31 s Dr. Herschel's Experiments on the solar, and 



mometer No. 1, than No. 4, from change of temperature, had 

 received behind the screen. Now, to determine whether this 

 was owing merely to a transmission of heat through the glass, 

 or to a condensation of the rays, by the refraction of the burning 

 lens, I took away the lens, as soon as the last observation of 

 the thermometers was written down, and continued to take 

 down their progress as follows. 





No. 1. 



No. 4 



9'i 



74 



61I 



11 



7°i 



6ii 



12 



7°i 



6if 



— 



6& 



6i-2 



Hi- 



fei 



6i* 



Here the direct rays of the fire, we see, could not keep up 

 the thermometer No. 1 ; which, lost 2± degrees of heat, not- 

 withstanding the lens intercepted no longer any of them. I 

 now restored the burning glass, and continued. 



15' 6& 611 



16 69% 61J 



17 70 6i\ 

 20 70J Gx-f 

 25 71 61J 



Here again, the lens acted as a condenser of heat, and gave 

 i-| degrees of it to the thermometer No. 1. I now once more 

 took away the lens, and continued the experiment. 



31 68 6ii 



This again confirms the same, by a loss of 3 degrees of heat. 

 I restored the lens once more, and had as follows. 



