WATER WHEELS AND WINDMILLS 201 



down. The weight and force of the water flowing into the 

 buckets turn the wheel. This overshot wheel is used where 

 the fall is not very great and its diameter is almost equal 

 to the distance the water falls. The waste in power is 

 due largely to the water spilling out of the buckets or 

 shooting over them. The efficiency of such a wheel is 

 from 80 per cent to 90 per cent. The power is transmitted 

 by a shaft and series of cogwheels or by a belt. 



133. The Undershot Water Wheel. This is used in 

 level countries where the fall of water is not great enough 

 for overshot wheels, 



but where the water 

 is in abundance. The 

 wheel is built some- 

 what like the pad- 

 dle-wheel on a 

 steamboat, and the 

 water strikes the 

 wheel at the bottom 

 with the force with 

 which it flows into UNDERSHOT WHEEL 



the mill-race from the 



bottom of the dam. A type of the undershot water wheel 

 is the one which boys usually make while playing in swiftly 

 running streams. The efficiency of the undershot wheel 

 is about 30 per cent when compared to the energy of the 

 water above the dam. 



134. The Pelton Water Wheel or Motor. This is a 

 modern form of the undershot wheel which has come into 

 use since 1880. Small forms of it are used for small 

 power machines in cities in which power can be had from 

 the waterworks. It is also used where water is con- 

 ducted down a mountain through pipes. The water 



