Aeronautics, accidents & safety questions, i, 49-50; accidents in World War, x, 246; aneroid barometer importance in, iv, 124; fog in, i, 94, 95, 300-2; history & future, 39-51; Langley's work in, iv, 43-4; pilot balloons in, i, 22; therapeutic possibilities, 51; weather importance, 284-6; wind & air currents, 126, 130, 289-300 (see also Aeroplanes, Balloons) Aeroplanes, altitudes attained, i, 22, 46; altitude effects, 303; astronomical use, ii, 208, 212, 225-6, 382; Brocken specters seen from, i, 185; engine efficiency, v, 170; gyroscopic stabilizing, 343-4; helicopter, i, 42; history & development, 40-1, iv, 43-4, v, 230-3, 382, 383-4; landings, i, 42, 45, 294 (fig.) 302; mail service, 44-5, vii, 76; meteorological uses, i, 22; passenger, 41-2, 43-5, 50; photographic mapping by, 45-8; principles, i, 286-305, v, 233-8; propellers (tractors) of, iv, 34; radiotelephony and, vii, 282-3; rise or "taking off" of, iv, 43; safety question, i, 49-50; stereograms from, xi, 180-1; uses, present & future, i, 41-2, 43-9; war uses, v, 107, 372-3, 375; wind effects, i, 285-6, 289-300; wireless directing, vii, 283; World War, i, 185, 308, 312, vii, 283, x, 246 (see also Aeronautics, Aviators) Æsculapius, x, 16, 17; temples of, 17, xvi, 44 Æsthetic Arts, development of, xv, 297-324 Æsthetic Instinct, xvi, 47, 48 Æther of Space, vi, 118-20; constitution, vii, 368; elastic solid theory, xvi, 137; universal presence of, iv, 180-1 Æther Waves, various kinds, vi, 119, 269, vii, 249, 250, 259-61, 371 Aetius, medieval writer, x, 31 Ætna (see Etna) Affection, emotion of, xi, 147; importance, 129; seat of, ix, 200