I4'2 On Elasticity. 



C. Barruel has proposed a theory different in some re- 

 spects from any of those I have mentioned, — more in ap- 

 pearance, however, than in reahty. He contends that ca- 

 loric acts a great sliare \\\ the phaenomcna of elasticity, and 

 maintains that it is itself elastic in consequence of the pro- 

 perty which the molecule of this fluid have of repelling each 

 other: a property, he says, the more probable as it is ob- 

 i'erved in the electric fluid, with which caloric has so great 

 an analogy. " In a word," savs Barruel, ^' we may be 

 satiilied with admitting its elasticity as a fact from v/hich 

 we may set out as from an incontestable principle." To 

 enter at great length into this theory, an account of which 

 may be seen in the sixth volume of the Philosophical Ma- 

 gazine, p. 52, would encroach too much on oin* present 

 time. The author presents, in his memoir'on this subject, 

 some curious thoughts, and well worthy of a perusal. It 

 is only necessary here, however, to state in few words the 

 substance of his reasoning. 1st, Every body in nature is 

 porous, and tiresc pores are proportioned to the density of 

 the substance : 2d, These pores are filled with different 

 fluids, and principally with caloric. But caloric possesses 

 a strong repulsive force ; from which it follows, that, when 

 an elastic body is compressed, the caloric in its pores drives 

 back, by its repulsive power, the displaced parts, and bringb 

 them to their former state. 



On this theory it may be observed, that however true it 

 may be that caloric acts a distinguishing part in the phae- 

 iiomena of elasticity, the author seems to have made hardly 

 any other use of the fact than to put that substance in the 

 place of the materia suhtiUs and ether of the earlier philo- 

 sophers. He assumes too that it necessarily possesses elas- 

 ticity ; but he ought either to have first proved it, or at 

 least to have demonstrated, that if that property be not in- 

 herent in caloric, there could be no elasticity in other mat- 

 ter. In short, were it even proved that caloric is naturally 

 and essentially elastic, and the cause of elasticity in other 

 matter, still the main question would remain unsolved, 

 which would then be — What is the physical cause of elas- 

 ticity in caloric ? 



Libes makes elasticity to depend on caloric interposed 

 either between the moleculse of bodies or combined with 

 them, and at the same time on the attractive force of these 

 molecidte. "This being premised," says he, " I say that 

 the restoration of solid bodies after compression is a com- 

 bined effect, which depends in part on the repulsive force 

 which their integral moleculae have received from ca- 

 loric. 



