Steam engine

A boiler heats water to produce steam, which expands under pressure and transfers part of its heat energy into mechanical work. In a reciprocating engine, steam moves a piston inside a cylinder; a connecting rod and crank can convert that back-and-forth motion into rotation. In early atmospheric engines such as Newcomen's, steam was condensed in the cylinder to create a partial vacuum, allowing atmospheric pressure to push the piston. Steam turbines use a different mechanism: flowing steam passes over blades attached to a rotor, producing continuous rotary motion.

Ancient devices such as Hero of Alexandria's aeolipile demonstrated that steam could produce motion, but they were not practical power sources. In 1698 Thomas Savery patented a steam-powered pump for raising water from mines. Around 1712 Thomas Newcomen developed a more serviceable atmospheric engine that used a piston and beam to operate mine pumps. Its main value was draining mines, helping workers reach deeper mineral deposits; it was not originally designed as a general-purpose factory engine.

James Watt did not invent the steam engine. After examining a model Newcomen engine, he identified the repeated heating and cooling of its cylinder as a major source of wasted heat. His separate condenser, conceived in 1765 and patented in 1769, let steam condense in a separate chamber while the main cylinder stayed hot, improving efficiency. Watt and his business partner Matthew Boulton later developed engines capable of delivering rotary motion, making steam power useful for a wider range of factory machinery. The innovation became one important contributor to industrialization, alongside other changes in energy supply, manufacturing, transport, and finance.

Once engines could provide sustained rotary power, steam was adapted to transport as well as pumping and manufacturing. Steam locomotives and ships altered the movement of people and goods during the nineteenth century. Engineers also developed higher-pressure engines and other designs, each balancing power, fuel consumption, reliability, and safety. In 1884 Charles Parsons developed a modern steam turbine, in which steam turns a rotor through rows of blades rather than driving a piston back and forth.

Reciprocating steam engines have largely given way to other prime movers in ordinary transport and industry, but steam remains significant in power engineering. In a steam-turbine power plant, a heat source produces steam that turns a turbine connected to an electric generator. The heat may come from burning a fuel or from sources such as nuclear reactors, solar-thermal systems, or geothermal systems. This distinction matters: modern electricity generation often uses steam turbines, not the piston engines commonly associated with nineteenth-century railways.