﻿FOWLE] absorption of water vapok II 



to follow the same law when the absorbent is in liquid form. 1 

 Saturated steam, according to Aery,- exercises more total absorption 

 over the whole spectrum than the same amount of water vapor under 

 atmospheric conditions. Water in liquid form goes still further in 

 this direction. " A layer of water 40 centimeters thick is almost 

 absolutely impervious to solar infra-red radiation beyond the wave- 

 length r.o/i. No such absorption occurs with the moist humid air 

 as the sun approaches the horizon, although the absolute amount 

 of water in a vaporous form interposed in the path of the rays must 

 be even greater than that contained in a layer 40 cm. thick." 



However, Paschen says : " In the liquid state there is a continuous 

 general absorption, whereas in the gaseous form only a discon- 

 tinuous absorption and emission spectrum is found, there being no 

 indication of a continuous superposed absorption or emission." It 

 may be very possible that the selective absorption in these water 

 vapor bands follows the same law of density when the absorbent is 

 in liquid form, and that the general absorption causes the great in- 

 crease in opacity observed. The last two curves in plate v certainly 

 show no differential effect between the maxima from p to 0, to W, 

 and to 8, due to a general water vapor absorption. It is hoped 

 to discuss this point further in a subsequent paper. 



Probably the only available measures on the absorption of liquid 

 water, comparable with those on water vapor, contained in this paper, 

 are those made by Abney and Festing. 4 Their results give, with 

 layers of y 2 inch and iyi inches liquid water respectively, in p } 

 78 and 19 percent transmitted, and for 0, 69 and 2 percent. The 

 logarithms of these numbers are 9.89, 9.28, 9.84, and 8.30, respect- 

 ively- The first three lie above, the last below the lines indicating 

 the absorption of aqueous vapor in plate 11. However, little weight 

 can probably be attached to the comparison, on account of the 

 probable difference in the effective purity of the spectroscopes used. 



SUMMARY 



The selective absorption of water vapor within the range of 

 densities observed seems to depend only on the amount of the 



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

 p. 547. 1880. G. D. Liveing and Dewar, Philosophical Magazine (5) 40, p. 

 268, 1895. 



' F. W. Very, Bulletin G, U. S. Weather Bureau, p. 94, Washington, 1900. 

 Angstrom finds the general absorption of C0 2 increases more rapidly than 

 with the first power of the density. Knut Angstrom, Annalen der Physik, 

 Band 6, p. 163, 1901. 



3 Annalen der Pliysik und Chcmic 52, p. 221, 1904. 



* Proceedings Royal Society of London, 35, p. 328, 1883. 



