544 SUBMARINE CABLE LAYING AND EEPAIEING. 



The fault being very close to the ship, a resistance of 1,342 

 ohms was inserted between bridge and cable to steady the 

 readings. 



A line of average drawn as nearly as possible through the 

 various graphic plottings of the means of the foregoing two 

 series of tests places the fault at 1,347 ohms away, and deduct- 

 ing the added resistance makes it 5 ohms from ship. 



Here the results of the tests are plotted in terms of bridge 



readings in ohms and -^ — i.e., the reciprocal of the square 



root of the current passing in each case, as read on a milam- 

 meter. 



This method for localising a •* partial earth," when there 

 happens to be no skilled assistance at the distant cable house 

 for "earth overlaps," is found very convenient. 



Betts' Partial Earth Simultaneous Method.— Mr. Walter 

 Betts, in an article entitled " A New Method of Localising a 



STATION A, STATION B 



CarboniJ,i,|,|,ZmG Zinc, |,|.|,|. (Carbon 



Fig. 310. — Betts' Simultaneous Method for Localisation of Partial Earth Fault. 



Fault in a Single Cable " {Electrical Revieiu, August 16, 1901, 

 p. 255), describes a deflection method by which a partial earth 

 fault may be localised by simultaneous observations, and which, 

 being independent of variation in the fault, is under the same 

 conditions and has all the accuracy of the loop. During a pre- 

 arranged period and at stated intervals both stations test, with 

 batteries in opposition, putting on the same direction of current 

 (zinc to line) as in Fig. 310. Low-shunted galvanometers 

 are in circuit at each end, and substitutional resistances ER 

 are provided for taking the galvanometer constants in the 

 usual way. 



It is not necessary to add resistance to the low side to 

 centralise the fault. Both stations use batteries of the 



