Hydrotherapy, x, 383 Hydroxides, viii, 93, 377; bases as, 115; commercial preparation, of, 276; metals found as, 130, 131, 198 Hydroxyl Derivatives, viii, 210, 212-14, 215, 218 Hydroxyl Group, viii, 377; in bases, 115; boiling point raised by, 299; negative ionization, 122; solubility, 112 Hyenas, xii, 351-2 Hygiene, among early Jews, x, 15; daily applications, xvi, 15; instruction in, remarks on, x, 282-5; mental, xi, 368-82; personal, disease prevention through, x, 302-17 Hygrometers, i, 78-9, 375; invention, 68-9 Hygroscope, i, 375 Hymenoptera, xii, 124-6 Hyperfunction, defined, x, 348 Hyperopia, ix, 113 Hypersensibility, x, 212-15 Hypnotism, xi, 311-22; use in medicine, xvi, 185-6 Hypo, of photography, viii, 140, 172 Hypofunction, meaning, x, 348 Hypophysis, (gland), x, 347, 352 Hysteresis, vi, 192, 213-14; in motors, 225; in transformers, 316 Hysteria, x, 360-3 Ianthena, xii, 19 Iatrochemical School, x, 69-70 Iatrophysical School, x, 69, 70-2 Iberian Racial Group, xvi, 49 Ibervillea, xiii, 106-7 Ibexes, xii, 325-6 Ibises, xii, 254, 255-6 Ibn-Yunos (Jounis), ii, 38, 210 Ice, ancient use in refrigeration, v, 349; artificial, iv, 188, v, 349-50, 354-8, viii, 69-70; color of, 40; comparative heat, v, 345; cooling by, iv, 178, v, 346; density of, iv, 149; disadvantages in refrigeration, vii, 230; erosion by, (see Glaciers); expansion of water in, viii, 38; heat conductivity, iv, 179; keeping of, v, 346, 349; melting point and requirements, iv, 152, 161, 162; melting point, pressure effects on, 163, 164, 164-6; mixture with salt, temperature resulting, 175; mixture with water, temperatures obtained, 160-1, v, 353-4; regelation of, iv, 164-6; specific gravity, iii, 321; specific heat of, iv, 155; temperatures at different pressures, v, 345; transformation of snow into, iii, 59-60; warming of, iv, 151-2 Ice Age, Great Quaternary, iii, 236-48, xv, 72-6; antiquity of, xiii, 209, 322; lakes formed, iii, 143-51; man during, 302, 303, xv, 102; Mississippi Valley remains, iii, 35; moraines left by, 67-8; sea level in, 83; subsidence of land in, 80; Yosemite Valley formed in, 48, 64 (see also Glacial Epoch) Ice Age, Permian, iii, 203-4 Ice Ages, theories of, iii, 247-8; volcanic dust theory, i, 58 Icebergs, submergence of, iv, 149 Ice Breakers, gyroscopes on, v, 342 Ice Caps, iii, 60, 61; of Greenland and Antarctica, xiv, 55 Ice Clouds, i, 92-3, 103; halos produced by, 177 Ice Dam Lakes, iii, 143-4, xiv, 201 Ice Crystals, i, 115-16; halos from, 177, 178, 182-3 Ice Fogs, i, 95-6 Ice Houses, insulation method in, iv, 178