James Watt

James Watt was a Scottish instrument maker, engineer and chemist whose improvements to the steam engine made it far more efficient and adaptable, turning it into a mainstay of the Industrial Revolution. He did not invent the steam engine, but his separate condenser and his later adaptation of the engine to drive machinery transformed mines, mills and factories across Britain and beyond. In partnership with the Birmingham manufacturer Matthew Boulton he became wealthy, and the unit of power, the watt, is named after him.

Watt was born in Greenock, in western Scotland, on 19 January 1736 by the old calendar (30 January by the modern one). His father was a shipwright, shipowner and merchant whose wealth came partly from trading in enslaved people and the goods they produced; his mother came from a well-educated family. He showed a gift for mathematics at school and for model-making in his father's workshops.

After a year's training as an instrument maker in London in 1755 and 1756, he settled in Glasgow. In 1757 the University of Glasgow let him open a small workshop on its premises, where he repaired and made scientific instruments. There he became friends with the chemist Joseph Black and the economist Adam Smith.

The engines of the day, designed by Thomas Newcomen in 1712, were used mainly to pump water from mines and wasted huge amounts of fuel. In 1763 Watt was asked to repair the university's model Newcomen engine and found that about three-quarters of the steam's heat went into reheating the cylinder after each stroke, because cold water was sprayed in to condense the steam. In May 1765, while walking across Glasgow Green, he hit on the solution: condense the steam in a separate chamber and keep the cylinder permanently hot. He had a working model that year.

Building a full-size engine proved much harder. With backing from Black and the ironmaster John Roebuck he patented the idea, but money ran short, and for about eight years he worked as a surveyor and civil engineer.

When Roebuck went bankrupt, Matthew Boulton, owner of the Soho Manufactory near Birmingham, took over his share of the patent, and Parliament extended it to 1800. Watt moved to Birmingham, and in 1775 the two men formed the partnership of Boulton and Watt, which lasted 25 years. The ironmaster John Wilkinson found a way to bore a precise cylinder, and in 1776 the first engines went to work, many of them pumping Cornish mines. The firm charged customers a third of the fuel savings compared with a Newcomen engine.

At Boulton's urging Watt converted the engine's up-and-down motion to rotary power, using a sun and planet gear in 1781, so that it could drive mills and textile machinery. Further patents followed for double-acting and compound engines, the parallel motion linkage he was proudest of, and a centrifugal governor. Together these meant his engines could burn as little as a fifth of the fuel that Newcomen's needed. In the 1790s the firm fought costly but ultimately successful court cases against infringers.

Watt also patented a letter-copying process in 1780, which remained in office use into the 20th century, and experimented with chlorine bleaching after witnessing work in Paris in 1786. He was a leading member of the Lunar Society of Birmingham, a circle of scientists and industrialists, and a fellow of the Royal Society of Edinburgh from 1784. He hated bargaining and suffered from headaches and depression.

Watt retired in 1800, when the patent and the original partnership expired, leaving the firm to his and Boulton's sons. He kept inventing in his garret workshop, including a machine for copying sculpture. In 1816 he sailed on the paddle-steamer Comet, a product of his inventions, to revisit Greenock. He died at his home, Heathfield Hall near Birmingham, on 25 August 1819, aged 83. In 1889, and internationally in 1960, the unit of power was named the watt in his honour.

Our 1783 and 1800 maps show Great Britain, the forerunner of today's United Kingdom, in the decades when his engines spread through its mines and mills.