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138 



MAT'HEMATICAL and 



are produced by the fame caufe, according to the medium 

 on which it operates. It alfo appears that the particular 

 aptitude of any body to be heated is nearly as the elaftici- 

 ty of that body, or the cohcfion of its parts. Whatever 

 produces a tremulous motion in the particles of any body^ 

 excites heat in that body, and 'vice verfa whatever excites 

 heat produces a tremulous motion in the particles of the 

 body. Does heat therefore confift in nothing elfe than 

 the rapid vibrations of the minute particles of any body? 

 or is there an elementary principle of fire difFufed through 

 all bodies, which is only excited or brought into adion 

 by any caufe which produces a tremulous motion in the 

 particles of thofe bodies ? The latter feems mod probable, 

 though in folving the prefent hypothecs there is no dif- 



\ 



fire 



h 



ference whether heat depends on the fimple vibration of 

 the particles of matter, or whether it depends on the 

 which was only brought into adion by the vibration of 

 thofe particles, provided it fhould appear that the heat 

 in every body is uniformly as the vibratory motion 

 of the particles of that body. — This I apprehend is the 

 cafe and fhall beg leave to mention fuch evidence as feems 

 to render the matter at leaft very probable. 



Philofophers have enumerated five methods by which 



heat it generated, viz. i. by attrition, 2. chymical mixture, 

 <5. fermentation, 4. inflammation, and 5. by the Sun. In all 

 thefe cafes it appears that the heat depends on a vibratory 

 motion which by one means or another is excited in the 

 particles of the body. 



I 



Heat 



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rubbing of one body againft another. In this cafe there 

 can be no doubt that the heat depends on the vibratory 

 motion of the particles, hence bodies are fooneft heated 

 where the fridion is confiderable, provided the bodies have 

 alfo a proper degree of elafticity. For the motion once 

 communicated to the particles of an elaflic body, are re- 

 tained a confiderable time, and increafcd by every fucceed- 



ix\<y ftroke of the caufe v/hich put them into motion. The 

 ^ quantity 





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