Chap. 1.1 [ 93 1 



CHAP. II. 



OF FIRE (CALORIC) AND ITS PROPERTIES. 



Inquiry whether Heat or Fire is a Subftance cr Quality, Fire a Sub- 

 Jiance. Application of this Doftrine. Analogy between Heat and 

 Light. Obje&ions. Properties of Fire or Caloric ; Minutenefs 

 if .Particles ; attraSed by all Bodies. Conducing Powers of dif- 

 ferent Bodies. Caufe of Fluidity. Why Heat is produced by 

 flacking Lime, and by certain Mixtures of cold Subftances. Freez- 

 ing of Water by the Fire Side explained. Fire the mojl elaftic 

 of all Bodies. 



THE element of fire is only known by its effects; 

 fo fubtile and evafive indeed is this wonderful 

 fluid, fo various are the forms which it alfumes in the 

 different departments of nature which it occupies, that 

 its very exiftence, we have feen, has been questioned 

 by fome philofophers. 



Heat, fay thefe theorifts, is nothing more than an 

 inteftine motion of the molt fubtile particles of bodies. 

 Fire is no other than this motion increafed to a cer- 

 tain degree, in other words, a body heated very hot ; 

 and flame is no more than ignited vapour, that is, va- 

 pour, the particles of which are agitated in an extra.-. 

 ordinary degree. 



In fupport of this theory it is alledged, i. That 

 motion in all cafes is known to generate heat; and if 

 continued to a certain degree, aclual ignition will be 

 produced, as the friction of two pieces of wood will 

 6rft produce heat; and afterwards tire; and the motion 

 of a glafs globe upon an elaftic cufhion will caafe a 

 Itream of fire to be copioufly emitted, adly, Bodies 

 which are molt fufceptible of inteftine motion, are 

 readily heated, jdly, Motion always accompa- 

 ' nies 



