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 have been moved so they do not break up paragraphs. Typographical and punctuation errors have been silently corrected. Page 41: “1,000,000 feet or 300,000 kilometres per second” changed to “1,000,000,000 feet or 300,000 kilometres per second” THE ATOM AND THE BOHR THEORY OF ITS STRUCTURE _Original Title: “Bohr’s Atomteori, almenfatteligt fremstillet”_ _Translated from the Danish by $1 Fellow of the American-Scandinavian Foundation, 1923, and RACHEL T. LINDSAY_ [Illustration: _Niels Bohr_] THE ATOM AND THE BOHR THEORY OF ITS STRUCTURE An Elementary Presentation BY H. A. KRAMERS LECTURER AT THE INSTITUTE OF THEORETICAL PHYSICS IN THE UNIVERSITY OF COPENHAGEN AND HELGE HOLST LIBRARIAN AT THE ROYAL TECHNICAL COLLEGE OF COPENHAGEN WITH A FOREWORD BY SIR ERNEST RUTHERFORD, F.R.S. [Illustration] NEW YORK ALFRED A. KNOPF 1923 PRINTED IN GREAT BRITAIN BY MORRISON AND GIBB LTD., EDINBURGH PREFACE