PHYSICS, PROGRESS OF, IN 1896. 



641 



tion spectra of fluorescent substances and ethereal 

 oils, making his measurements with a quartz prism 

 and replacing all lenses by mirrors. He finds that 

 uranin, eosin, fluoreseein, esculin. and chloro- 

 phyll show no thermal absorption down to wave 

 length 2 - ? p. Aymonnet (Paris Academy of Sci- 

 ences, Dec. 30. 1895), from a comparison of the re- 

 sults of various investigators, concludes that the 

 position of the heat maximum in the solar spectrum 

 depends not only on the composition of the prism, 

 but also on other parts of the spectroscope, and 

 that another source of error is the continual varia- 

 tion in the intensity of solar radiation. Jewell 

 ( Astrophysical Journal." February) considers that 

 he has established that the vibration period of an 

 atom depends to some extent upon its environ- 

 ment, an increase of the density of the material 

 (and presumably an increase of pressure) seeming to 

 produce a damping effect. He has done this by 

 study of the Rowland photographs of solar and 

 metallic spectra, and his results have important 

 bearings on solar physics. Ramsay (London Phys- 

 ical Society, Feb. 14) has devised a direct-vision 

 spectroscope in which the eyepiece can be moved 

 in a plane perpendicular to the axis. Pie reports 

 that it is of great utility in verifying the position 

 of spectrum lines. 



Color. Carey Lea (" American Journal of Sci- 

 ence," June), in investigations on the color relations 

 of atoms, ions, and molecules, has shown that if two 

 colorless substances unite to form a colored one, the 

 color belongs to the molecule, and hence a solvent 

 that separates the ions gives a colorless solution. 

 Mayer r American Journal of Science.'' January) 

 analyzes contrast colors by viewing through a re- 

 flecting tube a graded series of gray disks or rings 

 on colored surfaces. The method is based on the 

 fact, discovered by Rood, that black when mixed 

 with some colors darkens them, and with others 

 changes the hues. 



Polarization. Sohncke (Wiedemann's "An- 

 nalen," July) finds that, as theory requires, all 

 doubly refracting crystals emit polarized fluores- 

 cence. Wyrouboff (" Journal de Physique " (3). 3, 

 1894) has discovered a new substance which, like 

 quartz, possesses double rotatory power. It is the 

 neutral anhydrous tartrate of rubidium, and it is 

 unique in that its rotatory power in the crystalline 

 state is reversed in solution. " This wholly new phe- 

 nomenon,'' says Le Conte Stevens (address on " Re- 

 cent Progress in Optics," American Association, 

 1895), " introduces some perplexity in connection 

 with certain molecular theories that have been 

 formulated to account for double rotatory power." 



Longitudinal Vibration. Jaumann (Wiede- 

 mann's "Annalen." February) argues that since 

 both light and electric waves that strike a cathode 

 surface at right angles favor the dissipation of its 

 charge, they must have a component in the direc- 

 tion of propagation. He reconciles this with Max- 

 well's equations, which admit of no longitudinal com- 

 ponent, by supposing that the inductive capacity 

 and permeability of the medium are affected by 

 the oscillations themselves. Maxwell's constants 

 then become variables and the resulting equations 

 correspond to pencils of light that vibrate trans- 

 ly along their axes and more and more longi- 

 tudinally toward the edges (see R">XTGEX RAYS). 



Phosphorescence. Becquerel (Paris Academy) 

 finds that the salts of uranium emit invisible phos- 

 phorescent rays, some of whose properties are sim- 

 ilar to those of the Rontgen rays. They are emitted 

 not only after the salts have been illuminated, but 

 even when they have been kept in darkness for months. 

 They are reflected and refracted like light, affect a sen- 

 sitive plate, discharge electrified bodies, and traverse 

 substances that are opaque to visible light. The 

 VOL. xxxvi. 41 A 



invisible rays emitted by potassium uranyl sulphate 

 that has been kept several days in the dark can 

 discharge an electroscope even after passing through 

 a plate of aluminium two millimetres thick. Pow- 

 dered metallic uranium possesses the property in 

 an even stronger degree. In discussing these phe- 

 nomena. S. I*. Thompson (' Philosophical Maga- 

 zine." July) says: "The phenomenon of persistent 

 emission of these invisible rays by the uranium 

 compounds long after any electrical or luminous 

 stimulus has ceased to 'be applied would seem, 

 therefore, to bear the same relation to the transient 

 emission of them in the Crookes tube as the per- 

 sistent emission of visible light by phosphorescent 

 bodies does to the transient emission of light by 

 fluorescent bodies. Hence the writer ventures to 

 give to the new phenomenon thus independently 

 observed by M. Becquerel and by himself the name 

 of hyperphosphorescence. A hyperphosphorescent 

 bodv is one which, after due stimulus, exhibits a 

 persistent emission of invisible rays not included in 

 the hitherto recognized spectrum." Henry and 

 Seguy (Paris Academy of Sciences, May 26) find that 

 at a fixed pressure the brightness of zinc sulphate, 

 phosphorescing under the action of cathode rays in 

 a Crookes tube, decreases with time. There" is a 

 certain pressure at which the maximum brightness 

 is obtained ; a reversal of the current reduces this 

 to about one twenty-seventh of its original value. 

 Charles Henry (Paris Academy of Sciences, sum- 

 marized in " Cosmos." March 28) suggests what he 

 calls the " storage of light." based on the recent 

 discovery ("Annual Cyclopaedia," 1895. page 651) 

 that intense cold retards or prevents phosphores- 

 cence, thus, as it were, preserving in a latent condi- 

 tion the light to which the phosphorescent sub- 

 stance has been exposed. The light can be regained 

 by raising the temperature. 



Fluorescence. Wiedemann and Schmidt (Wie- 

 demann's "Annalen." March) find that the vapors 

 of potassium and sodium show brilliant fluorescence 

 when illuminated with bright sunlight. They show 

 also electro-luminescence. These results are of im- 

 portance in solar physics. Schmidt (Wiedemann's 

 " Annalen." May) maintains that all bodies are capa- 

 ble of fluorescence if dissolved in suitable solvents, 

 the most favorable form being a " solid solution," 

 as in sugar or gelatin. The color of fluorescence is 

 often nearly independent of the solvent. 



Dispersion. Guye and Jordan (Paris Academy 

 of Sciences. April 20) conclude from an experimental 

 study that active liquid bodies, not polymerized, 

 present only normal rotatory dispersion, and that 

 there is no simple relation between the refrangi- 

 bility of the radiations and the rotatory dispersion. 



So-called "Dark Lipht." Le Bon, in several 

 papers read before the Paris Academy of Sciences, 

 describes experiments on what he calls " dark " or 

 'black" light (himitre noire), an invisible form of 

 radiation arising from the passage of ordinary light 

 through apparently opaque metal plates, and capa- 

 ble of producing shadow pictures like those made 

 by Rontgen rays. His results have not been gener- 

 ally accepted. by physicists, it being generally as- 

 sumed that they are due to filtration of ordinary 

 light. Le Bon, however, asserts (May 11) that he 

 has taken all possible precautions against this. He 

 reports (Paris Academy of Sciences. Jan. 2?) that 

 when an ordinary photographic dry plate is placed 

 under a negative in a printing frame, and the nega- 

 tive is closely covered with a thin iron plate, if the 

 whole be exposed to the light of a paraffin lamp for 

 three hours, .a faint but well-defined image may be 

 brought out by prolonged development. If lead is 

 used to cover the plate instead of iron the image is 

 nearly as good as if no obstacle at all had inter- 

 vened. In another experiment (ibid.. May 11), after 



