d.

Professor Challis said he would conduct the search himself; and shortly
commenced a leisurely and dignified series of sweeps round about the
place assigned by theory, cataloguing all the stars which he observed,
intending afterwards 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. He thus, without giving an
excessive time to the business, accumulated a host of observations,
which he intended afterwards to reduce and sift at his leisure.

The wretched man thus actually saw the planet twice--on August 4th and
August 12th, 1846--without knowing it. If only he had had a map of the
heavens containing telescopic stars down to the tenth magnitude, and if
he had compared his observations with this map as they were made, the
process would have been easy, and the discovery quick. But he had no
such map. Nevertheless one was in existence: it had just been completed
in that country of enlightened method and industry--Germany. Dr.
Bremiker had not, indeed, completed his great work--a chart of the whole
zodiac down to stars of the tenth magnitude--but portions of it were
completed, and the special region where the new planet was expected
happened to be among the portions already just done. But in England
this was not known.

Meanwhile, Mr. Adams wrote to the Astronomer-Royal several additional
communications, making improvements in his theory, and giving what he
considered nearer and nearer approximations for the place of the planet.
He also now answered quite satisfactorily, but too late, the question
about the radius vector sent to him months before.

Let us return to Leverrier. This great man was likewise engaged in
improving his theory and in considering how best the optical search
could be conducted. Actuated, probably, by the knowledge that in such
matters as cataloguing and mapping Germany was then, as now, far ahead
of all the other nations of the world, he wrote in September (the same
September as Sir John Herschel delivered his eloquent address at
Southampton) to Berlin. Leverrier wrote, I say, to Dr. Galle, head of
the Observatory at Berlin, saying to him, clearly and decidedly, that
the new planet was now in or close to such and such a position, and that
if he would point his telescope to that part of the heavens he would see
it; and, moreover, that he would be able to tell it from a star by its
having a sen