to a small height. A metallic cylinder, sufficiently strong, and bored truly cylindrical within, has a solid piston fitted into it, which is made perfectly water-tight, by leather packing round its edge, or other means used in hydraulic engines. The bottom of the cylinder must be made sufficiently strong with the other parts of the surface, to resist the greatest strain which can ever be applied to it. In the bottom of the cylinder is inserted the end of the small tube, the aperture of which communicates with the inside of the cylinder, and introduces water or fluids into it; the other end of the pipe communicates with a small forcing-pump, by which the water can be injected into the cylinder beneath its piston; the pump has of course valves to prevent the return of the water. Now, suppose the diameter of the cylinder to be six inches, and the diameter of the piston of the small pump, or injector, only one-quarter of an inch; the proportions between the two surfaces or ends of the said pistons will be as the squares of their diameters, which are as 1 to 24; therefore the areas will be as 1 to 576; and supposing the intermediate space between them to be filled with water, or any other dense and incompressible fluid, any force applied to the small piston will operate on the other in the above proportion of 1 to 576. Suppose the small piston, or injector, to be forced down, when in the act of forcing or injecting, with a weight of 20 cwt., which can easily be done by means of a long lever, the piston of the great cylinder would then be moved up with a force equal to 1 ton multiplied by 576.

Fig. 343 represents a crane constructed upon the hydrostatical principle, that is, by the injection of water from a small pump into a large cylinder, which is fitted with a piston, having a rack attached to it for the purpose of turning a pinion upon the axis of a large drum-wheel or barrel, round which the rope is coiled, and from thence passes to the jib.

The figure A A represents the jib, made of iron, and supported upon two brackets a a, projecting from the wall of the warehouse in which the crane is supposed to be erected. The rope passes over the pulley S, and down through holes in the brackets a a, then turns under the pulley b, and comes to the lower side of the great drum-wheel B. The pinion C is fixed on the same axis with this, and its gudgeons turn in small iron frames d, bolted down to the floor of the warehouse. The pinion C is actuated by the teeth of the rack D, and a small roller, whose pivot is shown at e, presses against the back of the rack, to keep its teeth up to the pinion. The rack is attached to the piston D of the cylinder L, in which the power for working the crane is obtained. The piston passes through a tight collar of leather on the top of the cylinder at E, which does not admit of any leakage by the side of it, and therefore if any water is forced into the cylinder it must protrude the piston from it. The cylinder is supported in a wooden frame F F, and has a small copper

U

pipe gg, proceeding from the lower end of it, communicating with a small forcing-pump at h; this stands in an iron cistern H, which contains the water, and sustains the standard ii, for the centre of the handle G, with which the pump is worked by one or two men. The upper extremity of the standard i'i guides the piston-rod of the pump, to confine it to a vertical motion; 7 is a weight for counterbalancing the handle G of the pump. From what we have said before, the operation of this machine is evident; the power of the cylinder D is in proportion to its size compared with the size of the pump; but as it only acts through short limits, the pinion and drum B are necessary to raise the weight a sufficient height. The operation of lowering goods by this crane is extremely simple, as it is only necessary to open a cock at m, which suffers the water to escape from the cylinder into the cistern H, and the weight descends, but under the most perfect command of the person who regulates the opening of the cock; for by diminishing the aperture, he can increase the resistance at pleasure, or stop it altogether.

Fig. 345 is a side elevation of a crane. The post is immovable, and is fixed on an iron frame, with arms extending in the form of a cross, the extremities of which are bolted down by strong screws to large blocks of stone sufficiently heavy to more than counterpoise the weight to be raised by the crane. In the top of the post is fixed a wrought-iron pivot, by which the weight is supported, and a strong cast-iron cap bears on the pivot, and has attached to it two iron frames, one on each side, that receive the pres sure from the stay, as well as support the pull of the jib, which is formed of two bars of wrought-iron; the lateral pressure is borne by the bottom of the post, round which two friction-rollers turn to facilitate its motion. This crane will carry five tons with safety.

PRESSES.

THE press is a machine in most extensive use in the mechanic arts. It is usually made of wood, or iron, and serves to squeeze or compress any body very close.

Screw-presses generally consist of six members, or pieces; viz. two flat smooth tables of wood or metal, between which the substance to be pressed is placed; two screws, or worms, fastened to the lower plank, and passing through two holes in the upper; and two nuts, in form of an S, serving to drive the upper plank, which is movable, against the lower which is stable and without motion.

Presses used for expressing liquors, are of various kinds some, in most respects, the same as the common presses, excepting that the under plank is perforated with a great number of holes, to let the juice run through into a tub or receiver underneath.

1. An improved cider-press, turned by a windlass, is shown in fig. 284.

A A is the base or foundation with its supporting parts; B B the cheeks or sisters; DD the cross-piece at top, through which the screw passes, and which consequently contains the female screw; E the screw with its appendages; FF the bridge or cross-piece which acts on the pommage; GG is the wide plank or vat on which the pulp rests in the hair bags, in which the mode of the liquor's passing off is seen.

This kind of press may be advantageously employed for packing cloth, paper, and other goods; as also in paper-mills, for flattening and rendering paper solid; and in the manufacture of woollen cloth, for glazing and setting a finish upon the article in its last stage.

2. Two elevations of a very good screw-press for a papermill are given in figs. 285 and 286.

A A is the bed, formed of an immense beam of oak; and each of the cheeks, B, consists of a long iron bar bb, fig. 286, the ends of which are welded together, so that it forms a long sink, one end of which receives the end of the bed A, and the other the end of a massive cast-iron bar D, through which the screw E is received, and its nut fixed fast therein. The open spaces of the long links or cheeks, b, b, are filled up by rails of wood C, which support the weight of parts of the press when it is not in action, but these bear nothing when the press has any articles under pressure in it; these articles are laid at H, on the bed, and the follower, G, is pressed upon them by the screw, when it is turned by a long lever put through the holes in the screw-head F.

The screws employed for paper-presses are generally formed with such coarse threads, and so rapid a spiral, that the elasticity of the paper is sufficient to force it to run back. To these a ratchet-wheel, a, is fixed, and a click e, fig. 287, is applied to its teeth; to prevent its return, the click is supported on a bar bd, which moves on a centre at B, but the other end is retained by a catch or lever fg. When the press is to be relieved, the

end f, of the catch, is driven back; this relieves the bar db, and the click no longer detaining the ratchet-wheel, the screw runs back.

3. A very ingenious and useful packing-press has been invented by Mr. John Peek. It is represented in fig. 288.

A A, the frame of the press; B B, the large screws, which, in this press, contrary to those in common use, is fixed and immovable; C, a circular iron bar, extending beyond the sides of the press, and having thereon two worms, or endless screws EE, which work in two toothed wheels fixed to the nuts, and, by turning the winch D, drive the nuts and bed up and down the screws as may be found necessary; F, a stage, suspended from the bed, and on which the men stand who work the press; such a stage may, if found necessary, be fixed at the other end of the bar, as shown by the square shoulder G. The bed of this press must be formed of two pieces of strong wood, which are held together by screws and nuts, passed through them, as shown at hhhh. The great utility of this press consists in its being capable of packing two sets of bales at once; thus answering the purpose of two presses, with more expedition.

4. The hydrostatic or water-press, or as it is sometimes called Bramah's Press, has, for a great number of purposes, superseded the use of the screw-press, over which it possesses great advantages, in all cases where a strong pressure is required. It is one among the many useful inventions of the late Mr. Joseph Bramah, of Piccadilly; and is ingeniously contrived for applying the quaqua versum pressure of fluids as a powerful agent in many kinds of machinery.

These contrivances consist in the application of water, or other dense fluids, to various engines, so as, in some instances, to cause them to act with immense force; in others, to communicate the motion and powers of one part of a machine to some other part of the same machine; and, lastly, to communicate the motion and force of one machine to another, where their local situations preclude the application of all other methods of connection.

The first and most material part of this invention will be clearly understood by an inspection of fig. 289, where A is a cylinder of iron, or other materials, sufficiently strong, and bored perfectly smooth and cylindrical; into which is fitted the piston B, which must be made perfectly water-tight, by leather or other materials, as used in pump-making. The bottom of the cylinder must also be made sufficiently strong with the other part of the surface, to be capable of resisting the greatest force or strain that may at any time be required. In the bottom of the cylinder is inserted the end of the tube C; the aperture of which communicates with the inside of the cylinder, under the piston B, where it is shut with the small valve D, the same as the suction-pipe of a common pump. The other end of the tube C communicates with the small forcing-pump or injector E, by means of which water or other dense fluids can be forced or injected into the cylinder A, under the piston B. Now, suppose the diameter of the cylinder A be 12 inches, and the diameter of the piston of the small pump or injector E only one quarter of an inch, the proportion between the two surfaces or ends of the said piston will be as 1 to 2304; and supposing the intermediate