THE LOCALISATION OF BEEAKS AND FAULTS. 



385 



with a very variable earth current, but ordinarily the condi- 

 tions are quite satisfactory when the shunt is in circuit with 

 the galvanometer and the high resistance in series as in 

 Fig. 227. 



For bridge work the sensitiveness of the galvanometer should 

 be reduced as required by adjusting the high resistance in 

 series, the shunt slider being kept at or near the position for 

 maximum sensitiveness of the instrument. If the short-circuit 

 key is connected to the galvanometer direct it produces heavy 

 damping on the return to zero, due to the coil being short- 



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Fig. 228. — Galvanometer in Sensitive Condition. 



circuited on itself. If connected as in Fig. 226 this damping 

 only occurs when the slider is at the 10,000 end of the shunt. 

 In intermediate positions there is always some resistance inter- 

 posed between the galvanometer and one side of the short-cir- 

 cuit key which prevents the coil being short-circuited. 



When, as recommended, a high resistance is put in series 

 with the shunted galvanometer the best place for the 

 short-circuit key is right across the two points of the 

 bridge. In this position no damping can take place on the 

 return to zero as the high resistance prevents short-circuit- 

 ing of the coil quite independently of any position of the 

 shunt. 



