SUBMARINE CABLES.

LAYING.

Before the days of steam-ships it would have been almost if not quite impracticable to lay ocean cables; for in order to do so with accuracy and success, it is necessary to be independent of wind and weather as far as possible. The course and speed of the ship must be under the control of the navigator, not at the mercy of the winds and currents, so that he may economise cable, and prevent undue strain upon it as the depth varies. Then too it is necessary that the ship should answer swiftly and surely to his will; that she should vary her speed, stop, or turn round, as promptly as he desires. The telegraph-ship is the helot of her cargo, and should be completely subservient to the work of laying the cable. A well-found steam-ship answers all requirements. Up till a few years ago no specially built telegraph-ship existed. The majority of cables have been laid from ordinary iron screw-steamers, fitted with tanks to contain the cable and paying-out gear. Recently, however, the steam-ships Hooper and Faraday (the first belonging to Messrs Hooper, the other to Messrs Siemens) were specially constructed as telegraph-ships for their respective owners. These vessels are very much on a par in size and carrying capacity. The Faraday is a ship of five thousand tons burden, and capable of carrying fifteen hundred miles of main or deep-sea cable. She is fitted with screws both fore and aft, so that her motion can be reversed without turning her in the water. She can thus, without changing her position, begin hauling in a cable which she had previously been paying out. Both of these ships are fitted with three large iron water-tight tanks for containing the cable—one fore, one amidships, and one aft. The depth of these tanks varies from thirty to forty-five feet, and they are upwards of fifty feet in diameter. The Hooper has laid the Brazilian coast cables, and the Faraday the Direct United States Atlantic cable. Besides the tanks for holding the cable, the only other peculiarities of a cable-ship, as distinct from other steamers, are the heavy deck machinery for paying out the cable and for picking it up if necessary; the electrical testing-room; and the stock of large iron buoys she carries lashed to her gunwales for use in laying.

The cable-ship having been moored alongside the works where the cable is stored, shipment begins. The cable presents three aspects of increasing thickness, namely the shore-end, intermediate, and main; and thus graduated it is payed out of the tanks in the works into the tanks of the ship. When all is aboard, the tanks are filled with salt-water till the cable is soaked, and the ship puts to sea.

During her voyage to the place from which she is to start laying, electrical tests are taken daily of the cables on board, to see that they continue sound, and the machinery for laying is got ready. The souls on board may be divided into three classes. The engineers, or those in charge of the mechanical work of the laying, and their helps 'the cable-hands,' who do the rough work in the tanks and on deck, or in putting out buoys from the ship. The electricians, or those in charge of the electrical work of the laying, whose duty it is to see that the cable is all right electrically. The navigators, or those in charge of the sailing of the ship, including captain, officers, and seamen. The engineer-in-chief is generally the head of the entire expedition; he requires reports from the chief electrician, and instructs the captain where to put the ship.

Before laying a submarine cable between the proposed places it is extremely important to take soundings and otherwise survey the ocean, so as to determine the exact route the cable should take. A cable is too costly to be flung away anywhere on the sea-bottom, and the sea-bottom is sometimes of a very unfavourable character. It may be said that too little attention has hitherto been paid to this point in cable-laying. Expensive cables have been manufactured at home, with their relative lengths of shore-end, intermediate, and main determined by formula or usage, and then hid away in seas whose character had been largely taken for granted; the consequence being that weighty and very costly shore-end has been deposited in mud soft as butter where it would be out of harm's way; while unprotected main has been laid along the jagged surface of coral reefs. The depth and nature of the bottom, the strength and direction of currents, the temperature at the bottom, should all be ascertained beforehand by a special ship appointed to survey the proposed track of the cable. The best route for the cable is then laid down on the charts, as a guide to the navigator and engineers engaged in the laying.

Great improvements have recently been made