C. C. Hutchins — Radiation of Atmospheric Air. 361 



ing the failure to establish a connection between the absolute 

 amount of moisture and the radiation, the tabulated results 

 show a striking connection between the relative humidity and 

 the radiation, as is exhibited in the following table. 









Table T. 









a 



5 



m 



n 



t-t' 



/' 



h 



Oct. 20 



76-16 



14-7 



15-6 



88-2 



90- 



0-000002562 



Nov. 7 



76-41 



16-1 



23-9 



89-0 



40- 



1189 



Nov. 9 



76-76 



16.7 



22-8 



88-7 



50- 



1273 



Nov. 10 



76-76 



10-0 



139 



84-0 



57-5 



1559 



Nov. 11 



76-19 



14-4 



17-3 



84-5 



71- 



1812 



Nov. 1 1 



75-80 



18-9 



20-4 



87-7 



85-5 



1986 



Nov. 12 



75-99 



14-0 



17-9 



88-3 



62-5 



1597 



Nov. 13 



76-38 



136 



19-4 



82-6 



47- 



1513 



a is the date. 















b " barometer reading 













m " wet bulb. 













n " dry bulb. 













t-t' " difference of temp 



. between hot air 



and cube. 





/' <; relative 



humidity. 













h " absolute radiation. 













It will be seen that h increases quite regularly with/', though 

 the plotted observations do not lie well enough upon any 

 smooth curve to enable us to assert the law of connection, 

 which law it would be difficult to deduce without the means of 

 controlling the presence of other accidental constituents of the 

 atmosphere ; such as carbonic acid and gases resulting from 

 the decomposition of dust, coming in contact with the heated 

 tube. That these accidental impurities have a very great in- 

 fluence, is shown by the following experiment. On Dec. 7, 

 the mean deflection produced by the air column at 120° was 

 64 scale divisions. A small amount of pure dry carbonic acid 

 gas was allowed to mix, a bubble at a time with the air at the 

 entrance of the heated tube. The deflection rose to 140 or 

 more than doubled. When a very small amount of illumina- 

 ting gas was mixed with the air, the deflection was too great 

 to be recorded on the scale. As it is impossible at present to 

 allow for the presence of these impurities or even for the aque- 

 ous vapor in assigning a value to the absolute radiating power 

 of atmospheric air we are obliged to employ an average result 

 obtained from several days' observations. 



The following table presents the measures made on six days 

 after considerable practice had been had with the apparatus. 



The observations were made at four or more different tem- 

 peratures of the air column, with a view to learning the law 

 connecting the heat radiated and the temperature. 



