of the perfection to which astronomy had been brought, that
divergencies regarded as menacing the very foundation of its theories
never entered the range of unaided vision. In other words, if the
theoretical and the real Uranus had been placed side by side in the sky,
they would have seemed, to the sharpest eye, to form a single body.[215]

The idea that these enigmatical disturbances were due to the attraction
of an unknown exterior body was a tolerably obvious one; and we
accordingly find it suggested in many different quarters. Bouvard
himself was perhaps the first to conceive it. He kept the possibility
continually in view, and bequeathed to his nephew's diligence the
inquiry into its reality when he felt that his own span was drawing to a
close; but before any progress had been made with it, he had already
(June 7, 1843) "ceased to breathe and to calculate." The Rev. T. J.
Hussey actually entertained in 1834 the notion, but found his powers
inadequate to the task, of assigning an approximate place to the
disturbing body; and Bessel, in 1840, laid his plans for an assault in
form upon the Uranian difficulty, the triumphant exit from which fatal
illness frustrated his hopes of effecting or even witnessing.

The problem was practically untouched when, in 1841, an undergraduate of
St. John's College, Cambridge, formed the resolution of grappling with
it. The projected task was an arduous one. There were no guiding
precedents for its conduct. Analytical obstacles had to be encountered
so formidable as to appear invincible even to such a mathematician as
Airy. John Couch Adams, however, had no sooner taken his degree, which
he did as senior wrangler in January, 1843, than he set resolutely to
work, and on October 21, 1845, was able to communicate to the Astronomer
Royal numerical estimates of the elements and mass of the unknown
planet, together with an indication of its actual place in the heavens.
These results, it has been well said,[216] gave "the final and
inexorable proof" of the validity of Newton's Law. The date October 21,
1845, "may therefore be regarded as marking a distinct epoch in the
history of gravitational astronomy."

Sir George Biddell Airy had begun in 1835 his long and energetic
administration of the Royal Observatory, and was already in possession
of data vitally important to the momentous inquiry then on foot. At his
suggestion, and under his superintendence, the reduction of all the
planetary ob