Page:Reflections on the Motive Power of Heat.djvu/124

102 Let us suppose one kilogram of liquid water enclosed in the cylindrical vessel abcd (Fig. 4), between the bottom ab and the piston cd. Let us suppose, also, the two bodies A, B maintained each at a constant temperature, that of A being a very little above that of B. Let us imagine now the following operations:

(1) Contact of the water with the body A, movement of the piston from the position cd to the position ef, formation of steam at the temperature of the body A to fill the vacuum produced by the extension of volume. We will suppose the space abef large enough to contain all the water in a state of vapor.

(2) Removal of the body A, contact of the vapor with the body B, precipitation of a part of this vapor, diminution of its elastic force, return of the piston from ef to ab, liquefaction of the rest of the vapor through the effect of the pressure combined with the contact of the body B.

(3) Removal of the body B, fresh contact of the water with the body A, return of the water to the temperature of this body, renewal of the former period, and so on.

The quantity of motive power developed in a