[Footnote 869: _Mem. Roy. Astr. Soc._, vol. xlvii., pp. 77, 84.]

[Footnote 870: _Astr. Reg._, vol. xiii., p. 132.]

[Footnote 871: _L'Astronomie_, t. ii., p. 27; _Astr. Nach._, No. 2,021; _Am. Jour. of Sc._, vol. xxv., p. 430.]

[Footnote 872: _Mem. Spettr. Ital._, Dicembre, 1882; _Am. Jour. of Sc._, vol. xxv., p. 328.]

[Footnote 873: _Comptes Rendus_, t. cxvi., p. 288.]

[Footnote 874: Vogel, _Spectra der Planeten_, p. 15.]

[Footnote 875: _Nature_, vol. xix., p. 23.]

[Footnote 876: _Nova Acta Acad. Naturae Curiosorum_, Bd. x., 239.]

[Footnote 877: _Astr. Jahrbuch_, 1809, p. 164.]

[Footnote 878: _Month Not._, vol. xliii., p. 331.]

[Footnote 879: _Report Brit. a.s.s._, 1873, p. 407. The paper contains a valuable record of observations of the phenomenon.]

[Footnote 880: _Photom. Untersuchungen_, p. 301.]

[Footnote 881: _Bothkamp Beobachtungen_, Heft ii., p. 126.]

[Footnote 882: _Astr. Nach._, No. 2,818.]

[Footnote 883: _Memoires de l'Acad. de Bruxelles_, t. xlix., No. 5, 4to; _Astr. Nach._, No. 2,809; _f._ Schorr, _Der Venusmond_, 1875.]

[Footnote 884: _Phil. Trans._, 1839, 1841, 1842.]

[Footnote 885: Delaunay objected (_Comptes Rendus_, t. lxvii., p. 65) that the viscosity of the contained liquid (of which Hopkins took no account) would, where the movements were so excessively slow as those of the earth's axis, almost certainly cause it to behave like a solid. Lord Kelvin, however (_Report Brit. a.s.s._, 1876, ii., p. 1), considered Hopkins's argument valid as regards the comparatively quick solar semi-annual and lunar fortnightly nutations.]

[Footnote 886: _Phil. Trans._, cliii., p. 573.]

[Footnote 887: _Report Brit. a.s.s._, 1868, p. 494.]

[Footnote 888: _Ibid._, 1882, p. 474.]

[Footnote 889: Albrecht, _Astr. Nach._, No. 3,131.]

[Footnote 890: _Astr. Jour._, Nos. 248, 249.]

[Footnote 891: _Ibid._, No. 258.]

[Footnote 892: _Month. Not._, vol. lii., p. 336.]

[Footnote 893: _Astr. Nach._, No. 3,097; _Phil. Trans._, vol. clx.x.xvi., A., p. 469; _Proc. Roy. Soc._, vol. lix.]

[Footnote 894: See Chandler's searching investigations, _Astr. Jour._, Nos. 329, 344, 351, 392, 402, 406, 412, 446, 489, 490, 494, 495.]

[Footnote 895: Rees, _Pop. Astr._, No. 74, 1900.]

[Footnote 896: _Nature_, vol. lxi., p. 447; see also A. V. Backlund, _Astr. Nach._, No. 3,787.]

[Footnote 897: _Trans. Geol. Soc._, vol. iii. (2d ser.), p. 293.]

[Footnote 898: See his _Treatise on Astronomy_, p. 199 (1833).]

[Footnote 899: _Phil. Mag._, vol. xxviii. (4th ser.), p. 121.]

[Footnote 900: _Climate and Time_, 1875; _Discussions on Climate and Cosmology_, 1885.]

[Footnote 901: See for a popular account of the theory, Sir R. Ball's _The Cause of an Ice Age_, 1892.]

[Footnote 902: See A. Woeikof, _Phil. Mag._, vol. xxi., p. 223.]

[Footnote 903: _The Ice Age in North America_, London, 1890.]

[Footnote 904: _Phil. Trans._, vol. lxviii., p. 783.]

[Footnote 905: _Comptes Rendus_, t. lxxvi., p. 954.]

[Footnote 906: _Potsdam Publ._, Nos. 22, 23.]

[Footnote 907: _Phil. Trans._, vol. clx.x.xii., p. 565; _Adams Prize Essay for 1893._]

[Footnote 908: _Denkschriften Akad. der Wiss. Wien_, Bd. lxiv.; quoted by Poynting. _Nature_, vol. lxii., p. 404.]

[Footnote 909: _Report on the Geodetic Survey of S. Africa_, 1894.]

[Footnote 910: _Nature_, vol. lxii., p. 622; Hollis, _Observatory_, vol.

xxiii., p. 337; Poincare, _Comptes Rendus_, July 23, 1900.]

[Footnote 911: _Astr. Nach._, No. 2,228.]

[Footnote 912: Young's _Gen. Astr._, p. 601.]

[Footnote 913: _Astr. Constants_, p. 195.]

[Footnote 914: The second volume was published at Gottingen in 1802.]

[Footnote 915: _Ueber Rillen auf dem Monde_, p. 13. _Cf. The Moon_, by T. Gwyn Elger, p. 20. W. H. Pickering, _Harvard Annals_, vol. x.x.xii., p.

249.]

[Footnote 916: _The Moon_, p. 73.]

[Footnote 917: _Selen. Fragm._, Th. ii., p. 399.]