WOBK BY EUNNING WATEE 167 



185. Utilization of running water. The power of doing work 

 which running water possesses has long been recognized. Cen- 

 turies ago men devised water wheels, by means of which streams 

 of water were caused to turn the millstones which ground grain 

 into flour. In the United States small water-power flour mills 

 and saw-mills were formerly found in almost every neigh- 

 borhood. Many of these are no longer used, since it has been 

 found more satisfactory to carry on the work in a smaller num- 

 ber of larger and well-equipped mills. The larger mills often 

 owe their location and success to the abundance of water power, 

 as in the case of the flour mills of Minneapolis, which have been 

 built alongside the neighboring falls of the Mississippi River. 



FIG. 84. An important water power 



The dam in the Mississippi River at Keokuk, Iowa. It will supply 

 300,000 horse power 



In later years water power has been more largely used for 

 a great variety of industrial purposes. The water wheels are 

 usually caused to operate dynamos, and the electric current 

 thus generated is transmitted to trolley lines, factories, and 

 industrial plants of various sorts, where it is made to do work 

 through the agency of electric motors. These plants may be 

 several hundred miles from the location of. the water power. 

 A dam which has been built across the Mississippi River at 

 Keokuk, Iowa, is expected to produce electric energy equiva- 

 lent to more than 300,000 horse power (fig. 84). This is said 

 to be about three times the total amount of power now used 

 for manufacturing purposes in the whole state of Iowa. The 



