PHYSICS IN 1899. 



TOY 



the temperature at which this ratio is measured, 

 the amount of heat converted into vibratory mo- 

 tion is small compared with that which remains 

 as heat. The hypothesis that in gases energy 

 communicated to the molecules is distributed 

 equally through all the degrees of freedom must 

 apparently be given up, and so must that of gase- 

 ous atoms in the shape of rigid spheres, for such 

 an atom could acquire no internal motion from 

 heat communicated to it. Hemsalech (Comptes 

 Rendus, CXXIX, p. 285) finds that a self-induc- 

 tion in the discharge circuit affects the spectrum 

 of an oscillating spark discharge by lowering the 

 temperature, and thus eliminating the lines due 

 to the surrounding gas from the spectrum of the 

 spark. In hydrogen under atmospheric pressure 

 the lines due to the oscillating discharge have a 

 sharpness which is not interfered with by the 

 sparking distance. 



Magneto - optics ; Zeeman Effect. Poincare 

 (Eclair Electrique, XIX, p. 5) has elaborated 

 mathematically Lorentz's theory for Explaining 

 the resolution of spectral lines into complex forms 

 in a magnetic field. The supposition that the 

 ions are simple electrified particles accounts for 

 triplex forms, but not for the others. Lorentz's 

 theory supposes complex dynamical systems, 

 which explains some of the more complex results 

 of experiment. Kelvin (London Royal Society, 

 July 17) concludes from mathematical analysis 

 that a gyrostatic molecule could not in a strong 

 magnetic field give the Zeeman effect. Only a 

 broadening, not a splitting, of the spectrum lines 

 could occur. This agrees with Larmor's state- 

 ment. Voigt (Gottingen Nachrichten, IV, p. 

 329) concludes that the inverse Zeeman phenome- 

 non (alteration of selective absorption of a body 

 in the magnetic eld) is nothing else than the 

 Faraday phenomenon of magnetic rotatory po- 

 larization in substances possessing selective ab- 

 sorption. The author has developed a mathe- 

 matical theory in which these two effects appear 

 as special cases. Corbino (Academy of the Lincei, 

 VIII, p. 250) finds that the phenomena of anom- 

 alous magnetic rotatory polarization with all 

 their peculiarities can be deduced from the Zee- 

 man phenomenon by the admission of certain 

 postulates. The symmetry of the phenomenon 

 also follows with the aid of Helmholtz's anom- 

 alous-dispersion postulates, and also the phe- 

 nomenon of double refraction by absorbent va- 

 pors, normal to the lines of force. Voigt (Wiede- 

 mann's Annalen, LXVIII, 2, p. 352) shows that 

 observed deviations from the normal type of the 

 Zeeman effect are due to anomalous behavior of 

 the component of the electric force that is paral- 

 lel to the lines of force of the magnetic field. 

 On this basis the author works out modifications 

 of the Hertzian equations which account for the 

 quadruplets of Cornu and Becquerel and allied 

 forms. Preston, in a lecture before the Royal 

 Institution (May 12), finds evidence in the phe- 

 nomenon for a surmise that not only is the atom 

 composed of different ions, but the atoms of those 

 substances in the same chemical group are built 

 up from the same kind of ions. It may be, he 

 thinks, that all ions are fundamentally the same. 

 italdhammer (Wiedemann's Annalen, LXVII, 3, 

 p. GOO) shows that it is possible to explain the 

 effect on the basis of the older magneto-optical 

 theories, without calling in the conception of ionic 

 motion. Preston (Philosophical Magazine, XLVII, 

 p, 165) explains radiation phenomena in strong 

 magnetic fields by Larmor's electro-magnetic the- 

 ory. An ion describing an elliptic orbit is forced 

 by the magnetic field into a precessional move- 

 ment around the direction of the magnetic force. 



As a deduction from this, a single spectral line 

 should be tripled, and its constituents should be 

 plane polarized when viewed across the force 

 lines. The separation of the side lines of a triplet 

 should vary as the wave length. The author be- 

 lieves that the results of observation so far con- 

 firm this. Cotton (Comptes Rendus, CXXVI1I, 

 p. 294) has studied the polarization of rays from 

 sodium flames placed between the pole pieces of 

 an electro-magnet, and finds that the vibrations 

 in the neighborhood of the rays become elliptical 

 right-handed on one side and left-handed on 

 the other. For all radiations more refrangible 

 than one of the D lines the component perpen- 

 dicular to the field was in advance of the other. 

 For the less refrangible radiations the inverse is 

 true. This double refraction is connected with 

 the Zeeman effect, and is in accordance with 

 Becquerel's explanation. 



Kerr Effect. Abraham and Lemoine (Comptes 

 Rendus, CXXIX, p. 206) find that when the mag- 

 netic field productive of the Kerr phenomenon is 

 abolished the bi-refringence does not cease at 

 once, though the decay is rapid. The electro- 

 optic phenomenon is reduced by one half in 

 STnnroTnnnr P ar t of a second. Blondlot (Paris 

 Academy of Sciences, July 24) shows that the 

 time elapsing between the suppression of an elec- 

 tric field and the disappearance of the Kerr effect 

 can not exceed -^^1 ^^ of a second. 



Phosphorescence. Messrs. Lumiere (Comptes 

 Rendus, CXXVIII, p. 549) find that the phos- 

 phorescence of calcium and zinc sulphides after 

 exposure to the electric arc is enfeebled at 20 

 or 30 and disappears at about 50. When 

 the original source was the magnesium light the 

 disappearance took place at between 70 and 

 80. When the exposure to magnesium light 

 was at the temperature of liquid air ( 191) 

 the phosphorescence appeared at 180. 



Photo-action at Low Temperatures. A. and L. 

 Lumie're (Comptes Rendus, CXXVIII, p. 359) find 

 that ultrasensitive gelatino-bromide plates cooled 

 to the temperature of liquid air ( 191 C.) re- 

 quire 350 to 400 times as long exposure as at 

 ordinary temperatures. Less sensitive plates are 

 not acted upon at all. The plates are not altered 

 in any way, nor is any latent image in the film 

 affected. 



Fluorescence. Burke (Philosophical Transac- 

 tions, CXCI, p. 87) finds that fluorescing bodies 

 absorb differently, according as they are fluores- 

 cing or not, the rays that they give out while 

 fluorescing. 



"Dark Light." Le Bon (Comptes Rendus, 

 CXXVIII, p. 297) asserts that bodies inclosed in 

 opaque boxes can be photographed by exposure 

 for a few seconds to a plate of phosphorescent 

 zinc sulphide, which is then put into contact with 

 a sensitive plate. 



Monochromatism. Fabry and Perot (Comptes 

 Rendus, CXXVIII, p. 1156) recommend as a 

 source of monochromatic light the arc produced 

 between mercury electrodes in a Torricellian 

 vacuum. The principal radiations are: Violet, 

 which may be cut out by yellow glass or a thin 

 layer of bichromate-of-potash solution; green, 

 cut out with the preceding by a weak solution 

 of eosine; and two yellows, cut out by a con- 

 centrated solution of chloride of didymium. A 

 mixture of this solution with bichromate of pot- 

 ash cuts out all except the green rays. The violet 

 ray is useful for photography. For this the yel- 

 low and green need not be eliminated, but an 

 acid solution of sulphate of quinine must be in- 

 terposed in order to get rid of some ultraviolet 

 radiations. 



