During the short historic period there was no record of such an event;
still it would seem to be only through the collision of dark suns, of
which the number must be increasing, that a temporary rejuvenescence
of the heavens was possible, and by such ebbings and flowings of
stellar life that the inevitable end to which evolution in its
apparently uncompensated progress was carrying us could, even for a
little, be delayed. We could not refuse to admit as possible such an
origin for nebulæ. In considering, however, the formation of the
existing nebulæ we must bear in mind that, in the part of the heavens
within our ken, the stars still in the early and middle stages of
evolution exceeded greatly in number those which appeared to be in an
advanced condition of condensation. Indeed, we found some stars which
might be regarded as not far advanced beyond the nebular condition. It
might be that the cosmical bodies which were still nebulous owed their
later development to some conditions of the part of space where they
occurred, such as conceivably a greater original homogeneity, in
consequence of which condensation began less early. In other parts of
space condensation might have been still further delayed, or even have
not yet begun. If light matter were suggested by the spectrum of these
nebulæ, it might be asked further, as a pure speculation, whether in
them we were witnessing possibly a later condensation of the light
matter which had been left behind, at least in a relatively greater
proportion, after the first growth of worlds into which the heavier
matter condensed, though not without some entanglement of the lighter
substances. The wide extent and great diffuseness of this bright-line
nebulosity over a large part of the constellation of Orion might be
regarded, perhaps, as pointing in this direction. The diffuse nebulous
matter streaming round the Pleiades might possibly be another
instance, though the character of its spectrum had not yet been
ascertained.