perfection of the machine, and ne accomplished it by a very slight extension of his first idea. "He had introduced steam acting against a piston to press it downwards; be now formed a communication between both sides of the piston and the boiler, and also with the condenser, and made the steam act to press the piston upwards as well as downwards. "The mechanism was now, as far as the principle went, perfect; and it was reed, for the first time, from the enor mous dead weight of counterpoises, which had hung on it from the first attempts of Newcomen; and the equally enormous load which was used in the construction of the various parts, for the purpose of equalizing the motion." The drawing on page 392, illus◄ trates the application of this improve ment. "The cylinder a is inclosed in a jacket or casing like the single engine, having a similar interval, which may be filled with steam or air. The piston b is attached to the lever-beam by the rod x. 1 2 3 4 are the valves which admit steam to the cylinder, or open a communication between the upper and under sides of the piston, and the condenser. g is the pipe leading from the valves to the condenser. mm, the levers or spanaers, which are elevated or depressed by the lappets or pins nz, in the plugframe, and open or shut the valves to which they may be connected. h is the condenser; L, a pipe connecting it with the air-pump i, and a second air-pump E. c, the piston-rod of this second pump, attached, like the other, I, to the leverbeam. F, a pipe from the cold waterpump q, to supply the reservoir in which the condenser and its pumps are placed. k, a trough or reservoir into which the water heated by the condensation of zteam in the condenser, which is raised by the air-pump, is pumped back by M, anto the boiler. G, a pulley; and H, an endless chain moving over it, also going round a pulley fixed on the upright axis of the conical pendulum or governor z. The other pulley, which is fixed to the axis of the fly-wheel, is not shown in this figure, but its situation and connexion will be clearly seen. R, the handle of the lever which regulates the quantity of injection water admitted. PP, the ma sonry or wall on which the cylinder and other parts of the machine are placed. d, a pipe conveying steam from the boiler to the cylinder. », a cock or valve, called the throttle-vale or regu lator, placed on the pipe conveying the steam from the boiler, and which is moved by the levers shown as supported at D, and connected with the conical pendulum TQQQw are system of levers called the parallel mution. the axis of the lever-beam y. 1 is "The motion at first is produced in this machine in the same manner as 'in the single engine, by filling the con denser and cylinder with steam, and then opening the injection-cock. "This process may be considered to have been gone through, and that the piston has arrived at the top of the cylinder. At this moment the tappets n n, and levers m m, open the valves 1 and 4, and shut 3 and 2. The steam from the boiler now acts on the upper side of the piston, while a vacuum is formed under it by the valve 4 opening a communication between that part of the cylinder beneath it and the condenser. The piston is, therefore, pressed by the elasticity of the steam to the bottom: when it has arrived at the lowest point, the tappets on the plug-frame, which also descend with the piston-rod, shut the valves 1 and, and open 3 and 2. The steam from the boiler, instead of flowing in at the top of the cylinder, is admitted at the bottom, and a communication is opened between the upper end of the cylinder and the condenser: a vacuum is then produced above the piston, and the elasticity of the steam (instead of the counterpoise) forces it upwards. When it is elevated to the required height, the tappets again act on the spanners, and prevent the further flow of steam beneath the piston, and admits it at its upper end, opening at the same moment a communication between the lower end and condensing apparatus. The motion of the piston is then reversed, and this alternation may be continued indefinitely. "The mode of pumping out the water from the condenser being the same as • “We believe that until Mr. Watt went into Cornwall, the blowing valve (in the condenser) had never been applied to any of his engines, it being the usual method to pump out the air by a temporary brake attached to the discharging pump; and that this valve was first applied by Mr. Hornblower at an engine on a mine called Ting Tong, which engine was erected by him for the proprietors of the work. Hornblower in Gregory s Mechanics, p. 375, vol. II." that in the single engine, will be easily understood from an inspection of our figure. In order to show the four valves in section, a pipe placed in the same direction, and opposite to o, has been omitted in the engraving: it connects the top of the cylinder and the condenser together." * "When the impulse of the steam impelled the piston only in one direction (downwards), its motion could be imparted to the beam by means of chains, as in the following figure: but when the impulse was to be communicated upwards as well as downwards, some other contrivance for connecting the beam and piston became necessary; and one of the conditions of this contrivance must be, to convert the motion in a curved path of the end of the lever-beam, into a rectilineal motion of the cylinder piston-rod. Mr. Watt, in his earlier engines, used to form the end of the beam as a sector with teeth, which worked into a rack fixed on the end of the piston-rod: this allowed the rod to move perpendicularly upwards or downwards, but it was very inelegant in appearance, worked with a great noise, and was easily deranged, especially at the instant when the direc tion of the motion was changed. "Even after the motion of the piston was equalized by shutting off the steam Booner or later from the cylinder, another source of irregularity was found to arise from the varying quantity of steam, which in different states of the fire under the boiler was admitted into the cylinder: several modes of adjustment ocThe one must curred to Mr. Watt. generally employed, and probably as accurate as any, was, by placing a valve in the pipe connecting the boiler and the cylinder, which could be made to increase or diminish the steam way. The next improvement was to make this valve, called a throttle valve, a self. acting one, and to admit of its being so adjusted, that when the piston was moving with too great a velocity, it would admit less steam into the cylinder, and so diminish its speed, and on the contrary admit a greater quantity when it was moving too slow. "A similar irregularity in the motion of corn-mills from the varying quantity of water or resistance, had early exercised the ingenuity of millers, to obtain some means by which its injurious effects could be obviated. One of the most usual modes was by means of a couple of heavy balls, attached by a jointed rod, which were made to revolve by being connected with the spindle or axis of the mill-stones. When the stones were moving at a great speed, the meal, by the rise of the stones, was too coarse; and, on the contrary, when the motion was slow, the meal produced was small in quantity and too fine. The attached balls, which were called a lift-tenter, by their centrifugal force, either raised or lowered a stage in which the arbour of the spindle revolved, and brought the mill-stones nearer, or removed them farther from each other, as they might be adjusted. This most ingenious regu lator was adopted by Mr. Watt, and ap plied to regulate the opening and shutting of the throttle-valve of his improved engine." Mr. Watt, by these and other contrivances, having made the reciprocating motion of his engines very regular, next turned his attention to the important object of producing a continuous rotatory motion from a reciprocating one; and this he accomplished by what are now called the sun and planet wheels. It has been found, however, in practice, that nearly the same effect may be obtained in a much simpler manner, and at less expence, by the application of a crank, in the manner of a common turning lathe; and the crank accordingly is now generally employed. The application of the Steamengine to the moving of mill machinery gave birth to another contrivance. "In the patent of 1782, the double impulse was communicated to the working-beam by the intervention of a sector, placed on the end of the pump-rod, working into a sector placed on the end of the working-beam; but the motion was rough and jerking, and, above all, noisy; and the racks and sectors were very subject to wear. It occurred to Mr. Wett, that if some mechanism could be devised, moving on centres which would keep the piston-rods perpendicular, both in pulling and pushing, a smoother motion would be obtained. This problem was solved by the invention of the beau tiful mechanical combination called the parallel motion." The combination here mentioned is shown in the drawing (p. 392), and was first used in the engines erected at the Albion Mills, near London. with an elasticity equal to the pres sure of the atmosphere, he calculated that a saving of at least one-half of the fuel could be made. We extract Mr. Stuart's description of the engine which Dr. C. constructed on these principles: "The piston (see our second engraving in this Number), moving in the cylinder a, has its rod t prolonged downwards; another piston d, is attached to it, moving in the cylinder c, and which may be also considered as a prolongation of the steam cylinder. The steam cylinder is attached by the pipe g, to the condenser, placed in cold water, formed of two concentric circular vessels, between which the steam is admitted in a thin sheet, and is condensed by coming into contact with the cold sides of the condensing vessel. The water of condensation fails into the pipe e. To the bottom of the cylinder i, a pipe m is carried into a box n, having a float-ball o, which opens and shuts the valve p, communicating with the atmosphere; a pipe g, is also fitted to the box. There is a valve placed at i, opening into the cylinder c; another at n, also opening upwards. The pipes conveys steam from the boiler into the cylinder, which may be shut by the fall of the clack r. K is a valve made in the piston b. "In the figure, the piston b is shown as descending by the elasticity of the steam flowing from the boiler through s; the piston d, being attached to the same rod, is also descending. When the piston 6 reaches the bottom of the cylin dera, the tail or spindle of the valve k, being pressed upwards, opens the valve, and forms a communication between the upper side of the piston and the condenser; at the same moment the valve r is pressed into its seat by the descent of the cross arm on the piston, which prevents the further admission of steam from the boiler; this allows the piston to be drawn up to the top of the cylinder, by the momentum of the fly-wheel z, in a non-resisting medium. The piston dis also drawn up to the top of c, and the valve i is raised by the condensed water and air which have accumulated in e, and in the condenser g. At the moment when the piston l.as reached the top of the cylinder, the valve is pressed into its place y the pin or tail striking the cylinder cover; and at the same time, the piston b striking the tail of the valve , opens it; a communication is again established between the boiler and piston, and it is forced to the bottom as before." By the descent of the piston d, the waters and air which were under it in the cylin der c, being prevented from returning into the condensing cylinder by the valve under i, are driven up the pipe m, into the box. n, and are conveyed into the boiler again through the pipe q. The air rises above the water in a, and when, by its accumulation, its pressure is increased, it presses the float o down wards; this opens the vale p, and allows it to escape into the atmosphere. "The machine, from its refined simplicity, appears excellently adapted as first mover on a small scale. It bas never, however, had a fair trial; the objections which were urged against the condensing vessels at the time of their invention, have always appeared to us more specious than solid. To the great merit in the arrangement and simplification of parts shown in this engine, must be added one of immense importance to engines on every construction-the me tallic piston. Mr. Cartwright constructed his of two plates, between which were placed detached pieces of metal, instead of the usual packing; these pieces were acted on by a spring, so as always to be kept equally fight, whatever might be the wear of the piston. The manner of connecting the piston-rod and procuring a rotatory motion, is a beautiful specimen of mechanical invention." (To be concluded in our next.) PLAN FOR EXTINGUISHING FIRE AT SEA GENTLEMEN;-I take the liberty of offering a suggestion of mine to your notice, which, if carried into effect, may perhaps prove of service in case of accident by fire at sea. I propose that every ship of 500 tons should have a row of common hand-pumps affixed to each of her sides, outside the gunwale, not less than ten in number; these to have each a leather hose affixed to their spouts, and filled, as regards length, aperture, &c. in the manner of com mon fire-engine hose. I believe that twenty such pumps, which might be worked by forty men (one at each pump, and one to guide the hose) would throw in a sufficient quantity of water in any case to ensure the extinction of the raging element and by the hose being of a proper |