Transcriber’s Notes: Underscores “_” before and after a word or phrase indicate _italics_ in the original text. A single underscore after a symbol indicates a subscript. Carat symbol “^” designates a superscript. Small capitals have been converted to SOLID capitals. Illustrations have been moved so they do not break up paragraphs. Typographical errors have been silently corrected. The numerical references to the NOTES, e. g. [1] have been changed to “(see NOTE x)” in order to avoid confusion with the true footnotes. THE EVOLUTION OF WORLDS [Illustration] THE MACMILLAN COMPANY NEW YORK · BOSTON · CHICAGO ATLANTA · SAN FRANCISCO MACMILLAN & CO., LIMITED LONDON · BOMBAY · CALCUTTA MELBOURNE THE MACMILLAN CO. OF CANADA, LTD. TORONTO [Illustration: SATURN—PHOTOGRAPHED AT THE LOWELL OBSERVATORY BY MR. E. C. SLIPHER. SEPTEMBER, 1909.] THE EVOLUTION OF WORLDS BY PERCIVAL LOWELL, A.B., LL.D. AUTHOR OF “MARS AND ITS CANALS,” “MARS AS THE ABODE OF LIFE,” ETC. DIRECTOR OF THE OBSERVATORY AT FLAGSTAFF, ARIZONA; NON-RESIDENT PROFESSOR OF ASTRONOMY AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY; FELLOW OF THE AMERICAN ACADEMY OF ARTS AND SCIENCES; MEMBRE DE LA SOCIÉTÉ ASTRONOMIQUE DE FRANCE; MEMBER OF THE ASTRONOMICAL AND ASTROPHYSICAL SOCIETY OF AMERICA; MITGLIED DER ASTRONOMISCHE GESELLSCHAFT; MEMBRE DE LA SOCIÉTÉ BELGE D’ASTRONOMIE; HONORARY MEMBER OF THE SOCIEDAD ASTRONOMICA DE MEXICO; JANSSEN MEDALLIST OF THE SOCIÉTÉ ASTRONOMIQUE DE FRANCE, 1904, FOR RESEARCHES ON MARS; MEDALLIST OF THE SOCIEDAD ASTRONOMICA DE MEXICO FOR STUDIES ON MARS, 1908 _ILLUSTRATED_ New York THE MACMILLAN COMPANY 1909 _All rights reserved_ COPYRIGHT, 1909, BY THE MACMILLAN COMPANY. Set up and electrotyped. Published December, 1909. Norwood Press J. S. Cushing Co.—Berwick & Smith Co. Norwood, Mass., U.S.A.