It may here be mentioned that ocean cables are usually made in three sections, called, respectively, the shore-end, the intermediate section and the deep-sea section. It is clear that the submerged conductor needs the greatest protection in the shallow water that surrounds the coast, where it lies on a pebbly or rocky bottom, exposed to the drifting action of currents and tides, as well as to the haling flukes of the anchors of storm-tossed ships. In deep water, on the other hand, there is neither shingly bottom nor violent movement to displace and abrade the cable; for all is quiet and peaceful in the profound depths where the god of the trident holds his court; and hence few coverings and a light armor afford sufficient protection. The wear and tear in the ocean depths is a vanishing quantity when compared with the abrasive effects near coast-lines. Looking at the sections of an ocean cable, the biggest and heaviest is the shore-end, while the thinnest and lightest is that which goes down into the depths of the sea. The lengths of the various sections are determined by the survey of the route, which is always carefully made before completing the specification of the cable. Moreover, as the position of the cable-ship at noon every day is known from its longitude and latitude, it follows that the location of the cable on the bed of the ocean is also exactly known. When a cable is broken either by an upheaval or by a subsidence of the ocean floor, the distance of the rupture from the shore end is determined by an electrical test, after which a repair-ship is dispatched to the spot, when the cable is lifted, the "fault" cut away, a new length spliced on, and the amended cable allowed to settle down into its watery depths.
At the present time (July, 1909), there are sixteen cables carrying the work of the North Atlantic, at an average speed of 20 words a minute duplex, or 40 words a minute, counting both directions.
This cable narrative affords as striking an illustration of the triumph of failure as any recorded in the history of human enterprise. It was a victory of mind over matter; of character and tactfulness, energy and endurance over difficulties of every kind, moral and financial, mechanical and meteorological. The four expeditions of 1857, 1858, 1865 and 1866 represent years of hard work, anxiety and distressing failures; but, sustained by the patience of hope and by an unshaken confidence in the soundness of the enterprise as well as in the ability of their staff, the Directors of the Atlantic Company were well rewarded for the disappointment occasioned and the monetary losses incurred. "It has been a long struggle," said the initial promoter of the enterprise, Mr. Cyrus W. Field, speaking at a banquet given in his honor on November 15th, 1866, at the Metropolitan Hotel, New York, "a long struggle of nearly thirteen years of anxious watching and ceaseless toil. Often my heart was ready to sink. Many times, when wandering in the forests of Newfoundland in pelting rain, or on the decks of ships in dark, stormy nights, I almost accused myself of madness and folly to sacrifice the peace of my family for what might have proved but a dream. I have seen my companions, one after another, fall by my side, and I feared that I, too, might not live to see the end. And yet one hope has led me on; I prayed that I might not taste of death till the work was accomplished. That prayer has been answered; and now, beyond all acknowledgments to men, is the feeling of gratitude to Almighty God."
It was men like Field and Thomson that the poet had in mind when he wrote:
The wise and active conquer difficulties
By daring to attempt them. Sloth and folly
Shiver and shrink at sight of toil and labor,
And make the impossibility they fear.
Shortly after his return home, Prof. Thomson was knighted for his splendid services in connection with sub-oceanic cables, and was also honored with the freedom of the City of Glasgow.
If while journeying over land or sea, Sir William's mind was always active, his eyes were also open and observant. In the numerous voyages which he undertook in the interest of cable companies, he seems to have been struck by the unreliable character of the ordinary apparatus used in taking soundings, consisting of a heavy weight suspended by a thick hempen cord unwound from a reel. Owing to the massiveness of the cord, the motion of the ship and currents in the water would necessarily deflect it from the vertical, so that the soundings recorded would be in excess of the true depth. To remedy this defect, Thomson replaced the rope, at first by a steel wire, and later by a thin strand of steel wires, on which the speed of the ship has but little effect; the sinker descends vertically with considerable velocity, and is raised with equal rapidity by suitable winding-up machinery placed in the stern of the ship. The sinker carries a gauge consisting of a quill-tube open at the lower end and closed at the top. The inside, which is coated with silver chromate, shows by the discoloration produced by the action of the sea water how far the water has compressed the air in the tube. By comparison with a graduated ruler, the depth is then read off. When the sinker reaches bottom, the heavy weight is detached automatically, so that there is but little strain on the wire as it ascends with its thermometer and battery of tubes containing samples of the depths reached.
A story is told in connection with this sounding-machine which shows the vivacity and wit of the inventor. Having brought his friend Joule into White's one day, he pointed to a number of coils of steel wire lying on the floor, informing his English friend of "mechanical-equivalent" fame at the same time that he intended the wire for sounding purposes. Upon Joule's innocently asking what note it would sound, he received the prompt answer, "the deep sea"!
Another subject to which Sir William gave some attention after his experiences on the ocean is the navigating compass. His observations led him to distrust the long, heavy needles then in general use on shipboard. Besides the friction to which the pressure on the pivot gives rise and which necessarily diminishes the sensitiveness of the needle, there was another objection, due to the difficulty experienced in successfully applying steel magnets and soft-iron masses to compensate for the magnetism of the ship and for the changes induced in it by change of place in the earth's magnetic field.
As a result, Prof. Thomson devised a compass-card which is remarkable for its lightness and sensitiveness. It is made of two sets of magnets, containing four needles each, arranged symmetrically on the right and left of the pivot. The four needles, forming a set, are of unequal length, ranging from 3-1/4 to 2 inches, with the shortest outermost. Such a card, with its associated correctors of steel magnets and soft-iron balls, has added greatly to the safety and certainty of navigation; and as such, it is used to-day in the merchant service and in the navies of most countries of the world.