[Footnote 492: The Rev. A. Cortie (_Month. Not._, vol. lx., p. 538) detects the influence of a short subsidiary cycle, Dr. W. J. S. Lockyer that of a thirty-five year period (_Nature_, June 20, 1901). Professor Newcomb (_Astroph. Jour._, vol. xiii., p. 11) considers that solar activity oscillates uniformly in 11.13 years, with superposed periodic variations.] [Footnote 493: _Opere_, t. iii., p. 412.] [Footnote 494: _Mitth._, Nos. vii. and xviii.] [Footnote 495: _Observations at Redhill_, p. 248.] [Footnote 496: _Comptes Rendus_, t. xcv., p. 1249.] [Footnote 497: _Ibid._, t. xciii., p. 827; t. xcvi., p. 1418.] [Footnote 498: _Ibid._, t. c, p. 593.] [Footnote 499: Ellis, _Proc. Roy. Society_, vol. lxiii., p. 70.] [Footnote 500: Schultz, _Astr. Nach._, Nos. 2,817-18, 2,847-8; Wilsing, _Ibid._, No. 3,039; Bélopolsky, _Ibid._, No. 2,722.] [Footnote 501: _Report Brit. Ass._, 1892, p. 635.] [Footnote 502: A. W. Augur, _Astroph. Jour._, vol. xiii., p. 346.] [Footnote 503: _Report Brit. Ass._, 1862, p. 16 (pt. ii.).] [Footnote 504: _Mem. R. A. S._, vol. xxi., p. 161.] [Footnote 505: _Month. Not._, vol. xxiv., p. 162.] [Footnote 506: _Am. Jour. of Science_, vol. vii., 1874, p. 92.] [Footnote 507: Young, _The Sun_, p. 103.] [Footnote 508: _Ann. Bur. Long._, 1879, p. 679.] [Footnote 509: _Ibid._, 1878, p. 689.] [Footnote 510: _Himmelsphotographie_, p. 273.] [Footnote 511: Ranyard, _Knowledge_, vols. xiv., p. 14, xvi., p. 189; see also the accompanying photographs.] CHAPTER III _RECENT SOLAR ECLIPSES_ By observations made during a series of five remarkable eclipses, comprised within a period of eleven years, knowledge of the solar surroundings was advanced nearly to its present stage. Each of these events brought with it a fresh disclosure of a definite and unmistakable character. We will now briefly review this orderly sequence of discovery. Photography was first systematically applied to solve the problems presented by the eclipsed sun, July 18, 1860. It is true that a daguerreotype,[512] taken by Berkowski with the Königsberg heliometer during the eclipse of 1851, is still valuable as a record of the corona of that year; and some subsequent attempts were made to register partial phases of solar occultation, notably by Professor Bartlett at West Point in 1854;[513] but the ground remained practically unbroken until 1860.