Page:Incandescent electric lighting- A practical description of the Edison system.djvu/69

 lighting generally commences. If no lights are turned on there will be no current generated, because we shall have what is termed an open circuit; that is, there will be no connection between the outgoing and incoming, or what is known as the positive and negative wires, as there is when lamps are in circuit.

As soon, however, as a lamp is turned on, abridge is formed connecting the main wires and permitting the current to flow over the completed circuit, which includes the generator, the latter becoming active the moment the circuit is closed by the introduction of a lamp. A glance at the volt meter shows us that we have a pressure greater or less than 100, which is the pressure we require; and by operating the resistance boxes connected with the fields of the dynamos, we secure the proper pressure, and the current being proportional to the pressure divided by the resistance of the lamps in circuit will take care of itself.

As more lamps are turned on our pressure begins to fall below 100 and, we