drawn in by some of the greater planets.

As they come to us these meteorites often break up in the atmosphere,
the bits being scattered sometimes over a wide area of country. Thus,
in the case of the Cocke County meteorite of Tennessee, one of the
iron species, the fragments, perhaps thousands in number, which came
from the explosion of the body were scattered over an area of some
thousand square miles. When they reach the surface in their natural
form, these meteors always have a curious wasted and indented
appearance, which makes it seem likely that they have been subject to
frequent collisions in their journeys after they were formed by some
violent rending action.

In some apparent kinship with the meteorites may be classed the
comets. The peculiarity of these bodies is that they appear in most
cases to be more or less completely vaporous. Rushing down from the
depths of the heavens, these bodies commonly appear as faintly
shining, cloudlike masses. As they move in toward the sun long trails
of vapour stream back from the somewhat consolidated head. Swinging
around that centre, they journey again into the outer realm. As they
retreat, their tail-like streamers appear to gather again upon their
centres, and when they fade from view they are again consolidated. In
some cases it has been suspected that a part at least of the cometary
mass was solid. The evidence goes to show, however, that the matter is
in a dustlike or vaporous condition, and that the weight of these
bodies is relatively very small.

[Illustration: Fig. 2.--The Great Comet of 1811, one of the many
varied forms of these bodies.]

Owing to their strange appearance, comets were to the ancients omens
of calamity. Sometimes they were conceived as flaming swords; their
forms, indeed, lend themselves to this imagining. They were thought to
presage war, famine, and the death of kings. Again, in more modern
times, when they were not regarded as portents of calamity, it was
feared that these wanderers moving vagariously through our solar
system might by chance come in contact with the earth with disastrous
results. Such collisions are not impossible, for the reason that the
planets would tend to draw these errant bodies toward them if they
came near their spheres; yet the chance of such collisions happening
to the earth is so small that they may be disregarded.

MOTIONS OF THE SPHERES.

Although little is known of the motions whi