594 SCIENTIFIC RECORD FOR 1883. 



but as soon as solidification began at the edges of the mass, the radia- 

 tion from the liquid portion at the center remained constant until the 

 solidification was complete. The author recommends this constant 

 radiation of silver as a spectro-photometric standard. (-7. Phys., August, 

 1883, II, ii, 3GG ; G. R., xcvi, 1033.) 



Baur has investigated by means of the bolometer the radiation of rock 

 salt at different temperatures. He concludes that rock salt absorbs its 

 own radiations more strongly than it does those of other bodies; and 

 that the absorption increases as the difference of temperature between 

 the radiating and absorbing rock-salt plates diminishes ; reaching its 

 full value when this difference is zero. He does not believe that the 

 radiations emitted by rock-salt are homogeneous; but concludes that 

 long waves are accompanied by more or less longer and shorter waves, 

 just as a yellow glowing solid emits beside the yellow radiations of a 

 greater wave-length in addition. (Wied. Ann., xxiii, 17; Am. J. Sci., 

 June, 1883, III, xxv, 469.) 



Lecher has calculated the absolute emissive and absorbing powers 

 of a body as a function of the diffuse reflecting power and of the emissive 

 power of surrounding bodies. Conceding the former to be constant at 

 all temperatures, he concludes : (1) That a body emits radiations of all 

 refrangibilities whatever the temperature ; and (2) that the distribution 

 in the spectrum of the emitted radiations, is independent of the tempera- 

 ture. Placing, for example, between two thermo-batteries differentially 

 arranged an incandescent plate of platinum, he finds that certain bodies 

 interposed between the platinum and either battery maintain nearly the 

 same absorbing power however the temperature of the plate be varied. 

 Incandescent electric lamps give spectra of the same quality, whatever 

 may be the temperature of the carbon filament. He maintains therefore 

 that the emissive power of any body whatever is for any temperature 

 the same fraction of the function which expresses the emissive power of 

 a black body. (Ber. Al: Wien, 1882, 57; J. Phys., April, 1883, II, n, 195.) 



Abney and Festing have published an investigation into the relations 

 between radiation, energy, and temperature, using for the purpose the 

 incandescent lamps of Edison, Lane Fox, British Electric Company, 

 and Maxim. They express their results as follows: (1) the current can 

 be expressed as a function of the potential ; (2) the radiation, after a 

 certain temperature of the filament has been reached, bears a simple 

 proportion to the energy expended in the lamp ; (3) the resistance can 

 be formulated as a function of the energy and therefore of the radia- 

 tion ; and (4) the temperature appears to be nearly a simple function of 

 the resistance. These results are given also in the form of curves. 

 (Phil. Mag., September, 1883, V, xvr, 224.) 



Van Assche has proposed a thin plate of selenium as a medium of 

 isolating heat radiation from other radiations. Tbe light which it trans- 

 mits is monochromatic, of a reddish tint, its spectrum being comprised 

 between A and C. All radiations are interrupted by the selenium when 



