Elevation of a Watt 56 hp steam engine, 1797-1847.
© Science Museum / Science & Society Picture Library
Drawing of a steam engine designed by James Watt (1736-1819). Watt invented the modern steam engine, which became the main power source 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 cylinder 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.