486 SUBMAKINE CABLE LAYING AND EEPATRING. 



As the cable and condenser are charged together in series or 

 "cascade," the quantity of charge is the same on both, and, 

 therefore, their capacities are inversely proportional to the 

 difference of potential on each. It will be seen by Fig. 270 that 

 The potential on the cable is e, 

 The potential on the condenser is E - e, 

 where E is the full potential on the slides. And, by inverse 

 proportion, 



/_ e 

 F E - e * 



When there is no deflection on the galvanometer the potentials 

 on the resistances are balanced against those on the condenser 

 and cable, and we have 



Therefore 

 and 



If a and h together form the usual slides divisible into 10,000 

 equal parts, and if a is the slide reading on the cable side, 

 &= 10,000 - a, and we have 



F=/(i2:222_iY 



^ a J 



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

 condenser. 



Another arrangement for this test is shown in Fig. 271, in 

 which Sullivan's universal shunt (divisible into 10,000 equal 

 parts like the slides) is used for adjustment of balance. 



Muirhead's Absorption Correction for Gott's Test. — Dr. 

 Alexander Muirhead has shown that the above formula in Gott's 

 test is correct only when the balance has been obtained imme- 

 diately after " charge " and before the difference in the absorp- 

 tion of the cable and condenser has had time to take effect {The 

 Electrician, September 5, 1890). If there is delay in obtaining 

 balance or reading on the slides, more charge will be absorbed, 

 the potential V at the junction of cable and condenser will vary, 

 and the apparent capacity of the cable will be increased. A 



