Niagara River, drop in, vi, 368; due to Ice Age, iii, 243; first impressiveness, vii, 202; gorge of, xiv, 51 "Niagaras," Electric, i, 342, 343-4 Nickel, viii, 126-7, 154; affinity strength, 128; atomic weight and symbol, 383; classification place, 178, 183; electrical conductivity, iv, 283, vi, 77; fusibility, viii, 384; in earth's interior, xiv, 11; in steel alloys, xiv, 238; magnetic susceptibility, iv, 251; melting point and requirements, iv, 162; ores of, viii, 198, 270; positiveness, vi, 59; source, xiv, 238; test for, viii, 287, 289 Nickel-Iron Batteries, vi, 149-51 Nickel Plating, vii, 314, 316-17 Nicol's Prism, iv, 354 Nieve Penitente, i, 117, 377 Niger River, furrow of, xiv, 287; Park's explorations, xvi, 123 Night, cooling of earth at, i, 121; "falling" of, xi, 173; plant conduct at, xiii, 88-9, 113, 114, 126 Night Adders, xii, 232 Night-Blooming Plants, fertilization, xiii, 152-3 Nightingales, xii, 269 Nightjar Family, xii, 267 Nightshade, xiii, 250 Nile River, aerial photography, i, 46-7; ancient harnessing, v, 19; annual overflow of, xiv, 53, 70-1; bichir of, xii, 151; Bruce's exploration, xvi, 123; connections with Congo system, xiv, 186-7; course of, 120, 155; crocodiles of, xii, 199; dominance of Egyptian life, ii, 26; Egypt gift of, xiv, 71; gobar of upper region, i, 96; hippopotamus of, xii, 310; length and volume, xiv, 189; rafts used on, xv, 264-5; veneration in Egypt, v, 18; water supply of, xiv, 182-3 Nile Valley, antiquity of man in, xv, 84; fertility, xiv, 71; sand-abrasion of granite bluffs, 77 Nimbus Clouds, i, 98, 101, 103, 377 Ninevah, burying of, iii, 75 Ninevah Eclipse, ii, 209 Nipissing Lakes, iii, 150, 151 Nirvana, xv, 334 Niton, viii, 185; atomic weight and symbol, 383; in atmosphere, i, 11, 12 Nitrate Group, viii, 93; in explosives, 71 Nitrates, cellulose forms, viii, 254-5; Chilian deposits, i, 35; viii, 64, 197, xiv, 66; commercial production, i, 35-6, vii, 322, 323-4, viii, 74; formation in soil, i, 35, viii, 340, 345, xiii, 98; metal occurrence in, viii, 130; test, 290; uses, 72; arterial spasm, x, 381 (see also Potassium, Silver, Sodium Nitrates) Nitric Acid, character and uses, viii, 71-3, 115, 116; in atmosphere, i, 13; production of, 36, vii, 322, 323-4, viii, 74, 137, 275; solubility, 112; strength, 115 Nitro, defined, viii, 379 Nitrocellulose, viii, 255, 256, 261 Nitro Compounds, viii, 237; in explosives, 71