SUBMARINE TELEGRAPHY 213 



that is to say, by increasing its bulk relatively to its weight. 

 The Atlantic Cable, under the water, probably lay at an angle of 

 nearly 7 with the horizon ; on leaving the ship the angle was 

 9^. In this case, in a depth of two miles, a length of from 16^ 

 miles of cable would lie in the water between the point where 

 it left the ship and that where it touched the bottom. The 

 weight of this cable, weighed in water, would be 231 cwt. ; 

 fortunately, as the cable would break with about 154 cwt., only 

 a very small part of this weight is borne by the cable itself as 

 it leaves the ship. Even if the cable were to be laid absolutely 

 taut, a restraining force of 28 cwt. only would be necessary. 

 In practice. 12 cwt. to 14 cwt. was found quite sufficient. 



The cable, as it leaves the ship, may almost be said to lie on 

 a long inclined plane of water; if it lay on a solid inclined 

 plane, without friction, it might, by a well-known law of 

 mechanics, be balanced by a length of itself hanging vertically 

 from the apex of the inclined plane to the bottom, and this is 

 almost exactly the strain required to be given by the break on 

 board ship to balance the cable, or, in other words, to prevent it 

 from shooting back along the inclined plane, so as to lie slack 

 in folds at the bottom ; but the inclined plane of water is not at 

 rest, it yields under the cable at every instant, at every spot ; 

 yet if the cable were pressed through the water, so that the 

 water yielded before it, but did not slip along it at all, the ana- 

 logy of the inclined plane would be quite perfect. The resistance 

 of the water to displacement would supply the component of the 

 whole force required, perpendicular to the direction of the cable 

 exactly as in the case of a solid plane ; but on constructing a 

 diagram, it will at once be seen that the cable, as it descends, 

 slips a little along the plane, and the friction of the water op- 

 posing this slip slightly diminishes the strain required to lay 

 the cable taut. If, on board ship, this full strain is not pro- 

 duced by the brakes, the cable slips still faster back along the 

 inclined plane, and with such a velocity that the friction of the 

 water on the cable makes up for the insufficient tension given 

 by the brakes, and equilibrium is again restored, but at the 

 expense of a waste of cable. It will be clear that, with a 

 given depth, the greater the length of cable in the water the 

 less need this waste be, for the friction will be directly proper- 



