The photographs here reproduced were made at the Yerkes Observatory, and the most grateful acknowledgments are tendered to Prof. Edwin B. Frost, its director, for generously consenting to their use for this purpose. He could only have been induced to do so by his desire to see the fruits of the admirable work accomplished by his associates enjoyed by an ever-widening circle. The series of photographs representing the moon on successive evenings were taken with the 12-inch telescope of the Yerkes Observatory by Mr. James Wallace, who employed a color filter that he constructed specially for this telescope, which possesses a visual and not a photographic objective. The larger scale photographs, representing certain selected regions on the moon, were taken by Mr. Ritchey, now of the Carnegie Solar Observatory at Mount Wilson, California, with the great 40-inch telescope of the Yerkes Observatory. It is unnecessary to speak of the extraordinary quality of these photographs, which have been admired by astronomers in all lands. It should, perhaps, be added that while the director of the Yerkes Observatory has shown confidence in the author by intrusting to him the use of these photographs, yet, neither Professor Frost, nor Messrs. Wallace and Ritchey are in any way responsible for the statements made in this book. The author has taken pains to be accurate, but if any errors of fact or opinion have crept in, he alone must be blamed for them. GARRETT P. SERVISS. CHÂTEAU D’ARCEAU, CÔTE D’OR, FRANCE, June, 1907. ------------------------------------------------------------------------ CONTENTS PAGE INTRODUCTION 3 I. —NEW MOON TO FIRST QUARTER 47 II. —FIRST QUARTER TO FULL MOON 83 III. —FULL MOON TO OLD MOON 131 IV. —GREAT SCENES ON THE MOON 181 APPENDIX 239 INDEX 243 ------------------------------------------------------------------------ LIST OF ILLUSTRATIONS FULL-PAGE ILLUSTRATIONS Copernicus and the Carpathian Mountains _Frontispiece_ PHOTOGRAPHS OF THE MOON SHOWING PHASES OF CHANGE