s to the
number of stations is not the number that can be rung by a single
generator, or the number with which it is possible to transmit speech
properly, but rather the number of stations that may be employed
without causing undue interference between the various parties who may
desire to use the line. Overloaded party lines cause much annoyance,
not only for the reason that the subscribers are often not able to use
the line when they want it, but also, in non-selective lines, because
of the incessant ringing of the bells, and the liability of confusion
in the interpretation of the signaling code, which of course becomes
more complex as the number of stations increases.

The amount of business that is done over a telephone line is usually
referred to as the "traffic." It will be understood, however, in
considering party-line working that the number of calls per day or per
hour, or per shorter unit, is not the true measure of the traffic and,
therefore, not the true measure of the amount of possible interference
between the various subscribers on the line.

An almost equally great factor is the average length of the
conversation. In city lines, that is, in lines in city exchanges, the
conversation is usually short and averages perhaps two minutes in
duration. In country lines, however, serving people in rural
districts, who have poor facilities for seeing each other,
particularly during the winter time, the conversations will average
very much longer. In rural communities the people often do much of
their visiting by telephone, and conversations of half an hour in
length are not unusual. It is obvious that under such conditions a
party line having a great many stations will be subject to very grave
interference between the parties, people desiring to use the line for
business purposes often being compelled to wait an undue time before
they may secure the use of the line.

It is obvious, therefore, that the amount of traffic on the line,
whether due to many short conversations or to a comparatively few
long ones, is the main factor that should determine the number of
stations that, economically, may be placed on a line. The facilities
also for building lines enter as a factor in this respect, since it is
obvious that in comparatively poor communities the money may not be
forthcoming to build as many lines as are needed to properly take care
of the traffic. A compromise is, therefore, often necessary, and the
only rul