The Supply and Uses of Water 243 



Niagara Falls the. Ontario Power Company has now in operation 

 fourteen twin-wheel turbines, each of which, from a supply by 

 a pipe nine feet in diameter and with a fall of about 140 feet, 

 produces 12,500 to 13,000 horse power. The plant at Keokuk, 

 Iowa, on the Mississippi River, is equipped with turbines which 

 generate, besides the power utilized locally, 231,000 kilowatts of 

 electricity, equivalent to about 300,000 horse power, which is 

 transmitted to St. Louis, 144 miles distant. 



100. Horse power and efficiency of water wheels. In the 

 study of water power and machines for converting water power 

 into working energy, we have mentioned frequently " horse 

 power " and " efficiency." These terms are so commonly em- 

 ployed in describing power sources and machines that they need 

 to be understood . We may consider them in the following manner . 



Method of calculating energy of falling water. Assume that 

 the volume of a stream is two hundred cubic feet a minute, and 

 that it has a useful fall of fifteen feet. The weight of 200 cubic 

 feet of water is the product of 200 X 62.5 (pounds per cubic 

 foot), or 12,500 pounds. Energy is measured and expressed in 

 " foot-pounds," which means the amount required to lift verti- 

 cally one pound one foot (cf . page 269) . In this case the amount 

 of energy produced by one pound of water falling a distance of 

 one foot is one foot-pound. The total mass of water weighs 

 12,500 pounds, and in falling a distance of one foot gives 12,500 

 foot-pounds. But it falls 15 feet, and gives, therefore, 12,500 X 

 15 or 187,500, the number of foot-pounds of energy. This 

 may be expressed in a general proposition : The amount of 

 energy is found by multiplying the unit of energy (one foot-pound) 

 by the number of units of weight (pounds) and the number of 

 units of distance (feet). 



Calculation of horse power. We have now to find out what 

 horse power is represented by a body of falling water giving 

 187,500 foot-pounds per minute. First, what is a horse power? 

 An interesting story connected with this term makes clear its 

 meaning and use. 



