The actual features of our spiral nebulae
seem clearly to exhibit that stage. The shape of the
planets--globular bodies, flattened at the poles--strongly
suggests that they were once liquid. The condition in which we
find Saturn and Jupiter very forcibly confirms this suggestion;
the latest study of those planets supports the current opinion
that they are still red-hot, and even seems to detect the glow of
their surfaces in their mantles of cloud. These points will be
considered more fully presently. For the moment it is enough to
note that, as far as the early stages of planetary development
are concerned, the generally accepted theory rests on a mass of
positive evidence, while the new hypothesis is purely
theoretical. We therefore follow the prevailing view with some
confidence.
Those of the spiral nebulae which face the earth squarely afford
an excellent suggestion of the way in which planets are probably
formed. In some of these nebulae the arms consist of almost
continuous streams of faintly luminous matter; in others the
matter is gathering about distinct centres; in others again the
nebulous matter is, for the most part, collected in large glowing
spheres.
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