Watt's engine. Historical artwork of part of the steam engine designed by the British engineer James Watt (1736-1819). It was the first engine to give rotary rather than pumping motion. Watt's engine also drove steam out of a cylinder to be condensed in a separate vessel. Previous engines, based on a design by Newcomen, condensed the steam within the cylinder which was far less efficient. Watt coined the term 'horsepower' to describe how powerful his engines were. Watt's engines were used to pump water from mines and to drive looms in textile mills. Published in History and progress of the steam engine, England, 1830.