tions
it produces. This problem it was that Laplace worked out in the
_Mecanique Celeste_.

But the inverse problem: Given the perturbations, to find the planet
which causes them--such a problem had never yet been attacked, and by
only a few had its possibility been conceived. Bessel made preparations
for trying what he could do at it in 1840, but he was prevented by fatal
illness.

In 1841 the difficulties of the problem presented by these residual
perturbations of Uranus excited the imagination of a young student, an
undergraduate of St. John's College, Cambridge--John Couch Adams by
name--and he determined to have a try at it as soon as he was through
his Tripos. In January, 1843, he graduated as Senior Wrangler, and
shortly afterwards he set to work. In less than two years he reached a
definite conclusion; and in October, 1845, he wrote to the
Astronomer-Royal, at Greenwich, Professor Airy, saying that the
perturbations of Uranus would be explained by assuming the existence of
an outer planet, which he reckoned was now situated in a specified
latitude and longitude.

We know now that had the Astronomer-Royal put sufficient faith in this
result to point his big telescope to the spot indicated and commence
sweeping for a planet, he would have detected it within 1-3/4 deg. of the
place assigned to it by Mr. Adams. But any one in the position of the
Astronomer-Royal knows that almost every post brings an absurd letter
from some ambitious correspondent or other, some of them having just
discovered perpetual motion, or squared the circle, or proved the earth
flat, or discovered the constitution of the moon, or of ether, or of
electricity; and out of this mass of rubbish it requires great skill and
patience to detect such gems of value as there may be.

Now this letter of Mr. Adams's was indeed a jewel of the first water,
and no doubt bore on its face a very different appearance from the
chaff of which I have spoken; but still Mr. Adams was an unknown man: he
had graduated as Senior Wrangler it is true, but somebody must graduate
as Senior Wrangler every year, and every year by no means produces a
first-rate mathematician. Those behind the scenes, as Professor Airy of
course was, having been a Senior Wrangler himself, knew perfectly well
that the labelling of a young man on taking his degree is much more
worthless as a testimony to his genius and ability than the general
public are apt to suppose.

Was it likely tha