ld.
Herschel mentioned these particulars to no one save to his constant and
generous friend, Sir W. Watson, who exclaimed, "Never bought monarch
honour so cheap." To other enquirers, Herschel merely said that the King
had provided for him. In accepting this post, the great astronomer took
no doubt a serious step. He at once sacrificed entirely his musical
career, now, from many sources, a lucrative one; but his determination
was speedily taken. The splendid earnest that he had already given of
his devotion to astronomy was, he knew, only the commencement of a
series of memorable labours. He had indeed long been feeling that it was
his bounden duty to follow that path in life which his genius indicated.
He was no longer a young man. He had attained middle age, and the years
had become especially precious to one who knew that he had still a
life-work to accomplish. He at one stroke freed himself from all
distractions; his pupils and concerts, his whole connection at Bath,
were immediately renounced; he accepted the King's offer with alacrity,
and after one or two changes settled permanently at Slough, near
Windsor.

It has, indeed, been well remarked that the most important event in
connection with the discovery of Uranus was the discovery of Herschel's
unrivalled powers of observation. Uranus must, sooner or later, have
been found. Had Herschel not lived, we would still, no doubt, have known
Uranus long ere this. The really important point for science was that
Herschel's genius should be given full scope, by setting him free from
the engrossing details of an ordinary professional calling. The
discovery of Uranus secured all this, and accordingly obtained for
astronomy all Herschel's future labours.[30]

Uranus is so remote that even the best of our modern telescopes cannot
make of it a striking picture. We can see, as Herschel did, that it has
a measurable disc, and from measurements of that disc we conclude that
the diameter of the planet is about 31,700 miles. This is about four
times as great as the diameter of the earth, and we accordingly see that
the volume of Uranus must be about sixty-four times as great as that of
the earth. We also find that, like the other giant planets, Uranus seems
to be composed of materials much lighter, on the whole, than those we
find here; so that, though sixty-four times as large as the earth,
Uranus is only fifteen times as heavy. If we may trust to the analogies
of what we see ever