t acquired a fresh
interest when it was perceived that its least conspicuous member might
be a planetary shred or projectile in the dignified disguise of a
distant sun. Harding's "Celestial Atlas," designed for the special
purpose of facilitating asteroidal research, was the first systematic
attempt to represent to the eye the _telescopic_ aspect of the heavens.
It was while engaged on its construction that the Lilienthal observer
successfully intercepted Juno on her passage through the Whale in 1804;
whereupon promoted to Gottingen, he there completed, in 1822, the
arduous task so opportunely entered upon a score of years previously.
Still more important were the great star-maps of the Berlin Academy,
undertaken at Bessel's suggestion, with the same object of
distinguishing errant from fixed stars, and executed, under Encke's
supervision, during the years 1830-59. They have played a noteworthy
part in the history of planetary discovery, nor of the minor kind alone.

We have now to recount an event unique in scientific history. The
discovery of Neptune has been characterised as the result of a "movement
of the age,"[214] and with some justice. It had become necessary to the
integrity of planetary theory. Until it was accomplished, the phantom of
an unexplained anomaly in the orderly movements of the solar system must
have continued to haunt astronomical consciousness. Moreover, it was
prepared by many, suggested as possible by not a few, and actually
achieved, simultaneously, independently, and completely, by two
investigators.

The position of the planet Uranus was recorded as that of a fixed star
no less than twenty times between 1690 and the epoch of its final
detection by Herschel. But these early observations, far from affording
the expected facilities for the calculation of its orbit, proved a
source of grievous perplexity. The utmost ingenuity of geometers failed
to combine them satisfactorily with the later Uranian places, and it
became evident, either that they were widely erroneous, or that the
revolving body was wandering from its ancient track. The simplest course
was to reject them altogether, and this was done in the new Tables
published in 1821 by Alexis Bouvard, the indefatigable computating
partner of Laplace. But the trouble was not thus to be got rid of. After
a few years fresh irregularities began to appear, and continued to
increase until absolutely "intolerable." It may be stated as
illustrative