it, and
that, therefore, no current from the central office can affect them.
This general scheme of selection is a new-comer in the field, and for
certain classes of work it is of undoubted promise.

[Illustration: Fig. 187. Principle of Broken-Line System]

CHAPTER XVII

LOCK-OUT PARTY-LINE SYSTEMS

The party-line problem in rural districts is somewhat different from
that within urban limits. In the latter cases, owing to the closer
grouping of the subscribers, it is not now generally considered
desirable, even from the standpoint of economy, to place more than
four subscribers on a single line. For such a line selective ringing
is simple, both from the standpoint of apparatus and operation; and
moreover owing to the small number of stations on a line, and the
small amount of traffic to and from such subscribers as usually take
party-line service, the interference between parties on the same line
is not a very serious matter.

For rural districts, particularly those tributary to small towns,
these conditions do not exist. Owing to the remoteness of the stations
from each other it is not feasible from the standpoint of line cost to
limit the number of stations to four. A much greater number of
stations is employed and the confusion resulting is distressing not
only to the subscribers themselves but also to the management of the
company. There exists then the need of a party-line system which will
give the limited user in rural districts a service, at least
approaching that which he would get if served by an individual line.

The principal investment necessary to provide facilities for telephone
service is that required to produce the telephone line. In many cases
the cost of instruments and apparatus is small in comparison with the
cost of the line. By far the greater number of subscribers in rural
districts are those who use their instruments a comparatively small
number of times a day, and to maintain an expensive telephone line for
the exclusive use of one such subscriber who will use it but a few
minutes each day is on its face an economic waste. As a result, where
individual line service is practiced exclusively one of two things
must be true: either the average subscriber pays more for his service
than he should, or else the operating company sells the service for
less than it costs, or at best for an insufficient profit. Both of
these conditions are unnatural and cannot be permanent.

The party-l