six fathoms till it arrives at B, and thence through the engine from B to S two fathoms. At the turn B the water enters into a chamber C, the lower part of which terminates in two brass cylinders, four inches in diameter; in which two plugs or pistons of lead, D and E, are capable of moving up and down by their piston-rods, which pass through a close packing above, and are attached to the extremities of a chain leading over and properly attached to the wheel Q, so that it cannot slip.

The leaden pipes D and E are cast in their places, and have no packing whatever. They move very easily; and if at any time they should become loose, they may be spread out by a few blows with a proper instrument, without taking them out of their place. On the sides of the two brass cylinders in which D and E move, there are square holes communicating towards F and G, which is a horizontal trunk or square pipe, four inches wide and three inches deep. All the other pipes G, G, and R, are six inches in diameter, except the principal cylinder wherein the piston H moves; and this cylinder is ten inches in diameter, and admits a nine-foot stroke, though it is here delineated as if the stroke were only a three-foot.

The piston-rod works through a stuffing-box above, and is attached to MN, which is the pit-rod, or a perpendicular piece divided into two, so as to allow its alternate motion up and down, and leave a space between, without touching the fixed apparatus or great cylinder. The pit-rod is prolonged down into the mine, where it is employed to work the pumps; or if the engine were applied to mill-work, or any other use, this rod would form the communication of the first mover.

KL is a tumbler, or tumbling-bob, capable of being moved on the gudgeon V, from its present position to another, in which the weight L shall hang over the same inclination on the opposite side of the perpendicular, and consequently the end K will then be as much elevated as it is now depressed.

The pipe RS has its lower end immersed in a cistern, by which means it delivers its water without the possibility of the external air introducing itself; so that it constitutes a torricellian column, or water barometer, and renders the whole column from A to S effectual: as we shall see in our view of the operation..

Let us suppose the lower bar KV of the tumbler to be horizontal, and the rod PO so situated, as that the plugs or leaden pistons D and E shall lie opposite to each other, and stop the water-ways G and F. In this state of the engine, though each of these pistons is pressed by a force equivalent to more than 1000 pounds, they will remain motionless, because these actions being contrary to each other, they are constantly in equilibrio. The great piston H being here shown as at the bottom of its cylinder, the tumbler is to be thrown by hand into the position here delineated. Its action upon OP, and consequently upon the wheel Q, draws up the plug D, and depresses E, so that the water-way G becomes open from A B, and that of F to the pipe R: the water consequently descends from A to C; thence to GG G, until it acts beneath the piston H. This pressure raises the piston, and if there be any water above the piston, it causes it to rise and pass through F into R. During the rise of the piston (which carries the pit-rod MN along with it) a sliding block of wood I, fixed to this rod, is brought into contact with the tail K of the tumbler, and raises it to the horizontal position, beyond which it oversets by the acquired motion of the wheel L. The mere rise of the piston, if there were no additional motion in the tumbler, would only bring the two plugs D and E to the position of rest, namely, to close G and F, and then the engine would stop; but the fall of the tumbler carries the plug D downwards quite clear of the hole F, and

the other plug E upwards, quite clear of the hole G. These motions require no consumption of power, because the plugs are in equilibrio, as was just observed.

In this new situation the column A B no longer communicates with G, but acts through F upon the upper part of the piston H, and depresses it; while the contents of the great cylinder beneath that piston are driven out through G GG, and pass through the opening at E into R. It may be observed, that the column which acts against the piston is assisted by the pressure of the atmosphere, rendered active by the column of water hanging in R, to which that assisting pressure is equivalent, as has already been noticed.

When the piston has descended through a certain length, the slide or block at T, upon the pit-rod, applies against the tail K of the tumbler, which it depresses, and again oversets; producing once more the position of the plugs DE, here delineated, and the consequent ascent of the great piston H, as before described. The ascent produces its former effect on the tumbler and plugs; and in this manner it is evident that the alterations will go on without limit, or until the manager shall think fit to place the tumbler and plugs D E in the positions of rest; namely, so as to stop the passages F and G.

The length of the stroke may be varied by altering the positions of the pieces T and I, which will shorten the stroke the nearer they are together; as in that case they will sooner alternate upon the tail K.

As the sudden stoppage of the descent of the column A B, at the instant when the two plugs were both in the water-way, might jar and shake the apparatus, those plugs are made half an inch shorter than the depth of the side holes; so that in that case the water can escape directly through both the small cylinders to R. This gives a moment of time for the generation of the contrary motion in the piston and the water in G GG, and greatly deadens the concussion which might else be produced.

Some former attempts to make pressure-engines upon the principle of the steam-engine have failed; because water, not being elastic, could not be made to carry the piston onwards a little, so as completely to shut one set of valves and open another. In the present judicious construction, the tumbler performs the office of the expansive force of steam at the end of the stroke.

Mr. Boswell suggests, as a considerable improvement, that the action of this engine should be made elastic by the addition of an air-chamber, on the same principle as that used in fire-engines; this, he thinks, might be best effected by making the piston hollow, with a small orifice in the bottom, and of a larger size, to serve for this purpose, as the spring of the air would then act both on the upward and downward pressure of

the water.

There are many other ingenious hydraulic engines of great utility, which the limits of our work will not permit us to describe; in order, therefore, to supply the deficiency, we shall add a catalogue of the most important writings on this kind of engine,

Descriptio Machine Hydraulica curiosæ constructæ Joh. Geor. Faudieri. Venet. 1607.

Nouvelle Invention de lever l'Eau plus haut que la Source, avec quelque Machines Mouvantes par le Moyen de l'Eau, &c. par Isaac de Caus, 1657. Josephi Gregorii a Monte Sacr. Principia Physico-mechanica diversarum Machinarum seu Instrumentorum Pneumatices ac Hydraulices. Venet. 1664. Nouvelle Machine Hydraulique, par Francini. Journ. des Sçav. 1669. [An account of this machine is likewise given in the Architecture Hydraulique of Belidor, tom. 2. and in the 2d vol. of Desaguliers' Experimental Philosophy: in both which performances many other hydraulic machines are described.]

An Undertaking for raising Water, by Sir Samuel Moreland. Phil. Trans. 1674, No. 102.

Phil. Trans. 1675, No. 128.

An Hydraulic Engine, by....
A cheap Pump, by Mr. Conyers. Phil. Trans. 1677, No. 136.

M. de Hautefeuille, Réflexions sur quelques Machines à élever les Eaux, avec sa Description d'une nouvelle Pompe, sans Frottement et sans Piston, &c. 1682.

Elévation des Eaux par toute sorte de Machines, réduite à la mesure, au poids, à la balance, par le moyen d'un nouveau piston et corps de pompe, et d'un nouveau mouvement cyclo-elliptique, et rejetant l'usage de toute sorte de manivelles ordinaires, par le Chevalier Morland. 1685.

A new Way of raising Water, enigmatically proposed, by Dr. Papin. Phil. Trans. 1685, No. 173. The solutions by Dr. Vincent and Mr. R. A. in No. 177.

M. du Torax, Nouvelles Machines pour épuiser l'Eau des Fondations, qui, quoique très simples, font un effet surprenant. 1695. Journ. des Sçav. 1695, p. 293.

An Engine for raising Water by the help of Fire, by Mr. Tho. Savery. Phil. Trans. 1699, No. 253.

D. Papin, Nouvelle Manière pour lever l'Eau par la Force du Feu : à Cassel. 1707.

Mémoire pour la Construction d'une Pompe qui fournit continuellement de l'Eau dans le Réservoir, par M. de la Hire, Mem. Acad. Sci. Paris. 1716. Description d'une Machine pour élever des Eaux, par M. de la Faye, Mem. Acad. Sci. Paris. 1717.

Joh. Jac. Bruckmann's und Joh. Heinr. Weber's Elementar-maschine, oder universal-mittel bey allen wasser-hebungen. Cassel. 1720.

Jacob Leupold, Theatri Machinarum Hydraulicarum. 1724, 1725.

Joh. Frid. Weidleri Tractatus, de Machinis Hydraulicis toto terrarum orbe maximis Marlyensi et Londinensi, &c. 1727. Vide Act. erudit. Lips. 1728.

A Description of the Water-works at London-bridge, by H. Beighton, F.R.S. Phil. Trans. 1731, No. 417.

An Account of a new Engine for raising Water, in which horses or other animals draw without any loss of power (which has never yet been practised;) and how the strokes of the piston may be made of any length, to prevent the loss of water by the too frequent opening of valves, &c. by Walter Churchman. Phil. Trans. 1734.

Sur l'Effet d'une Machine Hydraulique proposée par M. Segner, par M. Leon. Euler, Mem. Acad. Sci. Berlin. 1750.

Application de la Machine Hydraulique de M. Segner à toutes sortes d'ouvrages, et de ses avantages sur les autres Machines Hydrauliques, par M. Leon. Euler, Mem. Acad. Sci. Berlin. 1751.

[M. Segner's machine is no other than the simple yet truly ingenious