The accuracy of Thomson's law was disputed in 1856 by Dr. Edward O. Wildman Whitehouse, the electrician of the Atlantic Telegraph Company, who had misinterpreted the results of his own experiments. Thomson disposed of his contention in a letter to the ATHENAEUM, and the directors of the company saw that he was a man to enlist in their adventure. It is not enough to say the young Glasgow professor threw himself heart and soul into their work. He descended in their midst like the very genius of electricity, and helped them out of all their difficulties. In 1857 he published in the ENGINEER the whole theory of the mechanical forces involved in the laying of a submarine cable, and showed that when the line is running out of the ship at a constant speed in a uniform depth of water, it sinks in a slant or straight incline from the point where it enters the water to that where it touches the bottom.

To these gifts of theory, electrical and mechanical, Thomson added a practical boon in the shape of the reflecting galvanometer, or mirror instrument. This measurer of the current was infinitely more sensitive than any which preceded it, and enables the electrician to detect the slightest flaw in the core of a cable during its manufacture and submersion. Moreover, it proved the best apparatus for receiving the messages through a long cable. The Morse and other instruments, however suitable for land lines and short cables, were all but useless on the Atlantic line, owing to the retardation of the signals; but the mirror instrument sprang out of Thomson's study of this phenomenon, and was designed to match it. Hence this instrument, through being the fittest for the purpose, drove the others from the field, and allowed the first Atlantic cables to be worked on a profitable basis.

The cable consisted of a strand of seven copper wires, one weighing 107 pounds a nautical mile or knot, covered with three coats of gutta- percha, weighing 261 pounds a knot, and wound with tarred hemp, over which a sheath of eighteen strands, each of seven iron wires, was laid in a close spiral. It weighed nearly a ton to the mile, was flexible as a rope, and able to withstand a pull of several tons. It was made conjointly by Messrs. Glass, Elliot & Co., of Greenwich, and Messrs. R. S. Newall & Co., of Liverpool.

The British Government promised Mr. Field a subsidy of L1,400 a year, and the loan of ships to lay the cable. He solicited an equal help from Congress, but a large number of the senators, actuated by a national jealousy of England, and looking to the fact that both ends of the line were to lie in British territory, opposed the grant. It appeared to these far-sighted politicians that England, the hereditary foe, was 'literally crawling under the sea to get some advantage over the United States.' The Bill was only passed by a majority of a single vote. In the House of Representatives it encountered a similar hostility, but was ultimately signed by President Pierce.

The Agamemnon, a British man-of-war fitted out for the purpose, took in the section made at Greenwich, and the Niagara, an American warship, that made at Liverpool. The vessels and their consorts met in the bay of Valentia Island, on the south-west coast of Ireland, where on August 5, 1857, the shore end of the cable was landed from the Niagara. It was a memorable scene. The ships in the bay were dressed in bunting, and the Lord Lieutenant of Ireland stood on the beach, attended by his following, to receive the end from the American sailors. Visitors in holiday attire collected in groups to watch the operations, and eagerly joined with his excellency in helping to pull the wire ashore. When it was landed, the Reverend Mr. Day, of Kenmore, offered up a prayer, asking the Almighty to prosper the undertaking, Next day the expedition sailed; but ere the Niagara had proceeded five miles on her way the shore-end parted, and the repairing of it delayed the start for another day.

At first the Niagara went slowly ahead to avoid a mishap, but as the cable ran out easily she increased her speed. The night fell, but hardly a soul slept. The utmost vigilance was maintained throughout the vessel. Apart from the noise of the paying-out machinery, there was an awful stillness on board. Men walked about with a muffled step, or spoke in whispers, as if they were afraid the sound of their voices would break the slender line. It seemed as though a great and valued friend lay at the point of death.

The submarine hill, with its dangerous slope, was passed in safety, and the 'telegraph plateau,' nearly two miles deep, was reached, when suddenly the signals from Ireland, which told that the conductor was intact, stopped altogether. Professor Morse and De Sauty, the electricians, failed to restore the communication, and the engineers were preparing to cut the cable, when quite as suddenly the signals returned, and every face grew bright. A weather-beaten old sailor said, 'I have watched nearly every mile of it as it came over the side, and I would have given fifty dollars, poor man as I am, to have saved it, although I don't expect to make anything by it when it is laid down.'

But the joy was short-lived. The line was running out at the rate of six miles an hour, while the vessel was only making four. To check this waste of cable the engineer tightened the brakes; but as the stern of the ship rose on the swell, the cable parted under the heavy strain, and the end was lost in the sea.