only pass into a gaseous or solid condition, in which
condition it will possess mass and weight, on the assumption that in the
aetherial condition it possesses the same properties, only in a modified
form, which it possesses after the process of condensation has taken
place. In a similar way that air can pass out of its gaseous condition
into a liquid condition, or any gas can pass out of its gaseous into a
liquid condition, so Aether, on the conception as given in Chapter IV.,
can pass out of its aetherial and rarefied condition into that form of
matter which is known as gaseous. We shall deal with this aspect of
Aether more fully when we come to deal with the Nebular Hypothesis, as
the same principle underlies that hypothesis as underlies the origin and
development of comets.

Thus, comets may be formed at any time in interstellar space out of the
Aether that exists there, provided the conditions of its formation are
to be found there. Then, as they are gradually formed, they would, like
any other bodies, come more directly under the influence of any large
bodies, as the sun, and be attracted by them.

This conception of the origin and development of a comet will also
account, and that on a logical and philosophical basis, for another fact
which is associated with cometary phenomena. I refer to the fact of the
expulsion of gaseous matter out of the head of a comet as it nears the
sun, which expulsion will be dealt with in the article on "Parts of a
Comet."

Another problem that might be solved by this conception of a comet lies
in the question, as to whether comets shine by their own light?

If comets are really formed of condensed Aether, as I believe them to
be, then, as light is due to a periodic wave motion of the Aether, as
soon as the Aether (of which the comets' tails, for example, were
formed) was made to vibrate with that rapidity sufficient to produce
light waves in the surrounding Aether, the tails would then shine by
their own light, in exactly the same way that any other body emits light
waves, as soon as its aetherial vibrations reach the rapidity necessary
to produce the waves of light, which vibrations would lie between 2000
to 8000 billions per second.

The number of the comets that exist in the solar system cannot be
ascertained with any degree of accuracy, but the total probably extends
into millions. They are of all sizes, from those which possess diameters
of several miles, to those extending