142 



INFRA-RED EMISSION SPECTRA. 



temperature, using the formula tf) x =E x (iR^), where R is the observed 

 reflecting power and E is the corresponding intensity of the full radiator. 

 It will be noticed that the radiation will be highly selective, and that at 

 10 p. it approaches closely to that of the complete radiator. If, then, one 

 were to observe the emission curve of carborundum, the maximum at 10 \i 

 would appear as an "emission band," but its explanation is different from 

 that of emission bands of hot vapors, e.g., C0 2 and H 2 in the Bunsen 

 flame. In fig. ioo is given the observed reflection curve, a, of quartz, and 

 the computed emission curves of a complete radiator, b, and of quartz, c, 

 at a temperature of 400 abs. 



5 



Fig. ioo. 



8 9 10 11 12/JL 



Reflecting power of quartz (a); Emission of complete radiator at 400 abs. (6); Emission 

 curve (c) of quartz at 400 abs. 



In fig. 1 01 are given the computed emission curves, a and b, for a com- 

 plete radiator, for temperatures 300 and 400 abs., respectively, and the 

 corresponding emission curves, c and d, of quartz, at the same temperature 

 using the values of the reflecting power of quartz given by Rosenthal 

 (loc. cit.). These values are somewhat lower than found by the writer. 

 In general, the difference in the emissivity of the silicates and that of a 

 full radiator at 8 to 10 /j. would not be so marked as in quartz. For mica 

 (see Carnegie Publication No. 65) the emission minima would occur at 

 9.1 and 9.8 //, while for granite the emission minimum would extend from 

 8.5 to 10 (x. The combination would have an appreciable effect upon the 

 radiation curve of a surface like that of the moon. Even, if we exclude 

 atmospheric absorption, the emission curve (a, fig. 102) will not be smooth 

 and continuous, as some writers seem to think. If we superpose atmos- 

 pheric absorption, the emission curve of quartz (curve c, fig. 101) will be 

 somewhat as shown in curve b, fig. 102. Transmission curve c (fig. 102) is 



