that angle is to radius nearly as to 1 : 687) a real diameter
1/687 of its distance from the eye, which, if we assume to be such as
would correspond to a parallax of 1/20 of a second, we find that the
cluster, outliers apart, measures 558,000 millions of miles across.
Light, in other words, occupies thirty-six days in traversing it, but
sixty-five years in journeying thence hither. Its components may be
regarded, on an average, as of the twelfth magnitude; for, although the
divergent stars rank much higher in the scale of brightness, the central
ones, there is reason to believe, are notably fainter. The sum total of
their light, if concentrated into one stellar point, would at any rate
very little (if at all) exceed that of a third-magnitude star. And one
star of the third is equivalent to just four thousand stars of the
twelfth magnitude. Hence we arrive at the conclusion that the stars in
the Hercules Cluster number much more nearly four than fourteen
thousand.'

For what purpose do those thousands of clustering orbs shine? Who can
tell? Night is unknown in the regions illumined by their brilliant
radiance. This stupendous aggregation of suns testifies to the
magnificence of the starry heavens, and to the omnipotence of the
Creator.

GALAXIES.--These consist of vast aggregations of stars which form
separate 'island universes' floating in the depths of space; they are
believed to equal in magnitude and magnificence the Milky Way--the
galaxy to which our system belongs.

NEBULAE.--We now reach the last, and what are believed to be the most
distant of the known contents of the heavens. They are all exceedingly
remote, devoid of any perceptible motion, faintly luminous, and, with
the exception of two of their number, invisible to the naked eye. Halley
was the first astronomer who paid any attention to those objects. In
1716 he enumerated six of them, but of this number only two can, in a
strict sense, be regarded as nebulae, the others since then have been
resolved into magnificent star clusters. In 1784, Messier catalogued 103
nebulae, and the Herschels--father and son--in their survey of the
stellar regions, discovered 4,000 of those objects. There are now 8,000
known nebulae in the heavens, but the majority of them are not of much
interest to astronomers. Prior to the invention of the spectroscope it
was believed that all nebulae were irresolvable star clusters, but the
analysis of their light by this instrument ind