ions with respect to the jack and
line-signal equipment of the multiple switchboard by saying that each
line has a multiple jack on each section of the board and in addition to
this has on one section of the board an answering jack and a line
signal. These answering jacks and line signals are distributed in groups
along the face of the board so that each operator will receive her
proper quota of the originating calls which she will answer and, by
virtue of the multiple jack, be able to complete the connections with
the desired subscribers without moving from her position.

=Cord Circuits.= Each operator is also provided with a number of pairs
of cords and plugs with proper supervisory or clearing-out signals and
ringing and listening keys, the arrangement in this respect being
similar to that already described in connection with the simple
switchboard.

=Guarding against Double Connections.= From what has been said it is
seen that a call originating on a given line may be answered at one
place only, but an outgoing connection with that line may be made at any
position. This fact that a line may be connected with when called for at
any one of the sections of the switchboard makes necessary the provision
that two or more connections will not be made with the same line at the
same time. For instance, if a call came in over a line whose signal was
located on the first position of the switchboard for a connection with
line No. 1,000, the operator at the first position would connect this
calling line with No. 1,000 through the multiple jack on the first
section of the switchboard. Assume now that some line, whose signal was
located on the 39th position of the switchboard, should call also for
line No. 1,000 while that line was still connected with the first
calling subscriber. Obviously confusion would result if the operator at
the 39th position, not knowing that line No. 1,000 was already busy,
should connect this second line with it, thereby leaving both of the
calling subscribers connected with line No. 1,000, and as a result all
of these three subscribers connected together.

The provisions for suitable means for preventing the making of a
connection with a line that is already switched at some other section of
the switchboard, has offered one of the most fertile fields for
invention in the whole telephone art. The ways that have been proposed
for accomplishing this are legion. Fortunately common practice has
settled o