it had been taken for granted that it was a star. It presented no
difference which was sufficient to arrest attention.

As the unknown body by which Uranus was disturbed was certainly much
more remote than Uranus, it seemed to be certain that though it might
show a disc perceptible to very close inspection, yet that the disc
must be so minute as not to be detected except with extreme care. In
other words, it seemed probable that the body which was to be sought
for could not readily be discriminated from a small star, to which
class of object it bore a superficial resemblance, though, as a
matter of fact, there was the profoundest difference between the two
bodies.

There are on the heavens many hundreds of thousands of stars, and the
problem of identifying the planet, if indeed it should lie among
these stars, seemed a very complex matter. Of course it is the
abundant presence of the stars which causes the difficulty. If the
stars could have been got rid of, a sweep over the heavens would at
once disclose all the planets which are bright enough to be visible
with the telescopic power employed. It is the fortuitous resemblance
of the planet to the stars which enables it to escape detection. To
discriminate the planet among stars everywhere in the sky would be
almost impossible. If, however, some method could be devised for
localizing that precise region in which the planet's existence might
be presumed, then the search could be undertaken with some prospect
of success.

To a certain extent the problem of localizing the region on the sky
in which the planet might be expected admitted of an immediate
limitation. It is known that all the planets, or perhaps I ought