|The early telephones worked on the Magneto system. The telephone was wired to a central
switchboard that would connect the caller to another telephone via cords.
The telephone microphone was powered by a local battery source and called the exchange
switchboard by means of a hand generator. The switchboard would also call telephones by
use of a hand generator. On finishing a call both users would crank their generators to
signal to the exchange switchboard that they had hung up (this is known as ringing off).
On lines within the same building, the battery-ringing telephone is generally adopted,
owing to its cheapness. On long lines it is necessary to introduce a relay to economise
battery power, and in such circumstances the magneto-ringing telephone is generally
preferred. It will be seen that the transmitter, the primary of the induction coil, and
the speaking battery form a local circuit. This circuit may be closed either by a gravity
switch or a microtelephone press key. With the telephone resting, the magneto bell in
series with a condenser is connected across the lines via the contacts of a switch forming
part of the magneto generator and a second switch forming a portion of the gravity switch.
When the handle of the magneto generator is turned, the bell is disconnected and the
generator is connected across the A and B wires. When the receiver or microtelephone is
removed from its rest, the local speaking circuit is closed, the magneto bell disconnected
from the line, and the receiver in series with the secondary winding of the induction coil
is connected across the A and B wires. The method in which these circuit changes are
effected in the types of telephone instrument used in a magneto system varies
considerably, but the principle remains the same.