432 Table 145 



SCATTERING OF SOLAR RADIATION BY WATER VAPOR 



From the Smithsonian Institution spectral observations at Mt. Wilson, Fowle 1 measured 

 the spectral transmission of solar radiation by a cloudless atmosphere (assumed dust-free) 

 and computed the spectral transmission coefficient a\ for a vertical path. Assuming 



ai = a a \a w \ w (1) 



where a a \ is the vertical transmission considering only the effect of scattering by pure 

 dry air, a w \ is the transmission considering only the effect of scattering by 1 centimeter 

 of precipitable water vapor, and w is the amount of precipitable water in the path, Fowle 

 plotted log a\ against zv (measured spectroscopically). The slope of the best-fitting 

 straight line gives log a w \, from which a w \ is computed. Table 145 gives a w \ as a function 

 of wave length; values are averages for the years 1910, 1911, and 1913.' 



1 Fowle, F. E., Astrophys. Journ., vol. 38, p. 392, 1913. 



8 Fowle, F. E., Smithsonian Misc. Coll., vol. 68, No. 8, p. 45, 1917. Additional data for X < .574/t 

 are given in Smithsonian Misc. Coll., vol. 69, No. 3, 1918. 



SMITHSONIAN METEOROLOGICAL TABLES 



