THE TELEGRAPH,. 
strands of hemp or jute, either tarred or preserved in tannin; 
and outside of this covering, galvanized iron or steel wires are 
twisted, in order that the cable may be able to bear a powerful 
strain and receive sufficient protection. The metallic covering 
is preserved from rust by two inverse layers of tow mixed with 
silicated bitumen. 
Two perfectly distinct operations must be gone through in 
Fig. 89.—Sir James Anderson, of the Eastern Telegraph Company. 
making a cable, and these operations are often conducted by 
different manufacturers. The first operation concerns the 
electrical conditions of the cable, and the second has for its 
object to enable the cable to resist the strains to which it will 
be exposed while being laid. According to the distances they 
traverse, and the depths to which they reach, cables have to 
fulfil certain electrical and mechanical conditions, which we 
shall here discuss. 
Copper is always used as the conductor, because this metal 
offers less resistance to the passage of electricity than any other 
