. A textbook on electric lighting and railways. International correspondence schools, Scranton, Pa. v. 1-3, 5 . thus giving the attendant an indicationas to whether the machine is picking up properly or the machine has come up to voltage, the switch ismoved to the position shown in the figure and the pilot lampis cut out. On some boards, five or six lamps in series areused in place of the resistance r and the single lamp /. Thepilot lamp / is inserted in the receptacle 4, shown in Fig. 19. Jer/esF/e/6f. + 63. Field Rheostats.—Field rheostats, or resistanceboxes, are used in connectio
. A textbook on electric lighting and railways. International correspondence schools, Scranton, Pa. v. 1-3, 5 . thus giving the attendant an indicationas to whether the machine is picking up properly or the machine has come up to voltage, the switch ismoved to the position shown in the figure and the pilot lampis cut out. On some boards, five or six lamps in series areused in place of the resistance r and the single lamp /. Thepilot lamp / is inserted in the receptacle 4, shown in Fig. 19. Jer/esF/e/6f. + 63. Field Rheostats.—Field rheostats, or resistanceboxes, are used in connection with all railway generators,and are connected in series with the shunt-field winding, sothat the field current, and hence the voltage of the generator, S20 ELECTRIC RAILWAYS. 51 may be adjusted. The field resistance is not intended to beused for rei;ulatino; the voltage to suit the variations in load,because the compound winding is su[)])osed to take care ofthat. It is used to adjust the voltage when the machine isfirst started, and it is also necessary to cut out some oi it astlie field coils warm Field rheostats used on railway boards are made in a greatvariety of designs, but in all cases they consist of a resist-ance split up into a large number of sections that are con-nected to a multipoint switch, so that any amount of resist-ance may be cut in or out. In some styles the resistance ismade up of German-silver or tinned-iron wire coiled intospirals and mounted in a well-ventilated iron box. Inothers, the wire is formed into zigzag shape and mounted inenamel on the back of cast-iron plates. In all cases, rheo-stats should be constructed so that they will be perfectlyfireproof and at the same time allow easy radiation of the 52 ELECTRIC RAILWAYS. 20 heat generated in them. If the latter point is not con-sidered, burn-outs are apt to result. In some rheostats theresistance is in the form of cast-iron grids of zigzag makes a substantial resistance that is we
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