Horse-Power

Unit of work, used to measure the performance of motors. When steam engines replaced animal power for hoisting and pumping at mines, it became desirable to state the capacity of the engine in terms of the power which it replaced. James Watt found by experiment with large and powerful roadsters that they could do a work in lifting or hauling which was equivalent to lifting 33,000 lbs. one foot high in one minute. This amount of work is known as a horse-power, in whatever way the factors of feet and pounds are made to vary, provided only the product and the time are constant. A horse could not work at this rate continuously for ten hours, but for a short time only (see ANIMAL STRENGTH). The French unit, force de cheval or cheval vapeur, is 4,500 kilogram meters (-32,549 foot pounds) and is the metric equivalent of the usual unit.