242 Introduction to the Study of Science 



turbine is supplied with water from a common pipe and dis- 

 charges it through a common pipe. The efficiency of the water 

 turbine varies from eighty to ninety-five per cent (page 245). 



FIG. 72. A ten thousand horse power water turbine for hydroelectric plant. 

 Diameter of valve (right of picture) is 5.5 feet. Estimate diameter of turbine 

 casing from height of man standing beside it. Turbine is adapted to a head 

 of 519 feet and about 450 cubic feet per second, and will make 350 revolutions 

 per minute. 



Turbines vary in size from a few inches to fifteen or more 

 feet in diameter, and in capacity from that of a toy pin wheel to 

 that of a wheel producing 18,000 or more horse power (Fig. 72). 

 A western plant has in operation four large turbines, each pro- 

 ducing 18,000 horse power from a fall of about 500 feet. At 



