AKING AND LAYING SUBMARINE CABLES. 181 
successively, at the same time laying it down again in its former 
position. This process can only be used where the depth is 
not great, and where the cable is not buried in sand, or 
entangled among rocks. But at the present day it has become 
almost unnecessary, as the position of the damaged point can 
be determined electrically with precision. 
To grapple the cables, strong irons with three or four arms 
are used (fig. 118). Their weight may be 30 or 40 lbs. They 
fall to the bottom, and of course rest upon two of their arms. 
A chain of about 20 or 30 fathoms in length is fastened to the 
ring of the grapnel, and to the chain a rope of a size suitable 
for the work to be done. This rope is, for great depths, made 
of hempen strands and steel wires twisted together. 
In shallow water a length of rope equal to three or four times 
the depth is used. Beyond 400 yards two or three times the 
