OCEAN TELEGRAPHY. * FORTUNATE has it been for the Electric Telegraph
that ifs infancy WO never subjected to the enervating influence of Glcvacionent • The. Edinburgh Review, No. 229, Jannaq 189L, Published biAamposo .01111 to.
aid, and that the slight patronage at first vouchsafed to it by two of the most powerful railway companies was so speedily withdrawn, as to leave it wholly dependant on its own resources for the suc- cess it has achieved on land. At sea, too, its most prosperous stept have been accomplished by its own unborrowed strength, while its failures date from the period when it first began to lean on the arm of the Government. The Dover and Calais telegraph, the earliest of the submarine kind, was laid down in 1852, and was followed, not long afterwards, by the Dover and Ostend line. In 1853, Orfordness, near Ipswich, was connected with the port of Schevening, in Holland, by a cable extending 125 miles under the turbulent North Sea, and which was paid out during a violent gale of wind without the slightest accident. In 1858, a line was laid from England to Denmark, 350 miles in length. All these lines are still in good working condition, and for not one of them has any Government aid been asked or given. They are all ex- posed to strong competition, and yet it has been found worth the while of private companies to lay them. Very different has been the fortune of the lines which have been inaugurated under the new policy adopted by the Government in 1856, since which period it has guaranteed five lines—one for the Atlantic, one for the Channel, two for the Mediterranean, and one for the Red Sea. One of these five, the Ragusa and Alexandria Telegraph, has
never been constructed, and the rest have all failed. The writer in the Edinburgh expresses his conviction, "that at no very dis- tant period submarine telegraphs, established on sound principles i and in a durable manner, will encircle the globe ; " but, for the present, he regards the whole matter of deep sea telegraphy as standing in a highly unsatisfactory condition, for which the Go- vernment is, to a great extent, answerable. He admits that a guarantee of interest, so long as it is limited to a certain amount, and so long as it is only to be paid while the line is capable of doing a specified amount of work, is one of the least objectionable modes of support which can be given; but objectionable it still is, as tending to diminish the habit of self-reliance, which is the source of our commercial success. When, however, the guarantee is given unconditionally, as in two instances it has been, when it insures to the shareholders a specified rate of interest for a speci- fied number of years, whatever the working expenses and what- ever the condition of the line may be, the injury done to the spirit of public enterprise is incalculable— "The history of the Atlantic enterprise shows that failure was its neces-
sary result ; and yet it was made under Government sanction, and by the help of assistance from Government. No doubt, the form in which this assistance was given was one of the least objectionable forms in which Government assistance could be given, viz., a payment conditional upon success; but there was no definition of what that success was to be; if one word per hour could have been transmitted, the company might have claimed the letter of its bond. It may, however, be fairly assumed that if the Go- vernment had declined to assist the undertaking, it would at that time have gone forward perhaps more slowly, but more surely, than it did with the flourish of the Government help: The shareholders who advanced 10001. apiece in London and Liverpool, did so for a national experiment, and not
with the sole thought of gain. But, even if it had not gone forward then, and if we had continued to advance by slow and sure steps in Goeaggele- graphy, it would have been better for science, better for our credit asitac- tical nation, and better for those whose property now lies irrecoverably lost at the bottom of the Atlantic. . . . .
" Guaranteed telegraphic lines have unfortunately been got up generally by persons unacquainted with the subject, and have been placed by the pro- moters in the hands either of contractors, who were, of course only inte- rested in the lines being laid in such a manner as to work for the few days required by the contract ; or in the hands of engineers, who, at the time when they undertook the work, had not attained the highest rank in their profession. The promoters appear to have studiously avoided the employ- ment of the leading engineering talent of the country ; and the Government, -when it had control, appears to have countenanced this line of conduct. Stephenson and Brunel would not have allowed the Atlantic Telegraph to be laid upon their responsibility without proper preliminary experiments being made; and it is to the absence of a proper scientific appreciation of the difficulties of these enterprises, that we entirely attribute the disasters and disappointments to which they have been subjected."
The primary cause of all these difficulties is the great re- tardation which a current of electricity experiences in passing along a conductor immersed in water, which is itself a conductor. The atmosphere being an admirable insulator, especially when dry, wires suspended in it by insulating supports may be prac- tically regarded as perfect transmitters of electricity, because they convey messages to any distance at a speed vastly surpassing that at which the operators at either end can deliver and receive them ; but it is quite otherwise with submarine wires. These must be surrounded by some non-conducting material—gutta percha for instance—and this again by a protecting sheath of iron or steel wire to save it from mechanical injury. Under these conditions, the phenomenon of induction comes in play, and the wire becomes a Leyden jar, so charged with electricity that a current cannot without the greatest difficulty move through it, and signals can only be made by charging and discharging the wire throughout its whole length for each of them. This is necessarily a slow process on long lines ; but, on shorter ones, no delay arises from this cause, because that which it tends to produce is exceeded by the me- chanical difficulties of manipulation : in other words, the speed of charge and discharge in a submarine line of 200 or 300 miles far exceeds that at which human hands can work upon any of the instruments hitherto in use. On the other hand, when the line passes 400 or 500 miles in length, the retardation from induction becomes very great, the mechanical difficulties disappear, and the inductive difficulties limit the speed. The means of diminishing the delay due to this cause are to be sought in such arrangements as shall best expedite the charge and discharge of the wire, but the laws which regulate these processes give opposite mechanical
indications. The capacity of the insulated conductor for charge, depends on the ratio of the diameter of the insulator to the diameter of the conductor, and is independent of the absolute dia- meter of either. Reasoning from this law alone, many electricians at first supposed that the much-desired saving of time would be effected by making the wire thinner, and its insulating covering thicker ; but, though this would shorten the time of charge, it would have just the opposite effect on the time of discharge, for the latter is diminished by increasing the gauge of the wire, and what is very important, it is diminished in inverse proportion to the square of the thickness, and not in the simple ratio. From all these considerations, it follows that the wire must be made of the best conducting material, namely copper, whilst iron, which has but one-seventh of its conducting power, serves very well for land lines, and that to produce increased rapidity of discharge without making the charging process slower, we must increase the thickness both of the wire and of its insulating wrapper to the ut- most practicable limits.
Unfortunately, those limits are greatly narrowed by the many mechanical difficulties attendant on the manufacture and laying down of bulky and heavy telegraph cables. The use of copper, too, as a conductor, is a serious, though necessary evil, for the metal has but little elasticity, and is liable to be permanently elongated or broken by the strains put upon it in the process of paying out, or to be bent into 'bights that force their way through the insulating covering. Gutta percha, the material which has hitherto been almost exclusively used for this covering, is very far from being perfect as an insulator, for the leakage of electricity through it is always very large, and is remarkably dependent upon temperature. At the freezing point of water, it is a minimum, but becomes three times, six times, and ten times as great at each successive increment of 20° F. Indiarubber is not affected in this way, and its insulation, as compared with that of gutta percha, is almost absolutely perfect. Still, the Edinburgh reviewer thinks we should be cautious in discarding gutta percha for this or other untried materials. " We know the faults of gutta percha from long experience. We know that indiarubber does not possess these faults, but we do not know yet whether it may not possess others equally serious." This is but one instance of the general need that exists for experimental inquiry, as the first step to any great extension of the range of Ocean Telegraphy. In 1857, the Treasury agreed to guarantee 5 per cent interest for twenty-five years upon a capital of 120,000/. for the construction of a line from Cagliari to Malta, and thence to Corfu. In support of their application for this aid, the company stated, that "submarine cables, when once laid down, are so little liable to accident, that it may be safely affirmed that they will work as efficiently at the end of fifty years as on the first day of their operation." About the same time, Messrs. Gisborne and Forde stated in a letter to the India Board, that " experience has shown that a good cable, once laid successfully, requires no maintenance." In whatever
degree this blind confidence may still prevail among companies and engineers, it is satisfactory to know that it is no longer enter- tained by her Majesty's Government, and that no more subsidies will be granted upon such fallacious assurances. Just before the Derby Administration went out of office, a cable was completed, which was to be laid down from this country to Gibraltar.
" When the present Government came into office, Mr. Gladstone directed that the control of this line should be transferred from the Treasury to the
Board of Trade ; that department reported that the knowledge possessed at the time was not such as to justify the submerging of another deep sea cable without further experiments being made, and they recommended the appointment of a committee to investigate the subject. The committee con- sisted of the late Mr. Robert Stephenson, Professor Wheatstone, and Cap- tain Douglas Galton, R.E., and with them was associated a committee formed by the Atlantic Telegraph Company. Upon the death of Mr. R. Stephenson, a modification of the committee took place, and Mr. Bidder, Mr. W. Fairbairn, Mr. Ed. L. Clark, and Mr. Varley, appear to have been added to it. The Government deserve great credit for the appointment of a committee to investigate the subject. It is the first and most important step which has yet been taken for placing the knowledge of deep sea tele- graphy upon a sound basis, by showing its present condition, and the steps which are necessary for its future success."
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