ance apart on one side of a
canal. Other plates were placed on the opposite side of the waterway
and were connected by a wire with a sensitive galvanometer in series
to act as a receiver. Currents sent from the opposite side were
recorded by the galvanometer and the possibility of communication
through the water was established. Others carried these experiments
further, it being even suggested that messages might be sent across
the Atlantic by this method.

But Bell's greatest contribution to the search for wireless telegraphy
was not his direct work in this field, but the telephone itself.
His telephone receiver provided the wireless experimenters with an
instrument of extreme sensitiveness by which they were able to detect
currents which the mirror galvanometer could not receive. While
experimenting with a telephone along a telegraph line a curious
phenomenon was noticed. The telephone experimenters heard music very
clearly. They investigated and found that another telegraph wire,
strung along the same poles, but at the usual distance and with
the usual insulation, was being used for a test of Edison's musical
telephone. Many other similar tests were made and the effect was
always noted. In some way the message on one line had been conveyed
across the air-gap and had been recorded by the telephones on the
other line. It was decided that this had been caused by induction.

Prof. John Trowbridge, of Harvard University, might well be termed
the grandfather of wireless telegraphy. He made the first extensive
investigation of the subject, and his experiments in sending
messages without wires and his discoveries furnished information and
inspiration for those who were to follow. His early experiments tested
the possibility of using the earth as a conductor. He demonstrated
that when an electric current is sent into the earth it spreads from
that point in waves in all directions, just as when a stone is cast
into a pond the ripples widen out from that point, becoming fainter
and fainter until they reach the shore. He further found that these
currents could be detected by grounding the terminals of a telephone
circuit. Telegraphy through the earth was thus possible. However, the
farther the receiving station was from the sending station the wider
must be the distance between the telephone terminals and the smaller
the current received. Professor Trowbridge did not find it possible to
operate his system at a sufficient dista