estate. The working pressure is 400 lbs. per square inch. The pumping station contains duplicate machinery, and is designed to work from 80 to 100 lifts of this class. The only water used is that required for filling the system of pipes, and to make up waste.

THE CITY AND SOUTH LONDON RAILWAY.*

The City and South London Railway Company was incorporated by an Act of Parliament in 1884, and empowered to construct its line from King William Street to the "Elephant and Castle," Newington, and by an Act of 1887 the line was extended to the Clapham Road at Stockwell. An Act of 1890 authorizes a further extension to Clapham Common.

The railway at present constructed (Fig. 1, Plate XL.) is rather more than three miles in length. The up and the down lines are carried in separate tunnels placed at such a depth under the surface of the roads as to avoid all interference with sewers and other underground structures. Except where the line is under the river and an adjoining wharf, it passes throughout its whole length under the streets -thus enabling it to accommodate the great stream of passenger traffic between the City and the Borough, Newington, Kennington, Stockwell. etc., now passing over London Bridge, without appreciable deviation from the present course of the traffic. There are stations at the Monument, King William Street; Great Dover Street (Borough); the "Elephant and Castle"; New Street, Kennington; the Oval; and Stockwell (Fig. 2, Plate XL.).

At each station powerful hydraulic lifts are provided in addition to stairways for the purpose of giving casy and speedy access between the street and the platform levels; and in order to avoid double establishments on opposite sides of the road, at each intermediate station, the up and down tunnels are placed at different levels, so that passengers may pass readily from the lifts or stairs on one side of the road to either platform.

The steepest gradient against the load is about 1 in 30.

The traffic is worked by electricity. The current, generated at Stockwell, is carried by a main insulated conductor through both tunnels. Between the rails is placed, upon glass blocks resting upon the cross sleepers, the working conductor of steel. This conductor is connected with the main conductor at the signal boxes along the line. Upon each locomotive are three collectors or shoes resting or sliding upon the working conductor, and taking up the current as required by the locomotive. A lever on the locomotive enables the driver to regulate the current or to cut it off altogether. Each locomotive, weighing about 10 tons, contains two motors capable of working up to 100 horse-power. By making the axles of the wheels the armatures, all gearing has been dispensed with. The rails form the return conductor and complete the circuit.

Steam locomotives being excluded, the question of ventilation is a very simple one; * The illustrations are reproduced by permission from the Engineer.

and the traffic in each tunnel being always in one direction, a continuous current

of air is established.

The whole of the

power required for

traction and lifts is concentrated at one point, at Stockwell. Hydraulic pressure and return water pipes are placed throughout the length of the line for the working of all the lifts, and the drainage of the line is secured by the use of small injector hydrants connected with the high pressure main.

The carriages are of the longitudinal type, with platforms and entrances at the ends.

In connexion with the permanent way, no ballast is used, the sleepers resting upon the iron lining of the tunnels.

Some details of

the mode of construction of the works may be interesting. The two tunnels for the up and down lines being absolutely separate and distinct between the termini, they were

Fig. 6.

capable of being carried in any desired position relatively to each other. Commencing side by side in the City (Fig. 6), the down line falls more rapidly than

the up, in order that when Swan Lane is reached the former may be immediately under the latter, because, except in this position, they could not be constructed without encroaching upon private property or rights. In this position they pass

TEMPORARY STAGE & SHAFT

NORTH

THAMES

HIGH WATER

RIVER

Fig. 7.

LOW WATER

UP LINE

DOWN LINE

CROSS HEADING

under the northern foreshore of the river Thames, but before the southern shore is reached they are again side by side, and at each intermediate station, as already described, they are at different levels.

Each of the tunnels is 10 feet to 10 feet 6 inches in diameter, and is formed of rings of cast iron segments (Figs. 3 and 4, Plate XL.) bolted together through internal flanges. The rings are 1 foot 8 inches long.

The first operation was to erect a staging in the river at Old Swan Pier for the purpose of sinking a temporary shaft, and constructing the river tunnels (Fig. 7). An iron lined shaft, 13 feet in diameter, was then sunk in the bed of the river, through sand and gravel into the London Clay. From this shaft were driven the two tunnels, northwards to the City terminus, and southwards to near the Borough Station. The second tunnel was driven immediately under, and within 4 feet 6 inches of the upper tunnel, for a considerable length; and after the river tunnels had been driven, work was commenced at the Borough, and subsequently in the City, and at the "Elephant and Castle," and, at a later date, the extension to Stockwell was proceeded with.

The first or upper tunnel has a dip under the river, and the second or lower tunnel rises continuously from the shaft (Fig. 7). A cross heading joining the two tunnels at the lowest point of the first provides for draining that tunnel to the sump at the temporary shaft, whence the small accumulation of water arising from condensation, is discharged by an injector hydrant, deriving its supply of high pressure water from the hydraulic main already referred to.

The mode of constructing the iron tunnels is very simple, and can be described in a few words. A steel cylinder, overlapping (like the cap of a telescope) the forward end of the iron tunnel, is provided, near its front end, with a strong diaphragm or face, having an opening or door in it (Fig. 8).

Beyond this face project adjustable steel cutters and wedges (Fig. 9), and behind it are ranged, round the circumference inside, six

STEEL CYLINDER

A

HYD' PRESS

hydraulic presses, so fixed as to abut against the last ring of completed tunnel. As the material is excavated from before the cap or shield by the miners and the action of the cutters and wedges, and thrown back through the opening in the face, the shield is forced forward by the hydraulic presses. The shield thus clears out an exact circle somewhat larger than the outside diameter of the iron lining of the tunnel. The small annular space thus left is filled with grout, composed of Blue Lias lime, by means of an apparatus to be presently described. When the shield has been forced forward sufficiently far a fresh ring of iron lining is built up inside, and under cover of the overlapping steel cylinder. Eight

of these rings were regularly erected

HYD
PRESS

HYD

PRESS

CAST IRON SECMENTAL RINCS OF END OF

COMPLETED TUNNEL.

STEEL CYLINDER

HYD' PRESS

A

SHIELD

TRANSVERSE & LONGITUDINAL SECTIONS OF TUNNEL

END AND SHIELD.

Fig. 8.

AJUSTABLE STEEL

CUTTERS >>

daily, representing a rate of progress of 13 feet 6 inches at each face, the maximum rate of speed being 16 feet per day.

A special apparatus was used for grouting (Fig. 5, Plate XL.). The lime was mixed with water in a cylindrical vessel, the lid closed, and compressed air, at a pressure of about 30 lbs per square inch, from a compressor at the shaft, was admitted through the upper valve, and the lower valve being opened, the contents of the vessel were discharged through a short length of hose pipe, a branch and a nozzle, into the annular space left outside the iron lining by the advance of the shield, holes being provided in each segment of the lining for the purpose. The grout was first of all forced through the lower holes in the segments until it appeared at the holes above; the lower holes were then plugged, and the grout forced into the next holes

Fig. 9.

above, and so on until the grout came out at the topmost hole in which the nozzle was then inserted, and the grout forced in by the full pressure of air until the space

was completely filled. By this appliance the iron lining was surrounded by a coating of lime or cement. The paddles upon the spindle were kept continually in motion to mix the grout, and to prevent its setting in the pan.

The tunnels were driven for considerable lengths through sand and gravel under water, at a lower rate of speed, but very successfully, under compressed air. It is interesting to note that since these tunnels were commenced several important tunnels have been constructed or are in progress, on the same plan, in this country and in America.

Mr. J. H. Greathead is the engineer who designed and executed the works, Sir John Fowler and Sir Benjamin Baker being consulting engineers. The main contract for the construction of the subway between the City and Newington was carried out, in part, by Mr. Edmund Gabbutt, of Liverpool, and the extension to Stockwell and the completion of the City section have been carried out by Messrs. Walter Scott & Co., of Newcastle-upon-Tyne.

The electrical plant and locomotives were constructed by Messrs. Mather & Platt, of Manchester, having been designed by Dr. Edward Hopkinson of that firm. Dr. John Hopkinson acted as their consulting engineer, and Mr. J. A. Grindle as their resident engineer throughout. The hydraulic lifts and plant were made by Sir W. G. Armstrong, Mitchell, & Co., Limited.

At the depôt at Stockwell the electricity for working the line is generated by three engines, made by Messrs. John Fowler & Co., Limited, of Leeds, each capable of working up to 375 horse-power and each driving an Edison-Hopkinson dynamo, the current from any two dynamos being capable of working the trains on the line at any time, leaving the third in reserve. The maximum tension of the current is 500 volts.

In the same engine house are three engines and pumps, any two of which will work the hydraulic lifts at all the stations. The water is delivered by the pumps into the accumulator at the engine house, at a pressure of 1,200 lbs. per square inch, and after having passed through the lifts and having done its work it is returned to a tank in the engine house to be taken again by the pumps.

The engines and carriages are conveyed from the railway to the depôt on the surface, by means of an inclined road worked by a small hauling engine.

The boilers are set on the Livet improved principles, by which means and by the use of the Vicars mechanical stokers, the formation of smoke is prevented, and considorable economy of fuel secured.