servations made at Greenwich from 1750 onwards had been
undertaken in 1833. The results, published in 1846, constituted a
permanent and universal stock of materials for the correction of
planetary theory. But in the meantime, investigators, both native and
foreign, were freely supplied with the "places and errors," which,
clearly exhibiting the discrepancies between observation and
calculation--between what _was_ and what was _expected_--formed the very
groundwork of future improvements.

Mr. Adams had no reason to complain of official discourtesy. His labours
received due and indispensable aid; but their purpose was regarded as
chimerical. "I have always," Sir George Airy wrote,[217] "considered the
correctness of a distant mathematical result to be a subject rather of
moral than of mathematical evidence." And that actually before him
seemed, from its very novelty, to incur a suspicion of unlikelihood. No
problem in planetary disturbance had heretofore been attacked, so to
speak, from the rear. The inverse method was untried, and might well be
deemed impracticable. For the difficulty of determining the
perturbations produced by a given planet is small compared with the
difficulty of finding a planet by its resulting perturbations. Laplace
might have quailed before it; yet it was now grappled with as a first
essay in celestial dynamics. Moreover, Adams unaccountably neglected to
answer until too late a question regarded by Airy in the light of an
_experimentum crucis_ as to the soundness of the new theory. Nor did he
himself take any steps to obtain a publicity which he was more anxious
to merit than to secure. The investigation consequently remained buried
in obscurity. It is now known that had a search been instituted in the
autumn of 1845 for the remote body whose existence had been so
marvellously foretold, it would have been found within _three and a half
lunar diameters_ (1 deg. 49') of the spot assigned to it by Adams.

A competitor, however, equally daring and more fortunate--_audax fortuna
adjutus_, as Gauss said of him--was even then entering the field. Urbain
Jean Joseph Leverrier, the son of a small Government _employe_ in
Normandy, was born at Saint-Lo, March 11, 1811. He studied with
brilliant success at the Ecole Polytechnique, accepted the post of
astronomical teacher there in 1837, and, "docile to circumstance,"
immediately concentrated the whole of his vast, though as yet
undeveloped powers upon the f