Submarine the year 1850, when a copper wire insulated with gutta-percha, submerged between Dover and Calais, continued in use for one day, the progress of submarine telegraphy has been as remarkable as that of telegraphy on terra firma. The Malta-Alexandria cable was laid in 1861, and continued in use till 1872, when, from repeated breakages in shallow water, its use was discarded. The core con sists of a strand of seven copper wires, covered by three layers of gutta-percha; outside of this, a serving • of tarred yarn; and, finally, eighteen iron wires, constituting the sheathing. This was the first long cable successfully laid (its total length, in three sec tions, being 1331 miles); and it was also the first properly tested under water before being laid, and carefully constructed with constant watchfulness as to its electrical and mechanical conditions. This cable was thrown out of use because the chafing it under went in shallow water made it too expensive in maintenance. So far as construction goes, it corresponds very nearly with sir James Anderson's typical "successful iron covered cable." With careful testing and supervision, and with the weight of cable, etc., duly proportioned to the strain, etc., a cable forms a permanent property of much value. A new form of cable, with lead as the conductor, has been suggested. In 1877 the task of duplexing a submarine cable was accomplished by Muirhead on the Aden and Bombay cable of the Eastern Telegraph company, and the " artificial line," or bal ance, has been since applied successfully to other cables, including two crossing the Atlantic. In view of the enormous cost of submarine telegraphy, the attainment of a means by which the carrying capacity of a cable is nearly doubled is of vast importance. In 1877 the Marseilles-Algiers cable, belonging to the French system, was duplexed by M. Ailhaud. The Journal Telegraphigue gave in 1877 a list of 149 cables belonging to companies, and 420 belonging to government systems, existing at that date. In point of
number, Norway stood first, with 193 cables, but the total length of these is only 233 nautical miles. The total length of the 420 government cables was 4,442 nautical miles of which Britain possessed 49, measuring 1338 miles. The longest of these (excludin& cables to the continent) is to Guernsey 70, and to Shetland 63 miles. The cables (of which 96 per cent had their administration in London) measured 59,547 nauti cal miles. The longest cable is that from France to America, 2,585 nautical miles, and the largest organization that of the Eastern and Eastern Extension companies. embrac ing 48 cables of a total length of 21,883 nautical miles, to which, since 1876, several thousand miles have been added in new routes or duplicated cables. In 1879 Great Britain was connected with Europe by eighteen cables, and with Ireland by five cables. From Europe to America seven cables crossed the Atlantic (five from Ireland, one from France, and one from Portugal to Brazil). A cable from Nagasaki to Shanghai joins the internal system of Japan with the outer world; while by cables of 557 miles from Singa pore to Batavia, and 1082 miles from Java to Australia, the distant colonies are brought into the telegraph system of the world. Many additional cables, including one to Natal and the Cape, are projected or in course of construction; and before long it cannot be doubted that the imagination of the poet, to "put a girdle round the earth in forty min utes," will be cast into the shade by the realities of the electric telegraph.
Soe works on Practical Telegraphy by Culley, Sabine, Preece and Siveright, etc; Journal of the Society of Telegraph Engineers; sir James Anderson's Lecture before the statistical society, London, June 1872 ; Mr. Scudamore's reports to the postmaster general, 1870 and 1872; estimates for the telegraph service, ]aid annually before parlia ment, etc.