Contact rails south of Reade Street are supplied from sub-station No. 11; from Reade Street to 19th Street they are supplied from sub-stations Nos. 11 and 12; from 19th Street they are supplied from sub-stations Nos. 12 and 13; from the point last named to 96th Street they are supplied from sub-stations Nos. 13 and 14; from 96th Street to 143d Street, on the West Side, they are supplied from sub-stations Nos. 14 and 15; from 143d Street to Dyckman Street they are supplied from sub-stations Nos. 15 and 17; and from that point to the terminal they are supplied from sub-station No. 17. On the East Side branch contact rails from 96th Street to 132d Street are supplied from sub-stations Nos. 14 and 16; from 132d to 165th Street they are supplied from sub-stations Nos. 16 and 18; and from 165th Street to 182d Street they are supplied from sub-station No. 18. Each contact rail is insulated from all contact rails belonging to adjacent tracks. This is done in order that in case of derailment or other accident necessitating interruption of service on a given track, trains may be operated upon the other tracks having their separate and independent channels of electrical supply. To make this clear, we may consider that section of the subway which lies between Reade Street and 19th Street. This section is equipped with four tracks, and the contact rail for each track, together with the direct current feeders which supply it from sub-stations Nos. 11 and 12, are electrically insulated from all other circuits. Of each pair of track rails one is used for the automatic block signaling system, and, therefore, is not used as a part of the negative or return side of the direct current system. The other four track rails, however, are bonded, and together with the negative feeders constitute the track return or negative side of the direct current system. The diagram on page 109 illustrates the connections of the contact rails, track rails and the positive and negative feeders. All negative as well as positive feeders are cables of 2,000,000 c. m. section and lead sheathed. In emergency, as, for example, in the case of the destruction of a number of the cables in a manhole, they are, therefore, interchangeable. The connections are such as to minimize "track drop," as will be evident upon examination of the diagram. The electrical separation of the several contact rails and the positive feeders connected thereto secures a further important advantage in permitting the use at sub-stations of direct-current circuit-breakers of moderate size and capacity, which can be set to open automatically at much lower currents than would be practicable were all contact rails electrically connected, thus reducing the limiting current and consequently the intensity of the arcs which might occur in the subway in case of short-circuit between contact rail and earth.