The actual type adopted (Fig. 34), on the recommendation of Sir Charles Bright and other engineers who were additionally consulted, was much the same in respect to the conductor and insulator—300 pounds copper to 400 pounds gutta-percha per nautical mile—as that which the former had suggested for the previous Atlantic line. This combination for the length involved was based on Professor Thomson’s law for the working speed of a cable, as depending inversely on the resistance of the conductor as well as on the electrostatic capacity of the core. The armor consisted of a combination of iron and hemp, each wire being enveloped in manila yarns. The object of incasing the separate wires in hemp was (1) to protect them from rust due to exposure to air and water, and (2) to reduce the specific gravity of the cable, with a view to rendering it more capable of supporting its own weight in{181} water. This form of cable, bearing a stress of about eight tons,[59] and suspending eleven miles of itself, was considered by most of the authorities at that period to perfectly fulfil the conditions required for deep-sea lines.[60] The claims of light hempen cables, without any iron, had been urged for meeting the difficulty of lay and recovery in deep water; and this type formed a sort of compromise, its total diameter being 1.1 inch, weighing 1 ton 16 hundredweight in air, and only 14 hundredweight in water. The shore end was to have a further outer sheathing of twelve strands, each strand containing three stout galvanized-iron wires of No. 2 B.W.G., bringing the weight up to 20 tons per mile. This was to be joined on to the main deep-sea type by a gradually tapering length of twenty-five fathoms.
Arrangements for Laying.—It was determined that this time the cable must be laid in one length, with the exception of the shore ends, by a single vessel. There was but one ship that could carry such a cargo. This ship was the Great Eastern, the conception of that distinguished engineer, Isambard Kingdom Brunel. She was in course of construction by the late Mr. Scott Russell at the time of the first cable, and it was a subject for regret that she was not then available. An enormous craft of 22,500 tons, she did not prove suitable at that time as a cargo-boat; and the laying of{182} the second Atlantic cable was the first piece of useful work she did, after lying more or less idle for nearly ten years.[61] It is sad to think of the way this poor old ship was metaphorically passed from hand to hand. Even at this period three separate companies had already been formed one after another to work her. As promoter and chairman of one of these, Mr. (afterward Sir Daniel) Gooch took an active part in arranging for her charter on this undertaking, and it was in this way that he became a prominent party in the enterprise.
All the cable machinery was fitted to the Great Eastern, on behalf of the Telegraph Construction Company, by Mr. Henry Clifford to the designs of Mr. Canning and himself. It was constructed and set up by the famous firm of engineers, Messrs. John Penn & Son, of Greenwich. In the main principles the apparatus employed was similar to that previously adopted in 1858 on the Agamemnon and Niagara. There were, however, several modifications introduced, as the result of the extra experience gained during the seven years’ interval. The main point of difference was the further application of jockeys to the paying-out gear in a more complete form.
As it was not practicable to moor so enormous a vessel off the works at East Greenwich, the cable had to be cut into lengths and coiled on two pontoons, and thence transferred to the big ship.
Landing the Irish End.—At length all the{183} cable having been manufactured and shipped from the Greenwich works, the Great Eastern, under the command of Captain (later Sir James) Anderson,[62] left the Thames on July 23, 1865, with a total dead weight of 21,000 tons, and proceeded to Foilhommerun Bay, Valentia. Here she joined up her cable to the shore end, which had been laid a day earlier by S.S. Caroline, a small vessel chartered and fitted up for the purpose. The great ship then started paying out as she steamed away on her journey to America, escorted by two British men-of-war, the Terrible and the Sphinx.