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The development of the steam engine provided a reason to compare the output of horses with that of the engines that could replace them.
In 1702, Thomas Savery wrote in The Miner's Friend: " So that an engine which will raise as much water as two horses, working together at one time in such a work, can do, and for which there must be constantly kept ten or twelve horses for doing the same.
Then I say, such an engine may be made large enough to do the work required in employing eight, ten, fifteen, or twenty horses to be constantly maintained and kept for doing such a work …" The idea was later used by James Watt to help market his improved steam engine.
He had previously agreed to take royalties of one third of the savings in coal from the older Newcomen steam engines.
This royalty scheme did not work with customers who did not have existing steam engines but used horses instead.
Watt determined that a horse could turn a mill wheel 144 times in an hour ( or 2. 4 times a minute ).
The wheel was 12 feet in radius ; therefore, the horse travelled 2. 4 × 2π × 12 feet in one minute.
Watt judged that the horse could pull with a force of 180 pounds.
So:

2.232 seconds.