Text extracted from opening pages of book: CONCERNING THE NATURE OF THINGS Six Lectures delivered at the Royal Institution By SIR WILLIAM BRAGG K. B. E., D. Sc., F. R. S LONDON G. BELL AND SONS LTD. * 19* 5 RO IN GRFAF BKITAIN BY KD CLAY & SONS, LIMIJED, BUNC. AY, SUFFOLK. PREFACE IT was my endeavour at the Christmas Lectures given at the Royal Institution in 1923-24 to describe certain features of the recent discoveries in physical science. Many of the facts that have come to light might well be the subject of Lectures adapted to a Juvenile Auditory/' and would be at the same time interesting and helpful ; interesting because they display a beautiful order in the fundamental arrangement of Nature, and helpful because they have given us light on many old questions, and will surely help us with many that are new. I was aware of two special diffi culties. The first was the difficulty of under standing the minuteness of the scale on which the action and properties of the atoms must be repre sented ; but, after all, this was only a difficulty due to unfamiliarity, and would come to a timely end. The other was the difficulty of grasping arrangements in space. There are some who think that this difficulty is incurable, and that it is due to the want of some special capacity, which only a few possess. I am persuaded that this is not the vi PREFACE case : we should have nearly as much difficulty in grasping events in two dimensions as in three were it not that we can so easily illustrate our two dimensional thoughts by pencil and paper. If one can turn over a model in one's hand, an idea can be seized in a mere fraction of the time that is required to read about it, and a still smaller fraction of the time that is required to prepare the description. Perhaps some of the readers of this book will be sufficiently interested to make models of the few crystal structures that are mentioned in it, and may even go on to other structures that are described in larger books or in original papers. I have added somewhat to the lectures as originally given. The additions are intended to make the treatment of the subject a little more complete : they were not very suitable for con sideration at the lectures, but are perhaps per missible in the book because the reader can omit them if he desires or read them more than once, or consider them with a model in his hand. At the end of the book there is a short note on the making of models. CONTENTS LECTURE I I'AGK THE ATOMS OF WHICH THINGS ARE MADE . . i LECTURE II THE NATURE OF GASES ..... 42 LECTURE III THE NATURE OF LIQUIDS ..... 83 LECTURE IV THE NATURE OF CRYSTALS: DIAMOND . .116 LECTURE V THE NATURE OF CRYSTALS : ICE AND SNOW . 160 LECTURE VI THE NATURE OF CRYSTALS : METALS . . . 200 LIST OF PLATES PI ATE To face page I. ( A) MODEL OF BISMUTH CRYSTAL. (&) THE SHAKING SAND BOX . . .17 II. SHIMIZU-WILSON RAY TRACK APPARATUS . 26 III. ALPHA RA. Y TRACKS .... 28 IV. ( A) BAR MAGNETS ON SPIRAL SPRINGS. ( B) MODELS OF ATOMS WITH ELECTRONS . 32 V. ( A) FLOATING MAGNETS. ( B) CRYSTALS IN TUBE CONTAINING EMANATION . . 38 VI. ( A) TUNING FORK OVER JAR. ( B) FOG APPA RATUS ...... 56 VII. CIGARETTE SMOKE ..... (> o VIII. EXPERIMENT SHOWING THE PRESSURE OF THE ATMOSPHERE .... 65 IX. CAVITATION CAUSING EROSION OF PROPELLER BLADES ..... 91 X. ( A) LARGE DROP OF ORTHOTOLUIDINE. ( B) ONE SOAP BUBBLE INSIDE ANOTHER . 95 XI. ( A) CIRCLES CLEARED BY MINUTE DROPS OF OIL. ( B) THE CAMPHOR BOAT . . 104 ix t LIST OF PLATES PLATE-To face page XII. ( A) STORMY WATER. ( fi) OIL STILLING THE STORM, ( c) GRAPE IN SODA WATER . 106 XIII. CRYSTALLINE FORMS .... 124 XIV. ( A) DIAMOND MODEL. ( B) PLANE LATTICE IN THE DESIGN OF A WALL-PAPER . 135 XV. THE CULLINAN DIAMOND . . - 145 XVI. ( A) LAYERS OF THE GRAPHITE CRYSTAL. ( B) POSSIBLE FORMS OF THE BENZENE RING 146 XVII. SNOW CRYSTALS OF VARIOUS FORMS . . l6o xviii. MORF: SNOW CRYSTALS . . . .161 XIX. A HALO AND MOCK SUNS. . . . 163 XX. ( A) GLACIER ICE. ( B) MODELS OF ICE STRUCTURE