FROM COPERNICUS TO EINSTEIN COPYRIGHT MCMXLII BY PHILOSOPHICAL LIBRARY, INC. 15 EAST 40TH STREET, NEW YORK Composed and Printed in the United States of America By Steingould Corp., New York TYPOGRAPHY BY SIDNEY SOLOMON CONTENTS CHAPTER 1. The Copernican View of the World 11 2. Ether 29 3. The Special Theory of Relativity 49 4. The Relativity of Motion 73 5. General Theory of Relativity 85 6. Space and Time 107 6201251 ILLUSTRATIONS FIGURE 1. A Tycho Brahe s Sextant 20 2. Roemer s Observation of Jupiter s Moon 32 3. The Phenomenon of Interference 38 4. The Total Spectrum 46 5. The Diagram of Michelson s Experiment 54 6. A Diagram of the Measurement of the Speed of Light 59 7. A Diagram of the Course of a Light-Signal 63 8. Einstein s quot Box Experiment quot 86 9. The Curvature of Light-Rays in Einstein s Box 95 10. The Einstein Tower in Potsdam 100 11. Major Segrave s 1,000 Horsepower Auto at Full Speed 1 10 FROM COPERNICUS TO EINSTEIN Chapter 1 THE COPERNICAN VIEW OF THE WORLD THIS little book purports to serve as an introduction to the great problems of space, time and motion. The in quiries it is concerned with are very old. Men have been forming ideas concerning space and time since times im memorial, and curiously enough, have been writing and fighting about these things with the greatest interest, even fanaticism. This has been a strange strife, indeed, having little to do with economic necessities it has always dealt with abstract things, far removed from our daily life and with no direct influence upon our daily activities. Why do we need to know whether the sun revolves around the earth or vice versa What business of ours is it, anyway Can this knowledge be of any use to us No sooner have we uttered these questions than we become aware of their foolishness. It may not be of any use to us, but we want to know something about these problems. We do not want to go blindly through the world. We desire more than a mere existence. We need these cosmic perspectives in order to be able to experi ence a feeling for our place in the world. The ultimate questions as to the meaning of our actions and as to the meaning of life in general always tend to involve astro nomical problems. Here lies the mystery surrounding 11 From Copernicus To Einstein astronomy, here lies the wonder we experience at the sight of the starry sky, the wonder growing in proportion to our understanding of immense distances of space and of the stars inner nature. Here is the source of scientific as well as popular astronomy. These two branches have diverged in the course of their development. Astronomy, as a science, has come to forget its primitive wonder instead, it approaches the realm of stars with sober research and calculation. This disenchantment with its subject-matter, which scientific study invariably entails, has permeated astronomy to a greater degree than the layman realizes. In observing the astronomers of today, how they measure, take notes, cal culate, how little attention fiiey pay to mysterious specu lations, one may be surprised to find the wonderful struc ture of learning so cut and dry at a close range. Yet nothing is more wrong and more objectionable than the feeling of a heartbreaking loss, with which some people regard the vanishing mysticism of the skies. Although science may have destroyed a few naive fantasies, what she has put in their place is so immensely greater that we can well bear the loss. It takes perseverance and energy, of course, to com prehend the discoveries of science but whoever under takes the study is bound to learn many more surprising things from it than a naive study of nature can disclose. Scientific astronomy has always exercised, in fact, a great influence upon everyday thinking and upon the popular conception of the universe. If it is difficult today to pro-12