Thus,
as Laplace ably remarks,* "An astronomer, without leaving his observatory,
may, by a comparison of lunar theory with true observations, not only be
enabled to determine the form and size 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."
[footnote] *Laplace, 'Expos. du Syst. du Monde', p. 231.
p 169
The compression which may be inferred from lunar inequalities affords an
advantage not yielded by individual measurements of degrees or experiments
with the pendulum, since it gives a mean amount which is referable to the
whole planet. The comparison of the Earth's compression with the velocity
of rotation shows, further, the increase of density from the strata from the
surface toward the center -- an increase which a comparison of the ratios of
the axes of Jupiter and Saturn with their times of rotation likewise shows
to exist in these two large planets. Thus the knowledge of the external
form of planetary bodies leads us to draw conclusions regarding their
internal character.
The northern and southern hemispheres appear to present nearly the same
curvature under equal degrees of latitude, but, as has already been
observed, pendulum experiments and measurements of degrees yield such
different results for individual portions of the Earth's surface that no
regular figure can be given which would reconcile all the results hitherto
obtained by this method.
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