Electric Railway. The proposal that electricity should furnish motive power on railways is nearly as old as the railway-system itself. In 1837, when it was still doubted whether steam locomotives would come into general use, an experiment in electric traction was made by Robert Davidson, who propelled a car on the Edinburgh and Glasgow Railway by an electro-magnetic engine, with a galvanic battery to supply the current. But the cost of producing electricity on a large scale by means of a battery is so great as to make such a method of locomotion impracticable, however perfectly the electric energy may afterwards be converted into mechanical work. And the electro-magnetic motor of those days was an extremely inefficient machine, which did not succeed in utilising more than a small fraction of the electric power supplied to it. The matter consequently fell into complete abeyance, and was not revived until engineers had at their command a much cheaper mode of producing electric energy, and a much more efficient mode of turning it to mechanical account. This came about with the introduction of the Dynamo-electric Machine (q.v.), which gave a cheap means of converting work done by a steam-engine or any other prime mover into the electrical form, and with the recognition that the operation of the dynamo was reversible—that it would serve as a motor, to do mechanical work by the agency of the electric current. Hence it became practicable to work a railway electrically, by having at one station a dynamo to produce the current, driven by a steam-engine, turbine, or any other source of power, and by using this current to drive another dynamo, as a motor, upon the train, electrical connection between the train and the source of supply being maintained by means of conductors with which the train should be kept in contact throughout its course.
This was first demonstrated on a practical scale at the Berlin Exhibition of 1879, by Werner Siemens, who made and worked with complete success a line 219 yards long, on which three carriages, carrying twenty people, ran at a speed of about 7 miles an hour, by means of the current from a fixed dynamo, which was driven by a steam-engine. The current reached the car through a special conducting rail placed between the wheel-rails, and insulated from the ground by blocks of wood. The motor on the car took the current from this rail by the rubbing contact of copper brushes, and the circuit was completed through the car wheels and the ordinary rails. In 1881 a permanent electric tramway, mile long, was established at Lichterfelde (Berlin), where a still simpler plan of conducting the current was employed: the two ordinary rails, insulated from the ground and from one another by wooden sleepers, formed the two conductors. Soon after that a number of electric tramways or railways were constructed in various parts of Europe and a very much greater number are at work in the United States, where, for example, the new St Louis and Chicago line is designed to run the 250 miles between the two cities in hours, with low cars shaped so as to cut the wind, there being a relay current-generating station at every 10 miles. The first permanent elevated electric railway in the United States is that of Chicago (over 16 miles, with 43 stations, in 1895). The Liverpool overhead railway, running the whole length of the docks (6 miles, with 14 stations), was opened in 1893. The City and South London underground electric railway was opened in 1890; and in 1896 the Central London line, also underground, miles long, from Shepherd's Bush to Liverpool Street, was begun, and opened in 1900.
The plan of using the rails themselves as the only conductors is obviously impracticable, except on very short lines and in special circumstances, on account of the difficulty of maintaining good insulation. In some lines, especially in quiet places, a special stiff conducting rail is used, raised from the ground on insulating supports. A stiff conductor, set alongside of the rails, is also used for electric traction on some portions of the New York elevated railroads. In many cases the conducting rail is put in a trench underground—an arrangement which allows this system to be applied to city tram-lines. But in by far the greater number of electrical railways or tramways, especially in America, the conductor is a wire carried on posts overhead, either immediately above the cars or alongside of them. In many instances the current is taken from the overhead conductor by means of a little carriage running on it, and drawn along by the car. An extremely simple overhead system has been suggested by Dr Hopkinson, in which the conductor is a wire, or strand of wires, supported by means of posts, so that it hangs slack over the line, at such a height that a metal rod, fixed on the top of the car, rubs against it. There are two rods—one near the front of the car and the other near the back—and these keep up continuity of contact as the car passes under the supports, from one to another of the slack spans in which the conductor hangs.
When there are several motor cars running on an electric railway at the same time, they are commonly arranged in electrical 'parallel'—that is to say, the motor of every train forms a cross connection between a single pair of positive and negative conducting mains. If, however, the line be divided into a sufficient number of short sections, it is possible to run the trains in electrical 'series,' each train spanning a gap in an otherwise continuous conductor, and the same current passing through all in succession. This plan, which has the advantage of requiring a smaller volume of current (but at a correspondingly greater potential), was patented by Fleening Jenkin in 1882.
All the arrangements for electric traction that have been referred to above are conductor systems. Energy is continuously passing to the car through the conductor which maintains connection between the distant dynamo and the motor on the car, and any break of continuity in the conductor, or any failure on the part of the car to make contact with it, deprives the car instantly of locomotive power. Another serious disadvantage of conductor systems is that under the powerful currents now necessary, escapes of current cause electrolysis of damp earth and rapid corrosion of gas and water pipes. The introduction of storage batteries (see ELECTRIC LIGHT) has made a very important alternative method of electric traction practicable—viz. the storage system, in which each car or train is self-contained as regards power. In this system there are no conductors along the line, but each locomotive is furnished with a set of storage cells, which are charged from time to time by means of a station dynamo, and carry enough energy to last during the trip. The storage system has been put in practice at Antwerp, Hamburg, Brussels, New York, London, and elsewhere, in some cases by placing the cells under the seats of the car, in others by using a separate locomotive car to carry them and the motor. For city tram-lines its advantages are obvious: it makes each car independent, it causes no obstruction of the street by troughs or posts to carry conductors, and it allows existing lines to be utilised for electric traction without change. Its chief drawbacks are the dead-weight of the batteries and the cost of renewing these when they are worn out or injured by the rather rough treatment they receive on the road. In conductor and storage systems alike there is a considerable loss of energy in the successive transformations, amounting generally to 40 or 50 per cent. On short lines this waste should be less when conductors are used; but on long lines the loss which is caused by the resistance of the conductors may be greater than the loss which the charging and discharging of a battery entails.
An important feature in conductor methods of electric traction is the possibility they afford of applying an absolute automatic block system, so as to make it impossible for trains to overtake one another, without any control being exercised from the trains themselves. When the line is divided into sections, it is possible to arrange matters so that the presence of a train on one section has the effect of cutting off the supply of electric energy to the section behind, and thus a train entering the latter finds itself unable to proceed until the train in front has advanced to the section beyond. A number of plans by which this idea may be carried out have been invented by Fleeming Jenkin and by Ayton and Perry. Fleeming Jenkin, too, it was who proposed the word Telpherage, as a distinctive name for electric traction developed on these lines. In one of his systems of telpherage, suitable for transporting minerals or goods in small parcels and at a low speed, the line consists of a series of short spans of steel cable, supported overhead upon stout posts, at a distance of some 70 feet apart. The train is a number of light cars, which hang from the line; they are free to swing, and are spaced and connected together by light coupling rods. A telpher line of this construction, about a mile long, was erected in 1885 at Glynde, in Sussex. See Reckenzaun's Electric Traction in Railways and Tramways (London, 1892), and Crosby & Bell, The Electric Railway (New York, 1893).