other, the secondary winding delivers the electrical energy to the circuit. The induction coil separates the circuit of the
telephone set two circuits, the transmitting circuit and the receiving circuit.
(1) The transmitting circuit is emphasized by the heavy lines in A. This circuit includes the primary winding of
the induction coil, the transmitter, the handset switch, and the battery, all in series. When the handset switch is closed,
direct current from the battery is supplied only to the primary circuit.
(2) The receiving circuit is shown by the heavy lines in B. This circuit includes the secondary winding of the
induction coil and the telephone receiver.
(3) The function of the transmitting and receiving circuits of the telephone set will be considered after the
following discussion of the basic principles of the induction coil.
Local-Battery Telephone Set
with Induction Coil.