66 MOTIVE POWER OF HEAT. 



executed in an inverse sense and order. Let us 

 imagine that, after the sixth period, that is to say 

 the piston having arrived at the position ef, we 

 cause it to return to the position ik, and that at 

 the same time we keep the air in contact with the 

 body A. The caloric furnished by this body 

 during the sixth period would return to its source, 

 that is, to the body A, and the conditions would 

 then become precisely the same as they were at the 

 end of the fifth period. If now we take away the 

 body A, and if we cause the piston to move from 

 ef to cd, the temperature of the air will diminish 

 as many degrees as it increased during the fifth 

 period, and will become that of the body B. We 

 may evidently continue a series of operations the 

 inverse of those already described. It is only 

 necessary under the same circumstances to exe- 

 cute for each period a movement of dilatation 

 instead of a movement of compression, and re- 

 ciprocally. 



The result of these first operations has been the 

 production of a certain quantity of motive power 

 and the removal of caloric from the body A to the 

 body B. The result of the inverse operations is 

 the consumption of the motive power produced and 

 the return of the caloric from the body B to the 

 body A ; so that these two series of operations annul 



