210 GENERAL SCIENCE 



there is in the piston of the double-action engine. The 

 principle of the steam turbine is the same as that of the 

 water turbine or the wheel of a windmill. A wheel 

 with a great number of blades like the wheel of a wind- 

 mill is firmly fastened to a shaft; steam from nozzles is 

 directed against the blades of the turbine wheel and the 

 wheel is thus caused to rotate at a very high speed. 



BLADES ON THE ROTATING SHAFT OF STEAM TURBINE 



The steam enters at the middle, divides, and goes toward 

 each end, causing the shaft to rotate at high speed. 



The steam can be used several times by allowing it to 

 pass over the blades of several wheels which are set in 

 series. Steam turbines are used where high speed and 

 great power are needed, as on modern ocean vessels, the 

 engines of some of which have 70,000 horse power. One 

 of the Pittsburgh city water pumping stations has a 

 steam turbine which runs a centrifugal pump that will 

 throw 100,000,000 gallons of water in 24 hours. 



142. Gas Engines. In recent years gas engines have 

 come into use for small power purposes and to a very 

 great extent have taken the place of steam engines. Gas 

 engines are driven by properly timed explosions by an 

 electric spark, of a mixture of gas and air within the 

 cylinder. A gas engine with a single cylinder has a 

 heavy pair of fly wheels, because the piston receives energy 



