372

XVIII. THE STARRY HEAVENS 409

XIX. THE DISTANT SUNS 425

XX. DOUBLE STARS 434

XXI. THE DISTANCES OF THE STARS 441

XXII. STAR CLUSTERS AND NEBULAE 461

XXIII. THE PHYSICAL NATURE OF THE STARS 477

XXIV. THE PRECESSION AND NUTATION OF THE EARTH'S AXIS 492

XXV. THE ABERRATION OF LIGHT 503

XXVI. THE ASTRONOMICAL SIGNIFICANCE OF HEAT 513

XXVII. THE TIDES 531

APPENDIX 558

LIST OF PLATES.

PLATE

I. The Planet Saturn _Frontispiece_

II. A Typical Sun-spot _To face page_ 9

A. The Sun " " 44

III. Spots and Faculae on the Sun " " 37

IV. Solar Prominences or Flames " " 57

V. The Solar Corona " " 62

VI. Chart of the Moon's Surface " " 81

B. Portion of the Moon " " 88

VII. The Lunar Crater Triesnecker " " 93

VIII. A Normal Lunar Crater " " 97

IX. The Lunar Crater Plato " " 102

X. The Lunar Crater Tycho " " 106

XI. The Planet Jupiter " " 254

XII. Coggia's Comet " " 340

C. Comet A., 1892, 1 Swift " " 358

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