I. THE CELESTIAL SPHERE 3

II. THE SOLAR SYSTEM 41

I. THEORY OF THE SOLAR SYSTEM 41

The Ptolemaic System 41

The Copernican System 44

Tycho Brahe's System 44

Kepler's System 44

The Newtonian System 48

II. THE SUN AND PLANETS 53

I. The Earth 53

Form and Size 53

Day and Night 57

The Seasons 64

Tides 68

The Day and Time 74

The Year 78

Weight of the Earth and Precession 83

II. The Moon 86

Distance, Size, and Motions 86

The Atmosphere of the Moon 109

The Surface of the Moon 114

III. Inferior and Superior Planets 130

Inferior Planets 130

Superior Planets 134

IV. The Sun 140

I. Magnitude and Distance of the Sun 140

II. Physical and Chemical Condition of the Sun 149

Physical Condition of the Sun 149

The Spectroscope 152

Spectra 158

Chemical Constitution of the Sun 164

Motion at the Surface of the Sun 168

III. The Photosphere and Sun-Spots 175

The Photosphere 175

Sun-Spots 179

IV. The Chromosphere and Prominences 196

V. The Corona 204

V. Eclipses 210

VI. The Three Groups of Planets 221

I. General Characteristics of the Groups 221

II. The Inner Group of Planets 225

Mercury 225

Venus 230

Mars 235

III. The Asteroids 241

IV. Outer Group of Planets 244

Jupiter 244

The Satellites of Jupiter 250

Saturn 255

The Planet and his Moons 255

The Rings of Saturn 261

Uranus 269

Neptune 271

VII. Comets and Meteors 274

I. Comets 274

General Phenomena of Comets 274

Motion and Origin of Comets 281

Remarkable Comets 290

Connection between Meteors and Comets, 300

Physical and Chemical Constitution of Comets 314

II. The Zodiacal Light 318

III. THE STELLAR UNIVERSE 322

I. General Aspect of the Heavens 322

II. The Stars 330

The Constellations 330

Clusters 350

Double and Multiple Stars 355

New and Variable Stars 358

Distance of the Stars 364

Proper Motion of the Stars 365

Chemical and Physical Constitution of the Stars 371

III. NebulÆ 373

Classification of NebulÆ 373

Irregular NebulÆ 376

Spiral NebulÆ 384

The Nebular Hypothesis 391

IV. The Structure of the Stellar Universe 396