acceleration might be forthcoming.

The capability of the sun for disturbing the earth-moon system is
obviously connected with the distance of the earth from the sun. If
the earth moved in an orbit which underwent no change whatever, then
the efficiency of the sun as a disturbing agent would not undergo any
change of the kind which was sought for. But if there were any
alteration in the shape or size of the earth's orbit, then that might
involve such changes in the distance between the earth and the sun as
would possibly afford the desired agent for producing the observed
lunar effect. It is known that the earth revolves in an orbit which,
though nearly circular, is strictly an ellipse. If the earth were
the only planet revolving around the sun then that ellipse would
remain unaltered from age to age. The earth is, however, only one of
a large number of planets which circulate around the great luminary,
and are guided and controlled by his supreme attracting power. These
planets mutually attract each other, and in consequence of their
mutual attractions the orbits of the planets are disturbed from the
simple elliptic form which they would otherwise possess. The
movement of the earth, for instance, is not, strictly speaking,
performed in an elliptical orbit. We may, however, regard it as
revolving in an ellipse provided we admit that the ellipse is itself
in slow motion.

It is a remarkable characteristic of the disturbing effects of the
planets that the ellipse in which the earth is at any moment moving
always retains the same length; that is to say, its longest diameter
is invariable. In all other respects the ellipse is continually
changing. It alters its position, it changes its plane, and, most
important of all, it changes its eccentricity. Thus, from age to age