: ey ns reang te atecind wari pre ES A art ee AAR ti Seen Sei Hie RCH et Am APA A t Potivy Ab Wa Ea rat THE ¥ y a x mS awe : we yl. n » " ' “ .e < - Pat gh adit aphid " Pape aa s (Ree A eat IH tee pee » Ho Dohme F deeb Hesiieon Al Fahad RL f < * 3 . VELMA AP Dh A ae ell end “FOE eh 8 tl BAe ern AE Sot fetes! aN read At ag at SAAN E LG VON OS ree elt a Both tt Delve EPsorewene~e. iret re trae Get PA nth Pe Weis tN Se Gebel Ming on pd So AE eth Rat Rat ed eng inte nb haa eaapahcentieg Wette® Se oy ue tri Blt fe Rare’ “Wow he - werd BA lol Sadie Merial Mus OVO Pee hie amy are ed vale-y ae t-cet Renae eae eins SOON A eR Fea Fe LLP PO Ee I ee FON THE LONDON, EDINBURGH, ann DUBLIN PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. CONDUCTED BY SIR DAVID BREWSTER, K.H. LL.D. F.R.S.L. & HE. &e. SIR ROBERT KANE, M.D. F.R.S. M.R.ILA. WILLIAM FRANCIS, Pu.D. F.L.S. F.R.A.S. F.C.S. “‘ Nec aranearum sane textus ideo melior quia ex se fila gignunt, nec noster vilior quia ex alienis libamus ut apes.” Just. Lips. Polit. lib. i. cap. 1. Not. VOL. XXVIII.— FOURTH SERIES. JULY—DECEMBER, 1864. LONDON. TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET, Printers and Publishers to the University of London ; SOLD BY LONGMAN, GREEN, LONGMAN, ROBERTS, AND GREEN; SIMPKIN, MARSHALL AND CO.; WHITTAKER AND CO.; AND PIPER AND CO., LONDON :— BY ADAM AND CHARLES BLACK, AND THOMAS CLARK, EDINBURGH ; SMITH AND SON, GLASGOW; HODGES AND SMITH, DUBLIN; AND PUTNAM, NEW YORK, “Meditationis est perscrutari occulta; contemplationis est admirari perspicua..... Admiratio generat questionem, queestio investigationem, investigatio mventionem.”—Hugo de S. Victore. —“ Cur spirent venti, cur terra dehiscat, Cur mare turgescat, pelago cur tantus amaror, Cur caput obscura Pheebus ferrugine condat, Quid toties diros cogat flagrare cometas ; Quid pariat nubes, veniant cur fulmina ccelo, Quo micet igne Iris, superos quis conciat orbes Tam vario motu.” J.B, Pinelli ad Mazonium, CONTENTS OF VOL. XXVIII. (FOURTH SERIES.) NUMBER CLXXXVI.—JULY 1864. Prof. J. C. ooo on the Extra Current of the Induction- Current. . Mr. C. Packe on the Discrepance between the “English and French Barometer Scales; and on the Corrections necessary in reducing the Readings to the Freezing-point .......... Mr. T. K. Abbott on the Probability of ve eae and ee ments. ne Prof. Tyndall’: s “Notes 0 on Scientific History . A A aca acta coke M. P. Tchébychef on a Modification of Watt’s Parallelogram. . Mr. P. E. Chase on the Barometer as an Indicator of the Earth’s Rotation and the Sun’s Distance . Notices respecting New Books: Dr. ‘Apjohn’s s Manual of the LS SIUC 5 oe Nr de aria em eae Pe Proceedings of the Royal Society :— Mr. G. G. Stokes on the supposed Identity of Biliverdine with Chlorophyll, with remarks on the Constitution of Reememeny RE Nin), Soe ee ees es een ee Drs. Plucker and Hittorf on the ea of Ignited Gases and Vapours ...... orgs oe RA drety hoe Mr. B. Stewart on Sun Spots Pe ae dear alae ace ae eesti Mr. J. P. Gassiot on a Train of Eleven Sulphide-of-carbon Prisms arranged for Spectrum Analysis .. icicles Proceedings of the Geological Society :-— Mr. J. W. Salter on some New Fossils from the Lingula- PE TEPMEMMN ALCS eet Ewer tats sm oat. Stet "sects! ata sos Greta nn ee a Messrs. Hull and Green on the Millstone-grit of North Staffordshire, and the adjoining parts of Derbyshire, Cheshire, and Lancashire .............. Mr. W. P. Blake on the Geology and Mines of the Nevada SEMI), 6 oo ade a due atta ete cleveue ete eet aah aha ay alte ton Mr. H. Seeley on the Red Rock in the Section at Hun- ECMEUEL cote ls ols e'o ¢ araleaicie ss = as shen 0 aorere The Rey. D. Honeyman on the Geology of Arisaig, “Nova OCIS PE Cai oo, SAC a a ea a ara are Mr. J. W. Kirkby on some Remains of Fishes from the ‘‘Upper Limestone” of the Permian Series of Durham. Mr. P. M. Duncan on the Fossil Corals of the West Indian Islands Beta Bie a eae eae : Neo ine Page lv CONTENTS OF VOL. XXVIII.—FOURTH SERIES. Page Remarks on the Distillation of Substances of different Volatili- ties, by M. Carey Lea .... . 75 Note on the Residual Charge af Blectrical ‘Conilenseas! “by "M. J.M. Gaugain ..... 76 On the Boiling of Water, ‘and on the Explosion ‘of Steam-boilers, by M. L. Dufour of Lausanne eesti. . 0 os or NUMBER CLXXXVII.—AUGUST. Prof. Tyndall on the Absorption and Radiation of Heat by Gaseous and Liquid Matter.— Fourth Memorr. . 81 Dr. Woods on the Relative Amounts of Heat produced by ‘the Chemical Combination of Ordinary and Ozonized Oxygen .. 106 Mr. W. F. Barrett on a Physical Analysis of the Human Breathe ono ose ow ele e's asain in od eee A ele aieyd ons rr 108 Mr. J. Croll on the Physical Cause of the Change of Climate dunng Geolopical: Epoch: 3).)7400 1.94 se ook eee 121 Prof. Stefan on che Dispersion of Light by Quarts, owing to the Rotation of the Plane of Polarization | ahige’ 137 Father Secchi on Earth Currents, and their “alien n Bice and Magnetic’ Phenomena. s.s0..0:s as sede a ete 2 140 Pof. Maskelyne and Dr. Lang’s Mineralogical Notes (With a Plate) cen ee) Dr. Joule on the History of the Dynamical Theory of Heat .. 150 Proceedings of the Royal Society :— Mr. W. Hugginsand Dr. A. Miller on the e OBE of some of the Fixed Stars . » 32 Mr. P. E. Chase on Aérial Tides ......../see0s-- eee 154 Mr. H. C. Sorby on the Microscopical ‘Structure of Me- teorites ... Werner co 5 Proceedings of the Geological Society : — Mr. T. Pe seEe ona Section with Mammalian Remains near Thame ... 159 Mr. E. Witchell on a . Deposit at Stroud containing Flint Implements, Land and Freshwater Shells, &c......... 159 Mr. A. Lennox on the White Limestone of Jamaica, and its associated intrusive rocks. ; 2.4; ....1./5. «1 eee 159 Fort-Major T. Austin on the Earthquake which occurred in England on the 6th of October, 1863 . . +h. eee Apjohn’s ‘ Manual of the Metalloids’ .. .. 160 On the Measurement of the Chemical Brightness of various “por- tions of the Sun’s Disk, by ‘Thomas Woods, M.D......... 166 On the Plena atte: of Emeralds, by MM. Wohler and G. Rose. Pele Researches on the Respiration of Flowers, by M.Cahours ... 167 On the Spectral Ray of Thallium, by M. J. Nicklés CONTENTS OF VOL. XXVIII.—FOURTH SERIES. NUMBER CLXXXVIIIL—SEPTEMBER. Prof. Mitscherlich on the Spectra of Compounds and of Simple Substances. (With Two Plates.) .........-00-. ee ee eeee Prof. Breithaupt on the Quartz from Euba, and on the Biaxial character of Pyramidal and Rhombohedral Crystals.. .. Prof. Norton on Molecular Physics ...... 2.1.0 -+ essere eee: The Hon. Chief Justice Cockle on the Operating Symbol of Witerential Covariants .....-.. 2... 0c ece eee settee Prof. Plateau on the Conditions of Stability of thin Films of Mr. G. F. Rodwell on some Effects produced by a Fluid in Motion.—No. II. On the Trompe. (With a Plate.) ...... Dr. Atkinson’s Chemical Notices from Foreign Journals Proceedings of the Royal Society :— Dr. T. R. Robinson on a New Mercurial Gasometer and /: She) UD LS ES ea ae pire ca ana ceo Proceedings of the Geological Society :— Captain Godwin-Austen on the Geology of part of the North-western Himalayas.... 6... -- +s eeeeeere cece Prof. Huxley on the Cetacean Fossils termed Ziphius by Cuvier, with a notice of a new species (Belemnoziphius compressus) from the Red Crag.......-ee-++s+-+--+- Mr. W. B. Dawkins on the Rhetic Beds and White Lias of Western and Central Somerset, and on the Discovery of a new Fossil Mammal in the Grey Marlstones beneath RREMEOME-DEO .... ce. s wees eye ere ne te tee tne Dr. Holl on the Geological Structure of the Malvern Hills and adjacent District .....-.2-+ +s eeeeeer ree eee: On the Kotatory Power of Active Liquids and of their Vapours, eM GLNEZ ee ee ee ee et as a Inversion of the Absorption Bands in the Spectrumof Didymium, DEVIC nw ce ee rc te ets Hee Ree ne On a New Polarizing Prism, by Prof. H. W. Dove.......... On the Optical Properties of Carthamine, by Prof. H.W. Dove. NUMBER CLXXXIX.—OCTOBER. Dr. H. Draper on the Photographic Use of a Silvered-Glass Menectine Telescope .......--222+-0sec cere: ee Prof. Tyndall on the Conformation of the Alps ..........-. Prof. Potter on the Law of the Expansion of the Gases by in- crease of Temperature. ........ : : Mee ceene Prof. Norton on Molecular Physics ........ 00.2 002+ se eres Dr. Rankine on the Properties of certain Stream-Lines...... Mr. P. G. Tait on the History of Thermo-dynamics. ...... eee Geet eiia) Loken en, 6.6.0 209 225 235 241 241 242 243 243 246 247 247 vi CONTENTS OF VOL. XXVIII.—FOURTH SERIES. Page Mr. A. C. Ramsay on the Erosion of Valleys and Lakes; a Renly. to Sir Roderick Murchison’s Anniversary Address to the Geoprephical Society. ..c. ..< 4.2.0; sisi sehen 293 Prof. Bohn’s Historic Notes on the Conservation of Energy .. 311 Proceedings of the Royal Society :— Mr. T. Graham on the Pr operties of Silicic Acid and other analogous Colloidal Substances .................. 814 Proceedings of the Geological Society :— Mr. J. Powrie on the Fossiliferous Rocks of Forfarshire and. Shem CQntentss a9. 6 eee ag, was sy nt p oe 321 Prof. R. Harkness on the Reptiliferous Rocks and Foot- print Strata of the North-east of Scotland .......... 321 Mr. J. Evans on some Bone- and Cave-deposits of the Reindeer-period in the South of France ............ 321 Prof. J. Helmersen on the Carboniferous Rocks of the Donetz and the Granite-gravel of St. Petersburg. . 322 Mr. G. Maw on a supposed Deposit of Boulder- clay it in North Devon ..... 322 Dr. Young on the former existence of Glaciers in the High Grounds of the South of Scotland ....... 323 Mr. T. Belt on the Formation and Preservation of Lakes by Ice-action .... thie. ee Mr. S. H. Wintle on the Geological Features of Hobart, Tasmania .... 323 On the Ebullition of Water, ‘and | on the Explosion of Steam- boilers, by My. Datour, cic. 6\ tied cn vee Spe ee On the Application of Zeiodelite, by R. Bottger icp Oe . 326 On the Determinations of Temperature in the depth of some = Ba- varian Mountain Lakes, by Prof. Jolly ..............--+: 326 On the Meteorite of Albareto in the Modenese, by Dr. W. MADMIN SET oy rols56 0:00 4-9 0 wings 2 8g, GOs Oh ere 327 NUMBER CXC.—NOVEMBER. Prof. Tyndall on Luminous and Obscure Radiation..... Sota MOS Mr. D. Forbes on Evansite, a new Mineral Species.......... 341 M. E. Jochmann on Induction in a Rotating Conductor .... 347 Mr. J. Bishop on the Influence of the Pitch of the Tuning- Fork on the Mechanism of the Human Voice............ 349 Mr. C. Yomlinson on the cee ee of Liquids. (With — Two Plates.)... Lie OOe Mr. E. J. Mills ona 1 Defect i in the Theory of Saturation .. .. 3864 Mr. J. Gill on the Dynamical Theory of Heat.............. 867 Father Secchi on Shooting-Stars,.....:3:...: eae ee ee 377 Prof, Norton on Molecular Physiesi ‘234... j eee ee Oe 382 Notices respecting New Books :—Prof. Church’s Laboratory Guide for Students of Agricultural Chemistéys 28 aio oe - 390 CONTENTS OF VOL. XXVIII.—FOURTH SERIES. Vill ; Page Proceedings of the Royal Society :— Prof. Stokes on the Reduction and Oxidation of the Co- fsumine Matter of the Blood... 02 .)00..300 0 Se 391 Influence of Heat-force on Vegetable Life, by George Bentham, F-is., President of the Linnzan Society .............. 400 Analysis of Langite, anew Mineral from Cornwall, by M. Pisani. 403 On the History of Energetics, by Prof. Rankine, LL.D.,F.R.S. 404 On the Temperature of Sea-water, by M. Charles Martins.... 405 On the Ancient Aqueduct of Alatri, by Father Secchi ...... 406 - Phenomena observed in the Spectra produced by the Light of Induction-Currents in traversing Rarefied Gases, by M. J. Paneer ne ee a I SORT 408 NUMBER CXCI.—DECEMBER. Prof. Lorenz on the Theory of Light.—Second Memoir...... 409 Eee Morten ow Molecular Physics ...........-0..--65% 425 M. G. Vander Mensbrugghe on some curious Effects of the meecrmiantorces of Liquids)... .. j. 2. «2:5 2.2 jo >.< toe oes 434 Prof. Tyndall’s Contributions to Molecular Physics. Being the Fifth Memoir of Researches on Radiant Heat . 438 Prof. Donkin on certain statements in Elementary Works con- cerning the Specific Heat of Gases ..... 458 Mr. C. J. Monro on the Nomenclature of the Physical ‘Sciences. 461 Prof. Church on Tasmanite, a new Mineral of Organic Origin. 465 Mee ee cin on, the History of Force-.. 2.6.0.0 et es 470 Proceedings of the Royal Society :— Comparison of Mr. W. De la Rue’s and Padre Secchi’s Eclipse Photographs, by Warren De la Rue, F.R.S. .. 477 A Letter from John Davy, M.D., F.R.S., to the Editors of the Philosophical Magazine in reply to certain charges made by C. Babbage, Esq., F.R.S., &c., against the late Sir Humphry Davy, when President of the Royal Society. . 480 On the Comparison between the English and Metrical Readings in Double-scale Barometers, by W. Mathews; Jun. 725... 484 On the Spectrum of Jupiter, by Father Secchi ............ 486 NUMBER CXCII.—SUPPLEMENT. Prof. Challis on the Dispersion of Light ..... 489 Prof. Maskelyne and Dr. Lang’s Mineralogical Notes. (With: a ET ee ol etaaie She eae cate eae eva we 502 Prof. Tyndall’s Contributions to Molecular Physics. Being the Fifth Memoir of Researches on Radiant Heat............ 508 MM. Pelouze and Maurey on Gun-cotton, with reference to the New Methods of General Baron von Lenk for preparing and employing this Substance......... Fo eC ROMER, Aca pce RAE » 335 Vill CONTENTS OF VOL. XXVIII.—FOURTH SERIES. Page M. F. M. Raoult on the Thermal Phenomena of Voltameters, and Measurement of the quantitiesof Heat absorbed in Electro- chemical Decompositions .... ..'/5, 5.8 f2.-2 944 ee 551 Dr. C. K. Akin on Ray-Transmutation’ 2... 52... . Js. eee 554 Notices respecting New Books :—Mr. W. A. Darby’s Astrono- mical Observer. A Handbook to the Observatory and the common Telescope... j ..'.. 5208 2.). 235K. Eee 561 Proceedings of the Geological Society :— Messrs. P. M. Duncan and G. P. Wall on the Geology of Jamaica; with Descriptions of new Species of Cretaceous, Eocene; and Miocene Corals’... ...-.2 2). i... eee 562 Mr. R. Tate on the Correlation of the Irish Cretaceous Strata. oso. ce oe ees wh eee 562 On the Verification of the Law of Electrolysis when external work is performed by the Galvanic Current, by M. J. L. Soret. 563 Ritter ee oye nee ie eee Perri > 564 PLATES. I. & II. Illustrative of Prof. Mitscherlich’s Paper on the Spectra of Compounds and of Simple Substances. III. Illustrative of Dr. Viktor yon Lang’s Paper on the Crystalline forms of Gadolinite. IV*. Illustrative of Mr. G. F. Rodwell’s Paper on the Trompe. V. & VI. Illustrative of Mr. C. Tomlinson’s Paper on the Cohesion-figures of Liquids. VII. Illustrative of Dr. Viktor von Lang’s Paper on some Crystalline forms of Malachite, Gismondine, and Herschelite. * To Binder :—By mistake, printed “ Plate III.” THE LONDON, EDINBURGH, ann DUBLIN PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. [FOURTH SERIES.] JULY 1864. I. On the Extra Current of the Induction Current. By J. C. PoagzenporrFr*. | Bs my latest investigation laid before the Royal Academy in August last, on the thermal action of electrical sparks, in order to test the view propounded by Reitlinger, that this action is proportional to the intensity of the current, I had interposed yery long wires, in the form of coils, in the path of an induction -eurrent. I thereby observed that the sparks, notwithstanding the considerable enfeeblement in intensity produced by this in- terposition, lost scarcely any of their heat, just as they have long been known to become thereby more fully luminous, but to lose little or none of their striking-distance. I observed on this occasion that when the circuit of the in- ductorium is completely metallic through such accessory coils, the current, in spite of this metallic circuit, and in spite of the great enfeeblement which it experiences through the resistance of a very long and thin wire, possesses such tension that ex- tremely piercing sparks are obtained if the wires are merely touched in one point with the hand.: I further found that the free electricity at the end of the ac- cessory coil turned towards the positive pole of the inductorium is positive, and negative at the other end; and that if two such accessory coils are placed end to end, the wire joining them ex- hibits far less tension than the two wires leading from the coils to the inductorium, from which I concluded that in the long metallic circuit there must be a zero point of tension. Finally, I convinced myself, by individual interruptions of the voltaic ex- * Translated from the Monatsbericht der Berliner Akademie, November 1863, by Dr. E. Atkinson. Phil. Mag. 8. 4, Vol. 28. No. 186. July 1864. B 2 Prof. J. C. Poggendorff on the Extra Current citing current, that the tension observed only belongs to the current when it is opened. These phenomena are certainly surprising when it is considered that the poles of the inductorium lose their tension coms sal when they are joined by a simple, by no means short, thic metallic wire. It is indeed stated that they retain even then a trace of tension; but with my apparatus I could not observe it, either by the gold-leaf electrometer or with the tongue. Even when I had approached the poles of a powerful apparatus till they produced sparks abundantly, I could, by means of 100 feet of a platinum wire 0:1 millim. in diameter, which was bent back- wards and forwards im the air, and was equal in resistance at least to 1000 feet of the induction wire, entirely take away not merely the sparks, but every perceptible trace of tension at the poles, when I connected them with the two ends of this wire. But these phenomena of tension were at once distinctly observed, though in a less degree, even with a copper wire of 0°66 millim. in thickness and not more than 400 feet long which was rolled in the form of coil. . ‘Non-metallic, relatively bad conductors alone exhibited a dif- ferent deportment in this respect. A hemp string, for instance, moistened with feebly acid water, showed not merely tension in the electrometer, but gave just as delicate sparks as a large coil of wire, even when its length was only an inch or less. It differed remarkably from metallic wires (in which, as is well known, ouly very feeble heating is perceptible) by the fact that it became considerably heated—so much so, that a thermometer round whose cylinder it was coiled once, rose in a minute from 40° to 50°, that it smoked visibly, gradually dried, then car- bonized, and finally disappeared with sparks. : Although it was not impossible that even straight wires of great thickness and length, simply in virtue of their resistance, might exhibit a certain tension when united with the poles of the inductorium, I was yet convinced that the phenomena mentioned were not phenomena of resistance, but arose from an induction which might indeed occur in a feeble degree in straight wires, and I designated it even then as the result of such a process, without expressing an opinion as to the particular manner: Continued occupation with the subject has confirmed me in the original view, and leads me to consider it as not doubtful that the tension observed proceeds from an induction current, which the current of the inductorium, the current of opening, produces in the spires of the accessory coil in the opposite direction to its own. As it is usual to designate the current of induction, which the voltaic current can produce in its own wire on opening and of the Induction Current. Agi 3 closing, as an extra current, I do not hesitate to designate the current in question as the extra current of the induction current. To test this view. more accurately, it appeared best to inves- tigate the deportment of various induction apparatus to each other . : I first combined two apparatus of this kind, as similar as pos- sible, in opposite directions, by joining in a corresponding manner the two external divisions of an inductorium with three divisions, by bright copper wires of small length. Although each of these divisions only contained 1200 feet of copper wire of 0:25 millim. in thickness, and, both united in the same direction, exhibited no perceptible trace of tension, yet when united in opposite direc- tions their junction wires gave painful sparks. There was no current in this; for an electrical egg interposed in one of the joining wires showed no luminous phenomena. Thereupon I combined this inductorium as a whole, in which it contained about 3800 feet of wire, in an opposite direction with another large apparatus whose induction coil consisted of 23,000 feet of wire 4th of a millim. in thickness, in which I passed one and the same voltaic current through the inducing coils of both, and interrupted them by one and the same hammer. I began by testing the induction coils singly, by causing one to give sparks at the micrometer while the other was closed by metal. As was to be presupposed, the larger apparatus was the more powerful ; the striking-distance of its sparks was more than double that of the sparks of the smaller. Whea they were now combined in an opposite direction (that is, the similar poles of both coils united) by bright copper wires of no great length, a current moved in the direction of the stronger apparatus accompanied by a tension upon the joming wires, which yielded even more piercing sparks than those in the former case*, Both these results serve doubtless as a support of my view, in so far as they show that when, in a closed circuit of wire, two induction currents (whether equally or unequally strong is quite immaterial) act in opposite directions to each other, free elec- tricity occurs. It was now necessary to furnish a proof that in the original experiment the current of the inductorium evoked an opposite eurrent (Gegenstrom) in the accessory wire. This was effected in two ways. * I will not omit to mention that even when both apparatus were joined im the same direction, a tension was indeed observed on the wires, though somewhat feeble. This, however, I can only consider as abnormal, arising from some not yet explained circumstance. For, if it were normal, it must occur in each individual inductorium, as that may always be supposed to consist of two unequal instruments ibis in the same direction. z 4 Prof. J. C. Poggendorff on the Extra Current First by a bundle of iron wire. If such a bundle is inserted in the accessory coil, tension and sparks are observed in the junction wires to a surprising degree. The supposition is most natural that this result arises from a strengthening of the opposite current ; and if this supposition is confirmed, the inducing induc- tion current must be enfeebled by the bundle of iron. This is in fact the case. I was convinced of this in the following manner. I joined an inductorium having 10,000 feet of wire to an accessory coil of 23,000 feet, interposing at the same time a galvanometer and a well-exhausted electrical egg—the latter for the double reason of observing the luminous phenomena in it, and removing the closing current, so that the hammer might be used; for indi- | dividual openings and closings of the battery of six elements had produced no result. By means of this arrangement, and without iron wire in the accessory coil, I obtained a deflection of about 20° in the gal- vanometer, and the well-known luminosity in the egg. When the iron was interposed in the coil, the deflection sank at least to half its amount, and the light in the egg disappeared almost completely, being reduced to a few irregular sparks. Hence the strengthening of the opposite current, and there- fore its existence, cannot be subject to any doubt. In what manner soft iron strengthens the opposite current does not come into consideration. I will, however, remark that an induction current magnetized the iron in the same direction as that in which it deflects a magnetic needle, that it gives therefore to Ampére’s molecular currents the same direction as its own; while in an adjacent wire, according to the observations of Henry and others, it produces an induction current of the second order in an opposite direction*. By its magnetization the iron reacts on the magnetizing induction wire, and as it produces in it an op- posite current, I conclude that this current is the product of the commencing magnetism, and the disappearing acts little, or not at all. If in the momentary magnetization which the soft iron experiences by the induction current, resulting from the opening of the voltaic current, both elements, the increase and decrease of the magnetism, were of equal influence upon that current, it could not be perceptibly affected. A closed coil inserted in the accessory coil acts differently, that is, enfeebles the opposite current, and therewith the tension ; * It is clear that an induction current, since in its transitory career it in- creases and decreases, must induce two currents as well in its own as in an adjacent wire, one of opposite and one of the same direction. But ac- cording to all observations the first is, in galvanic induction, the stronger ; hence I have only spoken of it, and called it opposite current. of the Induction Current. 5 for the inducing induction current produces in it a current of the same direction as the opposite current which reacts upon this. But I had no coil of a sufficient number of windings, which I might have inserted in the accessory coil, so as in this way com- pletely to destroy the opposite current. The inductorium itself gives the second proof of the existence of the supposed opposite current. For to produce the often mentioned phenomena of tension it is unnecessary to use an accessory coil; the inductorium itself is quite sufficient. Nothing more is necessary than that, after the poles of the instrument at work have been united with one another by a short wire, the inducing coil together with its iron core be par- tially withdrawn. On commencing, free electricity appears in the junction wire, and it increases until about two-thirds or three-fourths of the coil are withdrawn from the induction coil. It is true that in this case the empty part of the induction coil represents the position of the accessory coils in the earlier expe- riments, and so far this result is not surprising. If now the inducing coil is slowly reinserted, free electricity begins to decrease, and continues to entire disappearance when the coil has been restored to its original position. This also is natural. But, it may be asked, what happens in this second process? Obviously nothing else than that, in the coils of the empty part of the induction coil, the original mduction, partly or entirely removed, is reproduced. This induction destroys the earlier condition. But what destroys an induction can be only an in- duction, and one of opposite direction; hence by this experi- ment the existence of the opposite current is proved. I do not suppose that anything well founded can be urged against these simple conclusions. I will only add that the phenomenon of tension in question, if purely one of resistance, could never entirely disappear, but rather, even with the very best conduction between the poles of the instrument, must occur in full force ; for each partial current which is induced in an individual spire of the induction coil has to traverse the sum of all the other spires of the coil, and hence to overcome a resistance which would be quite sufficient to cause free electricity to appear if this were merely evoked by resistance. From all this I consider the origin of free electricity in the circuit of a metallic closed inductorium to be sufficiently esta- blished, and hence I think myself justified in passing over other experiments which I have undertaken in this direction. Yet I cannot help discussing an objection which seems to follow from the statement that the striking-distance of the in- duction spark undergoes no enfecblement from a wire ciremt 6 Prof. J. C. Poggendorff on the Extra Current introduced into the path of the current. The striking-distance stands obviously in a direct ratio to the electromotive force ; and when this latter is enfeebled by an opposite current, it can scarcely be otherwise than that the striking-distance should also be diminished. Although my earlier investigations seem to speak against this, I believe that such a diminution actually occurs whenever the interposed wire is used in the form of coil, and that it is only on the one hand the indefiniteness of the striking- distance, and on the other the weakness of the partial current, which may have prevented this diminution from being perceived. It does not here depend so much on the absolute length of the coil added, as upon its ratio to the length of the wire of the in- ductorium. With a certain ratio, the opposite current, or its en- feebling influence upon the inducing current, is most strongly developed, and then the diminution also naturally follows. Some experiments which I made in this respect were favourable to this view, although a repetition of them with greater méans than those at my command would not have been superfluous. For straight wires, the above statement, though not perhaps with the utmost rigidity, applies with tolerable approximation. In the foregoing I have only spoken of the developments of the opposite current in free air; its occurrence is extremely striking when part of the circuit is in a rarefied space. If under the receiver of an extra plate of an air-pump which is provided with the necessary insulated conductors, a bright copper wire is stretched, and the air is adequately exhausted, aud if the arrangement is placed in the circuit of an inducto- rium provided with its accessory coil, as soon as the instrument is set to work the wire is seen to become brightly luminous, and to send bright rays towards the bell. The phenomenon is im- proved by clothing the bell externally with a strip of tinfoil corresponding to the wire, which is placed in connexion with the ground ; and still more by bringing a small piece of phos- phorus under the bell. 8 In general the wire does not become continuously, but partially luminous; these luminous parts are in continual motion; run backwards and forwards on the wire, and send glimmering rays towards the tinfoil, which also becomes luminous on the inside, so that the whole, since at the same time the dark parts, by contrast, appear to emit dark rays, has an appearance like that of the aurora borealis. - I could see nothing of a stratification in this luminous phe- nomenon, although [ had first with this view allowed phospho- rus to evaporate under the bell; the formation of stratification is probably suppressed or concealed by the great mobility of the light. Nor could I perceive any material difference in the appear- of the Induction Current. - 7 ance and colour of the light when the receiver was alternately touchéd on the positive and on the negative side of the apparatus. Its colour is whitish throughout. This side light, as I will call it, as it is obviously analogous to the lateral emissions which have long been known in powerful electric discharges in free air, was most intense when the induc- torium was made to give sparks in the air, and at the same time the air surrounding part of the joining partially exhausted. The further apart the poles are moved, the more intense is the light, and of course the tension upon the wires. It i is, on the other hand, relatively feeble if the poles of the apparatus are con- nected with the armatures of a Leyden jar, in which, as is known, recurrent currents are formed, and the tension upon the wires is feebler. The side light is a useful indicator of the degree of free elec- tricity on the wires. If, for example, an induction coil is placed in metallic connexion with a larger one, and an induction current is alternately pro- duced in the first and in the second, while the other is used empty as an accessory coil, even the sensation of feeling shows that the tension in the wire is stronger when the current is in- duced in the smaller coil, although the current is feebler in that case than in the other; but this is shown much more convin- cingly by the side light. The strengthening action produced by introducing a bundle of iron wire into the accessory coil cannot be more surprisingly shown than by the side light. I must in conclusion mention that in 1859, Koosen*, on the occasion of another investigation, made observations which are closely allied to mine, but do not quite coincide with them. He observes the phenomenon in a form in which it is essentially a phenomenon of partial currents. He offers, that is, two paths for the induction current, one through air and one through metal, by letting the poles of the strument give sparks, and joining them at the same time by a very long wire, in which he finds that the striking-distance of the sparks, in spite of this metallic lateral circuit, is either not at all or not perceptibly diminished. The free electricity in the wire has not mdeed escaped him ; but since he only states that the wire has a certain tension which can be shown by the gold-leaf electrometer, while he does not mention the sparks and their piercing action, he has probably not seen the phenomenon in its full development, perhaps because he used covered and varnished wires, perhaps because he only studied it at one branch of the current. Finally, he does not dwell upon the cause of the phenomenon. Although he has in all pro- bability used the wire in the form of coil, yet he does not say * Poge. Ann. vol. evii. p. 211. 8 Mr. C, Packe on the Scales of the so, but always speaks of the length and resistance of the wire. So that I do not consider the publication of my experiments to be superfluous. : | I have, moreover, repeated the observations in the manner described by Koosen, and found them confirmed in the main point, as was to be expected; yet I have also observed that it depends on the relation between the length of wire in the accessory coil and in the inductorium. An accessory coil of 10,000 feet took away completely the sparks of an inductorium of 23,000 feet, while it left untouched those of a small instrument of 8000 feet. The phenomenon is best seen as one of partial currents and of resistance when a hemp thread 5 or 6 feet in length, moist- ened with spring-water, which is fixed insulated in the air, once backwards and forwards, and connected with the poles of the spark micrometer. By moving a wire bridge laid across, it can be shortened at pleasure for the current, and it may be observed that the first action upon the sparks consists in an attenuation of them. II. On the Discrepance between the English and French Baro- meter-Scales; and on the Corrections necessary in reducing the Readings to the Freezing-point. By Cuarues Packs, Esq. To the Editors of the Philosophical Magazine and Journal. GENTLEMEN, | H AVING brought out with me a barometer graduated with a double scale, reading millimetres on one side and inches on the other, I have been at some pains to investigate the slight apparent anomaly existing between the French and English scales as compared with the boiling-point, which I thittk may be satisfactorily accounted for in the following manner :— Boiling- Barometer. point. -¢ in, mm, in, mm. 212° F., [29:905 or 759°58, | _ [29-922 or 760, or = as given by the Kew;=) as given by Regnault in 100 C. | Committee of the British | his Tables of the Elasti- Association. city of Vapour. The larger portion of this discrepance arises from the differ- ence of the standard temperature of the scales of the English and French barometers ; the remainder is accounted for by the difference of latitude producing a variation of gravity. First as to the discrepance arising from the standard tempe- ratures. That of the English barometer being 30° F. higher than that of the French scale, when the mercurial column is re- English and French Barometers. 9 duced to the freezing-point, the scale of the French barometer is also reduced to the freezing-point, but the scale of the English one is only reduced to the temperature of 62° F. The consequence is that the French barometer, when reduced, will always read higher than the English barometer. Let A be the height of the barometer observed ; B the linear expansion of brass for 1° F. = 0000104344, as given by Laplace and Lavoisier, or (000018782 for PC. The French barometer, when reduced, will, on account of the difference of standard temperatures, read higher than the English barometer by an amount =30 AB; e. g., Let the height of the barometer be = the boiling-point 212°, t. e. 29°905 inches. B=:0000104344:= log 5018467 A=29-905 = log 1:475743 30 = log 1:477121 3:971331=:009361 inch excess of the French reading. By changing A it will be evident that we get the excess for any height of the barometer, but for the average height at the sea- level it may be taken as -009 inch. For exact observation, therefore, it is useless to have a baro- meter marked with a double scale,—the French and English : they cannot be made to coincide; e. g. Let the barometer read 29 inches = 736-59 millims. (temp. 62° F.=16°-67C.). Inthe English scale at 62° (the temperature of the standard) no correction is made for the brass scale. The only correction is for the expansion of the mercury —‘087, 29 — ‘087 reduced 28°913=734:°38 millims. But in the French scale, the temperature of the standard being 32° F., the correction to be made is for the expansion of the mercury — the expansion of the scale: Expansion of mercury for 16°67 C. = "2-212 Expansion of brass scale for 4, =—°231 EOS! 736°59 — 1-981 reduced 734°61 =28°9224 inches. 10 Mr. C. Packe on the Scales of the To reduce the barometer to the freezing-point, we have the following formule :— Let M = the cubic expansion of mercury for the number of degrees Centigrade or Fahrenheit, by which the observed temperature differs from the freezin #-point. B = the linear expansion of the brass scale for the num- ber of degrees by which the observed temperature differs from the standard. H= the observed height of the barometer in inches or | millimetres. > The formula for the reduction of the English barometer will be Above 62°F, . . « «. =—(M—B)xH Below 62°, above 832°. . —(M+B)xH Below 82° . . . . . +(M—B)xH For. the reduction of the French barometer, Above the freezing-point . —(M—B)xH Below the freezing-point. -+(M—B)xH ' By the difference in the standard temperatures we can thus account for ‘00986 inch out of the -017 by which the Kew equivalent to the boiling-point differs from that of Regnault. The remainder is almost exactly accounted for by the difference of gravitation. The inerease of gravitation, 2. ¢. gravity as diminished by the centrifugal force, is from the equator to the poles =-0052005, or ‘00260 to the 45th degree of latitude. _- Adopting the law that it increases as the square of the sine of the latitude, we find that in 51° 80!, the latitude of London, the inéfease of gravity is =‘0031852; in latitude 49°, that of Paris, the increase of gravity ‘0029621. Let D be the difference of these two gravities =:0002281 ; B! the height of the mercurial column at London, equiva- lent to a given pressure ; B the ne height of the mercurial column at Par B will be gual (B/+ BD): e.g. Gravity in lat. 51° 30/=:0031852 Gravity in lat. 49° = ‘0029621 Difference =:0002231 = log 4°348305 = D 29-905 = log 1-475744=B! 3:824049 —-006688=—B'T To compare, therefore, the barometric column at London with that representing a corresponding pressure at Paris, we English and French Barometers. . 11 must add two corrections—one for the difference of the tempe- rature of standard, and a second for the decrease of gravity. The corrections will be as follows :— Barometer at London observed and 99: 905 reduced to freezing-point 3 Correction for temperature of standard+ 009861 Correction for decrease of gravity . + ‘006688 | 29°921049 equivalent pressure at Paris. This is very close to the equivalent pressure which Regnault gives in his Tables, 760 millims. = 29-922 inches*. Of course in a lower latitude the accurate correction for gravity will be greater; but practically all Tables are made to corre- spond with that of London or Paris; or else the barometer is supposed to be reduced to the mean gravity of lat. 45°= -0026003. I am somewhat astonished to find that in all the Tables given for the reduction of the barometer to the freezing-point, the only elements taken into consideration in computing the dilatation of the mercurial column are the linear expansion of the brass scales, and the cubic expansion of mercury. Surely for real accuracy the superficial expansion of the glass tube (2. e. increase of its capacity) should also be allowed for, as was done by Mr Stewart in his experiment to determine the melting-point of mercury (see Phil. Trans. vol. clin. p. 430). Let the expansion in volume of mercury (i. e. cubic) be, as determined by Regnault, =-00018153 for each degree Centi- grade above the freezing-point, and the coefficient of linear ex- pansion of the glass tube be =:0000086130, as determined by Dulong and Petit; then the coefficient of ‘the superficial ex- pansion (2. e. capacity) of the glass tube will be =-000017226. Take M for the cubic expansion of the mercury, and G for the * T have taken the increase of gravity adopted by Guyot in his Tables = 000520048, which assumes the ellipticity of the earth sae If we take the ellipticity of the earth as given by the British Ordnance Survey.5e7 (see Phil. Mag. vol. xxiv. p. 413), we shall get the increase of gravity from the equator to the pole ='00527919, and this will give the difference between that of Paris and London ='00023642 = log 4°373684 29°905 = log 1°475743 3°849427 =:007070, the amount to be added for gravity. 12 Mr. 'T. K. Abbott on the Probability of superficial expansion of the glass tube, for the number of degrees observed above or below the freezing-point. The dilatation of the mercurial column will be =M—G, or 00018153 — 000017226 = ‘000164304 for each degree Centigrade, ='000091280 for each degree Fahrenheit. The Tables, French and English, give as the correction, 0001614: for 1° Centigrade; =-00008967 for 1° Fahrenheit ; but they all take Dulong and Petit’s coefficient for the cubic expansion of mercury, which is lower than that of Regnault, being only 000180180. When the column is thus reduced for the expansion of the mercury, the additional correction for that of the scale has to be applied. I am, Gentlemen, Yours faithfully, Gayarnie, Hautes Pyrénées, CHARLES PAcKE, April 22, 1864. III. On the Probability of Testimony and Arguments. By T.K. Aevsott, M.A., Fellow and Tutor of Trinity College, Dublin*. HERE are certain questions respecting the probability of testimony and argument which, although of considerable practical importance, have been either neglected or erroneously treated by writers on the subject. It is the purpose of the pre- sent paper to consider briefly a few of these, keepimg in view not so much theoretical generality or completeness, as the corre- spondence of the conditions assumed with those which occur in ordinary experience. The case of testimony is represented in the ordinary treatises as follows :—Suppose a witness, A, affirms that a certain event has occurred, the antecedent probability of which was p, and let the witness’s credibility be a. Then, it is said, there are only two possible cases. Hither he is right, the chance of which is a; and the event has occurred, the chance of which is] P; .”, the chance of this coincidence is ap. * Communicated by the Author. Testimony and Arguments. 13 Or he is wrong, l—a; and the event has not occurred, 1—p; .”. the chance of this coincidence is l—al—p. The sum of these gives the common denominator ; and hence the resulting probability, P, that the event has actually hap- pened is = =, ap+1l—al—p Now let there be two or more witnesses who agree in the same assertion, their respective credibility being a,, a,, &c. Then either they are together right, and the event has occurred, the chance of which is @y Ag+ ++ AnD or they are together wrong, and the event has not occurred, the chance of which is fad Gas ok as Lp: Hence the resulting probability of the event is = @y Ag+ 2-An Dp 4 ~~ Gy Ag +++ 4,p+1—a, 1—ay...1—p From the first formula it follows that, ifa=4, P=p; that is to say, if this witness attests an event, of the chances of which we know nothing, his affirmation is enough to make the odds on it even; but if we have any other means of estimating the chances, his testimony goes for nothing. This is certainly not practically true. But the second formula leads to a result more obviously absurd. Suppose a,=da,=...=a,=4; then in this case again P=p; that is to say, if any number of witnesses, supposed to be wholly independent, give coincident testimony, it adds nothing to the probability of the event, unless each separately is sufficiently credible to turn the odds in its favour. If the odds are against the truth of each witness separately, then the greater their number the less credit is due to their testimony. The weight usually attributed to the coincidence of independent wit- nesses is inconsistent with the formula, according to which agreement in truth is just as unlikely as agreement in falsehood. A calculation which yields such results as these must be erro- neous, or imply conditions very different from those of ordinary 14 M. T. K. Abbott on the Probability of experience. In fact we have taken no account of the datum that error is manifold, while truth is one. Laplace analyzes ihe case of single witnesses as follows. Hig method generally is, having stated the chances of every possible case, to multiply each by the chances of the hypothesis in that par- ticular case. Thus, suppose an urn contains 100 balls numbered consecutively, and one is drawn. The witness A, who knows how many balls there are, affirms that the ball drawn was No. 25. Let us suppose his general Sd high he to be e 33 3 we heres the fol- lowing cases :— Hypothesis. —A affirms No. 25. ; Either he is right = 2, and it was drawn = ;1>. i this case the hypothesis is certain, therefore the chances of this supposition =2545=74- Or he is wrong =4, and No. 25 was not drawn, = 7%%; but this must-now be multiplied by the chance of the hypothesis in this case, 7. e. the chance that when A is wrong, his false testi- mony wiil be borne to No. 25. There being 99 balls not drawn, any of which might be asserted falsely, this chance is thereeEe go and the total chances of this last supposition =} 75 gy=sdo- The aes of the two suppositions respeciively are therefore do and ;4,; and as these exhaust all possible cases, the total probability of the event affirmed is =) eee it is due Tz0 t+ 600 et the same as the witness’s general credibility. The erroneous formula first quoted \ would have given as the resulting proba- I toot dey, 104 Laplace, it will be seen, has taken account of the diversity of error ; yet his conditions do not corr espond perfectly with those of actual experience. In fact the resulting probability in the case supposed was found to depend solely on the credibility of the witness, not at all on the antecedent probability of the event. This is a consequence of the supposition that the witness knows the number of balls in the urn; so that the number of possible errors is 99, and the odds against any particular ball are also. 99 to 1. In fact the chance of any ball being named at random is the same as the chance of its being drawn. But there is a further condition implied in the mode of stating the problem. Let it be supposed.that there are 2 white balls, 3 yellow, 5 red, in all 10. The witness asserts that white is drawn, his credibility being still supposed =3. The chances in favour of his assertion are My Eee =, 6°10 If he is wrong, either yellow was drawn or red. The chances _. Testimony and Arguments. 15 of the former are ;%,; and as there are 7 balls not of this colour, of which 2 are white, and the witness knows this, the chances of white being falsely named in this case =7%5 # = 3%. Similarly, the ehances of a false assertion of white when red is drawn =,°,2=-5. Total false assertions of white =49, to be multiplied by the ehance that A speaks falsely = 4. Hence, finally, the probability of A’s assertion is ~ 4 % 7 $+h3$ 9 In general, on. this supposition, if there are n cases whose probabilities are p,, o, &c., the sum of these being &, the chances of a false assertion of p, are Pil Pe P3 Hay § .). > \2—po =—Ps Call the quantity within the brackets C; then if the credibility of the witness be a, and he asserts the event p,, the probability that he is right is ~ | : a If we suppose that the witness knows the colours of the balls, but not the number of each colour, the case is different. Sup- pose, with the same numbers, he affirms white. Lither he is right, and it is drawn | —— 1 = Ee Or he is wrong, and selects white from the ¢wo colours not drawn, —1i1 8 1|1— prot oy i) = T5° Resulting probability of white SiS «: h a7 In general, if there be n cases p,, Po, &c. as above, and the wit- ness, knowing only the number of possible cases, asserts the event p,, the probability that he is right is (n—1)ap, (n—1)ap,+ 1—a (3—p,) Thus it is clear that on either hypothesis the case assumed by Laplace is not general. The condition involved in it, stated generally, will be seen to be, that, if the antecedent probability of the eyent named be p, the chances of its being falsely named when it has not occurred are l—-p 16 Mr. T. K. Abbott on the Probability of Now let us see how Laplace treats the case of a witness attest- ing a fact of given antecedent probability. Suppose there are 100 balls, of which one is white and the rest black, The witness whose credibility is 2 asserts that the ball drawn was white. The cases are :— Hypothesis —A affirms white. Hither he is right =2, and white was drawn =+},; chances in favour of this supposition = <3. Or he is wrong = j, and black was drawn = 7%; chances in favour of this supposition = 25. For on this supposition the hypothesis is certain, inasmuch as A, if he is wrong, must bear witness to white. Hence the total probability of white is — br oT oe 5+99 ~~ 104. In general if the whole number of balls be n, of which one only is white, the rest being black, and the witness whose credibility is a asserts that white was drawn, the probability of this event is evidently a a+ (1—a) (n—1) The probability that the assertion is not true is a= il =«) 2 a+(n—1)(1—a) If nis very large, this will not differ much from unity, 7. e. certainty, if we suppose even a slight chance of mistake or decep- tion on the part of the witness. Now this is the case of an extra- ordinary event ; and the result, adds Laplace, confirms the judg- ment of common sense, that such an event requires far stronger evidence to prove it than an ordinary one. On the same conditions, if several (say 7) witnesses join in attesting the drawing of white, then if their credibility is the same, the resulting probability is a’ a” +(1—a)’(n—1) This corresponds with the formula quoted at the beginning of this paper, and the same consideration shows that it is not appli- cable te such cases as are met with in ordinary experience. Sup- pose, for instance, the number of balls is 10, and three indepen- dent witnesses testify that white was drawn. If the credibility of each is 3 (t.¢., it is 2 to 1 that his unsupported testimony Testimony and Arguments. 17 is true), then the three together do not make it an even chance that white was drawn. The odds are still 9 to 8 against it; and, as before noticed, if the testimony of these is supported by a number of independent witnesses whose average credibility is only 3, it does not become a whit more probable. Common sense shows that this is to allow too much to the extraordinary character of the event, and that some condition must be involved in the calculation which does not apply to the events of ordi- nary life. One such condition was introduced by the assumption that when the witness is mistaken or deceived, there is no diversity of error possible. There are only two colours, and he knows this; therefore if black is drawn and he is wrong, it can only be by testifying to white. In order to apply such a for- mula to the evidence for an extraordinary event in general, we must assume that, supposing it not to have occurred, any error on the part of the witnesses must have led to its being reported. Of course whenever this can be shown, the circumstance detracts immensely from the weight of the testimony; but it is very far indeed from being generally the case. Before examining the problem more generally, it is worth while to show that Laplace’s formula applies only to the particular case which he has selected ; and that the extension of it by subsequent writers, who substitute p (the antecedent probability) for = is fallacious, even when we frame our conditions in perfect analogy with those of Laplace. Thus suppose, besides the 99 black and one white ball, we put into the urn 99 blue and one yellow, 99 red and one green. The drawing of white is exactly as extraordinary as before, and the chances against it greater, viz. 322. Nevertheless when it is affirméd its probability becomes (the witness’s credibility being 3 a a Is 54 222 324 or more than half as much again as in the former case. We must therefore investigate the problem under more general con- ditions, Suppose then that the witness A does not know anything about the colours or number of the balls in the urn; his affir- mations, therefore, may range over all possible colours, say m. Nowif he states that the ball drawn was white, we have the following cases :— _ Aypothesis—A affirms white. Hither he is right and white is drawn, a n? Phil, Mag. 8. 4, Vol. 28. No. 186, July 1864. C 18 Mr. T. K. Abbott on the Probability of or he is wrong and black is drawn, (1—a) (=); on which supposition the probability of the hypothesis, 2. e. the chance that he affirms white out of the m—1 colours which are not drawn, is 1 m—1 The chances in favour of this supposition therefore are Hence the probability of the event affirmed sd (m—1)a : (m—1)a+(1—a) (n—1) If there are several (7) independent witnesses who give the same evidence, then, supposing their credibility to be the same, the probability of the event is (m—1)*a* (m—1)"a" + (1—a)"(n—1) In the example above given of 10 balls and 3 witnesses each of credibility 2, if we suppose only four colours capable of being mentioned, this formula gives as the probability of the event 24; that is, the odds in favour of the event are 24 to 1 instead of being only 8 to 9. . If now we return to the case put by Laplace, it may be asked, is it possible that the circumstance of the witness knowing or not knowing that there are only two colours in the urn can make such an enormous difference in the credibility of his testi- mony? I answer no; and for this reason, that a does not represent the same quantity in both cases. This will be at once obvious from the following consideration. When there are 100 numbered balls, a man whose announcements are made altogether at random will be right only once ina hundred times ; but a man whose credibility is 3, 7. e. who is right fifty times in a hundred, is a good witness. ‘Two such witnesses agreeing would be equi- valent to one whose credibility is °9,. But if there are fifty black and fifty white balls, so that there are only two pos- sibilities to choose from, and the chances of these are equal, the random speaker will be right fifty times in a hundred. In this case, therefore, the credibility represented by 4 is no credibility Testimony and Arguments. 19 at all, and two such witnesses are accordingly of no more value than one; so that the same degree of credibility is represented in the one case by ;4,, and in the other by}. The credibility, therefore, which was represented by 4 in the first case ought to be represented by a greater fraction in the second; the witness has not lost all his credibility because the event itself has become more probable. It is clear, then, that a represents not the antecedent credibility of the witness, but the chances of his announcement being right under the particular conditions sup- posed, To consider the matter practically :—the chances of the witness being mistaken in the colour of a black ball are the sum of the chances of his taking it for white, for yellow, for red, and the rest of the m colours. Now if it is known that there are only two colours in the urn, he is excluded from m—2 of the m—1 possible mistakes, but we have no reason to suppose that when he is dis- posed to mistake black for red for example, he has no choice but to affirm white if he knows that red is not present. If we know nothing further about the case, we must suppose that in all such instances (2. e. where he mistakes black or white for a colour known not to be present) he has no reason for choosing either black or white, and therefore divides his assertions equally between them. We have then the following cases :— Hypothesis.—He affirms white, the probability of which is p, and his credibility a. Case 1. He believes that white is drawn, and itis so; chances in favour of this supposition = ap. Case 2. White is drawn, and he mistakes it for some colour known to be absent ; chances = p ious (l—a). m—1 In half of these imstances he affirms black, and the other half white ; hence chances that he affirmswhite on this supposition=(1— pe. Case 3. Black is drawn, and he mistakes it for white ; 1 chances =(1 —a)(1—p) ——— ae Case 4. Black is drawn, and he mistakes it for an absent colour, ____m—2 (1—p) 7 (1-4); C2 20 Mr. T. K. Abbott on the Probability of in half of which instances he affirms white; hence chances that white is affirmed on this supposition | m—2 = Sa) a On the whole, therefore, he affirms white in m—2 m—2 ap + (le) Opreereneesy +(1—a)(1—p) Imag Cases of which he is right in ap+ (l—a)p = cases. Hence the probability that white was drawn is gr feta: << 3 ap + (1—a)p 2+ —P) ome or putting a+ (1—a) =. =, it 18 oP ap + (1—a)(1—p) His credibility in these particular circumstances, therefore, 1s a+l1 2 the odds in his favour, instead of a to l—a, are now 1+a to 1 —a, or more than double. ee The result will be the same if we introduce the supposition that the witness intends to deceive, since the motives which usually affect his veracity cannot be supposed to operate uni- formly in fayour of the assertion of white when the remaining colours are excluded. Indeed we ought rather to suppose that in the absence of these colours a proportionate number of the motives to deception disappears; so that if his veracity be : and his judgment 7, he now affirms white.truly in ap(1—v) 5 cases, in which, if the other colours were present, he would be induced to affirm some one of them falsely. But it is useless to pursue this hypothesis any further. Enough has been said to show that it is altogether unfit to furnish a general formula. It would be quite as reasonable to neglect the probability of the event, and limit ourselves to that of its assertion, as to neglect the latter probability altogether. The general formula already given is independent of any hy- pothesis with respect to the knowledge of the witness, or the not a, but « When m is considerable, « nearly = See Testimony and Arguments, 21 proportion between extraordinary and ordinary events in general. It may be stated somewhat differently thus:—A witness whose eredibility is a, announces an event, the antecedent probability of which is p, and the chance of its being announced without reason 7; then the resultant probability is ap(1—r) ap(1—r) + (L—a)(1—p)r If complete generality is desired, we must introduce separately the chances of the witness being mistaken 4, and of his intending to deceive f, and also the chances of the event being imvented 2, or being erroneously supposed to have happened s. It may be worth while to exhibit the formula in this shape. It is obvious that when the event has actually happened, it may or may not be that the causes which would lead to its being either invented or falsely believed have also existed, i. e. pz and ps are possible cases. ‘This consideration simplifies the formula, which will be found to give for the resulting probability of the event announced p§(1—f)(1—#) + frit py(L—f)(L—A) + fhit + (L—p) {(L—f)as + fe} When r= p, the probability just given is reduced to a, and accordingly it frequently happens that, although the event announced is extraordinary, the chances of fiction or mistake may be proportionately small, and in such cases we are satisfied with ordinary testimony. Mr. J. S. Mill has some useful observations on Laplace’s for- mula in the chapter on the “Grounds of Disbelief” in his ‘System of Logic.” He draws attention to the absolute identity supposed by hypothesis to exist between the 99 black balls, which renders the case unlike that of real events. I have not referred to this, because in fact it results from the nature of the problem to be solved, in which we compare events of different degrees of antecedent probability; the 99 black balls are not in- tended to represent 99 similar events, but one and the same event, For the purposes of calculation, the chances in favour of an event must be treated as representing so many cases of its occurrence. When we say that the chances are 9 to | in favour of a certain horse A beating another horse B, there are only two events conceivable, and only two sets of motives, &c. possible : we do not conceive A as made up of 9 parts, each having an equal chance of victory with B. We may speak, indeed, of 10 trials in which A will win 9 times; but in each trial both horses and both sets of motives are equally present. To express degrees of probability, then, the most convenient method is to suppose a proportionate number of identical events, as Laplace has done. 22 Mr. T. K. Abbott on the Probability of It is important, however, to consider that testimony, true or false, is not given without motives; and therefore it may seem more proper that the formula should represent the operation of these. Let the probability of the event be p; the probability that its occurrence would move the witness to announce it truly =t. The probability of the event not happening is 1—p; let the chances that its non-occurrence would move the witness to deny it truly =d. This may not be the same as ¢. . Now let the chances that a motive to lie exists be «, and the chances of A’s yielding to it be @, 7. e. the chances of his lying =ad=v. Then, supposing that A announces the event p, which is one of the possibilities : Hither the event occurs and moves him to speak the truth, the motives to lying or to mistake not operating =pi(1—v). Or the event does not oceur, which non-occurrence has no effect on the witness, the motives to lying operating =(1—p)(1—d) v; but this must be multiplied by the chances of the hypothesis, i. e. of A fixing on this particular event, on this supposition, namely =, This gives v (1—p)(1—d) =. Resulting probability that the event announced has occurred pt(1—v) v pi(l—v) + (L—p) (1-4) If there are r witnesses, and the quantities ¢, d, v the same for all, we have pt'(l—vy pe(l—o)r+ (1—p)—ay & In this formula ¢ may represent, for example, the interest which the witness would have in truly reporting the event if it happened, and d his interest in truly reporting its non-occurrence. The case of arguments conspiring or opposed is somewhat different from that of testimony; since an argument may be fallacious, and yet the conclusion true. In the case of argu- ments establishing the same conclusion with the probability a, d, &c. respectively, the resulting probability is clearly 1a) py If two arguments are opposed, we have these cases: Testimony and Arguments. 23 the argument a is invalid, 5 invalid =a(1—®d) ; mee valid 2 0... = O(L=—a); meamerisvaid . .°. . . « =(l—a)(l—d); Sam . oe le-4, then the common denominator is <1—4w, and the odds in favour of A are less than 2wtol—w. Thus if y=2, and X=2, the odds are only 4w to l—w. IV. Notes on Scientific History. By Joun Tynpaut, F.RSX* ip i: vs aed years ago, in a Friday evening discourse at the Royal Institution+, I drew attention to the scientific labours of Dr. Julius Robert Mayer, and since that time the knowledge of his writings has been widely diffused by the publication in English of four of the five memoirs which he completed before his health gave way. A translation of Mayer’s first paper (date 1842) will be found in the Philosophical Magazine, S. 4. vol. xxiv. p- 371. A résumé of this paper, written by myself, appears in the Philosophical Magazine, 8.4.vol. xxv. p.378. A translation of his third paper (date 184:8) will be found in the Philosophical Maga- zine, S. 4. vol. xxv. pp.241, 387, 417. A translation of his fourth paper (date 1851) in the Magazine, S. 4. vol. xxv. p. 493. No translation of his second paper (date 1845) has yet been published. Circumstances have recently compelled me to refer to this Essay ; and pending its full translation, I would ask per- mission to make such a résumé of its contents as will give the readers of this journal some notion of its merits. The extracts will show the relationship of its author to other writers with whom he has been recently compared. Irom the works of these writers, moreover, I shall extract the portions on which their claims mainly rest, and thus the public will be enabled to form an in- dependent estimate of this passage in scientific history. * Communicated by the Author. ome of the Royal Institution, June 1862, Phil. Mag. vol. xxiv. p- 57. 26 _ Prof. Tyndall’s Notes on Scientific History. 2. Mayer was led from the contemplation of organic nature to the publication of his first paper “On the Forces of Inorganic Nature.” An observation made in 1840, on the blood of a patient in a tropical climate, was the origin of his scientific writings. It led him to the consideration of those physical forces on which the phenomena of vitality depend. This, if the laws of life were ever to become amenable to scientific investi- gation, he knew must be his starting-point. The paper now under consideration may be broadly divided into two parts, in the first of which he deals with the law of the conservation of energy* as it manifests itself in inorganic nature, and in the second of which he applies the law to the phenomena of life. 3. At the outset of this paper he announces, as he had pre- viously done in that of 1842, the indestructibility of force, its convertibility, and its quantitative constancy. Chemistry, he says, teaches the qualitative changes which matter undergoes under different circumstances, the form of the matter and not its amount being changed. What chemistry does for matter, physics must do for force; the force is as unalterable as the matter, and the function of physics is to study force in its forms, and to ascertain the conditions of its metamorphoses. This is the sole problem with which natural philosophy has any concern ; for as to the creation or annihilation of force, either act lies as much beyond the range of human thought as of human power. 4, For thousands of years men have employed the powers of inorganic nature to obtain mechanical effects. But to the forces of moving air and of falling water a new force has been added in modern times—the force of heat, which may be converted into mechanical effect. Supposing that to a train weighing 100,000 lbs. a velocity of 30 feet a second is to be imparted ; this may be done by the expenditure of ordinary mechanical force—by permitting, for example, the train to roll down an incline until the required velocity has been obtained. ‘Trains, however, in general move without this exercise of gravitating force, and, despite the friction of their parts, they are kept in motion. Let this friction be supposed equivalent to a rise of 1 in 150, then with a velocity of 30 feet a second the weight of . the train will be lifted 720 feet in an hour, which corresponds to the work of about forty-five horses. This large quantity of ge- nerated motion implies the expenditure of an equal amount of force. The force expended in the case of the locomotive is heat. The quantity of heat taken up by the steam employed to work the engine is greater than that which can be obtained from the recondensation of the steam. The difference between both * Rankine’s terminology. Prof. Tyndall’s Notes on Scientifie History. 27. is the heat usefully applied; that is to say, this difference ex- presses the heat which has been converted into mechanical effect. The more perfect the machine, the less will be the amount of heat obtainable from the condensation of the steam. The best engines give a difference of about 5 per cent.; that is to say, 100 lbs. of coal, burnt in such a machine, give no more heat than 95 lbs. which are burnt without doing any work. (Considering the sort of criticism to which he has been re- peatedly subjected*, the manner in which Mayer establishes the result last mentioned is worthy of particular attention. It will be observed that he deliberately chooses a substance which experiment proves to be suited to his purpose—a substance, that is, in which the whole of the heat rendered latent is consumed in exterior work.) 5. To prove this important proposition, we must investigate the relationship of elastic fluids to heat and to mechanical work. Gay-Lussac has proved by experiment, that when an elastic fluid passes from one vessel into a second one of the same size, but exhausted, the vessel from which the elastic fluid issues is cooled, while that into which it enters is warmed by exactly the same number of degrees. This experiment, which is distin- guished for its simplicity, shows that a given weight and volume of an elastic fluid may expand to double, quadruple, &c. of its previous volume without experiencing any change of temperature, or, in other words, that for the simple expansion of the gas no expenditure of heat is necessary. 6. Let a cubic inch of air at O°} and under a pressure of 28 inches of mercury, be heated to 274°, and let the quantity of heat required to warm the air be When it streams into another exhausted recipient of the same volume, the air will retain its temperature of 274°; the medium surrounding the vessels will undergo no change of temperature. Again, let a cubic inch of air, not at constant volume but under a constant pressure of 28 inches of mercury, be heated from 0° to 274°, a greater quantity of heat is now needed than before: let the quantity be x+y. If the air be permitted to cool in the two cases, it will give back the heat communicated to it. The air which is not followed by a pressure will, on cooling from 274° to 0°, give out the heat xz; that which cools under a constant pressure will yield the heat “+y. 7. Steam in the engine, where it expands under the piston, * As an example, see ‘Good Words,’ October 1862, p. 604, note :— ** Mayer’s statements imply its indiscriminate application to all bodies in nature, whether gaseous, liquid, or solid.” ot what Mayer’s words ““imply,”’ but what they are is stated in the text. - 7 Ali through his papers Mayer uses Centigrade degrees. 28 Prof. Tyndall’s Notes on Scientific History. behaves like the air under constant pressure. The heat neces- sary to the expansion of the steam is X+Y.° When the steam is cooled, the pressure of the piston is absent, or it is exercised in a greatly diminished degree: hence, in cooling, the heat given out will be X. With every stroke of the piston, there- fore, there is the loss of heat Y; that is to say, with the action of the engine a consumption of heat is inseparably connected. 8. From the quantity of fuel consumed in an engine, the total expenditure of heat may be calculated. The loss by radia- tion, transmission, and convection being subtracted, the re- mainder is the usefully applied heat. As, however, by far the ereater part of the unused heat can be but roughly estimated, only an approximate result can be thus obtamed. More sharply and more simply the problem may be solved by calculating the quantity of heat rendered latent when a gas expands under pres- sure. Let the amount required to heat a gas at constant volume 1° be 2; to produce the same elevation of temperature under constant pressure the heat necessary will be e+y. Let the weight raised in the latter case be P, and the height to which it is raised A; then we have y=Pxh, A cubic centimetre of atmospheric air at O° and 76 millims. barometric pressure weighs 0:0013 of a gramme; warmed 1° under constant pressure, it expands 51,;th of its volume, and lifts a mercury column 76 centimetres long and of a square cen- timetre basis to a height of 54,th of a centimetre. The weight of this column is 1033 grammes; the specific heat of air, according to De la Roche and Berard, is 0°267 ; hence the heat communicated to our cubic centimetre of air in order to raise its temperature 1° is equal to that which would raise the temperature of 00013 x 0°267=0-000847 of a gramme of water 1°. According to Dulong, the specific heat at constant pressure is to that at constant volume as 1°421:1; therefore the quantity required to raise the temperature of our cubic centimetre of air at constant volume 1° would be sufficient to heat 0:000347 1421 of a gramme of water 1°. Hence the difference (v+y)—z, or y= 0°000347 —0-000244=0:000103 thermal units, by which a weight P=1033 grammes is raised to = 0:000244: Prof, Tyndall’s Notes on Scientific History. 29 a height =54,th of a centimetre. Reducing these numbers, we find 1 thermal unit (1 gramme of water heated 1° C)=1 gramme : ; 367 metres raised to a height of 1330 Par. feet. This is Mayer’s calculation of the mechanical equivalent of heat. He first published the result in 1842, making use of the specific heat of air 4s determined by De la Roche and Berard. Substituting for it the subsequent and more accurate determina- tion of M. Regnault, and changing in no particular the method of calculation, Mayer’s equivalent, instead of 367, becomes 426 kilogrammetres ; Joule’s equivalent is 425. II. It has been many times affirmed that, in the calculation of the mechanical equivalent of heat, M. Séguin had anticipated Dr. Mayer by three years—that he had, in fact, pursued the same method and published the “same result.” M. Séguin’s book is in but few hands; I shall therefore give, in his own language, the details of his calculation*. 9. “ Supposons donc que l’on ait renfermé dans un cylindre ABCD, ayant un métre de section, un métre cube de vapeur a 100°, et que cette vapeur soit contenue par un piston CD, dont le poids équivaut 4 un kilogramme par centimétre carré, et derriére lequel on a fait le vide; ce qui représente, a peu de chose prés, une pression égale a celle que l’atmosphére exerce sur tous les corps au niveau delamer. L’appareil, d’ailleurs, étant disposé de telle sorte qu’il ne puisse ni céder ni recevoir du dehors aucune portion de calorique. 19. “Si Pon augmente la charge du piston CD, en y ajoutant successivement des poids pour comprimer la vapeur, jusqu’a ce que sa température se soit élevée de 20°, son ressort fera alors équilibre 4 une pression de 2 kil. par centimétre carré; et, con- sidérant que son volume augmente de 0°00375 de ce qu'il était 2 100° par chaque degré de température, ’espace ABFE qu’elle occupera sera exprimé par 14+1x a0 0:00875 _p.naen On pourra donc considérer l’effet comme sensiblement représenté par la moyenne de toutes les pressions exercées par la vapeur depuis DC jusqu’en EF multipliée par espace parcouru DE. 11. “La pression étant de 1 kil. en DC et de 2 kil. en EF, * Sur ? Influence des Chemins de Fer (Paris, 1839), pp. 385-389 inclusive. 80 Prof. Tyndall’s Notes on Scientific History. et croissant en progression géométrique, en désignant par S la somme des termes, par n le nombre des termes, le dernier, a le premier, et g la raison, P la pression moyenne; faisant n= 100, ce qui suffit pour obtenir une valeur de P assez approchée, et observant que la valeur de/ ou la pression de la vapeur en EF, est égale a 2 kil. par centimétre carré, et celle de a qui se rap- porte 4 CD, égale a 1 kil., nous aurons pour déterminer g l=aq"", g=*/*=1:007, ie @l@preih) i AC OOT ad ais i n(g—1) — 100(1-007—1) me Multipliant cette valeur par l’espace DE parcouru par le piston, égal a AD—AEH=1—0'5375 =0°4625 et par 10,000 qui repré- sente le nombre de centimétres carrés contenus dans un métre carré, on obtient 1°43 x 0:4625 x 10,000= 6613 kil. ; | ce qui nous indique que l’effet théorique obtenu par la détente d’un métre cube de vapeur comprimée par un poids de 2 kil. par centimétre carré, qu’on laisse répandre dans un espace qui répond a une pression de 1 kil. et 4 un abaissement de tempéra- ture de 20°, est représenté par un poids de 6°6138 kil. élevé & un métre, ou par 6°613. 12. “ En faisant un calcul analogue pour connaitre les espaces qu’occupe la vapeur, lorsqu’on augmente sa pression de maniére a faire élever sa température de 20 en 20 degrés, on trouvera “1, Que pour 140° la pression en GH =3*"-61, ABHG = +++ * 40 x0°00879 _omaig, GE=0°537—0°319=0™-218; P=2kil-83 ; et pour leffet total, 2°83 x 0:218 x 10,000=6170 kil. «2. Pour 160° la pression en IK 6*7-15, ay Deel 60 x 0:00375 ES a... IG=0°319—0:199=0™ 120, P=4k!-82; et pour l’effet total, 4°32 x 0°128 x 10,000=5780 kil. «3, Enfin, pour 180° la pression LM=9!-93, 1+1 x 30x 0-003875 9°93 =0™-199, ABLM= =0™-131, Prof. Tyndall’s Notes on Scientific History. 31 LI=0-199—0°131=0™-068, P=8*00; et pour l’effet total, 8:00 x 0:068 x 10,000 =5440 kul. 13. “Si nous supposons ensuite que lorsque la vapeur pousse le piston devant elle, et que la chaudiére est en communication avec le cylindre, sa température s’abaisse d’une quantité propor- tionnelle A l’effet dynamique produit, nous trouverons que la vapeur s'introduisant dans le cylindre a 100°, et perdant 20° pendant le mouvement du piston, la température, a la fin de la course, sera de 80°, et la pression de O-485. La pression moyenne 01-727. Soit pour l’effet total, : 0:727 x1 x 10,000=7270 kil., valeur qui se trouve a peu pres classée suivant la méme loi que les autres quantités auxquelles nous sommes parvenus, en consi- dérant Veffet produit par la vapeur 4 des températures et 4 des pressions plus élevées. 14. “ En réunissant tous ces résultats, et en les comparant a Pélévation de température qui leur correspond, nous formerons le tableau suivant :— : Effet produit - |Températures Bygone n empénien|on bron | pitrenee, |, ee | Pires 1 métre. produit. os Se 5976) Oe 20 1 100 : 1:80 6613 657 18:20 2 120 : 1-23 6170 443 16°97 3°61 140 ; 1:07 5780 390 15:90 FS 6-15 160 5540 240) 15-24 0°66 9:93 180 15. We have now the means of comparing Séguin’s alleged cal- culation of the mechanical equivalent of heat with that of Mayer. With reference to the foregoing Table, Mr. Joule writes thus (Phil. Mag. August 1862) :—“In page 389 he [M. Séguin] gives a Table of the quantity of mechanical effect produced corresponding to the loss of temperature of steam on expanding. From this it appears that 1° Cent. corresponds with 363 kilogrammes raised to the height of 1 metre...... Mayer discourses to the same effect as Séguin, but at greater length, with greater perspicuity, and more copious illustration. He adopts the same hypothesis as the latter philosopher, viz. that the heat evolved on compress- ing an elastic fluid is exactly the equivalent of the compressing force, and thus arrives at the same equivalent, viz. 865 kilo- grammes per 1° Cent.” 32 Prof. Tyndall’s Notes on Scientific History. 16. In the Philosophical Magazine for April 1863, Prof. William Thomson of Glasgow, and Prof. Tait of Edinburgh, express themselves thus:— Does Prof. Tyndall know that Mayer’s paper has no claims to novelty or correctness at all, saving this, that by a lucky chance he got an approximation to a true result from an utterly false analogy; and that even on this point he had been anticipated by Séguin, who, three years before the appearance of Mayer’s paper, had obtained and published the same result from the same hypothesis.” I have nowhere in this paper introduced italics into quotations; wherever they occur. they are in the original. 17. And in reference to the same subject, a more recent anonymous northern writer* expresses himself thus: — “ Of Séguin and Mayer, it seems not very difficult to estimate the claims, so far as the true theory or the mechanical equivalent of heat is concerned. Séguin in 1839, and Mayer in 1842, gave as values of the mechanical equivalent: the first 363 kilogram- metres, or, in terms of the ordinary British units, 660 foot- pounds; the second the almost identical number 365 or 663. It is curious also to observe that the methods employed are almost identical.” 18. Did the reputation of Dr. Mayer depend on his calculation of the mechanical equivalent of heat, and were the statements here quoted correct, his right to the recognition which I have thought his due might fairly be questioned. But let us inquire whether this is really the case. The Table on which the claim for M. Séguin is founded is now before the reader ; and on referring to it, two columns will be seen, the one headed “ Effet produit en kilo- grammes élevés 4 1 metre,” and the other headed ‘“‘ Températures correspondantes a l’effet produit.”” The first number in the first of these columns is 7270 kilogrammetres, and the “température cor- respondante” is 20 degrees. Hence, dividing 7270 by 20, we have the quotient 363 as the number of kilogrammetres corresponding toa single degree. And so of the other pairs of numbers, which give 363, or thereabouts, as the mechanical effect due to a single degree. All this seems very plain; and did no text accompany the Table, and had not M. Séguin in that text explicitly defined his own terms, we might be justified in assuming that he meant the number 863 to stand for the mechanical equivalent of heat, in the same sense as Dr. Mayer meant the number 365 to stand for it. It is only necessary, however, to read the foregoing pages to see that Mayer and Séquin are speaking of two totally different things ; that the degrees of the one are not the degrees of the other ; that the “‘ températures correspondantes”’ of the latter, which refer * Not my Edinburgh reviewer, who, while he writes as a critic, knows how to preserve the style of a gentleman, Prof. Tyndall’s Notes on Scientific History. 30 to his compressed steam, are not thermal units at all, and that there is no determination whatever of the mechanical equivalent of heat in the above Table. 19. The number 363 has been found for M. Séguin, not by him: he never made the division which results in this quotient. In 1847, for the first time, and without giving any description of his method *, M. Séguin gives his results “reduced to the type of 1 gramme elevated 1 metre, and corrected with reference to the specific heat of water and vapour.” His equivalent there given varies from 395 to 529 kilogrammetres (Comptes Rendus, vol. xxv. p. 420). The data, moreover, on which M. Séguin founded this last calculation were subsequently declared erro- neous by himself: the experiments of M. Regnault, he states, * defeated the calculations” (Cosmos, vol. vi. p. 684); and Mr. Grove has shown that when the correct specific heat of steam, as determined by Regnault, is introduced into the calculations, M. Séguin’s equivalent becomes 1666 kilogrammetres instead of 363 (Proceedings of the Royal Institution, vol. ii. p. 155). We have already seen that in Mayer’s case, when the correct specific heat of air is employed, his resuit is almost identical with that derived from the mean of all the best experiments of Mr. Joule. The one is 426, the other is 4257. III. 20. After gomg formally through the calculation of the me- chanical equivalent of heat, Mayer proceeds to determine the useful effect in steam-engines, and finds it to be about 5 per cent. of the consumed fuel. He then determines the useful * Such a description would be a desirable addition to our knowledge. + Ihave already drawn attention to these facts (Phil. Mag. vol. xxv. p- 385), but have been met, not by explanation, but by iteration. This, I trust, willnow cease. It is no compliment to the scientific public to think that mere hardihood of assertion can decide this question. To illustrate the difficulty of satisfying rival claimants, I may remark that in 1862 I withdrew the name of Dr. Mayer from the list of candidates for the Copley medal, out of deference to an eminent man—not Mr. Joule— who thought his own claims prior to those of Mayer. What I have had to endure at the hands of two northern critics for my supposed depre- ciation and suppression of the claims of Mr. Joule is at least partially known to the scientific public. Again, a writer in M. Séguin’s periodical, Le Cosmos, while declaring that Mr. Joule must be entirely put aside, the question of priority resting solely between Séguin and Mayer, charges me with having manifested a wholly insufficient appreciation of M. Séguin. T should be a mere intellectual quicksand if I allowed myself to be swayed by such criticisms. I have, judging from the facts, steered through these rival claims with the best light that I possess, and not one of my censors appears to have gone to one-tenth of the trouble that I have incurred to inform myself of the rights of the question. Phil, Mag. 8. 4, Vol, 28, No. 186, July 1864. D 34 Prof. Tyndall’s Notes on Scientific History. effect in the case of gunpowder, and finds in certain cases that 9 per cent. of the force of the consumed charcoal is expended on the projectile. He gives various illustrations of the generation of heat by mechanical power, and describes some observations of his own, made in a paper-mill, in which were four pulping machines, each containing about 80 lbs. of paper and 1200 lbs. of water. The surrounding temperature being 15° C., the pulp rose in thirty-two minutes from 14° to 16°. The highest observed temperature, which remained uniform for several hours, was 30°. Assuming that in one minute a horse can raise 27,000 lbs. a foot high, the heating of 1280 lbs. of water 1 degree in sixteen minutes (not taking into account the heat communicated to the apparatus) is equivalent to 3:16-horse power. The estimate in the factory was, that the pulping machines were worked with 5-horse power. Does the mechanical action of the five horses become nothing in the machine? Fact replies, 7¢ becomes heat. 21. He then goes on to show the relationship of mechanical work to electricity and magnetism, and passes to the con- sideration of chemical processes as compared with mechanical operations. A weight at such a distance from the earth that the attraction is insensible, he regards as in a state of mechanical separation; the falling of the weight to the earth as a case of mechanical combination. Such a weight would reach the earth’s surface with a velocity of 34,440 feet a second, and the heat generated by its collision would raise the temperature of an equal weight of water 17,356°. Chemical combination is in principle the same. The chemical combination of 1 gramme of carbon and 2°6 grammes of oxygen is equivalent to the mechani- cal combination of a weight of 4a gramme with the earth. The chemical combination of 1 pramine of hydrogen with 8 grammes of oxygen is equivalent to the mechanical combination of a weight of 2 grammes with the earth. The heat here develops is equal to 34,700 thermal units*. * In 1843 Mr. Joule wrote the following remarkable passage :—* I had before endeavoured to prove that when two atoms combine together, the heat evolved is exactly that which would have been evolved by the electrie current due to the chemical action taking place, and is therefore propor- tional to the chemical force causing them to combine. I now venture to state more explicitly that it is not precisely the attraction of affinity, but vather the mechanical force expended by the atoms in fallmg towards one another, which determines the intensity of the current, and consequently the heat evolved” (Phil. Mag. 1843, vol. xxiii. p.442). I cite this as one of the points of osculation between these two remarkable men. They thus touched each other repeatedly, Joule being in advance sometimes, and Mayer sometimes. But their main achievements lie in distinct fields ; and these are, in my opinion, so balanced as to render them a kind of “double star, the light of each being, in a certain sense, can plea to that of the other.” (Phil. Mag. S. 4. vol. xxvi. p. 67.) Prof. Tyndall’s Notes on Scientific History. 35 The manner in which Mayer expands his conceptions from the union of atoms to the union of worlds is a remarkable illus- tration of his generalizing power. After discoursing thus, he goes on to say :— 22. “The earth moves in its orbit with a mean velocity of 93,700’. To produce this motion by the combustion of coal, fifteen times the earth’s weight of coal would have to be consumed, and the heat produced would be competent to raise the temperature of a quantity of water equal to the earth in weight 128,000°. A small portion therefore of the force with which the earth moves in its orbit would suffice to dissolve all mechanical connexion among its parts. Supposing a mass equal to the earth in weight to lie at rest on the surface of the sun, to raise that mass, place it at the earth’s distance from the sun (215 times the sun’s radius), and to impart to it there the velo- city of 93,700', would require 429 times the above quantity of coal, or a quantity 6435 times the weight of the earth.” 23. (In a letter published in the Philosophical Magazine for August 1862 Mr.Joule writes as follows :—“ In 1847, in a popular lecture published in the ‘ Manchester Courier,’ I explained the phenomena of shooting-stars, and also stated that the effect of the earth falling into the sun would be to increase the tempera- ture of that luminary.” The foregoing passage, giving the amount of the heat that would result from the falling of the earth into the sun, was published by Mayer in 1845 *.) 24, Mayer next briefly considers the case of the voltaic battery and the gas battery. He then draws out a scheme of the five principal forms of energy which he has been examining, and under five-and-twenty separate heads he states their relations and mutual conversions. ‘ Preconceived notions,” he says, ‘ sanc- tioned by time and diffusion, and not the phenomena of Nature, are opposed to the propositions here laid down. While,” he adds, “we ascribe substantiality to motion, we must entirely deny materiality to heat and electricity. I know quite well that we have against us here the most deeply rooted convic- tions—hypotheses canonized by the greatest authorities. With the theory of imponderables we banish from science the last remains of the mythology of Greece; but we know that Nature in her simple truth transcends in glory the devices of the human phantasy, as much as she excels the operations of the human hand.” * It has been said that in the application of the dynamical theory of heat to shooting-stars, “and some other points of celestial dynamics,” Mr. Joule had “at least one year’s priority.” (Phil. Mag. vol. xxv. p. 431.) The “some other points” shrink, if I mistake not, to the point referred to in the text, and the year’s priority is, in reality, two years’ posteriority. Mr. Joule’s remarks on shooting-stars shall be quoted further on. D2 36 Prof. Tyndall’s Notes on Scientific History. iv. Having cleared his way through the powers of inorganic nature, he turns to vital phenomena, and at once fixes the attention of his readers upon the sun. 25. Measured by human standards, the sun is an inexhaust- ible source of physical energy. This is the continually wound- up spring which is the source of all terrestrial activity. The vast amount of force sent by the earth into space in the form of wave motion would soon bring its surface to the temperature of death. But the light of the sun is an incessant compensation. It is the sun’s light, converted into heat, which sets our atmosphere in motion, which raises the water into clouds, and thus causes the rivers to flow*. The heat developed by friction in the wheels of our wind- and water-mills was sent from the sun to the earth in the form of vibratory motion. (The reader cannot fail to remark the insight implied in this Jast utterance. But a still higher order of thought immediately reveals itself.) 26. Nature has proposed to herself the task of storing up the light which streams earthward from the sun—of conyerting the most volatile of all powers into a rigid form, and thus preserving it for her purposes. To this end she has overspread the earth with organisms, which, living, take into them the solar light, and by the consumption of its energy generate incessantly che- mical forces. 27. These organisms are plants. The vegetable world con- stitutes the reservoir in which the fugitive solar rays are fixed, suitably deposited, and rendered ready for useful application. With this prevision the existence of the human race is also inse- parably connected. The reducing action of the sun’s rays on inorganic and organic substances is well known; this reduction takes place most copiously in full sunlight, less copiously in the shade, and is entirely absent in darkness, and even in candle- light. The reduction is a conversion of one form of force into another—of mechanical effect into chemical tensicn. 28. The time does not lie far behind us when it was a sub- ject of contention whether, during life, plants did not possess the power of changing the chemical elements, and indeed of creating them. Facts and experiments seemed to favour the notion, but a more accurate examination has proved the con- trary. We now know that the sum of the materials employed and excreted is equal to the total quantity of matter taken * This, and much more, was stated by Sir John Herschel in 1833 (Out- lines of Astronomy), but Mayer was the first to show the relation of all these actions to the law of the conservation of energy. Prof. Tyndall’s Notes on Scientific History. 37 up by the plant. The tree, for example, which weighs several thousand pounds, has taken every grain of its substance from its neighbourhood. In plants a conversion only, and not a generation of matter, takes place. | 29. Plants consume the force of light, and produce in its place chemical tensions. Since the time of Saussure, the action of light has been known to be necessary to the reduction. In the first place we must inquire whether the light which falls upon living plants finds a different application from that which falls upon dead matter; that is to say, whether, ceteris paribus, plants are less warmed by solar light than other bodies equally dark-coloured. The results of the observations hitherto made on a small scale seem to lie within the limits of possible error. On the other hand, every-day experience teaches us that the heating action of the sun’s rays on large areas of land is moderated by nothing more powerfully than by a rich vegetation, although plants, on account of the darkness of their leaves, must be able to absorb a greater quantity of heat than the bare earth. If, to account for this cooling action, the evaporation from the plants be not sufficient, then the question above proposed must be answered in the affirmative. 30. The second question refers to the cause of the chemical ten- sion produced in the plant. This tension is a physical force. Itis equivalent to the heat obtained from the combustion of the plant. Does this force, then, come from the vital processes, and without the expenditure of some other form of force? The creation of a physical force, of itself hardly thinkable, seems all the more paradoxical when we consider that it is only by the help of the sun’s rays that plants can perform their work. By the assump- tion of such a hypothetical action of the “ vital force”? all further investigation is cut off, and the application of the methods of exact science to the phenomena of vitality is rendered impos- sible. Those who hold a notion so opposed to the spirit of science would be thereby carried into the chaos of unbridled phantasy. I therefore hope that I may reckon on the reader’s assent when I state, as an axiomatic truth, that during vital pro- cesses only a conversion of matter, as well as of force, occurs, and that a creation of either the one or the other never takes place. (To the philosophy of vegetable life here so firmly sketched, nothing to my knowledge has been added since. It will be immediately seen that Mayer’s power does not relax when he treats of animal life and energy.) a's 31. The physical force collected by plants becomes the pro- perty of another class of creatures—of animals. ‘The living 38 Prof. Tyndall’s Notes on Scientific History. animal consumes combustible substances belonging to the vege- table world, and causes them to reunite with the oxygen of the atmosphere. Parallel to this process runs the work done by animals. This work is the end and aim of animal existence, Plants certainly produce mechanical effects, but it is evident that for equal masses and times the sum of the effects produced by a plant is vanishingly small, compared with those produced by an animal. While, then, in the plant the production of mechanical effects plays quite a subordinate part, the conversion of chemical tensions into useful mechanical effect is the charac- teristic sign of animal life. 32. In the animal body chemical forces are perpetually expended. Ternary and quaternary compounds undergo during the life of the animal the most important changes, and are, for the most part, given off in the form of binary compounds—as burnt substances. The magnitude of these forces, with re- ference to the heat developed in these processes, is by no means determined with sufficient accuracy; but here, where our object is simply the establishment of a principle, it will be sufficient to take into account the heat of combustion of the pure carbon. When additional data have been obtained, it will be easy to modify our numerical calculations so as to render them accordant with the new facts. 33. The heat of combustion of carbon I assume with Dulong to be 8550°. The mechanical work which corresponds to the combustion of one unit of weight of coal corresponds to the raising of 9,670,000 units to a height of 1 foot. If we express by a weight of carbon the quantity of chemical force which a horse must expend to perform the above amount of work, we find that the animal in one day must apply 1°34 Ib. ; in an hour 0°167 lb.; and in a minute 0°0028 lb. of carbon to the production of mechanical effect. According to current estimates, the work of a strong labourer is 1th of that ofa horse. A man who in one day lifts 1,850,000lbs. to a height of a foot must consume in the work 0:19 lb. of carbon. This for an hour (the day reckoned at eight hours) amounts to 0:024 1b. ; for a minute it amounts to 0:0004 lb. =3:2 grains of carbon. A bowler who throws an 8-lb. ball with a velocity of 30’ consumes in this effort th of a grain of carbon. A man who lifts his own weight (150 lbs.) 8 feet high, consumes in the act 1 grain of carbon. In climbing a mountain 10,000 feet high, the consumption (not taking into account the heat generated by the inelastic shock of the feet against the earth) is 0°155 lb. =2 ozs. 4.drs. 50 grs. of carbon. 34. If the animal organism applied the disposable com- bustible material solely to the performance of work, the quan- Prof. Tyndall’s Notes on Scientific History. 39 tities of carbon just calculated would suffice for the times men- tioned. In reality, however, besides the production of mecha- nical effects, there is in the animal body a continuous genera- tion of heat. The chemical force contained in the food and inspired oxygen is therefore the source of two other forms of power, namely, mechanical motion and heat; and the sum of these physical forces produced by an animal is the equivalent of the contemporaneous chemical process. Let the quantity of mechanical work performed by an animal in a given time be col- lected, and converted by friction or some other means into heat ; add to this the heat generated immediately in the animal body in the same time, we have then the exact quantity of heat corresponding to the chemical processes that have taken place. 35. In the active animal, continues Mayer, the chemical changes are much greater than in the resting one. Let the amount of the chemical processes accomplished in a certain time in the resting animal be z, and in the active one x+y. If during activity the same quantity of heat were generated as during rest, the additional chemical force y would correspond to the work performed. In general, however, more heat is produced in the active organism than in the resting one. During work, therefore, we shall have x plus a portion of y for heat, the residue of y being converted into mechanical effect. 36. I must now prove that the extra quantity of combustible matter consumed by the working animal contains the necessary force for the performance of the work. A strong horse, not working, is amply nourished on 15 lbs. of hay and 5 lbs. of oats a day. If the animal performed daily the work of lifting a weight of 12,960,000 lbs. 1 foot high, it could not exist on the same nu- triment. To keep it in good condition we must add 11 lbs. of oats. The 20]bs. of nutriment first mentioned is the quantity which we have named 2, and contains, according to Boussingault, 8074 lbs. of carbon. The additional 11 lbs. of oats, our quan- tity y, contains, according to the same authority, 4°734. According to Boussingault, also, the carbon introduced is to _ that excreted in a combustible form as 3938 : 1864°4. Caleu- lating from these data, we find z, or the quantity of carbon burnt by the resting animal, 5'2766 lbs., and y=3'094. lbs. The quan- 4 consumed in mechanical effect is 1°34 lb., which we will call z. 37. We have therefore the following relations:—1. The mechanical effect is to the total consumption as z:2+y=0°'16. 2. The mechanical effect is to the surplus consumption of the working animal as z:y=0'43. 3. The generation of heat at rest is to the generation of heat while working as #: w-+y—z=0°75. 40 Prof. Tyndall’s Notes on Scientific History. 38. In the same way Mayer, taking the data furnished by Liebig regarding the prisoners and soldiers at Giessen, deter- mines the following relations for a man. 1. The mechanical effect is to the total consumption as 95°7 : 540=0°177. 2. The mechanical effect is to the surplus consumption of the man at work as 957 : 285=0°336. 38. The generation of heat in the resting man to that in the working man as 255 : 540—95:7=0°57. 39. In these calculations, he continues, I have confined my- self to the consumed carbon. If the heat of combustion be set equal to the carbon+the hydrogen, the additional heat of the hydrogen may be regarded as nearly=1th of that of the carbon. According to the individual constitution and habits of life, the labour and the consumption must be liable to considerable va- riations. The above results, however, serve to demonstrate the following propositions :— (1.) The: surplus nutriment consumed in the working or- ganism completely suffices to account for the work done. (2.) The maximum mechanical effect produced by a working mammal hardly amounts to 1th of the force derivable from the total quantity of carbon consumed. The remaining #ths are devoted to the generation of heat. Vi 40. In order to enable them to convert chemical force into mechanical work, animals are provided. with specific organs, which are altogether wanting in plants... These are the muscles. 41. To the activity of a muscle two things are necessary :— 1. The influence of the motor nerves as the determining condi- tion; and 2. the material changes as the cause of the mecha- nical effect. 42. Like the whole organism, the organ itself, the muscle, has its psychical and its physical side. Under the former we include the nervous influence, under the latter the chemical processes. 43, The motions of the steamship are performed in obedience to the will of the steersman and engineer. The spiritual influence, however, without which the ship could not be set in motion, or, wanting which, would go to pieces on the nearest reef, guides, but moves not. For the progress of the vessel we need physical force—the force of coal; in its absence the ship, however strong the volition of its navigator, remains dead. VIL. Thus does this remarkable man, at a time when the writings of the most celebrated scientific professors were beset with mysticism as regards the operations of the vital force, pour light upon the darkness, and bring the processes of the animal body Prof. Tyndall’s Notes on Scientific History. 41 into harmony with the great law of conservation, which he himself, alone and unaided, had thought out. 44, Here follow a few of Mayer’s remarks on muscular motion. In the first part of this memoir, the part played by combus- tion in inorganic apparatus in the steam-engine, for instance was, in its main characters, explained. Our present problem is to consider the phenomena of vitality in connexion with their physical causes, and thus give to the propositions of physiology the basis of exact science. | 45. It has been already stated that an active working man converts in a day 0°19 lb. of carbon into mechanical effect. The weight of the whole muscles of such a man, who weighs 150 lbs., is 64 lbs. ; and, subtracting 77 per cent. of water, 15 lbs. of dry combustible material remains. Let it be assumed (though not granted) that the heat-giving power of this mass (with 40 per cent. of nitrogen and oxygen) is equal to that of an equal mass of pure carbon; then, if the work were done at the expense of the muscles themselves, the whole of the muscles must be oxidized and consumed in mechanical effect in eighty days. 46. This arithmetical deduction becomes still more evident if we confine our attention to the work performed by a single muscle—the heart. I assume, with Valentin, the quantity of blood in the left ventricle to be at every systole on an average 150 cubic centimetres. The hydrostatic pressure of the blood in the arteries is, according to Poiseuille, equal to the pressure of a column of mercury 16 centimetres in height. The me- chanical work done by the left ventricle during a systole may be calculated from these data. It is equal to the raising of a column of mercury 16 centimetres long, and with a base of a square centimetre to a height of 150 centimetres. The weight of the mercury amounts to 217 grammes. The mechanical effect of a systole therefore is _ { 825°6 grammes raised 1 metre, 7 2 lbs. sxade toot, which is equivalent to 0°887 of a thermal unit, or equivalent to the combustion of 0°0001037 of a gramme of carbon. Taking for a minute 70 strokes, and for a day 100800 strokes of the pulse, the work done by the left ventricle in a day is equivalent to the raising of 202000 lbs. to a height of one foot. This is equal to 89428 thermal units, which is equal to the combustion of tise fot carbon. According to Valentin, the work done by the right ventricle is half that done by the left. The work of both chambers in a single day is therefore equal to 42 Prof, Tyndall’s Notes on Scientific History. the raising of 303000 lbs. 1 foot high =134143 thermal units BEY [teiae gis. \ of carbon ~ | 252°4 grs, F 47. Assuming the weight of the whole heart to be 500 grammes, and deducting from this 77. per cent. of water, we have remaining 115 grammes of dry combustible material. Assuming this material to be equal to that of pure carbon, it would follow that the entire organ, if it had to furnish the matter necessary to its action, would be oxidized in eight days. Taking the weight of the two ventricles alone as 202 grammes, under the same conditions the complete combustion of this muscular tissue would be effected in 34 days. VIII. 48. This partial résumé of half of Mayer’s second memoir is now ended. It embraces only the first 56 pages of an essay which contains 112 pages. Mayer began, as has been stated, with the question of vital dynamics. The observation which led to his scientific labours was made on a patient at Java in 1840, and in 1842 he published his first paper. He informs us that he had put it briefly together to secure himself agaist casual- ties* ; and having done this, he continued his inquiries, and in 1845 published the memoir from which the foregoing extracts are taken. He did this in the intervals of a laborious profession, *‘ ohne dussere Ermunterung,” as he himself touchingly observes. The full translation of the essay can alone give an adequate idea of the research which it imphes. Mayer probably had not the means of making experiments himself, but he ransacked the records of experimental science for his data, and thus conferred upon his writings a strength which mere speculation can never possess. From the extracts which I have given, the reader may infer his strong desire for quantitative accuracy, the clearness of his insight, and the firmness of his grasp. Regarding the recog- nition which will be ultimately accorded to Dr. Mayer, a shade of trouble or of doubt has never crossed my mind. — Individuals may seek to pull him down, but their efforts will be unavailing as long as such evidence of his genius exists, and as long as the general mind of humanity is influenced by considerations of justice and of truth +. * Phil. Mag. vol. xxv. p. 501. + The paucity of facts in Mayer’s time has been urged as if it were a reproach to him, but it ought to be remembered that the quantity of fact necessary to a generalization is different for different minds. ‘A word to the wise is sufficient for them,” and a single fact in some minds bears fruit that a hundred cannot produce in others. _Mayer’s data were compara- tively scanty, but his genius went far to supply the lack of experiment, by Prof. Tyndall’s Notes on Scientific History. 43 rm 49. There are a few points remaining, which, to preserve the events of scientific history in their true relationship, ought to be referred to here. It has been asserted mildly (as is his wont) by Mr. Joule, less mildly (as is their wont) by his northern sup- orters, that, as regards vital dynamics, he anticipated Mayer - two years. In a letter published in the Philosophical Maga- zine for August 1862, Mr. Joule writes thus :—“‘ Permit me to remark, that I applied the dynamical theory of heat to vital pro- cesses in 1843.” Let all justice be done to Mr. Joule regarding his application of the theory. In a postscript to a paper in the December Number of the Philosophical Magazine for 1843 he writes thus :— 50. “ On conversing a few days ago with my friend Mr. John Davies, he told me that he had himself a few years ago at- tempted to account for that part of animal heat which Craw- ford’s theory had left unexplained, by the friction of the blood in the veins and arteries, but that, finding a similar hypothesis in Haller’s ‘ Physiology,’ he had not pursued the subject further. It is unquestionable that heat is produced by such friction, but it must be understood that the mechanical force expended in the friction is a part of the force of affinity, which causes the venous blood to unite with the oxygen, so that the whole heat of the system must still be referred to the chemical changes. But if the animal were engaged in turning a piece of machinery, or in ascending a mountain, | apprehend that, in proportion to the muscular effort put forth for the purpose, a diminution of the heat evolved in the system by a given chemical action would be experienced.” This citation embraces, I believe, every word that was written on “ yital dynamics” by Mr. Joule, before the appearance of Mayer’s paper on organic motion. It consists of a conjecture, the sagacity of which is in accordance with the insight always mani- fested by Mr. Joule. Let the reader compare it with sections 4 to 7 of this résumé, and make the deductions which he deems right from his estimate of Mayer’s work. 51, In 1852 Prof. Wm.Thomson wrote on the subject of “ vital dynamics,” and it will be instructive to compare what he has done with what had been done by Mayer seyen years earlier. enabling him to see clearly the bearing of such facts as he possessed. They enabled him to think out the law of conservation, and his conclusions - received the stamp of certainty from the subsequent experimental labours of Mr. Joule. In reference to their comparative merits, I would say that, as Seer and Generalizer, Mayer, in my opinion, stands first,—as Experi- mental Philosopher, Joule. Ach Prof. Tyndall’s Notes on Scientific History. The whole paper of Prof. Thomson, published in the Philoso- phical Magazine for 1852, vol. iv., may be compared with the writings of Dr. Mayer now before the reader. I, however, will limit myself here to the section “ On the Power of Animated Creatures over Matter” (p. 258). «A principal object of the present communication is to point out the relation of this theory [that of animal heat and motion] to the dynamical theory of heat. It is remarked, in the first place, that both animal heat and weights raised or resistance overcome, are mechanical effects of the chemical forces which act during the combination of food with oxygen. The former is a dynamical mechanical effect, being thermal motions excited ; the latter is a mechanical effect of the statical kind. The whole mechanical value of these effects, which are produced by means of the animal mechanism in any time, must be equal to the me- chanical value of the work done by the chemical forces. Hence, when an animal is going up-hill or working against resisting force, there is less heat generated than the amount due to the oxidation of the food, by the thermal equivalent of the mecha- nical effect produced. From an estimate made by Mr. Joule [in 1846, Phil. Mag. vol. xxvii. p. 454], it appears that from 1 to 1 of the mechanical equivalent of the complete oxidation of all the food consumed by a horse may be produced from day to day as weights raised [Mayer published the same result a year previous to Mr. Joule, see 39]. The oxidation of the whole food consumed being, in reality, far from complete [see Mayer, 36 to 39], it follows that a less proportion than 2, perhaps even less than 2 of the heat due to the whole chemical action that actually goes on in the body of the animal, is given out as heat. An estimate, according to the same principle, upon _ very imperfect data, however, is made by the author, regarding the relation between the thermal and the non-thermal mecha- nical effects produced by a man at work [Mayer made the same estimate, see 38]; by which it appears that probably as much as 1 of the whole work of the chemical forces arising from the oxidation of his food during the twenty-four hours may be directed to raising his own weight, by a man walking up-hill for eight hours a day; and perhaps even as much as 4 of the work of the chemical forces may be directed to the overcoming of external resistances by a man exerting nimself for six hours a day in such operations as pumping. In the former case there would not be more than 2, and in the latter not more than 2 of the thermal equivalent of the chemical action emitted as animal heat, on the whole, during twenty-four hours, and the quantity of heat emitted during the time of working would bear much smaller proportions respectively than these to the thermal Prof. Tyndall’s Notes on Scientific History. 45 equivalents of the chemical forces actually operating during those times” *, Comparing the foregoing remarks with what Mayer had written seven years earlier, the reader will draw his own conclu- sions as to their comparative completeness. In his writings upon yital dynamics Prof. Thomson never once mentions the name of Mayer; he is not, I presume, to be blamed for this omission ; for when he wrote in 1852 he knew nothing about Mayer’s most important labours. I state this because the opposite supposition is too unpleasant to be entertained. But in 1862 I gave him the titles of Mayer’s memoirs, and requested him and others to refer to them, and correct me if I had erro- neously estimated the merits of their author. To my great regret, Prof. Thomson, without giving himself the trouble of consulting the documents to which I had referred him, sanctions the publication of the statement, that, as far back as 1851, he had given to Mayer “the full credit which his scientific claims can possibly be admitted to deserve” +. 52. In the paper from which I have just quoted, Prof. Wm. Thomson also refers to the deoxidation of carbon and hydrogen from carbonic acid and water, effected by the action of solar light upon the green leaves of plants, as a mechanical effect of radiant heat. This action, he says, was pointed out by Helm- holtz in 1847. 53. The words of Helmholtz are as follows (Erhaltung der Kraft, p. 69 {) :—‘ There remains to us of known natural pro- cesses those of organic beings. In plants the processes are principally chemical, and besides this, in some of them, at least, a slight generation of heat takes place. Of foremost importance is the fact, that in them a great quantity of chemical forces is deposited, the equivalent of which we obtain as heat on the com- bustion of the plant. The only vis viva which, according to our present knowledge, is absorbed during the growth of the plant, consists of the chemical rays of the sun. Results are, however, still wanting to enable us to make a sure and strict comparison of the forces which here disappear and appear. For animals we have, however, some grounds of comparison. They take in the complicated oxidizable compounds which are produced by plants and oxygen, and return them for the most part burnt as carbonic acid and water ; partly, however, they are excreted, reduced to sim- * On first reading this passage I thought it might be an abstract of a fuller statement, but I have been unable to find anything more complete. 7 Phi. Mag. vol. xxv. p. 264. t This excellent essay was translated by myself many years ago, and published in the last volume of the Scientific Memoirs. (Taylor and Francis, Red Lion Court, Fleet Street.) 46 Prof. Tyndall’s Notes on Scientific History. pler combinations. They therefore consume a quantity of chemi- cal forces, and generate in their place heat and mechanical forces. As the last represent a comparatively small amount of work in — comparison with the amount of ‘heat, the question of the con- servation of force reduces itself to this :—Do the combustion and the change of materials in the nutriment generate an equal quantity of heat to that yielded up by the animal? According to the experiments of Dulong and Despretz, this question can, at least approximately, be answered in the affirmative.” 54. Helmholtz made this statement independently of Mayer, for when he wrote he did not know what had been published two years before at Heilbronn *; and clearly as the above paragraph illustrates his insight on this momentous point, it could not be accepted as an adequate abstract of Mayer’s previous writings on the same subject. In a lecture of varied excellence, trans- lated by myself, and published in the Philosophical Magazine, 1856, vol. u., Helmholtz expresses in clear and beautiful lan- guage the relation of animals to vegetables, and of both to the sun. The lecture was given at Konigsberg on the 7th of Fe- bruary 1854; andif the reader wishes to realize fully the extent to which Mayer had occupied this field, and the scantiness of the additions made to our knowledge of vital dynamics during the nine years following the publication of Mayer’s essay, he may compare pp. 509, 510, and 511 of Helmholtz’s lecture with see- tions 4, 5, 6, and 7 of this résumé. 55. One word more on this subject, which shall have as slight a personal tinge as I can under the circumstances impart to it. In a religious periodical, which we are informed numbers 120,000 readers, Prof. Thomson undertook to give an accurate account of the discovery, nature, and development of the law of the conserva- tion of energy, professedly with the view of correcting the errors which he believed me to be disseminating regarding Mayer. In that article he charged me with depreciation and suppression, and these bad words rest unretracted in the pages of ‘ Good Words’ to this hour. After dealing with various questions relating to the “ conservation of energy,” Prof. Thomson comes at length to the “grandest question of all,’ and states it thus :—‘‘ Whence do we derive the stores of potential energy which we employ as fuel and food? What produces the potential energy of a loaf or a beefsteak? What supplies the coal and the water power, without which our factories would stop?” And the answer to this question is “the sun.” Prof. Thomson can now name the man who answered this question seventeen years before he called it the grandest of all—the man * «T myself, without beg acquainted with either Mayer or Colding,” &c.—Phil. Mag. S. 4. vol. i. p. 409. Prof, Tyndall’s Notes on Scientific History. A7 whose name, to my deep regret, he has never yet named in con- nexion with this question, though Mayer’s relation to it has been now for two years known to him. But this is not all. In public and in private—in articles which are so far manly as to bear their author’s names, and in an article which bears no name, but which has been recently mentioned with commendation in the pages of this Magazine—I have been attacked for my support of Dr. Mayer in language which I would not stoop to characterize. While here, from the pen of the man who, in equal ignorance both of me and of the facts, instituted this ungentle crusade against me, I extract testimony to the greatness of Mayer’s work, stronger than I have ever uttered in attempting to vindi- cate his claims. xX 56. Sir W. Herschel had called the maintenance of solar heat “TheGreat Secret.” Mayer endeavoured to solve it, and published his essay on Celestial Dynamics in 1848. It will be seen, however, in a foregoing page that the idea of a meteoric source of solar heat was at his hand in 1845. His calculation of the quantity of heat which would be generated by the mechanical combination of the earth and sun proves this (see 22). But in 1848 he pub- lished a complete developmeut of his theory, and his essay is now readily accessible since its translation by Dr. Debus for the Philo- sophical Magazine*. There could scarcely be a closer coincidence between two independent scientific memoirs than that subsisting between the essay of Dr. Mayer and the paper of Prof. Thomson, published six years subsequentlyt. Thomson considers and rejects the assumption that the sun is a heated body, losing heat; Mayer did the same. Thomson considers and rejects the assumption that the heat of the sun is due to chemical action; so did Mayer. Thomson considers and embraces the theory that meteors falling into the sun give rise to his heat; so did Mayer. Thomson arrives at the conclusion that the main source of solar light and heat is the zodiacal light. This was also Mayer’s conclusion. Their calculations run parallel, and their deductions from them are the same. As an instance of coinci- dence in detail the following is worthy of notice:—“A dark body,” writes Prof. Thomson in 1854, “ of dimensicns such as the sun, in any part of space, might, by entering a cloud of meteors, become incandescent as intensely in a few seconds, as it could in years of continuance of the same meteoric circumstances, and again getting to a position in space comparatively free from meteors, it might almost as suddenly become dark again. It is far from improbable that this is the explanation of the appear- * Vol. xxv. pp. 241, 387, 417, + Phil. Mag. vol. viii. p. 409. 48 Prof. Tyndall’s Notes on Scientific History. ance and disappearance of bright stars, and the strange variations of brilliancy of others which have caused so much astonishment.” (Phil. Mag. vol. vii. p. 415). Three years previous to the publication of the above paragraph Dr. Mayer wrote thus :—“ It is more than probable that the earth has come into existence in some such way, and that in consequence of this process our sun, as seen from the distance of the fixed stars, exhibited at that epoch a transient burst of light. But what took place in our solar system perhaps millions of years ago, still goes on at the present time here and there among the fixed stars; and the transient appearance of certain stars, which in some cases, like the celebrated star Tycho, have at first an extraordinary degree of brilliance, may be satisfactorily explained by assuming the falling together of previously invisible double stars.”’? (Bemer- kungen ti. d. mech. Aequiv. d. Warme, p. 56; Phil. Mag. vol. xxv. p. 521. ae he the commencement of his paper “ On the Mechanical Energies of the Solar System,” Prof Thomson states that this theory was never brought forward in any definite form, so far as he was aware, “until Mr. Waterston communicated to the British Association at Hull a remarkable speculation on cosmical dynamics (Dynamik des Himmels), in which he proposed the theory that solar heat is produced by the impact of meteors.” Mayer is here definitely ignored; and I assume the reason to be the same that I have assigned for Prof. Thomson’s silence regarding Mayer’s writings on vital dynamics. But he was not left without information ; in my lecture in June 1862 I referred to those writings in the following words :—“ In 1853 Mr. Waterston proposed independently the meteoric theory of the sun’s heat, and in 1854 Prof. Wm. Thomson applied his admirable mathe- matical powers to the development of the theory; but six years previously the subject had been handled in a masterly manner by Mayer, and all that I have said on this question has been derived from him.” I do not see how I could have stated the truth in more considerate terms. Instead, however, of making him- self acquainted with the essay of Mayer and nobly bidding him welcome, Prof. Thomson permits himself to sanction the following language towards me. “ Prof. Tyndallis most unfortunate in the possession of a mental bias, which often prevents him (as, for instance, in the case of Rendu and glacier-motion) * from recog- nizing the fact that the claims of individuals whom he supposes * I have asked Prof. Thomson to point out the passages in my writings which justify this language, but he has not done so. The readiness of Prof. Thomson to make such statements and to neglect their proof has excited attention in other quarters, and will assuredly furnish him with its harvest of results. Prof. Tyndall’s Notes on Scientific History. 49 to have been wronged, have, before his intervention, been fully ventilated, discussed, and settled by the general award of scientific men.” Such rashness is rare in a man occupying so responsible a position. The fact really is that if it could be shown that Prof. Thomson had, “ before my intervention,” been aware of what Mayer had done, he would at the present moment be in as unenviable a position as could possibly be occupied by a scientific man. I may add that he has never yet rendered to Dr. Mayer the credit which belongs to him. 58. How far Mr. Joule’s lecture on shooting-stars (23) affects the essay of Dr. Mayer on Cosmical Dynamics the reader must himself determme. Here is the extract from the ‘ Manchester Courier’ (12th May 1847) referred to by Mr. Joule and printed in the Philosophical Magazine. ‘ You have no doubt frequently observed what are called shooting-stars, as they appear to emerge from the dark sky at night, pursue a short and rapid course, burst, and are dissipated in shining fragments. From the velocity with which these bodies travel there can be little doubt that they are small planets, which in the course of their revo- lution round the sun are attracted and drawn to the earth. Reflect for a moment on the consequences which would ensue if a hard meteoric stone were to strike the room in which you are assembled with a velocity sixty times as great as a cannon- ball. The dire effects of such a collision are effectually prevented by the atmosphere surrounding our globe, by which the velocity of the meteoric stone is checked, and its living force converted into heat, which at last becomes so intense as to melt the body and dissipate it in fragments, too small probably to be noticed in their fall to the ground. Hence it is that, though multitudes of shooting-stars appear every night, few meteoric stones have been found, those few corroborating the truth of our hypothesis by the marks of intense heat they bear on their surfaces.” Those who have read Mayer’s essay will never forget it, and will be able to judge how far its character could be affected by the above extract ; even had it been under the eyes of Mayer from the moment of its publication. Those who have not read Mayer, will find him translated in the Phil. Mag. vol. xxv. pp. 241, 387, 417. In my book on Heat I have given Mr. Joule due credit for the-above hypothesis*. 59. More than a year ago I addressed a letter to Prof. W. Thom- son which gave me great pain to write. I wrote it partly in de- fence of Dr. Mayer, partly in defence of my own character. It was, I am told, vigorously expressed, but it has never been intimated * The hypothesis of the cosmical origin of meteorolites is due to Chladni, the protective power of the atmosphere and its sutficiency to dis- sipate meteors being the point brought forward by Mr. Joule. Phil, Mag. 8, 4, Vol, 28, No, 186, July 1864. iE 50 Prof. Tyndall’s Notes on Scientific History. to me that it contained a single ungentlemanly term. It brought me expressions of approval and sympathy from some of the most eminent men in Europe; and I was so content with this, that I willingly—some thought, tamely—let the discussion drop. It was quite natural that my style and matter should be the reverse of agreeable to Prof. Thomson; and, as might be expected, he ex-. pressed himself to this effect. He complained of the liberties which I had taken with his name; of the liberties I had taken with other names. In short, he considered my whole tone “ unpre- cedented in scientific discussion,” and he declined having any- thing to do with me. On one technical question, moreover, he made a complaint, to which, as it involves a point of personal courtesy, I am anxious to reply. He complained that I had printed my letter in the Philosophical Magazine without sending him the original. I am informed by good authority that the course I pursued was the usual and proper one. Had it been customary to send the original in such a case, I should certainly not have failed in this act of courtesy to Prof. Thomson. Had I even known his personal views on the matter, I should have sent him the original, regardless of the general practice. Nor should I have allowed myself to be in any degree influenced by the fact that Prof. Thomson had inserted in ‘Good Words’ expressions injurious to my character, which circulated unknown to me among the 120,000 readers of that periodical, until their accidental discovery by my assistant gave mean opportunity of demonstra- ting their baselessness. I would at the same time remind him that, though there is a dignity in silence when exercised at the proper time and in the proper way, it is not dignity, nor even manliness as defined in England, that permits a man to make an unwarranted accusation, and prevents him from retracting it after its injustice has been exposed. It is with great reluctance that I refer to these topics; and were I alone concerned, | should give the world no further opportunity to animadvert on the dissensions of those among whom, in the interest of their common vocation, brotherly kind- ness ought to reign. But silence is scarcely becoming on my part when I see the reputation of a man, in whom the finest intellectual qualities are associated with the most shrinking modesty of character, made the target of anonymous reviewers. I néver had an interest in this controversy apart from the desire to do him justice. To me Dr. Mayer is personally unknown, and my own scientific labours, unlike those of my chief censor, are entirely unaffected by anything that he has done. I may add. that all that I had seen or known of Mr. Joule, previous to this discussion, had served to inspire me with respect and attach- ment for him. Personal liking and what has been called “ pa- M. P. Tchébychef on a Modification of Watt’s Parallelogram. 51 triotism ” added themselves to the exalted value which I attached to his researches. I held, and still bold, him to be one of the noblest workers of this age; and my estimate of his labours is not a shade lowered by this other conviction, that he must, in the history of science, accept Dr. Mayer as his scientific brother,— that the Thinker and Generalizer is fit to stand, and will be caused to stand, beside the Experimental Philosopher. To permit Dr. Mayer to remain in the position in which I found him, would be to fasten on myself the guilt of that neglect of which the plea of ignorance alone acquits his contemporaries. In every sen- tence that I have written in his favour I have felt that strength which perfect single-mindedness can alone impart, and, fearless alike of his fate and of my own, I now commit his reputation, and my conduct concerning it, to the impartial judgment of mankind. ) Royal Institution, June 1864. V. On a Modification of Watt’s Parallelogram. By P. Tcu&pycuer*. HE mechanism known as Watt’s parallelogram furnishes a solution of the following practically important problem: To produce, to a sufficient degree of approximation, rectilineal motion by a combination of circular motions. The degree of precision attainable by contrivances of this kind depends obviously upon the number of its disposable elements, and in this point of view the parallelogram of Watt is far from being satisfactory. In its structure, for instance, two rods more are employed than in the mechanism @ fléau, and yet the mo- tion produced is the same. In attempting to produce approxi- mate rectilineal motion by means of either of these two contri- vances, the motion really attained is an oval one, which has at most five elements in common with the desired rectilineal motion. Now this degree of approximation is unquestionably small when we take into consideration the degree of complication presented by Watt’s parallelogram. The latter, as is well known, pos- sesses four disposable elements, each of which, as therein em- ployed, furnishes two arbitrary parameters—its length and its direction. Seeing, therefore, that, on the whole, eight parame- ters are involved, we are justified in seeking a contrivance of the same degree of complexity as Watt’s parallelogram, but capable of furnishing a much more rectilineal motion—one, in fact, * From the Bulletin de Acad. Imp. des Sciences de St. Pétersbourg, vol, iv. p, 433, K2 52 M.P.Tchébychef on a Modification of Watt’s Parallelogram. which has with the desired motion eight, instead of five common elements. We have done this, and found that the approximation in question may be attained by articulating, with each other and with the beam, the four rods of Watt’s parallelogram in the fol- lowing manner. In this figure AB represents the semi-beam upon which it is required to construct a mechanism capable of producing approximately rectilineal motion along the vertical line V V', passing through the extre- mity B of the beam when the latter has a horizontal position. BC, DE, CF, FG are the four rods composing this mechanism ; C is the point whose motion is to be considered; and FG, : turning around a fixed axis G, repre- sents the counter-beam, as in Watt’s parallelogram. These rods are articulated with each other and with the beam in the same manner as in Watt’s parallelogram, with the sole difference that the rods DE and FC, instead of being connected with each other, are articulated with the counter- beam FG at two different points Eand F. The lengths and distances adopted are the following :— Fig. 1. CF =FG= NOES. AB, BD=KG= Y3—1 ap. Consequently BD is a mean proportional between AB and AD, and EF is the half of AD. The rods BC and DE have the same length; and provided the latter do not sensibly exceed the semi-path of the pomt C, it may be arbitrarily chosen. The centre of oscillation G of the counter-beam FG is chosen so that, when the beam is horizontal, the rods BC and DE may be vertical, and at the same time the rods Fig. 2. CF and FG may have the same hori- zontal position, as seen in fig. 2. Such is the composition of the me- chanism which, with the same number 4__ Dd, of rods as Watt employed, will give a motion having eight elements in com- mon with the desired rectilineal one. This fact may be very easily verified by determining, as a function of the incli- nation of the beam, the variable distance = M. P. Tchébychef on a Modification of Watt’s Parallelogram. 53 of the point C from the vertical line VV! (fig. 1)*. It will then be at once seen that the vertical VV! is a tangent, at the point corresponding to the horizontal position of the beam, to the curve described by C; further, that in the neighbourhood of this point the curve has seven elements in common with its tangent, and, lastly, that it cuts the same at a distance from G less than BC; so that, within the space described by C, the curve and the vertical have necessarily an eighth common element. We see from this with what extreme rapidity the deviations of the point C from the vertical line V V' (fig. 1) increase with the amplitude of the oscillations of the beam, the distances being of the seventh order with respect to the inclination of the beam. In ordinary practical cases, where the inclination is never great, the working of this mechanism would, as far as precision is con- cerned, be greatly superior to that of Watt. Take, as an ex- ample, the case treated by Prony in his well-known “ Note sur le parallélogramme du balancier dela machine a feu ”’+, where the length of the semi-beam AB is 2515 metres, that of the rod BC being 0°762 of a metre, and the greatest inclination of the beam 17° 35! 30”. With the improved mechanism the devia- tions from the vertical would be less than 0:05 of a millimetre, whereas, according to Prony, the deviations with Watt’s paral- lelogram would amount to 2 millimetres,—a quantity forty times the above, and far from being insignificant in the working of a machine of this description. Hitherto, m seeking to approach as closely as possible to a * This variable distance is expressed by the formula Nor. AB (cos — cos ), wherein the angles y and ¢ are functions of the inclination « of the beam which satisfy the two equations —NV5 a4 2 (ee a COs a — als * cos] BC 3-5 +(a5 25 2 2 Uae sin) — BC sin a+ 5 AB” (1 — cos a+ ae Mee) cost) BO. V541. V5+1.. ) BC? + a ame See EA ——— — ——e ( AB 2 + Z sin b+ A sin ~ AB? The approximate expression for the distance in question is consequently given by the series 7—3V5 AB’, ¥5—2 AB Huge BE Mera T Ey oe + Annales des Mines, vol. xii. } 54 M. P. Tehébychet on a Modification of Watt’s Parallelogram. vertical motion, we have only considered how many elements were common to the vertical and to the curve described by the point C; the degree of approximation of the two, however, depends also very essentially upon the position of these elements. We have already examined this question in the first part of a memolr entitled “Théorie des mécanismes connus sous le nom des parallélogrammes”*, and therein proposed methods for rendering such an approximation as perfect as possible. By applying these methods to the case under consideration, we should be led to introduce certain small changes in the values of the several parameters, in order to render the mechanism as perfect as possible. By means of these corrections, the devia- tions of the point C would be reduced in the proportion of about 1 to 27 (see § 5 of the memoir cited). But since, in practical cases, these deviations, as we have seen, are themselves very small—amounting at most to some hundredths of a millimetre, —it is evident that by the application of the above corrections the theoretical precision of the apparatus might be carried to a limit unattamable by the mechanician. For ordinary practical purposes, therefore, there is no inducement to seek a mecha- nism capable of giving rectilineal motion with greater accuracy. This improved mechanism is the more worthy of attention, since, as we have shown, the utmost desirable precision is attaied by employing the same number of pieces as in Watt’s parallelo- gram, whose practical defects are often experienced. We may observe, lastly, that the adjoming new form of the mechanism is obtained by changing the signs of the radicals in the foregoing values of the elements. In this new form, where Fig. 3. geare— *O-lap, V54+1 2 the degree of working precision is theoretically the same as before; its construction, however, would neces- sitate the prolongation of the beam, and thus be attended with great dis- advantages. BD=EG= AB, * Mémoires de Savants Etrangers, vol. vii. [ 55 |] VI. On the Barometer as an Indicator of the Earth's Rotation and the Sun’s Distance. By Puiny Harte CuHase*. ee existence of daily barometric tides has been known for more than a hundred and fifty years, but their cause is still a matter of dispute. It is evident that they cannot be accounted for by variations of temperature, for (1) their regula- rity is not perceived until all the known effects of temperature have been eliminated; (2) they occur in all climates, and at all seasons; (3) opposite effects are produced at different times, under the same average temperature. Thus at St. Helena the mean of three years’ hourly observation gives the following average barometric heights :-— h h in. h Bet vag From Oto1l2 282801 From 18 to 6 28°28388 From 12to O 282861 From 6to18 28:2784 The upper lines evidently embrace the coolest parts of the day, and the lower lines the warmest. Dividing the day im the first method, the barometer is highest when the thermometer is highest ; but in the second division the high barometer prevails during the coolest half of the day. On account of the combined effects of the earth’s rotation and revolution, each particle of air has a velocity in the direction of its orbit, varying at the equator from about 65,000 miles per hour at noon, to 67,000 miles per hour at midnight. The force of rotation may be readily compared with that of gravity by observing the effects produced by each in twenty-four hours, the interval that elapses between two successive returns of any point to the same relative position with the sun. The force of rota- tion producing a daily motion of 24,895 miles, and the force of terrestrial gravity a motion of 22,738,900 miles, the ratio of the former to the latter is 5 348°5,,, or ‘00109. This ratio repre- sents the proportionate elevation or depression of the barometer above or below its mean height that should be caused by the earth’s rotation, and it corresponds very nearly with the actual disturbance at stations near the equator. From 05 to 6" the air has a forward motion greater than that of the earth, so that it tends to fly away; its pressure is there- fore diminished, and the mercury falls. From 6" to 12" the earth’s motion is greatest ; it therefore presses against the lag- ging air, and the barometer rises. From 12" to 184 the earth moves away from the air, and the barometer falls; while from 18 to 244 the increasing velocity of the air urges it against the earth, and the barometer rises. If the force of rotation at each instant be resolved into two components, one in the direction of the radius vector, and the * From Silliman’s American Journal for May 1864. 56 Mr. P. E. Chase on the Barometer other parallel to the earth’s orbit, it will be readily perceived that whenever the latter tends to increase the aérial pressure, the former tends to diminish it, and vice versd. Let B= the height of the barometer at any given instant; M= the mean height at the place of observation; @—90°= the hour-angle; C= the earth’s circumference at the equator; ¢=24 hours; g= the terrestrial gravity ; /= the latitude: and a simple integration gives the theoretical formula _M (14 sin 6 eee eae cost 2C gf This formula gives a maximum . eeat at 9h and 215 anda minimum at 32and 155, The St. Helena observations place the maximum at 102 and 225 and the minimum at 45 and 164, an hour later in each instance than the theoretical time. This is the precise amount of retardation caused by the mertia of the mercury, as indicated by the comparisons with the water baro- meter of the Royal Society of London. Aérial currents, variations of temperature, moisture, and cen- trifugal force, solar and lunar attraction, the obliquity of the ecliptic, and various other disturbing causes, produce, as might be naturally expected, great differences between the results of theory and observation. But by taking the grand mean of a series of observations, sufficiently extended to balance and. elimi- nate the principal opposing inequalities, the two results present a wonderful coincidence. According to our formula, the differences of altitude at 1, 2, and 3 hours from the mean, should be in the respective ratios of ‘5, °866, and 1. The actual differences, according to the mean of the St Helena observations, are as follows :— Differences of Barometer. Ratios. Difference of time} 1h. 2 h. 3h. lh. 2h. 3h. Before Th. 7s. 0166 0298 "0365 °455 816 1 Adter Mhiviis.cadac 0159 0266 "0298 534 *893 1 Betore./n.coeeaees °0122 0202 "0243 502 831 1 After: (ii c.so tunes ‘0135 0239 0297 *455 *805 ] Before Van.,secsece. "0136 0248 0284 479 873 ] Aster Shh %2. ak 0131 “0215 6227 577 "947 1 Betore 4 Oh... ‘0161 0287 "0348 ‘463 ‘825 1 PMIEEDIN ON, see ssinceier | 0150 0265 0286 524 ‘927 1 WIGAN) Aes Aencien en's °0145 °0252 "0293 "495 *860 1 C An fi gf represents the effective ratio of an entire day. But there is in each day a half day of acceleration, and a half day of retardation, and the Cor Gh ratio for each half day is 57 an t= = le as an Indicator of the Earth’s Rotation, &c. 57 The mean of the above differences varies from the theoretical mean less than 5455 of an inch. Ifwe take the mean of the ratios instead of the ratios of the means of the observed differ- ences, the coincidence is still more striking. Difference of time......... coaes Te 2h. 3h. Means of observed ratios ..... : *498625 "864625 1-:000000 Theoretical Means sreceesereee -500000 *866025 1-000000 The calculated time for the above-observed means differs less than 20" from the actual time. Observed MEansS..ccccreccseses we §«=6. 498625 ~=—s °8 64625 1-000000 Theoretical difference of time. 59’ 48” 119’ 40" 180' Observed difference of time... 60 0 120 0 180 The varying centrifugal force to which the earth is subjected by the ellipticity of its orbit, must m like manner produce annual tides. The disturbing elements render it impossible to determine the average monthly height of the barometer with any degree of accuracy, from any observations that have hitherto been made. We may, however, make an interesting approxima- tion to the annual range, still using the St. Helena records, which are the most complete that have yet been published for any sta- tion near the equator. Comparing the mean daily range as de- termined by the average of the observations at each hour, with the mean yearly range as determined by the monthly averages, we obtain the following results :— ; Approximate Year. Daily range. Annual range. Ratio. solar distance, in. in. . 1844 “0672 "1650 2°4553 137,070,000 1845 "0646 71214 1:8793 80,300,000 1846 "0670 "1214 1:8120 74,650,000 3)°1988 3)°4078 3)6°1466 | 0663 "1359 2°0489 95,446,000 Mean _—--0663 1290 1-9457 86,056,000 2)°1326 2)°2649 2)3°9946 0663 "1324 1:9973 90,702,000 The approximate estimates of the solar distance are based on the following hypothesis :— Let e = effective ratio of daily rotation to gravity. a = arc described by force of rotation im a given time ¢. ry = radius of relative sphere of attraction, or distance through which a body would fall by gravity during the disturbance of its equilibrium by rotation. = area described by radius vector in time ¢. 58 On the Barometer as an Indicator of the Earth’s Rotation. Let e’, a’, 2’, A’ represent corresponding elements of the annual revolution. Then A:A’::ar:ar:: &:e?. But the forces of rotation and revolution are so connected that @ differs but slightly from a’. 2 aE RAE AT pond ty very nearly. 2 2 It may be interesting to observe how nearly r (22,738,900 miles) corresponds with Kirkwood’s value of = (24,932,000 miles). A more thorough comprehension of all the various effects of gravity and rotation on the atmosphere, would probably lead to modifications of our formule that would show a still closer correspondence.. There is a great discrepancy between the determinations of the solar distance that are based on the records of 1844 and 1846 ; but it is no greater than we might reasonably have anticipated. On the other hand, it could hardly have been expected that any comparisons based on the observations of so short a period as three years, would have furnished so near an approximation to the most recent and most accurate determination of the earth’s mean radius vector. In order to obtain that approximation, it will be seen that I took, 1st, the mean of the ranges and ratios for three successive years; 2nd, the ranges and ratios of the mean results of the three years; 3rd, the grand mean of these two primary means. I could think of no other method which would be so likely to destroy the effects of changing seasons, and other accidental disturbances. The following Table exhibits the effects of latitude on the aérobaric tides. The differences between the theoretical and observed ranges may be owing partly to the equatorial-polar currents, and partly to insufficient observations. Station. Latitude. helen. naa Ratio. bow dae in. in. Arctic Ocean ...... 78 37 | 29-739 ‘012 ‘000404 | 000527 Girard College ...| 39 58 | 29-938 060 002004 | -002046 Washington ...... 38 53 | 30-020 062 002065 | 002079 St. Helena ......... 15 57 | 28-282 066 002344 | -002567 EQUator, acscesre>sex 0 30°709 ‘082 ‘002670 | -002670 The theoretical ratios are determined by multiplying the equa- Notices respecting New Bocks. 59 torial ratios by sa The formula p= = : a (p indicatmg the ratio of the mean range to the mean height) gives— Theoretical Observed SANS ratio. ratio. Latitude .... O O “002190 -002670 Latitude .... 78 37 -000432 -000404 showing that the ratio is less near the pole and greater near the equator than our theory indicates, a natural consequence of the centrifugal force at the equator and the cold surface currents that produce the trade-winds. The revolution of the sun around the great Central Sun must also cause barometric fluctuations that may possibly be measured by delicate instruments and long and patient observation. The Torricellian column may thus become a valuable auxiliary in veri- fying or rectifying our estimates of the distances and masses of the principal heavenly bodies. VII. Notices respecting New Books. Manual of the Metalloids. By James Arsoun, M.D., F.R.S., M.R.I.A., Professor of Chemistry in the University of Dublin. London: Longmans, 1864, pp. vili and 596. «gin work forms one of the series of Scientific Manuals issued | under the auspices of Professurs Galbraith and Haughton of Trinity College, Dublin. With regard to its intended scope and aim, the author says, ‘‘ In preparing it my wish has been to produce a condensed, but at the same time tolerably comprehensive treatise, in which no topic of importance should be omitted, while all would be discussed with as much brevity as is consistent with clearness, It is intended as a Handbook in Chemistry for students in Medicine and Engineering, ....” In books intended for the use of students, completeness in relation to matters of detail is unattainable, and is not even to be desired ; but it is very important that such books should be as free as possible from errors, and that the knowledge gained by the study of them— though necessarily limited in extent—should be accurate, and should serve as a firm foundation for further acquisitions. In such works, even slight mistakes often amount to serious faults; and they are the less excusable, since the author, not being called upon to enter upon the more abstruse parts of the science, may generally ensure accuracy, upon the subjects of which it is desirable that he should treat, by exercising a moderate degree of care. In the present volume, errors in regard to the simplest matters of fact are, unfor- tunately, by no means rare, nor are they all of small importance. It would be tedious to the reader were we to quote all the passages upon which this assertion is founded : the following must suffice as specimens of many more that might be given. 60 Notices respecting New Books. At page 68 we read, ‘‘ The compound, for example, generally known under the name of Dutch lquor, C,H, Cl,, reacts upon water in the following manner :— €,H,Cl, + H, O= 2ClH + ©,H,9. Now, viewing this latter substance, €, H, O, as a derivative of water, it is clear that C, H,, now called ethylene, has replaced two atoms of hy drogen, and is "therefore a binatomic body.”” What a capital pro- cess this is for preparing oxide of ethylene—upon paper, and what a pity that it does not answer equally well in sealed tubes! On page 232 we are told that “ the compounds of nitrogen with hydrogen are three in number, viz. amidogen, ammonia, and ammo- nium, and have their composition represented by the following for- mule :— Amidogent Uh Ge ne cccetue aclw aloe ter ere NH, Ammonia == NH Ammonium! 0% ie See ee eee Bae Sy bcp A more misleading statement than this could not easily be put before the student; for not only are the first and last of the three substances named completely unknown, but the whole analogy of the ascertained combining properties of nitrogen is against even the possibility of their existence, the most characteristic of all these properties being that, with elements of the hydrogen-class, nitrogen unites in only one proportion, that namely of which ammonia is an example. But our author habitually pays little regard to fine-drawn distinctions between substances which are well known as having a material existence, and those which are at best the convenient fic- tions of past or present theoretical systems. For instance (p. 256), he tells us that ‘‘ There are seven known oxides of sulphur, all of which possess the properties of acids. The name and atomic compo- sition of each is given in the subjoined Table :— Sulphurons, acid. .:. . aeheeis «somes ee eee sO, Sulphuricacid isles dele mce ome F is ae Hyposuiphurous acidtepe.. 20% -- |: . as ceise S, O, Dithionic acid (Hyposulphuric) Apes OS Trithioni¢ acid g As: & sebiscealeeh-nietiee S, O,; ‘Tetrathionicjaeid 9 4.'c0,4 a, oo 3. beer S, 0, Péenfathigni¢e Acid. 10.012 Saleen sldetee sAOr The hyposulphurous and pentathionic acids are instances of poly- meric bodies, or of such as have the same percentage composition, but different atomic weights.” At page 478 occurs another example of the same kind: we there read, ‘‘ The oxides of carbon are six in number, and of these all but the first are possessed of acid characters. They are— Carbonic oxide .......... CO Carbonie acid! s).0f...¢m, sh1C@s Oxdheacid :.!)s 2.05) oe HO: C,0O, + 2HO Rhodizonic acid ........ Were, G) O, Creconicmendics.3c3.: sabe HO, C, 0, Mellitic acid. ovis),2c. 305u : HO; 0,27 Notices respecting New Books. 61 From these instances it will be seen that Dr. Apjohn’s lists of ‘‘known compounds” include many substances with which other chemists are by no means well acquainted: hence it is natural that he should require to make room for them by ignoring substances which often receive a considerable share of attention. Thus (p- 502) the usual list of hydrocarbons is very much curtailed: we are told that “‘The number of compounds of carbon and hydrogen is very great. Those at present known are reducible to three groups :—Those whose general formula is Cy Hn, those represented by C, Hn+:, and those by Cp Hy+2, n being always an even number.” Again (pp. 463, 464), ‘‘ The only known compounds of boron with the metalloids are the teroxide, tersulphide, terchloride, and ter- fluoride.” Surely Dr. Apjohn has heard of nitride of boron. No similarly distinct assertion is made of the non-existence of hydride of silicon and of the whole series of compounds corresponding with an oxide containing half as much oxygen as silica, discovered a few years ago by Wohler; but, from the absence of the slightest allusion to any of these interesting substances, we must suppose that their existence is not yet recognized by our author. If, from the enumeration of the compounds of the various elements, we turn to the detailed description of their properties and reactions, we find no greater accuracy. We will quote but one passage in illustration of this remark. It occurs on pages 561 and 562, and refers to the volumetric process for estimating cyanogen, in presence of excess of potash, by means of a standard solution of nitrate of silver. ‘* The free potash will develop oxide of silver; but this is immediately taken up by the cyanide of potassium, with a view [sic] to the formation of the double cyanide; so that, as long as there is uncombined cyanide of potassium, there will be no permanent pre- cipitate. But when the cyanide of potassium is altogether con- verted into the double cyanide of potassium and silver, if any addi- tional quantity of the nitrate be added, the oxide of silver separated from it by the potash will appear as a permanent precipitate.” It is difficult to suppose that the writer of this passage has ever performed the operation he professes to describe, otherwise he could hardly have failed to notice that in reality it is the white cyanide of silver, and not the brown-grey oxide which ‘‘ appears as a perma- nent precipitate.” But the most remarkable portions of Dr. Apjohn’s work are those in which he has occasion to refer to the past history of the science, or to record his opinion of the works of his contemporaries. At page 124, for instance, the relation of Lavoisier to the antiphlogistic system of chemistry is placed in a new light. ‘‘ Stahl conceived that combustible bodies, such as carbon, sulphur, phosphorus, and iron, included a fiery principle, which he called phlogiston; and that, when they underwent combustion, the fiery principle is evolved. This phlogistic theory is at the present day only interesting in con- nexion with the history of chemistry. It held, however, its ground for a long time, and was only abandoned when it was shown by Ray and Mayow that bodies in burning, instead of becoming lighter, augment in weight. 62 Notices respecting New Books. ‘Lavoisier put forward on this subject a very plausible theory, which was founded on the well-known fact that, if a gas be com- pressed, heat will be developed.”” ‘This passage not only contains a totally inadequate, and therefore erroneous statement of Lavoisier’s ‘plausible theory,” but implies what is directly contrary to facts well known to all who have paid any attention to the history of chemistry—namely, that the phlogistic theory held its ground long after it had been discovered that combustible bodies increase in weight when burned, and that this observation first came to be regarded as a serious objection to the theory when it was shown by Lavoisier to be connected with the disappearance of part of the atmo- sphere in which combustion takes place. Every one knows that the discovery of the composition of water is attributed by some authorities to Cavendish, and by others to James Watt: according to Dr. Apjohn, similar rival claims have been put forward to the discovery of hydrogen itself. He says (p. 130), “Hydrogen... .. was first distinguished by Cavendish in 1766, and to him the credit of its discovery is usually given, though in modern times it has been claimed for Watt.”’ Further on (p. 471) we are told that Lavoisier and De Morveau burned the diamond in oxygen (discovered by Priestley in August 1774) about the year 1764. On page 212, the ‘ difficulty of pro- curing absolute nitric acid, NO,, now called nitric anhydride,” is stated to have ‘‘ been recently overcome by Naeterer,’’ a chemist whose name we do not remember to have met with before; while nothing is said about M. H. Sainte-Claire Deville as having had any- thing to do with the matter. After these specimens of Professor Apjohn’s historical accuracy, the reader will not be surprised at slight peculiarities of spelling in the names of foreign chemists, such as Schonbein for Schénbein, Schrotter for Schrétter, or Lassaign for Lassaigne; but unless he is very well acquainted with the Professor’s style, he may be a little at a loss on reading Bertholon (p. 255, and repeated in the index) in- stead of Berthelot, or on being toid (p. 407) that Lavoisier, instead of Le Verrier, investigated oxide of phosphorus (or at least a substance so called). We draw attention to these matters, not because the exact spelling of a chemist’s name is of much importance to a student who is be- ginning the study of chemistry, but because they illustrate the inac- curacy and carelessness which pervade the whole book and give it throughout a slovenly air. Scrupulous accuracy in the statement of scientific facts and theories need not be expected from an author who thus wrongly names his authorities, or’ allows such examples of English composition as the following to go forth under his name :— Page 183. ‘‘ We now come to consider the relative proportions of the oxygen and nitrogen of which the atmosphere is chiefly composed. This is always done by condensing the oxygen of a known volume of atmospherical air, and measuring the nitrogen which is left.” Page 248. “Schlossing has ascertained that distillation by heat is not necessary; and that a solution of ammoniacal salt, to which a little hydrate of potash has been added, if placed for twenty-four _ Royal Society. 63 hours under a glass bell with a cup of dilute sulphuric acid, passes completely from the alkaline to the acid liquid.” Page 417. ‘“‘ TeriopipE or Pyospuorus, PI,=285.—This is ob- tained when into a thin test-tube, or small flask, containing phos- phorus, and from which the air has been displaced by dry carbonic acid, twelve times its weight of iodine is introduced.” Page 297. “Such a result indeed is always obtained when the nitric acid is concentrated, and that the bottle or flask (it should be a strong one) is immediately closed by the pressure of the thumb after the acid has been introduced.” In conclusion, we can conscientiously say, after a careful examina- tion of the book before us, that we have been unable to discover any one respect in which it is superior to the average of elementary works on chemistry, while, as we have pointed out, it frequently falls below the average. If such a work was to be published at all, it is to be regretted that it was issued as one of a series of educational works which have already acquired a certain reputation for general excel- lence, and are ‘‘recommended by the Committee of Council on Education.” VIII. Proceedings of Learned Societies. ROYAL SOCIETY. [Continued from vol. xxvii. p. 542.] February 25, 1864.— Major-General Sabine, President, im the Chair. f ae following communication was read :— “On the supposed Identity of Biliverdin with Chlorophyll, with remarks on the Constitution of Chlorophyll.” By G. G. Stokes, M.A., Sec.R.S. I have lately been enabled to examine a specimen, prepared by Professor Harley, of the green substance obtained from the bile, which has been named biliverdin, and which was supposed by Ber- zelius to be identical with chlorophyll. The latter substance yields with alcohol, ether, chloroform, &c., solutions which are characterized by a peculiar and highly distinctive system of bands of absorption, and by a strong fluorescence of a blood-red colour. In solutions of bili- verdin these characters are wholly wanting. There is, indeed, a vague minimum of transparency in the red; but it is totally unlike the intensely sharp absorption- band of chlorophyll, nor are the other bands of chlorophyll seen in biliverdin. In fact, no one who is in the habit of using a prism could suppose for a moment that the two were identical ; for an observation which can be made in a few seconds, which requires no apparatus beyond a small prism, to be used with the naked eye, and which as a matter of course would be made by any chemist working at the subject, had the use of the prism made its way into the chemical world, is sufficient to show that chlorophyll and biliverdin are quite distinct. I may take this opportunity of mentioning that I have been for a 64. Royal Society :— good while engaged at intervals with an optico-chemical examination of chlorophyll. I find the chlorophyll of land-plants to be a mix- ture of four substances, two green and two yellow, all possessing highly distinctive optical properties. The green substances yield solutions exhibiting a strong red fluorescence; the yellow substances do not. ‘The four substances are soluble in the same solvents, and three of them are extremely easily decomposed by acids or even acid salts, such as binoxalate of potash ; but by proper treatment each may be obtained in a state of very approximate isolation, so far at least as coloured substances are concerned. The phyllocyanine of Fremy* is mainly the product of decomposition by acids of one of the green bodies, and is naturally a substance of a nearly neutral tint, showing however extremely sharp bands of absorption in its neutral solutions, but dissolves m certain acids and acid solutions with a greenor blue colour. Fremy’s phylloxanthine differs accord- ing to the mode of preparation. When prepared by removing the green bodies by hydrate of alumina and a little water, it is mainly one of the yellow bodies; but when prepared by hydrochloric acid and ether, it is mainly a mixture of the same yellow body (partly, it may be, decomposed) with the product of decomposition by acids of the second green body. As the mode of preparation of phylloxan- theine is rather hinted at than described, I can only conjecture what the substance is ; but I suppose it to be a mixture of the second yellow substance with the products of decomposition of the other three bodies. Green seaweeds (Chlorospermee) agree with land- plants, except as to the relative proportion of the substances pre- sent ; but in olive-coloured sea-weeds (Melanospermee) the second green substance is replaced by a third green substance, and the first yellow substance by a third yellow substance, to the presence of which the dull colour of those plants is due. The red colouring- matter of the red sea-weeds (Rhodospermee), which the plants con- © tain in addition to chlorophyll, is altogether different in its nature from chlorophyll, as is already known, and would appear to be an albu- minous substance. I hope, before long, to present to the Royal Society the details of these researches. March 3.—Major-General Sabine, President, in the Chair. The following communication was read :— “Qn the Spectra of Ignited Gases and Vapours, with especial regard to the different Spectra of the same elementary gaseous sub- stance.” By Dr. Julius Plicker, of Bonn, For. Memb. R.S., and Dr. S. W. Hittorf, of Munster. In order to obtain the spectra of the elementary bodies, we may employ either flame or the electric current. The former is the more easily managed, but its temperature is for the most part too low to volatilize the body to be examined, or, if it be volatilized or already in the state of gas, to exhibit its characteristic lines. In most cases it is only the electric current that is fitted to produce these lines; and * Comptes Rendus, tom. 1. p. 405. Drs. Pliicker and Hittorf on the Spectra of Ignited Gases. 65 the current furnished by a powerful induction coil was what the authors generally employed. - In the application of the current, different cases may arise. The body to be examined may be either in the state of gas, or capable of being volatilized at a moderate temperature, such as glass will bear — softening, or its volatilization may require a temperature still igher. In the first two cases the body is enclosed in a blown-glass vessel consisting of two bulbs, with platinum wires for electrodes, connected by a capillary tube. In the case of a gas, the vessel is exhausted by means of Geissler’s exhauster, and filled with the gas at a suitable tension. In the case of a solid easily volatilized, a portion is intro- duced into the vessel, which is then exhausted as highly as possible, and the substance is heated by a lamp at the time of the observa- tion. In the third case the electric current is employed at the same time for volatilizing the body and rendering its vapour luminous. If the body be a conductor, the electrodes are formed of it; but the spectrum observed exhibits not only the lines due to the body to be examined, but also those which depend on the interposed gas. This mconyenience is partly remedied by using hydrogen for the interposed gas, as its spectrum under these circumstances approaches to a con- tinuous one. If the body to be examined be a non-conductor, the metallic electrodes are covered with it. In this case the spectrum observed contains the lines due to the metal of which the electrodes are formed, and to the interposed gas, as well as those due to the sub- stance to be examined. Among the substances examined, the authors commence with nitrogen, which first revealed to them the existence of two spectra belonging to the same substance. The phenomena presented by nitrogen are described in detail, which permits a shorter description to suffice for the other bodies examined. On sending through a capillary tube containing nitrogen, at a pres- sure of from 40 to 80 millimetres, the direct discharge of a powerful Ruhmkorff’s coil, a spectrum is obtained consisting, both in its more and in its less refrangible part, of a series of bright shaded bands: the middle part of the spectrum is usually less marked. In each of the two parts referred to, the bands are formed on the same type; but the type in the less refrangible part of the spectrum is quite different from that in the more refrangible. In the latter case the bands have a channeled appearance, an effect which is produced by a shading, the intensity of which decreases from the more to the less refracted part of each band. In a sufficiently pure and magnified spectrum, a small bright line is observed between the neighbouring channels, and the shading is resolved into dark lines, which are nearly equidistant, while their darkness decreases towards the least refracted limit of each band. With a similar power the bands in the less refrangible part of the spectrum are also seen to be traversed by fine dark lines, the arrangement of which, however, ‘while similar for the different bands, is quite different from that observed in the chan- neled spaces belonging to the more refrangible region. Phil. Mag. S. 4, Vol. 28. No. 186. July 1864. F 66 Royal Society :— If, instead of sending the direct discharge of the induction coil through the capillary tube containing nitrogen, a Leyden jar be interposed in the secondary circuit in the usual way, the spectrum obtained is totally different. Instead of shaded bands, we have now a spectrum consisting of brilliant lines having no apparent relation whatsoever to the bands before observed. If the nitrogen employed contains a slight admixture of oxygen, the bright lines due to oxygen are seen as well as those due to nitrogen, whereas in the former spectrum a slight admixture of oxygen produced no apparent effect. The different appearance of the bands in the more and in the less refracted portion of the spectrum first mentioned suggested to the authors that it was really composed of two spectra, which possibly might admit of being separated. This the authors succeeded in effect- ing by using a somewhat wider tube. Sent through this tube, the direct discharge gave a golden-coloured light, which was resolved by the prism into the shaded bands belonging to the less refrangible part of the spectrum, whereas with a small jar interposed the light was blue, and was resolved by the prism into the channeled spaces belong- ing to the more refrangible part. By increasing the density of the gas and at the same time the power of the current, or else, in case the gas be less dense, by inter- posing in the secondary circuit at the same time a Leyden jar and a stratum of air, the authors obtained lines of dazzling brilliancy. which were no longer well defined, but had become of appreciable breadth, while at the same time other lines, previously too faint to be seen, made their appearance. The number of these lines, how- ever, is not unlimited. By the expansion of some of the lines, espe- cially the brighter ones, the spectrum tended to become continuous. Those spectra which are composed of rather broad bands, which show different appearances according as they are differently shaded by fine dark lines, the authors generally call spectra of the first order, while those spectra which show brilliant coloured lines on a more or less dark ground they call spectra of the second order. Incandescent nitrogen accordingly exhibits two spectra of the first, and one of the second order. The temperature produced by the pas- sage of an electric current increases with the quantity of electricity which passes, and for a given quantity with the suddenness of the passage. When the temperature produced by the discharge is com- paratively low, incandescent nitrogen emits a golden-coloured light, which is resolved by the prism into shaded bands occupying chiefly the less refrangible part of the spectrum. At a higher temperature the light is blue, and is resolved by the prism into channeled bands filling the more refrangible part of the spectrum. At a still higher temperature the spectrum consists mainly of bright lines, which at the highest attaimable temperature begin to expand, so that the spectrum tends to become continuous. The authors think it probable that the three different spectra of the emitted light depend upon three allotropic states which nitrogen assumes at different temperatures. By similar methods the authors obtained two different spectra Drs. Pliicker and Hittorf on the Spectra of Ignited Gases. 67 of sulphur, one of the first and one of the second order. The spec- trum of the first order exhibited channeled spaces, like one of the two spectra of that order of nitrogen; but the direction in which the depth of shading increased was the reverse of what was observed with nitrogen, the darker side of each channeled space being in the ease of sulphur directed towards the red end of the spectrum. Selenium, like sulphur, shows two spectra, one of the first and one of the second order. Incandescent carbon, even in a state of the finest division, gives a continuous spectrum. Among the gases which by their decomposi- tion, whether in flame or in the electric current, give the spectrum of carbon, the authors describe particularly the spectra of cyanogen and olefiant gas when burnt with oxygen or with air, and of carbonic oxide, carbonic acid, marsh-gas, olefiant gas, and methyle rendered incan- descent by the electric discharge; they likewise describe the spec- trum of the electric discharge between electrodes of carbon in an atmosphere of hydrogen. The spectrum of carbon examined under these various conditions showed great varieties, but all the different types observed were represented, more or less completely, in the spectrum of cyanogen fed with oxygen. The authors think it pos- sible that certain bands, not due to nitrogen, seen in the flame of cyanogen, and not in any other compound of carbon, may have been due to the undecomposed gas. The spectrum of hydrogen, as obtained by a small Ruhmkorff’s coil, exhibited chiefly three bright lines. With the large coil em- ployed by the authors, the lines slightly and unequally expanded. On interposing the Leyden jar, and using gas of a somewhat higher pressure, the spectrum was transformed into a continuous one, with a red line at one extremity, while at a still higher pressure this red line expanded into a band. The authors also observed a new hydrogen spectrum, correspond- ing to a lower temperature, but having no resemblance at all to the spectra of the first order of nitrogen, sulphur, &c. Oxygen gave only a spectrum of the second order, the different lines of which, however, expanded under certain circumstances into narrow bands, but very differently in different parts of the spectrum. Phosphorus, when treated like sulphur, gave only a spectrum of the second order. Chlorine, bromine, and iodine, when examined by the electric dis- charge, gave only spectra of the second order, in which no two of the numerous spectral lines belonging to the three substances were coin- cident. The authors were desirous of examining whether iodine would give a spectrum of the first order the reverse of the absorption- Spectrum at ordinary temperatures. ‘The vapour of iodine in an oxyhydrogen jet gave, indeed, a spectrum of the first order, but it did not agree with what theory might have led us to expect. In the electric discharge, arsenic and mercury gave only spectra of the second order. The metals of the alkalies sodium, potassium, lithium, thallium show, even at the lower temperature of Bunsen’s lamp, spectra of the second order. FZ 68 Royal Society :— Barium, strontium, calcium in the flame of Bunsen’s lamp show bands like spectra of the first order, and in each case a well-defined line-like spectra of the second order. On introducing chloride of barium into an oxyhydrogen jet, the shading of the bands was resolved into fine dark lines, proving that the band spectrum of barium is in every respect a spectrum of the first order. Spectra of the first order were observed in the case of only a few of the heavy metals, among which may be particularly mentioned lead, which, when its chloride, bromide, iodide, or oxide was introduced into an oxyhydrogen jet, gave a spectrum with bands which had a channeled appearance in consequence of a shading by fine dark lines. Chloride, bromide, and iodide of copper gave in a Bunsen’s lamp, or the oxyhydrogen jet, spectra with bands, and besides a few bright lines. ‘The bands in the three cases were not quite the same, but differed from one another by additional bands. Manganese showed a curious spectrum of the first order. "When an induction discharge passed between electrodes of copper or of manganese, pure spectra of these metals, of the second order, were obtained. March 17.—Major-General Sabine, President, in the Chair. The following communication was read :— * Remarks on Sun Spots.” By Balfour Stewart, M.A., F.RB.S., Superintendent of the Kew Observatory. In the volume on Sun Spots which Carrington has recently pub? lished, we are furnished with a curve denoting the relative frequency of these phenomena from 1760 to the present time. This curve exhibits a maximum corresponding to 1788°6. Again, in Dalton’s ‘Meteorology ’ we have a list of aurore observed at Kendal and Kes- wick from May 1786 to May 1793. The observations at Kendal were made by Dalton himself, and those at Keswick by Crosthwaite. This list gives— For the year 1787 .... 27aurore, | For theyear1790.... 36auroree; MIRO oot DO. Mia 1701 eo eee WBS a gO eas 1792 ae showing a maximum about the middle, or near the end of 1788. This corresponds very nearly with 1788°6, which we have seen is one of Carrington’s dates of maximum sun spots. The following observation is unconnected with the aurora borealis. In examining the sun pictures taken with the Kew Heliograph under the superintendence of Mr. De la Rue, it appears to be a nearly uni- versal law that the faculee belonging to a spot appear to the left of that spot, the motion due to the sun’s rotation being across the pic- ture from left to right. These pictures comprise a few taken in 1858, more in 1859, a few in 1861, and many more in 1862 and 1863, and they have been care- fully examined by Mr. Beckley, of Kew Observatory, and pate The following Table expresses the result obtained :— Mr. Gassiot on a Train of Eleven Sulphide-of-carbon Prisms. 69 No. of cases of No. of cases of No. of cases of No. of cases of fa- Year. facula to left facula to right faculaequallyon cule mostly be- of spot. of spot. both sides ofspot. tween two spots. USES es ee | REE ante Pee Ue ate ast ete as 0 Se) oa Ov. (Panza. eS sen deere 3 Lass 2 SPEC eRe Oe eS BIO 0 Us. 1 CE es TB Steal 5 3 Dt Ley I EP EES Cee. We id Se ieee 2 14 8 |e Be ES 2S 71 Ee Ser 1 April 7.—Major-General Sabine, President, in the Chair. The following communication was read :— “Description of a train of Eleven Sulphide-of-Carbon Prisms arranged for Spectrum Analysis.” By J. P. Gassiot, F.R.S. The principles which should regulate the construction of a bat- tery of prisms have been alluded to in the description of the large spectroscope now at Kew Observatory, which has a train of nine dense glass prisms with refracting angles of 45°*. While for purposes of exactitude, such as mapping out the solar spectrum, flint glass stands unrivalled ; yet when the greatest amount of dispersion is the desideratum, prisms filled with bisulphide of carbon present obvious advantages, on account of the enormous dis- persive power of that liquid—the difference of its indices of refrac- tion for extreme rays being, according to Sir David Brewster, as 0-077 against 0:026 for flint glass. In the fluid prisms of the ordinary construction, the sides are ce- mented on with a mixture of glue and honey. This cement, on har- dening, warps the sides, and confusion of the spectral lines is the consequent result. To obviate this source of error, it has been pro- posed to attach an additional pair of parallel sides to such prisms, a thin film of castor-oil beg interposed between the surfaces. The outer plates are then secured by means of sealing-wax, or some cement, at the corners. In the battery of prisms now about to be described, Mr. Browning has dispensed with this attachment at the corners, which is likely to prove prejudicial, and has secured the second sides in their proper position by extremely light metal frames which clasp the plates only on their edges. Thus arranged, the frames exert no pressure on the surfaces of the plates, and are quite out of the field of view, and they can be handled without any fear of derangement. On account of the lower refractive power of bisulphide of carbon, as compared with flint glass, a refractive angle of 50° was given to the fluid prisms. Eight such prisms would cause a ray of light to travel more than a circle, and would be the greatest number that could be employed had the ordinary arrangement been adopted. In place, however, of giving to the fluid prisms two pairs of parallel sides, Mr. Browning, taking advantage of the difference between the refractive and dispersive properties of crown glass and bisulphide of carbon, has substituted a prism of crown glass having * Phil. Mag., vol. xxvii. p, 143. 70 Royal Society :— a refracting angle of 6° for one of the outer plates of each prism— the base of this crown-glass prism being brought to correspond with the apex of the fluid prism, thus :— % Crown-glass prism. By this means the angle of minimum deviation of the prisms is so much decreased, that eleven of them thus constructed can be used in a circle instead of eight. An increase of dispersive power, due to refracting angles of 150° of the bisulphide of carbon, is thus gained, minus only the small amount of dispersion counteracted owing to the dispersive power of the crown-glass prisms being employed in the contrary direction. From the well-known low dispersive power of this medium, however, this loss is inconsiderable, amounting tc scarcely more than a fifteenth of the power gained. Owing to the minimum angle of deviation being lowered, the further advantage is also secured of a larger field of view being presented to the telescope by the first and last prism of the train. Each prism, in addition to the aT light metal frame referred to, has | a separate stand, furnished with screws for adjusting the prisms, and securing them at the angle of minimum deviation for any particularray. The prism stands within a stirrup furnished with a welled head. By this arrangement the prisms can be removed and replaced without touching their sides—a matter of some import- ance, as all fluid prisms show dif- ferent results with every change of temperature. For the sake of simplicity, the * Direction of ray as it would pass through two pair of parallel sides. + Direction of ray as altered by interposing the crown-glass prism. Mr. Gassiot on a Train of Eleven Sulphide-of-carbon Prisms. 71 metal framing of the prisms, and the various adjusting-screws, have been omitted in the last sketch. _ The very unfavourable state of the weather prevented any observa- tions being made on the solar spectrum with these prisms until Saturday the 12th inst. The results then obtained may probably not be considered devoid of interest. They are as follows :— The prisms were arranged so as to enable that portion of the spec- trum to be observed in which the well-defined D line of Fraunhofer is situated. This line, long since resolved as double, presented an angular separation of 3! 6!’, measured from the centre of one to that of the other principal line, this measurement being made by Mr. Balfour Stewart by means of the micrometer attached to the tele- scope; the value of the divisions of the micrometer he had previously determined relatively to the divided circle of the spectroscope. A ~ centre line (clearly defined and figured in Kirchhoff and Bunsen’s map) was distinctly visible, and nearly equidistant from the centre towards the violet ; five clearly defined lines were perceptible, as also two faint lines on each side of the principal lines, between the centre line of Kirchhoff towards the red. Several faint lines were also per- ceptible. The lines as represented in the diagram were drawn by Mr. Whipple, one of the assistants in the Observatory, as they were observed by him about 3.45 p.m Some of these may possibly be due to the earth’s atmosphere, but the five most refrangible lines were observed at an earlier period of the day by Mr. Stewart, Mr. Browning, and myself. The great angular separation of the double D line to 3! 6" is a proof of the power of this arrangement of the sulphide-of-carbon prisms, and offers the means of mapping out the entire solar spectrum on a scale not hitherto attained. Note.—Since the preceding observations were recorded, an inspec- tion has been made of the region of the spectrum towards the refran- gible side of double D; and, from the comparisons made with a map of lines obtained by means of the battery of glass prisms with that given by those of the sulphide-of-carbon prisms, many new lines are produced in addition to those observable by the former, while the battery of glass prisms itself gives a number of additional lines to those that are depicted in Kirchhoff’s map. 72 Geological Society :— GEOLOGICAL SOCIETY. (Continued from vol. xxvii. p. 545. | March 23, 1864.—W. J. Hamilton, Esq., President, in the Chair. The following communications were read :— 1. “ On some new Fossils from the Lingula-flags of Wales.” By J. W. Salter, Esq., F.G.S., A.L.S. Since the author’s paper last session, on the discovery of Para- doxides in Britain, the researches of Mr. Hicks have brought to light so many new members of the hitherto scanty fauna of the Primordial zone, that Mr. Salter was now enabled to describe two new genera of Trilobites and a new genus of Sponges, and to complete the de- scription of Paradoxides Davidis. He also remarked that the fauna of the Lingula-flags shows an approximation, in some of its genera, to Lower Silurian forms, and some (the Shells and a Cystidean) are of genera common to both formations ; but the Crustacea, which are the surest indices of the age of Paleozoic rocks, are of entirely dis- tinct genera; and their evidence quite outweighs that of the other fossils. The Primordial zone is moreover in Britain, separated from the Caradoc and Llandeilo beds by the whole of the 'Tremadoc group, at least 2000 feet thick. 2. “On the Millstone-grit of North Staffordshire, and the ad- joining parts of Derbyshire, Cheshire, and Lancashire.” By E. Hull, Esq., B.A., F.G.S., and A. H. Green, Esq., M.A., F.G.S. In this paper the Millstone-grit series was described, from the eastern edge of the Lancashire Coal-field southwards to the Coal- fields of North Staffordshire. After giving a general sketch of the Geology of the district, and defining the upper and lower limits of the Millstone-grit, the authors - explained a series of sections, running from east to west, at intervals, across the country. In the most northerly of these the group con- sists of five thick gritstone-beds, separated by seams of shale, and attains a thickness of more than 2000 feet; while on the extreme south all but two of these beds have thinned away, and the whole thickness is there not more than 300 or 400 feet. Between the base of the Millstone-grit and the Carboniferous Limestone lies a group of shales and sandstones, with thin earthy limestones towards the bottom, which seem to hold the place of the Yoredale Rocks of Yorkshire. The mineral character of these beds was described, and their place noted on the sections. A short notice was also given of two small inliers of Carboniferous Limestone, namely, at Moxon, east of Leek, and at Astbury, near Congleton. April 13.—W. J. Hamilton, Esq., President, in the Chair. The following communications were read :— 1. “On the Geology and Mines of the Nevada Territory.” By W. Phipps Blake, Esq. In describing the physical features of the country, the author Mr. H. Seeley on the Red Rock in the Section at Hunstanton. 73 observed that it is an elevated semi-desert region, composed of a succession of longitudinal mountain-ranges with intermediate valleys and plains, the most abundant rocks being Metamorphic and Igneous; but Tertiary strata and Carboniferous Limestone also occur. The author then described the hot springs, which are extended along a line of fissure in a granitic rock, and parallel to the moun- tains, and which deposit silica in an amorphous and a granular state, sulphur being also seen in the cracks and cavities of the sili- ceous deposit. He considered these phenomena to illustrate the formation of a quartz-vein in a fissure. ’ Mr. Blake then gave an account of certain mineral veins in por- phyry, which yield sulphurets of silver (including crystals of Ste- phanite, but very little ruby silver) and a little gold; also galena, - copper pyrites, iron pyrites, and a little native silver, the veinstone being a friable quartz. The prevailing direction of the veins was stated to be nearly north and south; and the author remarked that they were richer in gold near the surface than at greater depths. 2. “On the Red Rock in the Section at Hunstanton.” By Harry Seeley, Esq., F.G.S., of the Woodwardian Museum, Cam- bridge. The physical structure of the rock was first considered, and it was shown to be divisible into three beds, the uppermost of which is of a much lighter colour than the rest, the middle being concretionary in structure, and the lower sandy. ‘These three beds, with the over- lying white sponge-bed, were considered to belong to one formation, and were treated of in this paper as the Hunstanton Rock; but the thin band of red chalk some distance above was considered, though of similar colour, to be quite distinct, as also was the Carstone below. Mr. Seeley then showed that near Cambridge the Shanklin Sands and the Gault have both become very thin, so that there is a great probability of the latter being unconformable to the beds above as well as to those below. He considered the lower part of the Car- stone to be of the age of the Shanklin sands; and as the Chalk is not unconformable to the Hunstanton Rock, he concluded that the latter could not be the Gault, but must be the Upper Greensand,— a conclusion which he afterwards showed was supported by the evidence of the fossils, and the occurrence of phosphate of lime. The seam of soapy clay which separates the Hunstanton Rock from the Chalk was supposed to have resulted from the disintegra- tion of a portion of the former, the red colour of ,which the author endeavoured to show was due to Glauconite. The upper part of the red rock of Speeton was thought to be possibly newer than that of Hunstanton, and perhaps to represent the time which elapsed between the formation of the latter and that of the band of red chalk. In conclusion, Mr. Seeley remarked that as the phosphate of lime is confined to Bed No. 2, and as many individuals of Gault species occur in Bed No. 3, while others of a Chalk character are met with 74 Geological Society. in Bed No. 1, it is very probable that the Hunstanton Rock is a more typical example of the Upper Greensand than is seen at Cam- bridge, and may represent also those periods which separate that formation from other divisions of the Cretaceous system. April 27.—W. J. Hamilton, Esq., President, in the Chair. The following communications were read :— 1. “On the Geology of Arisaig, Nova Scotia.” By the Rey. D. Honeyman, F.G.S. A careful examination of the country in the neighbourhood of Arisaig enabled the author to construct three sections and a map showing the geological constitution of the district. Two of these sections were nearly parallel to one another, running from N. to S., and taken some distance apart, while the third was nearly at right angles to the other two; thus a tolerably accurate idea of the geology of the country could be obtained. The author described each of these sections in detail, giving lists of the fossils found in the different beds, which proved them to be of Upper Silurian age; and. he further considered that they justified the adoption for the sub- divisions of these Nova-Scotian Silurians of the terms May-hill, Lower Ludlow, Aymestry, and Tilestones, the first and third of which had been used for them previously by Mr. Salter. Besides Silurian rocks, there occurs in the western part of this district a conglomerate of Lower Carboniferous age, while trap-rocks occur on the north and south. 2. ‘** On some Remains of Fishes from the ‘ Upper Limestone? of the Permian Series of Durham.” By J. W. Kirkby, Esq. The object of this paper was to record the discovery of Fish- remains in the upper Magnesian Limestone of the Permian forma- tion, which is higher in that series than any vertebrate remains had been previously known to occur. The strata exposed in the quarries were described in detail, especially the bed from which most of the Fishes were obtained, and which is known as the “‘ flexible limestone.” The author stated that at least nine-tenths of the specimens belong to Palgoniscus varians, the remainder belonging to two or three species of the same genus, and to a species of Acrolepis. Detailed descriptions of the different species of Fishes were given, as also were short notices of the species of Plants sometimes found associated with them, one of which he believed to be Calamites arenaceus, a Triassic species. ‘The occurrence of Paleonisci with smooth scales was stated to be antagonistic to Agassiz’s conclusion that the Permian species of that genus have striated, and the Coal- measure species smooth scales. In conclusion Mr. Kirkby re- marked that the fauna of the period appeared to have an Estuarine facies, and he expressed his opinion that the Fishes were imbedded suddenly, as a result of some general catastrophe. 3. ‘On the Fossil Corals of the West Indian Islands.—Part 3. Mineral Condition.” By P. Martin Duncan, M.B. Lond., Sec. G.S. The results of the process of fossilization, as seen in the West Indian fossil Corals, being very remarkable, and having much ob- Intelligence and Miscellaneous Articles. 75 scured their specific characters, thus rendering their determination extremely difficult, Dr. Duncan found it necessary to thoroughly examine their different varieties of mineralization, and to compare their present condition with the different stages in the decay and fossilization of recent Corals as now seen in progress. ‘Thus the author was enabled to show the connexion between the destruction of the minuter structures of the Coral by membrane decomposing and certain forms of fossilization in which those structures are im- perfectly preserved ; and he likewise stated that the filling-up of the interspaces by*granular carbonate of lime and other substances, as well as the induration of certain species, during a ‘‘ prefossil”’ and “‘ post-mortem” period, gave rise to certain varieties of fossilization, and that the results of those operations were perpetuated in a fossil state. The forms of mineralization described by Dr. Duncan are— (1) Calcareous; (2) Siliceous ; (3) Siliceous and Crystalline; (4) Siliceous and Destructive; (5) Siliceous Casts; (6) Calcareo- siliceous; (7) Calcareo-siliceous and Destructive; (8) Calcareo- siliceous Casts. In describing these forms, especial reference was made to those in which the structures were more or less destroyed during the re- placement (by silica) of the carbonate of lime which filled the inter- spaces, and during that of the ordinary hard parts of the Coral. In explaining the nature and mode of formation of the large casts of calices from Antigua, the author drew attention to the fact that the silicification is more intense on the surface and in the centre of the corallum than in the intermediate region; and, when examined microscopically, it could be seen that the replacement of the carbo- nate of lime began by the silica appearing as minute points in the centre of the interspaces and of the sclerenchyma, and not on their surface. In conclusion, the relation of hydrated silica to destruc- tive forms of fossilization was discussed, together with the influence of all the forms enumerated above in the preservation of organisms, and as one cause of the incompleteness of the geological record. IX. Intelligence and Miscellaneous Articles. REMARKS ON THE DISTILLATION OF SUBSTANCES OF DIFFERENT VOLATILITIES. BY M. CAREY LEA. a? experiments which have been recently published by M. Berthelot recall to me a similar and remarkable case which attracted my attention several years ago. M. Berthelot distilled 92 parts of alcohol and 8 of water, and found that the distillate at the beginning, middle, and end of the operation contained equal quantities of water and of alcohol. He distilled also a mixture containing a large quantity of sulphide of carbon and a small quantity of alcohol, and found that the least volatile body, the alcohol, passed over with the first portions of the 76 Intelligence and Miscellaneous Articles. distillate, so that toward the end of the operation the retort con- tained sulphide of carbon almost pure. To these facts, which tend to cast the greatest doubt on all the results obtained by the laborious process of fractional distillation, I now add the following. When a mixture containing the chlorides of ethylamine, diethyl- amine, and triethylamine is distilled with caustic alkali, we should, according to received ideas, expect to find the ethylamine, which is a gas at ordinary temperatures, distil over first. Triethylamine, which is at ordinary temperatures and pressures a liquid, separates as such when a strong solution of its chloride is treated with caustic alkali, and, floating on the surface, as I have before pointed out, we would naturally expect to find it principally in the latter stages of the distillation. The contrary is, however, the case when the less substituted ammonias predominate in quantity. Almost the whole of the triethylamine passes over in the first portions of the distillate, and subsequent ones, though rich in ethylamine and diethylamine, scarcely contain a trace of triethylamine.—Silliman’s American Jour- nal, May 1864, NOTE ON THE RESIDUAL CHARGE OF ELECTRICAL CONDENSERS. BY M.J.M. GAUGAIN. When after having discharged a Leyden jar it is left to itself and after some time a new metallic connexion is established between its armatures, we all know that a second spark is obtained, less strong than the first. This fact, generally known as the secondary discharge, has been designated by Mr. Faraday the residual charge. _I have adopted this latter name, slightly modifying the sense, to designate, not the quantity of electricity which passes in a second discharge, but all that remains after the original discharge, a quan- tity which may give rise to a multitude of successive secondary discharges. The existence of the residual charge is generally explained by saying that part of the electricity of the armatures penetrates slowly into the interior of the dielectric when the condenser is charged, and that this portion, slowly absorbed, is restored with equal slow- ness. But this explanation can certainly not apply to the experi- ments of which I am about to speak; for these experiments have been made in such conditions that the electricity of the armatures could not communicate itself to the dielectric, and yet the residual charge formed in certain cases more than three-quarters of the total charge. I worked, as in my former researches, on small fulminating panes, with moveable armatures: in certain cases the armatures were applied directly to the dielectric ; in other cases they were separated by small layers of air of uniform thickness. The general results were the same in either case. In a first series of researches I proposed to ascertain according to what law the residual charge varies when the duration of the charge Intelligence and Miscellaneous Articles. 77 varies—that is, the time during which the condenser is in connexion with the electrical source. I suppose the tension of this source to be invariable, as is the duration of the discharge. This was always a fraction of a second, the same in all the experiments. ‘The ob- servations were made in the following manner. The lower armature of the fulminating pane on which I worked being in connexion with the ground, I connect for a definite time the upper armature with a source of constant tension; the con- denser once charged, I detach the upper armature, and measure its total charge by the method which I have called gauging. Secondly, after this first operation, and when the dielectric has reverted to the neutral state, I charge the condenser again for the same time as at first, then I discharge it immediately by connecting for an instant the armatures ; that done, I remove the higher arma- ture, and gauge the quantity of electricity which it retains; this quantity represents the residual charge according to the definition given above. When this double series of operations is performed on the same condenser, giving successively different values to the duration of the discharge, this very simple result is attained—that the difference be- tween the total and the residual charge is constant. This difference, which represents the quantity of electricity which has disappeared in an instantaneous discharge, is precisely equal to the total instan- taneous charge. I denote in this manner the quantity of electricity which the influencing armature would receive if the condenser, com- pletely discharged, were put in connexion with the source of elec- tricity during a small interval of time equal to that taken for the discharge. ‘This law was verified by a great number of experiments, and on very different dielectrics. I worked successively on disks of shellac, of stearic acid, and of gutta percha, and on a cake made of flour of sulphur moistened by salad oil. I give the results obtained by a series of experiments made with the latter substance :— Duration of - Total Residual Differ- the charge. charge. charge. ence. Fraction of asecond ...... 26 ee 26 PRMOMIILES ois cs cs see pe es 44 18 26 4 minutes..... 49 23 26 . NS a rae 5d 28 27 MIIGES 5. cece sss oe. OF 33 26 The difference between the total and the residual discharge was sensibly the same for all durations of the charge, and equal to 26, a number which exactly represents the total instantaneous charge. Although observation alone would have enabled me to ascertain this relation, it is easy to see @ priori that it must exist if the bodies called insulating are generally formed, as I have been led to admit, of many elements of very different conductibilities. In the experiments I have just cited, the condenser was charged for a more or less long time, but always discharged immediately after being separated from the electric source, In another series of 78 Intelligence and Miscellancous Articles. researches the condenser was always charged for the same time, and discharged during the same fraction of a second; but the dis- charge was separated from the charge by longer or shorter intervals. This kind of observation appeared to me very suitable for putting in evidence the true origin of the residual charge. I shall cite the results of a series of experiments in which the duration of the charge was limited, like that of the discharge, to a fraction of a second; the dielectric was a disk of shellac 6 millims. in thickness. 1. The condenser was charged and gauged immediately after : the total charge was 45. 2. The condenser, after being charged, was left to itself for 15 minutes, and gauged at the end of this time: the total charge was again 45. : 3. The condenser was discharged immediately after being charged: the residual charge was zero. 4, Lastly, the condenser was discharged 15 minutes after the charge: the residual charge was 27. Experiments 1 and 2 prove clearly that in the interval of 15 minutes the armature gauged loses nothing of its charge, and that therefore no appreciable absorption is exerted by the shellac; and yet it follows, from experiments 3 and 4, that in this time of 15 minutes the residual charge rose from zero to 27. This increase of residual charge can only depend on a different arrangement of elec- tricity in the interior of the dielectric. When the charge has only been maintained for an instant, the parts of the dielectric which possess a great conductibility alone participate in the transmission of the influence; and as an instant is sufficient to polarize them, an instant is sufficient to restore them to the neutral state. If, on the contrary, the apparatus has been charged for a sufficiently long time, the elements endowed with a feeble conductibility come into play ; and as they cannot be restored to the neutral state in a very short time, they retain after the discharge almost all the electricity they had before. ‘This electricity retains a portion of the electricity of opposite kind which is accumulated on the armature. The residual charge is thus seen not to depend on a property of absorption specially belonging to insulating bodies; it depends simply on electrical movements which take place in the interior of these bodies in virtue of their conductibility.—Comptes Rendus, May 2, 1864. ON THE BOILING OF WATER, AND ON THE EXPLOSION OF STEAM- BOILERS. BY M. L. DUFOUR OF LAUSANNE. In the experiments which I have had the honour of communi- cating to the Academy, I have shown that the boiling-point of water and of other liquids may experience considerable retardation when these liquids are heated in the body of another liquid of the same density and without touching the sides of the vessels. In this mode of heating the liquids, it cannot be said that their boiling is Intelligence and Miscellaneous Articles. 79 produced at a fixed point; the change of state becomes possible when the temperature can give to the vapour an elastic force equal to the external pressure; but this change takes place only very rarely at the exact point at which its possibility commences. With a view to the study of ebullition, I have undertaken a great number of experiments; and among others, I have endeavoured to study ebullition by arriving at this phenomenon rather by a change of pressure, which the liquid undergoes, than by an increase of its temperature. The apparatus resembles, with certain modifica- tions, that which M. Regnault used in studying the elastic force of aqueous vapour. A sheet-iron vessel communicates, by suit- able tubes, (1) with an air-pump, (2) with a mercury manometer, (3) with a glass retort. In this retort were placed the liquids expe- rimented upon, and a thermometer with a small reservoir plunged in | the interior. By means of stopcocks, suitably arranged, the various parts of the apparatus could be connected. An observation of the manometer and of an external barometer obviously gave, at any moment, the external pressure of the apparatus. Studied under these circumstances, the boiling of water presents some characters worthy of attention. In the case of distilled water, it is soon seen that after.a first heating to 100°, boiling obtained by diminution of pressure is only produced at the temperature which the known law requires. Water remains liquid although the pressure is far below the tension of aqueous vapour for the temperature in question. When boiling commences, it is produced with tremulous violence, and usually part of the liquid is carried into the tubes with the first burst of vapour. These retardations are then more pronounced the more frequently water has been raised to a high temperature. They are more considerable when the water has been alternately heated to 110° and then cooled in the apparatus a certain number of times before being submitted to the test of dimi- nution of pressure. The following are some examples in which are noted in three successive columns, (1) the temperature of the liquid when boiling commences; (2) the pressure at this time; (3) the temperature at which normal ebullition would take place for this pressure :— 5 mm. 5 71 175 64 57 75 46 66 108 53°5 90°5 335 78°7 53 37 33 Retardations of 7°, 11°, 11°8, 20°, &c. are thus seen; that is, far more. considerable than those observed for water in glass vessels when ebullition is attained by reheating. Taking ordinary water, not distilled, and even tolerably calcareous, the same facts are observed; but it is necessary that the water should have been two or three times heated to boiling, then cooled in the vessel, or submitted to a very prolonged ebullition before being sub- mitted to diminutions of pressure. Normal ebullition is less rare 80 Intelligence and Miscellaneous Articles. than with distilled water; but nevertheless very frequent retarda- tions of 10°, 15°, and more are seen, as in preceding experiments. The presence of platinum, and in general of metallic substances, is known to have the reputation of hindering retardations of ebul- lition in glass vessels; and for a long time platinum wires have been used in concentrating liquids to prevent them from jumping over. Platinum wires placed in distilled water hinder, in fact, these retardations from being produced when, after having been heated once or twice to 100°, water is subjected to a diminution of pressure. But if the liquid containing platinum wire is heated to boiling for several times, and then allowed to cool—if especially platinum is for some days in contact with water at the bottom of the vessel, it is soon seen that the metal has become inactive, and then delays are observed as considerable as if water alone were in the retort. If ordinary water is taken abundantly carbonated, if along with it various solid bodies are introduced, facts are observed ana- logous to that which has been mentioned in the case of platinum. I have tried pieces of iron, lead, tin, zinc, copper, &c.; fragments of chalk, of wood, of quartz, paper, &c. In the first reheating, the presence of these bodies prevents any retardation, and ebullition takes place at the exact point at which the temperature of the liquid imparts to the vapour an elastic force equal to the superficial pres- sure. But if they are left for some time in contact with water, heated four or five times to ebullition, the contact of all these bodies appears to have become indifferent, and the liquid furnishes then very frequent examples of the retardation of ebullition. The fol- lowing are some examples in which the retort contained ordinary water, with fragments of iron, platinum, lead, chalk, and wood :— . mm. é 74 217 68°5 85 7% 63°2 67 wl 45 72 87 49. These correspond to retardations of 55, 21°8, 22°, 23°. Ebul- lition then commenced, sometimes spontaneously, sometimes by a blow given to the vessel; it was always very tumultuous and violent, almost explosive. These facts and others relative to other liquids, show that the ordinary law regarding the boiling-point of a liquid in reference to its pressure can only apply when ebullition is arrived at by a change in pressure rather than by a variation of temperature. These facts show, moreover, that water is susceptible of presenting great re- tardation in its ebullition, even when in contact with any metals and solid substances. Glass and porcelain vessels form by no means an exception. Lastly, it is seen that the contact of solids is some- times active and sometimes indifferent; and by analyzing the expe- riments of which I have given extracts, it is soon seen that the very — 3 probable cause of this change of influence is the presence or absence round these solids of a more or less condensed gaseous atmosphere. —Comptes Rendus, May 30, 1864. Lr. (tt wer 1644 THE LONDON, EDINBURGH, ann DUBLIN PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. ‘FOURTH SERIES.] AUGUST 1864, X. On the Absorption and Radiation of Heat by Gaseous and. Liquid Matter—Fourth Memoir. By Joun Tynpatt, HH... 5c 6 ae Royal Society has already done me the honour of pub- lishing in the Philosophical Transactions three memoirs on the relations of radiant heat to the gaseous form of matter. ‘In the first of these memoirs} it was shown that for heat ema- nating from the blackened surface of a cube filled with boiling water, a class of bodies which had been previously regarded as equally, and indeed, as far as laboratory experiments went, per- fectly diathermic, exhibited vast differences both as regards radia- tion and absorption. Atthe common tension of one atmosphere the absorptive energy of olefiant gas, for example, was found to © be 290 times that of air, while when lower pressures were em- ployed the ratio was still greater. The reciprocity of absorption and radiation on the part of gases was also experimentally esta- blished in this first vestigation. In the second inquryt I employed a different and more powerful source of heat, my desire being to bring out with still greater decision the differences which revealed themselves in the first investigation. By carefully purifying the transparent ele- mentary gases, and thus reducing the action upon radiant heat, the difference between them and the more strongly acting com- pound gases was greatly augmented. In this second inquiry, for example, olefiant gas at a pressure of one atmosphere was * From the Philosophical Transactions, Part II. 1864, having been read at the Royal Society June 18, 1863. t Phil. Trans. February 1861; and Phil. Mag. September 1861. ‘[ Phil. Trans. January 1862; and Phil. Mag. October 1862. Phil. Mag. 8. 4, Vol. 28. No. 187. Aug. 1864. G 82 Prof. Tyndall on the Absorption and Radiation shown to possess 970 times the absorptive energy of atmospheric air, while it was shown to be probable that, when pressures of zpth of an atmosphere were compared, the absorption of olefiant gas was nearly 8000 times that of air. A column of ammoniacal gas, moreover, 3 feet long, was found sensibly impervious to the heat employed in the inquiry, while the vapours of many of the volatile liquids were proved to be still more opake to radiant heat than even the most powerfully acting permanent gases. In this second investigation, the discovery of dynamic radiation and absorption is also announced and illustrated, and the action of odours and of ozone on radiant heat is made the subject of expe- riment. The third paper * of the series to which I have referred was devoted to the examination of one particular vapour, which, on account of its universal diffusion, possesses an interest of its own —1I mean of course the vapour of water. In this paper I con- sidered all the objections which had been urged against my results up to the time when the paper was written; I replied to each of them by definite experiments, removing them one by one, and finally placing, as I believe, beyond the pale of reason- able doubt the action of the aqueous vapour of our atmosphere. In this third paper, moreover, the facts established by experi- ment are applied to the explanation of various atmospheric phe- nomena. I have now the honour to lay before the Royal Society a fourth memoir, containing an account of further researches. Hitherto i have confined myself to experiments on radiation through gases and vapours which were introduced in succession into the same experimental tube, the heat being thus permitted to pass through the same thickness of different gases. A portion of the present inquiry is devoted to the examination of the transmission of radiant heat through different thicknesses of the same gaseous body. The brass tube with which my former experiments were conducted is composed of several pieces, which are screwed together when the tube is to be used as awhole; but the pieces may be dismounted and used separately, a series of lengths being thus attainable, varying from 2°8 inches to 49-4 inches. I wished, however, to operate upon gaseous strata much thinner than the thinnest of these; and for this purpose a special appa- ratus was devised, and with much time and trouble rendered at length practically effective. The apparatus is;sketched in fig. 1. C is the source of heat, which consists of a plate of copper against the back of which a steady sheet of flame is caused to play. The plate of copper forms one end of the chamber F (the “front chamber” of my * Phil. Trans. December 1862; and Phil. Mag. July 1863. of Heat by Gaseous and Liquid Matter. . 83 former memoirs). This chamber, as in my previous investiga- tions, passes through the vessel V, through which cold water igs. Bo 2 D A ras. D Oo S DO La Pp = VL o) > oun “ib Vee} r r= Wa pL Dg any (| ee INS AS \ WN continually circulates, entering at the bottom and escaping at the top. The heat is thus prevented from passing by conduction from the source C to the first plate of rock-salt S. This plate forms the end of the hollow cylinder AB, dividing it from the G2 84 Prof. Tyndall on the Absorption and Radiation front chamber F, with which the cylinder AB is connected by suitable screws and washers. Within the cylinder A B moves a second one, II, as an air-tight piston, and the bottom of the second cylinder is stopped by the plate of rock-salt S!. This plate projects a little beyond the end of the cylinder, and thus can be brought into flat contact with the plate S. Fixed firmly to A B is a graduated strip of brass, while fixed to the piston is a second strip, the two strips forming a vernier, vv. By means of the pinion R, which works in a rack, the two plates of salt may be separated, their exact distance apart being given by the ver- ner. P is the thermo-electric pile with its two conical reflectors ; C’' is the compensating cube, employed to neutralize the radiation from the source C. H is an adjusting screen, by the motion of which the neutralization may be rendered perfect, and the needle brought to zero under the influence of the two opposing radia- tions. The graduation of the vernier was so arranged as to permit of the employment of plates of gas varying from 0:01 to 2°8 inches in thickness. They were afterwards continued with the pieces of the experimental tube, already referred to, and in this way layers of gas were examined which varied in thickness in the ratio of 1 : 4900. In my former experiments the chamber F was always kept exhausted, so that the rays of heat passed immediately from the source through a vacuum; but in the present instance I feared the strain upon the plate S, and I also feared the possible intru- sion of a small quantity of the gas under examination into the front chamber F, if the latter were kept exhausted. Having established the fact that a length of 8 inches of dry air exerts no sensible action on the rays of heat, I had no scruple in filling the chamber F with dry air. Its absorption was nz/, and it merely had the effect of lowering in an infinitesimal degree the tempe- rature of the source. The two stopcocks ¢ and c! stand exactly opposite the junction of the two plates of salt S, S’ when they are in contact, and when they are drawn apart these cocks are in communication with the space between the plates. After many trials, the followmg mode of experiment was adopted :—The gas-holder contaming the gas to be examined was connected by an india-rubber tube with the cock ¢’, the other cock ¢ being at the same time left open. The piston was then moved by the screw R until the requisite distance between the plates was obtained. This space being filled with dry air, the radiations on the two faces of the pile were equalized, and the needle brought to zero. The gas-holder was now opened, and by gentle pressure the gas from the holder was forced first through a drying apparatus, and then into the space between the plates of salt. The air was quickly displaced, and a plate of of Heat by Gaseous and Liquid Matter. 85 the gas substituted for it. If the layer of gas possessed any sensible absorbing power, the equilibrium of the two sources of heat would be destroyed; the source C’ would triumph, and from the deflection due to its preponderance the exact amount of heat intercepted by the gas could be calculated. When oxygen, hydrogen, or nitrogen was substituted for atmospheric air, no change in the position of the galvanometer- needle occurred ; but when any one of the compound gases was allowed to occupy the space between the plates, a measurable deflection ensued. The plates of rock-salt were not so smooth, nor was their parallelism so perfect as entirely to exclude the gas when they were in contact. The contact was but partial, and hence a stratum of gas sufficient to effect a sensible absorp- tion could find its way between the plates even when they touched each other. On this account the first thickness in the following Tables was really a little more than 0-01 of an inch. The first column in each contains the thickness of the gaseous layer, while the second column contains the absorption expressed in hun- dredths of the total radiation. The first layer of carbonic oxide, for example, absorbed 0-2, and the second layer 0°5 per cent. of the entire heat. TasiE I1.—Carbonic Oxide. Absorption in Absorption in Thickness of hundredths of Thickness of hundredths gas. the total gas. of the total radiation. radiation. 0°01 of aninch 0-2 0-4 of aninech 375 0:02 3 0:5 0:5 ‘ 3'8 0:03 as O:7 0:6 es 4:Q 0:04 BF 0:9 1:0 9 5k 0-06 pA 1°4. 5 fe 6°1 0-1 Ae 1:6 2°0 - 6:8 0°3 i 3°0 Taste I].—Carboniec Acid. 0°01 of an inch 0°86 0'4 of aninch 5°3 0:02 re 1:2 0-5 ; 5:7 003 =, 1:5 Yates 5:9 0:04. € 1:9 0:7 4 6:0 0:05 - 21 0:8 Fy 6°] 006 ., 2:3 OO? s 62 Bia 3:3 Lge pe: 63 O20, 4:1 Pay 7-0 ay, 48 SO M 7-6 86 Prof. Tyndall on the Absorption and Radiation Tasxe III.—Nitrous Oxide. Absorption in Absorption in Thickness of hundredths Thickness of hundredths gas. of the total gas. of the total radiation. radiation. 0:01 of an inch 1°48 0:4 of an inch 10°20 0:02 As 2°33 0:5 5 11:00 0:03 HE 3°80 0:6 . 11:70 0:04: i 400 0°8 5 12°17 0:05 fn 4°20 1:0 5 12°80 O-l ne 6:00 5 - 14°20 0:2 cae Cee 2:0 a Lory TasLe [V.—Olefiant Gas. 0:01 of an inch 1:80 0:5 of an inch 23°30 0:02 ? 3°08 1:0 5 26°33 ~~ 0°05 5 5°37 2:0 4 32°80 0-1 a 9°14, We here find that a layer of olefiant gas only 2 inches in thick- ness intercepts nearly 33 per cent. of the radiation from our source. Supposing our globe to be encircled bya shell of olefiant gas only 2 inches in thickness, this shell would offer a scarcely sensible obstacle to the passage of the solar rays earthward, but it would cut off at least 33 per cent. of the terrestrial radiation and in great part return it. Under such a canopy, trifling as it may appear, the surface of the earth would be kept at a stiflmg temperature. The possible influence of an atmospheric envelope on the temperature of a planet is here forcibly illustrated. The only vapour which I have examined with the piston appa- ratus 1s that of sulphuric ether. Glass fragments were placed in a U tube and wetted with the ether. Through this tube dry air was gently forced, whence it passed, vapour-laden, into the space between the rock-salt plates SS’. The following Table contains the results. TasLe V.—Air saturated with the Vapour of Sulphuric Ether. Absorption in Absorption in Thickness of hundredths Thickness of hundredths vapour. of the total vapour. of the total radiation. radiation. 0:05 of an inch 2:07 0:8 of an inch 21:0 Ol » 46 1:5 a 34:6 0:2 - 8:7 DO ees 35:1 0:4, a 5 WA Fars Comparing these results with those obtained with olefiant gas, we find for thicknesses of 0:05 of an inch and 2 inches respect- ively the following absorptions :-— of Heat by Gaseous and Liquid Matter. 87 Olefiant gas. Sulphuric ether. Thickness of 0°05 . . 5°37 | Thickness of 0:05. . 2:07 Thickness of 2 inches. 32°80 | Thickness of 2 inches. 35°1 Sulphuric ether vapour, therefore, commences with an absorp- tion much lower than that of olefiant gas, and ends with a higher absorption. This is quite in accordance with the result esta- blished in my second memoir*, that in a short tube the absorp- tion effected by the sparsely scattered molecules of a vapour may be less than that of a gas at a tension of an atmosphere, while in a long tube the gas may be exceeded by the vapour. The deport- ment of sulphuric ether indicates what mighty changes of climate might be brought about by the introduction into the earth’s at- mosphere of an almost infinitesimal amount of a powerful vapour. And if aqueous vapour can be shown to be thus powerful, the effect of its withdrawal from our atmosphere may be inferred. § 2. The experiments with the piston apparatus being com- pleted, greater thicknesses of gas were obtained by means of the composite brass experimental tube already referred to. The arrangement adopted, however, was peculiar, being expressly intended to check the experiments, which were for the most part made by my assistants. The source of heat and the front cham- ber remained as usual, a plate of rock-salt dividing, as in my previous investigations, the front chamber from the experimental tube. The distant end of the tube was also stopped by a plate of salt; but instead of permitting the tube to remain continuous from beginning to end, it was divided, by a third plate of rock- salt, into two air-tight compartments. Thus the rays of heat from the source had to pass through three distinct chambers, and through three plates of salt. The first chamber was always kept filled with perfectly dry air, while either or both of the other chambers could be filled at pleasure with the gas or vapour to be examined. For the sake of convenience I will call the compartment of the tube nearest to the front chamber the first chamber, the compartment nearest to the pile the second chamber, the term ‘front chamber’ being, as before, restricted to that near- est to the source. The arrangement is sketched in outline in fig. 2. The entire length of the tube was 49°4 inches, and this was maintained throughout the whole of the experiments. The only change consisted in the shifting of the plate of salt S’ which formed the partition between the first and second chambers. Commencing with a first chamber of 2°8 inches long, and a second chamber 46-4 inches long, the former was gradually aug- mented, and the latter equally diminished. The experiments were executed in the following manner:—The first and second chambers were thoroughly cleansed and exhausted, and the needle * Phil. Trans. part 1, 1862; and Phil. Mag. vol. xxiv. p. 343. 88 Prof. Tyndall on the Absorption and Radiation brought to zero by the equalization of the radiations fallmg upon the opposite faces of the pile. Into the first chamber the gas or et :@ | I Front ch. 6 Re (As Tst Cham. Fig, 2 2nd, Cham. Fo By agree id ir : : -— ai vapour to be examined was introduced, and its absorption deter- mined. The first chamber was then cleansed, and the gas or - of Heat by Gaseous and Liquid Matter. 89 vapour was introduced into the second chamber, its absorption there being also determined. Finally the absorption exerted by the two chambers acting together was determined, both of them being occupied by the gas or vapour. The combination here described enabled me to check the expe- riments, and also to trace the influence of the first chamber on the quality of the radiation. In it the heat was more or less sifted, and it entered the second chamber deprived of certain con- stituents which it possessed on its entrance into the first. On this account the quantity absorbed in the second chamber when the first chamber is full of gas, must always be less than it would be if the rays had entered without first traversing the gas of the first chamber. From this it follows that the sum of the absorp- tions of the two chambers, taken separately, must always exceed the absorption of the tube taken as a whole. This may be briefly and conveniently expressed by saying that the sum of the absorp- tions exceeds the absorption of the sum. TasLe VI.—Carbonic Oxide. Length. Absorption per 100. — lst 2nd Ist 2nd Both chamber. chamber. chamber. chamber. chambers. 46°6 6:8 12:9 12°9 8:0 4.1°4, 9°6 12-2 12:9 1:2 37°2 LOz7. 12:2 12°9 15°4. 340 10°9 12:2 13°4 17°8 31°6 Teibeal 12:0 13°38 36°3 13°1 12°6 10°3 13°4 TaBLe VII.—Carboniec Acid. 2'8 46°6 8°6 13°8 13°3 8:0 4.) °4, . 9:9 12°7 13°0 12°2 37°2 11:0 11°4 13:0 15:4 340 11°8 12-1 13°9 23°8 25'6 127. 11°4 13°1 23'°8 25°6 dl ‘par key 12°6 23°8 25°6 10°4 10°5 12:0 36°3 13°1 11°6 10:0 12:3 Various causes have rendered these experiments exceedingly laborious. Could I have procured a sufficiently large quantity of gas in a single holder for an entire series of experiments it would not have been difficult to obtain concurrent results, but the slight variations in quality of the same gas generated at dif- ferent times tell upon the results and render perfect uniformity extremely difficult to obtain. The approximate constancy of the numbers in the third column is,. however, a guarantee that the 90 Prof. Tyndall on the Absorption and Radiation determinations are not very wide of the truth. Irregularities, however, are revealed. Some remarkable ones occur in the case of carbonic acid, with the chambers 23°8 and 25°6,—the absorp- tions in the first chamber varying in this instance from 11°7 to 10°4, and in the second chamber from 11:4 to 10°5, and in both chambers from 1371 to 12°0. The gas which gave the largest of these results was generated from marble and hydrochloric acid; the next was obtained from chalk and sulphuric acid, and the gas which gave the smallest result was obtained from bicar- bonate of soda and sulphuricacid. The slight differences accom- panying these different modes of generation made themselves felt in the manner recorded in the Table. TasiLE VIII.—WNitrous Oxide. Length. Absorption per 100. = SS as = lst 2nd lst 2nd Both chamber. chamber. chamber. chamber. chambers. 2°8 46°6 1671 32°9 33'°9 12°23 37°2 20'1 30:0 32°0 15:4 34°09 23°6 29°6 32°0 Lis 31°6 26:2 29:6 32°7 The differences arising from different modes of generation are most strikingly illustrated by the powerful gases. My friend Dr. Frankland, for example, was kind enough to superintend for me the formation of a large holder of olefiant gas by the so-called “continuous process,” in which the vapour of alcohol is led through sulphuric acid diluted with its own volume of water ; the following results were obtained :— TaspLe [X.—Olefiant Gas. Length. Absorption per 100. lst 2nd lst Sad > Both chamber. chamber. chamber. chamber. chambers. 2°8 46:6 346 66:1 62:7 8:0 4. -4, 4.4°2 65°3 67:5 15°4 34-0 53°6 62°3 67:0 Considering the difficulty of the experiments, the agreement of the absorption of both chambers, the sum of which was the constant quantity of 49-4 inches, must be regarded as satisfae- tory. ‘This is the general character of the results as long as we adhere to the same gas. Olefiant gas generated by mixing the Liquid alcohol with sulphuric acid and applying heat to the mix- ture, gave the results recorded in the following Table :— of Heat by Gaseous and Liquid Matter. 91 Table X.—Olefiant Gas. Length. Absorption per 100. lst 2nd Ast 2nd Both chamber. chamber. chamber. chamber. chambers. 12°2 37°2 548 70°0 76:3 15°4 34:0 59°1 eet EN 19°8 29°6 67°8 70:4: 77:0 23°8 25°6 69:2 70°2 77°6 36°3 lisial 728 60°3 73:8 The absorptions of both chambers in this Table are almost exactly 10 per cent. higher than those found with the gas gene- rated under Dr. Frankland’s superintendence. A few remarks on these results may be introduced here. In the case of carbonic oxide (Table VI.), we see that while a length of 2°8 inches of gas is competent, when acting alone, to intercept 6’8 per cent. of the radiant heat, the cutting off of this length from a tube 49:4 inches long, or, what is the same, the addition of this length to a tube 46°6 inches long, makes no sensible change inits absorption. The second chamber absorbs as much as both. The same remark applies to carbonic acid, and it is also true within the limits of error for nitrous oxide and olefiant gas. Indeed it is only when 8 inches or more of the column have been cut away that the difference begins to make itself felt. Thus, in carbonic oxide, the absorption of a length of 41°4 being 12:2, that of a chamber 49:4, or 8 inches longer, is only 12:9, making a difference of only 0°7 per cent., while the same 8 inches acting singly on the gas produces an absorption of 9°6 per cent. So also with regard to carbonic acid; a tube 41°4 absorbing 12°7 per cent., a tube 49°4 absorbs only 13-0 per cent., making a difference of only 0°3 per cent. As regards olefiant gas (Table TX.), while a distance of 8 inches acting singly effects an absorp- tion of 44 per cent., the addition of 8 inches to a tube already 41:4 inches in length raises the absorption only from 65:3 to 67°5, or 2°2 per cent. The reason is plain. In a length of 41°4 the rays capable of being absorbed by the gas are so much diminished, so few in fact remain to be attacked, that an addi- tional 8 inches of gas produces a scarcely sensible effect. Simi- lar considerations explain the fact that, while by augmenting the length of the first chamber from 2°8 inches to 15:4 inches we increase the absorption of olefiant gas nearly 20 per cent., the shortening of the second chamber by precisely the same amount effects a diminution of barely 4 per cent. of the absorption. All these results conspire to prove the heterogeneous character of the radiation from a source heated to about 250° C. The sum of the absorptions placed side by side with the 92 Prof. Tyndall on the Absorption and Radiation absorption of the sum exhibits the influence of sifting in an in- structive manner. Tables VI., VII., VIII., I[X., and X., thus treated, give the following comparative numbers :— TaBLE XI.—Carbonic Oxide. Length of chambers. Sum of absorptions. Absorption of sum. 2°8 46°6 19°7 12°9 8:0 Al:1 21°8 12°9 12:2 37:2 22°9 12°9 15:4 34:0 23°1 13:4 17°8 31:6 23°1 13°3 36°3 lisp 22:9 13:4: Means 22°3 Wei TasBLE XII.—Carbonie Acid. 2°8 46°6 22°4, 13°3 8:0 4.) °4, 22°6 13:0 13-2 BYP 22-4, 13:0 15°4 84:0 23°9 13:9 23°8 25:6 Pot 1371 36°3 13:1 21°6 12-3 Means 22°6 13:1 TaBLeE XIII.—Nitrous Oxide. 2°8 46:6 49-0 33°9 12:2 oe 53:1 32-0 15-4 34:0 53:2 32-0 17°8 31°6 55:8 oon Means 52°8 oot TasBLE XIV.—Olefiant Gas. 2:8 46°6 100°7 67°7 80 41:4 109°5 67°5 12-2 37:2 109°4: 65:0 15-4 340 115°9 67-0 Means 108°9 66°8 TaBLE X V.—Olefiant Gas. 192 37°2 124°8 76°3 15°4 340 131°8 iy | 19°8 29°6 138°2 100 23°8 25°6 139°4 77°6 36'3 13-1 133°1 78°8 Means 133°4 77°3 of Heat by Gaseous and Liquid Matter. 93 The conclusion that the sum of the absorptions is greater than the absorption of the sum is here amply verified. The Tables also show that the ratio of the sum of the absorptions to the absorption of the sum is practically constant for all the gases. Dividing the first mean by the second in the respective cases, we have the following quotients :— Warnonie Oxide -) s,s. eeee-70 Barbome acid 2c... weeed72 Nitrous oxide . . . 161 Olefiant gas (mean of both) eetos The sum of the absorptions ought to be a maximum when the two chambers are of equal length. Supposing them to be unequal, one being in excess of half the length of the tube, let us consider the action of this excess singly. Placed after the half-length, it receives the rays which have already traversed that half; placed after the shorter length, it receives the rays which have traversed the shorter length. In the former case, therefore, the excess will absorb less than in the latter, because the rays in the former case have been more thoroughly sifted before the heat reaches the excess. From this it is clear that, as regards absorption, more is gained by attaching the excess to the short length of the tube than to the half-length; in other words, the sum of the absorptions, when the tube is divided into two equal parts,isa maximum. ‘This reasoning is approximately verified by the experiments. Supposing, moreover, one of the lengths constantly to diminish, we thus constantly approach the limit when the sum of the absorptions and the absorption of the sum are equal to each other, the former being then a minimum. The effect of proximity to this limit is exhibited in the first expe- riment in each of the series; here the lengths of the compart- ments are very unequal, and the sum of the absorptions is, in general, a minimun. After the absorption by the permanent gases had been in this way examined, | passed on to the examination of vapours. They were all used at a common pressure of 0°5 of an inch of mer- cury, or about ;1,th of an atmosphere. The liquid which yielded the vapour was enclosed in the flasks described in my previous memoirs, and the pure vapour was allowed to enter the respec- tive compartments of the experimental tube without the slightest ebullition. The following series of Tables contains the results thus obtained. 94. Prof. Tyndall on the Absorption and Radiation Taste XVI.—Bisulphide of Carbon. Pressure 0°5 of an inch. Length. Absorption per 100. oO a Ist 2nd lst 2nd Both chamber. chamber. chamber. chamber. chambers. 2°8 46:6 3°6 7°6 8:0 4.1 +4: 44, 73 76 15°4 34:0 Nely/ 6:0 7°5 17°8 31:6 5:8 6:4: 75 23°8 25°6 6:7 6:0 78 Taste XVII.—Chloroform. Pressure 0°5 of an inch. 2°8 46°6 5:5 15:9 16°3 8:0 A +4: 9:2 15°6 16°8 122 O72 10:5 14:8 171 15°4 34:0 11:6 14-1 16°9 23°8 25'6 15:0 14:0 18°4 36'3 ‘Teja h 15°6 10:9 17:2 TasBLE XVIII.—Benzole. Pressure 0°5 of an inch. 2°8 46°6 AO 20:0 20:6 8-0 41-4, 8°4, 17°3 20:4: 12-2 af°2 9:8 16°5 19:0 17°8 31°6 11:9 15:7 20°1 23°8 25°6 14:3 15:1 21:0 Taste XIX.—Iodide of Ethyle. Pressure 0°5 of an inch. 2°8 46°6 71 23°5 25°4: 8:0 41-4, 9°1 De: 23°3 12:2 Sia 12°8 20°5 25:2 15:4 34-0 14°6 20°8 25:2 17°8 31:6 158 20:0 25°5 TasBLE XX.—Aleohol. Pressure 0:5 of an inch. 2°8 46:6 11°7 46°] - AG] 8:0 4.1 °4: 18:5 43°6 4.7°0 132 ouee 26:0 44] AT5 15°4 34:0 yew | 41-1 47:0 17°8 31°6 32°4 40:0 4.7°6 TasbLe XXI.—Aleohol. Pressure 0:1 of an inch. 8:0 414, 8-0 Peyaey 4 2409 15°4 34°0 12-1 20:0 24°7 17°8 31°6 13-1 19:7 25:7 23°83 25°6 148 18°4 25-2 36°3 131 oO 13°8 25°1 of Heat by Gaseous and Liquid Matter. 95 Taste XXIJ.—Sulphuric Ether. Pressure 0°5 of an inch. Length. Absorption per 100. lst 2nd 1st 2nd Both chamber. chamber. chamber. chamber. chambers. 2°8 46°6 14°8 50:0 51°6 8:0 4] °4, 23°9 51:0 53°9 12°2 37°2 30°9 48°83 53°6 15°4: 34:0 34:0 47°83 531 Taste XXIII.—Acetic Ether. Pressure 0°5 of an inch. 2°38 46°6 17:0 60°2 62°9 8:0 Al °4, 30°7 581 -64:°6 12°2 O72 41°6 55:1 64:2 15:4 34:0 A Av 4, 55:5 62:4, 23°38 25°6 50:9 52°7 64:7 36°3 : 1 58°] 42°6 64°83 Taste XXI1V.—Formic Ether. Pressure 0°5 of an inch. 2°8 46:6 17°4 63:0 64:4, 8:0 41:4, 33°93 591 63:4: 17°38 31°6 40:0 4:8°4: 60:3 Aes) 25°6 45°6 4.7 °2 60:2 I have already compared the sum of the absorptions for gases with the absorption of the sum; in the following Tables the same comparison is made for the vapours. Tasie XXV. Bisulphide of Carbon, 0°5 inch. Length of chambers. Sum of absorptions. Absorption of sum. 46°6 8:0 41:4, 11°7 7°6 15°4 34-0 lualsrg 7°5 17°8 31°6 12:2 75 23°8 25°6 12°7 78 Means 11°9 76 Taste XX VI.—Chloroform, 0°5 inch. 2°8 46°6 21°4 16°3 8:0 41 °4, 24°8 16°8 12-2 O72 25°3 Vk 15°4 34:0 25:2 16°9 23'8 25°6 29:0 18°4 36°3 13:1 26°5 172 Means 25:36 17-1 96 Prof. Tyndall on the Absorption and Radiation TasLE XX VII.—Benzole, 0°5 inch. Length of chambers. Sum of absorptions. Absorption of sum. 2°8 46°6 24-0 20°6 8:0 41 °4, 27 20°4: 123-2 37°2 26°3 19:0 17°8 31°6 27°6 20°1 23°8 25°6 29-4, 21:0 Means 26°6 20°2 TaBLeE XXVITI.—lodide of Ethyle, 0°5 inch. 2:3 6. 40:6 30°6 25°4 80 41:4 30°2 23°3 12-2 37°2 33°0 25:2 15:4 3840 35°4: 25-2 17°8 31:6 35°8 25:2 Means 383°] 249 TaBLe XXIX.—Alcohol, 0°5 inch. 28 46°6 57°8 “46-3 80 41°4 62°] 47°0 12-2 i ancmee 70°1 47°5 154 340 73°2 47-0 igre} 31:6 72°4 47°6 Means 67°] 47-0 TaBLE XXX.—Alcohol, 0:1 inch. 80 41°4 30°2 249 154 340 32:1 2407 12-8 alo 32°8 25m 93'S — 2556 30'2 25°2 36°3 13°1 32°9 25°1 Means 32:2 25°) Taste XXXJ.—Sulphuric Ether, 0°5 inch, 2°8 4.6°6 64°83 51°6 8:0 4.1 -4, 74:9 53°9 12-2 ore 79°7 536 15°4: 34:0 81:8 53°1 Means 75°3 53°05 of Heat by Gaseous and Liquid Matter. 97 Taste XX XIJ.—Formic Ether, 0°5 inch. Sum of Absorption Length of chambers. absorptions. of sum. . 80:4: 64:4: 8:0 41:4, 82°4 63°4: 17°8 31:6 88°4 60:3 23°83 25°6 92°83 60°2 Means 86:0 62:07 Taste XXXITI.—Acetic Ether, 0°5 inch. 2°8 46°6 77:2 62°9 8:0 4.) °4, 88°8 64:6 12°2 37°2 96°7 642 15:4 34-0 99-9 62°4: 23°8 25°6 103°6 64:7 363 131 100°7 64°8 Means 94:5 63°9 An inspection of the foregoing Tables discloses the fact that, in the case of vapours, the difference between the sum of the absorptions and the absorption of the sum is, in general, less than in the case of gases. This resolves itself into the proposi- tion that for equal lengths, within the limits of these experi- ments, the sifting power of the gas is greater than that of the vapour. The reason of this is that the vapours are examined in a state of tenuity which is only J,th of that possessed by the gases. Thus, no matter how powerful the individual molecules may be, their distance asunder renders a thin layer of them a comparatively open screen. § 8. The entrance of a gas into anexhausted vessel isaccompanied by the generation of heat; and the gas thus warmed, if a radia- tor, will emit the heat generated. Conversely, on exhausting a vessel containing any gas, the gas is chilled, and thus an exter- nal body, which prior to the act of exhaustion possessed the same temperature as the gas within the vessel, becomes, on the first stroke of the pump, a warm body with reference to the gas - remaining in the vessel; and if the external body be separated from the cooled gas by a diathermic partition, it will radiate into the gas and become chilled by this radiation. It was shown in my second memoir* that this mode of warming and of chilling a gas or vapour. furnished a practical means of determining, without any source of heat external to the gaseous body itself, both its radiative and absorptive energy. For the sake of con- * Phil. Trans. part 1, 1862; and Phil. Mag. vol. xxiv. p. 337. Phil. Mag. 8. 4. Vol. 28. No. 187. Aug. 1864. H 98 Prof. Tyndall on the Absorption and Radiation venience I have called the radiation and absorption of a gas or vapour thus dynamically heated and cooled, dynamic radiation and dynamic absorption. In illustration of the manner in which dynamic radiation may be applied in researches on radiant heat, I have had made, during the last half-year, a considerable number of experiments, some of which I will here describe. In the first place, the expe- rimental tube was divided into two compartments, as in the experiments described in the foregoing section. ‘The source of heat was abolished, and one end of the experimental tube was stopped by a plate of polished metai; the other end was stopped by a transparent plate of rock-salt, while the space between the ends was divided into two compartments by a second plate of rock-salt. The thermo-electric pile occupied its usual position at the end of the tube, the compensating cube, however, being abandoned. For the sake of convenient reference, I will call the compartment of the tube most distant from the pile the first chamber, and that adjacent to the pile the second chamber, An outline sketch of the arrangement is given in fig. 3. Fig. 3. i Ist. Chain. T J | IRD mee (ez tes) e || 3 . a): ‘The experiments were conducted in the following manner :— Both compartments being exhausted and the needle at zero, the gas was allowed to enter the first chamber through a gauge- cock which made its time of entry 40 seconds. The second chamber was preserved a vacuum; the gas on entering the first chamber was dynamically heated, and radiated its heat to the pile through the vacuous second chamber; the needle moved, and the limit of its excursion was noted. The first chamber was then exhausted and carefully cleansed with dry air. The second chamber was filled with the same gas, not with a view to determine its dynamic radiation, but to examine its effect upon the heat radiated from the first chamber. The needle being at of Heat by Gaseous and Liquid Matter. 99 zero, the gas was again permitted to enter the first chamber exactly as in the first experiment,—the only difference between the two experiments being, that in the first the heat passed through a vacuum to the pile, while in the second it had to pass through a column of the same kind of gas as that from which it emanated. In this way the absorption exerted by any gas upon heat radiated from the same gas, or from any other gas, may be accurately determined. Finally, the apparatus being cleansed and the needle at zero, the gas was permitted to enter the second chamber, and its dynamic radiation from this chamber was deter- mined. ‘The intermediate plate of salt S! was shifted, as in the former experiments, so as to alter the lengths of the two cham- bers, but the sum of both lengths remained constant as before. In the following Tables the three columns bracketed under the head of “ Deflection,” contain the arcs through which the needle moved in the three cases mentioned; (1) when the radia- tion from the gas in the first chamber passed through the empty second chamber; (2) when the radiation from the first chamber passed through the occupied second chamber ; and (3) when the radiation proceeded from the second chamber. Dynamic Radiation of Gases. Taste XXXIV.—Carbonic Oxide. Deflection. Length. oo ee — By lst By Ist lst 2nd chamber, chamber, By 2nd chamber. chamber. 2nd chamber gasin 2nd chamber. empty. chamber. 2-8 46°6 1:0 0-0 28-0 15°4, 34:0 3°8 AS | 24:4. 36'3 13:1 13:7 6°3 166 TaBLeE XXX V.—Carbonic Acid. 2°8 46°6 EO 0:0 33'6 15:4 34:0 3°7 29 Doo 36°3 13:1 16°8 6°6 75 TasLe XXXVI.—Nitrous Oxide. 2°83 46°6 1:0 0:2 44c5 15:4. 34:0 43 1:2 oy 36°3 13°1 19°5 6:2 22:0 Taste XXX VII.—Olefiant Gas. 15:4 340 11:9 1:0 68:0 23°83 25-6 22°8 Ow 36°3 ho"h 59:0 10:4: 65:0 H 2 100 Prof. Tyndall on the Absorption and Radiation The gases, it will be observed, exhibit a gradually increasing power of dynamic radiation from carbonic oxide up to olefiant gas. This is most clearly illustrated by reference to the results obtained in the respective cases with the first length of the second chamber. They are as follows :— Carbonic oxide. . . . . . 280 Carbonie:acids titeeyt se ee Nitrous oxudesccaise otic’ toe eae Olefiant easing Wie? 68:0 Its proximity to the pile, and the fact of its having to cross but one plate of salt, makes the action of the second chamber much greater than that of the first. Each of the Tables exhibits the fact that as the length of the chamber increases the dynamic radiation of the gas contained in it increases, and as the length diminishes the radiation diminishes. We also see how powerfully the gas in the second chamber acts upon the radiation from the first. With carbonic oxide, the pre- sence of the gas in the second chamber reduces the deflection from 13°°7 to 6°83; with carbonic acid it is reduced from 16°8 to 6°6; with nitrous oxide it is reduced from 19°5 to 6:2. Now this residual deflection, 6°:2, is not entirely due to the transpa- rency of the gas, to heat emitted by the gas. No matter how well polished the experimental tube may be, there is always a certain radiation from its interior surface when the gas enters it. With perfectly dry air this radiation amounts to 8 or 9 degrees. Thus the radiation is composite, in part emanating from the mole- cules in the first chamber, and in part emanating from the sur- face of the tube. ‘To these latter, the gas in the second cham- ber would be much more permeable than to the former; and to these latter, I believe, the residual deflection of 6 degrees, or thereabouts, is mainly due. That this number turns up so often, although the radiations from the various gases differ con- siderably, is in harmony with the supposition just made. In the case of carbonic oxide, for example, the deflection is reduced from 13°7 to 63, while in the case of nitrous oxide it is reduced from 19°°5 to 6°-2; in the case of olefiant gas it is reduced from 99° to 10°*4,, while in other experiments (not here recorded) the deflection by olefiant gas was reduced from 44° to 6°. As may be expected, this radiation from the interior surface augments with the tarnish of the surface, but the extent to which it may be increased is hardly sufficiently known. Indeed the gravest errors are possible in experiments of this nature if the influence of the interior be overlooked or misunderstood. An experiment or two will illustrate this more forcibly than any words of mine. of Heat by Gaseous and Liquid Matter. 101 A brass tube 3 feet long, and very slightly tarnished within, was used for dynamic radiation. Dry air on entering the tube produced a deflection of 12 degrees. The tube was then polished. within, and the experiment repeated; the action of dry air was instantly reduced to 7-5 degrees. The rock-salt plate at the end of the tube was then removed, and a lining of black paper 2 feet long was introduced within it. The tube was again closed, and the experiment of allowing dry air to enter it repeated. The deflections observed in three suc- . cessive experiments were 80°, ol hg 80°. This result might be obtained as long as the lining continued within the tube. The plate of rock-salt was again removed, and the length of the lining was reduced to a foot; the dynamic radiation on the entrance of dry air in three successive experiments gave the deflections ioe 74°, "o-. The plate was again removed and the lining reduced to 3 inches ; the deflections obtained in two successive experiments were 6G], 65°. Finally the lining was reduced to a ring only 12 inch in width ; the dynamic radiation from this small surface gave in two suc- cessive trials the deflections 56°, 56°°5. The lining was then entirely removed, and the deflection instantly fell to hey A coating of lampblack within the tube produced the same effect as the paper lining; common writing-paper was almost equally effective; a coating of varnish also produced large deflections, and the mere oxidation of the interior surface of the _ tube is also very effective. In the above experiments the lining was first heated, and it then radiated its heat through a thick plate of rock-salt against the pile. The effect of the heat was enfeebled by distance, by reflexion from the surfaces of the salt, and by partial absorption. Still we see that the radiation thus weakened was competent to drive the needle almost through the quadrant of a circle. If, instead of being thus separated from the lining, the face of the pile itself had formed part of the interior surface of the tube, receiving there the direct impact of the particles of air, of course the deflections would be far greater than the highest of those 102 Prof. Tyndall on the Absorption and Radiation above recorded. Indeed I do not doubt my ability to cause the needle of my galvanometer to whirl, by the dynamic heating of the surface of my pile, through an are of 1000 degrees. As- suredly an arrangement’ subject to disturbances of this character cannot be suitable in experiments in which the greatest delicacy is necessary. Experiments on dynamic radiation, similar to those executed with gases, were made with vapours. The tube was divided into two compartments as before. Both compartments being exhausted, vapour was permitted to enter the first chamber. Dry air was afterwards permitted to enter the same chamber ; the air was heated, it warmed the vapour, and the vapour radiated its heat against the pile. The heat passed in the first experiment through a vacuous second chamber, and in the second experiment through the same chamber when it contained O°5 of an inch of the same vapour as that from which the rays issued. A third experiment was made to determine the dynamic radiation from the second chamber. The following Tables con- tain the results :— Dynamic Radiation of Vapours. Taste XXX VIII.—Bisulphide of Carbon, 0°5 inch. Lenyth. Deflection. SSS Se ie By Ist By Ist Ist 2nd chamber, chamber. By 2nd chamber. chamber. 2ndchamber Vapourin — chamber. empty. 2nd chamber. 15-4 84-0 Dd. 1-6 14-2 36°3 13-1 9°75 5°5 9:0 TaBLE XXXIX.—Benzole, 0°5 inch. __ 15:4 34:0 3°0 Ail 34:0 36°3 13-1 21°6 Teg 15°] Taste XL.—lIodide of Ethyle, 0°5 inch. 15°4 340 3°4: alae 38'8 36°3 Lay 20°A 13°8 19:0 Taste XLI.—Chloroform, 0°5 inch. 15°4 340 45 2°] 41-0 36°3 13:1 22°3 10:0 19-0 TasLe XLIIT.—Alcohol, 0°5 inch. 15°4 34:0 4°9 2°0 53°8 36°3 13:1 33°8 16'9 34:9 of Heat by Gaseous and Liquid Matter. 103 Taste XLIII.—Alcohol, 0°1 inch. Length. Deflection. By Ist By Ist lst 2nd chamber, chamber. By 2nd chamber. chamber. 2nd chamber vapour in chamber. empty. 2nd chamber. 15-4 840 2-0 13 85-7 36°3 13°1 21:8 16:2 115 TasLe XLIV.—Boracic Ether, 0:1 inch. 15°4: 340 6°3 21 61:0 36°3 13-1 29°1 15°7 31:6 Taste XLV.— Formic Ether, 0°5 inch. 15°4 340 6°3 20 68:0 36°3 1371 46:0 23°8 41:0 Tasie XLVI.—Sulphuric Ether, 0°5 inch. 15:4 340 5°6 2°5 68:0 36°3 131 45°3 22°4: 36°5 TasLft XLVII.—Acetic Ether, 0°5 inch. 15°4 34°0 ef 1:0 73°9 36°3 131 49°] 22'°0 41:0 Collecting the radiations from the second chamber for the lengths 34 inches and 13:1 inches together in a single Table, we see at a glance how the radiation is affected by varying the length. TaBLe XLVIII, Dynamic radiation of various vapours at 0°5 inch pressure and a common thickness of ~) ar EMRE Eas > ———— 34 inches. 13°1 inches. Bisulphide of carbon . . . 142 9:0 te be a Nao L5sk Meme Of ethyle . nn sine BOTS 19:0 APOTOHOLT 5 pis ...af »...0. 14b0 19:0 PCG ee kw ai) mary = . OO DeM 34:9 Bemumiie ether. ss a)» 68°0 36°5 Pome ether oe ah 2 oc >,.09°0 41°0 PRECHICACLET: oni iw, (e,1.5) 004 AOD 41:0 At a pressure of 0:1 of an inch. PUMP ef in ay Binoy Manacic ether... . » «yp» 61°0 31°6 104 Prof. Tyndall on the Absorption and Radiation The extraordinary energy of boracic ether as a radiant may be inferred from the last experiment. Although attenuated to +4,,th of an atmosphere, its thinly scattered molecules are able to urge the needle through an arc of 61 degrees, and this merely by the warmth generated on the entrance of dry air into a vacuum. Arranging the gases in the same manner, we have the follow- ing results :— TaBLE XLIX. Dynamic radiation of gases at 1 atm. pressure and a common thickness of —_ 34 inches. 13'1 inches. Carponic oxime. {502-24 16°6 Carbonic acid ee Sa ee ee 5 Nitroussoxdede? “aud Fee ae 22:0 Olefiant pases os? Sains DCS 65:0 The influence of tenuity which renders the vapour at 0°5 of an inch a more open screen than the gas at 30 inches is here exhibited. In the case of the vapour, a greater length is avail- able for radiation than in the case of the gas, because the radia- tion from the hinder portion of the column of vapour is less interfered with by the molecules in front of it than is the case with the gas. By shortening the column we therefore do more injury to the vapour than to the gas; by lengthening it we pro- mote the radiation from the vapour more than that from the gas. Thus while a shortening of the gaseous column from 34 inches to 13-1 causes a fall in the case of carbonic oxide only from 23°°3 to 17°5, the same amount of shortening causes benzole vapour to fall from 34° to 15°:],—a much greater diminution. So also as regards olefiant gas, a shortening of the radiating column from 34 inches to 13°1 inches causes a fall in the deflection only from 68° to 65°; the same diminution produces with sulphuric ether a fall from 68° to 36°°5; and with acetic ether from 73°°9 to 41°. In the long column acetic ether vapour beats olefiant gas, but in the short column the gas beats the vapour. One of the earliest series of experiments of this nature which were executed last autumn, though not free from irregularities, is nevertheless worth recording. The experiments were made with a brass tube, slightly tarnished within, the tube being 49-4 inches long, and divided into two equal compartments, each 24-7 inches in length, by a partition of rock-salt placed at the centre of the tube. - of Heat by Gaseous and Liquid Matter. 105 Taste L.—Dynamic radiation of Vapours. Deflection. a a ae = SEBEL By lst chamber, By lst chamber, 2nd chamber vapour in 2nd_ By 2nd empty. chamber. chamber. Bisulphide of carbon . 8:2 5°8 21°2 Benzole .. . . 20°0 12°4 45°9 Siloroferm.. ...... « 243 10:9 55°2 Jodide of ethyle . . . 27:5 14:7 55°3 RCE nS 6! ue A°7 22°3 69-0 Sulphuricether . . . 46:3 a Gy 80°5 Formic ether. . aude 19°8 795 Propionate of ethyle. . 49°38 25°0 82:3 PEEEEGHEE fo. fs) DOD 30°0 82°1 To ascertain whether the absorption by the vapours bears any significant relation to the absorption by the liquids from which these vapours were derived, the transmission of radiant heat through those liquids was examined. The open flame of an oil- lamp was used, and the liquids were enclosed in rock-salt cells. Thus the total radiation from the lamp, with the exception of the minute fraction absorbed by the rock-salt, was brought to bear upon the liquid. In the following Table the liquids are arranged in the order of their powers of transmission. TasLe LI. Transmission in Name of liquid. ’ hundredths of the radiation. Bisulphide of carbon . . 5 se ehek Bisulphide of carbon saturated with sulphur . te) Bisulphide of carbon saturated with iodine . . 81 Ege age ana aaa ahaa seat mN: dy Chloroform .. . Sg teenie ee ete pede agi es Iodide of apy a 6S Ng ee Ba etn ge eae Ox ch Benzole . De ae ei ee ee ie ie Sons See Todide of ethyle REAR LTR Ase MEN Fis Amylene. . PRT ES SS MN Mae NC fanaa | Sulphuric Benes Yas 5; Oy Lae Va ee Org os VOSS Q, ERS NOS LD o Sea est ASR Re AO As in allother measurements of this kind, the 33 retarding influence of the sides of the glacier is manifest: the centre moves with the greatest velocity. Morteratsch Glacier, Line B No. of stake. Hourly motion. : 0:05 inch. er OP AP TIE ae att reee ape oP OIA RM ai ls yl U8 P= Pitteery eh MS Rents enone Seer agg mac cee a Orie Lee ERO rea | aoa Se eee rar re ayn Osis Oe a etre, Oe TORR hmnas er Ora PP Se eee. ee Oran The first stake of this line was quite close 32 33 to the edge of the glacier, and the ice was thin at the place, hence its slow motion. Crevasses prevented us from carrying the line sufficiently far across to render the retardation of the further side of the glacier fully evident. Morteratsch Glacier, Line C. No. of stake. Hourly motion. iy 0:05 inch. 2. O09 =. 3. OS: a: 4., Spon geet OOo 5. go te, Sree one es 6. : A pes Vs O25, 8. soir Ooo 0 a 9. tie iar cee ul ake ay aaa 10. Sohn tere et Ure as | cl ee cna ee OSLO Prof. Tyndall on the Conformation of the Alps. 269 Comparing the three lines together, it will be observed that the velocity diminishes as we descend the glacier. In 100 hours the maximum motion of the three lines respectively is as follows:— Mazimum Motion in 100 hours. ime Ay 3... Seen b5Gunehes. ean Obie Mo BN pee mg Oudkos. .) sOmiey This deportment explains an appearance which must strike every observer who looks upon this glacier from the Pitz Lan- guard, or from the new Bernina Road. A medial moraine runs along the glacier, commencing as a narrow streak high up; but towards the end the moraine extends in width, and finally quite covers the terminal portion of the glacier. The cause of this is revealed by the foregoing measurements, which prove that a stone on the moraine where it is crossed by the line A, ap- proaches a second stone on the moraine where it is crossed by the line C with a velocity of 26 inches in 100 hours. The moraine is in a state of longitudinal compression. Its materials are more and more crowded together, and must consequently move laterally and render the moraine at the terminal portion of the glacier wider than above. The motion of the Morteratsch glacier, then, diminishes as we descend. The maximum motion of the third line is 30 inches in 100 hours, or 7 inches a day—a very slow motion ; and had we run our lines nearer to the end of the glacier, the motion would have been slower still. At the end itself it is nearly insensible. Now I submit that this is not the place to seek for the scooping power of a glacier. The opinion appears to be pre- valent that it is the snout of a glacier that must act the part of ploughshare; and it is certainly an erroneous opinion. The scooping power will exert itself most where the weight, and con- sequently, other things being equal, the motion is greatest. A glacier’s snout often rests upon matter which has been scooped from the glacier’s bed higher up. I therefore do not think that the inspection of what the end of a glacier does or does not accomplish can decide this question. The snout of a glacier is potent to remove anything against which it can fairly abut; and this power, notwithstanding the slowness of the motion, manifests itself at the end of the Mor- teratsch glacier. A hillock, bearing pine trees, was in front of the glacier when Mr. Hirst and myself inspected its end ; and this hillock is being bodily removed by the thrust of the ice. Several of the trees are overturned; and in a few years, if the glacier continues its reputed advance, the mound will certainly be ploughed away. 270 Prof. Tyndall on the Conformation of the Alps. I will here add a few measurements executed on the Rosegg glacier: the line was staked out across the trunk formed by the junction of the Rosegg glacier proper with the Tschierva glacier, a short distance below the rocky promontory called Agaliogs. Rosegg Glacier. No. of stake. et Hourly motion. 1. * * den ye OO amehe 2. Nepean Os Ula ens 3. See | OL Oakey A, 0:10 ,, 5. on phe aces 6. O13 ,, is O14 ,, 8. of OLS aes Qe oe sr tdhiatstoyl uo iroheuOze-tkaane LQ. £80 disgslhey 081 RAG: Say ag Oe oaare 10 ae oes osiiinie dpi OAT aus This is an extremely slowly moving glacier; the maximum here found hardly amounts to 7 inches a day. Crevasses pre- vented me from continuing the line quite across the glacier. To return to the question of Alpine conformation,—it stands, I think, thus:—We have, in the first place, great valleys, such as those of the Rhine and the Rhone, to which we might conveniently give the name of valleys of the Ist order. The mountains which flank these main valleys are also cut by lateral valleys which run into the main one, and which may be called valleys of the 2nd order. When these latter are examined, smaller valleys are found running into them, which may be called valleys of the 3rd order. Smaller ravines and depressions, again, join the latter, which may be called valleys of the 4th order, and so on until we reach streaks and cuttings so minute as not to merit the name of valleys at all. At the bottom of every valley we have a stream, diminishing in magnitude as the order of the valley ascends, carving eternally at the earth and carrying its materials to lower levels. We find moreover that the larger valleys have been filled for untold ages by glaciers of enormous dimensions, and that these glaciers were always moving, grinding down and tearing away the rocks over which they past. We have, moreover, on the plains which extend at the feet of the mountains, and in enormous quantities, the very matter derived from the sculpture of the mountains themselves. The plains of Italy and Switzerland are cumbered by the débris of the Alps. The lower, wider, and more level valleys are also filled to unknown depths with the materials derived from the higher On the Expansion of Gases by increase of Temperature. 271 ones. In the vast quantities of moraine-matter which cum- ber many of the valleys we have also suggestions as to the magnitude of the erosion which has taken place. This moraine- matter, moreover, is only in part derived from the falling of rocks from the eminences upon the glacier ; it is also in great part derived from the grinding and the ploughing-out of the glacier itself, This accounts for the magnitude of many of these ancient moraines, which date from a period when almost all the moun- tains were covered with ice and snow, and when consequently the quantity of moraine-matter derived from the naked crests cannot have been considerable. The erosion theory ascribes the forma- tion of Alpine valleys to the agencies here briefly referred to. It invokes nothing but true causes. The artificers by which its work is performed are still there, though, it may be, in dimi- nished strength; and if they are granted sufficient time, it is demonstrable that they are competent to produce the effects ascribed to them. And what does the fracture theory offer in comparison? From no possible application of this theory, pure and simple, can we obtain the slopes and forms of the moun- tains. Erosion must in the long run be invoked, and its power therefore conceded. The fracture theory infers from the dis- turbances of the Alps the existence of fissures ; and this is a pro- bable inference. But that they were of a magnitude sufficient to determine the conformation of the Alps, and that they fol- lowed, as the Alpine valleys do, the lines of natural drainage of the country, are assumptions which do not appear to me to be justified either by reason or by observation. Royal Institution, September 1864, P.S.—The foregoing paper was in the printer’s hands before it was my privilege to read the last Anniversary Address to the Geographical Society by its President, Sir Roderick Murchison. I have since considered the arguments, and given, I trust, due weight to the authorities urged and cited in that excellent Address against the theory of erosion, as applied to the valleys of the Alps. But the effect on my mind is not such as to induce me to alter the opinions, based on observed facts, which I have yen- tured to express in these pages. XXXI. On the Law of the Expansion of the Gases by increase of Temperature. By Professor Porter, A.M.* i bad the theory of heat, the law of the expansion of the gases by increase of temperature is a most important subject, not only on account of the air-thermometer having been taken as the * Communicated by the Author. 272 Prof. Potter on the Law of the Expansion standard to which the liquid and solid thermometers were com- pared, but also with respect to the chemical hypothesis of equi- valent combining-volumes of gases. The laws of the expansion of the gases by equal increments, proposed by Gay-Lussac, and of uniform expansion, proposed by Dalton, give results which differ very little between the points of the freezing and boiling of water, but they diverge greatly at higher temperatures. Dalton’s law, expressed in the formula V=V,.¢*, where V is the volume of a gas at f° above the zero-point of the thermometric scale, and V, the volume at the zero of the scale, had a greater prima facie claim to be considered a physical law than that of Gay-Lussac, of which the formula is V=V,(1+a?°), because, the expansion for one degree in the \= 0 latter being =a, obtained by putting 2°=1°, we do not 0 see why any temperature for a gas may not be taken as reason- ably as the freezing-point of water, and that generally ~ =a constant: then integrating we obtain for Dalton’s law V=V).c* ; and expanding we have VV es (1 + at? +. arfo2 a3{°3 ) 119 1 a ee By stopping at the term with the first power of «= z}, on Fahrenheit’s scale nearly, we have Gay-Lussac’s law. Never- theless I now think that Gay-Lussac’s law is a nearer approxi- mation than Dalton’s in ordinary temperatures, and a very much nearer one for high temperatures. The important experiments of M. Regnault show that the coefficient of expansion for air increases with the density, or as the molecules are nearer together*. Carbonic acid gas exhibits the same property still more strongly, and sulphurous acid gas shows it in a still higher degree. The expansion or value of « for the interval between the freezing- and boiling-points of water at ordinary atmospheric pressure for carbonic acid gas being *37099, it becomes 38455 at a pressure of rather more than three atmo- spheres; whilst hydrogen gas shows no reliable variation. Now as the atoms of a gas approach each other when the temperature is diminished, we have a right to expect the same result at lower temperatures at the same pressure: and Gay- Lussac’s law gives such a result; for the constant mcrement Wie) o o— bears asmallerratioto the actualvolumeV = V,(1 + a?°) i) as the degrees 7° are increased, anda greater ratio as the degrees —?° are more below the freezing-point of water. * Relation des Expériences, &c., vol. i. p. 110, of the Gases by increase of Temperature. 273 The air-thermometer being taken as the standard, we are not able to employ it to show its own errors, but must have recourse to the liquefiable gases, where the deviation from Gay-Lussac’s law becomes very great compared with that of air, and will con- _ sequently be well ascertained by taking the air-thermometer as exact in the first instance, and afterwards attributing to air the same law, with different constants, as that found for the lique- fiable gas. In this manner we shall find that the air-thermo- meters must give place to a thermometer formed with hydrogen gas, or the mercurial thermometer accurately graduated for the law of uniform expansion, or otherwise for low temperatures the spirit-thermometer accurately graduated according to the law of the hyperbolic expansion of alcohol, when critically exact tempe- ratures are required to be known. M. Regnault found* that a thermometer formed with sulphu- rous acid gas, on being compared with an air-thermometer, gave the following results for the mean value of « for Centigrade degrees :— From 0 Centigrade to 98-12 C. the mean value of «=:003825] bs Mp 102:45 >) <: ‘: = ‘0038225 x BR e542. ¥ = -0037999 me MS 7 E+ i) F = 0037923 i pe 299'90.° % = ‘0037913 me eee BIOB! oy; ) = 0037893 In seeking for the law which will include these results, we shall find that they conform to a hyper- bolic law of expansion ; and Gay-Lussac’s lawarises from taking at great dis- tances from the centre the asymptote of the hy- perbola for the arc; and thus Gay-Lussac’s law be- comes an exceedingly near approximation for hydrogen gas, and a very near one for oxygen, nitrogen, and atmospheric air. To apply the equation of the hyperbola to the results for sul- phurous acid, in the figure let Cz, Cy be the axes of coordi- nates to the origin C as centre of the hyperbolic are P A P’; let CT, CT’ be the asymptotes; let O be any origin from which the temperatures are represented along the axis of 2, whilst the * Relation des Expériences, &c., vol. i. pp. 188, 189. 274 Prof. Potter on the Law of the Expansion volumes of the gas are represented by the ordinates, as PM=y when CM=x2. Let C A=a= semi-major axis of the hyperbola, C O=m, and O M=z’ the temperatures ¢ on the Centigrade scale, so that w=m-+w’; then, the equation of the hyperbola being b2 = zi (a? — a?) b2 a aC (m+2')?—a?), 2 we have to find from three conditions the values of - m, and a?. Now, taking the volume of the gas at the freezing-point of water, and (represented in the figure by »O =y,) as 100 measures, and OM=z" being the Centigrade degrees, we have, if PM=y/, 2 ye= Bln 2%), 2 i “7 ((m+2!)*—0?), and similarly 32 P= a((n+a!)?—<"), which by ars give (2 oe vie) _s ea? (y'®—y, a! = aa Can — — oF? gi! iors = Yo gic my *), ao Calculating the volumes y,, y., y¥3.+.Yg from ae Regnault’s values of « at the Centigrade temperatures 21) Uo ae ame have as follows: at = 98:12 C. then y,=y) x 1°375382, v= 10245 <) * yo=9, “arate. g5=185'42 ,, Yg= YX 1°70458, y= POTN i 5s ot Yat eee #29990) 5.) eos #.=31031 55 + Yg=9o 2717986, : b? Taking 2',%, #1 4;, Z's y5 to determine the constants 7 ts and a?, we find of the Gases by inerease of Temperature. 275 b2 b 7 ='18918, and - ='3730, a a m=277°464, a?=5111°2, and a=71°492. Applying these to find the remaining values of y by the equation of the hyperbola, we have Yo= 100 y, = 187°5338, Y= 139176, y3== 170°584, Y4= 197-628, Y= 213°700, Yg= 217618, and we see that the ordinates of the hyperbola furnish volumes as near to M. Regnault’s experimental results as can be expected. The value of : ='3730 is trig. tangent of the angle which the asymptote makes with the axis of x, and is the extreme value of a, which we see is not the same as for other gases, which M. Regnault expected* might be the case in the limit for very high temperatures, or in the state of extreme dilatation. By differentiating the equation of the hyperbola to the centre as origin, or y= a (z*—a*), we have iA BP LI, da bat a a? ‘ / bmige and when a= +a, then = = infinity ; and this must be at the point of liquefaction of the gas, which, when known under a given pressure, will give an important datum, and probably much more accurate than can be found from the discussion of experi- ments like the preceding. When z= infinity, we have = = g a which equals « in Gay-Lussac’s law. The law of Amontons being expressed in the form p=xp(1+ 7°), must be received as the true law within the limits of accuracy which can be attri- buted to the laws of Boyle and Gay-Lussac, of which it is com- pounded, but it is not an absolutely exact law for any gas. * Relation des Expériences, &c, vol. i. p. 120. [ 276 J XXXII. On Molecular Physics. By Prof. W. A. Norton. [Continued from p. 204.] Molecular Constitution and Mechanical Properties of Bodies. : als body of matter consists of separate particles, or mole- cules ina state of equilibrium under the action of the forces proper to the particles, or of these in connexion with extraneous forces taking effect upon the particles. The interstices between the molecules we conceive to be pervaded by both the electric and the universal ether, having probably different densities in different substances. The state of equilibrium in which each particle of the mass subsists, implies that the effective forces acting upon it, from opposite sides, are equal and directly op- posed, or else that the effective forces of each side are equal to zero. The. different mechanical properties of different sub- stances may be ascribed, primarily, to differences in the value of the ratio of the constants of electric attraction and repulsion Cs in Table I.}; and to a certain extent also to differences in the size of the molecular atmospheres, upon which the value of k in Table I. partly depends. In consequence of these sup- posed differences in the value of the ratio =, each substance should have its own special curve of molecular action. It is natural to suppose that the constant n of the force of attraction exerted by the atom upon its atmosphere would in general increase with the mass of the atom, and so that the force of cohesion would be greatest in those substances whose atomic weights are the greatest. But as we cannot affirm that the weight of an atom must necessarily be proportional to the force of attraction ex- erted by it upon its electric atmosphere, and as the constant m may also be subject to variations, substances of nearly equal atomic weights (e. g., gold, platinum, bismuth, and lead) may have different properties. The molecules of a substance in the solid state may be aggre- gated together as a homogeneous mass, or in groups more or less complex. The mechanical properties of the mass vary with the mode of aggregation. The form of aggregation assumed, in the process of solidification, depends upon the circumstances, with respect to cooling, pressure, &c., under which the solidification occurs. The effect of the same circumstances should vary with different substances, with their properties in relation to heat ; but these properties are primarily dependent upon the general fea- tures in the constitution and condition of the molecules, upon Prof. Norton on Molecular Physics. 277 which the laws of effective molecular action, as shown by the proper curve, depend. Contemplating from our present poimt of view the varying mechanical states and conditions which the same substance may assume under different circumstances, we are led to recognize, as» an essential physical feature, upon which such changes either wholly or partially depend, the fact that the mechanical condi- tion of the individual molecules is not fixed and unchangeable, but liable to material variations. We perceive their atmo- spheres expanding under the influence of heat, and contracting from the effect of external pressure, and that certam phenomena and permanent changes of property result from these atmospheric changes (e.g. changes of property in passing from the solid to the liquid form, or vice versé; permanent displacement of particles produced by the temporary action of forces of a cer- tain intensity upon bodies). States of Aggregation of Matter.—These are three essentially different states of equilibrium. In the sold form, the particles immediately contiguous to each other are in a condition of equi- librium under the action of their own molecular forces; if more distant particles exercise any effective action, it is attractive, and neutralized by a similar action on the other side of the particle. To be more definite, each molecule of the mass is surrounded by others at various orders of distance from it; and each pair of molecules at the first order of distance from each other are in a condition of equilibrium by themselves, which is equivalent to saying that their electric atmospheres are separated by the distance Oa, fig. 1 (p. 203). For the second order of distance the action should then be attractive; but it may very well be that when a permanent equilibrium of the mass has been reached, the atmo- spheres of two particles at this order of distance will be so ex- panded by their attractive action, on the line of their centres, that, for the diminished value of < thus resulting, the distance between the atmospheres on this line will be the increased dis- tance Oa for the curve corresponding to this diminished value of =. Upon this supposition, each particle would be separately in equilibrium with every particle contiguous to it, both at the first and second order of distance. We shall have occasion to note hereafter that this state of things is probably more or less perfectly realized under different circumstances of solidification. As to the action of more distant molecules, it is first to be observed that, if two molecules are in equilibrium under their mutual actions, the attractive and repulsive impulses exerted by each upon the central atom of the other must be equal, and therefore 278 Prof. Norton on Molecular Physics. that no effective action, either attractive or repulsive, can be transmitted to other more distant particles on the same line. Under these circumstances, one molecule, in receiving the action of another, intercepts the action that would otherwise take effect upon other more distant molecules. This being admitted, it may be perceived, on examining Table I., that the attractive actions of particles which lie beyond the second order of distance from a given particle, will be in a great measure intercepted by intervening particles. In what has now been stated with respect to the solid condition, we have had in mind a homogeneous mass of molecules only. We cannot here enter upon the considera- tion of the case in which the molecules are aggregated into groups. In the liquid state, the contiguous particles repel each other; and particles more distant exert no sensible action, or a feeble attractive one. Here, as in the case of a solid, the sensible action is confined chiefly to particles that he at the first and second orders of distance. These remarks apply to the general mass of the liquid. The molecular atmospheres are in an ex- panded condition from the effect of the heat of fluidity; and it is from this fact that the peculiar properties of the liquid state result. As we draw near the surface of the liquid, the atmo- spheres are in a condition of greater and greater expansion as the necessary result of the process of liquefaction, and therefore their proper attractive actions are less and less. From this cause it happens that each particle near the surface is more — effectively attracted by those below it, beyond the first order of distance, than by those above it, and thus each layer of parti- cles is compressed upon that immediately below it; also to a certain depth more particles will exert their attraction from below than from above. As a consequence, the density must increase from the surface toa certain small depth below it, and a force of compression be exerted throughout the whole liquid mass. This force determines, and is in equilibrium with, a mutual repulsion between the particles of the liquid. From the essential nature of a liquid, as we shall soon see, this increasing molecular repul- sion, from the surface downward, operates in all directions from each molecule, and so tends to neutralize the attractive actions between molecules separated by the second order of distance ; as the final result, therefore, at the depth at which the density ceases to increase, and all greater depths, the action between two such moleules should be either feebly attractive, or altogether evanescent *, * The theory of the existence of a contractile force at the surface of a liquid, as the result of molecular action, was advocated by Young and Poisson, and employed by them in explanation of the phenomena of capil- larity. It has also been ably sustained and illustrated by Professor Henry by many ingenious experiments. Prof. Norton on Molecular Physics. 279 The views which have now been presented enable us to form a definite conception of the probable arrangement of the mole- cules of a liquid. If the state of equilibrium be such as we have represented, we must conclude that a perfectly symmetrical ar- rangement of particles, similar to that which subsists in crystals, prevails throughout the whole mass. We conceive the fundamental distinction between a solid and a liquid, from the mechanical point of view, to be that the exter- nal impulses which fall upon the molecule of a solid, are propa- gated, either wholly or chiefly, in their original line of direction ; while those which fall upon the molecule of a liquid are radiated in every direction from it. The physical cause of this differ- ence in the mode of propagation of a force appears to be the simple fact that in the process of liquefaction the molecular atmospheres are forced by the heat of fluidity to a decidedly greater distance from the atoms which they surround; thus leaving below them a much larger volume of universal ether, to receive the impulses propagated down toit. If this difference between the mode of propagation of impulses by the molecules of a solid and liquid be admitted, it is not difficult to see that we have a sufficient cause for the different mechanical properties attendant upon these two states of aggregation, without having recourse to the prevalent idea of a permanent polarity of simple atoms. So far as any polarization of molecules comes into ope- ration, we shall have occasion to remark, in discussing briefly the topic of crystallization, that it is simply an induced, and for the most part a temporary condition of the molecular atmo- spheres, developed in the act of solidification. In the aériform state the particles are so widely separated that each is repelled by all those which surround it, within the limit of effective action, and the equilibrium is determined by external pressure. The properties of gases and vapours, and the laws of their expansion and contraction, are deducible from equation (3), p. 200, The value of z that obtains when a vapour formed at any temperature has its maximum tension, is the distance Od, fig. 1, answering to the maximum molecular repulsion dn; and this varies for different temperatures, because the ratio = m decreases as the temperature rises. (See different values of maximum repulsion answering to different values of the ratio - given in Table I., p. 200.) The process of transition from the solid to the liquid state occurs at the surface of the mass. As the heat is absorbed, the molecules near the surface recede from each other; and when this expansion has reached a certain point, the attractive forces 280 Prof. Norton on Molecular Physics. of the particles at the different orders of distance come succes- sively into action, being less intercepted by intervening particles. At the same time, the individual molecular atmospheres expand, or recede from their central atoms, under the action of the heat- pulses that penetrate to these atoms; and so the energy of the attractive force of each of these molecules declines. The sur- face particles will thus continue to recede at the same time that they are restrained by the attractions of those below them. This effect will extend from the surface downward; and as a final result, a certain number of layers are brought into the liquid condition, in which, as we have seen (p. 278), the particles mutually repel each other, in consequence of the exertion of a compressing force at the surface. In the case of a liquid that emits vapour at the temperature of liquefaction, we must con- clude that the particles at the very surface become ultimately subject to an effective repulsion from the united action of those below it, which is in equilibrium with the tension of the vapour resting on the surface; and that this effective repulsion extends to all points above the surface. The heat of fluidity is consumed in forcing up the molecular atmospheres. As a final result of the liquefaction, these atmo- spheres remain in an expanded condition. The effect of this expansion is to diminish the values of » given by equation (1) (see p. 200), and increase the distance Oa, fig. 1. The actual distance between two contiguous atmospheres is less than the increased distance Oa, by reason of the compressing force that takes effect throughout the liquid mass. But the ultimate com- pression imparted to the individual atmospheres will depend in a great degree upon the final value of the attractive action v between the molecules, and may therefore still be less than that which obtained in the solid state. In this diminished value of v we have, at the same time, the explanation of the dimi- nished force of cohesion attendant upon the liquid state. The comparative densities of the liquid and solid also depend upon v. For we have just seen that the distance between the con- tiguous atmospheres of two particles of the liquid is less than the increased value of Oa, but this distance may, according to the intensity of the attractive force v, be either greater or less than the original value of Oa, which was the distance between the atmospheres of the same particles in the solid condition. Accordingly the liquid may be either more or less dense than the solid from which it is derived. The passage from the liquid to the solid state is essentially - the inverse of that which has just been under consideration, and in the general survey we are now taking need not be considered in detail. The mass of molecules and their individual atmo- Prof. Norton on Molecular Physics. 281 spheres now contract instead of expanding; and in the final act of solidification the contiguous molecules assume the positions due to their own special forces. While all this is being accom- plished, the molecular atmospheres contract, and heat is given out. The explanation of the process of evaporation will be readily inferred from what has already been stated with regard to the condition of the surface of a liquid (p. 280). The nice equipoise of the surface particles may be disturbed either by a slight ele- vation of temperature, or a diminution of the tension of the vapour resting upon them. ‘The cooling effect of the evaporation is to be attributed to the expansion which the electric atmo- spheres experience on being freed from the compressing forces previously existing*. In the process of ebullition, the expansive action of the heat absorbed by the lower layers of the liquid increases until the superincumbent pressure, the cohesive attraction of the vessel for the liquid, and the effective attractions subsisting between the molecules of the liquid (represented by the ordinates be- tween a and 8, fig. 1), are overcome. When this point is reached at any part of the liquid stratum, the separated particles will expand rapidly into bubbles of vapour, in opposition to the pressure of the atmosphere, and the attractions denoted by the decreasing ordinates between 0 and e, fig. 1. The expansion should continue until the distance between the atmospheres of two particles increases to the limit Od, at which the repulsion attains to its maximum value; or rather to a limiting distance somewhat greater than Od, at which the repulsion due to the heat-pulses present in the molecules, plus the molecular repul- sion at that distance, is equal to the external pressure. It cannot proceed further than this without a direct expendi- ture of heat-force, which will raise the temperature of the vapour. The heat which becomes latent, as the phrase is, is expended in the act of expansion, and in forcing up the molecular atmo- spheres in opposition to the attractive action of the atoms and all compressing forces. The amount of work thus taken up by the atmospheres manifests itself also as work of expansion, since it is so much work of the atomic attraction and of the compressing forces neutralized. When the heat-pulses are not wholly ex- * It is apparently not necessary to suppose, as has been done on p. 280, that the tension of the vapour resting on the surface of a liquid, when at its maximum, is in equilibrium with the outward repulsion experienced by the outer layer of liquid particles. The equilibrium may be a dynamical one, the vapour may be continually rising at certain points of the surface and continually passing back into the liquid condition at other points, the condensation compensating exactly for the evaporation. Phil. Mag. 8. 4. Vol. 28. No. 189. Oct. 1864. U 282 Dr. Rankine on the Properties pended in this manner, a portion of them pass into the mole- cular atmospheres and elevate the temperature of the liquid. If the pressure upon the free surface of the liquid exceeds the pressure of the atmosphere, the molecular atmospheres are more oa compressed, the value of m becomes greater, and the ratio 7 diminishes in consequence ; from this cause the limit of the re- cess of the particles (Od, fig. 1) diminishes, and the maximum repulsion dn increases (see Table I.). The resulting vapour has, therefore, at the same time a higher tension and a greater density. According to the theoretical views now advanced, the “ inte- rior work” which Tyndall maintains is expended in the act of liquefaction, and also in that of vaporization, in “moving the atoms into new positions,” or in conferring “ potential energy ”’ upon them, is consumed in each instance in pressing up the electric atmospheres that surround the atoms of the substance ; and heat disappears in the process in proportion to the effect thus produced. [To be continued. | XXXIII. Summary of the Properties of certain Stream-Lines. By W. J. Macavorn Rankine, C.H., LL.D., F.R.SS.L.& £.* i HE investigation, of which the present paper is a sum- mary, consists of three parts. It is a sequel to one of which an abstract was read at the Meeting of the British Asso- ciation in 1863, and which has since been printed in full in the Philosophical Transactions}. It relates to the paths in which the particles of a liquid move pasta solid body. In the previous paper (which was confined to motion in two dimensions) those paths were called “ Water-Lines,” and were treated of with a view mainly to their use as figures for the horizontal or nearly hori- zontal water-lines of ships. In the present paper they are called “ Stream-Lines,” as being a more general term, and one less liable to be misunderstood when motion in three dimensions 1s con- sidered. The term “ Neoid ” (vjoevdys, ship-like) proposed in the pre- vious paper as a general name for water-line curves in two di- mensions, may be extended to all the stream-lmes discussed in . the present paper; for they are all applicable to certain lines on the surface of a ship. * Communicated by the Author, having been read at the British Asso- ciation Meeting, Bath, September 19, 1864. + An abstract of that previous investigation appeared in the Philoso- ~ phical Magazine for October 1863. of certain Stream-Lines. 283 Part 1.—On some Exponential Stream-Lines in two Dimensions. 2. It is well known that amongst the functions which satisfy the conditions of liquid motion in two dimensions, are Ue ~ hended all those of the form y +> .e% cos ax. Such functions as the above obviously represent curves consist- ing of an endless series of repetitions of the same figure; and many of those curves resemble the profiles of waves. 3. The first part of the investigation consists of a discussion of the properties of the curves represented by the simplest of those exponential stream-line functions, viz. Bae COS Peg eles coe ae alia) By giving to 0 a set of values in arithmetical progression, this function is made to represent a set of stream-lines, dividing an indefinitely extended plane layer of liquid into a series of curved streams of equal flow. Hach of those stream-lines consists of an endless series of repetitions of the same figure, the length parallel to z of each repetition being 27; and each repetition consists of a pair of symmetrical halves. 4. The graphic construction of those stream-lines is very easy, by the aid of a general method of constructing curves first used by Professor Clerk Maxwell, and applied by the present author to stream-lines in the previous investigation already referred to. Draw a series of straight lines parallel to z, and having for their equation Yeu —the values of m being in arithmetical progression, positive and negative, with a fraction for their common difference, which should be the smaller the more accurate the drawing is to be. Then draw a series of curves of hyperbolic-logarithmic cosines, having for their equation e 4 cosz=m, —the values of m!, positive and negative, forming an arithmetical progression, and having the same common difference with those of m. a curves with positive values of m! lie between »=0 and »= ~ oe those with negative values between x= 5 7 andz=7; : and the straight line parallel to y, at —, is an asymptote to them 9? all. One and the same toahe serves to trace all those curves ; for they differ only in the maximum value of y, which is U2 284 Dr. Rankine on the Properties +-hyp. log m’. Then trace a series of curves diagonally through the intersections of the network already drawn, in such a man- ner as to make m—m'=6 for each curve; these will be the required stream-lines. 5. The ordinates for which x is an odd multiple of + 5 are asymptotes to all the stream-lines at the negative side of the axis of #2, and are also intersected by each stream-line at the poimt where y=). | 6. Maximum values of y for all the stream-lines occur on the ordinates where & has the value 0, or any even multiple of +7. 7. Minimum values of +y and —y occur on each ordinate where # is an odd multiple of +7, but for those stream-lines only for which 6>1. The stream-lines for which 0<1 do not intersect those ordinates. 8. The stream-line for which °}=I1 consists of an endless series of equal and similar curves, each adjacent pair of which cut each other at right angles and the axis of # at angles of 45°, in the points where # is an odd multiple of +7. 9. Each stream-line for which 6<1 consists of an endless series of equal and similar detached curves, having maximum and minimum values of z given by the equation cosa=—e7'*’, 10. Hach stream-line for which 6>1 is made up as follows :— at the positive side of the axis of 2, a continuous curve, present- ing an endless series of equal and similar waves; at the negative side, an endless series of equal and similar detached curves. 11. The wave-line curves thus formed, as they become more remote from the axis of x (that is, as b increases), approximate more and more nearly to the trochoidal form, which is known to be that of free waves in deep water ; and so rapid is that approxi- mation, that though for b=1 the difference between the two kinds of wave-line is very great, it becomes almost undistin-- guishable for b=11. | 12. Quantities proportional to the component velocities of a particle and to the square of its resultant velocity, are derived from the stream-line function as follows: u= ab =l+e%cost=1+y—8, dy <1, ae u? +-0?=1 4 2e-4 cos a + e~¥ (II1.) =1+42(y—b) +e-™. \ - of certain Stream-Lines. 285 Ai the point where the curves 5=1 cross the axis of a, both the component velocities are null. The unit of velocity in each of those expressions is the velocity of a particle at an infinite - distance in the positive direction from the axis of x, for which particle we have u=1, v=0. 13. Suppose the plane of z and y to be vertical, and y to be positive downwards; let the absolute value of the unit of mea- sure (that is, the radius of the circle whose circumference is a wave-length) be denoted by R; and let the heaviness (or weight of a unit of volume) of the liquid be W. Then the stream- lines for which 0 is not less than 1 may represent the profiles of a series of forced waves, capable of travelling with the absolute velocity BAT IPs can giore oastsiehald le eens es mate being the same with that of free waves of the same length; and the absolute values of the velocities of any particle relatively to still water will be horizontal component, c(u—1)=ce-4 cos z; vertical component, cv= —ce-Y sin a; | be) resultant velocity, eV {(u—1)?-+07 =ce7Y, 14. Those forced waves differ from free waves in the following respects. First, in free or trochoidal waves, each wave-surface is a surface of constant pressure, so that the upper surface of the liquid needs no pressure to be applied to it to compel the waves to travel; whereas in the waves now in question the pressure at cach wave-surface is not constant, being expressed by the fol- lowing formula, WRe-* 2 of which the last term is variable ; and the upper surface requires a pressure varying according to this law to be applied to it, in order to compel the waves to travel. Secondly, free or trochoidal waves begin to break as they reach the cycloidal form, in which the surface near the crest is vertical, and the crest forms a cusp; whereas in the waves now in question the steepest possible form, which cannot be passed without breaking, is that of the stream-line 5B=1, whose crest is formed by two surfaces meeting each other at right angles, and sloping in opposite directions at 45°. Thirdly, the particles of water in free waves revolve in circles, and do not permanently advance ; whereas the orbit of each particle in the waves now in question is an endless coiled or looped curve, in which each revo- lution is accompanied by an advance. The figure of that orbit p=constant + Wb— 5 PAT MRT RE) 286 Dr, Rankine on the Properties is determined by the ratio which its radius of curvature bears to the unit of measure R, viz. a Seals Yess) a fl Se ee EL) The waves whose motion is investigated by Professor Stokes in the Cambridge Transactions are of a character intermediate between trochoidal waves and those here considered. 15. As waves are frequently observed whose figures present a general likeness to that now described, it is probable that a pres- sure approximating to the law expressed by eufeos (VI.) may be exerted upon them by the wind. 16. It is evident that a pressure varying according to that law, or nearly so, will be exerted by the bottom of a ship upon the water, when the figures of the buttock-lines, or vertical longitu- dinal sections of her after-body, are exponential stream-lmes, or trochoidal waves approximating to them, as in Mr. Scott Russell’s system of shipbuilding. Part II.—On Lissoneotds in three Dimensions. 17. The second part of the investigation relates to the mathe- matical properties of stream-lines of smoothest gliding in three dimensions. The properties of such lines in two dimensions were investigated, and the name “ Lissoneoids” proposed for them, in the previous paper already referredto. Their essential mechanical properties are, to have fewer and less abrupt maxima and minima of the speed of gliding of the particles on them than on other stream-lines belonging to the same mathematical class, and to be the fullest lines of their class consistently with not raising more waves than are unavoidable, when they are employed as the lines of a ship. 18. The mathematical condition which such a stream-line ful- fils is, that at the midship-section or broadest part of the solid to which the line belongs, two points of maximum and one of minimum speed of gliding coalesce into one point. 19. The investigation shows that the before-mentioned con- dition 1s expressed mathematically as follows, for any stream-line which at its greatest breadth is parallel to the axis of # Let u be the longitudinal component, and v and w the transverse com- ponents of the speed of gliding of a particle along the stream- line; then at the point where that line crosses the midship sec- tion, supposing that we have v=0, w=0, the following equation must be fulfilled: du dy? +25 = ie dz of certain Stream-Laines. 287 The corresponding equation in two dimensions is formed by omitting the term in ae dz Part III.—On some Stream-Lines of Revolution. 20. The third part of the investigation relates to the stream- limes in which particles flow past certain totally immersed oval solids of revolution, bearing the same relation to a sphere that the oval neoids described in the previous paper bear to a circle. These lie upon a series of surfaces of revolution, and are the sections of those surfaces by planes passing through the axis. 21. Let the axis of figure be that of wv, and let there be two points in it, called foci, situated at the distances +a and —a from the origin. The distance a may be called the excentricity. Let the perpendicular distance of any particle from the axis be denoted by y; let f be a constant length, called the parameter ; and let b be the radius of a cylinder which is an asymptote to a ~ given stream-line surface. Then the equation of that surface is as follows: Peete ee Deira eas: Or, in another form, let 6 and 6’ be the angles which two lines drawn from the given particle to the foci (+a) and (—a) respect- ively make with the axis of +; then py —F * (cos G'—cOs O) pis» yer sian Ne) 22. For the primitive oval solid, 5=0; and by giving 0? a series of values increasing in arithmetical progression, a series of stream-lie surfaces are formed, of gradually increasing width, which divide the liquid mass into a series of concentric tubular streams of equal discharge. 23. The graphic construction of the stream-lines is as follows. From each of the foci draw a set of diverging straight lines, making angles with the axis whose cosines are in arithmetical progression, the common difference bemg a sufficiently small fraction. Through the network formed by these lines trace dia- gonally a series of curves traversing the two foci. (The equa- tion of each of those curves is cos 6/—cos#=m, and they are identical with the lines of force of a magnet having its poles at the foci.) Multiply the parameter (f/f) by the square roots of the terms of the arithmetical progression, and draw a series of straight lines parallel to the axis and at the distances from it so found ; these will be the asymptotes expressed by the equation b=fVm. Then through the network formed by those parallel straight lines and the before-mentioned series of curves trace 288 Mr. P. G. Tait on the History of Thermo-dynamics. diagonally a new series of curves, which will be the stream-lines required. ‘ 24. The stream-lines thus drawn closely resemble those in two dimensions, but are somewhat fuller. For those at a distance from the axis, the difference of form is scarcely perceptible ; for those near the axis, and especially for the primitive oval, the greater fulness of form is conspicuous. 25. The ratios of the component velocities of a particle on a stream-line surface of revolution to the velocity of a particle at an infinite distance from the disturbing solid are given by the expressions 2 bdb © bdb em wage = willl 26. By applying to those stream-lines of revolution the prin- ciples of the second part of the investigation, it is found that the radius (0) of the asymptotic cylinder of a lissoneoid surface cf revolution bears the following relation to the greatest radius (7) of the surface itself, and to the excentricity (a) of the set of sur- faces to which it belongs: Dayo —2(a? +y9') « (XI) ° . > se In order that this equation may bé reai, ~ must not be less 9 4\G : than ry = nor greater than ee The corresponding para- meter is found by the general formula pe Wo) Vato ee 2a 2 In the oval lissoneoid of revolution, 6?=0, = = Lae 1:1547; 5 psibutivrit as and = = VV8+2 = 0°644. 2 vo September 1864. XXXIV. On the History of Thermo-dynamices. By PaG. Varn VAS sc. To the Editors of the Philosophical Magazine and Journal. GENTLEMEN, WISH to make a few additional remarks on this subject: especially as it appears to me, after a careful perusal of all that Dr. Tyndall has written upon it, that he does not yet quite understand the points which Prof. Thomson and I wished to esta- Mr. P.G. Tait on the History of Thermo-dynamics. 289 blish when, in consequence of his lecture on “ Force,” we wrote our article in ‘ Good Words’ nearly two years ago. We have all along held that the questions as to the nature of heat, and its equivalence to mechanical energy, were settled by Davy; and that Rumford experimentally obtained a very fair approximation to the equivalent. Also that, as Newton had completely enunciated the Conservation of Energy in ordinary mechanics, Davy’s experiments brought heat under the same law, and that, therefore, in the beginning of the present century the Dynamical Theory of Heat was compietely established, although not developed. The development has been since furnished by the experiments and reasonings of Joule on Electric Thermo-dyna- mics*, his experimental determinations of the mechanical equi- valent, his experiments and reasoning on the thermal effects of the condensation and rarefaction of art; and by the theoretical writings of Helmholtz, Clausius, Rankine, and Thomson. Hence, so far as regards the question of heat alone, Mayer has no title to the position Dr. Tyndall claims for him. He did no more than repeat what Davy and Rumford had done better ; and he has never, so far as even Dr. Tyndall’s partisan- ship can show, attempted anything of the nature of either the theoretical cr experimental developments which have advanced thermo-dynamic scienee during the present century. What, in point of fact, did Mayer do in thermo-dynamics? In 1842 he published a paper, of which Prof. Thomson and I remarked as follows. ‘In this paper the results obtained by preceding naturalists are stated with precision—among them the funda- mental one of Davy—new experiments are suggested, and a method for finding the dynamical equivalent of heat is pro- * Of these the followimg are perhaps the most important :— “On the Production of Heat by Voltaic Electricity ” (Prec. Roy. Soe. Dec. 17, 1840). Printed in Phil. Mag. 1841, with the title “On the Heat evolved by Metailic Conductors of Electricity, and in the Cells of a Bat- tery during Electrolysis.” * On the Electric Origin of the Heat of Combustion” (Phil. Mag. 1841). Extension of the same (Report of British Association, 1842). On the Heat evolved during the Electrolysis of Water” (Lit. and Plnl. Soe. of Manchester, Jan. 1843). * On the Calorifie Effects of Magneto-Electricity, and the Mechanical Value of Heat” (Phil. Mag. 1843). “On the Heat disengaged in Chemical Combinations,” sent to the French Academy in 1846 (Phil. Mag. 1852). “© On the Mechanical powers of Electro-magnetism, Steam, and Horses,” by Scoresby and Joule (Phil. Mag. 1846). “On the Economical Production of Mechanical Effect from Chemical Forces ” (Manchester Memoirs, 1852, and Phil. Mag. 1853). T “On the Changes of Temperature produced by Rarefaction and Con- densation of Air,” sent to the Royal Society, June 1844 (printed in Phil. Mag. 1845). 290 Mr. P. G. Tait on the History of Thermo-dynamies. pounded.” To this we added, in a note, as follows. ‘ Mayer’s method is founded on the supposition that diminution of the volume of a body implies an evolution or generation of heat ; and it involves essentially a false analogy between the natural fall of a body to the earth, and the condensation produced in an elastic fluid by the application of external force. The hypothesis on which he thus grounds a definite numerical estimate of the relation between the agencies here involved, is that the heat evolved when an elastic fluid 1s compressed and kept cool, is simply the dynamical equivalent of the work employed in com- pressing it. The experimental investigations of subsequent naturalists have shown that this hypothesis is altogether false, for the generality of fluids, especially liquids, and is at best only approximately true for air; whereas Mayer’s statements imply its indiscriminate application to all bodies in nature, whether gaseous, liquid, or solid, and show no reason for choosing air for the application of the supposed principle to calculation, but that at the time he wrote air was the only body for which the requi- site numerical data were known with any approximation to accu- racy.” ‘To every word of this, with the exception of the word “imply,” which is not strong enough, I still adhere. Dr. Tyn- dall’s mode of dealing with it is characteristic. He says— “not what Mayer’s words ‘imply,’ but what they are”—and then quotes, not from the paper of 1842, to which alone we _ referred (as the only one which could have a chance of priority over either Joule or Colding), but from a pamphlet published in 1845. As to the question which might have arisen between Séguin and Mayer, supposing nothing to have been done in the matter by Davy and Rumford; everything that was done by Mayer in 1842 (I still confine myself to the question of Heat alone) was done by Séguin in 1839. Dr. Tyndall is correct in his remark that Séguin did not, as was originally supposed by Joule, give 363 edearammne ines as the dynamical equivalent. But to say, as Dr. Tyndall does, that ‘‘ there is no determination whatever of the mechanical equivalent of heat in the above [1.e.Séguin’s] Table,” is simply an error, for Séguin gives all the requisite data, though | the thermal unit he employs is by no means convenient. Nothing can indeed be more distinct than his evaluation. An hypothesis explicitly stated by him as to the heat of condensation of vapour, now known to be wrong and to give much less than the true ther- mal effect, rendered the numbers in his Table largely in error. In Séguin’s work we find the following passages :-— “ Ceci reviendrait 4 dire que la vapeur n’est que l’intermédiaire du calorique pour produire la force, et qu'il doit exister entre le mouvement et le calorique un rapport direct, indépendant de Mr. P. G. Tait on the History of Thermo-dynamics. 291 Pintermédiaire de la vapeur ou de tout autre agent que l’on pour- rait y substituer.” Compare this with Dr. Tyndall’s quotation (Phil. Mag. Sept. 1862). “The law,” says Mayer, “ ‘Heat = Mechanical Effect’ is independent of the nature of an elastic fluid, which only serves as the apparatus, by means of which the one force is converted into the other.” Again, Séguin says, “ La force mécanique qui apparait pendant Vabaissement de température d’un gaz comme de tout autre corps qui se dilate, est la mesure et la représentation de cette diminu- - tion de chaleur ;” and further, in speaking of steam escaping into the air, “ L’effort qu’elle exerce en recul contre les appareils qui la laissent échapper, ou la vitesse qu’elle communique a l’air ambiant, forme un équivalent de la perte de chaleur qu'elle éprouve.” Yet, according to Dr. Tyndall, it was Mayer “who first used the term ‘equivalent’ in the precise sense in which you”? (Joule, to whom the letter is addressed) “have ap- plied it.” But there is more than this in Séguin’s very able work. He points out distinctly that steam which has done work in an engine ought not to heat the water in the condenser so much as if it had been led directly into it. He had made, he says, nu- merous experiments to test this, without however obtaining sufficiently decisive results. Again, he points out how very small a proportion of the heat of the steam is really employed im doing work. He says that the work obtained from a steam- engine, as ordinarily used, is represented by “un abaissement de température d’environ 20°, qui équivaut au trentiéme environ du calorique employé pour réduire en vapeur Veau nécessaire a sa formation.’ That is, only jth of the heat used, disappears as heat, and is given out as work. Thus we see that his 20° repre- sent =,th of the latent heat of steam, at 100° C. and at the atmospheric pressure: and his Table gives for the corresponding work done by a cubic metre of steam (in round numbers) about 7000 kilogrammetres. ‘aking 540 as the latent heat, and 0°6 kilogramme as the weight of a cubic metre, of steam, we have 30 x 7000 for the mechanical equivalent 0°6 x 540 =650, about 50 per cent. too great. As to the Conservation of Energy. Dr. Tyndall, in a note to his last paper, ascribes the term, or terms, to Rankine. I cannot ascertain precisely when the term “Conservation” was intro- duced, but it must have been suggested at once to an English writer by the old term “ Conservation of Vis Viva,” of which the Conservation of Energy is only an extension. At all events Helm- 292 Mr. P. G. Tait on the History of Thermo-dynamics. holtz’s “ Erhaltung” is an identical word, and was employed before Rankine wrote on the subject. But ‘the term Energy (as Dr. Tyndall surely is aware) is due to Young, who introduced it as a convenient English term synonymouswith vis viva. Its exten- sion to the two forms “static” and “dynamic” was made by Thomson. Rankine improved these to “potential” and “actual; and in ‘Good Words’ Thomson and I have employed “ kinetic ” as less ambiguous and more suggestive than ‘ actual.” As to the discovery of the Conservation of Energy, I hold that to lay down, without experimental bases, such a maxim as “ causa equat effectum”’ is entirely subversive of common sense and logic im an experimental science such as natural philosophy. The esta- blishment of the Conservation of Energy was utterly out of the sphere of the “ Thinker ;” and it would be absurd to give him more credit than is due to the promulgator of a clever specula- tion. Thousands of equally clever, but less lucky, though not more baseless, speculations are evely day mercilessly extermi- nated by experiment. Celestial Dearie forms no part of the ‘Thermo-dynamic theory, though it affords exceedingly beautiful applications of it. The same must be said of Animal and Vegetable Physiology. Such applications, as is well illustrated by the famous little sen- tence of Joule’s postscript of 1848, always attend careful work at a theory; they are not discoveries, but inevitable consequences, to the experimental or mathematical mvestigator. The word or two, required to complete the suggestions of Stephenson and Herschell, occurred to many minds, merely to be recorded in passing—as by Helmholtz in a popular lecture, and by Thomson in the proceedings of a socicty. I have written again to the Philosophical Magazine because I imagine that Dr. Tyndall still misunderstands the views which Prof. Thomson and I maintain on the history of the subject ; and that it is this which has led him to charge us with misrepre- sentations. His special charges against Prof. Thomson, which receive fresh development in every successive article, arc so ob- viously unfounded that he can hardly be surprised that Prof, Thomson has not judged it necessary even to notice them. I am, Gentlemen, &e. - &c., P. Gururiz Tarr. 6 Greenhill Gardens, Edinburgh, September 12, 1864. [ 293 J XXXV. On the Erosion of Valleys and Lakes; a Reply ta Sir Roprrick Murcuison’s Anniversary Address to the Geogra- phical Society. By A. C. Ramsay, F.R.S.* yA SE TER the publication of my memoir “On the Glacial Origin of certain Lakes in the Ice-worn regions of Europe and North America,” several eminent British and Continental geologists, and some other persons who have only a general literary acquaintance with physical geology, did me the honour, in special memoirs, or in letters in newspapers, to express opi- nions that my views were deserving of the strongest opposition. To none of these opponents have I heretofore made any, reply, and seme of them, I found, were dealt with by men who met their arguments more ably perhaps than I could have done myself. Besides, I considered that if my theory, as I believe, be true, it would be sure in the long run to make its way just in the slow and steady manner it seems to me to be now doing. We all profess to appeal to nature, and “in nature there is no opinion ; there is truth in everything that is in nature; and in man alone is error.” To those who are not geologists in any practical sense it would never occur to me to reply. Physical geology, in the true meaning of the term, does not exist without a thorough practical acquaintance with, and experience of, rocks of all kinds on a large scale. The man who merely wanders about a country and looks curiously at rocks, without a long course of severe training, has no more scientific right to form a definite opinion as to the causes that brought about the external configuration of the land than the father of a family would have to decide questions in comparative anatomy, because for half his life he had daily carved beef, mutton, pork, fowls, and fish. Of late, however, an exceedingly authoritative protest against my theory has been entered by Sir Roderick Murchison, in his Anniversary Address to the Geographical Society,—an address issued indeed to the geologists of Hurope; for the portion that bears upon icy phenomena has been printed separately for special distribution. It would almost be uncourteous on my part silently to pass over the remarks of one who in his own person has attained the highest honours in the Geological and the Geogra- phical Societies, and who is besides my oldest living geological friend. “ As a geologist, with wide experience, the President of the geographers clearly states his conviction” + that my theory of the origin of certain lakes and other theories of denudation connected therewith, are so opposed to obvious facts, that, if his conviction be well founded, the wonder scems to me that * Communicated by the Author. Tt Geological Magazine, No. 3, p. 127. 294: Prof. A. C. Ramsay on the Erosion any man of weight and knowledge could be found to follow me at all. I may therefore be pardoned if in this mstance I depart from the course of leaving the value of my theory to be worked out solely by time. I have said that Sir Roderick has entered an authoritative protest, because, as several persons have remarked to me, so much stress has been laid on the argumentum ad hominem, liberally as regards Continental geologists, and more sparingly with Ame- rican and English names. Indeed, in reading the Address, I was more than once reminded of the observation of one of my opponents, who in the ‘ Reader’ observed to this effect, “ that Professor Desor entirely disagrees with Professor Ramsay—how can he do otherwise? for Desor has lived among glaciers all his life.’ In like manner Studer and Escher von der Linth, “by numerous appeals to nature,” Gastaldi, De Mortillet, and many more are all arrayed in opposition to the theory, the presumption being that the chances are therefore infinitely against it, and I must needs be wrong because they are so eminent, and some of them: have lived so long among the Alps. For, differmg from them, how is it likely that a man can be right who has only ex- ' plored the Alps five or six times with a special object, even though he may have spent five-and-twenty years on subjects allied to or identical with it? Such is the general impression produced, not on myself alone, by many of Sir Roderick’s remarks. I have no objection to this kind of argument; it is so old in the history of science that its value is understood. To compare great things with our small matter, Copernicus and Galileo experienced it, Hutton and Playfair knew it well; the most eminent geologists were for long deaf to the voice of William Smith, let him charm ever so wisely; and Agassiz himself, in glacial geology, had among his chief opponents distinguished seniors, some of whom even now only hesitatingly follow him. It is easy to “ appeal to nature,” but the language of her reply is not always to be understood merely by long poring on her face; and it generally happens that many an abortive effort is made before some happy accident reveals the key. In my original memoir, when discussing the origin of the lake- basins, [ found it necessary in some degree to treat of disturb- ances of rocks in general. Accordingly, Sir Roderick very pro- perly regards the question as one not merely of lakes, but as involving his belief “with the vast majority of practical geologists, that the irregularities of the surface of the Alps have been primarily caused by dislocations and denudations ;” and again, that “ until lately geologists seemed so be generally agreed that most of the numerous deep openings and depressions which exist in all lofty mountains were primarily due to cracks which took place during of Valleys and Lakes. 295 the various movements which each chain has undergone at various periods,” &c. The meaning of this, I conceive to be, that moun- tain valleys lie in lines of curvature, dislocation, and fracture, and that the mountains on each side of them are mountains, far less because of denudation than by reason of operations of frac- ture and dislocation. Therefore important lakes that fill true rock-basins lie only in lines of fracture, or else, as in the myriad lakes of North America, in hollows of wider dislocation somewhat aided by subsequent denudations. Every reasoning mind respects authority when it bears on questions that have been reduced to demonstration; but this is precisely what has not been done with respect to the origin of special Alpine lakes and valleys by those whose main argument is disturbance of strata. Assertions and crude ideas in all kinds of books and papers are ‘as plenty as blackberries; ” but for clear demonstrations—none are given. Nor does Sir Roderick either attempt or point to any when he says that in the Alps he “long ago came to the conclusion that the chief cavities, vertical precipices, and subtending deep, narrow gorges, have been or7- ginally determined by movements and openings of the crust, whether arranged in anticlinal or synclinal lines, or not less fre- quently modified by great transversal or lateral breaks, at right angles to the longitudinal or main folds of elevation or depres- sion.” Now in my paper I gave six stratigraphical reasons to show why the lakes do not le in hollows of disturbance, and then pointed to ice as the only remaining agent by which they could be formed, thus attempting to reduce the matter as nearly as [ could to a demonstration ; and what I want is an attempt at demonstration in return. But where is the proof beyond the general assertion and impression that craggy-sided mountains and valleys prove dislocations which gape. If they were mere close or nearly close fractures and denudation did the rest, the argument is equally im favour of my view ; for valleys which have been scooped out by denudation often necessarily coincide with lines of fracture, a proposition obvious to every geologist. But I want the proof that the Alpine valleys are dislocations. Let any one go into them and prove it in numerous cases, with his geological map in his hand, by the arrangement of the rocks on either side, and by the fracture or fault visible, or otherwise cer- tainly demonstrable in the bottom. Where are these valley faults, whose name ought to be legion, marked in the best geological _ maps of Switzerland? If they exist, they remain yet to be indi- cated in definite lines; for indeed none know better than the many eminent geologists of Switzerland and the north of Italy, for whom and. for whose work I have the highest respect, that the geological map of their country is as yet but an admirable 296 Prof. A. C. Ramsay on the Erosion sketch, and in all probability will remain so till their governments authorize more general and uniform painstaking surveys. When this is done, and when all the faults and curvatures possible are actually laid down, and when geological sections on a true scale have been run across the Alps, it will then be possible to reason with precision on the denudation of the mountains; and it will be found (what is well known now) that before the present surface of the valleys saw the light, vast piles of strata, as in Wales, have been removed by denudation, and the valleys were formed long after the latest important disturbances of the strata took place. - And now to prove that I also respect authority, let me quote from books of immortal repute; and surely those who reverence authority most, will not disdain that of Hutton and Playfair. What say the father of physical geology and his great disciple? “Tf,” says Hutton, reasoning on this subject, “the valley was made for the rain by any other natural cause, either we should tell by what means this work had been performed, or all reason- ing on the subject is at end, and fancy substituted in its place. If, again, the river be considered as the means employed by nature in making this valley, then all the solid parts between the bounding mountains must have been removed.” Again, reasoning on the weathering and erosion that originated the py- ramids on and around Mont Blanc, he observes, “It is true, indeed, that geologists have everywhere imagined to themselves ereat events, or powerful causes, by which these changes in the earth should be brought about in a short space of time ; but they are under a double deception; first, with regard to time, which is unlimited*, whereas they want to expiain appearances by a cause acting in a limited time; secondly, with regard to operation, their supposition of a great débdcle is altogether incompetent for the end required.” Again, arguing on the approximately hori- zontal gneissic strata of the neighbourhood of Monte Rosa, he shows that the great isolated peaks have been separated by “ the greatest degradation, in bemg wasted by the hand of time.... Here,” he says, “is nothing but a truth that may almost every- where be perceived” if we had only faculties to perceive it. Again, reasoning on strata that correspond on opposite sides of valleys, Playfair, in the Huttcnian Illustrations, says, “there is no man, however little addicted to geological speculations, who does not immediately acknowledge that the mountain was once continued quite across the place in which the river now flows; and, if he ventures to reason concerning the cause of so wonder- ful a change, he ascribes it [in the modern fashion] to some great convulsion of nature, which has torn the mountain asunder * In the original, “limited.”’. This is an evident misprint. of Valleys and Lakes. 297 and opened a passage for the waters. It is only the philo- sopher, who has deeply meditated on the effects which action long continued is able to produce, and on the simplicity of the means which nature employs in all her operations, who sees in this nothing but the gradual working of a stream, that once flowed over the top of the ridge which it now so deeply inter- sects, and has cut its course through the rock, in the same way, and almost with the same instrument, by which the lapidary divides a bleck of marble or granite.” And in the Alps (p. 122) he shows that “the sharp peaks of the granite mountains... . but mark so many epochs in the progress of decay,” while the loftiness of the harder peaks is due not to mere upheaval but to the circumstance “that the waste and detritus to which all things are subject will not allow soft and weak substances to remain long in an exposed and elevated situation.” “Thus, with Dr. Hutton (p. 126), we shall be disposed to consider those great chains of mountains, which traverse the surface of the globe, as cut out of masses vastly greater, and more lofty than anything that now remains.” I could multiply sentences of this kind from the writings of these great philosophers; but enough has been said to recall to memory the fact that before the present race of “practical geologists” had written a line, men of rare knowledge, keen sagacity, and the highest intel- lectual powers, by appeals to nature already held those views which some of their degenerate descendants have so readily repu- diated, but to which a younger school show strong symptoms of returning. I doubt also if some of the Swiss and Italian geolo- gists will be quite content to stand godfathers to the opinion that the Alpine valleys generally are apt to lie in lines of mere curva- ture or fracture, whether close or gaping; but without further authority than that of personal conversation it would be impro- per to quote their names. Unless I were to write a special elementary treatise on denu- dation, enough has now been said to show that the theory of formation of great systems of valleys by erosion in which water and ice are main agents, is not a mere absurdity, and I do not therefore care minutely to analyze the assertions that many of the Alpine rivers “flow in fissures or deep chasms, ... which water alone never could have opened out;” or again, that the Rhine and the Danube “never could have eroded those deep abrupt gorges through which they here and there flow, and which are manifestly due to original ruptures of the rocks.” To the neglected and even half-forgotten school of Hutton and Playfair, and to many expert geologists of the present day whose lives have been spent in practically analyzing the rocky struc- tures of countries, the manifest nature of such “original rup- Phil. Mag. 8. 4. Vol. 28. No, 189. Oct, 1864. X 298 Prof. A. C. Ramsay on the Erosion tures’ is anything but evident; and I for one believe that the “ruptures” are only manifest to those who accept such hypotheses “ without inquiring into what has been the former state of things, or what will be the future”*. To this day there is no error so common, even among geologists, as that which vaguely attri- butes the form and nature of the present surface-outlines of the earth chiefly to the operation of violent disturbance in recent geological times, not clearly perceiving that the great and small outlines of mountain-chains, of valleys, of river-gorges and of plains are the combined results of an immense number of opera- tions, many of these going back to exceedingly remote periods of geological antiquity, and a great proportion of their details bemg lost even to probable conjecture. These operations, however, in the production of scenery mainly resolve themselves into the following series, the parts of which, ever since land and water first existed, may be arranged in any possible combination. a. Oscillation with respect to the sea-level of rocks that have or have not been contorted and metamorphosed, accompanied by pauses in oscillation of greater or less duration. b. Great plains of marine denudation. ce. Subaérial denudations of all kinds; wearing away of sea- coasts ; and in the interior of the country, chemical decompositions, frost, snow, ice, wind, rain, and rivers ; modified by height of land, and the various positions, hardness, and other characters of rocks. Contortion and metamorphism seem to be essential accompa- niments of all great mountain-chains. It may also possibly be proved that in intensely contorted regions mountain-chains are high or low according to the relative antiquity of disturb- ance, while sometimes the irregular protuberances, as in the Devonian and other rocks of the Rhine and Moselle, have been planed away altogether. Plains of marine denudation are sure to be inclined at a very low angle if formed during slow depression of the land. Further, while the sea helps to make bays, the other agents of waste enumerated above cut out all mountain-peaks not volcanic, all the minor valleys, in this term including such valleys as those of the Alps, the Highlands, Wales, &c., but not such a valley as the great one that les. between the Alps and the Jura. Fractures and volcanos, in the production of the great scenic features of continental physical geography, are, as a rule, mere subordinate and subsidiary accidents, the first modifying the effects of denudation by juxtaposition of different kinds of rocks, and the second (which seem to be connected with general ele- vations) forming accidental mountains, hills, and hilly regions, * Hutton, vol. u. p. 257. of Valleys and Lakes. 299 which, as in the Andes, may form non-essential parts of moun- tain-chains, I shall now make some remarks on what has been said in the Address respecting the action of ice in general, and its share in forming lakes that are true rock-basins in particular, taking these in connexion with other points at issue. *‘ Before entering on the consideration of the new theory of the power of moving ice,” Sir Roderick gives a brief review of the recent progress of Alpine glacial geology, meaning by recent principally those twenty-five or thirty years that have elapsed since Agassiz began to insist not only on the enormous size of the old glaciers of the Alps, but on what is now generally recognized as the true glacial theory. ‘‘ Granting to the land glacialists their full demand ” for the great size of the old glacier of the Rhone, it is stated by Sir Roderick, backed by the authority of Sir Charles Lyell, that there is nothing in that fact “which supports the opi- nion that the deep cavity in which the lake [of Geneva] lies was excavated by ice ;” for among other things it is “to be noticed in the case of the Lake of Geneva” that it “trends from H. to W., whilst the detritus and blocks sent forth by the old glacier of the Rhone have all proceeded to the N. and N.N.W., or in direct continuation of the line of march of the glacier which issued from the narrow gorge of the Rhone. By what momen- tum, then, was the glacier to be so deflected to the west that it could channel or scoop out, on flat ground, the great hollow now occupied by the Lake of Geneva? And, after effecting this wonderful operation, how was it to be propelled upwards from this cavity on the ascent, to great heights on the slopes of the Jura mountains?” The same argument it is stated holds good of the Rhine glacier, which I have attempted to show scooped out the shallow hollow of the Lake of Constance. One would suppose these questions to be so conclusive, that the mere asking is enough, and any opposite views must be absurdities which no man of any sound knowledge could entertain; and yet men are found who do entertain them in part or in whole, even authors of great authority on geological and physical subjects, not only in the three kingdoms, but on the continents of Europe and Ame- rica. Now with regard to the great old glacier of the Rhine, the sentence bearing on it isso worded that I am unable to make out whether it is implied that in the belief of Sir Roderick Murchi- son no great glacier issumg from the Upper Rhine valley ever overspread the region around the Lake of Constance, or whether he and M. Escher von der Linth simply at one time could not find signs of a glacier that so “plunged into the flat region on the east and north” (of the Hohe Sentis) “as to have scooped out the cavity in which the lake lies.” If the former, then Sir X 2 300 Prof. A. C. Ramsay on the Erosion Roderick’s opinion seems to have been formed a long time ago; for, adopting M. Escher’s authority, anyone who consults his map of the ancient extension of the Alpine glaciers, will see that he draws an enormous glacier, which issuing from the broad flat valley of the Rhine, tranquilly overspread the country on all sides of the lake, and without the necessity for any plunge, could only have been fed by smaller tributary streams of ice that, if such existed, descended on the northern slopes of the Hohe Sentis*. In like manner, Sir Roderick is of opinion that the basin of the Lake of Geneva was not scooped out by ice, because “it trends from east to west,” or at right angles to the main flow of the glacier—because ice, per se, neither has nor has had any excavating power’’—because (p. 12) “in valleys with a very slight descent, .... no erosion whatever takes place, particularly as the bottom of the glacier is usually separated from the sub- jacent rock or vegetable soil by water arising from the melting of the ice,” and because even in gorges ‘‘ whence the largest gla- ciers have advanced for ages, we meet with islands of solid rock and little bosses still standing out, even in the midst of the val- leys down which the icy stream has swept,” and “ there is no proof of wide erosion ”—and, yet again, because (p. 15) “ice has so much plasticity that it has always moulded itself upon the inequalities of the hard rocks over which it passed,” and “has never excavated the lateral valleys, nor even cleared out their old alluvia,” and furthermore, in general terms, because ice could not have been propelled up an inclination from the bottom of a lake, let the angle, I presume, he ever so small. | Now the east and west course of the lake is here treated as if the glacier of the Rhone which overspread it were the only gla- cier which helped to cover the area; but if any one will take the trouble to refer to the map which accompanies my memoir, or, better still, to M. Eschevr’s, he will see that the mass of ice must have been prodigiously swelled by the great tributary glacier of Chamouni, which, descending from Mont Blanc, filled a valley some fifty miles in length, and joined the Rhone glacier near the lower end of the Lake of Geneva. Neither does it require much reasoning to see that during the cold of the glacial epoch all the higher region south of the lake must have maintained its glaciers and filled the valleys that run north; for even now some of the * T have to apologize to my friend M. Escher von der Linth for not having used his map of the ancient glaciers as my chief authority when my Memoir on the Lakes was read. The first time I saw his map, which was sent me by Principal Forbes of St. Andrews, was after the publication of my memoir. Had I seen it in time, I would certamly have availed my- self, in the construction of my sketch map, of the authority of a geologist so accurate and distinguished as Escher von der Linth, of Valleys and Lakes, 301 peaks are tipped with perpetual snow. The Rhone glacier had therefore no lack of tributaries to maintain its mass over all the area of the Lake of Geneva, though towards the west, where the glacier thinned away, that mass would be less than over the eastern half of the lake, where weight and grinding-power must, I believe, on that account have necessarily been greater. But the main flow of the ice, after escaping from the Rhone valley, was necessarily of a mixed nature, partly to the N.W., and also to a great extent to the N.E. and S.W., simply because the N. W. face of the glacier abutted on the Jura. For it requires no pro- found knowledge of physics to perceive that any body, whether actually plastic like pitch, or of a modified plasticity that may be fractured and reunite like jelly*, or that by “ fracture and regela- tion” behaves like a plastic body,—I say it requires no profound knowledge of physics to understand that such a body, constantly renewed and pressed on from behind, when opposed by a high impassable barrier (like the Jura), will spread itself out in the direction of least resistance, that direction in the case of the Rhone glacier having been at right angles to the general pres- sure, or N.E. and S.W., whence I believe the general form and trend of the Lake of Neuchatel. But, in the second place, is there indeed no proof that ice “neither has nor has had any excavating power,” whether in val- leys of large or of low inclination, narrow or broad? Then why is it that all the rivers that flow from glaciers, great and small, are so muddy? Surely no one will contend that all “the flour of rocks” that gives to the rivers a pipeclay colour has been washed in by streams from the surface. Alpine club men who drink (rarely) of the brooks that run on the surface of the ice will repudiate the idea; those who fancy they see in the Loess of the Rhine the old glacier-ground mud of the Alps will shrink from it; and many, if not all the Alpine geologists versed in ice whom I have conversed with in Italy and Switzerland, will, I ven- ture to say, still hold that glaciers by erosion seriously affect their beds. What else is the meaning of the striation and deep grooving, the mammillation and the glassy polish, even of quartz, and of all the Alpine rocks, whether hard or soft? The mud of the rivers is chiefly derived from this incessant ice-waste; and that is why it is so wnearthy, so clean, fresh, andimpalpable. Were it merely or chiefly surface-wash, derived from the hills and washed underneath and carried forward below the glaciers, the sediment in great part would be dirty, torrential, and coarse enough, espe- cially if, as is stated, glaciers do not seriously grind along their rocky floors. So far from a glacier exercising only a trifling grind- ing-power, “because it is usually separated from the subjacent * T have obtained this comparison from the Master of the Mint. 302 Prof. A. C. Ramsay on the Erosion rock or vegetable soil by water arising from the melting of the ice,” the grinding power is so immense, that in unweathered ground comparatively recently covered by a glacier, every foot of surface is often polished and striated. If, indeed, water usually separates ice from the rock so that it does not press upon it, a glacier, whether 30 or 3000 feet thick, would need to be treated in the main as a floating body; and it is well known - that with floating ice there is some eight or ten times as much ice below as above the water. As for bosses “ still standing out in the midst of the valleys” proving that glaciers have no erosive power, the reader unlearned in theories of denudation will easily understand that the same kind of argument might be applied to the pillars of earth left for a time in the midst of a railway-cuttmg the actual exca- vation of which he had not seen; or because Goat Island still stands in the middle of the falls, the Niagara has not cut its gorge; or because other low islands le higher up, the river has not worn out a channel on either side of them and will not destroy them; or in marine denudation, that the chalk between Old Harry and his Wife and the mainland of Swanage Bay, and that between the Needles and the Isle of Wight, has not been washed away by the sea, because the islets still stand im the midst. If, however, it be said that the glacier-islets are the result of old subaérial denudations before the glacier began to flow, I might perhaps doubt it, but, for evident reasons, for the purpose of this argument, I will not quarrel with it. If they have not been left prominent either by streams or ice, then, according to the hypothesis which accounts for these valleys by disturbance, the bosses in the midst of the glaciers are the result of a process of dislocation of which I should like to see the spe- cial proof. The peculiarity and in part the amount of this wearing action of ice is indeed due to that very “ plasticity ” which enables ice to mould “itself upon the inequalities of the hard rock.” And itis just therein that its excavating power differs from that of water. Still water cannot excavate a large basin-shaped hollow, and in the depths of a lake water is still; but glacier-ice, having “moulded itself upon the inequalities of the hard rocks over which it passed,” can even move right over a barrier of rock and grind it into roches moutonnées. The very fact that a roche mou- tonnée has, as stated by Sir Roderick, a “Stoss-Seite,” is indeed proof that with sufficient pressure behind, a glacier can to some extent pass uphill; and those who remember the great size and height of many of these barriers in Switzerland, as, for instance, the Kirchet and the hill behind the Grimsel, will be prepared to follow the arguments urged in my original paper—and, for dif- of Valleys and Lakes. 503 ferent reasons, also held by De Mortillet—viz. that a glacier of sufficient thickness could not only fill a lake, but could flow up the low angle of the ascent towards the outflow and escape beyond its bounds*. If a glacier can round, polish, and cover with striations the rocks over which it passes—if, flowing from its caverns, it can charge rivers thickly with the finest mud, then it can wear away its rocky floor and sides. Here indeed an appeal to nature may safely be made, and the answer will be easily obtained; for, standing on the surface of scores of glaciers, such as those of the Aar, and casting the eye upward, the whole mountain-sides are moutonnés, and parallel striations running along and down the valley are universal; and not there alone, but miles and miles below the end of the puny glaciers of today the signs of the same wearing actions of grander ice-streams are visible both in and thousands of feet above the present bottoms of the valleys. It needs no subtle argument to prove it. Nature proclaims it ; we have but to open our eyes and look upon it to see that ice grinds, and has ground and planed away the surface of rocks, as surely as a planing machine cuts iron, and for much the same cause. ‘What more,” says Hutton, writing of analogous waste, “what more is required? Nothing but time. It is not any part of the process that will be disputed+; but after allowing all the parts the whole will be denied; and for what? only because we are not disposed to allow that quantity of time which the ablution of so much wasted mountain might require.” ‘Trmg,” says Playfair, “ performs the office of integrating the infinitesimal parts of which this progression is made up ;”” and though I have in this Magazine formerly attempted to show, for purely geolo- gical reasons, that the greater valleys in the Alps existed before the so-called glacial period, yet I know perfectly well, not only that since that time glaciers have worn a vast quantity of matter out of them, but that, given sufficient time, a glacier of itself might scoop out a valley of any depth, just as running water may do the same, or as surely as that, given sufficient time, the sea will wear away any island, soft or hard, large or small, that rises amidst its waves. In further proof of the assertion that glacier-ice can have no serious effect in wearing away its bottom, great stress is laid on the well-known fact that such short and steep glaciers as those * Unless I am much mistaken, geologists will some day be much sur- prised at the size and kind of hills that they will be obliged to allow that glaciers have travelled over. 7 Things, however, that he considered almost self-evident are now dis- puted every day. The tendency of opinion begins to set in the opposite direction. 304 Prof. A. C, Ramsay on the Erosion of the Brenva and Miage ride over their moraines. I know these glaciers well, and the statement that they do ride on their moraines is perfectly true; but few geologists, and probably no physical philosopher will rest his reputation on the assertion that, if those glaciers were to inerease till they attained their ancient size, when as mere tributary sources they helped to swell the enormous mass that ploughed all down the Val d’Aosta to beyond Ivrea,—will anyone, I say, rest his reputation on the belief that these moraine heaps would le where they now do, underneath a thousand or thousands of feet of ice, unmoved to all eternity, or at least till the complete decline of the glaciers permitted the loose material to be attacked by running water ? If so, again, whence the muddy glacier rivers, and whence the scratched stones that come from under the glaciers? Tyndall will not believe in their immobility, nor De Mortillet, nor Gastaldi, nor Darwin, who was the first to show that the larger glaciers of Wales had ploughed the drift out of some of the greater valleys - of the country ; and many other geologists of weight will equally shrink from the idea. Has ice noweight ? Dothe huge glaciers of Victoria-land and of Greenland exert no pressure on the ground over which they flow? and are there no stones and no powder of rocks beneath to help the grinding-power? Rub iron with your finger often and long enough, and it will wear a channel in the metal; for the skin, like the passing glacier, will be renewed, while the iron has no means of restoration. If yielding water can wear out a channel, which few people will deny, far more, then, must the weight of a thick glacier exercise a prodigious abrading-power ; for surely no one on reflection will be so bold as to assert that 50 feet, or one, two, or three thousand vertical feet of ice with a specific gravity of nearly 0°92 will everywhere, or nearly everywhere, be separated from its floor by a stra- tum of water so complete that the glacier rarely touches the bot- tom. If Agassiz, Forbes, and Tyndall, backed by Studer, Escher, and Gastaldi, were to tell me so (and they would not dream of it), my reverence for authority (and it is great) could not persuade me to believe them. If, then, glaciers can waste rocks and deepen valleys, is it possible that the great old glaciers under favourable circum- stances have excavated lake-basins, when rocks of unequal hard- ness came in their course, or when from special causes the pressure of ice was unusually great on certain areas? Or were they apt to do so by a combination of these causes, when, ceas- ing to flow through valleys of great or of moderate inc ination, they descended into regions that are comparatively level ? I will not repeat what I have elsewhere printed about the effect of ice passing over rocks of unequal hardness, nor yet what of Valleys and Lakes. 305 [have said of the confluence of immense glaciers like those that once united in the valley of the Lago Maggiore at what are now the Borromean Isles. But it seems to me that to any one who allows any excavating power to a glacier, it will be evident that when the general inclination of a valley was comparatively steep, a glacier could have had no opportunity of cutting for itself any special basin-shaped hollows. Its course, with a difference, is like that of a torrent. But in a flat-bottomed part of a valley, or in a comparative plain that lies at the base of a mountain- range, the case is not the same. For instance, to take an ex- treme case, if a glacier tumble over a slope of 45°, no one would dream of the ice-flow producing any special effect, except that in the long run, the upper edge of the rock that forms the cata- ract being worn away, its average angle would be lowered. And so of minor slopes; if the ice flowing fast (for a glacier) rendered the rocky surface underneath unequal, such inequalities could not become great and permanent ; for the rapidly flowing ice would attack the projecting parts with greater power and effect than the minor hollows, and so preserve an approximate uniformity, or an average angle of moderate inclination. But when a monstrous glacier descended into a comparative plain, or into a low, flat valley, the case was different. There, to use homely phrases, the ice had time to select soft places for excavation, and there, if, from the confluence of large glaciers, or for other reasons, the downward pressure of the ice was of extra amount, the excavating effect, I contend, must have been unusually great in special areas, and have resulted in the formation of rock-bound hollows. And though the glacier of Ivrea has been constantly quoted as a case that completely proves the absurdity of my theory, this merely shows the unwariness of those who quote it; for not only are there a great many rock-basins full of water above Ivrea in among the vast roches moutonnées near the opening of the plain, but, where beyond this point the glacier spread out so wide on the Pliocene plain, it has scooped away so much material that parts of that plain are below the average level of the plains of Piedmont that lie outside the great moraine. Given sufficient time and extension of the glacier, and more matter still would have gone away. The same argument equally applies to the case on the Lake of Zurich, where glacier débris is said to lie on alluvial detritus. In reply to the question why in the actual valley of Aosta there are no lake-basins, I might with equal propriety say, Many contorted regions are much faulted, and there is often an evident connexion between contortion and faults ; but in some contorted regions there are few or no faults, and the reason of their absence remains to be accounted for. I have attempted to explain why the rock-basins are present, and not 306 Prof. A. C. Ramsay on the Erosion why they are absent. It may be that some of the alluvial flats of the valley are lake-hollows filled up. But another statement urged by Sir Roderick against my theory is, that the scooping-out of such hollows by ice is im- possible, because ice canuot flow up an inclined plane. If so, I repeat, what is the meaning of the “ Stoss-Seite” or upper side of a roche moutonnée that bars a wide glacier valley, through which barrier perhaps a mere narrow river gorge passes—as, for instance, in the case of the Kirchet so well known to Alpine men, or, on a smaller scale, of the roches moutonnées near the slate-quarries in Nant Francon? In both cases the barrier re- mained intact till the draimage of the glacier-formed lakes cut gorges through them—or, if Sir Roderick prefer it, till convul- sions made gorges. Its moutonnée form will convince every accomplished glacialist that the ground was once covered by ice. The strike of the rocks will be enough for ordinary geolo- gists ; for no man can suppose who sees the corresponding forms of the roches moutonnées on either side of the narrow gorge of the Aar, that that gorge existed before the period of the great glacier, and that the glacier flowed entirely between the walls of the narrow passage. If Iam right in this, then the great old glacier of the Aar flowed right over the hill, from bottom to top, and away into regions far beyond, in the manner I have imper- fectly shown in my little book on the old glaciers of Switzerland and North Wales, and equally so whether the gorge was formed by sudden violence or by water. In the existence, therefore, of ‘ Stoss-Seiten,” and in their upward striations, both in small and large roches moutonnées, there is proof that the belief that glaciers cannot flow over hillocks, and even hills of considerable size, is a mere assertion founded on prejudice: to me the wonder is, that any one can ever have believed it who has truly observed phenomena in the Alps, or who is familiar even with the ancient glaciation of our own country. And if this be so, I see no difficulty in accepting the hypothesis that the length and inclination of the slope which the bottom of a glacier may ascend depend simply on the thickness of the ice, and on the amount of the propelling power behind, that power being due to the weight and mass of the descending ice, and the average angles of the valley behind the point whence the upward ascent begins*. Now, in dealing with this question, most of the geologists who have opposed me have treated the larger lake-hollows much as they do Jime. Unconsciously they seem to me to be afraid both of it and of them. ‘ Look,” they seem to say, “at these mountains, * T think it might be possible to make a very good approximate calcula- tion on this point, and I hope it may yet be done. —— of Valleys and Lakes. 307 how awfully high and rugged they are; can any amount of time, aided by weather, torrents, rivers, and glaciers produce such effects? Old writers, like Hutton and Playfair, and a few modern observers (some of whom, both in America and Europe, have great familiarity with rocks), say they can; but we know that rending and fracture is the chief agent, and denudation is in com- parison quite a trifling affair. Look, again, at the hollows of the lakes, how awfully deep they are! How isit possible for a glacier ever to have slid up a hill from a depth so profound?” In treating the slopes as great, consists the viciousness of this sup- posed argument. Unconsciously, some of the arguers are draw- ing exaggerated diagrams in their minds. They foreshorten the slope, increase in their mind’s eye its steepness, and forget their trigonometry altogether. But let me beg of them to try to realize the real state of the case, and see how small by com- parison the depth really is, and how gentle the slope. Were the bottom of the Lago Maggiore not undulated (for I believe the islands to be mere roches moutonnées), this slope from the deepest part of the lake (2600 feet) to its outflow would only be 2° 21! in a distance of about 12 miles, a slope so gentle that, were a man standing on it, by the eye he would barely be able to tell whether he was on an inclined plane or not*. Again, take the Lake of Geneva from the place where it is nearly a thousand feet deep to Geneva, the average slope is only about 25’, an angle so small that any geologist looking at it would be apt to consider the surface as horizontal. The question, then, as regards the lakes resolves itself into this: Is it possible that the ice of the great old glaciers could ever have travelled up these exceedingly small inclinations for a distance, say of 12 miles in the one case and 20 to 25 miles in the other? And now, in connexion with this point, I could wish that Sir Roderick had expressed an opinion whether or not he agrees with the old geologists, that (p. 7) “the Lakes of Geneva and Neufchatel were so filled up with snow and ice that the advancing glaciers travelled on them as bridges of ice, the foundations of which occupied the cavities.” If this were so, then, in other words, the lower strata of ice in the hollow of what is now a lake remained in a condition of static equilibrium, and over this ice the advancing part of the glacier slipped or was propelled. Strictly speaking, it is evident that this state of static equilibrium is impossible; for all the ice of a glacier a little below the sur- face being, even in winter, in a melting state, the lower strata * In my original paper on the glacial excavation of certain lakes, I made an unfortunate error in calculation, stating that the angle is about 5°. In an able article in the ‘ Reader,’ Professor Jukes corrected the error, and made the slope 2°. 308 Prof. A. C. Ramsay on the Erosion above alluded to must have been destroyed and renewed over and over again; and as glacier-ice is practically anything but a rigid body, I think it would be easy to show that, just asin Are- tie regions in winter the more rapid flow of the lower strata of ice, with a temperature of about 82°, shatters the more rigid and slowly-moving upper layers which have a temperature far below that point, so, for other reasons, the motion of some 2000 vertical feet of ice sliding over the basin, would be communicated | to the lower strata ; for pressure in ice produces adhesion of parts. I for one cannot conceive a horizontal fracture of 40 miles in length over the area of the Lake of Geneva, clearly dividing two bodies of ice, the lower of which was, where thickest, nearly 1000 feet, and the upper and sliding stratum must have been nearly 3000 feet thick. It is, im fact, a piece of mere elementary knowledge that any heavy body passing steadily across any other body, the parts of which are moveable, will communicate motion to the parts over which it passes, whether one or both of those bodies be viscid or plastic, or of some other compound character; and when I wrote my original paper it never occurred to me that there was any need of mentioning a point so obvious. But ina glacier that fills a lake-basin, this is by no means the only, and perhaps not the principal, cause of motion. A glacier does not throughout all its course move on simply by virtue of gravity. Pressure from behind has a great deal to do with it; as, for instance, in the case of the Rhone glacier, familiar to so many, and cited by Professor Merian and Dr. Tyndall. There, at the cataract, the ice fractures and slides down comparatively rapidly in masses, but at the base, where it moves slowly, pressure from behind causes the masses to touch and reunite, and the whole slides on, a re-formed mass, into the lower valley, the inclination of which issmall. So, in the case of the lakes, the depths of which seem so appalling, but the real angles of the beds of which are so small, there seems to me nothing either impossible or remarkable in the idea that the long and enormous onflowing inclined mass of the glacier of the Rhone pushed before it in the plain (for such it is) its own more sluggish continuation up a slope of 25! for a distance of 20 or 25 miles. I believe that the same argument is equally applicable to the Lago Maggiore, where the already vast glacier, swelled by the mighty tributary of the Val d’Ossola, was thus enabled to push along the low average slope of 2° 21' for a distance about half as great. The very islands in many a lake once filled with ice help to prove this; for, as in the case of Loch Lomond, they are mere roches moutonnées, and I for one cannot conceive that the mammillation ceases imme- diately below the surface of the water. Having got thus far, I will not repeat my arguments to show of Valleys aad Lakes. 309 that (as I attempted to prove in my original memoir) the Alpine and other ice-worn lakes known to me do not lie in areas of special subsidence, nor in gaping fractures, nor in simple synclinal basins, nor in hollows of watery erosion. If any one who reads this is curious about them, he must refer to that memoir* ; but this at least I may be permitted to say: I used at all events arguments, even somewhat elaborate, and not mere statements, and whether these arguments are fated to be successful. time alone will show. That they were at all events of some value, the names of the distinguished geologists who have accepted my theory helps to show; and I could add to these other names as high as the very highest of those on whose authority Sir Roderick so much depends, did propriety permit me to quote from letters and commit men to opinions which they have not expressed in rint. But before leaving the subject, let me say a little more about the possibility of these lakes lying in fractures. For this pur- pose let us take some of those that lie on the north side of the Alps, partly in the region of the Miocene strata. If they lie in lines of gaping fracture, nearly as wide as the present lakes, then on the hills, say between the Lake of Lucerne and Thun, and between Thun and the Lake of Zurich, the Miocene strata would be crumpled up in zigzag lines across the average line of strike, to an amount corresponding to the distance between the severed strata in the spaces now overlooking and occupied by the lakes. Thisis not the case. Again, if the fractures were mere narrow cracks, then the amount of denudation that took place so as to form the wide valleys has been enormous, and within a mere fraction of what I require, especially when we consider that the great denudation necessary to widen the fractures would have filled up the lake-basins. The theory of the chief forma- tion of Alpine valleys having been effected by weather, water, and ice, would therefore still hold good. I might continue these arguments, and discuss in detail what Sir Roderick has said about Scandinavia, North America, and other regions, and among other things show how unprecise is the knowledge that we actually possess respecting the details of the boulder-beds that overspread some of them, and how unsafe it is to conclude, because a country is not actually mountainous, and does not now lie high above the sea-level, that it was never covered by glacier-ice in motion, and may not at one time have lain much higher. In spite of Agassiz’s memoirs, it is not long since all the lower Till of Scotland was considered not to be ordinary moraine-matter at all, but to have been formed * They are also given in ‘The Physical Geology and Geography of Great Britain.’ 310 On the Erosion of Valleys and Lakes. solely in the sea by the transporting agency of icebergs. Let those who still believe it refer for proof to the contrary to Mr. Geikie’s admirable work ‘On the Phenomena of the Glacial Drift of Scotland.’ I know enough of the superficial strata in North America to foresee that the erratic deposits there will some day also be divided into terrestrial and marine series, and I am pretty sure that Sir William Logan will not deny the proba- bility. For the vast size of the ancient glaciers of that con- tinent, I would refer to Professor Dana’s admirable Manual of American Geology. It is a mistake to suppose that the stria- tions there merely run from north to south, for Sir William Logan, who has mapped them, proves that they often conform to the bends of the valleys. As regards the great lakes of that continent, so far from being “cavities originally due to a combination of ruptures and denu- dations of the rocks,” it is impossible intimately to know the country and believe it. There the Silurian strata, amid which the lakes lie, are arranged so tranquilly and at angles so low, that the flattest chalk of Great Britain may be almost said to be tumultuous in comparison; and the forthcoming sections of Sir William Logan conclusively prove that around the lakes there is no trace of dislocation to help to form the hollows, nor yet do they lie in hollows of special subsidence. Only Lake Superior covers a faint synclinal curve; and Lake Ontario, so far from occupying an area of special depression, actually lies on a very low anticlinal bend of soft strata, the top of which has been denuded away. That Sir William, who has been called the best stratigraphical geologist in America, believes that ice has some- thing to do with the scooping out of rock-basins, any one may see who refers to his late masterly report on the geology of Canada; and Professor Newberry, whom Sir Roderick knows asa physical geologist and geographer, adheres strongly tothat opinion. As for the observation of my friend M. de Verneuil, that the orographic hollows in Spain are precisely those that “a theorist ” might “attribute to excavation by ice,’ I decline to be judged by it, till I have seen them and declared that opinion. I object, both for myself and my supporters, that we should be judged in a manner so vague. And further, I think I appeal to Nature to some purpose when, neither for the first nor the second time, I ask philosophers to consider why it is that not only drift- and moraine-danimed lakes, but striated rock-basins of all sizes occur in such prodigious numbers in America, Scandinavia, the High- lands, and in all other rocky temperate regions, high or low, that have been glaciated, while in tropical and subtropical regions ~ they are so rare as to be quite exceptional elsewhere than in mountain areas that now or once maintained their glaciers. Prof. Bohn on the Conservation of Energy. 311 Several other points raised by Sir Roderick in that part of his Address that relates to physical geology, glaciers, and icebergs remain to be discussed. I have entered, however, on this argu- ment with great reluctance, and, unless circumstances again con- strain me, I shall leave the remaining questions untouched. XXXVI. Historic Notes on the Conservation of Energy. By Professor Bown. To Professor Tyndall, Esq., F.R.S. | READ your “ Notes on Scientific History” * with great plea- sure and satisfaction. I agree perfectly with all you say respecting Mayer’s researches as compared with those of others ; in some respects, indeed, I am inclined to go further than you do. Seven years ago I studied the history of the principle of the Conservation of Energy, and arrived at the same conclusion, with respect to the modern development of this theorem, as the one for which you so ably and warmly contend. Your recent disin- terested advocacy of Mayer’s claims, and my own conviction that historic truth is the sole object of your research, inspire the hope that the following remarks will be found worthy of atten- tive perusal. Descartes, so. far as 1 know, was the first to give expression to the thought that whatever is not material must necessarily be indestructible. This non-material something he called “ Force,” a word which subsequently had, for a long period, divers and consequently vague meanings. In Descartes’s Principia Philosophie (Pars II., § xxxvi.) we find the following :—“ Deum esse primariam motus causam et eandem semper motus quantitatem in universo conservare. “Mottis natura sic animadversd, considerare oportet ejus causam, eamque duplicem: Primo scilicet universalem et pri- mariam, que est causa generalis omnium motuum qui sunt in mundo; ac deinde particularem, a qua fit, ut singule materiz partes motus, quos pris non habuerunt, acquirant. Kt gene- ralem quod attinet, manifestum mihi videtur illam non aliam esse, quam Deum ipsum, qui materiam simul cum motu et quiete in principio creavitt, jamque per solum suum concursum ordinarium, tantundem motts et quietis in eA tota quantum tune posuit conservat. Nam quamvis ille motus nihil aliud sit in materia mota quam ejus modus; certam tamen et determinatam habet * Phil. Mag. S. 4. vol. xxviii. p. 25. 7 Phil. Mag. S. 3. vol. xxiii. p. 442 (1843): Mr. Joule, “That the grand agents of nature are by the Creator’s fiat indestructible.” 312 Prof. Bohn on the Conservation of Energy. quantitatem, quam facilé intelligimus eandem semper in tota rerum uniyersitate esse posse, quamvis in singulis ejus partibus mutetur. Ita scilicet ut putemus, cum una pars materia duplo celeritis movetur, quam altera, et hee altera duplo major est quam prior, tantundem motus esse in minore quam in majore, ac quanto motus unius partis lentior fit, tanto motum alicujus alterius ipsi zequalis fieri celeriorem. Intelligimus etiam per- fectionem esse in Deo, non solum quod in se ipso sit immu- tabilis, sed etiam quod modo quam maximé constanti et immu- tabili operetur: Adeo ut 1s mutationibus exceptis, quas evidens - experientia, vel divina revelatio certas reddit, quasque sine ulla in creatore mutatione fieri percipimus, aut credimus, nullas alias in ejus operibus supponere debeamus, ne qua inde inconstantia in ipso arguatur. Unde sequitur quam maximé rationi esse consentaneum, ut putemus ex hoc solo, quod Deus diversimodé moverit partes materiz, cum primum illas creavit, jamque totam istam materiam conservet, eodem plané modo, eademque ratione qua prius creavit, eum etiam tantundem motts in ipsa semper conservare.’ Descartes therefore, precisely like Colding, bases the pr oof of his theorem on a divine attribute. The unsatisfactory nature of such a proof is manifest. Are we not equally justified in assert- ing that the assumption of a constant quantity of motion involves a limitation of divine power? The almightiness of God must manifest itself by actual achievement, new motion must inces- santly be created; therefore, assuming with Descartes the inde- structibility of that which exists, the quantity of motion must increase. Every attempt to deduce a natural law from an @ priori con- ceived attribute of God must inevitably be utterly fruitless. Leibnitz was the first to publish, in its proper form, the general theorem of the conservation of vis viva, and to demonstrate the same by empirically ascertained and rationally established theorems. He at once opposes Descartes’s views, and introduces the important conception of wis viva. All this will be found in his article in the Acta Eruditorum, Lips. 1686, entitled: “ Brevis demonstratio erroris memorabilis Cartesii et aliorum circa legem nature, secundum quam volunt a Deo eandem semper quantita- tem motus conservari, qua et in re mechanica abutuntur.” In the warm discussion which arose, Leibnitz argued that the assumption of the incorrectness of his views involved the neces- sity, or at least the possibility of a perpetual motion; which lat- ter he urged is manifestly absurd. Colding employs the same argument; and Helmholtz, in 1847, in bis well-known work ‘On the Conservation of Force,’ attributes great importance to this theorem concerning the absur dity of perpetual motion. Prof. Bohn on the Conservation of Energy. g13 John Bernoulli, however, gave the clearest exposition of the principle of the conservation of vis viva, as will be admitted after a perusal of his correspondence with Leibnitz (Vivorum cel. G. C. Leibnitu et Joh. Bernoulli commercium phil. et math.), of lis “Discours sur les lois de la communication du mouvement ” (Opera omnia, tom. ii. p. 1), and especially of his memoir entitled “ De vera notione virlum vivarum earumque usu in dynamicis” (Opera omnia, tom. il. p. 239). Allow me to draw your particular attention to the following two passages of the last-named memoir :— “S$ IIl. Hine patet vim vivam [que aptius vocaretur faculias agendi, Gallice le pouvoir | esse aliquid reale et substantiale, quod per se subsistit, et quantum in se est, non dependet ab alio. Unde concludimus, quamlibet vim vivam habere suam determinatam quantitatem, de qua nihil perire potest, quod non in effectu -edito reperiatur. Hine sponte fluit, vim vivam semper conservari ; adeo ut quee ante actionem residebat in uno pluribusve corpo- ribus, nune post actionem reperiatur necessario in alio, vel allis pluribus corporibus, nisi quid in prioribus remanserit. Atque hoc est, quod vocamus conservationem virium vivarum.” One fact of peculiar interest is John Bernoulli’s assertion that the vis viva which apparently disappears—that is to say, the ws viva which is not employed in external work such as the raising of a weight—may be consumed in molecular work. The follow- ing extract from § 9 of the above memoir will establish this point, ‘Si corpora non sunt perfecte elastica, aliqua pars virium vivarum, quee periisse videtur, consumitur in compressione cor- porum, quando perfecte se non restituunt; a quo autem nunc abstrahimus, concipientes, compressionem illam esse similem compressicni elastri, quod post tensionem factam impediretur ab aliquo retinaculo, quo minus se rursus dilatare posset, et sic non redderet, sed in se retineret vim vivam, quam a corpore incur- rente accepisset; unde nihil virium periret, etsi perisse videretur.” The conversion of vis viva into heat, or at least the possibility of such a conversion, was first asserted by Augustin Fresnel. ‘The French translation of Thomson’s ‘Chemistry’ contains an ap- pendix “On Light” from Fresnel’s pen, wherein he says :-— “C’est un principe général du mouvement des fluides élas- tiques, que, de quelque fagon que l’ébranlement s’étende ou se subdivise, la somme totale des forces vives reste constante. Ht voila principalement pourquoi la force vive doit étre considérée comme la mesure de Ja lumiére, dont la quantité totale reste toujours a trés pew pres la méme, tant qu’elle ne traverse du moins que des milieux trés transparens. Les corps noirs et méme les surfaces métalliques les plus brillantes ne réflechissent pas a Phil, Mag. 8. 4. Vol. 28, No. 189. Oct, 1864: x 314 Royal Society :— beaucoup prés la totalité de la lumiére qui tombe sur leur surface ; les corps imparfaitement transparens, et méme les plus diaphanes, quand ils sont assez épais, absorbent aussi (pour me servir de Yexpression usitée) une quantité notable de la lumiére incidente ; mais il n’en faut pas conclure que le principe de la conservation des forces vives, n’est plus applicable & ces phénoménes; il résulte au contraire de Vidée la plus probable qu’on puisse se faire sur la constitution mécanique des corps, que la somme des forces vives doit toujours rester la méme (tant que les forces accélératrices qui tendent & ramener les molécules 4 leurs posi- tions d’équilibre n’ont pas changé d’intensité), et que la quantité de forces vives qui disparait comme lumiére est reproduite en chaleur.” Should you consider the contents of this letter suitable for the pages of the Philosophical Magazine, I should feel honoured by its publication in that journal. - Giessen, August 14, 1864. XXXVII. Proceedings of Learned Societies. ROYAL SOCIETY. [Continued from p. 240. ] June 16, 1864.—Major-General Sabine, President, in the Chair. HE following communication was read :— “On the Properties of Silicie Acid and other analogous Col- loidal Substances.” By Thomas Graham, F.R.S., Master of the Mint. The prevalent notions respecting solubility have been derived chiefly from observations on crystalline salts, and are very imperfectly appli- cable to the class of colloidal substances. Hydrated silicic acid, for instance, when in the soluble condition, is properly speaking a liquid body, like alcohol, miscible with water in all proportions. We have no degrees of solubility to speak of with respect to silicic acid, like the degrees of solubility of a salt, unless it be with reference to silicie acid in the gelatinous condition, which is usually looked upon as des- titute of solubility. The jelly of silicic acid may be more or Iess rich in combined water, as it is first prepared, and it appears to be soluble in proportion to the extent of its hydration. A jelly contain- ing 1 per cent. of silicic acid, gives with cold water a solution con- taining about 1 of silicic acid-in 5000 water; a jelly containing 5 per cent. of silicic acid, gives a solution containing about J part of acid in 10,000 water. A less hydrated jelly than the last mentioned is still less soluble; and finally, when the jelly is rendered anhydrous it gives gummy-looking white masses, which appear to be absolutely insoluble, like the light dusty silicic acid obtained by drying a jelly charged with salts, in the ordinary analysis of a silicate. Prof. Graham on the Properties of Silicic Acid &c. 315 The liquidity of silicic acid is only effected by a change which is per- manent (namely, coagulation or pectization), by which the acid is con- verted into the gelatinous or pectous form, and loses its miscibility with water. The liquidity is permanent in proportion to the degree of dilution of silicic acid, and appears to be favoured by a low tem- perature. It is opposed, on the contrary, by concentration, and by elevation of temperature. A liquid silicic acid of 10 or 12 per cent. pectizes spontaneously in a few hours at the ordinary temperature, and immediately when heated. A liquid of 5 per cent. may be preserved for five or six days; a liquid of 2 per cent. for two or three months; and a liquid of 1 per cent. has not pectized after two years. Dilute solutions of 0°1 per cent. or less are no doubt practically unalter- able by time, and hence the possibility of soluble silicic acid ex- isting in nature. I may add, however, that no solution, weak or strong, of silicic acid in water has shown any disposition to deposit erystals, but always appears on drying as a colloidal glassy hyalite. The formation of quartz crystals at a low temperature, of so frequent occurrence in nature, remains still a mystery. I can only imagine that such crystals are formed at an inconceivably slow rate, and from solutions of silicic acid which are extremely dilute. Dilution no doubt weakens the colloidal character of substances, and may there- fore allow their crystallizing tendency to gain ground and develope itself, particularly where the crystal once formed is completely inso- luble, as with quartz. The pectization of liquid silicic acid is expedited by contact with solid matter in the form of powder. By contact with pounded gra- phite, which is chemically inactive, the pectization of a 5 per cent. silicic acid is brought about in an hour or two, and that of a 2 per ceut. silicic acid in two days. A rise of temperature of 1%1 C. was observed during the formation of the 5 per cent. jelly. The ultimate pectization of silicic acid is preceded by a gradual thickening in the liquid itself. The flow of liquid colloids through a capillary tube is always slow compared with the flow of crystalloid solutions, so that a liquid-transpiration-tube may be employed as a colloidoscope. With a colloidal liquid alterable in viscosity, such as silicic acid, the increased resistance to passage through the colloi- doscope is obvious from day to day. Just before gelatinizing, silicic acid flows like an oil. A dominating quality of colloids is the tendency of their particles to adhere, aggregate, and contract. This idio-attraction is obvious in the gradual thickening of the liquid, and when it advances leads to pectization. In the jelly itself, the specific contraction in question, or syneresis, still proceeds, causing separation of water, with the divi- sion into a clot and serum; and ending in the production of a hard stony mass, of vitreous structure, which may be anhydrous, or nearly so, when the water is allowed to escape by evaporation. The intense syneeresis of isinglass dried in a glass dish over sulphuric acid in vacuo, enables the contracting gelatine to tear up the surface of the glass. Glass itself is a colloid, and the adhesion of colloid to colloid appears to be more powerful than that of colloid to crystalloid. Y 2 316 Royal Society :-— The gelatine, when dried in the manner described upon plates of cale- spar and mica, did not adhere to the crystalline surface, but detached itself on drying. Polished plates of glass must not be left in con- tact, as is well known, owing to the risk of permanent adhesion between their surfaces. The adhesion of broken masses of glacial phosphoric acid to each other is an old illustration of colloidal syneeresis. Bearing in mind that the colloidal phasis of matter is the result of a peculiar attraction and aggregation of molecules, properties never entirely absent from matter but greatly more developed in some substances than in others, it is not surprising that colloidal characters spread on both sides into the liquid and solid condi- tions. These characters appear in the viscidity of liquids, and in the softness and adhesiveness of certain crystalline substances. Metaphosphate of soda, after fusion by heat, is a true glass er col- loid; but when this glass is maintained for a few minutes at a tem- perature some degrees under its point of fusion, the glass assumes a crystalline structure without losing its transparency. Notwith- standing this change, the low diffusibility cf the salt is preserved, with other characters of a colloid. Water in the form of ice has elready been represented as a similar intermediate form, both col- loid and crystalline, and in the first character adhesive and capable of reunion or ‘‘ regelation.”’ It is unnecessary to return here to the fact of the ready pectiza- tion of liquid silicic acid by alkaline salts, including some of ver sparing solubility, such as carbonate of lime, beyond stating that the presence of carbonate of lime in water was observed to be imcompa- tible with the coexistence of soluble silicic acid, till the proportion of the latter was reduced to nearly 1 in 10,000 water. Certain liquid substances differ from the salts in exercising little or no pectizing influence upon liquid silicie acid. But, on the other hand, none of the liquids now referred to appear to conduce to the preservation of the fluidity of the colloid, at least not more than the addition of water would do. Among these inactive diluents of silicie acid are found hydrochloric, nitric, acetic, and tartaric acids, syrup of sugar, glycerine, and alcohol. But all the liquid substances named, and many others, appear to possess an important relation to silicic acid, of a very different nature from the pectizing action of salts. ‘They are capable of displacing the combined water of the silicie acid hydrate, whether that hydrate is in the liquid or gelatinous condition, and give new substitution-products. A liquid compound of alcohol and silicic acid is obtained by adding alcohol to aqueous silicic acid, and then employing proper means to withdraw the water from the mixture. For that purpose the mixture contained in a cup may be placed over dry carbonate of potash or quicklime, within the receiver of an air-pump. Or a dialyzing bag of parchment-paper containing the mixed alcohol and silicie acid may be suspended in a jar of alcohol: the water diffuses away, leaving in the bag a liquid composed of alcohol and silicic acid only. A point to be attended to is, that the silicic acid should never be Prof. Graham on the Properties of Silicic Acid Se. 317 allowed to form more than 1 per cent. of the alcoholic solution, otherwise it may gelatinize during the experiment. If I may be allowed to distinguish the liquid and gelatinous hydrates of silicic acid by the irregularly formed terms of hydrosol and hydrogel of silicic acid, the two corresponding alcoholic bodies now introduced may be named the alcosol and alcogel of silicic acid. The aleosol of silicic acid, containing | per cent. of the latter, is a colourless liquid, not precipitated by water or salts, nor by contact with insoluble powders, probably from the small proportion of silicic acid present in solution. It may be boiled and evaporated without change, but is gelatinized by a slight concentration. The alcohol is retained less strongly in the alcoso! of silicic acid than water is in the hydrosol, but with the same varying force, a small portion of the alcohol being held so strongly as to char when the resulting jelly is rapidly distilled at a high temperature. Not a trace of silicic ether is found in any compound of this class. The jelly burns readily in the air, leaving the whole silicie acid in the form of a white ash. The alcogel, or solid compound, is readily prepared by placing masses of gelatinous silicic acid, containing 8 or 10 per cent. of the dry acid, in absolute alcohol, and changing the latter repeatedly till the water of the hydrogel is fully replaced by alcohol. The alcogel is generally slightly opalescent, and is similar in aspect to the hydrogel, preserving very nearly its original bulk. The following is the com- position of an alcogel carefully pre paved from a hy drog el which con- tained 9°35 per cent. of silicie acid :—. f= TTL TL ce la elle aa ds 88°13 1 5S opsltpade tale de Payile ee e t 0°23 PIE ACIO oe cs ne eae 11°64 100°00 Placed in water, the alcogel is gradually decomposed—aleohol diffu- sing out and water entering instead, so that a hydrogel is reproduced. Further, the alcogel may be made the starting-point in the forma- tion of a great variety of other substitution jellies of analogous con- stitution, the only condition required appearing to be that the new liquid and alcohol should be intermiscible, that is, interdiffusible bodies. Compounds of ether, benzole, and bisulphide of carbon have thus been produced. Again, from etherogel another series of silicic acid jellies may be derived, containing fluids soluble in ether, such as the fixed oils. The preparation of the glycerine compound of silicic acid is faci- litated by the comparative fixity of that liquid. When hydrated silicie acid is first steeped in glycerine, and then boiled in the same liquid, water distils over, without any change in the appearance of the jelly, except that when formerly opalescent it becomes now entirely colourless, and ceases to be visible when covered by the liquid. But a portion of the silicic acid is dissolved, and a glycerosol is produced at the same time as the glycerine jelly. A glycerogel prepared from a hydrate containing 9°35 per cent. of silicic acid, was found by a combustion analysis to be composed of 318 Royal Society :— RrryCerme ets te el Ope EVCGRT ee Sine oh ee 3°78 Siliere atid’) 2. oS ee eee 100°17 The glycerogel has somewhat less bulk than the original hydrogel. When a glycerine jelly is distilled by heat, it does not fuse, but the whole of the glycerme comes over, with a slight amount of decom- position towards the end of the process. The compound of sulphuric acid, sulphagel, is also interesting from the facility of its formation, and the complete manner in which the water of the original hydrogel is removed. A mass of hydrated silicic acid may be preserved unbroken if it is first placed in sulphu- ric acid diluted with two or three volumes of water, and then trans- ferred gradually to stronger acids, till at last it is placed in concen- trated oil of vitriol. The sulphagel sinks in the latter fluid, and may be distilled with an excess of it for hours without losing its transpa- rency or gelatinous character. It is always somewhat less in bulk than the primary hydrogel, but not more, to the eye, than one-fifth or one-sixth part of the original volume. This sulphagel is transparent and colourless. Whena sulphagel is heated strongly in an open ves- sel, the last portions of the monohydrated sulphuric acid in combi- nation are found to require a higher temperature for their expulsion than the boiling-point of the acid. The whole silicic acid remains behind, forming a white, opaque, porous mass, like pumice. A sul- phagel placed in water is soon decomposed, and the original hydrogel reproduced. No permanent compound of sulphuric and silicic acids, of the nature of a salt, appears to be formed in any circumstances. A sulphagel placed in alcohol gives ultimately a pure alcogel. Similar jellies of silicic acid may readily be formed with the monohydrates of nitric, acetic, and formic acids, and are all perfectly transparent. The production of the compounds of silicic acid now described indicates the possession of a wider range of affinity by a colloid than could well be anticipated. The organic colloids are no doubt in- vested with similar wide powers of combination, which may become of interest to the physiologist. ‘The capacity of a mass of gelatinous silicic acid to assume alcohol, or even oleine, in the place of water of combination, without disintegration or alteration of form, may per- haps afford a clue to the penetration of the albuminous matter of mem- brane by fatty and other insoluble bodies, which seems to occur in the digestion of food. Still more remarkable and suggestive are the fuid compounds of silicic acid. The fluid alechol-compound favours the possibility of the existence of a compound of the colloid albumen with oleine, soluble also and capable of circulating with the blood. eer The feebleness of the force which holds together two substances belonging to different physical classes, one being a colloid and the other a crystalloid, is a subject deserving notice. ‘When such a com- pound is placed in a fluid, the superior diffusive energy of the crystal- loid may cause its separation from the colloid. Thus, of hydrated Prof, Graham on the Properties of Silicie Acid &c. 319 silicie acid, the combined water (a crystalloid) leaves the acid (a col- loid) to diffuse into alcohol; and if the alcohol be repeatedly - changed, the entire water is thus removed, alcohol (another crystal- loid) at the same time taking the place of water in combination with the silicic acid. The liquid in excess (here the alcohol) gains entire possession of the silicic acid. The process is reversed if an alcogel be placed in a considerable volume of water. Then alcohol separates from combination, in consequence of the opportunity it possesses to diffuse into water ; and water, which is now the liquid present in excess, recovers possession of the silicic acid. Such changes illus- trate the predominating influence of mass. Even the compounds of silicic acid with alkalies yield to the decom- posing force of diffusion. The compound of silicic acid with 1 or 2 per cent. of soda isa colloidal solution, and, when placed ina dialyzer over water 7m vacuo to exclude carbonic acid, suffers gradual decom- position. The soda diffuses off slowly in the caustic state, and gives the usual brown oxide of silver when tested with the nitrate of that base. The pectization of liquid silicic acid and many other liquid col- loids is effected by contact with minute quantities of salts in a way which is not understood. On the other hand, the gelatinous acid may again be liquefied and have its energy restored by contact with a very moderate amount of alkali. The latter change is gradual, 1 part of caustic soda, dissolved in 10,000 water, liquefying 200 parts of silicic acid (estimated dry) in 60 minutes at 100° C. Gelati- nous stannic acid also is easily liquefied by a small proportion of alkali, even at the ordinary temperature. The alkali, too, after liquefying the gelatinous colloid, may be separated again from it by diffusion into water upon a dialyzer. The solution of these colloids, in such circumstances, may be looked upon as analogous to the solu- tion of insoluble organic colloids witnessed in animal digestion, with the difference that the solvent fluid here is not acid but alkaline. Liquid silicic acid may be represented as the “ peptone”? of gelati- nous silicic acid; and the liquefaction of the latter by a trace of alkali may be spoken of as the peptization of the jelly. The pure jellies of alumina, peroxide of iron, and titanic acid, prepared by dialysis, are assimilated more closely to albumen, being peptized by minute quan- tities of hydrochloric acid. Inquid Stannie and Metastannic Acids.—Liquid stannic acid is prepared by dialyzing the bichloride of tin with an addition of alkali, or by dialyzing the stannate of soda with an addition of hydrochloric acid. In both cases a jelly is first formed on the dialyzer ; but, as the salts diffuse away, the jelly is again peptized by the small proportion of free alkali remaining: the alkali itself may be removed by con- tinued diffusion, a drop or two of the tincture of iodine facilitating the separation. The liquid stannic acid is converted on heating it into liquid metastannic acid. Both liquid acids are remarkable for the facility with which they are pectized by a minute addition of hydrochloric acid, as well as by salts. _Lnquid Titanic Acid is prepared by dissolving gelatinous titanic acid 320 Royal Society. in a small quantity of hydrochloric acid, without heat, and placing the lhquid upon a dialyzer for several days. The liquid must not contain more than | per cent. of titanic acid, otherwise it sponta- neously gelatinizes, but it appears more stable when dilute. Both titanic and the two stannic acids afford the same classes of com- pounds with alcohol &c. as are obtained with silicic acid. Liquid Tungstic Acid.—The obscurity which has so long hung over tungstic acid is removed by a dialytic examination. It is in fact a remarkable colloid, of which the pectous form alone has hitherto been known. Liquid tungstic acid is prepared by adding dilute hydrochloric acidcarefully to a 5 per cent. solution of tung- state of soda, in sufficient proportion to neutralize the alkali, and then placing the resulting liquid on a dialyser. In about three days the acid is found pure, with the loss of about 20 per cent., the salts having diffused entirely away. It is remarkable that the purified acid is not pectized by acids or salts even at the boiling tempe- rature. Evaporated to dryness, it forms vitreous scales, like gum or gelatine, which sometimes adhere so strongly to the surface of the evaporating dish as to detach portions of it. It may be heated to 200° C. without losing its solubility or passing into the pectous state, but at a temperature near redness it undergoes a molecular change, losing at the same time 2:42 per cent. of water. When water is added to unchanged tungstic acid, it becomes pasty and adhesive like gum; and it forms a liquid with about one-fourth its weight of water, which is so dense as to float glass. The solution effervesces with carbonate of soda, and tungstic acid is evidently associated with silicic and molybdic acids. The taste of tungstic acid dissolved in water is not metallic or acid, but rather bitter and astringent. Solutions of tungstic acid containing 5, 20, 50, 66°5, and 79°8 per cent. of dry acid, possess the following densities at 19°, 1:0475, _ 1°2168, 1°8001, 2°396, and 3°243. Lvaporated in vacuo liquid tungstie acid is colourless, but becomes green in air from the deoxi- dating action of organic matter. Liquid silicic acid is protected from pectizing when mixed with tungstic acid, a cireumstance pro- bably connected with the formation of the double compounds of these acids which M. Marignec has lately described. Molybdic Acid has hitherto been known (like tungstic acid) only in the insoluble form. Crystallized molybdate of soda dissolved in water is decomposed by the gradual addition of hydrochloric acid in excess without any immediate precipitation. The acid liquid thrown upon a dialyzer may gelatinize after a few hours, but again liquefies spontaneously, when the salts diffuse away. After a diffusion of three days, about 60 per cent. of the molybdic acid remains behind in a pure condition. The solution of pure molybdic acid is yellow, astringent to the taste, acid to test-paper, and possesses much stabi- lity. The acid may be dried at 100°, and then heated to 200° without losing its solubility. Soluble molybdic acid has the same gummy aspect as soluble tungstic acid, and deliquesces slightly when exposed to damp air. Both acids lose their colloidality when digested with soda for a short time, and give a variety of crystallizable salts. Geological Society. 321 GEOLOGICAL SOCIETY. [Continued from p. 243. ] June 22, 1864.—W. J. Hamilton, Esq., President, in the Chair. 1. “ Onthe Fossiliferous Rocks of Forfarshire and their contents.” By James Powrie, Esq., F.G.S. Referring to his former paper for a detailed description of the lower members of the Forfarshire Old Red Sandstone, the author now gave a general sketch of the relations of the several beds, and then descriptions of the species of Crustacea and Fish oc- curring in them. ‘The latter belong to five genera, two of which (Uschnacanthus and Euthacanthus) are new. After discussing the nature of Parka decipiens, and shortly noticing the genera of Crus- tacea that occur in the same rocks, Mr. Powrie concluded his paper with a short synopsis of the distribution of the members of the Old Red Sandstone in Forfarshire, and a discussion respecting the sub-. division of that formation, in which he stated that Péerygotus, Parka decipiens, and Cephalaspis are always associated in the same beds, and extend through all the fossiliferous rocks of Forfarshire, instead of the latter characterizing a higher horizon than the others. 2. On the Reptiliferous Rocks and Foot-print Strata of the North-east of Scotland.” By Prof. R. Harkness, F.R.SS. L. & E., F:G.5. The author showed that the foot-print sandstones of Ross-shire constitute the upper portion of the Old Red Sandstone formation, and that the strata embraced in a line of section from the Nigg to Cambus Shandwick, from above the Gneiss to the foot-print sand- stones of Tarbet Ness inclusive, are conformable throughout, and are referable to each of the three divisions of the Old Red Sand- stone,—namely, the conglomerates and yellow sandstones (of a thick- ness of 1500 feet) belonging to the Lower Old Red Sandstone; the grey flaggy sandstones and shales of Geanies—the equivalent of the Caithness flags—containing Osteolepis, Coccostevs, and Acan- thodes, and thus referable to the Middle Old Red; thirdly, conform- able strata, consisting of conglomerates and foot-bearing and other sandstones appertaining to the higher members of the system. The foot-bearing sandstones have a thickness of 400 feet, and re- present the reptiliferous sandstones of the Elgin area, though not overlain by Cornstones as in that district. The author, in conclusion, remarked that though Stagonolepis is decidedly Teleosaurian in its affinities, it does not consequently mark a Mesozoic group of rocks; for Mastodontosaurie, which abound in the Trias, occur in the Coal-measures ; and stratigraphical evidence shows us that Teleosaurian crocodiles have a wider geo- logical range, since they are met with in the Old Red Sandstone. 3. “On some Bone- and Cave-deposits of the Reindeer-period in the South of France.” By John Evans, Esq., F.R.S., F.G.S. The deposits to which the author particularly called attention in 822 Geological Society :— this paper are those which have been, and are still being explored under the direction of MM. Lartet and Christy, and which were visited by him under the guidance of the latter gentleman and ac- companied by Mr. Hamilton, Prof. Rupert Jones, Capt. Galton, Mr. Lubbock, and Mr. Franks. Mr. Evans first gave a detailed description of the physical features of the valley of the Vézére, and of the contents of the caverns of Badegoule, Le Moustier, La Madelaine, Laugerie-Haute, Laugerie- Basse, the Gorge d’Enfer, and Les Eyzies, giving a list of the animal-remains discovered, which are for the most part of the same species from all the caverns. The author then discussed the antiquity of the deposits according to four methods of inquiry,—namely, from geological considerations with regard to the character and position of the caves; from the palzeontological evidence of the remains found in them; from the archeological character of the objects of human workmanship; and from a comparison with similar deposits in neighbouring districts in France; and he came to the conclusion that they belonged to a period subsequent to that of the Hlephas primigenius and Rhinoceros tichorhinus, but characterized by the presence of the Reindeer and some other animals now extinct in that part of Europe. 4. “On the Carboniferous Rocks of the Donetz and the Granite- gravel of St. Petersburg.” By Prof. J. Helmersen. (In a letter to Sir R. I. Murchison, K.C.B., F.R.S., F.G.S., &c.) This letter relates (1) to the discovery in the Donetz Mountains of additional beds of coal and of iron-ore; (2) to the proposed use of this coal for steam-purposes on the Volga; (3) to two geological expeditions to be sent out in 1864 for the purpose of surveying the Permian basin of Russia; and lastly, to the successful completion of an Artesian boring at St. Petersburg. In this well the following beds were passed through :—Alluvium, 88 ft. ; Silurian clay, 300 ft. ; sandstone, 137 ft.; bed of gravel, the result of the degradation of granite. 5. “On a supposed Deposit of Boulder-clay in North Devon.” By George Maw, Esq., F.G.S., F.L.S. A deposit of brown clay which occurs near Fremington, in North Devon, and has been worked for several years, was described by the author in this paper, and referred by him to the Boulder-clay forma- tion. The smallest amount of subsidence necessary for the deposi- tion of this clay at its present highest level would place a large area of Devonshire under water. Mr. Maw considered the raised beach at Croyd as being a much more recent deposit than the gravel just described; and in con- nexion with the question of the former submergence of Devonshire during the glacial period, he discussed the relation of the latter to a deposit of granite-drift gravel at Petrochstow, concluding that it could only have been transported thither during the submergence of the high ridges which intersect at right angles the country between the two deposits. Mr T. Belt on the Formation of Lakes by Ice-action. 3238 6. ‘“‘ On the former existence of Glaciers in the High Grounds of the South of Scotland.” By J. Young, M.D., F.R.S.E. The heights bordering the counties of Peebles and Dumfries are stated by the author to contain well-preserved remains of a group of Glaciers belonging to a later period than the Boulder-clay, and some of which have been already alluded to by Mr. Geikie and Mr. Chambers. Dr. Young then describes the physical geography of the region, grouping the several hills into three ranges—the Broad Law Range, the White Coomb Range, and Hartfell—from which certain glaciers formerly descended into the valleys ; and he further divides the glaciers into two classes, which he terms respectively the ‘‘ Social” and the ‘‘Solitary.”” ‘The author then describes the form and extension of the masses of detritus which he considers to be glacial débris, contrasting their characters with those of the patches of Boulder-clay occurring in the neighbourhood. Many indications of glaciers are;shown to be much obscured by the prevalence of peat in the district; but, in addition to the mo- raine matter, smoothed surfaces and roches moutonnées are occa- sionally seen. 7. “On the Formation and Preservation of Lakes by Ice-action.” By Thomas Belt, Esq. During a residence of two years in the province of Nova Scotia, the author observed the remarkable number of lakes, great and small, occurring there, sometimes in connected chains and some- times on the sides and tops of hills. The lake-basins are stated to be chiefly in extremely hard quartzites and metamorphosed schists, irregularly studded with masses of Boulder-clay, beneath which are seen scratches, grooves, &c., that have been produced by ice-action. | The author then describes all the phenomena in detail, and gives a résumé of the theory of their glacial origin, as propounded by Pro- fessor Ramsay, coming to the conclusion that in this way only can the facts be consistently explained. 8. “ A Sketch of the Principal Geological Features of Hobart, Tasmania.” By S. H. Wintle, Esq. The hills upon which Hobart is built, as well as those in the vicinity, are mostly composed of New (?) Red Sandstone, capped with Greenstone of variable composition and of great thickness in some places. The Carboniferous Limestone(?) is stated to be very extensively developed throughout the island, and to be very fossiliferous; the author describes its lithological characters, as well as those of the Devonian rocks and the Silurian slates of Mount Wellington, which last have, as yet, proved unfossiliferous; but he states that Mr. Gould has found a Calymene Blumenbachii in similar rocks in the interior. He then, after describing the Coal-formation of the island, and remarking upon the anthracitic nature of the coal, passes on to the ‘‘ Boulder Drift (?),”’ which consists of immense boulders, prin- cipally of felspathic trap and greenstone, imbedded in stiff clay in some parts, and in loam in others. The boulders are also associated S24 Intelligence and Miscellaneous Articles. with fragments of New Red Sandstone and nodular masses of Dolomite. The author concludes by describing the mode of occurrence, in the valley of the Derwent, of a marine deposit which he considers of Postpliocene age, and which is found at an elevation of upwards of 100 ft. above the sea-level, and at a distance of from 50 to 100 yards from the water’s edge—thus showing that the valley of the Derwent and the neighbouring country had been recently upheaved. XXXVIII. Intelligence and Miscellaneous Articles. ON THE EBULLITION OF WATER, AND ON THE EXPLOSION OF STEAM-BOILERS. BY M. L. DUFOUR. ASES, it is known, tend eminently to promote the vaporization of liquids with which they are in contact. But the superficial gaseous layer which adheres to solids, acting at first like gases themselves, is gradually removed by prolonged and successive heat- ing. When the solid surfaces are deprived of it, they no longer by their contact excite changes of condition, but become indifferent in the liquid. What confirms this view is the circumstance that, by maintain- ing or producing on the surface of bodies a gaseous layer, ebullition of a liquid is immediately produced if the temperature is suitable, and any retardation of ebullition is avoided. The following experi- ment realizes these conditions. ‘Two platinum wires, communica- ting with the outside, pass through a cork in which a thermometer fits, and dip in water. ‘They are connected with the two poles of a galvanic element, and a slight disengagement of gas, due to electro- lysis, takes place on their surface. Under these circumstances, and so long as the current passes, it 1s impossible to obtain the least retardation of boiling. If these wires cease to be connected with a battery, after some successive heatings and by diminishing the super- ficial pressure, retardations are produced similar to those mentioned above. If the current is then made to pass, ebullition is imme- diately produced. If the retardation is considerable (from 15 to 20 degrees), closing the circuit produces so abundant a production of vapour as to resemble a true explosion. ‘The vapour appears to break away with an effort from the liquid mass, and the vessel experi- ences concussions almost strong enough to breakit. This experiment, which has frequently succeeded in my hands with ordinary water, is more striking in the case of slightly acidulated water, for then the retardations are more pronounced. It is therefore, I think, a property of water to tend in most cases ~ to retain the liquid state, even when ebullition ought to take place, provided the boiling-point has been reached by a diminution of the superficial pressure after the liquid has been already heated, and after it has been in contact for some time with the solid substances of the vessel. This property is perhaps not without interest in its applica- tion to the explosions of steam-boilers. This formidable phenome- non is still enveloped in much obscurity. Various attempts have Intelligence and Miscellaneous Articles. 325 been made to explain it; among others, by saying that in a perfect calm, while the issue of vapour is suspended, everything being mo- tionless in the apparatus, aud all the dissolved air expelled, the water may accidentally become heated beyond the point corresponding to its pressure, and then if ebullition sets in, it suddenly furnishes a mass of vapour which breaks the envelopes. But the embarrassing circumstance, and the one found in most cases, is that the accident takes place without the heating having been continued, while the workmen and the machine were at rest, and when, from cooling, the pressure in the machine had diminished. ‘These conditions, almost always mentioned with surprise in these accidents, exhibit an un- doubted analogy with the experiments which I have described. Is it net possible that at a moment of repose, and while the heating has been discontinued, the cooling which sets in at first diminishes the pressure of vapour existing in the boiler? As water, in virtue of its great specific heat, cools very slowly, it retains for a longer time a temperature which ought to produce ebullition under this diminished pressure. This ebullition doubtless takes place most frequently in proportion as the diminution of pressure permits; but it may happen that, under exceptional circumstances, a retardation similar to that described above is produced, and then after a longer or shorter delay ebullition sets in, either spontaneously, or in consequence of some foreign disturbance. This ebullition ought to manifest the charac- ters many times observed in my apparatus, where the concussions raised the heavy support to which the retort was fixed. From the large quantity of water contained in a boiler, these strokes might well cause a fracture of the sides, and the disastrous effects of this kind of accidents. The explanation which I attempt to give acccunts, it is seen, fora boiler-explosion, even when heating has ceased, when all the machine is in a state of cooling, and the pressure has been diminished. Com- paring the details ordinarily noted in this kind of explosion with the conditions of the experiment above mentioned, it is impossible not to observe a striking analogy, if the hints above given are correct; and it would remain to find out the means of preventing these de- plorable accidents. No solid body by its contact seemed to me to determine ebullition with certainty at the desired point; and all of them at length and by repeated heating become inactive. Contact of gases, on the contrary, invariably provokes ebullition as soon as the temperature makes it possible. Hence, as M. Donny hasalready said, it is desirable permanently to produce gases in the interior of the boiler. Wires or platinum plates which dip in the water, and by which enters the current of even a feeble battery, would very provably be sufficient to prevent retardations of ebullition. P.S.—Since writing this Note, I have read (Cosmos, April 7, 1864) of a fact which agrees very well with this proposed theory of the explosion of boilers. This is the explosion at Aberdare, where two boilers burst. The water supplied appeared to contain a little sulphuric acid. Some pieces of the sides presented by Mr. Fairbairn to the Manchester 326 Intelligence and Miscellaneous Articles. Philosophical Society were deeply corroded from chemical action. The explosion has naturally been attributed to this attack of the sides by the acid, and doubtless an acidulated liquid ought to attack the sides. Now we know that sulphuric acid, even in very small quantity, imparts to water the property of undergoing retardations of ebullition much more considerable and much more frequent than those of pure water. If, then, boiler explosions arise from a retardation in the ebullition of water when the pressure diminishes in the boiler, as I explain in my Note, it is seen that the two accidents in England are easily explained, inasmuch as the feeding water contained a little acid.—Comptes Rendus, June 6, 1864. APPLICATION OF ZEIODELITE. Zeiodelite is a mixture prepared by melting together 20 to 30 parts of roll sulphur with 24 parts of powdered glass or pumice, and which forms a mass as hard as stone, that resists the action of water and of the strongest acids. Prof. R. Bottger recommends it, therefore, for making water- and air-tight cells for galvanic batteries.—Pog- gendorff’s Annalen, July 1864. DETERMINATIONS OF TEMPERATURE IN THE DEPTH OF SOME BAVARIAN MOUNTAIN LAKES. In the Sitzungsberichte of the Royal Bavarian Academy of 1862, Prof. Jolly describes a bathometer and aminimum thermometer of his invention, and gives some observations of the temperature at various depths in the Konigssee, the Obersee, and the Walchensee, which may find a place here. Depth in Temperature Depth in Temperature metres. in degrees C. metres. in degrees C. Konigssee, 1862, Aug. Obersee, 1862, Sept. 0 14-9-15-2 0 151 22°6 7°89 27°1 7:55 26°8 6°61 31:4 9-12 37'8 6°58 62°3 6:59 67:2 6:00 95°5 5°83 Walchensee, 1862, Oct. 104°3 5°81 153°3 5°38 0 15:0 163-2 5:50 58°3 6°76 198-0 5-44 97°6 6:07 2041 5-52 98-6 6°12 216-5 5°34 107:0 5°91 248°8 SIV) Hence in these lakes (as in those of Switzerland) the temperature approaches, without actually attaining, that of the maximum density of water (from inadequate depth), and without following any regular progress in its decrease.—Poggendorff’s Annalen, August 1864. Intelligence and Miscellaneous Articles. 327 ON THE METEORITE OF ALBARETO IN THE MODENESE. BY DR. W. HAIDINGER*. This meteorite, and the pamphlet by the Jesuit Dominico Troili describing it, have been mentioned by Chladni (1798 and 1819), by Ende (1804), and by Sir D. Brewster (Edinburgh Journal of Science, 1819). Chladni, whose careful inquiries at Modena in 1819 could not make out any trace of this stone, thought it definitively lost. But lately a specimen of it was found to exist in the University Museum of Modena; and of this, Dr. Hérnes, kindly assisted by Messrs. Greg, Senoner, Bianconi, and Bombici, obtained for the Imperial Museum of Vienna a fragment of 13°31 grammes in weight. It is tufaceous in aspect, dark grey, with numerous globular concretions— some greenish grey (as the Piddingtonite of Skalka, or the Chladnite of Bishopville), others dark grey or black, one of them conspicuous for its less density, yellowish-grey tint, dark-brown crust, and atoms of native iron disseminated through it. The particles of native and protosulphuretted iron irregularly distributed through the whole mass are sometimes discernible to the unaided eye; in one place two brownish-black globules are united by metallic iron in such a way as to allow us to suppose the group to be a fragment of a larger piece of native iron including globules of silicates, like the Hima- layan iron. The globules are easily detached from the surrounding mass. The outer surface, offering the impressions common to all meteorites, is covered, on a surface of about 25 square lines, with a blackish-brown, nearly opake crust. In general aspect the Albareto meteorite stands next to those of Benares, Trenzano, and Weston. Its density, at 15° R., is 3°344. The sulphuretted iron of the me- teorites, generally passing under the denomination of magnetic iron- pyrites, is, according to Prof. Rammelsberg, a mechanical compound of protosulphuretted iron (75°37 percent.), sulphuretted copper (0°71 per cent.), chromate of iron (2°83 per cent.), and nickeliferous iron (19°83 per cent.), of 4°787 density, yellowish brown, soluble in acids without residuous sulphur, and magnetic in consequence of the nickel contained in it. The sulphuretted iron, in its state of purity, as it occurs in the Garnallee meteorite, in grains of the size of a pea, is, according to Prof. Wohler, a combination of 1 atom of iron with i atom of sulphur (Fe S or iron 63°64, sulphur 36°36). For this sulphuret, hitherto not known to exist among the minerals compo- sing the terrestrial crust, Dr. Haidinger proposes the denomination of Troilite (commemorative of the first describer of the Albareto meteorite), and the following mineralogical characters :—amor- phous, in minute particles, disseminated through the lithoid sub- stance of meteorites, metallic brightness, bronze-brown, streak black, hardness 4, density 4°5-4°6; chemical formula, FeS. Ac- cording to Troili’s pamphlet (Modena, 1766), the meteorite in ques- tion may have originally had a weight of about 25 lbs. It fell in the middle of July 1766, 5" p.m., the sky being serene, but covered westward with heavy clouds, with frequent thunder and lightuing. Witnesses assert its fall to have been preceded by a sound resem- * Communicated by Count Marschall. 328 Intelligence and Miscellaneous Articles, bling a cannonade and the hissing of a cannon-ball through the air ; some describe it as having been in a state of incandescence, while others saw it dark and smoking. It penetrated intothe ground to the depth of less than a ‘ braccio ” (about 21 Vienna feet), and was dug out still hot, spreading a sulphurous smell, and covered with a crust. Troili, although quite uncertain as to the nature of the phenomenon, which he ascribes to a subterraneous commotion having thrown the stone into the air, whence it fell again to the ground, was evidently highly anxious to state its reality and every circumstance con- cerning it. ‘This, at a time when the scepticism about these phe- nomena was such that anyone who asserted their reality could only expect incredulity and even ridicule, gave a most meritorious proof of moral courage. Supposing the Albareto meteorite to have fallen to the ground in a nearly vertical direction, and to have come from the west (as did the sounds preceding its fall), its point of de- parture may be traced to the constellation of Leo, well known to be the point from which the fallmg stars of the November epoch pro- ceed, Its trajectory may have been a segment of the elliptical orbit of a whole swarm of bodies moving within the sphere of terres- trial attraction on the branch of a hyperbolic orbit through cosmical space. Dr. Haidinger on this occasion recalled to mind his hypo- thesis on the cause of the high temperature in meteoric masses—pass- ing through the terrestrial atmosphere and generating heat by rapid compression, in the same way as in Prof. Mallet’s experiment, suc- cesstully repeated before the Academy of Paris in 1803. Of late years (1840-57) the experimental researches of Messrs. Bianconi, Thomson, Joule, and Tyndall have shown that the temperature of a thin string of water rapidly forced through a narrow spiral tube rises from 1° F’. to 4° F., that a solid body surrounded by a rapid air-current was more heated than the ambient air, and that, if the rapidity of the air-current be brought to 1780 feet in a second, this difference of temperature may be raised to 137°. Even in an atmo- sphere rarefied to the utmost limits, any solid progressing within it at the rate of meteorites (6-30 miles a second) would come to a far higher temperature, still increased by the transformation of active forces (light, electricity, magnetism, &c.) into heat, in consequence of the resistance opposed to the rapid career of such a body. Prof. Bunsen, in a note on the Meteoric Iron of Atacama (Leonhard and Bronn’s Jahrbuch, 1857, p. 265), calculated the loss of active force during the fall of a solid coming into the terrestrial atmosphere with a pla- netary celerity to be sufficient to heat it to 1,000,000° C. Supposing 925. of this heat to be lost in the ambient medium, such a body would still touch the ground with a temperature of 2000° C. What Dr. Haidinger has done for meteorites, Prof. Tyndall has ascertained for hailstones—the existence of a facial plane with inci- pient fusion in consequence of the condensation of the air, and of a dor- sal one, on which the rarefaction of the air has caused the congelation of atmospheric water. Similar circumstances have been observed by Prof. Goth, on hailstones fallen at Gratz in the summer of 1846 (Wiener Naturwissenschaftliche Abhandlungen, published by Haidin- ger, vol. i. p. 91).—Jmp. Acad. Sc. Vienna, March 27, 1864. arc r - 4 4 a : Aa 1BR a THE LONDON, EDINBURGH, ann DUBLIN PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. [FOURTH SERIES.] NOVEMBER 1864, XXXIX. On Luminous and Obscure Radiation. By Joun Tynvatt, F.R.S., &c.* 1. Gr WILLIAM HERSCHEL discovered the obscure rays of the sun, and proved that the position of maximum heat was beyond the red of the solar spectrum}. Forty years subsequently Sir John Herschel succeeded in obtaining a thermo- graph of the calorific spectrum, and in giving striking visible evi- dence of its extension beyond the redf. Melloni proved that an exceedingly large proportion of the emission from a flame of oil, of alcohol, and from incandescent platinum heated by a flame of alcohol, is obscure$. Dr. Akin inferred from the paucity of lumi- nous rays evident to the eye, and a like paucity of extra-violet rays, as proved by the experiments of Dr. Miller, that the radiation from a flame of hydrogen must be mainly extra-red ; and he con- cluded from this that the glowing of a platinum wire in a hy- drogen-flame, as also the brightness of the Drummond light in the oxyhydrogen-flame, was produced by a change in the period of vibration ||. By a different mode of reasoning I arrived at the same conclusion myself, and published the conclusion subse- quently]. 2. A direct experimental demonstration of the character of the radiation from a hydrogen-flame was, however, wanting, and this want I have sought to supply. I had constructed for me, by Mr. Becker, a complete rock-salt train of a size sufficient to * Communicated by the Author. T Phil. Trans. 1800. { Phil. Trans. 1840. I hope very soon to be able to turn my attention to the remarkable results described in Note III. of Sir J. Herschel’s paper. § La Thermochrose, p. 304. { Phil. Trans. vol. cliv. p. 327. || Reports of the British Association, 1863. Phil. Mag. S. 4. Vol. 28. No. 190. Nov. 1864. Z 330 Prof. Tyndall on Luminous and Obscure Radiation. permit of its being substituted for the ordinary glass train of a Duboscq’s electric lamp. A double rock-salt lens placed in the camera rendered the rays parallel; the parallel rays then passed through a slit, and a second rock-salt lens placed without the camera produced, at an appropriate distance, an image of this slit. Behind this lens was placed a rock-salt prism, while late- rally stood a thermo-electric pile intended to examine the spec- trum produced by the prism. Within the camera of the electric lamp was placed a burner with a single aperture, so that the flame issuing from it occupied the position usually taken up by the coal points. This burner was connected with a T-piece, from which two pieces of india-rubber tubing were carried, the one toa large hydrogen-holder, the other to the gas-pipe of the labo- ratory. It was thus in my power to have, at will, either the gas- flame or the hydrogen-flame. When the former was employed, I had a visible spectrum, which enabled me to fix the thermo- electric pile in its proper position. To obtain the hydrogen- flame, it was only necessary to turn on the hydrogen until it reached the gas-flame and was ignited ; then to turn off the gas and leave the hydrogen-flame behind. In this way, indeed, the one flame could be substituted for the other withcut opening the door of the camera, or producing any change in the positions of the source, the lenses, the prism, and the pile. 3. The thermo-electric pile employed is a beautiful instrument constructed by Ruhmkorff. It belongs to my friend Mr. Gassiot, and consists of a single row of elements properly mounted and attached to a double brass screen. It has in front two silvered edges, which, by means of a screw, can be caused to close upon the pile so as to render its face as narrow as desirable, reducing it to the width of the finest hair, or, indeed, shutting it off altogether. By means of a small handle and long screw, the plate of brass and the pile attached to it can be moved gently to and fro, and thus the vertical slit of the pile can be caused to traverse the entire spectrum, or to pass beyond it in both diree- tions. The width of the spectrum was in each case equal to the length of the face of the pile, which was connected with an ex- tremely delicate galvanometer. 4, 1 began with a luminous gas-flame. The spectrum being cast upon the brass screen (which, to render the colours more visible, was covered with tinfoil), the pile was gradually moved in the direction from blue to red, until the deflection of the gal- vanometer became a maximum. To reach this it was necessary to pass entirely through the spectrum and a little way beyond the red; the deflection then observed was 30°. When the pile was moved in either direction from this position, the deflection diminished. Prof. Tyndall on Luminous and Obscure Radiation. 331 5. The hydrogen-flame was now substituted for the gas-flame ; the visible spectrum disappeared, and the deflection fell to 12°. Hence, as regards rays of this particular refrangibility, the emis- sion from the luminous gas-flame was two-and-a-half times that from the hydrogen-flame. 6. The pile was now moved to and fro, and the movement in both directions was accompanied by a diminished deflection. Twelve degrees, therefore, was the maximum deflection for the hydrogen-flame ; and the position of the pile, determined pre- viously by means of the luminous flame, proves that this deflec- tion was produced by extra-red undulations. I moved the pilea little forwards, so as to reduce the deflection from 12° to 4°, and then, in order to ascertain the refrangibility of the rays which produced this small deflection, I relighted the gas. The recti- linear face of the pile was found invading the red. When the pile was caused to pass successively thr ough positions correspond- ing to the various colours of the spectrum, and to its extra-violet rays, no measurable deflection was produced by the hydrogen- flame. 7. I next placed the pile at some distance from the invisible spectrum of the flame of hydrogen, and fe/t for the spectrum by moving the pile to and fro. Having found it, I without diffi- culty ascertained the place of maximum heating. Changing nothing else, I substituted the Juminous flame for the non-lumi- nous one; the position of the pile when thus revealed, was beyond the red. 8. It is thus proved that the radiation from a hydrogen- flame is sensibly extra-red. The other constituents of the radiation are so feeble as to be thermally insensible. Hence, when a body is raised to incandescence by a hydrogen-flame, the vibrating periods of its atoms must be shorter than those to which the radiation of the flame itself is due. 9. The falling of the deflection from 80° to 12° when the hy- drogen-flame was substituted for the gas-flame is doubtless due to the absence of all solid matter in the former. We may, how- ever, introduce such matter, and thus make the radiation origi- nating in the hydrogen- flame much greater than that of the gas- flame. A spiral of platinum wire plunged in the former gave a maximum deflection of 52° at a time when the maximum deflection of the gas-flame was only 33°. 10, It is mainly by convection that the hydrogen-flame dis- perses its heat: though its temperature is higher, its sparsely- scattered molecules are not able to cope, in radiant ener gy, with Z 2 So2 Prof. Tyndall on Luminous and Obscure Radiation. the solid carbon of the luminous flame. The same is true for the flame of a Bunsen’s burner; the moment the air (which destroys the solid carbon-particles) mingles with the gas-flame, the radiation falls considerably. Conversely, a gush of radiant heat accompanies the shutting out of the air which deprives the gas-flame of its lummosity. When, therefore, we introduce a platinum wire into a hydrogen-flame, or carbon-particles into a Bunsen’s flame, we obtain not only waves of a new period, but also convert a large portion of the heat of convection into the heat of radiation. 11. The action was still very sensible when the distance of the pile from the red end of the spectrum on the one side was as great as that of the violet rays on the other, the heat-spectrum thus proving itself to be at least as long as the light-spectrum. 12. Bunsen and Kirchhoff have proved that, for incandescent metallic vapours, the period of vibration is, within wide limits, independent of temperature. My own experiments with flames of hydrogen and carbonic oxide as sources, and with cold aqueous vapour and cold carbonic acid as absorbing media, point to the same conclusion*. But in sod metals augmented temperature introduces waves of shorter periods into the radiation. It may be asked, “ What becomes of the long obscure periods when we heighten the temperature? Are they broken up or changed into shorter ones, or do they maintain themselves side by side with the new vibrations?” The question is worth an experimental answer. 13. A spiral of platinum wire suitably supported was placed within the camera of the electric lamp at the place usually occu- pied by the carbon points. This spiral was connected with a voltaic battery; and by varying the resistance to the current, it was possible to raise the spiral gradually from a state of darkness to an intense white heat. Jaising it to a white heat in the first instance, the rock-salt train was placed in the path of its rays, and a brilliant spectrum was obtained. The pile was then moved into the region of obscure rays beyond the red of the spectrum. Altering nothing but the strength of the current, the spiral was reduced to darkness, and lowered in temperature till the deflec- tion of the galvanometer fell to 1°. Our question is, “ What becomes of the waves which produce this deflection when new ones are introduced by augmenting the temperature of the spiral ?” 14, Causing the spiral to pass from this state of darkness through various degrees of incandescence, the following deflec- tions were obtained : — * Phil, Trans, vol. cliv. p. 327. Prof. Tyndall on Luminous and Obscure Radiation. 333 Taste I. Appearance of spiral. Deflection by obscure rays. oO 5 FEE eee nil toon os aac ae, 5” es ia mp ee Ree EO Mamiered ss to ey ele Or: Whulered oy. kn ace coe eee ERI oe a te td ec te OO ee eg ge we BME TE fe ee oe igs A Meaty white (6) 2°65 = D406 Mintiewhite o° . °°. 60:0 15. The deflection of 60° here obtained is equivalent to 122 of the first degrees of the galvanometer. Hence the intensity of the obscure rays in the case of the full white heat is 122 times that of the rays of the same refrangibility emitted by the dark spiral used at the commencement. Or, as the imtensity is pro- portional to the square of the amplitude, the height of the ethe- real waves which produced the last deflection was eleven times that of the waves which produced the first. The wave-length, of course, remained the same throughout. 16. The experimental answer, therefore, to the question above proposed is, that the amplitude of the old waves is augmented by the same accession of temperature that gives birth to the new ones. ‘The case of the obscure rays is, in fact, that of the lumi- nous ones (of the red of the spectrum, for example), which glow with augmented intensity as the temperature of the radiant source is heightened. 17. In my last memoir* I demonstrated the wonderful trans- parency of the element iodine to the extra-red undulations. A per- fectly opake solution of this substance was obtained by dissolving it in bisulphide of carbon, and it was shown in the memoir referred to that a quantity of iodine sufficient to quench the light of our most brilliant flames transmitted 99 per cent. of the radiation from a flame of hydrogen. 18. Fifty experiments on the radiant heat ofa hydrogen-flame, recently executed, make the transmission of its rays, through a quantity of iodine which is perfectly opake to light, 100 per cent. To the radiation from a hydrogen-flame the dissolved iodine is therefore, according to these experiments, perfectly transparent. 19. It is also sensibly transparent to the radiation from solid bodies heated under incandescence. 20. It is also sensibly transparent to the obscure rays emitted by luminous bodies. * Phil. Trans. vol. cliv. p.327. [This memoir will appear in the Decem- ber Number of the Philosophical Magazine. | 334 Prof. Tyndall on Luminous and Obscure Radiation. 21. To the mixed radiation which issues from solid bodies at a very high temperature, the pure bisulphide of carbon is also eminently transparent. Hence, as the bisulphide of carbon in- terferes but slightly with the obscure rays issuing from a highly luminous source, and as the dissolved iodine seems not at all to interfere with them, we have in a combination of both substances a means of almost entirely detaching the purely thermal rays from the luminous ones. , 22. Ifvibrations ofa long period, established when the radia- ting body is at a low temperature, maintain themselves, as indicated in paragraph 14, side by side with the new periods © which augmented temperature introduces, it would follow that a body once pervious to the radiation from any source must always remain pervious to it. We cannot so alter the character of the radiation that a body once in any measure transparent to it shall become quite opake to it. We may, by augmenting the temperature, diminish the percentage of the total radiation trans- mitted by the body; but inasmuch as the old vibrations have their amplitudes enlarged by the very accession of temperature which produces the new ones, the total quantity of heat of any given refrangibility transmitted by the body must increase with increase of temperature. 23. This conclusion is thus experimentally illustrated. A cell with parallel sides of polished rock-salt was filled with the solu- tion of iodine, and placed in front of the camera within which was the platinum spiral. Behind the rock-salt cell was placed an ordinary thermo-electric pile, to receive such rays as had passed through the solution. The rock-salt lens was in the camera in front, but a small sheaf only of the parallel beam emergent from the lamp was employed. Commencing at a very low dark heat, the temperature was gradually augmented to full incandescence with the following results :— TasueE II. Appearance of spiral. Deflection. Darke) pias TV ee ey Dark but hotter’. 3.9. 5 8 Dark bat stilvhotter’: 2s" 3 Dark but still hotter. . . 10 Feeblewteds wail cdinceortinu us LD Dial red chi écsidnae ae ee ee Red) .is 4 2 pls er eh eta Full reds. Camecpaaededere 1245 Bright..vedives \ us nanan hile eee Very brightredia nic, vn aGe Nearly white ejpa. wu --0¢ 69 WIIte 4 cilia sed hay (ondkeciseatenics Intense witite a ee 80 Prof, Tyndall on Luminous and Obscure Radiation. 305: 24. To the luminous rays from the intensely white spiral the solution was perfectly opake; but though by the introduction of such rays the transmission, as expressed in parts of the total radiation, was diminished, the quantity absolutely transmitted was enormously increased. The value of the last deflection is 440 times that of the first; by raising therefore the platinum spiral from darkness to whiteness, we augment the intensity of the obscure rays which it emits in the ratio of 1 : 440. 25. A rock-salt cell filled with the transparent bisulphide of carbon was placed in front of the camera which contained the platinum spiral raised to a dazzling white heat. The trans- parent liquid was then drawn off and its place supplied by the solution of iodine. The deflections observed in the respective cases are as follows :— Radiation from White-hot Platinum. Through transparent CS?. Through opake solution. 73:9 73:0 73:8 72:9 All the luminous rays passed through the transparent bisulphide, ~ none of them passed through the solution of iodine. Still we see what a small difference is produced by their withdrawal. The actual proportion of luminous to obscure, as calculated from the above observations, may be thus expressed :— 26. Dividing the radiation from a platinum wire raised to a dazzling whiteness by an electric current into twenty-four equal parts, one of these parts is luminous and twenty-three obscure. 27. A bright gas-flame was substituted for the platinum spiral, the top and bottom of the flame were shut off, and its most brilliant portion chosen as the source of rays. The result of forty experiments with this source may be thus expressed :— 28. Dividing the radiation from the most brilliant portion of a flame of coal-gas into twenty-five equal parts, one of those parts ts luminous and twenty-four obscure. - 29. I next examined the ratio of obscure to luminous rays in the electric light. A battery of fifty cells was employed, and the rock-salt lens was used to render the rays from the coal points parallel. To prevent the deflection from reaching an Inconvenient magnitude, the parallel rays were caused to issue from a circular aperture 0°1 of an inch in diameter, and were sent alternately through the transparent bisulphide and through the opake solution. It is not easy to obtain perfect steadiness on the part of the electric light ; but three experiments carefully executed gave the following deflections :— 306 Prof. Tyndall on Luminous and Obscure Radiation. Radiation from Electric Light.—Experiment No. I. Through transparent CS*. Through opake solution. 72°°0 70°:0 Experiment No. Il. 76°°5 75°0 Experiment No. III. vie bas 76°°5 Calculating from these measurements the proportion of lumi- nous to obscure heat, the result may be thus expressed :— 30. Dividing the radiation from the electric light emitted by car- bon points, and excited by a Grove's battery of forty cells, mto ten equal parts, one of those parts is luminous and nine obscure. 31. The results may be thus presented in a tabular form :— Taste I]].—Radiation through dissolved Iodine. Source. Absorption. Transmission. Park spiral Se 2 0 100 Lampblack at 212° Fahr. 0 100 Red-hot spical; . 5 oie pO 100 Hydrogen-flame . . ZU 100 Oi fiamte o Ve" es 3 97 Gas-flame . . ngewe! 96 White-hot spiral . tke te 95°4 dilectrie Ticht, 7°": eee 90 Repeated experiments may slightly alter these results, but they are extremely near the truth. 32. Having thus in the solution of iodine found a means of almost perfectly detaching the obscure from the luminous heat- rays of any source, we are able to operate at will upon the former. Here are some illustrations :—The rock-salt lens was so placed in the camera that the coal points themselves and their image beyond the lens were equally distant from the latter. A battery of forty cells being employed, the track of the cone of rays emer- gent from the lamp was plainly seen in the air, and their point of convergence therefore easily fixed. The cell containing the opake solution was now placed in front of the lamp. The lumi- nous cone was thereby entirely cut off, but the intolerable tem- perature of the focus, when the hand was placed there, showed that the calorific rays were still transmitted. Thin plates of tin and zinc were placed successively in the dark focus and speedily fused; matches were ignited, gun-cotton exploded, and brown paper set on fire. Employing the iodine solution and a battery of sixty of Grove’s cells, all these results were readily obtained Prof. Tyndall on Luminous and Obscure Radiation. aan with the ordinary glass lenses attached to Duboscq’s electric lamp. They cannot, I think, fail to give pleasure to those who repeat the experiments. It is extremely interesting to ob- serve in the middle of the air of a perfectly dark room a piece of black paper suddenly pierced by the invisible rays, and the burning ring expanding on all sides from the centre of ignition. 33. On the 15th of this month I made a few experiments on solar light. The‘heavens were not free from clouds, nor the London atmosphere from smoke, and at best I obtained only a portion of the action which a clear day would have given me. I happened to possess a hollow lens, which I filled with the con- centrated solution of iodine. Placed in the path of the solar rays, a faint red ring was imprinted on a sheet of white paper held behind the lens, the ring contracting to a famt red spot when the focus of the lens was reached. It was immediately found that this ring was produced by the light which had pene= trated the thin rim of the liquid lens. Pasting a zone of black paper round the rim, the ring was entirely cut off and no visible trace of solar light crossed the lens. At the focus, whatever hght passed would be intensified nine hundredfold; still even here no light was visible. 34. Not so, however with the sun’s obscure rays; the focus was burning hot. A piece of black paper placed there was in- stantly pierced and set on fire; and by shifting the paper, aperture after aperture was formed in quick succession. Gun- powder was also exploded. In fact we had in the focus of the sun’s dark rays a heat decidedly more powerful than that of the electric light similarly condensed, and all the effects obtained with the former could be obtained im an increased degree with the latter. 35. I introduced a plano-convex lens of glass, larger than the opake lens just referred to, into the path of the sun’s rays. The focus on white paper was of dazzling brilliancy ; and in this focus the results already described were obtained. I then introduced a cell containing a solution of alum in front of the focits. The intensity of the light at the focus was not sensibly changed ; still these almost intolerable visual rays, aided as they were by a considerable quantity of invisible rays which had also passed through the alum, were incompetent to produce effects which were obtained with ease in the perfectly dark focus of the opake lens. 36. Thinking that this reduction of power might be due to the withdrawal of heat by reflexion from the sides of the glass cell, I put in its place a rock-salt cell filled with the opake solu- tion. Behind this cell the rays manifested the power which they exhibited in the focus of the opake lens. 338 Prof. Tyndall on Luminous and Obscure Radiation. 37. The rendering of metals incandescent by obscure rays has not yet been accomplished. This is a question on which Dr. Akin has been engaged for some years, and -it is not my intention to publish anything relating to it until the very pro- mising arrangements which he has devised have had a sufficient trial. 38. Melloni’s experiments led him to conclude that rock- salt transmits obscure and luminous rays equally well, and that a solution of alum of moderate thickness entirely intercepts the invisible rays, while it allows all the luminous ones to pass. Hence the difference between the transmissions of rock-salt and alum ought to give the obscure radiation. In this way Melloni found that 10 per cent. only of the radiation from an oil-flame consists of luminous rays. The method above employed proves that the proportion of lumimous heat to obscure, in the case of an oil-flame, is probably not more than one-third of what Melloni made it. 39. In fact this distinguished man clearly saw the possible imaccuracy of the conclusion that none but luminous rays are transmitted by alum ; and the following experiments justify the clauses of limitation which he attached to his conclusion :— The solution of iodine was placed in front of the electric lamp, the luminous rays being thereby intercepted. Behind the rock- salt cell containing the opake solution was placed a glass cell, empty in the first instance. The deflection produced by the obscure rays which passed through both produced a defiec- tion of 80°. The glass cell was now filled with a concentrated solution of alum ; the deflection produced by the obscure rays passing through both solutions was 50°. Calculating from the values of these deflections, it was found that of the obscure heat emeryent from the solution of iodine, and from the side of the glass cell, 20 per cent. was transmitted by the alum. 40. A point of very considerable importance forces itself upon our attention here—namely the vast practical difference which may exist between the two phrases, ‘‘ obscure rays,” and “rays from an obscure source.” Many writers seem to regard these phrases as equivalent to each other, and are thus led into grave errors. A stratum of alum solution >:th of an inch in thickness 1s, ac- cording to Melloni, entirely opake to the radiation from all bodies heated under incandescence. In the foregoing experiments the layer of alum solution traversed by the obscure rays of our lumi- nous source was thirty times the thickness of the layer which Prof. Tyndall on Luminous and Obscure Radiation. 309 Melloni found sufficient to quench all rays emanatiug from cb- scure sources. 41. There cannot be a doubt that the invisible rays which have shown themselves competent to traverse such a thick- ness of the most powerful adiathermic liquid yet discovered are also able to pass through the humours of the eye. The very careful and interesting experiments of M. Janssen *, prove that the humours of the eye absorb an amount of radiant heat exactly equal to that absorbed by a layer of water of the same thickness, and in our solution the power of alum is added to that of water. Direct experiments on the vitreous humour of an ox lead me to conclude that one-fifth of the obscure rays emitted by an intense electric light reaches the retina ; and mas- much as in every ten equal parts of the radiation from an electric lamp nine consist of obscure rays, it follows that, in the case of the electric light, nearly two-thirds of the whole radiant energy which actually reaches the retina is competent to excite vision. With a white-hot platinum spiral as source, the mean of four good experiments gave a transmission of 11-7 per cent. of the obscure heat of the spiral through a layer of distilled water 1°2 inch in thickness. A larger proportion no doubt reaches the retina. 42. Converging the beam from the electric lamp by a glass lens, I placed the opake solution of iodine before my open eye, and brought the eye into the focus of obscure rays; the heat was immediately unbearable. But it seemed to me that the unpleasant effect was mainly due to the action of the obscure rays upon the eyelids and other opake parts round the eye. I therefore cut, in a card, an aperture somewhat larger than the pupil, and allowed the concentrated calorific beam to enter my eye through this aperture. The sense of heat entirely disap- peared. Not only were the rays thus received upon the retina incompetent to excite vision, but the optic nerve seemed un- conscious of their existence even as heat. What the consequences would have been had I permitted the luminous third of the condensed beam to enter my eye, I am not prepared to say, nor should I like to make the experiment. 43, On a tolerably clear night a candle-flame can be readily seen at the distance of a mile. The intensity of the electric light used by me is 650 times that of a good composite candle, and as the non-luminous radiation from the coal points which reaches the retina is equal to twice the luminous, it follows that at a common distance of a foot, the energy of the invisible rays * Annales de Chimie et de Physique, tom. Ix. p. 71. T M. Franz has shown that a portion of the sun’s obscure rays reach the retina. ; | 340 Prof. Tyndall on Luminous and Obscure Radiation. of the electric light which reach the optic nerve, but are incom- petent to provoke vision, is 1300 times that of the hight of a candle. But the intensity of the candle’s hght at the distance of a mile is Jess than one twenty-millionth of its intensity at the distance of a foot, hence the energy which renders the can- dle perfectly visible a mile off would have to be multiplied by 1300 x 20,000,000, or by twenty-six thousand millions, to bring it up to the intensity of that powerless radiation which the eye receives from the electric light at a foot distance. Nothing, I think, could more forcibly illustrate the special relationship which subsists between the optic nerve and the oscillating periods of luminous bodies. The nerve, like a musical string, responds to the periods with which it is in accordance, while it refuses to be excited by others of vastly greater energy which are not in unison with its own. 44, By means of the opake solution of iodme, I have already shown that the quantity of lummons heat emitted by a bright red platinum spiral is immeasurably small*. Here are some determinations since made with the same source of heat and a solution of iodine in iodide of ethyle, the strength and thickness of the solution being such as entirely to intercept the luminous rays. | : Radiation from Red-hot Platmum Spiral. Through transparent liquid. Through opake solution. 2) 43-7 43°7 43-7 43-7 These experiments were made with exceeding care, and all the conditions were favourable to the detection of the slightest difference in the amount of heat reaching the galvanometer ; still the quantity of heat transmitted by the opake solution was found to be the same as that transmitted by the transparent one. In other words, the luminous radiation intercepted by the former, though competent to excite vividly the sense of vision, was, when expressed in terms of actual energy, absolutely immeasurable. 45, And here we have the solution of various difficulties which from time to time have perplexed experimenters. When we see a vivid light incompetent to affect our most delicate thermo- scopic apparatus, the idea naturally presents itself that hight and heat must be totally different things. The pure light emerging from a combination of water and green glass, even when rendered intense by concentration, has, according to Melloni, no sensible heating power}. The light of the moon is alsoa case in point. Concentrated by a polyzonal lens more than a yard in diameter * Phil. Trans. vol. cliy. p. 327. + Taylor’s Scientific Memoirs, vol. i. p. 392, Mr. D. Forbes on Evansite, a new Mineral Species. 341 upon the face of his pile, it required all Mellomi’s acuteness to nurse the calorific action up to a measurable quantity. Such experiments, however, demonstrate, not that the two agents are dissimilar, but that the sense of vision can be excited by an amount of force almost infinitely small. 46. Here also we are able to offer a remark as to the appli- eability of radiant heat to fog-signalling. The proposition, in the abstract, is a philosophical one; for were our fogs of a physical character similar to that of the iodine held in solution by the bisulphide of carbon, or to that of iodine or bromine vapour, it would be possible to transmit through them powerful fluxes of radiant heat, even after the entire stoppage of the light from our signal lamps. But our fogs are not of this character. They are unfortunately so constituted as to act very destructively upon the purely calorific rays; and this fact, taken in conjunc- tion with the marvellous sensitiveness of the eye, leads to the conclusion that long before the light of our signals ceases to be visible, their radiant heat has lost the power of affecting, in any sensible degree, the most delicate thermoscopic apparatus that we could apply to their detection. Royal Institution, October 1864. XL. On Evansite, a new Mineral Species. By Davip Forszs, F.R.S., &¢.* ene mineral was brought from Hungary in the year 1855 by the late Mr. Brooke Evans of Birmingham+, and was then reported to be found in some abundance as an incrustation in drusi¢e cavities which occurred in the brown iron ores. It was regarded as pertaining to the mineral species allophane f, with which it agrees in many of its physical properties, as hard- ness, colour, specific gravity, &c., as well as in the percentage of loss sustained upon heating the mineral to redness. The specimen I received from Mr. Evans was labelled Allo- phane from Zsetcznik, Gomar Comitat, and was very beautiful im appearance, consisting of an agglomeration of small stalactites with reniform and globular excrescences on brown hematite, many of these excrescences much resembling artificial or natural pearls, having both the figure and characteristic pearly lustre of such. I doubted the identity of the mineral with allophane; and a * Communicated by the Author. t+ After whom the species is now named. i A considerable number of specimens had been given by Mr. Evans to private collections in England all labelled “ allophane,” and I understand that many more had likewise been distributed in Germany under the saine name, 342 Mr. D. Forbes on Evansite, a new Mineral Species. preliminary blowpipe examination immediately confirmed this opinion by proving the absence of silica in any quantity, and indicating the presence of phosphoric acid; and consequently I was more disposed to regard it as hydrargyllite or Gibbsite. I commenced, however, a systematic examination of the mineral, but my sudden departure and prolonged absence in South Ame- rica has prevented my having had an opportunity of making the results public until my recent return. The physical characters of Evansite are as follows :—Amor- phous and without trace of crystallization ; reniform or botryoi- dal; colourless or milk-white, and sometimes faintly tinged with yellow or blue, and occasionally presenting iridescent hues; streak white; translucent to semi-opake. Lustre, vitreous or resinous ; splendid and waxy internally; very brittle. Fracture semicon- choidal and shining. . Hardness 3°5 to 4, scratching cale-spar with facility but not fluor-spar ; one fragment, however, was found to leave a faint mark on fluor-spar. Specific gravity. Several determinations were carefully made, and precautions were taken to expel all air from between the laminee of the mineral by using boiling distilled water and allow- ing it to cool down to the temperature of 60° Fahr.; the results were as follows :— 1. Using 28°51 grains of the translucent colourless mineral in small fragments, the loss in water was found to be 15°59 grains, and the consequent specific gravity 1°822. 2. With 13°686 grains similar to last, the loss in water was 7°31 grains, and the calculated specific gravity consequently 1°872. 3. With 12°87 grains of faint-yellow-coloured mineral in frag- ments, the loss obtained was 6°13 grs., and the consequent spe- cific gravity would be 2-099. 4. When 18°793 grains of semiopake mineral in one piece was immersed under water, it lost 9°55 grains, and consequently had a specific gravity of 1-965. , The mean of these four determinations will give 1-939 as the specific gravity of Evansite. The behaviour of this mineral before the blowpipe was found to be as follows :— In a closed tube it immediately evolved water, decrepitated, and, on continued application of heat, gave off more water and remained behind in the form of a milk-white powder. On test- ing, the water evolved did not show any reaction with Brazil wood, red or blue litmus, or turmeric test papers. In an open tube the same reactions were observed. Heated between platinum points it very slightly swelled out, became of a milk-white colour, and presented, when viewed through the glass, Mr. D. Forbes on Evansite, a new Mineral Species. 843 an innumerable series of minute cracks; did not fuse in the strongest heat ; appeared to colour the outer flame bluish green, but so feebly as to be all but indistinct. On moistening the mineral with sulphuric acid, this reaction was rendered rather more apparent. On charcoal it proved infusible and unaltered, in both oxidizing and deoxidizing flames; but when heated, after moistening it with a solution of nitrate of cobalt, an intense blue colour was communicated to the assay. It dissolved readily both in borax-glass and phosphate of soda* in the oxidating flame, forming colourless glasses, which remain colourless on cooling: some of the faint-yellow-coloured specimens give a very light- coloured yellow glass when hot, but, on cooling, become colour- less, a reaction due to the presence of iron. In the reducing- flame both these fluxes give the same reactions. In a few cases the glass formed by phosphate of soda shows a trace apparently of silica floating in the clear glass bead. A qualitative chemical examination showed the mineral to be completely soluble in sulphuric, nitric, and hydrochloric acids. The solution, when treated by a stream of sulphuretted hydrogen gas passing through it, gave no precipitate whatever. The acid solution gaye a yellow precipitate, indicative of phosphoric acid, when treated with molybdate of ammonia; and further, alumina and a trace of oxide of iron were found, but no lime, glucina or zirconia, which were specially tested for. Fluorine was examined for by treating 12°10 grains in a pla- tinum crucible with sulphuric acid at a gentle heat, the crucible being at the same time covered with a glass plate waxed on the under side and kept cold on the upper side; some characters were traced through the wax with a fine point; no visible etch- ing was remarked after the operation. The mmeral, therefore, consisted only of water, alumina, and phosphoric acid with an accidental trace of oxide of iron and silica. Its quantitative analysis was conducted as follows :— Determination of the Water. 22°22 grs. of the transparent colourless mineral left, after heating to redness, 13°49 grs. residue ; also evolved 8°73 ers. grs. water, equivalent to 39'285 per cent. water in the mineral. 15°38 grs., same quality, left under same treatment 8:93 residue ; also 6:45 grs. water, equivalent to 41°18 per cent. 13°365 grs., translucent but of a faint yellow colour, left 8°105 grs. residue; also 5°26 grs. water, which would make 39°37 per cent. * Instead of, as commonly, using miciocosmic salt (phosphate of soda and ammonia), I prefer employing the dried phosphate of soda prepared by heating strongly the above until all ammonia is driven off. It will be found much more convenient in practice, as it melts gently, and does not froth and spit as the microcosmic salt does, 344 — Mr. D. Forbes on Evansite, a new Mineral Species. 24°877 grs., translucent and colourless, heated in a water- bath at 212° Fahr. for twenty hours, left 20°25 grs. residue, being 4627 grs. water, or equal to 13°69 per cent. water given off at 212° Fahr.; on further heating to redness left 14-94 grs. residue, thus giving a total of 5°31 grs. water, or equivalent to 39°91 per cent. The average of these four experiments affords 39-945 per cent. water. Determination of the Insoluble Matter (Silica). 18-07 grs. of the mineral were dissolved in hydrochloric acid with addition of a little nitric acid; some flakes remained persistently insoluble, and were collected on a filter, washed, dried and incinerated, and weighed 0:250 gr., or equal to 1:39 per cent. 13°365 grs. of the translucent but yellow-coloured mineral, after having been previously ignited to determine the amount of water present, were now dissolved in nitrohydrochloric acid; the insoluble residue collected on a filter, washed, and determined after incineration, weighed 0°46 gr., or equivalent to 3°44 per cent. I satisfied myself, however, that this result is quite erroneous and much too high, owing to a part of the phosphate of alumina in the mineral becoming itself insoluble, through the previous heating it had been submitted to in determining the percentage of water in it. Determination of the Phosphoric Acid. 22:22 grs. of the white translucent mineral were dissolved in nitrohydrochloric acid, and to the solution an excess of a so- lution of molybdate of ammonia, previously rendered strongly acid by addition of nitric acid in large excess, was added until all phosphoric acid present was precipitated in the form of the yellow phosphomolybdate of ammonia. After filtration this pre- cipitate was dissolved in ammonia, and the solution then preci- pitated by adding a mixed solution of sulphate of magnesia, chloride of ammonium, and caustic ammonia. The precipitate of phosphate of ammonia and magnesia was allowed to stand for twelve hours, then filtered off, washed with ammonia-water, and determined on ignition, affording 6°40 grs. pyrophosphate of magnesia, equivalent to 4°09 grs. phosphoric acid, or 18°42 per cent. phosphoric acid in the mineral. Another estimation of the phosphoric acid in the mineral was made by Girard’s modification of Reynoso’s process, as follows :— 15°38 grs. were dissolved in nitric acid, and 22 grs. of me- tallic tin then added to the solution and boiled until entirely oxidized ; the solution was then filtered off, and the insoluble oxide and phosphate of tin dissolved in excess of sulphide of ammonium by digestion; the solution was filtered from some Mr. D. Forbes on Evansite, a new Mineral Species. 345 little soluble residue, and then precipitated by the addition of a previously mixed solution of sulphate of magnesia, chloride of ammonium, and ammonia in excess, allowed to stand twelve hours, and the precipitated phosphate of ammonia and magnesia then filtered off and determined as in the last case ; the pyrophosphate of magnesia amounted to 4605 grs., equivalent to 2°944 grs. phosphoric acid, or 19-01 per cent. A third determination of the phosphoric acid was now made upon 13°365 grs. dissolved in hydrochloric acid, some 50 grs. crystallized tartaric acid added, and then ammonia in excess ; the solution remained clear, and was then precipitated by a mixed solution of sulphate of magnesia, chloride of ammonium, and liquid ammonia, and allowed to stand twelve hours. The supernatant solution was now carefully decanted, and the pre- cipitate redissolved in hydrochloric acid, a little tartaric acid added, and then ammonia in excess: after standing twelve hours the precipitated phosphate of ammonia and magnesia was col- lected and determined as usual; the pyrophosphate of magnesia weighed 4°14 grs., equivalent to 2°63 grs. phosphoric acid, or 19°73 per cent. in the mineral. The mean of these three de- terminations of phosphoric acid will consequently amount to 19:05 per cent. Determination of the Alumina. 22°22 ers. (the same as employed as before mentioned in deter- mining the phosphoric acid by the molybdate-of-ammonia me- thod) were here made use of, and the solution, after separating the precipitate of phosphomolybdate of ammonia, was now sub- jected to the action of a stream of sulphuretted hydrogen gas until no more precipitate of sulphide of molybdenum fell ; it was then filtered from this precipitate, and the solution, after boiling to remove any excess of the gas, precipitated by ammonia, by which the alumina present was thrown down, which, being washed, dried, and incinerated, weighed 8:90 grains, or conse- quently 40°05 per cent. in the mineral. Another determination of the alumina was made on the quantity of mineral (15°38 ers.) used in determining the phosphoric acid according to the tin method. The matter insoluble in sulphide of ammonium was, as far as_ possible, dissolved in nitrohydrochloric acid, this solution was added to the nitric-acid solution obtained in the first instance after filter- ing off the oxide and phosphate of tin, and the whole then pre- cipitated by ammonia and the alumina collected. From its ap- pearance, however, it was suspected that it might contain tin ; it was redissolved in sulphuric acid and a stream of sulphuretted hydrogen passed through the solution, when a considerable Phil. Mag. 8. 4. Vol. 28. No. 190. Nov. 1864. 2 A 346 Mr. D. Forbes on Evansite, a new Mineral Species. precipitate of the sulphides of lead and tin* fell, which was filtered off, and the alumina determined as usual by precipitation by am- monia. After ignition it weighed 5:90 grs., or equivalent to 38°36 per cent. in the mineral. The average of these two determinations of alumina will be 39°20 per cent. From the results of the above determinations the analyses will now stand as follows :— a. 6. c. Waters wus . Ove 6°45 5260 Phosphoric acid . 4:09 2°94 2°630 Alumina: [F022 OL 5:90 5°290+ Insoluble (silica) . 0°31 0-09+ 0:185 Loss in analysis . 0-19 sen353 Bo oecca 22°22 15°38 13°365 And calculating the percentages derived from these results,— a. b. c. Mean. Water! 2 80he 28929 41:18 89°37 = 39°95 Phosphoric acid . 18°42 19:01 19°73 19-05 Alumina . . . 40°05 38°36 Al‘S1+ 39°31 Insoluble (silica) . 1°39 145+ 1:39 1°41 TOSS Segoe, se) ash OOO casieee cceees 0:28 100:°00 = 100:00 100:00 100-00 From the above analysis the formula 3 Al? 03, PO®+18HO may, I think, be safely deduced. This formula will, on calcula- tion, represent the following percentage composition :— 3 Al? 03=153°78 = 39:75 Alumina. 6PO0® = 71:00 = 18:36 Phosphoric acid. 18HO =162:00 = 41°39 Water. 386'78 100-00 For comparison I annex a Table showing the chemical com- position of all the hydrated phosphates hitherto announced as having been found in the mineral kingdom. 2A1203,P05 2Al2 cat ey ae re Al?03, P09, 3A1]203, 2P05+ 12HO. 4+5HO. 46H 48H 48HO. (a Wavellite. Kapricite. Kalaite, wet Pie Gibbsite. = Barnstaple. Hungary. Silesia. Striegis. Nischna Tugal. Mass.U.S. Phosphoric acid. 34:98 35°49 30°90 30°49 29°03 37°62 Alumina... , 37°18 39°59 44°50 44°49 38°47 - 26°66 @xidé of ron"... Se 1°80 230 1:20 Oxide ofcopper. 5... «0% 3°70 fats 0°80 Gane Gs) j.'s \ erates 294 pen ee re ebooks 300°) eg Waters °s 40s 28:00: 424'92 19:00 22°82 27°50.) saa 100°16 100°00 99:90 100:00 100°00 100:00 Fuchs. Stddeler. Zellner, Hermann, Hermann. Hermann. * Doubtless the lead had been im the tin as an impurity. + Determined as loss. pease ery XLI. On Induction in a Rotating Conductor. By HK. JocoMann*. een equations (26) and (27) of my memoir “On the Elec- tric Currents induced by a Magnet in a Rotating Con- ductor” + can be easily integrated, by means of a development in series according to spherical functions, in the special case of a conducting sphere rotating around one of its diameters. The results, on account of their remarkable simplicity, shall be here given. Let s=i/P+P+e be the distance of an inducing pole from the centre of the sphere, and X denote the angle between the directions of s and 7, where par/ x+y? +22; then if p represent, as before, the distance of the point (a, y, 2), within the conductor, from the inducing pole, so that p?=r?+s*?—2rs cos X, we shall have rey r(er— sz cos d) ‘ie eae SC +s—r cosa) where the summation is to be extended to all the existing mag- netic poles. If, further, we put mee bz—ay v= QnkKS pu ‘ps(p-+s—r cos nr) the components of the current-density at the point (2, y, 2) will be ie Aas gle. Oz Oy st Ow —Z£ ov Ox Oz pe oe OY Ox From the form of these expressions it is manifest that the radial components of the current at each point within the sphere vanish,—in other words, that all the currents flow on concen- = is the Journal fiir die reine und angewandte Mathematik, vol. xxxvie 2 p- 329. f Phil. Mag.S. 4. vol, xxvii. p.522. 2A2 348 M. E, Jochmann on Induction in a Rotating Conductor. tric spherical surfaces. It likewise follows therefrom that the results are also immediately applicable to the case of a shell bounded by two concentric spherical surfaces. In this case, however, we must also assume a distribution of free electricity on the inner surface of the hollow sphere, of such a nature that, in virtue of its presence together with that of the electricity within the conductor and on its external surface, the potential V may acquire the above value. The form of the current- curves within the conductor is determined by the equations 7—= consts) = const, The components of the action of the system of induced currents upon an external magnetic pole m are Bu Sa Qasere ce: Oc On” org where &, , € are the coordinates of the pole, and 0 (qi } { y! Ol(Canz — ON gr at gt dot OV tL Aer yt gol ee WN tes Q SE y dee dy See Le dy Oe ia oe y de dy'de’, in which expression WY’ denotes what VY becomes when 2, y, z are changed into 2’, y', z', and, for brevity, we have put Pe (a — 6) eG) The integration can easily be effected when it is required to calculate the reaction of the system of induced currents upon a single inducing pole, or when, after differentiation, &, 7, € are made equal to a, b, ¢ respectively, and consequently r to p. For then, putting for simplicity 6=0, we have in the case of a solid sphere of radius R, sould nkK rap? = 9s?— R? he s—R]. % 2s? 2 anos 5 s+ Rk]? and in the case of a hollow sphere with internal and external radii equal to R,, R,, respectively, eae nkKrrap? = USTaTS.. ee ae ose s?—r? 2s eSar wy whilst in both cases 3 = UI // =O) The relation between these results and those obtained in the former memoir for the case of a plane disk is manifest. The result takes a remarkably simple form under the hypo- thesis of a sphere rotating under the influence of a constant magnetic force, such as that of the earth. The coordinate plane y= 0 may now be made to coincide with the plane of the axis of rotation and the direction of magnetic force, or, as we may call Mr. J. Bishop on the Pitch of the Tuning-Fork. 349 it, the plane of the magnetic meridian. This done, we must put 5=0, and afterwards allow s and wu to increase indefinitely in ew ites such a manner that the ratios sasiny and = = T may preserve constant values. The quantity T will then represent the inten- sity of the constant magnetic force, and y the angle between the direction of this force and the axis of rotation. In this case the current -curves reduce themselves to the system of circles repre- sented by the equations r=const., #=const., all of which lie in planes parallel to that of the magnetic meri- dian. The constant current-density within each current-curve will be ankKT sn y.Ar, if N= V7? —y? be the radius of the current-circle. With respect to its external action, the current-system deports itself like a magnet whose axis coincides with that of y, or, in other words, is perpendicular to the plane of the magnetic meridian. Worthy of notice is the analogy which exists between this result and the one deduced by Poisson from his magnetic theory of rotation-magnetism in his memoir ‘Sur le Magnétisme en mouvement’’*, as well as the one found by Green+, in the case where a sphere of imperfect electric conductibility is supposed to rotate under the influence of a constant electrostatic force, or where a sphere consisting of a magnetizable substance endued with coercive force rotates under the influence of a constant magnetizing force. Berlin, March 1864, XLII. On the Influence of the Pitch of the Tuning-Fork on the Mechanism of the Human Voice. By Joun Bisuopr, F.R.S.t i those who have paid attention to acoustics know that what is denominated pitch in musical science refers to a certain definite number of vibrations or undulations of the air, and also that, for musical purposes, a tuning-fork has been con- structed to yield a note or sound termed C, which we may assume as the fundamental note in the diatonic scale, or gamut. Since, then, the pitch of the tuning-fork determines that of all the other notes, both in music, musical instruments, and * Mém. de ? Acad. des Sciences, vol. vi. p. 497. + Journal fiir die reine und angewandte Mathematik, vol. xlvii. p. 187. { Communicated by the Author. 350 Mr. J. Bishop on the Influence of the Pitch of the tones of the human voice in singing, it is of the greatest import- ance, not only that the pitch of the fork should be uniform, but that it should be conformable to the structure and functions of the human organs of voice, to which all other instruments of sound ought to be subordinate. How widely this principle has been departed from, and how injurious these deviations have been to the vocal mechanism, it is the object of the following remarks to show. The pitch having once been disturbed, the Philharmonic Society adopted a particular one, the Opera another, and then almost every maker of musical instruments chose his own pitch, until at last it became difficult to get together performers on two or three instruments which were of the same pitch. The pitch of tuning-forks with “C Philharmonic” marked on them may be very different, and there seems no guarantee for the cor- rect pitch of many of these forks; and where the pitch is so various, singers do not know whether or not the music they have been accustomed to sing is within the compass of their voice. In this state of uncertainty, the Society of Arts appointed a committee to investigate the subject, and to discover and report. on the best means of remedying these difficulties. Upon this report being considered, 528 vibrations were recommended for adoption by the Society*. When the nature of sound was first investigated, the number of vibrations in the air which were necessary to constitute a sound of a given pitch was accurately ascertained. It was determined that any elastic body, such as a stretched cord or a spring, whose vibrations to and fro recurred every second, should be denomi-. nated C, and that every power of the number two, expressing vibrations within the limits of the range of musical instruments, should constitute C in the diatonic scale of music. On this system was the tuning-fork constructed, being taken for conve- nience at the 10th power of 2, consisting of 1024 vibrations, which will be according to the German and the French system of notation, and 512 double vibrations on the system of the English method of computation—this pitch, or some other of a less number, having obtained the sanction of all the musicians and mathematicians who had studied acoustics with reference to musical science. Among the latter may be noticed the names of Kuler, I. and D. Bernouilli, Riccati, Poisson, Savart, Dr. Young, Weber, and Sir John Herschel. Among those who com- posed music nearly on this pitch of the fork are Handel, Mozart, Beethoven, and nearly all the great composers up to the begin- ning of the present century ; and, moreover, musical-instrument * Journal of the Society of Arts, June 8, 1864. Tuning-Fork on the Mechanism of the Human Voice. 351 - makers had, up to this period, observed nearly the same funda- mental pitch for the tuning-fork. The following Table, with which I have been supplied by the kindness of my friend Mr. A. J. Ellis, will show the truth of the statement that the pitch of C has been arbitrarily raised, in various degrees in different countries, since the time of Handel, and also that the Italian-Opera pitch is such as to render a great deal of vocal music impossible to be sung by any vocalists except those who possess an unusually extended compass; also that the scale of the Society of Arts is too high for general use, and has failed to produce that uniformity which was designed by its members ; and the question resolves itself into whether the slight difference in the brilliancy of instrumental music is compensated for by the increase of difficulty and injury to the human organs of voice. Weall know that the performance of the most favour- ite overture, executed by the most perfect of orchestras, faded into comparative insignificance when the tones of a Pasta, a Malibran, or a Jenny Lind reached the ear. TABLE of the Varieties of Pitch. When any note but C is the pitch note, the pitch of C is cal- culated from it according to the semitonic temperament of twelve equal semitones if not otherwise expressed, or according to the mesotonic temperament or system of perfect major thirds. | Pitch notes. No. Authority. SS == | Brace a A C _ | ae —— shies 1, |Dr. Smith, organ of Trinity College, Cambridge, | 1758 ; = d =262 (mesotonic)......... | sie ak ae ; 233-42 | 2. |Usual organ pitch ........ sonanearepaesaeanasaaaeace | sonsseana 240-00 3. |Handel’s tuning-fork, 1740 (mesotonic) ........., 416 247°35 5. Theoretical pitch, Hullah and Tomlinson, 1842.) ......... 256 6. |Philharmonic (1812-42) ........0..cscccocscseceses | 433 257°47 10. |French normal diapason (1559).........c0e.ceseeeee! 435 258°66 14. |Stuttgardt Congress of Musicians (1834)......... | 440 261-63 17. |Vienna Orchestra, 1834 (Schleibler) ............ | 440-87 262-14 18. |Berlin Orchestra, 1834 (Schleibler) .........0.... | 441-625 262-59 19. |Society of Arts, London (1860) .................. prea 264 21. \Italian Opera, 1860 (Society of Arts’ Report)...| 455 270'55 _N.B.—The pitch is here considered as the number of double vibrations in a second. In France and Germany the number of single vibrations is usually taken, and hence the preceding figures would be doubled. Thus the French normal diapason is called870. 352 Mr. J. Bishop on the Influence of the Pitch of the Shortly after the commencement of the present century there arrived in this country German performers on wind instruments whose pitch was much more acute than that of our standard. An opinion then prevailed that the tones of wind mstruments were improved by this higher pitch, and under this impression the Philharmonic Society and the orchestral departments of the theatres acceded to this strange notion, or what might rather be termed delusion. The effect of this alteration in the fundamental pitch of music has been very important. The pianoforte-makers have been obliged to shorten the strings of their instruments ; the organ- builders to shorten their pipes; the flute-makers to cut off a por- tion of the length of their tubes; and what is termed the opera pitch has transformed the C of the olden time into D; and since Nature has made no corresponding change in the length of the cords of the vocal organs of the human race, it is manifest that some changes must be made, either to adapt musical composi- tions to the changes in musical pitch, or to reduce the standard pitch conformably to the structure of the human organs, in order to render their execution possible. It has been already stated that the greater portion of our best music was composed at a period when the tuning-fork made about 512 vibrations for C. This is the case in the works of Handel, Mozart, Beethoven, and in the old madrigals and masses. Let us suppose a person has a tenor voice whose limit on the old scale of pitch is A. He can no longer sing the same music when A is transformed into B. Take, again, the soprano or alto, where, with the new pitch, the music is rendered impossible of execution. We find accordingly that, in order to diminish the evils which the present pitch has inflicted on the human voice, a large number of Handel’s and Mozart’s popular songs have been transposed by Callcott and others into lower keys, so as to bring them, for private use, into a pitch as near as possible to that in use in the time of the composers. This is, however, only a partial remedy for the much greater evil, since it leaves the entire works of these great masters untouched as far as relates to their per- formance in public. Now, although this may be easily effected in short pieces of music, no one would think of changing the key for such a work as the Messiah, or a whole Mass; and yet many singers can no longer join in the execution of these cele- brated productions. It must not be forgotten that in this age of vocal harmony, music was intended for assemblages of choral performers, and not merely for the few who possess such an extended range of voice as would enable them to disregard the change of pitch. 3 We come now to the effects produced on the organs of voice Tuning-Fork on the Mechanism of the Human Voice. 353 by straining the vocal cords beyond their proper tension. A young lady, endowed with a fine soprano voice reaching to C in alt. or 1024 vibrations, by straining the vocal cords on that note raised to D, lost the power of exercising her voice for musical purposes during nearly three years. Even Madame Goldschmidt complains of the strain which the change of pitch has produced in her vocal organs; and it is well known what an extended range of flute-like sounds this charming and accomplished singer possessed. Further, it is well known that the tones at the extreme limits of phonation are never so pure in quality, or so agreeable to listen to, as the notes within those limits; and moreover, when in order to execute a given note the vocal cords are stretched beyond their normal elastic length, they do not always so readily regain their tone of elasticity ; and if this be permanently impaired, the voice loses some of its range of notes, and will be unable to regain the power to execute the melody_as before. The struggle to execute a pitch beyond the normal limits sometimes gives rise to spitting of blood, and has been known to produce apoplexy. These circumstances are surely sufficient to render the reduction of the pitch of C to its former limit of 512 vibrations imperatively necessary. The principle we wish to impress is, that the pitch of musical instruments intended to accompany the human voice should be made subordinate to the anatomical structure and mechanism of the human organs, instead of the latter beg rendered subor- dinate to the former. Consequently the pitch of C should again be 512 vibrations ; and we advise all persons interested in the choice of pianos and other musical instruments intended for vocal accompaniments, to insist upon having them of that pitch. There appears to have been a general complaint against the present pitch of our musical instruments by almost all the higher class of smgers; and on appealing to one of the most scientific of our pianoforte-makers for his opinion, he stated that the pitch had ruined many a fine voice, but, as long as the public demand for the higher pitch remains, it is not in the power of the imstrument-maker to remedy the evil. We know how strongly Sir John Herschel protested against the decision of the Committee of the Society of Arts, and all parties appear to have considered the decision at which they arrived as only a temporary measure; and its complete failure to produce uni- formity is a confirmation of his views, and shows the necessity for further investigation. These remarks have not been written as a mere theory, but in consequence of the numerous cases of injury to the human organs of voice from the above-mentioned causes which have been from time to time submitted to the author’s opinion. [ 354 ] XLIII. On the Cohesion-Figures of Liquids. By Cuarurs Tomurnson, F.C.S.* [With Two Plates. ] T the Meeting of the British Association at Manchester in 1861, I had the honour of submitting to the Chemical Section a subject then new to science, namely, the cohesion- figures of liquids. In the memoir that was read}, I endeavoured to show that when a drop of an independent liquid (that is, not a solution) is gently deposited from the end of a glass rod or from the point of a dropping-tube upon chemically clean water in a chemically clean glass, the drop flashes out into a definite figure as it enters into solution or diffuses over the surface. Each figure is characteristic of the liquid, and is a function of the cohesive force and diffusibility of the liquid, and the adhe- sion of the surface on which it is deposited. The figure may also probably be represented in other ways. It may bea function of the solubility and the diffusibility of the liquid in question, or of the solubility, the density, and the molecular attraction ; while in the case of certain figures which are produced beneath the surface, and which I have named submersion figures, each figure seems to be a function of the solubility, the density, and the molecular attraction. In the production of cohesion-figures, water is the most con- venient adhesion surface. It must be contained in a glass that is kept chemically clean by occasional washing in sulphuric acid or in a solution of caustic potash, so that the water, which need not be distilled, may present a chemically clean surface. A shallow glass about 4 inches in diameter is adapted to these experiments. I have had a number of such glasses made for the purpose, and have placed a couple of them upon the table. The temperature best adapted for these experiments is that of an ordinary room, which in winter or summer may be taken at about 60°. I have not studied these figures by artificial light, but have been informed that they admit of being reflected in an enlarged form so as to be seen by anaudience. I have published various precautions respecting these figures, both with respect to temperature and variations in the area of the adhesion surface. I have also shown how these figures may be applied to the de- tection of adulteration in liquids, and also how suggestive many of these figures might be to the pattern-designer, from the great beauty and novelty of form and the exquisite harmony of colours displayed in them. * Communicated by the Author, having been read before the British Association at Bath, September 15, 1864. + Phil. Mag. for October 1861. t Ibid. March 1862. Mr. C. Tomlinson on the Cohesion-Figures of Liquids. 355 In order that the application of this subject to qualitative analysis might be brought more directly before the attention of persons who would value an easy and expeditious test, I read a paper before the Pharmaceutical Society in February last, ‘On the Verification of Castor Oil and Balsam of Copaiba by means of their Cohesion-figures.” These two liquids were selected to in- troduce the subject of cohesion-figures in general, and its appli- cation as a rough and ready test. The members were so much interested in the subject that they requested me to furnish their engraver with some figures for insertion in their journal, and also to state what variations took place in the figure of castor oil from various markets and of various growths. Accordingly I examined twelve specimens of castor oil collected from different sources, together with three or four specimens of balsam copaibee, and wrote a report on the same, which will be found in the Society’s Journal*. In order to inyite attention to the commercial oils, I read a paper in March last before the Society of Arts, “On the Verifi- cation of Olive-oil by means of its Cohesion-figure.” The sub- ject excited some interest and discussion f. In these communications I endeavoured to show that the co- hesion-figure of the same substance is hable to certain variations in different specimens, especially in the case of the oils, which may be more or less viscid, more or less acidified or resinified. I do not here refer to the variations arising from adulteration and admixture; for this point is insisted on im all my papers. But I was not unmindful of the changes likely to be induced by age; for in my paper published in March 1862 (Philosophical Magazine), I state that the cohesion-figure of the oil of lavender, for example, may vary in different specimens, since it varies in density from 0°87 to 0:94. The cohesion-figure of the oil of laven- der is so striking that I was induced to try a number of speci- mens in 1861, and in all of them I obtained the peculiar Carra- geen-moss pattern—unless, as was often the case, the specimen had been adulterated with turpentine, in which case there was no difficulty in detecting the adulteration. I also found that an essential oil, entirely different from that of lavender in its pro- perties and cohesion-figure, and also of less density, might be made to give a somewhat similar cohesion-figure by dissolving a small portion of camphor in it under a gentle heat, so as to bring it to about the same density and texture as oil of lavender. I stated in my first paper, that if two independent liquids could be found of the same density and physical molecular constitution (that is, equally fluid or viscid, &c.), they would form the same * Pharmaceutical Journal for March and April 1864. T Society of Arts Journal for March 4, 1864. 356 Mr. C. Tomlinson on the Cohesion-Figures of Liquids. — cohesion-figure on water, although of different chemical consti- tution. Dr. Gladstone has has been so kind as to send me a specimen of salicylate of methyle, €H*,.€” H° 0°, which gives a figure somewhat resembling that of oil of lavender—arising, I have no doubt, from a similar physical constitution. Cases of this kind must be rare, and are not likely to interfere with the application of conesion-figures as a test. A much more serious objection is the alteration which oils undergo by long keeping. The specimens of oil of lavender, for example, which in 1861 gave the Carrigeen-moss-pattern figure, were so changed in 1864 as to give only a plain film without any distinctive character. On redistilling these oils, however, so as to get rid of oxidized products, the “distillate produced the lavender-oil pattern as it did in 1861. On the other hand, the method is occasionally so delicate as to excite the surprise of persons who have sought in vain for a method of detecting differences in oils &c. which they largely use in the course of their trade. For example, a manufacturer informed me that it would be a great thing for him to be able to detect the difference between beef-oleine and mutton-oleine. The respective cohesion-figures of these substances show the dif- ference plainly. Again, balsam copaibe is often adulterated with castor oil, for the detection of which the usual tests are either troublesome or inadequate. The method of cohesion- figures detects the adulteration immediately. Again, olive oil is frequently mixed with poppy oil, or sesame-seed oil; not only may these mixtures be detected by means of their cohesion- figures, but also the relative proportions of the respective oils. Although for all practical purposes water would be used as the adhesion surface in the production of these figures, consider- able interest arises from noting changes undergone by the figures when other surfaces are used. In my first paper, im 1861, it was stated that wood-spirit on the surface of mercury gave a very different figure from what it did on the surface of water ; and in my second paper (Phil. Mag. March 1862) I described the cohesion-figures of water, ether, and alcohol on the surface of sulphuric acid, and also those of one or two essential oils on the surface of acetic acid. I have lately obtained a large variety of figures by experimenting on such adhesion surfaces as those of cocoa-nut oil, castor oil, paraffin, spermaceti, white wax, olive oil, lard, and ‘sulphur. Of course the substances, such as pa- raffin, wax, &c., which are solid at ordinary temperatures, were melted for the purpose of these experiments. ‘Too high a tem- perature was found to be disadvantageous, on account of the ten- dency of the drop to assume the spheroidal state. Lard is ad- vantageous, on account of the length of time that it remains Mr. C. Tomlinson on the Cohesion-Figures of Liquids. 357 fluid after having been thoroughly melted. Castor oil was used at various temperatures, but some of the finest figures were ob- tained on its surface at the ordmary temperature of the air of the room. Fine figures were also obtamed on the surface of cold olive oil. Some of these figures are represented in Plate VI. Cocoa-nut Oil.—A drop of ether flattened into a very perfect disk about two-eighths of an inch in diameter: this was sur- rounded by a dentated ring, from which proceeded a multitude of rays, as shown in Pl. V. fig. 4. The best-defined figure was obtained when the temperature of the surface was about 80°. Aicohol produced a disk about three-fourths of an inch in dia- meter, with a small boss in the centre surrounded by a number of concentric circles faintly tinted with iridescent colours, while the edge of the disk was delicately frmged with very short radial Imes. The figure was first of the size shown in fig. 1, No. 1; it then expanded to No. 2, and disappeared by closing in upon its centre. The figure was quite sharp and distinct, giving the idea of a lid of a box turned in the lathe. The best result was obtained when the surface was at about 90°. Benzole gave a figure about 2 inches in diameter, consisting of a central depressed disk about three-eighths of an inch in diameter, with a slight conical projection in the centre and surrounded by a broad smooth flat rmg terminating in a sharply-cut edge. Oil of turpentine gave a somewhat similar figure, only the outer edge was wavy. Paraffin oil and Persian naphtha also give figures of the same type. Oil of lavender gave a central disk, from which issued wavy processes which were torn away by the adhesion of the surface. Castor Oil.— When the oil is at about 94° F., a drop of ether forms a large figure bounded by a well-defined circular edge, in the centre of which figure isa plain disk surrounded bya narrow plain line; just outside the disk is the engine-turned pattern, and beyond this, as far as the boundary edge, the disk is quite smooth. The engine-turned pattern seems to be produced by the revolution, or rather oscillation, of the central disk on the heated surface. On cold castor oil the ether figure consists of a central boss surrounded by rippled waves, very much like the rose-pattern of the turner. Tig. 3 represents these two figures. When the oil is at 94°, a drop of alcohol forms a central star in a large disk surrounded by iridescent rings. But a finer figure is produced on cold castor oil: the drop spreads out into a large disk with broad iridescent bands just within the sharp-cut edge ; having attained a diameter of about 3 inches, it retreats towards the centre, leaving a beautiful network of minute globules. A drop of camphorated spirit produces a still finer figure, an idea of the beauty of which can scarcely be conveyed in words. A 358 Mr. C. Tomlinson on the Cohesion-Figures of Liquids. figure of a similar type is produced on the surface of olive oil (see Pl. V. fig. 6), and will be described further on. The benzole figure at 83° consists of a small central disk sur- rounded by an engine-turned pattern, beyond which rippled waves extend to the circumference of a large figure. On the cold oil the engine-turned pattern is wanting (see fig. 11). Pa- raffin oil gives a somewhat similar figure. The turpentine figure consists of a central boss. surrounded by a large flat rmg. On the cold oil, a drop of oil of cajuput has a central depression sur- rounded by a large flat ring. Paraffn.—Solid paraffin was melted in an evaporating-dish, and after the heat had been removed and the surface had become tranquil, a drop of ether, allowed to fall on the surface at 180°, was at first spheroidal; it then flattened down, and by its evapo- ration solidified a portion of the paraffin with which it was in contact; the solidified portion rushed wildly about under the retroactive force of a little remaining ether, until it disappeared by solution in the liquid paraffin. Alcohol formed a disk which sailed about, shooting out flat disks resembling petals, so as to give the figure the appearance of a flower (see Pl. V. fig. 5). Paraffin oil formed a disk which sailed about with much agi- tation, sending off waving lines. The oils of turpentine and cajuput, and some others, solidified a portion of the paraffin—in some cases permanently, while in others the solidified portions moved about over the surface. Olive oil and pure tallow oil assumed the spheroidal state on the surface at 180°, and then sank. Spermaceti.—On the surface of melted spermaceti a drop of ether becomes spheroidal, or, if the temperature be not too high, flattens down into a small raised disk which spins rapidly ; or it may solidify a portion of the spermaceti, when the solid portion darts about in wide sweeps rapidly over the surface until it is again taken up by the liquid. Alcohol, when the surface is at about 160°, forms a relhdehimcst disk with a waving border and concentric rings, and a delicately fringed iridescent ‘edge (see fig. 2); but at a lower temperature (about 116°) it solidifies a portion of the spermaceti into the form of asmall coracle, which sails about carrying its small cargo of alcohol. Turpentine at 121° behaves in a similar manner, only the solidified portion breaks up and darts about. Oil of cajuput at 127° forms a large disk with a faint depressed centre. Benzole forms a large plain disk, in the centre of which is a small spinning disk with a raised conical projection in the centre. Camphorated spirit slightly chills the spermaceti, rotates in the form of a small lens or boss with an agitated kind of motion; Mr. C. Tomlinson on the Cohesion-Figures of Liquids. 359 then settles down into a charming star-like figure surrounded by rings and iridescent colours, and a sharp boundary line. In one case the central boss slipped off the figure, leaving the disk with its iridescent rings, &c. complete. White Wax.—W ith the surface at 142°, ether solidified a por- tion which rushed wildly about. Alcohol solidified a portion in the form of a ring, which immediately broke up and was dispersed in radial lines, while the alcohol settled down into a small sharply-defined disk. At a higher temperature, such as 170°, a drop of alcohol will solidify a cup-shaped cavity for its reception ; but if the drop be held for a short time over the surface so as to become warmed, it at once subsides into a sharp well-turned disk. Lard.—Good figures are formed on the surface of melted lard with ether, alcohol, and the oils of turpentine, savin, paraffin, lavender, and some others. A drop of camphorated spirit formed a very beautiful figure, some idea of which may be gathered from fig. 7. The rippled concentric circles display several of the orders of Newton’s, or rather of Nobili’s rings. Olive Oil.—A fresh flask of the variety of this oil known as extra sublime, was opened for the purpose, and portions of it were poured into the ordinary 4-inch cohesion-figure glasses. It answers admirably as an adhesion surface at ordinary tempera- tures. A drop of ether produces a small beautiful figure, con- sisting of a disk surrounded by rays. Alcohol formsa disk about 3 inches in diameter; the drop diffuses well, and the disk is perfectly circular, with a central boss. Iridescent rings contain- ing the colours of four or five orders fringe the edge of the disk in broad bands, and outside this large disk is a fainter and more shadowy disk. When the figure is fully developed, it rapidly opens, and closes in upon the centre like a curtain being drawn in, and so vanishes, leaving no trace behind. Camphorated spirit (fig. 6) is even more beautiful and persistent than alcohol ; the iridescent rings are dentated, and this adds greatly to their beauty ; the film, which is of a very large size, retreats slowly inwards to the centre, leaving the camphor in the form of minute dots disposed in radial lines; these lines in their turn retreat towards the centre, where the camphor collects in the form of a flat ring. Benzole forms a large plain disk with a cavity in the centre. Turpentine, cajuput, and lavender also form disks; but the most curious figure is given by a drop of pure wood-spirit. It flashes out into a disk about 14 inch in diameter, then retreats inwards with the elasticity of a spring, leaving a delicate fringe made up of innumerable small’ dots; the disk then becomes toothed at the edge so as to give it the appearance of a small circular saw; the disk retreats inwards, and the point of each 3860 Mr. C. Tomlinson on the Cohesion- Fiyures of Liquids. tooth projects a number of globules, the ultimate figure being a small disk in the centre with an immense number of dots radia- ting towards it. In fig. 9 an attempt is made to represent this effect, first as the figure is expanding, and secondly as it is retreat- ing. On cold castor oil a similar figure is produced, only the dots are more numerous and finer; and there is a very curious differ- ence in the figure of a drop of the wood-spirit of commerce as compared with that of the pure spirit. On cold olive oil and on lard at 120°, or on cocoa-nut oil at a lower temperature, the drop of impure spirit forms a small lens with ten or twelve short blunt arms projecting from it (see fig. 10), and each arm shoots out a multitude of globules; and not doing so in equal times from each arm, there is a reactionary movement, which causes the disk to describe half a turn in one direction and then half a turn in an opposite direction, the effect of which is to dispose the dots not in radial, but in curved lines, the curves often bend- ing in opposite directions. The formation of the figure is suffi- ciently slow to allow it to be studied, and the effect is very curious. The difference between the two figures distinguishes the pure from the impure spirit in a very marked manner. It should be noticed that the surface of the oil soon becomes saturated, so that not more than two or three figures can be produced in suc- cession ; but by wiping the surface with a piece of filtering paper, its adhesion 1s restored. Sulphur.—When sulphur is melted so as to be sufficiently liquid to pour easily, some good figures may be formed on its surface. A drop of ether at first assumes the spheroidal state; it then forms a boss surrounded by two or three rings of the thinnest orders of colour, steel-blue prevailing, and the figure is bounded by an excentric ring some way off. LBenzole forms a good figure, consisting of a boss, an irregular star from which small lenses are shot out, and these are circumscribed by a flat circle (Pl. V. fig. 15). Oil of lavender forms a boss surrounded by iridescent rings in waving lines, then a large silvery space, and a narrow boundary ring of iridescent colours (see fig. 13). The oils of rosemary, turpentine, and paraffin form each a boss sur- rounded by large wavy iridescent clouds of most brilliant metal- lic colours, paraffin oil being most brilliant of all. Creosote and carbolic acid form disks which flatten out into waving figures (see fig. 12). The figure formed by camphorated spirit is shown in fig. 8. Camphor moves about over the surface; water forms and occupies a cup-shaped cavity, solidifying the sulphur as it evaporates, Submersion Figures. In the Philosophical Magazine for June 1864, I have described a new variety of the cohesion-figures of liquids, in which the Mr. C. Tomlinson on the Cohesion-Figures of Liquids. 361 drop, instead of diffusing over the surface of the adhesion liquid, sinks into it and diffuses throughit. For this purpose a column of liquid in a cylindrical glassis employed. When water is used, a few drops of a strong solution of ammonia, or of oxalate of ammonia, or of alum are added, for the purpose of throwing down the lime, and also of assisting in the development of the figure. A strong solution of cochineal in water forms a figure which is typical of a number of cases of this kind of diffusion. A single drop on the surface sinks down, opens into a rmg, which becomes depressed at two opposite points, and lets down lines with other rings attached to them; while each ring, at 90° from the point of attachment of each line, lets fall two other lines with a ring attached, which ring in like manner, from two points 90° distant from the line, lets fall other lines; and in this way the figure is developed slowly and symmetrically. Oil of lavender in a column of spirits of wine behaves in a simi- lar manner, only the figure is much more complicated and crowded. A drop of fousel oil in a column of paraffin oil passes through some complicated changes resulting in a kind of pointed dome, the lower edge of which is cut into four symmetrical arches ; from the springing of each pair of arches a line is let down, and from the extremity of this proceeds four smaller domes similarly arched, and letting down four other lines and four other still smaller domes, forming a figure which lasts a considerable time, exciting surprise in all who have seen it by the kind of architectural symmetry produced. Figures of another type are formed in columns of benzole, of ether, &. In some cases very perfect rolling rings are formed, for the details of which I must refer to my paper, my business today being to point out a variety of other forms of cohesion-figures by submer- sion; for which purpose cylindrical columns of cocoa-nut oil, castor oil, paraffin, spermaceti, white wax, lard, and olive oil were used as in the case of cohesion-figures on the surface. Heat must be employed when necessary; but the best results are obtained with the cold oils, or with only just a sufficient amount of heat to render the solid substances fluid. Indeed the figures vary considerably with considerable differences of temperature, not only with substances which require to be melted, but with oils which are fluid at ordinary temperatures. Cocoa-nut Oil.— When a column was at about 160°, a drop of patchouli oil flashed out into rings and festoons. Oil of cloves formed a wide ring, from which proceeded numerous festoons and small rings; oil of cinnamon two or three large rings and festoons. Oil of cummin descended as a riband with a globule attached, from which proceeded upwards a dome cut into arches with lines terminated by knobs at the springing of each pair of Phil. Mag. 8, 4. Vol. 28. No. 190, Nov. 1864. 2B 362 Mr. C. Tomlinson on the Cohesion-Figures of Liquids. arches. Balsam copaibs (when the oil was at 165°) descended in the form of a single thick glassy ring of perfect structure. Some of the fixed oils formed pretty figures in a column at 110°. Colza descended in the form of a cup with the edges turned over and inwards, suspended by a line from the surface of the column to the centre of the cup. Linseed oil also forms a hemispherical cup with the edges turned over, but without the suspending line. Sesame a similar figure,’ only instead of the suspending line there was an arched projection in the centre of the cup. Castor oil sank rapidly in the form of a cup with the edges turned over and inwards. Some of these figures are represented in Plate VI. and are marked a, 0, ¢, d, e. Castor Oil, Olive Oil.—A column of each of these oils is well adapted for the exposition of sets of figures differmg in many particulars, but all distinguished by a bulb and a stem. Tach figure may be compared to a thermometer with a small bulb and a long delicate stem. For example, when a drop of oil of cloves is deposited on the surface of a column of cold castor oil, 6 or 7 inches in length, the greater portion sinks beneath the surface (see No.1), while the remaining portion forms a disk on the surface, attached to the submerged globule by means of a short neck (see No. 2). The weight of the globule drags upon the disk and forms it into a conical cavity, containing a speck of air, which, as the disk collapses by the weight of the descending globule, becomes enclosed and is drawn out with a portion of the oil of cloves into the form of a long narrow tube (No. 3): the disk at the surface, now reduced to the diameter of the tube, remains attached to the surface, and, indeed, is so persistent in its character that, long after the bulb has spread over the bot- tom of the vessel, this tube or thread remains attached to its moorings at the surface, and even interferes with the proper development of a second figure in the same column if the latter be narrow. As the tube is drawn out by the descending globule, its material is supplied partly by the surface of the globule, and partly by the medium, namely the castor or olive oil. The lat- ter, in passing over the surface of the oil-of-cloves spheroid, detaches a portion of its substance, and thus allows the tube to increase in length. In the meanwhile the original drop of oil of cloves, which near the surface was a sphere, flattens out into the form of a spheroid; and when it has descended about one-third of the length of the column it appears to open, and the apparent opening is ornamented on either side by the well-turned volutes of an Ionic capital (see No. 4, and the figure further developed in No. 5). This effect appears to be due to the pene- tration of the spheroid at its lower surface by a portion of the medium itself, which enters and diffuses within the spheroid in Mr. C. Tomlinson on the Cohesion-Figures of Liquids. 363 the form of a very perfect ring. The volutes are the effects of an optical illusion arising from seeing through a number of the segments which compose the ring on either side, while at the front and back of the ring the edges only of the segments are seen. Figures of this type, with variations in detail, which it would take too long to describe, are produced in cold castor oil by oil of cinnamon, creosote, carbolic acid, sulphuric acid, sul- phate of indigo, and glycerine. In a column of olive oil a drop of creosote, of carbolic acid, of oil of cinnamon, or of eugenic acid is similarly penetrated from below. Other oils, however, in olive oil are penetrated from aboye. For example, a drop of croton oil descends at first as a bulb and stem, the stem, as before, being moored to the surfaee*, The bulb flattens out into the form of an oblate sphe- roid, and in attempting to flatten still more it gets turned over at the upper part into the form of a ring, but presenting the appearance shown in A; the medium closes in upon the open- ing, which becomes deeper, as in B and C, until at length it penetrates to the bottom of the spheroid, forming a trumpet- shaped mouth asin D. In doing so it unites with the stem, which thus appears tq have penetrated to the very bottom of the spheroid; while, to supply its length, the medium licks over the outer surface of the spheroid, as in the former case, and thus allows the stem to accompany the altered spheroid to the bottom of the vessel. This series of processes, which it takes so long to describe, may be understood at a glance by a reference to the figures A to D. In some cases, instead of the voluted figure, the opening from below is pyriform, and as the spheroid descends the pear-shaped figure describes a circle within the spheroid, which gives it the appearance of rocking to and fro upon its stem (see figs. a', a?, a°). Thus while in a column of olive oil a drop of cinnamon or of eugenic acid opens from below and forms a figure with volutes, a drop of oil of cloves, or of creosote, or of carbolic acid is pene- trated from below and a pear-shaped opening is formed within the spheroid. We use the,word opening as we do the word volutes, to express the appearances presented. The opening, however, is a penetration of the spheroid by the medium in which it is subsiding. In a column of lard at about 170° and upwards, a drop of oil of cloves (and of some other oils) forms festoons and rings; but at lower temperatures, as from 140° down to 82° (at which point the lard used by me solidified), figures of the bulb-and-stem type are formed. But in the case of castor oil there is some varia- * In the figuresa portion only of the stem is shown. 364 Mr. E. J. Mills on a Defect in the Theory of Saturation. tion: the drop of castor oil forms a bulb and stem: the bulb is penetrated from above, separates from the stem, and descends as a rolling ring (see figs. 0!, 4°, 6°, 54). Croton oil also forms a beautiful large ring, from which festoons descend, and from the end of each festoon a ring separates and then commences rolling. A drop of balsam copaibe forms a bulb and stem; the bulb en- larges, expands upwards into a dome-shaped figure, from the lower edge of which festoons and rings are let down, which rings multiply and produce other festoons and rings. A drop of creo- sote forms rings and festoons when the lard is at about 130° or 140°; but at 110° it forms a bulb and stem, the bulb being penetrated from above. Carbolic acid at the lower temperature forms a bulb and stem, the bulb being penetrated from above. A drop of oil of cloves forms rings and festoons in hot lard, but a bulb and stem with penetration from below at a lower tempe- rature. The same remark applies to oil of cimnamon: at about 90° the spheroid is largely penetrated from below. It would occupy too much space and require too much picto- rial illustration to enter into further details respecting these submersion figures. They all admit of being grouped under some four or five types: not that the figures of any one type are identical; for whether they be rings and festoons, or bulb-and- stem figures, or dome-shaped, or cones or rolling rings, each liquid presents characters of its own, which are again subject to further variations in different media. King’s College, London, September 1864. XLIV. On a Defect in the Theory of Saturation. By Epmunp J. Mitts, B.Se.* HE theory of atomicity—or, as it should be more correctly termed, the theory of saturation—may be justly con- sidered, according to Wurtz’s suggestiont, as a development of the doctrine of multiple proportions. It expresses the result of an extensive induction, that there is a definite limit to the combination of one substance with another, and that this limit may be approached by successive stages. The atomicity or saturability of a given body is expressed by the number of unit weights of hydrogen which can be made to combine with a cer- tain standard weight of it. Thus the radicals represented by the following formule, * Communicated by the Author. + Lecons de Philosophie Chimique, p. 221. Mr. E. J. Mills on a Defect in the Theory of Saturation. 365 Pea a C2 CFE? C24, C25; haying the standard weights BAG 2D; 26, 27, 28, 29, are saturated respectively by til 4, 3, Dah, unit weights of hydrogen. Complete saturation, with respect to _ either, is represented in the formula Care: Owing, however, to the difficulty of always obtaining hydrogen- compounds, or to the absence of them, the following point has been allowed in practice—that a constant weight of any other element, equivalent to a unit weight of hydrogen, shall be ac- cepted in the place of the latter, and be considered, equally with it, a measure of the saturability of the given substance. This concession has been most frequently made in the case of chlo- rine-, bromine-, and iodine-compounds—an equivalent of either of the elements mentioned being supposed to function, with respect to saturation, in precisely the same manner as one part by weight of hydrogen. It is to this point that I wish briefly to direct attention. The question as to interchangeability of saturating function between any elements must depend not only on their being capable of transposition in terms of equivalent value, but also on their affinity for the substance to be saturated. For it would be impossible to attribute to the vicarious element (as, for ex- ample, chlorine used in the place of hydrogen) the power of satura- tion at all, unless it had an affinity for the substance employed ; nor could it conveniently be taken, if, as is sometimes the case, the affinity were variable in its nature. Furthermore this ex- change of function cannot be considered an equal one unless the two elements are precisely alike in their affinity for the third body. Let us suppose, for illustration’s sake, a radical X! combined with chlorine, bromine, and iodine, the last two being successively weaker compounds. The measure of the full saturability of X/ will be the largest possible quantity (say, of one of these three elements) which has the greatest affinity for it. Hence it is obvious that X'Cl will only be fully saturated; X’Br and X’I will be deficient by some portion of a saturability, a positive number, which may be termed # in the former, and («+y) in the latter case. Each of these quantities might of course ap- proach or exceed unity if X were poly-equivalentic; and it is hardly necessary to say that these remarks apply to any radicals 866 Mr. . J. Mills on a Defect in the Theory of Saturation. combined with X, so long as they are interchangeable and of the same equivalency. Such a doctrine of residual saturability appears of very consi- derable interest. Based as it is on the well-known phenomena of difference in affinity, it rests on a property of bodies still unsubmitted to numerical measurement, but always received as afact. The idea of unequal affinity rests chiefly on results derived from the decomposition of bodies—being thus comple- mentary to the current doctrine of saturation, which more ex- pressly leans on the facts of their synthesis. At the present moment especially it is desirable that the importance of connect- ing these should be taken into consideration. For unless we are prepared to recognize this connexion, we are logically bound to fall back on hydrogen-compounds only, and to content our- selves, in the prospect of much inconvenience, with a dogmatic announcement of merely partial value. But, on the other hand, by accepting it, we are able to explain the formation of certain compounds whose existence otherwise 1s quite anomalous. Thus chloride of silver is ordinarily considered a completely saturated compound. Silver, indeed, being mono-equivalentic, must, after combination with an equivalent of chlorme, be in- capable of entering, according to the common view, into any further union whatsoever. This chloride contains no poly-equi- valentic radical—that kind which is said to possess the power of “accumulating ”’ as its exclusive privilege. Yet the compound 3AgC1+2AgBr, long since described, is perfectly definite; and, to judge from its solubility in solutions of hydrochloric acid and of the chlo- rides of potassium and sodium, chloride of silver also combines with these bodies. The formula of chlorobromide of silver may be expressed under the general one mX!R! + nZ, Z being a quite undetermined body. We see that the residual saturability of three molecules of chloride of silver_is capable of causing them to unite with two of bromide of silver. This consi- deration is in favour of the chloride being the more saturated compound. | The following examples may also be adduced :— AgBr-+ HBr, Agl +2KI, Agl +KI, KI +I, and also the pair AgCl+ AgNO, Agi +AgNO3, Mr. J. Gill on the Dynamical Theory of Heat. 367 the occurrence of which will hardly be attributed to the di- equivalentic nature of oxygen. Again, certain chlorides, which are usually supposed to be fully saturated, unite with water, a substance in which the di- equivalentic oxygen is understood to be completely satisfied. Thus we have the hydrates liCl +nAq (n=1 or 2°), NaCl+ 2Aq, but not a hydrated chloride of potassium. The formation of many double salts, and of direct combinations with water, appear to me to be only explicable on the ground here proposed. This question is not verbal. Affinities are, tacitly at least, taken into account in all our reasonings ; it is impossible for the theory of saturation to be independent of them. The defect in the theory consists in this—omitting to notice the fact that in- terchangeable weights of the same equivalentic order do not usually represent precisely similar affinities. Hence we may arrive at the following general statement :—Any two radicals are not equal in saturating power for a third, unless they are equal 1a equivalency and affinity also; and in most cases of combina- tion there is still residual saturability, due to affinity, enabling the new compound itself to enter into combination. XLV. On the Dynamical Theory of Heat. By Jossru Giiu, Esq.* OTHING in the universe can be supposed to be in a state of isolation; a lone body is evidently a physical impossi= bility ; and therefore it seems impossible to trace back to an ultimate source any physical phenomenon displaying the action of energy or force; for we can perceive no material origin of power, but only a circulation of existing force distributed though- out all the matter of creation. Wherever an increase of energy appears in any portion of matter, we may assume that an equi- valent of energy must have disappeared from some other por- tion of matter, as the phenomena are only indications of dis- turbed equilibrium. When a weight is raised above the surface of the earth, it acquires potential energy in the shape of an in- creased amount of the attraction of gravitation, which must have cost an expenditure of an equal amount of energy from some other body. When a spring is wound up, or an elastic fluid compressed, potential energy appears in the shape of repulsion * Communicated by the Author. 368 Mr. J. Gill on the Dynamical Theory of Heat. in quantity equivalent to the force which had been expended in producing the tension. It seems impossible to form any satisfactory idea of the nature of the forces of attraction and repulsion; and after ages of research by intellects of the highest order the subject still remains enveloped in mystery. Chemical forces seem to be spe- cific properties inherent in matter; and the general forces of at- traction and repulsion are by some considered as essential pro- perties of ponderable matter, while others incline to attribute them to the action of a more subtle fluid medium present in all space, so that matter cannot be conceived of apart from the uni-. versal influence of this all-pervading fluid. The force or vis viva of motion may be conceived of as resulting from an original impression of mechanical power on matter at its creation, or as a consequence of the action of potential energies of attraction and repulsion resulting from primitive positions of disturbed equilibrium, in which atoms and masses may have been placed at their formation. The general sources from which we can derive ready-made elemental power are the natural movements of the atmosphere in the phenomena of the winds, and the fall of water under the influence of common terrestrial gravitation. But it is often more expedient to produce mechanical power by artificial means, or by the arbitrary employment of the natural atomic forces of inanimate matter; and for this purpose we preferably avail our- selves of the chemical forces, generally through the medium of heat. In the combustion of common carbon fuels the heat is supposed to arise from intensely active molecular motion caused by the clashing of the oxygen atoms against those of the carbon, in which process the rapid motion of translation of the excited particles falling violently together under the influence of chemi- cal attraction, is changed by the shock into intense molecular motion of vibration, or orbital movements, or perhaps some mode of individual expansion of the molecules, supposed to constitute the phenomena of heat or temperature. This clashing of the sympathetic particles in the act of combustion suggests the idea of a forcible separation of the same elements at some former period when the fuel was formed. Thus it is supposed that the solar energy at some remote time in the history of creation, when some of the common processes of nature were probably more vigorous than we now perceive them, enabled the vegetative vital principle in the ripe primeval productions of the teeming soil to separate the carbon from the carbonic acid gas of the atmosphere, and to assimilate it in a solid state in the gigantic grottoes of the ancient forests of the carboniferous epoch. In order that the oxygen may combine with the carbon and Mr. J. Gill on the Dynamical Theory of Heat. 369 form carbonic oxide and carbonic acid in the act of combustion, the particles must be brought so close together as to come within the spheres of chemical attraction under the influence of which they unite. It would be difficult to effect this approximation of the particles by gradually squeezing together the two bodies in mass, aS general molecular repulsion increases to a powerful degree under the compression of matter; but in electricity and heat we possess agencies which, operating directly on the indivi- dual particles of matter, can produce results of intensity of action incomparably more powerful than can be effected by any mecha- nical means which can be brought to bear on masses. Thus the friction of a chemical match, by concentrating the mecha- nical action, is sufficient at a few points of actual molecular con- tact to generate a very high local temperature, which throws the excited particles into such violent molecular motion as to impel them over the boundaries of repulsion fairly within the sphere of chemical attraction. Under the influence of this force they combine with intense atomic action, which, communicating from particle to particle, causes the rapid lighting of the whole mass ; and by the same play of molecular movements the phe- nomena of fire or flame may be supposed to originate, from the burning of the humblest rushlight to the most destructive con- flagration. The intense vibratory or orbital motions of the compound par- ticles formed in the act of combustion constitute the heat or temperature of the flame, while solid particles of carbon, ren- dered incandescent by the highly excited atmospheres in which they are enveloped, are supposed to increase its luminosity, giving consistence and body to the fainter light of the glowing gases. The attraction of chemical affinity no longer exists between the homogeneous compound particles resulting from the combustion, and they are now under the uncontrolled influ- ence of common molecular repulsion, which tends to separate the particles, increasing in intensity in some geometrical ratio of the inverse distances. In the case of gunpowder and other explosive compounds, in the solid form containing in themselves the elements whose combination gives rise to the phenomena of combustion, the action of the chemical forces can take place in a confined space, and the accompanying repulsion, resulting from both the tem- porary heat and the permanent expansion of the resulting gases, may be availed of as a direct dynamical agent not only in impel- ling projectiles, but also in giving motion to a piston acting in a cylinder like that of a steam-engine. The same result can be obtained from the close combustion of explosive gaseous mixtures ; and a considerable amount of power can be made 370 Mr. J. Gill on the Dynamical Theory of Heat. available from the direct pressure arising from the tempo- rary heat of the explosive action, even when the bulk of the resulting gases is not, after cooling, greater than that of their constituents,—as experiment shows that in some such cases a momentary increase of bulk of 14 or 15 times the volume when cold may result, indicating a temperature of at least 7000° F. But in obtaining motive power from fire, the molecular motion of the flame is generally transmitted to water in a closed boiler, where, by increasing the intestine movements of the liquid par- ticles, it raises the temperature until, at a pot depending on the superincumbent pressure, the particles in more immediate contact with the source of heat undergo a sudden change of condi- tion, and, absorbing instantaneously a large additional amount of heat (at the ordinary temperature of ebullition), assume the state of vapour and rise to the surface. Under a pressure of 1700 atmospheres water might be heated to about 1200° F. (or 1000° above the common boiling-point), in which condition it would contain heat enough to convert the whole mass into steam, the available amount of repulsion being in proportion; so that by expanding down to atmospheric pressure against a resistance gradually decreasing from 1700 atmospheres to 1, it might per- form a quantity of work eight or ten times as great as is gene- rally obtained from the best steam-engines. This enormous amount of potential energy stored up in the superheated water in the shape of highly excited repulsion, would seem to be due more to the concentration of the heat in possession than to any excess of quantitative heat which the hot fluid may be supposed to contain above the heat of conversion of the same weight of steam at atmospheric pressure. Energy may be put into an elastic fluid, or rather the fluid can be put into a condition of increased energy, either by com- pression or by the actual addition of heat ; and in both cases the quantity of sensible heat, or the temperature, is increased. I have before expressed my opinion that compression, apart from the idea of molecular friction, is not a source of quantitative heat, but only of concentration of heat or temperature. In the act of compression the particles are forced closer together; and supposing the total quantity of heat to remain unchanged, the increase of temperature may result from concentration of mo- lecular action as to the number of vibrations made by each particle in a given time. By the actual addition of heat to an elastic fluid under constant volume, the same effect may be produced of increasing the number of molecular vibrations in a given time. In both cases the heat-tone may be supposed to become more acute from a corresponding change of the thermic rhythm of the molecular vibrations. In compression the increased Mr. J. Gill on the Dynamical Theory of Heat. 371 repulsion is accounted for by the decrease of molecular distances, and by the addition of heat under constant volume the molecular distances are also in effect decreased; for by the addition of heat - or molecular vis viva, the particles of a gas moving with increased energy would approach closer together at some points of their orbits, and recede further asunder at the opposite points; and the general result of the increased energy of the molecular move- ments would be an increase of tension if the repulsion increases, in some geometrical ratio of the inverse distance, because the repulsion would increase by the closer approach of the particles at their points of greater vicinity more than it would diminish by the increased distance at the opposite points. Thus the tension of elastic fluids (and the activity of thermo-dynamical phencmena generally) may be referred to the common principle of mole- cular repulsion, called into action by heat considered as mole- cular motion. The motion of matter in masses may be stopped in various ways, and transformed into different shapes of energy; but it is difficult to conceive how molecular motion could be stopped by any arrangement or combination of common matter. Mole- cular motion is being continually produced in natural phe- nomena, and by artificial agencies, at the expense of energy in various shapes. It can be transferred from one body to another, and modified indefinitely as to its intensity; but its production being continual, it must be supposed to accumulate indefi- nitely, while the other forms of energy from which it has its origin must at the same time be decreasing in equal pro- portion—an assumption which is contrary to all rational proba- bility. This difficulty does not exist in the dynamical theory of heat, as this theory supposes a direct conversion of heat, or mole- cular motion of common matter, into work in the same proportion as work is actually proved to be convertible into heat or molecular motion by friction; and thus a continual and invariable circula- tion of phenomena by interchange or transformation in terrestrial dynatnics can be satisfactorily accounted for, if the direct con- version of heat into work can be proved to be true. _ Any theory of phenomena which involves the circumstance of a continually accumulating amount of disturbance of the mobile equilibrium requisite for the general permanence of physical ex- istence must be considered unsatisfactory. The meteoric theory of the sun’s replenishment, independently imagined by Mayer and by Mr. Waterston, and admirably developed by Professor W. Thomson, is based on reasoning which might obtain for it uni- versal favour, were it not for the idea it involves of a continual transfer of matter in one direction only, and its consequent accu- mulation in the sun, which is opposed to the ideas of constancy 372 Mr. J. Gill on the Dynamical Theory of Heat. and permanence which naturally present themselves to the unpre- judiced mind in contemplating these sublime phenomena. Now by an interesting coincidence it appears that, by supposing the meteoric theory so modified as to avoid the foregomg objection, it would result from this modification that terrestrial molecular motion may, in agreement with known physical laws, be con- verted into the force of gravitation by the agencies of the meteoric phenomena, thus removing a strong objection which would other- wise oppose the repulsion theory of thermo-dynamies which I am endeavouring to develope, while at the same time it supports the idea of a general cosmical stability and permanence. In specu- lations of this kind we cannot expect to arrive at conclusions beyond a mere preponderance of probability on one side or the other of any undecided point; and in such investigations the ardent study of the limited train of facts we possess imevitabl leads into the regions of the unknown; for the vast field of research offers no boundaries; no one part of the subject can be fairly detached from the apparently endless circuit of connexions and relations with which it is bound; and in directing our ex- perimental researches beyond the narrow limits of established fact in search of additional truth, it were unwise to reject the suggestions of analogical probability. Radiant heat is supposed to be propagated in the same manner as light. All bodies radiate heat, and every point of the surface of each is a distinct centre from which undulations of the uni- versal zether proceed in straight lines in all directions without interfering with each other, or with the innumerable waves with which space is filled. Heat in common terrestrial matter has been well designated a mode of motion; but it must be conceived of as molecular motion of a vibratory or orbital character, limited by the balance of forces affecting the particles of a mass under given circumstances. No uninterrupted independent rectilinear motion, either in an atom or a mass, or in the stright-line trans- mission of radiation or electricity, can be imagined of as heat, but rather as vis viva, which may become heat when the motion of a body is stopped and transformed into individual movements of its own particles, or of those of other matter. It is allowed that the chief physical source of terrestrial energy is the sun. The wonderful balance of the perturbations of the solar system, as shown by Laplace and other astronomers, and the rational probability of the immense antiquity of the earth’s existence indicated by geological evidence, suggest ideas of the measure of time in cosmical existence somewhat in agreement with the overwhelming measures of quantity and extension in the universe which even the limited powers of man can faintly appreciate. All things finite must have had a beginning, and Mr. J. Gill on the Dynamical Theory of Heat. 373 may have an end; though the certainty of the prospective eter- nity of our spiritual existence is gladly acknowledged by the wisest and the best, and it is difficult to conceive of the anni- hilation of even common matter. It is probable that our planet has already undergone changes the nature of which may never be clearly revealed to human intelligence; and whenever the great catastrophe may occur which is to change the present order of terrestrial existence, is it not probable that the agencies em- ployed, though not opposing or inverting natural law, may still differ essentially from the ordinary routine of physical phenomena which, with a continual rotation of periodic change, conveys the idea of general cosmical permanence ? Analogy would indicate the probability that the planets may be receiving from the sun something more than mere motion, or radiant heat and light, as generally described, and the idea is not perhaps without support from physical facts. The vital solar fluid which reaches the earth may become, as it were, analyzed and assimilated in the various active processes of nature by which organisms are built up; whilst, besides radiant heat, there is emanating from the earth into space a current of comparatively effete cosmical matter which joins the general effluent solar tide, carrying with it part of the vis viva of the terrestrial molecular motion which we call heat, and another portion of this heat is transferred by the universal ether, in the act of radiation, to the solar tide. The accumulation of molecular motion on the earth’s surface is thus prevented by a continual change into the vis viva of the motion of translation of the effluent particles, which, with the general solar tide in their outward progress, go on changing this vis viva into potential energy of centripetal gravitation. There is reason to believe that the idea of a universal ocean of interstellar ther has been entertained from the remotest times of physical speculation ; and this idea still prevails, being sup- ported by a strong preponderance of probability. The undula- tory theory of light shows that the mighty pulse of this cosmical vital fluid is beating throughout the universe at the amazing rate of four hundred and seventy-four millions of millions of strokes per second! All these pulsations are caught by the delicate eptical mechanism of the eye in a single second, and the resulting impression is that of light. From this single mani- festation some faint idea may be conceived of the wonderful pro- perties which should characterize this cosmical fluid. As com- pared with terrestrial matter, it is supposed to be imponderable and comparatively non-resisting, and to be universally present. It is known that the sun has an atmosphere containing in a state of vapour or gas several substances which exist on our planet in a solid form. How far may the solar atmosphere be 374 Mr. J. Gill on the Dynamical Theory of Heat. imagined probably to extend? The retardation of Eneke’s comet is generally attributed to the resistance of the interstellar ether ; but it is not improbable that the extension of the solar atmosphere may play an important part in producing the effects observed. The meteoric theory of the sun’s heat has much probability in its favour. The immense number of meteors which are periodically seen from some parts of the earth’s surface would seem to prove the existence of an incalculable crowd of small asteroids circula- ting round the sun. Moving through a resisting medium, these small masses may be naturally supposed to be continually suffer- ing a loss of projectile force or vis viva of orbital motion, and consequently to be gradually approaching nearer and nearer to the sun. The zodiacal light is supposed to owe its existence to these crowded meteoric masses. ‘‘ However this may be, it is at least proved that this phenomenon arises from matter which circulates in obedience to planetary laws; the entire mass con- stituting the zodiacal light must be continually approaching, and incessantly raining its substance down upon the sun”*. The heat produced by the collision of an incombustible asteroid thus falling imto the sun, has been calculated to be equal to 9000 times the heat generated by the combustion of an equal asteroid of solid coal. Thus in the force of gravitation we perceive an agency competent to maintain at the surface of the sun a tem- perature far surpassing anything we can conceive of terrestrial combustion. Helmholtz has shown that the force of gravitation now existing as potential energy in the principal bodies of the solar system might, if converted into heat, raise the temperature of a mass of water equal to the sun and planets in weight 28 millions of degrees Centigrade. From the incomparable penetrative power of the solar rays, it is inferred that the temperature of their source must be enormous; and is it not probable that the almost inconceivable temperature of the fiery ocean forming the sun’s surface should volatilize the meteoric matter continually falling ito it, reducing it to a state of gaseous tenuity far beyond anything we can perceive in terrestrial phenomena, and that from this vast alembic the subtle though still ponder- able matter of the sun’s atmosphere should be emitted in a con- tinuoys stream radiating into space? It has been supposed by eminent physicists that gaseous particles fly in straight lines through space; and if the atomic projectiles from the sun's sur- face be supposed to be uninterrupted in their outward pro- gress, they may be imagined to move with a velocity which, in combination with the outward impulsion of the excited ether, should carry them with gradually diminishing motion to an im- mense distance into space (probably far beyond the orbit of the * Prof, Tyndall. Mr. J. Gill on the Dynamical Theory of Heat, 375 most distant planet of the system), till, arrived at the limits where the repulsive force and the power of gravitation are in equili- brium, the outflowing current should come quietly to a state of rest on the vague shores of the solar aérial ocean in circumam- bient space. Here the solar atoms would have no motion, except perhaps some slight vibratory movement from the almost ex- hausted undulations of the ether in these distant regions of space; but gravitation would soon again begin to predominate, and each atom, like a pendulum in vibr ation, would begin gra- dually to return towards its centre of gravitation in the sun. While thus on the verge between their outward and inward movements, the atoms would be in a state of almost perfect equilibrium or neutrality of general forces; and the meeting of - the returning ripples with the spent waves still moving slowly on, under the expiring influence of outward repulsion, might induce an approach of the atoms sufficient to cause aggregation, from the effect of mutual attraction in the absence or abeyance of other forces. We nowhere perceive homogeneity in nature; and even the distribution of highly rarefied gaseous matter in space cannot be supposed to be effected with strict geometrical symmetry. The slightest mequalities of distance between the atoms hovering on their boundaries of solar gravitation would form centres of ag- eregation under the influence of mutual atomic attraction, which would become the nuclei of meteoric formations. In the agglo- merated masses some incipient heat would be generated in the act of aggregation, by converting the motion of translation with which the particles approached each other into reciprocating or orbital molecular motion; but the general temperature would probably be low, and the newly formed meteoric masses might be of considerable density. The return of the meteoric matter, in the shape of these newly formed or still forming masses, to its central source in the sun presents an interesting subject of speculation. Whatever ideas may be entertained of the interstellar zether as a resistin g medium, it seems certain that the meteorites falling towards the sun would meet with considerable resistance from the outflowing tide of the solar atmosphere. Many years ago a theory of the sun’s dyna- mical action appeared which was perhaps entitled to more atten- tion than it received. It supposed that the centrifugal action of the sun’s rotation on his axis causes his equatorial rays to issue obliquely in the direction of the motion of the planets, and thus to influence the planetary motions by direct dynamical action. The meteorites in their approach towards the sun would be deflected from a direct radial course by the slanting direction of the issuing lines of the solar current, and would thus be 376 Mr. J. Gill on the Dynamical Theory of Heat. gradually thrown into orbital courses which might continue for a long time under the influence of planetary laws. Finally, the effect of the resisting medium causes the sun’s attraction to preponderate more and more, and the great stream of meteoric matter rolls on, gradually approaching the sun, in a vast spiral vortex. As graphically imagined by Prof. W. Thomson, “ each meteor thus goes on moving faster and faster, and getting nearer and nearer the centre, until some time, very suddenly, it gets so much entangled in the solar atmosphere as to begin to lose velocity. Ina few seconds more it is at rest on the sun’s surface, and the energy given up is vibrated across the district where it was gathered during so many ages, ultimately to pene- trate, as light, the remotest regions of space.” It is supposed that the principal store of energy which is to furnish future sunlight is im the vis viva and the gravitating power of the meteoric bodies at present circulating inside the earth’s orbit, and probably giving origin to the zodiacal light. However vast these clouds of meteoric matter may be, analogy would certainly indicate that their decrease from the fiery rain which they are continually pouring down upon the sun should be made up from some perennial source of supply, and also that some cosmical process should prevent the continual growth of the sun’s mass which would result from the conditions of the meteoric theory in its present apparently incomplete form. If the idea of the volatilization of the meteoric matter from the sun’s surface, and its diffusion into space, does not involve any contradiction to known physical laws, the system of solar meteorology which I have endeavoured faintly to sketch would tend to show, Ist, that a continuous supply of solid meteoric matter may be accounted for; 2ndly, that the’sun’s mass may remain constant ; and drdly, that the molecular motion of common matter, supposed by the repulsion theory of thermo-dynamics to be directly imconver- tible into work, may be converted into the force of gravitation by the supposed phenomena of the meteoric theory; and hence would result strong presumptive evidence of a general stability of equilibrium in all the physical phenomena of the universe. The quantity of heat emanating from the sun is so vast that no phy- sical theory of its replenishment can be considered satisfactory which should not provide for an indefinite supply of heat-pro- ducing material; and no physical theory can meet this require- ment except on the principle of circulation and transformation. And are not all natural analogies im fayour of such a prin- ciple ? However attractive such speculations may be to the fancy, I should not choose to obtrude hypotheses of cosmical dynamics unconnected with practical objects. In my long observations on M. Secchi on Shooting-Stars, 377 the working of heat-engines, I have not been able to verify the dis- appearance of heat supposed by the dynamical theory to be con- verted into work; and no experiments that I have been able to devise, or that have, to my knowledge, been made by others, have proved the fact. Hence I have been led to investigate the subject from a different point of view, in the hope of disco- vering some satisfactory clue towards the unravelling of this very intricate inquiry. My chief aim in these pursuits has been, and is, to see a satisfactory application of sound thermo-dynamical principles to the improvement of our heat-engines. An eminent scientific authority has called the practical application of thermo- dynamics “the grandest question of all;” and while our prac- tical engineers and mechanicians should encourage the noble ambition of elevating their technical operations to the rank of true scientific performances, our eminent men of science should not disdain to study in its practical details the Titanic engine which forms one of Britain’s noblest boasts; and thus with united energies we may reasonably hope to achieve improve- ments hitherto unlooked for in our thermic prime movers.. Palermo, May 23, 1864. XLVI. On Shooting-Stars. “By Father Srccui*. ees year, as in 1861, the electric telegraph between the observatories at the Collegio Romano and at Civita Vecchia was employed in order to make simultaneous observations, at these places, on the shooting-stars of August, The object of these observations was to determine the height at which these meteors become luminous, and to ascertain the limits of our atmosphere. The observations were commenced on the 5th, and concluded on the 10th of August. There were four obser- vers at Rome, between whom the whole celestial vault was divided; and two at Civita Vecchia, who had instructions to observe the north-eastern half of the heavens from the Great Bear to Aquarius. M. Stabuti and Prof. F. Armellini had the kindness to assist me in these observations; the former, aided by MM. Devarno and Caravani at the chronometer, observed at Civita Vecchia; the latter, together with the other assistants of the observatory, observed with me at Rome. The object of these observations being to fix, precisely, the positions and trajectories, rather than the number of the meteors, many of the latter (con- teniporaneous ones included) were neglected when their number prevented the positions of all from being well determined. * From a letter to M. E. de Beaumont, published in the Comptes Rendus de ? Académie des Sciences, September 26, 1864. Phil. Mag. 8. 4. Vol. 28. No. 190. Nov. 1864, 2C 378 M. Seechi on Shooting-Stars. The apparition of a star was indicated from one place to the other by a touch of the telegraph, given at each place for each star seen; and when the touches at both places were contempo- raneous, the position as seen from CivitaVecchia was immediately telegraphed to Rome, so that we were able to see at once what parallax existed between the two stations. The following Table shows the results, relative to the number of meteors, which were obtained :— Number of stars observed. Period of observation. Date of _ | Propor- OUSCLV as) |e eee a ee ay ea Non-contempora- tional | Rectified tion in Contem- mou: number | number, ahs Sones End. {Duration Leet At Civita a ee ment. At Rome. Vesehies k m h m h m 5 8 48 | 10 14) 1 26 5 él 11 28-9 6 8 45 | 10 23 | 1 38 12 38 8 30°6 q 915 | 10 28 | ¥ 13 8 43 3 41°9 8 | 9389 | 10 37 |} 0 58 20 34 21 558 § | 9 8 | 10 48] 1 40 43:2 0 Oye 2D. lcs ules 45-7 | 63 The moon and mists were somewhat troublesome on the 9th and 10th; the rectified number expresses the result, m one hour, when moon and mist were both absent. The contemporaneous observations proved, as in 1861, that the parallaxes were, in general, enormous, but nevertheless such as to establish the con- siderable height of our atmosphere. Notwithstanding the inde- termination caused by errors of observation, it was impossible, even for an inexperienced observer, to be deceived, since the parallaxes changed the places of entire constellations. Neverthe- less we shall see that much uncertainty still remains with respect to the distances, and that the solution of the problem is not so simple as is generally believed. The determination of the heights of these meteors would be very easy if, in reality, the same point of the trajectory had been observed at the same instant from both stations. For if the two visual rays to this point (say the commencement) were drawn, from their intersection a perpendicular let fall on the plane of the horizon, and the foot of the latter joined to the two stations, a pyramid would be obtained the length of whose vertical edge would be the height of the star. The magnitude of this per- pendicular might be obtaimed, either from calculation, or by a graphic construction similar to that employed in gnomonies for vertical, declined dials. It is merely necessary to know the azi- muths observed at the two stations, and the angular altitudes. From this construction it follows, too, that the magnitude of the M. Secchi on Shooting-Stars. 379 perpendicular ought to remain the same when the elevations of the two stations areemployed; the degree of accordance between the two results serves as a criterion of the trustworthiness of the observation. Repeating the same construction for the end of the trajectory, another point is ascertained, after which the direction and inclination of the actual trajectory are readily de- duced. In order to determine the coordinates of altitude and azimuth, the trajectories were first transferred to a celestial globe 0°53 metre in diameter, the apparent trajectories corresponding to the two stations being marked with different colours. Afterwards all the altitudes and azimuths, of the sixty-nine contemporaneous trajectories which were visible from begimning to end, were determined on the globe itself (placed according to the sidereal hour, which had previously been calculated from the mean times of observation) by means of a moveable vertical quarter of a circle. These preliminaries completed, I proceeded to the gra- phical constructions, referring all to the horizon of Rome, con- sidered as parallel to that of Civita Vecchia; for the difference scarcely exceeds half a degree, the distance between the stations being merely 65 kilometres. The results of these constructions showed that in a great number of cases the values of the perpendicular heights agreed tolerably well, or at all events that they could be made to agree by supposing very probable errors of observation amounting to 1 or 2 degrees. ‘There were many cases, however, in which this agreement was inadmissible. Nevertheless, as no doubt could be entertained of the contemporaneity of the observations, and as the general directions of the apparent trajectories accorded with those which parallax required, we were compelled to admit that the same point of the actual trajectory had not in reality been observed, but that the star had been seen from the two stations at different points of its course. This conclusion involves no improbability ; for, first, the light of many stars is very feeble at the beginning and end of its visible course, and a difference of distance amounting to 60 or 70 kilometres might easily render it invisible from one of the two stations; secondly, notwithstanding all possible care and attention, the eye perceives the star only after its course has commenced, and itis not at all uncommon to find disaccordance even between two observers at the same place; and Jastly, the strength of the observer’s vision must affect essentially the result. This is proved indirectly by the fact that, for the observed ignition, at the middle of its course, of a star which burst into a red-coloured flame and was seen from both stations, 2C 2 380 M. Secchi on Shooting-Stars. the construction gave a height nearly identical for both stations, amounting to 105 kilometres. Here, then, is a new and unexpected difficulty in obtaining exact results. Its solution, nevertheless, is not difficult. It will suffice in fact to apply in such cases the principles of descrip- tive geometry, and to trace the direction of the real trajectory according to any two portions of the apparent trajectories seen from the two different stations. Prof. F. Armellini kindly undertook this determination in many of the cases which proved most difficult and rebellious to the simple geometrical construc- tion. His results were very satisfactory; it was thus proved that these cases followed the rule applicable to the others, but it was necessary to admit that the star had become visible at different times from the two stations. Another consequence of these more accurate constructions is the approximate correctness of the mean of the two heights deduced from the simple con- struction—at all events when the latter do not differ too greatly. This premised, I proceed to the results obtained for the heights of the meteors. In round numbers the mean of all these heights was from 101 to 100 kilometres. There were, in fact, 6 stars whose heights were between 40 and 60 kilometres. 7 99 ry) 33 60 ,, 80 ” 10). 99 Be) ) 80 ,, 100 9 1 7 23 33 33 100 PP) 120 bP) 3 39 39 33 120 33 140 33 5 ” ” ” 140° 34 LOO ae 2 33 33 3) 160 re) 1 80 93 1 33 PP) 33 180 2) 200 39 2 PP) 39 PP) 200 33 220 33 3 a os # 200 and upwards. Thus the heights of 27 out of the whole 56 stars (about 50 per cent.) fell between 80 and 120 kilometres. As in many cases the trajectory was perpendicular to the vertical plane pas- sing through the two stations, the height of the trajectory was constructed directly by the principle of parallaxes, and amounted to 93 kilometres. The mean of the heights of the points of extinction was 75 kilometres. The greatest of the observed heights amounted to between 240 and 260 kilometres; but it must not be forgotten that these values may have been influ- enced by the errors of observation above discussed. Neverthe- less in these cases the heights must have exceeded 200 kilo- metres. M. Secchi on Shooting-Stars. 381 Another remarkable circumstance isthe small horizontal distance of these meteors: in no case did it exceed 222 kilometres, or 2 geographical degrees. A somewhat curious consequence of this is that no meteor seen from one of two stations, more than 444 kilometres asunder, can be identical with any of those seen from the other. If the space that can be examined by an observer from a given station were referred to a globe half a metre (in diameter), we should find that a franc-piece would cover just as much of its surface. This explains why, in certain showers of shooting-stars, the latter have often been so concentrated in one place and wholly invisible in another, and also why the shooting-stars of the period of the 10th of August are not visible in the southern hemisphere. We may also obtain from the above considerations some conception of the prodigious number of these meteors; for if we were to take a circle whose radius is equal to the distance from Rome to Paris, and to suppose the density of these meteors to be 63 per hour (as actually found this year at Paris by M. Coulvier-Gravier, and at Rome by ourselves), the number of meteors falling thereon, daily, would be found to be 18,144. _ This density, however, is very small, and the surface in question is not even equal to the half that of the continent of Europe. In conclusion, we must, I think, admit that the height of our atmosphere exceeds 200 kilometres (1244 English miles), and that at this elevation the density of the air is sufficient to excite light when violently compressed at the surface of these bodies. I say to excite light, and not always to produce combustion ; for, - according to the observations where a veritable combustion was seen to be determined in the middle of the star’s course, it may be questioned whether in reality every train is an actual com- bustion, or whether it may not arise from the production of an electric light developed during the violent friction of the meteor against the air; the heat accompanying which, however, may sometimes elevate the temperature of the body to the point of fusion. Subsequent observations must decide this question. In closing this letter I may observe that the point of depar- ture of most of the shooting-stars always lay between Cepheus and Cassiopeia, but that the parallax must necessarily cause this point to vary for different stars as well as for the same star as seen from different stations. Thus a star which to us ap- peared to be altogether without tail, the eye being in its direction from Cassiopeia, was seen from Civita Vecchia with a pretty long tail and in another part of the heavens. Two, indeed, were ob- served to have opposite directions; but these manifestly moved very slowly. [ 382 ] XLVII. On Molecular Physics. By Prof. W. A. Norton. [Continued from p. 282. ] | considering the changes of state through which the same substance may pass, we have been led to recognize, as an important physical principle upon which the mechanical pro- perties manifested in each new condition in a great degree depend, that the physical condition of the individual molecules is liable to permanent variations from the effect of heat, and that these variations consist mm expansions of the electric atmospheres which surround the atoms of the molecules. If we take a more extended view, and consider the diverse permanent changes of condition which the same substance may experience while in the same state of aggregation, we may discern the operation of a still more comprehensive principle, viz., that the physical state of the atmosphere of a molecule, and therefore the curve which represents its action upon surrounding molecules, is liable to permanent alteration from the action of external forces gene- rally. It is well known that if a mechanical force, of conside- rable intensity, be applied for a short interval of time to a body, the result will be a permanent change in its form. The expe- riments of Hodgkinson have indeed established that a certain set may be imparted to bars of cast iron, by a temporary load which is but a small fraction of its breaking load, and that “there is no weight, however small, that will not injure the elasticity ” of such a bar. As we cannot suppose that a given mass of mole- cules, while retaining forces of mutual action of unvarying in- tensity, can take up an infinite number of positions of equili- brium, differing but slightly from each other, we must conclude that the individual molecules experience some change of condi- tion, which occasions a change in the intensities of the forces they exert in a given direction. From our present theoretical point of view, such possible changes of condition consist im compressions, or expansions, of the molecular atmospheres, either as a whole or unequally on different sides. In the former case there will be a variation in the size of the atmosphere, and in the intensities of the forces of attraction and repulsion exerted by the molecule at a given distance, but the forces exerted in different directions will have an equal intensity. In the latter case there will be a variation in the form of the atmosphere, and an inequality of action in different directions. The form assumed will be sphe- roidal, or approximately so, supposing it to have been origi- nally spherical; and the mechanical result will be the exer- tion of an increased force of attraction from the sides of the molecule at which its atmosphere is compressed, and a dimi- Prof. Norton o% Molecular Physics. 383 nished force from the sides at which the atmosphere is expanded. This follows, as a necessary consequence, from the fundamental conception of molecular forces, developed on pages 199 to 204, as may be distinctly seen by attending to the values of ~ andr. It will thus be seen that the molecular atmospheres, in assuming the spheroidal form, under special circumstances, determine the existence of molecular axes of cohesive attraction, “‘ whose force is inversely related to their length.” In the direc- tion of such axes, then, the limit of stable equilibrium (Oa, fig. 1, p. 203) will be least for the shorter axis, and greater for the longer axis. When a force of pressure applied to a body determines a per- manent compression, the molecular atmospheres remain com- pressed, or in closer proximity to their central atoms, and the force of cohesive attraction is permanently increased, and the limit of stable equilibrium diminished. The heat developed is a necessary result of the compression of the atmospheres. If the elastic reaction to the pressure after it is withdrawn were per- fect, the atmospheres would resume their original form and dimensions, the original molecular forces would be recovered, and the heat evolved would be absorbed again. In general when mechanical forces are applied to a body, the heat evolved, or absorbed, is a necessary accompaniment of the compressions, or expansions, superinduced in the atmospheres of the particles, and may be regarded as a sensible indication of the extent of such changes of molecular condition. The mechanical work, of which the heat evolved serves as the measure, is expended in urging the atmospheres nearer to their central atoms. On the other hand, if heat be directly applied to a body, it has a tendency opposite to that of a mechanical pressure, or to expand the molecular atmospheres, and so to reduce the inten- sity of the cohesive attraction at a given distance. It is to be observed also that heat has a tendency to dissolve the groups in which the particles of a solid may be aggregated, and, when the point of fusion is reached, will effectually break up such groups and bring the mass to the condition of a homogeneous and sym- metrical arrangement of molecules. Solidification, or Crystallization.—It is a well recognized prin- ciple that solidification and crystallization are the same process. This great principle was first propounded by the learned and acute Dr. Young in 1807, in his lectures on Natural Philosophy. It has also been advocated by Biot and other physicists, and more recently has been reasserted and ably sustained by Professor Dana, in his admirable paper “On Cohesive Attraction,” pub- lished in vol. iv. second series, of Silliman’s Journal. If now it 384 Prof. Norton on Molecular Physics. be admitted that solidification is in every instance but a more or less perfect crystallization, it will be perceived that the investi- gation of the mechanical process of crystallization must consist essentially in an inquiry into the conditions and results of the operation of the molecular forces under special circumstances. The general nature of these forces, and the laws of the variation of effective molecular action with the distance between two mo- lecules, have already been under discussion. We have also seen (pp. 882, 383) that the mechanical condition of an individual molecule is subject to change under the operation of heat, and external forces generally, by reason of a change produced either in the dimensions or form of the atmosphere of the molecule, and that it may thus acquire permanent axes of attractive force. To establish a sufficient basis for a general explanation of crys- tallization, we have only to remark further that the molecule of every particular substance has primarily and inherently its own special physical condition, by virtue of which it exercises an effective action that would be represented by a special curve, and experiences under the operation of heat and other causes its own peculiar changes of mechanical condition. Upon this idea it - - may be seen that every substance may have its particular form of crystallization, although the molecules should be devoid of all natural polarity. The different systems of crystallization may be regarded as so many different systems of equilibrium of masses of molecules, under the operation of molecular forces diversely modified by the circumstances that determine the crystallization. The gene- ral nature of the modifications consists in a spheroidal form im- parted to the molecular atmospheres, and the consequent deve- lopment of certain axes of attraction—that is, of diameters of least or greatest length, in the direction of which the attraction has at a given distance a maximum or minimum value, and the limit of stable equilibrium (Oa, fig. 1, p. 203) a minimum or maximum value. Crystallization begins at a certain point of a hquid, and is generally determined by the loss of heat, or the evaporation of the liquid solvent. We already have seen reason to believe that the molecules of the liquid have a symmetrical arrangemeut previous to the erystallization (p. 279). Whether this be ad- mitted or not, such an arrangement obtains in the crystal formed from the liquid. The particles successively take positions 1m the corners or angular points of a series of polyhedral figures; as cubes, prisms, octahedrons, &c. Any two such figures lymg contiguous to each other, have a common face, or, as in the case of the octahedron, a common angular pomt. ‘The crystalliza- tion takes place either successively or simultaneously in the Prof. Norton on Molecular Physics. 385 faces of these figures. We have then first to consider the pro- cess of crystallization as it may occur in a single plane. The result of every such process is the arrangement of the molecules in the angular points of a series of quadrilaterals ; - which may be squares, rectangles, rhombuses, or rhomboids. If we suppose, in the first instance, several molecules to unite along a single line, and molecules posited on either side of this line to unite with those already crystallized, three different general modes of arrangement may occur: the new particles may take up positions opposite those of the first line, or opposite the mid- die points of the intervals between these particles, or opposite other than the middle points of these intervals. In the first case, squares or rectangles will be formed; in the second, rhom- buses, which may in special cases be squares; and in the third, rhomboids, which in special cases may be rectangles. The ge- neral tendency of the crystallization occurring along the first line should be, by reason of the compression of the molecular atmo- spheres along this line, and the consequent expansion of them in a direction perpendicular to it, to develope an axis of in- creased attraction in this primary lime of crystallization, and an axis of diminished attraction in the perpendicular direction. When this result is reached, and successively along the lines of _ particles parailel to the first, the figure assumed will be either a square, a rectangle, or a riombus. The two molecular axes will be coincident with the sides of the minute rectangular figures that make up the larger rectangle, and with the diagonals of each minute rhombus. The condition essential to the forma- tion of a square 1s that the properties of the molecules in refer- ence to cooling (or, in general, in reference to the propagation and absorption of impulses) should be such that each set of four contiguous molecules are, when in the incipient state of crystal- lization, in the same physical condition. That a rectangle may be formed, a group of four particles must unite ; but the escape of the heat-pulses that occurs primarily in the direction of one of the sides of the rectangle must determine a greater compres- sion of the molecular atmospheres in this direction than in that of the other side. ‘That the figure of a rhombus may be assumed, two particles must first unite, and subsequently two other par- ticles must take up, under the attractive action of these, posi- tions opposite the middle of the interval between them. To understand how a rhomboid may result, we must observe that when a line of particles is crystallizing, each particle, m, as it becomes united, exerts a certain disturbing action upon a par- ticle m! next in the line, and also upon a contiguous particle » at one side of the line. When the particle m! unites, it also modifies the condition of n; but as its action is subsequent to 386 Prof. Norton on Molecular Physics. that of m, it is possible that in special cases the final result may be an inequality of disturbance, so that m and m! will attract unequally, and the position of equilibrium assumed by it will in consequence not be opposite the middle of the interval between mand m!. In this case the electric atmosphere of n will have a form differently modified, and its second axis will be oblique to the line of primary crystallization in which the axis first deve- loped les. The figure first assumed must then depend upon the ae mental properties, with respect to heat, &c., of the individual molecules of the substance; and the general tendency must be, for the first group of molecules to acquire increased dimensions by successive solidifications of a series of figures similar to the first. In what precedes, we have had regard only to the play of the ordinary molecular forces, and the modifications which the ordi- nary molecular action may experience from the loss of heat, and in the act of solidification ; but there must result in each instance of the union of two particles a modification of the condition of their atmospheres, which should develope a new force of attrac- tion that may play an important part in the continuation of the process of crystallization. For when two particles unite by crystallization, their atmospheres on their nearer sides will be- come compressed, and consequently on their further sides ex- panded. Lach molecule will thus virtually be brought into an electro-polar condition, with the positive pole turned outward. This positive pole, or excess of electric zther, tends to bring all the molecules lying in the prolongation of the line of the first two into the same electro-polar condition, and in this state of induced polarization a force of electric attraction will subsist between the particles. As one particle after another in the line comes to unite with those previously crystallized, its previous polarization will be enhanced, and it will exert an increased attractive force upon those not yet crystallized. At the same time, by the compressive and repulsive action of the contiguous atmospheres, the particle with which the new one unites will lose a considerable portion of its polarity. This reflex action, attendant upon every act of union, should eventually greatly diminish, if not wholly remove, the prior induced polarization. Another effect of this reflex action to be noticed i is, the in- creased expansion of the atmosphere of the molecule which experiences the reactive compression in the direction perpendi- cular to the line of crystallization. This molecule thus acquires an increased positive polarization on the outer side, lying in this perpendicular direction, and therefore exerts an increased force of electric attraction in this direction. In the varying operation Prof. Norton on Molecular Physics. 387 of this induced electric polarization, and of the reflex action just noticed, we may discern the probable origin of those supposed variations of axial attraction which Professor Dana has shown will suffice for the explanation of secondary planes in crystal- lization. To illustrate by a special case, let fig. 2 represent a process of crystalli- zation in which the particles are ar- ranged in successive squares. When ¢, c,c are the outer particles, their outer sides will be positively pola- rized, and will consequently exert an electric attraction, in addition to the increasing molecular attraction that results from the cooling, upon the molecules c’,c',c' immediately exterior to them. The next step in the pro- cess should be the union of the molecules thus attracted; and all of these molecules should have the same tendency to unite, unless there should bea material inequality in the physical con- dition of the outer particles c, c, c, c on different sides of the square, ccec. But the four corner particles, ec", c’, c’, cl", can- not thus be directly brought into union with the particles of the erystal. They must either unite with the nearest particles of those newly attached, or remain disunited, to become incorpo- rated at a later stage of the process. In the normal or complete growth of the crystal, the first would be the result. If, on the other hand, the forces of the new lines of outer particles c’, c! cc! should fall off materially in intensity, so that the corner particles c are not taken up in the same step of the process as the others, secondary lines would arise at the angles of the square ¢’, ce", c', cl’. In the whole cubical crystal, of which fig. 2 represents a section, secondary planes would be formed at the edges. very such line or plane may have different positions, according as the corner par- ticles in question (c’) become incorporated in the next stage of the growth of the crystal, or in some of the subsequent stages. This Professor Dana has distinctly shown. What we have here to observe is simply that, by reason of the reflex action above noticed (p. 386), when new particles become united to c’, c’, these particles, c’, c’, will in fact exert a more energetic attraction late- rally upon e”, c’’; and hence the union of ce”, c with the crystal may then be determined. If not, the next augmentation of the attractive force attendant upon the union of the next set of mo- lecules may determine this result. In order that a complete polyhedral crystal may be formed, it is necessary that molecules on one or both sides of a plane in 388 Prof. Norton on Molecular Physics. which crystallization occurs should become united with those that take up their positions at the angles of the plane figure. Thus two sets of four molecules in parallel planes may take up positions of equilibrium at the eight angular points of a cube, or six may form an octahedron, &c. The conditions that will determine the figure of equilibrium assumed may be inferred from the general considerations already presented (pp. 885 and 886). The compression of the molecular atmospheres in the first plane of crystallization will tend to develope a third axis of attraction perpendicular to thisplane. Various systems of crys- tallization are possible, since the particles on one side of the first plane may take up positions of equilibrium perpendicularly opposite to those that crystallize in this plane, or opposite the intervals between parallel pairs of these particles, or opposite the centre of the quadrilateral figure which they form*. Professor Dana has shown that the various fundamental forms of crystals may be obtained by regarding the crystal as a mass of bipolar molecules, of a spherical or spheroidal form, in con- tact along certain lines, which are the conjugate axes or conju- gate diameters of the spheroids. This conception of the consti- tution of a crystal is, in a geometrical point of view, equivalent to that which has now been given. For we have only to con- ceive spheroids to be inscribed in the polyhedral figures of the compound crystal molecules just supposed, to obtain the repre- sentative spheroidal molecules of Prof. Dana; which will also touch each other along similar conjugate diameters of the differ- ent spheroids. Itis not difficult to make out the various posi- tions of equilibrium of the particles that must obtain in the different fundamental forms, and the various physical conditions of the particles upon which these forms must dependy. In his paper On Cohesive Attraction,” Professor Dana has apparently put the explanation of the cleavage of crystals on the true basis, by attributing it to alternations in the intensity of the attraction in a series of parallel planes. If such alternations really exist, we naturally seek for the explanation of them in alternations of the mechanical condition of the molecules upon * This is only a partial view of the matter. + The hypothesis of a permanent polarity of atoms or molecules has subserved a valuable purpose in linking together phenomena under one physical conception in several departments of physical science; but the progress of science has materially tended of late to shake the confidence reposed in it as a supposed truth of Nature. It will be conceded that it is the dictate of true philosophy to hold it in abeyance until it shall have become abundantly evident that the phenomena in question cannot be deduced from the fundamental conception of the constitution of a mole- cule, and of the primary forces of attraction and repulsion, to which all other molecular phenomena can be referred. Prof. Norton on Molecular Physics. 389 which the energy of the molecular forces depend. It is conceiv- able that such differences may result from the heat evolved in the process of crystallization. Let fig. 8, d, b, c, d, e, &e., be a line of particles crystalli- aa in regular succession. ‘ hen aunites with b,the yw aaa heat given out will expand =-@- eS the atmosphere of ¢; and it is possible that, after this effect has been produced, the expanded atmosphere will not become condensed, under the operation of the crystallizing forces, as much as it otherwise would have been, and hence that the molecular attractive force of ¢ will be less than would have otherwise resulted. If the attraction between 6 and ¢ should thus be materially lessened, there would be in consequence less heat evolved in the union of the two, and so the attractive force of d would be less weak- ened than that of c has been. Accordingly, in the union of e and d an excess of heat would again be given out. In this Way a series of alternations in the intensity of the cohesive attraction might be brought about along the line of erystailized molecules. It will be observed that the same fundamental idea pervades all the explanations that have now been given of changes of molecular aggregation, whether these are attended with a change of state, or only with a change of density and form. This is the idea that the physical and mechanical condition of a mole- cule may change with varying circumstances, and that it may undergo a permanent change, although the temperature should remain the same. The change of condition consists simply in the expansion or contraction of the electric atmosphere of the molecule (p. 382). We have recognized, also, that while the processes of transformation are going on, the normal distribu- tion of the electric ether, that forms the atmosphere of a mole- cule, may become disturbed, and that thus a transient electric polarity of the molecule may be induced which may play an im- portant part in the process. Upon the theory of crystallization here offered, the pheno- menon of dimorphism, and all changes of form, in the same crys- tal, produced by heat and external causes generally, are but simple results of the modifications superinduced by these causes, in the form or distance from the central atoms of the molecular atmospheres—that is, in the physical features of the molecules, upon which the system of crystallization in everyinstance depends. [To be continued. | b fe eo0m sy XLVIII. Notices respecting New Books. The Laboratory Guide for Students of Agricultural Chemistry. Ar- ranged by Artuur Herspert Cuurcu, M.A., Professor of Che- mistry in the Royal Agricultural College, Cirencester. Post 8vo.: London: Van Voorst. 1864. Pp. viii and 94. HIS little work is divided into two Parts. The first, intended as an outline of the general course of qualitative analysis, begins with an enumeration and brief description of the more com- monly occurring elements; then follow concise directions for pre- paring and purifying the reagents required in the subsequent pro- cesses ; and next about twenty-three pages devoted to ‘“‘ The Method of Analysis.” The second Part consists of a series of examples for practice in quantitative analysis, selected from among such sub- stances as are most likely to come in the way of an agricultural chemist. It is this second part which gives to the book its distinctive cha- racter and its chief value. ‘The examples here given have been judi- ciously selected so as to embrace a considerable variety of processes, while the working directions are almost always clear and sufficient for the object in view. A few of the best volumetric methods have been included, among which are two very good ones that we do not remember to have frequently met with in works of this class—namely, Mohr’s process for the estimation of chlorine by nitrate of silver and chromate of potash, and the late Dr. Pugh’s method of estimating nitric acid. This portion of the work appears to us so well planned and so likely to be useful, that we should be glad to see it extended so as to occupy the whole book instead of the last fifty-three pages merely. On the other hand, we do not think that the consequent exclusion of the part devoted to qualitative analysis would greatly diminish the value of the work. As it is, Professor Church leaves so much, of what it is necessary for the student to know respecting this branch of the subject, to be supplied from other sources, that he might, without much danger, have left the whole of what is given in this portion of his book to be supplied in the same way. Indeed, were this a suitable occasion for discussing the question, very much might be said against that system of laboratory teaching in which a ‘‘Scheme” or ‘‘ Method” of qualitative analysis, such as that contained in the first part of this work, is put into the hands of the student at the very beginning of his course. We believe that the very opposite system to this would, more than anything else, tend to promote the rational study of chemistry. As far as possible, we would have students encouraged to rely upon their own experi- ence and observations rather than upon books of any sort; and most of all we would endeavour to persuade them to use no Analy-- tical Schemes or Tables until they can construct them from their own knowledge, or are independent of them altogether. Mr. Church’s work, however, not being addressed to students of scientific che- mistry, so much as to those whose object is merely to become ac- quainted with one of its most important practical applications, and _ Royal Society. 391 who perhaps in most cases have neither time nor inclination to devote much attention to the study of chemistry for its own sake, it would be unfair to charge upon it as a fault that it follows the most commonly received system of instruction in the science, even although we may be of opinion that that system is not the best possible. We have exceedingly little to say in the way of adverse criticism on the details of this work. Here and there, possibly, are signs of somewhat hasty composition or correction: to this cause, for instance, we attribute the occurrence of such an expression as ‘‘ oil of vitriol plus its own bulk of water”’ on page 77, an expression which is much less pleasant than “‘ oil of vitriol diluted with its own bulk of water,” which we find on the following page. Again, on page 17 we are told that solutions of silver yield ‘‘a buff precipitate with hydrate of soda,” where for hydrate we are doubtless intended to read carbonate. The method of preparing absolute alcohol, recommended on page 13, might likewise be improved; for alcohol can be more completely and easily dehydrated by using a sufficient quantity of good quicklime than by either carbonate of potash or sulphate of copper. In conclusion, we have again to express our conviction that Mr. Church has produced a book well qualified to be of use to those to whom it is addressed; and if we have suggested a plan by which, without increasing the size of the book, its utility might, in our opinion, be made still greater, it is by no means because we con- sider its value small in its present shape. XLIX. Proceedings of Learned Societies. ROYAL SOCIETY. [Continued from p. 320. ] June 16, 1864.—Major-General Sabine, President, in the Chair. Apne following communication was read :— “Qn the Reduction and Oxidation of the Colouring Matter of the Blood.” By G. G. Stokes, M.A., Sec. R.S., &c. 1..Some time ago my attention was called to a paper by Pro- fessor Hoppe*, in which he has pointed out the remarkable spec- trum produced by the absorption of light by a very dilute solution of blood, and applied the observation to elucidate the chemical nature of the colouring matter. I had no sooner looked at the spectrum, than the extreme sharpness and beauty of the absorption-bands of blood excited a lively interest in my mind, and I proceeded to try the effect of various reagents. The observation is perfectly simple, since nothing more is required than to place the solution to be tried, which may be contained in a test-tube, behind a slit, and view it through a prism applied to the eye. In this way it is easy to verify Hoppe’s statement, that the colouring matter (as may be presumed at least from the retention of its peculiar spectrum) is unaffected by * Virchow’s Archiv, vol. xxiii. p. 446 (1862), 392 | Royal Society :— alkaline carbonates and caustic ammonia, but is almost immediately decomposed by acids, and also, but more slowly, by caustic fixed alkalies, the coloured product of decomposition being the heematine of Lecanu, which is easily identified by its peculiar spectra. But it seemed to me to be a point of special interest to inquire whether we could imitate the change of colour of arterial into that of venous blood, on the supposition that it arises from reduction. 2. In my experiments I generally employed the blood of sheep or oxen obtained from a butcher ; but Hoppe has shown that the blood of animals in general exhibits just the same bands. To obtain the colouring matter in true solution, and at the same time to get rid of a part of the associated matters, I generally allowed the blood to coagulate, cut the clot small, rinsed it well, and extracted it with water. This, however, is not essential, and blood merely diluted with a large quantity of water may be used; but in what follows it is to be understood that the watery extract is used unless the contrary be stated. 3. Since the colouring matter is changed by acids, we must employ reducing agents which are compatible with an’alkaline solution. If to ‘a solution of protosulphate of iron enough tartaric acid be added to prevent precipitation by alkalies, and a small quantity of the solu- tion, previously rendered alkaline by either ammonia or carbonate of soda, be added to a solution of blood, the colour is almost instantly changed to a much more purple red as seen in small thicknesses, and a much darker red than before as seen in greater thickness. The change of colour, which recalls the difference between arterial and venous blood, is striking enough, but the change in the absorption spectrum is far more decisive. The two highly characteristic dark bands seen before are now replaced by a single band, somewhat broader and less sharply defined at its edges than either of the former, and occupying nearly the position of the bright band sepa- rating the dark bands of the original solution. The fluid is more transparent for the blue, and less so for the green than it was before. -If the thickness be increased till the whole of the spectrum more refrangible than the red be on the pomt of disappearing, the last - part to remain is green, a little beyond the fixed line 6, im the case of the original solution, and blue, some way beyond F, in the case of the modified fluid. Figs. 1 and 2 in the accompanying woodcut represent the bands seen in these two solutions respectively. 4. If the purple solution be exposed to the air in a shallow vessel, it quickly returns to its original condition, showing the two charac- teristic bands the same as before; and this change takes place imme- diately, provided a small quantity only of the reducing agent were employed, when the solution is shaken up with air. If an additional quantity of the reagent be now added, the same effect is produced as at first, and the solution may thus be made to go through its changes any number of times. 5. The change produced by the action of the air (that is, of course, by the absorption of oxygen) may be seen in an instructive form on partly filling a test- tube with a solution of blood suitably Prof. Stokes on the Colouring Matter of the Blood. 3893 diluted, mixing with a little of the reducing agent, and leaving the tube at rest for some time in a vertical position. The upper or oxidized Big. 1. portion of the solution is readily distinguished by its colour ; and if the tube be now placed behind a slit and viewed through a prism, a dark band is seen, having the general form of a tuning-fork, like figs. 1 and 2, regarded now as a single figure, the line of separation being supposed removed. 6. Of course it is necessary to assure oneself that the single band in the green is not due to absorption produced merely by the reagent, as is readily done by direct observation of its spectrum, not to men- tion that in the region of the previous dark bands, or at least the outer portions of it, the solution is actually more transparent than before, which could not be occasioned by an additional absorption. Indeed the absorption due to the reagent itself in its different stages of oxidation, unless it be employed in most unnecessary excess, may almost be regarded as evanescent in comparison with the absorp- tion due to the colouring matter ; though if the solution be repeatedly put through its changes, the accumulation of the persalt of iron will presently tell on the colour, making it sensibly yellower than at first for small thicknesses of the solution. 7. That the change which the iron salt produces in the spectrum is due to a simple reduction of the colouring matter, and not to the formation of some compound of the colouring matter with the re- agent, is shown by the fact that a variety of reducing agents of very different nature produce just the same effect. If protochloride of tin be substituted for protosulphate of iron in the experiment above de- scribed, the same changes take place as with the iron salt. The tin solution has the advantage of being colourless, and leaving the visi- ble spectrum quite unaffected, both before and after oxidation, and accordingly of not interfering in the slightest degree with the optical examination of the solutions, but permitting them to be seen with Phil. Mag. 8. 4. Vol. 28. No. 190. Nov. 1864. 2D 394 Royal Society :— exactly their true tints. The action of this reagent, however, takes some little time at ordinary temperatures, though it is very rapid if previously the solution be gently warmed. Hydrosulphate of am- monia again produces the same change, though a small fraction of the colouring matter is liable to undergo some different modification, as is shown by the occurrence of a slender band in the red, variable in its amount of development, which did not previously exist. In this case, as with the tin salt, the action is somewhat slow, requiring a few minutes unless it be assisted by gentle heat. Other reagents might be mentioned, but these will suffice. 8. We may infer from the facts above mentioned that the colour- ing matter of blood, like indigo, zs capable of existing in two states of oxidation, distinguishable by a difference of colour and a funda- mental difference in the action on the spectrum. It may be made to pass from the more to the less oxidized state by the action of suitable reducing agents, and recovers its oxygen by absorption from the air. As the term hematine has been appropriated to a product of decom- position, some other name must be given to the original colouring matter. As it has not been named by Hoppe, I propose to call it cruorine, as suggested to me by Dr. Sharpey ; and inits two states of oxidation it may conveniently be named scarlet cruorine and purple cruorine respectively, though the former is slightly purplish at a cer- tain small thickness, and the latter is of a very red purple colour, becoming red at a moderate increase of thickness. 9. When the watery extract from blood-clots is left aside in a corked bottle, or even in a tall narrow vessel open at the top, it pre- sently changes in colour froma bright to a dark red, decidedly purple in small thicknesses. This change is perceived even before the solu- tion has begun to stink in the least perceptible degree. The tint agrees with that of the purple cruorine cbtained immediately by reducing agents; and if a little of the solution be sucked up from the bottom into a quill-tube drawn to a capillary point, and the tube be then placed behind a slit, so as to admit of analyzing the trans- mitted light without exposing the fluid to the air, the spectrum will be found to agree with that of purple cruorme. On shakimg the solution with air it immediately becomes bright red, and now pre- sents the optical characters of scarlet cruorme. It thus appears that scarlet cruorine is capable of being reduced by certain sub- stances, derived from the blood, present in the solution, which must themselves be oxidized at its expense. 10. When the alkaline tartaric solution of protoxide of tin is added in moderate quantity to a solution of scarlet cruorme, the latter is presently reduced. If the solution is now shaken with air, the cruorine is almost instantly oxidized, as is shown by the colour of the solution and its spectrum by transmitted light. On standing for a little time, a couple of minutes or so, the cruorine is again reduced, © and the solution may be made to go through these changes a great number of times, though not of course indefinitely, as the tin must at last become completely oxidized. It thus appears that purple cruorine absorbs free oxygen with much greater avidity than the tin Prof. Stokes on the Colouring Matter of the Blood. 395 solution, notwithstanding that the oxidized cruorine is itself reduced by the tin salt. I shall return to this experiment presently. 11. When a little acid, suppose acetic or tartaric acid, which does not produce a precipitate, is added to a solution of blood, the colour is quickly changed from red to brownish red, and in place of the original bands (fig. 1) we have a different system, nearly that of fig. 3. This system is highly characteristic; but im order to bring it out a larger quantity of substance is requisite than in the case of scarlet eruorime. The figure does not exactly correspond to any one thickness, for the bands in the blue are best seen while the band in the red is still rather narrow and ill-defined at its edges, while the narrow inconspicuous band in the yellow hardly comes out till the whole of the blue and violet, and a good part of the green, are absorbed, The difference in the spectra figs. 1 and 3 does not alone prove that the colouring matter is decomposed by the acid (though the fact that the change is not instantaneous favours that supposition), for the one solution is alkaline, though it may be only slightly so, while the other is acid, and the difference of spectra might be due merely to this circumstance. As the direct addition of either ammonia or - carbonate of soda to the acid liquid causes a precipitate, it is requi- site in the first instance to separate the colouring matter from the substance so precipitated. This may be easily effected on a small scale by adding to the watery extract from blood-clots about an equal volume of ether, and then some glacial acetic acid, and gently mixing, but not violently shaking for fear of forming an emulsion. When enough acetic acid has been added, the acid ether rises charged with nearly the whole of the colouring matter, while the substance which caused the precipitate remains in the acid watery layer below*. ‘The acid ether solution shows in perfection the characteristic spectrum fig. 3. When most of the acid is washed out the substance falls, remaining in the ether near the common surface. If after removing the wash-water a solution, even a weak one, of ammonia or carbonate of soda be added, the colouring matter readily dissolves in the alkali. The spectrum of the transmitted light is quite different from that of scarlet cruorine, and by no means so remarkable. It presents a single band of absorption, very obscurely divided into two, the centre of which nearly coincides with the fixed line D, so that the band is decidedly less refrangible than the pair of bands of scarlet cruorine. The rela- tive proportion of the two parts of the band is liable to vary. The presence of alcohol, perhaps even of dissolved ether, seems to favour the first part, and an excess of caustic alkali the second, the fluid at the same time becoming more decidedly dichroitic. The blue end of the spectrum is at the same time absorbed. The band of absorption is by no means so definite at its edges as those of scarlet cruorine, and a far larger quantity of the substance is required to develope it. * If I may judge from the results obtained with the precipitate given by acetic acid and a neutral salt, a promising mode of separation of the proximate consti- tuents of blood-crystals would be to dissolve the crystalsin glacial acetic acid and. add pects which precipitates a white albuminous substance, leaving the hematine in solution. sss one 2D2 396 Royal Society :— This difference of spectra shows that the colouring matter (heema- tine) obtained by acids is a product of the decomposition, or meta- morphosis of some kind, of the original colouring matter. When hematine is dissolved in alcohol containing acid, the spec- trum nearly agrees with that represented in fig. 3. 12. Heematine is capable of reduction and oxidation like cruorine. If it be dissolved in a solution of ammonia or of carbonate of-soda, and a little of the iron salt already mentioned, or else of hydrosul- phate of ammonia, be added, a pair of very intense bands of absorp- tion is immediately developed (fig. 4). These bands are situated at about the same distance apart as those of scarlet cruorine, and are no less sharp and distinctive. They are a little more refrangible, a clear though narrow interval intervening between the first of them and the line D. They differ much from the bands of cruorine in the relative strength of the first and second band. With cruorine the second band appears almost as soon as the first, on increasing the strength or thickness of the solution from zero onwards, and when both bands are well developed, the second band is decidedly broader than the first. With reduced hematine, on the other kand, the first band is already black and intense by the time the second begins to appear; then both bands increase, the first retaining its superiority until the two are on the point of merging into one by the absorption of the intervening bright band, when the two appear about equal. Like cruorine, reduced hzematine is oxidized by shaking up its solution with air. I have not yet obtamed hematine in an acid solution in more than one form, that which gives the spectrum fig. 3, and which I have little doubt contains heematine in its oxidized form ; for when it is withdrawn from acid ether by an alkali, I have not seen any traces of reduced hzematine, even on taking some precau- tions against the absorption of oxygen. 4s the alkaline solution of ordinary hzmatine passes, with increase of thickness, through yellow, green, and brown to red, while that of reduced heematine is red throughout, the two kinds may be conveniently distinguished as brown hematine and red hematine respectively, the former or oxi- dized substance being the hzematine of chemists. 13. Although the spectrum of scarlet cruorine is not affected by the addition to the solution of either ammonia or carbonate of soda, yet if after such addition the solution be either heated or alcohol be added, although there is no precipitation decomposition takes place. The coloured product of decomposition is brown heematine, as may be inferred from its spectrum. Since, however, the spectrum of an alka- hne solution of brown hzematine is only moderately distinctive, and is somewhat variable according to the nature of the solvent, it is well to add hydrosulphate of ammonia, which immediately developes the remarkable bands of red heematine. This is the easiest way to obtain them; but the less refrangible edge of the first band as obtained in this way is hable to be not quite clean, in consequence of the pre- sence of a small quantity of cruorine which escaped decomposition. Some very curious reactions are produced in a solution of cruorine by gallic acid combined with other reagents, but these require further study. Prof. Stokes on the Colouring Matter of the Blood. 397 14. Hoppe proposed to employ the highly characteristic absorp- tion-bands of scarlet cruorine in forensic inquiries. Since, however, cruorine is very easily decomposed, as by hot water, alcohol, weak acids, &c., the method would often be inapplicable. But as in such cases the coloured product of decomposition is heematine, which is a very stable substance, the absorption-bands of red heematine in alka- line solution, which in sharpness, distinctive character and sensibi-. lity rival those of scarlet cruorine itself, may be employed instead of the latter. The absorption-bands of brown hematine dissolved in a mixture of ether and acetic acid, or in acetic acid alone, are hardly less characteristic, but are not quite so sensitive, requiring a somewhat larger quantity of the substance. 15..1 have purposely abstained from physiological speculations until I should have finished the chemico-optical part of the sub- ject; but as the facts which have been adduced seem calculated to throw considerable light on the function of crnorine in the animal economy, I may perhaps be permitted to make a few remarks on this subject. It has been a disputed pomt whether the oxygen introduced into the blood in its passage through the lungs is simply dissolved or is chemically combined with some constituent of the blood. The latter and more natural view seems for a time to have given place to the for- mer in consequence of the experiments of Magnus. But Liebig and others have since adduced arguments to show that the oxygen absorbed is, mainly at least, chemically combined, be it only in such a loose way, like a portion of the carbonic acid in bicarbonate of soda, that it is capable of being expelled by indifferent gases. It is known, too, that it is the red corpuscles in which the faculty of absorbing oxygen mainly resides. Now it has been shown in this paper that we have in cruorine a substance capable of undergoing reduction and oxidation, more espe- cially oxidation, so that if we may assume the presence of purple cruorine in venous blood, we have all that is necessary to account for the absorption and chemical combination of the inspired oxygen. 16. It is stated by Hoppe that venous as well as arterial blood shows the two bands which are characteristic of what has been called in this paper scarlet cruorine. As the precautions taken to prevent the absorption of oxygen are not mentioned, it seemed desirable to repeat the experiment, which Dr. Harley and Dr. Sharpey have kindly done. A pipette adapted to a syringe was filled with water which had been boiled and cooled without exposure to the air, and the pomt having been introduced into the jugular vein of a live dog, a little blood was drawn into the bulb. Without the water the blood would have been too dark for spectral analysis. The colour did not much differ from that of scarlet cruorine; certainly it was much nearer the scarlet than the purple substance. The spectrum showed the bands of scarlet cruorine. This, however, does not by any means prove the absence of purple cruorine, but only shows that the colouring matter present was chiefly scarlet cruorine. Indeed the relative proportions of the two present in a mixture of them with one another and with colourless 398 Royal Society :— substances, can be better judged of by the tint than by the use of the prism. With the prism the extreme sharpness of the bands of scarlet cruorine is apt to mislead, and to induce the observer greatly to exaggerate the relative proportion of that substance. Seeing then that the change of colour from arterial to venous blood as far as it goes is in the direction of the change from scarlet to purple cruorine, that scarlet cruorine is capable of reduction even in the cold by substances present in the blood (§ 9), and that the action of reducing agents upon it is greatly assisted by warmth (§ 7), we have every reason to believe that a portion of the cruorine present in venous blood exists in. the state of purple cruorine, and is reoxidized in passing through the lungs. _ 17. That it is only a rather small proportion of the cruorine pre- sent in venous blood which exists in the state of purple cruorine under normal conditions of life and health, may be inferred, not only from the colour, but directly from the results of the most recent experiments *. Were it otherwise, any extensive hemorrhage could hardly fail to be fatal, if, as there is reason to believe, cruorine be the substance on which the function of respiration mainly depends ; nor could chlorotic persons exhale as much carbonic acid as healthy subjects, as is found to be the case. But after death there is every reason to think that the process of reduction still goes on, especially in the case of warm-blooded animals, while the body is still warm. Hence the blood found in the veins of an animal some time after death can hardly be taken as a fair spe- cimen as to colour of the venous blood in the living animal. More- over the blood of an animal which has been subjected to abnormal conditions before death is of course liable to be altered thereby. The terms in which Lehmann has described the colour of the blood of frogs which had been slowly asphyxiated by being made to breathe a mixture of air and carbonic acid seem unmistakeably to point to purple cruorine*. 18. The effect of various indifferent reagents in changing the colour of defibrinated blood has been much studied, but not always with due regard to optical principles. The brightening of the colour, as seen by reflexion, produced by the first action of neutral salts, and the darkening caused by the addition of a little water, are, I con- celve, easily explained; but I have not seen stated what I feel satis- fied is the true explanation. In the former case the corpuscles lose water by exosmose, and become thereby more highly refractive, in consequence of which a more copious reflexion takes place at the common surface of the corpuscles and the surrounding fluid. In the latter case they gain water by endosmose, which makes their refrac- tive power more nearly equal to that of the fluid in which they are coutained, and the reflexion is consequently diminished. There is nothing in these cases to indicate any change in the mode in which light is absorbed by the colouring matter, although a change of tint to a certain extent, and not merely a change of intensity, may accom- * Funk’s Lehrbuch der Physiologie, 1863, vol. i. § 108. + Physiological Chemistry, vol. ii. p. 178. - Prof. Stokes on the Colouring Matter of the Blood. 399 pany the change of conditions under which the turbid mixture is seen, as I have elsewhere more fully explained*. No doubt the form of the corpuscles is changed by the action of the reagents introduced ; but to attribute the change of colour to this is, I apprehend, to mistake a concomitant for a cause, and to attribute, moreover, the change of colour to a cause inadequate to produce it. 19. Very different is the effect of carbonic acid. In this case ~ the existence of a fundamental change in the mode of absorption cannot be questioned, especially when the fluid is squeezed thin between two glasses and viewed by transmitted light. I took two portions of defibrinated blood; to one I added a little of the redu- cing iron solution, and passed carbonic acid into the other, and then compared them. They were as nearly as possible alike. We must not attribute these apparently identical changes to two totally differ- ent causes if one will suffice. Now in the case of the iron salt, the change of colour is plainly due to a deoxidation of the cruorine. On the other hand, Magnus removed as much as 10 or 12 per cent. by volume of oxygen from arterialized blood by shaking the blood with carbonic acid. If, as we have reason to believe, this oxygen was for the most part chemically combined, it follows that carbonic acid acts asif it were a reducing agent. We are led to regard the change of colour not as a direct effect of the presence of carbonic acid, but a consequence of the removal of oxygen. ‘There is this difference between carbonic acid and the veal reducing agents, that the former no longer acts on a dilute and comparatively pure solution of scarlet cruorine, while the latter act just as before. If even in the case of blood exposed to an atmosphere of carbonic acid we are not to attribute the change of colour to the direct pre- sence of the gas, much less should we attempt to account for the darker colour of venous than arterial blood by the small additional percentage of carbonic acid which the former contains. The ascer- tained properties of cruorine furnish us with a ready explanation, namely that it is due to a partial reduction of scarlet cruorine in supplying the wants of the system. 20. I am indebted to Dr. Akin for calling my attention to a very interesting pamphlet by A. Schmidt on the existence of ozone in the blood+. The author uses throughout the language of the ozone theory. If by ozone be meant the substance, be it allotropic oxygen or teroxide of hydrogen, which is formed by electric discharges in air, there is absolutely nothing to prove its existence in blood; for all attempts to obtain an oxidizing gas from blood failed. But if by ozone be merely meant oxygen in any such state, of combination or otherwise, as to be capable of producing certain oxidizing effects, such as turning guaiacum blue, the experiments of Schmidt have completely established its existence, and have connected it, too, with the colouring matter. Now in cruorine we have a substance admit- ting of easy oxidation and reduction; and connecting this with Schmidt’s results, we may infer that scarlet cruorine is not merely a * Philosophical Transactions, 1852, p. 527. + Ueber Ozon im Blute. Dorpat, 1862. 400 Intelligence and Miscellaneous Articles. greedy absorber and a carrier of oxygen, but also an oxidizing agent, and that it is by its means that the substances which enter the blood from the food, setting aside those which are either assimilated or excreted by the kidneys, are reduced to the ultimate forms of carbonic acid and water, as if they had been burnt in oxygen. 21. In illustration of the functions of cruorine, I would refer, in conclusion, to the experiment mentioned in § 10. As the purple cruorine in the solution was oxidized almost instantaneously on being presented with free oxygen by shaking with air, while the tin-salt remained in an unoxidized state, so the purple cruorine of the veins is oxidized during the time, brief though it may be, during which it is exposed to air in the lungs, while the substances derived from the food may have little disposition to combine with free oxygen. As the scarlet cruorine is gradually reduced, oxidizing thereby a portion of the tin-salt, so part of the scarlet cruorine is gradually reduced in the course of the circulation, oxidizing a portion of the substances derived from the food or of the tissues. The purplish colour now assumed by the solution illustrates the tinge of venous blood, and a fresh shake represents a fresh passage through the lungs. L. Intelligence and Miscellaneous Articles. INFLUENCE OF HEAT-FORCE ON VEGETABLE LIFE. BY GEORGE BENTHAM, PRESIDENT OF THE LINNZAN SOCIETY *. CANNOT conclude my remarks upon the recent progress of biological science without alluding to the modern discovery of the dynamical theory of heat, or equivalence of heat and force—a. wonderful theory, which the lectures of Tyndall have rendered prac- tically clear even to the unscientific mind, but which, nevertheless, it is difficult to follow in all its details without feeling a certain bewilderment of the brain. I may refer to Dr. Carpenter’s article “On the Application of the Principle of Conservative Force to Physiology,” in the ‘Quarterly Journal of Science’ for January and April of the present year, for a general review of the influence of this force on vegetable and animal life, and, for a more popular summary, to the graphic sketch of the relation of the sun to life, contained in the closing portion of Prof. Tyndall’s twelfth lec- ture. But in this summary occur the following passages, which, however correct in regard to the great principle they are intended to illustrate, might yet, I think, without explanation, lead the ordinary reader into considerable error with regard to some great biological facts, and upon which therefore, on account of the high standing of the distinguished author, and the general circulation which the work must command, I think it necessary to offer a few observations. “The earth’s atmosphere contains carbonic acid, and the earth’s surface bears living plants; the former is the nutriment of the latter. The plant apparently seizes the combined carbon and oxygen, tears them asunder, storing up the carbon, and letting the * From the Anniversary Address, delivered May 24, 1864. Intelligence and Miscellaneous Articles. 40] oxygen go free. By no special force, different in quality from other forces, do plants exercise this power: the real magician is here the sun.” (p. 430.) “But we cannot stop at vegetable life; for this is the source, mediate or immediate, of all animal life. In the animal body, vege- table substances are brought again into contact with their beloved oxygen, and they burn within us, as a fire burns ina grate. This is the source of all animal power, and the forces in play are the same in kind as those which operate in inorganic nature. In the plant the clock is wound up, in the animal it runs down. In the plant the atoms are separated, in the animal they recombine.” (p. 481.) Pthe sun “rears, as I have said, the whole vegetable world, and through it the animal. The lilies of the field are his workmanship, the verdure of the meadows, and the cattle upon a thousand hills. He forms the muscle; he urges the blood; he builds the brain. His fleetness is in the lion’s foot; he springs in the panther; he soars in the eagle; he glides in the snake. He builds the forest, and hews it down,—the power which raised the tree, and which wields the axe, being one and the same. The clover sprouts and blossoms, and the scythe of the mower swings, by the operation of the same force.”’ (p. 432.) Notwithstanding the assertion to the contrary, it must be ad- mitted that there is here a little of poetry mixed with rigid mechanical truth; and we, as special investigators of the complex phenomena of animal and vegetable life and living beings, ought not to allow this quiet and summary dismissal of what is ordinarily, though perhaps erroneously, called “ vital force’? without remark. Life may not be a force in the sense which natural philosophers give to the term, but it is a power which so materially modifies the action of heat-force, that it comes within the general and more popular meaning of the word. Life cannot indeed be set in action without the operation of heat-force ; but, on the other hand, the sun cannot build a tree without the assistance of life. What life really is we do not know: its origin is probably beyond our inves- tigation ; but its existence and continuity cannot be denied. Not- withstanding the objections of heterogenists, to which I had occasion last year to allude, I cannot but remind you that in the present state of science we have as yet no prospect of proofs that any new life is created, that any new living being is built, by the sun or any other force, out of matter organic or inorganic. Life is continuous, and has been so from a period beyond human cog- nizance. We witness its cessation, but it has never been known to commence. Every new being grows out of, and is a portion detached from, a preexisting one. We cannot even fix precisely the moment when its independent life commences. It is not when the detached bud first shoots out its own roots, not when the seed bursts, or the egg-shell is broken, or the young animal is born; for the bud, the embryo, or foetus had a previous existence, more or less independent of, or connected with, the parent, according to species. It is not at the moment of fertilization or impregnation ; 402 Intelligence and Miscellaneous Articles. for the bud, and even the ovum in cases of parthenogenesis, may grow into independent beings without ever being impregnated. Nor can our most powerful instruments perceive the moment when the first embryo-cell receives that impress which has irrevocably determined the form which the perfect being is to assume, within those narrow limits which neither impregnation nor any other in- fluences set in action by the sun can ever make it exceed. And if life is once stopped, if interrupted, be it for a moment, no force can set it in action again. It may lie dormant for a long (but not perhaps indefinite) succession of years; its action may be absolutely imperceptible or limited to the resistance of disorganization, until recalled into more active operation by the action of the sun on surrounding influences; but if during the dormant period (of the seed, egg, &c.) hfe has once ceased, nothing will restore it: the action of the same sun upon the same surrounding influences will produce decomposition, not growth. The word “force” may indeed be properly limited to mechanical force, and it may be incorrect to say that life is a force different in quality from other forces ; but, as we must have some term equivalent to the popular sense, we may call life a power different in quality fromforce. Dr. Car- penter (p.80) proposes to term it a germinal capacity; but it 1s surely much more than a capacity, to be paraphrased as the “ power of utilizing, after its own particular fashion, the heat which it re- ceives, and of applying it as a constructive power to the building up of its fabric after its characteristic type” (p. 87). There is here this difference between the term and its paraphrase, that the one expresses a passive, the other an active idea. “ Vegetable substances, brought into contact with their beloved oxygen in the animal body, will burn within it as a fire burns in the grate.” True; but that burning will be fermentation and corruption, unless brought under the influence of the living parts of the body to be converted into growth. I say growth, not build- ing; for building the brain and the forest is a metaphor which must lead the unscientific mind far astray from all that science has as yet taught us. Nothing in life is built, in the ordinary “sense” of the term; no portion, no single cell, has been exter- nally added to a living being; everything has grown out of it, every new cell is gradually compounded within a living cell. _ “The plant apparently seizes the combined carbon and oxygen, tears them asunder, storing up the carbon, and letting the oxygen free.” True; but it doesmuchmore. Every living being, animal or vegetable, absorbs compound substances, decomposes them, liberates at once a portion (chiefly oxygen in the case of most plants), and stores up a portion. Of this portion some may be deposited unchanged in visible particles in various parts of the animal or plant, but some also undergoes afurther decomposition and dilution into a state hitherto concealed from our observation, from which it emerges recombined, having already received a pe- culiar impress, definitely differing in every species, or even in every individual—differences then inappreciable, it is true, to our senses, but evidenced by the forms the animal or plant is compelled to Intelligence and Miscellaneous Articles. 4.03 assume as it grows. And the process is substantially the same in animals and plants; both absorb, decompose, select, reject, and recombine. An animal may select what a tree rejects; but so also may one plant select what another rejects. None feed upon carbon or oxygen alone. Some are not satisfied without drawing their nutriment direct from the living plant or animal ; many feed upon organic substances, in which the decomposition after death has scarcely commenced ; and most, if not all, appear to require for their support some small portion, at least, of matter in which life is or has been. In both animals and vegetables the clock is wound up, and itruns down; in both, the atoms are separated and recombined, and, in both, these operations take place in a totally different way from what they do in the same bodies under the same influences, the moment life is extinct, the moment the vital power ceases to act. It is this vital power, its continuity and infinite divisibility, its unity and infinite diversity, the concordances, discrepancies, and reciprocal action and influences of the infinity of forms it produces, that our Society is specially called upon to investigate. As systematists, we have so to discriminate, describe, and class these forms as to enable us readily to identify them, both in- dividually and collectively, to comprehend one another and our- selves in treating of them, and to retain and store in our minds and books what is known of their resemblances, differences, and peculiarities, of their influences and relations to each other and to the lifeless world, as a starting-point for future obser- vation. As biologists, we have to study life itself in all its phases, and the multifarious influences by which it is continued, preserved, multiplied, checked, injured, destroyed, or extinguished. But, in addition, we must not neglect to learn from natural phi- losophers what are those general forces which act on organic as well as on inorganic bodies, and whilst carefully watching every modification these forces undergo, when applied in combination with vital power, gratefully accept any proved identity of action in the living and inanimate world. ANALYSIS OF LANGITE, A NEW MINERAL FROM CORNWALL. i BY M. PISANI. Professor Maskelyne presented a short time ago to the Geolo- gical Society of London some specimens of a new mineral found in Cornwall, to which he has given the name Langite. It isa greenish- blue hydrated subsulphate of copper, forming crystalline crusts and small right rhomboidal prisms on a coarse argillaceous schist called killas in Cornwall. The crystals of Langite are small and short; by their union they form macles analogous to those of Arragonite. Translucid; lustre vitreous. Its colour is a beautiful greenish blue, and that of its powder a pale blue. MHardness, 3°5; specific gravity about 3°05. Heated in a test-tube it gives water. Before the blowpipe, on charcoal, it gives with soda a bead of copper. It is insoluble in water, but soluble in weak acids and ammonia. Its hydrochloric acid solution, 404. Intelligence and Miscellaneous Articles. when diluted, gives an abundant precipitate with chloride of barium. It differs from brochantite in containing more water; therefore, as its external aspect is also quite different, it deserves to form a separate species. It is to be noticed that Berthier formerly analyzed an amorphous brochantite from Mexico, in which he had found as much water as in Langite, while its colour was green like that of other brochantites. Langite gave on analysis— Oxygen. Ratios. Sulphuric acid ...... 16°77 10:0 3 Oxide of RRS Soe eo 13°3 Dime. sho ccs rsieek OS 0:2 >A SiGa ees Magnesia Bs SENG ee He 0°29 0-1 Wider cts ese 16°19 14-4 4 100-00 which corresponds to the formula 4CuO, 8O0°+4HO. This formula requires— Sulphuric acidvy.Ws. 3.812 lee Oxide of copper Hh. 2 ee 67°59 Wraterea) ues a eee Sloe 100-00 It thus only differs from brochantite by containing one more equiva- lent of water.—Comptes Rendus, October 10, 1864. ON THE HISTORY OF ENERGETICS. To the Editors of the Philosophical Magazine and Journal. University of Glasgow, GENTLEMEN, October 5, 1864. So far as I know, the earliest introduction of a distinct term to denote the mechanical form of what is now called “ potential energy ” is due to Carnot, who, ina scarce and little-known essay on Machines in general, uses the phrase “‘ force vive virtuelle”’ in that sense. * The step which I took in 1853, of applying the distinction between «« Actual Energy ”’ and “ Potential Energy,’’ not to motion and me- chanical power alone, but to all kinds of physical phenomena, was suggested to me, I think, by Aristotle’s use of the words duvayus and évépyea. I am, Gentlemen, Your most obedient Servant, W. J. Macauorn Rankine. Erratum in October Number. In Prof. Rankine’s paper on Stream-lines, Equation II., for — 7 —_ Intelligence and Miscellaneous’ Articles. 405 ON THE TEMPERATURE OF SEA-WATER. BY M. CHARLES MARTINS*, I have read with great interest M. Ediund’s Note on the Forma- tion of Ice in the Sea, published in the Archives des Sciences Natu- relies of July 20. His observations render it difficult not to admit that ground-ice may be formed in salt water as well as in fresh. The fact that, in nature, the temperature of sea-water descends below zero without ice being formed can no longer be contested. In the two voyages made in 1838 and 1839 by the corvette ‘ La Recherche’ to Spitzbergen, I determined the temperatures at the bottom of the sea in the neighbourhood of the glaciers, which, in that region, often descend to the sea, and even advance, overhang- ing the surface of the water, to some distance from the coast. In these experiments, published fifteen years ago in the Voyages de la corvette ‘la Recherche, vol. 1. p. 279, and in the Annales de Chimie et de Physique, 3° sér. vol. xxv. p. 172, I used, for temperatures above zero, Walferdin’s overflow-thermometers with arbitrary scales. For temperatures below zero, I employed thermometrographs with indexes unprotected from pressure; but I took care to correct their indications by means of coefficients obtained from comparative ex- periments made with overtlow-instruments, protected from pressure by tubes of crystal: besides this, I always took the precaution (in- dispensable in experiments of this kind) to employ several thermo- metrographs at the same time, in order that their indications might rectify each other. Most of the experiments were made in August 1839, opposite the great glacier at the bottom of Magdalena Bay, on the east coast of Spitzbergen, in latitude 79° 34’, and longitude 8° 49! east of Paris. The temperature of the surface was always a little above zero; it varied, in fact, from 0°°1 to 192. Nevertheless twice a day, at low water, enormous masses of ice fell down into and cooled the sea. The temperature of the air at the surface of the sea varied from 0°-7 to 6°°0. From the surface of the water down to a depth of 70 metres I never found the temperature to be below zero; but beyond this depth, and down to the bottom of the sea, the temperature was always below zero, its mean value being about —1°°75. The lowest temperature was found at a depth of 110 metres, and at a distance of 1350 metres from the glacier at the bottom; it was —1°°91. The most elevated of these low temperatures was found at the less con- siderable depth of 73 metres, and amounted to —1°-29. It would be wrong, however, to conclude that the temperature sinks regularly as the depth increases, for at 136 metres I only found it depressed to —1°78. In the open sea [ never observed a temperature lower than -zero at any depth whatever. For instance, on the 20th of July 1839, in 73° 36! north latitude, and longitude 18° 32! east of Paris, I lowered, to a depth of 870 metres, four of Walferdin’s thermometers protected from pressure by tubes of crystal soldered by the blowpipe. Their indications agreed wonderfully well with each other, and showed a * From a letter to M. E. Plantamour, published in the Bibliotheque Universelle, Archives des Sciences Phys. et Nat. vol. xxi. p. 37 (1864). 406 Intelligence and Miscellaneous Articles. mean temperature of 0°10 at the bottom of the sea. At less depths I always observed higher temperatures. I place very little Teliance on the two otek of Professor Nordenskidld. They were made in winter, on the coasts of the Island of Aland—at a depth of 21 feet, and at a distance of 100 feet from the coast—with a single alcohol thermometer provided with a mercury index. Neither the author nor M. Edlund describes the in- strument; they do not state whether it was protected from, or ex- posed to pressure; and no proof is given that the unique indication derived from the bottom of the sea was exact. I may venture to advise readers desirous of becoming acquainted with the minute precautions which, in experiments of this kind, are necessary in order to gain for the results the confidence of physicists, to refer to the memoir I published in 1848 and 1849 in the Voyages de ‘la Recherche,’ and in the Annales de Chimie et de Physique. 'To avoid the incessant recommencement of the study of a question, it is necessary to con- sult the works of those by whom we have been preceded. I have carefully analyzed those of Scoresby and of Parry, who, in 1811 and 1827, had already observed, on many occasions, temperatures of the sea below zero, both at the surface and at depths varying from 90 to 1814 metres. M. Edlund will find the tabular statement of them in my memoir. Doubtless the procedure and the instruments of the English navigators are not beyond the reach of criticism; but. the fact of the depression, below zero, of the temperature of sea- water was established by them at the above period, and has since been verified by other travellers. ON THE ANCIENT AQUEDUCT OF ALATRI. BY FATHER SECCHI1*, The town of Alatri, of Pelasgic origin, famous for its encircling walls of Cyclopean construction, is very ancient. Placed on the summit of a calcareous mountain, it was altogether deprived of water, and was separated from the nearest mountains by a valley, about 125 metres in depth. According to a celebrated inscription, the Censor L. Betilienus Varus conducted water to the town by means of an aqueduct 340 feet high, and for this purpose he caused arcades and strong pipes to be constructed: ‘“‘ fornices, fistulas solidas fecit.” The recent researches, made by the order of His Holiness Pius [X., in order again to provide this important town with pota- ble water, have led to the discovery of a large portion of the ancient aqueduct. The levels which I have made show that the lowest point of the aqueduct was 110 metres below the highest part of the town; this accords with the 340 feet mentioned in the inscription. We have here, therefore, a water-conduit in the form of an inverted siphon, under a pressure of 11 atmospheres, constructed 160 years before our present era. It is difficult to say what quantity of water was conducted; but the dimensions of the aqueduct (the buttresses of which measure 1°75 by 1°45 metre) show that it must have been sufficient to supply the baths of the town, several public fountains, and the whole of the town itself, now found to be traversed with pipes of lead and terra cotta. Near the Acropolis, pipes of bronze * From a letter to M. Elie de Beaumont, published in the Comptes Rendus of September 26, 1864. Intelligence and Miscellaneous Articles. 407 have also been discovered, so that the fistulas solidas of the inscription may possibly refer to pipes of this metal. | It is remarkable that the pipes of terra cotta which have been found agree precisely with the description given by Vitruvius (4rchi- tura, lib. viii. cap. vii. no. 51). The aqueduct itself is constructed according to the principles handed down to us by this author; for it is carried along a horizontal line, at the level of the acropolis, to a distance of about 7 kilometres; thence it descends, skirting the_ mountain, until, after reaching its lowest point, it proceeds once more horizontally for about 500 or 600 metres, and finally reascends (see Vitruvius, idid. no. 50). Thus the total length of the siphon amounts to 5 or 6 kilometres. All attempts to find the specus of the aqueduct have been unsuccessful ; for the demolition of these works —caused in the first place by the barbarians, and afterwards by peasants—has been enormous; the foundations alone have escaped destruction. The metals discovered, however, appear in many cases to indicate that the conduit was of a mixed kind; itis possible that it was formed of different kinds of substances, corresponding to the different heights to which the water was raised; for a large portion of the water was arrested at half the above height. Con- structions in mortar, of great beauty and solidity, have been found, and it appears probable that the Romans were in the habit of strengthening their pipes, externally, by imbedding them in this mor- tar (in Italian, calce-struzzo). A field was also discovered under which still exists a magnificent and complete system of drainage, by means of long lines of terra- cotta pipes. These pipes have a mean diameter of 0°45 of ametre, their length being 1°10 metre, and their thickness 0°025 of a metre. At present they are filled with a water-sediment and with clay ; their depth under the present soil is 2°50 metres, but it is evident that, originally, this depth was less and has since been increased by new soil. The ends of the pipes overlap each other about 4 centi- metres only. No cement was used at their junctions; but spaces of about 1 centimetre were left, in order, probably, to facilitate filtra- tion. This field was probably the one used for military exercises, to which reference is made in the same inscription as being one of the interesting works of Betilienus. We have here, therefore, a complete system of drainage, resembling the modern one, but constructed twenty centuries ago, and still in a state of perfect conservation. The utility of these works and the merits of the man of genius who constructed them are proved by the esteem in which he was evidently held by his fellow citizens. He was twice elected censor, a statue was erected to his memory, and his son was exempted from military service. As before observed, water is again about to be conducted to the town of Alatri. The success of the modern conduits employed at Anagui, where the water rises at one bound to a height of 221 metres under the action of force-pumps, leaves no doubt whatever of the ultimate success of the projected constructions, where the new con- duit will have a length of from 14 to 15 kilometres, and where the half of this space will be under a pressure of from 6 to 12 atmospheres. On a more recent visit I found several ancient flint weapons 408 Intelligence and Miscellaneous Articles. known to the peasants under the name of thunder stones. Generally speaking they lie at a very small depth below the soil. PHENOMENA OBSERVED IN THE SPECTRA PRODUCED BY THE LIGHT OF INDUCTION-CURRENTS IN TRAVERSING RAREFIED GASES. BY M. J. CHAUTARD. In examining the spectra produced by rarefied gases raised to in- candescence under the influence of the current of a Ruhmkorff’s coil, I have noticed various new phenomena. The degree of incandescence of the gas may vary either in conse- quence of the greater or less density of the ponderable matter in the tube, or from the intensity of the inducing current. M. Plicker has described the phenomena arising from variations in the elasticity of the gas, but he has not examined the different conditions of the spectra when the resistance offered to the current of the pile is made to vary. This variation of resistance in the inducing current may be pro- duced by two distinct methods—either by elongating the wire tra- versed by the current, or by introducing a bar of soft iron into an ~ auxiliary coil which is traversed by the circuit of the battery which works the Ruhmkorff’s apparatus. Working so as to vary gradually the intensity of the pile, I ob- served the following phenomena with the tubes at my disposal :— 1. The dazzling red light of the hydrogen-tube finishes by being changed into a livid whitish-green tint; the spectrum, instead of offering three magnificent rays, red, green, and violet, which cha- racterize this gas, and which occupy almost the position of the three Fraunhofer’s rays C, F, and G, only give a very pale green. The glass does not become appreciably heated in the hand. The stratification in the enlarged part of the tube has the same appearance and the same precision as in the case of the normal current. In using only the external pole of the induction apparatus, the current still traverses the gas, but the light becomes so pale that no shading can be distinguished by the prism. 2. In nitrogen the disappearance of several shades can be distin- guished; but here the vanishing of the colours seems to take place in inverse order. ‘Thus the rays of red and of orange first become weaker ; the violet only disappears finally; the yellow and green rays remain, spite of the diminution of the light. 3. The rays in carbonic acid are very numerous with the ordinary current of the coil; but if the tension of the inducing circuit is di- minished, the same absorption of the extreme shades is noticed. Red commences to disappear, then the violet rays, as well as the green ray nearest the red. The external circuit used alone does not allow the shades of the spectrum to be distinguished. 4. Bromine gives a magnificent spectrum furrowed by about nine- teen of the most beautiful rays separated by almost dark intervals. The introduction of a resistance into the inducing circuit modifies neither the nature of the spectrum nor the number of rays; there is seen only a simple enfeeblement in the general aspect of the tints, which never completely disappear.— Comples Rendus, Aug. 22, 1864. T°: Phe as at a = THE LONDON, EDINBURGH, ann DUBLIN PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. ‘FOURTH SERIES.] DECEMBER 1864. LI. On the Theory of Light.—Second Memoir. By Professor L. Lorenz, of Copenhagen*. HAVE communicated, in a previous memoir} “ On the Theory of Light,” certain theoretical investigations which I have since continued and further developed. But before enter- ing more fully upon the details of the results obtained, I may be allowed to take this opportunity of making a few remarks upon the fundamental principles of the theory, and upon the particular position which it occupies relatively to other theories. Researches into the region of mathematical physics bear wit- ness almost universally to a firm belief in the power of inductive reasoning to penetrate to the forces concealed in the interior of bodies, in order, starting from thence as from a centre, to con- struct the explanation and laws of phenomena. Thisis the path entered upon by Laplace and those of his school: it was sup- posed that the problems of mathematical physics, like those of astronomy, were accessible, even as to their innermost nature, by the inductive method. Molecular forces have been in all cases assumed as the starting-point, which, like the forces of universal attraction, are supposed to bea function of the mutual distances of the molecules, proportional to their masses, and to act only in the direction of the lines joining their centres. The sum of hypotheses involved in this assumption has scarcely been clearly seen ; but how wide the basis is which has been chosen for the erection of almost all manner of wonderful structures has been sufficiently shown by modern analysis. But have these conceptions respecting the nature of molecular forces led to con- * Translated from Poggendorff’s Annalen, vol. exxi. p. 579. fT Phil. Mag. S. 4. vol. xxvi. p. 81. Phil. Mag. 8. 4, Vol. 28. No. 191. Dec. 1864. 25 4.10 Prof. Lorenz on the Theory of Light. sequences which could have been arrived at in no other way? and have these consequences always been correct ? The Theory of Capillarity can be developed equally well with- out these hypotheses; and the only result to which they have led is the principle discovered by Laplace and Poisson, that the height of liquids in capillary tubes at different temperatures is proportional to the densities of the liquids. This principle, how- ever, is false. The same assumption, applied to the doctrine of Electricity, led Poisson to the determination of the relation between the two electric constants; but this conclusion also has turned out to be incorrect. Poisson’s calculation has been par- tially altered, and the final deductions veiled under an unsummed summation-formula; but does such a result give us any right to consider the accuracy of our previous hypotheses as established ? This assumption led, in Cauchy’s hands, to wonderful results by its application to the theory of light. Originally it served to explain the dispersion of light; it was, however, at once found that a materially vacuous space would disperse light, provided that a definite hypothesis was made regarding the nature of force as a function of the distance. One would have supposed that so important a glimpse into the nature of molecular forces would necessarily lead to further consequences; but this was not the case. On the contrary, it was found in this case as in others— for example, in the cases of the hypotheses which it was neces- sary to add in order to explain double refraction—that the new hypotheses were serviceable for those purposes only for which they had been invented: ulterior consequences could not and might not be drawn from them. I will not, however, dwell upon objections of this kind, since they have already been made, but still have not overthrown the theory. They have on their side only a certain degree of pro- bability, while against them are ranged all the important results which have hitherto been deduced from the theory. On the contrary, I will lay stress upon a new objection, inasmuch as it in reality upsets the theory, while the great results of the theory which can be opposed to the objection, are not so great but that, as I shall show, they can be much more completely attained by a different method. The phenomenon of circular polarization obliged Cauchy to assume a periodicity in the internal structure of bodies. Against this nothing can be objected; for such a heterogeneity is precisely the most general case, and homogeneity, on the contrary, a par- ticular case. Cauchy, however, committed the fundamental mistake of assuming that the mean values of the periodic dis- placements of the particles of the ether were approximately dependent merely on the mean values of the periodic coefficients Prof, Lorenz on the Theory of Light. 411 of his differential equations. This theorem, taken as one of general application, can be easily disproved by a simple example. The following differential equation may serve as such :— END eae (a+s cos =) iG +6=0, where we will assume a to be greater than 0, and « very small. The mean value of the periodic coefficient a+) cos is a, and the mean value of the integral would therefore, according to the above theorem, be approximately & c= — O— Cine. But this result is incorrect ; for integration gives exactly de d —_ on hax cos = and afterwards approximately, if a is very small, x OT) Nga SBa d =e Na ee a value which differs essentially from the foregoing, inasmuch as the constant of periodicity 5 enters into it. The theorem, therefore, cannot be maintained in all its gene- rality ; neither is it any more specially applicable to Cauchy’s dif- ferential equations. In the first place, not only circular polari- zation, but also double refraction, if the equations are otherwise correct, must result from the periodicity of the coefficients. In order to prove this, we have no need to lose ourselves in endless calculations, for nature herself has carried out the calcula- tion. Brewster and, more recently, M. Schultze (Verhandl. d. rheml. Gesellsch. 1861) have in fact shown that transparent sub- stances in thin layers are doubly refracting. This important fact therefore demonstrates that a periodicity in the interior of bodies must involve double refraction. In the second place, it is at once obvious that the thickness of the layers of a periodically heterogeneous body must exert an influence upon the course of the ray which will depend upon its wave-length, and therefore that, whatever differential equations we take as our basis, chromatic dispersion at least is deducible from the periodicity of the coefficients. This explanation of chromatic dispersion shows moreover very simply why it is that chromatic dispersion is peculiar to material bodies and is not possessed by a vacuum. If, however, we now find that theory requires us, on the one hand, to assume a periodicity in the internal structure of bodies, 2H2 412 Prof. Lorenz on the Theory of Light. but that, on the other hand, this assumption brings with it not only the explanation of circular polarization, which had necessi- tated its bemg made, but also the explanation of double refrac- tion and chromatic dispersion—phenomena which had given rise to the fundamental hypotheses of the molecular forces—these latter hypotheses become quite superfluous; and an hypothesis which is superfluous is false. The whole complicated apparatus of hypotheses becomes merely an arbitrary appendage to the theory as soon as all can be explained by periodicity. Thus, as in other branches of mathematical physics, so also in optics, we are obliged to give up the common conceptions con- cerning the nature of molecular forces. It would be of very little use to try to construct the theory of light upon new phy- sical hypotheses, or upon new conceptions of what goes on in the interior of bodies, concerning which we are probably quite unable to form any conception whatever. The science of our day takes a totally different direction, and seeks to free itself from all such conceptions, which are only ignes fatui, and perhaps no better guides than the conceptions of Bacon’s time were in their day. In the theory of light we do not require to know any magni- tudes but such as we can directly or indirectly take cognizance of. These magnitudes are, the Intensity, the Velocity, the Direc- tion of emission, the Colour, the Phase, and lastly the position of the Plane of Polarization. Light, as is well known, does not make a momentary impression upon our eye; and the intensity which we measure is therefore a mean intensity, or the sum of all the impressions made during a short interval of time; but if we suppose the eye capable of perceiving the intensity of every colour, at every single moment of time, and at every point in space, it would then be able to determine not merely the mean intensity, but also the velocity, the direction of emission, the colour, and the phase; for every alteration of any one of these would modify the impression. We may therefore comprehend all these magnitudes under one idea—that of Intensity in a wide sense. In addition to this function of the time and of the coordinates of space, we only require two more in order to be able to determine the position of the plane of polarization ; light is thus at every point and at every moment fully characterized by three magnitudes dependent upon the time (¢) and the coor- dinates of the point (a, y, 2). The problem of the theory now becomes to find three partial differential equations which hold good for all media, and express the dependence of these three magnitudes upon the independent variables (x, y, z, ft). From these equations we must then be able to deduce all the phenomena of light, those only excepted which depend upon unknown forces, such as electrical and che- Prof. Lorenz on the Theory of Light. 413 mical forces. Hence, conversely, only the fundamental equa- tions can be in turn deduced from these phenomena, but nothing like a physical theory: as well might we expect to deduce such a theory from the phenomena of reflexion in a concave mirror or frem the refraction of a lens, as from diffraction or double refrac- tion &c. _On the contrary, the physical explanation is probably hidden under the unknown forces already referred to. If we now try to find the three partial differential equations which are to be the foundation of the theory, we soon discover that the intensity and plane of polarization cannot be directly introduced into such equations, but that auxiliary magnitudes dependent upon these must be taken instead. Let these auxi- liary magnitudes be &, », €; they may be spoken of simply as light-components. I will not now dwell longer upon the manner in which the three differential equations are arrived at im my former memoir; for after they have been found it is immaterial how this has been done; their truth must be evidenced by their eapability of accounting for all the phenomena of light, with the exception of those which depend upon unknown forces. These equations, in a somewhat altered form and without the dashes over the components, are as follows :— d (dé in) ata a 1a dy\dy da) dz\de dz)” wd?” a (ina) (iE _ any _ 1 ay ‘a9 dz\dz dy) dx\dy dx) w? dt?’ d (d& dé d (dy aya | de (de ~ as) ay ae ~ ay) aba In addition to these equations, and complementary to them, we have two others, which express the dependence of the inten- sity and the position of the plane of polarization upon the com- ponents &, 7, ¢, the intensity of the light bemg determined by the equation ih I= Pre (2-7 ces and the plane of polarization by the equation E(w! — 2) + y(y'—y) + &(2!—2) =0, where a’, y', z' are the current coordinates of this plane. The components are therefore proportionate to the cosines of the angles which the perpendicular to the plane of polarization makes with the three axes of coordinates respectively. The magnitude o is a function of z, y, and z, which for homo- geneous media becomes a constant. In these cases the equations assume a well-known simple form, whence the well-known laws 414 Prof. Lorenz on the Theory of Light. of the propagation of light in homogeneous media can be deduced, as well as the laws of diffraction (when this is not complicated with simultaneous refraction and reflexion), those of interference, of the polarization of the diffracted ray, and of the decrease of the intensity of the light emitted by a luminous point with the square of the distance. I need not now stay to discuss the man- ner in which these laws are deduced from the familiar equations, and I will consider it as well known and established that the equations are true for homogeneous media. It results from the form of the integrals that light may be regarded as a wave-motion, without nevertheless our being able to form any kind of notion as to the nature of this wave-motion, as must be sufficiently evi- dent from what has gone before. The integrals further show that @ is the velocity of propagation. Passing on to heterogeneous bodies, we see at once that the determination of the notions of intensity and plane of polarization is toacertain extent arbitrary, inasmuch as these cannot be expe- rimentally ascertained for heterogeneous bodies. The plane of polarization is arbitrarily fixed as for homogeneous media, while for the determination of the intensity we have the rule that the intensity of all the refracted and reflected light is equal to that of the incident light when the refracting body is perfectly transparent and homogeneous: whether such a medium is actu- ally to be met with in nature is of no consequence. In order to arrive at this, we might have multiplied the components by some power of w and then have fixed this power by the condition already made, as was done in the previous memoir ; but we shall soon see that this is already accomplished in the above equation of intensity. In the previous memoir I have deduced the laws of double refraction, of circular polarization, and of chromatic dispersion from the differential equations; moreover the principles which are to serve to calculate the reflexion and refraction of light result from the integration of the equations, inasmuch as I have found that the four magnitudes an, Vide de) ne ae Pears tee a have the same value on both sides of the plane of coordinates y z, which we assume as the limiting surface of the two media. Before trying to develope further the consequences of the results already obtained, I will show how a theory of the reflexion and refraction of light which agrees perfectly with experiment, may be deduced from the last limiting conditions. It is well known that Neumann, in his classical work on the reflexion and refraction of light, treated this problem in a very Prof. Lorenz on the Theory of Light, 7 415 complete manner; and the results of his calculation have been universally confirmed by experiment. The suppositions from which he sets out seem, nevertheless, at the first glance quite opposed to ours: his luminous vibrations are situated in the plane of polarization and in the plane of the wave, the inten- sity of the light is measured by the square of these vibrations, and, finally, his four limiting conditions are quite different from ours. If, however, we disregard the arbitrary physical significa- tion which he has assigned to his lght-components, it appears at once that he has used different auxiliary magnitudes from ourselves. We will denote these new components by &', 7/, €, and we will in the first place investigate the relation between these and our own. In the previous memoir it has been shown that, for a periodi- cally heterogeneous body, the components &, 7, € can be deve- loped in series whose terms contain the variable factor cos (kt—le—my—nz—A), wherein kf, /, m, n are constants, and A, on the other hand, in general a function of x, y, z, which becomes a constant in the first three terms only. The portion of these series which con- tains A as a variable, indicates a periodic motion changing with the periodicity of the body; while the other portion of the com- ponents, which we will denote by &,, 7,, ¢,, represents the proper visible motion propagating itself in plane waves. In accordance with the differential equation (A), we have EE =m(mé,— ly) —n(lg—nk,) +... the subsequent terms containing merely the other portion of the components. By multiplication by & we get from this equation k2 oo E°=m€é,(mé,—In,) —né& (16, —n€,) +e re Sick The intensity of the visable light, which we will denote by I,, is that portion of the expression 2 (€? + y? + €?) which contains A only as a constant; and to determine this we easily get the equation 1 T= 75 [lom, mb)? + (ib, —n.)? + (mE, — In). The same intensity, expressed by means of Neumann’s compo- nents, gives T= 2? +77 + 0", Besides, &,, ,, €, are proportional to the cosines of the angles 416 Prof. Lorenz on the Theory of Light. contained between the perpendicular to the plane of polariza- tion of the visible light and the axes of coordinates, whereas Neumann’s resultants lie in this plane; thus we have ES + na! + 60=0. The last resultant, moreover, lies in the plane of the wave, whence we have lé! + my! +ne'=0. From these equations result the following relations between the two sets of components, namely, kF@=nn,—mé,, ky =lE—né, kl=mé,—In,, equations to which we can also give the form dg! _ any _ a, dn! _ do, _ dé, de! _ dé _ dn, dt dz dy’ dt de dz dt dy dx Our limiting equations, which we may write as follows, CIS x=e a d, Le to. wati-a [2-8-0 dx dy ad ke dé. Stel Spit iy este. daz dz z=0 3 where ¢ is an infinitely small quantity, shall now be expressed with the new components. From the last two equations we get at once [f= Ovende eo By the first equations, we have oe eet dz dy ‘ [é"],-0=0. Thus all the components, &', 7, &', take the same values at the limiting surface of the two media, which agrees perfectly with Neumann’s hypotheses. Lastly, the fourth limiting equation, which with our components we may express by [mn, at ng, | a = 0, may be arrived at as follows for the new components. Let g be the angle which the perpendicular to the plane of the wave makes with the ray of light. Since our resultant, as was shown in the previous memoir, makes the same angle with z=0 accordingly Prof. Lorenz on the Theory of Light. 417 the plane of the wave, we have lE +mn,+n€, sing=+ : shen ; VP + mbt? JEP +0, + be whence follows lE,-+mn,+n€, We get, further, from the above values of 7! and ©, k (nn! —mé!) =U(mn, + nf.) —(m2-+72)E., By eliminating & from these two equations, after having ex- changed the denominator of the first for k\/ 2? + 72+ €?, we have tan qG= As k Se A Beep (en — mel) + (m2 +08) tam ge/ FE PY; and this expression must therefore have the same value on both sides of the limiting surface. If, adopting Neumann’s notation, we call the angle which the plane of the wave and the plane of refraction (yz) make with each other ¢, and the angle which the new resultant makes with the line of intersection of the plane of the wave and the plane of refraction yr, we have l JP +m? +0 na! — mb! = + cos p/n? +m / EP + 1? + 6°, By introducing into it these magnitudes, the last limiting equa- tion becomes [/ £24 17+ EP(cos p sin ¢ cos y+ sin? p tan g)]*=*=0. This condition agrees exactly with Neumann’s hypothesis, if only we take the double sign arbitrarily, as Neumann did. Strictly speaking, Neumann started from the assumption that the intensity of the imecident lght is equal to the intensity of all the refracted and reflected light; he, however, refers this assumption back to the previous one. Conversely, there- fore, we may conclude that our four limiting equations imclude the principle of the maintenance of the intensity, and hence that our intensity equation, by which this condition must be fulfilled, is rightly chosen. Now that we have thus deduced Neumann’s hypotheses from our own, the problem we had proposed to ourselves is fully solved; for it follows from the results obtained that the same theory of reflexion and refraction, complete and accordant with experiment, which Neumann has developed, can likewise be mn +no= 2 = cos ¢, 418 Prof. Lorenz on the Theory of Light. deduced from our fundamental equations. Here, as previously in the theory of double refraction, we have arrived at one of the stations from which the formal part of the theory takes its start, and, thanks to the great development which this part of the theory has attaimed, a whole section of the doctrine of light again lies before us (without our needing to take one step fur- ther) as a simple consequence of our theory. If the theory of reflexion and refraction had not already been developed as it has been, we should not endeavour to express the limiting equations by means of any other auxiliary magnitudes than our compo- nents; for both the limiting equations and the law of double refraction, when expressed by means of these, assume their sim- plest form, and hence also the calculation with them would be simpler and more elegant. In the above calculation we have indeed taken into conside- ration the immediate effect of the periodic part of the compo- nents, which must accompany every wave of light in the periodi- cally heterogeneous body and is dependent upon it; there arises, however, also a secondary effect of the periodic motions of the two media, a mutual reflex action, which cannot be without influ- ence upon the visible light-motion. Here, as throughout all nature, we meet with a perturbation; and this small departure from the results obtained will probably be capable of confirma- tion by experiment. Were both media homogeneous, both the calculation and the principle of the maintenance of the in- tensity would be exactly true; not so, however, in the opposite case. This also may be made directly evident; for a part of the original quantity of light must necessarily be extinguished in the production of periodic wave-motions within the body. I will here pass over another perturbation, to which I have previously directed attention *, and which depends upon the fact that the two media are not separated by a perfectly sharp mathematical lane. i The loss of visible light above mentioned must not be con- founded with that which arises from simple absorption. The latter can be easily calculated. Modern investigations into the reflexion and refraction of imperfectly transparent and metallic bodies have, in fact, led to the remarkable result, that the same laws which apply in the case of transparent bodies apply here also, with the single difference, that the refractive ratio now assumes the complex form at” —1. From this fact we can draw the important conclusion that our differential equations hold good not only for transparent bodies, but for all bodies without exception. It is moreover apparent, if we endeavour to * Poggendorff’s Annalen, vol. exi. p. 111. Prof. Lorenz on the Theory of Light. 419 find the refractive ratio by means of the serial developments of the former memoir, that it can also assume this more general form ; but it is difficult to indicate the conditions under which this will occur. It appears, however, that this case must arise when the interval between two similar points of a body is not small rela- tively to the wave-length. For this reason, for instance, a trans- parent body ceases to be transparent when pulverized. If we now place the results of the former memoir side by side with our present ones, we perceive that our object—namely, to deduce all the phenomena of light, which do not depend upon unknown, electrical or chemical forces, from our fundamental equations—is now attained; for the explanation of Double Re- fraction, of Circular Polarization, of Chromatic Dispersion, of Re- flexion, and of Refraction results from them as a simple conse- quence. ‘The general theory of diffraction may here be passed by, for it can afford no control of our theory. For homogeneous bodies, it is easily deducible from our equations; but as soon as the phenomenon is complicated with simultaneous reflexion and refraction, the difficulty lies even more in finding the conditions which correspond to each particular experiment than in the cal- culation itself; and agreement between calculation and experi- ment would rather prove that the conditions had been rightly chosen, than be a control of the theory. I think therefore that I may regard the accuracy of our fundamental equations as fully established, and I will in the sequel direct attention only to a few further consequences of the results that have been obtained. The periodic coefficient occurring in our equations may be expressed, as has already been done in the previous memoir, in a general manner by the equation zs 21 a (1 Se con ee tt tee +) where ©), ¢,, &c. areconstants. According to this formula, we consider the body as made up of several systems of parallel layers, whose thickness is a, and whose perpendicular makes with the axes of coordinates angles which are determined by their cosines a@,, b,,c,. Further, let a, b, c be the velocities of pro- pagation which the components possess in the directions of the three axes, while @,, 2,2, d3,3 are connected therewith by the equations 0? oF AG gs Ai= FZ w= FW 13.3—= >5° ) a2? ) $2? raion These last magnitudes, like a5, &c., in the former memoir, can now be determined from the constants of the body; and for 4.20 Prof. Lorenz on the Theory of Light. a, =0 we easily find 2 6.2 4 ,=1—> Sita o.9==1— 25 b:3) Q3=1—S 5 cy? If a body is, for instance, | alt in one direction only, and we take the perpendicular to the layers as the axis of x, we have a=1, and b,=c,=0. Consequently the velocities b and ¢ become equal ‘to each other when a, or the velocity of propaga- tion of the components in the direction of the perpendicular, has reached its greatest value. Such a substance therefore behaves hike a doubly refracting, uniaxal, negative crystal, whose axes are perpendicular to the layers of the body. This result agrees with the experiments of M. Schultze (Verh. der rheinl. Gesellsch. 1861). If we call the velocity of light in vacuo O, the refractive : 2g PEEP) ; index corresponding to the velocity a is —, and a mean refractive a index will be expressed by n=/50'(a+ Rta) O(3 tata) This mean refraction coefficient is independent of the position of the axes chosen, even if the small magnitudes a, are not quite neglected ; for we find Ay.) = 2,9 + d33=3— sya: P+ Be? whence we have O? 4,0? 2 i 02 Q-; Bxe +5 1 0? DE” =) a value which is independent of the choice of the axes. oul Oy” QQ?’ ; é 2 In the last equation £ is put = — where A denotes the wave- length, in order that it may at once be evident that the mean refraction coefficient, or its square, assumes the form a+b where 0 is always a positive quantity. The smaller therefore the wave-length is, so much the more refrangible does the light become—a law which has universally proved true ; still, the above approximate formula might possibly not be sufficient for absorb- ent media, and in this way exceptions to the rule might arise. The form which we have given to the function » has been the most simple and convenient for the foregoing calculations ; but if we wish in addition to form any conclusions respecting ~ the internal constitution of bodies, it becomes necessary to de- Prof. Lorenz on the Theory of Light. 421 | 1 aa termine the constants more precisely. The coefficient 2 18 in general any function f(z, y, z) which satisfies the equation Se, Y; z) =f(@+ 2pe,, y+ 2qh,; 2+2ry,), if p, g, rare arbitrary whole numbers, and 4,, 6, y, are very small constants. This condition expresses that the body is he- terogeneous in such sort that the heterogeneity eludes observa- tion by a very quickly returning periodicity, and the body thus appears to be homogeneous. Such a function can be expressed by the well-known formula dos — ti (y—B) at) »Y,2) = \ —f(e,f,y)cosa| ——— + —*,—— + =——— ],, flesy.2)=3\ F fle,8,a)eosm(A—*) 4 HE) 4 le where 7, 7,, 7, are whole numbers which run through the series of numbers from —o to +o, and the integral is taken from —a,, —P), —y, to 2, B,, y,;. Further, dw is put in place of da df dy, and w,is the value of \do=8e, Bi: If the term which contains 2=7,=7,=0 is separately extracted from this sum, and if moreover the negative values of 2 are ex- cluded by multiplying the sum by 2 and taking the terms which contain 7=0 at half their value, we get, with the meaning of the sign of summation thus altered, L242) = aS +23( = =f cos (a4) “ 4 AWA) | aE), where f is put for f(a, £, af If we now compare this value of the coefficient = =f(x, y, 2) @ with the previous one, we have i! do aan abiands E, COS . =20(2 fcosm (#+ m4 +3) ea, hee Eafe ask cy e, sin 2 = —20? sin (* rye eT 92 ). 3 a, af Bp oN From the last two ul as we may deduce the value of Ye,”, and simplify the resulting expression by introducing the product of two equal integrals instead of the square of the definite inte- gral. If the variables of the one integral are then distinguished 422 Prof. Lorenz on the Theory of Light. by accents, and /’ put instead of f(«’, 6’, y'), we obtain = da (da! eteanrs | EFC where ife-ay | 658) ie | By v1 But in accordance with the above formula for f(z, y, z), we have / 23 ( = so =fle, B, ) 1 (= S(e', BY Y)s 1 J) 71 and therefore sqr=20'[ |Z r- (f=). oe) BP, C= cos x( ‘lB—#) , ily) The values of Q? and 2e,? can now be introduced into the above expression for the mean refractive index. Since, how- ever, We may suppose the perturbing effect of chromatic disper- sion to be eliminated by calculation, we may entirely disregard the smali quantity «,, and only introduce the new magnitudes into the equation 02 0? Q? 60? where 7 accordingly is the value of the reduced mean refractive index. We will now try to apply the results we have obtained. It must not, however, be overlooked that the last equation gives only an approximation to the value of 7, inasmuch as it was ori- ginally assumed that the magnitudes e, were small. I have indeed succeeded in developing the exact value of 7 in a series the first terms of which are the above, and I am ready to com- municate this calculation in case it shall be called for; but the above approximate formula may nevertheless be considered suffi- cient for the present purpose. It is well known how the idea of the absolute refractive power early arose in science, how it has been discarded by the prevailing theory as useless, and how it nevertheless, claiming a certain currency in spite of the theory, is perpetually reappearing. It is only needful to cast a glance at the general survey of refrac- tive powers of various bodies given by Albr. Schrauf in Poggen- dorff’s Annalen, vol. cxvi., to be convinced of a certain regularity. Especially it may be seen that the refractive power, freed from the influence of dispersion, as it is expressed by the formula te p oe Se, 3 Prof. Lorenz on the Theory of Light. 423 where p is the density of the substance, remains nearly constant for the same body at different densities, and that the refractive power of mixtures can be calculated from those of their separate constituents by the formula Mp=M,p,+Mopot «+. if p is the weight of the mixture, and the marked letters are taken as applying to the several constituents of the mixture. An additional law, which seems not to have been remarked, appears from the same table of refractive powers (loc. cit. p. 211), namely, that the refractive power always and without exception decreases somewhat with the refractive index. It was precisely the pre- sent theory which first drew my attention to this point. The above-mentioned empirical laws can in fact all be deduced from our theory, but only on the supposition that bodies are made up of transparent particles or molecules separated by in- terstices in which the velocity of light is the same as in a vacuum. The molecules must likewise, so far as these laws remain appli- cable, be unalterable, in the sense that any alteration of the body affects merely the size of these interstices and the arrangement of the molecules themselves. In the integral 1 ed Pele we may therefore separate the elements which belong to the empty spaces surrounding the molecules. Since the velocity of light (@) is here equal to O, and therefore ] f= Gy it 1 dax I! arat}E(- a) if we allow the integration now to extend only to the unalterable portion of the space «,, occupied by the molecules. If p is put for the density of the substance, then pa, remains a constant quantity, which may be denoted by c, for all altera- tions of density. According to this, we obtain i ] we obtain where | p=(S oy-y, a quantity which is independent of the density of the substance. 4.24: Prof. Lorenz on the Theory of Light. The integral can be transformed in the same way. If we put s=(F OF a where the integration has reference only to the portion of the space @, occupied by the molecules, we obtain S—2P—pP? oO p mig (ieepE) and hence 1 S—2P—pP? Tn PP Uns aa Since, according to our supposition, the last term is very small, the refractive power is nearly constant, namely 7y2—] p If we take into consideration the last term also, the refractive power assumes nearly the form R M= Q— od M= be where Q and R are two positive constants. The refractive power therefore diminishes with the refractive index. The above formula, 1 Ke = Gall +pP), holds good for mixtures as for substances in general. If the densities and volumes of the several constituents were originally Pir Par Pa-+> and ,, Vo,¥,-.., while the volume of, the eEua is v, the constituents possess in the mixture the densities py po, .«» The constants P,, P,,...of the constituents, bce do not alter with the ae ; thus we also have I (t= 5e(2 +p, LPs +p Po+.-. .) Now vp, ¥P1, VoPo,--- are aes to the weights of the mixture and of its several constituents; we thus obtain, if P> Pr» Po» --- are these weights, pPR=p,P\+pePot «. Prof. Norton on Molecular Physics. 425 In a similar manner we also obtain PQ=p,Q, + poe + one pR=p,R,+pokat ... The present theory therefore does not only afford an expla- nation of the constancy of the refractive power and of the for- mula for mixtures, but it defines these laws even more distinctly than before, and in particular shows that the refractive power must diminish with the refractive index: this is fully con- firemd by experiment. And these results may suffice us on this occasion ; for it is needless to enter further into the details of experiment, partly because it is self-evident that a closer agree- ment can be obtained with two constants than with one, and partly because our formule are yet only approximately true. In conclusion, it will not be uninteresting to see how the various phenomena of light instruct us as to the internal constitution of material bodies. Double refraction indicates to us, in the first place, the regular stratification of crystals, a character which is also revealed by their external properties. The thickness of the layers cannot, however, be deduced from double refraction, for this would not cease even if the thickness were infinitely small ; circular polarization, on the other hand, and especially the more general chromatic dispersion, prove that this is not the case, and that in all bodies, the elastic fluids scarcely excepted, there is a stratification of measurable dimensions. Circular polarization further indicates a want of symmetry in the interior of certain crystals, which is likewise evidenced by their external characters; and the rare occurrence of this kind of polarization teaches us that such a want of symmetry is not the common case. Finally, the refractive power indicates that the limit of the periodicity in the interior of bodies is on one side of a vacuum, and therefore that material bodies consist of separate transparent molecules. LIL. On Molecular Physics. By Prof. W. A. Norton. [Continued from p. 389.] Heat. cee general nature of heat, and the general cause of its evolu- tion, have already been considered (p. 196). According to the fundamental ideas presented, heat must be developed when- ever the electric atmospheres of the molecules of any substance are urged into closer proximity to the atoms which they surround. Any disturbance of the equilibrium of the particles of a given mass, or any change in the relations of the particles of any body to those of other bodies, which may have the effect of producing Phil. Mag. 8. 4, Vol. 28. No. 191. Dec. 1864. 2F 426 Prof. Norton on Molecular Physics. this compression of the molecular atmospheres, should, then, be a source of heat. Thus chemical combination of two particles in which they are drawn into close union, collision of bodies, external pressure, and friction are different sources of heat. The disturbance of the electric equilibrium of contiguous mole- cules may also give rise to the evolution of heat—by reason of the increased repulsion exerted by the excess of electric «ther accumulated upon certain of the molecules, or upon one side of them, or of a discharge of the ether occurring from one molecule to another: Propagation of Heat.—Primarily the heat-pulses are developed in the universal ether associated with the atoms of bodies. These pulses may be conveyed outward through the universal ether posited between the atoms, and in this way be freely ¢rans- mitted through substances; or they may be more or less taken up or absorbed by the electric atmospheres of the molecules which they encounter. Such absorbed pulses may be given out again or radiated in their original form, or they may pass on to conti- guous molecules through the electric ether that pervades the in- terval between them. It is probably in this latter mode chiefly that heat is conducted from particle to particle of a substance, though the pulses that are given out by any particle to the sur- rounding universal ether may.be in part propagated onward, absorbed by the particles they encounter, and partially propa- gated onward again in the same manner to the next particles. The flow of heat from one particle to another of a substance tends to disturb the electric condition of the particles; for the repulsive action of the heat-pulses in the atmosphere of one particle tends to urge away a portion of the electric zther from the contiguous side of the next particle in the line of propaga- tion, and so to induce a negative electric state upon that side, and a positive state on the further side. This disturbance of the electric equilibrium of contiguous molecules may give rise to a discharge of the electric «ther from the one to the other, and a consequent more ready propagation of the heat-pulses from the one to the other. Upon this idea there is a close analogy between the conduction of heat and the conduction of electricity in the galvanic current, both depending upon the facility with which .an electric polarization of contiguous particles is deter- mined. The origin of this propagated polarization in the one case is the addition of repulsive pulses to the atmosphere of a molecule, and in the other the accumulation of an excess of the repulsive electric zether around a molecule or upon one side of it. A confirmation of these views is afforded by certain pheno- mena of thermo-electric currents, from which it appears that the conduction of heat is in reality attended with the disturbance of Prof. Norton on Molecular Physics. 427 the electric equilibrium* ; and they are also sustained by the fact of the close agreement that subsists between the conducting- powers of the metals for heat and electricity. The analogy between the conduction of heat and the conduction of a galvanic current may be more fully stated thus:—A stream of heat con- sists of two sets of pulses, viz. those conveyed by the electric gether, and those conveyed by the universal ether; and the pro- pagation is attended with, and partly by means of, an induced molecular polarization. The pulses propagated by the electric zether tend to develope this polarization, which determines a discharge of zether from one atmosphere to the next. But the other set of pulses, in proportion as they are taken up by the nearer side of the next atmosphere, tend to weaken the induced polarization, and so to check the flow of the heat. A galvanic current comprises two similar sets of pulses, is attended and promoted still more effectually by a similar molecular polariza- tion ; and the absorption of the «ethereal pulses, and their subse- quent emission as heat, tends to check the flow of the current. The feeble conducting-power of many substances is probably due to an aggregation of their particles in groups, with large intervening spaces. The bad conductivity of gases and liquids, both for heat and galvanic electricity, agreeably to the views just offered, must be ascribed to a feeble polarizing action of one particle upon another. This appears to be a consequence of the peculiar state of the molecular atmospheres which deter- mines the fluid condition (p. 279), combined with the effective mutual repulsion of the particles in this condition. In the case of liquids like water, whose ultimate molecules are compound, a portion of the heat propagated should be consumed in expand- ing the compound molecules. Capacity of Bodies for Heat.—The fundamental law discovered by Dulong and Petit, that the specific heats of elementary sub- stances are inversely proportional to their chemical equivalents or atomic weights—or, in other words, that the atoms of such substances have the same capacity for heat—if interpreted in the language of the present theory, amounts to this, viz., what- ever may be the difference of condition of the molecular atmo- spheres of elementary substances, if the same amount of heat be imparted to these atmospheres, the same amount will be given off again and interchanged with surrounding bodies having the same temperature. This would seem to imply that the portion of the heat absorbed, which is consumed in expanding the atmo- sphere, is the same for different simple molecules, and that the remaining portion, which is taken up as new pulses by the atmo- sphere, is also the same for molecules of different elementary * See De la Rive’s Treatise = Electricity, vol. il. p. 536 &e, 2 428 Prof. Norton on Molecular Physics. substances. There is nothing in the conception we have formed of a molecule, and of the probable difference of physical condi- tion in molecules of different substances, that is apparently op- posed to this result. The capacity for heat of compound i is in general greater than that of simple molecules, and is greater in proportion as the molecule is more complex. This indicates that when the tem- perature is raised 1°, a certain portion of the heat is expended in urging asunder the constituents of the molecules, and that this portion is greater in proportion as the molecule is more complex. Heat-rays of different rates of vibration.—The calorific spec- trum shows that the heat emitted from a hot body is composed of rays of an infinite variety of rates of vibration between certain limits. The physical cause of this fact will appear if we reflect that the heat-rays have their origin in the vibrations of the atomettes of the molecular atmospheres, and that these are situ- ated at every variety of distance from the central atoms, between certain limits. For the circumstances of equilibrium of these atomettes are different, and their rates of vibration when dis- placed should be different. The fact that the most intense heat- rays, in ordinary cases of combustion, are those of low refrangibi- lity and the phenomena of the evolution of calorific and luminous rays when a body is heated to incandescence, indicate that the electric atomettes which are nearest the central atoms have the lowest rate of vibration. We have seen that the expansive action of heat is a necessary consequence of the fundamental principle that the heat-pulses constitute a repulsive force, and that they are absorbed, more or less, by the molecular atmospheres which they encounter. It may be urged as an objection to the notion that radiant heat is a repulsive force, that bodies when heated do not exert any sensible repulsive action upon other contiguous bodies. We are not prepared to admit that experiment has furnished no evidence of such repulsive action under any circumstances; but the entire absence of such action upon bodies of sensible magnitude would in fact be no decisive proof that waves of radiant heat do not convey a series of preponderating repulsive impulses; for if these impulses penetrate to the atoms of the molecules, they should be ultimately taken up by their atmospheres, and ex- ite as an expansive force upon these atmospheres, and in rging the molecules asunder; and if they do not reach the oak no motion should be imparted to them. Since it is im- probable that the more intense impulses of heat will be wholly absorbed by the particles immediately at the surface of the body upon which they fall, a direct repulsive action of the heat may take effect to a certain depth below the surface. Have we not Prof. Norton on Molecular Physics. 429 in the spheroidal state of liquids evidence of such action exerted by the radiant heat from the hot vessel upon the liquid resting upon its interior surface ? It is only when the heat-waves impinge upon isolated parti- cles, or a small group of particles, that a progressive motion should be imparted. This supposition is apparently realized in the case of cometary matter repelled by the sun*. Light. The question of the precise relation which the two physical agents, light and heat, bear to each other, has not been defini- tively settled; but the weight of evidence preponderates very decidedly in favour of the doctrine of their essential identity. The only “formidable outstanding objection ” to this view con- sists in the fact that a strong light may be obtained which has little, if any, heating powert. According to Melloni, the green- ish light obtained by transmission of white light through a peculiar species of green glass coloured by oxide of copper, * exhibits no calorific action capable of being rendered perceptible by the most delicate thermoscopes, even when it is so concen- trated by lenses as to rival the direct raysof the sun in brilliancy.” May it not be that the explanation of the possible existence of light without heat, thus made out, is to be found in the presence, in the luminous beam, of a certain number of radiations which have individually too feeble an intensity to exercise any calorific action upon bodies, but are still capable of producing a sensible impression upon the organ of vision? Upon the theory of the constitution of molecules adopted in the present paper, we may suppose that vision results from some action of the luminous pulses upon the molecular atmospheres merely, while heat-expan- sion is not produced unless the individual pulses have sufficient _ intensity to penetrate to the surface of the central atoms of the molecules. According to this idea, as rays that penetrate to different depths in the molecular atmospheres of a medium should be unequally absorbed, the rays of feeble imtensity or of pure light may be separated from those which, by reason of their * In the article by the author, ‘‘On the Theoretical Determination of the Dimensions of Donati’s Comet” (see Silliman’s Journal, vol. xxxii. No. 94. p. 54, &c.), it is established by rigorous calculation that the par- ticles of matter disseminated over the breadth of the tail of the comet were exposed to a force of repulsion from the sun, of various degrees of inten- sity, between two ascertained limits. In the light of the theoretical views now offered, we must conclude that the matter thus unequally repelled consisted of particles of different sizes, or different absorptive powers for heat, or of different-sized groups of particles. + See Report of Rev. Baden Powell, M.A., F.R.S., for 1854, on Radiant Heat, published in the Smithsonian Report for 1859, p. 368. 430 Prof. Norton on Molecular Physics. greater intensity, are capable of penetrating to the atoms of the medium and exercising a calorific action upon them. It is generally admitted that vision is produced by the trans- verse vibrations of the rays of light. The fact that when two rays of heat, polarized in perpendicular planes, meet in opposite states of vibration they do not neutralize each other, has been generally regarded as an indication that the calorific action of a ray must also result from transverse vibrations; but this does not appear to be a legitimate conclusion, if we adopt Professor Challis’s theory, that the luminiferous ether is a highly elastic fluid, having the same properties as elastic fluids in general, and that the ethereal undulations consist of simultaneous longitudinal and transverse vibrations, attended with variations in the density oi the medium, as in the case of waves of sound. For if trans- verse vibrations, in perpendicular planes, meet in opposite states they cannot neutralize each other, and must develope direct vibra- tions, which will take the place of those which counteract each other and will exert a calorific action. In fact Prof. Challis con- ceives that “heat is the result of the mechanical action of the direct vibrations ;” while “light is due to the transverse vibrations.” The intimate association of heat and light leads to the infer- ence that they emanate from the same source, viz. the mole- cular atmospheres of bodies; and if, as has been intimated, the two emanations are essentially the same, we infer that rays of light as well as of heat originate in vibratory movements of the atomettes of these atmospheres. The atomettes lying at different distances from the central atom of a molecule will have different rates of vibration, increasing with the distance; and so the waves proceeding from them will have every variety of pul- sation between the lowest limit, answering to the bottom, and the highest, answering to the top of a molecular atmosphere. Accordingly the red rays will proceed from the lower portions of the atmosphere, and the violet from more elevated portions. If the electric atmospheres diminish in density by insensible degrees from bottom to top, there should be no break in the con- tinuity of the rays between the two extremes. But we know, from the existence of bright bands in the spectra obtained from coloured flames and from the highly heated vapours of metals and. other substances, that the rates of vibration of the luminous rays given off by incandescent vapours seldom, if ever, vary by insensible degrees from one extreme to the other. -We must conclude therefore that the electric atmospheres of highly heated molecules are made up of distinct layers of unequal density. Phenomena attending the propagation of light—The absorp- tion of light by a medium may be regarded as the taking up of the «ethereal pulses by the electric atmospheres of the medium. Prof. Norton on Molecular Physics. 431 In order that a ray may be completely absorbed, it must en- counter a layer of the electric atmosphere of a molecule which pulsates naturally in unison with the wave-pulsation of the ray. The absorbing action of a molecule should therefore depend upon the physical condition of its atmosphere as to rates of pulsation, density, &c., and also upon the comparative extent of its electric and ethereal atmospheres. For example, a medium would per- mit the free passage of any ray that did not penetrate to the surface of the electric atmospheres of its molecules. On the other hand, a medium would intercept rays that should pene- trate to atmospheric layers that afte in unison with the rays. Accordingly, if an incandescent vapour should emit rays of cer- tain colours, as shown by bright bands in its spectrum, those colours, if transmitted through the vapours, should be absorbed, and the spectrum given by transmitted light should show dark lines answering to the bright lines of the other spectruam—which is the well-known discovery of Kirchhoff and Bunsen. According to the theory of crystallization presented on p. 384 &c., in all the systems of crystallization in which the axes of molecular attraction are unequal, the electric atmospheres of the molecules are compressed unequally in the lines of direction of these axes. Now, if these atmospheres are compressed unequally, the same will be true of the zthereal atmospheres which pervade them. Thus in all forms of crystals which have unequal axes, the zthereal atmospheres of its separate particles will have un- equal densities in the directions of the molecular axes. It is well known that all such crystals have the property of double refraction, and that this property is attributed to a supposed in- equality of density or of elasticity of the ether in the direction of certain molecular axes. A mechanical pressure exerted along a certain line or plane also developes the property of double refraction in ordinary refracting media; and such compression should give rise to an increased density of the zthereal atmo- spheres along the line of pressure. Accordingly our general theory of the constitution of molecules and of molecular forces conducts to the physical basis assumed, in the undulatory theory of light, in explanation of double refraction. The phenomenon of “ atomic circular polarization ” by liquids, discovered by Biot, who established that the effect depended solely upon the number of atoms encountered by the light, what- ever may be the density of the medium—and the phenomenon of “magnetic circular polarization,’ in which the direction of rotation of the plane of polarization corresponds with that of the revolution of the circular magnetic currents—are decided in- dications that optical phenomena result mainly from the action of the atmospheres of molecules upon the rays of light. Nume- 432 Prof. Norton on Molecular Physics. rous facts, which go to show that the absorptive action of media upon light and heat depends in a great degree upon the physical constitution of the separate molecules, confirm this conclusion. The general phenomena and laws of reflexion, refraction, polarization, diffraction, &c., should obtain upon this supposi- tion no less than upon the conception that the phenomena are to be referred to the interstitial ether. It remains to be seen whether the theorems and formule deduced by Fresnel and other physicists from the undulatory theory of light, can be shown to be substantially im accordance with this notion of molecular actions. Note.—Objections to the theoretical views offered in the pre- ceding pages will readily occur to the scientific reader; but it does not comport with the design of the present communication to anticipate objections, or to attempt to enforce the general conclusions deduced from the fundamental positions taken by appeals to special facts. We must be content for the present to rest our conclusions mainly upon general considerations. A connected view of the whole ground to be surveyed is almost a necessary preliminary to the many detailed investigations that must be undertaken before the theory can be established on a firm foundation. It will be perceived that the most characteristic feature of the general theory under discussion is that it locates the source of physical phenomena in the atmospheres of molecules, instead of in the atoms or in the interstitial ether. In pursuing our de- ductions into other departments of physics, other general con- ceptions have been reached, some of which it may be advisable to state here, as circumstances may delay somewhat the publi- cation of the remainder of the article. 1. An electric current (hydro-electric or thermo-electric) has its origin in the opposite polarization of the adjacent sides of contiguous molecules, developed by the play of the molecular forces, under special circumstances, or by an inequality in the action of the pulses of heat upon the atmospheres of the mole- cules. The current consists of an actual flow of electric ether from molecule to molecule, determined by a previous electric polarization propagated from that which is the source of the current. There are also conveyed, in the direction of the posi- tive current, streams of impulses, both by the electric and uni- versal zther, which, by a partial lateral dispersion, produce the magnetic effects of the current. 2. The mutual attractions or repulsions exerted between two electric currents may be ascribed to a change in the tension of the zther between the wires, produced by the lateral actions of the currents. Prof. Norton on Molecular Physics. 433 3. Induction-currents result from an electric polarization of the molecules, suddenly induced by the same lateral action of a primary current when first established, or by the increased action of a previous electric or magnetic current—or suddenly vanishing when the current is broken, or the force of action decreases. The polarization in the first instance is the opposite | to that which prevails in the primary current, owing to the indirect nature of the inducing action. ~4, The circular currents of a magnet consist of electric currents that follow continuous chains of particles lying in the surface of the compound molecules of the magnet. These currents have their origin in an electric polarization of the particles, developed by a direct action of the impulses propagated from the exciting current. In permanent magnets the polarization thus originated becomes permanently established, and a permanent current remains as a necessary consequence of the play of the molecular forces in the chain. A magnet therefore derives its power directly from the inexhaustible primary forces of attraction and repulsion, and must retain its virtue unimpaired until the chain of mole- cules is broken by heat, or the excited molecular conditions upon which the currents depend are removed by some external cause. 5. Terrestrial magnetism is due to electric currents in the mass of the earth running in the general direction from east to west, and developed by the collision of the molecules with the xther of space. Both the rotatory and orbital motion of the earth are concerned in producing these currents. A part of the force of such currents must be converted into heat, and the earth derive a portion of its heat from this source. If this be true, the remarkable formal relations that subsist between the magnetism and heat of the earth are probably the result in a great degree of this physical bond by which the two principles are partially united. (See the investigation, by the author, of these relations, in an article on Terrestrial Magnetism, published in vol. iy. second series, of Silliman’s Journal.) This theory of the origin of terrestrial magnetism, as a part of the general theory of molecular physics here presented, was brought by the author to the notice of the Connecticut Academy about two years since. It appears from a pamphlet recently received by the editors of Silliman’s Journal, that a theory quite similar to this was propounded several years since by Gustav Hinrichs of Copenhagen. Haunrich’s theory, or one having the same essential features, I find is advocated by Prof. Challis in the Number of the Philosophical Magazine published in Fe- bruary 1861. [ 484 ] LIII. On some curious Effects of the Molecular Forces op Liquids. By G. Vanper Mrnssprueeue*, 1. Formation of liquid bubbles in a peculiar condition. i meteorology the question as to the state of the vapour in mists is far from being definitively solved; the hypothesis of vesicles, although strongly opposed, is not yet disproved. It is well known that one of the principal arguments against this hypo- thesis is, that the mode of formation of these vesicles is inconceiv- able. We are now acquainted, however, with an interesting fact which shows that a liquid film, unclosed and of any curvature, may take the form of a hollow sphere. This experiment has, in fact, been described by M. Félix Plateau, son of the illustrious phy- sicist. The author operated, however, on soap-water solely; so that it might be urged that his results do not, strictly considered, apply to pure water. Thanks to special circumstances, however, I have been able to prove that pure water comports itself in this respect almost like soap-water. I observed it in the following manner. Having thrown from a window, 12 metres above the ground, some pure water contained in a cup, | noticed that the sheet of liquid became transformed into hollow spheres whose greatest diameters were about 4 centimetres in length; after a fall of from 8 to 10 metres the bubbles burst, and became scattered into innumerable droplets. I reproduced the phenomenon a great many times, with dis- tilled water, by taking vessels of different forms and changing the mode of projection; I succeeded almost invariably, though the bubbles varied greatly in number and diameter ; the greatest diameter, however, did not exceed 5 or 6 centimetres. The resolution of the liquid sheet into hollow spheres was effected with greater rapidity the narrower the sheet and the greater its curvature. This peculiarity, it may be observed, is easily ex- plained ; for the molecular pressure, directed towards the con- cave part of the sheet, must necessarily increase with the curva- ture of the liquid surface. The best results may be obtained thus :—A cup, about 10 cen- timetres broad and three-quarters full, being taken, the water is projected, with moderate velocity, by moving the hand from left to right (for example), in order that the bubbles which are formed may not mutually prevent themselves from being seen. The operator must place himself at least 6 metres above the * From the Bulletins de ? Acad. Roy. de Belgique, ser. 2. vol. xvii. No. 8. + “Sur un mode particulier de production de bulles de sayon,” Bull. de PAcad. de Belgique, ser. 2. vo]. xiii. p. 286. [Phil. Mag. S. 4. vol. xxvi. p. 407.] On some curious Effects of the Molecular Forces of Liquids. 435 eround; for otherwise either the liquid sheet will not have time to resolve itself into hollow spheres, or, should these spheres be produced, it will be found impossible to observe them and to notice their rupture. This experiment fully confirms the conclusion arrived at by M. Félix Plateau, according to whom the simultaneous agglo- meration of liquid molecules into perfectly closed envelopes cannot be regarded as a necessary condition of the formation of vesicles ; the admission of the generation of unclosed films of any curvature whatever will suffice—a generation which assuredly involves no impossibility. Without doubt the question of the duration of the bubbles remains to be resolved. The larger ones, it is true, burst in less than a second; but do the smaller spherules likewise do so? I have not been able to establish this point, in consequence of the difficulty of judging whether these small spheres are full or empty—a difficulty which is increased by the circumstance that the envelope is much thicker than that of the bubbles of soap-water. Apart from the meteorological question, ile application of the procedure above described to different kinds of liquid ap- peared to me to possess some interest. I first tried soap-water, and thus found that although bubbles form themselves very well, their diameters are not great; and moreover they burst as rapidly as when pure water is employed. If these results differ from those described by M. Félix Plateau, it is merely because, instead of turning rapidly round on projecting the liquid, I simply threw it with a relatively moderate velocity, so that the sheet was much less broad, and much thicker. I tried also a very great velocity, so as to render the sheet very thin, and I then obtained a very great number of small spheres accompanied by some very light bubbles more or less large and pretty durable; I even succeeded, by rapidly projecting a con- centrated solution of soap (qui s’était prise en gelée), in pro- ducing three bubbles, the largest of which had a diameter of at least 25 centimetres, whilst that of the two others amounted to about 8 or 10; all three had a duration of about half a minute. My. method succeeds very well with alcohol, though the bub- bles burst very quickly. Amongst the volatile oils, I operated with success upon oil of turpentine, and especially so upon petro- leum oil. With heavy oils (of which I only tried olive oil) the experiment is a little less successful: the bubbles which are formed are very small, in consequence of the liquid being pre- vented by its own viscosity from expanding into a broad shect. Lastly, I obtained good results with several saline solutions. I have not tried mercury. It appeared to me, in fact, scarcely 436 M. G. Vander Mensbrugghe on some curious Effects necessary to do so, since the pretty experiment of M. Melsens*, in which bubbles of mercury are produced by employing, it is true, a very different method, has long been known. When a large quantity of liquid is operated upon, it may easily be made to take the form of a sheet with determinate cur- vature. ‘To do so, it is merely necessary to propel it by a force- pump through tubes provided with suitable terminations. To apply this method I had two such terminations constructed ; the form of one was a semicylindrical canal, and that of the other a semiconical one. The length of the canal was about 50 millimetres, and the section of efflux was the space enclosed between two concentric semicircles whose radii were 20 and 17 millimetres respectively. I used both well-water and soap- water. The semicylindrical termination gave, with well-water, a multitude of bubbles, from 3 to 4 centimetres in diameter, which burst after a trajectory of some metres; and with soap- water, a great number of hollow bubbles which floated in the air. The semiconical termination produced, with ordinary water, a sheet which gradually became broader and thinner until it resolved itself into a shower of hollow bubbles which burst a few instants after their formation; with soap-water innumerable spherules were thus formed, of which a great number had very thin envelopes. I also employed terminations narrower than 3 millimetres, but they yielded results much less developed than were the pre- ceding ones. On the whole, these experiments appeared to me to prove that the majority of liquids, if not all, after being spread out in sheets of proper breadth and thickness, may assume the form of hollow spheres. 2. Floating globules of mercury.—Attractions and repulstons exhibited by these globules. For some time past physicists have been frequently occupied with the examination of the globular form assumed by a liquid, even at ordinary temperatures, at the surface of the same or of a different liquid. The communication of an experiment which I believe to be new, and which, whilst showing in a remarkable manner the effects of the molecular actions of liquids, also fur- nishes the means of proving capillary attractions and repulsions, will therefore be here not out of place. 1 operated thus: A broad capsule being filled with distilled water, a globule of mercury, of about 0°5 of a millimetre in diameter, was taken on the blade of a knife and brought into proximity with the liquid, the blade being inclined as little as possible. The latter was * See L’ Institut for 1845, p. 207. of the Molecular Forces of Liquids. 437 then turned very gently around its sharp edge so as to put the globule, placed very near this edge, into contact with the water. This contact established, the knife was carefully withdrawn, and the globule of mercury left floating on the surface of a liquid thirteen and a half times less dense than itself. This phenomenon suggests several remarks. In the first place, why is the globule not made wet by the liquid? The fact is due, I believe, to the layer of air condensed at the surface of the globule: this explanation appears to be the more probable, since I was able to make the globule float immediately after it had remained immersed in the water for more than a quarter of an hour, though not after it had been submerged for an hour or upwards; the layer of air in the latter case had been displaced, or at least partially so. In the second place, it may be asked, will it suffice, in explaining the present phenomenon, to say that the weight of the mercurial globule is equal to that of the dis- placed water, the depression formed around the mercury being, of course, included? Must we not take into account the fact that, the water being concave immediately beneath the globule, the capillary pressure there must be less than at surrounding points? or does there come into play in this case a special effect of cohesion, for instance a resistance opposed by the surs rounding liquid to the deformation of its surface? I have made a great number of experiments and calculations in order to elu- cidate these questions decisively, but up to the present time I have not been successful. — As already remarked, the experiment above described furnishes a very convenient method of showing, clearly, capillary attractions and repulsions. In fact at the moment of withdrawing the blade of the penknife, the globule of mercury is seen to suffer a quick repulsion. This is evidently a capillary effect due to the elevation of the water along the blade, and to the depression of this liquid around the mercury. The sides of the capsule also exert an energetic repulsion. To prove attraction, I endeavoured to make two globules float in such a manner that, when still, their distance asunder might be about 20 millimetres. Ina few moments they moved towards each other with a velocity which, from being very small at first, increased rapidly as the distance between them diminished. Immediately after contact the two globules united and formed one, the layer of air adhering to each of them having been so far displaced by the shock as to allow cohesion to produce its effect. This union of the globules does not readily take place unless the mercury is sufficiently pure, and the surface of the water free from small filaments and cor- puscles; for the latter interfere considerably with the capillary actions, and render the distance between the mercurial surfaces 438 — Prof. Tyndall’s Contributions to Molecular Physics. in question sufficiently great to prevent the manifestation of molecular attraction. An interest is given to these experiments by the fact that capillary actions make themselves felt therein at far greater dis- tances (20 millims. to 25 millims.) than with the bodies usually employed in order to exhibit these actions in physical lectures. I may add that, in spite of the smallness of the masses which act upon one another, all these movements may be followed with the greatest facility, im consequence of the large quantity of light reflected by the non-submerged zones. The effect of the cohesion between two spherules in juxta- position enabled me to increase gradually the volume of the initial globule. For this purpose, it was merely necessary to float successively several very small spherules, which ultimately — all united themselves to the first globule. I was thus enabled to seek experimentally the maximum diameter of a sphere able to maintain itself at the surface of distilled water. I found it to be very nearly 0°87 of a millimetre. With well-water, I found the maximum diameter to be about 1 millimetre. I also tried to make droplets of mercury float on olive oil, and succeeded perfectly ; the globules, however, had at most a diameter of a third of a millimetre. These experiments suggested the idea of floating small solid spheres of great density. To cite one case only, a spherule of platinum 0:3 to 0-4 of a millimetre in diameter, was easily made to float on the surface of water. In the last place I submitted several saline solutions to expe- riment; amongst others, solutions of chloride of sodium, nitrate of barytes, and carbonate of soda. It appeared to me that the maximum diameter increased at first with the degree of concen- tration, but that this augmentation had a limit, beyond which the maximum diameter diminished. I propose, however, to examine this point more closely on some future occasion. LIV. The Bakerian Lecture.—Contributions to Molecular Physics. Being the Fifth Memoir of Researches on Radiant Heat. By JoHN TynpalLt, F.R.S., &c.* § I. Preliminary considerations.—Description of apparatus. ck lt natural philosophy of the future must, I imagine, mainly consist in the investigation of the relations which subsist between the ordinary matter of the universe and * From the Philosophical Transactions, Part IJ. 1864, having been read at the Royal Society March 17, 1864. Prof. Tyndall’s Contributions to Molecular Physics. 439 the ether in which this matter is immersed. Regarding the motions of the ether itself, as illustrated by the phenomena of reflexion, refraction, interference, and diffraction, the optical investigations of the last half century have left nothing to be desired; but as regards the atoms and molecules, whence issue the undulations of light and heat, and their relations to the medium which they move, and by which they are set in motion, these investigations teach us nothing. To come closer to the origin of the zxthereal waves—to get, if possible, some experi- mental hold of the oscillating atoms themselves—has been the main object of the researches in which I have been engaged for the last five years. In these researches radiant heat has been used as an instrument for exploring molecular condition, and this is the object which I have kept constantly in view throughout the investigation which I have now the honour to submit to the Royal Society. The first part of these researches is devoted to the more com- plete examination of a subject which was briefly touched upon at the conclusion of my fourth memoir—namely, the action of liquids, as compared with that of their vapours, upon radiant heat. The differences which exist between different gaseous molecules, as regards their power of emitting and absorbing radiant heat, have been already amply illustrated. When a gas is condensed to a liquid, the molecules approach and grapple with each other by forces which are insensible as long as the gaseous state is maintained. But though thus condensed and enthralled, the ether still surrounds the molecules. If, then, the powers of radiation and absorption depend upon them indi- vidually, we may expect that the deportment towards radiant heat which experiment establishes in the case of the free mole- cule, will maintain itself after the molecule has relinquished its freedom and formed part of a liquid. If, on the other hand, the state of aggregation be of paramount importance, we may expect to find on the part of liquids a deportment altogether different from that of their vapours. Melloni, it is well known, examined the diathermancy of various liquids, but he employed for this purpose the flame of an oil-lamp, covered bya glass chimney. His liquids, moreover, were contained in glass cells; hence the radiation from the source was profoundly modified before it entered the liquid at all, for the glass was impervious to a considerable part of the radiation. It was my wish to interfere as little as possible with the primi- tive emission, and also to compare the action of liquids with that _ of their vapours, when examined in a tube stopped with plates of rock-salt. I therefore devised an apparatus in which a layer of liquid of any thickness could be enclosed between two polished 440 Prof. Tyndall’s Contributions to Molecular Physics. plates of rock-salt. It was skilfully constructed for me by Mr. Becker, and the same two plates have already done service in more than six hundred experiments. The apparatus consists of the following parts :—A B C (fig. 1) is a plate of brass, 3°4 inches long, 2:1 inches wide, and 0°3 of Ie A= === SS = i: n Ht qe ttn i Prof. Tyndall’s Contributions to Molecular Physics. 441 an inch thick. Into it, at its corners, are rigidly fixed four upright pillars, furnished at the top with screws, for the recep- tion of the nuts grst. DEF isa second plate of brass of the same size as the former, and pierced with holes at its four cor- ners, so as to enable it to slip over the four columns of the plate ABC. Both these plates are perforated by circular apertures, mn and op, 1:35 inch m diameter. GH1I isa third plate of brass of the same area as D EF, and, like it, having its centre and its corners perforated. The plate G HI is intended to sepa- rate the two plates of rock-salt, which are to form the walls of the cell, and its thickness determines that of the liquid layer. Thus when the plates A BC and DEF are in position, a space of the form of a shallow cylinder is enclosed between them, and this space can be filled with any liquid through the orifice f. The separating plate G HI was ground with the utmost accu- racy, and the surfaces of the plates of salt were polished with extreme care, with a view to rendering the contact between the salt and the brass water-tight. In practice, however, it was found necessary to introduce washers of thin letter-paper between the plates of salt and the separating plate. In arranging the cell for experiment, the nuts grst are un- screwed, and a washer of india-rubber is first placed on ABC. On this washer is placed one of the plates of rock-salt. On the plate of rock-salt is placed the washer of letter-paper, and on this again the separating plate G HI. A second washer of paper is placed on this plate; then comes the second plate of salt, on which another india-rubber washer is laid. The plate D EF is finally slipped over the columns, and the whole arrangement is tightly screwed together by the nuts grst. The use of the india-rubber washers is to relieve the crushimg pressure which would be ap- plied to the plates of salt if they were in actual contact with the brass plates; and the use of the paper washers is, as already explained, to render the cell liquid-tight. After each experi- ment, the apparatus is unscrewed, the plates of salt are removed and thoroughly cleansed; the cellis then remounted, and in two or three minutes all is ready for a new experiment. My next necessity was a perfectly steady source of heat, of sufficient intensity to penetrate the most absorbent of the liquids to be subjected to examination. This was found in a spiral of _ platinum wire, rendered incandescent by an electric current. The frequent use of this source of heat led me to construct the lamp shown in fig. 2. A isa globe of glass 3 inches in diameter, fixed upon a stand, which can be raised and lowered. At the top of the globe is a tubulure, into which a cork is fitted, and through the cork pass two wires whose ends are united by the platinum spiral s. The wires are carried down to the binding- Phil. Mag. S. 4. Vol. 28. No. 191. Dec. 1864. 2G 442 Prof. Tyndall’s Contributions to Molecular Physics. screws ab, which are fixed in the foot of the stand, so that when the instrument is attached to the battery no strain is ever exerted on the wires which carry the spiral. The ends of the thick wire to which the spiral is attached are also of stout platinum; for when it was attached to copper wires, unsteadiness was introduced through oxidation. The heat from the incandescent spiral issues by the opening d, which is an inch and a half in diameter. Behind the spiral, finally, is a metallic reflector, 7, which aug- ments the flux of heat without sensibly changing its quality. In the open air the red-hot spiral is a capricious source of heat ; but surrounded by its glass globe its steadiness is admirable. The whole experimental arrangement will be immediately un- derstood from the sketch given in fig. 3. A is the platinum lamp just described, heated by a current from a Grove’s battery of five cells. It is necessary that this lamp should remain per- fectly constant throughout the day ; and to keep it so, a tangent galvanometer and a rheocord are introduced into the circuit. In front of the spiral, and surrounding the tubulure of its globe, is the tube B with an interior reflecting surface, through which the heat passes to the rock-salt cell C. This cell is placed on a little stage soldered to the back of the perforated screen SS, so that the heat, after having crossed the cell, passes through the hole in the screen, and afterwards impinges on the thermo- electric pile P. The pile is placed at some distance from the screen SS, so as to render the temperature of the cell C itself of no account. C/! is the compensating cube, containing water kept boiling by steam from the pipe p. Between the cube C’ and the pile P is the screen Q, which regulates the amount of heat fall- ing on the posterior face of the pile. The whole arrangement is here exposed, but in practice the pile P and the cube C’ are care- fully protected from the capricious action of the surrounding air. The experiments are thus performed. The empty rock-salt cell C being placed on its stage, a double silvered screen (not shown in the figure) is first introduced between the end of the tube B and the cell C—the radiation from the spiral being thus totally cut off, and the pile subjected to the action of the cube C! alone. By means of the screen Q, the total heat to be adopted throughout the series of experiments is obtained: say that it is sufficient to produce a galvanometric deflection of 50 degrees. The double screen used to intercept the radiation from the spiral is then gradually withdrawn until this radiation completely neu- tralizes that from the cube C’, and the needle of the galvano- meter points steadily to zero. The position of the double screen, once fixed, remains subsequently unchanged, the slight and slow alteration of the source being neutralized by the rheocord. Thus the rays in the first instance pass from the spiral through the Prof. Tyndall’s Contributions to Molecular Physics. 448 empty rock-salt cell. A small funnel, supported by a suitable stand, dips into the aperture which leads into the cell, and through this the liquid is poured. The imtroduction of the 2G 2 444 Prof. Tyndall’s Contributions to Molecular Physics. liquid destroys the previous equilibrium, the galvanometer needle moves, and finally assumes a steady deflection; and from this deflection we can immediately calculate the quantity of heat ab- sorbed by the liquid, and express it in hundredths of the entire radiation. For example, the empty cell being placed upon its stand, and the needle being at O°, the introduction of iodide of methyle into the cell produced a deflection of 80°°8. The total radiation on this occasion was 44°:2. Taking the force necessary to move the needle from 0° to 1° as our unit, the deflection 30°°8 corre- sponds to 32 such units, while the deflection 44°2 corresponds to 58°3 such units. Hence the statement 58°3 : 100=82 : 549, which gives an absorption of 54°9 per cent. for a layer of liquid iodide of methyle 0°07 of an inch in thickness. § II. Absorption of radiant heat of a certain quality by eleven different liquids at five different thicknesses. The following Table contains the results obtained in this manner with the respective liquids there mentioned. It em- braces both the deflection produced by the introduction of the liquid, and the quantity per cent. intercepted of the entire radia- — tion. It has been intimated to me by some of my continental friends that the publication of such details as would enable a reader to judge of the precision attaimable by my apparatus would be desirable. In this paper I shall, to some extent, endeavour to satisfy this desire, making use, however, of my ordinary ex- periments. Tasie I.—Radiation of heat through Liquids. Source of heat, red-hot platinum spiral. Thickness of liquid layer 0:07 of an inch. Name of liquid. Deflection. Absorption per 100. Iodide of methyle . . 30°8 54:9 Todide of ethyle oo 4-s4o0W 60-4 Benzoles 36: 2S. ie eeoars 67:0 Amylene 200 s0e- te we porns 74:8 Sulphuric ether . . . 39°0 (O4Am Aceticether . . . . 3896 81:6 Aleohol 2% | 1.0 eA 866 Water¥ S42; 2 eae a aate 91°4 Total heat... < =o =.9,.., 7442 100 * To prevent the water from attacking the cell, it was always first satu- rated with the substance of the cell itself, namely, transparent rock-salt. Prof. Tyndall’s Contributions to Molecular Physics. 445 _In these experiments I employed a less delicate galvanometer than that used in my former researches. The experiments were made on the 29th of September, and on the following day I repeated them with the following results:— Tas ie I].—Radiation of heat through Liquids. Source of heat, red-hot platinum spiral. Thickness of liquid layer 0-07 of an inch. Name of liquid. Deflection. Absorption per 100. Iodide of methyle . . 33-5 53°7 Homideofethyle .,.. . -35°D 58:7 ese e ee dis OD 6404 PAMeMENe -. . +) oe | B9'D 70°7 Sulphuricether . . . 41:0 75°74: Aceticether ... . 41°5 76:9 Formic ether . . . . 42°4 80:0 Alcohol ee hie. decd 8402 NVaIeENI bs 6 cre. 44°7 90°5 Woralbeaty. oc. 46°7 100:0 On the 28th of October my most delicate galvanometer was at liberty, and with it I executed the experiments performed with the coarser one. The following are the results :— Tape I1I1.—Radiation of heat through Liquids. Source, red- hot platinum spiral. Thickness of liquid layer 0:07 of an inch. Name of liquid. Deflection. | Absorption 7 per 100. Eimpimemucarbon.. ..'. . . . 9:0 12:5 (Siew ES a So 35°0 Paeic@emethyle . .... . . « » 86:0 53°2 543 Ditto, strongly coloured with iodine . 36:0 53:2 Moote oiethvie . .(.,:. . . . 88'2 59:0 59°6 So . , a hc ws we ODD 62°5 65:7 PeCICMUEIE kk ote a os oe ABD 736 72°3 Pulpniea@etiier, .- . 1). . . » 42°56 ZO 177 -A PMGeMIGICpnCE)s . 5 wt te ww ew AS 78:0 79'3 OPIMIGHEEMOY = 2-6 ev fetis «ee 403 79:0 80:0 POGUE sw ws Sa ee knee GAA 83°6 85:4 CORP, gf ptie’ eo sw 456 88°8 90:9 eat wt ee sw ABO 100:0 I have here placed beside the results obtained with the deli- cate galvanometer, the means of those obtained with the coarser one. It is not my object to push these measurements to the last 446 Prof. Tyndall’s Contributions to Molecular Physics. degree of nicety; otherwise the satisfactory agreement here exhi- bited might be made still better. To render the experiments on liquid transmission more com- plete, I operated with layers of various thicknesses, employing throughout my most delicate galvanometer. The results of these measurements are recorded in the following series of Tables :— Tasie [V.—Radiation of heat through Liquids. Source, red- hot platinum spiral. Thickness of liquid layer 0:02 of an inch. Name of liquid. Deflection. Absorption per 100. Bisulphide of carbon . 40 5:5 Chloroform <2.7 ee) 57 12:0 16°6 Todide of methyle. . . 260 361 Iodide of ethyle . . . 275 38°2 ‘Benzoles 2.) 5 tnt ee ole 43 °4: Aimylene 2) save pip OOO 58°3 Boracic ether . .~.'* .- -d9:0 61'8 Sulphuric ether” 7 42 %.. (aoza 63°3 Pormic-ether?-.) 4242 740:0 65°2 Alcohols Soe ee ile awed 67°3 Water vies yt.) OE ayaa iit 80°7 Votal:heat?- 22st 2 ai FASO 100:0 TaBLe V.—Thickness of liquid layer 0:04 of an inch. Name of liquid. Deflection. Absorption per 100. Bisulphide of carbon . 6°] 8°4, Chioroformict-eeu so Ow 25:0 Todide of methyle . . 83:0 46:5 fodide otvethyle “<0 000 S077 Benzole.m S08... 5 tes 70) Nae FATMIGLCTIC Ue ee > i's eee a) 65:2 Boracie ether. -« «. °° 41:0 69°4. Sulphurieether™ 7% 42-0 73°5 Acetic, ctnert =. . *. 1. ark 74:0 Formic ether. 7.) %) 374275 1675 Alcohols... eae 78°6 Water. Fee. eA 86°1 Total heat.) % 5 «5.6 2 |, - A&2 31:4 Supmuceether .*. |. . . 58D 31:9 mero ectner . . . :'. . b99D 34:6 Mmeeeicat s.r 78O | 100°0 Placing these results beside those recorded in Table IX., the manner in which they check each other will appear. 450 Prof. Tyndall’s Contributions to Molecular Physics. Comparison of Tables IX. and X.—Absorption. Table IX. Table X. Bisulphide of carbon . . 4°7 4:7 Chloroform . 2 I SOS 6°5 Iodide of methyle Nae Mut eat its 0 1 / 9:6 Hodide of ethyleys. oyna Wise Benzole ©. 5) Meet 20°6 Am ylene== aetna 27°38 PASS The agreement, it will ee seen, 18 as perfect as could be desired. Augmenting the opening through which the heat passed from the source into the experimental tube, the total heat was increased, and the experiments with a few of the vapours were repeated. The total heat in the last case produced a deflection of 78°, which is equal to 350 units; the total heat now employed produced a deflection of 83°, which is equal to 605 units. It is easy to see that the experiments now to be recorded furnish a direct check on the calibration of the galvanometer. As long as the quality of the heat remains unchanged, the absorption ought to be the same with a high total heat as with a low one. But if experi- ment show that this is the case, it proves also that the calibra- tion on which the calculation of the absorption depends, cannot be in error. The following results were obtained on the 8th of October :— TABLE Xa. Deflection. Absorption. Anmnyletie a. ear mete OO;O. 23°7 Alcohol: 2s: 14 258 ge eOoA 29°2 Formic ether). %. 4, &3)463;5 32°5 Formic ethers.) 22. -, ) 08%) 32°5 Sulphuric ether -. . - 69:2 33°6 Sulphuric ether . . . 691 33°4 Acetic ether, <),. i. e697 34°5 Acetic ether 20 see oe Cenk 34°5 otalvheat .¢ Dcaae fs 83°0 100:0 Placing the results beside fine recorded in Table X., we have the following comparison :— Comparison of Tables X. and Xa. Ammylene 1) 245-4 ee ee eae 28°7 Alcohols. 2 mbes: ae OR 29°2 Hormic ether.) >... Pro Leas 32°5 Sulphune: ether). . >.) 419 33°5 Aceticvether lise sate deso4.0 34°5 —— ee ee ~: a Prof. Tyndall’s Contributions to Molecular Physics. 451 The differences here are inconsiderable, and lean to neither side ; within these limits, therefore, the calibration must be correct ; it shall be tested more severely in another part of this paper. § JV. Absorption of the same heat by the same vapours when the quantities of vapour are proportional to the quantities of hquid. —Comparative view of the action of liquids and their vapours on radiant heat. We are now in a condition to compare the action of a series of volatile liquids with that of the vapours of those liquids upon radiant heat. Commencing with the substance of the lowest absorptive energy, and proceeding to the highest, we have the following order of absorption :— Liquids. Vapours. Bisulphide of carbon. Bisulphide of carbon. Chloroform. Chloroform. Iodide of methyle. Todide of methyle. Iodide of ethyle. Todide of ethyle. Benzole. Benzole. Amylene. Amylene. Sulphuric ether. Alcohol. Acetic ether. Formic ether. Formic ether. Sulphuric ether. Alcohol. Acetic ether. Water. Here, as far as amylene, the order of absorption is the same for both hquids and vapours. But from amylene downwards, though strong liquid absorption is in a general way paralleled by strong vapour absorption, the order of both is not the same. There is not the slightest doubt that next to water alcohol is the most powerful absorber in the list of liquids; but there is just as little doubt that the position which it occupies in the list of vapours is the correct one. This has been established by reite- rated experiments. Acetic ether, on the other hand, though certainly the most energetic absorber in the state of vapour, falls behind both formic ether and alcohol in the liquid state. Still, on the whole, [ think it is impossible to contemplate these results without arriving at the general conclusion that the act of absorp- tion isin the main molecular, and that the molecule maintains its power as an absorber and radiator when it changes its state of ageregation. Should, however, any doubt linger as to the cor- rectness of this conclusion, it will speedily disappear. 452 Prof. Tyndall’s Contributions to Molecular Physics. A moment’s reflection will show that the comparison here in- stituted is not a strict one. We have taken the liquids at a common thickness, and the vapours at a common volume and pressure. But if the layers of liquid employed were turned bodily into vapour, the volumes obtained would not be the same. Hence the quantities of matter traversed by the radiant heat are neither equal nor proportional to each other in the two cases ; and to render the comparison strict they ought to be propor- tional. It is easy, of course, to make them so; for the liquids being examined at a constant volume, their specific gravities give us the relative quantities of matter traversed by the radiant heat, and from these and the vapour-densities we can immedi- ately deduce the corresponding volumes of the vapour. Calling the quantity of matter g, the vapour-density d, and the volume V, we have Vd=q, or xan Me d Dividing, therefore, the specific gravities of our liquids by the densities of their vapours, we obtain a series of volumes propor- tional to the masses of the liquids employed. The densities of both liquids and vapours are given in the following Table :— Table of Densities. Vapour. Liquid. Bisulphide of carbon. . 2°63 1:27 Chioratorm 4) 5 +4. «ale 1:48 Iodide of methyle . . 4°90 2°24: Iodide of ethyle . . . 5:39 1°95 Henzolec’ = ae, sr eee 0°85 PAVMVLCTION Petes yas) jis aed 0:64: PACOMO Le spe etic ror cat OD 0°79 Sulphuric ether’... . "2°56 0°71 Formic eter.) 27 2 206 0:91 Acetic ether . . . . 93°04 0:89 Water Sir See eet Oe 1:00 Substituting for g the numbers of the second column, and for d those of the first, we obtain the following series of vapour volumes, whose weights are proportional to the masses of liquid employed. Prof. Tyndall’s Contributions to Molecular Physics. 4538 Table of Proportional Volumes. Bisulphide of carbon . . 0°48 Chioroform oo! ow 1) O'S6 Iodide of methyle . . . 0°46 fodide of ethyle 2. ~~) 0°36 Benzle 80.) 28 eh Se prarylene %4 0s.) 3 TUS 0.26 PMeouGleite ie Ose AL VO Sulphuric ether. . . . O28 Formic ethers ©... ." . O36 Aeetie ether... 6 oe 4) 0°29 Ribena helio: 24th. WIh60 Employing the vapours in the volumes here indicated, the following results were obtained :— Tasie X1.—Radiation of heat through Vapours. Mass of vapour proportional to mass of liquid. Tension in part é Absorpti Name of vapour. lige ee eae ‘ Dy BCebon Far 00) eae : 8-4. Bisulphide of carbon . 0°48 8-5 } 43 13:0 Chiovoiorm . . - . 0°36 { 13-0 } 6°6 Iodide of methyle O46. linn. 10:2 pe a 20-4 . 30-6 Iodide of ethyle . . 0°36 | 30-6 } 15-4 : 33°44: : Benzole 0°32 { 33.1 } 16°38 Amylene . ote O26 O77 19-0 42°55 Sulphuric ether. . . 0°28 { Beh 215 440 Aeetic ether. . . . 0°29 { AAO 22°2 445 Formic ether 0:36 ‘ AA 4 22°5 45:0 : Alcohol . . . . . 0:50 1449, 22-7 Here the discrepancies revealed by our former series of expe- riments entirely disappear, and it is proved that for heat of the same quality the order of absorption for liquids and their vapours is the same. We may therefore safely infer that the position of a vapour as an absorber or radiator is determined by that of the liquid from which it is derived. Granting the validity of this 454 — Prof. Tyndall’s Contributions to Molecular Physics. inference, the position of water fixes that of aqueous vapour. From the first seven Tables of this memoir, or from the résumé of results in Table VIII., it will be seen that for all thicknesses water exceeds the other liquids in the energy of its absorption. Hence, if no single experiment on the vapour of water existed, we should be compelled to conclude, from the deportment of its liquid, that, weight for weight, aqueous vapour transcends all others in absorptive power. Add to this the direct and multi- plied experiments by which the action of this substance on radiant heat has been established, and we have before us a body of evidence sufficient, I trust, to set this question for ever at rest, and to induce the meteorologist to apply without misgiving the radiant and absorbent property of aqueous vapour to the pheno- mena of his science. § V. Remarks on the chemical constitution of bodies with reference to their powers of absorption. ‘The order and relative powers of absorption of our vapours, when equal volumes are compared, are given in Table X.: the chemical formule of the substances, and the number of atoms which their molecules embrace, are as follows :— Number of atoms ‘Formula. : in molecules. Bisulphide of carbon . C8? 3 Chiorcformije.7 . . . ~ OC 5 Iodide of methyle . . CHI 5 Todide of ethyle . . . C? HI 8 Benzole + FOR Am. eo 12 Amylenenieha-.. 0. Vy C2? 15 Alcona tacit < oy. eZee 9 Pormictetheria: ..: peace ©? 11 Palphuriciether . 3. 2 SC HI°@ 15 Acetictethersh:.. .. ..- (C2 oO? 14 Boracic ether. . . . BC®H!03 25 Here, for the first six vapours, the radiant and absorbent powers augment with the number of atoms contained in the molecules. Alcohol and amylene vapours, however, are nearly alike in absorptive power, the molecule of amylene containing 15 atoms, while that of alcohol embraces only 9. But in alcohol we have a third element introduced, which is absent in the amy- lene; the oxygen of the alcohol gives its molecule such a cha- racter as enables it to transcend that of the amylene, though the latter contains the greater number of atoms. Here the idea of quality superadds itself to that of number. Acetic ether also has a less number of atoms in its molecule than sulphuric ether ; Prof. Tyndall’s Contributions to Molecular Physics. ABS but whereas the latter has but one atom of oxygen, the former has two. Formic ether and sulphuric ether are almost identical in their absorptive powers for the heat here employed ; still formic ether has but 11 atoms in its molecule, while sulphuric has 15. But formic ether possesses two atoms of oxygen, while sulphuric possesses only one. Two things here suggest themselves as influential on the absorbent and radiant power, which may be expressed by the terms multitude and complexity. As a mole- cule of multitude, amylene, for example, exceeds alcohol; as a molecule of complexity, alcohol exceeds amylene; and im this case, as regards radiant and absorbent power, the complexity is more than a match for the multitude. The same remarks may be made with reference to sulphuric and formic ether: the for- mer excels in multitude, the latter in complexity, the excess in the one case almost exactly balancing that in the other. Adding two atoms of hydrogen and one of carbon to the formic ether, we obtain acetic ether, and by this addition the balance is turned ; for though acetic ether falls short of sulphuric ether in multi- tude, it transcends it in absorbent and radiant power. Out- standing from all others, when equal volumes are compared, and signalizing itself by the enormous magnitude of its absorption, we have boracic ether, each molecule of which embraces no less than 25 atoms. The time now at my disposal enables me to do little more than glance at these singular facts; but I must direct the attention of chemists to the water molecule: its power as a radiant and-an absorbent is perfectly unprecedented and anomalous, if the usually recognized formula be correct. § VI. Transmission of radiant heat through bodies opake to light. —Remarks on the physical cause of transparency and opacity. In Table III. a fact is revealed which is worth a little further attention. ‘The measurements there recorded show that the absorption of a layer of iodide of methyle, strongly coloured with iodine (which, doubtless, had been liberated by the action of light), was precisely the same as that of a perfectly transpa- rent layer of the liquid. The iodine, which produced so marked an effect on light, did not sensibly affect the radiant heat emitted by the platinum spiral. Here are the numbers :— Absorption. Todide of methyle (transparent) . 53:2 Iodide of methyle (strongly coloured with iodine) | 53-2 In this case, the incandescent spiral, or a flame, was visible when looked at through the liquid; I therefore intentionally deepened the colour (a rich brown), by adding iodine, until the layer was of sufficient opacity to cut off wholly the light of a brilliant jet 456 Prof. Tyndall’s Contributions to Molecular Physics. of gas. The transparency of the liquid to the radiant heat was not sensibly affected by the addition of the iodine. The lumi- nous heat was of course cut off; but this, as compared with the whole radiation, was so small as to be insensible in the expe- riments. It is known that iodine dissolves freely in the bisulphide of carbon, the colour of the solution in thin layers being a splendid purple; but in layers of moderate thickness it may be rendered perfectly opake to light. I dissolved in the liquid a quantity of the iodine sufficient, when introduced into a cell 0:07 of an inch wide, to cut off wholly the light of the most brilliant gas-flame. Comparing the opake solution with the transparent bisulphide, the following results were obtained :— Deflection. Absorption. Bisulphide of carbon (opake). . . 9:0 12°5 Bisulphide of carbon (transparent) . 9-0 1275 Here the presence of a quantity of iodine, perfectly opake to a brilliant light, was without measurable effect upon the heat emanating from our platinum spiral. The liquid was sensibly thickened by the quantity of iodine dissolved in it. The same liquid was placed in acell 0°27 of an inch in width ; that is to say, a solution which was perfectly opake to light, at a thickness of 0°07 was employed in a layer of nearly four times this thickness. Here are the results :— Deflection. Absorption. Bisulphide of carbon (transparent) . 13°6 18°8 Bisulphide of carbon (opake). . . 138°7 19-0 The difference between the two measurements lies within the limits of possible error. Bisulphide of carbon is commonly used to fill hollow prisms, when considerable dispersion is sought for in the decomposition of white light. Such prisms, filled with the opake solution, inter- cept entirely the luminous part of the spectrum, but allow the extra-red rays free passage. A heat-spectrum of the sun, or of the electric light, may be thus obtained entirely separated from the luminous one. By means of a prism of the transparent bisulphide, I determined the position of the spectrum of the electric light upon a screen, and behind the screen placed a thermo-electric pile so that when the screen was removed the extra-red rays fell upon the pile. I then substituted an opake prism for the transparent one: there was no visible spectrum on the screen; but the removal of the latter at once demonstrated the existence of an invisible spectrum by the thermo-electric cur- rent which it generated, and which was powerful enough to dash violently aside the needles of a large lecture-room galvanometer. Prof. Tyndall’s Contributions to Molecular Physics. 457 To what, then, are we to ascribe the deportment of iodine towards luminous and obscure heat? The difference between both qualities of heat is simply one of period: in the one case the waves which convey the energy are short and of rapid recur- rence ; in the other case they are Jong and of slow recurrence. The former are intercepted by the iodine, and the latter are allowed to pass. Why? There can, I think, be only one answer to this question—that the intercepted waves are these whose periods coincide with the periods of oscillation possible to the atoms of the dissolved iodine. Supposing waves of any period to impinge upon an assemblage of molecules of any other period, it is, | think, physically certain 'that a tremor of greater or less intensity will be set up among the molecules; but for the motion to accumulate so as to produce sensible absorption, coincidence of period is necessary. Briefly defined, therefore, transparency is synonymous with discord, while opacity is synonymous with accord between the periods of the waves of ether and those of the molecules of the body on which they impinge. The opacity, then, of our solution of iodine to light shows that its atoms are competent to vibrate in all periods which lie withm the limits of the visible spectrum; while its transparency to the extra-red undulations demonstrates the incompetency of its atoms to vibrate in unison with the longer waves. This simple conception will, I think, be found sufficient to conduct us with intellectual clearness through a multitude of otherwise perplexing phenomena. It may cf course be applied immediately to that numerous class of bodies which are transpa- rent to light, but opake in a greater or less degree to radiant heat. Water, for example, is an eminent example of this class of bodies: while it allows the luminous rays to pass with free- dom, it is highly opake to all radiations emanating from obscure sources. A layer of this substance one-twentieth of an inch: thick is competent, as Melloni has shown, to intercept all rays issuing from bodies heated under incandescence. Hence we may infer that, throughout the range of the visible spectrum, the periods of the water-molecules are in discord with those of the ethereal waves, while beyond the red we have coincidence between both. What is true of water is, of course, true in a less degree of glass, alum, calcareous spar, and of all the substances named in the first section of this paper. They are all in discord with the visible spectrum ; they are all more or less in accord with the extra-red undulations of the spectrum. Thus also as regards lampblack: the blackness of the sub- stance is due to the accord which reigns between the oscillating periods of its atoms and those of the waves embraced within the Phil. Mag. 8. 4. Vol. 28. No. 191. Dec. 1864. 2H 458 Prof. Donkin on certain statements in Elementary Works limits of the visible spectrum. The substance which is thus im- pervious to the luminous rays is moreover the very one from which the whitest light of our lamps is derived. It can absorb all the rays of the visible spectrum, it can also emit them. But though in a far less degree than iodine, lampblack is also to some extent transparent to the longer undulations. Melloni was the first to prove this; and in an experiment described in a former memoir, I myself found that 30 per cent. of the radiation from an obscure source found its way through a layer of lamp- black which cut off totally the light of the most’ brilliant jet of gas. I shall have occasion to show that, fer certain sources of heat of long period, between 40 and 50 per cent. of the entire radiation is transmitted by a layer of lampblack which is per- fectly opake to our most brilliant artificial lights. Hence, in the case of lampblack, while accord exists between the periods of its atoms and those of the light-exciting waves, discord, to a consi- derable extent, exists between the periods of the same atoms and those of the extra-red undulations. [To be continued. | LV. Note on certain statements in Elementary Works concerning the Specific Heat of Gases. By Professor Donkin, F.R.S.* A YOUNG student of natural science showed me a few days ago the following statement in Galloway’s ‘Second Step in Chemistry’ (London, 1864). It had naturally surprised him, and he asked for an explanation, which I was quite unable to ive. ae From the calculations of Laplace and Poisson, and the expe- riments of Clement and Desormes, of De la Roche and Berard, and of Gay-Lussac and Dulong, it has hitherto been assumed that the specific heat of a gas under a constant pressure is always greater than’ the specific heat under a constant volume ; but M. Regnault has lately found, by an entirely new method, that the difference between the two kinds of specific heat is either null or extremely small.” (P. 585, paragraph 1321.) This paragraph is not accompanied by any note or reference, but it is enclosed in inverted commas, and I soon discovered that it is a translation of a passage in Ganot’s Traité élémentaire de Physique (Paris, 1859). See p. 312, end of paragraph 334. There is an English translation of Ganot, in which the same passage occurs, and is left, as it is in the original, without note or comment. I applied for further information to some of my scientific * Communicated by the Author. concerning the Specific Heat of Gases. 459 friends, and Professor Price pointed out to me a note in Jamin’s Cours de Physique, which appeared at first sight to assert the equality of the two kinds of specific heat. The probable expla- nation of it (vide infra) was suggested to me by Professor H. Smith and Sir B. Brodie. At p. 491, vol. ii. of Jamin’s book, there is a note on the ve- locity of sound. If V be the velocity calculated on the suppo- sition that pressure is proportional to density, V /1-+8 the true velocity, ¢ the specific heat (or “capacity ” as it is here called) at constant pressure, and c’ at constant volume, the ordinary theory accepts the equation 14+0=—- In the note referred to, Jamin objects to this equation on the ground that the old proof of it involved the assumption that the temperature of a gas is lowered by free expansion. After de- scribing the process which he considers to imply this error, he says,— - Mais ce raisonnement est inexact. (Quand un gaz se dilate, il est vrai qu’habituellement il se refroidit, mais c’est parce qu’il produit du travail, et s’il arrive qu’on le dilate en le faisant pénétrer dans un vase vide, il ne change plus de température (page 435). Les deux capacités sont done nécessairement égales entre elles. Par conséquent, |’équation (@) est vraie, mais elle devient fausse si on y remplace 1+ par = (The equation (@) is velocity =V /1+4@.) This note is objectionable in several respects. In the first place, it is not a safe conclusion that a result is false because it has been obtained by fallacious reasoning. Secondly, although the reasoning objected to probably did contain, in the minds of its first authors, the fallacy attributed to it, it is capable of being so interpreted as not to contain it. Thirdly, the modern mecha- nical theory of heat supplies a demonstration* of the equation * Let p, V, p, t, h be the pressure, volume, density, temperature, and actual heat of a unit of mass of gas. Let E=A/A be the energy which dh would have to be spent in communicating the actual heat A, and let c= de be the real specific heat (or specific heat at constant volume), and c the specific heat at constant pressure. Then assuming that pV=a+at, we shall have EV-EV dp eaenry OS aig gi 1) Suppose the gas to be compressed to volume V+dV (dV being negative), then dp, di being the increments of pressure and temperature, the incre- ment of actual heat is c’dt, and the corresponding energy is Ac'dt. Now 460 Prof. Donkin on the Specific Heat of Gases. 1+0= 3 which can only be objected to on two grounds—viz. that some (or all) of the quantities assumed as constant are not rigorously constant, and that the usual mechanical theory of sound is not rigorously correct ; and both objections would be irrelevant to the present purpose. Lastly, the assertion that “the two capacities are necessarily equal,” appears at first sight to mean that ¢ and c! are neces- sarily equal. But as the author cannot have intended to deduce this conclusion from a fact which proves that c and c' are neces- sarily unequal, it is probable that he only meant to say that when heat is spent upon a given quantity of gas, how much of it goes to make the gas hot depends only upon the change of tempera- ture. If this be so, the language used is very inaccurate, and almost certain to mislead an ordinary student. But, whatever Jamin may have meant, it is certain that Ganot really did mean to say that Regnault had proved experimentally the equality (or near equality) of c and c. And neither he nor his translator, nor the author of the ‘Second Step,’ have noticed that to assert this equality is to deny the conservation of energy. It may be conjectured that Ganot had somewhere met with the statement “les deux capacités sont égales entre elles,” in- tended in the non-natural sense suggested above, and confirmed this must be equal to the whole energy spent in the operation, viz. —pdV ; for if the gas were now allowed to expand freely to its former volume, it would retain its new temperature, while nothing would have been spent except the work of compression. Hence —pdV=Ac'dt; and combining this equation with (1), we obtain by eliminating dt, dp i. a+Ac! dV s (2) Pp am Ac! Ngee e ‘ e . « e e Next, let the gas (in its original condition) be heated, and at the same time allowed to expand under constant pressure p, until its volume becomes V+dV and its temperature ¢+6¢. The increment of actual heat will be c'dt, and the whole energy required for the operation will therefore be Ac'ét+pdV. But, by the definition of c, the whole energy required is Acét. Hence, since in this case (1) gives pdV=adt (for dp=0), we have (Ac’+a)6t=Acét, or Ac'+a=Ac; hence from (2), pie: Ne) DN auetaips c of which, according to the ordinary theory of sound, the equation 1+0= 5 is @ consequence. eb It is hardly necessary to add that this demonstration is only given for convenience of reference, and not as containing anything new. ~ On the Nomenclature of the Physical Sciences. 4.61 an that sense by some experiment of Regnault’s, that he took it in its natural sense, and transferred it to his book. The character a elementary scientific books has become a matter of great importance since the recognition in our old Universities of physical studies as instruments of education. It is for this reason alone that I have thought it worth while to offer these remarks for publication in the Philosophical Magazine. Oxford, October 27, 1864. LVI. On the Nomenclature of the Physical Sciences. By C. J. Monro*, 1 a paper lately published in the Philosophical Transactions, Professor Thomson has called the Astronomer Royal a natu- ralist. It would not be more inconsistent with English usage to call him a physician; but the most startling innovation seemed better than to call anybody a natural philosopher. What- ever is or ought to be the meaning of philosophy, it has nothing to do with special branches of science. To use the word in this manner is to do violence to its history, and is inconsistent with its modern application in other connexions. But I venture to think that the reform leaves untouched the most serious vice of the misnomer. If philosophy is more grossly misused in the substantive, nature is more gravely misused in the adjective. Hven as far as it goes, the advantage of the change is not unqualified: by rescuing the word philosopht wy from its misuse in the term natural philosoph y, we shall sacrifice the distinction between natural philosophy and natural history. The distinction is ill expressed indeed, and even, if I rightly under- stand the usage on the subject, inaccurately drawn; but it is real at bottom. Natural history describes things, to speak roughly, as they come: it comprehends the typical examples of what Dr. Whewell calls the classificatory sciences. Natural phi- losophy analyzes its object ; but perhaps because we have a good deal restricted our view to a particular kind of analysis, mathe- matical analysis, it is assumed that its object consists exclusively of things without life. However, the whole system isin confusion. In the classifica- tion of the physical sciences we meet the word nature, or the cor- responding Greek word in different forms, of which none sug- gests its own meaning much more than the meaning of any other. In the first place we have the general term physical science, or, as Mr. Faraday apparently prefers to say, natural knowledge. * Communicated by the Author. 462 Mr. ©. J. Monro on the Nomenclature Under physical science we have the subdivisions natural history, physiology, and natural philosophy. 1 do not say these are exactly conterminous ; probably they are not all mvariably used in quite the same senses. Anatomy might sometimes be ad- mitted into one of them, and sometimes not. But all would be, at first sight, terms as general as physical science itself; and physiology, which is in fact the most restricted, is in form the most genera] of the three. Again, natural philosophy has for its principal subdivision physics, a term apparently more general than any we have yet met with. That is to say, the science of nature is divided into history of nature, discourse of nature, and philosophy of nature; and the philosophy of nature is divided, let us say, into chemistry and naturals. Considering that these sciences differ at least as much in their objects as in their methods, and that no one would ever think of dividing science into history, discourse, and philosophy, we may ask whether confusion could go further than this. Something like it might be found in Blackstone; elsewhere hardly. I shall not examine the history of these phrases. One of them, however (physics), the most unmeaning as it stands, but the most defensible in its origin, it is ae while to observe, because it suggests a practical lesson in the art of nomenclature which may be useful if the present system is to be reformed. As the word seems to exclude chemistry, I suppose it is short for mathematical physics. Now this term, though clumsy, is per- fectly correct if we accept the more general use of the word physical; for it suggests exactly what it denotes, that part namely of physical science which can be treated mathematically. The inconvenience of it is that it expresses its differentia in a word five syllables long; and now that this is dropped, we apply the name of the summum genus to an infima species. The moral is that an essential part of a compound term should not be ex- pressed by an adjective five syllables long. There is scarcely a chance of the general adoption of any reform deliberately suggested, especially if the suggestion comes with no sort of authority 5 ; but it is worth while at least to con- sider the materials we have to dispose of. The words physic, physical, physiology, come from the Greek representatives of a root which expresses growth. Natural comes from a root which has been used for scientific purposes in Latin as the equivalent of the other. But the idea of growth has been applied in two ways. First, to things which are the subjects of generation proper— plants and animals. Secondly, to things which are the subjects of generation in a of the Physical Sciences. 463 wide and metaphorical sense. In this application it was very early contrasted with artificial creation ; but in later times, per- haps under the influence of Plato, the Greek derivatives have more emphatically suggested a contrast with things supposed to be above growth, not below it, with things eternal. Hence the antithesis of moral and physical, even mental and physical. It is in the first application that we speak of physiology, and perhaps of natural history ; all the other terms above mentioned belong to the second application. Our materials would be most economically turned to account by using the word natura in the second and wider application, and p/y/sis in the first and narrower one. But there would be something arbitrary in the selection, and it would be the formal abandonment of perhaps the oldest generalization i in philosophy. The only practicable consistent system would consist in using both natura and phy’sis in the wider application ; to preserve, that is, the phrases physical and natural science or knowledge, and to find other terms for the subdivisions. But then what are we to do with physiology? It would probably be necessary to keep biology, although, as it ought properly to mean the science of lives, lifetimes, or livelihoods, it is not very good Greek for the science of life; zoology has been appropriated as the science of zéa, animals. But the main division of the province was ex- pressed in old times by the words émpsycha and dpsycha, corre- sponding to our correct but less manageable adjectives organic and imorganic. I see no good reason against empsychology and apsychology: the words are long, but easily pronounced and easily contrasted by their accentuation. For a different reason, apsychology might not be currently used—namely, because it is a negative word; it would not, in tact, be necessary to use it so often. Apsychology would approximately coincide with natural phi- losophy. It remains to consider its principal species, physics. This term is the easiest replaced of all. I propose a reform which would have the advantage of rescuing another word from a sense in which I contend it is used improperly at present. It is not quite true, as I shall show, that this section of physical science is distinguished by its mathematical treatment. But what does distinguish it is the idea of force conceived as funda- mentally the same throughout it. I would therefore call it dyna- mics. ‘That dynamics is used already in a more restricted sense in opposition to sfafics, is a reason in favour of the change; for it is wrongly so used. The idea of force is common to statics and. “ dynamics ;”” what distinguishes “ dynamics ” is the idea of motion. It should be called cinetics. This word may seem tainted with the heresy condemned by Sir John Herschel at the 4.64 On the Nomenclature of the Physical Sciences. opening of the eighth chapter of his ‘Astronomy.’ But I am not questioning the reality of force ; I merely object to its giving a name to a single subdivision of the science concerned with it. As the number of the convertible forms of force increases, dyna- mics will tend to swallow up apsychology and will extend far into empsychology. But by that time the nomenclature will be ready for reform again. At present, what I should call dynamics scarcely embraces chemistry, because it is not yet determined, I believe, what in the latter science is the analogue of the other forms of force. It must be admitted that the adoption of such a term as empsychology would somewhat disturb the modern use of one of the most famous words in the philosophical vocabulary: I mean the word psyche. But in Greek, | believe, of all ages, Pagan, Jewish, and Christian, psyche comprehends animal life, and in Aristotle it comprehends vegetable life. And though (again I suppose under the influence of Plato) psychology is especially contrasted with physics, this is because we are more Platonic than Plato. Ali or every life may be, as he says, wmmortal, un- born, and indestructible; but in the classical passage where he says it is all this, he applies the word p/y’szs to it, and the church accepted the application to more mysterious essences stil]. What- ever else the object of psychology may be, it is certainly some- thing that grows, and its method, so far as it has one, is the method of the physical sciences. The science of language is part of psychology, and Mr. Max Miiller claims a position for it among the physical sciences. If this is conceded, the theory of chances should take its place as the mathematical department of psychology, and as another of the physical sciences. It would be mathematical physics, but of course not dynamics. Psycho- logy would sound awkward, as I have admitted, by the side of empsychology, or as a subdivision of it; I should prefer to speak of mental science, and contrast it with material science: but 1 think the awkwardness would not be intolerable; it would be nothing to the present anomalies. This extension of the term physics would be the rectification of another frontier, that of metaphysics. Metaphysics will always be contrasted with physics, without reference to the history of the former word, ov to the exact sense of the Greek preposition. Accordingly it is now often confounded with psychology. But as soon as psychology or mental science is understood to be a part of physical science, metaphysics may be kept without diffi- culty to its proper sense, the science of existence as such. Whether there is such a science or not; 1s a distinct question: those who think there is, whether right or wrong, will want the word; and so will those who wish to contradict them. On Tasmanite, a new Mineral of Organic Origin. 465 It would be too much to expect that even one of my sugges- tions will be adopted; but I hope that somebody will make better ones. Of one thing I am pretty sure, that no one will say that the present state of things is not disgraceful. I know it is easy to overrate the importance of such matters, but I think it is also easy to underrate it. Hadley, Middlesex. LVI. On Tasmanite, a new Mineral of Organic Origin. By ArtHur H. Cuurcu, M.A. Oxon., Professor of Chemistry, Royal Agricultural College, Cirencester *. N the Tasmanian Court of the International Exhibition of 1862, a very remarkable kind of fuel was shown by the « Dysodile Company”; it was catalogued as “ resiniferous shale.” In the Jermyn Street Museum of the School of Mines a speci- men of the same mineral is termed “ Combustible Shale, River Mersey, north side of Tasmania.” In the British Museum the specimen is unlabelled. I have now completed the investigation, begun in 1862, of this mineral, and in the present communication give the chief results of my experiments. The true dysodile from Glimbach near Giessen, analysed by Delesse, does not seem to be identical either in chemical or phy- sical constitution with the Tasmanian mineral. I shall, how- ever, investigate this point fully if Lam successful im obtaming a sufficient supply of the true dysodile, which is said to occur at Mellih near Syracuse, aud at Salzhaufen in Hessia. The so-called resiniferous shale is distinctly laminated, the organic matter, which occurs in scales, being disposed in planes parallel to the lamination, and probably causing it. These scales are of a reddish-brown colour, and form from 80 to 40 per cent. of the rock. Their shape may be best judged of by the accompanying figures,—1, 2, and 3 representing the aspect of the scales as end fm Hers 4, 5, and 6 their appearance as seen edgewise. The average diameter of the disks is about :03 of an inch, while their thickness at the centre is sometimes as much as ‘007. Separation of the Organic Substance.—As none of the ordinary solvents of resinoids and similar bodies seemed capable of dissol- ving out the carbonaceous constituent of the mineral, the fol- lowing plan of oe the separation was adopted. A large quantity of the mineral was crushed to a coarse powder, placed * Communicated by the Author. 466 Prof. Church on Tasmanite, in a Phillips’s precipitating- glass, and strong hydrochloric acid poured upen it. A trace of carbonic anhydride was thus set free from the small quantity of carbonate of calcium present, while the alumina and ferric oxide of the mineral were partly dissolved. These chemical actions served to break up the mine- ral, and the organic ‘scales’ became for the most part disen- gaged, and floated, owing to the high gravity of the hydrochloric solution, which had been further increased by the addition of chloride of calcium. ‘The scales were collected from the surface by a strainer, and washed repeatedly by decantation; by this method of purification the imorganic matter in them was reduced to a minimum. The substance thus prepared presents such remarkably dis- tinct chemical and physical characters, that I venture to assign to it a distinct name, Tasmanite. I have already described the mode of occurrence and the phy- sical appearance of the Tasmanite scales; the action of certam chemical reagents and of heat upon this substance may now be recorded: I should mention that the density of the substance is about 1°18; its hardness2. It is translucent, of a reddish-brown colour. Lustre resinous, and fracture conchoidal. Hydrochloric acid has no action on Tasmanite; nitric acid slowly oxidizes it, disengaging carbonic acid and pernitric oxide, while the sulphur appears as sulphuric acid. If the action of the nitric acid be stopped before all the substance has disap- peared, the residue will be an orange-brown powder, which burns still more readily than Tasmanite, but it is not explosive. . a new Mineral of Organie Origin. 467 Sulphuric acid readily carbonizes Tasmanite, torrents of sulphu- rous anhydride being disengaged at the same time. Aqueous solutions of the alkalies appear to be without action on Tasmanite. Aleohol, ether, bisulphide of carbon, benzole, turpentine, mineral turpentine, and parafiine oil do not appear to exert the least solvent action upon Tasmanite, even on the application of heat: the result might be different under an increased pres- sure. When Tasmanite is heated in the air, it burns readily with a very smoky flame and offensive odour. Submitted to destructive distillation, it fuses partially and yields oily and solid products having a disagreeable smell, recalling that of some specimens of Canadian petroleum. One is tempted to suggest that the natural rock-oils may in some instances originate in the action of heat upon substances similar to Tasmanite shale. Composition of Tasmanite.—Qualitative analysis of Tasmanite showed it to contain not only a large quantity of carbon and hy- drogen, but also a very considerable proportion of sulphur; and it was found that the most careful mechanical treatment of the specimens failed to separate from them completely the mineral impurities. ‘That the sulphur detected was an integral part of the carbonaceous maiter itself, and was not owing to the presence of an inorganic sulphide or sulphate, was proved in several ways, and was further confirmed by the observation that the more completely the mineral matter had been removed, the more sul- phur was found in the specimen of Tasmanite operated upon. I am indebted to my friend Mr. W. H. Perkin for the first four of the following analyses of purified Tasmanite. In Nos. I., II., and II]. the substance was burnt in a current of air, and finally of oxygen, the sulphurous acid being absorbed by binoxide of lead; in analysis IV. the combustion was performed with chromate of lead. In analysis V. to XI. the sulphur or the ash were alone determined. The sulphur was obtained by oxidizing the mineral with strong nitric acid and bichromate of potassium in a capacious flask, diluting largely with water when complete solution had been effected, filtering to separate the silica of the ash, and precipitating with nitrate of barium. After standing twelve hours, the precipitated sulphate of barium was collected, washed completely, and ignited with the usual precautions. In analysis V. the sulphur was oxidized by means of the gradual addition of chlorate of ,potassium instead of bichromate to the mixture of nitric acid and Tasmanite. The mineral must be completely destroyed and dissolved in order to extract the whole of the sulphur. The two preparations submitted to analysis are distinguished as a and 0. 468 Prof. Church on Tasmanite, ; I. +4288 grm.° of substance gave 1:1466 grm. carbonic acid and 0°0354 grm. ash. II. +3535 grm. of substance gave -3049 germ. water and 0284 grm. ash. III. :3087 grm. of substance gave °2729 grm. water and a. 5 0248 grin. ash. IV. -3668 grm. of substance gave ‘9796 grm. carbonie acid and ‘315 grm. water. VY. -4785 grm. of substance gave ‘175 grm. of sulphate of barium. \ VI. +5125 grm. of substance gave ‘041 grm. of ash. ; VIL. 6°16 graims of substance gave 2-12 grains of sulphate | of barium. VIII. :337 grm. of substance gave °121 grm. of sulphate of b J barium. ') IX. -654 grm. of substance gave -2302 erm. of sulphate of | barium. | X. :421 germ. of substance gave ‘0525 grm. of ash. U XI. -482 erm. of substance gave ‘0580 grm. of ash. These results correspond to the following percentage num- bers :-— | | i fu. |rm.| qv. |v. | vi jvar. [vit 1x.) x. | x | | | =| || __ |__|» al ee | Carbon ...... Byes esi ee | 72:83} | | Hydrogen ...| ....-- 9°58, 9°82) 9°54 | Sulphur 5..--.]-<2--<- | <2s- "| v-0-). [pesos 2] Ai Alene, 1 Adee) emacs | Ash.......00..| 8°25] 8°03) 8-03]... 8-00] ... |... | --- | 12-427] 12°03} ; i | The following are the mean percentages, rejecting the hydrogen of analysis III. as evidently too high :— Carbon «..s41ia ee Hydrogen . . 9°56 Sulphur. . . 4°90 Ash (a2) .. .° 8:14 (6) 12°24. Before these numbers can be taken to represent the centesimal composition of pure Tasmanite, they require recalculation after deduction of the ash, which is, without doubt, an accidental im- purity. This ash mainly consists of silica and alumina ; it con- tains also a small quantity of ferric oxide and of some soluble sulphate, this latter compound being derived in all probability from the oxidation of the sulphur contained in the Tasmanite proper. Since this ash has almost exactly the same composition as the shaly rock in which the grains of Tasmanite occur, we may directly subtract it without introducing any appreciable error. The percentages deduced from analyses I. to IV. are given a new Mineral of Organie Origin. 469 below after deduction of the mean percentage of ash, 8°14; analysis V. after deduction of 8 per cent. of ash; and analyses VII. to XI. after deduction of 12°24 per cent. of ash. Carbon -.....+ 2) 79:34 Pydrogen =. +, OAT. Sulphary.5 .ioovlor pore Oxygen (by diff.) . 498 These numbers may fairly be taken as representing the cente- simal composition of Tasmanite; the most noteworthy point re- garding them is the high percentage of sulphur. Tasmanite is, I believe, the first carbonaceous mineral which has been found to contain a large amount of sulphur in combination, not with a metal as in pyritic coal, but in intimate union with the carbon _and hydrogen of the substance. It would seem to be allied to retinite, although that mineral contains no sulphur; yet the chief constituent of many specimens of retinite yields, on ana- lysis, percentages of carbon and hydrogen almost exactly the same as those just recorded. The formula C!° H!6O, orC? H™ O04, has been suggested for retinite. A similar formula, in which sulphur is introduced, requires nearly the same percentages as those yielded in the analysis of Tasmanite :— Experiment. Theory, C* H® G2, S. Carbon... . 79:34 79°21 Hydrogen. . 10°41 10:23 Sulphur . . 5°32 5:28 Oxyeen., . >...) 4:98 5°28 100-00 100-00 It will be seen that the experimental percentages of carbon and hydrogen are a little higher than the theoretical: as one can easily account for this excess in the case of a substance which is hygroscopic and contains sulphur, I have been led to prefer the suggested formula to one or two others which demand a higher percentage of carbon and hydrogen. The sulphur determina- tions are accordant ; but there is an apparent deficiency of oxygen —493 per cent. instead of 5°28. If, however, we accept the theoretical percentages of carbon and hydrogen and the experi- mental percentage of sulphur, we arrive, by difference, at the following percentage of oxygen :— Experiment. Theory, C* H® Q2,S. Oxygen .-. . 5°24 5°28 Sulphur . . . 5°32 5:28 If we accept the formule C*° H®O* and CH? O? § for pure retinite and for Tasmanite respectively, we may compare 470 Dr. C. K. Akin on the History of Force. them by assuming the latter mineral to differ from the former only by containing H?0O less, and by the presence of 1 atom of S in lieu of 1 Sebi of O:— OH? O84 B20: 2. paRetimute: O40H& O28 92. ae asmamnite: To suggest a rational formula for the remarkably complex molecules of retinite and Tasmanite may seem premature ; but it is possible that in these minerals we have the hydrated oxide (retinite gives off water when heated) and the anhydrous sul- phide respectively of an oxygenated radical, C?° H®! O— 20 {731 a a of O+Agq_ Retinite. 20 {731 oa ae o +s Tasmanite. These minerals may be derivatives of a turpentine, C*° H®; or the radical I have assumed them to contain may be a homo- logue of benzoyle, C? H°O+138CH?=C” H?! 0. LVIII. On the History of Force. Be Dr. C. K. One. N the Number of the Philosophical Magazine for October * last (p. 289), Professor Guthrie Tait repeats an assertion already made by him upon two previous occasions, first in the Philosophical Magazine (see vol. xxv. p. 429, 1863), and next in the Pr oceedings of the Royal Society of Hdinburgh (see No. 59, p. 122), that “ Newton had completely enunciated the Conservation of Energy in ordinary mechanics ;” and in another portion of the same Number of this Magazine (p. 311), Professor Bohn cites passages from the writings of Descartes and John Bernoulli bearmg on the same question of the Conservation of Force also. For nearly two years, I have been engaged at inter- vals in collecting materials for a History of the Philosophy of Force, but which circumstances now oblige me to lay for a while aside. I am thus induced to publish meanwhile part, at least, of what little I have hitherto discovered that is new or interesting, in the Philosophical Magazine; for doing which the publications above referred to at present afford me an additional incentive. I. On the Conservation and Conversion of Force. 1. Prof. Tait rests the claims which he advances in behalf of Newton, on the followimg passage from the scholium to the Third Law of Motion, in Newton’s Principia :— * Communicated by the Author. | Dr. C. K. Akin on the History of Force. 471 «Si estimetur agentis actio ex ejus vi et velocitate conjunctim, et similiter resistentis reactio eestimetur conjunctim ex ejus partium singularum velocitatibus et viribus resistendi ab earum attritione, coheesione, pondere, et acceleratione orlundis; eruntactio et reactio . . sibi invicem semper zequales.” The dots(...), mdicating an elision, stand for the words 2n omni in- strumentorum usu. Now, I cannot help thinking that the omis- sion of these words completely alters the meaning of the above passage. Newton, in the passages preceding the above, is bent upon showing that the effective force of a moving system may be measured by its momentum (mv); and he states that this as- sumption is proved by the fact that, in machines, the moving force may be so estimated,—the velocity being always inversely proportional to the mass or inertia, after the resistance has been subtracted. “Ceeterum mechanicam tractare,’ Newton adds, “non est hujus instituti. Hisce volui tantum ostendere, quam laté pateat quamque certa sit lex tertia motus,” 7. e., that action is always opposed by an equal reaction. Yet this law, however important, cannot but be considered as a corollary from, rather than equivalent to, the principle of the conservation of force itself. Moreover, in the same scholium occurs a passage relative to the state of imperfectly elastic bodies after collision, which will scarcely be considered to favour the advocacy of Prof. Tait :— «A congressu et collisione corporum nunquam mutabatur quan- titas motus, que ex summa motuum conspirantium et differentia contrariorum colligebatur .... Porro ne quis objiciat regulam .... preesupponere corpora vel absoluté dura esse, vel saltem perfecteé elastica. ... addo quod... siregula illa in corporibus non perfecté duris tentanda est, debebit solummodo reflexio minui in certa pro- portione pro quantitate vis elastice.” How does Newton account for, in this case, the velocities lost ? But doubtful, if not impossible, as Newton’s authorship of the principle in question appears from the above passages, Query dl in his ‘Optics’ will be found still less compatible with it. Perhaps the remark of John Bernoulli concerning parts of this query—“‘ridiculum dicerem, si a tanto Viro non scripta essent ” (Opera, vol. i. p. 253)—may be rather too severe, yet its con- tents wil! be found difficult to reconcile with the assertion of Prof. Tait :— “Some other principle [than inertia] was necessary for putting bodies into motion; and now they are in motion, some other prin- ciple is necessary for conserving the motion. For... . it appears, that motion may be got or lost. But .... motion is more apt to be lost than got, and is always upon the decay. For. ... if two equal bodies [e. g. ] meet directly zz vacuo, they will, by the laws of motion, stop where they meet, and lose all their motion ... . unless they be 472 Dr. C. K. Akin on the History of Force. elastick... . If it be said, that they can lose no motion, but what they communicate to other bodies, the consequence is, that in vacuo they must go on and penetrate one another’s dimensions. . . . Seeing there- fore the variety of motion, which we find in the world, is always de- creasing, there is a necessity of conserving and recruiting it by active principles ; such as are the cause of gravity ..... and the cause of fermentation.” I trust I shall be able to enter more fully upon some future occasion into a consideration of these statements of Newton, which are followed by others no less remarkable. 2. With regard to Prof. Bohn’s extracts, | would observe that both the principles, of the conservation of energy or motion, and of force, owe their first enunciation in a scientific form—at least, as regards particular instances—to Huyghens. It was Huyghens who, in the Journal des Savants for March 1699 (vol. 1. p. 534), first stated the following laws regarding the collision of perfectly elastic bodies :— (1) ‘La quantité du mouvement qu’ont deux corps, se peut aug-. menter ou diminuer par leur rencontre; mais il y reste toujours la méme quantité vers le méme cOté, en soustrayant la quantité du mouvement contraire.”’ (2) ‘La somme des produits faits de la grandeur de chaque corps dur, multiplié par le quarré de sa vitesse, est toujours la meme devant et apres la rencontre.” (See also Phil. Trans. vol. iv. p. 927.) In Huyghens’s posthu- mous dissertation, De Motu Corporum ex Percussione (Oper. rel. vol. 11.), the second of the two propositions quoted is reproduced ; but of the first proposition only one-half is given, in these words (p. 84) :— (3) ‘*Corperibus duobus sibi mutuo occurrentibus non semper post impactum eadem motus quantitas in utroque simul sumpto conservatur que fuit ante, sed vel augeri potest vel minui.”’ It is to this and the subsequent propositions that Bernoulli, wishing to disprove the anti-Leibnitzian estimate of force, refers in saying (Opera, vol. i. p. 254), «Observatum est a multis, presertim ab Hugenio ..... motus quantitatem, etiam in corporibus perfecte elasticis, in immensum posse augeri et minui.” And it is apparently with the very same object as that which Bernoulli had in view that Huyghens, who had adopted Leibnita’s measure of force, in reproducing his pr oposition in the treatise last quoted, omits that other portion which he had appended to it in the French journal. However, as is well known, the whole of gee (1) is perfectly correct* ; and proposition /3) appears * Cf. Cor. 3 to Newton’s Third Law of Motion :—‘‘ Quantitas motus que colligitur capiendo summam motuum factorum ad eandem partem, et differentiam factorum ad contrarias, non mutatur ab actione corporum iter se.’ Dr. C. K. Akin on the Mistory of Force. 473 incompatible with it only so long as it is not considered that what Huyghens calls qguantitas motus in the latter means, with reference to any two bodies proceeding to mutual impact, their relative velocity (y) multiplied into the mass () of the quicker body,—which is an arbitrary if not incorrect estimate of, and cer- tainly different from what is ordinarily (and also by Newton) called, quantity of motion or momentum. To the passages quoted already in the Philosophical Magazine from John Bernoulli’s De Vera Notione Virium Vivarum, the following extracts may be usefully added :—“ La force vive, produite dans un COrps ..-.. est équivalente a cette partie de la cause qui s’est consumée [italics by the transcriber | en la produisant ; puisque toute cause efficiente doit étre égale a son effet pleinement exécuté” (Discours sur le Mouvement, 1727, Opera, vol. ii. p. 386). And, “Tout le monde regarde comme un axiome incontestable, que toute cause caieenks ne saurait périr, ni tout ni en partie, qu’elle ne produise un effet égal a sa perte” (zbid. p. 56). 5. As for the principle of the conservation of force in its wider sense, it was first enunciated, by implication, in Huyghens’s Horologium Oscillatorium, published in 1673, Prop. 4 of Part 4 of which is as follows:—“Si pendulum é pluribus ponderibus compositum, atque € quicte dimissum, partem quamcunque oscillationis integre confecerit, atque inde porro intelligantur pondera ejus singula, relicto communi vinculo, celeritates acqui- sitas sursum convertere, ac quousque possunt ascendere; hoc facto, centrum gravitatis ex omnibus composite, ad eandem altitudinem reversum erit, quam ante inceptam oscillationem ob- tinebat” (Oper. var. vol. i. p. 126). James Bernoulli generalized this proposition, asserting “ quod commune centrum gravitatis plurium ponderum non possit ascendere altius per gravitatis eorum effectum, quam unde descendit” (zbid. p. 247). 4. Intimately connected with the principle of the Conservation of Energy strictly so called (taking the word energy, according to the proposition of Young, as English for vis viva) is that of the Correlation of Forces, or, as it has been called by a logician of great reputation, of the Allotropy of Force. There has been of late a good deal of controversy regarding the priority of inven- tion or discovery of this last-named principle; and it may con- sequently be interesting, in an historical point of view, to take cognizance of passages of much-earlier date than any hitherto relied upon as establishing such priority, and upon which [ have, in the majority of cases, rather accidentally lighted. The follow- ing is an extract from Placidus Heinrich’s Die Phosphorescenz, &c., published in 1812 :— ** Unterdessen wissen wir wenigstens so viel mit Zuverlissigkeit, Phil. Mag. 8, 4. Vol. 28. No. 191, Dec. 1864. 21 474, Dr. C, K. Akin on the History of Force. dass in der Natur nichts verloren geht . ... alles erhiilt sich durch einen steten Umtausch: das eine gewinnt durch den Verlust des andern: das eine entsteht durch das Verschwinden des andern. . Also im Universum nie Verlust, nur Wechsel und Umtausch.”’ (Vol. ll. p. 283.) The next quotation is from a paper by Dr. Mohr, of Coblentz, on Heat, published in 1837 :— ** Ausser den bekannten 54 chemischen Elementen gibt es in der Natur nur noch ein Agens, und dieses heisst Kraft; es kann unter den passenden Verhiltnissen als Bewegung, chemische Affinitat, Cohision, Elektricitat, Licht, Wirme und Magnetismus hervortreten, und aus jeder dieser Erscheinungsarten kénnen alle ubrigen hervor- gebracht werden . . . . Vermége der Kraft des Armes reisst man die Induktionsrolle von einem Magneten los, es entsteht in dem darum geschlungenen Schraubendrathe ein elektrischer Strom, welcher bei Unterbrechung als Funke, oder bei verengerter Leitung als glu- hender Drath (Warme und Licht) erscheint; derselbe erregt mag- netische Polaritit, wenn er als Schraubendrath um eine Stahlnadel geleitet wird; er zersetzt das Wasser wodurch er geleitet wird, und hebt zugieich seine Affinitat und Cohasion auf; und da nun der dunne Platindrath, die Ampére’sche Schraube und der Wasserzerset- zungs-Apparat in derselben Kette eingeschlossen sein konnen, so leuchtet ein, wie die Kraft des Armes unter verschiedenen Verhalt- nissen, als Warme, Licht, chemische Affinitét, Magnetismus und Cohasion zum Vorschein gekommen ist.” (Baumgartner’s Zezt- schrift fur Physik, vol. v. pp. 442-3.) This passage is followed by two more pages, showing in greater detail the connexion and transmutation of the several known forces, and a transcript or translation of which I hope to give upon some future occasion. The author concludes his observa- tions with the following judicious remarks :— 7 « Ohne Zweifel lassen sich alle physikalischen Erscheinungen der sogenannten Imponderabilien unter eine dieser Rubriken bringen. gierkh 2% Es bleibt aber von dieser fliichtigen Andeutung bis zur voll- kommnen Einsicht in die Natur der Sache noch unendlich viel zu thun ubrig.”’ (Lbid. p. 445.) With regard to heat, besides showing that its nature or form. is motion, which is the Set object of the paper, the writer states (p. 422) -— —‘‘ Was ... eine Kraft hervorbringt, muss selbst eine Kraft sem ;” and again (p. 421) :—“ Was... eine Kraft auf- hebt muss selbst eine Kraft sein”; whence he concludes, con- sidering the effects of heat :—‘ Die Warme erscheint in unzah- ligen Fallen als eine Kraft” (p. 421). In the last place, it gives me great pleasure to quote, among the earliest statements concerning the transmutation of forces, the following passage from the 18th series of Mr. Faraday’s electrical researches, published in January 1840:—“ We have Dr. C. K. Akin on the History of Force. 475 many processes by which the form of the power may be so changed that an apparent conversion of one into another takes place. So we can change chemical force into electric current, or the current into chemical force. The beautiful experiments of Seebeck and Peltier show the convertibility of heat and elec- tricity ; and others by Girsted and myself show the convertibility of electricity and magnetism” (Res. in Electr., § 207, 1.). If. On Gravitation. In his ‘life of ‘Newton,’ Sir D. Brewster states (vol. i. p- 268) :—‘“‘ Kepler could not fail to suspect that some power resided in [the sun] by which the motions of the planets were produced ; and he went so far as to conjecture that this power diminishes as the square of the distance of the body on which it is exerted; but he immediately rejects this law in favour of that of the simple distances.” Again, further on (p. 282) :— “ Bouillaud maintained that the force of attraction must vary reciprocally as the square, and not, as Kepler asserted, in the simple ratio of the distance.” In a similar manner, Sir I. Newton stated (see Rigaud’s Hist. Essay, App. p. 32) :—“ Bullialdus wrote that all force, respecting the sun as its centre... must be reciprocally in a duplicate. ratio of the distance from the centre.” A reference to the original writings of Kepler and Bouillaud has suggested to me the following remarks, which, as they may be of some general interest, 1 purpose herewith publishing. 5. In the Introduction to the Astronomia Nova, referred to also by Sir D. Brewster, Kepler indeed “distinctly recognizes the mutual gravitation of matter”; but he extends that notion only to terrestrial bodies and the moon (see Asir. Nova, p.** * 4), As regards the action of the sun upon the planets, Kepler states (1. c. p. 185) :—“ Virtus ex Sole in mundum per speciem egressa rapidus quidam torrens est, qui Planetas omnes adeoque totam forsan auram zxtheriam ab occasu in ortum rapit, se 1pso non aptus corpora ad Solem adducere vel ab eo longius propellere ; . quod esset infinite sollicitudimis opus.” Again, in enumerating .the six “axioms” which account for the planetary motions (p. 186), he distinguishes between a “ virtus, quee ex Sole,” and through which every planet “ de loco in locum, secundum longi- tudinem zodiaci transponatur,” and a “ virtus quee est propria Planet,” and from which he assumes “ accessus Planet ad Solem et ab eo recessus oriri.”” Hence it is evident that Kepler did not consider the idea of gravitation as applicable to the action of the sun on the planets; and from cap. 83, entitled “Virtutem que Planetas movet, residere in corpore Solis, wat appears also that the “ virtus” of which the “debilitas sequitur 212 3 476 Dr. C. K. Akin on the History of Force. proportionem distantiarum” (p. 168), according to Kepler, was a tangential, and not a centripetal force. 6. Again, as regards Bouillaud, he opens cap. 12 of his Astro- nomia Philolatca by the following observation (p. 21) :—“.... Constat quod veritati magis aptuin et congruens videtur, et quod valde probabilius sit planetas, et catera corpora ceelestia per propriam formam moverl, quam ab anima adsistente.” He then goes on to apimadvert upon the views of Kepler, enunciated in cap. 33 of the Astron. Nova and elsewhere. Now Kepler had stated (/. c. p. 178) :— Demonstratum est cap. 382 planetarum motus intensionem et remissionem sequi proportionem distanti- arum simplicem. At videtur virtus ex Sole emanans intendi et remitti debere in proportione duplicata vel triplicata distantiarum seu linearum effluxus”; and the chapter (84) in which this is stated is headed, “ Qua mensura virtus ex Sole motrix, per mundi amplitudinem attenuatur.” With regard to this passage, Bouil- laud observes (p. 28) :—‘‘ Hoe non negavit Keplerus, attamen [etc.] ....Sed hee Kepleri responsio levis admodum est. Nam si in superficiali quantitate considerat illam virtutem mo- tricem, necessario imminuere eam debuit in ratione dupla inter- vallorum: si vero in solis lineis superiori propositioni contra- dicit,”’ ete. Bouillaud closes this chapter with the following observations (p. 24) :—“ Dico Solem 4 propria sua forma cirea proprium axem moveri, qua ignitus et lucidus est, ceteris vero planetis nullam motus speciem imprimere, que illos vehat, ipsos vero singulos & singulis formis, quibus preediti sunt, circumduci.”’ From the passages quoted, it appears, in the first place, that Bouillaud denied altogether the existence of any reaction between the sun and the planets, and, in the next place, that the force regarding which Bouillaud contended that its magnitude must depend on the inverse ratio of the square of distance (for reasons which Kepler himself had previously fully developed) was the same tangential force before assumed by Kepler, and not a cen- tripetal force. It may not be superfluous to state also, re- garding this same force, that, so far as it appears, Kepler supposed the force to be exerted only on the part of the sun; the sun itself not being liable to any reciprocal action on the part of the planets. 7. A third name which figures prominently in the history of gravitation, after Kepler and Bouillaud, is that of Borelli.. Sir I. Newton wrote (see Rig. Ess. App. p. 30), “ Borelli did some- thing ;” and Sir D. Brewster adverts more fully to his specu- lations. Yet it remains to be stated more precisely what was the exact “ something ” that “ Borelli did.” In his Theorice Mediceorum Planetarum (p. 76), Borelli states : “ Supponamus preeditum planetam 4a vertigine solarium radi- orum in orbem ferri circa solem per circulorum peripherias ab Royal Society. 477 occasu ad ortum; et quoniam ut dictum est motus circularis naturaliter quemdam imprimit impetum ipsi mobili, quo me- diante & centro remoyetur, atque expellitur, veluti in funda ac rota observare licet, ergo, dum predictus planeta circulariter rotatur, removebitur 4 centro Solis... Promdeque his aderunt duo motus directi inter se contrarii, alter perpetuus, ac uni- formis, quo planeta impulsus a propria magnetica virtute sibi connaturali vero successive admovet solari corpori, alter vero dif- formis, et continué decrescens, quo planeta & puncto(H) expellitur.” Again (p. 78): “ Ut dictum est, virtus motiva planete ... com- ponitur ex circulari impulsu, et gradu virtutis prementis uni- formis, et ex gradu virtutis repellentis;”? and (p. 81) :—“< Ut supponamus predictum motum.... pendere A magnetica im- pellente virtute ..., et motum circularem planetz circa Solem.” Hence, it is certainly evident that Borelli extended the idea of gravitation also to the sun (as a one-sided action); but then it is equally evident also that he supposed the attraction of gravity to be uniform, 2. e. independent of distance (as may be seen more at large in the passages omitted from the above quotation) ,—and further, that he considered the motions of the planets to be the result of three forces—one circular, the other centrifugal, and the third attractive or centripetal. According to our present notions, a force acting circularly is impossible; and a centripetal force, although the expression is still used, is no force at all, but only a tendency produced by the possible resolution of velocities ; whilst the motions of the planets are supposed be the result of an attractive force acting conjointly with certain cps tangential velocities. London, November 1864. LIX. Proceedings of Learned Socictics. ROYAL SOCIETY. [Continued from p. 400. | November 17, 1864.— Major-General Sabine, President, in the Chair. r§NHE following communication was read :— “Comparison of Mr. De la Rue’s and Padre Secchi’s Eclipse Photographs.’ By Warren De la Rue, F.R.S. I have stated, in the Bakerian Lecture read at the Royal Society on April 10, 1862, that the boomerang (prominence E)* was not depicted on Senor Aguilar’s photographs. ‘This is true of the prints which came into my hands in England. A visit to Rome in Novem- ber 1862, however, afforded an opportunity for the examination of the first prints which had been taken in Spain on the day of the * See Index Map, Plate XV. Phil. Trans. Part I. 1862. 478 Royal Society :— eclipse, previous to those printed off for general distribution by Senor Aguilar. I was agreeably surprised to find that the photo- graph of the first phase of totality showed not only this prominence very distinctly, but also other details, presently to be described, which were quite invisible in Senor Aguilar’s copies. I had in fact experi- enced some difficulty in comparing measurements of my photographs with those of Senor Aguilar’s, on account of the indistinctness (wool- less) of the latter, which I have attributed to Padre Secchi’s tele- scope not having followed the stm’s motion perfectly. A careful examination of the prints in Padre Secchi’s possession has, however, convinced me that this was not the case during the period of expo- sure of the first negative ; for I have been able to identify with a mag- nifier many minute forms which could only have been depicted by the most perfect following of the sun’s apparent motion. For instance, my statement that the prominence H (the fallen tree) was not seen from having been mixed up with the prominence G, is not appli- cable to Padre Secchi’s copy of the first phase of totality, for in it every detail of the fallen tree can be made out. On expressing to Professor Secchi my surprise at the great discord- ance between the copy of the first phase of totality sent to me by Senor Aguilar and that of the same phase in his possession, I was informed that after a few positive prints had been taken from the then unvarnished negative, it was strengthened by the usual photo- graphic process with nitrate of silver. This I iook upon as an unfor- tunate mistake, as the images of the prominences were increased and their details hidden, and the beauty of the negative for ever lost. It occurred to Padre Secchi and myself-that although there was no hope of procuring more satisfactory prints from the original negative of the first phase of totality, yet some advantage would arise from taking an enlarged negative from the positive print in his possession, although it could not be expected to yield as perfect an impression as might have been obtained by enlarging from the original photo- graph. The enlargement has been successfully accomplished in my presence ; and although Padre Secchi will take such means as he may think proper to make known the results of comparisons he may make between my photographs and his own, it will not be out of place for me to add a few remarks by way of appendix to my paper. Taking the prominences in the order in my index map, Plate XV. :— _ Prominence A (the cauliflower or wheatsheaf) has the same form in Padre Secchi’s photograph asin mine. It extends considerably less in height above the moon’s edge in this copy than in that printed off from the strengthened negative (Senior Aguilar’s copy) ;_ the bright points of the two branching streams which issue from the summit towards the North are well depicted in the Secchi photograph, but not the fainter parts. There exists a faint indication of the minute prominence B in the S. photograph. The convolutions of the prominence C (the floating cloud) are seen in the S. photograph, and its form coincides absolutely with Mr. De la Rue’s and Father Secchi’s Kelipse Photographs. 479 that of mime; it is a little nearer the moon’s edge at the point e¢, probably because the telescope was uncovered EATEN GING a little later than at Rivabellosa. The prominence D cannot be clearly traced in the S. photograph. The boomerang E is distinctly visible in the 8. photograph ; the point e is apparently prolonged ; but this I attribute to an accidental photographic stain, for the bright part ¢’ can be well made out. The long prominence F cannot be made out in the S. photograph, robably from the cause explained in reference to C. The fallen tree (H in the 8. photograph) corresponds in its minutest details with its picture in my own. ‘The articulated extre- mity h, the round points h' h”, the “point h’’, and the connecting braneh joining it with the stem are clearly seen. The prominence G from g to g’ corresponds precisely in the S. photograph with its image in my own, and a dark marking near g also is seen ; the narrow portion of this prominence, from g to the point immediately below A, is not seen in the S. photograph. | _ The prominence I (the mitre) agrees in form in the S. photograph with its image in my own, even the faint point zis there seen. This prominence in the S. photograph extends further from the edge of the moon than in mine; and whereas in my photograph the convex boundary next the moon is cut off by the,moon’s limb, in Padre Seechi’s the convex boundary is complete, and hence in all probability the prominence I presented another case of a floating cloud. About midway between G and I there is a small round prominence visible in the S. photograph not seen in mine, which may be accounted for from our different positions in respect to the central line of the eclipse. Between I and K, at a distance from I equal to about two- thirds the angular interval, there isin the 8. photograph a prominence con- sisting of two round dots, which extend beyond the moon’s limb to precisely the same extent as the prominence K protrudes in Pro- fessor Secchi’s photograph beyond the moon’s limb in excess of what it does in my own. The prominence K has precisely the same form in every tide in the 8. photograph as in mine, so far as mine shows it ; but on account of parallax, more of it is seen in the 8. photograph than in mine. Beyond K is another prominence, visible in the 8. photograph about 17° distant from K, a small round prominence which could not have been visible from iny station. Of the remaining prominences, L, M, N, O, P, Q, R, none were visible at the epoch of the photograph. In conclusion, the photographic images of the prominences, so far as they are common to the two photographs taken at Miranda and Desierto de las Palmas, accord in their most minute details. The photographs must, from the difference of position of the two stations, have been made at an absolute interval of about seven minutes; and this fact, while it strongly supports the conclusion that the protu- berances belong to the sun, at the same time shows that there is no change in their form during an interval much greater than the whole duration of an eclipse. [ 480 ] LX. Intelligence and Miscellaneous Articles. A LETTER FROM JOHN DAVY, M.D., F.R.S., TO THE EDITORS OF THE PHILOSOPHICAL MAGAZINE IN REPLY: TO CERTAIN CHARGES MADE BY C. BABBAGE, ESQ., F.R.S, ETC., AGAINST THE LATE SIR HUMPHRY DAVY, WHEN PRESIDENT OF THE ROYAL SOCIETY. GENTLEMEN,— ME BABBAGE, in his recently published work, ‘ Passages from “the life of a Philosopher,’ has brought two charges against the late Sir Humphry Davy, when President of the Royal Society, both of them injurious to his character, if substantiated :—one, of a breach of promise ; the other, of “‘ transferring between three and four hundred pounds from the funds of the Royal Society into his own pocket’’*. These charges are contained in the thirteenth Chapter, under the heading of ‘“‘ Recollections of Wollaston, Davy, and Rogers,” and are incongruously associated with an account of “The Thauma- trope,’ and with anecdotes of the poet. Mr. Babbage, in his Pre- face to another workt, expresses the opinion ‘“‘that the famous maxim de mortuis nihil nisi bonum, appears to savour more of female weakness than of manly reason.” Jn these his ‘‘recollections,” or rather his assertions, so far as they relate to Sir Humphry Davy, he strictly confines himself to nihil nisi malum. As the brother of Sir Humphry Davy, will you allow me to reply to these charges in your pages; I shall endeavour to be as brief as the subject will permit. First, of the breach of promise.—Mr. Babbage’s statement is the following :—‘‘In 1826 one of the Secretaryships of the Royal So- ciety became vacant. Dr. Wollaston, and several other of the lead- ing members of the Society and of the Council wished that I should be appointed. This would have been the more agreeable to me, because my early friend Herschel was at that time the senior Secre- tary. “This arrangement was agreed to by Sir Humphry Davy, and I left town with the full assurance that I was to have the appoint- ment. In the mean time Sir Humphry Davy summoned a Council at an unusual hour—eight o’clock in the evening—for a special pur- pose, some arrangements of the Treasurer’s accounts. ‘After the business relating to the Treasurer was got threugh, Sir Humphry Davy observed that there was a Secretaryship vacant, and he proposed to fill it up. Dr. Wollaston then asked Sir H. Davy if he claimed the nomination as a right of the President, to which Sir H. Davy replied that he did, and then nominated Mr. Children. The President, as President, had no such right, and even if he had possessed it, he had promised Mr. Herschel that I should be his colleague. ‘There were upright and eminent men on that Council; yet not one of them had the moral courage to oppose the President’s * Op. cit. pp. 187-189. t+ Reflections on the Decline of Science in England. a Intelligence and Miscellaneous Articles. 481 dictation, or afterwards set it aside on the ground of its irregu- larity’’*. From whom, I would ask, and didask Mr. Babbage, had he this in- formation? Ina letter which I have received from him of the 17th of September in reply to one from me, he writes, ‘‘ With respect to what took place at that Council, the late Dr. Fitton, who was pre- sent, gave me the account I have stated.” Mr. Babbage added, «“Not long before his death, Dr. Fitton gave me several MSS. and other papers which he thought might be interesting to my family. He then again related the account of the Council which I have given in my work.” . On this I remark, that Dr. Fitton was not then on the Council}, and.that I have been assured by one of the three surviving members of that Council{, that no such words as those atttibuted to Dr. Wollaston were spoken, and that there was no discussion of any kind on the occasion. Mr. Herschel, now Sir John Herschel, was one of those present ; and I would ask, why has not Mr. Babbage adduced him as his in- formant? From what I have learnt he would not support Mr. Bab- bage in the statement, nor indeed in the statement that Sir Hum- phry Davy had promised him that Mr. Babbage should be his col- league. I would further remark that, inasmuch as Dr. Wollaston and Sir H. Davy had been so long Secretaries together, it seems highly im- probable that the former would question the latter in the manner asserted. It is true that the President has not the right of naming for a Secretaryship; but it is equally true that it had become the usage: Mr. Babbage himself was fully aware of this; for at p. 140 of his ‘ Reflections on the Decline of Science in England,’ published in 1830, he states, of the officers and Council of the Society, “ the fact is that they are the private nominations by the President;”’ and, at p. 72, on the authority of the late Mr. Barrow, he affirms, ‘‘ that it had been the custom for years for the President of the Royal So- ciety to nominate the Council.” In my letter to Mr. Babbage, adverting in conclusion to the affair of the Secretaryship, I wrote, ‘that you felt aggrieved is certain from what you have stated,” adding, ‘‘I need hardly remark that too often under that state of feeling, an animus is created which tends to misinterpretation. Had you called on the President for an explanation at the time, would it not lave beeu more in accordance with what is just and honourable than to have brought such a charge against him after his death [after an interval of 35 years]? He might have stated reasons, if not reconciling you to your disappoint- ment, yet amply justifying his conduct, or convincing you that you Jaboured under a mistake as to a promise.” * Op. cit. p. 187. + In the Council-book, I am informed by the Assistant-Secretary that there is no minute respecting either the nomination of Mr. Babbage or Mr. Children as Secretary at the Meeting in question, that held at 8 p.m., on the 16th November, 1826. } These were Mr. Gompertz, Mr. Herschel, and Mr. South. 482 Intelligence and Miscellaneous Articles. I shall now proceed to the more serious charge—the asserted ‘‘ transfer of between three and four hundred pounds from the funds of the Royal Society into his [Sir H. Davy’s]own pocket”’*. This charge, according to Mr. Babbage’s statement, is founded on the facts (and I do not question their accuracy) that the late Mr. Mur- ray purchased for 500 guineas the copyright of the President’s Dis- courses, which were published at the request of the Council, and that the Council, at a meeting held on the 31st of December, 1826, ““Resolved, that 500 copies of the President’s Discourses about to be printed by Mr. Murray be purchased by the Society at the usual trade price.” At that meeting the President was in the chair; the members present were Captain Beaufort, Messrs. Brown, Children, Gilbert, and Herschel, Sir E. Home, Captain Kater, Drs. Pearson, Prout, and Young. Mr. Babbage, in commenting on the transac- tion, exculpates Mr. Murray; the gravamen of the charge he lays on the President and the Council—he for selling the copyright of his Discourses (which he certainly had a right to do) and the Council for ordering the purchase of the copies at a cost of £381 5s. Mr. Babbage states that in the following year, when he was on the Council, he inquired why the ‘‘ Resolution of Council” above named was passed; and that Dr. Young’s reply was, that it was “in order to induce Mr. Murray to print the President’s speeches.” It would appear from the wording of the resolution, that, previous to its passing, Mr. Murray had undertaken to publish the Discourses ; nor does it appear that there was any previous promise? Be that as it may, the Council was responsible for their act. I have recently applied to Mr. John Murray, the son of the late Mr. Murray, for information on the subject: he has courteously re- plied, stating his regret that the only information he can give is contained in a schedule which he annexed, specifying the date of the publication and the results—he adding that all his search after letters and copies of letters which may have passed has proved fruitless. From this document, of which the subjoined { is a copy, it would * Op. cit. p. 189. + See advertisement to the ‘ Discourses’ by their author. + “Sir H. Davy’s Discourses, published by Mr. Murray in January 1827. 500 guineas paid by Mr. Murray to Sir H. Davy for the copyright. 850 copies printed, the cost of which (including the sum paid for the copyright) was £742 4s. 5d. LOWS 500 copies sold to the Royal Society at the trade price, LbSiSa is nea eri ghia eas io Fe orek Raat tote aan 381 5 O 25 sent out as presents from Sir H. Davy, according to his list. 11 to Stationers’ Hall. 152 copies sold at Mr. Murray’s Annual sale ............ 92) 19" a Ctepavions, fering, git Bi. HOMIE AUS ptt te ea sd 49 19 11 O) wasted, producing): (its ou. SS FS ye Pe ae 2 Ore Eventuallossto Mas Mirrtay se P23 F. od 0. 216 10 2 ——— 850 . £742 4 5” Intelligence and Miscellaneous Articles. 433° appear that, if the whole of the impression had been suld at trade price, Mr. Murray would have been a loser, and to no inconsiderable - amount, viz. £94 Is. lld. May I be allowed to ask what is the inference? Is it not a logical conclusion that the publisher expected that the demand for the ‘ Discourses’ would have been so great as to require more than one edition, so as to remunerate him for his out- lay? Nor, it may be presumed, was such an expectation, though not realized, unreasonable, taking into account the demand for apre- ceding work of the author’s, the ‘ Lectures on Agricultural Chemistry,’ which passed through several editions, and for the copyright of which he received £1000, and £50 for every fresh edition, and the demand also for alater and for a posthumous work, ‘ Salmonia’ and *Consolations in Travel.’ Nor, when we further consider how highly the ‘Discourses’ were approved, should the sum payed for them by a liberal and enterprising publisher, such as was the late Mr. Murray, excite surprise. - It may perhaps be said that the President should have presented the copyright of the ‘ Discourses’ to the Royal Society. Had the Society been in want of funds, there would have been a just reason for making a present to it; but as the Society’s funds were ample, such a present was no wise needed; at least, such we must infer was the opinion of the Council. That he was considered free from blame in the transaction, may be inferred from the circumstance that on his resigning the Chair of the Royal Society on account of failing health, a vote of thanks to him, proposed by the Council, of which Council Mr. Babbage was a member, was unanimously agreed to by the Society: the following isa copy of it; the original, now in my possession, is formally written on parchment :—“ At a meeting of the Royal Society, held on Thursday the 15th of November, 1827, the President stated from the chair that he was directed by the Council to submit the following resolution to the Society, which was unani- mously agreed to—That the regret of the Fellows of the Royal Society be expressed in the strongest terms to their late excellent President, Sir Humphry Davy, Baronet, for the state of health which has unhap- pily compelled him to relinquish the chair, together with their thanks for the unremitting diligence with which he has at all times en- deavoured to promote the interests of science and the welfare of the Royal Society, and for the learned and eloquent discourses with which at each Anniversary during his Presidency, he concluded the business cf the year.” I have repressed my feelings in writing thus calmly on such a subject. When I call to mind the little regard my brother had for wealth—that to enrich himself he would never take out a patent, though urged so to do, for the safety lamp, or for the protection of the copper sheathing of ships, at a time it promised to be of the greatest use *—I must confess at least astonishment that, when dead, * At that time, in a letter to me, expressing his sanguine expectations of success, after adverting to the fortune (‘‘ the immense fortune”’) he might make if he had chosen to take out a patent for the invention, and that he had determined to give it to his country, he added, “in everything con- 484 Intelligence and Miscellaneous Articles. an accusation should have been brought against him equivalent to that of robbery, and that stated to have been committed in the last stage of a life devoted to science with so much honour to himself, and benefit to his country and to mankind. It may be asked why I did not reply to this last charge at the time it was first made, viz. in 1830, in Mr. Babbage’s ‘ Reflections on the Decline of Science in England and_on some of its Causes.’ I was then abroad on foreign service, and did not return until the lapse of two years. Then Mr. Babbage’s book had almost passed into oblivion: moreover, as the Council of the Royal Society were included in the charge, its members (they so many and able) might be considered the proper persons to reply to it; indeed, even now, my giving it attention is by some friends I have consulted considered unnecessary ; and so I might consider it, did I not know that where- ever pitch is thrown it adheres, and that the renewal of the charge in a book such as Mr. Babbage’s is, which may be referred to here- after, if passed over in silence, might be supposed to be founded on truth. T am, Gentlemen, Lesketh How, near Ambleside, Your obedient Servant, October 20, 1864. Joun Davy. ON THE COMPARISON BETWEEN THE ENGLISH AND METRICAL READINGS IN DOUBLE-SCALE BAROMETERS. To the Editors of the Philosophical Magazine and Journal. GENTLEMEN, In the July Number of your Magazine is a paper by my friend Mr. Packe, in which he attributes the larger part of the discrepancy between the barometric pressures corresponding to the French and English boiling-points to the difference between the standard tem- peratures of the French and English units of length. I believe this conclusion to be erroneous, and I propose to state, as briefly as possible, my reasons for dissenting from it. ‘‘ First,’’ writes Mr. Packe, ‘‘as to the discrepance arising from the standard temperatures. That of the English barometer being 30° F. higher than that of the French scale, when the mercurial column is reduced to the freezing-point, the scale of the French barometer is also reduced to the freezing-point, but the scale of the English one is only reduced to the temperature of 62° F. “ The consequence is that the French barometer, when reduced, will always read higher than the English barometer.” The unsoundness of this inference will appear from the following considerations. By reducing the French barometer we obtain the length of a column of mercury at 0° C., estimated in millimetres, at the standard temperature of 0° C. By reducing the English barometer we obtain the length of the nected with interests [meaning moneyed interests] I am resolved to live and die at least sans tache.”—See my Memorurs of his Life, vol. ul. p. 176. Intelligence and Miscellaneous Articles. 485 same column of mercury, at the same temperature, estimated in English inches, at the standard temperature of 62° F. From Guyot’s Tables for the conversion of millimetres into English inches, and vice versd, we express millimetres at the standard tem- perature of 0° C. in terms of English inches at the standard tempe- rature of 62° F. The consequence is that the reading of the French barometer, when reduced and converted into English inches by Guyot’s Tables, ought always to coincide exactly with the reading of the English barometer. From the following further quotation from Mr. Packe’s paper, it is easy to see how he has arrived at a different conclusion :— «* For exact observation, therefore, it is useless to have a barometer marked with a double scale—the French and English: they cannot be made to coincide; e. g. “Let the barometer read 29 inches = 736°59 millims. (temp. 62° F. =16°-67 C.). In the English scale at 62° (the temperature of the standard) no correction is made for the brass scale. ‘The only correction is for the expansion of the mercury, —‘087, in. 29 — ‘087 reduced 28°913 = 734°38 millims. “But in the French scale, the temperature of the standard being 32° F., the correction to be made is for the expansion of the mer- cury —the expansion of the scale: mm. Expansion of mercury for 16°°67 C. = 27212 Expansion of brass scale for ,, =— ‘281 1981 mm, 736°59 = els sh reduced 734°61=28°9224 inches.” Mr. Packe evidently supposes that in a barometer with a double scale, when the attached thermometer is at 62° F. = 16°67 C., and the English reading is 29 inches, the metrical reading will be 736°59 millims. Now, if the metrical scale is properly graduated, this will not be the case. 736°59 millims. is what the reading would be if the metrical scale were at its standard temperature of 0° C. But by hypothesis it is at 62° F.; it has therefore expanded through the space due to an increase of temperature of 30° I’., that is, through °23 millim. If, then, the English reading be 29 inches, the corresponding me- trical reading will be 736°36 millims. mm. 736°36 Reduction for 16°67 C. 1:98 Reducedreading . . 734'38=28°918 inches; 486 Intelligence and Miscellaneous Articles. precisely the same result that is obtained by the direct reduction of the English reading. I make the proviso, if the metrical scale is properly graduated, as there is reason to fear that this is not the case with many double-scale barometers made in this country. I am, Gentlemen, Your obedient Servant, Witi1aM Maraews, Jun. 51 Carpenter Road, Edgbaston, November 7, 1864. OBSERVATIONS OF THE SPECTRUM OF JUPITER. LETTER FROM FATHER SECCHI TO M. DE BEAUMONT. In my last communication on the spectra of the celestial bodies I gave new observations, which confirmed for the planet Jupiter the existence of special bands due to its atmosphere. [I said that I hoped to be able to measure these bands with the greatest precision, and to learn whether or not they coincided with the terrestrial atmo- spheric bands. 1 can now communicate the result of these measure- . ments. To obtain them I constructed specially an excellent astronomic micrometer, with a screw having a thread of four-tenths of a milli- metre, the cross wires being replaced by a metal plate with a very fine slit. This single slit is used mstead of the graduated scale of the spectroscope which I used last year; it is illuminated im the same manner with light graduated at will; by moving the head of the screw, which is divided into 100 parts, this lummous line may be made to coincide with an obscure band or any given ray; but as its light would-efface the obscure ray if it extended throughout the spectrum, its length was limited so that it only encroached upon it to about one-third or one-fourth of the length of the latter. In this way the micrometric line could be placed in continuation of the spectral ray with an astonishing precision. The solar rays and that of sodium served as the starting-pomt for the measurements: the latter was introduced at the moment of ob- servation: the others were observed the same day, some time before sunset, with the same micrometer and spectrometer applied to Merz’s large refractor. Great care was taken to fix each time the micro- metric slit on one of the strongest atmospheric rays, to see if they coincided or not with those of Jupiter. In the interval between the observation of the terrestrial atmosphere and that of Jupiter the instrument was left untouched, although it was subsequently observed that this precaution was superfluous. The atmospheric rays were determined by observing the air near the horizon. I also sometimes made use of the moon, which was a little above the horizon; and then I had the advantage of making one observation on the planet and another on the moon, and then of returning to the planet, by which the control was made more exact. The various bands are not equally easy to measure, for some are Intelligence and Miscellaneous Articles. 487 more diffused on one side than on the other; that of the dark red is a little difficult, especially if the air is not very pure. In this case the observations were somewhat muitiplied. The following numbers are the result of at least three measurements. Those taken in suc- cession usually agree better with each other than those taken on different evenings ; perhaps we have here the same phenomenon as in the case of the double stars. I shall first give the results obtained for the terrestrial atmosphere, and then those of Jupiter, and I shall refer the position of the bands to the darker line of the band D. Relative position of the Terrestrial Atmospheric Rays. D-C*. D-C. D—B. r Tt. Tr. _ Ve 1-85 2°85 3°95 _ | ae 2°75 3°95 OP eee 'o ci. 1-70 2°72 411 tase gn. | 1°76 2°73 3°99 20 (Moon)... 2°03 3°93 Mean. ... “Te 2°74 3°98 For Jupiter I shall call D’, y, 6 the lines analogous to those of the terrestrial atmosphere D, C, B. The following are the intervals :— Intervals of the Bands of Jupiter. D'-y D’-8s rT. tr. a re 1°90 3°70 17 1°90 4:00 19 1-98 3°49 1 EE Ceres or. 3°79 Ui ete err ks aii mus 2°02 3°85 2) SF eas: Pe 7 1-93 3°78 Meanio.7i. 2 04-92 3°77 It is seen by these measurements that the bands y and # of Jupiter do not coincide in position with those of the terrestrial atmosphere, but that the two, C° and B, approach to some extent. Their relative distance is also different; for we have C*—B=2"721, while y—=1' 85. Their difference exceeds all possible limit of error. Hitherto we have only compared lines with each other as to their relative place; but it is interesting to see if the starting-point is the same—that is, if the line D’ in Jupiter coincides with D in the atmo- sphere. Several micrometric measurements gave a constant difference 488 Intelligence and Miscellaneous Articles. between D and D’, this being 0°:34 towards the red ; but the observa- tion was very difécult, and deserved a careful examination. For this purpose, during two successive evenings the slit was pointed on the line of maximum obscurity in the terrestrial atmospheric band, and it was found to be in the exact prolongation of that of sodium. The micrometer was left untouched until Jupiter appeared. It was observed that the darkest band of Jupiter was outside the slit and the ray D by its own size; so that even the maximum of this band does not coincide with that of the terrestrial atmosphere. If the bands y and # are referred to those of sodium, we find D—y=2°26, D—6=4:11. These numbers agree with those of our atmosphere no better than the preceding. The band @ is not far removed from B; and it might be said that the difficulty of the measurement would allow for the difference ; but it exceeds the probable error of the measurements. The ray C and its terrestrial atmospheric band are quite wanting in Jupiter ; and, on the other hand, y, which is greatly developed, sug- gests C° more than C. I may say that C° is very developed in our atmosphere on foggy days. These results were confirmed, as far as it was possible to rely upon them, by the observations and the figures published last year in the ‘Memoirs’ of the Observatory, where it might be seen that the system of Jupiter’s bands on the red parts differ from the terres- trial band. Besides these rays and several others, Jupiter at first sight shows another band ¢ outside D towards the blue, which is analogous to the ¢ of Brewster, and it would be necessary to proceed to further measurements even for this. But I would not delay the communi- cation of these results to you before the planet is too near the hori- zon, in order that these results, which are the most striking, may be confirmed by those who possess powerful instruments. Before finishing, I may reply to a possible objection: If the posi- tion of these lines is correct, the solar rays will not be visible upon Jupiter, which does not agree with received ideas. I answer that this does not necessarily follow from my measurements; the solar rays may in fact exist; but being very much spread out and very fine, they would be confounded with the penumbra of these bands themselves; for in fact the position of the solar rays falls so nearly in the neighbourhood of the bands, that for want of light in the planet it would be difficult to see them without a more powerful instrument. In fact, if the moon is viewed with a small diaphragm in front of the object-glass, so as to reduce the light of the spectrum almost as much as has been done for Jupiter, the red rays can only be distinguished with extreme difficulty. I think, therefore, that these observations do not disprove the existence of solar rays in the planet, but show that its atmosphere has a strong absorbing power, and a different one from ours.—Comptes Rendus, August 17, 1864. THE LONDON, EDINBURGH anv DUBLIN PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. SUPPLEMENT to VOL. XXVIII. FOURTH SERIES. LXI. Continuation of a Theory of the Dispersion of Light. By Professor Cuauuis, V.A., F.R.S., F.R.AS* t AVING been much occupied with preparing for publication a volume of astronomical observations, I have been hindered from proceeding with the researches relating to the Dispersion of Light, which were commenced in a communication to the Number of the Philosophical Magazine for last June. On account of this interruption, it will be expedient, before advancing beyond the point to which the investigation was brought in that communication, to mention briefly the principal steps of the antecedent reasoning. It was assumed that an ethereal wave within a transparent medium obeys the same laws as one without, but is propagated with less velocity in consequence of being acted upon by an extraneous force always opposite in direction, and proportional in magnitude, to the accelerative force due to the ether. The density of the ether was supposed to be the same within the medium as without, and the extraneous retarding force was considered to be the mean effect of the re- flexion of the motion of the ether from the atoms of the medium, a vast number of atoms being supposed to be contained in a portion of space the linear dimensions of which are ex- tremely small compared to the breadth (A) of a wave. The amount of retardation depending not only on the number of atoms in a given space and their arrangement, but also on their mobility, it is necessary, in order to calculate the rate of pro- pagation in the medium, to determine the motion of an individual atom as resulting both from the dynamical action of the waves and the molecular forces of the medium. The form of the atom being assumed to be spherical, the determination of the accelera- tion due to the waves was shown to depend on the solution of a hydrodynamical problem of which this is the enunciation :—A series of waves defined by the equations . 277 MTree) sin (xat—x“+c) * Communicated by the Author. Phil. Mag. 8.4. No. 192. Suppl. Vol. 28. 2K 490 Prof. Challis on the Dispersion of Light. is incident in the direction of the axis of x on a fixed smooth sphere of given radius; it is required to find the condensation at any point of the surface of the sphere at any instant. Accord- ingly the Article in the June Number consists almost exclusively of investigations preparatory to the solution of this problem. In the first place the solution was attempted by employing only the two usual fundamental equations, and results were arrived at which were subsequently shown to be incompatible with the given conditions of the problem. The third general equation was then taken into account, and another process of solution, in- volving the principle of the new equation, was then entered upon, but not brought to a conclusion. I propose now to resume the argument, taking it up from the point (in p. 458) at which the second process was commenced. It is unnecessary to repeat that part of the reasoning (ending in p. 461) by which the equation Ka? « 2 wil baal i) tg. ee ane was obtained. It will suffice to explain here that in this equation o is the condensation, and V the ‘otal velocity, at any point whose coordinates are z, y, z at the time ¢; do is the increment of condensation, at the given time, along the line of motion passing through that poimt, corresponding to the imcrement ds of space along the same line; and i is the partial differential coefficient of V with respect to ¢ The factor «?a?, which holds the place of a? in the usual mode of investigation, takes account of the composite character of the motion. The equation only embraces quantities of the first order, and is exclusive of the action of any extraneous force ; in other respects it is perfectly general. For our present purpose we have to apply it to cases in which the motion is symmetrical with respect to an azis. In such cases, if r be the distance of any point from the origin of coordinates, and @ the angle which this line makes with the axis of z, o and V are functions of r and @. Also, if U and W be the resolved parts of the velocity respectively along and perpendicular to the same line, V?= U?+ W?. Consequently we have the equations do do dr do rdd ds dr ds 7d) ds? We ater Later be i ~ de Vt rd) V? and ON i DU de NY, eel a dt Vd \ Prof. Challis on the Dispersion of Light. 491 Hence, by substituting in the equation («), (2° = Bee = (12a? : Le +o )w=o. - (8) At the same time the equation of constancy of mass to the same approximation is ds dU 2U dW W peat a. cia Cob 0 = Une ey) Now, if it be required to apply the equations (8) and (ry) to eases of motion in which there is no other relation between U and W than that which results from the mutual action of the parts of the fluid, since the analysis is required to determine that relation, we must equate separately to zero the quantities in brackets in the equation (8). In fact, if that equation be multiplied by 8¢, it will seem to be formed by a combination of D’Alembert’s Principle with the Principle of Virtual Velocities ; and as by hypothesis there is no given relation between the virtual motions Udé and Wé¢, the factors by which they are multiplied must separately vanish. If U and W be eliminated from the two equations thus obtained and the equation (ry), the result is mew on. @ or | (d*.or d vor, ae ae ae tal ae tp te) This equation has been employed to determine the resistance of the air to a vibrating sphere, the centre of the sphere being the origin of coordinates. It appears, however, to be only applicable to the case in which the fluid is confined within fixed boundaries. For it is evident that in that case just as much incompressible fluid must flow in the direction contrary to the motion of the sphere as the volume of the sphere displaces ; which is precisely the result to which the analysis conducts when the vibrations are not very rapid, and the movement of the fluid is consequently very nearly the same as if it were incompressible. The analysis also shows that the same equation applies to the case in which the sphere is fixed and the mass of fluid is caused to vibrate bodily. In fact we may pass from the one case to the other by conceiving motion equal and opposite to that of the sphere to be impressed both on the sphere and on the fluid, such impressed velocity not altering the value of o, and therefore not altering the function that o is of r, 0, and ¢, as given by the above equation. In both these cases the velocities U and W are related to each other in a manner depending only on the mutual action of the parts of the fluids, the fixed boundaries being supposed to -be so far distant from the sphere as not to affect the law of the motion. 2K 2 452 Prof. Challis on the Dispersion of Light. But the conditions of the problem are wholly different if, as I assume to be the case, the sphere vibrates in fluid of unlimited extent, and impresses disturbances upon it which are propagated indefinitely into space. By applying to this case the hydro- dynamical principles on which our reasoning is now proceeding, U and W are found to have a known relation to each other, by introducing which into the equations (8) and (y) and integrating, the motion of the fluid may be completely determined. I do not produce the details of this reasoning here, because they are contained in the former paper (pages 462 and 463), and have been given in several other communications. It results from the solution of this problem that the relative velocity of the fluid in contact with the sphere is T sin 0, —T being the velocity of the centre of the sphere, and the angle @ being reckoned from the axis of x on the negative side. This value, however, implies that terms involving the small ratio of the radius of the sphere to X have been neglected, or that the fluid comports itself as if it were incompressible. Suppose now the velocity T to be impressed at each instant on the sphere and the fluid, so that the sphere will be reduced to rest. The actual velocity of the fluid along its surface will then be Tsin@. But on this supposition the fluid through its whole extent moves with the velocity T, and, excepting so far as condensation is produced by impact on the sphere, all its parts have the same density asin the state of rest. To pass from this case to that of waves of variable density impinging on the sphere, it is sufficient for a first approximation, considering the small ratio of the radius of the sphere to the breadth of the waves, to substitute c—o, for o in the equation which gives the condensation in the first case, c, being the condensation at any instant of the incident wave at the points of incidence. Through the small extent of the hemispherical surface on which the waves impinge, 7, may be regarded as uniform, without omitting quantities more significant than those already neglected. But for the determination of the motion beyond the plane yz passing through the centre of the sphere other considerations are necessary, because, on account of the varying density of the incident wave, the impressed velocity is there altered by the mutual action of the parts of the fluid, and the effect of such action can be ascertained only by the solution of a partial dif- ferential equation. The course of the reasoning now requires an investigation of the amount of this modification of the im- pressed velocity. Since the equation (9) is perfectly general for motion symme- trical with respect to an axis, and applies to all points of the fluid at all times, it will be true if we pass from one point to Prof. Challis on the Dispersion of Light. 493 another contiguous point by substituting 0466 for 0, while r and ¢ are constant. Hence the equation obtained by differen- tiating (8) with respect to @ only will be true. We shall thus get 2 2 (ea ae = ue («20 . = ae) aM) dedr * dedi aE do do d2W Bie an qw aa Py oes SS =): ee es edt an +(« aaa Esa) er aay For the disturbance of the fluid produced by the first hemi- spherical surface, the relation between U and W and also that between wy and cit are known, and this equation is con- dé dé sequently not required for determining that part of the motion. But for the remainder of the motion, U and W, as we have WwW argued above, and by consequence = and _ are related to each other in part by modes of fluid action ascertainable only by integration. To find such relation between the latter two quantities, we must assume, according to a principle already applied, that i ee ag and «7a? - LE ON Wee ab rd0 dt Also, as consequences of these equations, we shall have ae. 22, 20 @o PW a dOdr * dOdt rd@>* dOdt~ The foregoing equation is therefore satistied on this assump- tion. But it is particularly to be remarked that this process implies that the relation between U and W does not depend wholly on the mutual action of the parts of the fluid. For if that were so, the two latter equations would not be required, and we should have the kind of motion which was previously shown to be inconsistent with the conditions of the present problem. Consequently the four equations will serve to deter- mine only those parts of U and W of which the relation is not otherwise assignable ; and it is clear that, since the original equations are linear with constant coefficients, this portion of the motion may be determined independently of the rest. mee, dU dW d?U d?W After eliminating le adr. ddi and Ted by means of the four equations above and the equation (fy), and substituting g 0. =A ORY 6 Of d : for ~, the result is dé Ly d*.gr_. d*. qr a (ae d.qr Kae dif? - dr? 2 de de cot @ oe . (€) sin?@ 494: Prof. Challis on the Dispersion of Light. which, as might have been anticipated, is the equation (6) dif- ferentiated with respect to @. By a like process we might have obtained the equation resulting from the differentiation of (6) with respect to 7; but the above equation suffices for the present purpose. I proceed now to obtain a particular and exact solution of it. Let it be assumed that gr=d sin @ cos, and that ¢ is a function of r and ¢ only. Then, by substituting this value of gr in the equation, the result is 2 2 — . es sin 6 cos 0=0, Ka? di®)=— dr? which accords with the assumption that ¢ is a function ofr and ¢. This differential equation, which admits of exact integration, gives for @ an expression containing arbitrary functions of r—kxat and r+xat. Excluding the function of r+ «at, which is inapplicable to the question, it will be found that do _(f(r—xat) f'(r—«at) f"(r—xat) az A oY 3 m2 3,2 r r ) sin 0 cos 0. But if W, be the part of W which depends only on the mutual action of the fluid elements, from what is said above the left- hand side of this equation is equal to — >> _ Hence, by integration, f(r — Kat r—kat "(r—xat)\ . W, =—=Ka. (Ais ee) Hie) a) sin @ cos 0, no arbitrary function of 7 and @ being added, because by the conditions of the problem W, is a periodic function of the time. The preceding investigation would suffice for finding the corre- sponding part of U, and the condensation at any point due to the mutual action of the parts of the fluid. But as the sequel of the reasoning requires only the knowledge of the velocity and condensation at the surface of the sphere, this inquiry may be omitted. It may also be here remarked that as the form of the function f is determined by the given expression for the velocity T of the incident waves, and as the conditions that W,=0 where é= 3 and 0=7 are satisfied, all the conditions of the problem are definitely satisfied by the foregoing value of W,, which may therefore be considered as the only solution of the equation (e) appropriate to the question. By supposing 7 in the general expression for W, to be equal to c the radius of the sphere, we obtain the velocity along the Prof. Challis on the Dispersion of Light. 495 surface of the sphere, which I shall henceforth designate by the same symbol W,. Since f isa periodic function having the same value of X as T, after the substitution of c for 7 the second term in the brackets will be of the order < x the first, and the third 2 : term of the order - x the first. Hence the second and third terms are insignificant in comparison with the first, and may be omitted. But whether they are omitted or not, we may put the expression for W, under the general form ve a+ 85) sin 8 cos 8, a and @ being unknown constants. We have thus arrived at a formula for the alteration which the impressed velocity along the second hemispherical surface undergoes by fluid action; and as the impressed velocity is T sin 0, the entire expression for the velocity along that surface is T sin # (l+e cos 0) +8 sin 6 eos 6. I have made use of this expression in the Philosophical Magazine for February 1860 (p. 90), but I had not then obtained it by so complete an investigation as that here given. We have now to determine by means of the velocities along the two hemispherical surfaces the total pressure on the sphere produced by the dyna- mical action of the waves, the sphere being at first supposed to be fixed. ; For the first hemispherical surface _Kads dW aT. 9 edo tat nae Hence integrating, and determining the arbitrary constant so that c= Ss where 6 =5: it will be found that ep ao=A*oy+ 3" cos 0, Consequently the whole pressure on the hemisphere, resolyed in the direction of the incidence of the waves, is 2rate*| oad sin 6 cos @ from 6=0 to 6=— 9? that is OO sane i 2 poe B pipet Sia ees 27 oi 5 +33 at: 496 Prof. Challis on the Dispersion of Light. Similarly for the second half of the surface, Katda dW dT ——5 =a = sin 0(1 +2008 8) +8. sin 8 cos 8. C Hence, by integrating from @=5 7 to 0=z, 2 dT cB d?T cos*6 ee me Sane ah rs aro =a a, + 3° HP (cos +5 costé) + a) 4 7a ae aoe ae and the whole pressure, resolved as before in the direction of inei- dence, is 6 ao50% Gs Be a*T oo 2 Ti de\8 8)” (eee eae Hence, if the mass of the sphere be A x its volume, A being au unknown constant, and if the sum of the two pressures above obtained be divided by this mass, the acceleration which the waves tend to uel in the direction of their propagation is = 88 aT = [a psa lead Sis GEE } Passing now to the case of a moveable sphere, it is allowable, on the principle of the coexistence of small vibrations, to deter- mine the dynamical effect of a given series of waves by consi- dering, apart from any other motion the sphere may have, that which the waves would produce by themselves. But it is evi- dent that the waves are effective only in proportion to the rela- tive velocity of the fluid and the sphere; that is, 2 being the coordinate of the centre of the sphere, and regarded positive in the direction of propagation, the effect 1s Sele to d. 2Q7r T— =) or msin— 5 (bt +e) — dt the term —zw in the expression re T being Re because the excursions of the sphere are supposed to be extremely small about a mean position, which may be taken for the origin of 2. Now = since it depends only on T, will be a periodic function having the same period as T, and consequently pa will be sunilarly periodic. Hence, calling this quantity T’, if we sub- stitute 'T’ for T in the foregoing expression for the accelerative force the sphere being fixed, we shall have the acceleration of the sphere in motion, so far as it is due to the action of the waves. Again, as I have argued in the article “ On Double Refrac- tion ”’ in the Philosophical Magazine for December 1863 (p. 472), Prof. Challis on the Dispersion of Light. 497 the displacement of any atom of the medium in which the light is propagated will necessarily bring into play the molecular forces of the medium. Having found that the reasoning on this point in the article just cited requires correction, I propose now to determine again the acceleration of the atom due to the elasticity of the medium. Suppose that by the action of the ethereal waves the mean interval between consecutive atoms, estimated in the direction of propagation, is diminished bya quantity (e) ex- tremely small compared to that interval. Then since the result- ing molecular action is proportional to the relative displacement of the atoms, the acceleration of an atom due to this cause is —eé. = e being considered to be a function of a, and e? being an unknown constant. But since the movements of the atoms are determined by the action of the waves, it follows that these movements and the values of e are propagated through the medium with the velocity (b) of the propagation of the waves. Hence, just as in any case of uniform propagation, v= be=f (z—Dt), v being the velocity of any atom. Consequently MP ebia Ps) OD, 6%, 6 2 (eda By di BO dt It should be remarked here that e? may be regarded as a mea- sure of the force by which an atom displaced relatively to sur- rounding atoms tends to return to a position of relative equili- brium. On account of the small movements with which we are concerned, which do not sensibly affect the density of the medium, this force must be very nearly the same as that by which a single atom displaced tends to return to its position of absolute equilibrium ; so that e? may be taken as the measure of molecular elasticity in the given direction of propagation. In the former investigation this quantity was incorrectly stated to be a measure of elasticity as inferred for a continuous body from a given relation between its pressure and density, which is dependent on the other measure, but not identical with it. It is possible that ¢?, as resulting from the immediate action of molecular forces, may be comparable in magnitude with 6”. The investigation has now conducted to the following equation for ee the motion of the atom: aT 86) 98, OP ee, =n Val )-%6 aes dt A is eel ie A sheen g1VES dx 1 [ee a at dt au, A(b2—e) ( TRIE eT ye 498 Prof. Challis on the Dispersion of Light. no arbitrary constant bemg added, because we have to consider no other motion than that which the waves originate, which, by hypothesis, is wholly periodic. At the same time we have o = =m sin 5 (bt+c)—T". Hence the last equation may be put under this form, o sik QT’= MQ ain — — (bt +c), m which Q=- PAG *A(1— “)+1- 22) and M= m(1—“359"): Consequently by a second integration, after substituting cot for T= = —Mssin ye0s($ (bt-+0) +4): Now the condition of transparency of the medium requires that T', the relative velocity of the ether and the atom, should be proportional, or very nearly so, to the velocity of the ether; for in that case the mean retardation of the waves is produced by the atoms in motion nearly in the same manner as by the atoms fixed. This condition is fulfilled if x be very nearly equal to i or if Q be a very large quantity, which is the case if @ be very small. We are thus led to conclude that the term containing 8 as a factor in the general value of W is insignificant when the problem is to determine the dynamical effect of the ethereal waves in producing vibrations of the atoms. I have elsewhere shown (Phil. Mag. for November 1859, p. 332) that, in inquiring whether the waves have the effect of producing permanent . motions of translation of the atoms, that term has to be taken into account. Supposing, therefore, that Va! the results obtarmedt after substituting for Q in the above se of M, are b?—e? 6? 3a qk Jette ate Perens (2 16 Let » represent the ratio of the rate of propagation (xa) out of the medium to the rate (6) within the medium. Then by the reasoning I have given in the article “On Double Refraction ” T=Msin= (+0), Mam- Prof. Challis on the Dispersion of Light. 499 (pp. 475, 476), if 5 be the density of the medium and p?—1= Ho, the atoms being supposed fixed, the mobility of the atoms is taken into account by multiplying the right-hand side of this equation by the factor that multiplies m in the above expression for M. Thus we have H6(«2a? — pe?) —1= mW KG) 272 — 42001 % (1 3% Ka" — p*e* + a (1 16 This equation to the first power of e? may be put under the form p?—1=A—Be?, A and B being positive quantities. Hence the equation I have employed in my theory of Double Refraction (Phil. Mag. for December 1863, p. 479) is verified by this new investigation. In all the foregoing reasoning » has been supposed to have a given value. To apply the equation (7) in accounting for the phenomenon of Dispersion, it is necessary to discuss the cha- racter of the factor a, this being the only quantity in it which can contain A explicitly. Now it was found that the velocity (W) of the zether along the second half of the spherical atom is given generally by the equation W=T sin 0+aT sin 0 cos 0. If the same kind of reasoning were applied to the case of a uni- form stream encountering the atom, which may be regarded as a case of vibratory motion for which % is indefinitely great, the second term of the value of W would be found to disappear. (See Phil. Mag. for November 1859, p. 324.) Hence a is a function of % which decreases as A increases. In general that term expresses the difference between the effect of a stream and that of a series of vibrations, which difference is owing to the prevention of lateral spreading by the state of vibration. I have remarked in the preceding paper on Dispersion (p, 460), that in consequence of waves being compounded of separate vibrations parallel and perpendicular to rectilinear axes, lateral spreading may be counteracted in such manner that the whole motion, direct and transverse, may be included in a cylindrical space of small transverse section. The same cause must operate in a degree to check the lateral spreading by which the portion of the incident waves that passes the atom tends to supply the place of the portion which the atom intercepts. In the paper “On Double Refraction ” (p. 468), an expression is given for the function f which defines the law of the diminution trans- versely of the vibrations parallel to a single axis. From this expression it may be inferred that at a given position the diminu- tion for any number of component vibrations, whether or not 500 Prof. Challis on the Dispersion of Light. their axes be parallel, may be denoted by such an expression as Al? Bld Cly6 oy hy gh pcm CE Sues ee piety Susie Mean et \, r, the distance from an axis, being different for every different axis. As, on account of the small Sas of the radius of the atom to A, we are concerned here only with values of 7 extremely small compared to X, it may be presumed that the first term of the series is much more considerable than the remainder. Guided by these considerations, I shall now assume that the h factor « is equal to <3 >, A being an unknown constant, but neces- sarily positive, tate cos @ is negative. This quantity being substituted for « in the equation (7), the relation between uw anda may be put under the form oe (Re 1)*—(e7—0) - (8) in which Ka? 3ha? A="* —14 oa B=4@ C= H8(‘S—1). These expressions show that A, B, and C are positive quantities ; but theory alone is incapable of determining their numerical values. I proceed now to test the equation (@) by experimental data. For this purpose I have adopted Fraunhofer’s values of i, and, for a first instance, have selected his values of w for Flint Glass, No. 18. (See arts. 437 and 751 of the “ Treatise on Light ” in the Encyclopedia Metropolitana.) To determine the constants of (@), three equations were formed by means of the values of pv and d for the rays B, E, and H, the solution of which gave the results A= 9712778, B=1°39857, 6 C=11-97Sas: The values of ) for the other rays were then calculated by the formula (@) from the corresponding values of mu, and compared as follows with observation :— Ab Ab Excess of Ray. Value of p. ce A: culenleaen. calcalaee B ; IeG27 75 2°041 (2°541) 0:000 C . 162968 2°4.22 2°4.25 +0:0038 D . 163504 2175 2°174 —0:001 E . 1°64202 1:945 (1:94) 0:000 F . 1°64826 1°794 1:796 + 0-002 G . 1:66029 1:587 1:592 +0:005 H . 1:67106 1:4.64. (1°464,) 0:000 Prof. Challis on the Dispersion of Light. 501 The values of % in brackets were those used in determining the constants. The adopted unit of 2, which is arbitrary, was chosen for convenience in calculating. The followimg results were obtained by a like comparison for oil of cassia, which was selected on account of its great disper- sive power. The numbers are taken from Professor Baden Powell’s paper in the Transactions of the Royal Society for 1837, Part I. p. 22. Ab Ab Excess of Ray. Value of p. Se ae deletion calculation. + 3a 1°5885 2°D41 (2°541) 0:000 Cr. 1:5918 2°4.22 2°4.28 + 0:006 0 1:6017 2°175 2°174 —0:001 E. P6L55 1°945 (1:94:55) 0:000 F, 1°6295 1:794 1:791 —0:0038 See 2 "6607 5S a Oo —0:004 Pee E7002 1-464. (1°4.64) 0-000 The equations for determining the constants gave A=455574, B=0°64905, C=4°46624. In the first example, the difference between the first and last values of w is 0:'0433, and that between the first and last values of X is 1:077. Hence a difference of 0-001 in X corresponds on the average to a difference of 000004 in w. In the same man- ner it will be found that in the second example a difference of 0001 in A corresponds to 0:00010 in w. Taking these propor- tions into account, it will be seen that the accordance between theory and observation is much more exact in the above com- parisons than in the corresponding ones made by Professor Powell in the Transactions of the Royal Society for 1835, Part I. p. 252, and in the paper above cited. The accordance might be made still closer by assuming « to be equal to Bass but as another constant would then have to be determined, the resulting equation would amount to little more than a formula of interpolation. The above comparisons, however, by showing that the equation (@), derived entirely from antecedent physical principles, is capable of giving results im accordance with expe- riment, afford evidence both of the truth of the theoretical expla- nation of dispersion, and also of the principles on which it rests. I had previously obtained other equations, none of which were found on trial to admit of satisfactory comparison with experi- ment; but at the same time, as the present more complete in- vestigation has shown, they were not strictly deduced from the a priort principles. 502 ~~ Prof. Maskelyne and Dr. Lang’s Mineralogical Notes. The applications of my hydrodynamical researches which I have made from time to time in the undulatory theory of light, have now embraced most of the leading phenomena, excepting that hitherto I have not indicated their application to the phe- nomena of Diffraction. The theoretical explanations that have been given of this class of facts rest maimly on an assumed law of limited lateral divergence, and on this assumption have been successful. Now, from reasoning contained in this and previous communications, | am justified in inferring that this law is a consequence of the composite character of waves, and of the circumstance that the component vibrations are partly direct and partly transversal. Also the supposition usually made in the mathematical treatment of problems of diffraction, that the waves are compounded of indefinitely small parts each possessing the property of limited lateral divergence, is im accordance with this hydrodynamical theory of the composition of waves. I have never been able to perceive how such a supposition is con~ sistent with a theory of light which regards the ether as com- posed of discrete atoms. On the whole the results of my re- searches give reasons for the conclusion that the undulatory theory of light rests legitimately on no other than a hydro- dynamical basis. Cambridge, November 21, 1864. LXII. Mineralogical Notes. By Professor N. 8. MaskELYNE and Dr. Vixtor von Lane, of the British Museum. [Continued from p. 150.] [With a Plate. | On the Crystalline Form of Malachite. By Viktor von Lang. bi ies I had published my first Note on this subject I came, in the mineral collection of the British Museum, upon several more tolerably well crystallized specimens of malachite, of which the following is a description. These new observations not only confirmed my previous ones, but also led me, as I believe, to a somewhat more accurate determination of the cry- stallographic elements of malachite, viz. a:b:¢ = 0°7823:1:0°4036. ie = Uaioe They were deduced from the angles 110.110=75 56 101,100 — 61 53 108.100 = 98 48, Prof. Maskelyne and Dr. Lang’s Mineralogical Notes. 503 which are the means of numerous measurements—the first angle being observed on crystals from Siegen*, the two others on cry- stals from Nijni Tagilsk. Including the new planes on the crystals I am going to de- scribe, we have for malachite the planes 100, 010, 001, 110, 101, 102, 1038, 104, P24 3 401.93, 1.12, 3235 221. for which we find the following angles calculated with the above elements :— 100./1:010.| 001.] 110.)| 110. 001 | 88 57/90 0] 0 0] 89 10] 89 10 110 | 37 58) 52 2)89 10} O Oj 75 56 101 | 61 53) 90 0/27 4] 68 11) 68 11 104 | 96 19] 90 O| 7 22] 94 59| 94 59 103 | 98 43) 90 0} 9 46} 96 53) 96 53 102 |103 29) 90 0| 14 32/100 36/100 36 124 | 96 11) 78 39/13 30| 87 56/101 54 134 | 96 3) 73 15/18 15| 84 36/106 32 “123 | 98 25| 75 817 44| 87 34/105 52 112 |103 14] 78 54/18 13] 93 33)107 23} 323 |114 38] 76 11/30 32/101 11/119 1) 221 |128 16] 60 27/53 10/100 39/142 20 The following newly observed combinations are, like all crystals of malachite, twinned on the axis (100). ’ Plate VII. fig. 1—100, 101, 221. The specimen on which this by no means small crystal occurred consists of larger crystals penetrating each other. But this crys- tal was the only one of which at least one end, formed by the enumerated planes, was not in contact with other crystals. The planes 101 on the top seem to have been produced by cleavage. The planes 221 are not good, and are striated parallel with their intersection with the prism 110. The observed angles are * These crystals were already described in the previous Note. 504 Prof. Maskelyne and Dr. Lang’s Mineralogical Notes. 110.221=39 appr. 37 40 cale. 921.221 = 57 -..) “Onde P2215 221) (110.110) 44 te 44sec [221.1¢¢)[110.0%1)—509) “oie The last two angles are angles between edges, and could be mea- sured pretty accurately with the microscope. Fig. 2.—100, 110, 101, 103, 123. Fig. 3.—100, 010, 110, 123, 323. These forms were observed on small crystals from Medno Roudiansky mine, near Nijni Tagilsk, Ural. They are, with regard to the distinctness of the smaller planes, the best crystals I had for measurement. I found on them the angles 101.1 00=062 58 \a Gi S3rcale 103.100= 98 48 98 43 103.101= 36 58 36 51 103.110= 96 52 96 53 1O3iG.010) 103.17 31) } saz 86 123.010= 74 54 hay is: 123.128= 29 33 29 44 123.110= 87 47 ~— 87-34 123.110=105 48 105 68 823.100= 66 appr. 65 22 320-923) 27125, 04 Oe Aes 329. 11.0=" 62 “+5: '60n49 33 Crystals from a specimen from an unknown locality were similar to fig. 2, only the planes 101 were wanting, and the planes 1 23 were more developed. The planes reflected the light very well. I observed . 100 1083=98 49 98 48 calc. 103 123= 380 appr. 29 44 ,, The collection of the British Museum contains also specimens from the now exhausted locality at Rheinbreitenbach. But the crystals from this locality, although the largest of all, are not good for measurement, as they penetrate each other very much, and are moreover coated with foreign matter. They seem to be combinations of 110 and 123, the prism 110 being not much developed, as in fig. 3. : Prof. Maskelyne and Dr. Lang’s Mineralogical Notes. 505 But, induced by the greater size of these crystals, I tried to determine directly the mean coefficient of refraction for this sub- _ stance. I obtained without great difficulty, out of a part ofa erystal, a prism formed by the cleavage-planes* of the two twinned individuals and by an artificial plane in one zone with the two other planes. This artificial plane formed in consequence two angles, the better one of them being 23° 26’. But for the mini- mum deviation of the ordinary ray through this angle I could only get the approximate value 20° 34’, having neither direct sunlight nor artificial light at my disposal—an essential condi- tion when one has to work with such small prisms. As the prism is parallel to the mean axis of elasticity, one finds from the given data for the mean coefficient of refraction the value B=1:887. On the Crystalline Form of Gismondine. By Viktor von Lang. Under the name of Gismondine a zeolithic mineral is desig- nated, which in the form of small square pyramids occurs on a basaltic lava in the neighbourhood of Rome. The British Museum contains two specimens of it, one from Valerano, the other from Capo di Bove, both localities near Rome. Some mineralogists were of the opimion that these square pyramids are only twin crystals of Phillipsite, which indeed is found in forms nearly approaching an octahedron; but then the lines of twinning may always be seen on the planes of the octahedron, of which not the least trace could be found on the crystals of the two specimens in the British Museum. Nor by polarized light could I detect in these crystals any twin structure, but I found by the aid of it that the crystals are single individuals which belong to the prismatic system. A closer inspection indeed of the twinned crystals shows at once that the four planes forming the top of the supposed pyramid never meet in one point; they are, in fact, combinations of a vertical prism (110) with a horizontal one (101), fig. 1, Pl. VII. A section perpendicular to the axis a became, when turned between two crossed Nicol prisms, dark and bright, show- ing by this fact that the axis @ cannot be the axis of a square pyramid; the planes of polarization were for this section parallel with its edges, rendering also impossible the supposition that * These two cleavage-planes formed an angle of 55° 28’ (56° 14’ calc.), which could be measured with great accuracy. From this it follows that the twin plane bisects the obtuse angle of the two cleavage-planes. These facts seem to prove that the crystals from Rheinbreitenbach are not twinned on the plane (00.1)—an opinion expressed by M. Hessenberg in the last Number of his valuable Mineralogical Notes, with which he favoured me while the above was going to press. Phil. Mag.8. 4. No. 192. Suppl. Vol. 28. 21 506 Prof. Maskelyne and Dr. Lang’s Mineralogical Notes. the crystals are prismatic pyramids. By means ofa second sec- tion perpendicular to the axis c, it was found that the plane of the optic axes is indeed perpendicular to the axis a, and that the character of the mean line (probably the first) coinciding with the axis ¢ is negative. The points of the axes themselves could not be seen, as the angle of the optic axes is too great for this; but another section, a little inclined to the former one, showed one axis, by which one could see that the negative angle of the optic axis is smaller for red than for blue light. | The planes of the crystals are not very good for measuring, but the crystals are cleavable parallel to planes (101), and by means of such cleavage-planes I determined the angles 101.101=98 41 1 1Or Ot Gouls 110.110 = — 90° 50! calc., whence we find a:b:c=1:0°9856 : 0:9377. As for the axes of optic elasticity, we found alle < bie, eyes the symbol of the optical orientation becomes bea. Last summer I had the opportunity of seeing two quite similar specimens in the mineralogical collection of the Berlin Univer- sity. The accompanying label gave, “‘ Gismondine [variété de- crite par Gismondi, qui est la plus rare]: Capo di Bove prés de Rome. Monsignore Lavinio de Medice, Speelo, Roma.” On the Crystalline Form of Herschelite. By Viktor von Lang. It has hitherto been supposed that Herschelite crystallizes in the hexagonal system; but the optical investigation of the nu- merous specimens in the mineralogical collection of the British Museum showed that Herschelite belongs to the prismatic system, and that its hexagonal forms are only produced by the twin association of six individuals. One has only to grind down the crystals a little, as the top plane is always rounded, to see with the polarizing apparatus the internal structure of the crystals as represented in fig. 4, Pl. VII. Hach triangular section is doubly refracting, and gives moreover two optic axes, the planes of which bisect the central angle of each section. The angle of the optic axes is very small, the character of the first mean line negative. In making these observations, one has only to take care that the crystal is not too thin, as, the double refraction being not Prof. Maskelyne and Dr. Lang’s Mineralogical Notes. 507 very considerable, it is then difficult to see the differences. of the intensity of the light in turning round the crystal. In conse- quence of these remarks, the prism-planes of the crystals of Herschelite obtain the symbol 100; and the planes in the zone [100, 001], 001 being the top plane, become planes of ho- rizontal prisms parallel to the shorter diagonal of a prism 1 1 0, on the planes of which the crystals are twinned. As none of the planes are very good for measurement, the following crystallo- graphic data of Herschelite can only be considered as approxi- mations. The observed planes seem to correspond to the symbols POO ws OF, 502, 201, 101, OOT. Taking for the elements a:6:c=1:0°5774:0°8576, we calculate for these planes the angles 301.100=21 14 502.100=25 0 201.100=30 15 101.100 = 49 23 110.100=60 0 The observed combinations are :— Pl. VII. fig. 1.—001, 502. | On a crystal from Aci Reale, Sicily. One of these crystals gav 502.502 = 49° 51! (50° 0 calc.) Fig. 2.—100, 301, 101, 001. _ From Aci Castello near Aci Reale, Sicily. I found ona crystal, 100.801=21 56 21 1d ale. 100.101 = 48 30 49 23 ,, 101.101=98 46 98 46 ,, These crystals, like the foregoing, occur on a sort of lava; they are often associated together in spherules, but are also found single, imbedded in the vesicular mass, from which they can easily. be got out. Such crystals, very small but with tolerably good planes, were combinations only of 8301 and 001, with an angle it 301.3801 =392°-42° (42° 28! calc.). The top face of these crystals was also tolerably plane, but rough. Fig. 3.—100, 201, 001. | These crystals, from Cyclops, Catanea, are also interesting on account of their association, coating with Phillipsite a mass of. 212 508 ~~ Prof. Tyndall’s Contributions to Molecular Physics. basalt. I observed P00. 20P= 315% (607 Wo calen PTO UDO 0) LT 0'= 59-o1°(G0 Ur aa The plane 101 seems also to occur on some of these crystals. The plane 001 on one of them showed re-entering angles, which, although not measurable, are also a proof of the twin structure. A very interesting specimen of Herschelite from Victoria, Australia, was lately given to the British Museum by Mr. Selwyn, the colonial geologist, who found it himself. The crys- tals, occurring, like those just described, on basalt, are aggre- gated together in a greater quantity; and although much larger than those from Italy, are still less fit for good measurements, the planes being broken in every direction. They have the form of fig. 1; and I observed on one of the erystais 502.5 0/2 =502° (507 0) ealege The angles of the top plane are very much rounded, so that the edges 502.50 2 are quite obliterated. The optical properties of these crystals areexactly the same as those of the Italian specimens. LXIII. The Bakerian Lecture.—Contributions to Molecular Physics. Being the Fifth Memoir of Researches on Radiant Heat. By Joun Tynpat., FRK.S., &e. [Continued from p. 458. | § VIL. Influence of temperature on the transmission of radiant heat. ae power of varying at will the temperature of the platinum spiral renders it peculiarly suitable for the examination of the influence of temperature on the transmission of radiant heat. To obtain sources of different temperatures, Mellon resorted to lamps, to spirals heated to incandescence by the flame of alcohol, to copper lamine heated by flame, and to the surfaces of vessels containing boiling water. No conclusions regarding temperature can, as will afterwards be shown, be drawn from such experiments; but by means of the platinum spiral we can go through all those changes of temperature, retaining throughout the same vibrating atoms, and we can there- fore investigate how the alteration of the rate of vibration affects the rate of absorption. The following series of experiments were executed on the 9th of October, with a platinum spiral raised to barely visible redness, and vapours at a tension of 0°5 of an inch. Prof. Tyndall’s Contributions to Molecular Physics. 509 TasLe XJ1.—Radiation of heat through Vapours. Source of heat, platinum spiral barely visible in the dark. Name of vapour. Deflection. Absorption per 100. Bisulphide of carbon . . 75 2 5 i Bisulphide of carbon . . 74d weermorm ~ . . . . 10:5 1 Saleriorm . . . . . 105 4 Eegideormethyle « . . 14rd 12 5 Haamicormethyle. .'). . 145 12°5 Wemide ofethyle . 2... 24r2 20°9 Woumeotethyle . 2° 2 . 245 21:1 } ese. | fs | O10 26°7 Pee. SS |. O00 25°9 } PCH i. se + LO 35°6 PEC ROs Ny.) > O18 35° 3} Suplumce ether. 2. . 41'] 43°4, pulphurieether . . . .. 41-0 43°4 } Became ester.) .), 0s, <,. Ale7 45°0 Peeuieciner. .) .)...,+ Als 45°3 } PmeeMpiernemy ss) «. 406 49°8 i eeHIECHHEr. .<.. 43°4: 49°3 On the 10th of October ae eae results were obtained with the same platinum spiral, raised toa white heat :— Taste XIIJ.—Radiation of heat through Vapours. Source, white-hot platinum spiral. Bisulphide of carbon. 3-5 2°9 Bisulphide of carbon . . 3°4 2°8 \ Oilertomm So. . . lw GF 5°6 Wileratorm (65 ei) 2) el 67 set Iodide of methyle . . . 9:2 rare Weade ot methyle ... . <9 fe, } Femme ouethyle 2 2°). -s 154 13:0 Mepmemcthyle .. . .- 15:0 12-6} ew» | LOG 16°6 MMe lew’ ew LOO 164 f Mee Meats 6G ow of) ey) O92 100-0 ene wf). eG 22°6 Pmeemlenen ya) si si. sl) otljon 202 22°7 } Mommies cthen.. 3.) sy 30° 2 Hemme ebicr’. ... «)\.. 80:7 25°2 Sulphuricether . . . . 31:4 25°7 \ pulgauic ether . . . . 3l:7 26°0 PRECHIG CLHEE ca) ss 80:0 oo MPEICCUNEB a ier) «jc 2 0a'e 27°3 MMIGAIMedE eae ne OOO 100-0 510 ~~ Prof. Tyndall’s Contributions to Molecular Physics. With the same spiral, brought still nearer to its poimt of fusion, the following results were obtaimed with four of the vapours :— Taste XIV.—Radiation through Vapours. Source, platinum ‘spiral at an intense white heat. Name of vapour. Deflection. Absorption. Bisulphide of carbon . 14:5 2°5 Bisulphide of carbon . . 14°5 29 Chibrotorm™ 9.) een 6 eae 3°9 } Ghioreform.. 0° eee ew 3°9 Formic ether . . . . . 60°4 ia Rormueg ether... Ve. (60a 21°3 Sulphuric ether . . . . 62:3 - 23'6 Sulpituric-ether >. (79% 73402747 em 7 23°8 } Total heat... es A eee ee 100-0 In the experiments recorded in the foregoing Table, a total heat of 82°7, or 588 units, was employed; and to test whether the absorption calculated from this high total agreed with the absorptions calculated from a low total, a portion of the current was diverted, the branch passing through the galvanometer pro- ducing a deflection of 49°4. This corresponds to 77 units. The source, it will be observed, is here quite unchanged; the rays are of the same quality, and pass through the tube in the same quantity as before; but in the one case the absorption is calculated from the deflection among the high degrees, and in the other case it is calculated from. deflections among the low degrees of the galvanometer. The experiments were limited to Pia and sulphuric ether, with the following results :— Deflection. Absorption from eflection. Absorption. Table STV Formic ether . . 17-7 23 -21°3 Sulphuricether: 0: 09-L.-) 2, 24:62) 47 eee The agreement is such as to prove that no material error can have crept into the calibration. Placing the results obtained with. the ae sources side by side, the influence of temperature on the transmission comes out in a very decided manner. ~ Prof. Tyndall’s Contributions to Molecular Physies. 511 TasLte XV.—Absorption of heat by Vapours. Tension 0°5 of an inch. Source, platinum spiral. ae Name of vapour. Barely Bright White Near visible. red. hot. fusion. Bisulphide of carbon . 6°5 Ae 2°9 2°5 Chloroform . . Ore 6°3 5°6 3°9 Iodide of methyle . . 12°5 9°6 CS Watmeeotethyle. . . 21:0 Lee 12°8 Beemer.) .. 3s! 263 20°6 16°5 pigeies ss e . . 4k 858 27°5 22°7 Sulphuric ether. . . 43:4 31°4: 25°9 23°7 Pure ciier ~. . . 45:2 31°9 25°1 21:3 Seeeetecrer. . |. 49°6 34:6 27°2 The gradual augmentation of penetrative power as the tem- perature is augmented is here very manifest. By raising the spiral from a barely visible heat to an intense white heat, we reduce the absorption, in the cases of bisulphide of carbon and chloroform, to less than one-half. At barely visible redness, moreover, 56°6 and 54°8 per 100 get through sulphuric and formic ether respectively ; while, of the intensely white-hot spiral, 76°3 and 78°7 per 100 pass through the same vapours. By augmenting the temperature of solid platinum, we introduce into the radiation waves of shorter period, which, being in discord with the periods of the vapours, get more easily through them. What becomes of the more slowly recurrent vibrations as the more rapid ones are introduced? Do the latter take the place of the former? This question is answered by experiments made with an opake solution of iodine, and with lampblack. As the temperature of the platinum spiral increases from a dark heat to the most intense white heat, the absolute quantity transmitted through both these bodies steadily augments. But this heat is wholly obscure, for both the solution and the lampblack intercept all the luminous heat. Hence the conclusion that the augmen- tation of temperature which introduces the shorter waves aug- ments at the same time the amplitude of the longer ones, and hence also the inference that a body like the sun must of neces- sity include in its radiation waves of the same period as those emitted by obscure bodies. § VIII. Changes of the position of diathermic bodies through changes of temperature of the same source.—Radiation from lampblack compared with that from platinum at the same tem- perature. Running the eye along the numbers which express the absorp- tions of sulphuric and for: mic ether in Table XV., we find that, for 512. Prof. Tyndall’s Contributions to Molecular Physics. the lowest heat, the absorption of the latter exceeds that of the former; for a bright red heat they are nearly equal, but the formic still retains a slight predomimance ; at a white heat, how- ever, the sulphuric slips in advance, and at the heat near fusion its predominance is decided. I have tested this result in various ways, and by multiplied experiments, and placed it beyond doubt. We may at once infer from it that the capacity of the molecule of formic ether to enter mto rapid vibration is less than that of sulphuric. By augmenting the temperature of the spiral we produce vibrations of quicker periods, and the more of these that are introduced, the more transparent, in comparison with sul- phuric ether, does formic ether become. Thus what I have called its complexity tells upon the vibrating periods of the formic ether; the atom of oxygen which it possesses in excess of sul- phurie ether renders it more sluggish as a vibrator. Experi- ments made with a source of 212° Fahr. establish more deci- dedly the preponderance of the formic ether for vibrations of slow period. TasLe X VI.—Radiation through Vapours. Source, Leslie’s cube, coated with lampblack. Temperature, 212° Fahr. Name of vapour. Absorption. Bisulphide of carbon . . . 6:4 lodide of methyle - - . 2 IS8-4 Chioroforin eS 8s 2 ch elias Nulphuric‘ether*. i: 3) So Ga ieace Pormiciether ys a) ee. Pe For heat issuing from this source, the absorption by formic ether Is 6:1 per cent. in excess of that by sulphuric. “ Deeming the result worthy of rigid confirmation, I repeated the experiments, and obtained the following deflections :— Taste XVII. Name of vapour. Deflections. _ Bisulphide of carbon . . 9:3 Iodide of methyle . . . 25:0 Chiorotorin’s 2 42% 2-stee eo Gs Todide of spe goa, ee, AD Benzole . . +), weet ebes Amylene™ )-3 a SS So Ss Nulphuric ether: 2). VPage Sulphuric ether *0.° 2. VAT Formic ether... « . .49°7 Formic ether ... . 499 Acetic ether 48 2002 (WO +he4 Prof. Tyndall’s Contributions to Molecular Physics. 5138 When the absorptions were calculated from these deflections, the absorption of formic ether was found to be 6°3 per cent, in advance of that of sulphuric. But in both Tables XVI. and XVII. we notice another case of reversal. In all the experiments with the platinum spiral recorded in Table XV., chloroform showed itself less energetic as an absorber than iodide of methyle; but in Tables XVI. and XVII. chloroform shows itself to be decidedly the more powerful of the two. Cases of this kind have, in my estimation, a pecu- liar significance, and I therefore take care to verify them. The experiments with all the vapours were therefore repeated, with the following results :— Taste XVIII.—Radiation through Vapours. Source, Leslie’s cube at 212° Fahr. Nam? of vapour. Deflection. Absorption. Bisulphide of carbon . 15-0 6°6 Iodide of methyle. . 38:3 18°8 Chloroform. . . . 40°7 21°6 Todide of ethyle . . 46:2 29°0 Bemis. DOO B34°5 Amylene. . = et 9 47°] Sulphuric ether . . 603 54:1 formecther . .°. 62:1 60:4 mveme@erner . .°. 64:3 69-9 Migpiemest . . . . 7/14 100°0 The absorption by formic ether is here also 6°3 per cent. in excess of that effected by sulphuric ether; while, as in the last two Tables, chloroform excels iodide of methyle. Preserving the quality of the heat unchanged, but reducing its quantity from 71°-4:=227 units to 52°3=86'5 units, the following results were obtained :— FaBLeE XIX. Name of vapour. Deflection. Absorption. Iodide of methyle. . 16:5 18:3 Choroform . 4... +. 185 20°6 Iodide of ethyle . . 244 27°71 enzo st wo 4 NV GOO 33'3 metviene (Fy. 4%. + 386 4.8°6 Sulphuric ether . . 40:3 53:2 Formicether . . . 428 60:0 514 Prof. Tyndall’s Contributions to Molecular Physics. Placing the figures of Tables XVI., XVIII., and XIX. side by side, we have an opportunity of seeing how results obtained on different days check each other. Taste XX.—Source, blackened cube of boiling water. Absorptions from aa ee Name of vapour. Table XVI. Table XVIII. Table XIX. Bisulphide of carbon . . 64 © 6°6 Iodide of methyle . . . 184 188 18°3 Chloroform: “a4. cee oo 21°6 20°6 Iodide of ethyle. . . . —— 29:0 27°1 Benzolee:- oa 845 83°38 Amylenei te 26s Pe 47°] 4.3°6 Sulphuric ether. . . .° 54°8 54e1 53°2 Hormic ethers, 260% he SOS 60:4: 60-0 Acetic ether =. 0 6... == 69:9 Were it essential to my purpose, I should certainly be able to make even the small differences which here show themselves to disappear. But the agreement is such as to place the reliability of the experiments beyond doubt. ft will be seen that, contrary to the results obtained with a white-hot_ spiral, in all three cases, where a blackened cube of boiling water was the source, chloroform exceeds iodide of methyle, and formic ether exceeds sulphuric in absorbent power. To confirm the demonstration, I once more resorted to the white-hot spiral, and obtained the following results :— | Taste XXI.—Radiation meee Vapours. Source, white-hot platinum spiral. Name of vapour. Deflection. Absorption. Chloroform. . . . 9:8 4:5 Chiorefomirux «\ stew soe 45 Iodide of methyle. . 16:0 7°3 Iodide of methyle. . 15°8 73 Pormie ether, oo pa. Ae) 24°2 Formic ether .‘ . . 42°3 24:5 Sulphuric ether . . 43°6 26:3 Sulphuric ether . . 40°5 26°2 Portal neat oss cena oo, ARON 100°:0 Here chloroform retreats once more behind iodide of methyle, and formic ether behind sulphuric. The positions of sulphuric and formic ether are reversed within the range of the experiments made with the platinum spiral, but this is not the case with the chloroform and the iodide of methyle. Prof. Tyndall’s Contributions to Molecular Physics. 515 Even when the spiral was at a barely visible heat, the iodide was decidedly the most opake of the two ; the same result was obtained with a spiral heated below redness, as proved by the following figures :— Name of vapour. Deflection. Absorption. Chloroform . . . 85 12-14 Chioratorm, §.°.,.. ° 8°5 12°14 Iodide of methyle . 10:0 14°28 Iodide of methyle . 10:0 14°28 Total heat. ... 3 47°3 100:0 Here the iodide is still predominant. Is it, then, a question of temperature merely ? or is there a special flux emitted by the lampblack, to which chloroform is particularly opake? In other words, is there a special accord between the rates of vibration of lampblack and chloroform? 'To answer this question I operated thus :—The platinum spiral was heated by only two cells, and the strength of this current was lowered by the introduction of resistance. When decidedly below a red heat, the spiral was plunged into boiling water. Bubbles of steam issued from it, proving that its temperature was above 212° Fahr. By augment- ing the resistance its heat was lowered, until it was no longer competent to produce the least ebullition. It was then with- drawn from the water, and employed as a source: the following are the results :— Taste XXII.—Source, platinum spiral at 100° C. Name of vapour. Deflection. Absorption. Bisulphide of carbon . . 5-7 7°08 Siocon = Wii. 140. 16°8 Precrimletnvie A... bo. |. |. 180 No reversal was here obtained. The temperature was then reduced so that the total heat fell from 81 units to 59 units; but not even in this case (when the temperature was considerably _ below that of boiling water) could the reversal be obtamed. The absorptions approach each other, but the iodide has still the ad- vantage of the chloroform. Taste XXIII.—Source, platinum spiral, heated under 100° C. Name of vapour. Deflection. Absorption. Bisulphide of carbon... 5:2 9°2 Siro TOO 17°3 Hodide of methyle “.*.* 108 18:2 It is not, therefore, temperature alone which determines the in- 516 ~~ Prof. Tyndall’s Contributions to Molecular Physics. version: the experiments prove that there is a greater synchro- nism between the vibrating periods of chloroform and lampblack than between those of chloroform and platinum raised to the temperature of the lampblack. It will be seen, however, that as the temperature of the platinum falls, the opacity of the chloro- form increases more quickly than that of the iodide: with an intensely white-hot spiral, as shown in Table XXI., the absorp- tion of chloroform is to that of the iodide as 100: 162, while, with the spiral heated to a temperature of 212° Fahr., the ratio of the absorptions isas 100: 105. § IX. Radiation from gas-flames through vapours.—Reversals of position. We have hitherto occupied ourselves with the radiation from heated solids: I will now pass on to the examimation of the radiation from flames. ‘The first experiments were made with a steady jet of gas issuing from a small circular burner, the flame being long and tapering. The top and bottom of the flame were excluded, ‘and its most brilliant portion was chosen as the source. The following results were obtained :— TasbLe XXIV.—Radiation of heat through Vapours. Source, a highly luminous jet of gas. White-hot Name of vapour. Deflection. Absorption. mer Bisulphide of carbon . . 8:9 9°38 2-9 @ilorotorm:,’ oi. se OD 12:0 5'6 Iodide of methyle . . . 15-4 16:5 he. Wodidesotiethiyie ofan) A 7a7 19°5 12°8 Genzlest: 2 eke » 200 22°0 16:5 Puy lene ogee tse iil fora 30°2 22°7 Hormic ethers 2. Fo sa OLD 34°6 25") pulpuureether af. ne Lae B0°7 ye eae Acetic ether” ot ss ie icone 38°7 27°2 Total Neat’. tse eo kts Ler nO 100:0 It is interesting to compare the heat emitted by the white-hot carbon with that emitted by the white-hot platinum; and to facilitate the comparison, I have placed beside the results in the last Table those recorded in Table XIII. The emission from the flame is thus proved to be far more powerfully absorbed than the emission from the spiral. Doubtless, however, the carbon, in reaching incandescence, passes through lower stages of tem- perature, and in those stages emits heat more in accord with the Prof. Tyndall’s Contributions to Molecular Physics. 517 vapours. It is also mixed with the vapour of water and carbonic acid, both of which contribute their quota to the total radiation. It is therefore probable that the greater accord between the periods of the flame and those of the vapours is due to the slower periods of the substances which are unavoidably mixed with the body to which the flame mainly owes its light. The next source of heat employed was the flame of a Bunsen’s burner, the temperature of which is known to be very high. The flame was of a pale-blue colour, and emitted a very feebl light. The following results were obtained :— Taste XX V.—Radiation of heat through Vapours. Source, pale-blue flame of Bunsen’s burner. From Table XXIV. Name of vapour. Deflection. Absorption. Y ; 4 Luminous jet of gas. Chloroform . . . 5:0 6:2 12:0 Bisulphide ofcarbon 9-0 Lk 9°38 Iodide of ethyle . 11:3 14:0 19°5 Beuvdle 3% 66 6 145 17:9 22:0 PCM fe.) 5p) 19°6 24°2 30°2 Sulphuric ether. . 25°8 31:9 B5°7 Formic ether . . 27:0 33°39 34:6 Acetic ether ibteuy, teed a 36°3 38:°7 aca wea. .-.. », 90°6 100:0 100:0 The total heat radiated from the flame of Bunsen’s burner is greatly less than that radiated when the incandescent carbon is present in the flame. The moment the air is permitted to mix with the luminous flame, the radiation falls so considerably that the diminution is at once detected, even by the hand or face brought near the flame. Comparing Tables XXIV. and XXV., we sce that the radiation from the Bunsen’s burner is, on the whole, less powerfully absorbed than that from the luminous gas jet. In some cases, as in that of formic ether, they come very close to each other; im the case of amylene and a few other substances they differ more markedly. But an extremely interesting case of reversal here shows itself. Bisulphide of carbon, instead of being first, stands decidedly below chloroform. With the lumi- nous jet, the absorption of bisulphide of carbon is to that of chloroform as 100 : 122, while with the flame of Bunsen’s burner the ratio is 100:56; the removal of the carbon from the flame more than doubles the relative transparency of the chloroform. The case is of too much interest to be passed over without veri- fication: here is the result obtained with a different total heat :— 518 Prof. Tyndall’s Contributions to Molecular Physies. Deflection. Absorption. CI GEDEORIN ic mvciuir-. a bs 16°5 8°4, Chioroform:. .,.4s .¢ sO 8°2 Bisulphide of carbon . 19:0 © 9°7 Bisulphide of carbon . 19°4 9:9 Total. heat. 14 sie Lowa oe 100°0 And again, with an intermediate total heat,— Deflection. Absorption. Chloroform . . . . 10:2 8°4, Chloroform > 2.36 sn #41050 8:4 Bisulphide of carbon . 12:0 9°8 Bisulphide of carbon . 11:8 OT Lotalaheat0/'3; ke), seit 1600 100-0 There is therefore no doubt that, while in the case of a platinum spiral at all temperatures, of a luminous gas-flame, and, more especially, in the case of lampblack heated to 212° Fahy. the absorption of chloroform exceeds that of bisulphide of carbon, for the flame of Bunsen’s burner the bisulphide is the more powerful absorber of the two. The absorptive energy of the chloroform, as shown in Table XX., is more than three times that of the bisulphide, while in Table XXV. the action of the bisulphide is nearly twice that of the chloroform. We have here, moreover, another instance of the reversal of formic and sulphuric ether. For the luminous jet the sulphuric ether is decidedly the more opake; for the flame of Bunsen’s burner it is excelled‘in opacity by the formic. a § X. Radiation from the flames of hydrogen and carbonic oxide through air and other media.—Influence of period with refer- ence to absorption. The main radiating bodies in the flame of a Bunsen’s burner are, no doubt, aqueous vapour and carbonic acid. Highly heated nitrogen is also present, which may produce a sensible effect: the unburnt gas, moreover, in proximity with the flame, and warmed by it, may contribute to the radiation, even before it unites with the atmospheric oxygen. But the main source of the radiation is, no doubt, the aqueous vapour and the carbonic acid. I wished to separate these two constituents, and to study them separately. The radiation of aqueous vapour could be ob- tained from a flame of pure hydrogen, while that of carbonic acid could be obtained from an ignited jet of carbonic oxide. Tome the radiation from the hydrogen-flame possessed a peculiar inter- est; for, notwithstanding the high temperature of such a flame, Prof. Tyndall’s Contributions to Molecular Physics. 519 I thought it likely that the accord between its periods of vibra- tion and those of the cool aqueous vapour of the atmosphere would still be such as to cause the atmospheric vapour to exert a special absorbent power upon the radiation. The following experiments test this surmise :— Taste XXVI.—Radiation through Atmospheric Air. Source, a hydrogen-flame. Deflection. Absorption. Deyn aks. 0 6) Dudcied air... oy 21°5 17°20 Worm heat... . 604: 100:0 Thus, in a polished tube 4 feet long, the aqueous vapour of our laboratory air absorbed 17 per cent. of the radiation from the hydrogen-flame. A platinum spiral, raised by electricity to a degree of incandescence not greater’ than that obtainable by plunging a wire into the hydrogen-flame, was used as a source of heat ; of its radiation, the undried air of the laboratory absorbed 5°8 per cent., or one-third of the quantity absorbed when the flame of hydrogen was employed. The plunging of a spiral of platinum wire into the flame reduces its temperature; but it at the same time introduces vibrations which are not in accord with those of aqueous vapour : the absorption by ordinary undried air of heat emitted by this composite source amounted to 8°6 per cent. On humid days the absorption of the rays emitted by a hy- drogen-flame exceeds even the above large figure. Employing the same experimental tube and a new burner, the experiments were repeated some days subsequently, with the following result :— TasLe XXVII.—Radiation through Air. Source, hydrogen- flame. Absorptjon. Dry air BOM 108 WY, Ps Wadried an? 2204" 203, The undried air here made use of embraced the carbonic acid of the atmosphere ; after the foregoing experiments, the air was conducted through a tube containing a solution of caustic pot- ash, in which the carbonic acid was intercepted, while the air charged itself with a little additional moisture. The absorption 520 Prof. Tyndall’s Contributions to Molecular Physics. then observed amounted to 20°3 per cent. of the entire radiation. The exact agreement of this with the last result is, of course, an accident; the additional humidity of the air derived from the solution of potash happened to compen- sate for the action of the carbonic acid withdrawn. The other component of the flame of Bunsen’s burner is ecar- bonic acid; and the radiation of this substance is immediately obtained from a flame of carbonic oxide. With the air of the laboratory the following results were obtained :— Taste XXVIII.—Radiation through Atmospheric Air. Source, carbonic-oxide flame (very small). Deflection. Absorption. oO Diy ait so eu ed tee 0 0 Undriedtir. (. 2 6 2 161 Ofthe heat emitted by carbonic acid, 16 per cent. was absorbed by the common air of the laboratory. After the air had been passed through sulphuric acid, the aqueous vapour being thus removed while the carbonic acid remained, the absorption was 13°8 per cent. An india-rubber bag was filled from the lungs; it contained therefore both the aqueous vapour and the carbonic acid of the breath. The air from the bag was conducted through a drying apparatus, the mixed air and carbonic acid being permitted to enter the experimental tube. The following results were obtained :— Taste XXIX.—Arr from the lungs containing CO?. Source, carbonic-oxide flame. Tension in inches. Deflection. Absorption. l iP 12-0 3 15:0 25°0 5 20°0 33'S © 30 30°8 50:0 . Thus the tube filled with dry air from the lungs intercepted 50 per cent. of the entire radiation from a carbonic-oxide flame. It is quite manifest that we have here a means of testing with sur- passing delicacy the amount of carbonic acid emitted under various circumstances by the act of expiration *. That pure carbonic acid is highly opake to the radiation from the carbonic-oxide flame, is forcibly evidenced by the results recorded in the following Table. * [See article by W. F. Barrett “On a Physical Analysis of the Human Breath,” at p. 108 of the present volume,—Eb., } Prof. Tyndall’s Contributions to Molecular Physics. 521 Taste XXX.—Radiation through dry Carbonic Acid. Source, carbonic-oxide flame. Tension in inches. Deflection. Absorption. 1-0 83°7 53-0 2°0 37°0 61-7 3°0 38°6 66:9 40 39°4 70:0 a0 40:0 72°3 10:0 41°4: 10°70 About four months subsequent to the performance of these experiments they were repeated, using asa source a much smaller flame of carbonic oxide. The absorptions were found somewhat less, but still very high. They follow in the next Table. Taste XXXI.—Radiation through dry Carbonic Acid. Source, small carbonic-oxide fame. Tension in inches. Defiection. Absorption. 1-0 173 48-0 2°0 20:0 55°5 3°0 21°7 60:3 40 22°8 65:1 5:0 24°0 68°6 10:0 26:0 74:3 For the rays emanating from the heated solids employed in all my former researches, carbonic acid proved to be one of the mest feeble absorbers; but here, when the waves sent into it emanate from molecules of its own substance, its absorbent energy is enormous. ‘The thirtieth of an atmosphere of the gas cuts off half the entire radiation; while at a tension of 4 inches, nearly 70 per cent. of the whole radiation is intercepted. The energy of olefiant gas, both as an absorbent and a radiant, is well known ; for the solid sources of heat just referred to, its power is incomparably greater than that of earbonic acid; but, for the radiation from the carbonic-oxide flame, the power of olefiant gas is feeble when compared with that of carbonic acid. This is proved by the experiments recorded in the following Table. Taste XXXII.—Radiation through dry Olefiant Gas. Source, carbonic-oxide flame. Tension in inches. Deflection. Absorption. 1 17-0 24-2 2 26:0 37°] 4, 33'0 49:1 Total heat . 47°3 100:0 Phil, Mag, 8, 4. No, 192, Suppl. Vol, 28. 2M 522 Prof. Tyndall’s Contributions to Molecular Physics, Four months subsequent to the performance of the above ex- periments, a second series were made with olefiant gas, and the following results obtained :— Taste XXXIII.—Radiation through dry Olefiant Gas. Source, small carbonic-oxide flame. Tension in inches. Deflection. Absorption. From Table XXXI. 1:0 114 23°2 48°0 20 17:0 3407 55°5 3°0 21°6 440 60°3 40 24°83 50°6 65°1 3°0 27:0 55°1 68°6 - 10:0 b2°1 65°5 74:3 Beside the absorption by olefiant gas, I have placed that by carbonic acid derived from Table XXXI. The superior power of the acid is most decided in the smaller tensions; at a tension of an inch it is twice that of the olefiant gas. The substances approach each other more closely as the quantity of gas aug- ments. Here, in fact, both of them approach perfect opacity ; and as they draw near to this common limit, their absorptions, as a matter of course, approximate. The temperature of a hydrogen-flame, as caleulated by Bun- sen, is 8259° C., while that of a carbonic-oxide flame is 8042° C. The foregoing experiments demonstrate that accord subsists between the oscillating periods of these sources and the periods of aqueous vapour and carbonic acid at a temperature of 15° C. The heat of the flame goes to augment the amplitude, and not to quicken the vibration. Sent through carbonic oxide, the radiation from the carbonic- oxide flame gave the following absorptions :— Tanie XXXIV.—Radiation through Carbonic Oxide. Souree, carbonic-oxide flame. Tension in inches. Deflection. } Absorption. 1 18-0 29-0 2 27:0 43°5 4. 34:0 56:4: 10 37°3 65°5 The absorptive energy is here high—greater, indeed, than that of olefiant gas; it falls considerably short, however, of that exhibited by carbonie acid. This result shows us that the main radiant in the flame is its product of combustion, and not the carbonic oxide heated prior to combustion. Prof. Tyndall’s Contributions to Molecular Physics. 528 Wishing to examine the radiation from a flame whose product of combustion is sulphurous acid, through sulphurous acid, I resorted to the flame of bisulphide of carbon. Here, however, we had carbonic acid mixed with the sulphurous acid of the flame. Of the heat radiated by this composite source, the absorption by an atmosphere of sulphurous acid amounted to 60 per cent. The gas was sent from its generating retort through drying- tubes of sulphuric acid into a glass experimental tube 2:8 feet long. The comparative shortness of the tube, and the mixed character of the radiation, rendered the absorption less than it would have been had a source of pure sulphurous acid and a tube as long as that used in the other experiments been employed. I subsequently caused the radiation from the carbonic-oxide flame to pass through a few of our vapours, with the followmg results :— | Taste XXX V.—Radiation through Vapours (tension 0:5 inch). Source, carbonic-oxide flame. Name of vapour. Deflection. | — Absorption. Bisulphide of carbon . 55 9°8 Chlsroform 3... 32. GO 10°7 Formic ether... . . 14°5 25°8 Sulphuric ether .- . . 18:0 32°1 atalheat <>» ., 40°0 100:0 The same vapours were employed to test the radiation from the hydrogen-flame, with the following results :— Tasie XXX VI.—Radiation through Vapours (tension 0°5 inch). Source, hydrogen-flame. _ Name of vapour. Deflection. Absorption. Bisulphide of carbon. 8:8 11-9 SMGrOTM og sia OS 13-4 Sulnnorc-ether.. ..,,. 02'0 42°2 Biocenter i), 4, is). 000 49°3 Por Weat <3. ee « ABD 100:0 We here find that, in the case of every one of the four vapours, the synchronism with hot aqueous vapour is greater than with hot carbonic aeid. The temperature of the hydrogen-flame is higher than that, of the carbonic oxide ; but the radiation from the more intense source is most copiously absorbed. It has been already proved that, for waves of slow period, formic ether is more absorbent than sulphuric ether; while for waves of rapid 2M 2 524 Prof. Tyndall’s Contributions to Molecular Physics. period, the sulphuric ether is the more powerful absorber. For the radiation from hot carbonic acid, the absorption of sulphuric ether, as shown in Table XXXYV., is between 6 and 7 per cent. in excess of that of formic ether; while for the radiation from hot aqueous vapour, the absorption by formic ether, as shown in Table XXXVI., is 7 per cent. in excess of that by sulphuric. That the periods of aqueous vapour, as compared with those of carbonic acid, are slow, may therefore be inferred from these experiments. The two following Tables illustrate the action of carbonic acid gas and olefiant gas respectively, on the radiation from a flame of hydrogen :-— Taste XXX VIJ.—Radiation through Carbonic Acid Gas. Source, hydrogen-flame. Tension ininches. Deflection. Absorption. 1 5°5 7°4 2 9°5 12°8 d. TdeO 149 30 19:0 20°7 Total heat. 48°5 100-:0 TaBLe XXXVIII.—Radiation through Olefiant Gas. Source, hydrogen-flame. Tension in inches. Deflection. Absorption. From Table XXXVII. 1 12:0 16:2 74: 2 18:0 24°3 12°8 4 24-0 32°4: 149 30 33°5 58°8 25°7 Total heat . 48°5 100:0 100:0 A comparison of the last two columns, one of which is trans- ferred from Table XXXVII., proves the absorption of the rays from a hydrogen-flame by olefiant gas to be about twice that of carbonic acid ; while, when the source was a carbonic-oxide flame, the absorption by carbonic acid at small tensions was more than twice that effected by olefiant gas. § XI. Radiation through liquids—Influence of period.—Conver- sion of long periods into short ones. Water at moderate thickness is a very transparent sub- stance; that is to say, the periods of its molecules are in discord with those of the visible spectrum. It is also highly transparent to the extra-violet rays ; so that we may safely infer Prof. Tyndall’s Contributions to Molecular Physics. 525 from the deportment of this substance its incompetence to enter into rapid molecular vibration. When, however, we once quit the visible spectrum for the rays beyond the red, the opacity of the substance begins to show itself: for such rays, indeed, its absorbent power is unequalled. The synchronism of the periods of the water-molecules with those of the extra-red waves is thus demonstrated. I have already proved that undried atmospheric air manifests an extracrdinary opacity for the radiation from a hydrogen-flame, and from this deportment I inferred the syn- chronism of the cold vapour of the air and the hot vapour of the flame. The vibrating-period of a molecule is, no doubt, determined by the elastic forces which separate it from other molecules, and it is worth inquiring how these forces are affected when a change so great as that of the passage of a vapour to a liquid occurs. The fact established im the earlier sections of this paper, that the order of absorption for liquids and their vapours is the same, renders it extremely probable that the period of vibration is not materially affected by the change from vapour to liquid; for,if changed, it would probably be changed in different degrees for the different liquids, and the order of absorption would be thereby disturbed*. The following Table, in which the deportment of our series of liquids towards the radiation from a hydrogen-flame is recorded, will throw additional hght upon this question :— Taste XXXIX.—Radiation through Liquids. Source, hydrogen-flame. Thickness of liquid layer 0-07 of an inch. Name of liquid. Absorption. Transmission. Bisulphide of carbon . . 27°'7 723 Chloroform) ~~ 6.~)o« va) AD8 50°7 Iodide of ethyle . . . 75°6 244, em ZB lee 6 iiss wil +) ol eouimaee 172 PeeDE es.) ie. of OAD 12°1 Sulphuric ether. . . . 92°6 7°4: Formicether . .. . 93°5 65 Weevelether.(. .-. « 939 61 Seereminnte Siac alc a) en L000 ‘0:0 Through a layer of water 9°21 millimetres thick, Mellom found a transmission of 11 per cent. of the heat of a Locatelli lamp. Here we employ a source of higher temperature, and a layer of water only one-fifth of the thickness used by Melloni, * The general agreement in point of colour between a liquid and its vapour favours the idea that the period, at all events in the great majority of cases, remains constan¢ when the state of aggregation is changed. 526 ~—- Prof. Tyndall’s Contributions to Molecular Physics. and still we find the whole of the heat intercepted*. A layer of water, 0°07 of an inch in thickness, is sensibly opake to the radiation from a hydrogen-flame. Hence we may infer the coin- cidence in period between cold water and aqueous vapour heated to a temperature of 3259° C.; and inasmuch as the period of the water-molecules has been proved to be extra-red, the period of the. vapour-molecules in the hydrogen-flame must be extra- red also. Another point of considerable imterest may here be adverted to. Professor Stokes has demonstrated that a change of period is possible to those rays which belong to the violet and extra- violet end of the spectrum, the change showing itself by a degradation of the refrangibility. That is to say, vibrations of a rapid period are absorbed, and the absorbing substance has become the source of vibrations of a longer period. Lfforts, I believe, have been made to obtain an analogous result at the red end of the spectrum, but hitherto without result ; and it has been considered improbable that a change of period can occur which should raise the refrangibility of the light or heat. Such a change, I believe, occurs when we plunge a platinum wire into a hydrogen-flame. The platinum is rendered white by the colli- sion of molecules whose periods of oscillation are incompetent to excite vision. There is in this common experiment an actual breaking up of the long periods into short ones—a true render- ing of unvisual periods visual. The change of refrangibility differs from that of Professor Stokes, firstly, in its being in the opposite direction—that is, from low to high; and secondly, in the circumstance that the platinum is heated by the collision of the: molecules of aqueous vapour, and before their heat has assumed the radiant form. But it cannot be doubted that the same effect would be produced by radiant heat of the same period, provided the motion of the ether could be raised to a sufficient intensity. The effect in principle is the same, whether we con- sider the platinum wire to be struck by a particle of aqueous vapour oscillating at a certaim rate, or by a particle of ether oscillating at the same rate. -And thus, I imagine, by a chain of rigid reasoning, we arrive at the conclusion that a degree of incandescence, equal to that of: the sun itself, might be produced by the impact of waves, of themselves incompetent to excite vision F. * From the opacity of water to the radiation from aqueous vapour, we may infer the opacity of aqueous vapour to the radiation from water, and hence conclude that the very act of nocturnal refrigeration which causes the condensation of water on the earth’s surface gives to terrestrial radia- tion that particular character which renders it most liable to be intercepted by the aqueous vapour of the air. + Some time after this was written I learned that Dr. Akin had _previ- Prof. Tyndall’s Contributions to Molecular Physics, 527 The change of quality produced in the radiation by the intro- duction of a platinum spiral into a hydrogen-flame is illustrated by a series of experiments, executed for me by my assistant, Mr. Barrett, and inserted subsequently to the presentation of this memoir. TaBLe XXXIX. a.—Radiation through Liquids. Sources: 1. Hydrogen-flame ; 2. Hydrogen-flame and platinum spiral. Transmission. ~ a Thiekness of liquid Thickness of liquid 0:04 inch.- 0:07 inch. Wade of liquid Flame Flame and Fiame Flame and % ; only. spiral. only. spiral. Bisulphide of carbon . 77:7 87:2 10:4¢.... 86°0 Ohlorsierm «<=. : . 540 72°8 50:7 2. .69-0 Iodide of methyle . . 31°6 42°; 26:2 36°2 Iodide of ethyle . . . 30°3 36°8 242 32°6 Bemggle 2. sss» 2401 32°6 179 288 iyi s 2 ss Ce (14D 25°8 12°4 = 243 Sulphuric ether . . . 13:1 22°6 Sl... 22°0 meemeenicr - is: . LO] 18°3 GG +88" Peer ts OT 14°7 aS = 1233 ee ee een be 75 20 6:4: Here the introduction of the platinum spiral changed the periods of the flame into others more in discord with the periods of the liquid-molecules, and hence the more copious transmission when the spiral was employed. It will be seen that a transmis- sion of 2 per cent. is here obtained through a layer of water 0°07 of an inch in thickness. Another series of experiments, also executed by my assistant, gave the following results of the radiation of a hydrogen-flame through layers of water of five different thicknesses :— Radiation through Water. Source, hydrogen-flame. Thickness of liquid. 0S SSS 0:0 0:04 0:07 0°14 0:27 inch. inch. ineh. inebh. inch. imnennssion per i008 6 6S 28 °° PT OS OO Wishing to compare the radiation from a flame of ordinary ously inferred, from the paucity of luminous and extra-violet rays in the hydrogen-flame, that its periods must be extra-red. And he deduced from this that the heating of a platimum wire in a hydrogen-flame must consist of a change of period. A very interesting communication from Dr. Akin en this and kindred subjects will be found im the ‘ Reader’ for the 26th of September 1863.—April 5th, 1864. 528 — Prof. Tyndall’s Contribuiions to Molecular Physics. coal-gas with that of our hydrogen-flame, I reduced the former to the dimensions of the latter. The fenwe thus diminished had a blue base and bright top, and the whole of it was permitted to radiate through our series of liquids... The following results were obtained :— Taste XL.—Radiation through Liquids. Source, small gas- flame. Thickness of liquid layer 0:07 of an inch. ath From _ Name of liquid. Dede tions: Absorption. Table XXXIX. Chloroform . . al ONL, 39°83 49°3 Bisulphide of Gabon 21136:0 How OT ee Podide offethyle, “i 4157 72°3 75'6 BPenzole, eS alee le ee oe 79°4: 82°3 Aaniy lee gyn. en 28) 86°] 87°9 Sulphuric ether . . 466 93°3 92°6 Formic ether?) ) 4 2 940:0 93°3 93°5 Micohol 3s. oice SO AOS 94°} Acetic ether. . . . 469 94°4: 93°9 Wialeriete ice inn tein eee 97°1 100:0 Potalaheat: Woot he eee) 100:0 I have placed the results obtained with the hydrogen-flame in the third column of figures. For some of the liquids it will be observed that the absorption of the heat issuing from the small gas-flame is nearly the same as that of the heat issuing from the flame of hydrogen. A very remarkable difference, however, shows itself in the deportment of bisulphide of carbon as com- pared with that of chloroform. For the small gas-flame chloro- form is the most transparent body in the list; it is markedly more transparent than the bisulphide of carbon, while for the hydrogen-flame the bisulphide greatly excels the chloroform in transparency. The large luminous gas-flame previously experi- mented with differs also from the small one here employed. With the large flame, the absorption by the bisulphide 1s to that by the chloroform as 100 : 121, while with the small flame the absorptions of the same two sub- stances stand to each other in the ratio of 100 : 76. Numerous experiments were subsequently made, with a view of testing this result, but in all cases the bisulphide was found more opake than the chloroform to the radiation of the small gas-flame. The same result was obtained when a very small oil- flame was employed; and it came out im a very decided manner Prof. Tyndall’s Contributions to Molecular Physics. 529 when the source of heat was a flame of bisulphide of carbon. J¢ was found moreover that, whenever two liquids underwent a change of position of this kind, the vapours of the liquids underwent a similar change; in its finest gradations, the deportment of the liquid was imitated by that of its vapour. § XII. Ezplanation of certain results of Melloni and. M. Knoblauch. And here we find ourselves in a position te offer solutions of various facts which have hitherto stood as enigmas in re- searches upon radiant heat. It was for a time generally sup- posed that the power of heat to penetrate diathermic substances augmented as the temperature of the source of heat became more elevated. Knoblauch contended against this notion, show- ing that the heat emitted by a platinum wire plunged into an alcohol flame was less absorbed by certain diathermic screens than the heat of the flame itself, and justly arguing that the temperature of the spiral could not be higher than that of the body from which it derived its heat. 55 in the course of an experiment : as the variation takes place uniformly, the value of e introduced * Comptes Rendus, vol. lix. p. 521 (September 19, 1864), Tt Comptes Rendus, Sept. 14, 1863. [Phil. Mag. 8. 4. vol. xxvi. p. 522.] 552 M. F. M. Raoult’s Researches on the into the formule is that taken at the middle of the time. d is measured by the method of opposition; f by the method of alter- nate circuits*, after a sufficient number of elements have been added to the battery to make the intermittent current transmitted by the commutator equal to the primitive continuous current 7. An element 2, without resistance, capable of producing in the voltameter the same current 7 as that of the battery P, would give, in the sine-compass with long wire B, a current of the inten- sity e—f (for the demonstration see the complete memoir). The electromotive force of the element z, compared with that ofa Daniell’s element, is therefore = Now since the quantity of voltaic heat evolved in the entire circuit, for the same fraction 2 316 tive force, it follows that the heat evolved in the voltameter, by reason of its resistance, is of electricity transmitted, is proportional to the electromo- ée= = °=1 93900 x ao a Such is the quantity of heat which would be evolved during the experiment in a metallic conductor of equal resistance with the voltameter. This quantity ¢, contrary to what has been hitherto asserted, is always less than T. The difference T—¢ represents, for the fraction of an equivalent of electricity transmitted, the ae Be 31°6 heat furnished to the calorimeter by a local action. The local heat K, evolved in the voltameter for 1 equivalent of electricity transmitted, or of substance decomposed, is therefore 31-6 (T—?) rae or K=Tx "°° ego000, 7 aes The inverse electromotive force f of the voltameter diminishes, by fx 239000 thermal units, the heat which the current 7 pro- duces in the circuit for 1 equivalent of electricity transmitted. (Comptes Rendus, 14th September, 1863 [Phil. Mag. loc. cit.]) The sum X of the calorific effects, positive or negative, pro- * The method of opposition and that of alternate circuits, which were devised by myself, were communicated to the Académie des Sciences on the 2lst of February, 1859, and are described in the Annales de Chimie et de Physique, 4th series, vol. ii. pp. 321 and 326, Thermal Phenomena of Voliameters. 553 duced by the voltameter during the decomposition of 1 equiva- lent of substance is therefore —X= —f x 239000 -+K, or X= 5 x 239000—T x aS: . (9) My research is divided into two parts. In the first part I give an experimental demonstration of the formule («#), (@), and (y), and I establish the laws, hitherto misconceived, which regulate the development of heat in volta- meters. The experiments related to sulphate of copper and acidulated water; they led to the following conclusion :— “A voltameter introduced into the circuit of a battery weakens the electromotive force, and thus destroys in the complete circuit a quantity of heat which is always greater than what is re- quired for the decomposition effected. The excess varies accord- ing to circumstances ; but in every case a secondary action takes place at the electrodes, whereby a quantity of heat is imparted to the voltameter equal to the excess of heat destroyed. And, finally, the sum of the various calorific effects of the voltameter is equal to the heat absorbed by the decomposition which goes on within it.” This effect can be explained if we suppose that the substances first formed at the electrodes, and which cause the polarization, are unstable compounds which, like binoxide of hydrogen, evolve heat by their decomposition. In the second part I have determined, according to equation (y), the quantities of heat, X, absorbed by the decomposition of 1 equivalent of sulphate of copper, of water, of cupric chloride, and of hydrochloric acid. In these experiments it is essential to avoid the local recom- bination of the gases in the voltameter. To effect this, the posi- tive electrode is placed inside a small closed pipe-bowl, luted with wax to the end of a thin glass tube of equal diameter, whereby the oxygen or chlorine liberated is conducted out of the apparatus. For the electrolysis of chlorides, a rod of retort-carbon, dip- ping into hydrochloric acid saturated with chlorine, is used as the positive pole. The following Table gives the mean of the results obtained, compared with the calorific equivalents of the same substances in a state of solution, determined by Favre and Silbermann and by myself (Comptes Rendus, July 4, 1864). Phil. Mag. 8. 4. No. 192. Suppl. Vol. 28. 20 554 Dr. C. K. Akin on Ray-Transmutation. . Heat evolved by combina- tion. Heat X absorbed by decompo- sition. F d soul Siiheranani: BV RUG co rese ase as. cc co cem ener ae —33803 | ...eee 34462 Sulphate of copper ............ —29895 | ....:. 29605 Hydrochloric acid (dilute) ...| —33859 35200 40192 Cupric chlonde 3.scc.-e5-se-eeees | — 28371 29500 34500 Observations. Water.—The number — 88803 is the mean of the results, agreeing within 3, obtained with water containing sulphuric acid or soda. | Sulphate of Copper.—The sulphate of copper employed was acidulated beforehand with th of sulphuric acid, in order that its conductivity might not alter during the experiment. Hydrochloric Acid.—The acid employed was of such a strength that it decomposed exactly into hydrogen and chlorine, but nevertheless evolved no heat when mixed with water. The concentrated acid gives a lower number; but if the heat which this acid evolves by combination with excess of water is added to the result, it makes up very nearly the mean value 33859. Cupric Chloride.—As this compound is converted into sub- chloride of copper in contact with the negative pole, it could not be employed. The difficulty was got over by putting acidu- lated sulphate of copper on the side of the negative electrode, and hydrochloric acid saturated with chlorine on the side of the positive electrode. According to the law of moduli, the quan- tity of heat (28871) destroyed by this voltameter ought to be that which corresponds to the decomposition of chloride of cop- per, CuCl. LXVI. Note on Ray-Transmutation. By Dr. C. K. Axin.* N a communication made by Prof. Tyndall to the (last) November Number of the Philosophical Magazine, entitled “ On Luminous and Obscure Radiation,” the following sentences occur :—“ Dr. Akin inferred from the paucity of luminous rays evident to the eye, and a like paucity of extra-violet rays, as proved by the experiments of Dr. Miller, that the radiation from a flame of hydrogen must be mainly extra-red ; and he con- cluded from this that the glowing of a platinum wire in a hy- drogen-flame, as also the brightness of the Drummond light in * Communicated by the Author. Dr. C. K. Akin on Ray-Transmutation. 555 the oxyhydrogen-flame, was produced by a change in the period of vibration. By a different mode of reasoning I arrived at the same conclusion myself, and published the conclusion subse- quently.”” The reference appended to the last sentence is to “ Phil. Trans. vol. cliv. p. 327.” The following passage is taken from a paper read before the Royal Society by Prof. Tyndall on March 17, 1864, and will be found in the place indicated, at p. 360 :— “ Professor Stokes has demonstrated that a change of period is possible to those rays which belong to the violet and extra-violet end of the spectrum, the change showing itself by a degradation of the refrangibility. That is to say, vibrations of a rapid period are ab- sorbed, and the absorbing substance has become the source of vibra- tions of a longer period. Efforts, I believe, have been made to obtain an analogous result at the red end of the spectrum, but hitherto without result; and it has been considered improbable that a change of period can occur which should raise the refrangibility of the light or heat. Such a change, I believe, occurs when we plunge a plati- num wire into a hydrogen-flame. The platinum is rendered white by the collision of molecules whose periods of oscillation are incom- petent to excite vision. ‘There is in this common experiment an actual breaking up of the long periods into short ones—a true ren- dering of unvisual periods visual. The change of refrangibility dif- fers from that of Professor Stokes, firstly, in its being in the oppo- site direction—that is, from low to high; and secondly, in the cir- cumstance that the platinum is heated by the collision of the mole- cules of aqueous vapour, and before their heat has assumed the radiant form. But it cannot be doubted that the same effect would be produced by radiant heat of the same period, provided the motion of the ether could be raised to a sufficient intensity. The effect in principle is the same, whether we consider the platinum wire to be struck by a particle of aqueous vapour oscillating at a certain rate, or by a particle of zther oscillating at the same rate. And thus, I imagine, by a chain of rigid reasoning, we arrive at the conclusion that a degree of incandescence, equal to that of the sun itself, might be produced by the impact of waves, of themselves incompetent to excite vision” *, 1. The important parts of the above passage are the two couples of sentences, the one beginning with the words ‘‘ The platinum is rendered white,” and concluding with “ unvisual periods visual ; ”” and the other beginning with the words ‘‘ But it cannot be doubted,” and concluding with “at the same rate.” The first two sentences in this “chain of reasoning” are “ different ” * To this passage the following footnote is appended :—“ Some time after this was written I learned that Dr. Akin had previously inferred, from the paucity of luminous and extra-violet rays m the hydrogen-flame, that its periods must be extra-red. And he deduced from this that the heating of a platinum wire in a hydrogen-flame must consist of a change of period. A... communication from Dr. Akin on this and kindred subjects will be found im the ‘ Reader’ for the 26th 5 A igaaeth 1863.—April 5, 1864, 2 556 Dr. C. K. Akin on Ray-Transmutation. from the corresponding parts of my own reasonings, in the same sense as two separate links of achain are different from the same links when held together by a third, connecting link. Prof. Tyndall states that the platinum is rendered “ white” by oscil- lations which are invisible; and he hence concludes at once that there is a “breaking up of long periods into short ones.” This, however, is simply a non-sequitur. I founded my own conclusions concerning the origin of lime-light, &e., upon the evident deficiency of the oxyhydrogen-flame in Newtonie or luminous rays, and upon its probable poverty in Ritteric or so- called chemical rays, as compared with lime-light. And what I had thus at first but conjectured, regarding the Ritteric rays, was soon after corroborated by Prof. W. A. Miller’s experiments on the comparative photographie effects of the oxyhydrogen-flame in its pure state, aud of lime-light produced by the oxyhy- drogen jet*. . 2. Before adverting to the second, principal part of Professor Tyndall’s argument, a word or two may be apposite regarding his intermediate statements. The change of refrangibility which takes place in the oxyhydrogen-flame by the introduction of lime, or in the simple hydrogen-flame by the introduction of platinum, according to Prof. Tyndall, differs from that taking place in fluorescence “in its being in the opposite direction.” This, as shown, Prof. Tyndall’s reasoning does not prove. He states also that the platinum is “ heated by the collision of the molecules of aqueous vapour, and before their heat has assumed the radiant form.” I expressed the same idea by saying that the act of transmutation, in the case of lime-hght, took place “in statu nascenti, as it were,” of the rayst. 3. The concluding part of Prof. Tyndall’s induction affirms that “the effect in principle is the same, whether we consider the platinum wire to be struck by a particle of aqueous vapour oscillating at a certain rate, or by a particle of ether oscillating at the same rate.” In our present ignorance concerning the mode in which material particles act upon each other, or of the real constitution of ether, an assertion like the above will scarcely be considered as contributing to render ‘a chain of reasoning ”” “rigid.” In my own case, I reasoned concerning this matter as follows} :— Every kind of radiation possesses, with respect to any given substance, a certain heating power, which depends (1) on the amplitude of the given ray; (2) on the absorptive power of the given substance for the given ray ; and (3) in some unknown manner on the length of undulation of the given radia- tion. Any kind of radiation may, hence, be competent to raise * Report of the British Association, 1863, p. 95. t+ Ibid. p. 101. t See ‘Reader,’ September 26, 1863, p. 349. col. 2. Dr. C. K. Akin on Ray-Transmutation. 557 any substance whatever to any required temperature, by a suit- able adjustment of the element of amplitude alone— provided the substance considered be not absolutely pervious to, or an abso- lute reflector of, the given radiation.” Now, since metals do absorb Herschellic rays, after some preliminary considerations it was concluded “ that incandescence, or an emission of Newtonic rays, which, as proved, might be engendered even by Ritteric rays, will be still more easy to produce by means of Herschellic rays, to which, for some reason or other, a greater heating power is universally acknowledged to belong.” In this manner, it was shown as at least highly probable (and no induction can be ab- solutely certain) that the effect which in the case of lime-light is produced zn statu nascenti of the rays, might ev entually be produced also by rays incident upon lime or platinum after ema- nation from a source placed at a distance. 4. It will be seen from the above quotations, to what extent, and in what sense, Prof. Tyndall’s “reasoning” was “ dif- ferent”? from my own. But I will venture to make yet one further remark, of more general application. The British Association is one of the foremost scientific bodies in the United - Kingdom; and it 1s well known that, soon after its annual meetings are over, an account of its proceedings, authentic for the most part, is published in the ‘ Atheneum’ newspaper. Clearly it is the duty of scientific persons to consult the ‘Athenzeum’ during such portion of the year, in the same way as it is their duty to consult the Philosophical Magazine all the year round. Now in No. 1872 of the ‘Atheneum,’ p. 337, column 3 (Sept. 12, 1863), the following was published :— “The author conceived that the action of carbon and lime ren- dering the strongest heat of burning hydrogen luminous, were instances of the Herschelian rays being raised to the Newtonian ; and as Prof. Stokes had termed the other influence ‘ fluorescence,’ Dr. Akin proposed to term this ‘ caleescence,’ from the power of lime to turn heat into powerful illumination 3k, These sentences are taken from an abstract of the first of the two papers read by me before the Mathematical and Physical Section of the British Association at Newcastle, but for which I am not responsible. It would be superfluous to point out here its inaccuracies ; but the explanation of lime-light proposed by me is but too transparent, and in fact twice repeated, in the passage I have quoted. Now I will allow, for argument’s sake, that the abstract referred to had escaped Prof. Tyndall’s notice. In January 1864 an article appeared in the ‘Saturday Review,’ * The term “calcescence’”’ was actually suggested to me by one of the Secretaries of the Section of the British Association before which the paper referred to was read at Newcastle.—C. K. A. 558 Dr. C. K. Akin on Rays Transmutation, giving the outlines of a discourse delivered by me at Cambridge on the subject of “Calcescence.” In that article only one of the three experiments suggested by me was mentioned ; and the explanation of lime-light, also, was not explicitly referred to ; but, on the other hand, it was stated that the matter had been more fully treated in papers read at the Meeting of the British Association at Newcastle. Surely any one, like Prof. Tyndall, feeling an interest in the subject, after reading the above- mentioned article (and which is actually adverted to, though not distinctly, in the passage quoted before from the Philo- sophical Transactions), ought to have referred, under such cir- cumstances, to the ‘Atheneum’ for 18638, to see whether there were to be found in it further particulars concerning this subject. Perhaps, the ‘ Reader ’ having become more extensively known by that time, the abstract published in its columns on Sept. 26, 1863, would have likewise fallen then into Professor Tyndall’s hands. In my own case, and regarding the matter now in hand, | searched the back volumes of every sort of accessible periodicals, and other works which might possibly bear on it, in order to discover whether I had been anticipated, perhaps by some author whose writings are now forgotten. Such a proceeding (in which I have but followed the example of Sir H. Davy and other philosophers too conscientious and rich in original ideas of their own to wish to appropriate those of others) I believe all the more necessary, as it frequently occurs that persons read about things which they afterwards forget having read of, and then fancy to be the original products of their own minds. Thus I should not be at all astonished if Prof. Tyn- dall, in September 1863, had read the abstract quoted from the ‘Atheneum,’ but, from shortness of memory, by January or March 1864 had forgotten all about it, so far at least as the mere fact of reading goes*. A search for precedents, if it will not always revive recollection, would at least prevent repetitions in such cases. But sufficient stress, I venture to think, cannot be laid on the necessity that scientific persons should not neglect any means which they have at command, in order to become acquainted with the current progress, not less than with the past advances, in science. It may be allowable for poets to ignore their con- temporaries or predecessors, in order to preserve their own origi- nality of thought, whether in form or in substance. In the case of discoverers, the public is interested to learn, not what they would be capable of doing if nobody else were or had been in the * Upon the whole, I cannot help thinking that the passage quoted above from the Philosophical Transactions reads more like an imperfect remi- niscence, supplemented by conversation and discussion (see the ‘ Reader,’ no. 67. p- 46]), than anything else. 7 Dr. C. K. Akin on Ray-Transmutation. 559 field, but what they are capable of doing that is new. It may be difficult to decide which habit is of more importance—to study the literature of the past, or to attend to the publications of the pre- sent day. Much waste of thought would be prevented by either ; but the latter proceeding has the additional advantage of pre- venting the necessity of such explanations as those preceding, extorted by the natural obligations of self-defence and the defence of right*. 5. Prof. Tyndall states (Phil. Mag. S. 4. vol. xxvii. p. 83388):— “The rendering of metals incandescent by obscure rays has not yet been accomplished. This is a question on which Dr. Akin has been engaged for some years, and it is not my intention to publish anything relating to it until the very promising arrange- ments which he has devised have had a sufficient trial” +. Regard- ing this statement, I think it useful to publish the substance of a letter lately addressed by me to the President of the British * Merely as an illustration of what has been stated above regarding for- getfulness, I shall mention the following instance. In the paper commented on in this Note, Prof. Tyndall says, amongst other things (p. 332) :—‘‘ In solid metals augmented temperature intro- duces waves of shorter periods into the radiation. It may be asked, ‘What becomes of the long obscure periods when we heighten the tem- perature? Are they broken up or changed into shorter ones, or do they _ maintain themselves side by side with the new vibrations?’ The question is worth an experimental answer.’ Now that question had been practically answered by Prof. Draper, as long ago as 1847. He said (Phil. Mag. S. 3. vol. xxx. p. 390 :—“ It is to be remarked that, while the more refrangible end [of the spectrum] undergoes a great expansion, the other extremity exhibits a corresponding thougha less change... . arising from the in- creased brilliancy of the light . . . [as the temperature rises].”” No doubt, Prof. Tyndall has read the paper from which these latter passages are taken, and which has generally been considered (and more especially so by Melloni) as of great importance. But Prof. Tyndall has evidently forgotten the fact, or else he would certainly have mentioned it; and yet it would be impossible for him to assert that his own query regarding the invisible rays would have been suggested to him had he not previously read the above statement concerning the visible rays. Ina similar manner, it would not be difficult to trace back what Prof. Tyndall says concerning the light and heat of a candle (/. ¢. p. 339) to what, it is at least likely, was its original source. + I must be allowed to express here a doubt whether Sir H. Davy, for instance, or any other predecessor of Prof. Tyndall at the Royal Institu- tion, having read in a public print that two persons were engaged in making researches upon a certain subject with the aid and sanction of the British Association, would have chosen ‘‘ that very subject” “for attack’ some little time after. Nor do I believe that Davy or Young, having publicly pledged themselves not to “publish” anything relating to the subject till a certain contingency, would have meanwhile proceeded with it pri- vately ; at all events they would not, as soon as they had obtained what might turn out to be the desired result, have rushed off to repeat (and thus, to all intents, publish) the experiment before their ‘‘ colleague ’”—the sheets in which that pledge was published being then scarcely dry, and the con- tingency referred to as yet unaccomplished. 560 Dr. C. K. Akin on Ray-Transmutation. Association, and which was as follows:—‘‘ Some time ago, I received a letter from the Assistant General Secretary of the British Association, in which my attention was requested to a Resolution, which was adopted by the General Committee at the last Meeting of the Association, and to the effect, ‘That Prof. Griffith and Dr. Akin be requested to continue their Report on the Transmutation of Spectral Rays.? In answer to this communication, I now beg leave to state that, after the expe- rience of the last two years, and more especially of last summer, I feel it would be a hopeless undertaking for me to continue, at Oxford, the experiments begun there. Moreover, I am not sure whether, after the end of the present year, I shall be able to give my attention any longer to scientific researches.” Thus, as far as I am concerned, the trial of the “arrangements devised by” me, and of the apparatus constructed for the experiments begun at Oxford, is at an end. Such being the case, I have no doubt that, with the means at his command and his experimental proficiency, Prof. Tyndall will now realize and “ publish” a dis- covery which I have assigned the methods for accomplishing, and which I should have probably effected myself, I may say, years ago, had I been seconded asI had hoped, either by per- sons or by circumstances. Astronomers have placed the merit of the mathematicians who first conjectured the existence of Neptune above that of the practical observers who actually dis- covered that planet. In my own case, I have made considerable sacrifices of time, and even of feeling, in order to prove by ex- periment what I had deduced originally from logical reasonings. Being now practically shut out from pursuing the subject any further, I shall leave it for physicists to decide whatever merit may belong to the originator of the research, as compared with the merit of him, whoever it may be, who, more fortunate, shall bring the research to a satisfactory close*. London, November 1864. * Prof. Tyndall’s experiments on rays transmitted by iodme dissolved in bisulphide of carbon, and reported in the November Number of the Philoso- phical Magazine, although they may ultimately prove to be correct, are evidently inconclusive when made in the manner reported—that is, appa- rently,in daylight. I have also observed that, in looking through a prism of such iodine solution, at certain thicknesses, a double image of objects appears—the one violet, the other red. Now, since bisulphide of carben is about equally powerful as an absorbent both of Ritteric or chemical and of Herschellic or caloric rays, it remains to be proved whether the Ritteric rays do not cling, as it were, in transmission to the violet rays, in a similar manner to that in which the Herschellic rays adhere to the red rays—the penetrative power of the invisible rays exceeding in both cases that of the corresponding visible rays. a LXVII. Notices respecting New Books. The Astronomical Observer. A Handbook to the Observatory and the common Telescope. By W.A. Darsy, M.A.,F.R.A.S. London: R. Hardwicke. 1864. > book contains in alphabetical order the constellations visible to an observer in lat. 50° N. Under each head the constellations are first briefly described, the nebulz within its limits are next given, then the star-clusters, and lastly the double stars. The right ascen- sion and declination of each object is given and the magnitudes of its components; directions are added for finding it with a common telescope. In many cases a brief description of the object is included : e. g., in the constellation Cygnus, under the head of ‘‘ Double Stars,” «8 6.—19h 25m 17s., N. 27°40'42". a3, topaz-yellow; 67, sap- phire-blue ; dist. 34-4. One of the finest of the double stars, the colours in brilliant contrast; on the Swan’s bill, in the base of the cross of Cygnus. Pointed at by a line from Vega carried 1° f. y Lyrae, and rather less than as faragain.”’ ‘The work will probably be useful to the persons for whom it is designed—amateurs who do not possess an equatorially-mounted telescope. Prefixed to the book is an Introduction not easy to describe. We should guess that Mr. Darby first wrote the catalogue, and then by way of introduction jotted down without order or method anything bearing on the subject just as it occurred to him. Accordingly some of the points mentioned are very pertinent, e. g. the description of Sir J. Herschel’s mode of observing and registering double stars, the tables of test objects, &c. Other parts are quite the reverse. The sketch of the history of astronomy is meagre and inaccurate. Mr. Darby appears to believe the assertion of Josephus, that ‘‘ Abraham was a most intense observer of the stars, and the first to bring astro- nomy from Chaldea into Egypt.” Shortly after, he informs his rea- ders that ‘‘ to Egypt, the oldest of nations, belongs the honour of producing the most eminent astronomers of ancient times. Pytha- goras, Euclid, Archimedes, Eratosthenes, Ptolemy, and Hipparchus were all of the Alexandrian school.” Now this is really too bad. Mr. Darby had no occasion to go into the history of his subject; but as hechose to do so he was bound to be accurate in his statements. Surely it is well enough known that the Alexandrian Greeks were not much more Egyptians than Englishmen living in Calcutta are Hindoos. Many of the most conspicuous of them were not so much as born in Egypt; e. g., Hipparchus was of Nice in Bithynia. Then what are we to say to Archimedes, whose name and fame are so indis- solubly bound up with Syracuse? or to Pythagoras, of whom at all events we know this, that he lived some few hundred years before the Alexandrian school was founded? | 562 ] LXVIII. Proceedings of Learned Societies. GEOLOGICAL SOCIETY. [Continued from p. 324. ] eee 9, 1864.—W. J. Hamilton, Esq., President, in the Chair. . “Notes on the Geology of Jamaica; with Descriptions of new A cctes of Cretaceous, Eocene, and Miocene Corals.”’ By P. Martin Duncan, M.B., Sec. G.S., and G. P. Wall, Esq., F.G.S. The authors first referred to the Miocene age of the Corals that have hitherto been described from the West Indies, and then stated that in this paper conclusive evidence was brought forward, for the first time, of the existence of an Eocene formation in Jamaica. ‘hey next noticed successively the lithological characters of the different members of the Jamaican fossiliferous rocks, and then de- scribed two new species of Corals from the Lower Cretaceous beds, and six from the Miocene, besides giving notices of additional known forms from all the strata; and the conclusion was drawn, that the facies of these Cretaceous Corals was suggestive of a close wlliance having existed between this fauna and that of Gosau in the Eastern Alps. The question of the existence of Lower Cretaceous strata in other West Indian islands having been discussed, attention was drawn to the character of the Eocene Corals, as being con- firmatory of Mr. Barrett’s views on the existence of that forfiatida in the island, and the paper was concluded by some additional re- marks on the Miocene beds, and their probable correlation with those of Trinidad, Antigua, &c. 2. «On the Correlation of the Irish Cretaceous Strata.” By Ralph Tate, Esq., F.G.S. : The non-existence in Ireland of the formations between the Lower Lias and the Upper Greensand having been stated, Mr. Tate first showed that the Cretaceous formations occurring near Belfast are referable to the so-called Upper Greensand (Hibernian Greensand of the author) and to the Upper Chalk, the latter con- sisting chiefly of a “‘ White Limestone ” with flints, and containing species known to occur in the Upper Chalk of Norwich and Meudon, ‘with others aliied to Maestricht forms. ‘The basement-beds, form- ing lithologically a passage to the Hibernian Greensand, are (1) chloritic limestone with Sponge-remains belonging to about thirty species, and (2) a calcareo-chloritic sandstone with three species of Echinoderms, the dominant form being Ananchytes gibba. ‘These passage-beds are only locally developed, and when they are absent the junction of the Greensand and the White Limestone is very abrupt. The Hibernian Greensand was considered by Mr. Tate to represent the Upper Greensand, the Chalk-marl, and the lower part of the Lower Chalk of England, and to be the miniature counter- part of D’Orbigny’s Etage Cenomanien. It nowhere exceeds 55 feet in thickness; but it nevertheless contains the following beds :— (1) Chloritic sands and sandstones of Colin Glen, or the Zone of Ezogyra columba; (2) Chloritic sandstones of Woodburn, or the Zone of Inoceramus Crispi ?; (8) Yellow-sandstones and Marls with Chert, or the Zone of Ostrea carinata ; and (4) Glauconitic sands, or the Zone of Ewogyra conica. [ 563 ] LXIX. Intelligence and Miscellaneous Articles. ’ VERIFICATION OF THE LAW OF ELECTROLYSIS WHEN EXTERNAL WORK IS PERFORMED BY THE GALVANIC CURRENT. BY M. J. L. SORET. hs order to explain, conformably with the mechanical theory of heat, the production by an electric current of effects external to the circuit which it traverses, such, for instance, as the performance of mechanical work or the generation of induced currents, recourse has been had to an hypothesis proposed by Helmholtz, Scoresby and Joule, Clausius, and other physicists. According to this hypothesis, the law of electrolytic action is regarded as still holding good for this special case. In order to supplement previous investigations, I un- dertook the verification of this point by comparing the amount of chemical action with the mean intensities of currents, usually dis- continuous, by which external work was performed. In order to produce powerful external effects, I have employed for the most part a Ruhmkorff’s coil, but I found it needful in most cases to substitute a contact-breaker formed of a toothed wheel and platinum spring for the ordinary contact-breaker of this apparatus. By this means | obtained a much more rapid succession of currents, and at the same time greater stability in the needle of the sine-com- pass by which the mean intensity of the current was measured. After a great number of experiments performed for the purpose of assuring myself of the exactitude of the method I was employing, I arrived at the following results, which confirm the law of electrolysis for these conditions. In a circuit of great resistance, containing a Daniell’s battery, the sine-compass, a voltameter charged with sulphate of copper, and the inducing coil of the Ruhmkorff’s apparatus, the weight of copper deposited in the voltameter was found to be always proportional to the mean intensity of the current, whether the current was conti- nuous (that is to say, when the contact-breaker of the Ruhmkorff’s apparatus was excluded from the circuit, in which case no external action took place) or whether it was discontinuous (that is to say, when the contact-breaker was put in action, in which case an ex- ternal action was set up, though this was certainly of small import- ance relatively to the total work performed by the current). A similar result was obtained with a circuit of small resistance, consisting only of the Ruhmkorff’s apparatus, the compass, and a single Daniell’s cell in which a plate of platinum was substituted for the copper. The chemical action was measured by the quantity of copper deposited upon the platinum plate. With this disposition of the apparatus, the proportion of external work when the contact- breaker was put in action was considerable, Under the same conditions, the quantity of electro-positive metal (cadmium) which is dissolved in the battery is also proportional to the intensity of the current. ‘This determination cannot be made with as much accuracy as that of the weight of copper deposited, but the mean result of the experiments agrees with the law of electro- lysis.—Comptes Rendus, vol. lix. p. 485 (September 12, 1864). INDEX to VOL. XXVIII. ABBOTT (T. K.) on the probability of testimony and arguments, 12. Aérolites, notes on, 148. Air-pump, on a new, 235. Akin (C. K.) on the history of force, 470; on ray-transmutation, 554. Alps, on the conformation of the, 255, 293. Aqueduct of Alatri, on the, 406. Arseniates, on some crystallized, 232. Atkinson (Dr. E.), chemical notices by, 225. Barometer, on the, as an indicator of the earth’s rotation and of the sun’s distance, 55. -scales, on the discrepance be- tween the English and French, 8, 484. Barrett (W. F.) on a physical analysis of the human breath, 108. Bentham (G.) on the influence of heat- force on vegetable life, 400. Biliverdine, on the supposed identity of, with chlorophyll, 63. Bishop (J.) on the influence of the pitch of the tuning-fork on the human voice, 349. Blood, on the reduction and oxidation of the colouring matter of the, 391. Bodies, on the molecular constitution and mechanical properties of, 276. Bottger (Prof. R.) on zeiodelite and its applications, 326. Bohn (Prof.) on the conservation of energy, 311. Books, new:—Apjohn’s Manual of the Metalloids, 59, 160; Church’s Agricultural Chemistry, 390; ae Astronomical Observer, 56). Breath, human, on a physical analy- sis of the, 108. Breithaupt (Prof. A.) on the quartz from Euba, and on the biaxial cha- racter of pyramidal and rhombo- hedral crystals, 190. Brunner (M.) on the action of hydro- gen on metallic solutions, 226. Buchner (M.) on the purification of sulphurie acid, 228. Bunsen (R.) on the inversion of the absorption bands in the spectrum of didymium, 246. Cahours (M.) on the respiration of flowers, 167. Carboniferous epoch, on the climate of the, 131. Carthamine, on the optical properties of, 247. Challis (Prof.) on a theory of the dispersion of light, 489. Chase (P. E.) on the barometer as an indicator of the earth’s rota= tion and of the sun’s distance, 55; on aérial tides, 154. Chautard (J.) on phenomena observed in the spectra produced by the light of induction-currents in rarefied gases, 408. Chemical notices, 225. Chlorophyll, on the constitution of, 63. Church (A. H.) on Tasmanite, 465. Claire Deville (M. St.-) on the per- meability of iron to hydrogen, 229; Climate, on the physical cause of the change of, during geological epochs, 12 Cockle (Hon. Chief Justice) on the operating symbol of differential co- variants, 205. Cohesion-figures of liquids, on the, 354. INDEX. Colloidal substances, on the properties ‘of, 514. Covariants, on the operating symbol of differential, 205. Croll (J.) on the physical cause of the change of climate during geological epochs, 121. Crystallization, observations on, 383. Crystals, on the biaxial character of pyramidal and rhombohedral, 190. Damour (M.) on the density and re- fractive index of some zircons, 23-4. Davy (Dr. J.) on certain charges made against Sir H. Davy, 480. Davy lamp, on the theory of the, 227. Debray (M.) on some crystallized arseniates and phosphates, 232. Delafontaine (M.) on thorium and its oxide, 228. De la Rue (W.) on eclipse photo- eraphs, 477. Didymium, on the inversion of the absorption bands in the spectrum of, 246. Donkin (Prof.) on certam statements concerning the specific heat of gases, 408. Dove (Prof.) on a new polarizing prism, 247; on the optical proper- ties of carthamine, 247. Draper (Dr. H.) on the photographic use of a silvered-glass reflecting telescope, 249. Dufour (L.) on the boiling of water, and on the explosion of steam- boilers, 78, 324. Earth currents, observations on, 140. Electrical condensers, on the residual charge of, 76. phenomena, on the relation of earth currents to, 140. pat on the thermal action of, 1. Electrolysis, on the verification of the law of, 563. Emeralds, on the colouring matter of, 167. Energetics, on the history of, 404. Energy, historic notes on the conser- vation of, 311. Evansite, on the new mineral, 341. Flowers, on the respiration of, 167. Fluid, on some effects produced by a, in motion, 209. Forbes (D.) on Evansite, a new mine- ral species, 341, 565 Force, on the history of, 470. Gadolinite, on some combinations of, 145. Gases, on the dynamic radiation of, 99; on the law of the expansion of, by increase of temperature, 271; on phenomena observed in the spectra produced by the light of induction-currents in rarefied, 408 ; on the specific heat of, 458. Gasometer, on a new mercurial, 235. Gassiot (J. P.) on a train of eleven sulphide-of-carbon prisms arranged for spectrum analysis, 69. Gaugain (J. M.) on the residual charge of electrical condensers, 76. Geological Society, proceedings of the, 72, 159, 241, 321, 562. Gernez (D.) on the rotatory power of active liquids and of their vapours, 243. Gill (J.) on the dynamical theory of heat, 367. Gismondine, on the crystalline form of, 505. Glacial epoch, on the physical cause of the, 121" Graham (T.) on the properties of sili- cic acid and other colloidal sub- stances, 314. Gravitation, observations on, 475. Guu-cotton, observations on, 535. Haidinger (Dr. W.) on the meteorite of Albareto, 327. Heat, on the dynamical theory of, 25, 150, 288, 311, 367; 470; on the absorption and radiation of, by gaseous and liquid matter, 81, 438, 508, 554; on the relative amounts of, produced by the combination of ordinary and ozonized oxygen, 106; on the general nature of, 425; on the measurement of the quantities of, absorbed in _ electro-chemical decompositions, 551. Herschelite, on the crystalline form of, 506. Hittorf (Dr. S. W.) on the spectra of ignited gases and vapours, 64. Huggins (W.) on the spectra of some of the fixed stars, 152. Hydrogen, on the action of, on metal- lic solutions, 226; on the radiation from a flame of, 329. Induction in a rotating conductor, on, 847, 566 Induction-eurrent, on the extra cur- rent of the, 1. Iron, on the permeability of, to hy- drogen, 229. Jochmann (E.) on induction im a rotating conductor, 347. Joule (Dr. J. P.) on the history of the dynamical theory of heat, 150. Jupiter, on the spectrum of, 486. Kronig (M.) on the theory of the Davy lamp, 227. Lakes, on the erosion of, 293; on the temperature in the depth of certain mountain-, 326. Lamarle (Prof.) on the conditions of stability of thin films of liquids, 206. Lang (V. von) on some combinations of Gadolinite, 145; on the crystal- line form of malachite, 502; on Gismondine, 505; on the crystal- line form of Herschelite, 506. Langite, analysis of, 403. Lea (M. C.) on the distillation of substances of different volatilities, 75. Lemoine (M.) on a new sulphide of phosphorus, 235. Lenk’s (Baron von) gun-cotton, ob- servations on, 535. Life, influence of heat-force on vege- table, 400. Light, on the dispersion of, by quartz, 137; on the theory of, 409; on the phenomena attending the pro- pagation of, 430; on a theory of the dispersion of, 489. _ Liquids, on the conditions of sta- bility of thin films of, 206; on the rotatory power of active, and of their vapours, 243; on the cohe- sion-figures of, 304; on some curious effects of the molecular forces of, 434. Lorenz (Prof. L.) on the theory of light, 409. Magnetic phenomena, on the rela- tion of earth currents to, 140. Malachite, on the crystalline form of, 502. Martins (C.) on the temperature of sea-water, 405. Maskelyne (Prof. N.S.) on aérolites, 148. Mathews (W.) on the comparison between the English and metrical INDEX. readings in double-scale barome- ters, 484. Maurey (M.) on gun-cotton, 535. Mayer (Dr. J. R.), on the scientific labours of, 25. Mensbrugghe (G. V.) on some curious effects of the molecular forces of liquids, 434. Metallic oxides, on the action of marsh and olefiant gases on, 225. Meteorite of Albareto, on the, 327. Meteorites, on the microscopical structure of, 157. Miller (Prof. W. A.) on the spectra of some of the fixed stars, 152. Mills (E. J.) on a defect in the theory of saturation, 364. Mineralogical notes, 145, 341, 403, 465, 502. Mitscherlich (Prof. A.) on the spec- tra of compounds and of simple sub- stances, 169. Molecular phenomena, researches on, 192, 276, 382, 425, 438. Monro (C. J.) on the nomenclature of the physical sciences, 461. Miller (M.) on the action of marsh and olefiant gases on metallic ox- ides, 225. Nicklés (J.) on the spectral ray of thallium, 168. Norton (Prof. W. A.) on molecular physics, 192, 276, 382, 425. Ber observations on the nature of, 106. ; Packe (C.) on the discrepance between the English and French barometer- seales, 8. Pelouze (M.) on gun-cotton, with reference to Lenk’s method of pre- paring and employing this sub- stance, 535. Phosphates, on some crystallized, 232. Phosphorus, on a new sulphide of, 23D. Photography, on celestial, 252. Physical sciences, on the nomencla- ture of the, 461. Physics, on molecular, 192, 276, 382. Pisani (M.) on the analysis of Lan- gite, 403. Plateau (Prof.) on the conditions of stability of thin films of liquids, 206. Plucker (Prof. J.) on the spectra of ignited gases and vapours, 64. INDEX. Poggendorff (Prof.) on the extra _ current of the induction-current, 1. Polarizing prism, on a new, 247. Potter (Prof.) on the law of the ex- pansion of gases by increase of temperature, 271. Probability of testimony and argu- ments, on the, 12. Quartz, on the dispersion of light by, 137 ; from Euba, on the, 190. Radiation, on luminous and obscure, 329. Ramsay (Prof. A. C.) on the erosion of valleys and lakes, 293. Rankine (Dr. W. J. M.) on the pro- perties of certain stream-lines, 282 ; on energetics, 404. Raoult (F. M.) on the thermal phe- nomena of voltameters, 551. Ray-transmutation, note on, 554. Robinson (Dr. T. R.) on a new mer- curial gasometer and air-pump, 235. Rodwell (G. F.) on the trompe, 209. Rose (Prof.G.) on the colouring matter of emeralds, 167. Royal Society, proceedings of the, 63, 152, 235, 314, 391, 477. Saturation, on a defect in the theory of, 364. Scientific history, notes on, 25. Sea-water, on the temperature of, 405. | Secchi (Father) on earth currents and their relation to electrical and mag- netic phenomena, 140; on shoot- ing-stars, 377; on the ancient aqueduct of Alatri, 406; on the spectrum of Jupiter, 486. Shooting-stars, observations on, 377. Silicie acid, on the properties of, 314. Sorby (H. C.) on the microscopical structure of meteorites, 157. Soret (J. L.) on the verification of the law of electrolysis when exter- nal work is performed by the gal- vanie current, 563. Spectra of ignited gases and vapours, on the, 64; of some of the fixed stars, on the, 152; of compounds and of simple substances, on the, 169; on phenomena observed in* the, produced by the light of in- oe coments in rarefied gases, 408. 567 Spectrum analysis, observations on, 69. Stars, on the spectra of some of the fixed, 152. Steam-boilers, on the explosion of, 78, 324. Stefan (Prof.) on the dispersion of light by quartz, 137. Stewart (B.) on sun spots, 68. Stokes (Prof. G. G.) on the supposed identity of biliverdine with chloro- phyll, 63; on the reduction and oxidation of the colourmg matter of the blood, 391. Stream-lines, on the properties of cer- tain, 282. Sulphuric acid, on the purification of, 2 Sun, observations on the spots of the, 68; on the measurement of the chemical brightness of various por- tions of the disk of the, 166. Tait (P. G.) on the history of thermo- dynamies, 288. Tasmanite, description and analysis of, 465. Tchébychef (P.) on a modification of Watt’s parallelogram, 51. Telescope, on the photographic use of a silvered-glass reflecting, 249. Thallium, on the spectral ray of, 168. Thermo-dynamics, on the history of, 288. Thorium, on the atomic weight of, 228. Tides, on aérial, 154. Tomlinson (C.) on the cohesion- figures of liquids, 354. Trompe, on the, 209. Troost (M.) on the permeability of iron to hydrogen, 229. Tuning-fork, on the influence of the pitch of the, on the human voice, 349. Tyndall (Prof.) on scientific history, 25; on the absorption and radia- tion of heat by gaseous and liquid matter, 81, 329, 438, 508; on the conformation of the Alps, 255. Valleys, on the erosion of, 293. Vapours, on the dynamic radiation of, 102. Voice, human, on the influence of the pitch of the tuning-fork on the, 349, 568 Voltameters, on the thermal phe- nomena of, 551. Water, on the boiling of, 78, 324. Watt’s parallelogram, on a modifica- tion of, 51. Wobhler (Prof.) on the colouring mat- ter of emeralds, 167. Woods (Dr. T.) on the relative amounts of heat produced by the INDEX. combination of ordinary and ozo- nized oxygen, 106; on the mea- surement of the chemical bright- ness of various portions of the sun’s disk, 166. Zeiodelite, on a new application of, 326. Zircons, on the density and refractive index of some, 234, END OF THE TWENTY-EIGHTH VOLUME. PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET, ALERE FLAMMAM. % < | | : ee 2 AM ALMOMOA UM ORAGA AURA TO MRUAORRORUACURUREPREAUORERGSURERIOSERUURORIUSRUDNURUCUENRUGHURO) NNN RETR HEE EEE EEE EEE 8 : A a sed ee se wo 3 N | Mm TN | S is iW | mini BE i ee oe $4. 43 ce tou Br. 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