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Synopsis: Two previous papers before the American Institute of Electrical Engineers discussed the activities of the Bell System in the development of multiplex telephone and telegraph systems using carrier current methods. The present paper describes developments which have resulted in improvements in the carrier telephone art during the past few years. A new, so‐called type “C” system is described in detail, together with suitable repeaters and pilot channel apparatus for insuring the stability of operation; the line problems are considered and typical installations pictured. The growth of the application of carrier telephone systems and their increasingly important part in providing long distance telephone service on open‐wire lines are shown.

Review of the Subject.-Some of the important developments important of these, including the telephone repeater equipment, contemplated in the apparatus and equipment for long toll cable test board equipment, and signaling equiipment, are described. circuits are described. The large number of equipment units per The necessity for compactness in the ditmensions of equipment station in the cable plant and the greater number of stations in a units, uniformity in assembly arrangements, and simplicity in given length of cable than in an opent-wire system, have made the design, together with the need of careful correlation of the electrical economnic importance of the equipment design such that a compre-and mechanical requirements, are emphasized. The methods hensive program of development, affecting many types of equipment, proposed for meeting these requirements generally, are described.has been undertaken. The outstanding features of some of the more

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