314, Dr. Herschkl's Experiments on the solar, and 



sation of it by the refraction of the lens ; and, in this case, the 

 thermometer No. 3, by its situation, must have been partly 

 within the reach of the heat-image formed in the focus. During 

 the experiment, the thermometers were alternately screened 

 two minutes from the effects of the lens, and exposed to it for 

 the same length of time ; and the result was as follows. 



No. 2 No. 3. 







In the Focus. 



Near the Focus. 



Screened 



0' 



56 



56 



Open 



2 



62 



60 



Screened 



4 



59 



58 



Open 



6 



61 



59 



Screened 



8 



5*i 



57i 



Open 



10 



59i 



5H 



Here, in the first and second minutes, No. 2 gained two 

 degrees of heat more than No. 3. In the third and fourth, it 

 lost one more than No. 3. In the fifth and sixth, it gained one 

 more. In the seventh and eighth, it lost if more ; and in the 

 ninth and tenth, it gained | more than the other thermometer. 

 This plainly indicates its being acted upon by refracted heat. 

 Lest there should remain a doubt upon the subject, I now 

 removed the lens, and, putting a plain glass in the room of it, I 

 repeated the experiment, with all the rest of the apparatus in its 

 former situation. 



5U &i 



6o± 60 



Screened 



0' 



Open 



2 



Screened 



4 



Open 



6 



Screened 



8 



Open 



10 



61 60 



60 59i 



6o± 6o± 



