II. DANTE’S STUDIES. Dante a representative of contemporary beliefs: his erudition; his education; Brunetto Latini’s influence; possible visits to universities of Bologna, Padua, Paris. 223 III. BOOKS ON ASTRONOMY USED BY DANTE. Dante’s wide reading; his diligence and memory. Ptolemy his supreme authority on astronomy; his principal text-books Alfraganus and Aristotle; versions used. Classical Latin authors; Greek; Arab; Christian 231 IV. ASTRONOMY IN DANTE’S WRITINGS. References to heavenly bodies in Vita Nuova, the Canzoniere, Convivio, Latin works and letters, Divine Comedy. Artistic use of the facts and theories of astronomy. 253 V. OBSERVATIONAL ASTRONOMY 1. Movements of the Moon 261 2. Movements of the Sun 270 3. The Stars 283 4. The Galaxy 303 5. The Planets 307 6. Eclipses 316 7. Comets and Meteors 318 8. The Sun’s Path in the Sky seen from different Parts of the Earth 322 9. Celestial Phenomena and Time 338 VI. DANTE’S JOURNEY THROUGH THE THREE REALMS: INDICATIONS OF TIME AND DIRECTION BY MEANS OF THE SKIES 1. Time references in the Divine Comedy 353 2. The Inferno 367 3. Purgatory 373 4. Paradise 391 5. Positions of Sun, Moon, and Planets among the Stars during Dante’s Vision 402 6. The Assumed Date of the Vision 409 VII. THEORETICAL AND SPECULATIVE ASTRONOMY 1. The Spheres 429 2. The Spheres and the four Elements 441 3. Dimensions and Physical Nature of the Universe 457 4. Influence of the Spheres on Human Affairs 471 5. The Motive Power 480 VIII. MEDIÆVAL AND MODERN VIEWS OF THE UNIVERSE 487 ILLUSTRATIONS.