ormidable problems, of celestial mechanics.
He lost no time in proving to the mathematical world that the race of
giants was not extinct. Two papers on the stability of the solar system,
presented to the Academy of Sciences, September 16 and October 14, 1839,
showed him to be the worthy successor of Lagrange and Laplace, and
encouraged hopes destined to be abundantly realised. His attention was
directed by Arago to the Uranian difficulty in 1845, when he cheerfully
put aside certain intricate cometary researches upon which he happened
to be engaged, in order to obey with dutiful promptitude the summons of
the astronomical chief of France. In his first memoir on the subject
(communicated to the Academy, November 10, 1845), he proved the
inadequacy of all known causes of disturbance to account for the
vagaries of Uranus; in a second (June 1, 1848), he demonstrated that
only an exterior body, occupying at a certain date a determinate
position in the zodiac, could produce the observed effects; in a third
(August 31, 1846), he assigned the orbit of the disturbing body, and
announced its visibility as an object with a sensible disc about as
bright as a star of the eighth magnitude.

The question was now visibly approaching an issue. On September 10, Sir
John Herschel declared to the British Association respecting the
hypothetical new planet: "We see it as Columbus saw America from the
coast of Spain. Its movements have been felt, trembling along the
far-reaching line of our analysis with a certainty hardly inferior to
that of ocular demonstration." Less than a fortnight later, September
23, Professor Galle, of the Berlin Observatory, received a letter from
Leverrier requesting his aid in the telescopic part of the inquiry
already analytically completed. He directed his refractor to the heavens
that same night, and perceived, within less than a degree of the spot
indicated, an object with a measurable disc nearly three seconds in
diameter. Its absence from Bremiker's recently-completed map of that
region of the sky showed it to be no star, and its movement in the
predicted direction confirmed without delay the strong persuasion of its
planetary nature.[218]

In this remarkable manner the existence of the remote member of our
system known as "Neptune" was ascertained. But the discovery, which
faithfully reflected the duplicate character of the investigation which
led to it, had been already secured at Cambridge before it was a