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A steam engine is an apparatus for converting heat energy into useful work by means of th expansive force of steam.
The earliest recorded attempt to construct a working steam engine was conducted by Hero of Alexandria about 130BC, whose engine was later adapted for use with water instead of steam and became known as the Barker's Mill. Giobvanni della Porta at the beginning of the 17th century adapted another of Hero's inventions, his famous fountain replacing the expanded air used in the original with steam. In 1655 the marquess of Worcester is credited with the invention of a steam engine for pumping water.
The first practical step towards the application of steam power as a motive force was taken by Thomas Savery who patented and exhibited a model of his steam engine at the Royal Institution in London in 1698. Thomas Savery's engine essentially consisted of a cylinder into which steam entered and forced out a charge of water, sucked into it by a previous charge of steam that was suddenly condensed by a jet of cold water allowed to flow over the outer surface of the cylinder. Thomas Savery's steam engines were erected in many parts of Great Britain to pump water. However, Dionysius Papin had published a design for a high-pressure steam engine in 1690, and it is probable that Savery took the plan from him.
Whether designed by Thomas Savery or Dionysius Papin, the early steam engine described was considerably improved by Thomas Newcomen and John Cawley who introduced a piston, driven down by atmospheric pressure as a vacuum was created in the cylinder by the condensation of the steam. This improved steam engine was also used for pumping water.
In 1769 James Watt patented a double-condenser which was another major improvement upon the efficiency of the steam engine, and in 1804 Richard Trevithick applied the steam engine to run along rails.
 Research Steam Engine
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