Interest, advertising value, xi, 345-6; associations determined by, 203, 205-6; attention and, 235-6; fatigue and, 275; in salesmanship, 341-2 Interference of Light, iv, 376-8 Interference of Sounds, iv, 218-22 Interferometer, ii, 151, 323 Interior Lighting Systems, vi, 275-8, vii, 68-72 Interior Wiring, vii, 51-72; insulators in, 370 Interlaken, Switzerland, lakes at, xiv, 202 Internal Combustion Engines, v, 155-70; in aeroplanes, 231; in automobiles, 213; in submarines, 199; efficiency, securing of, xvi, 135; Joule's equivalent and, 132-3 Internal Senses, ix, 86-91 Interoceptive Senses, xi, 63 Interpoles, of dynamos, vi, 190-1 Interurban Traction, vii, 181; automatic substations, 192-3; cars and motors, 186; voltage drop, 189 Intestinal Stasis, x, 220 Intestines, ix, 233 (fig.); development in black and white races, xv, 50; emotion effects on, xi, 135, 137; functions of, viii, 356-7, 358; functions, operations, and disorders of, ix, 232-4, 236-8, 242-52, x, 325-9; germs in, ix, 247-9, x, 193, 194, 201, 287-8; infections through, x, 198, 220, 221; in infants, ix, 346; inflammation of, cause, x, 224; length in animals and man, ix, 246; mucous membrane, functions of, x, 347; position in circulatory system, ix, 196 (fig.), 198; smooth muscles in, 74, 160-1, 162 Intrenched Meanders, xiv, 165 Intrusive Rocks, xiv, 105 Intrusive Sheets (sills), xiv, 108 Intuition, xi, 245-6; Bergson on, xvi, 196 Inventions, imagination in, xvi, 59; inspiration and labor in, xi, 226; method of great, xvi, 98; misuse of ancient, v, 15-16, 111; necessity and laziness in, 282; production increased by, 17-18; pure science preliminary to, iv, 44-5; summary of mechanical, v, 376-84; war as stimulus to, 12, 359-60, 375 Inverse Time Relays and Switches, vii, 37, 39-40, 41, 42 Invertases, viii, 357 Invertebrates, xii, 127; age of, iii, 20; largest, xii, 80 Invincible Armada, xiv, 280 Inyo Earthquake, iii, 225 Iodine, a halogen, viii, 18, 84-5, 86; as antiseptic, 333; atomic weight and symbol, 383; classification place, 182, 183; indicator uses, 294; in seaweed, 197; manufacture of, 274; physical state and, chemical properties, 22, 297-8; test of, 290; thyroid secretion of, x, 351 Iodoform, viii, 52, 212 Ion-Counters, i, 142-3, 375 Ionic Reactions, viii, 119-25 Ionization, vi, 133-5, vii, 247, 248, 370; defined, viii, 378; electron theory, 188; in electric precipitation, vii, 348-9; of atmosphere, i, 142-4, 146, 150; of solutions, viii, 119-25, 300-1; origin of theory, 296, 300-1 Ionogens, viii, 122, 125, 378