mmon point within that district and where the number of
such subscribers and lines is insufficient to establish a fully equipped
office, it is possible to establish a so-called sub-station or
sub-office connected with the main office of that district by trunk
lines. At this sub-office there are placed only line switches and
connectors. When a call is originated on one of these sub-office lines,
the line switch acts instantly to connect that line with one of the
trunks leading to the main office of that district, at which this trunk
terminates in a first selector. From there on, the connection is the
same as that in a system in which no sub-offices are employed. Calls
coming into this sub-office over trunk lines from the main office are
received on the connectors at the sub-office and the connection is made
with the sub-office line by the connector in the usual manner. This
arrangement, it is seen, amounts merely to a stretching of the connector
trunks for a given group of lines so that they will reach out from a
main office to a sub-office, it being more economical to lengthen the
smaller number of trunks and by so doing to decrease in length the
larger number of subscribers' lines.

=The Rotary Connector.= For certain purposes it becomes desirable in
automatic work to employ a special form of connector which will have in
itself a certain ability to make automatic selection of one of a group
of previously chosen trunks in much the same manner as the first and
second selectors automatically choose the first idle one of a group of
trunks.

Such a use is demanded in private branch-exchange working where a given
business establishment, for instance, has a plurality of lines
connecting its own private switchboard with the central office. The
directory number of all these lines is, for convenience, made the same,
and it is important, therefore, that when a person attempts to make a
connection with this establishment, he will not fail to get his
connection simply because the first one of these lines happens to be
busy. For such use a given horizontal row of connector terminals or a
part of such a row is assigned to the lines leading to the private
branch exchange and the connector is so modified as to have a certain
"discretionary" power of its own. As a result, when the common number of
all these lines is called, the connector will choose the first one, if
it is not already engaged by some other connector, but if it is, it w