Nerve-force of animals, ii. 4, 6 chemical powers generated by, ii. 6 Nerves of animals, structure and functions of, ii. 5 electric currents in the, ii. 7 structure and functions of the brain and spinal cord, ii. 8 the nervous systems of the higher and lower animals, ii. 9-11 Nervous system of animals, ii. 5 Nickel, i. 4, 5 crystals of, formed artificially by electricity, i. 74 effect of heat on the magnetism of, i. 77 atomic weight of, compared with that of hydrogen, i. 100 Nidulariacei, characters of the order of, i. 272, 273 structure and mode of reproduction of, i. 273 habitat of, i. 273 Nitella flexilis, structure and mode of reproduction of, i. 312 Nitophyllum, structure and fronds of, i. 238, 239 Nitric acid, combination forming, i. 95 Nitrogen gas, i. 12 combination of nitrogen with chlorine, i. 20 absorptive power of, i. 39, 41 fulminates compounds of, i. 92 number of combinations of, with oxygen, i. 95 atomic weight of, compared with that of hydrogen, i. 100 one of the illuminants in coal gas, i. 118 spectrum analysis of, i. 140, 145 in high temperature, i. 144 binoxide of, combination forming, i. 95 chloride of, catalysis of, i. 91 iodide of, catalysis of, i. 91 protoxide of, or laughing gas, combination forming, i. 95 Nitrous oxide, absorption of, radiant heat by, i. 41, 43 combination forming, i. 95 Noctiluca miliaris, structure and mode of propagation of, ii. 73, 74 Noctiluci, their food, i. 205 Nodosaria, characters of the genus, ii. 39 Nodosaria rugosa, shell of, ii. 28 structure of, ii. 39 Nodosaria spinicosta, form of, ii. 28 structure of, ii. 39 Nostoc commune, wide distribution of, i. 212 Nostochineæ, structure and habitat of, i. 211 reproduction of, i. 212 wide distribution of, i. 212 Nullipores, structure and habitat of, i. 142 Nummulites, structure of the, ii. 44-46 circumstances favouring their existence in the Tertiary period, ii. 53 O Ocean, force exerted in the creation of the, i. 31 Octoblepharum albidum, leaves of, i. 330 Octopods, structure of, ii. 245 Octopus vulgaris, or poulpe, structure of, ii. 245-247 Odonthalia, structure of, i. 242 Œdogonium capillare, reproduction of, i. 216 Oïdium, structure and habitat of, i. 290 Oïdium Tuckeri, or vine mildew, fungus producing, i. 295 Oils, dead, manufacture of, i. 120 essential, chemical combinations forming, i. 97 vegetable, i. 422 formation of fixed and essential, artificially, i. 424 Oleandra, characters of the genus, i. 347 Oleandra neriiformis, structure of, i. 347 Olefiant gas, absorptive power of, i. 39, 40, 41 amount of absorptive power, i. 41 great absorption of, i. 47 formation of, i. 97 amount of carbon in, i. 105 one of the illuminants in coal gas, i. 118 chemical composition of, i. 128 Olefiant oil, i. 104 Olive oil, i. 422