The gist of the theory is that these
curious objects are probably the result of close approaches to each
other of two independent suns, reminding us of what was said on this
subject when we were dealing with temporary stars. Of the previous
history of these appulsing suns the theory gives us no account; they
are simply supposed to arrive within what may be called an effective
tide-producing distance, and then the drama begins. Some of the
probable consequences of such an approach have been noticed in Chapter
5; let us now consider them a little more in detail.
Tides always go in couples; if there is a tide on one side of a globe
there will be a corresponding tide on the other side. The cause is to
be found in the law that the force of gravitation varies inversely as
the square of the distance; the attraction on the nearest surface of
the body exercised by another body is greater than on its center, and
greater yet than on its opposite surface. If two great globes attract
each other, each tends to draw the other out into an ellipsoidal
figure; they must be more rigid than steel to resist this -- and even
then they cannot altogether resist. If they are liquid or gaseous they
will yield readily to the force of distortion, the amount of which
will depend upon their distance apart, for the nearer they are the
greater becomes the tidal strain.
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