394 SUBMARINE CABLE LAYING AND REPAIEING. 



are in accord it is generally a dead certainty that the localisation 

 is correct. On the other hand, when the Schaefer and Ryxner- 

 Jones break tests (both two-current methods to true zero) are in 

 accord, which very frequently happens, it is best to be suspicious, 

 as events will probably show that a barnacle or zoophyte is 

 occupying the end and looking like three or four miles of cable. 

 Sometimes a steady series of observations is obtained by 

 different methods, all more or less in support of each other, 

 with the exception of one solitary result indicating something 

 about five miles nearer. That indication must not be dis- 

 carded on the supposition that the bridge was misread, but 

 followed up and confirmed one way or the other, as notable 

 exceptions to uniformity in results have been known to turn 

 out right after all. Faults and breaks will apparently contra- 

 vene every rule on occasions, and this will be readily under- 

 stood when it is considered that an exposed end may be buried 

 or half-buried, washed over by sand now and then, and occa- 

 sionally stretched or shifted under the influence of bottom 

 currents. Under these conditions it requires very close 

 scrutiny and comparison of figures to arrive at the correct 

 result. 



The localisation of a break is effected not so much by the 

 results of equations as by weighing the bridge readings and 

 reviewing each one in the light of the others. Personal equation 

 enters very considerably into the reliability or otherwise of the 

 results, aud an experienced man knows intuitively what his 

 readings are worth. 



Kennelly Two-current Break Test to False Zero. — When a 

 cable is fractured the resistance of exposure is usually very 

 different at the two broken ends. Therefore, it is no use 

 comparing results from both ends, even though a duplicate 

 cable permits of the results being communicated. Each end 

 must independently localise position of break, and the ship 

 when it cuts in depends only on tests on board. Dr. A. E. 

 Kennelly, as the result of a long series of observations with 

 different currents and areas of exposure, discovered the law 

 known as "the law of inverse square roots," which is briefly 

 stated as follows : — The resistance of an exposed conductor 

 varies inversely as the square root of the current sent through 



