TRANSCRIBERS NOTE: The plain text version of this ebook includes mathematical formulas in TeX notation. These formulas are enclosed between dollar signs. The HTML version includes the same formulas rendered in their original form. EINSTEIN'S THEORIES OF RELATIVITY AND GRAVITATION A SELECTION OF MATERIAL FROM THE ESSAYS SUBMITTED IN THE COMPETITION FOR THE EUGENE HIGGINS PRIZE OF $5,000 COMPILED AND EDITED, AND INTRODUCTORY MATTER SUPPLIED BY J. MALCOLM BIRD, Associate Editor, Scientific American NEW YORK SCIENTIFIC AMERICAN PUBLISHING CO., MUNN & CO. 1921 PREFACE The obstacles which the layman finds to understanding Einstein's relativity theories lie not so much in the inherent difficulty of these theories themselves as in the difficulty of preparing the mind for their reception. The theory is no more difficult than any scientific development of comparable depth; it is not so difficult as some of these. But it is a fact that for a decent understanding of it, a large background of scientific knowledge and scientific habit of thought is essential. The bulk of the writers who have attempted to explain Einstein to the general reader have not realized the great gulf which lies between the mental processes of the trained mathematician and those of the man in the street. They have not perceived that the lay reader must be personally conducted for a long distance from the vestibule of the temple of science before he comes to Einstein, and that he cannot by any possibility make this journey unaided. The result has been to pitchfork the reader into the intricacies of the subject without adequate preparation. The present volume avoids this mistake with the utmost care. It avoids it, in fact, with such deliberation as to make it in order to say a word in explanation of what will at first glance seem an extraordinary arrangement of material. It was to be expected, doubtless, that this book would open with a brief statement of the genesis and the outcome of the Einstein Prize Essay Contest for the $5,000 prize offered by Mr. Eugene Higgins. It was doubtless to be expected that, after this had been dismissed, the winning essay would be given the post of honor in advance of all other material bearing actually on the Einstein theories. When the reader observes that this has not been done, he will by all means expect a word of explanation; and it is mainly for the purpose of giving this that we make these introductory remarks.