hand gear, from their supplying the place of the catches and strings hitherto moved by the attendants, and consisted of a rod suspended from the balanced lever or beam, which by tappets acted on levers attached to the injection and steam cocks, and opened and shut them, as they might be adjusted.

The valve by which the flow of steam was shut off from the cylinder, was of the same form with that used by Savery, and called a sliding valve, and was also placed inside the boiler. The injection cock did not differ from the sort in common use. See figure marked BEIGHTON.

The axis or spindle, a, of the sliding valve, c, projected through the roof of the boiler, and a lever, b, was fixed to it. This was attached to another lever, d, having its opposite extremity, e, formed like a fork, and the two prongs, f, g, connected by a wire. This wire, i, in its turn formed the axis, to which was attached two pieces of iron, called the stirrup, o, m, fixed on an axle, s; between these two pieces, also on the same axle, was fixed the Y piece, so called from its resemblance to that letter, reversed; and had a weight placed on the stalk: this appendag was named the tumbling bob. The spanners, x, y, were also fixed on this axle and were so placedas to be moved upwards and downwards by tappets fixed in a rod, z, suspended from the balanced beam.

The toothed quadrant, p, fixed on the axis of the injection cock, was moved by another quadrant, r, attached to a lever, p, also acted upon by projecting pins or tappets fixed in the plug-frame. In the engraving the forks are shewn in a position as if the injection cock was open, and the steam valve shut; and that the piston has approached near to the bottom of the cylinder. The fall of the

plug frame makes a tappet strike on one of the arms of the spanners, which turns the axle, and by this means raises the tumbling bob beyond the perpendicular, and the weight causes it to fall with a considerable force in the other directionone of its prongs pressing upon the axis of the stirrup, pushes it forward, and moving the lever, opens the steam valve. At the same instant that the tappet moved the spanner, the tappet, 2, pressing upon the lever of the quadrant, shut the injection cock, and the piston now being in equilibrium, the counterpoise draws it upwards. When it has nearly arrived at the top of the cylinder, the tappet, 3, in the plug frame, also rising, strikes the spanner-this turns the axle. The Y piece is by this means again turned into the opposite position, and the weight of the tumbling bob, making it fall with a considerable velocity, the prong draws the fork into the former position, and the steam cock is again shut. The tappet during this operation has also depressed the lever, and shut the injection cock; and this operation may obviously be repeated as often as it may be necessary.

This apparatus does not differ essentially from that given by other authors; but Desaguliers, who describes it in 1743, may have unintentionally given a form of it more perfect than it possessed at the period of the erection of the Griff engine. But at all events, by its introduction, the atmospheric engine, for the first time, became a self-acting machine.

The engraving (marked NEW COMEN, F.) will suffice to give a general idea of the appearance of this machine, until the experiments of Smeaton. It is described and figured by Desaguliers, in his book which was published in 1743; a, is the boiler; b, steam-pipe; c, cylinder; d, injection

ACTION OF BUOY.

173

pipe and cock; e, its lever; f, the horizontal fork; g, the stirrup; h, the axis of the tumblingbob; i, k, the plug-frame, with the tappets, l, m, n; o, snifling-valve; p, eduction-pipe for condensed steam and injection water; q, gauge-cocks, r, safety-valve, or puppet-clack; s, pipe for supplying water to boiler; t, pipe from cup of the cylinder; u, pipe for waste water which was raised by piston; v, pipe from cistern; w, fire-place; x, piston-rod and chain; y, working-beam.

Steam being raised in the boiler, a, it flows through the pipe, b, into the cylinder; this produces an equilibrium between the upper and under sides of the piston, and it rises to the top of the cylinder by the weight of the counterpoise placed at the opposite end of the lever-beam. By its ascent the plug-frame is also raised, and one of the tappets, l, m, n, which are fixed into it, striking upon the end of the lever, e, fixed to the loaded quadrant, opens the injection-cock, d; a jet is thus introduced into the vapour which condenses it. At the time when the tappet struck on the lever of the injection-cock, another struck one of the spanners, and by this means, turning the axle on which it is fixed, the tumbling-bob is carried into the opposite position, and one of its prongs being thus made to act on the axis of the stirrup and horizontal fork, the lever attached to the steam-valve is thus drawn forward, and the flow of steam from the boiler is prevented. The tappets are so adjusted, that the steam-valve is perfectly shut, before the injection-cock is opened. The fall of the piston, by the pressure of the atmosphere, reverses all these motions-shutting the injection-cock;-opening the steam-valve by the action of other tappets; and thus a tolerably regular series of reciprocating motions is produced.

174

DESAGULIERS' ENGINE.

A simpler method than either of these, of opening the steam and injection cocks is described and figured by Leupold, as practised in a German engine, constructed by one Potter an Englishman, previous to 1724. The engraving marked NEWCOMEN, exhibits this contrivance: m, the plug-frame, or the perpendicular rod attached to the beam; k, the end of a lever moving on an axis, h, having a fixed piece, or staple, perforating the roof of the boiler, and pressing on the end of another lever, g. within the boiler, which has its other extremity, f, so constructed, as to close the orifice of the steam-pipe when it is raised into the proper position; the injection cock is opened and shut by means of a jointed lever, connected with the lever, k. The manner of its action will readily be understood from an inspection of the engraving.

The second figure in the same engraving shows the method in which the counterpoise was employed, which raised the pump-buckets in the same engine; n, the pump-rod attached to the lever-beam; k, a small lever-beam; i, the counterpoise.

In the engine described by Desaguliers, as well as that shown in Leupold's book, the buoy, which in the earlier engines, rose and fell, and opened the steam-cock, does not appear; from the notice of the improvement made upon it by the use of a Scoggan, and its absence in the machines which have just been detailed, it might be inferred, that the mechanism had given place to more perfect methods-but from an exceedingly rare and curious print, published in 1725, it is shown as then used in some engines. This engraving, it is true, may have been made from an engine constructed long before; but, on the other hand, it is

improbable that so much care would be taken in describing a mechanism, which was either considered to be obsolete, or not on the most improved construction then in use:-as it is the only one which we have met with in which the buoy is described, the detail of its parts are interesting, as filling up a step in the progress of invention, will be given at length.

In the figure (marked NEWCOMEN, 1725,) a, is the fire-place, b, the boiler, c, piston, d, steampipe, e, axis of the regulator, or steam-valve, d, steam-pipe, f, a loaded or safety valve, "which gives vent to the steam of the boiler in case it grows too strong; g, gauge cocks with their pipes, one of which goes down so far into the boiler, as to be two or three inches above, and the other so far below the surface of the water therein," the water being of a due height when the steam is emitted by the shorter, and water by the longest pipe; h, a pipe fixed to the head of the boiler, and called the buoy pipe, open at both ends, the lower end being a foot or more below the surface of the water in the boiler. Within this pipe is a cylindrical buoy that swims upon the water therein; and when the steam in the boiler is become so strong as, by its pressure, to force water up the said pipe, it then raises the buoy, whose axis, 12, causes the balance, r, and inceptor, 7, also to rise, and lifting the notch, 2 from 3, on one end of the lever, permits 13, a weight attached to it, to fall so far, till the injecting-cock at n, the axis of the said lever, is opened, by which an injection of cold water from the cap of the injection-pipe being made, and consequently a vacuum by the condensation of the steam; the pressure of the atmosphere brings down the inner end of the great lever, when one of the pins in the hanging-beam,