Water Power 75 



may be designed for a slight flow or for a heavy volume of 

 water, and for any amount of fall, or head. It acts on the same 

 principle as' the undershot wheel, except that it is placed hori- 

 zontally at the base of a pit, and water is conducted to it through 

 a pipe called a penstock. The water falling from the pipe strikes 

 the wheel blades at right angles to the wheel axis, exerting great 

 pressure, and escapes through an outlet as the wheel revolves. 

 Its energy is transformed into the motion energy of the wheel, 

 which revolves with great rapidity. The efficiency of the water 

 power plants at Niagara Falls and Keokuk is largely due to the 

 use of these turbines. 



The Pelton Wheel. The Pelton wheel is a modern inven- 

 tion adapted to great pressure but only to a limited amount of 

 water. On its rim are a large number of cup-shaped buckets. 

 The water is forced through nozzles under tremendous pres- 

 sure, and as it strikes the buckets of the wheel nearly all of its 

 energy is transferred to the wheel. It is used extensively in Cali- 

 fornia and other western states. 



Measurement of Power. Energy, as we have said, is the 

 ability to do work. It is measured in foot pounds. A foot pound 

 represents the amount of work required to lift a weight of one 

 pound a distance of one foot. The rate at which work is done 

 is called power. This power may be measured in terms of 

 horsepower. One horsepower represents 33,000 foot pounds per 

 minute. All water power is measured in terms of horsepower. 



The origin of the term horsepower is interesting. In the latter 

 part of the eighteenth century, James Watt, the inventor of the 

 steam engine, in trying to sell his engines to coal operators, found 

 that the horse was a rival of his business. He determined to 

 prove that his engine could do more work in the same amount of 

 time than a horse could. So he set out to show what a horse- 

 power represents in foot pounds per minute. He did this by a 

 series of experiments with horses at work, and found that the 

 distance in feet traveled by a horse in pulling coal and water up 

 from a mine, multiplied by the weight lifted, averaged 33,000 foot 

 pounds of work in one minute. This has been accepted as repre- 

 senting one horsepower. 



