COST OF ELECTRIC POWER 239 



power furnished by a current of one ampere with a voltage of 

 one volt. 



One watt represents a very small amount of electric power, 

 and for practical purposes a unit 1000 times as large is used, 

 namely, the kilowatt. By experiment it has been found that 

 one kilowatt is equivalent to about ij horse power. Electric 

 current is charged for by the watt hour. A current of one 

 ampere, having a voltage of one volt, will furnish in the course 

 of one hour one watt hour of energy. Energy for electric light- 

 ing is sold at the rate of about ten cents per kilowatt hour. 

 For other purposes it is less expensive. The meters commonly 

 used measure the amperes, volts, and time automatically, and 

 register the electric power supplied in watt hours. 



