no
series contacts in the jacks and no unbalancing of the line due to a
cutting off of a portion of the line circuit when a connection was made
with it. Furthermore, the test circuits were entirely local to the
central office and were not likely to be affected by outside conditions
on the line. This switchboard also added the feature of the automatic
restoration of the drops, thus relieving the operator of the burden of
doing that manually, and also permitting the drops to be mounted on a
portion of the switchboard that was not available for the mounting of
jacks, and thus permitting a greater capacity in jack equipment.

[Illustration: Fig. 338. Branch-Terminal Magneto Multiple Switchboard]

Each jack has five contacts, and the answering and multiple jacks are
alike, both in respect to their construction and their connection with
the line. The drops are the electrically self-restoring type shown in
Fig. 263. The line circuits extended permanently from the subscriber's
station to the line winding of the drop and the two limbs of the line
branched off to the tip and sleeve contacts _1_ and _2_ respectively of
each jack. Another pair of wires extended through the multiple parallel
to the line wires and these branched off respectively to the contact
springs _3_ and _4_ of each of the jacks. This pair of wires formed
portions of the drop-restoring circuit, including the restoring coil _6_
and the battery _7_, as indicated. The test thimble _5_ of each of the
jacks is connected permanently with the spring _3_ of the corresponding
jack and, therefore, with the wire which connects through the restoring
coil _6_ of the corresponding drop to ground through the battery _7_.

The plugs were each provided with three contacts. Two of these were the
usual tip and sleeve contacts connected with the two strands of the cord
circuit. The third contact _8_ was not connected with any portion of the
cord circuit, being merely an insulated contact on the plug adapted,
when the plug was fully inserted, to connect together the springs _3_
and _4_. The cord circuit itself is readily understood from the drawing,
having two features, however, which merit attention. One is the
establishing of a grounded battery connection to the center portion of
the winding of the receiver for the purposes of the busy test, and the
other is the provision of a restoring coil and restoring circuit for the
clearing-out drop, this circuit being closed by an additio