The Steam Engine

Based on Robert C. Allen, The British Industrial Revolution in Global Perspective (Cambridge University Press, 2009).

The steam engine was the most revolutionary invention of the Industrial Revolution. It powered a new generation of industrial machinery, and it gave rise to two transportation technologies, railways and steamships, that stitched the world together.

The Experimental Basis of Steam Power

A series of experiments in the middle of the seventeenth century had shown that the atmosphere had weight. This weight could be measured by the height of the mercury column in Torricelli’s barometer: the weight of the column exactly balanced the weight of the atmosphere.

In 1672 Otto von Guericke showed that the atmosphere’s weight could be made to perform work. He fitted a piston into a fixed cylinder that was closed at the bottom and open at the top. One end of a rope was attached to the top of the piston. After passing through a pair of pulleys fixed above the cylinder, the other end of the rope was attached to a weight. The experiment began with the piston at the top of the cylinder and the weight suspended in the air. Then von Guericke pumped the air out of the cylinder. As the air pressure below the piston fell, the weight of the atmosphere drove the piston downwards, drawing the rope through the pulleys and causing the weight to rise. A weight had been moved through a distance: work had been done.

Otto von Guericke's experiment of 1672
Otto von Guericke’s experiment of 1672

In 1675 Denis Papin employed a different method for reducing the pressure below a piston. He filled the cylinder with steam rather than air, and then used cold water to condense the steam, reducing the pressure inside the cylinder and allowing atmospheric pressure to push the piston downwards. As in von Guericke’s experiment, the work was done by the atmosphere, not by the steam.

Steam Engines

These experiments were the key to solving a serious problem confronting Britain’s coal miners. The mine shafts extended below the water table, so that water naturally seeped into the mines. Keeping the mines relatively dry was a task that never ended. In just one colliery in Warwickshire, 500 horses were employed to lift water out of the mine.1 Thomas Newcomen, an ironmonger whose firm designed and built machines for the mining industry, thought that he could find a better solution. He envisioned a machine that repeatedly performed von Guericke’s experiment, with the water in the mines being the weight lifted. Newcomen began experimenting with this concept in 1700 and installed his first commercial machine in 1712.

Newcomen's engine
Newcomen’s engine

Newcomen’s “atmospheric engine” is shown above. The ghost of von Guericke’s apparatus is still visible. The rope has been replaced with a pivoting beam. The lefthand side of the beam is heavier than the righthand side, so that it has a tendency to drop. The weight has been replaced by a pump. The piston and the cylinder are still there, but with three added valves: a steam intake (V), a water injector (V’), and a waste water drain (V’’). There is a firebox and boiler (A) below the cylinder, and a water reservoir (C) above it. The engine is operated by opening and closing the valves.

  • Begin with the injector and waste water valves closed and the steam intake valve open. Gravity pulls the lefthand side of the beam down, lifting the piston to the starting position of von Guericke’s experiment. As the piston rises, steam is drawn in from the boiler to fill the space below the piston.
  • Close the steam intake valve, and briefly open the water injector valve. Gravity forces a spurt of cold water into the cylinder, condensing the steam. There is now minimal pressure inside the cylinder, so atmospheric pressure pushes the piston down, causing the lefthand side of the beam to rise. As it rises, the attached chain pump lifts a volume of water.
  • Open the waste water drain valve, allowing the accumulated water to escape from the cylinder, and then close it.
  • Open the steam intake valve once again, equalizing the pressure on the top and bottom of the piston. Now the only pressure acting on the engine is gravity, which pulls down the lefthand side of the beam, and we are back in the first step.

The settings of the valves were linked to the position of the beam, so they opened and closed automatically.

Newcomen’s early engines were hideously inefficient, burning 45 pounds of coal for every horsepower-hour of energy. At this rate of consumption they could be used only in coal mines, where they burned the coal that was too fragmented to be sold. Numerous small improvements introduced by the engines’ operators gradually reduced fuel consumption to 30 pounds per horsepower-hour. Then, between 1769 and 1772, the engineer John Smeaton systematically fine-tuned all of the components of the atmospheric engine, further reducing fuel consumption to 17.6 pounds per horsepower-hour.

The next major innovation was James Watt’s separate condenser (1776). The separate condenser adds a step to the atmospheric engine’s cycle. After the piston has been drawn to the top of the cylinder, a valve to a low-pressure chamber is opened. The steam is drawn into this chamber, and then the valve is closed. In the cylinder the reduced pressure below the piston allows atmospheric pressure to drive the piston downward, just as it did in Newcomen’s engine. Meanwhile, the steam that has been drawn into the chamber is condensed with cold water and drained away, leaving the chamber again at low pressure. The use of the separate condenser means that the cylinder is not alternately heated by steam and cooled by water, which would waste energy. Smeaton found that a Watt engine burned 8.8 pounds of coal per horsepower-hour, exactly half the consumption of his own “best practice” Newcomen engine. The operators of Watt’s engine subsequently made many small improvements that reduced its fuel consumption to 3.5 pounds per horsepower-hour by the middle of the 1830s.

The early atmospheric engines were used only in pumping operations because their irregular motions made them unsuitable for powering other types of equipment. The waterwheel, which delivered smooth and steady power, continued to be the preferred power source at mills of all kinds. However, from the 1770s, inventors began to search for improvements in the atmospheric engine that would allow it to replace the waterwheel. A flywheel was added to the engine in 1779, and in 1780 James Pickard used a combination of flywheel and crank to produce rotary motion, so that the engine could be connected to a factory’s power shaft. James Watt produced a quartet of innovations:

  • A double-acting cylinder, in which steam was injected at both ends to produce two power strokes per cycle rather than one.
  • “Parallel motion” rods, which replaced the chain that connected the piston to the beam, so that the beam could be both driven upwards and pulled down.
  • “Sun and moon” gears, which turned the engine’s reciprocal motion into rotary motion without infringing on Pickard’s patents.
  • A centrifugal governor, which stabilized the speed of the engine by reducing the flow of steam when it ran too fast and increasing the flow when it ran too slow.

With these innovations the Watt engine was factory ready. It was first installed in a cotton mill in 1785. By 1800, 308 Watt engines had been sold to drive machinery, and a further 24 to power blowing engines, which were used to move large quantities of air in smelting operations.

The first high-pressure steam engine was built by Richard Trevithick in about 1800. It was perhaps the first true steam engine, in the sense that steam alone drove the piston. The pressure of the steam was less than two atmospheres,2 but this engine was lighter and more fuel efficient than the atmospheric engine.

Fuel efficiency was further increased by using steam expansively. The early engines had continued to inject steam into the cylinder until the piston reached the end of the cylinder. The later engines stopped injecting steam when the piston was perhaps a quarter of the way along the cylinder, and then the expansion of the steam drove the piston the rest of the way. Less fuel was burned because less steam was used. However, expansive steam also reintroduced the problem of temperature cycling in the cylinder. The pressure of the steam fell as it expanded, causing the temperature of the steam to fall. Exposure to cooler steam reduced the temperature of the cylinder, so that some of the energy in the next blast of steam was expended in reheating the cylinder. This problem was reduced by the compound engine, which was introduced by Arthur Woolf in 1813. In this engine the steam initially drives the piston in a high-pressure cylinder; but before its expansion is complete, the steam is led into a somewhat lower pressure cylinder where it expands further to drive the second piston. Most of the temperature variation is between the two cylinders, leaving more even temperatures within each cylinder.

The high-pressure engine was light, fuel efficient and adaptable. It was instrumental to the revolution in transportation.


Rails came before locomotives. British mines had to move their product overland in order to get it to market. Sometimes it was carried to a town or industrial center, but often it was carried to the nearest canal or river, water transport being much cheaper than land transport. Some mines further reduced their land transport costs by constructing “wagonways,” rail systems along which horse-drawn wagon trains carried the freight. The advantage of rail over road was reduced friction. The rails were wood, then wood with a top plate of metal, then cast iron, then wrought iron.

The Little Eaton wagonway continued to operate until July 1908.
The Little Eaton wagonway continued to operate until July 1908.

Collieries that had once used steam engines to pump water out of the mines were now using them to raise the coal to the surface. Using these engines to move coal overland must have been a fairly obvious next step; at any rate, a number of people began to experiment with “travelling engines,” including Richard Trevithick. However, it is George Stephenson who is most closely identified with the beginnings of commercial railways. He was employed as an engine-wright at a colliery when he designed the engine Blücher (1814), which was able to pull 30 tons of freight at a speed of four miles per hour. In 1821 Stephenson was hired to survey, and then build, a railway between a group of collieries in County Durham and the nearest port, Stockton. He then designed and built engines for the railway, including its first engine, Locomotion No. 1. When the Darlington-Stockton Railway opened for business in September 1825, it became the first commercial railway.

What's a hundred years? Locomotion No. 1 takes the star turn at the one-hundredth anniversary celebration of the Darlington-Stockton Railway.
What’s a hundred years? Locomotion No. 1 takes the star turn at the one-hundredth anniversary celebration of the Darlington-Stockton Railway.

Stephenson also surveyed and built the railway connecting Manchester, the center of Britain’s cotton textile industry, with Liverpool, its largest port. The railway held a contest in 1829 to choose the supplier of its locomotives; that contest was won by Stephenson’s Rocket, which pulled twenty tons at speeds up to twenty miles per hour. The Liverpool and Manchester Railway opened the following year.

Railways were cheaper than horse transport, and had the potential to vastly increase the volume of freight — and people — that could be moved around Britain. There was a boom in railroad construction. Britain had 2,400 kilometers of railway line in 1840, and 30,100 kilometers in 1900.

While many of the technologies of the Industrial Revolution were not immediately adopted outside of Britain, railways were almost immediately built on the Continent. Railways were almost a necessity for an industrializing country. As Germany grew to be Britain’s foremost commercial competitor, it built railways even faster than Britain. Germany had 500 kilometers of railway line in 1840, and 51,700 kilometers in 1900. The Americas and Asia also quickly adopted the railway.


The steamboat, like the locomotive, was a fairly obvious application of the steam engine. There were a number of attempts to build practical steamboats in France, England and the United States during the late eighteenth and early nineteenth centuries. The best method of propulsion was not immediately clear. John Fitch tried mechanized oars, but paddle wheels were dominant through much of the nineteenth century. The propellor was invented in 1827 by an Austrian, Josef Ressel, who shelved the concept after an unlucky trial. It was independently developed in Britain a few years later; its first use on a seagoing vessel was in 1833.

The steamboat was eagerly adopted in the United States, where the land was large and the population small. In 1807 Robert Fulton inaugurated the first commercial steamboat service, running between New York City and Albany. Within twenty years there were three hundred steamboats operating in North America. Steamboats and railroads competed for business; but rising population densities improved the economics of the railways, which eventually pushed aside the steamboats.

Isambard Kingdom Brunel poses by the chains of Great Eastern
Isambard Kingdom Brunel poses by the chains of Great Eastern

Britain’s rapid industrialization during the nineteenth century dramatically increased the volume of its trade, both imports of raw materials and exports of finished goods. Steamships had the potential to carry these products rapidly and cheaply. Many engineers were engaged in their development, but Isambard Kingdom Brunel was pre-eminent among them. He recognized that increasing the dimensions of a ship increased its cargo capacity by a greater proportion than it increased the drag on the ship’s hull: a bigger ship was a more efficient ship. This idea led him to build the steamship Great Western, which had a wood hull and was driven by both paddle wheels and sails. It was the largest ship in existence when it was launched in 1838. It could cross the Atlantic in fifteen days and was commercially successful. Brunel’s next steamship, Great Britain, was even larger. It was also more modern, with an iron hull and a propellor. Brunel then built Great Eastern, which was three times larger than Great Western, and driven by a combination of paddle wheels, propellors and sails. Great Eastern was not a commercial success as a passenger liner; after a refit, it was used to lay the first successful transatlantic telegraph cable.

Great Eastern
Great Eastern

Steam Turbines

A steam turbine directs a continuous flow of high pressure steam across a rotor (or, in the modern iteration, a set of rotors) attached to an axle. The steam spins the rotor and its axle, so that unlike the steam engine, the turbine has native rotary motion.

The steam turbine was developed in 1884 by a British scientist, Charles Parsons, who was probably inspired by the water turbines that had been developed by French scientists earlier in the century. It operated at high speeds and produced high torque, making it the ideal power source for a dynamo. He sold rights to his invention to George Westinghouse, who scaled up the technology to meet the rapidly growing demand for electricity. This technology has yet to be superceded: today’s thermal power plants still use steam turbines to turn dynamos. Likewise, a nuclear power plant is little more than a fancy boiler serving a steam turbine connected to a dynamo.

Parsons believed that the steam turbine could replace the steam engine in ships, and set up a company to develop the marine turbine. In 1894 the company commissioned a trial ship, Turbinia, that proved to be exceptionally fast. The first turbine-powered merchant ship was launched only a few years later. After some experimentation with smaller vessels, the British navy launched the turbine-powered battleship HMS Dreadnought in 1906. This ship was so superior to every earlier battleship that it caused a naval arms race around the world. A decade later it was obsolete.

  1. David Landes, The Unbound Prometheus (1969), p. 96.
  2. The steam pressure in locomotives toward the end of the steam era was in the neighbourhood of 15 atmospheres.