STEAM AND GAS ENGINES 



209 



proper moments to keep the piston moving back and 

 forth throughout the length of the cylinder. The shaft, 

 Sh, carries a heavy fly wheel, W, which, after being 

 started, keeps the engine running at constant speed. 

 The rotary motion of the shaft can be communicated to 

 any desired machin- 

 ery by means of 

 cogwheels or of a 

 belt which passes 

 over a pulley securely 

 fastened to the shaft. 



140. Uses of the 

 Steam Engine. ~ 

 Steam engines are 

 classed according to 

 use. Stationary en- 

 gines do not move 

 about and are used 

 to operate factory 

 machinery, run elec- 

 tric dynamos, etc. FIXED BLADES OF STEAM TURBINE ENGINE 



Traction engines are They direct the steam against the blades of 



the rotating shaft. 



used for drawing 



heavy loads through the country, for drawing gang 

 plows and harvesters on the Western plains, for run- 

 ning threshing machines, etc. Street steam rollers are 

 forms of traction engines. The railroad locomotive 

 is a form of traction engine fitted to run only on steel 

 rails. The power of ordinary traction engines varies 

 from 10 to 20 horse power, while railroad locomotives 

 vary from 500 to 1000 horse power. 



141. Steam Turbines. -- The steam turbine is a form 

 of steam engine without back-and-forth motion such as 



