Human beings have long used their toolmaking abilities to construct machines that convert one form of energy into another for their own benefit. In the medieval period, Europeans began to adopt water mills to grind their grain and windmills to pump water and drain swamps. More efficient use of water and wind in the sixteenth and seventeenth centuries enabled them to accomplish more. Nevertheless, even into the eighteenth century Europe, like other areas of the world, continued to rely mainly on wood for energy, and human beings and animals continued to perform most work. This dependence meant that Europe and the rest of the world remained poor in energy and power.

By the eighteenth century wood was in ever-shorter supply in Britain. Processed wood (charcoal) was the fuel that was mixed with iron ore in the blast furnace to produce pig iron, crude iron molded into ingots called “pigs” that could be processed into steel, cast iron, or wrought iron. The iron industry’s appetite for wood was enormous, and by 1740 the British iron industry was stagnating. Vast forests enabled Russia in the eighteenth century to become the world’s leading producer of iron, much of which was exported to Britain. As wood became ever more scarce, the British looked to coal (combustible rock composed of fossilized organic matter) as an alternative. They had first used coal in the late Middle Ages as a source of heat. By 1640 most homes in London were heated with coal, and it was also used in industry to provide heat for making beer, glass, soap, and other products. The breakthrough came when industrialists began to use coal to produce mechanical energy and to power machinery.

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To produce more coal, mines had to be dug deeper and deeper and, as a result, were constantly filling with water. Mechanical pumps, usually powered by animals walking in circles at the surface, had to be installed. Animal power was expensive and bothersome. In an attempt to overcome these disadvantages, Thomas Savery in 1698 and Thomas Newcomen in 1705 invented the first primitive steam engines. Both engines burned coal to produce steam, which was then used to operate a pump. Although both models were extremely inefficient, by the early 1770s many of the Savery engines and hundreds of the Newcomen engines were operating successfully in English and Scottish mines.

In 1763 a gifted young Scot named James Watt (1736–1819) was drawn to a critical study of the steam engine. Watt was employed at the time by the University of Glasgow as a skilled craftsman making scientific instruments. Scotland’s Enlightenment emphasis on practicality and social progress had caused its universities to become pioneers in technical education. In 1763 Watt was called on to repair a Newcomen engine being used in a physics course. After a series of observations, Watt saw that the Newcomen engine’s waste of energy could be reduced by adding a separate condenser. This splendid invention, patented in 1769, greatly increased the efficiency of the steam engine.

To invent something is one thing; to make it a practical success is quite another. Watt needed skilled workers, precision parts, and capital, and the relatively advanced nature of the British economy proved essential. A partnership in 1775 with Matthew Boulton, a wealthy English industrialist, provided Watt with adequate capital and exceptional skills in salesmanship. Among Britain’s highly skilled locksmiths, tinsmiths, and millwrights, Watt found mechanics who could install, regulate, and repair his sophisticated engines. From ingenious manufacturers such as the cannonmaker John Wilkinson, Watt was gradually able to purchase precision parts. This support allowed him to create an effective vacuum in the condenser and regulate a complex engine. In more than twenty years of constant effort, Watt made many further improvements. By the late 1780s the firm of Boulton and Watt had made the steam engine a practical and commercial success in Britain.

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The coal-burning steam engine of Watt and his followers was the Industrial Revolution’s most fundamental advance in technology. For the first time in history, humanity had, at least for a few generations, almost unlimited power at its disposal. For the first time, inventors and engineers could devise and implement all kinds of power equipment to aid people in their work. The steam-power plant began to replace waterpower in cotton-spinning factories during the 1780s, contributing greatly to that industry’s phenomenal rise. Steam also took the place of waterpower in flour mills, in the malt mills used in breweries, in the flint mills supplying the pottery industry, and in the mills exported by Britain to the West Indies to crush sugarcane.

The British iron industry was radically transformed. Originally, the smoke and fumes resulting from coal burning meant that coal could not be substituted for charcoal in smelting iron. Starting around 1710, ironmakers began to use coke — a smokeless and hot-burning fuel produced by heating coal to rid it of water and other impurities — to smelt pig iron. After 1770 the adoption of steam-driven bellows in blast furnaces allowed for great increases in the quantity of pig iron produced by British ironmakers. In the 1780s Henry Cort developed the puddling furnace, which allowed pig iron to be refined in turn with coke.

Strong, skilled ironworkers — the puddlers — “cooked” molten pig iron in a great vat, raking off globs of refined iron for further processing. Cort also developed steam-powered rolling mills, which were capable of turning out finished iron in every shape and form. The economic consequence of these technical innovations was a great boom in the British iron industry. In 1740 annual British iron production was only 17,000 tons. With the spread of coke smelting and the impact of Cort’s inventions, production had reached 260,000 tons by 1806. In 1844 Britain produced 3 million tons of iron. Once expensive, iron became the cheap, basic, indispensable building block of the British economy.