Watt's rotary engine. Historical artwork of part of a steam engine designed by the British engineer James Watt (1736-1819). It was the first engine to give rotary rather than pumping motion and opened up the possibility of using steam for transport. The rotary design was patented in 1769. 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.