On the Blackwall railway the traffic is carried on by means of ropes worked by stationary engines, erected at each end of the line. This system has been adopted on account of the number of intermediate stations along the line, the line being only about 3 3/4 miles long, and having five intermediate stations. And had locomotives been employed, the time lost in stopping and starting the trains would have exceeded that occupied in traversing the lines. The line is worked as follows: - supposing the train to be that which ispassingfrom London to Blackwall; at each of the intermediate stations is one or more carriages, for the conveyance of the passengers from those stations to the Blackwall terminus, and at the London terminus is ranged what may be termed " the train," consisting of one or more carriages for the Blackwall terminus, and one or more for each of the intermediate stations; the Blackwall carriages being the first in the train, and those for the intermediate stations being ranged in the order of the proximity of the stations to the Blackwall terminus.
The several carriages being attached to the rope, the engine at the Blackwall end of the line is put in motion, and the carriages from the intermediate stations arrive in succession, at intervals, at the Blackwall terminus; the carriages, being detached from the rope (without stopping the rope) as they successively arrive within a certain distance of the terminus, and being stopped at the proper point by a powerful brake attached to each carriage. In like manner the carriages for the first intermediate station from London (and which carriages will be the last in the train) will be detached from the rope as they arrive within the prescribed distance from the station, and so on with the carriages for the remaining stations, until the leading carriages from London arrive at the Black-wall terminus, which completes the operation, and the rope is then stopped. This system of working the line has the advantage of delivering the passengers at each intermediate station without detention to the other carriages, but it is attended with this inconvenience, that the intermediate stations have no communication one with the other, but only with the termini: for instance, a person could not proceed from Stepney to Poplar, but would have to go on to the Blackwall terminus.
The accompanying figure represents the apparatus for attaching the carriages to the rope, which combines the advantage of a powerful grip with a ready means of casting off the rope. a is a forked lever turning upon a fulcrum at b, at the fore end of the carriage, and carrying within the fork the hanging clutch or nipper c; d is a pinion supported by the lever a, and working in a toothed standard e, which is bolted to the frame of the carriage; by turning this pinion by means of the handlef, the lever a can be raised to any required position, and may be retained therein by the pall g, which takes into the teeth of a ratchet, h, cut on the back of the standard e: i is the traction rope, k a block of wood attached to the under side of the carriage, against which the rope is firmly jammed when in action; m, is a forked cheekpiece attached to the side of the block to prevent the rope flying off laterally. When the rope is detached, the apparatus assumes the position indicated by the dotted lines. To attach the carriage the rope is lifted on to the claw of the nipper, which is then thrown into a vertical position, and the lever a is wound up until the rope is bound firmly to the block, and the pall g is put down.
To release the rope, the pall is thrown back, and the lever a falls into a horizontal position, and the nipper being thrown into the inclined position shown by the dotted lines, the rope is thrown off.
The railway is worked by two pairs of stationary engines, of 400 and of 200 horse-power respectively, at the Minories and Blackwall termini. The ropes are not worked on the plan of endless ropes, but there are two distinct ropes, one to each line, extending along the length of the railway, guided by grooved pulleys, and coiled round drums, twenty-two feet in diameter, situated at each end of the line, and worked by the engines; the one drum giving out the rope as fast as the other winds it up, so that each rope is twice the length of the railway. The drums are formed like sheaves, or pulleys, with a very deep groove, which becomes gradually narrower as it approaches the centre, so that the rope, when coiled upon the drum, forms numerous layers; and this tends in some measure to equalize the load upon the engines; for, at starting, when the number of carriages is greatest, the virtual diameter of the drum is least, and the advance of the train during a revolution of the drum is, consequently, least; but, as the train advances and becomes lighter, by a portion of the carriages being detached as they successively arrive at the intermediate stations, the virtual diameter of the drum is increased by the additional layers of rope it has received, and the speed is consequently proportionately increased.
The carriages run each way upon each line; and' the signals for starting, and the general working of the train line, are given by the electric telegraph. At first, hempen ropes were employed, but, owing to the inconvenience and delay occasioned by their frequent breakage, wire ropes, with swivels at given distances, have been substituted; and now, in about 2,000 journeys each way per month, not above two fractures occur. The wire rope now used is formed of six strands laid round a hempen core, and each strand is composed of six wires, also laid round a hempen core. In a paper by Mr. A.J. Robertson, read at the Institution of Civil Engineers, it is stated, that the power to move the rope alone was about 200 horse power, for a hempen rope, and with the wire rope, on account of its greater weight, it required about 250 horse power. The expense of working the engine and rope is stated to be about fourteen-pence per train per mile, but the author observes that the question of expense must not be considered abstractedly; it must be remembered that the traffic could not be carried on at the requisite speed by locomotive engines if they had required to stop seven times in 3 1/2 miles, - it was, therefore, a question, whether the system of rope traction, by which the traffic could be carried at a given speed, or whether the intermediate traffic, should be abandoned.
The latter, commercially speaking, could not be done, and the rope system is therefore persevered in.*