the switchboard, of which there are 20
shown in this illustration. Beside the operator's plug there are a
number of pairs of plugs shown hanging from the switchboard cabinet.
These are connected straight through in pairs, there being no
clearing-out drops or keys associated with them in the arrangement.
Each line shown is provided with an extra jack, the purpose of which
will be presently understood.

The method of operation is as follows: When a subscriber on a certain
line desires to get connection through the switchboard he turns his
generator and throws the drop. The operator in order to communicate
with him inserts the plug in which her telephone terminates into the
jack, and removes her receiver from its hook. Having learned that it
is for a certain subscriber on another line, she withdraws her plug
from the jack of the calling line and inserts it into the jack of the
called line, then, hanging up her receiver, she turns the generator
crank in accordance with the proper code to call that subscriber. When
that subscriber responds she connects the two lines by inserting the
two plugs of a pair into their respective jacks, and the subscribers
are thus placed in communication. The extra jack associated with each
line is merely an open jack having its terminals connected
respectively with the two sides of the line. Whenever an operator
desires to listen in on two connected lines she does so by inserting
the operator's plug into one of these extra jacks of the connected
lines, and she may thus find out whether the subscribers are through
talking or whether either one of them desires another connection. The
drops in such switchboards are commonly high wound and left
permanently bridged across the line so as to serve as clearing-out
drops. The usual night-alarm attachment is provided, the buzzer being
shown at the upper right-hand portion of the cabinet.

[Illustration: Fig. 293. Combined Telephone and Switchboard]

Another type of switchboard commonly employed for this kind of
service is shown in Fig. 293, in which the telephone and the
switchboard cabinet are combined. The operation of this board is
practically the same as that of Fig. 292, although it has
manually-restored drops instead of self-restoring drops; the
difference between these two types, however, is not material for this
class of service. For such work the operator has ample time to attend
to the restoring of the drop and the only possible advantage in