﻿1S71.] L. Schvvendler — On the general Theory of Dicplex Telegraphi/. 3 



before the Academy of Science by M. Zantedeschi, he claims the honour of 

 having first suggested the idea of Duplex Telegraphy, for as early as 1829 

 he had proved the possibility of the simultaneous transmission of currents 

 in opposite directions through a single conductor. Having never seen his 

 original communication of 1829, it is impossible for me to say how far these 

 early ideas of Zantedeschi bear on the problem ; but it is certain that both 

 he and Dr. Gintl took a great deal of trouble to prove an erroneous theory, 

 viz., that two distinct electrical currents can pass simultaneously in opposite 

 directions through the same conductor without in 2,nj way interfering with 

 each other. Such a supposition is in direct opposition to the electrical laws 

 which were already known in 1829,* and besides is in no way required in 

 order to explain the simple phenomenon of Duplex Telegrapliy.f 



None of the above methods, however, came to have extended, or indeed 

 any, practical application. They appear to have been attempted doubtingly 

 and without confidence, and, although the trials are generally reported to 

 have been successful, yet the methods were rejected as impracticable, and 

 came to be regarded as merely of scientific interest.;];; 



Only recently, after a torpid existence of almost twenty years, has 

 Duplex Telegraphy been revived, and come to be the leading topic in 

 Telegraphy, securing, after such a lapse of time, the amount of public 

 interest it rightly deserves. 



To Mr. Stearns, an American Telegraph Engineer, is due the honour of 

 having appreciated the real value of Duplex Telegraphy, and of having (by 

 giving the system, modified by improvements of his own, an extended 

 application on the lines of the United States) proved its thorough practi- 

 cability. 



Enquiry into the Causes which hate delated the Inteoduction 



OF the System. 



When Steinheil in 1837 announced his discovery of the feasibility of 

 employing the earth to complete the electric circuit instead of a return wire. 

 Telegraph Engineers immediately recognized its immense mercantile value, 

 and did not delay to verify his results. 



Now, in the career of Telegraphy, the invention of duplex working 

 ranks second only in importance to Steinheil's discovery. The utilization 

 of the earth reduced by one half the number of wires required to carry a 

 given traffic : Duplex Telegraphy again almost halves this number. In 



* Ohm published his classical work " Die galvauishe Kette matliematisch bear- 

 beitet" in the year 1828. 



f Dr. Wr. Siemens, Pogg. Ann., vol. 98, page 123. 



X For the light in which Duplex Telegraphy was regarded up till quite lately, see 

 Schellen, Dub, Sabine, Blavier, Kuhn, &c. 



