Clothes, Clothing, body heat regulation by, v, 348, ix, 308-9, 311-12; civilization in relation to, ix, 308-9; colds in relation to, x, 240, 253; "habit" in, xi, 247; hygiene of, x, 306-10; infants, ix, 351-2; origin and purposes of, x, 306, xv, 252-5; primitive, v, 14, xv, 256-7; touch sensations of, ix, 92; warmth dependent on air insulation, iv, 178; working, xi, 279, 362 Clothes-driers, centrifugal, iv, 73 Clotting of Blood, ix, 180, 189 Cloud Banners, i, 104-5, 369 Cloudberry, spread, xiii, 342 Cloudbursts, i, 109, 110, 111, 369, vii, 218; destruction effected by, xiv, 41 Cloud Caps, i, 104-5, 369 Cloudiness, measurement, i, 85 Clouds, i, 90-105; aviation in, 300-2; Brocken specters in, 185; earth heat retention by, iv, 183, 184; electrical discharges, vii, 18, 207-10, 213; electrification, i, 150, 151, vii, 206, 207, 217; electrification of earth by, iv, 269, 270; formation and kinds, i, 90-105; formation, cause of rapid, viii, 304; formed by forest fires, i, 333; heights, 17-18, 103-4; light diffraction by, 183, 185; noctilucent, 17-18, 58, 377; none in stratosphere, 20; observation at weather stations, 85-6; paintings of, 105; pictures, where obtainable, 103; self-luminous, 149; snow and rain without, 119; thunderstorm, vii, 217 Clouet, steel experiment, xvi, 174 Cloven-footed Animals, xii, 310 Clover, fertilization, xiii, 138; nitrogen fixation, by, viii, 74, xiv, 66; sleeping of leaves, xiii, 113 Clover Seed, method of gathering, v, 240 Cloves, Clove Trees, xiii, 262-3 Club Mosses, fixity and variation, xiii, 326, 327; history, 305-6, 307, 314, 317, 323; number of species, 323; present and former species, iii, 254, xiii, 306, 308 Clutches, automobile, vii, 143; electromagnetic, vi, 104 Cnidus, School, of, x, 22-3 Coagulation, by cooking, viii, 368; of colloids, 315; of proteins, 352 Coal, "Blue," v, 174; carbon dioxide from, amount, i, 13; conversion to electric power, vi, 216; deposits in mountains, xiv, 237; deposits in U. S., iii, 345-8; excavating by machine, v, 262; formation, iii, 198-201, 253-4, 343-5, viii, 44-5, xiii, 10, 68, 311-13; handling in power plants, v, 353-4, 357; heat measurement, viii, 360-1; heat value, iv, 193; importance, iii, 343, 345-8; kinds, 344; not a mineral, 307; Permian deposits, 204; specific gravity of, iv, 112; supply, use, and waste, iii, 346, v, 171-2, vi, 352, viii, 283; water power and, xiv, 191; "white," v, 76; work value, how estimated, iv, 189-90, 193-4 Coal Age, iii, 202; insects of 279; landscape of, 272 (Pl. 15); length and antiquity, xiii, 314; plants, iii, 253-4, xiii, 307-11, 315-16 (see also Pennsylvanian Period) Coal Dust, as engine fuel, v, 156, 212; explosions, i, 63