CRANE, is a machine employed for raising weights vertically by means of a rope or chain acted upon by a windlass, but carried over a pulley or wheels attached to the extremity of a projecting arm or jib. The common ware house crane, which is usually formed of iron, may be compared to an inverted L, the verti cal portion of which is so mounted as to form a pivot or axis upon which the whole may be swung round; so that the horizontal arm, which is strengthed by diagonal struts, may extend in any direction. The rope or chain of such a crane is conducted along the hori zontal arm, and connected with a kind of windlass or crab, which is usually provided with two sets of gearing for working at dif ferent velocities, so that in raising light goods a much greater speed may be given to the chain with the same motion of the winch handles than when the load is very heavy. Wharf-cranes are frequently of somewhat different construction, owing to the circum stance that they usually stand alone, that is to say, that they are self-supported, instead of being attached to and supported by a wall or a post secured to a wall. There is a verti cal pillar of iron or wood, the lower end of which is firmly secured to a foundation of masonry, while the upper end terminates in a pointed or conical pin, upon which, as a pivot, the revolving part of the crane rests and turns. The arm or jib projects obliquely from the pillar, and is strengthened by diagonal braces. The windlass or crab for working the crane is attached to the central pillar. Some cranes are worked by a tread-mill moved by men; some by horses or oxen; some by the surplus power of a steam engine ; some by the compression of air in a.strong vessel ; some by hydrostatic pressure ; but the cus tomary mode is by a winch-handle. Many of
the cranes at the principal docks and quays are capable of raising immense weights.
Mr. W. G. Amstrong, who has introduced many ingenious applications of water power, has recently patented a singular method of working a crane by means of the pressure of the water in the common water pipes of a town. One such hydraulic crane was set up and worked on the quay at Newcastle in 1816. The machinery for working the crane is all underground. There is a sort of dial plate visible, with handles or indicators for guiding all the movements of the machine, such as raising, lowering, stopping, dic., these indicators act upon valves which regulate the water-pressure beneath, so that the move ments produced can be made exactly propor tionate to the work to be done.
Mr. Henderson's derrick crane, which has been so largely used by Messrs. Fox and Henderson at the Industrial Palace in Hyde Park, is especially adapted for circumstances where the crane is required to be moved from place to place during the progress of the works. This kind of crane has a derrick or jib, rising nearly from the ground, and hinged at its lower extremity to the upright post of the crane. This hinge enables the derrick to be moved to any required angle, so that the upper extremity may be near or far from the central post, according to the position of the load to be raised. While the derrick can thus move vertically on a horizontal hinge, the post can rotate horizontally on a vertical pivot ; so that the crane has a wide extended area of action.