DEFINITIONS AND MECHANICAL PRINCIPLES 2? 



is measured in pounds to the square inch, and the volume 

 by the area of the cross section' of the pipe. With an 

 electric current the pressure is measured in volts and the 

 volume or amount of current in amperes. Thus a current 

 may have a pressure or voltage of no volts and a volume 

 or amperage of 7 amperes. The product of volts into am- 

 peres gives watts. An electrical current of 746 watts is 

 equal to one horse power. Electric energy is bought and 

 sold by the watt-hour, or the larger unit, the kilowatt- 

 hour, which is 1,000 watt-hours. 



