Watt, James, 1736–1819, Scottish inventor. While working at the Univ. of Glasgow as an instrument maker, Watt was asked to repair a model of Thomas Newcomen's steam engine. He devised improvements that resulted in a new type of engine (patented 1769) with a separate condensing chamber, an air pump to bring steam into the chamber, and parts of the engine insulated. He also perfected a rotary engine. Matthew Boulton financed Watt's work and was his partner (1775–80) in manufacturing the engines at Soho near Birmingham. Watt coined the term horsepower. The watt, a unit of electrical power, was named for him.
See his correspondence, Partners in Science, ed. by E. H. Robinson and D. McKie (1970); study by E. H. Robinson and A. E. Musson (1969).