24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 68 



tube. Paschen ^ gives the following data relative to the amount of 

 absorption in these bands : 



Carbon Dioxide Band 4.26 to 5.12 m; Maximum at 4.63 m 



Equivalent path in cm. CO^. 76 cm. pressure. ... 0.08* 



Grams CO2, column i m" 1.6 



Absorption per cent I _9 



* Paschen in obtaining this figure assumes with Kayser (Wied. Ann. 42, p. 310, 1891) 

 that the CO„ in his laboratory had a partial pressure of about i/iooo atmosphere. In com- 

 puting the values given in the present work the partial pressure given by Hann of 0.23 mm. 

 or 3/10,000 of an atmosphere has been used, for the experiments were made under 

 out-of-door conditions. 



Remembering that there were respectively about 7 and 80 grams 

 ot CO2 in the meter square absorbing column producing the two 

 curves of figure 7, Paschen's results indicate that probably something- 

 like 20 per cent of the absorption in the water-vapor band at 2.65 /x, 

 and 60 to 70 per cent in that at 4.3 may be due to carbon dioxide. 

 For the carbon dioxide band at 4.63 /a Paschen considers that 650 

 grams is enough to produce practically complete absorption, the 10 

 per cent left in the table probably being accounted for by the impurity 

 of his spectrum. Accordingly 3,000 grams COo in a vertical atmos- 

 pheric column I meter in cross section would suffice to completely 

 extinguish the solar energy in the band whose center appears at 

 about 4.6 /A. It appears from Paschen's work that the absorption 

 for 0.004 cm. ppt. HoO in the form of steam at 100° C. and 76 cm. 

 pressure, is about equal to that of 0.008 cm. in the form of vapor at 

 somewhat less than 15° C. and 8 mm. partial water- vapor pressure. 



The region covered by figure 7 has been further subdivided and 

 the absorption measured is indicated in the following table. The next 

 to the last line summarizes the data of the absorption for the whole 

 region given in parts in the five lines just preceding. The last line 

 summarizes the data of absorption for the whole region from 1.3 to 

 8.0 /x. The last value, which gives the absorption percentage for the 

 radiation as a whole, depends greatly on the distribution of energy 

 in the spectrum of the beam to be absorbed. In the fourth column the 



' Annalen der Physik und Chemie, 51, p. 51, 1894. 



