himself directly to nature, become a creator of knowledge, and thus repay, by original labours ofhis own, the immense debt he owed to the labours of others. It wasthese which enabled him to supplement the knowledge derived from hisown researches, so as to render his culture rounded and not one-sided. 

As regards science, Fichte's idea is to some extent illustrated by theconstitution and labours of the British Association. We have here abody of men engaged in the pursuit of Natural Knowledge, but variouslyengaged. While sympathising with each of its departments, andsupplementing his culture by knowledge drawn from all of them, eachstudent amongst us selects one subject for the exercise of his ownoriginal faculty--one line, along which he may carry the light of hisprivate intelligence a little way into the darkness by which allknowledge is surrounded. Thus, the geologist deals with the rocks;the biologist with the conditions and phenomena of life; theastronomer with stellar masses and motions; the mathematician with therelations of space and number; the chemist pursues his atoms; whilethe physical investigator has his own large field in optical, thermal, electrical, acoustical, and other phenomena. The British Associationthen, as a whole, faces physical nature on all sides, and pushesknowledge centrifugally outwards, the sum of its labours constitutingwhat Fichte might call the sphere of natural knowledge. In themeetings of the Association it is found necessary to resolve thissphere into its component parts, which take concrete form under therespective letters of our Sections. 

Mathematics and Physics have been long accustomed to coalesce, andhere they form a single section. No matter how subtle a naturalphenomenon may be, whether we observe it in the region of sense, orfollow it into that of imagination, it is in the long run reducible tomechanical laws. But the mechanical data once guessed or given, mathematics are all-powerful as an instrument of deduction. Thecommand of Geometry over the relations of space, and the far-reachingpower which Analysis confers, are potent both As means of physicaldiscovery, and of reaping the entire fruits of discovery. Indeed, without mathematics, expressed or implied, our knowledge of physicalscience would be both friable and incomplete. 

Side by side with the mathematical method we have the method ofexperiment. Here from a starting-point furnished by his ownresearches or those of others, the investigator proceeds by combiningintuition and verication. He ponders the knowledge he possesses, andtries to push it further; he guesses, and checks his guess; heconjectures, and confirms or explodes his conjecture. These guessesand conjectures are by no means leaps in the dark; for knowledge oncegained casts a faint light beyond its own immediate boundaries. Thereis no discovery so limited as not to illuminate something beyonditself. The force of intellectual penetration into this penumbralregion which surrounds actual knowledge is not, as some seem to think, dependent upon method, but upon the genius of the investigator. Thereis, however, no genius so gifted as not to need control andverification. The profoundest minds know best that Nature's ways arenot at all times their ways, and that the brightest flashes in theworld of thought are incomplete until they have been proved to havetheir counterparts in the world of fact. Thus the vocation of thetrue experimentalist may be defined as the continued exercise ofspiritual insight, and its incessant correction and realisation. Hisexperiments constitute a body, of which his purified intuitions are, as it were, the soul. 

Partly through mathematical and partly through experimental research, physical science has, of late years, assumed a momentous position inthe world. Both in a material and in an intellectual point of view ithas produced, and it is destined to produce, immense changes--vastsocial ameliorations, and vast alterations in the popular conceptionof the origin, rule, and governance of natural things. By science, inthe physical world, miracles are wrought, while philosophy isforsaking its ancient metaphysical channels, and pursuing others whichhave been opened, or indicated by, scientific research. This mustbecome more and more the case as philosophical writers become moredeeply imbued with the methods of science, better acquainted with thefacts which scientific men have established, and with the greattheories which they have elaborated. 

If you look at the face of a watch, you see the hour and minute-hands, and possibly also a second-hand, moving over the graduated dial. Whydo these hands move? and why are their relative motions such as theyare observed to be? These questions cannot be answered withoutopening the watch, mastering its various parts, and ascertaining theirrelationship to each other. When this is done, we find that theobserved motion of the hands follows of necessity from the innermechanism of the watch when acted upon by the force invested in thespring. The motion of the hands may be called a phenomenon of art, but the case is similar with the phenomena of nature. These also havetheir inner mechanism and their store of force to set that mechanismgoing. The ultimate problem of physical science is to reveal thismechanism, to discern this store, and to show that from the combinedaction of both, the phenomena of which they constitute the basis, must, of necessity, flow. 

I thought an attempt to give you even a brief and sketchy illustrationof the manner in which scientific thinkers regard this problem, wouldnot be uninteresting to you on the present occasion; more especiallyas it will give me occasion to say a word or two on the tendencies andlimits of modern science; to point out the region which men of scienceclaim as their own, and where it is futile to oppose their advance;and also to define, if possible, the bourne between this and thatother region, to which the questionings and yearnings of thescientific intellect are directed in vain. 

But here your tolerance will be needed. It was the American Emerson, I think, who said that it is hardly possible to state any truthstrongly, without apparent injustice to some other truth. Truth isoften of a dual character, taking the form of a magnet with two poles;and many of the differences which agitate the thinking part of mankindare to be traced to the exclusiveness with which partisan reasonersdwell upon one half of the duality, in forgetfulness of the other. Theproper course appears to be to state both halves strongly, and alloweach its fair share in the formation of the resultant conviction. Butthis waiting for the statement of the two sides of a question impliespatience. It implies a resolution to suppress indignation, if thestatement of the one half should clash with our convictions; and torepress equally undue elation, if the half-statement should happen tochime in with our views. It implies a determination to wait calmlyfor the statement of the whole, before we pronounce judgment in theform of either acquiescence or dissent. 

This premised, and I trust accepted, let us enter upon our task. Therehave been writers who affirmed that the Pyramids of Egypt were naturalproductions; and in his early youth Alexander von Humboldt wrote alearned essay with the express object of refuting this notion. We nowregard the pyramids as the work of men's hands, aided probably bymachinery of which no record remains. We picture to ourselves theswarming workers toiling at those vast erections, lifting the inertstones, and, guided by the volition, the skill, and possibly at timesby the whip of the architect, placing them in their proper positions. The blocks, in this case, were moved and posited by a power externalto themselves, and the final form of the pyramid expressed the thoughtof its human builder. 

Let us pass from this illustration of constructive power to another ofa different kind. When a solution of common salt is slowlyevaporated, the water which holds the salt in solution disappears, butthe salt itself remains behind. At a certain stage of concentrationthe salt can no longer retain the liquid form; its particles, ormolecules, as they are called, begin to deposit themselves as minutesolids--so minute, indeed, as to defy all microscopic power. Asevaporation continues, solidification goes on, and we finally obtain, through the clustering together of innumerable molecules, a finitecrystalline mass of a definite form. What is this form? It sometimesseems a mimicry of the architecture of Egypt. We have little pyramidsbuilt by the salt, terrace above terrace from base to apex, forming aseries of steps resembling those up which the traveller in Egypt isdragged by his guides. The human mind is as little disposed to lookwithout questioning at these pyramidal salt-crystals, as to look atthe pyramids of Egypt, without enquiring whence they came. How, then, are those salt-pyramids built up?

Guided by analogy, you may, if you like, suppose that, swarming amongthe constituent molecules of the salt, there is an invisiblepopulation, controlled and coerced by some invisible master, placingthe atomic blocks in their positions. This, however, is not thescientific idea, nor do I think your good sense will accept it as alikely one. The scientific idea is, that the molecules act upon eachother without the intervention of slave labour; that they attract eachother, and repel each other, at certain definite points, or poles, andin certain definite directions; and that the pyramidal form is theresult of this play of attraction and repulsion. While, then, theblocks of Egypt were laid down by a power external to themselves, these molecular blocks of salt are self-posited, being fixed in theirplaces by the inherent forces with which they act upon each other. 

I take common salt as an illustration, because it is so familiar to usall; but any other crystalline substance would answer my purposeequally well. Everywhere, in fact, throughout inorganic nature, wehave this formative power, as Fichte would call it--this structuralenergy ready to come into play, and build the ultimate particles ofmatter into definite shapes. The ice of our winters, and of our polarregions, is its handiwork, and so also are the quartz, felspar, andmica of our rocks. Our chalk-beds are for the most part composed ofminute shells, which are also the product of structural energy; butbehind the shell, as a whole, lies a more remote and subtle formativeact. These shells are built up of little crystals of talc-spar, and, to form these crystals, the structural force had to deal with theintangible molecules of carbonate of lime. This tendency on the partof matter to organise itself, to grow into shape, to assume definiteforms in obedience to the definite action of force, is, as I havesaid, all-pervading. It is in the ground on which you tread, in thewater you drink, in the air you breathe. Incipient life, as it were, manifests itself throughout the whole of what we call inorganicnature. 

The forms of the minerals resulting from this play of polar forces arevarious, and exhibit different degrees of complexity. Men of scienceavail themselves of all possible means of exploring their moleculararchitecture. For this purpose they employ in turn, as agents ofexploration, light, heat, magnetism, electricity, and sound. Polarisedlight is especially useful and powerful here. A beam of such light, when sent in among the molecules of a crystal, is acted on by them, and from this action we infer with more or less clearness the mannerin which the molecules are arranged. That differences, for example, exist between the inner structure of rocksalt and that of crystallisedsugar or sugar-candy, is thus strikingly revealed. These actionsoften display themselves in chromatic phenomena of great splendour, the play of molecular force being so regulated as to cause the removalof some of the coloured constituents of white light, while others areleft with increased intensity behind. 

And now let us pass from what we are accustomed to regard as a deadmineral, to a living grain of corn. When this is examined bypolarised light, chromatic phenomena similar to those noticed incrystals are observed. And why? Because the architecture of thegrain resembles that of the crystal. In the grain also the moleculesare set in definite positions, and in accordance with theirarrangement they act upon the light. But what has built together themolecules of the corn? Regarding crystalline architecture, I havealready said that you may, if you please, consider the atoms andmolecules to be placed in position by a Power external to themselves. The same hypothesis is open to you now. But if in the case ofcrystals you have rejected this notion of an external architect, Ithink you are bound to reject it in the case of the grain, and toconclude that the molecules of the corn, also, are posited by theforces with which they act upon each other. It would be poorphilosophy to invoke an external agent in the one case, and to rejectit in the other. 

Instead of cutting our grain of corn into slices and subjecting it tothe action of polarised light, let us place it in the earth, andsubject it to a certain degree of warmth. In other words, let themolecules, both of the corn and of the surrounding earth, be kept inthat state of agitation which we call heat. Under thesecircumstances, the grain and the substances which surround itinteract, and a definite molecular architecture is the result. A budis formed; this bud reaches the surface, where it is exposed to thesun's rays, which are also to be regarded as a kind of vibratorymotion. And as the motion of common heat, with which the grain andthe substances surrounding it were first endowed, enabled the grainand these substances to exercise their mutual attractions andrepulsions, and thus to coalesce in definite forms, so the specificmotion of the sun's rays now enables the green bud to feed upon thecarbonic acid and the aqueous vapour of the air. The bud appropriatesthose constituents of both for which it has an elective attraction, and permits the other constituent to return to the atmosphere. Thusthe architecture is carried on. Forces are active at the root, forcesare active in the blade, the matter of the air and the matter of theatmosphere are drawn upon, and the plant augments in size. We have insuccession the stalk, the ear, the full corn in the ear; the cycle ofmolecular action being completed by the production of grains, similarto that with which the process began. 

Now there is nothing in this process which necessarily eludes theconceptive or imagining power of the human mind. An intellect thesame in kind as our own would, if only sufficiently expanded, be ableto follow the whole process from beginning to end. It would see everymolecule placed in its position by the specific attractions andrepulsions exerted between it and other molecules, the whole process, and its consummation, being an instance of the play of molecularforce. Given the grain and its environment, with their respectiveforces, the purely human intellect might, if sufficiently expanded, trace out _à priori_ every step of the process of growth, and, by theapplication of purely mechanical principles, demonstrate that thecycle must end, as it is seen to end, in the reproduction of formslike that with which it began. A necessity rules here, similar tothat which rules the planets in their circuits round the sun. 

You will notice that I am stating the truth strongly, as at thebeginning we agreed it should be stated. But I must go still further, and affirm that in the eye of science the animal body is just as muchthe product of molecular force as the chalk and the ear of corn, or asthe crystal of salt or sugar. Many of the parts of the body areobviously mechanical. Take the human heart, for example, with itssystem of valves, or take the exquisite mechanism of the eye or hand. Animal heat, moreover, is the same in kind as the heat of a fire, being produced by the same chemical process. Animal motion, too, isas certainly derived from the food of the animal, as the motion ofTrevethyck's walking-engine from the fuel in its furnace. As regardsmatter, the animal body creates nothing; as regards force, it createsnothing. Which of you by taking thought can add one cubit to hisstature? All that has been said, then, regarding the plant, may berestated with regard to the animal. Every particle that enters intothe composition of a nerve, a muscle, or a bone, has been placed inits position by molecular force. And unless the existence of law inthese matters be denied, and the element of caprice introduced, wemust conclude that, given the relation of any molecule of the body toits environment, its position in the body might be determinedmathematically. Our difficulty is not with the _quality_ of theproblem, but with its _complexity_; and this difficulty might be met bythe simple expansion of the faculties we now possess. Given thisexpansion, with the necessary molecular data, and the chick might bededuced as rigorously and as logically from the egg, as the existenceof Neptune from the disturbances of Uranus, or as conical refractionfrom the undulatory theory of light. 

You see I am not mincing matters, but avowing nakedly what manyscientific thinkers more or less distinctly believe. The formation ofa crystal, a plant, or an animal, is, in their eyes, a purelymechanical problem, which differs from the problems of ordinarymechanics, in the smallness of the masses, and the complexity of theprocesses involved. Here you have one half of our dual truth; let usnow glance at the other half. Associated with this wonderfulmechanism of the animal body we have phenomena no less certain thanthose of physics, but between which and the mechanism we discern nonecessary connection. A man, for example, can say 'I feel, ' 'Ithink, ' 'I love;' but how does consciousness infuse itself into theproblem? The human brain is said to be the organ of thought andfeeling: when we are hurt, the brain feels it; when we ponder, or whenour passions or affections are excited, it is through theinstrumentality of the brain. Let us endeavour to be a little moreprecise here. I hardly imagine there exists a profound scientificthinker, who has reflected upon the subject, unwilling to admit theextreme probability of the hypothesis, that for every fact ofconsciousness, whether in the domain of sense, thought, or emotion, adefinite molecular condition, of motion or structure, is set up in thebrain; or who would be disposed even to deny that if the motion, orstructure, be induced by internal causes instead of external, theeffect on consciousness will be the same? Let any nerve, for example, be thrown by morbid action into the precise state of motion whichwould be communicated to it by the pulses of a heated body, surelythat nerve will declare itself hot--the mind will accept thesubjective intimation exactly as if it were objective. The retina maybe excited by purely mechanical means. A blow on the eye causes aluminous flash, and the mere pressure of the finger on the externalball produces a star of light, which Newton compared to the circles ona peacock's tail. Disease makes people see visions and dream dreams;but, in all such cases, could we examine the organs implicated, weshould, on philosophical grounds, expect to find them in that precisemolecular condition which the real objects, if present, wouldsuperinduce. 

The relation of physics to consciousness being thus invariable, itfollows that, given the state of the brain, the corresponding thoughtor feeling might be inferred: or, given the thought or feeling, thecorresponding state of the brain might be inferred. But how inferred?It would be at bottom not a case of logical inference at all, but ofempirical association. You may reply, that many of the inferences ofscience are of this character--the inference, for example, that anelectric current, of a given direction, will deflect a magnetic needlein a definite way. But the cases differ in this, that the passagefrom the current to the needle, if not demonstrable, is conceivable, and that we entertain no doubt as to the final mechanical solution ofthe problem. But the passage from the physics of the brain to thecorresponding facts of consciousness is inconceivable as a result ofmechanics. Granted that a definite thought, and a definite molecularaction in the brain, occur simultaneously; we do not possess theintellectual organ, nor apparently any rudiment of the organ, whichwould enable us to pass, by a process of reasoning, from the one tothe other. They appear together, but we do not know why. Were ourminds and senses so expanded, strengthened, and illuminated, as toenable us to see and feel the very molecules of the brain; were wecapable of following all their motions, all their groupings, all theirelectric discharges, if such there be; and were we intimatelyacquainted with the corresponding states of thought and feeling, weshould be as far as ever from the solution of the problem, 'How arethese physical processes connected with the facts of consciousness?'The chasm between the two classes of phenomena would still remainintellectually impassable. Let the consciousness of love, forexample, be associated with a right-handed spiral motion of themolecules of the brain, and the consciousness of hate with aleft-handed spiral motion. We should then know, when we love, thatthe motion is in one direction, and, when we hate, that the motion isin the other; but the WHY?' would remain as unanswerable as before. 

In affirming that the growth of the body is mechanical, and thatthought, as exercised by us, has its correlative in the physics of thebrain, I think the position of the 'Materialist' is stated, as far asthat position is a tenable one. I think the materialist will be ablefinally to maintain this position against all attacks; but I do notthink, in the present condition of the human mind, that he can passbeyond this position. I do not think he is entitled to say that hismolecular groupings, and motions, explain everything. 

In reality they explain nothing. The utmost he can affirm is theassociation of two classes of phenomena, of whose real bond of unionhe is in absolute ignorance. The problem of the connection of bodyand soul is as insoluble, in its modern form, as it was in theprescientific ages. Phosphorus is known to enter into the compositionof the human brain, and a trenchant German writer has exclaimed, 'OhnePhosphor, kein Gedanke!' That may or may not be the case; but even ifwe knew it to be the case, the knowledge would not lighten ourdarkness. On both sides of the zone here assigned to the materialisthe is equally helpless. If you ask him whence is this 'Matter' ofwhich we have been discoursing--who or what divided it into molecules, who or what impressed upon them this necessity of running into organicforms--he has no answer. Science is mute in reply to these questions. But if the materialist is confounded and science rendered dumb, whoelse is prepared with a solution? To whom has this arm of the Lordbeen revealed? Let us lower our heads, and acknowledge our ignorance, priest and philosopher, one and all. 

Perhaps the mystery may resolve itself into knowledge at some futureday. The process of things upon this earth has been one ofamelioration. It is a long way from the Iguanodon and hiscontemporaries, to the President and Members of the BritishAssociation. And whether we regard the improvement from thescientific or from the theological point of view--as the result ofprogressive development, or of successive exhibitions of creativeenergy--neither view entitles us to assume that man's presentfaculties end the series, that the process of amelioration ends withhim. A time may therefore come when this ultra-scientific region, bywhich we are now enfolded, may offer itself to terrestrial, if not tohuman, investigation. Two-thirds of the rays emitted by the sun failto arouse the sense of vision. The rays exist, but the visual organrequisite for their translation into light does not exist. And sofrom this region of darkness and mystery which surrounds us, rays maynow be darting, which require but the development of the properintellectual organs to translate them into knowledge as far surpassingOurs, as ours surpasses that of the wallowing reptiles, which onceheld possession of this planet. Meanwhile the mystery is not withoutits uses. It certainly may made a power in the human soul; but it isa power which has feeling, not knowledge, for its base. It may be, will be, and I hope is turned to account, both in steadying andstrengthening intellect, and in; rescuing man from that littleness towhich, in the struggle for existence, or for precedence in the world, he is continually prone. 

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Musings on the Matterhorn, July 27, 1868. 

Hacked and hurt by time, the aspect of the mountain from its highercrags saddened me. Hitherto the impression it made was that of savagestrength; here we had inexorable decay. But this notion of decayimplied a reference to a period when the Matterhorn was in the fullstrength of mountainhood. Thought naturally ran back to its remoterorigin and sculpture. Nor did thought halt there, but wandered onthrough molten worlds to that nebulous haze which philosophers haveregarded, and with good reason, as the proximate source of allmaterial things. I tried to look at this universal cloud, containingwithin itself the prediction of all that has since occurred; I triedto imagine it as the seat of those forces whose action was to issue insolar and stellar systems, and all that they involve. Did thatformless fog contain potentially the _sadness_ with which I regarded theMatterhorn? Did the _thought_ which now ran back to it simply return toits primeval home? If so, had we not better recast our definitions ofmatter and force; for, if life and thought be the very flower of both, any definition which omits life and thought must be inadequate, if notuntrue. Are questions like these warranted? Why not? If the finalgoal of man has not been yet attained; if his development has not beenyet arrested, who can say that such yearnings and questionings are notnecessary to the opening of a finer vision, to the budding and thegrowth of diviner powers? When I look at the heavens and the earth, at my own body, at my strength and weakness, even at these ponderings, and ask myself, Is there no being or thing in the universe that knowsmore about these matters than I do; what is my answer? Supposing ourtheologic schemes of creation, condemnation, and redemption to bedissipated; and the warmth of denial which they excite, and which, asa motive force, can match the warmth of affirmation, dissipated at thesame time; would the undeflected human mind return to the meridian ofabsolute neutrality as regards these ultra-physical questions? Issuch a position one of stable equilibrium? The channels of thoughtbeing already formed, such are the questions, without replies, whichcould run athwart consciousness during a ten minutes' halt upon theweathered crest of the Matterhorn. 

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 Self-reverence, self-knowledge, self-control, These three alone lead life to sovereign power. Yet not for power (power of herself Would come uncalled for), but to live by law, Acting the law we live by without fear; And, because right is right, to follow right Were wisdom in the scorn of consequence. 

 TENNYSON. 

*****

VII. AN ADDRESS TO STUDENTS. 

[Footnote: Delivered at University College, London, Session 1968-69. ]

THERE is an idea regarding the nature of man which modern philosophyhas sought, and is still seeking, to raise into clearness; the idea, namely, of secular growth. Man is not a thing of yesterday; nor do Iimagine that the slightest controversial tinge is imported into thisaddress when I say that he is not a thing of 6, 000 years ago. Whetherhe came originally from stocks or stones, from nebulous gas or solarfire, I know not; if he had any such origin the process of histransformation is as inscrutable to you and me as that of the grandold legend, according to which 'the Lord God formed man of the dust ofthe ground, and breathed into his nostrils the breath of life; and manbecame a living soul. ' But however obscure man's origin may be, hisgrowth is not to be denied. Here a little and there a little addedthrough the ages have slowly transformed him from what he was intowhat he is. The doctrine has been held that the mind of the child islike a sheet of white paper, on which by education we can write whatcharacters we please. This doctrine assuredly needs qualification andcorrection. In physics, when an external force is applied to a bodywith a view of affecting its inner texture, if we wish to predict theresult, we must know whether the external force conspires with oropposes the internal forces of the body itself; and in bringing theinfluence of education to bear upon the new-born man his inner powersalso must be taken into account. He comes to us as a bundle ofinherited capacities and tendencies, labelled 'from the indefinitepast to the indefinite future;' and he makes his transit from the oneto the other through the education of the present time. The object ofthat education is, or ought to be, to provide wise exercise for hiscapacities, wise direction for his tendencies, and through thisexercise and this direction to furnish his mind with such knowledge asmay contribute to the usefulness, the beauty, and the nobleness of hislife. 

How is this discipline to be secured, this knowledge imparted? Tworival methods now solicit attention, --the one organised and equipped, the labour of centuries having been expended in bringing it to itspresent state of perfection; the other, more or less chaotic, butbecoming daily less so, and giving signs of enormous power, both as asource of knowledge and as a means of discipline. These two methodsare the classical and the scientific method. I wish they were notrivals; it is only bigotry and short-sightedness that make them so;for assuredly it is possible to give both of them fair play. Thoughhardly authorised to express an opinion upon the subject, Inevertheless hold the opinion that the proper study of a language isan intellectual discipline of the highest kind. If I exceptdiscussions on the comparative merits of Popery and Protestantism, English grammar was the most important discipline of my boyhood. Thepiercing through the involved and inverted sentences of 'ParadiseLost'; the linking of the verb to its often distant nominative, of therelative to its distant antecedent, of the agent to the object of thetransitive verb, of the preposition to the noun or pronoun which itgoverned, the study of variations in mood and tense, thetranspositions often necessary to bring out the true grammaticalstructure of a sentence--all this was to my young mind a discipline ofthe highest value, and a source of unflagging delight. How I rejoicedwhen I found a great author tripping, and was fairly able to pin himto a corner from which there was no escape! As I speak, some of thesentences which exercised me when a boy rise to my recollection. Forinstance, 'He that hath ears to hear, let him hear;' where the 'He'is left, as it were, floating in mid air without any verb to supportit. I speak thus of English because it was of real value to me. I donot speak of other languages because their educational value for mewas almost insensible. But knowing the value of English so well, Ishould be the last to deny, or even to doubt, the high disciplineinvolved in the proper study of Latin and Greek. 

That study, moreover, has other merits and recommendations. It is, asI have said, organised and systematised by long-continued use. It isan instrument wielded by some of our best intellects in the educationof youth; and it can point to results in the achievements of ourforemost men. What, then, has science to offer which is in the leastdegree likely to compete with such a system? I cannot better replythan by recurring to the grand old story from which I have alreadyquoted. Speaking of the world and all that therein is, of the sky andthe stars around it, the ancient writer says, 'And God saw all thathe had made, and behold it was very good. ' It is the body of thingsthus described which science offers to the study of man. There is avery renowned argument much prized and much quoted by theologians, inwhich the universe is compared to a watch. Let us deal practicallywith this comparison. Supposing a watchmaker, having completed hisinstrument, to be so satisfied with his work as to call it very good, what would you understand him to mean? You would not suppose that hereferred to the dial-plate in front and the chasing of the casebehind, so much as to the wheels and pinions, the springs and jewelledpivots of the works within--to those qualities and powers, in short, which enable the watch to perform its work as a keeper of time. Withregard to the knowledge of such a watch he would be a mere ignoramuswho would content himself with outward inspection. I do not wish tosay one severe word here to-day, but I fear that many of those who arevery loud in their praise of the works of the Lord know them only inthis outside and superficial way. It is the inner works of theuniverse which science reverently uncovers; it is the study of thesethat she recommends as a discipline worthy of all acceptation. 

The ultimate problem of physics is to reduce matter by analysis to itslowest condition of divisibility, and force to its simplestmanifestations, and then by synthesis to construct from these elementsthe world as it stands. We are still a long way from the finalsolution of this problem; and when the solution comes, it will be moreone of spiritual insight than of actual observation. But though weare still a long way from this complete intellectual mastery ofnature, we have conquered vast regions of it, have learned theirpolities and the play of their powers. We live upon a ball of 8, 000miles in diameter, swathed by an atmosphere of unknown height. Thisball has been molten by heat, chilled to a solid, and sculptured bywater. It is made up of substances possessing distinctive propertiesand modes of action, which offer problems to the intellect, someprofitable to the child, others taxing the highest powers of thephilosopher. Our native sphere turns on its axis, and revolves inspace. It is one of a band which all do the same. It is illuminatedby a sun which, though nearly a hundred millions of miles distant, canbe brought virtually into our closets and there subjected toexamination. It has its winds and clouds, its rain and frost, itslight, heat, sound, electricity, and magnetism. And it has its vastkingdoms of animals and vegetables. To a most amazing extent thehuman mind has conquered these things, and revealed the logic whichruns through them. Were they facts only, without logicalrelationship, science might, as a means of discipline, suffer incomparison with language. But the whole body of phenomena is instinctwith law; the facts are hung on principles, and the value of physicalscience as a means of discipline consists in the motion of theintellect, both inductively and deductively, along the lines of lawmarked out by phenomena. As regards the discipline to which I havealready referred as derivable from the study of languages, --that, andmore, is involved in the study of physical science. Indeed, I believeit would be possible so to limit and arrange the study of a portion ofphysics as to render the mental exercise involved in it almostqualitatively the same as that involved in the unravelling of alanguage. 

I have thus far confined myself to the purely intellectual side ofthis question. But man is not all intellect. If he were so, sciencewould, I believe, be his proper nutriment. But he feels as well asthinks; he is receptive of the sublime and beautiful as well as of thetrue. Indeed, I believe that even the intellectual action of acomplete man is, consciously or unconsciously, sustained by anundercurrent of the emotions. It is vain to attempt to separate themoral and emotional from the intellectual. Let a man but observehimself, and he will, if I mistake not, find that in nine cases out often, the emotions constitute the motive force which pushes hisintellect into action. The reading of the works of two men, neitherof them imbued with the spirit of modern science--neither of them, indeed, friendly to that spirit--has placed me here to-day. These menare the English Carlyle and the American Emerson. I must evergratefully remember that through three long cold German wintersCarlyle placed me in my tub, even when ice was on its surface, at fiveo'clock every morning--not slavishly, but cheerfully, meeting eachday's studies with a resolute will, determined whether victor orvanquished not to shrink from difficulty. I never should have gonethrough Analytical Geometry and the Calculus had it not been for thosemen. I never should have become a physical investigator, and hencewithout them I should not have been here to-day. They told me what Iought to do in a way that caused me to do it, and all my consequentintellectual action is to be traced to this purely moral source. ToCarlyle and Emerson I ought to add Fichte, the greatest representativeof pure idealism. These three unscientific men made me a practicalscientific worker. They called out 'Act!' I hearkened to thesummons, taking the liberty, however, of determining for myself thedirection which effort was to take. 

And I may now cry 'Act!' but the potency of action must be yours. Imay pull the trigger, but if the gun be not charged there is noresult. We are creators in the intellectual world as little as in thephysical. We may remove obstacles, and render latent capacitiesactive, but we cannot suddenly change the nature of man. The 'newbirth' itself implies the pre-existence of a character which requiresnot to be created but brought forth. You cannot by any amount ofmissionary labour suddenly transform the savage into the civilisedChristian. The improvement of man is _secular_--not the work of an houror of a day. But though indubitably bound by our organisations, noman knows what the potentialities of any human mind may be, requiringonly release to be brought into action. There are in the mineralworld certain crystals--certain forms, for instance, of fluor-spar, which have lain darkly in the earth for ages, but which neverthelesshave a potency of light locked up within them. In their case thepotential has never become actual--the light is in fact held back by amolecular detent. When these crystals are warmed, the detent islifted, and an outflow of light immediately begins. I know not howmany of you may be in the condition of this fluor-spar. For aught Iknow, every one of you may be in this condition, requiring but theproper agent to be applied--the proper word to be spoken--to remove adetent, and to render you conscious of light and warmth withinyourselves and sources of both to others. 

The circle of human nature, then, is not complete without the arc ofthe emotions. The lilies of the field have a value for us beyondtheir botanical ones--a certain lightening of the heart accompaniesthe declaration that 'Solomon in all his glory was not arrayed likeone of these. ' The sound of the village bell has a value beyond itsacoustical one. The setting sun has a value beyond its optical one. The starry heavens, as you know, had for Immanuel Kant a value beyondtheir astronomical one. I think it very desirable to keep thishorizon of the emotions open, and not to permit either priest orphilosopher to draw down his shutters between you and it. Here thedead languages, which are sure to be beaten by science in the purelyintellectual fight, have an irresistible claim. They supplement thework of science by exalting and refining the aesthetic faculty, andmust on this account be cherished by all who desire to see humanculture complete. There must be a reason for the fascination whichthese languages have so long exercised upon powerful and elevatedminds--a fascination which will probably continue for men of Greek andRoman mould to the end of time. 

In connection with this question one very obvious danger besets manyof the more earnest spirits of our day--the danger of _haste_ inendeavouring to give the feelings repose. We are distracted bysystems of theology and philosophy which were taught to us when young, and which now excite in us a hunger and a thirst for knowledge notproved to be attainable. There are periods when the judgment ought toremain in suspense, the data on which a decision might be based beingabsent. This discipline of suspending the judgment is a common one inscience, but not so common as it ought to be elsewhere. I walked downRegent Street some time ago with a man of great gifts andacquirements, discussing with him various theological questions. Icould not accept his views of the origin and destiny of the universe, nor was I prepared to enunciate any definite views of my own. Heturned to me at length and said, 'You surely must have a theory of theuniverse. ' That I should in one way or another have solved thismystery of mysteries seemed, to my friend a matter of course. 'I havenot even a theory of magnetism' was my reply. We ought to learn towait. We ought assuredly to pause before closing with the advances ofthose expounders of the ways of God to men, who offer us intellectualpeace at the modest cost of intellectual life. 

The teachers of the world ought to be its best men, and for thepresent at all events such men must learn self-trust. By the fullnessand freshness of their own Jives and utterances they must awaken lifein others. The hopes and terrors which influenced our fathers arepassing away, and our trust henceforth must rest on the innatestrength of man's moral nature. And here, I think, the poet will havea great part to play in the future culture of the world. To him, whenhe rightly understands his mission, and does not flinch from the tonicdiscipline which it assuredly demands, we have a right to look forthat heightening and brightening of life which so many of us need. Tohim it is given for a long time to come to fill those shores which therecession of the theologic tide has left exposed. Void of offence toscience, he may freely deal with conceptions which science shuns, andbecome the illustrator and interpreter of that Power which as

 'Jehovah, Jove, or Lord, '

has hitherto filled and strengthened the human heart. 

Let me utter one practical word in conclusion--take care of yourhealth. There have been men who by wise attention to this point mighthave risen to any eminence--might have made great discoveries, writtengreat poems, commanded armies, or ruled states, but who by unwiseneglect of this point have come to nothing. Imagine Hercules asoarsman in a rotten boat; what can he do there but by the very forceof his stroke expedite the ruin of his craft? Take care then of thetimbers of your boat, and avoid all practices likely to introduceeither wet or dry rot amongst them. And this is not to beaccomplished by desultory or intermittent efforts of the will, but bythe formation of _habits_. The will no doubt has sometimes to put forthits strength in order to crush the special temptation. But theformation of right habits is essential to your permanent security. They diminish your chance of falling when assailed, and they augmentyour chance of recovery when overthrown. 

********************

 If thou would'st know the mystic song Chaunted when the sphere was young, Aloft, abroad, the paean swells, O wise man, hear'st thou half it tells? To the open ear it sings The early genesis of things; Of tendency through endless ages Of star-dust and star-pilgrimages, Of rounded worlds, of space and time, Of the old floods' subsiding slime, Of chemic matter, force and form, Of poles and powers, cold, wet, and warm. The rushing metamorphosis Dissolving all that fixture is, Melts things that be to things that seem, And solid nature to a dream. '

 EMERSON. 

 Was waer' ein Gott der nur von aussen stiesse, Im Kreis das All am Finger laufen liesse Ihm ziemt's, die Welt im Innern zu bewegen, Natur in Sich, Sich in Natur zu hegen. '

 GOETHE. 

*****

VIII. SCIENTIFIC USE OF THE IMAGINATION. 

[Footnote: Discourse delivered before the British Association atLiverpool, September 16, 1870. ]

'Lastly, physical investigation, more than anything besides, helps toteach us the actual value and right use of the Imagination--of thatwondrous faculty, which, left to ramble uncontrolled, leads us astrayinto a wilderness of perplexities and errors, a land of mists andshadows; but which, properly controlled by experience and reflection, becomes the noblest attribute of man; the source of poetic genius, theinstrument of discovery in Science, without the aid of which Newtonwould never have invented fluxions, nor Davy have decomposed theearths and alkalies, nor would Columbus have found anotherContinent. '--Address to the Royal Society by its President SirBenjamin Brodie, November 30, 1859. 

I carried with me to the Alps this year the burden of this evening'swork. Save from memory I had no direct aid upon the mountains; but tospur up the emotions, on which so much depends, as well as to nourishindirectly the intellect and will, I took with me four works, comprising two volumes of poetry, Goethe's 'Farbenlehre, ' and the workon 'Logic' recently published by Mr. Alexander Bain. In Goethe, sonoble otherwise, I chiefly noticed the self-inflicted hurts of genius, as it broke itself in vain against the philosophy of Newton. Mr. BainI found, for the most part, learned and practical, shining generallywith a dry light, but exhibiting at times a flush of emotionalstrength, which proved that even logicians share the common fire ofhumanity. He interested me most when he became the mirror of my owncondition. Neither intellectually nor socially is it good for man tobe alone, and the sorrows of thought are more patiently borne when wefind that they have been experienced by another. From certainpassages in his book I could infer that Mr. Bain was no stranger tosuch sorrows. Speaking for example of the ebb of intellectual force, which we all from time to time experience, Mr. Bain says: 'Theuncertainty where to look for the next opening of discovery brings thepain of conflict and the debility of indecision. ' These words have inthem the true ring of personal experience. The action of theinvestigator is periodic. He grapples with a subject of enquiry, wrestles with it, and exhausts, it may be, both himself and it for thetime being. He breathes a space, and then renews the struggle inanother field. Now this period of halting between two investigationsis not always one of pure repose. It is often a period of doubt anddiscomfort--of gloom and ennui. 'The uncertainty where to look forthe next opening of discovery brings the pain of conflict and thedebility of indecision. ' It was under such conditions that I had toequip myself for the hour and the ordeal that are now come. 

*****

The disciplines of common life are, in great part, exercises in therelations of space, or in the mental grouping of bodies in space; and, by such exercises, the public mind is, to some extent, prepared forthe reception of physical conceptions. Assuming this preparation onyour part, the wish gradually grew within me to trace, and to enableyou to trace, some of the more occult features and operations of Lightand Colour. I wished, if possible, to take you beyond the boundary ofmere observation, into a region where things are intellectuallydiscerned, and to show you there the hidden mechanism of opticalaction. 

But how are those hidden things to be revealed? Philosophers may beright in affirming that we cannot transcend experience: we can, at allevents, carry it a long way from its origin. We can magnify, diminish, qualify, and combine experiences, so as to render them fitfor purposes entirely new. In explaining sensible phenomena, wehabitually form mental images of the ultra-sensible. There are Torieseven in science who regard Imagination as a faculty to be feared andavoided rather than employed. They have observed its action in weakvessels, and are unduly impressed by its disasters. But they mightwith equal justice point to exploded boilers as an argument againstthe use of steam. With accurate experiment and observation to workupon, Imagination becomes the architect of physical theory. Newton'spassage from a falling apple to a falling moon was an act of theprepared imagination, without which the 'laws of Kepler' could neverhave been traced to their foundations. Out of the facts of chemistrythe constructive imagination of Dalton formed the atomic theory. Davywas richly endowed with the imaginative faculty, while with Faradayits exercise was incessant, preceding, accompanying and guiding allhis experiments. His strength and fertility as a discoverer is to bereferred in great part to the stimulus of his imagination. Scientificmen fight shy of the word because of its ultra-scientificconnotations; but the fact is that without the exercise of this power, our knowledge of nature would be a mere tabulation of co-existencesand sequences. We should still believe in the succession of day andnight, of summer and winter; but the conception of Force would vanishfrom our universe; causal relations would disappear, and with themthat science which is now binding the parts of nature to an organicwhole. 

I should like to illustrate by a few simple instances the use thatscientific men have already made of this power of imagination, and toindicate afterwards some of the further uses that they are likely tomake of it. Let us begin with the rudimentary experiences. Observethe falling of heavy rain-drops into a tranquil pond. Each drop as itstrikes the water becomes a centre of disturbance, from which a seriesof ring-ripples expand outwards. Gravity and inertia are the agentsby which this wave-motion is produced, and a rough experiment willsuffice to show that the rate of propagation does not amount to a foota second. A series of slight mechanical shocks is experienced by abody plunged in the water, as the wavelets reach it in succession. Buta finer motion is at the same time set up and propagated. If the headand ears be immersed in the water, as in an experiment of Franklin's, the tick of the drop is heard. Now, this sonorous impulse ispropagated, not at the rate of a foot, but at the rate of 4, 700 feet asecond. In this case it is not the gravity but the elasticity of thewater that comes into play. Every liquid particle pushed against itsneighbour delivers up its motion with extreme rapidity, and the pulseis propagated as a thrill. The incompressibility of water, asillustrated by the famous Florentine experiment, is a measure of itselasticity; and to the possession of this property, in so high adegree, the rapid transmission of a sound-pulse through water is to beascribed. 

But water, as you know, is not necessary to the conduction of sound;air is its most common vehicle. And you know that when the airpossesses the particular density and elasticity corresponding to thetemperature of freezing water, the velocity of sound in it is 1, 090feet a second. It is almost exactly one-fourth of the velocity inwater; the reason being that though the greater weight of the watertends to diminish the velocity, the enormous molecular elasticity ofthe liquid far more than atones for the disadvantage due to weight. Byvarious contrivances we can compel the vibrations of the air todeclare themselves we know the length and frequency of the sonorouswaves, and we have also obtained great mastery over the variousmethods by which the air is thrown into vibration. We know thephenomena and laws of vibrating rods, of organ-pipes, strings, membranes, plates, and bells. We can abolish one sound by another. Weknow the physical meaning of music and noise, of harmony and discord. In short, as regards sound in general, we have a very clear notion ofthe external physical processes which correspond to our sensations. 

In the phenomena of sound, we travel a very little way from downrightsensible experience. Still the imagination is to some extentexercised. The bodily eye, for example, cannot see the condensationsand rarefactions of the waves of sound. We construct them in thought, and we believe as firmly in their existence as in that of the airitself. But now our experience is to be carried into a new region, where a new use is to be made of it. Having mastered the cause andmechanism of sound, we desire to know the cause and mechanism oflight. We wish to extend our enquiries from the auditory to the opticnerve. There is in the human intellect a power of expansion--I mightalmost call it a power of creation--which is brought into play by thesimple brooding upon facts. The legend of the spirit brooding overchaos may have originated in experience of this power. In the casenow before us it has manifested itself by transplanting into space, for the purposes of light, an adequately modified form of themechanism of sound. We know intimately whereon the velocity of sounddepends. When we lessen the density of the aerial medium, andpreserve its elasticity constant, we augment the velocity. When weheighten the elasticity, and keep the density constant, we alsoaugment the velocity. A small density, therefore, and a greatelasticity, are the two things necessary to rapid propagation. Nowlight is known to move with the astounding velocity of 186, 000 miles asecond. How is such a velocity to be obtained? By boldly diffusingin space a medium of the requisite tenuity and elasticity. 

Let us make such a medium our starting-point, and, endowing it withone or two other necessary qualities, let us handle it in accordancewith strict mechanical laws. Let us then carry our results from theworld of theory into the world of sense, and see whether ourdeductions do not issue in the very phenomena of light which ordinaryknowledge and skilled experiment reveal. If in all the multipliedvarieties of these phenomena, including those of the most remote andentangled description, this fundamental conception always brings usface to face with the truth; if no contradiction to our deductionsfrom it be found in external nature, but on all sides agreement andverification; if, moreover, as in the case of Conical Refraction andin other cases, it actually forces upon our attention phenomena whichno eye had previously seen, and which no mind had previouslyimagined--such a conception, must, we think, be something more than amere figment of the scientific fancy. In forming it, that compositeand creative power, in which reason and imagination are united, has, we believe, led us into a world not less real than that of the senses, and of which the world of sense itself is the suggestion and, to agreat extent, the outcome. 

Far be it from me, however, to wish to fix you immovably in this or inany other theoretic conception. With all our belief of it, it will bewell to keep the theory of a luminiferous aether plastic and capableof change. You may, moreover, urge that, although the phenomena occur_as if_ the medium existed, the absolute demonstration of its existenceis still wanting. Far be it from me to deny to this reasoning suchvalidity as it may fairly claim. Let us endeavour by means of analogyto form a fair estimate of its force. You believe that in society youare surrounded by reasonable beings like yourself. You are, perhaps, as firmly convinced of this as of anything. What is your warrant forthis conviction? Simply and solely this: your fellow-creatures behaveas if they were reasonable; the hypothesis, for it is nothing more, accounts for the facts. To take an eminent example: you believe thatour President is a reasonable being. Why? There is no known methodof superposition by which any one of us can apply himselfintellectually to any other, so as to demonstrate coincidence asregards the possession of reason. If, therefore, you hold ourPresident to be reasonable, it is because he behaves _as if_ he werereasonable. As in the case of the aether, beyond the _'as if'_ youcannot go. Nay, I should not wonder if a close comparison of the dataon which both inferences rest, caused many respectable persons toconclude that the aether had the best of it. 

This universal medium, this light-aether as it is called, is thevehicle, not the origin, of wave-motion. It receives and transmits, but it does not create. Whence does it derive the motions it conveys?For the most part from luminous bodies. By the motion of a luminousbody I do not mean its sensible motion, such as the flicker of acandle, or the shooting out of red prominences from the limb of thesun. I mean an intestine motion of the atoms or molecules of theluminous body. But here a certain reserve is necessary. Manychemists of the present day refuse to speak of atoms and molecules asreal things. Their caution leads them to stop short of the clear, sharp, mechanically intelligible atomic theory enunciated by Dalton, or any form of that theory, and to make the doctrine of 'multipleproportions' their intellectual bourne. I respect the caution, thoughI think it is here misplaced. The chemists who recoil from thesenotions of atoms and molecules accept, without hesitation, theUndulatory Theory of Light. Like you and me they one and all believein an aether and its light-producing waves. Let us consider what thisbelief involves. Bring your imaginations once more into play, andfigure a series of sound-waves passing through air. Follow them up totheir origin, and what do you there find? A definite, tangible, vibrating body. It may be the vocal chords of a human being, it maybe an organ-pipe, or it may be a stretched string. Follow in the samemanner a train of aether-waves to their source; remembering at thesame time that your aether is matter, dense, elastic, and capable ofmotions subject to, and determined by, mechanical laws. What then doyou expect to find as the source of a series of aether-waves? Askyour imagination if it will accept a vibrating multiple proportion--anumerical ratio in a state of oscillation? I do not think it will. You cannot crown the edifice with this abstraction. The scientificimagination, which is here authoritative, demands, as the origin andcause of a series of aether-waves, a particle of vibrating matterquite as definite, though it may be excessively minute, as that whichgives origin to a musical sound. Such a particle we name an atom or amolecule. I think the intellect, when focussed so as to givedefinition without penumbral haze, is sure to realise this image atthe last. 

*****

With the view of preserving thought continuous throughout thisdiscourse, and of preventing either failure of knowledge or of memory, from causing any rent in our picture, I here propose to run rapidlyover a bit of ground which is probably familiar to most of you, butwhich I am anxious to make familiar to you all. The waves generatedin the aether by the swinging atoms of luminous bodies are ofdifferent lengths and amplitudes. The amplitude is the width of swingof the individual particles of the waves. In water-waves it is thevertical height of the crest above the trough, while the length of thewave is the horizontal distance between two consecutive crests. Theaggregate of waves emitted by the sun may be broadly divided into twoclasses: the one class competent, the other incompetent, to excitevision. But the light-producing waves differ markedly amongthemselves in size, form, and force. The length of the largest ofthese waves is about twice that of the smallest, but the amplitude ofthe largest is probably a hundred times that of the smallest. Now theforce or energy of the wave, which, expressed with reference tosensation, means the intensity of the light, is proportional to thesquare of the amplitude. Hence the amplitude being one-hundredfold, the energy of the largest light-giving waves would be ten-thousandfoldthat of the smallest. This is not improbable. I use these figures notwith a view to numerical accuracy, but to give you definite ideas ofthe differences that probably exist among the light-giving waves. Andif we take the whole range of solar radiation into account--itsnon-visual as well as its visual waves--I think it probable that theforce, or energy, of the largest wave is more than a million timesthat of the smallest. 

Turned into their equivalents of sensation, the different light-wavesproduce different colours. Red, for example, is produced by thelargest waves, violet by the smallest, while green is produced by awave of intermediate length and amplitude. On entering from air intoa more highly refracting substance, such as glass or water, or thesulphide of carbon, all the waves are retarded, but the smallest onesmost. This furnishes a means of separating the different classes ofwaves from each other; in other words, of analysing the light. 

Sent through a refracting prism, the waves of the sun are turned asidein different degrees from their direct course, the red least, theviolet most. They are virtually pulled asunder, and they paint upon awhite screen placed to receive them 'the solar spectrum. ' Strictlyspeaking, the spectrum embraces an infinity of colours; but the limitsof language, and of our powers of distinction, cause it to be dividedinto seven segments: red, orange, yellow, green, blue, indigo, violet. These are the seven primary or prismatic colours. 

Separately, or mixed in various proportions, the solar waves yield allthe colours observed in nature and employed in art. Collectively, they give us the impression of whiteness. Pure unsifted solar lightis white; and, if all the wave-constituents of such light be reducedin the same proportion, the light, though diminished in intensity, will still be white. The whiteness of snow with the sun shining uponit, is barely tolerable to the eye. The same snow under an overcastfirmament is still white. Such a firmament enfeebles the light byreflecting it upwards; and when we stand above a cloud-field--on anAlpine summit, for instance, or on the top of Snowdon--and see, in theproper direction, the sun shining on the clouds below us, they appeardazzlingly white. Ordinary clouds, in fact, divide the solar lightimpinging on them into two parts--a reflected part and a transmittedpart, in each of which the proportions of wave-motion which producethe impression of whiteness are sensibly preserved. 

It will be understood that the condition of whiteness would fail ifall the waves were diminished _equally_, or by the same absolutequantity. They must be reduced _proportionately_, instead of equally. If by the act of reflection the waves of red light are split intoexact halves, then, to preserve the light white, the waves of yellow, orange, green, and blue, must also be split into exact halves. Inshort, the reduction must take place, not by absolutely equalquantities, but by equal fractional parts. In white light thepreponderance, as regards energy, of the larger over the smaller wavesmust always be immense. Were the case otherwise, the visualcorrelative, blue, of the smaller waves would have the upper hand inour sensations. 

Not only are the waves of aether reflected by clouds, by solids, andby liquids, but when they pass from light air to dense, or from denseair to light, a portion of the wave-motion is always reflected. Nowour atmosphere changes continually in density from top to bottom. Itwill help our conceptions if we regard it as made up of a series ofthin concentric layers, or shells of air, each shell being of the samedensity throughout, a small and sudden change of density occurring inpassing from shell to shell. Light would be reflected at the limitingsurfaces of all these shells, and their action would be practicallythe same as that of the real atmosphere. And now I would ask yourimagination to picture this act of reflection. What must become ofthe reflected light? The atmospheric layers turn their convexsurfaces towards the sun; they are so many convex mirrors of feeblepower; and you will immediately perceive that the light regularlyreflected from these surfaces cannot reach the earth at all, but isdispersed in space. Light thus reflected cannot, therefore, be thelight of the sky. 

But, though the sun's light is not reflected in this fashion from theaerial layers to the earth, there is indubitable evidence to show thatthe light of our firmament is scattered light. Proofs of the mostcogent description could be here adduced; but we need only considerthat we receive light at the same time from all parts of thehemisphere of heaven. The light of the firmament comes to us acrossthe direction of the solar rays, and even against the direction of thesolar rays; and this lateral and opposing rush of wave-motion can onlybe due to the rebound of the waves from the air itself, or fromsomething suspended in the air. It is also evident that, unlike theaction of clouds, the solar light is not reflected by the sky in theproportions which produce white. The sky is blue, which indicates anexcess of the shorter waves. In accounting for the colour of the sky, the first question suggested by analogy would undoubtedly be, Is notthe air blue? The blueness of the air has, in fact, been given as asolution of the blueness of the sky. But how, if the air be blue, canthe light of sunrise and sunset, which travels through vast distancesof air, be yellow, orange, or even red? The passage of white solarlight through a blue medium could by no possibility redden the light. 

The hypothesis of a blue air is therefore untenable. In fact theagent, whatever it is, which sends us the light of the sky, exercisesin so doing a dichroitic action. The light reflected is blue, thelight transmitted is orange or red. A marked distinction is thusexhibited between the matter of the sky, and that of an ordinarycloud, which exercises no such dichroitic action. 

By the scientific use of the imagination we may hope to penetrate thismystery. The cloud takes no note of size on the part of the waves ofaether, but reflects them all alike. It exercises no selectiveaction. Now the cause of this may be that the cloud particles are solarge, in comparison with the waves of aether, as to reflect them allindifferently. A broad cliff reflects an Atlantic roller as easily asa ripple produced by a seabird's wing; and in the presence of largereflecting surfaces, the existing differences of magnitude among thewaves of aether may disappear. But supposing the reflectingparticles, instead of being very large, to be very small in comparisonwith the size of the waves. In this case, instead of the whole wavebeing fronted and thrown back, a small portion only is shivered off. The great mass of the wave passes over such a particle withoutreflection. Scatter, then, a handful of such minute foreign particlesin our atmosphere, and set imagination to watch their action upon thesolar waves. Waves of all sizes impinge upon the particles, and yousee at every collision a portion of the impinging wave struck off; allthe waves of the spectrum, from the extreme red to the extreme violet, being thus acted upon. 

Remembering that the red waves stand to the blue much in the relationof billows to ripples, we have to consider whether those extremelysmall particles are competent to scatter all the waves in the sameproportion. If they be not--and a little reflection will make itclear that they are not--the production of colour must be an incidentof the scattering. Largeness is a thing of relation; and the smallerthe wave, the greater is the relative size of any particle on whichthe wave impinges, and the greater also the ratio of the portionscattered to the total wave A pebble, placed in the way of thering-ripples produced by heavy raindrops on a tranquil pond, willscatter a large fraction of each ripple, while the fractional part ofa larger wave thrown back by the same pebble might be infinitesimal. Now we have already made it clear to our minds that to preserve thesolar light white, its constituent proportions must not be altered;but in the act of division performed by these very small particles theproportions are altered; an undue fraction of the smaller waves isscattered by the particles, and, as a consequence, in the scatteredlight, blue will be the predominant colour. The other colours of thespectrum must, to some extent, be associated with the blue. They arenot absent, but deficient. We ought, in fact, to have them all, butin diminishing proportions, from the violet to the red. 

We have here presented a case to the imagination, pad, assuming theundulatory theory to be a reality, we have, I think, fairly reasonedour way to the conclusion, that were particles, small in comparison tothe sizes of the aether waves, sown in our atmosphere, the lightscattered by those particles would be exactly such as we observe inour azure skies. When this light is analysed, all the colours of thespectrum are found, and they are found in the proportions indicated byour conclusion. Blue is not the sole, but it is the predominantcolour. 

Let us now turn our attention to the light which passes unscatteredamong the particles. How must it be finally affected? By itssuccessive collisions with the particles the white light is more andmore robbed of its shorter waves; it therefore loses more and more ofits due proportion of blue. The result may be anticipated. Thetransmitted light, where short distances are involved, will appearyellowish. But as the sun sinks towards the horizon the atmosphericdistances increase, and consequently the number of the scatteringparticles. They abstract in succession the violet, the indigo, theblue, and even disturb the proportions of green. The transmittedlight under such circumstances must pass from yellow through orange tored. This also is exactly what we find in nature. Thus, while thereflected light gives us at noon the deep azure of the Alpine skies, the transmitted light gives us at sunset the warm crimson of theAlpine snows. The phenomena certainly occur as if our atmosphere werea medium rendered slightly turbid by the mechanical suspension ofexceedingly small foreign particles. 

Here, as before, we encounter our sceptical 'as if. ' It is one of theparasites of science, ever at hand, and ready to plant itself andsprout, if it can, on the weak points of our philosophy. But a strongconstitution defies the parasite, and in our case, as we question thephenomena, probability grows like growing health, until in the end themalady of doubt is completely extirpated. The first question thatnaturally arises is this: Can small particles be really proved to actin the manner indicated? No doubt of it. Each one of you can submitthe question to an experimental test. Water will not dissolve resin, but spirit will dissolve it; and when spirit holding resin in solutionis dropped into water, the resin immediately separates in solidparticles, which render the water milky. The coarseness of thisprecipitate depends on the quantity of the dissolved resin. You cancause it to separate either in thick clots or in exceedingly fineparticles. Professor Bruecke has given us the proportions whichproduce particles particularly suited to our present purpose. Onegramme of clean mastic is dissolved in eighty-seven grammes ofabsolute alcohol, and the transparent solution is allowed to drop intoa beaker containing clear water, kept briskly stirred. An exceedinglyfine precipitate is thus formed, which declares its presence by itsaction upon light. Placing a dark surface behind the beaker, andpermitting the light to fall into it from the top or front, the mediumis seen to be distinctly blue. It is not perhaps so perfect a blue asmay be seen on exceptional days among the Alps, but it is a very fairsky-blue. A trace of soap in water gives a tint of blue. London, andI fear Liverpool, milk makes an approximation to the same colour, through the operation of the same cause; and Helmholtz hasirreverently disclosed the fact that the deepest blue eye is simply aturbid medium. 

*****

The action of turbid media upon light was illustrated by Goethe, who, though unacquainted with the undulatory theory, was led by hisexperiments to regard the firmament as an illuminated turbid medium, with the darkness of space behind it. He describes glasses showing abright yellow by transmitted, and a beautiful blue by reflected, light. Professor Stokes, who was probably the first to discern thereal nature of the action of small particles on the waves of aether, [Footnote: This is inferred from conversation. I am not aware thatProfessor Stokes has published anything upon the subject. ] describesa glass of a similar kind. [Footnote: This glass, by reflected light, had a colour 'strongly resembling that of a decoction ofhorse-chestnut bark. ' Curiously enough, Goethe refers to this verydecoction: 'Man nehme einen Streifen frischer Rinds von derRosskastanie, man stecke denselben in ein Glas Wasser, und in derkuerzesten Zeit werden wir das vollkommenste Himmelblau entstehensehen. '--Goethe's Werke, B. Xxix. P. 24. ]

Capital specimens of such glass are to be found at Salviati's, in St. James's Street. What artists call 'chill' is no doubt an effect ofthis description. Through the action of minute particles, the brownsof a picture often present the appearance of the bloom of a plum. Byrubbing the varnish with a silk handkerchief optical continuity isestablished and the chill disappears. Some years ago I witnessed Mr. Hirst experimenting at Zermatt on the turbid water of the Visp. Whenkept still for a day or so, the grosser matter sank, but the finerparticles remained suspended, and gave a distinctly blue tinge to thewater. The blueness of certain Alpine lakes has been shown to be inpart due to this cause. Professor Roscoe has noticed several strikingcases of a similar kind. In a very remarkable paper the latePrincipal Forbes showed that steam issuing from the safety-valve of alocomotive, when favourably observed, exhibits at a certain stage ofits condensation the colours of the sky. It is blue by reflectedlight, and orange or red by transmitted light. The same effect, aspointed out by Goethe, is to some extent exhibited by peat-smoke. Morethan ten years ago, I amused myself by observing, on a calm day atKillarney, the straight smoke-columns rising from the cabin-chimneys. It was easy to project the lower portion of a column against a darkpine, and its upper portion against a bright cloud. The smoke in theformer case was blue, being seen mainly by reflected light; in thelatter case it was reddish, being seen mainly by transmitted light. Such smoke was not in exactly the condition to give us the glow of theAlps, but it was a step in this direction. Bruecke's fine precipitateabove referred to looks yellowish by transmitted light; but, by dulystrengthening the precipitate, you may render the white light of noonas ruby-coloured as the sun, when seen through Liverpool smoke, orupon Alpine horizons. I do not, however, point to the gross smokearising from coal as an illustration of the action of small particles, because such smoke soon absorbs and destroys the waves of blue, instead of sending them to the eyes of the observer. 

These multifarious facts, and numberless others which cannot now bereferred to, are explained by reference to the single principle, that, where the scattering particles are small in comparison to theaethereal waves, we have in the reflected light a greater proportionof the smaller waves, and in the transmitted light a greaterproportion of the larger waves, than existed in the original whitelight. The consequence, as regards sensation, is that in the one easeblue is predominant, and in the other orange or red. Our bestmicroscopes can readily reveal objects not more than 1/50000th of aninch in diameter. This is less than the length of a wave of redlight. Indeed a first-rate microscope would enable us to discernobjects not exceeding in diameter the length of the smallest waves ofthe visible spectrum. [Footnote: Dallinger and Drysdale have recentlymeasured cilia 1/200000th of an inch in diameter. 1878. ] By themicroscope, therefore, we can test our particles. If they be as largeas the light-waves they will infallibly be seen; and if they be not soseen, it is because they are smaller. Some months ago I placed in thehands of our President a liquid containing Bruecke's precipitate. Theliquid was milky blue, and Mr. Huxley applied to it his highestmicroscopic power. He satisfied me that had particles of even1/100000th of an inch in diameter existed in the liquid, they couldnot have escaped detection. But no particles were seen. Under themicroscope the turbid liquid was not to be distinguished fromdistilled water. [Footnote: Like Dr. Burdon Sanderson's 'pyrogen, 'the particles of mastic passed, without sensible hindrance, throughfiltering-paper. By such filtering no freedom from suspendedparticles is secured. The application of a condensed beam to thefiltrate renders this at once evident. ]

But we have it in our power to imitate, far more closely than we havehitherto done, the natural conditions of this problem. We cangenerate, in air, artificial skies, and prove their perfect identitywith the natural one, as regards the exhibition of a number of whollyunexpected phenomena. By a continuous process of growth, moreover, weare able to connect sky-matter, if I may use the term, with molecularmatter on the one side, and with molar matter, or matter in sensiblemasses, on the other. In illustration of this, I will take anexperiment suggested by some of my own researches, and described by M. Morren of Marseilles at the Exeter meeting of the British Association. Sulphur and oxygen combine to form sulphurous acid gas, two atoms ofoxygen and one of sulphur constituting the molecule of sulphurousacid. It has been recently shown that waves of aether issuing from astrong source, such as the sun or the electric light, are competent toshake asunder the atoms of gaseous molecules. [Footnote: See 'NewChemical Reactions produced by Light, ' vol. I. ] A chemist wouldcall this, 'decomposition' by light; but it behoves us, who areexamining the power and function of the imagination, to keepconstantly before us the physical images which underlie our terms. Therefore I say, sharply and definitely, that the components of themolecules of sulphurous acid are shaken asunder by the aether-waves. Enclosing sulphurous acid in a suitable vessel, placing it in a darkroom, and sending through it a powerful beam of light, we at first seenothing: the vessel containing the gas seems as empty as a vacuum. Soon, however, along the track of the beam a beautiful sky-blue colouris observed, which is due to light scattered by the liberatedparticles of sulphur. For a time the blue grows more intense; it thenbecomes whitish; and ends in a more or less perfect white. When theaction is continued long enough, the tube is filled with a dense cloudof sulphur particles, which by the application of proper means may berendered individually visible. [Footnote: M. Morren was mistaken insupposing that a modicum of sulphurous acid, in the drying tubes, hadany share in the production of the 'actinic clouds' described by me. Abeautiful case of molecular instability in the presence of light isfurnished by peroxide of chlorine as proved by Professor Dewar. 1878. ]

Here, then, our aether-waves untie the bond of chemical affinity, andliberate a body--sulphur--which at ordinary temperatures is a solid, and which therefore soon becomes an object of the senses. We havefirst of all the free atoms of sulphur, which are incompetent to stirthe retina sensibly with scattered light. But these atoms graduallycoalesce and form _particles_, which grow larger by continual accretion, until after a minute or two they appear as sky-matter. In thiscondition they are individually invisible; but collectively they sendan amount of wave-motion to the retina, sufficient to produce thefirmamental blue. The particles continue, or may be caused tocontinue, in this condition for a considerable time, during which nomicroscope can cope with them. But they grow slowly larger, and passby insensible gradations into the state of _cloud_, when they can nolonger elude the armed eye. Thus, without solution of continuity, westart with matter in the atom, and end with matter in the mass;sky-matter being the middle term of the series of transformations. Instead of sulphurous acid, we might choose a dozen other substances, and produce the same effect with all of them. In the case ofsome--probably in the case of all--it is possible to preserve matterin the firmamental condition for fifteen or twenty minutes under thecontinual operation of the light. During these fifteen or twentyminutes the particles constantly grow larger, without ever exceedingthe size requisite to the production of the celestial blue. 

Now when two vessels are placed before us, each containing sky-matter, it is possible to state with great distinctness which vessel containsthe largest particles. The eye is very sensitive to differences oflight, when, as in our experiments, it is placed in comparativedarkness, and the wave-motion thrown against the retina is small. Thelarger particles declare themselves by the greater whiteness of theirscattered light. Call now to mind the observation, or effort atobservation, made by our President, when he failed to distinguish theparticles of mastic in Bruecke's medium, and when you have done this, please follow me. 

A beam of light is permitted to act upon a certain vapour. In twominutes the azure appears, but at the end of fifteen minutes it hasnot ceased to be azure. After fifteen minutes its colour, and someother phenomena, pronounce it to be a blue of distinctly smallerparticles than those sought for in vain by Mr. Huxley. Theseparticles, as already stated, must have been less than 1/100000th ofan inch in diameter. 

And now I want you to consider the following question: Here areparticles which have been growing continually for fifteen minutes, andat the end of that time are demonstrably smaller than those whichdefied the microscope of Mr. Huxley--_What must have been the size ofthese particles at the beginning of their growth?_ What notion can youform of the magnitude of such particles? The distances of stellarspace give us simply a bewildering sense of vastness, without leavingany distinct impression on the mind; and the magnitudes with which wehave here to do, bewilder us equally in the opposite direction. Weare dealing with infinitesimals, compared with which the test objectsof the microscope are literally immense. 

From their perviousness to stellar light, and other considerations, Sir John Herschel drew some startling conclusions regarding thedensity and weight of comets. You know that these extraordinary andmysterious bodies sometimes throw out tails 100, 000, 000 miles inlength, and 50, 000 miles in diameter. The diameter of our earth is8, 000 miles. Both it and the sky, and a good portion of space beyondthe sky, would certainly be included in a sphere 10, 000 miles across. Let us fill a hollow sphere of this diameter with cometary matter, andmake it our unit of measure. To produce a comet's tail of the sizejust mentioned, about 300, 000 such measures would have to be emptiedinto space. Now suppose the whole of this stuff to be swept together, and suitably compressed, what do you suppose its volume would be? SirJohn Herschel would probably tell you that the whole mass might becarted away, at a single effort, by one of your dray-horses. In fact, I do not know that he would require more than a small fraction of ahorse-power to remove the cometary dust. After this, you will hardlyregard as monstrous a notion I have sometimes entertained, concerningthe quantity, of matter in our sky. Suppose a shell to surround theearth at a distance which would place it beyond the grosser matterthat hangs in the lower regions of the air--say at the height of theMatterhorn or Mont Blanc. Outside this shell we should have the deepblue firmament. Let the atmospheric space beyond the shell be sweptclean, and the sky-matter properly gathered up. What would be itsprobable amount? I have sometimes thought that a lady's portmanteauwould contain it all. I have thought that even a gentleman'sportmanteau--possibly his snuff-box--might take it in. And, whetherthe actual sky be capable of this amount of condensation or not, Ientertain no doubt that a sky quite as vast as ours, and as good inappearance, could be formed from a quantity of matter which might beheld in the hollow of the hand. 

Small in mass, the vastness in point of number of the particles of oursky may be inferred from the continuity of its light. It is not inbroken patches, nor at scattered points, that the heavenly azure isrevealed. To the observer on the summit of Mont Blanc, the blue is asuniform and coherent as if it formed the surface of the mostclose-grained solid. A marble dome would not exhibit a strictercontinuity. And Mr. Glaisher will inform you, that if ourhypothetical shell were lifted to twice the height of Mont Blanc abovethe earth's surface, we should still have the azure overhead. Everywhere through the atmosphere those sky-particles are strewn. Theyfill the Alpine valleys, spreading like a delicate gauze in front ofthe slopes of pine. They sometimes so swathe the peaks with light asto abolish their definition. This year I have seen the Weisshorn thusdissolved in opalescent air. By proper instruments the glare thrownfrom the sky-particles against the retina may be quenched, and thenthe mountain which it obliterated starts into sudden definition. [Footnote: See the 'Sky of the Alps, ' Art. Iv. Sec. 3, vol. I. ]Its extinction in front of a dark mountain resembles exactly thewithdrawal of a veil. It is then the light taking possession of theeye, not the particles acting as opaque bodies, that interferes withthe definition. By day this light quenches the stars; even bymoonlight it is able to exclude from vision all stars between thefifth and the eleventh magnitude. It may be likened to a noise, andthe feebler stellar radiance to a whisper drowned by the noise. 

What is the nature of the particles which shed this light? Thecelebrated De la Rive ascribes the haze of the Alps in fine weather tofloating organic germs. Now the possible existence of germs in suchprofusion has been held up as an absurdity. It has been affirmed thatthey would darken the air, and on the assumed impossibility of theirexistence in the requisite numbers, without invasion of the solarlight, an apparently powerful argument has been based by believers inspontaneous generation. Similar arguments have been used by theopponents of the germ theory of epidemic disease, who havetriumphantly challenged an appeal to the microscope and the chemist'sbalance to decide the question. Such arguments, however, are foundedon a defective acquaintance with the powers and properties of matter. Without committing myself in the least to De la Rive's notion, to thedoctrine of spontaneous generation, or to the germ theory of disease, I would simply draw attention to the demonstrable fact, that, in theatmosphere, we have particles which defy both the microscope and thebalance, which do not darken the air, and which exist, nevertheless, in multitudes sufficient to reduce to insignificance the Israelitishhyperbole regarding the sands upon the sea-shore. 

*****

The varying judgments of men on these and other questions may perhapsbe, to some extent, accounted for by that doctrine of Relativity whichplays so important a part in philosophy. This doctrine affirms thatthe impressions made upon us by any circumstance, or combination ofcircumstances, depend upon our previous state. Two travellers uponthe same height, the one having ascended to it from the plain, theother having descended to it from a higher elevation, will bedifferently affected by the scene around them. To the one nature isexpanding, to the other it is contracting, and impressions which havetwo such different antecedent states are sure to differ. In ourscientific judgments the law of relativity may also play an importantpart. To two men, one educated in the school of the senses, havingmainly occupied himself with observation; the other educated in theschool of imagination as well, and exercised in the conceptions ofatoms and molecules to which we have so frequently referred, a bit ofmatter, say 1/50000th of an inch in diameter, will present itselfdifferently. The one descends to it from his molar heights, the otherclimbs to it from his molecular lowlands. To the one it appearssmall, to the other large. So, also, as regards the appreciation ofthe most minute forms of life revealed by the microscope. To one ofthe men these naturally appear conterminous with the ultimateparticles of matter; there is but a step from the atom to theorganism. The other discerns numberless organic gradations betweenboth. Compared with his atoms, the smallest vibrios and bacteria ofthe microscopic field are as behemoth and leviathan. The law ofrelativity may to some extent explain the different attitudes of twosuch persons with regard to the question of spontaneous generation. Anamount of evidence which satisfies the one entirely fails to satisfythe other; and while to the one the last bold defence and startlingexpansion of the doctrine by Dr. Bastian will appear perfectlyconclusive, to the other it will present itself as merely imposing alabour of demolition on subsequent investigators. [Footnote: Whenthese words were uttered I did not imagine that the chief labour ofdemolition would fall upon myself. 1878. ]

Let me say here that many of our physiological observers appear toform a very inadequate estimate of the distance which separates themicroscopic from the molecular limit, and that, as a consequence, theysometimes employ a phraseology calculated to mislead. When, forexample, the contents of a cell are described as perfectly homogeneousor as absolutely structureless, because the microscope fails todiscover any structure; or when two structures are pronounced to bewithout difference, because the microscope can discover none, then, Ithink the microscope begins to play a mischievous part. A littleconsideration will make it plain that the microscope can have no voicein the question of germ structure. Distilled water is more perfectlyhomogeneous than any possible organic germ. What is it that causesthe liquid to cease contracting at 39 degrees Fahr, and to expanduntil it freezes? We have here a structural process of which themicroscope can take no note, nor is it likely to do so by anyconceivable extension of its powers. Place distilled water in thefield of an electro-magnet, and bring a microscope to bear upon it. Will any change be observed when the magnet is excited? Absolutelynone; and still profound and complex changes have occurred. First ofall, the particles of water have been rendered diamagnetically polar;and secondly, in virtue of the structure impressed upon it by themagnetic whirl of its molecules, the liquid twists a ray of light in afashion perfectly determinate both as to quantity and direction. 

Have the diamond, the amethyst, and the countless other crystalsformed in the laboratories of nature and of man no structure?Assuredly they have; but what can the microscope make of it? Nothing. It cannot be too distinctly borne in mind that between the microscopiclimit, and the true molecular limit, there is room for infinitepermutations and combinations. It is in this region that the poles ofthe atoms are arranged, that tendency is given to their powers; sothat when these poles and powers have free action, proper stimulus, and a suitable environment, they determine, first the germ, andafterwards the complete organism. This first marshalling of theatoms, on which all subsequent action depends, baffles a keener powerthan that of the microscope. When duly pondered, the complexity ofthe problem raises the doubt, not of the power of our instrument, forthat is nil, but whether we ourselves possess the intellectualelements which will ever enable us to grapple with the ultimatestructural energies of nature. [Footnote: 'In using the expression"one sort of living substance" I must guard against being supposed tomean that any kind of living protoplasm is homogeneous. Hyalinethough it may appear, we are not at present able to assign any limitto its complexity of structure. '--Burdon Sanderson, in the 'BritishMedical Journal, ' January 16, 1875. We have here scientific insight, and its correlative caution. In fact Dr. Sanderson' s importantresearches are a continued illustration of the position laid downabove. ]

In more senses than one Mr. Darwin has drawn heavily upon thescientific tolerance of his age. He has drawn heavily upon time inhis development of species, and he has drawn adventurously upon matterin his theory of pangenesis. According to this theory, a germ, already microscopic, is a world of minor germs. Not only is theorganism as a whole wrapped up in the germ, but every organ of theorganism has there its special seed. This, I say, is an adventurousdraft on the power of matter to divide itself and distribute itsforces. But, unless we are perfectly sure that he is overstepping thebounds of reason, that he is unwittingly sinning against observed factor demonstrated law--for a mind like that of Darwin can never sinwittingly against either fact or law--we ought, I think, to becautious in limiting his intellectual horizon. If there be the leastdoubt in the matter, it ought to be given in favour of the freedom ofsuch a mind. To it a vast possibility is in itself a dynamic power, though the possibility may never be drawn upon. It gives me pleasureto think that the facts and reasonings of this discourse tend rathertowards the justification of Mr. Darwin, than towards hiscondemnation; for they seem to show the perfect competence of matterand force, as regards divisibility and distribution, to bear theheaviest strain that he has hitherto imposed upon them. 

In the case of Mr. Darwin, observation, imagination, and reasoncombined have run back with wonderful sagacity and success over acertain length of the line of biological succession. Guided byanalogy, in his 'Origin of Species' he placed at the root of life aprimordial germ, from which he conceived the amazing variety of theorganisms now upon earth's surface might be deduced. If thishypothesis were even true, it would not be final. The human mindwould infallibly look behind the germ, and however hopeless theattempt, would enquire into the history of its genesis. In this dimtwilight of conjecture the searcher welcomes every gleam, and seeks toaugment his light by indirect incidences. He studies the methods ofnature in the ages and the worlds within his reach, in order to shapethe course of speculation in antecedent ages and worlds. And thoughthe certainty possessed by experimental enquiry is here shut out, weare not left entirely without guidance. From the examination of thesolar system, Kant and Laplace came to the conclusion that its variousbodies once formed parts of the same undislocated mass; that matter ina nebulous form preceded matter in its present form; that as the agesrolled away, heat was wasted, condensation followed, planets weredetached; and that finally the chief portion of the hot cloud reached, by self-compression, the magnitude and density of our sun. The earthitself offers evidence of a fiery origin; and in our day thehypothesis of Kant and Laplace receives the independent countenance ofspectrum analysis, which proves the same substances to be common tothe earth and sun. 

Accepting some such view of the construction of our system asprobable, a desire immediately arises to connect the present life ofour planet with the past. We wish to know something of our remotestancestry. On its first detachment from the central mass, life, as weunderstand it, could not have been present on the earth. How, then, did it come there? The thing to be encouraged here is a reverentfreedom--a freedom preceded by the hard discipline which checkslicentiousness in speculation--while the thing to be repressed, bothin science and out of it, is dogmatism. And here I am in the hands ofthe meeting--willing to end, but ready to go on. I have no right tointrude upon you, unasked, the unformed notions which are floatinglike clouds, or gathering to more solid consistency, in the modernspeculative scientific mind. But if you wish me to speak plainly, honestly, and undisputatiously, I am willing to do so. On the presentoccasion--

 You are ordained to call, and I to come. 

Well, your answer is given, and I obey your call. 

Two or three years ago, in an ancient London College, I listened to adiscussion at the end of a lecture by a very remarkable man. Three orfour hundred clergymen were present at the lecture. The orator beganwith the civilisation of Egypt in the time of 'Joseph; pointing outthe very perfect organisation of the kingdom, and the possession ofchariots, in one of which Joseph rode, as proving a long antecedentperiod of civilisation. He then passed on to the mud of the Nile, itsrate of augmentation, its present thickness, and the remains of humanhandiwork found therein: thence to the rocks which bound the Nilevalley, and which teem with organic remains. Thus in his own clearway he caused the idea of the world's age to expand itselfindefinitely before the minds of his audience, and he contrasted thiswith the age usually assigned to the world. During his discourse heseemed to be swimming against a stream, he manifestly thought that hewas opposing a general conviction. He expected resistance in thesubsequent discussion; so did I. But it was all a mistake; there wasno adverse current, no opposing conviction, no resistance; merely hereand there a half-humorous, but unsuccessful attempt to entangle him inhis talk. The meeting agreed with all that had been said regardingthe antiquity of the earth and of its life. They had, indeed, knownit all long ago, and they rallied the lecturer for coming amongst themwith so stale a story. It was quite plain that this large body ofclergymen, who were, I should say, to be ranked amongst the finestsamples of their class, had entirely given up the ancient landmarks, and transported the conception of life's origin to an indefinitelydistant past. 

This leads us to the gist of our present enquiry, which is this: Doeslife belong to what we call matter, or is it an independent principleinserted into matter at some suitable epoch--say when the physicalconditions became such as to permit of the development of life? Letus put the question with the reverence due to a faith and culture inwhich we all were cradled, and which are the undeniable historicantecedents of our present enlightenment. I say, let us put thequestion reverently, but let us also put it clearly and definitely. There are the strongest grounds for believing that during a certainperiod of its history the earth was not, nor was it fit to be, thetheatre of life. Whether this was ever a nebulous period, or merely amolten period, does not signify much; and if we revert to the nebulouscondition, it is because the probabilities are really on its side. Ourquestion is this: Did creative energy pause until the nebulous matterhad condensed, until the earth had been detached, until the solar firehad so far withdrawn from the earth's vicinity as to permit a crust togather round the planet? Did it wait until the air was isolated;until the seas were formed; until evaporation, condensation, and thedescent of rain had begun; until the eroding forces of the atmospherehad weathered and decomposed the molten rocks so as to form soils;until the sun's rays had become so tempered by distance, and by waste, as to be chemically fit for the decompositions necessary to vegetablelife? Having waited through these aeons until the proper conditionshad set in, did it send the flat forth, 'Let there be Life!'? Thesequestions define a hypothesis not without its difficulties, but thedignity of which in relation to the world's knowledge was demonstratedby the nobleness of the men whom it sustained. 

Modern scientific thought is called upon to decide between thishypothesis and another; and public thought generally will afterwardsbe called upon to do the same. But, however the convictions ofindividuals here and there may be influenced, the process must be slowand secular which commends the hypothesis of Natural Evolution to thepublic mind. For what are the core and essence of this hypothesis?Strip it naked, and you stand face to face with the notion that notalone the more ignoble forms of animalcular or animal life, not alonethe nobler forms of the horse and lion, not alone the exquisite andwonderful mechanism of the human body, but that the human minditself--emotion, intellect, will, and all their phenomena--were oncelatent in a fiery cloud. Surely the mere statement of such a notionis more than a refutation. But the hypothesis would probably go evenfarther than this. Many who hold it would probably assent to theposition that, at the present moment, all our philosophy, all ourpoetry, all our science, and all our art--Plato, Shakspeare, Newton, and Raphael--are potential in the fires of the sun. We long to learnsomething of our origin. If the Evolution hypothesis be correct, eventhis unsatisfied yearning must have come to us across the ages whichseparate the primeval mist from the consciousness of to-day. I do notthink that any holder of the Evolution hypothesis would say that Ioverstate or overstrain it in any way. I merely strip it of allvagueness, and bring before you, unclothed and unvarnished, thenotions by which it must stand or fall. 

Surely these notions represent an absurdity too monstrous to beentertained by any sane mind. But why are such notions absurd, andwhy should sanity reject them? The law of Relativity, of which wehave previously spoken, may find its application here. TheseEvolution notions are absurd, monstrous, and fit only for theintellectual gibbet, in relation to the ideas concerning matter whichwere drilled into us when young. Spirit and matter have ever beenpresented to us in the rudest contrast, the one as all-noble, theother as all-vile. But is this correct? Upon the answer to thisquestion all depends. Supposing that, instead of having the foregoingantithesis of spirit and matter presented to our youthful minds, wehad been taught to regard them as equally worthy, and equallywonderful; to consider them, in fact, as two opposite faces of theself-same mystery. Supposing that in youth we had been impregnatedwith the notion of the poet Goethe, instead of the notion of the poetYoung, and taught to look upon matter, not as 'brute matter, ' but asthe 'living garment of God;' do you not think that under thesealtered circumstances the law of Relativity might have had an outcomedifferent from its present one? Is it not probable that ourrepugnance to the idea of primeval union between spirit and mattermight be considerably abated? Without this total revolution of thenotions now prevalent, the Evolution hypothesis must stand condemned;but in many profoundly thoughtful minds such a revolution has alreadytaken place. They degrade neither member of the mysterious dualityreferred to; but they exalt one of them from its abasement, and repealthe divorce hitherto existing between them. In substance, if not inwords, their position as regards the relation of spirit and matter is:'What God hath joined together, let not man put asunder. '

You have been thus led to the outer rim of speculative science, forbeyond the nebulae scientific thought has never hitherto ventured. Ihave tried to state that which I considered ought, in fairness, to beoutspoken. I neither think this Evolution hypothesis is to be floutedaway contemptuously, nor that it ought to be denounced as wicked. Itis to be brought before the bar of disciplined reason, and therejustified or condemned. Let us hearken to those who wisely supportit, and to those who wisely oppose it; and let us tolerate those, whose name is legion, who try foolishly to do either of these things. The only thing out of place in the discussion is dogmatism on eitherside. Fear not the Evolution hypothesis. Steady yourselves, in itspresence, upon that faith in the ultimate triumph of truth which wasexpressed by old Gamaliel when he said: 'If it be of God, ye cannotoverthrow it; if it be of man, it will come to nought. ' Under thefierce light of scientific enquiry, it is sure to be dissipated if itpossess not a core of truth. Trust me, its existence as a hypothesisis quite compatible with the simultaneous existence of all thosevirtues to which the term 'Christian' has been applied. It does notsolve--it does not profess to solve--the ultimate mystery of thisuniverse. It leaves, in fact, that mystery untouched. For, grantingthe nebula and its potential life, the question, whence they came, would still remain to baffle and bewilder us. At bottom, thehypothesis does nothing more than 'transport the conception of life'sorigin to an indefinitely distant past. '

Those who hold the doctrine of Evolution are by no means ignorant ofthe uncertainty of their data, and they only yield to it a provisionalassent. They regard the nebular hypothesis as probable, and, in theutter absence of any evidence to prove the act illegal, they extendthe method of nature from the present into the past. Here the observeduniformity of nature is their only guide. Within the long range ofphysical enquiry, they have never discerned in nature the insertion ofcaprice. Throughout this range, the laws of physical and intellectualcontinuity have run side by side. Having thus determined the elementsof their curve in a world of observation and experiment, they prolongthat curve into an antecedent world, and accept as probable theunbroken sequence of development from the nebula to the present time. You never hear the really philosophical defenders of the doctrine ofUniformity speaking of impossibilities in nature. They never say, what they are constantly charged with saying, that it is impossiblefor the Builder of the universe to alter His work. Their business isnot with the possible, but the actual--not with a world which mightbe, but with a world that is. This they explore with a courage notunmixed with reverence, and according to methods which, like thequality of a tree, are tested by their fruits. They have but onedesire--to know the truth. They have but one fear--to believe a lie. And if they know the strength of science, and rely upon it withunswerving trust, they also know the limits beyond which scienceceases to be strong. They best know that questions offer themselvesto thought, which science, as now prosecuted, has not even thetendency to solve. They have as little fellowship with the atheistwho says there is no God, as with the theist who professes to know themind of God. 'Two things, ' said Immanuel Kant, 'fill me with awe: thestarry heavens, and the sense of moral responsibility in man. ' And inhis hours of health and strength and sanity, when the stroke of actionhas ceased, and the pause of reflection has set in, the scientificinvestigator finds himself overshadowed by the same awe. Breakingcontact with the hampering details of earth, it associates him with aPower which gives fulness and tone to his existence, but which he canneither analyse nor comprehend. 

********************

 There is one God supreme over all gods, diviner than mortals, Whose form is not like unto man's, and as unlike his nature; But vain mortals imagine that gods like themselves are begotten, With human sensations and voice and corporeal members; So, if oxen or lions had hands and could work in man's fashion, And trace out with chisel or brush their conception of Godhead, Then would horses depict gods like horses, and oxen like oxen, Each kind the divine with its own form and nature endowing. 

 XENOPHANES Of COLOPHON (six centuries B. C. ), Supernatural Religion, vol. 1. 

*****

IX. THE BELFAST ADDRESS. 

[Footnote: Delivered before the British Association on Wednesdayevening, August 19, 1874. ]

 1. 

AN impulse inherent in primeval man turned his thoughts andquestionings betimes towards the sources of natural phenomena. Thesame impulse, inherited and intensified, is the spur of scientificaction to-day. Determined by it, by a process of abstraction fromexperience we form physical theories which lie beyond the pale ofexperience, but which satisfy the desire of the mind to see everynatural occurrence resting upon a cause. In forming their notions ofthe origin of things, our earliest historic (and doubtless, we mightadd, our prehistoric) ancestors pursued, as far as their intelligencepermitted, the same course. They also fell back upon experience; butwith this difference--that the particular experiences which furnishedthe warp and woof of their theories were drawn, not from the study ofnature, but from what lay much closer to them--the observation ofmen. Their theories accordingly took an anthropomorphic form. Tosuper-sensual beings, which, 'however potent and invisible, werenothing but a species of human creatures, perhaps raised from amongmankind, and retaining all human passions and appetites, ' were handedover the rule and governance of natural phenomena. [Footnote: Hume, 'Natural History of Religion. ]

Tested by observation and reflection, these early notions failed inthe long run to satisfy the more penetrating intellects of our race. Far in the depths of history we find men of exceptional powerdifferentiating themselves from the crowd, rejecting theseanthropomorphic notions, and seeking to connect natural phenomena withtheir physical principles. But, long prior to these purer efforts ofthe understanding, the merchant had been abroad, and rendered thephilosopher possible; commerce had been developed, wealth amassed, leisure for travel and speculation secured, while races educated underdifferent conditions, and therefore differently informed and endowed, had been stimulated and sharpened by mutual contact. In those regionswhere the commercial aristocracy of ancient Greece mingled with theireastern neighbours, the sciences were born, being nurtured anddeveloped by free-thinking and courageous men. The state of things tobe displaced may be gathered from a passage of Euripides quoted byHume. 'There is nothing in the world; no glory, no prosperity. Thegods toss all into confusion; mix everything with its reverse, thatall of us, from our ignorance and uncertainty, may pay them the moreworship and reverence. ' Now as science demands the radical extirpationof caprice, and the absolute reliance upon law in nature, there grew, with the growth of scientific notions, a desire and determination tosweep from the field of theory this mob of gods and demons, and toplace natural phenomena on a basis more congruent with themselves. 

The problem which had been previously approached from above, was nowattacked from below; theoretic effort passed from the super- to thesub-sensible. It was felt that to construct the universe in idea, itwas necessary to have some notion of its constituent parts--of whatLucretius subsequently called the 'First Beginnings. ' Abstractingagain from experience, the leaders of scientific speculation reachedat length the pregnant doctrine of atoms and molecules, the latestdevelopments of which were set forth with such power and clearness atthe last meeting of the British Association. Thought, no doubt, hadlong hovered about this doctrine before it attained the precision andcompleteness which it assumed in the mind of Democritus, [Footnote:Born 460 B. C. ] a philosopher who may well for a moment arrest ourattention. 'Few great men, ' says Lange, a non-materialist, in hisexcellent 'History of Materialism, ' to the spirit and to the letterof which I am equally indebted, 'have been so despitefully used byhistory as Democritus. In the distorted images sent down to usthrough unscientific traditions, there remains of him almost nothingbut the name of "the laughing philosopher, " while figures ofimmeasurably smaller significance spread themselves out at full lengthbefore us. ' Lange speaks of Bacon's high appreciation ofDemocritus--for ample illustrations of which I am indebted to myexcellent friend Mr. Spedding, the learned editor and biographer ofBacon. It is evident, indeed, that Bacon considered Democritus to bea man of weightier metal than either Plato or Aristotle, though theirphilosophy 'was noised and celebrated in the schools, amid the dinand pomp of professors. ' It was not they, but Genseric and Attila andthe barbarians, who destroyed the atomic philosophy. 'For, at a timewhen all human learning had suffered shipwreck, these planks ofAristotelian and Platonic philosophy, as being of a lighter and moreinflated substance, were preserved and came down to us, while thingsmore solid sank and almost passed into oblivion. '

The son of a wealthy father, Democritus devoted the whole of hisinherited fortune to the culture of his mind. He travelledeverywhere; visited Athens when Socrates and Plato were there, butquitted the city without making himself known. Indeed, the dialecticstrife in which Socrates so much delighted, had no charm forDemocritus, who held that 'the man who readily contradicts, and usesmany words, is unfit to learn anything truly right. ' He is said tohave discovered and educated Protagoras the Sophist, being struck asmuch by the manner in which he, being a hewer of wood, tied up hisfaggots, as by the sagacity of his conversation. Democritus returnedpoor from his travels, was supported by his brother, and at lengthwrote his great work entitled 'Diakosmos, ' which he read publiclybefore the people of his native town. He was honoured by hiscountrymen in various ways, and died serenely at a great age. 

The principles enunciated by Democritus reveal his uncompromisingantagonism to those who deduced the phenomena of nature from thecaprices of the gods. They are briefly these:

1. From nothing comes nothing. Nothing that exists can be destroyed. All changes are due to the combination and separation of molecules. 

2. Nothing happens by chance; every occurrence has its cause, fromwhich it follows by necessity. 

3. The only existing things are the atoms and empty space; all else ismere opinion. 

4. The atoms are infinite in number and infinitely various in form;they strike together, and the lateral motions and whirlings which thusarise are the beginnings of worlds. 

5. The varieties of all things depend upon the varieties of theiratoms, in number, size, and aggregation. 

6. The soul consists of fine, smooth, round atoms, like those of fire. These are the most mobile of all: they interpenetrate the whole body, and in their motions the phenomena of life arise. 

The first five propositions are a fair general statement of the atomicphilosophy, as now held. As regards the sixth, Democritus made hisfiner atoms do duty for the nervous system, whose functions were thenunknown. The atoms of Democritus are individually without sensation;they combine in obedience to mechanical laws; and not only organicforms, but the phenomena of sensation and thought, are the result oftheir combination. 

That great enigma, 'the exquisite adaptation of one part of anorganism to another part, and to the conditions of life, ' moreespecially the construction of the human body, Democritus made noattempt to solve. Empedocles, a man of more fiery and poetic nature, introduced the notion of love and hate among the atoms, to account fortheir combination and separation; and bolder than Democritus, hestruck in with the penetrating thought, linked, however, with somewild speculation, that it lay in the very nature of those combinationswhich were suited to their ends (in other words, in harmony with theirenvironment) to maintain themselves, while unfit combinations, havingno proper habitat, must rapidly disappear. Thus, more than 2, 000years ago, the doctrine of the 'survival of the fittest, ' which in ourday, not on the basis of vague conjecture, but of positive knowledge, has been raised to such extraordinary significance, had received atall events partial enunciation. [Footnote: See 'Lange, ' 2nd edit, p. 23. ]

Epicurus, [Footnote: Born 342 B. C. ] said to be the son of a poorschoolmaster at Samos, is the next dominant figure in the history ofthe atomic philosophy. He mastered the writings of Democritus, heardlectures in Athens, went back to Samos, and subsequently wanderedthrough various countries. He finally returned to Athens, where hebought a garden, and surrounded himself by pupils, in the midst ofwhom he lived a pure and serene life, and died a peaceful death. Democritus looked to the soul as the ennobling part of man; evenbeauty, without understanding, partook of animalism. Epicurus alsorated the spirit above the body; the pleasure of the body being thatof the moment, while the spirit could draw upon the future and thepast. His philosophy was almost identical with that of Democritus; buthe never quoted either friend or foe. One main object of Epicurus wasto free the world from superstition and the fear of death. Death betreated with indifference. It merely robs us of sensation. As longas we are, death is not; and when death is, we are not. Life has nomore evil for him who has made up his mind that it is no evil not tolive. He adored the gods, but not in the ordinary fashion. The ideaof Divine power, properly purified, he thought an elevating one. Stillhe taught, 'Not he is godless who rejects the gods of the crowd, butrather he who accepts them. ' The gods were to him eternal and immortalbeings, whose blessedness excluded every thought of care or occupationof any kind. Nature pursues her course in accordance with everlastinglaws, the gods never interfering. They haunt:

 The lucid interspace Of world and world Where never creeps a cloud or moves a wind, Nor ever falls the least white star of snow, Nor ever lowest roll of thunder moans, Nor sound of human sorrow mounts to mar Their sacred everlasting calm. 

 Tennyson's 'Lucretius. '

Lange considers the relation of Epicurus to the gods subjective; theindication, probably, of an ethical requirement of his own nature. Wecannot read history with open eyes, or study human nature to itsdepths, and fail to discern such a requirement. Man never has been, and he never will be, satisfied with the operations and products ofthe Understanding alone; hence physical science cannot cover all thedemands of his nature. But the history of the efforts made to satisfythese demands might be broadly described as a history of errors--theerror, in great part, consisting in ascribing fixity to that which isfluent, which varies as we vary, being gross when we are gross, andbecoming, as our capacities widen, more abstract and sublime. On onegreat point the mind of Epicurus was at peace. He neither sought norexpected, here or hereafter, any personal profit from his relation tothe gods. And it is assuredly a fact, that loftiness and serenity ofthought may be promoted by conceptions which involve no idea of profitof this kind. 'Did I not believe, ' said a great man. [Footnote:Carlyle. ] to me once, 'that an Intelligence is at the heart ofthings, my life on earth would be intolerable. ' The utterer of thesewords is not, in my opinion, rendered less but more noble by the fact, that it was the need of ethical harmony here, and not the thought ofpersonal happiness hereafter, that prompted his observation. 

There are persons, not belonging to the highest intellectual zone, noryet to the lowest, to whom perfect clearness of exposition suggestswant of depth. They find comfort and edification in an abstract andlearned phraseology. To such people Epicurus, who spared no pains torid his style of every trace of haze and turbidity, appeared, on thisvery account, superficial. He had, however, a disciple who thought itno unworthy occupation to spend his days and nights in the effort toreach the clearness of his master, and to whom the Greek philosopheris mainly indebted for the extension and perpetuation of his fame. Some two centuries after the death of Epicurus, Lucretius [Footnote:Born 99 B. C. ] wrote his great poem, 'On the Nature of Things, ' inwhich he, a Roman, developed with extraordinary ardour the philosophyof his Greek predecessor. He wishes to win over his friend Memnius tothe school of Epicurus; and although he has no rewards in a futurelife to offer, although his object appears to be a purely negativeone, he addresses his friend with the heat of an apostle. His object, like that of his great forerunner, is the destruction of superstition;and considering that men in his day trembled before every naturalevent as a direct monition from the gods, and that everlasting torturewas also in prospect, the freedom aimed at by Lucretius might bedeemed a positive good. 'This terror, ' he says, 'and darkness ofmind, must be dispelled, not by the rays of the sun and glitteringshafts of day, but by the aspect and the law of nature. ' He refutesthe notion that anything can come out of nothing, or that what is oncebegotten can be recalled to nothing. The first beginnings, the atoms, are indestructible, and into them all things can be resolved at last. Bodies are partly atoms; and partly combinations of atoms; but theatoms nothing can quench. They are strong in solid singleness, and, bytheir denser combination, all things can be closely packed and exhibitenduring strength. He denies that matter is infinitely divisible. Wecome at length to the atoms, without which, as an imperishablesubstratum, all order in the generation and development of thingswould be destroyed. 

The mechanical shock of the atoms being, in his view, theall-sufficient cause of things, he combats the notion that theconstitution of nature has been in any way determined by intelligentdesign. The interaction of the atoms throughout infinite timerendered all manner of combinations possible. Of these, the fit onespersisted, while the unfit ones disappeared. Not after sagedeliberation did the atoms station themselves in their right places, nor did they bargain what motions they should assume. From alleternity they have been driven together, and, after trying motions andunions of every kind, they fell at length into the arrangements outof which this system of things has been evolved. 

'If you will apprehend and keep in mind these things, Nature, free atonce, and rid of her haughty lords, is seen to do all thingsspontaneously of herself, without the meddling of the gods. '[Footnote: Monro's translation. In his criticism of this work('Contemporary Review' 1867) Dr. Hayman does not appear to be aware ofthe really sound and subtile observations on which the reasoning ofLucretius, though erroneous, sometimes rests. ]

To meet the objection that his atoms cannot be seen, Lucretiusdescribes a violent storm, and shows that the invisible particles ofair act in the same way as the visible particles of water. Weperceive, moreover, the different smells of things, yet never see themcoming to our nostrils. Again, clothes hung up on a shore which wavesbreak upon, become moist, and then get dry if spread out in the sun, though no eye can see either the approach or the escape of thewater-particles. A ring, worn long on the finger, becomes thinner; awater-drop hollows out a stone; the ploughshare is rubbed away in thefield; the street-pavement is worn by the feet; but the particles thatdisappear at any moment we cannot see. Nature acts through invisibleparticles. That Lucretius had a strong scientific imagination theforegoing references prove. A fine illustration of his power in thisrespect, is his explanation of the apparent rest of bodies whose atomsare in motion. He employs the image of a flock of sheep with skippinglambs, which, seen from a distance, presents simply a white patch uponthe green hill, the jumping of the individual lambs being quiteinvisible. 

His vaguely grand conception of the atoms falling eternally throughspace, suggested the nebular hypothesis to Kant, its first propounder. Far beyond the limits of our visible world are to be found atomsinnumerable, which have never been united to form bodies, or which, ifonce united, have been again dispersed--falling silently throughimmeasurable intervals of time and space. As everywhere throughoutthe All the same conditions are repeated, so must the phenomena berepeated also. Above us, below us, beside us, therefore, are worldswithout end; and this, when considered, must dissipate every thoughtof a deflection of the universe by the gods. The worlds come and go, attracting new atoms out of limitless space, or dispersing their ownparticles. The reputed death of Lucretius, which forms the basis ofMr. Tennyson's noble poem, is in strict accordance with hisphilosophy, which was severe and pure. 

2. 

Still earlier than these three philosophers, and during the centuriesbetween the first of them and the last, the human intellect was activein other fields than theirs. Pythagoras had founded a school ofmathematics, and made his experiments on the harmonic intervals. TheSophists had run through their career. At Athens had appearedSocrates, Plato, and Aristotle, who ruined the Sophists, and whoseyoke remains to some extent unbroken to the present hour. Within thisperiod also the School of Alexandria was founded, Euclid wrote his'Elements' and made some advance in optics. Archimedes had propoundedthe theory of the lever, and the principles of hydrostatics. Astronomywas immensely enriched by the discoveries of Hipparchus, who wasfollowed by the historically more celebrated Ptolemy. Anatomy hadbeen made the basis of scientific medicine; and it is said by Draperthat vivisection had begun. [Footnote: 'History of the IntellectualDevelopment of Europe, ' p. 295. ] In fact, the science of ancient Greecehad already cleared the world of the fantastic images of divinitiesoperating capriciously through natural phenomena. It had shaken itselffree from that fruitless scrutiny 'by the internal light of the mindalone, ' which had vainly sought to transcend experience, and to reacha knowledge of ultimate causes. Instead of accidental observation, ithad introduced observation with a purpose; instruments were employedto aid the senses; and scientific method was rendered in a great measurecomplete by the union of Induction and Experiment. 

What, then, stopped its victorious advance? Why was the scientificintellect compelled, like an exhausted soil, to lie fallow for nearlytwo millenniums, before it could regather the elements necessary toits fertility and strength? Bacon has already let us know one cause;Whewell ascribes this stationary period to four causes--obscurity ofthought, servility, intolerance of disposition, enthusiasm of temper;and he gives striking examples of each. [Footnote: 'History of theInductive Sciences, ' vol. I. ] But these characteristics must havehad their antecedents in the circumstances of the time. Rome, and theother cities of the Empire, had fallen into moral putrefaction. Christianity had appeared, offering the Gospel to the poor, and bymoderation, if not asceticism of life, practically protesting againstthe profligacy of the age. The sufferings of the early Christians, and the extraordinary exaltation of mind which enabled them to triumphover the diabolical tortures to which they were subjected, must haveleft traces not easily effaced. [Footnote: Described with terriblevividness in Renan's 'Antichrist. '] They scorned the earth, in view ofthat 'building of God, that house not made with hands, eternal in theheavens. ' The Scriptures which ministered to their spiritual needswere also the measure of their Science. When, for example, thecelebrated question of Antipodes came to be discussed, the Bible waswith many the ultimate court of appeal. Augustine, who flourishedA. D. 400, would not deny the rotundity of the earth; but he woulddeny the possible existence of inhabitants at the other side, 'becauseno such race is recorded in Scripture among the descendants of Adam. 'Archbishop Boniface was shocked at the assumption of a 'world of humanbeings out of the reach of the means of salvation. ' Thus reined in, Science was not likely to make much progress. Later on, the politicaland theological strife between the Church and civil governments, sopowerfully depicted by Draper, must have done much to stifleinvestigation. 

Whewell makes many wise and brave remarks regarding the spirit of theMiddle Ages. It was a menial spirit. The seekers after naturalknowledge had forsaken the fountain of living waters, the directappeal to nature by observation and experiment, and given themselvesup to the remanipulation of the notions of their predecessors. It wasa time when thought had become abject, and when the acceptance of mereauthority led, as it always does in science, to intellectual death. Natural events, instead of being traced to physical, were referred tomoral, causes; while an exercise of the phantasy, almost as degradingas the spiritualism of the present day, took the place of scientificspeculation. Then came the mysticism of the Middle Ages, Magic, Alchemy, the Neoplatonic philosophy, with its visionary though sublimeabstractions, which caused men to look with shame upon their ownbodies, as hindrances to the absorption of the creature in theblessedness of the Creator. Finally came the scholastic philosophy, afusion, according to Lange, of the least mature notions of Aristotlewith the Christianity of the West. Intellectual immobility was theresult. As a traveller without a compass in a fog may wander long, imagining he is making way, and find himself after hours of toil athis starting-point, so the schoolmen, having 'tied and untied the sameknots, and formed and dissipated the same clouds, ' found themselvesat the end of centuries in their old position. [Footnote: Whewell. ]

With regard to the influence wielded by Aristotle in the Middle Ages, and which, to a less extent, he still wields, I would ask permissionto make one remark. 

When the human mind has achieved greatness and given evidence ofextraordinary power in one domain, there is a tendency to credit itwith similar power in all other domains. Thus theologians havefound comfort and assurance in the thought that Newton dealt withthe question of revelation--forgetful of the fact that the verydevotion of his powers, through all the best years of his life, toa totally different class of ideas, not to speak of any naturaldisqualification, tended to render him less, instead of more competentto deal with theological and historic questions. Goethe, startingfrom his established greatness as a poet, and indeed from his positivediscoveries in Natural History, produced a profound impression amongthe painters of Germany, when he published his 'Farbenlehre, ' inwhich he endeavoured to overthrow Newton's theory of colours. Thistheory he deemed so obviously absurd, that he considered its author acharlatan, and attacked him with a corresponding vehemence oflanguage. 

In the domain of Natural History, Goethe had made really considerablediscoveries; and we have high authority for assuming that, had hedevoted himself wholly to that side of science, he might have reachedan eminence comparable with that which he attained as a poet. Insharpness of observation, in the detection of analogies apparentlyremote, in the classification and organisation of facts according tothe analogies discerned, Goethe possessed extraordinary powers. Theseelements of scientific enquiry fall in with the disciplines of thepoet. But, on the other hand, a mind thus richly endowed in thedirection of natural history, may be almost shorn of endowment asregards the physical and mechanical sciences. Goethe was in thiscondition. He could not formulate distinct mechanical conceptions; hecould not see the force of mechanical reasoning; and, in regions wheresuch reasoning reigns supreme, he became a mere ignis fatuus to thosewho followed him. 

I have sometimes permitted myself to compare Aristotle with Goethe--tocredit the Stagirite with an almost superhuman power of amassing andsystematising facts, but to consider him fatally defective on thatside of the mind, in respect to which incompleteness has been justascribed to Goethe. Whewell refers the errors of Aristotle not to aneglect of facts, but to 'a neglect of the idea appropriate to thefacts: the idea of Mechanical cause, which is Force, and thesubstitution of vague or inapplicable notions, involving onlyrelations of space or emotions of wonder. ' This is doubtless true; butthe word 'neglect' implies mere intellectual misdirection, whereas inAristotle, as in Goethe, it was not, I believe, misdirection, butsheer natural incapacity which lay at the root of his mistakes. As aphysicist, Aristotle displayed what we should consider some of theworst of attributes in a modern physical investigator--indistinctnessof ideas, confusion of mind, and a confident use of language which ledto the delusive notion that he had really mastered his subject, whilehe had, as yet, failed to grasp even the elements of it. He putwords in the place of things, subject in the place of object. Hepreached Induction without practising it, inverting the true order ofenquiry, by passing from the general to the particular, instead offrom the particular to the general. He made of the universe a closedsphere, in the centre of which he fixed the earth, proving fromgeneral principles, to his own satisfaction and to that of the worldfor near 2, 000 years, that no other universe was possible. Hisnotions of motion were entirely unphysical. It was natural orunnatural, better or worse, calm or violent--no real mechanicalconception regarding it lying at the bottom of his mind. 

He affirmed that a vacuum could not exist, and proved that if it didmotion in it would be impossible. He determined _à priori_ how manyspecies of animals must exist, and showed on general principles whyanimals must have such and such parts. When an eminent contemporaryphilosopher, who is far removed from errors of this kind, remembersthese abuses of the _à priori_ method, he will be able to make allowancefor the jealousy of physicists as to the acceptance of so-called _àpriori_ truths. Aristotle's errors of detail, as shown by Eucken andLange, were grave and numerous. He affirmed that only in man we hadthe beating of the heart, that the left side of the body was colderthan the right, that men have more teeth than women, and that there isan empty space at the back of every man's head. 

There is one essential quality in physical conceptions, which wasentirely wanting in those of Aristotle and his followers--a capabilityof being placed as coherent pictures before the mind. The Germansexpress the act of picturing by the word vorstellen, and the picturethey call a Vorstellung. We have no word in English which comesnearer to our requirements than Imagination; and, taken with itsproper limitations, the word answers very well. But it is tainted byits associations, and therefore objectionable to some minds. Compare, with reference to this capacity of mental presentation, the case ofthe Aristotelian, who refers the ascent of water in a pump to Nature'sabhorrence of a vacuum, with that of Pascal when he proposed to solvethe question of atmospheric pressure by the ascent of the Puy de Dôme. In the one case the terms of the explanation refuse to fall into placeas a physical image; in the other the image is distinct, the descentand rise of the barometer being clearly figured beforehand as thebalancing of two varying and opposing pressures. 

3. 

During the drought of the Middle Ages in Christendom, the Arabianintellect, as forcibly shown by Draper, was active. With theintrusion of the Moors into Spain, order, learning, and refinementtook the place of their opposites. When smitten with disease, theChristian peasant resorted to a shrine, the Moorish one to aninstructed physician. The Arabs encouraged translations from theGreek philosophers, but not from the Greek poets. They turned indisgust 'from the lewdness of our classical mythology, and denouncedas an unpardonable blasphemy all connection between the impureOlympian Jove and the Most High God. ' Draper traces still fartherthan Whewell the Arab elements in our scientific terms. He givesexamples of what Arabian men of science accomplished, dwellingparticularly on Alhazen, who was the first to correct the Platonicnotion that rays of light are emitted by the eye. Alhazen discoveredatmospheric refraction, and showed that we see the sun and the moonafter they have set. He explained the enlargement of the sun andmoon, and the shortening of the vertical diameters of both thesebodies when near the horizon. He was aware that the atmospheredecreases in density with increase of elevation, and actually fixedits height at 58. 5 miles. In the 'Book of the Balance of Wisdom, ' hesets forth the connection between the weight of the atmosphere and itsincreasing density. He shows that a body will weigh differently in arare and dense atmosphere, and he considers the force with whichplunged bodies rise through heavier media. He understood the doctrineof the centre of gravity, and applied it to the investigation ofbalances and steelyards. He recognised gravity as a. Force, thoughhe fell into the error of assuming it to diminish simply as thedistance, and of making it purely terrestrial. He knew the relationbetween the velocities, spaces, and times of falling bodies, and haddistinct ideas of capillary attraction. He improved the hydrometer. The determinations of the densities of bodies, as given by Alhazen, approach very closely to our own. 'I join, ' says Draper, 'in thepious prayer of Alhazen, that in the day of judgment the All-Mercifulwill take pity on the soul of Abur-Raihân, because he was the first ofthe race of men to construct a table of specific gravities. ' If allthis be historic truth (and I have entire confidence in Dr. Draper), well may he 'deplore the systematic manner in which the literature ofEurope has, contrived to put out of sight our scientific obligationsto the Mahommedans. ' [Footnote: Intellectual Development of Europe, 'p. 359. ]

The strain upon the mind during the stationary period towardsultra-terrestrial things, to the neglect of problems close at hand, was sure to provoke reaction. But the reaction was gradual; for theground was dangerous, and a power was at hand competent to crush thecritic who went too far. To elude this power, and still allowopportunity for the expression of opinion, the doctrine of 'two-foldtruth' was invented, according to which an opinion might be held'theologically, ' and the opposite opinion 'philosophically. '[Footnote: 'Lange, ' 2nd edit. Pp. 181, 182. ] Thus, in the thirteenthcentury, the creation of the world in six days, and theunchangeableness of the individual soul, which had been so distinctlyaffirmed by St. Thomas Aquinas, were both denied philosophically, butadmitted to be true as articles of the Catholic faith. WhenProtagoras uttered the maxim which brought upon him so muchvituperation, that 'opposite assertions are equally true, ' he simplymeant to affirm men's differences to be so great, that what wassubjectively true to the one might be subjectively untrue to theother. The great Sophist never meant to play fast and loose with thetruth by saying that one of two opposite assertions, made by the sameindividual, could possibly escape being a lie. It was not'sophistry, ' but the dread of theologic vengeance, that generated thisdouble dealing with conviction; and it is astonishing to notice whatlengths were allowed to men who were adroit in the use of artificesof this kind. 

Towards the close of the stationary period a word-weariness, if I mayso express it, took more and more possession of men's minds. Christendom had become sick of the School Philosophy and its verbalwastes, which led to no issue, but left the intellect in everlastinghaze. Here and there was heard the voice of one impatiently crying inthe wilderness, 'Not unto Aristotle, not unto subtle hypothesis, notunto church, Bible, or blind tradition, must we turn for a knowledgeof the universe, but to the direct investigation of nature byobservation and experiment. ' In 1543 the epoch-marking work ofCopernicus on the paths of the heavenly bodies appeared. The totalcrash of Aristotle's closed universe, with the earth at its centre, followed as a consequence, and 'The earth moves!' became a kind ofwatchword among intellectual freemen. Copernicus was Canon of thechurch of Frauenburg in the diocese of Ermeland. For three-and-thirtyyears he had withdrawn himself from the world, and devoted himself tothe consolidation of his great scheme of the solar system. He madeits blocks eternal; and even to those who feared it, and desired itsoverthrow, it was so obviously strong, that they refrained for a timefrom meddling with it. In the last year of the life of Copernicus hisbook appeared: it is said that the old man received a copy of it a fewdays before his death, and then departed in peace. 

The Italian philosopher, Giordano Bruno, was one of the earliestconverts to the new astronomy. Taking Lucretius as his exemplar, herevived the notion of the infinity of worlds; and, combining with itthe doctrine of Copernicus, reached the sublime generalisation thatthe fixed stars are suns, scattered numberless through space, andaccompanied by satellites, which bear the same relation to them thatour earth does to our sun, or our moon to our earth. This was anexpansion of transcendent import; but Bruno came closer than this toour present line of thought. Struck with the problem of thegeneration and maintenance of organisms, and duly pondering it, hecame to the conclusion that Nature, in her productions, does notimitate the technic of man. Her process is one of unravelling andunfolding. The infinity of forms under which matter appears was notimposed upon it by an external artificer; by its own intrinsic forceand virtue it brings these forms forth. Matter is not the mere naked, empty capacity which philosophers have pictured her to be, but theuniversal mother, who brings forth all things as the fruit of her ownwomb. 

This outspoken man was originally a Dominican monk. He was accused ofheresy and had to fly, seeking refuge in Geneva, Paris, England, andGermany. In 1592 be fell into the hands of the Inquisition at Venice. He was imprisoned for many years, tried, degraded, excommunicated, andhanded over to the Civil power, with the request that he should betreated gently, and 'without the shedding of blood. ' This meant thathe was to be burnt; and burnt accordingly he was, on February 16, 1600. To escape a similar fate Galileo, thirty-three yearsafterwards, abjured upon his knees, with his hands upon the holyGospels, the heliocentric doctrine, which he knew to be true. AfterGalileo came Kepler, who from his German home defied the ultramontanepower. He traced out from pre-existing observations the laws ofplanetary motion. Materials were thus prepared for Newton, who boundthose empirical laws together by the principle of gravitation. 

4. 

In the seventeenth century Bacon and Descartes, the restorers ofphilosophy, appeared in succession. Differently educated and endowed, their philosophic tendencies were different. Bacon held fast toInduction, believing firmly in the existence of an external world, andmaking collected experiences the basis of all knowledge. Themathematical studies of Descartes gave him a bias towards Deduction;and his fundamental principle was much the same as that of Protagoras, who 'made the individual man the measure of all things. I think, therefore I am, ' said Descartes. Only his own identity was sure tohim; and the full development of this system would have led to anidealism, in which the outer world would have been resolved into amere phenomenon of consciousness. Gassendi, one of Descartes'scontemporaries, of whom we shall hear more presently, quickly pointedout that the fact of personal existence would be proved as well byreference to any other act, as to the act of thinking. I eat, therefore I am, or I love, therefore I am, would be quite asconclusive. Lichtenberg, indeed, showed that the very thing to beproved was inevitably postulated in the first two words, 'I think;'and it is plain that no inference from the postulate could, by anypossibility, be stronger than the postulate itself. 

But Descartes deviated strangely from the idealism implied in hisfundamental principle. He was the first to reduce, in a mannereminently capable of bearing the test of mental presentation, vitalphenomena to purely mechanical principles. Through fear or love, Descartes was a good churchman; he accordingly rejected the notion ofan atom, because it was absurd to suppose that God, if He so pleased, could not divide an atom; he puts in the place-of the atoms smallround particles, and light splinters, out of which he builds theorganism. He sketches with marvellous physical insight a machine, with water for its motive power, which shall illustrate vital actions. He has made clear to his mind that such a machine would be competentto carry on the processes of digestion, nutrition, growth, respiration, and the beating of the heart. It would be competent toaccept impressions from the external sense, to store them up inimagination and memory, to go through the internal movements of theappetites and passions, and the external movements of the limbs. Hededuces these functions of his machine from the mere arrangements ofits organs, as the movement of a clock, or other automaton, is deducedfrom its weights and wheels. As far as these functions areconcerned, ' he says, 'it is not necessary to conceive any othervegetative or sensitive soul, nor any other principle of motion or oflife, than the blood and the spirits agitated by the fire which burnscontinually in the heart, and which is in nowise different from thefires existing in inanimate bodies. ' Had Descartes been acquaintedwith the steam-engine, he would have taken it, instead of a fall ofwater, as his motive power. He would have shown the perfect analogywhich exists between the oxidation of the food in the body, and thatof the coal in the furnace. He would assuredly have anticipated Mayerin calling the blood which the heart diffuses, 'the oil of the lamp oflife, ' deducing all animal motions from the combustion of this oil, asthe motions of a steam-engine are deduced from the combustion of itscoal. As the matter stands, however, and considering thecircumstances of the time, the boldness, clearness, and precision, with which Descartes grasped the problem of vital dynamics constitutea marvellous illustration of intellectual power. [Footnote: SeeHuxley's admirable 'Essay on Descartes. ' Lay Sermons. ]

During the Middle Ages the doctrine of atoms had to all appearancevanished from discussion. It probably held its ground amongsober-minded and thoughtful men, though neither the church nor theworld was prepared to hear of it with tolerance. Once, in the year1348, it received distinct expression. But retractation by compulsionimmediately followed; and, thus discouraged, it slumbered till theseventeenth century, when it was revived by a contemporary and friendof Hobbes of Malmesbury, the orthodox Catholic provost of Digne, Gassendi. But, before stating his relation to the Epicurean doctrine, it will be well to say a few words on the effect, as regards science, of the general introduction of monotheism among European nations. 

'Were men, ' says Hume, 'led into the apprehension of invisibleintelligent power by contemplation of the works of Nature, they couldnever possibly entertain any conception but of one single Being, whobestowed existence and order on this vast machine, and adjusted allits parts to one regular system. ' Referring to the condition of theheathen, who sees a god behind every natural event, thus peopling theworld with thousands of beings whose caprices are incalculable, Langeshows the impossibility of any compromise between such notions andthose of science, which proceeds on the assumption of never-changinglaw and causality. 'But, ' he continues, with characteristicpenetration, 'when the great thought of one God, acting as a unit uponthe universe, has been seized, the connection of things in accordancewith the law of cause and effect is not only thinkable, but it is anecessary consequence of the assumption. For when I see ten thousandwheels in motion, and know, or believe, that they are all driven byone motive power, then I know that I have before me a mechanism, theaction of every part of which is determined by the plan of the whole. So much being assumed, it follows that I may investigate the structureof that machine, and the various motions of its parts. For the timebeing, therefore, this conception renders scientific action free. ' Inother words, were a capricious God at the circumference of every wheeland at the end of every lever, the action of the machine would beincalculable by the methods of science. But the actions of all itsparts being rigidly determined by their connections and relations, andthese being brought into play by a single motive power, then thoughthis last prime mover may elude me, I am still able to comprehend themachinery which it sets in motion. We have here a conception of therelation of Nature to its Author, which seems perfectly acceptable tosome minds, but perfectly intolerable to others. Newton and Boylelived and worked happily under the influence of this conception;Goethe rejected it with vehemence, and the same repugnance toaccepting it is manifest in Carlyle. [Footnote: Boyle's model of theuniverse was the Strasburg clock with an outside Artificer. Goethe, on the other hand, sang:

 'Ihm ziemt's die Welt im Innern zu bewegen, Natur in sich, sich in Natur zu hegen. '

See also Carlyle, 'Past and Present, ' chap. V. ]

The analytic and synthetic tendencies of the human mind are traceablethroughout history, great writers ranging themselves sometimes on theone side, sometimes on the other. Men of warm feelings, and mindsopen to the elevating impressions produced by nature as a whole, whosesatisfaction, therefore, is rather ethical than logical, lean to thesynthetic side; while the analytic harmonises best with the moreprecise and more mechanical bias which seeks the satisfaction of theunderstanding. Some form of pantheism was usually adopted by the one, while a detached Creator, working more or less after the manner ofmen, was often assumed by the other. Gassendi, as sketched by Lange, is hardly to be ranked with either. Having formally acknowledged Godas the great first cause, he immediately dropped the idea, applied theknown laws of mechanics to the atoms, and deduced from them all vitalphenomena. He defended Epicurus, and dwelt upon his purity, both ofdoctrine and of life. True he was a heathen, but so was Aristotle. Epicurus assailed superstition and religion, and rightly, because hedid not know the true religion. He thought that the gods neitherrewarded nor punished, and he adored them purely in consequence oftheir completeness: here we see, says Gassendi, the reverence of thechild, instead of the fear of the slave. The errors of Epicurus shallbe corrected, and the body of his truth retained. Gassendi thenproceeds, as any heathen might have done, to build up the world, andall that therein is, of atoms and molecules. God, who created earthand water, plants and animals, produced in the first place a definitenumber of atoms, which constituted the seed of all things. Then beganthat series of combinations and decompositions which now goes on, andwhich will continue in future. The principle of every change residesin matter. In artificial productions the moving principle isdifferent from the material worked upon; but in nature the agent workswithin, being the most active and mobile part of the material itself. Thus this bold ecclesiastic, without incurring the censure of thechurch or the world, contrives to outstrip Mr. Darwin. The same castof mind which caused him to detach the Creator from his universe, ledhim also to detach the soul from the body, though to the body heascribes an influence so large as to render the soul almostunnecessary. The aberrations of reason were, in his view, an affairof the material brain. Mental disease is brain disease; but then theimmortal reason sits apart, and cannot be touched by the disease. Theerrors of madness are those of the instrument, not of the performer. 

It may be more than a mere result of education, connecting itself, probably, with the deeper mental structure of the two men, that theidea of Gassendi, above enunciated, is substantially the same as thatexpressed by Professor Clerk Maxwell, at the close of the very ablelecture delivered by him at Bradford in 1873. According to bothphilosophers, the atoms, if I understand aright, are preparedmaterials, which, formed once for all by the Eternal, produce by theirsubsequent interaction all the phenomena of the material world. Thereseems to be this difference, however, between Gassendi and Maxwell. The one postulates, the other infers his first cause. In his'manufactured articles, ' as he calls the atoms, Professor Maxwellfinds the basis of an induction, which enables him to scalephilosophic heights considered inaccessible by Kant, and to take thelogical step from the atoms to their Maker. 

Accepting here the leadership of Kant, I doubt the legitimacy ofMaxwell's logic; but it is impossible not to feel the ethic glow withwhich his lecture concludes. There is, moreover, a very noble strainof eloquence in his description of the steadfastness of the atoms:Natural causes, as we know, are at work, which tend to modify, if theydo not at length destroy, all the arrangements and dimensions of theearth and the whole solar system. But though in the course of agescatastrophes have occurred and may yet occur in the heavens, thoughancient systems may be dissolved and new systems evolved out of theirruins, the molecules out of which these systems are built--thefoundation stones of the material universe--remain unbroken andunworn. '

The atomic doctrine, in whole or in part, was entertained by Bacon, Descartes, Hobbes, Locke, Newton, Boyle, and their successors, untilthe chemical law of multiple proportions enabled Dalton to confer uponit an entirely new significance. In our day there are secessions fromthe theory, but it still stands firm. Loschmidt, Stoney, and SirWilliam Thomson have sought to determine the sizes of the atoms, orrather to fix the limits between which their sizes lie; while thediscourses of Williamson and Maxwell delivered in Bradford in 1873illustrate the present hold of the doctrine upon the foremostscientific minds. In fact, it may be doubted whether, wanting thisfundamental conception, a theory of the material universe is capableof scientific statement. 

5. 

Ninety years subsequent to Gassendi the doctrine of bodilyinstruments, as it may be called, assumed immense importance in thehands of Bishop Butler, who, in his famous 'Analogy of Religion, 'developed, from his own point of view, and with consummate sagacity, asimilar idea. The Bishop still influences many superior minds; and itwill repay us to dwell for a moment on his views. He draws thesharpest distinction between our real selves and our bodilyinstruments. He does not, as far as I remember, use the word soul, possibly because the term was so hackneyed in his day, as it had beenfor many generations previously. But he speaks of 'living powers, ''perceiving or percipient powers, ' 'moving agents, ' 'ourselves, ' inthe same sense as we should employ the term soul. He dwells upon thefact that limbs may be removed, and mortal diseases assail the body, the mind, almost up to the moment of death, remaining clear. Herefers to sleep and to swoon, where the 'living powers' are suspendedbut not destroyed. He considers it quite as easy to conceive ofexistence out of our bodies as in them; that we may animate asuccession of bodies, the dissolution of all of them having no moretendency to dissolve our real selves, or 'deprive us of livingfaculties--the faculties of perception and action--than thedissolution of any foreign matter which we are capable of receivingimpressions from, or making use of for the common occasions of life. 'This is the key of the Bishop's position: 'our organised bodies areno more a part of ourselves than any other matter around us. ' In proofof this he calls attention to the use of glasses, which 'prepareobjects' for the 'percipient power' exactly as the eye does. The eyeitself is no more percipient than the glass; is quite as much theinstrument of the true self, and also as foreign to the true self, asthe glass is. 'And if we see with our eyes only in the same manner aswe do with glasses, the like may justly be concluded from analogy ofall our senses. '

Lucretius, as you are aware, reached a precisely opposite conclusion:and it certainly would be interesting, if not profitable, to us all, to hear what he would or could urge in opposition to the reasoning ofthe Bishop. As a brief discussion of the point will enable us to seethe bearings of an important question, I will here permit a discipleof Lucretius to try the strength of the Bishop's position, and thenallow the Bishop to retaliate, with the view of rolling back, if hecan, the difficulty upon Lucretius. 

The argument might proceed in this fashion:

'Subjected to the test of mental presentation (Vorstellung), yourviews, most honoured prelate, would offer to many minds a great, ifnot an insuperable, difficulty. You speak of "living powers, ""percipient or perceiving powers, " and "ourselves;" but can you form amental picture of any of these, apart from the organism through whichit is supposed to act? Test yourself honestly, and see whether youpossess any faculty that would enable you to form such a conception. The true self has a local habitation in each of us; thus localised, must it not possess a form? If so, what form? Have you ever for amoment realised it? When a leg is amputated the body is divided intotwo parts; is the true self in both of them or in one? Thomas Aquinasmight say in both; but not you, for you appeal to the consciousnessassociated with one of the two parts, to prove that the other isforeign matter. Is consciousness, then, a necessary element of thetrue self? If so, what do you say to the case of the whole body beingdeprived of consciousness? If not, then on what grounds do you denyany portion of the true self to the severed limb? It seems verysingular that from the beginning to the end of your admirable book(and no one admires its sober strength more than I do), you never oncemention the brain or nervous system. You begin at one end of thebody, and show that its parts may be removed without prejudice to theperceiving power. What if you begin at the other end, and remove, instead of the leg, the brain? The body, as before, is divided intotwo parts; but both are now in the same predicament, and neither canbe appealed to to prove that the other is foreign matter. Or, insteadof going so far as to remove the brain itself, let a certain portionof its bony covering be removed, and let a rhythmic series ofpressures and relaxations of pressure be applied to the softsubstance. At every pressure "the faculties of perception and ofaction" vanish; at every relaxation of pressure they are restored. Where, during the intervals of pressure, is the perceiving power? Ionce had the discharge of a large Leyden battery passed unexpectedlythrough me: I felt nothing, but was simply blotted out of consciousexistence for a sensible interval. Where was my true self during thatinterval? Men who have recovered from lightning-stroke have been muchlonger in the same state; and indeed in cases of ordinary concussionof the brain, days may elapse during which no experience is registeredin consciousness. Where is the man himself during the period ofinsensibility? You may say that I beg the question when I assume theman to have been unconscious, that he was really conscious all thetime, and has simply forgotten what had occurred to him. In reply tothis, I can only say that no one need shrink from the worst torturesthat superstition ever invented, if only so felt and so remembered. Ido not think your theory of instruments goes at all to the bottom ofthe matter. A telegraph-operator has his instruments, by means ofwhich he converses with the world; our bodies possess a nervoussystem, which plays a similar part between the perceiving power andexternal things. Cut the wires of the operator, break his battery, demagnetise his needle; by this means you certainly sever hisconnection with the world; but, inasmuch as these are realinstruments, their destruction does not touch the man who uses them. The operator survives, and he knows that he survives. What is there, I would ask, in the human system that answers to this conscioussurvival of the operator when the battery of the brain is so disturbedas to produce insensibility, or when it is destroyed altogether?

'Another consideration, which you may regard as slight, presses uponme with some force. The brain may change from health to disease, andthrough such a change the most exemplary man may be converted into adebauchee or a murderer. My very noble and approved good master had, as you know, threatenings of lewdness introduced into his brain by hisjealous wife's philter; and sooner than permit himself to run even therisk of yielding to these base promptings he slew himself. How couldthe hand of Lucretius have been thus turned against himself if thereal Lucretius remained as before? Can the brain or can it not act inthis distempered way without the intervention of the immortal reason?If it can, then it is a prime mover which requires only healthyregulation to render it reasonably self-acting, and there is noapparent need of your immortal reason at all. If it cannot, then theimmortal reason, by its mischievous activity in operating upon abroken instrument, must have the credit of committing every imaginableextravagance and crime. 

I think, if you will allow me to say so, that the gravest consequencesare likely to flow from your estimate of the body. To regard thebrain as you would a staff or an eyeglass--to shut your eyes to allits mystery, to the perfect correlation of its condition and ourconsciousness, to the fact that a slight excess or defect of blood init produces the very swoon to which you refer, and that in relation toit our meat, and drink, and air, and exercise, have a perfectlytranscendental value and significance--to forget all this does, Ithink, open a way to innumerable errors in our habits of life, and maypossibly, in some cases, initiate and foster that very disease, andconsequent mental ruin, which a wiser appreciation of this mysteriousorgan would have avoided. '

I can imagine the Bishop thoughtful after hearing this argument. Hewas not the man to allow anger to mingle with the consideration of apoint of this kind. After due reflection, and having strengthenedhimself by that honest contemplation of the facts which was habitualwith him, and which includes the desire to give even adversereasonings their due weight, I can suppose the Bishop to proceed thus:'You will remember that in the "Analogy of Religion, " of which youhave so kindly spoken, I did not profess to prove anything absolutely, and that I over and over again acknowledged and insisted on thesmallness of our knowledge, or rather the depth of our ignorance, asregards the whole system of the universe. My object was to show mydeistical friends, who set forth so eloquently the beauty andbeneficence of Nature and the Ruler thereof, while they had nothingbut scorn for the so-called absurdities of the Christian scheme, thatthey were in no better condition than we were, and that, for everydifficulty found upon our side, quite as great a difficulty was to befound upon theirs. I will now, with your permission, adopt a similarline of argument. You are a Lucretian, and from the combination andseparation of insensate atoms deduce all terrestrial things, includingorganic forms and their phenomena. Let me tell you in the firstinstance how far I am prepared to go with you. I admit that you canbuild crystalline forms out of this play of molecular force; that thediamond, amethyst, and snow-star are truly wonderful structures whichare thus produced. I will go farther and acknowledge that even a treeor flower might in this way be organised. Nay, if you can show me ananimal without sensation, I will concede to you that it also might beput together by the suitable play of molecular force. 

'Thus far our way is clear, but now comes my difficulty. Your atomsare individually without sensation, much more are they withoutintelligence. May I ask you, then, to try your hand upon thisproblem. Take your dead hydrogen atoms, your dead oxygen atoms, yourdead carbon atoms, your dead nitrogen atoms, your dead phosphorusatoms, and all the other atoms, dead as grains of shot, of which thebrain is formed. Imagine them separate and sensationless; observethem running together and forming all imaginable combinations. This, as a purely mechanical process, is seeable by the mind. But can yousee, or dream, or in any way imagine, how out of that mechanical act, and from these individually dead atoms, sensation, thought, andemotion are to rise? Are you likely to extract Homer out of therattling of dice, or the Differential Calculus out of the clash ofbilliard-balls? I am not all bereft of this Vorstellungs-Kraft ofwhich you speak, nor am I, like so many of my brethren, a mere vacuumas regards scientific knowledge. I can follow a particle of muskuntil it reaches the olfactory nerve; I can follow the waves of sounduntil their tremors reach the water of the labyrinth, and set theotoliths and Corti's fibres in motion; I can also visualise the wavesof aether as they cross the eye and hit the retina. Nay more, I amable to pursue to the central organ the motion thus imparted at theperiphery, and to see in idea the very molecules of the brain throwninto tremors. My insight is not baffled by these physical processes. What baffles and bewilders me is the notion that from those physicaltremors things so utterly incongruous with them as sensation, thought, and emotion can be derived. You may say, or think, that this issue ofconsciousness from the clash of atoms is not more incongruous than theflash of light from the union of oxygen and hydrogen. But I beg tosay that it is. For such incongruity as the flash possesses is thatwhich I now force upon your attention. The 'flash' is an affair ofconsciousness, the objective counterpart of which is a vibration. Itis a flash only by your interpretation. You are the cause of theapparent incongruity; and you are the thing that puzzles me. I neednot remind you that the great Leibnitz felt the difficulty which Ifeel; and that to get rid of this monstrous deduction of life fromdeath he displaced your atoms by his monads, which were more or lessperfect mirrors of the universe, and out of the summation andintegration of which he supposed all the phenomena of life--sentient, intellectual, and emotional--to arise. 

'Your difficulty, then, as I see you are ready to admit, is quite asgreat as mine. You cannot satisfy the human understanding in itsdemand for logical continuity between molecular processes and thephenomena of consciousness. This is a rock on which Materialism mustinevitably split whenever it pretends to be a complete philosophy oflife. What is the moral, my Lucretian? You and I are not likely toindulge in ill-temper in the discussion of these great topics, wherewe see so much room for honest differences of opinion. But there arepeople of less wit or more bigotry (I say it with humility), on bothsides, who are ever ready to mingle anger and vituperation with suchdiscussions. There are, for example, writers of note and influence atthe present day, who are not ashamed publicly to assume the "deeppersonal sin" of a great logician to be the cause of his unbelief in atheologic dogma. [Footnote: This is the aspect under which the lateEditor of the 'Dublin Review' presented to his readers the memory ofJohn Stuart Mill. I can only say, that I would as soon take my chancein the other world, in the company of the 'unbeliever, ' as in that ofhis Jesuit detractor. In Dr. Ward we have an example of a wholesomeand vigorous nature, soured and perverted by a poisonous creed. ] 'Andthere are others who hold that we, who cherish our noble Bible, wrought as it has been into the constitution of our forefathers, andby inheritance into us, must necessarily be hypocritical andinsincere. Let us disavow and discountenance such people, cherishingthe unswerving faith that what is good and true in both our argumentswill be preserved for the benefit of humanity, while all that is bador false will disappear. '

I hold the Bishop's reasoning to be unanswerable, and his liberalityto be worthy of imitation. 

It is worth remarking that in one respect the Bishop was a product ofhis age. Long previous to his day the nature of the soul had been sofavourite and general a topic of discussion, that, when the studentsof the Italian Universities wished to know the leanings of a newProfessor, they at once requested him to lecture upon the soul. Aboutthe time of Bishop Butler the question was not only agitated butextended. It was seen by the clear-witted men who entered this arena, that many of their best arguments applied equally to brutes and men. The Bishop's arguments were of this character. He saw it, admittedit, took the consequence, and boldly embraced the whole animal worldin his scheme of immortality. 

6. 

Bishop Butler accepted with unwavering trust the chronology of the OldTestament, describing it as confirmed by the natural and civil historyof the world, collected from common historians, from the state of theearth, and from the late inventions of arts and sciences. ' These wordsmark progress; and they must seem somewhat hoary to the Bishop'ssuccessors of today. It is hardly necessary to inform you that sincehis time the domain of the naturalist has been immensely extended--thewhole science of geology, with its astounding revelations regardingthe life of the ancient earth, having been created. The rigidity ofold conceptions has been relaxed, the public mind being renderedgradually tolerant of the idea that not for six thousand, nor forsixty thousand, nor for six thousand thousand, but for aeons embracinguntold millions of years, this earth has been the theatre of life anddeath. The riddle of the rocks has been read by the geologist andpalaeontologist, from sub-Cambrian depths to the deposits thickeningover the sea-bottoms of today. And upon the leaves of that stone bookare, as you know, stamped the characters, plainer and surer than thoseformed by the ink of history, which carry the mind back into abyssesof past time, compared with which the periods which satisfied BishopButler cease to have a visual angle. 

The lode of discovery once struck, those petrified forms in which lifewas at one time active, increased to multitudes and demandedclassification. They were grouped in genera, species, and varieties, according to the degree of similarity subsisting between them. Thusconfusion was avoided, each object being found in the pigeon-holeappropriated to it and to its fellows of similar morphological orphysiological character. The general fact soon became evident thatnone but the simplest forms of life lie lowest down; that, as we climbhigher among the superimposed strata, more perfect forms appear. Thechange, however, from form to form was not continuous, but bysteps--some small, some great. 'A section, ' says Mr. Huxley, 'ahundred feet thick will exhibit at different heights a dozen speciesof Ammonite, none of which passes beyond the particular zone oflimestone, or clay, into the zone below it, or into that above it. ' Inthe presence of such facts it was not possible to avoid the question:Have these forms, showing, though in broken stages, and with manyirregularities, this unmistakable general advance, being subjected tono continuous law of growth or variation? Had our education beenpurely scientific, or had it been sufficiently detached frominfluences which, however ennobling in another domain, have alwaysproved hindrances and delusions when introduced as factors into thedomain of physics, the scientific mind never could have swerved fromthe search for a law of growth, or allowed itself to accept theanthropomorphism which regarded each successive stratum as a kind ofmechanic's bench for the manufacture of new species out of allrelation to the old. 

Biassed, however, by their previous education, the great majority ofnaturalists invoked a special creative act to account for theappearance of each new group of organisms. Doubtless numbers of themwere clearheaded enough to see that this was no explanation atall--that, in point of fact, it was an attempt, by the introduction ofa greater difficulty, to account for a less. But, having nothing tooffer in the way of explanation, they for the most part held theirpeace. Still the thoughts of reflecting men naturally and necessarilysimmered round the question. De Maillet, a contemporary of Newton, has been brought into notice by Professor Huxley as one who 'had anotion of the modifiability of living forms. ' The late Sir BenjaminBrodie, a man of highly philosophic mind, often drew my attention tothe fact that, as early as 1794, Charles Darwin's grandfather wasthe pioneer of Charles Darwin. [Footnote: Zoonomia, ' vol. I. Pp. 500-510. ] In 1801, and in subsequent years, the celebrated Lamarck, who, through the vigorous exposition of his views by the author of the'Vestiges of Creation, ' rendered the public mind perfectly familiarwith the idea of evolution, endeavoured to show the development ofspecies out of changes of habit and external condition. In 1813 Dr. Wells, the founder of our present theory of Dew, read before the RoyalSociety a paper in which, to use the words of Mr. Darwin, 'hedistinctly recognises the principle of natural selection; and this isthe first recognition that has been indicated. ' The thoroughness andskill with which Wells pursued his work, and the obvious independenceof his character, rendered him long ago a favourite with me; and itgave me the liveliest pleasure to alight upon this additionaltestimony to his penetration. Professor Grant, Mr. Patrick Matthew, von Buch, the author of the 'Vestiges, ' D'Halloy, and others, by theenunciation of opinions more or less clear and correct, showed thatthe question had been fermenting long prior to the year 1858, when Mr. Darwin and Mr. Wallace simultaneously, but independently, placed theirclosely concurrent views before the Linnean Society. [Footnote: In1855 Mr. Herbert Spencer ('Principles of Psychology, ' 2nd edit. Vol. I. P. 465) expressed 'the belief that life under all its forms hasarisen by an unbroken evolution, and through the instrumentality ofwhat are called natural causes. ' This was my belief also at thattime. ]

These papers were followed in 1859 by the publication of the firstedition of the 'Origin of Species. ' All great things come slowly tothe birth. Copernicus, as I informed you, pondered his great work forthirty-three years. Newton for nearly twenty years kept the idea ofGravitation before his mind; for twenty years also he dwelt upon hisdiscovery of Fluxions, and doubtless would have continued to make itthe object of his private thought, had he not found Leibnitz upon histrack. Darwin for two-and-twenty years pondered the problem of theorigin of species, and doubtless he would have continued to do so hadhe not found Wallace upon his track. [Footnote: The behaviour of Mr. Wallace in relation to this subject has been dignified in the highestdegree. ] A concentrated, but full and powerful, epitome of hislabours was the consequence. The book was by no means an easy one;and probably not one in every score of those who then attacked it, hadread its pages through, or were competent to grasp their significanceif they had. I do not say this merely to discredit them: for therewere in those days some really eminent scientific men, entirely raisedabove the heat of popular prejudice, and willing to accept anyconclusion that science had to offer, provided it was duly backed byfact and argument, who entirely mistook Mr. Darwin's views. In fact, the work needed an expounder, and it found one in Mr. Huxley. I knownothing more admirable in the way of scientific exposition than thoseearly articles of his on the origin of species. He swept the curve ofdiscussion through the really significant points of the subject, enriched his exposition with profound original remarks andreflections, often summing up in a single pithy sentence an argumentwhich a less compact mind would have spread over pages. But there isone impression made by the book itself which no exposition of it, however luminous, can convey; and that is the impression of the vastamount of labour, both of observation and of thought, implied in itsproduction. Let us glance at its principles. 

It is conceded on all hands that what are called varieties' arecontinually produced. The rule is probably without exception. Nochick, or child, is in all respects and particulars the counterpart ofits brother and sister; and in such differences we have 'variety'incipient. No naturalist could tell how far this variation could becarried; but the great mass of them held that never, by any amount ofinternal or external change, nor by the mixture of both, could theoffspring of the same progenitor so far deviate from each other as toconstitute different species. The function of the experimentalphilosopher is to combine the conditions of Nature and to produce herresults; and this was the method of Darwin. [Footnote: The first steponly towards experimental demonstration has been taken. Experimentsnow begun might, a couple of centuries hence, furnish data ofincalculable value, which ought to be supplied to the science of thefuture. ] He made himself acquainted with what could, without anymanner of doubt, be done in the way of producing variation. Heassociated himself with pigeon-fanciers--bought, begged, kept, andobserved every breed that he could obtain. Though derived from acommon stock, the diversities of these pigeons were such that 'a scoreof them might be chosen which, if shown to an ornithologist, and hewere told that they were wild birds, would certainly be ranked by himas well-defined species. ' The simple principle which guides thepigeon-fancier, as it does the cattle-breeder, is the selection ofsome variety that strikes his fancy, and the propagation of thisvariety by inheritance. With his eye still directed to the particularappearance which he wishes to exaggerate, he selects it as itreappears in successive broods, and thus adds increment to incrementuntil an astonishing amount of divergence from the parent type iseffected. The breeder in this case does not produce the elements ofthe variation. He simply observes them, and by selection adds themtogether until the required result has been obtained. 'No man, ' saysMr. Darwin, 'would ever try to make a fantail till he saw a pigeonwith a tail developed in some slight degree in an unusual manner, or apouter until he saw a pigeon with a crop of unusual size. ' Thus naturegives the hint, man acts upon it, and by the law of inheritanceexaggerates the deviation. 

Having thus satisfied himself by indubitable facts that theorganisation of an animal or of a plant (for precisely the sametreatment applies to plants). Is to some extent plastic, he passesfrom variation under domestication to variation under nature. Hithertowe have dealt with the adding together of small changes by theconscious selection of man. Can Nature thus select? Mr. Darwin'sanswer is, 'Assuredly she can. ' The number of living things producedis far in excess of the number that can be supported; hence at someperiod or other of their lives there must be a struggle for existence. And what is the infallible result? If one organism were a perfectcopy of the other in regard to strength, skill, and agility, externalconditions would decide. But this is not the case. Here we have thefact of variety offering itself to nature, as in the former instanceit offered itself to man; and those varieties which are leastcompetent to cope with surrounding conditions will infallibly give wayto those that are most competent. To use a familiar proverb, theweakest goes to the wall. But the triumphant fraction again breeds toover-production, transmitting the qualities which secured itsmaintenance, but transmitting them in different degrees. The strugglefor food again supervenes, and those to whom the favourable qualityhas been transmitted in excess, will triumph as before. 

It is easy to see that we have here the addition of incrementsfavourable to the individual, still more rigorously carried out thanin the case of domestication; for not only are unfavourable specimensnot selected by nature, but they are destroyed. This is what Mr. Darwin calls 'Natural Selection, ' which acts by the preservation andaccumulation of small inherited modifications, each profitable to thepreserved being. With this idea he interpenetrates and leavens thevast store of facts that he and others have collected. We cannot, without shutting our eyes through fear or prejudice, fail to see thatDarwin is here dealing, not with imaginary, but with true causes; norcan we fail to discern what vast modifications may be produced bynatural selection in periods sufficiently long. Each individualincrement may resemble what mathematicians call a 'differential' (aquantity indefinitely small); but definite and great changes mayobviously be produced by the integration of these infinitesimalquantities, through practically infinite time. 

If Darwin, like Bruno, rejects the notion of creative power, actingafter human fashion, it certainly is not because he is unacquaintedwith the numberless exquisite adaptations, on which this notion of asupernatural Artificer has been founded. His book is a repository ofthe most startling facts of this description. Take the marvellousobservation which he cites from Dr. Krueger, where a bucket, with anaperture serving as a spout, is formed in an orchid. Bees visit theflower: in eager search of material for their combs, they push eachother into the bucket, the drenched ones escaping from theirinvoluntary bath by the spout. Here they rub their backs against theviscid stigma of the flower and obtain glue; then against the pollenmasses, which are thus stuck to the back of the bee and carried away. 'When the bee, so provided, flies to another flower, or to the sameflower a second time, and is pushed by its comrades into the bucket, and then crawls out by the passage, the pollen-mass upon its backnecessarily comes first into contact with the viscid stigma, ' whichtakes up the pollen; and this is how that orchid is fertilised. Ortake this other case of the Catasetum 'Bees visit these flowers inorder to gnaw the labellum; in doing this they inevitably touch along, tapering, sensitive projection. This, when touched, transmits asensation or vibration to a certain membrane, which is instantlyruptured, setting free a spring, by which the pollen-mass is shotforth like an arrow in the right direction, and adheres by its viscidextremity to the back of the bee. ' In this way the fertilising pollenis spread abroad. 

It is the mind thus stored with the choicest materials of theteleologist that rejects teleology, seeking to refer these wonders tonatural causes. They illustrate, according to him, the method ofnature, not the 'technic' of a manlike Artificer. The beauty offlowers is due to natural selection. Those that distinguishthemselves by vividly contrasting colours from the surrounding greenleaves are most readily seen, most frequently visited by insects, mostoften fertilised, and hence most favoured by natural selection. Coloured berries also readily attract the attention of birds andbeasts, which feed upon them, spread their manured seeds abroad, thusgiving trees and shrubs possessing such berries a greater chance inthe struggle for existence. 

With profound analytic and synthetic skill, Mr. Darwin investigatesthe cell-making instinct of the hive-bee. His method of dealing withit is representative. He falls back from the more perfectly to theless perfectly developed instinct--from the hive-bee to the humblebee, which uses its own cocoon as a comb, and to classes of bees ofintermediate skill, endeavouring to show how the passage might begradually made from the lowest to the highest. The saving of wax isthe most important point in the economy of bees. Twelve to fifteenpounds of dry sugar are said to be needed for the secretion of asingle pound of wax. The quantities of nectar necessary for the waxmust therefore be vast; and every improvement of constructive instinctwhich results in the saving of wax is a direct profit to the insect'slife. The time that would otherwise be devoted to the making of wax, is devoted to the gathering and storing of honey for winter food. Mr. Darwin passes from the humble bee with its rude cells, through theMelipona with its more artistic cells, to the hive-bee with itsastonishing architecture. The bees place themselves at equaldistances apart upon the wax, sweep and excavate equal spheres roundthe selected points. The spheres intersect, and the planes ofintersection are built up with thin laminae. Hexagonal cells are thusformed. This mode of treating such questions is, as I have said, representative. The expositor habitually retires from the moreperfect and complex, to the less perfect and simple, and carries youwith him through stages of perfecting--adds increment to increment ofinfinitesimal change, and in this way gradually breaks down yourreluctance to admit that the exquisite climax of the whole could be aresult of natural selection. 

Mr. Darwin shirks no difficulty; and, saturated as the subject waswith his own thought, he must have known, better than his critics, theweakness as well as the strength of his theory. This of course wouldbe of little avail were his object a temporary dialectic victory, instead of the establishment of a truth which he means to beeverlasting. But he takes no pains to disguise the weakness he hasdiscerned; nay, he takes every pains to bring it into the strongestlight. His vast resources enable him to cope with objections startedby himself and others, so as to leave the final impression upon thereader's mind that, if they be not completely answered, they certainlyare not fatal. Their negative force being thus destroyed, you arefree to be influenced by the vast positive mass of evidence he is ableto bring before you. This largeness of knowledge, and readiness ofresource, render Mr. Darwin the most terrible of antagonists. Accomplished naturalists have levelled heavy and sustained criticismsagainst him--not always with the view of fairly weighing his theory, but with the express intention of exposing its weak points only. Thisdoes not irritate him. He treats every objection with a soberness andthoroughness which even Bishop Butler might be proud to imitate, surrounding each fact with its appropriate detail, placing it in itsproper relations, and usually giving it a significance which, as longas it was kept isolated, failed to appear. This is done without atrace of ill-temper. He moves over the subject with the passionlessstrength of a glacier; and the grinding of the rocks is not alwayswithout a counterpart in the logical pulverisation of the objector. But though in handling this mighty theme all passion has been stilled, there is an emotion of the intellect, incident to the discernment ofnew truth, which often colours and warms the pages of Mr. Darwin. 

His success has been great; and this implies not only the solidity ofhis work, but the preparedness of the public mind for such arevelation. On this head, a remark of Agassiz impressed me more thananything else. Sprung from a race of theologians, this celebrated mancombated to the last the theory of natural selection. One of the manytimes I had the pleasure of meeting him in the United States was atMr. Winthrop's beautiful residence at Brookline, near Boston. Risingfrom luncheon, we all halted as if by common consent, in front of awindow, and continued there a discussion which had been started attable. The maple was in its autumn glory, and the exquisite beauty ofthe scene outside seemed, in my case, to interpenetrate withoutdisturbance the intellectual action. Earnestly, almost sadly, Agassizturned, and said to the gentlemen standing round, 'I confess that Iwas not prepared to see this theory received as it has been by thebest intellects of our time. Its success is greater than I could havethought possible. '

7. 

In our day grand generalisations have been reached. The theory of theorigin of species is but one of them. Another, of still wider graspand more radical significance, is the doctrine of the Conservation ofEnergy, the ultimate philosophical issues of which are as yet butdimly seen--that doctrine which 'binds nature fast in fate, ' to anextent not hitherto recognised, exacting from every antecedent itsequivalent consequent, from every consequent its equivalentantecedent, and bringing vital as well as physical phenomena under thedominion of that law of causal connection which, so far as the humanunderstanding has yet pierced, asserts itself everywhere in nature. Long in advance of all definite experiment upon the subject, theconstancy and indestructibility of matter had been affirmed; and allsubsequent experience justified the affirmation. Mayer extended theattribute of indestructibility to energy, applying it in the firstinstance to inorganic, and afterwards with profound insight to organicnature. [Footnote: Dr. Berthold has shown that Leibnitz had sound viewsregarding the conservation of energy in inorganic nature. ] Thevegetable world, though drawing all its nutriment from invisiblesources, was proved incompetent to generate anew either matter orforce. Its matter is for the most part transmuted gas; its forcetransformed solar force. The animal world was proved to be equallyuncreative, all its motive energies being referred to the combustionof its food. The activity of each animal, as a whole, was proved tobe the transferred activity of its molecules. The muscles were shownto be stores of mechanical energy, potential until unlocked by thenerves, and then resulting in muscular contractions. The speed atwhich messages fly to and fro along the nerves was determined byHelmholtz, and found to be, not, as had been previously supposed, equal to that of light or electricity, but less than the speed ofsound--less even than that of an eagle. 

This was the work of the physicist: then came the conquests of thecomparative anatomist and physiologist, revealing the structure ofevery animal, and the function of every organ in the whole biologicalseries, from the lowest zoophyte up to man. The nervous system hadbeen made the object of profound and continued study, the wonderfuland, at bottom, entirely mysterious controlling power which itexercises over the whole organism, physical and mental, beingrecognised more and more. Thought could not be kept back from asubject so profoundly suggestive. Besides the physical life dealtwith by Mr. Darwin, there is a psychical life presenting similargradations, and asking equally for a solution. How are the differentgrades and orders of Mind to be accounted for? What is the principleof growth of that mysterious power which on our planet culminates inReason? These are questions which, though not thrusting themselves soforcibly upon the attention of the general public, had not onlyoccupied many reflecting minds, but had been formally broached by oneof them before the 'Origin of Species' appeared. 

With the mass of materials furnished by the physicist and physiologistin his hands, Mr. Herbert Spencer, twenty years ago, sought to graftupon this basis a system of psychology; and two years ago a second andgreatly amplified edition of his work appeared. Those who haveoccupied themselves with the beautiful experiments of Plateau willremember that when two spherules of olive-oil suspended in a mixtureof alcohol and water of the same density as the oil, are broughttogether, they do not immediately unite. Something like a pellicleappears to be formed around the drops, the rupture of which isimmediately followed by the coalescence of the globules into one. There are organisms whose vital actions are almost as purely physicalas the coalescence of such drops of oil. They come into contact andfuse themselves thus together. From such organisms to others a shadehigher, from these to others a shade higher still, and on through anever-ascending series, Mr. Spencer conducts his argument. There aretwo obvious factors to be here taken into account--the creature andthe medium in which it lives, or, as it is often expressed, theorganism and its environment. Mr. Spencer's fundamental principle is, that between these two factors there is incessant interaction. Theorganism is played upon by the environment, and is modified to meetthe requirements of the environment. Life he defines to be 'acontinuous adjustment of internal relations to external relations. 

In the lowest organisms we have a kind of tactual sense diffused overthe entire body; then, through impressions from without and theircorresponding adjustments, special portions of the surface become moreresponsive to stimuli than others. The senses are nascent, the basisof all of them being that simple tactual sense which the sageDemocritus recognised 2, 300 years ago as their common progenitor. Theaction of light, in the first instance, appears to be a meredisturbance of the chemical processes in the animal organism, similarto that which occurs in the leaves of plants. By degrees the actionbecomes localised in a few pigment-cells, more sensitive to light thanthe surrounding tissue. The eye is incipient. At first it is merelycapable of revealing differences of light and shade produced by bodiesclose at hand. Followed, as the interception of the light commonlyis, by the contact of the closely adjacent opaque body, sight in thiscondition becomes a kind of 'anticipatory touch. ' The adjustmentcontinues; a slight bulging out of the epidermis over thepigment-granules supervenes. A lens is incipient, and, through theoperation of infinite adjustments, at length reaches the perfectionthat it displays in the hawk and eagle. So of the other senses; theyare special differentiations of a tissue which was originally vaguelysensitive all over. 

With the development of the senses, the adjustments between theorganism and its environment gradually extend in space, amultiplication of experiences and a corresponding modification ofconduct being the result. 

The adjustments also extend in time, covering continually greaterintervals. Along with this extension in space and time theadjustments also increase in speciality and complexity, passingthrough the various grades of brute life, and prolonging themselvesinto the domain of reason. Very striking are Mr. Spencer's remarksregarding the influence of the sense of touch upon the development ofintelligence. This is, so to say, the mother-tongue of all thesenses, into which they must be translated to be of service to theorganism. Hence its importance. The parrot is the most intelligentof birds, and its tactual power is also greatest. From this sense itgets knowledge, unattainable by birds which cannot employ their feetas hands. The elephant is the most sagacious of quadrupeds--itstactual range and skill, and the consequent multiplication ofexperiences, which it owes to its wonderfully adaptable trunk, beingthe basis of its sagacity. Feline animals, for a similar cause, aremore sagacious than hoofed animals, --atonement being to some extentmade in the case of the horse, by the possession of sensitiveprehensile lips. In the Primates the evolution of intellect and theevolution of tactual appendages go hand in hand. In the mostintelligent anthropoid apes we find the tactual range and delicacygreatly augmented, new avenues of knowledge being thus opened to theanimal. Alan crowns the edifice here, not only in virtue of his ownmanipulatory power, but through the enormous extension of his range ofexperience, by the invention of instruments of precision, which serveas supplemental senses and supplemental limbs. The reciprocal actionof these is finely described and illustrated That chastenedintellectual emotion to which I have referred in connection with Mr. Darwin, is not absent in Mr. Spencer. His illustrations possess attimes exceeding vividness and force; and from his style on suchoccasions it is to be inferred, that the ganglia of this Apostle ofthe Understanding are sometimes the seat of a nascent poetic thrill. 

It is a fact of supreme importance that actions, the performance ofwhich at first requires even painful effort and deliberation, may, byhabit, be rendered automatic. Witness the slow learning of itsletters by a child, and the subsequent facility of reading in a man, when each group of letters which forms a word is instantly, andwithout effort, fused to a single perception. Instance thebilliard-player, whose muscles of hand and eye, when he reaches theperfection of his art, are unconsciously co-ordinated. Instance themusician, who, by practice, is enabled to fuse a multitude ofarrangements, auditory, tactual, and muscular, into a process ofautomatic manipulation. Combining such facts with the doctrine ofhereditary transmission, we reach a theory of Instinct. A chick, after coming out of the egg, balances itself correctly, runs about, picks up food, thus snowing that it possesses a power of directing itsmovements to definite ends. How did the chick learn this very complexco-ordination of eyes, muscles, and beak? It has not beenindividually taught; its personal experience is nit; but it has thebenefit of ancestral experience. In its inherited organisation areregistered the powers which it displays at birth. So also as regardsthe instinct of the hive-bee, already referred to. The distance atwhich the insects stand apart when they sweep their hemispheres andbuild their cells is 'organically remembered. ' Man also carries withhim the physical texture of his ancestry, as well as the inheritedintellect bound up with it. The defects of intelligence duringinfancy and youth are probably less due to a lack of individualexperience, than to the fact that in early life the cerebralorganisation is still incomplete. The period necessary for completionvaries with the race, and with the individual. As a round shotoutstrips the rifled bolt on quitting the muzzle of the gun, so thelower race, in childhood, may outstrip the higher. But the highereventually overtakes the lower, and surpasses it in range. As regardsindividuals, we do not always find the precocity of youth prolonged tomental power in maturity; while the dulness of boyhood is sometimesstrikingly contrasted with the intellectual energy of after years. Newton, when a boy, was weakly, and he showed no particular aptitudeat school; but in his eighteenth year he went to Cambridge, and soonafterwards astonished his teachers by his power of dealing withgeometrical problems. During his quiet youth his brain was slowlypreparing itself to be the organ of those energies which hesubsequently displayed. 

By myriad blows (to use a Lucretian phrase) the image andsuperscription of the external world are stamped as states ofconsciousness upon the organism, the depth of the impression dependingon the number of the blows. When two or more phenomena occur in theenvironment invariably together, they are stamped to the same depth orto the same relief, and indissolubly connected. And here we come tothe threshold of a great question. Seeing that he could in no way ridhimself of the consciousness of Space and Time, Kant assumed them tobe necessary 'forms of intuition, ' the moulds and shapes into whichour intuitions are thrown, belonging to ourselves, and withoutobjective existence. With unexpected power and success, Mr. Spencerbrings the hereditary experience theory, as he holds it, to bear uponthis question. 'If there exist certain external relations which areexperienced by all organisms at all instants of their wakinglives--relations which are absolutely constant and universal--therewill be established answering internal relations, that are absolutelyconstant and universal. Such relations we have in those of Space andTime. As the substratum of all other relations of the Non-Ego, theymust be responded to by conceptions that are the substrata of allother relations in the Ego. Being the constant and infinitelyrepeated elements of thought, they must become the automatic elementsof thought--the elements of thought which it is impossible to get ridof--the "forms of intuition. "'

Throughout this application and extension of Hartley's and Mill's 'Lawof Inseparable Association, ' Mr. Spencer stands upon his own ground, invoking, instead of the experiences of the individual, the registeredexperiences of the race. His overthrow of the restriction ofexperience to the individual is, I think, complete. That restrictionignores the power of organising experience, furnished at the outset toeach individual; it ignores the different degrees of this powerpossessed by different races, and by different individuals of the samerace. Were there not in the human brain a potency antecedent to allexperience, a dog or a cat ought to be as capable of education as man. These predetermined internal relations are independent of theexperiences of the individual. The human brain is the 'organisedregister of infinitely numerous experiences received during theevolution of life, or rather during the evolution of that series oforganisms through which the human organism has been reached. Theeffects of the most uniform and frequent of these experiences havebeen successively bequeathed, principal and interest, and have slowlymounted to that high intelligence which lies latent in the brain ofthe infant. Thus it happens that the European inherits from twenty tothirty cubic inches more of brain than the Papuan. Thus it happensthat faculties, as of music, which scarcely exist in some inferiorraces, become congenital in superior ones. Thus it happens that outof savages unable to count up to the number of their fingers, andspeaking a language containing only nouns and verbs, arise at lengthour Newtons and Shakspeares. '

8. 

At the outset of this Address it was stated that physical theorieswhich lie beyond experience are derived by a process of abstractionfrom experience. It is instructive to note from this point of viewthe successive introduction of new conceptions. The idea of theattraction of gravitation was preceded by the observation of theattraction of iron by a magnet, and of light bodies by rubbed amber. The polarity of magnetism and electricity also appealed to the senses. It thus became the substratum of the conception that atoms andmolecules are endowed with attractive and repellent poles, by the playof which definite forms of crystalline architecture are produced. Thusmolecular force becomes structural. [Footnote: See Art. On Matter andForce, or 'Lectures on Light, ' No. III. ] It required no greatboldness of thought to extend its play into organic nature, and torecognise in molecular force the agency by which both plants andanimals are built up. In this way, out of experience ariseconceptions which are wholly ultra-experiential. None of the atomistsof antiquity had any notion of this play of molecular polar force, butthey had experience of gravity, as manifested by falling bodies. Abstracting from this, they permitted their atoms to fall eternallythrough empty space. Democritus assumed that the larger atoms movedmore rapidly than the smaller ones, which they therefore couldovertake, and with which they could combine. Epicurus, holding thatempty space could offer no resistance to motion, ascribed to all theatoms the same velocity; but he seems to have overlooked theconsequence that under such circumstances the atoms could nevercombine. Lucretius cut the knot by quitting the domain of physicsaltogether, and causing the atoms to move together by a kind ofvolition. 

Was the instinct utterly at fault which caused Lucretius thus toswerve from his own principles? Diminishing gradually the number ofprogenitors, Mr. Darwin comes at length to one 'primordial form;' buthe does not say, so far as I remember, how he supposes this form tohave been introduced. He quotes with satisfaction the words of acelebrated author and divine who had I gradually learnt to see that itwas just as noble a conception of the Deity to believe He created afew original forms, capable of self-development into other and needfulforms, as to believe He required a fresh act of creation to supply thevoids caused by the action of His laws. ' What Mr. Darwin thinks ofthis view of the introduction of life, I do not know. But theanthropomorphism, which it seemed his object to set aside, is asfirmly associated with the creation of a few forms as with thecreation of a multitude. We need clearness and thoroughness here. Twocourses and two only are possible. Either let us open our doorsfreely to the conception of creative acts, or abandoning them, let usradically change our notions of Matter. If we look at matter aspictured by Democritus, and as defined for generations in ourscientific text-books, the notion of conscious life coming out of itcannot be formed by the mind. The argument placed in the mouth ofBishop Butler suffices, in my opinion, to crush all such materialismas this. Those, however, who framed these definitions of matter werebut partial students. They were not biologists, but mathematicians, whose labours referred only to such accidents and properties of matteras could be expressed in their formulae. Their science was mechanicalscience, not the science of life. With matter in its wholeness theynever dealt; and, denuded by their imperfect definitions, 'the gentlemother of all' became the object of her children's dread. Let usreverently, but honestly, look the question in the face. Divorcedfrom matter, where is life? Whatever our faith may say, our knowledgeshows them to be indissolubly joined. Every meal we eat, and everycup we drink, illustrates the mysterious control of Mind by Matter. 

On tracing the line of life backwards, we see it approaching more andmore to what we call the purely physical condition. We come at lengthto those organisms which I have compared to drops of oil suspended ina mixture of alcohol and water. We reach the protogenes of Haeckel, in which we have 'a type distinguishable from a fragment of albumenonly by its finely granular character. ' Can we pause here? We break amagnet, and find two poles in each of its fragments. We continue theprocess of breaking; but, however small the parts, each carries withit, though enfeebled, the polarity of the whole. And when we canbreak no longer, we prolong the intellectual vision to the polarmolecules. Are we not urged to do something similar in the case oflife? Is there not a temptation to close to some extent withLucretius, when he affirms that 'Nature is seen to do all thingsspontaneously of herself without the meddling of the gods? or withBruno, when he declares that Matter is not 'that mere empty capacitywhich philosophers have pictured her to be, but the universal motherwho brings forth all things as the fruit of her own womb?' Believing, as I do, in the continuity of nature, I cannot stop abruptly where ourmicroscopes cease to be of use. Here the vision of the mindauthoritatively supplements the vision of the eye. By a necessityengendered and justified by science I cross the boundary of theexperimental evidence, [Footnote: This mode of procedure was notinvented in Belfast. ] and discern in that Matter which we, in ourignorance of its latent powers, and notwithstanding our professedreverence for its Creator, have hitherto covered with opprobrium, thepromise and potency of all terrestrial Life. 

If you ask me whether there exists the least evidence to prove thatany form of life can be developed out of matter, without demonstrableantecedent life, my reply is that evidence considered perfectlyconclusive by many has been adduced; and that were some of us who havepondered this question to follow a very common example, and accepttestimony because it falls in with our belief, we also should eagerlyclose with the evidence referred to. But there is in the true man ofscience a desire stronger than the wish to have his beliefs upheld;namely, the desire to have them true. And this stronger wish causeshim to reject the most plausible support, if he has reason to suspectthat it is vitiated by error. Those to whom I refer as having studiedthis question, believing the evidence offered in favour of'spontaneous generation' to be thus vitiated, cannot accept it. Theyknow full well that the chemist now prepares from inorganic matter avast array of substances, which were some time ago regarded as thesole products of vitality. They are intimately acquainted with thestructural power of matter, as evidenced in the phenomena ofcrystallisation. They can justify scientifically their belief in itspotency, under the proper conditions, to produce organisms. But, inreply to your question, they will frankly admit their inability topoint to any satisfactory experimental proof that life can bedeveloped, save from demonstrable antecedent life. As alreadyindicated, they draw the line from the highest organisms through lowerones down to the lowest; and it is the prolongation of this line bythe intellect, beyond the range of the senses, that leads them to theconclusion which Bruno so boldly enunciated. [Footnote: Bruno was aPantheist, ' not an 'Atheist' or a 'Materialist. ']

The 'materialism' here professed may be vastly different from what yousuppose, and I therefore crave your gracious patience to the end. 'Thequestion of an external world, ' says J. S. Mill, 'is the greatbattleground of metaphysics. ' [Footnote: 'Examination of Hamilton, ' p. 154. ] Mr. Mill himself reduces external phenomena to 'possibilitiesof sensation. ' Kant, as we have seen, made time and space 'forms' ofour own intuitions. Fichte, having first by the inexorable logic ofhis understanding proved himself to be a mere link in that chain ofeternal causation which holds so rigidly in nature, violently brokethe chain by making nature, and all that it inherits, an apparition ofthe mind. [Footnote: 'Bestimmung des Menschen. '] And it is by nomeans easy to combat such notions. For when I say 'I see you, ' andthat there is not the least doubt about it, the obvious reply is, thatwhat I am really conscious of is an affection of my own retina. Andif I urge that my sight can be checked by touching you, the retortwould be that I am equally transgressing the limits of fact; for whatI am really conscious of is, not that you are there, but that thenerves of my hand have undergone a change. 

All we hear, and see, and touch, and taste, and smell, are, it wouldbe urged, mere variations of our own condition, beyond which, even tothe extent of a hair's breadth, we cannot go. That anything answeringto our impressions exists outside of ourselves is not a fact, but aninference, to which all validity would be denied by an idealist likeBerkeley, or by a sceptic like Hume. Mr. Spencer takes another line. With him, as with the uneducated man, there is no doubt or question asto the existence of an external world. But he differs from theuneducated, who think that the world really is what consciousnessrepresents it to be. Our states of consciousness are mere symbols ofan outside entity which produces them and determines the order oftheir succession, but the real nature of which we can never know. [Footnote: In a paper, at once popular and profound, entitled 'RecentProgress in the Theory of Vision, ' contained in the volume of lecturesby Helmholtz, published by Longmans, this symbolism of our states ofconsciousness is also dwelt upon. The impressions of sense are themere signs of external things. In this paper Helmholtz contendsstrongly against the view that the consciousness of space is inborn;and he evidently doubts the power of the chick to pick up grains ofcorn without preliminary lessons. On this point, he says, furtherexperiments are needed. Such experiments have been since made by Mr. Spalding, aided, I believe, in some of his observations by theaccomplished and deeply lamented Lady Amberly; and they seem to proveconclusively that the chick does not need a single moment's tuition toenable it to stand, run, govern the muscles of its eyes, and peck. Helmholtz, however, is contending against the notion ofpre-established harmony; and I am not aware of his views as to theorganisation of experiences of race or breed. ] In fact, the wholeprocess of evolution is the manifestation of a Power absolutelyinscrutable to the intellect of man. As little in our day as in thedays of Job can man by searching find this Power out. Consideredfundamentally, then, it is by the operation of an insoluble mysterythat life on earth is evolved, species differentiated, and mindunfolded, from their prepotent elements in the immeasurable past. 

The strength of the doctrine of Evolution consists, not in anexperimental demonstration (for the subject is hardly accessible tothis mode of proof), but in its general harmony with scientificthought. From contrast, moreover, it derives enormous relativecogency. On the one side we have a theory (if it could with anypropriety be so called) derived, as were the theories referred to atthe beginning of this Address, not from the study of nature, but fromthe observation of men--a theory which converts the Power whosegarment is seen in the visible universe into an Artificer, fashionedafter the human model, and acting by broken efforts as man is seen toact. On the other side we have the conception that all we see aroundus, and all we feel within us--the phenomena; physical nature as wellas those of the human mind--have their unsearchable roots in acosmical life, if I dare apply the term, an infinitesimal span ofwhich is offered to the investigation of man. And even this span isonly knowable in part. We can trace the development of a nervoussystem, and correlate with it the parallel phenomena of sensation andthought. We see with undoubting certainty that they go hand in hand. But we try to soar in a vacuum the moment we seek to comprehend theconnection between them. An Archimedean fulcrum is here requiredwhich the human mind cannot command; and the effort to solve theproblem--to borrow a comparison from an illustrious friend of mine--islike that of a man trying to lift himself by his own waistband. Allthat has been said in this discourse is to be taken in connection withthis fundamental truth. 

When' nascent senses' are spoken of, when 'the differentiation of atissue at first vaguely sensitive all over' is spoken of, and whenthese possessions and processes are associated with 'the modificationof an organism by its environment, ' the same parallelism, withoutcontact, or even approach to contact, is implied. Man the object isseparated by an impassable gulf from man the subject. There is nomotor energy in the human intellect to carry it, without logicalrupture, from the one to the other. 

9. 

The doctrine of Evolution derives man, in his totality, from theinteraction of organism and environment through countless ages past. The Human Understanding, for example, --that faculty which Mr. Spencerhas turned so skilfully round upon its own antecedents--is itself aresult of the play between organism and environment through cosmicranges of time. Never, surely, did prescription plead so irresistiblea claim. But then it comes to pass that, over and above hisunderstanding, there are many other things appertaining to man, whoseprescriptive rights are quite as strong as those of the understandingitself. It is a result, for example, of the play of organism andenvironment that sugar is sweet, and that aloes are bitter; that thesmell of henbane differs' from the perfume of a rose. Such facts ofconsciousness (for which, by the way, no adequate reason has ever beenrendered) are quite as old as the understanding; and many other thingscan boast an equally ancient origin. Mr. Spencer at one place refersto that most powerful of passions--the amatory passion--as one which, when it first occurs, is antecedent to all relative experiencewhatever; and we may press its claim as being at least as ancient, andas valid, as that of the understanding itself. Then there are suchthings woven into the texture of man as the feeling of Awe, Reverence, Wonder--and not alone the sexual love just referred to, but the loveof the beautiful, physical, and moral, in Nature, Poetry, and Art. There is also that deep-set feeling, which, since the earliest dawn ofhistory, and probably for ages prior to all history, incorporateditself in the Religious of the world. You, who have escaped fromthese religions into the high-and-dry light of the intellect, mayderide them; but in so doing you deride accidents of form merely, andfail to touch the immovable basis of the religious sentiment in thenature of man. To yield this sentiment reasonable satisfaction is theproblem of problems at the present hour. And grotesque in relation toscientific culture as many of the religions of the world have been andare--dangerous, nay, destructive, to the dearest privileges of freemenas some of them undoubtedly have been, and would, if they could, beagain--it will be wise to recognise them as the forms of a force, mischievous if permitted to intrude on the region of objectiveknowledge, over which it holds no command, but capable of adding, inthe region of poetry and emotion, inward completeness and dignity toman. 

Feeling, I say again, dates from as old an origin and as high a sourceas intelligence, and it equally demands its range of play. The wiseteacher of humanity will recognise the necessity of meeting thisdemand, rather than of resisting it on account of errors andabsurdities of form. What we should resist, at all hazards, is theattempt made in the past, and now repeated, to found upon thiselemental bias of man's nature a system which should exercise despoticsway over his intellect. I have no fear of such a consummation. Science has already to some extent leavened the world; it will leavenit more and more. I should look upon the mild light of sciencebreaking in upon the minds of the youth of Ireland, and strengtheninggradually to the perfect day, as a surer check to any intellectual orspiritual tyranny which may threaten this island, than the laws ofprinces or the swords of emperors. We fought and won our battle evenin the Middle Ages: should we doubt the issue of another conflict withour broken foe?

The impregnable position of science may be described in a few words. We claim, and we shall wrest from theology, the entire domain ofcosmological theory. All schemes and systems which thus infringe uponthe domain of science must, in so far as they do this, submit to itscontrol, and relinquish all thought of controlling it. Actingotherwise proved always disastrous in the past, and it is simplyfatuous to-day. Every system which would escape the fate of anorganism too rigid to adjust itself to its environment, must beplastic to the extent that the growth of knowledge demands. When'this truth has been thoroughly taken in, rigidity will be relaxed, exclusiveness diminished, things now deemed essential will be dropped, and elements now rejected will be assimilated. The lifting of thelife is the essential point; and as long as dogmatism, fanaticism, andintolerance are kept out, various modes of leverage may be employed toraise life to a higher level. 

Science itself not unfrequently derives motive power from anultra-scientific source. Some of its greatest discoveries have beenmade under the stimulus of a non-scientific ideal. This was the caseamong the ancients, and it has been so amongst ourselves. Mayer, Joule, and Colding, whose names are associated with the greatest ofmodern generalisations, were thus influenced. With his usual insight, Lange at one place remarks, that 'it is not always the objectivelycorrect and intelligible that helps man most, or leads most quickly tothe fullest and truest knowledge. As the sliding body upon thebrachystochrone reaches its end sooner than by the straighter road ofthe inclined plane, so, through the swing of the ideal, we oftenarrive at the naked truth more rapidly than by the processes of theunderstanding. ' Whewell speaks of enthusiasm of temper as a hindranceto science; but he means the enthusiasm of weak heads. There is astrong and resolute enthusiasm in which science finds an ally; and itis to the lowering of this fire, rather than to the diminution ofintellectual insight, that the lessening productiveness of men ofscience, in their mature years, is to be ascribed. Mr. Buckle soughtto detach intellectual achievement from moral force. He gravelyerred; for without moral force to whip it into action, the achievementof the intellect would be poor indeed. 

It has been said by its opponents that science divorces itself fromliterature; but the statement, like so many others, arises from lackof knowledge. A glance at the less technical writings of itsleaders--of its Helmholtz, its Huxley, and its Du Bois-Reymond--wouldshow what breadth of literary culture they command. Where amongmodern writers can you find their superiors in clearness and vigour ofliterary style? Science desires not isolation, but freely combineswith every effort towards the bettering of man's estate. Single-handed, and supported, not by outward sympathy, but by inwardforce, it has built at least one great wing of the many-mansioned homewhich man in his totality demands. And if rough walls and protrudingrafter-ends indicate that on one side the edifice is still incomplete, it is only by wise combination of the parts required, with thosealready irrevocably built, that we can hope for completeness. Thereis no necessary incongruity between what has been accomplished andwhat remains to be done. The moral glow of Socrates, which we allfeel by ignition, has in it nothing incompatible with the physics ofAnaxagoras which he so much scorned, but which he would hardly scornto-day. And here I am reminded of one among us, hoary, but stillstrong, whose prophet-voice some thirty years ago, far more than anyother of this age, unlocked whatever of life and nobleness lay latentin its most gifted minds--one fit to stand beside Socrates or theMaccabean Eleazar, and to dare and suffer all that they suffered anddared--fit, as he once said of Fichte, Ito have been the teacher ofthe Stoa, and to have discoursed of Beauty and Virtue in the groves ofAcademe. ' With a capacity to grasp physical principles which hisfriend Goethe did not possess, and which even total lack of exercisehas not been able to reduce to atrophy, it is the world's loss thathe, in the vigour of his years, did not open his mind and sympathiesto science, and make its conclusions a portion of his message tomankind. Marvellously endowed as he was--equally equipped on the sideof the Heart and of the Understanding--he might have done much towardsteaching us how to reconcile the claims of both, and to enable them incoming times to dwell together, in unity of spirit and in the bond ofpeace. 

*****

And now the end is come. With more time, or greater strength andknowledge, what has been here said might have been better said, whileworthy matters, here omitted, might have received fit expression. Butthere would have been no material deviation from the views set forth. As regards myself, they are not the growth of a day; and as regardsyou, I thought you ought to know the environment which, with orwithout your consent, is rapidly surrounding you, and in relation towhich some adjustment on your part may be necessary. A hint ofHamlet's, however, teaches us how the troubles of common life may beended; and it is perfectly possible for you and me to purchaseintellectual peace at the price of intellectual death. The world isnot without refuges of this description; nor is it wanting in personswho seek their shelter, and try to persuade others to do the same. Theunstable and the weak have yielded and will yield to this persuasion, and they to whom repose is sweeter than the truth. But I would exhortyou to refuse the offered shelter, and to scorn the base repose--toaccept, if the choice be forced upon you, commotion before stagnation, the breezy leap of the torrent before the foetid stillness of theswamp. In the course of this Address I have touched on debatablequestions, and led you over what will be deemed dangerous ground--andthis partly with the view of telling you that, as regards thesequestions, science claims unrestricted right of search. It is not tothe point to say that the views of Lucretius and Bruno, of Darwin andSpencer, may be wrong. Here I should agree with you, deeming itindeed certain that these views will undergo modification. But thepoint is, that, whether right or wrong, we claim the right to discussthem. For science, however, no exclusive claim is here made; you arenot urged to erect it into an idol. The inexorable advance of man'sunderstanding in the path of knowledge, and those unquenchable claimsof his moral and emotional nature, which the understanding can neversatisfy, are here equally set forth. The world embraces not only aNewton, but a Shakspeare--not only a Boyle, but a Raphael--not only aKant, but a Beethoven--not only a Darwin, but a Carlyle. Not in eachof these, but in all, is human nature whole. They are not opposed, butsupplementary--not mutually exclusive, but reconcilable. 

And if, unsatisfied with them all, the human mind, with the yearningof a pilgrim for his distant home, will still turn to the Mystery fromwhich it has emerged, seeking so to fashion it as to give unity tothought and faith; so long as this is done, not only withoutintolerance or bigotry of any kind, but with the enlightenedrecognition that ultimate fixity of conception is here unattainable, and that each succeeding age must be held free to fashion the mysteryin accordance with its own needs--then, casting aside all therestrictions of Materialism, I would affirm this to be a field for thenoblest exercise of what, in contrast with the knowing faculties, maybe called the creative faculties of man. Here, however, I touch atheme too great for me to handle, but which will assuredly be handledby the loftiest minds, when you and I, like streaks of morning cloud, shall have melted into the infinite azure of the past. 

********************

X. APOLOGY FOR THE BELFAST ADDRESS. 

1874. 

THE world has been frequently informed of late that I have raised upagainst myself a host of enemies; and considering, with fewexceptions, the deliverances of the Press, and more particularly ofthe religious Press, I am forced to admit that the statement is onlytoo true. I derive some comfort, nevertheless, from the reflection ofDiogenes, transmitted to us by Plutarch, that 'he who would be savedmust have good friends or violent enemies; and that he is best off whopossesses both. ' This 'best' condition, I have reason to believe, ismine. 

Reflecting on the fraction I have read of recent remonstrances, appeals, menaces, and judgments--covering not only the world that nowis, but that which is to come--I have noticed with mournful interesthow trivially men seem to be influenced by what they call theirreligion, and how potently by that 'nature' which it is the allegedprovince of religion to eradicate or subdue. From fair and manlyargument, from the tenderest and holiest sympathy on the part of thosewho desire my eternal good, I pass by many gradations, throughdeliberate unfairness, to a spirit of bitterness, which desires with afervour inexpressible in words my eternal ill. Now, were religion thepotent factor, we might expect a homogeneous utterance from thoseprofessing a common creed, while, if human nature be the really potentfactor, we may expect utterances as heterogeneous as the characters ofmen. As a matter of fact we have the latter; suggesting to my mindthat the common religion, professed and defended by these differentpeople, is merely the accidental conduit through which they pour theirown tempers, lofty or low, courteous or vulgar, mild or ferocious, asthe case may be. Pure abuse, however, as serving no good end, I have, wherever possible, deliberately avoided reading, wishing, indeed, tokeep, not only hatred, malice, and uncharitableness, but even everytrace of irritation, far away from my side of a discussion whichdemands not only good-temper, but largeness, clearness, andmany-sidedness of mind, if it is to guide us to even provisionalsolutions. 

It has been stated, with many variations of note and comment, that inthe Address as subsequently published by Messrs. Longman I haveretracted opinions uttered at Belfast. A Roman Catholic writer isspecially strong upon this point. Startled by the deep chorus ofdissent which my 'dazzling fallacies' have evoked, I am now trying toretreat. This he will by no means tolerate. 'It is too late now toseek to hide from the eyes of mankind one foul blot, one ghastlydeformity. Professor Tyndall has himself told us how and where thisAddress of his was composed. It was written among the glaciers andthe solitudes of the Swiss mountains. It was no hasty, hurried, crudeproduction; its every sentence bore marks of thought and care. 

My critic intends to be severe: he is simply just. In the 'solitudes'to which he refers I worked with deliberation, endeavouring even topurify my intellect by disciplines similar to those enjoined by hisown Church for the sanctification of the soul. I tried, moreover, inmy ponderings to realise not only the lawful, but the expedient; andto permit no fear to act upon my mind, save that of uttering a singleword on which I could not take my stand, either in this or in anyother world. 

Still my time was so brief, the difficulties arising from my isolatedposition were so numerous, and my thought and expression so slow, that, in a literary point of view, I halted, not only behind theideal, but behind the possible. Hence, after the delivery of theAddress, I went over it with the desire, not to revoke its principles, but to improve it verbally, and above all to remove any word whichmight give colour to the notion of 'crudeness, hurry, or haste. '

In connection with the charge of Atheism my critic refers to thePreface to the second issue of the Belfast Address: 'Christian men, ' Ithere say, 'are proved by their writings to have their hours ofweakness and of doubt, as well as their hours of strength and ofconviction; and men like myself share, in their own way, thesevariations of mood and tense. Were the religious moods of many of myassailants the only alternative ones, I do not know how strong theclaims of the doctrine of "Material Atheism" upon my allegiance mightbe. Probably they would be very strong. But, as it is, I havenoticed during years of self-observation that it is not in hours ofclearness and vigour that this doctrine commends itself to my mind;that in the presence of stronger and healthier thought it everdissolves and disappears, as offering no solution of the mystery inwhich we dwell, and of which we form a part. '

With reference to this honest and reasonable utterance my censorexclaims, 'This is a most remarkable passage. Much as we dislikeseasoning polemics with strong words, we assert that this Apology onlytends to affix with links of steel to the name of Professor Tyndall, the dread imputation against which be struggles. '

Here we have a very fair example of subjective religious vigour. Butmy quarrel with such exhibitions is that they do not always representobjective fact. No atheistic reasoning can, I hold, dislodge religionfrom the human heart. Logic cannot deprive us of life, and religionis life to the religious. As an experience of consciousness it isbeyond the assaults of logic. But the religious life is oftenprojected in external forms--I use the word in its widest sense--andthis embodiment of the religious sentiment will have to bear more andmore, as the world become more enlightened, the stress of scientifictests. We must be careful of projecting into external nature thatwhich belongs to ourselves. My critic commits this mistake: he feels, and takes delight in feeling, that I am struggling, and he obviouslyexperiences the most exquisite pleasures of 'the muscular sense' inholding me down. His feelings are as real, as if his imagination ofwhat mine are were equally real. His picture of my 'struggles' is, however, a mere delusion. I do not struggle. I do not fear thecharge of Atheism; nor should I even disavow it, in reference to anydefinition of the Supreme which he, or his order, would be likely toframe. His 'links' and his 'steel' and his 'dread imputations' are, therefore, even more unsubstantial than my 'streaks of morningcloud, ' and they may be permitted to vanish together. 

*****

These minor and more purely personal matters at an end, the weightierallegation remains, that at Belfast I misused my position by quittingthe domain of science, and making an unjustifiable raid into thedomain of theology. This I fail to see. Laying aside abuse, I hopemy accusers will consent to reason with me. Is it not lawful for ascientific man to speculate on the antecedents of the solar system?Did Kant, Laplace, and William Herschel quit their legitimate spheres, when they prolonged the intellectual vision beyond the boundary ofexperience, and propounded the nebular theory? Accepting that theoryas probable, is it not permitted to a scientific man to follow up, inidea, the series of changes associated with the condensation of thenebulae; to picture the successive detachment of planets and moons, and the relation of all of them to the sun? If I look upon our earth, with its orbital revolution and axial rotation, as one small issue ofthe process which made the solar system what it is, will anytheologian deny my right to entertain and express this theoretic view?Time was when a multitude of theologians would have been found to doso--when that archenemy of science which now vaunts its tolerancewould have made a speedy end of the man who might venture to publishany opinion of the kind. But, that time, unless the world is caughtstrangely slumbering, is for ever past. 

As regards inorganic nature, then, we may traverse, without let orhindrance, the whole distance which separates the nebulae from theworlds of to-day. But only a few years ago this now conceded groundof science was theological ground. I could by no means regard this asthe final and sufficient concession of theology; and, at Belfast, Ithought it not only my right but my duty to state that, as regards theorganic world, we must enjoy the freedom which we have already won inregard to the inorganic. I could not discern the shred of atitle-deed which gave any man, or any class of men, the right to openthe door of one of these worlds to the scientific searcher, and toclose the other against him. And I considered it frankest, wisest, and in the long run most conducive to permanent peace, to indicate, without evasion or reserve, the ground that belongs to Science, and towhich she will assuredly make good her claim. 

I have been reminded that an eminent predecessor of mine in thePresidential chair, expressed a totally different view of the Cause ofthings from that enunciated by me. In doing so he transgressed thebounds of science at least as much as I did; but nobody raised anoutcry against him. The freedom he took I claim. And looking at whatI must regard as the extravagances of the religious world; at the veryinadequate and foolish notions concerning this universe which areentertained by the majority of our authorised religious teachers; atthe waste of energy on the part of good men over things unworthy, if Imay say it without discourtesy, of the attention of enlightenedheathens; the fight about the fripperies of Ritualism, and the verbalquibbles of the Athanasian Creed; the forcing on the public view ofPontigny Pilgrimages; the dating of historic epochs from thedefinition of the Immaculate Conception; the proclamation of theDivine Glories of the Sacred Heart--standing in the midst of thesechimeras, which astound all thinking men, it did not appear to meextravagant to claim the public tolerance for an hour and a half, forthe statement of more reasonable views--views more in accordance withthe verities which science has brought to light, and which many wearysouls would, I thought, welcome with gratification and relief. 

But to come to closer quarters. The expression to which the mostviolent exception has been taken is this: 'Abandoning all disguise, the confession I feel bound to make before you is, that I prolong thevision backward across the boundary of the experimental evidence, anddiscern in that Matter which we, in our ignorance, and notwithstandingour professed reverence for its Creator, have hitherto covered withopprobrium, the promise and potency of every form and quality oflife. ' To call it a 'chorus of dissent, ' as my Catholic critic does, is a mild way of describing the storm of opprobrium with which thisstatement has been assailed. But the first blast of passion beingpast, I hope I may again ask my opponents to consent to reason. Firstof all, I am blamed for crossing the boundary of the experimentalevidence. This, I reply, is the habitual action of the scientificmind--at least of that portion of it which applies itself to physicalinvestigation. Our theories of light, heat, magnetism, andelectricity, all imply the crossing of this boundary. My paper on the'Scientific Use of the Imagination, ' and my 'Lectures on Light, 'illustrate this point in the amplest manner; and in the Articleentitled 'Matter and Force' in the present volume I have sought, incidentally, to make clear, that in physics the experientialincessantly leads to the ultra-experiential; that out of experiencethere always grows something finer than mere experience, and that intheir different powers of ideal extension consists, for the most part, the difference between the great and the mediocre investigator. Thekingdom of science, then, cometh not by observation and experimentalone, but is completed by fixing the roots of observation andexperiment in a region inaccessible to both, and in dealing with whichwe are forced to fall back upon the picturing power of the mind. 

Passing the boundary of experience, therefore, does not, in theabstract, constitute a sufficient ground for censure. There must havebeen something in my particular mode of crossing it which provokedthis tremendous 'chorus of dissent. '

Let us calmly reason the point out. I hold the nebular theory as itwas held by Kant, Laplace, and William Herschel, and as it is held bythe best scientific intellects of to-day. According to it, our sunand planets were once diffused through space as an impalpable haze, out of which, by condensation, came the solar system. What caused thehaze to condense? Loss of heat. What rounded the sun and planets?That which rounds a tear--molecular force. For aeons, the immensityof which overwhelms man's conceptions, the earth was unfit to maintainwhat we call life. It is now covered with visible living things. Theyare not formed of matter different from that of the earth around them. They are, on the contrary, bone of its bone, and flesh of its flesh. How were they introduced? Was life implicated in the nebula--as part, it may be, of a vaster and wholly Unfathomable Life; or is it the workof a Being standing outside the nebula, who fashioned it, andvitalised it; but whose own origin and ways are equally past findingout? As far as the eye of science has hitherto ranged through nature, no intrusion of purely creative power into any series of phenomena hasever been observed. The assumption of such a power to account forspecial phenomena, though often made, has always proved a failure. Itis opposed to the very spirit of science; and I therefore assumed theresponsibility of holding up, in contrast with it, that method ofnature which it has been the vocation and triumph of science todisclose, and in the application of which we can alone hope forfurther light. Holding, then, 'that the nebulae and the solar system, life included, stand to each other in the relation of the germ to thefinished organism, I reaffirm here, not arrogantly, or defiantly, butwithout a shade of indistinctness, the position laid down at Belfast. 

Not with the vagueness belonging to the emotions, but with thedefiniteness belonging to the understanding, the scientific man has toput to himself these questions regarding the introduction of life uponthe earth. He will be the last to dogmatise upon the subject, for heknows best that certainty is here for the present unattainable. Hisrefusal of the creative hypothesis is less an assertion of knowledgethan a protest against the assumption of knowledge which must long, ifnot for ever, lie beyond us, and the claim to which is the source ofperpetual confusion upon earth. With a mind open to conviction heasks his opponents to show him an authority for the belief they sostrenuously and so fiercely uphold. They can do no more than point tothe Book of Genesis, or some other portion of the Bible. Profoundlyinteresting, and indeed pathetic, to me are those attempts of theopening mind of man to appease its hunger for a Cause. But the Bookof Genesis has no voice in scientific questions. To the grasp ofgeology, which it resisted for a time, it at length yielded likepotter's clay; its authority as a system of cosmogony beingdiscredited on all hands, by the abandonment of the obvious meaning ofits writer. It is a poem, not a scientific treatise. In the formeraspect it is for ever beautiful: in the latter aspect it has been, andit will continue to be, purely obstructive and hurtful. To knowledgeits value has been negative, leading, in rougher ages than ours, tophysical, and even in our own' free' age to moral, violence. 

*****

No incident connected with the proceedings at Belfast is moreinstructive than the deportment of the Catholic hierarchy of Ireland;a body usually too wise to confer notoriety upon an adversary byimprudently denouncing him. The 'Times, ' to which I owe a great dealon the score of fair play, where so much has been unfair, thinks thatthe Irish Cardinal, Archbishops, and Bishops, in a recent manifesto, adroitly employed a weapon which I, at an unlucky moment, placed intheir hands. The antecedents of their action cause me to regard it ina different light; and a brief reference to these antecedents will, Ithink, illuminate not only their proceedings regarding Belfast, butother doings which have been recently noised abroad. 

Before me lies a document bearing the date of November 1873, which, after appearing for a moment, unaccountably vanished from public view. It is a Memorial addressed, by Seventy of the Students and Ex-studentsof the Catholic University in Ireland, to the Episcopal Board of theUniversity; and it constitutes the plainest and bravest remonstranceever addressed by Irish laymen to their spiritual pastors and masters. It expresses the profoundest dissatisfaction with the curriculummarked out for the students of the University; setting forth theextraordinary fact that the lecture-list for the faculty of Science, published a month before they wrote, did not contain the name of asingle Professor of the Physical or Natural Sciences. 

The memorialists forcibly deprecate this, and dwell upon the necessityof education in science: 'The distinguishing mark of this age is itsardour for science. The natural sciences have, within the last fiftyyears, become the chiefest study in the world; they are in our timepursued with an activity unparalleled in the history of mankind. Scarce a year now passes without some discovery being made in thesesciences which, as with the touch of the magician's wand, shivers toatoms theories formerly deemed unassailable. It is through thephysical and natural sciences that the fiercest assaults are now madeon our religion. No more deadly weapon is used against our faith thanthe facts incontestably proved by modern researches in science. '

Such statements must be the reverse of comfortable to a number ofgentlemen who, trained in the philosophy of Thomas Aquinas, have beenaccustomed to the unquestioning submission of all other sciences totheir divine science of Theology. But this is not all:

One thing seems certain, ' say the memorialists, viz, that if chairsfor the physical and natural sciences be not soon founded in theCatholic University, very many young men will have their faith exposedto dangers which the creation of a school of science in the Universitywould defend them from. For our generation of Irish Catholics arewrithing under the sense of their inferiority in science, and aredetermined that such inferiority shall not long continue; and so, ifscientific training be unattainable at our University, they will seekit at Trinity or at the Queen's Colleges, in not one of which is therea Catholic Professor of Science. '

Those who imagined the Catholic University at Kensington to be due tothe spontaneous recognition, on the part of the Roman hierarchy, ofthe intellectual needs of the age, will derive enlightenment fromthis, and still more from what follows: for the most formidable threatremains. To the picture of Catholic students seceding to Trinity andthe Queen's Colleges, the memorialists add this darkest stroke of all:'They will, in the solitude of their own homes, unaided by any guidingadvice, devour the works of Haeckel, Darwin, Huxley, Tyndall, andLyell; works innocuous if studied under a professor who would pointout the difference between established facts and erroneous inferences, but which are calculated to sap the faith of a solitary student, deprived of a discriminating judgment to which he could refer for asolution of his difficulties. '

In the light of the knowledge given by this courageous memorial, andof similar knowledge otherwise derived, the recent Catholic manifestodid not at all strike me as a chuckle over the mistake of a maladroitadversary, but rather as an evidence of profound uneasiness on thepart of the Cardinal, the Archbishops, and the Bishops who signed it. They acted towards the Students' Memorial, however, with theiraccustomed practical wisdom. As one concession to the spirit which itembodied, the Catholic University at Kensington was brought forth, apparently as the effect of spontaneous inward force, and not ofoutward pressure becoming too formidable to be successfully opposed. 

The memorialists point with bitterness to the fact, that 'the name ofno Irish Catholic is known in connection with the physical and naturalsciences. ' But this, they ought to know, is the complaint of free andcultivated minds wherever a Priesthood exercises dominant power. Precisely the same complaint has been made with respect to theCatholics of Germany. The great national literature and thescientific achievements of that country, in modern times, are almostwholly the work of Protestants. A vanishingly small fraction of itonly is derived from members of the Roman Church, although the numberof these in Germany is at least as great as that of the Protestants. 'The question arises, ' says a writer in an able German periodical, 'what is the cause of a phenomenon so humiliating to the Catholics? Itcannot be referred to want of natural endowment due to climate (forthe Protestants of Southern Germany have contributed powerfully to thecreations of the German intellect), but purely to outwardcircumstances. And these are readily discovered in the pressureexercised for centuries by the Jesuitical system, which has crushedout of Catholics every tendency to free mental productiveness. ' It is, indeed, in Catholic countries that the weight of Ultramontanism hasbeen most severely felt. It is in such countries that the very finestspirits, who have dared, without quitting their faith, to plead forfreedom or reform, have suffered extinction. The extinction, however, was more apparent than real, and Hermes, Hirscher, and Gunther, thoughindividually broken and subdued, prepared the way, in Bavaria, for thepersecuted but unflinching Frohschammer, for Doellinger, and for theremarkable liberal movement of which Doellinger is the head and guide. 

Though moulded for centuries to an obedience unparalleled in any othercountry, except Spain, the Irish intellect is beginning to show signsof independence; demanding a diet more suited to its years than thepabulum of the Middle Ages. As for the recent manifesto in whichPope, Cardinal, Archbishops, and Bishops are united in one grandanathema, its character and fate are shadowed forth by the Vision ofNebuchadnezzar recorded in the Book of Daniel. It resembles theimage, whose form was terrible, but the gold, and silver, and brass, and iron of which rested upon feet of clay. And a stone smote thefeet of clay; and the iron, and the brass, and the silver, and thegold, were broken in pieces together, and became like the chaff of thesummer threshing-floors, and the wind carried them away. 

Monsignor Capel has recently been good enough to proclaim at once thefriendliness of his Church towards true science, and her right todetermine what true science is. Let us dwell for a moment on theproofs of her scientific competence. When Halley's comet appeared in1456 it was regarded as the harbinger of God's vengeance, thedispenser of war, pestilence, and famine, and by order of the Pope thechurch bells of Europe were rung to scare the monster away. Anadditional daily prayer was added to the supplications of thefaithful. The comet in due time disappeared, and the faithful werecomforted by the assurance that, as in previous instances relating toeclipses, droughts, and rains, so also as regards this 'nefarious'comet, victory had been vouchsafed to the Church. 

Both Pythagoras and Copernicus had taught the heliocentricdoctrine--that the earth revolves round the sun. In the exercise ofher right to determine what true science is, the Church, in thePontificate of Paul V, stepped in, and by the mouth of the holyCongregation of the Index, delivered, on March 5, 1616, the followingdecree:

And whereas it hath also come to the knowledge of the said holycongregation that the false Pythagorean doctrine of the mobility ofthe earth and the immobility of the sun, entirely opposed to Holywrit, which is taught by Nicolas Copernicus, is now published abroadand received by many. In order that this opinion may not furtherspread, to the damage of Catholic truth, it is ordered that this andall other books teaching the like doctrine be suspended, and by thisdecree they are all respectively suspended, forbidden, and condemned. 

But why go back to 1456 and 1616? Far be it from me to charge bygonesins upon Monsignor Capel, were it not for the practices he upholdsto-day. The most applauded dogmatist and champion of the Jesuits is, I am informed, Perrone. No less than thirty editions of a work of hishave been scattered abroad for the healing of the nations. Hisnotions of physical astronomy are virtually those of 1456. He teachesboldly that 'God does not rule by universal law... That when Godorders a given planet to stand still He does not detract from any lawpassed by Himself, but orders that planet to move round the sun forsuch and such a time, then to stand still, and then again to move, asHis pleasure may be. ' Jesuitism proscribed Frohschammer forquestioning its favourite dogma, that every human soul was created bya direct supernatural act of God, and for asserting that man, body andsoul, came from his parents. This is the system that now strives foruniversal power; it is from it, as Monsignor Capel graciously informsus, that we are to learn what is allowable in science, and what isnot!

In the face of such facts, which might be multiplied at will, itrequires extraordinary bravery of mind, or a reliance upon publicignorance almost as extraordinary, to make the claims made byMonsignor Capel for his Church. 

Before me is a very remarkable letter addressed in 1875 by theBishop of Montpellier to the Deans and Professors of Faculties ofMontpellier, in which the writer very clearly lays down the claims ofhis Church. He had been startled by an incident occurring in a courseof lectures on Physiology given by a professor, of whose scientificcapacity there was no doubt, but who, it was alleged, rightly orwrongly, had made his course the vehicle of materialism. 'Je ne mesuis point donne, ' says the Bishop, 'la mission que je remplis aumilieu de vous. "Personne, au temoignage de saint Paul, ne s'attribueà soi-même un pareil honneur; il y faut être appelé de Dieu, commeAaron. " Et pourquoi en est-il ainsi? C'est parse que, selon le mêmeApôtre, noun devons titre les ambassadeurs de Dieu; et it n'est pasdans les usages, pas plus qu'il n'est dans la raison et le droit, qu'un envoyé s'accrédite lui-même. Mais, si j'ai recu d'En-Haut unemission; si l'Eglise, au nom de Dieu lui-même, a souscrit me lettresde créance, me siéraitil de manquer aux instructions qu'elle m'adonnées et d'entendre, en un sens différent du sien, le rôle qu'ellem'a confié?

'Or, Messieurs, la sainte Eglise se croit investie du droit absolud'enseigner les hommes; elle se croit dépositaire de la vérité, nonpas de la vérité fragmentaire, incomplète, mêlée de certitude etd'hésitation, mais de la vérité totale, complète, au point de vuereligieux. Bien plus, elle est si sûre de l'infaillibilité que sonFondateur divin lui a communiquée, comme la dot magnifique de leurindissoluble alliance, que, même dans l'ordre naturel, scientifique ouphilosophique, moral ou politique, elle n'admet pas qu'un systèmepuisse être soutenu et adopté par des chrétiens, s'il contredit à desdogmes définis. Elle considère que la négation volontaire etopiniâtre d'un seul point de sa doctrine rend coupable du péchéd'hérésie; et elle pense que toute hérésie formelle, si on ne larejette pas courageusement avant de paraitre devant Dieu, entraineavec soi la perte certaine de la grâce et de l'éternité. '

The Bishop recalls those whom he addresses from the false philosophyof the present to the philosophy of the past, and foresees the triumphof the latter. 'Avant que le dix-neuvième siècle s'achève, la vieillephilosophie scolastique aura repris sa place dans la juste admirationdu monde. Il lui faudra pourtant bien du temps pour guérir les mauxde tout genre, causés par son indigne rivale; et pendant de longuesannées encore, ce nom de philosophie, le plus grand de la languehumaine après celui de religion, sera suspect aux âmes qui sesouviendront de la science impie et materialiste de Locke, deCondillac ou d'Helvétius. L'heure actuelle est aux sciencesnaturelles: c'est maintenant l'instrument de combat contre l'Eglise etcontre toute foi religieuse. Nous ne les redoutons pas. ' Further onthe Bishop warns his readers that everything can be abused. Poetry isgood, but in excess it may injure practical conduct. 'Lesmathématiques sont excellentes: et Bossuet les a louées "comme étantce qui sert le plus à la justesse du raisonnement;" mais si ons'accoutume exclusivement à leur méthode, rien de ce qui appartient àl'ordre moral ne parait plus pouvoir être démontré; et Fénelon a puparler de l'ensorcellement et des attraits diaboliqes de lageometrie. '

The learned Bishop thus finally accentuates the claims of the Church:'Comme le définissait le Pape Léon X, au cinquième concile oecuméniquede Latran, "Le vrai ne peut pas être contraire à lui-même: parconséquent, toute assertion contraire à une vérité de foi révélée estnécessairement et absolument fausse. " Il suit de là que, sans entrerdans l'examen scientifique de telle ou telle question de physiologie, mais par la seule certitude de nos dogmes, nous pouvons juger du sortde telle ou telle hypothèse, qui est une machine de guerreanti-chrétienne plutôt qu'une conquête sérieuse sur les secrets et lesmystères de la nature... C'est un dogme que l'homme a été formé etfaconné des mains de Dieu. Donc il est faux, hérétique, contraire àla dignité du Créateur et offensant pour son chef-d'oeuvre, de direque l'homme constitue la septième espèce des singes... Hérésie encorede dire que le genre humain n'est pas sorti d'un seul couple, et qu'ony peut compter jusqu'à douze races distinctes!'

*****

The course of life upon earth, as far as Science can see, has been oneof amelioration--a steady advance on the whole from the lower to thehigher. The continued effort of animated nature is to improve itscondition and raise itself to a loftier level. In man improvement andamelioration depend largely upon the growth of conscious knowledge, bywhich the errors of ignorance are continually moulted, and truth isorganised. It is the advance of knowledge that has given amaterialistic colour to the philosophy of this age. Materialism istherefore not a thing to be mourned over, but to be honestlyconsidered--accepted if it be wholly true, rejected if it be whollyfalse, wisely sifted and turned to account if it embrace a mixture oftruth and error. Of late years the study of the nervous system, andits relation to thought and feeling, have profoundly occupiedenquiring minds. It is our duty not to shirk--it ought rather to beour privilege to accept--the established results of such enquiries, for here assuredly our ultimate weal depends upon our loyalty to thetruth. Instructed as to the control which the nervous systemexercises over man's moral and intellectual nature, we shall be betterprepared, not only to mend their manifold defects, but also tostrengthen and purify both. Is mind degraded by this recognition ofits dependence? Assuredly not. Matter, on the contrary, is raised tothe level it ought to occupy, and from which timid ignorance wouldremove it. 

But the light is dawning, and it will become stronger as time goes on. Even the Brighton "Church Congress" affords evidence of this. Fromthe manifold confusions of that assemblage my memory has rescued twoitems, which it would fain preserve: the recognition of a relationbetween Health and Religion, and the address of the Rev. Harry Jones. Out of the conflict of vanities his words emerge wholesome and strong, because undrugged by dogma, coming directly from the warm brain of onewho knows what practical truth means, and who has faith in itsvitality and inherent power of propagation. 

I wonder whether he is less effectual in his ministry than his moreembroidered colleagues? It surely behoves our teachers to come tosome definite understanding as to this question of health; to see how, by inattention to it, we are defrauded, negatively and positively:negatively, by the privation of that 'sweetness and light' which isthe natural concomitant of good health; positively, by the insertioninto life of cynicism, ill-temper, and a thousand corroding anxietieswhich good health would dissipate. We fear and scorn 'materialism. 'But he who knew all about it, and could apply his knowledge, mightbecome the preacher of a new gospel. Not, however, through theecstatic moments of the individual does such knowledge come, butthrough the revelations of science, in connection with the history ofmankind. 

Why should the Roman Catholic Church call gluttony a mortal sin? Whyshould fasting occupy a place in the disciplines of religion? What isthe meaning of Luther's advice to the young clergyman who came to him, perplexed with the difficulties of predestination and election, if itbe not that, in virtue of its action upon the brain, when wiselyapplied, there is moral and religious virtue even in a hydro-carbon?To use the old language, food and drink are creatures of God, and havetherefore a spiritual value. Through our neglect of the monitions ofa reasonable materialism we sin and suffer daily. I might here pointto the train of deadly disorders over which science has given modernsociety such control--disclosing the lair of the material enemy, ensuring his destruction, and thus preventing that moral squalor andhopelessness which habitually tread on the heels of epidemics in thecase of the poor. 

Rising to higher spheres, the visions of Swedenborg, and the ecstasyof Plotinus and Porphyry, are phases of that psychical condition, obviously connected with the nervous system and state of health, onwhich is based the Vedic doctrine of the absorption of the individualinto the universal soul. Plotinus taught the devout how to pass intoa condition of ecstasy. Porphyry complains of having been only onceunited to God in eighty-six years, while his master Plotinus had beenso united six times in sixty years. [Footnote: I recommend to thereader's particular attention Dr. Draper's important work entitled, 'History of the Conflict between Religion and Science' (Messrs. H. S. King and Co. )] A friend who knew Wordsworth informs me that the poet, in some of his moods, was accustomed to seize hold of an externalobject to assure himself of his own bodily existence. As states ofconsciousness such phenomena have an undisputed reality, and asubstantial identity; but they are connected with the mostheterogeneous objective conceptions. The subjective experiences aresimilar, because of the similarity of the underlying organisations. 

But for those who wish to look beyond the practical facts, there willalways remain ample room for speculation. Take the argument of theLucretian introduced in the Belfast Address. As far as I am aware, not one of my assailants has attempted to answer it. Some of them, indeed, rejoice over the ability displayed by Bishop Butler in rollingback the difficulty on his opponent; and they even imagine that it isthe Bishop's own argument that is there employed. But the raising ofa new difficulty does not abolish--does not even lessen--the old one, and the argument of the Lucretian remains untouched by anything theBishop has said or can say. 

*****

And here it may be permitted me to add a word to an importantcontroversy now going on: and which turns on the question: Do statesof consciousness enter as links into the chain of antecedence andsequence, which give rise to bodily actions, and to other states ofconsciousness; or are they merely by-products, which are not essentialto the physical processes going on in the brain? Speaking for myself, it is certain that I have no power of imagining states ofconsciousness, interposed between the molecules of the brain, andinfluencing the transference of motion among the molecules. Thethought 'eludes all mental presentation;' and hence the logic seemsof iron strength which claims for the brain an automatic action, uninfluenced by states of consciousness. But it is, I believe, admitted by those who hold the automaton-theory, that states ofconsciousness are produced by the marshalling of the molecules of thebrain: and this production of consciousness by molecular motion is tome quite as inconceivable on mechanical principles as the productionof molecular motion by consciousness. If, therefore, I reject oneresult, I must reject both. I, however, reject neither, and thusstand in the presence of two Incomprehensibles, instead of oneIncomprehensible. While accepting fearlessly the facts of materialismdwelt upon in these pages, I bow my head in the dust before thatmystery of mind, which has hitherto defied its own penetrative power, and which may ultimately resolve itself into a demonstrableimpossibility of self-penetration. 

But the secret is an open one--the practical monitions are plainenough, which declare that on our dealings with matter depend our wealand woe, physical and moral. The state of mind which rebels againstthe recognition of the claims of 'materialism' is not unknown to me. I can remember a time when I regarded my body as a weed, so much morehighly did I prize the conscious strength and pleasure derived frommoral and religious feeling--which, I may add, was mine without theintervention of dogma. The error was not an ignoble one, but this didnot save it from the penalty attached to error. Saner knowledgetaught me that the body is no weed, and that treated as such it wouldinfallibly avenge itself. Am I personally lowered by this change offront? Not so. Give me their health, and there is no spiritualexperience of those earlier years--no resolve of duty, or work ofmercy, no work of self-renouncement, no solemnity of thought, no joyin the life and aspects of nature--that would not still be mine; andthis without the least reference or regard to any purely personalreward or punishment looming in the future. 

And now I have to utter a 'farewell' free from bitterness to all myreaders; thanking my friends for a sympathy more steadfast, I wouldfain believe, if less noisy, than the antipathy of my foes; andcommending to these a passage from Bishop Butler, which they haveeither not read or failed to lay to heart. 'It seems, ' saith theBishop, 'that men would be strangely headstrong and self-willed, anddisposed to exert themselves with an impetuosity which would rendersociety insupportable, and the living in it impracticable, were it notfor some acquired moderation and self-government, some aptitude andreadiness in restraining themselves, and concealing their sense ofthings. '

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XI. THE REV. JAMES MARTINEAU AND THE BELFAST ADDRESS. 

[Footnote: Fortnightly Review. ]

PRIOR to the publication of the Fifth Edition of these 'Fragments' myattention had been directed by several estimable, and indeed eminent, persons, to an essay by the Rev. James Martineau, as demandingserious consideration at my hands. I tried to give the essay theattention claimed for it, and published my views of it as anIntroduction to Part 11. Of the 'Fragments. ' I there referred, andhere again refer with pleasure, to the accord subsisting between Mr. Martineau and myself on certain points of biblical Cosmogony. 'In sofar, ' says he, 'as Church belief is still committed to a givenCosmogony and natural history of man, it lies open to scientificrefutation. ' And again: 'It turns out that with the sun and moon andstars, and in and on the earth, before and after the appearance of ourrace, quite other things have happened than those which the sacredCosmogony recites. ' Once more: 'The whole history of the genesis ofthings Religion must surrender to the Sciences. ' Finally, still moreemphatically: 'In the investigation of the genetic order of things, Theology is an intruder, and must stand aside. ' This expresses, onlyin words of fuller pith, the views which I ventured to enunciate inBelfast. 'The impregnable position of Science, ' I there say, 'may bestated in a few words. We claim, and we shall wrest from Theology, the entire domain of Cosmological theory. ' Thus Theology, so far as itis represented by Mr. Martineau, and Science, so far as I understandit, are in absolute harmony here. 

But Mr. Martineau would have just reason to complain of me, if, bypartial citation, I left my readers under the impression that theagreement between us is complete. At the opening of the eighty-ninthSession of the Manchester New College, London, on October 6, '1874, he, its principal, delivered an Address bearing the title 'Religion asaffected by Modern Materialism;' the references and general tone ofwhich make evident the depth of its author's discontent with myprevious deliverance at Belfast. I find it difficult to grapple withthe exact grounds of this discontent. Indeed, logically considered, the impression left upon my mind by an essay of great aesthetic merit, containing many passages of exceeding beauty, and many sentimentswhich none but the pure in heart could utter as they are uttered here, is vague and unsatisfactory. The author appears at times so brave andliberal, at times so timid and captious, and at times, if I dare sayit, so imperfectly informed, regarding the position he assails. 

At the outset of his Address Mr. Martineau states with somedistinctness his 'sources of religious faith. ' They are two--'thescrutiny of Nature' and 'the interpretation of Sacred Books. ' Itwould have been a theme worthy of his intelligence to have deducedfrom these two sources his religion as it stands. But not anotherword is said about the 'Sacred Books. ' Having swept with the besom ofScience various 'books' contemptuously away, he does not define theSacred residue; much less give us the reasons why he deems themsacred. [Footnote: Mr. Martineau's use of the term 'sacred' isunintentionally misleading. In his later essays we are taught that hedoes not mean to restrict it to the Bible. He does not, however, mention the 'books' beyond those of the Bible to which he would applythe term. 1879. ] His references to 'Nature, ' on the other hand, aremagnificent tirades against Nature, intended, apparently, to show thewholly abominable character of man's antecedents if the theory ofevolution be true. Here also his mood lacks steadiness. Whilejoyfully accepting, at one place, 'the widening space, the deepeningvistas of time, the detected marvels of physiological structure, andthe rapid filling-in of the missing links in the chain of organiclife, ' he falls, at another, into lamentation and mourning over thevery theory which renders 'organic life' 'a chain. ' He claims thelargest liberality for his sect, and avows its contempt for thedangers of possible discovery. But immediately afterwards he damagesthe claim, and ruins all confidence in the avowal. He professessympathy with modern Science, and almost in the same breath he treats, or certainly will be understood to treat, the Atomic Theory, and thedoctrine of the Conservation of Energy, as if they were a kind ofscientific thimble-riggery. 

His ardour, moreover, renders him inaccurate causing him to seediscord between scientific men where nothing but harmony reigns. Inhis celebrated Address to the Congress of German Naturforscher, delivered at Leipzig, three years ago, Du Bois-Reymond speaks thus:'What conceivable connection subsists between definite movements ofdefinite atoms in my brain, on the one hand, and on the other handsuch primordial, indefinable, undeniable, facts as these: I feel painor pleasure; I experience a sweet taste, or smell a rose, or hear anorgan, or see something red ... It is absolutely and for everinconceivable that a number of carbon, hydrogen, nitrogen, and oxygenatoms should be otherwise than indifferent as to their own positionand motion, past, present, or future. It is utterly inconceivable howconsciousness should result from their joint action. '

This language, which was spoken in 1872, Mr. Martineau 'freely'translates, and quotes against me. The act is due to misapprehension. Evidence is at hand to prove that I employed similar language twentyyears ago. It is to be found in the 'Saturday Review' for 1860; buta sufficient illustration of the agreement between my friend DuBois-Reymond and myself, is furnished by the discourse on 'ScientificMaterialism, ' delivered in 1868, then widely circulated, and reprintedhere. The reader who compares the two discourses will see that thesame line of thought is pursued in both, and that perfect agreementreigns between my friend and me. In the very Address he criticises, Mr. Martineau might have seen that precisely the same position ismaintained. A quotation will prove this: 'Thus far, ' I say, 'our wayis clear, but now comes my difficulty. Your atoms are individuallywithout sensation, much more are they without intelligence. May I askyou, then, to try your hand upon this problem? Take your deadhydrogen atoms, your dead oxygen atoms, your dead carbon atoms, yourdead nitrogen atoms, your dead phosphorus atoms, and all the otheratoms, dead as grains of shot, of which the brain is formed. Imaginethem separate and sensationless; observe them running together andforming all imaginable combinations. This, as a purely mechanicalprocess, is seeable by the mind. But can you see, or dream, or in anyway imagine, how out of that mechanical act, and from theseindividually dead atoms, sensation, thought, and emotion are to rise?Are you likely to extract Homer out of the rattling of dice, or theDifferential Calculus out of the clash of billiard balls? ... I canfollow a particle of musk until it reaches the olfactory nerve; I canfollow the waves of sound until their tremors reach the water of thelabyrinth, and set the otoliths and Corti's fibres in motion; I canalso visualise the waves of aether as they cross the eye and hit theretina. Nay, more, I am able to pursue to the central organ themotion thus imparted at the periphery, and to see in idea the verymolecules of the brain thrown into tremors. My insight is not baffledby these physical processes. What baffles and bewilders me is thenotion that from these physical tremors things so utterly incongruouswith them as sensation, thought, and emotion can be derived. ' It isonly a complete misapprehension of our true relationship that couldinduce Mr. Martineau to represent Du Bois-Reymond and myself asopposed to each other. 

'The affluence of illustration, ' writes an able and sympatheticreviewer of this essay, in the 'New York Tribune, ' 'in which Mr. Martineau delights often impairs the distinctness of his statements bydiverting the attention of the reader from the essential points of hisdiscussion to the beauty of his imagery, and thus diminishes theirpower of conviction. 'To the beauties here referred to I bear willingtestimony; but the reviewer is strictly just in his estimate of theireffect upon my critic's logic. The 'affluence of illustration, ' andthe heat, and haze, and haste, generated by its reaction upon Mr. Martineau's own mind, often produce vagueness where precision is theone thing needful--poetic fervour where we require judicial calm; andpractical unfairness where the strictest justice ought to be, and Iwillingly believe is meant to be, observed. 

In one of his nobler passages Mr. Martineau tells us how the pupils ofhis college have been educated hitherto: 'They have been trainedunder the assumptions (1) that the Universe which includes us andfolds us round is the life-dwelling of an Eternal Mind; (2) that theworld of our abode is the scene of a moral government, incipient butnot complete; and (3) that the upper zones of human affection, abovethe clouds of self and passion, take us into the sphere of a DivineCommunion. Into this over-arching scene it is that growing thoughtand enthusiasm have expanded to catch their light and fire. '

Alpine summits seem to kindle above us as we read these glowing words;we see their beauty and feel their life. At the close of one of theessays here printed, [Footnote: 'Scientific Use of the Imagination. ']I thus refer to the 'Communion' which Mr. Martineau calls 'Divine':"Two things, " said Immanuel Kant, "fill me with awe--the starry heavens, and the sense of moral responsibility in man. " And in his hours ofhealth and strength and sanity, when the stroke of action has ceased, and the pause of reflection has set in, the scientific investigatorfinds himself overshadowed by the same awe. Breaking contact with thehampering details of earth, it associates him with a power which givesfulness and tone to his existence, but which he can neither analysenor comprehend. Though 'knowledge' is here disavowed, the 'feelings', of Mr. Martineau and myself are, I think, very much alike. He, nevertheless, censures me--almost denounces me--for referring Religionto the region of Emotion. Surely he is inconsistent here. Theforegoing words refer to an inward hue or temperature, rather than toan external object of thought. When I attempt to give the Power whichI see manifested in the Universe an objective form, personal orotherwise, it slips away from me, declining all intellectualmanipulation. I dare not, save poetically, use the pronoun 'He'regarding it; I dare not call it a 'Mind;' I refuse to call it even a'Cause. ' Its mystery overshadows me; but it remains a mystery, whilethe objective frames which some of my neighbours try to make it fit, seem to me to distort and desecrate it. 

It is otherwise with Mr. Martineau, and hence his discontent. Heprofesses to know where I only claim to feel. He could make hiscontention good against me if, by a process of verification, he wouldtransform his assumptions into 'objective knowledge. ' But he makes noattempt to do so. They remain assumptions from the beginning of hisAddress to its end. And yet he frequently uses the word 'unverified, 'as if it were fatal to the position oh which its incidence falls. 'The scrutiny of Nature' is one of his sources of 'religious faith:'what logical foothold does that scrutiny furnish, on which any one ofthe foregoing three assumptions could be planted? Nature, according tohis picturing, is base and cruel: what is the inference to be drawnregarding its Author? If Nature be 'red in tooth and claw, ' who isresponsible? On a Mindless nature Mr. Martineau pours the fulltorrent of his gorgeous invective; but could the 'assumption' of 'anEternal Mind'--even of a Beneficent Eternal Mind--render the worldobjectively a whit less mean and ugly than it is? Not an iota. It isman's feelings, and not external phenomena, that are influenced by theassumption. It adds not a ray of light nor a strain of music to theobjective sum of things. It does not touch the phenomena of physicalnature--storm, flood, or fire--nor diminish by a pang the bloodycombats of the animal world. But it does add the glow of religiousemotion to the human soul, as represented by Mr. Martineau. Beyondthis I defy him to go; and yet he rashly--it might be saidpetulantly--kicks away the only philosophic foundation on which it ispossible for him to build his religion. 

He twits incidentally the modern scientific interpretation of naturebecause of its want of cheerfulness. Let the new future, ' he says, 'preach its own gospel, and devise, if it can, the means of making thetidings glad. ' This is a common argument: 'If you only knew thecomfort of belief!' My reply is that I choose the nobler part ofEmerson, when, after various disenchantments, he exclaimed, 'I covettruth!' The gladness of true heroism visits the heart of him who isreally competent to say this. Besides, 'gladness' is an emotion, andMr. Martineau theoretically scorns the emotional. I am not, however, acquainted with a writer who draws more largely upon this source, while mistaking it for something objective. 'To reach the Cause, ' hesays, 'there is no need to go into the past, as though being missedhere, He could be found there. But when once He has been apprehendedby the proper organs of divine apprehension, the whole life ofHumanity is recognised as the scene of His agency. ' That Mr. Martineaushould have lived so long, thought so much, and failed to recognisethe entirely subjective character of this creed, is highlyinstructive. His 'proper organs of divine apprehension '--given, wemust assume, to Mr. Martineau and his pupils, but denied to many ofthe greatest intellects and noblest men in this and other ages--lie atthe very core of his emotions. 

In fact, it is when Mr. Martineau is most purely emotional that hescorns the emotions; it is when he is most purely subjective that herejects subjectivity. He pays a just and liberal tribute to thecharacter of John Stuart Mill. But in the light of Mill's philosophy, benevolence, honour, purity, having 'shrunk into mere unaccreditedsubjective susceptibilities, have lost all support from Omniscientapproval, and all presumable accordance with the reality of things. 'If Mr. Martineau had given them any inkling of the process by which herenders the 'subjective susceptibilities' objective, or how he arrivesat an objective ground of 'Omniscient approval, ' gratitude from hispupils would have been his just meed. But, as it is, he leaves themlost in an iridescent cloud of words, after exciting a desire which heis incompetent to appease. 

'We are, ' he says, in another place, 'for ever shaping ourrepresentations of invisible things into forms of definite opinion, and throwing them to the front, as if they were the photographicequivalent of our real faith. It is a delusion which affects us all. Yet somehow the essence of our religion never finds its way into theseframes of theory: as we put them together it slips away, and, if weturn to pursue it, still retreats behind; ever ready to work with thewill, to unbind and sweeten the affections, and bathe the life withreverence, but refusing to be seen, or to pass from a divine hue ofthinking into a human pattern of thought. ' This is very beautiful, andmainly so because the man who utters it obviously brings it all out ofthe treasury of his own heart. But the 'hue' and 'pattern' here sofinely spoken of, the former refusing to pass into the latter, areneither more nor less than that 'emotion, ' on the one hand, and that'objective knowledge, ' on the other, which have drawn this suicidalfire from Mr. Martineau's battery. 

I now come to one of the most serious portions of Mr. Martineau'spamphlet--serious far less on account of its 'personal errors, ' thanof its intrinsic gravity, though its author has thought fit to give ita witty and sarcastic tone. He analyses and criticises 'thematerialist doctrine, which, in our time, is proclaimed with so muchpomp, and resisted with so much passion. "Matter is all I want, " saysthe physicist; "give me its atoms alone, and I will explain theuniverse. "' It is thought, even by Mr. Martineau's intimate friends, that in this pamphlet he is answering me. I must therefore ask thereader to contrast the foregoing travesty with what I really do sayregarding atoms: 'I do not think that he [the materialist] is entitledto say that his molecular groupings and motions _explain_ everything. In reality, they explain nothing. The utmost he can affirm is theassociation of two classes of phenomena, of whose real bond of unionhe is in absolute ignorance. ' [Footnote: Address on 'ScientificMaterialism. '] This is very different from saying, 'Give me its atomsalone, and I will explain the universe. ' Mr. Martineau continues hisdialogue with the physicist: '"Good, " he says; "take as many atoms asyou please. See that they have all that is requisite to Body [ametaphysical B], being homogeneous extended solids. " "That is notenough, " his physicist replies; "it might do for Democritus and themathematicians, but I must have something more. The atoms must notonly be in motion, and of various shapes, but also of as many kinds asthere are chemical elements; for how could I ever get water if I hadonly hydrogen elements to work with?" "So be it, " Mr. Martineauconsents to answer, "only this is a considerable enlargement of yourspecified datum [where, and by whom specified?]--in fact, a conversionof it into several; yet, even at the cost of its monism [put into itby Mr. Martineau], your scheme seems hardly to gain its end; for bywhat manipulation of your resources will you, for example, educeConsciousness?"'

This reads like pleasantry, but it deals with serious things. For thelast seven years the question here proposed by Mr. Martineau, and myanswer to it, have been accessible to all. The question, in my words, is briefly this: 'A man can say, "I feel, I think, I love, " but howdoes consciousness infuse itself into the problem?' And here is myanswer: The passage from the physics of the brain to the correspondingfacts of consciousness is unthinkable. Granted that a definitethought and a definite molecular action in the brain occursimultaneously; we do not possess the intellectual organ, norapparently any rudiment of the organ, which would enable us to pass, by a process of reasoning, from the one to the other. They appeartogether, but we do not know why. Were our minds and senses soexpanded, strengthened, and illuminated, as to enable us to see andfeel the very molecules of the brain; were we capable of following alltheir motions, all their groupings, all their electric discharges, ifsuch there be; and were we intimately acquainted with thecorresponding states of thought and feeling, we should be as far asever from the solution of the problem, "How are these physicalprocesses connected with the facts of consciousness?" The chasmbetween the two classes of phenomena would still remain intellectuallyimpassable. ' [Footnote: Bishop Butler's reply to the Lucretian in the'Belfast Address' is all in the same strain. ]

Compare this with the answer which Mr. Martineau puts into the mouthof his physicist, and with which I am generally credited by Mr. Martineau's readers, both in England and America--'"It [the problem ofconsciousness] does not daunt me at all. Of course you understandthat all along my atoms have been affected by gravitation andpolarity; and now I have only to insist with Fechner on a differenceamong molecules: there are the inorganic, which can change only theirplace, like the particles in an undulation; and there are the organic, which can change their order, as in a globule that turns itself insideout. With an adequate number of these our problem will bemanageable. " "Likely enough, " we may say ["entirely unlikely, " sayI], "seeing how careful you are to provide for all emergencies; andif any hitch should occur in the next step, where you will have topass from mere sentiency to thought and will, you can again look inupon your atoms, and fling among them a handful of Leibnitz's monads, to serve as souls in little, and be ready, in a latent form, with thatVorstellungs-faehigkeit which our picturesque interpreters of natureso much prize. "'

'But surely, ' continues Mr. Martineau, 'you must observe that this"matter" of yours alters its style with every change of service:starting as a beggar with scarce a rag of "property" to cover itsbones, it turns up as a prince when large undertakings are wanted. "Wemust radically change our notions of matter, " says Professor Tyndall;and then, he ventures to believe, it will answer all demands, carrying"the promise and potency of all terrestrial life. " If the measure ofthe required "change in our notions" had been specified, theproposition would have had a real meaning, and been susceptible of atest. It is easy travelling through the stages of such an hypothesis;you deposit at your bank a round sum ere you start, and, drawing on itpiecemeal at every pause, complete your grand tour without a debt. '

The last paragraph of this argument is forcibly and ably stated. Onit I am willing to try conclusions with Mr. Martineau. I may say, inpassing, that I share his contempt for the picturesque interpretationof nature, if accuracy of vision be thereby impaired. But the termVorstellungs-faehigkeit, as used by me, means the power of definitemental presentation, of attaching to words the corresponding objectsof thought, and of seeing these in their proper relations, without theinterior haze and soft penumbral borders which the theologian loves. To this mode of interpreting nature' I shall to the best of my abilitynow adhere. 

Neither of us, I trust, will be afraid or ashamed to begin at thealphabet of this question. Our first effort must be to understandeach other, and this mutual understanding can only be ensured bybeginning low down. Physically speaking, however, we need not gobelow the sea-level. Let us then travel in company to the CaribbeanSea, and halt upon the heated water. What is that sea, and what isthe sun that heats it? Answering for myself, I say that they are bothmatter. I fill a glass with the sea-water and expose it on the deckof the vessel; after some time the liquid has all disappeared, andleft a solid residue of salt in the glass behind. We have mobility, invisibility--apparent annihilation. In virtue of

 The glad and secret aid The sun unto the ocean paid, the water has taken to itself wings and flown off as vapour. From thewhole surface of the Caribbean Sea such vapour is rising: and now wemust follow it--not upon our legs, however, nor in a ship, nor even ina balloon, but by the mind's eye--in other words, by that power ofVorstellung which Mr. Martineau knows so well, and which he so justlyscorns when it indulges in loose practices. 

Compounding, then, the northward motion of the vapour with the earth'saxial rotation, we track our fugitive through the higher atmosphericregions, obliquely across the Atlantic Ocean to Western Europe, and onto our familiar Alps. Here another wonderful metamorphosis occurs. Floating on the cold calm air, and in presence of the cold firmament, the vapour condenses, not only to particles of water, but to particlesof crystalline water. These coalesce to stars of snow, which fallupon the mountains in forms so exquisite that, when first seen, theynever fail to excite rapture. As to beauty, indeed, they put the workof the lapidary to shame, while as to accuracy they render concretethe abstractions of the geometer. Are these crystals 'matter'?Without presuming to dogmatise, I answer for myself in theaffirmative. 

Still, a formative power has obviously here come into play which didnot manifest itself in either the liquid or the vapour. The questionnow is, Was not the power 'potential' in both of them, requiring onlythe proper conditions of temperature to bring it into action? Again Ianswer for myself in the affirmative. I am, however, quite willing todiscuss with Mr. Martineau the alternative hypothesis, that animponderable formative soul unites itself with the substance after itsescape from the liquid state. If he should espouse this hypothesis, then I should demand of him an immediate exercise of thatVorstellungs-faehigkeit, with which, in my efforts to think clearly, Ican never dispense. I should ask, At what moment did the soul comein? Did it enter at once or by degrees; perfect from the first, orgrowing and perfecting itself contemporaneously with its ownhandiwork? I should also ask whether it is localised or diffused?Does it move about as a lonely builder, putting the bits of solidwater in their places as soon as the proper temperature has set in? oris it distributed through the entire mass of the crystal? If thelatter, then the soul has the shape of the crystal; but if the former, then I should enquire after its shape. Has it legs or arms? If not, I would ask it to be made clear to me how a thing without theseappliances can act so perfectly the part of a builder? (I insist ondefinition, and ask unusual questions, if haply I might thereby banishunmeaning words. ) What were the condition and residence of the soulbefore it joined the crystal? What becomes of it when the crystal isdissolved? Why should a particular temperature be needed before itcan exercise its vocation? Finally, is the problem before us in anyway simplified by the assumption of its existence? I think itprobable that, after a full discussion of the question, Mr. Martineauwould agree with me in ascribing the building power displayed in thecrystal to the bits of water themselves. At all events, I shouldcount upon his sympathy so far as to believe that he would considerany one unmannerly who would denounce me for rejecting this notion ofa separate soul, and for holding the snow-crystal to be matter. '

But then what an astonishing addition is here made to the powers ofMatter! Who would have dreamt, without actually seeing its work, thatsuch a power was locked up in a drop of water? All that we needed tomake the action of the liquid intelligible was the assumption of Mr. Martineau's 'homogeneous extended atomic solids, ' smoothly glidingover one another. But had we supposed the water to be nothing morethan this, we should have ignorantly defrauded it of an intrinsicarchitectural power, which the art of man, even when pushed to itsutmost degree of refinement, is incompetent to imitate. I wouldinvite Mr. Martineau to consider how inappropriate his figure of afictitious bank deposit becomes under these circumstances. The'account current' of matter receives nothing at my hands which couldbe honestly kept back from it. If, then, 'Democritus and themathematicians' so defined matter as to exclude the powers here provedto belong to it, they were clearly wrong, and Mr. Martineau, insteadof twitting me with my departure from them, ought rather to applaud mefor correcting them. [Footnote: Definition implies previousexamination of the object defined, and is open to correction ormodification as knowledge of the object increases. Such increasedknowledge has radically changed our conceptions of the luminiferousaether, converting its vibrations from longitudinal into transverse. Such changes also Mr. Martineau's conceptions of matter are doomed toundergo. ]

The reader of my small contributions to the literature which dealswith the overlapping margins of Science and Theology, will havenoticed how frequently I quote Mr. Emerson. I do so mainly because inhim we have a poet and a profoundly religious man, who is really andentirely undaunted by the discoveries of Science, past, present, orprospective. In his case Poetry, with the joy of a bacchanal, takesher graver brother Science by the hand, and cheers him with immortallaughter. By Emerson scientific conceptions are continuallytransmuted into the finer forms and warmer hues of an ideal world. Ourpresent theme is touched upon in the lines--

 The journeying atoms, primordial wholes Firmly draw, firmly drive by their animate poles. 

As regards veracity and insight these few words outweigh, in myestimation, all the formal learning expended by Mr. Martineau in thosedisquisitions on Force, where he treats the physicist as a conjuror, and speaks so wittily of atomic polarity. In fact, without thisnotion of polarity--this 'drawing' and 'driving'--this attraction andrepulsion, we stand as stupidly dumb before the phenomena ofCrystallisation as a Bushman before the phenomena of the Solar System. The genesis and growth of the notion I have endeavoured to make clearin my third Lecture on Light, and in the article on 'Matter and Force'published in this volume. 

Our further course is here foreshadowed. A Sunday or two ago I stoodunder an oak planted by Sir John Moore, the hero of Corunna. On theground near the tree little oaklets were successfully fighting forlife with the surrounding vegetation. The acorns had dropped into thefriendly soil, and this was the result of their interaction. What isthe acorn? what the earth? and what the sun, without whose heat andlight the tree could not become a tree, however rich the soil, andhowever healthy the seed? I answer for myself as before--all'matter. ' And the heat and light which here play so potent a part areacknowledged to be motions of matter. By taking something much lowerdown in the vegetable kingdom than the oak, we might approach muchmore nearly to the case of crystallisation already discussed; but thisis not now necessary. 

If, instead of conceding the sufficiency of matter here, Mr. Martineaushould fly to the hypothesis of a vegetative soul, all the questionsbefore asked in relation to the snow-star become pertinent. I wouldinvite him to go over them one by one, and consider what replies hewill make to them. He may retort by asking me, 'Who infused theprinciple of life into the tree?' I say, in answer, that our presentquestion is not this, but another--not who made the tree, but what isit? Is there anything besides matter in the tree? If so, what, and where? Mr. Martineau may have begun by this time to discernthat it is not 'picturesqueness, ' but cold precision, that myVorstellungs-faehigkeit demands. How, I would ask, is this vegetativesoul to be presented to the mind? where did it flourish before thetree grew? and what will become of it when the tree is sawn intoplanks, or consumed in fire?

Possibly Mr. Martineau may consider the assumption of this soul to beas untenable and as useless as I do. But then if the power to build atree be conceded to pure matter, what an amazing expansion of ournotions of the 'potency of matter' is implied in the concession' Thinkof the acorn, of the earth, and of the solar light and heat--was eversuch necromancy dreamt of as the production of that massive trunk, those swaying boughs and whispering leaves, from the interaction ofthese three factors? In this interaction, moreover, consists what wecall life. It will be seen that I am not in the least insensible tothe wonder of the tree; nay, I should not be surprised if, in thepresence of this wonder, I feel more perplexed and overwhelmed thanMr. Martineau himself. 

Consider it for a moment. There is an experiment, first made byWheatstone, where the music of a piano is transferred from itssound-board, through a thin wooden rod, across several silent rooms insuccession, and poured out at a distance from the instrument. Thestrings of the piano vibrate, not singly, but ten at a time. Everystring subdivides, yielding not one note, but a dozen. All thesevibrations and subvibrations are crowded together into a bit of dealnot more than a quarter of a square inch in section. Yet no note islost. Each vibration asserts its individual rights; and all are, atlast, shaken forth into the air by a second sound-board, against whichthe distant end of the rod presses. Thought ends in amazement when itseeks to realise the motions of that rod as the music flows throughit. I turn to my tree and observe its roots, its trunk, its branches, and its leaves. As the rod conveys the music, and yields it up to thedistant air, so does the trunk convey the matter and the motion--theshocks and pulses and other vital actions--which eventually emerge inthe umbrageous foliage of the tree. I went some time ago through thegreenhouse of a friend. He had ferns from Ceylon, the branches ofwhich were in some cases not much thicker than an ordinary pin--hard, smooth, and cylindrical--often leafless for a foot or more. But atthe end of every one of them the unsightly twig unlocked the exuberantbeauty hidden within it, and broke forth into a mass of fronds, almostlarge enough to fill the arms. We stand here upon a higher level ofthe wonderful: we are conscious of a music subtler than that of thepiano, passing unheard through these tiny boughs, and issuing in whatMr. Martineau would opulently call the 'clustered magnificence' of theleaves. Does it lessen my amazement to know that every cluster, andevery leaf--their form and texture--lie, like the music in the rod, inthe molecular structure of these apparently insignificant stems? Notso. Mr. Martineau weeps for' the beauty of the flower fading into anecessity. ' I care not whether it comes to me through necessity orthrough freedom, my delight in it is all the same. I see what he seeswith a wonder superadded. To me, as to him, not even Solomon in allhis glory was arrayed like one of these. 

I have spoken above as if the assumption of a soul would save Mr. Martineau from the inconsistency of crediting pure matter with theastonishing building power displayed in crystals and trees. This, however, would not be the necessary result; for it would remain to beproved that the soul assumed is not itself matter. When a boy Ilearnt from Dr. Watts that the souls of conscious brutes are merematter. And the man who would claim for matter the human soul itself, would find himself in very orthodox company. 'All that is erected, 'says Fauste, a famous French bishop of the fifth century, 'is matter. The soul occupies a place; it is enclosed in a body; it quits the bodyat death, and returns to it at the resurrection, as in the case ofLazarus; the distinction between Hell and Heaven, between eternalpleasures and eternal pains, proves that, even after death, soulsoccupy a place and are corporeal. God only is incorporeal. 'Tertullian, moreover, was quite a physicist in the definiteness of hisconceptions regarding the soul. 'The materiality of the soul, ' hesays, 'is evident from the evangelists. A human soul is thereexpressly pictured as suffering in hell; it is placed in the middle ofa flame, its tongue feels a cruel agony, and it implores a drop ofwater at the hands of a happier soul. Wanting materiality, ' addsTertullian, 'all this would be without meaning. ' [Footnote: Theforegoing extracts, which M. Alglave recently brought to light for thebenefit of the Bishop of Orleans, are taken from the sixth Lecture ofthe 'Cours d'Histoire Moderns' of that most orthodox of statesmen, M. Guizot. 'I could multiply, ' continues M. Guizot, 'these citations toinfinity, and they prove that in the first centuries of our era themateriality of the soul was an opinion not only permitted, butdominant. ' Dr. Moriarty, and the synod which he recently addressed, obviously forget their own antecedents. Their boasted succession fromthe early Church renders them the direct offspring of a 'materialism'more 'brutal' than any ever enunciated by me. ]

I have glanced at inorganic nature--at the sea, and the sun, and thevapour, and the snow-flake, and at organic nature as represented bythe fern and the oak. That same sun which warmed the water andliberated the vapour, exerts a subtler power on the nutriment of thetree. It takes hold of matter wholly unfit for the purposes ofnutrition, separates its nutritive from its non-nutritive portions, gives, the former to the vegetable, and carries the others away. Planted in the earth, bathed by the air, and tended by the sun, thetree is traversed by its sap, the cells are formed, the woody fibre isspun, and the whole is woven to a texture wonderful even to the nakedeye, but a million-fold more so to microscopic vision. Doesconsciousness mix in any way with these processes? No man can tell. Our only ground for a negative conclusion is the absence of thoseoutward manifestations from which feeling is usually inferred. Buteven these are not entirely absent. In the greenhouses of Kew we maysee that a leaf can close, in response to a proper stimulus, aspromptly as the human fingers themselves; and while there Dr. Hookerwill tell us of the wondrous fly-catching and fly-devouring power ofthe Dionaea. No man can say that the feelings of the animal are notrepresented by a drowsier consciousness in the vegetable world. Atall events, no line has ever been drawn between the conscious and theunconscious; for the vegetable shades into the animal by such finegradations, that is impossible to say where the one ends and the otherbegins. 

In all such enquiries we are necessarily limited by our own powers: weobserve what our senses, armed with the aids furnished by Science, enable us to observe; nothing more. The evidences as to consciousnessin the vegetable world depend wholly upon our capacity to observe andweigh them. Alter the capacity, and the evidence would alter too. Would that which to us is a total absence of any manifestation ofconsciousness be the same to a being with our capacities indefinitelymultiplied? To such a being I can imagine not only the vegetable, butthe mineral world, responsive to the proper irritants, the responsediffering only in degree from those exaggerated manifestations, which, in virtue of their magnitude, appeal to our weak powers ofobservation. 

Our conclusion, however, must be based, not on powers that we imagine, but upon those that we possess. What do they reveal? As the earthand atmosphere offer themselves as the nutriment of the vegetableworld, so does the latter, which contains no constituent not found ininorganic nature, offer itself to the animal world. Mixed withcertain inorganic substances--water, for example--the vegetableconstitutes, in the long run, the sole sustenance of the animal. Animals may be divided into two classes, the first of which canutilise the vegetable world immediately, having chemical forces strongenough to cope with its most refractory parts; the second class usethe vegetable world mediately; that is to say, after its finerportions have been extracted and stored up by the first. But inneither class have we an atom newly created. The animal world is, soto say, a distillation through the vegetable world from inorganicnature. 

From this point of view all three worlds would constitute a unity, inwhich I picture life as immanent everywhere. Nor am I anxious to shutout the idea that the life here spoken of, may be but a subordinatepart and function of a Higher Life, as the living moving blood issubordinate to the living man. I resist no such idea as long as it isnot dogmatically imposed. Left for the human mind freely to operateupon, the idea has ethical vitality; but, stiffened into a dogma, theinner force disappears, and the outward yoke of a usurping hierarchytakes its place. 

The problem before us is, at all events, capable of definitestatement. We have on the one hand strong grounds for concluding thatthe earth was once a molten mass. We now find it not only swathed byan atmosphere, and covered by a sea, but also crowded with livingthings. The question is, How were they introduced? Certainty may beas unattainable here as Bishop Butler held it to be in matters ofreligion; but in the contemplation of probabilities the thoughtfulmind is forced to take a side. The conclusion of Science, whichrecognises unbroken causal connection between the past and thepresent, would undoubtedly be that the molten earth contained withinit elements of life, which grouped themselves into their present formsas the planet cooled. The difficulty and reluctance encountered bythis conception, arise solely from the fact that the theologicconception obtained a prior footing in the human mind. Did the latterdepend upon reasoning alone, it could not hold its ground for an houragainst its rival. But it is warmed into life and strength byassociated hopes and fears--and not only by these, which are more orless mean, but by that loftiness of thought and feeling which liftsits possessor above the atmosphere of self, and which the theologicidea, in its nobler forms, has engendered in noble minds. 

Were not man's origin implicated, we should accept without a murmurthe derivation of animal and vegetable life from what we callinorganic nature. The conclusion of pure intellect points this wayand no other. But the purity is troubled by our interests in thislife, and by our hopes and fears regarding the life to come. Reasonis traversed by the emotions, anger rising in the weaker heads to theheight of suggesting that the suppression of the enquirer by the armof the law would be an act agreeable to God, and serviceable to man. But this foolishness is more than neutralised by the sympathy of thewise; and in England at least, so long as the courtesy which befits anearnest theme is adhered to, such sympathy is ever ready for an honestman. None of us here need shrink from saying all that he has a rightto say. We ought, however, to remember that it is not only a band ofJesuits, weaving their schemes of intellectual slavery, under theinnocent guise 'of education, ' that we are opposing. Our foes are tosome extent of our own household, including not only the ignorant andthe passionate, but a minority of minds of high calibre and culture, lovers of freedom moreover, who, though its objective bull be riddledby logic, still find the ethic life of their religion unimpaired. Butwhile such considerations ought to influence the form of our argument, and prevent it from ever slipping out of the region of courtesy intothat of scorn or abuse, its substance, I think, ought to be maintainedand presented in unmitigated strength. 

In the year 1855 the chair of philosophy in the University of Munichhappened to be filled by a Catholic priest of great criticalpenetration, great learning, and great courage, who had borne thebrunt of battle long before Doellinger. His Jesuit colleagues, heknew, inculcated the belief that every human soul is sent into theworld from God by a separate and supernatural act of creation. In awork entitled the 'Origin of the Human Soul, ' Professor Frohschammer, the philosopher here alluded to, was hardy enough to question thisdoctrine, and to affirm that man, body and soul, comes from hisparents, the act of creation being, therefore, mediate and secondaryonly. The Jesuits keep a sharp look out on all temerities of thiskind; and their organ, the 'Civilità Cattolica, ' immediately pouncedupon Frohschammer. His book was branded as 'pestilent, ' placed in theIndex, and stamped with the condemnation of the Church. [Footnote:King Maximilian II. Brought Liebig to Munich, he helped Helmholtz inhis researches, and loved to liberate and foster science. But throughhis liberal concession of power to the Jesuits in the schools, he didfar more damage to the intellectual freedom of his country than hissuperstitious predecessor Ludwig I. Priding himself on being a GermanPrince, Ludwig would not tolerate the interference of the Roman partywith the political affairs of Bavaria. ] The Jesuit notion does noterr on the score of indefiniteness. According to it, the Power whomGoethe does not dare to name, and whom Gassendi and Clerk Maxwellpresent to us under the guise of a 'Manufacturer' of atoms, turns outannually, for England and Wales alone, a quarter of a million of newsouls. Taken in connection with the dictum of Mr. Carlyle, that thisannual increment to our population are 'mostly fools, ' but littleprofit to the human heart seems derivable from this mode of regardingthe Divine operations. 

But if the Jesuit notion be rejected, what are we to accept?Physiologists say that every human being comes from an egg not morethan the 1/120th of an inch in diameter. Is this egg matter? I holdit to be so, as much as the seed of a fern or of an oak. Nine monthsgo to the making of it into a man. Are the additions made during thisperiod of gestation drawn from matter? I think so undoubtedly. Ifthere be anything besides matter in the egg, or in the infantsubsequently slumbering in the womb, what is it? The questionsalready asked with reference to the stars of snow may be hererepeated. Mr. Martineau will complain that I am disenchanting thebabe of its wonder; but is this the case? I figure it growing in thewomb, woven by a something not itself, without conscious participationon the part of either father or mother, and appearing in due time aliving miracle, with all its organs and all their implications. Consider the work accomplished during these nine months in forming theeye alone--with its lens, and its humours, and its miraculous retinabehind. Consider the ear with its tympanum, cochlea, and Corti'sorgan--an instrument of three thousand strings, built adjacent to thebrain, and employed by it to sift, separate, and interpret, antecedentto all consciousness, the sonorous tremors of the external world. Allthis has been accomplished, not only without man's contrivance, butwithout his knowledge, the secret of his own organisation having beenwithheld from him since his birth in the immeasurable past, untilthese latter days. Matter I define as that mysterious thing by whichall this is accomplished. How it came to have this power is aquestion on which I never ventured an opinion. If, then, Matterstarts as 'a beggar, ' it is, in my view, because the Jacobs oftheology have deprived it of its birthright. Mr. Martineau need fearno disenchantment. Theories of evolution go but a short way towardsthe explanation of this mystery; the Ages, let us hope, will at lengthgive us a Poet competent to deal with it aright. 

There are men, and they include amongst them some of the best of therace of man, upon whose minds this mystery falls without producingeither warmth or colour. The 'dry light' of the intellect sufficesfor them, and they live their noble lives untouched by a desire togive the mystery shape or expression. There are, on the other hand, men whose minds are warmed and coloured by its presence, and who, under its stimulus, attain to moral heights which have never beenovertopped. Different spiritual climates are necessary for thehealthy existence of these two classes of men; and different climatesmust be accorded them. The history of humanity, however, proves theexperience of the second class to illustrate the most pervading need. The world will have religion of some kind, even though it should flyfor it to the intellectual whoredom of 'spiritualism. ' What is reallywanted is the lifting power of an ideal element in human life. Butthe free play of this power must be preceded by its release from thepractical materialism of the present, as well as from the tornswaddling bands of the past. It is now in danger of being stupefied bythe one, or strangled by the other. I look, however, forward to atime when the strength, insight, and elevation which now visit us inmere hints and glimpses, during moments 'of clearness and vigour, 'shall be the stable and permanent possession of purer and mightierminds than ours--purer and mightier, partly because of their deeperknowledge of matter and their more faithful conformity to its laws. 

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XII. FERMENTATION, & ITS BEARINGS ON SURGERY & MEDICINE. 

[Footnote: A Discourse delivered before the Glasgow Science LecturesAssociation, October 19, 1876. ]

ONE of the most remarkable characteristics of the age in which welive, is its desire and tendency to connect itself organically withpreceding ages--to ascertain how the state of things that now is cameto be what it is. And the more earnestly and profoundly this problemis studied, the more clearly comes into view the vast and varied debtwhich the world of to-day owes to that fore-world, in which man byskill, valour, and well-directed strength first replenished andsubdued the earth. Our prehistoric fathers may have been savages, butthey were clever and observant ones. They founded agriculture by thediscovery and development of seeds whose origin is now unknown. Theytamed and harnessed their animal antagonists, and sent them down to usas ministers, instead of rivals in the fight for life. Later on, whenthe claims of luxury added themselves to those of necessity, we findthe same spirit of invention at work. We have no historic account ofthe first brewer, but we glean from history that his art waspractised, and its produce relished, more than two thousand years ago. Theophrastus, who was born nearly four hundred years before Christ, described beer as the wine of barley. It is extremely difficult topreserve beer in a hot country, still, Egypt was the land in which itwas first brewed, the desire of man to quench his thirst with thisexhilarating beverage overcoming all the obstacles which a hot climatethrew in the way of its manufacture. 

Our remote ancestors had also learned by experience that wine makethglad the heart of man. Noah, we are informed, planted a vineyard, drank of the wine, and experienced the consequences. But, though wineand beer possess so old a history, a very few years ago no man knewthe secret of their formation. Indeed, it might be said that untilthe present year no thorough and scientific account was ever given ofthe agencies which come into play in the manufacture of beer, of theconditions necessary to its health, and of the maladies andvicissitudes to which it is subject. Hitherto the art and practice ofthe brewer have resembled those of the physician, both being foundedon empirical observation. By this is meant the observation of facts, apart from the principles which explain them, and which give the mindan intelligent mastery over them. The brewer learnt from longexperience the conditions, not the reasons, of success. But he had tocontend, and has still to contend, against unexplained perplexities. Over and over again his care has been rendered nugatory; his beer hasfallen into acidity or rottenness, and disastrous losses have beensustained, of which he has been unable to assign the cause. It is thehidden enemies against which the physician and the brewer havehitherto contended, that recent researches are dragging into the lightof day, thus preparing the way for their final extermination. 

*****

Let us glance for a moment at the outward and visible signs offermentation. A few weeks ago I paid a visit to a private still in aSwiss chalet; and this is what I saw. In the peasant's bedroom was acask with a very large bunghole carefully closed. The cask containedcherries which had lain in it for fourteen days. It was not entirelyfilled with the fruit, an air-space being left above the cherries whenthey were put in. I had the bung removed, and a small lamp dippedinto this space. Its flame was instantly extinguished. The oxygen ofthe air had entirely disappeared, its place being taken by carbonicacid gas. [Footnote: The gas which is exhaled from the lungs after theoxygen of the air has done its duty in purifying the blood, the samealso which effervesces from soda water and champagne. ] I tasted thecherries: they were very sour, though when put into the cask they weresweet. The cherries and the liquid associated with them were thenplaced in a copper boiler, to which a copper head was closely fitted. From the head proceeded a copper tube which passed straight through avessel of cold water, and issued at the other side. Under the openend of the tube was placed a bottle to receive the spirit distilled. The flame of small wood-splinters being applied to the boiler, after atime vapour rose into the head, passed through the tube, was condensedby the cold of the water, and fell in a liquid fillet into the bottle. On being tasted, it proved to be that fiery and intoxicating spiritknown in commerce as Kirsch or Kirschwasser. 

The cherries, it should be remembered, were left to themselves, noferment of any kind being added to them. In this respect what hasbeen said of the cherry applies also to the grape. At the vintage thefruit of the vine is placed in proper vessels, and abandoned to itsown action. It ferments, producing carbonic acid; its sweetnessdisappears, and at the end of a certain time the unintoxicatinggrape-juice is converted into intoxicating wine. Here, as in the caseof the cherries, the fermentation is spontaneous--in what sensespontaneous will appear more clearly by-and-by. 

It is needless for me to tell a Glasgow audience that the beer-brewerdoes not set to work in this way. In the first place the brewer dealsnot with the juice of fruits, but with the juice of barley. Thebarley having been steeped for a sufficient time in water, it isdrained and subjected to a temperature sufficient to cause the moistgrain to germinate; after which, it is completely dried upon a kiln. It then receives the name of malt. The malt is crisp to the teeth, and decidedly sweeter to the taste than the original barley. It isground, mashed up in warm water, then boiled with hops until all thesoluble portions have been extracted; the infusion thus produced beingcalled the wort. This is drawn off, and cooled as rapidly aspossible; then, instead of abandoning the infusion, as the wine-makerdoes, to its own action, the brewer mixes yeast with his wort, andplaces it in vessels each with only one aperture open to the air. Soonafter the addition of the yeast, a brownish froth, which is really newyeast, issues from the aperture, and falls like a cataract intotroughs prepared to receive it. This frothing and foaming of the wortis a proof that the fermentation is active. 

Whence comes the yeast which issues so copiously from the fermentingtub? What is this yeast, and how did the brewer become possessed ofit? Examine its quantity before and after fermentation. The brewerintroduces, say 10 cwts. Of yeast; he collects 40, or it may be 50, cwts. The yeast has, therefore, augmented from four to five foldduring the fermentation. Shall we conclude that this additional yeasthas been spontaneously generated by the wort? Are we not ratherreminded of that seed which fell into good ground, and brought forthfruit, some thirty fold, some sixty fold, some an hundred fold? Onexamination, this notion of organic growth turns out to be more than amere surmise. In the year 1680, when the microscope was still in itsinfancy, Leeuwenhoek turned the instrument upon this substance, andfound it composed of minute globules suspended in a liquid. Thusknowledge rested until 1835, when Cagniard de la Tour in France, andSchwann in Germany, independently, but animated by it common thought, turned microscopes of improved definition and heightened powers uponyeast, and found it budding and sprouting before their eyes. Theaugmentation of the yeast alluded to above was thus proved to arisefrom the growth of a minute plant now called Torula (or Saccharomyces)Cerevisiae. Spontaneous generation is therefore out of the question. The brewer deliberately sows the yeast-plant, which grows andmultiplies in the wort as its proper soil. This discovery marks anepoch in the history of fermentation. 

But where did the brewer find his yeast? The reply to this questionis similar to that which must be given if it were asked where thebrewer found his barley. He has received the seeds of both of themfrom preceding generations. Could we connect without solution ofcontinuity the present with the past, we should probably be able totrace back the yeast employed by my friend Sir Fowell Buxton to-day tothat employed by some Egyptian brewer two thousand years ago. But youmay urge that there must have been a time when the first yeast-cellwas generated. Granted--exactly as there was a time when the firstbarley-corn was generated. Let not the delusion lay hold of you thata living thing is easily generated because it is small. Both theyeast-plant and the barley-plant lose themselves in the dim twilightof antiquity, and in this our day there is no more proof of thespontaneous generation of the one, than there is of the spontaneousgeneration of the other. 

I stated a moment ago that the fermentation of grape-juice wasspontaneous; but I was careful to add, in what sense spontaneous willappear more clearly by-and-by. ' Now this is the sense meant. Thewine-maker does not, like the brewer and distiller, deliberatelyintroduce either yeast; or any equivalent of yeast, into his vats; hedoes not consciously sow in them any plant, or the germ of any plant;indeed, he has been hitherto in ignorance whether plants or germs ofany kind have had anything to do with his operations. Still, when thefermented grape-juice is examined, the living Torula concerned inalcoholic fermentation never fails to make its appearance. How isthis? If no living germ has been introduced into the wine-vat, whencecomes the life so invariably developed there?

You may be disposed to reply, with Turpin and others, that in virtueof its own inherent powers, the grape-juice when brought into contactwith the vivifying atmospheric oxygen, runs spontaneously and of itsown accord into these low forms of life. I have not the slightestobjection to this explanation, provided proper evidence can be adducedin support of it. But the evidence adduced in its favour, as far as Iam acquainted with it, snaps asunder under the strain of scientificcriticism. It is, as far as I can see, the evidence of men, whohowever keen and clever as observers, are not rigidly trainedexperimenters. These alone are aware of the precautions necessary ininvestigations of this delicate kind. In reference, then, to the lifeof the wine-vat, what is the decision of experiment when carried outby competent men? Let a quantity of the clear, filtered 'must' of thegrape be so boiled as to destroy such germs as it may have contractedfrom the air or otherwise. In contact with germless air theuncontaminated must never ferments. All the materials for spontaneousgeneration are there, but so long as there is no seed sown, there isno life developed, and no sign of that fermentation which is theconcomitant of life. Nor need you resort to a boiled liquid. Thegrape is sealed by its own skin against contamination from without. Byan ingenious device Pasteur has extracted from the interior of thegrape its pure juice, and proved that in contact with pure air itnever acquires the power to ferment itself, nor to producefermentation in other liquids. [Footnote: The liquids of the healthyanimal body are also sealed from external contamination. Pure blood, for example, drawn with due precautions from the veins, will neverferment or putrefy in contact with pure air. ] It is not, therefore, in the interior of the grape that the origin of the life observed inthe vat is to be sought. 

What then is its true origin? This is Pasteur's answer, which hiswell-proved accuracy renders worthy of all confidence. At the time ofthe vintage microscopic particles are observed adherent, both to theouter surface of the grape and of the twigs which support the grape. Brush these particles into a capsule of pure water. It is renderedturbid by the dust. Examined by a microscope, some of these minuteparticles are seen to present the appearance of organised--cells. Instead of receiving them in water, let them be brushed into the pureinert juice of the grape. Forty-eight hours after this is done, ourfamiliar Torula is observed budding and sprouting, the growth of theplant being accompanied by all the other signs of active fermentation. What is the inference to be drawn from this experiment? Obviouslythat the particles adherent to the external surface of the grapeinclude the germs of that life which, after they have been sown in thejuice, appears in such profusion. Wine is sometimes objected to onthe ground that fermentation is 'artificial;' but we notice here theresponsibility of nature. The ferment of the grape clings like aparasite to the surface of the grape; and the art of the wine-makerfrom time immemorial has consisted in bringing--and it may be added, ignorantly bringing--two things thus closely associated by nature intoactual contact with each other. For thousands of years, what has beendone consciously by the brewer, has been done unconsciously by thewine-grower. The one has sown his leaven just as much as the other. 

Nor is it necessary to impregnate the beer-wort with yeast to provokefermentation. Abandoned to the contact of our common air, it sooneror later ferments; but the chances are that the produce of thatfermentation, instead of being agreeable, would be disgusting to thetaste. By a rare accident we might get the true alcoholicfermentation, but the odds against obtaining it would be enormous. Pure air acting upon a lifeless liquid will never provokefermentation; but our ordinary air is the vehicle of numberless germswhich act as ferments when they fall into appropriate infusions. Someof them produce acidity, some putrefaction. The germs of ouryeast-plant are also in the air; but so sparingly distributed that aninfusion like beer-wort, exposed to the air, is almost sure to betaken possession of by foreign organisms. In fact, the maladies ofbeer are wholly due to the admixture of these objectionable ferments, whose forms and modes of nutrition differ materially from those of thetrue leaven. 

Working in an atmosphere charged with the germs of these organisms, you can understand how easy it is to fall into error in studying theaction of any one of them. Indeed it is only the most accomplishedexperimenter, who, moreover, avails himself of every means ofchecking his conclusions, that can walk without tripping through thisland of pitfalls. Such a man the French chemist Pasteur has hithertoproved himself to be. He has taught us how to separate the commingledferments of our air, and to study their pure individual action. Guidedby him, let us fix our attention more particularly upon the growth andaction of the true yeast-plant under different conditions. Let it besown in a fermentable liquid, which is supplied with plenty of pureair. The plant will flourish in the aerated infusion, and producelarge quantities of carbonic acid gas--a compound, as you know, ofcarbon and oxygen. The oxygen thus consumed by the plant is the freeoxygen of the air, which we suppose to be abundantly supplied to theliquid. The action is so far similar to the respiration of animals, which inspire oxygen and expire carbonic acid. If we examine theliquid even when the vigour of the plant has reached its maximum, wehardly find in it a trace of alcohol. The yeast has grown andflourished, but it has almost ceased to act as a ferment. And couldevery individual yeast-cell seize, without any impediment, free oxygenfrom the surrounding liquid, it is certain that it would cease to actas a ferment altogether. 

What, then, are the conditions under which the yeast-plant must beplaced so that it may display its characteristic quality? Reflectionon the facts already referred to suggests a reply, and rigidexperiment confirms the suggestion. Consider the Alpine cherries intheir closed vessel. Consider the beer in its barrel, with a singlesmall aperture open to the air, through which it is observed not toimbibe oxygen, but to pour forth carbonic acid. Whence come thevolumes of oxygen necessary to the production of this latter gas? Thesmall quantity of atmospheric air dissolved in the wort and overlyingit would be totally incompetent to supply the necessary oxygen. In noother way can the yeast-plant obtain the gas necessary for itsrespiration than by wrenching it from surrounding substances in whichthe oxygen exists, not free, but in a state of combination. Itdecomposes the sugar of the solution in which it grows, produces heat, breathes forth carbonic acid gas, and one of the liquid products ofthe decomposition is our familiar alcohol. The act of fermentation, then, is a result of the effort of the little plant to maintain itsrespiration by means of combined oxygen, when its supply of freeoxygen is cut off. As defined by Pasteur, fermentation is lifewithout air. 

But here the knowledge of that thorough investigator comes to our aidto warn us against errors which have 'been committed over and overagain. It is not all yeast-cells that can thus live without air andprovoke fermentation. They must be young cells which have caughttheir vegetative vigour from contact with free oxygen. But oncepossessed of this vigour the yeast may be transplanted into asaccharine infusion absolutely purged of air, where it will continueto live at the expense of the oxygen, carbon, and other constituentsof the infusion. Under these new conditions its life, as a plant, will be by no means so vigorous as when it had a supply of freeoxygen, but its action as a ferment will be indefinitely greater. 

Does the yeast-plant stand alone in its power of provoking alcoholicfermentation? It would be singular if amid the multitude of lowvegetable forms no other could be found capable of acting in a similarway. And here again we have occasion to marvel at that sagacity ofobservation among the ancients to which we owe so vast a debt. Notonly did they discover the alcoholic ferment of yeast, but they had toexercise a wise selection in picking it out from others, and giving itspecial prominence. Place an old boot in a moist place, or exposecommon paste or a pot of jam to the air; it soon becomes coated with ablue-green mould, which is nothing else than the fructification of alittle plant called Penicillium glaucum. Do not imagine that themould has sprung spontaneously from boot, or paste, or jam; its germs, which are abundant in the air, have been sown, and have germinated, inas legal and legitimate a way as thistle-seeds wafted by the wind to aproper soil. Let the minute spores of Penicillium be sown in afermentable liquid, which has been previously so boiled as to kill allother spores or seeds which it may contain; let pure air have freeaccess to the mixture; the Penicillium will grow rapidly, strikinglong filaments into the liquid, and fructifying at its surface. Testthe infusion at various stages of the plant's growth, you will neverfind in it a trace of alcohol. But forcibly submerge the littleplant, push it down deep into the liquid, where the quantity of freeoxygen that can reach it is insufficient for its needs, it immediatelybegins to act as a ferment, supplying itself with oxygen by thedecomposition of the sugar, and producing alcohol as one of theresults of the decomposition. Many other low microscopic plants actin a similar manner. In aerated liquids they flourish without anyproduction of alcohol, but cut off from free oxygen they act asferments, producing alcohol exactly as the real alcoholic leavenproduces it, only less copiously. For the right apprehension of allthese facts we are indebted to Pasteur. 

In the cases hitherto considered, the fermentation is proved to be theinvariable correlative of life, being produced by organisms foreign tothe fermentable substance. But the substance itself may also havewithin it, to some extent, the motive power of fermentation. Theyeast-plant, as we have learned, is an assemblage of living cells; butso at bottom, as shown by Schleiden and Schwann, are all livingorganisms. Cherries, apples, peaches, pears, plums, and grapes, forexample, are composed of cells, each of which is a living unit. Andhere I have to direct your attention to a point of extreme interest. In 1821, the celebrated French chemist, Bérard, established theimportant fact that all ripening fruit, exposed to the freeatmosphere, absorbed the oxygen of the atmosphere and liberated anapproximately equal volume of carbonic acid. He also found that whenripe fruits were placed in a confined atmosphere, the oxygen of theatmosphere was first absorbed, and an equal volume of carbonic acidgiven out. But the process did not end here. After the oxygen hadvanished, carbonic acid, in considerable quantities, continued to beexhaled by the fruits, which at the same time lost a portion of theirsugar, becoming more acid to the taste, though the absolute quantityof acid was not augmented. This was an observation of capitalimportance, and Bérard had the sagacity to remark that the processmight be regarded as a kind of fermentation. 

Thus the living cells of fruits can absorb oxygen and breathe outcarbonic acid, exactly like the living cells of the leaven of beer. Supposing the access of oxygen suddenly cut off, will the livingfruit-cells as suddenly die, or will they continue to live as yeastlives, by extracting oxygen from the saccharine juices round them?This is a question of extreme theoretic significance. It was firstanswered affirmatively by the able and conclusive experiments ofLechartier and Bellamy, and the answer was subsequently confirmed andexplained by the experiments and the reasoning of Pasteur. Bérardonly showed the absorption of oxygen and the production of carbonicacid; Lechartier and Bellamy proved the production of alcohol, thuscompleting the evidence that it was a case of real fermentation, though the common alcoholic ferment was absent. 

*****

So full was Pasteur of the idea that the cells of a fruit wouldcontinue to live at the expense of the sugar of the fruit, that oncein his laboratory, while conversing on these subjects with M. Dumas, he exclaimed, 'I will wager that if a grape be plunged into anatmosphere of carbonic acid, it will produce alcohol and carbonic acidby the continued life of its own cells--that they will act for a timelike the cells of the true alcoholic leaven. ' He made the experiment, and found the result to be what he had foreseen. He then extended the'enquiry. Placing under a bell-jar twenty-four plums, he filled thejar with carbonic acid gas; beside it he placed twenty-four similarplums uncovered. At the end of eight days, he removed the plums fromthe jar, and compared them with the others. The difference wasextraordinary. The uncovered fruits had become soft, watery, and verysweet; the others were firm and hard, their fleshy portions being notat all watery. They had, moreover, lost a considerable quantity oftheir sugar. They were afterwards bruised, and the juice wasdistilled. It yielded six and a half grammes of alcohol, or one percent. Of the total weight of the plums. Neither in these plums, norin the grapes first experimented on by Pasteur, could any trace of theordinary alcoholic leaven be found. As previously proved byLechartier and Bellamy, the fermentation was the work of the livingcells of the fruit itself, after air had been denied to them. When, moreover, the cells were destroyed by bruising, no fermentationensued. The fermentation was the correlative of a vital act, and itceased when life was extinguished. 

Luedersdorf was the first to show by this method that yeast acted, not, as Liebig had assumed, in virtue of its organic, but in virtue ofits organised character. He destroyed the cells of yeast by rubbingthem on a ground glass plate, and found that with the destruction ofthe organism, though its chemical constituents remained, the power toact as a ferment totally disappeared. 

One word more in reference to Liebig may find a place here. To thephilosophic chemist thoughtfully pondering these phenomena, familiarwith the conception of molecular motion, and the changes produced bythe interactions of purely chemical forces, nothing could be morenatural than to see in the process of fermentation a simpleillustration of molecular instability, the ferment propagating tosurrounding molecular groups the overthrow of its own totteringcombinations. Broadly considered, indeed, there is a certain amountof truth in this theory; but Liebig, who propounded it, missed thevery kernel of the phenomena when he overlooked or contemned the partplayed in fermentation by microscopic life. He looked at the mattertoo little with the eye of the body, and too much with the spiritualeye. He practically neglected the microscope, and was unmoved by theknowledge which its revelations would have poured in upon his mind. His hypothesis, as I have said, was natural--nay it was a strikingillustration of Liebig's power to penetrate and unveil molecularactions; but it was an error, and as such has proved an ignis fatuusinstead of a pharos to some of his followers. 

*****

I have said that our air is full of the germs of ferments differingfrom the alcoholic leaven, and sometimes seriously interfering withthe latter. They are the weeds of this microscopic garden which oftenovershadow and choke the flowers. Let us take an illustrative case. Expose milk to the air. It will, after a time, turn sour, separatinglike blood into clot and serum. Place a drop of this sour milk undera powerful microscope and watch it closely. You see the minutebutter-globules animated by that curious quivering motion called theBrownian motion. But let not this attract your attention too much, for it is another motion that we have now to seek. Here and there youobserve a greater disturbance than ordinary among the globules; keepyour eye upon the place of tumult, and you will probably see emergingfrom it a long eel-like organism, tossing the globules aside andwriggling more or less rapidly across the field of the microscope. Familiar with one sample of this organism, which from its motionsreceives the name of vibrio, you soon detect numbers of them. It isthese organisms, and other analogous though apparently motionlessones, which by decomposing the milk render it sour and putrid. Theyare the lactic and putrid ferments, as the yeast-plant is thealcoholic ferment of sugar. Keep them and their germs out of yourmilk and it will continue sweet. But milk may become putrid withoutbecoming sour. Examine such putrid milk microscopically, and you findit swarming with shorter organisms, sometimes associated with thevibrios, sometimes alone, and often manifesting a wonderful alacrityof motion. Keep these organisms and their germs out of your milk andit will never putrify. Expose a mutton-chop to the air and keep itmoist; in summer weather it soon stinks. Place a drop of the juice ofthe fetid chop under a powerful microscope; it is seen swarming withorganisms resembling those in the putrid milk. These organisms, whichreceive the common name of bacteria, [Footnote: Doubtless organismsexhibiting grave specific differences are grouped together under thiscommon name. ] are the agents of all putrefaction. Keep them and theirgerms from your meat and it will remain for ever sweet. Thus we beginto see that within the world of life to which we ourselves belong, there is another living world requiring the microscope for itsdiscernment, but which, nevertheless, has the most important bearingon the welfare of the higher life-world. 

And now let us reason together as regards the origin of thesebacteria. A granular powder is placed in your hands, and you areasked to state what it is. You examine it, and have, or have not, reason to suspect that seeds of some kind are mixed up in it. Todetermine this point you prepare a bed in your garden, sow in it thepowder, and soon after find a mixed crop of docks and thistlessprouting from your bed. Until this powder was sown neither docks northistles ever made their appearance in your garden. You repeat theexperiment once, twice, ten times, fifty times. From fifty differentbeds after the sowing of the powder, you obtain the same crop. Whatwill be your response to the question proposed to you? 'I am not in acondition, ' you would say, 'to affirm that every grain of the powderis a dock-seed, or a thistle-seed; but I am in a condition to affirmthat both dock and thistle-seeds form, at all events, part of thepowder. ' Supposing a succession of such powders to be placed in yourhands with grains becoming gradually smaller, until they dwindle tothe size of impalpable dust particles; assuming that you treat themall in the same way, and that from every one of them in a few days youobtain a definite crop--may be clover, it may be mustard, it may bemignonette, it may be a plant more minute than any of these, smallnessof the particles, or of the plants that spring from them, does notaffect the validity of the conclusion. Without a shadow of misgivingyou would conclude that the powder must have contained the seeds orgerms of the life observed. There is not in the range of physicalscience, an experiment more conclusive nor an inference safer thanthis one. 

Supposing the powder to be light enough to float in the air, and thatyou are enabled to see it there just as plainly as you saw the heavierpowder in the palm of hand. If the dust sown by the air instead of bythe hand produce a definite living crop, with the same logical rigouryou would conclude that the germs of this crop must be mixed with thedust. To take an illustration: the spores of the little plantPenicillium glaucum, to which I have already referred, are lightenough to float in the air. A cut apple, a pear, a tomato, a slice ofvegetable marrow, or, as already mentioned, an old moist boot, a dishof paste, or a pot of jam, constitutes a proper soil for thePenicillium. Now, if it could be proved that the dust of the air whensown in this soil produces this plant, while, wanting the dust, neither the air, nor the soil, nor both together can produce it, itwould be obviously just as certain in this case that the floating dustcontains the germs of Penicillium as that the powders sown in yourgarden contained the germs of the plants which sprung from them. 

But how is the floating dust to be rendered visible? In this way. Build a little chamber and provide it with a door, windows, andwindow-shutters. Let an aperture be made in one of the shuttersthrough which a sunbeam can pass. Close the door and windows so thatno light shall enter save through the hole in the shutter. The trackof the sunbeam is at first perfectly plain and vivid in the air of theroom. If all disturbance of the air of the chamber be avoided, theluminous track will become fainter and fainter, until at last itdisappears absolutely, and no trace of the beam is to be seen. Whatrendered the beam visible at first? The floating dust of the air, which, thus illuminated and observed, is as palpable to sense as dustor powder placed on the palm of the hand. In the still air the dustgradually sinks to the floor or sticks to the walls and ceiling, untilfinally, by this self-cleansing process, the air is entirely freedfrom mechanically suspended matter. 

Thus, far, I think, we have made our footing sure. Let us proceed. Chop up a beefsteak and allow it to remain for two or three hours justcovered with warm water; you thus extract the juice of the beef in aconcentrated form. By properly boiling the liquid and filtering it, you can obtain from it a perfectly transparent beef-tea. Expose anumber of vessels containing this tea to the moteless air of yourchamber; and expose a number of vessels containing precisely the sameliquid to the dust-laden air. In three days every one of the latterstinks, and examined with the microscope every one of them is foundswarming with the bacteria of putrefaction. After three months, orthree years, the beef-tea within the chamber is found in every case assweet and clear, and as free from bacteria, as it was at the momentwhen it was first put in. There is absolutely no difference betweenthe air within and that without save that the one is dustless and theother dust-laden. 

Clinch the experiment thus: Open the door of your chamber and allowthe dust to enter it. In three days afterwards you have every vesselwithin the chamber swarming with bacteria, and in a state of activeputrefaction. Here, also, the inference is quite as certain as in thecase of the powder sown in your garden. Multiply your proofs bybuilding fifty chambers instead of one, and by employing everyimaginable infusion of wild animals and tame; of flesh, fish, fowl, and viscera; of vegetables of the most various kinds. If in all thesecases you find the dust infallibly producing its crop of bacteria, while neither the dustless air nor the nutritive infusion, nor bothtogether, are ever able to produce this crop, your conclusion issimply irresistible that the dust of the air contains the germs of thecrop which has appeared in your infusions. I repeat there is noinference of experimental science more certain than this one. In thepresence of such facts, to use the words of a paper lately publishedin the 'Philosophical Transactions, ' it would be simply monstrous toaffirm that these swarming crops of bacteria are spontaneouslygenerated. 

Is there then no experimental proof of spontaneous generation? Ianswer without hesitation, none! But to doubt the experimental proofof a fact, and to deny its possibility, are two different things, though some writers confuse matters by making them synonymous. Infact, this doctrine of spontaneous generation, in one form or another, falls in with the theoretic beliefs of some of the foremost workers ofthis age; but it is exactly these men who have the penetration to see, and the honesty to expose, the weakness of the evidence adduced in itssupport. 

*****

And here observe how these discoveries tally with the common practicesof life. Heat kills the bacteria, colds numbs them. When myhousekeeper has pheasants in charge which she wishes to keep sweet, but which threaten to give way, she partially cooks the birds, killsthe infant bacteria, and thus postpones the evil day. By boiling hermilk she also extends its period of sweetness. Some weeks ago in theAlps I made a few experiments on the influence of cold upon ants. Though the sun was strong, patches of snow still maintained themselveson the mountain slopes. The ants were found in the warm grass and onthe warm rocks adjacent. Transferred to the snow the rapidity oftheir paralysis was surprising. Ina few seconds a vigorous ant, aftera few languid struggles, would wholly lose its power of locomotion andlie practically dead upon the snow. Transferred to the warm rock, itwould revive, to be again smitten with death-like numbness whenretransferred to the snow. What is true of the ant is specially trueof our bacteria. Their active life is suspended by cold, and with ittheir power of producing or continuing putrefaction. This is thewhole philosophy of the preservation of meat by cold. The fishmonger, for example, when he surrounds his very assailable wares by lumps ofice, stays the process of putrefaction by reducing to numbness andinaction the organisms which produce it, and in the absence of whichhis fish would remain sweet and sound. It is the astonishing activityinto which these bacteria are pushed by warmth that renders a singlesummer's day sometimes so disastrous to the great butchers of Londonand Glasgow. The bodies of guides lost in the crevasses of Alpineglaciers have come to the surface forty years after their interment, without the flesh showing any sign of putrefaction. But the mostastonishing case of this kind is that of the hairy elephant of Siberiawhich was found incased in ice. It had been buried for ages, but whenlaid bare its flesh was sweet, and for some time afforded copiousnutriment to the wild beasts which fed upon it. 

Beer is assailable by all the organisms here referred to, some ofwhich produce acetic, some lactic, and some butyric acid, while yeastis open to attack from the bacteria of putrefaction. In relation tothe particular beverage the brewer wishes to produce, these foreignferments have been properly called ferments of disease. The cells ofthe true leaven are globules, usually somewhat elongated. The otherorganisms are more or less rod-like or eel-like in shape, some of thembeing beaded so as to resemble necklaces. Each of these organismsproduces a fermentation and a flavour peculiar to itself. Keep themout of your beer and it remains for ever unaltered. Never withoutthem will your beer contract disease. But their germs are in the air, in the vessels employed in the brewery; even in the yeast used toimpregnate the wort. Consciously or unconsciously, the art of thebrewer is directed against them. His aim is to paralyze, if he cannotannihilate them. 

For beer, moreover, the question of temperature is one of supremeimportance; indeed, the recognised influence of temperature is causingon the continent of Europe a complete revolution in the manufacture ofbeer. When I was a student in Berlin, in 1851, there were certainplaces specially devoted to the sale of Bavarian beer, which was thenmaking its way into public favour. This beer is prepared by what iscalled the process of low fermentation; the name being given partlybecause the yeast of the beer, instead of rising to the top andissuing through the bunghole, falls to the bottom of the cask; butpartly, also, because it is produced at a low temperature. The otherand older process, called high fermentation, is far more handy, expeditious, and cheap. In high fermentation eight days suffice forthe production of the beer; in low fermentation, ten, fifteen, eventwenty days are found necessary. Vast quantities of ice, moreover, are consumed in the process of low fermentation. In the singlebrewery of Dreher, of Vienna, a hundred million pounds of ice areconsumed annually in cooling the wort and beer. Notwithstanding theseobvious and weighty drawbacks, the low fermentation is rapidlydisplacing the high upon the Continent. Here are some statisticswhich show the number of breweries of both kinds existing in Bohemiain 1860, 1865, and 1870:

 1860. 1865. 1870. 

High Fermentation 281 81 18

Low Fermentation 135 459 831

Thus in ten years the number of high-fermentation breweries fell from281 to 18, while the number of low-fermentation breweries rose from135 to 831. The sole reason for this vast change--a change whichinvolves a great expenditure of time, labour, and money--is theadditional command which it gives the brewer over the fortuitousferments of disease. These ferments, which, it is to be remembered, are living organisms, have their activity suspended by temperaturesbelow 10°C, and as long as they are reduced to torpor the beer remainsuntainted either by acidity or putrefaction. The beer of lowfermentation is brewed in winter, and kept in cool cellars; the brewerbeing thus enabled to dispose of it at his leisure, instead of forcingits consumption to avoid the loss involved in its alteration if kepttoo long. Hops, it may be remarked, act to some extent as anantiseptic to beer. The essential oil of the hop is bactericidal:hence the strong impregnation with hop juice of all beer intended forexportation. 

These low organisms, which one might be disposed to regard as thebeginnings of life, were we not warned that the microscope, preciousand perfect as it is, has no power to show us the real beginnings oflife, are by no means purely useless or purely mischievous in theeconomy of nature. They are only noxious when out of their properplace. They exercise a useful and valuable function as the burnersand consumers of dead matter, animal and vegetable, reducing suchmatter, with a rapidity otherwise unattainable, to innocent carbonicacid and water. Furthermore, they are not all alike, and it is onlyrestricted classes of them that are really dangerous to man. Onedifference in their habits is worthy of special reference here. Air, or rather the oxygen of the air, which is absolutely necessary to thesupport of the bacteria of putrefaction, is, according to Pasteur, absolutely deadly to the vibrios which provoke the butyric acidfermentation. This has been illustrated by the following beautifulobservation. 

A drop of the liquid containing those small organisms is placed uponglass, and on the drop is placed a circle of exceedingly thin glass;for, to magnify them sufficiently, it is necessary that theobject-glass of the microscope should come very close to theorganisms. Round the edge of the circular plate of glass the liquidis in contact with the air, and incessantly absorbs it, including theoxygen. Here, if the drop be charged with bacteria, we have a zone ofvery lively ones. But through this living zone, greedy of oxygen andappropriating it, the vivifying gas cannot penetrate to the centre ofthe film. In the middle, therefore, the bacteria die, while theirperipheral colleagues continue active. If a bubble of air chance tobe enclosed in the film, round it the bacteria will pirouette andwabble until its oxygen has been absorbed, after which all theirmotions cease. Precisely the reverse of all this occurs with thevibrios of butyric acid. In their case it is the peripheral organismsthat are first killed, the central ones remaining vigorous whileringed by a zone of dead. Pasteur, moreover, filled two vessels witha liquid containing these vibrios; through one vessel be led air, andkilled its vibrios in half an hour; through the other he led carbonicacid, and after three hours found the vibrios fully active. It waswhile observing these differences of deportment fifteen years ago thatthe thought of life without air, and its bearing upon the theory offermentation, flashed upon the mind of this admirable investigator. 

*****

We now approach an aspect of this question which concerns us stillmore closely, and will be best illustrated by an actual fact. A fewyears ago I was bathing in an Alpine stream, and returning to myclothes from the cascade which had been my shower-bath, I slipped upona block of granite, the sharp crystals of which stamped themselvesinto my naked shin. The wound was an awkward one, but being invigorous health at the time, I hoped for a speedy recovery. Dipping aclean pocket-handkerchief into the stream, I wrapped it round thewound, limped home, and remained for four or five days quietly in bed. There was no pain, and at the end of this time I thought myself quitefit to quit my room. The wound, when uncovered, was found perfectlyclean, uninflamed, and entirely free from matter. Placing over it abit of goldbeater's-skin, I walked about all day. Towards eveningitching and heat were felt; a large accumulation of matter followed, and I was forced to go to bed again. The water-bandage was restored, but it was powerless to check the action now set up; arnica wasapplied, but it made matters worse. The inflammation increasedalarmingly, until finally I had to be carried on men's shoulders downthe mountain and transported to Geneva, where, thanks to the kindnessof friends, I was immediately placed in the best medical hands. Onthe morning after my arrival in Geneva, Dr. Gautier discovered anabscess in my instep, at a distance of five inches from the wound. Thetwo were connected by a channel, or sinus, as it is technicallycalled, through which he was able to empty the abscess, without theapplication of the lance. 

By what agency was that channel formed--what was it that thus toreasunder the sound tissue of my instep, and kept me for six weeks aprisoner in bed? In the very room where the water dressing had beenremoved from my wound and the goldbeater's-skin applied to it, Iopened this year a number of tubes, containing perfectly clear andsweet infusions of fish, flesh, and vegetable. These hermeticallysealed infusions had been exposed for weeks, both to the sun of theAlps and to the warmth of a kitchen, without showing the slightestturbidity or sign of life. But two days after they were opened thegreater number of them swarmed with the bacteria of putrefaction, thegerms of which had been contracted from the dust-laden air of theroom. And had the matter from my abscess been examined, my memory ofits appearance leads me to infer that it would have been found equallyswarming with these bacteria--that it was their germs which got intomy incautiously opened wound, and that they were the subtile workersthat burrowed down my shin, dug the abscess in my instep, and producedeffects which might easily have proved fatal. 

This apparent digression brings us face to face with the labours of aman who combines the penetration of the true theorist with the skilland conscientiousness of the true experimenter, and whose practice isone continued demonstration of the theory that the putrefaction ofwounds is to be averted by the destruction of the germs of bacteria. Not only from his own reports of his cases, but from the reports ofeminent men who have visited his hospital, and from the opinionsexpressed to me by continental surgeons, do I gather that one of thegreatest steps ever made in the art of surgery was the introduction ofthe antiseptic system of treatment, introduced by Professor Lister. 

The interest of this subject does not slacken as we proceed. We beganwith the cherry-cask and beer-vat; we end with the body of man. Thereare persons born with the power of interpreting natural facts, asthere are others smitten with everlasting incompetence in regard tosuch interpretation. To the former class in an eminent degreebelonged the illustrious philosopher Robert Boyle, whose words inrelation to this subject have in them the forecast of prophecy. 'Andlet me add, ' writes Boyle in his 'Essay on the Pathological Part ofPhysic, ' 'that he that thoroughly understands the nature of fermentsand fermentations shall probably be much better able than he thatignores them, to give a fair account of divers phenomena of severaldiseases (as well fevers as others), which will perhaps be neverproperly understood without an insight into the doctrine offermentations. '

Two hundred years have passed since these pregnant words were written, and it is only in this our day that men are beginning to fully realisetheir truth. In the domain of surgery the justice of Boyle's surmisehas been most strictly demonstrated. But we now pass the bounds ofsurgery proper, and enter the domain of epidemic disease, includingthose fevers so sagaciously referred to by Boyle. The most strikinganalogy between a _contagium_ and a ferment is to be found in the powerof indefinite self-multiplication possessed and exercised by both. Youknow the exquisitely truthful figures regarding leaven employed in theNew Testament. A particle hid in three measures of meal leavens itall. A little leaven leaveneth the whole lump. In a similar manner, a particle of _contagium_ spreads through the human body and may be somultiplied as to strike down whole populations. Consider the effectproduced upon the system by a microscopic quantity of the virus ofsmallpox. That virus is, to all intents and purposes, a seed. It issown as yeast is sown, it grows and multiplies as yeast grows andmultiplies, and it always reproduces itself. To Pasteur we areindebted for a series of masterly researches, wherein he exposes thelooseness and general baselessness of prevalent notions regarding thetransmutation of one ferment into another. He guards himself againstsaying it is impossible. The true investigator is sparing in the useof this word, though the use of it is unsparingly ascribed to him;but, as a matter of fact, Pasteur has never, been able to effect thealleged transmutation, while he has been always able to point out theopen doorways through which the affirmers of such transmutations hadallowed error to march in upon them. [Footnote: 'Those who wish for anillustration of the care necessary in these researches, and of thecarelessness with which they have in some cases been conducted, willdo well to consult the Rev. W. H. Dallinger's excellent 'Notes onHeterogenesis' in the October number of the Popular Science Review. ]

The great source of error here has been already alluded to in thisdiscourse. The observers worked in an atmosphere charged with thegerms of different organisms; the mere accident of first possessionrendering now one organism, now another, triumphant. In differentstages, moreover, of its fermentative or putrefactive changes, thesame infusion may so alter as to be successively taken possession ofby different organisms. Such cases have been adduced to show that theearlier organisms must have been transformed into the later ones, whereas they are simply cases in which different germs, because ofchanges in the infusion, render themselves valid at different times. 

By teaching us how to cultivate each ferment in its purity--in otherwords, by teaching us how to rear the individual organism apart fromall others, --Pasteur has enabled us to avoid all these errors. Andwhere this isolation of a particular organism has been duly effectedit grows and multiplies indefinitely, but no change of it into anotherorganism is ever observed. In Pasteur's researches the Bacteriumremained a Bacterium, the Vibrio a Vibrio, the Penicillium aPenicillium, and the Torula a Torula. Sow any of these in a state ofpurity in an appropriate liquid; you get it, and it alone, in thesubsequent crop. In like manner, sow small-pox in the human body, your crop is small-pox. Sow there scarlatina, and your crop isscarlatina. Sow typhoid virus, your crop is typhoid--cholera, yourcrop is cholera. The disease bears as constant a relation to its_contagium_ as the microscopic organisms just enumerated do to theirgerms, or indeed as a thistle does to its seed. No wonder then, withanalogies so obvious and so striking, that the conviction is spreadingand growing daily in strength, that reproductive parasitic life is atthe root of epidemic disease--that living ferments finding lodgment inthe body increase there and multiply, directly ruining the tissue onwhich they subsist, or destroying life indirectly by the generation ofpoisonous compounds within the body. This conclusion, which comes tous with a presumption almost amounting to demonstration, is clinchedby the fact that virulently infective diseases have been discoveredwith which living organisms are as closely and as indissolublyassociated as the growth of Torula is with the fermentation of beer. 

And here, if you will permit me, I would utter a word of warning towell-meaning people. We have now reached a phase of this questionwhen it is of the very last importance that light should once for allbe thrown upon the manner in which contagious and infectious diseasestake root and spread. To this end the action of various ferments uponthe organs and tissues of the living body must be studied; the habitatof each special organism concerned in the production of each specificdisease must be determined, and the mode by which its germs are spreadabroad as sources of further infection. It is only by such rigidlyaccurate enquiries that we can obtain final and complete mastery overthese destroyers. Hence, while abhorring cruelty of all kinds, whileshrinking sympathetically from all animal suffering--suffering whichmy own pursuits never call upon me to inflict, --an unbiassed survey ofthe field of research now opening out before the physiologist causesme to conclude, that no greater calamity could befall the human racethan the stoppage of experimental enquiry in this direction. A ladywhose philanthropy has rendered her illustrious said to me some timeago, that science was becoming immoral; that the researches of thepast, unlike those of the present, were carried on without cruelty. Ireplied to her that the science of Kepler and Newton, to which shereferred, dealt with the laws and phenomena of inorganic nature; butthat one great advance made by modern science was in the direction ofbiology, or the science of life; and that in this new directionscientific enquiry, though at the outset pursued at the cost of sometemporary suffering, would in the end prove a thousand times morebeneficent than it had ever hitherto been. I said this because I sawthat the very researches which the lady deprecated were leading us tosuch a knowledge of epidemic diseases as will enable us finally tosweep these scourges of the human race from the face of the earth. 

This is a point of such capital importance that I should like to bringit home to your intelligence by a single trustworthy illustration. In1850, two distinguished French observers, MM. Davainne and Rayer, noticed in the blood, of animals which had died of the virulentdisease called splenic fever, small microscopic organisms resemblingtransparent rods, but neither of them at that time attached anysignificance to the observation. In 1861, Pasteur published a memoiron the fermentation of butyric acid, wherein he described the organismwhich provoked it; and after reading this memoir it occurred toDavainne that splenic fever might be a case of fermentation set upwithin the animal body, by the organisms which had been observed byhim and Rayer. This idea has been placed beyond all doubt bysubsequent research. 

Observations of the highest importance have also been made on splenicfever by Pollender and Brauell. Two years ago, Dr. Burdon Sandersongave us a very clear account of what was known up to that time of thisdisorder. With regard to the permanence of the _contagium_, it had beenproved to hang for years about localities where it had once prevailed;and this seemed to show that the rod-like organisms could notconstitute the _contagium_, because their infective power was found tovanish in a few weeks. But other facts established an intimateconnection between the organisms and the disease, so that a review ofall the facts caused Dr. Sanderson to conclude that the _contagium_existed in two distinct forms: the one 'fugitive' and visible astransparent rods; the other permanent but 'latent, ' and not yetbrought within the grasp of the microscope. 

At the time that Dr. Sanderson was writing this report, a young Germanphysician, named Koch, [Footnote: This, I believe, was the firstreference to the researches of Koch made in this country. 1879. ]occupied with the duties of his profession in an obscure countrydistrict, was already at work, applying, during his spare time, various original and ingenious devices to the investigation of splenicfever. He studied the habits of the rod-like organisms, and found theaqueous humour an ox's eye to be particularly suitable for theirnutria. With a drop of the aqueous humour he mixed tiniest speck of aliquid containing the rods, placed the drop under his microscope, warmed it suitably, and observed the subsequent action. During thefirst two hours hardly any change was noticeable; but at the end ofthis time the rods began to lengthen, and the action was so rapid thatat the end of three or four hours they attained from ten to twentytimes their original length. At the end of a few additional hoursthey had formed filaments in many cases a hundred times the length ofthe original rods. The same filament, in fact, was frequentlyobserved to stretch through several fields of the microscope. Sometimes they lay in straight lines parallel to each other, in othercases they were bent, twisted, and coiled into the most gracefulfigures; while sometimes they formed knots of such bewilderingcomplexity that it was impossible for the eye to trace the individualfilaments through the confusion. 

Had the observation ended here an interesting scientific fact wouldhave been added to our previous store, but the addition would havebeen of little practical value. Koch, however, continued to watch thefilaments, and after a time noticed little dots appearing within them. These dots became more and more distinct, until finally the wholelength of the organism was studded with minute ovoid bodies, which laywithin the outer integument like peas within their shell. By-and-bythe integument fell to pieces, the place of the organisms being takenby a long row of seeds or spores. These observations, which wereconfirmed in all respects by the celebrated naturalist, Cohn ofBreslau, are of the highest importance. They clear up the existingperplexity regarding the latent and visible _contagia_ of splenic fever;for in the most conclusive manner, Koch proved the spores, asdistinguished from the rods, to constitute the _contagium_ of the feverin its most deadly and persistent form. 

How did he reach this important result? Mark the answer. There wasbut one way open to him to test the activity of the _contagium_, andthat was the inoculation with it of living animals. He operated uponguinea-pigs and rabbits, but the vast majority of his experiments weremade upon mice. Inoculating them with the fresh blood of an animalsuffering from splenic fever, they invariably died of the same diseasewithin twenty or thirty hours after inoculation. He then sought todetermine how the _contagium_ maintained its vitality. Drying theinfectious blood containing the rod-like organisms, in which, however, the spores were not developed, he found the _contagium_ to be that whichDr. Sanderson calls 'fugitive. ' It maintained its power of infectionfor five weeks at the furthest. He then dried blood containing thefully-developed spores, and posed the substance to a variety ofconditions. He permitted the dried blood to assume the form of dust;wetted this dust, allowed it to dry again, permitted it to remain foran indefinite time in the midst of putrefying matter, and subjected itto various other tests. After keeping the spore-charged blood whichhad been treated in this fashion for four years, he inoculated anumber of mice with it, and found its action as fatal as that of bloodfresh from the veins of an animal suffering from splenic fever. Therewas no single escape from death after inoculation by this deadly_contagium_. Uncounted millions of these spores are developed in thebody of every animal which has died of splenic fever, and every sporeof these millions is competent to produce the disease. The name ofthis formidable parasite is Bacillus anthracis. [Footnote: Koch foundthat to produce its characteristic effects the _contagium_ of splenicfever must enter the blood; the virulently festive spleen of adiseased animal may be eaten with impunity by mice. On the otherhand, the disease refuses to be communicated by inoculation to dogs, partridges, or sparrows. In their blood Bacillus anthracis ceases toact as a ferment. Pasteur announced more than six years ago thepropagation of the vibrios of the silkworm disease called _flacherie_, both by fission and by spores. He also made some remarkableexperiments on the permanence of the _contagium_ in the form of spores. See 'Etudes sur la Maladie des Vers à Soie, ' pp. 168 and 256. ]

Now the very first step towards the extirpation of these _contagia_ isthe knowledge of their nature; and the knowledge brought to us by Dr. Koch will render as certain the stamping out of splenic fever as thestoppage of the plague of _pébrine_ by the researches of Pasteur. [Footnote: Surmising that the immunity enjoyed by birds might arisefrom the heat of their blood, which destroyed the bacillus, Pasteurlowered their temperature artificially, inoculated them, and killedthem. He also raised the temperature of guinea-pigs afterinoculation, and saved them. It is needless to dwell for a moment onthe importance of this experiment. ] One small item of statisticswill show what this implies. In the single district of Novgorod inRussia, between the years 1867 and 1870, over fifty-six thousand casesof death by splenic fever, among horses, cows, and sheep wererecorded. Nor did its ravages confine themselves to the animal world, for during the time and in the district referred to, five hundred andtwenty-eight human beings perished in the agonies of the same disease. 

A description of the fever will help you to come to a right decisionon the point which I wish to submit to your consideration. 'Ananimal, ' says Dr. Burdon Sanderson, 'which perhaps for the previousday has declined food and shown signs of general disturbance, beginsto shudder and to have twitches of the muscles of the back, and soonafter becomes weak and listless. In the meantime the respirationbecomes frequent and often difficult, and the temperature rises threeor four degrees above the normal; but soon convulsions, affectingchiefly the muscles of the back and loins, usher in the final collapseof which the progress is marked by the loss of all power of moving thetrunk or extremities, diminution of temperature, mucous andsanguinolent alvine evacuations, and similar discharges from the mouthand nose. ' In a single district of Russia, as above remarked, fifty-six thousand horses, cows, and sheep, and five hundred andtwenty-eight men and women, perished in this way during a period oftwo or three years. What the annual fatality is throughout Europe Ihave no means of knowing. Doubtless it must be very great. Thequestion, then, which I wish to submit to your judgment is this: Isthe knowledge which reveals to us the nature, and which assures theextirpation, of a disorder so virulent and so vile, worth the pricepaid for it? It is exceedingly important that assemblies like thepresent should see clearly the issues at stake in such questions asthis, and that the properly informed sense of the community shouldtemper, if not restrain, the rashness of those who, meaning to betender, become agents of cruelty by the imposition of short-sightedrestrictions upon physiological investigations. It is a moderninstance of zeal for God, but not according to knowledge, the excessesof which must be corrected by an instructed public opinion. 

*****

And now let us cast a backward glance on the field we have traversed, and try to extract from our labours such further profit as they canyield. For more than two thousand years the attraction of lightbodies by amber was the sum of human knowledge regarding electricity, and for more than two thousand years fermentation was effected withoutany knowledge of its cause. In science one discovery grows out ofanother, and cannot appear without its proper antecedent. Thus, before fermentation could be understood, the microscope had to beinvented, and brought to a considerable degree of perfection. Notethe growth of knowledge. Leeuwenhoek, in 1680, found yeast to be amass of floating globules, but he had no notion that the globules werealive. This was proved in 1835 by Cagniard de la Tour and Schwann. Then came the question as to the origin of such microscopic organisms, and in this connection '`the memoir of Pasteur, published in the'Annales de Chimie' for 1862, is the inauguration of a new epoch. 

On that investigation all Pasteur's subsequent labours were based. Ravages had over and over again occurred among French wines. Therewas no guarantee that they ould not become acid or bitter, particularlywhen exported. The commerce in wines was thus restricted, and disastrouslosses were ften inflicted on the wine-grower. Every one of thesediseases was traced to the life of an organism. Pasteur ascertained thetemperature which killed these ferments of disease, proving it to beso low as to be perfectly harmless to the wine. By the simpleexpedient of heating the wine to a temperature of fifty degreesCentigrade, he rendered it inalterable, and thus saved his country theloss of millions. He then went on to vinegar--vin aigre, acidwine--which he proved to be produced by a fermentation set up by alittle fungus called Mycoderma aceti. Torula, in fact, converts thegrape juice into alcohol, and Mycoderma aceti converts the alcoholinto vinegar. Here also frequent failures occurred, and severe losseswere sustained. Through the operation of unknown causes, the vinegaroften became unfit for use, sometimes indeed falling into utterputridity. It had been long known that mere exposure to the air wassufficient to destroy it. Pasteur studied all these changes, tracedthem to their living causes, and showed that the permanent health ofthe vinegar was ensured by the destruction of this life. He passedfrom the diseases of vinegar to the study of a malady which a dozenyears ago had all but ruined the silk husbandry of France. Thisplague, which received the name of _pébrine_, was the product of aparasite which first took possession of the intestinal canal of thesilkworm, spread throughout its body, and filled the sack which oughtto contain the viscid matter of the silk. Thus smitten, the wormwould go automatically through the process of spinning when it hadnothing to spin. 

Pasteur followed this parasitic destroyer from year to year, and ledby his singular power of combining facts with the logic of facts, discovered eventually the precise phase in the development of theinsect when the disease which assailed it could with certainty bestamped out. Pasteur's devotion to this enquiry cost him dear. Herestored to France her silk husbandry, rescued thousands of herpopulation from ruin, set the looms of Italy also to work, but emergedfrom his labours with one of his sides permanently paralysed. Hislast investigation is embodied in a work entitled 'Studies on Beer, 'in which he describes a method of rendering beer permanentlyunchangeable. That method is not so simple as those found effectualwith wine and vinegar, but the principles which it involves are sureto receive extensive application at some future day. 

There are other reflections connected with this subject which, evenwere they now passed over without remark, would sooner or later occurto every thoughtful mind in this assembly. I have spoken of thefloating dust of the air, of the means of rendering it visible, and ofthe perfect immunity from putrefaction which accompanies the contactof germless infusions and moteless air. Consider the woes which thesewafted particles, during historic and pre-historic ages, haveinflicted on mankind; consider the loss of life in hospitals fromputrefying wounds; consider the loss in places where there are plentyof wounds, but no hospitals, and in the ages before hospitals wereanywhere founded; consider the slaughter which has hitherto followedthat of the battlefield, when those bacterial destroyers are letloose, often producing a mortality far greater than that of the battleitself; add to this the other conception that in times of epidemicdisease the self-same floating matter has frequently, if not always, mingled with it the special germs which produce the epidemic, beingthus enabled to sow pestilence and death over nations andcontinents--consider all this, and you will come with me to theconclusion that all the havoc of war, ten times multiplied, would beevanescent if compared with the ravages due to atmospheric dust. 

This preventible destruction is going on to-day, and it has beenpermitted to go on for ages, without a whisper of informationregarding its cause being vouchsafed to the suffering sentient world. We have been scourged by invisible thongs, attacked from impenetrableambuscades, and it is only to-day that the light of science is beinglet in upon the murderous dominion of our foes. Facts like theseexcite in me the thought that the rule and governance of this universeare different from what we in our youth supposed them to be--that theinscrutable Power, at once terrible and beneficent, in whom we liveand move and have our being and our end, is to be propitiated by meansdifferent to those usually resorted to. The first requisite towardssuch propitiation is knowledge; the second is action, shaped andilluminated by that knowledge. Of knowledge we already see the dawn, which will open out by-and-by to perfect day; while the action whichis to follow has its unfailing source and stimulus in the moral andemotional nature of man--in his desire for personal well-being, in hissense of duty, in his compassionate sympathy with the sufferings ofhis fellow-men. 'How often, ' says Dr. William Budd in his celebratedwork on Typhoid Fever, --' How often have I seen in past days, in thesingle narrow chamber of the day-labourer's cottage the father in thecoffin, the mother in the sick-bed in muttering delirium, and nothingto relieve the desolation of the children but the devotion of somepoor neighbour, who in too many cases paid the penalty of kindness inbecoming herself the victim of the same disorder!' From the vantageground already won I look forward with confident hope to the triumphof medical art over scenes of misery like that here described. Thecause of the calamity being once clearly revealed, not only to thephysician, but to the public, whose intelligent co-operation isabsolutely essential to success, the final victory of humanity is onlya question of time. We have already a foretaste of that victory inthe triumphs f surgery as practised at your doors. 

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XIII. SPONTANEOUS GENERATION. 

[Footnote: The Nineteenth Century, January 1878. ]

WITHIN ten minutes' walk of a little cottage which I have recentlybuilt in the Alps, there is a small lake, fed by the melted snows ofthe upper mountains. During the early weeks of summer no trace oflife is to be discerned in this water; but invariably towards the endof July, or the beginning of August, swarms of tailed organisms areseen enjoying the sun's warmth along the shallow margins of the lake, and rushing with audible patter into deeper water at the approach ofdanger. The origin of this periodic crowd of living things is by nomeans obvious. For years I had never noticed in the lake either anadult frog, or the smallest fragment of frog spawn; so that were I nototherwise informed, I should have found the conclusion of Mathiole anatural one, namely, that tadpoles are generated in lake mud by thevivifying action of the sun. 

The checks which experience alone can furnish being absent, thespontaneous generation of creatures quite as high as the frog in thescale of being was assumed for ages to be a fact. Here, as elsewhere, the dominant mind of Aristotle stamped its notions on the world atlarge. For nearly twenty centuries after him men found no difficultyin believing in cases of spontaneous generation which would now berejected as monstrous by the most fanatical supporter of the doctrine. Shell-fish of all kinds were considered to be without parental origin. Eels were supposed to spring spontaneously from the fat ooze of theNile. Caterpillars were the spontaneous products of the leaves onwhich they fed; while winged insects, serpents, rats, and mice wereall thought capable of being generated without sexual intervention. 

The most copious source of this life without an ancestry wasputrefying flesh; and, lacking the checks imposed by fullerinvestigation, the conclusion that flesh possesses and exerts thisgenerative power is a natural one. I well remember when a child often or twelve seeing a joint of imperfectly salted beef cut into, andcoils of maggots laid bare within the mass. Without a moment'shesitation I jumped to the conclusion that these maggots had beenspontaneously generated in the meat. I had no knowledge which couldqualify or oppose this conclusion, and for the time it wasirresistible. The childhood of the individual typifies that of therace, and the belief here enunciated was that of the world for nearlytwo thousand years. 

To the examination of this very point the celebrated Francesco Redi, physician to the Grand Dukes Ferdinand II. And Cosmo III. OfTuscany, and a member of the Academy del Cimento, addressed himself in1668. He had seen the maggots of putrefying flesh, and reflected ontheir possible origin. But he was not content with mere reflection, nor with the theoretic guesswork which his predecessors had foundedupon their imperfect observations. Watching meat during its passagefrom freshness to decay, prior to the appearance of maggots heinvariably observed flies buzzing round the meat and frequentlyalighting on it. The maggots, he thought, might be the half-developedprogeny of these flies. 

The inductive guess precedes experiment, by which, however, it must befinally tested. Redi knew this, and acted accordingly. Placing freshmeat in a jar and covering the mouth with paper, he found that, thoughthe meat putrefied in the ordinary way, it never bred maggots, whilethe same meat placed in open jars soon swarmed with these organisms. For the paper cover he then substituted fine gauze, through which theodour of the meat could rise. Over it the flies buzzed, and on itthey laid their eggs, but, the meshes being too small to permit theeggs to fall through, no maggots were generated in the meat. Theywere, on the contrary, hatched upon the gauze. By a series of suchexperiments Redi destroyed the belief in the spontaneous generation ofmaggots in meat, and with it doubtless many related beliefs. Thecombat was continued by Vallisneri, Schwammerdam, and Réaumur, whosucceeded in banishing the notion of spontaneous generation from thescientific minds of their day. Indeed, as regards such complexorganisms as those which formed the subject of their researches, thenotion was banished for ever. 

But the discovery and improvement of the microscope, though giving adeath-blow to much that had been previously written and believedregarding spontaneous generation, brought also into view a world oflife formed of individuals so minute--so close as it seemed to theultimate particles of matter--as to suggest an easy passage from atomsto organisms. Animal and vegetable infusions exposed to the air werefound clouded and crowded with creatures far beyond the reach ofunaided vision, but perfectly visible to an eye strengthened by themicroscope. With reference to their origin these organisms werecalled 'Infusoria. Stagnant pools were found full of them, and theobvious difficulty of assigning a germinal origin to existences sominute furnished the precise condition necessary to give new play tothe notion of heterogenesis or spontaneous generation. 

The scientific world was soon divided into two hostile camps, theleaders of which only can here be briefly alluded to. On the oneside, we have Buffon and Needham, the former postulating his 'organicmolecules, ' and the latter assuming the existence of a special'vegetative force' which drew the molecules together so as to formliving things. On the other side, we have the celebrated Abbé LazzaroSpallanzani, who in 1777 published results counter to those announcedby Needham in 1748, and obtained by methods so precise as tocompletely overthrow the convictions based upon the labours of hispredecessor. Charging his flasks with organic infusions, he sealedtheir necks with the blowpipe, subjected them in this condition to theheat of boiling water, and subsequently exposed them to temperaturesfavourable to the development of life. The infusions continuedunchanged for months, and when the flasks were subsequently opened notrace of life was found. 

Here I may forestall matters so far as to say that the success ofSpallanzani's experiments depended wholly on the locality in which heworked. The air around him must have been free from the more obdurateinfusorial germs, for otherwise the process he followed would, as waslong afterwards proved by Wyman, have infallibly yielded life. Buthis refutation of the doctrine of spontaneous generation is not theless valid on this account. Nor is it in any way upset by the fact, that others in repeating his experiments obtained life where heobtained none. Rather is the refutation strengthened by suchdifferences. Given two experimenters equally skilful and equallycareful, operating in different places on the same infusion, in thesame way, and assuming the one to obtain life while the other fails toobtain it; then its well-established absence in the one case provesthat some ingredient foreign to the infusion must be its cause in theother. 

Spallanzani's sealed flasks contained but small quantities of air, andas oxygen was afterwards shown to be generally essential to life, itwas thought that the absence of life observed by Spallanzani mighthave been due to the lack of this vitalising gas. To dissipate thisdoubt, Schulze in 1836 half filled a flask with distilled water towhich animal and vegetable matters were added. First boiling hisinfusion to destroy whatever life it might contain, Schulze suckeddaily into his flask air which had passed through a series of bulbscontaining concentrated sulphuric acid, where all germs of lifesuspended in the air were supposed to be destroyed. From May toAugust this process was continued without any development ofinfusorial life. 

Here again the success of Schulze was due to his working incomparatively pure air, but even in such air his experiment is a veryrisky one. Germs will pass unwetted and unscathed through sulphuricacid unless the most special care is taken to detain them. I haverepeatedly failed, by repeating Schulze's experiments, to obtain hisresults. Others have failed likewise. The air passes in bubblesthrough the bulbs, and to render the method secure, the passage of theair must be so slow as to cause the whole of its floating matter, evento the very core of each bubble, to touch the surrounding liquid. Butif this precaution be observed, water will be found quite as effectualas sulphuric acid. By the aid of an air-pump, in a highly infectiveatmosphere I have thus drawn air for weeks without intermission, firstthrough bulbs containing water, and afterwards through vessels containingorganic infusions, without any appearance of life. The germs were notkilled by the water, but they were effectually intercepted, while theobjection that the air had been injured by being brought into contactwith strongly corrosive substances was avoided. 

The brief paper of Schulze, published in Poggendorf's Annalen for1836, was followed in 1837 by another short and pregnant communicationby Schwann. 

Redi, as we have seen, traced the maggots of putrefying flesh to theeggs of flies. But he did not and he could not know the meaning ofputrefaction itself. He had not the instrumental means to inform himthat it also is a phenomenon attendant on the development of life. This was first proved in the paper now alluded to. Schwann placedflesh in a flask filled to one-third of its capacity with water, sterilised the flask by boiling, and then supplied it for months withcalcined air. Throughout this time there appeared no mould, noinfusoria, no putrefaction; the flesh remained unaltered, while theliquid continued as clear as it was immediately after boiling. Schwannthen varied his experimental argument, with no alteration in theresult. His final conclusion was, that putrefaction is due todecompositions of organic matter attendant on the multiplicationtherein of minute organisms. These organisms were derived not fromthe air, but from something contained in the air, which was destroyedby a sufficiently high temperature. There never was a more determinedopponent of the doctrine of spontaneous generation than Schwann, though a strange attempt was made a year and a half ago to enlist himand others equally opposed to it on the side of the doctrine. 

The physical character of the agent which produces putrefaction wasfurther revealed by Helmholtz in 1843. By means of a membrane, heseparated a sterilised putrescible liquid from a putrefying one. Thesterilised infusion remained perfectly intact. Hence it was not theliquid of the putrefying mass--for that could freely diffuse throughthe membrane--but something contained in the liquid, and which wasstopped by the membrane, that caused the putrefaction. In 1854Schroeder and von Dusch struck into this enquiry, which wassubsequently followed up by Schroeder alone. These able experimentersemployed plugs of cotton-wool to filter the air supplied to theirinfusions. Fed with such air, in the great majority of cases theputrescible liquids remained perfectly sweet after boiling. Milkformed a conspicuous exception to the general rule. It putrefiedafter boiling, though supplied with carefully filtered air. Theresearches of Schroeder bring us up to the year 1859. 

In that year a book was published which seemed to overturn some of thebest established facts of previous investigators. Its title wasHétérogénie, and its author was F. A. Pouchet, Director of theMuseum of Natural History at Rouen. Ardent, laborious, learned, fullnot only of scientific but of metaphysical fervour, he threw his wholeenergy into the enquiry. Never did a subject require the exercise ofthe cold critical faculty more than this one--calm study in theunravelling of complex phenomena, care in the preparation ofexperiments, care in their execution, skilful variation of conditions, and incessant questioning of results until repetition had placed thembeyond doubt or question. To a man of Pouchet's temperament thesubject was full of danger--danger not lessened by the theoretic biaswith which he approached it. This is revealed by the opening words ofhis preface: 'Lorsque, par la meditation, it fut evident pour moi quela generation spontanée était encore Fun des moyens qu'emploie lanature pour la reproduction des êtres, je m'appliquai à découvrir parquell procédés on pouvait parvenir à en mettre les phénomènes enevidence: It is needless to say that such a prepossession required astrong curb. Pouchet repeated the experiments of Schulze and Schwannwith results diametrically opposed to theirs. He heaped experimentupon experiment and argument upon argument, spicing with the sarcasmof the advocate the logic of the man of science. In view of themultitudes required to produce the observed results, he ridiculed theassumption of atmospheric germs. This was one of his strongestpoints. 'Si les Proto-organismes que nous voyons pulluler partout etdans tout, avaient leurs germes dissembles dans l'atmosphère, dans laproportion mathématiquement indispensable a cet effet, l'air en seraittotalement obscurci, car ill devraient s 'y trouver beaucoup plusserrés que les globules d'eau qui forment, nos nuages épais. Il n'y apas là la moindre exagération. ' Recurring to the subject, heexclaims: 'L'air dans lequel noun vivons aurait presque la densité dufer. ' There is often a virulent contagion in a confident tone, andthis hardihood of argumentative assertion was sure to influence mindsswayed not by knowledge, but by authority. Had Pouchet known that'the blue ethereal sky' is formed of suspended particles, throughwhich the sun freely shines, he would hardly have ventured upon thisline of argument. 

Pouchet's pursuit of this enquiry strengthened the conviction withwhich he began it, and landed him in downright credulity in the end. Ido not question his ability as an observer, but the enquiry needed adisciplined experimenter. This latter implies not mere ability tolook at things as Nature offers them to our inspection, but to forceher to show herself under conditions prescribed by the experimenterhimself. Here Pouchet lacked the necessary discipline. Yet thevigour of his onset raised clouds of doubt, which for a time obscuredthe whole field of enquiry. So difficult indeed did the subject seem, and so incapable of definite solution, that when Pasteur made knownhis intention to take it up, his friends Biot and Dumas expressedtheir regret, earnestly exhorting him to set a definite and rigidlimit to the time he purposed spending in this apparently unprofitablefield. [Footnote: 'Je ne conseillerais à personne, ' said Dumas to hisalready famous pupil, 'de rester trop longtemps dans cesujet. '--Annales de Chimie et de Physique, 1862, vol. Lxiv. P. 22. Since that time the illustrious Perpetual Secretary of the Academy ofSciences has had good reason to revise this 'counsel. ']

Schooled by his education as a chemist, and by special researches onthe closely related question of fermentation, Pasteur took up thissubject under particularly favourable conditions. His work and hisculture had given strength and finish to his natural aptitudes. In1862, accordingly, he published a paper 'On the Organised Corpusclesexisting in the Atmosphere, ' which must for ever remain classical. Bythe most ingenious devices he collected the floating particles of theair surrounding his laboratory in the Rue d'Ulm, and subjected them tomicroscopic examination. Many of them he found to be organisedparticles. Sowing them in sterilised infusions, he obtained abundantcrops of microscopic organisms. By more refined methods he repeatedand confirmed the experiments of Schwann, which had been contested byPouchet, Montegazza, Joly, and Musset. He also confirmed theexperiments of Schroeder and von Dusch. He showed that the causewhich communicated life to his infusions was not uniformly diffusedthrough the air; that there were aerial interspaces which possessed nopower to generate life. Standing on the Mer de Glace, near theMontanvert, he snipped off the ends of a number of hermetically sealedflasks containing organic infusions. One out of twenty of the flasksthus supplied with glacier air showed signs of life afterwards, whileeight out of twenty of the same infusions, supplied with the air ofthe plains, became crowded with life. He took his flasks into thecaves under the Observatory of Paris, and found the still air in thesecaves devoid of generative power. These and other experiments, carried out with a severity perfectly obvious to the instructedscientific reader, and accompanied by a logic equally severe, restoredthe conviction that, even in these lower raches of the scale of being, life does not appear without the operation of antecedent life. 

The main position of Pasteur has been strengthened by practicalresearches of the most momentous kind. He has applied the knowledgewon from his enquiries to the preservation of wine and beer, to themanufacture of vinegar, to the staying of the plague which threatenedutter destruction of the silk husbandry of France, and to theexamination of other formidable diseases which assail the higheranimals, including man. His relation to the improvements whichProfessor Lister has introduced into surgery, is shown by a letterquoted in his Etudes sur la Bière. [Footnote: 1 P. 43. ] ProfessorLister there expressly thanks Pasteur for having given him the onlyprinciple which could have conducted the antiseptic system to asuccessful issue. The strictures regarding defects of reasoning, towhich we have been lately accustomed, throw abundant light upon theirauthor, but no shade upon Pasteur. 

Redi, as we have seen, proved the maggots of putrefying flesh to bederived from the eggs of flies; Schwann proved putrefaction itself tobe the concomitant of far lower forms of life than those dealt with byRedi. Our knowledge here, as elsewhere in connection with thissubject, has been vastly extended by Professor Cohn, of Breslau. 'Noputrefaction, ' he says, 'can occur in a nitrogenous substance if itsbacteria be destroyed and new ones prevented from entering it. Putrefaction begins as soon as bacteria, even in the smallest numbers, are admitted either accidentally or purposely. It progresses indirect proportion to the multiplication of the bacteria, it isretarded when they exhibit low vitality, and is stopped by allinfluences which either hinder their development or kill them. Allbactericidal media are therefore antiseptic and disinfecting. '[Footnote: In his last excellent memoir Cohn expresses himself thus:'Wer noch heut die Faeulniss von einer spontanen Dissociation derProteinmolecule, oder von einem unorganisirten Ferment ableitet, odergar aus "Stickstoffsplittern" die Balken zur Stuetze seinerFaeulnisstheorie zu zimmern versucht, hat zuerst den Satz "keineFaeulniss ohne Bacterium Termo" zu widerlegen. ']

It was these organisms acting in wound and abscess which so frequentlyconverted our hospitals into charnel-houses, and it is theirdestruction by the antiseptic system that now renders justifiableoperations which no surgeon would have attempted a few years ago. Thegain is immense--to the practising surgeon as well as to the patientpractised upon. Contrast the anxiety of never feeling sure whetherthe most brilliant operation might not be rendered nugatory by theaccess of a few particles of unseen hospital dust, with the comfortderived from the knowledge that all power of mischief on the part ofsuch dust has been surely and certainly annihilated. But the actionof living _contagia_ extends beyond the domain of the surgeon. The powerof reproduction and indefinite self-multiplication which ischaracteristic of living things, coupled with the undeviating fact of_contagia_ 'breeding true, ' has given strength and consistency to abelief long entertained by penetrating minds, that epidemic diseasesgenerally are the concomitants of parasitic life. 'There begins to befaintly visible to us a vast and destructive laboratory of naturewherein the diseases which are most fatal to animal life, and thechanges to which dead organic matter passively liable, appear boundtogether by what must least be called a very close analogy ofcausation. ' [Footnote: Report of the Medical Officer of the PrivyCouncil, 1874, p. 5. ] According to this view, which, as I have said, is daily gaining converts, a contagious disease may be defined aconflict between the person smitten by it and a specific organismwhich multiplies at his expense, appropriating his air and moisture, disintegrating his tissues, or poisoning him by the decompositionsincident to its growth. 

*****

During the ten years extending from 1859 to 1869, researches onradiant heat in its relations to the gaseous form of matter occupiedmy continual attention. When air was experimented on, I had tocleanse it effectually of floating matter, and while doing so I wassurprised to notice that, at the ordinary rate of transfer, suchmatter passed freely through alkalis, acids, alcohols, and ethers. Theeye being kept sensitive by darkness, a concentrated beam of light wasfound to be a most searching test for suspended matter both in waterand in air--a test indeed indefinitely more searching and severe thanthat furnished by the most powerful microscope. With the aid of sucha beam I examined air filtered by cotton-wool; air long kept free fromagitation, so as to allow the floating matter to subside; calcinedair, and air filtered by the deeper cells of the human lungs. In allcases the correspondence between my experiments and those ofSchroeder, Pasteur, and Lister in regard to spontaneous generation wasperfect. The air which they found inoperative was proved by theluminous beam to be optically pure and therefore germless. Havingworked at the subject both by experiment and reflection, on Fridayevening, January 21, 1870, I brought it before the members of theRoyal Institution. Two or three months subsequently, for sufficientpractical reasons, I ventured to direct public attention to thesubject in a letter to the Times. Such was my first contact with thisimportant question. 

This letter, I believe, gave occasion for the first public utteranceof Dr. Bastian in relation to this subject. He did me the honour toinform me, as others had informed Pasteur, that the subject 'pertainsto the biologist and physician: He expressed 'amazement' at myreasoning, and warned me that before what I had done could be undone'much irreparable mischief might be occasioned. ' With far lesspreliminary experience to guide and warn him, the English heterogenistwas far bolder than Pouchet in his experiments, and far moreadventurous in his conclusions. With organic infusions he obtainedthe results of his celebrated predecessor, but he did much more--theatoms and molecules of inorganic liquids passing under hismanipulation into those more 'complex chemical compounds, ' which wedignify by calling them 'living organisms. ' [Footnote: 'It is furtherheld that bacteria or allied organisms are prone to be engendered ascorrelative products, coming into existence in the severalfermentations, just as independently as other less complex chemicalcompounds. '--Bastian, Trans. Of Pathological Society, vol. Xxvi. 258. ]

As regards the public who take an interest in such things, andapparently also as regards a large portion of the medical profession, our clever countryman succeeded in restoring the subject to a state ofuncertainty similar to that which followed the publication ofPouchet's volume in 1859. 

It is desirable that this uncertainty should be removed from allminds, and doubly desirable on practical grounds that it should beremoved from the minds of medical men. In the present article, therefore, I propose discussing this question face to face with someeminent and fair-minded member of the medical profession who, asregards spontaneous generation, entertains views adverse to mine. Sucha one it would be easy to name; but it is perhaps better to rest inthe impersonal. I shall therefore simply call my proposed co-enquirermy friend. With him at my side, I shall endeavour, to the best of myability, so to conduct this discussion that he who runs may read andthat he who reads may understand. 

Let us begin at the beginning. I ask my friend to step into thelaboratory of the Royal Institution, where I place before him a basinof thin turnip slices barely covered with distilled water kept atemperature of 120° Fahr. After digesting the turnip for four or fivehours we pour off the liquid, boil it, filter it, and obtain aninfusion as clear as filtered drinking water. We cool the infusion, test its specific gravity, and find it to be 1006 or higher--waterbeing 1000. A number of small clean empty flasks, of the shape shownon the margin, are before us. One of them is slightly warmed with aspirit-lamp, and its open end is then dipped into the turnip infusion. The warmed glass is afterwards chilled, the air within the flaskscools, contracts, and is followed in its contraction by the infusion. Thus we get a small quantity of liquid into the flask. We now heatthis liquid carefully. Steam is produced, which issues from the openneck, carrying the air of the flask along with it. After a fewseconds' ebullition, the open neck is again Plunged into the infusion. The steam within the flask condenses, the liquid enters to supply itsplace, and in this way we fill our little flask to about four-fifthsof its volume. This description is typical; we may thus fill athousand flasks with a thousand different infusions. 

I now ask my friend to notice a trough made of sheet copper, with tworows of handy little Bunsen burners underneath it. This trough, orbath, is nearly filled with oil; a piece of thin plank constitutes akind of lid for the oil-bath. The wood is perforated with circularapertures wide enough to allow our small flask to pass through andplunge itself in the oil, which has been heated, say, to 250° Fahr. Clasped all round by the hot liquid, the infusion in the flask risesto its boiling point, which is not sensibly over 212° Fahr. Steamissues from the open neck of the flask, and the boiling is continuedfor five minutes. With a pair of small brass tongs, an assistant nowseizes the neck near its junction with the flask, and partially liftsthe latter out of the oil. The steam does not cease to issue, but itsviolence is abated. With a second pair of tongs held in one hand, theneck of the flask is seized close to its open end, while with theother hand a Bunsen's flame or an ordinary spirit flame is broughtunder the middle of the neck. The glass reddens, whitens, softens, and as it is gently drawn out the neck diminishes in diameter, untilthe canal is completely blocked up. The tongs with the fragment ofsevered neck being withdrawn, the flask, with its contents diminishedby evaporation, is lifted from the oil-bath perfectly sealedhermetically. 

Sixty such flasks filled, boiled, and sealed in the manner described, and containing strong infusions of beef, mutton, turnip, and cucumber, are carefully packed in sawdust, and transported to the Alps. Thither, to an elevation of about 7, 000 feet above the sea, I invite myco-enquirer to accompany me. It is the month of July, and the weatheris favourable to putrefaction. We open our box at the Bel-Alp, andcount out fifty-four flasks, with their liquids as clear as filtereddrinking water. In six flasks, however, the infusion is found muddy. We closely examine these, and discover that every one of them has hadits fragile end broken off in the transit from London. Air has enteredthe flasks, and the observed muddiness is the result. My colleagueknows as well as I do what this means. Examined with a pocket-lens, or even with a microscope of insufficient power, nothing is seen inthe muddy liquid; but regarded with a magnifying power of a thousanddiameters or so, what an astonishing appearance does it present!Leeuwenhoek estimated the population of a single drop of stagnantwater at 500, 000, 000: probably the population of a drop of our turbidinfusion would be this many times multiplied. The field of themicroscope is crowded with organisms, some wabbling slowly, othersshooting rapidly across the microscopic field. They dart hither andthither like a rain of minute projectiles; they pirouette and spin soquickly round, that the retention of the retinal impression transformsthe little living rod into a twirling wheel. And yet the mostcelebrated naturalists tell us they are vegetables. From the rod-likeshape which they so frequently assume, these organisms are called'bacteria'--a term, be it here remarked, which covers organisms ofvery diverse kinds. 

Has this multitudinous life been spontaneously generated in these sixflasks, or is it the progeny of living germinal matter carried intothe flasks by the entering air? If the infusions have aself-generative power, how are the sterility and consequent clearnessof the fifty-four uninjured flasks to be accounted for? My colleaguemay urge--and fairly urge--that the assumption of germinal matter isby no means necessary; that the air itself may be the one thing neededto wake up the dormant infusions. We will examine this pointimmediately. But meanwhile I would remind him that I am working onthe exact lines laid down by our most conspicuous heterogenist. Hedistinctly affirms that the withdrawal of the atmospheric pressureabove the infusion favours the production of organisms; and heaccounts for their absence in tins of preserved meat, fruit, andvegetables, by the hypothesis that fermentation has begun in suchtins, that gases have been generated, the pressure of which hasstifled the incipient life and stopped its further development. [Footnote: _Beginnings of Life_, vol. I. ] This is the newtheory of preserved meats. Had its author pierced a tin of preservedmeat, fruit, or vegetable under water with the view of testing itstruth, he would have found it erroneous. In well-preserved tins hewould have found, not an outrush of gas, but an inrush of water. Ihave noticed this recently in tins which have lain perfectly good forsixty-three years in the Royal Institution. Modern tins, subjected tothe same test, yielded the same result. From time to time, moreover, during the last two years, I have placed glass tubes, containing clearinfusions of turnip, hay, beef, and mutton, in iron bottles, andsubjected them to air-pressures varying from ten to twenty-sevenatmospheres--pressures, it is needless to say, far more thansufficient to tear a preserved meat tin to shreds. After ten daysthese infusions were taken from their bottles rotten with putrefactionand teeming with life. Thus collapses an hypothesis which had norational foundation, and which could never have seen the light had theslightest attempt been made to verify it. 

Our fifty-four vacuous and pellucid flasks also declare against theheterogenist. We expose them to a warm Alpine sun by day, and at nightwe suspend them in a warm kitchen. Four of them have beenaccidentally broken; but at the end of a month we find the fiftyremaining ones as clear as at the commencement. There is no sign ofputrefaction or of life in any of them. We divide these flasks intotwo groups of twenty-three and twenty-seven respectively (an accidentof counting rendered the division uneven). The question now iswhether the admission of air can liberate any generative energy in theinfusions. Our next experiment will answer this question andsomething more. We carry the flasks to a hayloft, and there, with apair of steel pliers, snip off the sealed ends of the group ofthree-and-twenty. Each snipping off is of course followed by aninrush of air. We now carry our twenty-seven flasks, our pliers, anda spirit-lamp, to a ledge overlooking the Aletsch glacier, about 200feet above the hayloft, from which ledge the mountain falls almostprecipitously to the north-east for about a thousand feet. A gentlewind blows towards us from the north-east--that is, across the crestsand snow-fields of the Oberland mountains. We are therefore bathed byair which must have been for a good while out of practical contactwith either animal or vegetable life. I stand carefully to leeward ofthe flasks, for no dust or particle from my clothes or body must beblown towards them. An assistant ignites the spirit-lamp, into theflame of which I plunge the pliers, thereby destroying all attachedgerms or organisms. Then I snip off the sealed end of the flask. Prior to every snipping the same process is gone through, no flaskbeing opened without the previous cleansing of the pliers by theflame. In this way we charge our seven-and-twenty flasks with cleanvivifying mountain air. 

We place the fifty flasks, with their necks open, over a kitchenstove, in a temperature varying from 50° to 90° Fahr, and in threedays find twenty-one out of the twenty-three flasks opened on thehayloft invaded by organisms--two only of the group remaining freefrom them. After three weeks' exposure to precisely the sameconditions, not one of the twenty-seven flasks opened in free air hadgiven way. No germ from the kitchen air had ascended the narrownecks, the flasks being shaped to produce this result. They are stillin the Alps, as clear, I doubt not, and as free from life as they werewhen sent off from London. [Footnote: An actual experiment made at theBel Alp is here described. ]

What is my colleague's conclusion from the experiment before us?Twenty-seven putrescible infusions, first in vacuo, and afterwardssupplied with the most invigorating air, have shown no sign ofputrefaction or of life. And as to the others, I almost shrink fromasking him whether the hayloft has rendered them spontaneouslygenerative. Is not the inference here imperative that it is not theair of the loft--which is connected through a constantly open doorwith the general atmosphere--but something contained in the air, thathas produced the effects observed? What is this something? A sunbeamentering through a chink in the roof or wall, and traversing the airof the loft, would show it to be laden with suspended dust particles. Indeed the dust is distinctly visible in the diffused daylight. Canit have been the origin of the observed life? If so, are we not boundby all antecedent experience to regard these fruitful particles as thegerms of the life observed?

The name of Baron Liebig has been constantly mixed up with thesediscussions. 'We have, ' it is said, 'his authority for assuming thatdead decaying matter can produce fermentation. ' True, but with Liebigfermentation was by no means synonymous with life. It meant, according to him, the shaking asunder by chemical disturbance ofunstable molecules. Does the life of our flasks, then, proceed fromdead particles? If my co-enquirer should reply 'Yes, ' then I wouldask him, 'What warrant does Nature offer for such an assumption?Where, amid the multitude of vital phenomena in which her operationshave been clearly traced, is the slightest countenance given to thenotion that the sowing of dead particles can produce a living crop?'With regard to Baron Liebig, had he studied the revelations of themicroscope in relation to these questions, a mind so penetrating couldnever have missed the significance of the facts revealed. He, however, neglected the microscope, and fell into error--but not intoerror so gross as that in support of which his authority has beeninvoked. Were he now alive, he would, I doubt not, repudiate the useoften made of his name--Liebig's view of fermentation was at least ascientific one, founded on profound conceptions of molecularinstability. But this view by no means involves the notion that theplanting of dead particles--'Stickstoffsplittern' as Cohncontemptuously calls them--is followed by the sprouting of infusoriallife. 

*****

Let us now return to London and fix our attention on the dust of itsair. Suppose a room in which the housemaid has just finished her workto be completely closed, with the exception of an aperture in ashutter through which a sunbeam enters and crosses the room. Thefloating dust reveals the track of the light. Let a lens be placed inthe aperture to condense the beam. Its parallel rays are nowconverged to a cone, at the apex of which the dust is raised to almostunbroken whiteness by the intensity of its illumination. Defendedfrom all glare, the eye is peculiarly sensitive to this, scatteredlight. The floating dust of London rooms is organic, and may beburned without leaving visible residue. The action of a spirit-lampflame upon the floating matter has been elsewhere thus described:

*****

In a cylindrical beam which strongly illuminated the dust of ourlaboratory, I placed an ignited spirit-lamp. Mingling with the flame, and round its rim, were seen curious wreaths of darkness resembling anintensely black smoke. On placing the flame at some distance belowthe beam, the same dark masses stormed upwards. They were blackerthan the blackest smoke ever seen issuing from the funnel of asteamer; and their resemblance to smoke was so perfect as to promptthe conclusion that the apparently pure flame of the alcohol-lamprequired but a beam of sufficient intensity to reveal its clouds ofliberated carbon. 

But is the blackness smoke? This question presented itself in amoment, and was thus answered: A red-hot poker was placed underneaththe beam; from it the black wreaths also ascended. A large hydrogenflame, which emits no smoke, was next employed, and it also producedwith augmented copiousness those whirling masses of darkness. Smokebeing out of the question, what is the blackness? It is simply thatof stellar space; that is to say, blackness resulting from the absencefrom the track of the beam of all matter competent to scatter itslight. When the flame was placed below the beam, the floating matterwas destroyed in situ; and the heated air, freed from this matter, rose into the beam, jostled aside the illuminated particles, andsubstituted for their light the darkness due to its own perfecttransparency. Nothing could more forcibly illustrate the invisibilityof the agent which renders all things visible. The beam crossed, unseen, the black chasm formed by the transparent air, while, at bothsides of the gap, the thick-strewn particles shone out like a luminoussolid under the powerful illumination. [Footnote: See Fragment: 'OnDust and Disease', vol. I. ]

*****

Supposing an infusion intrinsically barren, but readily susceptible ofputrefaction when exposed to common air, to be brought into contactwith this unilluminable air, what would be the result? It would neverputrefy. It might, however, be urged that the air is spoiled by itsviolent calcination. Oxygen passed through a spirit-lamp flame is, itmay be thought, no longer the oxygen suitable for the development andmaintenance of life. We have an easy escape from this difficulty, which is based, however, upon the unproved assumption that the air hasbeen affected by the flame. Let a condensed beam be sent through alarge flask or bolthead containing common air. The track of the beamis seen within the flask--the dust revealing the light, and the lightrevealing the dust. Cork the flask, stuff its neck with cotton-wool, or simply turn it mouth downwards and leave it undisturbed for a dayor two. Examined afterwards with the luminous beam, no track isvisible; the light passes through the flask as through a vacuum. Thefloating matter has abolished itself, being now attached to theinterior surface of the flask. 

Were it our object, as it will be subsequently, to effectually detainthe dirt, we might coat that surface with some sticky substance. Here, then, without 'torturing' the air in any way, we have found a means ofridding it, or rather of enabling it to rid itself, of floatingmatter. 

We have now to devise a means of testing the action of suchspontaneously purified air upon putrescible infusions. Woodenchambers, or cases, are accordingly constructed, having glass fronts, side-windows, and back-doors. Through the bottoms of the chamberstest-tubes pass air-tight; their open ends, for about one-fifth of thelength of the tubes, being within the chambers. Provision is made fora free connection rough sinuous channels between the inner and theouter air. Through such channels, though open, no dust will reach thechamber. The top of each chamber is perforated by a circular hole twoinches in diameter, closed air-tight by a sheet of India-rubber. Thisis pierced in the middle by a pin, and through the pin-hole is pushedthe shank of a long pipette, ending above in a small funnel. Theshank also passes through a stuffing-box of cotton-wool moistened withglycerine; so that, tightly clasped by the rubber and wool, thepipette is not likely in its motions up and down to carry any dustinto the chamber. The annexed woodcut shows a chamber, with sixtest-tubes, its side-windows w w, its pipette p c, and its sinuouschannels a b which connect the air of the chamber with the outer air. 

The chamber is carefully closed and permitted to remain quiet for twoor three days. Examined at the beginning by a beam sent through itswindows, the air is found laden with floating matter, which in threedays has wholly disappeared. To prevent its ever rising again, theinternal surface of the chamber was at the outset coated withglycerine. The fresh but putrescible liquid is introduced into thesix tubes in succession by means of the pipette. Permitted to remainwithout further precaution, every one of the tubes would putrefy andfill itself with life. The liquid has been in contact with thedust-laden air outside by which it has been infected, and theinfection must be destroyed. This is done by plunging the six tubesinto a bath of heated oil and boiling the infusion. The timerequisite to destroy the infection depends wholly upon its nature. Twominutes' boiling suffices to destroy some _contagia_, whereas twohundred minutes' boiling fails to destroy others. After the infusionhas been sterilised, the oil-bath is withdrawn, and the liquid, whoseputrescibility has been in no way affected by the boiling, isabandoned to the air of the chamber. 

With such chambers I tested, in the autumn and winter of 1875-6, infusions of the most various kinds, embracing natural animal liquids, the flesh and viscera of domestic animals, game, fish, and vegetables. More than fifty chambers, each with its series of infusions, weretested, many of them repeatedly. There was no shade of uncertainty inany of the results. In every instance we had, within the chamber, perfect limpidity and sweetness, which in some cases lasted for morethan a year--without the chamber, with the same infusion, putridityand its characteristic smells. In no instance was the leastcountenance lent to the notion that an infusion deprived by heat ofits inherent life, and placed in contact with air cleansed of itsvisibly suspended matter, has any power to generate life anew. 

Remembering then the number and variety of the infusions employed, andthe strictness of our adherence to the rules of preparation laid downby the heterogenists themselves; remembering that we have operatedupon the very substances recommended by them as capable of furnishing, even in untrained hands, easy and decisive proofs of spontaneousgeneration, and that we have added to their substances many others ofour own--if this pretended generative power were a reality, surely itmust have manifested itself somewhere. Speaking roundly, I should saythat in such closed chambers at least five hundred chances have beengiven to it, but it has nowhere appeared. 

The argument is now to be clenched by an experiment which will removeevery residue of doubt as to the ability of the infusions hereemployed to sustain life. We open the back doors of our sealedchambers, and permit the common air with its floating particles tohave access to our tubes. For three months they have remainedpellucid and sweet--flesh, fish, and vegetable extracts purer thanever cook manufactured. Three days' exposure to the dusty airsuffices to render them muddy, fetid, and swarming with infusoriallife. The liquids are thus proved, one and all, ready forputrefaction when the contaminating agent is applied. I invite mycolleague to reflect on these facts. How will he account for theabsolute immunity of a liquid exposed for months in a warm room tooptically pure air, and its infallible putrefaction in a few days whenexposed to dust-laden air? He must, I submit, bow to the conclusionthat the dust-particles are the cause of putrefactive life. Andunless he accepts the hypothesis that these particles, being dead inthe air, are in the liquid miraculously kindled into living things, hemust conclude that the life we have observed springs from germs ororganisms diffused through the atmosphere. 

The experiments with hermetically sealed flasks have reached thenumber of 940. A sample group of 130 of them were laid before theRoyal Society on January 13, 1876. They were utterly free from life, having been completely sterilised by three minutes' boiling. Specialcare had been taken that the temperatures to which the flasks wereexposed should include those previously alleged to be efficient. Theconditions laid down by the heterogenist were accurately copied, butthere was no corroboration of his results. Stress was then laid onthe question of warmth, thirty degrees being suddenly added to thetemperatures with which both of us had previously worked. Waiving allprotest against the caprice thus manifested, I met this newrequirement also. The sealed tubes, which had proved barren in theRoyal Institution, were suspended in perforated boxes, and placedunder the supervision of an intelligent assistant in the Turkish Bathin Jermyn Street. From two to six days had been allowed for thegeneration of organisms in hermetically sealed tubes. Mine remainedin the washing-room of the bath for nine days. Thermometers placed inthe boxes, and read off twice or three times a day, showed thetemperature to vary from a minimum of 101° to a maximum of 112° Fahr. At the end of nine days the infusions were as clear as at thebeginning. They were then removed to a warmer position. Atemperature of 115° had been mentioned as particularly favourable tospontaneous generation. For fourteen days the temperature of theTurkish Bath hovered about this point, falling once as low as 106°, reaching 116° on three occasions, 118° on one, and 119° on two. Theresult was quite the same as that just recorded. The highertemperatures proved perfectly incompetent to develope life. 

Taking the actual experiment we have made as a basis of calculation, if our 940 flasks were opened on the hayloft of the Bel Alp, 858 ofthem would become filled with organisms. The escape of the remaining82 strengthens our case, proving as it does conclusively that not inthe air, nor in the infusions, nor in anything continuous diffusedthrough the air, but in discrete particles, suspended in the air andnourished by the infusions, we are to seek the cause of life. Ourexperiment proves these particles to be in some cases so far apart onthe hayloft as to permit 10 per cent of our flasks to take in airwithout contracting contamination. A quarter of a century ago Pasteurproved the cause of 'so-called spontaneous generation' to bediscontinuous. I have already referred to his observation that 12 outof 20 flasks opened on the plains escaped infection, while 19 out of20 flasks opened on the Mer de Glace escaped. Our own experiment atthe Bel Alp is a more emphatic instance of the same kind, 90 per centof the flasks opened in the hayloft being smitten, while not one ofthose opened on the free mountain ledge was attacked. 

The power of the air as regards putrefactive infection is incessantlychanging through natural causes, and we are able to alter it at will. Of a number of flasks opened in 1876 in the laboratory of the RoyalInstitution, 42 per cent. Were smitten, while 58 per cent. Escaped. In 1877 the proportion in the same laboratory was 68 per cent. Smitten, to 32 intact. The greater mortality, so to speak, of theinfusions in 1877 was due to the presence of hay which diffused itsgerminal dust in the laboratory air, causing it to approximate asregards infective virulence to the air of the Alpine loft. I wouldask my friend to bring his scientific penetration to bear upon all theforegoing facts. They do not prove spontaneous generation to be'impossible. ' My assertions, however, relate not to 'possibilities, 'but to proofs, and the experiments just described do most 'distinctlyprove the evidence on which the heterogenist relies to be written onwaste paper. 

My colleague will not, I am persuaded, dispute these results; but hemay be disposed to urge that other able and honourable men working atthe same subject have arrived at conclusions different from mine. Mostfreely granted; but let me here recur to the remarks already made inspeaking of the experiments of Spallanzani, to the effect that thefailure of others to confirm his results by no means upsets theirevidence. To fix the ideas, let us suppose that my colleague comes tothe laboratory of the Royal Institution, repeats there my experiments, and obtains confirmatory results; and that he then goes to Universityor King's College where, operating with the same infusions, he obtainscontradictory results. Will he be disposed to conclude that theselfsame substance is barren in Albemarle Street and fruitful in GowerStreet or the Strand? His Alpine experience has already made known tohim the literally infinite differences existing between differentsamples of air as regards their capacity for putrefactive infection. And, possessing this knowledge, will he not substitute for theadventurous conclusion that an organic infusion is barren at one placeand spontaneously generative at another, the more rational and obviousone that the atmospheres of the two localities which have had accessto the infusion are infective in different degrees?

As regards workmanship, moreover, he will not fail to bear in mind, that fruitfulness may be due to errors of manipulation, whilebarrenness involves the presumption of correct experiment. It is onlythe careful worker that can secure the latter, while it is open toevery novice to obtain the former. Barrenness is the result at whichthe conscientious experimenter, whatever his theoretic convictions maybe, ought to aim, omitting no pains to secure it, and resorting onlywhen there is no escape from it to the conclusion that the lifeobserved comes from no source which correct experiment couldneutralise or avoid. 

Let us again take a definite case. Supposing my colleague to operatewith the same apparent care on 100 infusions--or rather on 100 samplesof the same infusion--and that 50 of them prove fruitful and 50barren. Are we to say that the evidence for and against heterogeny isequally balanced? There are some who would not only say this, but whowould treasure up the 50 fruitful flasks as 'positive' results, andlower the evidential value of the 50 barren flasks by labelling them'negative' results. This, as shown by Dr. William Roberts, is anexact inversion of the true order of the terms positive and negative. [Footnote: See his truly philosophical remarks on this head in the'British Medical Journal, ' 1876, p. 282. ] Not such, I trust, wouldbe the course pursued by my friend. As regards the 50 fruitful flaskshe would, I doubt not, repeat the experiment with redoubled care andscrutiny, and not by one repetition only, but by many, assure himselfthat he had not fallen into error. Such faithful scrutiny fullycarried out would infallibly lead him to the conclusion that here, asin all other cases, the evidence in favour of spontaneous generationcrumbles in the grasp of the competent enquirer. 

The botanist knows that different seeds possess different powers ofresistance to heat. [Footnote: I am indebted to Dr. Thiselton Dyer forvarious illustrations of such differences. It is, however, surprisingthat a subject of such high scientific importance should not have beenmore thoroughly explored. Here the scoundrels who deal in killedseeds might be able to add to our knowledge. ] Some are killed by amomentary exposure to the boiling temperature, while others withstandit for several hours. Most of our ordinary seeds are rapidly killed, while Pouchet made known to the Paris Academy of Sciences in 1866, that certain seeds, which had been transported in fleeces of wool fromBrazil, germinated after four hours' boiling. The germs of the airvary as much among themselves as the seeds of the botanist. In somelocalities the diffused germs are so tender that boiling for fiveminutes, or even less, would be sure to destroy them all; in otherlocalities the diffused germs are so obstinate, that many hours'boiling would be requisite to deprive them of their power ofgermination. The absence or presence of a truss of desiccated haywould produce differences as great as those here described. Thegreatest endurance that I have ever observed--and I believe it is thegreatest on record--was a case of survival after eight hours' boiling. 

As regards their power of resisting heat, the infusorial germs of ouratmosphere might be classified under the following and intermediateheads: Killed in five minutes; not killed in five minutes but killedin fifteen; not killed in fifteen minutes but killed in thirty; notkilled in thirty minutes but killed in an hour; not killed in an hourbut killed in two hours; not killed in two but killed in three hours;not killed in three but killed in four hours. I have had severalcases of survival after four and five hours' boiling, some survivalsafter six, and one after eight hours' boiling. Thus far hasexperiment actually reached; but there is no valid warrant for fixingupon even eight hours as the extreme limit of vital resistance. Probably more extended researches (though mine have been veryextensive) would reveal germs more obstinate still. It is alsocertain that we might begin earlier, and find germs which aredestroyed by a temperature far below that of boiling water. In thepresence of such facts, to speak of a death-point of bacteria andtheir germs would be unmeaning--but of this more anon. 

'What present warrant, ' it has been asked, 'is there for supposingthat a naked, or almost naked, speck of protoplasm can withstand four, six, or eight hours' boiling?' Regarding naked specks of protoplasm Imake no assertion. I know nothing about them, save as the creaturesof fancy. But I do affirm, not as a 'supposition, ' nor an'assumption, ' nor a 'probable guess, ' nor as 'a wild hypothesis, ' butas a matter of the most undoubted fact, that the spores of the haybacillus, when thoroughly desiccated by age, have withstood the ordealmentioned. And I further affirm that these obdurate germs, under theguidance of the knowledge that they are germs, can be destroyed byfive minutes' boiling, or even less. This needs explanation. Thefinished bacterium perishes at a temperature far below that of boilingwater, and it is fair to assume that the nearer the germ is to itsfinal sensitive condition the more readily will it succumb to heat. Seeds soften before and during germination. This premised, the simpledescription of the following process will suffice to make its meaningunderstood. 

An infusion infected with the most powerfully resistent germs, butotherwise protected against the floating matters of the air, isgradually raised to its boiling-point. Such germs as have reached thesoft and plastic state immediately preceding their development intobacteria are thus destroyed. The infusion is then put aside in a warmroom for ten or twelve hours. If for twenty-four, we might have theliquid charged with well-developed bacteria. To anticipate this, atthe end of ten or twelve hours we raise the infusion a second time tothe boiling temperature, which, as before, destroys all germs thenapproaching their point of final development. The infusion is againput aside for ten or twelve hours, and the process of heating isrepeated. We thus kill the germs in order of their resistance, andfinally kill the last of them. No infusion can withstand this processif it be repeated a sufficient number of times. Artichoke, cucumber, and turnip infusions, which had proved specially obstinate wheninfected with the germs of desiccated hay, were completely broken downby this method of discontinuous heating, three minutes being foundsufficient to accomplish what three hundred minutes' continuousboiling failed to accomplish. I applied the method, moreover, toinfusions of various kinds of hay, including those most tenacious oflife. Not one of them bore the ordeal. These results were clearlyforeseen before they were realised, so that the germ theory fulfilsthe test of every true theory, that test being the power of prevision. 

When 'naked or almost naked specks of protoplasm' are spoken of, theimagination is drawn upon, not the objective truth of Nature. Suchwords sound like the words of knowledge where knowledge is really nil. The possibility of a 'thin covering' is conceded by those who speak inthis way. Such a covering may, however, exercise a powerfulprotective influence. A thin pellicle of India-rubber, for example, surrounding a pea keeps it hard in boiling water for a time sufficientto reduce an uncovered pea to a pulp. The pellicle preventsimbibition, diffusion, and the consequent disintegration. A greasy oroily surface, or even the layer of air which clings to certain bodies, would act to some extent in a similar way. 'The singular resistanceof green vegetables to sterilisation, ' says Dr. William Roberts, 'appears to be due to some peculiarity of the surface, perhaps theirsmooth glistening epidermis which prevented complete wetting of theirsurfaces. ' I pointed out in 1876 that the process by which anatmospheric germ is wetted would be an interesting subject ofinvestigation. A dry microscope covering-glass may be caused to floaton water for a year. A sewing-needle may be similarly kept floating, though its specific gravity is nearly eight times that of water. 

Were it not for some specific relation between the matter of the germand that of the liquid into which it falls, wetting would be simplyimpossible. Antecedent, to all development there must be aninterchange of matter between the germ and its environment; and thisinterchange must obviously depend upon the relation of the germ to itsencompassing liquid. Anything that hinders this interchange retardsthe destruction of the germ in boiling water. In my paper publishedin the 'Philosophical Transactions' for 1877, I add the followingremark:

It is not difficult to see that the surface of a seed or germ may beso affected by desiccation and other causes as practically to preventcontact between it and the surrounding liquid. The body of a germ, moreover, may be so indurated by time and dryness as to resistpowerfully the insinuation of water between its constituent molecules. It would be difficult to cause such a germ to imbibe the moisturenecessary to produce the swelling and softening which precede itsdestruction in a liquid of high temperature. 

*****

However this may be--whatever be the state of the surface, or of thebody, of the spores of Bacillus subtilis, they do as a matter ofcertainty resist, under some circumstances, exposure for hours to theheat of boiling water. No theoretic scepticism can successfully standin the way of this fact, established as it has been by hundreds, ifnot thousands, of rigidly conducted experiments. 

*****

We have now to test one of the principal foundations of the doctrineof spontaneous generation as formulated in this country. With thisview, I place before my friend and co-enquirer two liquids which havebeen kept for six months in one of our sealed chambers, exposed tooptically pure air. The one is a mineral solution containing in properproportions all the substances which enter into the composition ofbacteria, the other is an infusion of turnip-it might be any one of ahundred other infusions, animal or vegetable. Both liquids are asclear as distilled water, and there is no trace of life in either ofthem. They are, in fact, completely sterilised. A mutton-chop, overwhich a little water has been poured to keep its juices from dryingup, has lain for three days upon a plate in our warm room. It smellsoffensively. Placing a drop of the fetid mutton-juice under amicroscope, it is found swarming with the bacteria of putrefaction. With a speck of the swarming liquid I inoculate the clear mineralsolution and the clear turnip infusion, as a surgeon might inoculatean infant with vaccine lymph. In four-and-twenty hours the transparentliquids have become turbid throughout, and instead of being barren asat first they are teeming with life. The experiment may be repeated athousand times with the same invariable result. To the naked eye theliquids at the beginning were alike, being both equally transparent-tothe naked eye they are alike at the end, being both equally muddy. Instead of putrid mutton-juice, we might take as a source of infectionany one of a hundred other putrid liquids, animal or vegetable. Solong as the liquid contains living bacteria a speck of it communicatedeither to the clear mineral solution, or to the clear turnip infusion, produces in twenty-four hours the effect here described. 

We now vary the experiment thus: Opening the back-door of anotherclosed chamber which has contained for months the pure mineralsolution and the pure turnip infusion side by side, I drop into eachof them a small pinch of laboratory dust. The effect here is tardierthan when the speck of putrid liquid was employed. In three days, however, after its infection with the dust, the turnip infusion ismuddy, and swarming as before with bacteria. But what about themineral solution which, in our first experiment, behaved in a mannerundistinguishable from the turnip-juice? At the end of three daysthere is not a bacterium to be found in it. At the end of three weeksit is equally innocent of bacterial life. We may repeat the experimentwith the solution and the infusion a hundred times with the sameinvariable result. Always in the case of the latter the sowing, of theatmospheric dust yields a crop of bacteria-never in the former doesthe dry germinal matter kindle into active life. [Footnote: This isthe deportment of the mineral solution as described by others. My ownexperiments would lead me to say that the development of thebacteria, though exceedingly slow and difficult, is not impossible. ]What is the inference which the reflecting mind must draw from thisexperiment? Is it not as clear as day that while both liquids areable to feed the bacteria and to enable them to increase and multiply, after they have been once, fully developed, only one of the liquids isable to develope into active bacteria the germinal dust of the air?

I invite my friend to reflect upon this conclusion he will, I think, see that there is no escape from it. He may, if he prefers, hold theopinion, which I consider erroneous, that bacteria exist in the air, not as germs but as desiccated organisms. The inference remains, thatwhile the one liquid is able to force the passage from the inactive tothe active state, the other is not. 

But this is not at all the inference which has been drawn fromexperiments with the mineral solution. 

Seeing its ability to nourish bacteria when once inoculated with theliving active organism, and observing that no bacteria appeared in thesolution after long exposure to the air, the inference was drawn thatneither bacteria nor their germs existed in the air. ThroughoutGermany the ablest literature of the subject, even that opposed toheterogeny, is infected with this error; while heterogenists at homeand abroad have based upon it a triumphant demonstration of, theirdoctrine. It is proved, they say, by the deportment of the mineralsolution that neither bacteria nor their germs exist in the air;hence, if, on exposing a thoroughly sterilised turnip infusion to theair, bacteria appear, they must of necessity have been spontaneouslygenerated. In the words of Dr. Bastian: 'We can only infer that whilstthe boiled saline solution is quite incapable of engendering bacteria, such organisms are able to arise _de novo_ in the boiled organicinfusion. ' [Footnote: 'Proceedings of the Royal Society, ' vol. Xxi. P. 130. ]

I would ask my eminent colleague what he thinks of this reasoning now?The datum is--'A mineral solution exposed to common air does notdevelope bacteria;' the inference is--'Therefore if a turnip infusionsimilarly exposed develope bacteria, they must be spontaneouslygenerated. ' The inference, on the face of it, is an unwarranted one. But while as matter of logic it is inconclusive, as matter of fact itis chimerical. London air is as surely charged with the germs ofbacteria as London chimneys are with smoke. The inference justreferred to is completely disposed of by the simple question: 'Why, when your sterilised organic infusion is exposed to optically pureeair, should this generation of life _de novo_ utterly cease? Why shouldI be able to preserve my turnip-juice side by side with your salinesolution for the three hundred and sixty-five days of the year, infree connection with the general atmosphere, on the sole conditionthat the portion of that atmosphere in contact with the juice shall bevisibly free from floating dust, while three days' exposure to thatdust fills it with bacteria?' Am I over sanguine in hoping that asregards the argument here set forth he who runs may read, and he whoreads may understand?

We now proceed to the calm and thorough consideration of anothersubject, more important if possible than the foregoing one, but likeit somewhat difficult to seize by reason of the very opulence of thephraseology, logical and rhetorical, in which it has been set forth. The subject now to be considered relates to what has been called 'thedeath-point of bacteria. ' Those who happen to be acquainted with themodern English literature of the question will remember how challengeafter challenge has been issued to panspermatists in general, and toone or two home workers in particular, to come to close quarters onthis cardinal point. It is obviously the stronghold of the Englishheterogenist. 'Water, ' he says, `is boiling merrily over a fire whensome luckless person upsets the vessel so that the heated fluidexercises its scathing influence upon an uncovered portion of thebody-hand, arm, or face. Here, at all events, there is no room fordoubt. Boiling water unquestionably exercises a most pernicious andrapidly destructive effect upon the living matter of which we arecomposed. ' [Footnote: Bastian, 'Evolution, ' p. 133. ] And lest itshould be supposed that it is the high organisation which, in thiscase, renders the body susceptible to heat, he refers to the action ofboiling water on the hen's egg to dissipate the notion. 'Theconclusion, ' he says, 'would seem to force itself upon us that thereis something intrinsically deleterious in the action of boiling waterupon living matter-whether this matter be of high or of loworganisation. ' [Footnote: Bastian, 'Evolution, ' p. 135. ] Again, atanother place: 'It has been shown that the briefest exposure to theinfluence of boiling water is destructive of all living matter. '[Footnote: Ibid. P. 46]

The experiments already recorded plainly show that there is a markeddifference between the dry bacterial matter of the air, and the wet, soft, and active bacteria of putrefying organic liquids. The one canbe luxuriantly bred in the saline solution, the others refuse to beborn there, while both of them are copiously developed in a sterilisedturnip infusion. Inferences, as we have already seen, founded on thedeportment of the one liquid cannot with the warrant of scientificlogic be extended to the other. But this is exactly what theheterogenist has done, thus repeating as regards the death-point ofbacteria the error into which he fell concerning the germs of the air. Let us boil our muddy mineral solution with its swarming bacteria forfive minutes. In the soft succulent condition in which they exist inthe solution not one of them escapes destruction. The same is true ofthe turnip infusion if it be inoculated with the living bacteriaonly-the aerial dust being carefully excluded. In both cases the deadorganisms sink to the bottom of the liquid, and without re-inoculationno fresh organisms will arise. But the case is entirely different whenwe inoculate our turnip infusion with the desiccated germinal matterafloat in the air. 

The 'death-point' of bacteria is the maximum temperature at which theycan live, or the minimum temperature at which they cease to live. If, for example, they survive a temperature of 140°, and do not survive atemperature of 150°, the death-point lies somewhere between these twotemperatures. Vaccine lymph, for example, is proved by Messrs. Braidwood and Vacher to be deprived of its power of infection by briefexposure to a temperature between 140° and 150° Fahr. This may beregarded as the death-point of the lymph, or rather of the particlesdiffused in the lymph, which constitute the real _contagium_. If notime, however, be named for the application of the heat, the term'death-point' is a vague one. An infusion, for example, which willresist five hours' continuous exposure to the boiling temperature, will succumb to five days' exposure to a temperature 50° Fahr. Belowthat of boiling. The fully developed soft bacteria of putrefyingliquids are not only killed by five minutes' boiling, but by less thana single minute's boiling--indeed, they are slain at about the sametemperature as the vaccine. The same is true of the plastic, activebacteria of the turnip infusion [Footnote: In my paper in the'Philosophical Transactions' for 1876, I pointed out and illustratedexperimentally the difference, as regards rapidity of development, between water-germs and air-germs; the growth from the alreadysoftened water-germs proving to be practically as rapid as fromdeveloped bacteria. This preparedness of the germ for rapiddevelopment is associated with its preparedness for rapiddestruction. ]

But, instead of choosing a putrefying liquid for inoculation, let usprepare and employ our inoculating substance in the following simpleway:-Let a small wisp of hay, desiccated by age, be washed in a glassof water, and let a perfectly sterilised turnip infusion be inoculatedwith the washing liquid. After three hours' continuous boiling theinfusion thus infected will often develope luxuriant bacterial life. Precisely the same occurs if a turnip infusion be prepared in anatmosphere well charged with desiccated hay-germs. The infusion inthis case infects itself without special inoculation, and itssubsequent resistance to sterilisation is often very great. On the1st of March last I purposely infected the air of our laboratory withthe germinal dust of a sapless kind of hay mown in 1875. Ten groupsof flasks were charged with turnip infusion prepared in the infectedlaboratory, and were afterwards subjected to the boiling temperaturefor periods varying from 15 minutes to 240 minutes. Out of the tengroups only one was sterilised--that, namely, which had been boiledfor four hours. Every flask of the nine groups which had been boiledfor 15, 30, 45, 60, 75, 90, 105, 120, and 180 minutes respectively, bred organisms afterwards. The same is true of other vegetableinfusions. On the 28th of February last, for example, I boiled sixflasks, containing cucumber infusion prepared in an infectedatmosphere, for periods of 15, 30, 45, 60, 120, and 180 minutes. Everyflask of the group subsequently developed organisms. On the same day, in the case of three flasks, the boiling was prolonged to 240, 300, and 360 minutes; and these three flasks were completely sterilised. Animal infusions, which under ordinary circumstances are renderedinfallibly barren by five minutes' boiling, behave like the vegetableinfusions in an atmosphere infected with hay-germs. On the 30th ofMarch, for example, five flasks were charged with a clear infusion ofbeef and boiled for 60 minutes, 120 minutes, 180 minutes, 240 minutes, and 300 minutes respectively. Every one of them became subsequentlycrowded with organisms, and the same happened to a perfectly pellucidmutton infusion prepared at the same time. The cases are to benumbered by hundreds in which similar powers of resistance weremanifested by infusions of the most diverse kinds. 

In the presence of such facts I would ask my colleague whether it isnecessary to dwell for a single instant on the one-sidedness of theevidence which led the conclusion that all living matter has its lifedestroyed by 'the briefest exposure to the influence of boilingwater. ' An infusion proved to be barren by six months' exposure tomoteless air maintained at a temperature of 90° Fahr, when inoculatedwith full-grown active bacteria, fills itself in two days withorganisms so sensitive as to be killed by a few minutes' exposure to atemperature much below that of boiling water. But the extension ofthis result to the desiccated germinal matter of the air is withoutwarrant or justification. This is obvious without going beyond theargument itself. But we have gone far beyond the argument, and provedby multiplied experiment the alleged destruction of all living matterby the briefest exposure to the influence of boiling water to be adefusion. The whole logical edifice raised upon this basis fallstherefore to the ground; and the argument that bacteria and theirgerms, being destroyed at 140°, must, if they appear after exposure to212°, be spontaneously generated, is, I trust, silenced for ever. 

Through the precautions, variations, and repetitions observed andexecuted with the view of rendering its results secure, the separatevessels employed in this enquiry have mounted up in two years tonearly ten thousand. 

Besides the philosophic interest attaching to the problem of life'sorigin, which will be always immense, there are the practicalinterests involved in the application of the doctrines here discussedto surgery and medicine. The antiseptic system, at which I havealready glanced, illustrates the manner in which beneficent results ofthe gravest moment follow in the wake of clear theoretic insight. Surgery was once a noble art; it is now, as well, a noble science. Prior to the introduction of the antiseptic system, the thoughtfulsurgeon could not have failed to learn empirically that there wassomething in the air which often defeated the most consummateoperative skill. That something the antiseptic treatment destroys orrenders innocuous. At King's College Mr. Lister operates and dresseswhile a fine shower of mixed carbolic acid and water, produced in thesimplest manner, falls upon the wound, the lint and gauze employed inthe subsequent dressing being duly saturated with the antiseptic. AtSt. Bartholomew's Mr. Callender employs the dilute carbolic acidwithout the spray; but, as regards the real point aimed at--thepreventing of the wound from becoming a nidus for the propagation ofseptic bacteria--the practice in both hospitals is the same. Commending itself as it does to the scientifically trained mind, theantiseptic system has struck deep root in Germany. 

Had space allowed, it would have given me pleasure to point out thepresent position of the 'germ theory' in reference to the phenomena ofinfectious disease, distinguishing arguments based on analogy--which, however, are terribly strong--from those based on actual observation. I should have liked to follow up the account I have already given[Footnote: 'Fortnightly Review, ' November 1876, see article'Fermentation. '] of the truly excellent researches of a young and anunknown German physician named Koch, on splenic fever, by an accountof what Pasteur has recently done with reference to the same subject. Here we have before us a living _contagium_ of the most deadly power, which we can follow from the beginning to the end of its life cycle. [Footnote: Dallinger and Drysdale had previously shown what skill andpatience can accomplish, by their admirable observations on the lifehistory of the monads. ] We find it in the blood or spleen of asmitten animal in the state say of short motionless rods. When theserods are placed in a nutritive liquid on the warm stage of themicroscope, we soon see them lengthening into filaments which lie, insome cases, side by side, forming in others graceful loops, orbecoming coiled into knots of a complexity not to be unravelled. Wefinally see those filaments resolving themselves into innumerablespores, each with death potentially housed within it, yet not to bedistinguished microscopically from the harmless germs of Bacillussubtilis. The bacterium of splenic fever is called BacillusAnthracis. This formidable organism was shown to me by M. Pasteur inParis last July. His recent investigations regarding the part itplays pathologically certainly rank amongst the most remarkablelabours of that remarkable man. Observer after observer had strayedand fallen in this land of pitfalls, a multitude of opposingconclusions and mutually destructive theories being the result. Inassociation with a younger physiological colleague, M. Joubert, Pasteur struck in amidst the chaos, and soon reduced it to harmony. They proved, among other things, that in cases where previousobservers in France had supposed themselves to be dealing solely withsplenic fever, another equally virulent factor was simultaneouslyactive. Splenic fever was often overmastered by septicaemia, andresults due solely to the latter had been frequently made the groundof pathological inferences regarding the character and cause of theformer. Combining duly the two factors, all the previousirregularities disappeared, every result obtained receiving thefullest explanation. On studying the account of this masterlyinvestigation, the words wherewith Pasteur himself feelingly alludesto the difficulties and dangers of the experimenter's art came home tome with especial force: 'J'ai tant de fois éprouvé que dans cet artdifficile de l'expérimentation les plus habiles bronchent à chaquepas, et que l'interprétation des faits nest pas moins périlleuse. '[Footnote: Comptes-Rendus, ' lxxxiii. P. 177. ]

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XIV SCIENCE AND MAN. 

[Footnote: Presidential Address, delivered before the Birmingham andMidland Institute, October 1877; with additions. ]

A MAGNET attracts iron; but when we analyse the effect we learn thatthe metal is not only attracted but repelled, the final approach tothe magnet being due to the difference of two unequal and opposingforces. Social progress is for the most part typified by this duplexor polar action. As a general rule, every advance is balanced by apartial retreat, every amelioration is associated more or less withdeterioration. No great mechanical improvement, for example, isintroduced for the benefit of society at large that does not bearhardly upon individuals. Science, like other things, is subject tothe operation of this polar law, what is good for it under one aspectbeing bad for it under another. 

Science demands above all things personal concentration. Its home isthe study of the mathematician, the quiet laboratory of theexperimenter, and the cabinet of the meditative observer of nature. Different atmospheres are required by the man of science, as such, andthe man of action. Thus the facilities of social and internationalintercourse, the railway, the telegraph, and the post-office, whichare such undoubted boons to the man of action, react to some extentinjuriously on the man of science. Their tendency is to break up thatconcentrativeness which, as I have said, is an absolute necessity tothe scientific investigator. 

The men who have most profoundly influenced the world from thescientific side have habitually sought isolation. Faraday, at acertain period of his career, formally renounced dining out. Darwinlives apart from the bustle of the world in his quiet home in Kent. Mayer and Joule dealt in unobtrusive retirement with the weightiestscientific questions. There is, however, one motive power in theworld which no man, be he a scientific student or otherwise, canafford to treat with indifference; and that is, the cultivation ofright relations with his fellow-men--the performance of his duty, notas an isolated individual, but as a member of society. It is duty inthis aspect, overcoming alike the sense of possible danger and thedesire for repose, that has placed me in your presence here to-night. 

To look at his picture as a whole, a painter requires distance; and tojudge of the total scientific achievement of any age, the standpointof a succeeding age is desirable. We may, however, transportourselves in idea into the future, and thus survey with more or lesscompleteness the science of our time. We sometimes hear it decried, and contrasted to its disadvantage with the science of other times. Ido not think that this will be the verdict of posterity. I think, onthe contrary, that posterity will acknowledge that in the history ofscience no higher samples of intellectual conquest are recorded thanthose which this age has made its own. One of the most salient ofthese I propose, with your permission, to make the subject of ourconsideration during the coming hour. 

It is now generally admitted that the man of to-day is the child andproduct of incalculable antecedent time. His physical andintellectual textures have been woven for him during his passagethrough phases of history and forms of existence which lead the mindback to an abysmal past. One of the qualities which he has derivedfrom that past is the yearning to let in the light of principles onthe otherwise bewildering flux of phenomena. He has been described bythe German Lichtenberg as 'das rastlose Ursachenthier'--the restlesscause-seeking animal--in whom facts excite a kind of hunger to knowthe sources from which they spring. Never, I venture to say, in thehistory of the world has this longing been more liberally respondedto, both among men of science and the general public, than during thelast thirty or forty years. I say 'the general public, ' because it isa feature of our time that the man of science no longer limits hislabours to the society of his colleagues and his peers, but shares, asfar as it is possible to share, with the world at large the fruits ofenquiry. 

The celebrated Robert Boyle regarded the universe as a machine; Mr. Carlyle prefers regarding it as a tree. He loves the image of theumbrageous Igdrasil better than that of the Strasburg clock. Amachine may be defined as an organism with life and direction outside;a tree may be defined as an organism with life and direction within. In the light of these definitions, I close with the conception ofCarlyle. The order and energy of the universe I hold to be inherent, and not imposed from without, the expression of fixed law and not ofarbitrary will, exercised by what Carlyle would call an AlmightyClockmaker. But the two conceptions are not so much opposed to eachother after all. In one fundamental particular they at all eventsagree. They equally imply the interdependence and harmoniousinteraction of parts, and the subordination of the individual powersof the universal organism to the working of the whole. 

Never were the harmony and interdependence just referred to so clearlyrecognised as now. Our insight regarding them is not that vague andgeneral insight to which our fathers had attained, and which, in earlytimes, was more frequently affirmed by the synthetic poet than by thescientific man. The interdependence of our day has becomequantitative--expressible by numbers--leading, it must be added, directly into that inexorable reign of law which so many gentle peopleregard with dread. In the domain now under review men of science hadfirst to work their way from darkness into twilight, and from twilightinto day. There is no solution of continuity in science. It is notgiven to any man, however endowed, to rise spontaneously intointellectual splendour without the parentage of antecedent thought. Great discoveries grow. Here, as in other cases, we have first theseed, then the ear, then the full corn in the ear, the last member ofthe series implying the first. Thus, as regards the discovery ofgravitation with which the name of Newton is identified, notions moreor less clear concerning it had entered many minds before Newton'stranscendent mathematical genius raised it to the level of ademonstration. The whole of his deductions, moreover, rested upon theinductions of Kepler. Newton shot beyond his predecessors; but histhoughts were rooted in their thoughts, and a just distribution ofmerit would assign to them a fair portion of the honour of discovery. 

Scientific theories sometimes float like rumours in the air beforethey receive complete expression. The doom of a doctrine is oftenpractically sealed, and the truth of one is often practicallyaccepted, long prior to the demonstration of either the error or thetruth. 

Perpetual motion was discarded before it was proved to be opposed tonatural law; and, as regards the connection and interaction of naturalforces, intimations of modern discoveries are strewn through thewritings of Leibnitz, Boyle, Hooke, Locke and others. 

Confining ourselves to recent times, Dr. Ingleby has pointed out to mesome singularly sagacious remarks bearing upon this question, whichwere published by: an anonymous writer in 1820. Roget's penetrationwas conspicuous in 1829. Mohr had grasped in 1837 some deep-lyingtruth. The writings of Faraday furnish frequent illustrations of hisprofound belief in he unity of nature. 'I have long, ' he writes in1845, 'held an opinion almost amounting to conviction, in common, Ibelieve, with other lovers of natural knowledge, that the variousforms under which the forces of matter are made manifest have onecommon origin, or, in other words, are so directly related andmutually dependent, that they are convertible, as it were, one intoanother, and possess equivalence of power in their action. ' His ownresearches on magneto-electricity, on electro-chemistry, and on the'magnetisation of light led him directly to this belief. At an earlydate Mr. Justice Grove made his mark upon this question. Colding, though starting from a metaphysical basis, grasped eventually therelation between heat and mechanical work, and sought to determine itexperimentally. And here let me say, that to him who has only thetruth at heart, and who in his dealings with scientific history keepshis soul unwarped by envy, hatred, or malice, personal or national, every fresh accession to historic knowledge must be welcome. Forevery new-comer of proved merit, more especially if that merit shouldhave been previously overlooked, he makes ready room in hisrecognition or his reverence. But no retrospect of scientificliterature has as yet brought to light a claim which can sensiblyaffect the positions accorded to two great Path-hewers, as the Germanscall them, whose names in relation to this subject are linked inindissoluble association. These names are Julius Robert Mayer andJames Prescott Joule. 

In his essay on 'Circles' Mr. Emerson, if I remember rightly, pictured intellectual progress as rhythmic. At a given momentknowledge is surrounded by a barrier which marks its limit. Itgradually gathers clearness and strength until by-and-by some thinkerof exceptional power bursts the barrier and wins a wider circle, within which thought once more entrenches itself. But the internalforce again accumulates, the new barrier is in its turn broken, andthe mind finds itself surrounded by a still wider horizon. Thus, according to Emerson, knowledge spreads by intermittent victoriesinstead of progressing at a uniform rate. 

When Dr. Joule first proved that a weight of one pound, fallingthrough a height of seven hundred and seventy-two feet, generated anamount of heat competent to warm a pound of water one degreeFahrenheit, and that in lifting the weight so much heat exactlydisappeared, he broke an Emersonian 'circle, ' releasing by the act anamount of scientific energy which rapidly overran a vast domain, andembodied itself in the great doctrine known as the 'Conservation ofEnergy. ' This doctrine recognises in the material universe a constantsum of power made up of items among which the most Proteanfluctuations are incessantly going on. It is as if the body of Naturewere alive, the thrill and interchange of its energies resemblingthose of an organism. The parts of the 'stupendous whole' shift andchange, augment and diminish, appear and disappear, while the total ofwhich they are the parts remains quantitatively immutable. Immutable, because when change occurs it is always polar--plus accompanies minus, gain accompanies loss, no item varying in the slightest degree withoutan absolutely equal change of some other item in the oppositedirection. 

*****

The sun warms the tropical ocean, converting a portion of its liquidinto vapour, which rises in the air and is recondensed on mountainheights, returning in rivers to the ocean from which it came. Up tothe point where condensation begins, an amount of heat exactlyequivalent to the molecular work of vaporisation and the mechanicalwork of lifting the vapour to the mountain-tops has disappeared fromthe universe. What is the gain corresponding to this loss? It willseem when mentioned to be expressed in a foreign currency. The lossis a loss of heat; the gain is a gain of distance, both as regardsmasses and molecules. Water which was formerly at the sea-level hasbeen lifted to a position from which it can fall; molecules which havebeen locked together as a liquid are now separate as vapour which canrecondense. After condensation gravity comes into effectual play, pulling the showers down upon the hills, and the rivers thus createdthrough their gorges to the sea. Every raindrop which smites themountain produces its definite amount of heat; every river in itscourse develops heat by the clash of its cataracts and the friction ofits bed. In the act of condensation, moreover, the molecular work ofvaporisation is accurately reversed. 'Compare, then, the primitiveloss of solar warmth with the heat generated by the condensation ofthe vapour, and by the subsequent fall of the water from cloud to sea. They are mathematically equal to each other. No particle of vapourwas formed and lifted without being paid for in the currency of solarheat; no particle returns as water to the sea without the exactquantitative restitution of that heat. There is nothing gratuitous inphysical nature, no expenditure without equivalent gain, no gainwithout equivalent expenditure. With inexorable constancy the oneaccompanies the other, leaving no nook or crevice between them forspontaneity to mingle with the pure and necessary play of naturalforce. Has this uniformity of nature ever been broken? The reply is:

'Not to the knowledge of science. '

What has been here stated regarding heat and gravity applies to thewhole of inorganic nature. Let us take an illustration fromchemistry. The metal zinc may be burnt in oxygen, a perfectlydefinite amount of heat being produced by the combustion of a givenweight of the metal. But zinc may also be burnt in a liquid whichcontains a supply of oxygen--in water, for example. It does not inthis case produce flame or fire, but it does produce heat which iscapable of accurate measurement. But the heat of zinc burnt in waterfalls short of that produced in pure oxygen, the reason being that toobtain its oxygen from the water the zinc must first dislodge thehydrogen. It is in the performance of this molecular work that themissing heat is absorbed. Mix the liberated hydrogen with oxygen andcause them to recombine; the heat developed is mathematically equal tothe missing heat. Thus in pulling the oxygen and hydrogen asunder anamount of heat is consumed which is accurately restored by theirreunion. 

This leads up to a few remarks upon the Voltaic battery. It is not mydesign to dwell upon the technical features of this wonderfulinstrument, but simply, by means of it, to show what varying shapes agiven amount of energy can assume while maintaining unvaryingquantitative stability. When that form of power which we call anelectric current passes through Grove's battery, zinc is consumed inacidulated water; and in the battery we are able so to arrange mattersthat when no current passes no zinc shall be consumed. Now thecurrent, whatever it may be, possesses the power of generating heatoutside the battery. We can fuse with it iridium, the most refractoryof metals, or we can produce with it the dazzling electric light, andthat at any terrestrial distance from the battery itself. 

We will now, however, content ourselves with causing the current toraise a given length of platinum wire, first to a blood-heat, then toredness, and finally to a white heat. The heat under thesecircumstances generated in the battery by the combustion of a fixedquantity of zinc is no longer constant, but it varies inversely as theheat generated outside. If the outside heat be nil, the inside heatis a maximum; if the external wire be raised to a blood-heat, theinternal heat falls slightly short of the maximum. If the wire berendered red-hot, the quantity of missing heat within the battery isgreater, and if the external wire be rendered white-hot, the defect isgreater still. Add together the internal and external heat producedby the combustion of a given weight of zinc, and you have anabsolutely constant total. The heat generated without is so much lostwithin, the heat generated within is so much lost without, the polarchanges already adverted to coming here conspicuously into play. Thusin a variety of ways we can distribute the items of a never-varyingsum, but even the subtle agency of the electric current places nocreative power in our hands. 

Instead of generating external heat, we may cause the current toeffect chemical decomposition at a distance from the battery. Let it, for example, decompose water into oxygen and hydrogen. The heatgenerated in the battery under these circumstances by the combustionof a given weight of zinc falls short of what is produced when thereis no decomposition. How far short? The question admits of aperfectly exact answer. When the oxygen and hydrogen recombine, theheat absorbed in the decomposition is accurately restored, and it isexactly equal in amount to that missing in the battery. We may, if welike, bottle up the gases, carry in this form the heat of the batteryto the polar regions, and liberate it there. The battery, in fact isa hearth on which fuel is consumed; but the heat of the combustion, instead of being confined in the usual manner to the hearth itself, may be first liberated at the other side of the world. 

And here we are able to solve an enigma which long perplexedscientific men, and which could not be solved until the bearing of themechanical theory of heat upon the phenomena of the Voltaic batterywas understood. The puzzle was, that a single cell could notdecompose water. The reason is now plain enough. The solution of anequivalent of zinc in a single cell develops not much more than halfthe amount of heat required to decompose an equivalent of water, andthe single cell cannot cede an amount of force which it does notpossess. But by forming a battery of two cells instead of one, wedevelop an amount of heat slightly in excess of that needed for thedecomposition of the water. The two-celled battery is therefore richenough to pay for that decomposition, and to maintain the excessreferred to within its own cells. 

Similar reflections apply to the thermo-electric pile, an instrumentusually composed of small bars of bismuth and antimony solderedalternately together. The electric current is here evoked by warmingthe soldered junctions of one face of the pile. Like the Voltaiccurrent, the thermo-electric current can heat wires, producedecomposition, magnetise iron, and deflect a magnetic needle at anydistance from its origin. You will be disposed, and rightly disposed, to refer those distant manifestations of power to the heatcommunicated to the face of the pile, but the case is worthy of closerexamination. In 1826 Thomas Seebeck discovered thermo-electricity, and six years subsequently Peltier made an observation which comeswith singular felicity to our aid in determining the material used upin the formation of the thermo-electric current. He found that when aweak extraneous current was sent from antimony to bismuth the junctionof the two metals was always heated, but that when the direction wasfrom bismuth to antimony the junction was chilled. Now the current inthe thermo-pile itself is always from bismuth to antimony, across theheated junction--a direction in which it cannot possibly establishitself without consuming the heat imparted to the junction. This heatis the nutriment of the current. Thus the heat generated by thethermo-current in a distant wire is simply that originally imparted tothe pile, which has been first transmuted into electricity, and thenretransmuted into its first form at a distance from its origin. Aswater in a state of vapour passes from a boiler to a distantcondenser, and there assumes its primitive form without gain or loss, so the heat communicated to the thermo-pile distils into the subtlerelectric current, which is, as it were, recondensed into heat in thedistant platinum wire. 

In my youth I thought an electro-magnetic engine which was shown to mea veritable perpetual motion--a machine, that is to say, whichperformed work without the expenditure of power. Let us consider theaction of such a machine. Suppose it to be employed to pump waterfrom a lower to a higher level. On examining the battery which worksthe engine we find that the zinc consumed does not yield its fullamount of heat. The quantity of heat thus missing within is the exactthermal equivalent of the mechanical work performed without. Let thewater fall again to the lower level; it is warmed by the fall. Addthe heat thus produced to that generated by the friction, mechanicaland magnetical, of the engine; we thus obtain the precise amount ofheat missing in the battery. All the effects obtained from themachine are thus strictly paid for; this 'payment for results' being, I would repeat, the inexorable method of nature. 

No engine, however subtly devised, can evade this law of equivalence, or perform on its own account the smallest modicum of work. Themachine distributes, but it cannot create. Is the animal body, then, to be classed among machines? When I lift a weight, or throw a stone, or climb a mountain, or wrestle with my comrade, am I not conscious ofactually creating and expending force? Let us look at the antecedentsof this force. We derive the muscle and fat of our bodies from whatwe eat. Animal heat you know to be due to the slow combustion of thisfuel. My arm is now inactive, and the ordinary slow combustion of myblood and tissue is going on. For every grain of fuel thus burnt aperfectly definite amount of heat has been produced. I now contractmy biceps muscle without causing it to perform external work. Thecombustion is quickened, and the heat is increased; this additionalheat being liberated in the muscle itself. I lay hold of a 56 lb. Weight, and by the contraction of my biceps lift it through thevertical space of a foot. The blood and tissue consumed during thiscontraction have not developed in the muscle their due amount of heat. A quantity of heat is at this moment missing in my muscle which wouldraise the temperature of an ounce of water somewhat more than onedegree Fahrenheit. I liberate the weight: it falls to the earth, andby its collision generates the precise amount of heat missing in themuscle. My muscular heat is thus transferred from its local hearth toexternal space. The fuel is consumed in my body, but the heat ofcombustion is produced outside my body. The case is substantially thesame as that of the Voltaic battery when it performs external work, orproduces external heat. All this points to the conclusion that theforce we employ in muscular exertion is the force of burning fuel andnot of creative will. In the light of these facts the body is seen tobe as incapable of generating energy without expenditure, as thesolids and liquids of the Voltaic battery. The body, in other words, falls into the catagory of machines. 

We can do with the body all that we have already done with thebattery--heat platinum wires, decompose water, magnetise iron, anddeflect a magnetic needle. The combustion of muscle may be made toproduce all these effects, as the combustion of zinc may be caused toproduce them. By turning the handle of a magneto-electric machine acoil of wire may be caused to rotate between the poles of a magnet. Aslong as the two ends of the coil are unconnected we have simply toovercome the ordinary inertia and friction of the machine in turningthe handle. But the moment the two ends of the coil are united by athin platinum wire a sudden addition of labour is thrown upon theturning arm. When the necessary labour is expended, its equivalentimmediately appears. The platinum wire glows. You can readilymaintain it at a white heat, or even fuse it. This is a veryremarkable result. From the muscles of the arm, with a temperature of100 degrees, we extract the temperature of molten platinum, which isnearly four thousand degrees. The miracle here is the reverse of thatof the burning bush mentioned in Exodus. There the bush burned, butwas not consumed--here the body is consumed, but does not burn. Thesimilarity of the action with that of the Voltaic battery when itheats an external wire is too obvious to need pointing out. When themachine is used to decompose water, the heat of the muscle, like thatof the battery, is consumed in molecular work, being fully restoredwhen the gases recombine. As before, also, the transmuted heat ofthe muscles may be bottled up, carried to the polar regions, and thererestored to its pristine form. 

*****

The matter of the human body is the same as that of the world aroundus; and here we find the forces of the human body identical with thoseof inorganic nature. Just as little as the Voltaic battery is theanimal body a creator of force. It is an apparatus exquisite andeffectual beyond all others in transforming and distributing theenergy with which it is supplied, but it possesses no creative power. Compared with the notions previously entertained regarding the play of'Vital force' this is a great result. The problem of vital dynamicshas been described by a competent authority as 'the grandest of all. 'I subscribe to this opinion, and honour correspondingly the man whofirst successfully grappled with the problem. He was no pope, in thesense of being infallible, but he was a man of genius whose work willbe held in honour as long as science endures I have already named himin connection with our illustrious countryman Dr. Joule. Othereminent men took up this subject subsequently and independently, butall that has been done hitherto enhances instead of diminishing themerits of Dr. Mayer. 

Consider the vigour of his reasoning. 'Beyond the power of generatinginternal heat, the animal organism can generate heat external toitself. A blacksmith by hammering can warm a nail, and a savage byfriction can heat wood to its point of ignition. Unless, then, weabandon the physiological axiom that the animal body cannot createheat out of nothing, we are driven to the conclusion that it is thetotal heat, within and without, that ought to be regarded as the realcalorific effect of the oxidation within the body. ' Mayer, however, not only states the principle, but illustrates numerically thetransfer of muscular heat to external space. A bowler who imparts avelocity of 30 feet to an 8-lb. Ball consumes in the act 0. 1 of agrain of carbon. The heat of the muscle is here distributed over thetrack of the ball, being developed there by mechanical friction. Aman weighing 150 lbs. Consumes in lifting his own body to a height of8 feet the heat of a grain of carbon. Jumping from this height theheat is restored. The consumption of 2 oz. 4 drs. 20 grs. Of carbonwould place the same man on the summit of a mountain 10, 000 feet high. In descending the mountain an amount of heat equal to that produced bythe combustion of the foregoing amount of carbon is restored. Themuscles of a labourer whose weight is 150 lbs. Weigh 64 lbs. Whendried they are reduced to 15 lbs. Were the oxidation corresponding toa day-labourer's ordinary work exerted on the muscles alone, theywould be wholly consumed in 80 days. Were the oxidation necessary tosustain the heart's action concentrated on the heart itself, it wouldbe consumed in 8 days. And if we confine our attention to the twoventricles, their action would consume the associated muscular tissuein 31 days. With a fulness and precision of which this is but asample did Mayer, between 1842 and, 1845, deal with the great questionof vital dynamics. 

In direct opposition, moreover, to the foremost scientific authoritiesof that day, with Liebig at their head, this solitary Heilbronn workerwas led by his calculations to maintain that the muscles, in the main, played the part of machinery, converting the fat, which had beenpreviously considered a mere heat-producer, into the motive power ofthe organism. Mayer's prevision has been justified by events, for thescientific world is now upon his side. 

We place, then, food in our stomachs as so much combustible matter. Itis first dissolved by purely chemical processes, and the nutritivefluid is poured into the blood. Here it comes into contact withatmospheric oxygen admitted by the lungs. It unites with the oxygenas wood or coal might unite with it in a furnace. The matter-productsof the union, if I may use the term, are the same in both cases, viz. Carbonic acid and water. The force-products are also the same--heatwithin the body, or heat and work outside the body. Thus far everyaction of the organism belongs to the domain either of physics or ofchemistry. But you saw me contract the muscle of my arm. Whatenabled me to do, so? Was it or was it not the direct action of mywill? The answer is, the action of the will is mediate, not direct. Over and above the muscles the human organism is provided with longwhitish filaments of medullary matter, which issue from the spinalcolumn, being connected by it on the one side with the brain, and onthe other side losing themselves in the muscles. Those filaments orcords are the nerves, which you know are divided into two kinds, sensor and motor, or, if you like the terms better, afferent andefferent nerves. The former carry impressions from the external worldto the brain; the latter convey the behests of the brain to themuscles. Here, as elsewhere, we find ourselves aided by the sagacityof Mayer, who was the first clearly to formulate the part played bythe nerves in the organism. Mayer saw that neither nerves nor brain, nor both together, possessed the energy necessary to animal motion;but he also saw that the nerve could lift a latch and open a door, bywhich floods of energy are let loose. 'As an engineer, ' he says withadmirable lucidity, 'by the motion of his finger in opening a valve orloosening a detent can liberate an amount of mechanical energy almostinfinite compared with its exciting cause; so the nerves, acting onthe muscles, can unlock an amount of power out of all proportion tothe work done by the nerves themselves. ' The nerves, according toMayer, pull the trigger, but the gunpowder which they ignite is storedin the muscles. This is the view now universally entertained. 

The quickness of thought has passed into a proverb, and the notionthat any measurable time elapsed between the infliction of a wound andthe feeling of the injury would have been rejected as preposterousthirty years ago. Nervous impressions, notwithstanding the results ofHaller, were thought to be transmitted, if not instantaneously, at allevents with the rapidity of electricity. Hence, when Helmholtz, in1851, affirmed, as the result of experiment, nervous transmission tobe a comparatively sluggish process, very few believed him. Hisexperiments may now be made in the lecture-room. 

Sound in air moves at the rate of 1, 100 feet a second; sound in watermoves at the rate of 5, 000 feet a second; light in aether moves at therate of 186, 000 miles a second, and electricity in free wires movesprobably at the same rate. But the nerves transmit their messages atthe rate of only 70 feet a second, a progress which in these quicktimes might well be regarded as inordinately slow. 

Your townsman, Mr. Gore, has produced by electrolysis a kind ofantimony which exhibits an action strikingly analogous to that ofnervous propagation. A rod of this antimony is in such a molecularcondition that when you scratch or heat one end of the rod, thedisturbance propagates itself before your eyes to the other end, theonward march of the disturbance being announced by the development ofheat and fumes along the line of propagation. In some such way themolecules of the nerves are successively overthrown; and if Mr. Gorecould only devise some means of winding up his exhausted antimony, asthe nutritive blood winds up exhausted nerves, the comparison would becomplete. The subject may be summed up, as Du Bois-Reymond has summedit up, by reference to the case of a whale struck by a harpoon in thetail. If the animal were 70 feet long, a second would elapse beforethe disturbance could reach the brain. But the impression after itsarrival has to diffuse itself and throw the brain into the molecularcondition necessary to consciousness. Then, and not till then, thecommand to the tail to defend itself is shot through the motor nerves. Another second must elapse before the command can reach the tail, sothat more than two seconds transpire between the infliction of thewound and the muscular response of the part wounded. The intervalrequired for the kindling of consciousness would probably more thansuffice for the destruction of the brain by lightning, or even by arifle-bullet. Before the organ can arrange itself it may, therefore, be destroyed, and in such a case we may safely conclude that death ispainless. 

*****

The experiences of common life supply us with copious instances of theliberation of vast stores of muscular power by an infinitesimal'priming' of the muscles by the nerves. We all know the effectproduced on a 'nervous' organisation by a slight sound which causesaffright. An aërial wave, the energy of which would not reach aminute fraction of that necessary to raise the thousandth of a grainthrough the thousandth of an inch, can throw the whole human frameinto a powerful mechanical spasm, followed by violent respiration andpalpitation. The eye of course, may be appealed to as well as theear. Of this the lamented Lange gives the following vividillustration:

A merchant sits complacently in his easy chair, not knowing whethersmoking, sleeping, newspaper reading, or the digestion of foodoccupies the largest portion of his personality. A servant enters theroom with a telegram bearing the words, 'Antwerp, &c... Jonasand Co. Have failed. ' 'Tell James to harness the horses!' The servantflies. Upstairs the merchant, wide awake; makes a dozen paces throughthe room, descends to the counting-house, dictates letters, andforwards despatches. He jumps into his carriage, the horses snort, and their driver is immediately at the Bank, on the Bourse, and amonghis commercial friends. Before an hour has elapsed he is again athome, where he throws himself once more into his easy chair with adeep-drawn sigh, 'Thank God I am protected against the worst, and nowfor further reflection. '

This complex mass of action, emotional, intellectual, and mechanical, is evoked by the impact upon the retina of the infinitesimal waves oflight coming from a few pencil marks on a bit of paper. We have, asLange says, terror, hope, sensation, calculation, possible ruin, andvictory compressed into a moment. What caused the merchant to springout of his chair? The contraction of his muscles. What made hismuscles contract? An impulse of the nerves, which lifted the properlatch, and liberated the muscular power. Whence this impulse? Fromthe centre of the nervous system. But how did it originate there?This is the critical question, to which some will reply that it hadits origin in the human soul. 

The aim and effort of science is to explain the unknown in terms ofthe known. Explanation, therefore, is conditioned by knowledge. Youhave probably heard the story of the German peasant, who, in earlyrailway days, was taken to see the performance of a locomotive. Hehad never known carriages to be moved except by animal power. Everyexplanation outside of this conception lay beyond his experience, andcould not be invoked. After long reflection therefore, and seeing nopossible escape from the conclusion, he exclaimed confidently to hiscompanion, 'Es muessen doch Pferde darin sein '--There must be horsesinside. Amusing as this locomotive theory may seem, it illustrates adeep-lying truth. 

With reference to our present question, some may be disposed to pressupon me such considerations as these: Your motor nerves are so manyspeaking-tubes, through which messages are sent from the man to theworld; and your sensor nerves are so many conduits through which thewhispers of the world are sent back to the man. But you have not toldus where is the man. Who or what is it that sends and receives thosemessages through the bodily organism? Do not the phenomena point tothe existence of a self within the self, which acts through the bodyas through a skilfully constructed instrument? You picture themuscles as hearkening to the commands sent through the motor nerves, and you picture the sensor nerves as the vehicles of incomingintelligence; are you not bound to supplement this mechanism by theassumption of an entity which uses it? In other words, are you notforced by Tour own exposition into the hypothesis of a free humansoul?

This is fair reasoning now, and at a certain stage of the world'sknowledge, it might well have been deemed conclusive. Adequatereflection, however, shows that instead of introducing light into ourminds, this hypothesis considered scientifically increases ourdarkness. You do not in this case explain the unknown in terms of theknown, which, as stated above, is the method of science, but youexplain the unknown in terms of the more unknown. Try to mentallyvisualise this soul as an entity distinct from the body, and thedifficulty immediately appears. From the side of science all that weare warranted in stating is that the terror, hope, sensation, andcalculation of Lange's merchant, are psychical phenomena produced by, or associated with, the molecular processes set up by waves of lightin a previously prepared brain. 

When facts present themselves let us dare to face them, but let theman of science equally dare to confess ignorance where it prevails. What then is the causal connection, if any, between the objective andsubjective--between molecular motions and states of consciousness? Myanswer is: I do not see the connection, nor have I as yet met anybodywho does. 

It is no explanation to say that the objective and subjective effectsare two sides of one and the same phenomenon. Why should thephenomenon have two sides? This is the very core of the difficulty. There are plenty of molecular motions which do not exhibit thistwo-sidedness. Does water think or feel when it runs into frost-fernsupon a window-pane? If not, why should the molecular motion of thebrain be yoked to this mysterious companion--consciousness? We canform a coherent picture of the physical processes--the stirring of thebrain, the thrilling of the nerves, the discharging of the muscles, and all the subsequent mechanical motions of the organism. But we canpresent to our minds no picture of the process whereby consciousnessemerges, either as a necessary link or as an accidental by-product ofthis series of actions. Yet it certainly does emerge--the prick of apin suffices to prove that molecular motion can produce consciousness. The reverse process of the production of motion by consciousness isequally unpresentable to the mind. We are here, in fact, upon theboundary line of the intellect, where the ordinary canons of sciencefail to extricate us from our difficulties. If we are true to thesecanons, we must deny to subjective phenomena all influence on physicalprocesses. Observation proves that they interact, but in passing fromone to the other, we meet a blank which mechanical deduction is unableto fill. Frankly stated, we have here to deal with facts almost asdifficult to seize mentally as the idea of a soul. And if you arecontent to make your 'soul' a poetic rendering of a phenomenon whichrefuses the yoke of ordinary physical laws, I, for one, would notobject to this exercise of ideality. Amid all our speculativeuncertainty, however, there is one practical point as clear as theday; namely, that the brightness and the usefulness of life, as wellas its darkness and disaster, depend to a great extent upon our ownuse or abuse of this miraculous organ. 

Accustomed as I am to harsh language, I am quite prepared to hear my'poetic rendering' branded as a 'falsehood' and a 'fib. ' Thevituperation is unmerited, for poetry or ideality, and untruth areassuredly very different things. The one may vivify, while the other, kills. When St. John extends the notion of a soul to 'souls washedin the blood of Christ' does he 'fib'? Indeed, if the appeal toideality is censurable, Christ himself ought not to have escapedcensure. Nor did he escape it. 'How can this man give us his flesh toeat?' expressed the sceptical flouting of unpoetic natures. Such arestill amongst us. Cardinal Manning would doubtless tell anyProtestant who rejects the doctrine of transubstantiation that he'fibs' away the plain words of his Saviour when he reduces 'the Bodyof the Lord' in the sacrament to a mere figure of speech. 

Though misuse may render it grotesque or insincere, the idealisationof ancient conceptions, when done consciously and above board, has, inmy opinion, an important future. We are not radically different fromour historic ancestors, and any feeling which affected themprofoundly, requires only appropriate clothing to affect us. Theworld will not lightly relinquish its heritage of poetic feeling, andmetaphysic will be welcomed when it abandons its pretensions toscientific discovery and consents to be ranked as a kind of poetry. 'Agood symbol, ' says Emerson, 'is a missionary to persuade thousands. The Vedas, the Edda, the Koran, are each remembered by its happiestfigure. There is no more welcome gift to men than a new symbol. Theyassimilate themselves to it, deal with it in all ways, and it willlast a hundred years. Then comes a new genius and brings another. 'Our ideas of God and the soul are obviously subject to this symbolicmutation. They are not now what they were a century ago. They willnot be a century hence what they are now. Such ideas constitute akind of central energy in the human mind, capable, like the energy ofthe physical universe, of assuming various shapes and undergoingvarious transformations. They baffle and elude the theologicalmechanic who would carve them to dogmatic forms. They offerthemselves freely to the poet who understands his vocation, and whosefunction is, or ought to be, to find 'local habitation' for thoughtswoven into our subjective life, but which refuse to be mechanicallydefined. 

*****

We now stand face to face with the final problem. It is this: Are thebrain, and the moral and intellectual processes known to be associatedwith the brain--and, as far as our experience goes, indissolublyassociated--subject to the laws which we find paramount in physicalnature? Is the will of man, in other words, free, or are it andnature equally 'bound fast in fate'? From this latter conclusion, after he had established it to the entire satisfaction of hisunderstanding, the great German thinker Fichte recoiled. You willfind the record of this struggle between head and heart in his book, entitled 'Die Bestimmung des Menschen'--The Vocation of Man. [Footnote: Translated by Dr. William Smith of Edinburgh; Truebner, 1873. ] Fichte was determined at all hazards to maintain his freedom, but the price he paid for it indicates the difficulty of the task. Toescape from the iron necessity seen everywhere reigning in physicalnature, he turned defiantly round upon nature and law, and affirmedboth of them to be the products of his own mind. He was not going tobe the slave of a thing which he had himself created. There is a gooddeal to be said in favour of this view, but few of us probably wouldbe able to bring into play the solvent transcendentalism wherebyFichte melted his chains. 

Why do some regard this notion of necessity with terror, while othersdo not fear it at all? Has not Carlyle somewhere said that a beliefin destiny is the bias of all earnest minds? 'It is not Nature, ' saysFichte, 'it is Freedom itself, by which the greatest and mostterrible disorders incident to our race are produced. Man is thecruellest enemy of man. ' But the question of moral responsibility hereemerges, and it is the possible loosening of this responsibility thatso many of us dread. The notion of necessity certainly failed tofrighten Bishop Butler. He thought it untrue even absurd--but he didnot fear its practical consequences. He showed, on the contrary, inthe 'Analogy, ' that as far as human conduct is concerned, the twotheories of free-will and necessity would come to the same in the end. 

What is meant by free-will? Does it imply the power of producingevents without antecedents?--of starting, as it were, upon a creativetour of occurrences without any impulse from within or from without?Let us consider the point. If there be absolutely or relatively noreason why a tree should fall, it will not fall; and if there beabsolutely or relatively no reason why a man should act, he will notact. It is true that the united voice of this assembly could notpersuade me that I have not, at this moment, the power to lift my armif I wished to do so. Within this range the conscious freedom of mywill cannot be questioned. But what about the origin of the 'wish'?Are we, or are we not, complete masters of the circumstances whichcreate our wishes, motives, and tendencies to action? Adequatereflection will, I think, prove that we are not. What, for example, have I had to do with the generation and development of that whichsome will consider my total being, and others a most potent factor ofmy total being--the living, speaking organism which now addresses you?As stated at the beginning of this discourse, my physical andintellectual textures were woven for me, not by me. Processes in theconduct or regulation of which I had no share have made me what I am. Here, surely, if anywhere, we are as clay in the hands of the potter. It is the greatest of delusions to suppose that we come into thisworld as sheets of white paper on which the age can write anything itlikes, making us good or bad, noble or mean, as the age pleases. Theage can stunt, promote, or pervert pre-existent capacities, but itcannot create them. The worthy Robert Owen, who saw in externalcircumstances the great moulders of human character, was obliged tosupplement his doctrine by making the man himself one of thecircumstances. It is as fatal as it is cowardly to blink factsbecause they are not to our taste. How many disorders, ghostly andbodily, are transmitted to us by inheritance? In our courts of law, whenever it is a question whether a crime has been committed under theinfluence of insanity, the best guidance the judge and jury can haveis derived from the parental antecedents of the accused. If amongthese insanity be exhibited in any marked degree, the presumption inthe prisoner's favour is enormously enhanced, because the experienceof life has taught both judge and jury that insanity is frequentlytransmitted from parent to child. 

I met, some years ago, in a railway carriage the governor of one ofour largest prisons. He was evidently an observant and reflectiveman, possessed of wide experience gathered in various parts of theworld, and a thorough student of the duties of his vocation. He toldme that the prisoners in his charge might be divided into threedistinct classes. The first class consisted of persons who oughtnever to have been in prison. External accident, and not internaltaint, had brought them within the grasp of the law, and what hadhappened to them might happen to most of us. They were essentiallymen of sound moral stamina, though wearing the prison garb. Then camethe largest class, formed of individuals possessing no strong bias, moral or immoral, plastic to the touch of circumstances, which couldmould them into either good or evil members of society. Thirdly camea class--happily not a large one--whom no kindness could conciliateand no discipline tame. They were sent into this world labelled'incorrigible', wickedness being stamped, as it were, upon theirorganisations. It was an unpleasant truth, but as a truth it ought tobe faced. For such criminals the prison over which he ruled wascertainly not the proper place. If confined at all, their prisonshould be on a desert island where the deadly _contagium_ of theirexample could not taint the moral air. But the sea itself he wasdisposed to regard as a cheap and appropriate substitute for theisland. It seemed to him evident that the State would benefit ifprisoners of the first class were liberated; prisoners of the secondclass educated; and prisoners of the third class put compendiouslyunder water. 

It is not, however, from the observation of individuals that theargument against 'free-will, ' as commonly understood, derives itsprincipal force. It is, as already hinted, indefinitely strengthenedwhen extended to the race. Most of you have been forced to listen tothe outcries and denunciations which rang discordant through the landfor some years after the publication of Mr. Darwin's 'Origin ofSpecies. ' Well, the world--even the clerical world--for the most partsettled down in the belief that Mr. Darwin's book simply reflects thetruth of nature: that we who are now 'foremost in the files of time'have come to the front through almost endless stages of promotion fromlower to higher forms of life. 

If to any one of us were given the privilege of looking back throughthe aeons across which life has crept towards its present outcome, hisvision, according to Darwin, would ultimately reach a point when theprogenitors of this assembly could not be called human. From thathumble society, through the interaction of its members and the storingup of their best qualities, a better one emerged; from this again abetter still; until at length, by the integration of infinitesimalsthrough ages of amelioration, we came to be what we are to-day. We ofthis generation had no conscious share in the production of this grandand beneficent result. Any and every generation which preceded us hadjust as little share. The favoured organisms whose garneredexcellence constitutes our present store owed their advantages, first, to what we in our ignorance are obliged to call accidental variation;'and, secondly, to a law of heredity in the passing of which oursuffrages were not collected. With characteristic felicity andprecision Mr. Matthew Arnold lifts this question into the free air ofpoetry, but not out of the atmosphere of truth, when he ascribes theprocess of amelioration to 'a power not ourselves which makes forrighteousness. ' If, then, our organisms, with all their tendenciesand capacities, are given to us without our being consulted; and if, while capable of acting within certain limits in accordance with ourwishes, we are not masters of the circumstances in which motives andwishes originate; if, finally, our motives and wishes determine ouractions--in what sense can these actions be said to be the result offree-will?

*****

Here, again, we are confronted with the question of moralresponsibility, which, as it has been much talked of lately, it isdesirable to meet. With the view of removing the fear of our fallingback into the condition of 'the ape and tiger, ' so sedulously excitedby certain writers, I propose to grapple with this question in itsrudest form, and in the most uncompromising way. 'If, ' says therobber, the ravisher, or the murderer, 'I act because I must act, whatright have you to hold me responsible for my deeds?' The reply is, 'The right of society to protect itself against aggressive andinjurious forces, whether they be bond or free, forces of nature orforces of man. ' 'Then, ' retorts the criminal, 'you punish me forwhat I cannot help. ' 'Let it be granted, ' says society, 'but had youknown that the treadmill or the gallows was certainly in store foryou, you might have "helped. " Let us reason the matter fully andfrankly out. We may entertain no malice or hatred against you; it isenough that with a view to our own safety and purification we aredetermined that you and such as you shall not enjoy liberty of evilaction in our midst. You, who have behaved as a wild beast, we claimthe right to cage or kill as we should a wild beast. The public safetyis a matter of more importance than the very limited chance of yourmoral renovation, while the knowledge that you have been hanged by theneck may furnish to others about to do as you have done the precisemotive which will hold them back. If your act be such as to invoke aminor penalty, then not only others, but yourself, may profit by thepunishment which we inflict. On the homely principle that "a burntchild dreads the fire, " it will make you think twice before venturingon a repetition of your crime. Observe, finally, the consistency ofour conduct. You offend, you say, because you cannot help offending, to the public detriment. We punish, is our reply, because we cannothelp punishing, for the public good. Practically, then, as BishopButler predicted, we act as the world acted when it supposed the evildeeds of its criminals to be the products of free-will. ' [Footnote:An eminent Church dignitary describes all this, not unkindly, as'truculent logic. ' I think it worthy of his Grace's graverconsideration. ]

'What, ' I have heard it argued, 'is the use of preaching about duty, if a man's predetermined position in the moral world renders himincapable of profiting by advice?' Who knows that he is incapable?The preacher's last word is a factor in the man's conduct, and it maybe a most important factor, unlocking moral energies which mightotherwise remain imprisoned and unused. If the preacher thoroughlyfeel that words of enlightenment, courage, and admonition enter intothe list of forces employed by Nature herself for man's amelioration, since she gifted man with speech, he will suffer no paralysis to fallupon his tongue. Dung the fig-tree hopefully, and not until itsbarrenness has been demonstrated beyond a doubt let the sentence goforth, 'Cut it down, why cumbereth it the ground?'

I remember when a youth in the town of Halifax, some two-and-thirtyyears ago, attending a lecture given by a young man to a small butselect audience. The aspect of the lecturer was earnest andpractical, and his voice soon rivetted attention. He spoke of duty, defining it as a debt owed, and there was a kindling vigour in hiswords which must have strengthened the sense of duty in the minds ofthose who heard him. No speculations regarding the freedom of thewill could alter the fact that the words of that young man did megood. His name was George Dawson. He also spoke, if you will allowme to allude to it, of a social subject much discussed at thetime--the Chartist subject of 'levelling. ' Suppose, he says, two mento be equal at night, and that one rises at six, while the othersleeps till nine next morning, what becomes of your levelling? And inso speaking be made himself the mouthpiece of Nature, which, as wehave seen, secures advance, not by the reduction of all to a commonlevel, but by the encouragement and conservation of what is best. 

It may be urged that, in dealing as above with my hypotheticalcriminal, I am assuming a state of things brought about by theinfluence of religions which include the dogmas of theology and thebelief in freewill--a state, namely, in which a moral majority controland keep in awe an immoral minority. The heart of man is deceitfulabove all things, and desperately wicked. Withdraw, then, ourtheologic sanctions, including the belief in free-will, and thecondition of the race will be typified by the samples of individualwickedness which have been above adduced. We shall all, that is, become robbers, and ravishers, and murderers. From much that has beenwritten of late it would seem that this astounding inference findshouse-room in many minds. Possibly, the people who hold such viewsmight be able to illustrate them by individual instances. 

 The fear of hell's a hangman's whip, To keep the wretch in order. 

Remove the fear, and the wretch, following his natural instinct, maybecome disorderly; but I refuse to accept him as a sample of humanity. 'Let us eat and drink, for to-morrow we die' is by no means theethical consequence of a rejection of dogma. To many of you the nameof George Jacob Holyoake is doubtless familiar, and you are probablyaware that at no man in England has the term 'atheist' been morefrequently pelted. There are, moreover, really few who have morecompletely liberated themselves from theologic notions. Amongworking-class politicians Mr. Holyoake is a leader. Does he exhorthis followers to 'Eat and drink, for to-morrow we die'? Not so. Inthe August number of the 'Nineteenth Century' you will find thesewords from his pen: 'The gospel of dirt is bad enough, but the gospelof mere material comfort is much worse. ' He contemptuously calls theComtist championship of the working man, 'the championship of thetrencher. ' He would place 'the leanest liberty which brought with itthe dignity and power of self-help' higher than 'any prospect of afull plate without it. ' Such is the moral doctrine taught by this'atheistic' leader; and no Christian, I apprehend, need be ashamed ofit. 

Most heartily do I recognise and admire the spiritual radiance, if Imay use the term, shed by religion on the minds and lives of manypersonally known to me. At the same time I cannot but observe howsignally, as regards the production of anything beautiful, religionfails in other cases. Its professor and defender is sometimes atbottom a brawler and a clown. These differences depend upon primarydistinctions of character which religion does not remove. It maycomfort some to know that there are amongst us many whom thegladiators of the pulpit would call 'atheists' and 'materialists, 'whose lives, nevertheless, as tested by any accessible standard ofmorality, would contrast more than favourably with the lives of thosewho seek to stamp them with this offensive brand. When I say'offensive, ' I refer simply to the intention of those who use suchterms, and not because atheism or materialism, when compared with manyof the notions ventilated in the columns of religious newspapers, hasany particular offensiveness for me. If I wished to find men who arescrupulous in their adherence to engagements, whose words are theirbond, and to whom moral shiftiness of any kind is subjectivelyunknown; if I wanted a loving father, a faithful husband, anhonourable neighbour, and a just citizen--I should seek him, and findhim among the band of 'atheists' to which I refer. I have known someof the most pronounced among them not only in life but in death seenthem approaching with open eyes the inexorable goal, with no dread ofa 'hangman's whip, ' with no hope of a heavenly crown, and still asmindful of their duties, and as faithful in the discharge of them, asif their eternal future depended upon their latest deeds. 

In letters addressed to myself, and in utterances addressed to thepublic, Faraday is often referred to as a sample of the association ofreligious faith with moral elevation. I was locally intimate with himfor fourteen or fifteen years of my life, and had thus occasion toobserve how nearly his character approached what might, withoutextravagance, be called perfection. He was strong but gentle, impetuous but self-restrained; a sweet and lofty courtesy marked hisdealings with men and women; and though he sprang from the body of thepeople, a nature so fine might well have been distilled from theflower of antecedent chivalry. Not only in its broader sense was theChristian religion necessary to Faraday's spiritual peace, but in whatmany would call the narrow sense held by those described by Faradayhimself as 'a very small and despised sect of Christians, known, ifknown at all, as Sandemanians, ' it constituted the light and comfortof his days. 

Were our experience confined to such cases, it would furnish anirresistible argument in favour of the association of dogmaticreligion with moral purity and grace. But, as already intimated, ourexperience is not thus confined. In further illustration of thispoint, we may compare with Faraday a philosopher of equal magnitude, whose character, including gentleness and strength, candour andsimplicity, intellectual power and moral elevation, singularlyresembles that of the great Sandemanian, but who has neither sharedthe theologic views nor the religious emotions which formed sodominant a factor in Faraday's life. I allude to Mr. Charles Darwin, the Abraham of scientific men--a searcher as obedient to the commandof truth as was the patriarch to the command of God. I cannottherefore, as so many desire, look upon Faraday's religious belief asthe exclusive source of qualities shared so conspicuously by oneuninfluenced by that belief. To a deeper virtue belonging to humannature in its purer forms I am disposed to refer the excellence ofboth. 

Superstition may be defined as constructive religion which has grownincongruous with intelligence. We may admit, with Fichte, 'thatsuperstition has unquestionably constrained its subjects to abandonmany pernicious practices and to adopt many useful ones;' the realloss accompanying its decay at the present day has been thus clearlystated by the same philosopher: 'In so far as these lamentations donot proceed from the priests themselves--whose grief at the loss oftheir dominion over the human mind we can well understand--but fromthe politicians, the whole matter resolves itself into this, thatgovernment has thereby become more difficult and expensive. The judgewas spared the exercise of his own sagacity and penetration when, bythreats of relentless damnation, he could compel the accused to makeconfession. The evil spirit formerly performed without rewardservices for which in later times judges and policemen have to bepaid. '

No man ever felt the need of a high and ennobling religion morethoroughly than this powerful and fervid teacher, who, by the way, didnot escape the brand of 'atheist. ' But Fichte asserted emphaticallythe power and sufficiency of morality in its own sphere. 'Let usconsider, ' he says, 'the highest which man can possess in the absenceof religion--I mean pure morality. The moral man obeys the law ofduty in his breast absolutely, because it is a law unto him; and hedoes whatever reveals itself to him as his duty simply because it isduty. Let not the impudent assertion be repeated that such anobedience, without regard for consequences, and without desire forconsequences, is in itself impossible and opposed to human nature. 'So much for Fichte. Faraday was equally distinct. 'I have nointention, ' he says, 'of substituting anything for religion, but Iwish to take that part of human nature which is independent of it. Morality, philosophy, commerce, the various institutions and habits ofsociety, are independent of religion and may exist without it. ' Thesewere the words of his youth, but they expressed his latestconvictions. I would add, that the muse of Tennyson never reached ahigher strain than when it embodied the sentiment of duty in AEnone:

 And, because right is right, to follow right Were wisdom in the scorn of consequence. 

Not in the way assumed by our dogmatic teachers has the morality ofhuman nature been built up. The power which has moulded us thus farhas worked with stern tools upon a very rigid stuff. What it has donecannot be so readily undone; and it has endowed us with moralconstitutions which take pleasure in the noble, the beautiful, and thetrue, just as surely as it has endowed us with sentient organisms, which find aloes bitter and sugar sweet. That power did not work withdelusions, nor will it stay its hand when such are removed. Facts, rather than dogmas, have been its ministers--hunger and thirst, heatand cold, pleasure and pain, fervour, sympathy, aspiration, shame, pride, love, hate, terror, awe--such were the forces whose interactionand adjustment throughout an immeasurable past wove the triplex web ofman's physical, intellectual, and moral nature, and such are theforces that will be effectual to the end. 

You may retort that even on my own showing 'the power which makes forrighteousness' has dealt in delusions; for it cannot be denied thatthe beliefs of religion, including the dogmas of theology and thefreedom of the will, have had some effect in moulding the moral world. Granted; but I do not think that this goes to the root of the matter. Are you quite sure that those beliefs and dogmas are primary, and notderived?--that they are not the products, instead of being thecreators, of man's moral nature? I think it is in one of theLatter-Day Pamphlets that Carlyle corrects a reasoner, who deduced thenobility of man from a belief in heaven, by telling him that he putsthe cart before the horse, the real truth being that the belief inheaven is derived from the nobility of man. The bird's instinct toweave its nest is referred to by Emerson as typical of the force whichbuilt cathedrals, temples, and pyramids:

 Knowest thou what wove yon woodbird's nest Of leaves and feathers from her breast, Or how the fish outbuilt its shell, Painting with morn each annual cell? Such and so grew these holy piles While love and terror laid the tiles; Earth proudly wears the Parthenon As the best gem upon her zone; And Morning opes with haste her lids To gaze upon the Pyramids; O'er England's abbeys bends the sky As on its friends with kindred eye; For out of Thought's interior sphere These wonders rose to upper air, And nature gladly gave them place, Adopted them into her race, And granted them an equal date With Andes and with Ararat. 

Surely, many utterances which have been accepted as descriptions oughtto be interpreted as aspirations, or, as having their roots inaspiration instead of in objective knowledge. Does the song of theherald angels, 'Glory to God in the highest, and on earth peace, goodwill toward men, ' express the exaltation and the yearning of ahuman soul? or does it describe an optical and acoustical fact--avisible host and an audible song? If the former, the exaltation andthe yearning are man's imperishable possession--a ferment longconfined to individuals, but which may by-and-by become the leaven ofthe race. If the latter, then belief in the entire transaction iswrecked by non-fulfilment. Look to the East at the present moment asa comment on the promise of peace' on earth and goodwill toward men. That promise is a dream ruined by the experience of eighteencenturies, and in that ruin is involved the claim of the 'heavenlyhost' to prophetic vision. But though the mechanical theory provesuntenable, the immortal song and the feelings it expresses are stillours, to be incorporated, let us hope, in purer and less shadowy formsin the poetry, philosophy, and practice of the future. 

Thus, following the lead of physical science, we are brought withoutsolution of continuity into the presence of problems which, as usuallyclassified, lie entirely outside the domain of physics. To theseproblems thoughtful and penetrative minds are now applying thosemethods of research which in physical science have proved their truthby their fruits. There is on all hands a growing repugnance to invokethe supernatural in accounting for the phenomena of human life; andthe thoughtful minds just referred to, finding no trace of evidence infavour of any other origin, are driven to seek in the interaction ofsocial forces the genesis and development of man's moral nature. Ifthey succeed in their search--and I think they are sure tosucceed--social duty will be raised to a higher level of significanceand the deepening sense of social duty will, it is to be hoped, lessen, if not obliterate, the strifes and heartburnings which nowbeset and disfigure our social life. Towards this great end itbehoves us one and all to work; and devoutly wishing its consummation, I have the honour, ladies and gentlemen, to bid you a friendlyfarewell. 

********************

XV. PROFESSOR VIRCHOW AND EVOLUTION. 

THIS world of ours has, on the whole, been an inclement region for thegrowth of natural truth; but it may be that the plant is all thehardier for the bendings and buffetings it has undergone. Thetorturing of a shrub, within certain limits, strengthens it Throughthe struggles and passions of the brute, man reaches his estate;through savagery and barbarism his civilisation; and through illusionand persecution his knowledge of nature, including that of his ownframe. The bias towards natural truth must have been strong to havewithstood and overcome the opposing forces. Feeling appeared in theworld before Knowledge; and thoughts, conceptions, and creeds, foundedon emotion, had, before the dawn of science, taken root in man. Suchthoughts, conceptions, and creeds must have met a deep and generalwant; otherwise their growth could not have been so luxuriant, northeir abiding power so strong. This general need--this hunger for theideal and wonderful--led eventually to the differentiation of a caste, whose vocation it was to cultivate the mystery of life and itssurroundings, and to give shape, name, and habitation to the emotionswhich that mystery aroused. Even the savage lived, not by breadalone, but in a mental world peopled with forms answering to hiscapacities and needs. As time advanced--in other words, as the savageopened out into civilised man--these forms were purified and ennobleduntil they finally emerged in the mythology and art of Greece:

 Where still the magic robe of Poesy Wound itself lovingly around the Truth. 

[Footnote:

 Da der Dichtung zauberische Huelle Sich noch lieblich um die Wahrheit wand. '--Schiller. ]

As poets, the priesthood would have been justified, their deities, celestial and otherwise, with all their retinue and appliances, beingmore or less legitimate symbols and personifications of the aspects ofnature and the phases of the human soul. The priests, however, orthose among them who were mechanics, and not poets, claimed objectivevalidity for their conceptions, and tried to base upon externalevidence that which sprang from the innermost need and nature of man. It is against this objective rendering of the emotions--this thrustinginto the region of fact and positive knowledge of conceptionsessentially ideal and poetic--that science, consciously orunconsciously, wages war. Religious feeling is as much a verity asany other part of human consciousness; and against it, on itssubjective side, the waves of science beat in vain. But when, manipulated by the constructive imagination, mixed with imperfect orinaccurate historic data, and moulded by misapplied logic, thisfeeling makes claims which traverse our knowledge of nature, science, as in duty bound, stands as a hostile power in its path. It isagainst the mythologic scenery, if I may use the term, rather thanagainst the life and substance of religion, that Science enters herprotest. Sooner or later among thinking people, that scenery will betaken for what it is worth--as an effort on the part of man to bringthe mystery of life and nature within the range of his capacities; asa temporary and essentially fluxional rendering in terms of knowledgeof that which transcends all knowledge, and admits only of idealapproach. 

The signs of the times, I think, point in this direction. It is, forexample, the obvious aim of Mr. Matthew Arnold to protect, amid thewreck of dogma, the poetic basis of religion. And it is to beremembered that under the circumstances poetry may be the purestaccessible truth. In other influential quarters a similar spirit isat work. In a remarkable article published by Professor Knight of St. Andrews in the September number of the 'Nineteenth Century, ' amidother free utterances, we have this one: 'If matter is not eternal, its first emergence into being is a miracle beside which all othersdwindle into absolute insignificance. But, as has often been pointedout, the process is unthinkable; the sudden apocalypse of a materialworld out of blank nonentity cannot be imagined; [Footnote: ProfessorKnight will have to reckon with the English Marriage Service, one ofwhose Collects begins thus: 'O God, who by thy mighty power halt madeall things of nothing. ] its emergence into order out of chaos when"without form and void" of life, is merely a poetic rendering of thedoctrine of its slow evolution. ' These are all bold words to be spokenbefore the moral philosophy class of a Scotch university, while thoseI have underlined show a remarkable freedom of dealing with the sacredtext. They repeat in terser language what I ventured to utter fouryears ago regarding the Book of Genesis. 'Profoundly interesting andindeed pathetic to me are those attempts of the opening mind of man toappease its hunger for a Cause. But the Book of Genesis has no voicein scientific questions. _It is a poem, not a scientific treatise. _ Inthe former aspect it is for ever beautiful; in the latter it has been, and it will continue to be, purely obstructive and hurtful. ' Myagreement with Professor Knight extends still further. 'Does thevital, ' he asks, 'proceed by a still remoter development from thenon-vital? Or was it created by a fiat of volition? Or'--and here heemphasises his question--'has it always existed in some form or otheras an eternal constituent of the universe? I do not see, ' he replies, 'how we can escape from the last alternative. ' With the whole force ofmy conviction I say, Nor do I, though our modes of regarding the'eternal constituent' may not be the same. 

When matter was defined by Descartes, he deliberately excluded theidea of force or motion from its attributes and from his definition. Extension only was taken into account. And, inasmuch as the impotenceof matter to generate motion was assumed, its observed motions werereferred to an external cause. God, resident outside of matter, gavethe impulse. In this connection the argument in Young's 'NightThoughts' will occur to most readers:

 Who Motion foreign to the smallest grain Shot through vast masses of enormous weight? Who bid brute Matter's restive lump assume Such various forms, and gave it wings to fly?

Against this notion of Descartes the great deist John Toland, whoseashes lie unmarked in Putney Churchyard, strenuously contended. Heaffirmed motion to be an inherent attribute of matter--that no portionof matter was at rest, and that even the most quiescent solids wereanimated by a motion of their ultimate particles. The success of hiscontention, according to the learned and laborious Dr. Berthold, [Footnote: 'John Toland und der Monismus der Gegenwart, ' Heidelberg, Carl Winter. ] entitles Toland to be regarded as the founder of thatmonistic doctrine which is now so rapidly spreading. 

It seems to me that the idea of vitality entertained in our day byProfessor Knight, closely resembles the idea of motion entertained byhis opponents in Toland's day. Motion was then virtually asserted tobe a thing sui generis, distinct from matter, and incapable of beinggenerated out of matter. Hence the obvious inference when matter wasobserved to move. It was the vehicle of an energy not its own--therepository of forces impressed on it from without--the purely passiverecipient of the shock of the Divine. The logical form continues, butthe subject-matter is changed. 'The evolution of nature, ' saysProfessor Knight, 'may be a fact; a daily and hourly apocalypse. Butwe have no evidence of the non-vital passing into the vital. Spontaneous generation is, as yet, an imaginative guess, unverified byscientific tests. And matter is not itself alive. Vitality, whetherseen in a single cell of protoplasm or in the human brain, is a thingsui generis, distinct from matter, and incapable of being generatedout of matter. ' It may be, however, that, in process of time, vitalitywill follow the example of motion, and, after the necessary antecedentwrangling, take its place among the attributes of that 'universalmother' who has been so often misdefined. 

That 'matter is not itself alive' Professor Knight seems to regard asan axiomatic truth. Let us place in contrast with this the notionentertained by the philosopher Ueberweg, one of the subtlest headsthat Germany has produced. 'What occurs in the brain' says Ueberweg'would, in my opinion, not be possible, if the process which hereappears in its greatest concentration did not obtain generally, onlyin a vastly diminished degree. Take a pair of mice and a cask offlour. By copious nourishment the animals increase and multiply, andin the same proportion sensations and feelings augment. The quantityof these latter possessed by the first pair, is not simply diffusedamong their descendants, for in that case the last must feel morefeebly than the first. The sensations and feelings must necessarily bereferred back to the flour, where they exist, weak and pale it istrue, and not concentrated as they are in the brain. ' [Footnote:Letter to Lange: 'Geschichte des Materialismus, ' zweite Aufl, vol. Ii. P. 521. ] We may not be able to taste or smell alcohol in atub of fermented cherries, but by distillation we obtain from themconcentrated Kirschwasser. Hence Ueberweg's comparison of the brainto a still, which concentrates the sensation and feeling, pre-existing, but diluted in the food. 

'Definitions, ' says Mr. Holyoake, [Footnote: 'Nineteenth Century, 'September 1878. ] 'grow as the horizon of experience expands. Theyare not inventions, but descriptions of the state of a question. Noman sees all through a discovery at once. ' Thus Descartes's notion ofmatter, and his explanation of motion, would be put aside as trivialby a physiologist or a crystallographer of the present day. They arenot descriptions of the state of the question. And yet a desiresometimes shows itself in distinguished quarters to bind us own toconceptions which passed muster in the infancy of knowledge, but whichare wholly incompatible with our present enlightenment. Mr. Martineau, I think, errs when he seeks to hold me to views enunciatedby 'Democritus and the mathematicians. ' That definitions should changeas knowledge advances is in accordance both with sound sense andscientific practice. When, for example, the undulatory theory wasstarted, it was not imagined that the vibrations of light could betransverse to the direction of propagation. The example of sound wasat hand, which was a case of longitudinal vibration. Now thesubstitution of transverse for longitudinal vibrations in the case oflight involved a radical change of conception as to the mechanicalproperties of the luminiferous medium. But though this change went sofar as to fill space with a substance, possessing the properties of asolid, rather than those of a gas, the change was accepted, becausethe newly discovered facts imperatively demanded it. Following Mr. Martineau's example, the opponent of the undulatory theory mighteffectually twit the holder of it on his change of front. 'Thisaether of yours, ' he might say, 'alters its style with every changeof service. Starting as a beggar, with scarce a rag of 'property' tocover its bones, it turns up as a prince when large undertakings arewanted. You had some show of reason when, with the case of soundbefore you, you assumed your aether to be a gas in the last extremityof attenuation. But now that new service is rendered necessary by newfacts, you drop the beggar's rags, and accomplish an undertaking, great and princely enough in all conscience; for it implies that notonly planets of enormous weight, but comets with hardly any weight atall, fly through your hypothetical solid without perceptible loss ofmotion. ' This would sound very cogent, but it would be very vain. Equally vain, in my opinion, is Mr. Martineau's contention that we arenot justified in modifying, in accordance with advancing knowledge, our notions of matter. 

Before parting from Professor Knight, let me commend his courage aswell as his insight. We have heard much of late of the peril tomorality involved in the decay of religious belief. What Mr. Knightsays under this head is worthy of all respect and attention. 'Iadmit, ' he writes, 'that were it proved that the moral faculty wasderived as well as developed, its present decisions would not beinvalidated. The child of experience has a father whose teachings aregrave, peremptory, and august; and an earthborn rule may be asstringent as any derived from a celestial source. It does not evenfollow that a belief in the material origin of spiritual existence, accompanied by a corresponding decay of belief in immortality, mustnecessarily lead to a relaxation of the moral fibre of the race. [Footnote: Is this really certain? Instead of standing in therelation of cause and effect, may not the 'decay' and 'relaxation' bemerely coexistent, both, perhaps, flowing from common historicantecedents?] It is certain that it has often done so. But it isequally certain that there have been individuals, and great historicalcommunities, in which the absence of the latter belief has neitherweakened moral earnestness, nor prevented devotional fervour. ' I haveelsewhere stated that some of the best men of my acquaintance--menlofty in thought and beneficent in act--belong to a class whoassiduously let the belief referred to alone. They derive from itneither stimulus nor inspiration, while--I say it with regret--were Iin quest of persons who, in regard to the finer endowments of humancharacter, are to be ranked with the unendowed, I should find somecharacteristic samples among the noisier defenders of the orthodoxbelief. These, however, are but 'hand-specimens' on both sides; thewider data referred to by Professor Knight constitute, therefore, awelcome corroboration of my experience. Again, my excellent critic, Professor Blackie, describes Buddha as being 'a great deal more than aprophet; a rare, exceptional, and altogether transcendentalincarnation of moral perfection. ' [Footnote: 'Natural History ofAtheism, ' p. 136. ] And yet, 'what Buddha preached was a gospel ofpure human ethics, divorced not only from Brahma and the BrahminicTrinity, but even from the existence of God. ' [Footnote: NaturalHistory of Atheism, ' p. 125. ] These civilised and gallant voicesfrom the North contrast pleasantly with the barbarous whoops whichsometimes come to us along the same meridian. 

*****

Looking backwards from my present standpoint over the earnest past, aboyhood fond of play and physical action, but averse to schoolwork, lies before me. The aversion did not arise from intellectual apathyor want of appetite for knowledge, but simply from the fact that myearliest teachers lacked the power of imparting vitality to what theytaught. Athwart all play and amusement, however, a thread ofseriousness ran through my character; and many a sleepless night of mychildhood has been passed, fretted by the question 'Who made God?' Iwas well versed in Scripture; for I loved the Bible, and was promptedby that love to commit large portions of it to memory. Later on Ibecame adroit in turning my Scriptural knowledge against the Church ofRome, but the characteristic doctrines of that Church marked only fora time the limits of enquiry. The eternal Sonship of Christ, forexample, as enunciated in the Athanasian Creed, perplexed me. Theresurrection of the body was also a thorn in my mind, and here Iremember that a passage in Blair's 'Grave' gave me momentary rest. 

 Sure the same power That rear'd the piece at first and took it down Can reassemble the loose, scatter'd parts And put them as they were. 

The conclusion seemed for the moment entirely fair, but with furtherthought, my difficulties came back to me. I had seen cows and sheepbrowsing upon churchyard grass, which sprang from the decaying mouldof dead men. The flesh of these animals was undoubtedly amodification of human flesh, and the persons who fed upon them were asundoubtedly, in part, a more remote modification of the samesubstance. I figured the self-same molecules as belonging first toone body and afterwards to a different one, and I asked myself how twobodies so related could possibly arrange their claims at the day ofresurrection. The scattered parts of each were to be reassembled andset as they were. But if handed over to the one, how could theypossibly enter into the composition of the other? Omnipotence itself, I concluded, could not reconcile the contradiction. Thus the plankwhich Blair's mechanical theory of the resurrection broughtmomentarily into sight, disappeared, and I was again cast abroad onthe waste ocean of speculation. 

At the same time I could by no means get rid of the idea that theaspects of nature and the consciousness of man implied the operationof a power altogether beyond my grasp--an energy the thought of whichraised the temperature of the mind, though it refused to accept shape, personal or otherwise, from the intellect. Perhaps the able criticsof the 'Saturday Review' are justified in speaking as they sometimesdo of Mr. Carlyle. They owe him nothing, and have a right to announcethe fact in their own way. I, however, owe him a great deal, and amalso in honour bound to acknowledge the debt. Few, perhaps, who areprivileged to come into contact with that illustrious man have shownhim a sturdier front than I have, or in discussing modern science havemore frequently withstood him. But I could see that his contention atbottom always was that the human soul has claims and yearnings whichphysical science cannot satisfy. England to come will assuredly thankhim for his affirmation of the ethical and ideal side of human nature. Be this as it may, at the period now reached in my story the feelingreferred to was indefinitely strengthened, my whole life being at thesame time rendered more earnest, resolute, and laborious by thewritings of Carlyle. Others also ministered to this result. Emersonkindled me, while Fichte powerfully stirred my moral pulse. [Footnote:The reader will find in the Seventeenth Lecture of Fichte's course onthe 'Characteristics of the Present Age' a sample of the vital powerof this philosopher. ] In this relation I cared little for politicaltheories or philosophic systems, but a great deal for the propagatedlife and strength of pure and powerful minds. In my laterschool-days, under a clever teacher, some knowledge of mathematics andphysics had been picked up: my stock of both was, however, scanty, andI resolved to augment it. But it was really with the view of learningwhether mathematics and physics could help me in other spheres, ratherthan with the desire of acquiring distinction in either science, thatI ventured, in 1848, to break the continuity of my life, and devotethe meagre funds then at my disposal to the study of science inGermany. 

But science soon fascinated me on its own account. To carry it dulyand honestly out, moral qualities were incessantly invoked. There wasno room allowed for insincerity--no room even for carelessness. Theedifice of science had been raised by men who had unswervinglyfollowed the truth as it is in nature; and in doing so had oftensacrificed interests which are usually potent in this world. Amongthese rationalistic men of Germany I found conscientiousness in workas much insisted on as it could be among theologians. And why, sincethey had not the rewards or penalties of the theologian to offer totheir disciples? Because they assumed, and were justified inassuming, that those whom they addressed had that within them whichwould respond to their appeal. If Germany should ever change forsomething less noble the simple earnestness and fidelity to duty, which in those days characterised her teachers, and through them hersons generally, it will not be because of rationalism. Such adecadent Germany might coexist with the most rampant rationalismwithout their standing to each other in the relation of cause andeffect. 

My first really laborious investigation, conducted jointly with myfriend Professor Knoblauch, landed me in a region which harmonisedwith my speculative tastes. It was essentially an enquiry inmolecular physics, having reference to the curious, and thenperplexing, phenomena exhibited by crystals when freely suspended inthe magnetic field. I here lived amid the most complex operations ofmagnetism in its twofold aspect of an attractive and a repellentforce. Iron was attracted by a magnet, bismuth was repelled, and thecrystals operated on ranged themselves under these two heads. Faradayand Pluecker had worked assiduously at the subject, and had invokedthe aid of new forces to account for the phenomena. It was soon, however, found that the displacement in a crystal of an atom of theiron class by an atom of the bismuth class, involving no change ofcrystalline form, produced a complete reversal of the phenomena. Thelines through the crystal which were in the one case drawn towards thepoles of the magnet, were driven, in the other case, from these poles. By such instances and the reasoning which they suggested, magne-crystallic action was proved to be due, not to the operation ofnew forces, but to the modification of the old ones by moleculararrangement. Whether diamagnetism, like magnetism, was a polar force, was in those days a subject of the most lively contention. It wasfinally proved to be so; and the most complicated cases ofmagne-crystallic action were immediately shown to be simple mechanicalconsequences of the principle of diamagnetic polarity. These earlyresearches, which occupied in all five years of my life, andthroughout which the molecular architecture of crystals was anincessant subject of mental contemplation, gave a tinge and bias to mysubsequent scientific thought, and their influence is easily traced inmy subsequent enquiries. For example, during nine years of labour onthe subject of radiation, heat and light were handled throughout byme, not as ends, but as instruments by the aid of which the mind mightperchance lay hold upon the ultimate particles of matter. 

Scientific progress depends mainly upon two factors which incessantlyinteract--the strengthening of the mind by exercise, and theillumination of phenomena by knowledge. There seems no limit to theinsight regarding physical processes which this interaction carries inits train. Through such insight we are enabled to enter and explorethat subsensible world into which all natural phenomena strike theirroots, and from which they derive nutrition. By it we are enabled toplace before the mind's eye atoms and atomic motions which lie farbeyond the range of the senses, and to apply to them reasoning asstringent as that applied by the mechanician to the motions andcollisions of sensible masses. But once committed to suchconceptions, there is a risk of being irresistibly led beyond thebounds of inorganic nature. Even in those early stages of scientificgrowth, I found myself more and more compelled to regard not onlycrystals, but organic structures, the body of man inclusive, as casesof molecular architecture, infinitely more complex, it is true, thanthose of inorganic nature, but reducible, in the long run, to the samemechanical laws. In ancient journals I find recorded ponderings andspeculations relating to these subjects, and attempts made, byreference to magnetic and crystalline phenomena, to present somesatisfactory image to the mind of the way in which plants and animalsare built up. Perhaps I may be excused for noting a sample of theseearly speculations, already possibly known to a few of my readers, butwhich here finds a more suitable place than that which it formerlyoccupied. 

*****

Sitting, in the summer of 1855, with my friend Dr. Rebus under theshadow of a massive elm on the bank of a river in Normandy, thecurrent of our thoughts and conversation was substantially this: Weregarded the tree above us. In opposition to gravity its moleculeshad ascended, diverged into branches, and budded into innumerableleaves. What caused them to do so--a power external to themselves, oran inherent force? Science rejects the outside builder; let us, therefore, consider from the other point of view the experience of thepresent year. A low temperature had kept back for weeks the life ofthe vegetable world. But at length the sun gained power--or, rather, the cloud-screen which our atmosphere had drawn between him and us wasremoved--and life immediately kindled under his warmth. But what islife, and how can solar light and heat thus affect it? Near our elmwas a silver birch, with its leaves rapidly quivering in the morningair. We had here motion, but not the motion of life. Each leaf movedas a mass under the influence of an outside force, while the motion oflife was inherent and molecular. How are we to figure this molecularmotion--the forces which it implies, and the results which flow fromthem? Suppose the leaves to be shaken from the tree and enabled toattract and repel each other. To fix the ideas, suppose the point ofeach leaf to repel all the other points and to attract the roots, andthe root of each leaf to repel all other roots, but to attract thepoints. The leaves would then resemble an assemblage of littlemagnets abandoned freely to the interaction of their own forces. Inobedience to these they would arrange themselves, and finally assumepositions of rest, forming a coherent mass. Let us suppose thebreeze, which now causes them to quiver, to disturb the assumedequilibrium. As often as disturbed there would be a constant efforton the part of the leaves to re-establish it; and in making thiseffort the mass of leaves would pass through different shapes andforms. If other leaves, moreover, were at hand endowed with similarforces, the attraction would extend to them--a growth of the mass ofleaves being the consequence. 

We have strong reason for assuming that the ultimate particles ofmatter--the atoms and molecules of which it is made up--are endowedwith forces coarsely typified by those here ascribed to the leaves. The phenomena of crystallisation load, of necessity, to thisconception of molecular polarity. Under the operation of such forcesthe molecules of a seed, like our fallen leaves in the first instance, take up positions from which they would never move if undisturbed byan external impulse. But solar light and heat, which come to us aswaves through space, are the great agents of molecular disturbance. Onthe inert molecules of seed and soil these waves impinge, disturbingthe atomic equilibrium, which there is an immediate effort to restore. The effort, incessantly defeated--for the waves continue to pourin--is incessantly renewed; in the molecular struggle matter isgathered from the soil and from the atmosphere, and built, inobedience to the forces which guide the molecules, into the specialform of the tree. In a general way, therefore, the life of the treemight be defined as an unceasing effort to restore a disturbedequilibrium. In the building of crystals Nature makes her firststructural effort; we have here the earliest groping of the so-called'vital force, ' and the manifestations of this force in plants andanimals, though, as already stated, indefinitely more complex, are tobe regarded of the same mechanical quality as those concerned in thebuilding of the crystal. 

Consider the cycle of operations by which the seed produces the plant, the plant the flower, the flower again the seed, the causal line, returning with the fidelity of a planetary orbit to its original pointof departure. Who or what planned this molecular rhythm? We do notknow--science fails even to inform us whether it was ever 'planned' atall. Yonder butterfly has a spot of orange on its wing; and if welook at a drawing made a century ago, of one of the ancestors of thatbutterfly, we probably find the selfsame spot upon the wing. For acentury the molecules have described their cycles. Butterflies havebeen begotten, have been born, and have died; still we find themolecular architecture unchanged. Who or what determined thispersistency of recurrence? We do not know; but we stand within ourintellectual range when we say that there is probably nothing in thatwing which may not yet find its Newton to prove that the principlesinvolved in its construction are qualitatively the same as thosebrought into play in the formation of the solar system. We may eventake a step further, and affirm that the brain of man--the organ ofhis reason--without which he can neither think nor feel, is also anassemblage of molecules, acting and reacting according to law. Here, however, the methods pursued in mechanical science come to an end; andif asked to deduce from the physical interaction of the brainmolecules the least of the phenomena of sensation or thought, Iacknowledge my helplessness. The association of both with the matterof the brain may be as certain as the association of light with therising of the sun. But whereas in the latter case we have unbrokenmechanical connection between the sun and our organs, in the formercase logical continuity disappears. Between molecular mechanics andconsciousness is interposed a fissure over which the ladder ofphysical reasoning is incompetent to carry us. We must, therefore, accept the observed association as an empirical fact, without beingable to bring it under the yoke of _à priori_ deduction. 

*****

Such were the ponderings which ran habitually through my mind in thedays of my scientific youth. They illustrate two things--adetermination to push physical considerations to their utmostlegitimate limit; and an acknowledgment that physical considerationsdo not lead to the final explanation of all that we feel and know. This acknowledgment, be it said in passing, was by no means made withthe view of providing room for the play of considerations other thanphysical. The same intellectual duality, if I may use the phrase, manifests itself in the following extract from an article entitled'Physics and Metaphysics, ' published in the 'Saturday Review' forAugust 4, 1860:

'The philosophy of the future will assuredly take more account thanthat of the past of the dependence of thought and feeling on physicalprocesses; and it may be that the qualities of the mind will bestudied through organic combinations as we now study the character ofa force through the affections of ordinary matter. We believe thatevery thought and every feeling has its definite mechanicalcorrelative--that it is accompanied by a certain breaking up andremarshalling of the atoms of the brain. This latter process ispurely physical; and were the faculties we now possess sufficientlyexpanded, without the creation of any new faculty, it would doubtlessbe within the range of our augmented powers to infer from themolecular state of the brain the character of the thought acting onit, and, conversely, to infer from the thought the exact molecularcondition of the brain. We do not say--and this, as will be seen, isall-important--that the inference here referred to would be an _àpriori_ one. But by observing, with the faculties we assume, the stateof the brain and the associated mental affections, both might be sotabulated side by side that, if one were given, a mere reference tothe table would declare the other. Our present powers, it is true, shrivel into nothingness when brought to bear on such a problem, butit is because of its complexity and our limits that this is the case. The quality of the problem and of our powers are, we believe, sorelated, that a mere expansion of the latter would enable them to copewith the former. Why, then, in scientific speculation should we turnour eyes exclusively to the past? May it not be that a time iscoming--ages no doubt distant, but still advancing--when the dwellersupon this fair earth, starting from the gross human brain of to-day asa rudiment, may be able to apply to these mighty questions facultiesof commensurate extent? Given the requisite expansibility to thepresent senses and intelligence of man--given also the time necessaryfor their expansion--and this high goal may be attained. Developmentis all that is required, and not a change of quality. There need beno absolute breach of continuity between us and our loftier brothersyet to come. 

We have guarded ourselves against saying that the inferring of thoughtfrom material combinations and arrangements would be an inference _àpriori_. The inference meant would be the same in kind as that whichthe observation of the effects of food and drink upon the mind wouldenable us to make, differing only from the latter in the degree ofanalytical insight which we suppose attained. Given the masses anddistances of the planets, we can infer the perturbations consequent ontheir mutual attractions. Given the nature of a disturbance in water, air, or aether--knowing the physical qualities of the medium we caninfer how its particles will be affected. In all this we deal withphysical laws. The mind runs with certainty along the line of thoughtwhich connects the phenomena, and from beginning to end there is nobreak in the chain. But when we endeavour to pass by a similarprocess from the phenomena of physics to those of thought, we meet aproblem which transcends any conceivable expansion of the powers whichwe now possess. We may think over the subject again and again, but iteludes all intellectual presentation. We stand at length face to facewith the Incomprehensible. The territory of physics is wide, but ithas its limits from which we look with vacant gaze into the regionbeyond. Let us follow matter to its utmost bounds, let us claim it inall its forms--even in the muscles, blood, and brain of manhimself--as ours to experiment with and to speculate upon. Castingthe term "vital force" from our vocabulary, let us reduce, if we can, the visible phenomena of life to mechanical attractions andrepulsions. Having thus exhausted physics, and reached its very rim, amighty Mystery still looms beyond us. We have, in fact, made no steptowards its solution. And thus it will ever loom, compelling thephilosophies of successive ages to confess that

 "We are such stuff As dreams are made of, and our little life Is rounded by a sleep. "

In my work on 'Heat, ' published in 1863 and republished many timessince, I employ the precise language thus extracted from the 'SaturdayReview. '

The distinction is here clearly brought out which I had resolved atall hazards to draw--that, namely, between what men knew or mightknow, and what they could never hope to know. Impart simplemagnifying power to our present vision, and the atomic motions of thebrain itself might be brought into view. Compare these motions withthe corresponding states of consciousness, and an empirical nexusmight be established; but 'we try to soar in a vacuum when weendeavour to pass by logical deduction from the one to the other. 'Among these brain-effects a new product appears which defiesmechanical treatment. We cannot deduce motion from consciousness orconsciousness from motion as we deduce one motion from another. Nevertheless observation is open to us, and by it relations may beestablished which are at least as valid as those of the deductivereason. The difficulty may really lie in the attempt to convert adatum into an inference--an ultimate fact into a product of logic. Mydesire for the moment, however, is not to theorise, but to let factsspeak in reply to accusation. 

The most 'materialistic' speculation for which I was responsible, prior to the 'Belfast Address, ' is embodied in the following extractfrom a brief article written as far back as 1865: 'Supposing themolecules of the human body, instead of replacing others, and thusrenewing a pre-existing form, to be gathered first-hand from nature, and placed in the exact relative positions which they occupy in thebody. Supposing them to have the same forces and distribution offorces, the same motions and distribution of motions--would thisorganised concourse of molecules stand before us as a sentient, thinking being? There seems no valid reason to assume that it wouldnot. Or supposing a planet carved from the sun, set spinning round anaxis, and sent revolving round the sun at a distance equal to that ofour earth, would one consequence of the refrigeration of the mass bethe development of organic forms? I lean to the affirmative. ' This isplain speaking, but it is without 'dogmatism. ' An opinion isexpressed, a belief, a leaning--not an established 'doctrine. '

The burthen of my writings in this connection is as much a recognitionof the weakness of science as an assertion of its strength. In 1867, I told the working men of Dundee that while making the largest demandfor freedom of investigation; while considering science to be alikepowerful as an instrument of intellectual culture, and as a ministrantto the material wants of men; if asked whether science has solved, oris likely in our day to solve, 'the problem of the universe, ' I mustshake my head in doubt. I compare the mind of man to a musicalinstrument with a certain range of notes, beyond which in bothdirections exists infinite silence. The phenomena of matter and forcecome within our intellectual range; but behind, and above, and aroundus the real mystery of the universe lies unsolved, and, as far as weare concerned, is incapable of solution. 

While refreshing my mind on these old themes I appear to myself as aperson possessing one idea, which so over-masters him that he is neverweary of repeating it. That idea is the polar conception of thegrandeur and the littleness of man--the vastness of his range in somerespects and directions, and his powerlessness to take a single stepin others. In 1868, before the Mathematical and Physical Section ofthe British Association, then assembled at Norwich, I repeat the samewell-worn note:

'In thus affirming the growth of the human body to be mechanical, andthought as exercised by us to have its correlative in the physics ofthe brain, the position of the "materialist, " as far as that positionis tenable, is stated. I think the materialist will be able finallyto maintain this position against all attacks, but I do not think hecan pass beyond it. The problem of the connection of body and soul isas insoluble in its modern form as it was in the pre-scientific ages. Phosphorus is a constituent of the human brain, and a trenchant Germanwriter has exclaimed, "Ohne Phosphor kein Gedanke!" That may or maynot be the case; but, even if we knew it to be the case, the knowledgewould not lighten our darkness. On both sides of the zone hereassigned to the materialist, he is equally helpless. If you ask himwhence is this "matter" of which we have been discoursing--who or whatdivided it into molecules, and impressed upon them this necessity ofrunning into organic forms--he has no answer. Science is also mute inregard to such questions. But if the materialist is confounded andscience is rendered dumb, who else is prepared with an answer? Let uslower our heads and acknowledge our ignorance, priest and philosopher, one and all. '

*****

The roll of echoes which succeeded the Lecture delivered by ProfessorVirchow at Munich on September 22, 1877, was long and loud. The'Times' published a nearly full translation of the lecture, and it waseagerly commented on in other journals. Glances from it to an Addressdelivered by me before the Midland Institute in the autumn of 1877, and published in this volume, were very frequent. Professor Virchowwas held up to me in some quarters as a model of philosophic caution, who by his reasonableness reproved my rashness, and by his depthreproved my shallowness. With true theologic courtesy I wassedulously emptied, not only of the 'principles of scientificthought, ' but of 'common modesty' and 'common sense. ' And though I amindebted to Professor Clifford for recalling in the 'NineteenthCentury' for April the public mind in this connection from heatedfancy to sober fact, I do not think a brief additional examination ofVirchow's views, and of my relation to them, will be out of placehere. 

The key-note of his position is struck in the preface to the excellentEnglish translation of his lecture--a preface written expressly byhimself. 'Nothing, ' he says, 'was farther from his intention than anywish to disparage the great services rendered by Mr. Darwin to theadvancement of biological science, of which no one has expressed moreadmiration than himself. On the other hand, it seemed high time tohim to enter an energetic protest against the attempts that are madeto proclaim the problems of research as actual facts, and the opinionsof scientists as established science. ' On the ground, among others, that it promotes the pernicious delusions of the Socialist, Virchowconsiders the theory of evolution dangerous; but his fidelity to truthis so great that he would brave the danger and teach the theory, if itwere only proved. 'However dangerous the state of things might be, let the confederates be as mischievous as they might, still I do nothesitate to say that from the moment when we had become convinced thatthe evolution theory was a perfectly established doctrine--so certainthat we could pledge our oath to it, so sure that we could say, "Thusit is"--from that moment we could not dare to feel any scruple aboutintroducing it into our actual life, so as not only to communicate itto every educated man, but to impart it to every child, to make it thefoundation of our whole ideas of the world, of society, and the State, and to base upon it our whole system of education. This I hold to bea necessity. '

It would be interesting to know the persons designated by the pronoun'we' in the first sentence of the foregoing quotation. No doubtProfessor Haeckel would accept this canon in all its fulness, andfound on it his justification. He would say without hesitation: 'I amconvinced that the theory of evolution is a perfectly establisheddoctrine, and hence on your own showing I am justified in urging itsintroduction into our schools. ' It is plain, however, that ProfessorVirchow would not accept this retort as valid. His 'we' must coversomething more than Professor Haeckel. It would probably cover moreeven than the audience he addressed; for he would hardly affirm, evenif every one of his hearers accepted the theory of evolution, thatthat would be a sufficient warrant for forcing it upon the public atlarge. His 'we, ' I submit, needs definition. If he means that thetheory of evolution ought to be introduced into our schools, not whenexperts are agreed as to its truth, but when the community is preparedfor its introduction, then, I think, he is right, and that, as amatter of social policy, Dr. Haeckel would be wrong in seeking toantedate the period of its introduction. In dealing with thecommunity great changes must have timeliness as well as truth upontheir side. But if the mouths of thinkers be stopped, the necessarysocial preparation will be impossible; an unwholesome divorce will beestablished between the expert and the public, and the slow andnatural process of leavening the social lump by discovery anddiscussion will be displaced by something far less safe and salutary. 

The burthen, however, of this celebrated lecture is a warning that amarked distinction ought to be made between that which isexperimentally proved and that which is still in the region ofspeculation. As to the latter, Virchow by no means imposes silence. He is far too sagacious a man to commit himself, at the present timeof day, to any such absurdity. But he insists that it ought not to beput on the same evidential level as the former. 'It ought, ' as hepoetically expresses it, I to be written in small letters under thetext. ' The audience ought to be warned that the speculative matter isonly _possible_, not _actual_ truth--that it belongs to the region of'belief, ' and not to that of demonstration. As long as a problemcontinues in this speculative stage it would be mischievous, heconsiders, to teach it in our schools. 'We ought not, ' he urges, 'torepresent our conjecture as a certainty, nor our hypothesis as adoctrine: this is inadmissible. ' With regard to the connection betweenphysical processes and mental phenomena he says: 'I will, indeed, willingly grant that we can find certain gradations, certain definitepoints at which we trace a passage from mental processes to processespurely physical, or of a physical character. Throughout thisdiscourse I am not asserting that it will never be possible to bringpsychical processes into an immediate connection with those that arephysical. All I say is that we have _at present_ no right to set upthis _possible_ connection as _a doctrine_ of science. ' In the nextparagraph be reiterates his position with reference to theintroduction of such topics into school teaching. 'We must draw, ' hesays, 'a strict distinction between what we wish to _teach_, and what wewish to _search for_. The objects of our research are expressed asproblems (or hypotheses). _We need not keep them to ourselves; we areready to communicate them to all the world_, and say "There is theproblem; that is what we strive for. " ... The investigation of suchproblems, in which the whole nation may be interested, cannot berestricted to any one. This is Freedom of Enquiry. But the problem(or hypothesis) is not, without further debate, to be made _adoctrine_. ' He will not concede to Dr. Haeckel 'that it is a questionfor the schoolmasters to decide, whether the Darwinian theory of man'sdescent should be at once laid down as the basis of instruction, andthe protoplastic soul be assumed as the foundation of all ideasconcerning spiritual being. ' The Professor concludes his lecture thus:'With perfect truth did Bacon say of old "_Scientia est potentia_. " Buthe also defined that knowledge; and the knowledge he meant was notspeculative knowledge, not the knowledge of hypotheses, but it wasobjective and actual knowledge. Gentlemen, I think we should beabusing our power, we should be imperilling our power, unless in ourteaching we restrict ourselves to this perfectly safe and unassailabledomain. From this domain _we may make incursions into the field ofproblems_, and I am sure that every venture of that kind will then findall needful security and support. ' I have emphasised by italics twosentences in the foregoing series of quotations; the other italics arethe author's own. 

Virchow's position could not be made clearer by any comments of minethan he has here made it himself. That position is one of the highestpractical importance. Throughout our whole German Fatherland, ' hesays, men are busied in renovating, extending, and developing thesystem of education, and in inventing fixed forms in which to mouldit. On the threshold of coming events stands the Prussian law ofeducation. In all the German States larger schools are being built, new educational establishments are set up, the universities areextended, "higher" and "middle" schools are founded. Finally comesthe question, What is to be the chief substance of the teaching?' WhatVirchow thinks it ought and ought not to be, is disclosed by theforegoing quotations. There ought to be a clear distinction madebetween science in the state of hypothesis, and science in the stateof fact. In school teaching the former ought to be excluded. And, ashe assumes it to be still in its hypothetical stage, the ban ofexclusion ought, he thinks, to fall upon the theory of evolution. 

*****

I now freely offer myself for judgment before the tribunal whose lawis here laid down. First and foremost, then, I have never advocatedthe introduction of the theory of evolution into our schools. Ishould even be disposed to resist its introduction before its meaninghad been better understood and its utility more fully recognised thanit is now by the great body of the community. The theory ought, Ithink, to bide its time until the free conflict of discovery, argument, and opinion has won for it this recognition. A necessarycondition here, however, is that free discussion should not beprevented, either by the ferocity of reviewers or the arm of the law;otherwise, as I said before, the work of social preparation cannot goon. On this count, then, I claim acquittal, being for the moment onthe side of Virchow. 

Besides the duties of the chair, which I have been privileged tooccupy in London for more than a quarter of a century, and which neverinvolved a word on my part, pro or con, in reference to the theory ofevolution, I have had the honour of addressing audiences in Liverpool, Belfast, and Birmingham; and in these addresses the theory ofevolution, and the connected doctrine of spontaneous generation, havebeen more or less touched upon. Let us now examine whether in myreferences I have departed from the views of Virchow or not. 

In the Liverpool discourse, after speaking of the theory of evolutionwhen applied to the primitive condition of matter, as belonging to'the dim twilight of conjecture, ' and affirming that 'the certaintyof experimental enquiry is here shut out, ' I sketch the nebular theoryas enunciated by Kant and Laplace, and afterwards proceed thus:'Accepting some such view of the construction of our system _asprobable_, a desire immediately arises to connect the present life ofour planet with the past. We wish to know something of our remotestancestry. On its first detachment from the sun, life, as weunderstand it, could not have been present on the earth. How, then, did it come there? The thing to be encouraged here is a reverentfreedom--a freedom preceded by the hard discipline which checkslicentiousness in speculation--while the thing to be repressed, bothin science and out of it, is dogmatism. And here I am in the hands ofthe meeting, willing to end but ready to go on. _I have no right tointrude upon you unasked the unformed notions which are floating likeclouds, or gathering to more solid consistency in the modernspeculative mind_. '

I then notice more especially the basis of the theory. Those who holdthe doctrine of evolution _are by no means ignorant of the uncertaintyof their data, and they only yield to it a provisional assent_. Theyregard the nebular hypothesis as probable; and, in the utter absenceof any proof of the illegality of the act, they prolong the method ofnature from the present into the past. Here the observed uniformity ofnature is their only guide. Having determined the elements of theircurve in a world of observation and experiment, they prolong thatcurve into an antecedent world, and accept as probable the unbrokensequence of development from the nebula to the present time. ' Thus itappears that, long antecedent to the publication of his advice, I didexactly what Professor Virchow recommends, showing myself as carefulas he could be not to claim for a scientific doctrine a certaintywhich did not belong to it. 

I now pass on to the Belfast Address, and will cite at once from itthe passage which has given rise to the most violent animadversion. 'Believing as I do in the continuity of nature, I cannot stop abruptlywhere our microscopes cease to be of use. At this point the vision ofthe mind authoritatively supplements that of the eye. By anintellectual necessity I cross the boundary of the experimentalevidence, and discern in that "matter" which we, in our ignorance ofits latent powers, and notwithstanding our professed reverence for itsCreator, have hitherto covered with opprobrium, the promise andpotency of all terrestrial life. ' Without halting for a moment I go onto do the precise thing which Professor Virchow declares to benecessary. 'If you ask me, ' I say, 'whether there exists the leastevidence to prove that any form of life can be developed out of matterindependently of antecedent life, my reply is that evidence consideredperfectly conclusive by many has been adduced, and that were we tofollow a common example, and accept testimony because it falls in withour belief, we should eagerly close with the evidence referred to. Butthere is in the true man of science a desire stronger than the wish tohave his beliefs upheld; namely, the desire to have them true. Andthose to whom I refer as having studied this question, believing theevidence offered in favour of "spontaneous generation" to be vitiatedby error, cannot accept it. They know full well that the chemist nowprepares from inorganic matter a vast array of substances, which weresome time ago regarded as the products solely of vitality. They areintimately acquainted with the structural power of matter, asevidenced in the phenomena of crystallisation. They can justifyscientifically their _belief_ in its potency, under the properconditions, to produce organisms. But, in reply to your question, they will frankly admit their inability to point to any satisfactoryexperimental proof that life can be developed, save from demonstrableantecedent life. ' [Footnote: Quoted by Clifford, 'Nineteenth Century, '3, p. 726. ]

Comparing the theory of evolution with other theories, I thus expressmyself: 'The basis of the doctrine of evolution consists, not in anexperimental demonstration--for the subject is hardly accessible tothis mode of proof--but in its general harmony with scientificthought. From contrast, moreover, it derives enormous relativestrength. On the one side we have a theory, which converts the Powerwhose garment is seen in the visible universe into an Artificer, fashioned after the human model, and acting by broken efforts, as manis seen to act. On the other side we have the conception that all wesee around us and feel within us--the phenomena of physical nature aswell as those of the human mind--have their unsearchable roots in acosmical life, if I dare apply the term, an infinitesimal span ofwhich is offered to the investigation of man. ' Among thinking people, in my opinion, this last conception has a higher ethical value thanthat of a personal artificer. Be that as it may, I make here no claimfor the theory of evolution which can reasonably be refused. 

'Ten years have elapsed' said Dr. Hooker at Norwich in 1868 [Footnote:President's Address to the British Association. ] 'since thepublication of "The Origin of Species by Natural Selection, " and it istherefore not too early now to ask what progress that bold theory hasmade in scientific estimation. Since the "Origin" appeared it haspassed through four English editions, ' [Footnote: Published by Mr. John Murray, the English publisher of Virchow's Lecture. Bane andantidote are thus impartially distributed by the same hand. ] twoAmerican, two German, two French, several Russian, a Dutch, and anItalian edition. So far from Natural Selection being a thing of thepast [the 'Athenaeum' had stated it to be so] it is an accepteddoctrine with almost every philosophical naturalist, including, itwill always be understood, a considerable proportion who are notprepared to admit that it accounts for all Mr. Darwin assigns to it. 'In the following year, at Innsbruck, Helmholtz took up the sameground. [Footnote: 'Noch besteht lebhafter Streit um die Wahrheit oderWahrscheinlichkeit von Darwin's Theorie; er dreht sich aber docheigentlich nur um die Grenzen, welche wir fuer die Veraenderlichkeitder Arten annehmen duerfen. Dass innerhalb derselben Species erblicheRacenverschiedenheiten auf die von Darwin beschriebene Weise zu kommenkoennen, ja dass viele der bisher als verschiedene Species derselbenGattung betrachteten Formen von derselben Urform abstammen, werdenauch seine Gegner kaum leugnen. '--(Populaere Vortraege. )] Anotherdecade has now passed, and he is simply blind who cannot see theenormous progress made by the theory during that time. Some of theoutward and visible signs of this advance are readily indicated. Thehostility and fear which so long prevented the recognition of Mr. Darwin by his own university have vanished, and this year Cambridge, amid universal acclamation, conferred on him her Doctor's degree. TheAcademy of Sciences in Paris, which had so long persistently closedits doors against Mr. Darwin, has also yielded at last; while sermons, lectures, and published articles plainly show that even the clergyhave, to a great extent, become acclimatised to the Darwinian air. Mybrief reference to Mr. Darwin in the Birmingham Address was based uponthe knowledge that such changes had been accomplished, and were stillgoing on. 

That the lecture of Professor Virchow can, to any practical extentdisturb this progress of public faith in the theory of evolution, I donot believe. That the special lessons of caution which he inculcateswere exemplified by me, years before his voice was heard upon thissubject, has been proved in the foregoing pages. In point of fact, ifhe had preceded me instead of following me, and if my desire had beento incorporate his wishes in my words, I could not have accomplishedthis more completely. It is possible, moreover, to draw thecoincident lines still further, for most of what he has said aboutspontaneous generation might have been uttered by me. I share hisopinion that the theory of evolution in its complete form involves thepassage from matter which we now hold to be inorganic into organisedmatter; in other words, involves the assumption that at some period orother of the earth's history there occurred what would be now called'spontaneous generation. ' I agree with him that the proofs of it arestill wanting. ' 'Whoever, ' he says, recalls to mind the lamentablefailure of all the attempts made very recently to discover a decidedsupport for the _generatio aequivoca_ in the lower forms of transitionfrom the inorganic to the organic world will feel it doubly serious todemand that this theory, so utterly discredited, should be in any wayaccepted as the basis of all our views of life. ' I hold with Virchowthat the failures have been lamentable, that the doctrine is utterlydiscredited. But my position here is so well known that I need notdwell upon it further. 

With one special utterance of Professor Virchow his translatorconnects me by name. 'I have no objection, ' observes the Professor, 'to your saying that atoms of carbon also possess mind, or that intheir connection with the Plastidule company they acquire mind; only Ido not know how I am to perceive this. ' This is substantially what Ihad said seventeen years previously in the 'Saturday Review. ' TheProfessor continues: 'If I explain attraction and repulsion asexhibitions of mind, as psychical phenomena, I simply throw the Psycheout of the window, and the Psyche ceases to be a Psyche. ' I may say, in passing, that the Psyche that could be cast out of the window isnot worth houseroom. At this point the translator, who is evidently aman of culture, strikes in with a foot-note. 'As an illustration ofProfessor Virchow's meaning, we may quote the conclusion at whichDoctor Tyndall arrives respecting the hypothesis of a human soul, offered as an explanation or a simplification of a series of obscurephenomena--psychical phenomena, as he calls them. "If you arecontent to make your soul a poetic rendering of a phenomenon whichrefuses the yoke of ordinary physical laws, I, for one, would notobject to this exercise of ideality. "' [Footnote: 'PresidentialAddress delivered before the Birmingham and Midland Institute, October1, 1877. Fortnightly Review, ' Nov. 1, 1877, p. 60] ProfessorVirchow's meaning, I admit, required illustration; but I do notclearly see how the quotation from me subserves this purpose. I donot even know whether I am cited as meriting praise or deservingopprobrium. In a far coarser fashion this utterance of mine has beendealt with in other places: it may therefore be worth while to spend afew words upon it. 

The sting of a wasp at the finger-end announces itself to the brain aspain. The impression made by the sting travels, in the first place, with comparative slowness along the nerves affected; and only when itreaches the brain have we the fact of consciousness. Those who thinkmost profoundly on this subject hold that a chemical change, which, strictly interpreted, is atomic motion, is, in such a case, propagatedalong the nerve, and communicated to the brain. Again, on feeling thesting I flap the insect violently away. What has caused this motionof my hand? The command from the brain to remove the insect travelsalong the motor nerves to the proper muscles, and, their force beingunlocked, they perform the work demanded of them. But what moved thenerve molecules which unlocked the muscle? The sense of pain, it maybe replied. But how can a sense of pain, or any other state ofconsciousness, make matter move? Not all the sense of pain orpleasure in the world could lift a stone or move a billiard-ball; whyshould it stir a molecule? Try to express the motion numerically interms of the sensation, and the difficulty immediately appears. Hencethe idea long ago entertained by philosophers, but lately brought intospecial prominence, that the physical processes are complete inthemselves, and would go on just as they do if consciousness were notat all implicated. Consciousness, on this view, is a kind ofby-product inexpressible in terms of force and motion, and unessentialto the molecular changes going on in the brain. 

Four years ago, I wrote thus: 'Do states of consciousness enter aslinks into the chain of antecedence and sequence, which gives rise tobodily actions? Speaking for myself, it is certain that I have nopower of imagining such states interposed between the molecules of thebrain, and influencing the transference of motion among the molecules. The thing "eludes all mental presentation. " Hence an iron strengthseems to belong to the logic which claims for the brain an automaticaction uninfluenced by consciousness. But it is, I believe, admittedby those who hold the automaton theory, that states of consciousnessare produced by the motion of the molecules of the brain; and thisproduction of consciousness by molecular motion is to me quite asunpresentable to the mental vision as the production of molecularmotion by consciousness. If I reject one result I must reject both. I, however, reject neither, and thus stand in the presence of twoIncomprehensibles, instead of one Incomprehensible. ' Here I secedefrom the automaton theory, though maintained by friends who have allmy esteem, and fall back upon the avowal which occurs with suchwearisome iteration throughout the foregoing pages; namely, my ownutter incapacity to grasp the problem. 

This avowal is repeated with emphasis in the passage to whichProfessor Virchow's translator draws attention. What, I thereask, is the causal connection between the objective and thesubjective--between molecular motions and states of consciousness?My answer is: I do not see the connection, nor am I acquainted withanybody who does. It is no explanation to say that the objectiveand subjective are two sides of one and the same phenomenon. Why should the phenomenon have two sides? This is the very coreof the difficulty. There are plenty of molecular motions whichdo exhibit this two-sidedness. Does water think or feel when itruns into frost-ferns upon a window pane? If not, why shouldthe molecular motion of the brain be yoked to this mysteriouscompanion--consciousness? We can form a coherent picture of all thepurely physical processes--the stirring of the brain, the thrilling ofthe nerves, the discharging of the muscles, and all the subsequentmotions of the organism. We are here dealing with mechanical problemswhich are mentally presentable. 

But we can form no picture of the process whereby consciousnessemerges, either as a necessary link, or as an accidental by-product, of this series of actions. The reverse process of the production ofmotion by consciousness is equally unpresentable to the mind. We arehere in fact on the boundary line of the intellect, where the ordinarycanons of science fail to extricate us. If we are true to thesecanons, we must deny to subjective phenomena all influence on physicalprocesses. The mechanical philosopher, as such, will never place astate of consciousness and a group of molecules in the relation ofmover and moved. Observation proves them to interact; but, in passingfrom the one to the other, we meet a blank which the logic ofdeduction is unable to fill. This, the reader will remember, is theconclusion at which I had arrived more than twenty years ago. I laybare unsparingly the central difficulty of the materialist, and tellhim that the facts of observation which he considers so simple are'almost as difficult to be seized mentally as the idea of a soul. ' I gofurther, and say, in effect, to those who wish to retain this idea, 'If you abandon the interpretations of grosser minds, who image thesoul as a Psyche which could be thrown out of the window--an entitywhich is usually occupied, we know not how, among the molecules of thebrain, but which on due occasion, such as the intrusion of a bullet orthe blow of a club, can fly away into other regions of space--if, abandoning this heathen notion, you consent to approach the subject inthe only way in which approach is possible--if you consent to makeyour soul a poetic rendering of a phenomenon which, as I have takenmore pains than anybody else to show you, refuses the yoke of ordinaryphysical laws--then I, for one, would not object to this exercise ofideality. ' I say it strongly, but with good temper, that thetheologian, or the defender of theology, who hacks and scourges me forputting the question in this light is guilty of black ingratitude. 

*****

Notwithstanding the agreement thus far pointed out, there are certainpoints in Professor Virchow's lecture to which I should feel inclinedto take exception. I think it was hardly necessary to associate thetheory of evolution with Socialism; it may be even questioned whetherit was correct to do so. As Lange remarks, the aim of Socialism, orof its extreme leaders, is to overthrow the existing systems ofgovernment, and anything that helps them to this end is welcomed, whether it be atheism or papal infallibility. For long years theSocialists saw Church and State united against them, and both weretherefore regarded with a common hatred. But no sooner does a seriousdifference arise between Church and State, than a portion of theSocialists begin immediately to dally with the former. [Footnote:'Geschichte des Materialismus, ' 2e Auflage, vol. Ii. P. 538. ] Theexperience of the last German elections illustrates Lange's position. Far nobler and truer to my mind than this fear of promoting Socialismby a scientific theory which the best and soberest heads in the worldhave substantially accepted, is the position assumed by Helmholtz, whoin his 'Popular Lectures' describes Darwin's theory as embracing 'anessentially new creative thought' (einen wesentlich neuenschoepferischen Gedanken), and who illustrates the greatness of thisthought by copious references to the solutions, previously undreamtof, which it offers of the enigmas of life and organisation. Hepoints to the clouds of error and confusion which it has alreadydispersed, and shows how the progress of discovery since its firstenunciation is simply a record of the approach of the theory towardscomplete demonstration. One point in this 'popular' expositiondeserves especial mention here. Helmholtz refers to the dominantposition acquired by Germany in physiology and medicine, while othernations have kept abreast of her in the investigation of inorganicnature. He claims for German men the credit of pursuing withunflagging and self-denying industry, with purely ideal aims, andwithout any immediate prospect of practical utility, the cultivationof pure science. But that which has determined German superiority inthe fields referred to was, in his opinion, something different fromthis. Enquiries into the nature of life are intimately connected withpsychological and ethical questions; and he claims for his countrymena greater fearlessness of the consequences which a full knowledge ofthe truth may here carry along with it, than reigns among theenquirers of other nations. And why is this the case? 'England andFrance, ' he says, 'possess distinguished investigators--men competentto follow up and illustrate with vigorous energy the methods ofnatural science; but they have hitherto been compelled to bend beforesocial and theological prejudices, and could only utter theirconvictions under the penalty of injuring their social influence andusefulness. Germany has gone forward more courageously. She hascherished the trust, which has never been deceived, that completetruth carries with it the antidote against the bane and danger whichfollow in the train of half knowledge. A cheerfully laborious andtemperate people--a people morally strong--can well afford to looktruth full in the face. Nor are they to be ruined by the enunciationof one-sided theories, even when these may appear to threaten thebases of society. ' These words of Helmholtz are, in my opinion, wiserand more applicable to the condition of Germany at the present momentthan those which express the fears of Professor Virchow. It will beremembered that at the time of his lecture his chief anxieties weredirected towards France; but France has since that time given ampleevidence of her ability to crush, not only Socialists, butanti-Socialists, who would impose on her a yoke which she refuses tobear. 

In close connection with these utterances of Helmholtz, I placeanother utterance not less noble, which I trust was understood andappreciated by those to whom it was addressed. 'If, ' said thePresident of the British Association in his opening address in Dublin, we could lay down beforehand the precise limits of possible knowledge, the problem of physical science would be already half solved. But thequestion to which the scientific explorer has often to address himselfis, not merely whether he is able to solve this or that problem; butwhether he can so far unravel the tangled threads of the matter withwhich he has to deal, as to weave them into a definite problem atall ... If his eye seem dim, he must look steadfastly and with hopeinto the misty vision, until the very clouds wreathe themselves intodefinite forms. If his ear seem dull, he must listen patiently andwith sympathetic trust to the intricate whisperings of Nature--thegoddess, as she has been called, of a hundred voices--until here andthere he can pick out a few simple notes to which his own powers canresound. If, then, at a moment when he finds himself placed on apinnacle from which he is called upon to take a perspective survey ofthe range of science, and to tell us what he can see from his vantageground; if at such a moment after straining his gaze to the very vergeof the horizon, and after describing the most distant of well-definedobjects, he should give utterance also to some of the subjectiveimpressions which he is conscious of receiving from regions beyond; ifhe should depict possibilities which seem opening to his view; if heshould explain why he thinks this a mere blind alley and that an openpath; _then the fault and the loss would be alike ours if we refused tolisten calmly, and temperately to form our own judgment on what wehear; then assuredly it is we who would be committing the error ofconfounding matters of fact with matters of opinion, if we failed todiscriminate between the various elements contained in such adiscourse, and assumed that they had been all put on the samefooting_. '

*****

While largely agreeing with him, I cannot quite accept the setting inwhich Professor Virchow places the confessedly abortive attempts tosecure an experimental basis for the doctrine of spontaneousgeneration. It is not a doctrine 'so discredited' that some of thescientific thinkers of England accept 'as the basis of all theirviews of life. ' Their induction is by no means thus limited. Theyhave on their side more than the 'reasonable probability' deemedsufficient by Bishop Butler for practical guidance in the gravestaffairs, that the members of the solar system which are now discreteonce formed a continuous mass; that in the course of untold ages, during which the work of condensation, through the waste of heat inspace, went on, the planets were detached; and that our present sun isthe residual nucleus of the flocculent or gaseous ball from which theplanets were successively separated. Life, as we define it, was notpossible for aeons subsequent to this separation. When and how did itappear? I have already pressed this question, but have received noanswer. [Footnote: In the 'Apology for the Belfast Address, ' thequestion is reasoned out. ] If, with Professor Knight, we regard theBible account of the introduction of life upon the earth as a poem, not as a statement of fact, where are we to seek for guidance as tothe fact? There does not exist a barrier possessing the strength of acobweb to oppose to the hypothesis, which ascribes the appearance oflife to that 'potency of matter' which finds expression in naturalevolution. [Footnote: 'We feel it an undeniable necessity, ' saysProfessor Virchow, not to sever the organic world from the whole, asif it were something disjoined from the whole. ' This grave statementcannot be weakened by the subsequent pleasantry regarding 'Carbon &Co. ']

This hypothesis is not without its difficulties, but they vanish whencompared with those which encumber its rivals. There are variousfacts in science obviously connected, and whose connections we areunable to trace; but we do not think of filling the gap between themby the intrusion of a separable spiritual agent. In like mannerthough we are unable to trace the course of things from the nebula, when there was no life in our sense, to the present earth where lifeabounds, the spirit and practice of science pronounce against theintrusion of an anthropomorphic creator. Theologians must liberateand refine their conceptions or be prepared for the rejection of themby thoughtful minds. It is they, not we, who lay claim to knowledgenever given to man. Our refusal of the creative hypothesis is less anassertion of knowledge than a protest against the assumption ofknowledge which must long, if not always, lie beyond us, and the claimto which is a source of perpetual confusion. ' At the same time, when Ilook with strenuous gaze into the whole problem as far as mycapacities allow, overwhelming wonder is the predominant feeling. Thiswonder has come to me from the ages just as much as my understanding, and it has an equal right to satisfaction. Hence I say, if, abandoning your illegitimate claim to knowledge, you place, with Job, your forehead in the dust and acknowledge the authorship of thisuniverse to be past finding out--if, having made this confession, andrelinquished the views of the mechanical theologian, you desire forthe satisfaction of feelings which I admit to be, in great part, thoseof humanity at large, to give ideal form to the Power that moves allthings--it is not by me that you will find objections raised to thisexercise of ideality, if it be only consciously and worthily carriedout. 

*****

Again, I think Professor Virchow's position, in regard to the questionof _contagium animatum_, is not altogether that of true philosophy. Hepoints to the antiquity of the doctrine. 'It is lost, ' he says, 'inthe darkness of the middle ages. We have received this name from ourforefathers, and it already appears distinctly in the sixteenthcentury. We possess several works of that time which put forward_contagium animatum_ as a scientific doctrine, with the same confidence, with the same sort of proof, with which the "Plastidulic soul" is nowset forth. '

These speculations of our 'forefathers' will appeal differently todifferent minds. By some they will be dismissed with a sneer; toothers they will appeal as proofs of genius on the part of those whoenunciated them. There are men, and by no means the minority, who, however wealthy in regard to facts, can never rise into the region ofprinciples; and they are sometimes intolerant of those who can. Theyare formed to plod meritoriously on the lower levels of thought, unpossessed of the pinions necessary to reach the heights. They cannotrealise the mental act--the act of inspiration it might well becalled--by which a man of genius, after long pondering and proving, reaches a theoretic conception which unravels and illuminates thetangle of centuries of observation and experiment. There are minds, it may be said in passing, who at the present moment stand in thisrelation to Mr. Darwin. For my part, I should be inclined to ascribeto penetration rather than to presumption the notion of a _contagiumanimatum_. He who invented the term ought, I think, to be held inesteem; for he had before him the quantity of fact, and the measure ofanalogy, that would justify a man of genius in taking a step so bold. 'Nevertheless, ' says Professor Virchow, 'no one was able throughouta long time to discover these living germs of disease. The sixteenthcentury did not find them, nor did the seventeenth, nor theeighteenth. ' But it may be urged, in reply to this, that the theoreticconjecture often legitimately comes first. It is the forecast ofgenius which anticipates the fact and constitutes a spur towards itsdiscovery. If, instead of being a spur, the theoretic guess renderedmen content with imperfect knowledge, it would be a thing to bedeprecated. But in modern investigation this is distinctly not thecase; Darwin's theory, for example, like the undulatory theory, hasbeen a motive power and not an anodyne. 'At last, ' continuesProfessor Virchow, 'in the nineteenth century we have begun little bylittle really to find _contagia animata_. ' So much the more honour, Iinfer, is due to those who, three centuries in advance, so puttogether the facts and analogies of contagious disease as to divineits root and character. Professor Virchow seems to deprecate the'obstinacy' with which this notion of a _contagium vivum_ emerged. HereI should not be inclined to follow him; because I do not know, nordoes he tell me, how much the discovery of facts in the nineteenthcentury is indebted to the stimulus derived from the theoreticdiscussions of preceding centuries. The genesis of scientific ideasis a subject of profound interest and importance. He would be but apoor philosopher who would sever modern chemistry from the efforts ofthe alchemists, who would detach modern atomic doctrines from thespeculations of Lucretius and his predecessors, or who would claim forour present knowledge of _contagia_ an origin altogether independent ofthe efforts of our 'forefathers' to penetrate this enigma. 

*****

Finally, I do not know that I should agree with Professor Virchow asto what a theory is or ought to be. I call a theory a principle orconception of the mind which accounts for observed facts, and whichhelps us to look for and predict facts not yet observed. Every newdiscovery which fits into a theory strengthens it. The theory is nota thing complete from the first, but a thing which grows, as it wereasymptotically, towards certainty. Darwin's theory, as pointed outnine and ten years ago by Helmholtz and Hooker, was then exactly inthis condition of growth; and had they to speak of the subject to-daythey would be able to announce an enormous strengthening of thetheoretic fibre. Fissures in continuity which then existed, and whichleft little hope of being ever spanned, have been since filled in, sothat the further the theory is tested the more fully does it harmonisewith progressive experience and discovery. We shall probably neverfill all the gaps; but this will not prevent a profound belief in thetruth of the theory from taking root in the general mind. Much lesswill it justify a total denial of the theory. The man of science whoassumes in such a case the position of a denier is sure to be strandedand isolated. The proper attitude, in my opinion, is to give to thetheory during the phases of its growth as nearly as possible aproportionate assent; and, if it be a theory which influencespractice, our wisdom is to follow its probable suggestions where morethan probability is for the moment unattainable. I write thus withthe theory of _contagium vivum_, more especially in my mind, and mustregret the attitude of denial assumed by Professor Virchow towardsthat theory. 'I must beg my friend Klebs to pardon me, ' he says, 'if, notwithstanding the late advances made by the doctrine of infectiousfungi, I still persist in my reserve so far as to admit only thefungus which is really proved while I deny all other fungi so long asthey are not actually brought before me. ' Professor Virchow, that isto say, will continue to deny the Germ Theory, however great theprobabilities on its side, however numerous be the cases of which itrenders a just account, until it has ceased to be a theory at all, andhas become a congeries of sensible facts. Had he said, 'As long as asingle fungus of disease remains to be discovered, it is your boundenduty to search for it, ' I should cordially agree with him. But by hisunreserved denial he quenches the light of probability which ought toguide the practice of the medical man. Both here and in relation tothe theory of evolution excess upon one side has begotten excess uponthe other. 

====================

NOTE. --As might have been expected, Professor Virchow, shows himselfin practice far too sound a philosopher to be restricted by the canonlaid down in his critique of Dr. Haeckel. In his recent discourseupon the plague, he asks and answers the question, 'What is the_contagium_?' in the following words: 'Et qu'est-ce que le _contagium_? Amon avis, l'analogie de la peste aver le charbon contagieux me paraîtsi grande qu'il me semble possible de trouver un organismemicroscopique qui contient le germe de l'affection. Mais jusqu' àprésent on a peu cherché à trouver cet organisme. '--RevueScientifique, March, 1879. 

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XVI. THE ELECTRIC LIGHT. 

[Footnote: A discourse delivered at the Royal Institution of GreatBritain on Friday, January 17, 1879, and introduced here as the latestFragment. ]

THE subject of this evening's discourse was proposed by our latehonorary secretary. [Footnote: Mr. William Spottiswoode, now Presidentof the Royal Society] That word 'late' has for me its ownconnotations. It implies, among other things, the loss of a comradeby whose side I have worked for thirteen years. On the other hand, regret is not without its opposite in the feeling with which I haveseen him rise by sheer intrinsic merit, moral and intellectual, to thehighest official position which it is in the power of English scienceto bestow. Well, he, whose constant desire and practice were topromote the interests and extend the usefulness of this institution, thought that at a time when the electric light occupied so much ofpublic attention, a few sound notions regarding it, on the more purelyscientific side, might, to use his own pithy expression, be 'planted'in the public mind. I am here to-night with the view of trying, tothe best of my ability, to realise the idea of our friend. 

In the year 1800, Volta announced his immortal discovery of the pile. Whetted to eagerness by the previous conflict between him and Galvani, the scientific men of the age flung themselves with ardour upon thenew discovery, repeating Volta's experiments, and extending them inmany ways. The light and heat of the voltaic circuit attracted markedattention, and in the innumerable tests and trials to which thisquestion was subjected, the utility of platinum and charcoal as meansof exalting the light was on all hands recognised. Mr. Children, witha battery surpassing in strength all its predecessors, fused platinumwires eighteen inches long, while 'points of charcoal produced a lightso vivid that the sunshine, compared with it, appeared feeble. '[Footnote: Davy, 'Chemical Philosophy, ' p. 110. ] Such effectsreached their culmination when, in 1808, through the liberality of afew members of the Royal Institution, Davy was enabled to construct abattery of two thousand pairs of plates, with which he afterwardsobtained calorific and luminous effects far transcending anythingpreviously observed. The arc of flame between the carbon terminalswas four inches long, and by its heat quartz, sapphire, magnesia, andlime, were melted like wax in a candle flame; while fragments ofdiamond and plumbago rapidly disappeared as if reduced to vapour. [Footnote: In the concluding lecture at the Royal Institution in June, 1810, Davy showed the action of this battery. He then fused iridium, the alloy of iridium and osmium, and other refractory substances. 'Philosophical Magazine, ' vol. Xxxv. P. 463. Quetelet assigns thefirst production of the spark between coal-points to Curtet in 1802. Davy certainly in that year showed the carbon light with a battery of150 pairs of plates in the theatre of the Royal Institution ('Jour. Roy. Inst. ' vol. I. P. 166). ]

The first condition to be fulfilled in the development of heat andlight by the electric current is that it shall encounter and overcomeresistance. Flowing through a perfect conductor, no matter what thestrength of the current might be, neither heat nor light could bedeveloped. A rod of unresisting copper carries away uninjured andunwarmed an atmospheric discharge competent to shiver to splinters aresisting oak. I send the self-same current through a wire composedof alternate lengths of silver and platinum. The silver offers littleresistance, the platinum offers much. The consequence is that theplatinum is raised to a white heat, while the silver is not visiblywarmed. The same holds good with regard to the carbon terminalsemployed for the production of the electric light. The intervalbetween them offers a powerful resistance to the passage of thecurrent, and it is by the gathering up of the force necessary to burstacross this interval that the voltaic current is able to throw thecarbon into that state of violent intestine commotion which we callheat, and to which its effulgence is due. The smallest interval ofair usually suffices to stop the current. But when the carbon pointsare first brought together and then separated, there occurs betweenthem a discharge of incandescent matter which carries, or may carry, the current over a considerable space. The light comes almost whollyfrom the incandescent carbons. The space between them is filled witha blue flame which, being usually bent by the earth's magnetism, receives the name of the Voltaic Arc. [Footnote: The part played byresistance is strikingly illustrated by the deportment of silver andthallium when mixed together and volatilised in the arc. The currentfirst selects as its carrier the most volatile metal, which in thiscase is thallium. While it continues abundant, the passage of thecurrent is so free--the resistance to it is so small--that the heatgenerated is incompetent to volatilise the silver. As the thalliumdisappears the current is forced to concentrate its power; it pressesthe silver into its service, and finally fills the space between thecarbons with a vapour which, as long as the necessary resistance isabsent, it is incompetent to produce. I have on a former occasiondrawn attention to a danger which besets the spectroscopist whenoperating upon a mixture of constituents volatile in differentdegrees. When, in 1872, I first observed the effect here described, had I not known that silver was present, I should have inferred itsabsence. ]

For seventy years, then, we have been in possession of thistranscendent light without applying it to the illumination of ourstreets and houses. Such applications suggested themselves at theoutset, but there were grave difficulties in their way. The firstdifficulty arose from the waste of the carbons, which are dissipatedin part by ordinary combustion, and in part by the electric transferof matter from the one carbon to the other. To keep the carbons atthe proper distance asunder regulators were devised, the earliest, Ibelieve, by Staite, and the most successful by Duboscq, Foucault, andSerrin, who have been succeeded by Holmes, Siemens, Browning, Carré, Gramme, Lontin, and others. By such arrangements the first difficultywas practically overcome; but the second, a graver one, is probablyinseparable from the construction of the voltaic battery. It arisesfrom the operation of that inexorable law which throughout thematerial universe demands an eye for an eye, and a tooth for a tooth, refusing to yield the faintest glow of heat or glimmer of lightwithout the expenditure of an absolutely equal quantity of some otherpower. Hence, in practice, the desirability of any transformationmust depend upon the value of the product in relation to that of thepower expended. The metal zinc can be burnt like paper; it might beignited in a flame, but it is possible to avoid the introduction ofall foreign heat and to burn the zinc in air of the temperature ofthis room. This is done by placing zinc foil at the focus of aconcave mirror, which concentrates to a point the divergent electricbeam, but which does not warm the air. The zinc burns at the focuswith a violet flame, and we could readily determine the amount of heatgenerated by its combustion. But zinc can be burnt not only in airbut in liquids. It is thus burnt when acidulated water is poured overit; it is also thus burnt in the voltaic battery. Here, however, toobtain the oxygen necessary for its combustion, the zinc has todislodge the hydrogen with which the oxygen is combined. Theconsequence is that the heat due to the combustion of the metal in theliquid falls short of that developed by its combustion in air, by theexact quantity necessary to separate the oxygen from the hydrogen. Fully four-fifths of the total heat are used up in this molecularwork, only one-fifth remaining to warm the battery. It is upon thisresidue that we must now fix our attention, for it is solely out of itthat we manufacture our electric light. 

Before you are two small voltaic batteries of ten cells each. The twoends of one of them are united by a thick copper wire, while into thecircuit of the other a thin platinum wire is introduced. The platinumglows with a white heat, while the copper wire is not sensibly warmed. Now an ounce of zinc, like an ounce of coal, produces by its completecombustion in air a constant quantity of heat. The total heatdeveloped by an ounce of zinc through its union with oxygen in thebattery is also absolutely invariable. Let our two batteries, then, continue in action until an ounce of zinc in each of them is consumed. In the one case the heat generated is purely domestic, being liberatedon the hearth where the fuel is burnt, that is to say in the cells ofthe battery itself. In the other case, the heat is in part domesticand in part foreign--in part within the battery and in part outside. One of the fundamental truths to be borne in mind is that the sum ofthe foreign and domestic--of the external and internal--heats is fixedand invariable. Hence, to have heat outside, you must draw upon theheat within. These remarks apply to the electric light. By theinter-mediation of the electric current the moderate warmth of thebattery is not only carried away, but concentrated, so as to produce, at any distance from its origin, a heat next in order to that of thesun. The current might therefore be defined as the swift carrier ofheat. Loading itself here with invisible power, by a process oftransmutation which outstrips the dreams of the alchemist, it candischarge its load, in the fraction of a second, as light and heat, atthe opposite side of the world. 

Thus, the light and heat produced outside the battery are derived fromthe metallic fuel burnt within the battery; and, as zinc happens to bean expensive fuel, though we have possessed the electric light formore than seventy years, it has been too costly to come into generaluse. But within these walls, in the autumn of 1831, Faradaydiscovered a new source of electricity, which we have now toinvestigate. On the table before me lies a coil of covered copperwire, with its ends disunited. I lift one side of the coil from thetable, and in doing so exert the muscular effort necessary to overcomethe simple weight of the coil. I unite its two ends and repeat theexperiment. The effort now required, if accurately measured, would befound greater than before. In lifting the coil I cut the lines of theearth's magnetic force, such cutting, as proved by Faraday, beingalways accompanied, in a closed conductor, by the production of an'induced' electric current which, as long as the ends of the coilremained separate, had no circuit through which it could pass. Thecurrent here evoked subsides immediately as heat; this heat being theexact equivalent of the excess of effort just referred to as over andabove that necessary to overcome the simple weight of the coil. Whenthe coil is liberated it falls back to the table, and when its endsare united it encounters a resistance over and above that of the air. It generates an electric current opposed in direction to the first, and reaches the table with a diminished shock. The amount of thediminution is accurately represented by the warmth which the momentarycurrent developer in the coil. Various devices were employed to exaltthese induced currents, among which the instruments of Pixii, Clarke, and Saxton were long conspicuous. Faraday, indeed, foresaw that suchattempts were sure to be made; but he chose to leave them in the handsof the mechanician, while he himself pursued the deeper study of factsand principles. 'I have rather, ' he writes in 1831, 'been desirousof discovering new facts and new relations dependent onmagneto-electric induction, than of exalting the force of thosealready obtained; being assured that the latter would find their fulldevelopment hereafter. '

For more than twenty years magneto-electricity had subserved its firstand noblest purpose of augmenting our knowledge of the powers ofnature. It had been discovered and applied to intellectual ends, itsapplication to practical ends being still unrealised. The Drummondlight had raised thoughts and hopes of vast improvements in publicillumination. Many inventors tried to obtain it cheaply; and in 1853an attempt was made to organise a company in Paris for the purpose ofprocuring, through the decomposition of water by a powerfulmagneto-electric machine constructed by M. Nollet, the oxygen andhydrogen necessary for the lime light. The experiment failed, but theapparatus by which it was attempted suggested to Mr. Holmes other andmore hopeful applications. Abandoning the attempt to produce the limelight, with persevering skill Holmes continued to improve theapparatus and to augment its power, until it was finally able to yielda magneto-electric light comparable to that of the voltaic battery. Judged by later knowledge, this first machine would be consideredcumbrous and defective in the extreme; but judged by the light ofantecedent events, it marked a great step forward. 

Faraday was profoundly interested in the growth of his own discovery. The Elder Brethren of the Trinity House had had the wisdom to make himtheir 'Scientific Adviser;' and it is interesting to notice in hisreports regarding the light, the mixture of enthusiasm and cautionwhich characterised him. Enthusiasm was with him a motive power, guided and controlled by a disciplined judgment. He rode it as acharger, holding it in by a strong rein. While dealing with Holmes, he states the case of the light pro and con. He checks the ardour ofthe inventor, and, as regards cost, rejecting sanguine estimates, heinsists over and over again on the necessity of continued experimentfor the solution of this important question. His matured opinion was, however, strongly in favour of the light. With reference to anexperiment made at the South Foreland on the 20th of April, 1859, hethus expresses himself: 'The beauty of the light was wonderful. Ata mile off, the Apparent streams of light issuing from the lanternwere twice as long as those from the lower lighthouse, and apparentlythree or four times as bright. The horizontal plane in which theychiefly took their way made all above or below it black. The tops ofthe bills, the churches, and the houses illuminated by it werestriking in their effect upon the eye. ' Further on in his report heexpresses himself thus: 'In fulfilment of this part of my duty, I begto state that, in my opinion, Professor Holmes has practicallyestablished the fitness and sufficiency of the magneto-electric lightfor lighthouse purposes, so far as its nature and management areconcerned. The light produced is powerful beyond any other that Ihave yet seen so applied, and in principle may be accumulated to anydegree; its regularity in the lantern is great; its management easy, and its care there may be confided to attentive keepers of theordinary degree of intellect and knowledge. ' Finally, as regards theconduct of Professor Holmes during these memorable experiments, it isonly fair to add the following remark with which Faraday closes thereport submitted to the Elder Brethren of the Trinity House on the29th of April, 1859: 'I must bear my testimony, ' he says, 'to theperfect openness, candour, and honour of Professor Holmes. He hasanswered every question, concealed no weak point, explained everyapplied principle, given every reason for a change either in this orthat direction, during several periods of close questioning, in amanner that was very agreeable to me, whose duty it was to search forreal faults or possible objections, in respect both of the presenttime and the future. ' [Footnote: Holmes's first offer of his machineto the Trinity House bears date February 2, 1857. ]

Soon afterwards the Elder Brethren of the Trinity House had theintelligent courage to establish the machines of Holmes permanently atDungeness, where the magneto-electric light continued to shine formany years. 

The magneto-electric machine of the Alliance Company soon succeeded tothat of Holmes, being in various ways a very marked improvement on thelatter. Its currents were stronger and its light was brighter thanthose of its predecessor. In it, moreover, the commutator, theflashing and destruction of which were sources of irregularity anddeterioration in the machine of Holmes, was, at the suggestion of M. Masson, entirely abandoned; alternating currents instead of the directcurrent being employed. [Footnote: Du Moncel, 'l'Electricité, 'August, 1878, p. 150. ] M. Serrin modified his excellent lamp withthe express view of enabling it to cope with alternating currents. During the International Exhibition of 1862, where the machine wasshown, M. Berlioz offered to dispose of the invention to the ElderBrethren of the Trinity House. They referred the matter to Faraday, and he replied as follows: 'I am not aware that the Trinity Houseauthorities have advanced so far as to be able to decide whether theywill require more magneto-electric machines, or whether, if theyshould require them, they see reason to suppose the means of theirsupply in this country, from the source already open to them, wouldnot be sufficient. Therefore I do not see that at present they wantto purchase a machine. ' Faraday was obviously swayed by the desire toprotect the interests of Holmes, who had borne the burden and heatwhich fall upon the pioneer. The Alliance machines were introducedwith success at Cape la Hève, near Havre; and the Elder Brethren ofthe Trinity House, determined to have the best available apparatus, decided, in 1868, on the introduction of machines on the Allianceprinciple into the lighthouses at Souter Point and the South Foreland. These, machines were constructed by Professor Holmes, and they stillcontinue in operation. With regard, then, to the application ofelectricity to lighthouse purposes, the course of events was this: TheDungeness light was introduced on January 31, 1862; the light at LaHève on December 26, 1863, or nearly two years later. But Faraday'sexperimental trial at the South Foreland preceded the lighting ofDungeness by more than two years. The electric light was afterwardsestablished at Cape Grisnez. The light was started at Souter Point onJanuary 11, 1871; and at the South Foreland on January 1, 1872. 

At the Lizard, which enjoys the newest and most powerful developmentof the electric light, it began to shine on January 1, 1878. 

*****

I have now to revert to a point of apparently small moment, but whichreally constitutes an important step in the development of thissubject. I refer to the form given in 1857 to the rotating armatureby Dr. Werner Siemens, of Berlin. Instead of employing coils woundtransversely round cores of iron, as in the machine of Saxton, Siemens, after giving a bar of iron the proper shape, wound his wirelongitudinally round it, and obtained thereby greatly augmentedeffects between suitably placed magnetic poles. Such an armature isemployed in the small magneto-electric machine which I now introduceto your notice, and for which the institution is indebted to Mr. HenryWilde, of Manchester. There are here sixteen permanent horse-shoemagnets placed parallel to each other, and between their poles aSiemens armature. The two ends of the wire which surrounds thearmature are now disconnected. In turning the handle and causing thearmature to rotate, I simply overcome ordinary mechanical friction. But the two ends of the armature coil can be united in a moment, andwhen this is done I immediately experience a greatly increasedresistance to rotation. Something over and above the ordinaryfriction of the machine is now to be overcome, and by the expenditureof an additional amount of muscular force I am able to overcome it. The excess of labour thus thrown upon my arm has its exact equivalentin the electric currents generated, and the heat produced by theirsubsidence in the coil of the armature. A portion of this heat may berendered visible by connecting the two ends of the coil with a thinplatinum wire. When the handle of the machine is rapidly turned thewire glows, first with a red heat, then with a white heat, and finallywith the heat of fusion. The moment the wire melts, the circuit roundthe armature is broken, an instant relief from the labour thrown uponthe arm being the consequence. Clearly realise the equivalent of theheat here developed. During the period of turning the machine acertain amount of combustible substance was oxidised or burnt in themuscles of my arm. Had it done no external work, the matter consumedwould have produced a definite amount of heat. Now, the muscular heatactually developed during the rotation of the machine fell short ofthis definite amount, the missing heat being reproduced to the lastfraction in the glowing platinum wire and the other parts of themachine. Here, then, the electric current intervenes between mymuscles and the generated heat, exactly as it did a moment ago betweenthe voltaic battery and its generated heat. The electric current isto all intents and purposes a vehicle which transports the heat bothof muscle and battery to any distance from the hearth where the fuelis consumed. Not only is the current a messenger, but it is also anintensifier of magical power. The temperature of my arm is, in roundnumbers, 100° Fahr, and it is by the intensification of this heat thatone of the most refractory of metals, which requires a heat of 3, 600°Fahr. To fuse it, has been reduced to the molten condition. 

Zinc, as I have said, is a fuel far too expensive to permit of theelectric light produced by its combustion being used for the commonpurposes of life, and you will readily perceive that the humanmuscles, or even the muscles of a horse, would be more expensivestill. Here, however, we can employ the force of burning coal to turnour machine, and it is this employment of our cheapest fuel, renderedpossible by Faraday's discovery, which opens out to us the prospect ofbeing able to apply the electric light to public use. 

In 1866 a great step in the intensification of induced currents, andthe consequent augmentation of the magneto-electric light, was takenby Mr. Henry Wilde. It fell to my lot to report upon them to theRoyal Society, but before doing so I took the trouble of going toManchester to witness Mr. Wilde's experiments. He operated in thisway: starting from a small machine like that worked in your presence amoment ago, he employed its current to excite an electro-magnet of apeculiar shape, between whose poles rotated a Siemens armature;[Footnote: Page and Moigno had previously shown that themagneto-electric current could produce powerful electro-magnets. ] fromthis armature currents were obtained vastly stronger than thosegenerated by the small magneto-electric machine. These currents mighthave been immediately employed to produce the electric light; butinstead of this they were conducted round a second electro-magnet ofvast size, between whose poles rotated a Siemens armature ofcorresponding dimensions. Three armatures therefore were involved inthis series of operations: first, the armature of the smallmagneto-electric machine; secondly, the armature of the firstelectro-magnet, which was of considerable size; and, thirdly, thearmature of the second electro-magnet, which was of vast dimensions. With the currents drawn from this third armature, Mr. Wilde obtainedeffects, both as regards heat and light, enormously transcending thosepreviously known. [Footnote: Mr. Wilde's paper is published in the'Philosophical Transactions 'for 1867, p. 89. My opinion regardingWilde's machine was briefly expressed in a report to the ElderBrethren of the Trinity House on May 17, 1866: 'It gives me pleasureto state that the machine is exceedingly effective, and that it fartranscends in power all other apparatus of the kind. ']

But the discovery which, above all others, brought the practicalquestion to the front is now to be considered. On the 4th ofFebruary, 1867, a paper was received by the Royal Society from Dr. William Siemens bearing the title, 'On the Conversion of Dynamic intoElectrical Force without the use of Permanent Magnetism. ' [Footnote: Apaper on the same subject, by Dr. Werner Siemens, was read on January17, 1867, before the Academy of Sciences in Berlin. In a letter to'Engineering, ' No. 622, p. 45, Mr. Robert Sabine states thatProfessor Wheatstone's machines were constructed by Mr. Stroh in themonths of July and August, 1866. I do not doubt Mr. Sabine'sstatement; still it would be dangerous in the highest degree to departfrom the canon, in asserting which Faraday was specially strenuous, that the date of a discovery is the date of its publication. Towardsthe end of December, 1866, Mr. Alfred Varley' also lodged aprovisional specification (which, I believe, is a sealed document)embodying the principles of the dynamo-electric machine, but someyears elapsed before he made anything public. His brother, Mr. Cromwell varlet', when writing on this subject in 1867, does notmention him (Proc. Roy. Soc, March 14, 1867). It probably marks anational trait, that sealed communications, though allowed in France, have never been recognised by the scientific societies of England. ] Onthe 14th of February a paper from Sir Charles Wheatstone was received, bearing the title, 'On the Augmentation of the Power of a Magnet bythe reaction thereon of Currents induced by the Magnet itself. ' Bothpapers, which dealt with the same discovery, and which wereillustrated by experiments, were read upon the same night, viz. The14th of February. It would be difficult to find in the whole field ofscience a more beautiful example of the interaction of natural forcesthan that set forth in these two papers. You can hardly find a bit ofiron--you can hardly pick up an old horse-shoe, for example--that doesnot possess a trace of permanent magnetism; and from such a smallbeginning Siemens and Wheatstone have taught us to rise by a series ofinteractions between magnet and armature to a magnetic intensitypreviously unapproached. Conceive the Siemens armature placed betweenthe poles of a suitable electro-magnet. Suppose this latter to possessat starting the faintest, trace of magnetism; when the armaturerotates, currents of infinitesimal strength are generated in its coil. Let the ends of that coil be connected with the wire surrounding theelectro-magnet. The infinitesimal current generated in the armaturewill then circulate round the magnet, augmenting its intensity by aninfinitesimal amount. The strengthened magnet instantly reacts uponthe coil which feeds it, producing a current of greater strength. This current again passes round the magnet, which immediately bringsits enhanced power to bear upon the coil. By this play of mutual giveand take between magnet and armature, the strength of the former israised in a very brief interval from almost nothing to completemagnetic saturation. Such a magnet and armature are able to producecurrents of extraordinary power, and if an electric lamp be introducedinto the common circuit of magnet and armature, we can readily obtaina most powerful light. [Footnote: In 1867 Mr. Ladd introduced themodification of dividing the armature into two separate coils, one ofwhich fed the electro-magnets, while the other yielded the inducedcurrents. ] By this discovery, then, we are enabled to avoid thetrouble and expense involved in the employment of permanent magnets;we are also enabled to drop the exciting magneto-electric machine, andthe duplication of the electro-magnets. By it, in short, the electricgenerator is so far simplified, and reduced in cost, as to enableelectricity to enter the lists as the rival of our present means ofillumination. 

Soon after the announcement of their discovery by Siemens andWheatstone, Mr. Holmes, at the instance of the Elder Brethren of theTrinity House, endeavoured to turn this discovery to account forlighthouse purposes. Already, in the spring of 1869, he hadconstructed a machine which, though hampered with defects, exhibitedextraordinary power. The light was developed in the focus of adioptric apparatus placed on the Trinity Wharf at Blackwall, andwitnessed by the Elder Brethren, Mr. Douglass, and myself, from anobservatory at Charlton, on the opposite side of the Thames. Fallingupon the suspended haze, the light illuminated the atmosphere formiles all round. Anything so sunlike in splendour had not, I imagine, been previously witnessed. The apparatus of Holmes, however, wasrapidly distanced by the safer and more powerful machines of Siemensand Gramme. 

As regards lighthouse illumination, the next step forward was taken bythe Elder Brethren of the Trinity House in 1876-77. Having previouslydecided on the establishment of the electric light at the Lizard inCornwall, they instituted, at the time referred to, an elaborateseries of comparative experiments wherein the machines of Holmes, ofthe Alliance Company, of Siemens, and of Gramme, were pitted againsteach other. The Siemens and the Gramme machines delivered directcurrents, while those of Holmes and the Alliance Company deliveredalternating currents. The light of the latter was of the sameintensity in all azimuths; that of the former was different indifferent azimuths, the discharge being so regulated as to yield agush of light of special intensity in one direction. The followingtable gives in standard candles the performance of the respectivemachines:

Name of Machines. Maximum. Minimum. 

Holmes 1, 523 1, 523

Alliance 1, 953 1, 953

Gramme (No. 1). 6, 663 4, 016

Gramme (No. 2). 6, 663 4, 016

Siemens (Large) 14, 818 8, 932

Siemens (Small, No. 1) 5, 539 3, 339

Siemens (Small, No. 2) 6, 864 4, 138

Two Holmes's coupled 2, 811 2, 811

Two Gramme's (Nos. 1 and 2) 11, 396 6, 869

Two Siemens' (Nos. 1 and 2) 14, 134 8, 520

[Footnote: Observations from the sea on the night of November 21, 1876, made the Gramme and small Siemens practically equal to theAlliance. But the photometric observations, in which the externalresistance was abolished, and previous to which the light-keepers hadbecome more skilled in the management of the direct current, showedthe differences recorded in the table. A close inspection of thesepowerful lights at the South Foreland caused my face to peel, as if ithad been irritated by an Alpine sun. ]

These determinations were made with extreme care and accuracy by Mr. Douglass, the engineer-in-chief, and Mr. Ayres, the assistant engineerof the Trinity House. It is practically impossible to comparephoto-metrically and directly the flame of the candle with thesesun-like lights. A light of intermediate intensity--that of thesix-wick Trinity oil lamp--was therefore in the first instancecompared with the electric light. The candle power of the oil lampbeing afterwards determined, the intensity of the electric lightbecame known. The numbers given in the table prove the superiority ofthe Alliance machine over that of Holmes. They prove the greatsuperiority both of the Gramme machine and of the small Siemensmachine over the Alliance. The large Siemens machine is shown toyield a light far exceeding all the others, while the coupling of twoGrammes, or of two Siemens together, here effected for the first time, was followed by a very great augmentation of the light, rising in theone case from 6663 candles to 11, 396, and in the other case from 6864candles to 14, 134. Where the arc is single and the externalresistance small, great advantages attach to the Siemens light. Afterthis contest, which was conducted throughout in the most amicablemanner, Siemens machines of type No. 2 were chosen for the Lizard. [Footnote: As the result of a recent trial by Mr. Schwendler, theyhave been also chosen for India. ]

*****

We have machines capable of sustaining a single light, and alsomachines capable of sustaining several lights. The Gramme machine, for example, which ignites the Jablochkoff candles on the ThamesEmbankment and at the Holborn Viaduct, delivers four currents, eachpassing through its own circuit. In each circuit are five lampsthrough which the current belonging to the circuit passes insuccession. The lights correspond to so many resisting spaces, overwhich, as already explained, the current has to leap; the force whichaccomplishes the leap being that which produces the light. Whetherthe current is to be competent to pass through five lamps insuccession, or to sustain only a single lamp, depends entirely uponthe will and skill of the maker of the machine. He has, to guide him, definite laws laid down by Ohm half a century ago, by which he mustabide. 

Ohm has taught us how to arrange the elements of a Voltaic battery soas to augment indefinitely its electromotive force--that force, namely, which urges the current forward and enables it to surmountexternal obstacles. We have only to link the cells together so thatthe current generated by each cell shall pass through all the others, and add its electro-motive force to that of all the others. Weincrease, it is true, at the same time the resistance of the battery, diminishing thereby the quantity of the current from each cell, but weaugment the power of the integrated current to overcome externalhindrances. The resistance of the battery itself may, indeed, berendered so great, that the external resistance shall vanish incomparison. What is here said regarding the voltaic battery isequally true of magneto-electric machines. If we wish our current toleap over five intervals, and produce five lights in succession, wemust invoke a sufficient electromotive force. This is done throughmultiplying, by the use of thin wires, the convolutions of therotating armature as, a moment ago, we augmented the cells of ourvoltaic battery. Each additional convolution, like each additionalcell, adds its electro-motive force to that of all the others; andthough it also adds its resistance, thereby diminishing the quantityof current contributed by each convolution, the integrated currentbecomes endowed with the power of leaping across the successive spacesnecessary for the production of a series of lights in its course. Thecurrent is, as it were, rendered at once thinner and more piercing bythe simultaneous addition of internal resistance and electro-motivepower. The machines, on the other hand, which produce only a singlelight have a small internal resistance associated with a smallelectro-motive force. In such machines the wire of the rotatingarmature is comparatively short and thick, copper riband instead ofwire being commonly employed. Such machines deliver a large quantityof electricity of low tension--in other words, of low leaping power. Hence, though competent when their power is converged upon a singleinterval, to produce one splendid light, their currents are unable toforce a passage when the number of intervals is increased. Thus, byaugmenting the convolutions of our machines we sacrifice quantity andgain electro-motive force; while by lessening the number of theconvolutions, we sacrifice electro-motive force and gain quantity. Whether we ought to choose the one form of machine or the otherdepends entirely upon the external work the machine has to perform. Ifthe object be to obtain a single light of great splendour, machines oflow resistance and large quantity must be employed. If we want toobtain in the same circuit several lights of moderate intensity, machines of high internal resistance and of correspondingly highelectro-motive power must be invoked. 

When a coil of covered wire surrounds a bar of iron, the two ends ofthe coil being connected together, every alteration of the magnetismof the bar is accompanied by the development of an induced current inthe coil. The current is only excited during the period of magneticchange. No matter how strong or how weak the magnetism of the bar maybe, as long as its condition remains permanent no current isdeveloped. Conceive, then, the pole of a magnet placed near one endof the bar to be moved along it towards the other end. During thetime of the pole's motion there will be an incessant change in themagnetism of the bar, and accompanying this change we shall have aninduced current in the surrounding coil. If, instead of moving themagnet, we move the bar and its surrounding coil past the magneticpole, a similar alteration of the magnetism of the bar will occur, anda similar current will be induced in the coil. You have here thefundamental conception which led M. Gramme to the construction of hisbeautiful machine. [Footnote: 'Comptes Rendus, ' 1871, p. 176. Seealso Gaugain on the Gramme machine, 'Ann. De Chem. Et de Phys, 'vol. Xxviii. P. 324] He aimed at giving continuous motion to sucha bar as we have here described; and for this purpose he bent it intoa continuous ring, which, by a suitable mechanism, he caused to rotaterapidly close to the poles of a horse-shoe magnet. The direction ofthe current varied with the motion and with the character of theinfluencing pole. The result was that the currents in the twosemicircles of the coil surrounding the ring flowed in oppositedirections. But it was easy, by the mechanical arrangement called acommutator, to gather up the currents and cause them to flow in thesame direction. The first machines of Gramme, therefore, furnisheddirect currents, similar to those yielded by the voltaic pile. M. Gramme subsequently so modified his machine as to produce alternatingcurrents. Such alternating machines are employed to produce thelights now exhibited on the Holborn Viaduct and the Thames Embankment. 

Another machine of great alleged merit is that of M. Lontin. Itresembles in shape a toothed iron wheel, the teeth being used ascores, round which are wound coils of copper wire. The wheel iscaused to rotate between the opposite poles of powerfulelectromagnets. On passing each pole the core or tooth is stronglymagnetised, and instantly evokes in its surrounding coil an inducedcurrent of corresponding strength. The currents excited inapproaching to and retreating from a pole, and in passing differentpoles, move in opposite directions, but by means of a commutator theseconflicting electric streams are gathered up and caused to flow in acommon bed. The bobbins, in which the currents are induced, can be soincreased in number as to augment indefinitely the power of themachine. To excite his electro-magnets, M. Lontin applies theprinciple of Mr. Wilde. A small machine furnishes a direct current, which is carried round the electro-magnets of a second and largermachine. Wilde's principle, it may be added, is also applied on theThames Embankment and the Holborn Viaduct; a small Gramme machinebeing used in each case to excite the electro-magnets of the largeone. 

The Farmer-Wallace machine is also an apparatus of great power. Itconsists of a combination of bobbins for induced currents, and ofinducing electro-magnets, the latter being excited by the methoddiscovered by Siemens and Wheatstone. In the machines intended forthe production of the electric light, the electromotive force is sogreat as to permit of the introduction of several lights in the samecircuit. A peculiarly novel feature of the Farmer-Wallace system isthe shape of the carbons. Instead of rods, two large plates ofcarbons with bevelled edges are employed, one above the other. Theelectric discharge passes from edge to edge, and shifts its positionaccording as the carbon is dissipated. The duration of the light inthis case far exceeds that obtainable with rods. I have myself seenfour of these lights in the same circuit in Mr. Ladd's workshop in theCity, and they are now, I believe, employed at the Liverpool StreetStation of the Metropolitan Railway. The Farmer-Wallace 'quantitymachine' pours forth a flood of electricity of low tension. It isunable to cross the interval necessary for the production of theelectric light, but it can fuse thick copper wires. When sent througha short bar of iridium, this refractory metal emits a light ofextraordinary splendour. [Footnote: The iridium light was shown by Mr. Ladd. It brilliantly illuminated the theatre of the RoyalInstitution. ]

The machine of M. De Méritens, which he has generously brought overfrom Paris for our instruction, is the newest of all. In itsconstruction he falls back upon the principle of the magneto-electricmachine, employing permanent magnets as the exciters of the inducedcurrents. Using the magnets of the Alliance Company, by a skilfuldisposition of his bobbins, M. De Méritens produces with eight magnetsa light equal to that produced by forty magnets in the Alliancemachines. While the space occupied is only one-fifth, the cost islittle more than one-fourth of the latter. In the de Méritens machinethe commutator is abolished. The internal heat is hardly sensible, and the absorption of power, in relation to the effects produced, issmall. With his larger machines M. De Méritens maintains aconsiderable number of lights in the same circuit. [Footnote: Thesmall machine transforms one-and-a-quarter horse-power into heat andlight, yielding about 1, 900 candles; the large machine transformsfive-horse power, yielding about 9, 000 candles. ]

*****

In relation to this subject, inventors fall into two classes, thecontrivers of regulators and the constructors of machines. M. Rapieffhas hitherto belonged to inventors of the first class, but I havereason to know that he is engaged on a machine which, when complete, will place him in the other class also. Instead of two single carbonrods, M. Rapieff employs two pairs of rods, each pair forming a V. Thelight is produced at the common junction of the four carbons. Thedevice for regulating the light is of the simplest character. At thebottom of the stand which supports the carbons are two smallelectro-magnets. One of them, when the current passes, draws thecarbons together, and in so doing throws itself out of circuit, leaving the control of the light to the other. The carbons are causedto approach each other by a descending weight, which acts inconjunction with the electro-magnet. Through the liberality of theproprietors of the Times, every facility has been given to M. Rapieffto develope and simplify his invention at Printing House Square. Theillumination of the press-room, which I had the pleasure ofwitnessing, under the guidance of M. Rapieff himself, is extremelyeffectual and agreeable to the eye. There are, I believe, five lampsin the same circuit, and the regulators are so devised that theextinction of any lamp does not compromise the action of the others. M. Rapieff has lately improved his regulator. 

Many other inventors might here be named, and fresh ones are dailycrowding in. Mr. Werdermann has been long known in connection withthis subject. Employing as negative carbon a disc, and as positivecarbon a rod, he has, I am assured, obtained very satisfactoryresults. The small resistances brought into play by his minute arcsenable Mr. Werdermann to introduce a number of lamps into a circuittraversed by a current of only moderate electro-motive power. M. Reynier is also the inventor of a very beautiful little lamp, in whichthe point of a thin carbon rod, properly adjusted, is caused to touchthe circumference of a carbon wheel which rotates underneath thepoint. The light is developed at the place of contact of rod andwheel. One of the last steps, though I am informed not quite thelast, in the improvement of regulators is this: The positive carbonwastes more profusely than the negative, and this is alleged to be dueto the greater heat of the former. It occurred to Mr. William Siemensto chill the negative artificially, with the view of diminishing orwholly preventing its waste. This he accomplishes by making thenegative pole a hollow cone of copper, and by ingeniously discharginga small jet of cold water against the interior of the cone. Hisnegative copper is thus caused to remain fixed in space, for it is notdissipated, the positive carbon only needing control. I have seenthis lamp in action, and can bear witness to its success. 

I might go on to other inventions, achieved or projected. Indeed, there is something bewildering in the recent rush of constructivetalent into this domain of applied electricity. The question and itsprospects are modified from day to day, a steady advance being madetowards the improvement both of machines and regulators. With regardto our public lighting, I strongly lean to the opinion that theelectric light will at no distant day triumph over gas. I am not sosure that it will do so in our private houses. As, however, I amanxious to avoid dropping a word here that could influence the sharemarket in the slightest degree, I limit myself to this generalstatement of opinion. 

To one inventor in particular belongs the honour of the idea, and therealisation of the idea, of causing the carbon rods to burn away likea candle. It is needless to say that I here refer to the youngRussian officer, M. Jablochkoff. He sets two carbon rods upright at asmall distance apart, and fills the space between them with aninsulating substance like plaster of Paris. The carbon rods are fixedin metallic holders. A momentary contact is established between thetwo carbons by a little cross-piece of the same substance placedhorizontally from top to top. This cross-piece is immediatelydissipated or removed by the current, the passage of which onceestablished is afterwards maintained. The carbons gradually waste, while the substance between them melts like the wax of a candle. Thecomparison, however, only holds good for the act of melting; for, asregards the current, the insulating plaster is practically inert. Indeed, as proved by M. Rapieff and Mr. Wilde, the plaster may bedispensed with altogether, the current passing from point to pointbetween the naked carbons. M. De Méritens has recently brought out anew candle, in which the plaster is abandoned, while between the twoprincipal carbons is placed a third insulated rod of the samematerial. With the small de Méritens machine two of these candles canbe lighted before you; they produce a very brilliant light. [Footnote:The machine of M. De Méritens and the Farmer-Wallace machine wereworked by an excellent gas-engine, lent for the occasion by theMessrs. Crossley, of Manchester. The Siemens machine was worked bysteam. ] In the Jablochkoff candle it is necessary that the carbonsshould be consumed at the same rate. Hence the necessity foralternating currents by which this equal consumption is secured. Itwill be seen that M. Jablochkoff has abolished regulators altogether, introducing the candle principle in their stead. In my judgment, theperformance of the Jablochkoff candle on the Thames Embankment and theHolborn Viaduct is highly creditable, notwithstanding a considerablewaste of light towards the sky. The Jablochkoff lamps, it may beadded, would be more effective in a street, where their light would bescattered abroad by the adjacent houses, than in the positions whichthey now occupy in London. 

*****

It was my custom some years ago, whenever I needed a new andcomplicated instrument, to sit down beside its proposed constructor, and to talk the matter over with him. The study of the inventor'smind which this habit opened out was always of the highest interest tome. I particularly well remember the impression made upon me on suchoccasions by the late Mr. Darker, a philosophical instrument maker inLambeth. This man's life was a struggle, and the reason of it was notfar to seek. No matter how commercially lucrative the work upon whichhe was engaged might be, he would instantly turn aside from it toseize and realise the ideas of a scientific man. He had an inventor'spower, and an inventor's delight in its exercise. The late Mr. Beckerpossessed the same power in a very considerable degree. On theContinent, Froment, Breguet, Sauerwald, and others might be mentionedas eminent instances of ability of this kind. Such minds resemble aliquid on the point of crystallisation. Stirred by a hint, crystalsof constructive thought immediately shoot through them. That Mr. Edison possesses this intuitive power in no common measure, is provedby what he has already accomplished. He has the penetration to seizethe relationship of facts and principles, and the art to reduce themto novel and concrete combinations. Hence, though he has thus faraccomplished nothing that we can recognise as new in relation to theelectric light, an adverse opinion as to his ability to solve thecomplicated problem on which he is engaged would be unwarranted. 

I will endeavour to illustrate in a simple manner Mr. Edison's allegedmode of electric illumination, taking advantage of what Ohm has taughtus regarding the laws of the current, and what Joule has taught usregarding the relation of resistance to the development of light andheat. From one end of a voltaic battery runs a wire, dividing at acertain point into two branches, which reunite in a single wireconnected with the other end of the battery. From the positive end ofthe battery the current passes first through the single wire to thepoint of junction, where it divides itself between the branchesaccording to a well-known law. If the branches be equally resistant, the current divides itself equally between them. If one branch beless resistant than the other, more than half the current will choosethe freer path. The strict law is that the quantity of current isinversely proportional to the resistance. A clear image of theprocess is derived from the deportment of water. When a river meetsan island it divides, passing right and left of the obstacle, andafterwards reuniting. If the two branch beds be equal in depth, width, and inclination, the water will divi de itself equally betweenthem. If they be unequal, the larger quantity of water will flowthrough the more open course. And, as in the case of the water we mayhave an indefinite number of islands, producing an indefinitesubdivision of the trunk stream, so in the case of electricity we mayhave, instead of two branches, any number of branches, the currentdividing itself among them, in accordance with the law which fixes therelation of flow to resistance. 

Let us apply this knowledge. Suppose an insulated copper rod, whichwe may call an 'electric main, ' to be laid down along one of ourstreets, say along the Strand. Let this rod be connected with one endof a powerful voltaic battery, a good metallic connection beingestablished between the other end of the battery and the water-pipesunder the street. As long as the electric main continues unconnectedwith the water-pipes, the circuit is incomplete and no current willflow; but if any part of the main, however distant from the battery, be connected with the adjacent water-pipes, the circuit will becompleted and the current will flow. Supposing our battery to be atCharing Cross, and our rod of copper to be tapped opposite SomersetHouse, a wire can be carried from the rod into the building, and thecurrent passing through the wire may be subdivided into any number ofsubordinate branches, which reunite afterwards and return through thewater-pipes to the battery. The branch currents may be employed toraise to vivid incandescence a refractory metal like iridium or one ofits alloys. Instead of being tapped at one point, our main may betapped at one hundred points. The current will divide in strictaccordance with law, its power to produce light being solely limitedby its strength. The process of division closely resembles thecirculation of the blood; the electric main carrying the outgoingcurrent representing a great artery, the water-pipes carrying thereturn current representing a great vein, while the intermediatebranches represent the various vessels by which the blood isdistributed through the system. This, if I understand aright, is Mr. Edison's proposed mode of illumination. The electric force is athand. Metals sufficiently refractory to bear being raised to vividincandescence are also at hand. The principles which regulate thedivision of the current and the development of its light and heat areperfectly well known. There is no room for a 'discovery, ' in thescientific sense of the term, but there is ample room for the exerciseof that mechanical ingenuity which has given us the sewing machine andso many other useful inventions. Knowing something of the intricacyof the practical problem, I should certainly prefer seeing it in Mr. Edison's hands to having it in mine. [Footnote: More than thirty yearsago the radiation from incandescent platinum was admirablyinvestigated by Dr. Draper of New York. ]

*****

It is sometimes stated as a recommendation to the electric light, thatit is light without heat; but to disprove this, it is only necessaryto point to the experiments of Davy, which show that the heat of thevoltaic arc transcends that of any other terrestrial source. Theemission from the carbon points is capable of accurate analysis. Tosimplify the subject, we will take the case of a platinum wire atfirst slightly warmed by the current, and then gradually raised to awhite heat. When first warmed, the wire sends forth rays which haveno power on the optic nerve. They are what we call invisible rays;and not until the temperature of the wire has reached nearly 1, 000°Fahr, does it begin to glow with a faint, red light. The rays whichit emits prior to redness are all invisible rays, which can warm thehand but cannot excite vision. When the temperature of the wire israised to whiteness, these dark rays not only persist, but they areenormously augmented in intensity. They constitute about 95 per cent. Of the total radiation from the white-hot platinum wire. They make upnearly 90 per cent. Of the emission from a brilliant electric light. You can by no means have the light of the carbons without thisinvisible emission as an accompaniment. The visible radiation is, asit were, built upon the invisible as its necessary foundation. 

It is easy to illustrate the growth in intensity of these invisiblerays as the visible ones enter the radiation and augment in power. Thetransparency of the elementary gases and metalloids--of oxygen, hydrogen, nitrogen, chlorine, iodine, bromine, sulphur, phosphorus, and even of carbon, for the invisible heat rays is extraordinary. Dissolved in a proper vehicle, iodine cuts the visible radiationsharply off, but allows the invisible free transmission. Bydissolving iodine in sulphur, Professor Dewar has recently added tothe number of our effectual ray-filters. The mixture may be made asblack as pitch for the visible, while remaining transparent for theinvisible rays. By such filters it is possible to detach theinvisible rays from the total radiation, and to watch theiraugmentation as the light increases. Expressing the radiation from aplatinum wire when it first feels warm to the touch--when, therefore, all its rays are invisible--by the number 1, the invisible radiationfrom the same wire raised to a white heat may be 500 or more. [Footnote: See article 'Radiation', vol. I. ]

It is not, then, by the diminution or transformation of thenon-luminous emission that we obtain the luminous; the heat raysmaintain their ground as the necessary antecedents and companions ofthe light rays. When detached and concentrated, these powerful heatrays can produce all the effects ascribed to the mirrors of Archimedesat the siege of Syracuse. While incompetent to produce the faintestglimmer of light, or to affect the most delicate air-thermometer, theywill inflame paper, burn up wood, and even ignite combustible metals. When they impinge upon a metal refractory enough to bear their shockwithout fusion, they can raise it to a heat so white and luminous asto yield, when analysed, all the colours of the spectrum. In this waythe dark rays emitted by the incandescent carbons are converted intolight rays of all colours. Still, so powerless are these invisiblerays to excite vision, that the eye has been placed at a focuscompetent to raise platinum foil to bright redness, withoutexperiencing any visual impression. Light for light, no doubt, theamount of heat imparted by the incandescent carbons to the air is farless than that imparted by gas flames. It is less, because of thesmaller size of the carbons, and of the comparative smallness of thequantity of fuel consumed in a given time. It is also less becausethe air cannot penetrate the carbons as it penetrates a flame. Thetemperature of the flame is lowered by the admixture of a gas whichconstitutes four-fifths of our atmosphere, and which, while itappropriates and diffuses the heat, does not aid in the combustion;and this lowering of the temperature by the inert atmosphericnitrogen, renders necessary the combustion of a greater amount of gasto produce the necessary light. In fact, though the statement mayappear paradoxical, it is entirely because of its enormous actualtemperature that the electric light seems so cool. It is thistemperature that renders the proportion of luminous to non-luminousheat greater in the electric light than in our brightest flames. Theelectric light, moreover, requires no air to sustain it. It glows inthe most perfect air vacuum. Its light and heat are therefore notpurchased at the expense of the vitalising constituent of theatmosphere. 

Two orders of minds have been implicated in the development of thissubject; first, the investigator and discoverer, whose object is, purely scientific, and who cares little for practical ends; secondly, the practical mechanician, whose object is mainly industrial. Itwould be easy, and probably in many cases true, to say that the onewants to gain knowledge, while the other wishes to make money; but Iam persuaded that the mechanician not unfrequently merges the hope ofprofit in the love of his work. Members of each of these classes aresometimes scornful towards those of the other. There is, for example, something superb in the disdain with which Cuvier hands over thediscoveries of pure science to those who apply them: 'Your grandpractical achievements are only the easy application of truths notsought with a practical intent--truths which their discoverers pursuedfor their own sake, impelled solely by an ardour for knowledge. Thosewho turned them into practice could not have discovered them, whilethose who discovered them had neither the time nor the inclination topursue them to a practical result. Your rising workshops, yourpeopled colonies, your vessels which furrow the seas; this abundance, this luxury, this tumult, '--this commotion, ' he would have added, werehe now alive, 'regarding the electric light'--'all come fromdiscoverers in Science, though all remain strange to them. The daythat a discovery enters the market they abandon it; it concerns themno more. '

In writing thus, Cuvier probably did not sufficiently take intoaccount the reaction of the applications of science upon scienceitself. The improvement of an old instrument or the invention of anew one is often tantamount to an enlargement and refinement of thesenses of the scientific investigator. Beyond this, the ameliorationof the community is also an object worthy of the best efforts of thehuman brain. Still, assuredly it is well and wise for a nation tobear in mind that those practical applications which strike the publiceye, and excite public admiration, are the outgrowth of longantecedent labours begun, continued, and ended, under the operation ofa purely intellectual stimulus. 'Few, ' says Pasteur, 'seem tocomprehend the real origin of the marvels of industry and the wealthof nations. I need no other proof of this than the frequentemployment in lectures, speeches, and official language of theerroneous expression, "applied science. " A statesman of the greatesttalent stated some time ago that in our day the reign of theoreticscience had rightly yielded place to that of applied science. Nothing, I venture to say, could be more dangerous, even to practical life, than the consequences which might flow from these words. They showthe imperious necessity of a reform in our higher education. Thereexists no category of sciences to which the name of "applied science"could be given. We have science and the applications of science whichare united as tree and fruit. '

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A final reflection is here suggested. We have amongst us a smallcohort of social regenerators--men of high thoughts andaspirations--who would place the operations of the scientific mindunder the control of a hierarchy which should dictate to the man ofscience the course that he ought to pursue. How this hierarchy is toget its wisdom they do not explain. They decry and denouncescientific theories; they scorn all reference to aether, and atoms, and molecules, as subjects lying far apart from the world's needs; andyet such ultra-sensible conceptions are often the spur to the greatestdiscoveries. The source, in fact, from which the true naturalphilosopher derives inspiration and unifying power is essentiallyideal. Faraday lived in this ideal world. Nearly half a century ago, when he first obtained a spark from the magnet, an Oxford donexpressed regret that such a discovery should have been made, as itplaced a new and facile implement in the hands of the incendiary. Toregret, a Comtist hierarchy would have probably added repression, sending Faraday back to his bookbinder's bench as a more dignified andpractical sphere of action than peddling with a magnet. And yet it isFaraday's spark which now shines upon our coasts, and promises toilluminate our streets, halls, quays, squares, warehouses, and, perhaps at no distant day, our homes. 

THE END. 

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