CONTENTS 



PAGE 



INTRODUCTION 



MODERN PHYSICS 13 



BY R. A. MILLIKAN 



THE STRUCTURE OF ATOMS AND ITS BEARING ON CHEMICAL 



VALENCE 23 



BY IRVING LANGMUIR 



ENGINEERING BEFORE AND AFTER THE WAR 34 



BY SIR CHARLES PARSONS 



METHODS OF GAS WARFARE 61 



BY S. J. M. AULD, D.S.M. 



WHAT ARE ENZYMES? 76 



BY BENJAMIN HARROW 



NATURAL DEATH AND THE DURATION OF LIFE 85 



BY JACQUES LOEB 



THE PHYSIOLOGY OF THE AVIATOR 95 



BY YANDELL HENDERSON 



TWENTY- FIVE YEARS OF BACTERIOLOGY: A FRAGMENT OF 



MEDICAL RESEARCH 115 



BY SIMON FLEXNER 



BEFORE AND AFTER LISTER 152 



BY W. W. KEEN 



THE MEASUREMENT AND UTILIZATION OF BRAIN POWER IN 



THE ARMY 192 



BY R. M. YERKES 



CONCEPTIONS AND MISCONCEPTIONS IN PSYCHOANALYSIS . . 211 

 BY TRIGANT BURROW, M.D. 



EINSTEIN'S LAW OF GRAVITATION 230 



BY J. S. AMES 



INDEX 247 



