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Page:Popular Science Monthly Volume 24.djvu/768

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748
THE POPULAR SCIENCE MONTHLY.

fuel, it possesses many points of superiority over the present cumbersome, noisy, smoky locomotive. Indeed, in long passages such as those in the mines at Zankerode, where a Siemens electric railway is now running, a steam-locomotive would be not only undesirable but impossible.

In the Zankerode-mine railway, the current is sent from the dynamo along the roof of the tunnel through one of the inverted T-rails shown in Fig. 2, which thus acts as a conductor, and upon which slides a contact-carriage connected with the motor on the car by one of the flexible conductors, also shown. The return current coming from the motor goes to the other inverted T-iron by the other flexible conductor, and thence back to the dynamo.

The most extensive electric railway now in use is that constructed by Messrs. Siemens in Ireland, which runs from Portrush to Bushmills, a distance of about six miles. As at present operated, a dynamo revolved by a stationary steam-engine supplies the necessary current; but it is intended to utilize the waste power of a waterfall situated about three quarters of a mile from the end of the line, as soon as the necessary works can be constructed. The cost of running the electric locomotives is found to be less than that of running steam-locomotives over the same track, and it will be much reduced as soon as the utilization of the power of the waterfall (twenty-four feet) is made possible.

By another system of electric propulsion, it has been attempted to carry batteries of electric accumulators in the car, instead of conveying the current to the car by conductors. By this system, as yet undeveloped, a large stationary engine is to be used to turn a dynamo which will generate a current that will charge the accumulators or "storage-batteries," as they are sometimes called; these accumulators to lie under the seats or in some other convenient place, and render the current to the motor direct.

As accumulators may play an important part in electric railroading, and as much that is incorrect has appeared in print concerning them, a few words of description may not be out of place.

Probably the most prevalent conception of an accumulator is a box or other receptacle in which electricity is put and from which it can be drawn when desired; and for practical purposes this idea is sufficiently correct. From a scientific point of view, however, it is more satisfactory to regard an accumulator as a battery in which the electrical energy of the current which it renders arises from a chemical action due primarily to another current which was sent through it. To speak more in detail, the ordinary accumulator (Fig. 3) consists of two lead plates standing in acidulated water and capable of behaving like an ordinary voltaic battery, after they have been acted upon by a strong current. This current, called the charging current, when it goes through the liquid, decomposes it, the oxygen, separated, going to one lead plate and the hydrogen to the other lead plate. The oxygen at-