be laid down that the opposite portions of the sky, whether in the
Milky Way itself, or in those regions distant from it, show a marked
degree of symmetry. The proper motions of stars in corresponding
portions of the sky reveal the same kind of harmony, a harmony which may
even be extended to the various colours of the stars. The stellar
system, which we see disposed all around us, appears in fine to bear all
the marks of an _organised whole_.

The older astronomers, to take Sir William Herschel as an example,
supposed some of the nebulae to be distant "universes." Sir William was
led to this conclusion by the idea he had formed that, when his
telescopes failed to show the separate stars of which he imagined these
objects to be composed, he must put down the failure to their stupendous
distance from us. For instance, he thought the Orion Nebula, which is
now known to be made up of glowing gas, to be an external stellar
system. Later on, however, he changed his mind upon this point, and came
to the conclusion that "shining fluid" would better account both for
this nebula, and for others which his telescopes had failed to separate
into component stars.

The old ideas with regard to external systems and distant universes have
been shelved as a consequence of recent research. All known clusters and
nebulae are now firmly believed to lie _within_ our stellar system.

This view of the universe of stars as a sort of island in the
immensities, does not, however, give us the least idea about the actual
extent of space itself. Whether what is called space is really infinite,
that is to say, stretches out unendingly in every direction, or whether
it has eventually a boundary somewhere, are alike questions which the
human mind seems utterly unable to picture to itself.

[35] The Ptolemaic idea dies hard!

[36] Even the Milky Way itself is far from being a blaze of light, which
shows that the stars composing it do not extend outwards indefinitely.

[37] Mr. Gore has recently made some remarkable deductions, with regard
to the amount of light which we get from the stars. He considers that
most of this light comes from stars below the sixth magnitude; and
consequently, if all the stars visible to the naked eye were to be
blotted out, the glow of the night sky would remain practically the same
as it is at present. Going to the other end of the scale, he thinks also
that the combined light which we get from all the stars below th