My thanks are due also to the _Scientific American_ and to _Aëronautics_ for the use of photographs for the illustrations, as also to the manufacturers of various aircraft, and to Mr. W. J. Hammer, Mr. Carl Dientsbach, and Mr. A. S. Levino. A. F. ZAHM. COSMOS CLUB WASHINGTON, D. C., January, 1911. CONTENTS CHAPTER PAGE INTRODUCTION INTRODUCTION 3 PART I GROWTH OF AËROSTATION I.—EARLY HISTORY OF PASSIVE BALLOONS 29 II.—PRACTICAL DEVELOPMENT OF PASSIVE BALLOONS 54 III.—EARLY HISTORY OF POWER BALLOONS 78 IV.—INTRODUCTION OF GASOLINE-DRIVEN DIRIGIBLES 101 V.—PRACTICAL DEVELOPMENT OF NON-RIGID DIRIGIBLES 115 VI.—DEVELOPMENT OF RIGID DIRIGIBLES 145 PART II GROWTH OF AVIATION VII.—MODEL FLYING MACHINES 173 VIII.—NINETEENTH CENTURY MAN-FLYERS 202 IX.—AËROPLANES OF ADEQUATE STABILITY AND POWER 235 X.—ADVENT OF PUBLIC FLYING 256 XI.—STRENUOUS COMPETITIVE FLYING 283 XII.—FORCING THE ART 307 PART III AËRONAUTIC METEOROLOGY XIII.—GENERAL PROPERTIES OF FREE AIR 347 XIV.—GENERAL DISTRIBUTION OF HEAT AND PRESSURE 363 XV.—PERMANENT AND PERIODIC WINDS 376 XVI.—CYCLONES, TORNADOES, WATERSPOUTS 394 XVII.—THUNDERSTORMS, WIND GUSTS 422 APPENDICES I.—STRESS IN A VACUUM BALLOON 443 II.—AËRONAUTIC LETTERS OF BENJAMIN FRANKLIN 446 III.—SUCCESSFUL MILITARY DIRIGIBLE BALLOONS 456 IV.—THE RELATIONS OF WEIGHT, SPEED, AND POWER OF FLYERS 478 V.—CURTISS’ HYDRO-AËROPLANE EXPERIMENTS 481 INDEX 487 LIST OF PLATES FACING PAGE PLATE I 66 Glaisher and Coxwell. Parseval Kite Balloon.