The conflicting movements
would be adjusted by collisions and gravitation, the smaller
bodies would be absorbed in the larger or enslaved as their
satellites, and the last state would be a family of smaller suns
circling at vast distances round the parent body. The planets,
moreover, would be caused to rotate on their axes, besides
revolving round the sun, as the particles at their inner edge
(nearer the sun) would move at a different speed from those at
the outer edge. In the course of time the smaller bodies, having
less heat to lose and less (or no) atmosphere to check the loss,
would cool down, and become dark solid spheres, lit only by the
central fire.
While the first stage of this theory of development is seen in
the spiral nebula, the later stages seem to be well exemplified
in the actual condition of our planets. Following, chiefly, the
latest research of Professor Lowell and his colleagues, which
marks a considerable advance on our previous knowledge, we shall
find it useful to glance at the sister-planets before we approach
the particular story of our earth.
Mercury, the innermost and smallest of the planets, measuring
only some 3400 miles in diameter, is, not unexpectedly, an
airless wilderness.
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