James Watt

person · earth · Greenock and Glasgow, Scotland; then Birmingham, England

Scottish instrument maker (1736–1819), employed by the University of Glasgow, who in 1765 realised while repairing a model Newcomen engine that the fatal loss was the reheating of the cylinder on every stroke, and that condensing the steam in a separate vessel would remove it. He patented the separate condenser in 1769 and spent the next six years failing to make it pay, because no British workshop could bore a cylinder round enough to hold the vacuum until John Wilkinson's cannon-boring machine of 1774. Watt is also the source of the unit: he defined horsepower as 33,000 foot-pounds of work per minute in order to price his engines against the animals they replaced, which is a commercial definition rather than a physical one. His reputation is double-edged in the modern literature. The 1769 patent, extended by Act of Parliament to 1800, was enforced aggressively by his partnership, and Watt's conviction that high-pressure steam was lethally dangerous — not an unreasonable view given contemporary boilers — meant the firm neither developed it nor let others do so freely until the patent lapsed.