Mr. Henry on ibe'Maler'uiVity of'Heiit. 53 



gneater' abfolute quantity of cabric than in a Uqind form. 

 Bttt fuch an interpretation of phsenoniena is directly can- 

 tradi<5lory to an ellabliilied principle, adniitted even by thofe 

 who prefer the doArnie of capacities, viz. that all bodies, 

 during their converfion from a fluid to a vaporous (late, ab- 

 forb caloric. It is at variance alio with obierved faSs : lor, 

 if a thernioiueter be inimerfed in a portion of ether, confined 

 under the receiver of an an--punip, the teniperatuve of the 

 ether will be found to fink gradually during tlie exbaiiftiou 

 of the air ; and the evaporation becomes proportion ally, 

 flower, till, at lali, it is fcarccly perceptible. We may there- 

 ioxQ infer, that, at a certain point of dimininicd temperature,' 

 the volatilization of ether would entirely ceafe, if the iupply 

 of caloric from furrounding bodies could be completcjy inter- 

 cepted. But, on the theTiry of capacities, the evapnratioUi 

 fliould proceed as rapidly at the dole as at the commence- 

 ment of the procefs ; or, in other words, evaporation flioulA 

 be wholly independent of temperature, which every on© 

 knows is contrary to faft. 



It may be confidcrcd, therefore, as extremely probable, 

 that the tendency of ether to alTume a gafeous form depends 

 on its chemical affinity for caloric. But, it may be a(kcd, 

 how is this affinitv counteraL^ed by an increafed prelfure, and 

 augmented by a dimininicd one? 



A cireumRance ablolutcly eillntial to the fv)rmation bf» 

 gafes is, that free fpace (half be allowed for their cxpanfion. 

 Mechanical preflTurc a£fs as a counteracting force to this ex-. 

 panfion, and either prevents it completely or partially, ac- 

 cording to the deirree of its application. But from this faft 

 no argument can be drawn againll the exiftence of cheujical, 

 affinity as an attribute of caloric. Two oppofite forces in 

 phyfics may be fo balanced, that neither fhall produce its 

 appropriate'effeil. Thus, a body impelled in contrary direc- 

 tions may remain at relt ; yet the operation of tht oppofmg 

 forces, in this cafe, cannot be denied. Even in chemiftry, 

 ■we have unequivocal examples in which the action ot the 

 affinities is fuppreiTed by more powerful Caufes. Thus, bodies 

 that havf a ftrong chemical affinity are kept perie<::lly diuinCt 

 even when placed in contaft by the atBnity of aggregation. 

 The only inference, then, that tan fairly be deduced from 

 the efTcAs of prelTurc in preventing the fornuuion of gafes,^ 

 18, that it is a power fometimes fuperior in energy to that of 

 chemical affinity. 



Since, therefore, caloric is charaAerizcd by all tlie proper- 

 ties, except gravity, that enter into the delinition ot matter, 

 W'c may venture to coufidcr it as a diltincl and peculiar body. 

 '•- E3 ^". 



