planet to that time-honoured number. It was
indeed on the 13th of March 1781, while engaged in observing the
constellation of the Twins, that the justly famous Sir William Herschel
caught sight of an object which he did not recognise as having met with
before. He at first took it for a comet, but observations of its
movements during a few days showed it to be a planet. This body, which
the power of the telescope alone had thus shown to belong to the solar
family, has since become known to science under the name of Uranus. By
its discovery the hitherto accepted limits of the solar system were at
once pushed out to twice their former extent, and the hope naturally
arose that other planets would quickly reveal themselves in the
immensities beyond.

For a number of years prior to Herschel's great discovery, it had been
noticed that the distances at which the then known planets circulated
appeared to be arranged in a somewhat orderly progression outwards from
the sun. This seeming plan, known to astronomers by the name of Bode's
Law, was closely confirmed by the distance of the new planet Uranus.
There still lay, however, a broad gap between the planets Mars and
Jupiter. Had another planet indeed circuited there, the solar system
would have presented an appearance of almost perfect order. But the void
between Mars and Jupiter was unfilled; the space in which one would
reasonably expect to find another planet circling was unaccountably
empty.

On the first day of the nineteenth century the mystery was however
explained, a body being discovered[1] which revolved in the space that
had hitherto been considered planetless. But it was a tiny globe hardly
worthy of the name of planet. In the following year a second body was
discovered revolving in the same space; but it was even smaller in size
than the first. During the ensuing five years two more of these little
planets were discovered. Then came a pause, no more such bodies being
added to the system until half-way through the century, when suddenly
the discovery of these so-called "minor planets" began anew. Since then
additions to this portion of our system have rained thick and fast. The
small bodies have received the name of Asteroids or Planetoids; and up
to the present time some six hundred of them are known to exist, all
revolving in the previously unfilled space between Mars and Jupiter.

In the year 1846 the outer boundary of the solar system was again
extended by th