nergy can be communicated from one
point to another without being carried by some intervening medium.
But, practically, the line will be suppressed if, instead of
constructing it artificially, we use to replace it one of the natural
media which separate two points on the earth. These natural media are
divided into two very distinct categories, and from this
classification arise two series of questions to be examined.

Between the two points in question there are, first, the material
media such as the air, the earth, and the water. For a long time we
have used for transmissions to a distance the elastic properties of
the air, and more recently the electric conductivity of the soil and
of water, particularly that of the sea.

Modern physics leads us on the other hand, as we have seen, to
consider that there exists throughout the whole of the universe
another and more subtle medium which penetrates everywhere, is endowed
with elasticity _in vacuo_, and retains its elasticity when it
penetrates into a great number of bodies, such as the air. This medium
is the luminous ether which possesses, as we cannot doubt, the
property of being able to transmit energy, since it itself brings to
us by far the larger part of the energy which we possess on earth and
which we find in the movements of the atmosphere, or of waterfalls,
and in the coal mines proceeding from the decomposition of carbon
compounds under the influence of the solar energy. For a long time
also before the existence of the ether was known, the duty of
transmitting signals was entrusted to it. Thus through the ages a
double evolution is unfolded which has to be followed by the historian
who is ambitious of completeness.

Sec. 3

If such an historian were to examine from the beginning the first
order of questions, he might, no doubt, speak only briefly of the
attempts earlier than electric telegraphy. Without seeking to be
paradoxical, he certainly ought to mention the invention of the
speaking-trumpet and other similar inventions which for a long time
have enabled mankind, by the ingenious use of the elastic properties
of the natural media, to communicate at greater distances than they
could have attained without the aid of art. After this in some sort
prehistoric period had been rapidly run through, he would have to
follow very closely the development of electric telegraphy. Almost
from the outset, and shortly after Ampere had made public the idea of
constru