nce to make it of value, but
he did demonstrate that the currents do travel through the earth and
that they can be set to carrying messages.

Professor Trowbridge also revived the idea of telegraphing across the
Atlantic by utilizing the conductivity of the sea-water to carry the
currents. In working out the plan theoretically he discovered that the
terminals on the American side would have to be widely separated--one
in Nova Scotia and the other in Florida--and that they would have to
be connected by an insulated cable. Two widely separated points on
the coast of France were suggested for the other terminals. He
also calculated that very high voltages would be necessary, and the
practical difficulties involved made it seem certain that such a
system would cost far too much to construct and to operate to be
profitable.

Trowbridge suggested the possibility of using such a system
for establishing communication between ships at sea. Ship could
communicate with ship, over short distances, during a fog. A trailing
wire was to be used to increase the sending and receiving power, and
Trowbridge believed that with a dynamo capable of supplying current
for a hundred lights, communication could be established at a distance
of half a mile.

Not satisfied with the earth or the sea as a medium for carrying the
current, Trowbridge essayed to use the air. He believed that this was
possible, and that it would be accomplished at no distant date. He
believed, however, that such a system could not be operated over
considerable distances because of the curvature of the earth. He
endeavored to establish communication through the air by induction.
He demonstrated that if one coil of wire be set up and a current sent
through it, a similar coil facing it will have like currents induced
within it, which may be detected with a telephone receiver. He also
determined that the currents were strongest in the receiving coil when
it was placed in a plane parallel with the sending coil. By turning
the receiving coil about until the sound was strongest in the
telephone receiver, it was thus possible to determine the direction
from which the messages were coming. Trowbridge recognized the great
value of this feature to a ship at sea.

But these induced currents could only be detected at a distance by
the use of enormous coils. To receive at a half-mile a coil of eight
hundred feet radius would have been necessary, and this was obviously
impossible