ry of the planet Mars. A full account
of this inquiry is contained in his famous work, 'De Stella Martis' [Of
the Planet Mars], published in 1609. The discovery of the third law was
announced to the world in his treatise on Harmonics (1628).

To seek a physical cause adequate to retain the planets in their closed
orbits; to make the stability of the universe depend on mechanical
forces, and not on solid supports like the crystalline spheres imagined
by our ancestors; to extend to the heavenly bodies in their courses the
laws of earthly mechanics,--such were the problems which remained for
solution after Kepler's discoveries had been announced. Traces of these
great problems may be clearly perceived here and there among ancient and
modern writers, from Lucretius and Plutarch down to Kepler, Bouillaud,
and Borelli. It is to Newton, however, that we must award the merit of
their solution. This great man, like several of his predecessors,
imagined the celestial bodies to have a tendency to approach each other
in virtue of some attractive force, and from the laws of Kepler he
deduced the mathematical characteristics of this force. He extended it
to all the material molecules of the solar system; and developed his
brilliant discovery in a work which, even at the present day, is
regarded as the supremest product of the human intellect.

The contributions of France to these revolutions in astronomical science
consisted, in 1740, in the determination by experiment of the spheroidal
figure of the earth, and in the discovery of the local variations of
gravity upon the surface of our planet. These were two great results;
but whenever France is not first in science she has lost her place. This
rank, lost for a moment, was brilliantly regained by the labors of four
geometers. When Newton, giving to his discoveries a generality which the
laws of Kepler did not suggest, imagined that the different planets were
not only attracted by the sun, but that they also attracted each other,
he introduced into the heavens a cause of universal perturbation.
Astronomers then saw at a glance that in no part of the universe would
the Keplerian laws suffice for the exact representation of the phenomena
of motion; that the simple regular movements with which the imaginations
of the ancients were pleased to endow the heavenly bodies must
experience numerous, considerable, perpetually changing perturbations.
To discover a few of these perturbations, and