146 On Elastktfi/. 



to reasonings on molion as connecled with matter, it ra.*- 

 nishes entirely when the continuity of matter is broken, ai 

 in the case we have stated. But if' in' he case of the trans- 

 misfion of caloric through a vacuum, caloric is proved to 

 exist independently of motion^ why in any other case should 

 the two be confounded ? 



But to return. — A bar of metal by being hammered has a 

 quantity of caloric expressed from it by mere mechanical 

 means, without undergoing any chemical change. In other 

 words, its capacity for holding caloric has been abridged, 

 without its affinity for that substance being lessened 5 and 

 the aggregation of the mass has been increased in a ratio 

 bearing some proportion to the diminution of its capacity 

 for caloric. 



When the hamm.er is first applied to the metal, the latter 

 is, comparatively speaking, plastic, and gives but Httle re- 

 sistance ; but as the parts are brought into a closer state of 

 aggregation the resistance increases, and the hammer recoils 

 in proportion to the force with which it is applied and the 

 degree of aggregation the mass has acquired : in other 

 words, the metal has acquired a degree of elasticity propor- 

 tioned to the time it has been subjected to the mechanical 

 process. It appears then that by diminishing the capacity 

 of the metal for heat, while its natural affinity remains un- 

 altered, it acquires the property of being elastic. 



Let us attend a little to the case before us. When the 

 metal has received a certain degree of compression from the 

 Ivammer, it refuses to receive more, and the hammer recoils; 

 that is, by mechanical means a certain degree of caloric may 

 be expressed from the metal, but as its affinity for caloric 

 cannot be destroyed, the last portions of it cannot be ex- 

 pelled by any such process y and even a portion of what 

 may be expelled can only be momentarily separated, viz. 

 only during the continuance of the impulse. It is this last 

 circumstance that occasions in the instance under examina- 

 tion an exhibition of what is called elasticity. That I may 

 be the better enabled to convey my ideas on this point, I 

 shall here call in the assistance of a figure to illustrate my 

 meaning. 



Let ABCD (Plate II. fig. 6.) be a mass of metal that 

 lias received all the density of which it is susceptible by 

 hammering, o- let it be a mass (as an anvil) hardened by 

 any other process,, in such a manner that it can receive no 

 more permanent compression from the action of a hammer. 

 If a stroke of a hammer be applied on the surface ABC, 

 a momcntar)' depression of the suiface will take place, pro- 

 portioned 



