over the circuit of the line from the central office would ring the bell of this station.  In Fig. 187 the switches of both Station A and Station B have been thus operated, and Station C is thus placed in circuit.  Inspection of this figure will show that the bells of Station A, Station B, and Station D are all cut out of circuit, 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-line 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.