of the universal law of gravitation (1685),
whereby he showed that "the motions of the solar system were due to the
action of a central force directed to the body at the centre of the
system, and varying inversely with the square of the distance from it."
After making this discovery, Newton himself, with the aid of others,
especially of the French mathematician Picard, labored for years to
verify it, and still further verification was necessary before it could
be fully comprehended and accepted by the scientific world. The
discovery of the asteroids or small planets revolving in orbits between
those of Mars and Jupiter, aided in confirming the Newtonian theory,
which the discovery of Uranus, by Sir William Herschel (1781), had done
much to establish.

From the time of Sir William Herschel the science of stellar astronomy,
revealing the enormous distances of the stars--none of them really
fixed, but all having real or apparent motions--was rapidly developed.
The discovery of stellar planets, at almost incalculable distances,
still further changed the aspect of the heavens as viewed by
astronomers, and when the capital discovery of Neptune was made those
men of science were well prepared for studying its nature and
importance. These matters, as well as the simultaneous calculation of
the place of Neptune by Adams and Leverrier, and its actual discovery by
Galle, are set forth by Sir Oliver Lodge in a manner as charming for
simplicity as it is valuable in its summary of scientific learning.

The explanation by Newton of the observed facts of the motion of the
moon, the way he accounted for precession and nutation and for the
tides; the way in which Laplace explained every detail of the planetary
motions--these achievements may seem to the professional astronomer
equally, if not more, striking and wonderful; but of the facts to be
explained in these cases the general public is necessarily more or less
ignorant, and so no beauty or thoroughness of treatment appeals to it or
excites its imagination. But to predict in the solitude of the study,
with no weapons other than pen, ink, and paper, an unknown and
enormously distant world, to calculate its orbit when as yet it had
never been seen, and to be able to say to a practical astronomer, "Point
your telescope in such a direction at such a time, and you will see a
new planet hitherto unknown to man"--this must always appeal to the
imagination with dramatic intensity, and must