382 SUBMARINE CABLE LAYING AND REPAIRING. 



meter is G+R — S, while the shunt path is S. Suppose in this 

 position the deflection produced is equal to cl divisions. Then 

 the deflection corresponding to the whole line current through 

 the galvanometer would be 



cl -^ — - — l!l- divisions, 

 ■=^d —^ — divisions. 

 The line current being the same in each case we have 



R S ' 



whence D=(^— . 



S 



That is, the multiplying power of the shunt is — , the high 



resistance permanent shunt divided by the slide reading. For 

 example, if the permanent high resistance, E, were 10,000 

 ohms, and the slider at 2,500, the multiplying power would be 



10,000_. 

 2,500 ~ ' 



That is, the deflection obtained when the slider is at 2,500 

 would have to be multiplied by 4 to give the deflection equiva- 

 lent to the whole line current. 



In any test involving the comparison between two line 

 currents in which different amounts of shunting are used for 

 each, we have, say — 



deflection d with shunt reading S 

 and „ d^ „ „ Si 



If now the line currents are proportional to D and Di respec- 

 tively, we have, as explained above, 



and Di = d^— 



R being constant for both cancels out and we have 



d:d.::^4 



