162 BELL SYSTEM TECHNICAL JOURNAL 



mode of transmission has spread rapidly so that in spite of the inter- 

 vening period of retarded business activity it now provides about 1| 

 miUion miles (2.4 X 10^ km.) of high-grade circuits throughout the 

 Bell System, Its use with variations has extended to other countries 

 so that it bids fair to become an outstanding means for providing over- 

 land telegraph facilities, particularly for long distances, where the 

 service is exacting. As indicating the general trend, it may be stated 

 that in England alone about 1700 voice-frequency telegraph channels 

 were reported as available for operation at the end of 1938.^ 



It is interesting to note the role played by carrier telegraph in the 

 evolution of the art of telegraphy. The three major telegraph systems 

 up to about 1890 were those of Hughes on the Continent, Wheatstone 

 in England, and the manual Morse system in the United States. As 

 electrical communication reached out to greater and greater distances, 

 the desire to utilize costly lines more effectively led inventors to con- 

 centrate their efforts in two different directions; namely, the develop- 

 ment of high-speed systems and of multiplex systems. In high-speed 

 systems, the object, as the name implies, is to secure increased line 

 output by speeding transmission well beyond the ability of a single 

 operator. These devices are characterized by automatic transmitters 

 which can be supplied with perforated tape prepared in advance by a 

 number of individuals. Typical high-speed systems are the Wheat- 

 stone automatic, the Murray automatic, the Siemens and Halske high- 

 speed, and the Creed high-speed.^ 



The first efforts at multiplexing circuits were based upon the sug- 

 gestions of Gintl and Highton, who proposed to take advantage of 

 directional and magnitude effects respectively, and whose ideas were 

 brought together by Edison in his invention of the quadruplex. The 

 multiplex system as we know it, however, was the invention of Baudot, 

 who, putting into practical form a suggestion made by Moses G. Farmer 

 as far back as 1853, produced a system whereby the line was assigned 

 successively to a number of operators. This process had the great 

 advantage that while maintaining the line speed which economy made 

 imperative, it permitted a number of messages to be transmitted 

 simultaneously without delay and with each operator working at his 

 normal pace. The chief examples of the multiplex are the Baudot, 

 Murray, and American.^' ^ 



Owing to the advantages of these higher output systems, the older 

 methods of operation were gradually supplanted for the longer com- 

 mercial message circuits. This was particularly true in Europe, since 

 certain conditions operating in America tended to favor the survival 

 of the simple Morse arrangement; the chief of these being the avail- 



