Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/581

Rh leucogcranus), of which tlie last is perhaps the finest of the family, with nearly the whole plumage of a snowy white. The Indian Region, besides being visited in winter by four of the species already named, has two that are peculiar to it (G, torquata and G. indica both commonly con founded under the name of G. antigone). The Australian Region possesses a large species known to the colonists as the &quot; Native Companion &quot; (G. australis] while the Nearctic is tenanted by three species (G. americana, G. canadensis, and G. fraterculus ), to say nothing of the possibility of a fourth (G. scldegeli), a little-known and somewhat obscure bird, finding its habitat here. In the Ethiopian Region we have two species (G. paradisea and G. carunculata) which do not occur out of Africa, as well as two others forming the group known as &quot; Crowned Cranes &quot; differing much from other members of the family, and justifiably placed in a separate genus, Balearica. One of these (B. pavonina) inhabits Northern and Western Africa, whila the other (B. regulorum) is confined to the eastern and southern parts of that continent.

1em  CRANE, a machine for raising and lowering heavy weights, and removing them from one place to another. Its chief parts are the jib, an inclined or horizontal beam at the end of which the weight is suspended ; the upright crane post or stalk, on which the crane turns ; the stay, beneath and supporting the jib; the barrel, round which the chain attached to the weight is coiled ; and the winch, pinion, and handles. In place of a stay, chains or tension- bars above the jib are commonly employed ; the latter at their upper end form eyes for the pivot of the sheave, or are pinned to the socket of the jib ; below they are fixed to the cast-iron framing that carries the wheel-work. To prevent the acceleration of the movement of descending weights brakes are employed, in one form of which a lever causes friction by bringing a piece of wood, strengthened with iron, into contact with a plain wheel attached to the barrel of the crane. The winch handle has given it a radius of about 18 inches, and its centre is placed at 3 feet or 3 feet 2 inches from the ground ; the limit of the average stress on it to be allowed for each labourer, working constantly at the rate of 220 feet a minute, has been found to be 15 ft). The length of the journals of the axles is made 1 to 2 times their diameter, which must bs proportionate to the torsion of the wheels to ba resisted. The diameter of the axles of the crane-barrel, if of cast-iron, should be pro portional to the- cube root of the strain upon them in cwts; if of wrought iron, to y^ths of the same. The chain or rope ought not to be worked with more than one-half the weight which it is estimated to be capable of bearing. The strength of the jib varies almost directly as the fourth power of its diameter, and inversely as the square of its length. In cranes for lifting great weights the jib may be made to rest against a circular rail let into masonry, instead of bearing against the crane post. The ends of the jib should not be rounded, but should be cut square, BO as to lie evenly against the iron sockets into which they fit. In iron cranes the post is a hollow pillar of cast-iron, fixed by means of cross-shaped framings of the same material into a block of masonry ; the jib is of iron, or of wood with terminal sockets of that metal. A crane at Earl Grey s Dock, Dundee Harbour, when worked by eight men, is capable of lifting 30 tons; it can be moved round by one man by the application of horizontal gearing ; its total weight is not above 60 tons. The double crane for wharfs and pier-heads is framed and braced so as to balance exactly when turned on its pivot. In another double crane, used in the building of breakwaters, one jib is employed in laying, while the other lifts a stone. The derrick is a temporary crane consisting of a spar supported by guys or stays ; in this crane the iron beam or derrick can, by raising or lowering, be set at any required angle. The cranes in general use in the earlier part of the last century were primitive contrivances worked by means of a large hollow wheel, within which a man walked .forwards or backwards according as goods were to be raised or lowered ; the jib of the crane was fixed on a pivot, so as to turn round about fths of a circle. After this a simpler form, still in use, was introduced, with the wheel fixed on a portion of the jib projecting behind the crane post. One of the first examples of traversing cranes was erected by Mr Rennie in the Mahogany Sheds at the West India Docks. For this kind of crane a railway is constructed on parallel frames of timber reaching across the roof of a building, and on this is a carriage supported on wheels, and capable, therefore, of being moved backwards or forwards by means of the machinery attached to it. The chain that bears the weight is connected with the carriage, and hangs down between the two lines of rails. By making the framework supporting the railway movable, as well as the carriage, goods can be transported in any required direction. The frames of railway traversing cranes are composed of two triangular timber structures, mounted on strong wheels; these by toothed wheels and pinions are caused to move along the railroad on which they are placed. At one time vacuum cranes were employed, to work which small oscillating cylinders, similar to those of high-pressure steam engines, were put in communication with a receiver exhausted of air by steam pumps. Afterwards steam came to be applied immediately as the motive power of cranes. In the direct-acting steam crane, the crane post itself is the steam cylinder, and the steel wire rope for lifting the load constitutes the piston-rod ; to turn the crane round, steam is admitted to a cylinder beneath and forming part of the bed-plate. The first crane worked by pistons acted on by water-power was established at Newcastle-on-Tyne in 1846. Reservoirs at great heights for providing water-pressuro can be dispensed with by the use of Sir W. Armstrong s accumulator, an apparatus consisting of a cast-iron cylinder in which the water supplied by an engine is pressed upon by a loaded plunger. The excess of water pumped into the accumulator at any time is employed in raising the plunger ; this, on reaching a certain height, begins to close a throttle-valve in the steam-pipe of the engine, and thus lessens its rate, until fresh demands are made upon the contents of the accumulator. The water discharged by the cranes may be led by a return-pipe to a cistern over the engine room, in order again to supply the force-pumps. To avoid jerks and concussions owing to the momentum of the jib after the closing of the water passages, a clack-valve is provided which opens up into the supply-pipe whenever the pressure in the cylinder of the hydraulic press becomes greater than that in the accumulator. The tubular cranes of Fairbairn are made of wrought-iron plates riretted together. The jib, which is curved, is rectangular in cross- section, and tapers upwards to its extremity, and below the ground to a considerable depth, where it terminates in a shoe of cast-iron on which the crane revolves. The plates forming the edges of the jib are connected by means 