188 report — 1865. 



a few mouths later, it was found, moreover, that the hemp had engendered millions 

 of small marine insects of a peculiar kind (the Xylophaga, according to Huxley), 

 which had not only completely destroyed the rope, but had eaten deep holes in the 

 gutta percha without reaching, however, the copper conductor. This action had 

 been accomplished at a depth of from 300 to 500 fathoms. 



Several heavy iron-covered cables have been laid into moderately deep water in 

 the Mediterranean, some of which were laid successfully, though at great risk, aud 

 with great loss of cable, and have worked for several years before giving way. The 

 most remarkable is the Spezzia aud Corsica cable, which consisted of six insulated 

 conductors served with tarred hemp, aud sheathed with twelve galvanized iron 

 wires of vo ths of an inch diameter, producing a weight of 8| tons per mile of cable. 

 This cable was laid in 1854 in a depth of 600 fathoms, and remained in good 

 working order till 1863, when it failed. 



The Red Sea and Indian cable was laid successfully in 1859-60, but failed after 

 nine months' exposure to the sea- water, when it was found that the iron sheathing, 

 consisting of sixteen wires, and weighing 2 tons per mile, had been completely cor- 

 roded through in places. 



The first Atlantic cable, which was laid in 1857, had a sheathing of a peculiar 

 form, consisting of 126 thin charcoal iron wires of No. 22^ B.W.G., giving it great 

 relative strength during the process of laying. Considering, however, the large 

 exposure of iron surface to corrosive action of the sea, this cable must have failed a 

 few weeks after submersion, if the insulated conductor had not been so defective 

 in itself as to render the cable unfit for regular telegraphic communication from the 

 first. 



Another type of sheathing for a deep-sea cable is that which was adapted for the 

 Toulon and Algiers line in i860 ; it consisted of ten steel wires, each of which had 

 been previously covered with tarred hemp, for the purpose of giving it additional 

 strength and protection against corrosion by sea-water. It was proved by experi- 

 ments that the strength of each steel wire was increased to the full amount of the 

 strength of the hemp serving, or about 20 per cent., while at the same time the 

 specific gravity of the cable was greatly decreased, and its descent through the 

 water further retarded, in consequence of the rough surface the hemp serving 

 presents. The insulated conductor of this cable was well proportioned and care- 

 fully tested, and its sheathing was found to be such that a moderate break-power 

 sufficed to prevent its running out too fast in the laying, while at the same time 

 the cable descended with sufficient rapidity to provide the necessary slack (about 

 10 per cent.). Thus far this compound sheathing of steel and hemp had proved a 

 complete success, when about six months after its submersion the continuity sud- 

 denly ceased, and in endeavouring to raise the cable it was found that the marine 

 insects {Xylophaga) had again done the work of destruction, having completely 

 eaten the hemp and left the steel wires like a loose cage around the insulated con- 

 ductor, and fully exposed to corrosive action. 



These repeated failures of the outer covering of deep-sea cables led the writer to 

 devise one which combines the requisites of low specific gravity and relative 

 strength with greater durability than could hitherto be attained. A cable of 

 this description actually forms an important link in the telegraphic chain which 

 now unites France with its African dependency, and is therefore practically entitled 

 to consideration. It consists of the ordinary insulated copper conductor,* which is 

 covered in one process with two layers of best Italian hemp moderately twisted in 

 opposite directions, and lastly with an outer binding sheathing of copper, which is 

 put on under great pressure, and in such a manner that the copper strips composing 

 the same overlap, and are, as it were, mortised into one another, producing practi- 

 cally the effect of a complete flexible tube. Each string of hemp is put on in the 

 machine under an equal strain, which gives to the rope a strength fully equal to the 

 sum of all its constituents. The metal of the outer sheathing is copper mixed with 

 about \ per cent, of phosphorus, which imparts to it greater tenacity, and an 

 increased power to resist chemical action in the sea-water. Instead of copper, 

 zinc has sometimes been used, which also resists sea-water in a remarkable degree. 



The hemp gives great relative strength to this cable. The Algeria cable, with 

 an outer diameter of only \ inch, bears a strain exceeding 1^ ton ; and a cable of 



