This is not the case with subaqueous lines. The employment of submarine,
as well as of subterranean conductors, occasions a small retardation in
the velocity of the transmitted electricity. This retardation is not due
to the length of the path which the electric current has to traverse,
since it does not take place with a conductor equally long, insulated in
the air. It arises, as Faraday has demonstrated, from a static reaction,
which is determined by the introduction of a current into a conductor
well insulated, but surrounded outside its insulating coating by a
conducting body, such as sea-water or moist ground, or even simply by
the metallic envelope of iron wires placed in communication with the
ground. When this conductor is presented to one of the poles of a
battery, the other pole of which communicates with the ground, it
becomes charged with static electricity, like the coating of a Leyden
jar,--electricity which is capable of giving rise to a discharge
current, even after the voltaic current has ceased to be transmitted.

Professor Wheatstone experimented upon the cable intended to unite La
Spezia, upon the coast of Piedmont, with the Island of Corsica. It was
one hundred and ten miles in length, and contained six copper wires
one-sixteenth of an inch in diameter, individually insulated, and
each covered with a coating of gutta-percha one-twelfth of an inch in
thickness. The cable was coiled in a dry pit in the yard, with its two
ends accessible. The ends of the different wires could be united, so as
to make of all these wires merely one wire six hundred and sixty miles
in length, through which the electric current could circulate in the
same direction. This current was itself furnished by an insulated
battery formed of one hundred and forty-four Wheatstone's pairs, equal
to fifty of Grove's. In the first series of experiments, it was proved,
that, if one of the ends of the long wire, whose other end remained
insulated, were made to communicate with one of the poles of the