without seeing or knowing of any more. In 1845 another was found,
however, in Germany, and a few weeks later two others by Mr. Hind in
England. Since then there seems no end to them; numbers have been
discovered in America, where Professors Peters and Watson have made a
specialty of them, and have themselves found something like a hundred.

Vesta is the largest--its area being about the same as that of Central
Europe, without Russia or Spain--and the smallest known is about twenty
miles in diameter, or with a surface about the size of Kent. The whole
of them together do not nearly equal the earth in bulk.

The main interest of these bodies to us lies in the question, What is
their history? Can they have been once a single planet broken up? or are
they rather an abortive attempt at a planet never yet formed into one?

The question is not _entirely_ settled, but I can tell you which way
opinion strongly tends at the present time.

Imagine a shell travelling in an elliptic orbit round the earth to
suddenly explode: the centre of gravity of all its fragments would
continue moving along precisely the same path as had been traversed by
the centre of the shell before explosion, and would complete its orbit
quite undisturbed. Each fragment would describe an orbit of its own,
because it would be affected by a different initial velocity; but every
orbit would be a simple ellipse, and consequently every piece would in
time return through its starting-point--viz. the place at which the
explosion occurred. If the zone of asteroids had a common point through
which they all successively passed, they could be unhesitatingly
asserted to be the remains of an exploded planet. But they have nothing
of the kind; their orbits are scattered within a certain broad zone--a
zone everywhere as broad as the earth's distance from the sun,
92,000,000 miles--with no sort of law indicating an origin of this kind.

It must be admitted, however, that the fragments of our supposed shell
might in the course of ages, if left to themselves, mutually perturb
each other into a different arrangement of orbits from that with which
they began. But their perturbations would be very minute, and moreover,
on Laplace's theory, would only result in periodic changes, provided
each mass were rigid. It is probable that the asteroids were at one time
not rigid, and hence it is difficult to say what may have happened to
them; but there is not the least reason to believ