164 
THE TELEGRAPH, 
so that the cable may when necessary be drawn np again over 
the stern, as it is in some cases a tedious and risky operation 
to pass the cable to the taking-lip machine in the fore-part of 
the vessel. 
Trains of wheel-work provided with a counter are connected 
with the axle of the machine, so that at any moment the 
quantity of cable paid out, and the rate at which it is passing 
out, can be ascertained. The ratio of the latter to the speed of 
the vessel is an important factor for calculating the strain. A 
simple arrangement indicates, by a stroke on a bell, the com¬ 
pletion of each nautical mile paid out. 
The Appold brakes, which are fixed on the axle of the drum, 
are smooth and rather convex wheels of about four feet dia¬ 
meter and nine inches width. These wheels are surrounded 
with steel hoops, to the inside of which blocks of hard wood 
are fitted at intervals. The ends of the hoops are attached at 
different points to the arm of a lever radial to the wheel. The 
apparatus is lubricated by being immersed in a tank of water. 
When the blocks are not sufficiently lubricated, or when the 
friction increases, the rim of the wheel tends to carrv the 
blocks round with it (fig. 105). The effect of this is to turn 
the lever, and the result a diminution of the force of the brake. 
The apparatus can to a certain extent adjust itself; for the 
difference of distance between c 5 and c a on the lever being 
very small, it follows that by placing a weight p at the point 
where the greatest effect is produced, that is to say, at a , the 
lever will be moved by the force exercised on the circumference, 
in proportion to the power acting at p and the difference of the 
force applied at a and b. The ratio ^ of the lengths of the 
lever represents the resultant. Assuming that the drum turns 
in the direction shown by the arrow, as soon as the weight p 
counterbalances the friction of the.brake, if the co-efficient of 
friction between the surface increases from any cause, the 
strain becomes greater on a than on 5, and the lever will be 
proportionately raised, so from the eccentric position of the 
points of attachment it will raise the hoop and diminish the 
friction. The reverse will take place if the co-efficient of fric¬ 
tion should diminish. 
The rod supporting the weight p is terminated by a piston 
that works in a cylinder filled with water. In this way the 
