years, and down to 1846 it responded punctually to the
astronomers who expected its return as fixed by calculation. But on
January 13, 1846, the celestial wanderer broke in half: each fragment
went its own way, side by side, to return within sight from the Earth in
1852. It was their last appearance. That year the twin comets could
still be seen, though pale and insignificant. Soon they vanished into
the depths of night, and never appeared again. They were looked for in
vain, and were despaired of, when on November 27, 1872, instead of the
shattered comet, came a magnificent rain of shooting stars. They fell
through the Heavens, numerous as the flakes of a shower of snow.

The same phenomenon recurred on November 27, 1885, and confirmed the
hypothesis of the demolition and disaggregation of Biela's Comet into
shooting stars.

* * * * *

There is an immense variety in the brilliancy of the shooting stars,
from the weak telescopic sparks that vanish like a flash of lightning,
to the incandescent _bolides_ or _fire-balls_ that explode in the
atmosphere.

Fig. 56 shows an example of these, and it represents a fire-ball
observed at the Observatory of Juvisy on the night of August 10, 1899.
It arrived from Cassiopeia, and burst in Cepheus.

This phenomenon may occur by day as well as by night. It is often
accompanied by one or several explosions, the report of which is
sometimes perceptible to a considerable distance, and by a shower of
meteorites. The globe of fire bursts, and splits up into luminous
fragments, scattered in all directions. The different parts of the
fire-ball fall to the surface of the Earth, under the name of aerolites,
or rather of uranoliths, since they arrive from the depths of space, and
not from our atmosphere.

From the most ancient times we hear of showers of uranoliths to which
popular superstitions were attached; and the Greeks even gave the name
of _Sideros_ to iron, the first iron used having been sidereal.

[Illustration: FIG. 56.--Fire-Ball seen from the Observatory at Juvisy,
August 10, 1899.]

[Illustration: FIG. 57.--Explosion of a Fire-Ball above Madrid,
February 10, 1896.]

No year passes without the announcement of several showers of
uranoliths, and the phenomenon sometimes causes great alarm to those who
witness it. One of the most remarkable explosions is that which occurred
above Madrid, February 10, 1896, a fragment from which, sent me by M.