section when it is subjected to continued tension. It is carried on the steel trucks, which can be tipped on either side, as the body is supported on two trunnions (H, Fig. 442). The device for attaching the rope to the waggon is very simple; the rope lies in a fork or "jockey," which is slightly out of the direct line of traction. The jockey is free to turn in a socket on the truck, and the slight bend given to the rope is sufficient to afford the necessary grip, even in going up an incline of 1 in 20. If the "blue" has to be deposited at a point nearer the mine than the terminus, the part of the rope beyond the place where the waggons are taken off is supported by pulleys.

Horses are employed to draw the trucks from the main rope haulage lines to the places on the floors where they have to be tipped.

The endless chain has been chosen for bringing down the ore from some of the mines of the Somorrostro Company, in a part where self-acting inclines cannot be used because there is not a descent all the way. A second reason for adopting this system was the fact that it admits of considerable changes in the amount of traffic, by altering the speed of the chain and the distance between two successive trucks. It further allows branch lines to be taken off from the main one. At Somorrostro there are in all very nearly two miles (3000 m.) of endless chain haulage.

The greatest difference of level between the highest point at the Sol mine and the terminus at the station of Cadegal is 802 feet (244 60 m.), and on one part of the line the gradient is as high as 29.5 per 100 or 1 in 3'4. The fall is so great that the chain requires no power but gravity to work it; in fact, it is necessary to use brakes to oppose the vis viva. Strap-brakes are employed in the same manner as they are on the inclines just described, solely for the purpose of stopping the chain. The danger of depending entirely upon such brakes for working inclines has already been pointed out, and a uniform speed is maintained by affixing fan-regulators working in water. They are chosen in this case in preference to the fans working in air, because the latter must revolve at a great velocity in order to be efficient, and therefore could not be applied to the slow chain haulage without gearing, which would introduce complications. These hydraulic governors are like the air-regulators in principle, except that the blades are immersed in water; the speed of the chain can be adjusted with the greatest nicety by altering the quantity of water in the tank in which the blades work, and so introducing the amount of resistance required.

The usual speed at which the chain is run is 5 feet (1.5 m.) per second, but it can be raised to 6 feet 6 inches. The chain is made of inch (22 mm.) iron, which corresponds to about 19 lbs. per

Exposition Universelle de 1889. Op. cit., p. 15.

yard (9.826 kil. per metre). The last section, however, has harder work, and the chain is of 1-inch iron (26 mm.) and weighs 28 lbs. per yard (14 kil. per metre). Each waggon holds 17 cwt. (900 kil.) of ore, and when the waggons are arranged 27 yards (252 m.) apart, the chain haulage is capable of transporting 2500 to 2600 tons of ore a day, in addition to a certain amount of rubbish which is tipped before arriving at the port.

6. Conveyance of Mineral by Boats from one part of a mine to another is exceptional; but transport by canal or sea to the consumer is common, and is chosen whenever available on account of its comparative cheapness. It is of the utmost importance when dealing with large quantities of mineral to have cheap and rapid methods of shipping it. At Huelva, the shipping port of the Rio Tinto mines, the trains of ore are drawn on to a part of the pier which has just enough inclination to make a truck run down of itself. A workman then uncouples a truck and allows it to run opposite a shoot, which leads to the hold of the vessel lying alongside the pier. The truck is emptied by opening the bottom and letting the contents drop into the mouth of the shoot. The bottom is then closed and the truck is allowed to run on a little further, when it is shunted back on to a side line, and made to join the train of empties ready to be drawn back to the mine. After the locomotive has once hauled a train on to the proper part of the pier, the discharge of its contents into the ship proceeds very rapidly and requires the attendance of only one man.

The arrangements are so perfect that 500 tons can easily be loaded in an hour, but naturally a good deal of time is lost in shifting the steamers and berthing them. The greatest amount of work in loading at Huelva pier has been a little over 3000 tons in a single day. A steamer has been known to come into Huelva harbour by one tide, and leave by the next with a cargo of 1500 tons of ore.

The Somorrostro Company loads its iron ore at Bilbao in a similar manner. The Company has three wharves, at each of which 2000 tons can be shipped in a day; indeed a ship of 1490 tons has been loaded in six hours.

7. Aërial Ropeways.-These ropeways may be divided into five classes:

a. Single supporting rope, with or without a hauling rope.

b. Endless rope, which is the supporting rope and hauling rope at the same time.

c. Two supporting ropes and an endless rope for hauling the load. d. Double endless travelling rope or cnain.

e. Telpherage line.

a. Lines erected on the first of these principles may be seen in hilly countries. An iron or steel wire rope is stretched across a valley, and forms the rail supporting the load, which is put into

a sack and hung on by a grooved pulley. If the heights of the departure and receiving stations are properly arranged, the load on going down the slope acquires enough momentum to bring it up to the station on the other side, without rushing in too violently. The objection to this system is that the sacks and the pulleys have to be carried back by men or women, but it has the merit of simplicity and cheapness. By the addition of a small hauling rope on a drum, the method is available for steep mountain sides; the load is lowered with use of the brake, and the drum is worked to draw up the empties along the supporting rope.

b. In this system there is an endless rope, supported by pulleys on strong wooden or iron posts placed at suitable intervals, which is set in motion by any available source of power. Suspended from the rope are the buckets or other vessels in which the mineral is carried. The buckets may be detachable at pleasure or they may be fixed. The former plan is the one brought out by Hodgson in 1869. The bucket or other receptacle is suspended by an iron hanger from a grooved block of wood which rests upon the rope. The carrying block has a spindle with a small grooved pulley, which can be made to run upon a rail at each terminus and so let the rope move on without the load. The bucket is filled from a shoot or hopper while hanging on the rail at the loading terminus. A workman then pushes it along the rail until the carrying block is taken up by the rope, which is always in motion; the load now travels along suspended from the rope, the carriers being constructed so as to pass over the pulleys. On reaching the unloading terminus, the carrying block is again shunted on to a rail, and the bucket is tipped by lifting up the catch which had kept it from turning about pivots; after having been put into position, it is brought round to the point where the rope, after passing round a terminal pulley, is about to begin its journey back to the loading station. Here it is shunted on to the rope and travels along with it.

One great disadvantage of this system, in the case of steep inclines, is that the carriers may slip upon the rope, and that the loads either fall off or do damage in some other way. To overcome this difficulty, some of the constructors of aerial ropeways attach the loads to a clip which is tightly fixed to the rope. The clip must be of such a nature that it will pass the supporting sheaves or pulleys. When the inclination is sufficient, an aërial line of this description will work automatically, the weight of the full loads being enough to draw up the empties.

c. The third system has two fixed ropes, which serve as aërial rails and act solely as supports, and an endless travelling rope, to which the loads are made fast at pleasure. It resembles, therefore, the endless rope haulage, of which mention has been made for underground work, save that the rails are above the load instead of being below it.

Ropeways working upon this plan have been perfected of late years by Otto and by Bleichert in Germany, where they are commoner than in this country. They are constructed for distances of from 2 to 8 or even 10 miles, with a carrying capacity of 600 to 800 tons per day of 10 hours. The separate loads may vary from cwt. to 1 ton each.

The points to be considered are:

Carrying rope and vessel.

Posts or standards.

Hauling rope and attachments.

Terminals and their shunting arrangements.

*

The kind of cable used on the most recent lines erected on the Otto system is that known as "locked coil wire rope," the construction of which is explained in the next chapter (Fig. 451). It has the advantage of presenting a perfectly smooth surface, admirably adapted for the running of the grooved pulleys by which the load is suspended. The vessel in which the mineral is conveyed

FIG. 423.

may be any convenient form of bucket or box, supported by pivots around which it can be easily tipped, or the actual mine-waggons may be slung up and the ore carried in them.

Each box, bucket, or waggon, is attached to a hanger suspended from a spindle placed midway between two grooved pulleys or wheels, which rest on the rope (Fig. 423).

The posts or standards are constructed of wood or iron, sometimes with two, and sometimes with four legs, suitably stiffened by braces and held in position by guy ropes or rods (Figs. 424 and 425). The four-legged standards are used for heavy loads or long spans. The distance between the standards varies according to the nature of the country, and is often about 30 to 60 yards; but where the country is much broken by ravines, these short spans are unattainable without standards of an impracticable height, and the cable is then made to stretch across very long intervals without intermediate supports. Spans of 550 yards (500 m.) are not unknown.

The hauling rope must be very flexible, and is made of fine steel wire with a hempen core. The mode of attachment of the load varies with the gradient of the line. If the gradient is less than

*J. Pohlig, "Aerial Ropeways, Otto System."-Trans. Amer. Inst. M.E., vol. xix. 1891, p. 760.

I in 6, the amount of friction necessary for gripping the rope tightly can be obtained by bringing it between two flat iron discs and clamping them together with a screw. One of these discs is rigidly attached to the hanger, and the tightening screw of the other can be loosened automatically by providing it with a projecting lever, which comes in contact with a stop at the terminus.

If the gradient is between 1 in 6 and 1 in 3, the discs are made

with corrugated instead of smooth surfaces. When the gradient exceeds 1 in 3, another device has to be employed; projecting knobs are inserted into the rope at regular intervals, and on meeting with properly arranged stops upon the loads they cause them to travel along. Figs. 426, 427 and 428 show the details of the arrangement.

Each terminus is provided with an iron rail which is fixed So as to meet the rope where the buckets have to be loaded or unloaded; by suitably arranging the end of the rail, the load passes quite smoothly from it to the rope and vice versa.