Transcriber’s Notes: Underscores “_” before and after a word or phrase indicate _italics_ in the original text. Equal signs “=” before and after a word or phrase indicate =bold= in the original text. Small capitals have been converted to SOLID capitals. Illustrations and footnotes have been moved so they do not break up paragraphs. Deprecated spellings have been preserved. Typographical and punctuation errors have been silently corrected. THE UNIVERSE AROUND US Cambridge University Press Fetter Lane, London _Bombay_, _Calcutta_, _Madras_ _Toronto_ Macmillan _Tokyo_ Maruzen Company, Ltd Copyrighted in the United States of America by the Macmillan Company All rights reserved [Illustration: _Lowell Observatory_ The Discovery of Pluto The two photographs were taken at the Lowell Observatory on the nights of March 2 and 5, 1930. The object indicated by arrows was seen to have moved considerably in the interval, and this proved that it was of planetary character. The bright object in the bottom left-hand corner is the star δ Geminorum (see p. 260).] THE UNIVERSE AROUND US _By_ SIR JAMES JEANS M.A., D.Sc., Sc.D. LL.D., F.R.S. [Illustration] CAMBRIDGE AT THE UNIVERSITY PRESS 1930 _First Edition, September 1929_ _Reprinted November 1929_ ” _January 1930_ _Second Edition, October 1930_ PRINTED IN GREAT BRITAIN PREFACE The present book contains a brief account, written in simple language, of the methods and results of modern astronomical research, both observational and theoretical. Special attention has been given to problems of cosmogony and evolution, and to the general structure of the universe. My ideal, perhaps never wholly attainable, has been that of making the entire book intelligible to readers with no special scientific knowledge. Parts of the book cover the same ground as various lectures I have recently delivered to University and other audiences, including a course of wireless talks I gave last autumn. It has been found necessary to re-write these almost in their entirety, so that very few sentences remain in their original form, but those who have asked me to publish my lectures and wireless talks will find the substance of them in the present book.