How It Compares with that of a Man.

At his very best, the strongest man stands in pretty poor comparison, even with a horse, for hard, continu-uous labor. He might perform for a few minutes one-half horse power of work, but to keep it up for any great length of time would be impossible. Thus the gain in forcing horses to do a part of the world's work was enormous. One horse could exhaust a dozen men in a single day, and still be ready for the next day's work.

The measurement of a horse's power for work was first ascertained by Watt, the father of the modern steam engine, and he expressed this in terms that hold today. He experimented with a great number of heavy brewery horses to satisfy himself that his unit of measurement for work was correct. After many trials he ascertained that the average brewery horse was doing work equal to that required to raise 330 pounds of weight 100 feet high in one minute. So he called this one horse power.

This work, however, is not continuous, for the horse would have to backup after each pull to lower the line of the pulley, and thus he would work four hours a day in pulling 330 pounds in the air at the rate of 100 feet per minute, and four hours in slacking up the rope. Consequently no horse can actually perform continuously what is generally called one-horse power. The horse was never born that could tug at a rope for eight honrs a day pulling 330 pounds each minute without rest or change. Consequently when we speak of horse-power we refer only to the average work a horse can do in one minute - that is to say, the rate at which he can work.

A strong man might pull half that weight 100 feet in the air in two minutes, but he could not repeat the operation many times without being exhausted .

For all needful purposes the expression of one-horse power is accurate enough, and practically shows the measurement of an average horse's abilities for working. As a rule a strong man can in eight hours work at a rate of about one-tenth of one horse power; that is, it would require ten men to pull 330 pounds 100 feet in the air in a minute, and then slack up and repeat the operation throughout the eight hours of a working day. The world's gain in labor when horses were first employed to help man in his work was then tenfold.