ntral star. Yet again, and most beautifully in the great nebula of
the constellation of Orion, the cloudy mass, though hardly visible to
the naked eye, shows a division into many separate parts, the whole
appearing as if in process of concentration about many distinct
centres.

The nebulas are reasonably believed by many astronomers to be examples
of the ancient condition of the physical universe, masses of matter
which for some reason as yet unknown have not progressed in their
consolidation to the point where they have taken on the
characteristics of suns and their attendant planets.

Many of the fixed stars, the incomplete list of which now amounts to
several hundred, are curiously variable in the amount of light which
they send out to the earth. Sometimes these variations are apparently
irregular, but in the greater number of cases they have fixed periods,
the star waxing and waning at intervals varying from a few months to a
few years. Although some of the sudden flashings forth of stars from
apparent small size to near the greatest brilliancy may be due to
catastrophes such as might be brought about by the sudden falling in
of masses of matter upon the luminous spheres, it is more likely that
the changes which we observe are due to the fact that two suns
revolving around a common centre are in different stages of
extinction. It may well be that one of these orbs, presumably the
smaller, has so far lost temperature that it has ceased to glow. If in
its revolution it regularly comes between the earth and its luminous
companion, the effect would be to give about such a change in the
amount of light as we observe.

The supposition that a bright sun and a relatively dark sun might
revolve around a common centre of gravity may at first sight seem
improbable. The fact is, however, that imperfect as our observations
on the stars really are, we know many instances in which this kind of
revolution of one star about another takes place. In some cases these
stars are of the same brilliancy, but in others one of the lights is
much brighter than the other. From this condition to the state where
one of the stars is so nearly dark as to be invisible, the transition
is but slight. In a word, the evidence goes to show that while we see
only the luminous orbs of space, the dark bodies which people the
heavens are perhaps as numerous as those which send us light, and
therefore appear as stars.

Besides the greater spheres of spa