Boulton and Watt rotative engine, 1788.

UNITED KINGDOM - DECEMBER 30: The first recorded steam engine was built in 1712 by Thomas Newcomen (1663-1729). James Watt (1736-1819) was asked to improve upon a model of the engine, with his solution being a separate condenser, which he patented in 1769. This, and various other features, meant that Watt and his partner Matthew Boulton (1728-1809) had an engine which was capable of driving machinery. This rotative engine was built to power a section of Boulton's own works in Soho, London. It was known as the Lap engine because it drove a number of metal polishing (or 'lapping') machines, and was the first engine ever to be fitted with a centrifugal governor to regulate its speed. By 1800, when Watt and Boulton�s partnership ended, 451 engines had been built of which 268 were rotative. (Photo by SSPL/Getty Images)