ae a) 4 ra. pay eri "ya. Coan ; - gpa Ata vi “% Foe ae od AF jae —% THE LONDON, EDINBURGH, ann DUBLIN PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. CONDUCTED BY SIR DAVID BREWSTER, K.H. LL.D. F.R.S.L.&E. &c. RICHARD TAYLOR, F.L.S. G.S, Astr.S. Nat.H.Mosc. &c. SIR ROBERT KANE, M.D. M.R.I.A. 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.” Jusr. Lirs, Polit. lib. i. cap. 1. Not. VOL. II].—FOURTH SERIES. JANUARY—JUNE, 1852. LONDON. TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET. Printers and Publishers to the University of London ; SOLD BY LONGMAN, BROWN, GREEN, AND LONGMANS ; SIMPKIN, MARSHALL AND CO.; S. HIGHLEY; WHITTAKER AND CO.; AND SHERWOOD, GILBERT, AND PIPER, LONDON: —— BY ADAM AND CHARLES BLACK, AND THOMAS CLARK, EDINBURGH; SMITH AND SON, GLASGOW ; HODGES AND SMITH, DUBLIN; AND WILEY AND PUTNAM, NEW YORK, “ Meditationis est perscrutari occulta; contemplationis est admirari perspicua ..... Admiratio generat queestionem, questio investigationem, inyestigatio inventionem.””—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 ecelo, Quo micet igne Iris, superos quis conciat orbes Tam vario motu,” J.B. Pinelli ad Mazonium. CONTENTS OF VOL. III. (FOURTH SERIES.) NUMBER XV.—JANUARY 1852. Dr. Schlagintweit’s Observations in the Alps on the Optical Phzenomena of the Atmosphere. (With a Plate.) ....... Sir D. Brewster’s Description of several New and Simple Ste- reoscopes for exhibiting, as solids, one or more Pepe: tions of them on a Binns: (With a Plate.) . ‘ Sir D. Brewster's Account of a Binocular Camera, and of a Method of obtaining Drawings of Full Length and Colossal Statues, and of Living Bodies, which can be exhibited as alias iy the’ Steteostopes ss ot cc's sages se cee sae “Ge Sir D. Brewster’s Notice of a Chromatic Stereoscope........ Mr. J. P. Joule’s Account of Experiments with a powerful Elec- ORIEN S teins ip locig. WAGGA Gt aclc sy ARICA Ags HiME GAOr Mr. R. Phillips on Frictional Electricity.................. Dr. Woods on the Heat of Chemical Combination.......... Prof. Challis on the Cause of the Aberration of Light........ Sir D. Brewster’s Explanation of an Optical Illusion . Notices respecting New Books :—Mr. R. Hunt’s Elementary Physics; Paterson’s Calculus of Operations; Four Intro- ductory Lectures delivered at the Government School of Mines and of Science applied to the Arts; Museum of Prac- Ele RONEN ateiergenays pmadicee amend Meer sia elolw are « ais «aie «x ofp Proucedinestel the Ipyal OOCICCy «cucu < sre cp se cra ys ee ess — Royal Astronomical Society............ On the production of Instantaneous Photographic Images, by Te LADLE BG acct teh se aiane'e =, pielsieiaia" ye’ ss 4.8.» On Copper Crystallized by means of Phosphorus, by F. Wohler On the Accidental Colours which result from looking at White Obsects. by M.D) Mu Bepping ca) Avercnleteeh sie @ac8 0's 0° Spe Matraordinary Spotsion the Sun... .. 22.62... sess -eeees Obituary.—Mr. Samuel Veall: 0. fc eee cae cee ee ee Meteorological Observations for November 1851............ Meteorological Observations made by Mr. Thompson at the Garden of the Horticultural Society at Chiswick, near London; by Mr. Veall at Boston; and by the Rev. C. Clouston at Sandwick Manse, Orkney.......... A ES Page 80 1V CONTENTS OF VOL. I1I.—FOURTH SERIES. NUMBER XVI.—FEBRUARY. Page Dr. Tyndall’s Reports on the Progress of the Physical Sciences. : (With a Plate.) .. 0.2... 02 cece ee ce eee eee tenet ee ge 81 On Thermo-electric Currents, by Prof. Magnus of Berlin. Experiments of MM. Svanberg and Franz on Mono- thermic Electricity. Application of the results of M. Magnus to the solution of certain difficulties encoun- tered by -M. Regnault .........-00+--+2- cece cone 81 Dr. Schlagintweit’s Observations in the Alps on the oR Phzenomena of the Atmosphere ..... 92 Dr. Andrews on a Method of obtaining a perfect Vacuum i in the Receiver of an Air-pump .......-..--esee+s cece cerees 104 Prof. Wartmann on the Polarization of Atmospheric Heat . 108 Mr. G. B. Jerrard’s Notes on the Resolution of Equations ‘of the Fifth Degree 2... uc ee nee ee eee or teens cee 112 Mr. M. Donovan on the supposed Identity of the Agent con- cerned in the Phenomena of ordinary Electricity, Voltaic Electricity, Electro- magnetism, Magneto-electricity, and Thermo-clectricity ..... 2.55 a0. 0 = 0j0 ds = « o000.0.0 be ipsa e = eeinin 117 Dr. Tyndall’s Remarks on the Researches of Dr. Goodman “On the Identity of the Existences or Forces, Light, Heat, Elec- tricity and. Mapnetinnn (0 %.. ae Sse tisin aes, ane ate ipsa nbd ope 127 Mr. R. Carmichael on Homogeneous Functions, and their Index SVMDOLE ys nsn, ci tess assis clea Sele he A Rie Rs “iat, t) Se 8 129 Prof. Chapman’s Mineralogical Notes ..........-... 0.00: 141 Prof. Buff on the Electrical Properties of Flame............ 145 Notices respecting New Books :—Ramchundra’s Treatise on Problems of Maxima and Minima, solved by Algebra...... 148 Proceedings of the Royal Society... .........-seecssee-ese 149 Light for Tilumination obtained from the Burning of Hydrogen, BIO) Ds TEAL so oc ns Shain ee aie anole hy abe s/h ms ate oe 152 On the Crystallization of Sulphur, by Ch. Brame .......... 154 On the Electro-magnetic Motor of Fessel, by M. Pliicker .... 155 Present condition SF Vecniiee. ee ee ne cee 156 On the Sulphur Deposits at Zwoszowice and Radoboj ...... 157 Meteorological Observatory of Mount Vesuvius ............ 158 Experiments on the Application of Electro-magnetism as a Mo- tive Force, by M. Aristide Dumont .............-0..-- 158 Meteorological Observations for December 1851............ 139 fa 0: ERP eS ERAS See PS a is ARNIS. Pa A 160 NUMBER XVII.—MARCH. Dr. Herapath on the Optical Properties of a newly-discovered Saltof Quinmes (Wath a-Plates) eo ose oS cinte perce 161 Dr. Tyndall’s Reports on the Progress of the Physical Sciences : P. Riess on Electric Currents of the First and Higher Orders 173 Mr. R. Adie on some Thermo-electrical Experiments........ 185 CONTENTS OF VOL. III.—FOURTH SERIES. The Rev. B. Bronwin on the Integration of Linear Differential EO URGOBSe: Jetta eitemas sis abt dy nl misma ate 38S]e2.052,5 Sir D. Brewster on the Development and Extinction of regular doubly-refracting Structures in the Crystalline Lenses of Ani- malsafter Death, ((With.a Plate.) occ 21 .aps.- 20 s.0 0 sre « Mr. M. Donovan on the supposed Identity of the Agent con- cerned in the Phenomena of ordinary Electricity, Voltaic Electricity, Electro- Magnetism, Magneto-electricity, and Thermo-electricity (continued) ......+. 00+ eee eee eee Mr. E. Schunck on Rubian and its Products of Decomposition Notices respecting New Books :—Three Introductory Lectures delivered at the Government School of Mines and of Science applied to the Arts; Museum of Practical Geology; Dr. v. Feilitzsch’s Optical Investigations occasioned by the Total Eclipse of the Sun on the 28th of July 1851 ...........--. 2 Proceedings of the Royal Society ......-...-+----++++-0>- On the Artificial Formation of several Minerals, by M. Becquerel Eloin’s Improved Miner’s Safety-Lamp ........-...+-+++5 Meteorological Observations for January 1852 .........-..- gE PR TACO NUMBER XVIII.—APRIL. Prof. Wheatstone’s Contributions to the Physiology of Vision.— Part the First. On some remarkable, and hitherto unobserved, Phzenomena of Binocular Vision. (With two Plates.)...... M. H. Kopp on the Expansion of some Solid Bodies by Heat Prof. Chapman on the Classification of the Silicates and their gilied Compounds) jc tayo jure «, 2} «fale aren incl Joie p> yams" im 0,919: 9.2 M. A. G. C. Martin on the Amylum Grains of the Potatoe. GWithia, Plate). 021s. Wcrespypism @nm)clegeda oe ib Ae go 0s 25 2s Sir D. Brewster on a Remarkable Property of the Diamond. (Wath a Plate.) i223 isewteni eee = 2+ neo ele ee a es Mr. T. S. Davies on Geometry and Geometers.—No. IX.,... Mr. M. Donovan on the supposed Identity of the Agent con- cerned in the Phenomena of ordinary Electricity, Voltaic Electricity, Electro - Magnetism, Magneto- electricity, and Thermo-electricity (continued) .. 1.1... ee. . cece ee ee eee Dr. Woods on the Heat of Chemical Combination .......... Proceedings of the Royal Society...... 1... .0-- eee eeeeee Royal Institution... 21... se. + ..0aisis late siele —____—_—_——— Cambridge Philosophical Society........ On Gas-Batteries, and on the Preparation of Hydriodic and Hy- drobromic Acids by the Galvanic Method, by M. Osann Meteorological Observations for February 1852 ............ DOD G asiaia ar» (ais itten iw anin hyo nvenee nueue Prat aes 198 213 268 vi CONTENTS OF VOL. I1I.—FOURTH SERIES. NUMBER XIX.—MAY. Page Dr. Tyndall’s Reports on the Progress of the Physical Sciences. a (With a Plate.) 20... 0.05 eee ce reece ees ce nete epee 321 Dr. Kohlrausch on the Electroscopic Properties of the Voltaic Gircuit 7 ois 22 0. athe oie geotelis stay ore)» cotaenge ere 321 Prof. Challis on a Mathematical Theory of M. Foucault’s Pen- dulum Experiment... .... 22. ee ess ese ee re rere ce eeeene 331 Mr. M. Donovan on the supposed Identity of the Agent con- cerned in the Phenomena of ordinary Electricity, Voltaic Electricity, Electro - magnetism, Magneto - electricity, and Thermo-electricity (continued) Mere niete o2-0:4 Sogisie sane 335 Prof. Ragona-Scina on the Longitudinal Lines of the Solar Spectrum. (With a Plate.) .... 2... cess eee eee ees ce ee 347 Mr. W. Spottiswoode on a Problem in Combinatorial Analysis 349 Dr. Schunck on Rubian and its Products of Decomposition (comoludhed \iishe iis (oisp in’ ojsiace a! + a a epometera eats pelea en ge 354 Sir W. R. Hamilton on Continued Fractions in Quaternions 371 Dr. Griffith on the Triple or Ammonio-magnesian Phosphates occurring in the Urine and other Animal Fluids .......... 373 Mr. J. J. Sylvester on a remarkable Theorem in the sitecag of Equal Roots and Multiple Points ...........0-.-+ee0ee2 375 Prof. Miller on a new Locality of Phenakite Peer orc ie eae Pane iis. Proceedings of the Royal Society. . 379 On the Compound Ammonias, and ‘the Bodies of the "Cacodyle Series; iby lie bunt te ois so cles = eesti alain Voisin atecole 392 On the Invention of the Stereoscope, by James Elliot, Esq... 397 On the Artificial Production of Crystallized Tungstate of Tine, Hy gIN AO SIVIAMYORS (ye: s-c.scceks ote eats pieces imei nteleiae a ee 397 On the Green Colouring Matter of Plants, and on the Red Matter of the Blood, by }. Verdeil: : 5 s/.0c nas ge mide we hee eee 398 Equivalent of Phosphorus, by Prof. Schritter ele phere fers etter 399 Production of Cyanide of Potassium, by M. Rieken ........ 399 Meteorological Observations for March 1852 ............. Habe is, ——- MBabbles sets as 2 Pegeace oeaees aise on ee 400 NUMBER XX.—JUNE. Dr. Faraday on the Physical Character of the Lines of Magnetic Force: (With a Plate.) 0c. . W nade cea 401 Dr. Lamont on the Ten-year Period which exhibits itself in the Diurnal Motion of the Magnetic Needle . ei .. 428 Mr. W. R. Grove on a Mode of reviving Dormant Impressions On the Retima. e's... 5 sau the Lal dele Die arent a a 435 Mr. J. Cockle on Algebraic Transformation, on Quadruple Algebra, and on the "Theory of Equations) .'iu. 1 aSaae 436 Prof. De Morgan on the Authorship of the Account of the Com- mercium Epistolicum, published in the Philosophical Transac- ONE Bi deters dhe cpires awk aap hace re eee ee -- 440 CONTENTS OF VOL. IIl.—FOURTH SERIES. vill Page Mr. M. Donovan on the supposed Identity of the Agent con- ; cerned in the Phenomena of ordinary Electricity, Voltaic Electricity, Electro- magnetism, Magneto-electricity, and Thermo-electricity (continued) ........ 00sec cee eeeeenee 445 Mr. G. B. Jerrard on the possibility of solving Equations of any MePree DOWOVERCIENALCE: Sorte tic cre cin ae ents elasep a s-< ge 457 Mr. J. J. Sylvester’s Observations on a New Theory of Multi- LICIEYER. Bash AS oh dae Spay og AOS Ne STs ss 460 Notices respecting New Books:—Mr. R.-Grant’s History of Physical Astronomy, from the earliest Ages to the middle of Pie NENCLCGHTM, CONUIEG oor count tepimetos = Sale ehe elena 3! 468 Proceedings of the Royal Society... 2. ........ 0.22.25 00 vide VO ———. Royal Institution ..... 2G Se TS On the Passive State of Meteoric Iron, by Prof. Wéhler .... 477 On the Invention of the Stereoscope, by C. Wheatstone .... 478 On the Sun Column as seen at Sandwick Manse, Orkney, in Aprild 852, by C. Clouston ......:....... nv ees Leese ee Os 478 Meteorological Observations for April 1852 ........ oat on e's 479 Wablevat. sete acs 2 Big ihare Pix oh ah olinat aie ah hes esl . 480 NUMBER XXI.—SUPPLEMENT TO VOL. III. Mr. J. P. Joule on the Heat disengaged in Chemical Combina- ROWIAOTSseM eI w ee ele sie ate oe dn wile PRT ees «6 481 Prof. Wheatstone’s Contributions to the Physiology of Vision. —Part the Second. On some remarkable, and hitherto un- observed, Phenomena of Binocular Vision (continued). (With RUPE Cr rates ee an cae oe Meietebims ue oh nial ra. dan slegn ecient 504 Mr. T. S. Davies on Geometry and Geometers. ca TD. 523 The Rev. T. P. Kirkman on the Puzzle of the Fifteen Young 2) Sugden Sf ae epecaets Bere ea eon earn anrantt 526 Mr. W. Herapath on early Egyptian Chemistry ............ 528 Proceedings of the Royal Society of Edinburgh ............ 529 PVOYral RESHIEMEIOM ss os qs lanicin ne «ee 535 Dr. Kemp’s Patent for a new Method of obtaining motive power by means of Electro-magnetism ...........-..ecce+0-- 541 Electro-chemical Researches on the Properties of Electrified Bodies, by MM. Fremy and Becquerel.................- 543 On the Allotropy of Selenium, by M. Hittorf.............. 546 Meteorological Observation, by P. J. Martin.............. 547 PC Tad ce Reo ee ar oe EOC. ha ae lade cet ceipe 548 ERRATA IN VOL. II. Page 488, line 13 from bottom, for continuously read cautiously. — 489, — 1 from top, for with all the rest read with all, the test. ERRATUM IN VOL III. Page 38 line 16 for +.4- +.4 +.— read +.+ +.+ a ee Siaeaa = Peer PLATES. I. Illustrative of Dr. Schlagintweit’s Paper on the Optical Pheenomena of the Atmosphere in the Alps. II. Illustrative of Sir D. Brewster’s Paper on several New Stereoscopes. III. Illustrative of Prof. Magnus’s Paper on Thermo-electric Currents. IV. Illustrative of Dr. W. Bird Herapath’s Paper on the Optical Proper- ties of a newly-discovered Salt of Quinine. V. Illustrative of Sir D. Brewster’s Paper on the Development and Ex- tinction of regular Doubly-refracting Structures in the Crystalline Lenses of Animals after Death. VI. Illustrative of M. A. G. C. Martin’s Paper on the Amylum Grains of the Potatoe; and Sir D. Brewster’s Paper on a Remarkable Property of the Diamond. VII. and VIII. Illustrative of Prof. Wheatstone’s Paper on the Physiology of Vision. IX. Illustrative of Dr. Kohlrausch’s Paper on the Electroscopic Proper- ties of the Voltaic Circuit; and Prof. Ragona-Scina’s Paper on the Longitudinal Lines of the Solar Spectrum. X. Ilustrative of Dr. Faraday’s Paper on the Physical Character of the Lines of Magnetic Force. XI. Illustrative of Mr. J. P. Joule’s Paper on the Heat disengaged in Chemical Combinations. XII. Illustrative of Prof. Wheatstone’s Paper on the Physiology of Vision. THE LONDON, EDINBURGH anv DUBLIN PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. [FOURTH SERIES.] JANUARY 1882. I. Observations in the Alps on the Optical Phenomena of the Atmosphere. By Dr. Hermann ScuoLaGintweitT*. [With a Plate. ] DEPORTMENT OF THE ATMOSPHERE TOWARDS HEAT AND LIGHT. TRANSMISSION OF HEAT. Pyrheliometer. Difference of the thermo- meter in the sun and in the shade. Thermometer with blackened bulb. Saussure’s heliothermometer. Nightly radiation. TRANSPARENCY. Absorption of light in general. Diaphanometer. Transparency of the atmosphere in large masses. Optical illusions through altered transpa- rency. pa PONG the optical phenomena of the atmosphere, those which relate to its colour and its deportment towards the rays of light and heat are peculiarly subject to alteration with the height. The investigation of this subject at great elevations, as, for instance, in the higher alpine regions, obtains an interest from the fact, that here, in regard to its weight, a considerable portion of the atmosphere is absent +. The experiments on the intensity of heat and light are, how- ever, subject to so many accidents and disturbances, that in the following pages we must sometimes limit ourselves to the results of single experiments. TRANSMISSION OF HEart. To convince ourselves of the high permeability of the atmo- sphere with regard to the rays of heat, we made use of one of * Extracted from the Researches on the Physical Geography of the Alps, by Hermann Schlagintweit and Adolph Schlagintweit. Leipzig. . A. Barth, 1850. + At a height of 12,000 feet the loss, in this respect, amounts to 0°37 ; at 14,500 feet, to 0°44 of the entire weight. Phil. Mag. 8. 4. Vol. 3. No. 15. Jan, 1852. B 2 Dr. H. Schlagintweit’s Observations in the Alps those ingenious instruments which have been devised by Pouillet*, The construction of the direct Pyrheliometer (Plate I. fig. 1) is’ as follows :—The vessel (aa) is a shallow metallic cylinder, with a blackened surface (5). The diameter of the cylinder is 1 deci- metre, and its height 1:5 centimetre; it can therefore contain 150 grammes of water. To the bottom of the vessel a cylinder is appended, within which is a thermometer held fast by a cork ; on the outside of this cylinder is a screw (c), by means of which the instrument may be fastened to a vertical stick. [In this way the stand recommended by Pouillet was superseded.] The double motion of the screw in horizontal and vertical direction enabled us to place the instrument so that the sun’s rays always fell perpendicularly upon the blackened upper surface. Of this we convinced ourselves by fixing a pasteboard disc (e) of the same diameter as the cylindrical vessel (aa), near the end of the ther- mometer. When the entire disc was shaded by the vessel at the other end, we might be sure that the rays fell perpendicularly upon the latter; and by this arrangement the thermometer-tube is protected from the direct action of the sun. The bulb of the thermometer is contained within the cylinder (aa), that is to say, it is directed upwards. Were the air completely removed from the thermometer, on placing it in this position the mereury would flow downwards, and thus render the reading of the instru- ment impossible; but a small quantity of air, left intentionally in the tube during its preparation, hindered this descent of the mercury, without however invading the exactitude of the results. To impart a uniform temperature to the entire mass of water, the pyrheliometer, during the experiment, is turned round its longer axis; to permit of this, the screw (c) must not be made too fast. In the fillmg of the instrument great care must be taken that no air remains in the cylinder, as this would spread itself between the water and the upper metallic plate, and thus modify the quantity of heat received by the water. During its exposure to the action of the sun, the instrument loses a quantity of heat by contemporaneous radiation from its surface. This source of disturbance cannot indeed be avoided, but its magnitude may be determined, by observation, for each experiment. The procedure is as follows :—The vessel is first filled with water, to which time is given to assume the tempe- rature of the surrounding air. The instrument is then brought into the vicinity of the spot where it is intended to be exposed to the action of the sun, and so placed in the shade that its * Mémoire sur la chaleur solaire, sur les pouvoirs rayonnants et ab- sorbants de Pair atmosphérique, et sur la température de l’espace.— Comptes Rendus, 1838, vol. vii. p. 24-65. Compare also Herschel’s actinometer, in Keemtz’s Treatise on Mineralogy, vol. iii. p. 14. on the Optical Phenomena of the Atmosphere. 3 blackened surface may radiate against an unclouded portion of the sky. After somewhat more than four minutes, the surface 1s covered with a screen and directed perpendicularly against the sun’s rays. At the end of the fifth minute the screen is removed, and the apparatus is permitted to remain five minutes longer in the sun. At the end of the tenth minute it is again, as at first, brought into the shade and permitted to radiate five minutes longer. This operation can be often repeated if necessary. The two quantities which are here to be made use of are, the increase of temperature during the five minutes’ exposure to the sun, and the decrease of temperature during the periods of radiation im- mediately before and after; the arithmetical mean of the two latter may be regarded as the quantity of heat lost by radiation during the five minutes in the sun. The action of the sun (2) alone will therefore be where T represents the observed temperature, r and 7! the amounts of the radiation before and after. After the second radiation we generally placed the instrument once more in the sun, and afterwards permitted it again to ra- diate; in this way two series of observations were obtained. To secure perfect accuracy in the experiments, it would be desirable that the temperature of the air during the time occu- pied by each should remain constant; for any inconstancy in this respect would be accompanied by an increased or diminished “cooling. But in experiments which occupy fifteen minutes and upwards, triflmg alterations are unavoidable; by taking the arithmetic mean, however, they are sufficiently compensated. Of the experiments with the pyrheliometer, the maxima alone are chosen for nearer consideration ; for in these cases only is it probable that no turbidity of the atmosphere by vapours, fine veils of clouds, &c. takes place. In making such experiments, deviations in the transparency are often recognised which are totally inappreciable with the telescope or with the naked eyes, but which afterwards announce themselves by the presence of thin clouds, &c. In the observations on the Johannishiitte (7581 P. F.), the maxima of the increase* in August and September 1848 were 4°9 to 5°-2 C.; the mean height of the barometer at the time of the experiment bemg =571 millims. All the observations were * Under ‘ increase’ is here to be understood the increase of temperature U with the radiated heat (* 5 ) added to it. B2 4 Dr. H. Schlagintweit’s Observations in the Alps made at midday, between 12 and 1 o’clock. The 4th of September 1848, on which the observations on the Rachern (10362 P. F.) were made, seems to have been a peculiarly favourable day. It was not only entirely cloudless, but its transparency, when the distant alps were observed, was very striking; on this day the difference between the sunned and shaded thermometer was un- usually great. The observations on the Rachern gave as follows :— Time of observation, Sept. 4, 1848, 15 10™ p.m.* Height in Parisian feet . . ein 10362 Reduced height of barometer in millimetres . . 512 Pemipembtuneopthe lair sweet! +) Aobiay lt oe 58 C. Temperature of the water at the commencement . 8°:3 C. Temperature after five minutes’ radiation . . . 6°°4 C. Temperature after five mimutes’ exposure tothe sun 10° 1 C. Temperature after five minutes’ further radiation 79:6. Increase for five minutes without radiation . . 5°75 The maximum of the increase obtained by Pouillet+, after the elimination of the radiation, was5°"1C. (Paris, May 11, 1838,124). The insolation was also determined by observations made with two thermometers ; one of which was set in the sun, and the other, in the usual manner, in the shade. Lambert t, Alexander von Humboldt$, De Gasparin||, and Quetelet], have pointed out the import of such determinations, and the two latter have applied the method in a long series of experiments. ‘ We here communicate a number of insolations which we have had opportunity to observe. They are the results of single ex- periments ; and perhaps, even as separate phenomena, on ac- count of the considerable elevation to which they refer, are deserving of some attention. * The insolation at 12 o’clock might be taken at something over 5:8. + For the limit of the atmosphere, the observations of Pouillet made at different hours of the day gave 6°27 C. If we omit to compare our obser- vations with those of Pouillet, and the similar ones made by Kemtz and Forbes with Herschel’s actinometer, our apology is, that for these investi- gations numerous observations are necessary, as the single observations are so liable to disturbances from the altered serenity of the sky. { Lambert, Pyrometrie, § 283; Photometrie, § 886. § Alexander von Humboldt, De Distributione Plantarum, 1813, p. 167. || De Gasparin, Cours d’ Agriculture, “| Quetelet, Instruction sur V observation des phénoménes périodiques, and Sur le Climat de la Belgique, chap. 4. 1846. From the Annales de ’Ob- servatoire de Bruzelles, on the Optical Phenomena of the Atmosphere. 5 A. Insolations on the summits of the Alps (1848). Height in Thermometer. Differ- No. Location. Parisian | Day and hour.|~—____._,... | ence. feet. In the shade.| In the sun. 1 |Grossglockner ......... 12,158 aaa } 38 49 | 17 2 |Adlersruhe .........++ 10,432 ne i i 10-2 1569 | 59 Aug. 29. Z ; ‘ 3 |Adlersruhe ..........-. 10,432 | { 3,8 } 9-1 115 24 Sept 4. ‘ .. 4 |Rachern ......s....-+. 10,362 || TP } 5:8 66 | 08 Sept. 4. : : ; 5 |Rachern ...........+0+- 10,362 | 4 nn. } 42 5:9 1-7 Sept. 4. ; ; : 6 |Rachern .........ss000. 10,362 | { yh } 3-9 45 | O6 7 \Todtenlécher ......... 10,340 eae 44 69 | 25 8 |Névé region of the Paseseaboette | 8,781 ae - 38 5-6 1:8 Burgstall rocks... Hig! 9 |Pasterze, on the Sept. 3 foot of the great }| 8,236 |4 5." 5-4 9°5 41 Burgstall ......... Le 10 |Wallnerhiitte ......... 6,510 figs 28.1) 145 186 | 41 11 |Gossnitz .......eee.. 5,796 Aug. 22. 17-4 235 | 6l 12 |Georgenstein ......... 4,697 | gee 20. 18-1 19-4 13 B. Insolations on Johannishiitte (7581 P. F.). Hour Shaded. /In the sun, | Increase in Hour. Shaded. |In the sun. Tperegecin ES soa ol ee eal 7 a.m —10 +15 2-5 1 p.m 10°4 12-1 17 +64 8:5 2] 9-1 15:2 61 9°5 12-2 27 2 54 9-5 41 46 9:4 48 12-0 12-4 0-4 87 115 2°8 9 5:8 co 2-1 3 11:0 14:0 3-0 671 9-1 30 8:9 141 5-2 10 9-3 13-0 37 4 11-4 12-2 0:8 07 71 6:4 Vik 12:8 17 ll 0-5 45 40 5 74 8:9 15 81 10:7 2°6 113 13°3 2:0 Noon. 11°8 151 33 12°1 16:2 41° + 6 Dr. H. Schlagintweit’s Observations in the Alps C. Insolations observed contemporaneously on Johannishiitte and on the Glacier (horizontal distance from the edge 900 P. F.). Thermometer. “Shaded. [In the sun. Difference. |Diff. G.—Diff. J. h = ° . - 7} 730 baht sat 0-9 a hae eee a clos}! fi] la | art] ° a. 11 4} oak besara (| eet oe ewe}! Na | im | at] 3 Mepis cose 1-46 The differences can in general be very considerable ; even on the higher alpine summits (Table A.), notwithstanding the low temperature of the air, they are always very appreciable. A dif- ference of 2°°5 is frequently observed even there, and on very favourable days it amounts even to 6°C, The experiments upon the Johannishiitte show that the msolations imerease towards midday, but many disturbances are at the same time observed during the process of experiment. We therefore limit ourselves to the results of the hours, with the remark, that the observa- tions were made on days widely separated from each other. The Table C. includes observations, every two of which contained between the braces are correspondent ; the upper one was made on the Johannishiitte, the other at the same time upon the gla- cier. The temperatures of the shadowed atmosphere are very dif- ferent at both points; the height of the thermometer in the sun is, however, in both cases very nearly the same. A disturbance due to the reflexion of light from the surface of the glacier might in the present case be expected ; but this was prevented by the introduction of a pasteboard screen beneath. The difference of the sunned and shaded thermometers is here always greater than that observed over the rocks which surround the glacier ; at noon the difference in the former case exceeds that m the latter by 1°-46 C. This deviation is due to the circumstance of our having in one case an atmosphere artificially cooled by the pecu- liar surface upon which it rests. Both thermometers indeed are hereby depressed ; the difference, however, must be greater on the glacier, as the intensity of the solar rays, in the observa- tions made contemporaneously at both places, is the same, and is therefore more appreciable in the relatively cold atmosphere. on the Optical Phenomena of the Atmosphere. 7 True, the radiation in the latter case is likewise more energetic, but not sufficiently so to annul the comparatively great increase of temperature observed upon the glacier. The reverse of this must take place when the observations are made immediately over the surface of the bare rocks, where the temperature of the air is known to be considerably heightened. In this case the thermometer placed in the sun could not differ so considerably from that im the shade. This suggests to us the great caution necessary to be observed in experiments of this nature. We have also made several observations with a thermometer with a blackened bulb, similar to the photometer of Leshe*. By the pyrheliometer we obtained the increase of the temperature of a quantity of water during an arbitrary unit of time ; while instru- ments of the present description exhibit how far the respective thermometers, in the sun and in the shade, can diverge from each other, and thus furnish results which, in comparison with the former, may be named absolute or maxima differences. In our experiments we used two thermometers, one of which was placed in the shade, and the other, the bulb of which was blackened, exposed to the direct sunlight. Instruments of this description can only be compared with each othert+. For the sake of bre- vity we will name the thermometer with the blackened bulb, and which stood in the sun, the photometer. Observations with the blackened Thermometer. y é Temperature | photo- No. Place of observation. Height.| Day. Hour. | of the airin | yneter, the shade. feet. h o 1 |Grossglockner, second peak/12,158 |Aug. 29. | I p.m. 32 16-1 2t |Similaun (summit) ......... 11,135 |Sept. 13.47/23 p.m. 08 13-7 3 |Adlersruhe .......cs0+.s000. 10,432 |Aug. 29. | 2 p.m. 10 34:0 ASI RACHERD cinacz.sesasseseasate 10,362 |Sept. 4. | 1 p.m. 58 17-3 5 |Todtenlocher ........+.++... 10,340 |Sept. 1. |12 44 19:2 \Névé of the great Petz- ene aihere - 52 a ane BHAL-CIACIES ccc.cceee | | apace ay ab ee 8 ee oes De Sept. 11.*| 3 p.m. 2-2 13°6 9 |Névé of the Niederjoch...| ...... Sept. 13.*| 3 p.m. 2:4 15-7 10 |Gossnitzthal ......seccessee| severe Aug. 21. {12 17-4 33'1 * John Leslie, Short notice of Experiments and Instruments which relate to the Deportment of the Air towards Heat and Moisture. Leipzie, 1828. 8vo. + The instrument of Leslie is a differential thermometer with a blackened bulb. It is placed under a glass shade and set in the sun ; notwithstanding this, however, the results given by different instruments cannot be well compared with each other. Compare Ritchie, Edinburgh Journal, Se. iii.p.106. { The observations marked thus * are from 1847. § Nos. 6 to 9 inclusive, immediately over the surface of the granular snow (névé). 8 Dr. H. Schlagintweit’s Observations in the Alps The days chosen were all very clear. The least shading of the heavens by clouds is, however, capable of causing such con- siderable changes in the maxima of insolation, that a relation between the latter and the height is not to be given with cer- tainty. The temperatures given by the photometer are, however, in the first place, deserving of some attention, because the dark rocks and the most elevated accumulations of earthy matters exhibit similar temperatures very often. They attain sometimes, even at considerable elevations, a temperature from 20 to 30 degrees, and again sink under zero by the radiation at night. Experiments on temperature in the direct sunshine which are made with the heliothermometer of Saussure*, are comparable with each other only so long as the same instrument is used. The thickness and transparency of the glass, the space of the cylinder, the conductive power of the material, the more or less air-tight closing, &c., are generally very different in different in- struments. It will therefore be sufficient, m the present case, to exhibit briefly those experiments which we made on the Johan- nishtitte (7581 P. F.). We placed the mstrument generally from 10 o’clock in the morning to 4 o’clock in the afternoon im the sunshine; after this hour there was no further increase of temperature observable. We obtained— I. 40° C. with 6°:7 C.) °o, a “3 3 a "** | temperature of air in the feat Spots eer Wako! ac Pie Oe eee The radiation also varies with the height; it becomes more energetic as we ascend. The experiments on radiation were made with a Rumford’s minimum, which was placed upon a layer of down and left uncovered. The down served to prevent any lateral conduction of heat to the instrument. This is Pouil- let’s arrangement{. The observations were made upon Johan- nishiitte in Heiligenblut. The minimum temperature of the night air was observed at the same time as the radiating instru- ment. (Column 4.) * The instrument consists of a wooden box, which is blackened inside, and in which the bulb of the thermometer is placed. It is closed above by three glass plates. Fourier has given the experiments made by Saussure with this instrument in his investigations on obscure heat. Mém. del’ Acad. des Sciences, Paris, vol. vii. p. 585. + Saussure saw his instrument upon Mount Cramont rise to 87° C., the temperature of the air at the time being 6° 2 C.— Voyages, § 932. { Comptes Rendus, vol. vii. 1838, p. 56. on the Optical Phenomena of the Atmosphere. 9 Collection of Night Temperatures with and without Radiation. 7581 P. F. 1848. No. | Month. Night. | Minimum.) Radiation.) M—R. Remarks. 1 | August. | 15—16 | +42:0 — 51) 7-1 |Very clear, 2 eee. | 26-27 | —4:1 — 43 | 0-2 |Fog in the morning. Ca re 30—31 | +5:0 — 29 | 7:9 |Very clear. 4 | Sept 2—3 2-5 — 395 | 6:0 |Light cirri in the morning. DM eisees 3—4 —3'1 —101 | 7:0 |Very clear. a) tees 4—5 +12 — 30) 4:2 |Fog in the morning. The last éolumn but one contains M—R, that is, the tempe- rature of the air on Johannishiitte minus the results of the radiation thermometer. The contemporaneous maximum of ra- diation in Heiligenblut, at a height of 4004’, amounted to 5°:2 C, In the peculiarly clear nights, Nos. 3, 1 and 5, the radiation was nearly constant, varying only from 7:9 to 7-0. As the minimum of the air varied from +5°0 to —3°1, we may con- clude that the differences in the temperature of the air have no influence upon the radiation. Similar results have long served to support the assumption of the intense cold of the planetary spaces, in comparison with which the differences of temperature observed on the earth’s surface almost vanish. It is very diffi- cult to fix upon proper nights for such observations, the latter are so often disturbed by light clouds or by the morning fog. At still greater altitudes, the temperature of the air and the results given by the radiation thermometer differ from each other still more. Martins and Bravais, during their ascent of Mont Blanc, found the following differences on the Grand Plateau :— Difference on the Grand Plateau. | Difference in Chamouni. Aug. 28, 29, 1844. 13-4* 5 Aug. 31—Sept.1,1844. 13°5 6° 7 1 These observations also were made with a thermometer placed upon down. Different substances exposed at night exhibit different powers of radiation. The temperature which they assume depends, in a great degree, as well upon their constitution as upon their form. This difference exhibits itself very evidently in nature, particularly in the case of plants. In connexion with this sub- ject we give the following extract from the exceedingly careful investigation of Glaisher+, which refers to various and very cha- * Monit. Univers., 1844, p. 2796. t “On the Amount of Radiation of Heat at night from the Earth, and 10 Dr. H. Schlagintweit’s Observations in the Alps racteristic localities. The difference between the temperature of the air and a thermometer placed in long grass is assumed to be 1000; the difference between the temperature of the air and the radiation thermometer in the remaining positions is expressed in parts of the above number. The thermometer used to determine the temperature of the air was placed four feet above the ground. Relative Powers of Radiation of different Bodies*, LODE STASS ...caceccecnscoeerses 1000 | 2 feet above the points of mb 86 Short grass ......... epeailns 9 660). CAO PTS toca = =psne tes sdeseucaannn An inch above the ground. 4 feet above the points of the ¢9 Covered with grass ........... . 209 OTASS cenneunyraaede Scucnarate see Onthegroundunderlonggrass _ 66 | 6 feet above the points of the} 55 Onthegroundundershortgrass 200 TENG we acedec.peeeaseuewa = eheees 1 inch f abovethe points of the 671 8 feet above the points of the 17 CS ee eee 26 QTASS -.cceseseenecarcosccescncs 2 inches above the points of \ 570 12 feet above the points of th } 14 EDC TASS Too a. Secptescccsrecee DAYAR Ieeeorsecsese tes Seatenen oo 3 inches above the points of } 477 Gardens earth Wi. verre see cseees 472 ERC PTRAS Weve a.2 | 7,600} ......| sssee0 | eee 1 32 times sche aimeait Lienz. On the plane between ‘ 7 the Drau and Isel ......... } sien ii) Seal ahead ome a pas The column for Circle a contains the distances at which the small circle disappeared ; the column Circle A, the distances at which the large circle vanished. In the two following columns stand the calculated angles under which the respective circles disappeared. The last column (Q) contains the ratio of the re- spective distances,—a number which, as already remarked, for a perfectly transparent medium ought to be =12, but in the pre- sent case is always less. In Nos. 4 and 6, though only one distance could be measured, the angle under which the objects disappeared was of interest. . In general the quotient increases with the height, 7. e. the * Compare Biot, Traité de Physique, vol. iv. p. 776. Black marble reflects, according to Bouguer, 600 rays of every 1000 under an angle of 3° 35’; under an angle of 30°, 50 of every 1000. Under an angle of 0°°3, white marble reflects 721; under an angle of 2°3, 614; and under an angle of 15°, 211 rays. + Notwithstanding this great transparency, no stars were visible. + This number is in reference to the rocks 10 feet broad, mentioned at No. 4. 14 Dr. H. Schlagintweit’s Observations in the Alps higher we ascend, the more nearly does the atmosphere approach the state of perfect transparency. When, however, the barometer stood at 479 millims., a loss of light was still appreciable. The degree of transparency during serene, and to all appearance, perfectly clear days, is subject to variation ; which perhaps de- pends upon general psychrometric circumstances, but more im- mediately upon the condensation of atmospheric moisture occa- sioned by the peculiarities of locality and temperature. To this may be attributed the difference between the Wasseradkopf and Adlersruhe. Water distributed throughout the atmosphere in a gaseous form increases the transparency. It is known, for in- stance, that the outlines of neighbourmg mountains are pecu- liarly visible immediately before the descent of rain. The greatest number of luminous rays are absorbed by the atmosphere in the immediate vicinity of the source from which they, either directly or by reflexion, proceed,—a law quite ana- logous to that which, as before observed, Melloni discovered for the rays of heat. The most evident case of this kind is obtained from a comparison of Nos. 3 and 4. An object at a distance a of 229! disappeared under 1! 15" i) see 2740! eee }! 16" C +. 26100! doe Lg". The differences of the distances increase here far more quickly than those of the angles. ? For a perfectly transparent atmosphere the quotients (column 8 of the table in page 13) would be =12. Calling this 1000, we obtain for the quotients due to the respective altitudes the following numbers :— On the Grossglockner . . . . 996 On the Adlersruhe .... Q91 Rachemn . .. . . 995 On the Johannishiitte . . . . 981 Inifiienzg -« sd 6) (hilo ties eee Differences which are great enough to be the cause of consider- able errors in judging of distances at great heights, show them- selves here. If objects, the size of which is approximately known to us, as men, animals, houses, &c., be observed at great elevations, we are generally induced to consider them nearer than they really are. Objects which enable us to draw no con- clusion as to distance, such as masses of projecting rock, &c., appear to us too small. The reverse of this property of transpa- rency to diminish the apparent size of bodies is exhibited when the atmosphere is obscured by fog, &c. In this case mountain summits are considerably elevated, and appear to us rougher and -_ on the Optical Phenomena of the Atmosphere. 15 steeper than usual. In one single instance the transparency of the atmosphere seems to increase the size of objects, and that is when the chain of the Alps are observed from the plain to the south or north. In moist weather, generally before the descent of rain, the mountains appear darker and at the same time some- what larger. This illusion appears to be due to the fact, that in the latter case they are much more clearly and sharply defined against the horizon*. The transparency of the atmosphere has the power to modify in a great measure the magnitude of the prospect commanded by a great altitude. This is never so great as to permit of being calculated from the curvature of the earth and the refraction, for in the lower portions the prospect is always considerably limited by vapourst. This explains why we see more clearly looking from below upwards, than from a height downwards. In the latter case, however, another influence operates. The objects seen from above exhibit a uniform obscure colouring, and do not present the same striking contrasts among themselves as the rocks and the snow-covered mountains against the sky. The greater transparency of the upper regions of the atmosphere is strikingly exhibited when we direct our glance to higher summits. It is surprising how plainly the latter stand out before us, and with what distinctness we can recognise the objects which rest upon them. The reason of this is, that we look through a higher and more rarified atmospheric region. The intensity of the rays of light can also be approximately determined by their chemical action upon colours { ; although the results depend upon the material, &c.,the crease of intensity with the height is plainly manifested. We made use of strips of paper on which a uniform wash of carmine was laid. In each experi- ment one-half of each strip was exposed to the sun fronr 11 to 2.0’clock, while the other half was shaded by an opake screen. The altered colours were imitated by carefully mixing together carmine and white in different proportions (the exact process may be learned where the cyanometer is described). In this way we obtained the following corresponding quantities; the * A very simple practical rule to calculate the circle of view from the height is that used by seamen. The square root of the height in Hamburg feet gives the radius in sea miles, 60 to the degree. The refraction is here taken into account. A Hamburg foot is =0°286 met. = 127-0 Parisian lines. For heights of 12,000 feet, we obtain 118 sea miles = 29 geogra- phical miles; for Mont: Blanc, Saussure gives 136 sea miles (Voyages, vol. iv. 4to, p. 194). + The same was observed by Humboldt and Bonpland (Tableau Physique des Régions Equinowiales. Paris, 1807, p. 135); and also by Gay-Lussac during his aéria! journeys. t Saussure, Mém. de Turin, vol. iv. p.441-453 ; Voyages, vol. iv. p. 297. 16 Sir D. Brewster on New Stereoscopes. percentage quantity of carmine present being estimated from a mixture of white and red of the same brightness. 2000'. | 4000!. 7000'. 10,000’. | | =P al See Differ- \In the lin the | Differ-|In the |In the Differ-|In the |In the Differ- ence. |shade. | sun. | ence. |shade. | sun. | ences shade. } sun. | ence. —— |_| | In the |In the shade. | sun. Ge ee — Cd hs 21 19 2 15 | 12 3 19 | 16 3 23 | 18 5 18 | 15 3 94 |} 21 3 LS. Ls 4 177 eS 2 21 | 18 3 23 | 18 5 os gpitanna NAA Nes, SES Ae eT a Ue eS a Mean diff. 2°5 | Mean diff. 2°7 Mean diff. 3°7 Mean diff. 5 The chemical action of the light attains its maximum a little before noon, which was demonstrated by experiments with Da- guerreotype plates. Alexander von Humboldt* has drawn attention to the fact, that at hours equally distant from noon, for example at 10 o’clock a.m. and 2 o’clock P.m., at 8 o’clock aM. and 4 0’clock p.m., &c., the most decided divergences are exhibited. This is chiefly due to the alteration in the transpa- rency of the atmosphere through the condensation of vapours, and hence in different localities may exhibit small variations : these depend upon the distribution of the relative moisture} at different elevations,—a subject which has been already treated of. [To be continued. ] Il. Description of several New and Simple Stereoscopes for exhi- biting, as solids, one or more representations of them on a Plane. By Sir Davip BREWSTER, KH, D.C.L.,F.R.S., and V.P.R.S. Edin.} [With a Plate. ] ee ingenious stereoscope, invented by Prof. Wheatstone, for representing solid figures by the union of dissimilar plane pictures, ‘s described in his very interesting paper “On some remarkable and hitherto unobserved Phenomena of Bino- cular Vision§” ; and im a paper published im a recent volume of the Edinburgh Transactions ||, T have investigated the cause of the perception of objects in relief, by the coalescence of dissi- milar pictures. Having had occasion to make numerous experiments on this * Asie Central, Mahlmann’s edition, vol. ii. p.-76. + See Physical Geography of the Alps, p. 398-425. + From the Transactions of the Royal Scottish Society of Arts, 1849. See also the Report of the British Association at Birmingham, 1849, Trans. of agit? § Phi . 47. Trans. 1838, p. 371. \| Ibid. vol. xv. part 3, p- 360. _ Sir David Brewster on New Stereoscopes. 17 subject, [ was led to construct the stereoscope in several new forms, which, while they possess new and important properties, have the additional advantages of cheapness and portability. The first and the most generally useful of these forms is— 1. The Lenticular Stereoscope. This instrument consists of two semilenses, placed at such a distance that each eye views the picture or drawing opposite to it through the margin of the semilens, or through parts of it equidistant from the margin. The distance of the portions of the lens through which we look must be equal to the distance of the centres of the pupils, which is, at an average, 2} inches. The semilenses should be placed in a frame, so that their distance may be adjusted to different eyes, as shown in Plate II. fig. 1. When we thus view two dissimilar drawings of a solid object, as it is seen by each eye separately, we are actually looking through two prisms, which produce a second image of each drawing ; and when these second images unite, or coalesce, we see the solid object which they represent. But in order that the two images may coalesce, without any effort or strain on the part of the eye, it is necessary that the distance of similar parts of the two drawings be equal to ¢wice the separation produced by the prism. For this purpose, measure the distance at which the semilenses give the most distinct view of the drawings; and having ascertained, by using one eye, the amount of the refrac- tion produced at that distance, or the quantity by which the image of one of the drawings is displaced, place the drawings at a distance equal to twice that quantity, that is, place the draw- ings so that the average distance of similar parts in each is equal to twice that quantity. If this is not correctly done, the eye of the observer will correct the error by making the images coalesce, without being sensible that it is making any such effort. When the dissimilar drawings are thus united, the solid will appear standing, as it were, in relief, between the two plane representa- tions of it. Tn looking through this stereoscope, the observer may pro- bably be perplexed by the vision of only the two dissimilar draw- ings. This effect is produced by the strong tendency of the eyes to unite two similar, or even dissimilar drawings. No sooner do the refracted images emerge from their respective draw- ings, than the eyes, in virtue of this tendency, force them back into union ; and though this is done by the convergency of the optic axes to a point nearer the eye than the drawings, yet the observer is scareely conscious of the muscular exertion by which this is effected. This effect, when it does occur, may be coun- teracted by drawing back the eyes from the lenses, and shutting Phil. Mag. 8. 4. Vol. 3. No. 15, Jan. 1852. C 18 Sir David Brewster on New Stereoscopes. them before they again view the drawings. _ It exists chiefly with short-sighted persons, for whom the stereoscope may be con- structed with concave semilenses or quarters of lenses, placed as in fig. 16; and when there are only ¢wo drawings, it may be prevented by a partition, which hides the right-hand drawing from the left eye, and the left-hand drawing from the night eye. The instrument, as fitted up for use, is. shown in fig. 2, where ABCD is a frame of tin or wood, consisting of an upper and a lower plate, and two ends, AB and CD. The semilenses are placed in CD, with an opening for the nose at NN, a part of the lower plate being cut away for this purpose. The three dis- similar drawings, as shown at C, fig. 4, are placed in the end AB, and are illuminated by the light which enters by the two open sides, AC, BD*. If the drawings are upon thin or trans- parent paper, or are executed as transparencies like the diagrams used in the magic lantern, the box ABCD may be closed, and the light admitted only through the end AB. In the form shown in fig. 2, where the drawings slide into an open frame, either opake or transparent figures may be used. It is often convenient to have the drawings separate, so that, like the semilenses, they may be made to approach to or recede from one another; and when the drawings are thus separate, we can obtain the arrange- ment at B, fig. 4, from the drawings at A, or all of them from the three drawings at C. While the semilenses thus double the drawings and enable us to unite two of the images, they at the same time magnify them, —an advantage of a very peculiar kind, when we wish to give a great apparent magnitude to drawings on a small scale, taken photographically with the camera. But while the magnifymg power of any lens is the same through whatever portion of it we look, its prismatic angle varies with the distance of that portion from the margin. In the semilens LL, for example, fig. 3, the prismatic angle is a maximum at the margin A, less at A’, and still less at A", so that when the drawing 1s very small, we can double it, and refract it sufficiently by looking through A", when larger through A’, and when larger still through A. By using a thicker lens, without changing the curvature of its surface, or its focal length, we can increase the prismatic angle at its margin, so as to produce any degree of refraction that may be required for the purposes of experiment, or for the duplication of large drawings. - * It is sometimes more convenient to close the sides, and leave the upper and under side8 open, or we may cut off a circular segment from its upper and lower plate, as shown in fig. 2. The use of this opening in the lower plate is to illuminate the drawings when we turn the stereoscope and figures upside down, which increases the relief in a surprising degree. Sir David Brewster on New Stereoscopes. 19 It is obvious, from the very nature of the lenticular stereo- scope, that it may be made of any size. The one from which fig. 2 is copied is 8 inches long, and 5 inches at its widest end; but I have made them only ¢hree inches long, and have now before me a microscopic stereoscope, which can be carried in the pocket, and which exhibits all the properties of the instrument to the greatest advantage*. If we suppose the two figures at A, fig. 4, to represent a cone, as seen by the right and left eye, the stereoscope will unite them into a raised cone, with the circular apex nearest the eye. If they are placed as at B, they will appear as a hollow cone, the apex being furthest from the eye. In Mr. Wheatstone’s stereo- scope, the drawmgs must be turned upside down, in order that the raised and hollow cone may be seen in succession; but with the lenticular stereoscope, we have only to place three figures, as at C, fig. 4, and between A, B, fig. 2, im order to see at the same time the raised and the hollow cone; the former bemg produced by the union of the first with the second, and the latter by the union of the second with the third figures. This method of exhibiting at the same time the raised and the hollow solid, enables us to give an ocular and experimental proof of the usual explanation of the cause of the large size of the horizontal moon, of her small size when in the meridian at a considerable altitude, and her termediate apparent magnitude at an intermediate altitude. As the summit of the raised cone appears to be nearest the eye of the observer, the summit of the hollow cone furthest off, and that of the flat drawing on each side at an intermediate distance, these distances will represent the apparent distancé of the moon in the zenith of the elliptical celestial vault, in the horizon, and at an altitude of 45°. The circular summits thus seen are in reality exactly of the same size, and at the same distance from the eye, and are therefore pre- cisely in the same circumstances as the moon in the three posi- tions already mentioned. If we now contemplate them in the stereoscope, we shall see the circular summit of the hollow cone the largest, like the horizontal moon, because it seems at the greatest distance from the eye ; the circular summit of the raised cone the smallest, because it appears at the least distance, like the zenith moon ; and the circular summit of the cones on each of an intermediate size, like the moon at an altitude of 45°, * Tn place of using semilenses, as I at first did, I now use quarters of lenses, which answer the purpose equally well. With a single Jens, there- fore, we can construct two stereoscopes of exactly the same power. This is the first time that a quadrant of a lens has been used in optics. The eye-end of the stereoscope should consist of two short tubes, with the lenses at their extremities. C2 20 Sir David Brewster on New Stereoscopes. because their distance from the eye is intermediate. In the accompanying model this effect will be distinctly seen, by placmg three small wafers of the same size and colour on the square summits of the drawings of the cones or four-sided pyramids. No change is produced in the apparent magnitude of these circles by making one or more of them less bright than the rest, and hence we see the incorrectness of the explanation of the size of the horizontal moon, as given by Dr. Berkeley*. When the observer fails to see the object in relief from the cause already mentioned, but sees only the two drawings, if there are two, or the three drawings, if there are three, the plane of the drawings appears deeply hollow ; and, what is very remark- able, if we look with the eccentric lenses at a flat table from aboye, it also appears deeply hollow; and if we touch it with the palm of our hand, it is felt as hollow, while we are looking at it, but the sensation of hollowness disappears upon shutting our eyes. The sense of sight, therefore, instead of being the pupil of the sense of touch, as Berkeley and others have believed, is In this, as in other cases, its teacher and its gwide+. 2. The Total-Reflexion Telescope. This form of the stereoscope is a very interesting one, and possesses valuable properties. It requires only a small prism and one diagram, or picture of the solid, as seen by one eye ; the other diagram, or picture which is to be combined with it, being created by total reflexion from the base of the prism. This in- strument is shown in fig. 5, where D is the picture of a cone as seen by the left eye L, and ABC a prism, whose base BC is so large, that when the eye is placed close to it, it may see, by reflexion, the whole of the diagram D. The angles ABC, ACB must be equal, but may be of any magnitude. Great accuracy in the equality of the angles is not necessary ; and a prism con- structed by a lapidary out of a fragment of thick plate-glass, the face BC being one of the surfaces of the plate, will answer the purpose{. When the prism is placed at adc, fig. 6, at one end of a conical! tube LD, and the diagram D, at the other end, na cap which can be turned round so as to have the line mn, which passes through the centre of the base and summit of the cone parallel to the line joining the two eyes, the instrument is ready for use. The observer places his left ‘eye at L, and views with * Berkeley’s Works, p. 98; Essay on the Theory of Vision, § 67-78. Lond. 1837. + See Edinburgh Transactions, vol. xv. p. 672. { Inthis case the prism may have the form BedC, fig, 5, the parallel sides BC, cd being the original faces of the piece of the plate-glass, and the in- clined faces Be, Cd only, the work of the lapidary. Sir David Brewster on New Stereoscopes. 21 it the picture D, as seen by total reflexion from the base BC or be of the prism, figs. 5 and 6, while with his right eye R, fig. 5, he views the same picture directly. The first of these pictures being the reverse of the second D, like all pictures formed by one reflexion, we thus combine two dissimilar pictures into a raised cone, as in the figure, or into a hollow one, if the picture at D is turned round 180°. If we place two diagrams, one like one of those at A, fig. 4, and the other lke the other at A, fig. 4, vertically above one another, we shall then see, at the same time, the raised and the hollow cone as produced in the lenti- cular stereoscope by the three diagrams in fig. 4 at C. When the prism is good, the dissimilar image produced by the two refractions at B and C, and the one reflexion at E, is of course more accurate than if it had been drawn by the most skilful artist ; and therefore this form of the stereoscope has in this respect an advantage over every other in which two dissimilar figures, executed by art, are necessary. In consequence of the length of the reflected pencil DB+ BE+EC+CL being a little greater than the direct pencil of rays DR, the two images com- bined have not exactly the same apparent magnitude; but the difference is not perceptible to the eye, and a remedy could easily be provided were it required. If the conical tube LD is held in the left hand, the left eye must be used; and if in the right hand, the right eye must be used; so that the hand may not obstruct the direct vision of the drawing by the eye which does not look through the prism. The cone LD must be turned round slightly in the hand till the line mn joining the centre and apex of the figure is parallel to » the line joining the two eyes. The same line must be parallel to the plane of reflexion from the prism; but this parallelism is secured by fixing the prism and the drawing. It is scarcely necessary to state, that this stereoscope is appli- cable only to those diagrams and forms where the one image is the reflected picture of the other. If we wish to make a microscopic stereoscope of this form, or to magnify the drawings, we have only to cement plano-convex lenses, of the requisite focal length, upon the faces AB, AC of the prism, or, what is simpler still, to use a section of a deeply convex lens ABC, fig. 7, and apply the other half of the lens to the right eye, the face BC having been previously ground flat and polished for the prismatic lens. By using a lens of larger focus for the right eye, we may correct, if required, the imper- fection arising from the difference of paths in the reflected and direct pencils. This difference is so trivial, that it might be corrected by applying to the right eye the central portion of the same lens whose margin is used for the prism, 22 Sir David Brewster on New Stereoscopes. 3. The Single Prismatic Stereoscope. The prismatic stereoscope, represented in fig. 8, consists of a single prism P, with a small refracting angle, capable of refract- ing the image of the figure A, so as just to combme it with the dissimilar figure B, seen directly by the right eye. The second picture should be placed close to A, in order that they may be united by a prism with the smallest refracting angle. There is a slight degree of colour in the refracted image, but it does not injure the general effect. The prism, therefore, should not be made of flint-glass, or any glass with a high dispersive power. A single face ground by a lapidary upon one of the faces of a morsel of plate-glass, the size of the pupil of the eye, will give a prism sufficient for every ordmary purpose. Any person may make one for himself by placing a little bit of wmdow-glass upon another piece inclined to it, and inserting in the angle between them a drop of water. When the figures are small and near one another, a water prism with the requisite angle will scarcely produce any perceptible colour*. If we make a double prism, as shown at PP’, fig. 9, and apply it to the two dissimilar figures A, B, so that with the left eye L looking through the prism P, we may place the refracted image of B upon A, as seen by the right eye R, we shall see a hollow cone; and if with the left eye L/, looking through the other prism P’, we place the refracted image of A upon B, as seen with the right eye R’, we shall see a raised cone. 4. The Singly-Reflecting Stereoscope. A very simple stereoscope may be constructed, as in fig. 10, by using a small piece of black glass, or plate-glass with one side covered with black wax. This piece of glass MN reflects to the left eye L a reverted image of the figure B, which, when seen in the direction LCA, and combined with the figure A, seen directly by the right eye R, gives a raised cone. The cone will be seen hollow by reversing the figures A, B. As BC+CLis greater than AR, the reflected image of B will be shghtly less than A; but the difference is so little, that it does not affect the appearance of the hollow or the raised cone. By bringing Ba little nearer the reflector MN, the two pictures may be made exactly the same. The small reflector and the dissimilar figures may be fitted up in a conical tube, like that shown in fig. 6, the tube having an elliptical section to accommodate two figures at its further end, the major axis of the ellipse being parallel to the line joming the two eyes. * Professor Wheatstone has, we believe, used two achromatic prisms, but they are not necessary. a Sir David Brewster on New Stereoscopes. 23 5. The Double-Reflecting Stereoscope. In this form of the istrument a second reflector is added for the right eye, as shown at M'N’, fig. 11, and the effect of this is to exhibit at the same instant the raised and the hollow cone. The image of B seen by reflexion from MN at the point C is combined with the direct picture of A, seen by the right eye, and forms a hollow cone; while the image of A seen by reflexion from M'N! at the point C’, is combined with the direct picture of B, seen by the left eye. These reflectors may be placed in an elliptical tube, with an opening near the end AB to illuminate the figures A, B, or we may dispense with an opening by having the figures drawn upon thin or transparent paper. When the figures are drawn in transparent lines on a ground of opake varnish, like the diagrams in the magic lantern, the effect is very fine. Another form of the double-reflecting stereoscope is shown in fig. 12, which differs from that shown in fig. 11 in the position of the two reflectors, and of the figures to be united.. The reflecting faces of the mirrors are turned outwards, their distance being less than the distance between the eyes ; and the effect of this is to unite into a hollow cone the same figures which the other form in fig. 11 unite into a raised one. The superiority of this position of the reflectors is, that they are more easily en- closed im a tube, and that the mstrument is more portable. In describing these various forms of the stereoscope, by which the instrument may not only be rendered portable, but may be constructed out of materials which every person possesses, and without the aid of an optician, we have supposed the two dissi- milar figures to be those of the frustum of a cone as seen by each eye separately ; the large circle bemg the representation of the base of the cone, and the small circle the representation of its truncated summit. If we join similar points of these two circles by lines, as is done in the figures, the conical figure wili be more distinct. If we take the drawing of a six-sided pyramid as seen by the right eye, as shown in fig. 13, and place it in the total-reflexion stereoscope at D, fig.5, so that the line MN coincides with mn, and is parallel to the line joining the eyes of the observer, we shall perceive a perfect raised pyramid of a given height, the reflected mage of CD, fig. 13, being combined with AF seen directly. If we now turn the figure round 30°, CD will come into the position AB, and unite with AB, and we shall still perceive a raised pyramid with less height and less symmetry. If we turn it round 30° more, CD will be combined with BC, and we shall still perceive 24 Sir David Brewster on New Stereoscopes. a raised pyramid.with still less height, and still less symmetry. When the figure is turned round other 30°, or 90° from its first position, CD will coincide with CD scen directly, and the com- bined figures will be perfectly flat. If we continue the rotation through other 30°, CD will coincide with DE, and a slightly hollow, but not very symmetrical pyramid, willbe seen. A rota- tion of other 30° will bring CD into coalescence with EF, and we shall see a still more hollow and more symmetrical pyramid. A further rotation of other 80°, making 180° from the commence- ment, will bring CD into union with AF; and we shall have a perfectly symmetrical hollow pyramid of still greater depth, and the exact counterpart of the raised pyramid which was seen be- fore the rotation of the figure commenced. If the pyramid had been square, the raised would have passed into the hollow pyramid by rotations of 45° each. If it had been rectangular, the change would have been effected by rotations of 90°. If the space between the two circular sections of the cone in fig. 12 had been uniformly shaded, or if lines had been drawn from every degree of the one circle to every corresponding degree in the other, m place of from every 90th degree, as in the figure, the raised cone would have gradually diminished in height by the rotation of the figure till it became flat, after a rotation of 90°; and by continuing the rotation, it would have become hollow, and gra- dually reached its maximum depth after a revolution of 180°. There are two classes of phenomena of a very interesting kind, to which the stereoscope is not properly applicable, namely, those where it is required to unite a great number of similar and equidistant patterns, such as those which compose paper-hangings, carpets, and the openings in the cane bottoms of chairs; and those in which we binocularly unite, and give a new position to, lines meeting at or converging to a point, the eye being placed at different heights above the plane of the paper, and at different distances from the angular pomt*. In studying these pheeno- mena, we produce the required union by strainmg the eyes, or by contemplating the objects while the eyes are directed toa point either nearer to or further from them. The power of doing this with facility is possessed by very few persons, and it is there- fore necessary to have a simple and infallible method of effecting the union of such objects without instrumental assistance. The following method, when practised for a short time, will answer this purpose. * These two classes of phenomena are described in my paper “ On the Knowledge of Distance given by Binocular Vision,”’ published in the Edin- burgh Transactions, vol. xv. p. 663. Sur David Brewster on New Stereoscopes. 25 6. Method of uniting Similar or Dissimilar Figures. Upon a piece of glass MN, fig. 14, place a very small circle of white paper D, and let A, B, C be similar patterns which we wish to unite, A with C, or A with B. Hold the piece of glass MN in both hands, and at such a distance from the eyes that, when with the left eye L, and shutting the right eye, we see the circle D covering C, we also, upon opening the right eye B, see with it the circle D covering A. By continuing for a short time to look at the circle D with both eyes open, we shall see the patterns all united, and the wall or plane which contains them situated at the same distance from the eye as the circle D. If there are one or more intermediate patterns, such as B, the piece of glass MN must be held further from the eyes in order to unite A with B instead of A with C. Those who acquire in this way the art of uniting dissimilar and similar figures, will not require in any case the aid of the stereoscope, unless when there is only one figure or object ; in which case they must have recourse to the total-reflexion stereoscope, in order to convert the single figure into a solid, by creating and uniting with it its op- posite or reflected image. 7. Method of Drawing on a Plane the Dissimilar Representations of Solids for the Stereoscope. Let L, R, fig. 15, be the left and right eye, and A the middle point between them. Let MN be the plane on which an object or solid, whose height is CB, is to be drawn. Through B draw LB, meeting MN mm e; then if the object is a solid, with its apex at B, Ce will be the distance of its apex from the centre C of its base, as seen by the left eye. As seen by the right eye R, Ce’ will have the same value, but c’ will lie on the left side of C. Calling E the distance between the two eyes, and / the height BC of the solid, we shall have AB: h= = Ce and Ce= == which will give us the results in the following table, AC being =8 and E=23} inches :— Height. BC=nh. AB. Ce. 1 A 0°:279 inch. 2 6 0°4166 ... 3 5 0°75 4 4 M2o 5 3 2°088 6 2 3°75 1f 1 8°75 8 0 Infinite. 26 Sir David Brewster on a Binocular Camera, &c. If we now wish, by directing the axes of the eyes beyond MN to b, to ascertain the value of Cc’, which will give different depths d of the hollow solids corresponding to different values of Cd, we a are jp ee ae shall have Abis =d:Cc' and Ce = AB? which, making AC8 inches as before, will give the following results :— Depth. Cb=d. Ab. Ce'. 1 9 0°139 inch. 2 10 O25 vee 3 11 O34 ase A 12 0°4166 ... 5 13 ~0:°48 ase 6 14 O'53D\" V. 7 15 0°58 ease 8 16 O625 , 3 9 17 0:663° si. 10 18 0:696 ~c5. 1l 19 O°F20 — o0s 12 20 0°75 The values of 2 and d, when the excentricities Ce, Cc’, as we may call them, are known, will be found by the formule U = ee and d= See As Cc is always equal to Ce’ in each pair of figures or dissimilar pictures, the depth of the hollow solid will always appear much greater than the height of the raised solid one. When Ce and Cd are both 0:75 h:d=3:12, and when they are both 0:4166, 4: d=2: 4, and when they are both 0:1389 4: d=0°8: 1-0. III. Account of a Binocular Camera, and of a Method of ob- taining Drawings of Full Length and Colossal Statues, and of Living Bodies, which can be exhibited as Solids by the Ste- reoscope. By Sir Davip Brewster, K.H., D.C.L., F.R.S., and V.P.R.S. Edin.* ie explaining the construction and use of the lenticular and other stereoscopes, I have referred only to the duplication and union of the dissimilar drawings on a plane of geometrical and symmetrical solids. The most interesting application, however, of these instruments is to the dissimilar representations of statues and living bodies of all sizes and forms, and also to natural scenery, and the objects which enter into itscomposition. Professor * From Trans. of Royal Scottish Society of Arts, 1849. See also Report of British Association at Birmingham, 1849, Trans. of Sect., p. 5. Sir David Brewster on a Binocular Camera, &c. 27 Wheatstone had previously applied his stereoscope to the union of dissimilar drawings of small statues, taken by the Daguerre- otype and Talbotype processes ; and in an essay on Photography, lately published*, I have mentioned its application to statues of all sizes, and even to living figures, by means of a binocular camera. The object of the present paper is to describe the binocular camera, and to explain the principles and methods by which this application of the stereoscope is to be carried into effect. The vision of bodies of three dimensions, or of groups of such bodies combined, has never been sufficiently studied either by artists or philosophers. Leonardo da Vinci, who united im a re- markable degree a knowledge of art and science, has, in a passage of his Trattato della Pittura, quoted by Dr. Smith of Cambridget, made a brief reference to it insofar as binocular vision is con- cerned; but till the publication of Professor Wheatstone’s in- teresting memoir “ On some remarkable and hitherto unobserved Phenomena of Binocular Vision {,” the subject had excited no attention. In order to understand the subject, we shall first consider the vision with one eye of objects of three dimensions, when of dif- ferent magnitudes and placed at different distances. When we thus view a building or a full-length or colossal statue at a short distance, a picture of all its visible parts is formed on the retina. | If we view it at a greater distance, certain parts cease to be seen, and other parts come into view; and this change on the picture will go on, but will become less and less perceptible as we retire from the original. If we now look at the building or statue from a distance through a telescope, so as to present it to us with the same distinctness, and of the same apparent magnitude as we saw it at our first position, the two pictures will be essen- tially different ; all the parts which ceased to be visible as we retired will still be invisible, and all the parts which were not seen at our first position, but became visible by retiring, will be seen in the telescopic picture. Hence the parts seen by the near eye, and not by the distant telescope, will be those towards the middle of the building or statue, whose surfaces converge, as it were, towards the eye; while those seen by the telescope, and not by the eye, will be the external parts of the object whose surfaces converge less, or approach to parallelism. It will depend on the nature of the building or the statue which of these pic- tures gives us the most favourable representation of it. * North British Review, vol. vii. p. 502, August 1847. t Complete System of Optics, vol. ii. Remarks, p. 41. § 244. { Phil. Trans., 1838, p. 371; see also Edinburgh Transactions, vol. xv. pp. 349 and 663, 28 Sir David Brewster on a Binocular Camera, &c. If we now suppose the building or statue to be reduced in the most perfect manner,—to half its size, for example,—then it is ob- vious that these two perfectly similar solids will afford a different picture, whether viewed by the eye or by the telescope. In the reduced copy, the inner surfaces visible in the original will dis- appear, and the outer surfaces become visible ; and, as formerly, it will depend on the nature of the building or the statue whether the reduced or the original copy gives the best picture. If we repeat the preceding experiments with two eyes in place of one, the building or statue will have a different appearance. Surfaces and parts, formerly invisible, will become visible, and the body will be better seen because we see more of it; but then the parts thus brought into view being seen, generally speaking, with one eye, will have only one-half the illumination of the rest of the picture. But, though we see more of the body in bin- ocular vision, it is only parts of vertical surfaces perpendicular to the line joining the eyes that are thus brought into view, the parts of similar horizontal surfaces remaining invisible as with one eye. It would require a pair of eyes placed vertically, that is, with the line joing them in a vertical direction, to enable us to see the horizontal as well as the vertical surfaces ; and it would require a pair of eyes inclined at all possible angles, that is, aring of eyes 23 inches in diameter, to enable us to have a perfectly symmetrical view of the statue. These observations will enable us to answer the question, whether or not a reduced copy of a statue, of precisely the same form in all its parts, will give us, either by monocular or bin- ocular vision, a better view of it as a work of art. As it is the outer parts or surfaces of a large statue that are invisible, its great outline and largest parts must be best seen in the reduced copy; and consequently its relief, or third dimension in space, must be much greater in the reduced copy. This will be better understood if we suppose a sphere to be substituted for the statue. If the sphere exceeds in diameter the distance between the pupils of the right and left eye, or 23 inches, we shall not see a complete hemisphere unless from an infinite distance. If the sphere is larger, we shall see only a segment, whose relief, im place of being equal to the radius of the sphere, is equal only to the versed sine of half the visible segment. Hence it is ob- vious that a reduced copy of a statue is not only better seen from more of its parts being visible, but is also seen in stronger relief. With these observations, we shall be able to determine the best method of obtaiming dissimilar plane drawings of full-length and colossal statues, &c., in order to reproduce them in three dimensions by means of the stereoscope. Were a painter called upon to take drawings of a statue, as seen by each eye, he would Sir David Brewster on a Binocular Camera, &c. 29 fix, at the height of his eyes, a metallic plate with two small holes in it, whose distance is equal to that of his eyes, and he would then draw the statue as seen through the holes by each eye. These pictures, however, whatever be his skill, would not be such as to reproduce the statue by their union. An accu- racy, almost mathematical, is necessary for this purpose ; and this can only be obtained from pictures executed by the processes of the Daguerreotype and Talbotype. In order to do this with the requisite nicety, we must construct a binocular camera, which will take the pictures simultaneously and of the same size; that is, a camera with two lenses of the same aperture and focal length, placed at the same distance as the two eyes. As it is impossible to grind and polish two lenses, whether single or achromatic, of exactly the same focal lengths, even if we had the very same glass for each, I propose to bisect the lenses, and con- struct the instrument with semilenses, which will give us pic- tures of precisely the same size and definition. These lenses should be placed with their diameters of bisection parallel to one another, and at the distance of 2} inches, which 1s the average distance of the eyes in man ; and, when fixed in a box of sutfti- cient size, will form a bimocular camera, which will give us, at the same instant, with the same lights and shadows, and of the same size, such dissimilar pictures of statues, buildings, land- scapes, and living objects, as will reproduce them in relief in the stereoscope. It is obvious, however, from observations previously made, that even this camera will only be applicable to statues of small dimensions, which have a high enough relief, from the eyes seeing, as it were, well around them, to give sufficiently dissi- milar pictures for the stereoscope. As we cannot increase the distance between our eyes, and thus obtain a higher degree of relief for bodies of large dimensions, how are we to proceed in order to obtain drawings of such bodies of the requisite relief ? Let us suppose the statue to be colossal, and ten feet wide, and that dissimilar drawings of it about three inches high are required for the stereoscope. These drawings are forty times narrower than the statue, and must be taken at such a distance that, with a binocular camera having its semilenses 23 inches distant, the relief would be almost evanescent. We must, there- fore, suppose the statue to be reduced n times, and place the semilenses of the binocular camera at the distance n x 2} inches. If n=10, the statue will be reduced to +9, or to 1 foot, and nx 22, or the distance of the semilenses will be 25 inches. If the semilenses are placed at this distance, and dissimilar pictures of the colossal statue taken, they will reproduce by their union a statue one foot high, which will have exactly the same appear- 30 Sir David Brewster on a Binocular Camera, &c. ance and relief as if we had viewed the colossal statue with eyes 25 inches distant. But the reproduced statue will have also the same appearance and relief as a statue a foot high, reduced from the colossal one with mathematical precision; and therefore it will be a better and a more relieved representation of the work of art than if we had viewed the colossal original with our own eyes, either under a greater, an equal, or a less angle of apparent magnitude. ' We have supposed that a statue a foot broad will be seen in proper relief by binocular vision; but it remains to be decided whether or not it would be more advantageously seen, if reduced with mathematical precision to a breadth of 24 inches, the width of the eyes, which gives the vision of a hemisphere 23 inches in diameter, with the most perfect relief. If we adopt this prin- ciple, and call B the breadth of the statue of which we require dissimilar pictures, we must make n= Bx and n x 21=B, that is, Qa the distance of the semilenses in the binocular camera, or of the semilenses in two cameras, if two are necessary, must be made equal to the breadth of the statue. In the same manner we may obtain dissimilar pictures of living bodies, buildings, natural scenery, machines, and objects of all kinds, of three dimensions, and reproduce them by the - stereoscope, so as to give the most accurate idea of them to those who could not understand them in drawings of the greatest accuracy. The art which we have now described cannot fail to be re- garded as of inestimable value to the sculptor, the painter, and the mechanist, whatever be the nature of his production in three dimensions. Lay figures will no longer mock the eye of the painter. He may delineate at leisure on his canvas, the forms of life and beauty, stereotyped by the solar ray and reconverted into the substantial objects from which they were obtained, bril- liant with the same lights and chastened with the same shadows as the originals. The sculptor will work with similar advantages. Superficial forms will stand before him in three dimensions, and while he summons into view the living realities from which they were taken, he may avail himself of the labours of all his prede- cessors, of Pericles as well as of Canova; and he may virtually carry in his portfolio the mighty lions and bulls of Nineveh,—the gigantic sphinxes of Egypt,—the Apollos and Venuses of Grecian art,—and all the statuary and sculpture which adorn the galleries and museums of civilized nations. PASE» | IV. Notice of a Chromatic Stereoscope. By Sir Davin Brewster, K.H., F.R.S., V.P.R.S. Edin.* ‘el the year 1848, I communicated to the British Association, at Swansea, a brief notice of the principle of this instru- menty. If we look with both eyes through a lens, about 24 inches in diameter or upwards, at an object having colours of different re- frangibilities, such as the coloured lines on a map, a red rose among green leaves, or any scarlet object upon a blue ground, or in general any two simple colours not of the same degree of refrangibility, the two colours will appear at different distances from the eye of the observer. In this experiment we are looking through the margin of two semilenses or virtual prisms, by which the more refrangible rays are more refracted than the less refrangible rays. The doubly- coloured object is thus divided imto two as it were, and the distance between the two blue portions is as much greater than the distance between the two red portions (red and blue being supposed to be the colours) as ¢wice the deviation produced by the virtual prism, if we use a large lens or two semilenses, or by the real prisms, if we use prisms. The images of different colowrs being thus separated, the eyes unite them as in the stereoscope, and the red image takes its place nearer the observer than the db/we one, in the very same manner as the two nearest portions of the dissimilar stereoscopic figures stand up in relief at a distance from their more remote portions. The reverse of this will take place if we use a concave lens, or if we turn the refracting angles of the two prisms in- wards. Hence it follows, and experiment confirms the inference, that we give solidity and relief to plane figures by a suitable applica- tion of colour to parts that are placed at different distances from the eye. These effects are greatly increased by using lenses of highly- dispersing flint glass, oil of cassia, and other fluids, and avoiding the use of compound colours in the objects placed in the stereo- scope. * Read before the Royal Scottish Society of Arts, Dec. 10, 1849. + See Report of the British Association at Swansea, 1848, Trans. of Sect., p. 48. [ 32 ] V. Account of Experiments with a powerful Electro-magnet. By J. P. Journ, F.R.S. &e.* OME years ago I announced that if a particle of wire con- ductmg a voltaic current be made to act upon a very large surface of iron, the intensity of the induced magnetism will not be much diminished by an increase in the distance of that par- ticle from the surface of the iron. Guided by this principle, I constructed a very powerful electro-magnet in 1843+, and soon after prepared the iron of the electro-magnet employed in the experments related in the present paper. This was a plate of the best wrought iron, 1 inch thick, 22 inches long, 12 inches broad at the centre, but tapered thence to the breadth of 3 inches, as represented in the adjoming sketch (fig. 1). The plate was then bent into a semicircular shape, so as to bring its ends within 12 inches of one another. Previously to fitting up this bar as an electro-magnet, I made a few experi- ments with a view to test the principle above named more completely than I had hitherto done. A length of about eight yards of insu- Figh lated copper wire, z,th of an inch in diameter, was divided mto two exactly equal portions, one of which was wound four times round the broadest part of the iron, and close to its surface ; the other was also wound four times round the broadest part of the iron, but was kept at the distance of one inch from its surface by means of interposed pieces of wood. A constant current of electricity was alternately passed through the wires; and the deflections of a magnetic needle half an inch long, placed at the distance of two feet from the iron bar, were observed to be as follows :— 6° 23! with the wire close to the surface of the iron. 6° 9! with the wire at the distance of one inch from the surface of the iron; showing only a trifling “diminution of effect in consequence of the removal of the wire to the distance of one inch from the surface. Having been thus fortified in my previous conclusion as to the propriety of enveloping broad electro-magnets with a very large quantity of coils, even though the outer ones should be * Communicated by the Author. + Philosophical Magazine, S. 3, vol. xxiii. p. 268. Account of Experiments with a powerful Electro-magnet. 33 removed to a considerable distance from the surface of the iron, I proceeded to fit up the large bar already described with a coil consisting of a bundle of copper wires 68 yards long, and weigh- ing 100 lbs. The electro-magnet thus formed was placed in a wooden box, on the side of which two large brass clamps were screwed, the latter being soldered to the terminals of the coil. The accompanying sketch represents the apparatus in its com- Fig 2 Ret an pleted state ; excepting, however, two brass straps, by means of which the coil is kept securely in its place, which are omitted for the sake of clearness. : In experimenting with the electro-magnet, I employed a bat- tery consisting of sixteen Daniell’s cells, the copper of each exposing an active surface of nearly two square feet. They were arranged so that I could with facility use either one cell alone, four cells in a series of two, or sixteen in a series of four elements. The cells and the liquids in them being similar in every respect, it was evident that these arrangements must produce through the electro-magnetic coils currents represented by 1, 2 and 4. I therefore was enabled 1o dispense with the use of a galvano- meter, which would have been acted upon by the powerful elec- tro-magnet, even if it had been placed at the distance of many yards from it. Experiment 1.—A magnetic needle, 1} inch long, was sus- pended at the distance of three feet from the electro-magnet measured on a line at right angles to that joining the poles. The northward tendency of the needle having been counteracted by means of a permanent magnet, I observed the following vibrations per minute resulting from the action of the electro- magnet :— With 1 cell ina seriesof1 . . 48 vibrations. eee Acells ... 2 capil (Oe ses coe 16 a A nay 2 8 aa The vibrations are evidently in the ratio of the square root of the quantity of current circulating around the electro-magnet, and consequently we may infer that the magnetism induced in the latter was simply in proportion to the current. Phil. Mag. 8. 4. Vol. 3. No. 15. Jan. 1852, D 34 Mr. J. P. Joule’s Account of Experiments : Experiment 11.—Having provided a pair of tapered poles ter- minating in vertical edges, 1 inch long and ith of an inch in breadth, I caused them to be slid on the poles of the electro- magnet until with 14 inch from each other. —‘‘ In conducting the business of this class, I look forward to ~ the holding of field excursions, regarding them to be quite as essen- tial as lectures for the instruction of the student, who, to benefit by his studies, must become a practical fossilist, and learn to observe carefully fossils iz situ, and appreciate on the spot the evidence afforded by their associations. During the progress of our Winter Courses this can be done effectually in the neighbourhood of London, or by means of the facilities of transport afforded by lines of railroad. I trust that before the end of this session a compact band of un- daunted investigators, belted, strapped, and bag-bearing, armed with stout hammers and sharp chisels, under the veteran generalship of our Director-in-chief, and officered by my mineral and geological colleagues and myself, will make the rocks shake and yield up their treasures for many a mile around the great metropolis.” Such ap- peals thrill the heart of the student like electric fire, and awaken an ardour which renders his task heroic. The lecturer assigns a high vocation to the naturalist. ‘It is not an uncommon fancy to suppose that naturalists are occupied entirely with the naming and describing of the kinds of animals and plants ; that provided they can enumerate, in clear though technical lan- guage, the characteristics or features of a being submitted to their examinations, usually in the state of a preserved specimen, and, on discovery of the species being one hitherto unnoticed, give it a name by which it may be remembered by their brother naturalists to the end of time, or thereabouts, they have attained all their aim and ful- filled all their ambition. This notion of their offices and duties is a libel. It takes notice of only a fragment of their labours. To name and describe are but to enrol an object with a true spelling and cor- rect definition, in the great dictionary of science. Words in diction- aries are exhibitions of the raw materials out of which literature is made ; and species arranged in zoological and botanical systems are orderly and beautiful displays of the raw materials of natural history science. Words may be wasted and species misused. But the study of species, which is the basis of all natural history science, does not take note merely of their external, or even their internal organiza- tion. It deals also with their relation to conditions in time and space. It seeks out the epoch of their first appearance, and traces them through their diffusion under favouring, or limitation and ex- Phil. Mag. 8, 4, Vol. 3. No. 15, Jan, 1852. . 66 Notices respecting New Books. tinction under unfavourable influences. It searches for the causes inherent in their organization, by which, of two similar, yet not identical creatures, the one has the power to battle with varied dnd very different forces, and to maintain a vitality which braves alike the freezing cold of the poles and the feverish warmth of the equator, to spread its individuals over more than half the globe. Whilst the other, distinguished it may be from its congener by-some apparently slight and useless difference,—though the mark be an indelible brand by which nattire has stamped that member of her flock, and that one only,—is incapable of asstiming protean variations, or of enduring even a slight chatige in the physical conditions under which it first appeared. It enjoys a fleeting existence during a short segment of time, dies out eré it has spread beyond a mere speck on the earth’s surface, disappearing never to reappear ;—perchance, if it belonged to some primeval fauna, never to become known to man with all his research, unless some bony or shelly frame-work gave consistence to its otherwise perishable substance.” The lecture is full of passages of exceeding force and beauty, and evinces a power of illustration which, without onee forsaking the precision of science, is almost poetic, Speaking of the service to be rendered by the naturalist to the designer, the lecturer concludes as follows :—‘‘ What is ornamental art but the isolation and embodi- ment in works of human skill of the beauty that is diffused through all the works of God? And that beauty lies not merely i in the bulk of objects, nor on their surface, but is as manifest in every part and atom composing them as in the combined whole. It is in itself com- posite; the combination, not of lesser, but of minuter beauties. To imitate—to approach—we must attempt a like arrangement, in order to obtain the same exquisite result. And how, except through earnest and scientific study, can we attain the knowledge that shall enable us to discover the pathway leading towards petfection ?” The fourth lecture, on the Importance of cultivating Habits of Observation, was delivered by Professor Hunt, Keeper of Mining Records. In illustration of his subject, he refers to the observation of Thales, that rubbed amber attracted light bodies; to the discoveries of Gal- vani and CErsted; to the attempts made to tum magnetism to account as a motive power; to Faraday’s discovery of induced cut- rents; to the discovery of the planet Neptune ; to the steam-engine; to the researches of Boutigny on the spheroidal condition of bodies ; and to the glass used to protect the plants in the palm-house in Kew Gardens. In his remarks on lightning-conductors, we eannot help thinking that the lecturer, in recoiling from one error, has fallén into another equal and opposite. The author concludes his discourse with the following quotation :— “ Divine Philosophy ! Not harsh and crabbed as dull fools suppose, But musical as is Apollo’s lute, And a perpetual feast of nectar’d sweets Where no crude surfeit reigns.” L 67 J XI. Proceedings of Learned Societies. ROYAL SOCIETY. [Continued from vol. ii. p. 568.] Dee. 11,” | ‘HE reading of Dr. Faraday’s paper, entitled “ Experi- 1851. mental Researches in Electricity. Twenty-cighth Series, On Lines of Magnetic Force; their definite character; and their distribution within a Magnet and through Space,” which was eommenced on the 27th November, was resumed and concluded. The author defines a line of magnetic force to be that described by a very small magnetic needle, when it is so moved, in either direction correspondent to its length, as to remain constantly a tangent to the line of motion; or as that along which if a transverse wire be moved in either direction, there is no tendency to the forma- tion of an electric current in the wire, whilst if moved in any other direction there is such a tendency. Such lines are indicated by iron filings sprinkled about a magnet. ‘These lines have a deter- minate direction; they have opposite qualities in and about this di- rection, and the forces in any part of them are determinate for a given magnet. ‘They may, as the author thinks, be employed with great advantage to represent the magnetic force as to its nature, condi- tion, direction, and comparative amount; and that in many cases when other repregentations of the force, as centres of action, will not apply. The term line of force, as defined above, is restricted to mean no more than the condition of the force in a given place, as to strength and direction; and not to include any idea of the nature of the physical cause of the phenomena: at the same time if reason should arise to think that the physical condition of the force partakes ge- nerally of the nature of a current or of a ray, a view which the author inclines to, he sees no objection in the term, any more than to the terms current and ray, as they are used in considerations regarding electricity and light, because it may accord with such a view. The lines of magnetic force, as defined above, may be recognized either by a magnetic needle or by a moving wire; but the two methods are founded on very different conditions and actions of the magnetic force, and the moving wire appears to have the largest application. Its principle can be applied in places which are inac- cessible to the needle, and it can sum up the forces in a given plane or surface at any distance from the central magnet. It has no re- ference to results of attraction or repulsion, and in some cases is opposed to them; but the author thinks it gives a true view of the disposition of the magnetic powers, and leads, and will lead to a more correct understanding of the nature of the force. For these reasons he advocates its adoption, not to the exclusion of the needle, but in conjunction with it; and proceeds to develope the experi- mental methods and their results, and first in the case of a bar magnet. Two bar magnets, each 12 inches long, 1 inch in width, and 0°4 F2 68 Royal Society. of an inch in thickness, were fixed, side by side, a little apart, with like ends in the same direction, on and parallel to an axis, so that they might act as one bar magnet and be revolved at pleasure about the common axial line. A wire, which entering at one pole was carried along the axis of the magnetic arrangement, was at the centre turned outwards at the equatorial part, and then made to return at a distance outside the magnet to the place from whence it commenced. At times this wire was in three parts; the axial part being one, a radial part extending from the centre to the surface at the equator and there connected with a copper ring surrounding the magnet, being another, and the part from this ring on the outside of the magnet, back to the place of commencement, being the third ; and each of these could revolve either separately or in conjunction with the other parts, the electric contact being complete in all the cases, whilst the wire was insulated from the magnet by the cover- ing of silk. The ends of this loop, as it may be called, were con- nected with a galvanometer, and thus the presence or absence of electric currents ascertained, and their amount measured. Two galvanometers were used; one by Rheinkorf, containing fine wire, and very delicate in its action ; the other, constructed by the author, of copper wire 0°2 of an inch thick, passing only once round each needle; this, for abundant currents of low intensity, such as those generated in the moving wire, was found many-fold more delicate in its indications than the former. The general relations of a moving wire to the magnetic lines of force are then specified, and a reference is made to their discovery and description by the author in the First Series of these Experimental Researches; and the law of the evolution of the induced electrical current is given. Referring to an easy natural standard, it may be said, that if a person in these latitudes, where the lines of force dip 69 degrees, as shown by the dipping-needle, move forward with arms extended, then the direction .of an electric current which would tend to be produced in a wire represented by the arms, would be from the right hand through the arms and body to the left. It will be seen, upon a little consideration, that a wire which touches a regular bar magnet at one end, and is then continued through the air until it touches it again at the equator, if moved once round the magnet, slipping at the equator contact so as to resume its first position at the end of the revolution, will have in- tersected, once, all the lines of force external to the magnet, and neither more nor less, whatever its course through the air, or distance in parts from the magnet, may be. Now when the external part of the loop above described is moved in this manner a certain number of degrees round the axis of the magnet, the latter being still, a current of electricity in a given direction is shown by the galvanometer; and the proper precautions (which are described) being taken, the current is of the same amount for the same number of degrees of revolution, whether the motion be quicker or slower, or whether the wire be at a greater or a less distance in its course from the magnet. Royal Society. 69 If the external part of the loop be retained fixed, as also the axial part, and the magnet with the short radial part of the wire be revolved, an electric current is again produced, of a strength exactly equal to the former for the same number of degrees of revolution; but its direction is the reverse of the first current, when the direction of revolution is the same. In either case, reversing the direction of the revolution reverses the current produced by it. The moving radial part of the wire is in this case insulated from the magnet, and many other experiments, as with discs at the ends of the magnet, show, that the motion of the magnet itself is indifferent; and that whether it revolve or is still, provided the wire move, the result is the same. When the radial wire or part of the loop, and the ex- ternal part move together, then their effects exactly neutralize each other, as they ought to do, being in contrary directions, for the same revolution; and not the slightest trace of a current under the extremest conditions of motion, or of the experiment, can be pers ceived. Such is the case, whatever the course or distance of the external part of the loop may be, or even when the loop is altogether external to the magnet, but moving at the same angular velocity either with or around it. When the axial part of the loop is revolved it produces no effect ; neither if this part revolve or be still does it produce the least influence on any of the results already described; it acts simply as a conductor, and is in other respects perfectly indifferent. This axial wire may be replaced by the magnet itself; for when it exists only from the magnetic pole outwards, and when the radial wire has contact with the magnets at the centre, so as to complete the electric circuit, the results are exactly the same as before: or the axial wire may proceed to the centre and then make contact with the magnet, and the radial wire be removed; when precisely the same results occur: or both axial and radial parts may be removed, the magnet serving both for conductor and moving radius, and still the results are unchanged. From such results as these, the author draws the following con- clusions, in relation to the lines of magnetic force as defined at the commencement. The amount of magnetic force (as shown by the electric current evolved) is determinate ; and the same for the same lines of force, whatever the distance of the point or plane on which their power is exerted is from the magnet: or it is the same in any two or more sections of the same lines of force. There is no loss or destructibility, or evanescence or latent state of the magnetic power. Convergence or divergence of the lines of force causes no difference in the amount of their power. Obliquity of intersection causes no difference. In an equal field of magnetic force the elec- tricity evolved is proportionate to the time of motion, or to the velocity of motion, or to the amount of lines of force intersected. The internal state of the magnet is then examined by means of the results obtained with the radial wire, or the moving magnet when the latter makes part of the circuit; and the conclusion is arrived at, that there are within the magnet lines of magnetic force 70 Royal Society. as defined as, and exactly equal in amount to, those outside of it; that these are continuations of the former; and that every line of magnetic force, whatever distance it may extend to from a magnet, (and in principle that is infinite,) is a closed curve, which in some part of its course passes through the magnet in conformity with what is called its polarity. A current being thus induced in a closed wire, when it travels across magnetic lines of force, an inquiry is next made into the effect of altering the mass or diameter of the wire, and another form of apparatus is employed, in which loops of wire are made to inter- sect a given amount of lines; each loop consisting of a given length of wire, but either of wires of different diameter, or of one or more wires of the same diameter. The conclusion arrived at is, that the current or amount of electricity evolved is not simply as the space oceupied by the breadth of the wire correspondent to the direction of the line of force, which has relation to the polarity of the power ; nor by that width or dimension of it which includes the number or amount of lines of force intersected, and, which corresponding to the direction of the motion has relation to the equatorial condition of the lines; but is jointly as the two, or as the mass of the wire. The moying wire was next surrounded by different media, as air, al- cohol, water, oil of turpentine, &c., but the result was the same in all. Wires of different metals were used, and results in accordance with those obtained and described in the Second Series of these Researches were obtained: the conclusion is, that the current excited appears to be directly as the conducting power of the substance employed. It has no particular reference to the magnetic character of the body; for iron’ comes between tin and platinum, presenting no other distinction than that due to conducting power, and differing far less from these metals than they do from metals not magnetic. Magnetic polarity then comes under consideration. The author understands by this phrase, the opposite and antithetical actions which are manifest at the opposite ends, or the opposite sides, of a limited portion of a line of force. He is of opinion that these qualities, or conditions, are not shown with certainty in every case, by attractions and repulsions; thus a solution of sulphate of iron will be attracted by a magnetic pole if surrounded by a solution weaker than itself, as shown in former researches on diamagnetic and paramagnetic action; but if surrounded by a solution stronger than itself it will be repelied. Yet the direction of the lines of force passing through it and the surrounding media cannot be reversed in these two cases, and therefore the polarity remains the same. The moving wire however shows, in similar cases, the true polarity or direction of the forces; and for an application cf its principles, in this respect, to the metals, an apparatus is described by which dises of different metals can be revolved between the poles of a horse-shoe magnet and the electric currents evolved in them carried off to the galvanometer. Now, whether the discs be of paramagnetic or dia- magnetic metals, whether of iron, or bismuth, or copper, or tin, or lead, the direction of the current produced shows, that the lines of Royal Astronomical Society. 71 magnetic force passing through the metals is the same in all the eases, and hence the polarity within them the same. The author then gives a more explicit meaning, in accordance with the definition of line of magnetic force contained in this paper, to some of the expressions used in the three last series of his Researches on Magnetic Condition, Atmospheric Magnetism, &c.: and by referring to former results obtained since the year 1830, illustrates how much the idea of lines of force has influenced the course of his investigations, and the results obtained at different times, and the extent to which he has been indebted to it; and then, recommending for many special reasons the mode of examining magnetic forces by the aid of a moving conductor, he brings for the present his subject to a conclusion. ROYAL ASTRONOMICAL SOCIETY. [Continued from vol. ii. p. 326.] June 13, 1851.—On some Improvements in Reflecting Instru- ments. By Prof. Piazzi Smyth. In the course of his lectures on Practical Astronomy to the students of the Edinburgh University last winter, Prof. P. Smyth had unusual opportunity of ascertaining those points in the making of the generality of the observations of navigators by sea and of trayellers on land, which presented the greatest difficulty to be- ginners. And as these points generally consisted of needless pe- culiarities, sometimes absolute imperfections in the instruments, the Professor proceeded to remove them as well as he could, and the result may, perhaps, be more extensively useful, especially as the difficulties were generally felt on the sextant being applied to observations of stars by night, a more exact means than the sun by day, and therefore to be encouraged and assisted in every way. In nayal obseryations the impediments were, both by the expe- rience of the class, and by the testimony of nayal ofticers,— Ist, Difficulty of seeing and of bringing down the star. 2nd. Difficulty of seeing the horizon line at night. 8rd. Difficulty of reading off the angle on the limb. The first of these, in so far as it depended on the dark field of the telescope, he proposed to remedy by employing a telescope of large aperture, say 2 inches, in place of the usual size, 4 or % inch; in so far as the loss of light was occasioned by reflexion and absorption at the glasses, he intended to remove this by employiug metal reflectors, by which, too, the occasional nuisance of second images would be avoided and greater accuracy obtained. He had tried speculum metal for the purpose with great advantage; but, under some circumstances, he was in hopes of being able to employ silyer, which has lately been found to be capable of reflecting near double the amount of light that speculum metal does, though that fetains more than quicksilvered glass; and then, in so far as the oss of the star in ‘ bringing down” is caused by the diminished surface exposed by the index-glass at large angles, he proposed to make that larger than usual; besides which, the reflexion taking 72 Royal Astronomical Society. place in the metal at the first surface, there would be no loss, as now, from the thickness of the edges of the glass or the sides of the brass box containing it. The second difficulty would be alleviated by the same adoption of the large object-glass: besides the loss of light by transmission through the so-called transparent part of the present horizon-glass would be done away with by the employment of the metal reflectors. The third difficulty was also shown to be gratuitous, for the reflector of the reading-glass was in general so placed that the light of the lamp could not get to it, and if it did, would be thrown away from the arc instead of on it: and were even that managed, the surface of the vernier and arc being in different planes, the same ray of light would not illumine them doth at the same time. By placing them, however, both in the same plane, and by putting the reflector at an angle of 45° to the limb, instead of parallel to it, so as to receive parallel light and throw it straight down to the divisions, it was found that they could easily be read by a very faint light. For accuracy, opposite readings were deemed essential, and a circle insisted on in place of a sextant or quadrant; and the author, considering that the failure of the reflecting circle in se- curing a permanent footing in the navy arose from its being made in general too large and heavy, and complicated, he had devised a very small, but strong and simple form; the telescope was more firmly connected by moving in grooves on the large surface of the face of the circle, instead of rising by the usual single screw; and in place of the inconvenient plan of having to reverse the hands so as to put the instrument into its box face uppermost (which makes the getting of it out again without pulling at the reflector or some such delicate parts, difficult), by placing the legs not on the back but on the face, the instrument may. be either put into its box, or down on the floor, or anywhere, face first, with the same hand which was moving it in the observation, with the divisions and the reflectors protected from all accidents, and the whole instru- ment ready at any time on a moment’s notice (for the telescope never need be taken off, with its improved fixing), to take advantage of an instantaneous opportunity of observation. So much for the use of the reflecting instrument at sea: as used on land, the following difficulties were found, and are generally re- cognised :— lst. The impossibility of measuring in the mercury either sun or star when within, say 20° of the zenith, from the reflecting instrument not taking in so large an angle; and again, when within, say 10° of the horizon, from the foreshortening of the reflecting surface. 2nd. The difficulty of seeing the referring point all night, viz. the reflected image of the star, when black glass is employed; and the trouble with wind when employing mercury, as well as with other causes producing vibration; and the great weight and liability to loss in long journeys through difficult and uncivilized countries. All these difficulties seemed to be met by making the reflecting Intelligence and Miscellaneous Articles. 73 surface of speculum metal, leveled by a spirit-level ; and when the reflected object could not be seen, attaching to the metal a col- limating telescope, whose optical axis was parallel with the pre- viously leveled surface, and was defined at the focus end by a horizontal slit, illuminated by a lamp at night, soas completely to remove all difficulty of seeing the referring object, and allowing of almost the whole object-glass being brought to bear on the star. Difficulty having been found by the students in keeping sight of an object reflected from the artificial horizon, the latter was generally placed on a stand so as to bring it near the eye, and make it thereby offer a large angular space, which was pretty sure not to be exceeded by the shaking of the hand or involuntary movement of the head of an unpractised observer ; but it was found requisite, nut only to make the stand firm, but to improve the steadiness of the leveling screws, which was done by making them parts of a fixed frame, with the reflector moveable on them, and capable of being fastened in any position between opposite nuts. A sextant with all the improvements (except the opposite read- ings), a full-sized model of a circle, and one of the reflecting horizon, were shown; but Prof. Smyth did not mean to claim any part of them as his own invention ; for without making any special inquiries as to how far he might have been preceded by any one else, he believed that he had only brought to bear on this subject individual improvements long and well known in other departments of the science ; but as they had never, he thought, been so com- pletely united before, and as such a reunion might enable observa- tions often to be obtained when now they are given up, he hoped that the communication might not be uninteresting to some of the numerous working members of the Society, XII. Intelligence and Miscellaneous Articles. ON THE PRODUCTION OF INSTANTANEOUS PHOTOGRAPHIC IMAGES. BY H. IF. TALBOT, ESQ. - will probably be in the recollection of some of your readers that in the month of June last a successful experiment was tried at the Royal Institution, in which the photographic image was obtained of a printed paper fastened upon a wheel, the wheel being made to revolve as rapidly as possible during the operation. From this experiment the conclusion is inevitable, that it is in our power to obtain the pictures of all moving objects, no matter in how rapid motion they may be, provided we have the means of sufficiently illuminating them with a sudden electric flash. But here we stand in need of the kind assistance of scientific men who may be acquainted with methods of producing electric discharges more powerful than those in ordinary use. What is required, is, vividly to light up a whole apartment with the discharge of a battery :—the photographic art will then do the rest, and depict whatever may be moving across the field of view. 74 Intelligence and Miscellaneous Articles. I had intended to communicate much earlier the details of this experiment at the Royal Institution, but was prevented from doing so at the time; and soon afterwards I went on the Continent in order to observe the total solar eclipse of the 28th of July. This most interesting phenomenon I had the pleasure of witnessing at the little town of Marienburg, in the north-eastern corner of Prussia. The observations will appear, I believe, in a forthcoming volume of the Transactions of the Royal Astronomical Society. Among other things, I was enabled to make a satisfactory estimate of the degree of darkness during the total obscuration ; which proved to be equal to that which existed one hour after sunset the same evening, the weather being during that evening peculiarly serene, so as to allow of a just comparison. This Continental journey having effectually interrupted my photo- graphic labours, I have only recently been able to resume them. I shall therefore now proceed to describe to you exactly the modein which the plates were prepared which we used at the Royal Institu- tion; at the same time not doubting that much greater sensibility will be attained by the efforts of the many ingenious persons who are now cultivating the art of photography. And it is evident that an increased sensibility would be as useful as an augmentation in the intensity of the electric discharge. The mode of preparing the plates was as follows :— 1. ‘Take the most liquid portion of the white of an egg, rejecting the rest. Mix it with an equal quantity of water. Spread it very evenly upon a plate of glass, and dry it at the fire. A strong heat may be used without injuring the plate. ‘The film of dried albumen ought to be uniform and nearly invisible. 2. To an aqueous solution of nitrate of silver add a considerable quantity of alcohol, so that an ounce of the mixture may contain three grains of the nitrate. I have tried various proportions, from one to six grains, but perhaps three grains answer best. More ex- periments are here required, since the results are much influenced by this part of the process. 3. Dip the plate into this solution, and then let it dry sponta- neously. Faint prismatic colours will then be seen upon the plate. It is important to remark, that the nitrate of silver appears to form a true chemical combination with the albumen, rendering it much harder, and insoluble in liquids which dissolved it previously. 4. Wash with distilled water to remove any superfluous portions of the nitrate of silver. ‘Then give the plate a second coating of albumen similar to the first; but in drying it avoid heating it too much, which would cause a commencement of decomposition of the silver. I haye endeavoured to dispense with this operation No. 4, as it is not so easy to give a perfectly uniform coating of albumen as in No. 1. But the inferiority of the results obtained without it induces me for the present to consider it as necessary. 5. To an aqueous solution of protiodide of iron add first an equal volume of acetic acid, and then ten volumes of alcohol. Allow the mixture to repose two or three days. At the end of that time it Intelligence and Miscellaneous Articles. 75 will have changed colour, and the odour of acetic acid as well as that of alcohol will have disappeared, and the liquid will have acquired a peculiar but agreeable vinous odour. It isin this state that I prefer to employ it. 6. Into the iodide thus prepared and modified the plate is dipped for a few seconds. All these operations may be performed by mode- rate daylight, avoiding however the direct solar rays. 7. Asolution is made of nitrate of silver, containing about 70 grains to one ounce of water. To three parts of this add two of acetic acid. Then if the prepared plate is rapidly dipped once or twice into this solution it acquires a very great degree of sensibility, and it ought then to be placed in the camera without much delay. 8. The plate is withdrawn from the camera, and in order to bring out the image it is dipped into a solution of protosulphate of iron, containing one part of the saturated solution diluted with two or three parts of water. The image appears very rapidly. 9. Having washed the plate with water, it is now placed in a so- lution of hyposulphite of soda, which in about a minute causes the image to brighten up exceedingly by removing a kind of veil which previously covered it. 10. The plate is then washed with distilled water, and the process is terminated. In order, however, te guard against future accidents, it i well to give the picture another coating of albumen or of varnish. These operations may appear long in the description, but they are rapidly enough executed after a little practice. {n the process which I have now described, I trust that I have effected a harmonious combination of several previously ascertained and valuable facts—especially of the photographic property of iodide of iron, which was discovered by Dr. Woods of Parsonstown, in Ireland, and that of sulphate of iron, for which science is indebted to the researches of Mr. Robert Hunt. In the true adjustment of the proportions, and in the mode of operation, lies the difficulty of these investigations ; since it is possible by adopting other propor- tions and manipulations not very greatly differing from the above, and which a careless reader might consider to be the same, not only to fail in obtaining the highly exalted sensibility which is desirable in this process, but actually to obtain scarcely any photographic re- sult at all. To return, however, from this digression.—The pictures obtained by the above-described process are negative by transmitted light and positive by reflected light. When I first remarked this, I thought it would be desirable to give these pictures a distinctive name, and I proposed that of Amphitype, as expressive of their double nature— at once positive and negative. Since the time when I first observed them, the Collodion process has become known, which produces pic- tures having almost the same peculiarity. In a scientific classifica- tion of photographic methods, these ought therefore to be ranked together as species of the same genus. ‘These Amphitype pictures differ from the nearly related Collodion ones in an important circum- stance, viz. the great hardness of the film and the firm fixation of the image, which is such that in the last washing, No, 10, the image 76 Intelligence and Miscellaneous Articles. may be rubbed strongly with cotton and water without any injury to it; but, on the contrary, with much improvement, as this removes any particles of dust or other impurity, and gives the whole picture a fresh degree of vivacity and lustre. A Daguerreotype picture would be destroyed by such rough usage before it was completely fixed and finished. In examining one of the Amphitype pictures, the first thing that strikes the observer is, the much greater visibility of the positive image than of the negative one ; which is at least in the proportion of ten to one, since it is not rare to obtain plates which are almost invisible by transmitted light, and which yet present a brilliant pic- ture full of details when seen by reflected light. The object of giving to the plates a second coating of albumen, as prescribed in No. 4, is chiefly in order to obtain this well-developed positive image; for it is a most extraordinary fact, that a small change in the relative proportions of the chemical substances em- ployed enables us at pleasure to cause the final image to be either entirely negative or almost entirely positive. In performing the ex- periment of the rotating wheel the latter process must be adopted, since the transmitted or negative image is not strong enoughto be vi- sible unless the electric flash producing it bean exceedingly bright one. I now proceed to mention a peculiarity of these images which ap- pears to me to justify still further the name of Amphitype, or, as it may be rendered in other words, “‘ ambiguous image.” Until lately I had imagined that the division of photographic images into positive and negative was a complete and rigorous one, and that all images must be of either the one or the other kind. But a third kind of image of a new and unexpected nature is observed upon the Amphi- type plates. In order to render this intelligible, I will first recall the general fact that the image seen by transmitted light is negative and that by reflected light positive. Yet, nevertheless, if we vary the inclination of the plate, holding it in various lights, we shall not fail speedily to discover a position in which the image is positive although seen by transmitted light. This is already a fact greatly requiring explanation. But the most singular part of the matter is, that in this new image (which I call the transmitted positive), the brightest objects (viz. those that really are brightest, and which ap- pear so in the reflected positive) are entirely wanting. In the places where these ought to have been seen, the picture appears pierced with holes, through which are seen the objects which are behind. Now, if this singularity occurred in all the positions in which the plate gives a positive image, I should be satisfied with the explana- tion that the too great brightness of the objects had destroyed the photographic effect which they had themselves at first produced. But since this effect takes place in the transmitted positive but not in the reflected positive, I am at a loss to suggest the reason of it, and can only say that this part of optical science, dependent upon the molecular constitution of bodies, is in great need of a most careful experimental investigation. The delicate experiment of the revolving wheel requires for its success that the iodide of iron employed should be in a peculiar or Intelligence and Miscellaneous Articles. o. definite chemical state. This substance presents variations and ano- malies in its action which greatly influence the result. Those pho- tographers, therefore, who may repeat the experiment will do well to fix their principal attention upon this point. It is also requisite in winter to warm the plates a little before placing them in the camera. In pursuing this investigation, I have been much struck with the wide field of research in experimental optics which it throws open. By treating plates of albumened glass with different chemical solu- tions, the most beautiful Newtonian colours, or “colours of thin plates,” may be produced. And it often happens that the landscapes and pictures obtained by the camera present lively though irregular colours. These not being in conformity with nature are at present useless ; with this exception, nevertheless, that in many pictures [ have found the colour of the sky to come out of a very natural azure blue. I hope soon to have the leisure requisite for pursuing this very interesting branch of inquiry, and in the mean time I venture to recommend it to the notice of your scientific readers.— Atheneum, Dec. 6, 1851. ON COPPER CRYSTALLIZED BY MEANS OF PHOSPHORUS. BY F. WOHLER. The experiments of Bock and Vogel, sen., have taught us that the whole of the copper in a solution of the sulphate contained in closed vessels is reduced by phosphorus ; crystalline laminz of greater or less thickness, according to the duration of the reaction, having the form of the piece of phosphorus and of a beautiful bright copper colour, being formed. If the pieces of phosphorus are placed in contact with bright copper wires, reduction of the copper also takes place upon them, and this in distinct, mostly well-formed octohedral crystals, the form of which, when the process is allowed to continue for weeks and months, with a quantity of undissolved crystals of the sulphate in the solution, is distinguishable to the naked eye; at the same time the whole of the phosphorus disappears, and the masses of copper reduced by it are found filled inside with black pulyerulent phosphuret of copper.—Ann. der Chem. und Pharm. vol. lxxix, p- 126. ON THE ACCIDENTAL COLOURS WHICH RESULT FROM LOOKING AT WHITE OBJECTS. BY M. D. M. SEGUIN. 1. If after having looked for some time at a white object the eyes are closed, a coloured image of the object is seen. ‘This image pre- sents a number of colours, which change little by little: as an ex- ample, I will narrate the following instance. After looking at a very brilliant object, such as a white screen seen by the transmitted light of the sun, on closing the eyes the image appears at the first moment green, olive-green or yellow; but there is a red border all round, followed by much darker tints. After a few mo- ments the image becomes decidedly yellow, but the coloured border approaches towards the centre of the image: the latter acquires a deeper yellow, a zone of orange and a zone of red gain gradually upon the yellow, and at the same time the dark tint which was 78 Intelligence and Miscellaneous Articles. beyond the red separates into a number of coloured zones of great intensity, presenting violet, indigo, blue, green. All the colours advance one after the other towards the centre of the image, which they successively occupy. By varying the brightness of the object, and the length of time of looking at it, I have been able to detect one or two constant series of colours, apparently very different, which these accidental images present, 2. When the accidental image is formed in the eyes, if they are opened towards a white surface, the image remains; but it generally passes from the tint which it has to one of those which it would assume at a later period if the eyes were kept closed, and at the same time the tints which still remain at the border advance more towards the centre, which they occupy successively. The white light which enters the eye has therefore the effect of accelerating the pro- gression of the colours from the circumference to the centre of the image. I have traced this influence of the exterior white light, whether by opening the eyes before a surface more or less lighted, or by gradually opening them, and I have found that the tint to which the image passes is more advanced in the series when the ex- terior light is more intense. 3. My experiments have enabled me to observe those instances in which the accidental image of a white object passes through alter- nations of brightness and darkness; I have always observed that the images are coloured. - In the hope of being able to account for these effects, I have en- tered upon the study of the accidental images produced by coloured objects. This part of the question has been much disputed. Ihave repeated almost all the experiments described by various authors, and have frequently been astonished at the results which I have ob- tained. I shall describe these in a second memoir.—Comptes Rendus, Dec. 8, 1851. EXTRAORDINARY SPOTS ON THE SUN. On Saturday last, the 29th of November, the solar macule, which have of late been very numerous, assumed a remarkable shape and occurred in very considerable number. Dr. Forster, who has been occupied of late in taking drawings of these spots, observes that he has never seen any spot on the sun’s disc so large or unusual in form as that which occurred on Saturday : it was of a long and irregular form, densely black, and surrounded with a widely-spreading greyish margin, as well as by several other smaller macule. Many other more round and compact spots appeared on other parts of the disc. But the most remarkable circumstance was the rapid changes ob- served in these phenomena. While Dr. Forster was observing them, several new spots broke out into view. The connexion of these phenomena with the abundance of wet and cold were formerly noticed by the late Dr. Herschel. Now that the weather has been dry in England, a more than ordinary quantity of snow and rain has fallen on the Continent. Bruges, Dee, 5, 1851. Meteorological Observations. 79 OBITUARY.—MR. SAMUEL VEALL. Died at Boston, Lincolnshire; on the 17th of August 1851, aged 71 years. It may be said of him, that in youth, and until his mental powers had become enfeebled by age, he was diligent in the attainment of knowledge. From his early days he was fond of books and expe- rimental science. At a time when philosophy was by no means fashionable, especially about 1808 and 1809, he was amongst the earliest projectors and friends of a Literary and Philosophical Society in Boston, his native town. In connection with this Society, he be- came Secretary, and delivered lectures on Electricity, Optics, Galva- nism, &c.; and it is believed continued his efforts so long as he could fitid coadjutors to act with him. He engaged in those pursuits simply for the improvement of himself and his neighbours. It may well be presumed, that his Meteorological Journal, which he kept methodically and perseveringly for many years, and commu- nicated to this Magazine from the year 1816, has aided in throwing some light upon the laws which govern the changes of the atmosphere, and may have induced others to contribute in lke manner to meteo- rological science. He was considerate to a fault of those whom he employed in busi- ness; and though often injured himself, he was not known to act injuriously towards others. Punctiliously honest, he even made scruples where many individuals esteemed upright would see nothing to blame. He has left a widow and family to revere his memory and imitate his virtues. METEOROLOGICAL OBSERVATIONS FOR Nov. 1851, Chiswick.—November 1. Overcast: very fine: clear: frosty. 2. Fine: hail-shower. 3. Hoar-frost: very fine: cloudy: rain. 4. Rain: fine, but cold. 5. Clear and frosty: slight rain at night. 6. Clear and fine: cloudy. 7. Clondyandcold. 8. Fine: rain. 9. Foggy: fine: rain. 10. Veryfine: drizzlyatnight. 11, 12. Very fine. 13. Foggy. 14. Clearandfine. 15. Frosty: very fine: clear. 16. Frosty: clear and fine: cloudy. 17. Clearand cold: frosty atnight. 18. Clear and cold: severe frost at night. 19. Sharp frost: fine: cloudy. 20. Clear and frosty: very clearthroughout. 21. Overcast. 22. Cloudy: fine. 23. Trosty: clear and fine: rain at night. 24. Densely clouded: foggy at night. 25. Frosty: veryfine. 26: Foggy. 27. Hazy. 28. Frosty: very fine: frosty. 29. Frosty, with fog: fine: foggy. 30. Dense fog. Mean temperature of the month ........ssseseseeseseeees “posers 35°86 Mean temperature of Noy. 1850 .........sseeeeseeseeee eee olsen ces 45 +29 Mean temperature of Noy. for the last twenty-five years ... 43 -43 Average amount of rain in NOV. ...tsseesssiseseseesvecscseeenes 2°35 inches. Boston—Nov. 1. Fine. 2. Rain: rain early a.m. 3,4. Fine. 5, 6. Fine: rainp.M. 7. Cloudy. 8. Cloudy: rainp.m. 9,10. Fine: rainp.m. 11. Foggy. 12—16. Fine. 17. Fine: snowr.m. 18. Fine. 19. Cloudy. 20. Fine. 21. Cloudy: rainp.m. 22. Cloudy: rain a.m. and p.m, 23. Cloudy: rain p.m. 24, 25, Fine. 26. Cloudy. 27. Fine. 28, Cloudy. 29. Fine. 30. Foggy. Sandwick Manse, Orkney.—Nov. 1, 2. Showers. 3. Snow-showers. 4. Snow- showers: rain. 5. Showers: cloudy. 6. Showers: cloudy: rain. 7. Rain: drizzle. 8. Drizzle. 9. Showers. 10. Bright: showers. 11. Bright: cloudy. 12. Cloudy. 13, Showers: hail-showers. 14. Sleet-showers: rain. 15. Showers: cloudy. 16. Sleet-showers: snow-showers. 17. Hail-showers: cloudy. 18. Cloudy: clear. 19. Cloudy: drops. 20. Bright: rain. 21. Showers: clear : aurora, 22. Bright: cloudy. 23. Cloudy: rain. 24. Clear: frost: aurora. 25. Frost: rain: clear. 26. Showers: fine. 27, 28. Fine: frost; fine. 29. Fine: frost: fine: showers, 30. 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By Joun Tynparz, Ph.D. [With a Plate.] On Thermo-electric Currents, by Prof. Macnus of Berlin*. Experiments of MM. Svanseret and Franzt on Monothermic Electricity§. Ap- _ plication of the results of M. Macnus fo the solution of certain difficul- ties encountered by M. REGNAULT. _ of a degree Centi- grade. A practised eye can easily estimate the tenth part of each of these spaces; consequently I could by these thermometers observe a difference of temperature not greater than 0°:005. The voltaic pile that I made use of was one of very large di- mensions, each cell being 2 feet high and 5 inches in diameter. The internal arrangements of the cells were similar to those of the ordinary pile of Daniell. 5. I shall now proceed to describe my experiments on the heat evolved by currents traversing metallic wires. The apparatus used consisted of a wire of pure silver, 8 metres long and about 0°6 of a millimetre in thickness, coiled upon a thin chimney- glass, the several coils being prevented from touching one an- other by means of silken threads. The ends of the silver wire were connected metallically with two thick copper wires, the ends of which dipped into cups of mercury. The coil, thus mounted, was immersed in a jar of tinned iron, capable of containing two pounds and a half of water. In order to prevent, as well as pos- sible, the influence of the surrounding atmosphere in raising or depressing the temperature of the water, the sides and bottom of this jar were made hollow by soldering two jars of unequal mag- nitude within each other. Fig. 4 represents a section of this double can, aa being the hollow part between the internal and external cans. The positions of the coil, thermometer and stirrer, are also shown in the same figure. At 7 o’clock a.m., Sept. 4, 1844+, having filled the jar with 22 Ibs. of distilled water, I immersed the coil of silver wire into * Annales de Chimie et de Physique, 1842, vol. v. p. 428, note. + My object in being so particular as to the dates of the experiments, was to eliminate the effects of any variation in the intensity of the earth’s magnetism. In the subsequent series of experiments I have not always thought it necessary to mention these dates, but I have nevertheless used the same precaution in all of them. in Chemical Combinations. 489 it, and caused it to form part of a circuit in which a pile consist- ing of sixteen of the large Daniell’s cells in series and the gal- vanometer were placed. The circuit remained closed for exactly five minutes, durmg which time the deflections of both ends of the pointer of the galvanometer were observed three times. The mean of all the observations, no two of which differed from each other more than a few minutes of a degree, when properly cor- rected for the error in the position of the pointer, was 72° 17/. The increase of the temperature of the water, ascertained with all proper precautions in stirring, &c., was indicated by 81:8 - divisions of the scale of the thermometer, each division corre- sponding to =+;th of a degree Cent. The temperature of the room was 2°07 Cent. lower than the mean temperature of the water. As soon as the experiment just described was finished, another was performed in exactly the same manner; only the direction of the current was reversed, in order that the deflections might be observed on the other side of the meridian. At 7 o’clock p.m. of the same day, two experiments were again made in the manner above described; but in these the quantity of electricity passed through the silver wire was only about half as much as before ; five cells of the pile being now employed, instead of sixteen as before. On the morning of September 5, two experiments of the same kind were made with a pile consisting of two cells in series; and on the evening of the same day, two experiments were made using only one of the constant cells. On the two succeeding days all the above experiments were gone over again in the reverse order, beginning with one cell and ending with sixteen. In this way I sought to get rid of the mischievous effects of any change in the intensity of the earth’s magnetism during the experiments. The table of these results which I subjoin will easily be un- derstood by means of the headings of the columns ; and the only thing, therefore, which it will be necessary for me to say in ex- planation of it is, that the last column contains the results of observation corrected for the cooling or heating effect of the sur- rounding air. The amount of this correction was estimated by simple and decisive experiments, and was in no one instance found to exceed one-tenth of the quantity of heat evolved, even in the experiments with one cell, in which the heat evolved was least. 490 Mr. J. P. Joule on the Heat disengaged Table I. Si f th - D pips Deflections of the feared a fected Ganges Heat evolved in ate of the in the | Reedle of the gal- | the mean |reduced to facili-|5’ in divisions of experiments. pile. vanometer. AeHections! or terse the thermometer. : with column 6. Sept. 4,7am.| 16 (72 17 7 mean 81-94) sean 1 ° My fe aoe ra a ie eo a7 p7a 46 | 32428 | 87-24 Bay P8724 .7,7 pm. Sept. 7,74 p.m.| 16 |72 58 89:90 Sept. 4, 7 p.m 5 |61 8 27:08 ay, D7. Bote 5 ane > (61 26 be0 503] 18015 | 26-92 37-98 \.26-56 a ih Sept. 7, 73 a.m 5 |60 28 25°79 Sept. 5, 7 a.m. 2 /41 8 6°23 1 . ces ai 7 am) Fy f f40 41 | 08634 eis | 237) eos Sept. 6, 74 p.m 2 140 23 5°87 Sept. 5, 7 p.m. 1 |25 57 2-01 hi 1 . Sent Pana, | 1 ied dog 25 Ha) Oarar | 185 | gp 71 Sept. 6, 74a 1 |24 18 1:53 1 2 3 4 5 6 In order to carry on the experiments with electric currents of feebler tension, I now introduced into the circuit an electrolytic cell, consisting of two plates of zinc immersed in a solution of sulphate of zinc. The results thus obtained are arranged in the following table. In order to collect an appreciable quantity of heat, the experiments were carried on for an hour with the lower intensities, and for half an hour with the highest intensity of current ; I have, however, reduced all the results to five minutes, in order that they might be more readily compared with those of Table I. Each of the results given in Table II. is the mean of four experiments tried at different times, according to the principles which guided me in the former experiments. Table II. Quantity of zine Squares of the Number|deposited on the |nefections of the| Corrected tan- | Corrected tan- | Heat evolved of cells} negative elec- | needle of the gents of the |gents reduced to |per 5 minutes in in the | trode per 5 mi- galyanometer. deflections. _ {facilitate compa- | divisions of the pile. | nutes in milli- rison with thermometer. grammes. column 6. real 4 143 19 22 0°3527 1:03 0:96 2 82 11 143 0:1991 0:33 0:29 1 44 6 23 01059 0:09 0:09 S—_—— | | 1 2 3 4 5 6 in Chemical Combinations. 491 By comparing the last two columns of the foregoing table with each other, we see that throughout a very extensive range of electric intensities the heat evolved in a given time remains proportional to the square of the quantity of transmitted elec- tricity. 6. Having thus succeeded in giving another proof of the law of voltaic heat as far as regards a change in the intensity of the current, we may now proceed to consider the effects produced by a change in the resistance of the wire. It will not be neces- sary for me to enter very largely upon this part of the subject, inasmuch as it has long been admitted by philosophers that the heat evolved by a current of given intensity is proportional to the resistance of the wire. I will, however, give one series of experiments, in which I have compared a wire of mercury with the coil of silver wire used in the previous experiments. The comparison of a fluid with a solid metal was, I thought, emi- nently calculated to test the accuracy of the law. A glass tube, 157 centimetres long and about 2°3 millimetres in internal diameter, was fashioned into a spiral, as represented in fig. 5. The tube was filled with mercury as high as the bulbs aa. Connexion could be established between the pile and the spiral by means of the copper wires 4), which dipped as far as the centre of the bulbs aa. The coil of mercury, thus prepared, was immersed in 2 Ibs. 11 oz. of water contained in a double-cased can, similar to the one I have already described, and a current from a pile of five cells was transmitted through it for ten minutes. The heat evolved, the temperature of the room, and the deflections of the galvanometer during the experiment, were carefully noted. Eight of these experiments were made, in four of which the deflections were on one side, and, in the other four, on the other side of the meridian. Four experiments were made in a similar way with the coil of silver wire. In order to avoid the effects of any change in the intensity of the earth’s magnetism, these four experiments were alternated with those made with the mercury coil. The thermo- meter used in all the experiments was one of great accuracy ; and each division of its scale corresponded to ;=4- of a degree of the Centigrade szale. 492 Mr. J. P. Joule on the Heat disengaged Table III. Deflections of |Corrected tan-|Squares of the Heat evolved Fay onan the galvano- | gents of the |corrected tan- | Per 10 of oe temperature of meter. eflections. gents. eons hog gees ae of 8 60 24 | 13-7696 | 31315 | 45:5 0-61 6.4 = 60 56 18086 | 32710 | 45-0 1:97) + 2's 57 203 1-5683 2-456 34:8 0:80 + Fe!) 58 17 16266 | 26458 | 38-4 0-80 + 2. J] 58 302 16409 | 26926 | 40-1 087- — S5|| 59 48 17271 29829 | 43:8 084 — Be || 57 1 15584 | 24286 | 35-2 1d S5]|| 56 30 15184 | 23055 | 34:7 084 — wn eS —_. a — Ss fel jek Mean ...... 27397 | 3969 | 005 + | ——— epi nae | 2 tae creer eS [| 55 543 14847 | 2-2043 | 426 004 — a 56 193 1:5083 2-2750 44-2 075 + Ss j| 54 38 14159 | 2-0048 | 39-4 040 — Eee | 54 52 14282 | 20398 | 39:5 019 — oo —— | ——_ ——— ee [ Mean ...... 21310 | 41-425 | 003 + The resistance of the mercury wire in comparison with that of the silver wire, was found by ascertaining the intensity of the current produced by a pile of five cells :—1st, when the pile was in direct communication with the galvanometer; 2nd, when the resistance of the circuit was increased by the addition to it of the coil of silver wire; and 3rd, when the mercury wire was substi- tuted in the circuit for the silver wire. Calling the intensity of the current in the first instance A, and the resistance y; in the second instance B, and the resistance 1+y; and in the third instance C, and the resistance w+ y, we have, by the laws of Ohm and Pouillet, _ B(A-0) "= CGB) The observations from which I have deduced the constant quantities of the above formula are arranged in the following table. In these experiments the precaution was taken that the temperature of the water in which the coils of mercury and silver were immersed should be as nearly as possible the same as in the experiments of Table III., in order to obviate the possibility of an alteration of the resistance arising from an alteration of the temperature of the metals. I may mention also, that each of the recorded deflections is the mean of two observations, one on one side, and the other (by reversing the direction of the cur- rent) on the other side of the magnetic meridian. The effect of any change in the intensity of the pile during any of the expe- in Chemical Combinations. 493 riments was carefully guarded against by a repetition of each experiment in the reverse order; 7. e. beginning with current C and ending with current A, and then taking the mean of the two sets of observations. Table IV. No. of| Deflection | Corrected | Deflection | Corrected | Deflection | Corrected | Resistance of experi- with resist-| tangent of |with resist-| tangent of |with resist-| tangent of | mercury spiral ment. ance deflection ance deflection ance deflection Ag B(A—C) or A. l+y. or B. x+y. or C, C(A—B) —— °o i i i 73 48 | 3-4635 | 57.10 | 15574 | 6056 | 1-8085| 0-74771 71 10 | 2:9492 | 55 2 | 1-4370| 5839 | 1-6501| 0-74814 72 25 | 31753 | 56 21 | 15098 | 59 542 | 1-7346 | 0-75292 75 24 | 3:8630| 58 37 | 16475 | 62 25 | 1-9242| 0-74997 7611 | 40916 | 58 47 | 1-6583 | 62 42 | 1-9477] 0-75015 Cum Cobo MEGATIT: ccndnanaaees 0:74964 On multiplying 0°74964 by 2°7397, the square of the inten- sity of the current to which the mercury wire was exposed (see Table III.), we obtain 2°0538, a quantity which ought to be proportional to the heat evolved, if our law be correct. From Table III. we see also, that, in the case of the silver wire, the square of the current multiplied by its resistance (which we called unity) is 2°131, while the heat evolved was 41°425. Hence we have for the heat which ought to have been evolved by the mer- cury spiral, 20538 he bad 1310 * 41:4.25 = 39:924, _ Referring again to Table III., we find that the heat actually evolved was 39°69. The difference between this number and the result of theory, trifling as it is, is almost entirely accounted for by the circumstance, that the capacity for heat of the mercury spiral exceeded that of the coil of silver wire by a quantity equal to the capacity of 5-64 grms. of water. Hence we must apply a correction of 735 to the observations with the mercurial appa- ratus. This brings the heat actually evolved up to 39°868, a quantity differmg from 39-924, the theoretical result, only by 0:056 of a division of the thermometer, or 0°-0024 of a degree Centigrade. 7. Having thus given fresh proofs of the accuracy of the law of the evolution of heat by voltaic electricity, we may now pro- ceed to apply it in order to determine the quantity of heat evolved in chemical combinations. The following is an outline of my process:—lI take a glass vessel filled with the solution of an elec- trolyte, and properly furnished with electrodes. I place this electrolytic cell in the voltaic circuit for a given length of time, 494 Mr. J. P. Joule on the Heat disengaged and carefully observe the quantity of decomposition and the heat evolved. By the law of Ohm I then ascertain the resistance of a wire capable of obstructing the current equally with the elec- trolytic cell. Then, by the law we have proved, I determine the quantity of heat which would have been evolved had a wire of such resistance been placed in the circuit instead of the electro- lytic cell: this theoretical quantity, being compared with the heat actually evolved in the electrolytic cell, is always found to exceed the latter considerably. The difference between the two results evidently gives the quantity of heat absorbed during the electrolysis, and is therefore equivalent to the heat which is due to the reverse chemical combination by combustion or other means, Having thus given a short outline of the process, I shall at once proceed to describe the experiments in detail. lst. Heat evolved by the Combustion of Copper. I took a glass jar, fig. 6, filled with 3 lbs. of a solution con- sisting of 24 parts of water, 7 parts of crystallized sulphate of copper, and 1 part of strong sulphuric acid. In this solution, two plates, one of platinum, the other of copper, were immersed, each being connected by means of a proper clamp with a thick copper wire passing through a cork in the mouth of the vessel, and terminating in a mereury cup a. A very delicate thermo- meter, each of whose divisions was equal to =~ of a degree Cent., was also fixed in the cork so as to have its bulb nearly in the centre of the liquid. Lastly, a glass stirrer b was introduced. The experiments were conducted in the following manner :—A pile consisting of four large cells of Daniell (a, fig. 7) was con- nected with the galvanometer b by means of two thick copper wires, one of which was continuous, while the other was divided at the mercury cups cc. The connexion between these mereury cups was first established by means of a short thick copper wire, and the deflection of the needle noted. The quantity of current indicated by this deflection I shall call A. The thick copper wire was now remoyed from the cups at cc, and the standard coil of silver wire (immersed in water to keep it cool) was put there instead, and the deflection again noted. The current ob- served in this second instance I shall call B. The coil of silver wire was now remoyed, and the electrolytic cell aboye described being put in its stead, electrolysis was carried on for exactly 10! of time, during which the deflections of the needle were noted at equal intervals of time. The current indicated by the mean of these obseryations I shall call C. Currents B and A were then again obseryed in the reverse order ; and the mean of these and in Chemical Combinations. 495 the former observations taken, so as to obviate the effects of any change that might be occurring in the intensity of the pile. The temperature of the solution was observed, with the usual precautions, immediately before and after the electrolysis was carried on. The amount of electrolysis was obtained by weigh- ing the negative copper electrode before and after each expe- riment. Putting a for the resistance of a metallic wire capable of retard- ing the passage of the current equally with the electrolytic cell, and calling the resistance of the coil of silver wire unity, we have, as in the case of the coil of mercury, ta SOAR he BIG: (A—C)BC this value, multiplied by C*, gives for the calorific A—B effect of the current C passing along a wire whose resistance =z, The calorific effects of the standard coil of silver wire were ascertained by experiments made on the day before, and on the day after the experiments on electrolysis were performed. In this way I sought, as before, to avoid the injurious influence of a change, either in the intensity of the earth’s magnetism, or in the resistance of the standard coil. The standard coil was im- mersed in a light tin can containing 2 lbs. 12 oz. of distilled water. The thermometer employed was that used in the experi- ments of electrolysis. Table V.—Experiments on the Electrolysis of the Solution of Sulphate of Copper, with a pile of 4 Daniell’s cells. f} ; eG Current A. Current B, Current C geeae sit ee : 5 Z 958628 las a5 lame g af | 24 | ef | 22] 28 | 3g [p23 lan | CEE eee se | £2) £8) £2] 28 | £8 \ssace oes |BS8é Se | 52 | =e | 56 | =a | 5s |B8 eos s-3 (5.5 Z| oF 3) °8 g | OF PRESSE HES |Sé ‘ i U 9° 73 31| 3-4006| 53 52 | 1:3764|35 553| 0°7275|1:24 C.—| 1:3223 |20:4 | 65686 74 59) 3°7510) 54 40) 1-4176/36 53 | 0°7535)0-43 —| 1:3722 |19-4 | 05777 75 22) 3°8538) 54 45 | 1-4220)37 18 | 0:7650)0-23 75 12) 3°8084) 54 47 | 1-4237/38 26 |0-7968/1:78 +) 1:4326 |17-4 |0-6153 Mean ..,.». 003 —| 1:3772 | 19-162) 0:5874 *Corrected for difference 0°03 — | 19-113 * The corrections I have applied to the quantities of heat evolved were derived from experiments on the cooling of the liquids reduced by the law of Leslie to the difference between the mean temperature of the liquids and that of the room. The signs + or — signify that the temperature of the liquid is greater or less than that of the room. 496 Mr. J. P. Joule on the Heat disengaged Table VI.—Experiments on the Heat evolved by the Standard Coil. Pile of 4 cells. Mean deflec- Difference be- tion of the | Corrected | ‘Wee? i cox Square “ the needle of the tangent. temperature of | corrected tan- Heat evolved in 10’ in divi- sions of the galvanometer. rey ind a Bent thermometer. si 7 | 12462 | f0sc,— | 15530 | 300 51 18 1:2544 003 + 15735 31:0 53 38 1:3648 019 + ° | 1:8627 371 54 47 14239 090 + 2:0275 36:9 IMIGAN vie as teatieepter 001 + 1:7542 33°75 Corrected for the difference 0°01+-| 33:76 In order to compare the results of the above tables, it now became necessary to ascertain the capacity for heat of the jars of liquid employed in the experiments. This was done in one or two instances by the method of mixtures. The jar along with its contents was heated to a certain point, and then having been immersed in a large can of cold water, the capacity was deter- mined by the decrease of temperature in the former and the in- crease in the latter. I felt, however, that this plan was on several accounts incapable of giving results of extreme accuracy, and had therefore recourse to a method founded upon the law of the development of heat by electricity. The spiral glass tube (fig. 5), filled with mercury, was immersed up to the bulbs aa in the jar whose capacity for heat was to be determined. A current of electricity was then passed through the mercury for a given time, and the heat thereby evolved was observed with the usual’ precautions. The capacity of the jar and its contents was of course directly proportional to the square of the intensity of the current, and inversely to the increase of temperature. Table VII.—Experiments on the Heat evolved by the Mereury Spiral in the jar of Solution of Copper used in the experiments of Table V. Pile of 4 cells. Difference be- Heat evolved Mean deflec- t th S f the |- haze tion of the sje tonpbttnre of Beal te tat i pa 57 34 15815 005 C.+ | 25011 391 | 58 10 | 16193 | 159 + | 26221 37-0 58 17 16261 123 — | 26442 43-4 59 0 16725 | 037. — | 27973 41:3 Mean ...... 001 + | 26412 402 Corrected for difference 0°-01-+ 40-216 Corrected for capacity «1... 40622 in Chemical Combinations. 497 Table VIIT.—Experiments on the Heat evolved by the Mereury Spiral in the can of water used in the experiments of Table VI. Pile of 4 cells. 2 Ibs. 11 oz. of water in the can. —— Difference be- ent evolved Mean deflec- | Corrected | tween the mean |Square of the | ? 10 in ong tion of the tangent. temperature of | corrected oe tee ra jgalvanometer. Se ine . tangent. themmcineter: 5726 | 15734 | fiec.— | 24756 | 35-6 57 27 15744 025 ~ + 2°4787 36°6 59 113 1-6853 101 — 2-8402 40:3 | 58 27 16367 185 + 2-6788 38-2 pee eee 2 ee SS es Mean joc: 002 — | 26183 | 37-675 Corrected for difference 0°-02—| 37-65 Corrected for capacity ............ 36:99 Besides the correction on account of the difference between the mean temperature of the liquid and that of the room in which the experiments were made, it was necessary to supply the second correction given in the above tables, on account of the capacity for heat of the jars being necessarily somewhat different from what it was in the experiments of Tables V. and VI. In Table VI. the can contained 2 Ibs. 12 oz. of water, and the coil of silver wire ; whereas it contained 2 Ibs. 11 oz. and the coil of mercur in Table VIII. Again, in the experiments of Table V. there were 3 lbs. of solution of copper along with the platinum and copper electrodes ; whereas in those of Table VII. the mercury coil was substituted for the electrodes, whilst the weight of the solu- tion was two grammes less than before. It would be tedious and unnecessary to give in detail the various reductions de- manded by these circumstances; suffice it to say, that the cal- culations were founded upon the best tables of specific heat, and were made with the most scrupulous care. The tin can containing (as in the experiments of Table VI.) the coil of silver wire and 2 Ibs. 12 02. of water, was found by careful calculations to be equivalent in its capacity for heat to 1283°7 grms. of water; consequently from Tables VII. and VIII. we obtain for the capacity of the jar of solution used in the experiments of Table V., 2°6412 36:99 Referring now to Tables V. and VI., and remembering that Phil. Mag, 8. 4. No. 21. Suppl. Vol. 3. 2K 498 Mr. J. P. Joule on the Heat disengaged 23°38 divisions of the scale of the thermometer employed are equal to one degree of the Centigrade scale, we obtain for the x BC, A—B 33°76 1:3772 23°38 ~ 1-7542 The quantity of heat actually evolved will be 19:113 is a @pbo. 93:38 * 1179 2=963""99. Subtracting the latter from the former result, we obtain 491°3 as the quantity of heat absorbed in the electrolysis of a quantity of sulphate of copper corresponding to 0°5874 of a gramme of copper. The quantity of heat absorbed per gramme of copper deposited will therefore be 836°°4. Two other series of experiments conducted in precisely the same manner, excepting that in the former of the two the spe- cific heat of the solution was obtained by the method of mixtures, gave, for the absorption of heat per gramme of copper deposited, respectively 856° and 796°:5. The mean of the three results is 829° 6. The above quantity of heat is that absorbed in separating the copper and oxygen gas from a solution of sulphate of oxide of copper. It is therefore necessary to subtract the absorption due to the transfer of the sulphuric acid from the oxide of copper to water, in order to obtaim the heat absorbed in the decomposition of oxide of copper into metal and oxygen gas. For this purpose, 8 grammes of oxide of copper, prepared by adding potash to a solution of the sulphate of copper, and then carefully washing and igniting the precipitate, were thrown into an acidulated solution of copper similar to that used in the above experiments, the capacity for heat of which had been previously ascertained. The mean of four experiments, tried in this way with every pos- sible precaution, gave 236° as the heat due to the solution of 1:252 gramme, the quantity of oxide corresponding to a gramme of copper. 829°'6 — 236°= 593°6 = the quantity of heat absorbed in the decomposition of oxide of copper into copper and oxygen gas, and which ought therefore to be the quantity of heat evolved by the combustion of a gramme of copper. quantity of heat due to x 1288°7 = 14553. Combustion of Zinc. My experiments on this metal were similar to those on copper ; they will not therefore require a very detailed description. The in Chemical Combinations. 499 solution employed was one consisting of 3 parts of crystallized sulphate of zinc and 8 parts of water, weighing 3 lbs. 2 oz. The electrodes were plates of platinum and zine, each plate exposing an active surface of about 8 square inches. At the conclusion of each experiment, oxide of zinc was thrown into the solution to replace that removed by electrolysis, in order to prevent the zinc electrode from being acted upon by free acid. Table [X.—Experiments on the Heat evolved by the Electrolysis of Sulphate of Zine. Pile of 7 cells. 5 Gt oe S&T AOR Current A Current B. Current C. sgoge cas SEs fae ° S89 ies: s : oF®sak P28 [2808 . . eee ce _ =a.29/9 S's sf | 3#| 28] 88 | eS | Se |BSESS |foGxzc.| S28 BEES = = r o _— Dl $2 | 2% |88| 28 | €3 | 2h lesess eeu loSsé Fe | & 22| 52 | Se | Be ESe2. B88 (9385 ae og S og S Ss |AeSes Sy |. 2 =>) ee ce aid ohoriicd 4°35 Keg ino Lo t iJ i °o i oo 74 103) 3-5500'61 46) 1-872235 31 | 0-7167|0-°83C. —| 2-2659 | 32-2 |0-5797 _ |75 554) 4:01383\63 9) 1-9858/35 14 | 0-7092/0-35 +) 2:2951 | 30-0 | 05647 75 18 | 3-8356,62 30) 1°9311387 134) 0°7573/0-40° —| 2°3688 | 31:3 | 0-6010 75 324) 39025 62 47| 1:9546/36 56 | 0:7548/0°84 +) 2-3841 (305 | 05991 LAA opdocetts 0-01 —| 2:3272 |31:0 | 05861 Corrected for difference 0°-01— | 30:984 Table X.—Experiments on the Heat evolved by the Standard Silver Coil. Pile of 5 cells. Difference be- H eat evolved Mean Corrected | tween the mean |Square of the |; 19, datlechon, tonvent temperature of | corrected F prlenie meres Seat the water and tangent. chermiticas. that of the room. 3 53 583 | 13820 | {-15c.— | 1-:9099 | 363 53 48 13731 025 + 1°8854 370 56 264 15150 044 — 2:2952 45-9 57 4k 15520 1:24 +4 2°4087 44-4 Mean......... 0:025 — 2°1248 409 Corrected for difference 0°-025—| 40°869 The following tables give the results of the experiments for ascertaining the capacity for heat of the jar of solution. 2K2 500 Mr. J. P. Joule on the Heat disengaged Table XI.—Experiments on the Heat evolved by the Mercury Spiral in the jar of Solution of Sulphate of Zinc used in the experiments of Table IX. Pile of 5 cells. Difference be- a " Heat evolved Mean Corrected | tween the mean /Square of the |i, 10’ in divi- deflection. tangent. temperature of | corrected sions of the the solution and| tangent. thermometer. that of the ae 61 173 | 1:8355 | 0-48C.— | 33691 | 51-1 : 6030 | 17768 | 161 + | 31570 | 45-6 5819 | 16987 | 0-47 — | 26527 | 427 59 183 1:6935 lll + 2:8679 40°5 \———————_- Mean ...... 0-442 + | 30117 44-975 Corrected for difference 0°442-+| 45-700 Corrected for capacity .......:...-| 46°269 Table XIJ.—Experiments on the Heat evolved by the Mercury Spiral in the can of water used im the experiments of Table X. Pile of 5 cells. 2 Ibs. 11 oz. of water in the can. Difference be- Heat evolved Mean Corrected | tween the mean |Square of the j, 10/ in diyi- deflection. tangent. | temperature of | corrected | sions of the | the water and tangent. |thermometer. that of the room. as 6021 | 1-7659 | O66C.— | 31184 | 44-4 60 24 1:7696 1:25 +4 31315 45:1 58 442 1:6561 ll7 - 2°7427 40:7 59 163 | 16913 | 05) + | 28605 | 40-4 Mean ...., 0018 — 2:9633 42°65 Corrected for difference 0°°018C.—| 42-628 Corrected for capacity ........4... 41881 From the last two tables we obtain for the capacity of the jar of solution used in the experiments of Table IX., 30117 — 41°881 From Tables IX. and X. we obtain for the quantity of heat AuRB * BC, ; 40-869 | 2°3272 siya. °, 93.38 * 3-1948 * 1283°7 = 2457"'7. And for the actual quantity of heat evolved during electrolysis, 30°984: Fatt ‘ due to in Chemical Combinations. 501 Hence 2457°:7 —1565°=892°'7= the quantity of heat ab- sorbed in the electrolysis of a quantity of sulphate of zinc cor- responding to 0°5861 of a gramme of zinc. The quantity of heat absorbed by the electrolysis of a quantity of sulphate of zine corresponding to a gramme of zinc will there- fore be 15231. The results of two other series of experiments, conducted in precisely the same manner as that I have just given, were 1547° and 1619° respectively. The mean of the three results is 1563°. The heat absorbed by the transfer of the sulphuric acid from the oxide of zinc to the water was ascertained in the following manner. A solution of zine similar to that employed in the experiments was acidulated with about 10 grammes of sulphuric acid. 7:9 grms. of oxide of zinc (prepared by igniting the car- bonate) were thrown into this solution; and the heat evolved by its union with the free sulphuric acid was carefully ascertained, _and properly corrected for the influence of the atmosphere. The capacity for heat of the jar of solution was then ascertained by the method of electrical currents. This being done, a fresh quantity of oxide of zinc was thrown into the solution, and the heat evolved again observed. The mean of the two experiments gave 378° for the quantity of heat evolved by the solution of 1:242 grm., the quantity of oxide of zinc corresponding to a gramme of zinc. 1563°—378°=1185°, the quantity of heat absorbed in the decomposition of oxide of zine into zine and oxygen gas; and which ought therefore to be the quantity of heat evolved by the combustion of a gramme of zinc. Combustion of Hydrogen Gas. The apparatus employed in the experiments on hydrogen is shown in fig. 8. a represents a glass jar nearly full of a solu- tion consisting of six parts of water and one of strong sulphuric acid, and containing platinum electrodes; 4 represents a glass tube for conveying the mixed gases to the pneumatic trough ec. The glass stirrer d, being inserted in the small cork e, can, when not in use, be made perfectly tight by inserting the latter into the large cork which stops up the mouth of the jar. A coating of a viscid solution of rosin in turpentine was applied wherever it appeared necessary, in order to ensure perfect tightness. The quantity of mixed gases evolved was ascertained by the weight of water displaced in the bottle f; and hence the weight of libe- rated hydrogen was computed with the assistance of the best tables, regard being paid to the temperature of the gas, its hy- grometric state, the barometric pressure, &c. 502 Mr. J. P. Joule on the Heat disengaged Table XIII.—Experiments on the Electrolysis of Dilute Sul- phuric Acid, spec. grav. 1:103. Pile of 6 cells. pf wo g sou] 3oe Current A. Current B. Current C. sgog8 “a8 |/Say y Saibeani ies aggss DSsgiSRES : zs 5 = 5 gage A-C B38 ge 8 won gil |. ihes A | Bs 8| Bs (22888 |Axcxpe.| Seg | 8S s.2 eo S.5 “qa e. 2a os ese Bred O° as 38 a3 26 ao 96 |x oy, | A—-B OC gZ RRO oo 2h oo ch oo SH |e BOs Bi | sub = Oo BS s2 5 =o Ba leSg'm #.49 BUS ae 3 3 68 S a [oo 8 Lo Diego 3 | 58 3 | 6s | S= |AESZS m2 |43& ° i ° 4 ° ce) 73 353) 3:4170|59 26, 1-702058 14) 1-6234'1-30C. 2°8897 |40°6 | 0-03978 75 41 | 3-9429/60 57| 1:8098 60 31 1:7780/0°34 3-2658 |37°8 | 0-04212 76 57 | 4:3412|62 0 1:890661 19) 1-8374/0-71 35492 | 41:7 | 004872 76 3 | 4-0508)/61 13) 1:8298 60 50) 1-8011|1-85 3°3382 | 388 |0:04411 +441 Mean ...... 0-40 +} 3:2607 | 39-725) 0:04243 Corrected for difference 0°-40-+4 40°381 Table XIV.—Experiments on the Heat evolved by the Standard Silver Coil. Pile of 5 cells. Difference be- Hi d Mean Corrected | tween the mean | Square of the erat ib oar in diyi- deflection. tangent. temperature of | corrected | ‘sions of the the water and tangent. |thermometer. that of the room. ‘ 56 12 1:5012 0-25 C 2°2536 42°] = oO i) 5 2 ~ a ee to 3 _— 3) — ~ to <4 nt Corrected for difference 0°45-++ | 42-642 Table XV.—Experiments on the Heat evolved by the Mercury Spiral in the jar of Dilute Sulphuric Acid used in the experi- ments of Table XIII. Pile of 5 cells. Difference be- Heat evolyed Mean Corrected | tween the mean /Square of the in 10! in divi- deflection. tangent. hy rh a eres sions of the that of the room. Ben’: |thermometer. 60 154 | 17594 | O46C.— | 3-:0955 | 499 60 39% 1:7883 159 + 3°1980 46:0 59 344 17117 155 — 2°9299 466 58 5224 16648 038 + 2:7716 43°9 Mean ...... 001 — 2:9987 46°6 Corrected for difference 0°°01—| 46-584 Corrected for capacity ..,......... 47-164 in Chemical Combinations. 503 Table XVI.-—Experiments on the Heat evolved by the Mereury Spiral in the can of water used in the experiments of Table XIV. Pile of 5 cells. 2 Ibs. 11 oz. of water in the can. Difference be- tween the mean | Square of the | temperature of | corrected | Heat evolved Mean Corrected in 10/ in divi- deflection tangent. | sions of the ‘h d tangent. | that of the room.| "thermometer. 59 39 1-7168 047C.— | 29474 41-9 59 462 | 17255 135 + | 29774 42-6 59 10 16841 101 — | 28362 428 59 373 | 17151 | 074 4 | 2-9416 40°5 Mean’ si... 0152 + 2:9256 41:95 Corrected for difference 0°152C.+} 42-141 Corrected for capacity .....+....0. 41-402 From the above tables we obtain for the capacity for heat of the jar of dilute sulphuric acid used in the experiments of Table XIII, 29987 41:402 a 9-9256 x eben 1283°7 =1155. For the quantity of heat due to a = BC, 42°642 _ 3:2607 Og 338 ~ 9-918] * 1283°7 =3441 And for the actual quantity of heat evolved in the electrolysis, 40°381 b “agg” * 1155=1994°-9. Hence 3441°8—1994°'9=1446°°9, the quantity of heat ab- sorbed during the electrolysis of a quantity of sulphate of water corresponding to 0:04.43 of a gramme of hydrogen. The quantity of heat absorbed by the electrolysis of a quantity of sulphate of water corresponding to a gramme of hydrogen will therefore be 34101°. Two other series of experiments conducted in precisely the same manner, excepting that in the former of the two the capa- city for heat of the jar of dilute acid was obtained by the method of mixtures, gave 34212° and 32358° respectively, as the heat absorbed per gramme « of hydrogen liberated. The mean of the three results is 33557° A small portion of this quantity of heat absorbed is that due to the removal of water from the dilute acid; but the correction on this account is so exceedingly small as to be hardly worth 504 Prof. Wheatstone on the Physiology of Vision. applying. Subtracting 4°, however, on this account, we obtain 335538° as the quantity of heat absorbed during the electrolysis of water, which ought therefore to be equal to the quantity of heat evolved by the combustion of a gramme of hydrogen gas. 8. By the inverse method of electrical currents, then, we have found that the quantities of heat evolved by the combustion of copper, zine and hydrogen, are respectively 594°, 1185°, and 33553°. These quantities agree so well with the results ob- tamed by Dulong, that I think I may assume that the principles admitted in this paper are demonstrated sufficiently to justify me in making them the basis of a few concluding observations. The fact that the heat evolved in a given time by a metallic wire is proportional to the square of the quantity of transmitted electricity, proves that the action of the current is of a strictly mechanical character ; for the force exerted by a fluid impinging against a solid body obeys the same law. Now I have shown in previous papers*, that when the temperature of a gramme of water is increased by 1° Centigrade, a quantity of vis viva is commu- nicated to its particles equal to that acquired by a weight of 448 grammes after falling from the perpendicular height of one metre. Hence the mechanical force of a voltaic pile may be calculated from the heat which it evolves. Hence also may the absolute force with which bodies enter into chemical combination be estimated by the quantity of heat evolved. Thus, from the data already given, the vis viva deve- loped by the combustion of a gramme of copper, a gramme of zine, and a gramme of hydrogen, will be respectively equivalent to the vis viva possessed by weights of 266112, 530880, and 15031744 grammes, after fallmg from the perpendicular height of one metre. LXX. The Bakerian Lecture.—Contributions to the Physiology of Vision.—Part the Second. _On some remarkable, and hitherto unobserved, Phenomena of Binocular Vision (continued). By Cuartes Wuearstone, F.R.S., Professor of Experimental Philosophy in King’s College, London+. [With a Plate. ] § 17. | fe § 3. of the first part of my “ Contributions to the Physio- logy of Vision,” published in the Philosophical Transactions for 1838}, speaking of the stereoscope, I stated, “The pictures * Philosophical Magazine, S. 3. vol. xxvii. p. 206. + From the Philosophical. Transactions for 1852, part i.; having been receiyed and read by the Royal Society January 15, 1852, _ { Reprinted in our April Number.—Ep. Phil. Mag. Prof. Wheatstone on the Physiology of Vision. 505 will indeed coincide when the sliding pannels are in a variety of different positions, and consequently when viewed under differ-' ent inclinations of the optic axes; but there is only one position in which the binocular image will be immediately seen single, of its proper magnitude, and without fatigue to the eyes, because in this position only the ordinary relations between the magni- tude of the pictures on the retina, the inclination of the optic axes, and the adaptation of the eye to distinct vision at different distances, are preserved. The alteration in the apparent magni- tude of the bmocular images, when these usual relations are disturbed, will be discussed in another paper of this series, with a variety of remarkable phenomena depending thereon.” In 18383, five years before the publication of the memoir just mentioned, these yet unpublished investigations were announced m the third edition of Herbert Mayo’s “Outlines of Human Physiology” in the following words :—“Mr. Wheatstone has shown, in a paper he is about to publish, that if by artificial means the usual relations which subsist between the degree of inclination of the optic axes and the visual angle which the object subtends on the retina be disturbed, some extraordinary illusions may be produced. Thus, the magnitude of the image remaining constant on the retina, its apparent size may be made to vary with every alteration of the angular inclination of the optic axes.” I shall resume the consideration of the phenomena of bin- ocular vision with this subject, because the facts I have ascer- tained regarding it are necessary to be understood before enter- ing on the new experiments relating to stereoscopic appearances which I intend to bring forward on the present occasion. Under the ordinary conditions of vision, when an object is placed at a certain distance before the eyes, several concurring circumstances remain constant, and they always vary in the same order when the distance of the object is changed. Thus, as we approach the object, or as it is brought nearer to us, the magni- tude of the picture on the retina increases ; the inclination of the optic axes, required to cause the pictures to fall on corresponding places of the retinee, becomes greater ; the divergence of the rays of light proceeding from each point of the object, and which determines the adaptation of the eyes to distinct vision of that point, increases ; and the dissimilarity of the two pictures pro- jected on the retinz also becomes greater. It is important to ascertain in what manner our perception of the magnitude and distance of objects depends on these various circumstances, and to inquire which are the most, and which the least influential in the judgements we form. ‘To advance this inquiry beyond the point to which it has hitherto been brought, it is not sufficient to content ourselves with drawing conclusions from observations 506 Prof. Wheatstone on the Physiology of Vision. on the circumstances under which vision naturally occurs, as preceding writers on this subject mostly have done, but it is necessary to have more extended recourse to the methods so successfully employed in experimental philosophy, and to endea- your, wherever it be possible, not only to analyse the elements of yision, but also to recombine them in unusual manners, so that they may be associated under circumstances that never naturally oceur. The instrument I shall proceed to describe enables these ab- normal combinations to be made in a very simple and effectual manner. Its principal object is to cause the bimocular pictures to coincide, with any inclination of the optic axes, while their magnitudes on the retin remain the same; or inversely, while the optic axes remain at the same angle, to cause the size of the pictures on the retine to vary in any manner. ~ Two plane mirrors inclined 90° to each other are placed toge- ther and fixed vertically upon a horizontal board. Two wooden arms move round a common centre situated on this board in the vertical plane which bisects the angle of the mirrors, and about 14 inch beyond their line of junction. Upon each of these arms is placed an upright pannel, at right angles thereto, for the pur- pose of receiving its appropriate picture, and each pannel is made to slide to and from the opposite mirror. The eyes being placed before the mirrors, the right eye to the right mirror and the left eye to the left mirror, and the pannels being adjusted to the same distances, however the arms be moved round their centre, the distance of the reflected image of each picture from the eye will remain exactly the same, and consequently its retinal magnitude will be unchanged. But as the two reflected images do not occupy the same place when the pictures are in different positions, to cause the former to coimcide the optic axes must converge differently. When the arms are in the same straight line, the images coincide while the optic axes are parallel; and as they form a less angle with each other, the optic axes converge more to occasion the coimeidence. When the arms remain in the same positions, while the pannels slide towards or from the mirrors, the convergence of the optic axes remains the same, but the magni- tude of the pictures on the retine increases as the distance de- creases. By the arrangement described, and which is repre- sented by figs. 1 and 2, Plate XII., the retlected pictures are always perpendicular to the optic axes, and the corresponding points of the pictures, when they are exactly similar, fall upon correspond- ing points of the retine. The instrument has an adjustment for otherwise inclining them if it be required. Let us now attend to the effects produced. The pictures being fixed at the same distance from the mirrors, there is a cer- Prof. Wheatstone on the Physiology of Vision. 507 tain adjustment of the arms at which the binocular image will appear of its natural size, that is, the size we judge the picture itself to be when we look at it directly ; in this case the magnitude of the pictures on the retine and the inclination of the optic axes preserve their usual relation to each other. If now the arms be moved back, so as to cause a less convergence of the axes, the image will appear to increase in magnitude until the arms are in a straight line and the optic axes are parallel; and, on the other hand, if the arms be moved forwards, so as to form a less angle, the optic axes will converge more, and the image will appear gradually smaller. In this manner, while the retinal magnitude remains the same, the perceived magnitude of the binocular object varies through a very considerable range. The instrument being again adjusted so that the image shall - be seen of its natural size; on sliding the pictures nearer the mirrors its perceived magnitude will be augmented, and on sli- ding them from the mirrors it will appear diminished in size. Durimg these variations of magnitude the inclination of the optic axes remains the same. ; The perceived magnitude of an object, therefore, diminishes as the inclination of the axes becomes greater, while the distance remains the same; and it increases, when the inclination of the axes remains the same, while the distance diminishes. When both these conditions vary inversely, as they do in ordinary vision when the distance of an object changes, the perceived magnitude remains the same*. Before I proceed further it will be proper to explain the mean- ing of some of the terms I employ. I call the magnitude of the object itself, the real or objective magnitude; the magnitude of the picture on the retina, the retinal magnitude; and the mag- nitude we estimate the object to be from its retinal magnitude and the inclination of the optic axes conjointly, I name the per- ceived magnitude. I do not use the term apparent magnitude, because, according to its ordinary acceptation, it sometimes means what I call retinal, and at other times what I name per- ceived magnitude. We have seen in what manner our perception of magnitude is modified by the new associations which this instrument enables us to form; let us now examine how our perception of distance * Several cases of the alteration of the perceived magnitude of ob- jects are mentioned by Dr. R. Smith (Complete System of Optics, 1738, vol. ii. p. 388, and rem. 526 and 532); and Dr. R. Darwin (Philosophical Transactions, vol. lxxvi. p. 313) observed that when an ocular spectrum was impressed on both eyes it appeared magnified when they were directed to a wall at a considerable distance. The facts noticed by these authors are satisfactorily explained by the above considerations. 508 Prof. Wheatstone on the Physiology of Vision. is affected bythem. If we continue to observe the binocular picture whilst it apparently increases or decreases, im consequence of the inclination of the’optic axes varying while the magnitude of the impressions on the retinze remains the same, it does not appear either to approach or to recede ; and yet if we attentively regard it in any fixed position, it is perceived to be at a different distance. On the other hand, if we continue to regard the binocular pic- ture, enlarging and diminishing in consequence of the change of retinal magnitude while the convergence of the axes remains the same, we perceive it to approach or recede in the most evident manner ; but on fixing the attention to it, when it is stationary, at any instant, it appears to be at the same distance at one time as it 1s at another. Convergence of the optic axes therefore suggests fixed distance to the mind; variation of retinal magnitude suggests change of distance. We may, as I have above shown, perceive an object approach or recede without appearing to change its distance, and an object to be at a different distance, without appearing to approach or recede; these paradoxical effects render it difficult, until the phenomena are well apprehended, to know, or to ex- press, what we actually do perceive. It is the prevalent opinion that the sensation which accom- panies the inclination of the optic axes immediately suggests distance, and that the perceived magnitude of an object is a judgement arising from our consciousness of its distance and of the magnitude of its picture on the retina. From the experi- ments I have brought forward, it rather appears to me that what the sensation which is connected with the convergence of the axes immediately suggests is a correction of the retinal magni- tude to make it agree with the real magnitude of the object ; and that distance, instead of being a simple perception, is a judge- ment arising from a comparison of the retinal and perceived magnitudes. However this may be, unless other signs accom- pany this sensation the notion of distance we thence derive is uncertain and obscure, whereas the perception of the change of magnitude it occasions is obvious and unmistakeable. To see, in their full extent, the variations of magnitude exhi- bited by the instrument I have described, it is necessary to attend to the following observations. As the inclination of the optic axes corresponding to a differ- ent distance is habitually, under ordinary circumstances, accom- panied with the particular adaptation of the eyes required for distinct vision at that distance, it is difficult to disassociate these two conditions so as to see with equal distinctness the bin- ocular picture when the optic axes are parallel, and when they converge greatly, although the pictures remain, in both cases, at Prof. Wheatstone on the Physiology of Vision. 509 the same distance from the eyes. The adaptation is, therefore, not entirely dependent on the divergence of the rays of light which proceed from the object regarded, but also, in some degree, on the inclination of the optic axes. I have acquired by practice considerable power of adjustment, or rather disadjustment, of the eyes, and can, without having recourse to artificial means, see the binocular picture distinctly when its perceived magnitude is widely different. ose to whom such an effort is painful may employ short-sighted spectacles to see the binocular picture when the eyes converge within the limit of distinct vision for the distance at which the pictures are placed; and long-sighted spectacles when the eyes converge beyond that limit, or become parallel. There is a means of avoiding to a very considerable extent the influence of the adjustment of the eyes, and thereby enabling the pictures to be seen distinctly within the entire range of the inclination of the optic axes. This is by looking at the reflected images in the mirrors through two very minute apertures, not larger than fine pin-holes, placed near each eye, and illuminating the pictures by a very strong light; sunshine in the middle of the day answers the purpose very well. By this expedient the divergence of the rays of light is greatly diminished, and the adaptation of the eyes does not materially influence the result. § 18. Leaving this subject, I will now revert to the stereoscope and its effects. Since 1838 numerous modifications of the stereoscope have occurred to me, and several ingenious arrangements have also been proposed by Sir David Brewster and Professor Dove; but there is no form of the instrument which has so many advan- tages for investigating the phenomena of binocular vision as the original reflecting stereoscope. Pictures of any size may be placed in it, and it admits of every kind of adjustment. I have constructed a very portable reflecting stereoscope which is represented at fig. 3. The sides fold over the mirrors, and the mirrors then fold into a box, which is not larger than six inches in any of its dimensions. To avoid the second feeble reflexion from the anterior surface of the silvered glass, which has a bad effect when the attention is attracted to it, I have sometimes employed reflecting prisms. The reflecting surfaces of the prisms should be silvered in order to obviate the unequal brightness of the field of view on each side of the limit of total reflexion ; and as it would be too costly to employ very large prisms, they should have an adjustment to accommodate their distance to the width between the eyes of the observer. 510 Prof. Wheatstone on the Physiology of Vision. I have, for many years past, employed also another means to occasion, without any straining of the eyes, the coincidence of the pictures so that the image in relief shall appear of the same magnitude and at the same distance as the object which they represent would do if it were itself directly regarded: In this apparatus, prisms being employed to deflect the rays of light proceeding from the pictures, so as to make them appear to oceupy the same place, I have called it the: refracting stereoscope. It is represented by fig. 4. It consists of a base 6 inches long and 4 inches broad, upon which stands an upright partition, 5 inches high, dividing it equally ; this partition 1s capable of extension by means of a slide to double the length, and carries at its upper extremity a board placed parallel to the base, and of the same dimensions. In this upper board there are two apertures an inch square, one on each side of the partition, the centres of which are 2} inches from each other; in these aper- tures are fixed a pair of glass prisms having their faces inclined 15°, and their refractive angles turned towards each other. The stereoscope pictures are to be placed on the base, and their centres ought not to exceed the distance of 23 inches. A pair of plate-glass prisms, their faces making with each other an angle of 12°, will bring two pictures, the corresponding points of which are 22 inches apart, to coincidence at a distance of 12 inches, and a pair with an angle of 15° will occasion coin- cidence at 8 inches. The refracting stereoscope has the advantage of portability, but it is limited to pictures of small dimensions. It is well suited for Daguerreotypes, which are usually of small size, and, on account of the nature of their reflecting surface, must be viewed in a particular direction with respect to the light which falls upon them; whereas in the reflecting stereoscope it is some- what difficult to render the two Daguerreotypes equally visible. For drawings and Talbotypes it however offers no advantages, though it is equally well suited for them when their dimensions are small. Stereoscopic drawings afford a means of illustrating works with figures of three dimensions, instead of with mere plane representations. Works on crystallography, solid geometry, spherical trigonometry, architecture, machinery, &c., might be thus rendered more instructive, from the perfect counterpart of the solid figure seen from a single point of view being represented instead of merely one of its plane projections. For this purpose the corresponding binocular figures must be engraved in parallel vertical columns, and their coalescence may be effected by view- ing them through a pair of prisms, similar to those employed in the refracting stereoscope, placed in a frame at the proper di- Prof. Wheatstone on the Physiology of Vision. 51k stance from each other. If the engravings should be less than 23 inches apart, the prisms may be dispensed with by persons who have command over the adaptation of their eyes, particularly if they be short-sighted. § 19. At the date of the publication of my experiments on binocular vision, the brilliant photographic discoveries of Talbot, Niepce and Daguerre, had not been announced to the world. To illus- trate the phenomena of the stereoscope I could therefore, at that time, only employ drawings made by the hands of an artist. Mere outline figures, or even shaded perspective drawings of simple objects, do not present much difficulty ; but it is evidently impossible for the most accurate and accomplished artist to deli- neate, by the sole aid of his eye, the two projections necessary to form the stereoscopic relief of objects as they exist in nature with their delicate differences of outline, light and shade. What the hand of the artist was unable to accomplish, the chemical action of light, directed by the camera, has enabled us to effect. It was at the beginning of 1839, about six months after the appearance of my memoir in the Philosophical Transactions, that the photographic art became known, and soon after, at my request, Mr. Talbot, the inventor, and Mr. Collen (one of the first culti- vators of the art) obligingly prepared for me stereoscopic Talbo- types of full-sized statues, buildimgs, and even portraits of living persons. M. Quetelet, to whom I communicated this application and sent specimens, made mention of it in the Bulletins of the Brussels Academy of October 1841. To M. Fizeau and M.Claudet I was indebted for the first Daguerreotypes executed for the stereoscope. The beautiful stereoscopic representations of sta- tuary, architecture, machinery, natural history specimens, por- traits of living persons, single and in groups, &c., which have recently been produced by M. Soleil and M. Claudet, are now too well known to the public to need more than a slight refer- ence to them. With respect to the means of preparing the binocular photo- graphs (and in this general term I include both Talbotypes and Daguerreotypes), little requires to be said beyond’a few diree- tions as to the proper positions in which it is necessary to place the camera in order to obtain the two required projections. We will suppose that the binocular pictures are required to be seen in the stereoscope at a distance. of 8 inches before the eyes, in which case the convergence of the optic axes is about 18°. To obtain the proper projections for this distance, the camera must be placed, with its lens accurately directed towards the object, successively in two points of the circumference of a circle 512 Prof, Wheatstone on the Physiology of Vision. of which the object is the centre, and the points at which the camera is so placed must have the angular distance of 18° from each other, exactly that of the optic axes in the stereoscope. The distance of the camera from the object may be taken arbi- trarily ; for, so long as the same angle is employed, whatever that distance may be, the pictures will exhibit in the stereoscope the same relief, and be seen at the same distance of 8 inches, only the magnitude of the picture will appear different. Minia- ture -stereoscopic representations of buildings and full-sized statues are therefore obtained merely by taking the two projec- tions of the object from a considerable distance, but at the same angle as if the object were only 8 inches distant, that is, at an angle of 18°. To produce the best effect, it is necessary that the pictures be so placed in the stereoscope that each eye shall see its respective picture at the proper point of sight: if this condition be not attended to, the binocular perspective will be incorrect. For obtaining binocular photographic portraits, it has been found advantageous to employ, simultaneously, two cameras fixed at the proper angular positions. I subjoi a Table of the inclinations of the optic axes which correspond to different distances; it also shows the angular positions of the camera required to obtain binocular pictures which shall appear at a given distance in the stereoscope in their true relief. 16° | 3°8 30° 4°6 6° 23°8 8° 12° 18°|20°|22°/24°|26°128° 6:4 Inclination of the optic axes | 2° | 4° 10° 14° Distance in inches.......... 71°5/35°7 17°8 |13*2/11°8|10°1 7°8\7°0 5*°8)5'4)5°0 0 : 5 cotang gi 4 denoting the distance between the two eyes, and @ the inclination of the optic axes. § 20. As the inclination of the optic axes diminishes by the removal of an object to which they are directed to a greater distance, not only does the magnitude of the pictures projected by it on the ~ retin proportionately diminish, but the dissimilarity of the pic- tures becomes less. The difference of distance between any two points of each of the pictures will diminish until the projections become sensibly similar. Under the usual circumstances attend- ing the vision of a solid object placed at a given distance, a par- ticular inclination of the axes is invariably accompanied by a specific pair of dissimilar projections; and if the distance be changed, a different inclination of the axes is accompanied by The distance is equal to Prof. Wheatstone on the Physiology of Vision. 513 another pair of projections ; but, by means of the stereoscope, we have it within our power to associate these circumstances abnormally, and to cause any degree of inclination of the axes to coexist with any dissimilarity of the two pictures. To ascertain experimentally what takes place under these circumstances, M. Claudet prepared for me a number of Daguerreotypes of the same bust, taken at a variety of different angles, so that I was enabled to place in the stereoscope two pictures taken at any angular distance from 2° to 18°, the former corresponding with a distance of about 6 feet, and the latter with a distance of about 8 inches. The effect of a pair of near projections seen with a distant convergence of the optic axes, is to give an undue elon- gation to lines joining two unequally distant points, so that all the features of a bust appear to be exaggerated in depth. The effect, on the contrary, of a pair‘of distant projections, seen with a near convergence of the axes, is to give an undue shortening to the same lines, so that the appearance of a bas-relief is ob- tained from the two projections of the bust. The apparent di- mensions in breadth and height remain in both cases the same. § 21. To reproduce the conditions of the binocular vision of a solid object as completely as possible by means of its two plane pro- jections, it is necessary, as I have before stated, that the projec-. tions shall be such as correspond exactly with the inclination of the optic axes under which they are viewed. I have already shown in § 20 what takes place when this condition is not strictly observed, and I may add, that the mind is not unplea- santly affected by a considerable incongruity in this respect ; on the contrary, the effect in many cases seems heightened by view- ing the solid appearance, intended for a determinate degree of inclination of the axes, under an angle several degrees less ; the reality is as it were exaggerated. When the optic axes are parallel, in strictness there should be no difference between the pictures presented to each eye, and in this case there would be no binocular relief; but I find that an excellent effect is pro- duced when the axes are nearly parallel by pictures taken at an inclination of 7° or 8°, and even a difference of 16° or 17° has no decidedly bad effect. This circumstance enables us to combine the ideal amplifica- tion arising from viewing pictures placed near the eyes under a small inclination, or even parallelism, of the optic axes mentioned in § 17, with the perception of solidity arising from the dissimi- larity of the projections; for this purpose, the pictures in the refracting stereoscope, or their reflected images in the reflecting instrument, must be viewed through lenses the focal distance of Phil, Mag. 8.4, No. 21. Suppl. Vol. 3. 21L 514 Prof. Wheatstone on the Physiology of Vision. which is equal to the distance between them and the pictures ; the perceived magnitude of the binocular image will increase with the nearness of the pictures, and depends almost entirely on the disassociation of the retinal magnitude from its usually aceom- panying inclination of the optic axes, the actual magnifying power of the lenses having a very small influence. The sole use of the lenses is to render the rays of light parallel, which it is necessary they should be for distinct vision when the optic axes are parallel. When the reflecting stereoscope is em- ployed, this means of magnifying the effect is not of much utility, as pictures of any size may be adapted to that instrument. But in the case of the refracting stereoscope it may be advantageously made use of. By combining lenses with the refracting stereo- scope, described in §18, Daguerreotypes somewhat wider than the width between the eyes may be-employed. Sir David Brewster has used, to effect the same purpose, semi-lenses with their edges directed towards each other, which serve at the same time to render the rays less convergent and slightly to displace the pictures towards each other. Two corresponding Daguerreo- types, each not exceeding in breadth the width between the eyes, being placed close to each other, and viewed with lenses of short focal distance, will, even without the aid of the prisms, give an apparently highly magnified binocular image in bold relief. There is a peculiarity in such images worthy of remark; although the optic axes are parallel, or nearly so, the image does not appear to be referred to the distance we should, from: this circumstance, suppose it to be, but it is perceived to be much nearer, and indeed more so, as the pictures are nearer the eyes, though the inclination of the optic axes remains the same, and should therefore suggest the same distance; it seems as if the dissimilarity of the projections, corresponding as they do to a nearer distance than that which would be suggested by the former circumstance alone, alters in some degree the perception of distance, I recommend, as a convenient arrangement of a refracting stereoscope for viewing Daguerreotypes of small dimensions, the instrument represented, Pl. XII. fig. 4, shortened in its length from 8 inches to 5, and lenses of 5 inches focal distance placed before and close to the prisms. § 22. I now proceed to another subject—to the consideration of those phenomena which I have termed Conversions of Relief. In § 5 of my first memoir I noticed the remarkable cireum- stance, that when the drawing intended to be seen by the right eye is presented to the left eye in the stereoscope, and vice versd, Prof. Wheatstone on the Physiology of Vision. 515 a totally different solid figure is perceived to that seen before the transposition. I called this the converse figure, and showed that it differs from the normal figure in the circumstance, that those points which appear the most distant in the latter, appear the nearest in the former. The pictures being, in the first place, presented directly to their corresponding eyes, as in the refracting stereoscope, and exhibiting therefore the resultant image in its normal relief, the conversion of the relief may be effected in three different ways,— 1st, by transposing the pictures from one eye to the other, as mentioned above; 2ndly, by reflecting the pictures, while they remain presented to the same eye, as in the reflecting stereo- scope; and 3rdly, by inverting the position of the pictures with- out transposing them. The following considerations will explain the cause of the con- version of relief in the preceding cases. If two different objects, or parts of an object (fig. 5a), have a greater lateral distance between them on the right-hand picture than that which they have on the left-hand picture, the optic axes must converge more to make the left-hand than to make the right-hand objects coincide, and the left-hand object will appear the nearest. If the pictures be now transposed from one eye to the other (fig. 5 a’), the greatest distance will be between the correspond- ing points of the picture presented to the left eye; the optic axes must therefore converge less to make the left-hand objects coincide, and the right-hand object will appear the nearest. If the pictures, remaiming untransposed, be each separately reflected (fig. 5 b), the relative distances of the corresponding objects remain the same to each eye, and the left-hand object will still appear nearest ; but in consequence of the lateral inver- sion of the objects in each picture by reflexion, that which was previously on the left will now be on the right, and therefore the object which before appeared nearest will now appear furthest. When the pictures are turned upside down, still remaining untransposed (fig. 5c), the objects are reversed with respect to the right and left, in the same manner as they are when reflected, and the lateral distances between the objects remaining the same to each eye, precisely the same conversion of relief is produced as in the preceding case, except that the resultant image is in- yerted. The diagram (fig. 5) represents all the possible changes of the two binocular pictures; those marked N show the normal relief, and those marked C the converse relief. But it may be asked why, if the reflexion or inversion of the binocular pictures of an object gives rise to the mental idea of the conyerse relief, the same converse relief is not observed when 2L2 516 Prof. Wheatstone on the Physiology of Vision. the object itself is reflected in a mirror, or inverted. The reason is this; that in the former cases the projections to each eye are separately reflected or inverted, still remaining presented to the same eye, whereas, by the reflexion or mversion of the object itself, not only are the projections reflected or inverted, but they are also transposed from one eye to the other; and these cir- cumstances occurring simultaneously reproduce the normal relief. Fig. 6 will render this evident in the case of reflexion: A is the object, B its reflexion in the mirror CD; RB and LB are the directions in which the right and left eyes view the reflected image respectively, and JA and rA the directions in which the eyes would view the corresponding face of the object directly. In the case of an inverted object, it is obvious that that pro- jection which was before seen by the right eye must be seen by the left eye, and the contrary. It is possible to make this normal or converse relief appear while one of the pictures remains constantly presented to the same eye. This result may be thus obtained. Having taken a photograph of the object, which should be one the converse of which has a meaning, take two others at the same angular di- stance (say 18°), one on the right side, the other on the left side of the original. Of the three pictures thus taken, if the middle one be presented to the right eye, and the left picture to the left eye, a normal relief will be seen; but if the right picture be presented to the left eye, the other remaining unchanged, a con- verse relief will be seen. In like manner, if the middle picture be presented to the left eye, and the right picture to the right eye, a normal relief will appear; but if the left picture be pre- sented to the right eye, the converse relief will present itself. It must be observed, that the normal and converse reliefs, when the same picture remains presented to the same eye, belong to two different positions of the object. § 23. Hitherto I have taken into consideration only those cases of the conversion of relief which are exhibited by binocular pictures in the stereoscope, when they are transposed, reflected or in- verted; I shall now proceed to show how phenomena of the same kind may be elicited by regarding objects themselves, by means of an instrument adapted for the purpose. As this m- strument conveys to the mind false perceptions of all external objects, I have called it the Pseudoscope. It is represented by fig. 7, and is thus constructed: two rectangular prisms of flint glass, the faces of which are 1:2 inch square, are placed in a frame with their hypothenuses parallel, and 2-1 inches from each other; each prism has a motion on an axis corresponding Prof. Wheatstone on the Physiology of Vision. 517 with the angle nearest the eyes, so that they may be adjusted that their bases may have any inclination towards each other ; and the frame itself is adjustable by a hinge at a, in order to bring the prisms nearer each other to suit the eyes of the observer. The instrument being held to the eyes, and adjusted to an object, so that it shall appear single, each eye will see a reflected image of that projection of the object which would be seen by the same eye without the pseudoscope. This is exactly the con- trary of what occurs when the eyes regard the reflected image of an object im a looking-glass ; the left eye then sees the re- flected image of the right-hand projection, and the right eye the reflected image of the left projection, as shown by fig. 6. Plane mirrors cannot be substituted for the reflecting prisms, for this reason ; the refraction of the rays of light at the incident and emergent surfaces of the prisms enables the reflexion of an object to be seen when the object is even behind the prolonga- tion of the reflecting surface, as shown at fig. 8, and thus the reflected binocular image may be seen in the same place as the object itself, whereas the images cannot be made by means of plane mirrors thus to coincide. When the pseudoscope is so adjusted as to see a near object while the optic axes are parallel, to view a more distant object with the same adjustment, the axes must converge, and the more so as the object is more distant; all nearer objects than that seen when the axes ave parallel, will appear double, because the optic axes can never be simultaneously directed to them. If this in- strument be so adjusted that very distant objects are seen single when the eyes are parallel, a// nearer objects will appear double, because the optic axes can never converge to make their bin- ocular images coincide. If the attention is required to be di- rected to an object at a particular distance, the best mode of viewing it with the pseudoscope is to adjust the instrument so that the object shall appear at the proper distance and of its natural size. In this case the more distant objects will appear nearer and smaller, and the nearer objects will appear more distant and larger. In ordinary vision, whenever the distance of an object varies, the magnitude of the picture on the retina, and the degree of convergence of the optic axes, always maintain a constant rela- tion to each other, both increasing or decreasing together; and the perceived magnitude, suggesting to the mind the real mag- nitude of the object, in consequence thereof remains the same. The instrument I described in § 17 shows what illusions arise when the usual relations of these elements of our perceptions are disturbed, by causing one to remain constant while the other varies. The pseudoscope exhibits the still more curious illusions 518 Prof. Wheatstone or the Physiology of Vision. which result from combining these elements inversely ; so that as an object becomes nearer, its larger picture on the retina is accompanied by a less convergence of the optic axes. With the pseudoscope we have a glance, as it were, into another visible world, in which external objects and our internal perceptions have no longer their habitual relation with each other. I will now proceed to describe some of the illusions produced by the aid of this instrument. Those which may be strictly designated conversions of relief, in which the illusive appearance has the same relation to that of the real object as a cast toa mould, or a mould to a cast, are very readily perceived. I must however remark, that it is necessary to illuminate the object equally, so as to allow no lights or shades to appear upon them, for their presence has a considerable influence on the judgement, and is one of the principal causes of the perception of the proper relief when a single eye is employed. ‘ The inside of a tea-cup appears as a solid convex body; the effect is more striking if there are painted figures within the cup. A china vase, ornamented with coloured flowers in relief, pre- sents a very remarkable appearance ; we apparently see a vertical section of the interior of the vase, with painted hollow impres- sions of the flowers. A small terrestrial globe appears as a concave hemisphere ; on turning it round on its axis, it was curious to see different portions of the spherical map appear and disappear in @ manner that nothing in external nature can imitate. A bust regarded in front becomes a deep hollow mask; the appearance when regarded in profile is equally striking. A framed picture hanging against a wall, appears as if im- bedded in a cavity made in the wall. A medal, or the impression of a seal, is perfectly converted into a representation of the die from which it has been struck ; and, on the other hand, the mould or die of a medal, or an en- egraved seal, becomes a fac-simile of the medal or raised impres- sion. It will also be observed, that if the medal be placed on a flat surface, as a sheet of paper, it will appear sunk beneath the surface ; and if it be placed in a hollow of the same size, it will appear to stand above the surface as much as it actually is below it. These appearances are not always immediately perceived ; and some much more readily present themselves than others. Those converse forms which have a meaning, and resemble real forms we have been accustomed to see, are those which are the most easily apprehended. Viewed with the pseudoscope, notwithstand- ing the inversion of the pictures on the retina, the natural ap- pearance of the object continues to intrude itself, when some- Prof. Wheatstone on the Physiology of Vision. 519 times suddenly, and at other times gradually, the converse oc- cupies its place. The reason of this is, that the relief and distance of objects is not suggested to the mind solely by the binocular pictures and the convergence of the optic axes, but also by other signs, which are perceived by means of each eye singly ; among which the most effective are the distributions of light and shade and the perspective forms which we have been accustomed to see accompany these appearances. One idea being therefore sug- gested to the mind by one set of signs, and another totally in- compatible idea by another set, according as the mental atten- tion is directed to the one and abstracted from the other, the normal form or its converse is perceived. This mental attention is involuntary; no immediate effort of the will can call up one idea while the other continues to present itself, though the trans- ition may be facilitated by intentionally removing some of the signs which suggest the preponderating idea; thus the converse form being perceived, closing either eye will most frequently cause an instant reversion to the normal form; and always, if the monocular signs of relief are sufficiently suggestive. I know of nothing more wonderful, among the phenomena of perception, than the spontaneous successive occurrence of these two very different ideas in the mind, while all external cir- cumstances remain precisely the same. Thus a small statuary group, an elegant and beautiful object, without any apparent cause becomes converted into another totally dissimilar object uncouth in appearance, and which gives rise to no agreeable emotions in the mind; yet in both cases all the sensations that intervene between objective reality and ideal conception continue unchanged. The effects of the pseudoscope I have already mentioned, may be strictly called conversions of relief, because the illusive appear- ance is in each case the converse impression of the relief of the real object. If, however, the object consists of parts detached from and behind each other, the preceding term is inappropriate to denote the effects which result, but the more general expres- sion conversion or inversion of distance may be employed to de- signate them. I proceed to call attention to a few such effects. Skeleton figures of geometrical solids, as cubes, pyramids, &e., readily show their converse. pad Je Two objects at different distances, being simultaneously re- garded, the most remote will appear the nearest and the nearest the most remote. An ivory foot-rule, held immediately before the eyes a little inclined to the horizon with its remote end elevated, appears inelined in the opposite way, its nearer end elevated, and as if the observer were looking at its lower surface. Its form also 520 Prof. Wheatstone on the Physiology of Vision. undergoes a change. Since the nearest end, the retinal magni- tude of which is the largest, appears farthest from the eyes, and the nearest end, the retinal magnitude of which is greatest, ap- pears near the eyes, the rule will no longer be perceived to be rectangular, but trapezoidal. If the rule be placed horizontally, and it be regarded with the pseudoscope at an angle of 45°, it will appear with the form just described standing vertically. Any object placed before the wall of a room will appear behind the wall, and as if an aperture of the proper dimensions had been made in the wall to allow it to be seen ; if the object be illumi- nated by a candle, its shadow will appear as far before the object as in reality it is behind. The appearance of a plant is very remarkable ; as the branches which are furthest from the eye are perceived to be the nearest, those parts which are actually obscured by the branches before them, appear broken away and allow the parts apparently behind them to be seen. A flowering shrub before a hedge appears to be transferred behind it; and a tree standing outside a window may be brought visibly within the room in which the observer is standing. I have before observed, that the transition from the normal to the converse perception is often gradual; I will give one instance of this as an illustration. The object was a page of medallions embossed on card-board, and the raised impressions were pro- tected from injury by a thick piece of mill-board having aper- tures in it made to correspond to each medallion. The page was placed horizontally, illuminated by a candle placed beyond it, and looked at through the pseudoscope at an angle of 45°; for the first moment the page appeared as it would have done without the instrument ; soon after the medallions appeared level with the upper surface, and the shadows on the upper parts of the circular apertures were converted mto deep depressions as if cut out with a tool ; they next, from horizontal, became vertical, each standing erect on the horizontal plane, and immediately afterwards the reliefs were all changed into hollows ; finally, the page itself stood vertical, but with that change of form which I indicated in the case of the rule, the upper edge appearing much shorter than the lower edge: the series of changes bemg now complete, the final form remained constant as long as the object was regarded. In endeavouring to analyse the phenomena of converse per- ception, it must be borne in mind that the transposition of distances has reference only to distances from the retinz, not to absolute horizontal distances in space. Thus, if a straight ruler be held in the vertical plane perpendicular to the optic base, and also inclined 45° to the horizon so that its wpper end shall be Prof. Wheatstone on the Physiology of Vision. 521 the most distant, when the eyes are directed horizontally towards it, the rule will appear exactly in the converse position. If the rule be now removed lower down in the same vertical plane, its inclination, remaining unchanged, so that to look upon it the plane of the optic axes must be inclined 45°, it will appear un- altered in position, because its two pictures are parallel on the retin, and the optic axes would require the same convergence to make the upper and lower ends coalesce. The rule bemg remoyed still lower down, instead of its position being apparently reversed, it will appear to have a greater inclination on the same side than the object itself has. In the first case the more distant end is actually furthest from the eyes; in the second, the near and remote ends are equally distant ; and in the third the nearest end is most distant. Attention to what I have just stated will explam many ano- malous circumstances which occur when the eyes are differently directed towards the same object. It may also be necessary to remark, that the conversion of distance takes place only within those limits im which the optic axes sensibly converge, or the pictures projected on the retin are sensibly dissimilar. Beyond this range there is no mutual transposition of the apparent distances of objects with the pseudoscope ; a distant view there- fore appears unchanged. Some very paradoxical results are obtained when objects in motion are viewed through the pseudoscope. When an object approaches, the magnitude of its picture on the retin increases as in ordinary vision; but the inclination of the optic axes, instead of increasing, becomes less, as I have already explained. Now an enlargement of the picture on the retina invariably sug- gests approach, and a less convergence of the optic axes indicates that the object is at a greater distance; and we have thus two contradictory suggestions. Hence, if two objects be placed side by side at a certain distance before the eyes, and one of them be moved forwards, so as to vary its distance from the other, its continually enlarging picture on the retina makes it appear to come towards the eyes, as it actually does, while at the same time it appears at every step at a greater distance beyond the fixed object ; from one suggestion the object appears to approach, from the other to have receded. I again observe that retinal magnitude does not itself suggest distance, but from its changes we infer changes of distance. I have hitherto only described the pseudoscope constructed with two reflecting prisms. This is the most convenient appa- ratus for effecting the conversion of distance and relief that has occurred to me; but other means may be employed, which I will briefly mention. 522 Prof. Wheatstone on the Physiology of Vision. lst. Two plane mirrors are placed together so as to form a very obtuse angle towards the eyes of the observer ; immediately before them the object is to be placed at such distance that a reflected image shall appear in each mirror. The eyes being placed before and a little above the object, must be caused to converge to a point between the object and the mirrors; the right-hand image of the left eye will then unite with the left- hand image of the right eye, and the converse relief will be per- ceived. The disadvantages of this method are that only parti- cular objects can be examined, and it requires a painful adapta- tion of the eye to distinct vision. 2ndly. Place between the object and each eye a lens of small focal distance, and adjust the distances of the object and the lenses so that distinct inverted images of the object shall be seen by each eye; on directing the eyes to the place of the object, the two images will unite, and the converse relief be perceived. As the rays of light proceeding from the images have a greater divergence than those which would proceed from the point to which the optic axes are directed, long-sighted persons will see the binocular image more distinctly by wearing a pair of short- sighted spectacles. In this experiment the field of view is very small, on account of the distance at which it is necessary to place the lenses from the eyes; but I have been enabled in this manner to see beautifully the converse relief of a small ivory bust and of other small objects, which, however, should be in- verted in order to see them direct. 8rdly. The inverted images of the lenses, instead of being received immediately by the eyes, as just described, may be thrown on a plate of ground glass, as in the case of the ordinary camera-obscura, and may be then caused to unite by the means employed in any form of the refracting stereoscope. § 24, The cases of the conversion of relief when the object is regarded with one eye only, some of which were known more than a cen- tury ago, were taken into consideration and endeavoured to be explained by me in § 1] of the first part of this memoir, and Sir David Brewster* has published some interesting and in- structive observations on the same subject ; I will therefore not revert to this matter here, but only to say that I have myself never observed the conversion of relief when looking with both eyes immediately on a solid object, and if it has been observed by others under such circumstances, I should be inclined to attribute the effect to an inequality in the impressions on the * Transactions of the Royal Society of Edinburgh, vol. xv. p. 365 & 657. Ree ea oe nade tk - Cyd ae etaa ot aet Mr. T. S. Davies on Geometry and Geometers. 528 two eyes so that one only is attended to. But the plane shaded representation of a solid object, the relief of which is not very deep, may easily be made to appear at will, either as the solid which it is intended to represent or as its converse, even when both eyes are employed. This effect is strikingly observed in the glyptographic engravings of medals of low relief, and depends entirely on whether the light is so placed that it would cast the same shadows on the real object as are represented in the picture, or that it would cast shadows in the opposite direction. In the former case the picture appears with the relief it was intended to suggest ; in the latter with the converse relief. I have ob- served similar effects with Daguerreotypes of medallions and cameos, and with carefully shaded drawings of simple objects. LXXI. Geometry and Geometers. Collected by the late Taomas SrerpHens Daviss, /.R.S.L.& £.§c.* No. X. {Continued from p. 290.] yHERe is another ground of embarrassment to the young mathematician in forming his estimate of the ancient geo- metry. It is the want of proper discrimination between classes af propositions which are in themselves of essentially distinct characters. This is traceable to our very elements ; for even the first three books of Euclid comprise indiscriminately almost every kind of proposition—determinate and indeterminate. I need only refer to Mr. Potts’s “ Appendix,” before referred to (p. 289), for proof of this; for it will there be seen how di- versified are the propositions as to logical character, which con- * Communicated by James Cockle, Esq., M.A., Barrister-at-Law, who adds the following note :— {“ The above autograph of the late Professor Davies (for this addition to which I am responsible) constitutes the residue of the paper of which the remaining portion appeared in the April Number of this Journal. I have now communicated to the Philosophical Magazine for publication all the manuscripts of my !:te friend, which Mrs. Davies has confided to me. But Ihave no doubt that, in the ample store which I believe still remains in her hands, much will be found of the working of his genius—much that, while it reminds science of the loss she has sustained, will render important ad- vantages to mathematical literature, and prove worthy of the name and re- putation of the departed philosopher. “James Cock ie. “2 Pump Court, Temple, May 11, 1852.”] 524 Mr. T. S. Davies on Geometry and Geometers. stitute our first “Elements.” In the more extended classes of research, however, this becomes much more embarrassing ; and it is to be regretted that no single work in which the different classes of geometric research are intelligibly defined, can be pointed out. With one more source of difficulty this formidable list will be concluded ; though others, and those not of a minor character, might have been added. The great object of the ancient geometers appears to have been the solution of problems ; and hence the investigation of theorems held no importance in their estimation, further than as they were subsidiary to the demonstration of the constructions arrived at, or in the analyses by which those constructions were obtained. Instead, therefore, of investigating the properties of figures and classing them according to any rule (good or bad), only those were recorded that became subservient to some step or other in the construction of a problem. This is strikingly manifested in the seventh book of the Mathematical Collections of Pappus; where we see given as isolated propositions many theorems _ which form parts of the most beautiful and interesting classes of research that have been yet discovered. That wonderful work of M. Chasles (Apergu Historique) bears witness to this in almost every page, and it prevents the necessity of my adducing illus- trative examples in this paper. It will probably be objected that the arbelon and some other speculations mentioned by Pappus, as well as some of the minor works of the ancients which have reached us, contravene this view of the leading objects of the Greek Geometry. I know of none of those ancient works, however, in which I cannot trace the ulti- mate object to be the solution of some specific problem or class of problems; and so far I see no force in such an objection. As regards any of the sets of properties mentioned by Pappus, we must recollect that he wrote and “ collected”’ long after the period when geometry could be said to “ flourish” m the school of Plato —long after the decadence of pure geometry amongst the Greeks, The arbelon is itself, beyond being “pretty and curious,” mere geometrical trifling ; just the kind of speculation that might be supposed to be indulged in the age when the weak Proclus pre- sided over that once illustrious school. Nothing of this kind appears to have engaged the attention of geometers during the period of Apollonius and Archimedes: even the various curves that were devised by the ancients were not devised for the pur- pose of investigating their properties, but of solving some in- tractable problem by means of them. The conic sections come the nearest to claiming an exemption from this general rule: but though many properties are given by Apollonius, the immediate application of which to constructive purposes might not readily Mr. T. 8. Davies on Geometry and Geometers. 525 strike the mind, yet so many of them are subsidiary to the de- monstration of properties which have that undoubted purpose, as to require little concession on this point. Besides, my remarks are more immediately made in reference to the propositions of plane geometry ; and I think we may infer that if such classes of properties had been investigated, the good taste and judgement of Pappus would have led him to substitute them for the arbelon at least*. * It is usually stated that the several treatises enumerated by Pappus in the celebrated preface to his seventh book, “ were written with a view of facilitating the study of the geometrical analysis.” High as is the authority with which this opinion is enforced, I can only adopt it in a very modified sense of the terms employed—and in a sense too, which its supporters do not seem to include in their mode of understanding the statement. It is only in the light of their forming exemplars of the geometrical analysis, that I can yiew it as approaching to the fact; although I should not, perhaps, dispute the question if it were stated that these treatises are in the main, solutions of the problems in which the analysis of other problems often terminate. My principal objection to this latter view would be, that though analyses do often terminate in one or other of these problems, they as often do not; and that even if they were found by experience to do so still more frequently, there appears to be no reason why other classes of problems may not present as much variety in respect to this circumstance as those upon which the Greeks happened to spend their powers presented of frequency. That Euclid’s Data and his Porisms were subservient to analysis, and intended to be so, there cannot exist a moment’s doubt. Like his Elements they are intended to be subsidiary, and appear to have no other object. The treatises of Apollonius, on the contrary, can only be viewed as final and complete, each in itself: the complete enumeration of the varieties of case and circumstance, and the solution of each in succession, is the obvious end of his undertakg—not the means of getting to something else beyond it, Indeed, we may ask, to what purpose could these solutions have been ren- dered subservient in the cultivation of analysis? 1 cannot form the least conjecture as to how they can be so employed. We are also compelled to ask what could have been the nature of those problems which required such an immense amount of preparation as these treatises would imply, even supposing we could see how to apply them? It is strange that no single hint should have escaped the pen of Pappus on this topic, had there been such wonderful problems or classes of problems. To me, therefore, every one of the treatises of Apollonius appears to have nothing further to do with analysis, than as far as analysis might have been employed in obtaining the constructions ; even this being an assumption for which it might be difficult to furnish convincing authority. Our yiews would be much more in keeping at all events with the disputational character of the intercourse of the geometers of those times, did we believe that the analysis was always concealed, and only the construction and demonstration given. [ 526] LXXII. On the Puzzle of the Fifteen Young Ladies. By the Rey. Tuomas P. Kirkman, M.4A., Rector of Croft with Southworth, Lancashire. To the Editors of the Philosophical Magazine and Journal. GENTLEMEN, \ N JHILE I fully appreciate the analytic value of Mr. Spottiswoode’s observations on my problem of the fifteen young ladies in your May Number, I shall hope for his pardon if I say, that, so far as I can discover from what he has written, his solution, like my own and all that I have yet heard of, is accomplished simply by the rule of thumb. When he has supplied the demonstration, that from his seven groups, each of eight terms, not one must, but one can, be selected “im such a manner that no combinations recur,” I will confess that all the tentative process is avoided. I do not believe, although I am far from denying, that 63 young ladies can be handled day after day like the 15, That this can be done with 5 x3”*' young ladies, I have proved at p. 259, vol. v. of the Cambridge and Dublin Mathematical Journal. The following arguments in support of the opinion that the problem cannot be generalized for the case of 8n young ladies, n being a prime number greater than 5, may be deserving of attention, although I do not offer them as a demonstration of the negative. Let it be required to march out day by day in threes, until every pair have walked together, all the 38x ladics,. G4 4 A b, b, bg C, N, Ny Ng, consisting of three sisters a, three sisters 4, three sisters ¢, &c., n being a prime number. As the data are symmetrical in a, ,c...N, and there is nothing in the restriction, that each pair shall walk once and once only together, which is unsymmetrical, and as the whole column is to walk out every day, it is to be expected that the sum of the columns will be also symmetrical in these n letters. The families will exhibit no special preferences or dislikes towards each other, when we consider the letters apart from the sub- On the Puzzle of the Fifteen Young Ladies. 527 indices. Now the number of triplets possible with n things is less than that of those which must be employed in the columns to be added to the given one. We have a right to expect that the pair ab will be associated equally with the remaining letters ; that is, the numberof triplets to be added, which is 2 3n(3n—1)—n, will be divisible by that of those possible with n symbols, which is-4n -n—1.n—2; in other words, 9 is divisible by n—2, which confines n to the values 8, 5, and 11. The force of this reason- ing lies in the position, that there cannot be less than n families, all being symmetrical. The problem can be solved for the two first values of n; but I doubt greatly its solvability for n=11. There are 11 x 15 triplets possible with 11 things, and 15 columns of 11 triads are required to be added in the solution ; thus we may safely predict that every triplet of the 11 x 15 will be once employed. And it is reasonable to anticipate, on account of the symmetry to be expected, that the 15 columns will fall into groups of one or more columns, which can all be formed from the first added group by cyclical permutation either of n, or of n—1, or of n—2 letters; for to suppose such permutation to be made with less than n—2 letters, would inyolve the ad- mission that some one triplet of the 11 x 15 would be unaffected by it, which is next door to absurd. The only groups into which the 15 columns of letters, considered apart from subindices, can fall, are groups of 1, or of 3, or of 5, if all is symmetrical ; and these cannot be produced from each other by cyclical permuta- tion of 11, nor of 10, nor of 9 letters. I venture to affirm, though I do not pretend to have demonstrated, that the problem cannot be solved for a prime number greater than 5. The following is a better arrangement than that which I have before given :— Aol abe, ade, Abad Ayala Mb3e, ay Csds5 byboby Agbele Alley Agbsd, Agel Abe, Aged, CoC Ase, AsbsCs Ase\C, 3b, AxColy Asbaeg ddd bgdyeg dgbyeo byeoe3 ey bods betsd, Cabge, €1Ca€3 Cylgt, eg bat deseo Cybga eed, dabyeg The second and third groups of added columns, looking at letters apart from subindices, are made by cyclical permutabion of cde in the first. The subindices are made by cyclical permu- tation of 128, under all the letters bede, the second and third groups from the first. £9528] LXXIII. Early Egyptian Chemistry. By W.Herarata, Esq. To the Editors of the Philosophical Magazine and Journal. GENTLEMEN, W HILE engaged in unrolling a mummy at the Bristol Philosophical Institution lately, I elicited a few chemical facts which might probably be interesting to some of your readers. On three of the bandages were hieroglyphical charac- ters of a dark colour, as well defined as if written with a modern pen; where the marking fluid had flowed more copiously than the characters required, the texture of the cloth had become de- composed and small holes had resulted. I have no doubt that the bandages were genuine, and had not been disturbed or un- folded: the colour of the marks were so similar to those of the present “ marking-ink,” that I was induced to try if they were produced by silver. With the blowpipe I immediately obtained a button of that metal; the fibre of the linen I proved by the microscope, and by chemical reagents, to be linen ; it is therefore certain that the ancient Egyptians were acquainted with the means of dissolving silver, and of applying it as a permanent ink ; but what was their solvent? I know of none that would act on the metal and decompose flax fibre but nitric acid, which we have been told was unknown until discovered by the alche- mists in the thirteenth century, which was about 2200 years after the date of this mummy, according as its superscription was read. A very probable speculation might be raised upon this to account for the solution of the golden calf by Moses, who had. all his mundane knowledge from the Egyptian priests. It has been supposed that he was acquainted with and used the sul- phuret of potassium for that purpose: how the inference arose I know not; but if the Egyptians obtained nitric acid, it could only have been by the means of sulphuric acid, through the agency of which, and by the same kind of process, they could have separated hydrochloric acid from common salt: it is there- fore more probable that the priests had taught Moses the’ use of the mixed nitric and hydrochloric acids with which he could dis- solve the statue, rather than a sulphuret, which we have no evi- dence of their being acquainted with. The yellow colour of the fine linen cloths which had not been stained by the embalming materials, I found to be the natural colouring matter of the flax; they therefore did not, if we judge from this specimen, practise bleaching. There were in some of the bandages near the selvage some twenty or thirty blue threads; these were dyed by indigo, but the tint was not so deep nor so equal as the work of the modern dyers; the colour had been given it in the skein. Royal Society of Edinburgh. 529 One of the outer bandages was of a reddish colour, which dye I found to be vegetable, but could not individualize it; my son Mr. Thornton J. Herapath analysed it for tin and alumina, but could not find any. The face and internal surfaces of the orbits had been painted white, which pigment I ascertained to be finely powdered chalk. I am, Gentlemen, Yours respectfully, Mansion House, Old Park, Wixiiam Herapatu. Bristol, June 10, 1852. LXXIV. Proceedings of Learned Societies. ROYAL SOCIETY OF EDINBURGH. Dec. 15,(yN the Quantities of Mechanical Energy contained in 1852. a Fluid Mass, in different states, as to Temperature and Density. By Professor William Thomson. Let p be the pressure of a fluid mass when its volume and tempe- rature are v and ¢ respectively, and let Mdv+Nd¢ be the quantity of heat that must be supplied to it to augment its volume by dv and its temperature by df. The mechanical value of the work done upon it to produce this change, is the excess of the mechanical value of the quantity of heat that has to be added above that of the work done by the fluid in expanding, and is therefore J(Mdv+Ndt)—pdv. It was shown in the author’s paper on the Dynamical Theory of Heat, that this expression is the differential of a function of v and ¢, so that, if this function be denoted by ¢, we have o(v, t)=/{IM—p)dv+Ndt}. This function would, if the constant of integration were properly assigned, express the absolute quantity of mechanical energy contained in the fluid mass. Failing an absolute determination of the constant, we may regard the function ¢ as expressing the mechanical value of the whole agency required to bring the fluid mass from a specified zero state to the state of occupying the volume v and being at the temperature ¢. In the present paper some formule are given, by means of which it is shown that nearly all the physical properties of a fluid may be deduced from a table of the values of ¢ for all values of v and ¢; and experimental methods connected with the experi- mental researches proposed in the author’s last paper, are suggested for determining values of @ for a gaseous fluid mass. On a Mechanical Theory of Thermo-Electric Currents. It was discovered by Peltier that heat is absorbed at a surface of contact of bismuth and antimony in a compound metallic conductor, when electricity traverses it from the bismuth to the antimony, and that heat is generated when electricity traverses it in the contrary direction. This fact, taken in connection with Joule’s law of the Phil. Mag. 8.4, No. 21. Suppl. Vol. 3. 2M 530 Royal Society of Edinburgh. electrical generation of heat in a homogeneous metallic conductor, suggests the following assumption, which is the foundation of the theory at present laid before the Royal Society. When electricity passes-in a current of uniform strength y through a heterogeneous linear conductor, no part of which is permitted to vary in temperature, the heat generated in a given time is expressible by the Formula Ay+By?, where A, which may be either positive or negative, and B, which is essentially positive, denote quantities independent of y. The fundamental equations of the theory are the following :— Py Jy se; PB yes ane C2 yy sols ae ee —1 f' pat Za,=a,(1 —e J oh ) . . . . . . . (6) where F denotes the electromotive force (considered as of the same sign with y, when it acts in the direction of the current) which must act to produce or to permit the current y to circulate uniformly through the conductor; J the mechanical equivalent of the thermal unit; «, y the quantity of heat evolved in the unit of time in all parts of the conductor which are at the temperature ¢ when y is in- finitely small; y ‘‘ Carnot’s function” of the temperature ¢*; T the temperature of the coldest part of the circuit ; and 2 a summation including all parts of the circuit. The first of these equations is a mere expression of the equivalence, according to the principles established by Joule, of the work, F yt, done in a unit of time by the electromotive force, to the heat deve- loped, which, in the circumstances, is the sole effect produced. The second is a consequence of the first and of the following equation :— p-y=piay.(t—T),. . . HIG S (c) where @ denotes the electromotive force when y is infinitely small, and when the temperatures in all parts of the circuit are infinitely nearly equal, This latter equation is an expression, for the present circumstances, of the proposition} (first enunciated by Carnot, and first established in the dynamical theory by Clausius) that the ob- taining of mechanical effect from heat, by means of a perfectly re- versible arrangement, depends in a definite manner on the transmis- sion of a certain quantity of heat from one body, to another at a lower temperature. There is a degree of uncertainty in the present appli- cation of this principle, on account of the conduction of heat that must necessarily go on from the hotter to the colder parts of the * The values of this function, calculated from Regnault’s observations, ’ andthe hypothesis that the density of saturated steam follows the “ gaseous laws,” for every degree of temperature from 0° to 230° Cent., are shown in Table I. of the author’s “ Account of Carnot’s Theory,”’ Transactions, vol. xvi. p. 541. t Bee Philosophical Magazine, Dec. 1851, “‘ On Applications of the Prin- ciple of Mechanical Effect,” &c. n { “ Dynamical Theory of Heat” (Transactions, vol. xx. part ii.), Prop. . &e, Royal Society of Edinburgh. 531 circuit; an agency which is not reversed when the direction of the current is changed. As it cannot be shown that the thermal effect of this agency is infinitely small, compared with that of the electric current, unless y be so large that the term By’, expressing the thermal effect of another irreversible agency, cannot be neglected, the conditions required for the application of Carnot and Clausius’s principle, according to the demonstrations of it which have been already given, are not completely fulfilled : the author therefore con- siders that at present this part of the theory requires experimental verification. 1. A first application of the theory-is to the case of antimony and bismuth ; and it is shown that the fact discovered by Seebeck is, ac- cording to equation (c), a consequence of the more recent discovery of Peltier referred to above,—a partial verification of the only doubtful part of the theory being thus afforded. 2. If Gy denote the quantity of heat evolved [or —Oy the quantity absorbed] at the surface of separation of two metals in a compound circuit, by the passage of a current of electricity of strength y across it, when the temperature ¢ is kept constant ; and if » denote the electromotive force produced in the same circuit by keeping the two junctions at temperatures ¢ and z', which differ from one another by an infinitely small amount, the magnitude of this force is given by the equation $=Opn(!—2): ks 9d). (d) and its direction is such, that a current produced by it would cause the absorption of heat at the hotter junction, and the evolution of heat at the colder. A complete experimental verification of this con- clusion would fully establish the theory. 3. If a current of electricity, passing from hot to cold, or from cold to hot, in the same metal produced the same thermal effects; that is, if no term of Za, depended upon variation of temperature from point to point of the same metal; we should have, by equation (a), de _1 Dag do_l g=I—(t t); and therefore, by (d), ao 59H From this we deduce 1 et 1 yt =f pat — | pdt Pong ty ; and ea(induaet® A table of the values of BEN for every tenth degree from 0 to 4 OS 230 is given, according to the values of »*, used in the author’s previous papers ; showing, that if the hypothesis just mentioned were true, the thermal electromotive force corresponding to a given very small difference of temperatures, would, for the same two metals, in- crease very slowly, as the mean absolute temperature is raised. Or, * The unit of force adopted in magnetic and electro-magnetic researches, being that force which, acting on a unit of matter, generates a unit of ve- locity in the unit of time, the values » and J used in this paper are obtained by multiplying the values used in at aa former papers, by 32"2, 532 Royal Society of Edinburgh. JE if Mayer’s hypothesis, which leads to the expression 1+Et for p, were true, the electromotive force of the same pair of metals would be the same, for the same difference of temperatures, whatever be the absolute temperatures. Whether the values of p previously found were correct or not, it would follow, from the preceding expres- sion for ¢, that the electromotive force of a thermo-electric pair is subject to the same law of variation, with the temperatures of the two junctions, whatever be the metals of which it iscomposed. This result being at variance with known facts, the hypothesis on which it is founded must be false; and the author arrives at the remark- able conclusion, that an electric current produces different thermal effects, according as it passes from hot to cold, or from cold to hot, in the same metal. 4. If 3(¢'/—#) be taken to denote the value of the part of Za, which depends on this circumstance, and which corresponds to all parts of the circuit of which the temperatures lie within an infinitely small range ¢ to ¢'; the equations to be substituted for the preceding are, p=IZ@ +90), Kinyo sh us Ot Sea OT and therefore, by (d), de 1 tea zOH ttre AD 5. The following expressions for F, the electromotive force in a thermo-electric pair, with the two junctions at temperatures S and T, differing by any finite amount, are then established in terms of the preceding notations, with the addition of suffixes to denote the par- ticular values of © for the temperatures of the junctions. F= /-,0dt=J{0,—0,,.+ f, Sdt} ( =J{0, Gnen Ue mt /S Serr pH) at) 9 6. it has been shown by Magnus, that no sensible electromotive force is produced by keeping the different parts of a circuit of one homogeneous metal at different temperatures, however different their sections may be. Itis concluded that for this case 3=0; and there- fore that, for a thermo-electric element of two metals, we must have S=V(t)—¥,(¢), where ¥, and ¥, denote functions depending solely on the qualities of the two metals, and expressing the thermal effects of a current passing through a conductor of either metal, kept at different uni- form temperatures in different parts. Thus, with reference to the metal to which , corresponds, if a current of strength y pass through a conductor consisting of it, the quantity of heat absorbed in any infinitely small part PP! is ¥, (¢) (t!—2)y, if ¢ and ¢' be the Royal Society of Edinburgh. 533 temperatures at P and P’ respectively, and if the current be in the direction from P to P’. An application to the case of copper and iron is made, in which it is shown that, if ¥, and ¥, refer to these me- tals respectively, if S be a certain temperature defined below (which, according to Regnault’s observations, cannot differ much from 240° Cent.), and if T be any lower temperature, we have Sv YO-¥ AD} UH 0, FE, since the experiments made by Becquerel lead to the conclusion, that at a certain high temperature iron and copper change their places in the thermo-electric series (a conclusion which the author has expe- rimentally verified), and if this temperature be denoted by S, we must consequently have 0,=0. The quantities denoted by ©, and F in the preceding equation being both positive, it is concluded that when a thermo-electric current passes through a piece of iron from one end kept at about 240° Cent., to the other end kept cold, in a circuit of which the remainder is copper, in- cluding a long resistance wire of uniform temperature throughout, or an electro-magnetic engine raising weights, there is heat evolved at the cold junction of the copper and iron, and (no heat being either absorbed or evolved at the hot junction) there must be a quantity of heat absorbed on the whole in the rest of the circuit. When there is no engine raising weights in the circuit, the sum of the quantities evolved at the cold junction and generated in the “ resistance wire” is equal to the quantity absorbed on the whole in the other parts of the circuit. When there is an engine in the circuit, the sum of the heat evolved at the cold junc- tion and the thermal equivalent of the weights raised, is equal to the quantity of heat absorbed on the whole in all the circuit except the cold Junction. 7. An application of the theory to the case of a circuit consisting of several different metals shows that if (A,B), 9(B,C), 9(C,D) . . . - (ZA) denote the electromotive forces in single elements, consisting respect- ively of different metals taken in order, with the same absolute tem- peratures of the junctions in each element, we have g(A,B)+9(B,C)+9(C,D) . . +9(Z,4)=0, which expresses a proposition, the truth of which was first pointed out and experimentally verified by Becquerel. A curious experi- mental verification of this proposition (so far as regards the signs of the terms of the equation) was made by the author, with refer- ence to certain specimens of platinum wire and iron and copper wires. He had observed that the platinum wire, with iron wires bent round its ends, constituted a less powerful thermo-electric ele- ment than an iron wire with copper wires bent round its ends, for temperatures within atmospheric limits. He tried, in consequence, the platinum wire with copper wires bent round its ends, and con- nected with the ends of a galvanometer coil ; and he found that, with temperatures within atmospheric limits, a current passed from the 534 Royal Society of Edinburgh. copper to the platinum through the hot junction, and concluded that, in the thermo-electric series sal Copper, 9 61, Antimony, Iron, Picket \ Bismuth, this platinum wire must, at ordinary temperatures, be between iron and copper. He found that the platinum wire retained the same properties after having been heated to redness in a spirit-lamp and cooled again; but with temperatures above some limit itself con- siderably below that of boiling water, he found that the iron and pla- tinum constituted a more powerful thermo-electric element than the iron and copper ; and he verified that for such temperatures, in the platinum and copper element the current was from the platinum to the copper through the hot junction, and therefore that the copper now lay between the iron and the platinum of the series, or in the position in which other observers have generally found copper to lie with reference to platinum. A second somewhat thinner platinum wire was found to lie invariably on the negative side of copper, for all temperatures above the freezing-point; but a third, still thinner, possessed the same property as the first, although in a less marked degree, as the superior limit of the range of temperatures for which it was positive towards copper was lower than in the case of the first wire. By making an element of the first and third platinum wire, it was found that the former was positive towards the latter, as was to be expected. In conclusion, various objects of experimental research regarding thermo-electric forces and currents are pointed out, and methods of experimenting are suggested. It is pointed out that, failing direct data, the absolute value of the electromotive force in an element of copper and bismuth, with its two junctions kept at the temperatures 0° and 100° Cent., may be estimated indirectly from Pouillet’s com- parison of the strength of the current it sends through a copper wire 20 metres long and 1 millimetre in diameter, with the strength of a current decomposing water at an observed rate; by means of determinations by Weber, and of others, of the specific resistance of copper and the electro-chemical equivalent of water, in absolute units. The specific resistances of different specimens of copper having been found to differ considerably from one another, it is impossible, with- out experiments on the individual wire used by M. Pouillet, to deter- mine with much accuracy the absolute resistance of his circuit; but the author has estimated it on the hypothesis that the specific resist- ance of its substance is 24 British units. Taking ‘02 as the electro- chemical equivalent of water in British absolute units, the author has thus found 16300 as the electromotive force of an element of cop- per and bismuth, with the two junctions at 0° and 100° respectively. About 154 of such elements would be required to produce the same electromotive force as a single cell of Daniell’s, if all the chemical action in a Daniell’s battery were electrically efficient A battery of 1000 copper and bismuth elements, with the two sets of junctions at 0° and 100° Cent,, employed to work a galvanic engine, if the resistance Royal Institution. 535 in the whole circuit be equivalent to that of a copper wire of about 100 feet long and about one-eighth of an inch in diameter, and if the engine be allowed to move at such a rate as by inductive reaction to diminish the strength of the current to the half of what it is when the engine is at rest, would produce mechanical effect at the rate of about one- fifth of a horse-power. ‘The electromotive force of a copper and bis- muth element, with its two junctions at 0° and 1°, being found by Pouillet to be about 10g of the electromotive force when the junc- tions are at 0° and 100°, must be about 168. The value of Q, for copper and bismuth, according to these results (and to the value 160°16 of at 0°), or the quantity of heat absorbed in a second of time by a current of unit strength in passing from bismuth to copper, when the temperature is kept at 0°, is jm, or very nearly equal to the quantity required to raise the temperature of a grain of water from 0° to 1° Cent. ROYAL INSTITUTION OF GREAT BRITAIN, April 23, 1852.—On the Analogies of Light and Heat. By the Rey. Baden Powell, M.A., F.R.S., &c., Savilian Professor of Geo- metry, Oxford. The researches of Sir W. Herschel, Sir J. Leslie, M. De la Roche, and others, long since established the existence of well-marked dif- ferences in character, not only between the radiation from the sun and that from terrestrial sources, but even among these latter, according as the source was luminous or not ; and this especially as regarded its transmissibility through various screens and the absorp- tive effect of different surfaces. But the most striking peculiarity in the radiation from flame was established by Sir W. Herschel and afterwards extended to gas-lights by Mr. Brande, in that, even at considerable distances, after passing through a thick glass lens, without heating it, the concentrated rays produced heat on a blackened thermometer at the focus, exactly as in the case of the solar rays. This pointed to a peculiar distinction (also recognised by Sir J. Leslie), and showed that the mere proportion of heat transmitted by a screen (as in De la Roche’s experiments) was not the essential characteristic, but that further distinction as to the specific nature of the rays, was wanted. This want it was attempted in some measure to supply in some experiments by the author of this paper (Phil. Trans. 1825), in which the character of the different rays as to TRANS- MISSIBILITY through screens was examined 1n comBinaTion with the conditions of the ABSORBING SURFACE. This last is a point even yet little understood ; but thus much is clear :— (1) A certain peculiarity of ¢evture in the external lamina is favourable to the absorption of radiant heat, probably in all cases. (2) Darkness of colour is peculiarly favourable to the effect for the sun’s rays, and wholly oyerrules the first condition. In terrestrial luminous hot bodies it does so to an extent sufficient to give very marked indications. But this (as the author showed, 536 Royal Institution. in the experiments referred to) applies to that portion only of the compound rays, which is ‘also transmissible through glass; the non-transmissible portion is subject wholly to the former condition, as are all the rays from non-luminous sources (as was shown by Leslie and others). Hence the distinction of at least two species of heating rays emanating at the same time from the same /uminous source. From the neglect of this distinction much confusion has been kept up; and statements involving such confusion have been repeated from one elementary treatise to another. Again, notwithstanding that the experiments of Leslie and others on the absorption of heat from non-luminous sources, as well as those of Professor Bache on the radiation from surfaces, demonstrate that the effect has zo relation whatever to colour, yet the contrary asser- tion has been often persisted in. Again, “dark heat” is often spoken of without recollecting that rays of the very same quality and properties exist in the compound radiation from /uminous sources. The conclusions drawn from later experiments (performed with all the advantages derived from the beautiful invention of the thermo- electric instrument of Nobili), in many instances, are still vague, from want of attention to the distinction of different species of heat emanating at the same time from the same source. Melloni, in a most extensive and valuable series of experiments, taking as the sources of heat successively flame, incandescent metal, boiling mercury, and boiling water, and applying in each instance a long series of substances as screens, estimated the proportion of rays out of 100 stopped, which was very different for each screen and each source: evincing wide differences in ‘‘ diathermaneity,” while rock-salt alone was almost totally ‘‘ diathermanous ” to rays from all sources alike. But we must still ask, what species of rays were those respectively stopped and transmitted? To take the per-centage simply is ambi- guous; the body of rays is not homogeneous; the property of trans- missibility should be viewed in combination with other properties of the specific rays, such as those evinced in their relations to the texture or colour of the absorbing surface. Nor is the ambiguity removed, though the difference of source is specially referred to, if the heterogeneity of rays from the same source be overlooked. The mere classification of sources into /umi- nous and non-luminous will not suffice; still less a reference to their temperatures, it being perfectly well known that the temperature of luminosity is very different for different substances *. Again, Melloni has shown that the diathermaneity is not proportional to transparency, by a classified series of transparent screens with the lamp. It must however be recollected that the term “ diathermaneity ” * References in detail to all the different researches here mentioned, will be found in the author’s two Reports on the state of our knowledge of Radiant Heat in the British Association Reports, 1832 and 1840, Royal Institution. 537 is applied indiscriminately to a heterogeneous body of rays; out of which some species of rays are entirely stopped, others entirely trans- mitted; and the great differences in “ diathermaneity ” for heat from different sources, which Melloni has also established, are nothing else than absorption of PECULIAR rays by each medium, not more anoma- lous than the corresponding absorptions of /uminous rays by different transparent media so little as yet reduced to law. While rock-salé is analogous to colourless media for light, alwm on the other hand is totally impermeable by heat from dark sources, and partially so by rays from the lamp ; that is, wholly impermeable for that portion of the rays which are of the same kind as those from non- luminous sources, and permeable to the others. By other sets of experiments Melloni showed that rays from the lamp transmitted in different proportions by various screens and then equalized, were afterwards transmitted by alum in equally various proportions; or as he expresses it, ‘‘ possess the diathermancy peculiar to the substances through which they had passed.” But this implies no new property communicated to the rays. It shows that as different specific rays out of the compound beam were transmitted in each case by the first screen, alum, though im- pervious to the lower heating rays, is permeable by these higher rays ; and in different degrees according to their nature; an effect simply dependent on the heterogeneity of the compound rays from a lamp. Again, with differently coloured glasses peculiar differences of dia- thermaneity were exhibited with rays from a lamp, incandescent metal, and the sun; but not more various or anomalous than the absorption of specific rays of light. And besides considerations of this kind, it must always be borne in mind that a blackened surface (like that which was used in all these experiments) itself is unequally absorptive for the different rays. The solar heat being freely transmissible through all colourless transparent media along with the light, there would be no peculiar advantage in experimenting on the solar spectrum formed by a rock-salt prism. Melloni however with such a prism, on interposing a thick screen of water, found the most heating rays (7. e. those at or beyond the red end) intercepted, as they are known to be by water ; and this caused the position of the redative maximum to be apparently shifted higher up in the spectrum, even to the position of the green ray. On the other hand, many coloured glasses, he found, absorbed the rays in various proportions, yet they left the point of maximum heat unaltered; i.e. though variously absorptive for the higher rays, they were not of a nature to stop the lower, or most heating rays. One result indeed is recorded which seems at variance with all other experiments on the solar rays: a peculiar green glass (tinged by oxide of copper) was found to absorb so entirely all the most heating rays that the remaining portion produced no heat, though when concentrated by a lens they gave a brilliant focus. Speaking generally, however, these experiments only confirm what is on all 538 Royal Institution. hands admitted, viz. that the i//uminating and heating powers follow very different laws with relation to the different rays. The grand discovery by Melloni of the true REFRACTION OF HEAT, even of that kind which constitutes the whole radiation from dark sources, by means of the rock-sait lens and prism, and its extension by Professor Forbes to the determination of the index of refraction («) for the most heating rays from all sources, both luminous and non-luminous, gave the first actual proof of the real analogy of the propagation of heat by waves in an etherial medium: which was further carried out when it was shown from Cauchy’s theory that for different wave-lengths (\) there must be in every medium a certain limit of all refrangibility : that is, as we suppose (A) to in- crease, large changes in (X) will give continually smaller changes in (), and when (A) is very great compared with (Az) the intervals of the molecules, then the index () assumes its limiting value, which is not greatly below that for the extreme red ray, and with this, the index for the lowest heat coincides. Rent is seen directly from the formula * == P-Q Cs). +R (=) —&e., which, when we suppose i = 0, will have for its limiting value (- )= /P The results from observation for rock-salt ee with this theory, are as follows :— Rock-Salt. [he Rays. Obs. Theory. Mean light............|, 1°598 iS 0 aR RTC IR HRB GY, 7 C106 OC eer ey hee bi 1°529 Dark hot metal ........| 1°528 LL LEL A RO PORE a O27 But it is to the capital fact established by Professor Forbes, of the polarization of heat from dark sources (for with /uminous sources little doubt could exist), with all its remarkable train of consequences, that the complete analogy with light is seen in the most uninter- rupted point of view ;—the transverse vibrations, the depolarization, the consequent interferences, the production of circular and elliptic vibrations under the proper ‘conditions, —to those familiar with the wave-theory present an irresistible accumulation of proof of the identity of the rays of heat with a succession of waves in an etherial medium; exhibiting different properties i in some dependence on their wave-lengths. * See the author’s Treatise ‘‘ On the Undulatory Theory applied to the Dispersion of Light,” &c. London, J. W. Parker, 1841, pp. 71-122. PN ES ee Royal Institution. 539 Among the most recent researches on the subject are those of Mr. Knoblauch (of which a translation is given in Taylor’s Foreign Scientific Memoirs, Part xviii. and xix.), and they are not to be sur- passed for extent and accuracy of detail. One series is devoted to the examination of the alleged differences in radiation of heat proportioned to the temperature of the source. This, as before observed, is an untenable hypothesis, but Mr. Knob- lauch distinctly refutes it by a series of experiments on alcohol flame, red-hot metal, hydrogen flame, and an Argand lamp, whose tempera- tures are in the order of enumeration beginning with the highest ; but the power of their heat to penetrate screens is found to follow exactly the reverse order. And even with lower stages of heat, the effects bear no proportion to the temperatures as such. Hence the effect is evidently not due to a mere extrication of the heat of tem- perature, but is of a peculiar kind. In a word, agreeably to the pre- ceding remarks, the different species of rays, more or less compounded together in the several cases, exhibit their diversities of character in developing heat by their absorption. One very peculiar result is, that platinum, at a stage intermediate between red and white heat, trans- mits through all the screens employed rather less heat than when at ared heat. That is, these intermediate rays are of such a wave- length as to be subject to a peculiar absorption by these screens ; while at the same time possibly less of the former may be emitted. In another section Mr. Knoblauch adverts to the effects of surfaces on the absorption of rays, and particularly remarks (p. 205), “ The experiments of B. Powell and Melloni have shown that one and the same body is not uniformly heated by rays from different sources, which exert the same direct action on a blackened thermoscope ; ” a statement which does not very intelligibly express any conclusion of the author’s. Mr. Knoblauch however supports it by elaborate experiments, showing, as might be anticipated, that an Argand lamp affects a surface of carmine less, and one of black paper more, while a cylinder heated to 212° affects the carmine more and the black paper less, Another extensive series, on the effect of surfaces on radiation, is directed to show that the effect is independent of the source whence the heat so radiated was originally obtained. Among the very multifarious results referring to screens and sur- faces obtained by Mr. Knoblauch, it can here only be remarked that none of those varied facts appear to present anything at variance with the principles here advocated, while in the general conclusions which he indicates at the close of his memoir, the author, though professedly avoiding all hypothesis, yet distinctly intimates his con- viction of the heterogeneity of the heating rays increasing as the condition of the source rises in the scale from a low heat up to lumi- nosity or combustion: and that the diversities of heating effect on different media are due to a selective absorption of particular species of rays, from peculiarities in the nature of those substances, and analogous to the absorption of particular rays of light by coloured media. 540 Royal Institution. It must: not however be omitted to notice, however briefly, another recent set of researches of high interest, those of M. Silberman ;’ in which (among others) the very remarkable fact is established, that on transmitting a narrow ray of heat from a heated wire, through rock-crystal, there is a singular difference according as the ray passes parallel or perpendicular to the axis of the crystal: the effect being indicated by having the further side of the crystal coated with a fine composition of wax, the portion of which in the direction of the ray is melted in a circular form in the first instance and in an elliptical in the second. The general fact of the heterogeneity of heating rays, especially from luminous sources, is fully recognised by Melloni as in some sense the conclusion from all his experiments. The hypothesis that this heterogeneity consists simply in differences of wave-length would seem a probable one ; though it is still possi- ble, as Professor Forbes suggests, that some other element may also enter into the conditions. This view has been extended by M. Ampere so as to refer both luminous and heating effects to the same rays :—a view controverted by Melloni, chiefly on the ground, evinced by several classes of experiments, that the intensity of the heating effect (especially in the solar rays) follows no proportion to that of illumination ; an argu- ment which really amounts to little, unless the theory obliged us to infer that the amount of illumination must follow the same law as that of heat; which it manifestly does not; since the nature of the effect in the one case is wholly dependent on the unknown constitution of the optic nerve ; according to which some precise proportion of the impinging vibrations, with a particular wave-length, is that which gives the greatest perfection of vision ; while for heat the effect has no reference to such peculiar conditions; but is dependent in some way on longer wave-lengths, and pro- bably more simply connected with the intensity or amplitude of the vibrations. On this theory our view of the case would be thus :— A body heated below luminosity begins to give out rays of large wave-length only. As it increases in luminosity it continues to send out these, and at the same time others of diminishing wave-lengths, till at the highest stage of luminosity it gives out rays of all wave- lengths from those of the limit greater than the red end of the spectrum, to those of the violet end, or possibly less. Rays of all these species are transmissible and refrangible by rock- salt; and many of them with numerous specific distinctions by other media. They are all more or less capable of exciting heat when absorbed or stopped; though in some the effect is perhaps insensible. Both this property and that of their transmissibility seems to depend in some way on the wave-length, though in no simple ratio to it. The absorptive effect due to texture of surfaces has some direct relation to the magnitude of the wave-length, especially near the limit; while that due to darkness of colour is connected with a A Intelligence and Miscellaneous Articles. 541 shorter wave-lengths, such as belong to rays within the limits of the light spectrum: and in any case when a ray impinges on any absorb- ing substance, its vibrations, being stopped, communicate to the mole- cules of the body vibratory movements of such a kind as constitute heat of temperature. The peculiar molecular constitution of bodies which determines their permeability or impermeability to rays of any species, gives rise to all the diversities of effect, whether luminous or calorific. We thus escape all such crude ideas, at once difficult and unphilosophical, as those either of two distinct material emanations producing respect- ively heat and light, or of a conversion of one into the other; and obtain a view far more simple and consistent with all analogy. LXXV. Intelligence and Miscellaneous Articles. DR. KEMP’S PATENT FOR A NEW METHOD OF OBTAINING MOTIVE POWER BY MEANS OF ELECTRO-MAGNETISM. MY invention of a new method of obtaining power by means of electro-magnetism consists of the mode hereinafter described of combining apparatus to be actuated by electro-magnets. And in order that my invention may be most fully understood and readily carried into effect, I will proceed to describe the means pursued by me. I so arrange electro-magneto apparatus that a series of electro- magnets are caused to act in succession by their armatures on the same bar or instrument, and by such bar or instrument I give motion to fluids in order to obtain and communicate power thereby. To accomplish this object the armatures of several electro-magnets are fixed to stems, and the stems of the armatures are to be free to move through the bar or instrument which carries them. For the purpose of enabling the armatures to be acted on in succession by their magnets, I make the stem of the armature which is to be first attracted somewhat longer than the next in succession, by which means the first armature will be as near as may be to its magnet ; and the next armatures being more and more distant from their electro-magnets, therefore when the first armature has been attracted by its electro-magnet, the others will be moved nearer to their electro-magnets, and will consequently be brought into the most advantageous position to be attracted thereby when their turns come. Thus, supposing it to be determined that each armature shall be attracted through a quarter of an inch by its electro-magnet, and that there are to be eight electro-magnets to act on the same bar or magnet, the first armature before being attracted would be at a di- stance of a quarter of an inch from its electro-magnet; the second would be half an inch from its magnet ; the third three quarters of an inch from its magnet, and so on; whereby the eighth armature would be two inches from its electro-magnet, and these differences of distance are to be obtained by the stems (by which the armatures are connected to the bar or instrument) being made shorter and shorter. By this arrangement it will be evident that if electric currents be caused to pass in succession to the coils of the several 542 Intelligence and Miscellaneous Articles. electro-magnets, and in such manner that the currents of electricity having caused the first electro-magnet to attract its armature, are cut off therefrom, and caused to pass to the next electro-magnet, and so on in regard to the eight electro-magnets and their armatures ; each armature before being attracted will have been brought by the movement of the bar or instrument to within about a quarter of an inch of its electro-magnet, the bar coming at each step of its move- ment nearer and nearer to the electro-magnets, which it is enabled to do by the stems of those armatures which have been previously attracted, being enabled to slide back freely through the bar or instru- ment which carries them. The stems of the armatures are enabled to draw the bar or instrument towards the electro-magnets (when their armatures are attracted by reason of the stems having projecting heads or end), which prevent the stems from being drawn through the bar or instrument which carries them, whereby, when all the electro-magnets have attracted their armatures, the bar or instru- ment will have been moved two inches or other distance according as arrangement is made for each of the electro-magnets to act through a less or larger space than a quarter of an inch. It will be evident that this bar or instrument may be arranged to give motion to machinery in various ways; but I believe the most convenient mode of applying the power thus derived from electro-magnets, will be found to be to affix one bar or instrument, such as herein de- scribed, to one end of the rod of a piston working in a cylinder, and another such bar or instrument to the other end of the piston-rod, the piston being in the middle of the piston-rod, and the piston-rod working through stuffing-boxes on the covers at either end of the cylinder. Each such bar or instrument is to be fixed in the manner of a cross-head to the piston-rod, and to be guided in its movement to and fro, and is to be provided with armatures on stems as herein described, and sets of electro-magnets to attract the same, and capable of being brought into action in succession, as above explain- ed, and as will be readily understood by workmen accustomed to making electro-magneto apparatus ; by which means the piston in the cylinder may be moved first in one direction and then in the other. In order that the armatures may be in a position to act cor- rectly, the ends of their stems, when being moved back towards the cylinder, should come against a stop or stops to move the heads or enlarged ends of the stems to the bar or instrument which carries them; they will thus be brought inte position to be again acted on by their electro-magnets so soon as the electro-magnets have, by attracting their armatures, drawn the piston, as far as it can go, in the other direction. Asa piston, by such means, cannot with con- venience be caused to move through an extended length of space, the cylinder is to be of comparatively large diameter to its length, and at either end it is to have passages for the water or other fluid (contained in the cylinder) to pass into and from the ends of another cylinder of less diameter, but of proportionably greater length, in which a piston also works ; and I prefer that the piston-rod of such second cylinder should also work through stuffing-boxes at either end of that cylinder; such piston-rod communicating the power Intelligence and Miscellaneous Articles. 543 obtained (by the means above described) by a connecting-rod and crank from one end of the piston-rod, or by other suitable means of communicating power from a piston, may be employed. From the above description it will be understood that great power may be ob- tained from a series of electro-magnets, each attracting its keeper or armature, and consequently moving the piston through only a small space; and such power being exerted over a large area of piston, moving a fluid and forcing it into a cylinder of smaller diameter, will cause the piston of that second cylinder to be moved through a longer stroke in proportion to the different capacities of the cylinders, and the piston of the second cylinder will consequently be moved at a greater speed than that in the larger cylinder, and the pressure per square inch on the smaller piston will be the same as that on the greater piston. All which will be readily understood by a workman acquainted with the pressure of fluids put in motion by one piston, and caused to act on another; and it will be at once perceived that the action will be the reverse of that in Bramah’s Press, wherein the water is put in motion by the power used acting on a piston or plunger of comparatively small diameter, and the water is caused to act on and to move a piston of much larger diameter. Whereas, in the present invention, a series of electro-magnets are caused to act in succession on a bar or instrument, as above explained, in such manner that when combined with a comparatively large piston the power will, by driving or forcing the water or fluid with a cylinder of less diameter and of greater length, cause the piston therein to be moved with less power, but with greater speed. And it will at once be understood that the power obtained will depend on the effort each magnet is capable of exerting; for it will be evident that the actual force which is kept up to and given off from the piston in the small cylinder will be equivalent to that exerted by one of the magnets, in attracting or drawing its armature through a compara- tively small space.—Repertory of Patent Inventions, February 1852. ELECTRO-CHEMICAL RESEARCHES ON THE PROPERTIES OF ELEC- TRIFIED BODIES. BY MM. FREMY AND BECQUEREL. For several years the attention of chemists and physicists has been directed to the very remarkable modifications which certain bodies present when submitted to the action of a moderate temperature. We know that, under this influence, sulphur and phosphorus acquire new properties. We propose to investigate whether electricity, like heat, can change the physical and chemical properties of different bodies. We must examine, in the first place, into the singular effects presented by oxygen in various circumstances, and referred to the formation of what has been called ozone; this body appears to be produced in all cases in which oxygen is submitted to the influence of electricity. Without wishing to cast doubt upon the sagacity of those who haye examined into the properties of ozone, it cannot be denied that there still exists great uncertainty in the minds of chemists and phi- losophers as to the interpretation of the phenomena observed; we 544 Intelligence and Miscellaneous Articles. have therefore thought that it was important to submit these phe- nomena to new experiments. We will confine ourselves here to reproducing some of the facts mentioned in the memoir which we have the honour to present to the Academy. 1. After going over all the experiments made on ozone, mention- ing in particular the important researches of Schdnbein, Marignac and De la Rive, we have examined, first the oxidizing properties of the oxygen procured by the decomposition of water by the galvanic pile ; the result of these researches is that the pile cannot be employed to determine the nature of ozone, because the active principle is found only in very small proportion in the oxygen of the pile. We have therefore been obliged to study successively all the methods which can be employed to electrify oxygen. 2. The are which is formed upon the interruption of the voltaic circuit does not appear to modify the oxygen in the same manner as the ordinary spark, because the elevation of temperature which accompanies it probably destroys that which the electricity might produce; but according to our observations, this are may determine the combination of gases amongst themselves, acting thus as spongy platinum and as electricity; under its influence we have combined nitrogen and oxygen directly, to form nitric acid, nitrogen and hydrogen to produce ammonia, and sulphurous acid and oxygen to form anhydrous sulphuric acid. 3. The spark proceeding from currents of induction, and produced by means of the ingenious apparatus lately constructed by M. Ruhmkorff, acts like the spark of the ordinary machines, and has enabled us to repeat, without fatigue, all the experiments made with the machine. 4. Pure oxygen, enclosed in glass tubes together with a band of starched and iodized paper, was electrified by means of « series of sparks striking the outer surface of the tube; the paper began to become blue after the passage of a few sparks. ‘This coloriza- tion depends on the electrization of the oxygen, and not on the de- composition of the iodide; for no effect takes place when the iodide is placed in hydrogen and operated on. This fact is so much the more remarkable, as the oxygen is electrified without the interven- tion of metallic wires, and consequently without the presence of particles transported by the electric spark. 5. Oxygen, prepared by the most different modes, such as the calcination of the oxides of manganese, mercury or silver, by the de- composition of chlorate of potash, or of water by means of the pile, acquires a very distinct odour, and strongly marked oxidizing pro- perties when it is subjected to the influence of electricity ; these properties are manifested by oxygen as pure as it is possible to ob- tain it. The oxygen thus electrified loses its oxidizing properties when exposed to iodide of potassium, but it regains its odour and chemical activity when again electrified; this experiment may be re- peated indefinitely on the same gas. All these facts show that the oxidizing power of electrified oxygen is not due to the presence of a foreign body contained in the gas; = Intelligence and Miscellaneous Articles. 545 the following experiments were directed to rendering a given volume of oxygen entirely absorbable whilst cold by mercury, silver, or iodide of potassium. 6. When pure and dry oxygen is enclosed in a series of glass tubes and subjected to the action of electric sparks, if after a time we break one of the extremities of these tubes to ascertain the volume of gas which has become immediately absorbable by alkaline iodide, we shall find that during several hours the modification increases in proportion to the time of electrization, and that afterwards it appears to diminish, probably because the spark destroys that which at first it produces. 7. The difficulties presented in the preceding experiment induced us to study the deportment of electrified oxygen with certain absorb- ing bodies capable of immediately seizing the modified oxygen and of withdrawing this gas from the decomposing action of the excess of electricity ; we therefore passed a series of electric sparks into small eudiometric tubes full of moist oxygen, and placed over either mer- cury or a solution of iodide of potassium, or containing in their in- terior a moistened leaf of silver; we then saw the oxygen become absorbed in a regular manner by the action of the electric spark, and in many experiments obtained a complete absorption. 8. Lastly, to get rid of all doubts about the particular activity im- parted to oxygen by the electric spark, we wished to verify the pre- ceding experiments in closed tubes. We therefore introduced into tubes filled with pure oxygen some iodide of potassium and moist- ened silver. We submitted these tubes for several days to the action of electricity ; the spark, which, during the first days was very brilliant, became palerand paler, and presently almost invisible. At this moment, on breaking the tubes under water, we saw this liquid rush into their interior and fill them entirely, thus showing that a vacuum had been produced, and consequently that the oxygen had become completely absorbable without heat, by the silver and iodide of potassium. We must add, that, to render these experiments de- cisive, we had previously ascertained—1st, that pure water, the sur- face of glass and the platinum wires conducting the spark, could not absorb oxygen; 2nd, that water is not necessary to develope the activity of oxygen, but to cause the active oxygen to react upon metals or iodide of potassium; 3rd, that the electric spark does not decompose the iodide of potassium. We think therefore that we have shown, by rigorous experiments, that oxygen, under the influence of electricity, can become com- pletely absorbable in the cold by iodide of potassium and several metals, such as mercury and silver. These facts confirm the last researches of MM. Schonbein, Ma- rignac and De la Rive, and show that electricity, in acting upon oxygen, developes properties in it which did not exist before its in- fluence; we propose therefore simply to give the name of electrified orygen to the gas, which, having been submitted to the action of electricity, acquires a particular state of chemical activity, and to abandon the name of ozone, which expresses the idea of the transfor- mation of the oxygen into a new body.—Comptes Rendus, March 15, 1852, p. 399. Phil. Mag. 8. 4. No, 21. Suppl. Vol. 8. 2N 546 Intelligence and Miscellaneous Articles. ON THE ALLOTROPY OF SELENIUM. BY M. HITTORF. It is well known that selenium is softened by heat, becomes semi- fluid at 212°, and melts at a few degrees higher. In cooling, it be- comes viscous, thickens more and more, like wax, and then solidifies into a reddish mass, with a shining surface and a conchoidal and vitreous fracture. _ Berzelius had already observed, that when the cooling takes place very slowly, the selenium acquires a reddish colour, a rough surface, and a dull granular fracture, but that it loses this appearance when it is melted again and cooled rapidly. The author, having attentively studied these phanomena, has found that they are due to the existence of an allotropic modifica- tion of selenium analogous to that presented by sulphur, and evi- denced by the fact that the crystallized selenium melts without any previous softening, but at a temperature of 4.22°°6 F. When the substance is melted and the temperature raised, for instance to 428°, and left to cool with a thermometer immersed in it, the temperature is seen to descend gradually without the ther- mometer becoming stationary, without its even being possible to ob- serve a single point where its cooling appears to slacken until it has attained the temperature of the medium. At the same time the selenium passes through all degrees of viscosity until at about 122° it entirely solidifies into a resinous mass. In these circumstances the substance has therefore solidified in the amorphous state without having lost its latent heat of fusion; and it may retain it indefinitely, for it persists in this amorphous state at the ordinary temperature. But it passes into the crystalline state when kept for some time at a temperature between 176°-4.22°, and it then parts with its latent heat. Between 176° and 212° the transformation requires several hours ; and in this case the disengagement of heat which accompanies it is not appreciable. Between 257° and 356° it is very rapid; and if we operate upon 20 grms. of selenium, which are heated in an oil- bath, a thermometer immersed in the interior of the substance, after having attained the temperature of the bath, will rapidly exceed it, and will rise from 70° to 90° above it for some minutes. This phznomenon is still more striking when a hot air-bath is substituted for an oil-bath. In one experiment, in which the bath was heated to 266°, the author observed the thermometer, after having risen slowly to 257°, ascend suddenly to between 410° and 419°. When the selenium is employed in the state of powder, its meta- morphosis is more rapid. In this case, even in a bath heated merely to 212°, the crystalline state may be developed so rapidly that the heat rises from 4.5° to 52° above that of the interior. These phenomena are exactly similar to those which are pre- sented by sulphur. When this substance is strongly heated, and it is then suddenly cooled, it is converted into an amorphous, soft and elastic mass. At the ordinary temperature it passes gradually, but very slowly, from this amorphous state into the hard and crystalline state in which it is ordinarily met with. At a temperature ap- proaching 212°, it passes in a few minutes into this state; and it is well known that M. Regnault noticed in this case the temperature of the soft sulphur rise spontaneously to 232° in a chamber heated Intelligence and Miscellaneous Articles. 547 to 208°. The only difference which exists between these two bodies is, that with sulphur the ordinary temperature is sufficiently near that at which the change of state takes place for the transformation to be gradually effected ; whilst in the case of selenium, it is requi- site to raise it to a more elevated temperature in order to cause it to pass from the amorphous into the crystalline state. In many chemical reactions the selenium is separated from its solutions in the form ef an amorphous red powder. It is obtained thus by precipitating selenious acid by sulphurous acid, by the chlorides of tin, zinc, iron, or by exposing a solution of hydroselenie acid to the atmosphere, or by diluting with water a solution of amorphous or crystallized selenium in concentrated sulphuric acid. These precipitates have only to be exposed to the action of the solar rays to make them gradually pass into the crystalline state. In other circumstances selenium may be precipitated at the ordi- nary temperature in the crystalline state; for iustance, when solu- tions of seleniuret of potassium or ammonium are exposed to the air. Selenium exhibits very different densities in its two allotropie modifications. In its amorphous-state the specific gravity is 4-26- 4°28, whilst in the crystalline it is 4°80; its conductibility for clec- tricity likewise varies considerably ; the vitreous selenium insulates almost perfectly, whilst the crystalline substance is a very excellent conductor. In this state it exhibits a very curious phenomenon, that of the resistance decreasing in proportion as the temperature rises, provided its point of fusion be not attained. The author concludes his memoir by some observations on the analogy which exists between the phenomena of allotropy presented by sulphur and selenium and that which M. Schreetter has published regarding phosphorus; he thinks that the latter ehemist conimits.a mistake in considering the red phosphorus. as amorphous; and although we have not yet been able to obtain this modification in the crystalline state, he believes that it is the state of phosphorus corresponding to the erystalline sulphur and selenium, and that very probably this body, in passing into that state, likewise disengages a quantity of heat.—Poggendorff’s Annalen, Ixxxiv. p. 214. METEOROLOGICAL OBSERVATION. BY P. J. MARTIN. The perpendicular column of light seen in the horizon at sunset in April, as described by your Orkney correspondent, was also seen in this part of Sussex. I did not get sight of it more than once; because, supposing it to be of a transient and local character, I did not look for it again. Here it was singularly vivid, and faded gradually away, or rather followed the sun, as described by your friend and the correspondents of the Times. It had none of the character of the zodiacal light, but rather looked like the columnar prolongation of the sun described by oriental travellers as frequent in the east; and it immediately suggested to my mind (as it seems to have done to some of the above-mentioned observers) the columnar light “in Martin’s ‘‘ Exodus,” the ‘pillar of fire’”’ moving before the Israeli- tish host. Pwhorough, June 4, 1852. 2N2 548 INDEX to VOL. III. ADIE (R.) on some thermo-electrical experiments, 185. ts Air-pump, method of obtaining a per- fect vacuum in the receiver of an, 104. Algebra, on quadruple, 436. Alizarime, properties and composition - of, 358. Ammonias, on the compound, 392. Andrews (Dr. T.) on a method of ob- taining a perfect vacuum in the receiver of an air-pump, 104. Astronomical Society, proceedings of the, 71.” Astronomy, Grant’s History of Phy- sical, noticed, 468. Atmosphere, observations on the op- tical phenomena of the, 1, 92. Barytine, on the crystalline form of, 144. Bats’ wings, on the rythmical con- tractility of the veins of, 383. Becquerel (M.) on the artificial forma- tion of several minerals, 235; on the properties of electrified bodies, 503. Blood, on the red matter of the, 398. Books, new :—Hunt’s Elementary Physics, 57; Paterson’s Calculus of Operations, 60; Introductory Lectures delivered at the Govern- ment School of Mines, 61, 227; Ramchundra’s Treatise on Pro- blems of Maxima and Minima, 148; Feilitzsch’s Optical Investigations, occasioned by the Total Eclipse of the Sun on the 28th of July 1851, 232; Grant’s History of Physical Astronomy, 468. Booth (Rey. J.) on the geometrical properties of elliptic integrals, 233. Brame (Ch.) on the crystallization of sulphur, 154. Brewster (Sir D.) on some new and simple stereoscopes, 16; on a bin- ocular camera, and on a method of obtaining drawings of full length and colossal statues, and of living bodies which can be exhibited as solids by the stereoscope, 26; on a chromatic stereoscope, 31 ; on an optical illusion, 55; on the deve- lopment and extinction of regular doubly-refracting structures in the crystalline lenses of animals after death, 192; on a remarkable pro- perty of the diamond, 284. Brodhurst (B. E.) on the motions of the iris, 390. Bronwin (Rey. B.) on the integration of linear differential equations, 187. Buff (Prof. H.) on the electrical pro- perties of flame, 145. Cae series, on the bodies of the, 392. Cambridge Philosophical proceedings of the, 316. Camera, account of a binocular, 26. Carmichael (R.) on homogeneous Eee and their index symbol, Challis (Prof.) on the cause of the aberration of light, 53; on a ma- thematical theory of M. Foucault’s pendulum experiment, 331. Chapman (Prof.), mineralogical notes, 141; on the elassification of the pat and their allied compounds, 270. Chemical combmation, on the heat of, 43, 299, 481. Chemistry, early Egyptian, observa- tions on, 528. Chlorite spar and chloritoid, notice respecting, 142. Clouston (Rev. C.) on the sun-column as seen at Sandwick Manse, Ork- ney, 478. Cockle (J.) on algebraic transforma- tion, on quadruple algebra, and on the theory of equations, 436. Society, INDEX. Colours, accidental, observations on, Commercium Epistolicum, on the au- thorship of the, 440. Copper, crystallization of, by means of phosphorus, 77. Crednerite, notice respecting, 141. Crystalline lens, on the changes in the structure of the, after death, 192. Cyanide of potassium, on the pro- duction of, 399. Cyanometer, description of the, 93. Davies (the late T. S.) on geometry and geometers, 286, 523. Davy (Dr. J.) on the ova of the Sal- monidz, 384. Diamond, on a remarkable property of the, 284. Donovan (M.) on the supposed iden- tity of the agent concerned in the phenomena of ordinary electricity, voltaic electricity, electro-magnet- ism, magneto-electricity, and ther- mo-electricity, 117, 198, 290, 335, 445. Doris, on the anatomy of, 470. Dumont (A.) on the application of electro-magnetism as a motive force, 158. Earth’s axis of rotation, on the stabi- lity of the, 386. Electric currents of the first and higher orders, on, 173. —— fluid, on the constitution of the, 117, 198, 290, 335, 445. Electricity, observations on frictional, 36; experimental researches in, 67; observations on monothermic, 81; magnetism, heat, light and, on the identity of, 127; of flame, on the, 145; on the heating effects of, 311. Electro-magnet, account of experi- ments with a powerful, 32. Electro-magnetism, on the application of, as a motive force, 158, 501, Elliot (J.) on the stereoscope, 397. Elliptic integrals, on the geometrical properties of, 233. Eloin’s improved miner’s safety-lamp, 238, Embleton (Dr.) on the anatomy of Doris, 470 Equations, on the integration of linear differential, 187 ; on the theory of, 436; of thé fifth degree, on the 549 resolution of, 112; of any degree, on the possibility of solving, 457. Faraday (Dr.) on lines of magnetic force ; their definite character ; and their distribution within a magnet and through space, 67, 309, 401. Feilitzsch’s (Dr. v.) optical investiga- tions occasioned by the total eclipse of the sun on the 28th of July 1851, 232. Fessel’s (M.) electro-magnetic motor, observations on, 155. be on the electrical properties of, 45. Forster (Dr.) on some extraordinary spots on the sun, 78 Foucault’s (M.) pendulum experi- ment, mathematical theory of, 331. Franz (M.) on monothermic electri- city, 81. Fremy (M.) on the properties of elec- trified bodies, 503. Garnet, on a false cleavage in, 141. Gas-batteries, observations on, 317. Geometry and geometers, observa- tions on, 286, 523. Gillard’s (M.) light for illumination obtained from the burning of hy- drogen, remarks on, 152. Glands of the chick, on the develop- ment of the ductless, 379. Grant’s (R.) History of Physical Astronomy, noticed, 468. Gray (H.) on the development of the ductless glands of the chick, 379. Griffith (Dr. J. W.) on the triple or ammonio-magnesian _ phosphates occurring in the urine and other animal fluids, 373. Grove (W. R.) on the heating effects of electricity and magnetism, 311 ; on a mode of reviving dormant im- pressions on the retina, 435. Haidinger (Prof.) on vibrations in a ray of polarized light, 385. Hamilton (Sir W. R.) on continued fractions in quaternions, 371. Hancock (A.) on the anatomy of Do- ris, 470. Heart, human, on the structure and connexion of the valves of the, 304. Heat, on the expansion of some solid bodies by, 268; of chemical com- bination, on the, 43, 299, 481. —— and light, on theanalogies of, 495. 550 Heat, light, electricity and magnet- ism, on the identity of, 127. , atmospheric, on the polariza- tion of, 108. Helvine, notice respecting, 141. Hennessy (H.) on the stability of the earth’s axis of rotation, 386. Herapath (W.) on early’ Egyptian chemistry, 528. Herapath (W. B.) on the optical pro- perties of a newly-discovered salt of quinine, 161. Hittorf (M.) on the allotrophy of se- lenium, 546. Homogeneous ‘functions and their index symbol, on, 129. Hunt’s (R.) Elementary Physics, no- ticed, 57. Hunt (T. S.) on the compound am- monias, and the bodies of the ca- codyle series, 392. Hydriodic and hydrobromic acids, on the preparation of, by the galvanic method, 317. Hydrogen, observations on M. Gil- lard’s light forillumimation obtained from the burning of, 152. Tris, on the motions of the, 390. + Tron, meteoric, on the passive state of, 477. Jerrard (G..B.) on the resolution of equations of the fifth degree, 112; on the possibility of solvmg equa- tions of any degree however ele- vated, 457. Jones (Dr. H.) on the structure of the liver, 381. : Jones (T. W.) on the rythmical con- tractility of the veins of the bat’s wing, 383. Joule (J. P.), account of experiments with a powerful electro-magnet, 32; on the heat disengaged in chemical combinations, 481. Kemp (Dr.) on a new method of ob- taining motive power by means of electro-magnetism, 501. Kirkman (Rev. T. P.) on the puzzle of the fifteen young ladies, 526. Kohlrausch (Dr.) on the electroscopic properties of the voltaic circuit, 321. Kopp (H.) on the expansion of some solid bodies by heat, 268. Lamont (Dr.) on the ten-year period which exhibits itself m the diumal motion of the magnetic needle, 428. INDEX. Light, on the cause of the aberration of, 53 and heat, on the analogies of,495. , heat, electricity and magnetism, on the identity of, 127. ——, polarized, on the composition and resolution of streams of, from different sources, 316; on vibra- tions ina ray of, 385. Liver, on the structure of the, 381. Lyell (Sir C.) on the Blackheath pebble-bed, and on certain pheeno- mena in the geology of the neigh- bourhood of London, 473. Madder, on the colouring matters of, BUSI Magnetic force, on the distribution of the lines of, 67, 309; on the phy- sical character of the lines of, 401. —— needle, on the ten-year period which exhibits itself in ‘the diurnal motion of the, 428. Magnetism, on the heating effects of, 311; on the identity of electricity, heat, and light with, 127. Magnus (Prof.) on thermo-electric currents, St. Manganese, detection of, in limestone rocks, 144. Manross (N. 8.) on the artificial pro- duction of crystallized tungstate of lime, 397. Martin (A. G. C.) on the amylum grains of the potato, 277. Martin (P. J.) on a remarkable meteo- rological phenomenon, 547. Matter, on the molecular constitution of, 43. Meteoric iron, on the passive state of, 477. Meteorological observations, 79, 159, 239, 319, 399, 479, 547. Miller (Prof.) on a new locality of phenakite, 378. Mineralogical notices, 141, 235, 378. Minerals, on the artificial formation of several, 235. Miner’s safety lamp, notice of an im- proved, 238. Morgan (Prof. de) on the authorship of the Account of the Commercium Epistolicum, 440. Multiplicity, on a new theory of, 460. Museum of Practical Geology, lec- tures delivered at the, noticed, 61, 227. q INDEX. Osann (M.) on gas-batteries, and on _ the preparation of hydriodic and hydrobromie acids by the galvanic method, 317. Ozone, on the nature of, 503. Paterson’s(J.) Caleulus of Operations, noticed, 60. Pendulum experiment, mathematical theory of M. Foucault’s, 331. Phenacite, notice respecting, 142, 378. ee (R.) on frictional electricity, 36. a gap on the equivalent of, 39 Photographic images, on the produc- tion of instantaneous, 73. Plants, on the green colouring matter of, 398. Pliicker (M.) on the electro-magnetic motor of Fessel, 155. Pollock (Sir F.), on a proof that every number is composed of four square numbers, or less, 304 Potato, en the amylum grains of the, os 77- Powell (Rev. B.) on the analogies of light and heat, 495. Problem in combinatorial analysis, on a, 349. ee description of the, 151, 516. Quaternions, on continued fractions in, 371. Quinine, on the optical properties of a newly discovered salt of, 161. Ragona-Scina (Prof.) on the longi- tudinal lines of the solar spectrum, 3 Ramehundra’s Treatise on Problems of Maxima and Minima, 148. Reflecting instruments, on improve- ments in, 71. Retina, on a mode of reviving dor- mant impressions on the, 435. Riecken (M.) on the production of cyanide of potassium, 399. Riess (P.) on electric currents of the first and higher orders, 173. Rohrs (J. H.) on the oscillations of suspension-bridges, 316. Royal Institution of Great Britain, proceedings of the, 311, 473, 495. Royal Society, proceedings of the, 67, 49, 233, 304, 379, 470. Royal Society of Edinburgh, pro- ceedings of the, 489. 551 Rubian and its products of decompo- sition, observations on, 213, 354. Rubiretine, properties and composi-~ tion of, 364. Safety-lamp, on an improved miner’s, 238. Salmonidz, observations on the ova of the, 384. Savory (W.) on the structure and con- nexion of the valves of the human heart, 304. Schlagintweit (Dr. H.) on the optical phznomenaoftheatmosphere, 1,92. Schrotter (Prof.) on the equivalent of phosphorus, 399. Schunck (E.) on rubian and its pro- ducts of decomposition, 213, 354. Seguin (M. D. M.) on the accidental colours which result from looking at white objects, 77. Selenium, on the allotropy of, 546. Sharpe (D.) on the arrangement of the foliation and cleavage of the rocks of the north of Scotland, 388. Silicates, on the classification of the, and their allied compounds, 270. Siliman (B., jun.) on M. Gillard’s light for ilumination obtained from the burning of hydrogen, 152; on oF present condition of Vesuvius, 1565.50, 05 Smyth (Prof. P.) on some improve- ments in reflecting instruments, 71. Solar spectrum, on the longitudinal lines of the, 347. Sphene and epidote, notice respect- ing, 142. Spottiswoode (W.) on a problem in combinatorial analysis, 349. Stereoscopes, description of several new and simple, 16, 31, 149, 245, 397, 478, 504. Stokes (Prof.) on the composition and resolution of streams of polar- ue light from different sources, 316. Sulphur, on the crystallization of, 154. Sulphur deposits at Swaszowice and Radobo}j, on the, 157. Sun, extraordinary spots on the, 78; on the late total eclipse of the, 232. Suspension bridges, on the oscillations of, 31 Svanberg (M.) on monothermic elec- tricity, 81. Sylvester (J. J.) on a remarkable 552 theorem in the theory of equal roots and multiple pomts, 375; on a new theory of multiplicity, 461. Talbot (H. F.) on the production of instantaneous photographic images, Thermo-electric currents, on a me- chanical theory of, 489. Thermo-electrical experiments, on some, 185. Thomson (Prof. W.) on the quanti- ties of mechanical energy contained in a fluid mass, 489; on a mecha- nical theory of thermo-electric cur- rents, 2b. Tungstate of lime, on the artificial production of erystallized, 397. Tyndall (Dr. J.) on the progress of the physical sciences, 81, 173, 321; on the measurement of thermo- electric currents, 90; on the re-» searches of Dr. Goodman on the identity of the existences or forces, light, heat, electricity and magnet- ism, 127. Urine, on the triple or ammonio- magnesian phosphates occurring in the, 373. INDEX. Veall (S.), notice of the late, 79. Verantine, properties and composition of, 360. Verdeil (F.) on the green colouring matter of plants, and on the red matter of the blood, 398. Vesuvius, on the present condition of, 156; meteorological observa- tory of, 158. Vision, on some phenomena of, 55, 149, 241, 504. Voltaic circuit, on the electroscopic properties of the, 321. Wartmann (Prof. E.) on the polari- zation of atmospheric heat, 108. Wheatstone (C.) on the physiology of vision, 149, 241, 504; on the invention of the stereoscope, 478. Wichtyne, notice respecting, 143. Wohler (Prof.) on copper erystallized by means of phosphorus, 77; on rE passive state of meteoric iron, 477. Woods (Dr. T.) on the heat of che- mical combination, 43, 299. Zeuschner (Prof. L.) on the sulphur deposits at Swaszowice and Rado- boj, 157. END OF THE THIRD VOLUME. PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET. -_ i - : x so Phil. Mag. Ser4#,Vol.3, P11. 2. 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