﻿1874.] L. Schwendler — On the general Theory of Duplex Telegraphy. 11 



Explanation of Diagram. 



JE, electromotive force of the sigualling battery. 



i8, internal resistance of the signalling battery. 



1c, Telegraph key of peculiar construction to be described hereafter. 



g, the receiving instrument connected up in that branch of the bridge which when 

 measuring resistances would contain the galvanometer. The letter g represents also the 

 resistance of the receiving instrument,* 



a, h, and d are the branches of the bridge. 

 f, the resistance between the rest-contact of the key and earth. 



w, an additional resistance to be inserted in the battery branch for reasons to be given 

 further on. 



i, the resistance of the residtant fault (" real absolute insulation" of the line) acting at 

 a distance I' from station I and at a distance I" from station II (both V and I" expressed 

 in resistances so that V -\- l'^ = I equal the " real conductor resistance" of the line). 



Further : 



i' the " measured conductor"! resistance of the line when measured from Station I, 



il" 



L" the " measured conductor"* resistance of the line when measured from station II, 



il' 

 .•.L"=l-+.-p, 



p' the complex resistance of the duplex arrangement in station I, i. e., the resistance 

 between point 1 and earth. 



p" the complex resistance of the duplex arrangement in station II, i. e. the resistance 

 between point 2 and earth. 



To be quite general we must suppose that the Telegraph line, which con- 

 nects the two stations I and II, has a different resistance when measured 

 from station I than when measured from station II, and that therefore the 

 best resistance arrangement of station I must be also different from that 

 of station II with respect to magnitude of resistances. 



The resistances which are similarly situated in both the stations will 

 be designated by the same letters, and to indicate the station to which they 

 belong, each letter will have one accent in station I and two accents in 

 station II. 



Mr. O. Heaviside Phil. Mag. Vol. XLV, 1873, states that Mr. Eden of Edinburgh 

 claims to have suggested this method at about the same time as Mr. Steai'ns of Boston 

 U. S. Am. took out a patent for it. 



* Siemens's polarized relays are well adapted for this purpose on account of their 

 great sensitiveness and wide range ; d'Arlincourt's relays would also answer well. 



f Generally these measured values i' and i" will be different from each other, 

 especiaRy for long overland lines. They can become equal only under two conditions, 

 either if the resistance of the resultant fault (^) is so great that the total conductor 

 resistance of the line (I' -f* I" = ^^^ ^® neglected against it, or for any magnitude of i, if 



the latter has a position in the middle of the conductor, L e. when I* z=z I" =z - 



2 



