EFFECT OF SURROUNDING MEDIUM. 151 



matter of speculation whether the earth would be at a much lower tem- 

 perature if its surface were composed of material not having bands of 

 selective emission. 



Rubens and Aschkinass (loc. cit.) found that after four reflections from 

 fluorite surfaces the deflection due to solar energy is reduced to zero, 

 showing that the opacity of the combined solar and terrestrial envelope is 

 practically total for wave-lengths 24 to 32 fi. In a recent communication 

 on the absence of very long waves from the sun's spectrum, Nichols 1 found 

 that the atmospheric transmission for wave-lengths ^=51/1 can not be 

 greater than 3 per cent. This, however, does not indicate that the sun 

 is lacking in radiation of wave-lengths ^=51 /, as the title of the paper 

 appears to imply, but that, whatever the intensity of the radiation emitted 

 at 51 n, it is almost entirely absorbed by the earth's atmosphere. 



1 E. F. Nichols: Astrophys. Jour., 26, p. 46, 1907. 



