ing in the dim future, the
earth and the moon will continue to perform this adjusted revolution
in a period of about fourteen hundred hours, the two bodies being
held, as it were, by invisible bands. Such an arrangement might be
eternal if there were no intrusion of tidal influence from any other
body; but of course in our system as we actually find it the sun
produces tides as well as the moon; and the solar tides being at
present much less than those originated by the moon, we have neglected
them in the general outlines of the theory. The solar tides, however,
must necessarily have an increasing significance. I do not mean that
they will intrinsically increase, for there seems no reason to
apprehend any growth in their actual amount; it is their relative
importance to the lunar tides that is the augmenting quantity. As the
final state is being approached, and as the velocity of the earth's
rotation is approximating to the angular velocity with which the moon
revolves around it, the ebbing and the flowing of the lunar tides must
become of evanescent importance; and this indeed for a double reason,
partly on account of the moon's greatly augmented distance, and
partly on account of the increasing length of the lunar day, and the
extremely tardy movements of ebb and flow that the lunar tides will
then have. Thus the lunar tides, so far as their dynamical importance
is concerned, will ultimately become zero, while the solar tides
retain all their pristine efficiency.

We have therefore to examine the dynamical effects of solar tides on
the earth and moon in the critical stage to which the present course
of things tends. The earth will then rotate in a period of about
fifty-seven of its present days; and considering that the length of
the day, though so much greater than our present day, is still much
less than the year, it follows that the solar tides must still
continue so as to bring the earth's velocity of rotation to a point
even lower than it has yet attained. In fact, if we could venture to
project our glance sufficiently far into the future, it would seem
that the earth must ultimately have its velocity checked by the
sun-raised tides, until the day itself had become equal to the year.
The dynamical considerations become, however, too complex for us to
follow them, so that I shall be content with merely pointing out that
the influence of the solar tides will prevent the earth and moon from
eternally preserving the