On the Maferialtty of Heat. 4^ 



thus be entirely cut off, fince it has been (hown by Count 

 Rumford that caloric pafles even through a torricellian va- 

 cuum. If, therefore, fridion produce in bodies fome chancre, 

 which enables them to attraft caloric from furroundintr fub- 

 ftances, this attraction may be equally efficient in an ex- 

 haufted receiver as in one containing an atmofphere of mean 

 dcnfity. It would be an interefting fubje6l of experiment to 

 determine the influence of atmofpheres of various denfitiesas 

 conduftors of caloric ; for, fince efftcls are proportionate to 

 their caufes, and it is afcertained that common air conducts 

 caloric (better than it is conveyed through a vacuum) as 

 Jooo is to 702, it may be e.xpefted that the ratio will hold 

 in all intermediate degrees. 



In Count Rumford's mafterly experiment, the metal fub- 

 niitted to fridlion was encompalled by water, and air was 

 carefully excluded from the furfaccs in motion: yet the v.'ater 

 became hot, and was kept boiling a confiderable time. In 

 this cafe, the only obvious fource of caloric, from without, was 

 through the borer employed in producing the fridlion ; if it 

 be true, as the Count has obferved, that the water could not, 

 at the fame inftant, be in the aft of giving out and receiving 

 heat. The fame objeftion to the communication of heat, 

 from an external fource, exifts alfo in thus explaining Mr. 

 Davy's experiment; but I cannot admit that the argument 

 is demon(lrative in proving the evolved caloric not to be de- 

 rived from external fubftancesj for no abfurdity is implied in 

 fuppofing that a body may be rcceivino; caloric in one ftate, 

 and giving it out in another. We have an example of the 

 (imultaneous admiflion and extrication of a fubtile fluid, the 

 materiality of which is admitted by Mr. Davy, in an excited 

 eledric, which, at the very fame inftant, receives the eleftric 

 fluid from without, and transfers it to the neighbouring con- 

 .du^lors. In an ignited body, alfo, the two proceflTes of ab- 

 lorption and irradiation of light are, perhaps, taking place 

 at the fame moment. 



II. Another caufe of the incrcafe of temperature in bodies, 

 is the liberation of their combined caloric ; and if ihi^ be a 

 fource of temperature, the abfolute quantity of caloric in a 

 body muft be diminilhed by fridtiou. That no fuch dimi- 

 nution really lakes place, we have the evidence of two expe- 

 riments, — the one of Mr. Davy, tiic other of Count Kumford. 

 Mr. Davy, by rubbing together two pieces of ice, converted 

 them into water. Now water, ex hjpothiji, contains more 

 caloric than the ice from which it was formed ; and, on the 

 fame hypothefis, tfie abiblute quantity of caloric in ice is 

 dimiuidjL'd by fri6tiuu and liquefaction; which is abfurd. 



Count 



