Submarine cable

“ A light cable or unprotected core must therefore be regarded at best as an experiment, with the chances against the successful laying, and still more against its existing as a permanent property.
I have written enough to illustrate that the present submarine cable is not a haphazard idea, but one which has grown out of many failures and thousands of experiments; all the principles of manufacture and laying down have been established by great anxiety and reflection on the part of the able men who gave their energies to this kind of enterprise prior to 1865. ”

“ Twenty-seven years ago the first submarine cable was laid across the Strait of Dover. This was a single copper wire covered in gutta-percha, which parted next day; and the first practicable submarine cable was laid in 1851, on the same route. Since then the progress of ocean telegraphy has been extraordinary ”

“ There are two forces, in fact, pulling against each other through the gutta-percha as a neutral medium,—that is, the electricity in the wire, and the opposite electricity in the film of water immediately surrounding the cable; and to that extent the power of the current in the enclosed wire is weakened. A submarine cable, when in the water, is virtually a lengthened-out Leyden jar; it transmits signals while being charged and discharged, instead of merely allowing a stream to flow evenly along it: it is a bottle for holding electricity rather than a pipe for carrying it ”

“ In all there are more than 150,000 miles of submarine cable under the waters of the globe, and there is a fleet of forty ships, large and small, fitted out solely for the purpose of laying and repairing submarine cables. Nowadays the laying of an Atlantic cable attracts no attention, and the fishing up of a slender rope less than an inch thick from the floor of the ocean, 12,000 or 15,000 feet down, is a thing done a dozen times a year. ”

“ According to recent statistics, the North Atlantic Ocean is now crossed by no less than 17 cables, the number of cables all over the world being 2937, with a total length of 291,137 nautical miles.
Before describing the actual working of a submarine cable, a few words on cable-laying may be of interest. Before the cable-ship starts, another vessel is sent over the proposed course to make soundings. Galvanized steel pianoforte wire is used for sounding, and it is wound in lengths of 3 or 4 nautical miles on gun-metal drums. ”

“ The practical working of a submarine cable differs in many respects from that of a land telegraph line. The currents used in submarine telegraphy are extremely small, contrary to the popular impression. An insulated cable acts like a Leyden jar, in the sense that it accumulates electricity and does not quickly part with it, as does a bare overhead wire. In the case of a very long cable, such as one across the Atlantic, a current continues to flow from it for some time after the battery is disconnected. ”

“ 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. ”

“ The receiving instruments for working a submarine cable are different from those used in working land-lines. Inasmuch as the current travels full strength, like a bullet, through a land-line, and in the form of an undulation or wave through a cable, so is it necessary to have different kinds of receiving instruments for each. In a land-line powerful currents can be used with impunity, and these can be made, by means of electro-magnetism, to move comparatively heavy pieces of mechanism in giving signals. ”

“ The science of making, testing, and laying cables has so much improved that an undetected fault in an insulated wire has now become literally impossible, while so much are the instruments for signalling improved, that not only can a slight fault be disregarded if necessary, but it is even easy to work through a submarine wire with a foot of its copper conductor stripped and bare to the water. This latter result, astonishing as it may appear, has actually been achieved for some days past with the whole Atlantic cable on board the Great Eastern. ”

“ Communication by wireless cannot be interrupted by a belligerent. With a submarine cable it is otherwise. The possibility of cutting the cable exists, and if a belligerent possesses naval superiority the cable is cut, as was the German cable near the Azores by one of Germany's enemies, and as was the British cable near Fanning Island by a German naval force. Since a cable is subject to hostile attack, the responsibility falls upon the belligerent, and not upon the neutral, to prevent cable communication. ”

“ Countries far apart, and isolated by oceans, have, by means of deep-sea cables, been brought into intimate relation, and made sharers of one another’s intelligence, enterprise, and civilizing instincts. What the overland telegraph has done toward bringing local states and communities into contact, the submarine cable has done for the remote nations.
In form, an ocean cable differs much from the simple wire which constitutes the conductor of an overland or even underground telegraph. ”

“ Owing to the small currents received and to prevent interference from earth currents it is necessary to use a complete metallic circuit. If an overhead line could be employed no difficulty would be experienced in working a distance of over 1000 miles, but a line of this length is impossible—at least in this country—and if transmission is attempted with any other country, a certain amount of submarine cable is essential. ”

“ All cables of any great length are worked by reverse currents. A modification (known as the cable code) of the ordinary single needle alphabet is used; that is to say, currents in one direction indicate dots and in the other direction dashes.
The general principle on which the instruments for working long submarine cables are based is that of making the moving parts very light and perfectly free to follow the comparatively slow rise and fall of the electric impulses or waves. The simplest form of receiving instrument (formerly much used) is known as the “mirror.” ”

“ It has been found that the electrostatic capacity of one mile of submarine cable is equal to the capacity of 20 miles of overhead line, and as the effect of capacity is to retard the current and reduce the speed of working, it is evident that where there is any great length of cable in the circuit the distance of possible transmission is enormously reduced. ”

“ We have many reasons to confirm the belief that a submarine cable, manufactured and laid with strict attention to all known principles, may be regarded as a substantial property, likely to last for any length of time; for there is no evidence whatever upon record which shows any decay of the insulating medium or copper conductor of a well-manufactured cable, i. e., there is no decay inherent in the nature of a cable; all deterioration is external ”

“ ELECTRICAL GRAPNEL FOR SUBMARINE CABLES AND TORPEDO LINES. By H. KINGSFORD.
All those who are acquainted with the cable-lifting branch of submarine telegraphy are well aware how important a matter it is in grappling to be certain of the instant the cable is hooked. This importance increases, of course, with the age and consequent weakness of the material, as the injury caused by dragging a cable along the bottom is obviously very great. ”

“ EVENTS FOLLOWING THE CIVIL WAR.
THE ATLANTIC CABLE.
Original
ARLY [318] in October, 1851, the first effort at laying a cable for a submarine telegraph was begun by the United States brig Dolphin, which carried a line of soundings across the Atlantic. At that time there were but eighty-seven nautical miles of submarine cable laid, while now there are nearly 200,000 statute miles. Some of these cables merely connect islands with the main shore, others are thousands of miles long. A cable is laid so far below the surface that neither storms, tides or currents can disturb it. ”

“ No insulation of a submarine cable is ever so perfect as to withstand the influence of these electrical phenomena, which correspond [Pg 286] in some particulars to storms in the ordinary atmosphere, their direction generally being from east to west. Their action is immediately communicated to all conductors of electricity, and a struggle set up between the natural current and that used artificially in sending messages. ”

“ The engineers were fast learning the rigorous conditions of submarine telegraphy; in its essentials the Dover-Calais line continues to be the type of deep-sea cables to-day. The success of the wire laid across the British Channel incited other ventures of the kind. Many of them, through careless construction or unskilful laying, were utter failures. At last, in 1855, a submarine line 171 miles in length gave excellent service, as it united Varna with Constantinople; this was the greatest length of satisfactory cable until the submergence of an Atlantic line. ”

“ From this the cable was led over a second pulley, and so into the sea by the stern-sheaves.” [24]
This entire apparatus—simplified as regards the brake—has since been universally adopted for submarine-cable work, [25] with the exception that a single-flanged drum, fitted with a sort of plow, skid, or knife-edge—to guide or “fleet” the incoming turn of cable correctly on to the drum—is now used in place of the grooved sheave, or sheaves. ”

“ All the experience we. have points to the value of protection, first, of the core, then of the external covering, and, if those responsible for the safety and maintenance of submarine cables could be allowed to dictate the most desirable conditions of safety, they would select, besides the strongest possible cable to be manufactured, and laid with extreme care, a depth of water of about 500 fathoms, and a bottom of sand or mud ”

“ The weight per nautical mile of dielectric is the same in both cables, but each copper conductor of the former weighs 300 lb. per mile as compared with 160 lb. per mile in the latter. The transmission efficiency of the cables is practically equal, but the continuously loaded cable provides an additional circuit by superposing. Experiments conducted on this cable in 1914 proved the possibility of obtaining four circuits from a continuously loaded 4-wire submarine cable by introducing an improved method of balancing the electrostatic capacity of the conductors. ”

“ Submarine cables have multiplied recently, and almost every ocean flows over the mysterious wires which flash intelligence beneath the rolling waters from point to point of the civilized world. By a telegraph-cable, which is partly submarine, the India Office in Westminster is united with the Governor-General and his Council at Calcutta. ”

“ The High Contracting Parties agree to insist, as far as possible, when they shall authorize the landing of a submarine cable, upon suitable conditions of safety, both as regards the track of the cable and its dimensions. ”

“ The difficulty of connecting lightships and isolated lighthouses to the mainland by submarine cables, owing to the destructive action of the tides and waves on rocky coasts on the shore ends, led many inventors to look for a way out of the difficulty by the adoption of some form of inductive or conductive telegraphy not necessitating a continuous cable. ”

“ In other words, the retardation is proportional to the product of the resistance of the copper conductor and the total capacity of the cable. This gave a practical rule of great importance for guidance in the manufacture of submarine cables. The conductor should have the highest conductivity obtainable, and should therefore be of pure copper; the insulating covering should, while forming a nearly absolutely non-conducting sheath, have as low a specific inductive capacity as possible. ”

“ Here, then, we have the first instance of an organized system of testing for conductivity at the cable factory—a system which has ever since been rigorously insisted on.
Professor Thomson’s Mirror Instrument.—And now, in the spring of 1858, an invention was perfected that was destined to have a remarkable effect on submarine-cable enterprise. ”

“ If it becomes absolutely necessary to reverse the propellers when paying out cable, men paying it out must haul it in taut and keep it above the wheel and clear of it. The planting vessel should not pass nearer than 25 feet to the distribution box boat when cable is leading out from the latter, nor should it pass over any cable, if it can be avoided, if the depth is less than 16 feet. ”

“ Its subsequent progress, such as it has been, was encouraged and fostered by the trade in provisions and gold induced by the workers at the northern territory gold-fields. There are now two submarine cables connecting Port Darwin with Singapore, viâ Java, and thence with Europe. The first was laid in 1872, and was found most difficult to maintain on account of the ravages made in it by a boring mollusc, a species of Teredo, which in an amazingly short space of time pierced the galvanized iron-wire sheathing of the cable, and destroyed the insulation of the copper core. ”

“ It may be well believed that the Directors have not decided upon a matter so all-important to success, without availing themselves of the most eminent talent and experience which could be commanded. The practical history of submarine telegraphs dates from the successful submersion of the cable between Dover and Calais in 1851, and advantage has been taken of whatever instruction this history could furnish or suggest. Of the submarine cables heretofore laid down, without enumerating others, the one between Dover and Calais weighs six tons to the mile ”