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 in the method of taking deep-sea soundings. The ordinary plan is to carry the lead-line (a strong line or small rope of fine tanned Manilla yarn) from the stern along the ship's side to the bows, and there drop the lead into the sea. As it sinks the rope runs out off the drum on which it is coiled, and when the lead strikes bottom the running ceases. The introduction of fine steel pianoforte-wire for the rope, by Sir William Thomson, is a great improvement upon this clumsy method. The wire sinks quickly through the water, and is pulled in again with a very great saving of time and labour. But the most ingenious of all contrivances for finding the depth of the sea is Siemen's Bathometer, a very recent invention. The bathometer simply stands in the captain's cabin like a barometer, and indicates the depth of the sea over which the ship is passing, just as a barometer indicates the height of the atmosphere above. The action of this ingenious contrivance depends on the attraction of the earth on a column of mercury. This attraction is proportional to the earth's density, and the relative distance of its crust from the mercury column. Earth being denser than water, exercises a greater downward attraction on the mercury. If then there are say a hundred fathoms of water just under the mercury instead of a hundred fathoms of earth or rock, there will be less downward attraction on it. Taking advantage of this law, the mercury column is adjusted so as to indicate the power of the attraction and give the depth of water it corresponds to.

Arrived at the place from which the cable is to be laid, the first thing done is the laying of the shore-end from the ship at her anchorage to the cable-hut on the beach. The cable-hut is generally a small erection of galvanised iron or stone and lime to contain the end of the cable and a few instruments. Cables are never if possible landed in harbours, or where there is danger from anchors. A suitable retired cove is generally selected, not far distant from the town where the telegraph office is, and a short land-line connects the end of the cable to the office. In the cable-hut the land-line and cable meet and are connected together.

The distance from the ship to the cable-hut is accurately measured by the ship's boats or steam-launch, so as to fix the amount of shore-end necessary to reach the shore. This is then coiled in a flat barge or raft, and payed out by hand as the launch tugs the raft ashore. When the water becomes too shallow for the raft to float, the men jump into the water and drag the heavy end ashore. A trench has been cut in the beach up to the cable-hut, and into this the end is laid. In a few moments a test from the cable-hut to the ship announces that the shore-end is successfully fixed.

Everything is now ready for the ship to begin paying out. The anchor has been got up; the paying-out gear is all in working order; the men are all at their appointed places. The cable is being held fast at the ship's stern, and the running out by its own weight is prevented. But directly all are aboard again, the word is given, the screw revolves, the cable is let go at the stern, and the real work of paying out begins.

The cable passes from the tank to the stern of the ship, and from thence to the bottom of the sea. The weight of that part which hangs in the water between the ship and the bottom pulls it out of the ship as the latter moves along. If the ship were stationary, still the cable would run out, but then it would simply coil or kink itself up on the bottom. The object is, however, to lay it evenly along the bottom, neither too tight nor too slack, so as at once to economise cable, and to allow of its being easily hooked and hauled up again from the bottom without breaking from over-tightness. The speed of the ship has therefore to be adjusted to the rate at which the cable runs out. It should be a little under the rate of the paying out, so that there is a slight excess of cable for the distance travelled over. Now the rate at which the cable runs out from the ship is greater, the greater the depth; therefore the speed of the ship must be varied as the depth changes. The rate at which the cable runs out, however, is not entirely dependent on the depth. It can be controlled on board by mechanism. The cable can be held back against the force pulling it overboard. But there is a limit to the extent to which it may be held back, and the tension on it must not be so great as to overstrain it. It is necessary, therefore, to know what tension there is on the cable at any time. To achieve this, two apparatus are used: the friction brake (for holding the cable back) and the dynamometer (for indicating its tension).

The cable is made to run cleanly out of the tank by being allowed to escape through a funnel-shaped iron framework called a 'crinoline.' This prevents it from lashing about or flying off as the ship rolls. It then passes over pulleys to the paying-out drum, round which it is passed several times. The paying-out drum is controlled by an Appold's friction brake, which is simply a belt or strap of iron with blocks of wood studded to it clasping the periphery of the drum and restraining its revolution by the friction of the wooden blocks. The tighter the belt is made to clasp the drum, the greater the friction on the drum, and the greater the force required to make it revolve. After passing several times round the drum, so as to get a good hold of it, the cable passes through the dynamometer to the sheave or grooved pulley projecting from the stern, and from thence it passes to the water. The dynamometer is simply a 'jockey pulley' riding on the cable; that is to say the cable is made to support a pulley of a certain weight; and according as the tension on the cable, due to the weight of cable in the water, is greater or less, so will the weight of this jockey pulley supported by the cable cause the cable to bend less or more. Although this jockey pulley is the essential part of the dynamometer, there are three pulleys altogether, two fixed pulleys at the same level, with the riding pulley between. The cable passes over both the fixed pulleys and under the riding pulley. The weight of the latter bends the cable into a V shape; and as explained above, the depth of this V is greater as the tension on the cable is less. In short the tension of the cable can be told from the depth of the V, which is therefore graduated into a scale of tensions.

By regulating the friction on the brake the cable can be held back, under restrictions of tension indicated by the dynamometer, and the speed of the ship adjusted to give the proper percentage of slack. Sixteen per cent. for a depth of two thousand fathoms is a usual allowance. The slack should vary with the depth, because of the possibility of having to hook the cable and raise it up from the bottom to the surface to repair it. The revolutions of the drum, the tension on the cable, the number of turns of the ship's screw, are constantly observed night and day as the laying goes on.

In the electrical testing-room the same watchful activity prevails. A continuous test is kept applied to the cable, to see that its insulating power keeps steady; in other words, to detect any 'fault' that may occur in the cable which is being laid. This is done by charging the cable throughout, from the end on board the ship to the end left behind in the cable-hut, with a current of electricity, and observing on a galvanometer (an instrument described in a recent paper) the amount of electricity which leaks through the gutta-percha from the copper wire inside to the sea-water outside. To shew that the copper wire too keeps continuous from ship to shore, a pulse of electricity is sent along the cable at stated intervals, usually every five minutes. This is either sent from the ship to the cable-hut, or from the cable-hut to the ship by the electricians left on duty there. The resistance too of the copper conductor is regularly taken at times, to see whether the conductor remains intact; for the pulse test only shews that it is continuous, and would not shew, for instance, that it had been half broken through.

The navigators of the ship are meanwhile as busy as the rest on board. It is important to keep the ship as nearly as possible up to the prescribed course marked on the chart, and in any case to determine accurately her place whatever it may be, so that the precise position of the cable on the bottom may be known, in order to facilitate future repairs, if necessary. Observations of the sun and other heavenly bodies are therefore made as often as feasible, and the navigation of the ship very carefully attended to.

If a fault should be reported from the testing-room, the engines are at once reversed and the ship stopped. The length of cable being payed out is cut in two within the ship, and that section still on board is tested first. If the fault is found to be there, a new length of cable is jointed on to the section in the sea, and the laying is again proceeded with. If, however, the fault is in the section already laid, special tests must be applied to locate the fault. If it should be proved to be but a few miles from the ship, she is 'put about;' the end of the section is taken to the bows, where the picking-up gear is situated, and the cable is hauled in slowly from the sea by the help of a steam-winch, the ship going slowly back the way she has come as the cable comes on board. This goes on until the fault is reached and cut out. If the fault should be proved to be twenty or more miles away, the end of the cable is buoyed, and the ship proceeds backward to the locality of the fault. Here she grapples for the cable, hooks it, and draws it up to the surface, where it is cut and the two parts tested separately. The flaw is then cut out of the faulty part and the cable made good. She then returns to her buoy, picks up the end there, joints on the cable on board to be paid out, and continues her voyage.

Arrived at her destination, the shore-end there is landed to its cable-hut. A test taken from there and signals exchanged between the two cable-huts proclaim the completion of her work. It only remains to test the cable daily for a specified period, generally thirty days; and if during this trial time it remains good and sound, it passes into the hands of the Company for whose use it has been laid, and is then employed for regular traffic and public benefit. In a concluding article we will describe the working of submarine cables.