THE FOUNDATIONS OF
EINSTEIN'S THEORY OF
GRAVITATION
BY
DIRECTOR OF THE EINSTEIN TOWER
WITH A PREFACE BY
TRANSLATED FROM THE FOURTH GERMAN EDITION,
WITH TWO ESSAYS, BY
CHRIST CHURCH, OXFORD
WITH AN INTRODUCTION BY
SAVILIAN PROFESSOR OF ASTRONOMY IN THE UNIVERSITY OF OXFORD
WITH FIVE DIAGRAMS
NEW YORK
E. P. DUTTON AND COMPANY
PUBLISHERS
PREFACE
DR. FREUNDLICH has undertaken in thefollowing essay to illumine the ideas and observations which gave riseto the general theory of relativity so as to make them available to awider circle of readers.
I have gained the impression in perusing these pages that the author hassucceeded in rendering the fundamental ideas of the theory accessible toall who are to some extent conversant with the methods of reasoning ofthe exact sciences. The relations of the problem to mathematics, to thetheory of knowledge, physics and astronomy are expounded in afascinating style, and the depth of thought of Riemann, a mathematicianso far in advance of his time, has in particular received warmappreciation.
Dr. Freundlich is not only highly qualified as a specialist in thevarious branches of knowledge involved to demonstrate the subject; he isalso the first amongst fellow-scientists who has taken pains to put thetheory to the test.
May his booklet prove a source of pleasure to many!
A. EINSTEIN
[Pg v]
INTRODUCTION
THE Universe is limited by the propertiesof light. Until half a century ago it was strictly true that we dependedupon our eyes for all our knowledge of the universe, which extended nofurther than we could see. Even the invention of the telescope did notdisturb this proposition, but it is otherwise with the invention of thephotographic plate. It is now conceivable that a blind man, by takingphotographs and rendering their records in some way decipherable by hisfingers, could investigate the universe; but still it would remain true,that all his knowledge of anything outside the earth would be derivedfrom the use of light and would therefore be limited by its properties.On this little earth there is, indeed, a tiny corner of the universeaccessible to other senses: but feeling and taste act only at thoseminute distances which separate particles of matter when "in contact:"smell ranges over, at the utmost, a mile or two; and the greatestdistance which sound is ever known to have travelled (when Krakatoaexploded in 1883) is but a few thousand miles—a mere fraction ofthe earth's girdle. The scale of phenomena manifested through agenciesother than light is so small that we are unlikely to reach an