Practical application of carrier telephone and telegraph in the Bell System

IN 1918 it was announced that the engineers of the Bell System had perfected carrier current telephone apparatus to such a point that four talking circuits had been added to one pair of wires already in use for telephone and telegraph communication and were being used commercially between Pittsburgh and Baltimore for providing needed telephone facilities. Since that time the growth of carrier application in the Bell System has been quite rapid. The purpose of this paper is to summarize the applications of carrier up to the present time and give a few typical examples where it has been found economical to provide circuits by means of carrier rather than by other types of facilities.