MOTIVE POWER OF HEAT. 141 



CARROT'S THEORY OF THE STEAM- ENGIKE. 



15. Let CDF^E^ be a cylinder, of which the 

 curved surface is perfectly impermeable to heat, 

 with a piston also impermeable to heat, fitted in it ; 

 while the fixed bottom CD, itself with no capacity 

 for heat, is possessed of perfect conducting power. 

 Let K be an impermeable stand, such that when 

 the cylinder is placed upon it the contents below 

 the piston can neither gain nor lose heat. Let A 

 and B be two bodies permanently retained at con- 

 stant temperatures, S and T, respectively, of which 

 the former is higher than the latter. Let the cyl- 

 inder, placed on the impermeable stand, K, be par- 

 tially filled with water, at the temperature S, of the 

 body A y and (there being no air below it) let the 

 piston be placed in a position EF, near the surface of 

 the water. The pressure of the vapor above the 

 water will tend to push up the piston, and must 

 be resisted by a force applied to the piston,* till 



* In all that follows, the pressure of the atmosphere on 

 the upper side of the piston will be included in the applied 

 forces, which, in the successive operations described, are 

 sometimes overcome by the upward motion, and some- 

 times yielded to in the motion downwards. It will be un- 

 necessary, in reckoning at the end of a cycle of operations, 

 to take into account the work thus spent upon the atmos- 

 phere, and the restitution which has been made, since 

 these precisely compensate for one another. 



