the main switch, the indicator lamp will not be lighted. [Illustration: MOTOR-GENERATOR SET SUPPLYING ALTERNATING CURRENT FOR BLOCK SIGNALS AND MOTOR-GENERATOR STARTING SET] The control board is divided into two parts--one for the connections of the alternators to the bus bars and the other for the connection of feeders to bus bars. The drawing on page 97 shows in plain view the essential features of the control boards. [Sidenote: _The Instrument Board_] A front view of the Instrument Board is shown on page 97. This board contains all indicating instruments for alternators and feeders. It also carries standardizing instruments and a clock. In the illustration the alternator panels are shown at the left and the feeder panels at the right. For the alternator panels, instruments of the vertical edgewise type are used. Each vertical row comprises the measuring instruments for an alternator. Beginning at the top and enumerating them in order these instruments are: Three ammeters, one for each phase, a volumeter, an indicating wattmeter, a power factor indicator and a field ammeter. The round dial instrument shown at the bottom of each row of instruments is a three-phase recording wattmeter. A panel located near the center of the board between alternator panels and feeder panels carries standard instruments used for convenient calibration of the alternator and feeder instruments. Provision is made on the back of the board for convenient connection of the standard instruments in series with the instruments to be compared. The panel which carries the standard instruments also carries ammeters used to measure current to auxiliary circuits in the power house. For the feeder board, instruments of the round dial pattern are used, and for each feeder a single instrument is provided, viz., an ammeter. Each vertical row comprises the ammeters belonging to the feeders which supply a given sub-station, and from left to right these are in order sub-stations Nos. 11, 12, 13, 14, 15, 16, 17, and 18; blank spaces are left for four additional sub-stations. Each horizontal row comprises the ammeter belonging to feeders which are supplied through a given group switch. This arrangement in vertical and horizontal lines, indicating respectively feeders to given sub-stations and feeders connected to the several group switches, is intended to facilitate the work of the operator. A glance down a vertical row without stopping to reach the scales of the instruments will tell him whether the feeders are dividing with approximate equality the load to a given sub-station. Feeders to different sub-stations usually carry different loads and, generally speaking, a glance along a horizontal row will convey no information of especial importance. If, however, for any reason the operator should desire to know the approximate aggregate load upon a group of feeders this systematic arrangement of the instruments is of use.