. Nach._, No. 1,631.]

[Footnote 931: Cf. Leo Brenner, _Naturwiss. Wochenschrift_, January 13,
1895; _Jour. Brit. Astr. Ass._, 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. Ass._, 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. xxxix., 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. xxxviii., 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. Institution_, 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. xxxiv., p. 422.]

[Footnote 958: _Saemmtl. Werke_ (ed. 1839), Th. vi., pp. 5-12. See a