ABSTRACTS 



Authors of scientific papers are requested to see that abstracts, preferably 

 prepared and signed by themselves, are forwarded promptly to the editors. Each 

 of the scientific bureaus in Washington has a representative authorized to for- 

 ward such material to this journal and abstracts of official publications should 

 be transmitted through the representative of the bureau in which they originate. 

 The abstracts should conform in length and general style to those appearing in 

 this issue. 



ASTROPHYSICS. — The non-selective transmissibility of radiation 

 through dry and moist air. F. E. Fowle, Astrophysical Journal 

 38:392. 1913. 

 The change in the transmissibihty of radiation associated with atmos- 

 pheric water-vapor between the wave-lengths 0.371/x and 1.74/z was 

 first determined; this rendered possible the evaluation of the trans- 

 missibility of radiation by dry air vertically above Mount Wilson (1730 

 meters). In the following table are given, for a few selected wave- 

 lengths, the coefficients of transmission for dry air, aa\, the factor for 

 the change produced by atmospheric water-vapor when the amount 

 of precipitable water is 1 cm., a^\, and the theoretical values for dry 

 air computed from the theory of molecular scattering. 



TTAVE-LEXOTH 



370 ; 0.400 I 0.430 \ 0.460 i 0.500 0.600 ; 0.750 1.000 i 1.500 



a^x I 0.957 0.962' 0.967; 0.9710.976 10.977 | 0.988 0.990 0.988 



ttax (observed) 0.683 0.757 0.808 0.85l|o. 885* 0.916* 0.977 0.98?' 0.990 



aa\ (computed) 0.680 0.755 0.808 0.8500.890*10.946* 0.977 0.987^ 0.986 



; , I '\ j ' 



* Places of selective transmission. 



The corresponding values of a^ for air containing w cm. of precipitable 

 water-vapor would be a^x ' «ax- 



The transmission coefficient for dry air was then used for the deter- 

 mination of the number of molecules, A'^o, per cc. of a gas at 760 mm. 

 pressure and at 0°C. The result was 



No = 25.6 X 1018, 



found to correspond very closely with the present best value from 

 other methods, 27 billion billion ( Alillikan) . This mode of analysis shows 

 that for dry air, except where selective absorption accurs, the deple- 

 tion of the beam from the sun or other celestial body, as observed in 



159 



