By means of a purely astronomical determination, based upon the action
which the earth exerts on the motion of the moon, or, in other words,
on the inequalities in lunar longitudes and latitudes, Laplace has
shown in one single result the mean Figure of the Earth.
It is very remarkable that an astronomer, without leaving his
observatory, may, merely by comparing his observations with
mean analytical results, not only be enabled to determine with
exactness the size and degree of ellipticity of the earth, but
also its distance from the sun and moon; results that otherwise
could only be arrived at by long and arduous expeditions to the
most remote parts of both hemispheres. The moon may therefore, by
the observation of its movements, render appreciable to the higher
departments of astronomy the ellipticity of the earth, as it taught
the early astronomers the rotundity of our earth by means of its
eclipses.--_Laplace’s Expos. du Syst. du Monde._