CONQUEST OF DISTANCE BY WIRE TELEPHONY 343 



2. Paper-insulated, twisted-pair cable construction dominated the ex- 

 change plant, with about 80% of the cable underground. 22-gauge 

 cable was coming into extensive use. 



3. The preparation of comprehensive conduit plans for the larger cities 

 had started soon after the development of paper-insulated cables in 

 the early nmeties. By 1906, this work had been broadened to in- 

 clude definite forecasts of the future requirements of those cities, and 

 the resulting development plans showed not only the most economical 

 size and distribution of the conduits and cables, for a period extending 

 about 15 years into the future, but also the proper number, locations, 

 and sizes of the central ofiices. This work, in later years termed 

 "Commercial Surveys and Fundamental Plans," enabled the operat- 

 ing companies to keep abreast of the continually advancing business 

 needs with a minimum of reconstruction. 



4. Common battery switchboards had been installed in all of the large 

 cities replacing the magneto boards, and were being installed in the 

 smaller cities and towns. The use of the new switchboards made 

 local batteries and magneto generators no longer necessary at the 

 individual subscriber stations, and resulted in great improvements in 

 the speed and quality of the telephone service. Switchboard lamps 

 used as line and supervisory signals were also factors in the improved 

 service. 



5. High-grade telephone instruments were in universal use, including the 

 "solid back" transmitter which was much superior to its predeces- 

 sors with respect to power and freedom from carbon packing. 



6. Message rate service had been introduced in the larger cities, supple- 

 menting flat rate service, and was still an important factor in the 

 rapid rate of station growth. 



7. An accompanying map shows the A. T. & T. Co. long distance lines 

 at the beginning of 1906. The long distance circuits were almost 

 entirely in open-wire construction, little cable being used except to 

 provide entrance facilities to city toll offices, and at river crossings. 

 The loading standardized in 1904 for 104 mil open- wire pairs made 

 such circuits approximately equivalent in transmission to non-loaded 

 165 mil pairs, their range being of the order of 1000 miles. Study of 

 the problems involved in loading 165 mil circuits had begun. 



8. The leased-wire telegraph business had expanded to become an im- 

 portant source of revenue and was becoming a basic factor in the ex- 

 pansion of the long distance telephone plant. The telegraph cir- 

 cuits that were leased as private lines were usually obtained by 

 compositing the telephone circuits, and thus the same wires were 

 used simultaneously for telephone and telegraph. 



