James Watt (1736-1819)

James Watt was a Scottish engineer most famous for his invention of the separate condenser for steam engines, which made steam power safer, more productive and much more efficient.

Watt was the son of a shipwright in Greenock, Scotland. In 1755 he spent a year in London training as a scientific instrument-maker. The experience affected Watt badly. He developed a ‘racking cough, a gnawing pain in the back and weariness all over the body’, and poor health that dogged him for the rest of his life.

While working as an instrument-maker at the University of Glasgow he was given a model steam engine to repair. He realised that, because the steam was being condensed in the engine cylinder, a great deal of energy was being wasted heating the cylinder. He found that condensing the steam in a separate chamber, and using a ‘steam jacket’ to maintain the temperature of the cylinder, made the engine far more efficient.

The scientist Joseph Black provided Watt with a generous loan to scale up the engine. Later, Watt went into partnership with John Roebuck - but in 1773 Roebuck was declared bankrupt. In 1775, Watt formed a new partnership with Matthew Boulton, a Birmingham engineer and manufacturer.

Their partnership lasted until 1800 and produced the steam engines that powered the Industrial Revolution. They both became very rich because a patent issued in 1755 prevented anyone else competing with them until 1800. They continued improving their engine designs - developments included solving the problem of converting the linear motion of a steam engine to a rotary one to power machinery, coining the term ‘horsepower’ as a measure, and the printing press for copying engineering drawings.

Boulton and Watt built pumping engines across the country, particularly in Cornwall, where they replaced every single Newcomen engine. At one mine, five Boulton and Watt engines replaced seven Newcomen engines and burned two-thirds less coal.

Watt retired in 1800, in the same year that his patent and partnership with Boulton expired. He continued to research and invent in a garret workshop in his house at Heathfield, Birmingham. The workshop survives today at the Science Museum, largely as it was when Watt died in 1819.