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 The Tuscarora was fitted out at the Navy Yard, Mare Island, Cal., in the summer of 1873, for the purpose of sounding between the shores of the U.S. and Japan, to ascertain the practicability of a cable route across the North Pacific. She was originally fitted with two machines; one, a heavy dynamometer, devised by Passed Assistant Engineer T. W. Rae, U. S. Navy, for sounding with a rope or cord; and the other, a small reel and dynamometer, invented by Sir William Thomson, of Glasgow University, to be used with fine piano wire.

The heavy dynamometer worked well at depths of 1,800 fathoms, beyond which it was not tried, as, owing to the sudden complications with Spain it was taken out of the ship to make room for a gun. Had that machine been kept on board, it was further intended to use with it a small cord, or rope of wire, instead of the hempen line, and the results would undoubtedly have been good. When sounding with that machine, the line passed from the reel with two or three turns round a large drum twelve feet in circumference,—the revolutions being registered by a counter, so that the length of line out was indicated both by the counter and the marks on the line. The principle upon which the working of the machine was based, was essentially the same as that which constitutes the chief merit of the Thomson dynamometer; but this machine being out of the question for the cause above given, the Thomson machine had it all its own way, and so admirable has been its working, and so accurate are its indications that, it seems to be no more than due the genius of Sir William to say, that the appliances for what may be, not inaptly called, the perfection of Deep Sea Sounding, originated with him. Wire had been tried by Lieut. Walsh on board the U. S. schooner Taney, so far back as 1849, but the happy thought had not occurred to him to measure the weight of the wire as it ran out, and applying a counterbalancing weight inside to restrain it in its descent, hence the specific gravity of the wire being so great, it would continue to run on forever, if permitted,