nebular lines, which are either straight throughout, or if they change
direction do so at an angle, little stars are strung like beads. In
one case seven or eight stars are thus aligned, and, as if to
emphasize their dependence upon the chain which connects them, when it
makes a slight bend the file of stars turns the same way. Many other
star rows in the group suggest by their arrangement that they, too,
were once strung upon similar threads which have now disappeared,
leaving the stars spaced along their ancient tracks. We seem forced to
the conclusion that there was a time when the Pleiades were embedded
in a vast nebula resembling that of Orion, and that the cloud has now
become so rare by gradual condensation into stars that the merest
trace of it remains, and this would probably have escaped detection
but for the remarkable actinic power of the radiant matter of which it
consists. The richness of many of these faint nebulous masses in
ultra-violet radiations, which are those that specifically affect the
photographic plate, is the cause of the marvelous revelatory power of
celestial photography. So the veritable unseen universe, as
distinguished from the ``unseen universe'' of metaphysical
speculation, is shown to us.

A different kind of association between stars and nebulæ is shown in
some surprising photographic objects in the constellation Cygnus,
where long, wispy nebulæ, billions of miles in length, some of them
looking like tresses streaming in a breeze, lie amid fields of stars
which seem related to them. But the relation is of a most singular
kind, for notwithstanding the delicate structure of the long nebulæ
they appear to act as barriers, causing the stars to heap themselves
on one side. The stars are two, three, or four times as numerous on
one side of the nebulæ as on the other. These nebulæ, as far as
appearance goes, might be likened to rail fences, or thin hedges,