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.
[THE ROMANCE OF A LODGING.]
IN TWO CHAPTERS.—CHAPTER II.
'Well, Fred, what will you say to all my sermons on extravagance, when I tell you that I have actually taken the landlady's first-floor rooms for a month; and that without any view to your advantage, which has hitherto actuated my movements? You will say it is only a preliminary step to my employing the artist—who by the way is not an artist after all—to take my portrait!'
Thus did Mrs Arlington announce her plans next morning at breakfast to Fred, who offered no remonstrance. It was enough for him that she chose to do it; he was too well satisfied and accustomed to her guidance and good sense not to fall in readily with everything she did, as the best possible that could be done; and so he assented without a remark.