XIV. Experimental Researches in Magnetism and Electricity.Second Series. By H. WILDE, Esq. (With a Plate).... page 81 § 3. On the Electric Condition of the Terrestrial Globe, and on the Absolute Character of the Law of Definite Electrolysis.. 81 § 4. On the Transmutable Nature of Water... 106 XV. On the Theory of Pressure in Fluids. By R. Moon, M.A., Honorary Fellow of Queen's College, Cambridge. 116 XVI. On the Diammonic Carbonate, or Normal Carbonate of Ammonium. By EDWARD DIVERS, M.D., F.C.S., Lecturer on Natural Philosophy, Charing Cross Hospital XVII. On a modified Spectroscope for use in the examination of Minerals. By J. EMERSON REYNOLDS, Member of the Royal College of Physicians, Edinburgh, Keeper of the Minerals and Analyst to the Royal Dublin Society 125 129 XVIII. The Internal Motions of Gases compared with the Motions of Waves of Light. By G. JOHNSTONE STONEY, M.A., F.R.S. .... 132 XIX. On Geological Time, and the probable Date of the Glacial and the Upper Miocene Period. By JAMES CROLL, of the Geological Survey of Scotland XX. Proceedings of Learned Societies : 141 ROYAL SOCIETY:-Mr. R. Moon on the Impact of Compressible 157-158 XXI. Intelligence and Miscellaneous Articles :- It is requested that all Communications for this Work may be addressed, post-paid, to the Care of Messrs. Taylor and Francis, Printing Office, Red Lion Court, Fleet Street, London. Published the First Day of every Month.-Price 2s. 6d. THE LONDON, EDINBURGH, AND DUBLIN PHILOSOPHICAL MAGAZINE, AND JOURNAL OF SCIENCE. Being a Continuation of Tilloch's Philosophical Magazine,' Nicholson's Journal,' and Thomson's Annals of Philosophy.' CONDUCTED BY SIR ROBERT KANE, M.D. F.R.S. M.R.I.A. AND WILLIAM FRANCIS, Ph.D. F.L.S. F.R.A.S. F.C.S. FOURTH SERIES. N° 242.-SEPTEMBER 1868. LONDON: PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET, Printers and Publishers to the University of London. 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Taylor and Francis, Red Lion Court, Fleet Street, E.C. [ADVERTISEMENTS continued on 3rd page of Cover. THE LONDON, EDINBURGH, AND DUBLIN PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. [FOURTH SERIES.] : SEPTEMBER 1868, IN XXII. On the Polarization of Heat at 100° C., and on the Motion accompanying Heat-conduction. By Professor MAGNUS*. Na former essay on the polarization of heat, and on its passage through parallel platest, it has been already shown that the heat radiated from a red-hot plate of platinum at an oblique angle only comes in part from the surface, another portion being radiated from the interior. This fact was deduced as a consequence of the polarization of the heat radiated from such a surface. For since the plane of polarization has the same position as that of light refracted at a certain angle, we are compelled to assume that, at all events, one portion of the emergent rays suffers a refraction at the surface; and in order that this may be the case, the heat must come from the interior of the plate. Since, however, this polarization takes place according to the same laws as that of light, we are further compelled to conclude that the propagation of the heat in the interior takes place in the same manner as that of light, namely in transverse oscillations. In the above-mentioned publication it was asserted that the conduction of heat depends upon this species of motion. This assertion, however, was only based upon the fact that the motion which is called heat cannot be of two kinds, and that, if its propagation through air, vacuum, or any other diathermanous substance takes place by means of transverse oscillations, its propagation in the interior of such bodies as are not diathermanous, which propagation we call conduction, must be of the same nature. This conclusion could not be drawn with certainty, because it * Monatsbericht der königlich preussischen Akademie der Wissenschaften zu Berlin. März 1868. † Monatsbericht, 1866, p. 62. Phil. Mag. S. 4. Vol. 36. No. 242. Sept. 1868. M was still possible that it was only the luminous portion of the heat which was polarizable. If, on the contrary, we could prove that the heat which is radiated at an oblique angle from bodies of any temperature, and therefore at a very low one, is also partly polarized, it would be proved that in the case of dark bodies the heat which they radiate comes in part from their interiors, and is propagated in them by transverse undulations. I think, then, we should be justified in asserting that the conduction of heat, or its propagation in athermanous bodies, also depends upon transverse oscillations. MM. La Provostaye and Desains state that they obtained polarized heat from a platinum plate whose temperature was below incandescence. Their experiments were made with platinized plates at a temperature of between 330° and 360° C.; and with these they say they have obtained very distinct polarization, though to a less degree than with smooth plates. It was shown in the abovementioned experiments with incandescent plates that these do not show any polarization if they are perfectly platinized. The plates used by MM. Provostaye and Desains, therefore, could not have been fully platinized. These experimenters do not enter into any explanation of the polarization of the heat radiated from these plates. It is also clear that by the employment of rough plates they were not in a position to arrive at the conclusion that the polarization depended upon the refraction of the heat issuing from the interior. For the same reason, their results, although very interesting, determine nothing in regard to the point at issue. It was therefore necessary to undertake new experiments, in order to decide whether the heat which is radiated from bodies of a lower temperature (say, 100° C.) is polarized. The means hitherto employed for the investigation of the polarization of heat depend upon its passage through double-refracting plates or through columns of mica plates. Neither of these could be here employed, because they do not allow the passage of the dark heat. There only remained, therefore, to make use of reflection for this purpose. Since, however, as is well known, only a small portion of the heat falling upon a mirror is reflected, especial precautions and arrangements had to be made in order to measure the reflected heat. The essential portion of the apparatus was a reflecting mirror, 65 millims. wide and 130 millims. long, of black polished glass. This was placed at the end of a horizontal tube of 60 millims. diameter and 120 millims. length. This tube was made of stout pasteboard, in order to prevent heat reaching the mirror by conduction. Both ends of the tube were closed by plates having circular openings of 35 millims. diameter. The axis of the tube, or the line joining the centres of the openings, passed, when produced, through the centre of the mirror, which could receive any |