426 



SUBMAEINE CABLE LAYING AND REPAIRING. 



can, of course, be made by altering the connections of the 

 wires by hand if necessary, without the use of commutators. 

 With the aid of this diagram any Iseys or commutators avail- 

 able can be adapted to make the connections required, so long 

 as the conditions of the test are carried out, and the parts are 

 well insulated. 



In the position shown the switch puts battery to line (com- 

 mutator plug being in 3) and in position E puts line to earth, 

 both charge and discharge passing through the galvanometer. 

 But the line can be discharged independently to earth without 

 affecting the galvanometer by closing the earthing key, which 



A^A/VWVWV- 



fn^ 



I\ 



Differential Galvanometer 

 with Universal Shimts 



Break 



Condenser Key 



Fig. 246. — Rymer- Jones High Resistance Break Test. 



at the same instant breaks the battery circuit. As it is the 

 quantity of charge that is observed in this method, the cable 

 can be discharged between each charge reading without affect- 

 ing the galvanometer, so that the latter is in a state of rest 

 ready to indicate the next charge throw. The play of the key 

 is made as small as possible, so that earthing immediately fol- 

 lows disconnection of the battery. There are four observations. 

 (1) OJwnic Balance. — Plugs 1 and 3 in. Battery switch to B 

 putting zinc to line. Galvanometer short-circuit key con- 

 nected across the two galvanometers as shown in full lines in 

 the diagram. Adjust galvanometer shunts and the variable 

 resistance (R in diagram) until the differential galvanometer is 

 balanced to zero. 



