ASTRONOMY FOR STUDENTS AND GENERAL READERS BY SIMON NEWCOMB, LL.D., SUPERINTENDENT AMERICAN EPHEMERIS AND NAUTICAL ALMANAC, AND EDWARD S. HOLDEN, M.A., PROFESSOR IN THE U. S. NAVAL OBSERVATORY. SECOND EDITION, REVISED NEW YORK HENRY HOLT AND COMPANY 1880 KE 3172 VARD COLLEGE Copyright, 1879, BY HENRY HOLT & Co. THE JOHN A. GRAY PRESS, NEW YORK. PREFACE. THE following work is designed principally for the use of those who desire to pursue the study of Astronomy as a branch of liberal education. To facilitate its use by students of different grades, the subject-matter is divided into two classes, distinguished by the size of the type, and the volume is thus made to contain two courses. The portions in large type form a complete course for the use of those who desire only such a general knowledge of the subject as can be acquired without the application of advanced mathematics. It is believed that this course can be mastered by persons having at command only those geometrical ideas which are familiar to most intelligent students in our advanced schools; though sometimes, especially in the earlier chapters, a knowledge of elementary trigonometry and physics will be found conducive to a full understanding of a few details. The portions in small type comprise additions for the use of those students who either desire a more detailed and precise knowledge of the subject, or who intend to make astronomy a special study. In this, as in the elementary course, the rule has been never to use more advanced mathematical methods than are necessary to the development of the subject, but in some cases a knowledge of Analytic Geometry, in others of the Differential Calculus, and in others of Elementary Mechanics, is neces sarily presupposed. The object aimed at has been to lay a broad foundation for further study rather than to attempt the detailed presentation of any special branch. As some students, especially in seminaries, may not desire so extended a knowledge of the subject as that embraced in the course in large type, the following hints are added for their benefit: Chapter I., on the relation of the earth to the heavens, Chapter III., on the motion of the earth, and the chapter on Chronology should, so far as possible, be mastered by all. The remaining parts of the course may be left to the selection of the teacher or student. Most persons will desire to know something of the telescope (Chapter II.), of the arrangement of the solar system (Chapter IV., §§ 1-2, and Part II., Chapter II.), of eclipses, of the phases of the moon, of the physical constitution of the sun (Part II., Chapter II.), and of the constellations (Part III., Chapter I.). It is to be expected that all will be interested in the subjects of the planets, comets, and meteors, treated in Part II., the study of which involves no difficulty. An acknowledgment is due to the managers of the Clarendon Press, Oxford, who have allowed the use of a number of electrotypes from CHAMBERS's Descriptive Astronomy. Messrs. FAUTH & Co., instrument-makers, of Washington, have also lent electrotypes of instruments, and a few electrotypes have been kindly furnished by the editors of the American Journal of Science and of the Popular Science Monthly. The greater part of the illustrations have, however, been prepared expressly for the work. CONTENTS. PAGE THE RELATION OF THE EARTH TO THE HEAVENS. The Earth-The Diurnal Motion and the Celestial Sphere-Corre- spondence of the Terrestrial and Celestial Spheres - The Diurnal Motion in different Latitudes-Relation of Time to the Sphere-Determination of Terrestrial Longitudes-Mathe- matical Theory of the Celestial Sphere-Determination of The Refracting Telescope-Reflecting Telescopes-Chronometers and Clocks-The Transit Instrument-Graduated Circles- Ancient Ideas of the Planets-Annual Revolution of the Earth- |