ated in practice.

[Illustration: Fig. 273. Circuit of Simple Magneto Switchboard]

Little need be said concerning this circuit in view of what has
already been said in connection with Figs. 240 to 245. It will be seen
in the particular sub-station circuit here represented, that the
talking apparatus is arranged in the usual manner and that the ringer
and generator are so arranged that when the generator is operated the
ringer will be cut out of circuit, while the generator will be placed
across the circuit; while, when the generator is idle, the ringer is
bridged across the circuit and the generator is cut out.

The line terminates in each case in the tip and sleeve contacts of the
jack, and in the normal condition of the jack the line drop is bridged
across the line. The arrangement by which the drop is restored and at
the same time cut out of circuit when the operator plugs in the jack,
is obvious from the diagrammatic illustration. The cord circuit is the
same as that already discussed, with the exception that two ringing
keys are provided, one in connection with the calling plug, as is
universal practice, and the other in connection with the answering plug
as is sometimes practiced in order that the operator may, when occasion
requires, ring back the calling subscriber without the necessity of
changing the plug in the jack. The outer contacts of these two ringing
keys are connected to the terminals of the ringing generator and, when
either key is operated, the connection between the plug, on which the
ringing is to be done, and the rest of the cord circuit will be broken,
while the generator will be connected with the terminals of the plug.
The listening key and talking apparatus need no further explanation, it
being obvious that when the key is operated the subscriber's telephone
set will be bridged across the cord circuit and, therefore, connected
with either or both of the talking subscribers.

[Illustration: Fig. 274. Night-Alarm Circuit]

Night-Alarm Circuits. The circuit of Fig. 273, while referred to as
a complete circuit, is not quite that. The night-alarm circuit is not
shown. In order to clearly indicate how a single battery and bell, or
buzzer, may serve in connecting a number of line drops, reference is
made to Fig. 274 which shows the connection between three different
line drops and the night-alarm circuit. The night-alarm apparatus
consists in the battery _1_ and the buzzer, or bell, _2_. A switc