394 THE ELECTRIC TELEGRAPH. 



form of slack, the more chance there is that the cable will 

 succeed. 



97. If the bottom were level, M. du Moncel's idea would 

 be just, and the speed of the ship could be made uniform with 

 the speed of the out- going cable, in which case, the cable 

 from the stern-pulley to the bottom would form, in the 

 water, a straight line. If the speed of the ship were increased 

 the line would bend over and form a curve concave with the 

 bottom ; and, if decreased, the cable would have a tendency 

 to form a curve convex towards the bottom. But these 

 curves can occur only after altering the relative speed of ship 

 and cable. 



We have heard some engineers question the truth of the 

 assertion that a cable descending in the water from the stern of 

 a ship whose speed is uniform must form a straight line inclined 

 to the bottom. The question admits of an easy solution. From 

 what was said of the descending weight used in sounding, it 

 will be remembered that when a heavy body is thrown into 

 water, after the first instant it descends to the bottom through 

 equal spaces in equal times. Suppose, therefore, from a ship 

 sailing with uniform speed, at distances of every fathom 

 travelled over a pellet were dropped overboard, it is evident 

 that by the time the second pellet touched the water the first 

 would have descended a depth say n feet below the surface ; 

 when the third was dropped, the second would be n feet below 

 the surface, and the first twice n feet ; when the fourth was 

 dropped, No. 1 would be thrice n feet, JNfo. 2 twice n feet, 

 and No. 3 only n feet down, and so on, forming always a 

 straight line. The same must necessarily apply to a cable 

 paid into the water at an uniform rate and descending uni- 

 formly ; it can take no other form in the water but that of 

 approximately a straight line. 



Messrs. Brook and Longridge* have demonstrated this 

 mathematically in a very able manner. 



The results of their developments are of great use in a 

 practical sense, instructing us, as they do, on the important 

 question of how much strain must be put upon the outgoing 

 * Minutes of Proc. Inst. Civil Eng., 1858. 



