68 



GENERAL SCIENCE 



The Undershot Wheel. This type of wheel (Figure 

 64) is much less efficient than the overshot wheel and is 

 used in more level regions where there is an abundance 

 of water and little fall. It utilizes the kinetic energy 

 of the water as it runs through the opening 0. Such a 

 wheel seldom develops more than 25 per cent of the po- 

 tential energy of the water above the dam. 



The Water Turbine. This form of water wheel is now 

 used more than any other. Figure 65 shows the instal- 

 lation of such a wheel. 

 It rotates in a horizontal 

 plane and stands at the 

 bottom of a turbine pit. 

 The power developed de- 

 pends upon the depth of 

 the pit and the amount 

 of water which passes 

 through the wheel. The 

 efficiency of the turbine 

 is often as high as 90 per 

 cent. It is used exclu- 

 sively in the power plants 

 at Niagara, where the 

 pits are about 135 feet 

 deep and where indi- 

 vidual turbines develop 

 as high as 5000 horse 

 power. 



Wind Power. Wind power like water power is to 

 be commended for its cheapness. The principle of the 

 windmill is exactly the same as that of the water wheel. 

 Moving air strikes the blades of the windmill and causes 

 the wheel to rotate (Figure 66) . This mechanical energy 



FIG. 65. Diagram of Water Turbine. 



