ing success was that put in at Richmond, Va., by F. J. Sprague in 1887, and most of the features that have been developed and used in our present street-systems of electric traction are found in Sprague's road. These features are one or two motors supported under the cars and geared to the axle; a switch and controller on the platform by which the speed and direction of the motor can be controlled; a single, overhead wire, suspended over the track by insulating supports, for bringing the current; a trolley-wheel carried on a pivoted pole from the car-top to connect the trolley-wire with the motor; a return-circuit through the rail and ground to the power-station. The currents are generally used at a pressure or potential of 500 volts. The current for the trolley-wire is carried by feeders, large wires, which run overhead (or underground in large cities) from the power-station, and are connected at various points with the trolley-wire. The return-currents through the ground have introduced most troublesome problems, owing to the electrolytic action on pipes for water and gas and on street-foundations. (See Electrolysis.) For means of suspension of motors from car, special trucks required, methods of control of motor-speeds, the question of lines and line-insulation and other special engineering problems that have been so successfully met, the reader must consult the technical books and journals. The overhead trolley-wire has been replaced in some large cities by an underground conduit-system and for most elevated railroads by the third-rail system. The underground conduit-system is used in Washington, D. C., in New York city and in several European cities where the overhead wire was not considered safe, and not sightly. A small tunnel or conduit runs below the surface between the tracks, and in this is a slit for an arm which extends down from the car. The trolley-wire is carried on insulated supports in this conduit, and contact is made with it by brushes on the arm from the car above. The success of this system depends on the maintenance of insulation of the wire in the conduit, often a difficult problem owing to moisture and dirt, but successfully solved in the cities mentioned. The installation of the conduit-system is very costly, and pays only in large cities where the traffic is large. In the third-rail system an ordinary steel track-rail is carried on the insulators, supported on the wooden sleepers about a foot to one side of the track. This third rail takes the place of the trolley-wire. It has proved successful on elevated railways, as in Chicago, and is to be installed on the New York elevated railroads.
A STREET-CAR MOTOR
The electric railway has practically superseded horse and cable-cars for general urban and suburban purposes. It was introduced in 1887. By 1890 there were over 2,000 miles of track operated by electric traction in the United States, as against 6,000 by horses, and 500 by cable. In 1911 there were 40,089 miles operated electrically. The number of electric cars in the United States is to-day 89,601. The capital invested in this industry of only two decades is over two billions of dollars, and the net revenue for 1911 was $195,324,698. (McGraw Electric Railway Manual, 1911.) The power-plants of some of the electric railways are the largest known. A single dynamo for a New York plant has an output of 3,500 K. W. or about 4,600 H. P. The Electric Railway Review estimates that the electric cars carry nearly 20,000,000 passengers per day in the United States. The reason for this rapid increase of electric railways is due to their being cheaper and more rapid than other means of transit. In New York city the percentage of operating expenses to gross receipts for horse railways in 1900 was 73.6%, for cable 51% and for electric 40.5%, and these figures agree with those of many other cities. The electric-railway systems have extended far out into the country-districts, making those districts residences for workers in the cities. They also to-day form connecting lines between cities. One can go from Portland, Me., through Boston to New York city by using the trolley-lines connecting the intervening towns. For underground railroads the electric system has not only the advantages of economy and efficiency but that of producing no smoke. The London Metropolitan Underground road is operated by electricity, and the new underground road in New York city uses the same method. At present no long overland trunk-railroad is operated by electricity, although such schemes have been suggested for the lines between Boston, New
