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III. Experiments on the folar and on the terrejlrial Rays that 

 occajion Heat ; with a comparative View of the Laws to 

 which Light and Heat, or rather the Rays which occajion 

 them, are j'ubjecl, in order to determine whether they arc the 

 fame, or different. By William Herschel, LL.D. 

 F.R.S.* 



Part I. 



T 



X HE word heat, in its mod common acceptation, denotes 

 a certain fenfation, which is well known to every perfon. 

 The caufe of this fenfation, to avoid ambiguity, ought to 

 have been diftinguifhed by a name different from that which 

 is ufed to point out its effecT:. Various authors, indeed, who 

 have treated on the fubjecl of heat, have occasionally added 

 certain terms to diflinguifh their conceptions, fuch as, latent, 

 abfolute, fpecific, fentible heat ; while others have adopted 

 the new expreffions of caloric, and the matter of heat. None 

 of thefe defcriptive appellations, however, would have com- 

 pletely anfvvered my purpofe. I might, as in the preceding 

 papers, have ufed the name radiant heat, which has been 

 introduced by a celebrated author, and which certainly is 

 not very different from the expreffions I have now adopted ; 

 but, by calling the fubjeel of my refearches, the rays that 

 occafion heat, I cannot be mifunderftood as meaning that 

 thefe rays themfelves are heat; nor do I in any refpecl engage 

 myfclf to fhow in what manner they produce heat. 



From what has been faid, it follows that any objections 

 that may be alleged from the fuppofed agency of heat in 

 other circumflanccs than in its ftate of radiance, or heat- 

 making rays, cannot be admitted againfl my experiments. 

 For, notwithstanding I may be inclined to believe that all 

 phaenomena in which heat is concerned, fuch as the expan- 

 fion of bodies, fluidity, congelation, fermentation, friction, 

 he. as well as heat, in its various ftates of being latent, fpe- 

 cific, abfolute, or fenfible, may be explained on the principle 

 of heat-mak.ng rays, and vibrations occafioned by them in 



* From the Traiifaflions of the Rqyal Society far i8oo» 



the 



