NO. 4 SOLAR RADIATION ABBOT, FOWLE, AND ALDRICH 



17 



Fowle has determined transmission coefficients similar in their 

 application to the values a given above, but dependent on the total 

 quantity of precipitable water in the atmosphere as determined spec- 

 troscopically. He gives the following values of the transmission 

 coefficients for dry air (a a \) and for the equal of 1 cm. of liquid as 

 water vapor (a w \) above Mt. Wilson. We employ values obtained 

 from observations of 1910 and 191 1, in preference to later ones, 

 because obtained prior to the volcanic eruption of 1912. 



Table 6 — Coefficients of Transmission for the Dry Atmosphere and for 

 Atmospheric Water Vapor (Fowle} 



Wa Ye 

 length X 



a ok- 



.350 

 .632 

 .917 



,360 



655 



940 



371 



686 

 959 



384 

 713 

 959 



397 

 752 

 062 



413 

 783 

 965 



431 j. 452 j. 47s .503 



808 L 840 .863 .885 

 968 .9671.973-976 



535 



980 



574 

 905 

 974 



•913 



.624 

 .929 



•9781 .977 



Wave 1'gthX. 





.653 

 .938 

 .987 



.686 

 • 959 



722 

 970 



764 

 979 



,812 



990 



987 

 .987 



.146 



.987 



1.302 



.990 



1.452 • 



1.603 



These water vapor coefficients apply to smoothed energy curves, 

 and are a measure of the general extinction associated with water 

 vapor apart from its selective absorption. 



By Rayleigh's theory the dry air coefficients may be calculated 

 from the known number of molecules of air per cm. 3 at standard 

 temperature and pressure. This computation is in close accord 

 with the values above given. We hold therefore that Rayleigh's 

 theory of scattering would yield proper values of general atmospheric 

 extinction, for clear days on Mt. Wilson, if water vapor were absent. 

 As our observed general transmission coefficients in the infra-red 

 spectrum are somewhat less accurate than elsewhere, owing to the 

 necessity of interpolating the curves over the water vapor bands, and 

 from other causes, we have thought it right to compute by Rayleigh's 

 theory the true transmission coefficients in this region as they would 

 be if molecular scattering alone were the active agent. 



Table 7 — Computed Atmospheric Transmission and Extinction Coefficients 



Wave length. . . 

 Computed a a ^. . 



*— «a\ 



1— aw K 



764 



■979 

 ,021 

 007 



812 



,0162 

 .005 



864 .922 



9873 -9903 

 0127 .0097 

 005 .005 



9925 

 0075 

 005 



1.062 



•9954 

 .0046 

 .005 



1. 146 1.226 

 .9959 .9969 

 .00411 .0031 

 .005 .005 



1.302 



• 9975 

 .0025 

 .005 



1-377 



.0020 

 .010 



