162 



Experimental Investigations 



80 F., a little more quickly, or in 23 minutes 40 sec- 

 onds. 



To raise the temperature of the reservoir A to 100 

 F., = 3of R., it was necessary to continue the experi- 

 ment for i hour 15 minutes 10 seconds, reckoning 

 from the commencement of it ; but the reservoir B 

 reached the same temperature in i hour 12 minutes 10 

 seconds. 



The progress of this experiment from the beginning 

 to the end is exhibited in the following table. 



This experiment was begun at 7 minutes 30 seconds 

 after n, and finished at 22 minutes 40 seconds after 12, 

 the sky being perfectly clear during the time. 



On comparing all the results of this experiment, we 

 see that the reservoir A, which was placed very near 

 the focus, was more slowly heated than the reservoir B, 

 which was at a considerable distance from it. The dif- 

 ferences of time, however, taken to heat them an equal 

 number of degrees were very trifling, and I think may 

 be easily explained without supposing the condensation 

 of light to increase its faculty of exciting heat. 



In both the preceding experiments the solar rays 

 striking on the reservoirs of heat were convergent, and 

 they were even equally so on both sides. To deter- 

 mine whether parallel rays have the same power of ex- 



