[Footnote 1631: A. A. Common, _Memoirs R. Astr. Soc._, vol. i., p. 118.]

[Footnote 1632: Newcomb, _Pop. Astr._, p. 137.]

[Footnote 1633: _Month. Not._, vol. liv., p. 67.]

[Footnote 1634: Keeler, _Publ. Astr. Pac. Soc._, vol. ii., p. 160.]

[Footnote 1635: H. Grubb, _Trans. Roy. Dub. Soc._, vol. i. (new ser.), p. 2.]

[Footnote 1636: Hale, nevertheless (_Astroph. Jour._, vol. v., p. 128), considers that refractors preserve their superiority of visual light-grasp over Newtonian reflectors up to an aperture of 52-1/2, while equalisation is reached for the photographic rays at 34 inches.]

[Footnote 1637: _Astroph. Jour._, vol. v., p. 130.]

[Footnote 1638: _Phil. Trans._, vol. cxlviii., p. 465.]

[Footnote 1639: _Optics_, p. 107 (2nd ed., 1719).]

[Footnote 1640: _Observatory_, vol. viii., p. 85.]

[Footnote 1641: Holden on Celestial Photography, _Overland Monthly_, Nov., 1886.]

[Footnote 1642: _Observatory_, vol. xv., p. 283.]

[Footnote 1643: Bailey, _Astroph. Jour._, vol. x., p. 255.]

[Footnote 1644: _Harvard Circulars_, Nos. 2, 18, 24, 33;]

[Footnote 1645: Loewy, _Bull. Astr._, t. i., p. 286; _Nature_, vol.

xxix., p. 36.]

[Footnote 1646: _Nature_, vol. xxiv., p. 389.]

[Footnote 1647: _Ibid._, vol. xxix., p. 470.]

[Footnote 1648: _Trans. R. Dublin Soc._, vol. iii., p. 61.]

[Footnote 1649: _Observatory_, vol. vii., p. 167.]

[Footnote 1650: Loewy, _Bull. Astr._, t. i., p. 265.]

[Footnote 1651: _Phil. Trans._, vol. clxxi., p. 653.]

[Footnote 1652: Janssen, _L'Astronomie_, t. ii., p. 121.]

[Footnote 1653: Rev. A. L. Cortie, _Astr. and Astrophysics_, vol. xi., p. 400.]

[Footnote 1654: _Phil. Mag._, vol. xiii., 1882, p. 469.]

[Footnote 1655: _Bull. Astr._, t. iii., p. 331.]

APPENDIX

TABLE I

CHRONOLOGY, 1774-1893

1774, March 4 Herschel's first observation. Subject, the Orion Nebula.

1774 Sun-spots geometrically proved to be depressions by Wilson.

1774 First experimental determination of the earth's mean density by Maskelyne.

1781, March 13 Discovery of Ura.n.u.s.

1782 Herschel's first Catalogue of Double Stars.

1783 Herschel's first investigation of the sun's movement in s.p.a.ce.

1783 Goodricke's discovery of Algol's law of variation.

1784 a.n.a.logy between Mars and the Earth pointed out by Herschel.

1784 Construction of the Heavens investigated by Herschel's method of star-gauging. "Cloven-disc" plan of the Milky Way.

1784 Discovery of binary stars antic.i.p.ated by Mich.e.l.l.

1786 Herschel's first Catalogue of Nebulae.

1787, Jan. 11 Discovery by Herschel of two Uranian moons (Oberon and t.i.tania).

1787, Nov. 19 Acceleration of the moon explained by Laplace.

1789 Herschel's second Catalogue of Nebulae, and cla.s.sification by age of these objects.

1789 Completion of Herschel's forty-foot reflector.

1789, Aug. 28 His discovery with it of the two inner Saturnian and Sept. 17 satellites.

1789 Repeating-circle invented by Borda.

1789 Five-foot circle constructed by Ramsden for Piazzi.

1790 Maskelyne's Catalogue of thirty-six fundamental stars.

1791 Herschel propounds the hypothesis of a fluid const.i.tution for nebulae.

1792 Atmospheric refraction in Venus announced by Schroter.

1794 Rotation-period of Saturn fixed by Herschel at 10h. 16m.

1795 Herschel's theory of the solar const.i.tution.

1796 Herschel's first measures of comparative stellar brightness.

1796 Laplace's Nebular Hypothesis published in _Exposition du Systeme du Monde_.

1797 Publication of Olbers's method of computing cometary orbits.

1798 Retrograde motions of Uranian satellites detected by Herschel.

1799 Publication of first two volumes of _Mecanique Celeste_.

1799, May 7 Transit of Mercury observed by Schroter.

1799, Nov. 12 Star-shower observed by Humboldt at c.u.mana.

1800 _Monatliche Correspondenz_ started by Von Zach.

1800 Invisible heat-rays detected in the solar spectrum by Herschel.

1801, Jan. 1 Discovery of Ceres by Piazzi.

1801 Publication of Lalande's _Histoire Celeste_.

1801 Investigation by Herschel of solar emissive variability in connection with spot-development.

1802, March 28 Discovery of Pallas by Olbers.

1802 Herschel's third Catalogue of Nebulae.