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 G G, 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 G G, 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 Hydraulicæ curiosa constructa 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.

An Hydraulic Engine, by

Phil. Trans. 1675, No. 128.

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

contrivance known by the name of Barker's mill, which had been described in the 2d volume of Desaguliers' Philosophy, some years before the German professor made any pretensions to the honour of the invention. The theory of it is likewise treated by John Bernoulli at the end of his Hydraulics.] Recherches sur une nouvelle manière d'élever de l'Eau proposée par M. de Mour, par M. L. Euler, Mem. Acad. Berlin. 1751.

Discussion particulière de diverses manières d'élever de l'Eau par le moyen des Pompes, par M. L. Euler, Mem. Acad. Ber. 1752.

Maximes pour arranger le plus avantageusement les Machines destinées à élever de l'Eau par le moyen des Pompes, par M. L. Euler, Mem. Acad. Ber. 1752.

Réflexions sur les Machines Hydrauliques, par M. le Chevalier D'Arcy, Mem. Acad. Sci. Paris. 1754.

Mémoire sur les Pompes, par M. le Chevalier de Borda, Mem. Acad. Sci. Paris. 1768.

Dan. Bernoulli Expositio Theoretica singularis Machine Hydraulieæ. Figuri helvetiorum, exstructæ. Nov. Com. Acad. Petrop. 1772.

Abhandlungen von der Wasserschraube, von D. Scherffer, Priester. Wien.

1774.

Recherches sur les Moyens d'exécuter sous l'Eau toutes sortes de Travaux Hydrauliques, sans employer aucun Epuisement, par M. Coulumb. 1779. Saemund Magnussen Holm, Efterretning om skye Pumpen. Kiobenhavn.

1779.

Moyen d'augmenter la Vitesse dans le Mouvement de la Vis d'Archimède sur son Axe, tiré des Mémoires Manuscrits de M. Pingeron, sur les Arts utiles et agréables. Journ. d'Agric. Juin, 1780.

The Theory of the Syphon, plainly and methodically illustrated. 1781. (Richardson.)

Memoria sopra la nuova Tromba Funiculare Umiliata, dal Can. Carlo Castelli. Milano. 1782.

Dissertation de M. de Parcieux, sur le moyen d'élever l'Eau par la rotation d'une corde verticale sans fin. Amsterdam et Paris, 1792.

Theorie der Wirzischen Spiral Pumpe, erläutert von Heinr. Nicander. Schwed. Abhandl. 1783.

Jac. Bernoulli, Essai sur une nouvelle Machine Hydraulique propre à élever de l'Eau, et qu'on peut nommer Machine Pitotienne. Nov. Act. Acad. Petrop. 1786.

K. Ch. Langsdorf's Berechnungen über die Vortheilhæftere Benutzung Angelegter Fammelteiche zur Betriebung der Maschinen. Act. Acad. Elect. Mogunt. 1784, 1785.

Nicander's Theorie der Spiral Pumpe. 1789.

Nouvelle Architecture Hydraulique, par M. Prony. 1790, 1796.

A short Account of the Invention, Theory, and Practice of Fire Machinery; or, Introduction to the Art of making Machines vulgarly called SteamEngines, in order to extract water from mines, convey it to towns, and jetsd'eaux in gardens; to procure water-falls for fulling, hammering, stamping, rolling, and corn-mills; by W. Blakey. 1793.

PUMPS.

1. The construction of pumps is usually explained by glass models, in which the action both of the pistons and valves may be seen.

In order to understand the structure and operation of the common pump, let the model DC BL, fig. 222, be placed upright in the vessel of water K, the water being deep enough to rise at least as high as from A to L. The

valve a on the movable bucket G, and the valve à on the fixed box H, (which box quite fills the bore of the pipe or barrel at H,) will each lie close by its own weight, upon the hole in the bucket and box, until the engine begins to work. The valves are made of brass, and covered underneath with leather, for closing the hole more exactly; and the bucket G is raised and depressed alternately by the handle E and rod D d, the bucket being supposed at B before the working begins.

Take hold of the handle E, and thereby draw up the bucket from B to C, which will make room for the air in the pump all the way below the bucket to dilate itself, by which its spring is weakened, and then its force is not equivalent to the weight or pressure of the outward air upon the water in the vessel K; and therefore, at the first stroke, the outward air will press up the water through the notched foot A, into the lower pipe, as far as e: this will condense the rarefied air in the pipe between e and С to the same state as it was in before; and then, as its spring within the pipe is equal to the force or pressure of the outward air, the water will rise no higher by the first stroke; and the valve b, which was raised a little by the dilatation of the air in the pipe, will fall, and stop the hole in the box H; and the surface of the water will stand at e. Then depress the piston or bucket from C to B, and as the air in the part B cannot get back again through the valve b, it will (as the bucket descends) raise the valve a, and so make its way through the upper part of the barrel d into the open air. But, upon raising the bucket G a second time, the air between it and the water, in the lower pipe at e, will be again left at liberty to fill a larger space; and so its spring being again weakened, the pressure of the outward air on the water in the vessel K will force more water up into the lower pipe from e to ƒ; and when the bucket is at its greatest height C, the lower valve b will fall, and stop the hole in the box H as before. At the next stroke of the bucket or piston, the water will rise through the box H towards B, and then the valve b, which was raised by it, will fall when the bucket G is at its greatest height. Upon depressing the bucket again, the water cannot be pushed back through the valve b, which keeps close upon the hole whilst the piston descends. And upon raising the piston again, the outward pressure of the air will force the water up through H, where it will raise the valve, and follow the bucket to C. Upon the next depression of the bucket G, it will go down into the water in the barrel B; and as the water cannot be driven back through the now close valve b, it will raise the valve a as the bucket descends, and will be lifted up by the bucket when it is next raised. And now, the whole space below the bucket being full, the water above it cannot sink when it is depressed; but upon its depression, the valve a will rise to let the bucket go down; and when it is quite down, the valve a will fall by its own weight, and stop the hole in the bucket. When the bucket is next raised, all the water above it will be lifted up, and begin to run off by the pipe F. And thus, by raising and depressing the bucket alternately, there is still more water raised by it; which getting above the pipe F, into the wide top I, will supply the pipe, and make it run with a continued stream.

So, at every time the bucket is raised, the valve b rises, and the valve a falls; and at every time the bucket is depressed, the valve o falls, and the valve a rises.

As it is the pressure of the air or atmosphere which causes the water to rise, and follow the piston or bucket G as it is drawn up; and since a column of water 32 feet high is of equal weight with as thick a column of the atmosphere, from the earth to the very top of the air; therefore the perpendicular height of the piston or bucket from the surface of the water in the well must always

THE OPERATIVE MECHANIC

be less than 32 feet; otherwise the water will never get above the bucket. But when the height is less, the pressure of the atmosphere will be greater than the weight of the water in the pump, and will therefore raise it above the bucket; and when the water has once got above the bucket, it may be lifted to any height, if the rod D be made long enough, and a sufficient degree of strength be employed, to raise it with the weight of the water above the bucket without ever lengthening the stroke.

The force required to work a pump will be as the height to which the water is raised, and as the square of the diameter of the pump-bore in that part where the piston works. So that if two pumps be made of equal heights, and one of them be twice as wide in the bore as the other, the widest will raise four times as much water as the narrowest, and will require therefore four times as much strength to work it.

The wideness or narrowness of the pump in any other part besides that in which the piston works, does not make the pump either more or less difficult to work, except what difference may arise from the friction of the water in the bore, which is always greater in a narrow bore than in a wide one, because of the great velocity of the water.

The pump-rod is never raised directly by such a handle as E at the top, but by means of a lever, whose longer arm (at the end of which the power is applied) generally exceeds the length of the shorter arm five or six times, and by that means gives five or six times as much advantage to the power. Upon these principles, it will be easy to find the dimensions of a pump that shall work with a given force, and draw water from any given depth.

;

The quantity of water raised by each stroke of the pumphandle is just as much as fills that part of the bore in which the piston works, be the size of the rest of the bore above and below the piston what it will. The pressure of the atmosphere will raise the water 32 feet in a pipe exhausted of air but it is advisable never to have the piston more than 20 or 24 feet above the level of the surface of the water in which the lower end of the pump is placed; and the power required to work the pump will be the same, whether the piston goes down to lie on a level with the surface of the well, or whether it works 30 feet above that surface, because the weight of the column of air that the piston lifts is equal to the weight or pressure of the column of water raised by the pressure of the air to the piston. And although the pressure of the air on the surface of the well will not raise or force up the water in the pump-bore more than 32 feet, yet when the piston goes down into the column so raised, the water gets above it, and