[Footnote 918: _Astr. Nach._, No. 263 (1834); _Pop. Vorl._, pp. 615-620 (1838).]

[Footnote 919: _Outlines of Astr._, par. 431.]

[Footnote 920: _Month. Not._, vol. xxv., p. 61.]

[Footnote 921: _Month. Not._, vol. xxv., p. 264.]

[Footnote 922: _Astroph. Jour._, vol. vi., p. 422.]

[Footnote 923: _Harvard Annals_, vol. x.x.xii., p. 81.]

[Footnote 924: _Astr. and Astrophysics_, vol. xi., p. 778.]

[Footnote 925: Neison, _The Moon_, p. 25.]

[Footnote 926: _Knowledge_, vol. xvii., p. 85.]

[Footnote 927: Neison, _The Moon_, p. 104.]

[Footnote 928: The combination of a uniform rotational with an unequal orbital movement causes a slight swaying of the moon's globe, now east, now west, by which we are able to see round the edges of the averted hemisphere. There is also a "parallactic" libration, depending on the earth's rotation; and a species of nodding movement--the "libration in lat.i.tude"--is produced by the inclination of the moon's axis to her orbit, and by her changes of position with regard to the terrestrial equator. Altogether, about 2/11 of the _invisible_ side come into view.]

[Footnote 929: _Cel. Objects_, p. 58 (4th ed.).]

[Footnote 930: _Astr. Nach._, No. 1,631.]

[Footnote 931: Cf. Leo Brenner, _Naturwiss. Wochenschrift_, January 13, 1895; _Jour. Brit. Astr. a.s.s._, vol. v., pp. 29, 222.]

[Footnote 932: Respighi, _Les Mondes_, t. xiv., p. 294; Huggins, _Month.

Not._, vol. xxvii., p. 298.]

[Footnote 933: Birt, _Ibid._, p. 95.]

[Footnote 934: _Report Brit. a.s.s._, 1872, p. 245.]

[Footnote 935: _Observatory_, vol. xv., p. 250.]

[Footnote 936: _Astr. Reg._, vol. xvi., p. 265; _Astr. Nach._, No.

2,275.]

[Footnote 937: Lindsay and Copeland, _Month. Not._, vol. x.x.xix., p.

195.]

[Footnote 938: _Observatory_, vols. ii., p. 296; iv., p. 373. N. E.

Green (_Astr. Reg._, vol. xvii., p. 144) concluded the object a mere "spot of colour," dark under oblique light.]

[Footnote 939: Webb, _Cel. Objects_, p. 101.]

[Footnote 940: _Publ. Lick Observatory_, vol. iii., p. 7.]

[Footnote 941: _Ibid._, p. 21; Mee, _Knowledge_, vol. xviii., p. 135.]

[Footnote 942: _Comptes Rendus_, t. cxxii., p. 967; _Bull. Astr._, August, 1899; _Ann. Bureau des Long._, 1898; _Nature_, vols. lii., p.

439; lvi., p. 280; lix., p. 304; lx., p. 491; _Astroph. Jour._ vol. vi., p. 51.]

[Footnote 943: _Comptes Rendus_, t. xxii., p. 541.]

[Footnote 944: _Phil. Trans._, vol. cxlviii., p. 502.]

[Footnote 945: _Proc. Roy. Soc._, vol. xvii., p. 443.]

[Footnote 946: _Phil. Trans._, vol. clxiii., p. 623.]

[Footnote 947: _Trans. R. Dublin Soc._, vol. iii., p. 321.]

[Footnote 948: _Science_, vol. vii., p. 9.]

[Footnote 949: _Amer. Jour. of Science_, vol. x.x.xviii., p. 428.]

[Footnote 950: "The Temperature of the Moon," _Memoirs National Acad. of Sciences_, vol. iv., p. 193, 1889.]

[Footnote 951: _Temperature of the Moon_, p. iii.; see also App. ii., p.

206.]

[Footnote 952: _Trans. R. Dublin Soc._, vol. iv., p. 481, 1891; Rosse, _Proc. Roy. Inst.i.tution_, May 31, 1895.]

[Footnote 953: _Astroph. Jour._, vol. viii., pp. 199, 265.]

[Footnote 954: Airy, _Observatory_, vol. iii., p. 420.]

[Footnote 955: _Phil. Trans._, vol. cxliii., p. 397; _Proc. Roy. Soc._, vol. vi., p. 321.]

[Footnote 956: _Comptes Rendus_, t. lxi., p. 1023.]

[Footnote 957: Professor Darwin calculated that the heat generated by tidal friction in the course of lengthening the earth's period of rotation from 23 to 24 hours, equalled 23 million times the amount of its present annual loss by cooling. _Nature_, vol. x.x.xiv., p. 422.]

[Footnote 958: _Sammtl. Werke_ (ed. 1839), Th. vi., pp. 5-12. See also C. J. Monro's useful indications in _Nature_, vol. vii., p. 241.]

[Footnote 959: _Dynamik des Himmels_, p. 40.]

[Footnote 960: Gould's _Astr. Jour._, vol. iii., p. 138.]

[Footnote 961: _Wash. Obs._ for 1875, vol. xxii., App. ii.]

[Footnote 962: _Comptes Rendus_, t. cxiii., p. 669; _Annuaire_, Paris, 1892.]

[Footnote 963: Newcomb, _Pop. Astr._ (4th ed.), p. 101.]

[Footnote 964: Sir W. Thomson, _Report Brit. a.s.s._, 1876, p. 12.]