[Footnote 1440: Pickering, _Am. Jour. of Sc._, vol. x.x.xix., 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 ma.s.ses 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. x.x.xix., 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., p. 125.]

[Footnote 1460: Myers, _Astroph. Jour._, vol. vii., p. 1; A. W. Roberts, _Ibid._, vol. xiii., p. 181.]

[Footnote 1461: _Proc. R. Irish Ac._, July, 1884.]

[Footnote 1462: _Ibid._, vol. i., p. 97.]

[Footnote 1463: _Astr. Jour._, Nos. 179, 180.]

[Footnote 1464: _Ibid._, Nos. 300, 379.]

[Footnote 1465: _Astr. Jour._, Nos. 491-2.]

[Footnote 1466: _System of the Stars_, p. 125.]

[Footnote 1467: _Proc. Roy. Soc._, vol. xv., p. 146.]

[Footnote 1468: Weiss, _Astr. Nach._, No. 1,590; Espin, _Ibid._, No.

3,200.]

[Footnote 1469: _Comptes Rendus_, t. lx.x.xiii., p. 1172.]

[Footnote 1470: _Monatsb._, Berlin, 1877, pp. 241, 826.]

[Footnote 1471: _Copernicus_, vol. ii., p. 101.]

[Footnote 1472: Burnham, _Month. Not._, vol. lii., p. 457.]

[Footnote 1473: _Astr. Nach._, No. 2,682.]

[Footnote 1474: A. Hall, _Am. Jour. of Sc._, vol. x.x.xi., p. 301.]

[Footnote 1475: Young, _Sid. Messenger_, vol. iv., p. 282; Ha.s.selberg, _Astr. Nach._, No. 2,690.]

[Footnote 1476: _Report Brit. a.s.soc._, 1885, p. 935.]

[Footnote 1477: _Month. Not._, vol. xlvii., p. 54.]

[Footnote 1478: _Nature_, vol. x.x.xii., p. 522.]

[Footnote 1479: _Astr. Nach._, Nos. 1,267, 2,715.]

[Footnote 1480: _Month. Not._, vol. xxi., p. 32.]

[Footnote 1481: _Observatory_, vol. viii., p. 335.]

[Footnote 1482: _Astr. Nach._, No. 3,118; _Astr. and Astroph._, vol.

xi., p. 907.]

[Footnote 1483: _Cape Results_, p. 137.]

[Footnote 1484: _Trans. R. Soc. of Edinburgh_, vol. xxvii., p. 51; _Astr. and Astroph._, August, 1892, p. 593.]

[Footnote 1485: Vogel, _Astr. Nach._, No. 3,079.]

[Footnote 1486: _Observatory_, vol. xv., p. 287; Seeliger, _Astr.