31 8 On ihc Nalurg of Heat. 



feck for an explanation of them in no way frt falisfa^lofily as 

 bv iuppofing- them to originate from the univerfal prefence of 

 a very fubtile fluid called by the French writers calorique, 

 which penetrates, without exception, all bodies, and is 

 equally diffufcd through all fpace. 



That heat is only a property of common matter, a fpecific 

 motion of the particle? of bodies, is an hypoihcfis perfeftly 

 inadequate to the folution of the phasnomena alluded to. 

 Lord Bacon is the Hrft modern philofopher who attempted 

 to elucidate at lenirth anv theory on this fubjetl:; and we find 

 him, in a treatife written exprefsly for this purpofe, and en- 

 titled De Forma Calidi, deducing, from an enumeration of 

 the feveral pheenomena and efietls of heat, its general pro- 

 pcrtie:^, and hence defining it to be an expanfive undulatory 

 ■Motion in the minuie particles of the body, by ivhich they tend 

 'Milh fome rapidity totuards the circumference^ and at the fame 

 time incline a little upiuards. 



This fyftem, which evidently confiders heat not as an ori- 

 ginal inherent property of any particular fort of body, but as 

 mechanically producible in it, was adopted by moft; of the 

 mechanical philofophers of that age. h\ Boyle, Newton, and 

 Defcartes ; and has been fuppofed to have received no incon- 

 ■Gderabte (bare of weight from the later experiments of Count 

 Rumford and Profeflbr Piiiiet. Before, however, we acknow- 

 ledge the truth of this hypolhefi?, it is neceffarv we (bould 

 firlf afcertain if it is capable, in its application, of accnuntmg 

 for the various pheenomena of nature; for, unlefs theie are 

 found to admit by it of a fimple and obvious interpretation, 

 \ye are juftificd in concluding that it is unequal to the pro- 

 vince afligned it. That the theory under confideralion will 

 not (land the teft that is here fubmitted as the criterion of its 

 truth, cannot be well doubted after an attention to the fol- 

 lowing facts: — 'If a thermometer be placed under the receiver 

 of an air pump, and the air be fuddenlv cxhauftcd from it, 

 the thermometer will fink feveral degrees, and very quickly 

 after will rife again to its nfual height. Now if heat confifts 

 in vibrations, according to the tenets of this hypothefis, it 

 may be afked, How comes it to pafs that the fmall quantity 

 of n)alter that remains within the receiver is fir(t infufficient, 

 and afterwards fufficient, to maintain the temperature oriiri- 

 naily indicated by the thermometer? This is afa(Slwhich no 

 reafoning can fatisfaftorily account for fimply on mechanical 

 principles, and can only be reconciled on the fuppofition that 

 there is fuch a fluid as caloric pofieOed of a nature peculiar 

 to itfclf. 



The univerfal power of expanfion that heat poflefiTcs (for 



we 



