the Asteroids were formed by the explosion of a planet circulating
between the orbits of Mars and Jupiter. The Asteroids, whatever their
manner of origin, form a ring around the sun; but, of course, the
explosion of a great independent body, not originally revolving about
a superior center of gravitational force, would not result in the
formation of a ring of small bodies, but rather of a dispersed mass of
them. But back of any speculation of this kind lies the problem, at
present insoluble: How could the explosion be produced? (See the
question of explosions in Chapters 6 and 14).

Then, on the other hand, we have the observation of Herschel, since
abundantly confirmed, that space is unusually vacant in the immediate
neighborhood of condensed star-clusters and nebulæ, which, as far as
it goes, might be taken as an indication that the assembled stars had
been drawn together by their mutual attractions, and that the tendency
to aggregation is still bringing new members toward the cluster. But
in that case there must have been an original condensation of stars at
that point in space. This could probably have been produced by the
coagulation of a great nebula into stellar nuclei, a process which
seems now to be taking place in the Orion Nebula.

A yet more remarkable globular star-cluster exists in the southern
hemisphere, Omega Centauri. In this case the central condensation of
stars presents an almost uniform blaze of light. Like the Hercules
cluster, that in Centaurus is surrounded with stars scattered over a
broad field and showing an appearance of radial arrangement. In fact,
except for its greater richness, Omega Centauri is an exact duplicate
of its northern rival. Each appears to an imaginative spectator as a
veritable ``city of suns.'' Mathematics shrinks from the task of
disentangling the maze of motions in such an assemblage. It would seem