Origin of term "horsepower"

[pluto]

In the misty corners of my memory there is a vague recollection that someone actually measured the power output of a horse in order to define one horse power.

Do any of you have better memories, or at least better search engines? Can you verify this apocryphal story for me?

[MEBuckner]

horsepower: the common unit of power; i.e., the rate at which work is done. In the English system, one horsepower equals 33,000 foot-pounds of work per minute—that is, the power necessary to lift a total of 33,000 pounds mass one foot in one minute. This value was adopted by the Scottish engineer James Watt in the late 18th century, after experiments with strong dray horses, and is actually about 50 percent more than the rate that an average horse can sustain for a working day.