Past failures are not to be regarded as the harbingers of future defeats, for it is only within the last few years that the subject of artificial flight has been taken up in a true scientific spirit. Within a comparatively brief period an enormous mass of valuable data has been collected. As societies for the advancement of aëronautics have been established in Britain, America, France, and other countries, there is reason to believe that our knowledge of this most difficult department of science will go on increasing until the knotty problem is finally solved. If this day should ever come, it will not be too much to affirm, that it will inaugurate a new era in the history of mankind; and that great as the destiny of our race has been hitherto, it will be quite out-lustred by the grandeur and magnitude of coming events. [Illustration] INDEX. PAGE Aerial creatures not stronger than terrestrial ones, 13 Aërial flight as distinguished from sub-aquatic flight, 92 Aëronautics, 209 Air cells in insects and birds not necessary to flight, 115 Albatross, flight of, compared to compass set upon gimbals, 199 Amphibia have larger travelling surfaces than land animals, but less than aërial ones, 8 Artificial fins, flippers, and wings, how constructed, 14 Artificial wings, Borelli, 219 Do. Marey, 226 Do. Chabrier, 233 Do. Straus-Durckheim, 233 Do. how to apply to the air, 245 Do. nature of forces required to propel, 246 Artificial _wave_ wing of Pettigrew, 236 Do. how to construct on insect type, 240 Do. how to construct to evade the superimposed air during the up stroke, 241 Do. can create currents and rise upon them, 253 Do. can be driven at any speed; can make new currents and utilize old ones, 251, 255 Do. as a propeller and aërial screw, 256 Do. compound rotation of: the different parts of the wing travel at different speeds, 252 Do. necessity for supplying root of, with elastic structures, 247 Artificial _compound wave_ wing of Pettigrew, 242 Atmospheric pressure, effects of, on limbs, 24 Axioms, fundamental, 17 Balancing, how effected in flight, 118 Balloon, 210 Bats and birds, lax condition of shoulder-joint in, 190 Birds, lifting capacity of, 205 Body and wing reciprocate in flight, and each describes a waved track, 12 Bones, 21 Bones of the extremities twisted and spiral, 28, 29 Bones of wing of bat--spiral configuration of their articular surfaces, 176 Bones of wing of bird--their articular surfaces, movements, etc., 178 Borelli’s artificial bird, 220 Chabrier’s artificial wings, 233 Elytra or wing cases and membranous wings, 170 Feathers, primary, secondary, and tertiary, 180 Fins, flippers, and wings form mobile helices or screws, 14 Flight, weight necessary to, 3, 4, 110, 111, 112, 113 Flight the poetry of motion, 6 Flight the least fatiguing kind of motion, 13