ine method of giving service, by which a single line is
made to serve a number of subscribers, offers a solution to this
difficulty, but the ordinary non-selective or even selective party
line has many undesirable features if the attempt is made to place on
it such a large number of stations as is considered economically
necessary in rural work. These undesirable features work to the
detriment of both the user of the telephone and the operating company.

Many attempts have been made to overcome these disadvantages of the
party line in sparsely settled communities, by producing what are
commonly called lock-out systems. These, as their name implies, employ
such an arrangement of parts that when the line is in use by any two
parties, all other parties are locked out from the circuit and cannot
gain access to it until the parties who are using it are through.
System after system for accomplishing this purpose has been announced
but for the most part these have involved such a degree of complexity
and have introduced so many undesirable features as to seriously
affect the smooth operation of the system and the reliability of the
service.

We believe, however, in spite of numerous failures, that the lock-out
selective-signaling party line has a real field of usefulness and that
operating companies as well as manufacturing companies are beginning
to appreciate this need, and as a result that the relief of the rural
subscriber from the almost intolerable service he has often had to
endure is at hand. A few of the most promising lock-out party-line
systems now before the public will, therefore, be described in some
detail.

Poole System. The Poole system is a lock-out system pure and simple,
its devices being in the nature of a lock-out attachment for
selective-signaling lines, either of the polarity or of the harmonic
type wherein common-battery transmission is employed. It will be here
described as employed in connection with an ordinary harmonic-ringing
system.

In Fig. 188 there is shown a four-station party line equipped with
Poole lock-out devices, it being assumed that the ringers at each
station are harmonic and that the keys at the central office are the
ordinary keys adapted to impress the proper frequency on the line for
ringing any one of the stations. In addition to the ordinary talking
and ringing apparatus at each subscriber's station, there is a relay
of special form and also a push-button key.

[Illustra