ine is busy is being told so by the
_A_-operator. This may be considered a special feature and it is
employed in New York because there the custom exists of telling a
calling subscriber, when the line he has called for has been found busy,
that the party will be secured for him and that he, the calling
subscriber, will be called, if he desires.

A modification of this busy-back feature that has been employed in
Boston, and perhaps in other places, is to associate with the busy-back
jack at the _B_-operator's position a phonograph which, like a parrot,
keeps repeating "Line busy--please call again." Where this is done the
calling subscriber, _if he understands what the phonograph says_, is
supposed to hang up his receiver, at which time the _A_-operator takes
down the connection and the _B_-operator follows in response to the
notification of her supervisory lamp. The phonograph busy-back scheme,
while ingenious, has not been a success and has generally been
abandoned.

As a rule the independent operating companies in this country have not
employed automatic ringing, and in this case the _B_-operators have
been required to operate their ringing keys and to watch for the
response of the called subscriber. In order to arrange for this, another
supervisory lamp, termed the _ringing lamp_, is associated with each
incoming trunk plug, the going out of this lamp being a notification to
the _B_-operator to discontinue ringing.

=Western Electric Trunk Circuits.= The principles involved in
inter-office trunking with automatic ringing, are well illustrated in
the trunk circuit employed by the Western Electric Company in connection
with its No. 1 relay boards. The dotted dividing line through the center
of Fig. 371 represents the separating space between two offices. The
calling subscriber's line in the first office is shown at the extreme
left and the called subscriber's line in the second office is shown at
the extreme right. Both of these lines are standard multiple switchboard
lines of the form already discussed. The equipment illustrated in the
first office is that of an _A_-board, the cord circuit shown being that
of the regular _A_-operator. The outgoing trunk jacks connecting with
the trunk leading to the other office are, it will be understood,
multipled through the _A_-sections of the board and contain no relay
equipment, but the test rings are connected to ground through a
resistance coil _1_, which takes the place of