546 SUBMARINE CABLE LADING AND REPAIRING. 



E is constant and equal at both ends. Also whatever changes 

 occur in e due to variation of the fault the difference of 

 potential E— e is always equal at both ends. 



Dividing (1) by (2) we obtain distance of fault from A 



X 



-H^,) <^) 



where L is the CR of the line. 



The resistances a and b are considerably higher than the 

 actual conductor resistances in circuit on account of the mutual 

 opposition of the testing currents. It must not be supposed 

 that the fault resistance is equal toa — x or to & — (L - a;). Both 

 testing currents traverse the fault and it is, therefore, lower in 

 resistance than either of these quantities. It is easily shown 

 that the fault resistance at the moment when any pair of ob- 

 servations are taken is 



/=(«-. )A^ ..... (4) 



If the resistance of shunted galvanometer plus battery at 

 either station is not negligible in comparison to that of the line 

 it must be taken account of as a correction. 



Including correction for both these quantities formula (3) 

 becomes 



x= 

 a 



U^+'---'D • ■• ■ • (^) 



Particulars of a test were given in Mr. Bett's article as 

 follows : — 



a b 



Pair 1 2,990 1,707 



„ 2 4,315 2,431 



„ 3 7,861 4,386 



„ 4 9,863 _5,286 



„ 5 17,288 8,600 



The CR of the cable was 3,940 ohms. 



Mr. Raymond-Barker has shown this test solved graphi- 

 cally without calculation {Electrical Eeview, September 13, 

 1901), the figures given above being plotted on the calculator 

 board, as in Fig. 312. The base line represents the CR of the 

 line (3,940 ohms) and the verticals at each end the equal vol- 



