The question of gearing was a troublesome one. The armature shaft of the motor was at first connected by friction gearing to the axle of two wheels of the locomotive. Later a belt and pulleys were used. An idler pulley was used to tighten the belt. When the motor was started and the belt quickly tightened the armature was burned out. This happened a number of times. Then Mr. Edison brought out from the laboratory a number of resistance-boxes, placed them on the locomotive, and connected them in series with the armature. These resistances would permit only a small current to flow through the motor as it was starting, and so prevent the burning-out of the armature coils. The locomotive was started with the resistance-boxes in circuit, and after gaining some speed the operator would plug the various boxes out of circuit, and in that way increase the speed. When the motor is running there is a back-pressure, or a pressure that would cause a current to flow in the opposite direction from that which is running the motor. Because of this back-pressure the current which actually flows through the motor is small, and the resistance-boxes may be safely taken out of the circuit. Finding the resistance-boxes scattered about under the seats and on the platform as they were a nuisance, Mr. Edison threw them aside, and used some coils of wire wound on the motor field-magnet which could be plugged out of the circuit in the same way as the resistance-boxes. This device of Edison's was the origin of the controller, though in the controller now used on street-cars not only is the resistance cut out as the speed of the car increases, but the electrical connections of the motor are changed in such a way as to increase its speed gradually. Fig. 56 shows Edison's first passenger locomotive. [Illustration: FIG. 56--EDISON'S FIRST PASSENGER LOCOMOTIVE] The news of the little electric railway at the Industrial Exposition in Berlin was soon noised abroad, and the German inventor received inquiries from all parts of the world, indicating that efforts would be made in other countries to develop practical electrical railways. The firm of Siemens & Halske therefore determined to build a line for actual traffic, not for profit, but that Germany might have the honor of building the first practical electric railway. The line was built between Berlin and Lichterfelde, a distance of about one and a half miles. A horse-car seating twenty-six persons was pressed into service. A motor was mounted between the axles, and a central-station dynamo exactly like the motor was installed. As in Edison's experimental railway, the two rails of the track were used to carry the current. This electric line replaced an omnibus line, and was immediately used for regular traffic, and thus the electric railway was launched upon its remarkable career. The first electric car used for commercial service is shown in Fig. 57.