CHAPTER XIX 

 STEAM ENGINES 



504. Early forms. Hero of Alexandria is given credit 

 for being the first man to use steam as an agent to con- 

 vert heat energy into mechanical energy. He produced 

 an aeopile which operated with steam upon the same 

 principle that our present-day centrifugal lawn sprinklers 

 work with water. 



History gives us ideas which were advanced by certain men, but 

 nothing of importance after Hero's machine until 1675, when, con- 

 jointly, Newcomen, Galley, and Savery invented what has been known 

 as the Newcomen engine. Fig. 242 is a drawing of this engine as 

 it was used for pumping water. A is the pump plunger and is always 

 held down by the weights B. The steam, after being generated in 

 the boiler C, is passed through valve D to the cylinder F. The piston 

 H, which is up as the steam enters, is connected with the pump by 

 means of the walking beam /. When the cylinder F is filled with 

 steam, the valve D is closed and the valve E opened, letting in a jet 

 of water from the previously filled tank G, As the water enters the 

 cylinder it condenses the steam F, thus producing a vacuum in the 

 cylinder, consequently the atmosphere will act upon the piston H and 

 force it down. As it forces the steam piston down it raises the 

 piston A, and with it the water. 



After Newcomen, Watt produced probably the most important im- 

 provement of the steam engine. It was in 1769 that he got out an 

 engine which would not condense the steam in the working cylinder, 

 and by so doing cool off the walls, but he condensed it in separate 

 vessels, which produced a continuous vacuum. The same principle 

 as that of Watt is in use in the condensing steam engine of to-day, 

 the only changes being in the mechanism for admitting and releasing 

 the steam, in mechanical make-up and methods whereby labor in the 

 machine shop is reduced. 



505. The present engine. The working parts of the 

 present engine are all of the same general plan, with dif- 



