over thousands of miles. They also
possess orbits, with which we will now deal.

ART. 112. _Orbits of Comets._--As has already been pointed out, comets
perform their journey round the sun, not only in the plane of the
ecliptic, but also at all angles relatively to that plane. In this
respect they differ from the orbits of planets and satellites, which
perform their journey in orbits situated wholly in the plane of the
ecliptic (Art. 109).

There is another important difference between the orbits of the comets
and those of the planets. In the case of the latter the orbit is that of
an ellipse, while in the case of the comet the orbit may be either that
of a parabola or a hyperbola, which may be looked upon as elongated
ellipses open at one end. There are, however, some comets whose orbits
are perfectly elliptical, and whose return may be calculated with a fair
amount of accuracy.

These are known either as Short Period Comets, as represented by Faye's
Comet, Encke's and De Vico's; or Long Period Comets, as represented by
the comets of 1811, 1844, and 1858. In the case of all these, as their
return to our solar system can be determined, it follows that they must
revolve around the sun in some sort of a closed orbit, probably that of
an exceedingly elongated ellipse.

There are, however, other comets which appear once, or it may be several
times only, and then disappear out of the solar system for ever. Now the
question arises, as to whether the orbits of the comets which are so
variable can be explained by the motions of the Aether which we have
already ascribed to it? We have seen (Art. 109) how it is possible to
account physically for the plane of the ecliptic from the motions of the
Aether, and how it is that all the planets move within that plane, but
here we have a phenomenon of a different kind, as observation distinctly
teaches us that the comets do not move in, or keep within the plane of
the ecliptic, but gravitate round the sun at all angles to that plane.

In order for us, therefore, to be able to account, and that on a
philosophical basis, for this fact, we must revert to our conception of
the sun in its relation to the solar system. In Art. 88 we learned that
the sun was an electro-magnet possessing its electro-magnetic field, and
generating electro-magnetic waves which were radiated forth from it on
every side. From Art. 89 we learn that an electro-magnetic body
possesses lines of force, and that the