hy to be called stars.

On the one hand, then, we see that the notion, of late years
uncritically received, that the nebulae are extremely remote galaxies of
stars like those which make up our own Milky Way, is totally
irreconcilable with the facts--involves us in sundry absurdities. On the
other hand, we see that the hypothesis of nebular condensation
harmonizes with the most recent results of stellar astronomy: nay
more--that it supplies us with an explanation of various appearances
which in its absence would be incomprehensible.

* * * * *

Descending now to the Solar System, let us consider first a class of
phenomena in some sort transitional--those offered by comets. In them,
or at least in those most numerous of them which lie far out of the
plane of the Solar System, and are not to be counted among its members,
we have, still existing, a kind of matter like that out of which,
according to the Nebular Hypothesis, the Solar System was evolved.
Hence, for the explanation of them, we must go back to the time when the
substances forming the sun and planets were yet unconcentrated.

When diffused matter, precipitated from a rarer medium, is aggregating,
there are certain to be here and there produced small flocculi, which
long remain detached; as do, for instance, minute shreds of cloud in a
summer sky. In a concentrating nebula these will, in the majority of
cases, eventually coalesce with the larger flocculi near to them. But it
is tolerably evident that some of those formed at the outermost parts of
the nebula, will _not_ coalesce with the larger internal masses, but
will slowly follow without overtaking them. The relatively greater
resistance of the medium necessitates this. As a single feather falling
to the ground will be rapidly left behind by a pillow-full of feathers;
so, in their progress to the common centre of gravity, will the
outermost shreds of vapour be left behind by the great masses of vapour
internally situated. But we are not dependent merely on reasoning for
this belief. Observation shows us that the less concentrated external
parts of nebulae, _are_ left behind by the more concentrated internal
parts. Examined through high powers, all nebulae, even when they have
assumed regular forms, are seen to be surrounded by luminous streaks, of
which the directions show that they are being drawn into the general
mass. Still higher powers bring into view still smaller, faint