real
cause of all phenomena which are due to light are due to the aetherial
waves which themselves give rise to the phenomena of light. Thus light
acts as a guide-post to us, pointing out the direction we should take in
order to find out the real centrifugal force or motion, and as plainly
as it possibly can, it indicates to us that the true solution of our
centrifugal motion that we are seeking for is to be found, and alone
found, in that universal aetherial medium which, by its vibrations and
wave motions, gives rise to that which we term Light. In conclusion of
this point, it may be pointed out that Professor Challis[20] also took
this view of light, as he distinctly states that "Light is to be ranked
with the physical forces, and its dynamical action is equally to be
ascribed to the pressure of the Aether," and then proceeded to show how
repulsion could be exerted on atoms by the periodic wave motion of the
Aether.

[Footnote 15: _Magnetism and Electricity._]

[Footnote 16: _Phil. Mag._, 1902.]

[Footnote 17: _Ibid._, 1872.]

[Footnote 18: _Burnet Lectures._]

[Footnote 19: _Burnet Lectures._]

[Footnote 20: _Phil. Mag._, 1872.]

ART. 78. _The Electro-Magnetic Theory of Light._--We have seen (Art.
71) that light is due to a periodic wave motion of the Aether, and we
have previously seen that heat is also due to a periodic wave motion of
the Aether. Thus in the phenomena of light and heat, Aether is the
medium in which the energy of light is stored, and by which it is
transmitted in its passage from a luminous body, as the sun, until it
comes into contact with a planet or satellite from which it is
reflected, thus giving rise to light and heat. When, however, we come to
deal with electro-magnetic phenomena, which are the results and effects
produced by electricity and magnetism, we find certain phenomena similar
to those that we find in relation to light and heat. Thus, when light is
emitted by a luminous body, a certain amount of energy is given out by
that body, and if such light is absorbed by another body, the latter
becomes heated, a clear proof that it has received energy or motion from
some outside source. From the time it left the luminous body till it
reached the lighted or absorbing body, it must have existed as energy,
that is, motion in the Aether. As we have already seen, Newton thought
that the transference of energy was accomplished by the actual
transference of certain small corpuscles or