than elsewhere. All these stars are
incomparably more distant than the sun, which they surround, so it is
evident that our sun and, of course, the system which attends him lie
actually inside the Milky Way. It seems tempting to pursue the thought
here suggested, and to reflect that the whole Milky Way may, after all,
be merely a star cluster, comparable in size with some of the other star
clusters which we see, and that, viewed from a remote point in space,
the Milky Way would seem to be but one of the many clusters of stars
containing our sun as an indistinguishable unit.

[Illustration: Fig. 96.--The Globular Cluster in Hercules.]

In the southern hemisphere there are two immense masses which are
conspicuously visible to the naked eye, and resemble detached portions
of the Milky Way. They cannot be seen by observers in our latitude, and
are known as the Magellanic clouds or the two nubeculae. Their structure,
as revealed to an observer using a powerful telescope, is of great
complexity. Sir John Herschel, who made a special study of these
remarkable objects, gives the following description of them: "The
general ground of both consists of large tracts and patches of
nebulosity in every stage of resolution, from light irresolvable, in a
reflector of eighteen inches aperture, up to perfectly separated stars
like the Milky Way, and clustering groups sufficiently insulated and
condensed to come under the designation of irregular and in some cases
pretty rich clusters. But besides these there are also nebulae in
abundance and globular clusters in every state of condensation." It can
hardly be doubted that the two nubeculae, which are, roughly speaking,
round, or, rather, oval, are not formed accidentally by a vast number of
very different objects being ranged at various distances along the same
line of sight, but that they really represent two great systems of
objects, widely different in constitution, which here are congregated in
each other's neighbourhood, whereas they generally do not co-exist close
to each other in the Milky Way, with which the mere naked-eye view would
otherwise lead us to associate the Magellanic clouds.

When we direct a good telescope to the heavens, we shall occasionally
meet with one of the remarkable celestial objects which are known as
nebulae. They are faint cloudy spots, or stains of light on the black
background of the sky. They are nearly all invisible to the naked eye.
These celestial ob