Chap. 2.] Caloric an elementary Principle. 97 



on the contrary, nothing is mose natural than that the 

 entrance of an exceedingly elaftic fubftance into the 

 pores of another body mould excite fome degree of 

 inteftine motion, as well as the emiffion of the fame 

 fubftance, which muft occafibn fome degree of con- 

 traction in the particles of the body. Heat is indeed 

 excited by the attrition of two pieces of wood ; but 

 why may not the fire in that cafe be expelled from the 

 wood by the vibration or contraction of its fibres *, 

 or from the air which occafionally interpofes itfelf ? In 

 the fame manner a piece of lead will become hot by 

 hammering ; but lead, and all metals, are known to 

 contain a quantity of fire in a latent ftate, which indeed 

 occafionally caufes their expanfion or dilatation ; it 

 is then the more probable fuppofition, that the fire 

 or caloric is expelled from the lead by the hammer- 

 ing and contraction of the metal, and this is rendered 

 ftill more probable, fmce the contraction or compref- 

 fion of the metal in a vice will produce the fame 

 effect. The inftance taken from the inflammability 

 of the fleam of fpirituous liquors will be. perfectly ex- 

 plained when I fpeak of fteam or vapour ; befides 

 that, thefe liquors are amongft the moft inflammable 

 fubftances with which we are acquainted, and their 

 particles, being in a rarefied ftate, will be more fubject 

 to thofe natural forces, which in all ftates are known 

 to act upon them. There is no increafe of gravity 

 in heated bodies, becaufe of the great elafticity of ca- 

 loric or the matter of fire, which expands the- bodies 

 into which it enters, and confequently rather dimiriifhes 

 their fpecific gravities. 



Sthly. All the other phenomena of nature are more 



* If the parts of a body, containing any fluid, are made to vi- 

 brate ftrongly, they will in general expel a part of the fluid out of 

 the pores. Nickclfin, Vol. II. p. 12?,. 



VOL. I. H fads factor ily 



