THE STEAM-ENGINE. 



419 



THE STEAM-ENGINE. 



(SECOND LECTURE.) 



Having explained in a former lecture the conditions under which, by sup- 

 plying heat to water, it is converted into steam, and, by abstracting heat from 

 steam, it may be reconverted into water, let us now consider the mechanical 

 force which is developed in these phenomena. 



Fig. 5. 



Let A B (fig. 5) be a tube, or cylinder, the base of which is equal to a 

 square inch, and let a piston P move in it so as to be steam-tight. Let it be 

 supposed, that under this piston there is, in the bottom of the cylinder, a cubic 

 inch of water between the bottom of the piston and the bottom of the tube ; 



