Visit any County Fair in England and you'll see about 25 of these beautiful steam driven Traction Engines. They were the work horses of the day from 1800 to 1870. They met the needs of the Industrial Revolution and farming.
They used the steam engine developed by James Watt, a Scotsman. When he was trying to sell them to farmers he was asked "How powerful are they ?" He answered "This steam engine will do the work of 7 horses" which was off the top of his head. So now we have all cars and trucks measured in HP. He also gave his name to the unit of Electricity - the Watt. And 746 watts make 1 Horse Power.