coat together. The third coat was communicated to a solitary strand. The strand and its triple coating of gutta percha were together designated “the core.”

[larger view]
F. Jones, lith from a drawing by R. Dudley
London, Day & Sons, Limited, Lith.
THE REELS OF GUTTA PERCHA COVERED CONDUCTING WIRE CONVEYED INTO TANKS AT THE WORKS AT GREENWICH.

[larger view]
R. M. Bryson, lith from a drawing by R. Dudley London,
Day & Sons, Limited, Lith.
VALENCIA IN 1857-1858 AT THE TIME OF THE LAYING OF THE FORMER CABLE.

The copper strand was formed and coated with gutta percha in two mile lengths. Each of these lengths, when completed, was immersed in water, and then carefully tested to prove that its continuity and insulation were both perfect. The continuity was ascertained by passing a voltaic current of low power through the strand from a battery of a single pair of plates, and causing it to record a signal after issuing from the wire. A different and very remarkable plan was adopted to determine the amount of insulation. One pole of a voltaic battery, consisting of 500 pairs of plates, was connected with the earth; the other pole was united to a wire which coiled round the needle of a very sensitive horizontal galvanometer, and then ran on into the insulated strand of the core, the end of which was turned up into the air, and left without any conducting communication. If the insulation was perfect, the earth would form one pole of the battery, and the end of the insulated strand the other pole, and the circuit be quite open and uninterrupted; consequently no current would pass, and the needle of the galvanometer would not be deflected in the slightest degree. If on the other hand there was any imperfection, or permeability in the sheath of gutta percha, a portion of the electricity would force its way from the strand through the faulty places and surrounding water to the earth, a current would be set up, and the needle of the galvanometer deflected; the deflection being in proportion to the current which passed, and therefore its degree would become a measure of the amount of imperfection.

When about fifty of the two-mile lengths of core were ready, these were placed in the water of the canal which ran past the gutta percha works, and were joined up by their ends into one continuous strand of 100 miles, the joints being covered with gutta percha. The hundred-mile length was then put through a careful scrutiny in the same way that the smaller portions were tried,—and next it was halved, quartered, and separated into groups of twenty, ten, and finally two miles, and each of these were again separately examined, and tested in comparison with similar lengths previously approved.

Whenever separate lengths of the gutta percha covered core were to be joined together, the gutta percha was scraped away for a short distance from the ends, and these were made to overlap. A piece of copper wire was then attached by firm brazing, an inch or two beyond the joint on one side, tightly bound round until it reached to the same extent on the other side, and then was there firmly brazed on again. A second binding was next rolled over the first in the same fashion, and extended a little way beyond it, and finally several layers of gutta percha were carefully laid over, and all round the joint by the agency of hot irons. If the core on each side of the joint was dragged opposite ways until the joint yielded, the outer investment of the wire unrolled spirally as the ends were pulled asunder, and so the conducting continuity of the strand was maintained, although the mechanical continuity of the strand itself was broken.

The two-mile coils of completed and proved core were wound on large drums with projecting flanges on each side, the rims of which were shod with iron tires, so that they might be rolled about as broad wheels, and made to perform their own locomotive offices as far as possible. When the core was in position on these channelled drums, the circumference of the drum was closed in carefully by a sheet of gutta percha, which thus constituted its core-filled channel a sort of cylindrical box or packing case. In this snug nest each completed coil of core was wheeled and dragged away to be transferred to the manufactory, either at Birkenhead or Greenwich.

The core-filled drums, having arrived at the factory of the Cable, the drums were mounted by axles, and kept ready so that one extremity of the length of core might be attached to the Cable as it was spun out, when the drum previously in use had been exhausted. During the unrolling of the core from the drum, it was wound tightly round by a serving of hemp, saturated with a composition made chiefly of pitch and tar, the winding being effected by revolving bobbins as the core was drawn along. This hempen serving constituted a bed for the external coat of metallic wires, and prevented the insulating sheath of gutta percha from being injured by pressure during the final stage of the construction. Each new length of core was attached to the Cable by precisely the same operation as that used at the gutta percha works in joining the two-mile coils for testing; shortly before an old drum was exhausted, its remainder was rapidly pulled off and placed in the joiner’s hands, so that it might be made continuous with the core on a new drum, before the outgoing Cable began to draw upon it.

When the core was covered in with its great coat of hemp and tar, and carefully gauged to ascertain the equality of its dimensions everywhere, it was ready to be turned into the completed Cable. This final operation was effected as the core was drawn up through the centre of a horizontally revolving wheel or table. The table turned with great rapidity, and carried near its circumference eighteen bobbins or drums. Each of these drums was filled with a strand of bright charcoal iron wire, and had two motions, one round its horizontal axis, and one round an upright pivot, inserted into the revolving table, so that it delivered its strand always towards the centre of the table as it was carried swiftly round by the revolution. The iron strand was of the same diameter as that which was used for the copper core. There were also seven iron wires in each strand, exactly like those for the copper strand. Eighteen iron strands were thus firmly twisted round the central core, as the “closing machine” whirled. The core, acted on by the rollers of the machinery, rose through the middle of the table, and went up towards the ceiling. The iron strands danced round it, as it went up, in a filmy-looking spectre-like cone, which narrowed and grew more matter-of-fact and distinct as it ascended, until it glittered in a compact metallic twist, tightly embracing the core. The eighteen strands of seven-thread wire were used for this metallic envelope in place of eighteen simple wires of the same size as the strand, because by this means greater flexibility and strength were obtained for the weight of material employed.

Each strand machine worked day and night, and in the twenty-four hours spun ninety-eight miles of