Indian rubber, dissolved by naphtha for waterproofing, i. 120 Indium, discovery of the metal so called, i. 137 properties of, i. 137 Infusoria, structure, form, and habitat of, ii. 63 abundance of infusoria in the atmosphere, ii. 63, 64 different states of development in one and the same animal, ii. 65 groups of, of opposite characters in the same liquid, ii. 66 the agents in the decomposition of animal matter, ii. 67 minuteness of the ferments, ii. 68 cilia of Infusoria, ii. 68 as organs of locomotion, ii. 69 cell constituting the body of Infusoria, ii. 70 food and organs of digestion of, ii. 70 transparent contractile vesicles, ii. 71 modes of propagation, ii. 74 _et seq._ in a state analogous to hybernation, ii. 78, 79 functions assigned to Infusoria in the economy of nature, ii. 79 Insects, phosphorescence of, i. 167 Intelligence, or the mental principle, of animals, ii. 11, 12 Iodine, i. 18, 21 whence obtained, i. 19 properties of, i. 21, 22 spectrum of, i. 21 atomic weight of, compared with that of hydrogen, i. 100 preparation of, from sea-weeds, i. 128 spectrum analysis of, i. 140, 141 iodine richer at Guernsey than elsewhere, i. 258 Iris germanica, vertical section showing the cellular tissue of, i. 173 Iron heated by percussion or impetus, i. 27 effect of electricity on, i. 32 effect of magnetism of, i. 75, 76, 77 and of heat on the magnetism of, i. 77 feeble affinity of iron for mercury, i. 98 atomic weight of, compared with that of hydrogen, i. 100 spectrum analysis of the rarefied vapour of, i. 142 Isaria, its structure and habitat, i. 282 its destruction of caterpillars, i. 282, 293 Isaria crassa, characters of, i. 283 Isaria farinosa, characters of, i. 283 Isariacei, structure and habitat of, i. 282 Isidæ, structure, habitat, and mode of reproduction of, ii. 125 Isis, structure of the genus, ii. 125 Isomeric substances, i. 104 law of the sequence of three isomeric bodies, and their respective atomic numbers, i. 105 Isomorphism, property of, in determining atomic weights, i. 99 Isomorphous substances, conduct of, under magnetic influence, i. 76 Isopoda, characters of the order, ii. 202 J Jam, greenish, and grey moulds on, i. 285 Jungermanniaceæ, or scale mosses, structure, fertilization, and development of, i. 320-322 Jupiter, the planet, spectrum of, i. 157, 161 constitution of, i. 158 K Katsup made from the morel, i. 292 Kelp, i. 258 former and present uses of, i. 128 Kerona silurus, structure and food of, ii. 69 L Labellum of orchids, i. 401 Lactarii, laticiferous vessels of, i. 263 Lady Fern, herbaceous caudex of, i. 340 structure and fructification of, i. 352, 353 Lagenidæ, characters and habitat of the family, ii. 39