Hero, a mathematician in Alexandria in about AD 75, enjoys inventing mechanical gadgets, which he describes in his work Pneumatica. Whether he has the technology to make them we do not know, but his scientific principles are correct.
One such gadget is a primitive version of a steam turbine. Hero says steam should be directed into a hollow globe with outlets through nozzles on opposite sides of the circumference. The nozzles are directed round the rim of the globe. As the steam rushes out, like sparks from a catherine wheel, the globe spins.
Hero makes another significant use of atmospheric pressure in a magic altar, putting to work the expansion and contraction of air. A fire heats the air in a container, causing it to expand and force water up a tube into a bucket. The increased weight of the bucket opens the doors of an altar. When the fire is extinguished, the air contracts, the water in the bucket is sucked out and the doors close.
Any temple managing to work this trick is certain to attract more pilgrims, and more money, than its rivals.
Pressure cooker and piston: AD 1685-1690
In about 1685 Denis Papin, a French scientist working in England, demonstrates his ‘digester’. It is a device familiar three centuries later as the pressure cooker. Papin’s version is a cast-iron cylinder, about 6 inches in diameter and 18 inches long – much like a short length of drainpipe. The top section, which can be removed, is provided with a tight seal.
Papin places meat, bones and water in his digester. The tube can contain atmospheric pressure up to the point at which tin melts (about 210° C). To everyone’s delight and amazement, the food is cooked very much sooner than the onlookers expect.
The digester includes an important mechanical innovation. Anticipating the danger that his scalding concoction of meat, bones and water may explode over the assembled company, Papin takes a crucial precaution. He provides the first recorded safety valve.
In addition to the main seal at the end of the cylinder, there is a second smaller aperture with its own seal. This smaller seal is held in place by a lever with an adjustable weight exerting the pressure.
By 1690 Papin is professor of mathematics at the university of Marburg. Here he makes a working model of a steam engine which is the first to incorporate one crucial element – the piston, forced up in its cylinder by the energy of expanding steam and then sucked down again by the vacuum when the steam cools and condenses.
Papin’s machine is extremely leisurely because he uses the same container as both boiler and cylinder. A small amount of water is boiled in the vessel, forcing up the piston; the heat is removed and the steam cools, condensing and eventually pulling down the piston. The pace is unbearably slow, but the principle has a great future.
Steam pump: AD 1698-1702
Thomas Savery has grown up in a mining district of Devon and knows the problem of flooded mines. In 1698 he obtains a patent for an engine to raise water ‘by the Impellent Force of Fire’. It turns out to be the world’s first practical steam engine. Designed purely as a pump, it has no piston but relies on the power of a vacuum.
A metal cylinder is filled with steam from a boiler. Cold water is poured over the outside, condensing the steam within and creating a vacuum which sucks water up through a pipe at the base. When the cylinder is full of water, the valve from below is closed. Steam is again introduced, forcing the water out of the cylinder through another valve. With the cylinder again full of steam, the process is repeated.
In 1702 Savery publishes a book about his invention, entitled The Miner’s Friend. In it he describes how the idea came to him. One evening, after finishing his wine, he threw the empty bottle into the fire and prepared to wash his hands in a basin of water. Noticing steam coming out of the neck of the bottle, he plucked it from the fire and stuck it neck down in the basin. As the bottle cooled, it sucked up the water.
The story sounds improbable, and it may be Savery’s way of trying to justify his patent – for the principles involved are already well known to contemporary scientists. What the pamphlet does show is that Savery intends to make money from his invention by supplying pumps to mines.
As it turns out, the maximum levels of pressure and vacuum achieved by Savery cannot lift water more than about twelve yards – too little for most mines.
Instead he finds his main customers among progressive country landowners, who are attracted by being at the cutting edge of technology. They use Savery’s pumps to raise water for their houses and gardens.
Boiler, cylinder and piston: AD 1704-1712
Two Devon metalworkers – Thomas Newcomen, a Dartmouth blacksmith, and his assistant John Calley, a glassblower and plumber – are making good progress in some potentially very profitable experiments. They know the high cost of the horse-driven pumps which raise water from the copper and tin mines of Devon and Cornwall. So they are working on a steam pump.
Though probably unaware of this, they are combining two elements pioneered separately by Denis Papin and Thomas Savery – Papin’s piston and Savery’s separation of the boiler (providing the supply of steam) from the cylinder (where the steam does its work).
In Newcomen’s engine the piston, emerging from the top of the cylinder, is attached by an iron chain to one end of a beam which seesaws on a central pivot. At the other end of the beam another chain leads down to the water-pumping mechanism.
Steam released from the boiler into the cylinder pushes up the piston. When the cylinder is full of steam, the same procedure follows as in Savery’s engine. Cold water poured on the outside condenses the steam and creates the vacuum. But in this case, instead of directly sucking up water, the vacuum causes the piston to descend in the cylinder. The chain drags down one end of the beam, activating the pump at the other end.
As so often in the advance of science and technology, an accident provides Newcomen with the refinement which brings his pump up to an economic speed. A flaw develops in one of the seams of his cylinder. As a result some cold water, intended only to flow down the outside, gets into the cylinder when it is full of steam. It creates a vacuum so rapid and so powerful that it snaps the chain attaching the piston to the beam.
With this event another lasting feature of the steam engine is discovered. In all Newcomen’s developed engines, which soon start work in England’s mines, the steam is condensed by a jet of cold water injected into the cylinder.
The first of Newcomen’s working engines is installed in 1712 at a colliery near Dudley Castle. It operates successfully here for some thirty years, as the first of many in the mining districts of Britain. Newcomen’s machine undoubtedly infringes Savery’s patent, for there is no denying that it works ‘by the Impellent Force of Fire’. But Savery is having no great commercial success with his own machine. The two men come to an amicable arrangement, the details of which are not known.
Even with Newcomen’s improvements, these machines are suitable only for the slow relentless work of pumping in the mines. Proof of the wider potential of the steam engine must await the inventive genius of James Watt.
James Watt and the condenser: AD 1764-1769
In 1764 a model of a Newcomen steam engine is brought for repair to the young James Watt, who is responsible for looking after the instruments in the physics department of the university of Glasgow. In restoring it to working order, he is astonished at how much steam it uses and wastes.
The reason, he realizes, is that the machine’s single cylinder is required to perform two opposing functions. It must receive the incoming steam at maximum pressure to force the piston up (for which it needs to be as hot as possible), and it must then condense the steam to form a vacuum to pull the cylinder down (for which it needs to be as cool as possible).
The solution occurs to Watt when he is walking near Glasgow one Sunday in May 1765. The two functions could be separated by providing a chamber, outside the cylinder but connecting with it, in which a jet of cold water will condense the steam and cause the vacuum.
This chamber is the condenser, for which Watt registers a patent in 1769. The principle has remained an essential part of all subsequent steam engines. It is the first of three major improvements which Watt makes in the basic design of steam-driven machinery. The other two are the double-acting engine and the governor, developed in the 1780s.
Double-acting engine and governor: AD 1782-1787
Just as James Watt applied a rational approach to improve the efficiency of the steam engine with the condenser, so now he takes a logical step forward in a modification patented in 1782. His new improvement is the double-acting engine.
Watt observes that the steam is idle for half of each cycle. During the downward stroke, when the vacuum is exerting atmospheric force on the piston, the valve between boiler and cylinder is closed. Watt takes the simple step of diverting the steam during this part of the cycle to the upper part of the cylinder, where it joins with the atmospheric pressure in forcing the cylinder down – and thus doubles its effective action.
The most elegant contraption devised by Watt is in use from 1787. It is the governor – the first example of the type of controlling device required in industrial automation, and a feature of all steam engines since Watt’s time.
Watt’s governor consists of two arms, hinged on a central pivot and rotated by the action of the steam engine. Each arm has a heavy ball at the end. As the speed increases, centrifugal force moves the balls and the arms outwards. This action narrows the aperture of a valve controlling the flow of steam to the engine. As the power is slowly cut off, the speed of the engine reduces and the balls subside nearer to the central column – thus slightly opening the valve again in a permanent process of adjustment.
Watt’s many improvements to the steam engine leave it poised to undertake a whole new range of tasks. Its new efficiency means that it can become mobile. Each engine can now generate more power than is required merely to move itself.
By the time of his death in 1819, in quiet retirement near Birmingham, Watt has seen the introduction of commercially successful steam boats and the dawn of the railway age. In each case the vehicles are powered by engines of the type which he has developed.