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Page:Popular Science Monthly Volume 56.djvu/590

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574
POPULAR SCIENCE MONTHLY.

shoes can be caught. Thus, unless the slot can be dispensed with the greater beauty overhead is obtained at the expense of increased danger on the street surface. There are quite a number of underground conductor systems in which the slot is not used, the current being conveyed to the car by contact made with plates set at suitable intervals between or along the sides of the tracks, and on a level with the street surface. Many of these arrangements appear to be quite practical, but none of them can attract the attention of railroad managers unless it can be constructed at a reasonable cost.

About two years ago the New York, New Haven, and Hartford Railroad published a report of the performance of a branch line that was equipped with electric motors, the current being conveyed to them by means of a third rail. Some of the sensational dailies at once took the matter up and heralded the third rail to the public as something entirely new and sure to supersede the trolley. Now, as a matter of fact, the third rail is one of the oldest arrangements that have been used, and was in daily operation in Baltimore in 1886. It is a very cheap system PSM V56 D0590 Modified third rail system.pngFig. 31.—Cross-section of Railway Track, showing a Modification of the Third-rail System. and well adapted to roads owning the right of way or running upon elevated tracks, but could not be used on public highways or streets. The third-rail system in its simplest form is shown m Fig. 29, which represents a section through the roadbed. The log A represents a tie or sleeper, and c c are the track rails, while b is the third rail through which the current passes to the motors. Between the rail b and the tie A is placed a piece of insulating material, a, of such dimensions as may be necessary. If the track is high above the surrounding ground, so as to not be submerged when there is a heavy fall of rain, a may be thin, but otherwise it must be of sufficient thickness to raise the rail above the high-water mark. The car is provided with a wheel or brush to bear upon the rail b.

This is the construction used upon the New York, New Haven, and Hartford Railroad, as can be seen from Fig. 30, which is a photograph of a section of the road. The third rail, it will be seen, is raised but slightly from the ties, just about as shown in Fig. 29. One objection to this construction is that persons and animals can receive shocks by touching the center rail and one of the side ones at the same time, as, for example, by standing with one foot on each. Such shocks would not prove fatal to men, as the currents used for railway work are not of a sufficiently high