286 Dr. Herschel's Experiments on the Refrangibility 



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



44 44 - . - 45 



47 44 ' - 45 



4 6 i - - 44 45 



4 6 t - " 44 45 



Here the thermometer No. 2 rose 2^ degrees, in 12 minutes; 

 and being, as has been noticed before, much more sensible than 

 No. 1, it came to the temperature of its situation in a short time; 

 but I left it exposed longer, on purpose to be perfectly assured 

 of the result. Its shewing but 2^ degrees advance, when No. 1 

 shewed 6±, has also been accounted for before. 



It being now evident that there was a refraction of rays coming 

 from the sun, which, though not fit for vision, were yet highly 

 invested with a power of occasioning heat, I proceeded to ex- 

 amine its extent as follows. 



The thermometers were arranged on the third line, instead 

 of the second ; and the stand was, as before, immersed up to the 

 first, in the coloured margin of the vanishing red rays. The 

 result was thus. 



No. 1. 



No. 2. 



No. 3 



46 



46 



45i 



50 



- 4^ " 



46 



5iJ 



- m - 



- 4S£ 



5*i 



47 



- 4^i 



Here the thermometer No. 1 rose 5^ degrees, in 13 minutes, 

 at 1 inch behind the visible light of the red rays. 



I placed now the thermometers on the 4th line, instead of 

 the 3d ; and, proceeding as before, I had the following result. 



