48. The stationary points of Jupiter 120 49. The alteration in a planet’s apparent position due to an alteration in the earth’s distance from the sun 122 50. Stellar parallax 124 51. Uraniborg 133 52. Tycho’s system of the world 137 PORTRAIT OF TYCHO BRAHE _To face p._ 139 53. One of Galilei’s drawings of the moon „ 150 54. Jupiter and its satellites as seen on January 7, 1610 152 55. Sun-spots _To face p._ 154 56. Galilei’s proof that sun-spots are not planets 156 57. The differential method of parallax 165 PORTRAIT OF GALILEI _To face p._ 171 58. The daily libration of the moon 173 PORTRAIT OF KEPLER _To face p._ 183 59. An ellipse 185 60. Kepler’s second law 186 61. Diagram used by Kepler to establish his laws of planetary motion 187 62. The “music of the spheres” according to Kepler 190 63. Kepler’s idea of gravity 196 64. Saturn’s ring, as drawn by Huygens _To face p._ 200 65. Saturn, with the ring seen edge-wise „ 200 66. The phases of Saturn’s ring 201 67. Early drawings of Saturn _To face p._ 202 68. Mars in opposition 206 69. The parallax of a planet 206 70. Motion in a circle 214 71. The moon as a projectile 220 72. The spheroidal form of the earth 234 73. An elongated ellipse and a parabola 238 PORTRAIT OF NEWTON _To face p._ 240 PORTRAIT OF BRADLEY „ 258 74, 75. The aberration of light 262, 263 76. The aberrational ellipse 264 77. Precession and nutation 268 78. The varying curvature of the earth 277 79. Tobias Mayer’s map of the moon _To face p._ 282 80. The path of Halley’s comet 294 81. A varying ellipse 303