towards the Milky Way.
If a point is at length reached beyond which there are but few
scattered stars, such a point would, for us, mark the boundary of our
system. From this point of view the answer does not seem to admit of
doubt. If, going in every direction, we mark the point, if any, at
which the great mass of the stars are seen behind us, the totality of
all these points will lie on a surface of the general form that
Herschel supposed.

There is still another direct indication of the finitude of our stellar
system upon which we have not touched. If this system extended out
without limit in any direction whatever, it is shown by a geometric
process which it is not necessary to explain in the present connection,
but which is of the character of mathematical demonstration, that the
heavens would, in every direction where this was true, blaze with the
light of the noonday sun. This would be very different from the
blue-black sky which we actually see on a clear night, and which, with
a reservation that we shall consider hereafter, shows that, how far
so-ever our stellar system may extend, it is not infinite. Beyond this
negative conclusion the fact does not teach us much. Vast, indeed, is
the distance to which the system might extend without the sky appearing
much brighter than it is, and we must have recourse to other
considerations in seeking for indications of a boundary, or even of a
well-marked thinning out, of stars.

If, as was formerly supposed, the stars did not greatly differ in the
amount of light emitted by each, and if their diversity of apparent
magnitude were due principally to the greater distance of the fainter
stars, then the brightness of a star would enable us to form a more or
less approximate idea of its distance. But the accumulated researches
of the past seventy years show that the stars differ so enormously in
their actual luminosity that the apparent brightness of a star affords
us only a very imperfect indication of its distance. While, in the
general average, the brighter stars must be nearer to us than the
fainter ones, it by no means follows that a very bright star, even of
the first magnitude, is among the nearer to our system. Two stars are
worthy of especial mention in this connection, Canopus and Rigel. The
first is, with the single exception of Sirius, the brightest star in
the heavens. The other is a star of the first magnitude in the
southwest corner of Orion. The most long-contin