458 SUBMARINE CABLE LAYING AND REPAIRING. 



And the corrected CE from B end would be 



5,050 + 34 = 5,084 ohms. 



Station B will then request A to balance his end anew to the 

 corrected CR (5,084 ohms). A's previous balance of 5,050 was 

 with an added resistance of 3,020, and he must therefore 

 increase this to about 3,020-f34 = 3,054. Af cer trial he obtains 

 the corrected balance (5,084) with 3,060 ohms added. The 

 corrected distance of the fault from the A end is then 



5,460-3,060 , ^„^ , 

 ^ =-1,200 ohms. 



That is, 20 ohms nearer than the uncorrected result put it. 

 It will be noticed here that the observed CR in the Rule for 

 NE.F correction includes the added resistance at the end of the 

 line. 



If the false zero is very unsteady or the readings variable 

 the balances may be taken to true zero eliminating the earth 

 current effect by Mance's method. This will take rather more 

 time as the observation at each end will then consist of two 

 balances with different currents worked out by the Mance 

 formula. In any case, it is useful to apply this or Schaefer's 

 method for eliminating earth-current effect taking observations 

 to true zero as a check on the false zero readings. 



Jordan and Schonau's Earth Overlap to False Zero. — 

 Messrs. Jordan and Schonau, of the Great Northern Telegraph 

 Company, have devised a modification of the above method (Elec- 

 trical Beview, 1894, Vol. XXXV., p. 427) in which, at both ends, 

 a fixed resistance is unplugged in the third arm of the bridge 

 and balance obtained by adjusting a variable resistance in 

 the line. Both ends test alternately by arrangement for a 

 given number of times without speaking, and add resistances to 

 bring up their respective balances to a pre-arranged amount. In 

 this way time is saved and sets of readings are obtained without 

 disturbance or polarisation of the fault by signalling currents. 



An arrangement is made between the stations that one end 

 tests, say, for two minutes, while the other earths for the same 

 time. Then the first station earths for two minutes while the 

 other tests, and so on for an agreed number of times, lasting 



