James Watt, Scottish engineer, 1801.
© Science Museum / Science & Society Picture Library
Oil painting by Abraham Wivell, 1856, after the original of 1801 by Sir William Beechey, RA. James Watt (1736-1819) invented the modern steam engine, which became the main source of power in 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.