tive wire indispensable? By no means! Is there a
connecting wire between the sun and the earth? Yet the spots on the
sun occasion rebounds in the variations of terrestrial magnetism. In
the photophone the conductive wire has already been dispensed with,
and a ray of light is used in its place. You speak behind a mirror,
and thus cause it to vibrate. These vibrations modify the reflection
of light from the vibrating mirror, which thus bears along your voice,
with which it becomes charged. Selenium, the chemical element used in
the operation, transmits the sound to the telephone, and your spoken
word is reproduced.

The principal of the transformation of forces is undoubtedly one of
the most prolific in modern physics. Heat can be transformed into
mechanical motion; mechanical motion may be transformed into heat.
Electricity is transformable into magnetism; and, reciprocally,
magnetism may change into electricity, into light. The motion of the
mill-wheel serves to illuminate your house. From Paris you can light a
lamp in Brussels. When you act from afar upon another mind, it is not
your thought which travels, as a mental condition; but your thought
traverses the intervening ether through a series of vibrations as yet
unknown to us, and only becomes thought again when brought into
contact with another brain, because the last transference brings the
impulse into a medium akin to that from which it started. It is
therefore necessary that this second brain should be in sympathy with
yours; that is to say, using one of Doctor Ochorowiez's expressions,
that "the dynamic tone" of the receiver should be in accord with your
own. It is, moreover, noticeable that there are periods when veritable
thought-currents affect thousands of brains at the same moment. At the
bottom of all this there is but one principle, and that is identical
with the relation existing between the magnet and the iron, between
the sun and the earth,--namely, the transmission and transformation of
motion. Herbert Spencer has said:--

The discovery that matter, so simple in appearance, is
wonderfully complicated in its vital structure,--and that
other discovery, that its molecules, oscillating with a
rapidity almost infinite, convey their impressions to the
surrounding ether, which, in turn, transmits them over
inconceivable distances, in an inconceivably short space of
time,--these discoveries lead us to the even more marvel