NATURAL PHILOSOPHY. 119 



dents have frequently occurred in the cables between England and the 

 Haggle, and there is not the least doubt that there are many scores of such 

 faults along the Atlantic wire. A good deal of attention has lately been 

 turned to the question of rope-covered wire, and there is now no doubt but 

 that all future attempts to connect Europe with America will be made with 

 cables so constructed. At the same time it will not be strands of hemp 

 loosely thrown around the gutta-percha covered wires that will make a ser- 

 viceable cable; but rope-yarns, bound in with the same fineness as the wires 

 are now twisted by the " closing machine." In fact, rope-covered wire 

 would have to be made by Glass and Elliot, or Newall, just in the same 

 manner, and on the same plan, as the wire-covered cables are now made by 

 those firms. 



There is one difficulty which many suppose will influence the success of 

 the deep sea cables in no slight degree namely, the pressure to which all 

 cables must be subjected at great depths. Some people are sufficiently ill- 

 informed to deny that there is any pressure exerted by the water of the 

 ocean at the bottom at all. Such absurd blunders only arise from ignorance 

 of the difference between density and weight. It does not follow that, 

 because water is almost incompressible, it weighs nothing, no more than 

 it follows that, because a block of granite is not elastic, it does not press 

 upon the spot on which it rests. The pressure of the water at the bottom of 

 the Atlantic averages about two tons and a half to a square inch. It is a 

 simple matter of calculation to ascertain the fact. At such a pressure as this, 

 wrought brass can be saturated with water like a sponge, and a block of it 

 so saturated requires days for it to ooze out again. 



ON THE SUBMERGENCE AND CONSTRUCTION OF SUBMARINE TELE- 

 GRAPH CABLES. 



At a recent meeting of the London Society of Civil Engineers, it was men- 

 tioned as a practical illustration of the facility with which light cables could 

 be laid, that, although the submarine telegraph between Varna and the Cri- 

 mea was submerged under considerable difficulties, and during a storm, yet 

 the actual length payed out was only 3 3-4 miles in excess of the distance 

 between those places, which was nearly 350 miles. The depth of the Black 

 Sea, where this cable was laid, was about 70 fathoms. The cable consisted, 

 throughout the greater portion of its length, simply of No. 16 copper wire, 

 covered with gutta-percha, and wholly unprotected. The shore ends had an 

 iron sheathing, extending to a distance of ten miles from Varna, and of six 

 miles from the Crimea. Its insulation was perfect; and it remained unin- 

 jured for twelve months, during the time of the Russian war, notwithstand- 

 ing the many violent storms to which it was exposed in the Black Sea, until, 

 during a storm of more than usual severity, it was broken on the 5th of De- 

 cember, 1855. 



With reference to the best form for a submarine cable, it had been proved 

 that, when great depths had to be traversed, one of light specific gravity was 

 to be preferred. The conductor, which constituted the weight to be carried, 

 should, therefore, be as light as possible ; and, to insure its continuity, it 

 should be relieved from strain by the external coating. The conductor, 

 when of copper, had a specific gravity of 11, the gutta-percha insulator was 

 nearly equal in weight to sea-water, and the iron external covering had a 

 specific gravity of 7. Probably, aluminium might be substituted for copper 



