6 volts × .1 ampere = .6 watts.
Telegraph line wires are usually bare, the insulation being merely the glass knobs at the poles. Clean water is a very good insulator but dirty water is a fairly good conductor. A wet telegraph pole may bring so much current to earth as to prevent all sounders on the line from operating. Hence the line is separated from the poles by glass. The poles are about one hundred and thirty-two feet apart, making forty to the mile. The wires are usually galvanized iron one sixth of an inch in diameter. Copper conducts six times as well as iron, and is now replacing iron in the lines.
Morse laid a submarine telegraph line in New York Harbour and suggested a cable across the ocean. But that gigantic undertaking had to await the masterful intelligence of Lord Kelvin and the indomitable will of Cyrus W. Field. A submarine cable was laid across the Strait of Dover in 1850. It was cut by the anchor of a fisherman a few hours after it was laid. The first attempt to lay a submarine cable across the Atlantic Ocean was made in 1857. Two ships of war, the Agamemnon of Great Britain and the Niagara of the United States, engaged in this undertaking. Three hundred miles had been laid when the cable parted where the ocean was more than two miles deep. William Thomson was on board the Agamemnon as electrical expert. He went home to study and improve the methods. The next year, 1858, the Agamemnon and the Niagara met in midocean each with a portion of the cable on board. The splice was made, and the Agamemnon started toward Ireland and the Niagara toward Newfoundland. When six miles apart the cable broke. The ships met again, made a new splice and again started in opposite directions. They laid eighty miles and the cable parted a second time. They met again, spliced and laid two hundred miles when it parted for the third time. They met a fourth time, made the splice and succeeded in laying the first cable from Ireland to Newfoundland on August 5, 1858.
In a few weeks the insulation failed and no more messages could be sent. Seven years were spent in studying the problem, and again in 1865 the Great Eastern, a mammoth ship, started to lay the cable. William Thomson was again on board as the expert. When twelve hundred miles had been laid the cable parted in deep water. Three times the cable was grappled and brought part way to the surface and lost again. The Great Eastern returned to land. The next year, 1866, the Great Eastern, having on board William Thomson (Lord Kelvin), Mr. Canning, the engineer of the expedition, and Captain Anderson, in command, laid the cable which has worked successfully ever since. Thomson, Canning, and Anderson were knighted as a result of their labours. Sir William Thomson (1824–1907), afterward Lord Kelvin, is credited with having solved the difficult electrical problems connected with this enterprise. Cyrus W. Field (1819–1892), born in Stockbridge, Mass., helped to secure the many millions of dollars necessary to carry the work to completion.
There are now seventy-three cables connecting Europe and America, and two across the Pacific Ocean. Cable rates are: New York to England, France, Germany, or Holland twenty-five cents a word, to Switzerland thirty cents a word, and to Japan one dollar and thirty-three cents a word.
The boys were kept very busy now looking up historical and biographical sketches, as well as working up the many applications of the electro-magnet. The next to be reported was:
Fig. 32
11. The Relay ([Fig. 32]).—Telegraphing from 3,000 to 10,000 miles under the ocean is full of difficulties not now to be explained.