143 On Elasticity. 



mass for caloric is lessened as its moleculae are brought 

 closer together. A sccoiui blow is iollowcd by a like effect, 

 which is in like manner increased by succeeding blows. It 

 is necessary, however, that these be given in such quick 

 succession that the bar may not have time between to give 

 off its caloric to surrounding bodies. If this be attended to, 

 an accumulation of caloric must take place in the bar ; for 

 by the second blow a larger quantity of heat is displaced 

 than by the first, and consequently a larger quantity is im- 

 bibed to be affected by the third blow ; the quantity dis- 

 placed by each blow being proportioned to that Vv-hich was 

 before present, and the quantity newly imbibed being pro- 

 portioned to what was displaced by the last blow. This 

 fact, with some latitude, will always be found to hold true. 

 Need we wonder then at seeing a dexterous artisan lighting 

 his forge without anv other heat than what he can furnish 

 to himself by means of his hammer and an iron rod? 



In the case which we have just examined the phsenome- 

 non appears to depend on the displacement of caloric in a 

 body by an external force, while the affinity of aggregatiori 

 endeavours to retain it. Will this be found to hold in other 

 cases ? — Yes, making allowance for the difference of cir- 

 cumstances. 



Let AB (fig. 7.) represent a spring of steel or any other 

 metal. By any external ibrce let it be bent into the form 

 CD. It is plain that one side of the spring has been elon- 

 gated and the other shortened. 



But the spring before flexure had its moleculas respec- 

 tively at those distances or in that arrangement in which 

 thev best balanced each other ; that is, the mutual effort of 

 all was to keep the sprino- in the state it exhibited before 

 any external force was applied ; and the quantity of caloric 

 resident in the mass was distributed throughout in propor- 

 tion to the affinity of all the parts. 



Let the proportion of caioric proper to anv part of the 

 mass in any common temperature be represented by the 

 space comprehended between the two parallel lines ab and 

 cd. 



When the bar is bent, the lines ah and cd are made to 

 approach each other, as at e on the concave side, and to re- 

 cede on the convex siJ'-;, suppose to f and g, so that they 

 no lonacr remain parallel. In other words, a quantity of 

 caloriclias been displaced from the one side, and has found 

 lf)duing-rooni in the other side of the bar ; and what is said 

 of tliis'is understood of every other part of the spring. But 

 the affinity of all the parts for caloric having undergone no 

 1 change. 



