Submarine Telegraphy. 119 



see at once that it will be of two kinds — mechanical and 

 chemical. Both of these have to be specially guarded against. 

 The mechanical action arises chiefly from the movement of 

 submarine currents, the direction and extent of which are very 

 imperfectly known to hydrographers. The superficial marine 

 currents, such as the Gulf Stream and others, have been 

 thoroughly explored ; and it may be safely inferred, from 

 hydrostatic principles, that where a superficial current exists, 

 there must be, in general, a submarine current somewhere 

 answering to it ; but beyond this, little can be stated positively 

 about them. Wherever they do exist in any force, their effect 

 on the bed of the ocean must be very considerable ; and if a 

 telegraphic cable should cross the course of such a current, it 

 would be liable to wear and tear, from the attrition of the cable, 

 upon the solid rocks, and from the action of the water, which > 

 would be often greatly aggravated by its holding in suspension, 

 fragments of rocks and mineral debris. As to the chemical 

 action of sea- water, its activity is well known ; and the iron 

 wires which surround the copper in a cable would stand no 

 chance at all, unless protected by " galvanizing" — that is, 

 covering them with a coating of zinc ; or, still further, by 

 " serving" them with tarred hemp. 



One might suppose that a cable so protected would be 

 tolerably safe from depredations of every kind. But in warm 

 latitudes, where animal life abounds in the ocean, cables have 

 been rendered quite useless, in consequence of the attacks of 

 these nnexpected foes. Nibbling at the hempen covering,, 

 they have laid bare the wires, which in turn soon yielded to the 

 corroding influences of the sea-water, and the utter destruction 

 of the cable was the result. In other instances, corals and 

 barnacles have attached themselves to the cable in positions 

 where it has been stretched from rock to rock, when, by their 

 united weight, they caused a strain which the wires could not- 

 resist. In more northerly latitudes, there is less to be feared 

 from this cause ; nevertheless, as any one who has spent a day 

 at the sea-side has had an opportunity of noticing, there are 

 many molluscs — the Pholas and Limpet to wit — which possess 

 an extraordinary power of abrading and boring the hardest 

 substances to which they attach themselves ; and one never 

 knows how far he is safe from the attacks of such minute 

 and insidious aggressors. 



The Atlantic telegraph cable, the object of so much interest 

 at the beginning of the past month, was constructed with due 

 regard to all the difficulties heretofore mentioned, and the 

 manner in which the projectors proposed to meet them can 

 scarcely fail to prove interesting. 



In Fig. 2 we have a chart of that portion of the Atlantic 



