THE NAUTICAL MAGAZINE AND Naval Chronicle. JANUARY, 1862. ON THE PROPER DEPTHS FOR ELECTRIC CABLES AS AT PRESENT CONSTRUCTED,By Captain T. Spratt, R.N., C.B., H.M.S. "Medina." The completion of the Malta and Alexandria submarine cable will no doubt revive public interest in submarine telegraphy, particularly after the appearance of the. Commissioners' inquiry into past failures and future practicability in this important subject. It was my lot to be connected with the Varna and Crimean cable, of 310 miles, one of the earliest laid of any great length. Instead of laying it direct, as intended, at my suggestion it was laid entirely in shallow water, by making a long detour, so that the uncertain risks of the direct deep route were avoided. Most of the Levant lines successfully laid or attempted in 1858 have shared my attention, so that my interest in these questions has been constantly kept on the alert, with the view to a right understanding of some of the difficulties and causes of immediate or subsequent failure. It was therefore very soon evident to me that deep sea cables of great length almost always failed from being cast into these depths without being in any way tested for the trying conditions to which they would be there subject, arising from pressure and its effect in the immediate or ultimate development of faults in the cable that would not be of material consequence in moderate depths. That, in fact, the fair test of efficiency was only made after they had reached great depths, and were then irrecoverable, either for repair or even that the real cause of their failure might be ascertained and corrected. NO. 1.-VOL. XXXI. B A consideration, therefore, of the possible effect of the enormous pressure of 1,000 or 2,000 fathoms of water on any part of the cable at all imperfect in its several coatings;-along with its multitude of splices, the spongy condition of certain parts from the impurity of the gutta percha, as well as the possibility that after long soaking under that pressure its particles might be displaced and water absorbed instead,-satisfied me that these were the main reasons for the failures of the several deep sea cables that had occurred, and induced me to foretell the same fate for cables laid in a similar manner; for who could ensure before laying the cable that the condition of the material part of the cable, namely its insulating covering, was perfect. Such were my views, and of which I made no secret in the autunn of 1858, after the failure of the first attempt with the Crete and Alexandria cable, which directed my attention to the subject. Previous to that time, however, some testing for the effect of pressure had been carried out before consigning cables to the great deeps. This I had presumed on, and was hopeful of ultimate success. But such was not the case, and my hopes that submarine cables were so tested before they were thrown to the ocean deeps went to the winds. It was a few months afterwards (the spring of 1859) that I had the good fortune to meet the talented and much lamented engineer, Mr. Stephenson, on his passage through Malta, to whom I communicated my views on this subject. The same apprehension as to the results of ocean pressure on deep sea cables was as fully entertained by him as by myself, and doubts of the efficiency of electric cables were equally as strong in his mind unless they were fairly tested for the conditions they would be subject to in those depths. It was not until the blue book on submarine cables was published, a few weeks since, that I was informed a Commission had been inquiring into the various questions connected with the causes of failure of submarine telegraphy, and that there had been so many important experiments carried out in reference to the subject. I was therefore both surprised and gratified to learn from the perusal of their report that so much had been done in the right way of obtaining a correct knowledge of the difficulties connected with submarine telegraphy in the deeper portions of the sea. But I regretted, notwithstanding the numerous experiments made as to ocean pressure on the various substances recommended as insulations, to find that one result was that although gutta percha, when freed of all its impurities, was almost impervious to water under a limited period of testing with very high pressure, yet that the risks were considered by these gentlemen to be still great, from the delicacy of this insulating material and the uncertainty of producing a perfect insulation throughout the entire length of cable,-in fact, to span the ocean's bed; and yet to know that a single defect entails the certain loss of the whole! The great desideratum, then, is unfortunately still, as I have from the first apprehended, the risk of ocean pressure on imperfect adhesion of the several coats of the insulating gutta percha, arising from positive spongy parts that rise imperceptibly under ordinary tests and from faulty manipulation of some one or two of the many hundreds of splices that must be formed in a long cable. Some eminent individuals, however, interested in its practicability, yet believe that success is not far distant, although not actually accomplished. The civilised world are interested in its success, and the motto must be nil desperandum. On this point the Gutta Percha Company entertain sanguine hopes as to the practicability of producing an insulator possessing the desired properties;-although it does not yet appear that any experiment has been prolonged sufficiently to prove that these will be gained in ocean depths;-in fact, that hundreds of miles of cable can be rendered perfect in insulation throughout, although they may be so in the distance of a few miles. There is one remark, however, in Mr. Chatterton's last letter in the blue book that deserves notice. It comes from the organ of the Gutta Percha Company, expressing their unbounded confidence in the practicability of gutta-percha-covered-wires, and says that their success is certain if laid in the sea uninjured." This of course includes all defects of manipulation, as well as injuries subsequently produced, defects which cannot be discovered by the test that can be applied to cables in their entirety on shore or in the vessel before being cast to the deep, and only when submerged for a certain time under the severe pressure of the ocean deeps, and after some hundreds of splices, &c., have been subjected to their effects. That "IF," then, embraces the whole question, considering the numerous chances against obtaining the required perfection, as the cable has to pass through many processes of manipulation, and many hands before it is laid in the sea. Hence it would seem that the question rests entirely with the Gutta Percha Company;-that they should be not only the makers and coverers but also the depositors of such cables, to ensure the best results for those who order them, since there are so many divided interests that do not suffer by the ultimate failure of a cable: first, the maker of the core; next, the party that covers it; and thirdly, the contractor who lays it, the latter of whom only is under any penalty for failure occurring within a brief period, which may be reckoned as a few hours in comparison with the period it is required to last before it can be assumed as a complete success. Again, the question seems to lie fairly and properly with the Gutta Percha Company, in respect of deep sea cables; for as these are by common consent considered to require no external wire covering for great depths, this company becomes the sole manufacturers of them, and should therefore be the sole parties to take the risk of laying them and the guarantee of their remaining efficient during a reasonable time. Now it might be fairly advanced that until an entire cable of some 500 or 600 miles in length can be tested for the pressures of the ocean at depths of 1,500 or 2,000 fathoms and upwards before it is laid in those depths, it is not in a fair condition to be depended on; as a defect of manufacture or injury cannot be discovered until too late to amend it because to recover the cable from these depths for |