ON THE 
 
 CONSERVATION OF SOLAR ENERGY. 
 
ON THE 
 
 CONSERVATION OF SOLAR ENERGY 
 
 A COLLECTION OF PAPERS AND 
 DISCUSSIONS 
 
 BY 
 
 C. WILLIAM SIEMENS, F.R.S, D.C.L. 
 
 LL.D., PH.D., MEM. INST. C.E k 
 
 WITH ILLUSTRATIONS 
 
 MACMILLAN AND CO. 
 
 1883 
 
 The Right of Translation and Reproduction it reserved 
 
LONDON : 
 R. CLAY, SONS, AND TAYLOR, 
 
 BREAD STREET HILL. 
 
5s- 
 
 DEDICATION. 
 
 SHERWOOD, TUNBRIDGE WELLS, 
 April tth, 1883. 
 
 DEAR MR. SPOTTISWOODE, 
 
 When, a twelvemonth ago, I ventured to communicate 
 to the Koyal Society my hypothesis regarding the Conser- 
 vation of Solar Energy, I thought it advisable to confine 
 myself to a concise statement of my views, in order to fix 
 the attention of iny audience upon the principles of action 
 which I wished to submit for their consideration. That 
 audience, comprising astronomers and physicists more familiar 
 with the intricacies of solar physics than I could pretend to 
 be, would, I thought, prefer the simple statement of my 
 views to an elaboration of proofs, some of which they might 
 possibly have deemed superfluous, and others objectionable 
 in leading their attention away from the simple conception 
 to matters of detail. In the short space of time which has 
 elapsed since the reading of my paper, the amount of 
 positive information regarding solar physics has been greatly 
 augmented. The elaborate report to the American Govern- 
 ment regarding the eclipse of 1880 had not appeared at the 
 time I prepared my paper, but has since furnished a 
 striking confirmation of the luminous equatorial extension of 
 the sun which I had represented in a hypothetical diagram ; 
 other valuable information has been furnished, by observations 
 in Egypt, of the solar eclipse of last year. The spectroscope, 
 in the hands of Captain Abney and of Professor Langley, has 
 
vi DEDICATION, 
 
 furnished important evidence to the effect that solar rays are 
 absorbed before they reach the outer confines of our atmo- 
 sphere, pointing to the existence between the two atmo- 
 spheres of a highly-attenuated medium comprising, according 
 to Captain Abney, hydrocarbons of the ethyle group. The 
 light thrown upon the differential motion of the photosphere by 
 Mr. Carrington has been supplemented by the elaborate series 
 of observations on the motion of sun-spots by Dr. Spoerer of 
 Potsdam, and by very recent communications to the Paris 
 Academy by M. Faye, who, although not admitting my 
 hypothesis of a polar inflow current, has resorted to a polar 
 outflow current in order to explain the photospheric polar 
 retardation, and the cyclonic action to which the appearance 
 and motion of sun-spots are attributable. 
 
 While thus encouraged by the accumulation of facts, and 
 further by the approval of friends to follow up the hypothesis, 
 upon which I had ventured, not without careful con- 
 sideration, I am chiefly indebted to those who have taken 
 opposite views for opportunities to enter upon further ex- 
 planations and additional investigations regarding the 
 principal conditions upon which the working out of my 
 hypothesis depends. It was necessary to prove, amongst other 
 things, that the temperature of the solar photosphere did 
 not exceed the limits at which the combustion of hydrogen 
 and of hydrocarbons can take place ; and here again observed 
 facts converge towards the conclusion that the former 
 estimates fixing that temperature at between 12,000 and 
 20,000 Centigrade are fallacious, and that the real 
 photospheric temperature does not exceed probably 2,800 C. 
 
 The effect of a resisting medium in space, in retarding 
 planetary motion, furnishes another consideration of im- 
 portance outside the question immediately involved ; proof 
 
DEDICATION. vii 
 
 has been brought forward to show that the basis upon which 
 such resistance has generally been calculated is untenable, 
 so that astronomers need no longer insist upon a perfect 
 vacuum in order to account for the diminutive amount of 
 the changes that have taken place in the length of our year 
 since the time of the first astronomical records of eclipses 
 3,000 years ago, 
 
 In putting forward my perhaps somewhat daring hypothesis, 
 I was animated by the feeling that although not prepared 
 certainly to discuss intricate questions of solar physics upon 
 equal terms with some of my hearers, I possessed special 
 advantages in having given a life-long attention to questions 
 of combustion, and to the utilisation of different forms of 
 energy upon a comparatively large scale. This led me to look 
 upon , the sun in the light of a vast piece of apparatus, 
 worked upon principles such as could be observed and appre- 
 ciated at their real value, in terrestrial practice. 
 
 The fan-like solar action upon which my hypothesis de- 
 pends has been well discussed in these pages ; and I may say 
 that I have not met with any adverse arguments calculated to 
 shake my conviction in the reality of such an action, provided 
 only that space is filled with matter however much attenuated. 
 The further question whether aqueous vapour and carbon- 
 compounds are capable of being dissociated by solar radiation 
 when so attenuated has been viewed favourably as regards my 
 hypothesis by eminent chemists ; and I need only refer the 
 reader to the concluding Appendix taken from Professor 
 Liveing as setting forth the accepted views regarding the 
 influence of attenuation upon dissociation ; but I am aware 
 some eminent physicists entertain a doubt of the sufficiency of 
 the avowedly incomplete experimental proof which I brought 
 forward in my original paper. I was in hopes that others 
 
viii DEDICATION. 
 
 would have taken up this experimental inquiry, but in default 
 of such aid I have pursued the subject in my own way, and 
 hope shortly to embody the results in a separate com- 
 munication. Suffice it for present purposes to say that 
 although the quantitative proof is necessarily very difficult, 
 considering the . extremely small amount of matter present 
 in a tube filled with highly-attenuated vapour, yet the 
 results of observation are decidedly corroborative of the 
 action which I supposed to take place. 
 
 But supposing that no such dissociation at the expense of 
 solar radiation does take place, we shall find ourselves between 
 two difficulties, which have been touched upon only very 
 lightly in this controversy and elsewhere, but which involve, 
 nevertheless, a question of vast importance to the maintenance 
 of a thermal condition of the universe. If space is filled 
 with vapour we shall surely have absorption of solar -energy, 
 resulting, unless chemical action be admitted, in thermal effect, 
 thus raising the highly-attenuated gases gradually but surely 
 up to the solar temperature ; for, although a boundless space 
 filled with attenuated matter has an infinite capacity for heat, 
 the space comprised between thousands of visible stars 
 being all Suns like our own constitutes, in a measure, an 
 interior region which could not remain permanently at a 
 temperature not exceeding probably 100 on the absolute 
 scale. If, on the contrary, we hold with M. Him that a 
 perfectly vacuous space can alone satisfy the astronomer, \ve 
 shall have to admit an expenditure of all but perhaps the 
 millionth part of the energy of the world without conceivable 
 result, an idea which appears to me as much opposed to the 
 modern conception of conservation of energy as the converse 
 case of perpetual motion. 
 
 I was much struck with jbhe impartiality with which you 
 
DEDICATION. ix 
 
 made allusion to my paper in your opening address to the 
 Royal Society in November last, when you expressed yourself 
 as follows : " Upon the questions therein raised the last word 
 has been by no means said; and whether the theory be 
 ultimately established, or whether, like a phoenix, it shall 
 hereafter give rise to some other outcome from its own 
 ashes, it will ever be remembered as having set many active 
 minds at work, and will always have a place in the history 
 of solar physics." 
 
 While cordially accepting the position you thus assign 
 to the question at issue, I have been induced by the advice 
 of several friends to combine in a small volume all the 
 discussion of a serious nature which has publicly appeared 
 (chiefly in the pages of Nature and in the Comptes Eendus of 
 the French Academy of Sciences), in order to prevent redis- 
 cussion of the same points, and to put those interested in 
 the question in possession of the arguments that have been 
 used, which would not otherwise be generally accessible. 
 
 All things considered, I have every reason to be satisfied 
 with the interest that has been taken in the question I 
 have ventured to bring forward, and I gladly accept the 
 permission, you kindly gave me, of dedicating these pages 
 to you, which I do as a token of that personal regard 
 
 With which I remain, 
 
 DEAR MR. SPOTTISWOODE, 
 Yours very sincerely, 
 
 C. WILLIAM SIEMENS. 
 
 WILLIAM SI-OTTISWOODE, ESQ., M.A., D.C.L., &c., &c., 
 President of the Royal Society, 
 
CONTENTS. 
 
 PAGE 
 
 ORIGINAL KOYAL SOCIETY PAPER, WITH ADDITIONS FROM ARTICLE 
 
 IN Nineteenth Century, BY C. W. SIEMENS 1 
 
 ON ELECTRICAL DISCHARGES IN VACUUM TUBES 22 
 
 LETTERS TO Nature BY CHARLES MORRIS AND T. STERRY HUNT . . 27 
 
 REPLY BY C. W. SIEMENS TO THE LETTERS OF C. MORRIS AND T. 
 
 STERRY HUNT 34 
 
 LETTER TO Nature BY E. DOUGLAS ARCHIBALD 37 
 
 REPLY BY C. "W. SIEMENS TO THE LETTER OF E. D. ARCHIBALD . 40 
 
 LETTER TO Nature BY GEO. FRAS. FITZGERALD 41 
 
 REPLY BY C. \V. SIEMENS TO THE LETTER OF GEO. FRAS. FITZ- 
 GERALD 42 
 
 LETTER TO Nature BY G. B. S 44 
 
 REPLY BY C. W. SIEMENS TO THE LETTER OF G. B. S 45 
 
 ON DR. C. W. SIEMENS'S NEW THEORY OF THE SUN BY M. FAYE . 46 
 
 REPLY BY C. W. SIEMENS TO THE NOTE OF M. FAYE 49 
 
 ON DR. C. W. SIEMENS'S NEW THEORY OF THE SUN BY M. G. A. 
 
 HIRN 53 
 
xii CONTENTS. 
 
 PAGE 
 
 REPLY BY C. W. SIEMENS TO THE LETTER OF M. G. A. HIRN . . 56 
 
 ON A LETTER OF M. SPOERER CONCERNING A PECULIARITY OF SOLAR 
 
 MECHANICS BY M. FAYE . 64 
 
 A REPLY BY M. G. A. HIRN TO THE NOTE OF M. C. "W. SIEMENS . 68 
 
 FURTHER REPLY BY C. W. SIEMENS TO MM. FAYE AND HIRN . . 71 
 
 OBSERVATIONS BY M. FAYE ON DR. SIEMENS'S LETTER 80 
 
 ON Two OBJECTIONS OF PROFESSOR YOUNG AGAINST THE CYCLONIC 
 
 THEORY OF SUN-SPOTS BY M. FAYE . 81 
 
 APPENDIX. 
 
 ON THE ELECTRIC FURNACE, BY C. W. SIEMENS AND A. K. HUN- 
 TINGTON 91 
 
 SUNLIGHT AND SKYLIGHT AT HIGH ALTITUDES, BY CAPTAIN ABNEY . 98 
 REMARKS OF PROFESSOR LANGLEY ON CAPTAIN ABNEY'S PAPER , . 99 
 
 DISSOCIATION OF ATTENUATED COMPOUND GASES, BY PROFESSOR 
 
 LIVEING . 108 
 
ANALYSIS OF SUBJECTS. 
 
 ON THE CONSERVATION OF SOLAR ENERGY. 
 
 Enormous amount of heat radiated, p. 1. Small quantity intercepted. No 
 diminution of solar temperature. Continuance of solar heat accounted for 
 by Helmholtz through shrinkage, p. 2, Examination of this hypothesis. 
 Fluid supposed in "critical" condition. Convection currents active both in 
 gaseous atmosphere and fluid ocean below, p. 3. Comparison with steam 
 boiler, p. 4. Sun spots occur only in two belts between equator and poles, 
 p. 5. Explained by currents from poles to equator causing cyclones. 
 Convection currents insufficient to account for amount of heat lost by 
 radiation. 
 
 Hypothesis that radiant energy is arrested in space and brought back to Sun 
 in another form, p. 6. Space assumed to contain highly-rarefied gaseous 
 matter. Each planet has its atmosphere. Grove, Humboldt, Zoellner, Mattieu 
 Williams, and also Sir Isaac Newton, have assumed matter in space, p. 7. 
 (History of Newton's paper), p. 8. The occluded gases in meteorolites, and 
 spectrum analysis, favour this view, p. 9 ; but want of retardation of planetary 
 motion opposes it ; consideration of this difficulty. 
 
 Why the Sun has an outer atmosphere of the light gases, p. 10. Mairan 
 and La Place on zodiacal light. Solar fan-action described, p. 11. 
 
 Dissociation of matter in space by solar heat energy. Bunsen and Sainte 
 Claire Deville on dissociation at high temperature. 
 
 Dissociation in leaf-cells of plants at ordinary temperature, p. 12. 
 
 The Author's experiments on dissociation in vacuum tubes at a pressure 
 of -J-/TPJ- atmosphere, p. 13. Professor Stokes's discovery that ultra-violet rays 
 are absorbed by clear glass. Hence dissociation in space likely to be more 
 active than in vacuum tubes, p. 14. Fan-like action draws dissociated 
 gases in at poles, and after combustion, it throws them out at the equatorial 
 regions into space. 
 
 Professor Piazzi Smyth finds that vacuum tubes containing attenuated 
 vapours become in time hydrogen tubes, p. 15. Professor Storey and Mr. 
 Meldola have found oxygen in outer solar atmosphere. 
 
 Calculation that 8 Ibs. of gas, developing 2,100 heat units per pound, flow- 
 ing at the rate of 100 ft. per second, per sq. ft. of solar heat-receiving surface, 
 would suffice to account for the radiation of heat from the Sun, p. 16. 
 
xiv ANALYSIS OF SUBJECTS. 
 
 Comparison of diagram of ideal corona, with real corona photographed 
 by Professor Langley in America, when the Sun was eclipsed on llth January 
 1880, p. 17. 
 
 Solar absorption spectra favour the view of the existence of gases in space ; 
 the metallic vapours in Sun supposed to form a lower atmosphere not partici- 
 pating in fan-action, which is only feasible if density of the inflowing is at 
 equal distance equal to that of the outflowing current ; denser vapours may 
 be blown out by explosions and carried away into space to form cosmic dust, 
 p. 18. 
 
 Variations in solar heat may be due to variations in condition of gaseous 
 matter in space. Zodiacal light may be due to particles of dust emitting light 
 reflected from the Sun, or to electrical tension similar to that observed by 
 Dr. Werner Siemens on the Chiops Pyramid in Egypt. Other electrical 
 considerations, p. 19. 
 
 Outflow from Sun may have caused the large amount of carbonic acid found 
 in the enormous beds of limestone on the earth, p. 20. 
 
 Considerations with regard to comets ; the nucleus an aggregation of stones ; 
 gases absorbed in space would be driven out with enormously increased 
 volume by heat when the comet is moving in perihelion ; the nucleus would 
 emit original light, p. 21. 
 
 Fundamental conditions of hypothesis : 1. That gases are present in space. 
 2. That compound gases, when extremely attenuated, can be dissociated by 
 radiant solar energy. 3. That solar rotation draws in dissociated gases at 
 the Sun's polar surfaces, and ejects them equatorially after combustion into 
 space. 
 
 ON ELECTRICAL DISCHARGES IN VACUUM TUBES, AND THEIR RELATION TO 
 SOLAR PHYSICS. 
 
 Dr. De la Rue's large battery of 14,400 cells, 14,832 Volt's electromotive 
 force, gave a current of '054 Ampere, with a discharge at 71 inch between 
 terminals, p. 22. 
 
 Phenomena of stratified discharge similar to those of electric arc, being 
 a disruptive discharge and not a current ; length of spark varies as square 
 of number of cells ; imitation of the aurora produced in vacuum tube, 
 p. 23. 
 
 Mr. Spottiswoode's experiments prove that the dissymmetry in electrical 
 discharges in vacuum tubes is an essential element in every disruptive dis- 
 charge, and that the phenomena of stratification are always present ; the 
 striae are actual aggregations of matter, p 24. 
 
 The importance of these investigations in connection with solar physios ; 
 the light thrown on the subject by the spectroscope, p. 25. 
 
 The results of the last eclipse expedition ; amongst others that hydro- 
 carbons exist between the Sun and earth ; absorption of actinic rays 
 shown to take place in solar atmosphere in Professor Langley's experiments, 
 and between solar and terrestrial atmosphere by Captain Abney, p. 26 ; mate- 
 rial continuity between Sun and earth thus established. 
 
ANALYSIS OF SUBJECTS. XY 
 
 LETTER FEOM MR. CHARLES MORRIS TO Nature. 
 
 Accepts fan- like action ; thinks space is occupied with matter of great 
 tenuity, p. 27. Nebular hypothesis of contracted matter in planets and 
 rarefied matter in space, p. 28. Owing to condensation and rarefaction of 
 gaseous matter, Sun would be hot, space cold, p. 29 ; Sun's heat would be main- 
 tained by condensation of inflowing matter ; and the outflow of the products 
 of combustion, at the expense of the rotatory energy of the Sun, p. 30. 
 
 LETTER FROM PROFESSOR STERRY HUNT TO Nature. 
 
 Reference to views of Sir Wm. Grove, of Mr. Mattieu Williams, and 
 Newton on the subject of matter in space, with quotations from these 
 writers, pp. 31-33. Considers that as far as the Sun's energy is concerned it 
 would be immaterial whether the matter in space was dissociated or merely 
 heated, p. 34. 
 
 C. W. SIEMENS'S REPLY, 
 
 Material in stellar space is intensely cold ; if it be assumed at 100 absolute 
 on the Centigrade scale, with density = y-^Vinr of an atmosphere, the tem- 
 perature of the solar photosphere due to adiabatic compression would be 
 2545 C., or below that of powerful electric arcs, p. 35 ; if this heat be 
 supplemented by that due to the combustion of combustible gases, the whole 
 of the radiant heat is accounted for, p. 36. 
 
 The amount of rotative force required to produce fan-action only that neces- 
 sary to cover frictional retardation, as the flow of gases, when once established, 
 has only to be changed in direction, p. 37. 
 
 LETTER FROM MR. ARCHIBALD TO Nature. 
 
 Objects that the centrifugal force is not adequate to produce fan-action, 
 owing to the large amount of solar gravity, p. 38 ; thinks the solar atmo- 
 sphere arranged in layers of relative density around the sun, p. 30. 
 
 C. W. SIEMENS'S REPLY. 
 
 Shows that the centrifugal force need not exceed that of gravitation. 
 Assumes two gaseous particles of equal masses at equal distances from 
 the Sun, one in polar, the other in equatorial plane ; if the latter revolve 
 around the Sun, the force of gravitation upon it will diminish, and the 
 inequality of attractive forces upon the two particles will cause polar inflow 
 and equatorial outflow, p. 40. 
 
 LETTER FROM PROFESSOR FITZGERALD TO Nature. 
 
 Asks 1. Why the gases near the Sun do not become an atmosphere around 
 him ? 2. Why the planets have not enormous atmospheres ? 3. Why the 
 earth is not deluged with the aqueous vapour passing it on the way to space 1 
 4. Why the stars are visible? p. 41. 
 
ANALYSIS OF SUBJECTS. 
 
 C. W. SIEMENS'S REPLY, 
 
 1. The gases flashing into flame have diminished specific gravity, causing 
 a rebound action, which, combined with acquired motion, and centrifugal 
 impulse from contact with lower atmosphere, constitutes a stream from the 
 poles to the equator, and thence into space. Rotatory motion of the Sun, 
 must cause outflow, p. 42. 
 
 2. The atmosphere of each spheroid would be that due to its mass ; the 
 moon's would be so small as to be scarcely perceptible by means of optical 
 instruments. 
 
 3. The amount of vapour that would condense on the earth would depend 
 on its mean temperature, and the vapour density of the stellar- atmosphere 
 surrounding it ; the earth would only acquire aqueous vapour if its tempera- 
 ture were lower than that of space, p. 43. 
 
 4. The stars may still be visible, notwithstanding selective dissociation 
 in space. 
 
 LETTER FROM G. B. S. TO Nature. 
 
 Asks what has become of the energy which was present as heat in the earth 
 and planets ? and whether the Sun radiates more heat than required for disso- 
 ciation of gases in space ? p. 44. 
 
 C. W. SIEMENS'S REPLY. 
 
 If the earth's rotatory velocity were formerly higher than now, and its 
 surface sufficiently hot to ignite gases, it would have the power of proportional 
 recuperation, until its temperature fell below that of ignition, when it would 
 cool rapidly until its own radiation of heat into space equalled that received 
 from the Sun, the present state, p. 45. 
 
 M. FAYE ON DR. SIEMENS'S NEW THEORY OF THE SUN. 
 
 Statement of the hypothesis, p. 46. A vacuum of yo \ very dense from 
 the astronomer's point of view, it would cause excessive resistance to planetary 
 motion, p. 47, and would add a mass of matter to the solar system 100,000 
 times as great as that of the Sun, p. 48. 
 
 C. W. SIEMENS'S REPLY. 
 
 The distribution in space is such as to insure statical equilibrium be- 
 tween the forces of expansion and diffusion on the one hand, and of attraction 
 towards the Sun and celestial bodies on the other, p. 49. Mariotte's law as 
 regards tension probably not of universal application, Crookes's experiments 
 favour this view, p. 50. 
 
 The amount of rarefaction, .nnnj, was that in the vacuum tubes experimented 
 on, and if dissociation took place in these it should a fortiori in space where 
 the gases must be much more rarefied. Comets in perihelion were assumed to 
 move in a medium of density not exceeding -y-^-y ; the density of space was 
 not fixed in original paper, p. 51. 
 
ANALYSIS OF SUBJECTS. xvii 
 
 Reference to Captain Abney's and Professor Langlcy's spectroscopic investiga- 
 tions, to the results of recent solar eclipses, and Professor Sehwedoff s obser- 
 vation of the fall of what appeared to be cosmical hailstones. 
 
 Density in space would be a function of the temperature ; the lowest 
 observed temperature 63 C., the absolute zero 274 C. ; that of space must 
 be between these ; Regnault's formula not applicable rigorously ; but at 
 - 130 C. the density about TTrTmnnF- Assuming this density at the distance of 
 Mercury, the area would supply in combustion all the heat the Sun requires 
 to keep up its radiation, p. 52. 
 
 M. HlRN ON DR. SlEMENS's THEORY OF THE SUN. 
 
 Thinks that Mr. Langley's experiments point to 20,000 C. as the minimum 
 temperature of the Sun, p. 53 ; hence argues, that if stellar matter were disso- 
 ciated, its recombination could only take place at an appreciable distance from 
 the photosphere, and in falling into the Sun it would be again dissociated, 
 and would hence contribute nothing to the continuous reproduction of solar 
 temperature. 
 
 The stars must lose a proportion of their light by dissociating matter in 
 space and the lustre of the Sun and stars must diminish in a ratio much more 
 rapid than the inverse square of the distance, p. 54. 
 
 As regards the necessary tenuity of gaseous matter in space so as not to 
 oppose planetary movements more than astronomical observations indicate, 
 there must not be more than one kilogramme of matteHn seven million millions 
 of cubic metres, and this tenuity must be diminished 10,000 times to prevent 
 our atmosphere from being swept away, p. 55. 
 
 The astronomer requires an absolute vacuum of matter, and Mr. Him 
 thinks this necessity upsets the materialistic theory, p. 56. 
 
 C. "W. SIEMENS'S REPLY. 
 
 Adherence to materialistic theory. Previously computed temperatures of the 
 Sun too high, including M. Hirn's of 20,000 C., p. '57 ; has estimated this 
 temperature at or below 3,000. Agreement of views between Professor 
 Langley and himself. 
 
 Analysis of Professor Tyndall's experiments on the proportional luminosity 
 of light from electric arc, incandescent wire and gas flame. 
 
 Calculation that an arc of temperature of 2,500 C. gives one-fourth of its 
 energy in light ; Professor Langley considers one-fourth of the Sun's energy 
 is luminous, p. 58 ; Dr. Siemens argues that, allowing for absorption, the 
 temperature of the photosphere is probably 2,800C., and that hence the 
 re-dissociation supposed by M. Him does not occur. 
 
 As regards the objection of a diminution in the visibility of stars, Dr. 
 Siemens thinks the law of the inverse square of the distance may not hold as 
 regards star light, p. 59 ; Professor Langley has proved absorption, and the 
 great gaps in his solar spectrum seem to indicate wave-lengths less favourable 
 to the decomposition of vapours, and hence capable of traversing space further 
 than other rays. 
 
 I 
 
xviii ANALYSIS OF SUBJECTS. 
 
 As regards mechanical resistance : asks whether M. Hirn, in his calculation, 
 had taken the tangential motion of the planet or the duration of its year into 
 account, p. 60 ; quotation from Froude as to stream-line theory ; want of con- 
 cordant results as to resistance of solids wholly immersed in fluids, p. 61 ; recent 
 experiments of Messrs. Fowler and Baker support Mr. Froude's theory that 
 an unbounded elastic fluid simply performs a lateral oscillation in allowing 
 a solid body to pass ; these experiments point to a diminution of pressure per 
 unit of surface as the surface increases in dimensions. 
 
 Reference to gases in meteorites, to zodiacal light, to equatorial extension 
 observed in eclipse in America, to researches of Captain Abney, p. 62, and 
 to Carrington's work on Sun-spots. The retardation in the motion of Sun- 
 spots due to matter flowing in at the polar surfaces, passing on to the equator, 
 and thence into space, p. 63. 
 
 A NOTE FROM M. FAYE ON A LETTER, OF M. SPOERER. 
 
 The centrifugal force of the sun being ^^5-5-^ of solar gravity, not competent 
 to throw matter into space, p. 64. 
 
 As regards the motion of Sun-spots, the observations of Langier, Car- 
 rington, and M. Spoerer, show that the displacement of the spots in 
 latitude is small, that those remote from the equator tend towards and not 
 away from the poles, p. 65. This M. Faye considers is opposed to Dr. 
 Siemens's hypothesis of motion in the other direction ; his own observations 
 are to the effect that the motion of the larger spots in latitude is oscillatory, 
 p. 66. 
 
 If M. Faye could harmonize the results of observation with the hypothesis 
 of a current from the pole to the solar equator, he would be inclined to accept 
 that hypothesis, p. 67. 
 
 A REPLY TO DR. SIEMENS BY M. HIRN. 
 
 Arguing from Mr. Langley's experiments M. Hirn thinks 20,000 C. is prob- 
 ably within the limit of the temperature of the Sun, as for equal surfaces of 
 radiation the radiation of the Sun is eighty-seven times that from steel in 
 fusion at a temperature of 2,000 C., p. 68. 
 
 The experiments of Clausius prove that the temperature in the focus 
 of a perfect concave mirror is always below that of the radiating surface, 
 and as with small mirrors platinum has been melted and the diamond 
 ignited, he argues that as !%ths of the disposable solar heat and light is 
 lost, a number is arrived at much larger than 2,000 C. as the temperature of 
 the Sun, p. 69. 
 
 As regards the resistance of fluids, M. Him thinks that a fluid which offers 
 no resistance to bodies moving in it is purely hypothetical, that the combus- 
 tion of shooting stars in a medium which he places at Tinnnnnrff f an atmo- 
 sphere proves high resistance, and finishes by placing the tenuity of gaseous 
 matter at the figure in his previous letter, p. 70. 
 
ANALYSIS OF SUBJECTS. xix 
 
 C. W. SIEMENS'S EEPLY TO MM. FAYE AND HIRN. 
 
 Statement of M. Faye's objections, p. 71 . By means of a hypothetical bent 
 tube extending from the Sun in the polar and equatorial directions, it is shown 
 how, if the equatorial branch is supposed to revolve, the matter within it 
 must become lighter and cause a continuous flow into the polar tube, p. 72, 
 the power necessary to maintain the current being derived from solar rotation, 
 p. 73. 
 
 Analogous but inverse conditions on the earth to the solar spots, in the 
 form of an equatorial or trade-wind current giving rise in our latitudes to 
 cyclones, p. 74 ; cause of the deviation of the Sun-spots in latitude is the less 
 resistance in the polar direction, p. 75. 
 
 Statement of M. Hirn's objections. Acceptance of Mr. Langley's con- 
 clusions that the solar temperature is above 1,800C., and that the radia- 
 tion from the Sun is 100 times greater than that from melted platinum, but 
 that this high radiation does not prove any particular temperature in excess of 
 his minimum, p. 76. Sir William Thomson accepts 3,000 C. as the probable 
 temperature of the Sun, p. 77. 
 
 The Author's experiments with parabolic reflector focussing the Sun's 
 rays upon burning gas proved a retardation of the combustion. Reference 
 to the regenerative gas furnace, to partial dissociation within it, and to the 
 radiation from the hot sides and the incandescent gas respectively. Experi- 
 ments with electric furnaces, p. 78. 
 
 With matter as attenuated as- M. Him calculates it, if at the distance of 
 Neptune or Uranus it would suffice for the purposes of the hypothesis. 
 
 As regards resistance of a medium to a large body moving in it, it appears 
 that this is likely to be found proportional to the circumferential develop- 
 ment rather than the area of the body, p. 79. 
 
 OBSERVATIONS BY M. FAYE. 
 
 M. Faye agrees that the hypothetical tube assumed by the Author would 
 be a means of supplying the gases to the Sun, but adds that the medium must 
 revolve as if rigidly connected with the Sun, p. 80. 
 
 The Author answers in a footnote that the matter would enter the polar 
 branch irrespective of any initial motion of the arm, and would he delivered 
 equatorially with the motion imparted to it by the tube, p. 81. 
 
 M. FAYE'S REPLY TO Two OBJECTIONS OF MR. YOUKG'S AGAINST THE 
 CYCLONIC THEORY OF SUN-SPOTS. 
 
 Explains that the edges of the Sun-spots do not appear torn and dis- 
 torted, because it is the upper edge that is visible where the motion is slow 
 and regular, whereas deep down the motion is very violent, p. 82 ; in ter- 
 restrial tornadoes the violent motion is felt on the earth, whilst the summit 
 is hidden in clouds, p. 83 ; a velocity of 2 per day in the visible motion of 
 the Sun-spot may mean 30,000 a day below in the deep, black, central 
 portion, p. 84. 
 
 Summary of reply to Mr. Young's objections, pp. 85-87. 
 
3X ANALYSIS OF SUBJECTS. 
 
 APPENDIX. 
 
 THE ELECTRIC FURNACE. 
 
 Short description of furnace, p. 91. Abstract of experiments on wrought 
 iron, p. 92 ; steel, p. 93 ; diagram of electric furnace ; white iron, cast iron, 
 siliceous pig iron, p. 94 ; nickel, copper, p. 95 ; platinum, and tungsten, 
 p. 96. Remarks on the experiments, p. 97. 
 
 SUNLIGHT AND SKYLIGHT AT HIGH ALTITUDES, BY CAPTAIN ABNEY, 
 AND REMARKS BY MR. LANGLEY. 
 
 Captain Abney's observations at high altitude show skies nearly black by 
 comparison with bright objects projected against them ; at 8,500 feet of 
 elevation the whole photographic spectrum is represented by a band ; the 
 reason of this is the existence of particles of reflecting matter, p. 98 ; con- 
 clusion that hydrocarbons must exist between our atmosphere and the Sun, 
 and it may be in space. 
 
 Captain Langley's remarks as to the influence of the selective absorption of 
 our atmosphere and that of the Sun on the spectrum, p. 99 ; outside the 
 earth's atmosphere the spectrum would be different from the ordinary one, 
 and if the solar atmosphere could be removed a third spectrum would be 
 obtained, p. 100. 
 
 Description of the diagrams, showing the distribution of energy in the 
 prismatic spectrum and the normal spectrum, p. 101 ; prismatic spectrum ; 
 extraordinary depression and interruptions of energy, p. 102. 
 
 Experiments with the bolometer ; labour of determination of wave-lengths, 
 p. 103 ; normal spectrum, p. 104 ; main results of observations, an enormous 
 and progressive increase of energy towards the shorter wave-lengths ; while 
 all radiations emanate from the solar surface, p. 106, the blue are so much 
 greater in proportion that the proper colour of the Sun as seen in the photo- 
 sphere is blue, p. 107. 
 
 DISSOCIATION OF ATTENUATED COMPOUND GASES, BY PROFESSOR 
 LIVEING. 
 
 Statement of the Author's hypothesis ; fan-action must be carried on at the 
 expense of the energy of the Sun's rotation, p. 108 ; the decomposition of 
 compound gases at low pressure not inconsistent with laws of dissociation ; 
 absorption of rays by our atmosphere, p. 109 ; spectrum of comets explained 
 by flame of gas containing hydrocarbons found in meteorites ; Dr. Huggins 
 found cyanogen in comets ; this may be due to ammonia in hydrocarbon flarne, 
 p. 110 ; interesting when Halley's comet returns, to see whether it shines only 
 by reflected light, or gives again the banded spectrum of hydrocarbons, p. 111. 
 
A COLLECTION 
 
 OF 
 
 PAPERS AND DISCUSSIONS 
 
 ON THE 
 
 CONSERVATION OF SOLAR ENERGY. 
 
 On the Conservation of Solar Energy. By C. WILLIAM 
 SIEMENS, D.C.L., LL.D., Ph.D., F.R.S., Mem. Inst. 
 C.E. [Received February 20, 1882]. 
 
 (From the Proceedings of the Royal Society, No. 219, 1882.) 
 
 Incorporated with this Paper are certain portions of an Article 
 entitled "A New Theory of the Sun," published in the Nineteenth 
 Century of April, 1882. The additions are printed in distinctive type. 
 
 THE question of the maintenance of Solar Energy is one 
 that has been looked upon with deep interest by astronomers 
 and physicists from the time of La Place downward. 
 
 The amount of heat radiated from the Sun has been 
 approximately computed, by the aid of the pyrheliometer 
 of Pouillet, and by the actinometers of Herschel at 
 18,000,000 of heat units from every square foot of his surface 
 per hour, 1 or, put popularly, as equal to the heat that woiild 
 
 1 " The classic value by Pouillet is about 1*7 calories. All the determina- 
 tions made during the last fifty years tend to augment this value ; the most 
 
 B 
 
2 CONSERVATION OF SOLAR ENERGY. 
 
 be produced by the perfect combustion every thirty-six hours 
 of a mass of coal (of specific gravity = T5) as great as that 
 of our earth. 
 
 If the Sun were surrounded by a solid sphere of the radius 
 equal to the mean distance of the Sun from the earth 
 (93,000,000 of miles), the whole of this prodigious amount 
 of heat would be intercepted ; but considering that the 
 earth's apparent diameter as seen from the Sun is only 
 seventeen seconds, the earth can intercept only the 2,250- 
 millionth part. 
 
 Assuming that the other planetary bodies swell the inter- 
 cepted heat by ten times this amount, there remains the 
 imposing fact that f |J of the solar energy is radiated 
 into space, and apparantly lost to the Solar System, and only 
 
 utilised. 
 
 2250000 
 
 Notwithstanding this enormous loss of heat, solar tempera- 
 ture has not diminished sensibly for centuries, if we neglect 
 the periodic changes apparently connected with the appear- 
 ance of Sun-spots which have been observed by Lockyer, 
 Janssen and others, and the question forces itself upon us 
 how this great loss can be sustained without producing an 
 observable diminution of solar temperature even within 
 a human lifetime. 
 
 Amongst the ingenious hypotheses intended to account for 
 a continuance of solar heat is that of shrinkage, or gradual 
 reduction of the Sun's volume, suggested by Helmholtz. It 
 may, however, be urged against this theory that the heat so 
 produced would be liberated throughout his mass, and would 
 have to be brought to the surface either by conduction or 
 by convection. 
 
 recent, due to Messrs. Soret, Crova, and Violle, lead from 2 '2 to 2 '5 calories. 
 On account of the large number of observations and very long calculations 
 which they necessitate, I cannot yet assign a definite value, but I find three 
 calories to be about the mean ; in other words, deducting the influence of our 
 atmosphere, the solar rays would raise 1 gramme of water 3 Centigrade per 
 minute, for every square centimetre of terrestrial surface normally exposed to 
 their action." Observations du Spectre Solaire par M. Langley, Comptes Rendus 
 de VAcadtmie des Sciences^ vol. xcv. p. 482* llth Sept. 1882. 
 
SHRINKAGE AND CONVECTION CURRENTS. 3 
 
 This theory as developed by Sir William Thomson has 
 certainly the advantage of accounting for the greatest 
 possible store of heat within the solar mass, because 
 it supposes the latter to consist in the main of a 
 fluid heated to such a degree that if it were relieved 
 at any point of the confining pressure, it would flash into 
 gas of a vastly inferior, but still of an elevated, tempera- 
 ture. It is supposed that such fluid material, or material 
 in the "critical" condition, as Professor Andrews, of 
 Belfast, has named it, is continually transferred to the 
 surface by means of convection currents, that is to say, 
 by currents forming naturally when a fluid substance is 
 cooled at its upper surface, and sinks down after cooling 
 to make room for ascending material at the compara- 
 tively higher temperature. It is owing to such convection 
 currents that the temperature of a roam is, generally 
 speaking, higher towards the ceiling than towards the 
 floor, and that upon plunging a thermometer into a tank 
 of heated water the surface temperature is found superior 
 to that near the bottom. 
 
 These convection currents owe their existence to a pre- 
 ponderance of the cooled descending over the ascending 
 current; but this difference being slight, and the as- 
 cending and descending currents intermixing freely, they 
 are, generally speaking, of a sluggish character ; hence 
 in all heating apparatus it is found essential to resort 
 either to artificial propulsion or to separating walls 
 between the ascending and the descending currents, in 
 order to give effect to the convective transfer of heat. 
 
 In the case of a fluid Sun another difficulty presents itself 
 through the circumstance that the vast liquid interior 
 is enveloped in a gaseous atmosphere, which, although 
 perhaps some thousands of miles in depth, represents a 
 relatively very small store of heat. Convection currents 
 may be supposed active in both the gaseous atmosphere 
 and in the fluid ocean below, but the surface of this 
 fluid must necessarily constitute a barrier between the 
 
 B 2 
 
CONSERVATION OF SOLAR ENERGY. 
 
 two convective systems, nor could the convective action 
 of the gaseous atmosphere, that is to say, the simple up 
 and down currents caused by surface refrigeration, be 
 such as to disturb the liquid surface below to any great 
 extent, because each descending current would have had 
 plenty of time to get intermixed with its neighbouring- 
 ascending current, and would therefore have reached 
 its least intensity on arriving on the liquid surface. 
 
 As regards the liquid, its most favourable condition for 
 heating purposes would be at the critical point, or that 
 at which the slightest diminution of superincumbent 
 pressure would make it flash off into gas ; but considering 
 that, by means of conduction and convection, the liquid 
 matter must have assumed in the course of ages a 
 practically uniform temperature to a very considerable 
 depth, it follows that the liquid below the surface, with 
 fluid pressure in addition to that of the superimposed 
 gaseous atmosphere, must be ordinary fluid, the critical 
 condition being essentially confined only to the surface. 
 
 Conditions analogous to those here contemplated are met 
 with in a high-pressure steam boiler, with its heated 
 water and dense vapour atmosphere. Suppose the fire 
 below such a boiler be withdrawn, and its roof be exposed 
 to active radiation into space, what, it may be asked, 
 should we observe through a strong pane of glass 
 inserted in the side of the boiler near the liquid surface, 
 lit up by an incandescent electric lamp within? The 
 loss of heat by radiation from the boiler would give 
 rise to convection currents, and partial condensation 
 of the vapour atmosphere ; then, if the motion of the 
 water was made visible by means of colouring matter, 
 we should observe convection currents in the fluid 
 mass separate and distinct from those in the gaseous 
 mass ; but these convection currents would cause no 
 visible disturbance of the liquid surface, which would 
 present itself to the eye with the smoothness of a mirror. 
 It is only in the event of the steam pressure being 
 
SUN SPOTS. 5 
 
 suddenly relieved at any point, that a portion of the 
 water would flash into steam, causing a violent upheaval 
 of the liquid. 
 
 The dark spots on the Sun appear to indicate commotion of 
 this description, but these are evidently not the result 
 of mere convection currents ; if they were, they would 
 
 Sir John Herscliel's Sun-Spot Belts. 
 
 occur indiscriminately over the entire surface of the Sun, 
 whereas telescopic observation has revealed the fact that 
 they do occur almost exclusively in two belts, between 
 the Equator and the polar surfaces on either side, as 
 originally shown by Sir John Herschel. Their occur- 
 rence could be satisfactorily explained" if we could 
 suppose the existence of strong lateral currents flowing 
 
6 CONSERVATION OF SOLAR ENERGY. 
 
 from the polar surfaces towards the Equator, which lateral 
 currents in the solar atmosphere would cause cyclones 
 extending into a lower and denser atmosphere and 
 consisting probably of metallic vapours; this cyclonic 
 action extending downward would relieve the fluid ocean 
 locally from pressure, and give rise to explosive out- 
 bursts of enormous magnitude, projecting the lower 
 substance high above the photosphere, with a velocity 
 measured, according to Lockyer, by a thousand miles a 
 second. It will be seen from what follows how, according 
 to my views, such cyclonic action in those intermediate 
 regions of the Sun would necessarily be produced. 
 But, supposing -that, notwithstanding the difficulties just 
 pointed out, convection currents sufficed to effect a 
 transfer of internal heat to the surface with sufficient 
 rapidity to account for the enormous surface-loss by 
 radiation, we should still be at a loss to account for 
 the heat so dispersed, and should only have the poor 
 satisfaction of knowing that the available store would 
 last longer than might have been expected, whereas 
 the only complete solution of the problem would be 
 furnished by a theory, according to which the radiant 
 energy which is now supposed to be dissipated into space 
 and irrecoverably lost to our Solar System, could be arrested 
 and brought back in another form to the Sun himself, there 
 to continue the work of solar radiation. 
 Some years ago it occurred to me that such a solution 
 of the solar problem might not be beyond the bounds of 
 possibility, and although I cannot claim intimate acquaintance 
 with the intricacies of solar physics, I have watched the 
 progress of this branch of science, and have engaged also 
 in some physical experiments bearing upon the question, 
 all of which have served to strengthen my confidence and 
 ripened in me the determination to submit my views, not 
 without some misgiving, to the touchstone of scientific 
 criticism. 
 
 For the purposes of my theory, stellar space is supposed 
 
GASEOUS MATTER IN SPACE. 7 
 
 to be filled with highly rarefied gaseous matter, including 
 probably hydrogen, oxygen, nitrogen, carbon, and their com- 
 pounds, besides solid materials in the form of dust. If this 
 be the case, each planetary body would attract to itself an 
 atmosphere depending for its density upon its relative attrac- 
 tive importance, and it would not seem unreasonable to sup- 
 pose that the heavier and less diffusible gases would form the 
 staple of these atmospheres ; that, in fact, they would consist 
 mostly of nitrogen, oxygen, and carbonic anhydride, whilst 
 hydrogen and its compounds would predominate in space. 
 
 But the planetary system, as a whole, would exercise an 
 attractive influence upon the gaseous matter diffused 
 through space, and would therefore be enveloped in an 
 atmosphere, holding an intermediate position between the 
 individual planetary atmospheres and the extremely rarefied 
 atmosphere of stellar space. 
 
 In support of this view it may be urged, that in following 
 out the molecular theory of gases as laid down by Clausius, 
 Clerk Maxwell, and Sir William Thomson, it would be diffi- 
 cult to assign a limit to a gaseous atmosphere in space l and 
 further, that some writers, among whom I will here mention 
 only Grove, Humboldt, Zoellner, and Mattieu Williams, have 
 boldly asserted the existence of matter occupying all space and 
 accomplishing important functions ; moreover, Newton him- 
 self, as Dr. Sterry Hunt tells us in an interesting paper which 
 has only just reached me, has expressed views in favour of 
 such an assumption. 
 
 The history of Newton's paper is remarkable and very 
 suggestive. It was read before the Royal Society on 
 the 9th and 16th of December, 1675, and remained 
 
 1 Except in assuming that the point of absolute zero is reached by adiabatic 
 expansion upward. Regarding this question much valuable information will 
 be found in the six treatises by Dr. A. Ritter, 1879, entitled, Anwendung der 
 Mechanischcn IVaermetheorie auf Kosmologische Probleme, in which he shows 
 that our atmosphere should, in obedience to the laws of adiabatic expansion, 
 be limited to a height of 40 kilometers, whereas Schiepperelli has observed at 
 the elevation of 200 kilometers an atmosphere of sufficient density to ignite 
 meteorolites by frictional resistance. 
 
8 CONSERVATION OF SOLAR ENERGY. , 
 
 unpublished until 1757, when it was printed by Birch, the 
 then secretary, in the third volume of his History of the 
 Royal Society, but received no attention ; in 1846 it was 
 published in the Philosophical Magazine at the suggestion 
 of Harcourt, but was again disregarded ; and now, once 
 more, only a few months since, an astronomer on the 
 other side of the Atlantic brings back to the birthplace 
 of Newton his forgotten and almost despised work of 200 
 years ago. 1 
 
 If at the time referred to, chemistry had been understood 
 as it now is, and if Newton had been armed moreover with 
 that most wonderful of all modern scientific instruments, 
 the spectroscope, the direct outcome of his own prismatic 
 analysis of light, there appears to be no doubt that 
 the author of the laws of gravitation would have so 
 developed his thoughts upon solar fuel, that they would 
 have taken the form rather of a scientific discovery 
 than of a mere speculation. 
 
 Further than this, we have the facts that meteorolites, 
 whose flight through stellar, or at all events through inter- 
 planetary space, is suddenly arrested by being brought into 
 
 1 Newton in his Hypothesis imagines "an ethereal medium much of the 
 same constitution with air, but far rarer, subtler, and more elastic." "But 
 it is not to be supposed that this medium is one uniform matter, but composed 
 partly of the main phlegmatic body of ether, partly of other various ethereal 
 spirits, much after the manner that air is compounded of the phlegmatic body 
 of air intermixed with various vapours and exhalations." Newton further 
 suggests in his Hypothesis that this complex spirit or ether, which by its 
 elasticity is extended throughout all space, is in continual movement and 
 interchange. " For Nature is a perpetual circulatory worker, generating fluids 
 out of solids, and solids out of fluids ; fixed things out of volatile, and 
 volatile out of fixed ; subtile out of gross, and 'gross out of subtile ; some 
 things to ascend and make the upper terrestrial juices, rivers, and the atmo- 
 sphere, and by consequence others to descend for a requital to the former. 
 And as the earth, so perhaps may the Sun imbibe this spirit copiously, to 
 conserve his Rhining, and keep the planets from receding farther from him ; 
 and they that will may also suppose that this spirit affords or carries with it 
 thither the solary fuel and material principle of life, and that the vast 
 ethereal spaces between us and the stars are for a sufficient repository for this 
 food of the Sun and planets." " Thus, perhaps, may all things be originated 
 from ether." 
 
GAS IN METEOROLITES. 9 
 
 collision with our earth, are known to contain as much as six 
 times their own volume of gases taken at atmospheric 
 pressure ; Dr. Flight has only very recently communicated 
 to the Royal Society the analysis of the occluded gases of one 
 of these meteorolites taken immediately after the descent 
 as follows : 
 
 C0 2 0-12 
 
 CO 31-88 
 
 H 4579 
 
 CH 4 4-55 
 
 N 17-66 
 
 100-00 
 
 It appears surprising that there was no aqueous vapour, 1 
 considering there was much hydrogen and oxygen in combi- 
 nation with carbon, but perhaps the vapour escaped observa- 
 tion, or was expelled to a greater extent than the other gases 
 by external heat when the meteorolite passed through our 
 atmosphere. Opinions concur that the gases found occluded 
 in meteorolites cannot be supposed to have entered into their 
 composition during the very short period of traversing our 
 atmosphere, but if any doubt should exist on this head, it 
 ought to be set at rest by the fact that the gas principally 
 occluded is hydrogen, which is not contained in our atmo- 
 sphere in any appreciable quantity. 
 
 Further proof of the fact that stellar space is filled with 
 gaseous matter is furnished by spectrum analysis, and it 
 appears from recent investigation, by Dr. Huggins and 
 others, that the nucleus of a comet contains very much the 
 same gases found occluded in meteorolites, including " carbon, 
 hydrogen, nitrogen, and probably oxygen," whilst, according 
 to the views set forth by Dewar and Liveing, it also contains 
 nitrogenous compounds such as cyanogen. 
 
 1 My attention has lately been directed to an article, by Dr. Mohr, in 
 Liebig's Annalen, vol. clxxix., proving 1*149 per cent, of water in a meteorite 
 that fell at Parnella in India. 
 
10 CONSERVATION OF SOLAR ENERGY. 
 
 Adversely to the assumption that interplanetary space is 
 filled with gases, it is urged that the presence of ordinary 
 matter would cause sensible retardation of planetary motion, 
 such as must have made itself felt before this ; but assuming 
 that the matter filling space is an almost perfect fluid not 
 limited by border surfaces, it can be shown on purely 
 mechanical grounds, that the retardation by friction through 
 such highly attenuated medium would be very slight indeed, 
 even at planetary velocities. 1 
 
 But it may be contended that, if the views here advocated 
 regarding the distribution of gases were true, the Sun should 
 draw to himself the bulk of the least diffusible, and there- 
 fore the heaviest gases, such as carbonic anhydride, carbonic 
 oxide, oxygen and nitrogen, whereas spectrum analysis has 
 proved on the contrary a prevalence of hydrogen in the 
 photosphere. 
 
 In explanation of this seeming anomaly, it can be shown 
 in the first place, that the temperature of the Sun is so high, 
 that such compound gases as carbonic anhydride and carbonic 
 oxide, could not exist within him; it has been contended, 
 indeed, by Mr. Lockyer, that none of the metalloids exist at 
 these temperatures, although as regards oxygen, Dr. Draper 
 asserts its presence in the solar photosphere. There must 
 be regions, however, outside that thermal limit, where their 
 existence would not be jeopardised by heat, and here great 
 accumulation of those comparatively heavy gases that con- 
 stitute our atmosphere would probably take place, were it 
 not for a certain counterbalancing action. 
 
 I here approach a point of principal importance in my 
 argument, upon the proof of which my further conclusions 
 must depend. 
 
 The Sun completes one revolution on his axis in 25 days, 
 and his diameter being taken at 882,000 miles, it follows 
 that the tangential velocity amounts to 1'25 miles per 
 second, or to 4 '41 times the tangential velocity of our earth. 
 This high rotative velocity of the Sun must cause an 
 1 See reply to Messrs. Faye and Him, pp. 61, 62 and 79. 
 
SOLAR FAN ACTION, 11 
 
 equatorial rise of the solar atmosphere to which Mairan, 
 in 1731, attributed the appearance of the zodiacal light. 
 La Place rejected this explanation on the ground that the 
 zodiacal light extended to a distance from the Sun exceeding 
 our own distance, whereas the equatorial rise of the solar 
 atmosphere due to his rotation could not exceed -^j-ths of the 
 distance of Mercury. But it must be remembered that 
 La Place based his calculation upon the hypothesis of an 
 empty stellar space (filled only with an ether not subject to 
 the laws of gravitation), and that the result of solar rotation 
 would be widely different, if it was supposed to take place 
 within a medium of unbounded extension. In this case 
 pressure would be balanced all round, and the Sun would 
 act mechanically upon the floating matter surrounding him in 
 the manner of a fan, drawing it towards himself upon the polar 
 surfaces, and projecting it outward in a continuous disk-like 
 stream. By this fan action, hydrogen, hydrocarbons, and oxy- 
 gen, are supposed to be drawn in enormous quantities toward 
 the polar surfaces of the Sun ; during their gradual approach, 
 they will pass from their condition of extreme attenuation 
 and extreme cold, to that of compression, accompanied with 
 rise of temperature, until on approaching the photosphere, 
 they burst into flame, giving rise to a great development of 
 heat, and a temperature commensurate with their point of 
 dissociation at the photospheric density. The result of their 
 combustion will be aqueous vapour and carbonic anhydride or 
 oxide according to the sufficiency or the insufficiency of oxygen 
 present to complete the combustion, and these products of com- 
 bustion in yielding to the influence of propulsive force will flow 
 toward the solar equator, and be thence projected into space. 1 
 
 The next question for consideration is : What would become 
 of these products of combustion when thus rendered back 
 into space ? Apparently they would gradually change the 
 condition of stellar material, rendering it more and more 
 neutral, but I venture to suggest the possibility, nay, the 
 probability, that solar radiation would, under these circum- 
 1 See replies to Messrs. Archibald and Faye, pp. 40, 41, and 72, 73. 
 
12 CONSERVATION OF SOLAR ENERGY. 
 
 stances, step in to bring lack the combined materials to a condi- 
 tion of separation by a process of dissociation carried into effect 
 at the expense of that solar energy which is now supposed to lie 
 lost to our planetary system. 
 
 According to the law of dissociation as developed by Bunsen 
 and Sainte-Claire Deville, the point of dissociation of different 
 compounds depends upon the temperature on the one hand, 
 and upon the pressure on the other. According to Sainte- 
 Claire Deville, the dissociation tension of aqueous vapour of 
 atmospheric pressure and at 2800 C. is - 5, that is to say 
 only half of the vapour can exist as such, its remaining half 
 being found as a mechanical mixture of hydrogen and oxygen ; 
 but with pressure, the temperature of dissociation rises in the 
 same ratio as the temperature of saturated steam rises with 
 its pressure. It is therefore conceivable that the temperature 
 of the solar photosphere may be raised by combustion to a 
 temperature exceeding 2800 C., 1 whereas dissociation may be 
 effected in space at comparatively low temperatures. 
 
 These investigations had reference only to heats measured 
 by means of pyrometers, but do not extend to the effects of 
 radiant heat. Dr. Tyndall has shown by his elaborate re- 
 searches that vapour of water and other gaseous compounds 
 intercept radiant heat in a most remarkable degree, and 
 there is other evidence to show that radiant energy from a 
 source of high intensity possesses a dissociating power far 
 surpassing the measurable temperature to which the com- 
 pound substance under its influence is raised. Thus carbonic 
 anhydride and water are dissociated in the leaf cells of plants, 
 under the influence of the direct solar ray at ordinary summer 
 temperature, and experiments in which I have been engaged 
 for nearly three years 2 go to prove that this dissociating 
 action is obtained also under the radiant influence of the 
 electric arc, although it is scarcely perceptible if the source 
 
 1 See pp. 58, 59 for other reasons why the temperature of the photosphere 
 does probably not exceed 2800 C. 
 
 2 See Proc. Hoy. Soc., vol. 30, p. 208, and paper read before Section A, 
 British Association, and printed in full in the Report for 1881, Part I., p. 
 474. 
 
DISSOCIATION IN VACUUM TUBES. 13 
 
 of radiant energy is such as can be produced by the combustion 
 of oil or gas. 
 
 The point of dissociation of aqueous vapour and carbonic 
 anhydride admits, however, of being determined by direct ex- 
 periment. It engaged my attention some years ago, but I 
 have hesitated to publish the qualitative results I then 
 obtained, in the hope of attaining to quantitative proofs. 
 
 These experiments consisted in the employment of glass 
 tubes, furnished with platinum electrodes, and filled with 
 aqueous vapour or with carbonic anhydride in the usual 
 manner, the latter being furnished with caustic soda to 
 regulate the vapour pressure by heating. Upon immersing 
 one end of the tube charged with aqueous vapour in a 
 refrigerating mixture of ice and chloride of calcium, its 
 temperature at that end was reduced to 32 C., correspond- 
 ing to a vapour pressure, according to Regnault, of y^Vtr f an 
 atmosphere. When so cooled no slow electric discharge 
 took place on connecting the two electrodes with a small 
 induction coil. I then exposed the end of the tube pro- 
 jecting out of the freezing mixture, backed by white paper, 
 to solar radiation (on a clear summer's day) for several 
 hours, when upon again connecting up to the inductorium, 
 a discharge, apparently that of a hydrogen vacuum, was 
 obtained. This experiment being repeated furnished un- 
 mistakable evidence, I thought, that aqueous vapour had been 
 dissociated by exposure to solar radiation. The carbonic anhy- 
 dride tubes gave, however, less reliable results. Not satisfied 
 with these qualitative results, I made arrangements to collect 
 the permanent gases so produced by means of a Sprengel 
 pump, but was prevented by lack of time from pursuing 
 the inquiry, which I purpose, however, to resume shortly, 
 being of opinion that, independently of my present speculation, 
 the experiments may prove useful in extending our know- 
 ledge regarding the laws of dissociation. 1 
 
 1 Further experiments in this direction are still in progress, in which 
 powerful arc light is substituted for solar rays. They furnish corroborative- 
 evidence, and will be made the subject-matter of a separate communication. 
 
14 CONSERVATION OF SOLAR ENERGY. 
 
 It should here be observed that, according to Professor 
 Stokes, the ultra-violet rays are in a large measure ab- 
 sorbed in passing through clear glass, and it follows from 
 this discovery that only a small portion of the chemical 
 rays found their way through the tubes to accomplish the 
 work of dissociation. 
 
 This circumstance being adverse to the experiment only 
 serves to increase the value of the effect observed, 
 whilst it appears to furnish additional proof of the 
 fact, first enunciated by Professor Draper, and corro- 
 borated by my own experiments on plants, that the 
 dissociating power of light is not confined to the 
 ultra-violet rays, but depends as regards the process of 
 vegetation chiefly upon the yellow ray. 
 Assuming, for my present purpose, that dissociation of 
 aqueous vapour was really effected in the experiment just 
 described, and assuming, further, that stellar space is filled 
 with aqueous and other vapour of a density not exceeding 
 the 2 O'Q o th part of our atmosphere, it seems reasonable to 
 suppose that its dissociation would be effected by solar 
 radiation, and that solar energy would thus be utilised. 1 
 The presence of carbonic anhydride and carbonic oxide 
 would only serve to facilitate the decomposition of the 
 aqueous vapour by furnishing substances to combine with 
 nascent oxygen and hydrogen. It is not necessary to 
 suppose that all the energy radiated from the Sun into 
 space would be intercepted, inasmuch as even a partial 
 return of heat in the manner described would serve to 
 supplement solar radiation, the balance being lost to the 
 Solar System. To this loss of energy must be added 
 that involved in keeping up the circulating movement of 
 the gases, which, however, would probably not be relatively 
 greater than that concerned in the tidal retardation of the 
 
 1 Mr. Faye has understood this passage to mean that I supposed stellar 
 space to be filled with gases of this density, whereas it was the limit imposed 
 by my experiment, and I have spoken of the gases in space as being ex- 
 tremely attenuated, which, according to Mr. Crookes, would mean about 
 aooooooo atmospheric pressure. 
 
DISSOCIATION IN VACUUM TUBES. 15 
 
 earth's rotation. By means of the fan-like action resulting 
 from the rotation of the Sun, the vapours dissociated in space 
 would be drawn towards the polar surfaces of the Sun, 
 be heated by increase in density, and would burst into flame 
 at a point where both their density and temperature had 
 reached the necessary elevation to induce combustion, each 
 complete cycle taking years or centuries to be accomplished. 
 The resulting aqueous vapour, carbonic anhydride and 
 carbonic oxide, would be drawn towards the equatorial 
 regions, and be then again projected into space by centri- 
 fugal force. 
 
 Doubts have been expressed as to the sufficiency of the 
 proof that dissociation of attenuated aqueous vapour 
 and carbonic acid is really effected by radiant solar 
 energy, and, if so effected, whether the amount of heat 
 so supplied to the Sun could be at all adequate in 
 amount to keep up the known rate of radiation. It 
 was admitted in my paper that my own experiments 
 on the dissociation of vapours within vacuum tubes 
 amounted to inferential rather than absolute proof ; 
 but the amount of inferential evidence in favour of my 
 views has been very much strengthened since by 
 chemical evidence received from various sources; I 
 will here only refer to one of these. 
 
 Professor Piazzi Smyth, the Astronomer Eoyal for Scotland, 
 has, in connection with Professor Herschel of Newcastle, 
 recently presented an elaborate paper or series of papers 
 to the Royal Society of Edinburgh "On the Gaseous 
 Spectra in Vacuum Tubes," of which he has kindly 
 forwarded me a copy. It appears from these memoirs 
 that when vacuum tubes, which contain attenuated 
 vapours, have been laid aside for a length of time, 
 they turn practically into hydrogen tubes. In another 
 very recent paper presented to the Royal Society of 
 Edinburgh, Professor Piazzi Smyth furnishes important 
 additional proof of the presence of oxygen in the outer 
 solar atmosphere, and gives an explanation why this 
 
16 CONSERVATION OF SOLAR ENERGY. 
 
 important element has escaped observation by the 
 spectroscope. Additional proof of the existence of 
 oxygen in the outer solar atmosphere, has been given 
 by Professor Stoney, the Astronomer Royal for Ireland, 
 and by Mr. R. Meldola in an interesting paper 
 communicated by him to the Philosophical Magazine 
 in June, 1878. 
 
 As regards the sufficiency of an inflowing stream of 
 dissociated vapours to maintain solar energy, the 
 following calculation may be of service. Let it be 
 assumed that the stream flowing in upon the polar 
 surfaces of the Sun flashes into flame when it has 
 attained the density of our atmosphere, that its velocity 
 at that time is 100 feet per second (the velocity of a 
 strong terrestrial wind) and that in its composition only 
 one-twentieth part is hydrogen and marsh gas in equal 
 proportions, the other nineteen-twentieths being made 
 up of oxygen, nitrogen, and neutral compounds. It 
 is well known that each pound of hydrogen develops 
 in burning about 60,000 heat units, and each pound 
 of marsh gas about 24,000; the average of the two 
 gases mixed in equal proportion would yield, roughly 
 speaking, 42,000 units ; but, considering that only one- 
 twentieth part of the inflowing current is assumed to 
 consist of such combustible matter, the amount of heat 
 developed per pound of inflowing current would be only 
 2,100 heat units. One hundred cubic feet, weighing 
 eight pounds, would enter into combustion every second 
 upon each square foot of the polar surface, and would 
 yield 8x60x60x2100 = 60,480,000 heat units per 
 hour. Assuming that one-third of the entire solar 
 surface may be regarded as polar heat-receiving surface, 
 this would give 20,000,000 heat units per square foot 
 of solar surface; whereas according to Herschel's and 
 Pouillet's measurements only 18,000,000 heat units per 
 square foot of solar surface are radiated away. There 
 would thus be no difficulty in accounting for the rnainten- 
 
IDEAL AND ACTUAL COEONAS. 17 
 
 ance of solar energy from the supposed source of supply. 
 On the other hand I wish to guard myself against the 
 assumption that appears to have been made by some 
 critics, that what I have advocated would amount to 
 the counterpart of "perpetual motion," and therefore 
 to an absurdity. The Sun cannot of course get back 
 any heat radiated by himself which has been turned to 
 a purpose ; thus the solar heat spent upon our earth 
 in effecting vegetation must be absolutely lost to him ; 
 but on the other hand the laws regarding the conservation 
 of energy make it impossible to suppose that heat 
 radiation into space can go on indefinitely without 
 producing tangible effects regarding which we are up 
 to the present without information. 
 
 My paper presented to the Royal Society was accompanied 
 by a diagram of an ideal corona representing an accu- 
 mulation of igneous matter upon the solar surfaces, 
 surrounded by disturbed regions pierced by occasional 
 cyclones and outbursts of metallic vapours, and culmi- 
 nating in two outward streams projecting from the 
 equatorial surfaces into space through many thousands 
 of miles. It was therefore a matter of great satisfaction 
 to me to be informed, as I have been by an excellent 
 authority and eye-witness, that my imaginary diagram 
 bore a very close resemblance to the corona observed 
 in America on the occasion of the total eclipse of 
 the Sun on the llth of January, 1880 ; a representa- 
 tion of this phenomenon as observed on the occasion 
 of the previous eclipse that of 1878 has appeared 
 since in the official American Report, of which the 
 diagram facing this page, taken by Professor Langley, 
 is a copy. 
 
 Space would, according to my views, be filled with 
 gaseous compounds in process of decomposition by solar 
 radiant energy, and the existence of these gases seems to 
 furnish an explanation of the solar absorption spectrum, in 
 which the lines of some of the substances may be entirely 
 
 c 
 
18 CONSERVATION OF SOLAR ENERGY. 
 
 neutralised and lost to observation. As regards the heavy 
 metallic vapours revealed in the Sun by the spectroscope, it is 
 assumed that these form a lower and denser solar atmosphere, 
 not participating in the fan-like action which is supposed to 
 affect the light outer atmosphere only, in which hydrogen is 
 the principal factor. 
 
 Such a dense metallic atmosphere could not participate in 
 the fan action affecting the lighter photosphere, because this 
 is only feasible on the supposition that the density of the in- 
 flowing current is, at equal distances from the gravitating 
 centre, equal or nearly equal to the outflowing current. It 
 is true that the products of combustion of hydrogen and 
 carbonic oxide are denser than their constituents, but this 
 difference may be balanced by their superior temperature on 
 leaving the Sun, whereas the metallic vapours would be 
 unbalanced, and would therefore obey the laws of gravitation, 
 recalling them to the Sun. On the surface of contact between 
 the two solar atmospheres intermixture, induced by friction, 
 must take place however, giving rise perhaps to those cyclones 
 and explosive effects which are revealed to us by the telescope 
 in the intermediate or stormy region of the Sun, and which have 
 been commented on by Sir John Herschel and other astro- 
 nomers. Some of the denser vapours would probably get 
 intermixed and carried away mechanically by the lighter 
 gases, and give rise to that cosmic dust which is observed to 
 fall upon our earth in not inappreciable quantities. Excessive 
 intermixture would be prevented by the intermediary neutral 
 atmosphere, the penumbra. 
 
 As the whole Solar System moves through space at a velocity 
 estimated at 150,000,000 of miles annually (being about 
 one -fourth of the velocity of the earth in its orbit), it 
 appears possible that the condition of the gaseous fuel 
 supplying the Sun may vary according to its state of pre- 
 vious decomposition, in which action other heavenly bodies 
 may have taken part. May it not be upon such differences in 
 the quality of the fuel supplied that the observed variations 
 of the solar heat may depend ? and may it not be in con- 
 
LUMINOSITY OF OUTFLOW CUERENT. 1$ 
 
 sequence of such changes in the thermal condition of the 
 photosphere that Sun-spots are formed ? 
 
 The views here advocated could not be thought accept- 
 able unless they furnished at any rate a consistent ex- 
 planation of the still somewhat mysterious phenomena of 
 the zodiacal light and of comets. Regarding the former, 
 we should be able to return to Mairan's views, the objection 
 by Laplace being met by a continuous outward flow from 
 the solar equator. Luminosity would be attributable to 
 particles of dust emitting light reflected from the Sun, or by 
 phosphorescence. But there is another cause for luminosity 
 of these particles which may deserve a passing consideration. 
 Each particle would be electrified by gaseous friction in its 
 acceleration, and its electric tension would be vastly increased 
 in its forcible removal, in the same way as the fine dust 
 of the desert has been observed by Werner Siemens to be in 
 a state of high electrification on the apex of the Cheops 
 Pyramid. Would not the zodiacal light also find explanation 
 by slow electric discharge backward from the dust towards 
 the Sun ? and would the same cause not account for a great 
 difference of potential between the Sun and earth, which 
 latter may be supposed to be washed by the solar radial 
 current ? May not the presence of the current also furnish 
 us with an explanation of the fact that hydrogen, while 
 abounding apparently in space, is practically absent in our 
 atmosphere, where aqueous vapour, which may be partly 
 derived from the Sun, takes its place ? An action analogous 
 to this, though on a much smaller scale, may be set up also 
 by terrestrial rotation, giving rise to an electrical discharge 
 from the outgoing equatorial stream to the polar regions, 
 where the atmosphere to be pierced by the return flood is of 
 least resistance. 
 
 The effect of this continuous outpour of solar materials 
 could not be without very important influences as 
 regards the geological conditions of our earth. Geolo- 
 gists have long acknowledged the difficulty of account- 
 ing for the amount of carbonic acid that must have 
 
 c 2 
 
20 CONSERVATION OF SOLAR ENERGY. 
 
 been in our atmosphere, at one time or another, in order 
 to form with lime those enormous beds of dolomite and 
 limestone, of which the crust of our earth is in great 
 measure composed. It has been calculated that if this 
 carbonic acid had been at one and the same time in 
 our atmosphere it would have caused an elastic pressure 
 fifty times that of our present atmosphere ; and if we 
 add the carbonic acid that must have been absorbed in 
 vegetation in order to form our coal-beds, we should 
 probably have to double that pressure. Animal life, of 
 which we find abundant traces in these " measures," 
 could not have existed under such conditions, and we 
 are almost forced to the conclusion that the carbonic 
 acid must have been derived from an external source. 
 It appears to me that the theory here advocated furnishes 
 a feasible solution of this geological difficulty. Our earth 
 being situated in the outflowing current of the solar pro- 
 ducts of combustion, or, as it were, in the solar chimney, 
 would be fed from day to day with its quota of carbonic 
 acid, of which our local atmosphere would assimilate as 
 much as would be necessary to maintain in it a carbonic 
 acid vapour density balancing that of the solar current ; 
 we should thus receive our daily supply of this important 
 constituent (with the regularity of fresh rolls for break- 
 fast), which, according to an investigation by M. E/eiset, 
 communicated to the French Academy of Sciences by 
 M. Dumas on the 6th of March last, amounts to the 
 constant factor of the three ten-thousandth part of our 
 atmosphere. The aqueous vapour in the air would be 
 similarly maintained as to its density, and its influx to, 
 or reflux from, our atmosphere would be determined by 
 the surface temperature of our earth. 
 
 It is also important to show how the phenomena of comets 
 could be harmonised with the views here advocated, and 
 I venture to hope that these occasional visitors will serve to 
 furnish us with positive evidence in my favour. Astronomical 
 physicists tell us that the nucleus of a comet consists of an 
 
COMETS AND OCCLUDED GASES. 21 
 
 aggregation of stones similar to meteoric stones. Adopting 
 this view, and assuming that the stones have absorbed in 
 stellar space gases to the amount of six times their volume, 
 taken at atmospheric pressure, what, it may be asked, will be 
 the effect of such a mass of stone advancing towards the Sun 
 at a velocity reaching in perihelion the prodigious rate of 366 
 miles per second (as observed in the comet of 1845), being 
 twenty-three times our orbital rate of motion. It appears 
 evident that the entry of such a divided mass into a compara- 
 tively dense atmosphere must be accompanied by a rise of 
 temperature by frictional resistance, aided by attractive 
 condensation. At a certain point the increase of -temperature 
 must cause ignition, and the heat thus produced must drive out 
 the occluded gases, which in an atmosphere say 3,000 times 
 less dense than that of our earth would produce 6 x 3,000 
 =18,000 times the volume of the stones themselves. These 
 gases would issue forth in all directions, but would remain 
 unobserved except in that of motion, in which they would 
 meet the interplanetary atmosphere with the compound 
 velocity, and form a zone of intense combustion, such as 
 Dr. Huggins has lately observed to surround the one side of 
 the ' nucleus, evidently the side of forward motion. The 
 nucleus would thus emit original light, whereas the tail may 
 be supposed to consist of stellar dust rendered luminous by 
 reflex action produced by the light of the Sun and comet 
 combined, as foreshadowed already by Tyndall and by Tait, 
 starting each from different assumptions. 
 
 These are in brief the outlines of my reflections regarding 
 this most fascinating question, which I now venture to put 
 before the Royal Society. I have long had a conviction, 
 derived principally from familiarity with some of the terrestrial 
 effects of heat, that the prodigious and seemingly wanton dis- 
 sipation of solar heat is unnecessary to satisfy accepted prin- 
 ciple's regarding the conservation of energy, but that this 
 heat apparently expended without producing any effect what- 
 ever may be effectively arrested and returned over and over 
 again to the Sun, in a manner somewhat analogous to the 
 
22 CONSERVATION OF SOLAR ENERGY. 
 
 action of the heat recuperator in the regenerative gas furnace. 
 The fundamental conditions are : 
 
 1. That aqueous vapour and carbon compounds are present 
 in stellar or interplanetary space. 
 
 2. That these gaseous compounds while in a state of 
 extreme attenuation are capable of being dissociated by 
 radiant solar energy. 
 
 3. That these dissociated vapours are capable of being 
 compressed into, the solar photosphere by a process of 
 interchange with an equal amount of reassociated vapours, 
 this interchange being effected by the centrifugal action of 
 the Sun himself. 
 
 If these conditions could be substantiated, we should gain 
 the satisfaction that our Solar System would no longer impress 
 us with the idea of prodigious waste through dissipation of 
 energy into space, but rather with that of well-ordered, 
 self-sustaining action, capable of continuing solar radiation 
 ta a very remote future. 
 
 ON ELECTEICAL DISCHARGES IN VACUUM TUBES AND THEIR 
 RELATION TO SOLAR PHYSICS. 
 
 An Extract from the Authors Presidential Address to the 
 Meeting of the British Association at Southampton, 
 August, 1882. 
 
 THE means usually employed to produce electrical discharge 
 in vacuum tubes was Ruhmkorff 's coil ; but Mr. Gassiot first 
 succeeded in obtaining the phenomena by means of a galvanic 
 battery of 3,000 Leclanch^ cells. Dr. De La Rue, in 
 conjunction with his friend Dr. Hugo Mliller, has gone 
 far beyond his predecessors in the production of batteries 
 of high potential. At his lecture " On the Phenomena of 
 Electric Discharge," delivered at the Royal Institution in 
 January, 1881, he employed a battery of his own invention 
 consisting of 14,400 cells (14,832 Volts), which gave a current 
 of 0'054 Ampere, and produced a discharge at a distance 
 
DISCHARGES IN VACUUM TUBES. 23 
 
 of 071 inch between the terminals. During last year he 
 increased the number of cells to 15,000 (15,450 Volts), and 
 increased the current to 0*4 Ampere, or eight times that 
 of the battery he used at the Royal Institution. 
 
 With the enormous potential and perfectly steady current 
 at his disposal, Dr. De La Rue has been able to contribute 
 many interesting facts to the science of electricity. He has 
 shown, for example, that the beautiful phenomena of the 
 stratified discharge in exhausted tubes are but a modification 
 and a magnification of those of the electric arc at ordinary 
 atmospheric pressure. Photography was used in his experi- 
 ments to record the appearance of the discharge, so as to 
 give a degree of precision otherwise unattainable in the 
 comparison of the phenomena. He has shown that between 
 two points the length of the spark, provided the insulation 
 of the battery is efficacious, is as the square of the number 
 of cells employed. Dr. De La Rue's experiments have 
 proved that at all pressures the discharge in gases is not 
 a current in the ordinary acceptation of the term, but is 
 of the nature of a disruptive discharge. Even in an appa- 
 rently perfectly steady discharge in a vacuum tube, when 
 the strata as seen in a rapidly revolving mirror are 
 immovable, he has shown that the discharge is a pulsating 
 one; but, of course, the period must be of a very high 
 order. 
 
 At the Royal Institution, on the occasion of his lecture, 
 he produced, in a very large vacuum tube, an imitation of 
 the Aurora Borealis; and he has deduced from his experi- 
 ments that the greatest brilliancy of Aurora displays must 
 be at an altitude of from thirty-seven to thirty-eight miles 
 a conclusion of the highest interest, and in opposition to 
 the extravagant estimate of 281 miles, at which it had 
 been previously put. 
 
 The President of the Royal Society has made the pheno- 
 mena of electrical discharge his study for several years, and 
 resorted in his important experiments to a special source of 
 electric power. In a note addressed to me, Mr. Spottiswoode 
 
24 CONSERVATION OF SOLAR ENERGY. 
 
 describes the nature of his investigations much more clearly 
 than I could venture to give them. He says : " It had long 
 been my opinion that the dissymmetry, shown in electrical 
 discharges through rarefied gases, must be an essential 
 element of every disruptive discharge, and that the phe- 
 nomena of stratification might be regarded as magnified 
 images of features always present, but concealed under 
 ordinary circumstances. It was with a view to the study 
 of this question that the researches by Moulton and myself 
 were undertaken. The method chiefly used consisted in 
 introducing into the circuit intermittence of a particular 
 kind, whereby one luminous discharge was rendered sensitive 
 to- the approach of a conductor outside the tube. The 
 application of this method enabled us to produce artificially 
 a variety of phenomena, including that of stratification. 
 We were thus led to a series of conclusions relating to the 
 mechanism of the discharge', among which the following may 
 be mentioned : 
 
 " 1. That a stria, with its attendant dark space, forms a 
 physical unit of a striated discharge ; that a striated column 
 is an aggregate of such units formed by means of a step-by- 
 step process ; and that the negative glow is merely a localised 
 stria, modified by local circumstances. 
 
 " 2. That the origin of the luminous, column is to be 
 sought for at its negative end; that the luminosity is an 
 expression of a demand for negative electricity; and that 
 the dark spaces are those regions where the negative 
 terminal, whether metallic or gaseous, is capable of exerting 
 sufficient influence to prevent such demand. 
 
 " 3. That the time occupied by electricity of either name 
 in traversing a tube is greater than that occupied in 
 traversing an equal length of wire, but less than that 
 occupied by molecular streams (Crooke's radiations) in 
 traversing the tubes. Also that, especially in high vacua, 
 the discharge from the negative terminal exhibits a 
 clurational character not found at the positive. 
 
 " 4. That the brilliancy of the light with so little heat 
 
SPECTROSCOPIC OBSERVATIONS. 25 
 
 may be due in part to brevity in the duration of the 
 discharge ; and that for action so rapid as that of individual 
 discharges, the mobility of the medium may count as 
 nothing ; and that for these infinitesimal periods of time 
 gas may itself be as rigid and as brittle as glass. 
 
 " 5. That striae are not merely loci in which electrical 
 is converted into luminous energy, but are actual aggregations 
 of matter. 
 
 " This last conclusion was based mainly upon experiments 
 made with an induction coil excited in a new way viz. 
 directly by an alternating machine, without the intervention 
 of a commutator or condenser. This mode of excitement 
 promises to be one of great importance in spectroscopic 
 work, as well as in the study of the discharge in a magnetic 
 field, partly on account of the simplification which it permits 
 in the construction of induction coils, but mainly on account 
 of the very great increase of strength in the secondary 
 currents to which it gives rise." 
 
 These investigations assume additional importance when 
 we view them in connection with solar I may even say 
 stellar physics, for evidence is augmenting. in favour of the 
 view that interstellar space is not empty, but is filled with 
 highly attenuated matter of such a nature as may be put 
 into our vacuum tubes. Nor can the matter occupying 
 stellar space be said any longer to be beyond our reach for 
 chemical and physical test. The spectroscope has already 
 thrown a flood of light upon the chemical constitution 
 and physical condition of the Sun, the stars, the comets, 
 and the far distant nebulae, which latter have yielded 
 spectroscopic photographs under the skilful management of 
 Dr. Huggins and Dr. Draper of New York. Armed with 
 greatly improved apparatus, the physical astronomer has 
 been able to reap a rich harvest of scientific information 
 during the short periods of the last two solar eclipses : that 
 of 1880, visible in America, and that of May last, observed in 
 Egypt by Lockyer, Schuster, and by Continental observers 
 of high standing. The result of this last eclipse expedition 
 
26 CONSERVATION OF SOLAR ENERGY. 
 
 has been summed up as follows : " Different temperature 
 levels have been discovered in the solar atmosphere; the 
 constitution of the corona has now the possibility of being 
 determined, and it is proved to shine with its own light. 
 A suspicion has been aroused once more as to the existence 
 of a lunar atmosphere, and the position of an important line 
 has been discovered. Hydro-carbons do not exist close to the 
 Sun, but may in space between us and it." 
 
 To me personally these reported results possess peculiar 
 interest, for in March last I ventured to bring before the 
 Royal Society a speculation regarding the conservation of 
 solar energy, which was based upon the three following 
 postulates, viz. : 
 
 1. That aqueous vapour and carbon compounds are present 
 in stellar or interplanetary space. 
 
 2. That these gaseous compounds while in a state of 
 extreme attenuation are capable of being dissociated by 
 radiant solar energy. 
 
 3. That the effect of solar rotation is to draw in dissociated 
 vapours upon the polar surfaces, and to eject them after 
 combustion back into space equatorially. 
 
 It is therefore a matter of peculiar gratification to me that 
 the results of observations here recorded give considerable 
 support to that speculation. The luminous equatorial exten- 
 tions of the Sun which the American observations revealed 
 in such a striking manner (with which I was not acquainted 
 when writing my paper) were not observed in Egypt ; but the 
 outflowing equatorial streams which I suppose to exist could 
 only be rendered visible by reflected sunlight, or by electric 
 discharge between the particles of dust, which may be pro- 
 duced by solar disturbances. Professor Langley, of Pittsburg, 
 has shown, by means of his bolometer, that the solar actinic 
 rays are absorbed chiefly in the solar instead of in the terres- 
 trial atmosphere, and Captain Abney has found, by his new 
 photometric method, that absorption, due to hydro-carbons, 
 takes place somewhere between the solar and terrestrial at- 
 mosphere ; in order to test this interesting result still further, 
 
HYDROCARBONS IN SPACE. 27 
 
 he has lately taken his apparatus to the top of the Eiffel with 
 a view of diminishing the amount of terrestrial atmospheric 
 air between it and the Sun, and intends to bring a paper on 
 this subject before Section A. 1 Stellar space filled with such 
 matter as hydro-carbon and aqueous vapour would establish a 
 material continuity between the Sun and his planets, and 
 between the innumerable solar systems of which the universe 
 is composed. If chemical action and reaction can further 
 be admitted, we may be able to trace certain conditions of 
 thermal dependence and maintenance, in which we may 
 recognise principles of high perfection, applicable also to 
 comparatively humble purposes of human life. 
 
 LETTERS ON THE CONSERVATION OF SOLAR ENERGY 
 ADDRESSED TO THE EDITOR OF "NATURE." 
 
 On the Conservation of Solar Energy. 
 
 WITH your permission I should like to offer a few remarks 
 upon the interesting paper of Dr. C. William Siemens on the 
 " Conservation of Solar Energy," published in Nature (vol. 
 xxv. p. 440). The main hypothesis upon, which that paper 
 is based, that of a fan-like action of the Sun, is not impro- 
 bable ; nor are the consequences drawn illogical, if we could 
 reasonably imagine space to be occupied by such condensed 
 molecules as he supposes. That space is everywhere occu- 
 pied by matter there is no just reason to doubt. The hypo- 
 thesis of an ether, specifically distinct from matter, is a 
 gratuitous assumption, and one of the last surviving relics of 
 eighteenth century science. Unless it can be proved that 
 highly disintegrated matter is positively incapable of con- 
 veying light vibrations, there is no warrant for assigning 
 this duty to a distinct form of substance. But that matter 
 exists in outer space in the same conditions as in the 
 planetary atmospheres is certainly improbable. Its duty as a 
 1 See Appendix, p. 98. 
 
28 CONSERVATION OF SOLAR ENERGY. 
 
 conveyer of radiant vibrations seems to require a far greater 
 tensity, and its disintegration is probably extreme. 
 
 If we assume, then, that matter exists throughout the 
 universe, here as condensed spheres, there as highly rarefied 
 substance, with the atmospheric envelopes of the spheres 
 gradually shading off into the excessively rare matter of 
 mid space; another hypothesis may be deduced, somewhat 
 different to that offered by Dr. Siemens. The views which I 
 desire to present have been already published, but they seem 
 worthy of repetition in connection with his solar theory. 
 
 On the nebular hypothesis, the matter of the Sun was once 
 disseminated through space. Gravitative attraction has, there- 
 fore, had a double effect. The greater portion of this matter 
 is now drawn together into a contracted mass. The remain- 
 ing portion yet occupies outer space, in a far more rarefied 
 condition than the original. But an important consequence 
 attends the condensation and rarefaction of gases. This is, that 
 condensed gases become heated, rarefied gases cooled, and 
 this without the aid of heat exchange with outer material. 
 In the one case a portion of the absolute heat of the gas, 
 formerly latent, becomes sensible ; in the other a portion of 
 the sensible heat becomes latent. If originally the absolute 
 contents and the temperatures were alike equal, condensation 
 and rarefaction would not, of themselves, change the heat 
 contents, but they would change the temperatures. In con- 
 densation, the latent heat is reduced, the sensible heat 
 increased, and the temperature rises. In rarefaction the 
 opposite effect is produced, and the temperature falls. 
 
 This consideration applies as well to the problem of the 
 condensation of nebulous as of terrestrial gases. The effect 
 of contraction of nebulous gas into a dense sphere, must 
 be a considerable rise in temperature if there be no 
 diminution of absolute heat contents. The effect of rare- 
 faction of the remaining matter of space must be a decrease 
 in temperature. Thus, if radiant outflow of heat from the 
 Sun had been prevented during his condensation, the eventual 
 result must have been that the Sun and the matter of outer 
 
NEBULAR HYPOTHESIS OF MATTER. 29 
 
 space would have continued equal, mass for mass, in absolute 
 heat contents, and yet have become immensely different in 
 temperature. 
 
 And from this must have come another interesting result, 
 namely, that their degree of disintegration would continue the 
 same. There could be no more chemical combination in the 
 Sun, if thus retaining all his heat, than in the rare matter of 
 space. For chemical condensation to take place, the heat 
 contents must be reduced. An equal degree of absolute heat 
 signifies an equal motive vigour of particles, and it is this 
 motive vigour which enables them to resist chemical attrac- 
 tion. It may be supposed, however, that in dense matter the 
 chemical attraction would be more effective from its increased 
 energy through contiguity. Yet this is an erroneous idea ; 
 there is no real greater contiguity between the particles of 
 dense than of rare matter. In both cases, the particles are 
 brought incessantly into absolute contact through their vibra- 
 tions. The number of contacts of dense as compared with 
 rare matter may be millions to one, but that can have no 
 effect upon the result. If the chemical vigour be stronger 
 than the vibratory vigour, it will overcome it in the contact ; 
 if it be weaker, it will fail to overcome it, and a more 
 frequent repetition of contacts cannot materially aid this 
 result. 
 
 Thus all substances of equal absolute heat must be equal 
 in degree of chemical integration, whatever their degrees of 
 tensity or condensation. But the assumed equality of absolute 
 heat cannot continue between dense and rare gases. The 
 sensible heat of the dense gas tends to radiate out into the 
 chilled rare gas. A constant and vigorous effort to equalise 
 temperatures takes place. With every outflow of radiant heat 
 from a sphere into space the absolute heat of the particles of 
 the sphere decreases, that of the rare matter of space in- 
 creases. The absolute heat contents grow more unequal with 
 every step towards equalisation of temperatures. Con- 
 sequently a variation in chemical condition arises. The loss 
 of heat by the Sun, for instance, reduces the vibratory 
 
30 CONSERVATION OF SOLAR ENERGY. 
 
 resistance to attraction, and with every such loss chemical 
 molecules of greater complexity are formed. This heat is 
 radiated into space. Probably some portion of this radiant 
 heat is arrested and becomes local heat in the matter of space. 
 If so the heat vigour of this matter increases, disintegration 
 must ensue, and the increasing chemical condensation in the 
 Sun must be matched by an increasing chemical disintegration 
 in outer matter. 
 
 During the myriad years of solar condensation, this process 
 of heat-outflow has been continuous, so that now, despite its 
 great excess of temperature, the absolute heat of solar matter 
 must be far below that of an equal mass of the matter of outer 
 space. Can the heat thus lost by the Sun be recovered ? If 
 it could, the solar heat emissions might continue indefinitely. 
 Dr. Siemens' hypothesis offers a method of recovery. If the 
 matter of outer space is drawn into the solar atmosphere by 
 such a polar inflow as he supposes, and subjected to the 
 vigorous condensing influence of solar gravity, its volume 
 must be very greatly decreased, and much of its latent heat 
 become sensible. And as its absolute heat-contents are far in 
 excess of those of solar matter, the result of such condensation 
 must be a high degree of temperature, and a continual re- 
 placement of the radiated heat of the Sun. Without any 
 chemical integration taking place in this inflowing matter, 
 the solar temperature may be kept up by its mere condensa- 
 tion, and by rendering available its great excess of absolute 
 heat. With chemical integration, and the consequent much 
 greater condensation, of course the heat-yielding effect must 
 be much more considerable. 
 
 This inflow of outer matter to the Sun is, in Dr. Siemens' 
 hypothesis, rendered possible by a continuous outflow of solar 
 matter to outer space, thus carrying substance of low heat 
 energy to be mingled with the rarefied exterior matter, whose 
 high heat energy is thereby somewhat reduced. Such a 
 process, however, has in it something of the flavour of perpetual 
 motion. The Sun is giving and taking, and his receptions may 
 be equal to his emissions. He would thus constitute a machine 
 
ATTENUATED MATTER IN SPACE, 31 
 
 yielding power to, and regaining power to be again yielded 
 from the same substance. Yet there is another element in 
 the case, which relieves it of this suspicious perpetual motion 
 flavour. If the Sun is constantly flinging off rare matter at a 
 tangent from his upper atmosphere, there must be a reaction 
 upon the rotatory energy of the solar sphere. He must be 
 gradually losing his energy of rotation, with extreme slowness, 
 of course, since the weight thrown off is very light, but in 
 time the effect cannot but become a marked one, and perhaps 
 this loss of solar energy may be the ultimate source of the 
 new heat obtained by such a process. We may conceive of a 
 like process taking place, to a less marked extent, in the large 
 and rapidly rotating planets, such as Jupiter. 
 
 CHAELES MORRIS. 
 
 PHILADELPHIA, U.S. 
 
 Under this title Dr. C. "W. Siemens, on March 2, presented 
 to the Royal Society a paper, which is published in Nature, 
 vol. xxv. p. 440. Therein, after noticing the hypotheses pro- 
 posed by Meyer, Helmholtz, and Sir William Thomson, to 
 explain the maintenance of solar heat, he endeavours to show 
 how the energy, apparently lost by radiation from the Sun into 
 space, may be gathered up and restored to the centre of our 
 system. This he conceives to be effected through the in- 
 tervention of attenuated matter diffused throughout space, 
 which is the recipient of the radiated energy, and is con- 
 tinuously absorbed and again reflected by the centrifugal 
 action of the Sun himself. The matter diffused through space 
 he supposes to include oxygen and nitrogen, hydrogen, aqueous 
 vapour, and carbon compounds, besides solid materials which 
 are probably exhalations from the Sun, and constitute the 
 so-called cosmic dust. 1 
 
 1 In a paper on the subject of an interstellar medium, read by me before 
 the French Academy of Sciences (Comptes Rcndus, September 23, 1878, page 
 453), I spoke of it as affording, in accordance with the ideas of Newton and of 
 Grove, a means of material communication between celestial bodies and added : 
 " Cette th^orie d'une echange universelle me paraissait fournir une explication 
 de 1'origine des poussieres cosmiques." 
 
32 CONSERVATION OF SOLAR ENERGY. 
 
 In support of this view of an interstellary nature Dr. 
 Siemens cites Grove and Mattieu Williams, among others, but 
 does not seem aware that its agency, in gathering up and 
 restoring to the Sun his lost radiant energy, has been 
 maintained by these writers. Sir William Grove, in his 
 address as President of the British Association in 1866, 
 attempted to find in this interstellar matter (whose nature 
 and relations to our atmosphere he had already considered in 
 1843, in his celebrated essay on " The Correlation of Forces ") 
 a source of solar heat, inasmuch as the Sun " may condense 
 gaseous matters as it travels in space, and so heat may be 
 produced." This same view suggests the title of " The Fuel 
 of the Sun," by Mattieu Williams, a book published in 1860, 
 the argument of which, as briefly resumed by me in an essay on 
 " The Chemical and Geological Eelations of the Atmosphere," 
 in the American Journal of Science for May, 1880, is as 
 follows : 
 
 " The solar heat, according to Williams, is maintained by 
 the Sun's condensation of the attenuated matter everywhere 
 encountered by that body in his motion through interstellar 
 space. The irregular movements impressed upon the Sun by 
 the varying attractions of the planets, stirring up and inter- 
 mingling the different strata of the solar atmosphere, and 
 producing the great perturbations therein, of which the 
 telescope affords evidence, are, in his hypothesis, the efficient 
 agents in the process. The diffused matter or ether, which is 
 the recipient of the heat-radiations of the universe, is thereby 
 drawn into the depths of the solar mass ; repelling thence the 
 previously condensed and thermally-exhausted ether, it be- 
 comes compressed and gives up its heat, to be, in turn, itself 
 driven out in a rarefied and cooled state, and to absorb a fresh 
 supply of heat, which he supposes to be, in this way, taken 
 up by the ether, and again concentrated and redistributed by 
 the suns of the universe." 
 
 The astronomer must judge between the different views of 
 the mechanism of what may be called the process of solar 
 respiration in this hypothesis, as put forward by Siemens and 
 
NEWTON'S VIEWS ON SOLAR FUEL, 33 
 
 Williams respectively. We may call attention in this con- 
 nection to Newton's Principia, book iii., proposition 12. 
 
 The views of Grove and of Williams, cited in my paper of 
 1880, are further considered in an essay on "Celestial Chemistry 
 from the time of Newton," read by me in November, 1881, 
 before the Philosophical Society of Cambridge, and reprinted 
 from its Proceedings both in the Chemical News and the 
 American Journal of Science for February, 1882. A perusal 
 of this paper, to which Dr. Siemens alludes, will show that 
 Sir Isaac Newton 200 years ago conceived the existence of an 
 interstellar ether made up in part from emanations and 
 exhalations from the atmospheres of the earth, the planets, 
 and the Sun, and from comets. He further conjectured this 
 interstellary medium to contain "the material principle of 
 life" and "the food of Sun and planets," furnishing "the 
 solary fuel," and being copiously absorbed by the Sun " to 
 conserve his shining/' The relations of this interstellary 
 matter to terrestrial life I have endeavoured to set forth in 
 the paper just noticed. In connection with Sir William 
 Thomson's calculation of the density of the luminiferous 
 medium therein mentioned, the reader is referred to a recent 
 examination of the subject by P. Glan, in the Annalen der 
 Physik und Chemie, No. viii. 1879, in which he concludes that 
 the lower limit of density would be more than 7,000 times 
 greater than that calculated by Thomson. 
 
 Dr. Siemens has, in his paper, further suggested that solar 
 radiation may effect the dissociation in interstellar space of 
 the compounds of oxygen with carbon and with hydrogen, so 
 that these elements may reach the Sun in an uncombined 
 state, and there be burned. He would thus make the Sun 
 not only a compressing-engine, but a furnace. While such a 
 dissociation in outer space is not impossible, it is to be said 
 that a preliminary decomposition, followed by reunion in the 
 solar sphere, would in no way augment the ultimate calorific 
 effect of compression there. The elements in the act of dis- 
 sociation in space would absorb just as much radiant energy 
 as would be set free by their subsequent combination, so that, 
 
 D 
 
34 CONSERVATION OF SOLAR ENERGY. 
 
 whether the solar radiations are expended in heating or in 
 dissociating the diffused matter, the final result in the Sun 
 would be the same. It may be further remarked, that 
 from what we know of solar chemistry, dissociation of 
 aqueous vapour and of carbonic dioxide is more likely to 
 take place in the Sun himself than in the cold regions of 
 outer space. 
 
 While, therefore, his suggested addition to the hypothesis 
 seems, if not untenable, unnecessary, we are grateful to Dr. 
 Siemens for again bringing before us the grand conception 
 which dawned upon the mind of Newton, but has found 
 its fuller expression in our own day, and, as I have 
 endeavoured to show in the papers already noticed, gives 
 us the elements of a rational Physiology of the Universe. 
 
 T. STERRY HUNT. 
 
 MONTKEAL, CANADA, April 3, 1882. 
 
 In the two preceding letters, by American men of science 
 of well-known position, one of the three postulates upon 
 which I grounded my solar plan is granted, that of space 
 filled with attenuated matter ; the second and all-important 
 one of the equatorial outflowing current is not objected to ; 
 but the third, that of dissociation of attenuated matter in 
 space by means of arrested solar energy, is called in question. 
 Both my critics think dissociation in space unnecessary for 
 the maintenance of solar energy, or as Dr. Sterry Hunt 
 very clearly puts it : " Whether the solar radiations are ex- 
 pended in heating or in dissociating the diffused matter, the 
 final result in the Sun would be the same/' 
 
 I would be disposed to agree with this dictum if taken as 
 an abstract proposition, but I do not think that my critics 
 can have subjected their view to calculation, the keystone 
 without which the arch of speculation cannot be considered 
 as secure. We know by experimental evidence that stellar 
 space, and the matter filling it, are intensely cold, as proved 
 by the winter temperature of the polar regions ; moreover 
 water exposed even in the tropics to free radiation while 
 
HEAT BY ADIABATIC COMPRESSION. 35 
 
 insulated from the warm earth, freezes to a considerable 
 thickness during a single night. 
 
 Let us suppose that the attenuated matter in space has a 
 temperature of 100 1 on the absolute scale (being* 174 below 
 the freezing-point of water), and that it is 100,000 times more 
 rarefied than when it reaches by adiabatic compression the 
 solar photosphere. The rise of temperature due to this 
 compression must be according to Rankine's well-known 
 formula 
 
 , n , H- 1 = -20 
 
 T 2 = T i ( - I 7 = 2819 absolute, 
 
 and this would make the solar photosphere 2545 on the 
 centigrade scale. This temperature is scarcely adequate to 
 produce the solar luminosity, which must require one 
 equalling, though probably not far exceeding, that of a 
 powerful electric arc ; but although a higher maximum tem- 
 perature could be reached by compression through a wider 
 range, very little of the heat due to it could be spared for 
 the purpose of radiation into space, because the gases so 
 refrigerated would obey the law of solar gravitation to a 
 greater extent than the heated in-coming gases, and would 
 certainly not pass away into space, unless acted upon by 
 a considerable extraneous force. The mere passage of the 
 solar orb through space at a majestic pace which does not 
 exceed one quarter of our orbital velocity, could not possibly 
 produce such a result, and even the fan action advocated 
 in my paper would fail to work in opposition to a large 
 determining influence of density on solar gravitation. 
 
 These conditions are entirely changed if we assume, in 
 addition to adiabatic compression and re-expansion, a further 
 source of heat such as is produced in combustion. One 
 
 1 In my original and somewhat hurried reply to Professor Sterry Hunt, I 
 assumed an initial temperature of 160 absolute, and an adiabatic compression 
 to only -^Vtr of the original volume. These figures would imply an action 
 within too narrow a limit of the solar atmosphere, and I have taken the 
 liberty of substituting figures more harmonious with the argument advanced 
 by me elsewhere. 
 
 D 2 
 
38 CONSERVATION OF SOLAR ENERGY. 
 
 pound of hydrogen develops in burning about 60,000 heat 
 units, and one pound of marsh gas 24,000 heat units. In my 
 article upon this subject, published in the April number of 
 the Nineteenth Century, I showed that if only one-twentieth 
 portion of the gases streaming in upon the polar surfaces at 
 the rate of 100 feet a second were combustible gases, they 
 could produce an amount of heat more than sufficient to 
 account for the entire solar radiation as determined by 
 Herschel and Pouillet. 
 
 There is no reason for supposing that the instreaming gases 
 would penetrate beyond the solar photosphere ; they would 
 flash into combustion whenever their temperature (by adiabatic 
 compression) had reached the limit of spontaneous ignition, 
 and the light igneous clouds so produced would flow on 
 above the denser metallic vapours which form part of the 
 permanent body of the Sun, towards the equatorial regions, 
 whence they would pass into space at a temperature still 
 exceeding, to some extent, that of the inflowing gases, the 
 heat radiated into space being made up by combustion of 
 photospheric matter. 
 
 The fan action itself would be produced, no doubt, at the 
 expense of solar rotation; but, in order to appreciate this 
 retarding influence at its true value, it must be borne in 
 mind that the flow of gases, when once established, has only 
 to be changed in direction, the velocity acquired by the 
 inflowing gases being simply transferred to the outflowing 
 current so that the amount of rotative force required need 
 only be sufficient to cover frictional retardation. The very 
 interesting leading article in last week's Nature, regarding 
 the solar observations in America during the last eclipses, 
 now published for the first time, furnishes an unexpected and 
 most striking corroboration'of the solar fan action which I 
 had ventured to put forward as a necessary consequence of 
 solar rotation in space filled with attenuated matter. 
 
 I am well aware that my paper read before the Royal 
 Society does scant justice to those who have devoted much 
 time and ingenuity to the subject of solar physics, and that, 
 
SOLAR FAN ACTION CRITICISED. 37 
 
 moreover, many points of considerable interest connected 
 with the views I advocate have been indicated only, instead 
 of having been fully developed ; but, on the whole, I thought 
 it was better to present my views in mere outline before an 
 audience well acquainted with our present information re- 
 garding solar physics, and with only half an hour's time at 
 their disposal. 
 
 The elaboration of such a subject would necessitate the 
 writing of a book rather than of a paper, and perhaps 
 Dr. Sterry Hunt, who has already done so much to elucidate 
 our present knowledge of solar physics, may be induced to 
 extend his labours in this direction. 
 
 C. W. SIEMENS. 
 
 12, QUEEN ANNE'S GATE, WESTMINSTER, 
 April 26, 1882. 
 
 CONSERVATION OF SOLAR ENERGY. 
 
 WHILE Dr. Siemens's novel and ingenious theory described 
 in his paper before the Royal Society, and published in 
 Nature, will doubtless be adequately criticised in its more 
 physical aspects by those who are better acquainted than 
 myself with " the intricacies of solar physics," I may perhaps 
 be allowed to point out one or two conclusions which appear 
 somewhat opposed to the laws of mechanics. The author, 
 for example, lays great stress upon the " high rotative 
 velocity of the Sun," which at the solar equator, according to 
 his figures, is four and a half times that at the terrestrial 
 equator. To this " high rotative velocity " Dr. Siemens 
 attributes the supposed expulsion from the solar equator 
 of the products of combustion of the gases drawn in by the 
 assumed fan action at the solar poles. 
 
 Mairan apparently thought the equatorial rise of the solar 
 atmosphere due to the centrifugal force engendered by this 
 velocity sufficient to account for the appearance of the zodiacal 
 light, and according to Dr. Siemens his supposition may 
 possibly be correct, if we suppose that space, instead of being 
 
38 CONSERVATION OF SOLAR ENERGY. 
 
 an ether-vacuum, is filled with highly attenuated gases. 
 It seems, however, that La Place, acting on the usual 
 supposition of an empty stellar space, calculated that the 
 solar atmosphere could not extend more than 9-20ths 
 of the distance of Mercury, or about 16,000,000 miles, at 
 which distance it would exist in such a highly rarefied 
 condition as almost to merit the designation of vacuum. 
 That this must be so, is evident when we remember that the 
 high superficial velocity at the solar equator, though 
 relatively larger than that at the terrestrial equator in the 
 proportion given by Dr. Siemens, so far from being able to 
 exert a powerful centrifugal force, is in this respect far less 
 effective than the smaller tangential velocity at the terrestrial 
 equator. This is chiefly due to the counteracting influence 
 of solar gravity, which, as is well known, is more than 
 twenty-seven times terrestrial gravity as represented by g. 
 It is also partly due to the large value of the solar radius, 
 since this also enters into the denominator of the expression 
 for centrifugal force in terms of the tangential velocity, 
 
 viz. v It is at least remarkable that Dr. Siemens has 
 
 T 
 
 made no allusion to either of these factors, which so 
 intimately affect the centrifugal efficiency of the centrifugal 
 force the motive-power on which the entire action depends 
 and has made it appear from his language that this is a 
 mere simple function of the tangential velocity at the 
 solar equator. 
 
 As it is, owing to these united circumstances, but mainly 
 to the former, the ratio of the centrifugal force acting on a 
 particle to its weight is, even at the solar equator, almost 
 infinitesimal. 
 
 To accentuate this astronomical platitude it is only 
 necessary to quote figures which may be found in every 
 popular work on the Sun, such as the fact that while the 
 centrifugal force at the terrestrial equator deprives a body 
 of 1 -289th of its weight at the poles, the amount it would 
 similarly lose at the solar equator would be 1-1 8,000th. 
 
SOLAR FAN ACTION CRITICISED. 39 
 
 Or again, to put it in another light, in order that solar 
 gravity and centrifugal force may equilibrate, and a particle 
 at the solar equator be without weight, the Sun would have 
 to turn upon his axis 133 times as fast as at present, while 
 in order that the same conditions should prevail on the 
 earth, its rotational velocity would only need to be increased 
 seventeen times. 
 
 Except, therefore, where they would be momentarily 
 affected by the local expulsive forces engendered by solar 
 combustion, the different layers of the solar atmosphere 
 would arrange themselves in the order of their relative 
 densities, and remain quietly attached to the surface of the 
 Sun, under an attraction fully twenty-seven times greater 
 than that which our earth exerts on its aerial envelope. 
 That, under such circumstances, the centrifugal force of the 
 Sun could cause him to project into space the products of 
 combustion seems most improbable. 
 
 Moreover, suppose, for the sake of argument, that this 
 action really does take place, can it be literally maintained, 
 according to Dr. Siemens's concluding sentence, that this 
 action is "capable of perpetuating solar radiation to the 
 remotest future " ? l The laws of energy tell us that work 
 cannot be done without expenditure of energy, and since the 
 primum mobile in this case is solar rotation, and the gases 
 entering at the solar poles must gradually acquire rotational 
 momentum at the Sun's expense, they must, in time, reduce 
 it to nought, when the supposed regenerative action would 
 cease, and so the Sun burn out. In any case, therefore, the 
 word " remotest " can only be understood to have a limited 
 signification. 
 
 E. DOUGLAS ARCHIBALD. 
 
 1 The expression used in the concluding paragraph of my original paper was 
 certainly calculated to mislead, although in the body of the paper I speak of 
 various losses of solar energy, showing that I did not contemplate actio in 
 pcrpetuum. 
 
40 CONSERVATION OF SOLAR ENERGY. 
 
 [To save time we submitted Mr. Archibald's letter to 
 Dr. Siemens, who sends the following reply. ED.] 
 
 This letter shows that Mr. Archibald has missed the 
 principal point of my argument concerning solar fan action. 
 I showed pretty clearly, I thought, that solar gravitation would 
 affect the inflowing and the outflowing currents equally, and 
 that centrifugal action must determine motion in the equa- 
 torial direction in a space filled with matter. But, to put the 
 problem into a mathematical garb, let us consider the con- 
 dition of two equal masses m p and m a , both at the radius R 
 from the solar centre, the one opposite either pole, and the 
 other opposite the equatorial region. The force of gravitation 
 acting on these masses will be represented respectively by 
 
 -- and ^j~, and supposing both masses to be gaseous, and of 
 
 the same chemical composition and temperature, they will 
 represent equal volumes, say one cube foot. 
 These conditions being granted, we may put 
 
 but the mass m a is subject to another force, that produced by 
 tangential motion, which shall be represented by v, and the 
 centrifugal force resulting from this motion by <f>v ; the force 
 of gravitation towards the Sun will then be reduced to 
 
 ^~ w a <#, and the latter factor being a positive quantity 
 we have 
 
 This inequality of attractive forces must determine motion 
 toward the Sun in favour of ^=^ and this condition holding 
 
 good for any value of g and R, it follows that the polar in- 
 flow and equatorial outflow must take place, provided only 
 
SOLAR FAN ACTION EXPLAINED. 41 
 
 that space is not empty, as supposed by La Place, but filled 
 with either an elastic or non-elastic fluid. 
 
 To put it in another way, Mr. Archibald imagines that 
 in order to determine an outflow from the Sun it is necessary 
 for the centrifugal force m a (ftv to exceed the force of gravita- 
 tion -^> whereas, according to my view, the value of the 
 
 former determines only the rate of outflow, but is immaterial 
 as regards the principle of action. The projection of dust 
 is entirely dependent upon the outflowing current. I leave 
 it for Mr. Archibald to determine for himself the velocity of 
 current necessary to move a particle of dust of given size 
 and weight away from the Sun in opposition to his force of 
 gravity, which I am well aware is twenty-seven times that of 
 the earth on its surface. 
 
 The gaseous current is of course produced at the expense 
 of solar rotation, but this expenditure of energy is relatively 
 much smaller than that lost to our earth through tidal action, 
 and may be neglected for our present purposes. It is more- 
 over counterbalanced by solar shrinkage as explained in 
 my paper. C. WM. SIEMENS. 
 
 Dr. Siemens's Solar Hypothesis. 
 
 I have been waiting for several weeks for answers to the 
 following rather obvious objections to Dr. Siemens's Solar 
 Hypothesis, but I have not seen them either asked by others 
 or answered by Dr. Siemens. 
 
 1. How the interplanetary gases near the Sun acquire a 
 sufficient radial velocity to prevent their becoming a dense 
 atmosphere round him ? 
 
 2. Why enormous atmospheres have not long ago become 
 attached to the planets, notably to the moon ? 
 
 3. Why the earth has not long ago been deluged when a 
 constant stream of aqueous vapour that would produce a rain 
 of more than 30 inches per annum all over the earth must 
 annually pass out past the earth in order to supply fuel to be 
 dissociated by the heat that annually passes the earth ? 
 
42 CONSERVATION OF SOLAR ENERGY. 
 
 4. Why we can see the stars although most of the solar 
 radiations are absorbed within some reasonable distance of 
 the Sun ? 
 
 GEO. FKAS. FITZGERALD. 
 
 40, TRINITY COLLEGE, DUBLIN, 
 May 16, 1882. 
 
 I have the pleasure to reply to the very pertinent questions 
 put by Prof. Fitzgerald as follows : 
 
 1. The gases being for the most part hydrogen and hydrogen 
 compounds, have a low specific gravity as compared with the 
 denser gases forming the permanent solar atmosphere. On 
 flashing into flame in the photosphere, their specific gravity 
 would be vastly diminished, thus giving rise to a certain 
 rebound action which, coupled with their acquired onward 
 motion and with the centrifugal impulse they receive by 
 frictional contact with the lower atmosphere, constitutes them 
 a surface stream flowing from the polar to the equatorial 
 regions, and thence out into space. (Lest I should be mis- 
 understood, allow me to add that I do not look upon centri- 
 fugal action as sufficing in any way to overcome solar 
 gravitation.) Astronomers are in the habit of regarding each 
 spheroid possessed of an atmosphere as rotating in vacuous 
 space ; under such circumstances the atmosphere must par- 
 take of the rotatory motion of the solid spheroid, and after 
 having attained an increased depth at the equator, will assume 
 a state of static equilibrium unless disturbed by external 
 influences. No such statical equilibrium is possible, however, 
 if we assume the same spheroid with its atmosphere, sur- 
 rounded by an ocean of indefinite dimensions, consisting of 
 gaseous matter not partaking of the rotation of the spheroid, 
 although subject to its attractive influence. Equal masses 
 will under those conditions be equally attracted both in the 
 polar and equatorial direction, and the continued disturbance 
 of equilibrium by rotatory motion must result in continuous 
 outflow. Nor need this outflow be accomplished entirely at 
 the expense of rotatory motion of the spheroid because the 
 inflowing polar current, when once established, will only have 
 
PLANETARY ATMOSPHERES. 43 
 
 to be changed in direction by frictional action in order to 
 convert it into the outflowing current. 
 
 2. Regarding the second question, I assume that the atmo- 
 sphere of each spheroid in space is precisely such as would 
 result from its mass, and if this view is correct, the moon also 
 must have an atmosphere, though of so attenuated a character 
 as to be scarcely perceptible by means of optical instruments ; 
 for as Wollaston put it in his celebrated paper read before 
 the Royal Society in January, 1822, "it would not be greater 
 than that of our atmosphere is, where the earth attraction is 
 equal to that of the moon at her surface, or about 5,000 miles 
 from the earth's surface." I am well aware that in assuming 
 atmospheric air to be a perfectly elastic fluid, the atmospheric 
 density would, at a height of only 70 kilometers, not exceed 
 the l-7000th part of atmospheric density, and would therefore 
 at greater distances become inappreciable ; but we have 
 evidence to show that Boyle and Mariotte's law holds good 
 only within comparatively narrow limits, 1 and there is other 
 evidence referred to in my paper in favour of the supposition 
 that such gases as are contained in meteorites are diffused 
 through space in appreciable amounts, or the meteorites 
 could not for millions of years have retained these gases, 
 notwithstanding the action of diffusion into empty space. 
 
 3. The amount of vapour that would condense upon the 
 earth under the conditions here assumed, would depend upon 
 its mean temperature on the one hand, and on the vapour- 
 density of the stellar atmosphere surrounding it on the other. 
 Assuming the density of the stellar atmosphere, which, while 
 surrounding the earth does not partake of its rotatory motion, 
 to be 1-1 0,000th part of atmospheric density, and saturated 
 with aqueous vapour, the point of condensation would be, 
 according to Regnault, 50 C. ; 2 if the outer regions of our 
 atmosphere should be at that temperature, and saturated with 
 
 1 See footnote under page 7. 
 
 2 This assumed temperature is decidedly too high ; if we assume it to be 
 100 absolute on the Centigrade scale, we should find a much lower vapour- 
 density in space, but one which Regnault's formula does not give us the means 
 of estimating. 
 
44 CONSERVATION OF SOLAR ENERGY. 
 
 aqueous vapour, the two would be in diffusive balance ; if they 
 were at a lower temperature they would acquire, and if at 
 a higher they would part with, aqueous vapour to the 
 surrounding medium. 
 
 4. It has long been held by astronomers that there are stars 
 beyond our range of vision, which hypothesis would involve 
 that of absorption of heat and light rays in stellar space ; 
 some rays are more easily absorbed than others ; thus it 
 appears to be the yellow ray which is most efficacious in 
 the decomposition of carbonic acid and aqueous vapour in the 
 vegetable cell. May not the same conditions prevail in space, 
 and allow probably the rays of highest refrangibility to pass 
 on to the greatest distance without being absorbed I should 
 say utilized in doing chemical work ? 
 
 C. WM. SIEMENS. 
 
 12, QUEEN ANNE'S GATE, S.W., 
 May 22, 1882. 
 
 ON THE CONSERVATION OF SOLAR RADIATION. 
 
 IT appears to me a difficulty arises with regard to Dr. 
 Siemens's theory when we consider the original condition of 
 the earth and of the other planets. What, in fact, has 
 become of the great amount of energy which was present 
 in the form of heat in those bodies ? 
 
 Just as in the case of the Sun, the rotation of the earth 
 would produce a continuous cycle current, the decrease of 
 rotatory energy being perhaps counterbalanced by shrinkage, 
 the radiant heat would become transformed into the potential 
 energy of dissociation, and this energy again would be given 
 back to the earth in the form of heat in another part of 
 the circuit where the elements recombine. Now it is quite 
 impossible that the whole of the heat radiated should be used 
 in this way, for after a lapse of years we should find a 
 considerable diminution of potential, or (perhaps) rotatory 
 energy, and we therefore should be forced to the conclusion 
 that the earth became continually hotter. Hence some of 
 
EARTH FORMERLY RECUPERATED ITS HEAT. 45 
 
 the radiant heat escaped must have escaped into space, never 
 to return. 
 
 Is it then a feasible solution that more heat is radiating 
 from the Sun than is necessary for the dissociation of the 
 elements ? If so, then at least we should have a satisfactory 
 explanation of its slowly-diminishing activity. G. B. S. 
 
 THE writer of this letter is right in concluding that in 
 accordance with my hypothesis the earth also must throw 
 out a stream of matter equatorially into space ; and if your 
 correspondent will refer to my article in the Nineteenth 
 Century of April last, he will find that at p. 522 I speak of 
 such a terrestrial outflow, with which I connect the pheno- 
 mena of Aurora Borealis. If at any period of the world's 
 history the rotatory velocity of the earth has been much 
 greater than it is now (as has been suggested lately by Mr. 
 G. Darwin), and its surface-temperature sufficiently high 
 to cause ignition of combustible gases, it may be reasonably 
 supposed that it had the power of recuperating its heat 
 of radiation. The amount of heat so recuperated would, 
 under all circumstances, be less than that received back 
 by combustion, and the result of gradual diminution of 
 temperature would be that on a certain day the temper- 
 ature must have fallen below the point of ignition, from 
 which day forward no further recuperation of heat can have 
 taken place. The process of cooling would then proceed at a 
 very rapid ratio, until the surface-temperature had reached 
 another point of comparative constancy, at which the radiation 
 into space was balanced by the heat received by solar 
 radiation, which is our present condition. 1 
 
 C. W. SIEMENS. 
 
 12, QUEEN ANNE'S GATE, S.W., 
 October 16, 1882. 
 
 1 Professor E. J. Stone lately called my attention to a most interesting 
 observation favouring my solar hypothesis, viz., that when (probably by collision) 
 a star, say of the third, suddenly lights up to one of the first magnitude, the 
 greater brilliancy thus produced by its increased temperature rapidly subsides 
 until its former degree of brilliancy is again reached, from which time forward 
 its condition is maintained, apparently by a process of recuperation depending 
 upon its rotation. 
 
46 CONSERVATION OF SOLAR ENERGY. 
 
 ON DR. C. W. SIEMENS'S NEW THEORY OF 
 THE SUN. BY M. FAYE. 
 
 A Communication addressed to the Academic des Sciences, and 
 published in the Comptes Rendus, October 9th, 1882. 1 
 
 IT would appear that this theory has greatly struck our 
 physicists; for it had scarcely appeared in London when it 
 was translated and published in France in various forms, and 
 especially in the last number of the Annales de Chimie et de 
 Physique. I suppose that the principal object of this haste 
 was the announcement of fresh experiments which have 
 been instituted by the author upon the chemical action of 
 light. It is well known that, under the action of light 
 and with the intervention of the chlorophyll of plants, aqueous 
 vapour and carbonic acid are decomposed at ordinary 
 temperatures, and brought back to the combustible form, 
 carbon and hydrogen variously associated. Dr. Siemens has 
 tried whether the action of the light of the Sun alone would 
 not produce this decomposition if we submit to him, without 
 any other intermediary, aqueous vapour and carbonic-acid 
 gas excessively rarefied, brought for example to the vacuum 
 of TsW His experiments, which, in my opinion, only require 
 a counter-test which it would be easy to institute, have given 
 perfectly affirmative results. Thus, the burnt gases having 
 been brought to such a rarefaction that they no longer 
 permitted the passage of the induction-spark, a few hours' 
 exposure to the light of the Sun sufficed to enable the 
 mixture to allow this spark to pass with the well-known 
 colouration that it acquires in hydro-carburetted media. 2 
 
 Regarding these beautiful experiments as decisive, Dr. 
 Siemens has been led to inquire whether this phenomenon 
 does not perform in the universe a part still more consider- 
 
 1 This communication was translated in the Philosophical Magazine of 
 November, whence the present translation is taken. 
 
 2 A vacuum produced in a bell-glass into which a drop of oil of turpentine 
 has previously been introduced, for example. 
 
ASTRONOMICAL AND PHYSICAL VACUA. 47 
 
 able than in vegetable life. Supposing space to be filled 
 with analogous gases, already burnt, the light of the Sun 
 would revivify the combustibles hydrogen and carbon, which 
 would then be quite ready to furnish the food of a fresh 
 combustion. 
 
 By drawing them to himself and burning them afresh, the 
 Sun would recuperate a good portion of the enormous heat 
 which one is grieved to see him radiating in pure loss into 
 celestial space. 
 
 Dr. Siemens has thus been lead to put forward the 
 following hypothesis : Space is filled with burnt gases, 
 aqueous vapour and carbonic acid, mixed with inert gases, 
 nitrogen, &c., pretty nearly the same as those of our atmo- 
 sphere, at a pressure of -a^nr- These gases are partially 
 converted into combustibles under the action of solar light ; 
 then, by a mechanism like that of a fan of a blower, the Sun 
 draws them to himself, burns them, and sends them back 
 again into space. This immense source of heat would be 
 continually resuscitated ; the only part of its radiation lost 
 would be that which is not absorbed by the cosmical medium 
 of a density of 2--^-. 
 
 It is perfectly true that, for the physicist, air at ^^ would 
 be an almost absolute vacuum, so much so indeed that in such 
 a vacuum the electric spark would no longer pass. But to the 
 astronomer such a medium would be very dense. When we 
 speak, in Astronomy, of the resistance of a medium or of the 
 ether, and when by the aid of the most delicate observations 
 and the most profound calculations, we seek for traces of this 
 resistance, we have to do with a very different 'thing. 
 
 Without entering upon these discussions, I will remark that 
 the trajectory of a cannon-ball with a velocity of 500 metres is 
 sufficiently altered at the end of a few seconds, to compel 
 artillerists to take into account the resistance of the air in 
 their tables. 
 
 If the air is reduced to 2 o 1 ooj but the velocity of the pro- 
 jectile becomes that of the celestial movements, sixty times as 
 much for example, these palpable effects will become, for a 
 
48 CONSERVATION OF SOLAR ENERGY. 
 
 multitude of celestial projectiles of dimensions comparable to 
 those of our cannon-balls, twice as great as in our firing- 
 grounds, and this not merely at the end of a few years or a 
 few centuries, but at the end of a few seconds. 
 
 In the second place, it seems to me that the celebrated 
 English physicist has somewhat neglected to examine into the 
 quantity of matter which he adds to the solar system. Under 
 the influence of attraction this matter would go to unite itself 
 with the pre-existing stars, with the Sun especially, and would 
 continually augment their mass. Nothing is easier than to 
 form an idea of this. A litre of air containing the required 
 proportion of aqueous vapour weighs at least 1 gramme at the 
 ordinary pressure. At a pressure of ^wo 1 th* 8 w ^ ^ e 0'0005 
 gramme, and a cubic metre will weigh 0'0005 kilogramme. 
 This being settled, if we restrict the Solar System to a 
 sphere including all the planets as far as Neptune, the weight 
 of the excessively rarefied matter added by the hypothesis 
 would be, in kilogrammes 
 
 | TT (6400000 X 24000 X 30) 3 X 0'0005 kilog. 1 
 The actual weight of the Sun is, in kilogrammes 
 | TT (64000000) 3 x 5-6 X 324000. 2 
 
 The first is 100,000 times as great as the second. It is 
 therefore 100,000 times the mass of the Sun that this hypo- 
 thesis adds to those of which celestial mechanics has hitherto 
 kept so minute an account. 
 
 It is not very probable that the astronomers will adopt such 
 hypotheses. No doubt they would be pleased to think that 
 Nature has provided the Sun with resources to make his heat 
 last longer ; but as his final refrigeration is still, under any 
 circumstances, a tolerably distant catastrophe, they will console 
 
 1 The first number is the radius of the earth in metres ; the second the 
 distance of our globe from the Sun in terrestrial radii ; the third the distance 
 of Neptune in parts of the distance of the Sun. 
 
 2 The first number is the radius of the earth in decimetres ; the second the 
 mean density of our globe referred to that of water ; the third the mass of 
 the Sun referred to that of the earth. 
 
DR. SIEMENS'S REPLY TO M. FAYE 49 
 
 themselves by the thought that the things of this world, even 
 the most beautiful, do not appear to be made to last for ever. 
 As to the fundamental experiments of Dr. Siemens, they 
 will lose none of their importance in their eyes. The business* 
 is to surprise a secret of living nature, one of the laws of the 
 organic world ; and their desire will be that Dr. Siemens may 
 pursue the course in which he has commenced so brilliantly, 
 even though they cannot hope to have a very bright light 
 thrown by it upon their own researches. 
 
 REPLY TO THE OBJECTIONS PRESENTED BY M. FAYE AGAINST 
 MR. C. W. SIEMENS'S NEW THEORY OF THE SUN. 
 
 Letter of Mr. C. W. Siemens to M. Dumas, and published in 
 the Comptes Rendus, October 30^, 1882. 1 
 
 I HAVE studied the note published by M. Faye in the 
 Comptes Rendus of October 9th, headed " On the New Theory 
 of the Sun by Mr. C. W. Siemens." This communication 
 has induced me to address to you some supplementary explan- 
 ations, trusting that you will be so good as to communicate 
 them to the Academie des Sciences, should you think them 
 worthy of that honour. 
 
 When I communicated to the Royal Society of London on 
 the 20th of February, 1882, my memoir " On the Conservation 
 of Solar Energy," I did not expect or desire that the astro- 
 nomical hypothesis, to which I had been led by observations 
 in the domain of physics, would be accepted without ob- 
 jections. It was therefore with great pleasure that I saw 
 in the Annales de Chimie et de Physique a translation of 
 my memoir in the more extended and generalised form ia 
 which I had given it in the April number of the Nineteenth 
 Century, and it was a source of still greater satisfaction to 
 find that an astronomer of the high reputation of M. Faye 
 had deemed it worthy of discussion before the Academie des 
 Sciences. 
 
 1 This letter was in part translated in the Philosophical Magazine of 
 December, 1882. 
 
 E 
 
50 CONSERVATION OF SOLAR ENERGY. 
 
 M. Faye, while approving generally of the physical part of 
 my investigations, questions their application to astronomy, 
 and for the following reasons : 
 
 1. That the presence of a universal gaseous medium at a 
 pressure of ^^^ atmosphere would oppose an excessive 
 resistance to the movements of the planets ; 2. That this 
 vapour, thus distributed, would be gradually attracted towards 
 the Sun, and would tend to augment his mass considerably. 
 
 Allow me to point out, as regards the second of M. Faye's 
 objections, that the degree of diffusion supposed by me to 
 obtain in space is such as will ensure the permanence of the 
 statical equilibrium between the forces of expansion and 
 diffusion on the one hand, and of attraction towards the Sun 
 and the celestial bodies on the other. If no such equilibrium 
 were established, M. Faye's objection would at once upset my 
 theory. I am, moreover, inclined to admit that if Mariotte's 
 law with regard to the tension of gases was to hold good in- 
 definitely, the pressure of the interplanetary gaseous medium 
 would be reduced almost beyond anything of which we can 
 form a conception ; but it seems to me, from considerations 
 drawn from the-dynamical theory of gases, and from the manner 
 in which, as demonstrated by Mr. Crookes, gases behave when 
 rarefied to an extraordinary degree in tubes it seems 
 to me, I say, that there exists no a priori reason why this 
 law should be extended rigorously to vapours beyond the 
 confines of our atmosphere and of that of the Sun. 1 
 
 As regards M. Faye's first objection, I admit that a density 
 of ^-o-Vtf atmosphere would have the consequences which he 
 so correctly establishes ; and I remember having said, (see 
 Proceedings of the Royal Society, p. 395,) that assuming the 
 results of my experiments on the dissociation of vapours by 
 solar energy to be proved, and assuming further that stellar 
 space is filled with vapour at a pressure not exceeding the 
 limit of 217017 atmosphere, which corresponds to the highest 
 rarefaction that I was able to obtain in my experiments, a 
 dissociation of this cosmical vapour must ensue by means of 
 1 See also footnote to p. 7. 
 
DK. SIEMENS'S REPLY TO M. FAYE. 51 
 
 the radiation of the Sun. It should be observed that this 
 passage only relates to the physical phenomena submitted to 
 my experiments, and that if the dissociation of aqueous 
 vapour and of carbon-compounds is effected by the direct 
 radiation of the Sun at so high a pressure as ^ITOTT atmo- 
 sphere, it would, a fortiori, be effected in the more rarefied 
 medium. 
 
 In another passage of my memoir, (p. 397,) when I apply 
 my hypothesis to comets, I assume that, even at their 
 perihelion, they move in a medium of a density not exceed- 
 ing ^^ atmosphere, and that this density would suffice to 
 give rise to incandescence by frictional compression. This 
 proves^ at any rate indirectly, that I regarded stellar space as 
 filled with vapour of a pressure much below -g^Ver atmosphere, 
 and (in the absence of all data of experiment and obser- 
 vation) I spoke of the stellar medium as in an extremely 
 rarefied state, without fixing any limit to this rarefaction. 
 
 Since then new facts of observation have tended to confirm 
 my hypothesis of a stellar space filled with rarefied matter 
 analogous to that which we can actually produce in our 
 vacuum-tubes. The equatorial prolongations of the solar 
 atmosphere observed in America during the eclipse of 1880 
 seem to demonstrate the existence of matter extending from 
 the Sun for several millions of leagues, and rendered visible, 
 no doubt, by solid particles, illuminated partly by the 
 reflection of the solar light, and partly by discharges of 
 electricity from particle to particle towards the Sun. 
 
 My hypothesis has found a still more direct confirmation in 
 the remarkable spectroscopic investigations communicated 
 by Capt. Abney to Section A of the British Association in 
 the month of August last, which prove that carbon-compounds 
 of the ethyl or alcohol group exist, at a low temperature, 
 between the Sun's atmosphere and our own, and recent 
 observations made in America by Prof. Langley with his bolo- 
 meter (although made with a totally different object in view) 
 tend to confirm the results obtained by Capt. Abney upon the 
 Riffel. We may also add to these proofs the interesting 
 
 E 2 
 
52 CONSERVATION OF SOLAR ENERGY. 
 
 observation of Prof. Schwedoff (communicated to Section A 
 of the British Association by Prof. Silvanus Thompson), 
 according to which large hailstones, seemingly of cosmical 
 origin, have on certain occasions been observed to fall upon 
 the earth. 
 
 Accepting these observations as founded upon facts, 
 physical considerations are not wanting for the approximate 
 determination of stellar vapour density, which, in this case 
 must be a function of the temperature in space. As 
 Gorschow, on 30th November, 1871, observed a temperature 
 of 63 C. in the Arctic regions, it follows that the stellar 
 medium (which, if it consists of a vapour, is capable of inter- 
 cepting calorific rays) must be at a temperature comprised 
 between 63 and the absolute zero (274). 
 
 It is to Regnault that we owe our most exact knowledge of 
 the density of vapours at different temperatures ; but his 
 researches did not extend below 32 C., and his formulae 
 cannot be rigorously applied below that point ; neverthe- 
 less they enable us to estimate approximately what may be 
 the densities of a vapour at lower temperatures ; and it is 
 thus that we are led to believe that at 130 the density of 
 aqueous vapour does not exceed ^cro^oir ^niosphere. If we 
 assume, further, that the gaseous mass which fills space 
 consists only one-fifth of aqueous vapour, the other four-fifths 
 being composed of hydrocarbons, carbonic acid, and nitrogen, 
 the total pressure of the vapour cannot exceed TOWO"OTJ- 
 atmosphere. 
 
 These vapours would traverse space with a velocity equal, 
 probably, to half the tangential velocity at the surface of the 
 Sun, or about 1 kilometre per second. It could be easily 
 demonstrated that a column of these dissociated gases 
 travelling with this velocity towards the polar surfaces of the 
 Sun, and taken at a distance of 5,500,000 kilom. from the Sun 
 (the mean distance of Mercury, the nearest of his planets) 
 would present a sectional area of flow towards the Sun 
 equal to 140,000 milliards of square kilometres, much more 
 than sufficient to furnish the material necessary to yield 
 
M. HIRN ON TEMPERATUKE OF THE SUN. 53 
 
 by combustion the heat required to maintain the solar 
 radiation. 
 
 Perhaps the eminent Director of the Bureau des Longi- 
 tudes may be inclined to think that a gaseous medium of a 
 density equal at most to T^RTO-OW f that of our atmosphere 
 might still interfere with planetary movements to a degree 
 incompatible with the facts ascertained by astronomical 
 observations. If this be the case, it would suffice to assume 
 a still lower temperature in space, and consequently a 
 still more attenuated rarefaction of the interstellar gaseous 
 matter. 
 
 ON MR. C. W. SIEMENS'S NEW THEORY OF THE SUN. 
 BY M. G. A. HIRN. 
 
 A communication addressed to the Academic des Sciences, and 
 published in the Comptes Rendus, November 6.th, 1882. 1 
 
 To the grave objection brought forward by M. Faye against 
 Mr. Siemens' s new theory of the conservation of solar 
 energy, another, also a very serious one, may be added. 
 This objection may be summed up in few words. 
 
 Up to the present time there is no general agreement as 
 to the real value of the Sun's temperature. Pere Secchi 
 carried it to millions of degrees. Other physicists, especially 
 in France, lowered it to about twenty thousand degrees. 
 According to the magnificent experiments of Mr. Langley 
 (of Alleghany) this latter amount is, at any rate, a minimum. 
 What is certain then, starting from the fine memoirs upon 
 dissociation of our lamented colleague Henri Sainte-Claire 
 Deville, is that none of the chemical compounds that we 
 know upon our earth could exist at the surface of the Sun. 
 All, even those which are most refractory in our laboratories, 
 would be dissociated and reduced to their constituent 
 elements. And this is what is admitted in M. Faye's theory 
 of the Sun. 
 
 1 This communication was translated in the Philosophical Magazine of 
 December, whence the present translation is taken. 
 
54 CONSERVATION OF SOLAR ENERGY. 
 
 The natural and direct consequences of the preceding fact 
 is, that the chemical compounds which Mr. Siemens supposes 
 to be dissociated by degrees in space by solar radiation, 
 might certainly, in returning under the action of gravity and 
 in the elementary state towards the central body, become 
 reformed, and regenerate the heat expended in their dissocia- 
 tion in space ; but this recombination could only be effected 
 at an appreciable distance from the solar photosphere, and 
 the compounds reproduced, on falling into the bosom of the 
 latter, would be again completely dissociated. This action, 
 therefore, would cause ' the expenditure of all the heat 
 previously developed by the combination. From this it 
 follows evidently that this return of the elements towards 
 the centre would contribute nothing at all towards the con- 
 servation, or rather the continuous reproduction, of the solar 
 temperature. 
 
 It seems to me that Mr. Siemens's theory maybe subjected 
 to another decisive critical test. If the solar radiation, or 
 say the heat, whether visible or not, emitted or sent off by 
 any celestial body during its course, effects the chemical 
 dissociation of the hypothetical compounds disseminated in 
 stellar space, the intensity of this radiation must necessarily 
 be reduced by the positive work effected, and all that serves 
 for this work is lost for the visibility of the star. 
 
 From this, then, it follows that the lustre of the Sun, of 
 the stars, and of the planets must diminish according to a 
 imtch more rapid law than that of the inverse proportion of 
 the square of the distances. I say much more rapid ; but we 
 must say extremely rapid. In fact, from the moment when 
 the recombination of the elements at the surface of the Sun 
 would be capable of regenerating the heat emitted, it is 
 evident that all this emitted heat would be employed in its 
 turn in dissociating the chemical compounds in space. In 
 order that the Sun could be thus continually maintained in 
 its energy, it would be necessary that the distance at which 
 it is visible, far from being unlimited as it probably is, should, 
 on the contrary, be restricted ; for wherever it would be still 
 
M. HIRN ON DENSITY OF GAS IN SPACE. 55 
 
 visible there would be light not employed in chemical dissocia- 
 tion, and consequently there would still be a definite loss 
 possible. Nothing in the aspect of our planets and their 
 satellites, it seems to me, authorises us to assume that there 
 is any other reduction in the brilliancy of the light than 
 that resulting from the inverse proportion of the square ot 
 their distance from the central body. We see stars the 
 light of which has taken at least three years, and others 
 of which the light has perhaps taken thousands of years to 
 reach us. None of this light, therefore, has been employed 
 in chemical dissociation ; nothing could have been restored 
 to them by the mode indicated by the ingenious theory of 
 Mr. Siemens. 
 
 May I be permitted, in concluding this note, to revert 
 to the objection formulated by M. Faye, and to render it in 
 some degree palpable by a numerical example ? In an 
 extensive work upon which I am engaged, upon the con- 
 stitution of stellar space, I naturally examine into the 
 consequences that the resistance of a gas diffused in space 
 would have upon the movements of the planets. From this 
 work I extract an example relating to the application of 
 analysis to the motion of our Earth. According to Laplace, 
 the diminution or augmentation which one may attribute 
 to the duration of our sidereal year 3000 years ago, taking 
 into account the uncertainty of the observations, would be 
 ninety seconds at the maximum (a modification of which, 
 however, there is nothing to demonstrate the reality). 
 Accepting a reduction of this amount as real, I inquire what 
 density a gas would need to have, to produce it ; and I show 
 that it would suffice if there were one kilogr. of matter 
 in vapour in 700 thousand millions of cubic metres in other 
 words, that the density would be O'OOO, 000, 000, 00143 
 kilogr. It will be seen that we are far from the reduction 
 to the ^VTTJ and even to the millionth assumed by Mr. 
 Siemens. If, instead of taking account only of the resistance 
 opposed by such a gas to the motion of our planet, we direct 
 our attention to the consequences which its existence would 
 
56 CONSERVATION OF SOLAR ENERGY. 
 
 have upon that of our atmosphere, we find that, unless we 
 multiply our 700 thousand millions of cubic metres by 10,000, 
 and reduce the density sought for to O'OOO, 000, 000, 000, 0001 
 kilogr., our atmosphere would be in a few moments swept 
 away by the pressure exerted above by the interstellar gas. 
 
 M. Faye is perfectly justified in saying that it is not such 
 or such a degree of rarefaction, but that it is the vacuum (of 
 matter, of course) that the astronomer requires, to ensure the 
 stability of the movements that his analysis shows. This 
 vacuum no doubt upsets the doctrine, supposed to be so 
 undeniable, which ascribes all the phenomena of the physical 
 world to movements and collisions of material atoms 
 independent of each other. Some day or other, no doubt, 
 this doctrine will have ta give up its existence, and its 
 defenders will have to resign themselves to admit in the 
 physical world something more than matter in motion. In 
 a remarkable letter to Bentley, Newton said that one must 
 be destitute of all aptitude for a serious philosophical discus- 
 sion to suppose that between two bodies which seem to 
 attract each other at an unlimited distance, there is not 
 something which establishes this relation ; but, he adds 
 immediately, is this intermediary material or immaterial? 
 This I leave to. the reader to decide. With that great 
 genius undoubtedly there was no uncertainty upon this latter 
 point ; but, perhaps justly, he refrained from putting before 
 his contemporaries a solution which might have seemed in- 
 comprehensible to them, as it still is, apparently, to so many 
 minds of the present day. 
 
 ON THE CONSERVATION OF SOLAR ENERGY. 
 
 A Reply, by C. W. Siemens, to the Note of M. G. A. Him, 
 and translated from the Comptes Rendus, November 27th, 
 1882. 
 
 M. G. A. HIRN has published in the Comptes Rendiis of 
 Nov. 6th a communication to the Academic des Sciences 
 
DR. SIEMENS 1 S REPLY TO M. HIRN ON SUN'S HEAT. 57 
 
 concerning my hypothesis regarding the conservation of solar 
 energy, to which I hasten to reply. At the same time I feel 
 some personal embarrassment, since M. Hirn declares his un- 
 compromising antagonism to those physicists who attribute 
 " all the phenomona of the physical world to movements and 
 collisions of material atoms independent of each other " ; and 
 considers that " the day will not be long in coming, when 
 physicists will be content to admit something in nature 
 beyond matter in motion." 
 
 For my part I must admit that I am an adherent of this 
 materialistic principle, being convinced that it alone can lead 
 us, when supported by experiment, to reliable conclusions 
 regarding the great phenomena of nature. 
 
 I shall reply to the physical and mathematical objections 
 of M. Hirn in the order in which they are severally 
 presented. 
 
 The French physicists have been the first to throw doubt 
 on the exaggerated estimates of the temperature of the Sun 
 formed by Pere Secchi and others, exaggerations that were 
 very common also regarding the fusing points of solids 
 previous to the brilliant researches of Pouillet, H. Sainte- 
 Claire Deville, and others. 
 
 M. Hirn estimates this temperature at 20,000, and very 
 justly concludes that all compound bodies produced during 
 approach will be again completely dissociated in these in- 
 tensely heated regions, and that this action will absorb all the 
 heat previously developed by combustion. M. Hirn regards 
 this temperature as a minimum, basing his view on the experi- 
 ments of Professor Langley ; but I venture to think that 
 regarding these he cannot be in possession of full information. 
 The instrument employed by Professor Langley, the Bolometer, 
 is a very ingenious development of my electrical pyrometer 
 (Proc. R. S. 1871, and Journal of the Society of Telegraph 
 Engineers, 1875), which has been frequently employed in 
 metallurgical investigations ; I have consequently followed 
 Professor Langley's researches with a very special interest, 
 and on the occasion of his recent visit to Europe I had the 
 
58 CONSERVATION OF SOLAR ENERGY. 
 
 opportunity during his stay at my country house of discussing 
 with him questions of solar physics, and have not found that 
 our opinions were very divergent. I have calculated the 
 temperature of the photosphere to be below 3,000, an 
 estimate based on comparative observations on gas-burners 
 and electric arcs. 
 
 The interesting experiments of Professor Tyndall, described 
 in his book on Radiant Heat (p. 260), show that a gas-burner, 
 giving an intense light, produces luminous and non-luminous 
 rays in the proportion of 1 to 25, and the temperature of 
 such a burner may be taken at 1,700. A platinum wire, 
 heated almost to the point of fusion (1,800 according to 
 H. Sainte-Claire Deville) by a galvanic current, emits in 
 luminous rays -^ of the energy imparted to it and f-J i n non ~ 
 luminous rays, while in Tyndall's electric arc produced by 
 50 Grove's elements ^ of the rays produced were luminous. 
 
 Proceeding on these important data I have first reproduced 
 a dynamo-electric current of the strength due to 50 Grove's 
 elements, and have found that Tyndall's arc would be produced 
 by a current of about 5 amperes and 36 volts, giving a light 
 of 20 carcels measured in a horizontal direction. The tem- 
 perature of an arc of this kind was given by M. Becquerel 
 in 1860 as between 2,070 and 2,100. An arc produced by 
 a current of 43 amperes and 42 volts according to my own 
 experiments gives 450 carcels ; whence it follows that in the 
 latter case Vo x A x II x TV = i approximately of the total 
 energy appears in the form of luminous rays. The tempera- 
 ture of this arc, following the analogy drawn from other 
 sources of light, cannot exceed 2,500. 
 
 According to the data of Professor Langley, a quarter only 
 of the energy which reaches us from the Sun is luminous 
 (including therein the ultra-violet rays), and admitting that a 
 considerable portion of the latter is absorbed before reaching 
 our atmosphere, it still follows that the temperature of the 
 photosphere cannot much exceed that of our most powerful 
 electric arcs, it may be 2,800. 
 
 The total quantity of radiant energy proceeding from a 
 
ABSORPTION OF SUN'S RAYS IN SPACE. 59 
 
 given surface is dependent in the first place on the nature 
 of the radiating body. This will be a minimum in the case 
 of a solid body with a smooth surface, and a maximum in a 
 thick mass of incandescent gas, for it is a known fact in 
 physics, and specially confirmed in the case of the photo- 
 sphere by the researches of Professor Langley, that heat- 
 rays traverse incandescent gas almost without absorption. 
 The prodigious radiation of the photosphere is then a 
 proof of its great thickness, while its temperature can 
 be determined by the proportion of luminous rays which it 
 emits, a proportion not greatly exceeding that which we meet 
 with in our electric arcs. It appears, then, that whatever may 
 be the interior temperature of the Sun, that of the photo- 
 sphere which surrounds it is not beyond the conditions 
 necessary for combustion, of which the temperature limit 
 is 3,000, supposing the density equal to that of our atmo- 
 sphere. But the current does not descend below the photo- 
 sphere, and it is therefore unnecessary to presume that a 
 second, decomposition of the matter combined in the 
 photosphere must take place. 
 
 Another objection raised by M. Hirn relates to the trans- 
 mission of the light of the stars through vast distances, 
 filled, according to my views, with an absorbing medium. It 
 appears to me that the doctrine of the diminution of the 
 intensity of light in proportion to the square of the distance 
 is not applicable without modification to the light of the 
 stars. Professor Langley has proved that a considerable 
 portion of the solar light is lost by absorption before reaching 
 our atmosphere, this being especially the case with the blue 
 rays ; further, Mr. J. W. Draper, of New York, has stated in 
 his scientific memoirs, that it is especially the yellow ray 
 which decomposes the carbonic acid and water in the leaf- 
 cells of plants, and my researches on the chemical effect of 
 electric light on vegetation, continued for four years, confirm 
 his observations. On the other hand the diagrams of the 
 solar spectrum 1 by Professor Langley show great gaps, where 
 1 See Appendix, pp. 102 aiid 104. 
 
60 CONSERVATION OF SOLAR ENERGY. 
 
 no effect is produced on the bolometer. May it not be possible 
 that there exist in the luminous spectrum wave-lengths less 
 favourable to the decomposition of certain vapours, and there- 
 fore capable of traversing space filled with these rarefied gases 
 to a far greater distance than other rays ? Several astronomers 
 have expressed the opinion that besides the visible stars 
 there exist millions of stars of which the light never reaches 
 us, a hypothesis which accords with my view of the existence 
 of a gradually absorbing medium. 
 
 The third objection of M. Hirn is based on the mechanical 
 resistance which a material gas diffused through space would 
 offer to the movements of the planets : he shows that to 
 satisfy the sidereal retardation admitted by Laplace of ninety 
 seconds in the last 3,000 years, a degree of rarefaction is 
 necessary such that one kilogram of gas occupies a volume to 
 700,000,000,000 cubic metres. The learned mathematician 
 does not tell us whether in his calculation he took account 
 of the tangential motion of the planet, or only of the duration 
 of its year. A diminution of tangential velocity would 
 involve a reduction of the mean distance from the Sun, and 
 consequently, following the third law of Kepler, the decrease 
 of velocity would have very little effect on the length of 
 the year. 
 
 It would be of interest to know what is the physical law 
 on which M. Hirn has based his calculations of air resistance ; 
 the classical researches of Poncelet and others relate almost 
 exclusively to the motion of fluids confined in channels, and are 
 therefore inapplicable, while for the motion of solids through 
 unconstrained fluids we are still in want of a well-founded 
 experimental basis. As far as I know, the only effective 
 experiments on a large scale on the resistance of uncon- 
 strained fluids are those undertaken at Torquay by the 
 late Mr. William Froude for the English Admiralty. The 
 striking results at which Mr. Froude arrived are described in 
 a paragraph of his presidential address to the Mechanical 
 Section of the British Association in 1875. He says : 
 
 " The theory of stream lines discloses to us the startling 
 
RESISTANCE OF FLUIDS TO SOLIDS. 61 
 
 but true proposition, that a submerged body, if moving at a 
 uniform speed through a perfect fluid, would encounter no 
 resistance whatever. By a perfect fluid, I mean a fluid which 
 is free from viscosity, or quasi-solidity, and in which no 
 friction is caused by the sliding of the particles of the fluid 
 past one another, or past the surface of the body." 
 
 He adds : 
 
 " I cannot pretend to frame a list of the many eminent 
 mathematicians who originated or perfected the stream line 
 theory; but I must name from amongst them Professor 
 Rankine, Sir William Thomson, and Professor Stokes, in 
 order to express my personal Indebtedness to them for 
 information and explanations, to which chiefly (however 
 imperfectly utilised) I owe such elementary knowledge of 
 the subject as alone I possess." 
 
 On the other hand, among the experiments made to 
 determine the resistance of solids wholly immersed in fluids, 
 we have anemometrical experiments, which give by no means 
 concordant results. The English meteorologists, in observing 
 wind-pressure on a surface one foot-square, have deduced a 
 resistance of 61 Ibs, (260 kilograms per square metre) for 
 a velocity of 50 metres per second ; whereas General Didion, 
 employing discs of one square metre area, has found for the 
 same velocity a total resistance of 194*7 kilograms, or only 
 40 Ibs. per square foot. 
 
 Our most eminent mathematicians have maintained 
 hitherto that these discrepancies arise from errors of obser- 
 vation, and that a given wind should produce at least as much 
 pressure per square foot on a large surface as on a small. 
 
 An important series of observations has however been 
 made very lately under the direction of Messrs. Fowler and 
 Baker (the well-known engineers of the great projected 
 bridge over the Frith of Forth), the result of which does not 
 accord with that view but is consistent with the theory 
 advanced by Mr. Froude. They have established on a small 
 island in the Frith of Forth three anemometrical plates, the 
 centre one having an area of 27 square metres (12 feet high 
 
62 CONSERVATION OF SOLAR ENERGY. 
 
 by 20 feet broad), and those on either side, circular in form, 
 being 1/6 ft. in diameter, equivalent to an area of '18 
 square metre. They found that the same wind, normal to 
 the surface, produced a pressure of 15*4 Ibs. per square foot 
 (65'1 kilograms per square metre) on the small, and 8*4 Ibs. 
 per square foot (35'3 kilograms per square metre) on the 
 large plate. 
 
 Following a like proportion, the pressure of the same wind 
 on the surface of an exposed building would probably not 
 exceed 3 Ibs. per square foot of surface, a pressure more 
 consistent with facts of observation than that deduced by a 
 calculation based on the uniformity of pressure per unit of 
 surface. Distributed over the enormous surface of a planet 
 the resistance would probably not exceed xoVir part of that 
 deducible from the laws of resistance hitherto assumed by 
 physicists, and based on the idea of actual impact ; whereas 
 according to the laws developed by Froude, the resisting 
 elastic fluid (without boundaries) simply performs a lateral 
 oscillation of small intensity in allowing the solid body to 
 pass. The atmosphere of our earth, instead of being swept 
 away, would, according to these views, have the useful effect 
 of rilling the space in front and in rear, and of thus acting 
 the part of lubricating matter. Unless all these physical 
 researches are without value, the resistance to the motion of 
 the planets in an elastic and very rare medium must be 
 a mere fraction of the amount hitherto generally accepted. 
 
 May I be permitted, before concluding, to recapitulate in 
 favour of my hypothesis the following points already brought 
 forward by me on previous occasions: the gas contained in 
 meteorites and in the nuclei of comets; the zodiacal 
 light ; the equatorial extension observed in America on the 
 occasion of the total eclipse of 1880 ; 1 the recent spectroscopic 
 researches by Captain Abney, showing the presence of hydro- 
 carbons in space between the solar and terrestrial atmospheres. 
 To these I may add the careful observations on the Sun 
 made by Mr. R. C. Carrington, and described in his work 
 
 1 See p. 91. 
 
SUN SPOTS AND THE EQUATORIAL CURRENT. 63 
 
 Observations on the Spots of the Sun, 1863 ; Mr. Carrington 
 has established by these important observations that the 
 angular motion of the photosphere is not the same from the 
 equator to the poles. A revolution is completed in 24'9 days 
 at the equator, in 26 at the latitude of 25, and in 27'4 days 
 at 50 latitude, the retardation in the two hemispheres being 
 almost identical. To what cause should we be able to 
 attribute such a retardation, if it is not to a current of new 
 matter, which, entering at the polar surfaces and receiving the 
 rotatory motion by friction against the penumbra, gives rise 
 in the intermediate zone to great disturbances the Sun spots ? 
 It is probable that such matter, entering the photosphere at 
 the poles, will cause a movement within the solar atmosphere 
 analogous to our terrestrial trade-winds; only it must be 
 remembered that the trade-winds are the result of the solar 
 rays in heating the terrestrial air in the tropics, whereas in the 
 Sun no similar cause of motion exists. It can easily be shown 
 on the contrary that if the Sun rotated with his atmosphere 
 in empty space, the only effect produced would be a moderate 
 accumulation in a direction normal to the axis of rotation ; 
 this eccentricity once established, all atmospheric motion in a 
 tangential direction must cease. The polar retardation, then, 
 which is observable in the photosphere, furnishes, I submit, an 
 incontestable proof of a great inflow from without of gaseous 
 matter at the polar surfaces, passing to the equator, and 
 thence into universal space. In the absence of an opposing 
 force, this vast current must expand in the plane of the 
 ecliptic, and become finally part of the interstellar material : 
 centuries may elapse before the same atoms, which thus leave 
 the Sun to-day in a state of combination, will return to him 
 again dissociated by solar radiant energy. 
 
64 CONSERVATION OF SOLAR ENERGY. 
 
 ON A LETTER OF M. SPOERER CONCERNING A PECULIARITY 
 OF SOLAR MECHANICS. 
 
 A Note communicated to the Academic des Sciences ly M. Faye, 
 and translated from the Comptes Rendus, December 4<th, 
 1882. 
 
 THE attention of the Academy has recently been specially 
 directed to the physical constitution of the Sun. According 
 to the theory of Dr. Siemens, the Sun is fed by matter 
 which enters at the poles, and having undergone combustion, 
 flows along the surface of the Sun towards the equator, 
 where by centrifugal force it is projected into space away 
 from the Sun. 
 
 It would appear that the centrifugal force is not capable of 
 producing such an effect, since solar gravity is 48,000 times 
 as great. 1 If, however, the existence of a surface current 
 from the poles to the equator be assumed, it would afford an 
 explanation of some of the phenomena of the photosphere 
 for example, the spots. These spots, especially the more 
 remote, would be urged towards the equator, their heliocentric 
 latitude diminishing with the time. The following letter of 
 M. Spoerer bears very directly on this hypothesis, though 
 undoubtedly the learned observer of Potsdam had no idea 
 of testing it, his object being to elucidate a delicate and 
 important point in the theory of Sun spots : 
 
 " POTSDAM, November 27th, 1882. 
 
 " Since my last letter, I have concluded my study on the motion in 
 latitude of the Sun spots, which I had undertaken on the appearance of 
 a work on the subject published by M. de Rico in the Memorie degli 
 Spettroscopisti italiana of June, 1882. 
 
 1 Unless gravitation towards the centre of the Sun should be almost counter- 
 balanced by the repulsive force which the Sun would exert on matter in a 
 state of extreme tenuity, as is the case with the tails of comets. 
 
M. SPOERER ON MOTION OF SUN SPOTS. 65 
 
 " M. de Rico found from observations in the year 1881 that between 
 the parallels of + 15 and- 15 of heliocentric latitude the majority of 
 the spots were directed towards the equator, whereas the motion in 
 latitude of spots more remote from the equator was towards the poles. 
 
 " Carrington had remarked the same, but had found the motion too 
 small to attach any importance to it. For my part I had not concerned 
 myself with the question, as it had appeared to me that these small 
 movements took place indifferently in either direction. I have just 
 resumed my observations of the last twenty years (1861 to 1880) on this 
 subject, and have arrived at the following results : 
 
 " The spots have been divided into two groups : 
 
 " 1. Those observed during a single rotation. 
 
 "2. The spots of longer duration observed during two rotations at 
 least. These latter results have the advantage that they are not sensibly 
 affected by the slight uncertainty regarding the position of the solar 
 equator. 
 
 I. 
 
 " In the following table I have included only those spots which have 
 changed at least 0'4 in latitude during n 2 days, n being the number 
 of observations on each spot. The sign -f- indicates increasing latitude, 
 the sign decreasing latitude, and the number includes those spots 
 which have changed less than 0'4. 
 
 Latitude. 
 
 Northern 
 Hemisphere. 
 
 Southern 
 Hemisphere. 
 
 On both 
 Hemispheres. 
 
 
 
 
 + 
 
 
 
 
 
 + 
 
 
 
 
 
 + 
 
 
 
 
 
 From 
 
 
 
 to 5 
 
 2 
 
 14 
 
 4 
 
 4 
 
 6 
 
 2 
 
 6 
 
 20 
 
 6 
 
 
 
 5 
 
 10 
 
 5 
 
 34 
 
 10 
 
 3 
 
 22 
 
 9 
 
 8 
 
 56 
 
 19 
 
 tt 
 
 10 
 
 15 
 
 4 
 
 25 
 
 6 
 
 9 
 
 33 
 
 5 
 
 13 
 
 58 
 
 11 
 
 
 
 15 
 
 20 
 
 5 
 
 16 
 
 5 
 
 
 24 
 
 8 
 
 5 
 
 40 
 
 13 
 
 
 
 20 
 
 25 
 
 5 
 
 10 
 
 2 
 
 2 
 
 11 
 
 1 
 
 7 
 
 21 
 
 3 
 
 Above 
 
 25 
 
 
 
 8 
 
 2 
 
 4 
 
 10 
 
 4 
 
 4 
 
 18 
 
 6 
 
 " From the above table it appears that there is a slight excess of spots 
 between the parallels 5 and 10, whose motion is towards the equator, 
 and also a slight excess of spots between 20 and 25, which move 
 towards the poles. 
 
 " The following series is rather more decisive. 
 
 II. 
 
 " Here the minimum displacement is 0'4 in twenty days, and the 
 sign -f and have the same meaning as before. The sign includes 
 those spots whose motion in latitude has been less than 0'4 in twenty 
 
 F 
 
66 CONSERVATION OF SOLAR ENERGY. 
 
 days. The last column indicates the motion during twenty- seven days 
 of all the spots indifferently. 
 
 Latitude. 
 
 Northern 
 Hemisphere. 
 
 + - 
 
 Southern 
 Hemisphere. 
 + - 
 
 On both 
 Hemispheres. 
 + - 
 
 Mean variation 
 for 27 days. 
 
 From 
 
 
 
 to 5 
 
 1 
 
 
 
 3 
 
 5 
 
 2 
 
 3 
 
 6 
 
 2 
 
 o-o 
 
 n 
 
 5 
 
 10 
 
 2 3 
 
 5 
 
 2 
 
 5 
 
 5 
 
 4 
 
 5- 
 
 10 
 
 -0-28 
 
 ,, 
 
 10 
 
 15 
 
 3 10 
 
 5 
 
 6 
 
 1 
 
 5 
 
 9 
 
 11 
 
 10 
 
 -0-04 
 
 ,, 
 
 15 
 
 20 
 
 5 9 
 
 3 
 
 1 
 
 3 
 
 1 
 
 6 
 
 12 
 
 4 
 
 + 0-19 
 
 ,, 
 
 20 
 
 25 
 
 7 2 
 
 2 
 
 1 
 
 3 
 
 1 
 
 8 
 
 5 
 
 3 
 
 + 0-63 
 
 Above 
 
 25 
 
 
 3 1 
 
 
 
 3 
 
 2 
 
 
 
 6 
 
 3 
 
 
 
 4-0-91 
 
 TOTALS 20 26 15 16 19 14 36 42 29 
 
 " The mean values given in the last column are for the most part 
 exceedingly small, and their significance depends entirely on the 
 regularity of their increase. 
 
 " The numbers themselves in this column are uncertain ; but it 
 would be useless to give the probable errors, as their uncertainty is 
 sufficiently shown by comparison with the numbers given in the 
 adjoining columns." 
 
 It is apparent that all these observations from Langier and 
 Carrington to M. Spoerer, extending over a great number of 
 years, agree in showing that the displacement of the spots 
 in latitude is either inappreciable or very small, and that the 
 spots remote from the equator tend towards the poles, rather 
 than in the opposite direction. 
 
 This result is in direct opposition to the theory, to which 
 I previously alluded. It is, moreover, confirmed by all that 
 we know of the other superficial formations of the Sun, 
 granulations, faculae, indentations of the chromosphere, pro- 
 tuberances. None of these give evidence of a great current 
 from the poles to the equator. Further, there remains the 
 crucial question, independent of all hypotheses, as to the 
 direction of the currents of the photosphere. I have carefully 
 studied this point, and confining myself exclusively to the 
 spots of long duration, have concluded that they move neither 
 towards the poles nor towards the equator, their small 
 movements in latitude being purely oscillatory and confined 
 within very narrow limits. 
 
 In the last very remarkable communication which 
 Dr. Siemens has addressed to us in reply to the objections 
 
M. FAYE ON MOTION OF SUN SPOTS. 67 
 
 of M. Him, he treats these questions fundamentally. He 
 believes that the increase in angular velocity of successive 
 zones, in proportion to their proximity to the equator, is due 
 to the retarding effect in the polar zones of the influx 
 of matter at the poles, not originally possessing any rotation. 
 This polar current, he says, would give rise in the intermediate 
 zone to those immense whirlpools, the spots. 
 
 It is precisely the hypothesis long ago adopted by Sir John 
 Herschel ; and I should myself have admitted the same, had 
 I been able to verify by the observations of Langier and 
 Carrington the existence of currents from the poles to the 
 equator. There would be, in fact, a phenomenon analogous 
 to that we are acquainted with in our own atmosphere, where 
 the lower currents flow towards the equator, and the upper 
 currents, which Herschel supposed also to exist in the Sun, 
 from the equator to the poles, forming and carrying with 
 them huge vortices, or cyclones. 
 
 But neither Langier nor Carrington nor I have found 
 anything similar in the Sun, and we have just seen that 
 M. Spoerer, during his twenty years' observations, has not 
 discovered the least trace of the movements from the pole 
 to the equator, which Dr. Siemens requires for his theory. 
 
 If, then, a retardation of the surface rotation takes place, 
 and the fact is beyond dispute, we must seek the cause, not 
 in a medium exterior to the Sun, as does Dr. Siemens, nor 
 in an inadmissible flattening of his atmosphere, like Sir 
 John Herschel, but in the ascending and descending move- 
 ments which are continually taking place in the internal 
 mass, and which incessantly bring into contact with the 
 photosphere masses having a smaller linear velocity, and 
 which then participate in the surface radiation, entirely 
 escaping solidification. 
 
 F 2 
 
68 CONSERVATION OF SOLAR ENERGY. 
 
 ON THE CONSERVATION OF SOLAR ENERGY. 
 
 A Reply, ly M. G. A. Him, to the Critical Note addressed 
 to the Academic des Sciences ly Mr. C. W. Siemens, and 
 translated from the Comptes Rendus, December llth, 1882. 
 
 IN the Comptes Rendus of November 27th, Mr. Siemens 
 endeavours to answer the various objections I put forward 
 against his new theory on the Conservation of Solar Energy. 
 It is easy to show that the reply of the eminent physicist 
 does not refute my arguments. 
 
 1. With regard to the temperature of the photosphere 
 of the Sun, I have relied on what Mr. Langley has published 
 in the Proceedings of the American Academy of Arts and 
 Sciences, October 9th, 1878, p. 116. 
 
 Having, with the aid of a new and original experimental 
 method compared the radiation of the Sun with .that of 
 Bessemer steel in fusion, Mr. Langley has found that for 
 an equal area of radiating surface, the first is eighty-seven 
 times as great as the second ; and this number is a minimum. 
 The actual number is necessarily much greater, according 
 to the author himself, if account be taken of the conditions 
 under which the experiment took place. Mr. Langley shows 
 besides that the temperature of this steel, when in fusion, 
 would be nearly 2,000. 
 
 If the description of the experiments of Mr. Langley be 
 carefully followed, and his judicious manner of employing 
 the thermo-electric pile noted, it is easy to see that the 
 expression "magnitude of radiation" does not mean the 
 " quantity of heat " emitted in a given time, but rather the 
 intensity of the heat, or, in other words, the temperature. 
 As all physicists will agree, the researches of Mr. Langley 
 are among the most beautiful on the subject, and in my 
 estimation are decisive in determining the minimum tem- 
 perature of the Sun, in assuming which at 20,000 I was 
 probably within the actual value. 
 
M. HIRN ON THE SUN'S TEMPERATURE. 69 
 
 In support of this I would farther put forward an argument 
 of a very different nature. Among the many claims of 
 Mr. Clausius to the gratitude of the scientific world, one of 
 the most prominent is the way in which he has analysed 
 what constitutes the temperature of a body. He shows that 
 a temperature cannot be raised by merely concentrating rays ; 
 that if, with a perfect concave mirror, we could gather together 
 all the heat radiated from a body at 100, for example, a 
 thermometer placed at the focus would not be raised above 
 100. I say " above," although in taking account of all the 
 causes of loss which would in this case intervene, it is evident 
 that the 100 would never be reached in reality. 
 
 It follows that if, by the aid of concave mirrors and lenses, 
 we could concentrate the solar rays on a very small surface, 
 the temperature indicated by a thermometer placed at the 
 point of concentration would only be a minimum in com- 
 parison with the real temperature of the Sun. Experiments 
 which have hitherto been made have shown that in the 
 proportion in which we increase the surface of the lenses 
 and reflectors, the temperature at the focus is raised, and 
 we can only guess a limit to this elevation. Now we know 
 that with the aid of the imperfect lenses at our disposal we 
 can ignite diamond and melt platinum ; it is then more than 
 probable that with larger and more perfect reflectors and 
 refractors, such as we could now construct, the effect would 
 be proportionately greater. Accepting, however, what we 
 have found as a limit, and noting that from the nature of 
 the experiment more than -$ of the disposable solar light and 
 heat is lost as far as regards its effect on the thermometer, we 
 still arrive at a number much larger than 2,000 as the real 
 temperature of the Sun. 
 
 If, then, the temperature of the Sun cannot be nearly so low 
 as that admitted by Mr. Siemens and others, my first objection 
 remains in its entirety : the chemical compounds supposed to 
 be produced during the approach to the Sun would be again 
 dissociated, and the heat thereby developed would be absorbed 
 in the dissociation. 
 
70 CONSERVATION OF SOLAR ENERGY. 
 
 2. I pass at once to the third objection. In the researches 
 which I have made to determine the various effects which 
 would result from the presence of a material fluid in space, 
 I have had recourse to some special analytical methods 
 which I cannot here explain. I confine myself to saying 
 that in forming the equations of the problem I started from 
 the principles generally admitted in Hydrodynamics, on the 
 validity of which I do not think there can be any serious 
 contest. 
 
 A fluid which "offers no resistance to bodies moving in 
 it," certainly does not exist in nature, and can only exist 
 as a mental conception, resting on hypotheses which have 
 not been verified. . . . The combustion of shooting stars, of 
 meteorites, and of aerolites at a height where the density 
 of the air is reduced to one ten-millionth, and perhaps even 
 further than this, show that these bodies experience an 
 enormous resistance on account of their planetary velocity, 
 and there is absolutely no distinction between these phe- 
 nomena and those we study on the surface of the earth. If 
 there is a part of applied mechanics where the laws 
 determined on a small scale hold in practice on an indefinite 
 scale, it is certainly the branch of Hydrodynamics which has 
 for its object the study of the laws of resistance of an 
 unlimited fluid to the motion of bodies, great or small, 
 which are immersed in it ; or inversely, of the pressure 
 exerted by an unlimited fluid in motion on bodies at rest. 
 The degree of precision attainable in ballistic calculations, 
 the exactitude with which it is possible to estimate the 
 mechanical effect of wind on such obstacles as buildings, 
 sails of ships, wind-mills, etc., fully confirm the validity of 
 the principles on which the calculations are founded. Except 
 by inventing new properties of matter, and entering into 
 the region of arbitrary hypothesis, we have no authority 
 whatever for saying that a material fluid extended through 
 space would behave with regard to the planets, comets, and 
 asteroids, otherwise than the air would behave, in a degree 
 proportional to its density, with regard to the bodies, great 
 
DR. SIEMENS'S REPLY TO M. FAYE AND M. HIRN. 71 
 
 or small, which move in it, and in particular with regard to 
 these same asteroids in the form of shooting stars, or meteorites. 
 In a word, I maintain the fraction 0'0,000,000,000,000,001 
 as expressing the density of a material interstellar fluid, 
 whose existence, if supposed real, would render our planetary 
 atmospheres impossible. 
 
 ON SOLAR ENERGY. 
 
 Further reply, by C. W. Siemens, to M. Faye and M. Him, and 
 published in the Comptes Rendus, January 2nd, 1883. 
 
 IT is with some hesitation that I again venture to address 
 the Academie des Sciences in defence of my hypothesis 
 regarding the conservation of solar energy ; I trust, however, 
 that M. Faye and M. Hirn will pardon me for pointing out 
 where they misapprehend, as it appears to me, some of the 
 physical laws and conditions upon which I rely for proof of 
 my views regarding a question which has attracted the 
 attention of physicists in several countries. 
 
 M. Faye, in answering Dr. Spoerer (Comptes Rendus, 
 4th December), makes two critical observations regarding my 
 hypothesis, which, if admitted, would destroy its very founda- 
 tion. He says that the centrifugal force upon the solar 
 equator amounts to only T 8innr P ar * f s l ar gravitation, and 
 .that expulsion into space by centrifugal force is out of the 
 question, unless we assume some imaginary expansive force 
 such as appears to be active on the tail of comets. I am 
 anxious to state that I am well aware of the great superiority of 
 solar attraction over centrifugal force at the solar surface 
 (which I had evaluated at T ^J^o) ; nor do I assume any 
 expansive forces different from what we can verify by experi- 
 ments in our laboratories. 
 
 In order to illustrate perhaps more clearly than I have 
 hitherto done the cause of the powerful outflowing current 
 which I regard as a necessary consequence of fluid material, 
 however attenuated, filling stellar space, I will suppose the 
 
72 CONSERVATION OF SOLAR ENERGY. 
 
 existence of a bent tube (similar to that referred to by 
 Newton in his Principia) passing from the solar centre in the 
 equatorial and the polar direction respectively, both branches 
 extending to an immaterial but equal distance into space. 
 The effect of solar gravitation on the matter contained within 
 the two branches of this tube, would be to cause the same 
 density in both at equal distances (the temperatures being 
 equal), according to the law of Mariotte. At any distance, 
 R, from the centre, an increment of, say, a centimetre in 
 length in one branch, would be precisely balanced by a similar 
 increment at the distance, R, in the other branch. If now the 
 equatorial arm of the tube was made to partake of the solar 
 rotation, the equilibrium of pressures towards the centre 
 would be immediately disturbed, the two increments at the 
 distance, R, would no longer balance, but the one in the 
 equatorial direction would move outwards, causing that in 
 the polar direction to move inwards; the places that had 
 been occupied by this matter would be immediately taken 
 up by similar matter within the tubes, and the same want 
 of equilibrium would be immediately applicable to these 
 similar volumes of fresh matter, causing them to move a 
 further step in the same direction. The same disturbing 
 cause of equilibrium being applicable continually and for 
 every value of R, and the stellar material beyond the tube 
 having free access to the same, it follows that a current must 
 be established passing towards the Sun in the polar and from 
 the Sun in the equatorial arm of the tube. 
 
 Solar gravitation determines the density of the gaseous 
 columns within the two arms of the tube equally without 
 impeding their flow ; on the contrary, the greater the density 
 due to solar gravitation, the greater will be the effect of 
 rotation upon the gaseous column, and the more determinedly 
 will the current flow through the hypothetical tube. I need 
 hardly add that what is proved for the confined area within 
 such a tube must be true also for all free matter, extending 
 from the Sun into space in the radial and equatorial directions, 
 and the amount of matter thus circulating has to be estimated 
 
SUN : S MECHANICAL AND CHEMICAL WOEK. 73 
 
 by the two factors its tangential velocity at the solar equator, 
 and the vast superficial area of the equatorial region. In 
 flowing outward this current would expand into larger and 
 larger sectional areas, causing its onward velocity, in reaching 
 stellar density, to diminish, whereby its kinetic energy will 
 be converted into potential energy or pressure, before mingling 
 with the great interstellar ocean of gaseous matter through 
 which our whole Solar System is supposed to move. This 
 potential energy or pressure, affecting matter in space, serves 
 to generate, by gradual acceleration, the polar current, in the 
 manner illustrated by the hypothetical bent tube. 
 
 The power necessary to maintain this current must be 
 derived from solar rotation, but considering that the matter 
 arrives at the surface of the Sun with a certain velocity, 
 the Sun has only to supply as much rotatory energy as is 
 necessary to effect a change of direction, and to make up 
 for intermolecular friction. As regards this mechanical 
 action, the second 1 law of Thermodynamics (as developed 
 chiefly by Clausius and Rankine) applies, that is to say, 
 a certain amount of solar heat must descend from a higher 
 to a lower potential ; but inasmuch as the mechanical power 
 required to maintain the current, is small in comparison with 
 the chemical work performed in dissociation (and to which 
 the second law of Thermodynamics does not apply), the 
 cooling effect involved must also be relatively small, and this 
 loss of heat may possibly be replaced by solar shrinkage 
 (the enormous value of which has been demonstrated by 
 Helmholtz), by the falling into the Sun of planetary matter 
 as suggested by Mayer, Waterston, and by convection currents 
 from the interior of the Sun, as suggested by Sir William 
 Thomson. It may be interesting to observe that the supposed 
 mechanical action of the Sun is accomplished with the least 
 possible expenditure of solar heat, because the range of 
 absolute temperatures, T T, upon which the economy of 
 every caloric engine depends, amounts in the case of the Sun, 
 to say 2930 Centigrade, as contrasted with 160, the greatest 
 working range of temperature obtainable in a steam-engine. 
 
74 CONSERVATION OF SOLAR ENERGY. 
 
 M. Faye, referring to the researches of Dr. Spoerer, and to 
 his own important investigations regarding the irregular 
 deviations in heliocentric latitude of Sun spots, points out that 
 Sir John Herschel was mistaken in ascribing the existence of 
 those spots to a solar equatorial current due to polar flattening 
 of the solar atmosphere. I accept M. Faye's view that the 
 polar depression of the Sun being very slight, no appreciable 
 equatorial current could be ascribed to it ; but I venture to 
 think that if Sir John Herschel had imagined the existence of 
 a polar current of light material, taking its origin outside 
 the solar atmosphere, his deductions regarding the cause of 
 Sun spots would have been consistent with the facts of 
 observation. 
 
 We have on our earth analogous conditions to those which 
 my hypothesis supposes to exist on the Sun (but in the inverse 
 order), in the form of a heated and expanded equatorial 
 current. The equatorial or trade-wind current gives rise in 
 our latitude to those cyclones, the approach of which on 
 western shores is very frequently communicated to us by the 
 Atlantic telegraph. These cyclonic currents pass across the 
 Atlantic, sometimes with a southern and at others with a 
 northern deviation ; but they necessarily follow in the main, 
 and in obedience to the laws of gyration, an easterly course, 
 and if they could be seen from a point in space would appear 
 to pass around the earth in about twenty-three hours and 
 forty minutes. The supposed solar current in passing from 
 the poles towards the equator would cause cyclones showing 
 an acceleration in the opposite sense, that is to say, would 
 effect a solar revolution in say twenty-seven instead of twenty- 
 five terrestrial days. Their deviations in heliocentric latitude 
 would be influenced on the one hand by the generating current 
 forcing them towards the equator, and on the other hand by 
 their own vortex action in the dense metallic vapour of the 
 Sun forcing them towards the pole. I shall be required, no 
 doubt, to furnish an explanation of this latter action, which 
 I attribute to the circumstance that a cyclone occupying 
 say 1 in 30 latitude would in advancing latitudinally have 
 
DR. SIEMENS ON SUN SPOTS OR CYCLONES. 75 
 
 less matter to displace on the side towards the pole, 
 where the solar diameter is inferior, than on that towards 
 the equator, where the solar diameter is superior. Having 
 less mass to move in the smaller circle facing the pole, it 
 will encounter less resistance in that direction and will there- 
 fore verge towards the pole. The relative importance of 
 the two forces would be determined by the depth to which 
 the cyclone is rooted in the inferior metallic vapour, or the size 
 of the spot, and by its angular distance from the pole. This 
 vortex pressure would increase necessarily with the degree of 
 solar latitude, and we should thus find a rational explanation of 
 Dr. Spoerer's important observations, to the effect that the spots 
 of high latitude tend towards the pole, while those of the 
 equatorial regions verge more frequently towards the equator. 
 It would be important to know whether in the same latitude 
 the deeply rooted or larger spots do not more frequently 
 verge towards the pole, and the smaller or superficial ones 
 towards the equator. 
 
 If the observed retardation of the solar photosphere were 
 due to the sudden transportation of matter from an inferior 
 to a superior radius of the Sun's body, the retarding effect 
 thus produced could certainly not be less near the equator 
 than near the pole, and there would apparently be no reason 
 why Sun spots should be seen any less at the pole or the 
 equator itself than within the two intermediate regions. If 
 we may suppose the lower atmosphere of the Sun to consist 
 of comparatively dense metallic gases at a high temperature, 
 cyclonic action would have the effect of drawing photospheric 
 matter into the vortex funnel ; here solar dissociation, alluded 
 to by M. Hirn, would undoubtedly take place, giving rise in 
 the first place to a local depression of temperature the 
 appearance of darkness and in the next to explosive action 
 caused by a temporary release from pressure at great solar depth. 
 Streams of vivid light must also appear on the dark back- 
 ground, whenever the dissociated matter again reached a 
 sufficient elevation to admit of recombustion. Thus far, then, 
 I am disposed to agree with M. Hirn, that redissociation upon 
 
76 CONSERVATION OF SOLAR ENERGY. 
 
 the solar surface may actually take place, but the ultimate 
 heating effect due to an inflowing and outflowing current 
 such as I suppose, must be determined by the chemical 
 condition of that current on entering and leaving the solar 
 photosphere, the intermediate changes being capable of producing 
 local disturbances without affecting the final balance of cause 
 and effect. 
 
 M. Him formulates his objection to the working of my 
 hypothesis under two distinct heads (Comptes Rendus, 
 December llth), to which I venture to make the following 
 reply. Regarding the temperature of the solar photosphere, 
 I admire with him the ingenuity and value of Mr. Langley's 
 investigation " On the Temperature of the Sun " as recorded 
 in the Proceedings of the American Academy of Arts and 
 Sciences, for May 1879, though I must differ from him as 
 regards some of the conclusions which he draws from Mr. 
 Langley's investigation. I fully accept Mr. Langley's conclu- 
 sion to the effect "that the determinations of M. Violle 
 placing the temperature of the photosphere at 1500C. are 
 evidently considerably too low, and that it is demonstrably 
 over 1800 C. and may be considerably above that temper- 
 ature ; " * nor do I disagree with Mr. Langley when he states 
 that the solar heat radiation must be as a minimum something 
 like 100 times greater than that from melted platinum, seeing 
 that he guards himself against being understood to say, that 
 this greater radiation proves any particular temperature 
 in excess of the 1800 C., which latter he adopts indeed as 
 his minimum. In his quantitative experiment a smooth 
 surface of fluid metal is compared with the gaseous photo- 
 sphere, and no allowance is made for the important factor, 
 ra, in Dulong and Petit's formula; nor does Mr. Langley 
 attempt to establish a ratio of dependence of radiation with 
 increase of temperature. I may here remark that the solar 
 
 1 M. Violle, in a letter addressed to the Academic des Sciences, and which 
 appeared in the Comptes Rendus of 22 January, 1883, admits that the temper- 
 ature of the solar photosphere must exceed 1800, and accepts my estimate 
 making it nearly 3000 Centigrade. 
 
DR. SIEMENS'S EXPERIMENTS WITH REFLECTOR. 77 
 
 temperature of 2800 C. at which I arrived by a different 
 process of reasoning is just 1000 G. above Mr. Langley's 
 minimum a difference quite sufficient I consider to harmonise 
 his observations as regards amount of radiation with my own. 
 The opinion on this question of Sir William Thomson, must 
 be deemed of great interest by all physicists ; in a paper 
 communicated by him quite recently to the Philosophical 
 Society of Glasgow on Photometric Measurement, he says : 
 " In the year 1878 Kosetti reckoned the solar temperature 
 to be about 9000, but possibly the most probable value 
 yet assigned was that of C. Wm. Siemens, about 3000 
 Centigrade." 
 
 When M. Hirn, referring to the investigation of Clausius, 
 says that the temperature of a focus of light or heat can 
 never exceed that of the surface, whence the radiant energy 
 is derived, I am fully prepared to agree with him. It is 
 evident that the temperature produced in the focus of a good 
 parabolic reflector directed towards the solar disc cannot 
 exceed the solar temperature, but I venture to maintain that 
 it can be made to approach that temperature much more 
 nearly than M. Hirn seems prepared to admit ; if the reflector 
 is carefully made, of sufficient size, and placed upon a 
 considerable elevation. The question is one which has 
 particularly attracted my attention, and a few years ago I 
 mounted a heliostat, with a carefully silvered parabolic reflec- 
 tor of 18 centimetres diameter, at my country house near 
 Tunbridge Wells, which is situated about 160 metres above 
 sea level. The principal object I had in view was to ascertain 
 whether dissociation could be produced within the focus. The 
 temperature produced was such that the point of a rod of 
 carbon pushed through a hole at the apex of the parabolic 
 reflector became vividly luminous when reaching the focus but 
 not more so than it would have been in an electric arc of small 
 power. One of the experiments I made consisted in directing 
 an ordinary gas flame through the focus, with the result 
 that the solar rays were sufficient to retard, without sus- 
 pending, the gaseous combustion ; the effect produced was 
 
78 CONSERVATION OF SOLAR ENERGY. 
 
 similar indeed to that observed in the Regenerative Gas 
 (or Siemens) furnace, when employed for the production of 
 mild steel, or fused iron (fer fondu). In this furnace the 
 metal attains approximately the same temperature as in the 
 Bessemer Converter, whereas the portion of the furnace 
 above the metallic bath is at a considerably higher temper- 
 ature, since the heat of the flame is communicated to the 
 metal through a certain thickness of scoria. It is interesting 
 to observe that when this furnace is at its highest heat, the 
 flame has a decidedly bluish appearance, and the rate of 
 combustion is considerably retarded by what constitutes a 
 partial dissociation. The sides of the furnace (of pure 
 silica) attain necessarily almost the same temperature as the 
 flame, yet in first opening the furnace door, and thereupon 
 shutting off the gas supply, an extraordinary decrease of 
 radiant energy is at once perceptible, showing that the 
 gaseous incandescent atmosphere is far superior to the solid 
 refractory substance of the sides in heat radiating power. 
 
 The only means by which I have succeeded in obtaining 
 calorific effects exceeding those of the regenerative gas furnace 
 have been by the use of my electric furnace, which M. 
 Dumas saw at the Electrical Exhibition at Paris, and thought 
 sufficiently interesting to make mention of before the 
 Academy. In employing a current ranging between 250 and 
 300 amperes, I succeeded in melting 4 kilogrammes of 
 platinum in 15 minutes, commencing with a cold crucible, 
 and being desirous of carrying out some further experiments 
 in electric fusion, I induced my friend Professor Huntington 
 to join me in a series of researches, the results of which 
 were communicated to the Chemical Section of the British 
 Association at Southampton in August last, and published in 
 The Engineer of the 8th September, 1882, a reprint from which 
 I enclose herewith. 1 
 
 The difficulty that presented itself in the practical applica- 
 tion of this furnace for metallurgical purposes, was principally 
 due to the circumstance, that during fusion a considerable 
 
 1 See Appendix, p. 91. 
 
DR. SIEMENS ON FLUID RESISTANCE. 79 
 
 portion of the material or metal under treatment assumed the 
 gaseous condition, and issued from the close chamber of the 
 furnace with considerable force through the smallest crevices. 
 Thus in one experiment a weight of 340 grammes of copper 
 was treated for about half an hour, when, at the end of that 
 time, only 21 grammes remained in the crucible, the remainder 
 filling the apartment in the form of a thick and not readily 
 condensible vapour. The furnace temperature was practically 
 limited in these experiments by the point, at which even the 
 most refractory materials, such as Tungsten, assumed the 
 gaseous condition, and considering that evaporation of the 
 metals took place before their fusion was accomplished, I 
 conclude that their evaporative point is not much above their 
 fusing point. 
 
 Regarding the frictional resistance of an attenuated medium, 
 M. Him thinks it necessary to adhere to the extraordinary 
 admissible degree of tenuity of 0*0,000,000,000,000,001 kilo- 
 gramme mentioned in his previous communication. Even this 
 degree of attenuation might suffice for my purpose if it was 
 taken to apply to a distance from the Sun equal to that of 
 Neptune or Uranus ; but I hope that further evidence will be 
 produced to establish my deductions to the effect that planetary 
 resistance, if calculated upon the formulae now generally applied 
 to ballistic problems, would enormously exceed the actual re- 
 sistance in a free medium. Mr. Froude' did not deny, nor do I 
 in any way overlook, the great frictional resistance which must 
 be encountered by a projectile of comparatively small dimen- 
 sions in passing through the air, or by a meteorolite passing 
 through the confines of our atmosphere, with a velocity greatly 
 accelerated by terrestrial attraction during its approach ; but 
 both the stream-line theory of Froude, and my own observations 
 regarding anemometer plates of large and small areas, go to 
 prove that the resistance of a comparatively large body or 
 surface encountering a free medium increases much more 
 nearly proportionately to its circumferential development than 
 to its area. I may add, that the further observations reported 
 to Messrs. Fowler and Baker from the Frith of Forth, confirm 
 
80 CONSERVATION OF SOLAR ENERGY. 
 
 those I mentioned in my last communication, and I hope soon 
 to be in a position to bring forward additional proof in support 
 of my views, by means of an apparatus now in course of 
 construction. 
 
 OBSERVATIONS ON THE LAST COMMUNICATION OF DR. 
 SIEMENS ON SOLAR ENERGY : BY M. FAYE. 
 
 Communicated to the Acade'mie des Sciences, and translated 
 from the Comptes Rendus, January 8th, 1883. 
 
 WHEN Mr. Siemens, who has been signally successful in 
 treating electrical forces and high temperatures, refers to his 
 experiments, the reader cannot but derive much advantage by 
 studying his communications; but when he discusses the 
 physical constitution of the Sun, we encounter much which 
 is hard to admit. 
 
 Thus I raised the objection that the equatorial centrifugal 
 force of the Sun is far too weak in comparison with solar 
 gravity to allow the Sun to project into space, the particles 
 arriving at the equator. 
 
 Mr. Siemens answers me by referring to the hypothetical 
 bent tube, to which Newton had recourse in discussing the 
 flattening of the poles of our globe, the tube having one branch 
 along the line of the poles, and the other directed towards any 
 point on the equator. But Newton made the two branches of 
 the tube emerge on the same surface of the planet, whereas 
 Mr. Siemens supposes, in the case of the Sun, a bent tube with 
 indefinite branches extending into cosmical space. When he 
 impresses on the equatorial branch of this tube the rotation of 
 the Sun, it is certain that the centrifugal force at the extremity 
 would increase indefinitely in proportion to the length of the 
 tube, whereas, gravity at the extremity will diminish more 
 rapidly still, in the inverse ratio of the square of the length. 
 Consequently, the equilibrium will be destroyed, the matter 
 will flow out from the extremity of the tube and form a sort 
 of equatorial current, while cosmical matter will be drawn into 
 
M. FAYE'S REPLY TO DR. SIEMENS. 81 
 
 the immovable polar branch. If necessary, Mr. Siemens would 
 make all the gas, with which he fills the universe, pass in this 
 way through his tube. 
 
 But the learned author has not remarked in applying this 
 action to the Sun, that he supposes the Sun has communicated 
 his rotation to the indefinitely extended medium, which 
 according to -the hypothesis surrounds him. This medium 
 would revolve, as if rigidly connected with the Sun, which 
 Mr. Siemens certainly has not in view ; on further reflection 
 I believe that he will find some difficulty on this point. 1 
 
 ON TWO OBJECTIONS OF PROFESSOR YOUNG, OF NEW JERSEY, 
 AGAINST THE CYCLONIC THEORY OF SUN SPOTS : BY M. FAYE. 
 
 A Communication to the Acaaemie des Sciences, and Translated 
 from the Comptes Rendus, December 26th, 1882. 2 
 
 IN Simon Newcomb's Popular Astronomy, Mr. Young, 
 whose beautiful spectroscopic researches on the sun 
 are well known, refers to this theory in the following 
 words : " The theory of M. Faye appears to me, on the 
 whole, to be the most reasonable of all which have been 
 put forward, but it is difficult to reconcile it with the want 
 of visible traces of rotation in the majority of the spots." 
 Quite recently, in a work on the Sun, which has just been 
 published in the International Library of M. Alglave, Mr. 
 Young again raised this objection, and points out a second 
 difficulty which appears to him decisive. It is known that 
 the successive zones of the photosphere have not the same 
 angular velocity. It is to these differences of velocity that 
 
 1 It will be seen from my previous communication regarding the solar fan 
 action that it does not depend on the rotation of the gaseous matter filling 
 space. This matter would enter the polar branch of the hypothetical tube 
 irrespective of any initial motion of the arm, and would be delivered equa- 
 torially with the motion imparted to it by the tube. C. "W. S. 
 
 2 This communication of M. Faye on the nature of Sun spots corroborates 
 in many remarkable points the views expressed by the author in his final 
 reply to MM. Faye and Him. M. Faye's Note, though preceding the author's 
 Letter in date of publication, appeared after the latter had been despatched. 
 
 G 
 
82 CONSERVATION OF SOLAR ENERGY. 
 
 I attribute the formation of the solar cyclones or spots. 
 On the other hand, Mr. Young, availing himself of the 
 formula I have given for the diurnal velocity in any helio- 
 centric latitude 1, viz. : 
 
 862'-186' Sin 2 1. 
 
 finds that the variation from 1 = 20 to 1=20. I' is only 4 J 
 miles per day, while the distance between the two parallels 
 is 123 miles. This appears to him to be insufficient to give 
 rise to cyclones in the Sun. 
 
 I appreciate these objections, but believe them to be 
 anticipated. Cyclones have been taken to imply violent 
 vortices ; and it has been imagined that, if the spots of the 
 Sun are cyclones, the edges should be violently torn and 
 distorted ; the whole should revolve rapidly about the centre, 
 the luminous filaments of the penumbra would be twisted 
 into spirals, etc. If such is necessarily the case, I would at 
 once admit that the appearance of the spots is by no means 
 cyclonic, and that a velocity of 4*1 miles, per day, at a radius 
 of 123 miles, only representing an angular velocity of 2 per 
 day at the edge of the vortex, does not at all correspond to 
 this view. 
 
 But I hope that Mr. Young will be impressed by the simple 
 remark I am about to make on this subject. 
 
 The upper part of the diagram represents a vertical 
 section of a terrestrial tornado ; the lower part represents 
 an ordinary Sun spot with the serrated edge of the photo- 
 sphere, the grey penumbra, the dark nucleus, and the 
 entirely black centre discovered by the Rev. Mr. Dawes, 
 with the exception of some details, physical rather than 
 geometrical. The two figures are the vertical and hori- 
 zontal sections of one and the same object; viz. a vortex 
 about a vertical axis. We see the terrestrial vortices from 
 the first point of view, quite low down, almost at the foot 
 of the vortex, where the motion is very violent, while the 
 upper opening is hidden by clouds. On the other hand we 
 see the solar vortices from above, from the second point of 
 
M. FAYE'S CYCLONIC THEORY OF SUN SPOTS. 
 
 83 
 
 view, showing the vortex projected on the surface of the 
 Sun ; the edge of the vast upper opening being alone visible 
 to us. There, contrary to the lower part, which we do not 
 see on the Sun, the velocity of rotation is very slow. 1 
 
 What we see on the Sun, we should see also on the earth, 
 could we raise ourselves high above the earth and contemplate 
 from a height a horizontal projection of the cyclone or 
 tornado in full action, making a vast opening in the midst 
 
 Earth 
 
 line. 
 
 of our aerial current charged with cirrus. If we were at a 
 sufficient distance, we should see hardly any rotation at the 
 edge, or at least, a very long time must elapse before it 
 
 1 I know nothing more striking than this simple geometrical identity of 
 two phenomena so different in appearance, viz. the Sun spots and terrestrial 
 cyclones. Since the nucleus of the solar cyclone is black, the matter which 
 moves in it is cold, consequently the vortex motion is downwards. Since 
 terrestrial mechanics ought not to differ from solar mechanics, the vortex 
 motion is also downwards in terrestrial cyclones, a conclusion which I have 
 verified with regard to our cyclones, waterspouts,, and tornadoes. 
 
 G 2 
 
84 CONSERVATION OF SOLAR ENERGY. 
 
 became very distinct. As to the dark centre of the cyclone, 
 we should see nothing of the enormous rotation there taking 
 place. 
 
 Almost the only law of Hydrodynamics, relating to vortices, 
 is that the angular velocity in a well-established vortex varies 
 from one point to another inversely as the square of the 
 distance from the axis. Further, if we examined a water- 
 spout having a base a few metres in diameter, and stretching 
 upwards to the clouds, which obscure the mouth of the 
 funnel an opening many hundred times larger than the 
 base we should find at the upper edge a rotation ten thousand 
 times slower and relatively imperceptible. Similarly a cyclone 
 or a waterspout, the angular velocity of whose lower edge is 
 180 per day, which is quite possible at the commencement 
 of a tempest, would not have a velocity of more than 2 per 
 day at the extreme upper edge, where the diameter is 
 perhaps ten times as great. 
 
 Further, the difference of 4*1 miles per day, which Mr. Young 
 finds between the velocities of two points on the photosphere 
 123 miles apart, corresponds exactly to an angular velocity 
 of 2 per day, and this does not preclude that at a sufficient 
 depth ; where the diameter of this imperceptible solar pore 
 is reduced to one mile, the angular velocity will be 30,000 
 per day. 
 
 This slowness of rotation at the edge of the vast funnel 
 of the spots, even when it is prolonged upwards into the 
 chromosphere, clearly explains the disappointment of observers, 
 who complain that they very rarely find any traces of rotation. 
 Such traces would only be visible at the edges, for in the 
 centre, where the rotation is more rapid, there is only the 
 dark and cold gas, which is being rapidly engulfed in the 
 dark hole, discovered by Dawes, corresponding precisely to 
 the constricted part of the funnel of our aerial vortices. 
 
 If the luminous clouds detached from the edges could 
 continue to shine in the cold centre, we should certainly see 
 them following the current in descending spirals. But they 
 are rapidly enveloped in the cold hydrogen flowing in from 
 
M. FAYE'S REPLY TO MR. YOUNG'S OBJECTIONS. 85 
 
 above, and die away not far from the edge. In the penumbra 
 it would be useless to seek for traces of rotation. It is no 
 more a part of the vortex than the envelope of clouds which 
 surrounds our waterspouts and tornadoes, and renders their 
 contour visible. It is composed of luminous clouds resembling 
 those of the photosphere, but much rarer. They originate 
 in the tranquil space situated above the funnel, on account 
 of a local depression of temperature ; and the penumbra so 
 formed ends abruptly, irregularly bounding the nucleus, 
 properly so called, because nearer the axis the ascending 
 currents, loaded with the vapour which gives rise to these 
 clouds, are thrust aside by the gas which is set free, and 
 mounts from the lower end of the cyclone. The gyratory 
 motion only encroaches on this envelope in case of 
 segmentation. The luminous threads are then twisted 
 locally in various directions, as shown in the beautiful 
 diagrams of Mr. Langley. 
 
 It is in this way (and it is necessary to insist on it) that 
 the clouds enveloping waterspouts and tornadoes do not in 
 general give any indication of the violent vortex which they 
 suiTOund. It is true that justly celebrated meteorologists 
 have long denied the internal rotation of tornadoes because 
 there are no indications of it on the outlines ; hence, in order 
 to convince them, it is necessary to seek traces on the earth 
 in the position of overturned trees and in the debris of our 
 houses. I have myself undertaken a discussion of this 
 subject before the Academie. 
 
 Briefly here is my reply to the objections of Mr. Young, 
 which at first sight appear so plausible : 
 
 1. The inequality of velocity (for which my formula gives 
 only a mean value, the accuracy of which is impaired by the 
 presence of the spots) between the parallel lines of the 
 currents of the photosphere, and without doubt, also of the 
 chromosphere, is amply sufficient to give rise on the Sun to 
 vortices of every size from the largest spots, which would 
 easily engulf our earth, down to the scarcely visible pores. 
 
 2. If in general no traces of rotation are visible at the 
 
86 CONSERVATION OF SOLAR ENERGY. 
 
 edge of the spots, it is on account of the slowness of rotation 
 there. They would not, moreover, be found in our cyclones 
 if viewed from above on the edges of their extended openings. 
 
 But, although we seldom meet with the indications sought 
 by Mr. Young, which in fact ought generally to be absent, 
 it is easy to find other very characteristic indications, which 
 are by no means accidental, but occur in every spot. I have 
 long ago pointed these out, and will now simply enumerate 
 them. They are the distinctive characteristics of all gyratory 
 motion, and are found both in the Sun, and in our own 
 atmosphere. 
 
 1. The circular form assumed by all the spots in their 
 earliest stages. 
 
 2. The extended conical form of their mouth. 
 
 3. The marked constriction which this form undergoes at 
 a lower level, made especially evident in the black hole 
 of Dawes. 
 
 4. Their tendency to enlarge, while almost always keeping 
 their circular form. 
 
 5. Their tendency to break into segments,- which, starting 
 with a certain degree of development, .form partial spots. 
 These in their turn, as soon as they have differentiated 
 themselves, and a narrow band of the photosphere has been 
 established between them and the ascending currents of the 
 interior, form complete spots with penumbra nucleus and the 
 black hole of Dawes more or less concentrically placed. 
 This phenomenon is so frequent and striking in our own 
 cyclones, that meteorologists have adopted the same word, 
 " segmentation," to distinguish it. 
 
 6. Their regular course following the line of the current 
 which has originated them. 
 
 7. Their long duration, comparable and often superior to 
 that of our cyclones, which extend over entire weeks, while 
 describing their enormous trajectories on our globe. This 
 long duration is compatible only with gyration round a 
 vertical axis. 
 
 8. Their mode of disappearance depending on their 
 
M. FAYE'S EEPLY TO MR. YOUNG'S OBJECTIONS. 87 
 
 mechanical action. This action has the effect of absorbing 
 the inequalities in the velocities of the surface currents, 
 which are drawn below, and having performed their peculiar 
 work disappear. When in this way a more uniform region 
 is momentarily established in a stream of water or gas, 
 the vortex ceases to be fed; and rapidly contracts and 
 disappears. 
 
 9. The reappearance around the spots (or the pores) of 
 the hydrogen, which has been engulfed by them, and which, 
 set free at a certain depth, rapidly remounts around the 
 vortex to the point whence it came, and even shoots beyond 
 by reason of its acquired velocity. Hence the production 
 of faculse, the appearance of the erruptive protuberances, 
 and the extraordinary vertical circulation of the hydrogen, 
 which takes place incessantly between the chromosphere and 
 lower strata, and vice versd. This is the only phenomenon 
 which is peculiar to solar vortices. 
 
 I have proved, and meteorologists are beginning to believe, 
 that the terrestrial vortices formed round a vertical axis have 
 their origin in the upper currents of our atmosphere ; thence 
 they descend to the earth, where they expend the energy 
 they have acquired above and concentrated in transmitting 
 it downwards. It is interesting to recognize on the Sun this 
 law of terrestrial mechanics even to the minutest details. 
 The identity established between the spots of the Sun and 
 our cyclones furnishes the key of these mysterious phenomena ; 
 and when, in passing from the earth to the Sun, we see these 
 phenomena successively projected on a vertical and then on 
 a horizontal plane, we are in a better position to form a more 
 complete idea of both. 1 
 
 1 It appears from this interesting communication that M. Faye attributes 
 the Sun spots to similar causes to those which I have assumed in my last 
 answer to him, the important difference between us being that M. Faye 
 supposes the generating currents to proceed from the interior whereas I 
 suppose them to come from sources exterior to the sun. The question being 
 thus narrowed it will most likely be determined absolutely before long by 
 independent observers. C. W. S. 
 
APPENDIX 
 
EXPERIMENTS WITH ELECTRIC FURNACE. 91 
 
 APPENDIX. 
 
 ON THE ELECTRIC FURNACE. 1 
 
 By C. W. SIEMENS, D.C.L., F.R.S., and A. K. HUNTING-TON, 
 
 Professor of Metallurgy, King's College, London. 
 
 THE electric furnace has previously been described in the 
 Journal of the Society of Telegraph Engineers, June 1880. It 
 has since been found advisable to surround the furnace with 
 a coil. By this means the direction of the arc can be 
 regulated at will, and the tendency which it has to fly to the 
 sides of the crucible be checked. 
 
 The furnace consists of a crucible, a, of any convenient size, 
 in the bottom of which is pierced a hole to receive the positive 
 electrode, c, the negative electrode, d, which passes through a 
 hole in the lid of the crucible, being suspended from one end 
 of a beam, the other end of which is attached to a hollow 
 cylinder of soft iron, e, free to move vertically within a solenoid 
 coil of wire. The force with which the cylinder is drawn into 
 the coil can be counterpoised by a sliding weight, #,on the beam. 
 One end of the solenoid coil is connected with the positive, 
 and the other with the negative pole. The coil having a high 
 resistance, its attractive force on the cylinder is proportional 
 to the electromotive force between the electrodes, i.e. to the 
 resistance of the arc. The length of the arc is therefore 
 regulated automatically. This is a point of great importance, 
 as, were it not so, the resistance of the arc would rapidly 
 diminish as the temperature of the atmosphere within the 
 crucible increased, and the result would be that heat would 
 be developed in the dynamo machine. The extinction of the 
 arc by sudden change in its resistance or by the sinking of 
 the material in the crucible is thus also avoided. The crucible 
 is surrounded with some infusible substance, 6, which is also 
 a bad conductor of heat. Gas retort carbon or sand answers 
 
 1 Read before Section B of the British Association at Southampton, 1882. 
 
92 APPENDIX. 
 
 well for the purpose. The electrodes may be of such carbon 
 as is used in electric lighting or of any other convenient 
 conducting substance. They may, if desired, be cooled by 
 circulating water through or round them, or by exposing 
 them as far as possible to the air. For example, in one 
 experiment a half-inch nickel positive pole was employed, the 
 lower end being inserted into a solid rod of copper about one 
 inch square by six inches long. With this pole, no other 
 means of keeping it cool being adopted, one pound of grain 
 nickel was fused in a clay crucible and poured in eight 
 minutes, starting with all cold. The electrode was but little 
 attacked, and no leakage occurred. 
 
 There are two great advantages possessed by the electric 
 furnace, viz. that the temperature attainable is practically 
 only limited by the refractoriness of the materials of which 
 the furnace is constructed, and that the heat is developed 
 immediately in the material to be fused, instead of first having 
 to pass through the containing vessel. The temperature to 
 be obtained by the use of fuel is limited by dissociation. 
 Deville has shown that carbonic acid undergoes dissociation 
 at the ordinary atmospheric pressure at about 2600 C. 
 
 In the experiments made by the authors, five D 2 machines 
 driven by a Marshall's twelve-horse power engine were 
 employed ; one being used as an exciter. The current ranged 
 between 250 and 300 amperes. The most refractory clay 
 crucibles supplied by the Patent Plumbago Crucible Company 
 were invariably cut through in a few minutes, and, except for 
 experiments of short duration, were useless. Plumbago 
 crucibles stood exceedingly well. Obviously, however, they 
 could not be employed for all purposes, owing to their 
 tendency to cause carburisation of the metal experimented 
 with. In some experiments the fusion of metal was effected 
 in a bed of lime, sand, or electric light carbon dust. The 
 latter is a very bad conductor, and, as in the case of lime and 
 sand, allows the arc when once formed to maintain a passage 
 through it to the metal beneath. 
 
 Wrought Iron. Six pounds of wrought iron were kept 
 under the action of the arc for twenty minutes and the metal 
 then poured into a mould. It was found to be crystalline, 
 and could not be forged. This is the result which has always 
 been obtaine'd when iron, nickel, or cobalt have been fused. 
 Although the remedy, viz. the addition of a little manganese 
 just before pouring, is well known, the cause remains still 
 unexplained. 
 
EXPERIMENTS WITH STEEL AND IRON. 
 
 93 
 
 Steel. As mucb as twenty pounds of steel files have been 
 melted in one charge, the time required being about one 
 hour, starting with the furnace hot. With such large 
 quantities the metal has invariably been full of blowholes. 
 
 White iron, fused in a clay crucible for thirty minutes, 
 when fractured did not appear to have undergone any change. 
 White iron and coke were introduced into the furnace ; the 
 
94 APPENDIX. 
 
 resultant metal was slightly grayer than the original. When, 
 however, retort carbon was substituted for the coke a good 
 gray iron, soft and easily workable, was readily obtained in 
 fifteen minutes, starting with the crucible hot. On another 
 occasion, starting all cold, at the end of thirty minutes the 
 metal, although it had been well fused, had not been rendered 
 grayer. The difference between these two results was possibly 
 due to the temperature being somewhat higher in the one 
 case than in the other. This is a point of considerable 
 practical interest. Four pounds of white iron, fused with 
 carbon dust for three-quarters of an hour, yielded a very gray 
 crystalline iron. In another experiment, in which eight ounces 
 of gray iron, produced in the electric furnace from white iron, 
 were re-melted in carbon dust for ten minutes a very gray 
 metal was obtained, from which on slow cooling a large 
 quantity of graphite separated. 
 
 Cast iron, fused and kept under the action of the arc for 
 forty-five minutes in carbon dust was not materially changed 
 as to grayness, and the general character of the metal as to 
 the way in which it worked under the tool was not materially 
 altered. The object of the experiment was to ascertain the 
 maximum amount of carbon iron is capable of taking up 
 under circumstances presumably the most favourable. The 
 result is hardly that which would have been anticipated. 
 Some of the same cast iron was fused for fifteen minutes 
 under lime, which nearly covered it. The character of the 
 fracture of the metal was but little altered by this treatment, 
 when slight differences, due to the rate of cooling, are taken 
 into account. A strong smell of phosphoretted hydrogen or 
 of a phosphite was perceived probably the latter. This was 
 only observed in the experiment in which lime was used. 
 The lime employed still retains a very offensive odour. 
 
 When spiegeleisen was fused in a plumbago or a clay 
 crucible graphite separated as the metal cooled. 
 
 Siliceous pig iron, containing about 10 per cent, silicon, was 
 fused by itself, it showed but little change, except that some 
 graphite separated. A similar result was obtained when five 
 pounds of the siliceous pig were fused for one hour in carbon 
 dust. On fracturing the ingot obtained, a large quantity of 
 scales of graphite was found in a hollow which traversed 
 nearly the whole length of the ingot at its centre. The 
 fracture of the metal was still that so characteristic of highly 
 siliceous iron, and was practically the same as that of the 
 original pig iron. 
 
EXPERIMENTS WITH NICKEL AND COPPER. 95 
 
 A series of experiments was made to determine the maximum 
 amount of carbon pig iron is capable of taking up in the 
 presence of a given quantity of silicon. Gray cast iron and 
 pig iron containing 10 per cent, of silicon were fused together 
 in carbon dust, the ratio between them being varied so as to 
 yield metal with from J per cent, to 9 per cent, of silicon. 
 
 A similar series was made, only substituting sulphur for 
 silicon. No odour of sulphurous acid was perceived ; there- 
 fore, presumably, no sulphur was volatilised. This is some- 
 what remarkable, considering the nature of the experiment. 
 It was thought that investigations of this kind might have 
 an important practical as well as more purely scientific 
 interest admitting, for the sake of argument, that any such 
 distinction really exists in assisting to determine the 
 conditions in the blast furnace, &c. 
 
 Nickel. A positive pole of this metal cast malleable by 
 Wiggin & Co.'s process 1 half inch in diameter, was passed 
 through a hole in the bottom of a clay crucible. A carbon 
 negative pole, was used, but soon after the commencement of 
 the experiment a deposit of nickel formed on the end of it, 
 so that practically it was a nickel pole. This deposition of 
 metal on the negative pole was also observed with some other 
 metals notably with tungsten. Whilst disclaiming any 
 special knowledge on the point, Professor Huntington sug- 
 gested whether this phenomenon which is the reverse of 
 that generally recognised as taking place might not depend 
 on the relative volatility of the matter composing the poles. 
 In the furnace arranged as just described, one pound of grain 
 nickel was fused and poured in eight minutes. The fused 
 metal had a brilliant granular fracture. It could not be cut 
 properly in the shaping machine, shearing off under the 
 tool. One pound of grain nickel fused in carbon dust for 
 twenty-five minutes yielded a dark gray carburised metal, 
 which worked well under the tool. On another occasion an 
 equal quantity of nickel, similarly treated, gave a " blowy " 
 metal, which could not be worked. Some carburised nickel, 
 made as described above, was fused in a clay crucible for 
 twelve minutes, and allowed to cool gradually in the furnace ; 
 the fracture became whiter, and the grain closer. 
 
 Copper. Three quarters of a pound of copper were fused 
 for about half an hour in carbon dust. On examining the 
 result, it was found that all but about three quarters of an 
 
 1 See paper on "Nickel and Cobalt," by A. K. Huntington, in July number 
 of the Journal of the Society of Chemical Industry* 
 
96 APPENDIX. 
 
 ounce had been vapourised. Those who were present during 
 the experiments suffered no ill effects from the atmosphere 
 charged with copper, which they must have breathed. 
 
 Platinum. Eight pounds of platinum were rendered 
 perfectly liquid in about a quarter of an hour. 
 
 Tungsten. Half a pound of tungsten in powder was sub- 
 jected to the action of the arc in a clay crucible. Dense 
 fumes were evolved, a cavity about one and a half inches 
 across the top being formed. The furnace was allowed to 
 cool down slowly. When the crucible was removed, it was 
 found to have been very much attacked below the point 
 to which the arc extended. The inference is that the crucible 
 had been attacked by the metal at the temperature of the 
 experiment. The metal was fused only to an inappreciable 
 depth beneath the cavity formed by the arc. The unfused 
 metal underneath was covered with very beautiful iridescent 
 crystals of tungsten, which under the microscope appeared to 
 be well-formed prisms. They have not yet been measured. 
 The crystals had evidently been formed by the slow cooling 
 of the vapour distilled down from the surface. 
 
 A very large number of experiments was made with 
 tungsten, the results of which showed that it could not be 
 fused, except in very small quantities at a time. It was 
 possible to build up a small ingot by fusing a little of the 
 tungsten, and then adding little by little gradually. Even 
 then the pieces obtained were for the most part spongy and 
 unsatisfactory. The best results arrived at were when tung- 
 sten which had already been fused was employed in the 
 building-up process. Once the metal had been fused, it did 
 not fume much in melting, doubtless owing to the greatly 
 reduced surface exposed. 
 
 Tungsten fused in the electric furnace is, when untarnished, 
 pure white, and brittle, the grain being very close. Tungsten 
 hitherto has only been obtained as a gray powder, by reducing 
 the oxide with carbon or hydrogen, or in minute globules in 
 the ordinary small electric arc. Tungsten has its fusing point 
 lowered by the addition to it of carbon. Under these con- 
 ditions a solid piece of moderate size can, without much 
 difficulty, be obtained. From 1000 grains of powder fused 
 in carbon dust 650 grains were recovered, the remainder 
 having been volatilised, and from 450 grains of the fused 
 metal 410 grains were obtained on refusion. One piece of 
 tungsten which had been treated under the conditions most 
 likely to cause it to be highly carburised was analysed. It 
 
DISCUSSION ON ELECTRIC FUSION. 97 
 
 contained 1*8 per cent, of carbon. The metal was very white, 
 close in grain, and brittle. 
 
 From the foregoing experiments it is clear that the amount 
 of any given metal which can be successfully fused in the 
 electric furnace, and the time required in effecting the fusion, 
 are dependent on (a) the relation between the volatilising 
 point and the fusing point, i.e. the extent to which the 
 volatilising point is higher than the fusing point; (&) the 
 conductivity of the metal for heat. 
 
 It thus happens that platinum can be more readily melted 
 than steel, and in greater quantity for a given expenditure of 
 energy. This inference is believed by Professor Huntington 
 to be justified by the observations and experiments so far 
 made. 
 
 It still remains to examine chemically the specimens 
 referred to in this paper. 
 
 In the discussion on the communication made by Professor 
 Huntington, Dr. Siemens remarked that the limit of the 
 temperature producible by means of the electric furnace is 
 as yet unknown, for although the resistance of the arc would 
 probably increase with temperature, that in itself would only 
 cause a further development of heat. The results obtained 
 with copper, although apparently pointing to a drawback in 
 the use of the furnace for melting purposes, yet might prove 
 of importance in dealing with metals in the vaporous con- 
 dition.- He could not agree with Professor Huntington's 
 suggestion as to the cause of the deposition of metal on the 
 negative pole. He thought it was due to the negative pole 
 being much cooler than the positive. 
 
 Dr. Gladstone inquired whether the deposit was crystalline 
 or in fused globules. 
 
 Professor Huntington replied that it was in the latter 
 condition. 
 
 Mr. Terrill (Swansea), remarked that the loss of copper 
 by volatilisation in smelting was much greater than it was 
 generally supposed. During an accidental escape of sulphur- 
 etted hydrogen in the works he had observed a thick deposit 
 of sulphide of copper extending over a large area. He had 
 detected copper deposited even on the zinc counter of the 
 refreshment bar at the railway station some distance from 
 the works. The discussion was continued by Mr. Maxwell 
 Lyte, Prof. Vernon Harcourt, and the president, Prof. Liveing, 
 who thought that such experiments as had been made might 
 be of great service in the study of metals. 
 
 H 
 
98 APPENDIX. 
 
 SUNLIGHT AND SKYLIGHT AT HIGH ALTITUDES. 
 
 An Abstract of a Paper by CAPTAIN ABNEY, F.R.S., read before 
 Section A of the Meeting of the British Association at Southampton, 
 1882 ; together with a Report of the Remarks made by PROFESSOR 
 LANGLEY in the subsequent Discussion.* 
 
 AT the Southampton meeting of the British Association, 
 Captain Abney read a paper in which he called attention 
 to the fact that photographs taken at high altitudes show 
 skies that are nearly black by comparison with bright objects 
 projected against them, and he went on to show that the 
 higher above the sea-level the observer went, the darker the 
 sky really is and the fainter the spectrum. In fact, the latter 
 shows but little more than a band in the violet and ultra- 
 violet at a height of 8,500 feet, whilst at sea-level it shows 
 nearly the whole photographic spectrum. The only reason of 
 this must be particles of some reflecting matter from which 
 sunlight is reflected. The author refers this to " water- 
 stuff" of which nine-tenths is left behind at the altitude at 
 which he worked. He then showed that the brightness of 
 the ultra-violet of direct sunlight increased enormously the 
 higher the observer went, but only to a certain point, for 
 the spectrum suddenly terminated at about 2,940 wave-length. 
 This abrupt absorption was due to extra atmospheric causes 
 and perhaps to space.. The increase dn brightness of the 
 ultra-violet was such that the usually invisible rays L, M, N, 
 could be distinctly seen showing that the visibility of these 
 rays depended on the intensity of the radiation. The red 
 and ultra-red part of the spectrum was also considered. 
 He showed that the absorption lines were present in 
 undiminished force and number at this high altitude, thus 
 placing their origin to extra atmospheric causes. The 
 absorption from atmospheric causes of radiant energy in 
 these parts he showed was due to " water-stuff," which he 
 hesitated to call aqueous vapour, since the banded spectrum 
 1 Printed in Nature, October 12th, 1882. 
 
HYDROCARBONS BETWEEN EARTH AND SUN. 99 
 
 of water was present, and not lines. The B and A line he 
 also stated could not be claimed as telluric lines, much less 
 as due to aqueous vapour, but must originate between the 
 Sun and our atmosphere. The author finally confirmed the 
 presence of benzene and ethyl in the same region. He had 
 found their presence indicated in the spectrum at sea-level, 
 and found their absorption lines with undiminished intensity 
 at 8,500 feet. Thus without much doubt hydrocarbons must 
 exist between our atmosphere and the Sun, and it may be 
 in space. 
 
 Prof. Langley, following Capt. Abney observed: The 
 very remarkable paper just read by Captain Abney has 
 already brought information, upon some points which the 
 one I am about, by the courtesy of the Association, to present, 
 leaves in doubt. It will be understood then that the 
 references here are to his published memoirs only, and 
 not to what we have just heard. 
 
 The solar spectrum is so commonly supposed to have been 
 mapped with completeness, that the statement that much 
 more than one half its extent is not only unmapped but 
 nearly unknown, may excite surprise. This statement is, 
 however, I think, quite within the truth, as to that almost 
 unexplored region discovered by the elder Herschel, which 
 lying below the red and invisible to the eye, is so compressed 
 by the prism, that though its aggregate heat effects have 
 been studied through the thermopile, it is only by the recent 
 researches of Captain Abney that we have any certain 
 knowledge of the lines of absorption there, even in part. 
 Though the last named investigator has extended our 
 knowledge of it to a point much beyond the lowest visible 
 ray, there yet remains a still remoter region, more extensive 
 than the whole visible spectrum, the study of which has 
 been entered on at Alleghany, by means of the linear 
 bolometer. 
 
 The whole spectrum, visible and invisible, is powerfully 
 affected by the selective absorption of our atmosphere, 
 and that of the Sun ; and we must first observe that could 
 we get outside our earth's atmospheric shell, we should see a 
 second and very different spectrum, and could we afterwards 
 remove the solar atmosphere also, we should have yet a third, 
 different from either. The charts exhibited show : 
 
 1st. The distribution of the solar energy as we receive 
 it, at the earth's surface, throughout the entire invisible 
 
 H 2 
 
100 APPENDIX. 
 
 as well as visible portion, both on the prismatic and normal 
 scales. This is what I have principally to speak of now, 
 but this whole first research is but incidental to others 
 upon the spectra before any absorption, which though 
 incomplete, I wish briefly to allude to later. The other 
 curves then indicate. 
 
 2nd. The distribution of energy before absorption by our 
 own atmosphere. 
 
 3rd. This distribution at the photosphere of the Sun. 
 
 The extent of the field, newly studied, is shown by this 
 drawing (chart exhibited). Between H in the extreme violet, 
 and A in the furthest red, lies the visible spectrum, with 
 which we are familiar, its length being about 4,000 of 
 Angstrom's units. If then, 4,000 represent the length of the 
 visible spectrum, the chart shows that the region below extends 
 through 24,000 more, and so much of this as lies below 
 wave-length, 12,000, I think, is now mapped for the 
 first time. 
 
 We have to \ 12,000, relatively complete photographs, 
 published by Captain Abney, but except some very slight 
 indications by Lamansky, Desains, and Mouton, no further 
 guide. 
 
 Deviations being proportionate to abscissae, and measured 
 solar energies to ordinates, we have here (1) the distribution 
 of energy in the prismatic and (2) its distribution in the 
 normal spectrum. The total energy is in each case propor- 
 tionate to the area of the curve, (the two very dissimilar 
 curves inclosing the same area,) and on each, if the total 
 energy be roughly divided into four parts, one of these will 
 correspond to the visible, and three to the invisible or ultra- 
 red part. The total energy at the ultra-violet end is so small 
 then as to be here altogether negligible. 
 
 We observe that (owing to the distortion introduced by the 
 prism) the maximum ordinate representing the heat in the 
 prismatic spectrum is, as observed by Tyndall, below the red, 
 while upon the normal scale the maximum ordinate is found 
 in the orange. 
 
 I would next ask your attention to the fact that in either 
 spectrum, below \ = 12,000 are most extraordinary depressions 
 and interruptions of the energy, to which, as will be seen, the 
 visible spectrum offers no parallel. As to the agent producing 
 these great gaps, which so strikingly interrupt the continuity 
 of the curve, and as you see, in one place, cut it completely in 
 two, I have as yet obtained no conclusive evidence. Knowing 
 
EXPERIMENTS WITH BOLOMETER 101 
 
 the great absorption of water vapour in this lowest region, as 
 we already do, from the observations of Tyndall, it would, a 
 priori, seem not unreasonable to look to it as the cause. On the 
 other hand, when I have continued observations from noon to 
 sunset, making successive measures of each ordinate, as the 
 sinking Sun sent its rays through greater depths of absorbing 
 atmosphere ; I have not found these gaps increasing, as much 
 as they apparently should, if due to a terrestrial cause, and so 
 far as this evidence goes, they might be rather thought to be 
 solar. But my own means of investigation are not so well 
 adapted to decide this important point, as those of photo- 
 graphy, to which we may yet be indebted for our final 
 conclusion. 
 
 I am led from a study of Captain Abney's photographs of 
 the region between X = 8,000 and \ = 12,000, to think that 
 these gaps are produced by the aggregation of finer lines, 
 which can best be discriminated by the camera, an instrument, 
 which, where it can be used at all, is far more sensitive than 
 the bolometer ; while the latter, I think, has on the other hand 
 some advantage in affording direct and trustworthy measures 
 of the amount of energy inhering in each ray. 
 
 One reason why the extent of this great region has been so 
 singularly under-estimated, is the deceptively small space into 
 which it appears to be compressed by the distortion of the 
 prism. To discriminate between these crowded rays I have 
 been driven to the invention of a special instrument. The 
 bolometer, which I have here, is an instrument depending 
 upon principles which I need not explain at length, since all 
 present may be presumed to be familiar with the success 
 which has before attended their application in another field, in 
 the hands of the President of this Association, Dr. Siemens. 
 
 I may remark, however, that this special construction has 
 involved very considerable difficulties and long labour. For 
 the instrument here shown, platinum has been rolled by 
 Messrs. Tiffany, of New York, into sheets, which, as determined 
 by the kindness of Professor Rood, reach the surprising tenuity 
 of less than ^rimy of an English inch (I have also iron rolled 
 to ITOIFII inch), and from this platinum a strip is cut -^^ of an 
 inch wide. This minute strip, forming one arm of a Wheat- 
 stone's bridge, and thus perfectly shielded from air currents, is 
 accurately centred by means of a compound microscope, in this 
 truly turned cylinder, and the cylinder itself is exactly directed 
 by the arms of this Y- 
 
 The attached galvanometer responds readily to changes of 
 
102 
 
 APPENDIX. 
 
 40 
 
DETERMINATION OF WAVE-LENGTHS. 103 
 
 temperature, of much less than -f^^ Fah. Since it is one 
 and the same solar energy, whose manifestations we call 
 " light " or " heat," according to the medium which interprets 
 them, what is "light" to the eye is "heat" to the bolometer, 
 and what is seen as a dark line by the eye is felt as a cold line 
 by the sentient instrument. Accordingly if lines analogous to 
 the dark " Fraunhofer lines " exist in this invisible region, 
 they will appear (if I may so speak), to the bolometer as cold 
 bands, and this hair-like strip of platina is moved along in the 
 invisible part of the spectrum, till the galvanometer indicates 
 the all but infinitesimal change of temperature caused by its 
 contact with such a " cold band." The whole work, it will be 
 seen, is necessarily very slow ; it is in fact a long groping in 
 the dark, and it demands extreme patience. A portion of its 
 results are now before you. 
 
 The most tedious part of the whole process, has been the 
 determination of the wave-lengths. It will be remembered 
 that we have (except through the work of Captain Abney, 
 already cited, and perhaps of M. Mouton), no direct knowledge 
 of the wave-lengths in the infra-red prismatic spectrum, but 
 have hitherto inferred them from formulas like the well-known 
 one of Cauchy's, all which known to me appear to be here 
 found erroneous by the test of direct experiment ; at least in 
 the case of the prism actually employed. 
 
 I have been greatly aided in this part of the work by the 
 remarkable concave gratings lately constructed by Professor 
 Rowland of Baltimore, one of which I have the pleasure of 
 showing you. 
 
 The spectra formed by this, fall upon a screen in which is a 
 fine slit, only permitting nearly homogeneous rays to pass, and 
 these, which may contain the rays of as many as four over- 
 lapping spectra, are next passed through a rock-salt or glass 
 prism placed with its refracting edge parallel to the grating 
 lines. This sorts out the different narrow spectral images, 
 without danger of overlapping, and after their passage through 
 the prism we find them again and fix their position by 
 means of the bolometer, which for this purpose is attached to 
 a special kind of spectrometer, where its platinum thread re- 
 places the reticule of the ordinary telescope. This is very 
 difficult work, especially in the lowermost spectrum, where 1 
 have spent over two weeks of consecutive labour, in fixing 
 a single wave-length. 
 
 The final result is I think worth the trouble, however, for 
 as you see here, we are now able to fix with approximate 
 
104 
 
 APPENDIX. 
 
NORMAL SPECTRUM. 105 
 
 precision, and by direct experiment, the wave-length of every 
 prismatic spectral ray. The terminal ray of the solar spectrum, 
 whose presence has been certainly felt by the bolometer, has a 
 wave-length of about 28,000 (or is nearly two octaves below 
 the " great A " of Fraunhofer). 
 
 So far it appears only that we have been measuring heat, 
 but I have called the curve that of solar " energy," because by 
 a series of independent investigations, not here given, the 
 selective absorption of the silver, the speculum-metal, the glass 
 and the lamp-black (the latter used on the bolometer-strip), 
 forming the agents of investigation, has been separately 
 allowed for. My study of lamp-black absorption, I should 
 add in qualification, is not quite complete, I have found it 
 quite transparent to certain infra-red rays, and it is very 
 possible that there may be some faint radiations yet to be 
 discovered even below 'those here indicated. 
 
 In view of the increased attention that is doubtless soon to 
 be given to this most interesting but strangely neglected 
 region, and which by photography and other methods, is 
 certain to be fully mapped hereafter, I can but consider this 
 present work less as a survey than as a sketch of this great 
 new field, and it is as such only that I here present it. 
 
 All that has preceded is subordinate to the main research, 
 on which I have occupied the past two years at Alleghany, in 
 comparing the spectra of the Sun at high and low altitudes, but 
 which I must here touch upon briefly. By the generosity of 
 a friend of the Alleghany Observatory, and by the aid of 
 General Hazen, Chief Signal Officer of the United States 
 Army, I was enabled last year to organise an expedition to 
 Mount Whitney in South Califorina, where the most important 
 of these latter observations were repeated at an altitude of 
 13,000 feet. Upon my return I made a special investigation 
 upon the selective absorption of the Sun's atmosphere, with 
 results which I can now only allude to. 
 
 By such observations, but by methods too elaborate for 
 present description, we can pass from the curve of energy 
 actually observed, to that which would be seen, if the observer 
 were stationed wholly above the earth's atmosphere, and freed 
 from the effect of its absorption. 
 
 The salient and remarkable result is the growth of the blue 
 end of the spectrum, and I would remark that while it has 
 been long known from the researches of Lockyer, Crova, and 
 others, that certain rays of short wave-length were more 
 absorbed than those of long, that these charts show how much 
 
106 APPENDIX. 
 
 separate each ray of the spectrum has grown, and bring, what 
 seems to me, conclusive evidence of the shifting of the point 
 of maximum energy without the atmosphere towards the blue. 
 Contrary to the accepted belief, it appears here also that the 
 absorption on the whole grows less and less, to the extreme 
 infra-red extremity ; and on the other hand, that the energy 
 before absorption was so enormously greater in the blue and 
 violet, that the Sun must have a decidedly bluish tint to the 
 naked eye, if we could rise above the earth's atmosphere to 
 view it. 
 
 But even were we placed outside the earth's atmosphere, 
 that surrounding the Sun itself would still remain, and exert 
 absorption. By special methods, not here detailed, we have 
 at Alleghany, compared the absorption, at various depths, of 
 the Sun's own atmosphere for each spectral ray, and are hence 
 enabled to show, with approximate truth, I think for the first 
 time, the original distribution of energy throughout the visible 
 and invisible spectrum, at the fount of that energy, in the Sun 
 itself. There is a surprising similarity you will notice, in the 
 character of the solar and telluric absorptions, and one which 
 we could hardly have anticipated a priori. 
 
 Here too, violet has been absorbed enormously more than 
 the green, and the green than the red, and so on, the difference 
 being so great, that if we were to calculate the thickness of 
 the solar atmosphere on the hypothesis of a uniform trans- 
 mission, we should obtain a very thick atmosphere, from the 
 rate of absorption in the infra-red alone, and a very thin one 
 from that in the violet alone. 
 
 But the main result, seems to be still this, that as we have 
 seen in the earth's atmosphere, so we see in the Sun's, an 
 enormous and progressive increase of the energy towards the 
 shorter wave-lengths. This conclusion, which I may be 
 permitted to remark, I anticipated in a communication 
 published in the Comptes Rendus of the Institute of France 
 as long since as 1875, is now fully confirmed, and I may 
 mention that it is so also by direct photometric methods, not 
 here given. 
 
 If then we ask how the solar photosphere would appear to 
 the eye, could we see it without absorption, these figures 
 appear to show conclusively that it would be blue. Not to 
 rely on any assumption, however, we have by various methods 
 at Alleghany, reproduced this colour. 
 
 Thus (to indicate roughly the principle used), taking three 
 Maxwell's discs, a red, green, and blue, so as to reproduce 
 
BLUE COLOUR OF THE SUN. 107 
 
 white, we note the three corresponding ordinates at the earth's 
 surface spectrum, and comparing these with the same ordinates 
 in the curve giving the energy at the solar surface ; we re- 
 arrange the discs, so as to give the proportion of red, green, 
 and blue, which would be seen there, and obtain by their 
 revolution a tint which must approximately represent that at 
 the photosphere, and which is most similar to that of a blue 
 near Fraunhofer's " F." 
 
 The conclusion then is, that while all radiations emanate 
 from the solar surface, including red and infra-red, in greater 
 degree than we receive them, that the blue end is so enormously 
 greater in proportion, that the proper colour of the Sun, as 
 seen at the photosphere, is blue not only " bluish," but 
 positively and distinctly blue ; a statement which I have not 
 ventured to make from any conjecture, or on any less cause 
 than on the sole ground of long continued experiments, which, 
 commenced some seven years since, have within the past two 
 years irresistibly tended to the present conclusion. 
 
 The mass of observations on which it rests must be reserved 
 for more detailed publication elsewhere, at present I can only 
 thank the Association for the courtesy which has given me 
 the much prized opportunity of laying before them this 
 indication of methods and results. 
 
108 APPENDIX 
 
 DISSOCIATION OF ATTENUATED COMPOUND 
 
 GASES. 
 
 BY PROFESSOR G. D. LIVEING, M.A., F.R.S., F.C.S. 
 
 Excerpt from the, Address to the Chemical Section of the 
 British Association at Southampton in 1882. 
 
 I CANNOT dismiss the subject of chemical dynamics with- 
 out alluding to the ingenious theory by which the President 
 of the Association has proposed to account for the conservation 
 of solar energy. He supposes planetary space to be pervaded 
 by an atmosphere which, except where it is condensed by the 
 attraction of the Sun and planets, is in a highly attenuated 
 state. The Sun and planets communicate some of their own 
 motion of rotation to the atmosphere condensed about them, 
 and he supposes that in this way an action like that of a 
 blowing fan is set up, by which the equatorial part of the 
 Sun's atmosphere acquires such a velocity as to stream out to 
 distances beyond the earth's orbit, while an equal quantity of 
 gas is drawn in at the poles to maintain equilibrium. The 
 gases thus driven to a distance in planetary space will of 
 course be enormously expanded and highly attenuated, and 
 in this state Dr. Siemens thinks that such of them as are 
 compound may be decomposed by absorbing the solar radia- 
 tion, and thus the kinetic energy of the Sun's rays be converted 
 into the potential energy of chemical separation. The separated 
 elements, or partial compounds, will in the circulation pro- 
 duced by the fanlike action of the solar rotation be carried 
 back to the polar regions of the Sun as fuel to maintain his 
 temperature by condensation and re-combination. I will not 
 discuss the mechanical .part of this theory further than to 
 remark that the fanlike action can only be carried on at the 
 expense of the energy of the Sun's rotation, which must in 
 consequence be continually diminishing, and must in time 
 become too slow to produce any sensible projection of the 
 
DISSOCIATION AT LOW PRESSURE. 109 
 
 atmosphere into distant regions of planetary space. As to 
 the chemical side of the theory, Dr. Siemens supposes the 
 gases which pervade the planetary space to be not only of the 
 same kind as the components of our own atmosphere, which 
 on the kinetic theory of gases must diffuse through that space, 
 but also such gases as are not found in our air, but are found 
 occluded in meteorites, which may be supposed to have ac- 
 quired them in their previous wanderings. Amongst these he 
 specially mentions hydrocarbons which form the self-luminous 
 part of most comets. It is to these gases, together with 
 aqueous vapour and carbonic acid, that he ascribes the prin- 
 cipal part in the conservation of solar energy. That compound 
 gases at the extremely low pressure of the planetary space are 
 decomposed by solar radiation is not inconsistent with the 
 laws of dissociation, for it is quite possible that some com- 
 pounds may be decomposed at ordinary temperatures by mere 
 reduction of pressure, and the radiation absorbed will be the 
 more effective because it will directly affect the vibratory 
 motion within the molecule, and may well produce chemical 
 decomposition before it can, when the free path of the mole- 
 cules is so much increased by the attenuation of the gas, 
 assume the form of an increased temperature. Dr. Siemens, 
 moreover, adduces a remarkable experiment in confirmation 
 of this supposition. We know, too, the power which our 
 atmosphere, and especially the water vapour in it, has of 
 absorbing the infra-red rays, and that amongst the Fraunhofer 
 lines some of the strongest groups are due to aqueous vapour ; 
 and the capital observation made by the spectroscopic ob- 
 servers at the last total eclipse, that the group of lines known 
 as " B," which is one of those produced by aqueous vapour, 
 is greatly strengthened when the Sun's light passes by the 
 edge of the moon and so through the lunar atmosphere, may 
 be taken as a confirmation of the theory that gases like our 
 atmosphere are diffused through space and concentrated about 
 the planets. But if it be true that the compounds are 
 decomposed by absorbing the Sun's rays, we r ought to find in 
 our atmosphere the products of decomposition, we ought to 
 find in it free hydrogen, carbonic oxide, and acetylene or some 
 other hydrocarbons. The hydrogen, from its small specific 
 gravity, would not be concentrated in the lower regions of our 
 atmosphere in the same proportions as the denser "gases, but 
 carbonic oxide and hydrocarbons could not fail to be detected 
 in the air if they formed any sensible proportion of the gases 
 in the planetary space. That a large portion of solar radiation 
 
110 APPENDIX. 
 
 is intercepted before it reaches the earth is no doubt 
 true, for there are not only the dark bands which are in- 
 creased by our atmosphere and may reasonably be attributed 
 to the action of like gases pervading planetary space, but there 
 is a continuous absorption of the ultra-violet spectrum beyond 
 the line U, and Cornu has found that this absorption is not 
 sensibly affected by our atmosphere, so that the substance, 
 whatever it be that produces it, may be an agent in the 
 process imagined by Dr. Siemens, but cannot be the means of 
 restoring to the sun any portion of his radiant energy which 
 reaches our distance from him. 
 
 Dr. Siemens explains the self-luminous character of comets 
 by the theory that the streams of meteoric stones of which 
 they are supposed to consist bring from stellar space hydro- 
 carbon and other gases occluded within them, and that in 
 consequence of the rise of temperature due to the frictional 
 resistance of such a divided mass moving with enormous 
 velocity, aided by attractive condensation, the occluded gases 
 will be driven out and burnt, the flame giving rise to the 
 original light emitted by the nucleus. Now the spectrum of 
 most comets shows only the principal bands of a Bunsen 
 burner, and is therefore adequately explained by the flame of 
 gas containing hydrocarbons such as have been found in 
 meteorites ; but Dr. Huggins has observed in the spectrum 
 of more than one comet, not only hydrocarbon, but cyanogen 
 bands ; and, although carbon and nitrogen combine readily in 
 the electric arc, a coal-gas flame in air shows no trace of the 
 spectrum of cyanogen, and it would certainly put some strain 
 on our credulity if it were asserted that cyanogen was one of 
 the gases brought ready-formed by meteorites from stellar 
 space. Dewar and I have, however, recently shown that if 
 nitrogen already in combination, as, for instance, ammonia, be 
 brought into a hydrocarbon flame, cyanogen is produced in 
 sufficient amount to give in a photograph (though not so as 
 to be directly visible) the characteristic spectrum of cyanogen 
 as it appears in the comet. It is therefore no longer necessary 
 to make any other supposition to account for the cyanogen 
 bands in the spectra of comets, than that ammonia, or some 
 such compound of nitrogen, is present as well as hydrocarbons 
 in a state of ignition. 
 
 Quite recently Dr. Huggins has observed that the principal 
 comet of this year has a spectrum of an entirely different 
 character, but he is not yet able to say to what elements or 
 compounds it is probably due. The notion that comets may 
 
OCCLUDED GASES IN COMETS. Ill 
 
 bring us news of distant parts of stellar space, towards which 
 our system is driving, where the atmosphere is not like ours 
 oxygen and nitrogen but hydrogen and hydrocarbons, may 
 fascinate the fancy, but the laws of occlusion oblige us to 
 think that the meteorites have not merely wandered through 
 an attenuated atmosphere of hydrogen and hydrocarbons, but 
 have cooled in a much denser atmosphere of those substances, 
 which we can only conceive as concentrated by the presence 
 of a star or some large aggregation of matter. They may, 
 perchance, have come from some nebulous mass, for Draper 
 and Huggins tell us that in the great nebula in Orion 
 hydrogen is dense enough and hot enough to show some of 
 its characteristic lines, besides the F line which is seen in 
 other nebulae, and is the last to disappear by reduction of 
 density. No comet on visiting our system a second time can 
 repeat the exclusion of its occluded gases unless its store has 
 been replenished in the interval. Tacchini has recently 
 observed that Encke's comet, which is one of short period 
 that does not travel beyond the limits of our system, shows 
 the usual spectrum of three bands. If this observation should 
 be confirmed it will be very difficult to account for the re- 
 plenishment of its occluded gases. But Encke's comet is a 
 very small object, and one cannot feel very certain about its 
 spectrum, and it will be interesting to see, when Halley's 
 comet next returns, whether it shines only by reflected light 
 or gives us, like so many others, the banded spectrum of 
 hydrocarbons. 
 
 THE END. 
 
 R. CLAY, SONS, AND TAYLOR, PRINTERS, BREAD STREET HILL 
 
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