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James Watt, c.1788  © Watt was a Scottish inventor and mechanical engineer, renowned for his improvements in steam engine technology.

James Watt was born in Greenock on 18 January 1736. His father was a prosperous shipwright. Watt initially worked as a maker of mathematical instruments, but soon became interested in steam engines.

The first working steam engine had been patented in 1698 and by the time of Watt's birth, Newcomen engines were pumping water from mines all over the country. In around 1764, Watt was given a model Newcomen engine to repair. He realised that it was hopelessly inefficient and began to work to improve the design. He designed a separate condensing chamber for the steam engine that prevented enormous losses of steam. His first patent in 1769 covered this device and other improvements on Newcomen's engine.

Watt's partner and backer was the inventor John Roebuck. In 1775, Roebuck's interest was taken over by Matthew Boulton who owned an engineering works in Birmingham. Together he and Watt began to manufacture steam engines. Boulton & Watt became the most important engineering firm in the country, meeting considerable demand. Initially this came from Cornish mine owners, but extended to paper, flour, cotton and iron mills, as well as distilleries, canals and waterworks. In 1785, Watt and Boulton were elected fellows of the Royal Society.

By 1790, Watt was a wealthy man and in 1800 he retired and devoted himself entirely to research work. He patented several other important inventions including the rotary engine, the double-action engine and the steam indicator, which records the steam pressure inside the engine.

Watt died on 19 August 1819. A unit of measurement of electrical and mechanical power - the watt - is named in his honour.