Agriculture, ancient centers of, xiii, 221; beginnings of, 209-10, xv, 200-2; civilization and, 128; fundamental importance, xiv, 218; grasslands and, 383; plains most favorable to, 218-19; possibilities, by what determined, 64; summer rain importance, 352 Ailerons, i, 289, 299, v, 238, 343 Air, amount consumed by breathing, ix, 256; ancient ideas, xvi, 79; as balloon ballast, v, 226; boiling point of, iv, 173; buoyant power of, 107, 108; burning of, in gas, viii, 55, 56; burning, in gasoline engines, v, 156-7; "change of" (vertical), i, 51; closeness or stuffiness of, (see Ventilation); combustion and, i, 10; composition, 9-16, vii, 321, viii, 66-8, ix, 254, 268; composition, discovery of, xvi, 120, 121; compressed (see Compressed Air); compressibility, v, 126; cooling power, i, 318, 319-21; critical temperature & pressure, iv, 172, 173; decay in relation to, xiii, 312-13; density of, iv, 113, 198; drying power, i, 77, 323; dryness & dampness, viii, 67, xiv, 353-4; elasticity of, iv, 198, v, 126; electrical conductivity, i, 144-5, iv, 259, 265; expansion by heat, 151; frozen, v, 345; health benefits of special types of, x, 241; heat conductivity, iv, 178, 179; ionization, i, 142-4, 146, 150; life without, (see Anaërobic); liquefaction of, iv, 171, 172; (see Liquid Air); moisture capacity, xiv, 352-4 (see also Humidity); molecular velocity in, iv, 133; necessity to life, ii, 244, 245; necessity to plants, xiii, 102, 109; physics of, historical development, iv, 28-30; popular & scientific conceptions, i, 9-10; pressure of, iv, 132 (see also Atmospheric Pressure); purifying by ozone, i, 15, vii, 354; purity tests, i, 321-2; resistance due to inertia, v, 234; resistance effects on aeroplanes, i, 286-9, iv, 43, v, 235-6; resistance to falling bodies, iv, 42, 97; resistance to projectiles, v, 369; saturated, i, 14, viii, 67; shimmering of, i, 174, iv, 328, 329; in soil, xiii, 92; solubility in water, viii, 111; sound transmission by, i, 186, iv, 195, 198-9, 201, ix, 98-9; specific heat of, iv, 161; specific heat ratio, 156; surfeit of, bodily effects, 31; ventilation of, (see Ventilation); vibrations of, 215; warming of, by sunshine, 182; warming of, by freezing water, 161; weight of, 107, 116, 124, v, 221-2, 230; weight, discovery of, iv, 29, 114-16; weight of heated, v, 223 (see also Atmosphere) Air Bladder, xii, 135-6, 164-5 Air Brakes, iv, 129, 200, v, 130-3, 380, 381; on electric cars, vii, 185-6 Air Columns, resonance of, iv, 226-31; vibrations of, 215 Air Compressors, i, 26-7, iv, 128, v, 89-93, 127-8 Air-cooled Engines, v, 160-1 Air Currents in aeronautics, i, 293-300; pilot balloons to discover, 21-2 Air Cushioning, v, 133-5