XIII. Spectra of the Sun and of three Stars " " 47 D. The Milky Way, near Messier II. " " 462 XIV. The Great Nebula in Orion " " 466 XV. The Great Nebula in Andromeda " " 468 E. Nebulae in the Pleiades " " 472 F. o Centauri " " 474 XVI. Nebulae observed with Lord Rosse's Telescope " " 476 XVII. The Comet of 1882 " " 357 XVIII. Schiaparelli's Map of Mars " " 221 LIST OF ILLUSTRATIONS. FIG. PAGE 1. Principle of the Refracting Telescope 11 2. Dome of the South Equatorial at Dunsink Observatory, Co. Dublin 12 3. Section of the Dome of Dunsink Observatory 13 4. The Telescope at Yerkes Observatory, Chicago 15 5. Principle of Herschel's Reflecting Telescope 16 6. South Front of the Yerkes Observatory, Chicago 17 7. Lord Rosse's Telescope 18 8. Meridian Circle 20 9. The Great Bear 27 10. Comparative Sizes of the Earth and the Sun 30 11. The Sun, photographed September 22, 1870 33 12. Photograph of the Solar Surface 35 13. An ordinary Sun-spot 36 14. Scheiner's Observations on Sun-spots 38 15. Zones on the Sun's Surface in which Spots appear 39 16. Texture of the Sun and a small Spot 43 17. The Prism 45 18. Dispersion of Light by the Prism 46 19. Prominences seen in Total Eclipses 53 20. View of the Corona in a Total Eclipse 62 21. View of Corona during Eclipse of January 22, 1898 63 22. The Zodiacal Light in 1874 69 23. Comparative Sizes of the Earth and the Moon 73 24. The Moon's Path around the Sun 76 25. The Phases of the Moon 76 26. The Earth's Shadow and Penumbra 78 27. Key to Chart of the Moon (Plate VI.) 81 28. Lunar Volcano in Activity: Nasmyth's Theory 97 29. Lunar Volcano: Subsequent Feeble Activity 97 30. " " Formation of the Level Floor by Lava 98 31. Orbits of the Four Interior Planets 115