arth, anything small enough, that is, and
not travelling at too great a pace, is bound to fall on to it. And,
however improbable it seems, it is undoubtedly true that masses of
matter do crash down upon the earth from time to time, and these are
called meteorites. When we think of the great expanse of the oceans, of
the ice round the poles, and of the desert wastes, we know that for
every one of such bodies seen to fall many more must have fallen unseen
by any human being. Meteors large enough to reach the earth are not very
frequent, which is perhaps as well, and as yet there is no record of
anyone's having been killed by them. Most of them consist of masses of
stone, and a few are of iron, while various substances resembling those
that we know here have been found in them. Chemists in analyzing them
have also come across certain elements so far unknown upon earth, though
of course there is no saying that these may not exist at depths to which
man has not penetrated.

A really large meteor is a grand sight. If it is seen at night it
appears as a red star, growing rapidly bigger and leaving a trail of
luminous vapour behind as it passes across the sky. In the daytime this
vapour looks like a cloud. As the meteor hurls itself along there may be
a deep continuous roar, ending in one supreme explosion, or perhaps in
several explosions, and finally the meteor may come to the earth in one
mass, with a force so great that it buries itself some feet deep in the
soil, or it may burst into numbers of tiny fragments, which are
scattered over a large area. When a meteor is found soon after its fall
it is very hot, and all its surface has 'run,' having been fused by
heat. The heat is caused by the friction of our atmosphere. The meteor
gets entangled in the atmosphere, and, being drawn by the attraction of
the earth, dashes through it. Part of the energy of its motion is turned
to heat, which grows greater and greater as the denser air nearer to the
earth is encountered; so that in time all the surface of the meteor runs
like liquid, and this liquid, rising to a still higher temperature, is
blown off in vapour, leaving a new surface exposed. The vapour makes the
trail of fire or cloud seen to follow the meteor. If the process went on
for long the meteor would be all dissipated in vapour, and in any case
it must reach the earth considerably reduced in size.

Numbers and numbers of comparatively small ones disappear, and for every
o