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XX. On the General Theory of Duplex Telegraphy. 

 By Louis Schwendler*. 



Introduction. 

 rjlHE name of " duplex telegraphy" has been given to that 

 J- mode of electric telegraphy which admits of the simulta- 

 neous transmission in opposite directions of signals between two 

 stations through a single wire. That this name is far from 

 happily chosen is evident • but as it is current and has already 

 gained a recognized footing, it is not considered advisable to en- 

 deavour to replace it now by a more rational one, and it will 

 therefore be adhered to throughout this paperf. 



In the following investigation I shall endeavour to develop 

 the mathematical theory of Ce duplex telegraphy " in its most 

 general form, with the object of determining not only the best 

 arrangement for any particular method, but also the relative 

 values of different methods. 



It is manifest that, having from general considerations decided 

 on the best method, and further determined the best arrange- 

 ment for this method, the remaining difficulties, due to the 

 nature of the problem itself, will be exhibited in a clearer light, 

 and the means of overcoming them may then be more easily 

 discerned. 



It is believed, however, that the sequel will show that, if the 

 best method be adopted, and for this method the best arrange- 

 ment 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 arc encoun- 

 tered every day in ordinary single telegraphy. 



Imperfect 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 im- 

 portant invention ; and consequently the following sketch is ne- 

 cessarily 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 simulta- 

 neously through a single wire is by no means a new one. As 



* From the * Journal of the Asiatic Society of Bengal/ vol. xliii. pt. 2, 

 18/4, having been read before the Society on the 4th of February, 18/4. 

 Communicated by the Author. 



t The German language possesses a peculiarly suitable word in "Gegen- 

 sprcchen ;" and the idea is fully rendered by " glcichzcitigcs Gcgcn- 

 sprtchen." 



