482 



SUBMARINE CABLE LAYING AND REPAIRING. 



smaller in the case of the cable, and, therefore, the resistance 

 a is small compared to h. Since the potentials are proportional 

 to the resistances, we have 



a _ e 



and the capacities being inversely proportional to the poten- 

 tials for equal quantities, we have 



f_ c 



f^a 

 F 6 



Therefore 



and 



a 



where F is the capacity of the cable and / is the capacity of the 

 condenser. 



To Galvanometer 



To Cable f 



To Conden-.eP 



Fig. 266. — Lambert's Mixing Key. 



On the slides a is the reading from zero, and h will be 

 10,000 - a. Consequently, we may put the formula in the 

 form 



\ a J 



Lambert's key for this test is illustrated in Fig. 266. Both 

 levers are pressed down at once by the insulated knob A for 

 "charge," and on releasing A the cable and condenser are 

 connected through the bar B and the charges mixed. The 



