Engineering Achievements
Watt adopted the centrifugal governor to regulate the speed of a steam engine. (This was already in use for governing wind and watermills.) He invented the parallel motion linkage to convert circular motion to an approximate straight line motion (of which he was most proud) and the steam indicator to measure steam pressure in the cylinder throughout the working cycle of the engine, so showing its efficiency.
Watt greatly helped the development of the embryonic steam engine into a viable and economic means of power generation. He realised that the Newcomen steam engine was wasting nearly three quarters of the steam energy in heating the piston and chamber. Watt developed a separate condenser chamber which significantly increased the efficiency. Further refinements (insulation of the steam cylinder, the double-acting engine, a counter, an indicator, and a throttle valve) made the steam engine his life's work.
Watt was opposed to the use of high pressure steam, and is held by some to have held back the technical development of the steam engine by other engineers, until his patents expired in 1800. With his partner Matthew Boulton he battled against rival engineers such as Jonathan Hornblower who tried to develop engines which did not fall foul of his 'catch-all' patents. Boulton proved an excellent businessman, and both men eventually made fortunes.
He introduced a unit called the horsepower to compare the power output of steam engines, his version of the unit being equivalent to 550 foot-pounds per second (about 745.7 watts).
Watt also invented several other things, not least a copying device for letters.
Legacy
James Watt's model of the steam engine converted a machine of limited use to one of efficiency and many applications. It was the foremost energy source in the emerging Industrial Revolution, and greatly multiplied its productive capacity. (Without it, humans might have continued to provide power.) It was also