The power required to work a pump, or any other hydraulic engine, must not only be equal to the whole column of water in the pump-bore, but as much superior to it as will overcome all the friction of the working parts of the engine.

2. In Dr. Gregory's Mechanics, vol. ii. is the following description of a pump, with little friction, which may be constructed in a variety of ways by any common carpenter, without the assistance of the pump-maker, or plumber, and which will be very effective for raising a great quantity of water to small heights, as in draining marshes, marle pits, quarries, &c., or even for the service of a house.

ABCD, fig. 223, is a square trunk of carpenter's work open at both ends, and having a little cistern and spout at top. Near the bottom there is a partition made of board, perforated with a hole E, and covered with a dock. ffff represent a long cylindrical bag made of leather or of double canvass, with a fold of thin leather, such as sheep skin, between the canvass bags. This is firmly nailed to the board E with soft leather between. The upper end of this bag is fixed on a round board having a hole and valve F. This board may be turned in the lathe with a groove round its edge, and the bag fastened to it by a cord bound tight round it. The fork of the piston-rod FG is firmly fixed into this board; the bag is kept distended by a number of wooden hoops or rings of strong wire, ff, ff, ff, &c. put into it at a few inches distance from each other. It will be proper to connect these hoops, before putting them in, by three or four cords from top to bottom, which will keep them at their proper distances. Thus will the bag have the form of a barber's bellows powder-puff. The distance between the hoops should be about twice the breadth of the rim of the wooden ring to which the upper valve and piston-rod are fixed.

It is evident that if the Now let this trunk be immersed in the water. bag be stretched from the compressed form which its own weight will give it by drawing up the piston-rod, its capacity will be enlarged, the valve F will be shut by its own weight, the air in the bag will be rarefied, and the atmosphere will press the water into the bag. When the rod is thrust down again, this water will come out by the valve F, and fill part of the trunk. A repetition of the operation will have a similar effect; the trunk will be filled, and the water will at last be discharged by the spout.

Here is a pump almost divested of friction, and perfectly light. For the leather between the folds of canvass renders the bag impervious both to air and water. And the canvass has very considerable strength. We know, from experience, that a bag of six inches diameter, made of sail-cloth No. 3, with a sheep-skin between, will bear a column of 15 feet of water, and six hours work per day for a month without failure, and that the pump is considerably superior in effect We must only to a common pump of the same dimensions. observe, that the length of the bag must be three times the intended length of the stroke; so that when the piston-rod is in its highest position, the angles or ridges of the bag may be pretty acute. If the bag be more stretched than this,

the force which must be exerted by the labourer becomes much greater than the weight of the column of water which he is raising. If the pump be laid aslope, which is very usual in these occasional and hasty drawings, it is necessary to make a guide for the piston-rod within the trunk, that the bag may play up and down without rubbing on the sides, which would quickly wear it out.

The experienced reader will see that this pump is very like that of Gosset and De la Deuille, described by Belidor, vol. ii. p. 120, and most writers on hydraulics. It would be still more like it, if the bag were on the under side of the partition E, and a valve placed further down the trunk. But we think that our form is greatly preferable in point of strength. When in the other situation, the column of water lifted by the piston tends to burst the bag, and this with a great force, as the intelligent reader well knows. But in the form recommended here, the bag is compressed, and the strain on each part may be made much less than that which tends to burst a bag of six inches diameter. The nearer the rings are placed to each other the smaller will the strain be.

The same bag-piston may be employed for a forcing-pump, by placing it below the partition, and inverting the valve; and it will then be equally strong, because the resistance in this case too will act by compression.

3. An ingenious variation in the construction of the suckingpump, is that with two piston-rods, in the same barrel, invented by Mr. Walter Taylor, of Southampton. A vertical section of this pump is given in fig. 224.

The piston-rods have racks at their upper parts working on the opposite sides of a pinion, and kept to their proper positions by friction-rollers. The valves used in this pump are of three kinds, as shown at a, b, and c. The former is a spheric segment which slides up and down on the pistonrod, and is brought down by its own weight; the second, b, is called the pendulum-valve; and the third, c, is a globe which is raised by the rising water, and falls again by its own weight. Each of these valves will disengage itself from chips, sand, gravel, &c. brought up by the water. In this kind of pump the pistons may either be put in motion by a handle in the usual way, or a rope may pass round the wheel de in a proper groove, the two ends of which, after crossing at the lower part of the wheel, may be pulled by one man or more on each side. A pump of this kind, with seven inch bore, heaves a ton 24 feet high in a minute, with ten men, five only working at a time on each side.

Another improvement of the common pump has been made by Mr. Todd, of Hull. This invention in some particulars bears a resemblance to the ordinary one, but he has contrived to double its powers by the following means:

Having prepared the piston-cylinder, which may be 12 feet high, he cuts from the bottom of it about three feet; at the end of the great cylinder he places an atmospheric-valve, and to the top of the small cylinder a serving-valve. In the bottom of the small cylinder, which contains the servingvalve, is inserted an oblong elliptical curved tube, of equal caliber with the principal cylinder, and the other end is again inserted in the top of the great cylinder. This tube is divided in the same manner as the first cylinder, with atmospheric and serving valves, exactly parallel with the valves of the first cylinder. The pump, thus having double valves, produces double effects, which effects may be still further increased by extending the dimensions.

The cylinder is screwed for service on a male tube screw, which projects from the side of a reservoir or water cistern, and is worked by hand.

The piston-plunger is worked by a toothed segment-wheel, similar to the principle of the one used in working the chainpumps of ships belonging to the royal navy; and the wheel receives its motion from a hand-winch, which is considerably accelerated by a fly-wheel of variable dimensions, at the opposite end.

This pump, in addition to its increased powers, possesses another very great and prominent advantage. By screwing to it the long leather tube and fire-pipe of the common engine, it is in a few minutes converted into an effective fire-engine. Hence, whoever possesses one may be said to have a convenient domestic apparatus against fire. Three men can work it, one to turn the winch, another to direct the firepipe, and a third to supply the water.

4. The Forcing-pump is represented in fig. 225.

It raises water through the box H, not in the same manner as the sucking or lifting pump does, when the plunger or piston g is lifted up by the rod Dd; but this plunger or forcer has no hole through it, to let the water in the barrel BC get above it, when it is depressed to B; and the valve b (which rose by the ascent of the water through the box H when the plunger g was drawn up) falls down and stops the hole in H the moment that the plunger is raised to its greatest height. Therefore as the water between the plunger g and the box H can neither get through the plunger upon its descent, nor back again into the lower part of the pump Le, but has a free passage by the cavity around H into the pipe MM, which opens into the air-vessel KK at P, the water is forced through the pipe M M by the descent of the plunger, and driven into the air-vessel, and in running up through the pipe at P, it opens the valve 4, which shuts at the moment the plunger begins to be raised, because the action of the water against the under side of the valve then ceases.

The water being thus forced into the air-vessel K K, by repeated strokes

of the plunger, gets above the lower end of the pipe G H I, and then begins to condense the air in the vessel K K. For as the pipe G H is fixed air-tight into the vessel below F, and the air has no way to get out of the vessel out through the mouth of the pipe at I, and cannot get out when the mouth I is covered with water, and is more and more condensed as the water rises upon the pipe, the air then begins to act forcibly by its spring against the surface of the water at H; and this action drives the water up through the pipe IHGF, from whence it spouts in a jet S to a great height, and is supplied by alternately raising and depressing the plunger g, which constantly forces the water that it raises through the valve H, along the pipe M M, into the air-vessel K K.

The higher the surface of the water II is raised in the air-vessel, the less space will the air be condensed into, which before filled that vessel; and therefore the force of its spring will be so much the stronger upon the water, and will drive it with the greater force through the pipe at F; and as the spring of the air continues whilst the plunger g is rising, the stream or jet S will be uniform as long as the action of the plunger continues; and when the valve b opens to let the water follow the plunger upward, the valve a shuts, to hinder the water, which is forced into the air-vessel, from running back by the pipe M M into the barrel of the pump.

If there was no air-vessel to this engine, the pipe & HỈ would be joined to the pipe M M N at P: and then the jet S would stop every time the plunger is raised, and run only when the plunger is depressed.

Mr. Newsham's Water-engine, for extinguishing fire, (see Fire-engine,) consists of two forcing-pumps, which alternately drive water into a close vessel of air; and by forcing the water into that vessel, the air in it is thereby condensed, and compresses the water so strongly, that it rushes out with great impetuosity and force through a pipe that comes down into it; and makes a continued uniform stream, by the condensation of the air upon its surface in the vessel.

By means of forcing-pumps, water may be raised to any height above the level of a river or spring; and machines may be contrived to work these pumps, either by a running stream, a fall of water, by horses, or by steam.

The rod of the bucket in a sucking-pump is sometimes made to work through a collar of oiled leathers and brass plates, connected with the barrel of the pump by screws, and kept moist by water contained in a vessel at the top: it prevents the water issuing from the top of the pump, and therefore by a pipe it will raise to any height. This is called, in the North a jackhead.

5. The Lifting-pump differs from the sucking-pump only in the disposition of its valves, and the form of its piston frame. This pump is represented in fig. 226.

A B is a barrel fixed in a frame IKLM, which is immovable, with its lower parts communicating with the water. GEQHO is a frame with two strong iron rods, movable through holes in the upper and lower parts of the pumps IK and LM; in the bottom of this frame