STEAM Engine, an engine for raising water, or for producing any powerful ef fect in moving machinery, &c. by the force of steam obtained from boiling wa ter. It is often called a fire-engine, on account, perhaps, of the fire employed in heating the water, in order to throw off the steam. This is unquestionably one of the most useful, curious, and important machines that has ever been and it is thought that without the aid of this, or some other engine adapted to the same purpose,we should long ere this have been deprived of the benefit of coal fires; as our forefathers, WI a century ago, had excavated almost all the mines of that substance as deep as they could be worked, without the aid of some engine to draw water from greater depths. The principle of this machine is as follows : there is a forcing pump, with its rod fixed to one end of a lever, which is worked by the weight or pressure of the atmosphere upon a piston at the other end, a tempo rary vacuum being made below it, by suddenly condensing the steam that had been let into the cylinder in which this piston works, by a jet of cold water thrown into it. A partial vacuum being thus made, the weight of the atmosphere presses down the piston, and raises the other end of the straight lever with water, &c. from the mine. Then immediately a hole is uncovered in the bottom of the cylinder, by which a fresh supply of hot steam rushes in from the boiler, which acts as a counterbalance for the atmos phere above the piston, and the weight of the pump rods at the other end of the lever carries that end down, and of course raises the piston of the steam cylinder. The orifice for the emission of the steam is immediately shut, and the cock open ed for injecting the cold water into the cylinder: this condenses it to water, and another vacuum is made below. the pis ton, which is now again forced down by the weight of the atmosphere, and thus the work is continued so long as water and fuel are supplied.
This is the common principle of the steam engine, but the methods of opera tion are very various ; there is seldom a year that passes away, that we have not new patents obtained for improvements, or professed improvements of this ma. chine. It is comparatively of modern in vention: the earliest account of any one is that in the Marquis of Worcester's His tory of Inventions, published in the year 1663; the description here is too scanty to work upon, but it furnished the idea, which has afforded to ingenious men of all nations the opportunity of putting forth their skill, and their talents, in executing a number of important improvements on the subject. Captain Savery was the first person who attempted to realize the no ble Marquis's project : he made the pres sure of steam act immediately on the sur face of water contained in a close vessel, and the water was forced, by the elastici ty of the steam, to ascend through a pipe. The objection to this was, the great heat required for raising water to any consi derable height: and also the waste of steam by its coming in contact with the cold water in the receiver, the surfaces of which required to be heated to its own temperature, before the water could be expelled. These inconveniences were in
a great measure avoided in Newcomen's engine, where the steam was gradually introduced into a cylinder, and suddenly condensed by a jet of water, so that the piston was forced down with great vio lence by the preaspre of the atmosphere, which produced the effective stroke : this effect was, however, partly employ. ed in raising a counterpoise, which de scended, upon the re-admission of the steam, and worked a forcing-pump in its return, when water was to be raised. Engines on this principle were common ly used in this country, till the improve ments on them were introduced by Mr. Watt, to whom the public, in this busi ness, is more indebted than to any other person. The engines constructed by this gentleman are said to save three-fourths of the fuel that was used in the beat con structed engines of Newcomen, with the waste of only one-fourth of the steam. He has contrived to observe an uniform heat in the cylinder of his engines, by suffer ing no cold water to touch it, and by pro. tecting it from the air, or other cold bo dies, by a surrounding case filled with steam, or with hot air, or water, and by coating it over with substances that con duct the heat very slowly and imperfect ly. He makes his vacuum to approach nearly in excellence to that of a barome ter, by condensing the steam in a sepa rate vessel, called the condenser, whteh may be cooled at pleasure, without cool ing the cylinder, either by an injection of cold water, or by surrounding the con denser with it. He extracts the injection water and detached air from the cylinder, or condenser, by pumps, which are work ed by the engine itself As the entrance of air into the cylinder would stop, or very much impede, the operation of the engines, and as it is almost impossible to expect such pistons to be absolutely air tight, a stream of water used to be kept running on the piston, to prevent the en try of the air, as the lighter fluid could not descend through the heavier: this mode, which was not injurious to the en gines on the old construction, could not fail to injure the modern ones of Mr. Watt. He therefore makes his pistons more ac curately ; and the outer cylinder having a lid, which covers it, the steam is intro duced above the piston, and when a va cuum is produced under it, acts upon it by its elasticity, as the atmosphere does upon common engines by its gravity. This method of working effectually excludes the air from the inner cylinder, and gives the advantage of adding to the power, by increasing the elasticity of the steam. We shall endeavour to give our readers an idea of the manner m which Mr. Watt's engine works, and then present the% with an accurate description, accompanied with engravings of one, to which our drafts man has had access for the purpose.