and which has
since borne his name, was moving in an orbit so contracted that it must
complete its circuit in about three and a half years. Shortly afterwards
another comet, revolving in a period of about six years, was discovered
by Biela, and given his name. Only two more of these short-period comets
were discovered during the first half of last century, but latterly they
have been shown to be a numerous family. Nearly twenty are known
which the giant Jupiter holds so close that the utmost reach of their
elliptical tether does not let them go beyond the orbit of Saturn. These
aforetime wanderers have adapted themselves wonderfully to planetary
customs, for all of them revolve in the same direction with the planets,
and in planes not wide of the ecliptic.

Checked in their proud hyperbolic sweep, made captive in a planetary
net, deprived of their trains, these quondam free-lances of the heavens
are now mere shadows of their former selves. Considered as to mere
bulk, they are very substantial shadows, their extent being measured in
hundreds of thousands of miles; but their actual mass is so slight that
they are quite at the mercy of the gravitation pulls of their captors.
And worse is in store for them. So persistently do sun and planets tug
at them that they are doomed presently to be torn into shreds.

Such a fate has already overtaken one of them, under the very eyes of
the astronomers, within the relatively short period during which these
ill-fated comets have been observed. In 1832 Biela's comet passed quite
near the earth, as astronomers measure distance, and in doing so created
a panic on our planet. It did no greater harm than that, of course, and
passed on its way as usual. The very next time it came within telescopic
hail it was seen to have broken into two fragments. Six years later
these fragments were separated by many millions of miles; and in 1852,
when the comet was due again, astronomers looked for it in vain. It had
been completely shattered.

What had become of the fragments? At that time no one positively knew.
But the question was to be answered presently. It chanced that just at
this period astronomers were paying much attention to a class of bodies
which they had hitherto somewhat neglected, the familiar shooting-stars,
or meteors. The studies of Professor Newton, of Yale, and Professor
Adams, of Cambridge, with particular reference to the great
meteor-shower of November, 1866, which Professor N