Radio or wireless telegraphy in principle is as old as mankind. Adam
delivered the first wireless when on awakening in the Garden of Eden
he discovered Eve and addressed her in the vernacular of Paradise in
that famous sentence which translated in English reads both ways the
same,--"Madam, I'm Adam." The oral words issuing from his lips created
a sound wave which the medium of the air conveyed to the tympanum of
the partner of his joys and the cause of his sorrows.

When one person speaks to another the speaker causes certain vibrations
in the air and these so stimulate the hearing apparatus that a series
of nerve impulses are conveyed to the sensorium where the meaning of
these signals is unconsciously interpreted.

In wireless telegraphy the sender causes vibrations not in the air but
in that all-pervading impalpable substance which fills all space and
which we call the ether. These vibrations can reach out to a great
distance and are capable of so affecting a receiving apparatus that
signals are made, the movements of which can be interpreted into a
distinct meaning and consequently into the messages of language.

Let us briefly consider the underlying principles at work. When we
cast a stone into a pool of water we observe that it produces a series
of ripples which grow fainter and fainter the farther they recede from
the centre, the initial point of the disturbance, until they fade
altogether in the surrounding expanse of water. The succession of these
ripples is what is known as _wave_ motion.

When the clapper strikes the lip of a bell it produces a sound and
sends a tremor out upon the air. The vibrations thus made are air