planation for the density of the Aether
and also for different degrees of density both in the atomic world, and
in the planetary and stellar world.

ART. 47. _Aether is Elastic._--In Art. 39, matter was shown to be
elastic, and on the assumption that Aether is matter, the elasticity of
the Aether, which has been postulated for it by various scientists, can
be logically and philosophically accounted for.

In view of the transmission of light through space with a definite and
finite velocity, we are compelled to regard Aether as possessing
elasticity, similar to that of an elastic solid body.

If we take the analogy of sound, we find that sound is transmitted and
propagated through matter, by waves of alternate condensation and
rarefaction, and that transmission is regulated by the relation of the
density of the medium to its elasticity. Light has been proved to be due
to the undulatory wave-motions of the Aether, and in order to account
for the transmission of the wave-motion, it is essential that the Aether
should possess the property of elasticity.

As Young points out in his First Hypothesis,[6] the Aether possesses
this property of elasticity, but with the advance of scientific
knowledge and research, the elasticity of the Aether may be said to have
passed out of the hypothetical stage, into the state of actual fact and
experiment. Both McCullagh and Fresnel have assumed this property of
elasticity for the aetherial medium in order to account for certain
phenomena of light.

Apart, however, from the atomicity of the Aether, it is exceedingly
difficult to understand how such a property can belong to it. Atoms are
exceedingly small particles, possessing the property of elasticity, or
the power to recover their original shape after distortion or change of
shape. If the Aether therefore be atomic, as is pointed out in Art. 44,
it can at once be readily understood how the Aether as a whole can
possess the property of elasticity. The atoms of the Aether must be
inconceivably small, as the light-waves travel with the enormous
velocity of 186,000 miles per second.

What must therefore be the atomic vibration which such a statement
implies? If, on the other hand, the Aether is assumed to be continuous
and non-atomic, it must be seen how exceedingly difficult it is to
account for the elasticity of the Aether, as it seems absolutely
impossible for a medium which is continuous, and non-atomic, to be able
to transmit the