steam-engines are machines employing steam pressure and condensation to generate motion. Thomas Savery's device (1698) pumped water by partial vacuum, without moving parts, and while engines on his principles were still in use in the 1790s, Newcomen's atmospheric cylinder/piston engine erected near Dudley in 1712 established the fundamental principles of steam power. James Watt's separate condenser of 1769 (and reciprocation from 1782) became a source of much-improved technical efficiency once Wilkinson's improved cylinder boring became available (1774), and expressed itself in economy of coal use: by the 1790s Watt engines consumed 70 per cent of the fuel of a comparable Smeaton atmospheric device. Higher capital costs meant that coal prices determined the adoption of Watt technology, and industry located onto the cheapest available coal, still providing half its steam-power in 1800 with atmospheric engines.

Mine drainage was its primary application, where coals were cheap and many engines ran on unsaleable slack, with brewing and milling, water supply, and textiles following, the last before the 1820s often employing stationary steam-power through water-wheels for the even torque needed by early machinery. Wider applications from the 1790s owed more to Trevithick's high-pressure non-condensing and direct acting engines, which powered the first successful marine applications with Symington's Charlotte Dundas (1802—though experimentally proven by Jouffroy at Lyons in 1781), and his validation of the steam carriage (1801) and locomotive (1804). Steam was proven at sea by the voyage of Dodd's Thames from Glasgow to London (1815) and entered general coastal service during the 1820s; and on railways by the Rainhill trials of 1829.

Steam-power in cotton more than doubled 1835–56, and was followed by woollens and linen; the Cornish boiler diffused to produce high pressures at reduced fuel costs; and Stephenson long-boiler and Kitson outside-frame locomotives established the basic pattern of railway motive power. From the Grand Junction's establishment of Crewe (1837), British railways manufactured their own locomotives, with occasional purchases from specialists such as Beyer Peacock, who were otherwise confined to export markets, producing long-term losses in standardization and technical progress. The economical compound steam-engine was little used on British railways, where coal was cheap, whereas it became a standard unit for factory power, and in its ultimate triple-expansion form (after 1880) the key to British shipping and shipbuilding dominance. From the early 1900s, Parsons's marine steam turbine provided still greater speed and economy. Plentiful coal supplies, and the extensive coal/steam engineering industrial base, hereafter represented elements of inertia slowing Britain's adoption of electricity and internal combustion.

J. A. Chartres