Condensing beam engine by James Watt & Co, late 18th century.
© Science Museum / Science & Society Picture Library
Plate taken from Michael Reynold's 'Stationary engine driving: a practical manual: for engineers in charge of stationary engines' (1881), showing a condensing beam engine made by James Watt & Co. James Watt (1736-1819) was the Scottish engineer and instrument maker who invented the modern steam engine. It was Watt's steam engine which became the main source of power in the textile mills in Britain during the Industrial Revolution. His engine had a separate condenser through which steam from the cylinder was pased and cooled, allowing the engine to be kept hot. This reduced fuel consumption and saved time. The SI (international standard) unit of power, the watt (W), is named after him.