, meet with greater
resistances on their inner sides than on their outer sides; and will be
thus made to diverge outwardly from their courses more than they would
otherwise do. Hence a tendency which, apart from other tendencies, will
cause them severally to go on one or other side of the centre of
gravity, and, approaching it, to get motions more and more tangential.
Observe, however, that their respective motions will be deflected, not
towards one side of the common centre of gravity, but towards various
sides. How then can there result a movement common to them all? Very
simply. Each flocculus, in describing its course, must give motion to
the medium through which it is moving. But the probabilities are
infinity to one against all the respective motions thus impressed on
this medium, exactly balancing one another. And if they do not balance
one another the result must be rotation of the whole mass of the medium
in one direction. But preponderating momentum in one direction, having
caused rotation of the medium in that direction, the rotating medium
must in its turn gradually arrest such flocculi as are moving in
opposition, and impress its own motion upon them; and thus there will
ultimately be formed a rotating medium with suspended flocculi partaking
of its motion, while they move in converging spirals towards the common
centre of gravity.[14]

Before comparing these conclusions with facts, let us pursue the
reasoning a little further, and observe certain subordinate actions. The
respective flocculi must be drawn not towards their common centre of
gravity only, but also towards neighbouring flocculi. Hence the whole
assemblage of flocculi will break up into groups: each group
concentrating towards its local centre of gravity, and in so doing
acquiring a vortical movement like that subsequently acquired by the
whole nebula. According to circumstances, and chiefly according to the
size of the original nebulous mass, this process of local aggregation
will produce various results. If the whole nebula is but small, the
local groups of flocculi may be drawn into the common centre of gravity
before their constituent masses have coalesced with one another. In a
larger nebula, these local aggregations may have concentrated into
rotating spheroids of vapour, while yet they have made but little
approach towards the general focus of the system. In a still larger
nebula, where the local aggregations are both greater and more re