WHAT HORSE-POWER MEANS.

Thames Star, Volume LVIII, Issue 10287, 8 January 1917, Page 3

WHAT HORSE-POWER MEANS.

The use of the"horse-power as a measure of an engine's work came naturally from the fact that the first engines were built to do work which had formerly been performed by horses. John Smeaton, who built atmospheric engines before Bolton and Watt placed their more complete machine upon the market, had valued the work done by a strong horse-as equal to lifting a weight of 22,000 ■pounds one foot high in a minute. When Bolton and Watt began to bid for public favour, they agreed to place their engines for "the value of onethird part of the coals which are saved in its use." They also increased the value of the horse-power to 33J000 foot-pounds, so that their engines were half again as powerful for their rated power as those of their competitors. In this way they established the value of the horse-power. The following are. the. various values of a horse-power: 33,000 footpounds per minute, 650 foot-pounds per second, 2,565 thermal units per hour, 42.75 thermal units per minute. The horse-power of a boiler depends upon its capacity for evaporation. The evaporation of 30 pounds of water from 100 degrees Fahrenheit ~ into steam at 70 pounds gauge pressure equals pounds lrom and at 212 decrees Fahrenheit is equivalent to!"a... korse-power.

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