the side of the cylinder a quantity of junk or oakum is stuffed, and kept down by weights, to prevent the entrance of air or water, and the escape of steam.

H, the chain and piston-shank, by which it is connected to the working beam by an arc of a circle.

I, I, the working beam, or lever, working on its centre, in the manner of a scale beam; it is made of two or more large logs of timber, bent together at each end, and kept at the distance of eight or nine inches from each other in the middle, by the gudgeon or centre, as represented in the plate. The arch heads I, I, at the ends of the beam, are for giving a perpendicular direction to the chains of the piston and pump-rods, which are suspended at the opposite ends.

N, the jack-head pump, which is a smaller sucking pump, wrought by a small lever or working beam, by means of a chain connected to the great beam or lever near the arch g, at the inner end; and the rod of the pump N is suspended by a chain at the outer end. This pump commonly stands near the corner or front of the house, and raises a column of water up to the cistern O, into which it is conducted by a trough.

O, the jack-head cistern, for supplying the injection; it is always kept full by the pump N, and is fixed so high above the cylinder bottom, as to give the jet of injection a sufficient velocity into the cylinder, when the cock is opened. This cistern has a waste-pipe on the opposite side for conveying away the superfluous water.

P, P, the injection pipe, of two or three inches diameter, which descends from the cistern O, to the injection cock r, after passing which it turns up in a curve at the lower end, and enters the cylinder bottom. It has a thin plate of iron screwed upon the end d, which is within the cylinder, with three or four ajutage holes in it, to cause the jet of cold water from the jack-head cistern to fly up in as many streams against the under surface of the piston, and condense the steam contained in the cylinder each stroke, when the injection cock is open.

e, a valve upon the upper end of the injection pipe,

which is shut, to prevent waste of water by leakage when the engine stands still; but before the engine is set to work this valve must be lifted up, and kept open by a string.

ƒ, a small pipe which branches off from the injection pipe, and has a cock to supply the piston with a little water to keep it air tight.

Q, the working plug, suspended by a chain to the small arch g, of the working beam. It is usually a heavy piece of timber, with a slit vertically down its middle, and holes bored horizontally through it to receive pins, for the purpose of opening and shutting the injection and steam cocks, as it ascends and descends by the motion of the working beam.

h, the handle of the steam cock, or regulator. It is fixed to the regulator by a spindle, which comes through the top of the receiver. The regulator itself is a sectorial plate of brass, shaped like a fan, which is moved horizontally by the handle h, and opens or shuts the communication at the lower end of the pipe E, within the receiver.

ii, the spanner, which is a long rod or bar of iron, for communicating motion to the handle of the regulator, to which it is fixed by means of a slit in the latter, and some pins put through to fasten it.

k, l, the vibrating lever, called the tumbling-bob, or the Y, having the weight k at one end, and the two forked legs at the other end, like the letter A turned. It is fixed to an horizontal axis, moveable about its centre pins or pivots mn, and is put in motion by means of two shanks, o, p, fixed to the same axis, which are alternately raised and depressed by means of two pins in the working plug, and the bob or weight at the top of the Y is thrown backwards and forwards; one pin on the outside, depressing the shank o, throws the loaded end k of the Y from the cylinder into the position represented in the drawing, and causes the leg, l, of the fork of the Y to strike against the end of the spanner, which forcing back the handle of the regulator, or steam cock, opens the communication, and permits the

steam to fly into the cylinder. The piston immediately rises by the weight of the pump rod, on the admission of the steam. The motion of the working beam, I, I, also raises the working plug; and another pin, which goes through the slit, raises the shank p of the axis, which throws the end, k, of the Y towards the cylinder, and the leg of the fork, striking the end of the spanner, forces it forwards, and shuts the regulator or steam cock.

q, r, is the lever for opening and shutting the injection cock, called the F. It has a rack or toothed sector fixed upon its axis, which takes the teeth of a pinion, fixed on the top of the plug, or key of the injection cock. When the working plug has ascended nearly to its greatest height, and shut the regulator, as above described, a pin catches the end q of the F, and raises it up, which opens the injection cock, and admits a jet of cold water to fly into the cylinder, and, condensing the steam, makes a vacuum within. Then the pressure of the atmosphere, forcing down the piston into the cylinder, causes the plug frame to descend, and another pin fixed in it catches the end of the lever q, in its descent, and by pressing it down shuts the injection cock, at the same time the regulator is opened to admit steam, and so on alternately; that when the regulator is shut, the injection cock shall be open, and when the former is open, the latter shall be shut.

R, the eduction pipe, to convey away the water which is injected into the cylinder at each stroke; its upper end is even with the cylinder bottom, and its lower end has a lid or cover, moveable on a hinge, which serves as a valve to let out the injection water, and shuts close each stroke of the engine, to prevent the water being forced up again, when the vacuum is made.

S, the hot well, which is a small cistern made of planks, to receive all the waste water from the cylinder, and keep it in reserve for feeding the boiler, to supply the waste occasioned by the continual evaporation of the

steam.

T, the feeding pipe, to supply the boiler with water from the hot well. It has a cock to let in a large or small

quantity of water, as occasion requires, to make up for what is evaporated; it goes nearly down to the boiler bottom, so that the lower end is always immersed in water.

s, the snifting valve, by which, at every ascent of the piston, the air is discharged from the cylinder which was admitted with the injection, and would otherwise obstruct the due operation of the engine.

t, t, the cylinder beams, which are strong girdles going through the house, for supporting or rather keeping down the cylinder.

v, the cylinder cup of lead surrounding the top of the cylinder, to prevent the water upon the piston from flashing over, when it rises too high.

W, the waste pipe, which conducts the superfluous water from the top of the cylinder to the hot well.

x, iron bars, called the catch pins, fixed horizontally through each arch head, to strike the floor, and prevent the beam descending too low, in case the chains at either end should break, or if the engine make too long a stroke. y, y, two strong wooden springs, to weaken the blow given by the catch pins when the stroke is too long.

z, z, two friction wheels, or sectors, on which the gudgeons, or centres of the great beam, are supported; they are the third or fourth part of a circle, and move a little each way, as the beam vibrates. Their use is to diminish the friction of the axis, which being necessarily very large for so heavy a lever, would otherwise be very great.

When this engine is to be set to work, the boiler must be filled about two or three feet deep with water, and a large fire made under it; and when the steam is heated to be of sufficient strength to exert a pressure of about one pound beneath each square inch of the safety valve, it will lift up the valve and escape. The water in the boiler being supposed to be in a strong state of ebullition, and the steam issuing by the safety valve, we will consider the machine in a state of rest, having both the steam cock and injection cock shut. The resting position or attitude of the machine is such as appears in the drawing, the pump

rods, K, preponderating by their weight, and the great piston being drawn to the top of the cylinder.

The man that attends the engine depresses the handle p, so as to throw the tumbling bob into the position of the figure; and the leg of the fork thrusting back the spanner i, i, opens the regulator, or steam cock, when the steam from the boiler immediately rushes in, and flying all over the cylinder, will mix with the air; much will be condensed by the cold surface of the cylinder and piston, and the water produced from it will trickle down the sides, and run off at the eduction pipe R, as soon as any quantity is accumulated. This condensation and waste of steam will continue, till the whole cylinder and piston are made as hot as boiling water.

When this happens, the steam will begin to open the snifting valve s, and issue through the pipe; at first, slowly and very cloudy, being mixed with much air, the cloudy appearance of steam being always owing to its mixture with common air. The blast at s will grow stronger by degrees, and more transparent, having already carried off the greatest part of the common air which filled the cylinder. We supposed, at first, that the water was boiling briskly, so that the steam was issuing by the safety valve, which is in the top of the boiler. The opening of the steam cock puts an end to this at once, secause the cold cylinder draws off the steam from the soiler with astonishing rapidity, until it becomes heated so as not to condense.

When the manager of the engine perceives that no only the blast at the snifting valve is strong and steady, but that the boiler is fully supplied with steam of a proper strength, which appears by the renewal of the discharge at the safety-valve, the engine is ready for starting. He now lifts up the handle o, or p, till the tumbling bob, Y, falls over the perpendicular towards the cylinder, and its leg striking the cross-pin of the spanner i, draws it forwards, and shuts the steam regulator; at the same instant he lifts up the handle, q, of the F, which opens the injection cock. The pressure of the column of water in the