James Watt, b. Jan. 19, 1736, d. Aug. 25, 1819, was a Scottish engineer and inventor who played an important part in the development of the steam engine as a practical power source. He studied instrument making and went (1755) to London at the age of 18 to study further and practice his trade. In 1757 he was appointed instrument maker at the University of Glasgow; there he met the physicist Joseph Black, who was studying the thermodynamic (heat) properties of steam. Watt studied the Newcomen steam engine then in use and made a number of important improvements. In 1769 he patented a separate condenser (a chamber for condensing the steam) for the engine. He formed (1774-1800) a partnership with the manufacturer Matthew Boulton. The Boulton and Watt steam engines soon replaced the Newcomen engines that were being used to pump water out of mines. Other improvements developed by Watt included the twin-action piston engine (in which steam is supplied to both sides of the piston), obtaining power from the expansion of the steam inside the cylinder, a mechanism for transforming the reciprocating motion of the piston into rotary motion, and the centrifugal governor (a device that made use of feedback to keep the engine at a constant speed). Although Watt did not invent the steam engine, his improved engine was really the first practical device for efficiently converting heat into useful work and was a key stimulus to the Industrial Revolution.
