The Thames Subway at Tower-Hilldetails

Several illustrations were lately given of the works in progress for the construction of the subway or tunnel under the Thames, from Tower-hill to Tooley-street, Southwark, designed and carried through by Mr W. H. Barlow, the engineer. It is now complete and ready for traffic. The subway consists of a narrow tunnel uniting two vertical shafts, the mouth of one being on Tower-hill and the other is in Vine-street, Toolet-street. The tunnel is lined with iron tubing, bolted together in short lengths by flanges projecting on the internal surface. This tube is 7ft. in clear internal diameter, or 6ft 8in between the flanges, and carries a railway of 2ft 6in gauge.

On the railway runs an omnibus conveying twelve passengers. The tube is about a quarter of a mile in length, and sinks from both ends towards the centre with a gradient of about 1 in 30. The omnibus is of iron—light, but very strong, and runs upon eight wheels. It is connected with a rope of steel wire by means of a gripe that can be tightened or relaxed at will. At each end of the tunnel this wire runs over a drum worked by a stationary engine. The declivity of the tunnel is such that, when once the omnibus is started, it requires only a small amount of traction, and the momentum acquired during its descent will carry it a long way up the opposite slope. It is said that the strain on the rope will never exceed 2cwt. The omnibus is provided with brakes, so that its motion is completely under the control of the man in charge.

At each end of the tunnel it is received by buffers, or catches, which are connected with very strong springs of vulcanised indiarubber.

The shafts at each end of the tunnel are 60ft in depth, and are lined partly with brickwork and partly with iron tubing. Within the shafts are lifts, carrying six passengers at once, and these lifts are raised and lowered by the same engines that work the drums. Each lift has a counterpoise equal to its own weight and to that of three average passengers; so that the weight of three passengers represents the maximum of work that will be demanded from the engine, either for raising or lowering.

At the top of each lift is a contrivance by which a breakage of the suspending chain would close iron claws upon the lateral guiding-rails, and would bring the machine to a standstill in the course of a few feet. The ascent of these lifts is checked by springs of steel and indiarubber, which the engine employed would not be strong enough to break. The wheel over which the suspending-chain runs is also dragged, so to speak, by revolving fans; and too great rapidity of either ascent or descent seems to be rendered impossible.

The arrangements visible from above are very simple. The upper opening of each shaft is covered by a small square building, at the door of which pas sengers take their tickets, then enter and descend in the lift. On reaching the bottom they find a space of a few feet between the shaft and the buffers fitted up with benches, as a waiting-room. When the omnibus arrives and has discharged its load, those who are waiting step in and start off for the other end. The descent of the shaft occupies twenty-five seconds, and the omnibus journey seventy seconds; so that a passenger may descend into the shaft at Tower-hill and emerge in Vine-street in a minute and three quarters from the time of his descent.

Allowing for all ordinary causes of detention—such as missing the lift at the moment of its descent, or being just too late for the omnibus—the journey from point to point cannot occupy more than five minutes. The lifts, as they only carry half as many passengers as the omnibus, will make twice as many journeys; and it is intended to give priority of ascent to first-class passengers who pay twopence while the second class pas sengers pay one penny. (p. 385)