NO. 8 WATER-VAPOR TRANSPARENCY — FOWLE 47 



C. ABSORPTION IN WATER VAPOR FOR WAVE-LENGTHS 9.O /x TO I4 /a 



AND BEYOND 



(l) LABORATORY CONDITIONS APPROXIMATING ATMOSPHERIC CONDITIONS AS TO 

 TEMPERATURE, TOTAL AND PARTIAL PRESSURES 



In the main body of this report will be found in detail the observa- 

 tions for this region made with a 15° rock-salt prism. The amounts 

 of vapor range from 0.003 cni. to 0.26 cm. ppt. H2O. Figure 8 shows 

 the appearance of a record of holographic observation, somewhat 

 complicated by the observations necessary to eliminate field light. 

 The principal results relating to the absorption of water vapor are 

 shown in figure 10 and table 7. 



For information on the effect of carbon dioxide in this spectrum 

 region (partially indicated by the shaded region in figure 10) the 

 main body of the paper must be consulted. A path through the 

 atmosphere of the order of 100 meters is sufficient to produce com- 

 plete absorption in the carbon dioxide band between 14 and 15.5 jw 

 (see fig. 11). Besides the work published by Rubens and Aschkinass, 

 and shown in figure 11, further data will be found in " Uber das 

 ultrarote Absorptions-spectrum der Kohlensaure in seiner Abhan- 

 gigkeit von Druck und Partial-druck," von G. Hertz, Verb. Deutsche 

 Physikalische Gesellschaft, 13, p. 617, 1911. 



(2) RESULTS FOR STEAM (7 TO 20 |x) 



In figure ii will be found the results of Rubens and Aschkinass. 

 They show the percentage absorption due to 0.045 cm. ppt. H2O in 

 the form of steam at 100° C. and 76 cm. pressure. Again by com- 

 parison with table 7 it will be noted that the same amount of water 

 in the form of steam gives a greater absorption than when at a 

 smaller partial pressure although the same total pressure. 



D. RESULTS FOR STEAM. WAVE-LENGTHS GREATER THAN 20 fx 



Isolated results for greater wave-lengths have been obtained by 

 the use of the " Restrahlungen " from various crystals. Rubens and 

 Wartenberg^ found that a column of steam 40 cm. long 100° C. 

 y6 cm. pressure (0.024 cm. ppt. HoO), transmits radiation as follows : 

 39.6 per cent at 23 fx, 0.7 at 52 fx, 19.6 at no /^ and 49.2 at 314 fi. 

 At the same wave-lengths 20 cm. of carbon dioxide at 76 cm. pres- 

 sure showed no absorption. Rubens ^ later found that water vapor 

 in the whole region between 45 and 120 fx causes many bands of great 



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



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



