tion of the formation of
the comet advanced in Art. 111, viz. that it is nothing more or less
than Aether in a state of condensation, and remembering the explanation
given of the parts of the comet, as the nucleus, and head or coma, we
are now in a position to give a philosophical account of the formation
of the tails of comets, which will satisfactorily fulfil all the Rules
of Philosophy. In addition to the facts already referred to in the
previous articles of this chapter, we must also recall our conception of
the Aether as given in Chapter IV., remembering that it gets denser
nearer the sun, and that it is not frictionless; therefore, when a body
is urged through it, friction is produced, and heat is generated.

We must also remember that the Aether is rotating round the sun as that
body proceeds through space. We have, therefore, to picture the
condensed mass of Aether situated out in the cold interstellar space,
gradually coming under the influence of the sun, as that body rushes on
its journey through space with a velocity of 500,000 miles per hour.

Slowly, but surely, the mass of condensed Aether begins to respond to
the attractive power of the sun, and to move through space towards the
sun. So long as it is moving towards the sun, it is encountering and
having to overcome the resistance of the Aether.

At first this resistance is very feeble, owing to the decreased density
of the Aether, but as it proceeds on its journey it is constantly
passing into denser parts of the aetherial electro-magnetic field around
the sun. The result is, that as the resistance is increased, so there is
greater friction between the matter of the comet and the atomic Aether
in space, and, in consequence, heat is generated.

In addition to the generated heat, the comet is all the while passing
into regions of greater intensity of heat. In both cases, the effect is
only manifested on that side of the comet which is approaching the sun;
for, if there be any friction at all, it will only be on that half of
the comet which encounters the Aether, so to speak, while the same part
will receive the added heat, as the distance between the comet and the
sun is decreased. As can readily be seen therefore, this added heat acts
only upon the half of the comet which is advancing, and which faces the
sun, and as the effect of heat is always to vaporise, so the effect on
the nucleus of the comet is to vaporise the condensed aetherial matter,
and th