48 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 68 



absorption. It is especially absorbing at 50 jjl, 66 /x and 79 /* and 

 apparently also at 58 /* and 103 /x. It is relatively more transparent 

 at 47 /^. 54 f^, 62 fx, 75 fx, 91 /^ and 115 /x. 



E. ABSORPTION BY LIQUID WATER 

 (l) FOR WAVE-LENGTHS LESS THAN 2 ^ 



It has been thought worth while both for comparison and for its 

 practical value to include the following data for liquid water. As 

 already stated, in giving the absorption of water vapor in terms of 

 the precipitable water, it should not be inferred equivalent to that of 

 the same quantity of liquid water. In general the absorption of an 

 equivalent amount of water is different in the three states, liquid, 

 atmospheric vapor, and steam. 



For the shorter wave-lengths data have been obtained by Kreusler,^ 

 Ewan,'' and Aschkinass ^ from which are taken the following values 

 of a in the formula i — ioe~'^'^ in which d is in cm., to the original in- 

 tensity of a ray and i its intensity after transmission. A more com- 

 plete table will be found in Kayser's Handbuch, Vol. 3. 



Table ii. — Absorption of Radiation by Liquid Water 

 Wave-lengths Less Than 0.5//. 



Between the two absorption bands at 0.115 (x (metallic absorp- 

 tion^) and at 0.50 /x these values of absorption are what would be 

 expected from purely molecular scattering.^ When the same water 

 is in the form of atmospheric vapor its absorption is greater. This 

 will be seen by comparing a^x of table 10, for example at .5 ix, with 

 the a in the above table at the same wave-length remembering 

 a-u,x=e~°'. The vapor value and liquid value in the same units are 

 0.33 and .0002 respectively. 



As the true absorption bands are approached the liquid water 

 rapidly becomes a far more effective absorber than the vapor. The 

 following coefficients, a, are given by Nichols " for the transmission 

 of a cell of water i cm. thick. 



^ Annalen der Physik, 6, p. 412, 1901. 



* Proceedings of the Royal Society, 57, 117, 1894. 

 " Annalen der Physik und Chemie, 55, 401, 1895. 



* Martens, Annalen der Piiysik, 6, p. 603, 1901. 



° Astrophysical Journal, 2^, p. 392, 1913, and unpublished data. 



* Physical Review, i, p. i, 1894. 



