contact, the object being, as with the more usual divided brush, to prevent the circuit being opened or a cell short-circuited as the switch passes

from one

cell to the next. A laminated brush, moved by means of a long screw and hand-wheel, enables any contact to be connected with the bar.

By means of these switches, any number of the twelve regulating cells

FIG. 119.-Battery Switchboard.

can be connected in series with the corresponding sub-battery before the main board is reached. By means of screwed plugs with collars, any horizontal bar can be connected to any vertical.

For discharging, the two-way switch is put over to the fifth bar, and the sub-batteries plugged on to the distributing mains in the desired order, the four single-pole switches being closed. By means of the regulating switches the pressure on each pair of mains can be independently varied.

For charging, the two-way switch is put over to the sixth bar, the three single-pole switches on the intermediate wires put off and the remaining one left on. The cells are thus left in series, and the motor-driven generator being run up, the added pressure supplied by it is available for charging, the Regulating

Cells

plug connecting the end cell having previously been transferred to the seventh bar.

The connections are made by means of solid round bare copper rods, supported on porcelain insulators, those joining up the sub-batteries being provided with oil insulators, those attached to the regulating cells being insulated from one another by porcelain insulators carried in a cast iron frame which is itself insulated from earth, as shown in fig. 120. The rods to the regulating cells are of smaller sectional area than those to the subbatteries, because they are in use for a much shorter time, and the waste of energy in them is of less importance than the capital expenditure on the copper.

The resistances between the cells are conveniently arranged in the form of straight iron bars about four feet long, as shown in fig. 121.

The instruments comprise four ammeters reading up to 700 amperes in one direction for the discharge, and 400 amperes for the charge. These are

of the moving coil type, connected across conductors of known resistance. Four voltmeters reading up to 150 volts, each connected by a two-way switch

either to the mains or to a pair of the vertical bars of the switchboard; one voltmeter reading to 200 volts connected to the booster; and another reading to 600 volts connected across the outermost bars of the switchboard. These are all mounted on a cast iron frame, as shown in fig.

122.

In addition to these, four Aron ampere-hour meters with a double set of dials show the quantity put in and taken out of the battery.

The cells are mounted in some cases in a single row and in others in two tiers, cast iron frames with wrought iron girders being used to support the upper one. The cells are insulated with glass insulators and oil, and are kept clear of the floor.