the movable pieces are covered two by two with leather as at ee e, fig. 261, upon which the weight of the water acts as upon the pieces themselves.

All these leathers last a very long time, as well as those of the suckers, because they are not exposed to any friction, which only acts upon the movable pieces of wood. When the piston descends, the water that raises the suckers finds an easy passage, without filtering between the piston and the interior of the barrel of the pump; an effect which has this additional convenience, that no dirt can be introduced into the joints, which might afterwards prevent the perfect contact of the different pieces.

In 1808, these pistons were tried in several mines in Saxony, and were found very satisfactory. It was only observed that there was some inconvenience attending the use of them where the wells were much inclined; as the pressure of the water above not being equal upon all the movable pieces of the piston, those that were least_pressed upon let some of the water pass between them. These inconveniences however exist only in the ordinary pistons.

In some departments pistons with springs are sometimes used, which are composed of movable rubbing-pieces, that are substituted for the leathers that are ordinarily employed. We know that these pistons are used with advantage in the cylinders of some blowing-engines; but in these pistons the rubbing-pieces are constantly forced against the interior surface of the cylinder by the springs

In the piston with the flexible crown of wood, which M. Bonnard has described, the movable pieces of wood that compose it do not rub against the interior surface of the barrel of the pump, except when the piston ascends, being then pushed by the weight of the column of water that is raised, and they scarcely rub at all against the surface when the piston descends. This peculiar effect assimilates this piston with those that have a flexible crown of leather, or a bucket, and gives it a decided advantage over pistons with springs and cushions. In other departments pistons with springs are sometimes used, which move in cylinders of cast-iron.

These pistons are composed of four pieces of brass, aa a a, figures 262 and 263, which are each about three centimetres in height and thickness, and are pushed horizontally by two springs, bbbb. Those pieces, which we shall call quadrants, in order that none of the air may escape when they play under the inequalities of the cylinder in which they rise and descend, are each of them something longer than a quarter of the circumference of the cylinder, and towards the extremities they are reduced to half the thickness.

By this means, these quadrants are perfectly covered at the extremities,

and prevent the passage of the air in a horizontal direction, while the springs bbbb prevent its passage vertically.

In conclusion we shall observe, that these pistons, perfectly joined, have been proved to be proper for driving air with great force. We shall likewise observe, that the quadrants aaaa being made of brass, and rubbing against cast-iron, ought to last a very long time; consequently, the blowing here mentioned have the advantage of not requiring frequent repairs.

19. The following piston, described and recommended by Belidor, seems as perfect as the nature of things will allow. We shall therefore describe it in the author's own words, as a model which may be adopted with confidence in the greatest works.

"The body of the piston is a truncated metal cone, (fig. 264,) having a small fillet at the greater end. Fig. 265 shows the profile, and fig. 266 the plan of its upper base, where appears a cross-bar D D, pierced with an oblong mortise E for receiving the tail of the piston-rod. A band of thick and uniform leather A A (figs. 265 and 267) is put round this cone, and secured by a brass hoop B B, firmly driven on its smaller end, where it is previously made thinner to give room for the hoop.

66

This piston is covered with a leather valve, fortified with metal plates GG (fig. 268.) These plates are wider than the hole of the piston, so as to rest on its rim. There are similar plates below the leathers, of a smaller size, that they may go into the hollow of the piston; and the leather is firmly held between the metal plates by screws H H, which go through all. This is represented by the dotted circle JK. Thus the pressure of the incumbent column of water is supported by the plates G G, whose circular edges rest on the brim of the water-way, and thus straight edges rest on the cross-bar DD of figs. 265 and 266. This valve is laid on the top of the conical box in such a manner that its middle F P rests on the cross-bar. To bind all together, the end of the piston-red is formed like a cross, and the arms MN (fig. 269) are made to rest on the diameter F F of the valve, the tail E F going through the hole E in the middle of the leather, and through the mortise E of the cross-bar of the box, as well as through another bar, QR, (figs. 267 and 268,) which is notched into the lower brim of the box. A key V is then driven into the hole I, in the piston-rod; and this wedges all fast. The bar QR is made strong; and its extremities project a little, so as to support the brass hoop B B, which binds the leather band to the piston-box.”

This piston has every advantage of strength, tightness, and large water-way. The form of the valve (which has given it the name of the butterfly-valve) is extremely favourable to the passage of the water; and as it has but half the motion of a complete circular valve, less water goes back while it is shutting.

FIRE-ENGINES.

WHEN fire breaks out in a crowded neighbourhood, it carries with it such devastating effects, that any individual who has seriously turned his attention to the constructing of an engine that is in the least calculated to check its progress, must ever be considered as deserving of our praise. Those who have most beneficially directed their attention this way are Messrs. Newsham and Rowntree, whose engines we shall now proceed to describe.

1. A perspective view of Mr. Newsham's fire-engine, ready for working, is represented in fig. 270.

It consists of a cistern A B, about three times as long as it is broad, made of thick oaken planks, the joints of which are lined with sheet copper, and easily movable by means of a pole and cross-bar Cm, the fore part of the engine, which is so contrived as to slip back under the cover of the cistern and on four solid wheels, two of which are seen at D and E. The hind axle-tree, to which the wheel E and its opposite are fixed, is fastened across under the bottom of the cistern; but the fore axle-tree, bearing the wheel D, &c. is put on a strong pin or bolt, strongly fastened in a horizontal situation in the middle of the front of the bottom of the cistern, by which contrivance the two fore-wheels and the axle-tree have a circular motion round the bolt, so that the engine may stand as firm on rough or sloping ground as if it were level.

Upon the ground next to the hind part of the engine may be seen a leather pipe F, one end of which may be screwed on and off upon occasion to a brass cock at the lower end of the cistern; the other end is immersed in water, supplied by a pond, fire-plug, &c. and the pipe becomes a sucking-pipe for furnishing the pump of the engine by its working, without pouring water into the cistern. To the hind part of the cistern is furnished a wooden trough G, with a copper grate for keeping out stones, sand, and dirt, through which the cistern is supplied with water when the sucking-pipe cannot be used. The fore part of the cistern is also separated from the rest of its cavity by another copper grate, through which water may be poured into the cistern. Those that work the pumps of this engine move the handles, visible at the long sides, up and down, and are assisted by others who stand on two suspended treadles, throwing their weight alternately upon each of them, and keeping themselves steady, by taking hold of two round horizontal rails H I, framed into four vertical stands which reach the bottom of the cistern, and are well secured to its sides. Over the hind trough there is an iron handle or key K, serving to open or shut a cock placed under it on the bottom of the cistern, the use of which we shall explain in the sequel of this article: L is an inverted pyramidal case which preserves the pumps and air-vessels from damage, and also supports a wooden frame M, on which stands a man, who, by raising or depressing, and turning about the spout N, directs the stream of water as occasion requires. This spout is made of two pieces of brass pipe, each of which has an elbow; the lower is screwed over the upper end F, (fig. 271,) of the pipe that goes through the air-vessel, and the upper part screws on to the lower by a screw of several threads, so truly turned as to be water-tight in every direction. The conic form of the spouting pipe serves for wiredrawing the water in its passage through it, which occasions a friction that produces such a velocity of the jet as to render it capable of