It was not until 1870, when Gramme had improved the dynamo, that power was practically transmitted in this way, and applied to pumping water, and other work. Since then great progress has been made, and electricity is now recognised, not only as a rival of steam, but as the best means of distributing steam, wind, water, or any other power to a distance, and bringing it to bear on the proper point. The first electric railway, or, rather, tramway, was built by Dr. Werner von Siemens at Berlin in 1879, and was soon followed by many others. The wheels of the car were driven by an electric motor drawing its electricity from the rails, which were insulated from the ground, and being connected to the generator, served as conductors. It was found very difficult to insulate the rails, and keep the electricity from leaking to the ground, however, and at the Pans Electrical Exhibition of 1881, von Siemens made a short tramway in which the current was drawn from a bare copper conductor running on poles, like a telegraph wire, along the line. The system will be understood from figure 77, where L is the overhead conductor joined to the positive pole of the dynamo or generator in the power house, and C is a rolling contact or trolley wheel travelling with the car and connected by the wire W to an electric motor M under the car, and geared to the axles. After passing through the motor the current escapes to the rail R by a brush or sliding contact C', and so returns to the negative pole of the generator. A very general way is to allow the return current to escape to the rails through the wheels. Many tramways, covering thousands of miles, are now worked on this plan in the United States. At Bangor, Maine, a modification of it is in use whereby the conductor is divided into sections, alternately connected to the positive and negative poles of two generators, coupled together as in the "three-wire system" of electric lighting (page 119), their middle poles being joined to the earth --that is to say, the rails. It enables two cars to be run on the same line at once, and with a considerable saving of copper. To make the car independent of the conductor L for a short time, as in switching, a battery of accumulators B may be added and charged from the conductor, so that when the motor is disconnected from the conductor, the discharge from the accumulator may still work it and drive the wheels. Attempts have been made to run tramcars with the electricity supplied by accumulators alone, but the system is not economical owing to the dead weight of the cells, and the periodical trouble of recharging them at the generating station.