HiXiracl of a Memoir on ^Jajllciiy. 53 



their dlftance is lefs than that diameter, their atmofpheres 

 will be comprefled, and the parts incontaft will afTunie 

 more denfity and a higher temperature, and which is not 

 in equilibrium with that in the reft of the receiver. Thefe 

 parts deprive ihemfelves of a portion of their caloric, which 

 is diftributcd among the other ftrata of thefe atmospheres 

 until the equilibrium is reftored. 



When the moleculag are made to approach each other 

 gently, the compreffion of the atmofpheres and their re- 

 eftablifliment take place peaceably; bm if the nioleculae are 

 brought into contart abruptly, the caloric is difengaged with 

 the greateft violence. It is to this rapid difengagement of 

 caloric, ftronglv comprefled, that we ought to afcribe the 

 detonations of the fuper-oxygenated muriat of pot-afli and 

 of gim-powder. 



The molecule aflluned, for example, retain a portion of 

 the comprefled caloric as long as they obey the force which 

 makes them approach each other. When they arrive at 

 that diftancc at which they exercife an aftion on each other, 

 their attraftive force is greater or iefs than that with which 

 their atmofpheres tend to recover their former ftate. If tlie 

 molcculs, then^ be left to themfelves, in the firft cafe the 

 fyftem retains its prefent ftate; in the other cafe it will re- 

 fume its primitive ftate; and it is in this that the greater 

 part of the phenomena of elafticity feem to confift. This 

 reafoning may be applied to every body, the molcculas of 

 which are feparatcd from each other by a certain quantity of 

 caloric. 



C. Barruel pays attention alio to the circumfta«ces under 

 which the elafticity of a body may be manifefted, and to the 

 means proper for increafing or producing this property. 

 Thefe circumftances are, compreflion, a fudden (liock, and 

 flexion. In either of thefe circumftimces it happens that 

 the adherence of the raoleculs cither is or is uot overcome. 

 In the firft cafe the moleculae are put out of their fphere of 

 aftivity, and the body is faid to be brittle. In the fecond 

 cafe the body is flexible, but the caloric interpofed between 

 its moleculae withdraws, or does not withdraw itfelf, from 

 compreffion. If it withdraws itfelf, there is only one difr 

 9 placement 



