On Elasticity. 151 



pressing force that was employed. In this case, then, a 

 mere abstraction of caloric annihilates a certain quantity 

 of elastic force which belongs to the air when the common 

 temperature is higher. 



Again : Inclose a given quantity of air, not compressed, 

 in any proper vessel, when the common temperature is ?,{f, 

 and it will be foinid when the temperature becomes high, 

 say 80°, that it has acquired an elastic force which it had 

 not before. 



The cause is obvious. The air inclosed. at 30° has as 

 strong an affinity for caloric when the common temperatur 

 comes to 80" as the air not inclosed, but is prevented b) 

 want of room from satisfying itself to the extent of its affi- 

 nity. On opening the vessel, however, the caloric finds an 

 easy admission; the volume of the mass becomes increased, 

 and a quantity equal to this increase discharges itself. 



But when by force we compress air which is to be again 

 liberated without waiting tor any remarkable change of tem- 

 perature, v.'e only accomplish by mechanical means what 

 nature effects by a mere change of temperature. We ex- 

 press a certain quantity of caloric from the air, while its 

 affinity for that substance remains undiminished. Remove 

 the restraint, and, the affinity exerting itself, a sudiSen in- 

 crease of volume takes place, exhibiting that phaenomenon 

 which is visually called elastic force. 



Ao;ain : When a foot-ball is struck (and so of similar 

 cases) there is a displacement of caloric proportioned to the 

 force applied and the nature of the covering. But this is 

 only momentary ; for, the affinity of the air for caloric re- 

 maming unaltered, a quantity of the latter, more than equal 

 to what was displaced by ths blow, is, for the reason before 

 pointed out, instantly taken in by the air, and with such 

 rapidity as to cause the ball to recoil from the foot in the 

 same manner as a hammer does when struck on an anvil, 

 but in a much mory remarkable degree; for the recoil will 

 always be proportioned to the force employed, compared 

 with the affinity of the bodies for caloric. 



ik-fore concluding, we may observe generally, that every 

 body in nature may be considered as in some measure 

 elastic, though many of them cannot manifest that property 

 to the extent which those bodies usually called elastic can: 

 that is, a certain force may he applied to all of them with- 

 out destroying their form, and by the application of thii 

 force a certain f[uantity of caloric may be lirst accumulatci 

 in and then given off from them. In every rase of th.^ 

 kind (ajid tluy include every species of frictiou) caloric ::i 

 K 4 first 



