tag="{http://www.w3.org/1999/xhtml}a">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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LETTERS ON ASTRONOMY.

LETTER I.

INTRODUCTORY OBSERVATIONS.

To Mrs. C——M——.

Dear Madam,—In the conversation we recently held on the study of Astronomy, you expressed a strong desire to become better acquainted with this noble science, but said you had always been repelled by the air of severity which it exhibits, arrayed as it is in so many technical terms, and such abstruse mathematical processes: or, if you had taken up some smaller treatise, with the hope of avoiding these perplexities, you had always found it so meager and superficial, as to afford you very little satisfaction. You asked, if a work might not be prepared, which would convey to the general reader some clear and adequate knowledge of the great discoveries in astronomy, and yet require for its perusal no greater preparation, than may be presumed of every well-educated English scholar of either sex.

You were pleased to add the request, that I would write such a work,—a work which should combine, with a luminous exposition of the leading truths of the science, some account of the interesting historical facts with which it is said the records of astronomical discovery abound. Having, moreover, heard much of the grand discoveries which, within the last fifty years, have been made among the fixed stars, you expressed a strong desire to learn more respecting these sublime researches. Finally, you desired to see the argument for the existence and natural attributes of the Deity, as furnished by astronomy, more fully and clearly exhibited, than is done in any work which you have hitherto perused. In the preparation of the proposed treatise, you urged me to supply, either in the text or in notes, every elementary principle which would be essential to a perfect understanding of the work; for although, while at school, you had paid some attention to geometry and natural philosophy, yet so much time had since elapsed, that your memory required to be refreshed on the most simple principles of these elementary studies, and you preferred that I should consider you as altogether unacquainted with them.

Although, to satisfy a mind, so cultivated and inquisitive as yours, may require a greater variety of powers and attainments than I possess, yet, as you were pleased to urge me to the trial, I have resolved to make the attempt, and will see how far I may be able to lead you into the interior of this beautiful temple, without obliging you to force your way through the "jargon of the schools."

Astronomy, however, is a very difficult or a comparatively easy study, according to the view we take of it.