to make a planetary system; all our sun's
planets and their satellites taken together amount to only 1/100th of
the mass of the solar system. We may assume, further, that the outpoured
matter would be a mixed cloud of gases and solid and liquid particles;
and that it would stream out, possibly in successive waves, from more
than one part of the disrupted sun, tending to form great spiral trails
round the parent mass. Some astronomers even suggest that, as there are
tidal waves raised by the moon at opposite points of the earth, similar
tidal outbursts would occur at opposite points on the disk of the
disrupted star, and thus give rise to the characteristic arms starting
from opposite sides of the spiral nebula. This is not at all clear,
as the two tidal waves of the earth are due to the fact that it has a
liquid ocean rolling on, not under, a solid bed.

In any case, we have here a good suggestion of the origin of the spiral
nebula and of its further development. As soon as the outbursts are
over, and the scattered particles have reached the farthest limit to
which they are hurled, the concentrating action of gravitation will
slowly assert itself. If we conceive this gravitational influence as the
pressure of the surrounding ether we get a wider understanding of the
process. Much of the dispersed matter may have been shot far enough into
space to escape the gravitational pull of the parent mass, and will be
added to the sum of scattered cosmic dust, meteors, and close shoals
of meteors (comets) wandering in space. Much of the rest will fall
back upon the central body But in the great spiral arms themselves the
distribution of the matter will be irregular, and the denser areas will
slowly gather in the surrounding material. In the end we would thus get
secondary spheres circling round a large primary.

This is the way in which astronomers now generally conceive the
destruction and re-formation of worlds. On one point the new
planetesimal theory differs from the other theories. It supposes that,
since the particles of the whirling nebula are all travelling in the
same general direction, they overtake each other with less violent
impact than the other theories suppose, and therefore the condensation
of the material into planets would not give rise to the terrific heat
which is generally assumed. We will consider this in the next chapter,
when we deal with the formation of the planets. As far as the central
body, the sun,