This book is the result of a special study of the planet made during the last opposition, at an observatory put up for the purpose of getting as good air as practicable, at Flagstaff, Arizona. A steady atmosphere is essential to the study of planetary detail: size of instrument being a very secondary matter. A large instrument in poor air will not begin to show what a smaller one in good air will. When this is recognized, as it eventually will be, it will become the fashion to put up observatories where they may see rather than be seen.
Next to atmosphere comes systematic study. Of the extent to which this was realized at Flagstaff, I need only say that the planet was observed there from May 24, 1894, to April 3, 1895, during which time, to mention nothing else, 917 drawings and sketches were made of it. Prof. W. H. Pickering and Mr. A. E.