James Watt

James Watt (born January 19, 1736, Greenock, Renfrewshire, Scotland—died August 25, 1819, Heathfield Hall, near Birmingham, Warwick, England) was a Scottish instrument maker and inventor whose steam engine contributed substantially to the Industrial Revolution. Watt was also known for patenting the double-acting engine and an early steam locomotive. He was elected fellow of the Royal Society of London in 1785.

(Read James Watt’s 1819 Britannica essay on the steam engine.)

Education and training

Watt’s father, the treasurer and magistrate of Greenock, ran a successful ship- and house-building business. A delicate child, Watt was taught for a time at home by his mother; later, in grammar school, he learned Latin, Greek, and mathematics. The source for an important part of his education was his father’s workshops, where, with his own tools, bench, and forge, he made models (e.g., of cranes and barrel organs) and grew familiar with ships’ instruments.

Deciding at age 17 to be a mathematical-instrument maker, Watt first went to Glasgow, where one of his mother’s relatives taught at the university, and then, in 1755, to London, where he found a master to train him. Although his health broke down within a year, he had learned enough in that time “to work as well as most journeymen.” Returning to Glasgow, he opened a shop in 1757 at the university and made mathematical instruments (e.g., quadrants, compasses, scales). He met many scientists and became a friend of British chemist and physicist Joseph Black, who developed the concept of latent heat. In 1764 he married his cousin Margaret Miller, who, before she died nine years later, bore him six children.

The Watt engine

While repairing a model Newcomen steam engine in 1764, Watt was impressed by its waste of steam. In May 1765, after wrestling with the problem of improving it, he suddenly came upon a solution—the separate condenser, his first and greatest invention. Watt had realized that the loss of latent heat (the heat involved in changing the state of a substance—e.g., solid or liquid) was the worst defect of the Newcomen engine and that therefore condensation must be effected in a chamber distinct from the cylinder but connected to it. Shortly afterward he met British physician, chemist, and inventor John Roebuck, the founder of the Carron Works, who urged him to make an engine. He entered into partnership with him in 1768, after having made a small test engine with the help of loans from Joseph Black. The following year Watt took out the famous patent for “A New Invented Method of Lessening the Consumption of Steam and Fuel in Fire Engines.”

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Meanwhile, Watt in 1766 became a land surveyor; for the next eight years he was continuously busy marking out routes for canals in Scotland, work that prevented his making further progress with the steam engine. After Roebuck went bankrupt in 1772, English manufacturer and engineer Matthew Boulton, the manufacturer of the Soho Works in Birmingham, took over a share in Watt’s patent. Bored with surveying and with Scotland, Watt immigrated to Birmingham in 1774.

After Watt’s patent was extended by an act of Parliament, he and Boulton in 1775 began a partnership that lasted 25 years. Boulton’s financial support made possible rapid progress with the engine. In 1776 two engines were installed—one for pumping water in a Staffordshire colliery, the other for blowing air into the furnaces of British industrialist John Wilkinson, the famous ironmaster. That year Watt married again; his second wife, Ann MacGregor, bore him two more children.

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During the next five years, until 1781, Watt spent long periods in Cornwall, where he installed and supervised numerous pumping engines for the copper and tin mines, the managers of which wanted to reduce fuel costs. Watt, who was no businessman, was obliged to endure keen bargaining in order to obtain adequate royalties on the new engines. By 1780 he was doing well financially, though Boulton still had problems raising capital. In the following year Boulton, foreseeing a new market in the corn, malt, and cotton mills, urged Watt to invent a rotary motion for the steam engine, to replace the reciprocating action of the original. He did that in 1781 with his so-called sun-and-planet gear, by means of which a shaft produced two revolutions for each cycle of the engine. In 1782, at the height of his inventive powers, he patented the double-acting engine, in which the piston pushed as well as pulled. The engine required a new method of rigidly connecting the piston to the beam. He solved that problem in 1784 with his invention of the parallel motion—an arrangement of connected rods that guided the piston rod in a perpendicular motion—which he described as “one of the most ingenious, simple pieces of mechanism I have contrived.” Four years later his application of the centrifugal governor for automatic control of the speed of the engine, at Boulton’s suggestion, and in 1790 his invention of a pressure gauge, virtually completed the Watt engine.