He will be told of a machine more potent in shaping the destinies of our race than warlike engines—the steam printing-press. He may hear of a chemistry which effects endless and marvellous transformations; which from dirt and dross extracts fragrant essences and dyes of resplendent hue. He may hear something of a wonderful instrument which can make a faint beam of light, reaching us after a journey of a thousand years, unfold its tale and reveal the secrets of the stars. Of these and of other inventions and discoveries which distinguish the present age it is the purpose of this work to give some account.
STEAM ENGINES.
To track the steps which led up to the invention of the Steam Engine, and fully describe the improvements by which the genius of the illustrious Watt perfected it at least in principle, are not subjects falling within the province of this work, which deals only with the discoveries and inventions of the present century. But as it does enter into our province to describe some of the more recent developments of Watt’s invention, it may be desirable to give the reader an idea of his engine, of which all the more recent applications of steam are modifications, with improvements of detail rather than of principle.
Watt took up the engine in the condition in which it was left by Newcomen; and what that was may be seen in Fig. [2], which represents Newcomen’s atmospheric engine—the first practically useful engine in which a piston moving in a cylinder was employed. In the cut, the lower part of the cylinder, c, is removed, or supposed to be broken off, in order that the piston, h, and the openings of the pipes, d, e, f, connected with the cylinder, may be exhibited. The steam was admitted beneath the piston by the attendant turning the cock k, and as the elastic force of the steam was only equal to the pressure of the atmosphere, it was not employed to raise the piston, but merely filled the cylinder, the ascent of the piston being caused by the weight attached to the other side of the beam, which at the same time sent down the pump-rod, m; and when this was at its lowest position, the piston was nearly at the top of the cylinder, which was open. The attendant then cut off the communication with the boiler by closing the cock, k, at the same time opening another cock which allowed a jet of cold water from the cistern, g, to flow through the opening, d, into the cylinder. The steam which filled the cylinder was, by contact with the cold fluid, instantly condensed into water; and as the liquefied steam would take up little more than a two-thousandth part of the space it occupied in the gaseous state, it followed that a vacuum was produced within the cylinder; and the weight of the atmosphere acting on the top of the piston, having no longer the elastic force of the steam to counteract it, forced the piston down, and thus raised the pump-bucket attached to the rod, m. The water which entered the cylinder from the cistern, together with that produced by the condensation of the steam, flowed out of the cylinder by the opening, f, the pipe from which was conducted downwards, and terminated under water, the surface of which was at least 34 ft. below the level of the cylinder; for the atmospheric pressure would cause the cylinder to be filled with water had the height been less. The improvements which Watt, reasoning from scientific principles, was enabled to effect on the rude engine of Newcomen, are well expressed by himself in the specification of his patent of 1769. It will be observed that the machine was formerly called the “fire engine.”
Fig. 2.—Newcomen’s Steam Engine.
Fig. 3.—Watt’s Double-action Steam Engine.
“My method of lessening the consumption of steam, and consequently fuel, in fire engines, consists of the following principles:—First. That vessel in which the powers of steam are to be employed to work the engine (which is called the cylinder in common fire engines, and which I call the steam-vessel), must, during the whole time the engine is at work, be kept as hot as the steam that enters it; first, by enclosing it in a case of wood, or any other materials that transmit heat slowly; secondly, by surrounding it with steam or other heated bodies; and thirdly, by suffering neither water nor any other substance colder than the steam to enter or touch it during that time.—Secondly. In engines that are to be worked either wholly or partially by condensation of steam, the steam is to be condensed in vessels distinct from the steam-vessels or cylinders, although occasionally communicating with them,—these vessels I call condensers; and whilst the engines are working, these condensers ought to be kept at least as cold as the air in the neighbourhood of the engines by the application of water or other cold bodies.—Thirdly. Whatever air or other elastic vapour is not condensed by the cold of the condenser, and may impede the working of the engine, is to be drawn out of the steam-vessels or condensers by means of pumps, wrought by the engines themselves or otherwise.—Fourthly. I intend in many cases to employ the expansive force of steam to press on the pistons, or whatever may be used instead of them, in the same manner in which the pressure of the atmosphere is now employed in common fire engines. In cases where cold water cannot be had in plenty, the engines may be wrought by this force of steam only, by discharging the steam into the air after it has done its office.—Lastly. Instead of using water to render the pistons and other parts of the engines air- and steam-tight, I employ oils, wax, resinous bodies, fat of animals, quicksilver, and other metals in their fluid state.”