168 STJBMAEINE CABLE LAYING AND REPAIEINCJ. 



For convenience, let 10,000 -?i. = m, then the potential pei 

 division is equal to 



— volts, 

 m 



and the potential p is equal to 



(10,000 -s)— volts, 



also the potential P is equal to 



10,000 X A volts, 

 m 



The values so determined are then used in the formula 

 a^^R^-^'Mohms, 



where x is the cable resistance to the fault. Or the ahove 



values may be first substituted in the formula, which then 



becomes in its complete form 



-p / 10,000 , p,m\ , 



x = si [ — '- — 1 - -t-I — ohms. 



\ s es J 



The shore simultaneously determines the potential p^ in volts 



by comparing the deflections throvigfh one nripgohm produced 



respectively by this potential and by the known E.M.F. of a 



standard cell. Shunts must, of course, be allowed for if used. 



It will be noticed that the expression comprising the first two 



terms within the brackets multiplied by R is identical with 



that given above as representing the whole resistance in 



circuit, which, when a fault is present, is the resistance from 



ship to earth through the fault. And, since the whole formula 



represents x, the distance in ohms to the fault, it follows that 



the remaining term Viv m 



-J-^ — ohms 

 es 



represents the resistance of the fault. 



If all goes well the ship will lay from 120 to 150 nautical 

 miles per day; and, if no mishap occurs, will lay about 1,800 

 nauts of main cable in a fortnight, including slowing-down for 

 changing tanks and passing out splices. By the drum record 

 of length paid out and the factory mile marks the time when 

 the next factory splice may be expected to come up from tank 

 is known. As soon as it is seen on the flake, warning is passed 

 up, and the order given to slow the ship's engines to half-speed 



