general terms, and we can safely take them as such; but in this, as in
other instances, it is well to qualify our acceptance of the
statements by the memory that all things are infinitely more
complicated than we can possibly conceive or represent them to be.

We have next to consider the rotations of the planetary spheres upon
their axes, together with the similar movement, or lack of it, in the
case of their satellites. This rotation, according to the nebular
hypothesis, may be explained by the movements which would set up in
the share of matter which was at first a ring of the solar nebula, and
which afterward gathered into the planetary aggregation. The way of it
may be briefly set forth as follows: Such a ring doubtless had a
diameter of some million miles; we readily perceive that the particles
of matter in the outer part of the belt would have a swifter movement
around the sun than those on the inside. When by some disturbance, as
possibly by the passage of a great meteoric body of a considerable
gravitative power, this ring was broken in two, the particles
composing it on either side would, because of their mutual attraction,
tend to draw away from the breach, widening that gap until the matter
of the broken ring was aggregated into a sphere of the star dust or
vapour. When the nebulous matter originally in the ring became
aggregated into a spherical form, it would, on account of the
different rates at which the particles were moving when they came
together, be the surer to fall in toward the centre, not in straight
lines, but in curves--in other words, the mass would necessarily take
on a movement of rotation essentially like that which we have
described in setting forth the nebular hypothesis.

In the stages of concentration the planetary nebulæ might well repeat
those through which the greater solar mass proceeded. If the volume of