sun.

[Illustration: FIG. 90.--Planetary orbits to scale; showing the
Asteroidal region between Jupiter and Mars. (The orbits of satellites
are exaggerated.)]

In 1800 the preliminaries were settled: the heavens near the zodiac
were divided into twenty-four regions, each of which was intrusted to
one observer to be swept. Meanwhile, however, quite independently of
these arrangements in Germany, and entirely unknown to this committee, a
quiet astronomer in Sicily, Piazzi, was engaged in making a catalogue of
the stars. His attention was directed to a certain region in Taurus by
an error in a previous catalogue, which contained a star really
non-existent.

In the course of his scrutiny, on the 1st of January, 1801, he noticed a
small star which next evening appeared to have shifted. He watched it
anxiously for successive evenings, and by the 24th of January he was
quite sure he had got hold of some moving body, not a star: probably, he
thought, a comet. It was very small, only of the eighth magnitude; and
he wrote to two astronomers (one of them Bode himself) saying what he
had observed. He continued to observe till the 11th of February, when he
was attacked by illness and compelled to cease.

His letters did not reach their destination till the end of March.
Directly Bode opened his letter he jumped to the conclusion that this
must be the missing planet. But unfortunately he was unable to verify
the guess, for the object, whatever it was, had now got too near the sun
to be seen. It would not be likely to be out again before September, and
by that time it would be hopelessly lost again, and have just as much to
be rediscovered as if it had never been seen.

Mathematical astronomers tried to calculate a possible orbit for the
body from the observations of Piazzi, but the observed places were so
desperately few and close together. It was like having to determine a
curve from three points close together. Three observations ought to
serve,[27] but if they are taken with insufficient interval between
them it is extremely difficult to construct the whole circumstances of
the orbit from them. All the calculations gave different results, and
none were of the slightest use.

The difficulty as it turned out was most fortunate. It resulted in the
discovery of one of the greatest mathematicians, perhaps the greatest,
that Germany has ever produced--Gauss. He was then a young man of
twenty-five, eking out a living by tuition.