The British instrument maker and engineer James Watt (1736-1819) developed an efficient steam engine which was a universal source of power and thereby provided one of the most essential technological components of the early industrial revolution.

James Watt was born on Jan. 19, 1736, in Greenock, Scotland, the son of a shipwright and merchant of ship's stores. He received an elementary education in school, but of much more interest to him was his father's store, where the boy had his own tools and forge and where he skillfully made models of the ship's gear surrounding him. In 1755 he was apprenticed to a London mathematical instrument maker; at that time the trade primarily produced navigational and surveying instruments. A year later he returned to Scotland. By late 1757 Watt was established in Glasgow as "mathematical instrument maker to the university."

About this time Watt met Joseph Black, who had already laid the foundations of modern chemistry and of the study of heat. Their friendship was of some importance in the early development of the steam engine.

Invention of the Steam Engine

In the meantime, Watt had become engaged in his first studies on the steam engine. During the winter of 1763/1764 he was asked to repair the university's model of the Newcomen steam engine. After a few experiments, Watt recognized that the fault with the model rested not so much in the details of its construction or in its malfunctioning as in its design. He found that a volume of steam three or four times the volume of the piston cylinder was required to make the piston move to the end of the cylinder. The solution Watt provided was to keep the piston at the temperature of the steam (by means of a jacket heated by steam) and to condense the steam in a separate vessel rather than in the piston. Such a separate condenser avoided the large heat losses that resulted from repeatedly heating and cooling the body of the piston, and so engine efficiency was improved.

There is a considerable gap between having a good idea for a commercial invention and in reducing it to practice. It took a decade for Watt to solve all the mechanical problems. Black lent him money and introduced him to John Roebuck of the Carron ironworks in Stirlingshire, Scotland. In 1765 Roebuck and Watt entered into a partnership. However, Watt still had to earn his own living, and his employment as surveyor of canal construction left little time for developing his invention. However, Watt did manage to prepare a patent application on his invention, and the patent was granted on Jan. 5, 1769.

By 1773 Roebuck's financial difficulties brought not only Watt's work on the engine to a standstill but also Roebuck's own business. Matthew Boulton, an industrialist of Birmingham, England, then became Watt's partner, and Watt moved to Birmingham. He was now able to work full time on his invention. In 1775 Boulton accepted two orders to erect Watt's steam engine; the two engines were set up in 1776 and their success led to many other orders.

Improvements in the Steam Engine

Between 1781 and 1788 Watt modified and further improved his engine. These changes combined to make as great an advance over his original engine as the latter was over the Newcomen engine. The most important modifications were a more efficient utilization of the steam, the use of a double-acting piston, the replacement of the flexible chain connection to the beam by the rigid threebar linkage, the provision of another mechanical device to change the reciprocating motion of the beam end to a rotary motion, and the provision of a centrifugal governor to regulate the speed.

Having devised a new rotary machine, the partners had next to determine the cost of constructing it. These rotary steam engines replaced animal power, and it was only natural that the new engine should be measured in terms of the number of horses it replaced. By using measurements that millwrights, who set up horse gins (animal-driven wheels), had determined, Watt found the value of one "horse power" to be equal to 33,000 pounds lifted one foot high per minute, a value which is still that of the standard American and English horsepower. The charge of erecting the new type of steam engine was accordingly based upon its horsepower.

Other Inventions

On Watt's many business trips, there was always a good deal of correspondence that had to be copied. To avoid this irksome task, he devised letter-press copying, in which, by writing the original with a special ink, copies could be made by simply placing another sheet of paper on the freshly written sheet and then pressing the two together.

Watt's interests in applied chemistry led him to introduce chlorine bleaching into Great Britain and to devise a famous iron cement. In theoretical chemistry, he was one of the first to argue that water was not an element but a compound.

In 1794 Watt and Boulton turned over their flourishing business to their sons. Watt maintained a workshop where he continued his inventing activities until he died on Aug. 25, 1819.

Further Reading

• Excellent biographies of Watt are H. W. Dickinson and Rhys Jenkins, James Watt and the Steam Engine (1927), and Dickinson's James Watt (1936). Eric Robinson and A. E. Musson, James Watt and the Steam Revolution (1969), is a documentary history that commemorates the bicentenary of Watt's patent for the separate condenser in his steam engine and includes extracts from Watt's personal letters and other documents not before published. For background material see H. W. Dickinson, A Short History of the Steam Engine (1939), and T. S. Ashton, The Industrial Revolution (1948).