James Watt (1736-1819), Scottish inventor who developed an improved steam engine (1769) and perfected a rotary engine. While working as an instrument maker at the University of Glasgow, Watt was asked to repair a model of Thomas Newcomen's steam engine. His repairs included so many improvements to Newcomen's original, that an entirely new and better engine emerged. His additions included a separate condensing chamber, a pump to distribute air, and insulation for heat and energy conservation. Watt quickly patented the new machine and went into business to manufacure it. The watt, an electrical unit of power, is named after him.