ELECTRO-TELEGRAPHY 247 



the-shore end of any cable is more exposed to the action of the waves than those parts 

 are which remain in a state of rest at the bottom of the deep soa, it becomes necessary 

 to give this portion a greatly-increased degree 

 of protection. Fig. 820, which is of the exact 

 size of the shore-end of the Atlantic cable, will 

 fully illustrate the conditions of this portion. 

 The core was formed by the main cable, which 

 was wrapped with a serving of yarn to a size 

 sufficient to receive round it 12 strands of iron 

 wire, each strand being composed of 3 galvanised 

 iron-wires, each of which being nearly a quarter 

 of an inch in diameter ; the weight of the com- 

 pleted shore-end was nearly 20 tons to the mile. 

 Its diameter is 2 inches, but at its junction with 

 the main cable it is made to taper down to the size 

 of the latter by a gradual diminution in diameter 

 extending over 500 yards. This shore-end was side view of the Atlantic Cable, 

 laid out for about 28 miles from the coast of 



Valentia Island, when it reached water of the depth of 100 fathoms. From Hope's 

 Content, Newfoundland, about 8 miles of shore-cable only would have been required. 



The weight of the deep-sea cable according to the Company's statement in air 

 was 35 cwts. 3 qrs. per nautical mile of 2,028 yards. Its weight in water, 14 cwts. to 

 each nautical mile, or equal to 1 1 times its weight in water per knot ; that is to say, 

 it will bear its own weight in 11 miles deep of water. Its breaking strain was 7 tons 

 15 cwts. The length of cable shipped was 2,300 nautical miles ; the actual distance 

 from the point of departure, Valentia, on the West of Ireland, to the point Heart's 

 Content, in Trinity Bay, Newfoundland, on which it was to have been landed, being 

 1,670 nautical miles. 



As every one knows, this great experiment failed, the cable breaking when the 

 Great Eastern had reached the mid-Atlantic. Another experiment was made in 

 1866, and the result has proved in the highest degree satisfactory. Not only has the 

 new cable been securely lowered to its ocean-bed in the depths of the Atlantic, but the 

 old cable has been recovered and repaired, and we have now several electrical nerves 

 uniting the new with the old continents. These electric cables have now been for 

 some time in constant use, and their powers of transmitting electric currents appear to 

 improve. 



It is not necessary in this place to notice the various electrical cables which now 

 girdle the earth. There are a few points, however, which are of sufficient interest to 

 find a place in these volumes. The condition of the cable in the ship is one of these. 

 For the following remarks we are indebted to Mr. Kobert Sabine's excellent work on 

 ' Electro-Telegraphy ' : 



' At present, all cables of any importance are sent to sea in water-tanks on board 

 the transport ships. The tanks are circular, with as large a diameter and as high as 

 the room of the ship will allow between the bottom of the tank and the deck ; they 

 are made of plates of iron, riveted together, caulked, and painted with red lead to pre- 

 vent rusting. There are usually two such tanks, the forehold and afterhold, on board 

 a cable ship. In the centre of each tank a hollow cone of iron is erected, and above 

 this a series of rings of 2-inch round iron, which are lowered in the tank as the cable 

 is paid out, are suspended for guiding the cable as it leaves the tanks, and preventing 

 it flying out by centrifugal force, and going into kinks. On leaving the tanks, the 

 cable passes through the rings in the circular space between them and the top of the 

 cone, which it rubs against continually. The friction which the cable exerts against 

 the sides and bottom of the trough assists the breaks in preventing its too rapid egress 

 from the ship. 



' No good electrical measurements are possible during the passage out on account of 

 the motion of the ship, and the difficulty of keeping the apparatus dry ; the measure- 

 ments which are made are only of value qualitatively and approximately in the event 

 of a fault occurring. The electrical conditions of the cable are, however, always kept 

 under surveillance. 



' Messrs. Siemens have constructed a galvanometer purposely for use on board ship. 

 It consists of an astatic system of magnetic needles on a vertical bar, moving in stone 

 pivots, and surmounted by an aluminium pointer. Each needle turns in the centre of 

 an independent coil of wire. Above the glass cover of the dial-plate is a tall rod of 

 brass carrying a horizontal adjusting magnet, which, in different positions and at 

 different distances from the magnet system, increases or diminishes its directive force, 

 and with this the sensibility of the instrument. 



' Professor Thompson has succeeded in eliminating the directive force of the earth's 



