52 



SUBMARINE CABLE LAYING AND REPAIRING. 



minimum thickness of insulator is, in fact, settled by a fixed 

 maximum ratio of weight of copper and gutta-percha for & 

 given Tcr per naut, as will be explained more fully later on. 



550 

 540 

 530 



520 



510 



500 



. 490 



8,480 



^470 



;l"460 



i 450 



5. 440 



£•430 



g420 



>410 



•| 400 



|~ 390 



^ 380 



■§370 



!§ 360 



E35O 



I 340 



1 330 



i^ 320 



310 



300 



290 



280 



270 



2€0 



^ ^ 



\© — — ^ 



_\^ ^ 



O,^ ^S 



&>- ^^ 



0-6 



0-7 0-! 



0-9 



1-0 



1-3 



1-4 1-5 



Ratios of Weights of Copper to Gutta-Percha, 



Fig. 29 — Curve B, showing Insulation Resistance at Standard Tempera- 

 ture and Pressure after one minute ; and Curve C, the Capacity per Naut 

 with Different Ratios of Weights of Copper and Gutta-Percha. 



The electrostatic capacity of a cable is directly proportional 

 to the mean effective area and inversely proportional to the 

 thickness of dielectric. The ratio of these two quantities is the 



