OCEAN-CABLES. 



4 



that condition until it was laid, was the Malta and Alexandria cable, 

 laid in 1861. This cable was submerged in too shallow water, for 

 many miles in less depth than 20 fathoms ; the result was the frequent 

 recurrence of fracture from being rolled about by the surf, and yet 

 this cable was only finally abandoned last year ; not because it could 

 not be kept in repair, but because it was too expensive to keep in 

 order. These and many other examples have established the principle 

 that no cable should be laid without first obtaining an accurate sur- 

 vey of the approach to the coast and landing-places, with accurate 

 soundings over the intended route, and as much knowledge as possible 

 of the nature of the bottom. Currents and anchorage should be 

 avoided, and, where that is impossible, the heaviest cable that can be 

 laid should be provided. Heavy cables should be laid out to depths 

 of 400 fathoms, where there are tide-ways. Where a current exists, a 

 position should be sought for as far removed from it as possible. A 

 great cause of injury to cables is the corrosion of the external wires, 

 caused by moving water or marine vegetation, etc., and this has 

 established the general practice of covering the external wires with 

 tarred yarn saturated with a mixture of pitch and silica. There is 

 still great room for improvement upon the present method of protect- 

 ing- the external covering; of cables, and I commend it to the further 

 careful study of telegraph-engineers as a subject of vital importance. 



Another enemy of submarine cables is the teredo * of all kinds ; there 

 is one kind which has proved destructive by boring through the core, 

 but that has only occurred in shallow water ; there is another kind 

 which destroys the hemp in a few months, and is then satisfied to fix 

 itself upon the gutta-percha and remain there. Cables have been re- 

 covered from depths of 1,200 fathoms with all the hemp eaten away, 

 and the core pitted with these marine animals. The recovery is then 

 only possible by the strength of the external wires. 



All the expei-ience we. have points to the value of protection, first, 

 of the core, then of the external covering, and, if those responsible for 

 the safety and maintenance of submarine cables could be allowed to 

 dictate the most desirable conditions of safety, they would select, be- 

 sides the strongest possible cable to be manufactured, and laid with 

 extreme care, a depth of water of about 500 fathoms, and a bottom of 

 sand or mud ; but, as this cannot always be secured, nothing should be 

 omitted in the direction of strength and quality. 



Lightning is still another source of injury to cables ; this is, how- 

 ever, so readily guarded against that we no longer hear of injury from 

 this cause : it is said to have destroyed three cables. Mr. Siemens 

 produced before the committee a piece of the core of the Corfu cable 

 injured by lightning ; the land-line had been struck, and, from the ab- 

 sence of any lightning-guards, the cable was damaged. Mr. Preece 

 described the Jersey cable as having been destroyed by lightning. Mr. 



See article, iu this number, on the " Borers of the Sea." 



