In the Sprague system each car is equipped with a controlling device operated by a pilot motor, the motor being operated through a cir cuit controlled by the motorman. The system is to a considerable extent automatic, as the rate at which the different positions of the con troller on each car are changed depends upon the flow of current into the motors, and is not determined by the motorman. This is an im portant feature of the apparatus and makes the acceleration uniform, and at a rate to give the greatest efficiency. The General Electric method of control is somewhat different from this, each car having a master-controller, very much like the ordinary tramway controller— the speed at which the current is cut into the motors being determinedthe rate at which the motorman turns the of the con troller. In the Westinghouse controller, the ap paratus which supplies current to the motor is operated pneumatically, the valves of the pneumatic system being worked by magnets in a local circuit, which has as a source of energy a few storage batteries on each car and is op erated by a master-controller on each car of the train. This makes all the operations inde pendent of the line current and gives very posi tive and efficient action.
Overhead Trolley For collecting the current to run electric cars, a number of devices were used, until finally Sprague's suc cess at Richmond fixed a type of collecting de vice that is still considered standard in this country and is largely used abroad. Until actu ally determined by experiments, it seemed im possible that a moving contact device could col lect the current necessary to supply the energy to the cars without such destructive sparking and heating that it would be inoperative. In the first experiments on electric railroading, the current was collected from the rails; afterward it was collected through small carriages running on the overhead wire; and finally it developed into a rotating wheel having a contact on the underside of the trolley wire and pressing against it by some spring arrangement. What is called a °bow" trolley was first used — that is, a wire bent into the shape of a bow, press ing against the underside of the wire, but hav ing no rolling contact. This is still used to a considerable extent abroad and presents some advantages over the trolley wheel used in this country. A number of modifications of both of these systems have been devised and employed. The overhead trolley wires, from which the current is collected, are usually of copper; they are either suspended from insulators fastened to a span wire between poles on the two sides of the track, or from brackets fastened to a pole and projecting over the track. In this country they are almost universally placed over the centre of the track, but abroad they are sometimes placed on the side of the •road, the trolley being so constructed as to make a side bearing contact.
Underground From the earliest application of electricity to railways, attempts were made to do away with the overhead wires used in the ordinary trolley systems. Conduits having a slot through which a current-collecting device could pass were placed beside the tracks or between the rails; conductors were placed in these conduits and the collecting devices on the cars were made to bear against the conductors. At first the conduits were not large enough, not enough space was given for insulation, and the results were unsatisfactory. The first success ful system to be installed was a tramway at Budapest, designed by the Siemens Company. Here the conduit was on the side of the track, the tram rail forming part of the slot. The con ductor was supported from below by insulators and the system was constructed on a larger scale than had been previously employed— the details were carefully worked out and the road has operated successfully from the time of its installation. In the meantime, in this country, the necessity of some such system in the cities of New York and Washington, where overhead wires were not permitted, had forced the differ ent electrical companies to take up seriously the question of conduit construction, with the result that successful systems were worked out for both Washington and New York, the sys tems being practically the same. The slot in these systems is in the middle of track. The conduit is constructed as follows: Cast-iron yokes supporting the tramrail and slot rail are placed at intervals of five feet, the rails are attached to the yokes and the whole structure is blocked up in its proper position; then sheet steel is placed between the yokes, forming a tunnel of the proper dimensions, and concrete is packed around the yokes and the forms, sup porting the structure in its proper position and forming a tunnel for the conductor rails. The steel forms are then taken out. The conductors are made of T-iron, held from above by porce lain insulators placed in cast-iron boxes along the track. The details of the different systems that have been installed vary, but the above is practically the standard type of construction. The current for the car is collected by means of what is known as the plow, which passes through the slot and has two cast-iron contact shoes held against the conductor rail by springs; the rail is supported on cross-rods on the car and has a wide limit of lateral motion. It is usual to place duCts beside the track, these ducts containing the feed wires that are connected at various intervals with the conducting rail.