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 im parted 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 sooner 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 occurred to Mr. Watt. The one most 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 increase or diminish the steam way. The next improvement was to make this valve, called a throttle valve, a selfacting 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. to "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 regulator was adopted by Mr. Watt, and applied to regulate the opening and shutting of the throttle-valve of his improved engine." Mr. Watt, by these and other contrivances, having made the recipro cating 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. Watt, 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 beautiful 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, pear London. with an elasticity equal to the pressure 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 b (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 falls into the pipe e. To the bottom of the cylinder i, a pipem is carried into a box n, having a float-ball o, which opens and shuts the valve p, communicating with the atmosphere; a pipe q, 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 pipe s 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 b reaches the bottom of the cylinder a, 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 has reached the top of the cylinder, the valve k 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 r, opens it; a cominunication 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 water and air which were under it in the cylinder 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 downwards; this opens the vale p, and allows it to escape into the atmosphere. "The machine, from its refined simplicity, appears excellently adapted as a It has first mover on a small scale. 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 metallic 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 tight, 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 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 common 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 length, the water might be all thrown on one spot, which must render its effect certain. You will see, Gentlemen, that these pumps being always in readiness, might be worked at a minute's notice, and that they would be no disadvantage to the appearance of a ship compared to the essential benefit they would afford in a moment of danger; besides which, they might be worked in all weathers, and would be of use in cleaning the ship, &c. The number might vary with the size of the vessel; for instance, fifteen on each side, or one between every two guns, would be sufficient for one of his majesty's frigates. 66 I have been led to this thought by reading the account of the tremendous fire which in ten minutes drove every soul from the ship Fame." What would have been the consequence if it had happened far at sea, and in a heavy gale of wind? I remain, Gentlemen, Your obedient servant, R. J. M., a Seaman. [We see no objection to this plan, provided the pumps are so fitted that the fulcrum of the brake shall be moveable, and the lower end of the pipe be so let in to the sheathing as not to impede the vessel's way. If pumps can be thus attached to ships, they would certainly be of great use in cases of fire, and give great facility to the daily operation of washing the deck, as at present it is necessary to carry the water for that purpose from the forecastle aft to the poop.EDIT. Here I will take the liberty to propose a plain question, viz.-Should a certain known quantity and fall of a stream of water be applied to act upon a common water-wheel made nearly in diameter equal to the fall of water, and the same water, both in quantity and fall, be put to act upon a piston constructed similar to the common steam-engine; which of these two applications of the same water will have most power to turn machinery? Should it be in favour of the water-wheel, then it follows that the piston acting in a cylinder will not be the way "to make the most of a water-fall." The true value of any thing is its usefulness; therefore, any thing of little use is of little value; this is the case with the piston moved by the pressure-water in a cylinder, &c. to giye motion and power to machinery, because, by actual trial, the water-wheel gives double the actual power to driving machinery. The truth of this assertion is evident to every person who will only consider the loss of power by the necessary parts required to take the power from a straight line, and apply it to that which is a circle. In effecting this circular motion, the parts used must contain a great weight of materials, which are caused to move alternately in different directions, having their accumulated (moving) power in opposition to the power applied for turning the machinery, every time these parts are caused to move in an opposite direction. Notwithstanding this impeding property, it is but little loss of power when compared to the loss arising from the different positions which the crank must be in during the time it receives and communicates power (by the aid of a fly-wheel) to machinery. For, take away the flywheel, and all motion ceases, although the pressure of the water remains the same; but this is not the case where the common water-wheel is used. These crude hints may be sufficient to show the inefficacy of using the piston and cylinder, &c. to make the most of a water-fall. there may be situations, &c. that may prevent the use of the water-wheel But |