e it would
still only look like a star, and it would require considerable labor and
watching to sift it out from the other stars surrounding it. We know
that Uranus had been seen twenty times, and thought to be a star, before
its true nature was discovered by Herschel; and Uranus is only about
half as far away as Neptune.

Neither at Paris nor at Greenwich was any optical search undertaken; but
Professor Airy wrote to ask M. Leverrier the same old question that he
had fruitlessly put to Adams: Did the new theory explain the errors of
the radius vector or not? The reply of Leverrier was both prompt and
satisfactory--these errors were explained, as well as all the others.
The existence of the object was then for the first time officially
believed in. The British Association met that year at Southampton, and
Sir John Herschel was one of its sectional presidents. In his inaugural
address, on September 10, 1846, he called attention to the researches of
Leverrier and Adams in these memorable words:

"The past year has given to us the new [minor] planet Astraea; it has
done more--it has given us the probable prospect of another. We see it
as Columbus saw America from the shores of Spain. Its movements have
been felt trembling along the far-reaching line of our analysis with a
certainty hardly inferior to ocular demonstration."

It was nearly time to begin to look for it. So the astronomer-royal
thought on reading Leverrier's paper. But as the national telescope at
Greenwich was otherwise occupied, he wrote to Professor Challis, at
Cambridge, to know whether he would permit a search to be made for it
with the Northumberland equatorial, the large telescope at Cambridge
University, presented to it by one of the Dukes of Northumberland.

Professor Challis said he would conduct the search himself, and shortly
began a leisurely and dignified series of sweeps around the place
designated by theory, cataloguing all the stars he observed, intending
afterward to sort out his observations, compare one with another, and
find out whether any one star had changed its position; because if it
had it must be the planet. Thus, without giving an excessive time to the
business, he accumulated a host of observations.

Professor Challis thus actually saw the planet twice--on August 4 and
August 12, 1846--without knowing it. If he had had a map of the heavens
containing telescopic stars down to the tenth magnitude, and if he had
compared his obs