396 THE ELECTRIC TELEGRAPH. 



into the error of giving too little slack just when it is most 

 needed, that is to say, on approaching a bank. 



In the late attempt to submerge the Atlantic Cable, the angle 

 at which the cable went to the bottom was 9 30 7 . The average 

 depth of the Atlantic is two knots, and, as the cable weighs 

 in sea water 14 cwt. per knot, it follows that in order to lay 

 out this cable on a plane bottom, a retarding force of 28 cwt. 

 would have been required. A very small fraction of this 

 retarding force is found by the cable itself, in the form of 

 friction against the water in sliding. But the strain put 

 upon the cable by the break on board was only 12 cwt., and 

 consequently 15 per cent, of cable slid uniformly down the 

 incline to accommodate accidental irregularities at the bottom, 

 and prevent it hanging suspended between them. 



98. The Break. In the early days of submarine tele- 

 graphy the breaks were, like many other of the appliances of 

 this art, somewhat crude. The best break which we know 

 of is that fitted up on board the French Government tele- 

 graph steamer Le Dix Decembre. 



The cable, guided on by a plough or knife-edge, is made 

 to pass four or five times round a hollow iron drum, which is 

 turned by the weight of the cable as 

 the ship goes on. On the axle, on each 

 side of this drum, is a break-wheel, of 

 nearly the same diameter, and about 9 

 inches broad. Around these breaks are 

 straps made of blocks of hard wood, 

 secured at regular distances to iron 

 bands, the ends of which terminate at 

 different distances from the centre in 

 leyer bars. This part of the arrangement 

 Fig. 180. is known as Appold's break. When 



insufficiently lubricated, or when the friction becomes great, 

 the wheels have an increased tendency to carry the wooden 

 blocks round with them ; this deflects the lever bars from the 

 vertical line, and opens out the iron bands sufficiently to 

 lessen the break power. 



Advantage is taken of this to make this break in a measure 



