140 On Elasticity. 



applied with so much success, since the lime of Newton, 

 to the solution of many other of the phasnomena of nature ; 

 and we are incHned to think that the n)ore this subject is 

 investigated the more will it appear that it acts an important 

 part in producing those effects ascribed to elasticity. Ac- 

 cording to this theory, when an elastic body is struck or 

 bent so that the component parts, or portions of them, are 

 moved a little from each other, but not beyond their spheres 

 of attraction, they must, on the cessation of the applied 

 force, spring; back to their natural state. 



Repulsion also has been held to be the cause of elasticity 

 in the case of aeriform fluids, and this repulsion is ascribed 

 to the presence of heat. \n this case repulsion is not made 

 use of as the last term of our knowledge, but merely as 

 expressive of a certain state of action ascribed to another 

 cause. Some, however, make use of the expression with- 

 out so defining it, and, if they mean any thing at all, use 

 it to express an abstract property of which they know not 

 the cause. We may tjiereforc observe, in passing, that 

 this term should be used as seldom as possible in philoso- 

 phical subjects, and never unless the author has defined the 

 sense in which he employs it. 



Another theory has been proposed, which has been ad- 

 mitted by many as suflicient to account for all the phseno- 

 mena, not of the elasticity of bodies only, but of matter in 

 general. This theory, which has the celebrated Boscovich 

 tor its autiior, supposes that the whole matter of the uni- 

 verse consists of a great but finite number of simple, indi- 

 visible, iNEXTENDED atoms, endued with repulsive and at- 

 ivactive forces, wliich vary and change from the one to the 

 other according to circumstances pointed out in his System 

 of Natural Philosophy, of which a good account may be seen 

 in the Supplement to the Ennjclopr^dia Br'ilaniiica, under 

 Boscovich. The most singular part of the system is, that 

 his atoms, in their least and innermost distances, repel each 

 other, and this power of repulsion increases as the distances 

 are diminished: insensible distances they attract each other, 

 and this power decreases as the squares of the distances in- 

 crease, constituting universal gravity : between the inner- 

 most repulsive force and the outermost attractive one, in 

 the insensible distances, many varieties occur ; at a certain 

 distance the repulsive force vanishes — increase that distance, 

 and attraction begins, increases, lessens, and vanishes, till, 

 at a certain increase of distance, the force becomes repul- 

 sive ; and so on alternately, always changing from the one 

 to the other with the increased distances ; sometimes more 



slowly, 



