THE LOCOMOTIVE 



been pushing, escapes into the air and ceases to act. 

 while on the other side a ]et of steam rushes in from 

 tin.' boiler and begins to push in the contrary direc- 

 tion/' 



"Let me repeat it," said Jules, "to see if I have 

 understood it properly. Steam comes from the 

 boiler, where it forms unceasingly. It goes into the 

 cylinder before and behind the piston by turns. 

 When it gets in front, that behind escapes into the 

 air and no longer pushes; when it gets behind, that 

 in front escapes. The piston, pushed first one way, 

 then the other, alternately, must advance and re- 

 treat, go and come, in the cylinder. And then .''' 



"The piston is in the form of a solid iron rod that 

 enters the cylinder through a hole pierced in the 

 middle of one of the ends, and just large enough to 

 irivc free passage to the rod, without letting the 

 steam escape. This rod is bound to another iron 

 piece called a crank, and finally the crank is at- 

 tached to the neighboring wheel. In the picture 

 all these things can easily be seen. The piston, ad- 

 vancing and retreating in turn in the cylinder, 

 pushes the crank forward and back, and the crank 

 thus makes the great wheel turn. On the other side 

 <>!' the locomotive the same things are taking place 

 by means of a second cylinder. Then the two great 

 win-els turn at the same time and the locomotive 

 moves forward/' 



"It isn't so hard as I thought," Jules remarked. 

 "Steam pushes the piston, the piston pushes tin- 

 crank, the crank pushes the wln-rl, and the engine 

 moves." 



