SCIENCE AND PRACTICE. 



377 



85. Finding the Place of a Fault in the Insulating Covering 

 when both ends of the cable are at hand. The advantage of 

 having both ends occurs before the cable is submerged, 

 and sometimes, but in rare instances, after it is submerged, 

 when the stations at the ends of the line are joined by 

 another wire, whose insulation is good, and which enables 

 the electrician to employ the " loop-method." In this event 

 the ends of the two cables are connected together at the 

 distant station, say at A, Fig. 174, forming a single line, E A d. 



Fig. 174, 



Two proportion resistances, r and f>, are connected together 

 in a point, a, with one pole of a battery whose opposite pole 

 is to earth ; their further ends b and d are severally connected 

 to the end of cable and the end of an adjustable resistance, 

 R, the remaining ends of the cable and resistance- coil meet- 

 ing in E. The resistance R is inserted in the cable circuit at 

 that end of it towards which the fault lies. A galvano- 

 scope is also inserted between b and d. The system thus 

 arranged forms the circuits of an ordinary Wheatstone's 

 balance, the sides of which are, respectively, 1) r, 2) p, 3) y, 

 4) R -|- x. The magnitude x is the resistance of the con- 

 ductor from the fault to E, y the resistance from the fault to 

 d ; therefore, the resistance of the whole conductor / is 



