Who invented the steam engine?

The first person to harness the power of steam was the Greek scientist Heron of Alexandria in the first century A.D. He developed several devices that were operated by water, steam, or compressed air, including a fountain, a fire engine, and the steam engine. The steam engine was significantly improved in 1711 by Englishman Thomas Newcomen (1663–1729), who created a machine that used steam to pump water. The Scottish inventor James Watt (1736–1819) substantially improved on Newcomen's model and patented (received exclusive rights to make, use, and sell) his own steam engine in 1769. Steam engines had previously depended on atmospheric pressure to push a piston (a sliding piece of metal moved by pressure) into a cylinder (a hollow tube) and create a vacuum by the cooling steam. Watt's invention was the first to employ a separate device, called a condenser, which performed this function. The condenser resulted in a 75-percent saving in fuel. It also allowed for the use of steam pressure to move the piston in both directions, giving the machine greater flexibility. Watt's advances paved the way for the Industrial Revolution (a period of technological development; c. 1750–c. 1850), which relied heavily on this machine to move from reliance on agriculture to an industrial-based economy. Watt's legacy also includes the terminology "horsepower" and "watts" as units for measuring the energy produced by an engine.

Further Information: Hills, Richard L. Power from Steam: A History of the Stationary Steam Engine. New York: Cambridge University Press, 1993; "Steam Engine." MSN Encarta. [Online] Available http://www.encarta.msn.com/find/search.asp?search=steam+engine, November 8, 2000.