On Elastlc'itij. 147 



portioned to the force that has been applicLl. Say that the 

 curved hue AflC represents this depression, and the area 

 A B Ca its quantity : a quantity of caloric equal to the space 

 ABCa is momentarily displaced bv the blow. 



But in this case an attempt is made to separate, by me- 

 chanical means, a portion of that caloric which the mass 

 demands by its affinity ; and this law, exerting itself to re- 

 store the equilibrium, takes back the quantity thus violently 

 attempted to be taken away, and with such rapidity that 

 the hammer is no sooner at a than it is instantly pushed 

 out by the reimbibed caloric. Nor is this all : caloric, being 

 matter, must, when put in motion, obey the same laws 

 that other matter would in similar circumstances. The re- 

 servoir that furnishes the supply (viz. the surrounding at- 

 mosphere) being inexhaustible, instead of the caloric ceasing 

 to operate when it lias brought the surface again to coincide 

 with ABC, it carries it to i, a distance as far above B, or 

 nearly so, as a was below it ; and it is not till after repeated 

 vibrations between these points that the surface at last comes 

 to rest in its first position. Any one may satisfy himself 

 of this fact by letting a hammer fall upon an anvil while 

 he holds the handle easily in his hand; it v>'lll not give one. 

 but several strokes, proportioned to the force employed. 



When the recoil of the stroke, as it is called, has carried 

 the surface to I, why does not the mass retain the caloric 

 (represented by the space A/'CB) which it has received by 

 the cflort thus made by its affinity for caloric? — Because the 

 affinity of aggregation of the mass forbids it. The two af- 

 finities — that of the whole mass for caloric, and thnt of the 

 molecular for each other — find their powers balanced when, 

 the surface comes to rest in the line ABC 



From what has been stated respecting the eflect produced 

 by the blow of a hammer on a hardened mass of metal, it 

 will not be difficult to trace the effi:^ct that will follow if a 

 soft bar of metal be interposed. Wc have seen tl";..t a quan- 

 tity of caloric is momentarily expelled from a hardened mass 

 of metal v.-hen struck by a hammer, and asquickly reimbibed 

 with an increase of quantity. When such a bar is stmek 

 on an anvil with a hannner, there is a displacement of tl:e 

 caloric from the part struck ; and at the same time an in- 

 crease in the aggregation of the moleeulai in the same part, 

 that is, an increase of its elasticity. The quick return of 

 caloric into the part makes the hammer reoil ; but the uu.- 

 Icculac having been brought closer together by ihe blow, the 

 caloric find^ less lodging-room than before, and of course 

 an iocrea-:c of temperature follows 3 for the affinity of the 

 K 2 niasa 



