George Westinghouse negotiated his first contract with Nikola Tesla on horsepower.
The figure, if the surviving historical record is accurate, was $2.50 per horsepower of alternating current generated from Tesla’s polyphase induction motor.
Tesla died destitute. But it wasn’t for lack of production despite horsepower, as a measurable power unit, being notoriously difficult to quantify.
The reason has a great deal to do with its origins to which Scottish engineer James Watt, who first adopted horsepower to promote his improved variant on the steam engine, played a significant role.
Watt was keen to impress upon a market still, by 1776, dominated by horse-drawn carriers, before he condemned it to obsolescence, the concept of horsepower.
To do this, he juxtaposed the amount of work a horse could do over a day, estimated ultimately as a force of 180 pounds, as a sustained output for an amount of energy transferred over time; besides oxen just doesn’t have the same ring to it.
Not that it ever did. Mass management and horsepower, as we shall see, have been entwined in perpetuity. Horses had for millennia been harnessed the same way as oxen.
Because such a harness could throttle a horse, load bearing legislation was put in place by the Romans.
The Theodosian Code decreed the severest of punishment for anyone who hooked a load to a horse more than the equivalent of 500 kilograms according to Jean Gimpel’s landmark study The Industrial Revolution in the Middle Ages.
It wasn’t until the erroneously named Dark Ages when a rigid, well-padded collar was adopted that properly placed the weight on the horse’s shoulders instead of its neck, enabling the horse to pull as much as the ox and to pull it much faster.
Having adopted the horse collar, European farmers soon switched from oxen to horses, with an immense gain in productivity — a horse could plow more than twice as much per day as an ox.
Having gained a much more efficient substitute for the ox, medieval Europeans promptly invented the heavy, wheeled plow to improve the productivity of their fertile but very heavy soil in the colder regions of Europe where deep furrows were required unlike the cross scratching in practice across the surface in the more arid regions of Mediterranean climes.
Today in motor vehicle specifications horsepower is mostly interchangeable with kilowatts and Newton metres in usage despite alluding to different metrics such as compound units of torque, in the latter example.
Horsepower need not be limited to land.
Callum Douglas makes an interesting case of such things in his WW2 book The Secret Horsepower Race, on the design and secret intelligence behind military air supremacy.
By this time Rudolf Diesel had made his indelible mark on industries that had until then primarily relied on heating water by burning coal as the predominant power source. It had been a 160-year reign all the same.
History, it would seem, is not yet done with the figure of James Watt who looms equally large over future industry.
Tesla, for the recent rehabilitation of his name and contribution to engineering, might have been better to have had a unit of power named after him.
One kilowatt is not, after all, the same as one horsepower.
Nor is a patent equal to a legacy, which is controlled by the many not the few.