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THE RADIATION OF THE PLANET EARTH TO SPACE 



By C. G. abbot 

 (With Two Plates) 



In an illuminating series of papers, G. C. Simpson recently has 

 approached the subject of terrestrial and atmospheric radiation to 

 outer space. The first of these papers is entitled " Some Studies in 

 Terrestrial Radiation." ' Here Simpson makes the unsatisfactory 

 assumption that the atmospheric water vapor behaves like a " grey 

 body " in absorbing radiation. That is, he assumes that general coeffi- 

 cients of absorption and of transmission may be employed, without 

 regard to the wave length of the radiation considered. Arriving in 

 this way at unexpected and questionable results, Simpson then modi- 

 fied his procedure in a second paper entitled " Further Studies in Ter- 

 restrial Radiation." ^ Here he makes the following important assump- 

 tions : (a) The stratosphere contains 0.3 mm. of precipitable water, 

 (b) The absorptive properties of atmospheric water vapor may be 

 regarded as so similar to those of steam that Hettner's ' observations 

 of the absorption of a layer of steam may be taken as representing the 

 coefficients of absorption of atmospheric water vapor between wave 

 lengths 4/x and 34jU.^ (c) " The stratosphere absorbs all radiation 

 between wave lengths 5^/i. and /jw, and from wave length 14/x, to the 

 end of the spectrum." 



As the Smithsonian Institution has hitherto published considerable 

 evidence relating to these three subjects, it has occurred to me to see 

 whether the use of our independently derived data would check well the 



^ Mem. Roy. Meteorol. Soc, \''ol. 2, No. 16, 1928. 



'^ Ibid., Vol. 3, No. 21, 1928. 



* Hettner, G., Ann. Physik. Leipzig, 4th Folge., Band 55, p. 476, 1918. 



■* Simpson nevertheless calls attention to the incomplete similarity between 

 the absorption of concentrated and unconcentrated vapors, and therefore cor- 

 rects Hettner's curve between S/x and ii;a from other data derived from atmos- 

 pheric experiments. 



Smithsonian Miscellaneous Collections. Vol. 82, No. 3. 



