of Duplex Telegraphy. 127 



L" the "measured conductor" resistance of the line when 

 measured from station II ; 



iff 



/. L"=Z"+ -A,- 



p r the complex resistance of the duplex arrangement in station 

 I,, i. e. the resistance between point 1 and earth. 



p n the complex resistance of the duplex arrangement in sta- 

 tion II., i. e. the resistance between point 2 and earth. 



E, electromotive force of the signalling-battery. 



the resistance of the receiving-instrument. 



K, 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*. 



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



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



iv, an additional resistance to be inserted in the battery-branch, for rea- 

 sons to be given further on. 



i, the resistance of the resultant fault (" real absolute insulation " of the 

 line) acting at a distance V from station I. and at a distance I" from sta- 

 tion II. (both V and X! expressed in resistances so that l'-{-l" = l equal the 

 "real conductor resistance" of the line). 



To be quite general, we must suppose that the telegraph-line 

 which connects the two stations I. and II. has a different resist- 

 ance 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. 



* 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. 



