the atmosphere in rushing in
toward the centre of upward movement take on the same whirling motion
as do the molecules of water in the basin--in fact, the two actions
are perfectly comparable in all essential regards, except that the
fluid is moving downward, while the air flows upward. Briefly stated,
the reason for the movement of fluid and gas in the whirling way is as
follows: If every particle on its way to the centre moved on a
perfectly straight line toward the point of escape, the flow would be
directly converging, and the paths followed would resemble the spokes
of a wheel. But when by chance one of the particles sways ever so
little to one side of the direct way, a slight lateral motion would
necessarily be established. This movement would be due to the fact
that the particle which pursued the curved line would press against
the particles on the out-curved side of its path--or, in other words,
shove them a little in that direction--to the extent that they
departed from the direct line they would in turn communicate the
shoving to the next beyond. When two particles are thus shoving on one
side of their paths, the action which makes for revolution is doubled,
and, as we readily see, the whole mass may in this way become quickly
affected, the particles driven out of their path, moving in a curve
toward the centre. We also see that the action is accumulative: the
more curved the path of each particle, the more effectively it shoves;
and so, in the case of the basin, we see the whirling rapidly
developed before our eyes.

In falling in toward the centre the particles of star dust or vapour
would no more have been able one and all to pursue a perfectly
straight line than the particles of water in the basin. If a man
should spend his lifetime in filling and emptying such a vessel, it is
safe to say that he would never fail to observe the whirling movement.
As the particles of matter in the nebular mass which was to become a
solar system are inconceivably greater than those of water in the
basin, or those of air in the atmospheric whirl, the chance of the
whirling taking place in the heavenly bodies is so great that we may
assume that it would inevitably occur.

As the vapours in the olden day tended in toward the centre of our
solar system, and the mass revolved, there is reason to believe that
ringlike separations took place in it. Whirling in the manner
indicated, the mass of vapour or dust would flatten into a