i66 
THE TELEGRAPH. 
less, this pulley rises or falls in the frame, and shows by a 
pointer the degree of strain on the cable. The scale is made by 
trial. 
Choice of Route.—We take the following considerations as to 
the choice of route from Delmarche’s “ Elements de Tele¬ 
graphic Sousmarine ” (Paris, 1858). Apart from political, 
commercial, or other reasons, the choice of route should be 
Fig. 106. 
determined by the shortest distance, the least and most regular 
depths. The shortest distance requires least length of cable and 
a smaller vessel; the smaller the depth the less is the strain 
upon the cable during its laying ; and the regularity of the 
depths obviates the dangers of suddenly varying strains. 
A profile of the sea bottom along the proposed route is indis¬ 
pensable, and it should be as exact as possible; it is also 
desirable that the contour to the right and the left of the route 
should be known, so that the proper course may be taken if 
the ship should be driven out of the route laid down. 
