that I had reasoned out the best type of a machine even before I commenced a stroke of the work. I have to thank Mr. Albert T. Thurston for reading the proofs of this work. H. S. M. CONTENTS. CHAPTER I. PAGE Introductory, 1 CHAPTER II. Air Currents and the Flight of Birds, 11 CHAPTER III. Flying of Kites, 25 CHAPTER IV. Principally Relating to Screws, 31 CHAPTER V. Experiments with Apparatus Attached to a Rotating Arm--Crystal Palace Experiments, 62 CHAPTER VI. Hints as to the Building of Flying Machines--Steering by Means of a Gyroscope, 77 CHAPTER VII. The Shape and Efficiency of Aeroplanes--The Action of Aeroplanes and the Power Required Expressed in the Simplest Terms--Some Recent Machines, 99 CHAPTER VIII. Balloons, 120 APPENDIX I., 125 APPENDIX II.-- Recapitulation of Early Experiments--Efficiency of Screw Propellers, Steering, Stability, &c.--The Comparative Value of Different Motors--Engines--Experiments with Small Machines Attached to a Rotating Arm, 130 INDEX, 163 INDEX OF ILLUSTRATIONS. FIG. PAGE