45 Oh the Mat'erialliy of Heht. 



A Review of fonie Experiments ivhieh have been fippofed Id 

 dif prove the j\Iaterialitj/ of Heat. 



It has long been a queftion among philofophers, whether 

 the lenlation elf heat, and the clafs of piisnoniena arifing 

 from the fame caufe, be produced by a peculiar kind of mat- 

 ter, or by niolion of the particles of bodies in general. The 

 former of ihcfc opinions, though far from being univerfally 

 admitted, is now moft generally received; and the peculiar 

 body, to which the phjenomena of heat are referred, has 

 been denominated by M. Lavoifier caloric. Againft the 

 doctrine of the French fchool, fdme forcible arguments have 

 lately been advanced by Count Rumford and by Mr. Davyj 

 both of whom have adopted that theory refpefting heat, 

 which adigns as its caufe a motion among the particles of 

 bodies. 



The method of rcafoning employed by Mr. Davy in prov- 

 ing the innnaterialilv of the caufe of heat, is the redu£ito ad 

 abfurdiun, i. e. the oppugned theory is affumed as true, to- 

 gether with its applications ; and fa6ts are adduced dirc6l!y 

 contradidory of the aflumed principles : I fliall take the li- 

 berty of oflering a fiatement of the argument, rather different 

 from that of Mr. Davy, though, I truft, without mifrepre- 

 fentatiin, or any material omiffion. 



Let heat be confidcred as matter; and let it be granted, 

 that the temperature of bodies depends on the prefence of 

 imcombiaed caloric. Now, if the temperature of a body 

 be incrtafed, the free caloric, occafioning that elevation, 

 muft proceed from one of two fources : either, illly. It may 

 be communicated bv furroundino- fubftances; or, adly, It 

 may proceed from an internal fourcc, i. e. from a dil'engage- 

 mentof what before exifted in the body, latent or combined. 

 But the temperature of bodies is unitbrmly increafed by fric- 

 tion and percuflion, and nccefl'arily in one of the foregoing 

 modes. 



1. Mr. Davy found, by experiment, that a thin metallic 

 plate was heated, bv friftion in the exhaufted receiver o\ 

 an air-pump, even when the apparatus was infulated, from 

 bodies capable of fupplying caloric, by being placed on ice< 

 'J'his experiment he confiders as demonftrating, that the 

 ♦"volved caloric could not be communicattjd by lurrounding 

 bodies. 



To the inference deduced from this experiment it may be 

 objected, that the mode of infulalion was by no means per- 

 fetit. Admitting the vacuum, produced bv the air-pump, 

 to have been complete, iViU the fupply of caloric could not 



thus 



