. A textbook on electric lighting and railways. International correspondence schools, Scranton, Pa. v. 1-3, 5 . ntact is made with it by means of a slidingshoe carried on the car. The rail is mounted on specialinsulators and is generally raised somewhat above the otherrails. The regular track rails constitute the return grade crossings the third rail is omitted, as the momen-tum of the car is sufficient to carry it over. Of course, thethird rail can only be used where there will be no liabilityof persons coming into contact with it, but for the class of 10 ELECTRIC RAILWAYS. 20 work
. A textbook on electric lighting and railways. International correspondence schools, Scranton, Pa. v. 1-3, 5 . ntact is made with it by means of a slidingshoe carried on the car. The rail is mounted on specialinsulators and is generally raised somewhat above the otherrails. The regular track rails constitute the return grade crossings the third rail is omitted, as the momen-tum of the car is sufficient to carry it over. Of course, thethird rail can only be used where there will be no liabilityof persons coming into contact with it, but for the class of 10 ELECTRIC RAILWAYS. 20 work mentioned above it gives very satisfactory service andits use is rapidly extending. For example, elevated trainsin New York, Chicago, and Boston are operated by meansof the third rail. 12. Fig. 6 shows a third-rail construction used on theNantasket Beach and East Weymouth Road. The thirdrail r is, in this case, of special shape, though ordinaryT rails are often used. The rail shown is made in 30-footlengths and weighs 93 pounds to the yard. It is shownsupported on posts a, which are treated with Electrical continuity between the rails is secured by fasten-ing them together by copper bonds. In the later styles ofthird-rail equipment, which will be described more fullywhen track construction is taken up, porcelain or graniteinsulators are used for supporting the rail. The shoe s, Fig. G, slides on the rail and conveys the cur-rent to the car by means of a cable fastened to the ter-minal /. The slotted links / allow the shoe to play verti-cally, so as to follow inequalities in the track. There aretwo contact shoes and frames to each car on this particular §20 ELECTRIC RAILWAYS. 11 road and they are placed :].] feet apart, so tliat at roadcrossings the third rail nuiy be omitted and the momentumof the moving car depended on to carry it over. When thewidth of the road is less than 3:3 feet, there is no break. CURRENT SUPPJ^Y. Iti. Direct Current vs. Alternatinpr.—Elec
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