Compressed air and coiled springs may both be consigned to pigeon-holes, labelled respectively “doubtful” and “impossible,” there being of the former scarcely half a dozen examples in Great Britain, though in America it is said to have worked well and on an extensive scale. Cable traction has many advantages, and for a long time was successfully adopted in America, but is now abandoned. With the funicular system, in vogue in Edinburgh, Birmingham, Paris, and Melbourne, travellers have long been familiar. Where a large number of cars are employed, it has the advantage of cheapness in working, and the machinery does not easily get out of order. But the initial cost is very heavy, and it is not suitable for complicated lines, or for tramways with several branches; and therefore extensions, unless straight, are almost impracticable, though it is superior to all others, save that of electricity, for very severe gradients. As the cable moves at a uniform rate, a car can neither vary its speed nor reverse its course. Then there is a difficulty in dealing with the gas and water-pipes during construction (that is, if they are near the surface), and the conduit forms a receptacle for street refuse, and becomes insanitary. But the chief defect is that three-fourths of the total power required to haul the cars is absorbed in driving the cable. On a small scale, and with but little success, gas traction has been recently tried. There is a difficulty in starting the engines, therefore they have to work continuously, which causes the unpleasant noise familiarised to us by petrol-driven motor-cars when standing still. There is a decided smell from the “exhaust” of the engine; the vibration is considerable; and, as at present designed, the cars cannot mount a moderately steep hill. Steam traction has been in use for some time, but has not improved, and is not popular. Great wear and tear of the track is caused by the weight of the locomotive, and the public object to the long intervals of service, consequent upon the necessity, for economical reasons, of using large cars. Steam involves sulphurous gases and general dirtiness, besides the apprehension, fanciful or real, of an occasional “blow up.” VARIOUS METHODS OF ELECTRIC TRAMWAY TRACTION Dismissing all these systems, we turn to electricity, as admittedly the best agent for tramway traction, and, until some marvellous discovery displaces it as a force, likely to remain and to become universally adopted. Blackpool was first in the field with an electric tramway in 1883. Several other provincial districts followed suit, including Bristol and Stockton-on-Tees. London, in 1900, welcomed the completion of Mr. J. Clifton Robinson’s great scheme for electrifying that portion of the London United Tramways running between Hammersmith and Kew.