308 Canadian Record of Science. 



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 

 surface is cold, the water does not teem with life in the same 

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

 deposit on the bottom of the ocean. 



A submarine cable consists, first, of a core, which com- 

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

 central heavy wire surrounded by copper strips as in the Paci- 

 fic cable, and the insulating covering, generally made of gutta 

 percha, occasionally of india rubber, 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 lay in the 

 ocean, and, secondly, would be too easily injured and destroyed 

 by the many vicissitudes to which it would be subjected. For 

 this reason, a protection in the form of a sheathing of iron or 

 steel wires surrounds the core ; the nature, size, and weight ot 

 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 in- 

 fluences outside of displacement of the earth's crust by earth- 

 quakes or volcanic action, is naturally the one of 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 must be very heavy. 

 So that while the deep sea cable is somewhat less than an inch 

 in diameter, that for the shore ends is nearly 2^/2 inches 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. 



The Pacific Cable is equipped with the most modern 

 apparatus at the various stations, and the cable is worked du- 

 plex, that is, messages are sent and received on the same cable 

 at the same time. 



