Part 1

From NEWTON to EINSTEIN

Changing Conceptions of THE UNIVERSE

BENJAMIN HARROW, Ph.D.

SECOND EDITION, REVISED AND ENLARGED

With Articles by Prof. Einstein, Prof. J. S. Ames (Johns Hopkins), Sir Frank Dyson (Astronomer Royal), Prof. A. S. Eddington (Cambridge) and Sir J. J. Thomson (President of the Royal Society)

Portraits and Illustrations

NEW YORK D. VAN NOSTRAND COMPANY Eight Warren Street 1920

PREFACE

Einstein's contributions to our ideas of time and space, and to our knowledge of the universe in general, are of so momentous a nature, that they easily take their place among the two or three greatest achievements of the twentieth century. This little book attempts to give, in popular form, an account of this work. As, however, Einstein's work is so largely dependent upon the work of Newton and Newton's successors, the first two chapters are devoted to the latter.

B. H.

PREFACE TO SECOND EDITION

The preparation of this new edition has made it possible to correct errors, to further amplify certain portions of the text and to enlarge the ever-increasing bibliography on the subject. Photographs of Professors J. J. Thomson, Michelson, Minkowski and Lorentz are also new features in this edition.

The explanatory notes and articles in the Appendix will, I believe, present no difficulties to readers who have mastered the contents of the book. They are in fact "popular expositions" of various phases of the Einstein theory; but experience has shown that even "popular expositions" of the theory need further "popular introductions."

I wish to take this opportunity of thanking Prof. Einstein, Prof. A. A. Michelson of the University of Chicago, Prof. J. S. Ames of Johns Hopkins University, and Professor G. B. Pegram of Columbia University for help in various ways which they were good enough to extend to me. Prof. J. S. Ames and the editor of Science have been kind enough to allow me to reprint the former's excellent presidential address on Einstein's theory, delivered before the members of the American Physical Society.

B. H.

TABLE OF CONTENTS

PAGE

I. Newton 1 II. The Ether and Its Consequences 27 III. Einstein 41 IV. Appendix 81

Time, Space and Gravitation, by Prof. Einstein 88 Einstein's Law of Gravitation, by Prof. J. S. Ames 93 The Deflection of light by Gravitation and the Einstein Theory of Relativity, by Sir Frank Dyson, Prof. A. S. Eddington and Sir J. J. Thomson 112

NEWTON

"Newton was the greatest genius that ever existed."--Lagrange, one of the greatest of French mathematicians.

"The efforts of the great philosopher were always superhuman; the questions which he did not solve were incapable of solution in his time."--Arago, famous French astronomer.

EINSTEIN

"This is the most important result obtained in connection with the theory of gravitation since Newton's day. Einstein's reasoning is the result of one of the highest achievements of human thought."--Sir J. J. Thomson, president of the British Royal Society and professor of physics at the University of Cambridge.

"It surpasses in boldness everything previously suggested in speculative natural philosophy and even in the philosophical theories of knowledge. The revolution introduced into the physical conceptions of the world is only to be compared in extent and depth with that brought about by the introduction of the Copernican system of the universe."--Prof. Max Planck, professor of physics at the University of Berlin and winner of the Nobel Prize.

NEWTON

In speaking of Newton we are tempted to paraphrase a line from the Scriptures: Before Newton the Solar System was without form, and void; then Newton came and there was light. To have discovered a law not only applicable to matter on this earth, but to the planets and sun and stars beyond, is a triumph which places Newton among the super-men.

What Newton's law of gravitation must have meant to the people of his day can be pictured only if we conceive what the effect upon us would be if someone--say Marconi--were actually to succeed in getting into touch with beings on another planet. Newton's law increased confidence in the universality of earthly laws; and it strengthened belief in the cosmos as a law-abiding mechanism.