t which they travel, we can at once compute the number which
occur in a second of time, and thus ascertain their pitch. By this
means we can follow for about three more octaves above the audible
limit, namely, up to 160,000 pulsations per second, with a length of
wave of one-twelfth of an inch.

Two and a half octaves above these numerically, _i.e._ at about the
twentieth octave, we reach the frequency of Electro-Magnetic Rills,
used by the Marconi System of wireless telegraphy, which pulsate at
about 950,000 per second, and have a wave-length of something like
1000 feet. The reason for this great increase in length of wave is
caused by these frequencies being propagated in the Ether at the rate
of 186,000 miles per second, instead of, as with sound waves, in the
air, at only 1130 feet per second. We can trace these particular
frequencies, called, after their discoverer, Hertzian waves, for about
fifteen octaves, when we arrive at the frequency of 32,000,000,000 in
a second, with a wave-length decreased to a quarter of an inch; we
can render the effect of these waves visible, but have no physical
organ by which we can feel these pulsations. After this, however, we
get into the region of frequencies which, though still of exactly the
same kind, we know and can feel as Radiant heat; these are situated in
the next fourteen octaves, and bring us up to those subtle frequencies
which affect another of our sense organs, and which we appreciate as
light; these we have already seen have the enormous frequency of
530,000,000,000,000 pulsations per second for red light, up to
930,000,000,000,000 per second for violet, and having wave-lengths so
small that it takes 40,000 and 70,000 of them respectively to cover
one inch in length. There is only a little over half an octave that
the eye can appreciate as light, and then all is darkness; but we can
still go on further by the help of Science: beyond the violet we have
the actinic or chemical rays, which are used in photography, and which
enable us to trace the frequencies for a further two octaves. Beyond
this we cannot pierce with our present knowledge; but there may be,
and probably are, latent in our nature, senses which, properly
developed, will be able to appreciate still more subtle vibrations,
and organs which, perhaps, even now are being prepared for the
reception of these influences.

We have no organs yet developed for receiving and appreciating what
are called Wireless w