Page:Popular Science Monthly Volume 3.djvu/52

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42
THE POPULAR SCIENCE MONTHLY.

Fleeming Jenkin has seen a fault 18 inches long due to this cause, and it is asserted that the same cause destroyed the Toulon-Algiers cable, which was connected to the land-lines without lightning-guards.

We are every now and then startled by the announcement that light cables are to be preferred to the present iron-clad type, and the object of this investigation has been to discover what data there are to justify any preference to one form of cable over another. I have said already that the committee called attention to the remarkable fact that, in almost all cases, small cables have been found liable to mishaps, while the heavier the cable the greater had been its durability.

Mr. Newall, in his evidence, said that the hemp-covered cable which he attempted to lay in 1859, between Candia and Egypt, had the hemp eaten off by the teredo in a very short time, and it was too weak to recover for repairing. The same firm laid an unprotected core from Varna to the Crimea, and it lasted until the winter set in; it is frequently said that it was cut by order of the French commander-in-chief, but there is no proof of this, and I am not disposed to believe it. Mr. Woodehouse, the engineer who laid this core, said in his evidence he "should not advise anybody to lay so light a cable across the Atlantic, because so small a strain would break it. If it is once safe at the bottom, perhaps it may rest." Mr. Newall said he thought it folly to lay any thing excepting unprotected core. Consistently with this conviction, he laid in 1869 several lines of unprotected India-rubber core, connecting the Grecian islands with the main-land; they were protected only near the shore. The sea is quiet and tideless in those parts; no better spot could be wished for the experiment, yet they every one of them gave out within two years.

The Red Sea cable, covered externally with light wires, and unprotected with bituminous compound, was so rusted in a short time that it could not be lifted for repairs.

Notwithstanding, Mr. Newall's partiality for light cables, he suggests at the close of his evidence what I assume he would consider the most perfect form of cable. He would cover the copper with India-rubber, protect this core with steel wires vulcanized, the whole then passed through heat; thus insulating all the wires, he would make the cable in one length, and have no joints. Mr. Fleeming Jenkin, in his report to the International Exhibition of 1862, says:

"So long as the iron wires lasted, the cables frequently continued to work in spite of faults, but sooner or later the iron wires of all these light cables rusted away in parts; so soon as this took place they one and all broke up into short sections; this fact has been observed in depths of 100 fathoms;" the reasons were not obvious to Mr. Jenkin, but he says: "Meanwhile the use of large iron wire seems a sure guarantee against this danger, for as yet no cable covered with wire of the large gauges has ever parted in the manner described. The difficulty is, to find a permanent material which shall retain its strength and continue to afford protection after the cable is laid."