note_.]

[Footnote 296: _Astr. Jahrbuch_, 1828, p. 151.]

[Footnote 297: Maedler, _Gesch. d. Astr._, Bd. ii., p. 412.]

[Footnote 298: _Recueil de l'Ac. Imp. de St. Petersbourg_, 1835, p.
143.]

[Footnote 299: Guillemin's _World of Comets_, trans, by J. Glaisher, p.
294, _note_.]

[Footnote 300: _Month. Not._, vol. viii., p. 9.]

[Footnote 301: A real, though only partial stoppage of light seems
indicated by Herschel's observations on the comet of 1807. Stars seen
through the tail, October 18, lost much of their lustre. One near the
head was only faintly visible by glimpses. _Phil. Trans._, vol. xcvii.,
p. 153.]

[Footnote 302: Arago, _Annuaire_, 1832, p. 205.]

[Footnote 303: _Ibid._, 1891, p. 290.]

[Footnote 304: Viz., Encke's, Biela's, Faye's, and Brorsen's.]

CHAPTER VI

_INSTRUMENTAL ADVANCES_

It is impossible to follow with intelligent interest the course of
astronomical discovery without feeling some curiosity as to the means by
which such surpassing results have been secured. Indeed, the bare
acquaintance with _what_ has been achieved, without any corresponding
knowledge of _how_ it has been achieved, supplies food for barren wonder
rather than for fruitful and profitable thought. Ideas advance most
readily along the solid ground of practical reality, and often find true
sublimity while laying aside empty marvels. Progress is the result, not
so much of sudden flights of genius, as of sustained, patient, often
commonplace endeavour; and the true lesson of scientific history lies in
the close connection which it discloses between the most brilliant
developments of knowledge and the faithful accomplishment of his daily
task by each individual thinker and worker.

It would be easy to fill a volume with the detailed account of the long
succession of optical and mechanical improvements by means of which the
observation of the heavens has been brought to its present degree of
perfection; but we must here content ourselves with a summary sketch of
the chief amongst them. The first place in our consideration is
naturally claimed by the telescope.

This marvellous instrument, we need hardly remind our readers, is of two
distinct kinds--that in which light is gathered together into a focus by
_refraction_, and that in which the same end is attained by
_reflection_. The image formed is in each case viewed through a
magnifying lens, or combi