MACHINES 



'67 



a force in the direction in which it is flowing. The power 



of many streams can be used in factories, in mills, and 



for making electricity, which can 



be utilized in numerous ways. 

 Some of the power of the 



Niagara River is used to turn 



great dynamos, which develop 



the electricity used in the near-by 



cities of the United States and 



Canada. The mills of many 



New England cities are run by 



water power. The largest flour 



mills in the world are run by 



the water of the Mississippi 



River (Fig. 62). 



Several types of water wheels 



are used to transform the poten- 

 tial energy of the water above into mechanical energy. 

 The Overshot Wheel. This type of wheel (Figure 63) 



utilizes the weight of 

 the water at A. The 

 work expended on the 

 wheel in a second is 

 the product of the 

 weight of" the water 

 which falls upon it in 

 a second and the dis- 

 tance through which 

 it falls. This is a 

 very efficient type of 

 water wheel and is 



the common type in hilly regions where the streams are 



small and have considerable fall. 



FIG. 63. Overshot Water 

 Wheel. 



FIG. 64. Undershot Water Wheel. 



