ion of the satellites is tipped
much farther backward. Since in every other case the satellites of a
planet are situated nearly in the plane of the planet's equator, it may
be assumed that the same rule holds with Uranus and Neptune; and, that
being so, we must conclude that those planets rotate backward on their
axes. This has an important bearing on the nebular hypothesis of the
origin of the solar system, and at one time was thought to furnish a
convincing argument against that hypothesis; but it has been shown that
by a modification of Laplace's theory the peculiar behavior of Uranus
and Neptune can be reconciled with it.

Very little is known of the surfaces of Uranus and Neptune. Indications
of the existence of belts resembling those of Jupiter have been found in
the case of both planets. There are similar belts on Saturn, and as they
seem to be characteristic of large, rapidly rotating bodies of small
density, it was to be expected that they would be found on Uranus and
Neptune.

The very interesting opinion is entertained by some astronomers that
there is at least one other great planet beyond Neptune. The orbits of
certain comets are relied upon as furnishing evidence of the existence
of such a body. Prof. George Forbes has estimated that this, as yet
undiscovered, planet may be even greater than Jupiter in mass, and may
be situated at a distance from the sun one hundred times as great as the
earth's, where it revolves in an orbit a single circuit of which
requires a thousand years.

Whether this planet, with a year a thousand of our years in length, will
ever be seen with a telescope, or whether its existence will ever, in
some other manner, be fully demonstrated, can not yet be told. It will
be remembered that Neptune was discovered by means of computations based
upon its disturbing attraction on Uranus before it had ever been
recognized with the telescope. But when the astronomers in the
observatories were told by their mathematical brethren where to look
they found the planet within half an hour after the search began. So it
is possible the suspected great planet beyond Neptune may be within the
range of telescopic vision, but may not be detected until elaborate
calculations have deduced its place in the heavens. As a populous city
is said to furnish the best hiding-place for a man who would escape the
attention of his fellow beings, so the star-sprinkled sky is able to
conceal among its multitudes world