Under this head we propose to notice various machines which are at times employed in lieu of pumps for raising water, or which have been proposed for that purpose. The most simple, as well, perhaps, as the most ancient (next to the bucket and windlass), is the Cochlion Water Screw of Archimedes. It consists of a cylinder of wood, of about a foot in diameter, and of any length at pleasure, and on this a leaden pipe of any bore is wound from the bottom to the top. When the bottom of the cylinder revolves in the water (by means of a common winch handle at top, and of a pintle hi the centre of its base, which rests in a bore or step for that purpose below,) the reclined portion, as shown in the following figure, occasions the water to enter the mouth of the pipe, and as by its gravity it naturally occupies the lowest part of the pipe, whilst by the revolution of the cylinder the orifice of the pipe is gradually elevated, and a different portion of the pipe occupies the lowest position, the water advances progressively along the pipe, always occupying the lowest portion of the bends or turns of the pipe, until it at length reaches he top of the cylinder, and is discharged into a vessel.

This, however, raises but a small quantity, although the height may be indefinite; therefore, when this machine is used, it will be found eligible to cover the whole surface of the cylinder with a number of pipes laid close together, or, what is a better method, and is that which is usually adopted, is to wind a number of spiral feathers round the cylinder, standing out from it at right angles like the square threads of a screw, and covering these feathers with an exterior case closely fitting in every part. These machines were formerly in great repute; but, owing to their liability to become choked with weeds and mud, they are not often employed at present.

Hydraulic Machines 677Hydraulic Machines 678

The figure on page 720 represents what is called the horn-drum; it is formed of a number of segments passing from the circumference of a large flat cylinder to its centre. This affords an easy mode of raising water. The mouths or scoops by turns dip into the water, and as they rise cause it to pass up the horn or segment, until it is discharged into a trough placed under the end of the axis, which is hollow, and is formed into a number of separate compartments, each communicating with one of the horns or segments. One disadvantage of this machine is that it raises water no higher than the axle, and is therefore only applicable in situations where the water is required to be raised to an inconsiderable height. This circumstance renders it necessary to construct it of double the diameter of wheels that discharge their water at their tops. This machine, however, might be altered to do so likewise, by confining the scoops to near the periphery of the wheel, and discharging them by means of lateral valves, to be opened by coming against a contrivance fixed at the top of the wheel for that purpose.

The Persian wheel, represented in the following engraving, is free from the defect of the last described.

In this machine a number of rectangular buckets a a a a are hung upon strong pins b b b b, fixed in the side of the rim, the diameter of which must somewhat exceed the height to which the water is required to be raised. As the wheel turns, the buckets on the right hand descend into the water, where they are filled, and return up full on the left hand, until they arrive at the top at k, where they strike against the end n of the fixed trough m by which they are overset, and thus discharge the water into the trough, from which it may be conducted by pipes to wherever it is required; and as each bucket gets over the trough, it falls again into a perpendicular position, and so goes down empty until it comes to the water at o, where it is filled as before. On each bucket is a spring r which, as it passes over the edge of the trough, elevates the end of the bucket above the level of its mouth so as to discharge the whole of the water into the trough. These springs are likewise useful in preventing the concussion of the buckets against the trough.

This machine, as well as the horn-drum, is frequently driven by means of floats attached to the opposite side of the rim.

Hydraulic Machines 679Hydraulic Machines 680

The Hungarian machine, so called from its having been employed in draining a mine in Chemnitz, in Hungary, produces its action by the condensation of a confined portion of air, produced by the descent of a high column of water contained in a pipe, and therefore acts with a force proportionate to the weight of such column. Its general form is shown in the annexed cut, by which it will appear that it is an exceedingly simple and useful machine, admitting of many modifications and applications; but it can be used only in hilly countries, or situations where the source of water by which it is to be worked is as much above the top of the well as the water to be raised is underneath it In this figure a is supposed to be a well, or the shaft of a mine, from the bottom of which it is necessary to raise the water standing at the level b b. c c is the surface of the ground at the top of the well or shaft, at which the discharged water must have an opportunity of escaping, either by running to waste, or being converted to some useful purpose; and d is the spring or other elevated source from whence the supply of water for working the machine may be obtained.

The machine itself consists of three cisterns, chests, or reservoirs, two of which at e and f must be made very strong, and perfectly air-tight, while the third at d may be weaker, and open at the top, as it is merely for collecting and retaining the spring, rain, or other water for working the machine. The lowest close chest or reservoir e must be sunk below the surface b b of the water in the shaft or well a, but must not come into contact with its bottom, otherwise the water would be prevented entering the chest by the valve g, which opens inwards for its admission. An open pipe h h passes from very near the bottom of this chest, through its top, in an airtight manner, and proceeds upwards in the shaft as far as the surface of the ground, where it bends over to deliver its water, as at h c. Another open pipe i i, which may be of rather smaller dimensions than the last, proceeds from the top of the lower chest e to very near the top of the second chest f; and a third pipe, k l, of the same capacity as the first, proceeds from very near the bottom of the second close chest, up to the bottom of the high reservoir d, but has a cock or valve at f, by which it can occasionally be shut or opened.