Other hypotheses, having the same end in view, are the meteoritic hypothesis of Lockyer and the planetesimal hypothesis that has been largely developed in the United States. These can best be read in the original papers to various journals, references to which may be found in the footnotes of Miss Clerke’s _History of Astronomy during the Nineteenth Century_. The same can be said of Bredichin’s hypothesis of comets’ tails, Arrhenius’s book on the applications of the theory of light repulsion, the speculations on radium, the origin of the sun’s heat and the age of the earth, the electron hypothesis of terrestrial magnetism, and a host of similar speculations, all combining to throw an interesting light on the evolution of a modern train of thought that seems to delight in conjecture, while rebelling against that strict mathematical logic which has crowned astronomy as the queen of the sciences. FOOTNOTES: [1] _R. S. Phil Trans_., 1810 and 1817-24. [2] One of the most valuable contributions to our knowledge of stellar parallaxes is the result of Gill’s work (_Cape Results_, vol. iii., part ii., 1900). [3] Taking the velocity of light at 186,000 miles a second, and the earth’s mean distance at 93,000,000 miles, 1 light-year=5,865,696,000,000 miles or 63,072 astronomical units; 1 astronomical unit a year=2.94 miles a second; and the earth’s orbital velocity=18.5 miles a second. [4] Ast. Nacht., 1889. [5] R. S. Phil. Trans., 1718. [6] Mem. Acad. des Sciences, 1738, p. 337. [7] R. S Phil. Trans., 1868. [8] _R.S. Phil Trans._, 1783. [9] See Kapteyn’s address to the Royal Institution, 1908. Also Gill’s presidential address to the British Association, 1907. [10] _Brit. Assoc. Rep._, 1905. [11] R. S. Phil. Trans., 1803, 1804. [12] Ibid, 1824. [13] Connaisance des Temps, 1830. [14] _R. A. S. Mem._, vol. xlvii., p. 178; _Ast. Nach._, No. 3,142; Catalogue published by Lick Observatory, 1901. [15] _R. A. S., M. N._, vol. vi. [16] _R. S. Phil. Trans._, vol. lxxiii., p. 484. [17] _Astr. Nach._, No. 2,947. [18] _R. S. E. Trans_., vol. xxvii. In 1901 Dr. Anderson discovered Nova Persei. [19] _Astr. Nach_., No. 3,079. [20] For a different explanation see Sir W. Huggins’s lecture, Royal Institution, May 13th, 1892. [21] For the early history of the proposals for photographic cataloguing of stars, see the _Cape Photographic Durchmusterung_, 3 vols. (_Ann. of the Cape Observatory_, vols. in., iv., and v., Introduction.) [22] _R. S. Phil. Trans._, 1850, p. 499 _et seq._ [23] _Ibid_, vol. cliv., p. 437. [24] _Brit. Assoc. Rep._, 1868, p. 165. ILLUSTRATIONS SIR ISAAC NEWTON (From the bust by Roubiliac In Trinity College, Cambridge.) CHALDÆAN BAKED BRICK OR TABLET Obverse and reverse sides, containing record of solar eclipse, 1062 B.C., used lately by Cowell for rendering the lunar theory more accurate than was possible by finest modern observations. (British Museum collection, No. 35908.)