of the system will frequently vary, and consequently often throw the system out of balance. To counteract this influence certain devices known as "Equalizers" are introduced into the system.
These equalizers consist of boxes containing coils of wire which offer a great deal of resistance to the passage of the current, and are so arranged that one coil after another may be brought into or out of the circuit, by simply rotating a handle placed on the outside of the box.
The general arrangement of this device is shown in Fig. 13, where DD are dynamos, and RR the equalizers.
When a number of lamps sufficient to destroy the equilibrium of the system are turned in or out of either side of the system, a proportionate amount of resistance is thrown in or out of the proper side by means of the regulators so as to restore the balance.
Where large districts of a city are to be lighted it is important that the pressure at all points of the circuit should
