hole comet. On the theory that a comet is due
to the condensation of Aether, the nucleus would represent the first act
in the process of condensation, as there would have to be some centre of
condensation, and that centre would be represented by the nucleus.
Further, the process of condensation would assume a spherical form, as
the conception of our aetherial atom is that of a sphere or an oblate
spheroid. As the process of condensation went on, the layers that would
be produced would form a kind of envelope around the point of
condensation, with the result that the nucleus would ultimately consist
of a large mass of gaseous matter, made up of layer upon layer of
condensed Aether around some central point, which formed the nucleus.

This hypothesis agrees with observed phenomena, because, when we deal
with the tails of comets, we shall see that the tail is simply formed by
the reverse process to that of condensation, as in the case of cometary
tails the gaseous envelopes so formed will be thrown off (either through
heat generated by friction, or by the increased heat as the comet nears
the sun), which are then repelled away from the sun by the centrifugal
force. Herschel,[41] referring to the nucleus, states, paragraph 559:
"An atmosphere free to expand in all directions would envelop the
nucleus spherically," while in his Reflection on Halley's Comet, he
states, Art. 570, "1st, That the matter of the nucleus of a comet is
powerfully excited and dilated into a vaporous state by the action of
the sun's rays, escaping in streams and jets at those points of its
surface which oppose the least resistance. 2nd, That the process chiefly
takes place in that portion of the nucleus which is turned towards the
sun, the vapour escaping in that direction. 3rd, That when so emitted,
it is prevented from proceeding in the direction originally impressed
upon it, by some force directed _from_ the sun, drifting it back and
carrying it out to vast distances behind the nucleus forming the tail."

When we come to deal with the question of the formation of the tail, we
shall find that every reflection made by Herschel is satisfactorily
fulfilled by the conception of a gravitating and condensing Aether.
Before considering the tail, however, we will deal with the head or
coma.

The head or coma is that part of the comet which exists round the
nucleus. It is less bright than the nucleus, and oftentimes appears as a
shadowy mass of light. Hers