132 INFRA-RED EMISSION SPECTRA. 



on the reflecting power of oxides at high temperatures will be necessary. 

 The emissivity of the sharp spectral lines in a magnetic field will also 

 require examination, although, on account of the wave-lengths involved, 

 the possibility of obtaining results is not promising. 



It may be added that the well-defined maxima of emission are not 

 affected by change in temperature, which is in marked contrast with the 

 results of Konigsberger 1 for the limited region of the visible spectrum. 

 Whether the emission maxima at 2.85 fi and 4.75 /x are due to the presence 

 of water, in the various minerals, remains to be determined. If they are 

 due to water, then one would expect to find them in calcium sulphate 

 (CaS0 4 + 2H 2 0), as well as in calcium oxide (CaO; probably some CaOH). 

 But in the sulphate no band was found at 2.9 n, where the emission should 

 be the most intense if due to water. The band at 4.75 \i is characteristic 

 of the sulphates (see Carnegie Publication No. 65). On the whole, the 

 assumption that these bands are due to the presence of water is no more 

 satisfactory than to ascribe them to the common constituent, viz, oxygen. 



The isochromatics of oligoclase show that the emissivity is proportional 

 to the energy in-put, thus differing from the other solids investigated ; but, 

 in view of the fact that in the oxyhydrogen flame the oligoclase emits 

 an intensely white light, it appears that the emissivity must suddenly 

 undergo a change in the visible spectrum, and perhaps form a more con- 

 tinuous spectrum in the infra-red. 



In considering the emissivity of these oxides in connection with the 

 radiation from the sun which is a mixture of these substances in various 

 conditions of temperature and physical state, and remembering that the 

 tendency of the solids is to emit a continuous spectrum at high tempera- 

 tures, it forms an interesting field for speculation as to what one ought to 

 expect for the composite radiation from the solar surface. The available 

 data show that gases radiating in a vacuum-tube and the metallic vapors 

 in the arc have their strongest emission lines in the region of 1 \i. In the 

 spark discharge the metallic vapors appear to have their maximum energy 

 in the ultra-violet. With data provided by the Astrophysical Observatory 

 (see vol. 2 of the Annals), giving the distribution of energy in the normal 

 solar spectrum, it has not been possible for me to compute a consistent >^ max 

 for different wave-lengths, nor a uniform value of the radiation constant a 

 (the value of a varied from 21.9 at 0.4 n, 15.6 at 0.5 /*, 11. o at 0.6 /*, 7.8 at 

 0.7// to 5.4 at 1.2 /i), by the methods given on a previous page, and it 

 seems evident that these laws are not applicable. If, as the data herewith 

 presented on the emissivity of the oxides seems to show (assuming the solar 

 surface to be solid, electrolytic conductor as compared with a pure metal 

 with high reflecting power) these radiation laws do not hold, how much 

 less must they be true in the case of the solar surface in its real condition. 



1 Konigsberger: Ann. der Phys. (4), 4, p. 796, 1901. 



