Langley, Prof. S. P., aeronautical work, iv, 43-4, v, 231, 382; astronomical work, ii, 144, 169, 213, 223-4; measurement of heat of moonbeams, iv, 301; on the camera, ii, 221; spectrobolometer, 128, 186 Language, xv, 141-2; association principle in, ix, 151-2; clearness of, xi, 379; importance of, ix, 152-3, xv, 68, 142, 143, 145-6; inadequacy in feelings, 143; making of, xv, 140-63; psychological importance, xi, 200, 224, 225; race and, xv, 159; thought and, 143-5, 146 Languages, Aryan and Semitic, xv, 161-3; changes in, 154-6; difficulty of learning new, xi, 201; foreign, advantages of learning, xv, 146; foreign, sound of, xi, 103; relationships and common origin, xv, 159-63 Lantern Gears, v, 27-8 Lanterns, enlarging and projecting, iv, 341-2 Lanthanum, symbol and atomic weight, viii, 383 Lap, cotton, v, 272; wood pulp, 293 Lapilli, volcanic, xiv, 323-4 Laplace, asteroid hypothesis, ii, 258; mathematical work, xvi, 105, 125; nebular hypothesis, ii, 369-72, 374-5, 378, 380 (see Nebular Hypothesis); on sound velocity, iv, 198-9; other work, ii, 15, 72, 73, 74, 87 La Plata River, connections of tributaries, xiv, 187; fish of, xii, 160 Lapwings, xii, 262, 263 Lard, animal fat, viii, 246; calories in, ix, 299; vitamins absent in, x, 261, 262 Larks, xii, 268 Larmor, light theory, xvi, 137-8; magnetism theory, 193 Larrey, Jean, x, 130 Larvæ, affected by light, x, 253; used in nest repairing, v, 10; "rains," i, 356-7 Larynx, aphonia of, x, 29-30; infection center, 220 La Salle, xiv, 192 La Soufriere, eruption of, xiv, 28, 338 Lassen Peak, iii, 103, 226, 176 (Pl. 10); activity of, xiv, 315 Latent Heat, iv, 152-3, v, 169, 353-4, viii, 37-8, 378; of fusion, iv, 152, 160, 161, 162; of vaporization, 173-4, 187 Latent Period, of pain, xi, 121; of sound, 105; of touch, 111 Lateral Line, of fishes, xii, 137 Lateral Moraines, lakes formed by, xiv, 202 Lathes, development of, v, 42-6, 47, 52-3, 376, 378, 380, 383 Latin, in animal classification, xii, 29; in cloud classification, i, 98; in plant classification, xiii, 169; languages derived from, xv, 160, 162 Latitude, barometric corrections for, iv, 122-3; color of skin and, xv, 36-7; of ships, how determined, v, 65; plant distribution determined by, xiv, 364-6; temperature and, 344-5; weight of bodies, affected by, iv, 101-2 Laudanum, discovery of uses, xvi, 109; first prepared by Paracelsus, x, 50 Laughing Gas, viii, 71, x, 123-4; critical temperature and pressure, iv, 172 Laughter, emotional control of, ix, 164; in infants, 349; kinetic theory, xi, 355-7; psychology of, 350-7 Laurel Family, xiii, 196-7 Laurel-leaf Points, xv, 109 Laurel Magnolia, xiii, 318 (fig.) Laurent, chemist, xvi, 162, 163