Seeds of two lobes, i. 177 of one lobe, i. 177 of plants, i. 381, 382, 383, 404 Selaginella, structure and habitat of, i. 374 Selenium, atomic weight of, i. 105 its properties analogous with those of sulphur and tellurium, i. 105 Sepedonium mycophilum, spores of, i. 286 Sepia, or cuttle fish, structure of, ii. 245, 246, 247 Serpentine marble of Tyree and of Connemara, composition of, ii. 56 Serpula, structure of, ii. 155 Sertularia cupressina, structure of, ii. 87 Sertulariidæ, characters of the family of, ii. 90, 91 modes of propagation of, ii. 91 Shells of mollusks, ii. 234 Shrimps, opossum, ii. 199, 200 Sigillaria, structure of the fossil, i. 375 Silex, quantity of, in the Equisetaceæ, i. 369 in the grasses, i. 386 Silica, abundance of, i. 17 in the stalks and leaves of the grasses, i. 386 effect of electricity on, i. 32 Silicon, i. 17 combined with oxygen gas forms rock-crystal, i. 17 three different states in which it exists, i. 18 analogy between silicon and carbon, i. 18 Professor Graham’s limpid solution of, i. 18 Silk, dyes for, i. 125 mode of preparing it if it is to be moiré, i. 125 advantages of the climate of Lyons in the manufacture of, i. 126 Silk-worm, a fungus parasite of the, i. 274 Silver, affinity of, for oxygen, i. 5 conduction of heat and radiation, i. 5 iodine found in combination with, i. 19 crystals of, formed artificially by electricity, i. 74 transmissive power of, of electricity, i. 90 Sipunculidæ, structure and mode of reproduction of, ii. 186, 187 Sky, probable cause of the blue colour of the, i. 58 Slate, polishing, of Bilin, of what it consists, i. 206 Smoke, i. 14 Smut of wheat, i. 281 Snails, structure of, ii. 235-237 Soda, chlorate of, singular property of, in crystallization, i. 75 Soda, oxalate of, formation of, i. 117 Soda, silicate of, i. 110 Prof. Graham’s dialysis of, i. 110 Soda, former and present mode of procuring, i. 128 yellow coloured light produced by the combustion of, i. 132 abundance in the Algæ, i. 414 Sodium, i. 3 atomic weight of, compared with that of hydrogen, i. 100 spectrum analysis of the rarefied vapour of, i. 141 chloride of, spectrum of, i. 146 reversion of the coloured lines of sodium burning in air, i. 150