Klotz. — Transpacific Longitudes. 51 



larian ooze, forty-five to coral mud or sand, twenty-seven to ptero- 

 pod ooze, twelve to blue or green muds, and eleven to organic 

 mud or clay.* 



The pressure at a depth of 3,000 fathoms, in which a con- 

 siderable portion of the Pacific cable is laid, is about i tons to 

 the square inch. When the cable is being laid at such depths, 

 it will be approximately twenty miles astern of the ship before 

 it touches bottom. 



Deep-sea cables last longer in the tropics than in the north- 

 ern oceans. The reason is to be found in the fact that in the 

 tropics marine life, from which globigerina ooze is derived, is 

 more abundant than in the more northerly or southerly waters. 

 It is the sun and the warmed surface-water that call into life 

 these countless globigerina, which live for a short space, then 

 die and fall to the bottom like dust, making such a good bed 

 for the cable to rest in. In the arctic currents where the sur- 

 face is cold the water does not teem with life iu the same way 

 as it does in the tropics, and consequently there is less deposit 

 on the bottom of the ocea,n. 



A submarine cable consists first of a core, which comprises 

 the conductor, made of a strand of copper wires, or of a central 

 heavy wire surrounded by copper strips as in the Pacific cable, 

 and the i»isulating covering, generally made of guttapercha, 

 occasionally of indiarubber, to prevent the escape of electricity. 

 As far as cabling is concerned, this is really all that is necessary 

 — an insulated conductor. This, however, would not, in the 

 first place, be sufficiently heavy to lie in the ocean, and, secondly, 

 would be too easily injured and destroyed by the many vicis- 

 situdes to which it would be subjected. For this reason a pro- 

 tection in Ihe form of a sheathing of iron or steel wires surrounds 

 the core, the nature, size, and weight of the sheathing being 

 dependent upon the depth of the water and kind of ground 

 over which it has to be laid. The deep-sea section, being the 

 best-protected from all disturbing influences outside of displace- 

 ment of the earth's crust by earthquakes or volcanic action, is 

 naturally the one of the smallest dimensions ; and for the shore 

 end, which is exposed to the action of the waves, to driftwood, 

 to the grinding of ice in the more northerly latitudes, and to the 

 danger of anchorage, especially of fishing-boats, the sheathing mast 

 be very heavy. So that, while the deep-sea cable is somewhat 

 less than 1 in. in diameter, that for the shore end is nearly 2| in. 

 in diameter. The action of the waves is limited to a depth of 

 only about 13 fathoms, so that their influence on the cable, 

 manifested by wear and chafing, is confined to the shore end. 



* Report of Sir John Murray. 



