modesty, which is the crown of all his other virtues, presenting such
a model of an accomplished philosopher as can rarely be found beyond
the regions of fiction, demand abler pens than mine to describe them
in adequate terms, however much inclined I might feel to undertake
the task."

The first few lines of the eulogium just quoted allude to Herschel's
absence from England. This was not merely an episode of interest in
the career of Herschel, it was the occasion of one of the greatest
scientific expeditions in the whole history of astronomy.

Herschel had, as we have seen, undertaken a revision of his father's
"sweeps" for new objects, in those skies which are visible from our
latitudes in the northern hemisphere. He had well-nigh completed
this task. Zone by zone the whole of the heavens which could be
observed from Windsor had passed under his review. He had added
hundreds to the list of nebulae discovered by his father. He had
announced thousands of double stars. At last, however, the great
survey was accomplished. The contents of the northern hemisphere, so
far at least as they could be disclosed by his telescope of twenty
feet focal length, had been revealed.

[PLATE: SIR JOHN HERSCHEL'S OBSERVATORY AT FELDHAUSEN,
Cape of Good Hope.]

But Herschel felt that this mighty task had to be supplemented by
another of almost equal proportions, before it could be said that the
twenty-foot telescope had done its work. It was only the northern
half of the celestial sphere which had been fully explored. The
southern half was almost virgin territory, for no other astronomer