A machine employed at wharfs, warehouses, &e. for raising and lowering goods; it consists of a long projecting arm, called the Jib, having a pulley at the outer end, over which passes the rope or chain by which the goods are raised, the other end of the rope being wound round a barrel either attached to the foot of the jib, or placed at any convenient distance from it. Various modes have been resorted to for turning the chain barrel; on piers and jetties it is frequently placed erect, and worked like a capstan: another method which was formerly very common, but is now little used, was to place it horizontally, and connect it with the axis of a large hollow drum, within which were placed a number of men, who, by stepping upon battens nailed upon the interior circumference parallel to the axis, caused the drum to revolve. But the most effective and best mode of employing the strength of men in working cranes (in situations which will admit of its application), is that invented and patented by Mr. Hardy: as in the preceding plan, the chain barrel is connected with a large drum fixed upon a horizontal axis, but the steps upon which the labourers tread are ranged upon the outside (instead of the inside) of the drum, radiating like the floats of an undershot water-wheel, and the labourers continually step upon that arm or step which is horizontal, so as always to act upon the longest lever. One or more of these cranes were erected at the East India Warehouses, and the principle has been since rendered familiar to one very numerous portion of the public by the invention ascribed to Mr. Cubitt, of Ipswich - called the treadmill.
The preceding figure represents a side elevation of Mr. L. Wright's patent crane, erected at the West India Docks, and which was the subject of much acrimonious controversy amongst some of the scientific periodicals of the time. a is the principal wheel, fixed to and revolving with the chain barrel b on the axis c; the periphery of the wheel c is made perfectly flat on both sides, for the reception of the numerous small wheels d, alternately placed on the opposite sides of the ring, with their axes fixed into it; these, which may be called friction wheels, are solid, about an inch thick, and five inches in diameter - they are turned smooth, and made bright in all parts; e e are two (of four) levers, worked by a four-throw crankffturned by the winches g g; the levers pass between guides at o, and slide over rollers at p, which form the fulcrum of the levers; and by the revolutions of the cranks the levers are successively projected against the under sides of the small wheels d, from whence they are, by the continued revolution of the cranks, again withdrawn, and again projected under the next little wheel below the former, each wheel being raised by the angular motion of the lever over which it rolls.
It should be observed that only one side or half of the machine is seen, the other side being a duplicate of it, having two similar levers, large wheel, and smaller wheels, etc. The machine (as delineated) is in gear; to put it out of gear a locking bar t is lifted, and thrown into the position shown by the dotted lines; then the framing r which carries the crank, inclined planes, and fly-wheel, and turns upon the centre s, is thrown back, by which the axis of the crank moves in the arc of a circle (shown by dots) to the position n. What mechanical advantage the inventor expected to obtain by this singular construction, it is hard to say; the machine is cumbersome and unsightly, has a complication of parts, in which the friction far exceeds that of a well-made crane of the common construction, to which it is also decidedly inferior in the circumstance of affording no means of altering the power or velocity according to the weight to be raised. The method adopted by the inventor for putting the machine in and out of gear is also very defective; but if the crane offered any advantages in other respects, this latter defect might be obviated.
In Mr. Revis's patent crane, which we are about to describe, the alternating motion of a single lever is employed to produce rotatory motion by means of a well-known mechanical arrangement, instead of producing such motion by turning a winch. The engraving on the succeeding page represents an elevation of this machine, a is the alternating lever (shown as broken into two parts for want of space), and having a counterbalance at x; it is on the opposite side of the machine to that represented, and its fulcrum being the axis of the toothed wheel b, which gears into another toothed wheel c, motion is given to both wheels in opposite directions. These two wheels are shown merely by two dotted circles, to avoid confusion in the drawing. On the axis of the wheels b and c are placed the wheels d and e, which are not fixed to the axles, but turn loosely upon, them; each of these wheels cany four palls or clicks, which fall into the notches of two ratchet wheels f and g that are fixed to the axis on which d and e turn loosely.
The operation of the lever, therefore, which causes the two first mentioned wheels b and c to revolve in opposite directions, produces precisely the same effect upon the ratchet wheels f g.
It will now be observed that the ratchet teeth and palls of both wheels incline, in respect to each other, in the same direction; and as the ratchets are turned round in opposite directions, the palls in one wheel slip over the ratchet teeth, while in the other wheel the palls catch into the ratchet; the latter is thereby locked to the toothed wheel, which now operates upon the toothed wheel f on the working barrel, upon which the rope or chain r is wound. During this process, the other wheel and ratchet (which we will suppose to be d f) has no effect, from their not being connected; but upon reversing the motion of the lever, these become fastened together* while the former are simultaneously loosened; and as the wheel d revolves in an opposite direction to e, the wheel f is turned round in the same direction as previously, and the rope or chain on the barrel proceeds in an uniform course. Having thus explained the manner in which the motion of the lever a is communicated to the other wheels b c, and thence to the rest of the machine, it is obvious that the putting of the wheel b out of gear with the wheel c, will stop the forward action of the crane; this is effected by means of the lever h, which turns horizontally upon a fulcrum pin at f, and slides the axis in its bearings, so that the wheels w and c are placed cut of contact with each other.