408 



SUBMARINE CABLE LAYING AND REPAIRING. 



versely as the l'3th root of the current or it would be nil,, 

 neither of which would be consistent with Kennelly's inverse 

 square root law. Mr. Schaefer suggests that the polari- 

 sation resistance may possibly act aa a shunt on the ex- 

 posure {The Electrician, February 25, 1898), and that no con- 

 nection can be established between the two sets of laws, as 

 each involves a particular method of testing and definite 

 ratios of currents. But although the relation between the 

 Kennelly and Schaefer laws is not clearly defined, the successful 

 use of the methods of localisation depending upon them is proof 



High Resistance 

 m Circuit 



Y This wire to Earth' 

 or to Earth Side of Key 



Standard Celt 

 Tig. 240. — Connections for taking the Constant m Schaefer's Test, 



that they are true as carried out in the manner specified, and 

 each with their particular ratios and limitations of current. 



The resistance effect of the earth current ( - ), which is 



in the nature of an increase or diminution of the observed CR, 

 according as the earth current is in the opposite or the same 

 direction as the testing current, is, of course, included in the 

 bridge balance, and its equivalent resistance must be deducted 

 from or added to the balance to obtain the correct result. Mr, 

 Schaefer showed how to determine the earth-current correction 

 which is of considerable usefulness when a long cable is in 

 circuit and enables very close results to be obtained. The 

 potential of the earth current is found by comparison with^a 



