Distance, method of measuring, ii, 197-8; perception of, ix, 118-19, 120, xi, 165-9, 173-89; units of, iv, 283 Distance Senses, ix, 86, 96-121; choice in relation to, 121, 140; connections with brain, 142 Distillation, alcoholic, viii, 249-50; apparatus, 213 (fig.); fractional, i, 32, iv, 168 Distillation of coal, vii, 252-3 Distractions, fatigue from, xi, 277 Distress Signals, vii, 284 Ditch Grass, fertilization, xiii, 151-2 Ditching Machines, v, 216, 253, 254-5 Divers, compression and decompression, v, 120-1; pressure on, i, 329 Diversion, need of, in brain work, ix, 138 Diving Bells, v, 115-16, 121 Divining Rods, iii, 123-4 Division of Labor, first form of, xv, 279; in plants, xiii, 61-2 Divorce, xv, 290-1 Dizziness, from over-ventilation of lungs, ix, 266-7; sensation of, xi, 64 "Doctor" Winds, i, 131, 371 Dodder, plant, xiii, 100, 101 (fig.) Dodo, xii, 265 Dog Family, xii, 338-46 Dogfish, xii, 143, 146; eggs of, 140; name changed, i, 224 Dogs, xii, 344-6; baboons and, 380; canine teeth of, 333; cat's hatred for, origin of, 355; domestication of, xii, 345-6, xv, 197, 198; embryological resemblances, 54; employment in hunting, 223; expression of emotions by, 64; heat-loss regulation by, ix, 307-8; hyenas and, xii, 351; imitation in, xv, 66; language methods of, 141; mode of attack, xii, 354; reasoning power in, xv, 68; sense of smell in, ix, 97, 117; wild, xii, 344-5; zoölogical interest, xvi, 16 Dogwood, xiii, 271; flowering, 45; index plant, i, 255 Doldrums, i, 127, 129, 136, 371, xiv, 348, 349 Dollond, telescopes, ii, 100, 103, xvi, 125 Dolomite, viii, 149; in refractories, vii, 307 Dolphins, xii, 297 Domestic Animals, development of, xii, 345-6, xv, 197-8 Dominants, in crosses, ix, 334, 335, x, 231, 233 Donati's Comet, ii, 275, 277, 280-1 Donkeys, xii, 308 Door-checks, pneumatic, v, 134 Doppler's Principle, ii, 119, iv, 209-10; astronomical applications, ii, 123, 129, 133, 363 Dormice, xii, 291 Double Decomposition, viii, 104-5, 375 Double Images, xi, 175-81 Double Stars, ii, 122-4, 334-5; colors, 296; connections, 340; proportion of, 320; telescopes required for, 97-8; theory of origin, 377 (see also Binary Stars) Doubt, reasoning and, xi, 239-40; retardization of impulses in, 20 Douglas Fir, forests, xiii, 340, xiv, 374 Dover, England, breakwater, xiv, 301 Doves, mating of, xv, 276; plumage of neck, xii, 245 (see also pigeons) Down, character of, xii, 244; warmth of, x, 309 Downs of England, dew ponds, i, 352-3 Dowry System, xv, 285 Dragon Flies, xii, 105-6; ancient, iii, 279, xiii, 308; eyes of, xii, 102 Dragon Tree, xiii, 183-4