94- Arguments to prove Fire not a Sub/lance. [Book II. 



nies fire or heat, as is evident on mixing oil of tur- 

 pentine and vitriolic acid ; and the heat feems in mod 

 cafes to bear a proportion to the degree of motion or 

 agitation. In the boilinp; of water, and in the hiflmg 

 of heated iron v hen applied to a fluid, this motion is 

 evidently manifefted. 4thly, If the particles of any 

 body are. excited to a violent decree of interline mo- 

 tion, by attrlrion, fermentation, &c. if they do not 

 actually emit flames, they will yet be difpofed to catch 

 fire with the ucmoft facility ; as in the diftillation of 

 ipirits, if the head of the (till is removed, the vapours 

 will inftantly be converted into flame if brought into 

 contact with a lighted candle, or any other ignited 

 body. Laftly, Heated bodies receive no acceffion of 

 weight, which they apparently ought to do, on another 

 body being introduced into their pores. 



Plaufible as this reafoning appears at firft fight, the 

 hypothefis which afllgns exiilence to the principle of 

 fire, as a diftinct elementary principle, is fupported by 

 snore numerous fads, and by more decifive reafons ; 

 it accounts better for all the phenomena of nature, and 

 even for thofe very phenomena which are adduced in 

 fupport of the contrary opinion. 



i ft. If it is admitted, as I apprehend it muft, by 

 the advocates for the contrary opinion, that the inter- 

 nal motion or agitation, which they fay conllitutcs heat, 

 is not equally felt by all the component particles of 

 bodies, but only by the minuter and more fubtile 

 particles ; and that thefe particles being afterwards 

 thrown into a projectile (late produce the effect of 

 light; thefe concefllons will almoft amount to the 

 eftabliftmient of the principle of fire as an elementary 

 principle. 



idly, That fire is really a fubftance, and not a qua- 

 lity, appears from its acting upon other fubftances, the 



reality 



