Entered according to Act of Congress, in the year 1850,

BY CROCKER AND BREWSTER,

In the Clerk's Office of the District Court of Massachusetts.

PREFACE.

THE apology for the present treatise on Astronomy is based on the nature of the subject; it is one which requires to be presented to the student from more than one point of view. He should learn from the original observer, the profound generalizer, the investigator of cause and effect in detail; and to prepare him for such studies, he needs the book of one who knows from experience his requirements and his capacity.

As such a book, "The Elements of Astronomy, or the World as it is, and as it appears," is offered by a teacher to the teaching and studying public. Had the writer aimed only to excite an interest in the subject, it would have been shorter and more attractive; but it is intended, likewise, to exercise the student's memory, reason, and imagination. The details introduced for this purpose serve also to keep each truth before the mind some time; they present it in different lights, and secure its being perceived by each pupil fully and in all its bearings.

This book has gradually grown out of lessons given orally during many years of teaching. These were written out for the author's own use, not for publication. Originality was not sought for, and all explanations and illustrations which could be of service to the pupils were adopted. As time passed on, and no book appeared precisely suited to the wants of these pupils, or of High Schools in general, the author began to entertain the idea that these lessons might in some measure supply the want so extensively felt. In this hope such completeness has been given to the work as a very limited leisure would allow. It has been revised in manuscript by George P. Bond, Esq., of the Cambridge Observatory, to whom the author is also indebted for superintending its passage through the press.

Boston, 1850.