only see Jupiter's first satellite at its greatest
elongation, 2' 15". He might, however, possibly have distinguished two
objects of _equal_ lustre at a lesser interval.]

[Footnote 216: J. W. L. Glaisher, _Observatory_, vol. xv., p. 177.]

[Footnote 217: _Mem. R. A. S._, vol. xvi., p. 399.]

[Footnote 218: For an account of D'Arrest's share in the detection see
_Copernicus_, vol. ii., pp. 63, 96.]

[Footnote 219: _Mem. R. A. S._, vol. xvi., p. 412.]

[Footnote 220: He had recorded the places of 3,150 stars (three of which
were different positions of the planet), and was preparing to map them,
when, October 1, news of the discovery arrived from Berlin. Prof.
Challis's _Report_, quoted in Obituary Notice, _Month. Not._, Feb.,
1883, p. 170.]

[Footnote 221: See Airy in _Mem. R. A. S._, vol. xvi., p. 411.]

[Footnote 222: He died January 21, 1892, in his 71st year.]

[Footnote 223: Ledger, _The Sun, its Planets and their Satellites_, p.
414.]

[Footnote 224: Presented by the Misses Lassell, after their father's
death, to the Greenwich Observatory.]

[Footnote 225: _Astr. Jour._, No. 508.]

[Footnote 226: _Report of U.S. Naval Observatory for 1900_, p. 15.]

[Footnote 227: Grant, _Hist. of Astr._, p. 271.]

[Footnote 228: _Month. Not._, vol. ix., p. 91.]

[Footnote 229: _Month. Not._, vol. xi., p. 21.]

[Footnote 230: _Astr. Nach._, No. 756 (May 2, 1851).]

[Footnote 231: _Phil. Trans._, vol. i., p. 246. See H. T. Vivian, _Engl.
Mech._, April 20, 1894.]

[Footnote 232: Secchi, _Month. Not._, vol. xiii., p. 248.]

[Footnote 233: Hind, _ibid._, vol. xv., p. 32.]

[Footnote 234: Lynn, _Observatory_, Oct. 1, 1883; Hadley, _Phil.
Trans._, vol. xxxii., p. 385.]

[Footnote 235: Proctor, _Saturn and its System_, p. 64.]

[Footnote 236: _Phil. Trans._, vol. lxxvii., p. 125.]

[Footnote 237: _Month. Not._, vol. xi., p. 248.]

[Footnote 238: _Ibid._, vol. xxxv., pp. 16-22.]

[Footnote 239: _Ibid._, p. 26.]

[Footnote 240: _Ibid._, vol. xli., p. 190.]

CHAPTER V

_COMETS_

Newton showed that the bodies known as "comets," or _hirsute_ stars,
obey the law of gravitation; but it was by no means certain that the
individual of the species observed by him in 1680 formed a permanent
member of the solar system. The velocity, in fact, of its rush round the
sun was quite possibly sufficient to carry it off for ever into the
depths of space,