  | Preface, | | 3 | | LETTER I. | | Introductory Observations, | | 9 | | LETTER II. | | Doctrine of the Sphere, | | 16 | | LETTER III. | | Astronomical Instruments.—Telescope, | | 29 | | LETTER IV | | Telescope continued, | | 36 | | LETTER V. | | Observatories, | | 42 | | LETTER VI. | | Time and the Calendar, | | 59 | | LETTER VII. | | Figure of the Earth, | | 69 | | LETTER VIII. | | Diurnal Revolution, | | 81 | | LETTER IX. | | Parallax and Refraction, | | 89 | | LETTER X. | | The Sun, | | 101 | | LETTER XI. | | Annual Revolution.—Seasons, | | 111 | | LETTER XII. | | Laws of Motion, | | 126 | | LETTER XIII. | | Terrestrial Gravity, | | 134 | | LETTER XIV. | | Sir Isaac Newton.—Universal Gravitation.—Figure | | of the Earth's Orbit.—Precession of the Equinoxes, | | 143 | | LETTER XV. | | The Moon, | | 157 | | LETTER XVI. | | The Moon.—Phases.—Harvest Moon.—Librations, | | 172 | | LETTER XVII. | | Moon's Orbit.—Her Irregularities, | | 180 | | LETTER XVIII. | | Eclipses, | | 195 | | LETTER XIX. | | Longitude.—Tides, | | 208 | | LETTER XX. | | Planets.—Mercury and Venus, | | 225 | | LETTER XXI. | | Superior Planets: Mars, Jupiter, Saturn, and Uranus, | | 243 | | LETTER XXII. | | Copernicus.—Galileo, | | 254 | | LETTER XXIII. | | Saturn.—Uranus.—Asteroids, | | 274 | | LETTER XXIV. | | The Planetary Motions.—Kepler's Laws.—Kepler, | | 291 | | LETTER XXV. | | Comets, | | 312 | | LETTER XXVI. | | Comets, | | 334 | | LETTER XXVII. | | Meteoric Showers, | | 346 | | LETTER XXVIII. | | Fixed Stars, | | 365 | | LETTER XXIX. | | Fixed Stars, | | 383 | | LETTER XXX. | | System of the World, | | 392 | | LETTER XXXI. | | Natural Theology, | | 406 | | LETTER XXXII. | | Recent Discoveries, | | 414 | | INDEX. | | 423 |
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