e one with positive the other with negative
electricity, separated from each other by air or some other insulating
material, and connected by a coil of wire called an inductance coil. To
explain the how and why, so far as these questions can be explained,
would involve a whole treatise on electricity; for the present purpose
it is enough to say that when the two plates are connected through the
coil, the electrical discharge is oscillatory in character, as the
current runs to and fro between the one plate and the other, and that
these oscillations are radiated into space in the form of waves. The
frequency of the waves, the rapidity, that is, with which wave follows
wave, depends on the size and proximity of the plates and on the length
and form of the coil which connects them. The receiving instrument is
similarly constructed, and can be so adjusted that the waves which it
would generate if it were a transmitter would have the same frequency as
those it is to receive. It is thus in resonance with the transmitter,
and the effect of the incoming impulses is greatly enhanced.

If the waves produced are to be perceptible at any considerable
distance, the transmitting instrument must be capable of absorbing a
large amount of energy and radiating this energy into space in the form
of waves.

The storing capacity of the instrument is increased by having large
plates close together, but its radiating properties are impaired if the
plates are too close.

The chief advance made by Signor Marconi lay in his use of the earth as
one of the plates. In his wireless installation, a network of insulated
wires, suspended in the air above, is one plate, the earth is the other;
and the two are connected by an inductance coil. This device cannot be
applied to aircraft, for obviously no connexion with the earth is
possible. Both of the plates, or networks of wire, have to be carried on
the airship or aeroplane. No great weight could be carried on the early
type of aeroplane, and no great space was available.

This brief and imperfect description has been given in order to make
clear some of the difficulties which attend the application of wireless
telegraphy to aircraft, and especially to aeroplanes.

The theory of flight was worked out by men of science in the laboratory;
flight itself was first achieved by men who had had no systematic
scientific training, but who endeavoured to acquaint themselves with
scientific results, and to app