No. 2. 



No. 3. 



In the Focus. 



In the Edge of it. 



64i 



64 



63 



^3i 



6si 



%i 



62! 



63 



*3» 



631 



322 Dr. Herschei/s Experiments on the solar y and 



Open - 11 



Screened 12-j 



Open 14, 



Screened 16 



Open 1 8 



Here the changes of the thermometer No. 2 were — f -|- -§• 

 — ii-j-2 — 1 -|- 1 ; and those of No. 3 were — £ -f- J — | 

 -j- i — |- + f- All which so clearly confirm the effect of the 

 refraction of the lens, that it must now be evident that there are 

 rays issuing from hot iron, which, though in a state of total in- 

 visibility, have a power of occasioning heat, and obey certain laws 

 of refraction, very nearly the same with those that affect light. 



As we have now traced the rays which occasion heat, both 

 solar and terrestrial, through all the varieties that were men- 

 tioned in the beginning of this paper, and have shewn that, in 

 every state, they are subject to the laws of reflection and of 

 refraction, it will be easy to perceive that I have made good a 

 proof of the three first of my propositions. For, the same 

 experiments which have convinced us that, according to our 

 second and third articles, heat is both reflexible and refrangible, 

 establish also its radiant nature, and thus equally prove the first 

 of them. 



END OF THE FIRST PART. 



Slough, near Windsor. 

 April 26, 1800. 



