xxx List of Illustrations 



FIG. PAOE 



33. Parallax 68 



34. Jupiter's epicycle and deferent 70 



35. Theequant 71 



36. The celestial spheres ... ... ... 89 



PORTRAIT OF COPPERNICUS ... ... ... To face p. 94 



37. Relative motion ... ... ... ... ... 102 



38. The relative motion of the sun and moon ... ... ... 103 



39. The daily rotation of the earth ... ... 104 



40. The solar system according to Coppernicus ... ... ... 107 



41. 42. Coppernican explanation of the seasons ... ... 108, 109 



43. The orbits of Venus and of the earth ... ... 113 



44. The synodic and sidereal periods of Venus ... ... ... 114 



45. The epicycle of Jupiter ... ... ... ... 116 



46. The relative sizes of the orbits of the earth and of a superior 



planet 117 



47. The stationary points of Mercury ... 119 



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 ... M 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 f dee 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. 2OO 



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 



