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XV. 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 I. 

 Read May 15, 1800 » 



1 he word heat, in its most common acceptation, denotes a 

 certain sensation, which is well known to every person. The 

 cause of this sensation, to avoid ambiguity, ought to have been 

 distinguished by a name different from that which is used to 

 point out its effect. Various authors indeed, who have treated 

 on the subject of heat, have occasionally added certain terms to 

 distinguish their conceptions, such as, latent, absolute, specific, 

 sensible heat ; while others have adopted the new expressions 

 of caloric, and the matter of heat. None of these descriptive 

 appellations however would have completely answered my 

 purpose. I might, as in the preceding papers, have used the name 

 radiant heat, which has been introduced by a celebrated author, 

 and which certainly is not very different from the expressions 

 I have now adopted ; but, by calling the subject of my researches, 

 the rays that occasion heat, I cannot be misunderstood as mean- 

 ing that these rays themselves are heat; nor do I in any respect 

 engage myself to shew in what manner they produce heat. 



From what has been said it follows, that any objections that 

 may be alleged, from the supposed agency of heat in other 



