. The Family tutor . a few movements of the piston, the lower end, I, of this tube becomeswater, and any further quantity now thrown in compresses the airin the space, H G, which, exerting its elastic force,drives out the water in a continuous jet, S. The reci-procating motion of the piston may, therefore, bemade to give rise to a continuous and unintermittingstream by the aid of the air-vessel, K K. Among other hydraulic machines may be mentionedVeras pump, more, however, from its peculiar con-struction than for any real value it possesses. It con-sists of a pair of pulleys, over which a rope
. The Family tutor . a few movements of the piston, the lower end, I, of this tube becomeswater, and any further quantity now thrown in compresses the airin the space, H G, which, exerting its elastic force,drives out the water in a continuous jet, S. The reci-procating motion of the piston may, therefore, bemade to give rise to a continuous and unintermittingstream by the aid of the air-vessel, K K. Among other hydraulic machines may be mentionedVeras pump, more, however, from its peculiar con-struction than for any real value it possesses. It con-sists of a pair of pulleys, over which a rope is madeto run rapidly ; the lower one is immersed in the waterto be raised. By adhesion a portion of the water fol-lows the rope in its movements, and is dischargedinto a receptacle placed above. (Fig- 73.) The chain-pump consists of a series of flat plates, d,held together by pieces of metal, so arranged that,by turning an upper wheel, e, the whole chain is madeto revolve, on one side ascending and on the other de-. 128 NATURAL PHILOSOPHY scending and passing over a lower wheel. As the flat plates pass upward they movethrough a trunk of suitable shape, a h, and therefore continually lift in it a column ofwater. The cliain-pump requires deep water to work in, and cannot completelyempty its reservoir, but it has the advantage of not being liable to be choked. CHAPTER XIV. HYDRAULIC MACHINES. Archimedes Screiv.—The Syphon acts by the Pressure of Air.—The Descent, Ascent,afid Floating of Solids in Liquids.— Quantity of Water displaced by a Floating Solid.—Case tvhere fluids of different densities are used.—Eqtiilibrium of Floating Solids. The screw of Archimedes is an ancient contrivance, invented by the philosopherwhose name it bears, for tlie purpose of raising water in Egypt. It consists of a hollowscrew-thread wound round an axis, upon wliich it can be worked by means of a lower end of this spiral tube dips in tlie reservoir from which the water is to ber
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