6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 68 



Paschen ' investigated the transparency of carbon dioxide and 

 water vapor. He used a column of steam 7 cm. long- at atmospheric 

 pressure. Between the wave-lengths i and 9 /x he showed definitely 

 the absorption due to each absorbent. He also gives four curves 

 showing the energy curves to about 9 /x of a blackened platinum 

 strip at 450° C. observed through an empty fluorite cell and with the 

 cell containing films of liquid water, o.oi to 0.02 mm., at least 

 0.03 mm., and 0.08 mm. thick. The principal liquid water bands 

 of this region lie at 2.9, 4.7, 6.1 fx. 



Rubens and Nichols ' found but a small absorption due to water 

 vapor for the energy from a terrestrial source selectively reflected 

 from fluorite at 24.4 jx. Energy of this wave-length could not have 

 been found in the solar spectrum by the earlier observers owing 

 to its absorption in their prisms of rock salt or fluorite. Rubens and 

 Aschkinass ^ pursued the experiments using selectively reflected 

 sun-light of the same wave-length, 24.4 /x, with purely negative 

 results, no deflections were obtained. They then proceeded to the 

 examination of the transmission of energy from a laboratory source 

 through 40 cm. of steam at atmospheric pressure. The results of 

 Rubens and Aschkinass and of Paschen will be given later in more 

 detail in connection with the results of the present research. Their 

 results were all obtained with steam at 100° C. and 76 cm. pressure 

 whereas the results of the present contribution were obtained at 

 atmospheric conditions both as to temperature and to total and partial 

 pressures. 



Rubens later, using the residual radiations selectively reflected 

 from various crystals, found that water vapor has strong absorption 

 between 45 and 120 fi, this being especially intense at 50 /x, 66 fx, and 

 79 fji. Relatively high transparency occurs at 47 fi, 54 fi, 62 fi, 75 fi, 

 91 /i,, and at 115 /x.* In an earlier research with Wartenberg' he 

 found that a column of steam 40 cm. long and at atmospheric pres- 

 sure transmits radiation as follows : 39.6 per cent at 23 fx, 0.7 per 

 cent at 52 /x, 19.6 per cent at 1 10 fi, and 49.2 per cent at 314 /x. These 

 results are not necessarily at variance with the earlier statement that 

 with selectively reflected sun-light purely negative results were 

 obtained at 24.4 fx by Rubens and Aschkinass. For some other 



^ Annalen der Physik und Chemie, 51, p. i, 1894; 52, p. 209, 1894. 



" Idem., 60, p. 418, 1897. 



^ Idem., 64, p. 548, 1898. 



* Berichte Kgl. Preuss. Akademie der Wissenschaften, 1913, p. 513. 



° Verb. Deutsche Physikalische Gesellschaft, 13, p. 797, 1911. 



