EXPERIMENTAL RESEARCHES IN ELECTRICITY

by

MICHAEL FARADAY, D. C. L. F. R. S. 

Fullerian Profesor of Chemistry in the Royal Institution. Corresponding Member, etc. Of the Royal and Imperial Academies ofScience of Paris, Petersburgh, Florence, Copenhagen, Berlin, Gottingen, Modena, Stockholm, Palermo, etc. Etc. 

In Two Volumes

VOL. I. 

Second Edition

Reprinted from the PHILOSOPHICAL TRANSACTIONS of 1831-1838. 

London:Richard and John Edward Taylor, Printers and Publishers to the University of London, Red Lion Court, Fleet Street

1849

PREFACE

I have been induced by various circumstances to collect in One Volume theFourteen Series of Experimental Researches in Electricity, which haveappeared in the Philosophical Transactions during the last seven years: thechief reason has been the desire to supply at a moderate price the whole ofthese papers, with an Index, to those who may desire to have them. 

The readers of the volume will, I hope, do me the justice to remember thatit was not written as a _whole_, but in parts; the earlier portions rarelyhaving any known relation at the time to those which might follow. If I hadrewritten the work, I perhaps might have considerably varied the form, butshould not have altered much of the real matter: it would not, however, then have been considered a faithful reprint or statement of the course andresults of the whole investigation, which only I desired to supply. 

I may be allowed to express my great satisfaction at finding, that thedifferent parts, written at intervals during seven years, harmonize so wellas they do. There would have been nothing particular in this, if the partshad related only to matters well-ascertained before any of them werewritten:--but as each professes to contain something of original discovery, or of correction of received views, it does surprise even my partiality, that they should have the degree of consistency and apparent generalaccuracy which they seem to me to present. 

I have made some alterations in the text, but they have been altogether ofa typographical or grammatical character; and even where greatest, havebeen intended to explain the sense, not to alter it. I have often addedNotes at the bottom of the page, as to paragraphs 59, 360, 439, 521, 552, 555, 598, 657, 883, for the correction of errors, and also the purpose ofillustration: but these are all distinguished from the Original Notes ofthe Researches by the date of _Dec. 1838_. 

The date of a scientific paper containing any pretensions to discovery isfrequently a matter of serious importance, and it is a great misfortunethat there are many most valuable communications, essential to the historyand progress of science, with respect to which this point cannot now beascertained. This arises from the circumstance of the papers having nodates attached to them individually, and of the journals in which theyappear having such as are inaccurate, i. E. Dates of a period earlier thanthat of publication. I may refer to the note at the end of the FirstSeries, as an illustration of the kind of confusion thus produced. Thesecircumstances have induced me to affix a date at the top of every otherpage, and I have thought myself justified in using that placed by theSecretary of the Royal Society on each paper as it was received. An authorhas no right, perhaps, to claim an earlier one, unless it has receivedconfirmation by some public act or officer. 

Before concluding these lines I would beg leave to make a reference or two;first, to my own Papers on Electro-magnetic Rotations in the QuarterlyJournal of Science, 1822. Xii. 74. 186. 283. 416, and also to my Letter onMagneto-electric Induction in the Annales de Chimie, li. P. 404. Thesemight, as to the matter, very properly have appeared in this volume, butthey would have interfered with it as a simple reprint of the "ExperimentalResearches" of the Philosophical Transactions. 

Then I wish to refer, in relation to the Fourth Series on a new law ofElectric Conduction, to Franklin's experiments on the non-conduction ofice, which have been very properly separated and set forth by ProfessorBache (Journal of the Franklin Institute, 1836. Xvii. 183. ). These, which Idid not at all remember as to the extent of the effect, though they in noway anticipate the expression of the law I state as to the general effectof liquefaction on electrolytes, still should never be forgotten whenspeaking of that law as applicable to the case of water. 

There are two papers which I am anxious to refer to, as corrections orcriticisms of parts of the Experimental Researches. The first of these isone by Jacobi (Philosophical Magazine, 1838. Xiii. 401. ), relative to thepossible production of a spark on completing the junction of the two metalsof a single pair of plates (915. ). It is an excellent paper, and though Ihave not repeated the experiments, the description of them convinces methat I must have been in error. The second is by that excellentphilosopher, Marianini (Memoria della Societa Italiana di Modena, xxi. 205), and is a critical and experimental examination of Series viii, and ofthe question whether metallic contact is or is not _productive_ of a partof the electricity of the voltaic pile. I see no reason as yet to alter theopinion I have given; but the paper is so very valuable, comes to thequestion so directly, and the point itself is of such great importance, that I intend at the first opportunity renewing the inquiry, and, if I can, rendering the proofs either on the one side or the other undeniable to all. 

Other parts of these researches have received the honour of criticalattention from various philosophers, to all of whom I am obliged, and someof whose corrections I have acknowledged in the foot notes. There are, nodoubt, occasions on which I have not felt the force of the remarks, buttime and the progress of science will best settle such cases; and, althoughI cannot honestly say that I _wish_ to be found in error, yet I dofervently hope that the progress of science in the hands of its manyzealous present cultivators will be such, as by giving us new and otherdevelopments, and laws more and more general in their applications, willeven make me think that what is written and illustrated in theseexperimental researches, belongs to the by-gone parts of science. 

MICHAEL FARADAY. 

Royal Institution, March, 1839. 

CONTENTS. 

 Par. Series I. §. 1. Induction of electric currents 6 §. 2. Evolution of electricity from magnetism 27 §. 3. New electrical state or condition of matter 60 §. 4. Explication of Arago's magnetic phenomena 81Series II. §. 5. Terrestrial magneto-electric induction 140 §. 6. Force and direction of magneto-electric induction generally 193Series III. §. 7. Identity of electricities from different sources 265 ---- ---- i Voltaic electricity 268 ---- ---- ii Ordinary electricity 284 ---- ---- iii Magneto-electricity 343 ---- ---- iv Thermo-electricity 349 ---- ---- v Animal electricity 351 §. 8. Relation by measure of common and voltaic electricity 361 ---- Note respecting Ampère's inductive results after 379Series IV. §. 9. New law of electric conduction 380 §. 10. On conducting power generally 418Series V. §. 11. Electro-chemical decomposition 450 ---- ¶ 1. New conditions of electro-chemical decomposition 453 ---- ¶ 2. Influence of water in such decomposition 472 ---- ¶ 3. Theory of electro-chemical decomposition 477Series VI. §. 12. Power of platina, &c. To induce combination 564Series VII. §. 11. * Electro-chemical decomposition continued (nomenclature) 661 ---- ¶ 4. Some general conditions of Electro-chemical decomposition 669 ---- ¶ 5. Volta-electrometer 704 ---- ¶ 6. Primary and secondary results 742 ---- ¶ 7. Definite nature and extent of electro-chemical forces 783 ---- ---- Electro-chemical equivalents 822 §. 13. Absolute quantity of Electricity in the molecules of matter 852Series VIII. §. 14. Electricity of the voltaic pile 875 ---- ¶ 1. Simple voltaic circles 875 ---- ¶ 2. Electrolytic intensity 966 ---- ¶ 3. Associated voltaic circles; or battery 989 ---- ¶ 4. Resistance of an electrolyte to decomposition 1007 ---- ¶ 5. General remarks on the active battery 1034Series IX. §. 15. Induction of a current on itself 1048 ---- Inductive action of currents generally 1101Series X. §. 16. Improved voltaic battery 1119 §. 17. Practical results with the voltaic battery 1136Series XI. §. 18. On static induction 1161 ---- ¶ 1. Induction an action of contiguous particles 1161 ---- ¶ 2. Absolute charge of matter 1169 ---- ¶ 3. Electrometer and inductive apparatus 1179 ---- ¶ 4. Induction in curved lines 1215 ---- ---- Conduction by glass, lac, sulphur, &c. 1283 ---- ¶ 5. Specific inductive capacity 1252 ---- ¶ 6. General results as to the nature of induction 1295 ---- ---- Differential inductometer 1307Series XII. ---- ¶ 7. Conduction or conductive discharge 1320 ---- ¶ 8. Electrolytic discharge 1343 ---- ¶ 9. Disruptive discharge 1359 ---- ---- ---- Insulation 1362 ---- ---- ---- as spark 1406 ---- ---- ---- as brush 1425 ---- ---- ---- positive and negative 1465Series XIII. ---- ---- ---- as glow 1526 ---- ---- ---- dark 1544 ---- ¶ 10. Convection; or carrying discharge 1562 ---- ¶ 11. Relation of a vacuum to electrical phenomena 1613 §. 19. Nature of the electric current 1617 ---- ---- its transverse forces 1653Series XIV. §. 20. Nature of the electric force or forces 1667 §. 21. Relation of the electric and magnetic forces 1709 §. 22. Note on electrical excitation 1737IndexNotes

EXPERIMENTAL RESEARCHESINELECTRICITY. 

FIRST SERIES. 

§ 1. _On the Induction of Electric Currents. _ § 2. _On the Evolution ofElectricity from Magnetism. _ § 3. _On a new Electrical Condition ofMatter. _ § 4. _On_ Arago's _Magnetic Phenomena. _

[Read November 24, 1831. ]

1. The power which electricity of tension possesses of causing an oppositeelectrical state in its vicinity has been expressed by the general termInduction; which, as it has been received into scientific language, mayalso, with propriety, be used in the same general sense to express thepower which electrical currents may possess of inducing any particularstate upon matter in their immediate neighbourhood, otherwise indifferent. It is with this meaning that I purpose using it in the present paper. 

2. Certain effects of the induction of electrical currents have alreadybeen recognised and described: as those of magnetization; Ampère'sexperiments of bringing a copper disc near to a flat spiral; his repetitionwith electro-magnets of Arago's extraordinary experiments, and perhaps afew others. Still it appeared unlikely that these could be all the effectswhich induction by currents could produce; especially as, upon dispensingwith iron, almost the whole of them disappear, whilst yet an infinity ofbodies, exhibiting definite phenomena of induction with electricity oftension, still remain to be acted upon by the induction of electricity inmotion. 

3. Further: Whether Ampère's beautiful theory were adopted, or any other, or whatever reservation were mentally made, still it appeared veryextraordinary, that as every electric current was accompanied by acorresponding intensity of magnetic action at right angles to the current, good conductors of electricity, when placed within the sphere of thisaction, should not have any current induced through them, or some sensibleeffect produced equivalent in force to such a current. 

4. These considerations, with their consequence, the hope of obtainingelectricity from ordinary magnetism, have stimulated me at various times toinvestigate experimentally the inductive effect of electric currents. Ilately arrived at positive results; and not only had my hopes fulfilled, but obtained a key which appeared to me to open out a full explanation ofArago's magnetic phenomena, and also to discover a new state, which mayprobably have great influence in some of the most important effects ofelectric currents. 

5. These results I purpose describing, not as they were obtained, but insuch a manner as to give the most concise view of the whole. 

§ 1. _Induction of Electric Currents. _

6. About twenty-six feet of copper wire one twentieth of an inch indiameter were wound round a cylinder of wood as a helix, the differentspires of which were prevented from touching by a thin interposed twine. This helix was covered with calico, and then a second wire applied in thesame manner. In this way twelve helices were superposed, each containing anaverage length of wire of twenty-seven feet, and all in the same direction. The first, third, fifth, seventh, ninth, and eleventh of these helices wereconnected at their extremities end to end, so as to form one helix; theothers were connected in a similar manner; and thus two principal heliceswere produced, closely interposed, having the same direction, not touchinganywhere, and each containing one hundred and fifty-five feet in length ofwire. 

7. One of these helices was connected with a galvanometer, the other with avoltaic battery of ten pairs of plates four inches square, with doublecoppers and well charged; yet not the slightest sensible reflection of thegalvanometer-needle could be observed. 

8. A similar compound helix, consisting of six lengths of copper and six ofsoft iron wire, was constructed. The resulting iron helix contained twohundred and fourteen feet of wire, the resulting copper helix two hundredand eight feet; but whether the current from the trough was passed throughthe copper or the iron helix, no effect upon the other could be perceivedat the galvanometer. 

9. In these and many similar experiments no difference in action of anykind appeared between iron and other metals. 

10. Two hundred and three feet of copper wire in one length were coiledround a large block of wood; other two hundred and three feet of similarwire were interposed as a spiral between the turns of the first coil, andmetallic contact everywhere prevented by twine. One of these helices wasconnected with a galvanometer, and the other with a battery of one hundredpairs of plates four inches square, with double coppers, and well charged. When the contact was made, there was a sudden and very slight effect at thegalvanometer, and there was also a similar slight effect when the contactwith the battery was broken. But whilst the voltaic current was continuingto pass through the one helix, no galvanometrical appearances nor anyeffect like induction upon the other helix could be perceived, although theactive power of the battery was proved to be great, by its heating thewhole of its own helix, and by the brilliancy of the discharge when madethrough charcoal. 

11. Repetition of the experiments with a battery of one hundred and twentypairs of plates produced no other effects; but it was ascertained, both atthis and the former time, that the slight deflection of the needleoccurring at the moment of completing the connexion, was always in onedirection, and that the equally slight deflection produced when the contactwas broken, was in the other direction; and also, that these effectsoccurred when the first helices were used (6. 8. ). 

12. The results which I had by this time obtained with magnets led me tobelieve that the battery current through one wire, did, in reality, inducea similar current through the other wire, but that it continued for aninstant only, and partook more of the nature of the electrical wave passedthrough from the shock of a common Leyden jar than of the current from avoltaic battery, and therefore might magnetise a steel needle, although itscarcely affected the galvanometer. 

13. This expectation was confirmed; for on substituting a small hollowhelix, formed round a glass tube, for the galvanometer, introducing a steelneedle, making contact as before between the battery and the inducing wire(7. 10. ), and then removing the needle before the battery contact wasbroken, it was found magnetised. 

14. When the battery contact was first made, then an unmagnetised needleintroduced into the small indicating helix (13. ), and lastly the batterycontact broken, the needle was found magnetised to an equal degreeapparently as before; but the poles were of the contrary kind. 

15. The same effects took place on using the large compound helices firstdescribed (6. 8. ). 

16. When the unmagnetised needle was put into the indicating helix, beforecontact of the inducing wire with the battery, and remained there until thecontact was broken, it exhibited little or no magnetism; the first effecthaving been nearly neutralised by the second (13. 14. ). The force of theinduced current upon making contact was found always to exceed that of theinduced current at breaking of contact; and if therefore the contact wasmade and broken many times in succession, whilst the needle remained in theindicating helix, it at last came out not unmagnetised, but a needlemagnetised as if the induced current upon making contact had acted alone onit. This effect may be due to the accumulation (as it is called) at thepoles of the unconnected pile, rendering the current upon first makingcontact more powerful than what it is afterwards, at the moment of breakingcontact. 

17. If the circuit between the helix or wire under induction and thegalvanometer or indicating spiral was not rendered complete _before_ theconnexion between the battery and the inducing wire was completed orbroken, then no effects were perceived at the galvanometer. Thus, if thebattery communications were first made, and then the wire under inductionconnected with the indicating helix, no magnetising power was thereexhibited. But still retaining the latter communications, when those withthe battery were broken, a magnet was formed in the helix, but of thesecond kind (14. ), i. E. With poles indicating a current in the samedirection to that belonging to the battery current, or to that alwaysinduced by that current at its cessation. 

18. In the preceding experiments the wires were placed near to each other, and the contact of the inducing one with the buttery made when theinductive effect was required; but as the particular action might besupposed to be exerted only at the moments of making and breaking contact, the induction was produced in another way. Several feet of copper wire werestretched in wide zigzag forms, representing the letter W, on one surfaceof a broad board; a second wire was stretched in precisely similar forms ona second board, so that when brought near the first, the wires shouldeverywhere touch, except that a sheet of thick paper was interposed. One ofthese wires was connected with the galvanometer, and the other with avoltaic battery. The first wire was then moved towards the second, and asit approached, the needle was deflected. Being then removed, the needle wasdeflected in the opposite direction. By first making the wires approach andthen recede, simultaneously with the vibrations of the needle, the lattersoon became very extensive; but when the wires ceased to move from ortowards each other, the galvanometer-needle soon came to its usualposition. 

19. As the wires approximated, the induced current was in the _contrary_direction to the inducing current. As the wires receded, the inducedcurrent was in the _same_ direction as the inducing current. When the wiresremained stationary, there was no induced current (54. ). 

20. When a small voltaic arrangement was introduced into the circuitbetween the galvanometer (10. ) and its helix or wire, so as to cause apermanent deflection of 30° or 40°, and then the battery of one hundredpairs of plates connected with the inducing wire, there was aninstantaneous action as before (11. ); but the galvanometer-needleimmediately resumed and retained its place unaltered, notwithstanding thecontinued contact of the inducing wire with the trough: such was the casein whichever way the contacts were made (33. ). 

21. Hence it would appear that collateral currents, either in the same orin opposite directions, exert no permanent inducing power on each other, affecting their quantity or tension. 

22. I could obtain no evidence by the tongue, by spark, or by heating finewire or charcoal, of the electricity passing through the wire underinduction; neither could I obtain any chemical effects, though the contactswith metallic and other solutions were made and broken alternately withthose of the battery, so that the second effect of induction should notoppose or neutralise the first (13. 16. ). 

23. This deficiency of effect is not because the induced current ofelectricity cannot pass fluids, but probably because of its brief durationand feeble intensity; for on introducing two large copper plates into thecircuit on the induced side (20. ), the plates being immersed in brine, butprevented from touching each other by an interposed cloth, the effect atthe indicating galvanometer, or helix, occurred as before. The inducedelectricity could also pass through a voltaic trough (20. ). When, however, the quantity of interposed fluid was reduced to a drop, the galvanometergave no indication. 

24. Attempts to obtain similar effects by the use of wires conveyingordinary electricity were doubtful in the results. A compound helix similarto that already described, containing eight elementary helices (6. ), wasused. Four of the helices had their similar ends bound together by wire, and the two general terminations thus produced connected with the smallmagnetising helix containing an unmagnetised needle (13. ). The other fourhelices were similarly arranged, but their ends connected with a Leydenjar. On passing the discharge, the needle was found to be a magnet; but itappeared probable that a part of the electricity of the jar had passed offto the small helix, and so magnetised the needle. There was indeed noreason to expect that the electricity of a jar possessing as it does greattension, would not diffuse itself through all the metallic matterinterposed between the coatings. 

25. Still it does not follow that the discharge of ordinary electricitythrough a wire does not produce analogous phenomena to those arising fromvoltaic electricity; but as it appears impossible to separate the effectsproduced at the moment when the discharge begins to pass, from the equaland contrary effects produced when it ceases to pass (16. ), inasmuch aswith ordinary electricity these periods are simultaneous, so there can bescarcely any hope that in this form of the experiment they can beperceived. 

26. Hence it is evident that currents of voltaic electricity presentphenomena of induction somewhat analogous to those produced by electricityof tension, although, as will be seen hereafter, many differences existbetween them. The result is the production of other currents, (but whichare only momentary, ) parallel, or tending to parallelism, with the inducingcurrent. By reference to the poles of the needle formed in the indicatinghelix (13. 14. ) and to the deflections of the galvanometer-needle (11. ), itwas found in all cases that the induced current, produced by the firstaction of the inducing current, was in the contrary direction to thelatter, but that the current produced by the cessation of the inducingcurrent was in the same direction (19. ). For the purpose of avoidingperiphrasis, I propose to call this action of the current from the voltaicbattery, _volta-electric induction_. The properties of the second wire, after induction has developed the first current, and whilst the electricityfrom the battery continues to flow through its inducing neighbour (10. 18. ), constitute a peculiar electric condition, the consideration of whichwill be resumed hereafter (60. ). All these results have been obtained witha voltaic apparatus consisting of a single pair of plates. 

§ 2. _Evolution of Electricity from Magnetism. _

27. A welded ring was made of soft round bar-iron, the metal beingseven-eighths of an inch in thickness, and the ring six inches in externaldiameter. Three helices were put round one part of this ring, eachcontaining about twenty-four feet of copper wire one twentieth of an inchthick; they were insulated from the iron and each other, and superposed inthe manner before described (6. ), occupying about nine inches in lengthupon the ring. They could be used separately or conjointly; the group maybe distinguished by the letter A (Pl. I. Fig. 1. ). On the other part of thering about sixty feet of similar copper wire in two pieces were applied inthe same manner, forming a helix B, which had the same common directionwith the helices of A, but being separated from it at each extremity byabout half an inch of the uncovered iron. 

28. The helix B was connected by copper wires with a galvanometer threefeet from the ring. The helices of A were connected end to end so as toform one common helix, the extremities of which were connected with abattery of ten pairs of plates four inches square. The galvanometer wasimmediately affected, and to a degree far beyond what has been describedwhen with a battery of tenfold power helices _without iron_ were used(10. ); but though the contact was continued, the effect was not permanent, for the needle soon came to rest in its natural position, as if quiteindifferent to the attached electro-magnetic arrangement. Upon breaking thecontact with the batterry, the needle was again powerfully deflected, butin the contrary direction to that induced in the first instance. 

29. Upon arranging the apparatus so that B should be out of use, thegalvanometer be connected with one of the three wires of A (27. ), and theother two made into a helix through which the current from the trough (28. )was passed, similar but rather more powerful effects were produced. 

30. When the battery contact was made in one direction, thegalvanometer-needle was deflected on the one side; if made in the otherdirection, the deflection was on the other side. The deflection on breakingthe battery contact was always the reverse of that produced by completingit. The deflection on making a battery contact always indicated an inducedcurrent in the opposite direction to that from the battery; but on breakingthe contact the deflection indicated an induced current in the samedirection as that of the battery. No making or breaking of the contact at Bside, or in any part of the galvanometer circuit, produced any effect atthe galvanometer. No continuance of the battery current caused anydeflection of the galvanometer-needle. As the above results are common toall these experiments, and to similar ones with ordinary magnets to behereafter detailed, they need not be again particularly described. 

31. Upon using the power of one hundred pairs of plates (10. ) with thisring, the impulse at the galvanometer, when contact was completed orbroken, was so great as to make the needle spin round rapidly four or fivetimes, before the air and terrestrial magnetism could reduce its motion tomere oscillation. 

32. By using charcoal at the ends of the B helix, a minute _spark_ could beperceived when the contact of the battery with A was completed. This sparkcould not be due to any diversion of a part of the current of the batterythrough the iron to the helix B; for when the battery contact wascontinued, the galvanometer still resumed its perfectly indifferent state(28. ). The spark was rarely seen on breaking contact. A small platina wirecould not be ignited by this induced current; but there seems every reasonto believe that the effect would be obtained by using a stronger originalcurrent or a more powerful arrangement of helices. 

33. A feeble voltaic current was sent through the helix B and thegalvanometer, so as to deflect the needle of the latter 30° or 40°, andthen the battery of one hundred pairs of plates connected with A; but afterthe first effect was over, the galvanometer-needle resumed exactly theposition due to the feeble current transmitted by its own wire. This tookplace in whichever way the battery contacts were made, and shows that hereagain (20. ) no permanent influence of the currents upon each other, as totheir quantity and tension, exists. 

34. Another arrangement was then employed connecting the former experimentson volta-electric induction (6-26. ) with the present. A combination ofhelices like that already described (6. ) was constructed upon a hollowcylinder of pasteboard: there were eight lengths of copper wire, containingaltogether 220 feet; four of these helices were connected end to end, andthen with the galvanometer (7. ); the other intervening four were alsoconnected end to end, and the battery of one hundred pairs dischargedthrough them. In this form the effect on the galvanometer was hardlysensible (11. ), though magnets could be made by the induced current (13. ). But when a soft iron cylinder seven eighths of an inch thick, and twelveinches long, was introduced into the pasteboard tube, surrounded by thehelices, then the induced current affected the galvanometer powerfully andwith all the phenomena just described (30. ). It possessed also the power ofmaking magnets with more energy, apparently, than when no iron cylinder waspresent. 

35. When the iron cylinder was replaced by an equal cylinder of copper, noeffect beyond that of the helices alone was produced. The iron cylinderarrangement was not so powerful as the ring arrangement already described(27. ). 

36. Similar effects were then produced by _ordinary magnets_: thus thehollow helix just described (34. ) had all its elementary helices connectedwith the galvanometer by two copper wires, each five feet in length; thesoft iron cylinder was introduced into its axis; a couple of bar magnets, each twenty-four inches long, were arranged with their opposite poles atone end in contact, so as to resemble a horse-shoe magnet, and then contactmade between the other poles and the ends of the iron cylinder, so as toconvert it for the time into a magnet (fig. 2. ): by breaking the magneticcontacts, or reversing them, the magnetism of the iron cylinder could bedestroyed or reversed at pleasure. 

37. Upon making magnetic contact, the needle was deflected; continuing thecontact, the needle became indifferent, and resumed its first position; onbreaking the contact, it was again deflected, but in the opposite directionto the first effect, and then it again became indifferent. When themagnetic contacts were reversed the deflections were reversed. 

38. When the magnetic contact was made, the deflection was such as toindicate an induced current of electricity in the opposite direction tothat fitted to form a magnet, having the same polarity as that reallyproduced by contact with the bar magnets. Thus when the marked and unmarkedpoles were placed as in fig. 3, the current in the helix was in thedirection represented, P being supposed to be the end of the wire going tothe positive pole of the battery, or that end towards which the zinc platesface, and N the negative wire. Such a current would have converted thecylinder into a magnet of the opposite kind to that formed by contact withthe poles A and B; and such a current moves in the opposite direction tothe currents which in M. Ampère's beautiful theory are considered asconstituting a magnet in the position figured[A]. 

 [A] The relative position of an electric current and a magnet is by most persons found very difficult to remember, and three or four helps to the memory have been devised by M. Ampère and others. I venture to suggest the following as a very simple and effectual assistance in these and similar latitudes. Let the experimenter think he is looking down upon a dipping needle, or upon the pole of the north, and then let him think upon the direction of the motion of the hands of a watch, or of a screw moving direct; currents in that direction round a needle would make it into such a magnet as the dipping needle, or would themselves constitute an electro-magnet of similar qualities; or if brought near a magnet would tend to make it take that direction; or would themselves be moved into that position by a magnet so placed; or in M. Ampère's theory are considered as moving in that direction in the magnet. These two points of the position of the dipping-needle and the motion of the watch hands being remembered, any other relation of the current and magnet can be at once deduced from it. 

39. But as it might be supposed that in all the preceding experiments ofthis section, it was by some peculiar effect taking place during theformation of the magnet, and not by its mere virtual approximation, thatthe momentary induced current was excited, the following experiment wasmade. All the similar ends of the compound hollow helix (34. ) were boundtogether by copper wire, forming two general terminations, and these wereconnected with the galvanometer. The soft iron cylinder (34. ) was removed, and a cylindrical magnet, three quarters of an inch in diameter and eightinches and a half in length, used instead. One end of this magnet wasintroduced into the axis of the helix (fig. 4. ), and then, thegalvanometer-needle being stationary, the magnet was suddenly thrust in;immediately the needle was deflected in the same direction as if the magnethad been formed by either of the two preceding processes (34. 36. ). Beingleft in, the needle resumed its first position, and then the magnet beingwithdrawn the needle was deflected in the opposite direction. These effectswere not great; but by introducing and withdrawing the magnet, so that theimpulse each time should be added to those previously communicated to theneedle, the latter could be made to vibrate through an arc of 180° or more. 

40. In this experiment the magnet must not be passed entirely through thehelix, for then a second action occurs. When the magnet is introduced, theneedle at the galvanometer is deflected in a certain direction; but beingin, whether it be pushed quite through or withdrawn, the needle isdeflected in a direction the reverse of that previously produced. When themagnet is passed in and through at one continuous motion, the needle movesone way, is then suddenly stopped, and finally moves the other way. 

41. If such a hollow helix as that described (34. ) be laid east and west(or in any other constant position), and a magnet be retained east andwest, its marked pole always being one way; then whichever end of the helixthe magnet goes in at, and consequently whichever pole of the magnet entersfirst, still the needle is deflected the same way: on the other hand, whichever direction is followed in withdrawing the magnet, the deflectionis constant, but contrary to that due to its entrance. 

42. These effects are simple consequences of the _law_ hereafter to bedescribed (114). 

43. When the eight elementary helices were made one long helix, the effectwas not so great as in the arrangement described. When only one of theeight helices was used, the effect was also much diminished. All care wastaken to guard against tiny direct action of the inducing magnet upon thegalvanometer, and it was found that by moving the magnet in the samedirection, and to the same degree on the outside of the helix, no effect onthe needle was produced. 

44. The Royal Society are in possession of a large compound magnet formerlybelonging to Dr. Gowin Knight, which, by permission of the President andCouncil, I was allowed to use in the prosecution of these experiments: itis at present in the charge of Mr. Christie, at his house at Woolwich, where, by Mr. Christie's kindness, I was at liberty to work; and I have toacknowledge my obligations to him for his assistance in all the experimentsand observations made with it. This magnet is composed of about 450 barmagnets, each fifteen inches long, one inch wide, and half an inch thick, arranged in a box so as to present at one of its extremities two externalpoles (fig. 5. ). These poles projected horizontally six inches from thebox, were each twelve inches high and three inches wide. They were nineinches apart; and when a soft iron cylinder, three quarters of an inch indiameter and twelve inches long, was put across from one to the other, itrequired a force of nearly one hundred pounds to break the contact. Thepole to the left in the figure is the marked pole[A]. 

 [A] To avoid any confusion as to the poles of the magnet, I shall designate the pole pointing to the north as the marked pole; I may occasionally speak of the north and south ends of the needle, but do not mean thereby north and south poles. That is by many considered the true north pole of a needle which points to the south; but in this country it in often called the south pole. 

45. The indicating galvanometer, in all experiments made with this magnet, was about eight feet from it, not directly in front of the poles, but about16° or 17° on one side. It was found that on making or breaking theconnexion of the poles by soft iron, the instrument was slightly affected;but all error of observation arising from this cause was easily andcarefully avoided. 

46. The electrical effects exhibited by this magnet were very striking. When a soft iron cylinder thirteen inches long was put through the compoundhollow helix, with its ends arranged as two general terminations (39. ), these connected with the galvanometer, and the iron cylinder brought incontact with the two poles of the magnet (fig. 5. ), so powerful a rush ofelectricity took place that the needle whirled round many times insuccession[A]. 

 [A] A soft iron bar in the form of a lifter to a horse-shoe magnet, when supplied with a coil of this kind round the middle of it, becomes, by juxta-position with a magnet, a ready source of a brief but determinate current of electricity. 

47. Notwithstanding this great power, if the contact was continued, theneedle resumed its natural position, being entirely uninfluenced by theposition of the helix (30. ). But on breaking the magnetic contact, theneedle was whirled round in the opposite direction with a force equal tothe former. 

48. A piece of copper plate wrapped _once_ round the iron cylinder like asocket, but with interposed paper to prevent contact, had its edgesconnected with the wires of the galvanometer. When the iron was brought incontact with the poles the galvanometer was strongly affected. 

49. Dismissing the helices and sockets, the galvanometer wire was passedover, and consequently only half round the iron cylinder (fig. 6. ); buteven then a strong effect upon the needle was exhibited, when the magneticcontact was made or broken. 

50. As the helix with its iron cylinder was brought towards the magneticpoles, but _without making contact_, still powerful effects were produced. When the helix, without the iron cylinder, and consequently containing nometal but copper, was approached to, or placed between the poles (44. ), theneedle was thrown 80°, 90°, or more, from its natural position. Theinductive force was of course greater, the nearer the helix, either with orwithout its iron cylinder, was brought to the poles; but otherwise the sameeffects were produced, whether the helix, &c. Was or was not brought intocontact with the magnet; i. E. No permanent effect on the galvanometer wasproduced; and the effects of approximation and removal were the reverse ofeach other (30. ). 

51. When a bolt of copper corresponding to the iron cylinder wasintroduced, no greater effect was produced by the helix than without it. But when a thick iron wire was substituted, the magneto-electric inductionwas rendered sensibly greater. 

52. The direction of the electric current produced in all these experimentswith the helix, was the same as that already described (38. ) as obtainedwith the weaker bar magnets. 

53. A spiral containing fourteen feet of copper wire, being connected withthe galvanometer, and approximated directly towards the marked pole in theline of its axis, affected the instrument strongly; the current induced init was in the reverse direction to the current theoretically considered byM. Ampère as existing in the magnet (38. ), or as the current in anelectro-magnet of similar polarity. As the spiral was withdrawn, theinduced current was reversed. 

54. A similar spiral had the current of eighty pairs of 4-inch plates sentthrough it so as to form an electro-magnet, and then the other spiralconnected with the galvanometer (58. ) approximated to it; the needlevibrated, indicating a current in the galvanometer spiral the reverse ofthat in the battery spiral (18. 26. ). On withdrawing the latter spiral, theneedle passed in the opposite direction. 

55. Single wires, approximated in certain directions towards the magneticpole, had currents induced in them. On their removal, the currents wereinverted. In such experiments the wires should not be removed in directionsdifferent to those in which they were approximated; for then occasionallycomplicated and irregular effects are produced, the causes of which will bevery evident in the fourth part of this paper. 

56. All attempts to obtain chemical effects by the induced current ofelectricity failed, though the precautions before described (22. ), and allothers that could be thought of, were employed. Neither was any sensationon the tongue, or any convulsive effect upon the limbs of a frog, produced. Nor could charcoal or fine wire be ignited (133. ). But upon repeating theexperiments more at leisure at the Royal Institution, with an armedloadstone belonging to Professor Daniell and capable of lifting aboutthirty pounds, a frog was very _powerfully convulsed_ each time magneticcontact was made. At first the convulsions could not be obtained onbreaking magnetic contact; but conceiving the deficiency of effect wasbecause of the comparative slowness of separation, the latter act waseffected by a blow, and then the frog was convulsed strongly. The moreinstantaneous the union or disunion is effected, the more powerful theconvulsion. I thought also I could perceive the _sensation_ upon the tongueand the _flash_ before the eyes; but I could obtain no evidence of chemicaldecomposition. 

57. The various experiments of this section prove, I think, most completelythe production of electricity from ordinary magnetism. That its intensityshould be very feeble and quantity small, cannot be considered wonderful, when it is remembered that like thermo-electricity it is evolved entirelywithin the substance of metals retaining all their conducting power. But anagent which is conducted along metallic wires in the manner described;which whilst so passing possesses the peculiar magnetic actions and forceof a current of electricity; which can agitate and convulse the limbs of afrog; and which, finally, can produce a spark[A] by its discharge throughcharcoal (32. ), can only be electricity. As all the effects can be producedby ferruginous electro-magnets (34. ), there is no doubt that arrangementslike the magnets of Professors Moll, Henry, Ten Eyke, and others, in whichas many as two thousand pounds have been lifted, may be used for theseexperiments; in which case not only a brighter spark may be obtained, butwires also ignited, and, as the current can pass liquids (23. ), chemicalaction be produced. These effects are still more likely to be obtained whenthe magneto-electric arrangements to be explained in the fourth section areexcited by the powers of such apparatus. 

 [A] For a mode of obtaining the spark from the common magnet which I have found effectual, see the Philosophical Magazine for June 1832, p. 5. In the same Journal for November 1834, vol. V. P. 349, will be found a method of obtaining the magneto-electric spark, still simpler in its principle, the use of soft iron being dispensed with altogether. --_Dec. 1838. _

58. The similarity of action, almost amounting to identity, between commonmagnets and either electro-magnets or volta-electric currents, isstrikingly in accordance with and confirmatory of M. Ampère's theory, andfurnishes powerful reasons for believing that the action is the same inboth cases; but, as a distinction in language is still necessary, I proposeto call the agency thus exerted by ordinary magnets, _magneto-electric_ or_magnelectric_ induction (26). 

59. The only difference which powerfully strikes the attention as existingbetween volta-electric and magneto-electric induction, is the suddenness ofthe former, and the sensible time required by the latter; but even in thisearly state of investigation there are circumstances which seem toindicate, that upon further inquiry this difference will, as aphilosophical distinction, disappear (68). [A]

 [A] For important additional phenomena and developments of the induction of electrical currents, see now the ninth series, 1048-1118. --_Dec. 1838. _

§ 3. _New Electrical State or Condition of Matter. _[A]

 [A] This section having been read at the Royal Society and reported upon, and having also, in consequence of a letter from myself to M. Hachette, been noticed at the French Institute, I feel bound to let it stand as part of the paper; but later investigations (intimated 73. 76. 77. ) of the laws governing those phenomena, induce me to think that the latter can be fully explained without admitting the electro-tonic state. My views on this point will appear in the second series of these researches. --M. F. 

60. Whilst the wire is subject to either volta-electric or magneto-electricinduction, it appears to be in a peculiar state; for it resists theformation of an electrical current in it, whereas, if in its commoncondition, such a current would be produced; and when left uninfluenced ithas the power of originating a current, a power which the wire does notpossess under common circumstances. This electrical condition of matter hasnot hitherto been recognised, but it probably exerts a very importantinfluence in many if not most of the phenomena produced by currents ofelectricity. For reasons which will immediately appear (71. ), I have, afteradvising with several learned friends, ventured to designate it as the_electro-ionic_ state. 

61. This peculiar condition shows no known electrical effects whilst itcontinues; nor have I yet been able to discover any peculiar powersexerted, or properties possessed, by matter whilst retained in this state. 

62. It shows no reaction by attractive or repulsive powers. The variousexperiments which have been made with powerful magnets upon such metals, ascopper, silver, and generally those substances not magnetic, prove thispoint; for the substances experimented upon, if electrical conductors, musthave acquired this state; and yet no evidence of attractive or repulsivepowers has been observed. I have placed copper and silver discs, verydelicately suspended on torsion balances in vacuo near to the poles of verypowerful magnets, yet have not been able to observe the least attractive orrepulsive force. 

63. I have also arranged a fine slip of gold-leaf very near to a bar ofcopper, the two being in metallic contact by mercury at their extremities. These have been placed in vacuo, so that metal rods connected with theextremities of the arrangement should pass through the sides of the vesselinto the air. I have then moved powerful magnetic poles, about thisarrangement, in various directions, the metallic circuit on the outsidebeing sometimes completed by wires, and sometimes broken. But I never couldobtain any sensible motion of the gold-leaf, either directed to the magnetor towards the collateral bar of copper, which must have been, as far asinduction was concerned, in a similar state to itself. 

64. In some cases it has been supposed that, under such circumstances, attractive and repulsive forces have been exhibited, i. E. That such bodieshave become slightly magnetic. But the phenomena now described, inconjunction with the confidence we may reasonably repose in M. Ampère'stheory of magnetism, tend to throw doubt on such cases; for if magnetismdepend upon the attraction of electrical currents, and if the powerfulcurrents at first excited, both by volta-electric and magneto-electricinduction, instantly and naturally cease (12. 28. 47. ), causing at the sametime an entire cessation of magnetic effects at the galvanometer needle, then there can be little or no expectation that any substances notpartaking of the peculiar relation in which iron, nickel, and one or twoother bodies, stand, should exhibit magneto-attractive powers. It seems farmore probable, that the extremely feeble permanent effects observed havebeen due to traces of iron, or perhaps some other unrecognised cause notmagnetic. 

65. This peculiar condition exerts no retarding or accelerating power uponelectrical currents passing through metal thus circumstanced (20. 33. ). Neither could any such power upon the inducing current itself be detected;for when masses of metal, wires, helices, &c. Were arranged in all possibleways by the side of a wire or helix, carrying a current measured by thegalvanometer (20. ), not the slightest permanent change in the indication ofthe instrument could be perceived. Metal in the supposed peculiar state, therefore, conducts electricity in all directions with its ordinaryfacility, or, in other words, its conducting power is not sensibly alteredby it. 

66. All metals take on the peculiar state. This is proved in the precedingexperiments with copper and iron (9. ), and with gold, silver, tin, lead, zinc, antimony, bismuth, mercury, &c. By experiments to be described in thefourth part (132. ), admitting of easy application. With regard to iron, theexperiments prove the thorough and remarkable independence of thesephenomena of induction, and the ordinary magnetical appearances of thatmetal. 

67. This state is altogether the effect of the induction exerted, andceases as soon as the inductive force is removed. It is the same state, whether produced by the collateral passage of voltaic currents (26. ), orthe formation of a magnet (34. 36. ), or the mere approximation of a magnet(39. 50. ); and is a strong proof in addition to those advanced by M. Ampère, of the identity of the agents concerned in these severaloperations. It probably occurs, momentarily, during the passage of thecommon electric spark (24. ), and may perhaps be obtained hereafter in badconductors by weak electrical currents or other means (74. 76). 

68. The state appears to be instantly assumed (12. ), requiring hardly asensible portion of time for that purpose. The _difference_ of time betweenvolta-electric and magneto-electric induction, rendered evident by thegalvanometer (59. ), may probably be thus explained. When a voltaic currentis sent through one of two parallel wires, as those of the hollow helix(34. ), a current is produced in the other wire, as brief in its continuanceas the time required for a single action of this kind, and which, byexperiment, is found to be inappreciably small. The action will seem stillmore instantaneous, because, as there is an accumulation of power in thepoles of the battery before contact, the first rush of electricity in thewire of communication is greater than that sustained after the contact iscompleted; the wire of induction becomes at the moment electro-tonic to anequivalent degree, which the moment after sinks to the state in which thecontinuous current can sustain it, but in sinking, causes an oppositeinduced current to that at first produced. The consequence is, that thefirst induced wave of electricity more resembles that from the discharge ofan electric jar, than it otherwise would do. 

69. But when the iron cylinder is put into the same helix (31. ), previousto the connexion being made with the battery, then the current from thelatter may be considered as active in inducing innumerable currents of asimilar kind to itself in the iron, rendering it a magnet. This is known byexperiment to occupy time; for a magnet so formed, even of soft iron, doesnot rise to its fullest intensity in an instant, and it may be because thecurrents within the iron are successive in their formation or arrangement. But as the magnet can induce, as well as the battery current, the combinedaction of the two continues to evolve induced electricity, until theirjoint effect is at a maximum, and thus the existence of the deflectingforce is prolonged sufficiently to overcome the inertia of the galvanometerneedle. 

70. In all those cases where the helices or wires are advanced towards ortaken from the magnet (50. 55. ), the direct or inverted current of inducedelectricity continues for the time occupied in the advance or recession;for the electro-tonic state is rising to a higher or falling to a lowerdegree during that time, and the change is accompanied by its correspondingevolution of electricity; but these form no objections to the opinion thatthe electro-tonic state is instantly assumed. 

71. This peculiar state appears to be a state of tension, and may beconsidered as _equivalent_ to a current of electricity, at least equal tothat produced either when the condition is induced or destroyed. Thecurrent evolved, however, first or last, is not to be considered a measureof the degree of tension to which the electro-tonic state has risen; for asthe metal retains its conducting powers unimpaired (65. ), and as theelectricity evolved is but for a moment, (the peculiar state beinginstantly assumed and lost (68. ), ) the electricity which may be led away bylong wire conductors, offering obstruction in their substance proportionateto their small lateral and extensive linear dimensions, can be but a verysmall portion of that really evolved within the mass at the moment itassumes this condition. Insulated helices and portions of metal instantlyassumed the state; and no traces of electricity could be discovered inthem, however quickly the contact with the electrometer was made, afterthey were put under induction, either by the current from the battery orthe magnet. A single drop of water or a small piece of moistened paper (23. 56. ) was obstacle sufficient to stop the current through the conductors, the electricity evolved returning to a state of equilibrium through themetal itself, and consequently in an unobserved manner. 

72. The tension of this state may therefore be comparatively very great. But whether great or small, it is hardly conceivable that it should existwithout exerting a reaction upon the original inducing current, andproducing equilibrium of some kind. It might be anticipated that this wouldgive rise to a retardation of the original current; but I have not beenable to ascertain that this is the case. Neither have I in any other way asyet been able to distinguish effects attributable to such a reaction. 

73. All the results favour the notion that the electro-tonic state relatesto the particles, and not to the mass, of the wire or substance underinduction, being in that respect different to the induction exerted byelectricity of tension. If so, the state may be assumed in liquids when noelectrical current is sensible, and even in non-conductors; the currentitself, when it occurs, being as it were a contingency due to the existenceof conducting power, and the momentary propulsive force exerted by theparticles during their arrangement. Even when conducting power is equal, the currents of electricity, which as yet are the only indicators of thisstate, may be unequal, because of differences as to numbers, size, electrical condition, &c. &c. In the particles themselves. It will only beafter the laws which govern this new state are ascertained, that we shallbe able to predict what is the true condition of, and what are theelectrical results obtainable from, any particular substance. 

74. The current of electricity which induces the electro-tonic state in aneighbouring wire, probably induces that state also in its own wire; forwhen by a current in one wire a collateral wire is made electro-tonic, thelatter state is not rendered any way incompatible or interfering with acurrent of electricity passing through it (62. ). If, therefore, the currentwere sent through the second wire instead of the first, it does not seemprobable that its inducing action upon the second would be less, but on thecontrary more, because the distance between the agent and the matter actedupon would be very greatly diminished. A copper bolt had its extremitiesconnected with a galvanometer, and then the poles of a battery of onehundred pairs of plates connected with the bolt, so as to send the currentthrough it; the voltaic circuit was then suddenly broken, and thegalvanometer observed for any indications of a return current through thecopper bolt due to the discharge of its supposed electro-tonic state. Noeffect of the kind was obtained, nor indeed, for two reasons, ought it tobe expected; for first, as the cessation of induction and the discharge ofthe electro-tonic condition are simultaneous, and not successive, thereturn current would only be equivalent to the neutralization of the lastportion of the inducing current, and would not therefore show anyalteration of direction; or assuming that time did intervene, and that thelatter current was really distinct from the former, its short, suddencharacter (12. 26. ) would prevent it from being thus recognised. 

75. No difficulty arises, I think, in considering the wire thus renderedelectro-tonic by its own current more than by any external current, especially when the apparent non-interference of that state with currentsis considered (62. 71. ). The simultaneous existence of the conducting andelectro-tonic states finds an analogy in the manner in which electricalcurrents can be passed through magnets, where it is found that both thecurrents passed, and those of the magnets, preserve all their propertiesdistinct from each other, and exert their mutual actions. 

76. The reason given with regard to metals extends also to fluids and allother conductors, and leads to the conclusion that when electric currentsare passed through them they also assume the electro-tonic state. Shouldthat prove to be the case, its influence in voltaic decomposition, and thetransference of the elements to the poles, can hardly be doubted. In theelectro-tonic state the homogeneous particles of matter appear to haveassumed a regular but forced electrical arrangement in the direction of thecurrent, which if the matter be undecomposable, produces, when relieved, areturn current; but in decomposable matter this forced state may besufficient to make an elementary particle leave its companion, with whichit is in a constrained condition, and associate with the neighbouringsimilar particle, in relation to which it is in a more natural condition, the forced electrical arrangement being itself discharged or relieved, atthe same time, as effectually as if it had been freed from induction. Butas the original voltaic current is continued, the electro-tonic state maybe instantly renewed, producing the forced arrangement of the compoundparticles, to be as instantly discharged by a transference of theelementary particles of the opposite kind in opposite directions, butparallel to the current. Even the differences between common and voltaicelectricity, when applied to effect chemical decomposition, which Dr. Wollaston has pointed out[A], seem explicable by the circumstancesconnected with the induction of electricity from these two sources (25. ). But as I have reserved this branch of the inquiry, that I might follow outthe investigations contained in the present paper, I refrain (though muchtempted) from offering further speculations. 

 [A] Philosophical Transactions, 1801, p. 247. 

77. Marianini has discovered and described a peculiar affection of thesurfaces of metallic discs, when, being in contact with humid conductors, acurrent of electricity is passed through them; they are then capable ofproducing a reverse current of electricity, and Marianini has well appliedthe effect in explanation of the phenomena of Ritter's piles[A]. M. A. De laRive has described a peculiar property acquired by metallic conductors, when being immersed in a liquid as poles, they have completed, for sometime, the voltaic circuit, in consequence of which, when separated from thebattery and plunged into the same fluid, they by themselves produce anelectric current[B]. M. A. Van Beek has detailed cases in which theelectrical relation of one metal in contact with another has been preservedafter separation, and accompanied by its corresponding chemical effects[C]. These states and results appear to differ from the electro-tonic state andits phenomena; but the true relation of the former to the latter can onlybe decided when our knowledge of all these phenomena has been enlarged. 

 [A] Annales de Chimie, xxxviii. 5. 

 [B] Ibid. Xxviii. 190. 

 [C] Ibid. Xxxviii. 49. 

78. I had occasion in the commencement of this paper (2. ) to refer to anexperiment by Ampère, as one of those dependent upon the electricalinduction of currents made prior to the present investigation, and havearrived at conclusions which seem to imply doubts of the accuracy of theexperiment (62. &c. ); it is therefore due to M. Ampère that I should attendto it more distinctly. When a disc of copper (says M. Ampère) was suspendedby a silk thread and surrounded by a helix or spiral, and when the chargeof a powerful voltaic battery was sent through the spiral, a strong magnetat the same time being presented to the copper disc, the latter turned atthe moment to take a position of equilibrium, exactly as the spiral itselfwould have turned had it been free to move. I have not been able to obtainthis effect, nor indeed any motion; but the cause of my failure in the_latter_ point may be due to the momentary existence of the current notallowing time for the inertia of the plate to be overcome (11. 12. ). M. Ampère has perhaps succeeded in obtaining motion from the superior delicacyand power of his electro-magnetical apparatus, or he may have obtained onlythe motion due to cessation of action. But all my results tend to invertthe sense of the proposition stated by M. Ampère, "that a current ofelectricity tends to put the electricity of conductors near which it passesin motion in the same direction, " for they indicate an opposite directionfor the produced current (26. 53. ); and they show that the effect ismomentary, and that it is also produced by magnetic induction, and thatcertain other extraordinary effects follow thereupon. 

79. The momentary existence of the phenomena of induction now described issufficient to furnish abundant reasons for the uncertainty or failure ofthe experiments, hitherto made to obtain electricity from magnets, or toeffect chemical decomposition or arrangement by their means[A]. 

 [A] The Lycée, No. 36, for January 1st, has a long and rather premature article, in which it endeavours to show anticipations by French philosophers of my researches. It however mistakes the erroneous results of MM. Fresnel and Ampère for true ones, and then imagines my true results are like those erroneous ones. I notice it here, however, for the purpose of doing honour to Fresnel in a much higher degree than would have been merited by a feeble anticipation of the present investigations. That great philosopher, at the same time with myself and fifty other persons, made experiments which the present paper proves could give no expected result. He was deceived for the moment, and published his imaginary success; but on more carefully repeating his trials, he could find no proof of their accuracy; and, in the high and pure philosophic desire to remove error as well as discover truth, he recanted his first statement. The example of Berzelius regarding the first Thorina is another instance of this fine feeling; and as occasions are not rare, it would be to the dignity of science if such examples were more frequently followed. --February 10th, 1832. 

80. It also appears capable of explaining fully the remarkable phenomenaobserved by M. Arago between metals and magnets when neither are moving(120. ), as well as most of the results obtained by Sir John Herschel, Messrs. Babbage, Harris, and others, in repeating his experiments;accounting at the same time perfectly for what at first appearedinexplicable; namely, the non-action of the same metals and magnets when atrest. These results, which also afford the readiest means of obtainingelectricity from magnetism, I shall now proceed to describe. 

§ 4. _Explication of Arago's Magnetic Phenomena. _

81. If a plate of copper be revolved close to a magnetic needle, or magnet, suspended in such a way that the latter may rotate in a plane parallel tothat of the former, the magnet tends to follow the motion of the plate; orif the magnet be revolved, the plate tends to follow its motion; and theeffect is so powerful, that magnets or plates of many pounds weight may bethus carried round. If the magnet and plate be at rest relative to eachother, not the slightest effect, attractive or repulsive, or of any kind, can be observed between them (62. ). This is the phenomenon discovered by M. Arago; and he states that the effect takes place not only with all metals, but with solids, liquids, and even gases, i. E. With all substances (130. ). 

82. Mr. Babbage and Sir John Herschel, on conjointly repeating theexperiments in this country[A], could obtain the effects only with themetals, and with carbon in a peculiar state (from gas retorts), i. E. Onlywith excellent conductors of electricity. They refer the effect tomagnetism induced in the plate by the magnet; the pole of the lattercausing an opposite pole in the nearest part of the plate, and round this amore diffuse polarity of its own kind (120. ). The essential circumstance inproducing the rotation of the suspended magnet is, that the substancerevolving below it shall acquire and lose its magnetism in sensible time, and not instantly (124. ). This theory refers the effect to an attractiveforce, and is not agreed to by the discoverer, M. Arago, nor by M. Ampère, who quote against it the absence of all attraction when the magnet andmetal are at rest (62. 126. ), although the induced magnetism should stillremain; and who, from experiments made with a long dipping needle, conceivethe action to be always repulsive (125. ). 

 [A] Philosophical Transactions, 1825, p. 467. 

83. Upon obtaining electricity from magnets by the means already described(36 46. ), I hoped to make the experiment of M. Arago a new source ofelectricity; and did not despair, by reference to terrestrialmagneto-electric induction, of being able to construct a new electricalmachine. Thus stimulated, numerous experiments were made with the magnet ofthe Royal Society at Mr. Christie's house, in all of which I had theadvantage of his assistance. As many of these were in the course of thesuperseded by more perfect arrangements, I shall consider myself at libertyinvestigation to rearrange them in a manner calculated to convey mostreadily what appears to me to be a correct view of the nature of thephenomena. 

84. The magnet has been already described (44. ). To concentrate the poles, and bring them nearer to each other, two iron or steel bars, each about sixor seven inches long, one inch wide, and half an inch thick, were putacross the poles as in fig. 7, and being supported by twine from slipping, could be placed as near to or far from each other as was required. Occasionally two bars of soft iron were employed, so bent that whenapplied, one to each pole, the two smaller resulting poles were verticallyover each other, either being uppermost at pleasure. 

85. A disc of copper, twelve inches in diameter, and about one fifth of aninch in thickness, fixed upon a brass axis, was mounted in frames so as toallow of revolution either vertically or horizontally, its edge being atthe same time introduced more or less between the magnetic poles (fig. 7. ). The edge of the plate was well amalgamated for the purpose of obtaining agood but moveable contact, and a part round the axis was also prepared in asimilar manner. 

86. Conductors or electric collectors of copper and lead were constructedso as to come in contact with the edge of the copper disc (85. ), or withother forms of plates hereafter to be described (101. ). These conductorswere about four inches long, one third of an inch wide, and one fifth of aninch thick; one end of each was slightly grooved, to allow of more exactadaptation to the somewhat convex edge of the plates, and then amalgamated. Copper wires, one sixteenth of an inch in thickness, attached, in theordinary manner, by convolutions to the other ends of these conductors, passed away to the galvanometer. 

87. The galvanometer was roughly made, yet sufficiently delicate in itsindications. The wire was of copper covered with silk, and made sixteen oreighteen convolutions. Two sewing-needles were magnetized and fixed on to astem of dried grass parallel to each other, but in opposite directions, andabout half an inch apart; this system was suspended by a fibre of unspunsilk, so that the lower needle should be between the convolutions of themultiplier, and the upper above them. The latter was by much the mostpowerful magnet, and gave terrestrial direction to the whole; fig. 8. Represents the direction of the wire and of the needles when the instrumentwas placed in the magnetic meridian: the ends of the wires are marked A andB for convenient reference hereafter. The letters S and N designate thesouth and north ends of the needle when affected merely by terrestrialmagnetism; the end N is therefore the marked pole (44. ). The wholeinstrument was protected by a glass jar, and stood, as to position anddistance relative to the large magnet, under the same circumstances asbefore (45. ). 

88. All these arrangements being made, the copper disc was adjusted as infig. 7, the small magnetic poles being about half an inch apart, and theedge of the plate inserted about half their width between them. One of thegalvanometer wires was passed twice or thrice loosely round the brass axisof the plate, and the other attached to a conductor (86. ), which itself wasretained by the hand in contact with the amalgamated edge of the disc atthe part immediately between the magnetic poles. Under these circumstancesall was quiescent, and the galvanometer exhibited no effect. But theinstant the plate moved, the galvanometer was influenced, and by revolvingthe plate quickly the needle could be deflected 90° or more. 

89. It was difficult under the circumstances to make the contact betweenthe conductor and the edge of the revolving disc uniformly good andextensive; it was also difficult in the first experiments to obtain aregular velocity of rotation: both these causes tended to retain the needlein a continual state of vibration; but no difficulty existed inascertaining to which side it was deflected, or generally, about what lineit vibrated. Afterwards, when the experiments were made more carefully, apermanent deflection of the needle of nearly 45° could be sustained. 

90. Here therefore was demonstrated the production of a permanent currentof electricity by ordinary magnets (57. ). 

91. When the motion of the disc was reversed, every other circumstanceremaining the same, the galvanometer needle was deflected with equal poweras before; but the deflection was on the opposite side, and the current ofelectricity evolved, therefore, the reverse of the former. 

92. When the conductor was placed on the edge of the disc a little to theright or left, as in the dotted positions fig. 9, the current ofelectricity was still evolved, and in the same direction as at first (88. 91. ). This occurred to a considerable distance, i. E. 50° or 60° on eachside of the place of the magnetic poles. The current gathered by theconductor and conveyed to the galvanometer was of the same kind on bothsides of the place of greatest intensity, but gradually diminished in forcefrom that place. It appeared to be equally powerful at equal distances fromthe place of the magnetic poles, not being affected in that respect by thedirection of the rotation. When the rotation of the disc was reversed, thedirection of the current of electricity was reversed also; but the othercircumstances were not affected. 

93. On raising the plate, so that the magnetic poles were entirely hiddenfrom each other by its intervention, (a. Fig. 10, ) the same effects wereproduced in the same order, and with equal intensity as before. On raisingit still higher, so as to bring the place of the poles to c, still theeffects were produced, and apparently with as much power as at first. 

94. When the conductor was held against the edge as if fixed to it, andwith it moved between the poles, even though but for a few degrees, thegalvanometer needle moved and indicated a current of electricity, the sameas that which would have been produced if the wheel had revolved in thesame direction, the conductor remaining stationary. 

95. When the galvanometer connexion with the axis was broken, and its wiresmade fast to two conductors, both applied to the edge of the copper disc, then currents of electricity were produced, presenting more complicatedappearances, but in perfect harmony with the above results. Thus, ifapplied as in fig. 11, a current of electricity through the galvanometerwas produced; but if their place was a little shifted, as in fig. 12, acurrent in the contrary direction resulted; the fact being, that in thefirst instance the galvanometer indicated the difference between a strongcurrent through A and a weak one through B, and in the second, of a weakcurrent through A and a strong one through B (92. ), and therefore producedopposite deflections. 

96. So also when the two conductors were equidistant from the magneticpoles, as in fig. 13, no current at the galvanometer was perceived, whichever way the disc was rotated, beyond what was momentarily produced byirregularity of contact; because equal currents in the same directiontended to pass into both. But when the two conductors were connected withone wire, and the axis with the other wire, (fig. 14, ) then thegalvanometer showed a current according with the direction of rotation(91. ); both conductors now acting consentaneously, and as a singleconductor did before (88. ). 

97. All these effects could be obtained when only one of the poles of themagnet was brought near to the plate; they were of the same kind as todirection, &c. , but by no means so powerful. 

98. All care was taken to render these results independent of the earth'smagnetism, or of the mutual magnetism of the magnet and galvanometerneedles. The contacts were made in the magnetic equator of the plate, andat other parts; the plate was placed horizontally, and the polesvertically; and other precautions were taken. But the absence of anyinterference of the kind referred to, was readily shown by the want of alleffect when the disc was removed from the poles, or the poles from thedisc; every other circumstance remaining the same. 

99. The _relation of the current_ of electricity produced, to the magneticpole, to the direction of rotation of the plate, &c. &c. , may be expressedby saying, that when the unmarked pole (44. 84. ) is beneath the edge of theplate, and the latter revolves horizontally, screw-fashion, the electricitywhich can be collected at the edge of the plate nearest to the pole ispositive. As the pole of the earth may mentally be considered the unmarkedpole, this relation of the rotation, the pole, and the electricity evolved, is not difficult to remember. Or if, in fig. 15, the circle represent thecopper disc revolving in the direction of the arrows, and _a_ the outlineof the unmarked pole placed beneath the plate, then the electricitycollected at _b_ and the neighbouring parts is positive, whilst thatcollected at the centre _c_ and other parts is negative (88. ). The currentsin the plate are therefore from the centre by the magnetic poles towardsthe circumference. 

100. If the marked pole be placed above, all other things remaining thesame, the electricity at _b_, fig. 15, is still positive. If the markedpole be placed below, or the unmarked pole above, the electricity isreversed. If the direction of revolution in any case is reversed, theelectricity is also reversed. 

101. It is now evident that the rotating plate is merely another form ofthe simpler experiment of passing a piece of metal between the magneticpoles in a rectilinear direction, and that in such cases currents ofelectricity are produced at right angles to the direction of the motion, and crossing it at the place of the magnetic pole or poles. This wassufficiently shown by the following simple experiment: A piece of copperplate one fifth of an inch thick, one inch and a half wide, and twelveinches long, being amalgamated at the edges, was placed between themagnetic poles, whilst the two conductors from the galvanometer were heldin contact with its edges; it was then drawn through between the poles ofthe conductors in the direction of the arrow, fig. 16; immediately thegalvanometer needle was deflected, its north or marked end passed eastward, indicating that the wire A received negative and the wire B positiveelectricity; and as the marked pole was above, the result is in perfectaccordance with the effect obtained by the rotatory plate (99. ). 

102. On reversing the motion of the plate, the needle at the galvanometerwas deflected in the opposite direction, showing an opposite current. 

103. To render evident the character of the electrical current existing invarious parts of the moving copper plate, differing in their relation tothe inducing poles, one collector (86. ) only was applied at the part to beexamined near to the pole, the other being connected with the end of theplate as the most neutral place: the results are given at fig. 17-20, themarked pole being above the plate. In fig. 17, B received positiveelectricity; but the plate moving in the same direction, it received on theopposite side, fig. 18, negative electricity: reversing the motion of thelatter, as in fig. 20, B received positive electricity; or reversing themotion of the first arrangement, that of fig. 17 to fig. 19, B receivednegative electricity. 

104. When the plates were previously removed sideways from between themagnets, as in fig. 21, so as to be quite out of the polar axis, still thesame effects were produced, though not so strongly. 

105. When the magnetic poles were in contact, and the copper plate wasdrawn between the conductors near to the place, there was but very littleeffect produced. When the poles were opened by the width of a card, theeffect was somewhat more, but still very small. 

106. When an amalgamated copper wire, one eighth of an inch thick, wasdrawn through between the conductors and poles (101. ), it produced a veryconsiderable effect, though not so much as the plates. 

107. If the conductors were held permanently against any particular partsof the copper plates, and carried between the magnetic poles with them, effects the same as those described were produced, in accordance with theresults obtained with the revolving disc (94. ). 

108. On the conductors being held against the ends of the plates, and thelatter then passed between the magnetic poles, in a direction transverse totheir length, the same effects were produced (fig. 22. ). The parts of theplates towards the end may be considered either as mere conductors, or asportions of metal in which the electrical current is excited, according totheir distance and the strength of the magnet; but the results were inperfect harmony with those before obtained. The effect was as strong aswhen the conductors were held against the sides of the plate (101. ). 

109. When a mere wire, connected with the galvanometer so as to form acomplete circuit, was passed through between the poles, the galvanometerwas affected; and upon moving the wire to and fro, so as to make thealternate impulses produced correspond with the vibrations of the needle, the latter could be increased to 20° or 30° on each side the magneticmeridian. 

110. Upon connecting the ends of a plate of metal with the galvanometerwires, and then carrying it between the poles from end to end (as in fig. 23. ), in either direction, no effect whatever was produced upon thegalvanometer. But the moment the motion became transverse, the needle wasdeflected. 

111. These effects were also obtained from _electro-magnetic poles_, resulting from the use of copper helices or spirals, either alone or withiron cores (34. 54. ). The directions of the motions were precisely thesame; but the action was much greater when the iron cores were used, thanwithout. 

112. When a flat spiral was passed through edgewise between the poles, acurious action at the galvanometer resulted; the needle first went stronglyone way, but then suddenly stopped, as if it struck against some solidobstacle, and immediately returned. If the spiral were passed through fromabove downwards, or from below upwards, still the motion of the needle wasin the same direction, then suddenly stopped, and then was reversed. But onturning the spiral half-way round, i. E. Edge for edge, then the directionsof the motions were reversed, but still were suddenly interrupted andinverted as before. This double action depends upon the halves of thespiral (divided by a line passing through its centre perpendicular to thedirection of its motion) acting in opposite directions; and the reason whythe needle went to the same side, whether the spiral passed by the poles inthe one or the other direction, was the circumstance, that upon changingthe motion, the direction of the wires in the approaching half of thespiral was changed also. The effects, curious as they appear whenwitnessed, are immediately referable to the action of single wires (40. 109. ). 

113. Although the experiments with the revolving plate, wires, and platesof metal, were first successfully made with the large magnet belonging tothe Royal Society, yet they were all ultimately repeated with a couple ofbar magnets two feet long, one inch and a half wide, and half an inchthick; and, by rendering the galvanometer (87. ) a little more delicate, with the most striking results. Ferro-electro-magnets, as those of Moll, Henry, &c. (57. ), are very powerful. It is very essential, when makingexperiments on different substances, that thermo-electric effects (producedby contact of the fingers, &c. ) be avoided, or at least appreciated andaccounted for; they are easily distinguished by their permanency, and theirindependence of the magnets, or of the direction of the motion. 

114. The relation which holds between the magnetic pole, the moving wire ormetal, and the direction of the current evolved, i. E. _the law_ whichgoverns the evolution of electricity by magneto-electric induction, is verysimple, although rather difficult to express. If in fig. 24, PN represent ahorizontal wire passing by a marked magnetic pole, so that the direction ofits motion shall coincide with the curved line proceeding from belowupwards; or if its motion parallel to itself be in a line tangential to thecurved line, but in the general direction of the arrows; or if it pass thepole in other directions, but so as to cut the magnetic curves[A] in thesame general direction, or on the same side as they would be cut by thewire if moving along the dotted curved line;--then the current ofelectricity in the wire is from P to N. If it be carried in the reversedirections, the electric current will be from N to P. Or if the wire be inthe vertical position, figured P' N', and it be carried in similardirections, coinciding with the dotted horizontal curve so far, as to cutthe magnetic curves on the same side with it, the current will be from P'to N'. If the wire be considered a tangent to the curved surface of thecylindrical magnet, and it be carried round that surface into any otherposition, or if the magnet itself be revolved on its axis, so as to bringany part opposite to the tangential wire, --still, if afterwards the wire bemoved in the directions indicated, the current of electricity will be fromP to N; or if it be moved in the opposite direction, from N to P; so thatas regards the motions of the wire past the pole, they may be reduced totwo, directly opposite to each other, one of which produces a current fromP to N, and the other from N to P. 

 [A] By magnetic curves, I mean the lines of magnetic forces, however modified by the juxtaposition of poles, which would be depicted by iron filings; or those to which a very small magnetic needle would form a tangent. 

115. The same holds true of the unmarked pole of the magnet, except that ifit be substituted for the one in the figure, then, as the wires are movedin the direction of the arrows, the current of electricity would be from Nto P, and when they move in the reverse direction, from P to N. 

116. Hence the current of electricity which is excited in metal when movingin the neighbourhood of a magnet, depends for its direction altogether uponthe relation of the metal to the resultant of magnetic action, or to themagnetic curves, and may be expressed in a popular way thus; Let AB (fig. 25. ) represent a cylinder magnet, A being the marked pole, and B theunmarked pole; let PN be a silver knife-blade, resting across the magnetwith its edge upward, and with its marked or notched side towards the poleA; then in whatever direction or position this knife be moved edgeforemost, either about the marked or the unmarked pole, the current ofelectricity produced will be from P to N, provided the intersected curvesproceeding from A abut upon the notched surface of the knife, and thosefrom B upon the unnotched side. Or if the knife be moved with its backforemost, the current will be from N to P in every possible position anddirection, provided the intersected curves abut on the same surfaces asbefore. A little model is easily constructed, by using a cylinder of woodfor a magnet, a flat piece for the blade, and a piece of thread connectingone end of the cylinder with the other, and passing through a hole in theblade, for the magnetic curves: this readily gives the result of anypossible direction. 

117. When the wire under induction is passing by an electromagnetic pole, as for instance one end of a copper helix traversed by the electric current(34. ), the direction of the current in the approaching wire is the samewith that of the current in the parts or sides of the spirals nearest toit, and in the receding wire the reverse of that in the parts nearest toit. 

118. All these results show that the power of inducing electric currents iscircumferentially exerted by a magnetic resultant or axis of power, just ascircumferential magnetism is dependent upon and is exhibited by an electriccurrent. 

119. The experiments described combine to prove that when a piece of metal(and the same may be true of all conducting matter (213. ) ) is passedeither before a single pole, or between the opposite poles of a magnet, ornear electro-magnetic poles, whether ferruginous or not, electricalcurrents are produced across the metal transverse to the direction ofmotion; and which therefore, in Arago's experiments, will approximatetowards the direction of radii. If a single wire be moved like the spoke ofa wheel near a magnetic pole, a current of electricity is determinedthrough it from one end towards the other. If a wheel be imagined, constructed of a great number of these radii, and this revolved near thepole, in the manner of the copper disc (85. ), each radius will have acurrent produced in it as it passes by the pole. If the radii be supposedto be in contact laterally, a copper disc results, in which the directionsof the currents will be generally the same, being modified only by thecoaction which can take place between the particles, now that they are inmetallic contact. 

120. Now that the existence of these currents is known, Arago's phenomenamay be accounted for without considering them as due to the formation inthe copper, of a pole of the opposite kind to that approximated, surroundedby a diffuse polarity of the same kind (82. ); neither is it essential thatthe plate should acquire and lose its state in a finite time; nor on theother hand does it seem necessary that any repulsive force should beadmitted as the cause of the rotation (82. ). 

121. The effect is precisely of the same kind as the electromagneticrotations which I had the good fortune to discover some years ago[A]. According to the experiments then made which have since been abundantlyconfirmed, if a wire (PN fig. 26. ) be connected with the positive andnegative ends of a voltaic buttery, so that the positive electricity shallpass from P to N, and a marked magnetic pole N be placed near the wirebetween it and the spectator, the pole will move in a direction tangentialto the wire, i. E. Towards the right, and the wire will move tangentiallytowards the left, according to the directions of the arrows. This isexactly what takes place in the rotation of a plate beneath a magneticpole; for let N (fig. 27. ) be a marked pole above the circular plate, thelatter being rotated in the direction of the arrow: immediately currents ofpositive electricity set from the central parts in the general direction ofthe radii by the pole to the parts of the circumference _a_ on the otherside of that pole (99. 119. ), and are therefore exactly in the samerelation to it as the current in the wire (PN, fig. 26. ), and therefore thepole in the same manner moves to the right hand. 

 [A] Quarterly Journal of Science, vol. Xii. Pp. 74. 186. 416. 283. 

122. If the rotation of the disc be reversed, the electric currents arereversed (91. ), and the pole therefore moves to the left hand. If thecontrary pole be employed, the effects are the same, i. E. In the samedirection, because currents of electricity, the reverse of those described, are produced, and by reversing both poles and currents, the visible effectsremain unchanged. In whatever position the axis of the magnet be placed, provided the same pole be applied to the same side of the plate, theelectric current produced is in the same direction, in consistency with thelaw already stated (114, &c. ); and thus every circumstance regarding thedirection of the motion may be explained. 

123. These currents are _discharged or return_ in the parts of the plate oneach side of and more distant from the place of the pole, where, of course, the magnetic induction is weaker; and when the collectors are applied, anda current of electricity is carried away to the galvanometer (88. ), thedeflection there is merely a repetition, by the same current or part of it, of the effect of rotation in the magnet over the plate itself. 

124. It is under the point of view just put forth that I have ventured tosay it is not necessary that the plate should acquire and lose its state ina finite time (120. ); for if it were possible for the current to be fullydeveloped the instant _before_ it arrived at its state of nearestapproximation to the vertical pole of the magnet, instead of opposite to ora little beyond it, still the relative motion of the pole and plate wouldbe the same, the resulting force being in fact tangential instead ofdirect. 

125. But it is possible (though not necessary for the rotation) that _time_may be required for the development of the maximum current in the plate, inwhich case the resultant of all the forces would be in advance of themagnet when the plate is rotated, or in the rear of the magnet when thelatter is rotated, and many of the effects with pure electro-magnetic polestend to prove this is the case. Then, the tangential force may be resolvedinto two others, one parallel to the plane of rotation, and the otherperpendicular to it; the former would be the force exerted in making theplate revolve with the magnet, or the magnet with the plate; the latterwould be a repulsive force, and is probably that, the effects of which M. Arago has also discovered (82. ). 

126. The extraordinary circumstance accompanying this action, which hasseemed so inexplicable, namely, the cessation of all phenomena when themagnet and metal are brought to rest, now receives a full explanation(82. ); for then the electrical currents which cause the motion ceasealtogether. 

127. All the effects of solution of metallic continuity, and the consequentdiminution of power described by Messrs. Babbage and Herschel[A], nowreceive their natural explanation, as well also as the resumption of powerwhen the cuts were filled up by metallic substances, which, thoughconductors of electricity, were themselves very deficient in the power ofinfluencing magnets. And new modes of cutting the plate may be devised, which shall almost entirely destroy its power. Thus, if a copper plate(81. ) be cut through at about a fifth or sixth of its diameter from theedge, so as to separate a ring from it, and this ring be again fastened on, but with a thickness of paper intervening (fig. 29. ), and if Arago'sexperiment be made with this compound plate so adjusted that the sectionshall continually travel opposite the pole, it is evident that the magneticcurrents will be greatly interfered with, and the plate probably lose muchof its effect[B]. 

 [A] Philosophical Transactions, 1825, p. 481. 

 [B] This experiment has actually been made by Mr. Christie, with the results here described, and is recorded in the Philosophical Transactions for 1827, p. 82. 

An elementary result of this kind was obtained by using two pieces of thickcopper, shaped as in fig. 28. When the two neighbouring edges wereamalgamated and put together, and the arrangement passed between the polesof the magnet, in the direction parallel to these edges, a current wasurged through the wires attached to the outer angles, and the galvanometerbecame strongly affected; but when a single film of paper was interposed, and the experiment repeated, no sensible effect could be produced. 

128. A section of this kind could not interfere much with the induction ofmagnetism, supposed to be of the nature ordinarily received by iron. 

129. The effect of rotation or deflection of the needle, which M. Aragoobtained by ordinary magnets, M. Ampère succeeded in procuring byelectro-magnets. This is perfectly in harmony with the results relative tovolta-electric and magneto-electric induction described in this paper. Andby using flat spirals of copper wire, through which electric currents weresent, in place of ordinary magnetic poles (Ill. ), sometimes applying asingle one to one side of the rotating plate, and sometimes two to oppositesides, I obtained the induced currents of electricity from the plateitself, and could lead them away to, and ascertain their existence by, thegalvanometer. 

130. The cause which has now been assigned for the rotation in Arago'sexperiment, namely, the production of electrical currents, seems abundantlysufficient in all cases where the metals, or perhaps even other conductors, are concerned; but with regard to such bodies as glass, resins, and, aboveall, gases, it seems impossible that currents of electricity, capable ofproducing these effects, should be generated in them. Yet Arago found thatthe effects in question were produced by these and by all bodies tried(81. ). Messrs. Babbage and Herschel, it is true, did not observe them withany substance not metallic, except carbon, in a highly conducting state(82. ). Mr. Harris has ascertained their occurrence with wood, marble, freestone and annealed glass, but obtained no effect with sulphuric acidand saturated solution of sulphate of iron, although these are betterconductors of electricity than the former substances. 

131. Future investigations will no doubt explain these difficulties, anddecide the point whether the retarding or dragging action spoken of isalways simultaneous with electric currents. [A] The existence of the actionin metals, only whilst the currents exist, i. E. Whilst motion is given (82. 88. ), and the explication of the repulsive action observed by M. Arago (82. 125. ), are powerful reasons for referring it to this cause; but it may becombined with others which occasionally act alone. 

 [A] Experiments which I have since made convince me that this particular action is always due to the electrical currents formed; and they supply a test by which it may be distinguished from the action of ordinary magnetism, or any other cause, including those which are mechanical or irregular, producing similar effects (254. )

132. Copper, iron, tin, zinc, lead, mercury, and all the metals tried, produced electrical currents when passed between the magnetic poles: themercury was put into a glass tube for the purpose. The dense carbondeposited in coal gas retorts, also produced the current, but ordinarycharcoal did not. Neither could I obtain any sensible effects with brine, sulphuric acid, saline solutions, &c. , whether rotated in basins, orinclosed in tubes and passed between the poles. 

133. I have never been able to produce any sensation upon the tongue by thewires connected with the conductors applied to the edges of the revolvingplate (88. ) or slips of metal (101. ). Nor have I been able to heat a fineplatina wire, or produce a spark, or convulse the limbs of a frog. I havefailed also to produce any chemical effects by electricity thus evolved(22. 56). 

134. As the electric current in the revolving copper plate occupies but asmall space, proceeding by the poles and being discharged right and left atvery small distances comparatively (123. ); and as it exists in a thick massof metal possessing almost the highest conducting power of any, andconsequently offering extraordinary facility for its production anddischarge; and as, notwithstanding this, considerable currents may be drawnoff which can pass through narrow wires, forty, fifty, sixty, or even onehundred feet long; it is evident that the current existing in the plateitself must be a very powerful one, when the rotation is rapid and themagnet strong. This is also abundantly proved by the obedience andreadiness with which a magnet ten or twelve pounds in weight follows themotion of the plate and will strongly twist up the cord by which it issuspended. 

135. Two rough trials were made with the intention of constructing_magneto-electric machines_. In one, a ring one inch and a half broad andtwelve inches external diameter, cut from a thick copper plate, was mountedso as to revolve between the poles of the magnet and represent a platesimilar to those formerly used (101. ), but of interminable length; theinner and outer edges were amalgamated, and the conductors applied one toeach edge, at the place of the magnetic poles. The current of electricityevolved did not appear by the galvanometer to be stronger, if so strong, asthat from the circular plate (88. ). 

136. In the other, small thick discs of copper or other metal, half an inchin diameter, were revolved rapidly near to the poles, but with the axis ofrotation out of the polar axis; the electricity evolved was collected byconductors applied as before to the edges (86. ). Currents were procured, but of strength much inferior to that produced by the circular plate. 

137. The latter experiment is analogous to those made by Mr. Barlow with arotating iron shell, subject to the influence of the earth[A]. The effectsobtained by him have been referred by Messrs. Babbage and Herschel to thesame cause as that considered as influential in Arago's experiment[B]; butit would be interesting to know how far the electric current which might beproduced in the experiment would account for the deflexion of the needle. The mere inversion of a copper wire six or seven times near the poles ofthe magnet, and isochronously with the vibrations of the galvanometerneedle connected with it, was sufficient to make the needle vibrate throughan arc of 60° or 70°. The rotation of a copper shell would perhaps decidethe point, and might even throw light upon the more permanent, thoughsomewhat analogous effects obtained by Mr. Christie. 

 [A] Philosophical Transactions, 1825. P. 317. 

 [B] Ibid. 1825. P. 485. 

138. The remark which has already been made respecting iron (66. ), and theindependence of the ordinary magnetical phenomena of that substance and thephenomena now described of magneto-electric induction in that and othermetals, was fully confirmed by many results of the kind detailed in thissection. When an iron plate similar to the copper one formerly described(101. ) was passed between the magnetic poles, it gave a current ofelectricity like the copper plate, but decidedly of less power; and in theexperiments upon the induction of electric currents (9. ), no difference inthe kind of action between iron and other metals could be perceived. Thepower therefore of an iron plate to drag a magnet after it, or to interceptmagnetic action, should be carefully distinguished from the similar powerof such metals as silver, copper, &c. &c. , inasmuch as in the iron by farthe greater part of the effect is due to what may be called ordinarymagnetic action. There can be no doubt that the cause assigned by Messrs. Babbage and Herschel in explication of Arago's phenomena is the true one, when iron is the metal used. 

139. The very feeble powers which were found by those philosophers tobelong to bismuth and antimony, when moving, of affecting the suspendedmagnet, and which has been confirmed by Mr. Harris, seem at firstdisproportionate to their conducting powers; whether it be so or not mustbe decided by future experiment (73. )[A]. These metals are highlycrystalline, and probably conduct electricity with different degrees offacility in different directions; and it is not unlikely that where a massis made up of a number of crystals heterogeneously associated, an effectapproaching to that of actual division may occur (127. ); or the currents ofelectricity may become more suddenly deflected at the confines of similarcrystalline arrangements, and so be more readily and completely dischargedwithin the mass. 

 [A] I have since been able to explain these differences, and prove, with several metals, that the effect is in the order of the conducting power; for I have been able to obtain, by magneto-electric induction, currents of electricity which are proportionate in strength to the conducting power of the bodies experimented with (211. ). 

§. _Royal Institution, November 1831. _

_Note. _--In consequence of the long period which has intervened between thereading and printing of the foregoing paper, accounts of the experimentshave been dispersed, and, through a letter of my own to M. Hachette, havereached France and Italy. That letter was translated (with some errors), and read to the Academy of Sciences at Paris, 26th December, 1831. A copyof it in _Le Temps_ of the 28th December quickly reached Signor Nobili, who, with Signor Antinori, immediately experimented upon the subject, andobtained many of the results mentioned in my letter; others they could notobtain or understand, because of the brevity of my account. These resultsby Signori Nobili and Antinori have been embodied in a paper dated 31stJanuary 1832, and printed and published in the number of the _Antologia_dated November 1831 (according at least to the copy of the paper kindlysent me by Signor Nobili). It is evident the work could not have been thenprinted; and though Signor Nobili, in his paper, has inserted my letter asthe text of his experiments, yet the circumstance of back date has causedmany here, who have heard of Nobili's experiments by report only, toimagine his results were anterior to, instead of being dependent upon, mine. 

I may be allowed under these circumstances to remark, that I experimentedon this subject several years ago, and have published results. (SeeQuarterly Journal of Science for July 1825, p. 338. ) The following also isan extract from my note-book, dated November 28, 1825: "Experiments oninduction by connecting wire of voltaic battery:--a battery of fourtroughs, ten pairs of plates, each arranged side by side--the polesconnected by a wire about four feet long, parallel to which was anothersimilar wire separated from it only by two thicknesses of paper, the endsof the latter were attached to a galvanometer:--exhibited no action, &c. &c. &c. --Could not in any way render any induction evident from theconnecting wire. " The cause of failure at that time is now evident(79. ). --M. F. April, 1832. 

SECOND SERIES. 

THE BAKERIAN LECTURE. 

§ 5. _Terrestrial Magneto-electric Induction. _ § 6. _Force and Direction ofMagneto-electric Induction generally. _

Read January 12, 1832. 

§ 5. _Terrestrial Magneto-electric Induction. _

140. When the general facts described in the former paper were discovered, and the _law_ of magneto-electric induction relative to direction wasascertained (114. ), it was not difficult to perceive that the earth wouldproduce the same effect as a magnet, and to an extent that would, perhaps, render it available in the construction of new electrical machines. Thefollowing are some of the results obtained in pursuance of this view. 

141. The hollow helix already described (6. ) was connected with agalvanometer by wires eight feet long; and the soft iron cylinder (34. )after being heated red-hot and slowly cooled, to remove all traces ofmagnetism, was put into the helix so as to project equally at both ends, and fixed there. The combined helix and bar were held in the magneticdirection or line of dip, and (the galvanometer needle being motionless)were then inverted, so that the lower end should become the upper, but thewhole still correspond to the magnetic direction; the needle wasimmediately deflected. As the latter returned to its first position, thehelix and bar were again inverted; and by doing this two or three times, making the inversions and vibrations to coincide, the needle swung throughan arc of 150° or 160°. 

142. When one end of the helix, which may be called A, was uppermost atfirst (B end consequently being below), then it mattered not in whichdirection it proceeded during the inversion, whether to the right hand orleft hand, or through any other course; still the galvanometer needlepassed in the same direction. Again, when B end was uppermost, theinversion of the helix and bar in any direction always caused the needle tobe deflected one way; that way being the opposite to the course of thedeflection in the former case. 

143. When the helix with its iron core in any given position was inverted, the effect was as if a magnet with its marked pole downwards had beenintroduced from above into the inverted helix. Thus, if the end B wereupwards, such a magnet introduced from above would make the marked end ofthe galvanometer needle pass west. Or the end B being downwards, and thesoft iron in its place, inversion of the whole produced the same effect. 

144. When the soft iron bar was taken out of the helix and inverted invarious directions within four feet of the galvanometer, not the slightesteffect upon it was produced. 

145. These phenomena are the necessary consequence of the inductivemagnetic power of the earth, rendering the soft iron cylinder a magnet withits marked pole downwards. The experiment is analogous to that in which twobar magnets were used to magnetize the same cylinder in the same helix(36. ), and the inversion of position in the present experiment isequivalent to a change of the poles in that arrangement. But the result isnot less an instance of the evolution of electricity by means of themagnetism of the globe. 

146. The helix alone was then held permanently in the magnetic direction, and the soft iron cylinder afterwards introduced; the galvanometer needlewas instantly deflected; by withdrawing the cylinder as the needlereturned, and continuing the two actions simultaneously, the vibrationssoon extended through an arc of 180°. The effect was precisely the same asthat obtained by using a cylinder magnet with its marked pole downwards;and the direction of motion, &c. Was perfectly in accordance with theresults of former experiments obtained with such a magnet (39. ). A magnetin that position being used, gave the same deflections, but stronger. Whenthe helix was put at right angles to the magnetic direction or dip, thenthe introduction or removal of the soft iron cylinder produced no effect atthe needle. Any inclination to the dip gave results of the same kind asthose already described, but increasing in strength as the helixapproximated to the direction of the dip. 

147. A cylinder magnet, although it has great power of affecting thegalvanometer when moving into or out of the helix, has no power ofcontinuing the deflection (39. ); and therefore, though left in, still themagnetic needle comes to its usual place of rest. But upon repeating (withthe magnet) the experiment of inversion in the direction of the dip (141), the needle was affected as powerfully as before; the disturbance of themagnetism in the steel magnet, by the earth's inductive force upon it, being thus shown to be nearly, if not quite, equal in amount and rapidityto that occurring in soft iron. It is probable that in this waymagneto-electrical arrangements may become very useful in indicating thedisturbance of magnetic forces, where other means will not apply; for it isnot the whole magnetic power which produces the visible effect, but onlythe difference due to the disturbing causes. 

148. These favourable results led me to hope that the directmagneto-electric induction of the earth might be rendered sensible; and Iultimately succeeded in obtaining the effect in several ways. When thehelix just referred to (141. 6. ) was placed in the magnetic dip, butwithout any cylinder of iron or steel, and was then inverted, a feebleaction at the needle was observed. Inverting the helix ten or twelve times, and at such periods that the deflecting forces exerted by the currents ofelectricity produced in it should be added to the momentum of the needle(39. ), the latter was soon made to vibrate through an arc of 80° or 90°. Here, therefore, currents of electricity were produced by the directinductive power of the earth's magnetism, without the use of anyferruginous matter, and upon a metal not capable of exhibiting any of theordinary magnetic phenomena. The experiment in everything represents theeffects produced by bringing the same helix to one or both poles of anypowerful magnet (50. ). 

149. Guided by the law already expressed (114. ), I expected that all theelectric phenomena of the revolving metal plate could now be producedwithout any other magnet than the earth. The plate so often referred to(85. ) was therefore fixed so as to rotate in a horizontal plane. Themagnetic curves of the earth (114. _note_), i. E. The dip, passes throughthis plane at angles of about 70°, which it was expected would be anapproximation to perpendicularity, quite enough to allow ofmagneto-electric induction sufficiently powerful to produce a current ofelectricity. 

150. Upon rotation of the plate, the currents ought, according to the law(114. 121. ), to tend to pass in the direction of the radii, through _all_parts of the plate, either from the centre to the circumference, or fromthe circumference to the centre, as the direction of the rotation of theplate was one way or the other. One of the wires of the galvanometer wastherefore brought in contact with the axis of the plate, and the otherattached to a leaden collector or conductor (86. ), which itself was placedagainst the amalgamated edge of the disc. On rotating the plate there was adistinct effect at the galvanometer needle; on reversing the rotation, theneedle went in the opposite direction; and by making the action of theplate coincide with the vibrations of the needle, the arc through which thelatter passed soon extended to half a circle. 

151. Whatever part of the edge of the plate was touched by the conductor, the electricity was the same, provided the direction of rotation continuedunaltered. 

152. When the plate revolved _screw-fashion_, or as the hands of a watch, the current of electricity (150. ) was from the centre to the circumference;when the direction of rotation was _unscrew_, the current was from thecircumference to the centre. These directions are the same with thoseobtained when the unmarked pole of a magnet was placed beneath therevolving plate (99. ). 

153. When the plate was in the magnetic meridian, or in any other plane_coinciding_ with the magnetic dip, then its rotation produced no effectupon the galvanometer. When inclined to the dip but a few degrees, electricity began to appear upon rotation. Thus when standing upright in aplane perpendicular to the magnetic meridian, and when consequently its ownplane was inclined only about 20° to the dip, revolution of the plateevolved electricity. As the inclination was increased, the electricitybecame more powerful until the angle formed by the plane of the plate withthe dip was 90°, when the electricity for a given velocity of the plate wasa maximum. 

154. It is a striking thing to observe the revolving copper plate becomethus a _new electrical machine_; and curious results arise on comparing itwith the common machine. In the one, the plate is of the bestnon-conducting substance that can be applied; in the other, it is the mostperfect conductor: in the one, insulation is essential; in the other, it isfatal. In comparison of the quantities of electricity produced, the metalmachine does not at all fall below the glass one; for it can produce aconstant current capable of deflecting the galvanometer needle, whereas thelatter cannot. It is quite true that the force of the current thus evolvedhas not as yet been increased so as to render it available in any of ourordinary applications of this power; but there appears every reasonableexpectation that this may hereafter be effected; and probably by severalarrangements. Weak as the current may seem to be, it is as strong as, ifnot stronger than, any thermo-electric current; for it can pass fluids(23. ), agitate the animal system, and in the case of an electro-magnet hasproduced sparks (32. ). 

155. A disc of copper, one fifth of an inch thick and only one inch and ahalf in diameter, was amalgamated at the edge; a square piece of sheet lead(copper would have been better) of equal thickness had a circular hole cutin it, into which the disc loosely fitted; a little mercury completed themetallic communication of the disc and its surrounding ring; the latter wasattached to one of the galvanometer wires, and the other wire dipped into alittle metallic cup containing mercury, fixed upon the top of the copperaxis of the small disc. Upon rotating the disc in a horizontal plane, thegalvanometer needle could be affected, although the earth was the onlymagnet employed, and the radius of the disc but three quarters of an inch;in which space only the current was excited. 

156. On putting the pole of a magnet under the revolving disc, thegalvanometer needle could be permanently deflected. 

157. On using copper wires one sixth of an inch in thickness instead of thesmaller wires (86. ) hitherto constantly employed, far more powerful effectswere obtained. Perhaps if the galvanometer had consisted of fewer turns ofthick wire instead of many convolutions of thinner, more striking effectswould have been produced. 

158. One form of apparatus which I purpose having arranged, is to haveseveral discs superposed; the discs are to be metallically connected, alternately at the edges and at the centres, by means of mercury; and arethen to be revolved alternately in opposite directions, i. E. The first, third, fifth, &c. To the right hand, and the second, fourth, sixth, &c. Tothe left hand; the whole being placed so that the discs are perpendicularto the dip, or intersect most directly the magnetic curves of powerfulmagnets. The electricity will be from the centre to the circumference inone set of discs, and from the circumference to the centre in those on eachside of them; thus the action of the whole will conjoin to produce onecombined and more powerful current. 

159. I have rather, however, been desirous of discovering new facts and newrelations dependent on magneto-electric induction, than of exalting theforce of those already obtained; being assured that the latter would findtheir full development hereafter. 

 * * * * *

160. I referred in my former paper to the probable influence of terrestrialmagneto-electric induction (137. ) in producing, either altogether or inpart, the phenomena observed by Messrs. Christie and Barlow[A], whilstrevolving ferruginous bodies; and especially those observed by the latterwhen rapidly rotating an iron shell, which were by that philosopherreferred to a change in the ordinary disposition of the magnetism of theball. I suggested also that the rotation of a copper globe would probablyinsulate the effects due to electric currents from those due to merederangement of magnetism, and throw light upon the true nature of thephenomena. 

 [A] Christie, Phil. Trans. 1825, pp. 58, 347, &c. Barlow, Phil. Trans. 1825, p. 317. 

161. Upon considering the law already referred to (114. ), it appearedimpossible that a metallic globe could revolve under natural circumstances, without having electric currents produced within it, circulating round therevolving globe in a plane at right angles to the plane of revolution, provided its axis of rotation did not coincide with the dip; and itappeared that the current would be most powerful when the axis ofrevolution was perpendicular to the dip of the needle: for then all thoseparts of the ball below a plane passing through its centre andperpendicular to the dip, would in moving cut the magnetic curves in onedirection, whilst all those parts above that plane would intersect them inthe other direction: currents therefore would exist in these moving parts, proceeding from one pole of rotation to the other; but the currents abovewould be in the reverse direction to those below, and in conjunction withthem would produce a continued circulation of electricity. 

162. As the electric currents are nowhere interrupted in the ball, powerfuleffects were expected, and I endeavoured to obtain them with simpleapparatus. The ball I used was of brass; it had belonged to an oldelectrical machine, was hollow, thin (too thin), and four inches indiameter; a brass wire was screwed into it, and the ball either turned inthe hand by the wire, or sometimes, to render it more steady, supported byits wire in a notched piece of wood, and motion again given by the hand. The ball gave no signs of magnetism when at rest. 

163. A compound magnetic needle was used to detect the currents. It wasarranged thus: a sewing-needle had the head and point broken off, and wasthen magnetised; being broken in halves, the two magnets thus produced werefixed on a stem of dried grass, so as to be perpendicular to it, and aboutfour inches asunder; they were both in one plane, but their similar polesin contrary directions. The grass was attached to a piece of unspun silkabout six inches long, the latter to a stick passing through a cork in themouth of a cylindrical jar; and thus a compound arrangement was obtained, perfectly sheltered from the motion of the air, but little influenced bythe magnetism of the earth, and yet highly sensible to magnetic andelectric forces, when the latter were brought into the vicinity of the oneor the other needle. 

164. Upon adjusting the needles to the plane of the magnetic meridian;arranging the ball on the outside of the glass jar to the west of theneedles, and at such a height that its centre should correspondhorizontally with the upper needle, whilst its axis was in the plane of themagnetic meridian, but perpendicular to the dip; and then rotating theball, the needle was immediately affected. Upon inverting the direction ofrotation, the needle was again affected, but in the opposite direction. When the ball revolved from east over to west, the marked pole wenteastward; when the ball revolved in the opposite direction, the marked polewent westward or towards the ball. Upon placing the ball to the east of theneedles, still the needle was deflected in the same way; i. E. When the ballrevolved from east over to west, the marked pole wont eastward (or towardsthe ball); when the rotation was in the opposite direction, the marked polewent westward. 

165. By twisting the silk of the needles, the latter were brought into aposition perpendicular to the plane of the magnetic meridian; the ball wasagain revolved, with its axis parallel to the needles; the upper wasaffected as before, and the deflection was such as to show that both hereand in the former case the needle was influenced solely by currents ofelectricity existing in the brass globe. 

166. If the upper part of the revolving ball be considered as a wire movingfrom east to west, over the unmarked pole of the earth, the current ofelectricity in it should be from north to south (99. 114. 150. ); if theunder part be considered as a similar wire, moving from west to east overthe same pole, the electric current should be from south to north; and thecirculation of electricity should therefore be from north above to south, and below back to north, in a metal ball revolving from east above to westin these latitudes. Now these currents are exactly those required to givethe directions of the needle in the experiments just described; so that thecoincidence of the theory from which the experiments were deduced with theexperiments themselves, is perfect. 

167. Upon inclining the axis of rotation considerably, the revolving ballwas still found to affect the magnetic needle; and it was not until theangle which it formed with the magnetic dip was rendered small, that itseffects, even upon this apparatus, were lost (153. ). When revolving withits axis parallel to the dip, it is evident that the globe becomesanalogous to the copper plate; electricity of one kind might be collectedat its equator, and of the other kind at its poles. 

168. A current in the ball, such as that described above (161. ), althoughit ought to deflect a needle the same way whether it be to the right or theleft of the ball and of the axis of rotation, ought to deflect it thecontrary way when above or below the ball; for then the needle is, or oughtto be, acted upon in a contrary direction by the current. This expectationwas fulfilled by revolving the ball beneath the magnetic needle, the latterbeing still inclosed in its jar. When the ball was revolved from east overto west, the marked pole of the needle, instead of passing eastward, wentwestward; and when revolved from west over to east, the marked pole wenteastward. 

169. The deflections of the magnetic needle thus obtained with a brass ballare exactly in the same direction as those observed by Mr. Barlow in therevolution of the iron shell; and from the manner in which iron exhibitsthe phenomena of magneto-electric induction like any other metal, anddistinct from its peculiar magnetic phenomena (132. ), it is impossible butthat electric currents must have been excited, and become active in thoseexperiments. What proportion of the whole effect obtained is due to thiscause, must be decided by a more elaborate investigation of all thephenomena. 

170. These results, in conjunction with the general law before stated(114. ), suggested an experiment of extreme simplicity, which yet, on trial, was found to answer perfectly. The exclusion of all extraneouscircumstances and complexity of arrangement, and the distinct character ofthe indications afforded, render this single experiment an epitome ofnearly all the facts of magneto-electric induction. 

171. A piece of common copper wire, about eight feet long and one twentiethof an inch in thickness, had one of its ends fastened to one of theterminations of the galvanometer wire, and the other end to the othertermination; thus it formed an endless continuation of the galvanometerwire: it was then roughly adjusted into the shape of a rectangle, or ratherof a loop, the upper part of which could be carried to and fro over thegalvanometer, whilst the lower part, and the galvanometer attached to it, remained steady (Plate II. Fig. 30. ). Upon moving this loop over thegalvanometer from right to left, the magnetic needle was immediatelydeflected; upon passing the loop back again, the needle passed in thecontrary direction to what it did before; upon repeating these motions ofthe loop in accordance with the vibrations of the needle (39. ), the lattersoon swung through 90° or more. 

172. The relation of the current of electricity produced in the wire, toits motion, may be understood by supposing the convolutions at thegalvanometer away, and the wire arranged as a rectangle, with its loweredge horizontal and in the plane of the magnetic meridian, and a magneticneedle suspended above and over the middle part of this edge, and directedby the earth (fig. 30. ). On passing the upper part of the rectangle fromwest to east into the position represented by the dotted line, the markedpole of the magnetic needle went west; the electric current was thereforefrom north to south in the part of the wire passing under the needle, andfrom south to north in the moving or upper part of the parallelogram. Onpassing the upper part of the rectangle from east to west over thegalvanometer, the marked pole of the needle went east, and the current ofelectricity was therefore the reverse of the former. 

173. When the rectangle was arranged in a plane east and west, and themagnetic needle made parallel to it, either by the torsion of itssuspension thread or the action of a magnet, still the general effects werethe same. On moving the upper part of the rectangle from north to south, the marked pole of the needle went north; when the wire was moved in theopposite direction, the marked pole went south. The same effect took placewhen the motion of the wire was in any other azimuth of the line of dip;the direction of the current always being conformable to the law formerlyexpressed (114. ), and also to the directions obtained with the rotatingball (101. ). 

174. In these experiments it is not necessary to move the galvanometer orneedle from its first position. It is quite sufficient if the wire of therectangle is distorted where it leaves the instrument, and bent so as toallow the moving upper part to travel in the desired direction. 

175. The moveable part of the wire was then arranged _below_ thegalvanometer, but so as to be carried across the dip. It affected theinstrument as before, and in the same direction; i. E. When carried fromwest to east under the instrument, the marked end of the needle went west, as before. This should, of course, be the case; for when the wire iscutting the magnetic dip in a certain direction, an electric current alsoin a certain direction should be induced in it. 

176. If in fig. 31 _dp_ be parallel to the dip, and BA be considered as theupper part of the rectangle (171. ), with an arrow _c_ attached to it, boththese being retained in a plane perpendicular to the dip, --then, however BAwith its attached arrow is moved upon _dp_ as an axis, if it afterwardsproceed in the direction of the arrow, a current of electricity will movealong it from B towards A. 

177. When the moving part of the wire was carried up or down parallel tothe dip, no effect was produced on the galvanometer. When the direction ofmotion was a little inclined to the dip, electricity manifested itself; andwas at a maximum when the motion was perpendicular to the magneticdirection. 

178. When the wire was bent into other forms and moved, equally strongeffects were obtained, especially when instead of a rectangle a doublecatenarian curve was formed of it on one side of the galvanometer, and thetwo single curves or halves were swung in opposite directions at the sametime; their action then combined to affect the galvanometer: but all theresults were reducible to those above described. 

179. The longer the extent of the moving wire, and the greater the spacethrough which it moves, the greater is the effect upon the galvanometer. 

180. The facility with which electric currents are produced in metals whenmoving under the influence of magnets, suggests that henceforth precautionsshould always be taken, in experiments upon metals and magnets, to guardagainst such effects. Considering the universality of the magneticinfluence of the earth, it is a consequence which appears veryextraordinary to the mind, that scarcely any piece of metal can be moved incontact with others, either at rest, or in motion with different velocitiesor in varying directions, without an electric current existing within them. It is probable that amongst arrangements of steam-engines and metalmachinery, some curious accidental magneto-electric combinations may befound, producing effects which have never been observed, or, if noticed, have never as yet been understood. 

 * * * * *

181. Upon considering the effects of terrestrial magneto-electric inductionwhich have now been described, it is almost impossible to resist theimpression that similar effects, but infinitely greater in force, may beproduced by the action of the globe, as a magnet, upon its own mass, inconsequence of its diurnal rotation. It would seem that if a bar of metalbe laid in these latitudes on the surface of the earth parallel to themagnetic meridian, a current of electricity tends to pass through it fromsouth to north, in consequence of the travelling of the bar from west toeast (172. ), by the rotation of the earth; that if another bar in the samedirection be connected with the first by wires, it cannot discharge thecurrent of the first, because it has an equal tendency to have a current inthe same direction induced within itself: but that if the latter be carriedfrom east to west, which is equivalent to a diminution of the motioncommunicated to it from the earth (172. ), then the electric current fromsouth to north is rendered evident in the first bar, in consequence of itsdischarge, at the same time, by means of the second. 

182. Upon the supposition that the rotation of the earth tended, bymagneto-electric induction, to cause currents in its own mass, these would, according to the law (114. ) and the experiments, be, upon the surface atleast, from the parts in the neighbourhood of or towards the plane of theequator, in opposite directions to the poles; and if collectors could beapplied at the equator and at the poles of the globe, as has been done withthe revolving copper plate (150. ), and also with magnets (220. ), thennegative electricity would be collected at the equator, and positiveelectricity at both poles (222. ). But without the conductors, or somethingequivalent to them, it is evident these currents could not exist, as theycould not be discharged. 

183. I did not think it impossible that some natural difference might occurbetween bodies, relative to the intensity of the current produced ortending to be produced in them by magneto-electric induction, which mightbe shown by opposing them to each other; especially as Messrs. Arago, Babbage, Herschel, and Harris, have all found great differences, not onlybetween the metals and other substances, but between the metals themselves, in their power of receiving motion from or giving it to a magnet in trialsby revolution (130. ). I therefore took two wires, each one hundred andtwenty feet long, one of iron and the other of copper. These were connectedwith each other at their ends, and then extended in the direction of themagnetic meridian, so as to form two nearly parallel lines, nowhere incontact except at the extremities. The copper wire was then divided in themiddle, and examined by a delicate galvanometer, but no evidence of anelectrical current was obtained. 

184. By favour of His Royal Highness the President of the Society, Iobtained the permission of His Majesty to make experiments at the lake inthe gardens of Kensington-palace, for the purpose of comparing, in asimilar manner, water and metal. The basin of this lake is artificial; thewater is supplied by the Chelsea Company; no springs run into it, and itpresented what I required, namely, a uniform mass of still pure water, withbanks ranging nearly from east to west, and from north to south. 

185. Two perfectly clean bright copper plates, each exposing four squarefeet of surface, were soldered to the extremities of a copper wire; theplates were immersed in the water, north and south of each other, the wirewhich connected them being arranged upon the grass of the bank. The plateswere about four hundred and eighty feet from each other, in a right line;the wire was probably six hundred feet long. This wire was then divided inthe middle, and connected by two cups of mercury with a delicategalvanometer. 

186. At first, indications of electric currents were obtained; but whenthese were tested by inverting the direction of contact, and in other ways, they were found to be due to other causes than the one sought for. A littledifference in temperature; a minute portion of the nitrate of mercury usedto amalgamate the wires, entering into the water employed to reduce the twocups of mercury to the same temperature; was sufficient to produce currentsof electricity, which affected the galvanometer, notwithstanding they hadto pass through nearly five hundred feet of water. When these and otherinterfering causes were guarded against, no effect was obtained; and itappeared that even such dissimilar substances as water and copper, whencutting the magnetic curves of the earth with equal velocity, perfectlyneutralized each other's action. 

187. Mr. Fox of Falmouth has obtained some highly important resultsrespecting the electricity of metalliferous veins in the mines of Cornwall, which have been published in the Philosophical Transactions[A]. I haveexamined the paper with a view to ascertain whether any of the effects wereprobably referable to magneto-electric induction; but, though unable toform a very strong opinion, believe they are not. When parallel veinsrunning east and west were compared, the general tendency of theelectricity _in the wires_ was from north to south; when the comparison wasmade between parts towards the surface and at some depth, the current ofelectricity in the wires was from above downwards. If there should be anynatural difference in the force of the electric currents produced bymagneto-electric induction in different substances, or substances indifferent positions moving with the earth, and which might be renderedevident by increasing the masses acted upon, then the wires and veinsexperimented with by Mr. Fox might perhaps have acted as dischargers to theelectricity of the mass of strata included between them, and the directionsof the currents would agree with those observed as above. 

 [A] 1830. P. 399. 

188. Although the electricity obtained by magneto-electric induction in afew feet of wire is of but small intensity, and has not yet been observedexcept in metals, and carbon in a particular state, still it has power topass through brine (23. ); and, as increased length in the substance actedupon produces increase of intensity, I hoped to obtain effects fromextensive moving masses of water, though quiescent water gave none. I madeexperiments therefore (by favour) at Waterloo Bridge, extending a copperwire nine hundred and sixty feet in length upon the parapet of the bridge, and dropping from its extremities other wires with extensive plates ofmetal attached to them to complete contact with the water. Thus the wireand the water made one conducting circuit; and as the water ebbed or flowedwith the tide, I hoped to obtain currents analogous to those of the brassball (161. ). 

189. I constantly obtained deflections at the galvanometer, but they werevery irregular, and were, in succession, referred to other causes than thatsought for. The different condition of the water as to purity on the twosides of the river; the difference in temperature; slight differences inthe plates, in the solder used, in the more or less perfect contact made bytwisting or otherwise; all produced effects in turn: and though Iexperimented on the water passing through the middle arches only; usedplatina plates instead of copper; and took every other precaution, I couldnot after three days obtain any satisfactory results. 

190. Theoretically, it seems a necessary consequence, that where water isflowing, there electric currents should be formed; thus, if a line beimagined passing from Dover to Calais through the sea, and returningthrough the land beneath the water to Dover, it traces out a circuit ofconducting matter, one part of which, when the water moves up or down thechannel, is cutting the magnetic curves of the earth, whilst the other isrelatively at rest. This is a repetition of the wire experiment (171. ), butwith worse conductors. Still there is every reason to believe that electriccurrents do run in the general direction of the circuit described, eitherone way or the other, according as the passage of the waters is up or downthe channel. Where the lateral extent of the moving water is enormouslyincreased, it does not seem improbable that the effect should becomesensible; and the gulf stream may thus, perhaps, from electric currentsmoving across it, by magneto-electric induction from the earth, exert asensible influence upon the forms of the lines of magnetic variation[A]. 

 [A] Theoretically, even a ship or a boat when passing on the surface of the water, in northern or southern latitudes, should have currents of electricity running through it directly across the line of her motion; or if the water is flowing past the ship at anchor, similar currents should occur. 

191. Though positive results have not yet been obtained by the action ofthe earth upon water and aqueous fluids, yet, as the experiments are verylimited in their extent, and as such fluids do yield the current byartificial magnets (23. ), (for transference of the current is proof that itmay be produced (213. ), ) the supposition made, that the earth producesthese induced currents within itself (181. ) in consequence of its diurnalrotation, is still highly probable (222, 223. ); and when it is consideredthat the moving masses extend for thousands of miles across the magneticcurves, cutting them in various directions within its mass, as well as atthe surface, it is possible the electricity may rise to considerableintensity. 

192. I hardly dare venture, even in the most hypothetical form, to askwhether the Aurora Borealis and Australia may not be the discharge ofelectricity, thus urged towards the poles of the earth, from whence it isendeavouring to return by natural and appointed means above the earth tothe equatorial regions. The non-occurrence of it in very high latitudes isnot at all against the supposition; and it is remarkable that Mr. Fox, whoobserved the deflections of the magnetic needle at Falmouth, by the AuroraBorealis, gives that direction of it which perfectly agrees with thepresent view. He states that all the variations at night were towards theeast[A], and this is what would happen if electric currents were settingfrom south to north in the earth under the needle, or from north to southin space above it. 

 [A] Philosophical Transactions, 1831, p. 202. 

§ 6. _General remarks and illustrations of the Force and Direction ofMagneto-electric Induction. _

193. In the repetition and variation of Arago's experiment by Messrs. Babbage, Herschel, and Harris, these philosophers directed their attentionto the differences of force observed amongst the metals and othersubstances in their action on the magnet. These differences were verygreat[A], and led me to hope that by mechanical combinations of variousmetals important results might be obtained (183. ). The followingexperiments were therefore made, with a view to obtain, if possible, anysuch difference of the action of two metals, [B] Philosophical Transactions, 1825, p. 472; 1831, p. 78. 

194. A piece of soft iron bonnet-wire covered with cotton was laid bare andcleaned at one extremity, and there fastened by metallic contact with theclean end of a copper wire. Both wires were then twisted together like thestrands of a rope, for eighteen or twenty inches; and the remaining partsbeing made to diverge, their extremities were connected with the wires ofthe galvanometer. The iron wire was about two feet long, the continuationto the galvanometer being copper. 

195. The twisted copper and iron (touching each other nowhere but at theextremity) were then passed between the poles of a powerful magnet arrangedhorse-shoe fashion (fig. 32. ); but not the slightest effect was observed atthe galvanometer, although the arrangement seemed fitted to show anyelectrical difference between the two metals relative to the action of themagnet, 196. A soft iron cylinder was then covered with paper at the middle part, and the twisted portion of the above compound wire coiled as a spiralaround it, the connexion with the galvanometer still being made at the endsA and B. The iron cylinder was then brought in contact with the poles of apowerful magnet capable of raising thirty pounds; yet no signs ofelectricity appeared at the galvanometer. Every precaution was applied inmaking and breaking contact to accumulate effect, but no indications of acurrent could be obtained. 

197. Copper and tin, copper and zinc, tin and zinc, tin and iron, and zincand iron, were tried against each other in a similar manner (194), but notthe slightest sign of electric currents could be procured. 

198. Two flat spirals, one of copper and the other of iron, containing eacheighteen inches of wire, were connected with each other and with thegalvanometer, and then put face to face so as to be in contrary directions. When brought up to the magnetic pole (53. ). No electrical indications atthe galvanometer were observed. When one was turned round so that both werein the same direction, the effect at the galvanometer was very powerful. 

199. The compound helix of copper and iron wire formerly described (8. ) wasarranged as a double helix, one of the helices being all iron andcontaining two hundred and fourteen feet, the other all copper andcontinuing two hundred and eight feet. The two similar ends AA of thecopper and iron helix were connected together, and the other ends BB ofeach helix connected with the galvanometer; so that when a magnet wasintroduced into the centre of the arrangement, the induced currents in theiron and copper would tend to proceed in contrary directions. Yet when amagnet was inserted, or a soft iron bar within made a magnet by contactwith poles, no effect at the needle was produced. 

200. A glass tube about fourteen inches long was filled with strongsulphuric acid. Twelve inches of the end of a clean copper wire were bentup into a bundle and inserted into the tube, so as to make good superficialcontact with the acid, and the rest of the wire passed along the outside ofthe tube and away to the galvanometer. A wire similarly bent up at theextremity was immersed in the other end of the sulphuric acid, and alsoconnected with the galvanometer, so that the acid and copper wire were inthe same parallel relation to each other in this experiment as iron andcopper were in the first (194). When this arrangement was passed in asimilar manner between the poles of the magnet, not the slightest effect atthe galvanometer could be perceived. 

201. From these experiments it would appear, that when metals of differentkinds connected in one circuit are equally subject in every circumstance tomagneto-electric induction, they exhibit exactly equal powers with respectto the currents which either are formed, or tend to form, in them. The sameeven appears to be the case with regard to fluids, and probably all othersubstances. 

202. Still it seemed impossible that these results could indicate therelative inductive power of the magnet upon the different metals; for thatthe effect should be in some relation to the conducting power seemed anecessary consequence (139. ), and the influence of rotating plates uponmagnets had been found to bear a general relation to the conducting powerof the substance used. 

203. In the experiments of rotation (81. ), the electric current is excitedand discharged in the same substance, be it a good or bad conductor; but inthe experiments just described the current excited in iron could not betransmitted but through the copper, and that excited in copper had to passthrough iron: i. E. Supposing currents of dissimilar strength to be formedin the metals proportionate to their conducting power, the stronger currenthad to pass through the worst conductor, and the weaker current through thebest. 

204. Experiments were therefore made in which different metals insulatedfrom each other were passed between the poles of the magnet, their oppositeends being connected with the same end of the galvanometer wire, so thatthe currents formed and led away to the galvanometer should oppose eachother; and when considerable lengths of different wires were used, feebledeflections were obtained. 

205. To obtain perfectly satisfactory results a new galvanometer wasconstructed, consisting of two independent coils, each containing eighteenfeet of silked copper wire. These coils were exactly alike in shape andnumber of turns, and were fixed side by side with a small interval betweenthem, in which a double needle could be hung by a fibre of silk exactly asin the former instrument (87. ). The coils may be distinguished by theletters KL, and when electrical currents were sent through them in the samedirection, acted upon the needle with the sum of their powers; when inopposite directions, with the difference of their powers. 

206. The compound helix (199. 8. ) was now connected, the ends A and B ofthe iron with A and B ends of galvanometer coil K, and the ends A and B ofthe copper with B and A ends of galvanometer coil L, so that the currentsexcited in the two helices should pass in opposite directions through thecoils K and L. On introducing a small cylinder magnet within the helices, the galvanometer needle was powerfully deflected. On disuniting the ironhelix, the magnet caused with the copper helix alone still strongerdeflection in the same direction. On reuniting the iron helix, andunconnecting the copper helix, the magnet caused a moderate deflection inthe contrary direction. Thus it was evident that the electric currentinduced by a magnet in a copper wire was far more powerful than the currentinduced by the same magnet in an equal iron wire. 

207. To prevent any error that might arise from the greater influence, fromvicinity or other circumstances, of one coil on the needle beyond that ofthe other, the iron and copper terminations were changed relative to thegalvanometer coils KL, so that the one which before carried the currentfrom the copper now conveyed that from the iron, and vice versa. But thesame striking superiority of the copper was manifested as before. Thisprecaution was taken in the rest of the experiments with other metals to bedescribed. 

208. I then had wires of iron, zinc, copper, tin, and lead, drawn to thesame diameter (very nearly one twentieth of an inch), and I comparedexactly equal lengths, namely sixteen feet, of each in pairs in thefollowing manner: The ends of the copper wire were connected with the endsA and B of galvanometer coil K, and the ends of the zinc wire with theterminations A and B of the galvanometer coil L. The middle part of eachwire was then coiled six times round a cylinder of soft iron covered withpaper, long enough to connect the poles of Daniell's horse-shoe magnet(56. ) (fig. 33. ), so that similar helices of copper and zinc, each of sixturns, surrounded the bar at two places equidistant from each other andfrom the poles of the magnet; but these helices were purposely arranged soas to be in contrary directions, and therefore send contrary currentsthrough the galvanometer coils K and L, 209. On making and breaking contact between the soft iron bar and the polesof the magnet, the galvanometer was strongly affected; on detaching thezinc it was still more strongly affected in the same direction. On takingall the precautions before alluded to (207. ), with others, it wasabundantly proved that the current induced by the magnet in copper was farmore powerful than in zinc. 

210. The copper was then compared in a similar manner with tin, lead, andiron, and surpassed them all, even more than it did zinc. The zinc was thencompared experimentally with the tin, lead, and iron, and found to producea more powerful current than any of them. Iron in the same manner provedsuperior to tin and lead. Tin came next, and lead the last. 

211. Thus the order of these metals is copper, zinc, iron, tin, and lead. It is exactly their order with respect to conducting power for electricity, and, with the exception of iron, is the order presented by themagneto-rotation experiments of Messrs. Babbage, Herschel, Harris, &c. Theiron has additional power in the latter kind of experiments, because of itsordinary magnetic relations, and its place relative to magneto-electricaction of the kind now under investigation cannot be ascertained by suchtrials. In the manner above described it may be correctly ascertained[A]. 

 [A] Mr. Christie, who being appointed reporter upon this paper, had it in his hands before it was complete, felt the difficulty (202. ); and to satisfy his mind, made experiments upon iron and copper with the large magnet(44. ), and came to the same conclusions as I have arrived at. The two sets of experiments were perfectly independent of each other, neither of us being aware of the other's proceedings. 

212. It must still be observed that in these experiments the whole effectbetween different metals is not obtained; for of the thirty-four feet ofwire included in each circuit, eighteen feet are copper in both, being thewire of the galvanometer coils; and as the whole circuit is concerned inthe resulting force of the current, tin's circumstance must tend todiminish the difference which would appear between the metals if thecircuits were of the same substances throughout. In the present case thedifference obtained is probably not more than a half of that which would begiven if the whole of each circuit were of one metal. 

213. These results tend to prove that the currents produced bymagneto-electric induction in bodies is proportional to their conductingpower. That they are _exactly_ proportional to and altogether dependentupon the conducting power, is, I think, proved by the perfect neutralitydisplayed when two metals or other substances, as acid, water, &c. &c. (201. 186. ), are opposed to each other in their action. The feeble currentwhich tends to be produced in the worse conductor, has its transmissionfavoured in the better conductor, and the stronger current which tends toform in the latter has its intensity diminished by the obstruction of theformer; and the forces of generation and obstruction are so perfectlyneutralize each other exactly. Now as the obstruction is inversely as thebalanced as to conducting power, the tendency to generate a current mustbe directly as that power to produce this perfect equilibrium. 

214. The cause of the equality of action under the various circumstancesdescribed, where great extent of wire (183. ) or wire and water (181. ) wereconnected together, which yet produced such different effects upon themagnet, is now evident and simple. 

215. The effects of a rotating substance upon a needle or magnet ought, where ordinary magnetism has no influence, to be directly as the conductingpower of the substance; and I venture now to predict that such will befound to be the case; and that in all those instances where non-conductorshave been supposed to exhibit this peculiar influence, the motion has beendue to some interfering cause of an ordinary kind; as mechanicalcommunication of motion through the parts of the apparatus, or otherwise(as in the case Mr. Harris has pointed out[A]); or else to ordinarymagnetic attractions. To distinguish the effects of the latter from thoseof the induced electric currents, I have been able to devise a most perfecttest, which shall be almost immediately described (243. ). 

 [A] Philosophical Transactions, 1831. P. 68. 

216. There is every reason to believe that the magnet or magnetic needlewill become an excellent measurer of the conducting power of substancesrotated near it; for I have found by careful experiment, that when aconstant current of electricity was sent successively through a series ofwires of copper, platina, zinc, silver, lead, and tin, drawn to the samediameter; the deflection of the needle was exactly equal by them all. Itmust be remembered that when bodies are rotated in a horizontal plane, themagnetism of the earth is active upon them. As the effect is general to thewhole of the plate, it may not interfere in these cases; but in someexperiments and calculations may be of important consequence. 

217. Another point which I endeavoured to ascertain, was, whether it wasessential or not that the moving part of the wire should, in cutting themagnetic curves, pass into positions of greater or lesser magnetic force;or whether, always intersecting curves of equal magnetic intensity, themere motion was sufficient for the production of the current. That thelatter is true, has been proved already in several of the experiments onterrestrial magneto-electric induction. Thus the electricity evolved fromthe copper plate (149. ), the currents produced in the rotating globe (161, &c. ), and those passing through the moving wire (171. ), are all producedunder circumstances in which the magnetic force could not but be the sameduring the whole experiments. 

218. To prove the point with an ordinary magnet, a copper disc was cementedupon the end of a cylinder magnet, with paper intervening; the magnet anddisc were rotated together, and collectors (attached to the galvanometer)brought in contact with the circumference and the central part of thecopper plate. The galvanometer needle moved as in former cases, and the_direction_ of motion was the _same_ as that which would have resulted, ifthe copper only had revolved, and the magnet been fixed. Neither was thereany apparent difference in the quantity of deflection. Hence, rotating themagnet causes no difference in the results; for a rotatory and a stationarymagnet produce the same effect upon the moving copper. 

219. A copper cylinder, closed at one extremity, was then put over themagnet, one half of which it inclosed like a cap; it was firmly fixed, andprevented from touching the magnet anywhere by interposed paper. Thearrangement was then floated in a narrow jar of mercury, so that the loweredge of the copper cylinder touched the fluid metal; one wire of thegalvanometer dipped into this mercury, and the other into a little cavityin the centre of the end of the copper cap. Upon rotating the magnet andits attached cylinder, abundance of electricity passed through thegalvanometer, and in the same direction as if the cylinder had rotatedonly, the magnet being still. The results therefore were the same as thosewith the disc (218. ). 

220. That the metal of the magnet itself might be substituted for themoving cylinder, disc, or wire, seemed an inevitable consequence, and yetone which would exhibit the effects of magneto-electric induction in astriking form. A cylinder magnet had therefore a little hole made in thecentre of each end to receive a drop of mercury, and was then floated poleupwards in the same metal contained in a narrow jar. One wire from thegalvanometer dipped into the mercury of the jar, and the other into thedrop contained in the hole at the upper extremity of the axis. The magnetwas then revolved by a piece of string passed round it, and thegalvanometer-needle immediately indicated a powerful current ofelectricity. On reversing the order of rotation, the electrical current wasreversed. The direction of the electricity was the same as if the coppercylinder (219. ) or a copper wire had revolved round the fixed magnet in thesame direction as that which the magnet itself had followed. Thus a_singular independence_ of the magnetism and the bar in which it resides isrendered evident. 

221. In the above experiment the mercury reached about halfway up themagnet; but when its quantity was increased until within one eighth of aninch of the top, or diminished until equally near the bottom, still thesame effects and the _same direction_ of electrical current was obtained. But in those extreme proportions the effects did not appear so strong aswhen the surface of the mercury was about the middle, or between that andan inch from each end. The magnet was eight inches and a half long, andthree quarters of an inch in diameter. 

222. Upon inversion of the magnet, and causing rotation in the samedirection, i. E. Always screw or always unscrew, then a contrary current ofelectricity was produced. But when the motion of the magnet was continuedin a direction constant in relation to its _own axis_, then electricity ofthe same kind was collected at both poles, and the opposite electricity atthe equator, or in its neighbourhood, or in the parts corresponding to it. If the magnet be held parallel to the axis of the earth, with its unmarkedpole directed to the pole star, and then rotated so that the parts at itssouthern side pass from west to east in conformity to the motion of theearth; then positive electricity may be collected at the extremities of themagnet, and negative electricity at or about the middle of its mass. 

223. When the galvanometer was very sensible, the mere spinning of themagnet in the air, whilst one of the galvanometer wires touched theextremity, and the other the equatorial parts, was sufficient to evolve acurrent of electricity and deflect the needle. 

224. Experiments were then made with a similar magnet, for the purpose ofascertaining whether any return of the electric current could occur at thecentral or axial parts, they having the same angular velocity of rotationas the other parts (259. ) the belief being that it could not. 

225. A cylinder magnet, seven inches in length, and three quarters of aninch in diameter, had a hole pierced in the direction of its axis from oneextremity, a quarter of an inch in diameter, and three inches deep. Acopper cylinder, surrounded by paper and amalgamated at both extremities, was introduced so as to be in metallic contact at the bottom of the hole, by a little mercury, with the middle of the magnet; insulated at the sidesby the paper; and projecting about a quarter of an inch above the end ofthe steel. A quill was put over the copper rod, which reached to the paper, and formed a cup to receive mercury for the completion of the circuit. Ahigh paper edge was also raised round that end of the magnet and mercuryput within it, which however had no metallic connexion with that in thequill, except through the magnet itself and the copper rod (fig. 34. ). Thewires A and B from the galvanometer were dipped into these two portions ofmercury; any current through them could, therefore, only pass down themagnet towards its equatorial parts, and then up the copper rod; or viceversa. 

226. When thus arranged and rotated screw fashion, the marked end of thegalvanometer needle went west, indicating that there was a current throughthe instrument from A to B and consequently from B through the magnet andcopper rod to A (fig. 34. ). 

227. The magnet was then put into a jar of mercury (fig. 35. ) as before(219. ); the wire A left in contact with the copper axis, but the wire Bdipped in the mercury of the jar, and therefore in metallic communicationwith the equatorial parts of the magnet instead of its polar extremity. Onrevolving the magnet screw fashion, the galvanometer needle was deflectedin the same direction as before, but far more powerfully. Yet it is evidentthat the parts of the magnet from the equator to the pole were out of theelectric circuit. 

228. Then the wire A was connected with the mercury on the extremity of themagnet, the wire B still remaining in contact with that in the jar (fig. 36. ), so that the copper axis was altogether out of the circuit. The magnetwas again revolved screw fashion, and again caused the same deflection ofthe needle, the current being as strong as it was in the last trial (227. ), and much stronger than at first (226. ). 

229. Hence it is evident that there is no discharge of the current at thecentre of the magnet, for the current, now freely evolved, is up throughthe magnet; but in the first experiment (226. ) it was down. In fact, atthat time, it was only the part of the moving metal equal to a little discextending from the end of the wire B in the mercury to the wire A that wasefficient, i. E. Moving with a different angular velocity to the rest of thecircuit (258. ); and for that portion the direction of the current isconsistent with the other results. 

230. In the two after experiments, the _lateral_ parts of the magnet or ofthe copper rod are those which move relative to the other parts of thecircuit, i. E. The galvanometer wires; and being more extensive, intersecting more curves, or moving with more velocity, produce the greatereffect. For the discal part, the direction of the induced electric currentis the same in all, namely, from the circumference towards the centre. 

 * * * * *

231. The law under which the induced electric current excited in bodiesmoving relatively to magnets, is made dependent on the intersection of themagnetic curves by the metal (114. ) being thus rendered more precise anddefinite (217. 220. 224. ), seem now even to apply to the cause in the firstsection of the former paper (26. ); and by rendering a perfect reason forthe effects produced, take away any for supposing that peculiar condition, which I ventured to call the electro-tonic state (60. ). 

232. When an electrical current is passed through a wire, that wire issurrounded at every part by magnetic curves, diminishing in intensityaccording to their distance from the wire, and which in idea may be likenedto rings situated in planes perpendicular to the wire or rather to theelectric current within it. These curves, although different in form, areperfectly analogous to those existing between two contrary magnetic polesopposed to each other; and when a second wire, parallel to that whichcarries the current, is made to approach the latter (18. ), it passesthrough magnetic curves exactly of the same kind as those it wouldintersect when carried between opposite magnetic poles (109. ) in onedirection; and as it recedes from the inducing wire, it cuts the curvesaround it in the same manner that it would do those between the same polesif moved in the other direction. 

233. If the wire NP (fig. 40. ) have an electric current passed through itin the direction from P to N, then the dotted ring may represent a magneticcurve round it, and it is in such a direction that if small magneticneedles lie placed as tangents to it, they will become arranged as in thefigure, _n_ and _s_ indicating north and south ends (14. _note_. ). 

234. But if the current of electricity were made to cease for a while, andmagnetic poles were used instead to give direction to the needles, and makethem take the same position as when under the influence of the current, then they must be arranged as at fig. 41; the marked and unmarked poles_ab_ above the wire, being in opposite directions to those _a'b'_ below. Insuch a position therefore the magnetic curves between the poles _ab_ and_a'b'_ have the same general direction with the corresponding parts of thering magnetic curve surrounding the wire NP carrying an electric current. 

235. If the second wire _pn_ (fig. 40. ) be now brought towards theprincipal wire, carrying a current, it will cut an infinity of magneticcurves, similar in direction to that figured, and consequently similar indirection to those between the poles _ab_ of the magnets (fig. 41. ), and itwill intersect these current curves in the same manner as it would themagnet curves, if it passed from above between the poles downwards. Now, such an intersection would, with the magnets, induce an electric current inthe wire from _p_ to _n_ (114. ); and therefore as the curves are alike inarrangement, the same effect ought to result from the intersection of themagnetic curves dependent on the current in the wire NP; and such is thecase, for on approximation the induced current is in the opposite directionto the principal current (19. ). 

236. If the wire _p'n'_ be carried up from below, it will pass in theopposite direction between the magnetic poles; but then also the magneticpoles themselves are reversed (fig. 41. ), and the induced current istherefore (114. ) still in the same direction as before. It is also, forequally sufficient and evident reasons, in the same direction, if producedby the influence of the curves dependent upon the wire. 

237. When the second wire is retained at rest in the vicinity the principalwire, no current is induced through it, for it is intersecting no magneticcurves. When it is removed from the principal wire, it intersects thecurves in the opposite direction to what it did before (235. ); and acurrent in the opposite direction is induced, which therefore correspondswith the direction of the principal current (19. ). The same effect wouldtake place if by inverting the direction of motion of the wire in passingbetween either set of poles (fig. 41. ), it were made to intersect thecurves there existing in the opposite direction to what it did before. 

238. In the first experiments (10. 13. ), the inducing wire and that underinduction were arranged at a fixed distance from each other, and then anelectric current sent through the former. In such cases the magnetic curvesthemselves must be considered as moving (if I may use the expression)across the wire under induction, from the moment at which they begin to bedeveloped until the magnetic force of the current is at its utmost;expanding as it were from the wire outwards, and consequently being in thesame relation to the fixed wire under induction as if _it_ had moved in theopposite direction across them, or towards the wire carrying the current. Hence the first current induced in such cases was in the contrary directionto the principal current (17. 235. ). On breaking the battery contact, themagnetic curves (which are mere expressions for arranged magnetic forces)may be conceived as contracting upon and returning towards the failingelectrical current, and therefore move in the opposite direction across thewire, and cause an opposite induced current to the first. 

239. When, in experiments with ordinary magnets, the latter, in place ofbeing moved past the wires, were actually made near them (27. 36. ), then asimilar progressive development of the magnetic curves may be considered ashaving taken place, producing the effects which would have occurred bymotion of the wires in one direction; the destruction of the magnetic powercorresponds to the motion of the wire in the opposite direction. 

240. If, instead of intersecting the magnetic curves of a straight wirecarrying a current, by approximating or removing a second wire (235. ), arevolving plate be used, being placed for that purpose near the wire, and, as it were, amongst the magnetic curves, then it ought to have continuouselectric currents induced within it; and if a line joining the wire withthe centre of the plate were perpendicular to both, then the inducedcurrent ought to be, according to the law (114. ), directly across theplate, from one side to the other, and at right angles to the direction ofthe inducing current. 

241. A single metallic wire one twentieth of an inch in diameter had anelectric current passed through it, and a small copper disc one inch and ahalf in diameter revolved near to and under, but not in actual contact withit (fig. 39). Collectors were then applied at the opposite edges of thedisc, and wires from them connected with the galvanometer. As the discrevolved in one direction, the needle was deflected on one side: and whenthe direction of revolution was reversed, the needle was inclined on theother side, in accordance with the results anticipated. 

242. Thus the reasons which induce me to suppose a particular state in thewire (60. ) have disappeared; and though it still seems to me unlikely thata wire at rest in the neighbourhood of another carrying a powerful electriccurrent is entirely indifferent to it, yet I am not aware of any distinct_facts_ which authorize the conclusion that it is in a particular state. 

 * * * * *

243. In considering the nature of the cause assigned in these papers toaccount for the mutual influence of magnets and moving metals (120. ), andcomparing it with that heretofore admitted, namely, the induction of afeeble magnetism like that produced in iron, it occurred to me that a mostdecisive experimental test of the two views could be applied (215. ). 

244. No other known power has like direction with that exerted between anelectric current and a magnetic pole; it is tangential, while all otherforces, acting at a distance, are direct. Hence, if a magnetic pole on oneside of a revolving plate follow its course by reason of its obedience tothe tangential force exerted upon it by the very current of electricitywhich it has itself caused, a similar pole on the opposite side of theplate should immediately set it free from this force; for the currentswhich tend to be formed by the action of the two poles are in oppositedirections; or rather no current tends to be formed, or no magnetic curvesare intersected (114. ); and therefore the magnet should remain at rest. Onthe contrary, if the action of a north magnetic pole were to produce asouthness in the nearest part of the copper plate, and a diffuse northnesselsewhere (82. ), as is really the case with iron; then the use of anothernorth pole on the opposite side of the same part of the plate should doublethe effect instead of destroying it, and double the tendency of the firstmagnet to move with the plate. 

245. A thick copper plate (85. ) was therefore fixed on a vertical axis, abar magnet was suspended by a plaited silk cord, so that its marked polehung over the edge of the plate, and a sheet of paper being interposed, theplate was revolved; immediately the magnetic pole obeyed its motion andpassed off in the same direction. A second magnet of equal size andstrength was then attached to the first, so that its marked pole shouldhang _beneath_ the edge of the copper plate in a corresponding position tothat above, and at an equal distance (fig. 37. ). Then a paper sheath orscreen being interposed as before, and the plate revolved, the poles werefound entirely indifferent to its motion, although either of them alonewould have followed the course of rotation. 

246. On turning one magnet round, so that _opposite_ poles were on eachside of the plate, then the mutual action of the poles and the moving metalwas a maximum. 

247. On suspending one magnet so that its axis was level with the plate, and either pole opposite its edge, the revolution of the plate caused nomotion of the magnet. The electrical currents dependent upon inductionwould now tend to be produced in a vertical direction across the thicknessof the plate, but could not be so discharged, or at least only to so slighta degree as to leave all effects insensible; but ordinary magneticinduction, or that on an iron plate, would be equally if not morepowerfully developed in such a position (251. ). 

248. Then, with regard to the production of electricity in thesecases:--whenever motion was communicated by the plate to the magnets, currents existed; when it was not communicated, they ceased. A marked poleof a large bar magnet was put under the edge of the plate; collectors (86. )applied at the axis and edge of the plate as on former occasions (fig. 38. ), and these connected with the galvanometer; when the plate wasrevolved, abundance of electricity passed to the instrument. The unmarkedpole of a similar magnet was then put over the place of the former pole, sothat contrary poles were above and below; on revolving the plate, theelectricity was more powerful than before. The latter magnet was thenturned end for end, so that marked poles were both above and below theplate, and then, upon revolving it, scarcely any electricity was procured. By adjusting the distance of the poles so as to correspond with theirrelative force, they at last were brought so perfectly to neutralize eachother's inductive action upon the plate, that no electricity could beobtained with the most rapid motion. 

249. I now proceeded to compare the effect of similar and dissimilar polesupon iron and copper, adopting for the purpose Mr. Sturgeon's very usefulform of Arago's experiment. This consists in a circular plate of metalsupported in a vertical plane by a horizontal axis, and weighted a littleat one edge or rendered excentric so as to vibrate like a pendulum. Thepoles of the magnets are applied near the side and edges of these plates, and then the number of vibrations, required to reduce the vibrating arc acertain constant quantity, noted. In the first description of thisinstrument[A] it is said that opposite poles produced the greatestretarding effect, and similar poles none; and yet within a page of theplace the effect is considered as of the same kind with that produced iniron. 

 [A] Edin. Phil. Journal, 1825, p. 124. 

250. I had two such plates mounted, one of copper, one of iron. The copperplate alone gave sixty vibrations, in the average of several experiments, before the arc of vibration was reduced from one constant mark to another. On placing opposite magnetic poles near to, and on each side of, the sameplace, the vibrations were reduced to fifteen. On putting similar poles oneach side of it, they rose to fifty; and on placing two pieces of wood ofequal size with the poles equally near, they became fifty-two. So that, when similar poles were used, the magnetic effect was little or none, (theobstruction being due to the confinement of the air, rather, ) whilst withopposite poles it was the greatest possible. When a pole was presented tothe edge of the plate, no retardation occurred. 

251. The iron plate alone made thirty-two vibrations, whilst the arc ofvibration diminished a certain quantity. On presenting a magnetic pole tothe edge of the plate (247. ), the vibrations were diminished to eleven; andwhen the pole was about half an inch from the edge, to five. 

252. When the marked pole was put at the side of the iron plate at acertain distance, the number of vibrations was only five. When the markedpole of the second bar was put on the opposite side of the plate at thesame distance (250. ), the vibrations were reduced to two. But when thesecond pole was an unmarked one, yet occupying exactly the same position, the vibrations rose to twenty-two. By removing the stronger of these twoopposite poles a little way from the plate, the vibrations increased tothirty-one, or nearly the original number. But on removing it _altogether_, they fell to between five and six. 

253. Nothing can be more clear, therefore, than that with iron, and bodiesadmitting of ordinary magnetic induction, _opposite_ poles on oppositesides of the edge of the plate neutralize each other's effect, whilst_similar_ poles exalt the action; a single pole end on is also sufficient. But with copper, and substances not sensible to ordinary magneticimpressions, _similar_ poles on opposite sides of the plate neutralize eachother; _opposite_ poles exalt the action; and a single pole at the edge orend on does nothing. 

254. Nothing can more completely show the thorough independence of theeffects obtained with the metals by Arago, and those due to ordinarymagnetic forces; and henceforth, therefore, the application of two poles tovarious moving substances will, if they appear at all magneticallyaffected, afford a proof of the nature of that affection. If opposite polesproduce a greater effect than one pole, the result will be due to electriccurrents. If similar poles produce more effect than one, then the power is_not_ electrical; it is not like that active in the metals and carbon whenthey are moving, and in most cases will probably be found to be not evenmagnetical, but the result of irregular causes not anticipated andconsequently not guarded against. 

255. The result of these investigations tends to show that there are reallybut very few bodies that are magnetic in the manner of iron. I have oftensought for indications of this power in the common metals and othersubstances; and once in illustration of Arago's objection (82. ), and inhopes of ascertaining the existence of currents in metals by the momentaryapproach of a magnet, suspended a disc of copper by a single fibre of silkin an excellent vacuum, and approximated powerful magnets on the outside ofthe jar, making them approach and recede in unison with a pendulum thatvibrated as the disc would do: but no motion could be obtained; not merely, no indication of ordinary magnetic powers, but none or _any electriccurrent_ occasioned in the metal by the approximation and recession of themagnet. I therefore venture to arrange substances in three classes asregards their relation to magnets; first, those which are affected when atrest, like iron, nickel, &c. , being such as possess ordinary magneticproperties; then, those which are affected when in motion, being conductorsof electricity in which are produced electric currents by the inductiveforce of the magnet; and, lastly, those which are perfectly indifferent tothe magnet, whether at rest or in motion. 

256. Although it will require further research, and probably closeinvestigation, both experimental and mathematical, before the exact mode ofaction between a magnet and metal moving relatively to each other isascertained; yet many of the results appear sufficiently clear and simpleto allow of expression in a somewhat general manner. --If a terminated wiremove so as to cut a magnetic curve, a power is called into action whichtends to urge an electric current through it; but this current cannot bebrought into existence unless provision be made at the ends of the wire forits discharge and renewal. 

257. If a second wire move in the same direction as the first, the samepower is exerted upon it, and it is therefore unable to alter the conditionof the first: for there appear to be no natural differences amongsubstances when connected in a series, by which, when moving under the samecircumstances relative to the magnet, one tends to produce a more powerfulelectric current in the whole circuit than another (201. 214. ). 

258. But if the second wire move with a different velocity, or in someother direction, then variations in the force exerted take place; and ifconnected at their extremities, an electric current passes through them. 

259. Taking, then, a mass of metal or an endless wire, and referring to thepole of the magnet as a centre of action, (which though perhaps notstrictly correct may be allowed for facility of expression, at present, ) ifall parts move in the same direction, and with the same angular velocity, and through magnetic curves of constant intensity, then no electriccurrents are produced. This point is easily observed with masses subject tothe earth's magnetism, and may be proved with regard to small magnets; byrotating them, and leaving the metallic arrangements stationary, no currentis produced. 

260. If one part of the wire or metal cut the magnetic curves, whilst theother is stationary, then currents are produced. All the results obtainedwith the galvanometer are more or less of this nature, the galvanometerextremity being the fixed part. Even those with the wire, galvanometer, andearth (170. ), may be considered so without any error in the result. 

261. If the motion of the metal be in the same direction, but the angularvelocity of its parts relative to the pole of the magnet different, thencurrents are produced. This is the case in Arago's experiment, and also inthe wire subject to the earth's induction (172. ), when it was moved fromwest to east. 

262. If the magnet moves not directly to or from the arrangement, butlaterally, then the case is similar to the last. 

263. If different parts move in opposite directions across the magneticcurves, then the effect is a maximum for equal velocities. 

264. All these in fact are variations of one simple condition, namely, thatall parts of the mass shall not move in the same direction across thecurves, and with the same angular velocity. But they are forms ofexpression which, being retained in the mind, I have found useful whencomparing the consistency of particular phenomena with general results. 

_Royal Institution, December 21, 1831. _

THIRD SERIES. 

§ 7. _Identity of Electricities derived from different sources. _ § 8. _Relation by measure of common and voltaic Electricity. _

[Read January 10th and 17th, 1833. ]

§ 7. _Identity of Electricities derived from different sources. _

265. The progress of the electrical researches which I have had the honourto present to the Royal Society, brought me to a point at which it wasessential for the further prosecution of my inquiries that no doubt shouldremain of the identity or distinction of electricities excited by differentmeans. It is perfectly true that Cavendish[A], Wollaston[B], Colladon[C], and others, have in succession removed some of the greatest objections tothe acknowledgement of the identity of common, animal and voltaicelectricity, and I believe that most philosophers consider theseelectricities as really the same. But on the other hand it is also true, that the accuracy of Wollaston's experiments has been denied[D]; and alsothat one of them, which really is no proper proof of chemical decompositionby common electricity (309. 327. ), has been that selected by severalexperimenters as the test of chemical action (336. 346. ). It is a fact, too, that many philosophers are still drawing distinctions between theelectricities from different sources; or at least doubting whether theiridentity is proved. Sir Humphry Davy, for instance, in his paper on theTorpedo[E], thought it probable that animal electricity would be found of apeculiar kind; and referring to it, to common electricity, voltaicelectricity and magnetism, has said, "Distinctions might be established inpursuing the various modifications or properties of electricity in thosedifferent forms, &c. " Indeed I need only refer to the last volume of thePhilosophical Transactions to show that the question is by no meansconsidered as settled[F]. 

 [A] Phil. Trans. 1779, p. 196. 

 [B] Ibid. 1801, p. 434. 

 [C] Annnles de Chimie, 1826, p. 62, &c. 

 [D] Phil. Trans. 1832, p. 282, note. 

 [E] Phil. Trans. 1892, p. 17. 

 "Common electricity is excited upon non-conductors, and is readily carried off by conductors and imperfect conductors. Voltaic electricity is excited upon combinations of perfect and imperfect conductors, and is only transmitted by perfect conductors or imperfect conductors of the best kind. Magnetism, if it be a form of electricity, belongs only to perfect conductors; and, in its modifications, to a peculiar class of them[1]. Animal electricity resides only in the imperfect conductors forming the organs of living animals, &c. "

 [1] Dr. Ritchie has shown this is not the case. Phil. Trans. 1832, p. 294. 

 [F] Phil. Trans. 1832, p. 259. Dr. Davy, in making experiments on the torpedo, obtains effects the same as those produced by common and voltaic electricity, and says that in its magnetic and chemical power it does not seem to be essentially peculiar, --p. 274; but he then says, p. 275, there are other points of difference; and after referring to them, adds, "How are these differences to be explained? Do they admit of explanation similar to that advanced by Mr. Cavendish in his theory of the torpedo; or may we suppose, according to the analogy of the solar ray, that the electrical power, whether excited by the common machine, or by the voltaic battery, or by the torpedo, is not a simple power, but a combination of powers, which may occur variously associated, and produce all the varieties of electricity with which we are acquainted?"

At p. 279 of the same volume of Transactions is Dr. Ritchie's paper, from which the following are extracts: "Common electricity is diffusedover the surface of the metal;--voltaic electricity exists within themetal. Free electricity is conducted over the surface of the thinnestgold leaf as effectually as over a mass of metal having the samesurface;--voltaic electricity requires thickness of metal for itsconduction, " p. 280: and again, "The supposed analogy between common andvoltaic electricity, which was so eagerly traced after the invention ofthe pile, completely fails in this case, which was thought to afford themost striking resemblance. " p. 291. 

266. Notwithstanding, therefore, the general impression of the identity ofelectricities, it is evident that the proofs have not been sufficientlyclear and distinct to obtain the assent of all those who were competent toconsider the subject; and the question seemed to me very much in thecondition of that which Sir H. Davy solved so beautifully, --namely, whethervoltaic electricity in all cases merely eliminated, or did not in someactually produce, the acid and alkali found after its action upon water. The same necessity that urged him to decide the doubtful point, whichinterfered with the extension of his views, and destroyed the strictness ofhis reasoning, has obliged me to ascertain the identity or difference ofcommon and voltaic electricity. I have satisfied myself that they areidentical, and I hope the experiments which I have to offer and the proofsflowing from them, will be found worthy the attention of the Royal Society. 

267. The various phenomena exhibited by electricity may, for the purposesof comparison, be arranged under two heads; namely, those connected withelectricity of tension, and those belonging to electricity in motion. Thisdistinction is taken at present not as philosophical, but merely asconvenient. The effect of electricity of tension, at rest, is eitherattraction or repulsion at sensible distances. The effects of electricityin motion or electrical currents may be considered as 1st, Evolution ofheat; 2nd, Magnetism; 3rd, Chemical decomposition; 4th, Physiologicalphenomena; 5th, Spark. It will be my object to compare electricities fromdifferent sources, and especially common and voltaic electricities, bytheir power of producing these effects. 

I. _Voltaic Electricity. _

268. _Tension. _--When a voltaic battery of 100 pairs of plates has itsextremities examined by the ordinary electrometer, it is well known thatthey are found positive and negative, the gold leaves at the same extremityrepelling each other, the gold leaves at different extremities attractingeach other, even when half an inch or more of air intervenes. 

269. That ordinary electricity is discharged by points with facilitythrough air; that it is readily transmitted through highly rarefied air;and also through heated air, as for instance a flame; is due to its hightension. I sought, therefore, for similar effects in the discharge ofvoltaic electricity, using as a test of the passage of the electricityeither the galvanometer or chemical action produced by the arrangementhereafter to be described (312. 316. ). 

270. The voltaic battery I had at my disposal consisted of 140 pairs ofplates four inches square, with double coppers. It was insulatedthroughout, and diverged a gold leaf electrometer about one third of aninch. On endeavouring to discharge this battery by delicate points verynicely arranged and approximated, either in the air or in an exhaustedreceiver, I could obtain no indications of a current, either by magnetic orchemical action. In this, however, was found no point of discordancebetween voltaic and common electricity; for when a Leyden battery (291. )was charged so as to deflect the gold leaf electrometer to the same degree, the points were found equally unable to discharge it with such effect as toproduce either magnetic or chemical action. This was not because commonelectricity could not produce both these effects (307. 310. ); but becausewhen of such low intensity the quantity required to make the effectsvisible (being enormously great (371. 375. ), ) could not be transmitted inany reasonable time. In conjunction with the other proofs of identityhereafter to be given, these effects of points also prove identity insteadof difference between voltaic and common electricity. 

271. As heated air discharges common electricity with far greater facilitythan points, I hoped that voltaic electricity might in this way also bedischarged. An apparatus was therefore constructed (Plate III. Fig. 46. ), in which AB is an insulated glass rod upon which two copper wires, C, D, are fixed firmly; to these wires are soldered two pieces of fine platinawire, the ends of which are brought very close to each other at _e_, butwithout touching; the copper wire C was connected with the positive pole ofa voltaic battery, and the wire D with a decomposing apparatus (312. 316. ), from which the communication was completed to the negative pole of thebattery. In these experiments only two troughs, or twenty pairs of plates, were used. 

272. Whilst in the state described, no decomposition took place at thepoint _a_, but when the side of a spirit-lamp flame was applied to the twoplatina extremities at _e_, so as to make them bright red-hot, decomposition occurred; iodine soon appeared at the point _a_, and thetransference of electricity through the heated air was established. Onraising the temperature of the points _e_ by a blowpipe, the discharge wasrendered still more free, and decomposition took place instantly. Onremoving the source of heat, the current immediately ceased. On putting theends of the wires very close by the side of and parallel to each other, butnot touching, the effects were perhaps more readily obtained than before. On using a larger voltaic battery (270. ), they were also more freelyobtained. 

273. On removing the decomposing apparatus and interposing a galvanometerinstead, heating the points _e_ as the needle would swing one way, andremoving the heat during the time of its return (302. ), feeble deflectionswere soon obtained: thus also proving the current through heated air; butthe instrument used was not so sensible under the circumstances as chemicalaction. 

274. These effects, not hitherto known or expected under this form, areonly cases of the discharge which takes place through air between thecharcoal terminations of the poles of a powerful battery, when they aregradually separated after contact. Then the passage is through heated airexactly as with common electricity, and Sir H. Davy has recorded that withthe original battery of the Royal Institution this discharge passed througha space of at least four inches[A]. In the exhausted receiver theelectricity would _strike_ through nearly half an inch of space, and thecombined effects of rarefaction and heat were such upon the inclosed air usto enable it to conduct the electricity through a space of six or seveninches. 

 [A] Elements of Chemical Philosophy, p. 153

275. The instantaneous charge of a Leyden battery by the poles of a voltaicapparatus is another proof of the tension, and also the quantity, ofelectricity evolved by the latter. Sir H. Davy says[A], "When the twoconductors from the ends of the combination were connected with a Leydenbattery, one with the internal, the other with the external coating, thebattery instantly became charged; and on removing the wires and making theproper connexions, either a shock or a _spark_ could be perceived: and theleast possible time of contact was sufficient to renew the charge to itsfull intensity. "

 [A] Elements of Chemical Philosophy, p. 154. 

276. _In motion:_ i. _Evolution of Heat. _--The evolution of heat in wiresand fluids by the voltaic current is matter of general notoriety. 

277. Ii. _Magnetism. _--No fact is better known to philosophers than thepower of the voltaic current to deflect the magnetic needle, and to makemagnets according to _certain laws_; and no effect can be more distinctiveof an electrical current. 

278. Iii. _Chemical decomposition. _--The chemical powers of the voltaiccurrent, and their subjection to _certain laws_, are also perfectly wellknown. 

279. Iv. _Physiological effects. _--The power of the voltaic current, whenstrong, to shock and convulse the whole animal system, and when weak toaffect the tongue and the eyes, is very characteristic. 

280. V. _Spark_. --The brilliant star of light produced by the discharge ofa voltaic battery is known to all as the most beautiful light that man canproduce by art. 

 * * * * *

281. That these effects may be almost infinitely varied, some being exaltedwhilst others are diminished, is universally acknowledged; and yet withoutany doubt of the identity of character of the voltaic currents thus made todiffer in their effect. The beautiful explication of these variationsafforded by Cavendish's theory of quantity and intensity requires nosupport at present, as it is not supposed to be doubted. 

282. In consequence of the comparisons that will hereafter arise betweenwires carrying voltaic and ordinary electricities, and also because ofcertain views of the condition of a wire or any other conducting substanceconnecting the poles of a voltaic apparatus, it will be necessary to givesome definite expression of what is called the voltaic current, incontradistinction to any supposed peculiar state of arrangement, notprogressive, which the wire or the electricity within it may be supposed toassume. If two voltaic troughs PN, P'N', fig. 42, be symmetrically arrangedand insulated, and the ends NP' connected by a wire, over which a magneticneedle is suspended, the wire will exert no effect over the needle; butimmediately that the ends PN' are connected by another wire, the needlewill be deflected, and will remain so as long as the circuit is complete. Now if the troughs merely act by causing a peculiar arrangement in the wireeither of its particles or its electricity, that arrangement constitutingits electrical and magnetic state, then the wire NP' should be in a similarstate of arrangement _before_ P and N' were connected, to what it isafterwards, and should have deflected the needle, although less powerfully, perhaps to one half the extent which would result when the communication iscomplete throughout. But if the magnetic effects depend upon a current, then it is evident why they could not be produced in _any_ degree beforethe circuit was complete; because prior to that no current could exist. 

283. By _current_, I mean anything progressive, whether it be a fluid ofelectricity, or two fluids moving in opposite directions, or merelyvibrations, or, speaking still more generally, progressive forces. By_arrangement_, I understand a local adjustment of particles, or fluids, orforces, not progressive. Many other reasons might be urged in support ofthe view of a _current_ rather than an _arrangement_, but I am anxious toavoid stating unnecessarily what will occur to others at the moment. 

II. _Ordinary Electricity. _

284. By ordinary electricity I understand that which can be obtained fromthe common machine, or from the atmosphere, or by pressure, or cleavage ofcrystals, or by a multitude of other operations; its distinctive characterbeing that of great intensity, and the exertion of attractive and repulsivepowers, not merely at sensible but at considerable distances. 

285. _Tension. _ The attractions and repulsions at sensible distances, caused by ordinary electricity, are well known to be so powerful in certaincases, as to surpass, almost infinitely, the similar phenomena produced byelectricity, otherwise excited. But still those attractions and repulsionsare exactly of the same nature as those already referred to under the head_Tension, Voltaic electricity_ (268. ); and the difference in degree betweenthem is not greater than often occurs between cases of ordinary electricityonly. I think it will be unnecessary to enter minutely into the proofs ofthe identity of this character in the two instances. They are abundant; aregenerally admitted as good; and lie upon the surface of the subject: andwhenever in other parts of the comparison I am about to draw, a similarcase occurs, I shall content myself with a mere announcement of thesimilarity, enlarging only upon those parts where the great question ofdistinction or identity still exists. 

286. The discharge of common electricity through heated air is a well-knownfact. The parallel case of voltaic electricity has already been described(272, &c. ). 

287. _In motion. _ i. _Evolution of heat. _--The heating power of commonelectricity, when passed through wires or other substances, is perfectlywell known. The accordance between it and voltaic electricity is in thisrespect complete. Mr. Harris has constructed and described[A] a verybeautiful and sensible instrument on this principle, in which the heatproduced in a wire by the discharge of a small portion of commonelectricity is readily shown, and to which I shall have occasion to referfor experimental proof in a future part of this paper (344. ). 

 [A] Philosophical Transactions, 1827, p. 18. Edinburgh Transactions, 1831. Harris on a New Electrometer, &c. &c. 

288. Ii. _Magnetism. _--Voltaic electricity has most extraordinary andexalted magnetic powers. If common electricity be identical with it, itought to have the same powers. In rendering needles or bars magnetic, it isfound to agree with voltaic electricity, and the _direction_ of themagnetism, in both cases, is the same; but in deflecting the magneticneedle, common electricity has been found deficient, so that sometimes itspower has been denied altogether, and at other times distinctions have beenhypothetically assumed for the purpose of avoiding the difficulty[A]. 

 [A] Demonferrand's Manuel d'Electricité dynamique, p. 121. 

289. M. Colladon, of Geneva, considered that the difference might be due tothe use of insufficient quantities of common electricity in all theexperiments before made on this head; and in a memoir read to the Academiedes Sciences in 1826[A], describes experiments, in which, by the use of abattery, points, and a delicate galvanometer, he succeeded in obtainingdeflections, and thus establishing identity in that respect. MM. Arago, Ampère, and Savary, are mentioned in the paper as having witnessed asuccessful repetition of the experiments. But as no other one has comeforward in confirmation, MM. Arago, Ampère, and Savary, not havingthemselves published (that I am aware of) their admission of the results, and as some have not been able to obtain them, M. Colladon's conclusionshave been occasionally doubted or denied; and an important point with mewas to establish their accuracy, or remove them entirely from the body ofreceived experimental research. I am happy to say that my results fullyconfirm those by M. Colladon, and I should have had no occasion to describethem, but that they are essential as proofs of the accuracy of the finaland general conclusions I am enabled to draw respecting the magnetic andchemical action of electricity (360. 366. 367. 377. &c. ). 

 [A] Annales de Chimie, xxxiii. P. 62. 

290. The plate electrical machine I have used is fifty inches in diameter;it has two sets of rubbers; its prime conductor consists of two brasscylinders connected by a third, the whole length being twelve feet, and thesurface in contact with air about 1422 square inches. When in goodexcitation, one revolution of the plate will give ten or twelve sparks fromthe conductors, each an inch in length. Sparks or flashes from ten tofourteen inches in length may easily be drawn from the conductors. Eachturn of the machine, when worked moderately, occupies about 4/5ths of asecond. 

291. The electric battery consisted of fifteen equal jars. They are coatedeight inches upwards from the bottom, and are twenty-three inches incircumference, so that each contains one hundred and eighty-four squareinches of glass, coated on both sides; this is independent of the bottoms, which are of thicker glass, and contain each about fifty square inches. 

292. A good _discharging train_ was arranged by connecting metallically asufficiently thick wire with the metallic gas pipes of the house, with themetallic gas pipes belonging to the public gas works of London; and alsowith the metallic water pipes of London. It was so effectual in its officeas to carry off instantaneously electricity of the feeblest tension, eventhat of a single voltaic trough, and was essential to many of theexperiments. 

293. The galvanometer was one or the other of those formerly described (87. 205. ), but the glass jar covering it and supporting the needle was coatedinside and outside with tinfoil, and the upper part (left uncoated, thatthe motions of the needle might be examined, ) was covered with a frame ofwire-work, having numerous sharp points projecting from it. When this frameand the two coatings were connected with the discharging train (292. ), aninsulated point or ball, connected with the machine when most active, mightbe brought within an inch of any part of the galvanometer, yet withoutaffecting the needle within by ordinary electrical attraction or repulsion. 

294. In connexion with these precautions, it may be necessary to state thatthe needle of the galvanometer is very liable to have its magnetic powerderanged, diminished, or even inverted by the passage of a shock throughthe instrument. If the needle be at all oblique, in the wrong direction, tothe coils of the galvanometer when the shock passes, effects of this kindare sure to happen. 

295. It was to the retarding power of bad conductors, with the intention ofdiminishing its _intensity_ without altering its _quantity_, that I firstlooked with the hope of being able to make common electricity assume moreof the characters and power of voltaic electricity, than it is usuallysupposed to have. 

296, The coating and armour of the galvanometer were first connected withthe discharging train (292. ); the end B (87. ) of the galvanometer wire wasconnected with the outside coating of the battery, and then both these withthe discharging train; the end A of the galvanometer wire was connectedwith a discharging rod by a wet thread four feet long; and finally, whenthe battery (291. ) had been positively charged by about forty turns of themachine, it was discharged by the rod and the thread through thegalvanometer. The needle immediately moved. 

297. During the time that the needle completed its vibration in the firstdirection and returned, the machine was worked, and the battery recharged;and when the needle in vibrating resumed its first direction, the dischargewas again made through the galvanometer. By repeating this action a fewtimes, the vibrations soon extended to above 40° on each side of the lineof rest. 

298. This effect could be obtained at pleasure. Nor was it varied, apparently, either in direction or degree, by using a short thick string, or even four short thick strings in place of the long fine thread. With amore delicate galvanometer, an excellent swing of the needle could beobtained by one discharge of the battery. 

299. On reversing the galvanometer communications so as to pass thedischarge through from B to A, the needle was equally well deflected, butin the opposite direction. 

300. The deflections were in the same direction as if a voltaic current hadbeen passed through the galvanometer, i. E. The positively charged surfaceof the electric battery coincided with the positive end of the voltaicapparatus (268. ) and the negative surface of the former with the negativeend of the latter. 

301. The battery was then thrown out of use, and the communications soarranged that the current could be passed from the prime conductor, by thedischarging rod held against it, through the wet string, through thegalvanometer coil, and into the discharging train (292), by which it wasfinally dispersed. This current could be stopped at any moment, by removingthe discharging rod, and either stopping the machine or connecting theprime conductor by another rod with the discharging train; and could be asinstantly renewed. The needle was so adjusted, that whilst vibrating inmoderate and small arcs, it required time equal to twenty-five beats of awatch to pass in one direction through the arc, and of course an equal timeto pass in the other direction. 

302. Thus arranged, and the needle being stationary, the current, directfrom the machine, was sent through the galvanometer for twenty-five beats, then interrupted for other twenty-five beats, renewed for twenty-five beatsmore, again interrupted for an equal time, and so on continually. Theneedle soon began to vibrate visibly, and after several alternations ofthis kind, the vibration increased to 40° or more. 

303. On changing the direction of the current through the galvanometer, thedirection of the deflection of the needle was also changed. In all casesthe motion of the needle was in direction the same as that caused either bythe use of the electric battery or a voltaic trough (300). 

304. I now rejected the wet string, and substituted a copper wire, so thatthe electricity of the machine passed at once into wires communicatingdirectly with the discharging train, the galvanometer coil being one of thewires used for the discharge. The effects were exactly those obtained above(302). 

305. Instead of passing the electricity through the system, by bringing thedischarging rod at the end of it into contact with the conductor, fourpoints were fixed on to the rod; when the current was to pass, they wereheld about twelve inches from the conductor, and when it was not to pass, they were turned away. Then operating as before (302. ), except with thisvariation, the needle was soon powerfully deflected, and in perfectconsistency with the former results. Points afforded the means by whichColladon, in all cases, made his discharges. 

306. Finally, I passed the electricity first through an exhausted receiver, so as to make it there resemble the aurora borealis, and then through thegalvanometer to the earth; and it was found still effective in deflectingthe needle, and apparently with the same force as before. 

307. From all these experiments, it appears that a current of commonelectricity, whether transmitted through water or metal, or rarefied air, or by means of points in common air, is still able to deflect the needle;the only requisite being, apparently, to allow time for its action: that itis, in fact, just as magnetic in every respect as a voltaic current, andthat in this character therefore no distinction exists. 

308. Imperfect conductors, as water, brine, acids, &c. &c. Will be foundfar more convenient for exhibiting these effects than other modes ofdischarge, as by points or balls; for the former convert at once the chargeof a powerful battery into a feeble spark discharge, or rather continuouscurrent, and involve little or no risk of deranging the magnetism of theneedles (294. ). 

309. Iii. _Chemical decomposition. _--The chemical action of voltaicelectricity is characteristic of that agent, but not more characteristicthan are the _laws_ under which the bodies evolved by decomposition arrangethemselves at the poles. Dr. Wollaston showed[A] that common electricityresembled it in these effects, and "that they are both essentially thesame"; but he mingled with his proofs an experiment having a resemblance, and nothing more, to a case of voltaic decomposition, which however hehimself partly distinguished; and this has been more frequently referred toby some, on the one hand, to prove the occurrence of electro-chemicaldecomposition, like that of the pile, and by others to throw doubt upon thewhole paper, than the more numerous and decisive experiments which he hasdetailed. 

 [A] Philosophical Transactions, 1801, pp. 427, 434. 

310. I take the liberty of describing briefly my results, and of thusadding my testimony to that of Dr. Wollaston on the identity of voltaic andcommon electricity as to chemical action, not only that I may facilitatethe repetition of the experiments, but also lead to some new consequencesrespecting electrochemical decomposition (376. 377. ). 

311. I first repeated Wollaston's fourth experiment[A], in which the endsof coated silver wires are immersed in a drop of sulphate of copper. Bypassing the electricity of the machine through such an arrangement, thatend in the drop which received the electricity became coated with metalliccopper. One hundred turns of the machine produced an evident effect; twohundred turns a very sensible one. The decomposing action was however veryfeeble. Very little copper was precipitated, and no sensible trace ofsilver from the other pole appeared in the solution. 

 [A] Philosophical Transactions, 1801, p. 429. 

312. A much more convenient and effectual arrangement for chemicaldecompositions by common electricity, is the following. Upon a glass plate, fig. 43, placed over, but raised above a piece of white paper, so thatshadows may not interfere, put two pieces of tinfoil _a, b_; connect one ofthese by an insulated wire _c_, or wire and string (301. ) with the machine, and the other _g_, with the discharging train (292. ) or the negativeconductor; provide two pieces of fine platina wire, bent as in fig. 44, sothat the part _d, f_ shall be nearly upright, whilst the whole is restingon the three bearing points _p, e, f_ place these as in fig. 43; the points_p, n_ then become the decomposing poles. In this way surfaces of contact, as minute as possible, can be obtained at pleasure, and the connexion canbe broken or renewed in a moment, and the substances acted upon examinedwith the utmost facility. 

313. A coarse line was made on the glass with solution of sulphate ofcopper, and the terminations _p_ and _n_ put into it; the foil _a_ wasconnected with the positive conductor of the machine by wire and wetstring, so that no sparks passed: twenty turns of the machine caused theprecipitation of so much copper on the end _n_, that it looked like copperwire; no apparent change took place at _p_. 

314. A mixture of equal parts of muriatic acid and water was rendered deepblue by sulphate of indigo, and a large drop put on the glass, fig. 43, sothat _p_ and _n_ were immersed at opposite sides: a single turn of themachine showed bleaching effects round _p_, from evolved chlorine. Aftertwenty revolutions no effect of the kind was visible at _n_, but so muchchlorine had been set free at _p_, that when the drop was stirred the wholebecame colourless. 

315. A drop of solution of iodide of potassium mingled with starch was putinto the same position at _p_ and _n_; on turning the machine, iodine wasevolved at _p_, but not at _n_. 

316. A still further improvement in this form of apparatus consists inwetting a piece of filtering paper in the solution to be experimented on, and placing that under the points _p_ and _n_, on the glass: the paperretains the substance evolved at the point of evolution, by its whitenessrenders any change of colour visible, and allows of the point of contactbetween it and the decomposing wires being contracted to the utmost degree. A piece of paper moistened in the solution of iodide of potassium andstarch, or of the iodide alone, with certain precautions (322. ), is a mostadmirable test of electro-chemical action; and when thus placed and actedupon by the electric current, will show iodine evolved at _p_ by only halfa turn of the machine. With these adjustments and the use of iodide ofpotassium on paper, chemical action is sometimes a more delicate test ofelectrical currents than the galvanometer (273. ). Such cases occur when thebodies traversed by the current are bad conductors, or when the quantity ofelectricity evolved or transmitted in a given time is very small. 

317. A piece of litmus paper moistened in solution of common salt orsulphate of soda, was quickly reddened at _p_. A similar piece moistened inmuriatic acid was very soon bleached at _p_. No effects of a similar kindtook place at _n_. 

318. A piece of turmeric paper moistened in solution of sulphate of sodawas reddened at _n_ by two or three turns of the machine, and in twenty orthirty turns plenty of alkali was there evolved. On turning the paperround, so that the spot came under _p_, and then working the machine, thealkali soon disappeared, the place became yellow, and a brown alkaline spotappeared in the new part under _n_. 

319. On combining a piece of litmus with a piece of turmeric paper, wettingboth with solution of sulphate of soda, and putting the paper on the glass, so that _p_ was on the litmus and _n_ on the turmeric, a very few turns ofthe machine sufficed to show the evolution of acid at the former and alkaliat the latter, exactly in the manner effected by a volta-electric current. 

320. All these decompositions took place equally well, whether theelectricity passed from the machine to the foil _a_, through water, orthrough wire only; by _contact_ with the conductor, or by _sparks_ there;provided the sparks were not so large as to cause the electricity to passin sparks from _p_ to _n_, or towards _n_; and I have seen no reason tobelieve that in cases of true electro-chemical decomposition by themachine, the electricity passed in sparks from the conductor, or at anypart of the current, is able to do more, because of its tension, than thatwhich is made to pass merely as a regular current. 

321. Finally, the experiment was extended into the following form, supplying in this case the tidiest analogy between common and voltaicelectricity. Three compound pieces of litmus and turmeric paper (319. ) weremoistened in solution of sulphate of soda, and arranged on a plate of glasswith platina wires, as in fig. 45. The wire _m_ was connected with theprime conductor of the machine, the wire _t_ with the discharging train, and the wires _r_ and _s_ entered into the course of the electrical currentby means of the pieces of moistened paper; they were so bent as to resteach on three points, _n, r, p; n, s, p_, the points _r_ and _s_ beingsupported by the glass, and the others by the papers; the threeterminations _p, p, p_ rested on the litmus, and the other three _n, n, n_on the turmeric paper. On working the machine for a short time only, acidwas evolved at _all_ the poles or terminations _p, p, p_, by which theelectricity entered the solution, and alkali at the other poles _n, n, n_, by which the electricity left the solution. 

322. In all experiments of electro-chemical decomposition by the commonmachine and moistened papers (316. ), it is necessary to be aware of and toavoid the following important source of error. If a spark passes overmoistened litmus and turmeric paper, the litmus paper (provided it bedelicate and not too alkaline, ) is reddened by it; and if several sparksare passed, it becomes powerfully reddened. If the electricity pass alittle way from the wire over the surface of the moistened paper, before itfinds mass and moisture enough to conduct it, then the reddening extends asfar as the ramifications. If similar ramifications occur at the termination_n_, on the turmeric paper, they _prevent_ the occurrence of the red spotdue to the alkali, which would otherwise collect there: sparks orramifications from the points _n_ will also redden litmus paper. If papermoistened by a solution of iodide of potassium (which is an admirablydelicate test of electro-chemical action, ) be exposed to the sparks orramifications, or even a feeble stream of electricity through the air fromeither the point _p_ or _n_, iodine will be immediately evolved. 

323. These effects must not be confounded with those due to the trueelectro-chemical powers of common electricity, and must be carefullyavoided when the latter are to be observed. No sparks should be passed, therefore, in any part of the current, nor any increase of intensityallowed, by which the electricity may be induced to pass between theplatina wires and the moistened papers, otherwise than by conduction; forif it burst through the air, the effect referred to above (322. ) ensues. 

324. The effect itself is due to the formation of nitric acid by thecombination of the oxygen and nitrogen of the air, and is, in fact, only adelicate repetition of Cavendish's beautiful experiment. The acid soformed, though small in quantity, is in a high state of concentration as towater, and produces the consequent effects of reddening the litmus paper;or preventing the exhibition of alkali on the turmeric paper; or, by actingon the iodide of potassium, evolving iodine. 

325. By moistening a very small slip of litmus paper in solution of causticpotassa, and then passing the electric spark over its length in the air, Igradually neutralized the alkali, and ultimately rendered the paper red; ondrying it, I found that nitrate of potassa had resulted from the operation, and that the paper had become touch-paper. 

326. Either litmus paper or white paper, moistened in a strong solution ofiodide of potassium, offers therefore a very simple, beautiful, and readymeans of illustrating Cavendish's experiment of the formation of nitricacid from the atmosphere. 

327. I have already had occasion to refer to an experiment (265. 309. ) madeby Dr. Wollaston, which is insisted upon too much, both by those who opposeand those who agree with the accuracy of his views respecting the identityof voltaic and ordinary electricity. By covering fine wires with glass orother insulating substances, and then removing only so much matter as toexpose the point, or a section of the wires, and by passing electricitythrough two such wires, the guarded points of which were immersed in water, Wollaston found that the water could be decomposed even by the current fromthe machine, without sparks, and that two streams of gas arose from thepoints, exactly resembling, in appearance, those produced by voltaicelectricity, and, like the latter, giving a mixture of oxygen and hydrogengases. But Dr. Wollaston himself points out that the effect is differentfrom that of the voltaic pile, inasmuch as both oxygen and hydrogen areevolved from _each_ pole; he calls it "a very close _imitation_ of thegalvanic phenomena, " but adds that "in fact the resemblance is notcomplete, " and does not trust to it to establish the principles correctlylaid down in his paper. 

328. This experiment is neither more nor less than a repetition, in arefined manner, of that made by Dr. Pearson in 1797[A], and previously byMM. Paets Van Troostwyk and Deiman in 1789 or earlier. That the experimentshould never be quoted as proving true electro-chemical decomposition, issufficiently evident from the circumstance, that the _law_ which regulatesthe transference and final place of the evolved bodies (278. 309. ) has noinfluence here. The water is decomposed at both poles independently of eachother, and the oxygen and hydrogen evolved at the wires are the elements ofthe water existing the instant before in those places. That the poles, orrather points, have no mutual decomposing dependence, may be shown bysubstituting a wire, or the finger, for one of them, a change which doesnot at all interfere with the other, though it stops all action at thechanged pole. This fact may be observed by turning the machine for sometime; for though bubbles will rise from the point left unaltered, inquantity sufficient to cover entirely the wire used for the othercommunication, if they could be applied to it, yet not a single bubble willappear on that wire. 

 [A] Nicholson's Journal, 4to. Vol. I. Pp. 311, 299. 349. 

329. When electro-chemical decomposition takes place, there is great reasonto believe that the _quantity_ of matter decomposed is not proportionate tothe intensity, but to the quantity of electricity passed (320. ). Of this Ishall be able to offer some proofs in a future part of this paper (375. 377. ). But in the experiment under consideration, this is not the case. If, with a constant pair of points, the electricity be passed from the machinein sparks, a certain proportion of gas is evolved; but if the sparks berendered shorter, less gas is evolved; and if no sparks be passed, there isscarcely a sensible portion of gases set free. On substituting solution ofsulphate of soda for water, scarcely a sensible quantity of gas could beprocured even with powerful sparks, and nearly none with the mere current;yet the quantity of electricity in a given time was the same in all thesecases. 

330. I do not intend to deny that with such an apparatus common electricitycan decompose water in a manner analogous to that of the voltaic pile; Ibelieve at present that it can. But when what I consider the true effectonly was obtained, the quantity of gas given off was so small that I couldnot ascertain whether it was, as it ought to be, oxygen at one wire andhydrogen at the other. Of the two streams one seemed more copious than theother, and on turning the apparatus round, still the same side in relationto the machine; gave the largest stream. On substituting solution ofsulphate of soda for pure water (329. ), these minute streams were stillobserved. But the quantities were so small, that on working the machine forhalf an hour I could not obtain at either pole a bubble of gas larger thana small grain of sand. If the conclusion which I have drawn (377. ) relatingto the amount of chemical action be correct, this ought to be the case. 

331. I have been the more anxious to assign the true value of thisexperiment as a test of electro-chemical action, because I shall haveoccasion to refer to it in cases of supposed chemical action bymagneto-electric and other electric currents (336. 346. ) and elsewhere. But, independent of it, there cannot be now a doubt that Dr. Wollaston wasright in his general conclusion; and that voltaic and common electricityhave powers of chemical decomposition, alike in their nature, and governedby the same law of arrangement. 

332. Iv. _Physiological effects. _--The power of the common electric currentto shock and convulse the animal system, and when weak to affect the tongueand the eyes, may be considered as the same with the similar power ofvoltaic electricity, account being taken of the intensity of the oneelectricity and duration of the other. When a wet thread was interposed inthe course of the current of common electricity from the battery (291. )charged by eight or ten[A] revolutions of the machine in good action(290. ), and the discharge made by platina spatulas through the tongue orthe gums, the effect upon the tongue and eyes was exactly that of amomentary feeble voltaic circuit. 

 [A] Or even from thirty to forty. 

333. V. _Spark. _--The beautiful flash of light attending the discharge ofcommon electricity is well known. It rivals in brilliancy, if it does noteven very much surpass, the light from the discharge of voltaicelectricity; but it endures for an instant only, and is attended by a sharpnoise like that of a small explosion. Still no difficulty can arise inrecognising it to be the same spark as that from the voltaic battery, especially under certain circumstances. The eye cannot distinguish thedifference between a voltaic and a common electricity spark, if they betaken between amalgamated surfaces of metal, at intervals only, and throughthe same distance of air. 

334. When the Leyden battery (291. ) was discharged through a wet stringplaced in some part of the circuit away from the place where the spark wasto pass, the spark was yellowish, flamy, having a duration sensibly longerthan if the water had not been interposed, was about three-fourths of aninch in length, was accompanied by little or no noise, and whilst losingpart of its usual character had approximated in some degree to the voltaicspark. When the electricity retarded by water was discharged between piecesof charcoal, it was exceedingly luminous and bright upon both surfaces ofthe charcoal, resembling the brightness of the voltaic discharge on suchsurfaces. When the discharge of the unretarded electricity was taken uponcharcoal, it was bright upon both the surfaces, (in that respect resemblingthe voltaic spark, ) but the noise was loud, sharp, and ringing. 

335. I have assumed, in accordance, I believe, with the opinion of everyother philosopher, that atmospheric electricity is of the same nature withordinary electricity (284. ), and I might therefore refer to certainpublished statements of chemical effects produced by the former as proofsthat the latter enjoys the power of decomposition in common with voltaicelectricity. But the comparison I am drawing is far too rigorous to allowme to use these statements without being fully assured of their accuracy;yet I have no right to suppress them, because, if accurate, they establishwhat I am labouring to put on an undoubted foundation, and have priority tomy results. 

336. M. Bonijol of Geneva[A] is said to have constructed very delicateapparatus for the decomposition of water by common electricity. Byconnecting an insulated lightning rod with his apparatus, the decompositionof the water proceeded in a continuous and rapid manner even when theelectricity of the atmosphere was not very powerful. The apparatus is notdescribed; but as the diameter of the wire is mentioned as very small, itappears to have been similar in construction to that of Wollaston (327. );and as that does not furnish a case of true polar electro-chemicaldecomposition (328. ), this result of M. Bonijol does not prove the identityin chemical action of common and voltaic electricity. 

 [A] Bibliothèque Universelle, 1830, tome xlv. P. 213. 

337. At the same page of the Bibliothèque Universelle, M. Bonijol is saidto have decomposed, _potash_, and also chloride of silver, by putting theminto very narrow tubes and passing electric sparks from an ordinary machineover them. It is evident that these offer no analogy to cases of truevoltaic decomposition, where the electricity only decomposes when it is_conducted_ by the body acted upon, and ceases to decompose, according toits ordinary laws, when it passes in sparks. These effects are probablypartly analogous to that which takes place with water in Pearson's orWollaston's apparatus, and may be due to very high temperature acting onminute portions of matter; or they may be connected with the results in air(322. ). As nitrogen can combine directly with oxygen under the influence ofthe electric spark (324. ), it is not impossible that it should even take itfrom the potassium of the potash, especially as there would be plenty ofpotassa in contact with the acting particles to combine with the nitricacid formed. However distinct all these actions may be from true polarelectro-chemical decompositions, they are still highly important, andwell-worthy of investigation. 

338. The late Mr. Barry communicated a paper to the Royal Society[A] lastyear, so distinct in the details, that it would seem at once to prove theidentity in chemical action of common and voltaic electricity; but, whenexamined, considerable difficulty arises in reconciling certain of theeffects with the remainder. He used two tubes, each having a wire within itpassing through the closed end, as is usual for voltaic decompositions. Thetubes were filled with solution of sulphate of soda, coloured with syrup ofviolets, and connected by a portion of the same solution, in the ordinarymanner; the wire in one tube was connected by a _gilt thread_ with thestring of an insulated electrical kite, and the wire in the other tube by asimilar _gilt thread_ with the ground. Hydrogen soon appeared in the tubeconnected with the kite, and oxygen in the other, and in ten minutes theliquid in the first tube was green from the alkali evolved, and that in theother red from free acid produced. The only indication of the strength orintensity of the atmospheric electricity is in the expression, "the usualshocks were felt on touching the string. "

 [A] Philosophical Transactions, 1831, p. 165. 

339. That the electricity in this case does not resemble that from anyordinary source of common electricity, is shown by several circumstances. Wollaston could not effect the decomposition of water by such anarrangement, and obtain the gases in _separate_ vessels, using commonelectricity; nor have any of the numerous philosophers, who have employedsuch an apparatus, obtained any such decomposition, either of water or of aneutral salt, by the use of the machine. I have lately tried the largemachine (290. ) in full action for a quarter of an hour, during which timeseven hundred revolutions were made, without producing any sensibleeffects, although the shocks that it would then give must have been farmore powerful and numerous than could have been taken, with any chance ofsafety, from an electrical kite-string; and by reference to the comparisonhereafter to be made (371. ), it will be seen that for common electricity tohave produced the effect, the quantity must have been awfully great, andapparently far more than could have been conducted to the earth by a giltthread, and at the same time only have produced the "usual shocks. "

340. That the electricity was apparently not analogous to voltaicelectricity is evident, for the "usual shocks" only were produced, andnothing like the terrible sensation due to a voltaic battery, even when ithas a tension so feeble as not to strike through the eighth of an inch ofair. 

341. It seems just possible that the air which was passing by the kite andstring, being in an electrical state sufficient to produce the "usualshocks" only, could still, when the electricity was drawn off below, renewthe charge, and so continue the current. The string was 1500 feet long, andcontained two double threads. But when the enormous quantity which musthave been thus collected is considered (371. 376. ), the explanation seemsvery doubtful. I charged a voltaic battery of twenty pairs of plates fourinches square with double coppers very strongly, insulated it, connectedits positive extremity with the discharging train (292. ), and its negativepole with an apparatus like that of Mr. Barry, communicating by a wireinserted three inches into the wet soil of the ground. This battery thusarranged produced feeble decomposing effects, as nearly as I could judgeanswering the description Mr. Barry has given. Its intensity was, ofcourse, far lower than the electricity of the kite-string, but the supplyof quantity from the discharging train was unlimited. It gave no shocks tocompare with the "usual shocks" of a kite-string. 

342. Mr. Barry's experiment is a very important one to repeat and verify. If confirmed, it will be, as far as I am aware, the first recorded case oftrue electro-chemical decomposition of water by common electricity, and itwill supply a form of electrical current, which, both in quantity andintensity, is exactly intermediate with those of the common electricalmachine and the voltaic pile. 

 * * * * *

III. _Magneto-Electricity. _

343. _Tension_. --The attractions and repulsions due to the tension ofordinary electricity have been well observed with that evolved bymagneto-electric induction. M. Pixii, by using an apparatus, clever in itsconstruction and powerful in its action[A], was able to obtain greatdivergence of the gold leaves of an electrometer[B]. 

 [A] Annales de Chimie, l. P. 322. 

 [B] Ibid. Li. P 77. 

344. _In motion_: i. _Evolution of Heat. _--The current produced bymagneto-electric induction can heat a wire in the manner of ordinaryelectricity. At the British Association of Science at Oxford, in June ofthe present year, I had the pleasure, in conjunction with Mr. Harris, Professor Daniell, Mr. Duncan, and others, of making an experiment, forwhich the great magnet in the museum, Mr. Harris's new electrometer (287. ), and the magneto-electric coil described in my first paper (34. ), were putin requisition. The latter had been modified in the manner I have elsewheredescribed[A] so as to produce an electric spark when its contact with themagnet was made or broken. The terminations of the spiral, adjusted so asto have their contact with each other broken when the spark was to pass, were connected with the wire in the electrometer, and it was found thateach time the magnetic contact was made and broken, expansion of the airwithin the instrument occurred, indicating an increase, at the moment, ofthe temperature of the wire. 

 [A] Phil, Mag. And Annals, 1832, vol. Xi. P. 405. 

315. Ii. _Magnetism. _--These currents were discovered by their magneticpower. 

346. Iii. _Chemical decomposition. _--I have made many endeavours to effectchemical decomposition by magneto-electricity, but unavailingly. In Julylast I received an anonymous letter (which has since been published[A], )describing a magneto-electric apparatus, by which the decomposition ofwater was effected. As the term "guarded points" is used, I suppose theapparatus to have been Wollaston's (327. &c. ), in which case the resultsdid not indicate polar electro-chemical decomposition. Signor Botto hasrecently published certain results which he has obtained[B]; but they are, as at present described, inconclusive. The apparatus he used was apparentlythat of Dr. Wollaston, which gives only fallacious indications (327. &c. ). As magneto-electricity can produce sparks, it would be able to show theeffects proper to this apparatus. The apparatus of M. Pixii alreadyreferred to (343. ) has however, in the hands of himself[C] and M. Hachctte[D], given decisive chemical results, so as to complete this linkin the chain of evidence. Water was decomposed by it, and the oxygen andhydrogen obtained in separate tubes according to the law governingvolta-electric and machine-electric decomposition. 

 [A] Lond. And Edinb. Phil. Mag. And Journ. , 1832, vol. I. P. 161. 

 [B] Ibid. 1832. Vol. I. P. 441. 

 [C] Annales de Chimie, li, p. 77. 

 [D] Ibid. Li. P. 72

347. Iv. _Physiological effects. _--A frog was convulsed in the earliestexperiments on these currents (56. ). The sensation upon the tongue, and theflash before the eyes, which I at first obtained only in a feeble degree(56. ), have been since exalted by more powerful apparatus, so as to becomeeven disagreeable. 

348. V. _Spark. _--The feeble spark which I first obtained with thesecurrents (32. ), has been varied and strengthened by Signori Nobili andAntinori, and others, so as to leave no doubt as to its identity with thecommon electric spark. 

 * * * * *

IV. _Thermo-Electricity. _

349. With regard to thermo-electricity, (that beautiful form of electricitydiscovered by Seebeck, ) the very conditions under which it is excited aresuch as to give no ground for expecting that it can be raised like commonelectricity to any high degree of tension; the effects, therefore, due tothat state are not to be expected. The sum of evidence respecting itsanalogy to the electricities already described, is, I believe, asfollows:--_Tension. _ The attractions and repulsions due to a certain degreeof tension have not been observed. _In currents_: i. _Evolution of Heat. _ Iam not aware that its power of raising temperature has been observed. Ii. _Magnetism. _ It was discovered, and is best recognised, by its magneticpowers. Iii. _Chemical decomposition_ has not been effected by it. Iv. _Physiological effects. _ Nobili has shown[A] that these currents are ableto cause contractions in the limbs of a frog. V. _Spark. _ The spark has notyet been seen. 

 [A] Bibliothèque Universelle, xxxvii. 15. 

350. Only those effects are weak or deficient which depend upon a certainhigh degree of intensity; and if common electricity be reduced in thatquality to a similar degree with the thermo-electricity, it can produce noeffects beyond the latter. 

 * * * * *

V. _Animal Electricity. _

351. After an examination of the experiments of Walsh[A] Ingenhousz[B], Cavendish[C], Sir H. Davy[D], and Dr. Davy[E], no doubt remains on my mindas to the identity of the electricity of the torpedo with common andvoltaic electricity; and I presume that so little will remain on the mindsof others as to justify my refraining from entering at length into thephilosophical proofs of that identity. The doubts raised by Sir H. Davyhave been removed by his brother Dr. Davy; the results of the latter beingthe reverse of those of the former. At present the sum of evidence is asfollows:--

 [A] Philosophical Transactions, 1773, p. 461. 

 [B] Ibid. 1775, p. 1. 

 [C] Ibid. 1776, p. 196. 

 [D] Ibid. 1829, p. 15. 

 [E] Ibid. 1832, p. 259. 

352. _Tension. _--No sensible attractions or repulsions due to tension havebeen observed. 

353. _In motion_: i. Evolution of Heat; not yet observed; I have little orno doubt that Harris's electrometer would show it (287. 359. ). 

354. Ii. _Magnetism. _--Perfectly distinct. According to Dr. Davy[A], thecurrent deflected the needle and made magnets under the same law, as todirection, which governs currents of ordinary and voltaic electricity. 

 [A] Philosophical Transactions, 1832, p. 260. 

355. Iii. _Chemical decomposition. _--Also distinct; and though Dr. Davyused an apparatus of similar construction with that of Dr. Wollaston(327. ), still no error in the present case is involved, for thedecompositions were polar, and in their nature truly electro-chemical. Bythe direction of the magnet it was found that the under surface of the fishwas negative, and the upper positive; and in the chemical decompositions, silver and lead were precipitated on the wire connected with the undersurface, and not on the other; and when these wires were either steel orsilver, in solution of common salt, gas (hydrogen?) rose from the negativewire, but none from the positive. 

356. Another reason for the decomposition being electrochemical is, that aWollaston's apparatus constructed with _wires_, coated by sealing-wax, would most probably not have decomposed water, even in its own peculiarway, unless the electricity had risen high enough in intensity to producesparks in some part of the circuit; whereas the torpedo was not able toproduce sensible sparks. A third reason is, that the purer the water inWollaston's apparatus, the more abundant is the decomposition; and I havefound that a machine and wire points which succeeded perfectly well withdistilled water, failed altogether when the water was rendered a goodconductor by sulphate of soda, common salt, or other saline bodies. But inDr. Davy's experiments with the torpedo, _strong_ solutions of salt, nitrate of silver, and superacetate of lead were used successfully, andthere is no doubt with more success than weaker ones. 

357. Iv. _Physiological effects. _--These are so characteristic, that bythem the peculiar powers of the torpedo and gymnotus are principallyrecognised. 

358. V. _Spark. _--The electric spark has not yet been obtained, or at leastI think not; but perhaps I had better refer to the evidence on this point. Humboldt, speaking of results obtained by M. Fahlberg, of Sweden, says, "This philosopher has seen an electric spark, as Walsh and Ingenhousz haddone before him in London, by placing the gymnotus in the air, andinterrupting the conducting chain by two gold leaves pasted upon glass, anda line distant from each other[A]. " I cannot, however, find any record ofsuch an observation by either Walsh or Ingenhousz, and do not know where torefer to that by M. Fahlberg. M. Humboldt could not himself perceive anyluminous effect. 

 [A] Edinburgh Phil. Journal, ii. P. 249. 

Again, Sir John Leslie, in his dissertation on the progress of mathematicaland physical science, prefixed to the seventh edition of the EncyclopædiaBritannica, Edinb. 1830, p. 622, says, "From a healthy specimen" of the_Silurus electricus, _ meaning rather the _gymnotus_, "exhibited in London, vivid sparks were drawn in a darkened room"; but he does not say he sawthem himself, nor state who did see them; nor can I find any account ofsuch a phenomenon; so that the statement is doubtful[A]. 

 [A] Mr. Brayley, who referred me to those statements, and has extensive knowledge of recorded facts, is unacquainted with any further account relating to them. 

359. In concluding this summary of the powers of torpedinal electricity, Icannot refrain from pointing out the enormous absolute quantity ofelectricity which the animal must put in circulation at each effort. It isdoubtful whether any common electrical machine has as yet been able tosupply electricity sufficient in a reasonable time to cause trueelectro-chemical decomposition of water (330. 339. ), yet the current fromthe torpedo has done it. The same high proportion is shown by the magneticeffects (296. 371. ). These circumstances indicate that the torpedo haspower (in the way probably that Cavendish describes, ) to continue theevolution for a sensible time, so that its successive discharges ratherresemble those of a voltaic arrangement, intermitting in its action, thanthose of a Leyden apparatus, charged and discharged many times insuccession. In reality, however, there is _no philosophical difference_between these two cases. 

360. The _general conclusion_ which must, I think, be drawn from thiscollection of facts is, that _electricity, whatever may be its source, isidentical in its nature_. The phenomena in the five kinds or speciesquoted, differ, not in their character but only in degree; and in thatrespect vary in proportion to the variable circumstances of _quantity_ and_intensity_[A] which can at pleasure be made to change in almost any one ofthe kinds of electricity, as much as it does between one kind and another. 

 [A] The term _quantity_ in electricity is perhaps sufficiently definiteas to sense; the term _intensity_ is more difficult to define strictly. I am using the terms in their ordinary and accepted meaning. 

Table of the experimental Effects common to the Electricities derived fromdifferent Sources[A]. 

Table headings

A: Physiological EffectsB: Magnetic Deflection. C: Magnets made. D: Spark. E: Heating Power. F: True chemical Action. G: Attraction and Repulsion. H: Discharge by Hot Air. _________________________________________________________| | | | | | | | | || | A | B | C | D | E | F | G | H ||_________________________|___|___|___|___|___|___|___|___|| | | | | | | | | || 1. Voltaic electricity | X | X | X | X | X | X | X | X ||_________________________|___|___|___|___|___|___|___|___|| | | | | | | | | || 2. Common electricity | X | X | X | X | X | X | X | X ||_________________________|___|___|___|___|___|___|___|___|| | | | | | | | | || 3. Magneto-Electricity | X | X | X | X | X | X | X | ||_________________________|___|___|___|___|___|___|___|___|| | | | | | | | | || 4. Thermo-Electricity | X | X | + | + | + | + | | ||_________________________|___|___|___|___|___|___|___|___|| | | | | | | | | || 5. Animal Electricity | X | X | X | + | + | X | | ||_________________________|___|___|___|___|___|___|___|___|

 [A] Many of the spaces in this table originally left blank may now be filled. Thus with _thermo-electricity_, Botto made magnets and obtained polar chemical decomposition: Antinori produced the spark; and if it has not been done before, Mr. Watkins has recently heated a wire in Harris's thermo-electrometer. In respect to _animal electricity_, Matteucci and Linari have obtained the spark from the torpedo, and I have recently procured it from the gymnotus: Dr. Davy has observed the heating power of the current from the torpedo. I have therefore filled up these spaces with crosses, in a different position to the others originally in the table. There remain but five spaces unmarked, two under _attraction_ and _repulsion_, and three under _discharge by hot air_; and though these effects have not yet been obtained, it is a necessary conclusion that they must be possible, since the _spark_ corresponding to them has been procured. For when a discharge across cold air can occur, that intensity which is the only essential additional requisite for the other effects must be present. --_Dec. 13 1838. _

§ 8. _Relation by Measure of common and voltaic Electricity. _[A]

 [A] In further illustration of this subject see 855-873 in Series VII. --_Dec. 1838. _

361. Believing the point of identity to be satisfactorily established, Inext endeavoured to obtain a common measure, or a known relation as toquantity, of the electricity excited by a machine, and that from a voltaicpile; for the purpose not only of confirming their identity (378. ), butalso of demonstrating certain general principles (366, 377, &c. ), andcreating an extension of the means of investigating and applying thechemical powers of this wonderful and subtile agent. 

362. The first point to be determined was, whether the same absolutequantity of ordinary electricity, sent through a galvanometer, underdifferent circumstances, would cause the same deflection of the needle. Anarbitrary scale was therefore attached to the galvanometer, each divisionof which was equal to about 4°, and the instrument arranged as in formerexperiments (296. ). The machine (290. ), battery (291. ), and other parts ofthe apparatus were brought into good order, and retained for the time asnearly as possible in the same condition. The experiments were alternatedso as to indicate any change in the condition of the apparatus and supplythe necessary corrections. 

363. Seven of the battery jars were removed, and eight retained for presentuse. It was found that about forty turns would fully charge the eight jars. They were then charged by thirty turns of the machine, and dischargedthrough the galvanometer, a thick wet string, about ten inches long, beingincluded in the circuit. The needle was immediately deflected fivedivisions and a half, on the one side of the zero, and in vibrating passedas nearly as possible through five divisions and a half on the other side. 

364. The other seven jars were then added to the eight, and the wholefifteen charged by thirty turns of the machine. The Henley's electrometerstood not quite half as high as before; but when the discharge was madethrough the galvanometer, previously at rest, the needle immediatelyvibrated, passing _exactly_ to the same division as in the former instance. These experiments with eight and with fifteen jars were repeated severaltimes alternately with the same results. 

365. Other experiments were then made, in which all the battery was used, and its charge (being fifty turns of the machine, ) sent through thegalvanometer: but it was modified by being passed sometimes through a merewet thread, sometimes through thirty-eight inches of thin string wetted bydistilled water, and sometimes through a string of twelve times thethickness, only twelve inches in length, and soaked in dilute acid (298. ). With the thick string the charge passed at once; with the thin string itoccupied a sensible time, and with the thread it required two or threeseconds before the electrometer fell entirely down. The current thereforemust have varied extremely in intensity in these different cases, and yetthe deflection of the needle was sensibly the same in all of them. If anydifference occurred, it was that the thin string and thread caused greatestdeflection; and if there is any lateral transmission, as M. Colladon says, through the silk in the galvanometer coil, it ought to have been so, because then the intensity is lower and the lateral transmission less. 

366. Hence it would appear that _if the same absolute quantity ofelectricity pass through the galvanometer, whatever may be its intensity, the dejecting force upon the magnetic needle is the same. _

367. The battery of fifteen jars was then charged by sixty revolutions ofthe machine, and discharged, as before, through the galvanometer. Thedeflection of the needle was now as nearly as possible to the eleventhdivision, but the graduation was not accurate enough for me to assert thatthe arc was exactly double the former arc; to the eye it appeared to be so. The probability is, that _the deflecting force of an electric current isdirectly proportional to the absolute quantity of electricity passed_, atwhatever intensity that electricity may be[A]. 

 [A] The great and general value of the galvanometer, as an actual measure of the electricity passing through it, either continuously or interruptedly, must be evident from a consideration of these two conclusions. As constructed by Professor Ritchie with glass threads (see Philosophical Transactions, 1830, p. 218, and Quarterly Journal of Science, New Series, vol. I. P. 29. ), it apparently seems to leave nothing unsupplied in its own department. 

368. Dr. Ritchie has shown that in a case where the intensity of theelectricity remained the same, the deflection of the magnetic needle wasdirectly as the quantity of electricity passed through the galvanometer[A]. Mr. Harris has shown that the _heating_ power of common electricity onmetallic wires is the same for the same quantity of electricity whateverits intensity might have previously been[B]. 

 [A] Quarterly Journal of Science, New Series, vol. I. P. 33. 

 [B] Plymouth Transactions, page 22. 

369. The next point was to obtain a _voltaic_ arrangement producing aneffect equal to that just described (367. ). A platina and a zinc wire werepassed through the same hole of a draw-plate, being then one eighteenth ofan inch in diameter; these were fastened to a support, so that their lowerends projected, were parallel, and five sixteenths of an inch apart. Theupper ends were well-connected with the galvanometer wires. Some acid wasdiluted, and, after various preliminary experiments, that adopted as astandard which consisted of one drop strong sulphuric acid in four ouncesdistilled water. Finally, the time was noted which the needle required inswinging either from right to left or left to right: it was equal toseventeen beats of my watch, the latter giving one hundred and fifty in aminute. The object of these preparations was to arrange a voltaicapparatus, which, by immersion in a given acid for a given time, much lessthan that required by the needle to swing in one direction, should giveequal deflection to the instrument with the discharge of ordinaryelectricity from the battery (363. 364. ); and a new part of the zinc wirehaving been brought into position with the platina, the comparativeexperiments were made. 

370. On plunging the zinc and platina wires five eighths of an inch deepinto the acid, and retaining them there for eight beats of the watch, (after which they were quickly withdrawn, ) the needle was deflected, andcontinued to advance in the same direction some time after the voltaicapparatus had been removed from the acid. It attained the five-and-a-halfdivision, and then returned swinging an equal distance on the other side. This experiment was repeated many times, and always with the same result. 

371. Hence, as an approximation, and judging from _magnetic force_ only atpresent (376. ), it would appear that two wires, one of platina and one ofzinc, each one eighteenth of an inch in diameter, placed five sixteenths ofan inch apart and immersed to the depth of five eighths of an inch in acid, consisting of one drop oil of vitriol and four ounces distilled water, at atemperature about 60°, and connected at the other extremities by a copperwire eighteen feet long and one eighteenth of an inch thick (being the wireof the galvanometer coils), yield as much electricity in eight beats of mywatch, or in 8/150ths of a minute, as the electrical battery charged bythirty turns of the large machine, in excellent order (363. 364. ). Notwithstanding this apparently enormous disproportion, the results areperfectly in harmony with those effects which are known to be produced byvariations in the intensity and quantity of the electric fluid. 

372. In order to procure a reference to _chemical action_, the wires werenow retained immersed in the acid to the depth of five eighths of an inch, and the needle, when stationary, observed; it stood, as nearly as theunassisted eye could decide, at 5-1/3 division. Hence a permanentdeflection to that extent might be considered as indicating a constantvoltaic current, which in eight beats of my watch (369. ) could supply asmuch electricity as the electrical battery charged by thirty turns of themachine. 

373. The following arrangements and results are selected from many thatwere made and obtained relative to chemical action. A platina wire onetwelfth of an inch in diameter, weighing two hundred and sixty grains, hadthe extremity rendered plain, so as to offer a definite surface equal to acircle of the same diameter as the wire; it was then connected in turn withthe conductor of the machine, or with the voltaic apparatus (369. ), so asalways to form the positive pole, and at the same time retain aperpendicular position, that it might rest, with its whole weight, upon thetest paper to be employed. The test paper itself was supported upon aplatina spatula, connected either with the discharging train (292. ), orwith the negative wire of the voltaic apparatus, and it consisted of fourthicknesses, moistened at all times to an equal degree in a standardsolution of hydriodate of potassa (316. ). 

374. When the platina wire was connected with the prime conductor of themachine, and the spatula with the discharging train, ten turns of themachine had such decomposing power as to produce a pale round spot ofiodine of the diameter of the wire; twenty turns made a much darker mark, and thirty turns made a dark brown spot penetrating to the second thicknessof the paper. The difference in effect produced by two or three turns, moreor less, could be distinguished with facility. 

375. The wire and spatula were then connected with the voltaic apparatus(369. ), the galvanometer being also included in the arrangement; and, astronger acid having been prepared, consisting of nitric acid and water, the voltaic apparatus was immersed so far as to give a permanent deflectionof the needle to the 5-1/3 division (372. ), the fourfold moistened paperintervening as before[A]. Then by shifting the end of the wire from placeto place upon the test paper, the effect of the current for five, six, seven, or any number of the beats of the watch (369. ) was observed, andcompared with that of the machine. After alternating and repeating theexperiments of comparison many times, it was constantly found that thisstandard current of voltaic electricity, continued for eight beats of thewatch, was equal, in chemical effect, to thirty turns of the machine;twenty-eight revolutions of the machine were sensibly too few. 

 [A] Of course the heightened power of the voltaic battery was necessary to compensate for the bad conductor now interposed. 

376. Hence it results that both in _magnetic deflection_ (371. ) and in_chemical force_, the current of electricity of the standard voltaicbattery for eight beats of the watch was equal to that of the machineevolved by thirty revolutions. 

377. It also follows that for this case of electro-chemical decomposition, and it is probable for all cases, that the _chemical power, like themagnetic force_ (36. ), _is in direct proportion to the absolute quantityof electricity_ which passes. 

378. Hence arises still further confirmation, if any were required, of theidentity of common and voltaic electricity, and that the differences ofintensity and quantity are quite sufficient to account for what weresupposed to be their distinctive qualities. 

379. The extension which the present investigations have enabled me to makeof the facts and views constituting the theory of electro-chemicaldecomposition, will, with some other points of electrical doctrine, bealmost immediately submitted to the Royal Society in another series ofthese Researches. 

_Royal Institution, 15th Dec. 1832. _

Note. --I am anxious, and am permitted, to add to this paper a correction ofan error which I have attributed to M. Ampère the first series of theseExperimental Researches. In referring to his experiment on the induction ofelectrical currents (78. ), I have called that a disc which I should havecalled a circle or a ring. M. Ampère used a ring, or a very short cylindermade of a narrow plate of copper bent into a circle, and he tells me thatby such an arrangement the motion is very readily obtained. I have notdoubted that M. Ampère obtained the motion he described; but merely mistookthe kind of mobile conductor used, and so far I described his _experiment_erroneously. 

In the same paragraph I have stated that M. Ampère says the disc turned "totake a position of equilibrium exactly as the spiral itself would haveturned had it been free to move"; and further on I have said that myresults tended to invert the sense of the proposition "stated by M. Ampère, _that a current of electricity tends to put the electricity of conductorsnear which it passes in motion in the same direction. _" M. Ampère tells mein a letter which I have just received from him, that he carefully avoided, when describing the experiment, any reference to the direction of theinduced current; and on looking at the passages he quotes to me, I findthat to be the case. I have therefore done him injustice in the abovestatements, and am anxious to correct my error. 

But that it may not be supposed I lightly wrote those passages, I willbriefly refer to my reasons for understanding them in the sense I did. Atfirst the experiment failed. When re-made successfully about a yearafterwards, it was at Geneva in company with M. A. De la Rive: the latterphilosopher described the results[A], and says that the plate of copperbent into a circle which was used as the mobile conductor "sometimesadvanced between the two branches of the (horse-shoe) magnet, and sometimeswas repelled, _according_ to the direction of the current in thesurrounding conductors. "

 [A] Bibliothèque Universelle, xxi. P. 48. 

I have been in the habit of referring to Demonferrand's _Manueld'Electricité Dynamique_, as a book of authority in France; containing thegeneral results and laws of this branch of science, up to the time of itspublication, in a well arranged form. At p. 173, the author, whendescribing this experiment, says, "The mobile circle turns to take aposition of equilibrium as a conductor would do in which the current movedin the _same direction_ as in the spiral;" and in the same paragraph headds, "It is therefore proved _that a current of electricity tends to putthe electricity of conductors, near which it passes, in motion in the samedirection. _" These are the words I quoted in my paper (78. ). 

Le Lycée of 1st of January, 1832, No. 36, in an article written after thereceipt of my first unfortunate letter to M. Hachette, and before my paperswere printed, reasons upon the direction of the induced currents, and says, that there ought to be "an elementary current produced in the samedirection as the corresponding portion of the producing current. " A littlefurther on it says, "therefore we ought to obtain currents, moving in the_same direction_, produced upon a metallic wire, either by a magnet or acurrent. M. Ampère _was so thouroughly persuaded that such ought to be thedirection of the currents by influence_, that he neglected to assurehimself of it in his experiment at Geneva. "

It was the precise statements in Demonferrand's Manuel, agreeing as theydid with the expression in M. De la Rive's paper, (which, however, I nowunderstand as only meaning that when the inducing current was changed, themotion of the mobile circle changed also, ) and not in discordance withanything expressed by M. Ampère himself where he speaks of the experiment, which made me conclude, when I wrote the paper, that what I wrote wasreally his avowed opinion; and when the Number of the Lycée referred toappeared, which was before my paper was printed, it could excite nosuspicion that I was in error. 

Hence the mistake into which I unwittingly fell. I am proud to correct itand do full justice to the acuteness and accuracy which, as far as I canunderstand the subjects, M. Ampère carries into all the branches ofphilosophy which he investigates. 

Finally, my note to (79. ) says that the Lycée, No. 36. "mistakes theerroneous results of MM. Fresnel and Ampère for true ones, " &c. &c. Incalling M. Ampère's results erroneous, I spoke of the results described in, and referred to by the Lycée itself; but _now_ that the expression of thedirection of the induced current is to be separated, the term _erroneous_ought no longer to be attached to them. 

April 29, 1833. M. F. ]

FOURTH SERIES. 

§ 9. _On a new Law of Electric Conduction. _ § 10. _On Conducting Powergenerally. _

Received April 24, --Read May 23, 1833. 

§ 9. _On a new Law of Electric Conduction. _[A]

 [A] In reference to this law see further considerations at 910. 1358. 1705. --_Dec. 1838. _

380. It was during the progress of investigations relating toelectro-chemical decomposition, which I still have to submit to the RoyalSociety, that I encountered effects due to a very _general law_ of electricconduction not hitherto recognised; and though they prevented me fromobtaining the condition I sought for, they afforded abundant compensationfor the momentary disappointment, by the new and important interest whichthey gave to an extensive part of electrical science. 

381. I was working with ice, and the solids resulting from the freezing ofsolutions, arranged either as barriers across a substance to be decomposed, or as the actual poles of a voltaic battery, that I might trace and catchcertain elements in their transit, when I was suddenly stopped in myprogress by finding that ice was in such circumstances a non-conductor ofelectricity; and that as soon as a thin film of it was interposed, in thecircuit of a very powerful voltaic battery, the transmission of electricitywas prevented, and all decomposition ceased. 

382. At first the experiments were made with common ice, during the coldfreezing weather of the latter end of January 1833; but the results werefallacious, from the imperfection of the arrangements, and the followingmore unexceptionable form of experiment was adopted. 

383. Tin vessels were formed, five inches deep, one inch and a quarter widein one direction, of different widths from three eighths to five eighths ofan inch in the other, and open at one extremity. Into these were fixed bycorks, plates of platina, so that the latter should not touch the tincases; and copper wires having previously been soldered to the plate, thesewere easily connected, when required, with a voltaic pile. Then distilledwater, previously boiled for three hours, was poured into the vessels, andfrozen by a mixture of salt and snow, so that pure transparent solid iceintervened between the platina and tin; and finally these metals wereconnected with the opposite extremities of the voltaic apparatus, agalvanometer being at the same time included in the circuit. 

384. In the first experiment, the platina pole was three inches and a halflong, and seven eighths of an inch wide; it was wholly immersed in thewater or ice, and as the vessel was four eighths of an inch in width, theaverage thickness of the intervening ice was only a quarter of an inch, whilst the surface of contact with it at both poles was nearly fourteensquare inches. After the water was frozen, the vessel was still retained inthe frigorific mixture, whilst contact between the tin and platinarespectively was made with the extremities of a well-charged voltaicbattery, consisting of twenty pairs of four-inch plates, each with doublecoppers. Not the slightest deflection of the galvanometer needle occurred. 

385. On taking the frozen arrangement out of the cold mixture, and applyingwarmth to the bottom of the tin case, so as to melt part of the ice, theconnexion with the battery being in the mean time retained, the needle didnot at first move; and it was only when the thawing process had extended sofar as to liquefy part of the ice touching the platina pole, thatconduction took place; but then it occurred effectually, and thegalvanometer needle was permanently deflected nearly 70°. 

386. In another experiment, a platina spatula, five inches in length andseven eighths of an inch in width, had four inches fixed in the ice, andthe latter was only three sixteenths of an inch thick between one metallicsurface and the other; yet this arrangement insulated as perfectly as theformer. 

387. Upon pouring a little water in at the top of this vessel on the ice, still the arrangement did not conduct; yet fluid water was evidently there. This result was the consequence of the cold metals having frozen the waterwhere they touched it, and thus insulating the fluid part; and it wellillustrates the non-conducting power of ice, by showing how thin a filmcould prevent the transmission of the battery current. Upon thawing partsof this thin film, at _both_ metals, conduction occurred. 

388. Upon warming the tin case and removing the piece of ice, it was foundthat a cork having slipped, one of the edges of the platina had been allbut in contact with the inner surface of the tin vessel; yet, notwithstanding the extreme thinness of the interfering ice in this place, no sensible portion of electricity had passed. 

389. These experiments were repeated many times with the same results. Atlast a battery of fifteen troughs, or one hundred and fifty pairs offour-inch plates, powerfully charged, was used; yet even here no sensiblequantity of electricity passed the thin barrier of ice. 

390. It seemed at first as if occasional departures from these effectsoccurred; but they could always be traced to some interferingcircumstances. The water should in every instance be well-frozen; forthough it is not necessary that the ice should reach from pole to pole, since a barrier of it about one pole would be quite sufficient to preventconduction, yet, if part remain fluid, the mere necessary exposure of theapparatus to the air or the approximation of the hands, is sufficient toproduce, at the _upper surface_ of the water and ice, a film of fluid, extending from the platina to the tin; and then conduction occurs. Again, if the corks used to block the platina in its place are damp or wet within, it is necessary that the cold be sufficiently well applied to freeze thewater in them, or else when the surfaces of their contact with the tinbecome slightly warm by handling, that part will conduct, and the interiorbeing ready to conduct also, the current will pass. The water should bepure, not only that unembarrassed results may be obtained, but also that, as the freezing proceeds, a minute portion of concentrated saline solutionmay not be formed, which remaining fluid, and being interposed in the ice, or passing into cracks resulting from contraction, may exhibit conductingpowers independent of the ice itself. 

391. On one occasion I was surprised to find that after thawing much of theice the conducting power had not been restored; but I found that a corkwhich held the wire just where it joined the platina, dipped so far intothe ice, that with the ice itself it protected the platina from contactwith the melted part long after that contact was expected. 

392. This insulating power of ice is not effective with electricity ofexalted intensity. On touching a diverged gold-leaf electrometer with awire connected with the platina, whilst the tin case was touched by thehand or another wire, the electrometer was instantly discharged (419. ). 

393. But though electricity of an intensity so low that it cannot divergethe electrometer, can still pass (though in very limited quantities(419. ), ) through ice; the comparative relation of water and ice to theelectricity of the voltaic apparatus is not less extraordinary on thataccount, Or less important in its consequences. 

394. As it did not seem likely that this _law of the assumption ofconducting power during liquefaction, and loss of it during congelation_, would be peculiar to water, I immediately proceeded to ascertain itsinfluence in other cases, and found it to be very general. For this purposebodies were chosen which were solid at common temperatures, but readilyfusible; and of such composition as, for other reasons connected withelectrochemical action, led to the conclusion that they would be able whenfused to replace water as conductors. A voltaic battery of two troughs, ortwenty pairs of four-inch plates (384. ), was used as the source ofelectricity, and a galvanometer introduced into the circuit to indicate thepresence or absence of a current. 

395. On fusing a little chloride of lead by a spirit lamp on a fragment ofa Florence flask, and introducing two platina wires connected with thepoles of the battery, there was instantly powerful action, the galvanometerwas most violently affected, and the chloride rapidly decomposed. Onremoving the lamp, the instant the chloride solidified all current andconsequent effects ceased, though the platina wires remained inclosed inthe chloride not more than the one-sixteenth of an inch from each other. Onrenewing the heat, as soon as the fusion had proceeded far enough to allowliquid matter to connect the poles, the electrical current instantlypassed. 

396. On fusing the chloride, with one wire introduced, and then touchingthe liquid with the other, the latter being cold, caused a little knob toconcrete on its extremity, and no current passed; it was only when the wirebecame so hot as to be able to admit or allow of contact with the liquidmatter, that conduction took place, and then it was very powerful. 

397. When chloride of silver and chlorate of potassa were experimentedwith, in a similar manner, exactly the same results occurred. 

398. Whenever the current passed in these cases, there was decomposition ofthe substances; but the electro-chemical part of this subject I purposeconnecting with more general views in a future paper[A]. 

 [A] In 1801, Sir H. Davy knew that "dry nitre, caustic potash, and soda are conductors of galvanism when rendered fluid by a high degree of heat, " (Journals of the Royal Institution, 1802, p. 53, ) but was not aware of the general law which I have been engaged in developing. It is remarkable, that eleven years after that, he should say, "There are no fluids known except such as contain water, which are capable of being made the medium of connexion between the metal or metals of the voltaic apparatus. "--Elements of Chemical Philosophy, p. 169. 

399. Other substances, which could not be melted on glass, were fused bythe lamp and blowpipe on platina connected with one pole of the battery, and then a wire, connected with the other, dipped into them. In this waychloride of sodium, sulphate of soda, protoxide of lead, mixed carbonatesof potash and soda, &c. &c. , exhibited exactly the same phenomena as thosealready described: whilst liquid, they conducted and were decomposed;whilst solid, though very hot, they insulated the battery current even whenfour troughs were used. 

400. Occasionally the substances were contained in small bent tubes ofgreen glass, and when fused, the platina poles introduced, one on eachside. In such cases the same general results as those already describedwere procured; but a further advantage was obtained, namely, that whilstthe substance was conducting and suffering decomposition, the finalarrangement of the elements could be observed. Thus, iodides of potassiumand lead gave iodine at the positive pole, and potassium or lead at thenegative pole. Chlorides of lead and silver gave chlorine at the positive, and metals at the negative pole. Nitre and chlorate; of potassa gaveoxygen, &c. , at the positive, and alkali, or even potassium, at thenegative pole. 

[Illustration]

401. A fourth arrangement was used for substances requiring very hightemperatures for their fusion. A platina wire was connected with one poleof the battery; its extremity bent into a small ring, in the mannerdescribed by Berzelius, for blowpipe experiments; a little of the salt, glass, or other substance, was melted on this ring by the ordinaryblowpipe, or even in some cases by the oxy-hydrogen blowpipe, and when thedrop, retained in its place by the ring, was thoroughly hot and fluid, aplatina wire from the opposite pole of the battery was made to touch it, and the effects observed. 

402. The following are various substances, taken from very differentclasses chemically considered, which are subject to this law. The listmight, no doubt, be enormously extended; but I have not had time to do morethan confirm the law by a sufficient number of instances. 

First, _water_. 

Amongst _oxides_;--potassa, protoxide of lead, glass of antimony, protoxideof antimony, oxide of bismuth. 

_Chlorides_ of potassium, sodium, barium, strontium, calcium, magnesium, manganese, zinc, copper (proto-), lead, tin (proto-), antimony, silver. 

_Iodides_ of potassium, zinc and lead, protiodide of tin, periodide ofmercury; _fluoride_ of potassium; _cyanide_ of potassium; _sulpho-cyanide_of potassium. 

_Salts. _ Chlorate of potassa; nitrates of potassa, soda, baryta, strontia, lead, copper, and silver; sulphates of soda and lead, proto-sulphate ofmercury; phosphates of potassa, soda, lead, copper, phosphoric glass oracid phosphate of lime; carbonates of potassa and soda, mingled andseparate; borax, borate of lead, per-borate of tin; chromate of potassa, bi-chromate of potassa, chromate of lead; acetate of potassa. 

_Sulphurets. _ Sulphuret of antimony, sulphuret of potassium made byreducing sulphate of potassa by hydrogen; ordinary sulphuret of potassa. 

Silicated potassa; chameleon mineral. 

403. It is highly interesting in the instances of those substances whichsoften before they liquefy, to observe at what period the conducting poweris acquired, and to what degree it is exalted by perfect fluidity. Thus, with the borate of lead, when heated by the lamp upon glass, it becomes assoft as treacle, but it did not conduct, and it was only when urged by theblowpipe and brought to a fair red heat, that it conducted. When renderedquite liquid, it conducted with extreme facility. 

404. I do not mean to deny that part of the increased conducting power inthese cases of softening was probably due to the elevation of temperature(432. 445. ); but I have no doubt that by far the greater part was due tothe influence of the general law already demonstrated, and which in theseinstances came gradually, instead of suddenly, into operation. 

405. The following are bodies which acquired no conducting power uponassuming the liquid state:--

Sulphur, phosphorus; iodide of sulphur, per-iodide of tin; orpiment, realgar; glacial acetic acid, mixed margaric and oleic acids, artificialcamphor; caffeine, sugar, adipocire, stearine of cocoa-nut oil, spermaceti, camphor, naphthaline, resin, gum sandarach, shell lac. 

406. Perchloride of tin, chloride of arsenic, and the hydrated chloride ofarsenic, being liquids, had no sensible conducting power indicated by thegalvanometer, nor were they decomposed. 

407. Some of the above substances are sufficiently remarkable as exceptionsto the general law governing the former cases. These are orpiment, realgar, acetic acid, artificial camphor, per-iodide of tin, and the chlorides oftin and arsenic. I shall have occasion to refer to these cases in the paperon Electro-chemical Decomposition. 

408. Boracic acid was raised to the highest possible temperature by anoxy-hydrogen flame (401. ), yet it gained no conducting powers sufficient toaffect the galvanometer, and underwent no apparent voltaic decomposition. It seemed to be quite as bad a conductor as air. Green bottle-glass, heatedin the same manner, did not gain conducting power sensible to thegalvanometer. Flint glass, when highly heated, did conduct a little anddecompose; and as the proportion of potash or oxide of lead was increasedin the glass, the effects were more powerful. Those glasses, consisting ofboracic acid on the one hand, and oxide of lead or potassa on the other, show the assumption of conducting power upon fusion and the accompanyingdecomposition very well. 

409. I was very anxious to try the general experiment with sulphuric acid, of about specific gravity 1. 783, containing that proportion of water whichgives it the power of crystallizing at 40° Fahr. ; but I found it impossibleto obtain it so that I could be sure the whole would congeal even at 0°Fahr. A ten-thousandth part of water, more or less than necessary, would, upon cooling the whole, cause a portion of uncongealable liquid toseparate, and that remaining in the interstices of the solid mass, andmoistening the planes of division, would prevent the correct observation ofthe phenomena due to entire solidification and subsequent liquefaction. 

410. With regard to the substances on which conducting power is thusconferred by liquidity, the degree of power so given is generally verygreat. Water is that body in which this acquired power is feeblest. In thevarious oxides, chlorides, salts, &c. &c. , it is given in a much higherdegree. I have not had time to measure the conducting power in these cases, but it is apparently some hundred times that of pure water. The increasedconducting power known to be given to water by the addition of salts, wouldseem to be in a great degree dependent upon the high conducting power ofthese bodies when in the liquid state, that state being given them for thetime, not by heat but solution in the water[A]. 

 [A] See a doubt on this point at 1356. --_Dec. 1838. _

411. Whether the conducting power of these liquefied bodies is aconsequence of their decomposition or not (413. ), or whether the twoactions of conduction and decomposition are essentially connected or not, would introduce no difference affecting the probable accuracy of thepreceding statement. 

412. This _general assumption of conducting power_ by bodies as soon asthey pass from the solid to the liquid state, offers a new andextraordinary character, the existence of which, as far as I know, has notbefore been suspected; and it seems importantly connected with someproperties and relations of the particles of matter which I may now brieflypoint out. 

413. In almost all the instances, as yet observed, which are governed bythis law, the substances experimented with have been those which were notonly compound bodies, but such as contain elements known to arrangethemselves at the opposite poles; and were also such as could be_decomposed_ by the electrical current. When conduction took place, decomposition occurred; when decomposition ceased, conduction ceased also;and it becomes a fair and an important question, Whether the conductionitself may not, wherever the law holds good, be a consequence not merely ofthe capability, but of the act of decomposition? And that question may beaccompanied by another, namely, Whether solidification does not preventconduction, merely by chaining the particles to their places, under theinfluence of aggregation, and preventing their final separation in themanner necessary for decomposition?

414. But, on the other hand, there is one substance (and others may occur), the _per-iodide of mercury_, which, being experimented with like the others(400. ), was found to insulate when solid, and to acquire conducting powerwhen fluid; yet it did not seem to undergo decomposition in the lattercase. 

415. Again, there are many substances which contain elements such as wouldbe expected to arrange themselves at the opposite poles of the pile, andtherefore in that respect fitted for decomposition, which yet do notconduct. Amongst these are the iodide of sulphur, per-iodide of zinc, per-chloride of tin, chloride of arsenic, hydrated chloride of arsenic, acetic acid, orpiment, realgar, artificial camphor, &c. ; and from these itmight perhaps be assumed that decomposition is dependent upon conductingpower, and not the latter upon the former. The true relation, however, ofconduction and decomposition in those bodies governed by the general lawwhich it is the object of this paper to establish, can only besatisfactorily made out from a far more extensive series of observationsthan those I have yet been able to supply[A]. 

 [A] See 673, &c. &c. --_Dec. 1838. _

416. The relation, under this law, of the conducting power for electricityto that for heat, is very remarkable, and seems to imply a naturaldependence of the two. As the solid becomes a fluid, it loses almostentirely the power of conduction for heat, but gains in a high degree thatfor electricity; but as it reverts hack to the solid state, it gains thepower of conducting heat, and loses that of conducting electricity. If, therefore, the properties are not incompatible, still they are moststrongly contrasted, one being lost as the other is gained. We may hope, perhaps, hereafter to understand the physical reason of this veryextraordinary relation of the two conducting powers, both of which appearto be directly connected with the corpuscular condition of the substancesconcerned. 

417. The assumption of conducting power and a decomposable condition byliquefaction, promises new opportunities of, and great facilities in, voltaic decomposition. Thus, such bodies as the oxides, chlorides, cyanides, sulpho-cyanides, fluorides, certain vitreous mixtures, &c. &c. , may be submitted to the action of the voltaic battery under newcircumstances; and indeed I have already been able, with ten pairs ofplates, to decompose common salt, chloride of magnesium, borax, &c. &c. , and to obtain sodium, magnesium, boron, &c. , in their separate states. 

§ 10. _On Conducting Power generally. _[A]

 [A] In reference to this § refer to 983 in series viii. , and the results connected with it. --_Dec. 1838. _

418. It is not my intention here to enter into an examination of all thecircumstances connected with conducting power, but to record certain factsand observations which have arisen during recent inquiries, as additions tothe general stock of knowledge relating to this point of electricalscience. 

419. I was anxious, in the first place, to obtain some idea of theconducting power of ice and solid salts for electricity of high tension(392. ), that a comparison might be made between it and the large accessionof the same power gained upon liquefaction. For this purpose the largeelectrical machine (290. ) was brought into excellent action, its conductorconnected with a delicate gold-leaf electrometer, and also with the platinainclosed in the ice (383. ), whilst the tin case was connected with thedischarging train (292. ). On working the machine moderately, the goldleaves barely separated; on working it rapidly, they could be opened nearlytwo inches. In this instance the tin case was five-eighths of an inch inwidth; and as, after the experiment, the platina plate was found verynearly in the middle of the ice, the average thickness of the latter hadbeen five-sixteenths of an inch, and the extent of surface of contact withtin and platina fourteen square inches (384. ). Yet, under thesecircumstances, it was but just able to conduct the small quantity ofelectricity which this machine could evolve (371. ), even when of a tensioncompetent to open the leaves two inches; no wonder, therefore, that itcould not conduct any sensible portion of the electricity of the troughs(384. ), which, though almost infinitely surpassing that of the machine inquantity, had a tension so low as not to be sensible to an electrometer. 

420. In another experiment, the tin case was only four-eighths of an inchin width, and it was found afterwards that the platina had been not quiteone-eighth of an inch distant in the ice from one side of the tin vessel. When this was introduced into the course of the electricity from themachine (419. ), the gold leaves could be opened, but not more than half aninch; the thinness of the ice favouring the conduction of the electricity, and permitting the same quantity to pass in the same time, though of a muchlower tension. 

421. Iodide of potassium which had been fused and cooled was introducedinto the course of the electricity from the machine. There were two pieces, each about a quarter of an inch in thickness, and exposing a surface oneach side equal to about half a square inch; these were placed upon platinaplates, one connected with the machine and electrometer (419. ), and theother with the discharging train, whilst a fine platina wire connected thetwo pieces, resting upon them by its two points. On working the electricalmachine, it was possible to open the electrometer leaves about two-thirdsof an inch. 

422. As the platina wire touched only by points, the facts show that thissalt is a far better conductor than ice; but as the leaves of theelectrometer opened, it is also evident with what difficulty conduction, even of the small portion of electricity produced by the machine, iseffected by this body in the solid state, when compared to the facilitywith which enormous quantities at very low tensions are transmitted by itwhen in the fluid state. 

423. In order to confirm these results by others, obtained from the voltaicapparatus, a battery of one hundred and fifty plates, four inches square, was well-charged: its action was good; the shock from it strong; thedischarge would _continue_ from copper to copper through four-tenths of aninch of air, and the gold-leaf electrometer before used could be openednearly a quarter of an inch. 

424. The ice vessel employed (420. ) was half an inch in width; as theextent of contact of the ice with the tin and platina was nearly fourteensquare inches, the whole was equivalent to a plate of ice having a surfaceof seven square inches, of perfect contact at each side, and only onefourth of an inch thick. It was retained in a freezing mixture during theexperiment. 

425. The order of arrangement in the course of the electric current was asfollows. The positive pole of the battery was connected by a wire with theplatina plate in the ice; the plate was in contact with the ice, the icewith the tin jacket, the jacket with a wire, which communicated with apiece of tin foil, on which rested one end of a bent platina wire (312. ), the other or decomposing end being supported on paper moistened withsolution of iodide of potassium (316. ): the paper was laid flat on aplatina spatula connected with the negative end of the battery. All thatpart of the arrangement between the ice vessel and the decomposing wirepoint, including both these, was insulated, so that no electricity mightpass through the latter which had not traversed the former also. 

426. Under these circumstances, it was found that, a pale brown spot ofiodine was slowly formed under the decomposing platina point, thusindicating that ice could conduct a little of the electricity evolved by avoltaic battery charged up to the degree of intensity indicated by theelectrometer. But it is quite evident that notwithstanding the enormousquantity of electricity which the battery could furnish, it was, underpresent circumstances, a very inferior instrument to the ordinary machine;for the latter could send as much through the ice as it could carry, beingof a far higher intensity, i. E. Able to open the electrometer leaves halfan inch or more (419. 420. ). 

427. The decomposing wire and solution of iodide of potassium were thenremoved, and replaced by a very delicate galvanometer (205. ); it was sonearly astatic, that it vibrated to and fro in about sixty-three beats of awatch giving one hundred and fifty beats in a minute. The same feeblenessof current as before was still indicated; the galvanometer needle wasdeflected, but it required to break and make contact three or four times(297. ), before the effect was decided. 

428. The galvanometer being removed, two platina plates were connected withthe extremities of the wires, and the tongue placed between them, so thatthe whole charge of the battery, so far as the ice would let it pass, wasfree to go through the tongue. Whilst standing on the stone floor, therewas shock, &c. , but when insulated, I could feel no sensation. I think afrog would have been scarcely, if at all, affected. 

429. The ice was now removed, and experiments made with other solid bodies, for which purpose they were placed under the end of the decomposing wireinstead of the solution of iodide of potassium (125. ). For instance, apiece of dry iodide of potassium was placed on the spatula connected withthe negative pole of the battery, and the point of the decomposing wireplaced upon it, whilst the positive end of the battery communicated withthe latter. A brown spot of iodine very slowly appeared, indicating thepassage of a little electricity, and agreeing in that respect with theresults obtained by the use of the electrical machine (421. ). When thegalvanometer was introduced into the circuit at the same time with theiodide, it was with difficulty that the action of the current on it couldbe rendered sensible. 

430. A piece of common salt previously fused and solidified beingintroduced into the circuit was sufficient almost entirely to destroy theaction on the galvanometer. Fused and cooled chloride of lead produced thesame effect. The conducting power of these bodies, _when fluid_, is verygreat (395. 402. ). 

431. These effects, produced by using the common machine and the voltaicbattery, agree therefore with each other, and with the law laid down inthis paper (394. ); and also with the opinion I have supported, in the ThirdSeries of these Researches, of the identity of electricity derived fromdifferent sources (360. ). 

432. The effect of heat in increasing the conducting power of manysubstances, especially for electricity of high tension, is well known. Ihave lately met with an extraordinary case of this kind, for electricity oflow tension, or that of the voltaic pile, and which is in direct contrastwith the influence of heat upon metallic bodies, as observed and describedby Sir Humphry Davy[A]. 

 [A] Philosophical Transactions, 1821, p. 131. 

433. The substance presenting this effect is sulphuret of silver. It wasmade by fusing a mixture of precipitated silver and sublimed sulphur, removing the film of silver by a file from the exterior of the fused mass, pulverizing the sulphuret, mingling it with more sulphur, and fusing itagain in a green glass tube, so that no air should obtain access during theprocess. The surface of the sulphuret being again removed by a file orknife, it was considered quite free from uncombined silver. 

434. When a piece of this sulphuret, half an inch in thickness, was putbetween surfaces of platina, terminating the poles of a voltaic battery oftwenty pairs of four-inch plates, a galvanometer being also included in thecircuit, the needle was slightly deflected, indicating a feeble conductingpower. On pressing the platina poles and sulphuret together with thefingers, the conducting power increased as the whole became warm. Onapplying a lamp under the sulphuret between the poles, the conducting powerrose rapidly with the heat, and at last-the galvanometer needle jumped intoa fixed position, and the sulphuret was found conducting in the manner of ametal. On removing the lamp and allowing the heat to fall, the effects werereversed, the needle at first began to vibrate a little, then graduallyleft its transverse direction, and at last returned to a position verynearly that which it would take when no current was passing through thegalvanometer. 

435. Occasionally, when the contact of the sulphuret with the platina poleswas good, the battery freshly charged, and the commencing temperature nottoo low, the mere current of electricity from the battery was sufficient toraise the temperature of the sulphuret; and then, without any applicationof extraneous heat, it went on increasing conjointly in temperature andconducting power, until the cooling influence of the air limited theeffects. In such cases it was generally necessary to cool the wholepurposely, to show the returning series of phenomena. 

436. Occasionally, also, the effects would sink of themselves, and couldnot be renewed until a fresh surface of the sulphuret had been applied tothe positive pole. This was in consequence of peculiar results ofdecomposition, to which I shall have occasion to revert in the section onElectro-chemical Decomposition, and was conveniently avoided by insertingthe ends of two pieces of platina wire into the opposite extremities of aportion of sulphuret fused in a glass tube, and placing this arrangementbetween the poles of the battery. 

437. The hot sulphuret of silver conducts sufficiently well to give abright spark with charcoal, &c. &c. , in the manner of a metal. 

438. The native grey sulphuret of silver, and the ruby silver ore, bothpresented the same phenomena. The native malleable sulphuret of silverpresented precisely the same appearances as the artificial sulphuret. 

439. There is no other body with which I am acquainted, that, likesulphuret of silver, can compare with metals in conducting power forelectricity of low tension when hot, but which, unlike them, duringcooling, loses in power, whilst they, on the contrary, gain. Probably, however, many others may, when sought for, be found[A]. 

 [A] See now on this subject, 1340, 1341. --_Dec. 1838. _

440. The proto-sulphuret of iron, the native per-sulphuret of iron, arsenical sulphuret of iron, native yellow sulphuret of copper and iron, grey artificial sulphuret of copper, artificial sulphuret of bismuth, andartificial grey sulphuret of tin, all conduct the voltaic battery currentwhen cold, more or less, some giving sparks like the metals, others notbeing sufficient for that high effect. They did not seem to conduct betterwhen heated, than before; but I had not time to enter accurately into theinvestigation of this point. Almost all of them became much heated by thetransmission of the current, and present some very interesting phenomena inthat respect. The sulphuret of antimony does not conduct the same currentsensibly either hot or cold, but is amongst those bodies acquiringconducting power when fused (402. ). The sulphuret of silver and perhapssome others decompose whilst in the solid state; but the phenomena of thisdecomposition will be reserved for its proper place in the next series ofthese Researches. 

441. Notwithstanding the extreme dissimilarity between sulphuret of silverand gases or vapours, I cannot help suspecting the action of heat upon themto be the same, bringing them all into the same class as conductors ofelectricity, although with those great differences in degree, which arefound to exist under common circumstances. When gases are heated, theyincrease in conducting power, both for common and voltaic electricity(271. ); and it is probable that if we could compress and condense them atthe same time, we should still further increase their conducting power. Cagniard de la Tour has shown that a substance, for instance water, may beso expanded by heat whilst in the liquid state, or condensed whilst in thevaporous state, that the two states shall coincide at one point, and thetransition from one to the other be so gradual that no line of demarcationcan be pointed out[A]; that, in fact, the two states shall becomeone;--which one state presents us at different times with differences indegree as to certain properties and relations; and which differences are, under ordinary circumstances, so great as to be equivalent to two differentstates. 

 [A] Annales de Chimie, xxi. Pp. 127, 178. 

442. I cannot but suppose at present that at that point where the liquidand the gaseous state coincide, the conducting properties are the same forboth; but that they diminish as the expansion of the matter into a rarerform takes place by the removal of the necessary pressure; still, however, retaining, as might be expected, the capability of having what feebleconducting power remains, increased by the action of heat. 

443. I venture to give the following summary of the conditions of electricconduction in bodies, not however without fearing that I may have omittedsome important points[A]. 

 [A] See now in relation to this subject, 1320--1242. --_Dec. 1838. _

444. All bodies conduct electricity in the same manner from metals to lacand gases, but in very different degrees. 

445. Conducting power is in some bodies powerfully increased by heat, andin others diminished, yet without our perceiving any accompanying essentialelectrical difference, either in the bodies or in the changes occasioned bythe electricity conducted. 

446. A numerous class of bodies, insulating electricity of low intensity, when solid, conduct it very freely when fluid, and are then decomposed byit. 

447. But there are many fluid bodies which do not sensibly conductelectricity of this low intensity; there are some which conduct it and arenot decomposed; nor is fluidity essential to decomposition[A]. 

 [A] See the next series of these Experimental Researches. 

448. There is but one body yet discovered[A] which, insulating a voltaiccurrent when solid, and conducting it when fluid, is not decomposed in thelatter case (414. ). 

 [A] It is just possible that this case may, by more delicate experiment, hereafter disappear. (See now, 1340, 1341, in relation to this note. --_Dec. 1838. _)

449. There is no strict electrical distinction of conduction which can, asyet, be drawn between bodies supposed to be elementary, and those known tobe compounds. 

_Royal Institution, April 15, 1833_. 

FIFTH SERIES. 

§ 11. _On Electro-chemical Decomposition. _ ¶ i. _New conditions ofElectro-chemical Decomposition. _ ¶ ii. _Influence of Water inElectro-chemical Decomposition. _ ¶ iii. _Theory of Electro-chemicalDecomposition. _

Received June 18, --Read June 20, 1833. 

§ 11. _On Electro-chemical Decomposition. _[A]

 [A] Refer to the note after 1047, Series viii. --_Dec. 1838. _

450. I have in a recent series of these Researches (265. ) proved (to my ownsatisfaction, at least, ) the identity of electricities derived fromdifferent sources, and have especially dwelt upon the proofs of thesameness of those obtained by the use of the common electrical machine andthe voltaic battery. 

451. The great distinction of the electricities obtained from these twosources is the very high tension to which the small quantity obtained byaid of the machine may be raised, and the enormous quantity (371. 376. ) inwhich that of comparatively low tension, supplied by the voltaic battery, may be procured; but as their actions, whether magnetical, chemical, or ofany other nature, are essentially the same (360. ), it appeared evident thatwe might reason from the former as to the manner of action of the latter;and it was, to me, a probable consequence, that the use of electricity ofsuch intensity as that afforded by the machine, would, when applied toeffect and elucidate electro-chemical decomposition, show some newconditions of that action, evolve new views of the internal arrangementsand changes of the substances under decomposition, and perhaps giveefficient powers over matter as yet undecomposed. 

452. For the purpose of rendering the bearings of the different parts ofthis series of researches more distinct, I shall divide it into severalheads. 

¶ i. _New conditions of Electro-chemical Decomposition. _

453. The tension of machine electricity causes it, however small inquantity, to pass through any length of water, solutions, or othersubstances classing with these as conductors, as fast as it can beproduced, and therefore, in relation to quantity, as fast as it could havepassed through much shorter portions of the same conducting substance. Withthe voltaic battery the case is very different, and the passing current ofelectricity supplied by it suffers serious diminution in any substance, byconsiderable extension of its length, but especially in such bodies asthose mentioned above. 

454. I endeavoured to apply this facility of transmitting the current ofelectricity through any length of a conductor, to an investigation of thetransfer of the elements in a decomposing body, in contrary directions, towards the poles. The general form of apparatus used in these experimentshas been already described (312. 316); and also a particular experiment(319. ), in which, when a piece of litmus paper and a piece of turmericpaper were combined and moistened in solution of sulphate of soda, thepoint of the wire from the machine (representing the positive pole) putupon the litmus paper, and the receiving point from the discharging train(292. 316. ), representing the negative pole, upon the turmeric paper, avery few turns of the machine sufficed to show the evolution of acid at theformer, and alkali at the latter, exactly in the manner effected by avolta-electric current. 

455. The pieces of litmus and turmeric paper were _now_ placed each upon aseparate plate of glass, and connected by an insulated string four feetlong, moistened in the same solution of sulphate of soda: the terminaldecomposing wire points were placed upon the papers as before. On workingthe machine, the same evolution of acid and alkali appeared as in theformer instance, and with equal readiness, notwithstanding that the placesof their appearance were four feet apart from each other. Finally, a pieceof string, seventy feet long, was used. It was insulated in the air bysuspenders of silk, so that the electricity passed through its entirelength: decomposition took place exactly as in former cases, alkali andacid appearing at the two extremities in their proper places. 

456. Experiments were then made both with sulphate of soda and iodide ofpotassium, to ascertain if any diminution of decomposing effect wasproduced by such great extension as those just described of the moistconductor or body under decomposition; but whether the contact of thedecomposing point connected with the discharging train was made withturmeric paper touching the prime conductor, or with other turmeric paperconnected with it through the seventy feet of string, the spot of alkalifor an equal number of turns of the machine had equal intensity of colour. The same results occurred at the other decomposing wire, whether the saltor the iodide were used; and it was fully proved that this great extensionof the distance between the poles produced no effect whatever on the amountof decomposition, provided the same _quantity_ of electricity were passedin both cases (377. ). 

457. The negative point of the discharging train, the turmeric paper, andthe string were then removed; the positive point was left resting upon thelitmus paper, and the latter touched by a piece of moistened string held inthe hand. A few turns of the machine evolved acid at the positive point asfreely as before. 

458. The end of the moistened string, instead of being held in the hand, was suspended by glass in the air. On working the machine the electricityproceeded from the conductor through the wire point to the litmus paper, and thence away by the intervention of the string to the air, so that therewas (as in the last experiment) but one metallic pole; still acid wasevolved there as freely as in any former case. 

459. When any of these experiments were repeated with electricity from thenegative conductor, corresponding effects were produced whether one or twodecomposing wires were used. The results were always constant, consideredin relation to the _direction_ of the electric current. 

460. These experiments were varied so as to include the action of only onemetallic pole, but that not the pole connected with the machine. Turmericpaper was moistened in solution of sulphate of soda, placed upon glass, andconnected with the discharging train (292. ) by a decomposing wire (312. ); apiece of wet string was hung from it, the lower extremity of which wasbrought opposite a point connected with the positive prime conductor of themachine. The machine was then worked for a few turns, and alkaliimmediately appeared at the point of the discharging train which rested onthe turmeric paper. Corresponding effects took place at the negativeconductor of a machine. 

461. These cases are abundantly sufficient to show that electrochemicaldecomposition does not depend upon the simultaneous action of two metallicpoles, since a single pole might be used, decomposition ensue, and one orother of the elements liberated, pass to the pole, according as it waspositive or negative. In considering the course taken by, and the finalarrangement of, the other element, I had little doubt that I should find ithad receded towards the other extremity, and that the air itself had actedas a pole, an expectation which was fully confirmed in the followingmanner. 

462. A piece of turmeric paper, not more than 0. 4 of an inch in length and0. 5 of an inch in width, was moistened with sulphate of soda and placedupon the edge of a glass plate opposite to, and about two inches from, apoint connected with the discharging train (Plate IV. Fig. 47. ); a piece oftinfoil, resting upon the same glass plate, was connected with the machine, and also with the turmeric paper, by a decomposing wire _a_ (312. ). Themachine was then worked, the positive electricity passing into the turmericpaper at the point _p_, and out at the extremity _n_. After forty or fiftyturns of the machine, the extremity _n_ was examined, and the two points orangles found deeply coloured by the presence of free alkali (fig. 48. ). 

463. A similar piece of litmus paper, dipped in solution of sulphate ofsoda _n_, fig. 49, was now supported upon the end of the discharging train_a_, and its extremity brought opposite to a point _p_, connected with theconductor of the machine. After working the machine for a short time, acidwas developed at both the corners towards the point, i. E. At both thecorners receiving the electricities from the air. Every precaution wastaken to prevent this acid from being formed by sparks or brushes passingthrough the air (322. ); and these, with the accompanying general facts, aresufficient to show that the acid was really the result of electro-chemicaldecomposition (466. ). 

464. Then a long piece of turmeric paper, large at one end and pointed atthe other, was moistened in the saline solution, and immediately connectedwith the conductor of the machine, so that its pointed extremity wasopposite a point upon the discharging train. When the machine was worked, alkali was evolved at that point; and even when the discharging train wasremoved, and the electricity left to be diffused and carried off altogetherby the air, still alkali was evolved where the electricity left theturmeric paper. 

465. Arrangements were then made in which no metallic communication withthe decomposing matter was allowed, but both poles (if they might now becalled by that name) formed of air only. A piece of turmeric paper _a_ fig. 50, and a piece of litmus paper _b_, were dipped in solution of sulphate ofsoda, put together so as to form one moist pointed conductor, and supportedon wax between two needle points, one, _p_, connected by a wire with theconductor of the machine, and the other, _n_, with the discharging train. The interval in each case between the points was about half an inch; thepositive point _p_ was opposite the litmus paper; the negative point _n_opposite the turmeric. The machine was then worked for a time, upon whichevidence of decomposition quickly appeared, for the point of the litmus _b_became reddened from acid evolved there, and the point of the turmeric _a_red from a similar and simultaneous evolution of alkali. 

466. Upon turning the paper conductor round, so that the litmus pointshould now give off the positive electricity, and the turmeric pointreceive it, and working the machine for a short time, both the red spotsdisappeared, and as on continuing the action of the machine no red spot wasre-formed at the litmus extremity, it proved that in the first instance(463. ) the effect was not due to the action of brushes or mere electricdischarges causing the formation of nitric acid from the air (322. ). 

467. If the combined litmus and turmeric paper in this experiment beconsidered as constituting a conductor independent of the machine or thedischarging train, and the final places of the elements evolved beconsidered in relation to this conductor, then it will be found that theacid collects at the _negative_ or receiving end or pole of thearrangement, and the alkali at the _positive_ or delivering extremity. 

468. Similar litmus and turmeric paper points were now placed upon glassplates, and connected by a string six feet long, both string and paperbeing moistened in solution of sulphate of soda; a needle point connectedwith the machine was brought opposite the litmus paper point, and anotherneedle point connected with the discharging train brought opposite theturmeric paper. On working the machine, acid appeared on the litmus, andalkali on the turmeric paper; but the latter was not so abundant as informer cases, for much of the electricity passed off from the string intothe air, and diminished the quantity discharged at the turmeric point. 

469. Finally, a series of four small compound conductors, consisting oflitmus and turmeric paper (fig. 51. ) moistened in solution of sulphate ofsoda, were supported on glass rods, in a line at a little distance fromeach other, between the points _p_ and _n_ of the machine and dischargingtrain, so that the electricity might pass in succession through them, entering in at the litmus points _b, b_, and passing out at the turmericpoints _a, a_. On working the machine carefully, so as to avoid sparks andbrushes (322. ), I soon obtained evidence of decomposition in each of themoist conductors, for all the litmus points exhibited free acid, and theturmeric points equally showed free alkali. 

470. On using solutions of iodide of potassium, acetate of lead, &c. , similar effects were obtained; but as they were all consistent with theresults above described, I refrain from describing the appearancesminutely. 

471. These cases of electro-chemical decomposition are in their natureexactly of the same kind as those affected under ordinary circumstances bythe voltaic battery, notwithstanding the great differences as to thepresence or absence, or at least as to the nature of the parts usuallycalled poles; and also of the final situation of the elements eliminated atthe electrified boundary surfaces (467. ). They indicate at once an internalaction of the parts suffering decomposition, and appear to show that thepower which is effectual in separating the elements is exerted there, andnot at the poles. But I shall defer the consideration of this point for ashort time (493. 518. ), that I may previously consider another supposedcondition of electro-chemical decomposition[A]. 

 [A] I find (since making and describing these results, ) from a note to Sir Humphry Davy's paper in the Philosophical Transactions, 1807, p. 31, that that philosopher, in repeating Wollaston's experiment of the decomposition of water by common electricity (327. 330. ) used an arrangement somewhat like some of those I have described. He immersed a guarded platina point connected with the machine in distilled water, and dissipated the electricity from the water into the air by moistened filaments of cotton. In this way he states that he obtained oxygen and hydrogen _separately_ from each other. This experiment, had I known of it, ought to have been quoted in an earlier series of these Researches (342. ); but it does not remove any of the objections I have made to the use of Wollaston's apparatus as a test of true chemical action (331. ). 

¶ ii. _Influence of Water in Electro-chemical Decomposition. _

472. It is the opinion of several philosophers, that the presence of wateris essential in electro-chemical decomposition, and also for the evolutionof electricity in the voltaic battery itself. As the decomposing cell ismerely one of the cells of the battery, into which particular substancesare introduced for the purpose of experiment, it is probable that what isan essential condition in the one case is more or less so in the other. Theopinion, therefore, that water is necessary to decomposition, may have beenfounded on the statement made by Sir Humphry Davy, that "there are nofluids known, except such as contain water, which are capable of being madethe medium of connexion between the metals or metal of the voltaicapparatus[A]:" and again, "when any substance rendered fluid by heat, consisting of _water_, oxygen, and inflammable or metallic matter, isexposed to those wires, similar phenomena (of decomposition) occur[B]. "

 [A] Elements of Chemical Philosophy, p. 160, &c. 

 [B] Ibid. Pp. 144, 145. 

473. This opinion has, I think, been shown by other philosophers not to beaccurate, though I do not know where to refer for a contradiction of it. Sir Humphry Davy himself said in 1801[A], that dry nitre, caustic potashand soda are conductors of galvanism when rendered fluid by a high degreeof heat, but he must have considered them, or the nitre at least, as notsuffering decomposition, for the statements above were made by him elevenyears subsequently. In 1826 he also pointed out, that bodies not containingwater, as _fused litharge_ and _chlorate of potassa_, were sufficient toform, with platina and zinc, powerful electromotive circles[B]; but he ishere speaking of the _production_ of electricity in the pile, and not ofits effects when evolved; nor do his words at all imply that any correctionof his former distinct statements relative to _decomposition_ was required. 

 [A] Journal of the Royal Institution, 1802, p. 53. 

 [B] Philosophical Transactions, 1826, p. 406. 

474. I may refer to the last series of these Experimental Researches (380. 402. ) as setting the matter at rest, by proving that there are hundreds ofbodies equally influential with water in this respect; that amongst binarycompounds, oxides, chlorides, iodides, and even sulphurets (402. ) wereeffective; and that amongst more complicated compounds, cyanides and salts, of equal efficacy, occurred in great numbers (402. ). 

475. Water, therefore, is in this respect merely one of a very numerousclass of substances, instead of being the _only one_ and _essential_; andit is of that class one of the _worst_ as to its capability of facilitatingconduction and suffering decomposition. The reasons why it obtained for atime an exclusive character which it so little deserved are evident, andconsist, in the general necessity of a fluid condition (394. ); in its beingthe _only one_ of this class of bodies existing in the fluid state atcommon temperatures; its abundant supply as the great natural solvent; andits constant use in that character in philosophical investigations, becauseof its having a smaller interfering, injurious, or complicating action uponthe bodies, either dissolved or evolved, than any other substance. 

476. The analogy of the decomposing or experimental cell to the other cellsof the voltaic battery renders it nearly certain that any of thosesubstances which are decomposable when fluid, as described in my last paper(402. ), would, if they could be introduced between the metallic plates ofthe pile, be equally effectual with water, if not more so. Sir Humphry Davyfound that litharge and chlorate of potassa were thus effectual[A]. I haveconstructed various voltaic arrangements, and found the above conclusion tohold good. When any of the following substances in a fused state wereinterposed between copper and platina, voltaic action more or less powerfulwas produced. Nitre; chlorate of potassa; carbonate of potassa; sulphate ofsoda; chloride of lead, of sodium, of bismuth, of calcium; iodide of lead;oxide of bismuth; oxide of lead: the electric current was in the samedirection as if acids had acted upon the metals. When any of the samesubstances, or phosphate of soda, were made to act on platina and iron, still more powerful voltaic combinations of the same kind were produced. When either nitrate of silver or chloride of silver was the fluid substanceinterposed, there was voltaic action, but the electric current was in thereverse direction. 

 [A] Philosophical Transactions, 1826, p. 406. 

iii. _Theory of Electro-chemical Decomposition. _

477. The extreme beauty and value of electro-chemical decompositions havegiven to that power which the voltaic pile possesses of causing theiroccurrence an interest surpassing that of any other of its properties; forthe power is not only intimately connected with the continuance, if notwith the production, of the electrical phenomena, but it has furnished uswith the most beautiful demonstrations of the nature of many compoundbodies; has in the hands of Becquerel been employed in compoundingsubstances; has given us several new combinations, and sustains us with thehope that when thoroughly understood it will produce many more. 

478. What may be considered as the general facts of electrochemicaldecomposition are agreed to by nearly all who have written on the subject. They consist in the separation of the decomposable substance acted uponinto its proximate or sometimes ultimate principles, whenever both poles ofthe pile are in contact with that substance in a proper condition; in theevolution of these principles at distant points, i. E. At the poles of thepile, where they are either finally set free or enter into union with thesubstance of the poles; and in the constant determination of the evolvedelements or principles to particular poles according to certainwell-ascertained laws. 

479. But the views of men of science vary much as to the nature of theaction by which these effects are produced; and as it is certain that weshall be better able to apply the power when we really understand themanner in which it operates, this difference of opinion is a stronginducement to further inquiry. I have been led to hope that the followinginvestigations might be considered, not as an increase of that which isdoubtful, but a real addition to this branch of knowledge. 

480. It will be needful that I briefly state the views of electro-chemicaldecomposition already put forth, that their present contradictory andunsatisfactory state may be seen before I give that which seems to me moreaccurately to agree with facts; and I have ventured to discuss them freely, trusting that I should give no offence to their high-minded authors; for Ifelt convinced that if I were right, they would be pleased that their viewsshould serve as stepping-stones for the advance of science; and that if Iwere wrong, they would excuse the zeal which misled me, since it wasexerted for the service of that great cause whose prosperity and progressthey have desired. 

481. Grotthuss, in the year 1805, wrote expressly on the decomposition ofliquids by voltaic electricity[A]. He considers the pile as an electricmagnet, i. E. As an attractive and repulsive agent; the poles having_attractive_ and _repelling_ powers. The pole from whence resinouselectricity issues attracts hydrogen and repels oxygen, whilst that fromwhich vitreous electricity proceeds attracts oxygen and repels hydrogen; sothat each of the elements of a particle of water, for instance, is subjectto an attractive and a repulsive force, acting in contrary directions, thecentres of action of which are reciprocally opposed. The action of eachforce in relation to a molecule of water situated in the course of theelectric current is in the inverse ratio of the square of the distance atwhich it is exerted, thus giving (it is stated) for such a molecule a_constant force_[B]. He explains the appearance of the elements at adistance from each other by referring to a succession of decompositions andrecompositions occurring amongst the intervening particles[C], and hethinks it probable that those which are about to separate at the polesunite to the two electricities there, and in consequence become gases[D]. 

 [A] Annales de Chimie, 1806, tom, lviii. P. 64. 

 [B] Ibid. Pp. 66, 67, also tom. Lxiii. P. 20. 

 [C] Ibid. Tom. Lviii. P. 68, tom, lxiii. P. 20. 

 [D] Ibid. Tom. Lxiii. P. 34. 

482. Sir Humphry Davy's celebrated Bakerian Lecture on some chemicalagencies of electricity was read in November 1806, and is almost entirelyoccupied in the consideration of _electro-chemical decompositions_. Thefacts are of the utmost value, and, with the general points established, are universally known. The _mode of action_ by which the effects take placeis stated very generally, so generally, indeed, that probably a dozenprecise schemes of electro-chemical action might be drawn up, differingessentially from each other, yet all agreeing with the statement theregiven. 

483. When Sir Humphry Davy uses more particular expressions, he seems torefer the decomposing effects to the attractions of the poles. This is thecase in the "general expression of facts" given at pp. 28 and 29 of thePhilosophical Transactions for 1807, also at p. 30. Again at p. 160 of theElements of Chemical Philosophy, he speaks of the great attracting powersof the surfaces of the poles. He mentions the probability of a successionof decompositions and recompositions throughout the fluid, --agreeing inthat respect with Grotthuss[A]; and supposes that the attractive andrepellent agencies may be communicated from the metallic surfacesthroughout the whole of the menstruum[B], being communicated from _oneparticle to another particle of the same kind_[C], and diminishing instrength from the place of the poles to the middle point, which isnecessarily neutral[D]. In reference to this diminution of power atincreased distances from the poles, he states that in a circuit of teninches of water, solution of sulphate of potassa placed four inches fromthe positive pole, did not decompose; whereas when only two inches fromthat pole, it did render up its elements[E]. 

 [A] Philosophical Transactions, 1807, pp. 29, 30. 

 [B] Ibid. P. 39. 

 [C] Ibid. P. 29. 

 [D] Ibid. P. 42. 

 [E] Ibid. P. 42. 

484. When in 1826 Sir Humphry Davy wrote again on this subject, he statedthat he found nothing to alter in the fundamental theory laid down in theoriginal communication[A], and uses the terms attraction and repulsionapparently in the same sense as before[B]. 

 [A] Philosophical Transactions, 1826, p. 383. 

 [B] Ibid. Pp. 389, 407, 115. 

485. Messrs. Riffault and Chompré experimented on this subject in 1807. They came to the conclusion that the voltaic current caused decompositionsthroughout its whole course in the humid conductor, not merely aspreliminary to the recompositions spoken of by Grotthuss and Davy, butproducing final separation of the elements in the _course_ of the current, and elsewhere than at the poles. They considered the _negative_ current ascollecting and carrying the acids, &c. To the _positive_ pole, and the_positive_ current as doing the same duty with the bases, and collectingthem at the _negative_ pole. They likewise consider the currents as _morepowerful_ the nearer they are to their respective poles, and state that thepositive current is _superior_ in power to the negative current[A]. 

 [A] Annales de Chimie, 1807, tom. Lxiii. P. 83, &c. 

486. M. Biot is very cautious in expressing an opinion as to the cause ofthe separation of the elements of a compound body[A]. But as far as theeffects can be understood, he refers them to the opposite electrical statesof the portions of the decomposing substance in the neighbourhood of thetwo poles. The fluid is most positive at the positive pole; that stategradually diminishes to the middle distance, where the fluid is neutral ornot electrical; but from thence to the negative pole it becomes more andmore negative[B]. When a particle of salt is decomposed at the negativepole, the acid particle is considered as acquiring a negative electricalstate from the pole, stronger than that of the surrounding _undecomposed_particles, and is therefore repelled from amongst them, and from out ofthat portion of the liquid towards the positive pole, towards which also itis drawn by the attraction of the pole itself and the particles of positive_undecomposed_ fluid around it[C]. 

 [A] Précis Elémentaire de Physique, 3me édition, 1824, tom. I. P. 641. 

 [B] Ibid. P. 637. 

 [C] Ibid. Pp. 641, 642. 

487. M. Biot does not appear to admit the successive decompositions andrecompositions spoken of by Grotthuss, Davy, &c. &c. ; but seems to considerthe substance whilst in transit as combined with, or rather attached to, the electricity for the time[A], and though it communicates thiselectricity to the surrounding undecomposed matter with which it is incontact, yet it retains during the transit a little superiority withrespect to that kind which it first received from the pole, and is, byvirtue of that difference, carried forward through the fluid to theopposite pole[B]. 

 [A] Précis Elémentaire de Physique, 3me édition, 1824, tom. I. P. 636. 

 [B] Ibid. P, 642. 

488. This theory implies that decomposition takes place at both poles upondistinct portions of fluid, and not at all in the intervening parts. Thelatter serve merely as imperfect conductors, which, assuming an electricstate, urge particles electrified more highly at the poles through them inopposite directions, by virtue of a series of ordinary electricalattractions and repulsions[A]. 

 [A] Précis Elémentaire de Physique, 3me édition, 1824, tom. I. Pp. 638, 642. 

489. M. A. De la Rive investigated this subject particularly, and publisheda paper on it in 1825[A]. He thinks those who have referred the phenomenato the attractive powers of the poles, rather express the general fact thangive any explication of it. He considers the results as due to an actualcombination of the elements, or rather of half of them, with theelectricities passing from the poles in consequence of a kind of play ofaffinities between the matter and electricity[B]. The current from thepositive pole combining with the hydrogen, or the bases it finds there, leaves the oxygen and acids at liberty, but carries the substances it isunited with across to the negative pole, where, because of the peculiarcharacter of the metal as a conductor[C], it is separated from them, entering the metal and leaving the hydrogen or bases upon its surface. Inthe same manner the electricity from the negative pole sets the hydrogenand bases which it finds there, free, but combines with the oxygen andacids, carries them across to the positive pole, and there depositsthem[D]. In this respect M. De la Rive's hypothesis accords in part withthat of MM. Riffault and Chompré (485. ). 

 [A] Annales de Chimie, tom, xxviii. P. 190. 

 [B] Ibid. Pp. 200, 202. 

 [C] Ibid. P. 202. 

 [D] Ibid. P. 201. 

490. M. De la Rive considers the portions of matter which are decomposed tobe those contiguous to _both_ poles[A]. He does not admit with others thesuccessive decompositions and recompositions in the whole course of theelectricity through the humid conductor[B], but thinks the middle parts arein themselves unaltered, or at least serve only to conduct the two contrarycurrents of electricity and matter which set off from the oppositepoles[C]. The decomposition, therefore, of a particle of water, or aparticle of salt, may take place at either pole, and when once effected, itis final for the time, no recombination taking place, except the momentaryunion of the transferred particle with the electricity be so considered. 

 [A] Annales de Chimie, tom, xxviii. Pp. 197, 198. 

 [B] Ibid. Pp. 192, 199. 

 [C] Ibid. P. 200. 

491. The latest communication that I am aware of on the subject is by M. Hachette: its date is October 1832[A]. It is incidental to the descriptionof the decomposition of water by the magneto-electric currents (346. ). Oneof the results of the experiment is, that "it is not necessary, as has beensupposed, that for the chemical decomposition of water, the action of thetwo electricities, positive and negative, should be simultaneous. "

 [A] Annales de Chimie, tom, xxviii. Tom. Li. P. 73. 

492. It is more than probable that many other views of electro-chemicaldecomposition may have been published, and perhaps amongst them some which, differing from those above, might, even in my own opinion, were Iacquainted with them, obviate the necessity for the publication of myviews. If such be the case, I have to regret my ignorance of them, andapologize to the authors. 

 * * * * *

493. That electro-chemical decomposition does not depend upon any directattraction and repulsion of the poles (meaning thereby the metallicterminations either of the voltaic battery, or ordinary electrical machinearrangements (312. ), ) upon the elements in contact with or near to them, appeared very evident from the experiments made in air (462, 465, &c. ), when the substances evolved did not collect about any poles, but, inobedience to the direction of the current, were evolved, and I would sayejected, at the extremities of the decomposing substance. Butnotwithstanding the extreme dissimilarity in the character of air andmetals, and the almost total difference existing between them as to theirmode of conducting electricity, and becoming charged with it, it mightperhaps still be contended, although quite hypothetically, that thebounding portions of air were now the surfaces or places of attraction, asthe metals had been supposed to be before. In illustration of this andother points, I endeavoured to devise an arrangement by which I coulddecompose a body against a surface of water, as well as against air ormetal, and succeeded in doing so unexceptionably in the following manner. As the experiment for very natural reasons requires many precautions, to besuccessful, and will be referred to hereafter in illustration of the viewsI shall venture to give, I must describe it minutely. 

494. A glass basin (fig. 52. ), four inches in diameter and four inchesdeep, had a division of mica _a_, fixed across the upper part so as todescend one inch and a half below the edge, and be perfectly water-tight atthe sides: a plate of platina _b_, three inches wide, was put into thebasin on one side of the division _a_, and retained there by a glass blockbelow, so that any gas produced by it in a future stage of the experimentshould not ascend beyond the mica, and cause currents in the liquid on thatside. A strong solution of sulphate of magnesia was carefully pouredwithout splashing into the basin, until it rose a little above the loweredge of the mica division _a_, great care being taken that the glass ormica on the unoccupied or _c_ side of the division in the figure, shouldnot be moistened by agitation of the solution above the level to which itrose. A thin piece of clean cork, well-wetted in distilled water, was thencarefully and lightly placed on the solution at the _c_ side, and distilledwater poured gently on to it until a stratum the eighth of an inch inthickness appeared over the sulphate of magnesia; all was then left for afew minutes, that any solution adhering to the cork might sink away fromit, or be removed by the water on which it now floated; and then moredistilled water was added in a similar manner, until it reached nearly tothe top of the glass. In this way solution of the sulphate occupied thelower part of the glass, and also the upper on the right-hand side of themica; but on the left-hand side of the division a stratum of water from _c_to _d_, one inch and a half in depth, reposed upon it, the two presenting, when looked through horizontally, a comparatively definite plane ofcontact. A second platina pole _e_, was arranged so as to be just under thesurface of the water, in a position nearly horizontal, a little inclinationbeing given to it, that gas evolved during decomposition might escape: thepart immersed was three inches and a half long by one inch wide, and aboutseven-eighths of an inch of water intervened between it and the solution ofsulphate of magnesia. 

495. The latter pole _e_ was now connected with the negative end of avoltaic battery, of forty pairs of plates four inches square, whilst theformer pole _b_ was connected with the positive end. There was action andgas evolved at both poles; but from the intervention of the pure water, thedecomposition was very feeble compared to what the battery would haveeffected in a uniform solution. After a little while (less than a minute, )magnesia also appeared at the negative side: _it did not make itsappearance at the negative metallic pole, but in the water_, at the planewhere the solution and the water met; and on looking at it horizontally, itcould be there perceived lying in the water upon the solution, not risingmore than the fourth of an inch above the latter, whilst the water betweenit and the negative pole was perfectly clear. On continuing the action, thebubbles of hydrogen rising upwards from the negative pole impressed acirculatory movement on the stratum of water, upwards in the middle, anddownwards at the side, which gradually gave an ascending form to the cloudof magnesia in the part just under the pole, having an appearance as if itwere there attracted to it; but this was altogether an effect of thecurrents, and did not occur until long after the phenomena looked for weresatisfactorily ascertained. 

496. After a little while the voltaic communication was broken, and theplatina poles removed with as little agitation as possible from the waterand solution, for the purpose of examining the liquid adhering to them. Thepole _c_, when touched by turmeric paper, gave no traces of alkali, norcould anything but pure water be found upon it. The pole _b_, though drawnthrough a much greater depth and quantity of fluid, was found so acid as togive abundant evidence to litmus paper, the tongue, and other tests. Hencethere had been no interference of alkaline salts in any way, undergoingfirst decomposition, and then causing the separation of the magnesia at adistance from the pole by mere chemical agencies. This experiment wasrepeated again and again, and always successfully. 

497. As, therefore, the substances evolved in cases of electrochemicaldecomposition may be made to appear against air (465. 469. ), --which, according to common language, is not a conductor, nor is decomposed, oragainst water (495. ), which is a conductor, and can be decomposed, --as wellas against the metal poles, which are excellent conductors, butundecomposable, there appears but little reason to consider the phenomenagenerally, as due to the _attraction_ or attractive powers of the latter, when used in the ordinary way, since similar attractions can hardly beimagined in the former instances. 

498. It may be said that the surfaces of air or of water in these casesbecome the poles, and exert attractive powers; but what proof is there ofthat, except the fact that the matters evolved collect there, which is thepoint to be explained, and cannot be justly quoted as its own explanation?Or it may be said, that any section of the humid conductor, as that in thepresent case, where the solution and the water meet, may be considered asrepresenting the pole. But such does not appear to me to be the view ofthose who have written on the subject, certainly not of some of them, andis inconsistent with the supposed laws which they have assumed, asgoverning the diminution of power at increased distances from the poles. 

499. Grotthuss, for instance, describes the poles as centres of attractiveand repulsive forces (481. ), these forces varying inversely as the squaresof the distances, and says, therefore, that a particle placed anywherebetween the poles will be acted upon by a constant force. But the compoundforce, resulting from such a combination as he supposes, would be anythingbut a constant force; it would evidently be a force greatest at the poles, and diminishing to the middle distance. Grotthuss is right, however, _inthe fact_, according to my experiments (502. 505. ), that the particles areacted upon by equal force everywhere in the circuit, when the conditions ofthe experiment are the simplest possible; but the fact is against histheory, and is also, I think, against all theories that place thedecomposing effect in the attractive power of the poles. 

500. Sir Humphry Davy, who also speaks of the _diminution_ of power withincrease of distance from the poles[A] (483. ), supposes, that when bothpoles are acting on substances to decompose them, still the power ofdecomposition _diminishes_ to the middle distance. In this statement offact he is opposed to Grotthuss, and quotes an experiment in which sulphateof potassa, placed at different distances from the poles in a humidconductor of constant length, decomposed when near the pole, but not whenat a distance. Such a consequence would necessarily result theoreticallyfrom considering the poles as centres of attraction and repulsion; but Ihave not found the statement borne out by other experiments (505. ); and inthe one quoted by him the effect was doubtless due to some of the manyinterfering causes of variation which attend such investigations. 

 [A] Philosophical Transactions, 1807, p. 42. 

501. A glass vessel had a platina plate fixed perpendicularly across it, soas to divide it into two cells: a head of mica was fixed over it, so as tocollect the gas it might evolve during experiments; then each cell, and thespace beneath the mica, was filled with dilute sulphuric acid. Two poleswere provided, consisting each of a platina wire terminated by a plate ofthe same metal; each was fixed into a tube passing through its upper end byan air-tight joint, that it might be moveable, and yet that the gas evolvedat it might be collected. The tubes were filled with the acid, and oneimmersed in each cell. Each platina pole was equal in surface to one sideof the dividing plate in the middle glass vessel, and the whole might beconsidered as an arrangement between the poles of the battery of a humiddecomposable conductor divided in the middle by the interposed platinadiaphragm. It was easy, when required, to draw one of the poles further upthe tube, and then the platina diaphragm was no longer in the middle of thehumid conductor. But whether it were thus arranged at the middle, ortowards one side, it always evolved a quantity of oxygen and hydrogen equalto that evolved by both the extreme plates[A]. 

 [A] There are certain precautions, in this and such experiments, which can only be understood and guarded against by a knowledge of the phenomena to be described in the first part of the Sixth Series of these Researches. 

502. If the wires of a galvanometer be terminated by plates, and these beimmersed in dilute acid, contained in a regularly formed rectangular glasstrough, connected at each end with a voltaic battery by poles equal to thesection of the fluid, a part of the electricity will pass through theinstrument and cause a certain deflection. And if the plates are alwaysretained at the _same distance from each other_ and from the sides of thetrough, are always parallel to each other, and uniformly placed relative tothe fluid, then, whether they are immersed near the middle of thedecomposing solution, or at one end, still the instrument will indicate thesame deflection, and consequently the same electric influence. 

503. It is very evident, that when the width of the decomposing conductorvaries, as is always the case when mere wires or plates, as poles, aredipped into or are surrounded by solution, no constant expression can begiven as to the action upon a single particle placed in the course of thecurrent, nor any conclusion of use, relative to the supposed attractive orrepulsive force of the poles, be drawn. The force will vary as the distancefrom the pole varies; as the particle is directly between the poles, ormore or less on one side; and even as it is nearer to or further from thesides of the containing vessels, or as the shape of the vessel itselfvaries; and, in fact, by making variations in the form of the arrangement, the force upon any single particle may be made to increase, or diminish, orremain constant, whilst the distance between the particle and the poleshall remain the same; or the force may be made to increase, or diminish, or remain constant, either as the distance increases or as it diminishes. 

504. From numerous experiments, I am led to believe the following generalexpression to be correct; but I purpose examining it much further, andwould therefore wish not to be considered at present as pledged to itsaccuracy. The _sum of chemical decomposition is constant_ for any sectiontaken across a decomposing conductor, uniform in its nature, at whateverdistance the poles may be from each other or from the section; or howeverthat section may intersect the currents, whether directly across them, orso oblique as to reach almost from pole to pole, or whether it be plane, orcurved, or irregular in the utmost degree; provided the current ofelectricity be retained constant in quantity (377. ), and that the sectionpasses through every part of the current through the decomposing conductor. 

505. I have reason to believe that the statement might be made still moregeneral, and expressed thus: That _for a constant quantity of electricity, whatever the decomposing conductor may be, whether water, saline solutions, acids, fused bodies, &c. , the amount of electro-chemical action is also aconstant quantity, i. E. Would always be equivalent to a standard chemicaleffect founded upon ordinary chemical affinity_. I have this investigationin hand, with several others, and shall be prepared to give it in the nextseries but one of these Researches. 

506. Many other arguments might be adduced against the hypotheses of theattraction of the poles being the cause of electro-chemical decomposition;but I would rather pass on to the view I have thought more consistent withfacts, with this single remark; that if decomposition by the voltaicbattery depended upon the attraction of the poles, or the parts about them, being stronger than the mutual attraction of the particles separated, itwould follow that the weakest _electrical_ attraction was stronger than, ifnot the strongest, yet very strong _chemical_ attraction, namely, such asexists between oxygen and hydrogen, potassium and oxygen, chlorine andsodium, acid and alkali, &c. , a consequence which, although perhaps notimpossible, seems in the present state of the subject very unlikely. 

507. The view which M. De la Rive has taken (489. ), and also MM. Riffaultand Chompré (485. ), of the manner in which electro-chemical decompositionis effected, is very different to that already considered, and is notaffected by either the arguments or facts urged against the latter. Considering it as stated by the former philosopher, it appears to me to beincompetent to account for the experiments of decomposition againstsurfaces of air (462. 469. ) and water (495. ), which I have described; forif the physical differences between metals and humid conductors, which M. De la Rive supposes to account for the transmission of the compound ofmatter and electricity in the latter, and the transmission of theelectricity only with the rejection of the matter in the former, be allowedfor a moment, still the analogy of air to metal is, electricallyconsidered, so small, that instead of the former replacing the latter(462. ), an effect the very reverse might have been expected. Or if eventhat were allowed, the experiment with water (495. ), at once sets thematter at rest, the decomposing pole being now of a substance which isadmitted as competent to transmit the assumed compound of electricity andmatter. 

508. With regard to the views of MM. Riffault and Chompré (485. ), theoccurrence of decomposition alone in the _course_ of the current is socontrary to the well-known effects obtained in the forms of experimentadopted up to this time, that it must be proved before the hypothesisdepending on it need be considered. 

509. The consideration of the various theories of electro-chemicaldecomposition, whilst it has made me diffident, has also given meconfidence to add another to the number; for it is because the one I haveto propose appears, after the most attentive consideration, to explain andagree with the immense collection of facts belonging to this branch ofscience, and to remain uncontradicted by, or unopposed to, any of them, that I have been encouraged to give it. 

510. Electro-chemical decomposition is well known to depend essentiallyupon the _current_ of electricity. I have shown that in certain cases(375. ) the decomposition is proportionate to the quantity of electricitypassing, whatever may be its intensity or its source, and that the same isprobably true for all cases (377. ), even when the utmost generality istaken on the one hand, and great precision of expression on the other(505. ). 

511. In speaking of the current, I find myself obliged to be still moreparticular than on a former occasion (283. ), in consequence of the varietyof views taken by philosophers, all agreeing in the effect of the currentitself. Some philosophers, with Franklin, assume but one electric fluid;and such must agree together in the general uniformity and character of theelectric current. Others assume two electric fluids; and here singulardifferences have arisen. 

512. MM. Riffault and Chompré, for instance, consider the positive andnegative currents each as causing decomposition, and state that thepositive current is _more powerful_ than the negative current[A], thenitrate of soda being, under similar circumstances, decomposed by theformer, but not by the latter. 

 [A] Annales de Chimie, 1807, tom, lxiii. P. 84. 

513. M. Hachette states[A] that "it is not necessary, as has been believed, that the action of the two electricities, positive and negative, should besimultaneous for the decomposition of water. " The passage implying, if Ihave caught the meaning aright, that one electricity can be obtained, andcan be applied in effecting decompositions, independent of the other. 

 [A] Annales de Chimie, 1832, tom. Li. P. 73. 

514. The view of M. De la Rive to a certain extent agrees with that of M. Hachette, for he considers that the two electricities decompose separateportions of water (490. )[A]. In one passage he speaks of the twoelectricities as two influences, wishing perhaps to avoid offering adecided opinion upon the independent existence of electric fluids; but asthese influences are considered as combining with the elements set free asby a species of chemical affinity, and for the time entirely masking theircharacter, great vagueness of idea is thus introduced, inasmuch as such aspecies of combination can only be conceived to take place between thingshaving independent existences. The two elementary electric currents, movingin opposite directions, from pole to pole, constitute the ordinary _voltaiccurrent. _

 [A] Annales de Chimie, 1825, tom, xxviii. Pp. 197, 201. 

515. M. Grotthuss is inclined to believe that the elements of water, whenabout to separate at the poles, combine with the electricities, and sobecome gases. M. De la Rive's view is the exact reverse of this: whilstpassing through the fluid, they are, according to him, compounds with theelectricities; when evolved at the poles, they are de-electrified. 

516. I have sought amongst the various experiments quoted in support ofthese views, or connected with electro-chemical decompositions or electriccurrents, for any which might be considered as sustaining the theory of twoelectricities rather than that of one, but have not been able to perceive asingle fact which could be brought forward for such a purpose: or, admitting the hypothesis of two electricities, much less have I been ableto perceive the slightest grounds for believing that one electricity in acurrent can be more powerful than the other, or that it can be presentwithout the other, or that one can be varied or in the slightest degreeaffected, without a corresponding variation in the other[A]. If, upon thesupposition of two electricities, a current of one can be obtained withoutthe other, or the current of one be exalted or diminished more than theother, we might surely expect some variation either of the chemical ormagnetical effects, or of both; but no such variations have been observed. If a current be so directed that it may act chemically in one part of itscourse, and magnetically in another, the two actions are always found totake place together. A current has not, to my knowledge, been producedwhich could act chemically and not magnetically, nor any which can act onthe magnet, and not _at the same time_ chemically[B]. 

 [A] See now in relation to this subject, 1627-1645. --_Dec. 1838. _

 [B] Thermo-electric currents are of course no exception, because when they fail to act chemically they also fail to be currents. 

517. _Judging from facts only_, there is not as yet the slightest reasonfor considering the influence which is present in what we call the electriccurrent, --whether in metals or fused bodies or humid conductors, or even inair, flame, and rarefied elastic media, --as a compound or complicatedinfluence. It has never been resolved into simpler or elementaryinfluences, and may perhaps best be conceived of as _an axis of powerhaving contrary forces, exactly equal in amount, in contrary directions_. 

 * * * * *

518. Passing to the consideration of electro-chemical decomposition, itappears to me that the effect is produced by an _internal corpuscularaction_, exerted according to the direction of the electric current, andthat it is due to a force either _super to_, or _giving direction to theordinary chemical affinity_ of the bodies present. The body underdecomposition may be considered as a mass of acting particles, all thosewhich are included in the course of the electric current contributing tothe final effect; and it is because the ordinary chemical affinity isrelieved, weakened, or partly neutralized by the influence of the electriccurrent in one direction parallel to the course of the latter, andstrengthened or added to in the opposite direction, that the combiningparticles have a tendency to pass in opposite courses. 

519. In this view the effect is considered as _essentially dependent_ uponthe _mutual chemical affinity_ of the particles of opposite kinds. Particles _aa_, fig. 53, could not be transferred or travel from one pole Ntowards the other P, unless they found particles of the opposite kind _bb_, ready to pass in the contrary direction: for it is by virtue of theirincreased affinity for those particles, combined with their diminishedaffinity for such as are behind them in their course, that they are urgedforward: and when any one particle _a_, fig. 54, arrives at the pole, it isexcluded or set free, because the particle _b_ of the opposite kind, withwhich it was the moment before in combination, has, under the superinducinginfluence of the current, a greater attraction for the particle _a'_, whichis before it in its course, than for the particle _a_, towards which itsaffinity has been weakened. 

520. As far as regards any single compound particle, the case may beconsidered as analogous to one of ordinary decomposition, for in fig. 54, _a_ may be conceived to be expelled from the compound _ab_ by the superiorattraction of _a'_ for _b_, that superior attraction belonging to it inconsequence of the relative position of _a'b_ and _a_ to the direction ofthe axis of electric power (517. ) superinduced by the current. But as allthe compound particles in the course of the current, except those actuallyin contact with the poles, act conjointly, and consist of elementaryparticles, which, whilst they are in one direction expelling, are in theother being expelled, the case becomes more complicated, but not moredifficult of comprehension. 

521. It is not here assumed that the acting particles must be in a rightline between the poles. The lines of action which may be supposed torepresent the electric currents passing through a decomposing liquid, havein many experiments very irregular forms; and even in the simplest case oftwo wires or points immersed as poles in a drop or larger single portion offluid, these lines must diverge rapidly from the poles; and the directionin which the chemical affinity between particles is most powerfullymodified (519. 520. ) will vary with the direction of these lines, accordingconstantly with them. But even in reference to these lines or currents, itis not supposed that the particles which mutually affect each other must ofnecessity be parallel to them, but only that they shall accord generallywith their direction. Two particles, placed in a line perpendicular to theelectric current passing in any particular place, are not supposed to havetheir ordinary chemical relations towards each other affected; but as theline joining them is inclined one way to the current their mutual affinityis increased; as it is inclined in the other direction it is diminished;and the effect is a maximum, when that line is parallel to the current[A]. 

 [A] In reference to this subject see now electrolytic induction and discharge, Series XII. ¶ viii. 1343-1351, &c. --_Dec. 1838. _

522. That the actions, of whatever kind they may be, take place frequentlyin oblique directions is evident from the circumstance of those particlesbeing included which in numerous cases are not in a line between the poles. Thus, when wires are used as poles in a glass of solution, thedecompositions and recompositions occur to the right or left of the directline between the poles, and indeed in every part to which the currentsextend, as is proved by many experiments, and must therefore often occurbetween particles obliquely placed as respects the current itself; and whena metallic vessel containing the solution is made one pole, whilst a merepoint or wire is used for the other, the decompositions and recompositionsmust frequently be still more oblique to the course of the currents. 

523. The theory which I have ventured to put forth (almost) requires anadmission, that in a compound body capable of electro-chemicaldecomposition the elementary particles have a mutual relation to, andinfluence upon each other, extending beyond those with which they areimmediately combined. Thus in water, a particle of hydrogen in combinationwith oxygen is considered as not altogether indifferent to other particlesof oxygen, although they are combined with other particles of hydrogen; butto have an affinity or attraction towards them, which, though it does notat all approach in force, under ordinary circumstances, to that by which itis combined with its own particle, can, under the electric influence, exerted in a definite direction, be made even to surpass it. This generalrelation of particles already in combination to other particles with whichthey are not combined, is sufficiently distinct in numerous results of apurely chemical character; especially in those where partial decompositionsonly take place, and in Berthollet's experiments on the effects of quantityupon affinity: and it probably has a direct relation to, and connexionwith, attraction of aggregation, both in solids and fluids. It is aremarkable circumstance, that in gases and vapours, where the attraction ofaggregation ceases, there likewise the decomposing powers of electricityapparently cease, and there also the chemical action of quantity is nolonger evident. It seems not unlikely, that the inability to sufferdecomposition in these cases may be dependent upon the absence of thatmutual attractive relation of the particles which is the cause ofaggregation. 

524. I hope I have now distinctly stated, although in general terms, theview I entertain of the cause of electro-chemical decomposition, _as far asthat cause can at present be traced and understood_. I conceive the effectsto arise from forces which are _internal_, relative to the matter underdecomposition--and _not external_, as they might be considered, if directlydependent upon the poles. I suppose that the effects are due to amodification, by the electric current, of the chemical affinity of theparticles through or by which that current is passing, giving them thepower of acting more forcibly in one direction than in another, andconsequently making them travel by a series of successive decompositionsand recompositions in opposite directions, and finally causing theirexpulsion or exclusion at the boundaries of the body under decomposition, in the direction of the current, _and that_ in larger or smallerquantities, according as the current is more or less powerful (377. ). Ithink, therefore, it would be more philosophical, and more directlyexpressive of the facts, to speak of such a body, in relation to thecurrent passing through it, rather than to the poles, as they are usuallycalled, in contact with it; and say that whilst under decomposition, oxygen, chlorine, iodine, acids, &c. , are rendered at its negativeextremity, and combustibles, metals, alkalies, bases, &c. , at its positiveextremity (467. ), I do not believe that a substance can be transferred inthe electric current beyond the point where it ceases to find particleswith which it can combine; and I may refer to the experiments made in air(465. ) and in water (495. ), already quoted, for facts illustrating theseviews in the first instance; to which I will now add others. 

525. In order to show the dependence of the decomposition and transfer ofelements upon the chemical affinity of the substances present, experimentswere made upon sulphuric acid in the following manner. Dilute sulphuricacid was prepared: its specific gravity was 1. 0212. A solution of sulphateof soda was also prepared, of such strength that a measure of it containedexactly as much sulphuric acid as an equal measure of the diluted acid justreferred to. A solution of pure soda, and another of pure ammonia, werelikewise prepared, of such strengths that a measure of either should beexactly neutralized by a measure of the prepared sulphuric acid. 

526. Four glass cups were then arranged, as in fig. 55; seventeen measuresof the free sulphuric acid (525. ) were put into each of the vessels _a_ and_b_, and seventeen measures of the solution of sulphate of soda into eachof the vessels A and B. Asbestus, which had been well-washed in acid, actedupon by the voltaic pile, well-washed in water, and dried by pressure, wasused to connect _a_ with _b_ and A with B, the portions being as equal asthey could be made in quantity, and cut as short as was consistent withtheir performing the part of effectual communications, _b_ and A wereconnected by two platina plates or poles soldered to the extremities of onewire, and the cups _a_ and B were by similar platina plates connected witha voltaic battery of forty pairs of plates four inches square, that in _a_being connected with the negative, and that in B with the positive pole. The battery, which was not powerfully charged, was retained incommunication above half an hour. In this manner it was certain that thesame electric current had passed through _a b_ and A B, and that in eachinstance the same quantity and strength of acid had been submitted to itsaction, but in one case merely dissolved in water, and in the otherdissolved and also combined with an alkali. 

527. On breaking the connexion with the battery, the portions of asbestuswere lifted out, and the drops hanging at the ends allowed to fall eachinto its respective vessel. The acids in _a_ and _b_ were then firstcompared, for which purpose two evaporating dishes were balanced, and theacid from _a_ put into one, and that from _b_ into the other; but as onewas a little heavier than the other, a small drop was transferred from theheavier to the lighter, and the two rendered equal in weight. Beingneutralized by the addition of the soda solution (525. ), that from _a_, orthe negative vessel, required 15 parts of the soda solution, and that from_b_, or the positive vessel, required 16. 3 parts. That the sum of these isnot 34 parts is principally due to the acid removed with the asbestus; buttaking the mean of 15. 65 parts, it would appear that a twenty-fourth partof the acid originally in the vessel _a_ had passed, through the influenceof the electric current, from _a_ into _b_. 

528. In comparing the difference of acid in A and B, the necessary equalityof weight was considered as of no consequence, because the solution was atfirst neutral, and would not, therefore, affect the test liquids, and allthe evolved acid would be in B, and the free alkali in A. The solution in Arequired 3. 2 measures of the prepared acid (525. ) to neutralize it, and thesolution in B required also 3. 2 measures of the soda solution (525. ) toneutralize it. As the asbestus must have removed a little acid and alkalifrom the glasses, these quantities are by so much too small; and thereforeit would appear that about a tenth of the acid originally in the vessel Ahad been transferred into B during the continuance of the electric action. 

529. In another similar experiment, whilst a thirty-fifth part of the acidpassed from _a_ to _b_; in the free acid vessels, between a tenth and aneleventh passed from A to B in the combined acid vessels. Other experimentsof the same kind gave similar results. 

530. The variation of electro-chemical decomposition, the transfer ofelements and their accumulation at the poles, according as the substancesubmitted to action consists of particles opposed more or less in theirchemical affinity, together with the consequent influence of the lattercircumstances, are sufficiently obvious in these cases, where sulphuricacid is acted upon in the _same quantity_ by the _same_ electric current, but in one case opposed to the comparatively weak affinity of water for it, and in the other to the stronger one of soda. In the latter case thequantity transferred is from two and a half to three times what it is inthe former; and it appears therefore very evident that the transfer isgreatly dependent upon the mutual action of the particles of thedecomposing bodies[A]. 

 [A] See the note to (675. ), --_Dec. 1838. _

531. In some of the experiments the acid from the vessels _a_ and _b_ wasneutralized by ammonia, then evaporated to dryness, heated to redness, andthe residue examined for sulphates. In these cases more sulphate was alwaysobtained from _a_ than from _b_; showing that it had been impossible toexclude saline bases (derived from the asbestus, the glass, or perhapsimpurities originally in the acid, ) and that they had helped intransferring the acid into _b_. But the quantity was small, and the acidwas principally transferred by relation to the water present. 

532. I endeavoured to arrange certain experiments by which saline solutionsshould be decomposed against surfaces of water; and at first worked withthe electric machine upon a piece of bibulous paper, or asbestus moistenedin the solution, and in contact at its two extremities with pointed piecesof paper moistened in pure water, which served to carry the electriccurrent to and from the solution in the middle piece. But I found numerousinterfering difficulties. Thus, the water and solutions in the pieces ofpaper could not be prevented from mingling at the point where they touched. Again, sufficient acid could be derived from the paper connected with thedischarging train, or it may be even from the air itself, under theinfluence of electric action, to neutralize the alkali developed at thepositive extremity of the decomposing solution, and so not merely preventits appearance, but actually transfer it on to the metal termination: and, in fact, when the paper points were not allowed to touch there, and themachine was worked until alkali was evolved at the delivering or positiveend of the turmeric paper, containing the sulphate of soda solution, it wasmerely necessary to place the opposite receiving point of the paperconnected with the discharging train, which had been moistened by distilledwater, upon the brown turmeric point and press them together, when thealkaline effect immediately disappeared. 

533. The experiment with sulphate of magnesia already described (495. ) is acase in point, however, and shows most clearly that the sulphuric acid andmagnesia contributed to each other's transfer and final evolution, exactlyas the same acid and soda affected each other in the results just given(527, &c. ); and that so soon as the magnesia advanced beyond the reach ofthe acid, and found no other substance with which it could combine, itappeared in its proper character, and was no longer able to continue itsprogress towards the negative pole. 

 * * * * *

534. The theory I have ventured to put forth appears to me to explain allthe prominent features of electro-chemical decomposition in a satisfactorymanner. 

535. In the first place, it explains why, in all ordinary cases, theevolved substances _appear only at the poles_; for the poles are thelimiting surfaces of the decomposing substance, and except at them, everyparticle finds other particles having a contrary tendency with which it cancombine. 

536. Then it explains why, in numerous cases, the elements or evolvedsubstances are not _retained_ by the poles; and this is no small difficultyin those theories which refer the decomposing effect directly to theattractive power of the poles. If, in accordance with the usual theory, apiece of platina be supposed to have sufficient power to attract a particleof hydrogen from the particle of oxygen with which it was the instantbefore combined, there seems no sufficient reason, nor any fact, exceptthose to be explained, which show why it should not, according to analogywith all ordinary attractive forces, as those of gravitation, magnetism, cohesion, chemical affinity, &c. _retain_ that particle which it had justbefore taken from a distance and from previous combination. Yet it does notdo so, but allows it to escape freely. Nor does this depend upon itsassuming the gaseous state, for acids and alkalies, &c. Are left equally atliberty to diffuse themselves through the fluid surrounding the pole, andshow no particular tendency to combine with or adhere to the latter. Andthough there are plenty of cases where combination with the pole does takeplace, they do not at all explain the instances of non-combination, and donot therefore in their particular action reveal the general principle ofdecomposition. 

537. But in the theory that I have just given, the effect appears to be anatural consequence of the action: the evolved substances are _expelled_from the decomposing mass (518. 519. ), not _drawn out by an attraction_which ceases to act on one particle without any assignable reason, while itcontinues to act on another of the same kind: and whether the poles bemetal, water, or air, still the substances are evolved, and are sometimesset free, whilst at others they unite to the matter of the poles, accordingto the chemical nature of the latter, i. E. Their chemical relation to thoseparticles which are leaving the substance under operation. 

538. The theory accounts for the _transfer of elements_ in a manner whichseems to me at present to leave nothing unexplained; and it was, indeed, the phenomena of transfer in the numerous cases of decomposition of bodiesrendered fluid by heat (380. 402. ), which, in conjunction with theexperiments in air, led to its construction. Such cases as the former wherebinary compounds of easy decomposability are acted upon, are perhaps thebest to illustrate the theory. 

539. Chloride of lead, for instance, fused in a bent tube (400. ), anddecomposed by platina wires, evolves lead, passing to what is usuallycalled the negative pole, and chlorine, which being evolved at the positivepole, is in part set free, and in part combines with the platina. Thechloride of platina formed, being soluble in the chloride of lead, issubject to decomposition, and the platina itself is gradually transferredacross the decomposing matter, and found with the lead at the negativepole. 

540. Iodide of lead evolves abundance of lead at the negative pole, andabundance of iodine at the positive pole. 

541. Chloride of silver furnishes a beautiful instance, especially whendecomposed by silver wire poles. Upon fusing a portion of it on a piece ofglass, and bringing the poles into contact with it, there is abundance ofsilver evolved at the negative pole, and an equal abundance absorbed at thepositive pole, for no chlorine is set free: and by careful management, thenegative wire may be withdrawn from the fused globule as the silver isreduced there, the latter serving as the continuation of the pole, until awire or thread of revived silver, five or six inches in length, isproduced; at the same time the silver at the positive pole is as rapidlydissolved by the chlorine, which seizes upon it, so that the wire has to becontinually advanced as it is melted away. The whole experiment includesthe action of only two elements, silver and chlorine, and illustrates in abeautiful manner their progress in opposite directions, parallel to theelectric current, which is for the time giving a uniform general directionto their mutual affinities (524. ). 

542. According to my theory, an element or a substance not decomposableunder the circumstances of the experiment, (as for instance, a dilute acidor alkali, ) should not be transferred, or pass from pole to pole, unless itbe in chemical relation to some other element or substance tending to passin the opposite direction, for the effect is considered as essentially dueto the mutual relation of such particles. But the theories attributing thedetermination of the elements to the attractions and repulsions of thepoles require no such condition, i. E. There is no reason apparent why theattraction of the positive pole, and the repulsion of the negative pole, upon a particle of free acid, placed in water between them, should not(with equal currents of electricity) be as strong as if that particle werepreviously combined with alkali; but, on the contrary, as they have not apowerful chemical affinity to overcome, there is every reason to supposethey would be stronger, and would sooner bring the acid to rest at thepositive pole[A]. Yet such is not the case, as has been shown by theexperiments on free and combined acid (526. 528. ). 

 [A] Even Sir Humphry Davy considered the attraction of the pole as being communicated from one particle to another of the _same_ kind (483. ). 

543. Neither does M. De la Rive's theory, as I understand it, _require_that the particles should be in combination: it does not even admit, wherethere are two sets of particles capable of combining with and passing byeach other, that they do combine, but supposes that they travel as separatecompounds of matter and electricity. Yet in fact the free substance_cannot_ travel, the combined one _can_. 

544. It is very difficult to find cases amongst solutions or fluids whichshall illustrate this point, because of the difficulty of finding twofluids which shall conduct, shall not mingle, and in which an elementevolved from one shall not find a combinable element in the other. _Solutions_ of acids or alkalies will not answer, because they exist byvirtue of an attraction; and increasing the solubility of a body in onedirection, and diminishing it in the opposite, is just as good a reason fortransfer, as modifying the affinity between the acids and alkaliesthemselves[A]. Nevertheless the case of sulphate of magnesia is in point(494. 495. ), and shows that _one element or principle only_ has no power oftransference or of passing towards either pole. 

 [A] See the note to (670. ). --_Dec. 1838. _

545. Many of the metals, however, in their solid state, offer very fairinstances of the kind required. Thus, if a plate of platina be used as thepositive pole in a solution of sulphuric acid, oxygen will pass towards it, and so will acid; but these are not substances having such chemicalrelation to the platina as, even under the favourable conditionsuperinduced by the current (518. 524. ), to combine with it; the platinatherefore remains where it was first placed, and has no tendency to passtowards the negative pole. But if a plate of iron, zinc or copper, besubstituted for the platina, then the oxygen and acid can combine withthese, and the metal immediately begins to travel (as an oxide) to theopposite pole, and is finally deposited there. Or if, retaining the platinapole, a fused chloride, as of lead, zinc, silver, &c. , be substituted forthe sulphuric acid, then, as the platina finds an element it can combinewith, it enters into union, acts as other elements do in cases of voltaicdecomposition, is rapidly transferred across the melted matter, andexpelled at the negative pole. 

546. I can see but little reason in the theories referring theelectro-chemical decomposition to the attractions and repulsions of thepoles, and I can perceive none in M. De la Rive's theory, why the metal ofthe positive pole should not be transferred across the interveningconductor, and deposited at the negative pole, even when it cannot actchemically upon the element of the fluid surrounding it. It cannot bereferred to the attraction of cohesion preventing such an effect; for ifthe pole be made of the lightest spongy platina, the effect is the same. Orif gold precipitated by sulphate of iron be diffused through the solution, still accumulation of it at the negative pole will not take place; and yetthe attraction of cohesion is almost perfectly overcome, the particles arein it so small as to remain for hours in suspension, and are perfectly freeto move by the slightest impulse towards either pole; and _if in relation_by chemical affinity to any substance present, are powerfully determined tothe negative pole[A]. 

 [A] In making this experiment, care must be taken that no substance be present that can act chemically on the gold. Although I used the metal very carefully washed, and diffused through dilute sulphuric acid, yet in the first instance I obtained gold at the negative pole, and the effect was repeated when the platina poles were changed. But on examining the clear liquor in the cell, after subsidence of the metallic gold, I found a little of that metal in solution, and a little chlorine was also present. I therefore well washed the gold which had thus been subjected to voltaic action, diffused it through other pure dilute sulphuric acid, and then found, that on subjecting it to the action of the pile, not the slightest tendency to the negative pole could be perceived. 

547. In support of these arguments, it may be observed, that as yet nodetermination of a substance to a pole, or tendency to obey the electriccurrent, has been observed (that I am aware of, ) in cases of mere mixture;i. E. A substance diffused through a fluid, but having no sensible chemicalaffinity with it, or with substances that may be evolved from it during theaction, does not in any case seem to be affected by the electric current. Pulverised charcoal was diffused through dilute sulphuric acid, andsubjected with the solution to the action of a voltaic battery, terminatedby platina poles; but not the slightest tendency of the charcoal to thenegative pole could be observed, Sublimed sulphur was diffused throughsimilar acid, and submitted to the same action, a silver plate being usedas the negative pole; but the sulphur had no tendency to pass to that pole, the silver was not tarnished, nor did any sulphuretted hydrogen appear. Thecase of magnesia and water (495. 533. ), with those of comminuted metals incertain solutions (546. ), are also of this kind; and, in fact, substanceswhich have the instant before been powerfully determined towards the pole, as magnesia from sulphate of magnesia, become entirely _indifferent to it_the moment they assume their independent state, and pass away, diffusingthemselves through the surrounding fluid. 

548. There are, it is true, many instances of insoluble bodies being actedupon, as glass, sulphate of baryta, marble, slate, basalt, &c. , but theyform no exception; for the substances they give up are in direct and strongrelation as to chemical affinity with those which they find in thesurrounding solution, so that these decompositions enter into the class ofordinary effects. 

549. It may be expressed as a general consequence, that the more directlybodies are opposed to each other in chemical affinity, the more _ready_ istheir separation from each other in cases of electro-chemicaldecomposition, i. E. Provided other circumstances, as insolubility, deficient conducting power, proportions, &c. , do not interfere. This iswell known to be the case with water and saline solutions; and I have foundit to be equally true with _dry_ chlorides, iodides, salts, &c. , renderedsubject to electro-chemical decomposition by fusion (402. ). So that inapplying the voltaic battery for the purpose of decomposing bodies not yetresolved into forms of matter simpler than their own, it must beremembered, that success may depend not upon the weakness, or failure uponthe strength, of the affinity by which the elements sought for are heldtogether, but contrariwise; and then modes of application may be devised, by which, in _association_ with ordinary chemical powers, and theassistance of fusion (394. 417. ), we may be able to penetrate much furtherthan at present into the constitution of our chemical elements. 

550. Some of the most beautiful and surprising cases of electro-chemicaldecomposition and _transfer_ which Sir Humphry Davy described in hiscelebrated paper[A], were those in which acids were passed throughalkalies, and alkalies or earths through acids[B]; and the way in whichsubstances having the most powerful attractions for each other were thusprevented from combining, or, as it is said, had their natural affinitydestroyed or suspended throughout the whole of the circuit, excited theutmost astonishment. But if I be right in the view I have taken of theeffects, it will appear, that that which made the _wonder_, is in fact the_essential condition_ of transfer and decomposition, and that the morealkali there is in the course of an acid, the more will the transfer ofthat acid be facilitated from pole to pole; and perhaps a betterillustration of the difference between the theory I have ventured, andthose previously existing, cannot be offered than the views theyrespectively give of such facts as these. 

 [A] Philosophical Transactions, 1807, p. 1. 

 [B] Ibid. P, 24, &c. 

551. The instances in which sulphuric acid could not be passed thoughbaryta, or baryta through sulphuric acid[A], because of the precipitationof sulphate of baryta, enter within the pale of the law already described(380. 412. ), by which liquidity is so generally required for conduction anddecomposition. In assuming the solid state of sulphate of baryta, thesebodies became virtually non-conductors to electricity of so low a tensionas that of the voltaic battery, and the power of the latter over them wasalmost infinitely diminished. 

 [A] Philosophical Transactions, 1807, p. 25, &c. 

552. The theory I have advanced accords in a most satisfactory manner withthe fact of an element or substance finding its place of rest, or rather ofevolution, sometimes at one pole and sometimes at the other. Sulphurillustrates this effect very well[A]. When sulphuric acid is decomposed bythe pile, sulphur is evolved at the negative pole; but when sulphuret ofsilver is decomposed in a similar way (436. ), then the sulphur appears atthe positive pole; and if a hot platina pole be used so as to vaporize thesulphur evolved in the latter case, then the relation of that pole to thesulphur is exactly the same as the relation of the same pole to oxygen uponits immersion in water. In both cases the element evolved is liberated atthe pole, but not retained by it; but by virtue of its elastic, uncombinable, and immiscible condition passes away into the surroundingmedium. The sulphur is evidently determined in these opposite directions byits opposite chemical relations to oxygen and silver; and it is to suchrelations generally that I have referred all electro-chemical phenomena. Where they do not exist, no electro-chemical action can take place. Wherethey are strongest, it is most powerful; where they are reversed, thedirection of transfer of the substance is reversed with them. 

 [A] At 681 and 757 of Series VII, will be found corrections of the statement here made respecting sulphur and sulphuric acid. At present there is no well-ascertained fact which proves that the same body can go directly to _either_ of the two poles at pleasure. --_Dec. 1838. _

553. _Water_ may be considered as one of those substances which can be madeto pass to _either_ pole. When the poles are immersed in dilute sulphuricacid (527. ), acid passes towards the positive pole, and water towards thenegative pole; but when they are immersed in dilute alkali, the alkalipasses towards the negative pole, and water towards the positive pole. 

554. Nitrogen is another substance which is considered as determinable toeither pole; but in consequence of the numerous compounds which it forms, some of which pass to one pole, and some to the other, I have not alwaysfound it easy to determine the true circumstances of its appearance. A purestrong solution of ammonia is so bad a conductor of electricity that it isscarcely more decomposable than pure water; but if sulphate of ammonia bedissolved in it, then decomposition takes place very well; nitrogen almostpure, and in some cases quite, is evolved at the positive pole, andhydrogen at the negative pole. 

555. On the other hand, if a strong solution of nitrate of ammonia bedecomposed, oxygen appears at the positive pole, and hydrogen, withsometimes nitrogen, at the negative pole. If fused nitrate of ammonia beemployed, hydrogen appears at the negative pole, mingled with a littlenitrogen. Strong nitric acid yields plenty of oxygen at the positive pole, but no gas (only nitrous acid) at the negative pole. Weak nitric acidyields the oxygen and hydrogen of the water present, the acid apparentlyremaining unchanged. Strong nitric acid with nitrate of ammonia dissolvedin it, yields a gas at the negative pole, of which the greater part ishydrogen, but apparently a little nitrogen is present. I believe, that insome of these cases a little nitrogen appeared at the negative pole. Isuspect, however, that in all these, and in all former cases, theappearance of the nitrogen at the positive or negative pole is entirely asecondary effect, and not an immediate consequence of the decomposing powerof the electric current[A]. 

 [A] Refer for proof of the truth of this supposition to 748, 752, &c. --_Dec. 1838. _

556. A few observations on what are called the _poles_ of the voltaicbattery now seem necessary. The poles are merely the surfaces or doors bywhich the electricity enters into or passes out of the substance sufferingdecomposition. They limit the extent of that substance in the course of theelectric current, being its _terminations_ in that direction: Hence theelements evolved pass so far and no further. 

557. Metals make admirable poles, in consequence of their high conductingpower, their immiscibility with the substances generally acted upon, theirsolid form, and the opportunity afforded of selecting such as are notchemically acted upon by ordinary substances. 

558. Water makes a pole of difficult application, except in a few cases(494. ), because of its small conducting power, its miscibility with most ofthe substances acted upon, and its general relation to them in respect tochemical affinity. It consists of elements, which in their electrical andchemical relations are directly and powerfully opposed, yet combining toproduce a body more neutral in its character than any other. So that thereare but few substances which do not come into relation, by chemicalaffinity, with water or one of its elements; and therefore either the wateror its elements are transferred and assist in transferring the infinitevariety of bodies which, in association with it, can be placed in thecourse of the electric current. Hence the reason why it so rarely happensthat the evolved substances rest at the first surface of the water, and whyit therefore does not exhibit the ordinary action of a pole. 

559. Air, however, and some gases are free from the latter objection, andmay be used as poles in many cases (461, &c. ); but, in consequence of theextremely low degree of conducting power belonging to them, they cannot beemployed with the voltaic apparatus. This limits their use; for the voltaicapparatus is the only one as yet discovered which supplies sufficientquantity of electricity (371. 376. ) to effect electro-chemicaldecomposition with facility. 

560. When the poles are liable to the chemical action of the substancesevolved, either simply in consequence of their natural relation to them, orof that relation aided by the influence of the current (518. ), then theysuffer corrosion, and the parts dissolved are subject to transference, inthe same manner as the particles of the body originally underdecomposition. An immense series of phenomena of this kind might be quotedin support of the view I have taken of the cause of electro-chemicaldecomposition, and the transfer and evolution of the elements. Thus platinabeing made the positive and negative poles in a solution of sulphate ofsoda, has no affinity or attraction for the oxygen, hydrogen, acid, oralkali evolved, and refuses to combine with or retain them. Zinc cancombine with the oxygen and acid; at the positive pole it does combine, andimmediately begins to travel as oxide towards the negative pole. Charcoal, which cannot combine with the metals, if made the negative pole in ametallic solution, refuses to unite to the bodies which are ejected fromthe solution upon its surface; but if made the positive pole in a dilutesolution of sulphuric acid, it is capable of combining with the oxygenevolved there, and consequently unites with it, producing both carbonicacid and carbonic oxide in abundance. 

561. A great advantage is frequently supplied, by the opportunity affordedamongst the metals of selecting a substance for the pole, which shall orshall not be acted upon by the elements to be evolved. The consequent useof platina is notorious. In the decomposition of sulphuret of silver andother sulphurets, a positive silver pole is superior to a platina one, because in the former case the sulphur evolved there combines with thesilver, and the decomposition of the original sulphuret is renderedevident; whereas in the latter case it is dissipated, and the assurance ofits separation at the pole not easily obtained. 

562. The effects which take place when a succession of conductingdecomposable and undecomposable substances are placed in the electriccircuit, as, for instance, of wires and solutions, or of air and solutions(465, 469. ), are explained in the simplest possible manner by thetheoretical view I have given. In consequence of the reaction of theconstituents of each portion of decomposable matter, affected as they areby the supervention of the electric current (524. ), portions of theproximate or ultimate elements proceed in the direction of the current asfar as they find matter of a contrary kind capable of effecting theirtransfer, and being equally affected by them; and where they cease to findsuch matter, they are evolved in their free state, i. E. Upon the surfacesof metal or air bounding the extent of decomposable matter in the directionof the current. 

563. Having thus given my theory of the mode in which electro-chemicaldecomposition is effected, I will refrain for the present from enteringupon the numerous general considerations which it suggests, wishing firstto submit it to the test of publication and discussion. 

_Royal Institution, June 1833. _

SIXTH SERIES. 

§ 12. _On the power of Metals and other Solids to induce the Combinationof Gaseous Bodies. _

Received November 30, 1833, --Read January 11, 1834. 

564. The conclusion at which I have arrived in the present communicationmay seem to render the whole of it unfit to form part of a series ofresearches in electricity; since, remarkable as the phenomena are, thepower which produces them is not to be considered as of an electric origin, otherwise than as all attraction of particles may have this subtile agentfor their common cause. But as the effects investigated arose out ofelectrical researches, as they are directly connected with other effectswhich are of an electric nature, and must of necessity be understood andguarded against in a very extensive series of electro-chemicaldecompositions (707. ), I have felt myself fully justified in describingthem in this place. 

565. Believing that I had proved (by experiments hereafter to be described(705. ), ) the constant and definite chemical action of a certain quantity ofelectricity, whatever its intensity might be, or however the circumstancesof its transmission through either the body under decomposition or the moreperfect conductors were varied, I endeavoured upon that result to constructa new measuring instrument, which from its use might be called, at leastprovisionally, a _Volta-electrometer_ (739. )[A]. 

 [A] Or Voltameter. --_Dec. 1838. _

566. During the course of the experiments made to render the instrumentefficient, I was occasionally surprised at observing a deficiency of thegases resulting from the decompositions of water, and at last an actualdisappearance of portions which had been evolved, collected, and measured. The circumstances of the disappearance were these. A glass tube, abouttwelve inches in length and 3/4ths of an inch in diameter, had two platinapoles fixed into its upper, hermetically sealed, extremity: the poles, where they passed through the glass, were of wire; but terminated below inplates, which were soldered to the wires with gold (Plate V. Fig. 56. ). Thetube was filled with dilute sulphuric acid, and inverted in a cup of thesame fluid; a voltaic battery was connected with the two wires, andsufficient oxygen and hydrogen evolved to occupy 4/5ths of the tube, or bythe graduation, 116 parts. On separating the tube from the voltaic batterythe volume of gas immediately began to diminish, and in about five hoursonly 13-1/2 parts remained, and these ultimately disappeared. 

567. It was found by various experiments, that this effect was not due tothe escape or solution of the gas, nor to recombination of the oxygen orhydrogen in consequence of any peculiar condition _they_ might be supposedto possess under the circumstances; but to be occasioned by the action ofone or both of the poles within the tube upon the gas around them. Ondisuniting the poles from the pile after they had acted upon dilutesulphuric acid, and introducing them into separate tubes containing mixedoxygen and hydrogen, it was found that the _positive_ pole effected theunion of the gases, but the negative pole apparently not (588. ). It wasascertained also that no action of a sensible kind took place between thepositive pole with oxygen or hydrogen alone. 

568. These experiments reduced the phenomena to the consequence of a powerpossessed by the platina, after it had been the positive pole of a voltaicpile, of causing the combination of oxygen and hydrogen at common, or evenat low, temperatures. This effect is, as far as I am aware, altogether new, and was immediately followed out to ascertain whether it was really of anelectric nature, and how far it would interfere with the determination ofthe quantities evolved in the cases of electro-chemical decompositionrequired in the fourteenth section of these Researches. 

569. Several platina plates were prepared (fig. 57. ). They were nearly halfan inch wide, and two inches and a half long: some were 1/200dth of aninch, others not more than 1/600dth, whilst some were as much as 1/70th ofan inch in thickness. Each had a piece of platina wire, about seven incheslong, soldered to it by pure gold. Then a number of glass tubes wereprepared: they were about nine or ten inches in length, 5/8ths of an inchin internal diameter, were sealed hermetically at one extremity, and weregraduated. Into these tubes was put a mixture of two volumes of hydrogenand one of oxygen, at the water pneumatic trough, and when one of theplates described had been connected with the positive or negative pole ofthe voltaic battery for a given time, or had been otherwise prepared, itwas introduced through the water into the gas within the tube; the wholeset aside in a test-glass (fig. 58. ), and left for a longer or shorterperiod, that the action might be observed. 

570. The following result may be given as an illustration of the phenomenonto be investigated. Diluted sulphuric acid, of the specific gravity 1. 336, was put into a glass jar, in which was placed also a large platina plate, connected with the negative end of a voltaic battery of forty pairs offour-inch plates, with double coppers, and moderately charged. One of theplates above described (569. ) was then connected with the positiveextremity, and immersed in the same jar of acid for five minutes, afterwhich it was separated from the battery, washed in distilled water, andintroduced through the water of the pneumatic trough into a tube containingthe mixture of oxygen and hydrogen (569. ). The volume of gases immediatelybegan to lessen, the diminution proceeding more and more rapidly untilabout 3/4ths of the mixture had disappeared. The upper end of the tubebecame quite warm, the plate itself so hot that the water boiled as it roseover it; and in less than a minute a cubical inch and a half of the gaseswere gone, having been combined by the power of the platina, and convertedinto water. 

571. This extraordinary influence acquired by the platina at the positivepole of the pile, is exerted far more readily and effectively on oxygen andhydrogen than on any other mixture of gases that I have tried. One volumeof nitrous gas was mixed with a volume of hydrogen, and introduced into atube with a plate which had been made positive in the dilute sulphuric acidfor four minutes (570. ). There was no sensible action in an hour: beingleft for thirty-six hours, there was a diminution of about one-eighth ofthe whole volume. Action had taken place, but it had been very feeble. 

572. A mixture of two volumes of nitrous oxide with one volume of hydrogenwas put with a plate similarly prepared into a tube (569. 570. ). This alsoshowed no action immediately; but in thirty-six hours nearly a fourth ofthe whole had disappeared, i. E. About half of a cubic inch. By comparisonwith another tube containing the same mixture without a plate, it appearedthat a part of the diminution was due to solution, and the other part tothe power of the platina; but the action had been very slow and feeble. 

573. A mixture of one volume olefiant gas and three volumes oxygen was notaffected by such a platina plate, even though left together for severaldays (640. 641. ). 

574. A mixture of two volumes carbonic oxide and one volume oxygen was alsounaffected by the prepared platina plate in several days (645, &c. ). 

575. A mixture of equal volumes of chlorine and hydrogen was used inseveral experiments, with plates prepared in a similar manner (570. ). Diminution of bulk soon took place; but when after thirty-six hours theexperiments were examined, it was found that nearly all the chlorine haddisappeared, having been absorbed, principally by the water, and that theoriginal volume of hydrogen remained unchanged. No combination of thegases, therefore, had here taken place. 

576. Reverting to the action of the prepared plates on mixtures of oxygenand hydrogen (570. ), I found that the power, though gradually diminishingin all cases, could still be retained for a period, varying in its lengthwith circumstances. When tubes containing plates (569. ) were supplied withfresh portions of mixed oxygen and hydrogen as the previous portions werecondensed, the action was found to continue for above thirty hours, and insome cases slow combination could be observed even after eighty hours; butthe continuance of the action greatly depended upon the purity of the gasesused (638. ). 

577. Some plates (569. ) were made positive for four minutes in dilutesulphuric acid of specific gravity 1. 336: they were rinsed in distilledwater, after which two were put into a small bottle and closed up, whilstothers were left exposed to the air. The plates preserved in the limitedportion of air were found to retain their power after eight days, but thoseexposed to the atmosphere had lost their force almost entirely in twelvehours, and in some situations, where currents existed, in a much shortertime. 

578. Plates were made positive for five minutes in sulphuric acid, specificgravity 1. 336. One of these was retained in similar acid for eight minutesafter separation from the battery: it then acted on mixed oxygen andhydrogen with apparently undiminished vigour. Others were left in similaracid for forty hours, and some even for eight days, after theelectrization, and then acted as well in combining oxygen and hydrogen gasas those which were used immediately after electrization. 

579. The effect of a solution of caustic potassa in preserving the platinaplates was tried in a similar manner. After being retained in such asolution for forty hours, they acted exceedingly well on oxygen andhydrogen, and one caused such rapid condensation of the gases, that theplate became much heated, and I expected the temperature would have risento ignition. 

580. When similarly prepared plates (569. ) had been put into distilledwater for forty hours, and then introduced into mixed oxygen and hydrogen, they were found to act but very slowly and feebly as compared with thosewhich had been preserved in acid or alkali. When, however, the quantity ofwater was but small, the power was very little impaired after three or fourdays. As the water had been retained in a wooden vessel, portions of itwere redistilled in glass, and this was found to preserve prepared platesfor a great length of time. Prepared plates were put into tubes with thiswater and closed up; some of them, taken out at the end of twenty-fourdays, were found very active on mixed oxygen and hydrogen; others, whichwere left in the water for fifty-three days, were still found to cause thecombination of the gases. The tubes had been closed only by corks. 

581. The act of combination always seemed to diminish, or apparentlyexhaust, the power of the platina plate. It is true, that in most, if notall instances, the combination of the gases, at first insensible, graduallyincreased in rapidity, and sometimes reached to explosion; but when thelatter did not happen, the rapidity of combination diminished; and althoughfresh portions of gas were introduced into the tubes, the combination wenton more and more slowly, and at last ceased altogether. The first effect ofan increase in the rapidity of combination depended in part upon the waterflowing off from the platina plate, and allowing a better contact with thegas, and in part upon the heat evolved during the progress of thecombination (630. ). But notwithstanding the effect of these causes, diminution, and at last cessation of the power, always occurred. It mustnot, however, be unnoticed, that the purer the gases subjected to theaction of the plate, the longer was its combining power retained. With themixture evolved at the poles of the voltaic pile, in pure dilute sulphuricacid, it continued longest; and with oxygen and hydrogen, of perfectpurity, it probably would not be diminished at all. 

582. Different modes of treatment applied to the platina plate, after ithad ceased to be the positive pole of the pile, affected its power verycuriously. A plate which had been a positive pole in diluted sulphuric acidof specific gravity 1. 336 for four or five minutes, if rinsed in water andput into mixed oxygen and hydrogen, would act very well, and condenseperhaps one cubic inch and a half of gas in six or seven minutes; but ifthat same plate, instead of being merely rinsed, had been left in distilledwater for twelve or fifteen minutes, or more, it would rarely fail, whenput into the oxygen and hydrogen, of becoming, in the course of a minute ortwo, ignited, and would generally explode the gases. Occasionally the timeoccupied in bringing on the action extended to eight or nine minutes, andsometimes even to forty minutes, and yet ignition and explosion wouldresult. This effect is due to the removal of a portion of acid whichotherwise adheres firmly to the plate [A]. 

 [A] In proof that this is the case, refer to 1038. --_Dec. 1838. _

583. Occasionally the platina plates (569. ), after being made the positivepole of the battery, were washed, wiped with filtering-paper or a cloth, and washed and wiped again. Being then introduced into mixed oxygen andhydrogen, they acted apparently as if they had been unaffected by thetreatment. Sometimes the tubes containing the gas were opened in the airfor an instant, and the plates put in dry; but no sensible difference inaction was perceived, except that it commenced sooner. 

584. The power of heat in altering the action of the prepared platinaplates was also tried (595. ). Plates which had been rendered positive indilute sulphuric acid for four minutes were well-washed in water, andheated to redness in the flame of a spirit-lamp: after this they acted verywell on mixed oxygen and hydrogen. Others, which had been heated morepowerfully by the blowpipe, acted afterwards on the gases, though not sopowerfully as the former. Hence it appears that heat does not take away thepower acquired by the platina at the positive pole of the pile: theoccasional diminution of force seemed always referable to other causes thanthe mere heat. If, for instance, the plate had not been well-washed fromthe acid, or if the flame used was carbonaceous, or was that of an alcohollamp trimmed with spirit containing a little acid, or having a wick onwhich salt, or other extraneous matter, had been placed, then the power ofthe plate was quickly and greatly diminished (634. 636. ). 

585. This remarkable property was conferred upon platina when it was madethe positive pole in sulphuric acid of specific gravity 1. 336, or when itwas considerably weaker, or when stronger, even up to the strength of oilof vitriol. Strong and dilute nitric acid, dilute acetic acid, solutions oftartaric, citric, and oxalic acids, were used with equal success. Whenmuriatic acid was used, the plates acquired the power of condensing theoxygen and hydrogen, but in a much inferior degree. 

586. Plates which were made positive in solution of caustic potassa did notshow any sensible action upon the mixed oxygen and hydrogen. Other platesmade positive in solutions of carbonates of potassa and soda exhibited theaction, but only in a feeble degree. 

587. When a neutral solution of sulphate of soda, or of nitre, or ofchlorate of potassa, or of phosphate of potassa, or acetate of potassa, orsulphate of copper, was used, the plates, rendered positive in them forfour minutes, and then washed in water, acted very readily and powerfullyon the mixed oxygen and hydrogen. 

588. It became a very important point, in reference to the _cause_ of thisaction of the platina, to determine whether the _positive_ pole _only_could confer it (567. ), or whether, notwithstanding the numerous contrarycases, the _negative_ pole might not have the power when such circumstancesas could interfere with or prevent the action were avoided. Three plateswere therefore rendered negative, for four minutes in diluted sulphuricacid of specific gravity 1. 336, washed in distilled water, and put intomixed oxygen and hydrogen. _All_ of them _acted_, though not so strongly asthey would have done if they had been rendered positive. Each combinedabout a cubical inch and a quarter of the gases in twenty-five minutes. Onevery repetition of the experiment the same result was obtained; and whenthe plates were retained in distilled water for ten or twelve minutes, before being introduced into the gas (582. ), the action was very muchquickened. 

589. But when there was any metallic or other substance present in theacid, which could be precipitated on the negative plate, then that plateceased to act upon the mixed oxygen and hydrogen. 

590. These experiments led to the expectation that the power of causingoxygen and hydrogen to combine, which could be conferred upon any piece ofplatina by making it the positive pole of a voltaic pile, was notessentially dependent upon the action of the pile, or upon any structure orarrangement of parts it might receive whilst in association with it, butbelonged to the platina _at all times_, and was _always effective_ when thesurface was _perfectly clean_. And though, when made the _positive_ pole ofthe pile in acids, the circumstances might well be considered as thosewhich would cleanse the surface of the platina in the most effectualmanner, it did not seem impossible that ordinary operations should producethe same result, although in a less eminent degree. 

591. Accordingly, a platina plate (569. ) was cleaned by being rubbed with acork, a little water, and some coal-fire ashes upon a glass plate: beingwashed, it was put into mixed oxygen and hydrogen, and was found to act atfirst slowly, and then more rapidly. In an hour, a cubical inch and a halfhad disappeared. 

592. Other plates were cleaned with ordinary sand-paper and water; otherswith chalk and water; others with emery and water; others, again, withblack oxide of manganese and water; and others with a piece of charcoal andwater. All of these acted in tubes of oxygen and hydrogen, causingcombination of the gases. The action was by no means so powerful as thatproduced by plates having been in communication with the battery; but fromone to two cubical inches of the gases disappeared, in periods extendingfrom twenty-five to eighty or ninety minutes. 

593. Upon cleaning the plates with a cork, ground emery, and dilutesulphuric acid, they were found to act still better. In order to simplifythe conditions, the cork was dismissed, and a piece of platina foil usedinstead; still the effect took place. Then the acid was dismissed, and asolution of _potassa_ used, but the effect occurred as before. 

594. These results are abundantly sufficient to show that the meremechanical cleansing of the surface of the platina is sufficient to enableit to exert its combining power over oxygen and hydrogen at commontemperatures. 

595. I now tried the effect of heat in conferring this property uponplatina (584. ). Plates which had no action on the mixture of oxygen andhydrogen were heated by the flame of a freshly trimmed spirit-lamp, urgedby a mouth blowpipe, and when cold were put into tubes of the mixed gases:they acted slowly at first, but after two or three hours condensed nearlyall the gases. 

596. A plate of platina, which was about one inch wide and two andthree-quarters in length, and which had not been used in any of thepreceding experiments, was curved a little so as to enter a tube, and leftin a mixture of oxygen and hydrogen for thirteen hours: not the slightestaction or combination of the gases occurred. It was withdrawn at thepneumatic trough from the gas through the water, heated red-hot by thespirit-lamp and blowpipe, and then returned when cold into the _same_portion of gas. In the course of a few minutes diminution of the gasescould be observed, and in forty-five minutes about one cubical inch and aquarter had disappeared. In many other experiments platina plates whenheated were found to acquire the power of combining oxygen and hydrogen. 

597. But it happened not infrequently that plates, after being heated, showed no power of combining oxygen and hydrogen gases, though leftundisturbed in them for two hours. Sometimes also it would happen that aplate which, having been heated to dull redness, acted feebly, upon beingheated to whiteness ceased to act; and at other times a plate which, havingbeen slightly heated, did not act, was rendered active by a more powerfulignition. 

598. Though thus uncertain in its action, and though often diminishing thepower given to the plates at the positive pole of the pile (584. ), still itis evident that heat can render platina active, which before was inert(595. ). The cause of its occasional failure appears to be due to thesurface of the metal becoming soiled, either from something previouslyadhering to it, which is made to adhere more closely by the action of theheat, or from matter communicated from the flame of the lamp, or from theair itself. It often happens that a polished plate of platina, when heatedby the spirit-lamp and a blowpipe, becomes dulled and clouded on itssurface by something either formed or deposited there; and this, and muchless than this, is sufficient to prevent it from exhibiting the curiouspower now under consideration (634. 636. ). Platina also has been said tocombine with carbon; and it is not at all unlikely that in processes ofheating, where carbon or its compounds are present, a film of such acompound may be thus formed, and thus prevent the exhibition of theproperties belonging to _pure_ platina[A]. 

 [A] When heat does confer the property it is only by the destruction or dissipation of organic or other matter which had previously soiled the plate (632. 633. 634. ). --_Dec. 1838. _

599. The action of alkalies and acids in giving platina this property wasnow experimentally examined. Platina plates (569. ) having no action onmixed oxygen and hydrogen, being boiled in a solution of caustic potassa, washed, and then put into the gases, were found occasionally to act prettywell, but at other times to fail. In the latter case I concluded that theimpurity upon the surface of the platina was of a nature not to be removedby the mere solvent action of the alkali, for when the plates were rubbedwith a little emery, and the same solution of alkali (592. ), they becameactive. 

600. The action of acids was far more constant and satisfactory. A platinaplate was boiled in dilute nitric acid: being washed and put into mixedoxygen and hydrogen gases, it acted well. Other plates were boiled instrong nitric acid for periods extending from half a minute to fourminutes, and then being washed in distilled water, were found to act verywell, condensing one cubic inch and a half of gas in the space of eight ornine minutes, and rendering the tube warm (570. ). 

601. Strong sulphuric acid was very effectual in rendering the platinaactive. A plate (569. ) was heated in it for a minute, then washed and putinto the mixed oxygen and hydrogen, upon which it acted as well as if ithad been made the positive pole of a voltaic pile (570. ). 

602. Plates which, after being heated or electrized in alkali, or afterother treatment, were found inert, immediately received power by beingdipped for a minute or two, or even only for an instant, into hot oil ofvitriol, and then into water. 

603. When the plate was dipped into the oil of vitriol, taken out, and thenheated so as to drive off the acid, it did not act, in consequence of theimpurity left by the acid upon its surface. 

604. Vegetable acids, as acetic and tartaric, sometimes rendered inertplatina active, at other times not. This, I believe, depended upon thecharacter of the matter previously soiling the plates, and which may easilybe supposed to be sometimes of such a nature as to be removed by theseacids, and at other times not. Weak sulphuric acid showed the samedifference, but strong sulphuric acid (601. ) never failed in its action. 

605. The most favourable treatment, except that of making the plate apositive pole in strong acid, was as follows. The plate was held over aspirit-lamp flame, and when hot, rubbed with a piece of potassa fusa(caustic potash), which melting, covered the metal with a coat of verystrong alkali, and this was retained fused upon the surface for a second ortwo[A]: it was then put into water for four or five minutes to wash off thealkali, shaken, and immersed for about a minute in hot strong oil ofvitriol; from this it was removed into distilled water, where it wasallowed to remain ten or fifteen minutes to remove the last traces of acid(582. ). Being then put into a mixture of oxygen and hydrogen, combinationimmediately began, and proceeded rapidly; the tube became warm, the platinabecame red-hot, and the residue of the gases was inflamed. This effectcould be repeated at pleasure, and thus the maximum phenomenon could beproduced without the aid of the voltaic battery. 

 [A] The heat need not be raised so much as to make the alkali tarnish the platina, although if that effect does take place it does not prevent the ultimate action. 

606. When a solution of tartaric or acetic acid was substituted, in thismode of preparation, for the sulphuric acid, still the plate was found toacquire the same power, and would often produce explosion in the mixedgases; but the strong sulphuric acid was most certain and powerful. 

607. If borax, or a mixture of the carbonates of potash and soda, be fusedon the surface of a platina plate, and that plate be well-washed in water, it will be found to have acquired the power of combining oxygen andhydrogen, but only in a moderate degree; but if, after the fusion andwashing, it be dipped in the hot sulphuric acid (601. ), it will become veryactive. 

608. Other metals than platina were then experimented with. Gold andpalladium exhibited the power either when made the positive pole of thevoltaic battery (570. ), or when acted on by hot oil of vitriol (601. ). Whenpalladium is used, the action of the battery or acid should be moderated, as that metal is soon acted upon under such circumstances. Silver andcopper could not be made to show any effect at common temperatures. 

 * * * * *

609. There can remain no doubt that the property of inducing combination, which can thus be conferred upon masses of platina and other metals byconnecting them with the poles of the battery, or by cleansing processeseither of a mechanical or chemical nature, is the same as that which wasdiscovered by Döbereiner[A], in 1823, to belong in so eminent a degree tospongy platina, and which was afterwards so well experimented upon andillustrated by MM. Dulong and Thenard[B], in 1823. The latter philosopherseven quote experiments in which a very fine platina wire, which had beencoiled up and digested in nitric, sulphuric, or muriatic acid, becameignited when put into a jet of hydrogen gas[C]. This effect I can nowproduce at pleasure with either wires or plates by the processes described(570. 601. 605. ); and by using a smaller plate cut so that it shall restagainst the glass by a few points, and yet allow the water to flow off(fig. 59. ), the loss of heat is less, the metal is assimilated somewhat tothe spongy state, and the probability of failure almost entirely removed. 

 [A] Annales de Chimie, tom. Xxiv. P. 93. 

 [B] Ibid. Tom. Xxiii. P. 440; tom. Xxiv. P. 380. 

 [C] Ibid. Tom. Xxiv. P. 383. 

610. M. Döbereiner refers the effect entirely to an electric action. Heconsiders the platina and hydrogen as forming a voltaic element of theordinary kind, in which the hydrogen, being very highly positive, represents the zinc of the usual arrangement, and like it, therefore, attracts oxygen and combines with it[A]. 

 [A] tom. Xxiv. Pp. 94, 95. Also Bibliothèque Universelle, tom. Xxiv. P. 54. 

611. In the two excellent experimental papers by MM. Dulong and Thenard[A], those philosophers show that elevation of temperature favours the action, but does not alter its character; Sir Humphry Davy's incandescent platinawire being the same phenomenon with Döbereiner's spongy platina. They showthat _all_ metals have this power in a greater or smaller degree, and thatit is even possessed by such bodies as charcoal, pumice, porcelain, glass, rock crystal, &c. , when their temperatures are raised; and that another ofDavy's effects, in which oxygen and hydrogen had combined slowly togetherat a heat below ignition, was really dependent upon the property of theheated glass, which it has in common with the bodies named above. Theystate that liquids do not show this effect, at least that mercury, at orbelow the boiling point, has not the power; that it is not due to porosity;that the same body varies very much in its action, according to its state;and that many other gaseous mixtures besides oxygen and hydrogen areaffected, and made to act chemically, when the temperature is raised. Theythink it probable that spongy platina acquires its power from contact withthe acid evolved during its reduction, or from the heat itself to which itis then submitted. 

 [A] Annales de Chimie, tom. Xxiii. P. 440; tom. Xxiv. P, 380. 

612. MM. Dulong and Thenard express themselves with great caution on thetheory of this action; but, referring to the decomposing power of metals onammonia when heated to temperatures not sufficient alone to affect thealkali, they remark that those metals which in this case are mostefficacious, are the least so in causing the combination of oxygen andhydrogen; whilst platina, gold, &c. , which have least power of decomposingammonia, have most power of combining the elements of water:--from whichthey are led to believe, that amongst gases, some tend to _unite_ under theinfluence of metals, whilst others tend to _separate_, and that thisproperty varies in opposite directions with the different metals. At theclose of their second paper they observe, that the action is of a kind thatcannot be connected with any known theory; and though it is very remarkablethat the effects are transient, like those of most electrical actions, yetthey state that the greater number of the results observed by them areinexplicable, by supposing them to be of a purely electric origin. 

613. Dr. Fusinieri has also written on this subject, and given a theorywhich he considers as sufficient to account for the phenomena[A]. Heexpresses the immediate cause thus: "The platina determines upon itssurface a continual renovation of _concrete laminæ_ of the combustiblesubstance of the gases or vapours, which flowing over it are burnt, passaway, and are renewed: this combustion at the surface raises and sustainsthe temperature of the metal. " The combustible substance, thus reduced intoimperceptible laminæ, of which the concrete parts are in contact with theoxygen, is presumed to be in a state combinable with the oxygen at a muchlower temperature than when it is in the gaseous state, and more in analogywith what is called the nascent condition. That combustible gases shouldlose their elastic state, and become concrete, assuming the form ofexceedingly attenuated but solid strata, is considered as proved by facts, some of which are quoted in the Giornale di Fisica for 1824[B]; and thoughthe theory requires that they should assume this state at hightemperatures, and though the _similar_ films of aqueous and other matterare dissipated by the action of heat, still the facts are considered asjustifying the conclusion against all opposition of reasoning. 

 [A] Giornale di Fisica, &c. , 1825, tom. Viii. P. 259. 

 [B] pp. 138, 371. 

614. The power or force which makes combustible gas or vapour abandon itselastic state in contact with a solid, that it may cover the latter with athin stratum of its own proper substance, is considered as being neitherattraction nor affinity. It is able also to extend liquids and solids inconcrete laminæ over the surface of the acting solid body, and consists ina _repulsion_, which is developed from the parts of the solid body by thesimple fact of attenuation, and is highest when the attenuation is mostcomplete. The force has a progressive development, and acts mostpowerfully, or at first, in the direction in which the dimensions of theattenuated mass decrease, and then in the direction of the angles orcorners which from any cause may exist on the surface. This force not onlycauses spontaneous diffusion of gases and other substances over thesurface, but is considered as very elementary in its nature, and competentto account for all the phenomena of capillarity, chemical affinity, attraction of aggregation, rarefaction, ebullition, volatilization, explosion, and other thermometric effects, as well as inflammation, detonation, &c. &c. It is considered as a form of heat to which the term_native calorie_ is given, and is still further viewed as the principle ofthe two electricities and the two magnetisms. 

615. I have been the more anxious to give a correct abstract of Dr. Fusinieri's view, both because I cannot form a distinct idea of the powerto which he refers the phenomena, and because of my imperfect knowledge ofthe language in which the memoir is written. I would therefore beg to referthose who pursue the subject to the memoir itself. 

616. Not feeling, however, that the problem has yet been solved, I ventureto give the view which seems to me sufficient, upon _known principles_, toaccount for the effect. 

617. It may be observed of this action, that, with regard to platina, itcannot be due to any peculiar, temporary condition, either of an electricor of any other nature: the activity of plates rendered either positive ornegative by the pole, or cleaned with such different substances as acids, alkalies, or water; charcoal, emery, ashes, or glass; or merely heated, issufficient to negative such an opinion. Neither does it depend upon thespongy and porous, or upon the compact and burnished, or upon the massiveor the attenuated state of the metal, for in any of these states it may berendered effective, or its action may be taken away. The only essentialcondition appears to be a _perfectly clean_ and _metallic surface_, forwhenever that is present the platina acts, whatever its form and conditionin other respects may be; and though variations in the latter points willvery much affect the rapidity, and therefore the visible appearances andsecondary effects, of the action, i. E. The ignition of the metal and theinflammation of the gases, they, even in their most favourable state, cannot produce any effect unless the condition of a clean, pure, metallicsurface be also fulfilled. 

618. The effect is evidently produced by most, if not all, solid bodies, weakly perhaps by many of them, but rising to a high degree in platina. Dulong and Thenard have very philosophically extended our knowledge of theproperty to its possession by all the metals, and by earths, glass, stones, &c. (611. ); and every idea of its being a known and recognised electricaction is in this way removed. 

619. All the phenomena connected with this subject press upon my mind theconviction that the effects in question are entirely incidental and of asecondary nature; that they are dependent upon the _natural conditions_ ofgaseous elasticity, combined with the exertion of that attractive forcepossessed by many bodies, especially those which are solid, in an eminentdegree, and probably belonging to all; by which they are drawn intoassociation more or less close, without at the same time undergoingchemical combination, though often assuming the condition of adhesion; andwhich occasionally leads, under very favourable circumstances, as in thepresent instance, to the combination of bodies simultaneously subjected tothis attraction. I am prepared myself to admit (and probably many othersare of the same opinion), both with respect to the attraction ofaggregation and of chemical affinity, that the sphere of action ofparticles extends beyond those other particles with which they areimmediately and evidently in union (523. ), and in many cases produceseffects rising into considerable importance: and I think that this kind ofattraction is a determining cause of Döbereiner's effect, and of the manyothers of a similar nature. 

620. Bodies which become wetted by fluids with which they do not combinechemically, or in which they do not dissolve, are simple and well-knowninstances of this kind of attraction. 

621. All those cases of bodies which being insoluble in water and notcombining with it are hygrometric, and condense its vapour around or upontheir surface, are stronger instances of the same power, and approach alittle nearer to the cases under investigation. If pulverized clay, protoxide or peroxide of iron, oxide of manganese, charcoal, or evenmetals, as spongy platina or precipitated silver, be put into an atmospherecontaining vapour of water, they soon become moist by virtue of anattraction which is able to condense the vapour upon, although not tocombine it with, the substances; and if, as is well known, these bodies sodamped be put into a dry atmosphere, as, for instance, one confined oversulphuric acid, or if they be heated, then they yield up this water againalmost entirely, it not being in direct or permanent combination[A]. 

 [A] I met at Edinburgh with a case, remarkable as to its extent, of hygrometric action, assisted a little perhaps by very slight solvent power. Some turf had been well-dried by long exposure in a covered place to the atmosphere, but being then submitted to the action of a hydrostatic press, it yielded, _by the mere influence of the pressure_, 54 per cent. Of water. 

622. Still better instances of the power I refer to, because they are moreanalogous to the cases to be explained, are furnished by the attractionexisting between glass and air, so well known to barometer and thermometermakers, for here the adhesion or attraction is exerted between a solid andgases, bodies having very different physical conditions, having no power ofcombination with each other, and each retaining, during the time of action, its physical state unchanged[A]. When mercury is poured into a barometertube, a film of air will remain between the metal and glass for months, or, as far as is known, for years, for it has never been displaced except bythe action of means especially fitted for the purpose. These consist inboiling the mercury, or in other words, of forming an abundance of vapour, which coming in contact with every part of the glass and every portion ofsurface of the mercury, gradually mingles with, dilutes, and carries offthe air attracted by, and adhering to, those surfaces, replacing it byother vapour, subject to an equal or perhaps greater attraction, but whichwhen cooled condenses into the same liquid as that with which the tube isfilled. 

 [A] Fusinieri and Bellani consider the air as forming solid concrete films in these cases. --Giornale di Fisica, tom. Viii, p. 262. 1825. 

623. Extraneous bodies, which, acting as nuclei in crystallizing ordepositing solutions, cause deposition of substances on them, when it doesnot occur elsewhere in the liquid, seem to produce their effects by a powerof the same kind, i. E. A power of attraction extending to neighbouringparticles, and causing them to become attached to the nuclei, although itis not strong enough to make them combine chemically with their substance. 

624. It would appear from many cases of nuclei in solutions, and from theeffects of bodies put into atmospheres containing the vapours of water, orcamphor, or iodine, &c. , as if this attraction were in part elective, partaking in its characters both of the attraction of aggregation andchemical affinity: nor is this inconsistent with, but agreeable to, theidea entertained, that it is the power of particles acting, not upon otherswith which they can immediately and intimately combine, but upon such asare either more distantly situated with respect to them, or which, fromprevious condition, physical constitution, or feeble relation, are unableto enter into decided union with them. 

625. Then, of all bodies, the gases are those which might be expected toshow some _mutual_ action whilst _jointly_ under the attractive influenceof the platina or other solid acting substance. Liquids, such as water, alcohol, &c. , are in so dense and comparatively incompressible a state, asto favour no expectation that their particles should approach much closerto each other by the attraction of the body to which they adhere, and yetthat attraction must (according to its effects) place their particles asnear to those of the solid wetted body as they are to each other, and inmany cases it is evident that the former attraction is the stronger. Butgases and vapours are bodies competent to suffer very great changes in therelative distances of their particles by external agencies; and where theyare in immediate contact with the platina, the approximation of theparticles to those of the metal may be very great. In the case of thehygrometric bodies referred to (621. ), it is sufficient to reduce thevapour to the fluid state, frequently from atmospheres so rare that withoutthis influence it would be needful to compress them by mechanical forceinto a bulk not more than 1/10th or even 1/20th of their original volumebefore the vapours would become liquids. 

626. Another most important consideration in relation to this action ofbodies, and which, as far as I am aware, has not hitherto been noticed, isthe condition of elasticity under which the gases are placed against theacting surface. We have but very imperfect notions of the real and intimateconditions of the particles of a body existing in the solid, the liquid, and the gaseous state; but when we speak of the gaseous state as being dueto the mutual repulsions of the particles or of their atmospheres, althoughwe may err in imagining each particle to be a little nucleus to anatmosphere of heat, or electricity, or any other agent, we are still notlikely to be in error in considering the elasticity as dependent on_mutuality_ of action. Now this mutual relation fails altogether on theside of the gaseous particles next to the platina, and we might be led toexpect _à priori_ a deficiency of elastic force there to at least one half;for if, as Dalton has shown, the elastic force of the particles of one gascannot act against the elastic force of the particles of another, the twobeing as vacua to each other, so is it far less likely that the particlesof the platina can exert any influence on those of the gas against it, suchas would be exerted by gaseous particles of its own kind. 

627. But the diminution of power to one-half on the side of the gaseousbody towards the metal is only a slight result of what seems to me to flowas a necessary consequence of the known constitution of gases. Anatmosphere of one gas or vapour, however dense or compressed, is in effectas a vacuum to another: thus, if a little water were put into a vesselcontaining a dry gas, as air, of the pressure of one hundred atmospheres, as much vapour of the water would _rise_ as if it were in a perfect vacuum. Here the particles of watery vapour appear to have no difficulty inapproaching within any distance of the particles of air, being influencedsolely by relation to particles of their own kind; and if it be so withrespect to a body having the same elastic powers as itself, how much moresurely must it be so with particles, like those of the platina, or otherlimiting body, which at the same time that they have not these elasticpowers, are also unlike it in nature! Hence it would seem to result thatthe particles of hydrogen or any other gas or vapour which are next to theplatina, &c. , must be in such contact with it as if they were in the liquidstate, and therefore almost infinitely closer to it than they are to eachother, even though the metal be supposed to exert no attractive influenceover them. 

628. A third and very important consideration in favour of the mutualaction of gases under these circumstances is their perfect miscibility. Iffluid bodies capable of combining together are also capable of mixture, _they do combine_ when they are mingled, not waiting for any otherdetermining circumstance; but if two such gases as oxygen and hydrogen areput together, though they are elements having such powerful affinity as tounite naturally under a thousand different circumstances, they do notcombine by mere mixture. Still it is evident that, from their perfectassociation, the particles are in the most favourable state possible forcombination upon the supervention of any determining cause, such either asthe negative action of the platina in suppressing or annihilating, as itwere, their elasticity on its side; or the positive action of the metal incondensing them against its surface by an attractive force; or theinfluence of both together. 

629. Although there are not many distinct cases of combination under theinfluence of forces external to the combining particles, yet there aresufficient to remove any difficulty which might arise on that ground. SirJames Hull found carbonic acid and lime to remain combined under pressureat temperatures at which they would not have remained combined if thepressure had been removed; and I have had occasion to observe a case ofdirect combination in chlorine[A], which being compressed at commontemperatures will combine with water, and form a definite crystallinehydrate, incapable either of being formed or of existing if that pressurebe removed. 

 [A] Philosophical Transactions, 1823, p. 161. 

630. The course of events when platina acts upon, and combines oxygen andhydrogen, may be stated, according to these principles, as follows. Fromthe influence of the circumstances mentioned (619. &c. ), i. E. Thedeficiency of elastic power and the attraction of the metal for the gases, the latter, when they are in association with the former, are so farcondensed as to be brought within the action of their mutual affinities atthe existing temperature; the deficiency of elastic power, not merelysubjecting them more closely to the attractive influence of the metal, butalso bringing them into a more favourable state for union, by abstracting apart of that power (upon which depends their elasticity, ) which elsewherein the mass of gases is opposing their combination. The consequence oftheir combination is the production of the vapour of water and an elevationof temperature. But as the attraction of the platina for the water formedis not greater than for the gases, if so great, (for the metal is scarcelyhygrometric, ) the vapour is quickly diffused through the remaining gases;fresh portions of this latter, therefore, come into juxtaposition with themetal, combine, and the fresh vapour formed is also diffused, allowing newportions of gas to be acted upon. In this way the process advances, but isaccelerated by the evolution of heat, which is known by experiment tofacilitate the combination in proportion to its intensity, and thetemperature is thus gradually exalted until ignition results. 

631. The dissipation of the vapour produced at the surface of the platina, and the contact of fresh oxygen and hydrogen with the metal, form nodifficulty in this explication. The platina is not considered as causingthe combination of any particles with itself, but only associating themclosely around it; and the compressed particles are as free to move fromthe platina, being replaced by other particles, as a portion of dense airupon the surface of the globe, or at the bottom of a deep mine, is free tomove by the slightest impulse, into the upper and rarer parts of theatmosphere. 

632. It can hardly be necessary to give any reasons why platina does notshow this effect under ordinary circumstances. It is then not sufficientlyclean (617. ), and the gases are prevented from touching it, and sufferingthat degree of effect which is needful to commence their combination atcommon temperatures, and which they can only experience at its surface. Infact, the very power which causes the combination of oxygen and hydrogen, is competent, under the usual casual exposure of platina, to condenseextraneous matters upon its surface, which soiling it, take away for thetime its power of combining oxygen and hydrogen, by preventing theircontact with it (598. ). 

633. Clean platina, by which I mean such as has been made the positive poleof a pile (570. ), or has been treated with acid (605. ), and has then beenput into distilled water for twelve or fifteen minutes, has a _peculiarfriction_ when one piece is rubbed against another. It wets freely withpure water, even after it has been shaken and dried by the heat of aspirit-lamp; and if made the pole of a voltaic pile in a dilute acid, itevolves minute bubbles from every part of its surface. But platina in itscommon state wants that peculiar friction: it will not wet freely withwater as the clean platina does; and when made the positive pole of a pile, it for a time gives off large bubbles, which seem to cling or adhere to themetal, and are evolved at distinct and separate points of the surface. These appearances and effects, as well as its want of power on oxygen andhydrogen, are the consequences, and the indications, of a soiled surface. 

634. I found also that platina plates which had been cleaned perfectly soonbecame soiled by mere exposure to the air; for after twenty-four hours theyno longer moistened freely with water, but the fluid ran up into portions, leaving part of the surface bare, whilst other plates which had beenretained in water for the same time, when they were dried (580. ) didmoisten, and gave the other indications of a clean surface. 

635. Nor was this the case with platina or metals only, but also withearthy bodies, Rock crystal and obsidian would not wet freely upon thesurface, but being moistened with strong oil of vitriol, then washed, andleft in distilled water to remove all the acid, they did freely becomemoistened, whether they were previously dry or whether they were left wet;but being dried and left exposed to the air for twenty-four hours, theirsurface became so soiled that water would not then adhere freely to it, butran up into partial portions. Wiping with a cloth (even the cleanest) wasstill worse than exposure to air; the surface either of the minerals ormetals immediately became as if it were slightly greasy. The floating uponwater of small particles of metals under ordinary circumstances is aconsequence of this kind of soiled surface. The extreme difficulty ofcleaning the surface of mercury when it has once been soiled or greased, isdue to the same cause. 

636. The same reasons explain why the power of the platina plates in somecircumstances soon disappear, and especially upon use: MM. Dulong andThenard have observed the same effect with the spongy metal[A], as indeedhave all those who have used Döbereiner's instantaneous light machines. Ifleft in the air, if put into ordinary distilled water, if made to act uponordinary oxygen and hydrogen, they can still find in all these cases _that_minute portion of impurity which, when once in contact with the surface ofthe platina, is retained there, and is sufficient to prevent its fullaction upon oxygen and hydrogen at common temperatures: a slight elevationof temperature is again sufficient to compensate this effect, and causecombination. 

 [A] Annales de Chimie, tom. Xxiv. P. 386. 

637. No state of a solid body can be conceived more favourable for theproduction of the effect than that which is possessed by platina obtainedfrom the ammonio-muriate by heat. Its surface is most extensive and pure, yet very accessible to the gases brought in contact with it: if placed inimpurity, the interior, as Thenard and Dulong have observed, is preservedclean by the exterior; and as regards temperature, it is so bad a conductorof heat, because of its divided condition, that almost all which is evolvedby the combination of the first portions of gas is retained within themass, exalting the tendency of the succeeding portions to combine. 

 * * * * *

638. I have now to notice some very extraordinary interferences with thisphenomenon, dependent, not upon the nature or condition of the metal orother acting solid, but upon the presence of certain substances mingledwith the gases acted upon; and as I shall have occasion to speak frequentlyof a mixture of oxygen and hydrogen, I wish it always to be understood thatI mean a mixture composed of one volume of oxygen to two volumes ofhydrogen, being the proportions that form water. Unless otherwiseexpressed, the hydrogen was always that obtained by the action of dilutesulphuric acid on pure zinc, and the oxygen that obtained by the action ofheat from the chlorate of potassa. 

639. Mixtures of oxygen and hydrogen with _air_, containing one-fourth, one-half, and even two-thirds of the latter, being introduced with preparedplatina plates (570. 605. ) into tubes, were acted upon almost as well as ifno air were present: the retardation was far less than might have beenexpected from the mere dilution and consequent obstruction to the contactof the gases with the plates. In two hours and a half nearly all the oxygenand hydrogen introduced as mixture was gone. 

640. But when similar experiments were made with _olefiant gas_ (theplatina plates having been made the positive poles of a voltaic pile (570. )in acid), very different results occurred. A mixture was made of 29. 2volumes hydrogen and 14. 6 volumes oxygen, being the proportions for water;and to this was added another mixture of 3 volumes oxygen and one volumeolefiant gas, so that the olefiant gas formed but 1/40th part of the whole;yet in this mixture the platina plate would not act in forty-five hours. The failure was not for want of any power in the plate, for when after thattime it was taken out of this mixture and put into one of oxygen andhydrogen, it immediately acted, and in seven minutes caused explosion ofthe gas. This result was obtained several times, and when largerproportions of olefiant gas were used, the action seemed still morehopeless. 

641. A mixture of forty-nine volumes oxygen and hydrogen (638. ) with onevolume of olefiant gas had a well-prepared platina plate introduced. Thediminution of gas was scarcely sensible at the end of two hours, duringwhich it was watched; but on examination twenty-four hours afterwards, thetube was found blown to pieces. The action, therefore, though it had beenvery much retarded, had occurred at last, and risen to a maximum. 

642. With a mixture of ninety-nine volumes of oxygen and hydrogen (638. )with one of olefiant gas, a feeble action was evident at the end of fiftyminutes; it went on accelerating (630. ) until the eighty-fifth minute, andthen became so intense that the gas exploded. Here also the retardingeffect of the olefiant gas was very beautifully illustrated. 

643. Plates prepared by alkali and acid (605. ) produced effectscorresponding to those just described. 

644. It is perfectly clear from these experiments, that _olefiant gas_, even in small quantities, has a very remarkable influence in preventing thecombination of oxygen and hydrogen under these circumstances, and yetwithout at all injuring or affecting the power of the platina. 

645. Another striking illustration of similar interference may be shown in_carbonic oxide_; especially if contrasted with _carbonic acid_. A mixtureof one volume oxygen and hydrogen (638. ) with four volumes of carbonic acidwas affected at once by a platina plate prepared with acid, &c. (605. ); andin one hour and a quarter nearly all the oxygen and hydrogen was gone. Mixtures containing less carbonic acid were still more readily affected. 

646. But when carbonic oxide was substituted for the carbonic acid, not theslightest effect of combination was produced; and when the carbonic oxidewas only one-eighth of the whole volume, no action occurred in forty andfifty hours. Yet the plates had not lost their power; for being taken outand put into pure oxygen and hydrogen, they acted well and at once. 

647. Two volumes of carbonic oxide and one of oxygen were mingled with ninevolumes of oxygen and hydrogen (638. ). This mixture was not affected by aplate which had been made positive in acid, though it remained in itfifteen hours. But when to the same volumes of carbonic oxide and oxygenwere added thirty-three volumes of oxygen and hydrogen, the carbonic oxidebeing then only 1/18th part of the whole, the plate acted, slowly at first, and at the end of forty-two minutes the gases exploded. 

648. These experiments were extended to various gases and vapours, thegeneral results of which may be given as follow. Oxygen, hydrogen, nitrogen, and nitrous oxide, when used to dilute the mixture of oxygen andhydrogen, did not prevent the action of the plates even when they madefour-fifths of the whole volume of gas acted upon. Nor was the retardationso great in any case as might have been expected from the mere dilution ofthe oxygen and hydrogen, and the consequent mechanical obstruction to itscontact with the platina. The order in which carbonic acid and thesesubstances seemed to stand was as follows, the first interfering least withthe action; _nitrous oxide, hydrogen, carbonic acid, nitrogen, oxygen_: butit is possible the plates were not equally well prepared in all the cases, and that other circumstances also were unequal; consequently more numerousexperiments would be required to establish the order accurately. 

649. As to cases of _retardation_, the powers of olefiant gas and carbonicoxide have been already described. Mixtures of oxygen and hydrogen, containing from 1/16th to 1/20th of sulphuretted hydrogen or phosphurettedhydrogen, seemed to show a little action at first, but were not furtheraffected by the prepared plates, though in contact with them for seventyhours. When the plates were removed they had lost all power over pureoxygen and hydrogen, and the interference of these gases was therefore of adifferent nature from that of the two former, having permanently affectedthe plate. 

650. A small piece of cork was dipped in sulphuret of carbon and passed upthrough water into a tube containing oxygen and hydrogen (638. ), so as todiffuse a portion of its vapour through the gases. A plate being introducedappeared at first to act a little, but after sixty-one hours the diminutionwas very small. Upon putting the same plate into a pure mixture of oxygenand hydrogen, it acted at once and powerfully, having apparently sufferedno diminution of its force. 

651. A little vapour of ether being mixed with the oxygen and hydrogenretarded the action of the plate, but did not prevent it altogether. Alittle of the vapour of the condensed oil-gas liquor[A] retarded the actionstill more, but not nearly so much as an equal volume of olefiant gas wouldhave done. In both these cases it was the original oxygen and hydrogenwhich combined together, the ether and the oil-gas vapour remainingunaffected, and in both cases the plates retained the power of acting onfresh oxygen and hydrogen. 

 [A] Philosophical Transactions, 1825, p. 440. 

652. Spongy platina was then used in place of the plates, and jets ofhydrogen mingled with the different gases thrown against it in air. Theresults were exactly of the same kind, although presented occasionally in amore imposing form. Thus, mixtures of one volume of olefiant gas orcarbonic oxide with three of hydrogen could not heat the spongy platinawhen the experiments were commenced at common temperatures; but a mixtureof equal volumes of nitrogen and hydrogen acted very well, causingignition. With carbonic acid the results were still more striking. Amixture of three volumes of that gas with one of hydrogen caused _ignition_of the platina, yet that mixture would not continue to burn from the jetwhen attempts were made to light it by a taper. A mixture even of _seven_volumes of carbonic acid and _one_ of hydrogen will thus cause the ignitionof cold spongy platina, and yet, as if to supply a contrast, than whichnone can be greater, _it cannot burn at a taper_, but causes the extinctionof the latter. On the other hand, the mixtures of carbonic oxide orolefiant gas, which can do nothing with the platina, are _inflamed_ by thetaper, burning well. 

653. Hydrogen mingled with the vapour of ether or oil-gas liquor causes theignition of the spongy platina. The mixture with oil-gas burns with a flamefar brighter than that of the mixture of hydrogen and olefiant gas alreadyreferred to, so that it would appear that the retarding action of thehydrocarbons is not at all in proportion merely to the quantity of carbonpresent. 

654. In connexion with these interferences, I must state, that hydrogenitself, prepared from steam passed over ignited iron, was found whenmingled with oxygen to resist the action of platina. It had stood overwater seven days, and had lost all fetid smell; but a jet of it would notcause the ignition of spongy platina, commencing at common temperatures;nor would it combine with oxygen in a tube either under the influence of aprepared plate or of spongy platina. A mixture of one volume of this gaswith three of pure hydrogen, and the due proportion of oxygen, was notaffected by plates after fifty hours. I am inclined to refer the effect tocarbonic oxide present in the gas, but have not had time to verify thesuspicion. The power of the plates was not destroyed (640. 646. ). 

655. Such are the general facts of these remarkable interferences. Whetherthe effect produced by such small quantities of certain gases depends uponany direct action which they may exert upon the particles of oxygen andhydrogen, by which the latter are rendered less inclined to combine, orwhether it depends upon their modifying the action of the plate temporarily(for they produce no real change on it), by investing it through the agencyof a stronger attraction than that of the hydrogen, or otherwise, remainsto be decided by more extended experiments. 

 * * * * *

656. The theory of action which I have given for the original phenomenaappears to me quite sufficient to account for all the effects by referenceto known properties, and dispenses with the assumption of any new power ofmatter. I have pursued this subject at some length, as one of greatconsequence, because I am convinced that the superficial actions of matter, whether between two bodies, or of one piece of the same body, and theactions of particles not directly or strongly in combination, are becomingdaily more and more important to our theories of chemical as well asmechanical philosophy[A]. In all ordinary cases of combustion it is evidentthat an action of the kind considered, occurring upon the surface of thecarbon in the fire, and also in the bright part of a flame, must have greatinfluence over the combinations there taking place. 

 [A] As a curious illustration of the influence of mechanical forces over chemical affinity, I will quote the refusal of certain substances to effloresce when their surfaces are perfect, which yield immediately upon the surface being broken, If crystals of carbonate of soda, or phosphate of soda, or sulphate of soda, having no part of their surfaces broken, be preserved from external violence, they will not effloresce. I have thus retained crystals of carbonate of soda perfectly transparent and unchanged from September 1827 to January 1833; and crystals of sulphate of soda from May 1832 to the present time, November 1833. If any part of the surface were scratched or broken, then efflorescence began at that part, and covered the whole. The crystals were merely placed in evaporating basins and covered with paper. 

657. The condition of elasticity upon the exterior of the gaseous orvaporous mass already referred to (626. 627. ), must be connected directlywith the action of solid bodies, as nuclei, on vapours, causingcondensation upon them in preference to any condensation in the vapoursthemselves; and in the well-known effect of nuclei on solutions a similarcondition may have existence (623. ), for an analogy in condition existsbetween the parts of a body in solution, and those of a body in thevaporous or gaseous state. This thought leads us to the consideration ofwhat are the respective conditions at the surfaces of contact of twoportions of the same substance at the same temperature, one in the solid orliquid, and the other in the vaporous state; as, for instance, steam andwater. It would seem that the particles of vapour next to the particles ofliquid are in a different relation to the latter to what they would be withrespect to any other liquid or solid substance; as, for instance, mercuryor platina, if they were made to replace the water, i. E. If the view ofindependent action which I have taken (626. 627. ) as a consequence ofDalton's principles, be correct. It would also seem that the mutualrelation of similar particles, and the indifference of dissimilar particleswhich Dalton has established as a matter of fact amongst gases and vapours, extends to a certain degree amongst solids and fluids, that is, when theyare in relation by contact with vapours, either of their own substance orof other bodies. But though I view these points as of great importance withrespect to the relations existing between different substances and theirphysical constitution in the solid, liquid, or gaseous state, I have notsufficiently considered them to venture any strong opinions or statementshere[A]. 

 [A] In reference to this paragraph and also 626, see a correction by Dr. C. Henry, in his valuable paper on this curious subject. Philosophical Magazine, 1835. Vol. Vi. P. 305. --_Dec. 1838. _

658. There are numerous well-known cases, in which substances, such asoxygen and hydrogen, act readily in their _nascent_ state, and producechemical changes which they are not able to effect if once they haveassumed the gaseous condition. Such instances are very common at the polesof the voltaic pile, and are, I think, easily accounted for, if it beconsidered that at the moment of separation of any such particle it isentirely surrounded by other particles of a _different_ kind with which itis in close contact, and has not yet assumed those relations and conditionswhich it has in its fully developed state, and which it can only assume byassociation with other particles of its own kind. For, at the moment, itselasticity is absent, and it is in the same relation to particles withwhich it is in contact, and for which it has an affinity, as the particlesof oxygen and hydrogen are to each other on the surface of clean platina(626. 627. ). 

659. The singular effects of retardation produced by very small quantitiesof some gases, and not by large quantities of others (640. 645. 652. ), ifdependent upon any relation of the added gas to the surface of the solid, will then probably be found immediately connected with the curiousphenomena which are presented by different gases when passing throughnarrow tubes at low pressures, which I observed many years ago[A]; and thisaction of surfaces must, I think, influence the highly interestingphenomena of the diffusion of gases, at least in the form in which it hasbeen experimented upon by Mr. Graham in 1829 and 1831[B], and also by Dr. Mitchell of Philadelphia[C] in 1830. It seems very probable that if such asubstance as spongy platina were used, another law for the diffusion ofgases under the circumstances would come out than that obtained by the useof plaster of Paris. 

 [A] Quarterly Journal of Science, 1819, vol. Vii. P. 106. 

 [B] Quarterly Journal of Science, vol. Xxviii. P. 74, and Edinburgh Transactions, 1831. 

 [C] Journal of the Royal Institution for 1831, p. 101. 

660. I intended to have followed this section by one on the secondary pilesof Ritter, and the peculiar properties of the poles of the pile, or ofmetals through which electricity has passed, which have been observed byRitter, Van Marum, Yelin, De la Rive, Marianini, Berzelius, and others. Itappears to me that all these phenomena bear a satisfactory explanation onknown principles, connected with the investigation just terminated, and donot require the assumption of any new state or new property. But as theexperiments advanced, especially those of Marianini, require very carefulrepetition and examination, the necessity of pursuing the subject ofelectro-chemical decomposition obliges me for a time to defer theresearches to which I have just referred. 

_Royal Institution, November 30, 1833. _

SEVENTH SERIES. 

§ 11. _On Electro-chemical Decomposition, continued. _[A] ¶ iv. _On somegeneral conditions of Electro-decomposition. _ ¶ v. _On a new Measurer ofVolta-electricity. _ ¶ vi. _On the primary or secondary character of bodiesevolved in Electro-decomposition. _ ¶ vii. _On the definite nature andextent of Electro-chemical Decompositions. _ § 13. _On the absolute quantityof Electricity associated with the particles or atoms of Matter. _

 [A] Refer to the note after 1047, Series VIII. --_Dec. 1838. _

Received January 9, --Read January 23, February 6 and 13, 1834. 

_Preliminary. _

661. The theory which I believe to be a true expression of the facts ofelectro-chemical decomposition, and which I have therefore detailed in aformer series of these Researches, is so much at variance with thosepreviously advanced, that I find the greatest difficulty in statingresults, as I think, correctly, whilst limited to the use of terms whichare current with a certain accepted meaning. Of this kind is the term_pole_, with its prefixes of positive and negative, and the attached ideasof attraction and repulsion. The general phraseology is that the positivepole _attracts_ oxygen, acids, &c. , or more cautiously, that it_determines_ their evolution upon its surface; and that the negative poleacts in an equal manner upon hydrogen, combustibles, metals, and bases. According to my view, the determining force is _not_ at the poles, but_within_ the body under decomposition; and the oxygen and acids arerendered at the _negative_ extremity of that body, whilst hydrogen, metals, &c. , are evolved at the _positive_ extremity (518. 524. ). 

662. To avoid, therefore, confusion and circumlocution, and for the sake ofgreater precision of expression than I can otherwise obtain, I havedeliberately considered the subject with two friends, and with theirassistance and concurrence in framing them, I purpose henceforward usingcertain other terms, which I will now define. The _poles_, as they areusually called, are only the doors or ways by which the electric currentpasses into and out of the decomposing body (556. ); and they of course, when in contact with that body, are the limits of its extent in thedirection of the current. The term has been generally applied to the metalsurfaces in contact with the decomposing substance; but whetherphilosophers generally would also apply it to the surfaces of air (465. 471. ) and water (493. ), against which I have effected electro-chemicaldecomposition, is subject to doubt. In place of the term pole, I proposeusing that of _Electrode_[A], and I mean thereby that substance, or rathersurface, whether of air, water, metal, or any other body, which bounds theextent of the decomposing matter in the direction of the electric current. 

 [A] [Greek: elektron], and [Greek: -odos] _a way_. 

663. The surfaces at which, according to common phraseology, the electriccurrent enters and leaves a decomposing body, are most important places ofaction, and require to be distinguished apart from the poles, with whichthey are mostly, and the electrodes, with which they are always, incontact. Wishing for a natural standard of electric direction to which Imight refer these, expressive of their difference and at the same time freefrom all theory, I have thought it might be found in the earth. If themagnetism of the earth be due to electric currents passing round it, thelatter must be in a constant direction, which, according to present usageof speech, would be from east to west, or, which will strengthen this helpto the memory, that in which the sun appears to move. If in any case ofelectro-decomposition we consider the decomposing body as placed so thatthe current passing through it shall be in the same direction, and parallelto that supposed to exist in the earth, then the surfaces at which theelectricity is passing into and out of the substance would have aninvariable reference, and exhibit constantly the same relations of powers. Upon this notion we purpose calling that towards the east the _anode_[A], and that towards the west the _cathode_[B]; and whatever changes may takeplace in our views of the nature of electricity and electrical action, asthey must affect the _natural standard_ referred to, in the same direction, and to an equal amount with any decomposing substances to which these termsmay at any time be applied, there seems no reason to expect that they willlead to confusion, or tend in any way to support false views. The _anode_is therefore that surface at which the electric current, according to ourpresent expression, enters: it is the _negative_ extremity of thedecomposing body; is where oxygen, chlorine, acids, &c. , are evolved; andis against or opposite the positive electrode. The _cathode_ is thatsurface at which the current leaves the decomposing body, and is its_positive_ extremity; the combustible bodies, metals, alkalies, and bases, are evolved there, and it is in contact with the negative electrode. 

 [A] [Greek: ano] _upwards_, and [Greek: -odos] _a way_; the way whichthe sun rises. 

 [B] [Greek: kata] _downwards_, and [Greek: -odos] _a way_; the way which the sun sets. 

664. I shall have occasion in these Researches, also, to class bodiestogether according to certain relations derived from their electricalactions (822. ); and wishing to express those relations without at the sametime involving the expression of any hypothetical views, I intend using thefollowing names and terms. Many bodies are decomposed directly by theelectric current, their elements being set free; these I propose to call_electrolytes_. [A] Water, therefore, is an electrolyte. The bodies which, like nitric or sulphuric acids, are decomposed in a secondary manner (752. 757. ), are not included under this term. Then for _electro-chemicallydecomposed_, I shall often use the term _electrolyzed_, derived in the sameway, and implying that the body spoken of is separated into its componentsunder the influence of electricity: it is analogous in its sense and soundto _analyse_, which is derived in a similar manner. The term_electrolytical_ will be understood at once: muriatic acid iselectrolytical, boracic acid is not. 

 [A] [Greek: elektron], and [Greek: lyo], _soluo_. N. Electrolyte, V. Electrolyze. 

665. Finally, I require a term to express those bodies which can pass tothe _electrodes_, or, as they are usually called, the poles. Substances arefrequently spoken of as being _electro-negative_, or _electro-positive_, according as they go under the supposed influence of a direct attraction tothe positive or negative pole. But these terms are much too significant forthe use to which I should have to put them; for though the meanings areperhaps right, they are only hypothetical, and may be wrong; and then, through a very imperceptible, but still very dangerous, because continual, influence, they do great injury to science, by contracting and limiting thehabitual views of those engaged in pursuing it. I propose to distinguishsuch bodies by calling those _anions_[A] which go to the _anode_ of thedecomposing body; and those passing to the _cathode, cations_[B]; and whenI have occasion to speak of these together, I shall call them _ions_. Thusthe chloride of lead is an _electrolyte_, and when _electrolyzed_ evolvesthe two _ions_, chlorine and lead, the former being an _anion_, and thelatter a _cation_. 

 [A] [Greek: aniôn] _that which goes up. _ (Neuter participle. )

 [B] [Greek: katiôn] _that which goes down. _

666. These terms being once well-defined, will, I hope, in their use enableme to avoid much periphrasis and ambiguity of expression. I do not mean topress them into service more frequently than will be required, for I amfully aware that names are one thing and science another. 

667. It will be well understood that I am giving no opinion respecting thenature of the electric current now, beyond what I have done on formeroccasions (283. 517. ); and that though I speak of the current as proceedingfrom the parts which are positive to those which are negative (663. ), it ismerely in accordance with the conventional, though in some degree tacit, agreement entered into by scientific men, that they may have a constant, certain, and definite means of referring to the direction of the forces ofthat current. 

 [Since this paper was read, I have changed some of the terms which werefirst proposed, that I might employ only such as were at the same timesimple in their nature, clear in their reference, and free fromhypothesis. 

¶ iv. _On some general conditions of Electro-chemical Decomposition. _

669. From the period when electro-chemical decomposition was first effectedto the present time, it has been a remark, that those elements which, inthe ordinary phenomena of chemical affinity, were the most directly opposedto each other, and combined with the greatest attractive force, were thosewhich were the most readily evolved at the opposite extremities of thedecomposing bodies (549. ). 

670. If this result was evident when water was supposed to be essential to, and was present in, almost every case of such decomposition (472. ), it isfar more evident now that it has been shown and proved that water is notnecessarily concerned in the phenomena (474. ), and that other bodies muchsurpass it in some of the effects supposed to be peculiar to thatsubstance. 

671. Water, from its constitution and the nature of its elements, and fromits frequent presence in cases of electrolytic action, has hitherto stoodforemost in this respect. Though a compound formed by very powerfulaffinity, it yields up its elements under the influence of a very feebleelectric current; and it is doubtful whether a case of electrolyzation canoccur, where, being present, it is not resolved into its first principles. 

672. The various oxides, chlorides, iodides, and salts, which I have shownare decomposable by the electric current when in the liquid state, underthe same general law with water (402. ), illustrate in an equally strikingmanner the activity, in such decompositions, of elements directly andpowerfully opposed to each other by their chemical relations. 

673. On the other hand, bodies dependent on weak affinities very rarelygive way. Take, for instance, glasses: many of those formed of silica, lime, alkali, and oxide of lead, may be considered as little more thansolutions of substances one in another[A]. If bottle-glass be fused, andsubjected to the voltaic pile, it does not appear to be at all decomposed(408. ). If flint glass, which contains substances more directly opposed, beoperated upon, it suffers some decomposition; and if borate of lead glass, which is a definite chemical compound, be experimented with, it readilyyields up its elements (408. ). 

 [A] Philosophical Transactions, 1830, p. 49. 

674. But the result which is found to be so striking in the instancesquoted is not at all borne out by reference to other cases where a similarconsequence might have been expected. It may be said, that my own theory ofelectro-chemical decomposition would lead to the expectation that allcompound bodies should give way under the influence of the electric currentwith a facility proportionate to the strength of the affinity by whichtheir elements, either proximate or ultimate, are combined. I am not surethat that follows as a consequence of the theory; but if the objection issupposed to be one presented by the facts, I have no doubt it will beremoved when we obtain a more intimate acquaintance with, and precise ideaof, the nature of chemical affinity and the mode of action of an electriccurrent over it (518. 524. ): besides which, it is just as directly opposedto any other theory of electro-chemical decomposition as the one I havepropounded; for if it be admitted, as is generally the case, that the moredirectly bodies are opposed to each other in their attractive forces, themore powerfully do they combine, then the objection applies with equalforce to any of the theories of electrolyzation which have been considered, and is an addition to those which I have taken against them. 

675. Amongst powerful compounds which are not decomposed, boracic acidsstand prominent (408. ). Then again, the iodide of sulphur, and thechlorides of sulphur, phosphorus, and carbon, are not decomposable undercommon circumstances, though their elements are of a nature which wouldlead to a contrary expectation. Chloride of antimony (402. 690. ), thehydro-carbons, acetic acid, ammonia, and many other bodies undecomposableby the voltaic pile, would seem to be formed by an affinity sufficientlystrong to indicate that the elements were so far contrasted in their natureas to sanction the expectation that, the pile would separate them, especially as in some cases of mere solution (530. 544. ), where theaffinity must by comparison be very weak, separation takes place[A]. 

 [A] With regard to solution, I have met with some reasons for supposing that it will probably disappear as a cause of transference, and intend resuming the consideration at a convenient opportunity. 

676. It must not be forgotten, however, that much of this difficulty, andperhaps the whole, may depend upon the absence of conducting power, which, preventing the transmission of the current, prevents of course the effectsdue to it. All known compounds being non-conductors when solid, butconductors when liquid, are decomposed, with _perhaps_ the single exceptionat present known of periodide of mercury (679. 691. )[A]; and even wateritself, which so easily yields up its elements when the current passes, ifrendered quite pure, scarcely suffers change, because it then becomes avery bad conductor. 

 [A] See now, 1340, 1341. --_Dec. 1838. _

677. If it should hereafter be proved that the want of decomposition inthose cases where, from chemical considerations, it might be so stronglyexpected (669, 672. 674. ), is due to the absence or deficiency ofconducting power, it would also at the same time be proved thatdecomposition _depends_ upon conduction, and not the latter upon the former(413. ); and in water this seems to be very nearly decided. On the otherhand, the conclusion is almost irresistible, that in electrolytes the powerof transmitting the electricity across the substance is _dependent_ upontheir capability of suffering decomposition; taking place only whilst theyare decomposing, and being proportionate to the quantity of elementsseparated (821. ). I may not, however, stop to discuss this pointexperimentally at present. 

678. When a compound contains such elements as are known to pass towardsthe opposite extremities of the voltaic pile, still the proportions inwhich they are present appear to be intimately connected with capability inthe compound of suffering or resisting decomposition. Thus, theprotochloride of tin readily conducts, and is decomposed (402. ), but theperchloride neither conducts nor is decomposed (406. ). The protiodide oftin is decomposed when fluid (402. ); the periodide is not (405. ). Theperiodide of mercury when fused is not decomposed (691. ), even though itdoes conduct. I was unable to contrast it with the protiodide, the latterbeing converted into mercury and periodide by heat. 

679. These important differences induced me to look more closely to certainbinary compounds, with a view of ascertaining whether a _law_ regulatingthe _decomposability_ according to some _relation of the proportionals orequivalents_ of the elements, could be discovered. The proto compoundsonly, amongst those just referred to, were decomposable; and on referringto the substances quoted to illustrate the force and generality of the lawof conduction and decomposition which I discovered (402. ), it will be foundthat all the oxides, chlorides, and iodides subject to it, except thechloride of antimony and the periodide of mercury, (to which may nowperhaps be added corrosive sublimate, ) are also decomposable, whilst manyper compounds of the same elements, not subject to the law, were not so(405. 406. ). 

680. The substances which appeared to form the strongest exceptions to thisgeneral result were such bodies as the sulphuric, phosphoric, nitric, arsenic, and other acids. 

681. On experimenting with sulphuric acid, I found no reason to believethat it was by itself a conductor of, or decomposable by, electricity, although I had previously been of that opinion (552. ). When very strong itis a much worse conductor than if diluted[A]. If then subjected to theaction of a powerful battery, oxygen appears at the _anode_, or positiveelectrode, although much is absorbed (728. ), and hydrogen and sulphurappear at the _cathode_, or negative electrode. Now the hydrogen has withme always been pure, not sulphuretted, and has been deficient in proportionto the sulphur present, so that it is evident that when decompositionoccurred water must have been decomposed. I endeavoured to make theexperiment with anhydrous sulphuric acid; and it appeared to me that, whenfused, such acid was not a conductor, nor decomposed; but I had not enoughof the dry acid in my possession to allow me to decide the pointsatisfactorily. My belief is, that when sulphur appears during the actionof the pile on sulphuric acid, it is the result of a secondary action, andthat the acid itself is not electrolyzable (757. ). 

 [A] De la Rive. 

682. Phosphoric acid is, I believe, also in the same condition; but I havefound it impossible to decide the point, because of the difficulty ofoperating on fused anhydrous phosphoric acid. Phosphoric acid which hasonce obtained water cannot be deprived of it by heat alone. When heated, the hydrated acid volatilizes. Upon subjecting phosphoric acid, fused uponthe ring end of a wire (401. ), to the action of the voltaic apparatus, itconducted, and was decomposed; but gas, which I believe to be hydrogen, wasalways evolved at the negative electrode, and the wire was not affected aswould have happened had phosphorus been separated. Gas was also evolved atthe positive electrode. From all the facts, I conclude it was the water andnot the acid which was decomposed. 

683. _Arsenic acid_. This substance conducted, and was decomposed; but itcontained water, and I was unable at the time to press the investigation soas to ascertain whether a fusible anhydrous arsenic acid could be obtained. It forms, therefore, at present no exception to the general result. 

684. Nitrous acid, obtained by distilling nitrate of lead, and keeping itin contact with strong sulphuric acid, was found to conduct and decomposeslowly. But on examination there were strong reasons for believing thatwater was present, and that the decomposition and conduction depended uponit. I endeavoured to prepare a perfectly anhydrous portion, but could notspare the time required to procure an unexceptionable result. 

685. Nitric acid is a substance which I believe is not decomposed directlyby the electric current. As I want the facts in illustration of thedistinction existing between primary and secondary decomposition, I willmerely refer to them in this place (752. ). 

686. That these mineral acids should confer facility of conduction anddecomposition on water, is no proof that they are competent to favour andsuffer these actions in themselves. Boracic acid does the same thing, though not decomposable. M. De la Rive has pointed out that chlorine hasthis power also; but being to us an elementary substance, it cannot be dueto its capability of suffering decomposition. 

687. _Chloride of sulphur_ does not conduct, nor is it decomposed. Itconsists of single proportionals of its elements, but is not on thataccount an exception to the rule (679. ), which does not affirm that _all_compounds of single proportionals of elements are decomposable, but thatsuch as are decomposable are so constituted. 

688. _Protochloride of phosphorus_ does not conduct nor become decomposed. 

689. _Protochloride of carbon_ does not conduct nor suffer decomposition. In association with this substance, I submitted the _hydro-chloride ofcarbon_ from olefiant gas and chlorine to the action of the electriccurrent; but it also refused to conduct or yield up its elements. 

600. With regard to the exceptions (679. ), upon closer examination some ofthem disappear. Chloride of antimony (a compound of one proportional ofantimony and one and a half of chlorine) of recent preparation was put intoa tube (fig. 68. ) (789. ), and submitted when fused to the action of thecurrent, the positive electrode being of plumbago. No electricity passed, and no appearance of decomposition was visible at first; but when thepositive and negative electrodes were brought very near each other in thechloride, then a feeble action occurred and a feeble current passed. Theeffect altogether was so small (although quite amenable to the law beforegiven (394. )), and so unlike the decomposition and conduction occurring inall the other cases, that I attribute it to the presence of a minutequantity of water, (for which this and many other chlorides have strongattractions, producing hydrated chlorides, ) or perhaps of a trueprotochloride consisting of single proportionals (695, 796. ). 

691. _Periodide of mercury_ being examined in the same manner, was foundmost distinctly to insulate whilst solid, but conduct when fluid, accordingto the law of _liquido-conduction_ (402. ); but there was no appearance ofdecomposition. No iodine appeared at the _anode_, nor mercury or othersubstance at the _cathode_. The case is, therefore, no exception to therule, that only compounds of single proportionals are decomposable; but itis an exception, and I think the only one, to the statement, that allbodies subject to the law of liquido-conduction are decomposable. Iincline, however, to believe, that a portion of protiodide of mercury isretained dissolved in the periodide, and that to its slow decomposition thefeeble conducting power is due. Periodide would be formed, as a secondaryresult, at the _anode_; and the mercury at the _cathode_ would also form, as a secondary result, protiodide. Both these bodies would mingle with thefluid mass, and thus no final separation appear, notwithstanding thecontinued decomposition. 

692. When _perchloride of mercury_ was subjected to the voltaic current, itdid not conduct in the solid state, but it did conduct when fluid. I think, also, that in the latter case it was decomposed; but there are manyinterfering circumstances which require examination before a positiveconclusion can be drawn[A]. 

 [A] With regard to perchloride and periodide of mercury, see now 1340, 1341. --_Dec. 1838. _

693. When the ordinary protoxide of antimony is subjected to the voltaiccurrent in a fused state, it also is decomposed, although the effect fromother causes soon ceases (402, 801. ). This oxide consists of oneproportional of antimony and one and a half of oxygen, and is therefore anexception to the general law assumed. But in working with this oxide andthe chloride, I observed facts which lead me to doubt whether the compoundsusually called the protoxide and the protochloride do not often containother compounds, consisting of single proportions, which are the true protocompounds, and which, in the case of the oxide, might give rise to thedecomposition above described. 

694. The ordinary sulphuret of antimony its considered as being thecompound with the smallest quantity of sulphur, and analogous in itsproportions to the ordinary protoxide. But I find that if it be fused withmetallic antimony, a new sulphuret is formed, containing much more of themetal than the former, and separating distinctly, when fused, both from thepure metal on the one hand, and the ordinary gray sulphuret on the other. In some rough experiments, the metal thus taken up by the ordinarysulphuret of antimony was equal to half the proportion of that previouslyin the sulphuret, in which case the new sulphuret would consist of _single_proportionals. 

695. When this new sulphuret was dissolved in muriatic acid, although alittle antimony separated, yet it appeared to me that a true protochloride, consisting of _single_ proportionals, was formed, and from that byalkalies, &c. , a true protoxide, consisting also of _single_ proportionals, was obtainable. But I could not stop to ascertain this matter strictly byanalysis. 

696. I believe, however, that there is such an oxide; that it is oftenpresent in variable proportions in what is commonly called protoxide, throwing uncertainty upon the results of its analysis, and causing theelectrolytic decomposition above described[A]. 

 [A] In relation to this and the three preceding paragraphs, and also 801, see Berzelius's correction of the nature of the supposed now sulphuret and oxide, Phil. Mag. 1836, vol. Viii. 476: and for the probable explanation of the effects obtained with the protoxide, refer to 1340, 1341. --_Dec. 1838. _

697. Upon the whole, it appears probable that all those binary compounds ofelementary bodies which are capable of being electrolyzed when fluid, butnot whilst solid, according to the law of liquido-conduction (394. ), consist of single proportionals of their elementary principles; and it maybe because of their departure from this simplicity of composition, thatboracic acid, ammonia, perchlorides, periodides, and many other directcompounds of elements, are indecomposable. 

698. With regard to salts and combinations of compound bodies, the samesimple relation does not appear to hold good. I could not decide this bybisulphates of the alkalies, for as long as the second proportion of acidremained, water was retained with it. The fused salts conducted, and weredecomposed; but hydrogen always appeared at the negative electrode. 

699. A biphosphate of soda was prepared by heating, and ultimately fusing, the ammonia-phosphate of soda. In this case the fused bisalt conducted, andwas decomposed; but a little gas appeared at the negative electrode; andthough I believe the salt itself was electrolyzed, I am not quite satisfiedthat water was entirely absent. 

700. Then a biborate of soda was prepared; and this, I think, is anunobjectionable case. The salt, when fused, conducted, and was decomposed, and gas appeared at both electrodes: even when the boracic acid wasincreased to three proportionals, the same effect took place. 

701. Hence this class of compound combinations does not seem to be subjectto the same simple law as the former class of binary combinations. Whetherwe may find reason to consider them as mere solutions of the compound ofsingle proportionals in the excess of acid, is a matter which, with someapparent exceptions occurring amongst the sulphurets, must be left fordecision by future examination. 

702. In any investigation of these points, great care must be taken toexclude water; for if present, secondary effects are so frequently producedas often seemingly to indicate an electro-decomposition of substances, whenno true result of the kind has occurred (742, &c. ). 

703. It is evident that all the cases in which decomposition _does notoccur, may_ depend upon the want of conduction (677. 413. ); but that doesnot at all lessen the interest excited by seeing the great difference ofeffect due to a change, not in the nature of the elements, but merely intheir proportions; especially in any attempt which may be made to elucidateand expound the beautiful theory put forth by Sir Humphry Davy[A], andillustrated by Berzelius and other eminent philosophers, that ordinarychemical affinity is a mere result of the electrical attractions of theparticles of matter. 

 [A] Philosophical Transactions, 1807, pp. 32, 39; also 1826, pp. 387, 389. 

¶ v. _On a new measure of Volta-electricity. _

704. I have already said, when engaged in reducing common and voltaicelectricity to one standard of measurement (377. ), and again whenintroducing my theory of electro-chemical decomposition (504. 505. 510. ), that the chemical decomposing action of a current _is constant for aconstant quantity of electricity_, notwithstanding the greatest variationsin its sources, in its intensity, in the size of the _electrodes_ used, inthe nature of the conductors (or non-conductors (307. )) through which it ispassed, or in other circumstances. The conclusive proofs of the truth ofthese statements shall be given almost immediately (783, &c. ). 

705. I endeavoured upon this law to construct an instrument which shouldmeasure out the electricity passing through it, and which, being interposedin the course of the current used in any particular experiment, shouldserve at pleasure, either as a _comparative standard_ of effect, or as a_positive measurer_ of this subtile agent. 

706. There is no substance better fitted, under ordinary circumstances, tobe the indicating body in such an instrument than water; for it isdecomposed with facility when rendered a better conductor by the additionof acids or salts; its elements may in numerous cases be obtained andcollected without any embarrassment from secondary action, and, beinggaseous, they are in the best physical condition for separation andmeasurement. Water, therefore, acidulated by sulphuric acid, is thesubstance I shall generally refer to, although it may become expedient inpeculiar cases or forms of experiment to use other bodies (843. ). 

707. The first precaution needful in the construction of the instrument wasto avoid the recombination of the evolved gases, an effect which thepositive electrode has been found so capable of producing (571. ). For thispurpose various forms of decomposing apparatus were used. The firstconsisted of straight tubes, each containing a plate and wire of platinasoldered together by gold, and fixed hermetically in the glass at theclosed extremity of the tube (Plate V. Fig. 60. ). The tubes were abouteight inches long, 0. 7 of an inch in diameter, and graduated. The platinaplates were about an inch long, as wide as the tubes would permit, andadjusted as near to the mouths of the tubes as was consistent with the safecollection of the gases evolved. In certain cases, where it was required toevolve the elements upon as small a surface as possible, the metallicextremity, instead of being a plate, consisted of the wire bent into theform of a ring (fig. 61. ). When these tubes were used as measurers, theywere filled with the dilute sulphuric acid, inverted in a basin of the sameliquid (fig. 62. ), and placed in an inclined position, with their mouthsnear to each other, that as little decomposing matter should intervene aspossible; and also, in such a direction that the platina plates should bein vertical planes (720). 

708. Another form of apparatus is that delineated (fig. 63. ). The tube isbent in the middle; one end is closed; in that end is fixed a wire andplate, _a_, proceeding so far downwards, that, when in the positionfigured, it shall be as near to the angle as possible, consistently withthe collection, at the closed extremity of the tube, of all the gas evolvedagainst it. The plane of this plate is also perpendicular (720. ). The othermetallic termination, _b_, is introduced at the time decomposition is to beeffected, being brought as near the angle as possible, without causing anygas to pass from it towards the closed end of the instrument. The gasevolved against it is allowed to escape. 

709. The third form of apparatus contains both electrodes in the same tube;the transmission, therefore, of the electricity, and the consequentdecomposition, is far more rapid than in the separate tubes. The resultinggas is the sum of the portions evolved at the two electrodes, and theinstrument is better adapted than either of the former as a measurer of thequantity of voltaic electricity transmitted in ordinary cases. It consistsof a straight tube (fig. 64. ) closed at the upper extremity, and graduated, through the sides of which pass platina wires (being fused into the glass), which are connected with two plates within. The tube is fitted by grindinginto one mouth of a double-necked bottle. If the latter be one-half ortwo-thirds full of the dilute sulphuric acid (706. ), it will, uponinclination of the whole, flow into the tube and fill it. When an electriccurrent is passed through the instrument, the gases evolved against theplates collect in the upper portion of the tube, and are not subject to therecombining power of the platina. 

710. Another form of the instrument is given at fig. 65. 

711. A fifth form is delineated (fig. 66. ). This I have found exceedinglyuseful in experiments continued in succession for days together, and wherelarge quantities of indicating gas were to be collected. It is fixed on aweighted foot, and has the form of a small retort containing the twoelectrodes: the neck is narrow, and sufficiently long to deliver gasissuing from it into a jar placed in a small pneumatic trough. Theelectrode chamber, sealed hermetically at the part held in the stand, isfive inches in length, and 0. 6 of an inch in diameter; the neck about nineinches in length, and 0. 4 of an inch in diameter internally. The figurewill fully indicate the construction. 

712. It can hardly be requisite to remark, that in the arrangement of anyof these forms of apparatus, they, and the wires connecting them with thesubstance, which is collaterally subjected to the action of the sameelectric current, should be so far insulated as to ensure a certainty thatall the electricity which passes through the one shall also be transmittedthrough the other. 

 * * * * *

713. Next to the precaution of collecting the gases, if mingled, out ofcontact with the platinum, was the necessity of testing the law of a_definite electrolytic_ action, upon water at least, under all varieties ofcondition; that, with a conviction of its certainty, might also be obtaineda knowledge of those interfering circumstances which would require to bepractically guarded against. 

714. The first point investigated was the influence or indifference ofextensive variations in the size of the electrodes, for which purposeinstruments like those last described (709. 710. 711. ) were used. One ofthese had plates 0. 7 of an inch wide, and nearly four inches long; anotherhad plates only 0. 5 of an inch wide, and 0. 8 of an inch long; a third hadwires 0. 02 of an inch in diameter, and three inches long; and a fourth, similar wires only half an inch in length. Yet when these were filled withdilute sulphuric acid, and, being placed in succession, had one commoncurrent of electricity passed through them, very nearly the same quantityof gas was evolved in all. The difference was sometimes in favour of oneand sometimes on the side of another; but the general result was that thelargest quantity of gases was evolved at the smallest electrodes, namely, those consisting merely of platina wires. 

715. Experiments of a similar kind were made with the single-plate, straight tubes (707. ), and also with the curved tubes (708. ), with similarconsequences; and when these, with the former tubes, were arranged togetherin various ways, the result, as to the equality of action of large andsmall metallic surfaces when delivering and receiving the same current ofelectricity, was constantly the same. As an illustration, the followingnumbers are given. An instrument with two wires evolved 74. 3 volumes ofmixed gases; another with plates 73. 25 volumes; whilst the sum of theoxygen and hydrogen in two separate tubes amounted to 73. 65 volumes. Inanother experiment the volumes were 55. 3, 55. 3, and 54. 4. 

716. But it was observed in these experiments, that in single-plate tubes(707. ) more hydrogen was evolved at the negative electrode than wasproportionate to the oxygen at the positive electrode; and generally, also, more than was proportionate to the oxygen and hydrogen in a double-platetube. Upon more minutely examining these effects, I was led to refer them, and also the differences between wires and plates (714. ), to the solubilityof the gases evolved, especially at the positive electrode. 

717. When the positive and negative electrodes are equal in surface, thebubbles which rise from them in dilute sulphuric acid are always differentin character. Those from the positive plate are exceedingly small, andseparate instantly from every part of the surface of the metal, inconsequence of its perfect cleanliness (633. ); whilst in the liquid theygive it a hazy appearance, from their number and minuteness; are easilycarried down by currents, and therefore not only present far greatersurface of contact with the liquid than larger bubbles would do, but areretained a much longer time in mixture with it. But the bubbles at thenegative surface, though they constitute twice the volume of the gas at thepositive electrode, are nevertheless very inferior in number. They do notrise so universally from every part of the surface, but seem to be evolvedat different parts; and though so much larger, they appear to cling to themetal, separating with difficulty from it, and when separated, instantlyrising to the top of the liquid. If, therefore, oxygen and hydrogen hadequal solubility in, or powers of combining with, water under similarcircumstances, still under the present conditions the oxygen would be farthe most liable to solution; but when to these is added its well-knownpower of forming a compound with water, it is no longer surprising thatsuch a compound should be produced in small quantities at the positiveelectrode; and indeed the blenching power which some philosophers haveobserved in a solution at this electrode, when chlorine and similar bodieshave been carefully excluded, is probably due to the formation there, inthis manner, of oxywater. 

718. That more gas was collected from the wires than from the plates, Iattribute to the circumstance, that as equal quantities were evolved inequal times, the bubbles at the wires having been more rapidly produced, inrelation to any part of the surface, must have been much larger; have beentherefore in contact with the fluid by a much smaller surface, and for amuch shorter time than those at the plates; hence less solution and agreater amount collected. 

719. There was also another effect produced, especially by the use of largeelectrodes, which was both a consequence and a proof of the solution ofpart of the gas evolved there. The collected gas, when examined, was foundto contain small portions of nitrogen. This I attribute to the presence ofair dissolved in the acid used for decomposition. It is a well-known fact, that when bubbles of a gas but slightly soluble in water or solutions passthrough them, the portion of this gas which is dissolved displaces aportion of that previously in union with the liquid: and so, in thedecompositions under consideration, as the oxygen dissolves, it displaces apart of the air, or at least of the nitrogen, previously united to theacid; and this effect takes place _most extensively_ with large plates, because the gas evolved at them is in the most favourable condition forsolution, 720. With the intention of avoiding this solubility of the gases as much aspossible, I arranged the decomposing plates in a vertical position (707. 708. ), that the bubbles might quickly escape upwards, and that the downwardcurrents in the fluid should not meet ascending currents of gas. Thisprecaution I found to assist greatly in producing constant results, andespecially in experiments to be hereafter referred to, in which otherliquids than dilute sulphuric acid, as for instance solution of potash, were used. 

721. The irregularities in the indications of the measurer proposed, arising from the solubility just referred to, are but small, and may bevery nearly corrected by comparing the results of two or three experiments. They may also be almost entirely avoided by selecting that solution whichis found to favour them in the least degree (728. ); and still further bycollecting the hydrogen only, and using that as the indicating gas; forbeing much less soluble than oxygen, being evolved with twice the rapidityand in larger bubbles (717. ), it can be collected more perfectly and ingreater purity. 

722. From the foregoing and many other experiments, it results that_variation in the size of the electrodes causes no variation in thechemical action of a given quantity of electricity upon water_. 

723. The next point in regard to which the principle of constantelectro-chemical action was tested, was _variation of intensity_. In thefirst place, the preceding experiments were repeated, using batteries of an_equal_ number of plates, _strongly_ and _weakly_ charged; but the resultswere alike. They were then repeated, using batteries sometimes containingforty, and at other times only five pairs of plates; but the results werestill the same. _Variations therefore in the intensity_, caused bydifference in the strength of charge, or in the number of alternationsused, _produced no difference as to the equal action of large and smallelectrodes_. 

724. Still these results did not prove that variation in the intensity ofthe current was not accompanied by a corresponding variation in theelectro-chemical effects, since the actions at _all_ the surfaces mighthave increased or diminished together. The deficiency in the evidence is, however, completely supplied by the former experiments on different-sizedelectrodes; for with variation in the size of these, a variation in theintensity must have occurred. The intensity of an electric currenttraversing conductors alike in their nature, quality, and length, isprobably as the quantity of electricity passing through a given sectionalarea perpendicular to the current, divided by the time (360. _note_); andtherefore when large plates were contrasted with wires separated by anequal length of the same decomposing conductor (714. ), whilst one currentof electricity passed through both arrangements, that electricity must havebeen in a very different state, as to _tension_, between the plates andbetween the wires; yet the chemical results were the same. 

725. The difference in intensity, under the circumstances described, may beeasily shown practically, by arranging two decomposing apparatus as in fig. 67, where the same fluid is subjected to the decomposing power of the samecurrent of electricity, passing in the vessel A. Between large platinaplates, and in the vessel B. Between small wires. If a third decomposingapparatus, such as that delineated fig. 66. (711. ), be connected with thewires at _ab_, fig. 67, it will serve sufficiently well, by the degree ofdecomposition occurring in it, to indicate the relative state of the twoplates as to intensity; and if it then be applied in the same way, as atest of the state of the wires at _a'b'_, it will, by the increase ofdecomposition within, show how much greater the intensity is there than atthe former points. The connexions of P and N with the voltaic battery areof course to be continued during the whole time. 

726. A third form of experiment, in which difference of intensity wasobtained, for the purpose of testing the principle of equal chemicalaction, was to arrange three volta-electrometers, so that after theelectric current had passed through one, it should divide into two parts, each of which should traverse one of the remaining instruments, and shouldthen reunite. The sum of the decomposition in the two latter vessels wasalways equal to the decomposition in the former vessel. But the _intensity_of the divided current could not be the same as that it had in its originalstate; and therefore _variation of intensity has no influence on theresults if the quantity of electricity remain the same_. The experiment, infact, resolves itself simply into an increase in the size of the electrodes(725. ). 

727. The _third point_, in respect to which the principle of equalelectro-chemical action on water was tested, was _variation of the strengthof the solution used_. In order to render the water a conductor, sulphuricacid had been added to it (707. ); and it did not seem unlikely that thissubstance, with many others, might render the water more subject todecomposition, the electricity remaining the same in quantity. But such didnot prove to be the case. Diluted sulphuric acid, of different strengths, was introduced into different decomposing apparatus, and submittedsimultaneously to the action of the same electric current (714. ). Slightdifferences occurred, as before, sometimes in one direction, sometimes inanother; but the final result was, that _exactly the same quantity of waterwas decomposed in all the solutions by the same quantity of electricity_, though the sulphuric acid in some was seventy-fold what it was in others. The strengths used were of specific gravity 1. 495, and downwards. 

728. When an acid having a specific gravity of about 1. 336 was employed, the results were most uniform, and the oxygen and hydrogen (716. ) mostconstantly in the right proportion to each other. Such an acid gave moregas than one much weaker acted upon by the same current, apparently becauseit had less solvent power. If the acid were very strong, then a remarkabledisappearance of oxygen took place; thus, one made by mixing two measuresof strong oil of vitriol with one of water, gave forty-two volumes ofhydrogen, but only twelve of oxygen. The hydrogen was very nearly the samewith that evolved from acid of the specific gravity 1. 232. I have not yethad time to examine minutely the circumstances attending the disappearanceof the oxygen in this case, but imagine it is due to the formation ofoxywater, which Thenard has shown is favoured by the presence of acid. 

729. Although not necessary for the practical use of the instrument I amdescribing, yet as connected with the important point of constantchemical action upon water, I now investigated the effects produced by anelectro-electric current passing through aqueous solutions of acids, salts, and compounds, exceedingly different from each other in their nature, andfound them to yield astonishingly uniform results. But many of them whichare connected with a secondary action will be more usefully describedhereafter (778. ). 

730. When solutions of caustic potassa or soda, or sulphate of magnesia, orsulphate of soda, were acted upon by the electric current, just as muchoxygen and hydrogen was evolved from them as from the diluted sulphuricacid, with which they were compared. When a solution of ammonia, rendered abetter conductor by sulphate of ammonia (554. ), or a solution ofsubcarbonate of potassa was experimented with, the _hydrogen_ evolved wasin the same quantity as that set free from the diluted sulphuric acid withwhich they were compared. Hence _changes in the nature of the solution donot alter the constancy of electrolytic action upon water_. 

731. I have already said, respecting large and small electrodes, thatchange of order caused no change in the general effect (715. ). The same wasthe case with different solutions, or with different intensities; andhowever the circumstances of an experiment might be varied, the resultscame forth exceedingly consistent, and proved that the electro-chemicalaction was still the same. 

732. I consider the foregoing investigation as sufficient to prove the veryextraordinary and important principle with respect to WATER, _that whensubjected to the influence of the electric current, a quantity of it isdecomposed exactly proportionate to the quantity of electricity which haspassed_, notwithstanding the thousand variations in the conditions andcircumstances under which it may at the time be placed; and further, thatwhen the interference of certain secondary effects (742. &c. ), togetherwith the solution or recombination of the gas and the evolution of air, areguarded against, _the products of the decomposition may be collected withsuch accuracy, as to afford a very excellent and valuable measurer of theelectricity concerned in their evolution_. 

733. The forms of instrument which I have given, figg. 64, 65, 66. (709. 710. 711. ), are probably those which will be found most useful, as theyindicate the quantity of electricity by the largest volume of gases, andcause the least obstruction to the passage of the current. The fluid whichmy present experience leads me to prefer, is a solution of sulphuric acidof specific gravity about 1. 336, or from that to 1. 25; but it is veryessential that there should be no organic substance, nor any vegetableacid, nor other body, which, by being liable to the action of the oxygen orhydrogen evolved at the electrodes (773. &c. ), shall diminish theirquantity, or add other gases to them. 

734. In many cases when the instrument is used as a _comparative standard_, or even as _a measurer_, it may be desirable to collect the hydrogen only, as being less liable to absorption or disappearance in other ways than theoxygen; whilst at the same time its volume is so large, as to render it agood and sensible indicator. In such cases the first and second form ofapparatus have been used, figg. 62, 63. (707. 708. ). The indicationsobtained were very constant, the variations being much smaller than inthose forms of apparatus collecting both gases; and they can also beprocured when solutions are used in comparative experiments, which, yielding no oxygen or only secondary results of its action, can give noindications if the educts at both electrodes be collected. Such is the casewhen solutions of ammonia, muriatic acid, chlorides, iodides, acetates orother vegetable salts, &c. , are employed. 

735. In a few cases, as where solutions of metallic salts liable toreduction at the negative electrode are acted upon, the oxygen may beadvantageously used as the measuring substance. This is the case, forinstance, with sulphate of copper. 

736. There are therefore two general forms of the instrument which I submitas a measurer of electricity; one, in which both the gases of the waterdecomposed are collected (709. 710. 711. ); and the other, in which a singlegas, as the hydrogen only, is used (707. 708. ). When referred to as a_comparative instrument_, (a use I shall now make of it very extensively, )it will not often require particular precaution in the observation; butwhen used as an _absolute measurer_, it will be needful that the barometricpressure and the temperature be taken into account, and that the graduationof the instruments should be to one scale; the hundredths and smallerdivisions of a cubical inch are quite fit for this purpose, and thehundredth may be very conveniently taken as indicating a DEGREE ofelectricity. 

737. It can scarcely be needful to point out further than has been done howthis instrument is to be used. It is to be introduced into the course ofthe electric current, the action of which is to be exerted anywhere else, and if 60° or 70° of electricity are to be measured out, either in one orseveral portions, the current, whether strong or weak, is to be continueduntil the gas in the tube occupies that number of divisions or hundredthsof a cubical inch. Or if a quantity competent to produce a certain effectis to be measured, the effect is to be obtained, and then the indicationread off. In exact experiments it is necessary to correct the volume of gasfor changes in temperature and pressure, and especially for moisture[A]. For the latter object the volta-electrometer (fig. 66. ) is most accurate, as its gas can be measured over water, whilst the others retain it overacid or saline solutions. 

 [A] For a simple table of correction for moisture, I may take the liberty of referring to my Chemical Manipulation, edition of 1830, p. 376. 

738. I have not hesitated to apply the term _degree_ (736. ), in analogywith the use made of it with respect to another most important imponderableagent, namely, heat; and as the definite expansion of air, water, mercury, &c. , is there made use of to measure heat, so the equally definiteevolution of gases is here turned to a similar use for electricity. 

739. The instrument offers the only _actual measurer_ of voltaicelectricity which we at present possess. For without being at all affectedby variations in time or intensity, or alterations in the current itself, of any kind, or from any cause, or even of intermissions of action, ittakes note with accuracy of the quantity of electricity which has passedthrough it, and reveals that quantity by inspection; I have therefore namedit a VOLTA-ELECTROMETER. 

740. Another mode of measuring volta-electricity may be adopted withadvantage in many cases, dependent on the quantities of metals or othersubstances evolved either as primary or as secondary results; but I refrainfrom enlarging on this use of the products, until the principles on whichtheir constancy depends have been fully established (791. 848. );

741. By the aid of this instrument I have been able to establish thedefinite character of electro-chemical action in its most general sense;and I am persuaded it will become of the utmost use in the extensions ofthe science which these views afford. I do not pretend to have made itsdetail perfect, but to have demonstrated the truth of the principle, andthe utility of the application[A]. 

 [A] As early as the year 1811, Messrs. Gay-Lussac and Thénard employed chemical decomposition as a measure of the electricity of the voltaic pile. See _Recherches Physico-chymiques_, p. 12. The principles and precautions by which it becomes an exact measure were of course not then known. --_Dec. 1838. _

¶ vi. _On the primary or secondary character of the bodies evolved at theElectrodes. _

742. Before the _volta-electrometer_ could be employed in determining, as a_general law_, the constancy of electro-decomposition, it became necessaryto examine a distinction, already recognised among scientific men, relativeto the products of that action, namely, their primary or secondarycharacter; and, if possible, by some general rule or principle, to decidewhen they were of the one or the other kind. It will appear hereafter thatgreat mistakes inspecting electro-chemical action and its consequences havearisen from confounding these two classes of results together. 

743. When a substance under decomposition yields at the electrodes thosebodies uncombined and unaltered which the electric current has separated, then they may be considered as primary results, even though themselvescompounds. Thus the oxygen and hydrogen from water are primary results; andso also are the acid and alkali (themselves compound bodies) evolved fromsulphate of soda. But when the substances separated by the current arechanged at the electrodes before their appearance, then they give rise tosecondary results, although in many cases the bodies evolved areelementary. 

744. These secondary results occur in two ways, being sometimes due to themutual action of the evolved substance and the matter of the electrode, andsometimes to its action upon the substances contained in the body itselfunder decomposition. Thus, when carbon is made the positive electrode indilute sulphuric acid, carbonic oxide and carbonic acid occasionally appearthere instead of oxygen; for the latter, acting upon the matter of theelectrode, produces these secondary results. Or if the positive electrode, in a solution of nitrate or acetate of lead, be platina, then peroxide oflead appears there, equally a secondary result with the former, but nowdepending upon an action of the oxygen on a substance in the solution. Again, when ammonia is decomposed by platina electrodes, nitrogen appearsat the _anode_[A]; but though an _elementary_ body, it is a _secondary_result in this case, being derived from the chemical action of the oxygenelectrically evolved there, upon the ammonia in the surrounding solution(554. ). In the same manner when aqueous solutions of metallic salts aredecomposed by the current, the metals evolved at the _cathode_, thoughelements, are _always_ secondary results, and not immediate consequences ofthe decomposing power of the electric current. 

 [A] Annales de Chimie, 1801, tom. Li. P. 167. 

745. Many of these secondary results are extremely valuable; for instance, all the interesting compounds which M. Becquerel has obtained by feebleelectric currents are of this nature; but they are essentially chemical, and must, in the theory of electrolytic action, be carefully distinguishedfrom those which are directly due to the action of the electric current. 

746. The nature of the substances evolved will often lead to a correctjudgement of their primary or secondary character, but is not sufficientalone to establish that point. Thus, nitrogen is said to be attractedsometimes by the positive and sometimes by the negative electrode, according to the bodies with which it may be combined (554. 555. ), and itis on such occasions evidently viewed as a primary result[A]; but I think Ishall show, that, when it appears at the positive electrode, or rather atthe _anode_, it is a secondary result (748. ). Thus, also, Sir HumphryDavy[B], and with him the great body of chemical philosophers, (includingmyself, ) have given the appearance of copper, lead, tin, silver, gold, &c. , at the negative electrode, when their aqueous solutions were acted upon bythe voltaic current, as proofs that the metals, as a class, were attractedto that surface; thus assuming the metal, in each case, to be a primaryresult. These, however, I expect to prove, are all secondary results; themere consequence of chemical action, and no proofs either of the attractionor of the law announced respecting their places[C]. 

 [A] Annales de Chimie, 1804, tom. Li. P. 172. 

 [B] Elements of Chemical Philosophy, pp. 144. 161. 

 [C] It is remarkable that up to 1804 it was the received opinion that the metals were reduced by the nascent hydrogen. At that date the general opinion was reversed by Hisinger and Berzelius (Annales de Chimie, 1804, tom. Li. P. 174, ), who stated that the metals were evolved directly by the electricity: in which opinion it appears, from that time, Davy coincided (Philosophical Transactions, 1826, p. 388). 

747. But when we take to our assistance the law of _constantelectro-chemical action_ already proved with regard to water (732. ), andwhich I hope to extend satisfactorily to all bodies (821. ), and considerthe _quantities_ as well as the _nature_ of the substances set free, agenerally accurate judgement of the primary or secondary character of theresults may be formed: and this important point, so essential to the theoryof electrolyzation, since it decides what are the particles directly underthe influence of the current, (distinguishing them from such as are notaffected, ) and what are the results to be expected, may be established withsuch degree of certainty as to remove innumerable ambiguities and doubtfulconsiderations from this branch of the science. 

748. Let us apply these principles to the case of ammonia, and the supposeddetermination of nitrogen to one or the other _electrode_ (554. 555, ). Apure strong solution of ammonia is as bad a conductor, and therefore aslittle liable to electrolyzation, as pure water; but when sulphate ofammonia is dissolved in it, the whole becomes a conductor; nitrogen_almost_ and occasionally _quite_ pure is evolved at the _anode_, andhydrogen at the _cathode_; the ratio of the volume of the former to that ofthe latter varying, but being as 1 to about 3 or 4. This result would seemat first to imply that the electric current had decomposed ammonia, andthat the nitrogen had been determined towards the positive electrode. Butwhen the electricity used was measured out by the volta-electrometer (707. 736. ), it was found that the hydrogen obtained was exactly in theproportion which would have been supplied by decomposed water, whilst thenitrogen had no certain or constant relation whatever. When, uponmultiplying experiments, it was found that, by using a stronger or weakersolution, or a more or less powerful battery, the gas evolved at the_anode_ was a mixture of oxygen and nitrogen, varying both in proportionand absolute quantity, whilst the hydrogen at the _cathode_ remainedconstant, no doubt could be entertained that the nitrogen at the _anode_was a secondary result, depending upon the chemical action of the nascentoxygen, determined to that surface by the electric current, upon theammonia in solution. It was the water, therefore, which was electrolyzed, not the ammonia. Further, the experiment gives no real indication of thetendency of the element nitrogen to either one electrode or the other; nordo I know of any experiment with nitric acid, or other compounds ofnitrogen, which shows the tendency of this element, under the influence ofthe electric current, to pass in either direction along its course. 

749. As another illustration of secondary results, the effects on asolution of acetate of potassa, may be quoted. When a very strong solutionwas used, more gas was evolved at the _anode_ than at the _cathode_, in theproportion of 4 to 3 nearly: that from the _anode_ was a mixture ofcarbonic oxide and carbonic acid; that from the _cathode_ pure hydrogen. When a much weaker solution was used, less gas was evolved at the _anode_than at the _cathode_; and it now contained carburetted hydrogen, as wellas carbonic oxide and carbonic acid. This result of carburetted hydrogen atthe positive electrode has a very anomalous appearance, if considered as animmediate consequence of the decomposing power of the current. It, however, as well as the carbonic oxide and acid, is only a _secondary result_; forit is the water alone which suffers electro-decomposition, and it is theoxygen eliminated at the _anode_ which, reacting on the acetic acid, in themidst of which it is evolved, produces those substances that finally appearthere. This is fully proved by experiments with the volta-electrometer(707. ); for then the hydrogen evolved from the acetate at the _cathode_ isalways found to be definite, being exactly proportionate to the electricitywhich has passed through the solution, and, in quantity, the same as thehydrogen evolved in the volta-electrometer itself. The appearance of thecarbon in combination with the hydrogen at the positive electrode, and itsnon-appearance at the negative electrode, are in curious contrast with theresults which might have been expected from the law usually acceptedrespecting the final places of the elements. 

750. If the salt in solution be an acetate of lead, then the results atboth electrodes are secondary, and cannot be used to estimate or expressthe amount of electro-chemical action, except by a circuitous process(843. ). In place of oxygen or even the gases already described (749. ), peroxide of lead now appears at the positive, and lead itself at thenegative electrode. When other metallic solutions are used, containing, forinstance, peroxides, as that of copper, combined with this or any otherdecomposable acid, still more complicated results will be obtained; which, viewed as direct results of the electro-chemical action, will, in theirproportions, present nothing but confusion, but will appear perfectlyharmonious and simple if they be considered as secondary results, and willaccord in their proportions with the oxygen and hydrogen evolved from waterby the action of a definite quantity of electricity. 

751. I have experimented upon many bodies, with a view to determine whetherthe results were primary or secondary. I have been surprised to find howmany of them, in ordinary cases, are of the latter class, and howfrequently water is the only body electrolyzed in instances where othersubstances have been supposed to give way. Some of these results I willgive in as few words as possible. 

752. _Nitric acid. _--When very strong, it conducted well, and yieldedoxygen at the positive electrode. No gas appeared at the negativeelectrode; but nitrous acid, and apparently nitric oxide, were formedthere, which, dissolving, rendered the acid yellow or red, and at last eveneffervescent, from the spontaneous separation of nitric oxide. Upondiluting the acid with its bulk or more of water, gas appeared at thenegative electrode. Its quantity could be varied by variations, either inthe strength of the acid or of the voltaic current: for that acid fromwhich no gas separated at the _cathode_, with a weak voltaic battery, didevolve gas there with a stronger; and that battery which evolved no gasthere with a strong acid, did cause its evolution with an acid more dilute. The gas at the _anode_ was always oxygen; that at the _cathode_ hydrogen. When the quantity of products was examined by the volta-electrometer(707. ), the oxygen, whether from strong or weak acid, proved to be in thesame proportion as from water. When the acid was diluted to specificgravity 1. 24, or less, the hydrogen also proved to be the same in quantityas from water. Hence I conclude that the nitric acid does not undergoelectrolyzation, but the water only; that the oxygen at the _anode_ isalways a primary result, but that the products at the _cathode_ are oftensecondary, and due to the reaction of the hydrogen upon the nitric acid. 

753. _Nitre. _--A solution of this salt yields very variable results, according as one or other form of tube is used, or as the electrodes arelarge or small. Sometimes the whole of the hydrogen of the water decomposedmay be obtained at the negative electrode; at other times, only a part ofit, because of the ready formation of secondary results. The solution is avery excellent conductor of electricity. 

754. _Nitrate of ammonia_, in aqueous solution, gives rise to secondaryresults very varied and uncertain in their proportions. 

755. _Sulphurous acid. _--Pure liquid sulphurous acid does not conduct norsuffer decomposition by the voltaic current[A], but, when dissolved inwater, the solution acquires conducting power, and is decomposed, yieldingoxygen at the _anode_, and hydrogen and sulphur at the _cathode_. 

 [A] See also De la Rive, Bibliothèque Universelle, tom. Xl. P. 205; or Quarterly Journal of Science, vol. Xxvii. P, 407. 

756. A solution containing sulphuric acid in addition to the sulphurousacid, was a better conductor. It gave very little gas at either electrode:that at the _anode_ was oxygen, that at the _cathode_ pure hydrogen. Fromthe _cathode_ also rose a white turbid stream, consisting of diffusedsulphur, which soon rendered the whole solution milky. The volumes of gaseswere in no regular proportion to the quantities evolved from water in thevoltameter. I conclude that the sulphurous acid was not at all affected bythe electric current in any of these cases, and that the water present wasthe only body electro-chemically decomposed; that, at the _anode_, theoxygen from the water converted the sulphurous acid into sulphuric acid, and, at the _cathode_, the hydrogen electrically evolved decomposed thesulphurous acid, combining with its oxygen, and setting its sulphur free. Iconclude that the sulphur at the negative electrode was only a secondaryresult; and, in fact, no part of it was found combined with the smallportion of hydrogen which escaped when weak solutions of sulphurous acidwere used. 

757. _Sulphuric acid. _--I have already given my reasons for concluding thatsulphuric acid is not electrolyzable, i. E. Not decomposable directly by theelectric current, but occasionally suffering by a secondary action at the_cathode_ from the hydrogen evolved there (681. ). In the year 1800, Davyconsidered the sulphur from sulphuric acid as the result of the action ofthe nascent hydrogen[A]. In 1804, Hisinger and Berzelius stated that it wasthe direct result of the action of the voltaic pile[B], an opinion whichfrom that time Davy seems to have adopted, and which has since beencommonly received by all. The change of my own opinion requires that Ishould correct what I have already said of the decomposition of sulphuricacid in a former series of these Researches (552. ): I do not now think thatthe appearance of the sulphur at the negative electrode is an immediateconsequence of electrolytic action. 

 [A] Nicholson's Quarterly Journal, vol. Iv. Pp. 280, 281. 

 [B] Annales de Chimie, 1804, tom. Li. P. 173. 

758. _Muriatic acid. _--A strong solution gave hydrogen at the negativeelectrode, and chlorine only at the positive electrode; of the latter, apart acted on the platina and a part was dissolved. A minute bubble of gasremained; it was not oxygen, but probably air previously held in solution. 

759. It was an important matter to determine whether the chlorine was aprimary result, or only a secondary product, due to the action of theoxygen evolved from water at the _anode_ upon the muriatic acid; i. E. Whether the muriatic acid was electrolyzable, and if so, whether thedecomposition was _definite_. 

760. The muriatic acid was gradually diluted. One part with six of watergave only chlorine at the _anode_. One part with eight of water gave onlychlorine; with nine of water, a little oxygen appeared with the chlorine;but the occurrence or non-occurrence of oxygen at these strengths depended, in part, on the strength of the voltaic battery used. With fifteen parts ofwater, a little oxygen, with much chlorine, was evolved at the _anode_. Asthe solution was now becoming a bad conductor of electricity, sulphuricacid was added to it: this caused more ready decomposition, but did notsensibly alter the proportion of chlorine and oxygen. 

761. The muriatic acid was now diluted with 100 times its volume of dilutesulphuric acid. It still gave a large proportion of chlorine at the_anode_, mingled with oxygen; and the result was the same, whether avoltaic battery of 40 pairs of plates or one containing only 5 pairs wereused. With acid of this strength, the oxygen evolved at the _anode_ was tothe hydrogen at the _cathode_, in volume, as 17 is to 64; and therefore thechlorine would have been 30 volumes, had it not been dissolved by thefluid. 

762. Next with respect to the quantity of elements evolved. On using thevolta-electrometer, it was found that, whether the strongest or the weakestmuriatic acid were used, whether chlorine alone or chlorine mingled withoxygen appeared at the _anode_, still the hydrogen evolved at the _cathode_was a constant quantity, i. E. Exactly the same as the hydrogen which the_same quantity of electricity_ could evolve from water. 

763. This constancy does not decide whether the muriatic acid iselectrolyzed or not, although it proves that if so, it must be in definiteproportions to the quantity of electricity used. Other considerations may, however, be allowed to decide the point. The analogy between chlorine andoxygen, in their relations to hydrogen, is so strong, as to lead almost tothe certainty, that, when combined with that element, they would performsimilar parts in the process of electro-decomposition. They both unite withit in single proportional or equivalent quantities; and the number ofproportionals appearing to have an intimate and important relation to thedecomposability of a body (697. ), those in muriatic acid, as well as inwater, are the most favourable, or those perhaps even necessary, todecomposition. In other binary compounds of chlorine also, where nothingequivocal depending on the simultaneous presence of it and oxygen isinvolved, the chlorine is directly eliminated at the _anode_ by theelectric current. Such is the case with the chloride of lead (395. ), whichmay be justly compared with protoxide of lead (402. ), and stands in thesame relation to it as muriatic acid to water. The chlorides of potassium, sodium, barium, &c. , are in the same relation to the protoxides of the samemetals and present the same results under the influence of the electriccurrent (402. ). 

764. From all the experiments, combined with these considerations, Iconclude that muriatic acid is decomposed by the direct influence of theelectric current, and that the quantities evolved are, and therefore thechemical action is, _definite for a definite quantity of electricity_. Forthough I have not collected and measured the chlorine, in its separatestate, at the _anode_, there can exist no doubt as to its beingproportional to the hydrogen at the _cathode_; and the results aretherefore sufficient to establish the general law of _constantelectro-chemical action_ in the case of muriatic acid. 

765. In the dilute acid (761. ), I conclude that a part of the water iselectro-chemically decomposed, giving origin to the oxygen, which appearsmingled with the chlorine at the _anode_. The oxygen _may_ be viewed as asecondary result; but I incline to believe that it is not so; for, if itwere, it might be expected in largest proportion from the stronger acid, whereas the reverse is the fact. This consideration, with others, alsoleads me to conclude that muriatic acid is more easily decomposed by theelectric current than water; since, even when diluted with eight or ninetimes its quantity of the latter fluid, it alone gives way, the waterremaining unaffected. 

766. _Chlorides. _--On using solutions of chlorides in water, --for instance, the chlorides of sodium or calcium, --there was evolution of chlorine onlyat the positive electrode, and of hydrogen, with the oxide of the base, assoda or lime, at the negative electrode. The process of decomposition maybe viewed as proceeding in two or three ways, all terminating in the sameresults. Perhaps the simplest is to consider the chloride as the substanceelectrolyzed, its chlorine being determined to and evolved at the _anode_, and its metal passing to the _cathode_, where, finding no more chlorine, itacts upon the water, producing hydrogen and an oxide as secondary results. As the discussion would detain me from more important matter, and is not ofimmediate consequence, I shall defer it for the present. It is, however, of_great consequence_ to state, that, on using the volta-electrometer, thehydrogen in both cases was definite; and if the results do not prove thedefinite decomposition of chlorides, (which shall be provedelsewhere, --789. 794. 814. , ) they are not in the slightest degree opposedto such a conclusion, and do support the _general law_. 

767. _Hydriodic acid. _--A solution of hydriodic acid was affected exactlyin the same manner as muriatic acid. When strong, hydrogen was evolved atthe negative electrode, in definite proportion to the quantity ofelectricity which had passed, i. E. In the same proportion as was evolved bythe same current from water; and iodine without any oxygen was evolved atthe positive electrode. But when diluted, small quantities of oxygenappeared with the iodine at the _anode_, the proportion of hydrogen at the_cathode_ remaining undisturbed. 

768. I believe the decomposition of the hydriodic acid in this case to bedirect, for the reasons already given respecting muriatic acid (763. 764. ). 

769. _Iodides. _--A solution of iodide of potassium being subjected to thevoltaic current, iodine appeared at the positive electrode (without anyoxygen), and hydrogen with free alkali at the negative electrode. The sameobservations as to the mode of decomposition are applicable here as weremade in relation to the chlorides when in solution (766. ). 

770. _Hydro-fluoric acid and fluorides. _--Solution of hydrofluoric acid didnot appear to be decomposed under the influence of the electric current: itwas the water which gave way apparently. The fused fluorides wereelectrolysed (417. ); but having during these actions obtained _fluorine_ inthe separate state, I think it better to refer to a future series of theseResearches, in which I purpose giving a fuller account of the results thanwould be consistent with propriety here[A]. 

 [A] I have not obtained fluorine: my expectations, amounting to conviction, passed away one by one when subjected to rigorous examination; some very singular results were obtained; and to one of these I refer at 1340. --_Dec. 1838. _

771. _Hydro-cyanic acid_ in solution conducts very badly. The definiteproportion of hydrogen (equal to that from water) was set free at the_cathode_, whilst at the _anode_ a small quantity of oxygen was evolved andapparently a solution of cyanogen formed. The action altogethercorresponded with that on a dilute muriatic or hydriodic acid. When thehydrocyanic acid was made a better conductor by sulphuric acid, the sameresults occurred. 

_Cyanides. _--With a solution of the cyanide of potassium, the result wasprecisely the same as with a chloride or iodide. No oxygen was evolved atthe positive electrode, but a brown solution formed there. For the reasonsgiven when speaking of the chlorides (766. ), and because a fused cyanide ofpotassium evolves cyanogen at the positive electrode[A], I incline tobelieve that the cyanide in solution is _directly_ decomposed. 

 [A] It is a very remarkable thing to see carbon and nitrogen in this case determined powerfully towards the positive surface of the voltaic battery; but it is perfectly in harmony with the theory of electro-chemical decomposition which I have advanced. 

772. _Ferro-cyanic acid_ and the _ferro-cyanides_, as also _sulpho-cyanicacid_ and the _sulpho-cyanides_, presented results corresponding with thosejust described (771. ). 

773. _Acetic acid. _--Glacial acetic acid, when fused (405. ), is notdecomposed by, nor does it conduct, electricity. On adding a little waterto it, still there were no signs of action; on adding more water, it actedslowly and about as pure water would do. Dilute sulphuric acid was added toit in order to make it a better conductor; then the definite proportion ofhydrogen was evolved at the _cathode_, and a mixture of oxygen in verydeficient quantity, with carbonic acid, and a little carbonic oxide, at the_anode_. Hence it appears that acetic acid is not electrolyzable, but thata portion of it is decomposed by the oxygen evolved at the _anode_, producing secondary results, varying with the strength of the acid, theintensity of the current, and other circumstances. 

774. _Acetates. _--One of these has been referred to already, as affordingonly secondary results relative to the acetic acid (749. ). With many of themetallic acetates the results at both electrodes are secondary (746. 750. ). 

Acetate of soda fused and anhydrous is directly decomposed, being, as Ibelieve, a true electrolyte, and evolving soda and acetic acid at the_cathode_ and _anode_. These however have no sensible duration, but areimmediately resolved into other substances; charcoal, sodiuretted hydrogen, &c. , being set free at the former, and, as far as I could judge under thecircumstances, acetic acid mingled with carbonic oxide, carbonic acid, &c. At the latter. 

775. _Tartaric acid. _--Pure solution of tartaric acid is almost as bad aconductor as pure water. On adding sulphuric acid, it conducted well, theresults at the positive electrode being primary or secondary in differentproportions, according to variations in the strength of the acid and thepower of the electric current (752. ). Alkaline tartrates gave a largeproportion of secondary results at the positive electrode. The hydrogen atthe negative electrode remained constant unless certain triple metallicsalts were used. 

776. Solutions, of salts containing other vegetable acids, as thebenzoates; of sugar, gum, &c. , dissolved in dilute sulphuric acid; ofresin, albumen, &c. , dissolved in alkalies, were in turn submitted to theelectrolytic power of the voltaic current. In all these cases, secondaryresults to a greater or smaller extent were produced at the positiveelectrode. 

777. In concluding this division of these Researches, it cannot but occurto the mind that the final result of the action of the electric currentupon substances, placed between the electrodes, instead of being simple maybe very complicated. There are two modes by which these substances may bedecomposed, either by the direct force of the electric current, or by theaction of bodies which that current may evolve. There are also two modes bywhich new compounds may be formed, i. E. By combination of the evolvingsubstances whilst in their nascent state (658. ), directly with the matterof the electrode; or else their combination with those bodies, which beingcontained in, or associated with, the body suffering decomposition, arenecessarily present at the _anode_ and _cathode_. The complexity isrendered still greater by the circumstance that two or more of theseactions may occur simultaneously, and also in variable proportions to eachother. But it may in a great measure be resolved by attention to theprinciples already laid down (747. ). 

778. When _aqueous_ solutions of bodies are used, secondary results areexceedingly frequent. Even when the water is not present in large quantity, but is merely that of combination, still secondary results often ensue: forinstance, it is very possible that in Sir Humphry Davy's decomposition ofthe hydrates of potassa and soda, a part of the potassium produced was theresult of a secondary action. Hence, also, a frequent cause for thedisappearance of the oxygen and hydrogen which would otherwise be evolved:and when hydrogen does _not_ appear at the _cathode_ in an _aqueoussolution_, it perhaps always indicates that a secondary action has takenplace there. No exception to this rule has as yet occurred to myobservation. 

779. Secondary actions are _not confined to aqueous solutions_, or caseswhere water is present. For instance, various chlorides acted upon, whenfused (402. ), by platina electrodes, have the chlorine determinedelectrically to the _anode_. In many cases, as with the chlorides of lead, potassium, barium, &c. , the chlorine acts on the platina and forms acompound with it, which dissolves; but when protochloride of tin is used, the chlorine at the _anode_ does not act upon the platina, but upon thechloride already there, forming a perchloride which rises in vapour (790. 804. ). These are, therefore, instances of secondary actions of both kinds, produced in bodies containing no water. 

780. The production of boron from fused borax (402. 417. ) is also a case ofsecondary action; for boracic acid is not decomposable by electricity(408. ), and it was the sodium evolved at the _cathode_ which, re-acting onthe boracic acid around it, took oxygen from it and set boron free in theexperiments formerly described. 

781. Secondary actions have already, in the hands of M. Becquerel, producedmany interesting results in the formation of compounds; some of them new, others imitations of those occurring naturally[A]. It is probable they mayprove equally interesting in an opposite direction, i. E. As affording casesof analytic decomposition. Much information regarding the composition, andperhaps even the arrangement, of the particles of such bodies as thevegetable acids and alkalies, and organic compounds generally, willprobably be obtained by submitting them to the action of nascent oxygen, hydrogen, chlorine, &c. At the electrodes; and the action seems the morepromising, because of the thorough command which we possess over attendantcircumstances, such as the strength of the current, the size of theelectrodes, the nature of the decomposing conductor, its strength, &c. , allof which may be expected to have their corresponding influence upon thefinal result. 

782. It is to me a great satisfaction that the extreme variety of secondaryresults has presented nothing opposed to the doctrine of a constant anddefinite electro-chemical action, to the particular consideration of whichI shall now proceed. 

¶ vii. _On the definite nature and extent of Electro-chemicalDecomposition. _

783. In the third series of these Researches, after proving the identity ofelectricities derived from different sources, and showing, by actualmeasurement, the extraordinary quantity of electricity evolved by a veryfeeble voltaic arrangement (371. 376. ), I announced a law, derived fromexperiment, which seemed to me of the utmost importance to the science ofelectricity in general, and that branch of it denominated electro-chemistryin particular. The law was expressed thus: _The chemical power of a currentof electricity is in direct proportion to the absolute quantity ofelectricity which passes_ (377. ). 

 [A] Annales de Chimie, tom, xxxv. P. 113. 

784. In the further progress of the successive investigations, I have hadfrequent occasion to refer to the same law, sometimes in circumstancesoffering powerful corroboration of its truth (456. 504. 505. ); and thepresent series already supplies numerous new cases in which it holds good(704. 722. 726. 732. ). It is now my object to consider this great principlemore closely, and to develope some of the consequences to which it leads. That the evidence for it may be the more distinct and applicable, I shallquote cases of decomposition subject to as few interferences from secondaryresults as possible, effected upon bodies very simple, yet very definite intheir nature. 

785. In the first place, I consider the law as so fully established withrespect to the decomposition of _water_, and under so many circumstanceswhich might be supposed, if anything could, to exert an influence over it, that I may be excused entering into further detail respecting thatsubstance, or even summing up the results here (732. ). I refer, therefore, to the whole of the subdivision of this series of Researches which containsthe account of the _volta-electrometer_ (704. &c. ). 

786. In the next place, I also consider the law as established with respectto _muriatic acid_ by the experiments and reasoning already advanced, whenspeaking of that substance, in the subdivision respecting primary andsecondary results (758. &c. ). 

787. I consider the law as established also with regard to _hydriodic acid_by the experiments and considerations already advanced in the precedingdivision of this series of Researches (767. 768. ). 

788. Without speaking with the same confidence, yet from the experimentsdescribed, and many others not described, relating to hydro-fluoric, hydro-cyanic, ferro-cyanic, and sulpho-cyanic acids (770. 771. 772. ), andfrom the close analogy which holds between these bodies and the hydracidsof chlorine, iodine, bromine, &c. , I consider these also as coming undersubjection to the law, and assisting to prove its truth. 

789. In the preceding cases, except the first, the water is believed to beinactive; but to avoid any ambiguity arising from its presence, I soughtfor substances from which it should be absent altogether; and, takingadvantage of the law of conduction already developed (380. &c. ), I soonfound abundance, amongst which _protochloride of tin_ was first subjectedto decomposition in the following manner. A piece of platina wire had oneextremity coiled up into a small knob, and, having been carefully weighed, was sealed hermetically into a piece of bottle-glass tube, so that the knobshould be at the bottom of the tube within (fig. 68. ). The tube wassuspended by a piece of platina wire, so that the heat of a spirit-lampcould be applied to it. Recently fused protochloride of tin was introducedin sufficient quantity to occupy, when melted, about one-half of the tube;the wire of the tube was connected with a volta-electrometer (711. ), whichwas itself connected with the negative end of a voltaic battery; and aplatina wire connected with the positive end of the same battery was dippedinto the fused chloride in the tube; being however so bent, that it couldnot by any shake of the hand or apparatus touch the negative electrode atthe bottom of the vessel. The whole arrangement is delineated in fig. 69. 

790. Under these circumstances the chloride of tin was decomposed: thechlorine evolved at the positive electrode formed bichloride of tin (779. ), which passed away in fumes, and the tin evolved at the negative electrodecombined with the platina, forming an alloy, fusible at the temperature towhich the tube was subjected, and therefore never occasioning metalliccommunication through the decomposing chloride. When the experiment hadbeen continued so long as to yield a reasonable quantity of gas in thevolta-electrometer, the battery connexion was broken, the positiveelectrode removed, and the tube and remaining chloride allowed to cool. When cold, the tube was broken open, the rest of the chloride and the glassbeing easily separable from the platina wire and its button of alloy. Thelatter when washed was then reweighed, and the increase gave the weight ofthe tin reduced. 

791. I will give the particular results of one experiment, in illustrationof the mode adopted in this and others, the results of which I shall haveoccasion to quote. The negative electrode weighed at first 20 grains; afterthe experiment, it, with its button of alloy, weighed 23. 2 grains. The tinevolved by the electric current at the _cathode_: weighed therefore 3. 2grains. The quantity of oxygen and hydrogen collected in thevolta-electrometer = 3. 85 cubic inches. As 100 cubic inches of oxygen andhydrogen, in the proportions to form water, may be considered as weighing12. 92 grains, the 3. 85 cubic inches would weigh 0. 49742 of a grain; thatbeing, therefore, the weight of water decomposed by the same electriccurrent as was able to decompose such weight of protochloride of tin ascould yield 3. 2 grains of metal. Now 0. 49742 : 3. 2 :: 9 the equivalent ofwater is to 57. 9, which should therefore be the equivalent of tin, if theexperiment had been made without error, and if the electro-chemicaldecomposition _is in this case also definite_. In some chemical works 58 isgiven as the chemical equivalent of tin, in others 57. 9. Both are so nearto the result of the experiment, and the experiment itself is so subject toslight causes of variation (as from the absorption of gas in thevolta-electrometer (716. ), &c. ), that the numbers leave little doubt of theapplicability of the _law of definite action_ in this and all similar casesof electro-decomposition. 

792. It is not often I have obtained an accordance in numbers so near asthat I have just quoted. Four experiments were made on the protochloride oftin, the quantities of gas evolved in the volta-electrometer being from2. 05 to 10. 29 cubic inches. The average of the four experiments gave 58. 53as the electro-chemical equivalent for tin. 

793. The chloride remaining after the experiment was pure protochloride oftin; and no one can doubt for a moment that the equivalent of chlorine hadbeen evolved at the _anode_, and, having formed bichloride of tin as asecondary result, had passed away. 

794. _Chloride of lead_ was experimented upon in a manner exactly similar, except that a change was made in the nature of the positive electrode; foras the chlorine evolved at the _anode_ forms no perchloride of lead, butacts directly upon the platina, it produces, if that metal be used, asolution of chloride of platina in the chloride of lead; in consequence ofwhich a portion of platina can pass to the _cathode_, and would thenproduce a vitiated result. I therefore sought for, and found in plumbago, another substance, which could be used safely as the positive electrode insuch bodies as chlorides, iodides, &c. 

The chlorine or iodine does not act upon it, but is evolved in the freestate; and the plumbago has no re-action, under the circumstances, upon thefused chloride or iodide in which it is plunged. Even if a few particles ofplumbago should separate by the heat or the mechanical action of theevolved gas, they can do no harm in the chloride. 

795. The mean of three experiments gave the number of 100. 85 as theequivalent for lead. The chemical equivalent is 103. 5. The deficiency in myexperiments I attribute to the solution of part of the gas (716. ) in thevolta-electrometer; but the results leave no doubt on my mind that both thelead and the chlorine are, in this case, evolved in _definite quantities_by the action of a given quantity of electricity (814. &c. ). 

796. _Chloride of antimony. _--It was in endeavouring to obtain theelectro-chemical equivalent of antimony from the chloride, that I foundreasons for the statement I have made respecting the presence of water init in an earlier part of these Researches (690. 693. &c. ). 

797. I endeavoured to experiment upon the _oxide of lead_ obtained byfusion and ignition of the nitrate in a platina crucible, but found greatdifficulty, from the high temperature required for perfect fusion, and thepowerful fluxing qualities of the substance. Green-glass tubes repeatedlyfailed. I at last fused the oxide in a small porcelain crucible, heatedfully in a charcoal fire; and, as it is was essential that the evolution ofthe lead at the _cathode_ should take place beneath the surface, thenegative electrode was guarded by a green-glass tube, fused around it insuch a _manner as to expose only the knob of platina_ at the lower end(fig. 70. ), so that it could be plunged beneath the surface, and thusexclude contact of air or oxygen with the lead reduced there. A platinawire was employed for the positive electrode, that metal not being subjectto any action from the oxygen evolved against it. The arrangement is givenin fig. 71. 

798. In an experiment of this kind the equivalent for the lead came out93. 17, which is very much too small. This, I believe, was because of thesmall interval between the positive and negative electrodes in the oxide oflead; so that it was not unlikely that some of the froth and bubbles formedby the oxygen at the _anode_ should occasionally even touch the leadreduced at the _cathode_, and re-oxidize it. When I endeavoured to correctthis by having more litharge, the greater heat required to keep it allfluid caused a quicker action on the crucible, which was soon eatenthrough, and the experiment stopped. 

799. In one experiment of this kind I used borate of lead (408. 673. ). Itevolves lead, under the influence of the electric current, at the _anode_, and oxygen at the _cathode_; and as the boracic acid is not either directly(408. ) or incidentally decomposed during the operation, I expected a resultdependent on the oxide of lead. The borate is not so violent a flux as theoxide, but it requires a higher temperature to make it quite liquid; and ifnot very hot, the bubbles of oxygen cling to the positive electrode, andretard the transfer of electricity. The number for lead came out 101. 29, which is so near to 103. 5 as to show that the action of the current hadbeen definite. 

800. _Oxide of bismuth. _--I found this substance required too high atemperature, and acted too powerfully as a flux, to allow of any experimentbeing made on it, without the application of more time and care than Icould give at present. 

801. The ordinary _protoxide of antimony_, which consists of oneproportional of metal and one and a half of oxygen, was subjected to theaction of the electric current in a green-glass tube (789. ), surrounded bya jacket of platina foil, and heated in a charcoal fire. The decompositionbegan and proceeded very well at first, apparently indicating, according tothe general law (679. 697. ), that this substance was one containing suchelements and in such proportions as made it amenable to the power of theelectric current. This effect I have already given reasons for supposingmay be due to the presence of a true protoxide, consisting of singleproportionals (696. 693. ). The action soon diminished, and finally ceased, because of the formation of a higher oxide of the metal at the positiveelectrode. This compound, which was probably the peroxide, being infusibleand insoluble in the protoxide, formed a crystalline crust around thepositive electrode; and thus insulating it, prevented the transmission ofthe electricity. Whether, if it had been fusible and still immiscible, itwould have decomposed, is doubtful, because of its departure from therequired composition (697. ). It was a very natural secondary product at thepositive electrode (779. ). On opening the tube it was found that a littleantimony had been separated at the negative electrode; but the quantity wastoo small to allow of any quantitative result being obtained[A]. 

 [A] This paragraph is subject to the corrective note now appended to paragraph 696. --_Dec. 1838. _

802. _Iodide of lead. _--This substance can be experimented with in tubesheated by a spirit-lamp (789. ); but I obtained no good results from it, whether I used positive electrodes of platina or plumbago. In twoexperiments the numbers for the lead came out only 75. 46 and 73. 45, insteadof 103. 5. This I attribute to the formation of a periodide at the positiveelectrode, which, dissolving in the mass of liquid iodide, came in contactwith the lead evolved at the negative electrode, and dissolved part of it, becoming itself again protiodide. Such a periodide does exist; and it isvery rarely that the iodide of lead formed by precipitation, andwell-washed, can be fused without evolving much iodine, from the presenceof this percompound; nor does crystallization from its hot aqueous solutionfree it from this substance. Even when a little of the protiodide andiodine are merely rubbed together in a mortar, a portion of the periodideis formed. And though it is decomposed by being fused and heated to dullredness for a few minutes, and the whole reduced to protiodide, yet that isnot at all opposed to the possibility, that a little of that which isformed in great excess of iodine at the _anode_, should be carried by therapid currents in the liquid into contact with the _cathode_. 

803. This view of the result was strengthened by a third experiment, wherethe space between the electrodes was increased to one third of an inch; fornow the interfering effects were much diminished, and the number of thelead came out 89. 04; and it was fully confirmed by the results obtained inthe cases of _transfer_ to be immediately described (818. ). 

The experiments on iodide of lead therefore offer no exception to the_general law_ under consideration, but on the contrary may, from generalconsiderations, be admitted as included in it. 

804. _Protiodide of tin. _--This substance, when fused (402. ), conducts andis decomposed by the electric current, tin is evolved at the _anode_, andperiodide of tin as a secondary result (779. 790. ) at the _cathode_. Thetemperature required for its fusion is too high to allow of the productionof any results fit for weighing. 

805. _Iodide of potassium_ was subjected to electrolytic action in a tube, like that in fig. 68. (789. ). The negative electrode was a globule of lead, and I hoped in this way to retain the potassium, and obtain results thatcould be weighed and compared with the volta-electrometer indication; butthe difficulties dependent upon the high temperature required, the actionupon the glass, the fusibility of the platina induced by the presence ofthe lead, and other circumstances, prevented me from procuring suchresults. The iodide was decomposed with the evolution of iodine at the_anode_, and of potassium at the _cathode_, as in former cases. 

806. In some of these experiments several substances were placed insuccession, and decomposed simultaneously by the same electric current:thus, protochloride of tin, chloride of lead, and water, were thus acted onat once. It is needless to say that the results were comparable, the tin, lead, chlorine, oxygen, and hydrogen evolved being _definite in quantity_and electro-chemical equivalents to each other. 

 * * * * *

807. Let us turn to another kind of proof of the _definite chemical actionof electricity_. If any circumstances could be supposed to exert aninfluence over the quantity of the matters evolved during electrolyticaction, one would expect them to be present when electrodes of differentsubstances, and possessing very different chemical affinities for suchmatters, were used. Platina has no power in dilute sulphuric acid ofcombining with the oxygen at the _anode_, though the latter be evolved inthe nascent state against it. Copper, on the other hand, immediately uniteswith the oxygen, as the electric current sets it free from the hydrogen;and zinc is not only able to combine with it, but can, without any helpfrom the electricity, abstract it directly from the water, at the same timesetting torrents of hydrogen free. Yet in cases where these threesubstances were used as the positive electrodes in three similar portionsof the same dilute sulphuric acid, specific gravity 1. 336, precisely thesame quantity of water was decomposed by the electric current, andprecisely the same quantity of hydrogen set free at the _cathodes_ of thethree solutions. 

808. The experiment was made thus. Portions of the dilute sulphuric acidwere put into three basins. Three volta-electrometer tubes, of the formfigg. 60. 62. Were filled with the same acid, and one inverted in eachbasin (707. ). A zinc plate, connected with the positive end of a voltaicbattery, was dipped into the first basin, forming the positive electrodethere, the hydrogen, which was abundantly evolved from it by the directaction of the acid, being allowed to escape. A copper plate, which dippedinto the acid of the second basin, was connected with the negativeelectrode of the _first_ basin; and a platina plate, which dipped into theacid of the third basin, was connected with the negative electrode of the_second_ basin. The negative electrode of the third basin was connectedwith a volta-electrometer (711. ), and that with the negative end of thevoltaic battery. 

809. Immediately that the circuit was complete, the _electro-chemicalaction_ commenced in all the vessels. The hydrogen still rose in, apparently, undiminished quantities from the positive zinc electrode in thefirst basin. No oxygen was evolved at the positive copper electrode in thesecond basin, but a sulphate of copper was formed there; whilst in thethird basin the positive platina electrode evolved pure oxygen gas, and wasitself unaffected. But in _all_ the basins the hydrogen liberated at the_negative_ platina electrodes was the _same in quantity_, and the same withthe volume of hydrogen evolved in the volta-electrometer, showing that inall the vessels the current had decomposed an equal quantity of water. Inthis trying case, therefore, the _chemical action of electricity_ proved tobe _perfectly definite_. 

810. A similar experiment was made with muriatic acid diluted with its bulkof water. The three positive electrodes were zinc, silver, and platina; thefirst being able to separate and combine with the chlorine _without_ theaid of the current; the second combining with the chlorine only after thecurrent had set it free; and the third rejecting almost the whole of it. The three negative electrodes were, as before, platina plates fixed withinglass tubes. In this experiment, as in the former, the quantity of hydrogenevolved at the _cathodes_ was the same for all, and the same as thehydrogen evolved in the volta-electrometer. I have already given my reasonsfor believing that in these experiments it is the muriatic acid which isdirectly decomposed by the electricity (764. ); and the results prove thatthe quantities so decomposed are _perfectly definite_ and proportionate tothe quantity of electricity which has passed. 

811. In this experiment the chloride of silver formed in the second basinretarded the passage of the current of electricity, by virtue of the law ofconduction before described (394. ), so that it had to be cleaned off fouror five times during the course of the experiment; but this caused nodifference between the results of that vessel and the others. 

812. Charcoal was used as the positive electrode in both sulphuric andmuriatic acids (808. 810. ); but this change produced no variation of theresults. A zinc positive electrode, in sulphate of soda or solution ofcommon salt, gave the same constancy of operation. 

813. Experiments of a similar kind were then made with bodies altogether ina different state, i. E. With _fused_ chlorides, iodides, &c. I have alreadydescribed an experiment with fused chloride of silver, in which theelectrodes were of metallic silver, the one rendered negative becomingincreased and lengthened by the addition of metal, whilst the other wasdissolved and eaten away by its abstraction. This experiment was repeated, two weighed pieces of silver wire being used as the electrodes, and avolta-electrometer included in the circuit. Great care was taken towithdraw the negative electrodes so regularly and steadily that thecrystals of reduced silver should not form a _metallic_ communicationbeneath the surface of the fused chloride. On concluding the experiment thepositive electrode was re-weighed, and its loss ascertained. The mixture ofchloride of silver, and metal, withdrawn in successive portions at thenegative electrode, was digested in solution of ammonia, to remove thechloride, and the metallic silver remaining also weighed: it was thereduction at the _cathode_, and exactly equalled the solution at the_anode_; and each portion was as nearly as possible the equivalent to thewater decomposed in the volta-electrometer. 

814. The infusible condition of the silver at the temperature used, and thelength and ramifying character of its crystals, render the above experimentdifficult to perform, and uncertain in its results. I therefore wroughtwith chloride of lead, using a green-glass tube, formed as in fig. 72. Aweighed platina wire was fused into the bottom of a small tube, as beforedescribed (789. ). The tube was then bent to an angle, at about half an inchdistance from the closed end; and the part between the angle and theextremity being softened, was forced upward, as in the figure, so as toform a bridge, or rather separation, producing two little depressions orbasins _a, b_, within the tube. This arrangement was suspended by a platinawire, as before, so that the heat of a spirit-lamp could be applied to it, such inclination being given to it as would allow all air to escape duringthe fusion of the chloride of lead. A positive electrode was then provided, by bending up the end of a platina wire into a knot, and fusing abouttwenty grains of metallic lead on to it, in a small closed tube of glass, which was afterwards broken away. Being so furnished, the wire with itslead was weighed, and the weight recorded. 

815. Chloride of lead was now introduced into the tube, and carefullyfused. The leaded electrode was also introduced; after which the metal, atits extremity, soon melted. In this state of things the tube was filled upto _c_ with melted chloride of lead; the end of the electrode to berendered negative was in the basin _b_, and the electrode of melted leadwas retained in the basin _a_, and, by connexion with the proper conductingwire of a voltaic battery, was rendered positive. A volta-electrometer wasincluded in the circuit. 

816. Immediately upon the completion of the communication with the voltaicbattery, the current passed, and decomposition proceeded. No chlorine wasevolved at the positive electrode; but as the fused chloride wastransparent, a button of alloy could be observed gradually forming andincreasing in size at _b_, whilst the lead at _a_ could also be seengradually to diminish. After a time, the experiment was stopped; the tubeallowed to cool, and broken open; the wires, with their buttons, cleanedand weighed; and their change in weight compared with the indication of thevolta-electrometer. 

817. In this experiment the positive electrode had lost just as much leadas the negative one had gained (795. ), and the loss and gain were verynearly the equivalents of the water decomposed in the volta-electrometer, giving for lead the number 101. 5. It is therefore evident, in thisinstance, that causing a _strong affinity_, or _no affinity_, for thesubstance evolved at the _anode_, to be active during the experiment(807. ), produces no variation in the definite action of the electriccurrent. 

818. A similar experiment was then made with iodide of lead, and in thismanner all confusion from the formation of a periodide avoided (803. ). Noiodine was evolved during the whole action, and finally the loss of lead atthe _anode_ was the same as the gain at the _cathode_, the equivalentnumber, by comparison with the result in the volta-electrometer, being103. 5. 

819. Then protochloride of tin was subjected to the electric current in thesame manner, using of course, a tin positive electrode. No bichloride oftin was now formed (779. 790. ). On examining the two electrodes, thepositive had lost precisely as much as the negative had gained; and bycomparison with the volta-electrometer, the number for tin came out 59. 

820. It is quite necessary in these and similar experiments to examine theinterior of the bulbs of alloy at the ends of the conducting wires; foroccasionally, and especially with those which have been positive, they arecavernous, and contain portions of the chloride or iodide used, which mustbe removed before the final weight is ascertained. This is more usually thecase with lead than tin. 

821. All these facts combine into, I think, an irresistible mass ofevidence, proving the truth of the important proposition which I at firstlaid down, namely, _that the chemical power of a current of electricity isin direct proportion to the absolute quantity of electricity which passes_(377. 783. ). They prove, too, that this is not merely true with onesubstance, as water, but generally with all electrolytic bodies; and, further, that the results obtained with any _one substance_ do not merelyagree amongst themselves, but also with those obtained from _othersubstances_, the whole combining together into _one series of definiteelectro-chemical actions_ (505. ). I do not mean to say that no exceptionswill appear: perhaps some may arise, especially amongst substances existingonly by weak affinity; but I do not expect that any will seriously disturbthe result announced. If, in the well-considered, well-examined, and, I maysurely say, well-ascertained doctrines of the definite nature of ordinarychemical affinity, such exceptions occur, as they do in abundance, yet, without being allowed to disturb our minds as to the general conclusion, they ought also to be allowed if they should present themselves at this, the opening of a new view of electro-chemical action; not being held up asobstructions to those who may be engaged in rendering that view more andmore perfect, but laid aside for a while, in hopes that their perfect andconsistent explanation will ultimately appear. 

 * * * * *

822. The doctrine of _definite electro-chemical action_ just laid down, and, I believe, established, leads to some new views of the relations andclassifications of bodies associated with or subject to this action. Someof these I shall proceed to consider. 

823. In the first place, compound bodies may be separated into two greatclasses, namely, those which are decomposable by the electric current, andthose which are not: of the latter, some are conductors, othersnon-conductors, of voltaic electricity[A]. The former do not depend fortheir decomposability upon the nature of their elements only; for, of thesame two elements, bodies may be formed, of which one shall belong to oneclass and another to the other class; but probably on the proportions also(697. ). It is further remarkable, that with very few, if any, exceptions(414. 691. ), these decomposable bodies are exactly those governed by theremarkable law of conduction I have before described (694. ); for that lawdoes not extend to the many compound fusible substances that are excludedfrom this class. I propose to call bodies of this, the decomposable class, _Electrolytes_ (664. ). 

 [A] I mean here by voltaic electricity, merely electricity from a most abundant source, but having very small intensity. 

824. Then, again, the substances into which these divide, under theinfluence of the electric current, form an exceedingly important generalclass. They are combining bodies; are directly associated with thefundamental parts of the doctrine of chemical affinity; and have each adefinite proportion, in which they are always evolved during electrolyticaction. I have proposed to call these bodies generally _ions_, orparticularly _anions_ and _cations_, according as they appear at the_anode_ or _cathode_ (665. ); and the numbers representing the proportionsin which they are evolved _electro-chemical equivalents_. Thus hydrogen, oxygen, chlorine, iodine, lead, tin are _ions_; the three former are_anions_, the two metals are _cations_, and 1, 8, 3, 125, 104, 58, aretheir _electro-chemical equivalents_ nearly. 

825. A summary of certain points already ascertained respecting_electrolytes, ions_, and _electro-chemical equivalents_, may be given inthe following general form of propositions, without, I hope, including anyserious error. 

826. I. A single _ion_, i. E. One not in combination with another, will haveno tendency to pass to either of the electrodes, and will be perfectlyindifferent to the passing current, unless it be itself a compound of moreelementary _ions_, and so subject to actual decomposition. Upon this factis founded much of the proof adduced in favour of the new theory ofelectro-chemical decomposition, which I put forth in a former series ofthese Researches (518. &c. ). 

827. Ii. If one _ion_ be combined in right proportions (697. ) with anotherstrongly opposed to it in its ordinary chemical relations, i. E. If an_anion_ be combined with a _cation_, then both will travel, the one to the_anode_, the other to the _cathode_, of the decomposing body (530, 542. 547. ). 

828. Iii. If, therefore, an _ion_ pass towards one of the electrodes, another _ion_ must also be passing simultaneously to the other electrode, although, from secondary action, it may not make its appearance (743. ). 

829. Iv. A body decomposable directly by the electric current, i. E. An_electrolyte_, must consist of two _ions_, and must also render them upduring the act of decomposition. 

830. V. There is but one _electrolyte_ composed of the same two elementary_ions_; at least such appears to be the fact (697. ), dependent upon a law, that _only single electro-chemical equivalents of elementary ions can go tothe electrodes, and not multiples_. 

831. Vi. A body not decomposable when alone, as boracic acid, is notdirectly decomposable by the electric current when in combination (780. ). It may act as an _ion_ going wholly to the _anode_ or _cathode_, but doesnot yield up its elements, except occasionally by a secondary action. Perhaps it is superfluous for me to point out that this proposition has _norelation_ to such cases as that of water, which, by the presence of otherbodies, is rendered a better conductor of electricity, and _therefore_ ismore freely decomposed. 

832. Vii. The nature of the substance of which the electrode is formed, provided it be a conductor, causes no difference in theelectro-decomposition, either in kind or degree (807. 813. ): but itseriously influences, by secondary action (714. ), the state in which thefinally appear. Advantage may be taken of this principle in combining and_ions_ collecting such _ions_ as, if evolved in their _free_ state, wouldbe unmanageable[A]. 

 [A] It will often happen that the electrodes used may be of such a nature as, with the fluid in which they are immersed, to produce an electric current, either according with or opposing that of the voltaic arrangement used, and in this way, or by direct chemical action, may sadly disturb the results. Still, in the midst of all these confusing effects, the electric current, which actually passes in any direction through the body suffering decomposition, will produce its own definite electrolytic action. 

833. Viii. A substance which, being used as the electrode, can combine withthe _ion_ evolved against it, is also, I believe, an _ion_, and combines, in such cases, in the quantity represented by its _electro-chemicalequivalent_. All the experiments I have made agree with this view; and itseems to me, at present, to result as a necessary consequence. Whether, inthe secondary actions that take place, where the _ion_ acts, not upon thematter of the electrode, but on that which is around it in the liquid(744. ), the same consequence follows, will require more extendedinvestigation to determine. 

834. Ix. Compound _ions_ are not necessarily composed of electro-chemicalequivalents of simple _ions_. For instance, sulphuric acid, boracic acid, phosphoric acid, are _ions_, but not _electrolytes_, i. E. Not composed ofelectro-chemical equivalents of simple _ions_. 

835. X. Electro-chemical equivalents are always consistent; i. E. The samenumber which represents the equivalent of a substance A when it isseparating from a substance B, will also represent A when separating from athird substance C. Thus, 8 is the electro-chemical equivalent of oxygen, whether separating from hydrogen, or tin, or lead; and 103. 5 is theelectrochemical equivalent of lead, whether separating from oxygen, orchlorine, or iodine. 

836. Xi. Electro-chemical equivalents coincide, and are the same, withordinary chemical equivalents. 

837. By means of experiment and the preceding propositions, a knowledge of_ions_ and their electro-chemical equivalents may be obtained in variousways. 

838. In the first place, they may be determined directly, as has been donewith hydrogen, oxygen, lead, and tin, in the numerous experiments alreadyquoted. 

839. In the next place, from propositions ii. And iii. , may be deduced theknowledge of many other _ions_, and also their equivalents. When chlorideof lead was decomposed, platina being used for both electrodes (395. ), there could remain no more doubt that chlorine was passing to the _anode_, although it combined with the platina there, than when the positiveelectrode, being of plumbago (794. ), allowed its evolution in the freestate; neither could there, in either case, remain any doubt that for every103. 5 parts of lead evolved at the _cathode_, 36 parts of chlorine wereevolved at the _anode_, for the remaining chloride of lead was unchanged. So also, when in a metallic solution one volume of oxygen, or a secondarycompound containing that proportion, appeared at the _anode_, no doubtcould arise that hydrogen, equivalent to two volumes, had been determinedto the _cathode_, although, by a secondary action, it had been employed inreducing oxides of lead, copper, or other metals, to the metallic state. Inthis manner, then, we learn from the experiments already described in theseResearches, that chlorine, iodine, bromine, fluorine, calcium, potassium, strontium, magnesium, manganese, &c. , are _ions_ and that their_electro-chemical equivalents_ are the same as their _ordinary chemicalequivalents_. 

840. Propositions iv. And v. Extend our means of gaining information. Forif a body of known chemical composition is found to be decomposable, andthe nature of the substance evolved as a primary or even a secondary result(743. 777. ) at one of the electrodes, be ascertained, the electro-chemicalequivalent of that body may be deduced from the known constant compositionof the substance evolved. Thus, when fused protiodide of tin is decomposedby the voltaic current (804. ), the conclusion may be drawn, that both theiodine and tin are _ions_, and that the proportions in which they combinein the fused compound express their electro-chemical equivalents. Again, with respect to the fused iodide of potassium (805. ), it is an electrolyte;and the chemical equivalents will also be the electro-chemical equivalents. 

841. If proposition viii. Sustain extensive experimental investigation, then it will not only help to confirm the results obtained by the use ofthe other propositions, but will give abundant original information of itsown. 

842. In many instances, the _secondary results_ obtained by the action ofthe evolved _ion_ on the substances present in the surrounding liquid orsolution, will give the electro-chemical equivalent. Thus, in the solutionof acetate of lead, and, as far as I have gone, in other proto-saltssubjected to the reducing action of the nascent hydrogen at the _cathode_, the metal precipitated has been in the same quantity as if it had been aprimary product, (provided no free hydrogen escaped there, ) and thereforegave accurately the number representing its electro-chemical equivalent. 

843. Upon this principle it is that secondary results may occasionally beused as measurers of the volta-electric current (706. 740. ); but there arenot many metallic solutions that answer this purpose well: for unless themetal is easily precipitated, hydrogen will be evolved at the _cathode_ andvitiate the result. If a soluble peroxide is formed at the _anode_, or ifthe precipitated metal crystallize across the solution and touch thepositive electrode, similar vitiated results are obtained. I expect to findin some salts, as the acetates of mercury and zinc, solutions favourablefor this use. 

844. After the first experimental investigations to establish the definitechemical action of electricity, I have not hesitated to apply the morestrict results of chemical analysis to correct the numbers obtained aselectrolytic results. This, it is evident, may be done in a great number ofcases, without using too much liberty towards the due severity ofscientific research. The series of numbers representing electro-chemicalequivalents must, like those expressing the ordinary equivalents ofchemically acting bodies, remain subject to the continual correction ofexperiment and sound reasoning. 

845. I give the following brief Table of _ions_ and their electro-chemicalequivalents, rather as a specimen of a first attempt than as anything thatcan supply the want which must very quickly be felt, of a full and completetabular account of this class of bodies. Looking forward to such a table asof extreme utility (if well-constructed) in developing the intimaterelation of ordinary chemical affinity to electrical actions, andidentifying the two, not to the imagination merely, but to the convictionof the senses and a sound judgement, I may be allowed to express a hope, that the endeavour will always be to make it a table of _real_, and not_hypothetical_, electro-chemical equivalents; for we shall else overrun thefacts, and lose all sight and consciousness of the knowledge lying directlyin our path. 

846. The equivalent numbers do not profess to be exact, and are takenalmost entirely from the chemical results of other philosophers in whom Icould repose more confidence, as to these points, than in myself. 

847. TABLE OF IONS. 

_Anions_. 

Oxygen 8Chlorine 35. 5Iodine 126Bromine 78. 3Fluorine 18. 7Cyanogen 26Sulphuric acid 40Selenic acid 64Nitric acid 54Chloric acid 75. 5Phosphoric acid 35. 7Carbonic acid 22Boracic acid 24Acetic acid 51Tartaric acid 66Citric acid 58Oxalic acid 36Sulphur (?) 16Selenium (?)Salpho-cyanogen

_Cations_. 

Hydrogen 1Potassium 39. 2Sodium 23. 3Lithium 10Barium 68. 7Strontium 43. 8Calcium 20. 5Magnesium 12. 7Manganese 27. 7Zinc 32. 5Tin 57. 9Lead 103. 5Iron 28Copper 31. 6Cadmium 55. 8Cerium 46Cobalt 29. 5Nickel 29. 5Antimony 61. 67Bismuth 71Mercury 200Silver 108Platina 98. 6?Gold (?)

Ammonia 17Potassa 47. 2Soda 31. 3Lithia 18Baryta 76. 7Strontia 51. 8Lime 28. 5Magnesia 20. 7Alumina. (?)Protoxides generally. Quinia 171. 6Cinchona 160Morphia 290Vegeto-alkalies generally. 

848. This Table might be further arrange into groups of such substances aseither act with, or replace, each other. Thus, for instance, acids andbases act in relation to each other; but they do not act in associationwith oxygen, hydrogen, or elementary substances. There is indeed little orno doubt that, when the electrical relations of the particles of mattercome to be closely examined, this division must be made. The simplesubstances, with cyanogen, sulpho-cyanogen, and one or two other compoundbodies, will probably form the first group; and the acids and bases, withsuch analogous compounds as may prove to be _ions_, the second group. Whether these will include all _ions_, or whether a third class of morecomplicated results will be required, must be decided by futureexperiments. 

849. It is _probable_ that all our present elementary bodies are _ions_, but that is not as yet certain. There are some, such as carbon, phosphorus, nitrogen, silicon, boron, alumium, the right of which to the title of _ion_it is desirable to decide as soon as possible. There are also many compoundbodies, and amongst them alumina and silica, which it is desirable to classimmediately by unexceptionable experiments. It is also _possible_, that allcombinable bodies, compound as well as simple, may enter into the class of_ions_; but at present it does not seem to me probable. Still theexperimental evidence I have is so small in proportion to what mustgradually accumulate around, and bear upon, this point, that I am afraid togive a strong opinion upon it. 

850. I think I cannot deceive myself in considering the doctrine ofdefinite electro-chemical action as of the utmost importance. It touches byits facts more directly and closely than any former fact, or set of facts, have done, upon the beautiful idea, that ordinary chemical affinity is amere consequence of the electrical attractions of the particles ofdifferent kinds of matter; and it will probably lead us to the means bywhich we may enlighten that which is at present so obscure, and eitherfully demonstrate the truth of the idea, or develope that which ought toreplace it. 

851. A very valuable use of electro-chemical equivalents will be to decide, in cases of doubt, what is the true chemical equivalent, or definiteproportional, or atomic number of a body; for I have such conviction thatthe power which governs electro-decomposition and ordinary chemicalattractions is the same; and such confidence in the overruling influence ofthose natural laws which render the former definite, as to feel nohesitation in believing that the latter must submit to them also. Suchbeing the case, I can have, no doubt that, assuming hydrogen as 1, anddismissing small fractions for the simplicity of expression, the equivalentnumber or atomic weight of oxygen is 8, of chlorine 36, of bromine 78. 4, oflead 103. 5, of tin 59, &c. , notwithstanding that a very high authoritydoubles several of these numbers. 

§ 13. _On the absolute quantity of Electricity associated with theparticles or atoms of Matter. _

852. The theory of definite electrolytical or electro-chemical actionappears to me to touch immediately upon the _absolute quantity_ ofelectricity or electric power belonging to different bodies. It isimpossible, perhaps, to speak on this point without committing oneselfbeyond what present facts will sustain; and yet it is equally impossible, and perhaps would be impolitic, not to reason upon the subject. Although weknow nothing of what an atom is, yet we cannot resist forming some idea ofa small particle, which represents it to the mind; and though we are inequal, if not greater, ignorance of electricity, so as to be unable to saywhether it is a particular matter or matters, or mere motion of ordinarymatter, or some third kind of power or agent, yet there is an immensity offacts which justify us in believing that the atoms of matter are in someway endowed or associated with electrical powers, to which they owe theirmost striking qualities, and amongst them their mutual chemical affinity. As soon as we perceive, through the teaching of Dalton, that chemicalpowers are, however varied the circumstances in which they are exerted, definite for each body, we learn to estimate the relative degree of forcewhich resides in such bodies: and when upon that knowledge comes the fact, that the electricity, which we appear to be capable of loosening from itshabitation for a while, and conveying from place to place, _whilst itretains its chemical force_, can be measured out, and being so measured isfound to be _as definite in its action_ as any of _those portions_ which, remaining associated with the particles of matter, give them their_chemical relation_; we seem to have found the link which connects theproportion of that we have evolved to the proportion of that belonging tothe particles in their natural state. 

853. Now it is wonderful to observe how small a quantity of a compound bodyis decomposed by a certain portion of electricity. Let us, for instance, consider this and a few other points in relation to water. _One grain_ ofwater, acidulated to facilitate conduction, will require an electriccurrent to be continued for three minutes and three quarters of time toeffect its decomposition, which current must be powerful enough to retain aplatina wire 1/104 of an inch in thickness[A], red-hot, in the air duringthe whole time; and if interrupted anywhere by charcoal points, willproduce a very brilliant and constant star of light. If attention be paidto the instantaneous discharge of electricity of tension, as illustrated inthe beautiful experiments of Mr. Wheatstone[B], and to what I have saidelsewhere on the relation of common and voltaic electricity (371. 375. ), itwill not be too much to say that this necessary quantity of electricity isequal to a very powerful flash of lightning. Yet we have it under perfectcommand; can evolve, direct, and employ it at pleasure; and when it hasperformed its full work of electrolyzation, it has only separated theelements of _a single grain of water_. 

 [A] I have not stated the length of wire used, because I find by experiment, as would be expected in theory, that it is indifferent. The same quantity of electricity which, passed in a given time, can heat an inch of platina wire of a certain diameter red-hot, can also heat a hundred, a thousand, or any length of the same wire to the same degree, provided the cooling circumstances are the same for every part in all cases. This I have proved by the volta-electrometer. I found that whether half an inch or eight inches were retained at one constant temperature of dull redness, equal quantities of water were decomposed in equal times. When the half-inch was used, only the centre portion of wire was ignited. A fine wire may even be used as a rough but ready regulator of a voltaic current; for if it be made part of the circuit, and the larger wires communicating with it be shifted nearer to or further apart, so as to keep the portion of wire in the circuit sensibly at the same temperature, the current passing through it will be nearly uniform. 

 [B] Literary Gazette, 1833, March 1 and 8. Philosophical Magazine, 1833, p. 201. L'Institut, 1833, p. 261. 

854. On the other hand, the relation between the conduction of theelectricity and the decomposition of the water is so close, that one cannottake place without the other. If the water is altered only in that smalldegree which consists in its having the solid instead of the fluid state, the conduction is stopped, and the decomposition is stopped with it. Whether the conduction be considered as depending upon the decomposition, or not (443. 703. ), still the relation of the two functions is equallyintimate and inseparable. 

855. Considering this close and twofold relation, namely, that withoutdecomposition transmission of electricity does not occur; and, that for agiven definite quantity of electricity passed, an equally definite andconstant quantity of water or other matter is decomposed; considering alsothat the agent, which is electricity, is simply employed in overcomingelectrical powers in the body subjected to its action; it seems a probable, and almost a natural consequence, that the quantity which passes is the_equivalent_ of, and therefore equal to, that of the particles separated;i. E. That if the electrical power which holds the elements of a grain ofwater in combination, or which makes a grain of oxygen and hydrogen in theright proportions unite into water when they are made to combine, could bethrown into the condition of _a current_, it would exactly equal thecurrent required for the separation of that grain of water into itselements again. 

856. This view of the subject gives an almost overwhelming idea of theextraordinary quantity or degree of electric power which naturally belongsto the particles of matter; but it is not inconsistent in the slightestdegree with the facts which can be brought to bear on this point. Toillustrate this I must say a few words on the voltaic pile[A]. 

 [A] By the term voltaic pile, I mean such apparatus or arrangement of metals as up to this time have been called so, and which contain water, brine, acids, or other aqueous solutions or decomposable substances (476. ), between their plates. Other kinds of electric apparatus may be hereafter invented, and I hope to construct some not belonging to the class of instruments discovered by Volta. 

857. Intending hereafter to apply the results given in this and thepreceding series of Researches to a close investigation of the source ofelectricity in the voltaic instrument, I have refrained from forming anydecided opinion on the subject; and without at all meaning to dismissmetallic contact, or the contact of dissimilar substances, beingconductors, but not metallic, as if they had nothing to do with the originof the current, I still am fully of opinion with Davy, that it is at least continued bychemical action, and that the supply constituting the current is almostentirely from that source. 

858. Those bodies which, being interposed between the metals of the voltaicpile, render it active, _are all of them electrolytes_ (476. ); and itcannot but press upon the attention of every one engaged in consideringthis subject, that in those bodies (so essential to the pile) decompositionand the transmission of a current are so intimately connected, that onecannot happen without the other. This I have shown abundantly in water, andnumerous other cases (402. 476. ). If, then, a voltaic trough have itsextremities connected by a body capable of being decomposed, as water, weshall have a continuous current through the apparatus; and whilst itremains in this state we may look at the part where the acid is acting uponthe plates, and that where the current is acting upon the water, as thereciprocals of each other. In both parts we have the two conditions_inseparable in such bodies as these_, namely, the passing of a current, and decomposition; and this is as true of the cells in the battery as ofthe water cell; for no voltaic battery has as yet been constructed in whichthe chemical action is only that of combination: _decomposition is alwaysincluded_, and is, I believe, an essential chemical part. 

859. But the difference in the two parts of the connected battery, that is, the decomposition or experimental cell, and the acting cells, is simplythis. In the former we urge the current through, but it, apparently ofnecessity, is accompanied by decomposition: in the latter we causedecompositions by ordinary chemical actions, (which are, however, themselves electrical, ) and, as a consequence, have the electrical current;and as the decomposition dependent upon the current is definite in theformer case, so is the current associated with the decomposition alsodefinite in the latter (862. &c. ). 

860. Let us apply this in support of what I have surmised respecting theenormous electric power of each particle or atom of matter (856. ). I showedin a former series of these Researches on the relation by measure of commonand voltaic electricity, that two wires, one of platina and one of zinc, each one-eighteenth of an inch in diameter, placed five-sixteenths of aninch apart, and immersed to the depth of five-eighths of an inch in acid, consisting of one drop of oil of vitriol and four ounces of distilled waterat a temperature of about 60° Fahr. , and connected at the other extremitiesby a copper wire eighteen feet long, and one-eighteenth of an inch inthickness, yielded as much electricity in little more than three seconds oftime as a Leyden battery charged by thirty turns of a very large andpowerful plate electric machine in full action (371. ). This quantity, though sufficient if passed at once through the head of a rat or cat tohave killed it, as by a flash of lightning, was evolved by the mutualaction of so small a portion of the zinc wire and water in contact with it, that the loss of weight sustained by either would be inappreciable by ourmost delicate instruments; and as to the water which could be decomposed bythat current, it must have been insensible in quantity, for no trace ofhydrogen appeared upon the surface of the platina during those threeseconds. 

861. What an enormous quantity of electricity, therefore, is required forthe decomposition of a single grain of water! We have already seen that itmust be in quantity sufficient to sustain a platina wire 1/104 of an inchin thickness, red-hot, in contact with the air, for three minutes and threequarters (853. ), a quantity which is almost infinitely greater than thatwhich could be evolved by the little standard voltaic arrangement to whichI have just referred (860. 871. ). I have endeavoured to make a comparisonby the loss of weight of such a wire in a given time in such an acid, according to a principle and experiment to be almost immediately described(862. ); but the proportion is so high that I am almost afraid to mentionit. It would appear that 800, 000 such charges of the Leyden battery as Ihave referred to above, would be necessary to supply electricity sufficientto decompose a single grain of water; or, if I am right, to equal thequantity of electricity which is naturally associated with the elements ofthat grain of water, endowing them with their mutual chemical affinity. 

862. In further proof of this high electric condition of the particles ofmatter, and the _identity as to quantity of that belonging to them withthat necessary for their separation_, I will describe an experiment ofgreat simplicity but extreme beauty, when viewed in relation to theevolution of an electric current and its decomposing powers. 

863. A dilute sulphuric acid, made by adding about one part by measure ofoil of vitriol to thirty parts of water, will act energetically upon apiece of zinc plate in its ordinary and simple state: but, as Mr. Sturgeonhas shown[A], not at all, or scarcely so, if the surface of the metal hasin the first instance been amalgamated; yet the amalgamated zinc will actpowerfully with platina as an electromotor, hydrogen being evolved on thesurface of the latter metal, as the zinc is oxidized and dissolved. Theamalgamation is best effected by sprinkling a few drops of mercury upon thesurface of the zinc, the latter being moistened with the dilute acid, andrubbing with the fingers or two so as to extend the liquid metal over thewhole of the surface. Any mercury in excess, forming liquid drops upon thezinc, should be wiped off[B]. 

 [A] Recent Experimental Researches, &c. , 1830, p. 74, &c. 

 [B] The experiment may be made with pure zinc, which, as chemists well know, is but slightly acted upon by dilute sulphuric acid in comparison with ordinary zinc, which during the action is subject to an infinity of voltaic actions. See De la Rive on this subject, Bibliothèque Universelle, 1830, p. 391. 

864. Two plates of zinc thus amalgamated were dried and accurately weighed;one, which we will call A, weighed 163. 1 grains; the other, to be called B, weighed 148. 3 grains. They were about five inches long, and 0. 4 of an inchwide. An earthenware pneumatic trough was filled with dilute sulphuricacid, of the strength just described (863. ), and a gas jar, also filledwith the acid, inverted in it[A]. A plate of platina of nearly the samelength, but about three times as wide as the zinc plates, was put up intothis jar. The zinc plate A was also introduced into the jar, and brought incontact with the platina, and at the same moment the plate B was put intothe acid of the trough, but out of contact with other metallic matter. 

 [A] The acid was left during a night with a small piece of unamalgamated zinc in it, for the purpose of evolving such air as might be inclined to separate, and bringing the whole into a constant state. 

865. Strong action immediately occurred in the jar upon the contact of thezinc and platina plates. Hydrogen gas rose from the platina, and wascollected in the jar, but no hydrogen or other gas rose from _either_ zincplate. In about ten or twelve minutes, sufficient hydrogen having beencollected, the experiment was stopped; during its progress a few smallbubbles had appeared upon plate B, but none upon plate A. The plates werewashed in distilled water, dried, and reweighed. Plate B weighed 148. 3grains, as before, having lost nothing by the direct chemical action of theacid. Plate A weighed 154. 65 grains, 8. 45 grains of it having been oxidizedand dissolved during the experiment. 

866. The hydrogen gas was next transferred to a water-trough and measured;it amounted to 12. 5 cubic inches, the temperature being 52°, and thebarometer 29. 2 inches. This quantity, corrected for temperature, pressure, and moisture, becomes 12. 15453 cubic inches of dry hydrogen at meantemperature and pressure; which, increased by one half for the oxygen thatmust have gone to the _anode_, i. E. To the zinc, gives 18. 232 cubic inchesas the quantity of oxygen and hydrogen evolved from the water decomposed bythe electric current. According to the estimate of the weight of the mixedgas before adopted (791. ), this volume is equal to 2. 3535544 grains, whichtherefore is the weight of water decomposed; and this quantity is to 8. 45, the quantity of zinc oxidized, as 9 is to 32. 31. Now taking 9 as theequivalent number of water, the number 32. 5 is given as the equivalentnumber of zinc; a coincidence sufficiently near to show, what indeed couldnot but happen, that for an equivalent of zinc oxidized an equivalent ofwater must be decomposed[A]. 

 [A] The experiment was repeated several times with the same results. 

867. But let us observe _how_ the water is decomposed. It is electrolyzed, i. E. Is decomposed voltaically, and not in the ordinary manner (as toappearance) of chemical decompositions; for the oxygen appears at the_anode_ and the hydrogen at the _cathode_ of the body under decomposition, and these were in many parts of the experiment above an inch asunder. Again, the ordinary chemical affinity was not enough under thecircumstances to effect the decomposition of the water, as was abundantlyproved by the inaction on plate B; the voltaic current was essential. Andto prevent any idea that the chemical affinity was almost sufficient todecompose the water, and that a smaller current of electricity might, underthe circumstances, cause the hydrogen to pass to the _cathode_, I need onlyrefer to the results which I have given (807. 813. ) to shew that thechemical action at the electrodes has not the slightest influence over the_quantities_ of water or other substances decomposed between them, but thatthey are entirely dependent upon the quantity of electricity which passes. 

868. What, then, follows as a necessary consequence of the wholeexperiment? Why, this: that the chemical action upon 32. 31 parts, or oneequivalent of zinc, in this simple voltaic circle, was able to evolve suchquantity of electricity in the form of a current, as, passing throughwater, should decompose 9 parts, or one equivalent of that substance: andconsidering the definite relations of electricity as developed in thepreceding parts of the present paper, the results prove that the quantityof electricity which, being naturally associated with the particles ofmatter, gives them their combining power, is able, when thrown into acurrent, to separate those particles from their state of combination; or, in other words, that _the electricity which decomposes, and that which isevolved by the decomposition of a certain quantity of matter, are alike. _

869. The harmony which this theory of the definite evolution and theequivalent definite action of electricity introduces into the associatedtheories of definite proportions and electrochemical affinity, is verygreat. According to it, the equivalent weights of bodies are simply thosequantities of them which contain equal quantities of electricity, or havenaturally equal electric powers; it being the ELECTRICITY which_determines_ the equivalent number, _because_ it determines the combiningforce. Or, if we adopt the atomic theory or phraseology, then the atoms ofbodies which are equivalents to each other in their ordinary chemicalaction, have equal quantities of electricity naturally associated withthem. But I must confess I am jealous of the term _atom_; for though it isvery easy to talk of atoms, it is very difficult to form a clear idea oftheir nature, especially when compound bodies are under consideration. 

870. I cannot refrain from recalling here the beautiful idea put forth, Ibelieve, by Berzelius (703. ) in his development of his views of theelectro-chemical theory of affinity, that the heat and light evolved duringcases of powerful combination are the consequence of the electric dischargewhich is at the moment taking place. The idea is in perfect accordance withthe view I have taken of the _quantity_ of electricity associated with theparticles of matter. 

871. In this exposition of the law of the definite action of electricity, and its corresponding definite proportion in the particles of bodies, I donot pretend to have brought, as yet, every case of chemical orelectro-chemical action under its dominion. There are numerousconsiderations of a theoretical nature, especially respecting the compoundparticles of matter and the resulting electrical forces which they ought topossess, which I hope will gradually receive their development; and thereare numerous experimental cases, as, for instance, those of compoundsformed by weak affinities, the simultaneous decomposition of water andsalts, &c. , which still require investigation. But whatever the results onthese and numerous other points may be, I do not believe that the factswhich I have advanced, or even the general laws deduced from them, willsuffer any serious change; and they are of sufficient importance to justifytheir publication, though much may yet remain imperfect or undone. Indeed, it is the great beauty of our science, CHEMISTRY, that advancement in it, whether in a degree great or small, instead of exhausting the subjects ofresearch, opens the doors to further and more abundant knowledge, overflowing with beauty and utility, to those who will be at the easypersonal pains of undertaking its experimental investigation. 

872. The definite production of electricity (868. ) in association with itsdefinite action proves, I think, that the current of electricity in thevoltaic pile: is sustained by chemical decomposition, or rather by chemicalaction, and not by contact only. But here, as elsewhere (857. ), I beg toreserve my opinion as to the real action of contact, not having yet beenable to make up my mind as to whether it is an exciting cause of thecurrent, or merely necessary to allow of the conduction of electricity, otherwise generated, from one metal to the other. 

873. But admitting that chemical action is the source of electricity, whatan infinitely small fraction of that which is active do we obtain andemploy in our voltaic batteries! Zinc and platina wires, one-eighteenth ofan inch in diameter and about half an inch long, dipped into dilutesulphuric acid, so weak that it is not sensibly sour to the tongue, orscarcely to our most delicate test-papers, will evolve more electricity inone-twentieth of a minute (860. ) than any man would willingly allow to passthrough his body at once. The chemical action of a grain of water upon fourgrains of zinc can evolve electricity equal in quantity to that of apowerful thunder-storm (868. 861. ). Nor is it merely true that the quantityis active; it can be directed and made to perform its full equivalent duty(867. &c. ). Is there not, then, great reason to hope and believe that, by acloser _experimental_ investigation of the principles which govern thedevelopment and action of this subtile agent, we shall be able to increasethe power of our batteries, or invent new instruments which shall athousandfold surpass in energy those which we at present possess?

874. Here for a while I must leave the consideration of the _definitechemical action of electricity_. But before I dismiss this series ofexperimental Researches, I would call to mind that, in a former series, Ishowed the current of electricity was also _definite in its magneticaction_ (216. 366. 367. 376. 377. ); and, though this result was not pursuedto any extent, I have no doubt that the success which has attended thedevelopment of the chemical effects is not more than would accompany aninvestigation of the magnetic phenomena. 

_Royal Institution, December 31st, 1833. _

EIGHTH SERIES. 

§14. _On the Electricity of the Voltaic Pile; its source, quantity, intensity, and general characters. _ ¶ i. _On simple Voltaic Circles. _ ¶ ii. _On the intensity necessary for Electrolyzation. _ ¶ iii. _On associatedVoltaic Circles, or the Voltaic Battery. _ ¶ iv. _On the resistance of anElectrolyte to Electrolytic action. _ ¶ v. _General remarks on the activeVoltaic Battery. _

Received April 7, --Read June 5, 1831. 

¶ i. _On simple Voltaic Circles. _

875. The great question of the source of electricity, in the voltaic pilehas engaged the attention of so many eminent philosophers, that a man ofliberal mind and able to appreciate their powers would probably conclude, although he might not have studied the question, that the truth wassomewhere revealed. But if in pursuance of this impression he were inducedto enter upon the work of collating results and conclusions, he would findsuch contradictory evidence, such equilibrium of opinion, such variationand combination of theory, as would leave him in complete doubt respectingwhat he should accept as the true interpretation of nature: he would beforced to take upon himself the labour of repeating and examining thefacts, and then use his own judgement on them in preference to that ofothers. 

876. This state of the subject must, to those who have made up their mindson the matter, be my apology for entering upon its investigation. The viewsI have taken of the definite action of electricity in decomposing bodies(783. ), and the identity of the power so used with the power to be overcome(855. ), founded not on a mere opinion or general notion, but on factswhich, being altogether new, were to my mind precise and conclusive, gaveme, as I conceived, the power of examining the question with advantages notbefore possessed by any, and which might compensate, on my part, for thesuperior clearness and extent of intellect on theirs. Such are theconsiderations which have induced me to suppose I might help in decidingthe question, and be able to render assistance in that great service ofremoving _doubtful knowledge_. Such knowledge is the early morning light ofevery advancing science, and is essential to its development; but the manwho is engaged in dispelling that which is deceptive in it, and revealingmore clearly that which is true, is as useful in his place, and asnecessary to the general progress of the science, as he who first brokethrough the intellectual darkness, and opened a path into knowledge beforeunknown to man. 

877. The identity of the force constituting the voltaic current orelectrolytic agent, with that which holds the elements of electrolytestogether (855. ), or in other words with chemical affinity, seemed toindicate that the electricity of the pile itself was merely a mode ofexertion, or exhibition, or existence of _true chemical action_, or ratherof its cause; and I have consequently already said that I agree with thosewho believe that the _supply_ of electricity is due to chemical powers(857. ). 

878. But the great question of whether it is originally due to metalliccontact or to chemical action, i. E. Whether it is the first or the secondwhich _originates_ and determines the current, was to me still doubtful;and the beautiful and simple experiment with amalgamated zinc and platina, which I have described minutely as to its results (863, &c. ), did notdecide the point; for in that experiment the chemical action does not takeplace without the contact of the metals, and the metallic contact isinefficient without the chemical action. Hence either might be looked uponas the _determining_ cause of the current. 

879. I thought it essential to decide this question by the simplestpossible forms of apparatus and experiment, that no fallacy might beinadvertently admitted. The well-known difficulty of effectingdecomposition by a single pair of plates, except in the fluid exciting theminto action (863. ), seemed to throw insurmountable obstruction in the wayof such experiments; but I remembered the easy decomposability of thesolution of iodide of potassium (316. ), and seeing no theoretical reason, if metallic contact was not _essential_, why true electro-decompositionshould not be obtained without it, even in a single circuit, I perseveredand succeeded. 

880. A plate of zinc, about eight inches long and half an inch wide, wascleaned and bent in the middle to a right angle, fig. 73 _a_, Plate VI. Aplate of platina, about three inches long and half an inch wide, wasfastened to a platina wire, and the latter bent as in the figure, _b_. These two pieces of metal were arranged together as delineated, but as yetwithout the vessel _c_, and its contents, which consisted of dilutesulphuric acid mingled with a little nitric acid. At _x_ a piece of foldedbibulous paper, moistened in a solution of iodide of potassium, was placedon the zinc, and was pressed upon by the end of the platina wire. Whenunder these circumstances the plates were dipped into the acid of thevessel _c_, there was an immediate effect at _x_, the iodide beingdecomposed, and iodine appearing at the _anode_ (663. ), i. E. Against theend of the platina wire. 

881. As long as the lower ends of the plates remained in the acid theelectric current continued, and the decomposition proceeded at _x_. Onremoving the end of the wire from place to place on the paper, the effectwas evidently very powerful; and on placing a piece of turmeric paperbetween the white paper and zinc, both papers being moistened with thesolution of iodide of potassium, alkali was evolved at the _cathode_ (663. )against the zinc, in proportion to the evolution of iodine at the _anode_. Hence the decomposition was perfectly polar, and decidedly dependent upon acurrent of electricity passing from the zinc through the acid to theplatina in the vessel _c_, and back from the platina through the solutionto the zinc at the paper _x_. 

882. That the decomposition at _x_ was a true electrolytic action, due to acurrent determined by the state of things in the vessel _c_, and notdependent upon any mere direct chemical action of the zinc and platina onthe iodide, or even upon any _current_ which the solution of iodide mightby its action on those metals tend to form at _x_, was shown, in the firstplace, by removing the vessel _c_ and its acid from the plates, when alldecomposition at _x_ ceased, and in the next by connecting the metals, either in or out of the acid, together, when decomposition of the iodide at_x_ occurred, but in a _reverse order_; for now alkali appeared against theend of the platina wire, and the iodine passed to the zinc, the currentbeing the contrary of what it was in the former instance, and produceddirectly by the difference of action of the solution in the paper on thetwo metals. The iodine of course _combined_ with the zinc. 

883. When this experiment was made with pieces of zinc amalgamated over thewhole surface (863. ), the results were obtained with equal facility and inthe same direction, even when only dilute sulphuric acid was contained inthe vessel _c_ (fig. 73. ). Whichsoever end of the zinc was immersed in theacid, still the effects were the same: so that if, for a moment, themercury might be supposed to supply the metallic contact, the inversion ofthe amalgamated piece destroys that objection. The use of _unamalgamatedzinc_ (880. ) removes all possibility of doubt[A]. 

 [A] The following is a more striking mode of making the above elementary experiment. Prepare a plate of zinc, ten or twelve inches long and two inches wide, and clean it thoroughly: provide also two discs of clean platina, about one inch and a half in diameter:--dip three or four folds of bibulous paper into a strong solution of iodide of potassium, place them on the clean zinc at one end of the plate, and put on them one of the platina discs: finally dip similar folds of paper or a piece of linen cloth into a mixture of equal parts nitric acid and water, and place it at the other end of the zinc plate with the second platina disc upon it. In this state of things no change at the solution of the iodide will be perceptible; but if the two discs be connected by a platina (or any other) wire for a second or two, and then that over the iodide be raised, it will be found that the _whole_ of the surface beneath is deeply stained with _evolved iodine_. --_Dec. 1838. _

884 When, in pursuance of other views (930. ), the vessel _c_ was made tocontain a solution of caustic potash in place of acid, still the sameresults occurred. Decomposition of the iodide was effected freely, thoughthere was no metallic contact of dissimilar metals, and the current ofelectricity was in the _same direction_ as when acid was used at the placeof excitement. 

885. Even a solution of common salt in the glass _c_ could produce allthese effects. 

886. Having made a galvanometer with platina wires, and introduced it intothe course of the current between the platina plate and the place ofdecomposition _x_, it was affected, giving indications of currents in thesame direction as those shown to exist by the chemical action. 

887. If we consider these results generally, they lead to very importantconclusions. In the first place, they prove, in the most decisive manner, that _metallic contact is not necessary for the production of the voltaiccurrent. _ In the next place, they show a most extraordinary mutual relationof the chemical affinities of the fluid which _excites_ the current, andthe fluid which is _decomposed_ by it. 

888. For the purpose of simplifying the consideration, let us take theexperiment with amalgamated zinc. The metal so prepared exhibits no effectuntil the current can pass: it at the same time introduces no new action, but merely removes an influence which is extraneous to those belongingeither to the production or the effect of the electric current underinvestigation (1000. ); an influence also which, when present, tends only toconfuse the results. 

889. Let two plates, one of amalgamated zinc and the other of platina, beplaced parallel to each other (fig. 74. ), and introduce a drop of dilutesulphuric acid, _y_, between them at one end: there will be no sensiblechemical action at that spot unless the two plates are connected somewhereelse, as at PZ, by a body capable of conducting electricity. If that bodybe a metal or certain forms of carbon, then the current passes, and, as itcirculates through the fluid at _y_, decomposition ensues. 

890. Then remove the acid from _y_, and introduce a drop of the solution ofiodide of potassium at _x_ (fig. 75. ). Exactly the same set of effectsoccur, except that when the metallic communication is made at PZ, theelectric current is in the opposite direction to what it was before, as isindicated by the arrows, which show the courses of the currents (667. ). 

891. Now _both_ the solutions used are conductors, but the conduction inthem is essentially connected with decomposition (858. ) in a certainconstant order, and therefore the appearance of the elements in certainplaces _shows_ in what direction a current has passed when the solutionsare thus employed. Moreover, we find that when they are used at oppositeends of the plates, as in the last two experiments (889. 890. ), metalliccontact being allowed at the other extremities, the currents are inopposite directions. We have evidently, therefore, the power of opposingthe actions of the two fluids simultaneously to each other at the oppositeends of the plates, using each one as a conductor for the discharge of thecurrent of electricity, which the other tends to generate; in fact, substituting them for metallic contact, and combining both experiments intoone (fig. 76. ). Under these circumstances, there is an opposition offorces: the fluid, which brings into play the stronger set of chemicalaffinities for the zinc, (being the dilute acid, ) overcomes the force ofthe other, and determines the formation and direction of the electriccurrent; not merely making that current pass through the weaker liquid, butactually reversing the tendency which the elements of the latter have inrelation to the zinc and platina if not thus counteracted, and forcing themin the contrary direction to that they are inclined to follow, that its owncurrent may have free course. If the dominant action at _y_ be removed bymaking metallic contact there, then the liquid at _x_ resumes its power; orif the metals be not brought into contact at _y_ but the affinities of thesolution there weakened, whilst those active _x_ are strengthened, then thelatter gains the ascendency, and the decompositions are produced in acontrary order. 

892. Before drawing a _final_ conclusion from this mutual dependence andstate of the chemical affinities of two distant portions of acting fluids(916. ), I will proceed to examine more minutely the various circumstancesunder which the re-action of the body suffering decomposition is renderedevident upon the action of the body, also undergoing decomposition, whichproduces the voltaic current. 

893. The use of _metallic contact_ in a single pair of plates, and thecause of its great superiority above contact made by other kinds of matter, become now very evident. When an amalgamated zinc plate is dipped intodilute sulphuric acid, the force of chemical affinity exerted between themetal and the fluid is not sufficiently powerful to cause sensible actionat the surfaces of contact, and occasion the decomposition of water by theoxidation of the metal, although it _is_ sufficient to produce such acondition of the electricity (or the power upon which chemical affinitydepends) as would produce a current if there were a path open for it (916. 956. ); and that current would complete the conditions necessary, under thecircumstances, for the decomposition of the water. 

894. Now the presence of a piece of platina touching both the zinc and thefluid to be decomposed, opens the path required for the electricity. Its_direct communication_ with the zinc is effectual, far beyond anycommunication made between it and that metal, (i. E. Between the platinaand zinc, ) by means of decomposable conducting bodies, or, in other words, _electrolytes_, as in the experiment already described (891. ); because, when _they_ are used, the chemical affinities between them and the zincproduce a contrary and opposing action to that which is influential in thedilute sulphuric acid; or if that action be but small, still the affinityof their component parts for each other has to be overcome, for they cannotconduct without suffering decomposition; and this decomposition is found_experimentally_ to re-act back upon the forces which in the acid tend toproduce the current (904. 910. &c. ), and in numerous cases entirely toneutralize them. Where direct contact of the zinc and platina occurs, theseobstructing forces are not brought into action, and therefore theproduction and the circulation of the electric current and the concomitantaction of decomposition are then highly favoured. 

895. It is evident, however, that one of these opposing actions may bedismissed, and yet an electrolyte be used for the purpose of completing thecircuit between the zinc and platina immersed separately into the diluteacid; for if, in fig. 73, the platina wire be retained in metallic contactwith the zinc plate _a_, at _x_, and a division of the platina be madeelsewhere, as at _s_, then the solution of iodide placed there, being incontact with platina at both surfaces, exerts no chemical affinities forthat metal; or if it does, they are equal on both sides. Its power, therefore, of forming a current in opposition to that dependent upon theaction of the acid in the vessel _c_, is removed, and only its resistanceto decomposition remains as the obstacle to be overcome by the affinitiesexerted in the dilute sulphuric acid. 

896. This becomes the condition of a single pair of active plates where_metallic contact_ is allowed. In such cases, only one set of opposingaffinities are to be overcome by those which are dominant in the vessel_c_; whereas, when metallic contact is not allowed, two sets of opposingaffinities must be conquered (894. ). 

897. It has been considered a difficult, and by some an impossible thing, to decompose bodies by the current from a single pair of plates, even whenit was so powerful as to heat bars of metal red-hot, as in the case ofHare's calorimeter, arranged as a single voltaic circuit, or of Wollaston'spowerful single pair of metals. This difficulty has arisen altogether fromthe antagonism of the chemical affinity engaged in producing the currentwith the chemical affinity to be overcome, and depends entirely upon theirrelative intensity; for when the sum of forces in one has a certain degreeof superiority over the sum of forces in the other, the former gain theascendency, determine the current, and overcome the latter so as to makethe substance exerting them yield up its elements in perfect accordance, both as to direction and quantity, with the course of those which areexerting the most intense and dominant action. 

898. Water has generally been the substance, the decomposition of which hasbeen sought for as a chemical test of the passage of an electric current. But I now began to perceive a reason for its failure, and for a fact whichI had observed long before (315. 316. ) with regard to the iodide ofpotassium, namely, that bodies would differ in facility of decomposition bya given electric current, according to the condition and intensity of theirordinary chemical affinities. This reason appeared in their _re-action uponthe affinities_ tending to cause the current; and it appeared probable, that many substances might be found which could be decomposed by thecurrent of a single pair of zinc and platina plates immersed in dilutesulphuric acid, although water resisted its action. I soon found this to bethe case, and as the experiments offer new and beautiful proofs of thedirect relation and opposition of the chemical affinities concerned inproducing and in resisting the stream of electricity, I shall brieflydescribe them. 

899. The arrangement of the apparatus was as in fig. 77. The vessel _v_contained dilute sulphuric acid; Z and P are the zinc and platina plates;_a_, _b_, and _c_ are platina wires; the decompositions were effected at_x_, and occasionally, indeed generally, a galvanometer was introduced intothe circuit at _g_: its place only is here given, the circle at _g_ havingno reference to the size of the instrument. Various arrangements were madeat _x_, according to the kind of decomposition to be effected. If a drop ofliquid was to be acted upon, the two ends were merely dipped into it; if asolution contained in the pores of paper was to be decomposed, one of theextremities was connected with a platina plate supporting the paper, whilstthe other extremity rested on the paper, _e_, fig. 81: or sometimes, aswith sulphate of soda, a plate of platina sustained two portions of paper, one of the ends of the wires resting upon each piece, _c_, fig. 86. Thedarts represent the direction of the electric current (667. ). 

900. Solution of _iodide of potassium_, in moistened paper, being placed atthe interruption of the circuit at _x_, was readily decomposed. Iodine wasevolved at the _anode_, and alkali at the _cathode_, of the decomposingbody. 

901. _Protochloride of tin_, when fused and placed at _x_, was also readilydecomposed, yielding perchloride of tin at the _anode_ (779. ), and tin atthe _cathode_. 

902. Fused chloride of silver, placed at _x_, was also easily decomposed;chlorine was evolved at the _anode_, and brilliant metallic silver, eitherin films upon the surface of the liquid, or in crystals beneath, evolved atthe _cathode_. 

903. Water acidulated with sulphuric acid, solution of muriatic acid, solution of sulphate of soda, fused nitre, and the fused chloride andiodide of lead were not decomposed by this single pair of plates, excitedonly by dilute sulphuric acid. 

904. These experiments give abundant proofs that a single pair of platescan electrolyze bodies and separate their elements. They also show in abeautiful manner the direct relation and opposition of the chemicalaffinities concerned at the two points of action. In those cases where thesum of the opposing affinities at _x_ was sufficiently beneath the sum ofthe acting affinities in _v_, decomposition took place; but in those caseswhere they rose higher, decomposition was effectually resisted and thecurrent ceased to pass (891. ). 

905. It is however, evident, that the sum of acting affinities in _v_ maybe increased by using other fluids than dilute sulphuric acid, in whichlatter case, as I believe, it is merely the affinity of the zinc for theoxygen already combined with hydrogen in the water that is exerted inproducing the electric current (919. ): and when the affinities are soincreased, the view I am supporting leads to the conclusion, that bodieswhich resisted in the preceding experiments would then be decomposed, because of the increased difference between their affinities and the actingaffinities thus exalted. This expectation was fully confirmed in thefollowing manner. 

906. A little nitric acid was added to the liquid in the vessel _r_, so asto make a mixture which I shall call diluted nitro-sulphuric acid. Onrepeating the experiments with this mixture, all the substances beforedecomposed again gave way, and much more readily. But, besides that, manywhich before resisted electrolyzation, now yielded up their elements. Thus, solution of sulphate of soda, acted upon in the interstices of litmus andturmeric paper, yielded acid at the _anode_ and alkali at the _cathode_;solution of muriatic acid tinged by indigo yielded chlorine at the _anode_and hydrogen at the _cathode_; solution of nitrate of silver yielded silverat the _cathode_. Again, fused nitre and the fused iodide and chloride oflead were decomposable by the current of this single pair of plates, thoughthey were not by the former (903. ). 

907. A solution of acetate of lead was apparently not decomposed by thispair, nor did water acidulated by sulphuric acid seem at first to give way(973. ). 

908. The increase of intensity or power of the current produced by a simplevoltaic circle, with the increase of the force of the chemical action atthe exciting place, is here sufficiently evident. But in order to place itin a clearer point of view, and to show that the decomposing effect was notat all dependent, in the latter cases, upon the mere capability of evolving_more_ electricity, experiments were made in which the quantity evolvedcould be increased without variation in the intensity of the excitingcause. Thus the experiments in which dilute sulphuric acid was used (899. ), were repeated, using large plates of zinc and platina in the acid; butstill those bodies which resisted decomposition before, resisted it alsounder these new circumstances. Then again, where nitro-sulphuric acid wasused (906. ), mere wires of platina and zinc were immersed in the excitingacid; yet, notwithstanding this change, those bodies were now decomposedwhich resisted any current tending to be formed by the dilute sulphuricacid. For instance, muriatic acid could not be decomposed by a single pairof plates when immersed in dilute sulphuric acid; nor did making thesolution of sulphuric acid strong, nor enlarging the size of the zinc andplatina plates immersed in it, increase the power; but if to a weaksulphuric acid a very little nitric acid was added, then the electricityevolved had power to decompose the muriatic acid, evolving chlorine at the_anode_ and hydrogen at the _cathode_, even when mere wires of metals wereused. This mode of increasing the intensity of the electric current, as itexcludes the effect dependent upon many pairs of plates, or even the effectof making any one acid stronger or weaker, is at once referable to thecondition and force of the chemical affinities which are brought intoaction, and may, both in principle and practice, be considered as perfectlydistinct from any other mode. 

909. The direct reference which is thus experimentally made in the simplevoltaic circle of the _intensity_ of the electric current to the_intensity_ of the chemical action going on at the place where theexistence and direction of the current is determined, leads to theconclusion that by using selected bodies, as fused chlorides, salts, solutions of acids, &c. , which may act upon the metals employed withdifferent degrees of chemical force; and using also metals in associationwith platina, or with each other, which shall differ in the degree ofchemical action exerted between them and the exciting fluid or electrolyte, we shall be able to obtain a series of comparatively constant effects dueto electric currents of different intensities, which will serve to assistin the construction of a scale competent to supply the means of determiningrelative degrees of intensity with accuracy in future researches[A]. 

 [A] In relation to this difference and its probable cause, see considerations on inductive polarization, 1354, &c. --_Dec. 1838. _

910. I have already expressed the view which I take of the decomposition inthe experimental place, as being the direct consequence of the superiorexertion at some other spot of the same kind of power as that to beovercome, and therefore as the result of an antagonism of forces of the_same_ nature (891. 904. ). Those at the place of decomposition have are-action upon, and a power over, the exerting or determining setproportionate to what is needful to overcome their own power; and hence acurious result of _resistance_ offered by decompositions to the originaldetermining force, and consequently to the current. This is well shown inthe cases where such bodies as chloride of lead, iodide of lead, and waterwould not decompose with the current produced by a single pair of zinc andplatina plates in sulphuric acid (903. ), although they would with a currentof higher intensity produced by stronger chemical powers. In such cases nosensible portion of the current passes (967. ); the action is stopped; and Iam now of opinion that in the case of the law of conduction which Idescribed in the Fourth Series of these Researches (413. ), the bodies whichare electrolytes in the fluid state cease to be such in the solid form, because the attractions of the particles by which they are retained incombination and in their relative position, are then too powerful for theelectric current[A]. The particles retain their places; and asdecomposition is prevented, the transmission of the electricity isprevented also; and although a battery of many plates may be used, yet ifit be of that perfect kind which allows of no extraneous or indirect action(1000. ), the whole of the affinities concerned in the activity of thatbattery are at the same time also suspended and counteracted. 

 [A] Refer onwards to 1705. --_Dec. 1838. _

911. But referring to the _resistance_ of each single case ofdecomposition, it would appear that as these differ in force according tothe affinities by which the elements in the substance tend to retain theirplaces, they also would supply cases constituting a series of degrees bywhich to measure the initial intensities of simple voltaic or othercurrents of electricity, and which, combined with the scale of intensitiesdetermined by different degrees of _acting force_ (909. ), would probablyinclude a sufficient set of differences to meet almost every important casewhere a reference to intensity would be required. 

912. According to the experiments I have already had occasion to make, Ifind that the following bodies are electrolytic in the order in which Ihave placed them, those which are first being decomposed by the current oflowest intensity. These currents were always from a single pair of plates, and may be considered as elementary _voltaic forces_. 

Iodide of potassium (solution). Chloride of silver (fused). Protochloride of tin (fused). Chloride of lead (fused). Iodide of lead (fused). Muriatic acid (solution). Water, acidulated with sulphuric acid. 

913. It is essential that, in all endeavours to obtain the relativeelectrolytic intensity necessary for the decomposition of different bodies, attention should be paid to the nature of the electrodes and the otherbodies present which may favour secondary actions (986. ). If inelectro-decomposition one of the elements separated has an affinity for theelectrode, or for bodies present in the surrounding fluid, then theaffinity resisting decomposition is in part balanced by such power, and thetrue place of the electrolyte in a table of the above kind is not obtained:thus, chlorine combines with a positive platina electrode freely, butiodine scarcely at all, and therefore I believe it is that the fusedchlorides stand first in the preceding Table. Again, if in thedecomposition of water not merely sulphuric but also a little nitric acidbe present, then the water is more freely decomposed, for the hydrogen atthe _cathode_ is not ultimately expelled, but finds oxygen in the nitricacid, with which it can combine to produce a secondary result; theaffinities opposing decomposition are in this way diminished, and theelements of the water can then be separated by a current of lowerintensity. 

914. Advantage may be taken of this principle to interpolate more minutedegrees into the scale of initial intensities already referred to (909. 911. ) than is there spoken of; for by combining the force of a current_constant_ in its intensity, with the use of electrodes consisting ofmatter, having more or less affinity for the elements evolved from thedecomposing electrolyte, various intermediate degrees may be obtained. 

 * * * * *

915. Returning to the consideration of the source of electricity (878. &c. ), there is another proof of the most perfect kind that metallic contacthas nothing to do with the _production_ of electricity in the voltaiccircuit, and further, that electricity is only another mode of the exertionof chemical forces. It is, the production of the _electric spark_ beforeany contact of metals is made, and by the exertion of _pure and unmixedchemical forces_. The experiment, which will be described further on(956. ), consists in obtaining the spark upon making contact between a plateof zinc and a plate of copper plunged into dilute sulphuric acid. In orderto make the arrangement as elementary as possible, mercurial surfaces weredismissed, and the contact made by a copper wire connected with the copperplate, and then brought to touch a clean part of the zinc plate. Theelectric spark appeared, and it must of necessity have existed and passed_before the zinc and the copper were in contact_. 

916. In order to render more distinct the principles which I have beenendeavouring to establish, I will restate them in their simplest form, according to my present belief. The electricity of the voltaic pile (856. Note) is not dependent either in its origin or its continuance upon thecontact of the metals with each other (880. 915. ). It is entirely due tochemical action (882. ), and is proportionate in its intensity to theintensity of the affinities concerned in its production (908. ); and in itsquantity to the quantity of matter which has been chemically active duringits evolution (869. ). This definite production is again one of thestrongest proofs that the electricity is of chemical origin. 

917. As _volta-electro-generation_ is a case of mere chemical action, so_volta-electro-decomposition_ is simply a case of the preponderance of oneset of chemical affinities more powerful in their nature, over another setwhich are less powerful: and if the instance of two opposing sets of suchforces (891. ) be considered, and their mutual relation and dependence bornein mind, there appears no necessity for using, in respect to such cases, any other term than chemical affinity, (though that of electricity may bevery convenient, ) or supposing any new agent to be concerned in producingthe results; for we may consider that the powers at the two places ofaction are in direct communion and balanced against each other through themedium of the metals (891. ), fig. 76, in a manner analogous to that inwhich mechanical forces are balanced against each other by the interventionof the lever (1031. ). 

918. All the facts show us that that power commonly called chemicalaffinity, can be communicated to a distance through the metals and certainforms of carbon; that the electric current is only another form of theforces of chemical affinity; that its power is in proportion to thechemical affinities producing it; that when it is deficient in force it maybe helped by calling in chemical aid, the want in the former being made upby an equivalent of the latter; that, in other words, _the forces termedchemical affinity and electricity are one and the same. _

919. When the circumstances connected with the production of electricity inthe ordinary voltaic circuit are examined and compared, it appears that thesource of that agent, always meaning the electricity which circulates andcompletes the current in the voltaic apparatus, and gives that apparatuspower and character (947. 996. ), exists in the chemical action which takesplace directly between the metal and the body with which it combines, andnot at all in the subsequent action of the substance so produced with theacid present[A]. Thus, when zinc, platina, and dilute sulphuric acid areused, it is the union of the zinc with the oxygen of the water whichdetermines the current; and though the acid is essential to the removal ofthe oxide so formed, in order that another portion of zinc may act onanother portion of water, it does not, by combination with that oxide, produce any sensible portion of the current of electricity whichcirculates; for the quantity of electricity is dependent upon the quantityof zinc oxidized, and in definite proportion to it: its intensity is inproportion to the intensity of the chemical affinity of the zinc for theoxygen under the circumstances, and is scarcely, if at all, affected by theuse of either strong or weak acid (908. ). 

 [A] Wollaston, Philosophical Transactions, 1801, p. 427. 

920. Again, if zinc, platina, and muriatic acid are used, the electricityappears to be dependent upon the affinity of the zinc for the chlorine, andto be circulated in exact proportion to the number of particles of zinc andchlorine which unite, being in fact an equivalent to them. 

921. But in considering this oxidation, or other direct action upon theMETAL itself, as the cause and source of the electric current, it is of theutmost importance to observe that the oxygen or other body must be in apeculiar condition, namely, in the state of _combination_; and not only so, but limited still further to such a state of combination and in suchproportions as will constitute an _electrolyte_ (823. ). A pair of zinc andplatina plates cannot be so arranged in oxygen gas as to produce a currentof electricity, or act as a voltaic circle, even though the temperature maybe raised so high as to cause oxidation of the zinc far more rapidly thanif the pair of plates were plunged into dilute sulphuric acid; for theoxygen is not part of an electrolyte, and cannot therefore conduct theforces onwards by decomposition, or even as metals do by itself. Or if itsgaseous state embarrass the minds of some, then liquid chlorine may betaken. It does not excite a current of electricity through the two platesby combining with the zinc, for its particles cannot transfer theelectricity active at the point of combination across to the platina. It isnot a conductor of itself, like the metals; nor is it an electrolyte, so asto be capable of conduction during decomposition, and hence there is simplechemical action at the spot, and no electric current[A]. 

 [A] I do not mean to affirm that no traces of electricity ever appear in such cases. What I mean is, that no electricity is evolved in any way, due or related to the causes which excite voltaic electricity, or proportionate to them. That which does appear occasionally is the smallest possible fraction of that which the acting matter could produce if arranged so as to act voltaically, probably not the one hundred thousandth, or even the millionth part, and is very probably altogether different in its source. 

922. It might at first be supposed that a conducting body not electrolytic, might answer as the third substance between the zinc and the platina; andit is true that we have some such capable of exerting chemical action uponthe metals. They must, however, be chosen from the metals themselves, forthere are no bodies of this kind except those substances and charcoal. Todecide the matter by experiment, I made the following arrangement. Meltedtin was put into a glass tube bent into the form of the letter V, fig. 78, so as to fill the half of each limb, and two pieces of thick platina wire, _p_, _w_, inserted, so as to have their ends immersed some depth in thetin: the whole was then allowed to cool, and the ends _p_ and _w_ connectedwith a delicate galvanometer. The part of the tube at _x_ was now reheated, whilst the portion _y_ was retained cool. The galvanometer was immediatelyinfluenced by the thermo-electric current produced. The heat was steadilyincreased at _x_, until at last the tin and platina combined there; aneffect which is known to take place with strong chemical action and highignition; but not the slightest additional effect occurred at thegalvanometer. No other deflection than that due to the thermo-electriccurrent was observable the whole time. Hence, though a conductor, and onecapable of exerting chemical action on the tin, was used, yet, not being an_electrolyte_, not the slightest effect of an electrical current could beobserved (947. ). 

923. From this it seems apparent that the peculiar character and conditionof an electrolyte is _essential_ in one part of the voltaic circuit; andits nature being considered, good reasons appear why it and it alone shouldbe effectual. An electrolyte is always a compound body: it can conduct, butonly whilst decomposing. Its conduction depends upon its decomposition andthe _transmission of its particles_ in directions parallel to the current;and so intimate is this connexion, that if their transition be stopped, thecurrent is stopped also; if their course be changed, its course anddirection change with them; if they proceed in one direction, it has nopower to proceed in any other than a direction invariably dependent onthem. The particles of an electrolytic body are all so mutually connected, are in such relation with each other through their whole extent in thedirection of the current, that if the last is not disposed of, the first isnot at liberty to take up its place in the new combination which thepowerful affinity of the most active metal tends to produce; and then thecurrent itself is stopped; for the dependencies of the current and thedecomposition are so mutual, that whichsoever be originally determined, i. E. The motion of the particles or the motion of the current, the other isinvariable in its concomitant production and its relation to it. 

924. Consider, then, water as an electrolyte and also as an oxidizing body. The attraction of the zinc for the oxygen is greater, under thecircumstances, than that of the oxygen for the hydrogen; but in combiningwith it, it tends to throw into circulation a current of electricity in acertain direction. This direction is consistent (as is found by innumerableexperiments) with the transfer of the hydrogen from the zinc towards theplatina, and the transfer in the opposite direction of fresh oxygen fromthe platina towards the zinc; so that the current _can pass_ in that oneline, and, whilst it passes, can consist with and favour the renewal of theconditions upon the surface of the zinc, which at first determined both thecombination and circulation. Hence the continuance of the action there, andthe continuation of the current. It therefore appears quite as essentialthat there should be an electrolyte in the circuit, in order that theaction may be transferred forward, in a _certain constant direction, _ asthat there should be an oxidizing or other body capable of acting directlyon the metal; and it also appears to be essential that these two shouldmerge into one, or that the principle directly active on the metal bychemical action should be one of the _ions_ of the electrolyte used. Whether the voltaic arrangement be excited by solution of acids, oralkalies, or sulphurets, or by fused substances (476. ), this principle hasalways hitherto, as far as I am aware, been an _anion_ (943. ); and Ianticipate, from a consideration of the principles of electric action, thatit must of necessity be one of that class of bodies. 

925. If the action of the sulphuric acid used in the voltaic circuit beconsidered, it will be found incompetent to produce any sensible portion ofthe electricity of the current by its combination with the oxide formed, for this simple reason, it is deficient in a most essential condition: itforms no part of an electrolyte, nor is it in relation with any other bodypresent in the solution which will permit of the mutual transfer of theparticles and the consequent transfer of the electricity. It is true, thatas the plane at which the acid is dissolving the oxide of zinc formed bythe action of the water, is in contact with the metal zinc, there seems nodifficulty in considering how the oxide there could communicate anelectrical state, proportionate to its own chemical action on the acid, tothe metal, which is a conductor without decomposition. But on the side ofthe acid there is no substance to complete the circuit: the water, aswater, cannot conduct it, or at least only so small a proportion that it ismerely an incidental and almost inappreciable effect (970. ); and it cannotconduct it as an electrolyte, because an electrolyte conducts inconsequence of the _mutual_ relation and action of its particles; andneither of the elements of the water, nor even the water itself, as far aswe can perceive, are _ions_ with respect to the sulphuric acid (848. )[A]. 

 [A] It will be seen that I here agree with Sir Humphry Davy, who has experimentally supported the opinion that acids and alkalies in combining do not produce any current of electricity. Philosophical Transactions, 1826, p. 398. 

926. This view of the secondary character of the sulphuric acid as an agentin the production of the voltaic current, is further confirmed by the fact, that the current generated and transmitted is directly and exactlyproportional to the quantity of water decomposed and the quantity of zincoxidized (868. 991. ), and is the same as that required to decompose thesame quantity of water. As, therefore, the decomposition of the water showsthat the electricity has passed by its means, there remains no otherelectricity to be accounted for or to be referred to any action other thanthat of the zinc and the water on each other. 

927. The general case (for it includes the former one (924. ), ) of acids andbases, may theoretically be stated in the following manner. Let _a_, fig. 79, be supposed to be a dry oxacid, and _b_ a dry base, in contact at _c_, and in electric communication at their extremities by plates of platina_pp_, and a platina wire _w_. If this acid and base were fluid, andcombination took place at _c_, with an affinity ever so vigorous, andcapable of originating an electric current, the current could not circulatein any important degree; because, according to the experimental results, neither _a_ nor _b_ could conduct without being decomposed, for they areeither electrolytes or else insulators, under all circumstances, except tovery feeble and unimportant currents (970. 986. ). Now the affinities at _c_are not such as tend to cause the _elements_ either of _a_ or _b_ toseparate, but only such as would make the two bodies combine together as awhole; the point of action is, therefore, insulated, the action itselflocal (921. 947. ), and no current can be formed. 

928. If the acid and base be dissolved in water, then it is possible that asmall portion of the electricity due to chemical action may be conducted bythe water without decomposition (966. 984. ); but the quantity will be sosmall as to be utterly disproportionate to that due to the equivalents ofchemical force; will be merely incidental; and, as it does not involve theessential principles of the voltaic pile, it forms no part of the phenomenaat present under investigation[A]. 

 [A] It will I trust be fully understood, that in these investigations I am not professing to take an account of every small, incidental, or barely possible effect, dependent upon slight disturbances of the electric fluid during chemical action, but am seeking to distinguish and identify those actions on which the power of the voltaic battery essentially depends. 

929. If for the oxacid a hydracid be substituted (927. ), --as one analogousto the muriatic, for instance, --then the state of things changesaltogether, and a current due to the chemical action of the acid on thebase is possible. But now both the bodies act as electrolytes, for it isonly one principle of each which combine mutually, --as, for instance, thechlorine with the metal, --and the hydrogen of the acid and the oxygen ofthe base are ready to traverse with the chlorine of the acid and the metalof the base in conformity with the current and according to the generalprinciples already so fully laid down. 

930. This view of the oxidation of the metal, or other _direct_ chemicalaction upon it, being the sole cause of the production of the electriccurrent in the ordinary voltaic pile, is supported by the effects whichtake place when alkaline or sulphuretted solutions (931. 943. ) are used forthe electrolytic conductor instead of dilute sulphuric acid. It was inelucidation of this point that the experiments without metallic contact, and with solution of alkali as the exciting fluid, already referred to(884. ), were made. 

931. Advantage was then taken of the more favourable condition offered, when metallic contact is allowed (895. ), and the experiments upon thedecomposition of bodies by a single pair of plates (899. ) were repeated, solution of caustic potassa being employed in the vessel _v_, fig. 77. Inplace of dilute sulphuric acid. All the effects occurred as before: thegalvanometer was deflected; the decompositions of the solutions of iodideof potassium, nitrate of silver, muriatic acid, and sulphate of soda ensuedat _x_; and the places where the evolved principles appeared, as well asthe deflection of the galvanometer, indicated a current in the _samedirection_ as when acid was in the vessel _v_; i. E. From the zinc throughthe solution to the platina, and back by the galvanometer and substancesuffering decomposition to the zinc. 

932. The similarity in the action of either dilute sulphuric acid orpotassa goes indeed far beyond this, even to the proof of identity in_quantity_ as well as in _direction_ of the electricity produced. If aplate of amalgamated zinc be put into a solution of potassa, it is notsensibly acted upon; but if touched in the solution by a plate of platina, hydrogen is evolved on the surface of the latter metal, and the zinc isoxidized exactly as when immersed in dilute sulphuric acid (863. ). Iaccordingly repeated the experiment before described with weighed plates ofzinc (864. &c. ), using however solution of potassa instead of dilutesulphuric acid. Although the time required was much longer than when acidwas used, amounting to three hours for the oxidizement of 7. 55 grains ofzinc, still I found that the hydrogen evolved at the platina plate was theequivalent of the metal oxidized at the surface of the zinc. Hence thewhole of the reasoning which was applicable in the former instance appliesalso here, the current being in the same direction, and its decomposingeffect in the same degree, as if acid instead of alkali had been used(868. ). 

933. The proof, therefore, appears to me complete, that the combination ofthe acid with the oxide, in the former experiment, had nothing to do withthe production of the electric current; for the same current is hereproduced when the action of the acid is absent, and the reverse action ofan alkali is present. I think it cannot be supposed for a moment, that thealkali acted chemically as an acid to the oxide formed; on the contrary, our general chemical knowledge leads to the conclusion, that the ordinarymetallic oxides act rather as acids to the alkalies; yet that kind ofaction would tend to give a reverse current in the present case, if anywere due to the union of the oxide of the exciting metal with the bodywhich combines with it. But instead of any variation of this sort, thedirection of the electricity was constant, and its quantity also directlyproportional to the water decomposed, or the zinc oxidized. There arereasons for believing that acids and alkalies, when in contact with metalsupon which they cannot act directly, still have a power of influencingtheir attractions for oxygen (941. ); but all the effects in theseexperiments prove, I think, that it is the oxidation of the metalnecessarily dependent upon, and associated as it is with, theelectrolyzation of the water (921. 923. ) that produces the current; andthat the acid or alkali merely acts as solvents, and by removing theoxidized zinc, allows other portions to decompose fresh water, and socontinues the evolution or determination of the current. 

934. The experiments were then varied by using solution of ammonia insteadof solution of potassa; and as it, when pure, is like water, a badconductor (554. ), it was occasionally improved in that power by addingsulphate of ammonia to it. But in all the cases the results were the sameas before; decompositions of the same kind were effected, and the electriccurrent producing these was in the same direction as in the experimentsjust described. 

935. In order to put the equal and similar action of acid and alkali tostronger proof, arrangements were made as in fig. 80. ; the glass vessel Acontained dilute sulphuric acid, the corresponding glass vessel B solutionof potassa, PP was a plate of platina dipping into both solutions, and ZZtwo plates of amalgamated zinc connected with a delicate galvanometer. Whenthese were plunged at the same time into the two vessels, there wasgenerally a first feeble effect, and that in favour of the alkali, i. E. Theelectric current tended to pass through the vessels in the direction of thearrow, being the reverse direction of that which the acid in A would haveproduced alone: but the effect instantly ceased, and the action of theplates in the vessels was so equal, that, being contrary because of thecontrary position of the plates, no permanent current resulted. 

936. Occasionally a zinc plate was substituted for the plate PP, andplatina plates for the plates ZZ; but this caused no difference in theresults: nor did a further change of the middle plate to copper produce anyalteration. 

937. As the opposition of electro-motive pairs of plates produces resultsother than those due to the mere difference of their independent actions(1011. 1045. ), I devised another form of apparatus, in which the action ofacid and alkali might be more directly compared. A cylindrical glass cup, about two inches deep within, an inch in internal diameter, and at least aquarter of an inch in thickness, was cut down the middle into halves, fig. 81. A broad brass ring, larger in diameter than the cup, was supplied witha screw at one side; so that when the two halves of the cup were within thering, and the screw was made to press tightly against the glass, the cupheld any fluid put into it. Bibulous paper of different degrees ofpermeability was then cut into pieces of such a size as to be easilyintroduced between the loosened halves of the cup, and served when thelatter were tightened again to form a porous division down the middle ofthe cup, sufficient to keep any two fluids on opposite sides of the paperfrom mingling, except very slowly, and yet allowing them to act freely asone _electrolyte_. The two spaces thus produced I will call the cells A andB, fig. 82. This instrument I have found of most general application in theinvestigation of the relation of fluids and metals amongst themselves andto each other. By combining its use with that of the galvanometer, it iseasy to ascertain the relation of one metal with two fluids, or of twometals with one fluid, or of two metals and two fluids upon each other. 

938. Dilute sulphuric acid, sp. Gr. 1. 25, was put into the cell A, and astrong solution of caustic potassa into the cell B; they mingled slowlythrough the paper, and at last a thick crust of sulphate of potassa formedon the side of the paper next to the alkali. A plate of clean platina wasput into each cell and connected with a delicate galvanometer, but noelectric current could be observed. Hence the _contact_ of acid with oneplatina plate, and alkali with the other, was unable to produce a current;nor was the combination of the acid with the alkali more effectual (925. ). 

939. When one of the platina plates was removed and a zinc platesubstituted, either amalgamated or not, a strong electric current wasproduced. But, whether the zinc were in the acid whilst the platina was inthe alkali, or whether the reverse order were chosen, the electric currentwas always from the zinc through the electrolyte to the platina, and backthrough the galvanometer to the zinc, the current seeming to be strongestwhen the zinc was in the alkali and the platina in the acid. 

940. In these experiments, therefore, the acid seems to have no power overthe alkali, but to be rather inferior to it in force. Hence there is noreason to suppose that the combination of the oxide formed with the acidaround it has any direct influence in producing the electricity evolved, the whole of which appears to be due to the oxidation of the metal (919. ). 

941. The alkali, in fact, is superior to the acid in bringing a metal intowhat is called the positive state; for if plates of the same metal, aszinc, tin, lead, or copper, be used both in the acid or alkali, theelectric current is from the alkali across the cell to the acid, and backthrough the galvanometer to the alkali, as Sir Humphry Davy formerly stated[A]. This current is so powerful, that if amalgamated zinc, or tin, or leadbe used, the metal in the acid evolves hydrogen the moment it is placed incommunication with that in the alkali, not from any direct action of theacid upon it, for if the contact be broken the action ceases, but becauseit is powerfully negative with regard to the metal in the alkali. 

 [A] Elements of Chemical Philosophy, p. 149; or Philosophical Transactions, 1826, p. 403. 

942. The superiority of alkali is further proved by this, that if zinc andtin be used, or tin and lead, whichsoever metal is put into the alkalibecomes positive, that in the acid being negative. Whichsoever is in thealkali is oxidized, whilst that in the acid remains in the metallic state, as far as the electric current is concerned. 

943. When sulphuretted solutions are used (930. ) in illustration of theassertion, that it is the chemical action of the metal and one of the_ions_ of the associated electrolyte that produces all the electricity ofthe voltaic circuit, the proofs are still the same. Thus, as Sir HumphryDavy[A] has shown, if iron and copper be plunged into dilute acid, thecurrent is from the iron through the liquid to the copper; in solution ofpotassa it is in the same direction, but in solution of sulphuret ofpotassa it is reversed. In the two first cases it is oxygen which combineswith the iron, in the latter sulphur which combines with the copper, thatproduces the electric current; but both of these are _ions_, existing assuch in the electrolyte, which is at the same moment sufferingdecomposition; and, what is more, both of these are _anions_, for theyleave the electrolytes at their _anodes_, and act just as chlorine, iodine, or any other _anion_ would act which might have been previously chosen asthat which should be used to throw the voltaic circle into activity. 

 [A] Elements of Chemical Philosophy, p. 148. 

944. The following experiments complete the series of proofs of the originof the electricity in the voltaic pile. A fluid amalgam of potassium, containing not more than a hundredth of that metal, was put into purewater, and connected, through the galvanometer with a plate of platina inthe same water. There was immediately an electric current from the amalgamthrough the electrolyte to the platina. This must have been due to theoxidation only of the metal, for there was neither acid nor alkali tocombine with, or in any way act on, the body produced. 

945. Again, a plate of clean lead and a plate of platina were put into_pure_ water. There was immediately a powerful current produced from thelead through the fluid to the platina: it was even intense enough todecompose solution of the iodide of potassium when introduced into thecircuit in the form of apparatus already described (880. ), fig. 73. Here noaction of acid or alkali on the oxide formed from the lead could supply theelectricity: it was due solely to the oxidation of the metal. 

 * * * * *

946. There is no point in electrical science which seems to me of moreimportance than the state of the metals and the electrolytic conductor in asimple voltaic circuit _before and at_ the moment when metallic contact isfirst completed. If clearly understood, I feel no doubt it would supply uswith a direct key to the laws under which the great variety of voltaicexcitements, direct and incidental, occur, and open out new fields ofresearch for our investigation[A]. 

 [A] In connexion with this part of the subject refer now to Series XI. 1164, Series XII. 1343-1358, and Series XIII. 1621. &c. --_Dec. 1838. _

947. We seem to have the power of deciding to a certain extent in numerouscases of chemical affinity, (as of zinc with the oxygen of water, &c. &c. )which of _two modes of action of the attractive power_ shall be exerted(996. ). In the one mode we can transfer the power onwards, and make itproduce elsewhere its equivalent of action (867. 917. ); in the other, it isnot transferred, but exerted wholly at the spot. The first is the case ofvolta-electric excitation, the other ordinary chemical affinity: but bothare chemical actions and due to one force or principle. 

948. The general circumstances of the former mode occur in all instances ofvoltaic currents, but may be considered as in their perfect condition, andthen free from those of the second mode, in some only of the cases; as inthose of plates of zinc and platina in solution of potassa, or ofamalgamated zinc and platina in dilute sulphuric acid. 

949. Assuming it sufficiently proved, by the preceding experiments andconsiderations, that the electro-motive action depends, when zinc, platina, and dilute sulphuric acid are used, upon the mutual affinity of the metalzinc and the oxygen of the water (921. 924. ), it would appear that themetal, when alone, has not power enough, under the circumstances, to takethe oxygen and expel the hydrogen from the water; for, in fact, no suchaction takes place. But it would also appear that it has power so far toact, by its attraction for the oxygen of the particles in contact with it, as to place the similar forces already active between these and the otherparticles of oxygen and the particles of hydrogen in the water, in apeculiar state of tension or polarity, and probably also at the same timeto throw those of its own particles which are in contact with the waterinto a similar but opposed state. Whilst this state is retained, no furtherchange occurs; but when it is relieved, by completion of the circuit, inwhich case the forces determined in opposite directions, with respect tothe zinc and the electrolyte, are found exactly competent to neutralizeeach other, then a series of decompositions and recompositions takes placeamongst the particles of oxygen and hydrogen constituting the water, between the place of contact with the platina and the place where the zincis active; these intervening particles being evidently in close dependenceupon and relation to each other. The zinc forms a direct compound withthose particles of oxygen which were, previously, in divided relation toboth it and the hydrogen: the oxide is removed by the acid, and a freshsurface of zinc is presented to the water, to renew and repeat the action. 

950. Practically, the state of tension is best relieved by dipping a metalwhich has less attraction for oxygen than the zinc, into the dilute acid, and making it also touch the zinc. The force of chemical affinity, whichhas been influenced or polarized in the particles of the water by thedominant attraction of the zinc for the oxygen, is then transferred, in amost extraordinary manner, through the two metals, so as to re-enter uponthe circuit in the electrolytic conductor, which, unlike the metals in thatrespect, cannot convey or transfer it without suffering decomposition; orrather, probably, it is exactly balanced and neutralized by the force whichat the same moment completes the combination of the zinc with the oxygen ofthe water. The forces, in fact, of the two particles which are actingtowards each other, and which are therefore in opposite directions, are theorigin of the two opposite forces, or directions of force, in the current. They are of necessity equivalent to each other. Being transferred forwardin contrary directions, they produce what is called the voltaic current:and it seems to me impossible to resist the idea that it must be precededby a _state of tension_ in the fluid, and between the fluid and the zinc;the _first consequence_ of the affinity of the zinc for the oxygen of thewater. 

951. I have sought carefully for indications of a state of tension in theelectrolytic conductor; and conceiving that it might produce something likestructure, either before or during its discharge, I endeavoured to makethis evident by polarized light. A glass cell, seven inches long, one inchand a half wide, and six inches deep, had two sets of platina electrodesadapted to it, one set for the ends, and the other for the sides. Those forthe _sides_ were seven inches long by three inches high, and when in thecell were separated by a little frame of wood covered with calico; so thatwhen made active by connexion with a battery upon any solution in the cell, the bubbles of gas rising from them did not obscure the central parts ofthe liquid. 

952. A saturated solution of sulphate of soda was put into the cell, andthe electrodes connected with a battery of 150 pairs of 4-inch plates: thecurrent of electricity was conducted across the cell so freely, that thedischarge was as good as if a wire had been used. A ray of polarized lightwas then transmitted through this solution, directly across the course ofthe electric current, and examined by an analysing plate; but though itpenetrated seven inches of solution thus subject to the action of theelectricity, and though contact was sometimes made, sometimes broken, andoccasionally reversed during the observations, not the slightest trace ofaction on the ray could be perceived. 

953. The large electrodes were then removed, and others introduced whichfitted the _ends_ of the cell. In each a slit was cut, so as to allow thelight to pass. The course of the polarized ray was now parallel to thecurrent, or in the direction of its axis (517. ); but still no effect, underany circumstances of contact or disunion, could be perceived upon it. 

954. A strong solution of nitrate of lead was employed instead of thesulphate of soda, but no effects could be detected. 

955. Thinking it possible that the discharge of the electric forces by thesuccessive decompositions and recompositions of the particles of theelectrolyte might neutralize and therefore destroy any effect which thefirst state of tension could by possibility produce, I took a substancewhich, being an excellent electrolyte when fluid, was a perfect insulatorwhen solid, namely, borate of lead, in the form of a glass plate, andconnecting the sides and the edges of this mass with the metallic plates, sometimes in contact with the poles of a voltaic battery, and sometimeseven with the electric machine, for the advantage of the much higherintensity then obtained, I passed a polarized ray across it in variousdirections, as before, but could not obtain the slightest appearance ofaction upon the light. Hence I conclude, that notwithstanding the new andextraordinary state which must be assumed by an electrolyte, either duringdecomposition (when a most enormous quantity of electricity must betraversing it), or in the state of tension which is assumed as precedingdecomposition, and which might be supposed to be retained in the solid formof the electrolyte, still it has no power of affecting a polarized ray oflight; for no kind of structure or tension can in this way be renderedevident. 

956. There is, however, one beautiful experimental proof of a state oftension acquired by the metals and the electrolyte before the electriccurrent is produced, and _before contact_ of the different metals is made(915. ); in fact, at that moment when chemical forces only are efficient asa cause of action. I took a voltaic apparatus, consisting of a single pairof large plates, namely, a cylinder of amalgamated zinc, and a doublecylinder of copper. These were put into a jar containing dilute sulphuricacid[A], and could at pleasure be placed in metallic communication by acopper wire adjusted so as to dip at the extremities into two cups ofmercury connected with the two plates. 

 [A] When nitro-sulphuric acid is used, the spark is more powerful, but local chemical action can then commence, and proceed without requiring metallic contact. 

957. Being thus arranged, there was no chemical action whilst the plateswere not connected. On _making_ the connexion a spark was obtained[A], andthe solution was immediately decomposed. On breaking it, the usual sparkwas obtained, and the decomposition ceased. In this case it is evident thatthe first spark must have occurred before metallic contact was made, for itpassed through an interval of air; and also that it must have tended topass before the electrolytic action began; for the latter could not takeplace until the current passed, and the current could not pass before thespark appeared. Hence I think there is sufficient proof, that as it is thezinc and water which by their mutual action produce the electricity of thisapparatus, so these, by their first contact with each other, were placed ina state of powerful tension (951. ), which, though it could not produce theactual decomposition of the water, was able to make a spark of electricitypass between the zinc and a fit discharger as soon as the interval wasrendered sufficiently small. The experiment demonstrates the directproduction of the electric spark from pure chemical forces. 

 [A] It has been universally supposed that no spark is produced on making the contact between a single pair of plates. I was led to expect one from the considerations already advanced in this paper. The wire of communication should be short; for with a long wire, circumstances strongly affecting the spark are introduced. 

958. There are a few circumstances connected with the production of thisspark by a single pair of plates, which should be known, to ensure successto the experiment[B]. When the amalgamated surfaces of contact are quiteclean and dry, the spark, on making contact, is quite as brilliant as onbreaking it, if not even more so. When a film of oxide or dirt was presentat either mercurial surface, then the first spark was often feeble, andoften failed, the breaking spark, however, continuing very constant andbright. When a little water was put over the mercury, the spark was greatlydiminished in brilliancy, but very regular both on making and breakingcontact. When the contact was made between clean platina, the spark wasalso very small, but regular both ways. The true electric spark is, infact, very small, and when surfaces of mercury are used, it is thecombustion of the metal which produces the greater part of the light. Thecircumstances connected with the burning of the mercury are most favourableon breaking contact; for the act of separation exposes clean surfaces ofmetal, whereas, on making contact, a thin film of oxide, or soiling matter, often interferes. Hence the origin of the general opinion that it is onlywhen the contact is broken that the spark passes. 

 [B] See in relation to precautions respecting a spark, 1074. --_Dec. 1838. _

959. With reference to the other set of cases, namely, those of localaction (947. ) in which chemical affinity being exerted causes notransference of the power to a distance where no electric current isproduced, it is evident that forces of the most intense kind must beactive, and in some way balanced in their activity, during suchcombinations; these forces being directed so immediately and exclusivelytowards each other, that no signs of the powerful electric current they canproduce become apparent, although the same final state of things isobtained as if that current had passed. It was Berzelius, I believe, whoconsidered the heat and light evolved in cases of combustion as theconsequences of this mode of exertion of the electric powers of thecombining particles. But it will require a much more exact and extensiveknowledge of the nature of electricity, and the manner in which it isassociated with the atoms of matter, before we can understand accuratelythe action of this power in thus causing their union, or comprehend thenature of the great difference which it presents in the two modes of actionjust distinguished. We may imagine, but such imaginations must for the timebe classed with the great mass of _doubtful knowledge_ (876. ) which weought rather to strive to diminish than to increase; for the very extensivecontradictions of this knowledge by itself shows that but a small portionof it can ultimately prove true[A]. 

 [A] Refer to 1738, &c. Series XIV. --_Dec. 1838. _

960. Of the two modes of action in which chemical affinity is exerted, itis important to remark, that that which produces the electric current is as_definite_ as that which causes ordinary chemical combination; so that inexamining the _production_ or _evolution_ of electricity in cases ofcombination or decomposition, it will be necessary, not merely to observecertain effects dependent upon a current of electricity, but also their_quantity_: and though it may often happen that the forces concerned in anyparticular case of chemical action may be partly exerted in one mode andpartly in the other, it is only those which are efficient in producing thecurrent that have any relation to voltaic action. Thus, in the combinationof oxygen and hydrogen to produce water, electric powers to a most enormousamount are for the time active (861. 873. ); but any mode of examining theflame which they form during energetic combination, which has as yet beendevised, has given but the feeblest traces. These therefore may not, cannot, be taken as evidences of the nature of the action; but are merelyincidental results, incomparably small in relation to the forces concerned, and supplying no information of the way in which the particles are activeon each other, or in which their forces are finally arranged. 

961. That such cases of chemical action produce no _current ofelectricity_, is perfectly consistent with what we know of the voltaicapparatus, in which it is essential that one of the combining elementsshall form part of, or be in direct relation with, an electrolyticconductor (921. 923. ). That such cases produce _no free electricity oftension_, and that when they are converted into cases of voltaic actionthey produce a current in which the opposite forces are so equal as toneutralize each other, prove the equality of the forces in the opposedacting particles of matter, and therefore the equality of electric power inthose quantities of matter which are called _electro-chemical equivalents_(824). Hence another proof of the definite nature of electro-chemicalaction (783. &c. ), and that chemical affinity and electricity are forms ofthe same power (917. &c. ). 

962. The direct reference of the effects produced by the voltaic pile atthe place of experimental decomposition to the chemical affinities activeat the place of excitation (891. 917. ), gives a very simple and naturalview of the cause why the bodies (or _ions_) evolved pass in certaindirections; for it is only when they pass in those directions that theirforces can consist with and compensate (in direction at least) the superiorforces which are dominant at the place where the action of the whole isdetermined. If, for instance, in a voltaic circuit, the activity of whichis determined, by the attraction of zinc for the oxygen of water, the zincmove from right to left, then any other _cation_ included in the circuit, being part of an electrolyte, or forming part of it at the moment, willalso move from right to left: and as the oxygen of the water, by itsnatural affinity for the zinc, moves from left to right, so any other bodyof the same class with it (i. E. Any other _anion_), under its governmentfor the time, will move from left to right. 

963. This I may illustrate by reference to fig. 83, the double circle ofwhich may represent a complete voltaic circuit, the direction of its forcesbeing determined by supposing for a moment the zinc _b_ and the platina _c_as representing plates of those metals acting upon water, _d, e_, and othersubstances, but having their energy exalted so as to effect severaldecompositions by the use of a battery at _a_ (989. ). This supposition maybe allowed, because the action in the battery will only consist ofrepetitions of what would take place between _b_ and _c_, if they reallyconstituted but a single pair. The zinc _b_, and the oxygen _d_, by theirmutual affinity, tend to unite; but as the oxygen is already in associationwith the hydrogen _e_, and has its inherent chemical or electric powersneutralized for the time by those of the latter, the hydrogen _e_ mustleave the oxygen _d_, and advance in the direction of the arrow head, orelse the zinc _b_ cannot move in the same direction to unite to the oxygen_d_, nor the oxygen _d_ move in the contrary direction to unite to the zinc_b_, the relation of the _similar_ forces of _b_ and _c_, in contrarydirections, to the _opposite_ forces of _d_ being the preventive. As thehydrogen _e_ advances, it, on coming against the platina _c, f_, whichforms a part of the circuit, communicates its electric or chemical forcesthrough it to the next electrolyte in the circuit, fused chloride of lead, _g, h_, where the chlorine must move in conformity with the direction ofthe oxygen at _d_, for it has to compensate the forces disturbed in itspart of the circuit by the superior influence of those between the oxygenand zinc at _d, b_, aided as they are by those of the battery _a_; and fora similar reason the lead must move in the direction pointed out by thearrow head, that it may be in right relation to the first moving body ofits own class, namely, the zinc _b_. If copper intervene in the circuitfrom _i_ to _k_, it acts as the platina did before; and if anotherelectrolyte, as the iodide of tin, occur at _l, m_, then the iodine _l_, being an _anion_, must move in conformity with the exciting _anion_, namely, the oxygen _d_, and the _cation_ tin _m_ move in correspondencewith the other _cations b, e_, and _h_, that the chemical forces may be inequilibrium as to their direction and quantity throughout the circuit. Should it so happen that the anions in their circulation can combine withthe metals at the _anodes_ of the respective electrolytes, as would be thecase at the platina _f_ and the copper _k_, then those bodies becomingparts of electrolytes, under the influence of the current, immediatelytravel; but considering their relation to the zinc _b_, it is evidentlyimpossible that they can travel in any other direction than what willaccord with its course, and therefore can never tend to pass otherwise than_from_ the anode and _to_ the cathode. 

964. In such a circle as that delineated, therefore, all the known _anions_may be grouped within, and all the _cations_ without. If any number of thementer as _ions_ into the constitution of _electrolytes_, and, forming onecircuit, are simultaneously subject to one common current, the anions mustmove in accordance with each other in one direction, and the cations in theother. Nay, more than that, equivalent portions of these bodies must soadvance in opposite directions: for the advance of every 32. 5 parts of thezinc _b_ must be accompanied by a motion in the opposite direction of 8parts of oxygen at _d_, of 36 parts of chlorine at _g_, of 126 parts ofiodine at _l_; and in the same direction by electro-chemical equivalents ofhydrogen, lead, copper and tin, at _e, h, k_. And _m_. 

965. If the present paper be accepted as a correct expression of facts, itwill still only prove a confirmation of certain general views put forth bySir Humphry Davy in his Bakerian Lecture for 1806[A], and revised andre-stated by him in another Bakerian Lecture, on electrical and chemicalchanges, for the year 1826[B]. His general statement is, that "_chemicaland electrical attractions were produced by the same cause, acting in onecase on particles, in the other on masses, of matter; and that the sameproperty, under different modifications, was the cause of all the phenomenaexhibited by different voltaic combinations_[C]. " This statement I believeto be true; but in admitting and supporting it, I must guard myself frombeing supposed to assent to all that is associated with it in the twopapers referred to, or as admitting the experiments which are there quotedas decided proofs of the truth of the principle. Had I thought them so, there would have been no occasion for this investigation. It may besupposed by some that I ought to go through these papers, distinguishingwhat I admit from what I reject, and giving good experimental orphilosophical reasons for the judgment in both cases. But then I should beequally bound to review, for the same purpose, all that has been writtenboth for and against the necessity of metallic contact, --for and againstthe origin of voltaic electricity in chemical action, --a duty which I maynot undertake in the present paper[D]. 

 [A] Philosophical Transactions, 1807. 

 [B] Ibid. 1826, p. 383. 

 [C] Ibid. 1826, p. 389. 

 [D] I at one time intended to introduce here, in the form of a note, a table of reference to the papers of the different philosophers who have referred the origin of the electricity in the voltaic pile to contact, or to chemical action, or to both; but on the publication of the first volume of M. Becquerel's highly important and valuable Traité de l'Electricité et du Magnétisme, I thought it far better to refer to that work for these references, and the views held by the authors quoted. See pages 86, 91, 104, 110, 112, 117, 118, 120, 151, 152, 224, 227, 228, 232, 233, 252, 255, 257, 258, 290, &c. --July 3rd, 1834. 

¶ ii. _On the Intensity necessary for Electrolyzation. _

966. It became requisite, for the comprehension of many of the conditionsattending voltaic action, to determine positively, if possible, whetherelectrolytes could resist the action of an electric current when beneath acertain intensity? whether the intensity at which the current ceased to actwould be the same for all bodies? and also whether the electrolytes thusresisting decomposition would conduct the electric current as a metal does, after they ceased to conduct as electrolytes, or would act as perfectinsulators?

967. It was evident from the experiments described (904. 906. ) thatdifferent bodies were decomposed with very different facilities, andapparently that they required for their decomposition currents of differentintensities, resisting some, but giving way to others. But it was needful, by very careful and express experiments, to determine whether a currentcould really pass through, and yet not decompose an electrolyte (910. ). 

968. An arrangement (fig. 84. ) was made, in which two glass vesselscontained the same dilute sulphuric acid, sp. Gr. 1. 25. The plate _z_ wasamalgamated zinc, in connexion, by a platina wire _a_, with the platinaplate _e_; _b_ was a platina wire connecting the two platina plates PP';_c_ was a platina wire connected with the platina plate P". On the plate_e_ was placed a piece of paper moistened in solution of iodide ofpotassium: the wire _c_ was so curved that its end could be made to rest atpleasure on this paper, and show, by the evolution of iodine there, whethera current was passing; or, being placed in the dotted position, it formed adirect communication with the platina plate _e_, and the electricity couldpass without causing decomposition. The object was to produce a current bythe action of the acid on the amalgamated zinc in the first vessel A; topass it through the acid in the second vessel B by platina electrodes, thatits power of decomposing water might, if existing, be observed; and toverify the existence of the current at pleasure, by decomposition at _e_, without involving the continual obstruction to the current which wouldarise from making the decomposition there constant. The experiment, beingarranged, was examined and the existence of a current ascertained by thedecomposition at _e_; the whole was then left with the end of the wire _c_resting on the plate _e_, so as to form a constant metallic communicationthere. 

969. After several hours, the end of the wire _c_ was replaced on thetest-paper at _e_: decomposition occurred, and _the proof_ of a passingcurrent was therefore complete. The current was very feeble compared towhat it had been at the beginning of the experiment, because of a peculiarstate acquired by the metal surfaces in the second vessel, which causedthem to oppose the passing current by a force which they possess underthese circumstances (1040. ). Still it was proved, by the decomposition, that this state of the plates in the second vessel was not able entirely tostop the current determined in the first, and that was all that was needfulto be ascertained in the present inquiry. 

970. This apparatus was examined from time to time, and an electric currentalways found circulating through it, until twelve days had elapsed, duringwhich the water in the second vessel had been constantly subject to itsaction. Notwithstanding this lengthened period, not the slightestappearance of a bubble upon either of the plates in that vessel occurred. From the results of the experiment, I conclude that a current _had_ passed, but of so low an intensity as to fall beneath that degree at which theelements of water, unaided by any secondary force resulting from thecapability of combination with the matter of the electrodes, or of theliquid surrounding them, separated from each other. 

971. It may be supposed, that the oxygen and hydrogen had been evolved insuch small quantities as to have entirely dissolved in the water, andfinally to have escaped at the surface, or to have reunited into water. That the hydrogen can be so dissolved was shown in the first vessel; forafter several days minute bubbles of gas gradually appeared upon a glassrod, inserted to retain the zinc and platina apart, and also upon theplatina plate itself, and these were hydrogen. They resulted principally inthis way:--notwithstanding the amalgamation of the zinc, the acid exerted alittle direct action upon it, so that a small stream of hydrogen bubbleswas continually rising from its surface; a little of this hydrogengradually dissolved in the dilute acid, and was in part set free againstthe surfaces of the rod and the plate, according to the well-known actionof such solid bodies in solutions of gases (623. &c. ). 

972. But if the gases had been evolved in the second vessel by thedecomposition of water, and had tended to dissolve, still there would havebeen every reason to expect that a few bubbles should have appeared on theelectrodes, especially on the negative one, if it were only because of itsaction as a nucleus on the solution supposed to be formed; but noneappeared even after twelve days. 

973. When a few drops only of nitric acid were added to the vessel A, fig. 84, then the results were altogether different. In less than five minutesbubbles of gas appeared on the plates P' and P" in the second vessel. Toprove that this was the effect of the electric current (which by trial at_c_ was found at the same time to be passing, ) the connexion at _c_ wasbroken, the plates P'P" cleared from bubbles and left in the acid of thevessel B, for fifteen minutes: during that time no bubbles appeared uponthem; but on restoring the communication at _c_, a minute did not elapsebefore gas appeared in bubbles upon the plates. The proof, therefore, ismost full and complete, that the current excited by dilute sulphuric acidwith a little nitric acid in vessel A, has intensity enough to overcome thechemical affinity exerted between the oxygen and hydrogen of the water inthe vessel B, whilst that excited by dilute sulphuric acid alone has _not_sufficient intensity. 

974. On using a strong solution of caustic potassa in the vessel A, toexcite the current, it was found by the decomposing effects at _e_, thatthe current passed. But it had not intensity enough to decompose the waterin the vessel B; for though left for fourteen days, during the whole ofwhich time the current was found to be passing, still not the slightestappearance of gas appeared on the plates P'P", nor any other signs of thewater having suffered decomposition. 

975. Sulphate of soda in solution was then experimented with, for thepurpose of ascertaining with respect to it, whether a certain electrolyticintensity was also required for its decomposition in this state, in analogywith the result established with regard to water (974). The apparatus wasarranged as in fig. 85; P and Z are the platina and zinc plates dippinginto a solution of common salt; _a_ and _b_ are platina plates connected bywires of platina (except in the galvanometer _g_) with P and Z; _c_ is aconnecting wire of platina, the ends of which can be made to rest either onthe plates _a, b_, or on the papers moistened in solutions which are placedupon them; so that the passage of the current without decomposition, orwith one or two decompositions, was under ready command, as far asarrangement was concerned. In order to change the _anodes_ and _cathodes_at the places of decomposition, the form of apparatus fig. 86, wasoccasionally adopted. Here only one platina plate, _c_, was used; bothpieces of paper on which decomposition was to be effected were placed uponit, the wires from P and Z resting upon these pieces of paper, or upon theplate _c_, according as the current with or without decomposition of thesolutions was required. 

976. On placing solution of iodide of potassium in paper at one of thedecomposing localities, and solution of sulphate of soda at the other, sothat the electric current should pass through both at once, the solution ofiodide was slowly decomposed, yielding iodine at the _anode_ and alkali atthe _cathode_; but the solution of sulphate of soda exhibited no signs ofdecomposition, neither acid nor alkali being evolved from it. On placingthe wires so that the iodide alone was subject to the action of the current(900. ), it was quickly and powerfully decomposed; but on arranging them sothat the sulphate of soda alone was subject to action, it still refused toyield up its elements. Finally, the apparatus was so arranged under a wetbell-glass, that it could be left for twelve hours, the current passingduring the whole time through a solution of sulphate of soda, retained inits place by only two thicknesses of bibulous litmus and turmeric paper. Atthe end of that time it was ascertained by the decomposition of iodide ofpotassium at the second place of action, that the current was passing andhad passed for the twelve hours, and yet no trace of acid or alkali fromthe sulphate of soda appeared. 

977. From these experiments it may, I think, be concluded, that a solutionof sulphate of soda can conduct a current of electricity, which is unableto decompose the neutral salt present; that this salt in the state ofsolution, like water, requires a certain electrolytic intensity for itsdecomposition; and that the necessary intensity is much higher for thissubstance than for the iodide of potassium in a similar state of solution. 

978. I then experimented on bodies rendered decomposable by fusion, andfirst on _chloride of lead_. The current was excited by dilute sulphuricacid without any nitric acid between zinc and platina plates, fig. 87, andwas then made to traverse a little chloride of lead fused upon glass at_a_, a paper moistened in solution of iodide of potassium at _b_, and agalvanometer at _g_. The metallic terminations at _a_ and _b_ were ofplatina. Being thus arranged, the decomposition at _b_ and the deflectionat _g_ showed that an electric current was passing, but there was noappearance of decomposition at _a_, not even after a _metallic_communication at _b_ was established. The experiment was repeated severaltimes, and I am led to conclude that in this case the current has notintensity sufficient to cause the decomposition of the chloride of lead;and further, that, like water (974. ), fused chloride of lead can conduct anelectric current having an intensity below that required to effectdecomposition. 

979. _Chloride of silver_ was then placed at _a_, fig. 87, instead ofchloride of lead. There was a very ready decomposition of the solution ofiodide of potassium at _b_, and when metallic contact was made there, veryconsiderable deflection of the galvanometer needle at _g_. Platina alsoappeared to be dissolved at the anode of the fused chloride at _a_, andthere was every appearance of a decomposition having been effected there. 

980. A further proof of decomposition was obtained in the following manner. The platina wires in the fused chloride at _a_ were brought very neartogether (metallic contact having been established at _b_), and left so;the deflection at the galvanometer indicated the passage of a current, feeble in its force, but constant. After a minute or two, however, theneedle would suddenly be violently affected, and indicate a current asstrong as if metallic contact had taken place at _a_. This I actually foundto be the case, for the silver reduced by the action of the currentcrystallized in long delicate spiculæ, and these at last completed themetallic communication; and at the same time that they transmitted a morepowerful current than the fused chloride, they proved that electro-chemicaldecomposition of that chloride had been going on. Hence it appears, thatthe current excited by dilute sulphuric acid between zinc and platina, hasan intensity above that required to electrolyze the fused chloride ofsilver when placed between platina electrodes, although it has notintensity enough to decompose chloride of lead under the samecircumstances. 

981. A drop of _water_ placed at _a_ instead of the fused chlorides, showedas in the former case (970. ), that it could conduct a current unable todecompose it, for decomposition of the solution of iodide at _b_ occurredafter some time. But its conducting power was much below that of the fusedchloride of lead (978. ). 

982. Fused _nitre_ at _a_ conducted much better than water: I was unable todecide with certainty whether it was electrolyzed, but I incline to thinknot, for there was no discoloration against the platina at the _cathode_. If sulpho-nitric acid had been used in the exciting vessel, both the nitreand the chloride of lead would have suffered decomposition like the water(906. ). 

983. The results thus obtained of conduction without decomposition, and thenecessity of a certain electrolytic intensity for the separation of the_ions_ of different electrolytes, are immediately connected with theexperiments and results given in § 10. Of the Fourth Series of theseResearches (418. 423. 444. 419. ). But it will require a more exactknowledge of the nature of intensity, both as regards the first origin ofthe electric current, and also the manner in which it may be reduced, orlowered by the intervention of longer or shorter portions of badconductors, whether decomposable or not, before their relation can beminutely and fully understood. 

984. In the case of water, the experiments I have as yet made, appear toshow, that, when the electric current is reduced in intensity below thepoint required for decomposition, then the degree of conduction is the samewhether sulphuric acid, or any other of the many bodies which can affectits transferring power as an electrolyte, are present or not. Or, in otherwords, that the necessary electrolytic intensity for water is the samewhether it be pure, or rendered a better conductor by the addition of thesesubstances; and that for currents of less intensity than this, the water, whether pure or acidulated, has equal conducting power. An apparatus, fig. 84, was arranged with dilute sulphuric acid in the vessel A, and puredistilled water in the vessel B. By the decomposition at _c_, it appearedas if water was a _better_ conductor than dilute sulphuric acid for acurrent of such low intensity as to cause no decomposition. I am inclined, however, to attribute this apparent superiority of water to variations inthat peculiar condition of the platina electrodes which is referred tofurther on in this Series (1040. ), and which is assumed, as far as I canjudge, to a greater degree in dilute sulphuric acid than in pure water. Thepower therefore, of acids, alkalies, salts, and other bodies in solution, to increase conducting power, appears to hold good only in those caseswhere the electrolyte subject to the current suffers decomposition, andloses all influence when the current transmitted has too low an intensityto affect chemical change. It is probable that the ordinary conductingpower of an electrolyte in the solid state (419. ) is the same as that whichit possesses in the fluid state for currents, the tension of which isbeneath the due electrolytic intensity. 

985. Currents of electricity, produced by less than eight or ten series ofvoltaic elements, can be reduced to that intensity at which water canconduct them without suffering decomposition, by causing them to passthrough three or four vessels in which water shall be successivelyinterposed between platina surfaces. The principles of interference uponwhich this effect depends, will be described hereafter (1009. 1018. ), butthe effect may be useful in obtaining currents of standard intensity, andis probably applicable to batteries of any number of pairs of plates. 

986. As there appears every reason to expect that all electrolytes will befound subject to the law which requires an electric current of a certainintensity for their decomposition, but that they will differ from eachother in the degree of intensity required, it will be desirable hereafterto arrange them in a table, in the order of their electrolytic intensities. Investigations on this point must, however, be very much extended, andinclude many more bodies than have been here mentioned before such a tablecan be constructed. It will be especially needful in such experiments, todescribe the nature of the electrodes used, or, if possible, to select suchas, like platina or plumbago in certain cases, shall have no power ofassisting the separation of the _ions_ to be evolved (913). 

987. Of the two modes in which bodies can transmit the electric forces, namely, that which is so characteristically exhibited by the metals, andusually called conduction, and that in which it is accompanied bydecomposition, the first appears common to all bodies, although it occurswith almost infinite degrees of difference; the second is at presentdistinctive of the electrolytes. It is, however, just possible that it mayhereafter be extended to the metals; for their power of conducting withoutdecomposition may, perhaps justly, be ascribed to their requiring a veryhigh electrolytic intensity for their decomposition. 

987-1/2. The establishment of the principle that a certain electrolyticintensity is necessary before decomposition can be effected, is of greatimportance to all those considerations which arise regarding the probableeffects of weak currents, such for instance as those produced by naturalthermo-electricity, or natural voltaic arrangements in the earth. For toproduce an effect of decomposition or of combination, a current must notonly exist, but have a certain intensity before it can overcome thequiescent affinities opposed to it, otherwise it will be conducted, producing no permanent chemical effects. On the other hand, the principlesare also now evident by which an opposing action can be so weakened by thejuxtaposition of bodies not having quite affinity enough to cause directaction between them (913. ), that a very weak current shall be able to raisethe sum of actions sufficiently high, and cause chemical changes to occur. 

988. In concluding this division _on the intensity necessary forelectrolyzation_, I cannot resist pointing out the following remarkableconclusion in relation to intensity generally. It would appear that when avoltaic current is produced, having a certain intensity, dependent upon thestrength of the chemical affinities by which that current is excited(916. ), it can decompose a particular electrolyte without relation to thequantity of electricity passed, the _intensity_ deciding whether theelectrolyte shall give way or not. If that conclusion be confirmed, then wemay arrange circumstances so that the _same quantity_ of electricity maypass in the _same time_, in at the _same surface_, into the _samedecomposing body in the same state_, and yet, differing in intensity, will_decompose in one case and in the other not_:--for taking a source of toolow an intensity to decompose, and ascertaining the quantity passed in agiven time, it is easy to take another source having a sufficientintensity, and reducing the quantity of electricity from it by theintervention of bad conductors to the same proportion as the formercurrent, and then all the conditions will be fulfilled which are requiredto produce the result described. 

¶ iii. _On associated Voltaic Circles, or the Voltaic Battery. _

989. Passing from the consideration of single circles (875. &c. ) to theirassociation in the voltaic battery, it is a very evident consequence, thatif matters are so arranged that two sets of affinities, in place of beingopposed to each other as in figg. 73. 76. (880. 891. ), are made to act inconformity, then, instead of either interfering with the other, it willrather assist it. This is simply the case of two voltaic pairs of metalsarranged so as to form one circuit. In such arrangements the activity ofthe whole is known to be increased, and when ten, or a hundred, or anylarger number of such alternations are placed in conformable associationwith each other, the power of the whole becomes proportionally exalted, andwe obtain that magnificent instrument of philosophic research, the _voltaicbattery_. 

990. But it is evident from the principles of definite action already laiddown, that the _quantity_ of electricity in the current cannot be increasedwith the increase of the _quantity of metal_ oxidized and dissolved at eachnew place of chemical action. A single pair of zinc and platina platesthrows as much electricity into the form of a current, by the oxidation of32. 5 grains of the zinc (868. ) as would be circulated by the samealteration of a thousand times that quantity, or nearly five pounds ofmetal oxidized at the surface of the zinc plates of a thousand pairs placedin regular battery order. For it is evident, that the electricity whichpasses across the acid from the zinc to the platina in the first cell, andwhich has been associated with, or even evolved by, the decomposition of adefinite portion of water in that cell, cannot pass from the zinc to theplatina across the acid in the second cell, without the decomposition ofthe same quantity of water there, and the oxidation of the same quantity ofzinc by it (924. 949. ). The same result recurs in every other cell; theelectro-chemical equivalent of water must be decomposed in each, before thecurrent can pass through it; for the quantity of electricity passed and thequantity of electrolyte decomposed, _must_ be the equivalents of eachother. The action in each cell, therefore, is not to increase the quantityset in motion in any one cell, but to aid in urging forward that quantity, the passing of which is consistent with the oxidation of its own zinc; andin this way it exalts that peculiar property of the current which weendeavour to express by the term _intensity_, without increasing the_quantity_ beyond that which is proportionate to the quantity of zincoxidized in any single cell of the series. 

991. To prove this, I arranged ten pairs of amalgamated zinc and platinaplates with dilute sulphuric acid in the form of a battery. On completingthe circuit, all the pairs acted and evolved gas at the surfaces of theplatina. This was collected and found to be alike in quantity for eachplate; and the quantity of hydrogen evolved at any one platina plate was inthe same proportion to the quantity of metal dissolved from any one zincplate, as was given in the experiment with a single pair (864. &c. ). It wastherefore certain, that, just as much electricity and no more had passedthrough the series of ten pair of plates as had passed through, or wouldhave been put into motion by, any single pair, notwithstanding that tentimes the quantity of zinc had been consumed. 

992. This truth has been proved also long ago in another way, by the actionof the evolved current on a magnetic needle; the deflecting power of onepair of plates in a battery being equal to the deflecting power of thewhole, provided the wires used be sufficiently large to carry the currentof the single pair freely; but the _cause_ of this equality of action couldnot be understood whilst the definite action and evolution of electricity(783. 869. ) remained unknown. 

993. The superior decomposing power of a battery over a single pair ofplates is rendered evident in two ways. Electrolytes held together by anaffinity so strong as to resist the action of the current from a singlepair, yield up their elements to the current excited by many pairs; andthat body which is decomposed by the action of one or of few pairs ofmetals, &c. , is resolved into its _ions_ the more readily as it is actedupon by electricity urged forward by many alternations. 

994. Both these effects are, I think, easily understood. Whatever_intensity_ may be, (and that must of course depend upon the nature ofelectricity, whether it consist of a fluid or fluids, or of vibrations ofan ether, or any other kind or condition of matter, ) there seems to be nodifficulty in comprehending that the _degree_ of intensity at which acurrent of electricity is evolved by a first voltaic element, shall beincreased when that current is subjected to the action of a second voltaicelement, acting in conformity and possessing equal powers with the first:and as the decompositions are merely opposed actions, but exactly of thesame kind as those which generate the current (917. ), it seems to be anatural consequence, that the affinity which can resist the force of asingle decomposing action may be unable to oppose the energies of manydecomposing actions, operating conjointly, as in the voltaic battery. 

995. That a body which can give way to a current of feeble intensity, should give way more freely to one of stronger force, and yet involve nocontradiction to the law of definite electrolytic action, is perfectlyconsistent. All the facts and also the theory I have ventured to put forth, tend to show that the act of decomposition opposes a certain force to thepassage of the electric current; and, that this obstruction should beovercome more or less readily, in proportion to the greater or lessintensity of the decomposing current, is in perfect consistency with allour notions of the electric agent. 

996. I have elsewhere (947. ) distinguished the chemical action of zinc anddilute sulphuric acid into two portions; that which, acting effectually onthe zinc, evolves hydrogen at once upon its surface, and that which, producing an arrangement of the chemical forces throughout the electrolytepresent, (in this case water, ) tends to take oxygen from it, but cannot doso unless the electric current consequent thereon can have free passage, and the hydrogen be delivered elsewhere than against the zinc. The electriccurrent depends altogether upon the second of these; but when the currentcan pass, by favouring the electrolytic action it tends to diminish theformer and increase the latter portion. 

997. It is evident, therefore, that when ordinary zinc is used in a voltaicarrangement, there is an enormous waste of that power which it is theobject to throw into the form of an electric current; a consequence whichis put in its strongest point of view when it is considered that threeounces and a half of zinc, properly oxidized, can circulate enoughelectricity to decompose nearly one ounce of water, and cause the evolutionof about 2100 cubic inches of hydrogen gas. This loss of power not onlytakes place during the time the electrodes of the battery are incommunication, being then proportionate to the quantity of hydrogen evolvedagainst the surface of any one of the zinc plates, but includes also _all_the chemical action which goes on when the extremities of the pile are notin communication. 

998. This loss is far greater with ordinary zinc than with the pure metal, as M. De la Rive has shown[A]. The cause is, that when ordinary zinc isacted upon by dilute sulphuric acid, portions of copper, lead, cadmium, orother metals which it may contain, are set free upon its surface; andthese, being in contact with the zinc, form small but very active voltaiccircles, which cause great destruction of the zinc and evolution ofhydrogen, apparently upon the zinc surface, but really upon the surface ofthese incidental metals. In the same proportion as they serve to dischargeor convey the electricity back to the zinc, do they diminish its power ofproducing an electric current which shall extend to a greater distanceacross the acid, and be discharged only through the copper or platina platewhich is associated with it for the purpose of forming a voltaic apparatus. 

 [A] Quarterly Journal of Science, 1831, p. 388; or Bibliothèque Universelle, 1830, p. 391. 

999. All these evils are removed by the employment of an amalgam of zinc inthe manner recommended by Mr. Kemp[A], or the use of the amalgamated zincplates of Mr. Sturgeon (863. ), who has himself suggested and objected totheir application in galvanic batteries; for he says, "Were it not onaccount of the brittleness and other inconveniences occasioned by theincorporation of the mercury with the zinc, amalgamation of the zincsurfaces in galvanic batteries would become an important improvement; forthe metal would last much longer, and remain bright for a considerabletime, even for several successive hours; essential considerations in theemployment of this apparatus[B]. "

 [A] Jameson's Edinburgh Journal, October 1828. 

 [B] Recent Experimental Researches, p. 42, &c. Mr. Sturgeon is of course unaware of the definite production of electricity by chemical action, and is in fact quoting the experiment as the strongest argument _against_ the chemical theory of galvanism. 

1000. Zinc so prepared, even though impure, does not sensibly decompose thewater of dilute sulphuric acid, but still has such affinity for the oxygen, that the moment a metal which, like copper or platina, has little or noaffinity, touches it in the acid, action ensues, and a powerful andabundant electric current is produced. It is probable that the mercury actsby bringing the surface, in consequence of its fluidity, into one uniformcondition, and preventing those differences in character between one spotand another which are necessary for the formation of the minute voltaiccircuits referred to (998. ). If any difference does exist at the firstmoment, with regard to the proportion of zinc and mercury, at one spot onthe _surface_, as compared with another, that spot having the least mercuryis first acted on, and, by solution of the zinc, is soon placed in the samecondition as the other parts, and the whole plate rendered superficiallyuniform. One part cannot, therefore, act as a discharger to another; andhence _all_ the chemical power upon the water at its surface is in thatequable condition (949. ), which, though it tends to produce an electriccurrent through the liquid to another plate of metal which can act as adischarger (950. ), presents no irregularities by which any one part, havingweaker affinities for oxygen, can act as a discharger to another. Twoexcellent and important consequences follow upon this state of the metal. The first is, that _the full equivalent_ of electricity is obtained for theoxidation of a certain quantity of zinc; the second, that a batteryconstructed with the zinc so prepared, and charged with dilute sulphuricacid, is active only whilst the electrodes are connected, and ceases to actor be acted upon by the acid the instant the communication is broken. 

1001. I have had a small battery of ten pairs of plates thus constructed, and am convinced that arrangements of this kind will be very important, especially in the development and illustration of the philosophicalprinciples of the instrument. The metals I have used are amalgamated zincand platina, connected together by being soldered to platina wires, thewhole apparatus having the form of the couronne des tasses. The liquid usedwas dilute sulphuric acid of sp. Gr. 1. 25. No action took place upon themetals except when the electrodes were in communication, and then theaction upon the zinc was only in proportion to the decomposition in theexperimental cell; for when the current was retarded there, it was retardedalso in the battery, and no waste of the powers of the metal was incurred. 

1002. In consequence of this circumstance, the acid in the cells remainedactive for a very much longer time than usual. In fact, time did not tendto lower it in any sensible degree: for whilst the metal was preserved tobe acted upon at the proper moment, the acid also was preserved almost atits first strength. Hence a constancy of action far beyond what can beobtained by the use of common zinc. 

1003. Another excellent consequence was the renewal, during the interval ofrest, between two experiments of the first and most efficient state. Whenan amalgamated zinc and a platina plate, immersed in dilute sulphuric acid, are first connected, the current is very powerful, but instantly sinks verymuch in force, and in some cases actually falls to only an eighth or atenth of that first produced (1036. ). This is due to the acid which is incontact with the zinc becoming neutralized by the oxide formed; thecontinued quick oxidation of the metal being thus prevented. With ordinaryzinc, the evolution of gas at its surface tends to mingle all the liquidtogether, and thus bring fresh acid against the metal, by which the oxideformed there can be removed. With the amalgamated zinc battery, at everycessation of the current, the saline solution against the zinc is graduallydiffused amongst the rest of the liquid; and upon the renewal of contact atthe electrodes, the zinc plates are found most favourably circumstanced forthe production of a ready and powerful current. 

1004. It might at first be imagined that amalgamated zinc would be muchinferior in force to common zinc, because, of the lowering of its energy, which the mercury might be supposed to occasion over the whole of itssurface; but this is not the case. When the electric currents of two pairsof platina and zinc plates were opposed, the difference being that one ofthe zincs was amalgamated and the other not, the current from theamalgamated zinc was most powerful, although no gas was evolved against it, and much was evolved at the surface of the unamalgamated metal. Again, asDavy has shown[A], if amalgamated and unamalgamated zinc be put in contact, and dipped into dilute sulphuric acid, or other exciting fluids, the formeris positive to the latter, i. E. The current passes from the amalgamatedzinc, through the fluid, to the unprepared zinc. This he accounts for bysupposing that "there is not any inherent and specific property in eachmetal which gives it the electrical character, but that it depends upon itspeculiar state--on that form of aggregation which fits it for chemicalchange. "

 [A] Philosophical Transactions, 1826, p. 405. 

1005. The superiority of the amalgamated zinc is not, however, due to anysuch cause, but is a very simple consequence of the state of the fluid incontact with it; for as the unprepared zinc acts directly and alone uponthe fluid, whilst that which is amalgamated does not, the former (by theoxide it produces) quickly neutralizes the acid in contact with itssurface, so that the progress of oxidation is retarded, whilst at thesurface of the amalgamated zinc, any oxide formed is instantly removed bythe free acid present, and the clean metallic surface is always ready toact with full energy upon the water. Hence its superiority (1037. ). 1006. The progress of improvement in the voltaic battery and itsapplications, is evidently in the contrary direction at present to what itwas a few years ago; for in place of increasing the number of plates, thestrength of acid, and the extent altogether of the instrument, the changeis rather towards its first state of simplicity, but with a far moreintimate knowledge and application of the principles which govern its forceand action. Effects of decomposition can now be obtained with ten pairs ofplates (417. ), which required five hundred or a thousand pairs for theirproduction in the first instance. The capability of decomposing fusedchlorides, iodides, and other compounds, according to the law beforeestablished (380. &c. ), and the opportunity of collecting certain of theproducts, without any loss, by the use of apparatus of the nature of thosealready described (789. 814. &c. ), render it probable that the voltaicbattery may become a useful and even economical manufacturing instrument;for theory evidently indicates that an equivalent of a rare substance maybe obtained at the expense of three or four equivalents of a very commonbody, namely, zinc: and practice seems thus far to justify the expectation. In this point of view I think it very likely that plates of platina orsilver may be used instead of plates of copper with advantage, and thatthen the evil arising occasionally from solution of the copper, and itsprecipitation on the zinc, (by which the electromotive power of the zinc isso much injured, ) will be avoided (1047. ). 

¶ iv. _On the Resistance of an Electrolyte to Electrolytic Action, and onInterpositions. _

1007. I have already illustrated, in the simplest possible form ofexperiment (891. 910. ), the resistance established at the place ofdecomposition to the force active at the exciting place. I purposeexamining the effects of this resistance more generally; but it is ratherwith reference to their practical interference with the action andphenomena of the voltaic battery, than with any intention at this time tooffer a strict and philosophical account of their nature. Their general andprincipal cause is the resistance of the chemical affinities to beovercome; but there are numerous other circumstances which have a jointinfluence with these forces (1034. 1040. &c. ), each of which would requirea minute examination before a correct account of the whole could be given. 

1008. As it will be convenient to describe the experiments in a formdifferent to that in which they were made, both forms shall first beexplained. Plates of platina, copper, zinc, and other metals, about threequarters of an inch wide and three inches long, were associated together inpairs by means of platina wires to which they were soldered, fig. 88, theplates of one pair being either alike or different, as might be required. These were arranged in glasses, fig. 89, so as to form Volta's crown ofcups. The acid or fluid in the cups never covered the whole of any plate;and occasionally small glass rods were put into the cups, between theplates, to prevent their contact. Single plates were used to terminate theseries and complete the connexion with a galvanometer, or with adecomposing apparatus (899. 968. &c. ), or both. Now if fig. 90 be examinedand compared with fig. 91, the latter may be admitted as representing theformer in its simplest condition; for the cups i, ii, and iii of theformer, with their contents, are represented by the cells i, ii, and iii ofthe latter, and the metal plates Z and P of the former by the similarplates represented Z and P in the latter. The only difference, in fact, between the apparatus, fig. 90, and the trough represented fig. 91, is thattwice the quantity of surface of contact between the metal and acid isallowed in the first to what would occur in the second. 

1009. When the extreme plates of the arrangement just described, fig. 90, are connected metallically through the galvanometer _g_, then the wholerepresents a battery consisting of two pairs of zinc and platina platesurging a current forward, which has, however, to decompose water unassistedby any direct chemical affinity before it can be transmitted across thecell iii, and therefore before it can circulate. This decomposition ofwater, which is opposed to the passage of the current, may, as a matter ofconvenience, be considered as taking place either against the surfaces ofthe two platina plates which constitute the electrodes in the cell in, oragainst the two surfaces of that platina plate which separates the cells iiand iii, fig. 91, from each other. It is evident that if that plate wereaway, the battery would consist of two pairs of plates and two cells, arranged in the most favourable position for the production of a current. The platina plate therefore, which being introduced as at _x_, has oxygenevolved at one surface and hydrogen at the other (that is, if thedecomposing current passes), may be considered as the cause of anyobstruction arising from the decomposition of water by the electrolyticaction of the current; and I have usually called it the interposed plate. 

1010. In order to simplify the conditions, dilute sulphuric acid was firstused in all the cells, and platina for the interposed plates; for then theinitial intensity of the current which tends to be formed is constant, being due to the power which zinc has of decomposing water; and theopposing force of decomposition is also constant, the elements of the waterbeing unassisted in their separation at the interposed plates by anyaffinity or secondary action at the electrodes (744. ), arising either fromthe nature of the plate itself or the surrounding fluid. 

1011. When only one voltaic pair of zinc and platina plates was used, thecurrent of electricity was entirely stopped to all practical purposes byinterposing one platina plate, fig. 92, i. E. By requiring of the currentthat it should decompose water, and evolve both its elements, before itshould pass. This consequence is in perfect accordance with the viewsbefore given (910. 917. 973. ). For as the whole result depends upon theopposition of forces at the places of electric excitement andelectro-decomposition, and as water is the substance to be decomposed atboth before the current can move, it is not to be expected that the zincshould have such powerful attraction for the oxygen, as not only to be ableto take it from its associated hydrogen, but leave such a surplus of forceas, passing to the second place of decomposition, should be there able toeffect a second separation of the elements of water. Such an effect wouldrequire that the force of attraction between zinc and oxygen should underthe circumstances be _at least_ twice as great as the force of attractionbetween the oxygen and hydrogen. 

1012. When two pairs of zinc and platina exciting plates were used, thecurrent was also practically stopped by one interposed platina plate, fig. 93. There was a very feeble effect of a current at first, but it ceasedalmost immediately. It will be referred to, with many other similareffects, hereafter (1017. ). 

1013. Three pairs of zinc and platina plates, fig. 94, were able to producea current which could pass an interposed platina plate, and effect theelectrolyzation of water in cell iv. The current was evident, both by thecontinued deflection of the galvanometer, and the production of bubbles ofoxygen and hydrogen at the electrodes in cell iv. Hence the accumulatedsurplus force of three plates of zinc, which are active in decomposingwater, is more than equal, when added together, to the force with whichoxygen and hydrogen are combined in water, and is sufficient to cause theseparation of these elements from each other. 

1014. The three pairs of zinc and platina plates were now opposed by twointervening platina plates, fig. 95. In this case the current was stopped. 

1015. Four pairs of zinc and platina plates were also neutralized by twointerposed platina plates, fig. 96. 

1016. Five pairs of zinc and platina, with two interposed platina plates, fig. 97, gave a feeble current; there was permanent deflection at thegalvanometer, and decomposition in the cells vi and vii. But the currentwas very feeble; very much less than when all the intermediate plates wereremoved and the two extreme ones only retained: for when they were placedsix inches asunder in one cell, they gave a powerful current. Hence fiveexciting pairs, with two interposed obstructing plates, do not give acurrent at all comparable to that of a single unobstructed pair. 

1017. I have already said that a _very feeble current_ passed when theseries included one interposed platina and two pairs of zinc and platinaplates (1012. ). A similarly feeble current passed in every case, and evenwhen only one exciting pair and four intervening platina plates were used, fig. 98, a current passed which could be detected at _x_, both by chemicalaction on the solution of iodide of potassium, and by the galvanometer. This current I believe to be due to electricity reduced in intensity belowthe point requisite for the decomposition of water (970. 984. ); for watercan conduct electricity of such low intensity by the same kind of powerwhich it possesses in common with metals and charcoal, though it cannotconduct electricity of higher intensity without suffering decomposition, and then opposing a new force consequent thereon. With an electric currentof, or under this intensity, it is probable that increasing the number ofinterposed platina plates would not involve an increased difficulty ofconduction. 

1018. In order to obtain an idea of the additional interfering power ofeach added platina plate, six voltaic pairs and four intervening platinaswere arranged as in fig. 99; a very feeble current then passed (985. 1017. ). When one of the platinas was removed so that three intervened, acurrent somewhat stronger passed. With two intervening platinas a stillstronger current passed; and with only one intervening platina a very faircurrent was obtained. But the effect of the successive plates, taken in theorder of their interposition, was very different, as might be expected; forthe first retarded the current more powerfully than the second, and thesecond more than the third. 

1019. In these experiments both amalgamated and unamalgamated zinc wereused, but the results generally were the same. 

1020. The effects of retardation just described were altered altogetherwhen changes were made in the _nature of the liquid_ used between theplates, either in what may be called the _exciting_ or the _retarding_cells. Thus, retaining the exciting force the same, by still using puredilute sulphuric acid for that purpose, if a little nitric acid were addedto the liquid in the _retarding_ cells, then the transmission of thecurrent was very much facilitated. For instance, in the experiment with onepair of exciting plates and one intervening plate (1011. ), fig. 92, when afew drops of nitric acid were added to the contents of cell ii, then thecurrent of electricity passed with considerable strength (though it soonfell from other causes (1036; 1040. ), ) and the same increased effect wasproduced by the nitric acid when many interposed plates were used. 

1021. This seems to be a consequence of the diminution of the difficulty ofdecomposing water when its hydrogen, instead of being absolutely expelled, as in the former cases, is transferred to the oxygen of the nitric acid, producing a secondary result at the _cathode_ (752. ); for in accordancewith the chemical views of the electric current and its action alreadyadvanced (913. ), the water, instead of opposing a resistance todecomposition equal to the full amount of the force of mutual attractionbetween its oxygen and hydrogen, has that force counteracted in part, andtherefore diminished by the attraction of the hydrogen at the _cathode_ forthe oxygen of the nitric acid which surrounds it, and with which itultimately combines instead of being evolved in its free state. 

1022. When a little nitric acid was put into the exciting cells, then againthe circumstances favouring the transmission of the current werestrengthened, for the _intensity_ of the current itself was increased bythe addition (906. ). When therefore a little nitric acid was added to boththe _exciting_ and the _retarding_ cells, the current of electricity passedwith very considerable freedom. 

1023. When dilute muriatic acid was used, it produced and transmitted acurrent more easily than pure dilute sulphuric acid, but not so readily asdilute nitric acid. As muriatic acid appears to be decomposed more freelythan water (765. ), and as the affinity of zinc for chlorine is verypowerful, it might be expected to produce a current more intense than thatfrom the use of dilute sulphuric acid; and also to transmit it more freelyby undergoing decomposition at a lower intensity (912. ). 

1024. In relation to the effect of these interpositions, it is necessary tostate that they do not appear to be at all dependent upon the size of theelectrodes, or their distance from each other in the acid, except that whena current _can pass_, changes in these facilitate or retard its passage. For on repeating the experiment with one intervening and one pair ofexciting plates (1011. ), fig. 92, and in place of the interposed plate Pusing sometimes a mere wire, and sometimes very large plates (1008. ), andalso changing the terminal exciting plates Z and P, so that they weresometimes wires only and at others of great size, still the results werethe same as those already obtained. 

1025. In illustration of the effect of distance, an experiment like thatdescribed with two exciting pairs and one intervening plate (1012. ), fig. 93, was arranged so that the distance between the plates in the third cellcould be increased to six or eight inches, or diminished to the thicknessof a piece of intervening bibulous paper. Still the result was the same inboth cases, the effect not being sensibly greater, when the plates weremerely separated by the paper, than when a great way apart; so that theprincipal opposition to the current in this case does not depend upon the_quantity_ of intervening electrolytic conductor, but on the _relation ofits elements to the intensity of the current_, or to the chemical nature ofthe electrodes and the surrounding fluids. 

1026. When the acid was sulphuric acid, _increasing its strength_ in any ofthe cells, caused no change in the effects; it did not produce a moreintense current in the exciting cells (908. ), or cause the current producedto traverse the decomposing cells more freely. But if to very weaksulphuric acid a few drops of nitric acid were added, then either one orother of those effects could be produced; and, as might be expected in acase like this, where the exciting or conducting action bore a _direct_reference to the acid itself, increasing the strength of this (the nitricacid), also increased its powers. 

1027. The _nature of the interposed plate_ was now varied to show itsrelation to the phenomena either of excitation or retardation, andamalgamated zinc was first substituted for platina. On employing onevoltaic pair and one interposed zinc plate, fig. 100, there was as powerfula current, apparently, as if the interposed zinc plate was away. Hydrogenwas evolved against P in cell ii, and against the side of the second zincin cell i; but no gas appeared against the side of the zinc in cell ii, noragainst the zinc in cell i. 

1028. On interposing two amalgamated zinc plates, fig. 101, instead of one, there was still a powerful current, but interference had taken place. Onusing three intermediate zinc plates, fig. 102, there was still furtherretardation, though a good current of electricity passed. 

1029. Considering the retardation as due to the inaction of the amalgamatedzinc upon the dilute acid, in consequence of the slight though generaleffect of diminished chemical power produced by the mercury on the surface, and viewing this inaction as the circumstance which rendered it necessarythat each plate should have its tendency to decompose water assistedslightly by the electric current, it was expected that plates of the metalin the unamalgamated state would probably not require such assistance, andwould offer no sensible impediment to the passing of the current. Thisexpectation was fully realized in the use of two and three interposedunamalgamated plates. The electric current passed through them as freely asif there had been no such plates in the way. They offered no obstacle, because they could decompose water without the current; and the latter hadonly to give direction to a part of the forces, which would have beenactive whether it had passed or not. 

1030. Interposed plates of copper were then employed. These seemed at firstto occasion no obstruction, but after a few minutes the current almostentirely ceased. This effect appears due to the surfaces taking up thatpeculiar condition (1010. ) by which they tend to produce a reverse current;for when one or more of the plates were turned round, which could easily beeffected with the couronne des tasses form of experiment, fig. 90, then thecurrent was powerfully renewed for a few moments, and then again ceased. Plates of platina and copper, arranged as a voltaic pile with dilutesulphuric acid, could not form a voltaic trough competent to act for morethan a _few_ minutes, because of this peculiar counteracting effect. 

1031. All these effects of retardation, exhibited by decomposition againstsurfaces for which the evolved elements have more or less affinity, or arealtogether deficient in attraction, show generally, though beautifully, thechemical relations and source of the current, and also the balanced stateof the affinities at the places of excitation and decomposition. In thisway they add to the mass of evidence in favour of the identity of the two;for they demonstrate, as it were, the antagonism of the _chemical powers_at the electromotive part with the _chemical powers_ at the interposedparts; they show that the first are _producing_ electric effects, and thesecond _opposing_ them; they bring the two into direct relation; they provethat either can determine the other, thus making what appears to be causeand effect convertible, and thereby demonstrating that both chemical andelectrical action are merely two exhibitions of one single agent or power(916. &c. ). 

1032. It is quite evident, that as water and other electrolytes can conductelectricity without suffering decomposition (986. ), when the electricity isof sufficiently low intensity, it may not be asserted as absolutely true inall cases, that whenever electricity passes through an electrolyte, itproduces a definite effect of decomposition. But the quantity ofelectricity which can pass in a given time through an electrolyte withoutcausing decomposition, is so small as to bear no comparison to thatrequired in a case of very moderate decomposition, and with electricityabove the intensity required for electrolyzation, I have found no sensibledeparture as yet from the law of _definite electrolytic action_ developedin the preceding series of these Researches (783. &c. ). 

1033. I cannot dismiss this division of the present Paper without making areference to the important experiments of M. Aug. De la Rive on the effectsof interposed plates[A]. As I have had occasion to consider such platesmerely as giving rise to new decompositions, and in that way only causingobstruction to the passage of the electric current, I was freed from thenecessity of considering the peculiar effects described by thatphilosopher. I was the more willing to avoid for the present touching uponthese, as I must at the same time have entered into the views of SirHumphry Davy upon the same subject[B] and also those of Marianini[C] andHitter[D], which are connected with it. 

 [A] Annales de Chimie, tom. Xxviii. P 190; and Mémoires de Génève. 

 [B] Philosophical Transactions, 1826, p. 413. 

 [C] Annales de Chimie, tom. Xxxiii. Pp. 117, 119, &c. 

 [D] Journal de Physique, tom. Lvii. Pp. 319, 350. 

¶ v. _General Remarks on the active Voltaic Battery. _

1034. When the ordinary voltaic battery is brought into action, its veryactivity produces certain effects, which re-act upon it, and cause seriousdeterioration of its power. These render it an exceedingly inconstantinstrument as to the _quantity_ of effect which it is capable of producing. They are already, in part, known and understood; but as their importance, and that of certain other coincident results, will be more evident byreference to the principles and experiments already stated and described, Ihave thought it would be useful, in this investigation of the voltaic pile, to notice them briefly here. 

1035. When the battery is in action, it causes such substances to be formedand arranged in contact with the plates as very much weaken its power, oreven tend to produce a counter current. They are considered by Sir HumphryDavy as sufficient to account for the phenomena of Ritter's secondarypiles, and also for the effects observed by M. A. De la Rive with interposedplatina plates[A]. 

 [A] Philosophical Transactions, 1826, p. 113. 

1036. I have already referred to this consequence (1003. ), as capable, insome cases, of lowering the force of the current to one-eighth or one-tenthof what it was at the first moment, and have met with instances in whichits interference was very great. In an experiment in which one voltaic pairand one interposed platina plate were used with dilute sulphuric acid inthe cells fig. 103, the wires of communication were so arranged, that theend of that marked 3 could be placed at pleasure upon paper moistened inthe solution of iodide of potassium at _x_, or directly upon the platinaplate there. If, after an interval during which the circuit had not beencomplete, the wire 3 were placed upon the paper, there was evidence of acurrent, decomposition ensued, and the galvanometer was affected. If thewire 3 were made to touch the metal of _p_, a comparatively strong suddencurrent was produced, affecting the galvanometer, but lasting only for amoment; the effect at the galvanometer ceased, and if the wire 3 wereplaced on the paper at _x_, no signs of decomposition occurred. On raisingthe wire 3, and breaking the circuit altogether for a while, the apparatusresumed its first power, requiring, however, from five to ten minutes forthis purpose; and then, as before, on making contact between 3 and _p_, there was again a momentary current, and immediately all the effectsapparently ceased. 

1037. This effect I was ultimately able to refer to the state of the filmof fluid in contact with the zinc plate in cell i. The acid of that film isinstantly neutralized by the oxide formed; the oxidation of the zinccannot, of course, go on with the same facility as before; and the chemicalaction being thus interrupted, the voltaic action diminishes with it. Thetime of the rest was required for the diffusion of the liquid, and itsreplacement by other acid. From the serious influence of this cause inexperiments with single pairs of plates of different metals, in which I wasat one time engaged, and the extreme care required to avoid it, I cannothelp feeling a strong suspicion that it interferes more frequently andextensively than experimenters are aware of, and therefore direct theirattention to it. 

1038. In considering the effect in delicate experiments of this source ofirregularity of action, in the voltaic apparatus, it must be rememberedthat it is only that very small portion of matter which is directly incontact with the oxidizable metal which has to be considered with referenceto the change of its nature; and this portion is not very readily displacedfrom its position upon the surface of the metal (582. 605. ), especially ifthat metal be rough and irregular. In illustration of this effect, I willquote a remarkable experiment. A burnished platina plate (569. ) was putinto hot strong sulphuric acid for an instant only: it was then put intodistilled water, moved about in it, taken out, and wiped dry: it was putinto a second portion of distilled water, moved about in it, and againwiped: it was put into a third portion of distilled water, in which it wasmoved about for nearly eight seconds; it was then, without wiping, put intoa fourth portion of distilled water, where it was allowed to remain fiveminutes. The two latter portions of water were then tested for sulphuricacid; the third gave no sensible appearance of that substance, but thefourth gave indications which were not merely evident, but abundant for thecircumstances under which it had been introduced. The result sufficientlyshows with what difficulty that portion of the substance which is in_contact_ with the metal leaves it; and as the contact of the fluid formedagainst the plate in the voltaic circuit must be as intimate and as perfectas possible, it is easy to see how quickly and greatly it must vary fromthe general fluid in the cells, and how influential in diminishing theforce of the battery this effect must be. 

1039. In the ordinary voltaic pile, the influence of this effect will occurin all variety of degrees. The extremities of a trough of twenty pairs ofplates of Wollaston's construction were connected with thevolta-electrometer, fig. 66. (711. ), of the Seventh Series of theseResearches, and after five minutes the number of bubbles of gas issuingfrom the extremity of the tube, in consequence of the decomposition of thewater, noted. Without moving the plates, the acid between the copper andzinc was agitated by the introduction of a feather. The bubbles wereimmediately evolved more rapidly, above twice the number being produced inthe same portion of time as before. In this instance it is very evidentthat agitation by a feather must have been a very imperfect mode ofrestoring the acid in the cells against the plates towards its first equalcondition; and yet imperfect as the means were, they more than doubled thepower of the battery. The _first effect_ of a battery which is known to beso superior to the degree of action which the battery can sustain, isalmost entirely due to the favourable condition of the acid in contact withthe plates. 

1040. A _second_ cause of diminution in the force of the voltaic battery, consequent upon its own action, is that extraordinary state of the surfacesof the metals (969. ) which was first described, I believe, by Ritter[A], towhich he refers the powers of his secondary piles, and which has been sowell experimented upon by Marianini, and also by A. De la Rive. If theapparatus, fig. 103. (1096. ), be left in action for an hour or two, withthe wire 3 in contact with the plate _p_, so as to allow a free passage forthe current, then, though the contact be broken for ten or twelve minutes, still, upon its renewal, only a feeble current will pass, not at all equalin force to what might be expected. Further, if P^{1} and P^{2} beconnected by a metal wire, a powerful momentary current will pass fromP^{2} to P^{1} through the acid, and therefore in the reverse direction tothat produced by the action of the zinc in the arrangement; and after thishas happened, the general current can pass through the whole of the systemas at first, but by its passage again restores the plates P^{2} and P^{1}into the former opposing condition. This, generally, is the fact describedby Ritter, Marianini, and De la Rive. It has great opposing influence onthe action of a pile, especially if the latter consist of but a smallnumber of alternations, and has to pass its current through manyinterpositions. It varies with the solution in which the interposed platesare immersed, with the intensity of the current, the strength of the pile, the time of action, and especially with accidental discharges of the platesby inadvertent contacts or reversions of the plates during experiments, andmust be carefully watched in every endeavour to trace the source, strength, and variations of the voltaic current. Its effect was avoided in theexperiments already described (1036. &c. ), by making contact between theplates P^{1} and P^{2} before the effect dependent upon the state of thesolution in contact with the zinc plate was observed, and by otherprecautions. 

 [A] Journal de Physique, lvii. P. 349. 

1041. When an apparatus like fig. 98. (1017. ) with several platina plateswas used, being connected with a battery able to force a current throughthem, the power which they acquired, of producing a reversed current, wasvery considerable. 

1042. _Weak and exhausted charges_ should never be used at the same timewith _strong and fresh ones_ in the different cells of a trough, or thedifferent troughs of a battery: the fluid in all the cells should be alike, else the plates in the weaker cells, in place of assisting, retard thepassage of the electricity generated in, and transmitted across, thestronger cells. Each zinc plate so circumstanced has to be assisted indecomposing power before the whole current can pass between it and theliquid. So, that, if in a battery of fifty pairs of plates, ten of thecells contain a weaker charge than the others, it is as if ten decomposingplates were opposed to the transit of the current of forty pairs ofgenerating plates (1031. ). Hence a serious loss of force, and hence thereason why, if the ten pairs of plates were removed, the remaining fortypairs would be much more powerful than the whole fifty. 

1043. Five similar troughs, of ten pairs of plates each, were prepared, four of them with a good uniform charge of acid, and the fifth with thepartially neutralized acid of a used battery. Being arranged in rightorder, and connected with a volta-electrometer (711. ), the whole fiftypairs of plates yielded 1. 1 cubic inch of oxygen and hydrogen in oneminute: but on moving one of the connecting wires so that only the fourwell-charged troughs should be included in the circuit, they produced withthe same volta-electrometer 8. 4 cubical inches of gas in the same time. Nearly seven-eighths of the power of the four troughs had been lost, therefore, by their association with the fifth trough. 

1044. The same battery of fifty pairs of plates, after being thus used, wasconnected with a volta-electrometer (711. ), so that by quickly shifting thewires of communication, the current of the whole of the battery, or of anyportion of it, could be made to pass through the instrument for givenportions of time in succession. The whole of the battery evolved 0. 9 of acubic inch of oxygen and hydrogen in half a minute; the forty platesevolved 4. 6 cubic inches in the same time; the whole then evolved 1 cubicinch in the half-minute; the ten weakly charged evolved 0. 4 of a cubic inchin the time given: and finally the whole evolved 1. 15 cubic inch in thestandard time. The order of the observations was that given: the resultssufficiently show the extremely injurious effect produced by the mixture ofstrong and weak charges in the same battery[A]. 

 [A] The gradual increase in the action of the whole fifty pairs of plates was due to the elevation of temperature in the weakly charged trough by the passage of the current, in consequence of which the exciting energies of the fluid within were increased. 

1045. In the same manner associations of _strong and weak_ pairs of platesshould be carefully avoided. A pair of copper and platina plates arrangedin _accordance_ with a pair of zinc and platina plates in dilute sulphuricacid, were found to stop the action of the latter, or even of two pairs ofthe latter, as effectually almost as an interposed plate of platina(1011. ), or as if the copper itself had been platina. It, in fact, becamean interposed decomposing plate, and therefore a retarding instead of anassisting pair. 

1046. The _reversal_, by accident or otherwise, of the plates in a batteryhas an exceedingly injurious effect. It is not merely the counteraction ofthe current which the reversed plates can produce, but their effect also inretarding even as indifferent plates, and requiring decomposition to beeffected upon their surface, in _accordance_ with the course of thecurrent, before the latter can pass. They oppose the current, therefore, inthe first place, as interposed platina plates would do (1011-1018. ); and tothis they add a force of opposition as counter-voltaic plates. I find that, in a series of four pairs of zinc and platina plates in dilute sulphuricacid, if one pair be reversed, it very nearly neutralizes the power of thewhole. 

1047. There are many other causes of reaction, retardation, andirregularity in the voltaic battery. Amongst them is the not unusual one ofprecipitation of copper upon the zinc in the cells, the injurious effect ofwhich has before been adverted to (1006. ). But their interest is notperhaps sufficient to justify any increase of the length of this paper, which is rather intended to be an investigation of the theory of thevoltaic pile than a particular account of its practical application[A]. 

 [A] For further practical results relating to these points of the philosophy of the voltaic battery, see Series X. § 17. 1163. --1160. --_Dec. 1838. _

_Note_. --Many of the views and experiments in this Series of myExperimental Researches will be seen at once to be corrections andextensions of the theory of electro-chemical decomposition, given in theFifth and Seventh Series of these Researches. The expressions I would nowalter are those which concern the independence of the evolved elements inrelation to the poles or electrodes, and the reference of their evolutionto powers entirely internal (524. 537. 661. ). The present paper fully showsmy present views; and I would refer to paragraphs 891. 904. 910. 917. 918. 947. 963. 1007. 1031. &c. , as stating what they are. I hope this note willbe considered as sufficient in the way of correction at present; for Iwould rather defer revising the whole theory of electro-chemicaldecomposition until I can obtain clearer views of the way in which thepower under consideration can appear at one time as associated withparticles giving them their chemical attraction, and at another as freeelectricity (493. 957. ). --M. F. 

_Royal Institution, March 31st, 1834. _

NINTH SERIES. 

§ 15. _On the influence by induction of an Electric Current on itself:--andon the inductive action of Electric Currents generally. _

Received December 18, 1834, --Read January 29, 1835. 

1048. The following investigations relate to a very remarkable inductiveaction of electric currents, or of the different parts of the same current(74. ), and indicate an immediate connexion between such inductive actionand the direct transmission of electricity through conducting bodies, oreven that exhibited in the form of a spark. 

1049. The inquiry arose out of a fact communicated to me by Mr. Jenkin, which is as follows. If an ordinary wire of short length be used as themedium of communication between the two plates of an electromotorconsisting of a single pair of metals, no management will enable theexperimenter to obtain an electric shock from this wire; but if the wirewhich surrounds an electro-magnet be used, a shock is felt each time thecontact with the electromotor is broken, provided the ends of the wire begrasped one in each hand. 

1050. Another effect is observed at the same time, which has long beenknown to philosophers, namely, that a bright electric spark occurs at theplace of disjunction. 

1051. A brief account of these results, with some of a correspondingcharacter which I had observed in using long wires, was published in thePhilosophical Magazine for 1834[A]; and I added to them some observationson their nature. Further investigations led me to perceive the inaccuracyof my first notions, and ended in identifying these effects with thephenomena of induction which I had been fortunate enough to develop in theFirst Series of these Experimental Researches (1. -59. )[B]. Notwithstandingthis identity, the extension and the results supply, lead me to believethat they will be found worthy of the attention of the Royal Society. 

 [A] Vol. V. Pp. 349, 444. 

 [B] Philosophical Transactions, 1832, p. 126. 

1052. The _electromotor_ used consisted of a cylinder of zinc introducedbetween the two parts of a double cylinder of copper, and preserved frommetallic contact in the usual way by corks. The zinc cylinder was eightinches high and four inches in diameter. Both it and the copper cylinderwere supplied with stiff wires, surmounted by cups containing mercury; andit was at these cups that the contacts of wires, helices, orelectro-magnets, used to complete the circuit, were made or broken. Thesecups I will call G and E throughout the rest of this paper (1079. ). 

1053. Certain _helices_ were constructed, some of which it will benecessary to describe. A pasteboard tube had four copper wires, onetwenty-fourth of an inch in thickness, wound round it, each forming a helixin the same direction from end to end: the convolutions of each wire wereseparated by string, and the superposed helices prevented from touching byintervening calico. The lengths of the wires forming the helices were 48, 49. 5, 48, and 45 feet. The first and third wires were united together so asto form one consistent helix of 96 feet in length; and the second andfourth wires were similarly united to form a second helix, closelyinterwoven with the first, and 94. 5 feet in length. These helices may bedistinguished by the numbers i and ii. They were carefully examined by apowerful current of electricity and a galvanometer, and found to have nocommunication with each other. 

1054. Another helix was constructed upon a similar pasteboard tube, twolengths of the same copper wire being used, each forty-six feet long. Thesewere united into one consistent helix of ninety-two feet, which thereforewas nearly equal in value to either of the former helices, but was not inclose inductive association with them. It may be distinguished by thenumber iii. 

1055. A fourth helix was constructed of very thick copper wire, beingone-fifth of an inch in diameter; the length of wire used was seventy-ninefeet, independent of the straight terminal portions. 

1056. The principal _electro-magnet_ employed consisted of a cylindricalbar of soft iron twenty-five inches long, and one inch and three quartersin diameter, bent into a ring, so that the ends nearly touched, andsurrounded by three coils of thick copper wire, the similar ends of whichwere fastened together; each of these terminations was soldered to a copperrod, serving as a conducting continuation of the wire. Hence any electriccurrent sent through the rods was divided in the helices surrounding thering, into three parts, all of which, however, moved in the same direction. The three wires may therefore be considered as representing one wire, ofthrice the thickness of the wire really used. 

1057. Other electro-magnets could be made at pleasure by introducing a softiron rod into any of the helices described (1053, &c. ). 

1058. The _galvanometer_ which I had occasion to use was rough in itsconstruction, having but one magnetic needle, and not at all delicate inits indications. 

1059. The effects to be considered _depend on the conductor_ employed tocomplete the communication between the zinc and copper plates of theelectromotor; and I shall have to consider this conductor under fourdifferent forms: as the helix of an electro-magnet (1056); as an ordinaryhelix (1053, &c. ); as a _long_ extended wire, having its course such thatthe parts can exert little or no mutual influence; and as a _short_ wire. In all cases the conductor was of copper. 

1060. The peculiar effects are best shown by the _electro-magnet_ (1056. ). When it was used to complete the communication at the electromotor, therewas no sensible spark on _making_ contact, but on _breaking_ contact therewas a very large and bright spark, with considerable combustion of themercury. Then, again, with respect to the shock: if the hands weremoistened in salt and water, and good contact between them and the wiresretained, no shock could be felt upon _making_ contact at the electromotor, but a powerful one on _breaking_ contact. 

1061. When the _helix_ i or iii (1053, &c. ) was used as the connectingconductor, there was also a good spark on breaking contact, but none(sensibly) on making contact. On trying to obtain the shock from thesehelices, I could not succeed at first. By joining the similar ends of i andii so as to make the two helices equivalent to one helix, having wire ofdouble thickness, I could just obtain the sensation. Using the helix ofthick wire (1055. ) the shock was distinctly obtained. On placing the tonguebetween two plates of silver connected by wires with the parts which thehands had heretofore touched (1064. ), there was a powerful shock on_breaking_ contact, but none on _making_ contact. 

1062. The power of producing these phenomena exists therefore in the simplehelix, as in the electro-magnet, although by no means in the same highdegree. 

1063. On putting a bar of soft iron into the helix, it became anelectro-magnet (1057. ), and its power was instantly and greatly raised. Onputting a bar of copper into the helix, no change was produced, the actionbeing that of the helix alone. The two helices i and ii, made into onehelix of twofold length of wire, produced a greater effect than either i orii alone. 

1064. On descending from the helix to the mere _long wire_, the followingeffects were obtained, A copper wire, 0. 18 of an inch in diameter, and 132feet in length, was laid out upon the floor of the laboratory, and used asthe connecting conductor (1059. ); it gave no sensible spark on makingcontact, but produced a bright one on breaking contact, yet not so brightas that from the helix (1061. ) On endeavouring to obtain the electric shockat the moment contact was broken, I could not succeed so as to make it passthrough the hands; but by using two silver plates fastened by small wiresto the extremity of the principal wire used, and introducing the tonguebetween those plates, I succeeded in obtaining powerful shocks upon thetongue and gums, and could easily convulse a flounder, an eel, or a frog. None of these effects could be obtained directly from the electromotor, i. E. When the tongue, frog, or fish was in a similar, and thereforecomparative manner, interposed in the course of the communication betweenthe zinc and copper plates, separated everywhere else by the acid used toexcite the combination, or by air. The bright spark and the shock, producedonly on breaking contact, are therefore effects of the same kind as thoseproduced in a higher degree by the helix, and in a still higher degree bythe electro-magnet. 

1065. In order to compare an extended wire with a helix, the helix i, containing ninety-six feet, and ninety-six feet of the same-sized wirelying on the floor of the laboratory, were used alternately as conductors:the former gave a much brighter spark at the moment of disjunction than thelatter. Again, twenty-eight feet of copper wire were made up into a helix, and being used gave a good spark on disjunction at the electromotor; beingthen suddenly pulled out and again employed, it gave a much smaller sparkthan before, although nothing but its spiral arrangement had been changed. 

1066. As the superiority of a helix over a wire is important to thephilosophy of the effect, I took particular pains to ascertain the factwith certainty. A wire of copper sixty-seven feet long was bent in themiddle so as to form a double termination which could be communicated withthe electromotor; one of the halves of this wire was made into a helix andthe other remained in its extended condition. When these were usedalternately as the connecting wire, the helix half gave by much thestrongest spark. It even gave a stronger spark than when it and theextended wire were used conjointly as a double conductor. 

1067. When a _short wire_ is used, _all_ these effects disappear. If it beonly two or three inches long, a spark can scarcely be perceived onbreaking the junction. If it be ten or twelve inches long and moderatelythick, a small spark may be more easily obtained. As the length isincreased, the spark becomes proportionately brighter, until from extremelength the resistance offered by the metal as a conductor begins tointerfere with the principal result. 

1068. The effect of elongation was well shown thus: 114 feet of copperwire, one-eighteenth of an inch in diameter, were extended on the floor andused as a conductor; it remained cold, but gave a bright spark on breakingcontact. Being crossed so that the two terminations were in contact nearthe extremities, it was again used as a conductor, only twelve inches nowbeing included in the circuit: the wire became very hot from the greaterquantity of electricity passing through it, and yet the spark on breakingcontact was scarcely visible. The experiment was repeated with a wireone-ninth of an inch in diameter and thirty-six feet long with the sameresults. 

1069. That the effects, and also the action, in all these forms of theexperiment are identical, is evident from the manner in which the formercan be gradually raised from that produced by the shortest wire to that ofthe most powerful electro-magnet: and this capability of examining whatwill happen by the most powerful apparatus, and then experimenting for thesame results, or reasoning from them, with the weaker arrangements, is ofgreat advantage in making out the true principles of the phenomena. 

1070. The action is evidently dependent upon the wire which serves as aconductor; for it varies as that wire varies in its length or arrangement. The shortest wire may be considered as exhibiting the full effect of sparkor shock which the electromotor can produce by its own direct power; allthe additional force which the arrangements described can excite being dueto some affection of the current, either permanent or momentary, in thewire itself. That it is a _momentary_ effect, produced only at the instantof breaking contact, will be fully proved (1089. 1100. ). 

1071. No change takes place in the quantity or intensity of the currentduring the time the latter is _continued_, from the moment after contact ismade, up to that previous to disunion, except what depends upon theincreased obstruction offered to the passage of the electricity by a longwire as compared to a short wire. To ascertain this point with regard to_quantity_, the helix i (1053. ) and the galvanometer (1055. ) were both madeparts of the metallic circuit used to connect the plates of a smallelectromotor, and the deflection at the galvanometer was observed; then asoft iron core was put into the helix, and as soon as the momentary effectwas over, and the needle had become stationary, it was again observed, andfound to stand exactly at the same division as before. Thus the quantitypassing through the wire when the current was continued was the same eitherwith or without the soft iron, although the peculiar effects occurring atthe moment of disjunction were very different in degree under suchvariation of circumstances. 

1072. That the quality of _intensity_ belonging to the constant current didnot vary with the circumstances favouring the peculiar results underconsideration, so as to yield an explanation of those results, wasascertained in the following manner. The current excited by an electromotorwas passed through short wires, and its intensity tried by subjectingdifferent substances to its electrolyzing power (912. 966. &c. ); it wasthen passed through the wires of the powerful electro-magnet (1056. ), andagain examined with respect to its intensity by the same means and foundunchanged. Again, the constancy of the _quantity_ passed in the aboveexperiment (1071. ) adds further proof that the intensity could not havevaried; for had it been increased upon the introduction of the soft iron, there is every reason to believe that the quantity passed in a given timewould also have increased. 

1073. The fact is, that under many variations of the experiments, thepermanent current _loses_ in force as the effects upon breaking contactbecome _exalted_. This is abundantly evident in the comparative experimentswith long and short wires (1068. ); and is still more strikingly shown bythe following variation. Solder an inch or two in length of fine platinawire (about one-hundredth of an inch in diameter) on to one end of the longcommunicating wire, and also a similar length of the same platina wire onto one end of the short communication; then, in comparing the effects ofthese two communications, make and break contact between the platinaterminations and the mercury of the cup G or E (1079. ). When the short wireis used, the platina will be _ignited by the constant current_, because ofthe quantity of electricity, but the spark on breaking contact will behardly visible; on using the longer communicating wire, which byobstructing will diminish the current, the platina will remain cold whilstthe current passes, but give a bright spark at the moment it ceases: thusthe strange result is obtained of a diminished spark and shock from thestrong current, and increased effects from the weak one. Hence the sparkand shock at the moment of disjunction, although resulting from greatintensity and quantity, of the current _at that moment_, are no directindicators or measurers of the intensity or quantity of the constantcurrent previously passing, and by which they are ultimately produced. 

 * * * * *

1074. It is highly important in using the spark as an indication, by itsrelative brightness, of these effects, to bear in mind certaincircumstances connected with its production and appearance (958. ). Anordinary electric spark is understood to be the bright appearance ofelectricity passing suddenly through an interval of air, or other badlyconducting matter. A voltaic spark is sometimes of the same nature, but, generally, is due to the ignition and even combustion of a minute portionof a good conductor; and that is especially the case when the electromotorconsists of but one or few pairs of plates. This can be very well observedif either or both of the metallic surfaces intended to touch be solid andpointed. The moment they come in contact the current passes; it heats, ignites, and even burns the touching points, and the appearance is as ifthe spark passed on making contact, whereas it is only a case of ignitionby the current, contact being previously made, and is perfectly analogousto the ignition of a fine platina wire connecting the extremities of avoltaic battery. 

1075. When mercury constitutes one or both of the surfaces used, thebrightness of the spark is greatly increased. But as this effect is due tothe action on, and probable combustion of, the metal, such sparks must onlybe compared with other sparks also taken from mercurial surfaces, and notwith such as may be taken, for instance, between surfaces of platina orgold, for then the appearances are far less bright, though the samequantity of electricity be passed. It is not at all unlikely that thecommonly occurring circumstance of combustion may affect even the durationof the light; and that sparks taken between mercury, copper, or othercombustible bodies, will continue for a period sensibly longer than thosepassing between platina or gold. 

1076. When the end of a short clean copper wire, attached to one plate ofan electromotor, is brought down carefully upon a surface of mercuryconnected with the other plate, a spark, almost continuous, can beobtained. This I refer to a succession of effects of the following nature:first, contact, --then ignition of the touching points, --recession of themercury from the mechanical results of the heat produced at the place ofcontact, and the electro-magnetic condition of the parts at the moment[A], --breaking of the contact and the production of the peculiar intense effectdependent thereon, --renewal of the contact by the returning surface of theundulating mercury, --and then a repetition of the same series of effects, and that with such rapidity as to present the appearance of a continueddischarge. If a long wire or an electro-magnet be used as the connectingconductor instead of a short wire, a similar appearance may be produced bytapping the vessel containing the mercury and making it vibrate; but thesparks do not usually follow each other so rapidly as to produce anapparently continuous spark, because of the time required, when the longwire or electro-magnet is used, both for the full development of thecurrent (1101. 1106. ) and for its complete cessation. 

 [A] Quarterly Journal of Science, vol. Xii, p. 420. 

1077. Returning to the phenomena in question, the first thought that arisesin the mind is, that the electricity circulates with something like_momentum or inertia_ in the wire, and that thus a long wire produceseffects at the instant the current is stopped, which a short wire cannotproduce. Such an explanation is, however, at once set aside by the fact, that the same length of wire produces the effects in very differentdegrees, according as it is simply extended, or made into a helix, or formsthe circuit of an electro-magnet (1069. ). The experiments to be adduced(1089. ) will still more strikingly show that the idea of momentum cannotapply. 

1078. The bright spark at the electromotor, and the shock in the arms, appeared evidently to be due to _one_ current in the long wire, dividedinto two parts by the double channel afforded through the body and throughthe electromotor; for that the spark was evolved at the place ofdisjunction with the electromotor, not by any direct action of the latter, but by a force immediately exerted in the wire of communication, seemed tobe without doubt (1070. ). It followed, therefore, that by using a betterconductor in place of the human body, the _whole_ of this extra currentmight be made to pass at that place; and thus be separated from that whichthe electromotor could produce by its immediate action, and its _direction_be examined apart from any interference of the original and originatingcurrent. This was found to be true; for on connecting the ends of theprincipal wire together by a cross wire two or three feet in length, applied just where the hands had felt the shock, the whole of the extracurrent passed by the new channel, and then no better spark than oneproducible by a short wire was obtained on disjunction at the electromotor. 

1079. The _current_ thus separated was examined by galvanometers anddecomposing apparatus introduced into the course of this wire. I willalways speak of it as the current in the cross wire or wires, so that nomistake, as to its place or origin, may occur. In the wood-cut, Z and Crepresent the zinc and copper plates of the electromotor; G and E the cupsof mercury where contact is made or broken (1052. ); A and B theterminations of D, the long wire, the helix or the electro-magnet, used tocomplete the circuit; N and P are the cross wires, which can either bebrought into contact at _x_, or else have a galvanometer (1058. ) or anelectrolyzing apparatus (312. 316. ) interposed there. 

[Illustration]

The production of the _shock_ from the current in the cross wire, whether Dwas a long extended wire, or a helix, or an electro-magnet, has beenalready described (1060. 1061. 1064. ). 

1080. The _spark_ of the cross-wire current could be produced at _x_ in thefollowing manner: D was made an electro-magnet; the metallic extremities at_x_ were held close together, or rubbed lightly against each other, whilstcontact was broken at G or E. When the communication was perfect at _x_, little or no spark appeared at G or E. When the condition of vicinity at_x_ was favourable for the result required, a bright spark would pass thereat the moment of disjunction, _none_ occurring at G and E: this spark wasthe luminous passage of the extra current through the cross-wires. Whenthere was no contact or passage of current at _x_, then the spark appearedat G or E, the extra current forcing its way through the electromotoritself. The same results were obtained by the use of the helix or theextended wire at D in place of the electro-magnet. 

1081. On introducing a fine platina wire at _x_, and employing theelectro-magnet at D, no visible effects occurred as long as contact wascontinued; but on breaking contact at G or E, the fine wire was instantlyignited and fused. A longer or thicker wire could be so adjusted at _x_ asto show ignition, without fusion, every time the contact was broken at Gor E. 

1082. It is rather difficult to obtain this effect with helices or wires, and for very simple reasons: with the helices i, ii, or iii, there was suchretardation of the electric current, from the length of wire used, that afull inch of platina wire one-fiftieth of an inch in diameter could beretained ignited at the cross-wires during the _continuance of contact_, bythe portion of electricity passing through it. Hence it was impossible todistinguish the particular effects at the moments of making or breakingcontact from this constant effect. On using the thick wire helix (1055. ), the same results ensued. 

1083. Proceeding upon the known fact that electric currents of greatquantity but low intensity, though able to ignite thick wires, cannotproduce that effect upon thin ones, I used a very fine platina wire at _x_, reducing its diameter until a spark appeared at G or E, when contact wasbroken there. A quarter of an inch of such wire might be introduced at _x_without being ignited by the _continuance_ of contact at G or E; but whencontact was broken at either place, this wire became red-hot; proving, bythis method, the production of the induced current at that moment. 

1084. _Chemical decomposition_ was next effected by the cross-wire current, an electro-magnet being used at D, and a decomposing apparatus, withsolution of iodide of potassium in paper (1079. ), employed at _x_. Theconducting power of the connecting system A B D was sufficient to carry allthe primary current, and consequently no chemical action took place at _x_during the _continuance_ of contact at G and E; but when contact wasbroken, there was instantly decomposition at _x_. The iodine appearedagainst the wire N, and not against the wire P; thus demonstrating that thecurrent through the cross-wires, when contact was broken, was in the_reverse direction_ to that marked by the arrow, or that which theelectromotor would have sent through it. 

1085. In this experiment a bright spark occurs at the place of disjunction, indicating that only a small part of the extra current passed the apparatusat _x_, because of the small conducting power of the latter. 

1086. I found it difficult to obtain the chemical effects with the simplehelices and wires, in consequence of the diminished inductive power ofthese arrangements, and because of the passage of a strong constant currentat _x_ whenever a very active electromotor was used (1082). 

1087. The most instructive set of results was obtained, however, when the_galvanometer_ was introduced at _x_. Using an electro-magnet at D, andcontinuing contact, a current was then indicated by the deflection, proceeding from P to N, in the direction of the arrow; the cross-wireserving to carry one part of the electricity excited by the electromotor, and that part of the arrangement marked A B D, the other and far greaterpart, as indicated by the arrows. The magnetic needle was then forced back, by pins applied upon opposite sides of its two extremities, to its naturalposition when uninfluenced by a current; after which, contact being_broken_ at G or E, it was deflected strongly in the opposite direction;thus showing, in accordance with the chemical effects (1084), that theextra current followed a course in the cross-wires _contrary_ to thatindicated by the arrow, i. E. Contrary to the one produced by the directaction of the electromotor[A]. 

 [A] It was ascertained experimentally, that if a strong current was passed through the galvanometer only, and the needle restrained in one direction as above in its natural position, when the current was stopped, no vibration of the needle in the opposite direction took place. 

1088. With the _helix_ only (1061. ), these effects could scarcely beobserved, in consequence of the smaller inductive force of thisarrangement, the opposed action from induction in the galvanometer wireitself, the mechanical condition and tension of the needle from the effectof blocking (1087. ) whilst the current due to continuance of contact waspassing round it; and because of other causes. With the _extended wire_(1064. ) all these circumstances had still greater influence, and thereforeallowed less chance of success. 

1089. These experiments, establishing as they did, by the quantity, intensity, and even direction, a distinction between the primary orgenerating current and the extra current, led me to conclude that thelatter was identical with the induced current described (6. 26. 74. ) in theFirst Series of these Researches; and this opinion I was soon able to bringto proof, and at the same times obtained not the partial (1078. ) but entireseparation of one current from the other. 

1090. The double helix (1053. ) was arranged so that it should form theconnecting wire between the plates of the electromotor, in being out of thecurrent, and its ends unconnected. In this condition it acted very well, and gave a good spark at the time and place of disjunction. The oppositeends of ii were then connected together so as to form an endless wire, iremaining unchanged: but now _no spark_, or one scarcely sensible, could beobtained from the latter at the place of disjunction. Then, again, the endsof ii were held so nearly together that any current running round thathelix should be rendered visible as a spark; and in this manner a spark wasobtained from ii when the junction of i with the electromotor was broken, in place of appearing at the disjoined extremity of i itself. 

1091. By introducing a galvanometer or decomposing apparatus into thecircuit formed by the helix ii, I could easily obtain the deflections anddecomposition occasioned by the induced current due to the breaking contactat helix i, or even to that occasioned by making contact of that helix withthe electromotor; the results in both cases indicating the contrarydirections of the two induced currents thus produced (26. ). 

1092. All these effects, except those of decomposition, were reproduced bytwo extended long wires, not having the form of helices, but placed closeto each other; and thus it was proved that the _extra current_ could beremoved from the wire carrying the original current to a neighbouring wire, and was at the same time identified, in direction and every other respect, with the currents producible by induction (1089. ). The case, therefore, ofthe bright spark and shock on disjunction may now be stated thus: If acurrent be established in a wire, and another wire, forming a completecircuit, be placed parallel to the first, at the moment the current in thefirst is stopped it induces a current in the _same_ direction in thesecond, the first exhibiting then but a feeble spark; but if the secondwire be away, disjunction of the first wire induces a current in itself inthe same direction, producing a strong spark. The strong spark in thesingle long wire or helix, at the moment of disjunction, is therefore theequivalent of the current which would be produced in a neighbouring wire ifsuch second current were permitted. 

1093. Viewing the phenomena as the results of the induction of electricalcurrents, many of the principles of action, in the former experiments, become far more evident and precise. Thus the different effects of shortwires, long wires, helices, and electro-magnets (1069. ) may becomprehended. If the inductive action of a wire a foot long upon acollateral wire also a foot in length, be observed, it will be found verysmall; but if the same current be sent through a wire fifty feet long, itwill induce in a neighbouring wire of fifty feet a far more powerfulcurrent at the moment of making or breaking contact, each successive footof wire adding to the sum of action; and by parity of reasoning, a similareffect should take place when the conducting wire is also that in which theinduced current is formed (74. ): hence the reason why a long wire gives abrighter spark on breaking contact than a short one (1068. ), although itcarries much less electricity. 

1094. If the long wire be made into a helix, it will then be still moreeffective in producing sparks and shocks on breaking contact; for by themutual inductive action of the convolutions each aids its neighbour, andwill be aided in turn, and the sum of effect will be very greatlyincreased. 

1095. If an electro-magnet be employed, the effect will be still morehighly exalted; because the iron, magnetized by the power of the continuingcurrent, will lose its magnetism at the moment the current ceases to pass, and in so doing will tend to produce an electric current in the wire aroundit (37. 38. ), in conformity with that which the cessation of current in thehelix itself also tends to produce. 

1096. By applying the laws of the induction of electric currents formerlydeveloped (6. &c. ), various new conditions of the experiments could bedevised, which by their results should serve as tests of the accuracy ofthe view just given. Thus, if a long wire be doubled, so that the currentin the two halves shall have opposite actions, it ought not to give asensible spark at the moment of disjunction: and this proved to be thecase, for a wire forty feet long, covered with silk, being doubled and tiedclosely together to within four inches of the extremities, when used inthat state, gave scarcely a perceptible spark; but being opened out and theparts separated, it gave a very good one. The two helices i and ii beingjoined at their similar ends, and then used at their other extremities toconnect the plates of the electromotor, thus constituted one long helix, ofwhich one half was opposed in direction to the other half: under thesecircumstances it gave scarcely a sensible spark, even when the soft ironcore was within, although containing nearly two hundred feet of wire. Whenit was made into one consistent helix of the same length of wire it gave avery bright spark. 

1097. Similar proofs can be drawn from the mutual inductive action of twoseparate currents (1110. ); and it is important for the general principlesthat the consistent action of two such currents should be established. Thus, two currents going in the same direction should, if simultaneouslystopped, aid each other by their relative influence; or if proceeding incontrary directions, should oppose each other under similar circumstances. I endeavoured at first to obtain two currents from two differentelectromotors, and passing them through the helices i and ii, tried toeffect the disjunctions mechanically at the same moment. But in this Icould not succeed; one was always separated before the other, and in thatcase produced little or no spark, its inductive power being employed inthrowing a current round the remaining complete circuit (1090. ): thecurrent which was stopped last always gave a bright spark. If it were everto become needful to ascertain whether two junctions were accurately brokenat the same moment, these sparks would afford a test for the purpose, having an infinitesimal degree of perfection. 

1098. I was able to prove the points by other expedients. Two short thickwires were selected to serve as terminations, by which contact could bemade or broken with the electromotor. The compound helix, consisting of iand ii (1053. ), was adjusted so that the extremities of the two helicescould be placed in communication with the two terminal wires, in such amanner that the current moving through the thick wires should be dividedinto two equal portions in the two helices, these portions travelling, according to the mode of connexion, either in the same direction or incontrary directions at pleasure. In this manner two streams could beobtained, both of which could be stopped simultaneously, because thedisjunction could be broken at G or F by removing a single wire. When thehelices were in contrary directions, there was scarcely a sensible spark atthe place of disjunction; but when they were in accordance there was a verybright one. 

1099. The helix i was now used constantly, being sometimes associated, asabove, with helix ii in an according direction, and sometimes with helixiii, which was placed at a little distance. The association i and ii, whichpresented two currents able to affect each other by induction, because oftheir vicinity, gave a brighter spark than the association i and iii, wherethe two streams could not exert their mutual influence; but the differencewas not so great as I expected. 

1100. Thus all the phenomena tend to prove that the effects are due to aninductive action, occurring at the moment when the principal current isstopped. I at one time thought they were due to an action continued duringthe _whole time_ of the current, and expected that a steel magnet wouldhave an influence according to its position in the helix, comparable tothat of a soft iron bar, in assisting the effect. This, however, is not thecase; for hard steel, or a magnet in the helix, is not so effectual as softiron; nor does it make any difference how the magnet is placed in thehelix, and for very simple reasons, namely, that the effect does not dependupon a permanent state of the core, but a _change of state_; and that themagnet or hard steel cannot sink through such a difference of state as softiron, at the moment contact ceases, and therefore cannot produce an equaleffect in generating a current of electricity by induction (34. 37. ). 

 * * * * *

1101. As an electric current acts by induction with equal energy at themoment of its commencement as at the moment of its cessation (10. 26. ), butin a contrary direction, the reference of the effects under examination toan inductive action, would lead to the conclusion that correspondingeffects of an opposite nature must occur in a long wire, a helix, or anelectro-magnet, every time that _contact is made with_ the electromotor. These effects will tend to establish a resistance for the first moment inthe long conductor, producing a result equivalent to the reverse of a shockor a spark. Now it is very difficult to devise means fit for therecognition of such negative results; but as it is probable that somepositive effect is produced at the time, if we knew what to expect, I thinkthe few facts bearing upon this subject with which I am acquainted areworth recording. 

1102. The electro-magnet was arranged with an electrolyzing apparatus at_x_, as before described (1084. ), except that the intensity of the chemicalaction at the electromotor was increased until the electric current wasjust able to produce the feeblest signs of decomposition whilst contact wascontinued at G and E (1079. ); (the iodine of course appearing against theend of the cross wire P;) the wire N was also separated from A at _r_, sothat contact there could be made or broken at pleasure. Under thesecircumstances the following set of actions was repeated several times:contact was broken at _r_, then broken at G, next made at _r_, and lastlyrenewed at G; thus any current from N to P due to _breaking_ of contact wasavoided, but any additional force to the current from P to N due to_making_ contact could be observed. In this way it was found, that a muchgreater decomposing effect (causing the evolution of iodine against P)could be obtained by a few completions of contact than by the current whichcould pass in a much longer time if the contact was _continued_. This Iattribute to the act of induction in the wire ABD at the moment of contactrendering that wire a worse conductor, or rather retarding the passage ofthe electricity through it for the instant, and so throwing a greaterquantity of the electricity which the electromotor could produce, throughthe cross wire passage NP. The instant the induction ceased, ABD resumedits full power of carrying a constant current of electricity, and couldhave it highly increased, as we know by the former experiments (1060. ) bythe opposite inductive action brought into activity at the moment contactat Z or C was _broken_. 

1103. A galvanometer was then introduced at _x_, and the deflection of theneedle noted whilst contact was continued at G and E: the needle was thenblocked as before in one direction (1087. ), so that it should not returnwhen the current ceased, but remain in the position in which the currentcould retain it. Contact at G or E was broken, producing of course novisible effect; it was then renewed, and the needle was instantlydeflected, passing from the blocking pins to a position still further fromits natural place than that which the constant current could give, and thusshowing, by the temporary excess of current in this cross communication, the temporary retardation in the circuit ABD. 

1104. On adjusting a platina wire at _x_ (1081. ) so that it should not beignited by the current passing through it whilst contact at G and E was_continued_, and yet become red-hot by a current somewhat more powerful, Iwas readily able to produce its ignition upon _making contact_, and againupon _breaking contact_. Thus the momentary retardation in ABD on makingcontact was again shown by this result, as well also as the opposite resultupon breaking contact. The two ignitions of the wire at _x_ were of courseproduced by electric currents moving in opposite directions. 

1105. Using the _helix_ only, I could not obtain distinct deflections at_x_, due to the extra effect on making contact, for the reasons alreadymentioned (1088. ). By using a very fine platina wire there (1083. ), I didsucceed in obtaining the igniting effect for making contact in the samemanner, though by no means to the same degree, as with the electro-magnet(1104). 

1106. We may also consider and estimate the effect on _making contact_, bytransferring the force of induction from the wire carrying the originalcurrent to a lateral wire, as in the cases described (1090. ); and we thenare sure, both by the chemical and galvanometrical results (1091. ), thatthe forces upon making and breaking contact, like action and reaction, areequal in their strength but contrary in their direction. If, therefore, theeffect on making contact resolves itself into a mere retardation of thecurrent at the first moment of its existence, it must be, in its degree, equivalent to the high exaltation of that same current at the momentcontact is broken. 

1107. Thus the case, under the circumstances, is, that the intensity andquantity of electricity moving in a current are smaller when the currentcommences or is increased, and greater when it diminishes or ceases, thanthey would be if the inductive action occurring at these moments did nottake place; or than they are in the original current wire if the inductiveaction be transferred from that wire to a collateral one (1090. ). 

1108. From the facility of transference to neighbouring wires, and from theeffects generally, the inductive forces appear to be lateral, i. E. Exertedin a direction perpendicular to the direction of the originating andproduced currents: and they also appear to be accurately represented by themagnetic curves, and closely related to, if not identical with, magneticforces. 

1109. There can be no doubt that the current in one part of a wire can actby induction upon other parts of the _same_ wire which are lateral to thefirst, i. E. In the same vertical section (74. ), or in the parts which aremore or less oblique to it (1112. ), just as it can act in producing acurrent in a neighbouring wire or in a neighbouring coil of the same wire. It is this which gives the appearance of the current acting upon itself:but all the experiments and all analogy tend to show that the elements (ifI may so say) of the currents do not act upon themselves, and so cause theeffect in question, but produce it by exciting currents in conductingmatter which is lateral to them. 

1110. It is possible that some of the expressions I have used may seem toimply, that the inductive action is essentially the action of one currentupon another, or of one element of a current upon another element of thesame current. To avoid any such conclusion I must explain more distinctlymy meaning. If an endless wire be taken, we have the means of generating acurrent in it which shall run round the circuit without adding anyelectricity to what was previously in the wire. As far as we can judge, theelectricity which appears as a current is the same as that which before wasquiescent in the wire; and though we cannot as yet point out the essentialcondition of difference of the electricity at such times, we can easilyrecognize the two states. Now when a current acts by induction uponconducting matter lateral to it, it probably acts upon the electricity inthat conducting matter whether it be in the form of a _current_ or_quiescent_, in the one case increasing or diminishing the currentaccording to its direction, in the other producing a current, and the_amount_ of the inductive action is probably the same in both cases. Hence, to say that the action of induction depended upon the mutual relation oftwo or more currents, would, according to the restricted sense in which theterm current is understood at present (283. 517. 667. ), be an error. 

1111. Several of the effects, as, for instances, those with helices(1066. ), with according or counter currents (1097. 1098. ), and those on theproduction of lateral currents (1090. ), appeared to indicate that a currentcould produce an effect of induction in a neighbouring wire more readilythan in its own carrying wire, in which case it might be expected that somevariation of result would be produced if a bundle of wires were used as aconductor instead of a single wire. In consequence the followingexperiments were made. A copper wire one twenty-third of an inch indiameter was cut into lengths of five feet each, and six of these beinglaid side by side in one bundle, had their opposite extremities soldered totwo terminal pieces of copper. This arrangement could be used as adischarging wire, but the general current could be divided into sixparallel streams, which might be brought close together, or, by theseparation of the wires, be taken more or less out of each other'sinfluence. A somewhat brighter spark was, I think, obtained on breakingcontact when the six wires were close together than when held asunder. 

1112. Another bundle, containing twenty of these wires, was eighteen feetlong: the terminal pieces were one-fifth of an inch in diameter, and eachsix inches long. This was compared with nineteen feet in length of copperwire one-fifth of an inch in diameter. The bundle gave a smaller spark onbreaking contact than the latter, even when its strands were held togetherby string: when they were separated, it gave a still smaller spark. Uponthe whole, however, the diminution of effect was not such as I expected:and I doubt whether the results can be considered as any proof of the truthof the supposition which gave rise to them. 

1113. The inductive force by which two elements of one current (1109. 1110. ) act upon each other, appears to diminish as the line joining thembecomes oblique to the direction of the current and to vanish entirely whenit is parallel. I am led by some results to suspect that it then evenpasses into the repulsive force noticed by Ampère[A]; which is the cause ofthe elevations in mercury described by Sir Humphry Davy[B], and which againis probably directly connected with the quality of intensity. 

 [A] Recueil d'Observations Electro-Dynamiques, p. 285. 

 [B] Philosophical Transactions, 1823, p. 155. 

1114. Notwithstanding that the effects appear only at the making andbreaking of contact, (the current remaining unaffected, seemingly, in theinterval, ) I cannot resist the impression that there is some connected andcorrespondent effect produced by this lateral action of the elements of theelectric stream during the time of its continuance (60. 242. ). An action ofthis kind, in fact, is evident in the magnetic relations of the parts ofthe current. But admitting (as we may do for the moment) the magneticforces to constitute the power which produces such striking and differentresults at the commencement and termination of a current, still thereappears to be a link in the chain of effects, a wheel in the physicalmechanism of the action, as yet unrecognised. If we endeavour to considerelectricity and magnetism as the results of two forces of a physical agent, or a peculiar condition of matter, exerted in determinate directionsperpendicular to each other, then, it appears to me, that we must considerthese two states or forces as convertible into each other in a greater orsmaller degree; i. E. That an element of an electric current has not adeterminate electric force and a determinate magnetic force constantlyexisting in the same ratio, but that the two forces are, to a certaindegree, convertible by a process or change of condition at present unknownto us. How else can a current of a given intensity and quantity be able, byits direct action, to sustain a state which, when allowed to react, (at thecessation of the original current, ) shall produce a second current, havingan intensity and quantity far greater than the generating one? This cannotresult from a direct reaction of the electric force; and if it result froma change of electrical into magnetic force, and a reconversion back again, it will show that they differ in something more than mere direction, asregards _that agent_ in the conducting wire which constitutes theirimmediate cause. 

1115. With reference to the appearance, at different times, of the contraryeffects produced by the making and breaking contact, and their separationby an intermediate and indifferent state, this separation is probably moreapparent than real. If the conduction of electricity be effected byvibrations (283. ), or by any other mode in which opposite forces aresuccessively and rapidly excited and neutralized, then we might expect apeculiar and contrary development of force at the commencement andtermination of the periods during which the conducting action should last(somewhat in analogy with the colours produced at the outside of animperfectly developed solar spectrum): and the intermediate actions, although not sensible in the same way, may be very important and, forinstance, perhaps constitute the very essence of conductibility. It is byviews and reasons such as these, which seem to me connected with thefundamental laws and facts of electrical science, that I have been inducedto enter, more minutely than I otherwise should have done, into theexperimental examination of the phenomena described in this paper. 

1116. Before concluding, I may briefly remark, that on using a voltaicbattery of fifty pairs of plates instead of a single pair (1052. ), theeffects were exactly of the same kind. The spark on making contact, for thereasons before given, was very small (1101. 1107. ); that on breakingcontact, very excellent and brilliant. The _continuous_ discharge did notseem altered in character, whether a short wire or the powerfulelectro-magnet were used as a connecting discharger. 

1117. The effects produced at the commencement and end of a current, (whichare separated by an interval of time when that current is supplied from avoltaic apparatus, ) must occur at the same moment when a common electricdischarge is passed through a long wire. Whether, if happening accuratelyat the same moment, they would entirely neutralize each other, or whetherthey would not still give some definite peculiarity to the discharge, is amatter remaining to be examined; but it is very probable that the peculiarcharacter and pungency of sparks drawn from a long wire depend in part uponthe increased intensity given at the termination of the discharge by theinductive action then occurring. 

1118. In the wire of the helix of magneto-electric machines, (as, forinstance, in Mr. Saxton's beautiful arrangement, ) an important influence ofthese principles of action is evidently shown. From the construction of theapparatus the current is permitted to move in a complete metallic circuitof great length during the first instants of its formation: it graduallyrises in strength, and is then suddenly stopped by the breaking of themetallic circuit; and thus great intensity is given _by induction_ to theelectricity, which at that moment passes (1064. 1060. ). This intensity isnot only shown by the brilliancy of the spark and the strength of theshock, but also by the necessity which has been experienced ofwell-insulating the convolutions of the helix, in which the current isformed: and it gives to the current a force at these moments very far abovethat which the apparatus could produce if the principle which forms thesubject of this paper were not called into play. 

_Royal Institution, December 8th, 1834. _

TENTH SERIES. 

§ 16. _On an improved form of the Voltaic Battery. _ § 17. _Some practicalresults respecting the construction and use of the Voltaic Battery. _

Received June 16, --Read June 18, 1835. 

1119. I Have lately had occasion to examine the voltaic trough practically, with a view to improvements in its construction and use; and though I donot pretend that the results have anything like the importance whichattaches to the discovery of a new law or principle, I still think they arevaluable, and may therefore, if briefly told, and in connexion with formerpapers, be worthy the approbation of the Royal Society. 

§ 16. _On an improved form of the Voltaic Battery. _

1120. In a simple voltaic circuit (and the same is true of the battery) thechemical forces which, during their activity, give power to the instrument, are generally divided into two portions; one of these is exerted locally, whilst the other is transferred round the circle (947. 996. ); the latterconstitutes the electric current of the instrument, whilst the former isaltogether lost or wasted. The ratio of these two portions of power may bevaried to a great extent by the influence of circumstances: thus, in abattery not closed, _all_ the action is local; in one of the ordinaryconstruction, _much_ is in circulation when the extremities are incommunication: and in the perfect one, which I have described (1001. ), _all_ the chemical power circulates and becomes electricity. By referringto the quantity of zinc dissolved from the plates (865. 1120. ), and thequantity of decomposition effected in the volta-electrometer (711. 1126, )or elsewhere, the proportions of the local and transferred actions underany particular circumstances can be ascertained, and the efficacy of thevoltaic arrangement, or the waste of chemical power at its zinc plates, beaccurately determined. 

1121. If a voltaic battery were constructed of zinc and platina, the lattermetal surrounding the former, as in the double copper arrangement, and thewhole being excited by dilute sulphuric acid, then no insulating divisionsof glass, porcelain or air would be required between the contiguous platinasurfaces; and, provided these did not touch metallically, the same acidwhich, being between the zinc and platina, would excite the battery intopowerful action, would, between the two surfaces of platina, produce nodischarge of the electricity, nor cause any diminution of the power of thetrough. This is a necessary consequence of the resistance to the passage ofthe current which I have shown occurs at the place of decomposition (1007. 1011. ); for that resistance is fully able to stop the current, andtherefore acts as insulation to the electricity of the contiguous plates, inasmuch as the current which tends to pass between them never has a higherintensity than that due to the action of a single pair. 

1122. If the metal surrounding the zinc be copper (1045. ), and if the acidbe nitro-sulphuric acid (1020. ), then a slight discharge between the twocontiguous coppers does take place, provided there be no other channel openby which the forces may circulate; but when such a channel is permitted, the return or back discharge of which I speak is exceedingly diminished, inaccordance with the principles laid down in the Eighth Series of theseResearches. 

1123. Guided by these principles I was led to the construction of a voltaictrough, in which the coppers, passing round both surfaces of the zincs, asin Wollaston's construction, should not be separated from each other exceptby an intervening thickness of paper, or in some other way, so as toprevent metallic contact, and should thus constitute an instrument compact, powerful, economical, and easy of use. On examining, however, what had beendone before, I found that the new trough was in all essential respects thesame as that invented and described by Dr. Hare, Professor in theUniversity of Pennsylvania, to whom I have great pleasure in referring it. 

1124. Dr. Hare has fully described his trough[A]. In it the contiguouscopper plates are separated by thin veneers of wood, and the acid is pouredon to, or off, the plates by a quarter revolution of an axis, to which boththe trough containing the plates, and another trough to collect and holdthe liquid, are fixed. This arrangement I have found the most convenient ofany, and have therefore adopted it. My zinc plates were cut from rolledmetal, and when soldered to the copper plates had the form delineated, fig. 1. These were then bent over a gauge into the form fig. 2, and when packedin the wooden box constructed to receive them, were arranged as in fig. 3[B], little plugs of cork being used to keep the zinc plates from touchingthe copper plates, and a single or double thickness of cartridge paperbeing interposed between the contiguous surfaces of copper to prevent themfrom coming in contact. Such was the facility afforded by this arrangement, that a trough of forty pairs of plates could be unpacked in five minutes, and repacked again in half an hour; and the whole series was not more thanfifteen inches in length. 

[Illustration: Fig. 1. ]

[Illustration: Fig. 2. ]

[Illustration: Fig. 3. ]

 [A] Philosophical Magazine, 1824, vol. Lxiii. P. 241; or Silliman's Journal, vol. Vii. See also a previous paper by Dr. Hare, Annals of Philosophy, 1821, vol. I. P. 329, in which he speaks of the non-necessity of insulation between the coppers. 

 [B] The papers between the coppers are, for the sake of distinctness, omitted in the figure. 

1125. This trough, of forty pairs of plates three inches square, wascompared, as to the ignition of a platina wire, the discharge betweenpoints of charcoal, the shock on the human frame, &c. , with forty pairs offour-inch plates having double coppers, and used in porcelain troughsdivided into insulating cells, the strength of the acid employed to exciteboth being the same. In all these effects the former appeared quite equalto the latter. On comparing a second trough of the new construction, containing twenty pairs of four-inch plates, with twenty pairs of four-inchplates in porcelain troughs, excited by acid of the same strength, the newtrough appeared to surpass the old one in producing these effects, especially in the ignition of wire. 

1126. In these experiments the new trough diminished in its energy muchmore rapidly than the one on the old construction, and this was a necessaryconsequence of the smaller quantity of acid used to excite it, which in thecase of the forty pairs of new construction was only one-seventh part ofthat used for the forty pairs in the porcelain troughs. To compare, therefore, both forms of the voltaic trough in their decomposing powers, and to obtain accurate data as to their relative values, experiments of thefollowing kind were made. The troughs were charged with a known quantity ofacid of a known strength; the electric current was passed through avolta-electrometer (711. ) having electrodes 4 inches long and 2. 3 inches inwidth, so as to oppose as little obstruction as possible to the current;the gases evolved were collected and measured, and gave the quantity ofwater decomposed. Then the whole of the charge used was mixed together, anda known part of it analyzed, by being precipitated and boiled with excessof carbonate of soda, and the precipitate well-washed, dried, ignited, andweighed. In this way the quantity of metal oxidized and dissolved by theacid was ascertained; and the part removed from each zinc plate, or fromall the plates, could be estimated and compared with the water decomposedin the volta-electrometer. To bring these to one standard of comparison, Ihave reduced the results so as to express the loss at the plates inequivalents of zinc for the equivalent of water decomposed at thevolta-electrometer: I have taken the equivalent number of water as 9, andof zinc as 32. 5, and have considered 100 cubic inches of the mixed oxygenand hydrogen, as they were collected over a pneumatic trough, to resultfrom the decomposition of 12. 68 grains of water. 

1127. The acids used in these experiments were three, --sulphuric, nitric, and muriatic. The sulphuric acid was strong oil of vitriol; one cubicalinch of it was equivalent to 486 grains of marble. The nitric acid was verynearly pure; one cubical inch dissolved 150 grains of marble. The muriaticacid was also nearly pure, and one cubical inch dissolved 108 grains ofmarble. These were always mixed with water by volumes, the standard ofvolume being a cubical inch. 

1128. An acid was prepared consisting of 200 parts water, 4-1/2 partssulphuric acid, and 4 parts nitric acid; and with this both my troughcontaining forty pairs of three-inch plates, and four porcelain troughs, arranged in succession, each containing ten pairs of plates with doublecoppers four inches square, were charged. These two batteries were thenused in succession, and the action of each was allowed to continue fortwenty or thirty minutes, until the charge was nearly exhausted, theconnexion with the volta-electrometer being carefully preserved during thewhole time, and the acid in the troughs occasionally mixed together. Inthis way the former trough acted so well, that for each equivalent of waterdecomposed in the volta-electrometer only from 2 to 2. 5 equivalents of zincwere dissolved from each plate. In four experiments the average was 2. 21equivalents for each plate, or 88. 4 for the whole battery. In theexperiments with the porcelain troughs, the equivalents of consumption ateach plate were 3. 51, or 141. 6 for the whole battery. In a perfect voltaicbattery of forty pairs of plates (991. 1001. ) the consumption would havebeen one equivalent for each zinc plate, or forty for the whole. 

1129. Similar experiments were made with two voltaic batteries, onecontaining twenty pairs of four-inch plates, arranged as I have described(1124. ), and the other twenty pairs of four-inch plates in porcelaintroughs. The average of five experiments with the former was a consumptionof 3. 7 equivalents of zinc from each plate, or 74 from the whole: theaverage of three experiments with the latter was 5. 5 equivalents from eachplate, or 110 from the whole: to obtain this conclusion two experimentswere struck out, which were much against the porcelain troughs, and inwhich some unknown deteriorating influence was supposed to be accidentallyactive. In all the experiments, care was taken not to compare _new_ and_old_ plates together, as that would have introduced serious errors intothe conclusions (1146. ). 

1130. When ten pairs of the new arrangement were used, the consumption ofzinc at each plate was 6. 76 equivalents, or 67. 6 for the whole. With tenpairs of the common construction, in a porcelain trough, the zinc oxidizedwas, upon an average, 15. 5 equivalents each plate, or 155 for the entiretrough. 

1131. No doubt, therefore, can remain of the equality or even the greatsuperiority of this form of voltaic battery over the best previously inuse, namely, that with double coppers, in which the cells are insulated. The insulation of the coppers may therefore be dispensed with; and it isthat circumstance which principally permits of such other alterations inthe construction of the trough as gives it its practical advantages. 

1132. The advantages of this form of trough are very numerous and great. I. It is exceedingly compact, for 100 pairs of plates need not occupy a troughof more than three feet in length, ii. By Dr. Hare's plan of making thetrough turn upon copper pivots which rest upon copper bearings, the latterafford _fixed_ terminations; and these I have found it very convenient toconnect with two cups of mercury, fastened in the front of the stand of theinstrument. These fixed terminations give the great advantage of arrangingan apparatus to be used in connexion with the battery _before_ the latteris put into action, iii. The trough is put into readiness for use in aninstant, a single jug of dilute acid being sufficient for the charge of 100pairs of four-inch plates, iv. On making the trough pass through a quarterof a revolution, it becomes active, and the great advantage is obtained ofprocuring for the experiment the effect of the _first contact_ of the zincand acid, which is twice or sometimes even thrice that which the batterycan produce a minute or two after (1036. 1150. ). V. When the experiment iscompleted, the acid can be at once poured from between the plates, so thatthe battery is never left to waste during an unconnected state of itsextremities; the acid is not unnecessarily exhausted; the zinc is notuselessly consumed; and, besides avoiding these evils, the charge is mixedand rendered uniform, which produces a great and good result (1039. ); and, upon proceeding to a second experiment, the important effect of _firstcontact_ is again obtained. Vi. The saving of zinc is very great. It is notmerely that, whilst in action, the zinc performs more voltaic duty (1128. 1129. ), but _all_ the destruction which takes place with the ordinary formsof battery between the experiments is prevented. This saving is of suchextent, that I estimate the zinc in the new form of battery to be thrice aseffective as that in the ordinary form. Vii. The importance of this savingof metal is not merely that the value of the zinc is saved, but that thebattery is much lighter and more manageable; and also that the surfaces ofthe zinc and copper plates may be brought much nearer to each other whenthe battery is constructed, and remain so until it is worn out: the latteris a very important advantage (1148. ). Viii. Again, as, in consequence ofthe saving, thinner plates will perform the duty of thick ones, rolled zincmay be used; and I have found rolled zinc superior to cast zinc in action;a superiority which I incline to attribute to its greater purity (1144. ). Ix. Another advantage is obtained in the economy of the acid used, which isproportionate to the diminution of the zinc dissolved. X. The acid also ismore easily exhausted, and is in such small quantity that there is neverany occasion to return an old charge into use. The acid of old chargeswhilst out of use, often dissolves portions of copper from the blackflocculi usually mingled with it, which are derived from the zinc; now anyportion of copper in solution in the charge does great harm, because, bythe _local_ action of the acid and zinc, it tends to precipitate upon thelatter, and diminish its voltaic efficacy (1145. ). Xi. By using a duemixture of nitric and sulphuric acid for the charge (1139. ), no gas isevolved from the troughs; so that a battery of several hundred pairs ofplates may, without inconvenience, be close to the experimenter. Xii. If, during a series of experiments, the acid becomes exhausted, it can bewithdrawn, and replaced by other acid with the utmost facility; and afterthe experiments are concluded, the great advantage of easily washing theplates is at command. And it appears to me, that in place of making, underdifferent circumstances, mutual sacrifices of comfort, power, and economy, to obtain a desired end, all are at once obtained by Dr. Hare's form oftrough. 

1133. But there are some disadvantages which I have not yet had time toovercome, though I trust they will finally be conquered. One is the extremedifficulty of making a wooden trough constantly water-tight under thealternations of wet and dry to which the voltaic instrument is subject. Toremedy this evil, Mr. Newman is now engaged in obtaining porcelain troughs. The other disadvantage is a precipitation of copper on the zinc plates. Itappears to me to depend mainly on the circumstance that the papers betweenthe coppers retain acid when the trough is emptied; and that this acidslowly acting on the copper, forms a salt, which gradually mingles with thenext charge, and is reduced on the zinc plate by the local action (1120. ):the power of the whole battery is then reduced. I expect that by usingslips of glass or wood to separate the coppers at their edges, theircontact can be sufficiently prevented, and the space between them be leftso open that the acid of a charge can be poured and washed out, and so beremoved from _every part_ of the trough when the experiments in which thelatter is used are completed. 

1134. The actual superiority of the troughs which I have constructed onthis plan, I believe to depend, first and principally, on the closerapproximation of the zinc and copper surfaces;--in my troughs they are onlyone-tenth of an inch apart (1148. );--and, next, on the superior quality ofthe rolled zinc above the cast zinc used in the construction of theordinary pile. It cannot be that insulation between the contiguous coppersis a disadvantage, but I do not find that it is any advantage; for when, with both the forty pairs of three-inch plates and the twenty pairs offour-inch plates, I used papers well-soaked in wax[A], these being so largethat when folded at the edges they wrapped over each other, so as to makecells as insulating as those of the porcelain troughs, still no sensibleadvantage in the chemical action was obtained. 

 [A] A single paper thus prepared could insulate the electricity of a trough of forty pairs of plates. 

1135. As, upon principle, there must be a discharge of part of theelectricity from the edges of the zinc and copper plates at the sides ofthe trough, I should prefer, and intend having, troughs constructed with aplate or plates of crown glass at the sides of the trough: the bottom willneed none, though to glaze that and the ends would be no disadvantage. Theplates need not be fastened in, but only set in their places; nor need theybe in large single pieces. 

§ 17. _Some practical results respecting the construction and use of theVoltaic Battery_ (1034. &c. ). 

1136. The electro-chemical philosopher is well acquainted with somepractical results obtained from the voltaic battery by MM. . Gay-Lussac andThenard, and given in the first forty-five pages of their 'RecherchesPhysico-Chimiques'. Although the following results are generally of thesame nature, yet the advancement made in this branch of science of lateyears, the knowledge of the definite action of electricity, and the moreaccurate and philosophical mode of estimating the results by theequivalents of zinc consumed, will be their sufficient justification. 

1137. _Nature and strength of the acid. _--My battery of forty pairs ofthree-inch plates was charged with acid consisting of 200 parts water and 9oil of vitriol. Each plate lost, in the average of the experiments, 4. 66equivalents of zinc for the equivalent of water decomposed in thevolta-electrometer, or the whole battery 186. 4 equivalents of zinc. Beingcharged with a mixture of 200 water and 16 of the muriatic acid, each platelost 3. 8, equivalents of zinc for the water decomposed, or the wholebattery 152 equivalents of zinc. Being charged with a mixture of 200 waterand 8 nitric acid, each plate lost 1. 85, equivalents of zinc for oneequivalent of water decomposed, or the whole battery 74. 16 equivalents ofzinc. The sulphuric and muriatic acids evolved much hydrogen at the platesin the trough; the nitric acid no gas whatever. The relative strengths ofthe original acids have already been given (1127. ); but a difference inthat respect makes no important difference in the results when thusexpressed by equivalents (1140. ). 

1138. Thus nitric acid proves to be the best for this purpose; itssuperiority appears to depend upon its favouring the electrolyzation of theliquid in the cells of the trough upon the principles already explained(905. 973, 1022. ), and consequently favouring the transmission of theelectricity, and therefore the production of transferable power (1120. ). 

1139. The addition of nitric acid might, consequently, be expected toimprove sulphuric and muriatic acids. Accordingly, when the same trough wascharged with a mixture of 200 water, 9 oil of vitriol, and 4 nitric acid, the consumption of zinc was at each plate 2. 786, and for the whole battery111. 5, equivalents. When the charge was 200 water, 9 oil of vitriol, and 8nitric acid, the loss per plate was 2. 26, or for the whole battery 90. 4, equivalents. When the trough was charged with a mixture of 200 water, 16muriatic acid, and 6 nitric acid, the loss per plate was 2. 11, or for thewhole battery 84. 4, equivalents. Similar results were obtained with mybattery of twenty pairs of four-inch plates (1129. ). Hence it is evidentthat the nitric acid was of great service when mingled with the sulphuricacid; and the charge generally used after this time for ordinaryexperiments consisted of 200 water, 4-1/2 oil of vitriol, and 4 nitricacid. 

1140. It is not to be supposed that the different strengths of the acidsproduced the differences above; for within certain limits I found theelectrolytic effects to be nearly as the strengths of the acids, so as toleave the expression of force, when given in equivalents, almost constant. Thus, when the trough was charged with a mixture of 200 water and 8 nitricacid, each plate lost 1. 854 equivalent of zinc. When the charge was 200water and 16 nitric acid, the loss per plate was 1. 82 equivalent. When itwas 200 water and 32 nitric acid, the loss was 2. 1 equivalents. Thedifferences here are not greater than happen from unavoidableirregularities, depending on other causes than the strength of acid. 

1141. Again, when a charge consisting of 200 water, 4-1/2 oil of vitriol, and 4 nitric acid was used, each zinc plate lost 2. 16 equivalents; when thecharge with the same battery was 200 water, 9 oil of vitriol, and 8 nitricacid, each zinc plate lost 2. 26 equivalents. 

1142. I need hardly say that no copper is dissolved during the regularaction of the voltaic trough. I have found that much ammonia is formed inthe cells when nitric acid, either pure or mixed with sulphuric acid, isused. It is produced in part as a secondary result at the cathodes (663. )of the different portions of fluid constituting the necessary electrolyte, in the cells. 

1143. _Uniformity of the charge. _--This is a most important point, as Ihave already shown experimentally (1042. &c. ). Hence one great advantage ofDr. Hare's mechanical arrangement of his trough. 

1144. _Purity of the zinc. _--If pure zinc could be obtained, it would bevery advantageous in the construction of the voltaic apparatus (998. ). Mostzincs, when put into dilute sulphuric acid, leave more or less of aninsoluble matter upon the surface in the form of a crust, which containsvarious metals, as copper, lead, zinc, iron, cadmium, &c. , in the metallicstate. Such particles, by discharging part of the transferable power, render it, as to the whole battery, local; and so diminish the effect. Asan indication connected with the more or less perfect action of thebattery, I may mention that no gas ought to rise from the zinc plates. Themore gas which is generated upon these surfaces, the greater is the localaction and the less the transferable force. The investing crust is alsoinconvenient, by preventing the displacement and renewal of the charge uponthe surface of the zinc. Such zinc as, dissolving in the cleanest manner ina dilute acid, dissolves also the slowest, is the best; zinc which containsmuch copper should especially be avoided. I have generally found rolledLiege or Mosselman's zinc the purest; and to the circumstance of havingused such zinc in its construction attribute in part the advantage of thenew battery (1134. ). 

1145. _Foulness of the zinc plates. _--After use, the plates of a batteryshould be cleaned from the metallic powder upon their surfaces, especiallyif they are employed to obtain the laws of action of the battery itself. This precaution was always attended to with the porcelain trough batteriesin the experiments described (1125, &c. ). If a few foul plates are mingledwith many clean ones, they make the action in the different cellsirregular, and the transferable power is accordingly diminished, whilst thelocal and wasted power is increased. No old charge containing copper shouldbe used to excite a battery. 

1146. _New and old plates. _--I have found voltaic batteries far morepowerful when the plates were new than when they have been used two orthree times; so that a new and an used battery cannot be compared together, or even a battery with itself on the first and after times of use. Mytrough of twenty pairs of four-inch plates, charged with acid consisting of200 water, 4-1/2 oil of vitriol, and 4 nitric acid, lost, upon the firsttime of being used, 2. 82 equivalents per plate. When used after the fourthtime with the same charge, the loss was from 3. 26 to 4. 47 equivalents perplate; the average being 3. 7 equivalents. The first time the forty pair ofplates (1124. ) were used, the loss at each plate was only 1. 65 equivalent;but afterwards it became 2. 16, 2. 17, 2. 52. The first time twenty pair offour-inch plates in porcelain troughs were used, they lost, per plate, only3. 7 equivalents; but after that, the loss was 5. 25, 5. 36, 5. 9 equivalents. Yet in all these cases the zincs had been well-cleaned from adheringcopper, &c. , before each trial of power. 

1147. With the rolled zinc the fall in force soon appeared to becomeconstant, i. E. To proceed no further. But with the cast zinc platesbelonging to the porcelain troughs, it appeared to continue, until at last, with the same charge, each plate lost above twice as much zinc for a givenamount of action as at first. These troughs were, however, so irregularthat I could not always determine the circumstances affecting the amount ofelectrolytic action. 

1148. _Vicinity of the copper and zinc. _--The importance of this point inthe construction of voltaic arrangements, and the greater power, as toimmediate action, which is obtained when the zinc and copper surfaces arenear to each other than when removed further apart, are well known. I findthat the power is not only greater on the instant, but also that the sum oftransferable power, in relation to the whole sum of chemical action at theplates, is much increased. The cause of this gain is very evident. Whatevertends to retard the circulation of the transferable force, (i. E. Theelectricity, ) diminishes the proportion of such force, and increases theproportion of that which is local (996. 1120. ). Now the liquid in the cellspossesses this retarding power, and therefore acts injuriously, in greateror less proportion, according to the quantity of it between the zinc andcopper plates, i. E. According to the distances between their surfaces. Atrough, therefore, in which the plates are only half the distance asunderat which they are placed in another, will produce more transferable, andless local, force than the latter; and thus, because the electrolyte in thecells can transmit the current more readily; both the intensity andquantity of electricity is increased for a given consumption of zinc. Tothis circumstance mainly I attribute the superiority of the trough I havedescribed (1134. ). 

1149. The superiority of _double coppers_ over single plates also dependsin part upon diminishing the resistance offered by the electrolyte betweenthe metals. For, in fact, with double coppers the sectional area of theinterposed acid becomes nearly double that with single coppers, andtherefore it more freely transfers the electricity. Double coppers are, however, effective, mainly because they virtually double the acting surfaceof the zinc, or nearly so; for in a trough with single copper plates andthe usual construction of cells, that surface of zinc which is not opposedto a copper surface is thrown almost entirely out of voltaic action, yetthe acid continues to act upon it and the metal is dissolved, producingvery little more than local effect (947. 996). But when by doubling thecopper, that metal is opposed to the second surface of the zinc plate, thena great part of the action upon the latter is converted into transferableforce, and thus the power of the trough as to quantity of electricity ishighly exalted. 

1150. _First immersion of the plates. _--The great effect produced at thefirst immersion of the plates, (apart from their being new or used(1146. ), ) I have attributed elsewhere to the unchanged condition of theacid in contact with the zinc plate (1003. 1037. ): as the acid becomesneutralized, its exciting power is proportionally diminished. Hare's formof trough secures much advantage of this kind, by mingling the liquid, andbringing what may be considered as a fresh surface of acid against theplates every time it is used immediately after a rest. 

1151. _Number of plates. _[A]--The most advantageous number of plates in abattery used for chemical decomposition, depends almost entirely upon theresistance to be overcome at the place of action; but whatever thatresistance may be, there is a certain number which is more economical thaneither a greater or a less. Ten pairs of four-inch plates in a porcelaintrough of the ordinary construction, acting in the volta-electrometer(1126. ) upon dilute sulphuric acid of spec. Grav. 1. 314, gave an averageconsumption of 15. 4 equivalents per plate, or 154 equivalents on the whole. Twenty pairs of the same plates, with the same acid, gave only aconsumption of 5. 5 per plate, or 110 equivalents upon the whole. When fortypairs of the same plates were used, the consumption was 3. 54 equivalentsper plate, or 141. 6 upon the whole battery. Thus the consumption of zincarranged as _twenty_ plates was more advantageous than if arranged eitheras _ten_ or as _forty_. 

 [A] Gay-Lussac and Thenard, Recherches Physico-Chimiques, tom. I. P. 29. 

1152. Again, ten pairs of my four-inch plates (1129. ) lost 6. 76 each, orthe whole ten 67. 6 equivalents of zinc, in effecting decomposition; whilsttwenty pairs of the same plates, excited by the same acid, lost 3. 7equivalents each, or on the whole 74 equivalents. In other comparativeexperiments of numbers, ten pairs of the three inch-plates, (1125. ) lost3. 725, or 37. 25 equivalents upon the whole; whilst twenty pairs lost 2. 53each, or 50. 6 in all; and forty pairs lost on an average 2. 21, or 88. 4altogether. In both these cases, therefore, increase of numbers had notbeen advantageous as to the effective production of _transferable chemicalpower_ from the _whole quantity of chemical force_ active at the surfacesof excitation (1120. ). 

1153. But if I had used a weaker acid or a worse conductor in thevolta-electrometer, then the number of plates which would produce the mostadvantageous effect would have risen; or if I had used a better conductorthan that really employed in the volta-electrometer, I might have reducedthe number even to one; as, for instance, when a thick wire is used tocomplete the circuit (865. , &c. ). And the cause of these variations is veryevident, when it is considered that each successive plate in the voltaicapparatus does not add anything to the _quantity_ of transferable power orelectricity which the first plate can put into motion, provided a goodconductor be present, but tends only to exalt the _intensity_ of thatquantity, so as to make it more able to overcome the obstruction of badconductors (994. 1158. ). 

1154. _Large or small plates. _[A]--The advantageous use of large or smallplates for electrolyzations will evidently depend upon the facility withwhich the transferable power of electricity can pass. If in a particularcase the most effectual number of plates is known (1151. ), then theaddition of more zinc would be most advantageously made in increasing the_size_ of the plates, and not their _number_. At the same time, largeincrease in the size of the plates would raise in a small degree the mostfavourable number. 

 [A] Gay-Lussac and Thenard, Recherches Physico-Chimiques, tom, i. P. 20. 

1155. Large and small plates should not be used together in the samebattery: the small ones occasion a loss of the power of the large ones, unless they be excited by an acid proportionably more powerful; for with acertain acid they cannot transmit the same portion of electricity in agiven time which the same acid can evolve by action on the larger plates. 

1156. _Simultaneous decompositions. _--When the number of plates in abattery much surpasses the most favourable proportion (1151--1153. ), two ormore decompositions may be effected simultaneously with advantage. Thus myforty pairs of plates (1124. ) produced in one volta-electrometer 22. 8 cubicinches of gas. Being recharged exactly in the same manner, they produced ineach of two volta-electrometers 21 cubical inches. In the first experimentthe whole consumption of zinc was 88. 4 equivalents, and in the second only48. 28 equivalents, for the whole of the water decomposed in bothvolta-electrometers. 

1157. But when the twenty pairs of four-inch plates (1129. ) were tried ina similar manner, the results were in the opposite direction. With onevolta-electrometer 52 cubic inches of gas were obtained; with two, only14. 6 cubic inches from each. The quantity of charge was not the same inboth cases, though it was of the same strength; but on rendering theresults comparative by reducing them to equivalents (1126. ), it was foundthat the consumption of metal in the first case was 74, and in the secondcase 97, equivalents for the _whole_ of the water decomposed. Theseresults of course depend upon the same circumstances of retardation, &c. , which have been referred to in speaking of the proper number of plates(1151. ). 

1158. That the _transferring_, or, as it is usually called, _conducting, power_ of an electrolyte which is to be decomposed, or other interposedbody, should be rendered as good as possible[A], is very evident (1020. 1120. ). With a perfectly good conductor and a good battery, nearly all theelectricity is passed, i. E. _nearly all_ the chemical power becomestransferable, even with a single pair of plates (807. ). With an interposednonconductor none of the chemical power becomes transferable. With animperfect conductor more or less of the chemical power becomes transferableas the circumstances favouring the transfer of forces across the imperfectconductor are exalted or diminished: these circumstances are, actualincrease or improvement of the conducting power, enlargement of theelectrodes, approximation of the electrodes, and increased intensity of thepassing current. 

 [A] Gay-Lussac and Thenard, Recherches Physico-Chimiques, tom. I. Pp. 13, 15, 22. 

1159. The introduction of common spring water in place of one of thevolta-electrometers used with twenty pairs of four-inch plates (1156. )caused such obstruction as not to allow one-fifteenth of the transferableforce to pass which would have circulated without it. Thusfourteen-fifteenths of the available force of the battery were destroyed, local force, (which was rendered evident by the evolution of gas from thebeing converted into zincs, ) and yet the platina electrodes in the waterwere three inches long, nearly an inch wide, and not a quarter of an inchapart. 

1160. These points, i. E. The increase of conducting power, the enlargementof the electrodes, and their approximation, should be especially attendedto in _volta-electrometers_. The principles upon which their utility dependare so evident that there can be no occasion for further development ofthem here. 

_Royal Institution, October 11, 1834. _

ELEVENTH SERIES. 

§ 18. _On Induction. _ ¶ i. _Induction an action of contiguous particles. _¶ ii. _Absolute charge of matter. _ ¶ iii. _Electrometer and inductiveapparatus employed. _ ¶ iv. _Induction in curved lines. _ ¶ v. _Specificinductive capacity. _ ¶ vi. _General results as to induction. _

Received November 30, --Read December 21, 1837. 

¶ i. _Induction an action of contiguous particles. _

1161. The science of electricity is in that state in which every part of itrequires experimental investigation; not merely for the discovery of neweffects, but what is just now of far more importance, the development ofthe means by which the old effects are produced, and the consequent moreaccurate determination of the first principles of action of the mostextraordinary and universal power in nature:--and to those philosophers whopursue the inquiry zealously yet cautiously, combining experiment withanalogy, suspicious of their preconceived notions, paying more respect to afact than a theory, not too hasty to generalize, and above all things, willing at every step to cross-examine their own opinions, both byreasoning and experiment, no branch of knowledge can afford so fine andready a field for discovery as this. Such is most abundantly shown to bethe case by the progress which electricity has made in the last thirtyyears: Chemistry and Magnetism have successively acknowledged itsover-ruling influence; and it is probable that every effect depending uponthe powers of inorganic matter, and perhaps most of those related tovegetable and animal life, will ultimately be found subordinate to it. 

1162. Amongst the actions of different kinds into which electricity hasconventionally been subdivided, there is, I think, none which excels, oreven equals in importance, that called _Induction_. It is of the mostgeneral influence in electrical phenomena, appearing to be concerned inevery one of them, and has in reality the character of a first, essential, and fundamental principle. Its comprehension is so important, that I thinkwe cannot proceed much further in the investigation of the laws ofelectricity without a more thorough understanding of its nature; howotherwise can we hope to comprehend the harmony and even unity of actionwhich doubtless governs electrical excitement by friction, by chemicalmeans, by heat, by magnetic influence, by evaporation, and even by theliving being?

1163. In the long-continued course of experimental inquiry in which I havebeen engaged, this general result has pressed upon me constantly, namely, the necessity of admitting two forces, or two forms or directions of aforce (516. 517. ), combined with the impossibility of separating these twoforces (or electricities) from each other, either in the phenomena ofstatical electricity or those of the current. In association with this, theimpossibility under any circumstances, as yet, of absolutely chargingmatter of any kind with one or the other electricity only, dwelt on mymind, and made me wish and search for a clearer view than any that I wasacquainted with, of the way in which electrical powers and the particles ofmatter are related; especially in inductive actions, upon which almost allothers appeared to rest. 

1164. When I discovered the general fact that electrolytes refused to yieldtheir elements to a current when in the solid state, though they gave themforth freely if in the liquid condition (380. 394. 402. ), I thought I sawan opening to the elucidation of inductive action, and the possiblesubjugation of many dissimilar phenomena to one law. For let theelectrolyte be water, a plate of ice being coated with platina foil on itstwo surfaces, and these coatings connected with any continued source of thetwo electrical powers, the ice will charge like a Leyden arrangement, presenting a case of common induction, but no current will pass. If the icebe liquefied, the induction will fall to a certain degree, because acurrent can now pass; but its passing is dependent upon a _peculiarmolecular arrangement_ of the particles consistent with the transfer of theelements of the electrolyte in opposite directions, the degree of dischargeand the quantity of elements evolved being exactly proportioned to eachother (377. 783. ). Whether the charging of the metallic coating be effectedby a powerful electrical machine, a strong and large voltaic battery, or asingle pair of plates, makes no difference in the principle, but only inthe degree of action (360). Common induction takes place in each case ifthe electrolyte be solid, or if fluid, chemical action and decompositionensue, provided opposing actions do not interfere; and it is of highimportance occasionally thus to compare effects in their extreme degrees, for the purpose of enabling us to comprehend the nature of an action in itsweak state, which may be only sufficiently evident to us in its strongercondition (451. ). As, therefore, in the electrolytic action, _induction_appeared to be the _first_ step, and _decomposition_ the _second_ (thepower of separating these steps from each other by giving the solid orfluid condition to the electrolyte being in our hands); as the inductionwas the same in its nature as that through air, glass, wax, &c. Produced byany of the ordinary means; and as the whole effect in the electrolyteappeared to be an action of the particles thrown into a peculiar orpolarized state, I was led to suspect that common induction itself was inall cases an _action of contiguous particles_[A], and that electricalaction at a distance (i. E. Ordinary inductive action) never occurred exceptthrough the influence of the intervening matter. 

 [A] The word _contiguous_ is perhaps not the best that might have been used here and elsewhere; for as particles do not touch each other it is not strictly correct. I was induced to employ it, because in its common acceptation it enabled me to state the theory plainly and with facility. By contiguous particles I mean those which are next. --_Dec. 1838. _

1165. The respect which I entertain towards the names of Epinus, Cavendish, Poisson, and other most eminent men, all of whose theories I believeconsider induction as an action at a distance and in straight lines, longindisposed me to the view I have just stated; and though I always watchedfor opportunities to prove the opposite opinion, and made such experimentsoccasionally as seemed to bear directly on the point, as, for instance, theexamination of electrolytes, solid and fluid, whilst under induction bypolarized light (951. 955. ), it is only of late, and by degrees, that theextreme generality of the subject has urged me still further to extend myexperiments and publish my view. At present I believe ordinary induction inall cases to be an action of contiguous particles consisting in a speciesof polarity, instead of being an action of either particles or masses atsensible distances; and if this be true, the distinction and establishmentof such a truth must be of the greatest consequence to our further progressin the investigation of the nature of electric forces. The linked conditionof electrical induction with chemical decomposition; of voltaic excitementwith chemical action; the transfer of elements in an electrolyte; theoriginal cause of excitement in all cases; the nature and relation ofconduction and insulation of the direct and lateral or transverse actionconstituting electricity and magnetism; with many other things more or lessincomprehensible at present, would all be affected by it, and perhapsreceive a full explication in their reduction under one general law. 

1166. I searched for an unexceptionable test of my view, not merely in theaccordance of known facts with it, but in the consequences which would flowfrom it if true; especially in those which would not be consistent with thetheory of action at a distance. Such a consequence seemed to me to presentitself in the direction in which inductive action could be exerted. If instraight lines only, though not perhaps decisive, it would be against myview; but if in curved lines also, that would be a natural result of theaction of contiguous particles, but, as I think, utterly incompatible withaction at a distance, as assumed by the received theories, which, accordingto every fact and analogy we are acquainted with, is always in straightlines. 

1167. Again, if induction be an action of contiguous particles, and alsothe first step in the process of electrolyzation (1164. 919. ), there seemedreason to expect some particular relation of it to the different kinds ofmatter through which it would be exerted, or something equivalent to a_specific electric induction_ for different bodies, which, if it existed, would unequivocally prove the dependence of induction on the particles; andthough this, in the theory of Poisson and others, has never been supposedto be the case, I was soon led to doubt the received opinion, and havetaken great pains in subjecting this point to close experimentalexamination. 

1168. Another ever-present question on my mind has been, whetherelectricity has an actual and independent existence as a fluid or fluids, or was a mere power of matter, like what we conceive of the attraction ofgravitation. If determined either way it would be an enormous advance inour knowledge; and as having the most direct and influential bearing on mynotions, I have always sought for experiments which would in any way tendto elucidate that great inquiry. It was in attempts to prove the existenceof electricity separate from matter, by giving an independent charge ofeither positive or negative power only, to some one substance, and theutter failure of all such attempts, whatever substance was used or whatevermeans of exciting or _evolving_ electricity were employed, that first droveme to look upon induction as an action of the particles of matter, eachhaving _both_ forces developed in it in exactly equal amount. It is thiscircumstance, in connection with others, which makes me desirous of placingthe remarks on absolute charge first, in the order of proof and argument, which I am about to adduce in favour of my view, that electric induction isan action of the contiguous particles of the insulating medium or_dielectric_[A]. 

 [A] I use the word _dielectric_ to express that substance through or across which the electric forces are acting. --_Dec. 1838. _

¶ ii. _On the absolute charge of matter. _

1169. Can matter, either conducting or non-conducting, be charged with oneelectric force independently of the other, in any degree, either in asensible or latent state?

1170. The beautiful experiments of Coulomb upon the equality of action of_conductors_, whatever their substance, and the residence of _all_ theelectricity upon their surfaces[A], are sufficient, if properly viewed, toprove that _conductors cannot be bodily charged_; and as yet no means ofcommunicating electricity to a conductor so as to place its particles inrelation to one electricity, and not at the same time to the other inexactly equal amount, has been discovered. 

 [A] Mémoires de l'Académie, 1786, pp. 67. 69. 72; 1787, p. 452. 

1171. With regard to electrics or non-conductors, the conclusion does notat first seem so clear. They may easily be electrified bodily, either bycommunication (1247. ) or excitement; but being so charged, every case insuccession, when examined, came out to be a case of induction, and not ofabsolute charge. Thus, glass within conductors could easily have parts notin contact with the conductor brought into an excited state; but it wasalways found that a portion of the inner surface of the conductor was in anopposite and equivalent state, or that another part of the glass itself wasin an equally opposite state, an _inductive_ charge and not an _absolute_charge having been acquired. 

1172. Well-purified oil of turpentine, which I find to be an excellentliquid insulator for most purposes, was put into a metallic vessel, and, being insulated, an endeavour was made to charge its particles, sometimesby contact of the metal with the electrical machine, and at others by awire dipping into the fluid within; but whatever the mode of communication, no electricity of one kind only was retained by the arrangement, exceptwhat appeared on the exterior surface of the metal, that portion beingpresent there only by an inductive action through the air to thesurrounding conductors. When the oil of turpentine was confined in glassvessels, there were at first some appearances as if the fluid did receivean absolute charge of electricity from the charging wire, but these werequickly reduced to cases of common induction jointly through the fluid, theglass, and the surrounding air. 

1173. I carried these experiments on with air to a very great extent. I hada chamber built, being a cube of twelve feet. A slight cubical wooden framewas constructed, and copper wire passed along and across it in variousdirections, so as to make the sides a large net-work, and then all wascovered in with paper, placed in close connexion with the wires, andsupplied in every direction with bands of tin foil, that the whole might bebrought into good metallic communication, and rendered a free conductor inevery part. This chamber was insulated in the lecture-room of the RoyalInstitution; a glass tube about six feet in length was passed through itsside, leaving about four feet within and two feet on the outside, andthrough this a wire passed from the large electrical machine (290. ) to theair within. By working the machine, the air in this chamber could bebrought into what is considered a highly electrified state (being, in fact, the same state as that of the air of a room in which a powerful machine isin operation), and at the same time the outside of the insulated cube waseverywhere strongly charged. But putting the chamber in communication withthe perfect discharging train described in a former series (292. ), andworking the machine so as to bring the air within to its utmost degree ofcharge if I quickly cut off the connexion with the machine, and at the samemoment or instantly after insulated the cube, the air within had not theleast power to communicate a further charge to it. If any portion of theair was electrified, as glass or other insulators may be charged (1171. ), it was accompanied by a corresponding opposite action _within_ the cube, the whole effect being merely a case of induction. Every attempt to chargeair bodily and independently with the least portion of either electricityfailed. 

1174 I put a delicate gold-leaf electrometer within the cube, and thencharged the whole by an _outside_ communication, very strongly, for sometime together; but neither during the charge or after the discharge did theelectrometer or air within show the least signs of electricity. I chargedand discharged the whole arrangement in various ways, but in no case couldI obtain the least indication of an absolute charge; or of one by inductionin which the electricity of one kind had the smallest superiority inquantity over the other. I went into the cube and lived in it, and usinglighted candles, electrometers, and all other tests of electrical states, Icould not find the least influence upon them, or indication of any thingparticular given by them, though all the time the outside of the cube waspowerfully charged, and large sparks and brushes were darting off fromevery part of its outer surface. The conclusion I have come to is, thatnon-conductors, as well as conductors, have never yet had an absolute andindependent charge of one electricity communicated to them, and that to allappearance such a state of matter is impossible. 

1175. There is another view of this question which may be taken under thesupposition of the existence of an electric fluid or fluids. It may beimpossible to have one fluid or state in a free condition without itsproducing by induction the other, and yet possible to have cases in whichan isolated portion of matter in one condition being uncharged, shall, by achange of state, evolve one electricity or the other: and though suchevolved electricity might immediately induce the opposite state in itsneighbourhood, yet the mere evolution of one electricity without the otherin the _first instance_, would be a very important fact in the theorieswhich assume a fluid or fluids; these theories as I understand themassigning not the slightest reason why such an effect should not occur. 

1176. But on searching for such cases I cannot find one. Evolution byfriction, as is well known, gives both powers in equal proportion. So doesevolution by chemical action, notwithstanding the great diversity of bodieswhich may be employed, and the enormous quantity of electricity which canin this manner be evolved (371. 376. 861. 868. 961. ). The more promisingcases of change of state, whether by evaporation, fusion, or the reverseprocesses, still give both forms of the power in _equal_ proportion; andthe cases of splitting of mica and other crystals, the breaking of sulphur, &c. , are subject to the same law of limitation. 

1177. As far as experiment has proceeded, it appears, therefore, impossibleeither to evolve or make disappear one electric force without equal andcorresponding change in the other. It is also equally impossibleexperimentally to charge a portion of matter with one electric forceindependently of the other. Charge always implies _induction_, for it canin no instance be effected without; and also the presence of the _two_forms of power, equally at the moment of the development and afterwards. There is no _absolute_ charge of matter with one fluid; no latency of asingle electricity. This though a negative result is an exceedinglyimportant one, being probably the consequence of a natural impossibility, which will become clear to us when we understand the true condition andtheory of the electric power. 

1178. The preceding considerations already point to the followingconclusions: bodies cannot be charged absolutely, but only relatively, andby a principle which is the same with that of _induction_. All _charge_ issustained by induction. All phenomena of _intensity_ include the principleof induction. All _excitation_ is dependent on or directly related toinduction. All _currents_ involve previous intensity and therefore previousinduction. INDUCTION appears to be the essential function both the firstdevelopment and the consequent phenomena of electricity. 

¶ iii. _Electrometer and inductive apparatus employed. _

1179. Leaving for a time the further consideration of the preceding factsuntil they can be collated with other results bearing directly on the greatquestion of the nature of induction, I will now describe the apparatus Ihave had occasion to use; and in proportion to the importance of theprinciples sought to be established is the necessity of doing this soclearly, as to leave no doubt of the results behind. 

1180. _Electrometer. _--The measuring instrument I have employed has beenthe torsion balance electrometer of Coulomb, constructed, generally, according to his directions[A], but with certain variations and additions, which I will briefly describe. The lower part was a glass cylinder eightinches in height and eight inches in diameter; the tube for the torsionthread was seventeen inches in length. The torsion thread itself was not ofmetal, but glass, according to the excellent suggestion of the late Dr. Ritchie[B]. It was twenty inches in length, and of such tenuity that whenthe shell-lac lever and attached ball, &c. Were connected with it, theymade about ten vibrations in a minute. It would bear torsion through fourrevolutions or 1440°, and yet, when released, return accurately to itsposition; probably it would have borne considerably more than this withoutinjury. The repelled ball was of pith, gilt, and was 0. 3 of an inch indiameter. The horizontal stem or lever supporting it was of shell-lac, according to Coulomb's direction, the arm carrying the ball being 2. 4inches long, and the other only 1. 2 inches: to this was attached the vane, also described by Coulomb, which I found to answer admirably its purpose ofquickly destroying vibrations. That the inductive action within theelectrometer might be uniform in all positions of the repelled ball and inall states of the apparatus, two bands of tin foil, about an inch wideeach, were attached to the inner surface of the glass cylinder, goingentirely round it, at the distance of 0. 4 of an inch from each other, andat such a height that the intermediate clear surface was in the samehorizontal plane with the lever and ball. These bands were connected witheach other and with the earth, and, being perfect conductors, alwaysexerted a uniform influence on the electrified balls within, which theglass surface, from its irregularity of condition at different times, Ifound, did not. For the purpose of keeping the air within the electrometerin a constant state as to dryness, a glass dish, of such size as to entereasily within the cylinder, had a layer of fused potash placed within it, and this being covered with a disc of fine wire-gauze to render itsinductive action uniform at all parts, was placed within the instrument atthe bottom and left there. 

 [A] Mémoires de l'Académie, 1785, p. 570. 

 [B] Philosophical Transactions, 1830. 

1181. The moveable ball used to take and measure the portion of electricityunder examination, and which may be called the _repelling_, or the_carrier_, ball, was of soft alder wood, well and smoothly gilt. It wasattached to a fine shell-lac stem, and introduced through a hole into theelectrometer according to Coulomb's method: the stem was fixed at its upperend in a block or vice, supported on three short feet; and on the surfaceof the glass cover above was a plate of lead with stops on it, so that whenthe carrier ball was adjusted in its right position, with the vice abovebearing at the same time against these stops, it was perfectly easy tobring away the carrier-ball and restore it to its place again veryaccurately, without any loss of time. 

1182. It is quite necessary to attend to certain precautions respectingthese balls. If of pith alone they are bad; for when very dry, thatsubstance is so imperfect a conductor that it neither receives nor gives acharge freely, and so, after contact with a charged conductor, it is liableto be in an uncertain condition. Again, it is difficult to turn pith sosmooth as to leave the ball, even when gilt, so free from irregularities ofform, as to retain its charge undiminished for a considerable length oftime. When, therefore, the balls are finally prepared and gilt they shouldbe examined; and being electrified, unless they can hold their charge withvery little diminution for a considerable time, and yet be dischargedinstantly and perfectly by the touch of an uninsulated conductor, theyshould be dismissed. 

1183. It is, perhaps, unnecessary to refer to the graduation of theinstrument, further than to explain how the observations were made. On acircle or ring of paper on the outside of the glass cylinder, fixed so asto cover the internal lower ring of tinfoil, were marked four pointscorresponding to angles of 90°; four other points exactly corresponding tothese points being marked on the upper ring of tinfoil within. By these andthe adjusting screws on which the whole instrument stands, the glasstorsion thread could be brought accurately into the centre of theinstrument and of the graduations on it. From one of the four points on theexterior of the cylinder a graduation of 90° was set off, and acorresponding graduation was placed upon the upper tinfoil on the oppositeside of the cylinder within; and a dot being marked on that point of thesurface of the repelled ball nearest to the side of the electrometer, itwas easy, by observing the line which this dot made with the lines of thetwo graduations just referred to, to ascertain accurately the position ofthe ball. The upper end of the glass thread was attached, as in Coulomb'soriginal electrometer, to an index, which had its appropriate graduatedcircle, upon which the degree of torsion was ultimately to be read off. 

1184. After the levelling of the instrument and adjustment of the glassthread, the blocks which determine the place of the _carrier ball_ are tobe regulated (1181. ) so that, when the carrier arrangement is placedagainst them, the centre of the ball may be in the radius of the instrumentcorresponding to 0° on the lower graduation or that on the side of theelectrometer, and at the same level and distance from the centre as the_repelled ball_ on the suspended torsion lever. Then the torsion index isto be turned until the ball connected with it (the repelled ball) isaccurately at 30°, and finally the graduated arc belonging to the torsionindex is to be adjusted so as to bring 0° upon it to the index. This stateof the instrument was adopted as that which gave the most direct expressionof the experimental results, and in the form having fewest variable errors;the angular distance of 30° being always retained as the standard distanceto which the balls were in every case to be brought, and the whole of thetorsion being read off at once on the graduated circle above. Under thesecircumstances the distance of the balls from each other was not merely thesame in degree, but their position in the instrument, and in relation toevery part of it, was actually the same every time that a measurement wasmade; so that all irregularities arising from slight difference of form andaction in the instrument and the bodies around were avoided. The onlydifference which could occur in the position of anything within, consistedin the deflexion of the torsion thread from a vertical position, more orless, according to the force of repulsion of the balls; but this was soslight as to cause no interfering difference in the symmetry of form withinthe instrument, and gave no error in the amount of torsion force indicatedon the graduation above. 

1185. Although the constant angular distance of 30° between the centres ofthe balls was adopted, and found abundantly sensible, for all ordinarypurposes, yet the facility of rendering the instrument far more sensible bydiminishing this distance was at perfect command; the results at differentdistances being very easily compared with each other either by experiment, or, as they are inversely as the squares of the distances, by calculation. 

1186. The Coulomb balance electrometer requires experience to beunderstood; but I think it a very valuable instrument in the hands of thosewho will take pains by practice and attention to learn the precautionsneedful in its use. Its insulating condition varies with circumstances, andshould be examined before it is employed in experiments. In an ordinary andfair condition, when the balls were so electrified as to give a repulsivetorsion force of 100° at the standard distance of 30°, it took nearly fourhours to sink to 50° at the same distance; the average loss from 400° to300° being at the rate of 2°. 7 per minute, from 300° to 200° of 1°. 7 perminute, from 200° to 100° of 1°. 3 per minute, and from 100° to 50° of 0°. 87per minute. As a complete measurement by the instrument may be made in muchless than a minute, the amount of loss in that time is but small, and caneasily be taken into account. 

1187. _The inductive apparatus. _--My object was to examine inductive actioncarefully when taking place through different media, for which purpose itwas necessary to subject these media to it in exactly similarcircumstances, and in such quantities as should suffice to eliminate anyvariations they might present. The requisites of the apparatus to beconstructed were, therefore, that the inducing surfaces of the conductorsshould have a constant form and state, and be at a constant distance fromeach other; and that either solids, fluids, or gases might be placed andretained between these surfaces with readiness and certainty, and for anylength of time. 

1188. The apparatus used may be described in general terms as consisting oftwo metallic spheres of unequal diameter, placed, the smaller within thelarger, and concentric with it; the interval between the two being thespace through which the induction was to take place. A section of it isgiven (Plate VII. Fig. 104. ) on a scale of one-half: _a, a_ are the twohalves of a brass sphere, with an air-tight joint at _b_, like that of theMagdeburg hemispheres, made perfectly flush and smooth inside so as topresent no irregularity; _c_ is a connecting piece by which the apparatusis joined to a good stop-cock _d_, which is itself attached either to themetallic foot _e_, or to an air-pump. The aperture within the hemisphere at_f_ is very small: _g_ is a brass collar fitted to the upper hemisphere, through which the shell-lac support of the inner ball and its stem passes;_h_ is the inner ball, also of brass; it screws on to a brass stem _i_, terminated above by a brass ball B, _l, l_ is a mass of shell-lac, mouldedcarefully on to _i_, and serving both to support and insulate it and itsballs _h_, B. The shell-lac stem _l_ is fitted into the socket _g_, by alittle ordinary resinous cement, more fusible than shell-lac, applied at_mm_ in such a way as to give sufficient strength and render the apparatusair-tight there, yet leave as much as possible of the lower part of theshell-lac stem untouched, as an insulation between the ball _h_ and thesurrounding sphere _a, a_. The ball _h_ has a small aperture at _n_, sothat when the apparatus is exhausted of one gas and filled with another, the ball _h_ may itself also be exhausted and filled, that no variation ofthe gas in the interval _o_ may occur during the course of an experiment. 

1189. It will be unnecessary to give the dimensions of all the parts, sincethe drawing is to a scale of one-half: the inner ball has a diameter 2. 33inches, and the surrounding sphere an internal diameter of 3. 57 inches. Hence the width of the intervening space, through which the induction is totake place, is 0. 62 of an inch; and the extent of this place or plate, i. E. The surface of a medium sphere, may be taken as twenty-seven square inches, a quantity considered as sufficiently large for the comparison of differentsubstances. Great care was taken in finishing well the inducing surfaces ofthe ball _h_ and sphere _a, a_; and no varnish or lacquer was applied tothem, or to any part of the metal of the apparatus. 

1190. The attachment and adjustment of the shell-lac stem was a matterrequiring considerable care, especially as, in consequence of its cracking, it had frequently to be renewed. The best lac was chosen and applied to thewire _i_, so as to be in good contact with it everywhere, and in perfectcontinuity throughout its own mass. It was not smaller than is given byscale in the drawing, for when less it frequently cracked within a fewhours after it was cold. I think that very slow cooling or annealingimproved its quality in this respect. The collar _g_ was made as thin ascould be, that the lac might be as wide there as possible. In order that atevery re-attachment of the stem to the upper hemisphere the ball _h_ mighthave the same relative position, a gauge _p_ (fig. 105. ) was made of wood, and this being applied to the ball and hemisphere whilst the cement at _m_was still soft, the bearings of the ball at _qq_, and the hemisphere at_rr_, were forced home, and the whole left until cold. Thus all difficultyin the adjustment of the ball in the sphere was avoided. 

1191. I had occasion at first to attach the stem to the socket by othermeans, as a band of paper or a plugging of white silk thread; but thesewere very inferior to the cement, interfering much with the insulatingpower of the apparatus. 

1192. The retentive power of this apparatus was, when in good condition, better than that of the electrometer (1186. ), i. E. The proportion of lossof power was less. Thus when the apparatus was electrified, and also theballs in the electrometer, to such a degree, that after the inner ball hadbeen in contact with the top _k_ of the ball of the apparatus, it caused arepulsion indicated by 600° of torsion force, then in falling from 600° to400° the average loss was 8°. 6 per minute; from 400° to 300° the averageloss was 2°. 6 per minute; from 300° to 200° it was 1°. 7 per minute; from200° to 170° it was 1° per minute. This was after the apparatus had beencharged for a short time; at the first instant of charging there is anapparent loss of electricity, which can only be comprehended hereafter(1207. 1250. ). 

1193. When the apparatus loses its insulating power suddenly, it is almostalways from a crack near to or within the brass socket. These cracks areusually transverse to the stem. If they occur at the part attached bycommon cement to the socket, the air cannot enter, and thus constitutingvacua, they conduct away the electricity and lower the charge, as fastalmost as if a piece of metal had been introduced there. Occasionally stemsin this state, being taken out and cleared from the common cement, may, bythe careful application of the heat of a spirit-lamp, be so far softenedand melted as to restore the perfect continuity of the parts; but if thatdoes not succeed in replacing things in a good condition, the remedy is anew shell-lac stem. 

1194. The apparatus when in order could easily be exhausted of air andfilled with any given gas; but when that gas was acid or alkaline, it couldnot properly be removed by the air-pump, and yet required to be perfectlycleared away. In such cases the apparatus was opened and emptied of gas;and with respect to the inner ball _h_, it was washed out two or threetimes with distilled water introduced at the screw-hole, and then beingheated above 212°, air was blown through to render the interior perfectlydry. 

1195. The inductive apparatus described is evidently a Leyden phial, withthe advantage, however, of having the _dielectric_ or insulating mediumchanged at pleasure. The balls _h_ and B, with the connecting wire _i_, constitute the charged conductor, upon the surface of which all theelectric force is resident by virtue of induction (1178. ). Now though thelargest portion of this induction is between the ball _h_ and thesurrounding sphere _aa_, yet the wire _i_ and the ball B determine a partof the induction from their surfaces towards the external surroundingconductors. Still, as all things in that respect remain the same, whilstthe medium within at _oo_, may be varied, any changes exhibited by thewhole apparatus will in such cases depend upon the variations made in theinterior; and these were the changes I was in search of, the negation orestablishment of such differences being the great object of my inquiry. Iconsidered that these differences, if they existed, would be mostdistinctly set forth by having two apparatus of the kind described, precisely similar in every respect; and then, _different insulating media_being within, to charge one and measure it, and after dividing the chargewith the other, to observe what the ultimate conditions of both were. Ifinsulating media really had any specific differences in favouring oropposing inductive action through them, such differences, I conceived, could not fail of being developed by such a process. 

1196. I will wind up this description of the apparatus, and explain theprecautions necessary to their use, by describing the form and order of theexperiments made to prove their equality when both contained common air. Inorder to facilitate reference I will distinguish the two by the terms App. I. And App. Ii. 

1197. The electrometer is first to be adjusted and examined (1184. ), andthe app. I. And ii. Are to be perfectly discharged. A Leyden phial is to becharged to such a degree that it would give a spark of about one-sixteenthor one-twentieth of an inch in length between two balls of half an inchdiameter; and the carrier ball of the electrometer being charged by thisphial, is to be introduced into the electrometer, and the lever ballbrought by the motion of the torsion index against it; the charge is thusdivided between the balls, and repulsion ensues. It is useful then to bringthe repelled ball to the standard distance of 30° by the motion of thetorsion index, and observe the force in degrees required for this purpose;this force will in future experiments be called _repulsion of the balls_. 

1198. One of the inductive apparatus, as, for instance, app. I. , is now tobe charged from the Leyden phial, the latter being in the state it was inwhen used to charge the balls; the carrier ball is to be brought intocontact with the top of its upper ball (_k_, fig. 104. ), then introducedinto the electrometer, and the repulsive force (at the distance of 30°)measured. Again, the carrier should be applied to the app. I. And themeasurement repeated; the apparatus i. And ii. Are then to be joined, so asto _divide_ the charge, and afterwards the force of each measured by thecarrier ball, applied as before, and the results carefully noted. Afterthis both i. And ii. Are to be discharged; then app. Ii. Charged, measured, divided with app. I. , and the force of each again measured and noted. If ineach case the half charges of app. I. And ii. Are equal, and are togetherequal to the whole charge before division, then it may be considered asproved that the two apparatus are precisely equal in power, and fit to beused in cases of comparison between different insulating media or_dielectrics_. 

1199. But the _precautions_ necessary to obtain accurate results arenumerous. The apparatus i. And ii. Must always be placed on a thoroughlyuninsulating medium. A mahogany table, for instance, is far fromsatisfactory in this respect, and therefore a sheet of tinfoil, connectedwith an extensive discharging train (292. ), is what I have used. They mustbe so placed also as not to be too near each other, and yet equally exposedto the inductive influence of surrounding objects; and these objects, again, should not be disturbed in their position during an experiment, orelse variations of induction upon the external ball B of the apparatus mayoccur, and so errors be introduced into the results. The carrier ball, whenreceiving its portion of electricity from the apparatus, should always beapplied at the same part of the ball, as, for instance, the summit _k_, andalways in the same way; variable induction from the vicinity of the head, hands, &c. Being avoided, and the ball after contact being withdrawnupwards in a regular and constant manner. 

1200. As the stem had occasionally to be changed (1190. ), and the changemight occasion slight variations in the position of the ball within, I madesuch a variation purposely, to the amount of an eighth of an inch (which isfar more than ever could occur in practice), but did not find that itsensibly altered the relation of the apparatus, or its inductive condition_as a whole_. Another trial of the apparatus was made as to the effect ofdampness in the air, one being filled with very dry air, and the other withair from over water. Though this produced no change in the result, exceptan occasional tendency to more rapid dissipation, yet the precaution wasalways taken when working with gases (1290. ) to dry them perfectly. 

1201. It is essential that the interior of the apparatus should beperfectly free from _dust or small loose particles_, for these very rapidlylower the charge and interfere on occasions when their presence and actionwould hardly be expected. To breathe on the interior of the apparatus andwipe it out quietly with a clean silk handkerchief, is an effectual way ofremoving them; but then the intrusion of other particles should becarefully guarded against, and a dusty atmosphere should for this andseveral other reasons be avoided. 

1202. The shell-lac stem requires occasionally to be well-wiped, to remove, in the first instance, the film of wax and adhering matter which is uponit; and afterwards to displace dirt and dust which will gradually attach toit in the course of experiments. I have found much to depend upon thisprecaution, and a silk handkerchief is the best wiper. 

1203. But wiping and some other circumstances tend to give a charge to thesurface of the shell-lac stem. This should be removed, for, if allowed toremain, it very seriously affects the degree of charge given to the carrierball by the apparatus (1232. ). This condition of the stem is best observedby discharging the apparatus, applying the carrier ball to the stem, touching it with the finger, insulating and removing it, and examiningwhether it has received any charge (by induction) from the stem; if it has, the stem itself is in a charged state. The best method of removing thecharge I have found to be, to cover the finger with a single fold of a silkhandkerchief, and breathing on the stem, to wipe it immediately after withthe finger; the ball B and its connected wire, &c. Being at the same time_uninsulated_: the wiping place of the silk must not be changed; it thenbecomes sufficiently damp not to excite the stem, and is yet dry enough toleave it in a clean and excellent insulating condition. If the air bedusty, it will be found that a single charge of the apparatus will bring onan electric state of the outside of the stem, in consequence of thecarrying power of the particles of dust; whereas in the morning, and in aroom which has been left quiet, several experiments can be made insuccession without the stem assuming the least degree of charge. 

1204. Experiments should not be made by candle or lamp light except withmuch care, for flames have great and yet unsteady powers of affecting anddissipating electrical charges. 

1205. As a final observation on the state of the apparatus, they shouldretain their charges well and uniformly, and alike for both, and at thesame time allow of a perfect and instantaneous discharge, giving afterwardsno charge to the carrier ball, whatever part of the ball B it may beapplied to (1218. ). 

1206. With respect to the balance electrometer, all the precautions thatneed be mentioned, are, that the carrier ball is to be preserved during thefirst part of an experiment in its electrified state, the loss ofelectricity which would follow upon its discharge being avoided; and thatin introducing it into the electrometer through the hole in the glass plateabove, care should be taken that it do not touch, or even come near to, theedge of the glass. 

1207. When the whole charge in one apparatus is divided between the two, the gradual fall, apparently from dissipation, in the apparatus which has_received_ the half charge is greater than in the one _originally_ charged. This is due to a peculiar effect to be described hereafter (1250. 1251. ), the interfering influence of which may be avoided to a great extent bygoing through the steps of the process regularly and quickly; therefore, after the original charge has been measured, in app. I. For instance, i. And ii. Are to be symmetrically joined by their balls B, the carriertouching one of these balls at the same time; it is first to be removed, and then the apparatus separated from each other; app. Ii. Is next quicklyto be measured by the carrier, then app. I. ; lastly, ii. Is to bedischarged, and the discharged carrier applied to it to ascertain whetherany residual effect is present (1205. ), and app. I. Being discharged isalso to be examined in the same manner and for the same purpose. 

1208. The following is an example of the division of a charge by the twoapparatus, air being the dielectric in both of them. The observations areset down one under the other in the order in which they were taken, theleft-hand numbers representing the observations made on app. I. , and theright-hand numbers those on app. Ii. App. I. Is that which was originallycharged, and after two measurements, the charge was divided with app. Ii. 

App. I. App. Ii. Balls 160°

 . . . . 0°254° . . . . 250 . . . . Divided and instantly taken . . . . 122124 . . . . 1 . . . . After being discharged. . . . . 2 after being discharged. 

1209. Without endeavouring to allow for the loss which must have beengradually going on during the time of the experiment, let us observe theresults of the numbers as they stand. As 1° remained in app. I. In anundischargeable state, 249° may be taken as the utmost amount of thetransferable or divisible charge, the half of which is 124°. 5. As app. Ii. Was free of charge in the first instance, and immediately after thedivision was found with 122°, this amount _at least_ may be taken as whatit had received. On the other hand 124° minus 1°, or 123°, may be taken asthe half of the transferable charge retained by app. I. Now these do notdiffer much from each other, or from 124°. 5, the half of the full amount oftransferable charge; and when the gradual loss of charge evident in thedifference between 254° and 250° of app. I. Is also taken into account, there is every reason to admit the result as showing an equal division ofcharge, _unattended by any disappearance of power_ except that due todissipation. 

1210. I will give another result, in which app. Ii. Was first charged, andwhere the residual action of that apparatus was greater than in the formercase. 

App. I. App. Ii. Balls 150°

 . . . . 152° . . . . 148divided and instantly taken 70° . . . . . . . . 78 . . . . 5 immediately after discharge. 0 . . . . Immediately after discharge. 

1211. The transferable charge being 148° - 5°, its half is 71°. 5, which isnot far removed from 70°, the half charge of i. ; or from 73°, the halfcharge of ii. : these half charges again making up the sum of 143°, or justthe amount of the whole transferable charge. Considering the errors ofexperiment, therefore, these results may again be received as showing thatthe apparatus were equal in inductive capacity, or in their powers ofreceiving charges. 

1212. The experiments were repeated with charges of negative electricitywith the same general results. 

1213. That I might be sure of the sensibility and action of the apparatus, I made such a change in one as ought upon principle to increase itsinductive force, i. E. I put a metallic lining into the lower hemisphere ofapp. I. , so as to diminish the thickness of the intervening air in thatpart, from 0. 62 to 0. 435 of an inch: this lining was carefully shaped androunded so that it should not present a sudden projection within at itsedge, but a gradual transition from the reduced interval in the lower partof the sphere to the larger one in the upper. 

1214. This change immediately caused app. I. To produce effects indicatingthat it had a greater aptness or capacity for induction than app. Ii. Thus, when a transferable charge in app. Ii. Of 469° was divided with app. I. , the former retained a charge of 225°, whilst the latter showed one of 227°, i. E. The former had lost 244° in communicating 227° to the latter: on theother hand, when app. I. Had a transferable charge in it of 381° divided bycontact with app. Ii. , it lost 181° only, whilst it gave to app. Ii. Asmany as 194:--the sum of the divided forces being in the first instance_less_, and in the second instance _greater_ than the original undividedcharge. These results are the more striking, as only one-half of theinterior of app. I. Was modified, and they show that the instruments arecapable of bringing out differences in inductive force from amongst theerrors of experiment, when these differences are much less than thatproduced by the alteration made in the present instance. 

¶ iv. _Induction in curved lines. _

1215. Amongst those results deduced from the molecular view of induction(1166. ), which, being of a peculiar nature, are the best tests of the truthor error of the theory, the expected action in curved lines is, I think, the most important at present; for, if shown to take place in anunexceptionable manner, I do not see how the old theory of action at adistance and in straight lines can stand, or how the conclusion thatordinary induction is an action of contiguous particles can be resisted. 

1216. There are many forms of old experiments which might be quoted asfavourable to, and consistent with the view I have adopted. Such are mostcases of electro-chemical decomposition, electrical brushes, auras, sparks, &c. ; but as these might be considered equivocal evidence, inasmuch as theyinclude a current and discharge, (though they have long been to meindications of prior molecular action (1230. )) I endeavoured to devise suchexperiments for first proofs as should not include transfer, but relatealtogether to the pure simple inductive action of statical electricity. 

1217. It was also of importance to make these experiments in the simplestpossible manner, using not more than one insulating medium or dielectric ata time, lest differences of slow conduction should produce effects whichmight erroneously be supposed to result from induction in curved lines. Itwill be unnecessary to describe the steps of the investigation minutely; Iwill at once proceed to the simplest mode of proving the facts, first inair and then in other insulating media. 

1218. A cylinder of solid shell-lac, 0. 9 of an inch in diameter and seveninches in length, was fixed upright in a wooden foot (fig. 106. ): it wasmade concave or cupped at its upper extremity so that a brass ball or othersmall arrangement could stand upon it. The upper half of the stem havingbeen excited _negatively_ by friction with warm flannel, a brass ball, B, 1inch in diameter, was placed on the top, and then the whole arrangementexamined by the carrier ball and Coulomb's electrometer (1180. &c. ). Forthis purpose the balls of the electrometer were charged _positively_ toabout 360°, and then the carrier being applied to various parts of the ballB, the two were uninsulated whilst in contact or in position, theninsulated[A], separated, and the charge of the carrier examined as to itsnature and force. Its electricity was always positive, and its force at thedifferent positions _a, b, c, d, _ &c. (figs. 106. And 107. ) observed insuccession, was as follows:

at _a_ above 1000° _b_ it was 149 _c_ 270 _d_ 512 _b_ 130

 [A] It can hardly be necessary for me to say here, that whatever general state the carrier ball acquired in any place where it was uninsulated and then insulated, it retained on removal from that place, notwithstanding that it might pass through other places that would have given to it, if uninsulated, a different condition. 

1219. To comprehend the full force of these results, it must first beunderstood, that all the charges of the ball B and the carrier are chargesby induction, from the action of the excited surface of the shell-laccylinder; for whatever electricity the ball B received by _communication_from the shell-lac, either in the first instance or afterwards, was removedby the uninsulating contacts, only that due to induction remaining; andthis is shown by the charges taken from the ball in this its uninsulatedstate being always positive, or of the contrary character to theelectricity of the shell-lac. In the next place, the charges at _a_, _c_, and _d_ were of such a nature as might be expected from an inductive actionin straight lines, but that obtained at _b_ is _not so_: it is clearly acharge by induction, but _induction_ in _a curved line_; for the carrierball whilst applied to _b_, and after its removal to a distance of sixinches or more from B, could not, in consequence of the size of B, beconnected by a straight line with any part of the excited and inducingshell-lac. 

1220. To suppose that the upper part of the _uninsulated_ ball B, should insome way be retained in an electrified state by that portion of the surfaceof the ball which is in sight of the shell-lac, would be in opposition towhat we know already of the subject. Electricity is retained upon thesurface of conductors only by induction (1178. ); and though some personsmay not be prepared as yet to admit this with respect to insulatedconductors, all will as regards uninsulated conductors like the ball B; andto decide the matter we have only to place the carrier ball at _e_ (fig. 107. ), so that it shall not come in contact with B, uninsulate it by ametallic rod descending perpendicularly, insulate it, remove it, andexamine its state; it will be found charged with the same kind ofelectricity as, and even to a _higher degree_ (1224. ) than, if it had beenin contact with the summit of B. 

1221. To suppose, again, that induction acts in some way _through oracross_ the metal of the ball, is negatived by the simplest considerations;but a fact in proof will be better. If instead of the ball B a small discof metal be used, the carrier may be charged at, or above the middle of itsupper surface: but if the plate be enlarged to about 1-1/2 or 2 inches indiameter, C (fig. 108. ), then no charge will be given to the carrier at_f_, though when applied nearer to the edge at _g_, or even _above themiddle_ at _h_, a charge will be obtained; and this is true though theplate may be a mere thin film of gold-leaf. Hence it is clear that theinduction is not _through_ the metal, but through the surrounding air or_dielectric_, and that in curved lines. 

1222. I had another arrangement, in which a wire passing downwards throughthe middle of the shell-lac cylinder to the earth, was connected with theball B (fig. 109. ) so as to keep it in a constantly uninsulated state. Thiswas a very convenient form of apparatus, and the results with it were thesame as those just described. 

1223. In another case the ball B was supported by a shell-lac stem, independently of the excited cylinder of shell-lac, and at half an inchdistance from it; but the effects were the same. Then the brass ball of acharged Leyden jar was used in place of the excited shell-lac to produceinduction; but this caused no alteration of the phenomena. Both positiveand negative inducing charges were tried with the same general results. Finally, the arrangement was inverted in the air for the purpose ofremoving every possible objection to the conclusions, but they came outexactly the same. 

1224. Some results obtained with a brass hemisphere instead of the ball Bwere exceedingly interesting, It was 1. 36 of an inch in diameter, (fig. 110. ), and being placed on the top of the excited shell-lac cylinder, thecarrier ball was applied, as in the former experiments (1218. ), at therespective positions delineated in the figure. At _i_ the force was 112°, at _k_ 108°, at _l_ 65°, at _m_ 35°; the inductive force graduallydiminishing, as might have been expected, to this point. But on raising thecarrier to the position _n_, the charge increased to 87°; and on raising itstill higher to _o_, the charge still further increased to 105°: at ahigher point still, _p_, the charge taken was smaller in amount, being 98°, and continued to diminish for more elevated positions. Here the inductionfairly turned a corner. Nothing, in fact, can better show both the curvedlines or courses of the inductive action, disturbed as they are from theirrectilineal form by the shape, position, and condition of the metallichemisphere; and also a _lateral tension, _ so to speak, of these lines onone another:--all depending, as I conceive, on induction being an action ofthe contiguous particles of the dielectric, which being thrown into a stateof polarity and tension, are in mutual relation by their forces in alldirections. 

1225. As another proof that the whole of these actions were inductive I maystate a result which was exactly what might be expected, namely, that ifuninsulated conducting matter was brought round and near to the excitedshell-lac stem, then the inductive force was directed towards it, and couldnot be found on the top of the hemisphere. Removing this matter the linesof force resumed their former direction. The experiment affords proofs ofthe lateral tension of these lines, and supplies a warning to remove suchmatter in repeating the above investigation. 

1226. After these results on curved inductive action in air I extended theexperiments to other gases, using first carbonic acid and then hydrogen:the phenomena were precisely those already described. In these experimentsI found that if the gases were confined in vessels they required to be verylarge, for whether of glass or earthenware, the conducting power of suchmaterials is so great that the induction of the excited shell-lac cylindertowards them is as much as if they were metal; and if the vessels be small, so great a portion of the inductive force is determined towards them thatthe lateral tension or mutual repulsion of the lines of force before spokenof, (1224. ) by which their inflexion is caused, is so much relieved inother directions, that no inductive charge will be given to the carrierball in the positions _k, l, m, n, o, p_ (fig. 110. ). A very good mode ofmaking the experiment is to let large currents of the gases ascend ordescend through the air, and carry on the experiments in these currents. 

1227. These experiments were then varied by the substitution of a liquiddielectric, namely, _oil of turpentine_, in place of air and gases. A dishof thin glass well-covered with a film of shell-lac (1272. ), which wasfound by trial to insulate well, had some highly rectified oil ofturpentine put into it to the depth of half an inch, and being then placedupon the top of the brass hemisphere (fig. 110. ), observations were madewith the carrier ball as before (1224. ). The results were the same, and thecircumstance of some of the positions being within the fluid and somewithout, made no sensible difference. 

1228. Lastly, I used a few solid dielectrics for the same purpose, and withthe same results. These were shell-lac, sulphur, fused and cast borate oflead, flint glass well-covered with a film of lac, and spermaceti. Thefollowing was the form of experiment with sulphur, and all were of the samekind. A square plate of the substance, two inches in extent and 0. 6 of aninch in thickness, was cast with a small hole or depression in the middleof one surface to receive the carrier ball. This was placed upon thesurface of the metal hemisphere (fig. 112. ) arranged on the excited lac asin former cases, and observations were made at _n, o, p_, and _q_. Greatcare was required in these experiments to free the sulphur or other solidsubstance from any charge it might previously have received. This was doneby breathing and wiping (1203. ), and the substance being found free fromall electrical excitement, was then used in the experiment; after which itwas removed and again examined, to ascertain that it had received nocharge, but had acted really as a dielectric. With all these precautionsthe results were the same: and it is thus very satisfactory to obtain thecurved inductive action through _solid bodies_, as any possible effect fromthe translation of charged particles in fluids or gases, which some personsmight imagine to be the case, is here entirely negatived. 

1229. In these experiments with solid dielectrics, the degree of chargeassumed by the carrier ball at the situations _n, o, p_ (fig. 112. ), wasdecidedly greater than that given to the ball at the same places when aironly intervened between it and the metal hemisphere. This effect isconsistent with what will hereafter be found to be the respective relationsof these bodies, as to their power of facilitating induction through them(1269. 1273. 1277. ). 

1230. I might quote _many_ other forms of experiment, some old and somenew, in which induction in curved or contorted lines takes place, but thinkit unnecessary after the preceding results; I shall therefore mention buttwo. If a conductor A, (fig. 111. ) be electrified, and an uninsulatedmetallic ball B, or even a plate, provided the edges be not too thin, beheld before it, a small electrometer at _c_ or at _d_, uninsulated, willgive signs of electricity, opposite in its nature to that of A, andtherefore caused by induction, although the influencing and influencedbodies cannot be joined by a right line passing through the air. Or if, theelectrometers being removed, a point be fixed at the back of the ball inits uninsulated state as at C, this point will become luminous anddischarge the conductor A. The latter experiment is described byNicholson[A], who, however, reasons erroneously upon it. As to itsintroduction here, though it is a case of discharge, the discharge ispreceded by induction, and that induction must be in curved lines. 

 [A] Encyclopædia Britannica, vol. Vi. P. 504. 

1231. As argument against the received theory of induction and in favour ofthat which I have ventured to put forth, I cannot see how the precedingresults can be avoided. The effects are clearly inductive effects producedby electricity, not in currents but in its statical state, and thisinduction is exerted in lines of force which, though in many experimentsthey may be straight, are here curved more or less according tocircumstances. I use the term _line of inductive force_ merely as atemporary conventional mode of expressing the direction of the power incases of induction; and in the experiments with the hemisphere (1224. ), itis curious to see how, when certain lines have terminated on the undersurface and edge of the metal, those which were before lateral to them_expand and open out from each other_, some bending round and terminatingtheir action on the upper surface of the hemisphere, and others meeting, asit were, above in their progress outwards, uniting their forces to give anincreased charge to the carrier ball, at an _increased distance_ from thesource of power, and influencing each other so as to cause a second flexurein the contrary direction from the first one. All this appears to me toprove that the whole action is one of contiguous particles, related to eachother, not merely in the lines which they may be conceived to form throughthe dielectric, between the _inductric_ and the _inducteous_ surfaces(1483. ), but in other lateral directions also. It is this which gives aneffect equivalent to a lateral repulsion or expansion in the lines of forceI have spoken of, and enables induction to turn a corner (1304. ). Thepower, instead of being like that of gravity, which causes particles to acton each other through straight lines, whatever other particles may bebetween them, is more analogous to that of a series of magnetic needles, orto the condition of the particles considered as forming the whole of astraight or a curved magnet. So that in whatever way I view it, and withgreat suspicion of the influence of favourite notions over myself, I cannotperceive how the ordinary theory applied to explain induction can be acorrect representation of that great natural principle of electricalaction. 

1232. I have had occasion in describing the precautions necessary in theuse of the inductive apparatus, to refer to one founded on induction incurved lines (1203. ); and after the experiments already described, it willeasily be seen how great an influence the shell-lac stem may exert upon thecharge of the carrier ball when applied to the apparatus (1218. ), unlessthat precaution be attended to. 

1233. I think it expedient, next in the course of these experimentalresearches, to describe some effects due to _conduction_, obtained withsuch bodies as glass, lac, sulphur, &c. , which had not been anticipated. Being understood, they will make us acquainted with certain precautionsnecessary in investigating the great question of specific inductivecapacity. 

1234. One of the inductive apparatus already described (1187, &c. ) had ahemispherical cup of shell-lac introduced, which being in the intervalbetween the inner bull and the lower hemisphere, nearly occupied the spacethere; consequently when the apparatus was charged, the lac was thedielectric or insulating medium through which the induction took place inthat part. When this apparatus was first charged with electricity (1198. )up to a certain intensity, as 400°, measured by the COULOMB'S electrometer(1180. ), it sank much faster from that degree than if it had beenpreviously charged to a higher point, and had gradually fallen to 400°; orthan it would do if the charge were, by a second application, raised upagain to 400°; all other things remaining the same. Again, if after havingbeen charged for some time, as fifteen or twenty minutes, it was suddenlyand perfectly discharged, even the stem having all electricity removed fromit (1203. ), then the apparatus being left to itself, would graduallyrecover a charge, which in nine or ten minutes would rise up to 50° or 60°, and in one instance to 80°. 

1235. The electricity, which in these cases returned from an apparentlylatent to a sensible state, was always of the same kind as that which hadbeen given by the charge. The return took place at both the inducingsurfaces; for if after the perfect discharge of the apparatus the whole wasinsulated, as the inner ball resumed a positive state the outer sphereacquired a negative condition. 

1236. This effect was at once distinguished from that produced by theexcited stem acting in curved lines of induction (1203. 1232. ), by thecircumstance that all the returned electricity could be perfectly andinstantly discharged. It appeared to depend upon the shell-lac within, andto be, in some way, due to electricity evolved from it in consequence of aprevious condition into which it had been brought by the charge of themetallic coatings or balls. 

1237. To examine this state more accurately, the apparatus, with thehemispherical cup of shell-lac in it, was charged for about forty-fiveminutes to above 600° with positive electricity at the balls _h_ and B. (fig. 104. ) above and within. It was then discharged, opened, the shell-lactaken out, and its state examined; this was done by bringing the carrierball near the shell-lac, uninsulating it, insulating it, and then observingwhat charge it had acquired. As it would be a charge by induction, thestate of the ball would indicate the opposite state of electricity in thatsurface of the shell-lac which had produced it. At first the lac appearedquite free from any charge; but gradually its two surfaces assumed oppositestates of electricity, the concave surface, which had been next the innerand positive ball; assuming a positive state, and the convex surface, whichhad been in contact with the negative coating, acquiring a negative state;these states gradually increased in intensity for some time. 

1238. As the return action was evidently greatest instantly after thedischarge, I again put the apparatus together, and charged it for fifteenminutes as before, the inner ball positively. I then discharged it, instantly removing the upper hemisphere with the interior ball, and, leaving the shell-lac cup in the lower uninsulated hemisphere, examined itsinner surface by the carrier ball as before (1237. ). In this way I foundthe surface of the shell-lac actually _negative_, or in the reverse stateto the ball which had been in it; this state quickly disappeared, and wassucceeded by a positive condition, gradually increasing in intensity forsome time, in the same manner as before. The first negative condition ofthe surface opposite the positive charging ball is a natural consequence ofthe state of things, the charging ball being in contact with the shell-laconly in a few points. It does not interfere with the general result andpeculiar state now under consideration, except that it assists inillustrating in a very marked manner the ultimate assumption by thesurfaces of the shell-lac of an electrified condition, similar to that ofthe metallic surfaces opposed to or against them. 

1239. _Glass_ was then examined with respect to its power of assuming thispeculiar state. I had a thick flint-glass hemispherical cup formed, whichwould fit easily into the space _o_ of the lower hemisphere (1188. 1189. );it had been heated and varnished with a solution of shell-lac in alcohol, for the purpose of destroying the conducting power of the vitreous surface(1254. ). Being then well-warmed and experimented with, I found it couldalso assume the _same state_, but not apparently to the same degree, thereturn action amounting in different cases to quantities from 6° to 18°. 

1240. _Spermaceti_ experimented with in the same manner gave strikingresults. When the original charge had been sustained for fifteen or twentyminutes at about 500°, the return charge was equal to 95° or 100°, and wasabout fourteen minutes arriving at the maximum effect. A charge continuedfor not more than two or three seconds was here succeeded by a returncharge of 50° or 60°. The observations formerly made (1234. ) held good withthis substance. Spermaceti, though it will insulate a low charge for sometime, is a better conductor than shell-lac, glass, and sulphur; and thisconducting power is connected with the readiness with which it exhibits theparticular effect under consideration. 

1241. _Sulphur. _--I was anxious to obtain the amount of effect with thissubstance, first, because it is an excellent insulator, and in that respectwould illustrate the relation of the effect to the degree of conductingpower possessed by the dielectric (1247. ); and in the next place, that Imight obtain that body giving the smallest degree of the effect now underconsideration for the investigation of the question of specific inductivecapacity (1277. ). 

1242. With a good hemispherical cup of sulphur cast solid and sound, Iobtained the return charge, but only to an amount of 17° or 18°. Thus glassand sulphur, which are bodily very bad conductors of electricity, andindeed almost perfect insulators, gave very little of this return charge. 

1243. I tried the same experiment having _air_ only in the inductiveapparatus. After a continued high charge for some time I could obtain alittle effect of return action, but it was ultimately traced to theshell-lac of the stem. 

1244. I sought to produce something like this state with one electric powerand without induction; for upon the theory of an electric fluid or fluids, that did not seem impossible, and then I should have obtained an absolutecharge (1169. 1177. ), or something equivalent to it. In this I could notsucceed. I excited the outside of a cylinder of shell-lac very highly forsome time, and then quickly discharging it (1203. ), waited and watchedwhether any return charge would appear, but such was not the case. This isanother fact in favour of the inseparability of the two electric forces(1177. ), and another argument for the view that induction and itsconcomitant phenomena depend upon a polarity of the particles of matter. 

1245. Although inclined at first to refer these effects to a peculiarmasked condition of a certain portion of the forces, I think I have sincecorrectly traced them to known principles of electrical action. The effectsappear to be due to an actual penetration of the charge to some distancewithin the electric, at each of its two surfaces, by what we call_conduction_; so that, to use the ordinary phrase, the electric forcessustaining the induction are not upon the metallic surfaces only, but uponand within the dielectric also, extending to a greater or smaller depthfrom the metal linings. Let _c_ (fig. 113. ) be the section of a plate ofany dielectric, _a_ and _b_ being the metallic coatings; let _b_ beuninsulated, and _a_ be charged positively; after ten or fifteen minutes, if _a_ and _b_ be discharged, insulated, and immediately examined, noelectricity will appear in them; but in a short time, upon a secondexamination, they will appear charged in the same way, though not to thesame degree, as they were at first. Now suppose that a portion of thepositive force has, under the coercing influence of all the forcesconcerned, penetrated the dielectric and taken up its place at the line_p_, a corresponding portion of the negative force having also assumed itsposition at the line _n_; that in fact the electric at these two parts hasbecome charged positive and negative; then it is clear that the inductionof these two forces will be much greater one towards the other, and less inan external direction, now that they are at the small distance _np_ fromeach other, than when they were at the larger interval _ab_. Then let _a_and _b_ be discharged; the discharge destroys or neutralizes all externalinduction, and the coatings are therefore found by the carrier ballunelectrified; but it also removes almost the whole of the forces by whichthe electric charge was driven into the dielectric, and though probably apart of that charge goes forward in its passage and terminates in what wecall discharge, the greater portion returns on its course to the surfacesof _c_, and consequently to the conductors _a_ and _b_, and constitutes therecharge observed. 

1246. The following is the experiment on which I rest for the truth of thisview. Two plates of spermaceti, _d_ and, _f_ (fig. 114. ), were put togetherto form the dielectric, _a_ and _b_ being the metallic coatings of thiscompound plate, as before. The system was charged, then discharged, insulated, examined, and found to give no indications of electricity to thecarrier ball. The plates _d_ and _f_were then separated from each other, and instantly _a_ with _d_ was found in a positive state, and _b_ with _f_in a negative state, nearly all the electricity being in the linings _a_and _b_. Hence it is clear that, of the forces sought for, the positive wasin one-half of the compound plate and the negative in the other half; forwhen removed bodily with the plates from each other's inductive influence, they appeared in separate places, and resumed of necessity their power ofacting by induction on the electricity of surrounding bodies. Had theeffect depended upon a peculiar relation of the contiguous particles ofmatter only, then each half-plate, _d_ and _f_, should have shown positiveforce on one surface and negative on the other. 

1247. Thus it would appear that the best solid insulators, such asshell-lac, glass, and sulphur, have conductive properties to such anextent, that electricity can penetrate them bodily, though always subjectto the overruling condition of induction (1178. ). As to the depth to whichthe forces penetrate in this form of charge of the particles, theoretically, it should be throughout the mass, for what the charge of themetal does for the portion of dielectric next to it, should be close by thecharged dielectric for the portion next beyond it again; but probably inthe best insulators the sensible charge is to a very small depth only inthe dielectric, for otherwise more would disappear in the first instancewhilst the original charge is sustained, less time would be required forthe assumption of the particular state, and more electricity wouldre-appear as return charge. 

1248. The condition of _time_ required for this penetration of the chargeis important, both as respects the general relation of the cases toconduction, and also the removal of an objection that might otherwiseproperly be raised to certain results respecting specific inductivecapacities, hereafter to be given (1269. 1277. )

1249. It is the assumption for a time of this charged state of the glassbetween the coatings in the Leyden jar, which gives origin to a well-knownphenomenon, usually referred to the diffusion of electricity over theuncoated portion of the glass, namely, the _residual charge_. The extent ofcharge which can spontaneously be recovered by a large battery, afterperfect uninsulation of both surfaces, is very considerable, and by far thelargest portion of this is due to the return of electricity in the mannerdescribed. A plate of shell-lac six inches square, and half an inch thick, or a similar plate of spermaceti an inch thick, being coated on the sideswith tinfoil as a Leyden arrangement, will show this effect exceedinglywell. 

 * * * * *

1250. The peculiar condition of dielectrics which has now been described, is evidently capable of producing an effect interfering with the resultsand conclusions drawn from the use of the two inductive apparatus, whenshell-lac, glass, &c. Is used in one or both of them (1192. 1207. ), forupon dividing the charge in such cases according to the method described(1198. 1207. ), it is evident that the apparatus just receiving its halfcharge must fall faster in its tension than the other. For suppose app. I. First charged, and app. Ii. Used to divide with it; though both mayactually lose alike, yet app. I. , which has been diminished one-half, willbe sustained by a certain degree of return action or charge (1234. ), whilstapp. Ii. Will sink the more rapidly from the coming on of the particularstate. I have endeavoured to avoid this interference by performing thewhole process of comparison as quickly as possible, and taking the force ofapp. Ii. Immediately after the division, before any sensible diminution ofthe tension arising from the assumption of the peculiar state could beproduced; and I have assumed that as about three minutes pass between thefirst charge of app. I. And the division, and three minutes between thedivision and discharge, when the force of the non-transferable electricityis measured, the contrary tendencies for those periods would keep thatapparatus in a moderately steady and uniform condition for the latterportion of time. 

1251. The particular action described occurs in the shell-lac of the stems, as well as in the _dielectric_ used within the apparatus. It thereforeconstitutes a cause by which the outside of the stems may in someoperations become charged with electricity, independent of the action ofdust or carrying particles (1203. ). 

¶ v. _On specific induction, or specific inductive capacity. _

1252. I now proceed to examine the great question of specific inductivecapacity, i. E. Whether different dielectric bodies actually do possess anyinfluence over the degree of induction which takes place through them. Ifany such difference should exist, it appeared to me not only of highimportance in the further comprehension of the laws and results ofinduction, but an additional and very powerful argument for the theory Ihave ventured to put forth, that the whole depends upon a molecular action, in contradistinction to one at sensible distances. 

The question may be stated thus: suppose A an electrified plate of metalsuspended in the air, and B and C two exactly similar plates, placedparallel to and on each side of A at equal distances and uninsulated; Awill then induce equally towards B and C. If in this position of the platessome other dielectric than air, as shell-lac, be introduced between A andC, will the induction between them remain the same? Will the relation of Cand B to A be unaltered, notwithstanding the difference of the dielectricsinterposed between them?[A]

 [A] Refer for the practical illustration of this statement to the supplementary note commencing 1307, &c. --_Dec. 1838. _

1253. As far as I recollect, it is assumed that no change will occur undersuch variation of circumstances, and that the relations of B find C to Adepend entirely upon their distance. I only remember one experimentalillustration of the question, and that is by Coulomb[A], in which he showsthat a wire surrounded by shell-lac took exactly the same quantity ofelectricity from a charged body as the same wire in air. The experimentoffered to me no proof of the truth of the supposition: for it is not themere films of dielectric substances surrounding the charged body which haveto be examined and compared, but the _whole mass_ between that body and thesurrounding conductors at which the induction terminates. Charge dependsupon induction (1171. 1178. ); and if induction is related to the particlesof the surrounding dielectric, then it is related to _all_ the particles ofthat dielectric inclosed by the surrounding conductors, and not merely tothe few situated next to the charged body. Whether the difference I soughtfor existed or not, I soon found reason to doubt the conclusion that mightbe drawn from Coulomb's result; and therefore had the apparatus made, which, with its use, has been already described (1187, &c. ), and whichappears to me well-suited for the investigation of the question. 

 [A] Mémoires de l'Académie, 1787, pp. 452, 453. 

1254. Glass, and many bodies which might at first be considered as very fitto test the principle, proved exceedingly unfit for that purpose. Glass, principally in consequence of the alkali it contains, however well-warmedand dried it may be, has a certain degree of conducting power upon itssurface, dependent upon the moisture of the atmosphere, which renders itunfit for a test experiment. Resin, wax, naphtha, oil of turpentine, andmany other substances were in turn rejected, because of a slight degree ofconducting power possessed by them; and ultimately shell-lac and sulphurwere chosen, after many experiments, as the dielectrics best fitted for theinvestigation. No difficulty can arise in perceiving how the possession ofa feeble degree of conducting power tends to make a body produce effects, which would seem to indicate that it had a greater capability of allowinginduction through it than another body perfect in its insulation. Thissource of error has been that which I have found most difficult to obviatein the proving experiments. 

 * * * * *

1255. _Induction through shell-lac. _--As a preparatory experiment, I firstascertained generally that when a part of the surface of a thick plate ofshell-lac was excited or charged, there was no sensible difference in thecharacter of the induction sustained by that charged part, whether exertedthrough the air in the one direction, or through the shell-lac of the platein the other; provided the second surface of the plate had not, by contactwith conductors, the action of dust, or any other means, become charged(1203. ). Its solid condition enabled it to retain the excited particles ina permanent position, but that appeared to be all; for these particlesacted just as freely through the shell-lac on one side as through the airon the other. The same general experiment was made by attaching a disc oftinfoil to one side of the shell-lac plate, and electrifying it, and theresults were the same. Scarcely any other solid substance than shell-lacand sulphur, and no liquid substance that I have tried, will bear thisexamination. Glass in its ordinary state utterly fails; yet it wasessentially necessary to obtain this prior degree of perfection in thedielectric used, before any further progress could be made in the principalinvestigation. 

1256. _Shell-lac and air_ were compared in the first place. For thispurpose a thick hemispherical cup of shell-lac was introduced into thelower hemisphere of one of the inductive apparatus (1187, &c. ), so asnearly to fill the lower half of the space _o, o_ (fig. 104. ) between itand the inner ball; and then charges were divided in the manner alreadydescribed (1198. 1207. ), each apparatus being used in turn to receive thefirst charge before its division by the other. As the apparatus were knownto have equal inductive power when air was in both (1209. 1211. ), anydifferences resulting from the introduction of the shell-lac would show apeculiar action in it, and if unequivocally referable to a specificinductive influence, would establish the point sought to be sustained. Ihave already referred to the precautions necessary in making theexperiments (1199, &c. ); and with respect to the error which might beintroduced by the assumption of the peculiar state, it was guarded against, as far as possible, in the first place, by operating quickly (1248); and, afterwards, by using that dielectric as glass or sulphur, which assumed thepeculiar state most slowly, and in the least degree (1239. 1241. ). 

1257. The shell-lac hemisphere was put into app. I. , and app. Ii. Leftfilled with air. The results of an experiment in which the charge throughair was divided and reduced by the shell-lac app. Were as follows:

App. I. Lac. App. Ii. Air. Balls 255°. 

 0° . . . . . . . . 304° . . . . 297 Charge divided. 113 . . . . . . . . 121 0 . . . . After being discharged. . . . . 7 after being discharged. 

1258. Here 297°, minus 7°, or 290°, may be taken as the divisible charge ofapp. Ii. (the 7° being fixed stem action (1203. 1232. )), of which 145° isthe half. The lac app. I. Gave 113° as the power or tension it had acquiredafter division; and the air app. Ii. Gave 121°, minus 7°, or 114°, as theforce it possessed from what it retained of the divisible charge of 290°. These two numbers should evidently be alike, and they are very nearly so, indeed far within the errors of experiment and observation, but thesenumbers differ very much from 145°, or the force which the half chargewould have had if app. I. Had contained air instead of shell-lac; and itappears that whilst in the division the induction through the air has lost176° of force, that through the lac has only gained 113°. 

1259. If this difference be assumed as depending entirely on the greaterfacility possessed by shell-lac of allowing or causing inductive actionthrough its substance than that possessed by air, then this capacity forelectric induction would be inversely as the respective loss and gainindicated above; and assuming the capacity of the air apparatus as 1, thatof the shell-lac apparatus would be 176/113 or 1. 55. 

1260. This extraordinary difference was so unexpected in its amount, as toexcite the greatest suspicion of the general accuracy of the experiment, though the perfect discharge of app. I. After the division, showed that the113° had been taken and given up readily. It was evident that, if it reallyexisted, it ought to produce corresponding effects in the reverse order;and that when induction through shell-lac was converted into inductionthrough air, the force or tension of the whole ought to be _increased_. Theapp. I. Was therefore charged in the first place, and its force dividedwith app. Ii. The following were the results:

App. I. Lac. App. Ii. Air. . . . . 0° 215° . . . . 204 . . . . Charge divided. . . . . 118 118 . . . . . . . . 0 after being discharged. 0 . . . . After being discharged. 

1261. Here 204° must be the utmost of the divisible charge. The app. I. Andapp. Ii. Present 118° as their respective forces; both now much _above_ thehalf of the first force, or 102°, whereas in the former case they werebelow it. The lac app. I. Has lost only 86°, yet it has given to the airapp. Ii. 118°, so that the lac still appears much to surpass the air, thecapacity of the lac app. I. To the air app. Ii. Being as 1. 37 to 1. 

1262. The difference of 1. 55 and 1. 37 as the expression of the capacity forthe induction of shell-lac seems considerable, but is in reality veryadmissible under the circumstances, for both are in error in _contrarydirections_. Thus in the last experiment the charge fell from 215° to 204°by the joint effects of dissipation and absorption (1192. 1250. ), duringthe time which elapsed in the electrometer operations, between theapplications of the carrier ball required to give those two results. Nearlyan equal time must have elapsed between the application of the carrierwhich gave the 204° result, and the division of the charge between the twoapparatus; and as the fall in force progressively decreases in amount(1192. ), if in this case it be taken at 6° only, it will reduce the wholetransferable charge at the time of division to 198° instead of 204°; thisdiminishes the loss of the shell-lac charge to 80° instead of 86°; and thenthe expression of specific capacity for it is increased, and, instead of1. 37, is 1. 47 times that of air. 

1263. Applying the same correction to the former experiment in which airwas _first_ charged, the result is of the _contrary_ kind. No shell-lachemisphere was then in the apparatus, and therefore the loss would beprincipally from dissipation, and not from absorption: hence it would benearer to the degree of loss shown by the numbers 304° and 297°, and beingassumed as 6° would reduce the divisible charge to 284°. In that case theair would have lost 170°, and communicated only 113° to the shell-lac; andthe relative specific capacity of the latter would appear to be 1. 50, whichis very little indeed removed from 1. 47, the expression given by the secondexperiment when corrected in the same way. 

1264. The shell-lac was then removed from app. I. And put into app. Ii. Andthe experiments of division again made. I give the results, because I thinkthe importance of the point justifies and even requires them. 

App. I. Air. App. Ii. Lac. Balls 200°. 

 . . . . 0°. 286° . . . . 283 . . . . Charge divided. . . . . 110 109 . . . . . . . . 0. 25 after discharge. Trace . . . . After discharge. 

Here app. I. Retained 109°, having lost 174° in communicating 110° to app. Ii. ; and the capacity of the air app. Is to the lac app. , therefore, as 1to 1. 58. If the divided charge be corrected for an assumed loss of only 3°, being the amount of previous loss in the same time, it will make thecapacity of the shell-lac app. 1. 55 only. 

1265. Then app. Ii. Was charged, and the charge divided thus:

App. I. Air. App. Ii. Lac, 0° . . . . . . . . 250° . . . . 251 Charge divided. 146 . . . . . . . . 149a little . . . . After discharge. . . . . A little after discharge. 

Here app. I. Acquired a charge of 146°, while app. Ii. Lost only 102° incommunicating that amount of force; the capacities being, therefore, toeach other as 1 to 1. 43. If the whole transferable charge be corrected fora loss of 4° previous to division, it gives the expression of l. 49 for thecapacity of the shell-lac apparatus. 

1266. These four expressions of 1. 47, 1. 50, 1. 55, and 1. 49 for the power ofthe shell-lac apparatus, through the different variations of theexperiment, are very near to each other; the average is close upon 1. 5, which may hereafter be used as the expression of the result. It is a veryimportant result; and, showing for this particular piece of shell-lac adecided superiority over air in allowing or causing the act of induction, it proved the growing necessity of a more close and rigid examination ofthe whole question. 

1267. The shell-lac was of the best quality, and had been carefullyselected and cleaned; but as the action of any conducting particles in itwould tend, virtually, to diminish the quantity or thickness of thedielectric used, and produce effects as if the two inducing surfaces of theconductors in that apparatus were nearer together than in the one with aironly, I prepared another shell-lac hemisphere, of which the material hadbeen dissolved in strong spirit of wine, the solution filtered, and thencarefully evaporated. This is not an easy operation, for it is difficult todrive off the last portions of alcohol without injuring the lac by the heatapplied; and unless they be dissipated, the substance left conducts toowell to be used in these experiments. I prepared two hemispheres this way, one of them unexceptionable; and with it I repeated the former experimentswith all precautions. The results were exactly of the same kind; thefollowing expressions for the capacity of the shell-lac apparatus, whetherit were app. I. Or ii. , being given directly by the experiments, 1. 46, 1. 50, 1. 52, 1. 51; the average of these and several others being very nearly1. 5. 

1268. As a final check upon the general conclusion, I then actually broughtthe surfaces of the air apparatus, corresponding to the place of theshell-lac in its apparatus, nearer together, by putting a metallic lininginto the lower hemisphere of the one not containing the lac (1213. ). Thedistance of the metal surface from the carrier ball was in this waydiminished from 0. 62 of an inch to 0. 435 of an inch, whilst the intervaloccupied by the lac in the other apparatus remained O. 62 of an inch asbefore. Notwithstanding this change, the lac apparatus showed its formersuperiority; and whether it or the air apparatus was charged first, thecapacity of the lac apparatus to the air apparatus was by the experimentalresults as 1. 45 to 1. 

1269. From all the experiments I have made, and their constant results, Icannot resist the conclusion that shell-lac does exhibit a case of_specific inductive capacity_. I have tried to check the trials in everyway, and if not remove, at least estimate, every source of error. That thefinal result is not due to common conduction is shown by the capability ofthe apparatus to retain the communicated charge; that it is not due to theconductive power of inclosed small particles, by which they could acquire apolarized condition as conductors, is shown by the effects of the shell-lacpurified by alcohol; and, that it is not due to any influence of thecharged state, formerly described (1250. ), first absorbing and thenevolving electricity, is indicated by the _instantaneous_ assumption anddischarge of those portions of the power which are concerned in thephenomena, that instantaneous effect occurring in these cases, as in allothers of ordinary induction, by charged conductors. The latter argument isthe more striking in the case where the air apparatus is employed to dividethe charge with the lac apparatus, for it obtains its portion ofelectricity in an _instant_, and yet is charged far above the _mean_. 

1270. Admitting for the present the general fact sought to be proved; then1. 5, though it expresses the capacity of the apparatus containing thehemisphere of shell-lac, by no means expresses the relation of lac to air. The lac only occupies one-half of the space _o, o_, of the apparatuscontaining it, through which the induction is sustained; the rest is filledwith air, as in the other apparatus; and if the effect of the two upperhalves of the globes be abstracted, then the comparison of the shell-lacpowers in the lower half of the one, with the power of the air in the lowerhalf of the other, will be as 2:1; and even this must be less than thetruth, for the induction of the upper part of the apparatus, i. E. Of thewire and ball B. (fig. 104. ) to external objects, must be the same in both, and considerably diminish the difference dependent upon, and reallyproducible by, the influence of the shell-lac within. 

 * * * * *

1271. _Glass. _--I next worked with glass as the dielectric. It involved thepossibility of conduction on its surface, but it excluded the idea ofconducting particles within its substance (1267. ) other than those of itsown mass. Besides this it does not assume the charged state (1239. ) soreadily, or to such an extent, as shell-lac. 

1272. A thin hemispherical cup of glass being made hot was covered with acoat of shell-lac dissolved in alcohol, and after being dried for manyhours in a hot place, was put into the apparatus and experimented with. Itexhibited effects so slight, that, though they were in the directionindicating a superiority of glass over air, they were allowed to pass aspossible errors of experiment; and the glass was considered as producing nosensible effect. 

1273. I then procured a thick hemispherical flint glass cup resembling thatof shell-lac (1239. ), but not filling up the space _o, o_, so well. Itsaverage thickness was 0. 4 of an inch, there being an additional thicknessof air, averaging 0. 22 of an inch, to make up the whole space of 0. 62 of aninch between the inductive metallic surfaces. It was covered with a film ofshell-lac as the former was, (1272. ) and being made very warm, wasintroduced into the apparatus, also warmed, and experiments made with it asin the former instances (1257. &c. ). The general results were the same aswith shell-lac, i. E. Glass surpassed air in its power of favouringinduction through it. The two best results as respected the state of theapparatus for retention of charge, &c. , gave, when the air apparatus wascharged first 1. 336, and when the glass apparatus was charged first 1. 45, as the specific inductive capacity for glass, both being withoutcorrection. The average of nine results, four with the glass apparatusfirst charged, and five with the air apparatus first charged, gave 1. 38 asthe power of the glass apparatus; 1. 22 and 1. 46 being the minimum andmaximum numbers with all the errors of experiment upon them. In all theexperiments the glass apparatus took up its inductive charge instantly, andlost it as readily (1269. ); and during the short time of each experiment, acquired the peculiar state in a small degree only, so that the influenceof this state, and also of conduction upon the results, must have beensmall. 

1274. Allowing specific inductive capacity to be proved and active in thiscase, and 1. 38 as the expression for the glass apparatus, then the specificinductive capacity of flint glass will be above 1. 76, not forgetting thatthis expression is for a piece of glass of such thickness as to occupy notquite two-thirds of the space through which the induction is sustained(1253. 1273. ). 

 * * * * *

1275. _Sulphur. _--The same hemisphere of this substance was used in app. Ii. As was formerly referred to (1242. ). The experiments were well made, i. E. The sulphur itself was free from charge both before and after eachexperiment, and no action from the stem appeared (1203. 1232. ), so that nocorrection was required on that account. The following are the results whenthe air apparatus was first charged and divided:

App. I. Air, App. Ii. Sulphur. Balls 280°. 

 0° . . . . . . . . 0° 438 . . . . 434 . . . . Charge divided. . . . . 162 164 . . . . . . . . 160 162 . . . . . . . . 0 after discharge. 0 . . . . After discharge. 

Here app. I. Retained 164°, having lost 276° in communicating 162° to app. Ii. , and the capacity of the air apparatus is to that of the sulphurapparatus as 1 to 1. 66. 

1276. Then the sulphur apparatus was charged first, thus:

 . . . . 0° 0° . . . . . . . . 395 . . . . 388 Charge divided. 237 . . . . . . . . 238 0 . . . . After discharge. . . . . 0 after discharge. 

Here app. Ii. Retained 238°, and gave up 150° in communicating a charge of237° to app. I. , and the capacity of the air apparatus is to that of thesulphur apparatus as 1 to 1. 58. These results are very near to each other, and we may take the mean 1. 62 as representing the specific inductivecapacity of the sulphur apparatus; in which case the specific inductivecapacity of sulphur itself as compared to air = 1 (1270. ) will be about orabove 2. 24. 

1277. This result with sulphur I consider as one of the mostunexceptionable. The substance when fused was perfectly clear, pellucid, and free from particles of dirt (1267. ), so that no interference of smallconducting bodies confused the result. The substance when solid is anexcellent insulator, and by experiment was found to take up, with greatslowness, that state (1244. 1242. ) which alone seemed likely to disturb theconclusion. The experiments themselves, also, were free from any need ofcorrection. Yet notwithstanding these circumstances, so favourable to theexclusion of error, the result is a higher specific inductive capacity forsulphur than for any other body as yet tried; and though this may in partbe clue to the sulphur being in a better shape, i. E. Filling up morecompletely the space _o, o_, (fig. 104. ) than the cups of shell-lac andglass, still I feel satisfied that the experiments altogether fully provethe existence of a difference between dielectrics as to their power offavouring an inductive action through them; which difference may, for thepresent, be expressed by the term _specific inductive capacity_. 

1278. Having thus established the point in the most favourable cases that Icould anticipate, I proceeded to examine other bodies amongst solids, liquids, and gases. These results I shall give with all convenient brevity. 

 * * * * *

1279. _Spermaceti. _--A good hemisphere of spermaceti being tried as toconducting power whilst its two surfaces were still in contact with thetinfoil moulds used in forming it, was found to conduct sensibly evenwhilst warm. On removing it from the moulds and using it in one of theapparatus, it gave results indicating a specific inductive capacity between1. 3 and 1. 6 for the apparatus containing it. But as the only mode ofoperation was to charge the air apparatus, and then after a quick contactwith the spermaceti apparatus, ascertain what was left in the former(1281. ), no great confidence can be placed in the results. They are not inopposition to the general conclusion, but cannot be brought forward asargument in favour of it. 

 * * * * *

1280. I endeavoured to find some liquids which would insulate well, andcould be obtained in sufficient quantity for these experiments. Oil ofturpentine, native naphtha rectified, and the condensed oil gas fluid, appeared by common experiments to promise best as to insulation. Being leftin contact with fused carbonate of potassa, chloride of lime, and quicklime for some days and then filtered, they were found much injured ininsulating power; but after distillation acquired their best state, thougheven then they proved to be conductors when extensive metallic contact wasmade with them. 

1281. _Oil of turpentine rectified. _--I filled the lower half of app. I. With the fluid: and as it would not hold a charge sufficiently to enable mefirst to measure and then divide it, I charged app. Ii. Containing air, anddividing its charge with app. I. By a quick contact, measured thatremaining in app. Ii. : for, theoretically, if a quick contact would divideup to equal tension between the two apparatus, yet without sensible lossfrom the conducting power of app. I. ; and app. Ii. Were left charged to adegree of tension above half the original charge, it would indicate thatoil of turpentine had less specific inductive capacity than air; or, ifleft charged below that mean state of tension, it would imply that thefluid had the greater inductive capacity. In an experiment of this kind, app. Ii. Gave as its charge 390° before division with app. I. , and 175°afterwards, which is less than the half of 390°. Again, being at 176°before division, it was 79° after, which is also less than half the dividedcharge. Being at 79°, it was a third time divided, and then fell to 36°, less than the half of 79°. Such are the best results I could obtain; theyare not inconsistent with the belief that oil of turpentine has a greaterspecific capacity than air, but they do not prove the fact, since thedisappearance of more than half the charge may be due to the conductingpower merely of the fluid. 

1282. _Naphtha. _--This liquid gave results similar in their nature anddirection to those with oil of turpentine. 

 * * * * *

1283. A most interesting class of substances, in relation to specificinductive capacity, now came under review, namely, the gases or aëriformbodies. These are so peculiarly constituted, and are bound together by somany striking physical and chemical relations, that I expected someremarkable results from them: air in various states was selected for thefirst experiments. 

1284. _Air, rare and dense. _--Some experiments of division (1208. ) seemedto show that dense and rare air were alike in the property underexamination. A simple and better process was to attach one of the apparatusto an air-pump, to charge it, and then examine the tension of the chargewhen the air within was more or less rarefied. Under these circumstances itwas found, that commencing with a certain charge, that charge did notchange in its tension or force as the air was rarefied, until therarefaction was such that _discharge_ across the space _o_, _o_ (fig. 104. )occurred. This discharge was proportionate to the rarefaction; but havingtaken place, and lowered the tension to a certain degree, that degree wasnot at all affected by restoring the pressure and density of the air totheir first quantities. 

 inches of mercury. Thus at a pressure of 30 the charge was 88°Again 30 the charge was 88Again 30 the charge was 87Reduced to 11 the charge was 87Raised again to 30 the charge was 86Being now reduced to 3. 4 the charge fell to 81Raised again to 30 the charge was still 81

1285. The charges were low in these experiments, first that they might notpass off at low pressure, and next that little loss by dissipation mightoccur. I now reduced them still lower, that I might rarefy further, and forthis purpose in the following experiment used a measuring interval in theelectrometer of only 15° (1185. ). The pressure of air within the apparatusbeing reduced to 1. 9 inches of mercury, the charge was found to be 29°;then letting in air till the pressure was 30 inches, the charge was still29°. 

1286. These experiments were repeated with pure oxygen with the sameconsequences. 

1287. This result of _no variation_ in the electric tension being producedby variation in the density or pressure of the air, agrees perfectly withthose obtained by Mr. Harris[A], and described in his beautiful andimportant investigations contained in the Philosophical Transactions;namely that induction is the same in rare and dense air, and that thedivergence of an electrometer under such variations of the air continuesthe same, provided no electricity pass away from it. The effect is oneentirely independent of that power which dense air has of causing a highercharge to be _retained_ upon the surface of conductors in it than can beretained by the same conductors in rare air; a point I propose consideringhereafter. 

 [A] Philosophical Transactions, 1834, pp. 223, 224, 237, 244. 

1288. I then compared _hot and cold air_ together, by raising thetemperature of one of the inductive apparatus as high as it could bewithout injury, and then dividing charges between it and the otherapparatus containing cold air. The temperatures were about 50° and 200°, Still the power or capacity appeared to be unchanged; and when Iendeavoured to vary the experiment, by charging a cold apparatus and thenwarming it by a spirit lamp, I could obtain no proof that the inductivecapacity underwent any alteration. 

1289. I compared _damp and dry air_ together, but could find no differencein the results. 

 * * * * *

1290. _Gases. _--A very long series of experiments was then undertaken forthe purpose of comparing _different gases_ one with another. They were allfound to insulate well, except such as acted on the shell-lac of thesupporting stem; these were chlorine, ammonia, and muriatic acid. They wereall dried by appropriate means before being introduced into the apparatus. It would have been sufficient to have compared each with air; but, inconsequence of the striking result which came out, namely, that _all hadthe same power of_ or _capacity for_, sustaining induction through them, (which perhaps might have been expected after it was found that novariation of density or pressure produced any effect, ) I was induced tocompare them, experimentally, two and two in various ways, that nodifference might escape me, and that the sameness of result might stand infull opposition to the contrast of property, composition, and conditionwhich the gases themselves presented. 

1291. The experiments were made upon the following pairs of gases. 

 1. Nitrogen and Oxygen. 2. Oxygen Air. 3. Hydrogen Air. 4. Muriatic acid gas Air. 5. Oxygen Hydrogen. 5. Oxygen Carbonic acid. 7. Oxygen Olefiant gas. 8. Oxygen Nitrous gas. 9. Oxygen Sulphurous acid. 10. Oxygen Ammonia. 11. Hydrogen Carbonic acid. 12 Hydrogen Olefiant gas. 13. Hydrogen Sulphurous acid. 14. Hydrogen Fluo-silicic acid. 15. Hydrogen Ammonia. 16, Hydrogen Arseniuretted hydrogen. 17. Hydrogen Sulphuretted hydrogen. 18, Nitrogen Olefiant gas. 19. Nitrogen Nitrous gas. 20. Nitrogen Nitrous oxide. 21. Nitrogen Ammonia. 22. Carbonic oxide Carbonic acid. 23. Carbonic oxide Olefiant gas. 24. Nitrous oxide Nitrous gas. 25. Ammonia Sulphurous acid. 

1292. Notwithstanding the striking contrasts of all kinds which these gasespresent of property, of density, whether simple or compound, anions orcations (665. ), of high or low pressure (1284. 1286. ), hot or cold (1288. ), not the least difference in their capacity to favour or admit electricalinduction through them could be perceived. Considering the pointestablished, that in all these gases induction takes place by an action ofcontiguous particles, this is the more important, and adds one to the manystriking relations which hold between bodies having the gaseous conditionand form. Another equally important electrical relation, which will beexamined in the next paper[A], is that which the different gases have toeach other at the _same pressure_ of causing the retention of the _same ordifferent degrees of charge_ upon conductors in them. These two resultsappear to bear importantly upon the subject of electrochemical excitationand decomposition; for as _all_ these phenomena, different as they seem tobe, must depend upon the electrical forces of the particles of matter, thevery distance at which they seem to stand from each other will do much, ifproperly considered, to illustrate the principle by which they are held inone common bond, and subject, as they must be, to one common law. 

 [A] See in relation to this point 1382. &c. --_Dec. 1838. _

1293. It is just possible that the gases may differ from each other intheir specific inductive capacity, and yet by quantities so small as not tobe distinguished in the apparatus I have used. It must be remembered, however, that in the gaseous experiments the gases occupy all the space _o, o_, (fig. 104. ) between the inner and the outer ball, except the smallportion filled by the stem; and the results, therefore, are twice asdelicate as those with solid dielectrics. 

1294. The insulation was good in all the experiments recorded, except Nos. 10, 15, 21, and 25, being those in which ammonia was compared with othergases. When shell-lac is put into ammoniacal gas its surface graduallyacquires conducting power, and in this way the lac part of the stem withinwas so altered, that the ammonia apparatus could not retain a charge withsufficient steadiness to allow of division. In these experiments, therefore, the other apparatus was charged; its charge measured and dividedwith the ammonia apparatus by a quick contact, and what remained untakenaway by the division again measured (1281. ). It was so nearly one-half ofthe original charge, as to authorize, with this reservation, the insertionof ammoniacal gas amongst the other gases, as having equal power with them. 

¶ vi. _General results as to induction. _

1295. Thus _induction_ appears to be essentially an action of contiguousparticles, through the intermediation of which the electric force, originating or appearing at a certain place, is propagated to or sustainedat a distance, appearing there as a force of the same kind exactly equal inamount, but opposite in its direction and tendencies (1164. ). Inductionrequires no sensible thickness in the conductors which may be used to limitits extent; an uninsulated leaf of gold may be made very highly positive onone surface, and as highly negative on the other, without the leastinterference of the two states whilst the inductions continue. Nor is itaffected by the nature of the limiting conductors, provided time beallowed, in the case of those which conduct slowly, for them to assumetheir final state (1170. ). 

1296. But with regard to the _dielectrics_ or insulating media, matters arevery different (1167. ). Their thickness has an immediate and importantinfluence on the degree of induction. As to their quality, though all gasesand vapours are alike, whatever their state; yet amongst solid bodies, andbetween them and gases, there are differences which prove the existence of_specific inductive capacities_, these differences being in some cases verygreat. 

1297. The direct inductive force, which may be conceived to be exerted inlines between the two limiting and charged conducting surfaces, isaccompanied by a lateral or transverse force equivalent to a dilatation orrepulsion of these representative lines (1224. ); or the attractive forcewhich exists amongst the particles of the dielectric in the direction ofthe induction is accompanied by a repulsive or a diverging force in thetransverse direction (1304. ). 

1298. Induction appears to consist in a certain polarized state of theparticles, into which they are thrown by the electrified body sustainingthe action, the particles assuming positive and negative points or parts, which are symmetrically arranged with respect to each other and theinducting surfaces or particles[A]. The state must be a forced one, for itis originated and sustained only by force, and sinks to the normal orquiescent state when that force is removed. It can be _continued_ only ininsulators by the same portion of electricity, because they only can retainthis state of the particles (1304). 

 [A] The theory of induction which I am stating does not pretend to decide whether electricity be a fluid or fluids, or a mere power or condition of recognized matter. That is a question which I may be induced to consider in the next or following series of these researches. 

1299. The principle of induction is of the utmost generality in electricaction. It constitutes charge in every ordinary case, and probably in everycase; it appears to be the cause of all excitement, and to precede everycurrent. The degree to which the particles are affected in this theirforced state, before discharge of one kind or another supervenes, appearsto constitute what we call _intensity_. 

1300. When a Leyden jar is _charged_, the particles of the glass are forcedinto this polarized and constrained condition by the electricity of thecharging apparatus. _Discharge_ is the return of these particles to theirnatural state from their state of tension, whenever the two electric forcesare allowed to be disposed of in some other direction. 

1301. All charge of conductors is on their surface, because beingessentially inductive, it is there only that the medium capable ofsustaining the necessary inductive state begins. If the conductors arehollow and contain air or any other dielectric, still no _charge_ canappear upon that internal surface, because the dielectric there cannotassume the polarized state throughout, in consequence of the opposingactions in different directions. 

1302. The known influence of _form_ is perfectly consistent with thecorpuscular view of induction set forth. An electrified cylinder is moreaffected by the influence of the surrounding conductors (which complete thecondition of charge) at the ends than at the middle, because the ends areexposed to a greater sum of inductive forces than the middle; and a pointis brought to a higher condition than a ball, because by relation to theconductors around, more inductive force terminates on its surface than onan equal surface of the ball with which it is compared. Here too, especially, can be perceived the influence of the lateral or transverseforce (1297. ), which, being a power of the nature of or equivalent torepulsion, causes such a disposition of the lines of inductive force intheir course across the dielectric, that they must accumulate upon thepoint, the end of the cylinder, or any projecting part. 

1303. The influence of _distance_ is also in harmony with the same view. There is perhaps no distance so great that induction cannot take placethrough it[A]; but with the same constraining force (1298. ) it takes placethe more easily, according as the extent of dielectric through which it isexerted is lessened. And as it is assumed by the theory that the particlesof the dielectric, though tending to remain in a normal state, are throwninto a forced condition during the induction; so it would seem to followthat the fewer there are of these intervening particles opposing theirtendency to the assumption of the new state, the greater degree of changewill they suffer, i. E. The higher will be the condition they assume, andthe larger the amount of inductive action exerted through them. 

 [A] I have traced it experimentally from a ball placed in the middle of the large cube formerly described (1173. ) to the sides of the cube six feet distant, and also from the same ball placed in the middle of our large lecture-room to the walls of the room at twenty-six feet distance, the charge sustained upon the ball in these cases being solely due to induction through these distances. 

1304. I have used the phrases _lines of inductive force_ and _curved lines_of force (1231. 1297. 1298. 1302. ) in a general sense only, just as wespeak of the lines of magnetic force. The lines are imaginary, and theforce in any part of them is of course the resultant of compound forces, every molecule being related to every other molecule in _all_ directions bythe tension and reaction of those which are contiguous. The transverseforce is merely this relation considered in a direction oblique to thelines of inductive force, and at present I mean no more than that by thephrase. With respect to the term _polarity_ also, I mean at present only adisposition of force by which the same molecule acquires opposite powers ondifferent parts. The particular way in which this disposition is made willcome into consideration hereafter, and probably varies in different bodies, and so produces variety of electrical relation[A]. All I am anxious aboutat present is, that a more particular meaning should not be attached to theexpressions used than I contemplate. Further inquiry, I trust, will enableus by degrees to restrict the sense more and more, and so render theexplanation of electrical phenomena day by day more and more definite. 

 [A] See now 1685. &c. --_Dec. 1838. _

1305. As a test of the probable accuracy of my views, I have throughoutthis experimental examination compared them with the conclusions drawn byM. Poisson from his beautiful mathematical inquiries[A]. I am quite unfitto form a judgment of these admirable papers; but as far as I can perceive, the theory I have set forth and the results I have obtained are not inopposition to such of those conclusions as represent the final dispositionand state of the forces in the limited number of cases be has considered. His theory assumes a very different mode of action in induction to thatwhich I have ventured to support, and would probably find its mathematicaltest in the endeavour to apply it to cases of induction in curved lines. Tomy feeling it is insufficient in accounting for the retention ofelectricity upon the surface of conductors by the pressure of the air, aneffect which I hope to show is simple and consistent according to thepresent view[B]; and it does not touch voltaic electricity, or in any wayassociate it and what is called ordinary electricity under one commonprinciple. 

 [A] Mémoires de L'Institut, 1811, tom. Xii. The first page 1, and thesecond paging 163. 

 [B] Refer to 1377, 1378, 1379, 1398. --_Dec. 1838. _

I have also looked with some anxiety to the results which thatindefatigable philosopher Harris has obtained in his investigation of thelaws of induction[A], knowing that they were experimental, and having afull conviction of their exactness; but I am happy in perceiving nocollision at present between them and the views I have taken. 

 [A] Philosophical Transactions, 1834, p. 213. 

1306. Finally, I beg to say that I put forth my particular view with doubtand fear, lest it should not bear the test of general examination, forunless true it will only embarrass the progress of electrical science. Ithas long been on my mind, but I hesitated to publish it until theincreasing persuasion of its accordance with all known facts, and themanner in which it linked together effects apparently very different inkind, urged me to write the present paper. I as yet see no inconsistencybetween it and nature, but, on the contrary, think I perceive much newlight thrown by it on her operations; and my next papers will be devoted toa review of the phenomena of conduction, electrolyzation, current, magnetism, retention, discharge, and some other points, with an applicationof the theory to these effects, and an examination of it by them. 

_Royal Institution, November 16, 1837. _

 * * * * *

_Supplementary Note to Experimental Researches in Electricity. _

_Eleventh Series. _

Received March 29, 1838. 

1307. I have recently put into an experimental form that general statementof the question of _specific inductive capacity_ which is given at No. 1252of Series XI. , and the result is such as to lead me to hope the Council ofthe Royal Society will authorize its addition to the paper in the form of asupplementary note. Three circular brass plates, about five inches indiameter, were mounted side by side upon insulating pillars; the middleone, A, was a fixture, but the outer plates B and C were moveable onslides, so that all three could be brought with their sides almost intocontact, or separated to any required distance. Two gold leaves weresuspended in a glass jar from insulated wires; one of the outer plates Bwas connected with one of the gold leaves, and the other outer plate withthe other leaf. The outer plates B and C were adjusted at the distance ofan inch and a quarter from the middle plate A, and the gold leaves werefixed at two inches apart; A was then slightly charged with electricity, and the plates B and C, with their gold leaves, thrown out of insulation_at the same time_, and then left insulated. In this state of things A wascharged positive inductrically, and B and C negative inducteously; the samedielectric, air, being in the two intervals, and the gold leaves hanging, of course, parallel to each other in a relatively unelectrified state. 

1308. A plate of shell-lac three-quarters of an inch in thickness, and fourinches square, suspended by clean white silk thread, was very carefullydeprived of all charge (1203. ) (so that it produced no effect on the goldleaves if A were uncharged) and then introduced between plates A and B; theelectric relation of the three plates was immediately altered, and the goldleaves attracted each other. On removing the shell-lac this attractionceased; on introducing it between A and C it was renewed; on removing itthe attraction again ceased; and the shell-lac when examined by a delicateCoulomb electrometer was still without charge. 

1309. As A was positive, B and C were of course negative; but as thespecific inductive capacity of shell-lac is about twice that of air(1270. ), it was expected that when the lac was introduced between A and B, A would induce more towards B than towards C; that therefore B would becomemore negative than before towards A, and consequently, because of itsinsulated condition, be positive externally, as at its back or at the goldleaves; whilst C would be less negative towards A, and therefore negativeoutwards or at the gold leaves. This was found to be the case; for onwhichever side of A the shell-lac was introduced the external plate at thatside was positive, and the external plate on the other side negativetowards each other, and also to uninsulated external bodies. 

1310. On employing a plate of sulphur instead of shell-lac, the sameresults were obtained; consistent with the conclusions drawn regarding thehigh specific inductive capacity of that body already given (1276. ). 

1311. These effects of specific inductive capacity can be exalted invarious ways, and it is this capability which makes the great value of theapparatus. Thus I introduced the shell-lac between A and B, and then for amoment connected B and C, uninsulated them, and finally left them in theinsulated state; the gold leaves were of course hanging parallel to eachother. On removing the shell-lac the gold leaves attracted each other; onintroducing the shell-lac between A and C this attraction was _increased_, (as had been anticipated from theory, ) and the leaves came together, thoughnot more than four inches long, and hanging three inches apart. 

1312. By simply bringing the gold leaves nearer to each other I was able toshow the difference of specific inductive capacity when only thin plates ofshell-lac were used, the rest of the dielectric space being filled withair. By bringing B and C nearer to A another great increase of sensibilitywas made. By enlarging the size of the plates still further power wasgained. By diminishing the extent of the wires, &c. Connected with the goldleaves, another improvement resulted. So that in fact the gold leavesbecame, in this manner, as delicate a test of _specific inductive action_as they are, in Bennet's and Singer's electrometers, of ordinary electricalcharge. 

1313. It is evident that by making the three plates the sides of cells, with proper precautions as regards insulation, &c. , this apparatus may beused in the examination of gases, with far more effect than the formerapparatus (1187. 1290), and may, perhaps, bring out differences which haveas yet escaped me (1292. 1293. )

1314. It is also evident that two metal plates are quite sufficient to formthe instrument; the state of the single inducteous plate when thedielectric is changed, being examined either by bringing a body excited ina known manner towards its gold leaves, or, what I think will be better, employing a carrier ball in place of the leaf, and examining that ball bythe Coulomb electrometer (1180. ). The inductive and inducteous surfaces mayeven be balls; the latter being itself the carrier ball of the Coulomb'selectrometer (1181. 1229. ). 

1315. To increase the effect, a small condenser may be used with greatadvantage. Thus if, when two inducteous plates are used, a little condenserwere put in the place of the gold leaves, I have no doubt the threeprincipal plates might be reduced to an inch or even half an inch indiameter. Even the gold leaves act to each other for the time as the platesof a condenser. If only two plates were used, by the proper application ofthe condenser the same reduction might take place. This expectation isfully justified by an effect already observed and described (1229. ). 

1316. In that case the application of the instrument to very extensiveresearch is evident. Comparatively small masses of dielectrics could beexamined, as diamonds and crystals. An expectation, that the specificinductive capacity of crystals will vary in different directions, accordingas the lines of inductive force (1304. ) are parallel to, or in otherpositions in relation to the axes of the crystals, can be tested[A]: Ipurpose that these and many other thoughts which arise respecting specificinductive action and the polarity of the particles of dielectric matter, shall be put to the proof as soon as I can find time. 

 [A] Refer for this investigation to 1680-1698. --_Dec. 1838. _

1317. Hoping that this apparatus will form an instrument of considerableuse, I beg to propose for it (at the suggestion of a friend) the name of_Differential Inductometer_. 

_Royal Institution, March 29, 1838. _

TWELFTH SERIES. 

§ 18. _On Induction (continued). _ ¶ vii. _Conduction, or conductivedischarge. _ ¶ viii. _Electrolytic discharge. _ ¶ ix. _Disruptivedischarge--Insulation--Spark--Brush--Difference of discharge at thepositive and negative surfaces of conductors. _

Received January 11, --Read February 8, 1838. 

1318. I Proceed now, according to my promise, to examine, by the greatfacts of electrical science, that theory of induction which I have venturedto put forth (1165. 1295. &c. ). The principle of induction is so universalthat it pervades all electrical phenomena; but the general case which Ipurpose at present to go into consists of insulation traced into andterminating with discharge, with the accompanying effects. This caseincludes the various _modes_ of discharge, and also the condition andcharacters of a current; the elements of magnetic action being amongst thelatter. I shall necessarily have occasion to speak theoretically, and evenhypothetically; and though these papers profess to be experimentalresearches, I hope that, considering the facts and investigations containedin the last series in support of the particular view advanced, I shall notbe considered as taking too much liberty on the present occasion, or asdeparting too far from the character which they ought to have, especiallyas I shall use every opportunity which presents itself of returning to thatstrong test of truth, experiment. 

1319. Induction has as yet been considered in these papers only in cases ofinsulation; opposed to insulation is _discharge_. The action or effectwhich may be expressed by the general term _discharge_, may take place, asfar as we are aware at present, in several modes. Thus, that which iscalled simply _conduction_ involves no chemical action, and apparently nodisplacement of the particles concerned. A second mode may be called_electrolytic discharge_; in it chemical action does occur, and particlesmust, to a certain degree, be displaced. A third mode, namely, that bysparks or brushes, may, because of its violent displacement of theparticles of the _dielectric_ in its course, be called the _disruptivedischarge_; and a fourth may, perhaps, be conveniently distinguished for atime by the words _convection_, or _carrying discharge_, being that inwhich discharge is effected either by the carrying power of solidparticles, or those of gases and liquids. Hereafter, perhaps, all thesemodes may appear as the result of one common principle, but at present theyrequire to be considered apart; and I will now speak of the _first_ mode, for amongst all the forms of discharge, that which we express by the termconduction appears the most simple and the most directly in contrast withinsulation. 

¶ vii. _Conduction, or conductive discharge. _

1320. Though assumed to be essentially different, yet neither Cavendish norPoisson attempt to explain by, or even state in, their theories, what theessential difference between insulation and conduction is. Nor have Ianything, perhaps, to offer in this respect, _except_ that, according to myview of induction, insulation and conduction depend upon the same molecularaction of the dielectrics concerned; are only extreme degrees of _onecommon condition_ or effect; and in any sufficient mathematical theory ofelectricity must be taken as cases of the same kind. Hence the importanceof the endeavour to show the connection between them under my theory of theelectrical relations of contiguous particles. 

1321. Though the action of the insulating dielectric in the charged Leydenjar, and that of the wire in discharging it, may seem very different, theymay be associated by numerous intermediate links, which carry us on fromone to the other, leaving, I think, no necessary connection unsupplied. Wemay observe some of these in succession for information respecting thewhole case. 

1322. Spermnceti has been examined and found to be a dielectric, throughwhich induction can take place (1240. 1246. ), its specific inductivecapacity being about or above 1. 8 (1279. ), and the inductive action hasbeen considered in it, as in all other substances, an action of contiguousparticles. 

1323. But spermaceti is also a _conductor_, though in so low a degree thatwe can trace the process of conduction, as it were, step by step throughthe mass (1247. ); and even when the electric force has travelled through itto a certain distance, we can, by removing the coercitive (which is at thesame time the inductive) force, cause it to return upon its path andreappear in its first place (1245. 1246. ). Here induction appears to be anecessary preliminary to conduction. It of itself brings the contiguousparticles of the dielectric into a certain condition, which, if retained bythem, constitutes _insulation_, but if lowered by the communication ofpower from one particle to another, constitutes _conduction_. 

1324. If _glass_ or _shell-lac_ be the substances under consideration, thesame capabilities of suffering either induction or conduction through themappear (1233. 1239. 1247. ), but not in the same degree. The conductionalmost disappears (1239. 1242. ); the induction therefore is sustained, i. E. The polarized state into which the inductive force has brought thecontiguous particles is retained, there being little discharge actionbetween them, and therefore the _insulation_ continues. But, what dischargethere is, appears to be consequent upon that condition of the particlesinto which the induction throws them; and thus it is that ordinaryinsulation and conduction are closely associated together or rather areextreme cases of one common condition. 

1325. In ice or water we have a better conductor than spermaceti, and thephenomena of induction and insulation therefore rapidly disappear, becauseconduction quickly follows upon the assumption of the inductive state. Butlet a plate of cold ice have metallic coatings on its sides, and connectone of these with a good electrical machine in work, and the other with theground, and it then becomes easy to observe the phenomena of inductionthrough the ice, by the electrical tension which can be obtained andcontinued on both the coatings (419. 426. ). For although that portion ofpower which at one moment gave the inductive condition to the particles isat the next lowered by the consequent discharge due to the conductive act, it is succeeded by another portion of force from the machine to restore theinductive state. If the ice be converted into water the same succession ofactions can be just as easily proved, provided the water be distilled, and(if the machine be not powerful enough) a voltaic battery be employed. 

1326. All these considerations impress my mind strongly with theconviction, that insulation and ordinary conduction cannot be properlyseparated when we are examining into their nature; that is, into thegeneral law or laws under which their phenomena are produced. They appearto me to consist in an action of contiguous particles dependent on theforces developed in electrical excitement; these forces bring the particlesinto a state of tension or polarity, which constitutes both _induction_ and_insulation_; and being in this state, the continuous particles have apower or capability of communicating their forces one to the other, bywhich they are lowered, and discharge occurs. Every body appears todischarge (444. 987. ); but the possession of this capability in a _greateror smaller degree_ in different bodies, makes them better or worseconductors, worse or better insulators; and both _induction_ and_conduction_ appear to be the same in their principle and action (1320. ), except that in the latter an effect common to both is raised to the highestdegree, whereas in the former it occurs in the best cases, in only analmost insensible quantity. 

1327. That in our attempts to penetrate into the nature of electricalaction, and to deduce laws more general than those we are at presentacquainted with, we should endeavour to bring apparently opposite effectsto stand side by side in harmonious arrangement, is an opinion of longstanding, and sanctioned by the ablest philosophers. I hope, therefore, Imay be excused the attempt to look at the highest cases of conduction asanalogous to, or even the same in kind with, those of induction andinsulation. 

1328. If we consider the slight penetration of sulphur (1241. 1242. ) orshell-lac (1234. ) by electricity, or the feebler insulation sustained byspermaceti (1279. 1240. ), as essential consequences and indications oftheir _conducting_ power, then may we look on the resistance of metallicwires to the passage of electricity through them as _insulating_ power. Ofthe numerous well-known cases fitted to show this resistance in what arecalled the perfect conductors, the experiments of Professor Wheatstone bestserve my present purpose, since they were carried to such an extent as toshow that _time_ entered as an element into the conditions of conduction[A]even in metals. When discharge was made through a copper wire 2640 feet inlength, and 1/15th of an inch in diameter, so that the luminous sparks ateach end of the wire, and at the middle, could be observed in the sameplace, the latter was found to be sensibly behind the two former in time, they being by the conditions of the experiment simultaneous. Hence a proofof retardation; and what reason can be given why this retardation shouldnot be of the same kind as that in spermaceti, or in lac, or sulphur? Butas, in them, retardation is insulation, and insulation is induction, whyshould we refuse the same relation to the same exhibitions of force in themetals?

 [A] Philosophical Transactions, 1834, p. 583. 

1329. We learn from the experiment, that if _time_ be allowed theretardation is gradually overcome; and the same thing obtains for thespermaceti, the lac, and glass (1248. ); give but time in proportion to theretardation, and the latter is at last vanquished. But if that be the case, and all the results are alike in kind, the only difference being in thelength of time, why should we refuse to metals the previous inductiveaction, which is admitted to occur in the other bodies? The diminution of_time_ is no negation of the action; nor is the lower degree of tensionrequisite to cause the forces to traverse the metal, as compared to thatnecessary in the cases of water, spermaceti, or lac. These differenceswould only point to the conclusion, that in metals the particles underinduction can transfer their forces when at a lower degree of tension orpolarity, and with greater facility than in the instances of the otherbodies. 

1330. Let us look at Mr. Wheatstone's beautiful experiment in another pointof view, If, leaving the arrangement at the middle and two ends of the longcopper wire unaltered, we remove the two intervening portions and replacethem by wires of iron or platina, we shall have a much greater retardationof the middle spark than before. If, removing the iron, we were tosubstitute for it only five or six feet of water in a cylinder of the samediameter as the metal, we should have still greater retardation. If fromwater we passed to spermaceti, either directly or by gradual steps throughother bodies, (even though we might vastly enlarge the bulk, for thepurpose of evading the occurrence of a spark elsewhere (1331. ) than at thethree proper intervals, ) we should have still greater retardation, until atlast we might arrive, by degrees so small as to be inseparable from eachother, at actual and permanent insulation. What, then, is to separate theprinciple of these two extremes, perfect conduction and perfect insulation, from each other; since the moment we leave in the smallest degreeperfection at either extremity, we involve the element of perfection at theopposite end? Especially too, as we have not in nature the case ofperfection either at one extremity or the other, either of insulation orconduction. 

1331. Again, to return to this beautiful experiment in the various formswhich may be given to it: the forces are not all in the wire (after theyhave left the Leyden jar) during the whole time (1328. ) occupied by thedischarge; they are disposed in part through the surrounding dielectricunder the well-known form of induction; and if that dielectric be air, induction takes place from the wire through the air to surroundingconductors, until the ends of the wire are electrically related through itslength, and discharge has occurred, i. E. For the _time_ during which themiddle spark is retarded beyond the others. This is well shown by the oldexperiment, in which a long wire is so bent that two parts (Plate VIII. Fig. 115. ), _a, b_, near its extremities shall approach within a shortdistance, as a quarter of an inch, of each other in the air. If thedischarge of a Leyden jar, charged to a sufficient degree, be sent throughsuch a wire, by far the largest portion of the electricity will pass as aspark across the air at the interval, and not by the metal. Does not themiddle part of the wire, therefore, act here as an insulating medium, though it be of metal? and is not the spark through the air an indicationof the tension (simultaneous with _induction_) of the electricity in theends of this single wire? Why should not the wire and the air both beregarded as dielectrics; and the action at its commencement, and whilstthere is tension, as an inductive action? If it acts through the contortedlines of the wire, so it also does in curved and contorted lines throughair (1219, 1224, 1231. ), and other insulating dielectrics (1228); and wecan apparently go so far in the analogy, whilst limiting the case to theinductive action only, as to show that amongst insulating dielectrics somelead away the lines of force from others (1229. ), as the wire will do fromworse conductors, though in it the principal effect is no doubt due to theready discharge between the particles whilst in a low state of tension. Theretardation is for the time insulation; and it seems to me we may just asfairly compare the air at the interval _a, b_ (fig. 115. ) and the wire inthe circuit, as two bodies of the same kind and acting upon the sameprinciples, as far as the first inductive phenomena are concerned, notwithstanding the different forms of discharge which ultimatelyfollow[A], as we may compare, according to Coulomb's investigations[B]_different lengths_ of different insulating bodies required to produce thesame amount of insulating effect. 

 [A] These will be examined hereafter (1348. &c. ). 

 [B] Mémoires de l'Académie, 1785, p. 612. Or Ency. Britann. First Supp. Vol. I. P. 614. 

1332. This comparison is still more striking when we take intoconsideration the experiment of Mr. Harris, in which he stretched a finewire across a glass globe, the air within being rarefied[A]. On sending acharge through the joint arrangement of metal and rare air, as much, if notmore, electricity passed by the latter as by the former. In the air, rarefied as it was, there can be no doubt the discharge was preceded byinduction (1284. ); and to my mind all the circumstances indicate that thesame was the case with the metal; that, in fact, both substances aredielectrics, exhibiting the same effects in consequence of the action ofthe same causes, the only variation being one of degree in the differentsubstances employed. 

 [A] Philosophical Transactions, 1834, p, 212. 

1333. Judging on these principles, velocity of discharge through the _samewire_ may be varied greatly by attending to the circumstances which causevariations of discharge through spermaceti or sulphur. Thus, for instance, it must vary with the tension or intensity of the first urging force (1234. 1240. ), which tension is charge and induction. So if the two ends of thewire, in Professor Wheatstone's experiment, were immediately connected withtwo large insulated metallic surfaces exposed to the air, so that theprimary act of induction, after making the contact for discharge, might bein part removed from the internal portion of the wire at the first instant, and disposed for the moment on its surface jointly with the air andsurrounding conductors, then I venture to anticipate that the middle sparkwould be more retarded than before; and if these two plates were the innerand outer coating of a large jar or a Leyden battery, then the retardationof that spark would be still greater. 

1334. Cavendish was perhaps the first to show distinctly that discharge wasnot always by one channel[A], but, if several are present, by many at once. We may make these different channels of different bodies, and byproportioning their thicknesses and lengths, may include such substances asair, lac, spermaceti, water, protoxide of iron, iron and silver, and by_one_ discharge make each convey its proportion of the electric force. Perhaps the air ought to be excepted, as its discharge by conduction isquestionable at present (1336. ); but the others may all be limited in theirmode of discharge to pure conduction. Yet several of them suffer previousinduction, precisely like the induction through the air, it being anecessary preliminary to their discharging action. How can we thereforeseparate any one of these bodies from the others, as to the _principles andmode_ of insulating and conducting, except by mere degree? All seem to meto be dielectrics acting alike, and under the same common laws. 

 [A] _Philosophical Transactions_, 1776, p. 197. 

1335. I might draw another argument in favour of the general sameness, innature and action, of good and bad conductors (and all the bodies I referto are conductors more or less), from the perfect equipoise in action ofvery different bodies when opposed to each other in magneto-electricinductive action, as formerly described (213. ), but am anxious to be asbrief as is consistent with the clear examination of the probable truth ofmy views. 

1336. With regard to the possession by the gases of any conducting powerof the simple kind now under consideration, the question is a verydifficult one to determine at present. Experiments seem to indicate thatthey do insulate certain low degrees of tension perfectly, and that theeffects which may have appeared to be occasioned by _conduction_ have beenthe result of the carrying power of the charged particles, either of theair or of dust, in it. It is equally certain, however, that with higherdegrees of tension or charge the particles discharge to one another, andthat is conduction. If the gases possess the power of insulating a certainlow degree of tension continuously and perfectly, such a result may be dueto their peculiar physical state, and the condition of separation underwhich their particles are placed. But in that, or in any case, we must notforget the fine experiments of Cagniard de la Tour[A], in which he hasshown that liquids and their vapours can be made to pass gradually intoeach other, to the entire removal of any marked distinction of the twostates. Thus, hot dry steam and cold water pass by insensible gradationsinto each other; yet the one is amongst the gases as an insulator, and theother a comparatively good conductor. As to conducting power, therefore, the transition from metals even up to gases is gradual; substances make butone series in this respect, and the various cases must come under onecondition and law (444. ). The specific differences of bodies as toconducting power only serves to strengthen the general argument, thatconduction, like insulation, is a result of induction, and is an action ofcontiguous particles. 

 [A] Annales de Chimie, xxi. Pp. 127, 178, or Quarterly Journal of Science, xv. 145. 

1337. I might go on now to consider induction and its concomitant, _conduction_, through mixed dielectrics, as, for instance, when a chargedbody, instead of acting across air to a distant uninsulated conductor, actsjointly through it and an interposed insulated conductor. In such a case, the air and the conducting body are the mixed dielectrics; and the latterassumes a polarized condition as a mass, like that which my theory assumes_each particle_ of the air to possess at the same time (1679). But I fearto be tedious in the present condition of the subject, and hasten to theconsideration of other matter. 

1338. To sum up, in some degree, what has been said, I look upon the firsteffect of an excited body upon neighbouring matters to be the production ofa polarized state of their particles, which constitutes _induction_; andthis arises from its action upon the particles in immediate contact withit, which again act upon those contiguous to them, and thus the forces aretransferred to a distance. If the induction remain undiminished, thenperfect insulation is the consequence; and the higher the polarizedcondition which the particles can acquire or maintain, the higher is theintensity which may be given to the acting forces. If, on the contrary, thecontiguous particles, upon acquiring the polarized state, have the power tocommunicate their forces, then conduction occurs, and the tension islowered, conduction being a distinct act of discharge between neighbouringparticles. The lower the state of tension at which this discharge betweenthe particles of a body takes place, the better conductor is that body. Inthis view, insulators may be said to be bodies whose particles can retainthe polarized state; whilst conductors are those whose particles cannot bepermanently polarized. If I be right in my view of induction, then Iconsider the reduction of these two effects (which have been so long helddistinct) to an action of contiguous particles obedient to one common law, as a very important result; and, on the other hand, the identity ofcharacter which the two acquire when viewed by the theory (1326. ), isadditional presumptive proof in favour of the correctness of the latter. 

 * * * * *

1339. That heat has great influence over simple conduction is well known(445. ), its effect being, in some cases, almost an entire change of thecharacters of the body (432. 1340. ). Harris has, however, shown that it inno respect affects gaseous bodies, or at least air[A]; and Davy has taughtus that, as a class, metals have their conducting power _diminished_ byit[B]. 

 [A] _Philosophical Transactions_, 1834, p. 230

 [B] Ibid. 1821, p. 431. 

1340. I formerly described a substance, sulphuret of silver, whoseconducting power was increased by heat (433. 437. 438. ); and I have sincethen met with another as strongly affected in the same way: this isfluoride of lead. When a piece of that substance, which had been fused andcooled, was introduced into the circuit of a voltaic battery, it stoppedthe current. Being heated, it acquired conducting powers before it wasvisibly red-hot in daylight; and even sparks could be taken against itwhilst still solid. The current alone then raised its temperature (as inthe case of sulphuret of silver) until it fused, after which it seemed toconduct as well as the metallic vessel containing it; for whether the wireused to complete the circuit touched the fused fluoride only, or was incontact with the platina on which it was supported, no sensible differencein the force of the current was observed. During all the time there wasscarcely a trace of decomposing action of the fluoride, and what did occur, seemed referable to the air and moisture of the atmosphere, and not toelectrolytic action. 

1341. I have now very little doubt that periodide of mercury (414. 448. 691. ) is a case of the same kind, and also corrosive sublimate (692. ). I amalso inclined to think, since making the above experiments, that theanomalous action of the protoxide of antimony, formerly observed anddescribed (693. 801. ), may be referred in part to the same cause. 

1342. I have no intention at present of going into the particular relationof heat and electricity, but we may hope hereafter to discover byexperiment the law which probably holds together all the above effects withthose of the _evolution_ and the _disappearance_ of heat by the current, and the striking and beautiful results of thermo-electricity, in one commonbond. 

¶ viii. _Electrolytic discharge. _

1343. I have already expressed in a former paper (1164. ), the view by whichI hope to associate ordinary induction and electrolyzation. Under thatview, the discharge of electric forces by electrolyzation is rather aneffect superadded, in a certain class of bodies, to those already describedas constituting induction and insulation, than one independent of anddistinct from these phenomena. 

1344. Electrolytes, as respects their insulating and conducting forces, belong to the general category of bodies (1320. 1334. ); and if they are inthe solid state (as nearly all can assume that state), they retain theirplace, presenting then no new phenomenon (426. &c. ); or if one occur, beingin so small a proportion as to be almost unimportant. When liquefied, theyalso belong to the same list whilst the electric intensity is below acertain degree; but at a given intensity (910. 912. 1007. ), fixed for each, and very low in all known cases, they play a new part, causing discharge inproportion (783. ) to the development of certain chemical effects ofcombination and decomposition; and at this point, move out from the generalclass of insulators and conductors, to form a distinct one by themselves. The former phenomena have been considered (1320. 1338. ); it is the latterwhich have now to be revised, and used as a test of the proposed theory ofinduction. 

1345. The theory assumes, that the particles of the dielectric (now anelectrolyte) are in the first instance brought, by ordinary inductiveaction, into a polarized state, and raised to a certain degree of tensionor intensity before discharge commences; the inductive state being, infact, a _necessary preliminary_ to discharge. By taking advantage of thosecircumstances which bear upon the point, it is not difficult to increasethe tension indicative of this state of induction, and so make the stateitself more evident. Thus, if distilled water be employed, and a longnarrow portion of it placed between the electrodes of a powerful voltaicbattery, we have at once indications of the intensity which can besustained at these electrodes by the inductive action through the water asa dielectric, for sparks may be obtained, gold leaves diverged, and Leydenbottles charged at their wires. The water is in the condition of thespermaceti (1322. 1323. ) a bad conductor and a bad insulator; but what itdoes insulate is by virtue of inductive action, and that induction is thepreparation for and precursor of discharge (1338. ). 

1346. The induction and tension which appear at the limits of the portionof water in the direction of the current, are only the sums of theinduction and tension of the contiguous particles between those limits; andthe limitation of the inductive tension, to a certain degree shows (timeentering in each case as an important element of the result), that when theparticles have acquired a certain relative state, _discharge_, or atransfer of forces equivalent to ordinary conduction, takes place. 

1347. In the inductive condition assumed by water before discharge comeson, the particles polarized are the particles of the _water_ that being thedielectric used[A]; but the discharge between particle and particle is not, as before, a mere interchange of their powers or forces at the polar parts, but an actual separation of them into their two elementary particles, theoxygen travelling in one direction, and carrying with it its amount of theforce it had acquired during the polarization, and the hydrogen doing thesame thing in the other direction, until they each meet the nextapproaching particle, which is in the same electrical state with that theyhave left, and by association of their forces with it, produce whatconstitutes discharge. This part of the action may be regarded as acarrying one (1319. 1572. 1622. ), performed by the constituent particles ofthe dielectric. The latter is always a compound body (664. 823. ); and bythose who have considered the subject and are acquainted with thephilosophical view of transfer which was first put forth by Grotthuss[B], its particles may easily be compared to a series of metallic conductorsunder inductive action, which, whilst in that state, are divisible intothese elementary moveable halves. 

 [A] See 1699-1708. --_Dec. 1838_

 [B] Annales de Chimie, lviii. 60. And lxiii, 20. 

1348. Electrolytic discharge depends, of necessity, upon the non-conductionof the dielectric as a whole, and there are two steps or acts in theprocess: first a polarization of the molecules of the substance and then alowering of the forces by the separation, advance in opposite directions, and recombination of the elements of the molecules, these being, as itwere, the halves of the originally polarized conductors or particles. 

1349. These views of the decomposition of electrolytes and the consequenteffect of discharge, which, as to the particular case, are the same withthose of Grotthuss (481. ) and Davy (482. ), though they differ from those ofBiot (487. ), De la Rive (490. ), and others, seem to me to be fully inaccordance not merely with the theory I have given of induction generally(1165. ), but with all the known _facts_ of common induction, conduction, and electrolytic discharge; and in that respect help to confirm in my mindthe truth of the theory set forth. The new mode of discharge whichelectrolyzation presents must surely be an evidence of the _action ofcontiguous particles_; and as this appears to depend directly upon aprevious inductive state, which is the same with common induction, itgreatly strengthens the argument which refers induction in all cases to anaction of contiguous particles also (1295, &c. ). 

1350. As an illustration of the condition of the polarized particles in adielectric under induction, I may describe an experiment. Put into a glassvessel some clear rectified oil of turpentine, and introduce two wirespassing through glass tubes where they coincide with the surface of thefluid, and terminating either in balls or points. Cut some very clean drywhite silk into small particles, and put these also into the liquid: thenelectrify one of the wires by an ordinary machine and discharge by theother. The silk will immediately gather from all parts of the liquid, andform a band of particles reaching from wire to wire, and if touched by aglass rod will show considerable tenacity; yet the moment the supply ofelectricity ceases, the band will fall away and disappear by the dispersionof its parts. The _conduction_ by the silk is in this case very small; andafter the best examination I could give to the effects, the impression onmy mind is, that the adhesion of the whole is due to the polarity whicheach filament acquires, exactly as the particles of iron between the polesof a horse-shoe magnet are held together in one mass by a similardisposition of forces. The particles of silk therefore represent to me thecondition of the molecules of the dielectric itself, which I assume to bepolar, just as that of the silk is. In all cases of conductive dischargethe contiguous polarized particles of the body are able to effect aneutralization of their forces with greater or less facility, as the silkdoes also in a very slight degree. Further we are not able to carry theparallel, except in imagination; but if we could divide each particle ofsilk into two halves, and let each half travel until it met and united withthe next half in an opposite state, it would then exert its carrying power(1347. ), and so far represent electrolytic discharge. 

1351. Admitting that electrolytic discharge is a consequence of previousinduction, then how evidently do its numerous cases point to induction incurved lines (521. 1216. ), and to the divergence or lateral action of thelines of inductive force (1231. ), and so strengthen that part of thegeneral argument in the former paper! If two balls of platina, forming theelectrodes of a voltaic battery, are put into a large vessel of dilutesulphuric acid, the whole of the surfaces are covered with the respectivegases in beautifully regulated proportions, and the mind has no difficultyin conceiving the direction of the curved lines of discharge, and even theintensity of force of the different lines, by the quantity of gas evolvedupon the different parts of the surface. From this condition of the linesof inductive force arise the general effects of diffusion; the appearanceof the anions or cathions round the edges and on the further side of theelectrodes when in the form of plates; and the manner in which the currentor discharge will follow all the forms of the electrolyte, howevercontorted. Hence, also, the effects which Nobili has so well examined anddescribed[A] in his papers on the distribution of currents in conductingmasses. All these effects indicate the curved direction of the currents ordischarges which occur in and through the dielectrics, and these are inevery case _preceded_ by equivalent inductive actions of the contiguousparticles. 

 [A] Bibliothèque Universelle, 1835, lix. 263. 416. 

1352. Hence also the advantage, when the exciting forces are weak orrequire assistance, of enlarging the mass of the electrolyte; of increasingthe size of the electrodes; of making the coppers surround the zincs:--allis in harmony with the view of induction which I am endeavouring toexamine; I do not perceive as yet one fact against it. 

1353. There are many points of _electrolytic discharge_ which ultimatelywill require to be very closely considered, though I can but slightly touchupon them. It is not that, as far as I have investigated them, they presentany contradiction to the view taken (for I have carefully, thoughunsuccessfully, sought for such cases), but simply want of time as yet topursue the inquiry, which prevents me from entering upon them here. 

1354. One point is, that different electrolytes or dielectrics requiredifferent initial intensities for their decomposition (912. ). This maydepend upon the degree of polarization which the particles require beforeelectrolytic discharge commences. It is in direct relation to the chemicalaffinity of the substances concerned; and will probably be found to have arelation or analogy to the specific inductive capacity of different bodies(1252. 1296. ). It thus promises to assist in causing the great truths ofthose extensive sciences, which are occupied in considering the forces ofthe particles of matter, to fall into much closer order and arrangementthan they have heretofore presented. 

1355. Another point is the facilitation of electrolytic conducting power ordischarge by the addition of substances to the dielectric employed. Thiseffect is strikingly shown where water is the body whose qualities areimproved, but, as yet, no general law governing all the phenomena has beendetected. Thus some acids, as the sulphuric, phosphoric, oxalic, andnitric, increase the power of water enormously; whilst others, as thetartaric and citric acids, give but little power; and others, again, as theacetic and boracic acids, do not produce a change sensible to thevoltameter (739. ). Ammonia produces no effect, but its carbonate does. Thecaustic alkalies and their carbonates produce a fair effect. Sulphate ofsoda, nitre (753. ), and many soluble salts produce much effect. Percyanideof mercury and corrosive sublimate produce no effect; nor does iodine, gum, or sugar, the test being a voltameter. In many cases the added substance isacted on either directly or indirectly, and then the phenomena are morecomplicated; such substances are muriatic acid (758. ), the solubleprotochlorides (766. ), and iodides (769. ), nitric acid (752. ), &c. In othercases the substance added is not, when alone, subject to or a conductor ofthe powers of the voltaic battery, and yet both gives and receives powerwhen associated with water. M. De la Rive has pointed this result out insulphurous acid[A], iodine and bromine[B]; the chloride of arsenic producesthe same effect. A far more striking case, however, is presented by thatvery influential body sulphuric acid (681. ): and probably phosphoric acidalso is in the same peculiar relation. 

 [A] Quarterly Journal, xxvii. 407. Or Bibliothèque Universelle, xl. 205. Kemp says sulphurous acid is a very good conductor, Quarterly Journal, 1831, p. 613. 

 [B] Quarterly Journal, xxiv, 465. Or Annales de Chimie, xxxv. 161. 

1356. It would seem in the cases of those bodies which suffer no changethemselves, as sulphuric acid (and perhaps in all), that they affect waterin its conducting power only as an electrolyte; for whether little or muchimproved, the decomposition is proportionate to the quantity of electricitypassing (727. 730. ), and the transfer is therefore due to electrolyticdischarge. This is in accordance with the fact already stated as regardswater (984. ), that the conducting power is not improved for electricity offorce below the electrolytic intensity of the substance acting as thedielectric; but both facts (and some others) are against the opinion whichI formerly gave, that the power of salts, &c. Might depend upon theirassumption of the liquid state by solution in the water employed (410. ). Itoccurs to me that the effect may perhaps be related to, and have itsexplanation in differences of specific inductive capacities. 

1357. I have described in the last paper, cases, where shell-lac wasrendered a conductor by absorption of ammonia (1294. ). The same effecthappens with muriatic acid; yet both these substances, when gaseous, arenon-conductors; and the ammonia, also when in strong solution (718. ). Mr. Harris has mentioned instances[A] in which the conducting power of metalsis seriously altered by a very little alloy. These may have no relation tothe former cases, but nevertheless should not be overlooked in the generalinvestigation which the whole question requires. 

 [A] Philosophical Transactions, 1827, p. 22. 

1358. Nothing is perhaps more striking in that class of dielectrics whichwe call electrolytes, than the extraordinary and almost complete suspensionof their peculiar mode of effecting discharge when they are rendered_solid_ (380, &c. ), even though the intensity of the induction actingthrough them may be increased a hundredfold or more (419. ). It not onlyestablishes a very general relation between the physical properties ofthese bodies and electricity acting by induction through them, but drawsboth their physical and chemical relations so near together, as to make ushope we shall shortly arrive at the full comprehension of the influencethey mutually possess over each other. 

¶ ix. _Disruptive discharge and insulation. _

1359. The next form of discharge has been distinguished by the adjective_disruptive_ (1319. ), as it in every case displaces more or less theparticles amongst and across which it suddenly breaks. I include under it, discharge in the form of sparks, brushes, and glow (1405. ), but exclude thecases of currents of air, fluids, &c. , which, though frequentlyaccompanying the former, are essentially distinct in their nature. 

1360. The conditions requisite for the production of an electric spark inits simplest form are well-known. An insulating dielectric must beinterposed between two conducting surfaces in opposite states ofelectricity, and then if the actions be continually increased in strength, or otherwise favoured, either by exalting the electric state of the twoconductors, or bringing them nearer to each other, or diminishing thedensity of the dielectric, a _spark_ at last appears, and the two forcesare for the time annihilated, for _discharge_ has occurred. 

1361. The conductors (which may be considered as the termini of theinductive action) are in ordinary cases most generally metals, whilst thedielectrics usually employed are common air and glass. In my view ofinduction, however, every dielectric becomes of importance, for as theresults are considered essentially dependent on these bodies, it was to beexpected that differences of action never before suspected would be evidentupon close examination, and so at once give fresh confirmation of thetheory, and open new doors of discovery into the extensive and variedfields of our science. This hope was especially entertained with respect tothe gases, because of their high degree of insulation, their uniformity inphysical condition, and great difference in chemical properties. 

1362. All the effects prior to the discharge are inductive; and the degreeof tension which it is necessary to attain before the spark passes istherefore, in the examination I am now making of the new view of induction, a very important point. It is the limit of the influence which thedielectric exerts in resisting discharge; it is a measure, consequently, ofthe conservative power of the dielectric, which in its turn may beconsidered as becoming a measure, and therefore a representative of theintensity of the electric forces in activity. 

1363. Many philosophers have examined the circumstances of this limitingaction in air, but, as far as I know, none have come near Mr. Harris as tothe accuracy with, and the extent to, which he has carried on hisinvestigations[A]. Some of his results I must very briefly notice, premising that they are all obtained with the use of air as the_dielectric_ between the conducting surfaces. 

 [A] Philosophical Transactions, 1834, p. 225. 

1364. First as to the _distance_ between the two balls used, or in otherwords, the _thickness_ of the dielectric across which the induction wassustained. The quantity of electricity, measured by a unit jar, orotherwise on the same principle with the unit jar, in the charged orinductive ball, necessary to produce spark discharge, was found to varyexactly with the distance between the balls, or between the dischargingpoints, and that under very varied and exact forms of experiment[A]. 

 [A] Philosophical Transactions, 1834, p. 225. 

1365. Then with respect to variation in the _pressure_ or _density_ of theair. The quantities of electricity required to produce discharge across a_constant_ interval varied exactly with variations of the density; thequantity of electricity and density of the air being in the same simpleratio. Or, if the quantity was retained the same, whilst the interval anddensity of the air were varied, then these were found in the inverse simpleratio of each other, the same quantity passing across twice the distancewith air rarefied to one-half[A]. 

 [A] Philosophical Transactions, 1834, p. 229. 

1366. It must be remembered that these effects take place without anyvariation of the _inductive_ force by condensation or rarefaction of theair. That force remains the same in air[A], and in all gases (1284. 1292. ), whatever their rarefaction may be. 

 [A] Philosophical Transactions, 1834, p. 237, 244. 

1367. Variation of the _temperature_ of the air produced no variation ofthe quantity of electricity required to cause discharge across a giveninterval[A]. 

 [A] Philosophical Transactions, 1834, p. 230

Such are the general results, which I have occasion for at present, obtained by Mr. Harris, and they appear to me to be unexceptionable. 

1368. In the theory of induction founded upon a molecular action of thedielectric, we have to look to the state of that body principally for thecause and determination of the above effects. Whilst the inductioncontinues, it is assumed that the particles of the dielectric are in acertain polarized state, the tension of this state rising higher in eachparticle as the induction is raised to a higher degree, either byapproximation of the inducing surfaces, variation of form, increase of theoriginal force, or other means; until at last, the tension of the particleshaving reached the utmost degree which they can sustain without subversionof the whole arrangement, discharge immediately after takes place. 

1369. The theory does not assume, however, that _all_ the particles of thedielectric subject to the inductive action are affected to the same amount, or acquire the same tension. What has been called the lateral action of thelines of inductive force (1231. 1297. ), and the diverging and occasionallycurved form of these lines, is against such a notion. The idea is, that anysection taken through the dielectric across the lines of inductive force, and including _all of them, _ would be equal, in the sum of the forces, tothe sum of the forces in any other section; and that, therefore, the wholeamount of tension for each such section would be the same. 

1370. Discharge probably occurs, not when all the particles have attainedto a certain degree of tension, but when that particle which is mostaffected has been exalted to the subverting or turning point (1410. ). Forthough _all_ the particles in the line of induction resist charge, and areassociated in their actions so as to give a sum of resisting force, yetwhen any one is brought up to the overturning point, _all_ must give way inthe case of a spark between ball and ball. The breaking down of that onemust of necessity cause the whole barrier to be overturned, for it was atits utmost degree of resistance when it possessed the aiding power of thatone particle, in addition to the power of the rest, and the power of thatone is now lost. Hence _tension_ or _intensity_[A] may, according to thetheory, be considered as represented by the particular condition of theparticles, or the amount in them of forced variation from their normalstate (1298. 1368. ). 

 [A] See Harris on proposed particular meaning of these terms, Philosophical Transactions, 1834, p. 222. 

1371. The whole effect produced by a charged conductor on a distantconductor, insulated or not, is by my theory assumed to be due to an actionpropagated from particle to particle of the intervening and insulatingdielectric, all the particles being considered as thrown for the time intoa forced condition, from which they endeavour to return to their normal ornatural state. The theory, therefore, seems to supply an easy explanationof the influence of _distance_ in affecting induction (1303. 1364. ). As thedistance is diminished induction increases; for there are then fewerparticles in the line of inductive force to oppose their united resistanceto the assumption of the forced or polarized state, and _vice versa. _Again, as the distance diminishes, discharge across happens with a lowercharge of electricity; for if, as in Harris's experiments (1364), theinterval be diminished to one-half, then half the electricity required todischarge across the first interval is sufficient to strike across thesecond; and it is evident, also, that at that time there are only half thenumber of interposed molecules uniting their forces to resist thedischarge. 

1372. The effect of enlarging the conducting surfaces which are opposed toeach other in the act of induction, is, if the electricity be limited inits supply, to lower the intensity of action; and this follows as a verynatural consequence from the increased area of the dielectric across whichthe induction is effected. For by diffusing the inductive action, which atfirst was exerted through one square inch of sectional area of thedielectric, over two or three square inches of such area, twice or threetimes the number of molecules of the dielectric are brought into thepolarized condition, and employed in sustaining the inductive action, andconsequently the tension belonging to the smaller number on which thelimited force was originally accumulated, must fall in a proportionatedegree. 

1373. For the same reason diminishing these opposing surfaces must increasethe intensity, and the effect will increase until the surfaces becomepoints. But in this case, the tension of the particles of the dielectricnext the points is higher than that of particles midway, because of thelateral action and consequent bulging, as it were, of the lines ofinductive force at the middle distance (1369. ). 

1374. The more exalted effects of induction on a point _p_, or any smallsurface, as the rounded end of a rod, when it is opposed to a largesurface, as that of a ball or plate, rather than to another point or end, the distance being in both cases the same, fall into harmonious relationwith my theory (1302. ). For in the latter case, the small surface _p_ isaffected only by those particles which are brought into the inductivecondition by the equally small surface of the opposed conductor, whereaswhen that is a ball or plate the lines of inductive force from the latterare concentrated, as it were, upon the end _p_. Now though the molecules ofthe dielectric against the large surface may have a much lower state oftension than those against the corresponding smaller surface, yet they arealso far more numerous, and, as the lines of inductive force convergetowards a point, are able to communicate to the particles contained in anycross section (1369. ) nearer the small surface an amount of tension equalto their own, and consequently much higher for each individual particle; sothat, at the surface of the smaller conductor, the tension of a particlerises much, and if that conductor were to terminate in a point, the tensionwould rise to an infinite degree, except that it is limited, as before(1368. ), by discharge. The nature of the discharge from small surfaces andpoints under induction will be resumed hereafter (1425. &c. )

1375. _Rarefaction_ of the air does not alter the _intensity_ of inductiveaction (1284. 1287. ); nor is there any reason, as far as I can perceive, why it should. If the quantity of electricity and the distance remain thesame, and the air be rarefied one-half, then, though one-half of theparticles of the dielectric are removed, the other half assume a doubledegree of tension in their polarity, and therefore the inductive forces arebalanced, and the result remains unaltered as long as the induction andinsulation are sustained. But the case of _discharge_ is very different;for as there are only half the number of dielectric particles in therarefied atmosphere, so these are brought up to the discharging intensityby half the former quantity of electricity; discharge, therefore, ensues, and such a consequence of the theory is in perfect accordance with Mr. Harris's results (1365. ). 

1376. The _increase_ of electricity required to cause discharge over thesame distance, when the pressure of the air or its density is increased, flows in a similar manner, and on the same principle (1375. ), from themolecular theory. 

1377. Here I think my view of induction has a decided advantage overothers, especially over that which refers the retention of electricity onthe surface of conductors in air to the _pressure of the atmosphere_(1305. ). The latter is the view which, being adopted by Poisson andBiot[A], is also, I believe, that generally received; and it associates twosuch dissimilar things, as the ponderous air and the subtile and evenhypothetical fluid or fluids of electricity, by gross mechanical relations;by the bonds of mere static pressure. My theory, on the contrary, sets outat once by connecting the electric forces with the particles of matter; itderives all its proofs, and even its origin in the first instance, fromexperiment; and then, without any further assumption, seems to offer atonce a full explanation of these and many other singular, peculiar, and, Ithink, heretofore unconnected effects. 

 [A] Encyclopædia Britannica, Supplement, vol. Iv. Article Electricity, pp. 76, 81. &c. 

1378. An important assisting experimental argument may here be adduced, derived from the difference of specific inductive capacity of differentdielectrics (1269. 1274. 1278. ). Consider an insulated sphere electrifiedpositively and placed in the centre of another and larger sphereuninsulated, a uniform dielectric, as air, intervening. The case is reallythat of my apparatus (1187. ), and also, in effect, that of any ballelectrified in a room and removed to some distance from irregularly-formedconductors. Whilst things remain in this state the electricity isdistributed (so to speak) uniformly over the surface of the electrifiedsphere. But introduce such a dielectric as sulphur or lac, into the spacebetween the two conductors on one side only, or opposite one part of theinner sphere, and immediately the electricity on the latter is diffusedunequally (1229. 1270. 1309. ), although the form of the conductingsurfaces, their distances, and the _pressure_ of the atmosphere remainperfectly unchanged. 

1379. Fusinieri took a different view from that of Poisson, Biot, andothers, of the reason why rarefaction of air caused easy diffusion ofelectricity. He considered the effect as due to the removal of the_obstacle_ which the air presented to the expansion of the substances fromwhich the electricity passed[A]. But platina balls show the phenomena _invacuo_ as well as volatile metals and other substances; besides which, whenthe rarefaction is very considerable, the electricity passes with scarcelyany resistance, and the production of no sensible heat; so that I thinkFusinieri's view of the matter is likely to gain but few assents. 

 [A] Bib. Univ. 1831, xlviii. 375. 

1380. I have no need to remark upon the discharging or collecting power offlame or hot air. I believe, with Harris, that the mere heat does nothing(1367. ), the rarefaction only being influential. The effect of rarefactionhas been already considered generally (1375. ); and that caused by the heatof a burning light, with the pointed form of the wick, and the carryingpower of the carbonaceous particles which for the time are associated withit, are fully sufficient to account for all the effects. 

1381. We have now arrived at the important question, how will the inductivetension requisite for insulation and disruptive discharge be sustained ingases, which, having the same physical state and also the _samepressure_ and the _same temperature_ as _air_, differ from it in specificgravity, in chemical qualities, and it may be in peculiar relations, whichnot being as yet recognized, are purely electrical (1361. )?

1382. Into this question I can enter now only as far as is essential forthe present argument, namely, that insulation and inductive tension do notdepend merely upon the charged conductors employed, but also, andessentially, upon the interposed dielectric, in consequence of themolecular action of its particles (1292. ). 

1383. A glass vessel _a_ (fig. 127. )[A] was ground at the top and bottom soas to be closed by two ground brass plates, _b_ and _c_; _b_ carried astuffing-box, with a sliding rod _d_ terminated by a brass ball _s_ below, and a ring above. The lower plate was connected with a foot, stop-cock, andsocket, _e_, _f_ and _g_; and also with a brass ball _l_, which by means ofa stem attached to it and entering the socket _g_, could be fixed atvarious heights. The metallic parts of this apparatus were not varnished, but the glass was well-covered with a coat of shell-lac previouslydissolved in alcohol. On exhausting the vessel at the air-pump it could befilled with any other gas than air, and, in such cases, the gas so passedin was dried whilst entering by fused chloride of calcium. 

 [A] The drawing is to a scale of 1/6. 

1384. The other part of the apparatus consisted of two insulating pillars, _h_ and _i_, to which were fixed two brass balls, and through these passedtwo sliding rods, _k_ and _m_, terminated at each end by brass balls; _n_is the end of an insulated conductor, which could be rendered eitherpositive or negative from an electrical machine; _o_ and _p_ are wiresconnecting it with the two parts previously described, and _q_ is a wirewhich, connecting the two opposite sides of the collateral arrangements, also communicates with a good discharging train _r_ (292. ). 

1385. It is evident that the discharge from the machine electricity maypass either between _s_ and _l_, or S and L. The regulation adopted in thefirst experiments was to keep _s_ and _l_ with their distance _unchanged_, but to introduce first one gas and then another into the vessel _a_, andthen balance the discharge at the one place against that at the other; forby making the interval at _a_ sufficiently small, all the discharge wouldpass there, or making it sufficiently large it would all occur at theinterval _v_ in the receiver. On principle it seemed evident, that in thisway the varying interval _u_ might be taken as a measure, or ratherindication of the resistance to discharge through the gas at the constantinterval _v_. The following are the constant dimensions. 

 Ball _s_ 0. 93 of an inch. Ball S 0. 96 of an inch. Ball _l_ 2. 02 of an inch. Ball L 0. 62 of an inch. Interval _v_ 0. 62 of an inch. 

1386. On proceeding to experiment it was found that when air or any gas wasin the receiver _a_, the interval _u_ was not a fixed one; it might bealtered through a certain range of distance, and yet sparks pass eitherthere or at _v_ in the receiver. The extremes were therefore noted, i. E. The greatest distance short of that at which the discharge _always_ tookplace at _v_ in the gas, and the least distance short of that at which it_always_ took place at _u_ in the air. Thus, with air in the receiver, theextremes at _u_ were 0. 56 and 0. 79 of an inch, the range of 0. 23 betweenthese distances including intervals at which sparks passed occasionallyeither at one place or the other. 

1387. The small balls _s_ and S could be rendered either positive ornegative from the machine, and as gases were expected and were found todiffer from each other in relation to this change (1399. ), the resultsobtained under these differences of charge were also noted. 

1388. The following is a Table of results; the gas named is that in thevessel _a_. The smallest, greatest, and mean interval at _u_ in air isexpressed in parts of an inch, the interval _v_ being constantly 0. 62 of aninch. 

 Smallest. Greatest. Mean. _| Air, _s_ and S, pos. 0. 60 0. 79 0. 695|_Air, _s_ and S, neg. 0. 59 0. 68 0. 635 _| Oxygen, _s_ and S, pos. 0. 41 0. 60 0. 505|_Oxygen, _s_ and S, neg. 0. 50 0. 52 0. 510 _| Nitrogen, _s_ and S, pos. 0. 55 0. 68 0. 615|_Nitrogen, _s_ and S, neg. 0. 59 0. 70 0. 645 _| Hydrogen, _s_ and S, pos. 0. 30 0. 44 0. 370|_Hydrogen, _s_ and S, neg. 0. 25 0. 30 0. 275 _| Carbonic acid, _s_ and S, pos. 0. 56 0. 72 0. 640|_Carbonic acid, _s_ and S, neg. 0. 58 0. 60 0. 590 _| Olefiant gas, _s_ and S, pos. 0. 64 0. 86 0. 750|_Olefiant gas, _s_ and S, neg. 0. 69 0. 77 0. 730 _| Coal gas, _s_ and S, pos. 0. 37 0. 61 0. 490|_Coal gas, _s_ and S, neg. 0. 47 0. 58 0. 525 _| Muriatic acid gas, _s_ and S, pos. 0. 89 1. 32 1. 105|_Muriatic acid gas, _s_ and S, neg. 0. 67 0. 75 0. 710

1389. The above results were all obtained at one time. On other occasionsother experiments were made, which gave generally the same results as toorder, though not as to numbers. Thus:

 Hydrogen, _s_ and S, pos. 0. 23 0. 57 0. 400 Carbonic acid, _s_ and S, pos. 0. 51 1. 05 0. 780 Olefiant gas, _s_ and S, pos. 0. 66 1. 27 0. 965

I did not notice the difference of the barometer on the days ofexperiment[A]. 

 [A] Similar experiments in different gases are described at 1507. 1508. --_Dec. 1838. _

1390. One would have expected only two distances, one for each interval, for which the discharge might happen either at one or the other; and thatthe least alteration of either would immediately cause one to predominateconstantly over the other. But that under common circumstances is not thecase. With air in the receiver, the variation amounted to 0. 2 of an inchnearly on the smaller interval of 0. 6, and with muriatic acid gas, thevariation was above 0. 4 on the smaller interval of 0. 9. Why is it that whena fixed interval (the one in the receiver) will pass a spark that cannot goacross 0. 6 of air at one time, it will immediately after, and apparentlyunder exactly similar circumstances, not pass a spark that can go across0. 8 of air?

1391. It is probable that part of this variation will be traced toparticles of dust in the air drawn into and about the circuit (1568. ). Ibelieve also that part depends upon a variable charged condition of thesurface of the glass vessel _a_. That the whole of the effect is nottraceable to the influence of circumstances in the vessel _a_, may bededuced from the fact, that when sparks occur between balls in free airthey frequently are not straight, and often pass otherwise than by theshortest distance. These variations in air itself, and at different partsof the very same balls, show the presence and influence of circumstanceswhich are calculated to produce effects of the kind now underconsideration. 

1392. When a spark had passed at either interval, then, generally, moretended to appear at the _same_ interval, as if a preparation had been madefor the passing of the latter sparks. So also on continuing to work themachine quickly the sparks generally followed at the same place. Thiseffect is probably due in part to the warmth of the air heated by thepreceding spark, in part to dust, and I suspect in part, to somethingunperceived as yet in the circumstances of discharge. 

1393. A very remarkable difference, which is _constant_ in its direction, occurs when the electricity communicated to the balls _s_ and S is changedfrom positive to negative, or in the contrary direction. It is that therange of variation is always greater when the small bulls are positive thanwhen they are negative. This is exhibited in the following Table, drawnfrom the former experiments. 

 Pos. Neg. In Air the range was 0. 19 0. 09 Oxygen 0. 19 0. 02 Nitrogen 0. 18 0. 11 Hydrogen 0. 14 0. 05 Carbonic acid 0. 16 0. 02 Olefiant gas 0. 22 0. 08 Coal gas 0. 24 0. 12 Muriatic acid 0. 43 0. 08

I have no doubt these numbers require considerable correction, but thegeneral result is striking, and the differences in several cases verygreat. 

 * * * * *

1394. Though, in consequence of the variation of the striking distance(1386. ), the interval in air fails to be a measure, as yet, of theinsulating or resisting power of the gas in the vessel, yet we may forpresent purposes take the mean interval as representing in some degree thatpower. On examining these mean intervals as they are given in the thirdcolumn (1388. ), it will be very evident, that gases, when employed asdielectrics, have peculiar electrical relations to insulation, andtherefore to induction, very distinct from such as might be supposed todepend upon their mere physical qualities of specific gravity or pressure. 

1395. First, it is clear that at the _same pressure_ they are not alike, the difference being as great as 37 and 110. When the small balls arecharged positively, and with the same surfaces and the same pressure, muriatic acid gas has three times the insulating or restraining power(1362. ) of hydrogen gas, and nearly twice that of oxygen, nitrogen, or air. 

1396. Yet it is evident that the difference is not due to specific gravity, for though hydrogen is the lowest, and therefore lower than oxygen, oxygenis much beneath nitrogen, or olefiant gas; and carbonic acid gas, thoughconsiderably heavier than olefiant gas or muriatic acid gas, is lower thaneither. Oxygen as a heavy, and olefiant as a light gas, are in strongcontrast with each other; and if we may reason of olefiant gas fromHarris's results with air (1365. ), then it might be rarefied to two-thirdsits usual density, or to a specific gravity of 9. 3 (hydrogen being 1), andhaving neither the same density nor pressure as oxygen, would have equalinsulating powers with it, or equal tendency to resist discharge. 

1397. Experiments have already been described (1291. 1292. ) which show thatthe gases are sensibly alike in their inductive capacity. This result isnot in contradiction with the existence of great differences in theirrestraining power. The same point has been observed already in regard todense and rare air (1375. ). 

1398. Hence arises a new argument proving that it cannot be mere pressureof the atmosphere which prevents or governs discharge (1377. 1378. ), but aspecific electric quality or relation of the gaseous medium. Hence alsoadditional argument for the theory of molecular inductive action. 

1399. Other specific differences amongst the gases may be drawn from thepreceding series of experiments, rough and hasty as they are. Thus thepositive and negative series of mean intervals do not give the samedifferences. It has been already noticed that the negative numbers arelower than the positive (1393. ), but, besides that, the _order_ of thepositive and negative results is not the same. Thus, on comparing the meannumbers (which represent for the present insulating tension, ) it appearsthat in air, hydrogen, carbonic acid, olefiant gas and muriatic acid, thetension rose higher when the smaller ball was made positive than whenrendered negative, whilst in oxygen, nitrogen, and coal gas, the reversewas the case. Now though the numbers cannot be trusted as exact, and thoughair, oxygen, and nitrogen should probably be on the same side, yet some ofthe results, as, for instance, those with muriatic acid, fully show apeculiar relation and difference amongst gases in this respect. This wasfurther proved by making the interval in air 0. 8 of an inch whilst muriaticacid gas was in the vessel _a_; for on charging the small balls _s_ and Spositively, _all_ the discharge took place through the _air_; but oncharging them negatively, _all_ the discharge took place through the_muriatic acid gas_. 

1400. So also, when the conductor _n_ was connected _only_ with themuriatic acid gas apparatus, it was found that the discharge was morefacile when the small ball _s_ was negative than when positive; for in thelatter case, much of the electricity passed off as brush discharge throughthe air from the connecting wire _p_ but in the former case, it all seemedto go through the muriatic acid. 

1401. The consideration, however, of positive and negative discharge acrossair and other gases will be resumed in the further part of this, or in thenext paper (1465. 1525. ). 

1402. Here for the present I must leave this part of the subject, which hadfor its object only to observe how far gases agreed or differed as to theirpower of retaining a charge on bodies acting by induction through them. Allthe results conspire to show that Induction is an action of contiguousmolecules (1295. &c. ); but besides confirming this, the first principleplaced for proof in the present inquiry, they greatly assist in developingthe specific properties of each gaseous dielectric, at the same timeshowing that further and extensive experimental investigation is necessary, and holding out the promise of new discovery as the reward of the labourrequired. 

 * * * * *

1403. When we pass from the consideration of dielectrics like the gases tothat of bodies having the liquid and solid condition, then our reasoningsin the present state of the subject assume much more of the character ofmere supposition. Still I do not perceive anything adverse to the theory, in the phenomena which such bodies present. If we take three insulatingdielectrics, as air, oil of turpentine, and shell-lac, and use the sameballs or conductors at the same intervals in these three substances, increasing the intensity of the induction until discharge take place, weshall find that it must be raised much higher in the fluid than for thegas, and higher still in the solid than for the fluid. Nor is thisinconsistent with the theory; for with the liquid, though its molecules arefree to move almost as easily as those of the gas, there are many moreparticles introduced into the given interval; and such is also the casewhen the solid body is employed. Besides that with the solid, the cohesiveforce of the body used will produce some effect; for though the productionof the polarized states in the particle of a solid may not be obstructed, but, on the contrary, may in some cases be even favoured (1164. 1344. ) byits solidity or other circumstances, yet solidity may well exert aninfluence on the point of final subversion, (just as it prevents dischargein an electrolyte, ) and so enable inductive intensity to rise to a muchhigher degree. 

1404. In the cases of solids and liquids too, bodies may, and most probablydo, possess specific differences as to their ability of assuming thepolarized state, and also as to the extent to which that polarity must risebefore discharge occurs. An analogous difference exists in the specificinductive capacities already pointed out in a few substances (1278. ) in thelast paper. Such a difference might even account for the various degrees ofinsulating and conducting power possessed by different bodies, and, if itshould be found to exist, would add further strength to the argument infavour of the molecular theory of inductive action. 

 * * * * *

1405. Having considered these various cases of sustained insulation innon-conducting dielectrics up to the highest point which they can attain, we find that they terminate at last in _disruptive discharge_; the peculiarcondition of the molecules of the dielectric which was necessary to thecontinuous induction, being equally essential to the occurrence of thateffect which closes all the phenomena. This discharge is not only in itsappearance and condition different to the former modes by which thelowering of the powers was effected (1320. 1343. ), but, whilst really thesame in principle, varies much from itself in certain characters, and thuspresents us with the forms of _spark_, _brush_, and _glow_ (1359. ). I willfirst consider _the spark_, limiting it for the present to the case ofdischarge between two oppositely electrified conducting surfaces. 

_The electric spark or flash. _

1406. The _spark_ is consequent upon a discharge or lowering of thepolarized inductive state of many dielectric particles, by a particularaction of a few of the particles occupying a very small and limited space;all the previously polarized particles returning to their first or normalcondition in the inverse order in which they left it, and uniting theirpowers meanwhile to produce, or rather to continue, (1417. --1436. ) thedischarge effect in the place where the subversion of force first occurred. My impression is, that the few particles situated where discharge occursare not merely pushed apart, but assume a peculiar state, a highly exultedcondition for the time, i. E. Have thrown upon them all the surroundingforces in succession, and rising up to a proportionate intensity ofcondition, perhaps equal to that of chemically combining atoms, dischargethe powers, possibly in the same manner as they do theirs, by someoperation at present unknown to us; and so the end of the whole. Theultimate effect is exactly as if a metallic wire had been put into theplace of the discharging particles; and it does not seem impossible thatthe principles of action in both cases, may, hereafter, prove to be thesame. 

1407. The _path of the spark_, or of the discharge, depends on the degreeof tension acquired by the particles in the line of discharge, circumstances, which in every common case are very evident and by thetheory easy to understand, rendering it higher in them than in theirneighbours, and, by exalting them first to the requisite condition, causingthem to determine the course of the discharge. Hence the selection of thepath, and the solution of the wonder which Harris has so well described[A]as existing under the old theory. All is prepared amongst the moleculesbeforehand, by the prior induction, for the path either of the electricspark or of lightning itself. 

 [A] Nautical Magazine, 1834, p 229. 

1408. The same difficulty is expressed as a principle by Nobili for voltaicelectricity, almost in Mr. Harris's words, namely[A], "electricity directsitself towards the point where it can most easily discharge itself, " andthe results of this as a principle he has well wrought out for the case ofvoltaic currents. But the _solution_ of the difficulty, or the proximatecause of the effects, is the same; induction brings the particles up to ortowards a certain degree of tension (1370. ); and by those which firstattain it, is the discharge first and most efficiently performed. 

 [A] Bibliothèque Universelle, 1835, lix. 275. 

1409. The _moment_ of discharge is probably determined by that molecule ofthe dielectric which, from the circumstances, has its tension most quicklyraised up to the maximum intensity. In all cases where the discharge passesfrom conductor to conductor this molecule must be on the surface of one ofthem; but when it passes between a conductor and a nonconductor, it is, perhaps, not always so (1453. ). When this particle has acquired its maximumtension, then the whole barrier of resistance is broken down in the line orlines of inductive action originating at it, and disruptive dischargeoccurs (1370. ): and such an inference, drawn as it is from the theory, seems to me in accordance with Mr. Harris's facts and conclusionsrespecting the resistance of the atmosphere, namely, that it is not reallygreater at any one discharging distance than another[A]. 

 [A] Philosophical Transactions, 1834, pp. 227, 229. 

1410. It seems probable, that the tension of a particle of the samedielectric, as air, which is requisite to produce discharge, is a _constantquantity_, whatever the shape of the part of the conductor with which it isin contact, whether ball or point; whatever the thickness or depth ofdielectric throughout which induction is exerted; perhaps, even, whateverthe state, as to rarefaction or condensation of the dielectric; andwhatever the nature of the conductor, good or bad, with which the particleis for the moment associated. In saying so much, I do not mean to excludesmall differences which may be caused by the reaction of neighbouringparticles on the deciding particle, and indeed, it is evident that theintensity required in a particle must be related to the condition of thosewhich are contiguous. But if the expectation should be found to approximateto truth, what a generality of character it presents! and, in thedefiniteness of the power possessed by a particular molecule, may we nothope to find an immediate relation to the force which, being electrical, isequally definite and constitutes chemical affinity?

1411. Theoretically it would seem that, at the moment of discharge by thespark in one line of inductive force, not merely would all the other linesthrow their forces into this one (1406. ), but the lateral effect, equivalent to a repulsion of these lines (1224. 1297. ), would be relievedand, perhaps, followed by a contrary action, amounting to a collapse orattraction of these parts. Having long sought for some transverse force instatical electricity, which should be the equivalent to magnetism or thetransverse force of current electricity, and conceiving that it might beconnected with the transverse action of the lines of inductive force, already described (1297. ), I was desirous, by various experiments, ofbringing out the effect of such a force, and making it tell upon thephenomena of electro-magnetism and magneto-electricity[A]. 

 [A] See further investigations of this subject, 1658-1666. 1709-1735. --_Dec. 1838. _

1412. Amongst other results, I expected and sought for the mutualaffection, or even the lateral coalition of two similar sparks, if theycould be obtained simultaneously side by side, and sufficiently near toeach other. For this purpose, two similar Leyden jars were supplied withrods of copper projecting from their balls in a horizontal direction, therods being about 0. 2 of an inch thick, and rounded at the ends. The jarswere placed upon a sheet of tinfoil, and so adjusted that their rods, _a_and _b_, were near together, in the position represented in plan at fig. 116: _c_ and _d_ were two brass balls connected by a brass rod andinsulated: _e_ was also a brass ball connected, by a wire, with the groundand with the tinfoil upon which the Leyden jars were placed. By laying aninsulated metal rod across from _a_ to _b_, charging the jars, and removingthe rod, both the jars could be brought up to the same intensity of charge(1370. ). Then, making the ball _e_ approach the ball _d_, at the moment thespark passed there, two sparks passed between the rods _n_, _o_, and theball _c_; and as far as the eye could judge, or the conditions determine, they were simultaneous. 

1413. Under these circumstances two modes of discharge took place; eithereach end had its own particular spark to the ball, or else one end only wasassociated by a spark with the ball, but was at the same time related tothe other end by a spark between the two. 

1414. When the ball _c_ was about an inch in diameter, the ends _n_ and_o_, about half an inch from it, and about 0. 4 of an inch from each other, the two sparks to the ball could be obtained. When for the purpose ofbringing the sparks nearer together, the ends, _n_ and _o_, were broughtcloser to each other, then, unless very carefully adjusted, only one endhad a spark with the ball, the other having a spark to it; and the leastvariation of position would cause either _n_ or _o_ to be the end which, giving the direct spark to the ball, was also the one through, or by meansof which, the other discharged its electricity. 

1415. On making the ball _c_ smaller, I found that then it was needful tomake the interval between the ends _n_ and _o_ larger in proportion to thedistance between them and the ball _c_. On making _c_ larger, I found Icould diminish the interval, and so bring the two simultaneous separatesparks closer together, until, at last, the distance between them was notmore at the widest part than 0. 6 of their whole length. 

1416. Numerous sparks were then passed and carefully observed. They werevery rarely straight, but either curved or bent irregularly. In the averageof cases they were, I think, decidedly convex towards each other; perhapstwo-thirds presented more or less of this effect, the rest bulging more orless outwards. I was never able, however, to obtain sparks which, separately leaving the ends of the wires _n_ and _o_, conjoined into onespark before they reached or communicated with the ball _c_. At present, therefore, though I think I saw a tendency in the sparks to unite, I cannotassert it as a fact. 

1417. But there is one very interesting effect here, analogous to, and itmay be in part the same with, that I was searching for: I mean theincreased facility of discharge where the spark passes. For instance, inthe cases where one end, as _n_, discharged the electricity of both ends tothe ball _c_, fig. 116, the electricity of the other end _o_, had to passthrough an interval of air 1. 5 times as great as that which it might havetaken, by its direct passage between the end and the ball itself. In suchcases, the eye could not distinguish, even by the use of Wheatstone'smeans[A], that the spark from the end _n_, which contained both portions ofelectricity, was a double spark. It could not have consisted of two sparkstaking separate courses, for such an effect would have been visible to theeye; but it is just possible, that the spark of the first end _n_ and itsjar, passing at the smallest interval of time before that of the other _o_had heated and expanded the air in its course, and made it so much morefavourable to discharge, that the electricity of the end _o_ preferredleaping across to it and taking a very circuitous route, rather than themore direct one to the ball. It must, however, be remarked, in answer tothis supposition, that the one spark between _d_ and _e_ would, by itsinfluence, tend to produce simultaneous discharges at _n_ and _o_, andcertainly did so, when no preponderance was given to one wire over theother, as to the previous inductive effect (1414. ). 

 [A] Philosophical Transactions, 1834, pp. 584, 585. 

1418. The fact, however, is, that disruptive discharge is favourable toitself. It is at the outset a case of tottering equilibrium: and if _time_be an element in discharge, in however minute a proportion (1436. ), thenthe commencement of the act at any point favours its continuance andincrease there, and portions of power will be discharged by a course whichthey would not otherwise have taken. 

1419. The mere heating and expansion of the air itself by the first portionof electricity which passes, must have a great influence in producing thisresult. 

1420. As to the result itself, we see its effect in every electric spark;for it is not the whole quantity which passes that determines thedischarge, but merely that small portion of force which brings the decidingmolecule (1370. ) up to its maximum tension; then, when its forces aresubverted and discharge begins, all the rest passes by the same course, from the influence of the favouring circumstances just referred to; andwhether it be the electricity on a square inch, or a thousand square inchesof charged glass, the discharge is complete. Hereafter we shall find theinfluence of this effect in the formation of brushes (1435. ); and it is notimpossible that we may trace it producing the jagged spark and the forkedlightning. 

 * * * * *

1421. The characters of the electric spark in _different gases_ vary, andthe variation _may_ be due simply to the effect of the heat evolved at themoment. But it may also be due to that specific relation of the particlesand the electric forces which I have assumed as the basis of a theory ofinduction; the facts do not oppose such a view; and in that view thevariation strengthens the argument for molecular action, as it would seemto show the influence of the latter in every part of the electrical effect(1423. 1454. ). 

1422. The appearances of the sparks in different gases have often beenobserved and recorded[A], but I think it not out of place to notice brieflythe following results; they were obtained with balls of brass, (platinasurfaces would have been better, ) and at common pressures. In _air_, thesparks have that intense light and bluish colour which are so well known, and often have faint or dark parts in their course, when the quantity ofelectricity passing is not great. In _nitrogen_, they are very beautiful, having the same general appearance as in air, but have decidedly morecolour of a bluish or purple character, and I thought were remarkablysonorous. In _oxygen_, the sparks were whiter than in air or nitrogen, andI think not so brilliant. In _hydrogen_, they had a very fine crimsoncolour, not due to its rarity, for the character passed away as theatmosphere was rarefied (1459. )[B]. Very little sound was produced in thisgas; but that is a consequence of its physical condition[C]. In _carbonicacid gas_, the colour was similar to that of the spark in air, but with alittle green in it: the sparks were remarkably irregular in form, more sothan in common air: they could also, under similar circumstances as to sizeof ball, &c. , be obtained much longer than in air, the gas showing asingular readiness to cause the discharge in the form of spark. In_muriatic acid gas_, the spark was nearly white: it was always brightthroughout, never presenting those dark parts which happen in air, nitrogen, and some other gases. The gas was dry, and during the wholeexperiment the surface of the glass globe within remained quite dry andbright. In _coal gas_, the spark was sometimes green, sometimes red, andoccasionally one part was green and another red: black parts also occurvery suddenly in the line of the spark, i. E. They are not connected by anydull part with bright portions, but the two seem to join directly one withthe other. 

 [A] See Van Marum's description of the Teylerian machine, vol. I. P. 112, and vol. Ii. P. 196; also Ency. Britan. , vol. Vi. , Article Electricity, pp. 505, 507. 

 [B] Van Marum says they are about four times as large in hydrogen as in air. Vol. I. P. 122. 

 [C] Leslie. Cambridge Phil. Transactions, 267. 

1423. These varieties of character impress my mind with a feeling, thatthey are due to a direct relation of the electric powers to the particlesof the dielectric through which the discharge occurs, and are not the mereresults of a casual ignition or a secondary kind of action of theelectricity, upon the particles which it finds in its course and thrustsaside in its passage (1454. ). 

1424. The spark may be obtained in media which are far denser than air, asin oil of turpentine, olive oil, resin, glass, &c. : it may also be obtainedin bodies which being denser likewise approximate to the condition ofconductors, as spermaceti, water, &c. But in these cases, nothing occurswhich, as far as I can perceive, is at all hostile to the general views Ihave endeavoured to advocate. 

_The electrical brush. _

1425. The _brush_ is the next form of disruptive discharge which I shallconsider. There are many ways of obtaining it, or rather of exalting itscharacters; and all these ways illustrate the principles upon which it isproduced. If an insulated conductor, connected with the positive conductorof an electrical machine, have a metal rod 0. 3 of an inch in diameterprojecting from it outwards from the machine, and terminating by a roundedend or a small ball, it will generally give good brushes; or, if themachine be not in good action, then many ways of assisting the formation ofthe brush can be resorted to; thus, the hand or any _large_ conductingsurface may be approached towards the termination to increase inductiveforce (1374. ): or the termination may be smaller and of badly conductingmatter, as wood: or sparks may be taken between the prime conductor of themachine and the secondary conductor to which the termination giving brushesbelongs: or, which gives to the brushes exceedingly fine characters andgreat magnitude, the air around the termination may be rarefied more orless, either by heat or the air-pump; the former favourable circumstancesbeing also continued. 

1426. The brush when obtained by a powerful machine on a ball about 0. 7 ofan inch in diameter, at the end of a long brass rod attached to thepositive prime conductor, had the general appearance as to form representedin fig. 117: a short conical bright part or root appeared at the middlepart of the ball projecting directly from it, which, at a little distancefrom the ball, broke out suddenly into a wide brush of pale ramificationshaving a quivering motion, and being accompanied at the same time with alow dull chattering sound. 

1427. At first the brush seems continuous, but Professor Wheatstone hasshown that the whole phenomenon consists of successive intermittingdischarges[A]. If the eye be passed rapidly, not by a motion of the head, but of the eyeball itself, across the direction of the brush, by firstlooking steadfastly about 10° or 15° above, and then instantly as muchbelow it, the general brush will be resolved into a number of individualbrushes, standing in a row upon the line which the eye passed over; eachelementary brush being the result of a single discharge, and the spacebetween them representing both the time during which the eye was passingover that space, and that which elapsed between one discharge and another. 

 [A] Philosophical Transactions, 1834, p. 586. 

1428. The single brushes could easily be separated to eight or ten timestheir own width, but were not at the same time extended, i. E. They did notbecome more indefinite in shape, but, on the contrary, less so, each beingmore distinct in form, ramification, and character, because of itsseparation from the others, in its effects upon the eye. Each, therefore, was instantaneous in its existence (1436. ). Each had the conical rootcomplete (1426. ). 

1429. On using a smaller ball, the general brush was smaller, and thesound, though weaker, more continuous. On resolving the brush into itselementary parts, as before, these were found to occur at much shorterintervals of time than in the former case, but still the discharge wasintermitting. 

1430. Employing a wire with a round end, the brush was still smaller, but, as before, separable into successive discharges. The sound, though feebler, was higher in pitch, being a distinct musical note. 

1431. The sound is, in fact, due to the recurrence of the noise of eachseparate discharge, and these, happening at intervals nearly equal underordinary circumstances, cause a definite note to be heard, which, rising inpitch with the increased rapidity and regularity of the intermittingdischarges, gives a ready and accurate measure of the intervals, and so maybe used in any case when the discharge is heard, even though theappearances may not be seen, to determine the element of _time_. So when, by bringing the hand towards a projecting rod or ball, the pitch of thetone produced by a brushy discharge increases, the effect informs us thatwe have increased the induction (1374. ), and by that means increased therapidity of the alternations of charge and discharge. 

1432. By using wires with finer terminations, smaller brushes wereobtained, until they could hardly be distinguished as brushes; but as longas _sound_ was heard, the discharge could be ascertained by the eye to beintermitting; and when the sound ceased, the light became _continuous_ as aglow (1359. 1405. 1526-1543. ). 

1433. To those not accustomed to use the eye in the manner I havedescribed, or, in cases where the recurrence is too quick for anyunassisted eye, the beautiful revolving mirror of Professor Wheatstone[A]will be useful for such developments of condition as those mentioned above. Another excellent process is to produce the brush or other luminousphenomenon on the end of a rod held in the hand opposite to a chargedpositive or negative conductor, and then move the rod rapidly from side toside whilst the eye remains still. The successive discharges occur ofcourse in different places, and the state of things before, at, and after asingle coruscation or brush can be exceedingly well separated. 

 [A] Philosophical Transactions, 1834, pp. 581, 585. 

1434. The _brush_ is in reality a discharge between a bad or anon-conductor and either a conductor or another non-conductor. Under commoncircumstances, the brush is a discharge between a conductor and air, and Iconceive it to take place in something like the following manner. When theend of an electrified rod projects into the middle of a room, inductiontakes place between it and the walls of the room, across the dielectric, air; and the lines of inductive force accumulate upon the end in greaterquantity than elsewhere, or the particles of air at the end of the rod aremore highly polarized than those at any other part of the rod, for thereasons already given (1374. ). The particles of air situated in sectionsacross these lines of force are least polarized in the sections towards thewalls and most polarized in those nearer to the end of the wires (1369. ):thus, it may well happen, that a particle at the end of the wire is at atension that will immediately terminate in discharge, whilst in those evenonly a few inches off, the tension is still beneath that point. But supposethe rod to be charged positively, a particle of air A, fig. 118, next it, being polarized, and having of course its negative force directed towardsthe rod and its positive force outwards; the instant that discharge takesplace between the positive force of the particle of the rod opposite theair and the negative force of the particle of air towards the rod, thewhole particle of air becomes positively electrified; and when, the nextinstant, the discharged part of the rod resumes its positive state byconduction from the surface of metal behind, it not only acts on theparticles beyond A, by throwing A into a polarized state again, but Aitself, because of its charged state, exerts a distinct inductive acttowards these further particles, and the tension is consequently so muchexalted between A and B, that discharge takes place there also, as well asagain between the metal and A. 

1435. In addition to this effect, it has been shown, that, the act ofdischarge having once commenced, the whole operation, like a case ofunstable equilibrium, is hastened to a conclusion (1370. 1418. ), the restof the act being facilitated in its occurrence, and other electricity thanthat which caused the first necessary tension hurrying to the spot. When, therefore, disruptive discharge has once commenced at the root of a brush, the electric force which has been accumulating in the conductor attached tothe rod, finds a more ready discharge there than elsewhere, and will atonce follow the course marked out as it were for it, thus leaving theconductor in a partially discharged state, and the air about the end of thewire in a charged condition; and the time necessary for restoring the fullcharge of the conductor, and the dispersion of the charged air in a greateror smaller degree, by the joint forces of repulsion from the conductor andattraction towards the walls of the room, to which its inductive action isdirected, is just that time which forms the interval between brush andbrush (1420. 1427. 1431. 1447. ). 

1436. The words of this description are long, but there is nothing in theact or the forces on which it depends to prevent the discharge being_instantaneous_, as far as we can estimate and measure it. Theconsideration of _time_ is, however, important in several points of view(1418. ), and in reference to disruptive discharge, it seemed from theoryfar more probable that it might be detected in a brush than in a spark; forin a brush, the particles in the line through which the discharge passesare in very different states as to intensity, and the discharge is alreadycomplete in its act at the root of the brush, before the particles at theextremity of the ramifications have yet attained their maximum intensity. 

1437. I consider _brush_ discharge as probably a successive effect in thisway. Discharge begins at the root (1426. 1553. ), and, extending itself insuccession to all parts of the single brush, continues to go on at the rootand the previously formed parts until the whole brush is complete; then, bythe fall in intensity and power at the conductor, it ceases at once in allparts, to be renewed, when that power has risen again to a sufficientdegree. But in a _spark_, the particles in the line of discharge being, from the circumstances, nearly alike in their intensity of polarization, suffer discharge so nearly at the same moment as to make the time quiteinsensible to us. 

1438. Mr. Wheatstone has already made experiments which fully illustratethis point. He found that the brush generally had a sensible duration, butthat with his highest capabilities he could not detect any such effect inthe spark[A]. I repeated his experiment on the brush, though with moreimperfect means, to ascertain whether I could distinguish a longer durationin the stem or root of the brush than in the extremities, and theappearances were such as to make me think an effect of this kind wasproduced. 

 [A] Philosophical Transactions, 1836, pp. 586, 590. 

1439. That the discharge breaks into several ramifications, and by thempasses through portions of air alike, or nearly alike, as to polarizationand the degree of tension the particles there have acquired, is a verynatural result of the previous state of things, and rather to be expectedthan that the discharge should continue to go straight out into space in asingle line amongst those particles which, being at a distance from the endof the rod, are in a lower state of tension than those which are near: andwhilst we cannot but conclude, that those parts where the branches of asingle brush appear, are more favourably circumstanced for discharge thanthe darker parts between the ramifications, we may also conclude, that inthose parts where the light of concomitant discharge is equal, there thecircumstances are nearly equal also. The single successive brushes are byno means of the same particular shape even when they are observed withoutdisplacement of the rod or surrounding objects (1427. 1433. ), and thesuccessive discharges may be considered as taking place into the mass ofair around, through different roads at each brush, according as minutecircumstances, such as dust, &c. (1391. 1392. ), may have favoured thecourse by one set of particles rather than another. 

1440. Brush discharge does not essentially require any current of themedium in which the brush appears: the current almost always occurs, but isa consequence of the brush, and will be considered hereafter (1562-1610. ). On holding a blunt point positively charged towards uninsulated water, astar or glow appeared on the point, a current of air passed from it, andthe surface of the water was depressed; but on bringing the point so nearthat sonorous brushes passed, then the current of air instantly ceased, andthe surface of the water became level. 

1441. The discharge by a brush is not to all the particles of air that arenear the electrified conductor from which the brush issues; only thoseparts where the ramifications pass are electrified: the air in the centraldark parts between them receives no charge, and, in fact, at the time ofdischarge, has its electric and inductive tension considerably lowered. Forconsider fig. 128 to represent a single positive brush;--the inductionbefore the discharge is from the end of the rod outwards, in diverginglines towards the distant conductors, as the walls of the room, &c. , and aparticle at _a_ has polarity of a certain degree of tension, and tends witha certain force to become charged; but at the moment of discharge, the airin the ramifications _b_ and _d_, acquiring also a positive state, opposesits influence to that of the positive conductor on _a_, and the tension ofthe particle at _a_ is therefore diminished rather than increased. Thecharged particles at _b_ and _d_ are now inductive bodies, but their linesof inductive action are still outwards towards the walls of the room; thedirection of the polarity and the tendency of other particles to chargefrom these, being governed by, or in conformity with, these lines of force. 

1442. The particles that are charged are probably very highly charged, but, the medium being a non-conductor, they cannot communicate that state totheir neighbours. They travel, therefore, under the influence of therepulsive and attractive forces, from the charged conductor towards thenearest uninsulated conductor, or the nearest body in a different state tothemselves, just as charged particles of dust would travel, and are thendischarged; each particle acting, in its course, as a centre of inductiveforce upon any bodies near which it may come. The travelling of thesecharged particles when they are numerous, causes wind and currents, butthese will come into consideration under _carrying discharge_ (1319. 1562. &c. ). 

1443. When air is said to be electrified, and it frequently assumes thisstate near electrical machines, it consists, according to my view, of amixture of electrified and unelectrified particles, the latter being invery large proportion to the former. When we gather electricity from air, by a flame or by wires, it is either by the actual discharge of theseparticles, or by effects dependent on their inductive action, a case ofeither kind being produceable at pleasure. That the law of equality betweenthe two forces or forms of force in inductive action is as strictlypreserved in these as in other cases, is fully shown by the fact, formerlystated (1173. 1174. ), that, however strongly air in a vessel might becharged positively, there was an exactly equal amount of negative force onthe inner surface of the vessel itself, for no residual portion of eitherthe one or the other electricity could be obtained. 

1444. I have nowhere said, nor does it follow, that the air is charged onlywhere the luminous brush appears. The charging may extend beyond thoseparts which are visible, i. E. Particles to the right or left of the linesof light may receive electricity, the parts which are luminous being soonly because much electricity is passing by them to other parts (1437. );just as in a spark discharge the light is greater as more electricitypasses, though it has no necessary relation to the quantity required tocommence discharge (1370. 1420. ). Hence the form we see in a brush may byno means represent the whole quantity of air electrified; for an invisibleportion, clothing the visible form to a certain depth, may, at the sametime, receive its charge (1552. ). 

1445. Several effects which I have met with in muriatic acid gas tend tomake me believe, that that gaseous body allows of a dark discharge. At thesame time, it is quite clear from theory, that in some gases, the reverseof this may occur, i. E. That the charging of the air may not extend even sofar as the light. We do not know as yet enough of the electric light to beable to state on what it depends, and it is very possible that, whenelectricity bursts forth into air, all the particles of which are in astate of tension, light may be evolved by such as, being very near to, arenot of, those which actually receive a charge at the time. 

1446. The further a brush extends in a gas, the further no doubt is thecharge or discharge carried forward; but this may vary between differentgases, and yet the intensity required for the first moment of discharge notvary in the same, but in some other proportion. Thus with respect tonitrogen and muriatic acid gases, the former, as far as my experiments haveproceeded, produces far finer and larger brushes than the latter (1458. 1462. ), but the intensity required to commence discharge is much higher forthe muriatic acid than the nitrogen (1395. ). Here again, therefore, as inmany other qualities, specific differences are presented by differentgaseous dielectrics, and so prove the special relation of the latter to theact and the phenomena of induction. 

1447. To sum up these considerations respecting the character and conditionof the brush, I may state that it is a spark to air; a diffusion ofelectric force to matter, not by conduction, but disruptive discharge, adilute spark which, passing to very badly conducting matter, frequentlydischarges but a small portion of the power stored up in the conductor; foras the air charged reacts on the conductor, whilst the conductor, by lossof electricity, sinks in its force (1435. ), the discharge quickly ceases, until by the dispersion of the charged air and the renewal of the excitedconditions of the conductor, circumstances have risen up to their firsteffective condition, again to cause discharge, and again to fall and rise, 1448. The brush and spark gradually pass into one another, Making a smallball positive by a good electrical machine with a large prime conductor, and approaching a large uninsulated discharging ball towards it, verybeautiful variations from the spark to the brush may be obtained. Thedrawings of long and powerful sparks, given by Van Marum[A], Harris[B], andothers, also indicate the same phenomena. As far as I have observed, whenever the spark has been brushy in air of common pressures, the whole ofthe electricity has not been discharged, but only portions of it, more orless according to circumstances; whereas, whenever the effect has been adistinct spark throughout the whole of its course, the discharge has beenperfect, provided no interruption had been made to it elsewhere, in thedischarging circuit, than where the spark occurred. 

 [A] Description of the Teylerian machine, vol. I. Pp. 28. 32. ; vol. Ii. P. 226, &c. 

 [B] Philosophical Transactions, 1834, p. 213. 

1449. When an electrical brush from an inch to six inches in length or moreis issuing into free air, it has the form given, fig. 117. But if the hand, a ball, of any knobbed conductor be brought near, the extremities of thecoruscations turn towards it and each other, and the whole assumes variousforms according to circumstances, as in figs. 119, 120, and 121. Theinfluence of the circumstances in each case is easily traced, and I mightdescribe it here, but that I should be ashamed to occupy the time of theSociety in things so evident. But how beautifully does the curvature of theramifications illustrate the curved form of the lines of inductive forceexisting previous to the discharge! for the former are consequences of thelatter, and take their course, in each discharge, where the previousinductive tension had been raised to the proper degree. They representthese curves just as well as iron filings represent magnetic curves, thevisible effects in both cases being the consequences of the action of theforces in _the places where_ the effects appear. The phenomena, therefore, constitute additional and powerful testimony (1216. 1230. ) to that alreadygiven in favour both of induction through dielectrics in curved lines(1231. ), and of the lateral relation of these lines, by an effectequivalent to a repulsion producing divergence, or, as in the casesfigured, the bulging form. 

1450. In reference to the theory of molecular inductive action, I may alsoadd, the proof deducible from the long brushy ramifying spark which, may beobtained between a small ball on the positive conductor of an electricalmachine, and a larger one at a distance (1448. 1504. ). What a fineillustration that spark affords of the previous condition of _all_ theparticles of the dielectric between the surfaces of discharge, and howunlike the appearances are to any which would be deduced from the theorywhich assumes inductive action to be action at a distance, in straightlines only; and charge, as being electricity retained upon the surface ofconductors by the mere pressure of the atmosphere!

 * * * * *

1451. When the brush is obtained in rarefied air, the appearances varygreatly, according to circumstances, and are exceedingly beautiful. Sometimes a brush may be formed of only six or seven branches, these beingbroad and highly luminous, of a purple colour, and in some parts an inch ormore apart: by a spark discharge at the prime conductor (1455. ) singlebrushes may be obtained at pleasure. Discharge in the form of a brush isfavoured by rarefaction of the air, in the same manner and for the samereason as discharge in the form of a spark (1375. ); but in every case thereis previous induction and charge through the dielectric, and polarity ofits particles (1437. ), the induction being, as in any other instance, alternately raised by the machine and lowered by the discharge. In certainexperiments the rarefaction was increased to the utmost degree, and theopposed conducting surfaces brought as near together as possible withoutproducing glow (1529. ): the brushes then contracted in their lateraldimensions, and recurred so rapidly as to form an apparently continuous arcof light from metal to metal. Still the discharge could be observed tointermit (1427. ), so that even under these high conditions, inductionpreceded each single brush, and the tense polarized condition of thecontiguous particles was a necessary preparation for the discharge itself. 

1452. The brush form of disruptive discharge may be obtained not only inair and gases, but also in much denser media. I procured it in _oil ofturpentine_ from the end of a wire going through a glass tube into thefluid contained in a metal vessel. The brush was small and very difficultto obtain; the ramifications were simple, and stretched out from eachother, diverging very much. The light was exceedingly feeble, a perfectlydark room being required for its observation. When a few solid particles, as of dust or silk, were in the liquid, the brush was produced with muchgreater facility. 

1453. The running together or coalescence of different lines of discharge(1412. ) is very beautifully shown in the brush in air. This point maypresent a little difficulty to those who are not accustomed to see in everydischarge an equal exertion of power in opposite directions, a positivebrush being considered by such (perhaps in consequence of the common phrase_direction of a current_) as indicating a breaking forth in differentdirections of the original force, rather than a tendency to convergence andunion in one line of passage. But the ordinary case of the brush may becompared, for its illustration, with that in which, by holding the knuckleopposite to highly excited glass, a discharge occurs, the ramifications ofa brush then leading from the glass and converging into a spark on theknuckle. Though a difficult experiment to make, it is possible to obtaindischarge between highly excited shell-lac and the excited glass of amachine: when the discharge passes, it is, from the nature of the chargedbodies, brush at each end and spark in the middle, beautifully illustratingthat tendency of discharge to facilitate like action, which I havedescribed in a former page (1418. ). 

1454. The brush has _specific characters_ in different gases, indicating arelation to the particles of these bodies even in a stronger degree thanthe spark (1422. 1423. ). This effect is in strong contrast with thenon-variation caused by the use of different substances as _conductors_from which the brushes are to originate. Thus, using such bodies as wood, card, charcoal, nitre, citric acid, oxalic acid, oxide of lead, chloride oflead, carbonate of potassa, potassa fusa, strong solution of potash, oil ofvitriol, sulphur, sulphuret of antimony, and hæmatite, no variation in thecharacter of the brushes was obtained, except that (dependent upon theireffect as better or worse conductors) of causing discharge with more orless readiness and quickness from the machine[A]. 

 [A] Exception must, of course, be made of those cases where the root of the brush, becoming a spark, causes a little diffusion or even decomposition of the matter there, and so gains more or less of a particular colour at that part. 

1455. The following are a few of the effects I observed in different gassesat the positively charged surfaces, and with atmospheres varying in theirpressure. The general effect of rarefaction was the same for all the gases:at first, sparks passed; these gradually were converted into brushes, whichbecame larger and more distinct in their ramifications, until, upon furtherrarefaction, the latter began to collapse and draw in upon each other, tillthey formed a stream across from conductor to conductor: then a few lateralstreams shot out towards the glass of the vessel from the conductors; thesebecame thick and soft in appearance, and were succeeded by the fullconstant glow which covered the discharging wire. The phenomena varied withthe size of the vessel (1477. ), the degree of rarefaction, and thedischarge of electricity from the machine. When the latter was insuccessive sparks, they were most beautiful, the effect of a spark from asmall machine being equal to, and often surpassing, that produced by the_constant_ discharge of a far more powerful one. 

1456. _Air. _--Fine positive brushes are easily obtained in air at commonpressures, and possess the well-known purplish light. When the air israrefied, the ramifications are very long, filling the globe (1477. ); thelight is greatly increased, and is of a beautiful purple colour, with anoccasional rose tint in it. 

1457. _Oxygen. _--At common pressures, the brush is very close andcompressed, and of a dull whitish colour. In rarefied oxygen, the form andappearance are better, the colour somewhat purplish, but all the charactersvery poor compared to those in air. 

1458. _Nitrogen_ gives brushes with great facility at the positive surface, far beyond any other gas I have tried: they are almost always fine in form, light, and colour, and in rarefied nitrogen, are magnificent. They surpassthe discharges in any other gas as to the quantity of light evolved. 

1459. _Hydrogen_, at common pressures, gave a better brush than oxygen, butdid not equal nitrogen; the colour was greenish gray. In rarefied hydrogen, the ramifications were very fine in form and distinctness, but pale incolour, with a soft and velvety appearance, and not at all equal to thosein nitrogen. In the rarest state of the gas, the colour of the light was apale gray green. 

1460. _Coal gas. _--The brushes were rather difficult to produce, thecontrast with nitrogen being great in this respect. They were short andstrong, generally of a greenish colour, and possessing much of the sparkcharacter: for, occurring on both the positive and negative terminations, often when there was a dark interval of some length between the twobrushes, still the quick, sharp sound of the spark was produced, as if thedischarge had been sudden through this gas, and partaking, in that respect, of the character of a spark. In rare coal gas, the brush forms were better, but the light very poor and the colour gray. 

1461. _Carbonic acid gas_ produces a very poor brush at common pressures, as regards either size, light, or colour; and this is probably connectedwith the tendency which this gas has to discharge the electricity as aspark (1422. ). In rarefied carbonic acid, the brush is better in form, butweak as to light, being of a dull greenish or purplish line, varying withthe pressure and other circumstances. 

1462. _Muriatic acid gas. _--It is very difficult to obtain the brush inthis gas at common pressures. On gradually increasing the distance of therounded ends, the sparks suddenly ceased when the interval was about aninch, and the discharge, which was still through the gas in the globe, wassilent and dark. Occasionally a very short brush could for a few moments beobtained, but it quickly disappeared. Even when the intermitting sparkcurrent (1455. ) from the machine was used, still I could only withdifficulty obtain a brush, and that very short, though I used rods withrounded terminations (about 0. 25 of an inch in diameter) which had beforegiven them most freely in air and nitrogen. During the time of thisdifficulty with the muriatic gas, magnificent brushes were passing off fromdifferent parts of the machine into the surrounding air. On rarefying thegas, the formation of the brush was facilitated, but it was generally of alow squat form, very poor in light, and very similar on both the positiveand negative surfaces. On rarefying the gas still more, a few largeramifications were obtained of a pale bluish colour, utterly unlike thosein nitrogen. 

 * * * * *

1463. In all the gases, the different forms of disruptive discharge may belinked together and gradually traced from one extreme to the other, i. E. From the spark to the glow (1405. 1526. ), or, it may be, to a still furthercondition to be called dark discharge (1544-1560. ); but it is, nevertheless, very surprising to see what a specific character each keepswhilst under the predominance of the general law. Thus, in muriatic acid, the brush is very difficult to obtain, and there comes in its place almosta dark discharge, partaking of the readiness of the spark action. Moreover, in muriatic acid, I have _never_ observed the spark with any dark intervalin it. In nitrogen, the spark readily changes its character into that ofbrush. In carbonic acid gas, there seems to be a facility to occasion sparkdischarge, whilst yet that gas is unlike nitrogen in the facility of thelatter to form brushes, and unlike muriatic acid in its own facility tocontinue the spark. These differences add further force, first to theobservations already made respecting the spark in various gases (1422. 1423. ), and then, to the proofs deducible from it, of the relation of theelectrical forces to the particles of matter. 

1464. The peculiar characters of nitrogen in relation to the electricdischarge (1422. 1458. ) must, evidently, have an important influence overthe form and even the occurrence of lightning. Being that gas which mostreadily produces coruscations, and, by them, extends discharge to a greaterdistance than any other gas tried, it is also that which constitutesfour-fifths of our atmosphere; and as, in atmospheric electrical phenomena, one, and sometimes both the inductive forces are resident on the particlesof the air, which, though probably affected as to conducting power by theaqueous particles in it, cannot be considered as a good conductor; so thepeculiar power possessed by nitrogen, to originate and effect discharge inthe form of a brush or of ramifications, has, probably, an importantrelation to its electrical service in nature, as it most seriously affectsthe character and condition of the discharge when made. The whole subjectof discharge from and through gases is of great interest, and, if only inreference to atmospheric electricity, deserves extensive and closeexperimental investigation. 

_Difference of discharge at the positive and negative conducting surfaces. _

1465. I have avoided speaking of this well-known phenomenon more than wasquite necessary, that I might bring together here what I have to say on thesubject. When the brush discharge is observed in air at the positive andnegative surfaces, there is a very remarkable difference, the true and fullcomprehension of which would, no doubt, be of the utmost importance to thephysics of electricity; it would throw great light on our present subject, i. E. The molecular action of dielectrics under induction, and itsconsequences; and seems very open to, and accessible by, experimentalinquiry. 

1466. The difference in question used to be expressed in former times bysaying, that a point charged positively gave brushes into the air, whilstthe same point charged negatively gave a star. This is true only of badconductors, or of metallic conductors charged intermittingly, or otherwisecontrolled by collateral induction. If metallic points project _freely_into the air, the positive and negative light upon them differ very littlein appearance, and the difference can be observed only upon closeexamination. 

1467. The effect varies exceedingly under different circumstances, but, aswe must set out from some position, may perhaps be stated thus: if ametallic wire with a rounded termination in free air be used to produce thebrushy discharge, then the brushes obtained when the wire is chargednegatively are very poor and small, by comparison with those produced whenthe charge is positive. Or if a large metal ball connected with theelectrical machine be charged _positively_, and a fine uninsulated point begradually brought towards it, a star appears on the point when at aconsiderable distance, which, though it becomes brighter, does not changeits form of a star until it is close up to the ball: whereas, if the ballbe charged negatively, the point at a considerable distance has a star onit as before; but when brought nearer, (in my case to the distance of 1-1/2inch, ) a brush formed on it, extending to the negative ball; and when stillnearer, (at 1/8 of an inch distance, ) the brush ceased, and bright sparkspassed. These variations, I believe, include the whole series ofdifferences, and they seem to show at once, that the negative surface tendsto retain its discharging character unchanged, whilst the positive surface, under similar circumstances, permits of great variation. 

1468. There are several points in the character of the negative dischargeto air which it is important to observe. A metal rod, 0. 3 of an inch indiameter, with a rounded end projecting into the air, was chargednegatively, and gave a short noisy brush (fig. 122. ). It was ascertainedboth by sight (1427. 1433. ) and sound (1431. ), that the successivedischarges were very rapid in their recurrence, being seven or eight timesmore numerous in the same period, than those produced when the rod wascharged positively to an equal degree. When the rod was positive, it waseasy, by working the machine a little quicker, to replace the brush by aglow (1405. 1463. ), but when it was negative no efforts could produce thischange. Even by bringing the hand opposite the wire, the only effect was toincrease the number of brush discharges in a given period, raising at thesame time the sound to a higher pitch. 

1469. A point opposite the negative brush exhibited a star, and as it wasapproximated caused the size and sound of the negative brush to diminish, and, at last, to cease, leaving the negative end silent and dark, yeteffective as to discharge. 

1470. When the round end of a smaller wire (fig. 123. ) was advanced towardsthe negative brush, it (becoming positive by induction) exhibited the quietglow at 8 inches distance, the negative brush continuing. When nearer, thepitch of the sound of the negative brush rose, indicating quickerintermittences (1431. ); still nearer, the positive end threw offramifications and distinct brushes; at the same time, the negative brushcontracted in its lateral directions and collected together, giving apeculiar narrow longish brush, in shape like a hair pencil, the two brushesexisting at once, but very different in their form and appearance, andespecially in the more rapid recurrence of the negative discharges than ofthe positive. On using a smaller positive wire for the same experiment, theglow first appeared on it, and then the brush, the negative brush beingaffected at the same time; and the two at one distance became exceedinglyalike in appearance, and the sounds, I thought, were in unison; at allevents they were in harmony, so that the intermissions of discharge wereeither isochronous, or a simple ratio existed between the intervals. With ahigher action of the machine, the wires being retained unaltered, thenegative surface became dark and silent, and a glow appeared on thepositive one. A still higher action changed the latter into a spark. Finerpositive wires gave other variations of these effects, the description ofwhich I must not allow myself to go into here. 

1471. A thinner rod was now connected with the negative conductor in placeof the larger one (1468. ), its termination being gradually diminished to ablunt point, as in fig. 124; and it was beautiful to observe that, notwithstanding the variation of the brush, the same general order ofeffects was produced. The end gave a small sonorous negative brush, whichthe approach of the hand or a large conducting surface did not alter, untilit was so near as to produce a spark. A fine point opposite to it wasluminous at a distance; being nearer it did not destroy the light and soundof the negative brush, but only tended to have a brush produced on itself, which, at a still less distance, passed into a spark joining the twosurfaces. 

1472. When the distinct negative and positive brushes are producedsimultaneously in relation to each other in air, the former almost alwayshas a contracted form, as in fig. 125, very much indeed resembling thefigure which the positive brush itself has when influenced by the lateralvicinity of positive parts acting by induction. Thus a brush issuing from apoint in the re-entering angle of a positive conductor has the samecompressed form (fig. 126. ). 

1473. The character of the negative brush is not affected by the chemicalnature of the substances of the conductors (1454. ), but only by theirpossession of the conducting power in a greater or smaller degree. 

1474. Rarefaction of common air about a negative ball or blunt pointfacilitated the development of the negative brush, the effect being, Ithink, greater than on a positive brush, though great on both. Extensiveramifications could be obtained from a ball or end electrified negativelyto the plate of the air-pump on which the jar containing it stood. 

1475. A very important variation of the relative forms and conditions ofthe positive and negative brush takes place on varying the dielectric inwhich they are produced. The difference is so very great that it points toa specific relation of this form of discharge to the particular gas inwhich it takes place, and opposes the idea that gases are but obstructionsto the discharge, acting one like another and merely in proportion to theirpressure (1377. ). 

1476. In _air_, the superiority of the positive brush is well known (1467. 1472. ). In _nitrogen_, it is as great or even greater than in air (1458. ). In _hydrogen_, the positive brush loses a part of its superiority, notbeing so good as in nitrogen or air; whilst the negative brush does notseem injured (1459. ). In _oxygen_, the positive brush is compressed andpoor (1457); whilst the negative did not become less: the two were so alikethat the eye frequently could not tell one from the other, and thissimilarity continued when the oxygen was gradually rarefied. In _coal gas_, the brushes are difficult of production as compared to nitrogen (1460. ), and the positive not much superior to the negative in its character, eitherat common or low pressures. In _carbonic acid gas_, this approximation ofcharacter also occurred. In _muriatic acid gas_, the positive brush wasvery little better than the negative, and both difficult to produce (1462. )as compared with the facility in nitrogen or air. 

1477. These experiments were made with rods of brass about a quarter of aninch thick having rounded ends, these being opposed in a glass globe 7inches in diameter, containing the gas to be experimented with. Theelectric machine was used to communicate directly, sometimes the positive, and sometimes the negative state, to the rod in connection with it. 

1478. Thus we see that, notwithstanding there is a general difference infavour of the superiority of the positive brush over the negative, thatdifference is at its maximum in nitrogen and air; whilst in carbonic acid, muriatic acid, coal gas, and oxygen, it diminishes, and at last almostdisappears. So that in this particular effect, as in all others yetexamined, the evidence is in favour of that view which refers the resultsto a direct relation of the electric forces with the molecules of thematter concerned in the action (1421. 1423. 1463. ). Even when specialphenomena arise under the operation of the general law, the theory adoptedseems fully competent to meet the case. 

1479. Before I proceed further in tracing the probable cause of thedifference between the positive and negative brush discharge, I wish toknow the results of a few experiments which are in course of preparation:and thinking this Series of Researches long enough, I shall here close itwith the expectation of being able in a few weeks to renew the inquiry, andentirely redeem my pledge (1306. ). 

_Royal Institution, Dec. 23rd, 1837. _

THIRTEENTH SERIES. 

§ 18. _On Induction (continued). _ ¶ ix. _Disruptive discharge(continued)--Peculiarities of positive and negative discharge either asspark or brush--Glow discharge--Dark discharge. _ ¶ x. _Convection, orcarrying discharge. _ ¶ xi. _Relation of a vacuum to electrical phenomena. _§ 19. _Nature of the electrical current. _

Received February 22, --Read March 15, 1838. 

¶ ix. _Disruptive discharge (continued). _

1480. Let us now direct our attention to the general difference of thepositive and negative disruptive discharge, with the object of tracing, asfar as possible, the cause of that difference, and whether it depends onthe charged conductors principally, or on the interposed dielectric; and asit appears to be great in air and nitrogen (1476. ), let us observe thephenomena in air first. 

1481. The general case is best understood by a reference to surfaces ofconsiderable size rather than to points, which involve (as a secondaryeffect) the formation of currents (1562). My investigation, therefore, wascarried on with balls and terminations of different diameters, and thefollowing are some of the principal results. 

1482. If two balls of very different dimensions, as for instance one-halfan inch, and the other three inches in diameter, be arranged at the ends ofrods so that either can be electrified by a machine and made to dischargeby sparks to the other, which is at the same time uninsulated; then, as iswell known, far longer sparks are obtained when the small ball is positiveand the large ball negative, than when the small ball is negative and thelarge ball positive. In the former case, the sparks are 10 or 12 inches inlength; in the latter, an inch or an inch and a half only. 

 * * * * *

1483. But previous to the description of further experiments, I willmention two words, for which with many others I am indebted to a friend, and which I think it would be expedient to introduce and use. It isimportant in ordinary inductive action, to distinguish at which chargedsurface the induction originates and is sustained: i. E. If two or moremetallic balls, or other masses of matter, are in inductive relation, toexpress which are charged originally, and which are brought by them intothe opposite electrical condition. I propose to call those bodies which areoriginally charged, _inductric_ bodies; and those which assume the oppositestate, in consequence of the induction, _inducteous_ bodies. Thisdistinction is not needful because there is any difference between the sumsof the _inductric_ and the _inducteous_ forces; but principally because, when a ball A is inductric, it not merely brings a ball B, which isopposite to it, into an inducteous state, but also many other surroundingconductors, though some of them may be a considerable distance off, and theconsequence is, that the balls do not bear the same precise relation toeach other when, first one, and then the other, is made the inductric ball;though, in each case, the _same ball_ be made to assume the _same state. _

1484, Another liberty which I may also occasionally take in language I willexplain and limit. It is that of calling a particular spark or brush, _positive_ or _negative_, according as it may be considered as_originating_ at a positive or a negative surface. We speak of the brush aspositive or negative when it shoots out from surfaces previously in thosestates; and the experiments of Mr. Wheatstone go to prove that it _reallybegins_ at the charged surface, and from thence extends into the air (1437. 1438. ) or other dielectric. According to my view, _sparks_ also originateor are determined at one particular spot (1370. ), namely, that where thetension first rises up to the maximum degree; and when this can bedetermined, as in the simultaneous use of large and small balls, in whichcase the discharge begins or is determined by the latter, I would call thatdischarge which passes _at once_, a positive spark, if it was at thepositive surface that the maximum intensity was first obtained; or anegative spark, if that necessary intensity was first obtained at thenegative surface. 

 * * * * *

1485. An apparatus was arranged, as in fig. 129. (Plate VIII. ): A and Bwere brass balls of very different diameters attached to metal rods, movingthrough sockets on insulating pillars, so that the distance between theballs could be varied at pleasure. The large ball A, 2 inches in diameter, was connected with an insulated brass conductor, which could be renderedpositive or negative directly from a cylinder machine: the small ball B, 0. 25 of an inch in diameter, was connected with a discharging train (292. )and perfectly uninsulated. The brass rods sustaining the balls were 0. 2 ofan inch in thickness. 

1486. When the large ball was _positive_ and inductric (1483. ), negativesparks occurred until the interval was 0. 49 of an inch; then mixed brushand spark between that and 0. 51; and from 0. 52 and upwards, negative brushalone. When the large ball was made _negative_ and inductric, then positivespark alone occurred until the interval was as great as 1. 15 inches; sparkand brush from that up to 1. 55; and to have the positive brush alone, itrequired an interval of at least 1. 65 inches. 

1487. The balls A and B were now changed for each other. Then making thesmall ball B inductric _positively_, the positive sparks alone continuedonly up to 0. 67; spark and brush occurred from 0. 68 up to 0. 72; andpositive brush alone from 0. 74 and upwards. Rendering the small ball Binductric and _negative_, negative sparks alone occurred up to 0. 40; thenspark and brush at 0. 42; whilst from 0. 44 and upwards the noisy negativebrush alone took place. 

1488. We thus find a great difference as the balls are rendered inductricor inducteous; the small ball rendered _positive_ inducteously giving aspark nearly twice as long as that produced when it was charged positiveinductrically, and a corresponding difference, though not, under thecircumstances, to the same extent, was manifest, when it was rendered_negative_[A]. 

 [A] For similar experiments on different gases, see 1518. --_Dec. 1838. _

1489. Other results are, that the small ball rendered positive gives a muchlonger spark than when it is rendered negative, and that the small ballrendered negative gives a brush more readily than when positive, inrelation to the effect produced by increasing the distance between the twoballs. 

1490. When the interval was below 0. 4 of an inch, so that the small ballshould give sparks, whether positive or negative, I could not observe thatthere was any constant difference, either in their ready occurrence or thenumber which passed in a given time. But when the interval was such thatthe small ball when negative gave a brush, then the discharges from it, asseparate negative brushes, were far more numerous than the correspondingdischarges from it when rendered positive, whether those positivedischarges were as sparks or brushes. 

1491. It is, therefore, evident that, when a ball is dischargingelectricity in the form of brushes, the brushes are far more numerous, andeach contains or carries off far less electric force when the electricityso discharged is negative, than when it is positive. 

1492. In all such experiments as those described, the point of change fromspark to brush is very much governed by the working state of the electricalmachine and the size of the conductor connected with the discharging ball. If the machine be in strong action and the conductor large, so that muchpower is accumulated quickly for each discharge, then the interval isgreater at which the sparks are replaced by brushes; but the general effectis the same[A]. 

 [A] For similar experiments in different gases, see 1510-1517. --_Dec. 1838. _

1493. These results, though indicative of very striking and peculiarrelations of the electric force or forces, do not show the relative degreesof charge which the small ball acquires before discharge occurs, i. E. Theydo not tell whether it acquires a higher condition in the negative, or inthe positive state, immediately preceding that discharge. To illustratethis important point I arranged two places of discharge as represented, fig130. A and D are brass balls 2 inches diameter, B and C are smaller brassballs 0. 25 of an inch in diameter; the forks L and R supporting them wereof brass wire 0. 2 of an inch in diameter; the space between the large andsmall ball on the same fork was 5 inches, that the two places of discharge_n_ and _o_ might be sufficiently removed from each other's influence. Thefork L was connected with a projecting cylindrical conductor, which couldbe rendered positive or negative at pleasure, by an electrical machine, andthe fork R was attached to another conductor, but thrown into anuninsulated state by connection with a discharging train (292. ). The twointervals or places of discharge _n_ and _o_ could be varied at pleasure, their extent being measured by the occasional introduction of a diagonalscale. It is evident, that, as the balls A and B connected with the sameconductor are always charged at once, and that discharge may take place toeither of the balls connected with the discharging train, the intervals ofdischarge _n_ and _o_ may be properly compared to each other, as respectsthe influence of large and small balls when charged positively andnegatively in air. 

1494. When the intervals _n_ and _o_ were each made = 0. 9 of an inch, andthe balls A and B inductric _positively_, the discharge was all at _n_ fromthe small ball of the conductor to the large ball of the discharging train, and mostly by positive brush, though once by a spark. When the balls A andB were made inductric _negatively_, the discharge was still from the samesmall ball, at _n_, by a constant negative brush. 

1495. I diminished the intervals _n_ and _o_ to 0. 6 of an inch. When A andB were inductric _positively_, all the discharge was at _n_ as a positivebrush: when A and B were inductric _negatively_, still all the dischargewas at _n_, as a negative brush. 

1496. The facility of discharge at the positive and negative small balls, therefore, did not appear to be very different. If a difference hadexisted, there were always two small balls, one in each state, that thedischarge might happen at that most favourable to the effect. The onlydifference was, that one was in the inductric, and the other in theinducteous state, but whichsoever happened for the time to be in thatstate, whether positive or negative, had the advantage. 

1497. To counteract this interfering influence, I made the interval _n_ =0. 79 and interval _o_ = 0. 58 of an inch. Then, when the balls A and B were_inductric positive_, the discharge was about equal at both intervals. When, on the other hand, the balls A and B were inductric _negative_, therewas discharge, still at both, but most at _n_, as if the small ball_negative_ could discharge a little easier than the same ball _positive_. 

1498. The small balls and terminations used in these and similarexperiments may very correctly be compared, in their action, to the sameballs and ends when electrified in free air at a much greater distance fromconductors, than they were in those cases from each other. In the firstplace, the discharge, even when as a spark, is, according to my view, determined, and, so to speak, begins at a spot on the surface of the smallball (1374. ), occurring when the intensity there has risen up to a certainmaximum degree (1370. ); this determination of discharge at a particularspot first, being easily traced from the spark into the brush, byincreasing the distance, so as, at last, even to render the time evidentwhich is necessary for the production of the effect (1436. 1438. ). In thenext place, the large balls which I have used might be replaced by largerballs at a still greater distance, and so, by successive degrees, may beconsidered as passing into the sides of the rooms; these being undergeneral circumstances the inducteous bodies, whilst the small ball renderedeither positive or negative is the inductric body. 

1499. But, as has long been recognised, the small ball is only a blunt end, and, electrically speaking, a point only a small ball; so that when a pointor blunt end is throwing out its brushes into the air, it is acting exactlyas the small balls have acted in the experiments already described, and byvirtue of the same properties and relations. 

1500. It may very properly be said with respect to the experiments, thatthe large negative ball is as essential to the discharge as the smallpositive ball, and also that the large negative ball shows as muchsuperiority over the large positive ball (which is inefficient in causing aspark from its opposed small negative ball) as the small positive ball doesover the small negative ball; and probably when we understand the realcause of the difference, and refer it rather to the condition of theparticles of the dielectric than to the sizes of the conducting balls, wemay find much importance in such an observation. But for the present, andwhilst engaged in investigating the point, we may admit, what is the fact, that the forces are of higher intensity at the surfaces of the smallerballs than at those of the larger (1372. 1374. ); that the former, therefore, determine the discharge, by first rising up to that exaltedcondition which is necessary for it; and that, whether brought to thiscondition by induction towards the walls of a room or the large balls Ihave used, these may fairly be compared one with the other in theirinfluence and actions. 

1501. The conclusions I arrive at are: first, that when two equal smallconducting surfaces equally placed in air are electrified, one positivelyand the other negatively, that which is negative can discharge to the airat a tension a little lower than that required for the positive ball:second, that when discharge does take place, much more passes at each timefrom the positive than from the negative surface (1491. ). The lastconclusion is very abundantly proved by the optical analysis of thepositive and negative brushes already described (1468. ), the latter set ofdischarges being found to recur five or six times oftener than theformer[A]. 

 [A] A very excellent mode of examining the relation of small positive and negative surfaces would be by the use of drops of gum water, solutions, or other liquids. See onwards (1581. 1593. ). 

1502. If, now, a small ball be made to give brushes or brushy sparks by apowerful machine, we can, in some measure, understand and relate thedifference perceived when it is rendered positive or negative. It is knownto give when positive a much larger and more powerful spark than whennegative, and with greater facility (1482. ): in fact, the spark, althoughit takes away so much more electricity at once, commences at a tensionhigher only in a small degree, if at all. On the other hand, if renderednegative, though discharge may commence at a lower degree, it continues butfor a very short period, very little electricity passing away each time. These circumstances are directly related; for the extent to which thepositive spark can reach, and the size and extent of the positive brush, are consequences of the capability which exists of much electricity passingoff at one discharge from the positive surface (1468. 1501. ). 

1503. But to refer these effects only to the form and size of theconductor, would, according to my notion of induction, be a very imperfectmode of viewing the whole question (1523. 1600. ). I apprehend that theeffects are due altogether to the mode in which the particles of theinterposed dielectric polarize, and I have already given some experimentalindications of the differences presented by different electrics in thisrespect (1475. 1476. ). The modes of polarization, as I shall have occasionhereafter to show, may be very diverse in different dielectrics. Withrespect to common air, what seems to be the consequence of a superiority inthe positive force at the surface of the small ball, may be due to the moreexalted condition of the negative polarity of the particles of air, or ofthe nitrogen in it (the negative part being, perhaps, more compressed, whilst the positive part is more diffuse, or _vice versa_ (1687. &c. )); forsuch a condition could determine certain effects at the positive ball whichwould not take place to the same degree at the negative ball, just as wellas if the positive ball had possessed some special and independent power ofits own. 

1504. The opinion, that the effects are more likely to be dependent uponthe dielectric than the ball, is supported by the character of the twodischarges. If a small positive ball be throwing off brushes withramifications ten inches long, how can the ball affect that part of aramification which is five inches from it? Yet the portion beyond thatplace has the same character as that preceding it, and no doubt has thatcharacter impressed by the same general principle and law. Looking upon theaction of the contiguous particles of a dielectric as fully proved, I see, in such a ramification, a propagation of discharge from particle toparticle, each doing for the one next it what was done for it by thepreceding particle, and what was done for the first particle by the chargedmetal against which it was situated. 

1505. With respect to the general condition and relations of the positiveand negative brushes in dense or rare air, or in other media and gases, ifthey are produced at different times and places they are of courseindependent of each other. But when they are produced from opposed ends orballs at the same time, in the same vessel of gas (1470. 1477. ), they arefrequently related; and circumstances may be so arranged that they shall beisochronous, occurring in equal numbers in equal times; or shall occur inmultiples, i. E. With two or three negatives to one positive; or shallalternate, or be quite irregular. All these variations I have witnessed;and when it is considered that the air in the vessel, and also the glass ofthe vessel, can take a momentary charge, it is easy to comprehend theirgeneral nature and cause. 

 * * * * *

1506. Similar experiments to those in air (1485. 1493. ) were made indifferent gases, the results of which I will describe as briefly aspossible. The apparatus is represented fig. 131, consisting of a bell-glasseleven inches in diameter at the widest part, and ten and a half incheshigh up to the bottom of the neck. The balls are lettered, as in fig. 130, and are in the same relation to each other; but A and B were on separatesliding wires, which, however, were generally joined by a cross wire, _w_, above, and that connected with the brass conductor, which received itspositive or negative charge from the machine. The rods of A and B weregraduated at the part moving through the stuffing-box, so that theapplication of a diagonal scale applied there, told what was the distancebetween these balls and those beneath them. As to the position of the ballsin the jar, and their relation to each other, C and D were three and aquarter inches apart, their height above the pump plate five inches, andthe distance between any of the balls and the glass of the jar one inch andthree quarters at least, and generally more. The balls A and D were twoinches in diameter, as before (1493. ); the balls B and C only 0. 15 of aninch in diameter. 

Another apparatus was occasionally used in connection with that justdescribed, being an open discharger (fig. 132. ), by which a comparison ofthe discharge in air and that in gases could be obtained. The balls E andF, each 0. 6 of an inch in diameter, were connected with sliding rods andother balls, and were insulated. When used for comparison, the brassconductor was associated at the same time with the balls A and B of figure131 and ball E of this apparatus (fig. 132. ); whilst the balls C, D and Fwere connected with the discharging train. 

1507. I will first tabulate the results as to the _restraining power_ ofthe gases over discharge. The balls A and C (fig. 131. ) were thrown out ofaction by distance, and the effects at B and D, or the interval _n_ in thegas, compared with those at the interval _p_ in the air, between E and F(fig. 132. ). The Table sufficiently explains itself. It will be understoodthat all discharge was in the air, when the interval there was less thanthat expressed in the first or third columns of figures; and all thedischarge in the gas, when the interval in air was greater than that in thesecond or fourth column of figures. At intermediate distances the dischargewas occasionally at both places, i. E. Sometimes in the air, sometimes inthe gas. 

 _____________________________________________________________________| | || | Interval _p_ in parts of an inch ||_________________|___________________________________________________|| | | || | When the small ball B | When the small ball B || Constant inter- | was inductric and | was inductric and || val _n_ between | _positive_ the | _negative_ the || B and D = 1 | discharge was all | discharge was all || inch | at _p_ in at _n_ in | at _p_ in at _n_ in || | air before the gas | air before the gas || | after | after ||_________________|_________________________|_________________________|| | _p_ = | _p_ = | _p_ = | _p_ = ||In Air | 0. 10 | 0. 50 | 0. 28 | 0. 33 ||In Nitrogen | 0. 30 | 0. 65 | 0. 31 | 0. 40 ||In Oxygen | 0. 33 | 0. 52 | 0. 27 | 0. 30 ||In Hydrogen | 0. 20 | 0. 10 | 0. 22 | 0. 24 ||In Coal Gas | 0. 20 | 0. 90 | 0. 20 | 0. 27 ||In Carbonic Acid | 0. 61 | 1. 30 | 0. 30 | 0. 15 ||_________________|____________|____________|____________|____________|

1508. These results are the same generally, as far as they go, as those ofthe like nature in the last series (1388. ), and confirm the conclusion thatdifferent gases restrain discharge in very different proportions. They areprobably not so good as the former ones, for the glass jar not beingvarnished, acted irregularly, sometimes taking a certain degree of chargeas a non-conductor, and at other times acting as a conductor in theconveyance and derangement of that charge. Another cause of difference inthe ratios is, no doubt, the relative sizes of the discharge balls in air;in the former case they were of very different size, here they were alike. 

1509. In future experiments intended to have the character of accuracy, theinfluence of these circumstances ought to be ascertained, and, above allthings, the gases themselves ought to be contained in vessels of metal, andnot of glass. 

 * * * * *

1510. The next set of results are those obtained when the intervals _n_ and_o_ (fig. 131. ) were made equal to each other, and relate to the greaterfacility of discharge at the small ball, when rendered positive or negative(1493. ). 

1511. In _air_, with the intervals = 0. 4 of an inch, A and B beinginductric and positive, discharge was nearly equal at _n_ and _o_; when Aand B were inductric and negative, the discharge was mostly at _n_ bynegative brush. When the intervals were = 0. 8 of an inch, with A and Binductric positively, all discharge was at _n_ by positive brush; with Aand B inductric negatively, all the discharge was at _n_ by a negativebrush. It is doubtful, therefore, from these results, whether the negativeball has any greater facility than the positive. 

1512. _Nitrogen. _--Intervals _n_ and _o_ = 0. 4 of an inch: A, B inductricpositive, discharge at both intervals, most at _n_, by positive sparks; A, B inductric negative, discharge equal at _n_ and _o_. The intervals made =0. 8 of an inch: A, B inductric positive, discharge all at _n_ by positivebrush; A, B inductric negative, discharge most at _o_ by positive brush. Inthis gas, therefore, though the difference is not decisive, it would seemthat the positive small ball caused the most ready discharge. 

1513. _Oxygen. _--Intervals _n_ and _o_ = 0. 4 of an inch: A, B inductricpositive, discharge nearly equal; inductric negative, discharge mostly at_n_ by negative brush. Made the intervals = 0. 8 of an inch: A, B inductricpositive, discharge both at _n_ and _o_; inductric negative, discharge allat _o_ by negative brush. So here the negative small ball seems to give themost ready discharge. 

1514. _Hydrogen. _--Intervals _n_ and _o_ = 0. 4 of an inch: A, B inductricpositive, discharge nearly equal: inductric negative, discharge mostly at_o_. Intervals = 0. 8 of an inch: A and B inductric positive, dischargemostly at _n_, as positive brush; inductric negative, discharge mostly at_o_, as positive brush. Here the positive discharge seems most facile. 

1515. _Coal gas. _--_n_ and _o_ = 0. 4 of an inch: A, B inductric positive, discharge nearly all at _o_ by negative spark: A, B inductric negative, discharge nearly all at _n_ by negative spark. Intervals = 0. 8 of an inch, and A, B inductric positive, discharge mostly at _o_ by negative brush: A, B inductric negative, discharge all at _n_ by negative brush. Here thenegative discharge most facile. 

1516. _Carbonic acid gas. _--_n_ and _o_ = 0. 1 of an inch: A, B inductricpositive, discharge nearly all at _o_, or negative: A, B inductricnegative, discharge nearly all at _n_, or negative. Intervals = 0. 8 of aninch: A, B inductric positive, discharge mostly at _o_, or negative. A, Binductric negative, discharge all at _n_, or negative. In this case thenegative had a decided advantage in facility of discharge. 

1517. Thus, if we may trust this form of experiment, the negative smallball has a decided advantage in facilitating disruptive discharge over thepositive small ball in some gases, as in carbonic acid gas and coal gas(1399. ), whilst in others that conclusion seems more doubtful; and inothers, again, there seems a probability that the positive small ball maybe superior. All these results were obtained at very nearly the samepressure of the atmosphere. 

 * * * * *

1518. I made some experiments in these gases whilst in the air jar (fig. 131. ), as to the change from spark to brush, analogous to those in the openair already described (1486. 1487. ). I will give, in a Table, the resultsas to when brush began to appear mingled with the spark; but the afterresults were so varied, and the nature of the discharge in different gasesso different, that to insert the results obtained without furtherinvestigation, would be of little use. At intervals less than thoseexpressed the discharge was always by spark. 

 _______________________________________________________________________| | | || | Discharge between | Discharge between || | balls B and D. | balls A and C. || |___________________________|___________________________|| | | | | || | Small ball | Small ball | Large ball | Large ball || | B inductric | B inductric | A inductric | A inductric || | _pos_. | _neg_. | _pos_. | _neg_. ||_______________|_____________|_____________|_____________|_____________|| | | | | || Air | 0. 55 | 0. 30 | 0. 40 | 0. 75 || Nitrogen | 0. 30 | 0. 40 | 0. 52 | 0. 41 || Oxygen | 0. 70 | 0. 30 | 0. 45 | 0. 82 || Hydrogen | 0. 20 | 0. 10 | | || Coal gas | 0. 13 | 0. 30 | 0. 30 | 0. 44 || Carbonic acid | 0. 82 | 0. 43 | 1. 60 | {above 1. 80;|| | | | | had not || | | | | space. ) ||_______________|_____________|_____________|_____________|_____________|

1519. It is to be understood that sparks occurred at much higher intervalsthan these; the table only expresses that distance beneath which alldischarge was as spark. Some curious relations of the different gases todischarge are already discernible, but it would be useless to consider themuntil illustrated by further experiments. 

 * * * * *

1520. I ought not to omit noticing here, that Professor Belli of Milan haspublished a very valuable set of experiments on the relative dissipation ofpositive and negative electricity in the air[A]; he finds the latter farmore ready, in this respect, than the former. 

 [A] Bibliothèque Universelle, 1836, September, p. 152. 

1521. I made some experiments of a similar kind, but with sustained highcharges; the results were less striking than those of Signore Belli, and Idid not consider them as satisfactory. I may be allowed to mention, inconnexion with the subject, an interfering effect which embarrassed me fora long time. When I threw positive electricity from a given point into theair, a certain intensity was indicated by an electrometer on the conductorconnected with the point, but as the operation continued this intensityrose several degrees; then making the conductor negative with the samepoint attached to it, and all other things remaining the same, a certaindegree of tension was observed in the first instance, which also graduallyrose as the operation proceeded. Returning the conductor to the positivestate, the tension was at first low, but rose as before; and so also whenagain made negative. 

1522. This result appeared to indicate that the point which had been givingoff one electricity, was, by that, more fitted for a short time to give offthe other. But on closer examination I found the whole depended upon theinductive reaction of that air, which being charged by the point, andgradually increasing in quantity before it, as the positive or negativeissue was continued, diverted and removed a part of the inductive action ofthe surrounding wall, and thus apparently affected the powers of the point, whilst really it was the dielectric itself that was causing the change oftension. 

 * * * * *

1523. The results connected with the different conditions of positive andnegative discharge will have a far greater influence on the philosophy ofelectrical science than we at present imagine, especially if, as I believe, they depend on the peculiarity and degree of polarized condition which themolecules of the dielectrics concerned acquire (1503. 1600. ). Thus, forinstance, the relation of our atmosphere and the earth within it, to theoccurrence of spark or brush, must be especial and not accidental (1464. ). It would not else consist with other meteorological phenomena, also ofcourse dependent on the special properties of the air, and which beingthemselves in harmony the most perfect with the functions of animal andvegetable life, are yet restricted in their actions, not by looseregulations, but by laws the most precise. 

1524. Even in the passage through air of the voltaic current we see thepeculiarities of positive and negative discharge at the two charcoalpoints; and if these discharges are made to take place simultaneously tomercury, the distinction is still more remarkable, both as to the sound andthe quantity of vapour produced. 

1525. It seems very possible that the remarkable difference recentlyobserved and described by my friend Professor Daniell[A], namely, that whena zinc and a copper ball, the same in size, were placed respectively incopper and zinc spheres, also the same in size, and excited by electrolytesor dielectrics of the same strength and nature, the zinc ball far surpassedthe zinc sphere in action, may also be connected with these phenomena; forit is not difficult to conceive how the polarity of the particles shall beaffected by the circumstance of the positive surface, namely the zinc, being the larger or the smaller of the two inclosing the electrolyte. It iseven possible, that with different electrolytes or dielectrics the ratiomay be considerably varied, or in some cases even inverted. 

 [A] Philosophical Transactions, 1838, p. 47. 

 * * * * *

_Glow discharge. _

1526. That form of disruptive discharge which appears as a _glow_ (1359. 1405. ), is very peculiar and beautiful: it seems to depend on a quick andalmost continuous charging of the air close to, and in contact with, theconductor. 

1527. _Diminution of the charging surface_ will produce it. Thus, when arod 0. 3 of an inch in diameter, with a rounded termination, was renderedpositive in free air, it gave fine brushes from the extremity, butoccasionally these disappeared, and a quiet phosphorescent continuous glowtook their place, covering the whole of the end of the wire, and extendinga very small distance from the metal into the air. With a rod 0. 2 of aninch in diameter the glow was more readily produced. With still smallerrods, and also with blunt conical points, it occurred still more readily;and with a fine point I could not obtain the brush in free air, but onlythis glow. The positive glow and the positive star are, in fact, the same. 

1528. _Increase of power in the machine_ tends to produce the glow; forrounded terminations which will give only brushes when the machine is inweak action, will readily give the glow when it is in good order. 

1529. _Rarefaction of the air_ wonderfully favours the glow phenomena. Abrass ball, two and a half inches in diameter, being made positivelyinductric in an air-pump receiver, became covered with glow over an area oftwo inches in diameter, when the pressure was reduced to 4. 4 inches ofmercury. By a little adjustment the ball could be covered all over withthis light. Using a brass ball 1. 25 inches in diameter, and making itinducteously positive by an inductric negative point, the phenomena, athigh degrees of rarefaction, were exceedingly beautiful. The glow came overthe positive ball, and gradually increased in brightness, until it was atlast very luminous; and it also stood up like a low flame, half an inch ormore in height. On touching the sides of the glass jar this lambent flamewas affected, assumed a ring form, like a crown on the top of the ball, appeared flexible, and revolved with a comparatively slow motion, i. E. About four or five times in a second. This ring-shape and revolution arebeautifully connected with the mechanical currents (1576. ) taking placewithin the receiver. These glows in rarefied air are often highly exaltedin beauty by a spark discharge at the conductor (1551. _Note_. ). 

1530. To obtain a _negative glow_ in air at common pressures is difficult. I did not procure it on the rod 0. 3 of an inch in diameter by my machine, nor on much smaller rods; and it is questionable as yet, whether, even onfine points, what is called the negative star is a very reduced and minute, but still intermitting brush, or a glow similar to that obtained on apositive point. 

1531. In rarefied air the negative glow can easily be obtained. If therounded ends of two metal rods, about O. 2 of an inch in diameter, areintroduced into a globe or jar (the air within being rarefied), and beingopposite to each other, are about four inches apart, the glow can beobtained on both rods, covering not only the ends, but an inch or two ofthe part behind. On using _balls_ in the air-pump jar, and adjusting thedistance and exhaustion, the negative ball could be covered with glow, whether it were the inductric or the inducteous surface. 

1532. When rods are used it is necessary to be aware that, if placedconcentrically in the jar or globe, the light on one rod is often reflectedby the sides of the vessel on to the other rod, and makes it apparentlyluminous, when really it is not so. This effect may be detected by shiftingthe eye at the time of observation, or avoided by using blackened rods. 

1533. It is curious to observe the relation _of glow, brush_, and _spark_to each other, as produced by positive or negative surfaces; thus, beginning with spark discharge, it passes into brush much sooner when thesurface at which the discharge commences (1484. ) is negative, than it doeswhen positive; but proceeding onwards in the order of change, we find thatthe positive brush passes into _glow_ long before the negative brush does. So that, though each presents the three conditions in the same generalorder, the series are not precisely the same. It is probable, that, whenthese points are minutely examined, as they must be shortly, we shall findthat each different gas or dielectric presents its own peculiar results, dependent upon the mode in which its particles assume polar electriccondition. 

1534. The glow occurs in all gases in which I have looked for it. These areair, nitrogen, oxygen, hydrogen, coal gas, carbonic acid, muriatic acid, sulphurous acid and ammonia. I thought also that I obtained it in oil ofturpentine, but if so it was very dull and small. 

1535. The glow is always accompanied by a wind proceeding either directlyout from the glowing part, or directly towards it; the former being themost general case. This takes place even when the glow occurs upon a ballof considerable size: and if matters be so arranged that the ready andregular access of air to a part exhibiting the glow be interfered with orprevented, the glow then disappears. 

1536. I have never been able to analyse or separate the glow into visibleelementary intermitting discharges (1427. 1433. ), nor to obtain the otherevidence of intermitting action, namely an audible sound (1431. ). The wantof success, as respects trials made by ocular means, may depend upon thelarge size of the glow preventing the separation of the visible images:and, indeed, if it does intermit, it is not likely that all parts intermitat once with a simultaneous regularity. 

1537. All the effects tend to show, that _glow_ is due to a continuouscharge or discharge of air; in the former case being accompanied by acurrent from, and in the latter by one to, the place of the glow. As thesurrounding air comes up to the charged conductor, on attaining that spotat which the tension of the particles is raised to the sufficient degree(1370. 1410. ), it becomes charged, and then moves off, by the joint actionof the forces to which it is subject; and, at the same time that it makesway for other particles to come and be charged in turn, actually helps toform that current by which they are brought into the necessary position. Thus, through the regularity of the forces, a constant and quiet result isproduced; and that result is, the charging of successive portions of air, the production of a current, and of a continuous glow. 

1538. I have frequently been able to make the termination of a rod, which, when left to itself, would produce a brush, produce in preference a glow, simply by aiding the formation of a current of air at its extremity; and, on the other hand, it is not at all difficult to convert the glow intobrushes, by affecting the current of air (1574. 1579. ) or the inductiveaction near it. 

1539. The transition from glow, on the one hand, to brush and spark, on theother, and, therefore, their connexion, may be established in various ways. Those circumstances which tend to facilitate the charge of the air by theexcited conductor, and also those which tend to keep the tension at thesame degree notwithstanding the discharge, assist in producing the glow;whereas those which tend to resist the charge of the air or otherdielectric, and those which favour the accumulation of electric force priorto discharge, which, sinking by that act, has to be exalted before thetension can again acquire the requisite degree, favour intermittingdischarge, and, therefore, the production of brush or spark. Thus, rarefaction of the air, the removal of large conducting surfaces from theneighbourhood of the glowing termination, the presentation of a sharp pointtowards it, help to sustain or produce the glow: but the condensation ofthe air, the presentation of the hand or other large surface, the gradualapproximation of a discharging ball, tend to convert the glow into brush oreven spark. All these circumstances may be traced and reduced, in a mannereasily comprehensible, to their relative power of assisting to produce, either a _continuous_ discharge to the air, which gives the glow; or an_interrupted_ one, which produces the brush, and, in a more exaltedcondition, the spark. 

1540. The rounded end of a brass rod, 0. 3 of an inch in diameter, wascovered with a positive glow by the working of an electrical machine: onstopping the machine, so that the charge of the connected conductor shouldfall, the glow changed for a moment into brushes just before the dischargeceased altogether, illustrating the necessity for a certain high continuouscharge, for a certain sized termination. Working the machine so that theintensity should be just low enough to give continual brushes from the endin free air, the approach of a fine point changed these brushes into aglow. Working the machine so that the termination presented a continualglow in free air, the gradual approach of the hand caused the glow tocontract at the very end of the wire, then to throw out a luminous point, which, becoming a foot stalk (1426. ), finally produced brushes with largeramifications. All these results are in accordance with what is statedabove (1539. ). 

1541. Greasing the end of a rounded wire will immediately make it producebrushes instead of glow. A ball having a blunt point which can be made toproject more or less beyond its surface, at pleasure, can be made toproduce every gradation from glow, through brush, to spark. 

1542. It is also very interesting and instructive to trace the transitionfrom spark to glow, through the intermediate condition of stream, betweenends in a vessel containing air more or less rarefied; but I fear to beprolix. 

1543. All the effects show, that the glow is in its nature exactly the sameas the luminous part of a brush or ramification, namely a charging of air;the only difference being, that the glow has a continuous appearance fromthe constant renewal of the same action in the same place, whereas theramification is due to a momentary, independent and intermitting action ofthe same kind. 

 * * * * *

_Dark discharge. _

1544. I will now notice a very remarkable circumstance in the luminousdischarge accompanied by negative glow, which may, perhaps, be correctlytraced hereafter into discharges of much higher intensity. Two brass rods, 0. 3 of an inch in diameter, entering a glass globe on opposite sides, hadtheir ends brought into contact, and the air about them very much rarefied. A discharge of electricity from the machine was then made through them, andwhilst that was continued the ends were separated from each other. At themoment of separation a continuous glow came over the end of the negativerod, the positive termination remaining quite dark. As the distance wasincreased, a purple stream or haze appeared on the end of the positive rod, and proceeded directly outwards towards the negative rod; elongating as theinterval was enlarged, but never joining the negative glow, there beingalways a short dark space between. This space, of about 1/16th or 1/20th ofan inch, was apparently invariable in its extent and its position, relativeto the negative rod; nor did the negative glow vary. Whether the negativeend were inductric or inducteous, the same effect was produced. It wasstrange to see the positive purple haze diminish or lengthen as the endswere separated, and yet this dark space and the negative glow remainunaltered (fig. 133). 

1545. Two balls were then used in a large air-pump receiver, and the airrarefied. The usual transitions in the character of the discharge tookplace; but whenever the luminous stream, which appears after the spark andthe brush have ceased, was itself changed into glow at the balls, the darkspace occurred, and that whether the one or the other ball was madeinductric, or positive, or negative. 

1546. Sometimes when the negative ball was large, the machine in powerfulaction, and the rarefaction high, the ball would be covered over half itssurface with glow, and then, upon a hasty observation, would seem toexhibit no dark space: but this was a deception, arising from theoverlapping of the convex termination of the negative glow and the concavetermination of the positive stream. More careful observation and experimenthave convinced me, that when the negative glow occurs, it never visiblytouches the luminous part of the positive discharge, but that the darkspace is always there. 

1547. This singular separation of the positive and negative discharge, asfar as concerns their luminous character, under circumstances which onewould have thought very favourable to their coalescence, is probablyconnected with their differences when in the form of brush, and is perhapseven dependent on the same cause. Further, there is every likelihood thatthe dark parts which occur in feeble sparks are also connected with thesephenomena[A]. To understand them would be very important, for it is quiteclear that in many of the experiments, indeed in all that I have quoted, discharge is taking place across the dark part of the dielectric to anextent quite equal to what occurs in the luminous part. This difference inthe result would seem to imply a distinction in the modes by which the twoelectric forces are brought into equilibrium in the respective parts; andlooking upon all the phenomena as giving additional proofs, that it is tothe condition of the particles of the dielectric we must refer for theprinciples of induction and discharge, so it would be of great importanceif we could know accurately in what the difference of action in the darkand the luminous parts consisted. 

 [A] See Professor Johnson's experiments. Silliman's Journal, xxv. P. 57. 

1548. The dark discharge through air (1552. ), which in the case mentionedis very evident (1544. ), leads to the inquiry, whether the particles of airare generally capable of effecting discharge from one to another withoutbecoming luminous; and the inquiry is important, because it is connectedwith that degree of tension which is necessary to originate discharge(1368. 1370. ). Discharge between _air and conductors_ without luminousappearances are very common; and non-luminous discharges by carryingcurrents of air and other fluids (1562. 1595. ) are also common enough: butthese are not cases in point, for they are not discharges betweeninsulating particles. 

1549. An arrangement was made for discharge between two balls (1485. ) (fig. 129. ) but, in place of connecting the inducteous ball directly with thedischarging train, it was put in communication with the inside coating of aLeyden jar, and the discharging train with the outside coating. Thenworking the machine, it was found that whenever sonorous and luminousdischarge occurred at the balls A B, the jar became charged; but that whenthese did not occur, the jar acquired no charge: and such was the case whensmall rounded terminations were used in place of the balls, and also inwhatever manner they were arranged. Under these circumstances, therefore, discharge even between the air and conductors was always luminous. 

1550. But in other cases, the phenomena are such as to make it almostcertain, that dark discharge can take place across air. If the rounded endof a metal rod, 0. 15 of an inch in diameter, be made to give a goodnegative brush, the approach of a smaller end or a blunt point opposite toit will, at a certain distance, cause a diminution of the brush, and a glowwill appear on the positive inducteous wire, accompanied by a current ofair passing from it. Now, as the air is being charged both at the positiveand negative surfaces, it seems a reasonable conclusion, that the chargedportions meet somewhere in the interval, and there discharge to each other, without producing any luminous phenomena. It is possible, however, that theair electrified positively at the glowing end may travel on towards thenegative surface, and actually form that atmosphere into which the visiblenegative brushes dart, in which case dark discharge need not, of necessity, occur. But I incline to the former opinion, and think, that the diminutionin size of the negative brush, as the positive glow comes on to the end ofthe opposed wire, is in favour of that view. 

1551. Using rarefied air as the dielectric, it is very easy to obtainluminous phenomena as brushes, or glow, upon both conducting balls orterminations, whilst the interval is dark, and that, when the action is somomentary that I think we cannot consider currents as effecting dischargeacross the dark part. Thus if two balls, about an inch in diameter, and 4or more inches apart, have the air rarefied about them, and are theninterposed in the course of discharge, an interrupted or spark currentbeing produced at the machine[A], each termination may be made to showluminous phenomena, whilst more or less of the interval is quite dark. Thedischarge will pass as suddenly as a retarded spark (295. 334. ), i. E. In aninterval of time almost inappreciably small, and in such a case, I think itmust have passed across the dark part as true disruptive discharge, and notby convection. 

 [A] By spark current I mean one passing in a series of spark between the conductor of the machine and the apparatus: by a continuous current one that passes through metallic conductors, and in that respect without interruption at the same place. 

1552. Hence I conclude that dark disruptive discharge may occur (1547. 1550. ); and also, that, in the luminous brush, the visible ramificationsmay not show the full extent of the disruptive discharge (1444. 1452. ), butthat each may have a dark outside, enveloping, as it were, every partthrough which the discharge extends. It is probable, even, that there aresuch things as dark discharges analogous in form to the brush and thespark, but not luminous in any part (1445. ). 

1553. The occurrence of dark discharge in any case shows at how low atension disruptive discharge may occur (1548, ), and indicates that thelight of the ultimate brush or spark is in no relation to the intensityrequired (1368. 1370. ). So to speak, the discharge begins in darkness, andthe light is a mere consequence of the quantity which, after discharge hascommenced, flows to that spot and there finds its most facile passage(1418. 1435. ). As an illustration of the growth generally of discharge, Imay remark that, in the experiments on the transition in oxygen of thedischarge from spark to brush (1518. ), every spark was immediately precededby a short brush. 

1554. The phenomena relative to dark discharge in other gases, thoughdiffering in certain characters from those in air, confirm the conclusionsdrawn above. The two rounded terminations (1544. ) (fig. 133. ), were placedin _muriatic acid gas_ (1445. 1463. ) at the pressure of 6. 5 inches ofmercury, and a continuous machine current of electricity sent through theapparatus: bright sparks occurred until the interval was about or above aninch, when they were replaced by squat brushy intermitting glows upon bothterminations, with a dark part between. When the current at the machine wasin spark, then each spark caused a discharge across the muriatic acid gas, which, with a certain interval, was bright; with a larger interval, wasstraight across and flamy, like a very exhausted and sudden, but not adense sharp spark; and with a still larger interval, produced a feeblebrush on the inductric positive end, and a glow on the inducteous negativeend, the dark part being between (1544. ); and at such times, the spark atthe conductor, instead of being sudden and sonorous, was dull and quiet(334. ). 

1555. On introducing more muriatic acid gas, until the pressure was 29. 97inches, the same terminations gave bright sparks within at small distances;but when they were about an inch or more apart, the discharge was generallywith very small brushes and glow, and frequently with no light at all, though electricity had passed through the gas. Whenever the bright sparkdid pass through the muriatic acid gas at this pressure, it was brightthroughout, presenting no dark or dull space. 

1556. In _coal gas_, at common pressures, when the distance was about aninch, the discharge was accompanied by short brushes on the ends, and adark interval of half an inch or more between them, notwithstanding thedischarge had the sharp quick sound of a dull spark, and could not havedepended in the dark part on _convection_ (1562. ). 

1557. This gas presents several curious points in relation to the brightand dark parts of spark discharge. When bright sparks passed between therod ends 0. 3 of an inch in diameter (1544. ), very sudden dark parts wouldoccur next to the brightest portions of the spark. Again with these endsand also with balls (1422. ), the bright sparks would be sometimes red, sometimes green, and occasionally green and red in different parts of thesame spark. Again, in the experiments described (1518. ), at certainintervals a very peculiar pale, dull, yet sudden discharge would pass, which, though apparently weak, was very direct in its course, andaccompanied by a sharp snapping noise, as if quick in its occurrence. 

1558. _Hydrogen_ frequently gave peculiar sparks, one part being brightred, whilst the other was a dull pale gray, or else the whole spark wasdull and peculiar. 

1559. _Nitrogen_ presents a very remarkable discharge, between two balls ofthe respective diameters of 0. 15 and 2 inches (1506. 1518. ), the smallerone being rendered negative either directly inducteously. The peculiardischarge occurs at intervals between 0. 42 and 0. 68, and even at 1. 4 incheswhen the large ball was inductric positively; it consisted of a littlebrushy part on the small negative ball, then a dark space, and lastly adull straight line on the large positive ball (fig. 134. ). The position ofthe dark space was very constant, and is probably in direct relation to thedark space described when negative glow was produced (1544. ). When by anycircumstance a bright spark was determined, the contrast with the peculiarspark described was very striking; for it always had a faint purple part, but the place of this part was constantly near the positive ball. 

1560. Thus dark discharge appears to be decidedly established. But itsestablishment is accompanied by proofs that it occurs in different degreesand modes in different gases. Hence then another specific action, added tothe many (1296. 1398. 1399. 1423. 1454. 1503. ) by which the electricalrelations of insulating dielectrics are distinguished and established, andanother argument in favour of that molecular theory of induction, which isat present under examination[A]. 

 [A] I cannot resist referring here by a note to Biot's philosophical view of the nature of the light of the electric discharge, Annales de Chimie, liii. P. 321. 

 * * * * *

1561. What I have had to say regarding disruptive discharge has extended tosome length, but I hope will be excused in consequence of the importance ofthe subject. Before concluding my remarks, I will again intimate in theform of a query, whether we have not reason to consider the tension orretention and after discharge in air or other insulating dielectrics, asthe same thing with retardation and discharge in a metal wire, differingonly, but almost infinitely, in degree (1334. 1336. ). In other words, canwe not, by a gradual chain of association, carry up discharge from itsoccurrence in air, through spermaceti and water, to solutions, and then onto chlorides, oxides and metals, without any essential change in itscharacter; and, at the same time, connecting the insensible conduction ofair, through muriatic acid gas and the dark discharge, with the betterconduction of spermaceti, water, and the all but perfect conduction of themetals, associate the phenomena at both extremes? and may it not be, thatthe retardation and ignition of a wire are effects exactly correspondent intheir nature to the retention of charge and spark in air? If so, here againthe two extremes in property amongst dielectrics will be found to be inintimate relation, the whole difference probably depending upon the modeand degree in which their particles polarize under the influence ofinductive actions (1338. 1603. 1610. ). 

 * * * * *

¶ x. _Convection, or carrying discharge. _

1562. The last kind of discharge which I have to consider is that effectedby the motion of charged particles from place to place. It is apparentlyvery different in its nature to any of the former modes of discharge(1319. ), but, as the result is the same, may be of great importance inillustrating, not merely the nature of discharge itself, but also of whatwe call the electric current. It often, as before observed, in cases ofbrush and glow (1440. 1535. ), joins its effect to that of disruptivedischarge, to complete the act of neutralization amongst the electricforces. 

1563. The particles which being charged, then travel, may be either ofinsulating or conducting matter, large or small. The consideration in thefirst place of a large particle of conducting matter may perhaps help ourconceptions. 

1564. A copper boiler 3 feet in diameter was insulated and electrified, butso feebly, that dissipation by brushes or disruptive discharge did notoccur at its edges or projecting parts in a sensible degree. A brass ball, 2 inches in diameter, suspended by a clean white silk thread, was broughttowards it, and it was found that, if the ball was held for a second or twonear any part of the charged surface of the boiler, at such distance (twoinches more or less) as not to receive any direct charge from it, it becameitself charged, although insulated the whole time; and its electricity wasthe _reverse_ of that of the boiler. 

1565. This effect was the strongest opposite the edges and projecting partsof the boiler, and weaker opposite the sides, or those extended portions ofthe surface which, according to Coulomb's results, have the weakest charge. It was very strong opposite a rod projecting a little way from the boiler. It occurred when the copper was charged negatively as well as positively:it was produced also with small balls down to 0. 2 of an inch and less indiameter, and also with smaller charged conductors than the copper. It is, indeed, hardly possible in some cases to carry an insulated ball within aninch or two of a charged plane or convex surface without its receiving acharge of the contrary kind to that of the surface. 

1566. This effect is one of induction between the bodies, not ofcommunication. The ball, when related to the positive charged surface bythe intervening dielectric, has its opposite sides brought into contrarystates, that side towards the boiler being negative and the outer sidepositive. More inductric action is directed towards it than would havepassed across the same place if the ball had not been there, for severalreasons; amongst others, because, being a conductor, the resistance of theparticles of the dielectric, which otherwise would have been there, isremoved (1298. ); and also, because the reacting positive surface of theball being projected further out from the boiler than when there is nointroduction of conducting matter, is more free therefore to act throughthe rest of the dielectric towards surrounding conductors, and so favoursthe exaltation of that inductric polarity which is directed in its course. It is, as to the exaltation of force upon its outer surface beyond thatupon the inductric surface of the boiler, as if the latter were itselfprotuberant in that direction. Thus it acquires a state like, but higherthan, that of the surface of the boiler which causes it; and sufficientlyexalted to discharge at its positive surface to the air, or to affect smallparticles, as it is itself affected by the boiler, and they flying to it, take a charge and pass off; and so the ball, as a whole, is brought intothe contrary inducteous state. The consequence is, that, if free to move, its tendency, under the influence of all the forces, to approach the boileris increased, whilst it at the same time becomes more and more exalted inits condition, both of polarity and charge, until, at a certain distance, discharge takes place, it acquires the same state as the boiler, isrepelled, and passing to that conductor most favourably circumstanced todischarge it, there resumes its first indifferent condition. 

1567. It seems to me, that the manner in which inductric bodies affectuncharged floating or moveable conductors near them, is very frequently ofthis nature, and generally so when it ends in a carrying operation (1562. 1602. ). The manner in which, whilst the dominant inductric body cannot giveoff its electricity to the air, the inducteous body _can_ effect thedischarge of the same kind of force, is curious, and, in the case ofelongated or irregularly shaped conductors, such as filaments or particlesof dust, the effect will often be very ready, and the consequent attractionimmediate. 

1568. The effect described is also probably influential in causing thosevariations in spark discharge referred to in the last series (1386. 1390. 1391. ): for if a particle of dust were drawn towards the axis of inductionbetween the balls, it would tend, whilst at some distance from that axis, to commence discharge at itself, in the manner described (1566. ), and thatcommencement might so far facilitate the act (1417. 1420. ) as to make thecomplete discharge, as spark, pass through the particle, though it mightnot be the shortest course from ball to ball. So also, with equal balls atequal distances, as in the experiments of comparison already described(1493. 1506. ), a particle being between one pair of balls would causedischarge there in preference; or even if a particle were between each, difference of size or shape would give one for the time a predominance overthe other. 

1569. The power of particles of dust to carry off electricity in cases ofhigh tension is well known, and I have already mentioned some instances ofthe kind in the use of the inductive apparatus (1201. ). The generaloperation is very well shown by large light objects, as the toy called theelectrical spider; or, if smaller ones are wanted for philosophicalinvestigation, by the smoke of a glowing green wax taper, which, presentinga successive stream of such particles, makes their course visible. 

1570. On using oil of turpentine as the dielectric, the action and courseof small conducting carrying particles in it can be well observed. A fewshort pieces of thread will supply the place of carriers, and theirprogressive action is exceedingly interesting. 

1571. A very striking effect was produced on oil of turpentine, which, whether it was due to the carrying power of the particles in it, or to anyother action of them, is perhaps as yet doubtful. A portion of that fluidin a glass vessel had a large uninsulated silver dish at the bottom, and anelectrified metal rod with a round termination dipping into it at the top. The insulation was very good, and the attraction and other phenomenastriking. The rod end, with a drop of gum water attached to it, was thenelectrified in the fluid; the gum water soon spun off in fine threads, andwas quickly dissipated through the oil of turpentine. By the time that fourdrops had in this way been commingled with a pint of the dielectric, thelatter had lost by far the greatest portion of its insulating power; nosparks could be obtained in the fluid; and all the phenomena dependent uponinsulation had sunk to a low degree. The fluid was very slightly turbid. Upon being filtered through paper only, it resumed its first clearness, andnow insulated as well as before. The water, therefore, was merely diffusedthrough the oil of turpentine, not combined with or dissolved in it: butwhether the minute particles acted as carriers, or whether they were notrather gathered together in the line of highest inductive tension (1350. ), and there, being drawn into elongated forms by the electric forces, combined their effects to produce a band of matter having considerableconducting power, as compared with the oil of turpentine, is as yetquestionable. 

1572. The analogy between the action of solid conducting carrying particlesand that of the charged particles of fluid insulating substances, acting asdielectrics, is very evident and simple; but in the latter case the resultis, necessarily, currents in the mobile media. Particles are brought byinductric action into a polar state; and the latter, after rising to acertain tension (1370. ), is followed by the communication of a part of theforce originally on the conductor; the particles consequently becomecharged, and then, under the joint influence of the repellent andattractive forces, are urged towards a discharging place, or to that spotwhere these inductric forces are most easily compensated by the contraryinducteous forces. 

1573. Why a point should be so exceedingly favourable to the production ofcurrents in a fluid insulating dielectric, as air, is very evident. It isat the extremity of the point that the intensity necessary to charge theair is first acquired (1374. ); it is from thence that the charged particlerecedes; and the mechanical force which it impresses on the air to form acurrent is in every way favoured by the shape and position of the rod, ofwhich the point forms the termination. At the same time, the point, havingbecome the origin of an active mechanical force, does, by the very act ofcausing that force, namely, by discharge, prevent any other part of the rodfrom acquiring the same necessary condition, and so preserves and sustainsits own predominance. 

1574. The very varied and beautiful phenomena produced by sheltering orenclosing the point, illustrate the production of the current exceedinglywell, and justify the same conclusions; it being remembered that in suchcases the effect upon the discharge is of two kinds. For the current may beinterfered with by stopping the access of fresh uncharged air, or retardingthe removal of that which has been charged, as when a point is electrifiedin a tube of insulating matter closed at one extremity; or the _electriccondition_ of the point itself may be altered by the relation of otherparts in its neighbourhood, also rendered electric, as when the point is ina metal tube, by the metal itself, or when it is in the glass tube, by asimilar action of the charged parts of the glass, or even by thesurrounding air which has been charged, and which cannot escape. 

1575. Whenever it is intended to observe such inductive phenomena in afluid dielectric as have a direct relation to, and dependence upon, thefluidity of the medium, such, for instance, as discharge from points, orattractions and repulsions, &c. , then the mass of the fluid should begreat, and in such proportion to the distance between the inductric andinducteous surfaces as to include all the _lines of inductive force_(1369. ) between them; otherwise, the effects of currents, attraction, &c. , which are the resultants of all these forces, cannot be obtained. Thephenomena, which occur in the open air, or in the middle of a globe filledwith oil of turpentine, will not take place in the same media if confinedin tubes of glass, shell-lac, sulphur, or other such substances, thoughthey be excellent insulating dielectrics; nor can they be expected: for insuch cases, the polar forces, instead of being all dispersed amongst fluidparticles, which tend to move under their influence, are now associated inmany parts with particles that, notwithstanding their tendency to motion, are constrained by their solidity to remain quiescent. 

1576. The varied circumstances under which, with conductors differentlyformed and constituted, currents can occur, all illustrate the samesimplicity of production. A _ball_, if the intensity be raised sufficientlyon its surface, and that intensity be greatest on a part consistent withthe production of a current of air up to and off from it, will produce theeffect like a point (1537); such is the case whenever the glow occurs upona ball, the current being essential to that phenomenon. If as large asphere as can well be employed with the production of glow be used, theglow will appear at the place where the current leaves the ball, and thatwill be the part directly opposite to the connection of the ball and rodwhich supports it; but by increasing the tension elsewhere, so as to raiseit above the tension upon that spot, which can easily be effectedinductively, then the place of the glow and the direction of the currentwill also change, and pass to that spot which for the time is mostfavourable for their production (1591. ). 

1577. For instance, approaching the hand towards the ball will tend tocause brush (1539. ), but by increasing the supply of electricity thecondition of glow may be preserved; then on moving the hand about from sideto side the position of the glow will very evidently move with it. 

1578. A point brought towards a glowing ball would at twelve or fourteeninches distance make the glow break into brush, but when still nearer, glowwas reproduced, probably dependent upon the discharge of wind or airpassing from the point to the ball, and this glow was very obedient to themotion of the point, following it in every direction. 

1579. Even a current of wind could affect the place of the glow; for avarnished glass tube being directed sideways towards the ball, air wassometimes blown through it at the ball and sometimes not. In the formercase, the place of the glow was changed a little, as if it were blown awayby the current, and this is just the result which might have beenanticipated. All these effects illustrate beautifully the general causesand relations, both of the glow and the current of air accompanying it(1574. ). 

1580. Flame facilitates the production of a current in the dielectricsurrounding it. Thus, if a ball which would not occasion a current in theair have a flame, whether large or small, formed on its surface, thecurrent is produced with the greatest ease; but not the least difficultycan occur in comprehending the effective action of the flame in this case, if its relation, as part of the surrounding dielectric, to the electrifiedball, be but for a moment considered (1375. 1380. ). 

1581. Conducting fluid terminations, instead of rigid points, illustrate ina very beautiful manner the formation of the currents, with their effectsand influence in exalting the conditions under which they were commenced. Let the rounded end of a brass rod, 0. 3 of an inch or thereabouts indiameter, point downwards in free air; let it be amalgamated, and have adrop of mercury suspended from it; and then let it be powerfullyelectrized. The mercury will present the phenomenon of _glow_; a current ofair will rush along the rod, and set off from the mercury directlydownwards; and the form of the metallic drop will be slightly affected, theconvexity at a small part near the middle and lower part becoming greater, whilst it diminishes all round at places a little removed from this spot. The change is from the form of _a_ (fig. 135. ) to that of _b_, and is duealmost, if not entirely, to the mechanical force of the current of airsweeping over its surface. 

1582. As a comparative observation, let it be noticed, that a ballgradually brought towards it converts the glow into brushes, and ultimatelysparks pass from the most projecting part of the mercury. A point does thesame, but at much smaller distances. 

1583. Take next a drop of strong solution of muriate of lime; beingelectrified, a part will probably be dissipated, but a considerableportion, if the electricity be not too powerful, will remain, forming aconical drop (fig. 136. ), accompanied by a strong current. If glow beproduced, the drop will be smooth on the surface. If a short low brush isformed, a minute tremulous motion of the liquid will be visible; but botheffects coincide with the principal one to be observed, namely, the regularand successive charge of air, the formation of a wind or current, and theform given by that current to the fluid drop, if a discharge ball begradually brought toward the cone, sparks will at last pass, and these willbe from the apex of the cone to the approached ball, indicating aconsiderable degree of conducting power in this fluid. 

1584. With a drop of water, the effects were of the same kind, and werebest obtained when a portion of gum water or of syrup hung from a ball(fig. 137. ). When the machine was worked slowly, a fine large quiet conicaldrop, with concave lateral outline, and a small rounded end, was produced, on which the glow appeared, whilst a steady wind issued, in a directionfrom the point of the cone, of sufficient force to depress the surface ofuninsulated water held opposite to the termination. When the machine wasworked more rapidly some of the water was driven off; the smaller pointedportion left was roughish on the surface, and the sound of successive brushdischarges was heard. With still more electricity, more water wasdispersed; that which remained was elongated and contracted, with analternating motion; a stronger brush discharge was heard, and thevibrations of the water and the successive discharges of the individualbrushes were simultaneous. When water from beneath was brought towards thedrop, it did not indicate the same regular strong contracted current of airas before; and when the distance was such that sparks passed, the waterbeneath was _attracted_ rather than driven away, and the current of air_ceased_. 

1585. When the discharging ball was brought near the drop in its firstquiet glowing state (1582. ), it converted that glow into brushes, andcaused the vibrating motion of the drop. When still nearer, sparks passed, but they were always from the metal of the rod, over the surface of thewater, to the point, and then across the air to the ball. This is a naturalconsequence of the deficient conducting power of the fluid (1584. 1585. ). 

1586. Why the drop vibrated, changing its form between the periods ofdischarging brushes, so as to be more or less acute at particular instants, to be most acute when the brush issued forth, and to be isochronous in itsaction, and how the quiet glowing liquid drop, on assuming the conicalform, facilitated, as it were, the first action, are points, as to theory, so evident, that I will not stop to speak of them. The principal thing toobserve at present is, the formation of the carrying current of air, andthe manner in which it exhibits its existence and influence by giving formto the drop. 

1587. That the drop, when of water, or a better conductor than water, isformed into a cone principally by the current of air, is shown amongstother ways (1594. ) thus. A sharp point being held opposite the conicaldrop, the latter soon lost its pointed form; was retraced and became round;the current of air from it ceased, and was replaced by one from the pointbeneath, which, if the latter were held near enough to the drop, actuallyblew it aside, and rendered it concave in form. 

1588. It is hardly necessary to say what happened with still worseconductors than water, as oil, or oil of turpentine; the fluid itself wasthen spun out into threads and carried off, not only because the airrushing over its surface helped to sweep it away, but also because itsinsulating particles assumed the same charged state as the particles ofair, and, not being able to discharge to them in a much greater decree thanthe air particles themselves could do, were carried off by the same causeswhich urged those in their course. A similar effect with melted sealing-waxon a metal point forms an old and well-known experiment. 

1589. A drop of gum water in the exhausted receiver of the air-pump was notsensibly affected in its form when electrified. When air was let in, itbegun to show change of shape when the pressure was ten inches of mercury. At the pressure of fourteen or fifteen inches the change was more sensible, and as the air increased in density the effects increased, until they werethe same as those in the open atmosphere. The diminished effect in the rareair I refer to the relative diminished energy of its current; thatdiminution depending, in the first place, on the lower electric conditionof the electrified ball in the rarefied medium, and in the next, on theattenuated condition of the dielectric, the cohesive force of water inrelation to rarefied air being something like that of mercury to dense air(1581. ), whilst that of water in dense air may be compared to that ofmercury in oil of turpentine (1597. ). 

1590. When a ball is covered with a thick conducting fluid, as treacle orsyrup, it is easy by inductive action to determine the wind from almost anypart of it (1577. ); the experiment, which before was of rather difficultperformance, being rendered facile in consequence of the fluid enablingthat part, which at first was feeble in its action, to rise into an exaltedcondition by assuming a pointed form. 

1591. To produce the current, the electric intensity must rise and continueat _one spot_, namely, at the origin of the current, higher than elsewhere, and then, air having a uniform and ready access, the current is produced. If no current be allowed (1574. ), then discharge may take place by brush orspark. But whether it be by brush or spark, or wind, it seems very probablethat the initial intensity or tension at which a particle of a givengaseous dielectric charges, or commences discharge, is, under theconditions before expressed, always the same (1410. ). 

1592. It is not supposed that all the air which enters into motion iselectrified; on the contrary, much that is not charged is carried on intothe stream. The part which is really charged may be but a small proportionof that which is ultimately set in motion (1442. ). 

1593. When a drop of gum water (1584. ) is made _negative_, it presents alarger cone than when made positive; less of the fluid is thrown off, andyet, when a ball is approached, sparks can hardly be obtained, so pointedis the cone, and so free the discharge. A point held opposite to it did notcause the retraction of the cone to such an extent as when it was positive. All the effects are so different from those presented by the positive cone, that I have no doubt such drops would present a very instructive method ofinvestigating the difference of positive and negative discharge in air andother dielectrics (1480. 1501. ). 

1594. That I may not be misunderstood (1587. ), I must observe here that Ido not consider the cones produced as the result _only_ of the current ofair or other insulating dielectric over their surface. When the drop is ofbadly conducting matter, a part of the effect is due to the electrifiedstate of the particles, and this part constitutes almost the whole when thematter is melted sealing-wax, oil of turpentine, and similar insulatingbodies (1588. ). But even when the drop is of good conducting matter, aswater, solutions, or mercury, though the effect above spoken of will thenbe insensible (1607. ), still it is not the mere current of air or otherdielectric which produces all the change of form; for a part is due tothose attractive forces by which the charged drop, if free to move, wouldtravel along the line of strongest induction, and not being free to move, has its form elongated until the _sum_ of the different forces tending toproduce this form is balanced by the cohesive attraction of the fluid. Theeffect of the attractive forces are well shown when treacle, gum water, orsyrup is used; for the long threads which spin out, at the same time thatthey form the axes of the currents of air, which may still be considered asdetermined at their points, are like flexible conductors, and show by theirdirections in what way the attractive forces draw them. 

1595. When the phenomena of currents are observed in dense insulatingdielectrics, they present us with extraordinary degrees of mechanicalforce. Thus, if a pint of well-rectified and filtered (1571. ) oil ofturpentine be put into a glass vessel, and two wires be dipped into it indifferent places, one leading to the electrical machine, and the other tothe discharging train, on working the machine the fluid will be thrown intoviolent motion throughout its whole mass, whilst at the same time it willrise two, three or four inches up the machine wire, and dart off jets fromit into the air. 

1596. If very clean uninsulated mercury be at the bottom of the fluid, andthe wire from the machine be terminated either by a ball or a point, andalso pass through a glass tube extending both above and below the surfaceof the oil of turpentine, the currents can be better observed, and will beseen to rush down the wire, proceeding directly from it towards themercury, and there, diverging in all directions, will ripple its surfacestrongly, and mounting up at the sides of the vessel, will return tore-enter upon their course. 

1597. A drop of mercury being suspended from an amalgamated brass ball, preserved its form almost unchanged in air (1581. ); but when immersed inthe oil of turpentine it became very pointed, and even particles of themetal could be spun out and carried off by the currents of the dielectric. The form of the liquid metal was just like that of the syrup in air(1584. ), the point of the cone being quite as fine, though not so long. Bybringing a sharp uninsulated point towards it, it could also be effected inthe same manner as the syrup drop in air (1587. ), though not so readily, because of the density and limited quantity of the dielectric. 

1598. If the mercury at the bottom of the fluid be connected with theelectrical machine, whilst a rod is held in the hand terminating in a ballthree quarters of an inch, less or more, in diameter, and the ball bedipped into the electrified fluid, very striking appearances ensue. Whenthe ball is raised again so as to be at a level nearly out of the fluid, large portions of the latter will seem to cling to it (fig. 138. ). If it beraised higher, a column of the oil of turpentine will still connect it withthat in the basin below (fig. 139. ). If the machine be excited into morepowerful action, this will become more bulky, and may then also be raisedhigher, assuming the form (fig. 140); and all the time that these effectscontinue, currents and counter-currents, sometimes running very closetogether, may be observed in the raised column of fluid. 

1599. It is very difficult to decide by sight the direction of the currentsin such experiments as these. If particles of silk are introduced theycling about the conductors; but using drops of water and mercury the courseof the fluid dielectric seems well indicated. Thus, if a drop of water beplaced at the end of a rod (1571. ) over the uninsulated mercury, it is soonswept away in particles streaming downwards towards the mercury. If anotherdrop be placed on the mercury beneath the end of the rod, it is quicklydispersed in all directions in the form of streaming particles, theattractive forces drawing it into elongated portions, and the currentscarrying them away. If a drop of mercury be hung from a ball used to raisea column of the fluid (1598. ), then the shape of the drop seems to showcurrents travelling in the fluid in the direction indicated by the arrows(fig. 141. ). 

1600. A very remarkable effect is produced on these phenomena, connectedwith positive and negative charge and discharge, namely, that a ballcharged positively raises a much higher and larger column of the oil ofturpentine than when charged negatively. There can be no doubt that this isconnected with the difference of positive and negative action alreadyspoken of (1480. 1525. ), and tends much to strengthen the idea that suchdifference is referable to the particles of the dielectric rather than tothe charged conductors, and is dependent upon the mode in which theseparticles polarize (1503. 1523. ). 

1601. Whenever currents travel in insulating dielectrics they really effectdischarge; and it is important to observe, though a very natural result, that it is indifferent which way the current or particles travel, as withreversed direction their state is reversed. The change is easily made, either in air or oil of turpentine, between two opposed rods, for aninsulated ball being placed in connexion with either rod and brought nearits extremity, will cause the current to set towards it from the oppositeend. 

1602. The two currents often occur at once, as when both terminationspresent brushes, and frequently when they exhibit the glow (1531. ). In suchcases, the charged particles, or many of them, meet and mutually dischargeeach other (1518. 1612. ). If a smoking wax taper be held at the end of aninsulating rod towards a charged prime conductor, it will very often happenthat two currents will form, and be rendered visible by its vapour, onepassing as a fine filament of smoky particles directly to the chargedconductor, and the other passing as directly from the same taper wickoutwards, and from the conductor: the principles of inductric action andcharge, which were referred to in considering the relation of a carrierball and a conductor (1566. ), being here also called into play. 

 * * * * *

1603. The general analogy and, I think I may say, identity of action foundto exist as to insulation and conduction (1338. 1561. ) when bodies, thebest and the worst in the classes of insulators or conductors, werecompared, led me to believe that the phenomena of _convection_ in badlyconducting media were not without their parallel amongst the bestconductors, such even as the metals. Upon consideration, the cones producedby Davy[A] in fluid metals, as mercury and tin, seemed to be cases inpoint, and probably also the elongation of the metallic medium throughwhich a current of electricity was passing, described by Ampère (1113)[B];for it is not difficult to conceive, that the diminution of convectiveeffect, consequent upon the high conducting power of the metallic mediaused in these experiments, might be fully compensated for by the enormousquantity of electricity passing. In fact, it is impossible not to expect_some_ effect, whether sensible or not, of the kind in question, when sucha current is passing through a fluid offering a sensible resistance to thepassage of the electricity, and, thereby, giving proof of a certain degreeof insulating power (1328. ). 

 [A] Philosophical Transactions, 1823, p. 155. 

 [B] Bibliothèque Universelle, xxi, 417. 

1604. I endeavoured to connect the convective currents in air, oil ofturpentine, &c. And those in metals, by intermediate cases, but found thisnot easy to do. On taking bodies, for instance, which, like water, adds, solutions, fused salts or chlorides, &c. , have intermediate conductingpowers, the minute quantity of electricity which the common machine cansupply (371. 861. ) is exhausted instantly, so that the cause of thephenomenon is kept either very low in intensity, or the instant of timeduring which the effect lasts is so small, that one cannot hope to observethe result sought for. If a voltaic battery be used, these bodies are allelectrolytes, and the evolution of gas, or the production of other changes, interferes and prevents observation of the effect required. 

1605. There are, nevertheless, some experiments which illustrate theconnection. Two platina wires, forming the electrodes of a powerful voltaicbattery, were placed side by side, near each other, in distilled water, hermetically sealed up in a strong glass tube, some minute vegetable fibresbeing present in the water. When, from the evolution of gas and theconsequent increased pressure, the bubbles formed on the electrodes were sosmall as to produce but feebly ascending currents, then it could beobserved that the filaments present were attracted and repelled between thetwo wires, as they would have been between two oppositely charged surfacesin air or oil of turpentine, moving so quickly as to displace and disturbthe bubbles and the currents which these tended to form. Now I think itcannot be doubted, that under similar circumstances, and with an abundantsupply of electricity, of sufficient tension also, convective currentsmight have been formed; the attractions and repulsions of the filamentswere, in fact, the elements of such currents (1572. ), and therefore water, though almost infinitely above air or oil of turpentine as a conductor, isa medium in which similar currents can take place. 

1606. I had an apparatus made (fig. 142. ) in which _a_ is a plate ofshell-lac, _b_ a fine platina wire passing through it, and having only thesection of the wire exposed above; _c_ a ring of bibulous paper resting onthe shell-lac, and _d_ distilled water retained by the paper in its place, and just sufficient in quantity to cover the end of the wire _b_; anotherwire, _e_, touched a piece of tinfoil lying in the water, and was alsoconnected with a discharging train; in this way it was easy, by rendering_b_ either positive or negative, to send a current of electricity by itsextremity into the fluid, and so away by the wire _e_. 

1607. On connecting _b_ with the conductor of a powerful electricalmachine, not the least disturbance of the level of the fluid over the endof the wire during the working of the machine could be observed; but at thesame time there was not the smallest indication of electrical charge aboutthe conductor of the machine, so complete was the discharge. I concludethat the quantity of electricity passed in a _given time_ had been toosmall, when compared with the conducting power of the fluid to produce thedesired effect. 

1608. I then charged a large Leyden battery (291. ), and discharged itthrough the wire _b_, interposing, however, a wet thread, two feet long, toprevent a spark in the water, and to reduce what would else have been asudden violent discharge into one of more moderate character, enduring fora sensible length of time (334. ). I now did obtain a very brief elevationof the water over the end of the wire; and though a few minute bubbles ofgas were at the same time formed there, so as to prevent me from assertingthat the effect was unequivocally the same as that obtained by DAVY in themetals, yet, according to my best judgement, it was partly, and I believeprincipally, of that nature. 

1609. I employed a voltaic battery of 100 pair of four-inch plates forexperiments of a similar nature with electrolytes. In these cases theshell-lac was cupped, and the wire _b_ 0. 2 of an inch in diameter. Sometimes I used a positive amalgamated zinc wire in contact with dilutesulphuric acid; at others, a negative copper wire in a solution of sulphateof copper; but, because of the evolution of gas, the precipitation ofcopper, &c. , I was not able to obtain decided results. It is but right tomention, that when I made use of mercury, endeavouring to repeat DAVY'sexperiment, the battery of 100 pair was not sufficient to produce theelevations[A]. 

 [A] In the experiments at the Royal Institution, Sir H. Davy used, I think, 500 or 600 pairs of plates. Those at the London Institution were made with the apparatus of Mr. Pepys (consisting of an enormous single pair of plates), described in the Philosophical Transactions for 1832, p. 187. 

1610. The latter experiments (1609. ) may therefore be considered as failingto give the hoped-for proof, but I have much confidence in the former(1605. 1608. ), and in the considerations (1603. ) connected with them. If Ihave rightly viewed them, and we may be allowed to compare the currents atpoints and surfaces in such extremely different bodies as air and themetals, and admit that they are effects of the _same_ kind, differing onlyin degree and in proportion to the insulating or conducting power of thedielectric used, what great additional argument we obtain in favour of thattheory, which in the phenomena of insulation and conduction also, as inthese, would link _the same_ apparently dissimilar substances together(1336. 1561. ); and how completely the general view, which refers all thephenomena to the direct action of the molecules of matter, seems to embracethe various isolated phenomena as they successively come underconsideration!

 * * * * *

1611. The connection of this convective or carrying effect, which dependsupon a certain degree of insulation, with conduction; i. E. The occurrenceof both in so many of the substances referred to, as, for instance, themetals, water, air, &c. , would lead to many very curious theoreticalgeneralizations, which I must not indulge in here. One point, however, Ishall venture to refer to. Conduction appears to be essentially an actionof contiguous particles, and the considerations just stated, together withothers formerly expressed (1326, 1336, &c. ), lead to the conclusion, thatall bodies conduct, and by the same process, air as well as metals; theonly difference being in the necessary degree of force or tension betweenthe particles which must exist before the act of conduction or transferfrom one particle to another can take place. 

1612. The question then arises, what is this limiting condition whichseparates, as it were, conduction and insulation from each other? Does itconsist in a difference between the two contiguous particles, or thecontiguous poles of these particles, in the nature and amount of positiveand negative force, no communication or discharge occurring unless thatdifference rises up to a certain degree, variable for different bodies, butalways the same for the same body? Or is it true that, however small thedifference between two such particles, if _time_ be allowed, equalizationof force will take place, even with the particles of such bodies as air, sulphur or lac? In the first case, insulating power in any particular bodywould be proportionate to the degree of the assumed necessary difference offorce; in the second, to the _time_ required to equalize equal degrees ofdifference in different bodies. With regard to airs, one is almost led toexpect a permanent difference of force; but in all other bodies, time seemsto be quite sufficient to ensure, ultimately, complete conduction. Thedifference in the modes by which insulation may be sustained, or conductioneffected, is not a mere fanciful point, but one of great importance, asbeing essentially connected with the molecular theory of induction, and themanner in which the particles of bodies assume and retain their polarizedstate. 

 * * * * *

¶ xi. _Relation of a vacuum to electrical phenomena. _

1613. It would seem strange, if a theory which refers all the phenomena ofinsulation and conduction, i. E. All electrical phenomena, to the action ofcontiguous particles, were to omit to notice the assumed possible case of a_vacuum_. Admitting that a vacuum can be produced, it would be a verycurious matter indeed to know what its relation to electrical phenomenawould be; and as shell-lac and metal are directly opposed to each other, whether a vacuum would be opposed to them both, and allow neither ofinduction or conduction across it. Mr. Morgan[A] has said that a vacuumdoes not conduct. Sir H. Davy concluded from his investigations, that asperfect a vacuum as could be made[B] did conduct, but does not consider theprepared spaces which he used as absolute vacua. In such experiments Ithink I have observed the luminous discharge to be principally on the innersurface of the glass; and it does not appear at all unlikely, that, if thevacuum refused to conduct, still the surface of glass next it might carryon that action. 

 [A] Philosophical Transactions, 1785, p. 272

 [B] Ibid. 1822, p. 64. 

1614. At one time, when I thought inductive force was exerted in rightlines, I hoped to illustrate this important question by making experimentson induction with metallic mirrors (used only as conducting vessels)exposed towards a very clear sky at night time, and of such concavity thatnothing but the firmament could be visible from the lowest part of theconcave _n_, fig. 143. Such mirrors, when electrified, as by connexion witha Leyden jar, and examined by a carrier ball, readily gave electricity atthe lowest part of their concavity if in a room; but I was in hopes offinding that, circumstanced as before stated, they would give little ornone at the same spot, if the atmosphere above really terminated in avacuum. I was disappointed in the conclusion, for I obtained as muchelectricity there as before; but on discovering the action of induction incurved lines (1231. ), found a full and satisfactory explanation of theresult. 

1615. My theory, as far as I have ventured it, does not pretend to decideupon the consequences of a vacuum. It is not at present limitedsufficiently, or rendered precise enough, either by experiments relating tospaces void of matter, or those of other kinds, to indicate what wouldhappen in the vacuum case. I have only as yet endeavoured to establish, what all the facts seem to prove, that when electrical phenomena, as thoseof induction, conduction, insulation and discharge occur, they depend on, and are produced by the action of _contiguous_ particles of matter, thenext existing particle being considered as the contiguous one; and I havefurther assumed, that these particles are polarized; that each exhibits thetwo forces, or the force in two directions (1295. 1298. ); and that they actat a distance, only by acting on the _contiguous_ and intermediateparticles. 

1616. But assuming that a perfect vacuum were to intervene in the course ofthe lines of inductive action (1304. ), it does not follow from this theory, that the particles on opposite sides of such a vacuum could not act on eachother. Suppose it possible for a positively electrified particle to be inthe centre of a vacuum an inch in diameter, nothing in my present viewsforbids that the particle should act at the distance of half an inch on allthe particles forming the inner superficies of the bounding sphere, andwith a force consistent with the well-known law of the squares of thedistance. But suppose the sphere of an inch were full of insulating matter, the electrified particle would not then, according to my notion, actdirectly on the distant particles, but on those in immediate associationwith it, employing _all_ its power in polarizing them; producing in themnegative force equal in amount to its own positive force and directedtowards the latter, and positive force of equal amount directed outwardsand acting in the same manner upon the layer of particles next insuccession. So that ultimately, those particles in the surface of a sphereof half an inch radius, which were acted on _directly_ when that sphere wasa vacuum, will now be acted on _indirectly_ as respects the centralparticle or source of action, i. E. They will be polarized in the same way, and with the same amount of force. 

§ 19. _Nature of the electric current. _

1617. The word _current_ is so expressive in common language, that whenapplied in the consideration of electrical phenomena we can hardly divestit sufficiently of its meaning, or prevent our minds from being prejudicedby it (283. 511. ). I shall use it in its common electrical sense, namely, to express generally a certain condition and relation of electrical forcessupposed to be in progression. 

1618. A current is produced both by excitement and discharge; andwhatsoever the variation of the two general causes may be, the effectremains the same. Thus excitement may occur in many ways, as by friction, chemical action, influence of heat, change of condition, induction, &c. ;and discharge has the forms of conduction, electrolyzation, disruptivedischarge, and convection; yet the current connected with these actions, when it occurs, appears in all cases to be the same. This constancy in thecharacter of the current, notwithstanding the particular and greatvariations which may be made in the mode of its occurrence, is exceedinglystriking and important; and its investigation and development promise tosupply the most open and advantageous road to a true and intimateunderstanding of the nature of electrical forces. 

1619. As yet the phenomena of the current have presented nothing inopposition to the view I have taken of the nature of induction as an actionof contiguous particles. I have endeavoured to divest myself of prejudicesand to look for contradictions, but I have not perceived any in conductive, electrolytic, convective, or disruptive discharge. 

1620. Looking at the current as a _cause_, it exerts very extraordinary anddiverse powers, not only in its course and on the bodies in which itexists, but collaterally, as in inductive or magnetic phenomena. 

1621. _Electrolytic action. _--One of its direct actions is the exertion ofpure chemical force, this being a result which has now been examined to aconsiderable extent. The effect is found to be _constant_ and _definite_for the quantity of electric force discharged (783. &c. ); and beyond that, the _intensity_ required is in relation to the intensity of the affinity orforces to be overcome (904. 906. 911. ). The current and its consequencesare here proportionate; the one may be employed to represent the other; nopart of the effect of either is lost or gained; so that the case is astrict one, and yet it is the very case which most strikingly illustratesthe doctrine that induction is an action of contiguous particles (1164. 1343. ). 

1622. The process of electrolytic discharge appears to me to be in closeanalogy, and perhaps in its nature identical with another process ofdischarge, which at first seems very different from it, I mean _convection_(1347. 1572. ). In the latter case the particles may travel for yards acrossa chamber; they may produce strong winds in the air, so as to movemachinery; and in fluids, as oil of turpentine, may even shake the hand, and carry heavy metallic bodies about[A]; and yet I do not see that theforce, either in kind or action, is at all different to that by which aparticle of hydrogen leaves one particle of oxygen to go to another, or bywhich a particle of oxygen travels in the contrary direction. 

 [A] If a metallic vessel three or four inches deep, containing oil of turpentine, be insulated and electrified, and a rod with a ball (an inch or more in diameter) at the end have the ball immersed in the fluid whilst the end is held in the hand, the mechanical force generated when the ball is moved to and from the sides of the vessel will soon be evident to the experimenter. 

1623. Travelling particles of the air can effect chemical changes just aswell as the contact of a fixed platina electrode, or that of a combiningelectrode, or the ions of a decomposing electrolyte (453. 471. ); and in theexperiment formerly described, where eight places of decomposition wererendered active by one current (469. ), and where charged particles of airin motion were the only electrical means of connecting these parts of thecurrent, it seems to me that the action of the particles of the electrolyteand of the air were essentially the same. A particle of air was renderedpositive; it travelled in a certain determinate direction, and coming to anelectrolyte, communicated its powers; an equal amount of positive force wasaccordingly acquired by another particle (the hydrogen), and the latter, socharged, travelled as the former did, and in the same direction, until itcame to another particle, and transferred its power and motion, making thatother particle active. Now, though the particle of air travelled over avisible and occasionally a large space, whilst the particle of theelectrolyte moved over an exceedingly small one; though the air particlemight be oxygen, nitrogen, or hydrogen, receiving its charge from force ofhigh intensity, whilst the electrolytic particle of hydrogen had a naturalaptness to receive the positive condition with extreme facility; though theair particle might be charged with very little electricity at a very highintensity by one process, whilst the hydrogen particle might be chargedwith much electricity at a very low intensity by another process; these arenot differences of kind, as relates to the final discharging action ofthese particles, but only of degree; not essential differences which makethings unlike, but such differences as give to things, similar in theirnature, that great variety which fits them for their office in the systemof the universe. 

1624. So when a particle of air, or of dust in it, electrified at anegative point, moves on through the influence of the inductive forces(1572. ) to the next positive surface, and after discharge passes away, itseems to me to represent exactly that particle of oxygen which, having beenrendered negative in the electrolyte, is urged by the same disposition ofinductive forces, and going to the positive platina electrode, is theredischarged, and then passes away, as the air or dust did before it. 

1625. _Heat_ is another direct effect of the _current_ upon substances inwhich it occurs, and it becomes a very important question, as to therelation of the electric and heating forces, whether the latter is alwaysdefinite in amount[A]. There are many cases, even amongst bodies whichconduct without change, that at present are irreconcileable with theassumption that it is[B]; but there are also many which indicate that, whenproper limitations are applied, the heat produced is definite. Harris hasshown this for a given length of current in a metallic wire, using commonelectricity[C]; and De la Rive has proved the same point for voltaicelectricity by his beautiful application of Breguet's thermometer[D]. 

 [A] See De la Rive's Researches, Bib. Universelle, 1829, xl. P. 40. 

 [B] Amongst others, Davy, Philosophical Transactions, 1821, p. 438. Pelletier's important results, Annales de Chimie, 1834, lvi. P. 371. And Becquerel's non-heating current, Bib. Universelle, 1835, lx. 218. 

 [C] Philosophical Transactions, 1824, pp. 225. 228. 

 [D] Annales de Chimie, 1836, lxii. 177. 

1626. When the production of heat is observed in electrolytes underdecomposition, the results are still more complicated. But important stepshave been taken in the investigation of this branch of the subject by De laRive[A] and others; and it is more than probable that, when the rightlimitations are applied, constant and definite results will here also beobtained. 

 [A] Bib. Universelle, 1829, xl. 49; and Ritchie, Phil. Trans. 1832. P. 296. 

 * * * * *

1627. It is a most important part of the character of the current, andessentially connected with its very nature, that it is always the same. Thetwo forces are everywhere in it. There is never one current of force or onefluid only. Any one part of the current may, as respects the presence ofthe two forces there, be considered as precisely the same with any otherpart; and the numerous experiments which imply their possible separation, as well as the theoretical expressions which, being used daily, assume it, are, I think, in contradiction with facts (511, &c. ). It appears to me tobe as impossible to assume a current of positive or a current of negativeforce alone, or of the two at once with any predominance of one over theother, as it is to give an absolute charge to matter (516. 1169. 1177. ). 

1628. The establishment of this truth, if, as I think, it be a truth, or onthe other hand the disproof of it, is of the greatest consequence. If, as afirst principle, we can establish, that the centres of the two forces, orelements of force, never can be separated to any sensible distance, or atall events not further than the space between two contiguous particles(1615. ), or if we can establish the contrary conclusion, how much moreclear is our view of what lies before us, and how much less embarrassed theground over which we have to pass in attaining to it, than if we remainhalting between two opinions! And if, with that feeling, we rigidly testevery experiment which bears upon the point, as far as our prejudices willlet us (1161. ), instead of permitting them with a theoretical expression topass too easily away, are we not much more likely to attain the real truth, and from that proceed with safety to what is at present unknown?

1629. I say these things, not, I hope, to advance a particular view, but todraw the strict attention of those who are able to investigate and judge ofthe matter, to what must be a turning point in the theory of electricity;to a separation of two roads, one only of which can be right: and I hope Imay be allowed to go a little further into the facts which have driven meto the view I have just given. 

1630. When a wire in the voltaic circuit is heated, the temperaturefrequently rises first, or most at one end. If this effect were due to anyrelation of positive or negative as respects the current, it would beexceedingly important. I therefore examined several such cases; but when, keeping the contacts of the wire and its position to neighbouring thingsunchanged, I altered the direction of the current, I found that the effectremained unaltered, showing that it depended, not upon the direction of thecurrent, but on other circumstances. So there is here no evidence of adifference between one part of the circuit and another. 

1631. The same point, i. E. Uniformity in every part, may be illustrated bywhat may be considered as the inexhaustible nature of the current whenproducing particular effects; for these effects depend upon transfer only, and do not consume the power. Thus a current which will heat one inch ofplatina wire will heat a hundred inches (853. Note). If a current besustained in a constant state, it will decompose the fluid in onevoltameter only, or in twenty others if they be placed in the circuit, ineach to an amount equal to that in the single one. 

1632. Again, in cases of disruptive discharge, as in the spark, there isfrequently a dark part (1422. ) which, by Professor Johnson, has been calledthe neutral point[A]; and this has given rise to the use of expressionsimplying that there are two electricities existing separately, which, passing to that spot, there combine and neutralize each other[B]. But ifsuch expressions are understood as correctly indicating that positiveelectricity alone is moving between the positive ball and that spot, andnegative electricity only between the negative ball and that spot, thenwhat strange conditions these parts must be in; conditions, which to mymind are every way unlike those which really occur! In such a case, onepart of a current would consist of positive electricity only, and thatmoving in one direction; another part would consist of negative electricityonly, and that moving in the other direction; and a third part wouldconsist of an accumulation of the two electricities, not moving in eitherdirection, but mixing up together! and being in a relation to each otherutterly unlike any relation which could be supposed to exist in the twoformer portions of the discharge. This does not seem to me to be natural. In a current, whatever form the discharge may take, or whatever part of thecircuit or current is referred to, as much positive force as is thereexerted in one direction, so much negative force is there exerted in theother. If it were not so we should have bodies electrified not merelypositive and negative, but on occasions in a most extraordinary manner, onebeing charged with five, ten, or twenty times as much of both positive andnegative electricity in equal quantities as another. At present, however, there is no known fact indicating such states. 

 [A] Silliman's Journal, 1834, xxv. P. 57. 

 [B] Thomson on Heat and Electricity, p. 171. 

1633. Even in cases of convection, or carrying discharge, the statementthat the current is everywhere the same must in effect be true (1627. ); forhow, otherwise, could the results formerly described occur? When currentsof air constituted the mode of discharge between the portions of papermoistened with iodide of potassium or sulphate of soda (465. 469. ), decomposition occurred; and I have since ascertained that, whether acurrent of positive air issued from a spot, or one of negative air passedtowards it, the effect of the evolution of iodine or of acid was the same, whilst the reversed currents produced alkali. So also in the magneticexperiments (307. ) whether the discharge was effected by the introductionof a wire, or the occurrence of a spark, or the passage of convectivecurrents either one way or the other (depending on the electrified state ofthe particles), the result was the same, being in all cases dependent uponthe perfect current. 

1634. Hence, the section of a current compared with other sections of thesame current must be a constant quantity, if the actions exerted be of thesame kind; or if of different kinds, then the forms under which the effectsare produced are equivalent to each other, and experimentally convertibleat pleasure. It is in sections, therefore, we must look for identity ofelectrical force, even to the sections of sparks and carrying actions, aswell as those of wires and electrolytes. 

1635. In illustration of the utility and importance of establishing thatwhich may be the true principle, I will refer to a few cases. The doctrineof unipolarity, as formerly stated, and I think generally understood[A], isevidently inconsistent with my view of a current (1627. ); and the latersingular phenomena of poles and flames described by Erman and others[B]partake of the same inconsistency of character. If a unipolar body couldexist, i. E. One that could conduct the one electricity and not the other, what very new characters we should have a right to expect in the currentsof single electricities passing through them, and how greatly ought they todiffer, not only from the common current which is supposed to have bothelectricities travelling in opposite directions in equal amount at the sametime, but also from each other! The facts, which are excellent, have, however, gradually been more correctly explained by Becquerel[C], Andrews[D], and others; and I understand that Professor Ohms[E] hasperfected the work, in his close examination of all the phenomena; andafter showing that similar phenomena can take place with good conductors, proves that with soap, &c. Many of the effects are the mere consequences ofthe bodies evolved by electrolytic action. 

 [A] Erman, Annales de Chimie, 1807. Lxi. P. 115. Davy's Elements, p. 168. Biot, Ency. Brit. Supp, iv. P. 444. Becquerel, Traité, i. P. 167. De la Rive, Bib. Univ. 1837. Vii. 392. 

 [B] Erman, Annales de Chimie, 1824. Xxv. 278. Becquerel, Ibid. Xxxvi. P. 329

 [C] Becquerel, Annales de Chimie, 1831. Xlvi. P. 283. 

 [D] Andrews, Philosophical Magazine, 1836. Ix. 182. 

 [E] Schweigger's Jahrbuch de Chimie, &c. 1830. Heft 8. Not understanding German, it is with extreme regret I confess I have not access, and cannot do justice, to the many most valuable papers in experimental electricity published in that language. I take this opportunity also of stating another circumstance which occasions me great trouble, and, as I find by experience, may make, me seemingly regardless of the labours of others:--it is a gradual loss of memory for some years past; and now, often when I read a memoir, I remember that I have seen it before, and would have rejoiced if at the right time I could have recollected and referred to it in the progress of my own papers. --M. F. 

1636. I conclude, therefore, that the _facts_ upon which the doctrine ofunipolarity was founded are not adverse to that unity and indivisibility ofcharacter which I have stated the current to possess, any more than thephenomena of the pile itself (which might well bear comparison with thoseof unipolar bodies, ) are opposed to it. Probably the effects which havebeen called effects of unipolarity, and the peculiar differences of thepositive and negative surface when discharging into air, gases, or otherdielectrics (1480. 1525. ) which have been already referred to, may haveconsiderable relation to each other[A]. 

 [A] See also Hare in Silliman's Journal, 1833. Xxiv. 246. 

 * * * * *

1637. M. De la Rive has recently described a peculiar and remarkable effectof heat on a current when passing between electrodes and a fluid[A]. It is, that if platina electrodes dip into acidulated water, no change is producedin the passing current by making the positive electrode hotter or colder;whereas making the negative electrode hotter increased the deflexion of agalvanometer affected by the current, from 12° to 30° and even 45°, whilstmaking it colder diminished the current in the same high proportions. 

 [A] Bibliothèque Universelle, 1837, vii. 388. 

1638. That one electrode should have this striking relation to heat whilstthe other remained absolutely without, seem to me as incompatible with whatI conceived to be the character of a current as unipolarity (1627. 1635. ), and it was therefore with some anxiety that I repeated the experiment. Theelectrodes which I used were platina; the electrolyte, water containingabout one sixth of sulphuric acid by weight: the voltaic battery consistedof two pairs of amalgamated zinc and platina plates in dilute sulphuricacid, and the galvanometer in the circuit was one with two needles, andgave when the arrangement was complete a deflexion of 10° or 12°. 

1639. Under these circumstances heating either electrode increased thecurrent; heating both produced still more effect. When both were heated, ifeither were cooled, the effect on the current fell in proportion. Theproportion of effect due to heating this or that electrode varied, but onthe whole heating the negative seemed to favour the passage of the currentsomewhat more than heating the positive. Whether the application of heatwere by a flame applied underneath, or one directed by a blowpipe fromabove, or by a hot iron or coal, the effect was the same. 

1640. Having thus removed the difficulty out of the way of my viewsregarding a current, I did not pursue this curious experiment further. Itis probable, that the difference between my results and those of M. De laRive may depend upon the relative values of the currents used; for Iemployed only a weak one resulting from two pairs of plates two inches longand half an inch wide, whilst M. De la Rive used four pairs of plates ofsixteen square inches in surface. 

 * * * * *

1641. Electric discharges in the atmosphere in the form of balls of firehave occasionally been described. Such phenomena appear to me to beincompatible with all that we know of electricity and its modes ofdischarge. As _time_ is an element in the effect (1418. 1436. ) it ispossible perhaps that an electric discharge might really pass as a ballfrom place to place; but as every thing shows that its velocity must bealmost infinite, and the time of its duration exceedingly small, it isimpossible that the eye should perceive it as anything else than a line oflight. That phenomena of balls of fire may appear in the atmosphere, I donot mean to deny; but that they have anything to do with the discharge ofordinary electricity, or are at all related to lightning or atmosphericelectricity, is much more than doubtful. 

 * * * * *

1642. All these considerations, and many others, help to confirm theconclusion, drawn over and over again, that the current is an indivisiblething; an axis of power, in every part of which both electric forces arepresent in equal amount[A] (517. 1627. ). With conduction andelectrolyzation, and even discharge by spark, such a view will harmonizewithout hurting any of our preconceived notions; but as relates toconvection, a more startling result appears, which must therefore beconsidered. 

 [A] I am glad to refer here to the results obtained by Mr. Christie with magneto-electricity, Philosophical Transactions, 1833, p. 113 note. As regards the current in a wire, they confirm everything that I am contending for. 

1643. If two balls A and B be electrified in opposite states and heldwithin each other's influence, the moment they move towards each other, acurrent, or those effects which are understood by the word current, will beproduced. Whether A move towards B, or B move in the opposite directiontowards A, a current, and in both cases having the same _direction_, willresult. If A and B move from each other, then a _current_ in the oppositedirection, or equivalent effects, will be produced. 

1644. Or, as charge exists only by induction (1178. 1299. ), and a body whenelectrified is necessarily in relation to other bodies in the oppositestate; so, if a ball be electrified positively in the middle of a room andbe then moved in any direction, effects will be produced, as _current_ inthe same direction (to use the conventional mode of expression) hadexisted: or, if the ball be negatively electrified, and then moved, effectsas if a current in a direction contrary to that of the motion had beenformed, will be produced. 

1645. I am saying of a single particle or of two what I have before said, in effect, of many (1633. ). If the former account of currents be true, thenthat just stated must be a necessary result. And, though the statement mayseem startling at first, it is to be considered that, according to mytheory of induction, the charged conductor or particle is related to thedistant conductor in the opposite state, or that which terminates theextent of the induction, by all the intermediate particles (1165, 1295. ), these becoming polarized exactly as the particles of a solid electrolyte dowhen interposed between the two electrodes. Hence the conclusion regardingthe unity and identity of the current in the case of convection, jointlywith the former cases, is not so strange as it might at first appear. 

 * * * * *

1646. There is a very remarkable phenomenon or effect of the electrolyticdischarge, first pointed out, I believe, by Mr. Porrett, of theaccumulation of fluid under decomposing action in the current on one sideof an interposed diaphragm[A]. It is a mechanical result; and as the liquidpasses from the positive towards the negative electrode in all the knowncases, it seems to establish a relation to the polar condition of thedielectric in which the current exists (1164. 1525. ). It has not as yetbeen sufficiently investigated by experiment; for De la Rive says[B], itrequires that the water should be a bad conductor, as, for instance, distilled water, the effect not happening with strong solutions; whereas, Dutrochet says[C] the contrary is the case, and that, the effect is notdirectly due to the electric current. 

 [A] Annals of Philosophy, 1816. Viii. P. 75. 

 [B] Annales de Chimie, 1835. Xxviii. P. 196. 

 [C] Annales de Chimie, 1832, xlix. P. 423. 

1647. Becquerel, in his Traité de l'Electricité, has brought together theconsiderations which arise for and against the opinion, that the effectgenerally is an electric effect[A]. Though I have no decisive fact to quoteat present, I cannot refrain from venturing an opinion, that the effect isanalogous both to combination and convection (1623. ), being a case ofcarrying due to the relation of the diaphragm and the fluid in contact withit, through which the electric discharge is jointly effected; and further, that the peculiar relation of positive and negative small and largesurfaces already referred to (1482. 1503. 1525. ), may be the direct causeof the fluid and the diaphragm travelling in contrary but determinatedirections. A very valuable experiment has been made by M. Becquerel withparticles of clay[B], which will probably bear importantly on this point. 

 [A] Vol. Iv. P. 192, 197. 

 [B] Traité de l'Electricité, i. P. 285. 

 * * * * *

1648. _As long as_ the terms _current_ and _electro-dynamic_ are used toexpress those relations of the electric forces in which progression ofeither fluids or effects are supposed to occur (283. ), _so long_ will theidea of velocity be associated with them; and this will, perhaps, be moreespecially the case if the hypothesis of a fluid or fluids be adopted. 

1649. Hence has arisen the desire of estimating this velocity eitherdirectly or by some effect dependent on it; and amongst the endeavours todo this correctly, may be mentioned especially those of Dr. Watson[A] in1748, and of Professor Wheatstone[B] in 1834; the electricity in the earlytrials being supposed to travel from end to end of the arrangement, but inthe later investigations a distinction occasionally appearing to be madebetween the transmission of the effect and of the supposed fluid by themotion of whose particles that effect is produced. 

 [A] Philosophical Transactions, 1748. 

 [B] Ibid. 1834, p. 583. 

1650. Electrolytic action has a remarkable bearing upon this question ofthe velocity of the current, especially as connected with the theory of anelectric fluid or fluids. In it there is an evident transfer of power withthe transfer of each particle of the anion or cathion present, to the nextparticles of the cathion or anion; and as the amount of power is definite, we have in this way a means of localizing as it were the force, identifyingit by the particle and dealing it out in successive portions, which leads, I think, to very striking results. 

1651. Suppose, for instance, that water is undergoing decomposition by thepowers of a voltaic battery. Each particle of hydrogen as it moves one way, or of oxygen as it moves in the other direction, will transfer a certainamount of electrical force associated with it in the form of chemicalaffinity (822. 852. 918. ) onwards through a distance, which is equal tothat through which the particle itself has moved. This transfer will beaccompanied by a corresponding movement in the electrical forces throughoutevery part of the circuit formed (1627. 1634. ), and its effects may beestimated, as, for instance, by the heating of a wire (853. ) at anyparticular section of the current however distant. If the water be a cubeof an inch in the side, the electrodes touching, each by a surface of onesquare inch, and being an inch apart, then, by the time that a tenth of it, or 25. 25 grs. , is decomposed, the particles of oxygen and hydrogenthroughout the mass may be considered as having moved relatively to eachother in opposite directions, to the amount of the tenth of an inch; i. E. That two particles at first in combination will after the motion be thetenth of an inch apart. Other motions which occur in the fluid will not atall interfere with this result; for they have no power of accelerating orretarding the electric discharge, and possess in fact no relation to it. 

1652. The quantity of electricity in 25. 25 grains of water is, according toan estimate of the force which I formerly made (861. ), equal to above 24millions of charges of a large Leyden battery; or it would have kept anylength of a platina wire 1/104 of an inch in diameter red-hot for an hourand a half (853. ). This result, though given only as an approximation, Ihave seen no reason as yet to alter, and it is confirmed generally by theexperiments and results of M. Pouillet[A]. According to Mr. Wheatstone'sexperiments, the influence or effects of the current would appear at adistance of 576, 000 miles in a second[B]. We have, therefore, in this viewof the matter, on the one hand, an enormous quantity of power equal to amost destructive thunder-storm appearing instantly at the distance of576, 000 miles from its source, and on the other, a quiet effect, inproducing which the power had taken an hour and a half to travel throughthe tenth of an inch: yet these are the equivalents to each other, beingeffects observed at the sections of one and the same current (1634. ). 

 [A] Becquerel, Traité de l'Electricité, v. P. 278. 

 [B] Philosophical Transactions, 1834, p. 589. 

 * * * * *

1653. It is time that I should call attention to the lateral or transverseforces of the _current_. The great things which have been achieved byOersted, Arago, Ampère, Davy, De la Rive, and others, and the high degreeof simplification which has been introduced into their arrangement by thetheory of Ampère, have not only done their full service in advancing mostrapidly this branch of knowledge, but have secured to it such attentionthat there is no necessity for urging on its pursuit. I refer of course tomagnetic action and its relations; but though this is the only recognisedlateral action of the current, there is great reason for believing thatothers exist and would by their discovery reward a close search for them(951. ). 

1654. The magnetic or transverse action of the current seems to be in amost extraordinary degree independent of those variations or modes ofaction which it presents directly in its course; it consequently is of themore value to us, as it gives us a higher relation of the power than anythat might have varied with each mode of discharge. This discharge, whetherit be by conduction through a wire with infinite velocity (1652. ), or byelectrolyzation with its corresponding and exceeding slow motion (1651. ), or by spark, and probably even by convection, produces a transversemagnetic action always the same in kind and direction. 

1655. It has been shown by several experimenters, that whilst the dischargeis of the _same kind_ the amount of lateral or magnetic force is veryconstant (216. 366. 367. 368. 376. ). But when we wish to compare dischargeof different kinds, for the important purpose of ascertaining whether thesame amount of current will in its _different forms_ produce the sameamount of transverse action, we find the data very imperfect. Davy noticed, that when the electric current was passing through an aqueous solution itaffected a magnetic needle[A], and Dr. Ritchie says, that the current inthe electrolyte is as magnetic as that in a metallic wire[B], and hascaused water to revolve round a magnet as a wire carrying the current wouldrevolve. 

 [A] Philosophical Transactions, 1821, p. 426. 

 [B] Ibid. 1832, p. 294. 

1656. Disruptive discharge produces its magnetic effects: a strong spark, passed transversely to a steel needle, will magnetise it as well as if theelectricity of the spark were conducted by a metallic wire occupying theline of discharge; and Sir H. Davy has shown that the discharge of avoltaic battery in vacuo is affected and has motion given to it byapproximated magnets[A]. 

 [A] Philosophical Transactions, 1821, p. 427. 

1657. Thus the three very different modes of discharge, namely, conduction, electrolyzation, and disruptive discharge, agree in producing the importanttransverse phenomenon of magnetism. Whether convection or carryingdischarge will produce the same phenomenon has not been determined, and thefew experiments I have as yet had time to make do not enable me to answerin the affirmative. 

 * * * * *

1658. Having arrived at this point in the consideration of the current andin the endeavour to apply its phenomena as tests of the truth or fallacy ofthe theory of induction which I have ventured to set forth, I am now verymuch tempted to indulge in a few speculations respecting its lateral actionand its possible connexion with the transverse condition of the lines ofordinary induction (1165, 1304. )[A]. I have long sought and still seek foran effect or condition which shall be to statical electricity what magneticforce is to current electricity (1411. ); for as the lines of discharge areassociated with a certain transverse effect, so it appeared to meimpossible but that the lines of tension or of inductive action, which ofnecessity precede that discharge, should also have their correspondenttransverse condition or effect (951. ). 

 [A] Refer for further investigations to 1709. --1736. --_Dec. 1838. _

1659. According to the beautiful theory of Ampère, the transverse force ofa current may be represented by its attraction for a similar current andits repulsion of a contrary current. May not then the equivalent transverseforce of static electricity be represented by that lateral tension orrepulsion which the lines of inductive action appear to possess (1304. )?Then again, when current or discharge occurs between two bodies, previouslyunder inductrical relations to each other, the lines of inductive forcewill weaken and fade away, and, as their lateral repulsive tensiondiminishes, will contract and ultimately disappear in the line ofdischarge. May not this be an effect identical with the attractions ofsimilar currents? i. E. May not the passage of static electricity intocurrent electricity, and that of the lateral tension of the lines ofinductive force into the lateral attraction of lines of similar discharge, have the same relation and dependences, and run parallel to each other?

1660. The phenomena of induction amongst currents which I had the goodfortune to discover some years ago (6. &c. 1048. ) may perchance here form aconnecting link in the series of effects. When a current is first formed, it tends to produce a current in the contrary direction in all the matteraround it; and if that matter have conducting properties and be fitlycircumstanced, such a current is produced. On the contrary, when theoriginal current is stopped, one in the same direction tends to form allaround it, and, in conducting matter properly arranged, will be excited. 

1661. Now though we perceive the effects only in that portion of matterwhich, being in the neighbourhood, has conducting properties, yethypothetically it is probable, that the nonconducting matter has also itsrelations to, and is affected by, the disturbing cause, though we have notyet discovered them. Again and again the relation of conductors andnon-conductors has been shown to be one not of opposition in kind, but onlyof degree (1334, 1603. ); and, therefore, for this, as well as for otherreasons, it is probable, that what will affect a conductor will affect aninsulator also; producing perhaps what may deserve the term of theelectrotonic state (60. 242. 1114. ). 

1662. It is the feeling of the necessity of some lateral connexion betweenthe lines of electric force (1114. ); of some link in the chain of effectsas yet unrecognised, that urges me to the expression of these speculations. The same feeling has led me to make many experiments on the introduction ofinsulating dielectrics having different inductive capacities (1270. 1277. )between magnetic poles and wires carrying currents, so as to pass acrossthe lines of magnetic force. I have employed such bodies both at rest andin motion, without, as yet, being able to detect any influence produced bythem; but I do by no means consider the experiments as sufficientlydelicate, and intend, very shortly, to render them more decisive[A]. 

 [A] See onwards 1711. --1726. --_Dec. 1838. _

1663. I think the hypothetical question may at present be put thus: cansuch considerations as those already generally expressed (1658. ) accountfor the transverse effects of electrical currents? are two such currents inrelation to each other merely by the inductive condition of the particlesof matter between them, or are they in relation by some higher quality andcondition (1654. ), which, acting at a distance and not by the intermediateparticles, has, like the force of gravity, no relation to them?

1664. If the latter be the case, then, when electricity is acting upon andin matter, its direct and its transverse action are essentially differentin their nature; for the former, if I am correct, will depend upon thecontiguous particles, and the latter will not. As I have said before, thismay be so, and I incline to that view at present; but I am desirous ofsuggesting considerations why it may not, that the question may bethoroughly sifted. 

1665. The transverse power has a character of polarity impressed upon it. In the simplest forms it appears as attraction or repulsion, according asthe currents are in the same or different directions: in the current andthe magnet it takes up the condition of tangential forces; and in magnetsand their particles produces poles. Since the experiments have been madewhich have persuaded me that the polar forces of electricity, as ininduction and electrolytic action (1298. 1343. ), show effects at a distanceonly by means of the polarized contiguous and intervening particles, I havebeen led to expect that _all polar forces_ act in the same general manner;and the other kinds of phenomena which one can bring to bear upon thesubject seem fitted to strengthen that expectation. Thus incrystallizations the effect is transmitted from particle to particle; andin this manner, in acetic acid or freezing water a crystal a few inches oreven a couple of feet in length will form in less than a second, butprogressively and by a transmission of power from particle to particle. And, as far as I remember, no case of polar action, or partaking of polaraction, except the one under discussion, can be found which does not act bycontiguous particles[A]. It is apparently of the nature of polar forcesthat such should be the case, for the one force either finds or developedthe contrary force near to it, and has, therefore, no occasion to seek forit at a distance. 

 [A] I mean by contiguous particles those which are next to each other, not that there is _no_ space between them. See (1616. ). 

1666. But leaving these hypothetical notions respecting the nature of thelateral action out of sight, and returning to the direct effects, I thinkthat the phenomena examined and reasoning employed in this and the twopreceding papers tend to confirm the view first taken (1464. ), namely, thatordinary inductive action and the effects dependent upon it are due to anaction of the contiguous particles of the dielectric interposed between thecharged surfaces or parts which constitute, as it were, the terminations ofthe effect. The great point of distinction and power (if it have any) inthe theory is, the making the dielectric of essential and specificimportance, instead of leaving it as it were a mere accidental circumstanceor the simple representative of space, having no more influence over thephenomena than the space occupied by it. I have still certain other resultsand views respecting the nature of the electrical forces and excitation, which are connected with the present theory; and, unless upon furtherconsideration they sink in my estimation, I shall very shortly put theminto form as another series of these electrical researches. 

_Royal Institution. February 14th, 1838. _

FOURTEENTH SERIES. 

§ 20. _Nature of the electric force or forces. _ § 21. _Relation of theelectric and magnetic forces. _ § 22. _Note on electrical excitation. _

Received June 21, 1838. --Read June 21, 1838. 

§ 20. _Nature of the electric force or forces. _

1667. The theory of induction set forth and illustrated in the threepreceding series of experimental researches does not assume anything new asto the nature of the electric force or forces, but only as to theirdistribution. The effects may depend upon the association of one electricfluid with the particles of matter, as in the theory of Franklin, Epinus, Cavendish, and Mossotti; or they may depend upon the association of twoelectric fluids, as in the theory of Dufay and Poisson; or they may notdepend upon anything which can properly be called the electric fluid, buton vibrations or other affections of the matter in which they appear. Thetheory is unaffected by such differences in the mode of viewing the natureof the forces; and though it professes to perform the important office ofstating _how_ the powers are arranged (at least in inductive phenomena), itdoes not, as far as I can yet perceive, supply a single experiment whichcan be considered as a distinguishing test of the truth of any one of thesevarious views, 1668. But, to ascertain how the forces are arranged, to trace them in theirvarious relations to the particles of matter, to determine their generallaws, and also the specific differences which occur under these laws, is asimportant as, if not more so than, to know whether the forces reside in afluid or not; and with the hope of assisting in this research, I shalloffer some further developments, theoretical and experimental, of theconditions under which I suppose the particles of matter are placed whenexhibiting inductive phenomena. 

1669. The theory assumes that all the _particles_, whether of insulating orconducting matter, are as wholes conductors. 

1670. That not being polar in their normal state, they can become so by theinfluence of neighbouring charged particles, the polar state beingdeveloped at the instant, exactly as in an insulated conducting _mass_consisting of many particles. 

1671. That the particles when polarized are in a forced state, and tend toreturn to their normal or natural condition. 

1672. That being as wholes conductors, they can readily be charged, either_bodily_ or _polarly_. 

1673. That particles which being contiguous[A] are also in the line ofinductive action can communicate or transfer their polar forces one toanother _more_ or _less_ readily. 

 [A] See note to 1164. --_Dec. 1838. _

1674. That those doing so less readily require the polar forces to beraised to a higher degree before this transference or communication takesplace. 

1675. That the _ready_ communication of forces between contiguous particlesconstitutes _conduction_, and the _difficult_ communication _insulation_;conductors and insulators being bodies whose particles naturally possessthe property of communicating their respective forces easily or withdifficulty; having these differences just as they have differences of anyother natural property. 

1676. That ordinary induction is the effect resulting from the action ofmatter charged with excited or free electricity upon insulating matter, tending to produce in it an equal amount of the contrary state. 

1677. That it can do this only by polarizing the particles contiguous toit, which perform the same office to the next, and these again to thosebeyond; and that thus the action is propagated from the excited body to thenext conducting mass, and there renders the contrary force evident inconsequence of the effect of communication which supervenes in theconducting mass upon the polarization of the particles of that body(1675. ). 

1678. That therefore induction can only take place through or acrossinsulators; that induction is insulation, it being the necessaryconsequence of the state of the particles and the mode in which theinfluence of electrical forces is transferred or transmitted through oracross such insulating media. 

1679. The particles of an insulating dielectric whilst under induction maybe compared to a series of small magnetic needles, or more correctly stillto a series of small insulated conductors. If the space round a chargedglobe were filled with a mixture of an insulating dielectric, as oil ofturpentine or air, and small globular conductors, as shot, the latter beingat a little distance from each other so as to be insulated, then thesewould in their condition and action exactly resemble what I consider to bethe condition and action of the particles of the insulating dielectricitself (1337. ). If the globe were charged, these little conductors wouldall be polar; if the globe were discharged, they would all return to theirnormal state, to be polarized again upon the recharging of the globe. Thestate developed by induction through such particles on a mass of conductingmutter at a distance would be of the contrary kind, and exactly equal inamount to the force in the inductric globe. There would be a lateraldiffusion of force (1224. 1297. ), because each polarized sphere would be inan active or tense relation to all those contiguous to it, just as onemagnet can affect two or more magnetic needles near it, and these again astill greater number beyond them. Hence would result the production ofcurved lines of inductive force if the inducteous body in such a mixeddielectric were an uninsulated metallic ball (1219. &c. ) or other properlyshaped mass. Such curved lines are the consequences of the two electricforces arranged as I have assumed them to be: and, that the inductive forcecan be directed in such curved lines is the strongest proof of the presenceof the two powers and the polar condition of the dielectric particles. 

1680. I think it is evident, that in the case stated, action at a distancecan only result through an action of the contiguous conducting particles. There is no reason why the inductive body should polarize or affect_distant_ conductors and leave those _near_ it, namely the particles of thedielectric, unaffected: and everything in the form of fact and experimentwith conducting masses or particles of a sensible size contradicts such asupposition. 

1681. A striking character of the electric power is that it is limited andexclusive, and that the two forces being always present are exactly equalin amount. The forces are related in one of two ways, either as in thenatural normal condition of an uncharged insulated conductor; or as in thecharged state, the latter being a case of induction. 

1682. Cases of induction are easily arranged so that the two forces beinglimited in their direction shall present no phenomena or indicationsexternal to the apparatus employed, Thus, if a Leyden jar, having itsexternal coating a little higher than the internal, be charged and then itscharging ball and rod removed, such jar will present no electricalappearances so long as its outside is uninsulated. The two forces which maybe said to be in the coatings, or in the particles of the dielectriccontiguous to them, are entirely engaged to each other by induction throughthe glass; and a carrier ball (1181. ) applied either to the inside oroutside of the jar will show no signs of electricity. But if the jar beinsulated, and the charging ball and rod, in an uncharged state andsuspended by an insulating thread of white silk, be restored to theirplace, then the part projecting above the jar will give electricalindications and charge the carrier, and at the same time the _outside_coating of the jar will be found in the opposite state and inductrictowards external surrounding objects. 

1683. These are simple consequences of the theory. Whilst the charge of theinner coating could induce only through the glass towards the outercoating, and the latter contained no more of the contrary force than wasequivalent to it, no induction external to the jar could be perceived; butwhen the inner coating was extended by the rod and ball so that it couldinduce through the air towards external objects, then the tension of thepolarized glass molecules would, by their tendency to return to the normalstate, fall a little, and a portion of the charge passing to the surface ofthis new part of the inner conductor, would produce inductive actionthrough the air towards distant objects, whilst at the same time a part ofthe force in the outer coating previously directed inwards would now be atliberty, and indeed be constrained to induct outwards through the air, producing in that outer coating what is sometimes called, though I thinkvery improperly, free charge. If a small Leyden jar be converted into thatform of apparatus usually known by the name of the electric well, it willillustrate this action very completely. 

1684. The terms _free charge_ and _dissimulated electricity_ conveytherefore erroneous notions if they are meant to imply any difference as tothe mode or kind of action. The charge upon an insulated conductor in themiddle of a room is in the same relation to the walls of that room as thecharge upon the inner coating of a Leyden jar is to the outer coating ofthe same jar. The one is not more _free_ or more _dissimulated_ than theother; and when sometimes we make electricity appear where it was notevident before, as upon the outside of a charged jar, when, afterinsulating it, we touch the inner coating, it is only because we divertmore or less of the inductive force from one direction into another; fornot the slightest change is in such circumstances impressed upon thecharacter or action of the force. 

 * * * * *

1685. Having given this general theoretical view, I will now noticeparticular points relating to the nature of the assumed electric polarityof the insulating dielectric particles. 

1686. The polar state may be considered in common induction as a forcedstate, the particles tending to return to their normal condition. It mayprobably be raised to a very high degree by approximation of the inductricand inducteous bodies or by other circumstances; and the phenomena ofelectrolyzation (861. 1652. 1796. ) seem to imply that the quantity of powerwhich can thus be accumulated on a single particle is enormous. Hereafterwe may be able to compare corpuscular forces, as those of gravity, cohesion, electricity, and chemical affinity, and in some way or other fromtheir effects deduce their relative equivalents; at present we are not ableto do so, but there seems no reason to doubt that their electrical, whichare at the same time their chemical forces (891. 918. ), will be by far themost energetic. 

1687. I do not consider the powers when developed by the polarization aslimited to two distinct points or spots on the surface of each particle tobe considered as the poles of an axis, but as resident on large portions ofthat surface, as they are upon the surface of a conductor of sensible sizewhen it is thrown into a polar state. But it is very probable, notwithstanding, that the particles of different bodies may presentspecific differences in this respect, the powers not being equally diffusedthough equal in quantity; other circumstances also, as form and quality, giving to each a peculiar polar relation. It is perhaps to the existence ofsome such differences as these that we may attribute the specific actionsof the different dielectrics in relation to discharge(1394. 1508. ). Thuswith respect to oxygen and nitrogen singular contrasts were presented whenspark and brush discharge were made to take place in these gases, as may beseen by reference to the Table in paragraph 1518 of the Thirteenth Series;for with nitrogen, when the small, negative or the large positive ball wasrendered inductric, the effects corresponded with those which in oxygenwere produced when the small positive or the large negative ball wasrendered inductric. 

1688. In such solid bodies as glass, lac, sulphur, &c. , the particlesappear to be able to become polarized in all directions, for a mass whenexperimented upon so as to ascertain its inductive capacity in three ormore directions (1690. ), gives no indication of a difference. Now as theparticles are fixed in the mass, and as the direction of the inductionthrough them must change with its change relative to the mass, the constanteffect indicates that they can be polarized electrically in any direction. This accords with the view already taken of each particle as a whole beinga conductor (1669. ), and, as an experimental fact, helps to confirm thatview. 

1689. But though particles may thus be polarized in _any_ direction underthe influence of powers which are probably of extreme energy (1686. ), itdoes not follow that each particle may not tend to polarize to a greaterdegree, or with more facility, in one direction than another; or thatdifferent kinds may not have specific differences in this respect, as theyhave differences of conducting and other powers (1296. 1326. 1395. ). Isought with great anxiety for a relation of this nature; and selectingcrystalline bodies as those in which all the particles are symmetricallyplaced, and therefore best fitted to indicate any result which might dependupon variation of the direction of the forces to the direction of theparticles in which they were developed, experimented very carefully withthem. I was the more strongly stimulated to this inquiry by the beautifulelectrical condition of the crystalline bodies tourmaline and boracite, andhoped also to discover a relation between electric polarity and that ofcrystallization, or even of cohesion itself (1316. ). My experiments havenot established any connexion of the kind sought for. But as I think it ofequal importance to show either that there is or is not such a relation, Ishall briefly describe the results. 

1690. The form of experiment was as follows. A brass ball 0. 73 of an inchin diameter, fixed at the end of a horizontal brass rod, and that at theend of a brass cylinder, was by means of the latter connected with a largeLeyden battery (291. ) by perfect metallic communications, the object beingto keep that ball, by its connexion with the charged battery in anelectrified state, very nearly uniform, for half an hour at a time. Thiswas the inductric ball. The inducteous ball was the carrier of the torsionelectrometer (1229. 1314. ); and the dielectric between them was a cube cutfrom a crystal, so that two of its faces should be perpendicular to theoptical axis, whilst the other four were parallel to it. A small projectingpiece of shell-lac was fixed on the inductric ball at that part opposite tothe attachment of the brass rod, for the purpose of preventing actualcontact between the ball and the crystal cube. A coat of shell-lac was alsoattached to that side of the carrier ball which was to be towards the cube, being also that side which was furthest from the repelled ball in theelectrometer when placed in its position in that instrument. The cube wascovered with a thin coat of shell-lac dissolved in alcohol, to prevent thedeposition of damp upon its surface from the air. It was supported upon asmall table of shell-lac fixed on the top of a stem of the same substance, the latter being of sufficient strength to sustain the cube, and yetflexible enough from its length to act as a spring, and allow the cube tobear, when in its place, against the shell-lac on the inductric ball. 

[Illustration:]

1691. Thus it was easy to bring the inducteous ball always to the samedistance from the inductric bull, and to uninsulate and insulate it againin its place; and then, after measuring the force in the electrometer(1181. ), to return it to its place opposite to the inductric ball for asecond observation. Or it was easy by revolving the stand which supportedthe cube to bring four of its faces in succession towards the inductricball, and so observe the force when the lines of inductive action (1304. )coincided with, or were transverse to, the direction of the optical axis ofthe crystal. Generally from twenty to twenty-eight observations were madein succession upon the four vertical faces of a cube, and then an averageexpression of the inductive force was obtained, and compared with similaraverages obtained at other times, every precaution being taken to secureaccurate results. 

1692. The first cube used was of _rock crystal_; it was 0. 7 of an inch inthe side. It presented a remarkable and constant difference, the average ofnot less than 197 observations, giving 100 for the specific inductivecapacity in the direction coinciding with the optical axis of the cube, whilst 93. 59 and 93. 31 were the expressions for the two transversedirections. 

1693. But with a second cube of rock crystal corresponding results were notobtained. It was 0. 77 of an inch in the side. The average of manyexperiments gave 100 for the specific inductive capacity coinciding withthe direction of the optical axis, and 98. 6 and 99. 92 for the two otherdirections. 

1694. Lord Ashley, whom I have found ever ready to advance the cause ofscience, obtained for me the loan of three globes of rock crystal belongingto Her Grace the Duchess of Sutherland for the purposes of thisinvestigation. Two had such fissures as to render them unfit for theexperiments (1193. 1698. ). The third, which was very superior, gave me noindications of any difference in the inductive force for differentdirections. 

1695. I then used cubes of Iceland spar. One 0. 5 of an inch in diametergave 100 for the axial direction, and 98. 66 and 95. 74 for the two crossdirections. The other, 0. 8 of an inch in the side, gave 100 for the axialdirection, whilst 101. 73 and 101. 86 were the numbers for the crossdirection. 

1696. Besides these differences there were others, which I do not think itneedful to state, since the main point is not confirmed. For though theexperiments with the first cube raised great expectation, they have notbeen generalized by those which followed. I have no doubt of the results asto that cube, but they cannot as yet be referred to crystallization. Thereare in the cube some faintly coloured layers parallel to the optical axis, and the matter which colours them may have an influence; but then thelayers are also nearly parallel to a cross direction, and if at allinfluential should show some effect in that direction also, which they didnot. 

1697. In some of the experiments one half or one part of a cube showed asuperiority to another part, and this I could not trace to any charge thedifferent parts had received. It was found that the varnishing of the cubesprevented any communication of charge to them, except (in a fewexperiments) a small degree of the negative state, or that which wascontrary to the state of the inductric ball (1564. 1566. ). 

1698. I think it right to say that, as far as I could perceive, theinsulating character of the cubes used was perfect, or at least so nearlyperfect, as to bear a comparison with shell-lac, glass, &c. (1255). As tothe cause of the differences, other than regular crystalline structure, there may be several. Thus minute fissures in the crystal insensible to theeye may be so disposed as to produce a sensible electrical difference(1193. ). Or the crystallization may be irregular; or the substance may notbe quite pure; and if we consider how minute a quantity of matter willalter greatly the conducting power of water, it will seem not unlikely thata little extraneous matter diffused through the whole or part of a cube, may produce effects sufficient to account for all the irregularities ofaction that have been observed. 

1699. An important inquiry regarding the electrical polarity of theparticles of an insulating dielectric, is, whether it be the molecules ofthe particular substance acted on, or the component or ultimate particles, which thus act the part of insulated conducting polarizing portions(1669. ). 

1700. The conclusion I have arrived at is, that it is the molecules of thesubstance which polarize as wholes (1347. ); and that however complicatedthe composition of a body may be, all those particles or atoms which areheld together by chemical affinity to form one molecule of the resultingbody act as one conducting mass or particle when inductive phenomena andpolarization are produced in the substance of which it is a part. 

1701. This conclusion is founded on several considerations. Thus if weobserve the insulating and conducting power of elements when they are usedas dielectrics, we find some, as sulphur, phosphorus, chlorine, iodine, &c. , whose particles insulate, and therefore polarize in a high degree;whereas others, as the metals, give scarcely any indication of possessing asensible proportion of this power (1328. ), their particles freelyconducting one to another. Yet when these enter into combination they formsubstances having no direct relation apparently, in this respect, to theirelements; for water, sulphuric acid, and such compounds formed ofinsulating elements, conduct by comparison freely; whilst oxide of lead, flint glass, borate of lead, and other metallic compounds containing veryhigh proportions of conducting matter, insulate excellently well. Takingoxide of lead therefore as the illustration, I conceive that it is not theparticles of oxygen and lead which polarize separately under the act ofinduction, but the molecules of oxide of lead which exhibit this effect, all the elements of one particle of the resulting body, being held togetheras parts of one conducting individual by the bonds of chemical affinity;which is but another term for electrical force (918. ). 

1702. In bodies which are electrolytes we have still further reason forbelieving in such a state of things. Thus when water, chloride of tin, iodide of lead, &c. In the solid state are between the electrodes of thevoltaic battery, their particles polarize as those of any other insulatingdielectric do (1164. ); but when the liquid state is conferred on thesesubstances, the polarized particles divide, the two halves, each in ahighly charged state, travelling onwards until they meet other particles inan opposite and equally charged state, with which they combine, to theneutralization of their chemical, i. E. Their electrical forces, and thereproduction of compound particles, which can again polarize as wholes, andagain divide to repeat the same series of actions (1347. ). 

1703. But though electrolytic particles polarize as wholes, it would appearvery evident that in them it is not a matter of entire indifference _how_the particle polarizes (1689. ), since, when free to move (380, &c. ) thepolarities are ultimately distributed in reference to the elements; andsums of force equivalent to the polarities, and very definite in kind andamount, separate, as it were, from each other, and travel onwards with theelementary particles. And though I do not pretend to know what an atom is, or how it is associated or endowed with electrical force, or how this forceis arranged in the cases of combination and decomposition, yet the strongbelief I have in the electrical polarity of particles when under inductiveaction, and the hearing of such an opinion on the general effects ofinduction, whether ordinary or electrolytic, will be my excuse, I trust, for a few hypothetical considerations. 

1704 In electrolyzation it appears that the polarized particles would(because of the gradual change which has been induced upon the chemical, i. E. The electrical forces of their elements (918. )) rather divide thandischarge to each other without division (1348. ); for if their division, i. E. Their decomposition and recombination, be prevented by giving them thesolid state, then they will insulate electricity perhaps a hundredfold moreintense than that necessary for their electrolyzation (419, &c. ). Hence thetension necessary for direct conduction in such bodies appears to be muchhigher than that for decomposition (419. 1164. 1344. ). 

1705. The remarkable stoppage of electrolytic conduction by solidification(380. 1358. ), is quite consistent with these views of the dependence ofthat process on the polarity which is common to all insulating matter whenunder induction, though attended by such peculiar electro-chemical resultsin the case of electrolytes. Thus it may be expected that the first effectof induction is so to polarize and arrange the particles of water that thepositive or hydrogen pole of each shall be from the positive electrode andtowards the negative electrode, whilst the negative or oxygen pole of eachshall be in the contrary direction; and thus when the oxygen and hydrogenof a particle of water have separated, passing to and combining with otherhydrogen and oxygen particles, unless these new particles of water couldturn round they could not take up that position necessary for theirsuccessful electrolytic polarization. Now solidification, by fixing thewater particles and preventing them from assuming that essentialpreliminary position, prevents also their electrolysis (413. ); and so thetransfer of forces in that manner being prevented (1347. 1703. ), thesubstance acts as an ordinary insulating dielectric (for it is evident byformer experiments (419. 1704. ) that the insulating tension is higher thanthe electrolytic tension), induction through it rises to a higher degree, and the polar condition of the molecules as wholes, though greatly exalted, is still securely maintained. 

1706. When decomposition happens in a fluid electrolyte, I do not supposethat all the molecules in the same sectional plane (1634. ) part with andtransfer their electrified particles or elements at once. Probably the_discharge force_ for that plane is summed up on one or a few particles, which decomposing, travelling and recombining, restore the balance offorces, much as in the case of spark disruptive discharge (1406. ); for asthose molecules resulting from particles which have just transferred powermust by their position (1705. ) be less favourably circumstanced thanothers, so there must be some which are most favourably disposed, andthese, by giving way first, will for the time lower the tension and producedischarge. 

1707. In former investigations of the action of electricity (821, &c. ) itwas shown, from many satisfactory cases, that the quantity of electricpower transferred onwards was in proportion to and was definite for a givenquantity of matter moving as anion or cathion onwards in the electrolyticline of action; and there was strong reason to believe that each of theparticles of matter then dealt with, had associated with it a definiteamount of electrical force, constituting its force of chemical affinity, the chemical equivalents and the electro-chemical equivalents being thesame (836. ). It was also found with few, and I may now perhaps say with noexceptions (1341. ), that only those compounds containing elements in singleproportions could exhibit the characters and phenomena of electrolytes(697. ); oxides, chlorides, and other bodies containing more than oneproportion of the electro-negative element refusing to decompose under theinfluence of the electric current. 

1708. Probable reasons for these conditions and limitations arise out ofthe molecular theory of induction. Thus when a liquid dielectric, aschloride of tin, consists of molecules, each composed of a single particleof each of the elements, then as these can convey equivalent oppositeforces by their separation in opposite directions, both decomposition andtransfer can result. But when the molecules, as in the bichloride of tin, consist of one particle or atom of one element, and two of the other, thenthe simplicity with which the particles may be supposed to be arranged andto act, is destroyed. And, though it may be conceived that when themolecules of bichloride of tin are polarized as wholes by the inductionacross them, the positive polar force might accumulate on the one particleof tin whilst the negative polar force accumulated on the two particles ofchlorine associated with it, and that these might respectively travel rightand left to unite with other two of chlorine and one of tin, in analogywith what happens in cases of compounds consisting of single proportions, yet this is not altogether so evident or probable. For when a particle oftin combines with two of chlorine, it is difficult to conceive that thereshould not be some relation of the three in the resulting moleculeanalogous to fixed position, the one particle of metal being perhapssymmetrically placed in relation to the two of chlorine: and, it is notdifficult to conceive of such particles that they could not assume thatposition dependent both on their polarity and the relation of theirelements, which appears to be the first step in the process ofelectrolyzation (1345. 1705. ). 

§ 21. _Relation of the electric and magnetic forces. _

1709. I have already ventured a few speculations respecting the probablerelation of magnetism, as the transverse force of the current, to thedivergent or transverse force of the lines of inductive action belonging tostatic electricity (1658, &c. ). 

1710. In the further consideration of this subject it appeared to me to beof the utmost importance to ascertain, if possible, whether this lateralaction which we call magnetism, or sometimes the induction of electricalcurrents (26. 1048, &c. ), is extended to a distance _by the action of theintermediate particles_ in analogy with the induction of staticelectricity, or the various effects, such as conduction, discharge, &c. , which are dependent on that induction; or, whether its influence at adistance is altogether independent of such intermediate particles (1662. ). 

1711. I arranged two magneto-electric helices with iron cores end to end, but with an interval of an inch and three quarters between them, in whichinterval was placed the end or pole of a bar magnet. It is evident, that onmoving the magnetic pole from one core towards the other, a current wouldtend to form in both helices, in the one because of the lowering, and inthe other because of the strengthening of the magnetism induced in therespective soft iron cores. The helices were connected together, and alsowith a galvanometer, so that these two currents should coincide indirection, and tend by their joint force to deflect the needle of theinstrument. The whole arrangement was so effective and delicate, thatmoving the magnetic pole about the eighth of an inch to and fro two orthree times, in periods equal to those required for the vibrations of thegalvanometer needle, was sufficient to cause considerable vibration in thelatter; thus showing readily the consequence of strengthening the influenceof the magnet on the one core and helix, and diminishing it on the other. 

1712. Then without disturbing the distances of the magnet and cores, platesof substances were interposed. Thus calling the two cores A and B, a plateof shell-lac was introduced between the magnetic pole and A for the timeoccupied by the needle in swinging one way; then it was withdrawn for thetime occupied in the return swing; introduced again for another equalportion of time; withdrawn for another portion, and so on eight or ninetimes; but not the least effect was observed on the needle. In other casesthe plate was alternated, i. E. It was introduced between the magnet and Afor one period of time, withdrawn and introduced between the magnet and Bfor the second period, withdrawn and restored to its first place for thethird period, and so on, but with no effect on the needle. 

1713. In these experiments _shell-lac_ in plates 0. 9 of an inch inthickness, _sulphur_ in a plate 0. 9 of an inch in thickness, and _copper_in a plate 0. 7 of an inch in thickness were used without any effect. And Iconclude that bodies, contrasted by the extremes of conducting andinsulating power, and opposed to each other as strongly as metals, air, andsulphur, show no difference with respect to magnetic forces when placed intheir lines of action, at least under the circumstances described. 

1714. With a plate of iron, or even a small piece of that metal, as thehead of a nail, a very different effect was produced, for then thegalvanometer immediately showed its sensibility, and the perfection of thegeneral arrangement. 

1715. I arranged matters so that a plate of _copper_ 0. 2 of an inch inthickness, and ten inches in diameter, should have the part near the edgeinterposed between the magnet and the core, in which situation it was firstrotated rapidly, and then held quiescent alternately, for periods accordingwith that required for the swinging of the needle; but not the least effectupon the galvanometer was produced. 

1716. A plate of shell-lac 0. 6 of an inch in thickness was applied in thesame manner, but whether rotating or not it produced no effect. 

1717. Occasionally the plane of rotation was directly across the magneticcurve: at other times it was made as oblique as possible; the direction ofthe rotation being also changed in different experiments, but not the leasteffect was produced. 

1718. I now removed the helices with their soft iron cores, and replacedthem by two _flat helices_ wound upon card board, each containing forty-twofeet of silked copper wire, and having no associated iron. Otherwise thearrangement was as before, and exceedingly sensible; for a very slightmotion of the magnet between the helices produced an abundant vibration ofthe galvanometer needle. 

1719. The introduction of plates of shell-lac, sulphur, or copper into theintervals between the magnet and these helices (1713. ), produced not theleast effect, whether the former were quiescent or in rapid revolution(1715. ). So here no evidence of the influence of the intermediate particlescould be obtained (1710. ). 

1720. The magnet was then removed and replaced by a flat helix, corresponding to the two former, the three being parallel to each other. The middle helix was so arranged that a voltaic current could be sentthrough it at pleasure. The former galvanometer was removed, and one with adouble coil employed, one of the lateral helices being connected with onecoil, and the other helix with the other coil, in such manner that when avoltaic current was sent through the middle helix its inductive action(26. ) on the lateral helices should cause currents in them, having contrarydirections in the coils of the galvanometer. By a little adjustment of thedistances these induced currents were rendered exactly equal, and thegalvanometer needle remained stationary notwithstanding their frequentproduction in the instrument. I will call the middle coil C, and theexternal coils A and B. 

1721. A plate of copper 0. 7 of an inch thick and six inches square, wasplaced between coils C and B, their respective distances remainingunchanged; and then a voltaic current from twenty pairs of 4 inch plateswas sent through the coil C, and intermitted, in periods fitted to producean effect on the galvanometer (1712. ). If any difference had been producedin the effect of C on A and B. But notwithstanding the presence of air inone interval and copper in the other, the inductive effect was exactlyalike on the two coils, and as if air had occupied both intervals. So thatnotwithstanding the facility with which any induced currents might form inthe thick copper plate, the coil outside of it was just as much affected bythe central helix C as if no such conductor as the copper had been there(65. ). 

1722. Then, for the copper plate was substituted one of sulphur 0. 9 of aninch thick; still the results were exactly the same, i. E. There was noaction at the galvanometer. 

1723. Thus it appears that when a voltaic current in one wire is exertingits inductive action to produce a contrary or a similar current in aneighbouring wire, according as the primary current is commencing orceasing, it makes not the least difference whether the intervening space isoccupied by such insulating bodies as air, sulphur and shell-lac, or suchconducting bodies as copper, and the other non-magnetic metals. 

1724. A correspondent effect was obtained with the like forces whenresident in a magnet thus. A single flat helix (1718. ) was connected with agalvanometer, and a magnetic pole placed near to it; then by moving themagnet to and from the helix, or the helix to and from the magnet, currentswere produced indicated by the galvanometer. 

1725. The thick copper plate (1721. ) was afterwards interposed between themagnetic pole and the helix; nevertheless on moving these to and fro, effects, exactly the same in direction and amount, were obtained as if thecopper had not been there. So also on introducing a plate of sulphur intothe interval, not the least influence on the currents produced by motion ofthe magnet or coils could be obtained. 

1726. These results, with many others which I have not thought it needfulto describe, would lead to the conclusion that (judging by the _amount_ ofeffect produced at a distance by forces transverse to the electric current, i. E. Magnetic forces, ) the intervening matter, and therefore theintervening particles, have nothing to do with the phenomena; or in otherwords, that though the inductive force of static electricity is transmittedto a distance by the action of the intermediate particles (1164. 1666. ), the transverse inductive force of currents, which can also act at adistance, is not transmitted by the intermediate particles in a similarway. 

1727. It is however very evident that such a conclusion cannot beconsidered as proved. Thus when the metal copper is between the pole andthe helix (1715. 1719. 1725. ) or between the two helices (1721. ) we knowthat its particles are affected, and can by proper arrangements make theirpeculiar state for the time very evident by the production of eitherelectrical or magnetical effects. It seems impossible to consider thiseffect on the particles of the intervening matter as independent of thatproduced by the inductric coil or magnet C, on the inducteous coil or coreA (1715. 1721. ); for since the inducteous body is equally affected by theinductric body whether these intervening and affected particles of copperare present or not (1723. 1725. ), such a supposition would imply that theparticles so affected had no reaction back on the original inductricforces. The more reasonable conclusion, as it appears to me, is, toconsider these affected particles as efficient in continuing the actiononwards from the inductric to the inducteous body, and by this verycommunication producing the effect of _no loss_ of induced power at thelatter. 

1728. But then it may be asked what is the relation of the particles ofinsulating bodies, such as air, sulphur, or lac, when _they_ intervene inthe line of magnetic action? The answer to this is at present merelyconjectural. I have long thought there must be a particular condition ofsuch bodies corresponding to the state which causes currents in metals andother conductors (26. 53. 191. 201. 213. ); and considering that the bodiesare insulators one would expect that state to be one of tension. I have byrotating non-conducting bodies near magnetic poles and poles near them, andalso by causing powerful electric currents to be suddenly formed and tocease around and about insulators in various directions, endeavoured tomake some such state sensible, but have not succeeded. Nevertheless, as anysuch state must be of exceedingly low intensity, because of the feebleintensity of the currents which are used to induce it, it may well be thatthe state may exist, and may be discoverable by some more expertexperimentalist, though I have not been able to make it sensible. 

1729. It appears to me possible, therefore, and even probable, thatmagnetic action may be communicated to a distance by the action of theintervening particles, in a manner having a relation to the way in whichthe inductive forces of static electricity are transferred to a distance(1677. ); the intervening particles assuming for the time more or less of apeculiar condition, which (though with a very imperfect idea) I haveseveral times expressed by the term _electro-tonic state_ (60. 242. 1114. 1661. ). I hope it will not be understood that I hold the settled opinionthat such is the case. I would rather in fact have proved the contrary, namely, that magnetic forces are quite independent of the matterintervening between the inductric and the inductions bodies; but I cannotget over the difficulty presented by such substances as copper, silver, lead, gold, carbon, and even aqueous solutions (201. 213. ), which thoughthey are known to assume a peculiar state whilst intervening between thebodies acting and acted upon (1727. ), no more interfere with the finalresult than those which have as yet had no peculiarity of conditiondiscovered in them. 

1730. A remark important to the whole of this investigation ought to bemade here. Although I think the galvanometer used as I have described it(1711. 1720. ) is quite sufficient to prove that the final amount of actionon each of the two coils or the two cores A and B (1713. 1719. ) is equal, yet there is an effect which _may_ be consequent on the difference ofaction of two interposed bodies which it would not show. As time enters asan element into these actions[A] (125. ), it is very possible that theinduced actions on the helices or cores A, B, though they rise to the samedegree when air and copper, or air and lac are contrasted as interveningsubstances, do not do so in the same time; and yet, because of the lengthof time occupied by a vibration of the needle, this difference may not bevisible, both effects rising to their maximum in periods so short as tomake no sensible portion of that required for a vibration of the needle, and so exert no visible influence upon it. 

 [A] See Annnles de Chimie, 1833, tom. Li. Pp. 422, 428. 

 * * * * *

1731. If the lateral or transverse force of electrical currents, or whatappears to be the same thing, magnetic power, could be proved to beinfluential at a distance independently of the intervening contiguousparticles, then, as it appears to me, a real distinction of a high andimportant kind, would be established between the natures of these twoforces (1654. 1664. ). I do not mean that the powers are independent of eachother and might be rendered separately active, on the contrary they areprobably essentially associated (1654. ), but it by no means follows thatthey are of the same nature. In common statical induction, in conduction, and in electrolyzation, the forces at the opposite extremities of theparticles which coincide with the lines of action and have commonly beendistinguished by the term electric, are polar, and in the cases ofcontiguous particles act only to insensible distances; whilst those whichare transverse to the direction of these lines, and are called magnetic, are circumferential, act at a distance, and if not through the mediation ofthe intervening particles, have their relations to ordinary matter entirelyunlike those of the electrical forces with which they are associated. 

1732. To decide this question of the identity or distinction of the twokinds of power, and establish their true relation, would be exceedinglyimportant. The question seems fully within the reach of experiment, andoffers a high reward to him who will attempt its settlement. 

1733. I have already expressed a hope of finding an effect or conditionwhich shall be to statical electricity what magnetic force is to currentelectricity (1658. ). If I could have proved to my own satisfaction thatmagnetic forces extended their influence to a distance by the conjoinedaction of the intervening particles in a manner analogous to that ofelectrical forces, then I should have thought that the natural tension ofthe lines of inductive action (1659. ), or that state so often hinted at asthe electro-tonic state (1661. 1662. ), was this related condition ofstatical electricity. 

1734. It may be said that the state of _no lateral action_ is to static orinductive force the equivalent of _magnetism_ to current force; but thatcan only be upon the view that electric and magnetic action are in theirnature essentially different (1664. ). If they are the same power, the wholedifference in the results being the consequence of the difference of_direction_, then the normal or _undeveloped_ state of electric force willcorrespond with the state of _no lateral action_ of the magnetic state ofthe force; the electric current will correspond with the lateral effectscommonly called magnetism; but the state of static induction which isbetween the normal condition and the current will still require acorresponding lateral condition in the magnetic series, presenting its ownpeculiar phenomena; for it can hardly be supposed that the normal electric, and the inductive or polarized electric, condition, can both have the samelateral relation. If magnetism be a separate and a higher relation of thepowers developed, then perhaps the argument which presses for this thirdcondition of that force would not be so strong. 

1735. I cannot conclude these general remarks upon the relation of theelectric and magnetic forces without expressing my surprise at the resultsobtained with the copper plate (1724. 1725. ). The experiments with the flathelices represent one of the simplest cases of the induction of electricalcurrents (1720. ); the effect, as is well known, consisting in theproduction of a momentary current in a wire at the instant when a currentin the contrary direction begins to pass through a neighbouring parallelwire, and the production of an equally brief current in the reversedirection when the determining current is stopped (26. ). Such being thecase, it seems very extraordinary that this induced current which takesplace in the helix A when there is only air between A and C (1720. ). Shouldbe equally strong when that air is replaced by an enormous mass of thatexcellently conducting metal copper (1721. ). It might have been supposedthat this mass would have allowed of the formation and discharge of almostany quantity of currents in it, which the helix C was competent to induce, and so in some degree have diminished if not altogether prevented theeffect in A: instead of which, though we can hardly doubt that an infinityof currents are formed at the moment in the copper plate, still not thesmallest diminution or alteration of the effect in A appears (65. ). Almostthe only way of reconciling this effect with generally received notions is, as it appears to me, to admit that magnetic action is communicated by theaction of the intervening particles (1729. 1733. ). 

1736. This condition of things, which is very remarkable, accords perfectlywith the effects observed in solid helices where wires are coiled overwires to the amount of five or six or more layers in succession, nodiminution of effect on the outer ones being occasioned by those within. 

§ _22. Note on electrical excitation. _

1737. That the different modes in which electrical excitement takes placewill some day or other be reduced under one common law can hardly bedoubted, though for the present we are bound to admit distinctions. It willbe a great point gained when these distinctions are, not removed, butunderstood. 

1738. The strict relation of the electrical and chemical powers renders thechemical mode of excitement the most instructive of all, and the case oftwo isolated combining particles is probably the simplest that we possess. Here however the action is local, and we still want such a test ofelectricity as shall apply to it, to cases of current electricity, and alsoto those of static induction. Whenever by virtue of the previously combinedcondition of some of the acting particles (923. ) we are enabled, as in thevoltaic pile, to expand or convert the local action into a current, thenchemical action can be traced through its variations to the production of_all_ the phenomena of tension and the static state, these being in everyrespect the same as if the electric forces producing them had beendeveloped by friction. 

1739. It was Berzelius, I believe, who first spoke of the aptness ofcertain particles to assume opposite states when in presence of each other(959. ). Hypothetically we may suppose these states to increase in intensityby increased approximation, or by heat, &c. Until at a certain pointcombination occurs, accompanied by such an arrangement of the forces of thetwo particles between themselves as is equivalent to a discharge, producingat the same time a particle which is throughout a conductor (1700. ). 

1740. This aptness to assume an excited electrical state (which is probablypolar in those forming non-conducting matter) appears to be a primary fact, and to partake of the nature of induction (1162. ), for the particles do notseem capable of retaining their particular state independently of eachother (1177. ) or of matter in the opposite state. What appears to bedefinite about the particles of matter is their assumption of a_particular_ state, as the positive or negative, in relation to each other, and not of either one or other indifferently; and also the acquirement offorce up to a certain amount. 

1741. It is easily conceivable that the same force which causes localaction between two free particles shall produce current force if one of theparticles is previously in combination, forming part of an electrolyte(923. 1738. ). Thus a particle of zinc, and one of oxygen, when in presenceof each other, exert their inductive forces (1740. ), and these at last riseup to the point of combination. If the oxygen be previously in union withhydrogen, it is held so combined by an analogous exertion and arrangementof the forces; and as the forces of the oxygen and hydrogen are for thetime of combination mutually engaged and related, so when the superiorrelation of the forces between the oxygen and zinc come into play, theinduction of the former or oxygen towards the metal cannot be brought onand increased without a corresponding deficiency in its induction towardsthe hydrogen with which it is in combination (for the amount of force in aparticle is considered as definite), and the latter therefore has its forceturned towards the oxygen of the next particle of water; thus the effectmay be considered as extended to sensible distances, and thrown into thecondition of static induction, which being discharged and then removed bythe action of other particles produces currents. 

1742. In the common voltaic battery, the current is occasioned by thetendency of the zinc to take the oxygen of the water from the hydrogen, theeffective action being at the place where the oxygen leaves the previouslyexisting electrolyte. But Schoenbein has arranged a battery in which theeffective action is at the other extremity of this essential part of thearrangement, namely, where oxygen goes to the electrolyte[A]. The first maybe considered as a case where the current is put into motion by theabstraction of oxygen from hydrogen, the latter by that of hydrogen fromoxygen. The direction of the electric current is in both cases the same, when referred to the direction in which the elementary particles of theelectrolyte are moving (923. 962. ), and both are equally in accordance withthe hypothetical view of the inductive action of the particles justdescribed (1740. ). 

 [A] Philosophical Magazine, 1838, xii. 225, 315. Also De la Rive's results with peroxide of manganese. Annales de Chimie, 1836, lxi. P. 40. --_Dec. 1838. _

1743. In such a view of voltaic excitement, the action of the particles maybe divided into two parts, that which occurs whilst the force in a particleof oxygen is rising towards a particle of zinc acting on it, and fallingtowards the particle of hydrogen with which it is associated (this beingthe progressive period of the inductive action), and that which occurs whenthe change of association takes place, and the particle of oxygen leavesthe hydrogen and combines with the zinc. The former appears to be thatwhich produces the current, or if there be no current, produces the stateof tension at the termination of the battery; whilst the latter, byterminating for the time the influence of the particles which have beenactive, allows of others coming into play, and so the effect of current iscontinued. 

1744. It seems highly probable, that excitement by friction may veryfrequently be of the same character. Wollaston endeavoured to refer suchexcitement to chemical action[A]; but if by chemical action ultimate unionof the acting particles is intended, then there are plenty of cases whichare opposed to such a view. Davy mentions some such, and for my own part Ifeel no difficulty in admitting other means of electrical excitement thanchemical action, especially if by chemical action is meant a finalcombination of the particles. 

 [A] Philosophical Transactions, 1801, p. 427. 

1745. Davy refers experimentally to the opposite states which two particleshaving opposite chemical relations can assume when they are brought intothe close vicinity of each other, but _not_ allowed to combine[A]. This, Ithink, is the first part of the action already described (1743. ); but in myopinion it cannot give rise to a continuous current unless combination takeplace, so as to allow other particles to act successively in the samemanner, and not even then unless one set of the particles be present as anelement of an electrolyte (923. 963. ); i. E. Mere quiescent contact alonewithout chemical action does not in such cases produce a _current_. 

 [A] Philosophical Transactions, 1807, p. 31. 

1746. Still it seems very possible that such a relation may produce a highcharge, and thus give rise to excitement by friction. When two bodies arerubbed together to produce electricity in the usual way, one at least mustbe an insulator. During the act of rubbing, the particles of opposite kindsmust be brought more or less closely together, the few which are mostfavourably circumstanced being in such close contact as to be short only ofthat which is consequent upon chemical combination. At such moments theymay acquire by their mutual induction (1740. ) and partial discharge to eachother, very exalted opposite states, and when, the moment after, they areby the progress of the rub removed from each other's vicinity, they willretain this state if both bodies be insulators, and exhibit them upon theircomplete separation. 

1747. All the circumstances attending friction seem to me to favour such aview. The irregularities of form and pressure will cause that the particlesof the two rubbing surfaces will be at very variable distances, only a fewat once being in that very close relation which is probably necessary forthe development of the forces; further, those which are nearest at one timewill be further removed at another, and others will become the nearest, andso by continuing the friction many will in succession be excited. Finally, the lateral direction of the separation in rubbing seems to me the bestfitted to bring many pairs of particles, first of all into that closevicinity necessary for their assuming the opposite states by relation toeach other, and then to remove them from each other's influence whilst theyretain that state. 

1748. It would be easy, on the same view, to explain hypothetically, how, if one of the rubbing bodies be a conductor, as the amalgam of anelectrical machine, the state of the other when it comes from under thefriction is (as a mass) exalted; but it would be folly to go far into suchspeculation before that already advanced has been confirmed or corrected byfit experimental evidence. I do not wish it to be supposed that I think allexcitement by friction is of this kind; on the contrary, certainexperiments lead me to believe, that in many cases, and perhaps in all, effects of a thermo-electric nature conduce to the ultimate effect; andthere are very probably other causes of electric disturbance influential atthe same time, which we have not as yet distinguished. 

_Royal Institution. June, 1838. _

INDEX. 

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N. B. A dash rule represents the _italics_ immediately preceding it. Thereferences are sometimes to the individual paragraph, and sometimes to thatin conjunction with those which follow. 

 * * * * *

_Absolute_ charge of matter, 1169. ---- quantity of electricity in matter, 852, 861, 873. Acetate of potassa, its electrolysis, 749. Acetates, their electrolysis, 774. Acetic acid, its electrolysis, 773. _Acid_, nitric, formed in air by a spark, 324. ----, or alkali, alike in exciting the pile, 932. ----, transference of, 525. ---- _for battery_, its nature and strength, 1128, 1137. ---- ----, nitric, the best, 1138. ---- ----, effect of different strengths, 1139. ---- _in voltaic pile_, does not evolve the electricity, 925, 933. ---- ----, its use, 925. Acids and bases, their relation in the voltaic pile, 927, 933. Active battery, general remarks on, 1034, 1136. Adhesion of fluids to metals, 1038. Advantages of a new voltaic battery, 1132. _Affinities, chemical_, opposed voltaically, 891, 904, 910. ----, their relation in the active pile, 949. _Air_, its attraction by surfaces, 622. ----, _charge of_, 1173. ----, ----, by brush, 1434, 1441. ----, ----, by glow, 1537, 1543. ----, convective currents in, 1572, 1576, 1581. ----, dark discharge in, 1548. ----, disruptive discharge in, 1359, 1406, 1425, 1526. ----, induction in, 1208, 1215, 1284, 1362. ----, its insulating and conducting power, 411, 1332, 1336, 1362. ----, its rarefaction facilitates discharge, 1375. ----, electrified, 1443. ----, electro-chemical decompositions in, 454, 1623. ----, hot, discharges voltaic battery, 271, 274. ----, poles of, 455, 461, 559. ----, _positive and negative_ brush in, 1467, 1472, 1476. ----, ---- glow in, 1526, 1530. ----, ---- spark in, 1485. ----, rarefied, brush in, 1451, 1456. ----, retention of electricity on conductors by, 1377, 1398. ----, _specific inductive capacity of_, 1284. ----, ----, not varied by temperature or pressure, 1287, 1288. _Alkali_ has strong exciting power in voltaic pile, 884, 931, 941. ----, transference of, 525. _Amalgamated zinc_, its condition, 1000. ----, how prepared, 863. ----, its valuable use, 863, 999. ---- battery, 1001. _Ammonia_, nature of its electrolysis, 748. ----, solution of, a bad conductor, 554, 748. Ampère's inductive results, 78, 255, 379 _note_. _Anions_ defined, 665, 824. ----, table of, 847. ---- related through the entire circuit, 963. ----, their action in the voltaic pile, 924. ----, their direction of transfer, 962, Anode defined, 663. _Antimony_, its relation to magneto-electric induction, 139. ----, chloride of, not an electrolyte, 690, 796. ----, oxide of, how affected by the electric current, 801. ---- _supposed new_ protoxide, 693. ---- ----, sulphuret, 694. _Animal electricity_, its general characters considered, 351. ---- is identical with other electricities, 354, 360. ----, its chemical force, 355. ----, enormous amount, 359. ----, evolution of heat, 353, ----, magnetic force, 351. ----, physiological effects, 357. ----, spark, 358. ----, tension, 352. Apparatus, inductive, 1187. _See_ Inductive apparatus. _Arago's magnetic phenomena_, their nature, 81, 120. ----, reason why no effect if no motion, 126, ----, direction of motion accounted for, 121. ----, due to induced electric currents, 119, 248. ----, like electro-magnetic rotations in principle, 121. ----, not due to direct induction of magnetism, 128, 138, 215, 243, 248. ----, obtained with electro-magnets, 129. ----, produced by conductors only, 130, 215. ----, time an element in, 124. ----, Babbage and Hershel's results explained, 127. Arago's experiment, Sturgeon's form of, 219. Associated voltaic circles, 989. _Atmospheric_ balls of fire, 1611. ----, electricity, its chemical action, 336. Atomic number judged of from electrochemical equivalent, 851. _Atoms of matter_, 869, 1703. ----, their electric power, 856, 860. Attraction of particles, its influence in Döbereiner's phenomena, 619. _Attractions_, electric, their force, 1022 _note_. ----, _chemic, produce_ current force, 852, 918, 947, 996, 1741. ----, ---- local force, 852, 921, 947, 959, 1739. ----, hygrometric, 621. Aurora borealis referred to magneto-electric induction, 192. Axis of power, the electric current on, 517, 1627, 1642. 

Balls of fire, atmospheric, 1611. Barlow's revolving globe, magnetic effects explained, 137, 160. Barry, decomposed bodies by atmospheric electricity, 338. Bases and acids, their relation in the pile, 927. Battery, Leyden, that generally used, 291. _Battery, voltaic_, its nature, 856, 989. ----, _origin of its power_, 878, 989. ----, ---- not in contact, 887, 915, ----, ---- chemical, 879, 916, 919, 1741. ----, ----, oxidation of the zinc, 919, 944. ----, its circulating force, 858, 1120. ----, its local force, 1120. ----, quantity of electricity circulating, 990. ----, intensity of electricity circulating, 990, 993. ----, _intensity of its current_, 909, 994. ----, ---- increased, 905, 989. ----, _its diminution in power_, 1035. ----, ---- _from_ adhesion of fluid, 1003, 1136. ----, ---- ---- peculiar state of metal, 1040. ----, ---- ---- exhaustion of charge, 1042. ----, ---- ---- irregularity of plates, 1045, 1146. ----, use of metallic contact in, 893, 896. ----, _electrolytes essential to it_, 921. ----, ----, why, 858, 923. ----, state of metal and electrolyte before contact, 916. ----, conspiring action of associated affinities, 989. ----, purity of its zinc, 1144. ----, use of amalgamated zinc in, 999. ----, _plates, their_ number, 1151. ----, ---- size, 1154. ----, ---- vicinity, 1148. ----, ---- immersion, 1150. ----, ---- relative age, 1146. ----, ---- foulness, 1145. ----, _excited by_ acid, 880, 926, 1137. ----, ---- alkali, 931, 934, 941. ----, ---- sulphuretted solutions, 943. ----, the acid, its use, 925, ----, acid for, 1128, 1137. ----, nitric acid best for, 1137. ----, construction of, 989, 1001, 1121. ----, with numerous alternations, 989. ----, Hare's, 1123. ----, general remarks on, 1031. 1136. ----, simultaneous decompositions with, 1156. ----, practical results with, 1136. ----, _improved_, 1001, 1006, 1120. ----, ----, its construction, 1124. ----, ----, power, 1125, 1128. ----, ----, advantages, 1132. ----, ----, disadvantages, 1132. Batteries, voltaic, compared, 1126. Becquerel, his important secondary results, 745, 784. Berzelius, his view of combustion, 870, 959. Biot's theory of electro-chemical decomposition, 486. Bismuth, its relation to magneto-electric induction, 139. _Bodies_ classed in relation to the electric current, 823. ---- classed in relation to magnetism, 255. Bodies electrolyzable, 824. Bonijol decomposed substances by atmospheric electricity, 336. Boracic acid a bad conductor, 408. _Brush, electric_, 1425. ----, produced, 1425. ----, not affected by nature of conductors, 1454, 1473. ----, is affected by the dielectrics, 1455, 1463, 1475. ----, not dependent on current of air, 1440. ----, proves molecular action of dielectric, 1449, 1450. ----, its analysis, 1427, 1433. ----, nature, 1434, 1441, 1447. ----, form, 1428, 1449, 1451. ----, _ramifications_, 1439. ---- ----, their coalescence, 1453. ----, sound, 1426, 1431. ----, requisite intensity for, 1446. ---- has sensible duration, 1437. ---- is intermitting, 1427, 1431, 1451. ----, _light of_, 1444, 1445, 1451. ----, ----, in different gases, 1446, 1454. ----, dark? 1444, 1552. ----, passes into spark, 1448. ----, spark and glow relation of, 1533, 1539, 1542. ----, in gases, 1454, 1463, 1476. ----, oxygen, 1457, 1476. ----, nitrogen, 1458, 1476. ----, hydrogen, 1459, 1476. ----, coal-gas, 1460, 1476. ----, carbonic acid gas, 1461, 1476. ----, muriatic acid gas, 1462, 1476. ----, rare air, 1451, 1455, 1474. ----, oil of turpentine, 1452. ----, positive, 1455, 1467, 1484. ----, _negative_, 1468, 1472, 1484. ----, ----, of rapid recurrence, 1468, 1491. ----, positive and negative in different gases, 1455, 1475, 1506. 

_Capacity, specific inductive_, 1252. ----. _See_ Specific inductive capacity. _Carbonic acid gas_ facilitates formation of spark, 1463. ----, brush in, 1461, 1476. ----, glow in, 1534. ----, spark in, 1422, 1463. ----, _positive and negative_ brush in, 1476. ----, ---- discharge in, 1546. ----, non-interference of, 645, 652. Carbonic oxide gas, interference of, 645, 652. _Carrying discharge_, 1562. ----. _See_ Discharge convective. Cathode described, 663, 824. _Cations_, or cathions, described, 665, 824. ----, table of, 817. ----, direction of their transfer, 962. Cations, are in relation through the entire circuit, 963. _Characters of_ electricity, table of, 360. ---- the electric current, constant, 1618, 1627. ---- voltaic electricity, 268. ---- ordinary electricity, 284. ---- magneto-electricity, 343. ---- thermo-electricity, 349. ---- animal electricity, 351. _Charge_, free, 1684. ---- is always induction, 1171, 1177, 1300, 1682. ---- on surface of conductors: why, 1301. ----. _influence of_ form on, 1302. ----, ---- distance on, 1303. ----, loss of, by convection, 1569. ----, removed from good insulators, 1203. ---- of matter, absolute, 1169. ---- _of air_, 1173. ---- ---- by brush, 1434, 1441. ---- ---- by glow, 1526, 1537, 1543. ---- of particles in air, 1564. ---- of oil of turpentine, 1172. ---- of inductive apparatus divided, 1208. ----, residual, of a Leyden jar, 1249. ----, _chemical, for battery_, good, 1137. -----, ----, weak and exhausted, 1042, 1143. _Chemical action_, the, exciting the pile is oxidation, 921. ---- _superinduced by_ metals, 564. ---- ---- platina, 564, 617, 630. ---- tested by iodide of potassium, 315. Chemical actions, distant, opposed to each other, 891, 910, 1007. _Chemical affinity_ influenced by mechanical forces, 656. ---- transferable through metals, 918. ---- statical or local, 852, 921, 917, 959. ---- current, 852, 918, 947, 996. _Chemical decomposition by_ voltaic electricity, 278, 450, 661. ---- common electricity, 309, 453. ---- magneto-electricity, 346. ---- thermo-electricity, 349. ---- animal electricity, 355. ----. _See_ Decomposition electro-chemical. Chemical and electrical forces identical, 877, 918, 947, 960, 965, 1031. _Chloride of_ antimony not an electrolyte, 690. ---- _lead_, its electrolysis, 794, 815. ---- ----, electrolytic intensity for, 978. ---- _silver_, its electrolysis, 541, 813, 902. ---- ----, electrolytic intensity for, 979. ---- tin, its electrolysis, 789, 819. _Chlorides in_ solution, their electrolysis, 766. ---- fusion, their electrolysis, 789, 813. Circle of anions and cathions, 963. _Circles_, simple voltaic, 875. ----, associated voltaic, 989. Circuit, voltaic, relation of bodies in, 962. _Classification of bodies in relation to_ magnetism, 255. ---- the electric current, 823, 817. Cleanliness of metals and other solids, 633. _Clean platina_, its characters, 633, 717. ----, _its power of effecting combination_, 590, 605, 617, 632. ----, ----. _See_ Plates of platina. _Coal gas_, brush in, 1460. ----, dark discharge in, 1556. ----, positive and negative brush in, 1476. ----, positive and negative discharge in, 1515. ----, spark in, 1422. Colladon on magnetic force of common electricity, 289. Collectors, magneto-electric, 86. _Combination effected by_ metals, 564, 608. ---- solids, 564, 618. ---- poles of platina, 566. ---- _platina_, 564, 568, 571, 590, 630. ---- ----, as plates, 569. ---- ----, as sponge, 609, 636. ---- ----, cause of, 590, 616, 625, 656. ---- ----, how, 630. ---- ----, interferences with, 638, 652, 655. ---- ---- _retarded by_ olefiant gas, 640. ---- ---- ---- carbonic oxide, 645, 652. ---- ---- ---- sulphuret of carbon, 650. ---- ---- ---- ether, 651. ---- ---- ---- other substances, 649, 653, 654. Comparison of voltaic batteries, 1126, 1146. _Conditions_, general, of voltaic decomposition, 669. ----, new, of electro-chemical decomposition, 453. _Conducting power_ measured by a magnet, 216. ---- of solid electrolytes, 419. ---- of water, constant, 984. _Conduction_, 418, 1320. ----, its nature, 1320, 1326, 1611. ----, of two kinds, 987. ----, preceded by induction, 1329, 1332, 1338. ---- and insulation, cases of the same kind, 1320, 1326, 1336, 1338, 1561. ----, its relation to the intensity of the current conducted, 419. ---- common to all bodies, 444, 449. ---- by a vacuum, 1613. ---- by lac, 1234, 1324. ---- by sulphur, 1241, 1328. ---- by glass, 1239, 1324. ---- by spermaceti, 1240, 1323. ---- by gases, 1336. ----, slow, 1233, 1245, 1328. ---- affected by temperature, 445, 1339. ---- by metals diminished by heat, 432, 445. ---- increased by heat, 432, 441, 445. ---- of electricity and heat, relation of, 416. ----, _simple, can occur in electrolytes_, 967, 983. ----, ---- with very feeble currents, 970. ---- by electrolytes without decomposition, 968, 1017, 1032. ---- and decomposition associated in electrolytes, 413, 676, 854. ---- facilitated in electrolytes, 1355. ---- _by water_ bad, 1159. ---- ---- improved by dissolved bodies, 984, 1355. ----, electrolytic, stopped, 380, 1358, 1705. ---- of currents stopped by ice, 381. ---- conferred by liquefaction, 394, 410. ---- _taken away by solidification_, 394, 1705. ---- ---- why, 910, 1705. ----, _new law of_, 380, 394, 410. ----, ----, supposed exception to, 691, 1340. ----, general results as to, 443. Conductive discharge, 1320. _Conductors_, electrolytic, 474. ----, magneto-electric, 86. ----, their nature does not affect the electric brush, 1454. ----, size of, affects discharge, 1372. ----, form of, affects discharge, 1374, 1425. ----, _distribution of electricity on_, 1368. ----, ----, _affected by_ form, 1374. ----, ----, ---- distance, 1364, 1371. ----, ----, ---- air pressure, 1375. ----, ----, irregular with equal pressure, 1378. Constancy of electric current, 1618. _Constitution of electrolytes as to_ proportions, 679, 697, 830, 1708. ---- liquidity, 394, 823. _Contact of metals_ not necessary for electrolyzation, 879. ----, its use in the voltaic battery, 893. ---- not necessary for spark, 915, 956. _Contiguous particles_, their relation to induction, 1165, 1679. ---- active in electrolysis, 1349, 1703. _Convection_, 1562, 1642. ---- or convective discharge. _See_ Discharge convective. Copper, iron, and sulphur circle, 943. Coruscations of lightning, 1464. _Coulomb's electrometer_, 1180. ----, precautions in its use, 1182, 1186, 1206. Crystals, induction through, 1689. Cube, large, electrified, 1173. Cubes of crystals, induction through, 1692, 1695. Current chemical affinity, 852, 918, 947, 996. Current, voltaic, without metallic contact, 879, 887. _Current, electric_, 1617. ----, defined, 282, 511. ----, nature of, 511, 667, 1617, 1627. ----, variously produced, 1618. ----, _produced by_ chemical action, 879, 916, 1741. ----, ---- animals, 351. ----, ---- friction, 301, 307, 311. ----, ---- heat, 349, ----, ---- discharge of static electricity, 296, 307, 363. ----, ---- _induction by_ other currents, 6, 1089. ----, ---- ---- magnets, 30, 88, 344. ----, evolved in the moving earth, 181. ----, in the earth, 187. ----, natural standard of direction, 663. ----, none of one electricity, 1627, 1632, 1635. ----, two forces everywhere in it, 1627, 1632, 1635, 1642. ----, one, and indivisible, 1627. ----, an axis of power, 517, 1642. ----, constant in its characters, 1618, 1627. ----, inexhaustibility of, 1631. ----, _its velocity in_ conduction, 1648. ----, ---- electrolyzation, 1651. ----, regulated by a fine wire, 853, _note_. ----, affected by heat, 1637. ----, stopped by solidification, 381. ----, _its section_, 498, 504, 1634. ----, ---- presents a constant force, 1634. ----, _produces_ chemical phenomena, 1621. ----, ---- heat, 1625. ----, its heating power uniform, 1630. ----, produces magnetism, 1653. ----, Porrett's effects produced by, 1646. ----, _induction of_, 1, 6, 232, 241, 1101, 1048. ----, ----, on itself, 1048. ----, ----. _See_ Induction of electric current. ----, its inductive force lateral, 1108. ----, induced in different metals, 193, 213, 201, 211. ----, _its transverse effects_, 1653. ----, ---- constant, 1655. ----, _its transverse forces_, 1658. ----, ---- are in relation to contiguous particles, 1664. ----, ---- their polarity of character, 1665. ---- and magnet, their relation remembered, 38, _note_. _Currents_ in air by convection, 1572, 1581. ----, metals by convection, 1603. ----, oil of turpentine by convection, 1595, 1598. Curved lines, induction in, 1215. Curves, magnetic, their relation to dynamic induction, 217, 232. 

Daniell on the size of the voltaic metals, 1525. _Dark discharge_, 1444, 1544. ----. _See_ Discharge, dark. Dates of some facts and publications, 139, _note after_. _Davy's_ theory of electro-chemical decomposition, 482, 500. ---- electro-chemical views, 965. ---- mercurial cones, convective phenomena, 1603. _Decomposing force_ alike in every section of the current, 501, 505. ----, variation of, on each particle, 503. _Decomposition_ and conduction associated in electrolytes, 413, 854. ----, primary and secondary results of, 742, 777. ---- _by common electricity_, 309, 454. ---- ----, precautions, 322. _Decomposition, electro-chemical_, 450, 669. ----, nomenclature of, 661. ----, new terms relating to, 662. ----, its distinguishing character, 309. ----, by common electricity, 309, 454. ----, by a single pair of plates, 862, 897, 904, 931. ----, by the electric current, 1621. ----, without metallic contact, 880, 882. ----, its cause, 891, 904, 910. ----, not due to direct attraction or repulsion of poles, 493, 497, 536, 542, 5460. ----, _dependent on_ previous induction, 1345. ----, ---- the electric current, 493, 510, 524, 854. ----, ---- intensity of current, 905. ----, ---- chemical affinity of particles, 519, 525, 519. ----, resistance to, 891, 910, 1007. ----, intensity requisite for, 966, 1354. ----, stopped by solidification, 380, 1358, 1705. ----, retarded by interpositions, 1007. ----, assisted by dissolved bodies, 1355. ----, division of the electrolyte, 1347, 1623, 1701. ----, transference, 519, 525, 538, 550, 1347, 1706. ----, why elements appear at the poles, 535. ----, uncombined bodies do not travel, 544, 546. ----, circular series of effects, 562, 962. ----, simultaneous, 1156, ----, _definite_, 329, 372, 377, 504, 704, 714, 722, 726, 732, 764, 783, 807, 821, 960. ----, ---- independent of variations of electrodes, 714, 722, 807, 832. ----, necessary intensity of current, 911, 966, 1345, 1354. ----, influence of water in, 472. ----, in air, 451, 461, 469. ----, some general conditions of, 669. ----, new conditions of, 453. ----, primary results, 742. ----, secondary results, 702, 742, 748, 777. ----, of acetates, 774. ----, acetic acid, 773. ----, ammonia, 748. ----, _chloride of_ antimony, 690, 796. ----, ---- lead, 794, 815. ----, ---- silver, 541, 813, 979. ----, _chlorides in_ solution, 766. ----, ---- fusion, 789, 913. ----, fused electrolytes, 789. ----, hydriodic acid and iodides, 767, 787. ----, hydrocyanic acid and cyanides, 771. ----, hydrofluoric acid and fluorides, 770. ----, _iodide of_ lead, 802, 818. ----, ---- potassium, 805. ----, muriatic acid, 758, 780. ----, nitre, 753. ----, nitric acid, 752. ----, _oxide_ antimony, 801. ----, ---- lead, 797. ----, protochloride of tin, 789, 819. ----, protiodide of tin, 804. ----, sugar, gum, &c. , 776. ----, of sulphate of magnesia, 495. ----, sulphuric acid, 757. ----, sulphurous acid, 755. ----, tartaric acid, 775. ----, water, 704, 785, 807. ----, _theory of_, 477, 1345. ----, ----, by A. De la Rive, 489, 507, 514, 543. ----, ----, Biot, 486. ----, ----, Davy, 482, 500. ----, ----, Grotthuss, 481, 499, 515. ----, ----, Hachette, 491, 513, ----, ----, Riffault and Chompré, 485, 507, 512. ----, author's theory, 518, 524, 1345, 1623, 1703, 1766. _Definite_ decomposing action of electricity, 329, 372, 377, 504, 704, 783, 821. ----, magnetic action of electricity, 216, 362, 367, 377. ----, _electro-chemical action_, 822, 869, 960. ----, ----, general principles of, 822, 862. ----, ----, _in chloride of lead_, 815. ----, ----, ---- silver, 813. ----, ----, in hydriodic acid, 767, 787. ----, ----, iodide of lead, 802, 818. ----, ----, muriatic acid, 758, 786, ----, ----, protochloride of tin, 819. ----, ----, water, 732, 785, 807. Degree in measuring electricity, proposal for, 736. _De la Rive_ on heat at the electrodes, 1637. ----, his theory of electro-chemical decomposition, 489, 507, 514, 543. _Dielectrics_, what, 1168. ----, their importance in electrical actions, 1666. ----, their relation to static induction, 1296. ----, their condition under induction, 1369, 1679. ----, their nature affects the brush, 1455. ----, their specific electric actions, 1296, 1398, 1423, 1454, 1503, 1560. Difference of positive and negative discharge, 1465, 1480, 1485. Differential inductometer, 1307. _Direction of_ ions in the circuit, 962. ----, the electric current, 563. ----, the magneto-electric current, 114, 116. ----, the induced volta-electric current, 19, 26, 1091. Disruptive discharge, 1359, 1405. _See_ Discharge, disruptive. _Discharge, electric_, as balls of fire, 1641. ----, of Leyden jar, 1300. ----, _of voltaic battery by_ hot air, 271, 274. ----, ---- points, 272. ----, velocity of, in metal, varied, 1333. ----, varieties of, 1319. ----, brush, 1425. _See_ Brush. ----, carrying, 1562. _See_ Discharge, convective. ----, conductive, 1320. _See_ Conduction. ----, dark, 1444, 1544. ----, disruptive, 1359, 1405. ----, electrolytic, 1343, 1622, 1704. ----, glow, 1526. _See_ Glow. ----, positive and negative, 1465. ----, spark, 1406. _See_ Spark, electric. _Discharge, connective_, 1442, 1562, 1601, 1623, 1633, 1642. ----, in insulating media, 1562, 1572. ----, in good conductors, 1603. ----, _with fluid terminations in_ air, 1581, 1589. ----, ---- liquids, 1597. ----, from a ball, 1576, 1590. ----, influence of points in, 1573. ----, _affected by_ mechanical causes, 1579. ----, ---- flame, 1580. ----, with glow, 1576. ----, _charge of a particle in_ air, 1564. ----, ---- oil of turpentine, 1570. ----, charge of air by, 1442, 1592. ----, _currents produced in_ air, 1572, 1581, 1591. ----, ---- oil of turpentine, 1595, 1598. ----, direction of the currents, 1599, 1645. ----, Porrett's effects, 1646, ----, positive and negative, 1593, 1600, 1643. ----, related to electrolytic discharge, 1622, 1633. _Discharge, dark_, 1444, 1544, 1560. ----, with negative glow, 1544. ----, between positive and negative glow, 1547. ----, in air, 1548. ----, muriatic acid gas, 1554. ----, coal gas, 1556. ----, hydrogen, 1558. ----, nitrogen, 1559. _Discharge, disruptive_, 1405. ----, preceded by induction, 1362. ----, determined by one particle, 1370, 1409. ----, necessary intensity, 1409, 1553. ----, determining intensity constant, 1410. ----, related to particular dielectric, 1503. ----, facilitates like action, 1417, 1435, 1453, 1553. ----, its time, 1418, 1436, 1498, 1641. ----, _varied by_ form of conductors, 1302, 1372, 1374. ----, ---- change in the dielectric, 1395, 1422, 1454. ----, ---- rarefaction of air, 1365, 1375, 1451. ----, ---- temperature, 1367, 1380. ----, ---- distance of conductors, 1303, 1364, 1371. ----, ---- size of conductors, 1372. ----, in liquids and solids, 1403. ----, in _different gases_, 1381, 1388, 1421. ----, ---- not alike, 1395. ----, ---- specific differences, 1399, 1422, 1687. ----, _positive and negative_, 1393, 1399, 1465, 1524. ----, ----, distinctions, 1467, 1475, 1482. ----, ----, differences, 1485, 1501. ----, ----, relative facility, 1496, 1520. ----, ----, dependent on the dielectric, 1503. ----, ----, in different gases, 1506, 1510, 1518, 1687. ----, ----, of voltaic current, 1524. ----, brush, 1425. ----, collateral, 1412. ----, dark, 1444, 1544, 1560. ----, glow, 1526. ----, spark, 1406. ----, theory of, 1308, 1406, 1434. _Discharge, electrolytic_, 1164, 1343, 1621, 1703, 1706. ----, previous induction, 1345, 1351. ----, necessary intensity, 912, 966, 1346, 1354. ----, division of the electrolyte, 1347, 1704. ----, stopped by solidifying the electrolyte, 380, 1358, 1705. ----, facilitated by added bodies, 1355. ----, in curved lines, 521, 1216, 1351. ----, proves action of contiguous particles, 1349. ----, positive and negative, 1525. ----, velocity of electric current in, 1650. ----, related to convective discharge, 1622. ----, theory of, 1344, 1622, 1704. Discharging train generally used, 292. Disruptive discharge, 1405. _See_ Discharge, disruptive. Dissimulated electricity, 1684. _Distance, its influence_ in induction, 1303, 1364, 1371. ---- over disruptive discharge, 1364, 1371. Distant chemical actions, connected and opposed, 891, 909. Distinction of magnetic and magneto-electric action, 138, 215, 243, 253. Division of a charge by inductive apparatus, 1208. Döbereiner on combination effected by platina, 609, 610. Dulong and Thenard on combination by platina and solids, 609, 611. Dust, charge of its particles, 1567. 

Earth, natural magneto-electric induction in, 181, 190, 192. _Elasticity of_ gases, 626. ---- gaseous particles, 658. _Electric_ brush, 1425. _See_ Brush, electric. ---- condition of particles of matter, 862, 1669. ---- conduction, 1320. _See_ Conduction. ---- _current_ defined, 283, 511. ---- ----, nature of, 511, 1617, 1627. ---- ----. _See_ Current, electric. ---- ----, _induction of_, 6, 232, 241, 1048, 1101. _See_ Induction of electric current. ---- ----, ----, on itself, 1048. ---- discharge, 1319. _See_ Discharge. ---- force, nature of, 1667. _See_ Forces. ---- induction, 1162. _See_ Induction. ---- inductive capacity, 1252. _See_ Specific inductive capacity. ---- polarity, 1685. _See_ Polarity, electric. ---- spark, 1406. _See_ Spark, electric. ---- and magnetic forces, their relation, 118, 1411, 1653, 1658, 1709, 1731. Electrics, charge of, 1171, 1247. _Electrical_ excitation, 1737. _See_ Excitation. ---- machine generally used, 290. ---- battery generally used, 291. ---- and chemical forces identical, 877, 917, 947, 960, 965, 1031. _Electricities_, their identity, however excited, 265, 360. ----, one or two, 516, 1667. ----, _two_, 1163. ----, ----, their independent existence, 1168. ----, ----, their inseparability, 1168, 1177, 1244. ----, ----, never separated in the current, 1628. _Electricity_, quantity of, in matter, 852, 861. ----, _its distribution on conductors_, 1368. ----, ---- _influenced by_ form, 1302, 1374. ----, ---- ---- distance, 1303, 1364, 1371. ----, ---- ---- air's pressure, 1375. ----, relation of a vacuum to, 1613. ----, dissimulated, 1684. ----, common and voltaic, measured, 361, 860. ----, _its definite_ decomposing action, 329, 377, 783, 1621. ----, ---- heating action, 1625. ----, ---- magnetic action, 216, 366. ----, animal, its characters, 351. ----, magneto-, its characters, 343. ----, ordinary, its characters, 284. ----, thermo-, its characters, 349. ----, voltaic, its characters, 268. _Electricity from magnetism_, 27, 36, 57, 83, 135, 140. ----, _on magnetisation of soft iron by_ currents, 27, 34, 57, 113. ---- ---- magnets, 36, 44. ----, _employing_ permanent magnets, 39, 84, 112. ----, ---- terrestrial magnetic force, 140, 150, 161. ----, ---- _moving conductors_, 55, 83, 132, 139, 149, 161, 171. ----, ---- ---- essential condition, 217. ---- _by revolving plate_, 83, 149, 240. ---- ---- a constant source of electricity, 89, 90, 154. ---- ----, law of evolution, 114. ---- ----, direction of the current evolved, 91, 99, 110, 116, 117. ---- ----, course of the currents in the plate, 123, 150. ---- by a revolving globe, 137, 160. ---- by plates, 94, 101. ---- by a wire, 49, 55, 109, 112, 137. ----, conductors and magnet may move together, 218. ----, _current produced_ in a single wire, 49, 55, 170. ----, ---- a ready source of electricity, 46, _note_. ----, ---- momentary, 28, 30, 47. ----, ---- permanent, 89, 154. ----, ---- deflects galvanometer, 30, 39, 46. ----, ---- makes magnets, 34. ----, ----, shock of, 56. ----, ----, spark of, 32. ----, ---- traverses fluids, 23, 33. ----, ----, its direction, 30, 38, 41, 52, 53, 54, 78, 91, 99, 114, 142, 166, 220, 222. ----, effect of approximation and recession, 18, 39, 50. ----, the essential condition, 217. ----, general expression of the effects, 256. ----, from magnets alone, 220. _Electricity of the voltaic pile_, 875. ---- _its source_, 875. ---- ---- not metallic contact, 887, 915. ---- ---- is in chemical action, 879, 916, 919, 1738, 1741. _Electro-chemical decomposition_, 450, 661. ----, nomenclature, 661. ----, general conditions of, 669. ----, new conditions of, 453, ----, influence of water in, 472. ----, primary and secondary results, 742. ----, definite, 732, 783. ----, theory of, 477. ----. _See_ also Decomposition, electrochemical. _Electro-chemical equivalents_, 824, 833, 835, 855. ----, table of, 847. ----, how ascertained, 837. ---- always consistent, 835. ---- same as chemical equivalents, 836, 839. ---- able to determine atomic number, 851. Electro-chemical excitation, 878, 919, 1738. Electrode defined, 662. _Electrodes_ affected by heat, 1637. ----, _varied in_ size, 714, 722. ----, ---- nature, 807. ----. _See_ Poles. Electrolysis, resistance to, 1007. _Electrolyte_ defined, 664. ---- _exciting, solution of_ acid, 881, 925. ---- ---- alkali, 931, 941. ---- _exciting_, water, 944, 945. ---- ---- sulphuretted solution, 943. _Electrolytes_, their necessary constitution, 669, 823, 829, 858, 921, 1347, 1708. ---- consist of single proportionals of elements, 679, 697, 830, 1707. ---- _essential to voltaic pile_, 921. ---- ----, why, 858, 923. ---- conduct and decompose simultaneously, 413. ---- can conduct feeble currents without decomposition, 967. ----, as ordinary conductors, 970, 983, 1344. ----, solid, their insulating and conducting power, 419. ----, real conductive power not affected by dissolved matters, 1356. ----, needful conducting power, 1158. ---- are good conductors when fluid, 394, 823. _Electrolytes non-conductors when solid_ 381, 394. ----, why, 910, 1705. ----, the exception, 1032. _Electrolytes_, their particles polarize as wholes, 1700. ----, polarized light sent across, 951. ----, relation of their moving elements to the passing current, 923, 1704. ----, their resistance to decomposition, 891, 1007, 1705. ----, and metal, their states in the voltaic pile, 946. ----, salts considered as, 698. ----, acids not of this class, 681. _Electrolytic_ action of the current, 478, 518, 1620. ---- conductors, 474. ---- discharge, 1343. _See_ Discharge, electrolytic. ---- induction, 1164, 1343. ---- _intensity_, 911, 966, 983. ---- ---- varies for different bodies, 912, 986, 1354. ---- ---- of chloride of lead, 978. ---- ---- chloride of silver, 979. ---- ---- sulphate of soda, 975. ---- ---- water, 968, 981. ---- ---- its natural relation, 987. _Electrolyzation_, 450, 661, 1164, 1347, 1704. _See_ Decomposition electro-chemical. ---- defined, 664. ---- facilitated, 394, 417, 549, 1355. ---- in a single circuit, 863, 879. ----, intensity needful for, 919, 966, ---- of chloride of silver, 541, 979. ---- sulphate of magnesia, 495. ---- and conduction associated, 413, 676. Electro-magnet, inductive effects in, 1060. Electro-magnetic induction definite, 216, 366. _Electrometer, Coulomb's_, described, 1180. ----, how used, 1183. _Electro-tonic state_, 60, 231, 242, 1114, 1661, 1729. ---- _considered common to all_ metals, 66. ---- ---- conductors, 76. ---- is a state of tension, 71. ---- is dependent on particles, 73. Elementary bodies probably ions, 849. _Elements evolved_ by force of the current, 493, 520, 524. ---- at the poles, why, 535. ---- determined to either pole, 552, 681, 757. ----, transference of, 454, 538. ----, if not combined, do not travel, 544, 546. _Equivalents_, electro-chemical, 824, 833, 855. ----, chemical and electro-chemical, the same, 836, 839. Ether, interference of, 651. _Evolution_ of electricity, 1162, 1737. ---- of one electric force impossible, 1175. ---- of elements at the poles, why, 535. _Excitation_, electrical, 1737. ---- by chemical action, 878, 916, 1739. ---- by friction, 1744. Exclusive induction, 1681. 

Flame favours convectivc discharge, 1580. Flowing water, electric currents in, 190. Fluid terminations for convection, 1581. Fluids, their adhesion to metals, 1038. Fluoride of lead, hot, conducts well, 1340. _Force, chemical_, local, 947, 959, 1739. ----, circulating, 917, 947, 996, 1120. _Force_, electric, nature of, 1163, 1667. ----, inductive, of currents, its nature, 60, 1113, 1735. _Forces, electric_, two, 1163. ----, inseparable, 1163, 1177, 1244, 1627. ---- and chemical, are the same, 877, 916. ---- _and magnetic_, relation of, 1411, 1653, 1658, 1709. ---- ----, are they essentially different? 1663, 1731. _Forces, exciting, of voltaic apparatus_, 887, 916. ----, exalted, 905, 994, 1138, 1148. _Forces_, polar, 1665. ---- _of the current_, direct, 1620. ---- ----, lateral or transverse, 1653, 1709. _Form, its influence on_ induction, 1302, 1374. ---- discharge, 1372, 1374. Fox, his terrestrial electric currents, 187. _Friction_ electricity, its characters, 284. ----, excitement by, 1744. Fusion, conduction consequent upon, 394, 402. Fusinieri, on combination effected by platina, 613. 

_Galvanometer_, affected by common electricity, 289, 366. ----, a correct measure of electricity, 367, _note_. _Gases_, their elasticity, 626, 657. ----, conducting power, 1336. ----, _insulating power_, 1381, 1507. ----, ---- not alike, 1395, 1508. ----, _specific inductive capacity_, 1283, 1290. ----, ---- alike in all, 1292. ----, specific influence on brush and spark, 1463, 1687. ----, discharge, disruptive, through, 1381. ----, brush in, 1454. ----, spark in, 1421. ----, _positive and negative brushes in_, 1475. ----, ----, their differences, 1476. ----, positive and negative discharge in, 1393, 1506, 1687. ----, solubility of, in cases of electrolyzation, 717, 728. ----, from water, spontaneous recombination of, 566. ----, mixtures of, affected by platina plates, 571. ----, mixed, relation of their particles, 625. _General_ principles of definite electrolytic action, 822. ---- remarks on voltaic batteries, 1031, 1136. ---- _results as to_ conduction, 443. ---- ---- induction, 1295. _Glass_, its conducting power, 1239. ----, its specific inductive capacity, 1271. ----, _its attraction for_ air, 622. ----, ---- water, 1251. _Globe, revolving of Barlow_, effects explained, 137, 160. ----, is magnetic, 164. _Glow_, 1405, 1525. ----, produced, 1527. ----, positive, 1527. ----, negative, 1530. ----, favoured by rarefaction of air, 1529. ----, is a continuous charge of air, 1526, 1537, 1543. ----, occurs in all gases, 1534. ----, accompanied by a wind, 1535. ----, its nature, 1543, ----, discharge, 1526. ----, brush and spark relation of, 1533, 1538, 1539, 1542. Grotthuss' theory of electro-chemical decomposition, 481, 499, 515. _Growth of a_ brush, 1437. ---- spark, 1553. 

Hachette's view of electro-chemical decomposition, 491. Hare's voltaic trough, 1123, 1132. Harris on induction in air, 1363. _Heat_ affects the two electrodes, 1637. ---- increases the conducting power of some bodies, 432, 438, 1340. ----, its conduction related to that of electricity, 416. ----, as a result of the electric current, 853, _note_, 1625, 1630. ---- _evolved by_ animal electricity, 353. ---- ---- common electricity, 287. ---- ---- magneto-electricity, 344. ---- ---- thermo-electricity, 349. ---- ---- voltaic electricity, 276. Helix, inductive effects in, 1061, 1094. Hydriodic acid, its electrolyses, 767, 787. Hydrocyanic acid, its electrolyses, 771, 788. Hydrofluoric acid, not electrolysable, 770. _Hydrogen_, brush in, 1459. ----, _positive and negative_ brush in, 1476. ----, ---- discharge in, 1514. _Hydrogen and oxygen combined by_ platina plates, 570, 605. ---- spongy platina, 609. 

_Ice_, its conducting power, 419. ---- a non-conductor of voltaic currents, 381. Iceland crystal, induction across, 1695. _Identity_, of electricities, 265, 360. ---- of chemical and electrical forces, 877, 917, 947, 961, 1031. Ignition of wire by electric current, 853, _note_, 1630. Improved voltaic battery, 1006, 1120. Increase of cells in voltaic battery, effect of, 990. Inducteous surfaces, 1483. _Induction apparatus_, 1187. ----, fixing the stem, 1190, 1193, 1200. ----, precautions, 1194, 1199, 1213, 1232, 1250. ----, removal of charge, 1203. ----, retention of charge, 1205, 1207. ----, a charge divided, 1208. ----, peculiar effects with, 1233. _Induction, static_, 1161. ----, an action of contiguous particles, 1165, 1231, 1253, 1295, 1450, 1668, 1679. ----, consists in a polarity of particles, 1298, 1670, 1679. ----, continues only in insulators, 1298, 1324, 1338. ----, intensity of, sustained, 1362. ----, _influenced by the_ form of conductors, 1302. ----, ---- distance of conductors, 1303. ----, ---- relation of the bounding surfaces, 1483. ----, charge, a case of, 1171, 1177, 1300. ----, exclusive action, 1681. ----, towards space, 1614. ----, across a vacuum, 1614. ---- _through_ air, 1217, 1284. ---- ---- different gases, 1381, 1395. ---- ---- crystals, 1689, ---- ---- lac, 1228, 1255, 1308. ---- ---- metals, 1329, 1332. ---- ---- all bodies, 1331, 1334. ----, _its relation to_ other electrical actions, 1165, 1178. ----, ---- insulation, 1324, 13602, 1368, 1678. ----, ---- conduction, 1320. ----, ---- discharge, 1319, 1323, 1362. ----, ---- electrolyzation, 1164, 1343. ----, ---- intensity, 1178, 1362. ----, ---- excitation, 1178, 1740. ----, its relation to charge, 1177, 1299. ---- an essential general electric function, 1178, 1299. ----, general results as to, 1295. ----, theory of, 1165, 1231, 1295, 1667, 1669. ---- _in curved lines_, 1166, 1215, 1679. ---- ----, _through_ air, 1218, 1449. ---- ----, ---- other gases, 1226. ---- ----, ---- lac, 1228. ---- ----, ---- sulphur, 1228. ---- ----, ---- oil of turpentine, 1227. _induction, specific_, 1167, 1252, 1307. ----, _the problem_ stated, 1252. ----, ---- solved, 1307. ----, _of air_, 1284. ----, ----, invariable, 1287, 1288. ----, _of gases_, 1283, 1290. ----, ---- alike in all, 1292. ----, of shell-lac, 1256, 1269. ----, glass, 1271. ----, sulphur, 1275. ----, spermaceti, 1279. ----, certain fluid insulators, 1280. _Induction of electric currents_, 6, 34, 232, 241, 1048, 1089, 1101, 1660, 1718. ----, on aiming the principal current, 10, 238, 1101. ----, on stopping the principal current, 10, 17, 238, 1087, 1100. ---- by approximation, 18, 236. ---- by increasing distance, 19, 237. ---- _effective through_ conductors, 1719, 1721, 1735. ---- ---- insulators, 1719, 1722, 1735. ---- in different metals, 193, 202, 211, 213. ---- in the moving earth, 181. ---- in flowing water, 190. ---- in revolving plates, 85, 240. ----, _the induced current, its_ direction, 26, 232. ----, ---- duration, 19, 47, 89. ----, ----, traverses fluids, 20, 23. ----, ----, its intensity in different conductors, 183, 193, 201, 211, 213. ----, ----, not obtained by Leyden discharge, 24. ----, Ampère's results, 78, 255, 379, _note_. _Induction of a current on itself_, 1048, 1109. ----, apparatus used, 1052. ----, _in a_ long wire, 1064, 1068, 1092, 1118. ----, ---- doubled wire, 1096. ----, ---- helix, 1053, 1061. ---- in doubled helices, 1096. ---- in an electro-magnet, 1056, 1060. ----, wire and helix compared, 1065. ----, short wire, effects with, 1067. ----, action momentary, 1070, 1091, 1100. ----, causes no permanent change in the current, 1071. ----, not due to momentum, 1077. ----, induced current separated, 1078, 1089. ----, _effect at_ breaking contact, 1060, 1081, 1084, 1087. ----, ---- making contact, 1101, 1106. ----, _effects produced_, shock, 1060, 1064, 1079. ----, ---- spark, 1060, 1064, 1080. ----, ---- chemical decomposition, 1084. ----, ---- ignition of wire, 1081, 1104. ----, cause is in the conductor, 1059, 1070. ----, general principles of the action, 1093, 1107. ----, direction of the forces lateral, 1108. _induction, magnetic_, 255, 1658, 1710. ----, by intermediate particles, 1663, 1710, 1729, 1735. ----, _through_ quiescent bodies, 1712, 1719, 1720, 1735. ----, ---- moving bodies, 1715, 1716, 1719. ---- and magneto-electric, distinguished, 138, 215, 243, 253. _Induction_, magneto-electric, 27, 58, 81, 140, 193, 1709. _See_ Arago's magnetic phenomena. ----, magnelectric, 58. ----, electrolytic, 1164, 1345, 1702, 1740. ----, volta-electric, 26. Inductive capacity, specific, 1167, 1252. _Inductive force of currents_ lateral, 26, 1108. ----, its nature, 1113, 1660, 1663, 1709. _Inductive force, lines of_, 1231, 1297, 1304. ----, often curved, 1219, 1224, 1230. ----, exhibited by the brush, 1449. ----, their lateral relation, 1231, 1297, 1304. ----, their relation to magnetism, 1411, 1658, 1709. Inductometer, differential, 1307, 1317. Inductric surfaces, 1483. Inexhaustible nature of the electric current, 1631. Inseparability of the two electric forces, 1163, 1177, 1244, 1628. Insulating power of different gases, 1388, 1395, 1507. _Insulation_, 1320, 1359, 1361. ----, its nature, 1321. ---- is sustained induction, 1324. ----, degree of induction sustained, 1362. ---- _dependent on the_ dielectrics, 1368. ---- ---- distance in air, 1303, 1364, 1371. ---- ---- density of air, 1365, 1375. ---- ---- induction, 1368. ---- ---- form of conductors, 1302, 1374. ----, as affected by temperature of air, 1367, 1380. ---- _in different gases_, 1381, 1388. ---- ---- differs, 1395. ---- in liquids and solids, 1403. ---- in metals, 1328, 1331, 1332. ---- and conduction not essentially different, 1320, 1326, 1336, 1338, 1561. ----, its relation to induction, 1324, 1362, 1368, 1678. _Insulators_, liquid, good, 1172. ----, solid, good, 1254. ----, the best conduct, 1233, 1241, 1245, 1247, 1254. ---- tested as to conduction, 1255. ---- and conductors, relation of, 1328, 1334, 1338. _Intensity_, its influence in conduction, 419. ----, inductive, how represented, 1370. ----, relative, of magneto-electric currents, 183, 193, 211, 213. ---- of disruptive discharge constant, 1410. ----, electrolytic, 912, 966, 983, 1354. ---- necessary for electrolyzation, 911, 966. ---- _of the current of single circles_, 904. ---- ---- increased, 906. ---- of electricity in the voltaic battery, 990, 993. ---- of voltaic current increased, 906, 990. _Interference with combining power of platina_, 638, 655. ---- by olefiant gas, 640. ---- carbonic oxide, 645. ---- sulphuret of carbon, 650. ---- ether, 651. Interpositions, their retarding effects, 1018. _Iodides in_ solution, their electrolysis, 769. ---- fusion, their electrolysis, 802, 813. _Iodide_ of lead, electrolysed, 802, 818. ---- of potassium, test of chemical action, 316. _Ions_, what, 665, 824, 833, 834, 849. ---- not transferable alone, 542, 547, 826. ----, table of, 847. _Iron_, both magnetic and magneto-electric at once, 138, 254. ----, copper and sulphur circles, 943. 

Jenkin, his shock by one pair of plates, 1049. 

Kemp, his amalgam of zinc, 999. Knight, Dr. Gowin, his magnet, 44. 

_Lac_, charge removed from, 1203. ----, induction through, 1255. ----, specific inductive capacity of, 1256, 1269. ----, effects of its conducting power, 1234. ----, its relation to conduction and insulation, 1324. _Lateral_ direction of inductive forces of currents, 26, 1108. ---- forces of the current, 1653, 1709. _Law of_ conduction, new, 380, 394, 410. ---- magneto-electric induction, 114. ---- volta-electric induction, 26. _Lead_, chloride of, electrolysed, 794, 815. ----, fluoride of, conducts well when heated, 1340. ----, iodide of, electrolysed, 802, 818. ----, oxide of, electrolysed, 797. _Leyden jar_, condition of its charge, 1682. ----, its charge, nature of, 1300. ----, its discharge, 1300. ----, its residual charge, 1249. _Light_, polarized, passed across electrolytes, 951. ----, _electric_, 1405, 1445, 1560, _note_. ----, ----, spark, 1406, 1553. ----, ----, brush, 1425, 1444, 1445. ----, ----, glow, 1526. Lightning, 1420, 1404, 1641. _Lines of inductive force_, 1231, 1304, ---- often curved, 1219, 1224, 1230. ----, as shown by the brush, 1449. ----, their lateral relation, 1231, 1297, 1304. ----, their relation to magnetism, 1411, 1658, 1709. Liquefaction, conduction consequent upon, 380, 394, 410. Liquid bodies which are non-conductors, 405. Local chemical affinity, 947, 959, 961, 1739. 

_Machine_, electric, evolution of electricity by, 1748. ------, magneto-electric, 135, 154, 158, 1118. _Magnelectric_ induction, 58. ----, collectors or conductors, 86. _Magnesia_, sulphate, decomposed against water, 494, 533. ----, transference of, 495. _Magnet_, a measure of conducting power, 216. ---- _and_ current, their relation remembered, 38, _note_. ---- ---- plate revolved together, 218. ---- ---- cylinder revolved together, 219. ---- revolved alone, 220, 223. ---- and moving conductors, their general relation, 256. ---- made by induced current, 13, 14. ----, electricity from, 36, 220, 223. _Magnetic_ bodies, but few, 255. ----, curves, their inductive relation, 217, 232. ---- _effects of_ voltaic electricity, 277. ---- ---- common electricity, 288, 367. ---- ---- magneto-electricity, 27, 83, 345. ---- ---- thermo-electricity, 349. ---- ---- animal electricity, 354. ---- and electric forces, their relation, 118, 1411, 1653, 1658, 1709, 1731. ---- forces active through intermediate particles, 1663, 1710, 1729, 1735. ---- _forces of the current_, 1653. ---- ---- very constant, 1654. ---- deflection by common electricity, 289, 296. ---- phenomena of Arago explained, 81. ---- induction. _See_ Induction, magnetic. ---- _induction through_ quiescent bodies, 1712, 1719, 1720, 1735. ---- ---- moving bodies, 1715, 1719. ---- and magneto-electric action distinguished, 138, 215, 243, 253. _Magnetism_, electricity evolved by, 27. ----, its relation to the lines of inductive force, 1411, 1658, 1709. ---- bodies classed in relation to, 255. _Magneto-electric currents_, their intensity, 183, 193, 211, 213. ----, their direction, 114, 110. ---- traverse fluids, 33. ---- momentary, 30. ---- permanent, 89. ---- in all conductors, 193, 213. _Magneto-electric induction_, 27, 58. ----, terrestrial, 110, 181. ----, law of, 114. ----. _See_ Arago's magnetic phenomena. _Magneto-electric machines_, 135, 154, 158. ----, inductive effects in their wires, 1118, _Magneto-electricity_, its general characters considered, 343, &c. ---- identical with other electricities, 360. ----, its tension, 343. ----, evolution of heat, 344. ----, magnetic force, 345. ----, chemical force, 346. ----, spark, 348. ----, physiological effects, 347. ----. _See_ Induction, magnetic. _Matter_, atoms of, 869, 1703. ----, new condition of, 60, 231, 242, 1114, 1661, 1729. ----, quantity of electricity in, 852, 861, 873, 1652. ----, absolute charge of, 1169. _Measures of electricity_, galvanometer, 367, _note_. ----, voltameter, 704, 736, 739. ----, metal precipitated, 740, 842. Measure of specific inductive capacity, 1307, 1600. _Measurement of_ common and voltaic electricities, 361, 860, 1652. ---- _electricity_, degree, 736, 738. ---- ---- by voltameter, 704, 736, 739. ---- ---- by galvanometer, 367, _note_. ---- ---- by metal precipitated, 740, 842. Mechanical forces affect chemical affinity, 656. Mercurial terminations for convection, 1581. _Mercury_, periodide of, an exception to the law of conduction? 691, 1341. ----, perchloride of, 692, 1341. _Metallic contact_ not necessary for electrolyzation, 879. ---- not essential to the voltaic current, 879, 887, 915. ---- its use in the pile, 893, 896. Metallic poles, 557. Metal and electrolyte, their state, 946. _Metals_, adhesion of fluids to, 1038. ----, _their power of inducing combination_ 564, 608. ----, ---- interfered with, 638. ----, static induction in, 1329, 1332. ----, different, currents induced in, 193, 211. ----, generally secondary results of electrolysis, 746. ---- transfer chemical force, 918. ----, transference of, 539, 545. ---- insulate in a certain degree, 1328. ----, convective currents in, 1603. ----, but few magnetic, 255. Model of relation of magnetism and electricity, 116. Molecular inductive action, 1164, 1669. _Motion_ essential to magneto-electric induction, 39, 217, 256. ---- across magnetic curves, 217. ---- _of conductor and magnet, relative_, 114. ---- ---- not necessary, 218. Moving magnet is electric, 220. _Muriatic acid gas_, its high insulating power, 1395. ----, brush in, 1462. ----, dark discharge in, 1554. ----, glow in, 1534. ----, positive and negative brush in, 1476. ----, _spark in_, 1422, 1463. ----, ----, has no dark interval, 1463, 1555. _Muriatic acid_ decomposed by common electricity, 314. ----, its electrolysis (primary), 758, 786. 

Nascent state, its relation to combination, 658, 717. _Natural_ standard of direction for current, 663. ---- relation of electrolytic intensity, 987. _Nature of the electric_ current, 1617. ---- force or forces, 1667. _Negative_ current, none, 1627, 1632. ---- _discharge_, 1465, 1484. ---- ----, as Spark, 1467, 1482. ---- ----, as brush, 1466, 1502. ---- spark or brush, 1484, 1502. _Negative and positive discharge_, 1465, 1482, 1525---- in different gases, 1393. _New_ electrical condition of matter, 60, 231, 242, 1114, 1661, 1729. ---- law of conduction, 380, 394, 410. _Nitric acid_ formed by spark in air, 324. ---- _favours_ excitation of current, 906, 1138---- ---- transmission of current, 1020. ---- is best for excitation of battery, 1137. ----, nature of its electrolysis, 752. _Nitrogen_ determined to either pole, 554, 748, 752. ---- a secondary result of electrolysis, 746, 748. ----, brush in, 1458. ----, dark discharge in, 1559. ----, glow in, 1534. ----, spark in, 1422, 1463. ----, _positive and negative_ brush in, 1476. ----, ---- discharge in, 1512. ----, its influence on lightning, 1464. Nomenclature, 662, 1483. Nonconduction by solid electrolytes, 381, 1358, 1705. Note on electrical excitation, 1737. Nuclei, their action, 623, 657. 

Olefiant gas, interference of, 610, 652. _Ordinary electricity_, its tension, 285. ---- evolution of heat, 287. ---- magnetic force, 288, 362. ---- _chemical force_, 309, 454. ---- ----, precautions, 322. ---- spark, 333. ---- physiological effect, 332. ---- general characters considered, 284. ----, identity with other electricities, 360. Origin of the force of the voltaic pile, 878, 910, 919. Oxidation the origin of the electric current in the voltaic pile, 919, 930. Oxide of lead electrolysed, 797. _Oxygen_, brush in, 1457. ----, _positive and negative_ brush in, 1476, ----, ---- discharge in, 1513. ----, solubility of, in cases of electrolyzation, 717, 728. ----, spark in, 1422. ---- _and hydrogen combined by_ platina plates, 570, 605, 630. ---- ---- spongy platina, 609, 636. ---- ---- other metals, 608. 

_Particles_, their nascent state, 658. ---- in air, how charged, 1564. ----, neighbouring, their relation to each other, 619, 624, 657. ----, contiguous, active in induction, 1165, 1677. ---- of a dielectric, their inductive condition, 1369, 1410, 1669. ----, polarity of, when under induction, 1298, 1676. ----, _how polarised_, 1669, 1679. ----, ----, in any direction, 1689. ----, ----, as wholes or elements, 1699. ----, ----, in electrolytes, 1702. ----, crystalline, 1689. ----, contiguous, active in electrolysis, 1349, 1702. ----, _their_ action in electrolyzation, 520, 1343, 1703. ----, ---- local chemical action, 961, 1739. ----, ---- relation to electric action, 73. ----, ---- electric action, 1669, 1679, 1740. Path of the electric spark, 1107. Phosphoric acid not an electrolyte, 682. _Physiological effects of_ voltaic-electricity, 279. ---- common electricity, 332. ---- magneto-electricity, 56, 347. ---- thermo-electricity, 349. ---- animal electricity, 357. _Pile, voltaic_, electricity of, 875. ----. _See_ Battery, voltaic. _Plates of platina_ effect combination, 568, 571, 590, 630. ---- _prepared by_ electricity, 570, 585, 588. ---- ---- friction, 591. ---- ---- heat, 595. ---- ---- chemical cleansing, 599, 605, ----, clean, their general properties, 633, 717. ----, _their power preserved_, 576. ----, ---- in water, 580. ----, _their power diminished by_ action, 581. ----, ---- exposure to air, 636. ----, _their power affected by_ washing in water, 582. ----, ---- heat, 584, 597. ----, ---- presence of certain gases, 638, 655. ----, their power, cause of, 590, 616, 630. ----, _theory of their action_, Döbereiner's, 610. ----, ----, Dulong and Thenard's, 611. ----, ----, Fusinieri's, 613. ----, ----, author's, 619, 626, 630, 656. _Plates of voltaic battery_ foul, 1145. ----, new and old, 1116. ----, vicinity of, 1148. ----, immersion of, 1003, 1150. ----, number of, 989, 1151. ----, large or small, 1154. _Platina_, clean, its characters, 633, 717. ---- attracts matter from the air, 634. ----, spongy, its state, 637. ----, _clean, its power of effecting combination_, 564, 590, 605, 617, 630. ----, ---- interfered with, 638. ----, _its action retarded by_ olefiant gas, 640, 652. ----, ----, carbonic oxide, 645, 652. ----. _See_ Combination, Plates of platina, and Interference. ---- poles, recombination effected by, 567, 588. Plumbago poles for chlorides, 794. Poisson's theory of electric induction, 1305. _Points_, favour convective discharge, 1573. ----, fluid for convection, 1581. _Polar_ forces, their character, 1665. ---- decomposition by common electricity, 312, 321, 469. _Polarity_, meaning intended, 1304, 1685. ---- of particles under induction, 1298, 1676. ----, _electric_, 1070, 1085. ----, ----, its direction, 1688, 1703, ----, ----, its variation, 1687. ----, ----, its degree, 1686. ----, ----, in crystals, 1689. ----, ----, in molecules or atoms, 1699. ----, ----, in electrolytes, 1702. Polarized light across electrolytes, 951. _Poles, electric_, their nature, 461, 498, 556, 662. ----, appearance of evolved bodies at, accounted for, 535. ---- one element to either? 552, 681, 757. ----, of air, 455, 461, 559. ----, of water, 491, 558. ----, of metal, 557. ----, of platina, recombination effected by, 567, 588. ----, of plumbago, 794. Poles, magnetic, distinguished, 44, _note_. Porrett's peculiar effects, 1646. _Positive_ current none, 1627, 1632. ---- _discharge_, 1465, 1480. ---- ----, as spark, 1467, 1482. ---- ----, as brush, 1467, 1476. ---- spark or brush, 1484, 1502. ---- _and negative_, convective discharge, 1600. ---- ---- _disruptive discharge_, 1465, 1482, 1485, 1525. ---- ---- ---- in different gases, 1393. ---- ---- voltaic discharge, 1524. ---- ---- electrolytic discharge, 1525. Potassa acetate, nature of its electrolysis, 749. Potassium, iodide of, electrolysed, 805. Power of voltaic batteries estimated, 1126. Powers, their state of tension in the pile, 949. Practical results with the voltaic battery, 1136. Pressure of air retains electricity, explained, 1377, 1398. Primary electrolytical results, 742. Principles, general, of definite electrolytic action, 822. Proportionals in electrolytes, single, 679, 697. 

_Quantity of electricity in_ matter, 852, 861, 873, 1652. ---- voltaic battery, 990. 

Rarefaction of air facilitates discharge, why, 1375. Recombination, spontaneous, of gases from water, 566. _Relation_, by measure, of electricities, 361. ---- of magnets and moving conductors, 256. ---- of magnetic induction to intervening bodies, 1662, 1728. ---- of a current and magnet, to remember, 38, _note_. ---- of electric and magnetic forces, 118, 1411, 1653, 1658, 1709, 1731. ---- of conductors and insulators, 1321, 1326, 1334, 1338. ---- of conduction and induction, 1320, 1337. ---- _of induction and_ disruptive discharge, 1362. ---- ---- electrolyzation, 1164, 1343. ---- ---- excitation, 1178, 1740. ---- ---- charge, 1171, 1177, 1300. ---- of insulation and induction, 1324, 1362, 1368, 1678. ----, lateral, of lines of inductive force, 1231, 1297, 1304. ---- of a vacuum to electricity, 1613. ---- of spark, brush, and glow, 1533, 1539, 1542. ---- of gases to positive and negative discharge, 1510. ---- of neighbouring particles to each other, 619, 624. ---- _of elements in_ decomposing electrolytes, 923, 1702. ---- ---- exciting electrolytes, 921. ---- of acids and bases voltaically, 927, 933. Remarks on the active battery, 1034, 1136. Residual charge of a Leyden jar, 1249. _Resistance_ to electrolysis, 891, 904, 911, 1007. ---- of an electrolyte to decomposition, 1007. _Results_ of electrolysis, primary or secondary, 742, 777. ----, practical, with the voltaic battery, 1136. ----, general, as to induction, 1295, 1669. Retention of electricity by pressure of the atmosphere explained, 1377, 1398. _Revolving_ plate. _See_ Arago's phenomena. ---- _globe, Barlow's_, effect explained, 137, 160, 169. ---- ----, magnetic, 164. ---- ----, direction of currents in, 161, 166. Riffault's and Chompré's theory of electro-chemical decomposition, 485, 507, 512. Rock crystal, induction across, 1692. Room, insulated and electrified, 1173. Rotation of the earth a cause of magneto-electric induction, 181. 

Salts considered as electrolytes, 698. Scale of electrolytic intensities, 912. _Secondary electrolytical results_, 702, 742, 748, 777. ---- become measures of the electric current, 843. _Sections of the current_, 498, 1634. ----, decomposing force alike in all, 501, 1621. _Sections of lines of inductive action_, 1369. ----, amount of force constant, 1369. Shock, strong, with one voltaic pair, 1049. _Silver, chloride of_, its electrolyzation, 541, 813, 902. ----, electrolytic intensity for, 979. Silver, sulphuret of, hot, conducts well, 433. _Simple voltaic circles_, 875. ----, decomposition effected by, 897, 904, 931. Single and many pairs of plates, relation of, 990. _Single voltaic circuits_, 875. ---- without metallic contact, 879. ---- with metallic contact, 893. ---- their force exalted, 906. ---- _give_ strong shocks, 1049. ---- ---- a bright spark, 1050. _Solid electrolytes are non-conductors_, 394, 402, 1358. ----, why, 910, 1705. _Solids, their power of inducing combination_, 564, 618. ---- interfered with, 638. Solubility of gases in cases of electrolyzation, 717, 728. _Source of electricity in the voltaic pile_, 875. ---- is chemical action, 879, 916, 919, 1741. Spark, 1360, 1406. _Spark, electric, its_ conditions, 1360, 1406, 1553. ---- path, 1407. ---- light, 1553. ---- insensible duration or time, 1438. ---- accompanying dark parts, 1547, 1632. ---- determination, 1370. 1409. _Spark is affected by the_ dielectrics, 1395, 1421. ---- size of conductor, 1372. ---- form of conductor, 1302, 1374. ---- rarefaction of air, 1375. _Spark_, atmospheric or lightning, 1464, 1641. ----, negative, 1393, 1467, 1482, 1484, 1502. ----, positive, 1393, 1448, 1467, 1482, 1484, 1502. ----, ragged, 1420, 1448. ----, when not straight, why, 1568. ----, variation in its length, 1381. ----, tendency to its repetition, 1392. ----, facilitates discharge, 1417, 1553. ----, passes into brush, 1448. ----, preceded by induction, 1362. ----, forms nitric acid in air, 324. ----, in gases, 1383, 1421. ----, in air, 1422. ----, in nitrogen, 1422, 1463. ----, in oxygen, 1422. ----, in hydrogen, 1422. ----, in carbonic acid, 1422, 1463. ----, in muriatic acid gas, 1422, 1463. ----, in coal-gas, 1422. ----, in liquids, 1424. ----, precautions, 958, 1074. ----, voltaic, without metallic contact, 915, 956. ---- from single voltaic pair, 1050. ---- from common and voltaic electricity assimilated, 334. ----, first magneto-electric, 32. ---- of voltaic electricity, 280. ---- of common electricity, 333. ---- of magneto-electricity, 348. ---- of thermo-electricity, 349. ---- of animal electricity, 358. ----, brush and glow related, 1533, 1539, 1542. Sparks, their expected coalition, 1412. Specific induction. _See_ Induction, specific, 1252. _Specific inductive capacity_, 1252. ----, apparatus for, 1187. ---- of lac, 1256, 1270, 1308. ---- of sulphur, 1275, 1310. ---- of air, 1284. ---- of gases, 1283, 1290. ---- of glass, 1271. _Spermaceti_, its conducting power, 1240, 1323. ----, its relation to conduction and insulation, 1322. Standard of direction in the current, 663. State, electrotonic, 60, 231, 242, 1114, 1661, 1729. Static induction. _See_ Induction, static. _Sturgeon_, his form of Arago's experiment, 249. ----, use of amalgamated zinc by, 863, 999. _Sulphate of soda_, decomposed by common electricity, 317. ----, electrolytic intensity for, 975. _Sulphur_ determined to either pole, 552, 681, 757. ----, its conducting power, 1241, 1245. ----, its specific inductive capacity, 1275. ----, copper and iron, circle, 943. _Sulphuret of_ carbon, interference of, 650. ---- silver, hot, conducts well, 433. Sulphuretted solution excites the pile, 943. _Sulphuric acid_, conduction by, 409, 681. ----, magneto-electric induction on, 200, 213. ---- in voltaic pile, its use, 925. ---- not an electrolyte, 681. ----, its transference, 525. ----, its decomposition, 681, 757. Sulphurous acid, its decomposition, 755. _Summary of_ conditions of conduction, 443. ---- molecular inductive theory, 1669. 

_Table of_ discharge in gases, 1388. ---- electric effects, 360. ---- electro-chemical equivalents, 847. ---- electrolytes affected by fusion, 402. ---- insulation in gases, 1388. ---- ions, anions, and cathions, 847. Tartaric acid, nature of its electrolysis, 775. _Tension_, inductive, how represented, 1370. ---- of voltaic electricity, 268. ---- of common electricity, 285. ---- of thermo-electricity, 349. ---- of magneto-electricity, 343. ---- of animal electricity, 352. ---- of zinc and electrolyte in the voltaic pile, 949. Terrestrial electric currents, 187. _Terrestrial magneto-electric induction_, 140. ---- cause of aurora borealis, 192. ----, _electric currents produced by_, 141, 150. ----, ----, _in helices_ alone, 148. ----, ----, ---- with iron, 141, 146. ----, ----, ---- with a magnet, 147. ----, ---- a single wire, 170. ----, ---- a revolving plate, 149. ----, ---- a revolving ball, 160. ----, ---- the earth, 173. Test between magnetic and magneto-electric action, 215, 243. _Theory of_ combination of gases by clean platina, 619, 626, 630, 656. ---- electro-chemical decomposition, 477, 661, 1623, 1704. ---- the voltaic apparatus, 875, 1741. ---- static induction, 1165, 1231, 1295, 1666, 1667. ---- disruptive discharge, 1368, 1406, 1434. ---- Arago's phenomena, 120. _Thermo-electricity_, its general characters, 349. ---- identical with other electricities, 360. ----, its evolution of heat, 349. ----, magnetic, force, 349. ----, physiological effects, 349. ----, spark, 349. Time, 59, 68, 124, 1248, 1328, 1346, 1418, 1431, 1436, 1439, 1612, 1641, 1730. _Tin_, iodide of, electrolysed, 804. ----, protochloride, electrolysis of, definite, 789, 819. _Torpedo_, nature of its electric discharge, 359. ----, its enormous amount of electric force, 359. Transfer of elements and the current, their relation, 923, 962. _Transference_ is simultaneous in opposite directions, 542, 828. ----, uncombined bodies do not travel, 544, 546, 826. ---- _of elements_, 454, 507, 539, 550, 826. ---- ---- across great intervals, 455, 468. ---- ----, its nature, 519, 525, 538, 549. ---- of chemical force, 918. Transverse forces of the current, 1653, 1709. Travelling of charged particles, 1563. Trough, voltaic. _See_ Battery, voltaic. _Turpentine, oil of_, a good fluid insulator, 1172. ----, its insulating power destroyed, 1571. ---- charged, 1172. ----, brush in, 1452, ----, electric motions in, 1588, 1595, ----, convective currents in, 1595, 1598. 

Unipolarity, 1635. 

Vacuum, its relation to electricity, 1613. Vaporization, 657. _Velocity of_ conduction in metals varied, 1333. ---- the electric discharge, 1641, 1649. ---- conductive and electrolytic discharge, difference of, 1650. Vicinity of plates in voltaic battery, 1148. Volta-electric induction, 26. _Volta-electrometer_, 704, 736. ----, fluid decomposed in it, water, 706, 728, 732. ----, forms of, 707, 734. ---- _tested for variation of_ electrodes, 714, 722. ---- ---- fluid within, 727. ---- ---- intensity, 723. ----, strength of acid used in, 728, 733. ----, _its indications by_ oxygen and hydrogen, 736. ----, ---- hydrogen, 734. ----, ---- oxygen, 735. ----, how used, 737. Voltameter, 704. _Voltaic battery_, its nature, 875, 989. ----, remarks on, 1034, 1136. ----, improved, 1001, 1119. ----, practical results with, 1136. ----. _See_ Battery, voltaic. _Voltaic circles, simple_, 875. ----, decomposition by, 897. Voltaic circles associated, or battery, 989. _Voltaic circuit_, relation of bodies in, 962. ----, defined, 282, 511. ----, origin of, 916, 1741. ----, its direction, 663, 925, ----, intensity increased, 905, 990. ----, produced by oxidation of zinc, 919, 930. ---- not due to combination of oxide and acid, 925, 933. ----, _its relation to the_ combining oxygen, 921, 962. ----, ---- combining sulphur, 943. ----, ---- the transferred elements, 923, 962. ----, relation of bodies in, 962. Voltaic current, 1617. _See_ Current, electric. Voltaic discharge, positive and negative, 1524. Voltaic decomposition, 450, 600. _See_ Decomposition, electro-chemical. _Voltaic electricity_, identical with electricity, otherwise evolved, 268, 360. ----, _discharged by_ points, 272. ----, ---- hot air, 271, 274. ----, its tension, 268, 275. ----, evolution of heat by, 276. ----, its magnetic force, 277. ----, its chemical force, 278. ----, its spark, 280. ----, its physiological effects, 279. ----, its general characters considered, 268. _Voltaic pile_ distinguished, 856, _note_. ----, electricity of, 875. ----, depends on chemical action, 872. ----, relation of acid and bases in the, 927. ----. _See_ Battery, voltaic. _Voltaic spark_ without contact, 915, 956. ----, precautions, 958, 1074. Voltaic trough, 989. _See_ Battery, voltaic. 

_Water_, flowing, electric currents in, 190. ----, retardation of current by, 1159. ----, _its direct conducting power_, 1017, 1159, 1355. ----, ---- constant, 984. ----, electro-chemical decomposition against, 494, 532. ----, poles of, 494, 533, 558. ----, its influence in electro-chemical decomposition, 472. ---- is the great electrolyte, 924. ----, _the exciting electrolyte when_ pure, 944. ----, ---- acidulated, 880, 926, 1137. ----, ---- alkalized, 931, 934, 941. ----, electrolytic intensity for, 968, 981, 1017. ---- electrolyzed in a single circuit, 862. ----, its electrolysis definite, 732, 785, 807. ----, decomposition of by fine wires, 327. ----, quantity of electricity in its elements, 853, 861. ----, determined to either pole, 553. _Wheatstone's_ analysis of the electric brush, 1427. ---- measurement of conductive velocity in metals, 1328. _Wire, ignition of, by the electric current_, 853, _note_, 1631. ---- is uniform throughout, 1630. _Wire_ a regulator of the electric current, 853, _note_. ----, velocity of conduction in, varied, 1333. ----, single, a current induced in, 170. ----, long, inductive effects in, 1064, 1118. _Wollaston on_ decomposition by common electricity, 309. ---- decomposition of water by points, 327. 

_Zinc, amalgamated_, its condition, 863, 1000. ----, used in pile, 999. _Zinc_, how amalgamated, 863. ----, of troughs, its purity, 1144. ----, its relation to the electrolyte, 949. ----, its oxidation is the source of power in the pile, 919. ---- _plates of troughs_, foul, 1145. ---- ----, new and old, 1146. ----, waste of, in voltaic batteries, 997. 

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