tage of being removable from one place to another. Next to the cheap transport of material across rough country, perhaps the most important application of aerial cableways is for building and excavating operations. For this purpose they are a cheap, and often more efficient means, than an ordinary rigid traveller or a travelling crane. In bridge building, for instance, an aerial cable can be extended across a river, and the materials for the bridge can be deposited where required without having to carry it out in barges, and have the difficulties of current and tide to contend with. In excavating a canal or dock, an overhead cable attached to a travelling tower on rails on each bank will carry the excavators, and obviate the necessity of employing a number of cranes, with rails laid to run them on. In the loading and unloading of ships, an aerial cable is often more suitable than cranes. The cargo can be deposited or brought from places some distance back from the edge of the dock, or quay wall, and the tower on the dock side can be provided with a boom for running the carriers out over the vessel. In cases where there is no dock, as in Fig. 14, Plate I., a ship may lie at some distance from the shore, and cargo be transported by means of a connecting cable. In the construction of Beachy Head Lighthouse, Fig. 15, Plate I., communication with the shore was by means of cables. In the coaling of warships at sea, aerial transport is recognised as being the only economic method possible. Except in still water, ships cannot lie side by side. A space of not less than 300 feet is necessary for safety, and the communication must be by cable, means being provided to compensate as much as possible for increased or relaxed tension of the cable. In large factories and mills, products can often be best conveyed from the floors of one building to the floors of another building at some distance away, by an aerial cable, or a very light aerial railway. This is especially an advantage where constant communication between upper floors of separate buildings is necessary. Aerial transport is often the only way of conveying material across a railway. In such cases a light guard bridge is generally built beneath the cableway as a precaution against anything falling on to the line. For passenger transport, aerial cables are used to some extent. The earliest and simplest type of aerial cableway was an endless rope passing round a pulley at each terminus, and having carriers attached to it, which travelled with the rope. This type is still used, and for very light work is generally considered the more suitable, because of its cheapness. The later type, and the one more commonly used, has a fixed rope which serves as a rail for the carrier to run on, and a separate travelling rope which pulls the carrier along. In the simple type, one rope both supports and carries the load. In the other kind there is a separate rope for each of these purposes, and this gives much greater power and efficiency. Details vary considerably, but all the systems in use may be roughly reduced to the two mentioned. The system best suited for any particular case depends on the conditions, and on the work required of it. With the steel ropes of modern times there is scarcely a limit to the loads that can be transported, and there is no limit to the inclines that can be followed. For transportation on a level, or up inclines, or for hoisting, motive power is necessary. For carrying loads down inclines the force of gravity alone generally does the work, and in some cases even supplies power for other purposes. On level ground the motive power required is often reduced by making the tower from which the loads are despatched, higher than the tower at the other end of the cable. Cableways of great length are supported at frequent intervals, as in Fig. 16, Plate II., but when necessary very long unsupported spans can be employed. Cableways of comparatively short length, which are supported only by a tower at each end, are made movable, if the work they are intended for requires it. They are thus enabled to cover an immense area of ground. The two towers may be mounted on wheels and travel parallel with each other on lines of rails, or one tower may wheel in an arc, and provision be made for sufficient amount of swivel at the rope connections on the fixed tower. In the fixed rope type of cableway, the fixed ropes are generally anchored at one end, and kept to a proper tension by counterweights or springs at the other end. The load carriers which travel along the cables are made in forms suitable for the goods they have to carry. When they travel on a fixed rope they are provided with sheave wheels to fit the rope. The carriers are stopped and started by a locking grip which can be made to grip or to release its hold on the hauling rope at any place desired. When carriers are required to stop only at terminal stations, this is generally done automatically. If carriers have to be hoisted and lowered, as in building and excavating operations, ropes are required for this purpose in addition to the traversing rope. All operations are generally All operations are generally performed by one engine situated at the head tower. When two sets of cableways are used, there may be an engine for each, and sometimes engines are employed for moving the towers themselves. The photos, Figs. 14-16, Plates I. and II., are selected from installations by Messrs Bullivant & Co., Ltd., of London. The subject of aerial transportation, of which this is a general account only, involves many mechanical details which will be found treated and illustrated under their proper heads of Cables, and Cableways. Aerial Navigation. See Flying Machines. Aeroplanes. See Flying Machines. A-Frame. So called from its general resemblance to the letter A. It is admirably suited for vertical engines, pumps, and crabs, the spread of the legs and the greater mass about the base ensuring stability under working stresses. These frames are made both cast and plated, and in small and large dimensions. Also termed A-Standard. After-Blow. The operation of blowing air through the metal in a Bessemer converter after the removal of the carbon, in order to oxidise the phosphorus. See Bessemer Converter. Agglomerate Cell.-A modification of the Leclanché cell, in which the negative element consists of a carbon block or plate having blocks of agglomerated carbon and manganese in contact with it. These are prepared by mixing 40 parts of manganese oxide, 55 parts of gas car bon, and 5 parts of gum-lac resin. The mixture is placed in a steel mould and subjected to considerable pressure at a temperature of 100° Cent. The advantage gained is that the porous pot in the older type, which is required to sustain the loose mixture of carbon and manganese oxide, is dispensed with, and the internal resistance of the cell lessened thereby, indiarubber bands being substituted for it. Aggregate Motion.-Denotes cases in which a moving body receives more than one independent motion concentrated upon it at the same instant of time. The lazy tongs furnishes the most obvious exponent of motion of this kind. In these the sum of the circular movements of the ends of each separate pair of bars is concentrated at the end of the last pair of bars. The familiar and perennial problem of a rotating cart wheel is another example. The upper portion of the rim of a wheel on a moving vehicle moves with twice the linear velocity of the centre of the axle, while the part on the ground is for an instant at rest. The explanation is that this point is for any moment the fulcrum on which the wheel is turning. The differential screw is another case in point, in which the aggregate motion is equal to the difference in the pitch of two screws if of the same hand, or by the sum of the pitches if of opposite hands. Other examples are furnished by systems of pulleys, epicyclic trains, and other mechanisms. Agitator. A stirrer composed of blades set on a revolving shaft, which has its utilities in numerous industries. Agricultural Engine. See Portable Engine. Agricultural Machinery.-This comprises the machinery as distinguished from engines used in the processes of agriculture. There are few operations in this connection, for the performance of which highly efficient machines are not displacing hand work and horse power. In modern times such work has to be done on a larger scale and more rapidly than was formerly the case; and in agricultural work, as in everything else, the old methods are being abandoned except for operations on a very small scale. Portable and stationary engines are very commonly used for supplying power for all purposes. Steam ploughs that cut a number of furrows simultaneously are displacing single-furrow horse-drawn ploughs. The thrashing machine receives the corn as it is reaped and separates the various constituents and ejects them separately from different parts of the machine. All the minor operations in the treatment of the soil are performed by suitable machines, such as cultivators, harrows, rakes, sowers, diggers, rollers. In some cases several operations are combined in one machine. Similarly in the operations of gathering and treating the products of the soil, mowing and reaping machines, swath turners, trussers, presses, elevators, chaff cutters, corn grinders, and numerous other machines are used. Most of these machines are treated under their separate heads. Aich's Metal.-An alloy patented by Johann Aich of Venice, for guns. It is composed of copper 60, zinc 38-125, and iron 1.5. There are several alloys having a very similar composition, the principal feature of which is the addition of iron to copper-zinc alloys (see Sterro-Metal). The cause of the strength of the alloy, formerly obscure, was elucidated in the Fourth Report of the Alloys Research Committee. The iron enters into combination with a low eutectic, forming with it a less fusible compound, so removing the source of weakness. Brass, with, or without the 1.5 per cent. of iron added, has very different tenacities. Thus, two mixtures as follows, were tested at different temperatures. Brass: Copper 61-2, zinc 38.8 per cent. Aich's metal:Copper 59-8, zinc 37.9, tin 0-8, iron 15 per cent. The tenacity at different temperatures was TENACITY PER SQUARE INCH. : Air.-See Atmosphere. Air Belt, Air Chest, or Wind Chest.The belt put round many cupola furnaces to receive, and distribute the blast through the tuyeres. See Cupola Furnace. Air Blast.-See Blast. Air Brake.-See Brakes,-Railway. Air Chamber.-The chamber in a torpedo which receives a supply of compressed air for the working of the three-cylinder propelling engines. It occupies about half the length of the torpedo, and the air is forced into it by air-compressing pumps to a pressure of about 1,350 lb. The chamber is of Whitworth compressed steel barely of an inch thick, with convex ends. The pressure is so enormous that the effect of explosions, which are on record, is like that of gunpowder. See also Caisson. Air Chest. See Air Belt, Cupola Furnace. 3 Air Chuck.-See Pneumatic Chuck. Air Cock-Cocks used in air vessels, and in compressed air machinery, for relief, and regulation of pressure, &c. Air, Compressed. -See Compressed Air. Air-Compressing Machinery.—This includes the air compressor, the air receiver, the pumps, and the transmission pipes with the various connections to the machines used. Air Compressor. The employment of air under pressure as a motive power has grown enormously of late years. It is a rather more difficult task to say for what purposes it is not used than for what it is. The following is a brief résumé of some of its principal appli cations. For hoisting machinery of various kinds, for rock drills, for brakes, for riveting, caulking, chipping, for power hammers, sand blast apparatus, moulding machines, for spraying oil in furnaces, for oil lights, for pneumatic transmission, for machinery and motors used in mines, as coal cutters, and locomotives in tunneling, for caissons, for inflating tyres, for testing tubes, for raising submerged vessels, for divers, for ventilation, and refrigeration, for sucking, or blowing loose sand away from moulds, and chips from milling cutters, shavings and chips |