MOTIVE POWER OF HEAT. 



The only means of fulfilling the prescribed con- 

 dition would be to act upon the solid body exactly 

 as we did on the air in the operations described on 

 page 92. But for this we must be able to pro- 

 duce, by a single change of volume of the solid 

 body, considerable changes of temperature, that is, 

 if we should want to utilize considerable falls of 

 caloric. Now this appears impracticable. In 

 short, many considerations lead to the conclusion 

 that the changes produced in the temperature of 

 solid or liquid bodies through the effect of com- 

 pression and rarefaction would be but slight. 



(1) We often observe in machines (particularly 

 in steam-engines) solid pieces which endure con- 

 siderable strain in one way or another, and 

 although these efforts may be sometimes as great 

 as the nature of the substances employed permits, 

 the variations of temperature are scarcely per- 

 ceptible. 



(2) In the action of striking medals, in that of the 

 rolling-mill, of the draw-plate, the metals undergo 

 the greatest compression to which we can submit 

 them, employing the hardest and strongest tools. 

 Nevertheless the elevation of temperature is not 

 great. If it were, the pieces of steel used in these 

 operations would soon lose their temper. 



(3) We know that it would be necessary to exert 



