CONVEYANCE.] COAL power, boys being employed to push the trams before them to the main roads. In the thin seams jf South York shire and other places, considerable journeys are often performed in this way, the boys known, as " hurriers" or " putters" being obliged to crawl at full length, owing to the lowness of the excavation. As a general rule boys are not allowed to work in collieries when below 12 years of age, but in these thin mines special exemptions are granted, permitting the use of younger boys as putters when re quired. Where the levels are large, horse traction is in common use; the trams are formed up into trains, and from 6 to 15 vehicles are drawn by one horse. A considerable number of ponies are imported into the northern ports of this country from Norway and Iceland for this purpose every year. The supply of horses is, however, becoming scarcer, and the price higher, so that the use of under ground engines is generally adopted where the output is sufficiently large to justify the expenditure. This is done by hauling or, as it is called in the North of England, lead ing the trains of tubs by rope traction. In a large colliery where the shafts are situated near the centre of the field, and the workings extend on all sides, both to the dip and rise, the drawing roads for the coal may be of three differ ent kinds, (1) levels driven at right angles to the dip, suitable for horse roads, (2) rise ways, known as jinny roads, jig-brows, or up-brows, which, when of sufficient slope, may be used as self-acting planes, i.e., the loaded waggons may be made to pull back the empty ones to the working faces, and (3) dip or down-brows, requiring engine power. A road may be used as a self-acting or gravitating incline when the gradient is 1 in 30 or steeper, in which case the train is lowered by a rope passing over a pulley or brake drum at the upper end, the return empty train being attached to the opposite end of the rope and hauled up by the descend ing load. The arrangements for this purpose vary, of course, with the amount of work to be done with one fixing of the machinery ; where it is likely to be used for a considerable time, the drum and brake are solidly constructed, and the ropes of steel or iron wire carefully guided over fric tion rollers, placed at intervals between the rails to pre vent them from chafing and wearing out on the ground. Where the load has to be hauled up a rising gradient, underground engines, driven by steam or compressed air, are now generally used. In some cases steam generated in boilers at the surface is carried in pipes to the engines below, but this can be done with less loss of power by send ing down compressed air in the same way. The use of underground boilers placed near the upcast pit, as in fig. 6, so that the smoke and gases help the ventilat ing furnace, is most convenient in the majority of cases. Water-pressure engines, driven by a column of water equal to the depth of the pit, have also been employed for hauling. These can, however, only be used advantageously where there are fixed pumps, the fall of water generating the power resulting in a load to be removed by the expen diture of an equivalent amount of power in the pumping engine above that necessary for keeping down the mine water. There are four principal methods in which steam power can be applied to underground traction. These, which have been discussed in the fullest manner in the Report of the North of England Institute of Mining Engineers for 1867- 68, are as follows : 1. Tail rope system. 2. Endless chain system. 3. Endless rope system on the ground. 4. Endless rope system overhead. The three last may be considered as modifications of the same principle. In the first, which is that generally used in Northumberland and Durham, a single line of rails is used, the loaded tubs being drawn "out bye," i.e., towards the shaft, and the empty ones returned " in bye," or towards the working faces, by reversing the engine ; while in the other systems, double lines, with the rope travelling continu ously in the same direction, are the rule. On the tail rope plan the engine has two drums worked by spur gearing-, which can be connected with, or cast loose from, the driving shaft at pleasure. The main rope, which draws out the loaded tubs, coils upon one drum, and passes near the floor over guide sheaves placed about 20 feet apart. The tail rope, which is of lighter section than the main one, is coiled on the second drum, passes over similar guide sheaves placed near the roof or side of the gallery round a pulley at the bottom of the plane, and is fixed to the end of the train or set of tubs. When the load is being drawn out, the engine pulls directly on the main rope, coiling it on to its own drum, while the tail drum runs loose pay ing out its rope, a slight brake pressure being used to pre vent its running out too fast. When the set arrives out bye, the main rope will be wound up, and the tail rope pass out from the drum to the end and back, i.e., twice the length of the way; the. set is returned in bye, by reversing the engine, casting loose the main, and coupling up the tail drum, so that the tail rope is wound up, and the main rope paid out. This method, which is the oldest, having been in use for twenty-five years or more in the North of Eng land, is best adapted for ways that are nearly level, or when many branches are intended to be worked from one engine, and can be carried round curves of small radius without deranging the trains; but as it is intermittent in action, considerable engine-power is required in order to get up the required speed, which is from 8 to 10 miles per hour. From 8 to 10 tubs are usually drawn in a set, the ways being often from 2000 to 3000 yards long. In dip workings the tail rope is often made to work a pump con nected with the bottom pulley, which forces the water back to the cistern of the main pumping engine in the pit. For the endless chain system, which is much iised in the Wigan district a double line of way is necessary, one line for full and the other for empty tubs. The chain passes over a pulley driven by the engine, placed at such a height as to allow it to rest upon the tops of the tubs, and round a similar pulley at the far end of the plane. The forward edge of the tub carries a projecting pin or horn, with a notch into which the chain falls which drags the tub forward. The road at the outer end is made of a less slope than the chain, so that on arrival the tub is lowered, clears the pin, and so becomes detached from the chain. The tubs are placed on at intervals of about 20 yards, the chain moving continuously at a speed of from 2^ to 4 miles per hour. This system presents the greatest advantages in point of economy of driving power, especially where the gradients are variable, but is expensive in first cost, and is not well suited for curves, and branch roads cannot be worked con tinuously, as a fresh set of pulleys worked by bevel gear ing is required for each branch. The endless rope system may be used with either a single or double line of way, but the latter is more gene rally advantageous. The rope, which is guided upon sheaves between the rails, is taken twice round the head pulley; or a Fowler s clip pulley may be used. It is also customary to use a stretching pulley to keep the rope strained when the pull of the load diminishes. This is done by passing a loop at the upper end round a pulley mounted in a travelling frame, to which is attached a weight of about 15 cwt. hanging by a chain. This weight pulls directly against the rope ; so if the latter slacks, the weight pulls out the pulley frame and tightens it up again. The tubs are usually formed into sets of from 2 to 12,
the front one being coupled up by a short length of chain