F. W. Very — Note on Atmospheric Radiation. 535 



simply proportional to the depth of the layers and to the 

 fourth power of the absolute temperature, we get the values in 

 the third column of the following table. This, however, in no 

 case represents the direct radiation of the atmosphere from 

 layer to layer, because the selective radiations of the gaseous 

 molecules can proceed but a little way before they are absorbed 

 by other molecules of the same gas. These in turn radiate 

 again to cooler ones at a still higher level, and so on,* but the 

 number of successive transferences of heat is very great even 

 in a layer no more than one thousand meters thick, and the 

 process is a slow one, not to be compared for rapidity with the 

 rate of escape of unimpeded radiation. 



Talcing averages through the first 15,000 meters of air, we 

 get the following mean values of energy expended as radia- 

 tion in large calories per square meter, for comparison with 

 Bigelow's AQ, or " heat expended." 





Per thousand meters 



Elevation 



AT 



R (computed) 



AQ (observed) 



Upper layer 15000 — 10000" 1 

 Middle layer 10000— 5000 

 Lower layer 5000— 



0-96 C. 



7'3 



5-4 



0-057 

 0-429 

 0-314 



0-408 

 0-237 

 0-090 



The sudden diminution of the computed radiation (from 

 stratum to stratum) in the upper layer follows from the en- 

 trance into the isothermal region, and from the diminution of 

 A T ; but this does not imply a cessation of atmospheric radia- 

 tion in this nonadiabatic layer. On the contrary, the observed 

 increase of A Q in the upper layer is presumably due very 

 largely to direct radiation to outer space. That this outgoing 

 radiation produces no appreciable fall of temperature with 

 increasing elevation, appears to be because the heat of the 

 upper layer is continually replenished by absorption of the 

 radiation from the lower air, but especially because the solar 

 rays are undergoing their initial absorption, and though some 

 of the absorbent material, such as aqueous vapor, is excessively 

 rarefied, there are certain rays which are so powerfully 

 absorbed that they suffer loss in passing through the most ten- 

 uous layer, f 



The values of R, computed on the above assumption, are con- 

 siderably greater than those of A Q in the lower atmosphere, 



* Op. eit., pp. 114-115. + F. W. Very— Atmospheric Radiation, p. 123. 



