320 On the Nature of Heat. 



reafonings ; and, from the later experiments of Dr. Tlinmp- 

 fon, and Mr. Murray of Edinburgh, is perfe6tlv inadmillible. 

 If, however, the experiments of Count Rumford to prove 

 that heat is conveyed with much greater difficulty down- 

 wards than upwaids, be allowed to be fufficiently conclufive, 

 how is this phsenomenon to be reconciled bv the theory of 

 thofe who make all heat to be generated bv motion ? The 

 cftecl is not at all proportionate to the caufe ; for no good 

 reafon can be fliown, according to this hypolhefis, why heat 

 ihouW with more ditficulty be made to defcend in bodies 

 than lo afcend in them; for the fame motion will be com- 

 municated to the furrounding medium in all direftions. Is 

 not this fatl irreconcileablc with the doftrine alluded to? If, 

 however, we aflume the theory that heat is a peculiar ethe- 

 real fluid, all the difficulties that have before been enume- 

 rated will admit of an eafy folution, and the phaenomena of 

 beat will be reconciled in a fimple and beautiful manner: 

 indeed, on any other principle it would be extremely difficult 

 to account for mod of the operations in chemiftry, and it 

 would introduce a degree of uncertainty into the theory of 

 that fcience that would go very nearly to dedroy it altogether. 

 Thus, if we do not coniider caloric as a fubllance, we are 

 no longer at liberty to conceive that it is capable of attraftion. 

 Oxvireu gas, we are told, is oxygen combined with heat and 

 light ; and thus we find that, when oxygen enters into com- 

 bination with anv body, the two latter are always evolved. 

 If oxygen gas and phofjihorus be prefented to each other, the 

 oxveen combines with the phofphorus, and the caloric flies 

 oft'. This is readily accounted for on the fuppofition that 

 caloric is a fluid fui generis, and therefore capable of attrac- 

 tion ; and confequcntly we find this opinion very generally 

 adopted by chemUls, as alone able to aft'ord an adequate lo- 

 hition of the phenomena in queilion. The names of Boer- 

 haave, Lavoifier, Black, Crawford, and Fourcroy, are among 

 the moft celebrated partifans of this do\"trine, which, for its 

 beautiful (rmplicity, its pevfpicuity, and the eafe with which 

 it is applicable to all the phaenomena of heat, is much fupe- 

 rior to that which Hill divides in opinion many of the philo- 

 fophcrs of Europe. The ftrongeft, and indeed the only ar- 

 gument of weight that has been adduced againft this theory, 

 is that of Count Rumford, arifing from fome experiments 

 made by him concerning the fource of the heat excited by 

 friclion. From the accuracy with which thefe experiments 

 were condufted, and the nature of the refult, it certainly is 

 not very eafy to draw any inference thai is perfeftly fatisfac- 

 tory. It is evident that a change of capacity in the body, as 

 . ' . has 



