THE LOCALISATtON OF BREAKS AND FAULTS. 



487 



certain time must, tiowever, be allowed for the cable to charge, 

 and Dr. Muirhead's correction overcomes the obvious difficulty 

 of balancing to exactly the necessary time, as it is applicable 

 to any period of charge. The battery having been applied by 

 closing the charge key, and balance obtained afcer a given 

 duration of charge as already explained, the charge key is raised, 

 thus disconnecting the battery and earthing the condenser. 

 The condenser and cable then discharge, but the point V be- 

 tween them does not immediately fall to zero potential 

 on account of the slow discharge due to the oozing out of 

 the charge which has been absorbed by the dielectrics. The 

 correction observation in respect of this absorptioa is now 



Cable 



Standard 

 Condenser 



Earth 



Fig 271. — Gott's Capacity Test with Sullivan Universal Shunt as Slides. 



taken by connecting the poiat V through the galvanometer to 

 earth and reading the throw (d). This is done by moving the 

 slides index to zero (the earthed end) and closing the galvano- 

 meter key. 



The equivalent of this throw in divisions of the slides must 

 then be obtained to bring the correction in the formula. To 

 do this the slides index is run back to a position a little way 

 from zero, say, 10 stops, and the battery being connected to 

 slides the galvanometer key is closed and the throw d^^ observed. 

 If cZj is the exact reproduction of d the slide reading producing 

 it 13 the correction to apply. It is not necessary, however, to 

 adjust the slides to exactly reproduce the throw. Let the slide 

 reading be j^ divisions with d^ throw ; then the equivalent of 



