Engineering Wonders of the World
Volume I

310 ENGINEERING WONDERS OF THE WORLD. pumps to remove the water from the invert of the small tunnel. In one case, where the works were constructed in fine running sand under 15 to 20 lbs. per square inch, compressed air, a somewhat novel method of getting rid of the water was carried out. In this instance it was known that at GRADIENTS. A peculiar feature in connection with the London Tube railways, and one that tends to great economy in the cost of operation, is the method used, where possible, of so grading the tubes that between stations there may be a THE “ DIPPING GRADIENT ” SYSTEM (GRADES GREATLY EXAGGERATED) USED ON SOME OF THE TUBE RAILWAYS. a depth of some 200 feet below the tunnels water-bearing flints would be encountered in the chalk, and as the water-level in the chalk stood at a level several feet below the tubes, it was thought that the water which came by leakage into the tubes would itself drain away by gravity down a bore-hole ; so one was made. This is rather an “ upside-down way ” of dip or depression, each station being, as it were, on a summit. To show that this is nothing new, however, it may be mentioned that so long ago as the year 1833 a model of a spring locomo- . ? Gradients. tive and a short length or track with gradients dipping between the stations was made by some persons interested in railway construction ; and that a largo num- HAMPSTEAD UPHILL GRADE, WITH LEVELS AT STATIONS, AS ON CHARING CROSS AND HAMPSTEAD RAILWAY. doing things, as it is usual to put down borings specifically for the purpose of obtaining water from the chalk, and not for draining away water which it is inconvenient to deal with other- wise. However, in this case complete success attended the experiment, and the railway company now do no pumping whatever, as the water passes down the bore-hole and mingles in the chalk with the great body of water from which Londoners obtain so large a proportion of their supply. ber of the shareholders of the London and Birmingham Railway petitioned the directors to stop the construction of that railway, and also to proceed with the section between Liverpool and Birmingham on the principle of dipping gradients. They maintained that the experimental spring locomotive had demon- strated that, as compared with a level line, a railway with dipping gradients enabled the journey to be done in two-thirds of the time for the same expenditure of power.