railway, and accordingly obtained permission to lay down, at their own expense, an experimental length upon a short line at Wormwood Scrubs, which had been made to connect the London and Birmingham and the Great Western Railways with the Kensington Canal, and which, though only a mile or two in length, was dignified with the name of the 'Birmingham, Bristol, and Thames Junction Railway.' A vacuum pipe, half a mile long and nine inches internal diameter, was laid down on the part of the line between the Great Western Railway and the Uxbridge Road, where the gradient was about 1 in 115, and where therefore the efficiency of the power in ascending inclines was put to the test.

This was set to work in June 1840; and as it was a complete exemplification, on a real scale, of the proposed plan of atmospheric propulsion, it may be as well to insert in this place, once for all, the description of the apparatus as given by the inventors.

The accompanying figures will serve to illustrate the description.

Fig. 1 is a general side view of the front part of the train and the atmospheric tube, the latter being delineated partly in longitudinal section to show the piston, and its attachment to the leading carriage.

Fig. 2 is a transverse section of the same parts.

Figs. 3, 4, and 5 are transverse sections of the tube only, enlarged to show the details more clearly, and to explain the action of the valve.

In fig. 3 the valve is shown open, the piston passing through; fig. 4 shows the method of closing the valve

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

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

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

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

FIG. 5.

μα

A

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 H HHH, fixed to the piston rod