384 



SUBMARINE CABLE LAYING AND REPAIRING. 



damping on the instrument. When the slider is in an inter- 

 mediate position the damping effect of the bridge arm shunt 

 is less because the resistance between G^ ^^^ ^^® slider is 

 added to it. When the slider is nearly at the G^Ti end this 

 added resistance is so great as to practically annul the damp- 

 ing by the bridge arm shunt, but the galvanometer is then in 

 its least sensitive condition. In bridge work, of course, the 

 final adjustments to balance are made with the galvanometer 

 in the most sensitive condition, and when balancing to false 

 zero the deflections and return to zero should be quick, so that 



I ///////, 



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Fig. 227. — High Resistance to Prevent Bridge Arm Damping. 



the readings can be taken before any great change takes place 

 in the earth current. It is therefore better to have a high 

 resistance available in series with the galvanometer as in 

 Fig. 227, which may be used in combination with the shunt. 

 If, then, the galvanometer is too sensitive it may be reduced 

 by the high resistance in series, keeping the shunt in or near 

 the position for maximum sensitiveness of the instrument and 

 so avoiding the bridge arm damping referred to. 



It may in some cases be desirable to do without the shunt 

 altogether and use only a high resistance in series with the 

 galvanometer, as in Fig. 228. This would permit of a little 

 quicker working as might be necessary on a false zero test 



