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and sealing the composition; and Fig. 5 represents the valve as finally left after the carriage has passed by.

The same letters refer to the same parts in all the figures.

The moving power is communicated to the train by means of a continuous pipe or main A, laid between the rails, and divided by separating valves into suitable and convenient lengths for exhaustion. A partial vacuum is

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formed in each length of pipe by steam engines and air pumps fixed at intervals along the road. The separating valves are opened by the train as it advances, without stoppage or reduction of speed.

A piston B, which is made to fit air-tight by a leather

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packing surrounded by tallow, is introduced into the main pipe, and connected with the leading carriage

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of the train by an iron plate c, which travels through a longitudinal opening made along the top of the pipe

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for its whole length. This opening is covered by a valve G, extending also the whole length, formed of a

strip of leather riveted between iron plates; the top plates are wider than the groove, and serve to prevent the external air from forcing the leather into the pipe when the vacuum is formed; the lower plates fit the groove when the valve is shut, as shown in Figs. 4 and 5, and, by making up the circle of the pipe, prevent the air passing the piston. One edge of this valve is securely held down by iron bars a a fastened by screw bolts bb to a longitudinal rib c, cast on the pipe on one side of the opening; and the leather between the plates and the bar, being flexible, forms a hinge as in a common pump valve; the other edge of the valve falls on the surface of the pipe on the opposite side of the opening, thus forming one side of a trough F, as shown in Figs. 4 and 5. This trough is filled with a composition of bees'-wax and tallow, which is solid at ordinary temperatures, but softens when slightly heated. The composition, when so heated and pressed down, adheres to the edge of the valve, which forms one side of the trough, and to that part of the pipe which forms the other, and so makes an air-tight junction between them.

Supposing now the air to be exhausted from the part of the tube in front of the piston; the atmosphere having free access to the part behind it, will press upon it with a force proportional to its area and the degree of exhaustion; and the effect of this pressure will be to propel the piston along the tube, dragging with it the leading carriage to which it is attached, and the train coupled behind.

As the piston advances, the valve G must be raised to allow the connecting plate c to pass, and this is effected by four wheels HHHH, fixed to the piston rod

behind the piston: the aperture thus formed serves also for the free admission of air to press on the back of the piston. When the wheels have passed by, the valve falls again by its own weight.

But by the operation of raising the valve out of the trough, the composition between it and the main pipe has been broken, and the air-tight contact must be reproduced. To effect this, another wheel R (Fig. 4) is attached to the carriage, which serves to ensure the perfect closing of the valve by running over the top plates immediately after the piston rod has passed; and a copper tube or heater N, about five feet long, filled with burning charcoal, is also fixed to the under side of the carriage, and passes over the surface of the composition, softening it and pressing it down, so that when on cooling it becomes solid, it seals the joint air-tight as before. Thus each train, in passing, leaves the pipe in a fit state to receive the next train.

A protecting flap or cover 1, formed of thin plates of iron about five feet long, hinged with leather, is made to lie over the valve, to preserve it from snow or rain; the end of each plate underlaps the next in the direction of the piston's motion, being lifted up by wheels D (Fig. 3), fixed under the advancing carriage, and allowed to close again as it retires.

The parts above described constitute the essence of the plan. Much ingenuity and care were bestowed on the arrangement of other details, such as the entrance, exit, and separating valves, the mode of effecting junctions and crossings, the construction of the tube, the manner of connecting together the pipes of which it was formed, the

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