or. In the evolution of our system,
the central mass of the nebula became the Sun and each of the revolving
rings, by their condensation into one mass, formed a planet. In a
similar manner, though on a diminished scale, the elementary planets,
whilst in a nebulous state, parted with annular portions of their
substance, out of which were evolved their systems of satellites. This
theory furnished a plausible reason, which was capable of explaining how
the orbs which constitute the solar system came into existence, and,
though hypothetical, yet the manner in which it accounted for the
orderly and symmetrical genesis of the system rendered it attractive and
fascinating to scientific minds.

The evidence in support of the nebulous origin of the solar system, if
not conclusive, is of much weight and importance. The remarkable harmony
with which the orbs of the system perform their motions is strongly
indicative of their common origin and that their evolution occurred in
subordination to the law of universal gravitation. The following are the
characteristic points in favour of this theory:--

1. All the planets revolve round the Sun in the same direction, and they
all occupy nearly the same plane.

2. Their satellites, with the exception of those of Uranus and Neptune,
perform their revolutions in obedience to the same law.

3. The rotation on their axes of the Sun, planets, and satellites is in
the same direction as their orbital motion.

Between the orbits of Mars and Jupiter there revolves a remarkable group
of small planets or planetoids. On account of the absence of a planet in
this region, where, according to the laws of planetary distances, one
ought to be found, the existence of those small bodies was suspected for
some years prior to their discovery. The first was detected by Piazzi at
Palermo in 1801; two others were discovered by Olbers in 1802 and 1807,
and one by Harding in 1804. For some time it was believed that no more
planetoids existed, but in 1845 a fifth was detected by Hencke, and from
that year until now upwards of 300 of those small bodies have been
discovered. Their magnitudes are of varied extent; the diameter of the
largest is believed not to exceed 450 miles, and that of the smaller
ones from twenty to thirty miles. It was surmised at one time, when only
a few of those bodies were known, that they were the fragments of a
planet which met with some terrible catastrophe; but since the discovery
of