Hundred Years Of Physics

A Hundred Years of Physics by WILLIAM WILSON F. R. S., PH. D., D. SC. Emeritus Professor of Physics University of London GERALD DUCKWORTH CO. LTD. 5 HENRIETTA STREET, LONDON, W. C. 2 First published 1950 All rights reserved PRINTED IN GREAT BRITAIN BY WESTERN PRINTING SERVICES LTD., BRISTOL PREFACE To understand most of this book the reader needs very little previous knowledge of the science of physics and a very slight mathematical equipment. It is hardly an exaggeration to say that mathematics is absent in most of the chapters. I have been forced to introduce a little in dealing with parts of relativity and quantum mechanics but even that is of the most elementary kind. The . work is intended, as its title suggests, to present as clearly as possible the essential features in the development of the science during the past hundred years, or to be more precise-since the beginning of Queen Victorias reigri. The discovery of the cardinal facts of physics and the growth of its unifying theoretical structure are described and discussed together. There is much in it that is addressed to both students and teachers of science and a little of it, here and there, even to the great pundits of physics. Figures IV 1, VII-5 and XV 1 are borrowed from my Theoretical Physics, and I wish to express my thanks to Messrs. Methuen Co. for permitting me to use them. My thanks are also due to Messrs. Kdward Arnold Co. for Figure VII-1 which appeared in my article on The Origin and Nature of Wave Mechanics in Science Progress, 32, p. 209 1937. W. W. April 1950 CONTENTS Chaptci PROLOGUE ..... 9 I. THERMAL PHENOMENA . . . .15 II. ANOTHER ASPECT OF THERMAL PHENOMENA . 51 III. AN EXPERIMENTAL MISCELLANY . .46 IV.THE STATISTICAL THEORY OF HEAT I. KINETIC THEORY OF GASES . . 62 V. THE STATISTICAL THEORY OF HEAT II. STATISTICAL MECHANICS . . 80 VI. LIGHT ..... 86 VII. MORE ABOUT LIGHT . . . .106 VIII. INTEGRATION OF ELECTROMAGNETISM . . 118 ix. MAXWELLS ELECTROMAGNETIC THEORY . . 137 X. THE AETHER . . . . .148 XI. NEWTONIAN AND SPECIAL RELATIVITY . .155 xii. EINSTEINS GENERAL THEORY . . .174 XIII. RADIANT HEAT AND THE EMERGENCE OF THE QUANTUM THEORY . . . .182 XIV. CONDUCTION OF ELECTRICITY AND ASSOCIATED PHENOMENA .... 203 XV. MISCELLANEOUS SUBJECTS . . .212 XVI. ATOMIC STRUCTURE .... 228 XVII. THE CORRESPONDENCE PRINCIPLE AND ITS APPLICATION ..... 244 XVIII. QUANTUM MECHANICS .... 249 XIX, RADIOACTIVITY AND COSMIC RADIATION . . 263 XX. THE ATOMIC NUCLEUS .... 276 XXI. ASTROPHYSICS AND COSMOLOGICAL SPECULATION 282 EPILOGUE ..... 298 INDEX ...... 309 7 Dedicated to my former students at Bedford College and at Kings College, London PROLOGUE AT the beginning of Victorias reign physical and chemical phenomena, that is to say, the phenomena of the inorganic world, were regarded as the manifestation of the motions of material bodies, ranging from John Daltons atoms to planets and stars, under the influence of forces. In one set of phenomena the forces were gravitational, in another electrical, in still another chemical, and so on. The physicists and chemists of that time had fairly clear notions of what they meant by these terms. They were philosophers though perhaps not in the special and rather restricted present-day sense of the term. For them the investi gator of natural phenomena was a philosopher. Physical science was usually called natural philosophy. Their geometry was Euclidean and the inversesquare law of force had for them an almost a priori character, and indeed in a Euclidean world it would seem to be as inevitable as it is for the illumination of a surface by a point source of light. The mechanical principles to which the motions of bodies, under the influence of forces, were found to conform were those laid down by Sir Isaac Newton 16421727 in the great work Philosophiae naturalis principia mathematica usually referred to as the Principia. No physicist of 1857 could contemplate any other attitude to physical pheno mena...