5* JiiXtraSl of a Mei7io'ir on Elajlictty. 



exiftence of this force is merely hypothetical. Nor can it 

 be faid that the elafticity is owing to air interpofed between 

 the moleculce, fince the phenomena of elalticity manifeft 

 themfelves in vacuo. 



C. Barruel is of opinion, that if we {liould afcribe the 

 caufe of elafticity to caloric, this queftion would remain to be 

 anfwered, Why is caloric fo eminently elaftic ? We know, 

 indeed, fays he, that the affinity of moleculae of water to 

 thofe of fponge, into the pores of which they introduce 

 themfelves, produces an increafe of the volume of that 

 fponge ; but the caufe of the reciprocal attraftion of thefe 

 different moleculag remains unknown. Befides, we could not 

 refufe to admit that the elafticity of caloric would arife from 

 the property which the molecular of this fluid might have of 

 repelling each other : a property the more probable, as it is 

 obferved in the eleftric fluid, with which caloric has fo great 

 an analogy. In a word, we may be fatisfied with admitting 

 its elafticity as a faft from which we fet out, as from an 

 inconteftible principle. 



The author then proceeds immediately to his objeA, and 

 examines in what manner caloric afts upon bodies. It di- 

 lates them by means of a reciprocal affinity between it and 

 their moleculae. Thefe affinities are variable ; but it is cer- 

 tain that, in regard to the fame fubftance, they decreafe in 

 proportion as the diftanccs increafe, and that their aftion is 

 at length reduced to zero. 



Now, if we fuppofe a given quantity of caloric inclofed in 

 a receiver incapable of adling on this fluid, it will every-where 

 diffufe itfelf in an uniform manner. If we then introduce a 

 molecule of matter, the caloric will be unequally condcnfcd 

 around it, in virtue of the unequal aftion which it exercifes 

 on the parts of the fluid at ditterent diftanccs from it, and it 

 will be furrounded by a kind of igneous atmofphere, com- 

 pofed of ftrata of diflTerent denfities. If a fecond molecule 

 be introduced, the fame efiefts will tak(? place, and every 

 thing will remain in the fame ftate as long as the molecules 

 are at a diftance from each other equal to the diameter of 

 their atmofpheres ; nothing is changed but the temperature. 

 But when the moleculae are brought fo near each other that 



their 



