200 



GENERAL SCIENCE 



would develop enough power to supply the needs of 

 many cities. But the natural scenery of such a cataract 

 is considered to be worth more to civilization than the 

 work which could be done by using its power. 



To make waterfalls for the development of power, a 

 dam is usually built in rivers and mountain streams. 

 These dams also help to regulate the supply of water 

 and to keep it under control. The supply of water 

 must be constant in order to operate machinery success- 

 fully. Nearly all of the flour mills built by the early 

 settlers of the United States were run by water power. 

 Many of these can now be found in ruins. The largest 

 flour mills in the world are run by water from the Missis- 

 sippi river at St. Paul, Minnesota. Nearly all of the 

 water of the Androscoggin River is used for power in 

 Lewiston, Maine. This is true of many other rivers. 

 There are several types of water wheels now in use. 



They are all made to receive 

 the energy of the flowing 

 water and transform it into 

 mechanical energy. The type 

 of wheel used is determined by 

 the quantity of water avail- 

 able and the distance that it 

 falls. The various types are 

 the following. 



132. The Overshot Wheel. 

 -The overshot wheel as 

 shown in the illustration is 

 made of a series of trough- 

 like buckets into which the 

 water pours at the top. The buckets empty their water 

 at the bottom of the wheel and go up empty and upside 



OVERSHOT WATER WHEEL 



