This work must, however, be regarded as merely introductory to the
main labours of John Herschel's life. His father devoted the greater
part of his years as an observer to what he called his "sweeps" of
the heavens. The great reflecting telescope, twenty feet long, was
moved slowly up and down through an arc of about two degrees towards
and from the pole, while the celestial panorama passed slowly in the
course of the diurnal motion before the keenly watching eye of the
astronomer. Whenever a double star traversed the field Herschel
described it to his sister Caroline, who, as we have already
mentioned, was his invariable assistant in his midnight watches. When
a nebula appeared, then he estimated its size and its brightness, he
noticed whether it had a nucleus, or whether it had stars disposed in
any significant manner with regard to it. He also dictated any other
circumstance which he deemed worthy of record. These observations
were duly committed to writing by the same faithful and indefatigable
scribe, whose business it also was to take a memorandum of the exact
position of the object as indicated by a dial placed in front of her
desk, and connected with the telescope.
John Herschel undertook the important task of re-observing the
various double stars and nebulae which had been discovered during
these memorable vigils.
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