﻿V( )i.. 47 



Smithsonian 

 Miscellaneous Collections 



V< )L. 2 Quarterly Issue Part I 



THE ABSORPTION OF WATER VAPOR IN THE INFRA- 

 RED SOLAR SPECTRUM 



By F. E. FOWLE, Jr. 



(Communicated by S. P. Langley, Secretary of the Smithsonian Institution.) 



PURPOSE OF THE PAPER 



The quantitative investigation of the relationship between the 

 amount of water vapor in the terrestrial atmosphere and the corre- 

 sponding changes in the transmissibility of the latter to the incoming 

 solar energy, is the primary object of this paper. Bouguer's formula, 

 which will later be treated in detail, furnishes an analytical means 

 for this study. As generally used, however, it would indicate that 

 the absorption depends only on the amount of vapor present as an 

 absorbent ; that is. the same absorption would be produced bv a 

 given quantity of water in the form of vapor, whether the path were 

 long through a small density, or short through a great densitv. In 

 order to determine spectroscopically the amount of aqueous vapor 

 present in our atmosphere, it is necessary that such a condition should 

 be trne ; in such a case, only, is it immaterial what distribution of 

 densities exists in the atmospheric strata. 



Janssen 1 finds, however, that certain oxygen bands do not satisfy 

 this condition: neither does carbonic acid gas, according to Ang- 

 strom.- Consequently it is important to find whether or not the 

 absorption due to water vapor is expressed by Bouguer's formula in 

 its ordinarv form. 



1 J. Janssen, Report British Association for Advancement of Science, Bath, 

 p. 547, iSSo. 



z Knut Angstrom, Annalen der Physik, Band 6, p. 163. 1901. Somewhat 

 analogous variations are observed with some salt solutions. See E. Midler, 

 Annalen der Physik. Band 12, p. 767, 1903. 

 1 1 



