and iron wire. It is the general type of all the submarine cables
which have been deposited since then in every part of the world.
As a rule, the armour or sheathing is made heavier for shore water
than it is for the deep sea, but the electrical portion, or
"core," that is to say, the insulated conductor, is the same
throughout.

The first Atlantic cable was laid in 1858 by Cyrus W. Field and a
company of British capitalists, but it broke down, and it was not
until 1866 that a new and successful cable was laid to replace it.
Figure 51 represents various cross-sections of an Atlantic cable
deposited in 1894.

The inner star of twelve copper wires is the conductor, and the
black circle round it is the gutta-percha or insulator which keeps
the electricity from escaping into the water. The core in shallow
water is protected from the bites of teredoes by a brass tape, and
the envelope or armour consists of hemp and iron wire preserved
from corrosion by a covering of tape and a compound of mineral
pitch and sand.

The circuit of a submarine line is essentially the same as that of
a land line, except that the earth connection is usually the iron
sheathing of the cable in lieu of an earth-plate. On a cable,
however, at least a long cable, the instruments for sending and
receiving the messages are different from those employed on a land
line. A cable is virtually a Leyden jar or condenser, and the
signal currents in the wire induce opposite currents in the water
or earth. As these charges hold each other the signals are
retarded in their progress, and altered from sharp sudden jets to