Engineering Wonders of the World
Volume III

THE LAYING OF SUBMARINE CABLES. 361 Shore-end cables of this description are now largely used where local conditions demand sheathing which, besides being especially heavy, also offers a large metallic surface as a defence against trawlers, etc. The largest type of cable in existence weighs as much as 62j tons per mile, being designed to resist the crushing strain of icebergs grounding on the coast of Newfoundland, where it was landed but a few months ago. cent, greater than was obtained in the earliest cables. LAYING. Strictly speaking, the manufacture of a sub- marine cable should not be embarked on until a survey of Preliminary ,, , , , ™ , Submarine the route has been effected Survey. for determining the types to be adopted and the length of each. In any Compounded Hemp Cotton Taping. Steel Wires. Jute Inner Serving Gutta Percha Copper Insulator Conductor Dielectric Newfoundland Shore-End Irish Shore-End* Fig. 6.—MODERN ATLANTIC CABLE TYPES (4 ACTUAL SIZE). Deep Light. Heavy Seex Intermediate Intermediate DeepSeaC^ble Deep-sea (main type) cable of the descrip- tion depicted in the sectional elevation view is intended for maximum ocean depths of three or four miles. It will bear a strain of seven tons ; and being, in consequence, cap- able of supporting a considerable length of itself, can be recovered and repaired in very deep water. Though the general principles underlying all ocean telegraphy remain peculiarly the same as at first, steady advance has been made in the quality of the materials used in submarine cable manufacture. Indeed, the available strength of a modern deep-sea line, such as that represented by Fig. 6, is some 30 per case such a survey is essential before the actual laying proceeds. In early days several disasters occurred owing to the lack of pre- liminary soundings, and the want of even a general knowledge of the bod on which the cable was destined to rest. Some idea of what happens when a cable is laid over a sea bottom that has not been surveyed may be gathered from Fig. 7. In this example it may be observed that even if the cable did not break during the operation of laying, it would be pretty certain to do so soon after, due to the strain of being sus- pended from point to point. Such irregu- larities as are here depicted would require