The
current through this circuit energizes the release magnet of the second
selector and restores it to its normal position and also energizes the
back release relay of the first selector. This, in turn, closes the
circuit from the battery through the release magnet of the first
selector and contacts of the back release relay to ground. This works
the release magnet of the first selector and restores that selector to
normal. The contacts on the first selector release magnet, shown in Fig.
390, are closed by the action of the release magnet and this closes the
path from ground back through the first selector release wire, and
through the contacts _13_ and _14_ of the line switch, through the line
switch release magnet to battery, and this restores the line switch to
normal.

The reason for the term _back release_ will now be apparent. The release
operation at the connector is relayed back to the second selector; that
of the second selector back to the first selector; and that of the first
selector back to the line switch. Until this plan was adopted, the
release magnet of each selector and connector involved in a connection
was left bridged across the talking circuit so as to be available for
release; and it sometimes occurred that a first selector would be
released before a second selector or connector, which latter switches
would thus be left off-normal until rescued by an attendant. The back
release plan makes it impossible for the connection necessary for the
release of a switch to be torn down until the release is actually
accomplished.

Called Line Found Idle:--It will be remembered that, before the
digression necessary to trace through the operations occurring upon the
finding of a busy line, the connector wipers had been brought, by the
influence of the calling subscriber's impulses, into engagement with the
contacts of the desired line; that the connector side switch was in its
second position; and that the final rotary impulse following the last
series of selecting impulses had not been sent. The condition now to be
assumed is that the called subscriber's line is free and the private
wiper, therefore, has found and rests on an ungrounded private bank
contact. The final rotary impulse which immediately follows will operate
the rotary relay and this, in turn, will operate the private magnet.
This happened under the assumed condition that the line was busy, but in
that case the release magnet was also operated a