or planet as the case may be, in accordance with the Law of
Gravitation. We shall consider this view of the subject later on.

[Illustration: Fig: 5.]

Thus we learn that every particle of matter, and every body in the
universe has its aetherial atmosphere so to speak, to which it is held
bound by the universal Law of Gravitation. In the case of a satellite
or planet or sun or star, that atmosphere will be more or less spherical
in shape, decreasing in density as it recedes from the attracting body.
As we saw in the previous chapter, Tyndall stated that the waves of
light really formed spherical shells which surrounded the luminous body.
In the conception of an atomic and gravitating Aether we can form a
physical conception of these aetherial shells, which can be pictured as
elastic envelopes, or rather series of envelopes surrounding each
particle of matter, and also surrounding each satellite, planet, sun,
and star; each envelope getting gradually less and less dense as the
distance from the central body is increased.

Now we learn from experiments that the vibration is always in the wave
front, but the wave front is coincident with the surface of each
aetherial spherical shell, therefore the vibration must be in, and
coincide with, the surfaces of the spherical shells that are formed
around every body in the universe.

We are now, however, dealing specially with one body which is the source
of light, viz. the sun, and have therefore to picture the sun as being
surrounded by these aetherial elastic envelopes, which gradually get
less and less dense as they recede from it. What, therefore, will be the
effect of the heat of that body as it is poured forth into space? We
have already learned (Art. 63) of the untold quantity of heat that is
continually being poured forth into space from the sun with its diameter
of 856,000 miles, and its circumference of over 2-1/2 million miles.
What intense activity it must generate in the Aether near its surface!
and what must be the direct effect of that heat upon the aetherial
elastic envelopes or shells which surround it?

Perhaps the answer can be best illustrated by a simple experiment. Let
us take an ordinary toy balloon, with its elastic envelope, and fill it
moderately full with air, and observe what the effect on it is when we
put it near the fire. Gradually, as heat is imparted to the air in the
balloon, the air which is also elastic expands, with the result that the
env