now no available
moment of momentum, and all the moment of momentum required to account
for her retreat has of late come from the rotation of the earth; but
suppose that the moon still had some liquid on its surface which could
be agitated by tides, suppose further that it did not always bend the
same face towards us, that it therefore had some available moment of
momentum due to its rotation on which the tides could operate, then
see how the argument would have been altered. The gradual increase of
the moon's distance could be provided for by a transfer of moment of
momentum from two sources, due of course to the rotational velocities
of the two bodies. Here again the moon and the earth will contribute
according to that dynamical but very iniquitous principle which
regulated the appropriations from the purses of Dives and Lazarus. The
moon must give not according to her abundance, but in the inverse
ratio thereof--because she has little she must give largely. Nor shall
we make an erroneous estimate if we say that nine-tenths of the whole
moment of momentum necessary for the enlargement of the orbit would
have been exacted from the moon; that means that the moon must once
have had about five or six times as much moment of momentum as the
earth possesses at this moment. Considering the small size of the
moon, this could only have arisen by terrific velocity of rotation,
which it is inconceivable that its materials could ever have
possessed.

This presents the demonstration of tidal evolution in a fresh light.
If the moon now departed to any considerable extent from showing the
constant face to the earth, it would seem that its retreat could not
have been caused by tides. Some other agent for producing the present
configuration would be necessary, just as we found that some other
agent than the tides has been necessary in the case of Jupiter.

But I must say a few words as to the attitude of this question with
regard to the entire solar system. This system consists of the sun
presiding at the centre, and of the planets and their satellites in
revolution around their respective primaries, and each also animated
by a rotation on its axis. I shall in so far depart from the actual
configuration of the system as to transform it into an ideal system,
whereof the masses, the dimensions, and the velocities shall all be
preserved; but that the several planes of revolution shall be all
flattened into one plane, instead of being