e received wireless signals near St. John's, Newfoundland,
sent from Poldhu, Cornwall, England, or a distance of 1,800 miles,--a
feat which astonished the world. In many cases the telegraphic business
to an island is too small to warrant the laying of a cable; hence we
find that Trinidad and Tobago are to be joined by the wireless system,
as also five islands of the Hawaiian group, eight to sixty-one miles
apart.

A weak point in the first Marconi apparatus was that anybody within the
working radius of the sending-instrument could read its messages. To
modify this objection secret codes were at times employed, as in
commerce and diplomacy. A complete deliverance from this difficulty is
promised in attuning a transmitter and a receiver to the same note, so
that one receiver, and no other, shall respond to a particular frequency
of impulses. The experiments which indicate success in this vital
particular have been conducted by Professor Lodge.

When electricians, twenty years ago, committed energy to a wire and thus
enabled it to go round a corner, they felt that they had done well. The
Hertz waves sent abroad by Marconi ask no wire, as they find their way,
not round a corner, but through a corner. On May 1, 1899, a party of
French officers on board the _Ibis_ at Sangatte, near Calais, spoke to
Wimereux by means of a Marconi apparatus, with Cape Grisnez, a lofty
promontory, intervening. In ascertaining how much the earth and the sea
may obstruct the waves of Hertz there is a broad and fruitful field for
investigation. "It may be," says Professor John Trowbridge, "that such
long electrical waves roll around the surface of such obstructions very
much as waves of sound and of water would do."

[Illustration: Fig. 73--Discontinuous electric waves]

[Illustration: Fig. 74--Wehnelt interrupter]

It is singular how discoveries sometimes arrive abreast of each other so
as to render mutual aid, or supply a pressing want almost as soon as it
is felt. The coherer in its present form is actuated by waves of
comparatively low frequency, which rise from zero to full height in
extremely brief periods, and are separated by periods decidedly longer
(Fig. 73). What is needed is a plan by which the waves may flow either
continuously or so near together that they may lend themselves to
attuning. Dr. Wehnelt, by an extraordinary discovery, may, in all
likelihood, provide the lacking device in the form of his interrupter,
which breaks an