PROCEEDINGS OP THE ROYAL GEOGRAPHICAL SOCIETY. 43 would be instantaneous, and on such lines the art of telegraphy is but a question of mechanism. On a telegraphic line constructed through the air, perfectly insulated, and traversing an even and favourable temperature, a thousand words can be transmitted in one minute by the aid of mechanism. The ordinary manipulation, however, is with the hand, by the opening and closing of a given metallic circuit charged with electricity. The maximum trans- mission in this manner may be considered at about forty words per minute. The speed of transmission of the electric force through submarine cables depends upon the conductibility of the metal, its insulation, and length of circuit. I have good authority for saying that experiments instituted in England with No. 16 copper wire, have proved that the electric current requires one-third of a second for the first 500 miles, and one second for 1000 miles. According to this progression, the time required to transmit an electrical impulse 2000 miles would be about nine seconds. This delay or hindrance is called “retardation.” The cable becomes a Leyden jar, and the current transmitted is, more or less, held in suspension until discharged by some contrivance. It is owing to this suspension or retardation, and the irregularity of its time, that long submarine telegraphs cannot be made effective for commercial purposes. Circuits of the Northern Route.—The electric circuits of the North Atlantic telegraph will be short—the longest about 600 miles, and cables can be laid capable of transmitting at least twenty words per minute. It will be a financial question that will determine the capacity of the cables for the commercial telegraphy. Between Scotland and the Faroes, and between the Farcies and Iceland, cables can be laid that can equal the working of a double line of cables across the other sections of the route, or perhaps it may be found best to construct them for the short sections with two wires for telegraphing, and on the other sections with three or more conducting wires. If either one of the sections fail, the whole are not lost, and another cable can be promptly submerged. The Seas.—The depths of the seas are but little known. A few soundings were taken on the route last autumn. The water between Scotland and the Faroe Islands, and thence to Iceland, is not very deep, not exceeding perhaps, 1000 fathoms, and there can be no doubt but that the bottom is very deep mud. The sound- ings taken last autumn between Iceland and Greenland proved the bottom in that sea to be deep mud. The greatest depth of water was 1540 fathoms. The mud brought from the bottom has been

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