James Watt, Scottish engineer, late 18th century.
© Science Museum / Science & Society Picture Library
Engraving by W H Mote after William Beecheys' portrait, with Watt's (1736-1819) signature. Frontispiece from 'Stationary engine driving: a practical manual for engineers in charge of stationary engines' by Michael Reynolds, published in London in 1881. Watt 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 remain hot, thus reducing fuel consumption. The SI (international standard) unit of power, the watt (W), is named after him.