We shall proceed to describe some other cranes that are much in use in the present day. Fig. 1. Plate Cranes, is an elevation of a crane sideways, and fig. 2. is a plan ; A B is a stout beam, turning in a cast iron collar at B, affixed to beams in the floor of the wharf ; it goes down about twelve feet below this, and has a steel pivot in the lower end, which works in a brass collar, so that the beam A B can turn round freely without shake ; C D are the two beams of the jib, with a gully at E, over which the chain for hoist ing the goods works ; the other end of this chain is wound round a roll, e,1 foot diameter ; a cog wheel, marked 100, of 100 teeth, turned by a pinion of 7 leaves, on the same axle with another wheel 31, of 31 teeth : this is turned by a pinion, 14, of 14 teeth. If great power is requir ed, thewinch handle is applied to a square on the end of the spindle of the last pi nion, less weight the winch is put on the axle of 31 : when this is the case, the pinion 14 must be disengaged from its wheel, by sliding its axle lengthways. G is a clip, to keep the pinion in or out of gear, as it has been placed by the atten dant. A plan of it is also shewn in fig. 2: the two semicircular bands in it fit into grooves turned in the spindles, and the weight a at the end keeps them I ii this prevents them moving endways ; when the weight a is raised, it releases them both ; and when they are moved, the clip fits into another groove turned in them, so as to prevent their return. The frame containing the wheels is form ed by two cast iron crosses, bolted to the main beam A B by the ends of their ver tical arms, the two other arms forming the bearing for the wheels.
Cranes of this kind are now coming in to very general use in London, as they require no expensive framing over them, and they can be turned all round. A fur ther advantage they possess, in common with several other kinds, is, the chain not being bent suddenly round the small pullies over the jib when they are swing ing overland, as in the cofinnon kind, and fig. 4.
A crane of this kind, which we saw at Woolwich Warren, had an apparatus (shewn in fig 3.) attached to it for lower ing with safety great weights without any exertion of the workmen. It consists of a cylinder, b d e, of cast iron, smoothly bored through ; f g is a passage connect ing the top and bottom of the cylinder, and h a cock by which this passage can be closed ; i is a piston fitting the cylin der, and k the rod affixed to it, moving through a stuffing box in the lid of the cy linder; the axis of the wheel 31 (fig 1 and 2.) or one in the place of it, has a crank on it working the piston rod of the cylinder (fig. 3.) which is bolted fast to the back of the beam A B, with the usage sliding motion to render its motion parallel. The
cylinder is filled full of oil, and as the han dle of the crane is turned, the piston is moved up and down in the cylinder : now if the cock h is open, the oil flows freely from one part of the cylinder to the other, without obstructing the motion of the crane ; but if it is closed, the oil, finding no other passage, and being an incompressible fluid, stops the piston, and the descent of the goods suspended by the crane. By opening the cock partial ly, the friction (or, as it is technically termed, the wiredrawing) of the oil im pedes the motion of the wheels, so as to lower the greatest weights with any ve locity required. A portion of the circle ni is fastened to the cock, with fine teeth cut in it ; a click takes into these teeth, to hold the cock at any opening it may be set to. This contrivance is described in Gregory's Mechanics, published in 1806, applied to a different kind of crane, but the invention is ascribed to Nr. David Hardie. We consider it a contrivance of great utility, and likely to prove extreme ly useful.
Fig. 4, is an elevation of a crane at Queenhithe wharf, London. A II is a very strong upright beam, firmly bolted to beams running inland, and further se cured by curved stays D: a el e is a cast iron frame, bolted to the beam at one end and the stays D at the other. This forms the frame for the wheelwork, which is the same as fig. 1; the chain, after going round the roll, goes over a large wheel f, and passes through the beam to the jib. E is a cast-iron frame, bolted to the top of the beam A B, to receive the upper pivot of the jib ; g is one of the small pulleys, round which the chain bends when the jib is turned overland to raise or lower goods. F is another cast-iron frame, to support the lower pi vot of the jib, and G is a pile bolted to it, to assist. A few boards nailed over the . two 'stays D forms a cover for the whole machinery, and defends the wheel-work. The jib and its iron-work will be under stood by inspection of the figure. All cranes where chains are used for hoisting the goods should have barrels, with a spiral groove cut in them, and the lower half of the chain lay in the groove, as in fig. 5. This was applied, in 1789, by Mr. John Smeaton, to a crane designed by him, and executed in the Wool-quay, Custom-house, and found to be of great advantage. In 1805, Mr. Gilbert Gilpin received the silver medal of the Society of Arts for the same invention, without perhaps knowing it had been used before. The pulleys should also be grooved, to receive the lower half of the links of the chain in the same manner.