that tides raised on the moon by the earth would
be greater than the tides raised on the earth by the moon. The
question is, however, not a very simple one, for it depends on the
masses of both bodies as well as on their relative dimensions. In so
far as the masses are concerned, the earth being more than eighty
times as heavy as the moon, the tides would on this account be vastly
larger on the moon than on the earth. On the other hand, the moon's
diameter being much less than that of the earth, the efficiency of a
tide-producing body in its action on the moon would be less than that
of the same body at the same distance in its action on the earth; but
the diminution of the tides from this cause would be not so great as
their increase from the former cause, and therefore the net result
would be to exhibit much greater tides on the moon than on the earth.

Suppose that the moon had been originally endowed with a rapid
movement of rotation around its axis, the effect of the tides on that
rotation would tend to check its velocity just in the same way as the
tides on the earth have effected a continual elongation of the day.
Only as the tides on the moon were so enormously great, their capacity
to check the moon's speed would have corresponding efficacy. In
addition to this, the mass of the moon being so small, it could only
offer feeble resistance to the unceasing action of the tide, and
therefore our satellite must succumb to whatever the tides desired
ages before our earth would have been affected to a like extent. It
must be noticed that the influence of the tidal friction is not
directed to the total annihilation of the rotation of the two bodies
affected by it; the velocity is only checked down until it attains
such a point that the speed in which each body rotates upon its axis
has become equal to that in which it revolves around the
tide-producer. The practical effect of such an adjustment is to make
the tide-agitated body turn a constant face towards its tormentor.

I may here note a point about which people sometimes find a little
difficulty. The moon constantly turns the same face towards the earth,
and therefore people are sometimes apt to think that the moon performs
no rotation whatever around its own axis. But this is indeed not the
case. The true inference to be drawn from the constant face of the
moon is, that the velocity of rotation about its own axis is equal to
that of its rotation around the earth; i