1. There is a very complete paper on “How to find Easter,” by Dr. Downing, in the Journal of the British Astronomical Association, vol. ii., p. 264.
2. The application of Kepler’s third law gives us P = a³⁄₂ years, but as this is not strictly true, both P and a must be given where the greatest possible accuracy is desired.
3. The diagram is based upon one given by Prof. Albrech in the Astronomische Nachrichten, No. 3333. The dotted part of the curve could not be directly derived on account of insufficient observations.
4. The focal length of a lens is the distance from its centre at which an image of a very distant object, such as the sun, is formed.
5. In a British inch there are 25·4 millimetres.
6. Proctor: “Old and New Astronomy,” p. 327.
7. Langley: “The New Astronomy,” p. 108.
8. The “bolometer,” invented by Langley, measures heat with exquisite refinement by means of its electrical effects.
9. W. E. Wilson: Monthly Notices, vol. lv., p. 457.
10. Observatory, vol. xviii., p. 344.
11. Frost-Scheiner: “Astronomical Spectroscopy,” p. 177.
12. Astronomische Nachrichten, No. 3330.
13. Knowledge, vol. vi., p. 13.
14. “The Sun,” p. 206, first edition.
15. “Memoirs of the Royal Astronomical Society,” vol. xli., p. 435.
16. Astronomy and Astro-Physics, vol. xiii., p. 122.
17. Comptes Rendus, December 26, 1893.
18. Knowledge, vol. iv., p. 105.
19. “Rapport de la Mission envoyée an Sénégal,” p. 31.
20. “Harvard Annals,” vol. xix., part ii.; 1893.
21. “The Solar Corona discussed by Spherical Harmonics;” Washington, 1889.
22. Bulletin Astronomique, April, 1896.
23. According to G. Müller, Potsdam Publicationen, No. 30, p. 369, Zöllner fixed the albedo of Mercury at 0·13.
24. Astr. Nach., No. 3171.
25. Astr. Nach., No. 3406.
26. Ibid., No. 2944.
27. Astr. Nach., No. 3332.
28. This was in principle suggested by Proctor in “The Old and New Astronomy.”
29. Nature, vol. li., p. 227.
30. Kelvin, Nature, p. 440; Clarence King, American Journal of Science, January, 1893.
31. Ciel et Terre, 16th March, 1895.
32. Himmel und Erde, Feb., 1889; Astr. Nach., No. 3347; A. Battandier, L’Astronomie, 1894.
33. Balfour Stewart: “Ency. Brit.,” vol. xvi. pp. 164, 165.
34. A. Paulsen: Ciel et Terre, 1 Juillet, 1895, p. 202.
35. Elger: “The Moon,” p. 73.
36. “Publications, Astronomical Society of the Pacific,” vol. vii., p. 144.
37. “Harvard Annals,” vol. xxxii., part i., p. 109.
38. Astronomy and Astro-Physics, Nov., 1894, p. 718.
39. “Popular Astronomy,” 1895, p. 347.
40. Astr. Nach., No. 3271 (Schiaparelli).
41. “Popular Astronomy,” vol. i., p. 348.
42. Scientific American, Feb. 29, 1896.
43. Schiaparelli: Astronomy and Astro-Physics, Nov., 1894, p. 720.
44. Astronomy and Astro-Physics, August, 1894, p. 554.
45. “Publ. Astro. Soc. of the Pacific,” vol. iv., p. 196.
46. Monthly Notices, vol. lvi., p. 166.
47. Campbell: “Publ. A. S. P.,” vol. vi., p. 273.
48. Ibid., vol. ii., p. 248.
49. Ibid., vol. vi., p. 110.
50. Astronomy and Astro-Physics, October, 1894, p. 640.
51. Potsdam Publicationen, No. 30, 1893.
52. Barnard: Monthly Notices, vol. lvi., p. 55.
53. John Hopkins’ University Circular, Jan., 1895.
54. Astr. Nach., No. 3359.
55. Monthly Notices, vol. lvi., p. 250.
56. Barnard: Astr. Journal, No. 325, 1894.
57. “Publ. A. S. P.,” vol. ii., p. 286.
58. Maunder: Knowledge, vol. xix., p. 5.
59. Monthly Notices, vol. lvi., p. 143.
60. “Scientific Proceedings, R. Dublin Society,” vol. viii., p. 398.
61. Astro.-Phys. Journal, May, 1896, p. 394; “Rapport de l’Observatoire de Paris,” 1895, p. 22.
62. Proctor: “Old and New Astronomy,” p. 584.
63. “The subject of slant-markings,” Mr. Stanley Williams remarks (loc. cit.), “has only just begun to be investigated.”
64. “Jupiter and his System,” by Ellen M. Clerke, p. 43.
65. Comptes Rendus, t. cxix., p. 581.
66. G. H. Darwin: Harper’s Magazine, June, 1889.
67. Barnard, Monthly Notices, vol. lvi., p. 163.
68. Lewis: Observatory, vol. xviii., p. 379.
69. Monthly Notices, vol. lii., p. 419.
70. “Abhandlungen Akad. der Wissensch.” München, Bl. xvi., p. 403.
71. Astro-Physical Journal, May, June, 1895.
72. “Old and New Astronomy,” p. 640.
73. “Phil. Trans.,” vol. lxxxii., p. 17.
74. “Publications Astr. Soc. of the Pacific,” vol. iii., p. 284.
75. Astr. Journal, No. 370.
76. Perrotin: “Vierteljahrsschrift Astr. Ges.,” Jahrg. xxiv., p. 267.
77. “Annales de l’Observatoire de Nice,” t. ii., 1887.
78. Keeler: Astr. Nach., No. 2927.
79. Gregory: Nature, vol. xl., p. 236.
80. “General Astronomy,” p. 372.
81. Astronomical Journal, No. 342.
82. Tisserand: Astronomy and Astro-Physics, vol. xiii., p. 291 (1894).
83. Comptes Rendus, t. cvii., p. 804.
84. Astronomical Journal, No. 186.
85. “General Astronomy,” p. 372.
86. “Observations at the Cape of Good Hope,” p. 396.
87. “Monat. Correspondenz,” Bd. xxv., pp. 3–22, 1812.
88. Fessenden: Astro-Physical Journal, vol. iii., p. 40.
89. Astr. Nach., No. 2837.
90. Guillemin: “The World of Comets,” p. 282.
91. Astr. Nach., No. 2437.
92. Knowledge, Feb., 1896, p. 41.
93. For an account of its spectral changes, see Campbell in Astr. and Astr.-Physics, vol. xi., p. 698.
94. Barnard, Knowledge, vol. viii., p. 229.
95. Denning: Astronomy and Astro-Physics, vol. xii., p. 371.
96. Astroph. Journal, Jan., 1896, p. 42.
97. Ranyard: Knowledge, vol. ix., p. 159.
98. “Publications Astr. Pac. Society,” vol. vii., p. 166.
99. Hussey: loc. cit., p. 171.
100. Holden: “Publ. Astr. Pac. Society,” vol. ii., p. 19. H. A. Newton: Ibid., vol. iii., p. 91.
101. “Report Bri. Ass.,” 1891, p. 805.
102. S. Meunier: “Encycl. Chimique,” t. ii., p. 461.
103. Young: “Gen. Astr.,” p. 435.
104. Cornish: Knowledge, vol. vi., p. 163.
105. Journal Brit. Astr. Ass., vol. vi., p. 432.
106. H. A. Newton: “Proc. Amer. Phil. Society,” vol. xxxii.
107. Quoted by Sir F. Palgrave: “Phil. Trans.,” vol. cxxx., p. 175.
108. Observatory, April, 1895.
109. Observatory, Jan., 1896.
110. It has been recently seen again in America.
111. Journal of the British Astronomical Association, March, 1891.
112. Nature, Feb. 13, 1896.
113. “Planetary and Stellar Studies,” p. 257.
114. See Chapter V.
115. Comptes Rendus, March 30, 1896.
116. Nature, April 30, 1896.
117. “Cape Observations,” p. 34.
118. Journal of the British Astronomical Association, vol. iv., No. 11, p. 21.
119. Journal of the British Astronomical Association, vol. vi., No. 6, p. 312.
120. Recent observations show that the total variation is 2·71 magnitudes—the largest variation known for an Algol star.
121. “Cosmos,” Bohn’s edition, vol. iii., p. 205.
122. It was, however, asserted by Herlicius that he had seen it on Sept. 27.
123. The spectrum, however, seems to have since become continuous.
124. Astronomical Journal, No. 100.
125. Journal of the British Astronomical Association, March, 1892.
126. Journal of the British Astronomical Association, February, 1895, vol. v. No. 4.
127. Ibid., April, 1895, p. 328.
128. Journal of the British Astronomical Association, February, 1892.
129. The Observatory, December, 1895.
130. “Planetary and Stellar Studies,” p. 188.
131. Nature, September 6, 1894.
132. Nature, June 4, 1896.
133. “Cosmos,” vol. iii., Bohn’s edition, p. 192.
134. Humboldt’s “Cosmos,” Bohn’s edition, vol. iv., pp. 327, 328.
135. Monthly Notices, Royal Astronomical Society, June, 1888.
136. “Old and New Astronomy,” p. 794.
137. Nature, June 4, 1896.
138. Nature, September, 1894.
139. Ibid., October 4, 1894.
140. “Outlines of Astronomy,” tenth edition, p. 657.
141. Nature, November, 21, 1895.
142. Nature, January 16, 1896.
143. Nature, August 9, 1888.
144. Humboldt’s “Cosmos,” Bohn’s edition, vol, iii., p. 143.
145. See Knowledge, June, 1895.
146. “The Universe and the Coming Transits,” p. 200.
147. Journal of the British Astronomical Association, May, 1895, p. 383.
148. Knowledge, May, 1896.
149. Knowledge, July, 1891.
150. Knowledge, January, 1894, p. 17.
151. Journal of the British Astronomical Association, April, 1895, p. 304.
152. The Italics are Herschel’s.
153. A full discussion of Struve’s views will be found in Chapter XVI. of “The Visible Universe,” by the present writer.
154. “The Meteoritic Theory,” pp. 380, 381.