MOTIVE POWER OF HEAT. 



63 



periment has taught us nothing on this subject. It 

 has only shown us that this caloric is developed in 

 greater or less quantity by the compression of the 

 elastic fluids. 



This preliminary idea being established, let us 

 imagine an elastic fluid, atmospheric air for exam- 

 ple, shut up in a cylindrical vessel, abed. (Fig. 1), 

 provided with a movable dia- 

 phragm or piston, cd. Let 

 there be also two bodies, A and 

 B, kept each at a constant 

 temperature, that of A being 

 higher than that of B. Let 

 us picture to ourselves now 

 the series of operations which 

 are to be described : 



(1) Contact of the body 

 A with the air enclosed in the 

 space abed or with the wall 

 of this space a wall that we 

 will suppose to transmit the 

 caloric readily. The air be- 

 comes by such contact of the 



same temperature as the body A\ cd is the actual 

 position of the piston. 



(2) The piston gradually rises and takes the 

 position ef. The body A is all the time in con- 



FlG. 1 



