490 Addilional Notes. 



lity of matter, and depends on a peculiar vibration of its par* 

 tides. This opinion was afterwards adopted by Boyle and 

 Newton, whose authority rendered it considerably popular; 

 the ancient opinl6n, however, was still held by many. Boer^ 

 HAAVE, at an early period of the eighteendi century, entered 

 the lists against Newton on this subject, and maintained, with 

 great force of argument, that heat is a distinct substance. From 

 the time of Boerhaave, till towards the close of the cen* 

 tury under review, diis doctrine was almost universally re- 

 ceived. Stahl, Macquer, Black, Priestley, Scheele, 

 Bergman, Lavoisier, Crawford, Irvine, Kirvvan, 

 Pictet, De la Place, and most other distinguished che- 

 mists, though differing as to some details of opinion on thl» 

 subject, all agreed in considering heat as a distinct positive 

 substance* 



But, towards the close of the century, the doctrine of Ba- 

 con was revived by Count Rumford and Mr. Davy. 

 These philosophers, observing that caloric continues to be ex- 

 tricated from a body subjected to friction, so long as the fric- 

 tion is kept up, and the texture or form of the body is not de- 

 stroyed, and that this heat-yielding process goes on to an in- 

 definite extent, concluded that this phenomenon is inexplicable 

 on the supposition of heat being matter; and that those effects 

 which have been referred to the operation of a peculiar calorific 

 matter, depend entirely on a vibratorj/ motion of the particles 

 of bodies ; and that from the generation, communication, or 

 abstraction of this motion, all the phenomena abscribed to ca- 

 loric are to be explained. — See Rumford'^ Essays^ vol. ii. 

 and Contributions to Medical and Physical Knowledge, 



This doctrine, however, has but few advocates. The suf- 

 frages of modern philosophers are almost unanimous in favour 

 of the opinion, that caloric or heat is a distinct fluid. The 

 latter opinion, indeed, seems to be confirmed to a degree little 

 short of demonstration, by the late experiments of Dr. Hers- 

 chell on this subject, who has shown, that the rays oilight^ 

 and the Ta.yso( heat emitted from the sun, are distinct and se- 

 parable ; that the latter, as well as the former, are refracted 

 by transparent bodies, and reflected by polished surfaces ; and 

 that both consist of particles which mutually repel each other, 

 and which produce no sensible effect upon the weight of other 

 bodies. — See the Philosophical Transactions ioi 1800. 



It cannot be denied, indeed, that some difficulties attend the 

 doctrine of heat, being a distinct and positive substance. Nor 

 is that by any means one of the smallest which Count Rum- 



