panies. "Long Distance" makes the connection in much the same
way as the branch city exchanges. As the charges for long-distance calls
depend on the length of the conversation, so the connection is made by
an operator whose business it is to make a record of the length in
minutes of the conversation and the place with which the city subscriber
is connected. An automatic time stamp accomplishes this without
possibility of error.

Sometimes the calls come from a pay station, in which case a record must
be kept of the time occupied. This kind of call is indicated by the glow
of a red light instead of a white one, and so "central" is warned to
keep track, and the supervisors or monitors who constantly pass to and
fro can note the kind of calls that come in, and so keep tab on the
operators.

Other coloured lights indicate that the chief operator wishes to send
out a general order and wishes all operators to listen. Another
indicates that there is trouble somewhere on the line which needs the
attention of the wire chief and repair department.

[Illustration: THE BACK OF A TELEPHONE SWITCHBOARD
A section of one of several central station switchboards necessary to
carry the telephone traffic of a great city.]

The switchboards themselves are made of hard, black rubber, and are
honeycombed with innumerable holes, each of which is connected with a
subscriber. Below the switchboard is a broad shelf in which are set the
miniature lamps and from which project the brass plugs in rows. The
flexible cords containing the connecting wires are weighted and hang
below, so that when a plug is pulled out of a socket and dropped it
slides back automatically to its proper place, ready for use.

Many subscribers nowadays have their own private exchanges and several
lines running to central. Perhaps No. 4341 Eighteenth Street, for
instance, has 4342 and 4344 as well. This is indicated on the
switchboard by a line of red or white drawn under the three
switch-holes, so that central, finding one line busy, may be able to
make connection with one of the other two, the line underneath showing
at a glance which numbers belong to that particular subscriber.

If a subscriber is away temporarily, a plug of one colour is inserted
in his socket, or if he is behind in his payments to the company a plug
of another colour is put in, and if the service to his house is
discontinued still another plug notifies the operator of the fact, and
it remains the