of the invisible Rays of the Sun. 289 



just at the vanishing of the red colour, so that half its ball was 

 within, and half without, the visible rays of the sun. 



No. 1. No. 2. No. 3. 



4 8i - . 4 8i - - 48 



55i - - 48* " " 48 

 57 " - 49 4 8 i 



Here the thermometer No. 1 rose 8 degrees, in 10 minutes. 



By way of not losing time, in order to connect these last 

 observations the better together, I did not bring back the ther- 

 mometer No. 1 to the temperature of the room, being already 

 well acquainted with its rate of shewing, compared to that of 

 No. 2, but went on to the next experiment, by withdrawing the 

 stand, till the whole ball of No. 1 was completely out of the sun's 

 visible rays, yet so as to bring the termination of the line of the 

 red colour as near the outside of the ball as could be, without 

 touching it. 



No. 1. 





No. 2. 





No. % 



57 





49 



- 



^i 



5H - 



- 



49i 



- 



49 



59 



- 



5°i 



- 



49i 



59 



- 



50 



- 



49i 



Here the thermometer No. 1 rose, in 10 minutes, another 

 degree higher than in its former situation it could be brought 

 up to ; and was now 9 degrees above the standard. The ball 

 of this thermometer, as has been noticed, is exactly half an inch 

 in diameter; and its centre therefore was ~ inch beyond the 

 visible illumination, to which no part of it was exposed. 



It would not have been proper to compare these last obser- 

 vations with those taken at an earlier period this morning, in 



Pp2 



