﻿12 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vol. 47 



absorbent present, and is well expressed by Bouguers formula. In 

 other words, the absorption produced by a given quantity of water 

 in the form of vapor is the same whether the path is great through 

 a small density or vice-versa. Considering successive bands, for 

 example 0.81 u, par, 0, W, ii, it may be noted that the selective 

 absorption of water vapor is not greatest, like the general absorption, 

 at the shorter wavelengths, but increases as the wavelengths of the 

 bands increase. It varies from 10 percent in the more shallow bands 

 near A, at 0.76//, to nearly 100 percent in the bottom of SJ at 1.80/7, 

 where only on exceedingly dry days is much indication of energy 

 detected. 



However, in the separate bands themselves, where the increase in 

 absorption on reaching the bands from the shorter wavelength side 

 is quite sudden, the absorption then more slowly decreases, like the 

 general absorption, with increasing wavelength. 



The best values for the transmission coefficients are those in the 

 third column of Table iv. They give the fractional amount of the 

 incident energy transmitted by a layer of water 1 cm. thick in the 

 form of vapor. 



No indication of a general water vapor absorption in the region 

 from 0.68 a to 2.0011 has been found. 



