46 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



liable to give too high values at the higher altitude as compared with 

 the lower one. This is actually the result of the observations. It 

 therefore appears to me that the observations lend support to the 

 view that the variations produced in the radiation of the lower atmos- 

 phere by a change of locality or by other influences are due to 

 changes in the radiating power of the water vapor; changes that 

 we are able to define, within certain limits, from observations of 

 the temperature and the humidity at the surface of the earth. 



I have now, without venturing to emphasize the absolute reliability 

 of the procedure, applied a correction to the observed vapor pres- 

 sure at different altitudes, in order that the pressure may give a 

 true measure of the integral radiating power of the water vapor. 

 Considering that at the altitude of Mount Whitney, the constant K 

 in Suring's formula is 1.8, and that the total pressure there is only 

 44 cm., so that the absorption coefficient according to Miss v. Bahr's 



16 ^ 

 observations should be — — of the value corresponding to p = 66 cm. 



21-5 



(Lone Pine, Bassour), and finally that the pressure ought to be 



reduced to the temperature 20° C, I have used the reduction factor 

 l^.^S.m =0.68 



2.2 21.5 293 



for the humidity values taken at the summit of Mount Whitney 

 (4,420 m.) and also for Mount San Gorgonio (3,500 m). 

 A similar consideration gives the reduction factor 



2.2 21.5 273 



for the measurements at Mount San Antonio (3,000 m.) and at 

 Lone Pine Canyon (2,500 m.). 



In this way the values plotted in figure 5 are obtained. We are 

 now able to draw a continuous curve through the points given by 

 the observations corresponding to various altitudes. With regard 

 to the considerations that I have brought forward in the theoretical 

 part, I have tried an expression of the form 



E a =K-Ce-^ 

 where 



K = 0.439, C = 0.158, and 7 = 0.069. 



This gives a fairly good idea of the relation between the radiation of 

 the atmosphere at 20 C. and the humidity. The curve corresponding 

 to this equation is given by a dotted line in figure 5. The expression 

 adopted here does not fit the observations at high pressures so 



