[Illustration]

SCIENTIFIC AMERICAN SUPPLEMENT NO. 595

NEW YORK, MAY 28, 1887. 

Scientific American Supplement. Vol. XXIII, No. 595. 

Scientific American established 1845

Scientific American Supplement, $5 a year. 

Scientific American and Supplement, $7 a year. 

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TABLE OF CONTENTS. 

I. BOTANY. --The Relation of Tabasheer to Mineral Substances. --The composition of this curious secretion of the bamboo. --Analyses and properties of the material, according to various observers. --Its appearance under the microscope. 1 illustration. 

II. CHEMISTRY. --Apparatus for Drying Flour. --An apparatus for determining the moisture in flour. 1 illustration. 

III. ELECTRICITY. --Automatic Commutator for Incandescent Lamps. --An apparatus for lighting automatically a new lamp to replace one that has failed. 1 illustration. 

 Definitions and Designations in Electro-Technics. --Mr. Jamieson's proposed code of electric symbols--literal and graphic. 4 illustrations. 

IV. ENGINEERING. --New Dredging Machinery. --The dredger Ajax, recently built in California. --Its dimensions and capacity. 1 illustration. 

 Reservoir Dams. --By DAVID GRAVELL. --The engineering details of dams. --Typical masonry and earthwork dams of the world. 23 illustrations. 

 The Flexible Girder Tramway. --A new type of suspended railway--a modification of the wire tramway system. 21 illustrations. 

V. HYGIENE. --Climate in its Relation to Health. --By G. V. POORE, M. D. --The third lecture of this series. --Consideration of the floating matter of the air and diseases caused thereby. --Causation of hay fever. 

VI. MATHEMATICS. --Radii of Curvature Geometrically Determined. --By Prof. C. W. MACCORD, Sc. D. --No. VII. Path of a point on a connecting rod. 3 illustrations. 

VII. MICROSCOPY. --Improved Microscopical Settling Tube. --By F. VANDERPOEL. --New tubes for use in urinary analysis. 4 illustrations. 

VIII. MISCELLANEOUS. --Apparatus for Manufacturing Bouquets. --An ingenious machine for facilitating the construction of bouquets. 1 illustration. 

 Bozerian's Refrigerant Punkas. --A fan worked by the feet, a substitute for the Indian punka. 2 illustrations. 

 How to Make a Kite without a Tail. --An improved form of kite described and illustrated. 1 illustration. 

 Punkas. --By J. WALLACE, C. E. --The mechanics of punkas; experiments on their rate of swing. 

 The Edible Earth of Java. --An account of this curious substance, its taste and appearance. 

IX. NAVAL ENGINEERING. --Another Remarkable Torpedo Boat. --Over twenty-eight miles an hour. --Full particulars of the trial of one of the new Italian torpedo boats, built by Yarrow & Co. 

 Copeman & Pinhey's Life Rafts. --A new life raft for use on steamers, folding into deck settees. 3 illustrations. 

X. PHYSICS. --Sunlight Colors--By Capt. W. DE W. ABNEY. --A valuable lecture on the cause of the colors of the sun, and their relative intensities. 3 illustrations. 

 The Wave Theory of Sound Considered. --By HENRY A. MOTT, Ph. D. , LL. D. --Arguments against the generally accepted theory of sound. 

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COPEMAN & PINHEY'S LIFE RAFTS. 

The experiments with life saving appliances which Mr. Copeman broughtbefore the delegates of the Colonial Conference, on the 13th April, atthe Westminster Aquarium, had a particular interest, due to the late andlamentable accident which befell the Newhaven-Dieppe passenger steamerVictoria. In many cases of this nature, loss of life must rather beattributed to panic than to a want of life saving appliances; but, as ageneral rule, an abundant supply of such apparatus will tend to givepassengers confidence, and prevent the outbreak of such discreditablescenes on the part of passengers as took place on the Victoria. 

[Illustration: FIG. 1. --COPEMAN & PINHEY'S LIFE RAFTS. ]

Messrs. Copeman & Pinhey have, for some years past, done good work inthis direction, and at the recent meeting of the Institution of NavalArchitects, Mr. Copeman showed several models of the latest types oftheir life saving apparatus, both for use on torpedo boats and passengersteamers. Our illustration (Fig. 1) represents the kind of rafts suppliedto her Majesty's troop ships, while Figs. 2 and 3 show deck seatsconvertible into rafts, which are intended for ordinary passengersteamers. The raft shown in Fig. 1 consists of two pontoons, joined bystrong cross beams, and fitted with mast, sail, and oars. When not inuse, the pontoons form deck seats, covered by a wooden grating, which inour illustration forms the middle part of the raft. Each pontoon has acompartment for storing provisions, and when rigged as a raft, there is arailing to prevent persons being washed overboard. 

[Illustration: FIG. 2. ]

[Illustration: FIG. 3. ]

The seat life buoy, shown in Fig. 2, serves as an ordinary deck seat, being about 8 ft. Long, and it consists of two portions, hinged at theback. When required for use as a life buoy, it is simply thrown forward, the seat being at the same time lifted upward, so that the top rail ofthe back engages with the two clips, shown at either end of the seat, andthe whole structure then forms a rigid raft, as will be seen from Fig. 3. Several other appliances were shown at the Westminster Aquarium on April13, but the two rafts we have selected for illustration will give asufficiently correct idea of the general principles upon which theapparatus is based. --_Industries. _

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ANOTHER REMARKABLE TORPEDO BOAT--OVER TWENTY-EIGHT MILES AN HOUR. 

In a recent impression we gave some particulars of the trial trip of aboat built for the Italian government by Messrs. Yarrow & Co. , whichattained the highest speed known, namely, as nearly as possible, 28 milesan hour. On the 14th April the sister boat made her trial trip in theLower Hope, beating all previous performances, and attaining a mean speedof 25. 101 knots, or over 28 miles an hour. The quickest run made with thetide was at the rate of 27. 272 knots, or 31. 44 miles per hour, past theshore. This is a wonderful performance. 

In the following table we give the precise results:

 +-------+---------+-------+-----+-------+-------+-------+ | | | | | | | Second| |Boiler. |Receiver. |Vacuum. |Revs. | Speed. | Means. | Means. | +-------+---------+-------+-----+-------+-------+-------+ | | | | per | Knots | Knots | Knots | | lb. | lb. | in. | min. |per hr. |per hr. |per hr. | +-------+---------+-------+-----+-------+-------+-------+ 1 | 130 | 32 | 28 |373 | 22. 641| 24. 956| | 2 | 130 | 32 | 28 |372. 7| 27. 272| 25. 028| 24. 992| 3 | 130 | 32 | 28 |372 | 22. 784| 25. 028| 25. 028| 4 | 130 | 32 | 28 |377 | 27. 272| 25. 248| 25. 138| 5 | 130 | 32 | 28 |375 | 23. 225| 25. 248| 25. 248| 6 | 130 | 32 | 28 |377 | 27. 272| | |------+-------+---------+-------+-----+-------+-------+-------+Means | 130 | 32 | 28 |374. 5| | | 25. 101|------+-------+---------+-------+-----+-------+-------+-------+

The boat is 140 ft. Long, and fitted with twin screws driven by compoundengines, one pair to each propeller. These engines are of the usual type, constructed by Messrs. Yarrow. Each has two cylinders with cranks at 90°. The framing, and, indeed, every portion not of phosphor-bronze or gunmetal, is of steel, extraordinary precautions being taken to securelightness. Thus the connecting rods have holes drilled through them fromend to end. The low pressure cylinders are fitted with slide valves. Thehigh pressure valves are of the piston type, all being worked by theordinary link motion and eccentrics. The engine room is not far from themid length of the boat, and one boiler is placed ahead and the otherastern of it. Each boiler is so arranged that it will supply eitherengine or both at pleasure. The boat has therefore two funnels, oneforward and the other aft, and air is supplied to the furnaces by twofans, one fixed on the forward and the other on the aft bulkhead of theengine room. 

The fan engines have cylinders 5½ in. Diameter and 3½ in. Stroke, andmake about 1, 100 revolutions per minute when at full speed, causing aplenum in the stokeholes of about 6 in. Water pressure. Double steamsteering gear is fitted, for the forward and aft rudder respectively, andsafety from foundering is provided to an unusual degree by thesubdivision of the hull into numerous compartments, each of which isfitted with a huge ejector, capable of throwing overboard a great body ofwater. A body of water equal to the whole displacement of the boat can bedischarged in less than seven minutes. There is also a centrifugal pumpprovided, which can draw from any compartment. The circulating pump isnot available, because it has virtually no existence, a very small pumpon the same shaft as the centrifugal being used merely to drain thecondensers. These last are of copper, cylindrical, and fitted with pipesthrough which a tremendous current of water is set up by the passage ofthe boat through the sea. Thus the space and weight due to a circulatingpump is saved and complication avoided. The air and feed pumps arecombined in one casting let into the engine room floor, quite out of theway, and worked by a crank pin in a small disk on the forward end of thepropeller shaft. This is an admirable arrangement, and works toperfection. 

The armament of the boat consists of two torpedo tubes in her bows, and asecond pair set at a small angle to each--Yarrow's patent--carried aft ona turntable for broadside firing. There are also two quick firing 3 lb. Guns on her deck. The conning tower forward is rifle proof, and beneathit and further forward is fixed the steering engine, and a compressingengine, by which air is compressed for starting the torpedoes overboardand for charging their reservoirs. A small dynamo and engine are alsoprovided for working a search light, if necessary. The accommodationprovided for the officers and crew is far in advance of anything hithertofound on board a torpedo boat. 

The weather on the morning of Thursday, April 14, was anything ratherthan that which would be selected for a trial, or indeed any, trip on theThames. At 11 A. M. , the hour at which the boat was to leave Messrs. Yarrow's yard, Isle of Dogs, the wind was blowing in heavy squalls fromthe northeast, accompanied by showers of snow and hail. The Italiangovernment was represented by Count Gandiani and several officers andengineers. In all there were about thirty-three persons on board. Thedisplacement of the vessel was as nearly as might be 97 tons. A start wasmade down the river at 11:15 A. M. , the engines making about 180revolutions per minute, and the boat running at some 11½ or 12 knots. 

During this time the stokehole hatches were open, but the fans were keptrunning at slow speed to maintain a moderate draught. The fuel usedthroughout the trip was briquettes made of the best Welsh anthraciteworked up with a little tar. The briquettes were broken up to convenientsizes before being put in the bunkers. This fuel is not of so highevaporative efficiency as Nixon's navigation coal, but it is moresuitable for torpedo boat work, because it gives out Very little dust, while the coal in closed stokeholes half smothers the firemen. Wateringonly partially mitigates the evil. Besides this, the patent fuel does notclinker the tube ends--a matter of vital importance. 

During the run down to Gravesend, the small quantity of smoke given outwas borne down and away from the tops of the funnels by the fierce headwind, and now and then a heavy spray broke on the bows, wettingeverything forward. In the engine room preparations were made for takingindicator diagrams. No attempt was made to drive the boat fast, becausehigh speeds are prohibited by the river authorities on account of theheavy swell set up. 

The measured mile on the Lower Hope is on the southern bank of the river, about three miles below Gravesend. Just as the boat passed the town, inthe midst of a heavy rain squall, the stokehole hatches in the deck wereshut, and the dull humming roar of the fans showed that the fires werebeing got up. The smoke no longer rose leisurely from the funnels. Itcame up now with a rush and violence which showed the powerful agency atwork below. A rapid vibrating motion beneath the feet was the firstevidence that the engines were away full speed. As the boat gathered wayshe seemed to settle down to her work, and the vibration almost ceased. The measured mile was soon reached, and then in the teeth of thenortheaster she tore through the water. The tide and wind were bothagainst her. Had the tide and wind been opposed, there would have been aheavy sea on. As it was, there was quite enough; the water, breaking onher port bow, came on board in sheets, sparkling in the sun, which, therain squall having passed, shone out for the moment. As the wind wasblowing at least thirty miles an hour, and the boat was going at sometwenty-six miles an hour against it, the result was a moderate hurricaneon board. It was next to impossible to stand up against the fury of theblast without holding on. The mile was traversed in less than 2½ minutes, however; but the boat had to continue her course down the river fornearly another mile to avoid some barges which lay in the way, andprevented her from turning. Then the helm was put over, and she cameround. There was no slacking of the engines, and astern of her the waterleaped from her rudder in a great upheaved, foaming mass, some 7 ft. Or 8ft. High. Brought round, she once more lay her course. This time the windwas on her starboard quarter, or still more nearly aft. The boat wentliterally as fast as the wind, and on deck it was nearly calm. The lightsmoke from the funnels, no longer beaten down by wind, leaped up highinto the air. Looking over the side, it was difficult to imagine that theboat was passing through water at all. The enormous velocity gave thesurface of the river the appearance of a sheet of steel for 1 ft. Or moreoutside the boat. Standing right aft, the sight was yet more remarkable. Although two 6 ft. Screws were revolving at nearly 400 revolutions perminute almost under foot, not a bubble of air came up to break thesurface. There was no wave in her wake; about 70 ft. Behind her rose agentle swelling hill. 

Her wake was a broad smooth brown path, cut right through the roughsurface of the river. On each side of this path rose and broke the angrylittle seas lashed up by the scourging wind. Along the very center of thebrown track ran a thin ridge of sparkling foam, some 2 ft. High and some20 ft. Long, caused by the rudder being dragged through the water. Therewas scarcely any vibration. The noise was not excessive. A rapid whirrdue to the engines, and a rythmical clatter due to the relief valve onone of the port engine cylinders not being screwed down hard enough, andtherefore lifting a little in its seat at each stroke, made the most ofit. The most prominent noise perhaps was the hum of the fans. Standingforward, the deck seems to slope away downward aft, as indeed it does, for it is to be noted that at these high speeds the forefoot of the boatis always thrown up clean out of the water--and the whole aspect of theboat: the funnels vomiting thin brown smoke, and occasionally, when afire door is opened, a lurid pillar of flame for a moment; the whirr inthe engine room; the dull thunder of the fans, produce an impression onthe mind not easily expressed, and due in some measure no doubt to theexhilaration caused by the rapid motion through the air. 

The best way to convey what we mean is to say that the whole craft seemsto be alive, and a perfect demon of energy and strength. Many personshold that a torpedo boat is likely to be more useful in terrifying anenemy than in doing him real harm, and we can safely say that the captainof an ironclad who saw half a dozen of these vessels bearing down on him, and did not wish himself well out of a scrape, has more nerve than mostmen. 

The second mile was run in far less time than that in which what we havewritten concerning it can be read, and then the boat turned again, andonce more the head wind with all its discomforts was encountered. Eventsrepeated themselves, and so at last the sixth trip was completed, and theboat proceeded at a leisurely pace back again to Poplar. Mr. Crohn, representing Messrs. Yarrow on board, and all concerned, might well feelsatisfied. We had traveled at a greater speed than had ever before beenreached by anything that floats, and there was no hitch or impediment ortrouble of any kind. 

The Italian government may be congratulated on possessing the two fastestand most powerful torpedo boats in the world. We believe, however, thatMessrs. Yarrow are quite confident that, with twin screw triple expansionengines, they can attain a speed of 26 knots an hour, and we have noreason to doubt this. --_The Engineer. _

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RESERVOIR DAMS. 

[Footnote: Paper, with slight abbreviation, read by Mr. David Gravell, Assoc. M. Inst. C. E. , before the Society of Civil and MechanicalEngineers. The paper brings together in a convenient form the sectionsand salient facts concerning many dams. It was illustrated by numerousdiagrams, from which our engravings have been prepared. --_The Engineer. _]

By DAVID GRAVELL. 

The construction of dams, in some form or other, may probably rank amongthe very earliest of engineering works. Works of this character are notinfrequently referred to in the accounts of the earliest historians; butit is to be feared that they are not always perfectly trustworthy. Thesubscribers to the Mudie of the period had to be considered, and theirtaste for the marvelous was probably not much inferior to that of our ownday. When, therefore, Herodotus describes the reservoir of Moeris asformed for the control of the river floods of Nile-nourished Egypt, andof another constructed by Nebuchadnezzar at Sippara, of 140 miles incircumference, we must make allowances. But there is no question as tothe existence in the East at the present day, and especially in India andCeylon, of the remains of what may correctly be termed stupendous works;and the date of the construction of which, as regards India, is in manycases prehistoric. In Spain also the Moors, whose occupation of thepeninsula terminated in the thirteenth century, have left reservoir damsof great magnitude, situated mostly in the south-eastern provinces ofMurcia and Alicante, and many of which are still serviceable. 

In India and Ceylon the greater number of the ancient dams or bunds arenow in ruins, and this can occasion but little surprise, considering themeteorological condition of these countries. In Ceylon, for instance, thewhole rainfall of the year occurs within a period of six to eight weeks, and often amounts to as much as 12 in. In the twenty-four hours, and hasbeen known, comparatively recently, to reach nearly 19 in. , the latter anamount only 2 in. Or 3 in. Less than the average rainfall of Lincolnshirefor the whole year. In London it is only 25 in. And in the wettestdistrict in Great Britain, viz. , Cumberland, averages not more than 70in. Per annum. 

The rainfall in Bombay is from 80 in. To 100 in. Per annum, andthroughout India may be taken as from 50 in. To 130 in. , varying, as isthe general rule, in direct ratio with the altitude, and limited to a fewweeks in the year. Notwithstanding this, there still exist in the MadrasPresidency a not inconsiderable number of ancient bunds which serve theirintended purpose at the present day as well as ever. Slight mistakes didoccasionally occur, as they ever will till no more dams are wanted, as isproved by the remains of some works in Ceylon, where the failure wasevidently due to error, possibly due to the instruments being out ofadjustment, as their base is at a higher level than the bed of the streamat the point where water from the latter was to be diverted to afford thesupply. 

Among the most remarkable of these ancient works is the Horra-Bera tank, the bund of which is between three and four miles in length and from 50to 70 ft. In height, and although now in ruins would formerly impound areservoir lake of from eight to ten miles long and three to four milesbroad. There is also the Kala-Weva tank, with a bund of twelve miles inlength, which would, if perfect, create a lake of forty miles incircumference. Both of these ruined works are situated in Ceylon. Thethird embankment of a similar character is that of the Cummum tank, situated in the Madras Presidency, and which, though ranking among theearliest works of Hindoo history, is still in such a condition as tofulfill its original intention. The area of the reservoir is aboutfifteen square miles, the dam about 102 ft. High, with a breadth at thecrest of 76 ft. , and of the section shown in the diagram. 

The by-wash is cut in the solid rock altogether clear of the dam; theoutlet culverts, however, are carried under the bank. We will nowconsider generally the methods employed in determining the site, dimensions, and methods of construction of reservoir dams adapted to thevarying circumstances and requirements of modern times, with a fewreferences to some of the more important works constructed or inprogress, which it will be endeavored to make as concise and burdenedwith as few enumerations of dimensions as possible. 

The amount of the supply of water required, and the purposes to which itis to be applied, whether for household, manufacturing, or irrigationuses, are among the first considerations affecting the choice of the siteof the reservoir, and is governed by the amount of rainfall available, after deducting for evaporation and absorption, and the nature of thesurface soil and vegetation. The next important point is to determine theposition of the dam, having regard to the suitability of the ground foraffording a good foundation and the impoundment of the requisite body ofwater with the least outlay on embankment works. 

It has been suggested that the floods of the valley of the Thames mightbe controlled by a system of storage reservoirs, and notice wasespecially drawn to this in consequence of the heavy floods of the winterof 1875. From evidence given before the Royal Commission on Water Supply, previous to that date it was stated that a rainfall of 1 in. Over theThames basin above Kingston would give, omitting evaporation andabsorption, a volume of 53, 375, 000, 000 gallons. To prevent floods, arainfall of at least 3 in. Would have to be provided against, which wouldmean the construction of reservoirs of a storage capacity of say160, 000, 000, 000 gallons. Mr. Bailey Denton, in his evidence before thatcommission, estimated that reservoirs to store less than one tenth thatquantity would cost £1, 360, 000, and therefore a 3 in. Storage as abovewould require an outlay of, say, £15, 000, 000 sterling; and it will beseen that 3 in. Is by no means too great a rainfall to allow for, as inJuly of 1875, according to Mr. Symons, at Cirencester, 3. 11 in. Fellwithin twenty-four hours. Supposing serious attention were to be given tosuch a scheme, there would, without doubt, be very great difficulty infinding suitable situations, from an engineering and land owner's pointof view, for the requisite dams and reservoir areas. 

In Great Britain and many European countries rain gauges have beenestablished at a greater or less number of stations for many years past, and data thereby afforded for estimating approximately the rainfall ofany given district or catchment basin. The term "watershed" is one whichit appears to me is frequently misapplied; as I understand it, watershedis equivalent to what in America is termed the "divide, " and means theboundary of the catchment area or basin of any given stream, although Ibelieve it is frequently made use of as meaning the catchment areaitself. When saying that the rain gauges already established in most ofthe older civilized countries afford data for an approximate estimateonly, it is meant that an increase in the number of points at whichobservations are made is necessary, previous to the design of a reservoirdam on the catchment area above, the waters of which are proposed to beimpounded, and should be continuous for a series of five or six years, and these must be compared with the observations made with the oldestablished rain gauges of the adjacent district, say for a period oftwenty years previously, and modified accordingly. This is absolutelynecessary before an accurate estimate of the average and maximum andminimum rainfall can be arrived at, as the rainfall of each square mileof gathering ground may vary the amount being affected by the altitudeand the aspect as regards the rainy quarter. 

But this information will be of but little service to the engineerwithout an investigation of the loss due to evaporation and absorption, varying with the season of the year and the more or less degree ofsaturation of the soil; the amount of absorption depending upon thecharacter of the ground, dip of strata, etc. , the hydrographic areabeing, as a rule, by no means equal to the topographic area of a givenbasin. From this cursory view of the preliminary investigations necessarycan be realized what difficulties must attend the design of dams forreservoirs in newly settled or uncivilized countries, where there are nodata of this nature to go on, and where if maps exist they are probablyof the roughest description and uncontoured; so that before any projectcan be even discussed seriously special surveys have to be made, theresults of which may only go to prove the unsuitability of the site underconsideration as regards area, etc. The loss due to evaporation, according to Mr. Hawksley, in this country amounts to a mean of about 15in. ; this and the absorption must vary with the geological conditions, and therefore to arrive at a satisfactory conclusion regarding the amountof rainfall actually available for storage, careful gaugings have to bemade of the stream affected, and these should extend over a lengthenedperiod, and be compounded with the rainfall. A certain loss of water, intimes of excessive floods, must, in designing a dam, be ever expected, and under favorable conditions may be estimated at 10 per cent. Of thetotal amount impounded. 

As regards the choice of position for the dam of a reservoir, supposingthat it is intended to impound the water by throwing an obstructionacross a valley, it may be premised that to impound the largest quantityof water with the minimum outlay, the most favorable conditions arepresent where a more or less broad valley flanked by steep hills suddenlynarrows at its lower end, forming a gorge which can be obstructed by acomparatively short dam. The accompanying condition is that the nature ofthe soil, i. E. , the character, strata, and lie of the rock, clay, etc. , as the case may be, is favorable to assuring a good foundation. In GreatBritain, as a rule, dams for reservoirs have been constructed ofearthwork with a puddle core, deemed by the majority of English engineersas more suitable for this purpose than masonry. 

Earthwork, in some instances combined with masonry, was also a form usualin the ancient works of the East, already referred to; but it wouldappear from the experience of recent years that masonry dams are likelyto become as common as those of earthwork, especially in districtsfavorable to the construction of the former, where the natural ground isof a rocky character, and good stone easily obtained. 

As to the stability of structures of masonry for this purpose, ascompared with earthwork, experience would seem to leave the question anopen one. Either method is liable to failure, and there certainly are asmany cases on record of the destruction of masonry dams as there are ofthose constructed of earthwork, as instanced in Algeria within the pastfew years. As regards masonry dams, the question of success does not seemso much to depend upon their design, as far as the mere determination ofthe suitable profile or cross section is concerned, as that has been veryexhaustively investigated, and fairly agreed upon, from a mathematicalpoint of view, but to be principally due to the correctness of theestimate of the floods to be dealt with, and a sufficient provision ofby-wash allowed for the most extreme cases; and, lastly, perhaps the mostimportant of all, the securing a thoroughly good foundation, and acareful execution of the work throughout. 

These remarks equally apply to earthwork dams, as regards sufficientprovision of by-wash, careful execution of work, and security offoundation, but their area of cross section, supposing them to bewater-tight, on account of the flatness of their slopes and consequentbreadth of base, is, of course, far in excess of that merely required forstability; but in these latter, the method adopted for the water supplydischarge is of the very greatest importance, and will be again referredto. 

Before commencing the excavation for the foundations of a dam, it is mostessential that the character of the soil or rock should be examinedcarefully, by sinking a succession of small shafts, not mere borings, along the site, so that the depth to which the trench will have to becarried, and the amount of ground water likely to be encountered, can bereliably ascertained, as this portion of the work cannot be otherwiseestimated, and as it may bear a very large proportion of the totalexpense of construction, and in certain cases may demonstrate that thesite is altogether unsuitable for the proposed purpose. 

The depth to which puddle trenches have been carried, for the purpose ofpenetrating water-bearing strata, and reaching impenetrable ground, insome cases, has been as much as 160 ft. Below the natural surface of theground, and the expense of timbering, pumping, and excavation in such aninstance can be easily imagined. This may be realized by referring toFig. 4, giving a cross-section of the Yarrow dam, in which the bottom ofthe trench is there only 85 ft. Below the ground surface. In the DaleDyke dam, Fig. 2, the bottom of the trench was about 50 ft. Below theground surface. 

There is one other point which should be mentioned in connection with theform of the base of the puddle trench--that instead of cutting the bottomof the trench at the sides of the valley in steps, it should be merelysloped, so that the puddle, in setting, tends to slide down each inclinedplane toward the bottom of valley, thereby becoming further compressed;whereas, should the natural ground be cut in steps, the puddle in settingtends to bulge at the side of each riser, as it may be termed, and socause fissures. It will be noticed that the slopes of these earthworkdams vary from 7 to 1 to 2 to 1. 

The depths to which some puddle trenches are carried has been objected toby some engineers, and among them Sir Robert Rawlinson, as excessive andunnecessary, and, in the opinion of the latter, the same end might beobtained by going down to a depth say of 30 ft. Only, and putting in athick bed of concrete, and also carrying up the concrete at the back ofthe puddle trench, with a well for collecting water, and a pipe leadingthe same off through the back of the dam to the down stream side. Anarrangement of this kind is shown in the Yarrow dam, Fig. 4. 

The thickness of the puddle wall varies considerably in the differentexamples given in the diagrams before you, a fair average being the Rowbank of the Paisley Water Works, Fig. 6; and although in instances ofdams made early in the century, such as the Glencorse dam--Fig. 5--of theEdinburgh Water Works, the puddle was of very considerable thickness, andit would appear rightly so. This practice does not seem to have beenfollowed in many cases, as, for instance, again referring to the DaleDyke dam, Fig. 2, where the thickness of the top was only 4 ft. , with abatter of 1 in 16 downward, giving a thickness of 16 ft. At the base. Fora dam 95 ft. In height this is very light, compared with that of theVehui dam at Bombay, of which the engineer was Mr. Conybeare--Fig. 7--where the puddle wall is 10 ft. Wide at the top, with a batterdownward of 1 in 8, the Bann reservoir--Fig. 8--of Mr. Bateman's design, where the puddle is 8 ft. Broad at the top, and other instances. The samedimension was adopted for the puddle wall of the Harelaw reservoir, atPaisley, by Mr. Alexander Leslie, an engineer of considerable experiencein dam construction. 

There appears to be a question as to what the composition of puddleshould be, some advocating a considerable admixture of gravel with clay. There is no doubt that clay intended for puddle should be exposed to theweather for as long previous to use as possible, and subject to theaction of the air at any rate, of sunshine if there be any, or of frost. When deposited in the trench, it should be spread in layers of not morethan 6 in. In thickness, cut transversely in both directions, thoroughlywatered, and worked by stamping. 

The position of the puddle wall is, as a rule, in the center of the bankand vertical; but laying a thickness of puddle upon the inner or upstream slope, say 3 ft. Thick, protected by a layer of gravel andpitching, has been advocated as preventing any portion of the dam frombecoming saturated. There are, however, evident objections to thismethod, as the puddle being comparatively unprotected would be moreliable to damage by vermin, such as water rats, etc. ; and in case of theearthwork dam at the back settling, as would certainly be the case, unless its construction extended over a very lengthened period, thepuddle would be almost certain to become fissured and leaky; in addition, the comparative amounts of puddle used in this manner, as compared withthe vertical wall, would be so much increased. With the puddle wall inthe position usually adopted, unequal settlement of the bank on eitherside is less liable to affect the puddle, being vertical. 

It would be interesting to refer to the embankment of the Bann, or LoughIsland Reavy reservoir, Fig. 8, designed by Mr. Bateman, now nearly fiftyyears ago, where a layer of peat was adopted both on the slope, 15 in. Thick, and in front or on the up stream side of the puddle wall, 3 ft. Thick. The object was, that should the puddle become fissured and leaky, the draught so created would carry with it particles of peat, which wouldchoke up the cracks and so reduce the leakage that the alluvial matterwould gradually settle over it and close it up. On the same diagram willbe noticed curved lines, which are intended to delineate the way in whichthe earthwork of the embankment was made up. The layers were 3 ft. Inthickness, laid in the curved layers as indicated. 

It is a moot question whether, in making an earthwork embankment, dependence, as far as stanchness is concerned, should be placed upon thepuddle wall alone or upon the embankments on either side, and especiallyupon the up-stream side in addition. Supposing the former idea prevails, then it can be of little moment as to how or of what material the bank oneither side is made up--whether of earth or stone--placed in thin layersor tipped in banks of 3 ft. Or 4 ft. High; but the opinion of themajority of engineers seems to be in favor of making the banks act notmerely as buttresses to the puddle wall, and throwing the whole onus, asit may be termed, of stanchness upon that, but also sharing theresponsibility and lessening the chances of rupture thereby. But toinsure this, the material must be of the very best description for thepurpose. Stones, if allowed at all--and in the author's opinion theyshould not be--should be small, few, and far between. Let those that aresifted out be thrown into the tail of the down stream slope. They will dono harm there, but the layers of earth must not approach 3 ft. Inthickness nor 1 ft. --the maximum should be six in. , and this applies alsoto the puddle. Let the soil be brought on by say one-horse carts, spreadin six inch layers, and well watered. The traffic of the carts willconsolidate it, and in places where carts cannot traverse it should bepunned. In the Parvy reservoir dam a roller was employed for thispurpose. It comprised a small lorry body holding about a yard and a halfof stone, with two axles, on each of which was keyed a row of five or sixwheels. 

At the Oued Meurad dam, in Algeria, 95 ft. High, constructed about 23years ago, the earthwork layers were deposited normal to the outer slope, and as the bank was carried up the water was admitted and allowed to riseto near the temporary crest, and as soon as the bank had settled, theearthwork continued another grade, and the same process repeated. 

It was the practice until comparatively recently to make the dischargeoutlet by laying pipes in a trench under the dam, generally at the lowestpoint in the valley, or constructing a culvert in the same position andcarrying the pipes through this, and in the earlier works the valves orsluices regulating the outflow were placed at the tail of the down streambank, the pipes under the bank being consequently at all times subject tothe pressure of the full head of the water in the reservoir. An instanceof the first mentioned method is afforded by the Dale Dyke reservoir, Fig. 2, where two lines of pipes of 18 in. Diameter were laid in a trenchexcavated in the rock and resting upon a bed of puddle 12 in. Inthickness, and surrounded by puddle; the pipes were of cast iron, of thespigot and faucet type, probably yarned and leaded at the joints asusual, and the sluice valves were situated at the outer end of the pipes. As the failure of this embankment was, as we all know, productive of suchterrible consequences, it may be of interest to enter a little more fullyinto the details of its construction. It was situated at Bradfield, sixor seven miles from Sheffield, and at several hundred feet higher level. Its construction was commenced in 1858, the puddle trench was probablytaken down to a depth of 40 ft. To 50 ft. , a considerable amount of waterbeing encountered. This trench was 15 ft. To 20 ft. Broad at the top, andof course had to be crossed by the before mentioned line of pipes; andalthough the trench was filled with puddle, and the gullet cut in therock already mentioned for carrying the pipes under the site of the damwas "padded" with a layer of 12 in. Of puddle, we can imagine that theeffect of the weight of the puddle wall and bank upon this line of pipeswould be very different at the point where they crossed the puddle trenchto what it would be where they were laid in the rock gullet and partiallyprotected from pressure by the sides of the latter. At the trenchcrossing there would be a bed of puddle 50 ft. In thickness beneath thepipe, in the gullet a bed of 1 ft. In thickness. So much as regards thelaying of the pipes. 

The embankment had scarcely been completed when, on March 11, 1864, astorm of rain came on and nearly filled it up to the by-wash, when thebank began slowly to subside. The engineer was on the crest at the verytime, and remained until the water was running over his boots; he thenrushed down the other slope and was snatched out of the way as the bankburst, and the whole body of water, about 250, 000, 000 gallons, rushed outthrough the trench, carrying with it in the course of about twentyminutes 92, 000 cubic yards, or say one fourth of the total mass ofearthwork, causing the death of 250 human beings, not to mention cattle, and destruction of factories, dwellings, and bridges, denuding the rockof its surface soil, and, as it were, obliterating all the landmarks inits course. The greatest depth of the bank from ground level to crest was95 ft. , the top width 12 ft. , and the slopes, both on the up stream anddown stream sides, 2½ to 1, and the area of the reservoir 78 acres. 

Mr. --now Sir Robert--Rawlinson, together with Mr. Beadmore, were calledin to make a report, to lay before Parliament, upon this disaster; andhaving made a careful examination of the ruins, and taken evidence, theywere of opinion that the mode of laying the pipes, and in such anunprotected way, was faulty, and that subsidence of the pipes probablyoccurred at the crossing of the puddle trench. A fissure in the puddlewas created, affording a creep for the water, which, once set up, wouldrapidly increase the breach by scour; and this event was favored by themanner in which the bank had been constructed and the unsuitability ofthe material used, which, in the words of one engineer, had more theappearance of a quarry tip than of a bank intended to store water. Thisopinion of the cause of failure was, however, not adopted universally byengineers, the line of pipes when examined being found to be, althoughdisjointed, fairly in line; and there having occurred a land slip in theimmediate neighborhood, it was suggested that the rupture might be causedby a slip also having taken place here, especially as the substratum wasof flagstone rock tilted at a considerable angle. The formation wasmillstone grit. This catastrophe induced an examination to be made ofother storage reservoir dams in the same district, and a report on thesubject was presented to Parliament by Sir Robert Rawlinson. 

[Illustration: TYPICAL MASONRY AND EARTHWORK DAMS OF THE WORLD. ]

The dam of Stubden reservoir, of the Bradford water supply, also on themillstone grit, was constructed about 1859, and caused considerableanxiety for a length of time, as leakage occurred in the culvert carryingthe pipes, under the embankment at a point a short distance on the downstream side of the puddle trench. This was repaired to some extent bylining with cast iron plates; and an entirely independent outlet was madeby driving a curved tunnel into the hill side clear of the ends of thedam and lining it with cast iron plates. In this tunnel was then laid themain of 2 ft. Diameter, and as the original culvert again became leaky, the water had to be lowered, the old masonry pulled out, and the spacefilled in with puddle. 

The Leeming compensation reservoir of the same water supply, with a damof 50 ft. In height, and culvert outlet, had to be treated somewhat inthe same manner, as, although the reservoir had never been filled withwater, in 1875, when it was examined previous to filling, it was foundthat the culvert was cracked in all directions; and it was deemed best tofill it up with Portland cement concrete, and drive a tunnel outletthrough the hill side, as described in the case of the Stubden reservoir. The Leeshaw dam, which was being constructed at that time upon the samelines, viz. , with culvert outlet under the dam, was, at the advice of SirRobert Rawlinson, altered to a side tunnel outlet clear of the dam. 

Some years previous to the failure of the Dale Dyke reservoir thereoccurred, in 1852, a failure of a similar character--though, as far asthe author is aware, unattended by such disastrous results--at theBilberry reservoir at Holmfirth, near Huddersfield, which had never beenfilled previous to the day of its failure, and arose from the dam havingsunk, and being allowed to remain at a level actually below that of theby-wash; so that when the storm occurred, the dam was topped anddestroyed. An after examination proved that the bank was badlyconstructed and the foundation imperfect. 

Besides the above instances, there have been numerous failures withinrecent times of earthwork dams in Spain, the United States, Algeria, andelsewhere, such as that which occurred at Estrecho de Rientes, nearLorca, in Murcia, where a dam 150 ft. High, the construction of which forirrigation purposes was commenced in 1755 and completed in 1789, wasfilled for the first time in February, 1802, and two months later gaveway, destroying part of the town of Lorca and devastating a large tractof the most fertile country, and causing the death of 600 people. Theimmediate cause of failure in this case the author has been unable toascertain. In Algeria the Sig and Tlelat dams were destroyed in 1865; andin the United States of America, at Williamsburg, Hampshire Co. , Massachusetts, in 1874, an earthwork dam gave way, by which 159 liveswere lost and much damage done to property. In another case, viz. , thatof the Worcester dam, in the United States of America--impounding avolume of 663, 330, 000 gallons, and 41 ft. High, 50 ft. Broad at thecrest, and formed with a center wall of masonry, with earthwork on eachside--which gave way in 1875, four years after its completion; here, asin almost all other instances of failure, the leakage commenced at apoint where the pipes traverse the dam. In this case they were carried ina masonry culvert, and the leak started at about 20 ft. On the up streamside of the central wall. The opinion of Mr. McAlpine as to the cause offailure, which agrees with that of the most eminent of our own waterengineers, was to the effect that "earthen dams rarely fail from anyfault in the artificial earthwork, and seldom from any defect in thenatural soil. The latter may leak, but not so as to endanger the dam. Innine tenths of the cases, the dam is breached along the line of the wateroutlet passages. "

The method of forming the discharge outlet by the construction of amasonry culvert in the open has no doubt many advantages over that oftunnel driving through the hill side clear of the dam, permitting as itdoes of an easy inspection and control of the work as it proceeds; but aslight leakage in the instance of a side tunnel probably means nothingmore than the waste of so much water, whereas in the case of the culverttraversing the site of the bank, the same amount or less imperils thestability of the bank, and in ninety-nine cases out of a hundred would, if not attended to, sooner or later be the cause of its destruction. Ithink the majority will therefore agree that the method of dischargeoutlets under the site of embankments should not be tolerated where it ispossible to make an outlet in the flank of the hill, to one side, andaltogether clear of the dam. 

At Fig. 9 is a diagram of the Roundwood dam of the Vartry Water Works, supplying Dublin, which is a fair specimen of the class of earthwork damwith the outlet pipes carried in a culvert under the embankment, andwhich, perhaps, is one of the most favorable specimens of this method ofconstruction, as the inlet valves are on the up stream of the dam, andconsequently when necessary the water can be cut off from the length ofpipes traversing the dam. A short description will be given. This dam is66 ft. High at the deepest point and 28 ft. Wide at the crest, having tocarry a public road. The slope on the inner face is 3 to 1, and on theouter 2½ to 1. The by-wash is 6 ft. Below the crest, which is about theaverage difference. The storage capacity of the reservoir is2, 400, 000, 000 gallons, or sufficient for 200 days' supply to the city. The puddle wall is 6 ft. Wide at the top and 18 ft. At ground level, thebottom of the puddle trench about 40 ft. Below the surface of the ground. The culvert was formed by cutting a gullet 14 ft. Wide with nearlyvertical sides through the rock, and covering it with a semicircular arch4 ft. In thickness. Through this tunnel are laid a 33 in. And 48 in. Main; the former for the water supply, and the latter for scouring or foremptying the reservoir on an emergency. There is a plugging of brickworkin cement under the center of the dam in the line of the puddle wall, andthen stop walls built at the end of the plugging, projecting 25 ft. Beyond the sides of the culvert and 8 ft. Above, the space between thembeing filled up with cement concrete tied into the rock, and on this thepuddle wall rests. This bank, like almost all others pierced by outletpipes or culverts, was not destined to be perfect. In 1867, four yearsafter the completion, spurts of water showed themselves in the culvertin front of the puddle wall, which began to settle, and the water had tobe drawn off to admit of repairs. Diagram No. 10 shows a structure of adifferent character to any of these already described. This character ofwork is adopted on the North Poudre Irrigation Canal, in N. E. Colorado. Timber is there plentiful, and a dam of this character can be rapidlyconstructed, although probably not very durable, owing to liability todecay of timber. That represented is about 25 ft. High. 

The author has now concluded the consideration of earthwork dams, andproposes making a few remarks upon those of masonry or concrete, withreference to some of the most important, as shown on the diagrams. Theirstability, unlike those of earthwork, may be considerably increased wherethe contour and nature of the ground is favorable by being curved inplan, convex toward the water, and with a suitable radius. They areespecially suitable for blocking narrow rocky valleys, and as suchsituations must, from the character of the ground, be liable to suddenand high floods, great care is necessary to make sufficient provision foroverflow. 

When of masonry, the stones should be bonded, not merely as they would bein an ordinary vertical wall, where the direction of the stress isperpendicular, but each course should be knit in with that above andbelow it in a somewhat similar manner to what is termed "random" work. And lastly, if hydraulic mortar be used, a sufficient time should elapseafter construction before being subjected to strain, or in other words, before water is allowed to rise in the reservoir. For this latter reason, and also the liability to damage by sudden floods during the progress ofthe works, dams of Portland cement concrete, on account of their quickconsolidation, possess advantages over those of hydraulic masonry apartfrom the necessity in the latter instance of constant supervision toprevent "scamping" by leaving chinks and spaces vacant, especially wherelarge masses of stone or Cyclopean rubble are used. 

Again, should the dam be drowned by flood during its erection, no harmwould accrue were it composed of Portland cement concrete, whereas shouldit be of hydraulic mortar masonry, the wall would probably be destroyedor, at all events, considerably injured by the mortar being washed out ofthe joints. Portland cement, however, is only suitable for situationswhere the foundation is absolutely firm, as, should there be theslightest settlement, fissures would certainly be produced. 

As regards foundations, the dam of the Puentes reservoir in Spain issomewhat remarkable--see Fig. 12. Its height is 164 ft. , and the profileor cross section is of precisely the same character as that of theAlicante dam, the latter being 135 ft. In height, 65 ft. Wide at thecrest, and 65 ft. At the base, and erected about 300 years ago. At thePuentes dam the flanks of the valley were reliable, but, as must befrequently the case in such situations, the bed of the valley wascomposed to a great depth of gravel, _debris_, and shaky strata. Thedifficulty was overcome by throwing an arch, or arches, across thevalley, the abutments being formed by the solid rock on each side, andbuilding the dam upon this arching and filling in below the latter downto a sufficient depth with walling. 

Bearing in mind the sudden and great floods to which dams constructed insuch situations must be subjected, and, if the valley be very narrow, theprobability that sufficient space at the side for a by-wash will bedifficult to obtain, it would seem reasonable that in the calculation fortheir section allowance should be made for the possible condition of thewhole length of the dam being converted into a weir, over which thewaters may flow without risk of injury to the dam, to a depth of, say, atleast twice that ever probable. 

The topping of dams by floods is not uncommon, and if the extra strainthus induced has not been allowed for, their destruction is nearlycertain, as instanced in more than one case in Algeria, where, althoughthe average rainfall is only 15 in. Yearly, a depth of 6¼ in. , or morethan one-third of the annual total, has been known to fall in twenty-fourhours. 

The Habra dam--see Fig. No. 13--completed in 1871, was destroyed by asudden flood of this kind in December, 1881. This reservoir, with astorage capacity of 6, 600, 000, 000 gallons, was intended for theirrigation of a cultivated bordering on the Mediterranean and the storageof floods. The height of the dam was 116. 7 ft. And was provided with aby-wash of 394 ft. In length, and outlets for irrigation formed by fourcast iron pipes of 31½ in. Diameter through the dam. It was composed ofrubble set in hydraulic mortar, the latter composed of two parts of sandto one of hydraulic lime. 

For getting rid of the large deposits of sand to which all reservoirs inthat country are liable, two scouring outlets were provided of the samedescription as those in the old Moorish dams. The profile was calculatedfrom Delocre's formula, and was correct in this respect, supposing theby-wash to have been sufficient. But as it was otherwise, and the floodswept over the crest to the depth of about 3 ft. , the enormous extrastrain thus induced overthrew the dam and caused the destruction ofseveral villages and the death of 209 persons. It must be mentioned thatwhen the reservoir was filling, the water percolated through the masonry, giving the face wall the appearance of a huge filter, which at the timewas attributed to the porous nature of the sandstone used inconstruction, but which more probably was due to the washing of the greenmortar out of the joints. 

At the Hamiz dam, also in Algeria, the water was admitted in 1884, but itshowed immediately signs of weakness, so that the water had to be run outand an immense retaining wall erected to strengthen the main dam. Algeriaseems to have been singularly unfortunate as regards the success of worksof this description. Water was admitted to the Cheurfas reservoir inJanuary, 1885, and it at once began to make its way through permeableground at one end of the dam. The flushing sluice in the deepest part ofthe dam had become jammed, so that the pressure could not be relieved, and in February 30 ft. Length of the dam was carried away, causing aflood in the river below. At some distance down stream was the Sigreservoir. The flood rushing down, topped this dam by 18 ft. Andoverthrew it also. 

Allusion has been made to provision for scouring out sand and deposit, especially in the dams of Algeria and of Spain. The amount of sand, etc. , brought down by the floods is something enormous, and the question of thebest means of getting rid of it has occupied much attention. In the oldMoorish reservoirs the flushing gallery, piercing the lower part of thedam, was closed by iron doors on the down stream face and blocked withtimber at the upper end. When required to be flushed out, laborers passedthrough the gallery and broke down the timber barrier, the silt forming awall sufficiently thick to resist the pressure of the water for the timebeing, and allow of the retreat of the Forlorn Hope--if the latter hadluck--before giving way. 

One method adopted in Algeria, which has the advantage of permitting thesediment to be utilized together with the irrigation, this sediment beingvery fertilizing, is to pump air down through hose extending to thebottom of the reservoir, the pumps being actuated by steam power orturbine, and the sediment thus stirred up and run off with the waterthrough the irrigation pipes. As an example of one of the early types ofmasonry dams in France, reference may be made to Fig. 13, on which isshown an elevation and cross section of the Lampy dam, forming a largereservoir for feeding the Languedoc canal. 

I will now refer to some of the most notable masonry dams in existence, commencing with France, where perhaps the finest is that known as theFurens, in connection with the St. Etienne Water Works, constructedbetween the years 1859-66, and designed by the engineers Graiff andGrandchamps. It is curved in plan, struck with a radius of 828 ft. From acenter on the down stream side, and founded upon compact granite, thefootings being carried down to a depth of 3 ft. 3 in. Below the surfaceof the rock. It is of rubble masonry, in hydraulic mortar, carried up incourses of 5 ft. In depth. 

The height is 170 ft. On the up stream side and 184 ft. High on the lowerside, with a breadth of 9 ft. 8 in. At the crest and 110 ft. At the base, and the cross section is so designed that the pressure is nearly constantin all parts, and nowhere exceeds 93 lb. To the square inch--13, 392 lb. To the square foot. The contents is equal to 52, 000 cubic yards ofmasonry, and the cost of erection was £36, 080. The capacity of thereservoir is equal to 352, 000, 000 gallons. 

The reservoir discharges into two tunnels (see Fig. 11), driven one abovethe other through a hill into an adjacent valley. The lower tunnelcontains three cast iron pipes, with a masonry stopping of 36 ft. Long. Two of these pipes are 16 in. Diameter, with regulating valves, anddischarge into a well, from whence the water can be directed for the townsupply or into the river. The third pipe, of 8½ in. Diameter, is alwaysopen, and serves to remove any deposit in the reservoir, and to furnish aconstant supply for the use of manufacturers. 

The author drew attention to the difference in the section of the Furensdam, Fig. 11, as compared with that of Alicante, and of Puentes, which issimilar to the latter. These two last illustrate the ancient Moorishtype, and the former that of the present day. The Gileppe dam atVerviers, in Belgium, Fig. 14, although quite recently erected, viz. , between the years 1869 and 1875, differs very much from the Furens type, in so far as it is of very much larger sectional area in proportion toits height, but this is accounted for by the desire of the engineer, M. Bodson, to overcome the opposition to its construction, and meet theobjections and combat the fears of those whose interests--and thoseserious ones, no doubt--would be affected in the event of its rupture, the body of water stored being 2, 701, 687, 000 gallons, or about eighttimes as much as the capacity of the Furens reservoir. 

In addition to this, there was another reason, which was quite sufficientin itself to account for the extra substantiality of the dam. Thisreservoir is for supplying water to the cloth factories of Verviers, onthe Belgian-German frontier. It is curved in plan to a radius of 1, 640ft. , with a length of 771 ft. , and the additional strength of thestructure due to so flat a curve is probably slight. 

It is built of rubble masonry, with ashlar facework, laid in hydraulicmortar. The total amount of masonry is 325, 000 cubic yards. There are twoweirs, at a level of 6 ft. Below the crest, each 82 ft. Wide. The totalheight, including the foundations, which are carried down from 3 ft. To 5ft. Into the rock, is 154 ft. , and the breadth of the crest, whichcarries a road, is 49 ft. 3 in. , and at the base 216 ft. The outlet pipesare carried through tunnels, which are driven on the curve into the hillside a considerable distance clear of each end of the dam. 

Another very important structure is the Villar dam, Fig. 15, inconnection with the water supply of Madrid, and situated on the riverLozoya. The storage capacity of this reservoir is very considerable, viz. , 4, 400, 000, 000, or nearly thirteen times as great as that of Furens. The height of the dam is 162 ft. , with a breadth of 14 ft. 9 in. At thecrest. It is built on the curve to a radius of 440 ft. , and the length ofthe dam measured along the crest is 546 ft. , of which 197 ft. Is by-wash, thus describing nearly one-fifth of a circle, and consequently welldesigned to resist pressure. The dam is built of rubble masonry inhydraulic mortar, and cost £80, 556. 

The Stony Creek lower reservoir dam of the Geelong water supply, Fig. 16, colony of Victoria, is interesting as being constructed of concrete, inthe proportion of 1 to 8½. Its erection occupied eighteen months, andcost about £18, 000. It is curved in plan to a radius of 300 ft. , and thegreatest depth or head of water is 52 ft. 4 in. The width at the crest isonly 2 ft. 8 in. , although surmounted by a heavy coping of bluestone 3ft. 3 in. Broad and 1 ft. 9 in. Deep. There being no facility for makinga by-wash at the side, the center of the dam is dished to form a weir 30ft. Long. There are both outlet and scour pipes, and valves of 2 ft. Diameter, and the capacity of the reservoir is 143, 145, 834 gallons. 

The Paramatta dam, in New South Wales, built of masonry in hydraulicmortar, is another instance of a dam built on the curve, and which hasresisted a flood of water 4 ft. In depth over the crest; and in the caseof a dam of about 40 ft. High across the river Wyre, in connection withthe Lancaster Water Works, made of cement concrete in proportion of 4 to1, there has, according to Mr. Mansergh, frequently been a depth of 5 ft. Of flow over it. This dam is built to a radius of 80 ft. Only, and as itmeasures 100 ft. Along the crest, must include about the fifth of acircle. 

There now remain only two other examples of masonry dams, the first beingthat in connection with the Liverpool water supply, and known as theVyrnwy dam, Fig. 17, this being thrown across a stream of that name inNorth Wales. It is now under construction, and when completed willimpound an area of 1, 115 acres. 

The dam will be 1, 255 ft. Long, and formed of Cyclopean rubble set incement mortar, and the interstices or spaces between the large masses ofstone, which are rough hewn and not squared, are filled with cementconcrete. The proportion of the cement mortar is 2½ to 1. These masses ofstone weigh from two to eight tons each, and it is expected that the wallwill be of a most solid description, as great care is being taken to fillup all spaces. The face next to the water is cemented. The area of thecross section shown on the diagram, which is at one of the deepestpoints, is 8, 972 square feet, and the height from foundation to floodlevel is 129 ft. , the breadth at the base being 117 ft. 9 in. 

The existing dam of the New York water supply, Fig. 18, known as theCroton reservoir, is shown on the diagram. Its capacity is 364, 000, 000gallons and the area 279 acres. The height is 78 ft. And width at crest 8ft. 6 in. , and is built of masonry in hydraulic mortar. The face wallsare of stone laid in courses of 14 in. To 26 in. , and are vertical on theup stream side, and with a batter of 1 in 2½ on the down. The hearting isof concrete for a depth of 45 ft. From the top, and the remaining depthis in Cyclopean rubble. 

At Fig. 19 is shown the section of the Quaker Bridge dam, which whencompleted will be the largest structure of the kind in existence. It issituated on the Croton River, which is a tributary of the Hudson, aboutfour miles below the present Croton dam. The length will be 1, 300 ft. Andthe height 170 ft. Above the river bed, or 277 ft. Above the foundation. The water by-wash is 7 ft. Below the crest, and the dam is 26 ft. Broadat the crest and 216 ft. At the base. The capacity of the reservoir willbe 32, 000, 000, 000 gallons, or nearly a hundred times as great as that ofFurens. The geological formation at the site is sienitic gneiss. The costof the dam is estimated at £500, 000. 

[Illustration: TYPICAL MASONRY AND EARTHWORK DAMS OF THE WORLD. ]

The accompanying table gives the pressures to which various dams aresubjected, and it may be noted with regard to the weight of water, generally assumed as 62. 4 lb. Per cubic foot, that it will, in somedistricts, in time of flood, carry so much matter in suspension as to beincreased to as much as 75 lb. Weight, or an addition of 20 per cent. , which, it may be easily imagined, will affect the conditions of stabilityvery seriously. 

TABLE OF MAXIMUM PRESSURES. 

 Lb. Per sq. In. Gileppe (Verviers). 88Furens (St. Etienne). 93Puentes. 112De Ban. 113St. Chamond. 114Alicante. 154Hamiz (Algeria)--failed. 157Habra (Algeria)--failed. 185

A diagram comparing the section derived from Molesworth's formula andthose of Furens, Gileppe, Vyrnwy, and Quaker Bridge, is given at Fig. 20, the limit of pressure assumed for the masonry being 93 lb. Per squareinch, which is that of the Furens, the Gileppe being 88. 

 * * * * *

NEW DREDGING MACHINERY. 

We illustrate the new dredger Ajax, recently built for Mr. Geo. F. Smith, of Stockton, Cal. 

The dredger has now been working for two weeks at Wakefield, and, we areinformed, is giving entire satisfaction; having been repeatedly timed tobe discharging clay at the rate of 220 cubic yards per hour. 

[Illustration: THE NEW DREDGER AJAX. ]

The Ajax is almost a duplicate of the last dredger designed by Mr. Ferrisfor levee building on Roberts Island, with such modifications andimprovements as have suggested themselves in the two years it has beenworking. 

The hull, oval in plan, is 36 ft. 10 in. By 60 ft. Over all; it has foursolid fore and aft bulkheads, and a well hole 5 × 12 ft. At one end forthe bucket ladder. 

The main engine is 10 × 24, operating, by bevel gearing and a 3½ in. Vertical shaft, a 4 sided upper tumbler with 21 in. Sides. This engineworks also a gypsy shaft for swinging, and the conveyer that carries themud ashore. A steam hoist with 6 × 11 engines raises and lowers thebucket ladder. The buckets, at 4 foot centers, have a struck capacity of5 cubic feet, and are speeded to deliver from 18 to 20 a minute, according to the character of the material being handled. They are ofboiler iron, with a 5 in. Steel nosing. The links are of wrought iron, with cast bushings. The lower tumbler is hexagonal, on a 4 in. Shaft. 

The conveyer, projecting 72 ft. From the center of the boat, consists ofa 5 ply rubber belt 36 in. Wide; running over iron drums at each end andintermediate iron friction rollers at 3 foot centers. Ratchet and pinionon each side of conveyer ladder give means for taking up the slack of thebelt and adjusting the drums to maintain them parallel. 

This conveyer is the important feature of the dredge. It is entirelysatisfactory in its working and delivers its material, as nearly as maybe, in a dry state upon the levee. It was feared the rubber belt would beshortlived, but a 4 ply belt ran continuously for over two years on theRoberts Island dredge before it needed replacing. 

The boiler is of the marine type, 52 in. By 10 ft. 6 in. , with 3 in. Tubes and 14 in. Flues; and burns about 1, 400 lb. Of steam coal in a dayof 12 hours. There are three pumps aboard--a hand force pump for washingboiler, a plunger pump for boiler feed, and an Evans steam pump to throwa jet of water into the delivery hopper when digging in any verytenacious material. All three are connected with the boiler. 

Water tanks below deck serve to trim the boat and furnish a supply forthe boiler. The dredger cuts by swinging on a center spud 16 in. Indiameter, and moves forward from 8 to 10 ft. At each fleet. 

The Roberts Island dredger, of which the Ajax is an improved copy, handles steadily 700 yards per day of 12 hours, in the stiffest and mosttenacious clay in which it has been worked; and ranges from that averageto 1, 500 yards per day in soft, peaty mud. 

The Ajax was built by Farrington, Hyatt & Co. , of the Stockton IronWorks. 

This type of dredger can be built for about $12, 500, and we are informedcan be relied on for a monthly average of 26, 000 yards in any materialmet with in the overflowed lands near Stockton, delivered 50 ft. Ashore, at a height of 10 or 12 ft. Above the ground line. --_Min. And Sci. Press_. 

 * * * * *

THE FLEXIBLE GIRDER TRAMWAY. 

This is an ingenious proposition for utilizing a modification of the wiretramway system for overcoming obstacles (while retaining the ordinarywire tramway or any light railway on other parts of the line), made byMr. Charles Ball, of London. 

The flexible girder tramway is an improved system of constructing amodification of the well known and extensively used rope or wire tramway, and it is claimed that it will revolutionize the transport of theproducts of industrial operations from the place of production to theworks or manufactory, railway station, shipping ports, or place ofconsumption; and that in the result the introduction of the flexiblegirder tramway will in many cases enable profits to be earned inbusinesses which have hitherto been unremunerative. It is declared to beat once simple, cheap, durable, and efficient. The improvement consistsin the employment, in addition to the usual tram wire (a hempen rope, awire rope, or a metallic or other rod), along which the load istransported, of a second or suspension wire or rope to which the tramwire is connected by tension rods or their equivalent at intervalsbetween the rigid supports or piers, the object being to diminish ordistribute the sagging or deflection of the tram wire, and thus lessenthe steepness of the gradients over which the load has to be transported. The combined tram wire, tension rods, suspension wire, and accessoriesare, for convenience, designated a "flexible girder. "

Another improvement consists in using, when a double line is employed, stretchers or crossheads to keep the flexible girders nearly parallel toeach other, so that when necessary the load to be transported may besuspended from or borne by both tram wires jointly or simultaneously, thus permitting a load of greater weight than that for which each singletram wire is intended to be carried over the system. One indisputableclaim for confidence in the flexible girder principle is said to be that, although the peculiar combination of parts constitutes a striking andvaluable novelty, it contains nothing that has not been proved by theexperience of years--nay, generations--to be useful, economic, andreliable. The usual practice followed in erecting suspension bridges isapplicable in mounting the line, and the carriers, supports, andcarriages may be of any of the usual forms. For the rapid removal oflimited loads wire tramways are in universal favor, and are recognizednot only as very economic and quickly constructed, but also as being inmany cases the only means of transport available except by the adoptionof elaborate and costly engineering works. 

It has, it seems, been suggested by some who have examined theconstruction of the flexible girder tramway for mineral and producetraffic that it would be an additional advantage if arrangements weremade for the carriage of small loads--half a dozen or so--of passengers, the primary intention being to carry the workpeople backward and forwardbetween comparatively inaccessible mines, works, or plantations and aneighboring village or town. Compared with every other system where theline over which the load travels is elevated, the flexible girder tramwayis claimed to possess many advantages--the center of gravity is kept welldown, the liability of the wheels leaving the line is reduced to theminimum, the gradients are the easiest that can be obtained, there is anentire absence of jolting and extremely little vibration, and the motionis altogether smooth and regular; yet it is very questionable whether, when human life is at stake, any but an ordinary ground line should berelied upon. A living freight is far more liable than a dead freight tomove during the journey; and as the safety of all overhead lines dependsupon what is scientifically designated "unstable equilibrium, " theflexible girder tramway is not recommendable for passenger lines, although it can, of course, be fitted for passenger traffic, a suitablevehicle and ten or a dozen good stout workmen coming well within atwo-ton load, which can be readily carried. 

[Illustration: BALL'S FLEXIBLE WIRE TRAMWAY. ]

Rope traction or animal traction--practically speaking--is aloneavailable for wire tramways (that is to say, if the trains are each to bepropelled by its own locomotive--whether steam, springs, orelectricity--the cost of construction and maintenance becomes so seriousthat overhead lines, however well designed, are no longer economic); andexperience gained with rope traction in numerous collieries in the Northof England and Lancashire districts--where it is highly appreciated--hasshown that, all circumstances considered, the endless rope is preferable. The chief objection urged against wire tramways as hitherto constructedhas been that the "sag" of the rope has sometimes caused annoyance tothose using the property passed over, and has always added much to thecost of traction, owing to the increased power required for moving theload; this has also resulted in vastly increased wear and tear and therapid deterioration and destruction of the wire rope. The flexible girdersystem so reduces the "sag" that the maximum economy and durability areobtained, and the gradients over which the load has to travel can be madeas easy and regular as those upon an ordinary railway. This advantagewill be the more readily appreciated when it is considered that with agiven load on a gradient of 1 in 30 the resistance due to gravity aloneis 200 per cent. Greater than on a gradient of 1 in 150, and that theretardation and wear and tear due to friction, greater curves, andimperfections increase still more rapidly with increase of gradient, soonrendering the old sagging wire line practically worthless. 

To construct an entire line of flexible girders would be not onlyunnecessary, but so costly as to neutralize any advantage which it maypossess, yet for surmounting occasional obstacles the claim made forit--that it will sometimes permit of a line otherwise impracticable beingcheaply made--seems justified. One can readily imagine a light narrowgauge line costing £1, 000 per mile being laid, for example, between amine and the shipping place, and that a swamp, river, or valley wouldcost more to bridge over than the whole line besides. If at this obstaclethe trucks or carriages could be lifted bodily, passed along the flexiblegirder, and again placed on the line the other side of the obstacle, theadvantage to be derived is obvious; and as the flexible girder is reallylittle more than a suspension bridge _minus_ the platform, and having buttwo suspension wires, the cost and the difficulties should both be verysmall. --_Industrial Review_. 

 * * * * *

BOZERIAN'S REFRIGERANT PUNKAS. 

Punkas (also called pankasor tankas) are apparatus that serve for fanningrooms throughout the entire extent of English India. These devicesconsist of a light wooden frame covered with canvas, from the bottom ofwhich depends a fringe. These frames are suspended from the ceiling insuch a way as to occupy nearly the entire width and length of the room. To the base of the frame is attached a cord which passes over a wheel, and which is pulled by a Hindoo domestic. After the frame has beenlifted, a weight fastened to the lower part causes it to fall back again. The result of the continuous motion of this colossal fan is a coolnessthat is highly appreciated in a country where the temperature is at timesincredibly high, and where, without the factitious breeze created by thepunka, living would not be endurable. This breeze prevents perspiration, or evaporates the same as soon as it is formed. Sometimes it sinks to alight zephyr; then, if you are reading or writing, you may continue yourwork, but in a distracted way, with a moist brow, and with a feeling ofannoyance that soon makes you leave book or pen. 

[Illustration: FIG. 1. --TENT OR TABLE FAN OR PUNKA. ]

Looking around you, you find the punka immovable. The bahi still holdsthe cord that pulls it, but it is because he has tied it to his hand. Hehas gently slid to the floor in a squatting posture. He is asleep and youare burning. A vigorous exclamation brings him to his feet all standing, and he begins to pull the punka with all his might, and you have afeeling of ease and coolness. It is like the passage from an attack offever to a state of comfort in an intermittent disease. So the punka isseen everywhere--in the temple and court room and other public places, aswell as in private dwellings. It is one of the first things to astonishthe European upon his arrival in India, and it is not long before he hasto bless the happy invention. 

Although, in a country where the temperature generally reaches, and evenoften exceeds, 40° C. , it is absolutely necessary to obtain by everymeans possible a factitious coolness without which the Indies would notbe habitable for Europeans; and although there is no hesitancy in puttingup these punkas everywhere to be maneuvered by bahis, the elevation ofthe temperature is not such in France that we are obliged to haverecourse to such processes. But, without being forced thereto by nature, it is none the less true that we are often the more incommoded by heat inthat we are not accustomed to it, and that in southern France, at certainhours of the day, such heat becomes absolutely unbearable. We can, it istrue, obtain a little air by moving a fan, but, aside from the fact thatthis exercise soon becomes tiresome, it prevents the use of the hand thatis fanning. 

[Illustration: FIG 2. --AN APARTMENT FAN. ]

The new apparatus which have just been devised by Mr. G. Bozerian permitof one's fanning himself all day long if he wants to, without anyfatigue, and while he is eating, reading, writing, etc. 

In one of these apparatus, designed to be used in the open air (Fig. 1), we find a table, a tent, and a fan combined; but as each part isindependent, we can have the table and fan without tent, or the fan andpedals alone without table or tent. Under the tent there is arranged aframe which pivots freely in apertures formed in the uprights thatsupport both the tent and table. This frame is connected, through twolevers, with the pedals upon which one's feet rest. The motion of thepedals is an alternating one like those of sewing machines; but while inthe case of the latter a pressure has to be exerted that soon becomesvery tiresome, the motion in Mr. Bozerian's apparatus is so easy that itis only necessary to raise the toes of each foot in succession in orderto produce a swing of the fan through the weight alone of the foot thatis pressing. The frame, which when at rest hangs perpendicularly, describes about a quarter of a circle when the extremity of the foot israised about an inch. In consequence of the absence of passiveresistances, motion occurs without any stress, and almost mechanically, giving air not only to him who is actuating the fan, but also to hisvis-a-vis. 

Fig. 2 represents an apartment apparatus designed to be placed in frontof a table or desk, in order that one can fan himself while eating orwriting. Being mounted upon casters, it can be readily moved about fromone place to another. At the extremity of a wooden support, whose heightmay be varied at will, there is arranged a flexible fan whose handle isfixed near a pulley. A small piece of lead forms the counterpoise of thefan, which is thus completely balanced. Over the pulley runs a cord, eachend of which is attached to a pedal. It will be seen that the alternatemotion of these pedals must cause a rotation of the pulley in onedirection or the other, and that consequently the fan will rise or fallmore or less rapidly, and give a quantity of air that varies according tothe rapidity with which the toes are moved. --_La Nature_. 

 * * * * *

PUNKAS. 

[Footnote: Extract from a lecture recently delivered at Bombay. ]

By J. WALLACE, C. E. 

The function of a punka is to cause a current of air to pass the humanbody so that the animal heat may escape more rapidly. This has nothing todo with ventilation; for if the punka were used in a closed room, itwould still produce a cooling effect on the skin. 

Let us for a moment examine into what takes place in this operation, fora clear idea of the cause of our sensations of heat is absolutelynecessary to enable us to go directly to the simplest and best form ofremedy. The heat we feel, and which sometimes renders us uncomfortable, is produced _within us_ by the slow combustion of the food we eat. 

This heat continues to escape from the whole surface of the body duringthe whole lifetime, and if anything occurs to arrest it to any greatextent, the result is fatal. 

In cold weather, and especially when there is much wind, the animal heatescapes very rapidly from the body, and extra clothing is used, not forany heat it imparts, but simply because it interrupts the escape of theheat, and thus maintains the temperature of the skin--that part of uswhich is most sensible of change of temperature. It is a wonderful factthat the heat of the interior of the body varies very little in a healthyman between India and Greenland. 

The skin may bear a good many degrees of change of temperature withimpunity, but the blood will only suffer a very small variation from thenormal temperature of 98-4/10° Fahrenheit without serious consequences. 

Well, to keep the skin at an agreeable temperature in India we generallywear a minimum of clothing, and when there is no breeze, we try toproduce one with the punka. 

The escape of animal heat from the body forms a subject which is muchmore complicated, and much more important, than the one we have met toconsider, but it is impossible within the limits of our time to refer toit, except in the measure that is strictly necessary to elucidate theprinciples that should control the construction of the punka. 

It has often been said that every engineer on his arrival in India setsabout improving this useful apparatus; but if we may judge from theendless variety of forms which may be seen in shops and offices, inpublic and in private buildings, no general principle of construction hasbeen recognized, and the punka, as we see it, seems to depend, for itsform, more upon the taste of the workman who makes it than on anythingelse. 

We shall begin by directing our attention to the suspended punka, whichis usually hung from the ceiling, and put in movement by a cord. Theobject of this class of punka is to produce a downward current of air byswinging to and fro, and the best punka is the one which throws downwardthe greatest quantity of air with the smallest applied force. 

The swinging punka is one of the simplest forms of mechanism; it can befitted up with the most primitive materials, and however badly made, itwill always have _some_ effect. This fact has its good and its badaspects; it brings a certain comfort within the reach of all, but itremoves a great part of that _necessity_ which, as we all know, is themother of invention. 

There are some very important natural laws which are illustrated in thepunka. The first is that which governs the movement of the pendulum. Thenumber of swings it makes per minute depends on the length of thesuspending cords; a pendulum three feet long will swing 62½ times perminute, and a pendulum six feet long will swing 44¼ times per minute. Whether the swings are long ones or short ones, the number per minute isstill the same. You cannot, therefore, alter the natural rate of movementof a punka unless you pull it at both sides. 

The next law is that which determines that the angles of incidence and ofreflection are equal. This in simple language means that it is useless toexpect a good downward current of air from a slow moving and heavy punka, with long suspending cords which keep it nearly always in a verticalposition to its plane of movement. Striking the air squarely as it doesin its forward and backward movement, it throws almost as much air upwardas downward, and of course all the air that is propelled in any otherthan a downward direction represents just so much power wasted. 

One more law, and then we may proceed to demonstration. 

As the air weighs 0. 072 lb. Per cubic foot at 82° Fahrenheit, and as aconsiderable quantity of air is put in motion, the power required todrive a punka depends upon the quantity of air it puts in motion in agiven time. 

The _useful effect_ is a separate matter; it depends on the amount of airthrown in a downward direction. 

To summarize; all punkas of the same size or surface, and going at thesame speed, require the same amount of pulling. The best one is thatwhich will throw down more air than any other of the same size. 

To obtain the greatest result from the power expended in driving it, thepunka should be placed as near as possible to the person to be cooled, as the loss of effect, due to distance, increases not in direct ratio, but in proportion to the square of the distance between punka and person. If at two feet of distance he receives one eighth of the total effect, hewill at four feet of distance obtain only one thirty-second part. 

In practice, the punka should just clear his head when standing, and theweighting of the curtain should be of some yielding material, so as notto damage any person who might stand in its course. 

We shall now proceed to examine several forms of punka, all made to thesame size, and, for purposes of comparison, we shall drive them all atthe same speed. And in order that their effects may be visible to you, Ihave prepared an indicator which resembles more than anything else thekeyboard of a piano. It consists of a series of balanced levers withblades or keys attached, forming a keyboard four feet long. The levers, each three feet long, are delicately hung on fine brass centers, and eachlever is counterbalanced by a weight hung in a vessel of water, whichacts as a hydraulic brake, and checks any spasmodic movement in theapparatus. 

On the end of each blade is fixed a disk of white Bristol board fourinches in diameter, forming a row which faces the audience. 

This apparatus is so sensitive that a slight change in the humidity ofthe atmosphere is sufficient to throw it out of balance. 

The power required to drive a punka is nearly all due to the resistanceof the air; that part due to the force of gravity, and the friction ofthe suspending joints, is scarcely worth counting. We may readily observethe effect of the resistance of the air by swinging two pendulums ofequal length and having each a large cardboard disk attached. One of thedisks shall present its edge to the line of movement, and the other itsface. 

_Exp. 1. _--They are now swinging, and being both of the same gravitylength, they should swing together and for an equal length of time. Thisthey would do in a vacuum, but you have already observed that one of themis lagging, and will evidently soon come to a standstill. It is the one_facing_ the air. 

If punkas were pulled from both sides, they might be made very muchlighter than they are at present, but for the sake of simplicity a singlepull is preferred. They must, therefore, be made of such a weight thatthey will swing nearly as far on the opposite side as they are pulled onthe near side; any greater weight is useless and only serves to wear outthe suspending cords, which, by the way, are nearly always too numerousand too thick for their purpose. 

_Exp. 2. _--Here is a panel punka which we shall try to use without thecustomary swing bar. It is of calico stretched on a light wooden frame, and you will be able to judge if it swings equally on each side of thepost which supports it. The irregularity of its movement shows that it istoo light, so we shall add, by way of swing bar, a bar of round iron oneand a quarter inch thick. 

_Exp. 3. _--It is now swinging regularly, and experiments have alreadyproved that the swing bar should not be lighter than this one, whichweighs four and a sixth lb. Per foot of length. Iron is the best materialfor this purpose, as it offers the smallest surface to the resistance ofthe air. The length of the suspending cords is usually a matter ofaccident in the construction of a punka, but a little attention to thesubject will soon convince us that it is one of the most importantconsiderations. 

The limit of movement of a punka is to be found in the man who pulls it. Twenty-four pulls a minute of a length of 36 inches give in practice aspeed of 168 linear feet to the punka curtain. This speed is found toproduce a current sufficiently rapid for practical purposes, andtwenty-four pulls or beats per minute correspond to a length ofsuspending cord of fifty inches. 

 * * * * *

HOW TO MAKE A KITE WITHOUT A TAIL. 

The following is the method of making a kite without a tail: All thecalculations necessary in order to obtain the different proportions arebased upon the length of the stick, A'A, employed. Such length beingfound, we divide it by ten, and thus obtain what is called the unit oflength. With such unit it is very easy to obtain all the proportions. Thebow, K'K, consists of two pieces of osier each 5½ units in length, thatform, through their union, a total length of 7 units. 

[Illustration: KITE WITHOUT A TAIL. ]

After the bow has been constructed according to these measurements, itonly remains to fix it to the stick in such a way that it shall be twounits distant from the upper end of the stick. The balance, CC', whoseaccuracy contributes much to the stability of the whole in the air, consists of a string fixed at one end to the junction, D, of the bow andstick, and at the other to the stick itself at a distance of three unitsfrom the lower extremity. Next, a cord, B, is passed around the frame, and the whole is covered with thin paper. 

Before raising the kite, the string, which hangs from K', is made fast atK in such a way as to cause the bow to curve backward. This curvature isincreased or diminished according to the force of the wind. 

Nothing remains to be done but to attach the cord to the balance, andraise the kite. --_La Nature_. 

 * * * * *

APPARATUS FOR DRYING FLOUR. 

The accompanying drawing represents a simple but effective apparatus fordrying flour and ascertaining the quantity of water contained therein. Itconsists of four pieces, the whole being made of block tin. A is a simplesaucepan for containing the water. B is the lid, which only partiallycovers the top of the pan, to which it is fixed by two slots, a holebeing left in the middle for the placing of the vessel which contains theflour to be operated upon, and is dropped in in the same way as the pancontaining the glue is let into an ordinary glue pot. C is the spout, which serves as an outlet for the steam arising from the boiling water. Dis the vessel in which the flour is placed to be experimented upon; andEE are the funnels of the lid which covers the said vessel, and whichserve as escapes for the steam arising from the moisture contained in theflour. 

[Illustration: APPARATUS FOR DRYING FLOUR]

_Directions for use_. --Partially fill the pan with water and allow it toboil. Place a given quantity of flour in the inner vessel, D, taking carefirst to weigh it. Subject it to the action of the boiling water until itis perfectly dry, which will be indicated by the steam ceasing to issuefrom the funnels. Then weigh again, and the difference in the weight willrepresent the quantity of moisture contained in it, dried at atemperature of 212 degrees Fahr. , that of boiling water. --_The Miller_. 

 * * * * *

APPARATUS FOR MANUFACTURING BOUQUETS. 

For some years past, the sale of flowers has been gradually increasing. Into the larger cities, such as Paris for example, they are introduced bythe car load, and along about the first of January the consumption ofthem is extraordinary. All choice flowers are now being cultivated byimproved methods that assure of an abundant production of them. Whattwenty years ago would have appeared to be an antiquated mechanism, viz. , an apparatus for making bouquets, has now become a device of primenecessity by reason of the exigencies of an excessive demand. 

Mr. Myard, a gardener of Chalon-sur-Saone, and vice-president of thehorticultural society of that city, has devised a curious apparatus, which we represent herewith from a photograph. 

This bouquet machine, which the inventor styles a _bouquetiere_, consistsof a stationary rod (shown to the right of the figure), upon which slidesa spool wound with twine, and the lower part of which is provided withthree springs for keeping the twine taut. A horizontal arm at the topsupports a guide or pattern whose curve is to be followed, on placing theflowers in position. This arm is removed or turned aside after thebinding screw has been loosened, in order that the rod to the left thatcarries the bouquet may be taken out. A guide, formed of a steel ribbon, is fixed to the arm and to its movable rod by means of binding screws, which permit of its being readily elongated. This central rod can beraised or lowered at will, and, owing to these combinations, everydesired form of bouquet may be obtained. 

[Illustration: APPARATUS FOR MAKING BOUQUETS. ]

The rod to the left is provided with a steel pivot, and contains severalapertures, into which a pin enters, thus rendering it easy to beginbouquets at different heights. 

The bouquet is mounted upon the rod to the left, as shown in the figure. The pin passes through the rod and enters a loop formed at the extremityof the twine, and thus serves as a point of support, and prevents thebouquet from falling, no matter what its weight is. When the pin isremoved in order that the bouquet may be taken out, the loop escapes. 

At the lower part of the rod upon which the bouquet is mounted, there isa collar with three branches, by means of which a rotary motion is givento the flowers through the aid of the hand. The twine used for tying isthus wound around the stems. When the apparatus is in motion, the twineunwinds from the spool, and winds around the rod that carries theflowers, and twists about and holds every stem. 

An experienced operator can work very rapidly with this little apparatus, which has been constructed with much care and ingenuity, and which entersinto a series of special mechanisms that is always of interest to knowabout. 

The manufacturer was advised to construct his apparatus so that it couldbe run by foot power, but, after some trials, it was found that theaddition of a pedal and the mechanism that it necessitates was absolutelysuperfluous, the apparatus working very well such as it is. --_La Nature_. 

 * * * * *

[Continued from SUPPLEMENT, No. 567, page 9057. ]

RADII OF CURVATURE GEOMETRICALLY DETERMINED. 

By Prof. C. W. MACCORD, Sc. D. 

NO. VII. --PATH OF A POINT ON A CONNECTING ROD. 

The motion of the connecting rod of a reciprocating steam engine is veryclearly understood from the simple statement that one end travels in acircle and the other in a right line. From this statement it is alsoreadily inferred that the path of any point between the centers of thecrank and crosshead pins will be neither circular nor straight, but anelongated curve. This inference is so far correct, but the very commonimpression that the middle point of the rod always describes an ellipseis quite erroneous. The variation from that curve, while not conspicuousin all cases, is nevertheless quite sufficient to prevent the use of thismovement for an elliptograph. To this there is, abstractly, oneexception. Referring to Fig. 22 in the preceding article, it will be seenthat if the crank OH and the connecting HE are of equal length, any pointon the latter or on its prolongation, except E, H, and F, will describean exact ellipse. But the proportions are here so different from anythingused in steam engines (the stroke being four times the length of thecrank), that this particular arrangement can hardly be considered as whatis ordinarily understood by a "crank and connecting rod movement, " suchas is shown in Fig. 23. 

The length DE of the curve traced by the point P will evidently be equalto A'B', the stroke of the engine, and that again to AB, the throw of thecrank. The highest position of P will be that shown in the figure, determined by placing the crank vertically, as OC. At that instant themotions of C and C' are horizontal, and being inclined to CC' they mustbe equal. In other words, the motion is one of translation, and theradius of curvature at P is infinite. 

To find the center of curvature at D, assume the crank pin A to have avelocity A_a_. Then, since the rod is at that instant turning about thefarther end A', we will have D_d_ for the motion of D. The instantaneousaxis of the connecting rod is found by drawing perpendiculars to thedirections of the simultaneous motions of its two ends, and it thereforefalls at A', in the present position. But the perpendicular to the motionof the crank pin is the line of the crank itself, and consequently isrevolving about O with an angular velocity represented by AO_a_. Themotion of A' is in the direction A'B', but its velocity at the instant iszero. Hence, drawing a vertical line at A', limited by the prolongationof _a_O, we have A'_a_' for the motion of the instantaneous axis. Therefore, by drawing _a_'_d_, cutting the normal at _x_, we determineD_x_, the radius of curvature. 

Placing the crank in the opposite position OB, we find by a constructionprecisely similar to the above, the radius of curvature E_z_ at the otherextremity of the axis of the curve. It will at once be seen that E_z_ isless than D_x_, and that since the normal at P is vertical and infinite, the evolute of DPE will consist of two branches _x_N, _z_M, to which thevertical normal PL is a common asymptote. These two branches will not besimilar, nor is the curve itself symmetrical with respect to PL or to anytransverse line; all of which peculiarities characterize it as somethingquite different from the ellipse. 

[Illustration: FIG. 23. ]

[Illustration: FIG. 24. ]

[Illustration: FIG. 25. ]

Moreover, in Fig. 22, the locus of the instantaneous axis of the trammelbar (of which the part EH corresponds to the connecting rod, when a crankOH is added to the elliptograph there discussed) was found to be acircle. But in the present case this locus is very different. Beginningat A', the instantaneous axis moves downward and to the right, as thecrank travels from A in the direction of the arrow, until it becomesvertical, when the axis will be found upon C'R, at an infinite distancebelow AB', the locus for this quarter of the revolution being a curveA'G, to which C'R is an asymptote. After the crank pin passes C, the axiswill be found above AB' and to the right of C'R, moving in a curve HB', which is the locus for the second quadrant. Since the path of P issymmetrical with respect to DE, the completion of the revolution willresult in the formation of two other curves, continuous and symmetricalwith those above described, the whole appearing as in Fig. 24, thevertical line through C' being a common asymptote. 

In order to find the radius of curvature at any point on the generatedcurve, it is necessary to find not only the location of the instantaneousaxis, but its motion. This is done as shown in Fig. 25. P being the givenpoint, CD is the corresponding position of the connecting rod, OC that ofthe crank. Draw through D a perpendicular to OD, produce OC to cut it inE, the instantaneous axis. Assume C A perpendicular to OC, as the motionof the crank. Then the point E in OC produced will have the motion EFperpendicular to OE, of a magnitude determined by producing OA to cutthis perpendicular in F. But since the _intersection_ E of the crankproduced is to be with a vertical line through the other end of the rod, the instantaneous axis has a motion which, so far as it depends upon themovement of C only, is in the direction DE. Therefore EF is a component, whose resultant EG is found by drawing FG perpendicular to EF. Now D ismoving to the left with a velocity which may be determined either bydrawing through A a perpendicular to CD, and through C a horizontal lineto cut this perpendicular in H, or by making the angle DEI equal to theangle CEA, giving on DO the distance DI, equal to CH. Make EK = DI orCH, complete the rectangle KEGL, and its diagonal ES is, finally, themotion of the instantaneous axis. 

EP is the normal, and the actual motion of P is PM, perpendicular to EP, the angle PEM being made equal to CEA. Find now the component EN of themotion ES, which is perpendicular to EP. Draw NM and produce it to cut EPproduced in R the center of curvature at P. 

This point evidently lies upon the branch _z_M of the evolute in Fig. 23. The process of finding one upon the other branch _x_N is shown in thelower part of the diagram, Fig. 25. The operations being exactly likethose above described, will be readily traced by the reader withoutfurther explanation. 

 * * * * *

AUTOMATIC COMMUTATOR FOR INCANDESCENT LAMPS. 

Incandescent electric lighting, already pushed to such a degree ofperfection in the details of construction and installation, continuallyfinds new exigencies that have to be satisfied. As it is more and morefirmly established, it has to provide for all the comforts of existenceby simple solutions of problems of the smaller class. 

Take for example this case: Suppose a room, such as an office, lighted bya single lamp. The filament breaks; the room becomes dark. The bell pushis not always within reach of the arm, and it is by haphazard that onehas to wander around in the dark. This is certainly an unpleasantsituation. The comfort we seek for in our houses is far from beingprovided. 

M. Clerc, the well known inventor of the sun lamp, has tried to overcometroubles of this sort, and has attained a simple, elegant, and at thesame time cheap solution. The cut shows the arrangement. The apparatus isconnected at the points, BB', with the lighting circuit. The currententering by the terminal, B', passes through the coils of a bobbin, S, before reaching the points of attachment, a and b, of the lamp, L, thenormally working one. Thence the circuit runs to B. Within the coil, S, is a small hollow cylinder, T, of thin sheet iron, which is raisedparallel with the axis of the bobbin during the passage of the currentthrough the latter. At its base the cylinder is prolonged into two littlerods, h and h', which plunge into two mercury cups, G and G'. The cutshows that one of the cups, G', is connected to the terminal, B', and theother, G, to the terminal, a', of the other lamp, L'. An inspection ofthe cut shows just what ensues when an accident happens to the first lampwhile burning. The first circuit being broken at ab, the magnetizingaction of the current in the bobbin ceases, the cylinder, T, descends, and the rods, h and h', dip into the mercury. It follows that thecurrent, always starting from the terminal, B', will by means of thecups, G and G', pass through the lamp, L', to go by the original returnwire to B. 

[Illustration]

The substitution of the lamp, L, for L' is almost instantaneous. It canscarcely be perceived. It goes without saying that such an arrangement ofautomatic commutation is applicable to lamps with two or more filamentsof which only one is to be lighted at a time. The apparatus costs little, and can be made as ornamental as desired. No exaggeration is indulged inif we pronounce it simple and ingenious. It may be used in a greatvariety of eases. The diameter of the wire is 55/100 (22 mm. ), its lengtheighteen meters (60 feet), its resistance one ohm; ¾ ampere is needed towork it, and less than a watt is absorbed by it. --_Electricite_. 

 * * * * *

DEFINITIONS AND DESIGNATIONS IN ELECTROTECHNICS. 

We may discourse for some time to come upon the uniformity of electriclanguage, for universal agreement is far from being established. Animportant step toward the unity of this language was taken in 1881 by thecongress of Paris, which rendered the use of the C. G. S. System definitiveand universal. This labor was completed in 1884 by the meeting of a newcongress at Paris, at which a definition of the C. G. S. And practicalunits was distinctly decided upon. That the unit of light defined by thecongress has not rapidly come into favor is due to the fact that itspractical realization is not within everybody's reach. 

The work of unification should not come to a standstill on so good aroad. How many times in scientific works or in practical applications dowe find the same physical magnitude designated by different names, oreven the use of the same expression to designate entirely differentthings!

The result is an increase of difficulties and confusions, not only forpersons not thoroughly initiated into these notions, but also for adepts, even, in this new branch of the engineer's art. The effects of suchconfusion make themselves still further felt in the reading of foreignpublications. Thus, for example, in Germany that part of a dynamoelectric machine that is called in France the _induit_ (armature) issometimes styled _anker_, and more rarely _armatur_. The _north pole_ ofa freely suspended magnetized needle is the one that points toward thegeographical north of the earth. In France, and by some English authors, this pole is called the _south_ one. Among electricians of the samecountry, what by one is called _electro-motive force_ is by anotherstyled _difference of potential_, by a third _tension_, and even_difference of tension_. 

Our confrere Ruhlmann, of the _Elektrotechnische Zeitschrift_, gives astill more remarkable example yet of such confusion. The word_polarization_, borrowed from optics, where it has an unequivocal sense, serves likewise to designate the development of the counterelectro-motive force of galvanic elements, and also that essentiallydifferent condition of badly conducting substances that is brought aboutby the simultaneous influence of quantities of opposite electricity. 

In Germany, the word _induction_, coupled with the word _wire_, forexample, according to the formation of compound words in that language, may also have a double meaning, and it is by the sense alone of thephrase that we learn whether we have to do with an induced wire or aninducting one. The examples might be multiplied. 

At its session of November 5, 1884, the International Society ofElectricians, upon a motion of Mr. Hospitalier, who had made acommunication upon this question, appointed a committee to study it andreport upon it. The English Society of Electricians likewise took thesubject into consideration, and one of its most active and distinguishedmembers, Mr. Jamieson, presented the result of his labors at the Maysession of the society in 1885. 

A discussion arose in which the committee of the International Society ofElectricians was invited to take part. The committee was represented byits secretary, Mr. Hospitalier, who expressed himself in about thesewords: "The committee on electric notations presided over by Mr. Blauvelthas finished a part of its task, that relative to abbreviations, notations, and symbols. It will soon take up the second part, whichrelates to definitions and agreements. " He broadly outlined thecommittee's ideas as follows:

In all physical magnitudes that are made use of, we have: (1) thephysical magnitude itself, aside from the units that serve to measure it;(2) the C. G. S. Unit that serves to measure such grandeur (granted theadoption of the C. G. S. System); (3) practical units, which, in general, have a special name for each kind of magnitude, and are a decimalmultiple or sub-multiple of the C. G. S. Unit, except for time and angles;(4) finally, decimal multiples and sub-multiples of these practicalunits, that are in current use. 

The committee likewise decided always to adopt a large capital todesignate the physical magnitude; a small capital to designate the C. G. S. Unit, when it has a special name; a "lower case" letter for theabbreviation of each practical unit; and prefixes, always the same, forthe decimal multiples and sub-multiples of the practical units. 

Thus, for example, work would be indicated by the letter W (initial ofthe word); the C. G. S. Unit is the _erg_, which would be written withoutabbreviation, on account of its being short; and the practical unitswould be the kilogrammeter (_kgm_), the grammeter (_gm_), etc. Themultiples would be the _meg-erg_, the tonne-meter (_t-m_), etc. 

Mr. Jamieson's propositions have been in great part approved. Somecriticisms, however, were made during the course of the discussion, andit is for this reason that the scheme still remains open to improvements. The proposed symbols are as follows:

A. --PRACTICAL ELECTRIC UNITS. 

Total resistance of a circuit. RInternal resistance of a source of current. R_{1}Resistance of the separate parts of a current. _r__{1}, _r__{2}, etc. Specific resistance. [rho]1 ohm. [omega]1 megohm. [Omega]Intensity of a current. CMagnitude of 1 ampere. A1 milliampere. [alpha]Electro-motive force. EMagnitude of 1 volt. _v_Capacity. KConstant of specific induction. [sigma]1 farad. [Phi]1 microfarad. [phi]Quantity of electricity. Q1 coulomb. CElectric work (volt coulomb). _v_CElectric effect (volt ampere, watt in one second). WHorse power. HP

B. --MAGNETISM. 

Pole of magnet pointing toward the north. NThe opposite pole. SForce of a pole, quantity of magnetism. _m_Distance of the poles of a magnet. _l_Magnetic moment. M = _m. L_Intensity of magnetization. JIntensity of the horizontal component of terrestrialmagnetism. H

C. --ELECTRIC MEASUREMENTS. 

Galvanometer and its resistance. GResistance of the shunt of a galvanometer. _s_Battery and its internal resistance. B

For dynamo machines, the following designationsare proposed:

The machine itself. DPositive terminal. +TNegative terminal. -TMagnet forming the field. FMCurrent indicator (amperemeter). AMTension indicator (voltameter). MVElectro-magnet. EMLuminous intensity of a lamp, in candles. _c. P_. Resistance of the armature. R_{a}Resistance of the magnet forming the field. R_{m}Resistance of the external circuit. R_{o}Intensity in the armature. C_{a}Intensity in the coils of the magnet. C_{m}Intensity in the external circuit. C_{e}Coefficient of self-induction. L_{s}Coefficient of mutual induction. L_{m}

A primary battery would be represented as in Fig. 1, and a battery ofaccumulators as in Fig. 2. 

[Illustration: FIG. 1. ]

[Illustration: FIG. 2. ]

In order to designate incandescent lamps, circles would be used, andstars for arc lamps. A system of incandescent lamps arranged in multiplearc would be represented as in Fig. 3. 

[Illustration: FIG. 3. ]

Fig. 4 and the formula

R = B + Gs/(G + s) + r

would serve for the total resistance, R, of an electric circuit, upongiving the letters the significations adopted. 

[Illustration: FIG. 4. ]

Such is, in brief, the present state of the question. The scientificbodies that have taken hold of it have not as yet furnished a fullyco-ordinated work on the subject. Let us hope, however, that we shall nothave to wait long. The question is of as much interest to scientific menas to practical ones. 

A collection of identical symbols would have the advantage of permittingus to abridge explanations in regard to the signification of terms usedin mathematical formulas. A simple examination of a formula would sufficeto teach us its contents without the aid of tiresome explanatory matter. 

But in order that the language shall be precise, it will be necessary forthe words always to represent precise ideas that are universallyaccepted, and for their sense not to depend upon the manner ofunderstanding the idea according to their arrangement in the phrase. 

Nothing can be more desirable than that the societies of electricians ofall countries shall continue the study of these questions with the desireof coming to a common understanding through a mutual sacrifice of certainpreferences and habitudes. --_E. Dieudonne, in La Lumiere Electrique_. 

 * * * * *

IMPROVED MICROSCOPICAL SETTLING TUBE. 

By F. VANDERPOEL, of Newark, New Jersey. 

In the February number of this _Journal_ the writer described a newsettling tube for urinary deposits which possessed several advantagesover the old method with conical test-glass and pipette. For severalreasons, however, the article was not illustrated, and it is for thepurpose of elucidation by means of illustration, as well as to bringbefore the readers of the _Journal_ two new and improved forms of thetube, that space in these columns is again sought. The first two of thefigures, 1 and 2, represent the tube as originally devised; 1 denotingthe tube with movable cap secured to it by means of a rubber band, and 2the tube with a ground glass cap and stop cock. The first departure fromthese forms is shown at 3, and consists of a conical tube, as before, butprovided with a perforated stopper, the side opening in whichcommunicates with a side tube. The perforation in the stopper, which iseasily made by a glass blower, thus allows the overflow, when the stopperis inserted into the full tube, to pass into the side tube. The stopperis then turned so as to cut off the urine in the latter from that in thelarge tube, and the latter is thus made tight. After allowing it toremain at rest long enough to permit subsidence of all that will settle, the stopper is gently turned and a drop taken off the lower end upon aslide, to be examined at leisure with the microscope. The cap, ground andfitted upon the lower end, is put there as a precautionary measure, aswill be seen farther on. 

[Illustration: VANDERPOEL'S SETTLING TUBES. ]

The tube shown at 4 is, we think, an improvement upon all of theforegoing, for upon it there is no side tube to break off, and everythingis comprised in a small space. As will be seen by referring to thefigure, there is a slight enlargement in the ground portion of thestopper end of the tube, this protuberance coming down about one-half thelength of the stopper, which is solid and ground to fit perfectly. Thelower half, however, is provided with a small longitudinal slit orgroove, the lower end of which communicates with the interior of thetube, while the upper end just reaches the enlargement in the side of thelatter. Thus in one position of the stopper there is a communicationbetween the tube and the outer air, while in all other positions the tubeis quite shut. In all these tubes care must be taken to fill them_completely_ with the urine, and to allow no bubbles of air to remaintherein. 

The first of these settling tubes was made without the ground cap on thelower end, the latter being inserted into a small test tube for safety. At the suggestion of Mr. J. L. Smith the test tube was made a part of theapparatus by fitting it (by grinding) upon the conical end, and in itspresent form it serves to protect the latter from dust and to preventevaporation of the urine (or other liquid), and consequent deposition ofsalts, if, for any reason, the user should allow the tube to remainsuspended for several days. 

These tubes will be found very useful for collecting and concentratinginto a small bulk the sediment contained in any liquid, whether it becomposed of urinary deposits, diatoms in process of being cleaned, or anything of like nature; and, as the parts are all of glass, the strongestacids may be used, excepting, of course, hydrofluoric acid, without harmto the tubes. --_American Microscopical Journal_. 

 * * * * *

[Continued from SUPPLEMENT, No. 594, page 9491. ]

CLIMATE IN ITS RELATION TO HEALTH. By G. V. POORE, M. D. 

[Footnote: Three lectures before the Society of Arts, London. From theJournal of the Society. ]

LECTURE III. DISEASES CAUSED BY FLOATING MATTER IN THE AIR. 

The information which modern methods of research have given us withregard to the floating matter in the air is of an importance which cannotbe overestimated. 

That the air is full of organic particles capable of life and growth isnow a matter of absolute certainty. It has long been a matter ofspeculation, but there is a great difference between a fact and aspeculation. An eminent historian has recently deprecated the distinctionwhich is conventionally drawn between science and knowledge, but, nevertheless, such a distinction is useful, and will continue to bedrawn. A man's head may be filled with various things. His inclinationmay lead him, for example, to study archaic myths in the various dialectswhich first gave them birth; he may have a fancy for committing to memorythe writings of authors on astrology, or the speculations of ancientphilosophers, from Aristotle and Lucretius downward. Such a one may havea just claim to be considered a man of learning, and far be it from me todespise the branches of knowledge toward which his mind has a naturalbent. But in so far as his knowledge is a knowledge of fancies ratherthan facts, it has no claim to be called science. 

Fancies, however beautiful, cannot form a solid basis for action orconduct, whereas a scientific fact does. It is all very well to supposethat such and such things may be, but mere possibilities, or evenprobabilities, do not breed a living faith. They often foster schism, andgive rise to disunited or opposed action on the part of those who thinkthat such and such things may not be. 

When, however, a fancy or a speculation becomes a fact which is capableof demonstration, its universal acceptance is only a matter of time, andthe man who neglects such facts in regulating his actions or conduct isrightly regarded as insane all the world over. 

The influence of micro-organisms on disease is emerging more and more, day by day, from the regions of uncertainty, and what once were thespeculations of the few are now the accepted facts of the majority. 

Miquel's experiments show very clearly that the number of microbes in theair corresponds with tolerable closeness to the density of population. From the Alpine solitudes of the Bernese Oberland to the crowded ward ofa Parisian hospital, we have a constantly ascending ratio of microbes inthe air, from zero to 28, 000 per cubic meter. Their complete absence onthe Alps is mainly due to the absence of productive foci. Organic mattercapable of nourishing microbes is rare, and the dryness and cold preventany manifestation of vitality or increase. Whence come the large numberof microbes in the crowded places and in hospitals?

Every individual, even in health, is a productive focus for microbes;they are found in the breath, and flourish luxuriantly in the mouth ofthose especially who are negligent in the use of the tooth brush. When wespeak of "flourishing luxuriantly, " what do we mean? Simply that thesemicrobes, under favorable circumstances, increase by simple division, andthat one becomes about 16, 000, 000 in twenty-four hours. 

The breath, even of healthy persons, contains ammonia and organic matterwhich we can smell. When the moisture of the breath is condensed andcollected, it will putrefy. Every drop of condensed moisture that formson the walls of a crowded room is potentially a productive focus formicrobes. Every deposit of dirt on persons, clothing, or furniture isalso a productive focus, and production is fostered in close apartmentsby the warmth and moisture of the place. In hospitals productive foci aremore numerous than in ordinary dwellings. 

If microbes are present in the breath of ordinary individuals, what canwe expect in the breath of those whose lungs are rotten with tuberculardisease? Then we have the collections of expectorated matter and of otherorganic secretions, which all serve as productive foci. Every wound andsore, when antiseptic precautions are not used, becomes a most active anddangerous focus, and every patient suffering from an infective disease isprobably a focus for the production of infective particles. When weconsider, also, that hospital wards are occupied day and night, andcontinuously for weeks, it is not to be wondered at that microbes areabundant therein. 

I want especially to dwell upon the fact that foci, and probablyproductive foci, may exist outside the body. It is highly probable, judging from the results of experiments, that every collection ofputrescible matter is potentially a productive focus of microbes. Thethought, of a pit or sewer filled with excremental matters mixed withwater, seething and bubbling in its dark warm atmosphere, andcommunicating directly (with or without the intervention of thattreacherous machine called a trap) with a house, is enough to make oneshudder, and the long bills of mortality already chargeable to thisarrangement tell us that if we shudder we do not do so without cause. Asan instance of the way in which dangers may work in unsuspected ways, Imay mention the fact that Emmerich, in examining the soil beneath a wardof a hospital at Amberg, discovered therein the peculiar bacillus whichcauses pneumonia, and which had probably been the cause of an outbreak ofpneumonia that had occurred in that very ward. 

The importance of "Dutch cleanliness" in our houses, and the abolition ofall collections of putrescible matter in and around our houses, isabundantly evident. 

It will not be without profit to examine some well-known facts, by theaids of the additional light which has been thrown upon them by the studyof the microbes which are in the media around us. 

There is no better known cause of a high death rate than overcrowding. Overcrowding increases the death rate from infectious diseases, especially such as whooping cough, measles, scarlet fever, diphtheria, small-pox, and typhus. The infection of all these diseases iscommunicable through the air, and where there is overcrowding, the chanceof being infected by infective particles, given off by the breath orskin, is of course very great. Where there is overcrowding, thecollections of putrescible filth are multiplied, and with them probablythe productive foci of infective particles. Tubercular disease, commonsore throat, chicken-pox, and mumps, are also among the diseases whichare increased by overcrowding. 

To come to details which are more specific, let us consider the case ofsome diseases which are definitely caused by floating matter in the air. First, let us take one which is apparently attributable to pollen. 

HAY FEVER. 

Among diseases which are undoubtedly caused by floating matter in the airmust be reckoned the well-known malady "hay fever, " which is a veritablescourge during the summer months to a certain percentage of persons, whohave, probably, a peculiarly sensitive organization to begin with, andare, in a scientific sense, "irritable. "

This disease has been most thoroughly and laboriously investigated by Mr. Charles Blackley, of Manchester, who, being himself a martyr to hayfever, spent ten years in investigating the subject, and published theresult in 1873, in a small work entitled "Experimental Researches on theCauses and Nature of _Catarrhus aestivus_ (hay fever or hay asthma). "

Mr. Blackley had little difficulty in determining that the cause of histrouble was the pollen of grasses and flowers, and his investigationsshowed that the pollen of some plants was far more irritating than thepollen of others. The pollen of rye, for example, produced very severesymptoms of catarrh and asthma, when inhaled by the nose or mouth. Mr. Blackley came to the conclusion that the action of the pollen was partlychemical and partly mechanical, and that the full effect was not produceduntil the outer envelope burst and allowed of the escape of the granularcontents. 

Having satisfied himself that pollen was capable of producing all thesymptoms of hay fever, Mr. Blackley next sought to determine, by a seriesof experiments, the quantity of pollen found floating in the atmosphereduring the prevalence of hay fever, and its relation to the intensity ofthe symptoms. The amount of pollen was determined by exposing slips ofglass, each having an area of a square centimeter, and coated with asticky mixture of glycerine, water, proof spirit, and a little carbolicacid. Mr. Blackley gives two tables, showing the average number of pollengrains collected in twenty-four hours on one square of glass, between May28 and August 21, in both a rural and an urban position. The maximum bothin town and country was reached on June 28, when in the town 105 pollengrains were deposited, and in the country 880 grains. The number ofgrains deposited was found to vary much, falling almost to zero duringheavy rain and rising to a maximum if the rain were followed by brightsunshine. Mr. Blackley found that the severity of his own symptomsclosely corresponded to the number of pollen grains deposited on hisglasses. Mr. Blackley devised some very ingenious experiments todetermine the number of grains floating in the air at differentaltitudes. The experiments were conducted by means of a kite, to whichthe slips of glass were attached, fixed in an ingenious apparatus, bymeans of which the surface of the glass was kept covered until aconsiderable altitude had been reached. Mr. Blackley's first experimentgave as a result that 104 pollen grains were deposited in the glassattached to the kite, while only 10 were deposited on a glass near theground. This experiment was repeated. Again and again, and always withthe same result, there was more pollen in the upper strata of the airthan in the lower. 

A very interesting experiment was performed at Filey, in June, 1870. Abreeze was blowing from the sea, and had been blowing for 12 or 15hours. Mr. Blackley flew his kite to an elevation of 1, 000 feet. Theglass attached to the kite was exposed for three hours, and on it therewere 80 grains of pollen, whereas a similar glass, exposed at the marginof the water, showed no pollen nor any organic form. Whence came thispollen collected on the upper glass? Probably from Holland or Denmark. Possibly from some point nearer the center of Europe. 

POTATO DISEASE. 

A study of the terrible disease which so often attacks the potato crop inthis country will serve, I think, to bring forcibly before you certainuntoward conditions which may be called climatic, and which areattributable to fungoid spores in the air. 

With the potato disease you are all, probably, more or less practicallyacquainted. When summer is at its height, and when the gardeners andfarmers are all looking anxiously to the progress of their crops, howoften have we heard the congratulatory remark of "How well and strongthose potatoes look!" Such a remark is most common at the end of July orthe beginning of August, when the green part, or haulm, of the plant islooking its best, and when the rows of potatoes, with their elegant richfoliage and bunches of blossom, have an appearance which would almostmerit their admission to the flower border. The same evening, it may be, there comes a prolonged thunder storm, followed by a period of hot, close, moist, muggy weather. Four-and-twenty hours later, the haplessgardener notices that certain of his potato plants have dark spots uponsome of their leaves. This, he knows too well, is the "plague spot, " andif he examine his plants carefully, he will perhaps find that there isscarcely a plant which is not spotted. If the thunder shower which wehave imagined be followed by a long period of drought, the plague may bestayed and the potatoes saved; but if the damp weather continue, thenumber of spotted leaves among the potatoes increases day by day, untilthe spotted leaves are the majority; and then the haulm dies, gets slimy, and emits a characteristic odor; and it will be found that the tubersbeneath the soil are but half developed, and impregnated with the diseaseto an extent which destroys their value. 

Now, the essential cause of the potato disease is perfectly wellunderstood. It is parasitical, the parasite being a fungus, the_Peronospora infestans_, which grows at the expense of the leaves, stems, and tubers of the plant until it destroys their vitality. If a diseasedpotato leaf be examined with the naked eye, it will be seen that, on theupper surface, there is an irregular brownish black spot, and if theunder surface of the leaf be looked at carefully, the brown spot is alsovisible, but it will be seen to be covered with a very faint white bloom, due to the growth of the fungus from the microscopic openings or"stomata, " which exist in large numbers on the under surface of mostgreen leaves. The microscope shows this "bloom" to be due to theprotrusion of the fungus in the manner stated, and on the free ends ofthe minute branches are developed tiny egg shaped vessels, called"conidia, " in which are developed countless "spores, " each one of whichis theoretically capable of infecting neighboring plants. 

Now, it is right to say that, with respect to the mode of spread of thedisease, scientific men are not quite agreed. All admit that it may beconveyed by contact, that one leaf may infect its neighbors, and thatbirds, flies, rabbits, and other ground game may carry the disease fromone plant to another and from one crop to another. This is insufficientto account for the sudden onset and the wide extent of potato"epidemics, " which usually attack whole districts at "one fell swoop. "Some of those best qualified to judge believe that the spores are carriedthrough the air, and I am myself inclined to trust in the opinionexpressed by Mr. William Carruthers, F. R. S. , before the select committeeon the potato crop, in 1880. Mr. Carruthers' great scientificattainments, and his position as the head of the botanical department ofthe British Museum, and as the consulting naturalist of the RoyalAgricultural Society, at least demand that his opinion should be receivedwith the greatest respect and consideration. Mr. Carruthers said (reporton the potato crop, presented to the House of Commons, July 9, 1880, question 143 _et seq. _): "The disease, I believe, did not exist at all inEurope before 1844.... Many diseases had been observed; many injuries topotatoes had been observed and carefully described before 1844; but thisparticular disease had not. It is due to a species of plant, and althoughthat species is small, it is as easily separated from allied plants asspecies of flowering plants can be separated from each other. This plantwas known in South America before it made its appearance in this country. It has been traced from South America to North America, and to Australia, and it made its first appearance in Europe in Belgium, in 1844, andwithin a very few days after it appeared in Belgium, it was noticed inthe Isle of Wight, and then within almost a few hours after that itspread over the whole of the south of England and over Scotland.... Whenthe disease begins to make its appearance, the fungus produces theselarge oblong bodies (_conidia_), and the question is how these bodies arespread, and the disease scattered.... I believe that these bodies, whichare produced in immense quantities, and very speedily, within a few hoursafter the disease attacks the potato, are floating in the atmosphere, andare easily transplanted by the wind all over the country. I believe thisis the explanation of the spread of the disease in 1844, when it made itsappearance in Belgium. The spores produced in myriads were brought overin the wind, and first attacked the potato crops in the Isle of Wight, and then spread over the south of England. The course of the disease isclearly traced from the south of England toward the midland counties, andall over the island, and into Scotland and Ireland. It was a progressnorthward.... This plant, the _Peronospora infestans_, will only grow onthe _Solanum tuberosum_, that is, the cultivated potato.... Just asplants of higher organization choose their soils, some growing in thewater and some on land, so the _Peronospora infestans_ chooses its hostplant; and its soil is this species, the _Solatium tuberosum_. It willnot grow if it falls on the leaves of the oak or the beech, or on grass, because that is not its soil, so to speak. Now, the process of growth issimply this: When the conidia fall on the leaf, they remain thereperfectly innocent and harmless unless they get a supply of water toenable them to germinate.... The disease makes its appearance in the endof July or the beginning of August, when we have, generally, very hotweather. The temperature of the atmosphere is very high, and we haveheavy showers of rain. "

The warmth and moisture are, in fact, the conditions necessary for thegermination of the conidia. Their contents (zoospores) are liberated, andquickly grow in the leaf, and soon permeate every tissue of the plant. 

It was clearly established before the committee that not all potatoeswere equally liable to the disease. The liability depends upon strengthof constitution. It is well known that potatoes are usually, almostinvariably, propagated by "sets, " that is, by planting tubers, orportions of tubers, and this method of propagation is analogous to thepropagation of other forms of plants by means of "cuttings. " Whenpotatoes are raised from seed, it is found that some of the "seedlings"present a strength of constitution which enables them to resist thedisease for some years, even though the subsequent propagation of theseedling is entirely from "sets. " The raising of seedling potatoes is atedious process, but the patience of the grower is often rewarded bysuccess, and I may allude to the fact that the so-called "Championpotato, " raised from seed in the first instance by Mr. Nicoll, inForfarshire, and since propagated all over the country, has enjoyed, deservedly as it would appear, a great reputation as a disease-resistingpotato; but all who have a practical knowledge of potato growing seemagreed that we cannot expect its disease-resisting quality to last atmost more than twenty years from its first introduction (in 1877), andthat in time the constitution of the "Champion" will deteriorate, and itwill become a prey to disease. 

There is some evidence to show, also, that the constitution of the potatomay be materially influenced by good or bad culture. Damp soils, insufficient or badly selected manures, the selection of ill developedpotatoes for seed, and the overcrowding of the "sets" in the soil, allseem to act as causes which predispose the potatoes to the attacks of theparasite. Strong potatoes resist disease, just as strong children will;while weak potatoes, equally with weak children, are liable to succumb toepidemic influences. 

The following account of some exact experiments carried out by Mr. GeorgeMurray, of the Botanical Department of the British Museum, seems to showthat Mr. Carruthers' theory as to the diffusion of conidia through theair is something more than a speculation:

"In the middle of August, 1876, " says Mr. Murray, "I instituted thefollowing experiments, with the object of determining the mode ofdiffusion of the conidia of _Peronospora infestans_. 

"The method of procedure was to expose on the lee side of a field ofpotatoes, of which only about two per cent, were diseased, ordinarymicroscopic slides, measuring two inches long by one inch broad, coatedon the exposed surface with a thin layer of glycerine, to which objectsalighting would adhere, and in which, if of the nature of conidia, theywould be preserved. These slides were placed on the projecting stones ofa dry stone wall which surrounded the field, and was at least five yardsfrom the nearest potato plant. During the five days and nights of theexperiment, a gentle wind blew, and the weather was, on the whole, dryand clear. Every morning, about nine o'clock, I placed fourteen slides onthe lee side of the field, and every evening, about seven o'clock, Iremoved them, and placed others till the following morning at nineo'clock. The fourteen slides exposed during the day, when examined in theevening, showed (among other objects):

On the first day. 15 conidia. " second day. 17 " " third day. 27 " " fourth day. 4 " " fifth day. 9 "

"On none of the five nights did a single conidium alight on the slides. This seemed to me to prove that during the day the conidia, through thedryness of the atmosphere and the shaking of the leaves, became detatchedand wafted by the air; while during the night the moisture (in the formof dew, and on one occasion of a slight and gently falling shower)prevented the drying of the conidia, and thus rendered them less easy ofdetachment. 

"I determined the nature of the conidia (1) by comparing them withauthentic conidia directly removed from diseased plants; (2) by therebeing attached to some of them portions of the characteristicconidiaphores; and (3) by cultivating them in a moist chamber, the resultof which was, that five conidia, not having been immersed in theglycerine, retained their vitality, which they showed by bursting andproducing zoospores in the manner characteristic of _Peronosporainfestans_. "

INFLUENZA. 

Let us look at another disease by the light of recent knowledge, viz. , the epidemic influenza, concerning which I remember hearing much talk, asa child, in 1847-48. There has been no epidemic of this disease in theBritish Isles since 1847, but we may judge of its serious nature from thecomputation of Peacock that in London alone 250, 000 persons were strickendown with it in the space of a few days. It is characteristic of thisdisease that it invades a whole city, or even a whole country, at "onefell swoop, " resembling in its sudden onset and its extent the potatodisease which we have been considering. 

The mode of its spreading forbids us to attribute it, at least in anymaterial degree, although it may be partially so, to contagion in theordinary sense, i. E. , contagion passing from person to person along thelines of human intercourse. It forbids us also to look at community ofwater supply or food, or the peculiarities of soil, for the source of thedisease virus. We look, naturally, to some atmospheric condition for theexplanation. That the atmosphere is the source of the virus is made morelikely from the fact that the disease has broken out on board ship in aremarkable way. In 1782, there was an epidemic, and on May 2 in thatyear, says Sir Thomas Watson--

"Admiral Kempenfelt sailed from Spithead with a squadron, of which theGoliah was one. The crew of that vessel were attacked with influenza onMay 29, and the rest were at different times affected; and so many of themen were rendered incapable of duty by this prevailing sickness, that thewhole squadron was obliged to return into port about the second week inJune, not having had communication with any port, but having cruisedsolely between Brest and the Lizard. In the beginning of the same monthanother large squadron sailed, all in perfect health, under Lord Howe'scommand, for the Dutch coast. Toward the end of the month, just at thetime, therefore, when the Goliah became full of the disease, it appearedin the Rippon, the Princess Amelia, and other ships of the last mentionedfleet, although there had been no intercourse with the land. "

Similar events were noticed during the epidemic of 1833:

"On April 3, 1833, the very day on which I saw the first two cases that Idid see of influenza--all London being smitten with it on that and thefollowing day--the Stag was coming up the Channel, and arrived at twoo'clock off Berry Head on the coast of Devonshire, all on board being atthat time well. In half an hour afterward, the breeze being easterly andblowing off the land, 40 men were down with the influenza, by six o'clockthe number was increased to 60, and by two o'clock the next day to 160. On the self-same evening a regiment on duty at Portsmouth was in aperfectly healthy state, but by the next morning so many of the soldiersof the regiment were affected by the influenza that the garrison dutycould not be performed by it. "

After reviewing the various hypotheses which had been put forward toaccount for the disease, sudden thaws, fogs, particular winds, swarms ofinsects, electrical conditions, ozone, Sir Thomas Watson goes on to say:

"Another hypothesis, more fanciful perhaps at first sight than these, yetquite as easily accommodated to the known facts of the distemper, attributes it to the presence of innumerable minute substances, endowedwith vegetable or with animal life, and developed in unusual abundanceunder specific states of the atmosphere in which they float, and by whichthey are carried hither and thither. "

This hypothesis has certainly more facts in support of it now than it hadwhen Sir Thomas Watson gave utterance to it in 1837. And when anotherepidemic of influenza occurs, we may look with some confidence to havingthe hypothesis either refuted or confirmed by those engaged in thesystematic study of atmospheric bacteria. Among curious facts inconnection with influenza, quoted by Watson, is the following: "Duringthe raging of one epidemic, 300 women engaged in coal dredging atNewcastle, and wading all day in the sea, escaped the complaint. " Readingthis, the mind naturally turns to Dr. Blackley's glass slide exposed onthe shore at Filey, and upon which no pollen was deposited, while eightypollen grains were deposited on a glass at a higher elevation. 

SMALL-POX. 

Let us next inquire into the evidence regarding the conveyence ofsmall-pox through the air. In the supplement to the Tenth Report of theLocal Government Board for 1880-81 (c. 3, 290) is a report by Mr. W. H. Power on the influence of the Fulham, Hospital (for small-pox) on theneighborhood surrounding it. Mr. Power investigated the incidence ofsmall-pox on the neighborhood, both before and after the establishment ofthe hospital. He found that, in the year included between March, 1876, and March, 1877, before the establishment of the hospital, the incidenceof small-pox on houses in Chelsea, Fulham and Kensington amounted to 0. 41per cent. (i. E. , that one house out of every 244 was attacked bysmall-pox in the ordinary way), and that the area inclosed by a circlehaving a radius of one mile round the spot where the hospital wassubsequently established (called in the report the "special area") was, as a matter of fact, rather more free from small-pox than the rest of thedistrict. After the establishment of the hospital in March, 1877, theamount of small-pox in the "special area" round the hospital very notablyincreased, as is shown by the table by Mr. Power, given below. 

This table shows conclusively that the houses nearest the hospital werein the greatest danger of small-pox. It might naturally be supposed thatthe excessive incidence of the disease upon the houses nearest to thehospital was due to business traffic between the hospital and thedwellers in the neighborhood, and Mr. Power admits that he started on hisinvestigation with this belief, but with the prosecution of his work hefound such a theory untenable. 

ADMISSIONS OF ACUTE SMALL-POX TO FULHAM HOSPITAL, AND INCIDENCE OFSMALL-POX UPON HOUSES IN SEVERAL DIVISIONS OF THE SPECIAL AREA DURINGFIVE EPIDEMIC PERIODS. 

+-------+---------------------+------------------------------------------------+ | | Incidence on every 100 houses within the | | | special area and its divisions. |Cases of|The epidemic periods +--------+---------+---------+---------+---------+acute |since opening |On total|On small |On first |On second|On third |small- |of hospital. |special | circle, | ring, | ring, | ring, |pox. | | area. |0-¼ mile. |¼-½ mile. |½-¾ mile. |¾-1 mile. |--------+---------------------+--------+---------+---------+---------+---------+ 327 |March-December 1877 | 1. 10 | 3. 47 | 1. 37 | 1. 27 | 0. 36 | 714 |January- | | | | | | | September, 1878 | 1. 80 | 4. 62 | 2. 55 | 1. 84 | 0. 67 | 679 |September 1878- | | | | | | | October 1879 | 1. 68 | 4. 40 | 2. 63 | 1. 49 | 0. 64 | 292 |October, 1879- | | | | | | | December, 1880 | 0. 58 | 1. 85 | 1. 06 | 0. 30 | 0. 28 | 515 |December 1880- | | | | | | | April 1881 | 1. 21 | 2. 00 | 1. 54 | 1. 25 | 0. 61 |--------+---------------------+--------+---------+---------+---------+---------+ 2, 527 |Five periods | 6. 37 | 16. 34 | 9. 15 | 6. 15 | 2. 56 |--------+---------------------+--------+---------+---------+---------+---------+

Now, the source of infection in cases of small-pox is often more easy tofind than in cases of some other forms of infectious disease, and mainlyfor two reasons:

1. That the onset of small-pox is usually sudden and striking, such as isnot likely to escape observation. 

2. That the so-called incubative period is very definite and regular, being just a fortnight from infection to eruption. 

The old experiments of inoculation practiced on our forefathers havetaught us that from inoculation to the first appearance of the rash isjust twelve days. Given a case of small-pox, then one has only to gocarefully over the doings and movements of the patient on the days abouta fortnight preceding in order to succeed very often in finding thesource of infection. 

In the fortnight ending February 5, 1881, forty-one houses were attackedby small-pox in the special mile circle round the hospital, and in thislimited outbreak it was found, as previously, that the severity ofincidence bore an exact inverse proportion to the distance from thehospital. 

The greater part of these were attacked in the five days January 26-30, 1881, and in seeking for the source of infection of these cases, specialattention was directed to the time about a fortnight previous viz. , January 12-17, 1881. The comings and goings of all who had been directlyconnected with the hospital (ambulances, visitors, patients, staff, nurses, etc. ) were especially inquired into, but with an almost negativeresult, and Mr. Power was reluctantly forced to the conclusion thatsmall-pox poison had been disseminated through the air. 

During the period when the infection did spread, the atmosphericconditions were such as would be likely to favor the dissemination ofparticulate matter. Mr. Power says: "Familiar illustration of thatconveyance of particulate matter which I am here including in the termdissemination is seen, summer and winter, in the movements of particlesforming mist and fog. The chief of these are, of course, water particles, but these carry gently about with them, in an unaltered form, othermatters that have been suspended in the atmosphere, and these othermatters, during the almost absolute stillness attending the formation ofdew and hoar frost, sink earthward, and may often be recognized aftertheir deposit. 

"As to the capacity of fogs to this end, no Londoner needs instruction;and few persons can have failed to notice the immense distances thatodors will travel on the 'air breaths' of a still summer night. And thereare reasons which require us to believe particulate matter to be moreeasy of suspension in an unchanged form during any remarkable calmness ofatmosphere. Even quite conspicuous objects, such as cobwebs, may be heldup in the air under such conditions. Probably there are few observantpersons of rural habits who cannot call to mind one or another stillautumn morning, when from a cloudless, though perhaps hazy, sky, theyhave noted, over a wide area, steady descent of countless spider webs, many of them well-nigh perfect in all details of their construction. "

A reference to the meteorological returns issued by the registrar-generalshows that on the 12th of January, 1881, began a period of severe frost, characterized by still, sometimes foggy, weather, with occasional lightairs from nearly all points of the compass. This state of affairscontinued till January 18, when there was a notable snow storm, and agale from the E. N. E. For four days, up to and inclusive of January 8, ozone was present in more than its usual amounts. During January 9-16, itwas absent. On January 17 it reappeared, and on January 18 it wasabundant. Similar meteorological conditions (calm and no ozone) werefound to precede previous epidemics. 

Mr. Power's report, with regard to Fulham, seems conclusive, and there isa strong impression that hospitals, other than Fulham, have served ascenters of dissemination. 

In the last lecture I gave you the opinion of M. Bertillon, of Paris, andquoted figures in support of that opinion. It is a fact of someimportance to remember that small-pox is one of those diseases which hasa peculiar odor, recognizable by the expert. As to its conveyance forlong distances through the air, there are some curious facts quoted byProfessor Waterhouse, of Cambridge, Massachusetts, in a letter addressedto Dr. Haygarth at the close of the last century. Professor Waterhousestates that at Boston there was a small-pox hospital on one side of ariver, and opposite it, 1, 500 yards away, was a dockyard, where, on acertain misty, foggy day, with light airs just moving in a direction fromthe hospital to the dockyard, ten men were working. Twelve days later allbut two of these men were down with small-pox, and the only possiblesource of infection was the hospital across the river. (_To becontinued_. )

 * * * * *

SUNLIGHT COLORS. 

[Footnote: Lecture delivered by Capt. W. De W. Abney, R. E. , P. B. S. , atthe Royal Institution, on February 25, 1887. --_Nature_. ]

By Capt. W. DE W. ABNEY. 

Sunlight is so intimately woven up with our physical enjoyment of lifethat it is perhaps not the most uninteresting subject that can be chosenfor what is--perhaps somewhat pedantically--termed a Friday evening"discourse. " Now, no discourse ought to be be possible without a text onwhich to hang one's words, and I think I found a suitable one whenwalking with an artist friend from South Kensington Museum the other day. The sun appeared like a red disk through one of those fogs which the eastwind had brought, and I happened to point it out to him. He looked, andsaid, "Why is it that the sun appears so red?" Being near the railwaystation, whither he was bound, I had no time to enter into the subject, but said if he would come to the Royal Institution this evening I wouldendeavor to explain the matter. I am going to redeem that promise, and todevote at all events a portion of the time allotted to me in answeringthe question why the sun appears red in a fog. I must first of all appealto what every one who frequents this theater is so accustomed, viz. , thespectrum. I am going not to put it in the large and splendid stripe ofthe most gorgeous colors before you, with which you are so wellacquainted, but my spectrum will take a more modest form of purer colors, some twelve inches in length. 

I would ask you to notice which color is most luminous. I think that noone will dispute that in the yellow we have the most intense luminosity, and that it fades gradually in the red on the one side and in the violeton the other. This, then, may be called a qualitative estimate ofrelative brightnesses; but I wish now to introduce to you what was novellast year, a quantitative method of measuring the brightness of any part. 

Before doing this I must show you the diagram of the apparatus which Ishall employ in some of my experiments. 

[Illustration: FIG. 1. --COLOR PHOTOMETER. ]

RR are rays (Fig. I) coming from the arc light, or, if we were usingsunlight, from a heliostat, and a solar image is formed by a lens, L_{1}, on the slit, S_{1} of the collimator, C. The parallel rays produced bythe lens, L_{2}, are partially refracted and partially reflected. Theformer pass through the prisms, P_{1}P_{2}, and are focused to form aspectrum by a lens, L_{3}, on D, a movable ground glass screen. The raysare collected by a lens, L_{4}, tilted at an angle as shown, to form awhite image of the near surface of the second prism on F. 

Passing a card with a narrow slit, S_{2}, cut in it in front of thespectrum, any color which I may require can be isolated. The consequenceis that, instead of the white patch upon the screen, I have a coloredpatch, the color of which I can alter to any hue lying between the redand the violet. Thus, then, we are able to get a real patch of veryapproximately homogeneous light to work with, and it is with thesepatches of color that I shall have to deal. Is there any way of measuringthe brightness of these patches? was a question asked by General Festingand myself. After trying various plans, we hit upon the method I shallnow show you, and if any one works with it he must become fascinated withit on account of its almost childish simplicity--a simplicity, I mayremark, which it took us some months to find out. Placing a rod beforethe screen, it casts a black shadow surrounded with a colored background. Now I may cast another shadow from a candle or an incandescence lamp, andthe two shadows are illuminated, one by the light of the colored patchand the other by the light from an incandescence lamp which I am usingtonight. [Shown. ] Now one stripe is evidently too dark. By an arrangementwhich I have of altering the resistance interposed between the batteryand the lamp, I can diminish or increase the light from the lamp, firstmaking the shadow it illuminates too light and then too dark comparedwith the other shadow, which is illuminated by the colored light. Evidently there is some position in which the shadows are equallyluminous. When that point is reached, I can read off the current which ispassing through the lamp, and having previously standardized it for eachincrement of current, I know what amount of light is given out. Thisvalue of the incandescence lamp I can use as an ordinate to a curve, thescale number which marks the position of the color in the spectrum beingthe abscissa. This can be done for each part of the spectrum, and so acomplete curve can be constructed, which we call the illumination curveof the spectrum of the light under consideration. 

Now, when we are working in the laboratory with a steady light, we may beat ease with this method, but when we come to working with light such asthe sun, in which there may be constant variation, owing to passing, andmay be usually imperceptible, mist, we are met with a difficulty; and inorder to avoid this, General Festing and myself substituted anothermethod, which I will now show you. We made the comparison light part ofthe light we were measuring. Light which enters the collimating lenspartly passes through the prisms and is partly reflected from the firstsurface of the prism; that we utilize, thus giving a second shadow. Thereflected rays from P_{1} fall on G, a silver on glass mirror. They arecollected by L_{5}, and form a white image of the prism also at F. 

The method we can adopt of altering the intensity of the comparison lightis by means of rotating sectors, which can be opened or closed at will, and the two shadows thus made equally luminous. [Shown. ] But althoughthis is an excellent plan for some purposes, we have found it better toadopt a different method. You will recollect that the brightest part ofthe spectrum is in the yellow, and that it falls off in brightness oneach side, so instead of opening and closing the sectors, they are set atfixed intervals, and the slit is moved in front of the spectrum, justmaking the shadow cast by the reflected beam too dark or too light, andoscillating between the two till equality is discovered. The scale numberis then noted, and the curve constructed as before. It must be rememberedthat, on each side of the yellow, equality can be established. 

This method of securing a comparison light is very much better for sunwork than any other, as any variation in the light whose spectrum is tobe measured affects the comparison light in the same degree. Thus, suppose I interpose an artificial cloud before the slit of thespectroscope, having adjusted the two shadows, it will be seen that thepassage of steam in front of the slit does not alter the relativeintensities; but this result must be received with caution. [The lecturerthen proceeded to point out the contrast colors that the shadow of therod illuminated by white light assumed. ]

I must now make a digression. It must not be assumed that every one hasthe same sense of color, otherwise there would be no color blindness. Part of the researches of General Festing and myself have been on thesubject of color blindness, and these I must briefly refer to. We testall who come by making them match the luminosity of colors with whitelight, as I have now shown you. And as a color blind person has only twofundamental color perceptions instead of three, his matching ofluminosities is even more accurate than is that made by those whose eyesare normal or nearly normal. It is curious to note how many people aremore or less deficient in color perception. Some have remarked that it isimpossible that they were color blind and would not believe it, andsometimes we have been staggered at first with the remarkable manner inwhich they recognized color to which they ultimately proved deficient inperception. For instance, one gentleman when I asked him the name of ared color patch, said it was sunset color. He then named green and bluecorrectly, but when I reverted to the red patch he said green. 

On testing further, he proved totally deficient in the color perceptionof red, and with a brilliant red patch he matched almost a black shadow. The diagram shows you the relative perceptions in the spectrum of thisgentleman and myself. There are others who only see three-quarters, others half, and others a quarter the amount of red that we see, whilesome see none. Others see less green and others less violet, but I havemet with no one that can see more than myself or General Festing, whosecolor perceptions are almost identical. Hence we have called our curve ofillumination the "normal curve. "

We have tested several eminent artists in this manner, and about one halfof the number have been proved to see only three quarters of the amountof red which we see. It might be thought that this would vitiate theirpowers of matching color, but it is not so. They paint what they see; andalthough they see less red in a subject, they see the same deficiency intheir pigments; hence they are correct. If totally deficient, the case ofcourse would be different. 

Let us carry our experiments a step further, and see what effect what isknown as a turbid medium has upon the illuminating value of differentparts of the spectrum. I have here water which has been rendered turbidin a very simple manner. In it has been very cautiously dropped analcoholic solution of mastic. Now mastic is practically insoluble inwater, and directly the alcoholic solution comes in contact with thewater it separates out in very fine particles, which, from their veryfineness, remain suspended in the water. I propose now to make anexperiment with this turbid water. 

I place a glass cell containing water in front of the slit, and on thescreen I throw a patch of blue light. I now change it for turbid water ina cell. This thickness much dims the blue; with a still greater thicknessthe blue has almost gone. If I measure the intensity of the light at eachoperation, I shall find that it diminishes according to a certain law, which is of the same nature as the law of absorption. For instance, ifone inch diminishes the light one half, the next will diminish it half ofthat again, the next half of that again, while the fourth inch will causea final diminution of the total light of one sixteenth. If the first inchallows only one quarter of the light, the next will only allow onesixteenth, and the fourth inch will only permit 1/256 part to pass. 

Let us, however, take a red patch of light and examine it in the sameway. We shall find that, when the greater thickness of the turbid mediumwe used when examining the blue patch of light is placed in front of theslit, much more of this light is allowed to pass than of the blue. If wemeasure the light, we shall find that the same law holds good as before, but that the proportion which passes is invariably greater with the redthan the blue. The question then presents itself: Is there any connectionbetween the amounts of the red and the blue which pass?

Lord Rayleigh, some years ago, made a theoretical investigation of thesubject. But, as far as I am aware, no definite experimental proof of thetruth of the theory was made till it was tested last year by GeneralFesting and myself. His law was that for any ray, and through the samethickness, the light transmitted varied inversely as the fourth power ofthe wave length. The wave length 6, 000 lies in the red, and the wavelength 4, 000 in the violet. Now 6, 000 is to 4, 000 as 3 to 2, and thefourth powers of these wave lengths are as 81 to 16, or as about 5 to 1. If, then, the four inches of our turbid medium allowed three quarters ofthis particular red ray to be transmitted, they would only allow (¾)^{5}, or rather less than one fourth, of the blue ray to pass. 

Now, this law is not like the law of absorption for ordinary absorbingmedia, such as colored glass for instance, because here we have anincreased loss of light running from the red to the blue, and it mattersnot how the medium is made turbid, whether by varnish, suspended sulphur, or what not. It holds in every case, so long as the particles which makethe medium turbid are small enough. And please to recollect that itmatters not in the least whether the medium which is rendered turbid issolid, liquid, or air. Sulphur is yellow in mass, and mastic varnish isnearly white, while tobacco smoke when condensed is black, and veryminute particles of water are colorless; it matters not what the coloris, the loss of light is _always_ the same. The result is simply due tothe scattering of light by fine particles, such particles being small indimensions compared with a wave of light. Now, in this trough issuspended 1/1000 of a cubic inch of mastic varnish, and the water in itmeasures about 100 cubic inches, or is 100, 000 times more in bulk thanthe varnish. Under a microscope of ordinary power it is impossible todistinguish any particles of varnish; it looks like a homogeneous fluid, though we know that mastic will not dissolve in water. 

Now a wave length in the red is about 1/40000 of an inch, and a littlecalculation will show that these particles are well within the necessarylimits. Prof. Tyndall has delighted audiences here with an exposition ofthe effect of the scattering of light by small particles in the formationof artificial skies, and it would be superfluous for me to enter moreinto that. Suffice it to say that when particles are small enough to formthe artificial blue sky, they are fully small enough to obey the abovelaw, and that even larger particles will suffice. We may sum up by sayingthat very fine particles scatter more blue light than red light, and thatconsequently more red light than blue light passes through a turbidmedium, and that the rays obey the law prescribed by theory. 

I will exemplify this once more by using the whole spectrum and placingthis cell, which contains hyposulphite of soda in solution in water, infront of the slit. By dropping in hydrochloric acid, the sulphurseparates out in minute particles; and you will see that, as theparticles increase in number, the violet, blue, green, and yellowdisappear one by one and only red is left, and finally the red disappearsitself. 

Now let me revert to the question why the sun is red at sunset. Those whoare lovers of landscape will have often seen on some bright summer's daythat the most beautiful effects are those in which the distance is almostof a match to the sky. Distant hills, which when viewed close to aregreen or brown, when seen some five or ten miles away appear of adelicate and delicious, almost of a cobalt, blue color. Now, what is thecause of this change in color? It is simply that we have a sky formedbetween us and the distant ranges, the mere outline of which loomsthrough it. The shadows are softened so as almost to leave no trace, andwe have what artists call an atmospheric effect. If we go into anotherclimate, such as Egypt or among the high Alps, we usually lose thiseffect. Distant mountains stand out crisp with black shadows, and thewant of atmosphere is much felt. [Photographs showing these differenceswere shown. ] Let us ask to what this is due. In such climates as Englandthere is always a certain amount of moisture present in the atmosphere, and this moisture may be present as very minute particles of water--sominute indeed that they will sink down in an atmosphere of normaldensity--or as vapor. When present as vapor the air is much moretransparent, and it is a common expression to use, that when distanthills look "so close" rain may be expected shortly to follow, since thewater is present in a state to precipitate in larger particles. But whenpresent as small particles of water the hills look very distant, owing towhat we may call the haze between us and them. In recent weeks every onehas been able to see very multiplied effects of such haze. The ends oflong streets, for instance, have been scarcely visible, though the sunmay have been shining, and at night the long vistas of gas lamps haveshown light having an increasing redness as they became more distant. Every one admits the presence of mist on these occasions, and this mistmust be merely a collection of intangible and very minute particles ofsuspended water. In a distant landscape we have simply the same or asmaller quantity of street mist occupying, instead of perhaps 1, 000yards, ten times that distance. Now I would ask, What effect would such amist have upon the light of the sun which shone through it?

It is not in the bounds of present possibility to get outside ouratmosphere and measure by the plan I have described to you the differentilluminating values of the different rays, but this we can do: First, wecan measure these values at different altitudes of the sun, and thismeans measuring the effect on each ray after passing through differentthicknesses of the atmosphere, either at different times of day or atdifferent times of the year, about the same hour. Second, by taking theinstrument up to some such elevation as that to which Langley took hisbolometer at Mount Whitney, and so to leave the densest part of theatmosphere below us. 

[Illustration: FIG. 2. --RELATIVE LUMINOSITIES. ]

Now, I have adopted both these plans. For more than a year I have takenmeasurements of sunlight in my laboratory at South Kensington, and I havealso taken the instrument up to 8, 000 feet high in the Alps, and madeobservations _there_, and with a result which is satisfactory in thatboth sets of observations show that the law which holds with artificiallyturbid media is under ordinary circumstances obeyed by sunlight inpassing through our air: which is, you will remember, that more of thered is transmitted than of the violet, the amount of each depending onthe wave length. The luminosity of the spectrum observed at the Riffel Ihave used as my standard luminosity, and compared all others with it. Theresult for four days you see in the diagram. 

I have diagrammatically shown the amount of different colors whichpenetrated on the same days, taking the Riffel as ten. It will be seenthat on December 23 we have really very little violet and less than halfthe green, although we have four fifths of the red. 

The next diagram before you shows the minimum loss of light which I haveobserved for different air thicknesses. On the top we have the calculatedintensities of the different rays outside our atmosphere. Thus we havethat through one atmosphere, and two, three, and four. And you will seewhat enormous absorption there is in the blue end at four atmospheres. The areas of these curves, which give the total luminosity of the light, are 761, 662, 577, 503, and 439; and if observed as astronomers observethe absorption of light, by means of stellar observations, they wouldhave had the values, 761, 664, 578, 504, and 439--a very closeapproximation one to the other. 

Next notice in the diagram that the top of the curve gradually inclinesto go to the red end of the spectrum as you get the light transmittedthrough more and more air, and I should like to show you that this is thecase in a laboratory experiment. Taking a slide with a wide and long slotin it, a portion is occupied by a right angled prism, one of the anglesof 45° being toward the center of the slot. By sliding this prism infront of the spectrum I can deflect outward any portion of the spectrum Ilike, and by a mirror can reflect it through a second lens, forming apatch of light on the screen overlapping the patch of light formed by theundeflected rays. If the two patches be exactly equal, white light isformed. Now, by placing a rod as before in front of the patch, I have twocolored stripes in a white field, and though the background remains ofthe same intensity of white, the intensities of the two stripes can bealtered by moving the right angled prism through the spectrum. The twostripes are now apparently equally luminous, and I see the point ofequality is where the edge of the right angled prism is in the green. Placing a narrow cell filled with our turbid medium in front of the slit, I find that the equality is disturbed, and I have to allow more of theyellow to come into the patch formed by the blue end of the spectrum, andconsequently less of it in the red end. I again establish equality. Placing a thicker cell in front, equality is again disturbed, and I haveto have less yellow still in the red half, and more in the blue half. Inow remove the cell, and the inequality of luminosity is still moreglaring. This shows, then, that the rays of maximum luminosity musttravel toward the red as the thickness of the turbid medium is increased. 

The observations at 8, 000 feet, here recorded, were taken on September15, at noon, and of course in latitude 46° the sun could not be overhead, but had to traverse what would be almost exactly equivalent to theatmosphere at sea level. It is much nearer the calculated intensity forno atmosphere intervening than it is for one atmosphere. The explanationof this is easy. The air is denser at sea level than at 8, 000 feet up, and the lower stratum is more likely to hold small water particles ordust in suspension than is the higher. 

[Illustration: FIG. 3. --PROPORTIONS OF TRANSMITTED COLORS. ]

For, however small the particles may be, they will have a greatertendency to sink in a rare air than in a denser one, and less water vaporcan be held per cubic foot. Looking, then, from my laboratory at SouthKensington, we have to look through a proportionately larger quantity ofsuspended particles than we have at a high altitude when the airthicknesses are the same. And consequently the absorption isproportionately greater at sea level that at 8, 000 feet high. This leadsus to the fact that the real intensity of illumination of the differentrays outside the atmosphere is greater than it is calculated fromobservations near sea level. Prof. Langley, in this theater, in aremarkable and interesting lecture, in which he described his journey upMount Whitney to about 12, 000 feet, told us that the sun was really blueoutside our atmosphere, and at first blush the amount of extra blue whichhe deduced to be present in it would, he thought, make it so. But thoughhe surmised the result from experiments made with rotating disks ofcolored paper, he did not, I think, try the method of using pure colors, and consequently, I believe, slightly exaggerated the blueness whichwould result. 

I have taken Prof. Langley's calculations of the increase of intensityfor the different rays, which I may say do not quite agree with mine, andI have prepared a mask which I can place in the spectrum, giving thedifferent proportions of each ray as calculated by him, and this whenplaced in front of the spectrum will show you that the real color ofsunlight outside the atmosphere, as calculated by Langley, can scarcelybe called bluish. Alongside I place a patch of light which is veryclosely the color of sunlight on a July day at noon in England. Thiscomparison will enable you to gauge the blueness, and you will see thatit is not very blue, and, in fact, not bluer perceptibly than that wehave at the Riffel, the color of the sunlight at which place I show in asimilar way. I have also prepared some screens to show you the value ofsunlight after passing through five and ten atmospheres. On an ordinaryclear day you will see what a yellowness there is in the color. It seemsthat after a certain amount of blue is present in white light, theaddition of more makes but little difference in the tint. But these lastpatches show that the light which passes through the atmosphere when itis feebly charged with particles does not induce the red of the sun asseen through a fog. It only requires more suspended particles in anythickness to induce it. 

In observations made at the Riffel, and at 14, 000 feet, I have found thatit is possible to see far into the ultra-violet, and to distinguish andmeasure lines in the sun's spectrum which can ordinarily only be seen bythe aid of a fluorescent eye piece or by means of photography. Circumstantial evidence tends to show that the burning of the skin, whichalways takes place in these high altitudes in sunlight, is due to thegreat increase in the ultra-violet rays. It may be remarked that the samekind of burning is effected by the electric arc light, which is known tobe very rich in these rays. 

Again, to use a homely phrase, "You cannot eat your cake and have it. "You cannot have a large quantity of blue rays present in your directsunlight and have a luminous blue sky. The latter must always be lightscattered from the former. Now, in the high Alps you have, on clear day, a deep blue-black sky, very different indeed from the blue sky of Italyor of England; and as it is the sky which is the chief agent in lightingup the shadows, not only in those regions do we have dark shadows onaccount of no intervening--what I will call--mist, but because the skyitself is so little luminous. In an artistic point of view this isimportant. The warmth of an English landscape in sunlight is due to thehighest lights being yellowish, and to the shadows being bluish from thesky light illuminating them. In the high Alps the high lights are colder, being bluer, and the shadows are dark, and chiefly illuminated byreflected direct sunlight. Those who have traveled abroad will know whatthe effect is. A painting in the Alps, at any high elevation, is rarelypleasing, although it may be true to nature. It looks cold, and somewhatharsh and blue. 

In London we are often favored with easterly winds, and these, unpleasantin other ways, are also destructive of that portion of the sunlight whichis the most chemically active on living organisms. The sunlightcomposition of a July day may, by the prevalence of an easterly wind, bereduced to that of a November day, as I have proved by actualmeasurement. In this case it is not the water particles which act asscatterers, but the carbon particles from the smoke. 

Knowing, then, the cause of the change in the color of sunlight, we canmake an artificial sunset, in which we have an imitation light passingthrough increasing thicknesses of air largely charged with waterparticles. [The image of a circular diaphragm placed in front of theelectric light was thrown on the screen in imitation of the sun, and acell containing hyposulphite of soda placed in the beam. Hydrochloricacid was then added; as the fine particles of sulphur were formed, thedisk of light assumed a yellow tint, and as the decomposition of thehyposulphite progressed, it assumed an orange and finally a deep redtint. ] With this experiment I terminate my lecture, hoping that in somedegree I have answered the question I propounded at the outset--why thesun is red when seen through a fog. 

 * * * * *

THE WAVE THEORY OF SOUND CONSIDERED. 

By HENRY. A. MOTT, Ph. D. , LL. D. 

Before presenting any of the numerous difficulties in the way ofaccepting the wave theory of sound as correct, it will be best to brieflyrepresent its teachings, so that the reader will see that the writer isperfectly familiar with the same. 

The wave theory of sound starts off with the assumption that theatmosphere is _composed of molecules_, and that these supposed moleculesare free to vibrate when acted upon by a vibrating body. When a tuningfork, for example, is caused to vibrate, it is _assumed_ that thesupposed molecules in front of the advancing fork are crowded closelytogether, thus forming a condensation, and on the retreat of the fork areseparated more widely apart, thus forming a rarefaction. On account ofthe crowding of the molecules together to form the condensation, the airis supposed to become more dense and of a higher temperature, while inthe rarefaction the air is supposed to become less dense and of lowertemperature; but the heat of the condensation is supposed to just satisfythe cold of the rarefaction, in consequence of which the averagetemperature of the air remains unchanged. 

The supposed increase of temperature in the condensation is supposed tofacilitate the transference of the sound pulse, in consequence of which, sound is able to travel at the rate of 1, 095 feet a second at 0°C. , whichit would not do if there was no heat generated. 

In other words, the supposed increase of temperature is supposed to add1/6 to the velocity of sound. 

If the tuning fork be a _Koenig C^{3}_ fork, which makes 256 _full_vibrations in one second, then there will be 256 sound waves in onesecond of a length of 1095/256 or 4. 23 feet, so that at the end of asecond of time from the commencement of the vibration, the foremost wavewould have reached a distance of 1, 095 feet, at 0°C. 

The motion of a sound wave must not, however, be confounded with themotion of the molecules which at any moment form the wave; for during itspassage every molecule concerned in its transference makes only a smallexcursion to and fro, the length of the excursion being the amplitude ofvibration, on which the intensity of the sound depends. 

Taking the same tuning fork mentioned above, the molecule would take1/256 of a second to make a full vibration, which is the length of timeit takes for the pulse to travel the length of the sound wave. 

For different intensities, the amplitude of vibration of the molecule isroughly 1/50 to 1/1000000 of an inch. That is to say, in the case of thesame tuning fork, the molecules it causes to vibrate must either travel adistance of 1/56 or 1/1000000 of an inch forward and back in the 1/256 ofa second or in one direction in the 1/512 of a second. 

I might further state that the pitch of the sound depends on the numberof vibrations and the intensity, as already indicated by the amplitude ofstroke--the timbre or quality of the sound depending upon factors whichwill be clearly set forth as we advance. 

Having now clearly and correctly represented the wave theory of sound, without touching the physiological effect perceived by means of the ear, we will proceed to consider it. 

We must first consider the state in which the supposed molecules existin the air, before making progress. 

The present science teaches that the diameter of the supposed moleculesof the air is about 1/250000000 of an inch (Tait); that the distancebetween the molecules is about 8/100000 of an inch; that the velocity ofthe molecules is about 1, 512 feet a second at 0°C. , in its free path;that the number of molecules in a cubic inch at 0°C. Is3, 505, 519, 800, 000, 000, 000 or 35 followed by 17 ciphers (35)^{17}; andthat the number of collisions per second that the molecules make is, according to Boltzmann, for hydrogen, 17, 700, 000, 000, that is to say, ahydrogen molecule in one second has its course wholly changed overseventeen billion times. Assuming seventeen billion or million to beright for the supposed air molecules, we have a very interesting problemto consider. 

The wave theory of sound requires, if we expect to hear sound by means ofa C^{3} fork of 256 vibrations, that the molecules of the air composingthe sound wave must not be interfered with in such a way as to preventthem from traveling a distance of at least 1/50 to 1/1000000 of an inchforward and back in the 1/256 of a second. The problem we have to explainis, how a molecule traveling at the rate of 1, 512 feet a second through amean path of 8/100000 of an inch, and colliding seventeen billion ormillion times a second, can, by the vibration of the C^{3} fork, be madeto vibrate so as to have a pendulous motion for 1/256 of a second andvibrate through a distance of 1/50 to the 1/1000000 of an inch withoutbeing changed or mar its harmonic motion. 

It is claimed that the range of sound lies between 16 vibrations and30, 000 (about); in such extreme cases the molecules would require 1/16and 1/30000 of a second to perform the same journey. 

It must not be forgotten that a mass moving through a given distance hasthe power of doing work, and the amount of energy it will exercise willdepend on _its_ velocity. Now, a molecule of oxygen or nitrogen, according to modern science, is a _mass_ 1/250000000 of an inch indiameter, and an oxygen molecule has been calculated to weigh0. 0000000054044 ounce. Taking this weight traveling with a velocity of1, 512 feet a second through an average distance of 8/100000 of an inch, the battering power or momentum it would have can be shown to be in roundnumbers capable of moving 1/200000 of an ounce. 

Now, when the C^{3} tuning fork has been vibrating for some time, butstill sounding audibly, Prof. Carter determined that its amplitude ofstroke was only the 1/17000 of an inch, or its velocity of motion was atthe rate of 1/33 of an inch in one second, or one inch in 33 seconds(over half a minute), or less than one foot in one hour. 

Assuming one prong to weigh two ounces, we have a two-ounce mass moving1/17000 of an inch with a velocity of 1/33 of an inch in one second. Theprong, then, has a momentum or can exercise an amount of energyequivalent to 1/200 of an ounce, or can overcome the momentum of 1, 000molecules. 

It would be difficult to discover not only how a locust can expendsufficient energy to impart to molecules of the air, so as to set them ina _forced_ vibration, and thus enable a pulse of the energy imparted tocontrol the motion of the supposed molecules of the air for a mile in alldirections, but also to estimate the amount of energy the locust mustexpend. 

According to the wave theory, a condensation and rarefaction arenecessary to constitute a sound wave. Surely, if a condensation is notproduced, there can be no sound wave! We have then no need to consideranything but the condensation or compression of the supposed airmolecules, which will shorten the discussion. The property of mobility ofthe air and fluidity of water are well known. In the case of water, whichis almost incompressible, this property is well marked, andunquestionably would be very nearly the same if water were whollyincompressible. In the case of the air, it is conceded by Tyndall, Thomson, Daniell, Helmholtz, and others that any compression orcondensation of the air must be well marked or defined to secure thetransmission of a sound pulse. The reason for this is on account of thisvery property of mobility. Tyndall says: "The prong of the fork in itsswift advancement condenses the air. " Thomson says: "If I move my handvehemently through the air, I produce a condensation. " Helmholtz says:"The pendulum swings from right to left with a uniform motion. Near toeither end of its path it moves slowly, and in the middle fast. Amongsonorous bodies which move in the same way, only very much faster, we maymention tuning forks. " Tyndall says again: "When a common pendulumoscillates, it tends to form a condensation in front and a rarefactionbehind. But it is only a tendency; the motion is so slow, and the air soelastic, that it moves away in front before it is sensibly condensed, andfills the space behind before it can become sensibly dilated. Hence wavesor pulses are not generated by the pendulum. " And finally, Daniell says:"A vibrating body, _before it can act_ as a sounding body, must producealternate compressions and rarefactions in the air, and these must bewell marked. If, however, the vibrating body be so small that at eachoscillation the surrounding air has time to _flow round_ it, there is atevery oscillation a local rearrangement--a local flow and reflow of theair; but the air at a distance is almost wholly unaffected by this. "

Now, as Prof. Carter has shown by experiment that a tuning fork _whilestill sounding_ had only an amplitude of swing of 1/17000 of an inch, andonly traveled an aggregate distance of 1/33 of an inch in one second, orone inch in 33 seconds, surely such a motion is neither "swift, " "fast, "nor "vehement, " and is unquestionably much "slower" than the motion of apendulum. We have only to consider one forward motion of the prong, andif that motion cannot condense the air, then no wave can be produced; forafter a prong has advanced and stopped moving (no matter for how short atime), if it has not compressed the air, its return motion (on the sameside) cannot do anything toward making a compression. If one such motionof 1/17000 of an inch in 1/512 of a second cannot compress the air, thenthe remaining motions cannot. There is unquestionably a "union limit"between mobility and compressibility, and unless this limit is passed, mobility holds sway and prevents condensation or compression of the air;but when this limit is passed by the exercise of sufficient energy, thencompression of the air results. Just imagine the finger to be movedthrough the air at a velocity of one foot in one hour; is it possiblethat any scientist who considers the problem in connection with themobility of the air, could risk his reputation by saying that the airwould be compressed? Heretofore it was supposed that a praeong of a tuningfork was traveling _fast_ because it vibrated so many times in a second, never stopping to think that its velocity of motion was entirelydependent upon the distance it traveled. At the start the prong travels1/20 of an inch, but in a short time, _while still sounding_, thedistance is reduced to 1/17000 of an inch. While the first motion wasquite fast, about 25 inches in a second, the last motion was only about1/33 of an inch in the same time, and is consequently 825 times slowermotion. The momentum of the prong, the amount of work it can do, islikewise proportionately reduced. 

Some seem to imagine, without thinking, that the elasticity of the aircan add additional energy. This is perfectly erroneous; for elasticity isa mere property, which permits a body to be compressed on the applicationof a force, and to be dilated by the exercise of the force stored up init by the compression. No property of the air can impart any energy. Ifthe momentum of a molecule or a series of molecules extending in alldirections for a mile is to be overcome so as to control the character ofthe movements of the molecules, then sufficient _external_ energy must beapplied to accomplish the task: and when we think that one cubic inch ofair contains 3, 505, 519, 800, 000, 000, 000 molecules, to say nothing aboutthe number in a cubic mile, which a locust can transmit sound through, weare naturally compelled to stop and think whether the vibrations of_supposed_ molecules have anything or can have anything to do with thetransference of sound through the air. 

If control was only had of the distance the vibrating molecule travelsfrom its start to the end of its journey, then only the intensity of thesound would be under subjection; but if at every _infinitesimal instant_control was had of its amplitude of swing, then the character, timbre, orquality of the sound is under subjection. It is evident, then, that theblows normally given by one molecule to another in their supposedconstant bombardment must not be sufficient to alter the character ofvibration a molecule set in oscillation by a sounding body must maintain, to preserve the timbre or quality of the sound in process oftransmission; for if any such alteration should take place, then, naturally, while the pitch, and perhaps intensity, might be transmitted, the quality of the sound would be destroyed. 

Again, it is certain that no molecule can perform two sets of vibrations, two separate movements, at the same time, any more than it can be in twoplaces at the same time. 

When a band of music is playing, the molecule is supposed to make acomplex vibration, a resultant motion of all acting influences, which theear is supposed to analyze. It remains for the mathematician to show howa molecule influenced by twenty or more degrees of applied energy, andtwenty or more required number of frequences of vibration at the sametime, can establish a resultant motion which will transmit the requiredpitch, intensity, and timbre of each instrument. 

When a molecule is acted on by various forces, a resultant motion isunquestionably produced, but this would only tend to send the moleculeforward and back in _one_ direction, and, in fact, a direction it mighthave taken in the first place if hit properly. 

How any resultant can be established as regards the time necessary forthe molecule to take so as to complete a full vibration for the noteC_{11}, which requires 1/16 of a second, and for other notes up toC''''', which only requires 1/4176 of a second, as when an orchestra isplaying, is certainly beyond human comprehension, if it is not beyond the"transcendental mathematics" of the present day. 

Unquestionably, the able mathematicians Lord Rayleigh, Stokes, orMaxwell, if the problem was submitted to them, would start directly towork, and deduce by so called "higher mathematics" the required motionsthe molecules would have to undergo to accomplish this marveloustask--the same as they have established the diameter of the _supposed_molecules, their velocity, distance apart, and number of bombardments, without any shadow of _positive_ proof that any such things as moleculesexist. 

As S. Caunizzana has said: "Some of the followers of the modern schoolpush their faith to the borders of fanaticism; they often speak onmolecular subjects with as much dogmatic assurance as though they hadactually realized the ingenious fiction of Laplace, and had constructed amicroscope by which they could detect the molecule and count the numberof its constituent atoms. "

Speaking of the "modern manufacturers of mathematical hypotheses, "Mattieu Williams says: "It matters not to them how 'wild and visionary, 'how utterly gratuitous, any assumption may be, it is not unscientificprovided it can be vested in formulae and worked out mathematically. 

"These transcendental mathematicians are struggling to carry philosophyback to the era of Duns Scotus, when the greatest triumph of learning wasto sophisticate so profoundly an obvious absurdity that no ordinaryintellect could refute it.... The close study of _pure_ mathematics, bydirecting the mind to processes of calculation rather than to phenomena, induces that sublime indifference to facts which has characterized thepurely mathematical intellect of all ages. "

Tyndall, however, states in all frankness, and without the aid ofmathematical considerations, that "when we try to visualize the motionsof the air having one thousand separate tones, to present to the eye ofthe mind the battling of the pulses, direct and reverberated, theimagination retires baffled at the attempt;" and he might have added, theshallowness and fallacy of the wave theory of sound was made apparent. He, however, does express himself as follows: "Assuredly, no question ofscience ever stood so much in need of revision as this of thetransmission of sound through the atmosphere. Slowly but surely wemastered the question, and the further we advance, the more plainly itappeared that our reputed knowledge regarding it was erroneous frombeginning to end. "

Until physicists are willing to admit that the physical forces of natureare objective things--actual entities, and not mere modes of motion--afull and clear comprehension of the phenomena of nature will never berevealed to them. The motion of all bodies, whether small or great, isdue to the entitative force stored up in them, and the energy theyexercise is in proportion to the stored-up force. 

Tyndall says that "_heat itself_, its _essence and quiddity_, IS MOTION, AND NOTHING ELSE. " Surely, no scientist who considers what motion is canadmit such a fallacious statement, for motion is simply "position inspace changing;" it is a phenomenon, the result of the application ofentitative force to a body. It is no more an entity than shadow, which islikewise a phenomenon. Motion, _per se_, is nothing and can do nothing inphysics. Matter and force are the two great entities of theuniverse--both being objective things. Sound, heat, light, electricity, etc. , are different forms of manifestation of an all-pervading forceelement--substantial, yet not material. 

 * * * * *

[NATURE. ]

THE RELATION OF TABASHEER TO MINERAL SUBSTANCES. 

Mr. Thiselton Dyer has rendered a great service, not only to botanists, but also to physicists and mineralogists, by recalling attention to thevery interesting substance known as "tabasheer. " As he truly states, verylittle fresh information has been published on the subject during recentyears, a circumstance for which I can only account by the fact thatbotanists may justly feel some doubt as to whether it belongs to thevegetable kingdom, while mineralogists seem to have equal ground forhesitation in accepting it as a member of the mineral kingdom. 

It is very interesting to hear that so able a physiologist as Prof. Cohnintends to investigate the conditions under which living plants separatethis substance from their tissues. That unicellular algae, like theDiatomaceae, living in a medium which may contain only one part in 10, 000by weight of dissolved silica, or even less than that amount, should beable to separate this substance to form their exquisitely ornamentedfrustules is one of the most striking facts in natural history, whetherwe regard it in its physiological or its chemical aspects. 

Sir David Brewster long ago pointed out the remarkable physicalcharacters presented by the curious product of the vegetable world knownas "tabasheer, " though so far as I can find out it has not in recentyears received that attention from physicists which the experiments andobservations of the great Scotch philosopher show it to be worthy of. 

Tabasheer seems to stand in the same relation to the mineral kingdom asdo ambers and pearls. It is in fact an _opal_ formed under somewhatremarkable and anomalous conditions which we are able to study; and inthis aspect I have for some time past been devoting a considerable amountof attention to the minute structure of the substance by making thinsections and examining them under the microscope. It may be as well, perhaps, to give a short sketch of the information upon the subject whichI have up to the present time been able to obtain, and in this way tocall attention to points upon which further research seems to benecessary. 

From time immemorial tabasheer has enjoyed a very high reputation inEastern countries as a drug. Its supposed medicinal virtues, like thoseof the fossil teeth of China and the belemnites ("thunderbolts") of thiscountry, seem to have been suggested by the peculiarity of its mode ofoccurrence. A knowledge of the substance was introduced into WesternEurope by the Arabian physicians, and the name by which the substance isgenerally known is said to be of Arabic origin. Much of the materialwhich under the name of "tabasheer" finds its way to Syria and Turkey issaid, however, to be fictitious or adulterated. 

In 1788 Dr. Patrick Russell, F. R. S. , then resident at Vizagapatam, wrotea letter to Sir Joseph Banks in which he gave an account of all the factswhich he had been able to collect with respect to this curious substanceand its mode of occurrence, and his interesting letter was published inthe Philosophical Transactions for 1790 (vol. Lxxx. , p. 273). 

Tabasheer is said to be sometimes found among the ashes of bamboos thathave been set on fire (by mutual friction?). Ordinarily, however, it issought for by splitting open those bamboo stems which give a rattlingsound when shaken. Such rattling sounds do not, however, affordinfallible criteria as to the presence or absence of tabasheer in abamboo, for where the quantity is small it is often found to be closelyadherent to the bottom and sides of the cavity. Tabasheer is by no meansfound in all stems or in all joints of the same stem of the bamboos. Whether certain species produce it in greater abundance than others, andwhat is the influence of soil, situation, and season upon the productionof the substance, are questions which do not seem as yet to have beenaccurately investigated. 

Dr. Russell found that the bamboos which produce tabasheer often containa fluid, usually clear, transparent, and colorless or of greenish tint, but sometimes thicker and of a white color, and at other times darker andof the consistency of honey. Occasionally the thicker varieties werefound passing into a solid state, and forming tabasheer. 

Dr. Russell performed the interesting experiment of drawing off theliquid from the bamboo stem and allowing it to stand in stopperedbottles. A "whitish, cottony sediment" was formed at the bottom, with athin film of the same kind at the top. When the whole was well shakentogether and allowed to evaporate, it left a residue of a whitish browncolor resembling the inferior kinds of tabasheer. By splitting updifferent joints of bamboo Dr. Russell was also able to satisfy himselfof the gradual deposition within them of the solid tabasheer by theevaporation of the liquid solvent. 

In 1791, Mr. James Louis Macie, F. R. S. (who afterward took the name ofSmithson), gave an account of his examination of the properties of thespecimens of tabasheer sent home by Dr. Russell (Phil. Trans. , vol. Lxxxi. , 1791, p. 368). These specimens came from Vellore, Hyderabad, Masulipatam, and other localities in India. They were submitted to anumber of tests which induced Mr. Macie to believe that they consistedprincipally of silica, but that before calcination some vegetable mattermust have been present. A determination of the specific gravity of thesubstance by Mr. Macie gave 2. 188 as the result. Another determination byMr. Cavendish gave 2. 169. 

In this same paper it is stated that a bamboo grown in a hot-house atIslington gave a rattling noise, and on being split open by Sir JosephBanks yielded, not an ordinary tabasheer, but a small pebble about thesize of half a pea, externally of a dark brown or black color, andwithin of a reddish brown tint. This stone is said to have been so hardas to cut glass, and to have been in parts of a crystalline structure. Its behavior with reagents was found to be different in many respectsfrom that of the ordinary tabasheer; and it was proved to contain silicaand iron. The specimen is referred to in a letter to Berthollet publishedin the _Annales de Chimie_ for the same year (October, 1791). There maybe some doubt as to whether this specimen was really of the nature oftabasheer. If such were the case, it would seem to have been a tabasheerin which a crystalline structure had begun to be set up. 

In the year 1806, MM. Foureroy and Vauquelin gave an account of aspecimen of tabasheer brought from South America in 1804 by Humboldt andBonpland (_Mem. De l'Inst_. , vol. Vi. , p. 382). It was procured from aspecies of bamboo growing on the west of Pichincha, and is described asbeing of a milk white color, in part apparently crystalline in structure, and in part semi-transparent and gelatinous. It was seen to containtraces of the vegetable structure of the plant from which it had beenextracted. On ignition it became black, and emitted pungent fumes. 

An analysis of this tabasheer from the Andes showed that it contained 70per cent. Of silica and 30 per cent. Of potash, lime, and water, withsome organic matter. It would, perhaps, be rash to conclude from thissingle observation that the American bamboo produced tabasheer ofdifferent composition from that of the Old World; but the subject isevidently one worthy of careful investigation. 

It was in the year 1819 that Sir David Brewster published the firstaccount of his long and important series of observations upon thephysical peculiarities of tabasheer (Phil. Trans. , vol. Cix. , 1819, p. 283). The specimens which he first examined were obtained from India byDr. Kennedy, by whom they were given to Brewster. 

Brewster found the specimens which he examined to be perfectly_isotropic_, exercising no influence in depolarizing light. When heated, however, it proved to be remarkably _phosphorescent_. The translucentvarieties were found to transmit a yellowish and to reflect a bluishwhite light--or, in other words, to exhibit the phenomenon of_opalescence_. When tabasheer is slightly wetted, it becomes white andopaque; but when thoroughly saturated with water, perfectly transparent. 

By preparing prisms of different varieties of tabasheer, Brewsterproceeded to determine its refractive index, arriving at the remarkableresult that tabasheer "has a lower index of refraction than any otherknown solid or liquid, and that it actually holds an intermediate placebetween water and gaseous bodies!" This excessively low refractive powerBrewster believes to afford a complete explanation of the extraordinarybehavior exhibited by tabasheer when wholly or partially saturated withfluids. A number of interesting experiments were performed by saturatingthe tabasheer with oils of different refractive powers, and by heating itin various ways and under different conditions, and also by introducingcarbonaceous matter into the minute pores of the substance by settingfire to paper in which fragments were wrapped. 

The mean of experiments undertaken by Mr. James Jardine, on behalf ofBrewster, for determining the specific gravity of tabasheer, gave as aresult 2. 235. From these experiments Brewster concluded that the spaceoccupied by the pores of the tabasheer is about two and a half times asgreat as that of the colloid silica itself!

From this time forward Brewster seems to have manifested the keenestinterest in all questions connected with the origin and history of asubstance possessing such singular physical properties. By the aid of Mr. Swinton, secretary to the government at Calcutta, he formed a large andinteresting collection of all the different varieties of tabasheer fromvarious parts of India. He also obtained specimens of the bamboo with thetabasheer _in situ_. In 1828 he published an interesting paper on "TheNatural History and Properties of Tabasheer" (_Edinburgh Journal ofScience_, vol. Viii. , 1828, p. 288), in which he discussed many of theimportant problems connected with the origin of the substance. From hisinquiries and observations, Brewster was led to conclude that tabasheerwas only produced in those joints of bamboos which are in an injured, unhealthy, or malformed condition, and that the siliceous fluid onlyfinds its way into the hollow spaces between the joints of the stem whenthe membrane lining the cavities is destroyed or rent by disease. 

Prof. Edward Turner, of the University of London, undertook an analysisof tabasheer, the specimens being supplied from Brewster's collection(_Edinburgh Journal of Science_, vol. Viii. , 1828, p. 335). Hisdeterminations of the specific gravities of different varieties were asfollows:

Chalky tabasheer. 2. 189Translucent tabasheer. 2. 167Transparent tabasheer. 2. 160

All the varieties lose air and hygroscopic water at 100° C. , and a largerquantity of water and organic matter (indicated by faint smoke and anempyreumatic odor) at a red heat. The results obtained were as follows:

 Loss at 100° C. Loss at red heat. Chalky tabasheer. 0. 838 per cent. 1. 277 per cent. Translucent tabasheer. 1. 620 " " 3. 840 " "Transparent tabasheer. 2. 411 " " 4. 518 " "

Dr. Turner found the ignited Indian tabasheer to consist almost entirelyof pure silica with a minute quantity of lime and vegetable matter. Hefailed to find any trace of alkalies in it. 

In 1855, Guibourt (_Journ. De Pharm_. [3], xxvii. , 81, 161, 252; _Phil. Mag_, [4], x. , 229) analyzed a specimen of tabasheer having a specificgravity of 2. 148. It gave the following result:

Silica. = 96. 94Potash and lime. = 0. 13Water. = 2. 93Organic matter. = trace

Guibourt criticised some of the conclusions arrived at by Brewster, andsought to explain the source of the silica by studying the composition ofdifferent parts of the bamboo. While the ashes of the wood contained0. 0612 of the whole weight of the wood, the pith was found to contain0. 448 per cent. , the inner wood much less, and the greatest proportionoccurred in the external wood. On these determinations Guibourt founded atheory of the mode of formation of tabasheer based on the suggestion thatat certain periods of its growth the bamboo needed less silica than atother times, and that when not needed, the silica was carried inward anddeposited in the interior. 

In the year 1857, D. W. Host van Tonningen, of Buitenzorg, undertook aninvestigation of the tabasheer of Java, which is known to the natives ofthat island under the name of "singkara" (_Naturkundig Tijdschrift voorNederlandsch Indie_, vol. Xiii. , 1857, p. 391). The specimens examinedwere obtained from the _Bambusa apus_, growing in the Residency ofBantam. It is described as resembling in appearance the Indiantabasheers. Its analysis gave the following result:

Silica. = 86. 387Iron oxide. = 0. 424Lime. = 0. 244Potash. = 4. 806Organic matter. = 0. 507Water. = 7. 632 ------Total. 100. 000

Apart from the question of its singular mode of origin, however, and itsremarkable and anomalous physical properties, tabasheer is of muchinterest to mineralogists and geologists. All the varieties hithertoexamined, with the exception of the peculiar one from the Andes, are incomposition and physical characters true opals. This is the case with allthe Indian and Java varieties. They consist essentially of silica in itscolloidal form, the water, lime, potash, and organic matter being assmall and variable in amount as in the mineral opals; and, as in them, these substances must be regarded merely as mechanical impurities. 

The tabasheers must be studied in their relations on the one hand withcertain varieties of the natural semi-opals, hydrophanes, beekites, andfloatstones, some of which they closely resemble in their physicalcharacters, and on the other hand with specimens of artificiallydeposited colloid silica formed under different conditions. Prof. Church, who has so successfully studied the beekites, informs me that some ofthose remarkable bodies present singular points of analogy withtabasheer. 

By the study of thin sections I have, during several years, beenendeavoring to trace the minute structure of some of these substances. Inno class of materials is it more necessary to guard one's self againsterrors of observation arising from changes induced in the substanceduring the operations which are necessary to the preparation oftransparent sections of hard substances. Unfortunately, too, it is thecustom of the natives to prepare the substance for the market by animperfect calcination, and hitherto I have only been able to studyspecimens procured in the markets which have been subjected to thisprocess. It is obviously desirable, before attempting to interpret thestructures exhibited, under the microscope, to compare the fresh anduncalcined materials with those that have been more or less altered byheat. 

Tabasheer would seem, from Brewster's experiments, to be a very intimateadmixture of two and a half parts of air with one part of colloidalsilica. The interspaces filled with air appear, at all events, in mostcases, to be so minute that they cannot be detected by the highest powersof the microscope which I have been able to employ. It is this intimateadmixture of a solid with a gas which probably gives rise to the curiousand anomalous properties exhibited by this singular substance. 

The ultra-microscopical vesicles filled with air in all probability giverise to the opalescence which is so marked a property of the substance. Their size is such as to scatter and throw back the rays at the blue endof the spectrum and to transmit those at the red end. 

When the vesicles of the substance are filled with Canada balsam, and athin slice is cut from it, this opalescence comes out in the moststriking manner. Very thin sections are of a rich orange yellow bytransmitted light, and a delicate blue tint by reflected light. I do notknow of any substance which in such thin films displays such strikingopalescence. 

That the excessively low refractive power of tabasheer is connected withthe mechanical admixture of the colloidal silica with air seems to beproved by the experiments of Brewster, showing that with increase ofdensity there was an increase in the refractive index from 1. 111 inspecimens of the lowest specific gravity to 1. 182 in those of the highestspecific gravity. Where the surface was hard and dense, Brewster foundthe refractive index to approach that of semi opal. The wonderful thingis that a substance so full of cavities containing gas shouldnevertheless be transparent. 

By the kindness of Mr. F. Rutley, F. G. S. , I am able to supply a drawingtaken from one of my sections of tabasheer. 

The accompanying woodcut gives some idea of the interesting structuresexhibited in some sections of tabasheer, though much of the delicacy andfidelity of the original drawing has been lost in transferring it to thewood. 

In this particular case, the faint punctation of the surface may possiblyindicate the presence of air vesicles of a size sufficiently great to bevisible under the microscope. But in many other instances I have failedto detect any such indication, even with much higher powers. The smallramifying tubules might at first sight be taken for some traces of avegetable tissue, but my colleague, Dr. Scott, assures me that they donot in the least resemble any tissue found in the bamboo. I have myselfno doubt that it is an inorganic structure. It is not improbablyanalogous to the peculiar ramifying tubules formed in a solution of waterglass when a crystal of copper sulphate is suspended in it, as shown byDr. Heaton (Proc. Brit. Assoc. , 1869, p. 127). Similar forms also occuron a larger scale in some agates, and the artificial cells of Traube mayprobably be regarded as analogous phenomena. 

The aggregates of globular bodies seen in the section so greatly resemblethe globulites of slags and natural glasses, and in their arrangement soforcibly recall the structures seen in the well known pitchstone ofCorriegills in Arran, that one is tempted to regard them as indicatingthe beginnings of the development of crystalline structure in thetabasheer. But I have good grounds for believing the structure to have atotally different origin. They seem in fact to be the portions of themass which the fluid Canada balsam has not succeeded in penetrating. Byheating they may be made to grow outward, and as more balsam is imbibedthey gradually diminish, and finally disappear. 

I must postpone till a future occasion a discussion of all the structuresof this remarkable substance and of the resemblances and differenceswhich they present to the mineral opals on the one hand, and to those ofthe opals of animal origin found in sponge spicules, radiolarians, andthe rocks formed from them, some of which have recently been admirablyinvestigated by Dr. G. J. Hinde (Phil. Trans. , 1885, pp. 425-83). 

I cannot, however, but think that it would be of the greatest service tobotanists, physicists, and mineralogists alike, if some resident in Indiawould resume the investigations so admirably commenced by Dr. PatrickRussell nearly a century ago; and it is in the hope of inducing some oneto undertake this task that I have put together these notes. There arecertain problems with regard to the mode of occurrence of this singularsubstance which could only be solved by an investigator in the countrywhere it is found. 

[Illustration: SECTION OF INDIAN TABASHEER, SEEN WITH A MAGNIFYING POWER OF250 DIAMETERS. ]

Most parcels of the commercial tabasheer appear to contain differentvarieties, from the white, opaque, chalk like forms through thetranslucent kinds to those that are perfectly transparent. It would be ofmuch interest if the exact relation and modes of origin of thesedifferent varieties could be traced. It would also be important todetermine if Brewster was right in his conclusion that the particularinternodes of a bamboo which contain tabasheer always have their innerlining tissue rent or injured. The repetition of Dr. Russell's experimentof drawing off the liquids from the joints of bamboos and allowing themto evaporate is also greatly to be desired. My colleague, Prof. Rucker, F. R. S. , has kindly undertaken to re-examine the results arrived at byBrewster in the light of more recent physical investigations, and I doubtnot that some of the curious problems suggested by this very remarkablesubstance may ere long find a solution. 

JOHN W. JUDD. 

 * * * * *

THE EDIBLE EARTH OF JAVA. 

In 1883 Mr. Hekmeyer, pharmaceutist in chief of the Dutch Indies, exhibited at Amsterdam some specimens of Javanese edible earth, both in anatural state and in the form of various natural objects. A portion ofthis collection he has placed at our disposal, and has given us someinformation regarding its nature, use, etc. 

These clays, which are eaten not only in Java, but also in Sumatra, NewCaledonia, Siberia, Guiana, Terra del Fuego, etc. , are essentiallycomposed of silex, alumina, and water in variable proportions, and arecolored with various metallic oxides. They are in amorphous masses, areunctuous to the touch, stick to the tongue, and form a fine, smooth pastewith water. The natives of Java and Sumatra prepare them in a peculiarway. They free them of foreign substances, spread them out in thinsheets, which they cut into small pieces and parch in an iron saucepanover a coal fire. 

Each of these little cakes, when shrunken up into a little roll, lookssomewhat like a grayish or reddish fragment of cinnamon bark. The clay isalso formed into imitations of various objects. 

We have tasted this Javanese dainty, and we must very humbly confess thatwe have found nothing attractive in the earthy and slightly empyreumatictaste of this singular food. However, a sweet and slightly aromatic tastethat follows the first impression is an extenuating circumstance. 

According to the account given by Labillardiere, confirmed by theinformation given by Mr. Hekmeyer, the figures are often craunched bywomen and children, to the latter of whom they serve as dolls, toys, andeven money-boxes, as shown by the slits formed in the upper part of thelarger objects, which are usually hollow. 

We have not sufficient documents to carry us back to the origin of thattradition that would have it that the human form has been given tocertain food preparations from remote times. Savants will not be slow tosee in this a vague relic of the horrible festivities that succeededhuman sacrifices among primitive peoples. For want of prisoners and ofdesignated victims, a symbolic representation would have graduallydeveloped, and been kept up, though losing its religious character. Wemerely call brief attention to this obscure problem, not having thepretension to solve it. --_Revue d'Ethnographie_. 

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