cate observations. The two parts of the ring,
being at different distances from the planet, could not fail to be given
different movements of precession by the action of the sun. Hence it
would seem that the planes of both rings ought in general to be inclined
toward each other, whereas they appear from observation always to
coincide. It was necessary then that some physical cause capable of
neutralizing the action of the sun should exist. In a memoir published
in February, 1789, Laplace found that this cause depended on the
ellipticity of Saturn produced by a rapid movement of rotation of the
planet, a movement whose discovery Herschel announced in November of the
same year.

If we descend from the heavens to the earth, the discoveries of Laplace
will appear not less worthy of his genius. He reduced the phenomena of
the tides, which an ancient philosopher termed in despair "the tomb of
human curiosity," to an analytical theory in which the physical
conditions of the question figure for the first time. Consequently, to
the immense advantage of coast navigation, calculators now venture to
predict in detail the time and height of the tides several years in
advance. Between the phenomena of the ebb and flow, and the attractive
forces of the sun and moon upon the fluid sheet which covers three
fourths of the globe, an intimate and necessary connection exists; a
connection from which Laplace deduced the value of the mass of our
satellite the moon. Yet so late as the year 1631 the illustrious
Galileo, as appears from his 'Dialogues,' was so far from perceiving the
mathematical relations from which Laplace deduced results so beautiful,
so unequivocal, and so useful, that he taxed with frivolousness the
vague idea which Kepler entertained of attributing to the moon's
attraction a certain share in the production of the diurnal and
periodical movements of the waters of the ocean.

Laplace did not confine his genius to the extension and improvement of
the mathematical theory of the tide. He considered the phenomenon from
an entirely new point of view, and it was he who first treated of the
stability of the ocean. He has established its equilibrium, but upon the
express condition (which, however, has been amply proved to exist) that
the mean density of the fluid mass is less than the mean density of the
earth. Everything else remaining the same, if we substituted an ocean of
quicksilver for the actual ocean, this stability would d