22 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 68 



pheric gases and vapors. Curve a' of figure 6 is an energy curve so 

 made and it will be noted that even with the comparatively short path 

 through the spectroscope (11.5 meters) some of the^ absorption bands 

 are still quite pronounced. A black-body curve tangent to the curve 

 a' and corresponding to a temperature of 2,200° K. was thought to 

 be the best means of representing what might be expected as the form 

 of the energy curve were there no absorption bands present. This 

 is curve c which is tangent to curve a' at deviations ±5', at 100' to 

 140' (8 to 9 /x) and nearly so at 40' (5 /x) . 



In figure 7 are plotted the results obtained by dividing by values 

 read from curve c those obtained from curves similar to a' and b. 

 The solid points with the dashed lines connecting the mean values, 

 belong to the class a\ and show the absorption produced by the water 

 vapor and carbon dioxide in the path through the spectroscope alone. 

 The aqueous vapor corresponds to 0.008 cm. ppt. HoO, the carbon 

 dioxide, to about 7.4 grams ^ in a column of the length of the path 

 (11. 5 meters) and a meter square in section. The curve plotted with 

 open circles, squares and diamonds with the solid connecting line 

 corresponds to the class b. This curve shows the absorption due to 

 the medium contained in the path of 117 m. through the great tube. 

 The aqueous vapor corresponds to 0.082 cm. ppt. HoO and the carbon 

 dioxide to 83 grams in a column of the length of the path and of a 

 square meter in section. Probably the increase in absorption indi- 

 cated by the increase in the area of the absorption bands of the two 

 observed curves is more accurate than the absolute values of absorp- 

 tion for these involve the assumption that the black-body curve of 

 2,200° K. would represent the distribution of energy if there was no 

 absorption. 



There is also reproduced in the dotted curve extending from 5 to 

 about /'.y jx the work of Rubens and Aschkinass (1. c.) taken with a 

 column of steam 30 cm. long- at 100° C. and corresponding to 

 0.0042 cm. ppt. HoO. 



In the region shown here there are two important bands with 

 maximum absorption according to Paschen at wave-lengths 2.73 and 

 4.63 /x respectively due to carbon dioxide. Unfortunately it was not 

 feasible to remove this gas from either the spectroscope or the large 



^The total CO^, similarly measured, vertically from the surface of the 

 earth outwards is about 3,000 grams. 



