182 SUBJIARINE CABLE LAYING AND EEPAIEING. 



The number of degrees (t) above standard temperature is 

 found from the equation 



9-477 = 9-396 (1+ 0-0021 «), 

 which gives # = 4-7, and hence the mean temperature of the 

 cable is 79-7° F. 



Deep Water Cable. — (Bonny-Island of Principe section) : — 

 Length between cable houses ... 192-747 nauts 



Distance over water 180-88 „ 



Percentage slack 6-56 



Maximum depth 1,444 fathoms 



Mean depth 712 „ 



Observed resistance of line 1,292-5 ohms 



Corrected for temperature 1,298-3 „ 



Eesistance per knot 6-736 „ 



Ditto at 75°F 7-126 „ 



The number of degrees (t) below standard temperature is 

 found from the equation 



7-126 = 6-736 (1+0-0021 «), 



which gives ^ = 26-6, and hence the mean temperature of the 

 cable is 48-4^F. 



Tests of the electrostatic capacity of the cable are also made 

 during this period with the greatest attainable accuracy. At 

 the final test, on the expiration of the period of guarantee, the 

 insulation resistance is taken with zinc to line for 30 (some- 

 times 60) minutes, then 10 or 15 minutes' observation with 

 cable earthed to completely discharge it, followed by 30 minutes 

 with carbon to line. The deflections are observed at the first, 

 fifth, tenth, twentieth and thirtieth minutes, with both currents 

 and the resistances per knot worked out for each. The records 

 of the tests made at the factory, after shipment, on arrival out 

 and after submersion, afford the requisite data for future work 

 on the cable and give a summary of its state at these stages 

 from the time of manufacture till it is safely laid in the sea. 



