Cooke. — On Telegraph Cables. 329 



any way for the transmission of the current. There would 

 be little need for this sheathing if it could be insured that the 

 cable should lie on a smooth bed in water sufficiently deep to 

 be removed from the influence of tides and currents. Unfor- 

 tunately for submarine cable enterprise, the bottom of the 

 ocean is as diversified as the land-surface. There are hills 

 and dales, mountains and rugged crags, against which the 

 cable may chafe vmtil it is destroyed. There are precipices 

 and narrow ravines across which the cable lies supported from 

 the two sides and not sinking to the bottom. In such a posi- 

 tion it is more liable to injury. A cable was broken in the 

 Persian Gulf by a whale getting its tail entangled in it, while 

 near the mouth of the Amazon parts of the cable have been 

 raised with fish-teeth sticking in them. All these things show 

 the need of a cable being well protected. 



That the iron sheathing is very efficacious is shown by the 

 fact of comparatively few cables having ceased to work while 

 the sheathing has remained intact, although the insulation in 

 many cases has been far from perfect. 



From time to time proposals come up for what are known 

 as "light cables" — that is, cables in which the iron-wire 

 sheathing is replaced by hemp or sheet copper — but experience 

 does not serve to recommend them. 



From what has been said it will be seen that cables are 

 more liable to injury near the shore, hence those parts are 

 enveloped in much stronger sheathing. Often a second or 

 eVen a third spiral of stout wires is coiled on the part of the 

 cable meant to be laid near the shore, each wire being covered 

 with hemp and the whole passed into a bath of a preparation 

 of tar as it is being coiled on the cable. The cable thus pre- 

 pared is technically known as " shore end," the main part of 

 the cable being known as "deep sea." From the time the 

 insulator is placed on the copper the core is kept wet, and is 

 stored in tanks, where it is covered with water. When the 

 sheathing is put on the water penetrates it and reaches the 

 insulator. This is found necessary, as otherwise chemical 

 changes may cTause heating and consequent destruction of the 

 latter. It also insures the cable being stored under condi- 

 tions similar to those wjien it is in actual use. 



During the whole process of manufacture the cable is sub- 

 jected to electrical tests — continuous tests, where the instru- 

 ments are observed every few minutes, and special tests two 

 or three times a day. The least flaw is thus discovered at 

 once, its locality sought for, and the faulty piece cut out. 

 During the manufacture of the " shore end " the tests are more 

 rigid still, as the removal of a faulty piece in that part in- 

 volves the labour of cutting through a number of stout iron 

 wires and a great loss of material. 



