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James Watt's prototype steam engine 'Old Bess', c1778. Scottish engineer and inventor Watt (1736-1819) formed a successful partnership with the entrepreneur Matthew Boulton in 1775, building steam engines to power mills, factories and mines. Watt's designs with a separate condenser were more efficient than earlier steam engines. In this engine, which was erected at the Soho works, Birmingham, England, in 1777-1778, reciprocating motion was turned into rotary motion by a sun-and-planet gear train. (KEYSTONE/HERITAGE IMAGES/Oxford Science Archive)