3 i6 



THE POWER BEHIND THE ENGINE 



The steam turbine is very much more efficient than its 

 forerunner, the steam engine. The installation of turbines 

 on ocean liners has been accompanied by great increase in 

 speed, and by an almost corresponding decrease in the cost 

 of maintenance. 



Steam engines. A very simple illustration of the working 

 of a steam engine is given in Figure 189. Steam under pressure 



enters through the open- 

 ing F, passes through TV, 

 and presses upon the pis- 

 ton M. As a result M 

 moves downward, and 

 thereby induces rotation 

 in the large wheel L. 



As M falls, it drives the 

 air in D out through 

 and P (the opening P is 

 not visible in the dia- 

 gram). 



As soon as this is ac- 

 complished, a mechanical 

 device draws up the rod 

 E 9 which in turn closes 

 the opening N, and thus 

 prevents the steam from 

 passing into the part of D 

 above M. 



Fte. 189. The principle of the steam engine _ . . . . 



But when the rod E is 



in such a position that N is closed, on the other hand is 

 open, and steam rushes through it into D and forces up the 

 piston. This up-and-down motion of the piston causes con- 

 tinuous rotation of the wheel L, If the fire is hot, steam is 

 formed quickly and the piston moves rapidly; if the fire is 



