But the great majority are only as bright as stars of
the second, third, or fourth magnitude. As the amount of light given by
a meteor depends on its mass and velocity, we can form some idea as to
the actual weight of one of these meteors, and it appears that most of
them do not weigh nearly as much as a quarter of an ounce; indeed, it is
probable that many do not weigh a single grain. But we have seen that a
comet in all probability is nothing but a very loose swarm of small
particles surrounded by gas of very slight density, and we have also
seen that the material of a comet must by degrees be more or less
dissipated through space. We have still to tell a wonderful story of the
breaking up of a comet and what appears to have become of the particles
thereof.

A copious meteoric shower took place on the night of the 27th November,
1872. On this occasion the shooting stars diverged from a radiant point
in the constellation of Andromeda. As a spectacle, it was unquestionably
inferior to the magnificent display of 1866, but it is difficult to say
which of the two showers has been of greater scientific importance.

It surely is a remarkable coincidence that the earth should encounter
the Andromedes (for so this shower is called) at the very moment when it
is crossing the track of Biela's comet. We have observed the direction
from which the Andromedes come when they plunge into the atmosphere; we
can ascertain also the direction in which Biela's comet is moving when
it passes the earth's track, and we find that the direction in which the
comet moves and the direction in which the meteors move are identical.
This is, in itself, a strong and almost overwhelming presumption that
the comet and the shooting stars are connected; but it is not all. We
have observations of this swarm dating back to the eighteenth century,
and we find that the date of its appearance has changed from the 6th or
7th of December to the end of November in perfect accordance with the
retrograde motion of the crossing-point of the earth's orbit and the
orbit of Biela's comet. This comet was observed in 1772, and again in
1805-6, before its periodic return every seven years was discovered. It
was discovered by Biela in 1826, and was observed again in 1832. In 1846
the astronomical world was startled to find that there were now two
comets in place of one, and the two fragments were again perceived at
the return in 1852. In 1859 Biela's comet could not be se