PHILOSOPHICAL 

 TRANSACTIONS. 



XIX. Experiments on the solar, and on the terrestrial Rays that 

 occasion Heat ; with a comparative View of the Laws to which 

 Light and Heat, or rather the Rays which occasion them, are 

 subject, in order to determine whether they are the same, or 

 different. By William Herschel, LL. D. F. R. S. 



Part II.* 

 Read November 6, 1800. 



In the first part of this Paper it has been shewn, that heat 

 derived immediately from the sun, or from candent terrestrial 

 substances, is occasioned by rays emanating from them ; and 

 that such heat-making rays are subject to the laws of reflection, 

 and of refraction. The similarity between light and heat, in these 

 points, is so great, that it did not appear necessary to notice 

 some small difference between them, relating to the refraction 

 of rays to a certain focus, which will be mentioned hereafter. 

 But the next three articles of this Paper will require, that while 

 we shew the similarity between light and heat, we should at 



* For the First Part of this Paper, see page 293. 

 MDCCC. 3L 



