on the terrestrial Rays that occasion Heat. 441 



which occasion illumination, over the areas ASQA, and GRQG, 

 of our two spectra ! These rays neither agree in their mean 

 refrangibility, nor in the situation of their maxima. At R, where 

 we have most light, there is but little heat ; and at S, where we 

 have most heat, we find no light at all ! 



zist Experiment. The Sines of Refraction of the heat-making 

 Rays, are in a constant Ratio to the Sines of Incidence. 



I used a prism with a refracting angle of 61 degrees ; and, 

 placing the thermometer No. 4 half an inch, and No. 1 one 

 inch, beyond the last visible red colour, I kept No. 2 by the side 

 of the spectrum, as a standard for temperature. 



At 1 inch. Standard. 



No. 1. No. 2. 



64 - - 6%\ 



66 6& 



- 67 - - 6 s i 



- *1\ " 6 3 | 

 Here, in eight minutes, the thermometer at half an inch from 



visible colour, rose $\ degrees ; and, at one inch from the same, 

 the other thermometer rose 3^ ; while the temperature, as ap- 

 pears by No. 2, remained without change. 



I now took a prism with an angle of forty-five degrees, and, 

 placing the thermometers as before, I had as follows : 

 55 - - 55 - - 55 



59 " - 57 54rt 



61 - - 58 - - 55 



62 - - 5 8! - - 55 



Here we likewise had, in 10 minutes, a rise of 7 degrees in the 





At i inch 





No. 4. 



o' 



64 



2 



67 



5 



69 



8 



69i 



