PREFACE TO THE SECOND EDITION
Reading edition
In the present edition of this book I have endeavored to present a simple treatment of all the developments in physics to date which have caused a modification or extension of any of the viewpoints expressed just seven years ago. In its preparation I have been very much impressed to find how uniformly the changes represent additions rather than subtractions—a striking illustration of the great truth that science, like a plant, grows in the main by the process of accretion. If I have succeeded in interesting some old friends and making a few new ones for one of the most fascinating of subjects, I shall be content.
ROBERT ANDREWS MILLIKAN
NORMAN BRIDGE LABORATORY OF PHYSICS CALIFORNIA INSTITUTE OF TECHNOLOGY PASADENA, CALIFORNIA MAY 18, 1924