STEAM-ENGINE

The expansive power of steam was known to the ancients, and its earliest use in connection with a mechanical contrivance is noted by Hero of Alexandria (about 130 B.C.) in his Pneumatica. In this treatise Hero describes an æolipile or hollow spherical vessel turning on an axis, supplied with steam, and driven by the reaction from the escaping jets of steam, much in the same way as Barker's mill is driven by escaping water.

This invention had no practical result, and it was not until the 17th century that the power of steam was again recognized by Giovanni Battista della Porta (1601), Solomon de Caus (1615), Giovanni Branca (1629), and the Marquis of Worcester (1663). Their various inventions were an adaptation of the principle that a mechanical power is obtained by the pressure of steam acting on the surface of water placed in a closed vessel. This principle was put to practical use by Captain Thomas Savery (1698) in a steam-engine which he constructed for the purpose of raising water out of mines; and with the elevation of water by pressure he also combined the principle of obtaining a vacuum by condensation.

This principle, however, was made more practically effective by Denis Papin (1690), who constructed a steam-engine in which a piston was forced down through the vacuum made by condensation.

Thomas Newcomen, a locksmith at Dartmouth, in Devonshire, towards the close of the 17th century, conceived the idea of producing a vacuum below the piston of a steam-engine after it had been raised by the expansive force of the steam, which he effected by the injection of cold water to condense the vapour. This first conception of a piston working in a cylinder was further developed by Newcomen and his assistant Cawley. In their engine the boiler and furnace were separated from the cylinder and piston, and its chief characteristic was an oscillating beam connected on one side with the piston and on the other side with a pump-rod in the mine. When a vacuum was made under the piston in the cylinder by the injection of a jet of water, causing condensation, the piston was driven down by the pressure of the atmosphere, and as that end of the beam was lowered, the other end attached to the pump-rod was raised with its load of water. The merit of first applying the steam-engine to practical purposes is thus due to Newcomen, who, in conjunction with Captain Savery and John Cowley, took out a patent for the invention in 1705.

Various improvements were made upon this atmospheric steam-engine by Smeaton and others, but its greatest development was effected by James Watt (1769). His improvement consisted in condensing the steam, not in the cylinder, but in a separate condenser, thus preventing the waste occasioned previously by the chilling and heating of the cylinder. Besides this, he preserved the heat in the cylinder by surrounding it with a layer of hot steam inside of an external casing; and with the same object he employed steam, instead of air, to press down the piston from above. Thus he obtained the double-acting engine, which is so named because both the up-stroke and the down-stroke are produced by means of steam. Further, he devised a crank motion which converted the alternating motion of the oscillating beam into a continuous rotatory motion; but as this invention was pirated he patented the 'sun and-planet' wheel as a substitute for the crank, returning afterwards to the crank. To these improvements he subsequently added a fly-wheel, in order to equalize the motion so as to drive the crank past the dead-points; a governor, whose purpose was to regulate the quantity of steam passing into the cylinder; an indicator, to measure the pressure upon the piston; and a slide-valve, moved automatically by an eccentric, the object of which was to regulate the action of the steam in the cylinder. The steam-engine, as thus developed by Watt, was in nearly all essential points the same as the present-day engine. Probably the only improvement of primary importance which has been made in the steam-engine since the time of Watt, is the manner in which steam is now used expansively.

It was Jonathan Hornblower (1781) who first adopted the principle of expanding steam in two cylinders of different sizes. This form of compound engine, as it was called, was employed by Woolf (1814) in the Cornish mines, while it was improved by M'Naught (1845), and adapted by Elder (1854) to the use of marine engines. In the compound engine the steam receives the greater part of its expansion in a second cylinder of much larger diameter than the first, and by this means greater steadiness of piston-stroke, economy of fuel, and increased driving power have been obtained. The use of expanded steam has been especially notable in the marine engine, where it is now expanded successively in three or even four cylinders

The Road-locomotive was first suggested by William Symington in Scotland, and developed for practical purposes about 1800 by Oliver Evans in America and Trevethick in Wales.

		It was used to propel carriages from town to town, but the badness of the turnpike roads and the subsequent introduction of railways brought the road-locomotive, as a means of transit, into disuse. Later it was used to draw heavy loads along the highway or over fields in farming operations. The chief characteristics of this traction engine, as it is called, is the great width of the wheels, which were supplied by some makers with protected india-rubber tires to prevent slipping. It could be made to run backwards or forwards by means of reversing gear, while its course was guided by a steering wheel acting upon a vertical shaft.
A steam plough built by John Fowler of Leeds fueled by straw.

The Railway - locomotive is a steam. engine and boiler placed upon wheels and employed to transport a train of wagons or carriages upon a railway. Various attempts had been made to construct a steam-engine to run upon rails by Blenkinsop (1811), Blackett (1812), Hedley (1813), Dodds & Stephenson (1815), and others. It was not, however, until the opening of the Liverpool and Manchester Railway in 1829 that the modern high-speed locomotive came into use.

The steam Tramway-locomotive was in many respects similar to the railway-locomotive. It had usually two sloping cylinders in front connected with the hindmost of two coupled driving axles, and the waste steam is exhausted into an atmospheric condenser on the to of the engine.