﻿2 L. Schwcndler — On the general Theory of Duplex Telegraghy. [No. 1, 



It is believed, however, that the sequel will shew, that if the best 

 method be ado])ted, and for this method the best arrangement be selected, 

 to suit the particular line on which the method is to be employed, the 

 difficulties that stand in the way of Duplex Telegraphy will hardly be 

 greater than those which are encountered every day in ordinary single 

 Telegraphy. 



iMPERrECT Historical Sketch. 



Having access to but scanty records in this country, I am not in a 

 position to give an exhaustive history of this most important invention, 

 and consequently the following sketch is necessarily incomplete, and 

 must be taken as merely introductory, it being relegated to those better 

 situated in this respect than myself to clear up the doubtful points of 

 priority, and produce, what is much required, a complete history. 



The idea of sending signals in opposite directions simultaneously 

 through a single wire is by no means a new one. As early as 1849, Messrs. 

 Siemens and Halske of Berlin took out a patent in England* for the 

 simultaneous transmission of a plurality of messages by a suitable combina- 

 tion of wires, and, although this patent does not refer directly to Duplex 

 Telegraphy as it was subsequently understood, it must notwithstanding be 

 regarded as a forerunner of it. In point of fact Dr. Wr. Siemens's idea 

 represents the general problem of which Duplex Telegraphy is only a 

 particular case. 



In 1854 Dr. Gintl of Vienna tried his " compensation" method of 

 " duplex" working between that capital and Prague,t and on the 30th 

 November of the same year read a paper before the Kaiserlich Konig- 

 liche Acadamie of Science of Vienna]: on the practical solution of the same 

 problem by employing a Bain's electro-chemical Telegraph apparatus instead 

 of a Morse's receiving instrument. 



In the summer of 1854, after Dr. Gintl's experiments between Vienna 

 and Prague had brought the subject prominently to notice, Messrs. Siemens 

 and Halske of Berlin, and Hr. Frischen independently, invented the 

 " differential" method. 



In January 1855, Edlund§ made experiments on the line between 

 Stockholm and Gothenburg. He employed a " ditferential" method, which 

 he had invented in 1848 for the purpose of measuring accurately Faraday's 

 " extra-currents." 



In papers read at Paris on the 16th July and 6th August 1855|| 



* 23rd October, 18 19. The actual wording of the English patent is unknown to me. 



t Polyt. Central bl., 1853, p. 1475. 



X Wieu Akad. Sitzungsber., XIV. 



§ Pogg. Ann., 1856, vol. 98, page 634. 



II Fogg. Ann., 1856, vol. 98, page 123. 



