DcSrine efHeat, tvith refpeB to denfe and elaflic Fluids. , jjjp 



evident from the variety of cafes in which we fee It to take place during chenucal 

 changes of the moft different kinds, and even in feme modifications which muft. be ac- 

 counted purely mechanical. Before, therefore, the latent combination of caloric can ferve 

 as any Index of phyfical analogy between two phenomena, there muft be Ihown to exift a 

 correfpondence in the other changes with which it is refpeiSlively aflbciated. So little do we 

 find of this correfpondence here, however, that the changes moft intimately and effentially 

 conneiSed with it are in the one cafe an expanfion, and in the other a diminution of 

 bulk. 



Nor do we find the comparifon at all better fupported, if, attributing the latent abforp- 

 tion of caloric to a previous change of capacity, we attempt to fubftitute this as an Indication 

 of the analogy in queftion*. This change of capacity itfelf requires, no lefs than the 

 abforption of caloric, the fuppofition of a previous modification, and if, with the generality 

 of authors, we refer this modification to change of form, the fame difficulty occurs as 

 before, viz. that of conceiving how a fimilar change of form can be attended with 

 augmentation of volume in one cafe, and diminution of it in the other. BeGdes that to 

 , afcribe the change of capacity in vaporization and liquefa£tion to change of form, inftead 

 of bringing us to the caufe of the phenomena, is only leading us back to the phenomena 

 themfelves, and thus returning to the fame point from which we fet out. The only way 

 ■by which It has been attempted to efcape from this circle has been by refting the Im- 

 mediate occafion of the phenomena on the change of temperature : and how very littlfi 

 this is to be trufted to as an index of analogy between vaporization and liquefa£lion, has 

 already been feen. 



But we may eafily fatisfy ourfelves of the fallacy of the fuppofed analogy between thefe 

 two modifications of any body, if we attempt to infer from it the correfpondence of the 

 changes which fuch a body fliould exhibit with refpe(ft to both In confequence of the fame 

 changes in the conftitution. Thus, if the analogy were to be depended on, the fame 

 change of conftitution by which the freezing point of water becomes lowered, Ihould 

 lower alfo its boiling point. I need not point out how grofsly fuch inferences would mif- 

 lead us. And if the folvent adion of the air may ferve to fcreen this analogy from the 

 abfurdity of fome of thefe implications, it has at the fame tune introduced other incon- 

 fiftencies which are equally grofs. According to this, the influence of air and of caloric 

 In producing evaporation being fimilar, we fliould expe£l: that when the aiflion of the 

 former is added to that of the latter, the evaporation fltould be more fpeedy than when the 

 latter exerts itfelf alone. In other words, that the fame quantity of evaporation fhould be 



* How little information we derive, however, from being told that the abforption of caloric is a <on- 

 fequence of increafe of capacity, is eafily feen by attending to the meaning cf the term. An increafe of fa* 

 pacity is a power of combining with a greater proportion of caloric at the fame temperature. The whole 

 fecret of the explanation tlierefore confifts in this : that folid bodies, in becoming liquid, combine with a 

 greater proportion of caloric at t!ie fame temperature, becaufe they thereby acquirt the power of combining 

 with a greater proportion of caloric at the fame temperature. 



Vol. V. — April i8oi. E produced 



