f superintendence) there is no prospect whatever of its
being made with any chance of success, except with the Northumberland
telescope.

"Now, I should be glad to ask you, in the first place, whether you
could make such an examination?

"Presuming that your answer would be in the negative, I would ask,
secondly, whether, supposing that an assistant were supplied to you
for this purpose, you would superintend the examination?

"You will readily perceive that all this is in a most unformed state
at present, and that I am asking these questions almost at a venture,
in the hope of rescuing the matter from a state which is, without the
assistance that you and your instruments can give, almost desperate.
Therefore I should be glad to have your answer, not only responding
simply to my questions, but also entering into any other
considerations which you think likely to bear on the matter.

"The time for the said examination is approaching near."

[Sidenote: Challis undertakes the search.]

[Sidenote: He finds too late that he had observed the planet.]

Professor Challis did not require an assistant, but determined to
undertake the work himself, and devised his own plan of procedure; but he
also set out on the undertaking with the expectation of a long and arduous
search. No such idea as that of finding the planet on the first night ever
entered his head. For one thing, he had no map of the region to be
examined, for although the map used by Galle had been published, no copy
of it had as yet reached Cambridge, and Professor Challis had practically
to construct a map for himself. In these days of photography to make such
a map is a simple matter, but at that time the process was terribly
laborious. "I get over the ground very slowly," he wrote on September 2nd
to Airy, "thinking it right to include all stars to 10-11 magnitude; and I
find that to scrutinise thoroughly in this way the proposed portion of the
heavens will require many more observations than I can take this year."
With such a prospect, it is not surprising that one night's observations
were not even compared with the next; there would be a certain economy in
waiting until a large amount of material had been accumulated, and then
making the comparisons all together, and this was the course adopted. But
when Le Verrier's third paper, with the decided opinion that the planet
would be brig