[Footnote 244: Considerable uncertainty, however, still prevails on the point. The inverse relation a.s.sumed by Lagrange to exist between distance from the sun and density brought out the Mercurian ma.s.s 1/2025810 that of the sun (Laplace, _Exposition du Syst. du Monde_, t.

ii., p. 50, ed. 1824). Von Asten deduced from the movements of Encke's comet, 1818-48, a value of 1/7636440; while Backlund from its seven returns, 1871-1891, derived 1/9647000 (_Comptes Rendus_, Oct. 1, 1894).]

[Footnote 245: Arago, _Annuaire_ (1832), p. 218.]

[Footnote 246: Hind, _The Comets_, p. 20.]

[Footnote 247: _Phil. Trans._, vol. xlvi., p. 204.]

[Footnote 248: _Astr. Nach._, No. 2,134.]

[Footnote 249: _Comptes Rendus_, t. cvii., p. 588.]

[Footnote 250: _Mem. de St. Petersbourg_, t. x.x.xii., No. 3, 1884; _Astr.

Nach._, No. 2,727.]

[Footnote 251: _Month. Not._, vol. xix., p. 72.]

[Footnote 252: _Mecanique Celeste_, t. ii., p. 197.]

[Footnote 253: See Berberich, _Astr. Nach._, Nos. 2,836-7, 3,125; Deichmuller, _Ibid._, No. 3,123.]

[Footnote 254: _Month. Not._, vol. ii., p. 117.]

[Footnote 255: _Astr. Nach._, No. 128.]

[Footnote 256: _Annuaire_, 1832, p. 186.]

[Footnote 257: _Am. Journ. of Science_, vol. i. (2nd series), p. 293.

Prof. Hubbard's calculations indicated a probability that the definitive separation of the two nuclei occurred as early as September 30, 1884.

_Astronomical Journal_ (Gould's), vol. iv., p. 5. See also, on the subject of this comet, W. T. Lynn, _Intellectual Observer_, vol. xi., p.

208; E. Ledger, _Observatory_, August, 1883, p. 244; and H. A. Newton, _Am. Journ. of Science_, vol. x.x.xi., p. 81, February, 1886.]

[Footnote 258: _Month. Not._, vol. vii., p. 73.]

[Footnote 259: _Bulletin Ac. Imp. de St. Petersbourg_, t. vi., col. 77.

The latest observation of the parent nucleus was that of Argelander, April 27, at Bonn.]

[Footnote 260: D'Arrest, _Astr. Nach._, No. 1,624.]

[Footnote 261: _Der Brorsen'sche Comet._ Von Dr. E. Lamp, Kiel, 1892; Plummer, _Knowledge_, vol. xix., p. 41.]

[Footnote 262: Schulhof, _Astr. Nach._, No. 3,267; _Observatory_, vol.

xviii., p. 64; F. H. Seares, _Astr. Nach._, Nos. 3,606-7; Plummer, _Knowledge_, vol. xix., p. 156.]

[Footnote 263: _Comptes Rendus_, t. xxv., p. 570.]

[Footnote 264: _Month. Not._, vol. xii., p. 248.]

[Footnote 265: _Bull. Astr._, t. vi., pp. 241, 289.]

[Footnote 266: _etude sur la Theorie des Cometes periodiques. Annales de l'Observatoire_, t. xx., Paris, 1891.]

[Footnote 267: _Amer. Journ. of Science_, vol. xlii., pp. 183, 482, 1891.]

[Footnote 268: _Observatory_, vol. xiv., p. 194.]

[Footnote 269: _Phil. Trans._, vol. cii., pp. 118-124.]

[Footnote 270: _Ueber den Schweif des grossen Cometen von 1811, Monat.

Corr._, vol. xxv., pp. 3-22. Reprinted by Zollner. _Ueber die Natur der Cometen_, pp. 3-15.]

[Footnote 271: _Natur der Cometen_, p. 148.]

[Footnote 272: The subject of a cla.s.sical memoir by Bessel, published in 1810.]

[Footnote 273: A fresh investigation of its...o...b..t has been published by N. Herz of Vienna. See _Bull. Astr._, t. ix., p. 427.]

[Footnote 274: _Astr. Jahrbuch_ (Bode's), 1823, p. 134.]

[Footnote 275: Reproduced in Webb's _Celestial Objects_, 4th ed.]

[Footnote 276: _Month. Not._, vol. x.x.xvi., p. 309.]

[Footnote 277: _Celestial Objects_, p. 40, note.]

[Footnote 278: See Airy's Address, _Mem. R. A. S._, vol. x., p. 376.

Rosenberger calculated no more, though he lived until 1890. W. T. Lynn, _Observatory_, vol. xiii., p. 125.]

[Footnote 279: Hind, _The Comets_, p. 47.]

[Footnote 280: Arago, _Annuaire_, 1836, p. 228.]

[Footnote 281: _Astr. Nach._, No. 300.]

[Footnote 282: It deserves to be recorded that Robert Hooke drew a very similar inference from his observations of the comets of 1680 and 1682.

_Month. Not._, vol. xiv., pp. 77-83.]

[Footnote 283: _Briefwechsel zwischen Olbers und Bessel_, Bd. ii., p.

390.]

[Footnote 284: Herschel, _Results_, p. 405.]

[Footnote 285: _Mem. R. A. S._, vol. x., p. 92,]

[Footnote 286: _Results_, p. 401.]

[Footnote 287: Pontecoulant, _Comptes Rendus_, t. lviii., p. 825.]