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ART. V.-1. Correspondence respecting the establishment of Tele
graphic Communication in the Mediterranean and with India. Presented to the House of Commons by Command: 1858,
1859, 1860. 2. Report of Committee on Packet and Telegraphic Contracts :
1860. It may be asserted without exaggeration that the mechanical
genius of this country has, within the last eighty years, brought about a series of discoveries and inventions, which have changed the whole face of society, altered the conditions of life, and powerfully affected the destiny of mankind. Other nations, our rivals in science, ingenuity and enterprise-profound as the Germans, skilful as the French, daring as the Americans—have in some degree shared in these discoveries, and have not been slow to adopt their results. But in almost every instance the first successful application may fairly be said to have been made in these islands. Let us briefly enumerate the familiar, but surprising, series of them.
To begin with Watt, it was his vigorous Scottish intellect which perfected the steam-engine, and gave a new motive force to man. That power once discovered, and placed under regular control, its applications became innumerable. Every branch of textile manufactures felt the impulse - the power loom and the spinning jenny began to clothe the world; colossal engines pumped out the deepest mines; even rural economy in Britain has since allied itself to steam; and a new era of locomotion com. menced. The invention of the steam-boat is American, but one of its first successful applications was on the Clyde, and we may claim a large share in the most useful improvement yet made in marine engines by the introduction of the screwpropeller. Locomotion by land owes yet more to England. Macadam taught us, and through us all other civilised countries, the art of making a road, which simple as it now appears, is in truth a very modern invention: but before long the most perfect roads which had ever been constructed were superseded by iron tracks, along which the genius and perseverance of George Stephenson drove the first locomotive engine. Artificial light of the utmost brilliancy was conveyed in tubes through our cities and our dwellings, and there is now scarcely a capital in Europe which is not lit by the gasworks of an English company. To descend from these great works to minor contrivances, which, however, have enormously increased the aggregate
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of social convenience and human happiness, within a few years Macintosh has clothed our bodies in impermeable garments ; Sir Rowland Hill has shown that an adhesive stamp and a uniform rate of postage incalculably augments the intercourse of mankind by letters; Dr. Simpson has accomplished the most blessed work of all, by the discovery and introduction of those anæsthetic agents which have the marvellous property of rendering man unconscious of pain ; Mr. Fox Talbot must divide with M. Daguerre that pleasing art which perpetuates on paper the most delicate impressions of light; and Mr. Wheatstone has explained by an elegant application of the same device, the mystery of binocular vision. All these things are novelties of the most extraordinary kind. There is hardly an incident of our daily lives which would not have seemed altogether impossible or miraculous half a century back. Several of these discoveries may be ranked in importance with the three great inventions of the Middle Ages—the mariner's compass, gunpowder, and the printing press, which had hitherto stood almost alone in their momentous consequences to modern society. They have all suddenly sprung up to perfection amongst us — they are all in daily and familiar use. We could no longer exist without them.
But the greatest and most incredible of these achievements we have designedly left to the last. It need hardly be added that we mean the Electric Telegraph, and more especially that portion of the science of telegraphy which is now employed to place in instantaneous transmarine communication the distant islands and continents of the globe. The history of this marvellous invention has more than once been published with great minuteness in other places, and we do not here propose to revert to it. But the truth is that although this instrument is the most extraordinary production of scientific ingenuity, it is by no means the most perfect. Much experiment is still required to ascertain the true physical conditions to which a coil of wire is subjected, when it is used to put a girdle round this planet; much contrivance is still required to provide against the strange and unknown phenomena which have been, or will be, discovered in these vast operations. The grand principle of communication by electricity is established ; and as the discoverers, and first masters of that principle, the names of Wheatstone and of Morse will be transmitted to posterity among the names of the greatest benefactors of the human race. But beyond a certain point, which was speedily attained by the original inventors, the progress of the electric telegraph has been less rapid and satisfactory than is commonly supposed. Undertakings on a vast scale, in which large amounts of public and of private capital are sunk, have been begun and have failed. The art of submarine telegraphic communication is by no means so far advanced as we had hoped, some little time ago indeed, owing to the destruction of several of the longest and most useful electric cables, it has, at this moment rather retrograded. The questions we are about to submit to our readers involve therefore not only facts of extreme interest, but certain problems which have yet to be fully solved. The evidence taken by the scientific Committee recently appointed to investigate the whole subject, is the first precise and authoritative account of it; and with these new and ample materials before us, we propose to trace the history of the more important cables which have been laid; to consider the causes of their failure; and then to discuss the position which the Government has assumed with reference to this species of commercial enterprise.
The general principles upon which electric telegraphs, whether by land or sea, are constructed, are too well known to need repetition here. If a wire insulated from the earth be connected with the earth at one end, and with a battery communicating with the earth at the other, a current may be transmitted along the wire-the strength of the current diminishing in an inverse ratio to the length of the wire. Or if both ends of a long wire be connected with the earth, currents will pass through the line apparently in consequence of variations in the electrical condition of the earth in different places - these are termed earth currents. Mr. Varley, the able electrician of the Electric and International Telegraph Company, observes that these currents are continually flowing about the earth, either in one direction or the other, throughout the day, and reach their maximum about 2.40 P.M. When magnetic storms or the aurora borealis occur, currents sufficiently powerful to interrupt the working of the lines flow sometimes in one direction, sometimes in the other, and often change from one direction to the other in the course of a few seconds. He has observed that there is no general line across England for these currents, but that the lines from London to King's Lynn and London to Southampton are frequently neutral, and the lines from London to Ipswich, London to Bristol, Hull to Manchester are powerfully affected. Professor Thomson gives in his evidence before the Government Telegraph Committee, the following account of a thunderstorm in Newfoundland being registered in Valentia, viz. :
On one occasion, whilst waiting for signals from Newfoundland, the mirror was found to be violently deflected at Valentia, so much so, that it had the appearance of being broken from its suspending tbread; it turned out to be simply that the mirror was pressed forcibly against the stop at the extreme end of its range. While I was looking into the mirror to ascertain whether there was any such accident, it suddenly turned round and went to the other side, there being no battery applied at all at the Valentia end. When communication was re-established, I asked what was wrong, and was told that a violent thunderstorm had been experienced at Newfoundland. “Great deflections and end put to earth for half an hour.” This precaution having been very properly taken by the director of the station there to prevent the possibility of damage to the cable from lightning.'
In land lines the wires are generally insulated from the earth by being attached to supports made of some good insulating material, such as china or glass, which are fixed to the top of poles, twelve to fourteen feet high, placed from forty to sixty yards apart; the atmosphere being itself an admirable insulator especially when dry. But in crossing the sea it is necessary to cover the whole length of wire with an insulating material, and this insulating covering must itself be encased in a protecting sheath. Hence it will be seen that whilst for electric communication by land, only two elements, viz., the conducting wire and the insulators, are needed, the submarine telegraphic line must consist of three parts, viz.:-1st, the conducting wire ; 2nd, the insulating covering; and 3rd, the protecting sheath.
Before describing these several component parts of a submarine cable, it is necessary, in order to elucidate the subject, to state the laws which govern the flow of electricity through insulated circuits of great length.
The conducting power of a conductor, as shown by Ohm, is in simple proportion to the area of its section and inversely to its length, when the quality of metal of the conductor is constant. The capacity of the insulated conductor for charge, or the electrostatic capacity, which influences most seriously the rate of signalling through it, depends on the ratio of the diameter of the insulator to the diameter of the conductor, and is independent of the absolute diameter of either; the facility for charging and discharging the cable is moreover proportioned to the square of the length, other things being the same. Professor Wheatstone gives as a practical rule, that the induction varies directly with the length, and inversely with the square root of the diameter of the conductor and thickness of the insulating covering. Professor Thomson observes in his evidence given before the Committee on Submarine Telegraphs:
"The rate of signalling depends ultimately on the rapidity with which charge and discharge can be effected. I say ultimately; but before we reach this limit, there are many other considerations as regards
the sluggishness of the instruments, the system of more or less convenience for manipulation, and the susceptibility of the system for accuracy, all of which are to some extent uncertain. When these various circumstances are met in the most advantageous possible way, we come to a rate of speed in a line of 200 or 300 miles, which far exceeds the ordinary working rate. A machine could be got which could be worked through 200 or 300 miles at a very much greater rate than has yet been attained by any instrument in practical use. In estimating the speed of working through a long line we must consider the mere mechanical difficulties of very rapid action to be so completely overcome, as to give an extremely high speed in short lines ; and from that basis proceed to estimate the rate of signalling through any length. If we could get three words a minute through 2000 miles, through 200 miles there would be 300 words a minute possible.
The mechanical difficulties of manipulation, however, prevent this high speed being attained on the short lines, but on long lines when the retardation from induction is very great, the mechanical difficulties disappear, and the inductive difficulties limit the speed.
Another cause, which, curiously enough, limits the rate of speed is, that working a telegraph appears to cause nervous irritation in the clerks, and renders them prone to quarrel : if, for instance, one of the clerks carelessly sends a message indistinctly, the receiving clerk frequently gets out of temper, and serious delay results.
The conducting wire is of copper, and is usually made in a strand to diminish the chances of fracture to which a single wire is exposed. Copper is selected on account of the very superior conducting capacity of that metal, viz., seven times greater than that of iron, Copper wire is, however, deficient in strength, and it becomes permanently elongated when extended to a comparatively small amount. It has, therefore, been the practice to depend mainly for the strength of the cable on the protecting sheath. The insulating covering and the protecting sheath of a submarine cable, as generally made, possess more elasticity than copper wire. Consequently it has frequently happened that these after having been extended have returned to the original length, whilst the copper wire inside, which was equally extended, has remained permanently elongated, and has forced its way through its insulating covering of gutta percha. In order to prevent the undue extension of the copper wire, when a strain is brought on a cable, Mr. Allan, who has taken out several patents on the subject, proposes to place the strength of the cable close to the copper wire ; for which purpose he covers it with fine steel wires, and covers these