The author has been sparing in the use of diagrams, because he believes that, in many cases, they have been over-pressed. There is a tendency to try to represent everything to the eye. This is well to a certain extent, but there is danger that by pursuing this method too far the power of mental comprehension will be weakened. After all, it is only by an intelligent use of the imagination that progress can be made in such a science as astronomy. The reader is urged to make a serious effort to understand what is said in the text, and to picture it in his mind's eye, before referring to the diagrams. After he has thus presented the subject to his imagination, he may refer to the illustrations, and correct with their aid any misapprehension. For this reason the cuts, with their descriptions, have been made independent of the regular text, although they are placed in their proper connections throughout the book. G. P. S. April, 1912. ------------------------------------------------------------------------ CONTENTS PART I—THE CELESTIAL SPHERE. PAGES Definition of Astronomy—Fundamental Law of the 3-64 Stars—Relations of the Earth to the Universe—Ordinary Appearance of the Sky—The Horizon, the Zenith, and the Meridian—Locating the Stars—Altitude and Azimuth—Circular or Angular Measure—Altitude Circles and Vertical Circles—The Apparent Motion of the Heavens—The North Star and Phenomena Connected with it—Revolution of the Stars round the Pole—Locating the Stars on the Celestial Sphere—Astronomical Equivalents of Latitude and Longitude—Parallels of Declination and Hour Circles—“The Greenwich of the Sky”—Effects Produced by Changing the Observer's Place on the Earth—The Parallel Sphere, the Right Sphere, and the Oblique Sphere—The Astronomical Clock—The Ecliptic—Apparent Annual Revolution of the Sun round the Earth—Inclination of the Ecliptic to the Equator: its Cause and its Effects—The Equinoxes—Importance of the Vernal Equinox—The Equinoctial Colure—The Solstices—Poles of the Ecliptic—Celestial Latitude and Longitude—The Zodiac—The Precession of the Equinoxes: its Cause and Effects—Revolution of the Celestial Poles—Past and Future Pole Stars PART II—THE EARTH. PAGES