Stea m Mack inery. 



Blackboard Drawing-. On the right is a furnace, on which is 

 the boiler, partly filled with water. Steam collects in the 

 curved top of the boiler, and is let into the cylinder, first at A, 

 then at B, then A, then B, or one after another, so as to push 

 the piston, E, up and down rapidly, thus moving- the larg-e 

 working-beam, which sets the whole machinery in motion. C 

 and D are exhaust-pipes. 



13. Here is a rough drawing to show how the 

 steam does its work. When the steam comes 

 fro'm boiling water it expands very much, and 

 this expansion is the power we employ. 



14. The cylinder is a strong vessel of iron or 

 steel in shape like one joint of a stovepipe, but 

 very much larger. The steam comes out very 

 hot, as well as very powerful and expansive, and 

 getting in under the piston, pushes it up, and, 

 consequently, pushes the piston-rod which is 

 attached to it. This rod sets the machinery in 

 motion, and works the paddle-wheels of the 

 steamboat or the great revolving screw or pro- 

 peller of the steamship. 



15. When the steam has pushed the piston 

 up to the top of the cylinder the steam-pipe in- 

 let is shut off below and let on above. At the 



