h the rarefied
air at considerable distances. Alternate currents, especially of high
frequencies, pass with astonishing freedom through even slightly
rarefied gases. The upper strata of the air are rarefied. To reach a
number of miles out into space requires the overcoming of difficulties
of a merely mechanical nature. There is no doubt that with the
enormous potentials obtainable by the use of high frequencies and oil
insulation luminous discharges might be passed through many miles of
rarefied air, and that, by thus directing the energy of many hundreds
or thousands of horse-power, motors or lamps might be operated at
considerable distances from stationary sources. But such schemes are
mentioned merely as possibilities. We shall have no need to transmit
power in this way. We shall have no need to _transmit_ power at all.
Ere many generations pass, our machinery will be driven by a power
obtainable at any point of the universe. This idea is not novel. Men
have been led to it long ago by instinct or reason. It has been
expressed in many ways, and in many places, in the history of old and
new. We find it in the delightful myth of Antheus, who derives power
from the earth; we find it among the subtile speculations of one of
your splendid mathematicians, and in many hints and statements of
thinkers of the present time. Throughout space there is energy. Is
this energy static or kinetic? If static our hopes are in vain; if
kinetic--and this we know it is, for certain--then it is a mere
question of time when men will succeed in attaching their machinery to
the very wheelwork of nature. Of all, living or dead, Crookes came
nearest to doing it. His radiometer will turn in the light of day and
in the darkness of the night; it will turn everywhere where there is
heat, and heat is everywhere. But, unfortunately, this beautiful
little machine, while it goes down to posterity as the most
interesting, must likewise be put on record as the most inefficient
machine ever invented!

The preceding experiment is only one of many equally interesting
experiments which may be performed by the use of only one wire with
alternate currents of high potential and frequency. We may connect an
insulated line to a source of such currents, we may pass an
inappreciable current over the line, and on any point of the same we
are able to obtain a heavy current, capable of fusing a thick copper
wire. Or we may, by the help of some artifice, decompose a so