n the
same plane. This is not true of the orbits of the planets around the
sun, nor is it true of the orbits of any other system of satellites
around their primary. The most singular circumstance attending the
Uranian system is, however, found in the position which this plane
occupies. This is indeed almost as great an anomaly in our system as are
the rings of Saturn themselves. We have already had occasion to notice
that the plane in which the earth revolves around the sun is very nearly
coincident with the planes in which all the other great planets revolve.
The same is true, to a large extent, of the orbits of the minor planets;
though here, no doubt, we meet with a few cases in which the plane of
the orbit is inclined at no inconsiderable angle to the plane in which
the earth moves. The plane in which the moon revolves also approximates
to this system of planetary planes. So, too, do the orbits of the
satellites of Saturn and of Jupiter, while even the more recently
discovered satellites of Mars form no exception to the rule. The whole
solar system--at least so far as the great planets are concerned--would
require comparatively little alteration if the orbits were to be
entirely flattened down into one plane. There are, however, some notable
exceptions to this rule. The satellites of Uranus revolve in a plane
which is far from coinciding with the plane to which all other orbits
approximate. In fact, the paths of the satellites of Uranus lie in a
plane nearly at right angles to the orbit of Uranus. We are not in a
position to give any satisfactory explanation of this circumstance. It
is, however, evident that in the genesis of the Uranian system there
must have been some influence of a quite exceptional and local
character.

Soon after the discovery of the planet Uranus, in 1781, sufficient
observations were accumulated to enable the orbit it follows to be
determined. When the path was known, it was then a mere matter of
mathematical calculation to ascertain where the planet was situated at
any past time, and where it would be situated at any future time. An
interesting enquiry was thus originated as to how far it might be
possible to find any observations of the planet made previously to its
discovery by Herschel. Uranus looks like a star of the sixth magnitude.
Not many astronomers were provided with telescopes of the perfection
attained by Herschel, and the personal delicacy of perception
characteristic of Hersch