1. Diagram showing the reduction of the projected horizontal area, 2 2. Professor Langley’s experiments, 5 3. Eagles balancing themselves on an ascending current of air, 14 4. Air currents observed in Mid-Atlantic, 16 5. Glassy streaks in the Bay of Antibes, 17 6. Air currents observed in the Mediterranean, 18 7. The circulation of air produced by a difference in temperature, 27 8. Kite flying, 29 9. Group of screws and other objects used in my experiments, 32 10. Some of the principal screws experimented with, 32 11. The three best screws, 33 12. Apparatus for testing the thrust of screws, 34 13. Apparatus for testing the direction of air currents, 35 14. The ends of screw blades, 36 15. The manner of building up the large screws, 39 16. A fabric-covered screw, 40 17. The hub and one of the blades of the screw on the Farman machine, 42 18. Section of screw blades having radial edges, 43 19. Form of the blade of a screw made of sheet metal, 44 20. New form of hub, 45 21. Small apparatus for testing fabrics for aeroplanes, 50 22. Apparatus for testing the lifting effect of aeroplanes and condensers, 51 23. Apparatus for testing aeroplanes, condensers, &c., 52 24. Cross-sections of bars of wood, 53 25. Sections of bars of wood, 54 26. A flat aeroplane placed at different angles, 55 27. Group of aeroplanes used in experimental research, 56 28. An 8-inch aeroplane which did very well, 57 29. Resistance due to placing objects in close proximity to each other, 58 30. Cross-section of condenser tube made in the form of Philipps’ sustainers, 60 31. The grouping of condenser tubes made in the form of Philipps’ sustainers, 61 32. Machine with a rotating arm, 63 33. A screw and fabric-covered aeroplane in position for testing, 64 34. The rotating arm of the machine with a screw and aeroplane