3^ Mr. Henry on the Materiality of Hfaf. 



chemical facts are refohx-d into tlie law of douhle "ffimfyf 

 which aie at picfent explained by that of fingle eieciive at-» 

 tra6lion. 



4. Caloric a<5ls fometimes as an intermedltim in eombin- 

 in"" bodies which, without its aid, are not fufceptihle of com- 

 bination. Thus carbon and oxygen do not evince any ten-t 

 dency to cbmbinalion at the ordinary temperature of the at-* 

 mofphere; but caloric brings them into union, and confti- 

 tutes itieU'part of the rcUilting compound. This/ and a va-» 

 rifity of other Lnftances, have a llrikiug refemblance to what 

 is called intcrmcdiaie ajjinily. 



In the theorv of Dr. Crawfoi-d, no influence is allowed to 

 chemical, affinity over the pluv.nouKiia of heat ; and, indeed, 

 ihat philofopher cxpreills a decided opinion that elementary 

 heat is not capable of uniting chemically with bodies. Hence 

 it appears, that the difference between the terms ajfirtity and 

 capacity is not merely a verbal one, but that they are a6lually 

 wpreffive of difieHent powers or caufes; and the queflion, 

 therefore, which of thefe terms fliall be adopted in the de- 

 fbri^^uion of fads, is one involving the determination of caufes. 



Tiic term capacity for heat is employed, by Dr. Crawford 

 and other?, to denote, in the abltracf, ^'lat- power by which 

 difterent kinds of matter acquire different quantities of caloric. 

 Jlut in the various applications that are made of this theory, 

 ^tf'.more prccife meaning is often affixed to it; and the terra 

 is applied in much the fame fenfe which it has in common 

 language. When thus underdood, a difference of capacity 

 necellarilv implies a difference in the extent of the fpaces 

 between the minute particles of bodies ; and that thefe dif- 

 ferences occafion the varieties obfervcd in the acquirement of 

 heat by dilferent bodies. On ihi^ theory there is no active 

 principle or power inlierent in bodies, and more a6live irt 

 ibme than in others, — no tendency in the matter of heat tb 

 attach itlelf, in preference, to any one fubfl;ance. The af- 

 ligned caufe of the phsp.noniena of heat is not, I apprehend^ 

 Adequate to produce the effects afcribedto it. 



On the theory of capacities, a change of form is, in cer- 

 tain inltances, antecedent to the abloq)tion of caloric. Thirs, 

 when ether is converted into gas, on removing the preflure 

 of the atmofphere, according to this hypothefis, the capacity 

 ef the ether is increafed by its volatilization ; and the change 

 of form is prior to, and the caufc of, the ablbrption of calo- 

 ric. The order of events, then,, in the volatilization of ether 

 is firft an alteration of form; next, a change of capacity; 

 and, laUly, an abforption of caloric. On ilxis hypolhefis^ 

 ether may cxift in the. Itate of gas without containing jf 

 ;; . ' . 1 " greater 



