ootnote 1433: _Harvard Annals_, vol. xxvii.]

[Footnote 1434: _Harvard Annals_, vol. xxviii., parts i. and ii.]

[Footnote 1435: See _ante_, p. 201.]

[Footnote 1436: _Phil. Trans._, vol. clviii., p. 529.]

[Footnote 1437: Schellen, _Die Spectralanalyse_, Bd. ii., p. 326 (ed.
1883).]

[Footnote 1438: _Proc. Roy. Soc._, vol. xx., p. 386.]

[Footnote 1439: _System of the Stars_, p. 199.]

[Footnote 1440: Pickering, _Am. Jour. of Sc._, vol. xxxix., p. 46;
Vogel, _Astr. Nach._ No. 3,017.]

[Footnote 1441: _Sitzungsberichte_, Berlin, May 2, 1901; _Astroph.
Jour._, vol. xiii., p. 324.]

[Footnote 1442: The "relative orbit" of a double star is that described
by one round the other as a fixed point. Micrometrical measures are
always thus executed. But in reality both stars move in opposite
directions, and at rates inversely as their masses round their common
centre of gravity.]

[Footnote 1443: Vogel, _Astr. Nach._, Nos. 3,017, 3,039.]

[Footnote 1444: Huggins, _Pres. Address_, 1891; Cornu, _Sur la Methode
Doppler-Fizeau_ p. D. 38.]

[Footnote 1445: _Sitzungsb._, Berlin, 1890, p. 401; _Astr. Nach._, No.
2,995.]

[Footnote 1446: _Ibid._]

[Footnote 1447: _Astroph. Jour._, vol. v., p. 1; Newall, _Month. Not._,
vol. lvii., p. 575.]

[Footnote 1448: _Bull. de l'Acad. de St. Petersb._, tt. vi., viii.]

[Footnote 1449: _Astroph. Jour._, vol. x., p. 177; _Month. Not._, vol.
lx., p. 418; Vogel, _Sitzungsb._, Berlin, April 19, 1900.]

[Footnote 1450: _Month. Not._, vol. lx., p. 595.]

[Footnote 1451: Hussey, _Astr. Jour._, No. 484.]

[Footnote 1452: _Astroph. Jour._, vols. x, p. 180; xiv., p. 140; _Lick
Bulletin_, No. 4; Belopolsky, _Astr. Nach._, No. 3,637.]

[Footnote 1453: The significance of the name "El Ghoul" leaves little
doubt that the Arab astronomers took note of this star's variability. E.
M. Clerke, _Observatory_, vol. xv., p. 271.]

[Footnote 1454: _Phil. Trans._, vol. lxxiii., p. 484.]

[Footnote 1455: _Proc. Amer. Acad._, vol. xvi., p. 17; _Observatory_,
vol. iv., p. 116. For a preliminary essay by T. S. Aldis, see _Phil.
Mag._, vol. xxxix., p. 363, 1870.]

[Footnote 1456: _Astr. Nach._, No. 2,947.]

[Footnote 1457: _Astr. Jour._, Nos. 165-6, 255-6, 509. See also
_Knowledge_, vol. xv., p. 186.]

[Footnote 1458: Bauschinger, _V. J. S. Astr. Ges._, Jahrg. xxix.; but
_cf._ Searle, _Harvard Annals_, vol. xxix., p. 223; Boss, _Astr. Jour._,
No. 343.]

[Footnote 1459: _Comptes Rendus_, t. cxx.,