486 BELL SYSTEM TECHNICAL JOURNAL 



Introduction 



THE rapidity with which telephone service has been extended to 

 world-wide proportions during the past few years is perhaps one 

 of the most remarkable of man's conquests over time and distance. 

 Already it is a commonplace to hear the human voice from thousands 

 of miles away, over land and sea. Distance and the great natural 

 barriers of the world no longer prevent us from talking with each other. 

 Across oceans and over high sierras the voice now carries its full 

 message. Furthermore, these results have been accomplished within 

 a few years. Telephony has demonstrated its international and 

 intercontinental services. The development and extension of those 

 services lies before us. It seems an appropriate time, therefore, to 

 review some of the problems and possibilities in this extension of the 

 application of the electrical arts to the service of mankind. 



World-wide telephony has as its foundation the wire line networks 

 on the various continents with their millions of users. The first step 

 was taken toward overcoming the great barrier presented by the 

 oceans in 1891 when the first submarine telephone cable was laid 

 between Dover and Calais. Further submarine cable developments 

 followed including the laying of a continuously loaded cable between 

 Denmark and Sweden in 1902. 



In the meantime the problems of spanning great distances over 

 land were being rapidly solved, both in North America and in Europe, 

 through the application of the loading coil and other transmission 

 improvements. In 1911 service was opened between New York and 

 Denver, a distance of 2000 miles (3300 kilometers). By 1913 the de- 

 velopment of underground cable had progressed so that a cable was 

 placed in service between Boston, New York and Washington, a distance 

 of over 420 miles (700 kilometers). 



But it required still further improvements in the whole art of long 

 distance telephone transmission, including amplifiers and their appli- 

 cation to wire lines before long distance telephony could develop 

 beyond the semi-continental stage to truly transcontinental and 

 transoceanic distances. With improved amplifier elements and the 

 perfection of means for applying repeaters came the opening of trans- 

 continental service in America in 1915 initially between New York and 

 San Francisco, 3200 miles (5300 kilometers). This was followed after 

 the close of the war by the rapid development of telephony of conti- 

 nental scope throughout Europe, stimulated by the close cooperation 

 of the European Administrations through the International Advisory 

 Committee on Long Distance Telephony. In South America the 

 trans-Andean telephone line between Buenos Aires and Santiago was 



