CRANE

machine by which a load may be raised or lowered vertically and moved horizontally. When the machine lifts vertically only it is called a winch, hoist, or lift, and when coal, cereals, and other materials are moved, not in loads but continuously, the appliance is termed a conveyor. Cranes may be cla ified as revolving or non-revolving. Manual, hydraulic, steam, and electric power are used, the latter “especially in travelling cranes. The jib and derrick crane consist mainly of a revolving pillar or mast for the slewing movement, a jib which may be lowered or raised for the vertical movement, and the tackle pa ing from a winding drum along and over the end of the jib, and provided with a hook for attaching the load. Davits are an example of crane where jib and mast are in one piece,’ Portable cranes are mounted on trucks or gantries —(e.g.) running on rails alongside harbor quays. ‘Traveling cranes consist of a bridge resting on wheels running on rails —say on two opposite walls of a shed— and the jenny or crab carrying the hoisting mechanism, which runs on rails along the bridge. Many varieties of crane have been constructed—(e.g.) the Titian crane, a combination of the travelling and revolving type, used in constructing piers and breakwaters.