Gases, absorption and radiation of radiant heat by gases and vapours, i. 38 relation between the density of the gas and the quantity of heat extinguished or absorbed, i. 40 experiments on coloured gases, i. 40 table showing the absorption of various gases at a common pressure, or tension of one atmosphere, i. 41 table of absorption for one inch of tension, i. 4 causes of the difference between the absorptive power of compound and simple gases and vapours, i. 42 radiation equal to absorption, i. 46 action of different thicknesses of the same gas or vapour on radiant heat, i. 47 dynamic absorption and radiation, i. 49 great opacity of a gas to radiations from the same gas, i. 52 the specific heat of compound gases generally greater than that of their component elements, i. 101 law of equivalency in weight of, i. 102 diffusion of, i. 111 Prof. Graham’s experiments, i. 112 effusion of, 109, 110, 113 Prof. Graham’s experiments, i. 113 atmolysis, or method of analysing gases, i. 111, 112, 114 internal movement of molecules of matter in a gaseous state, i. 113 coal gas, i. 117 spectrum analysis of, i. 139 oxygen, i. 139 hydrogen, i. 139 nitrogen, i. 140 chlorine, i. 140 bromine, i. 140 iodine, i. 140 superposed spectra of rarefied compound gases, i. 141 researches of M.M. Bunsen and Kirchhoff, i. 141 spectra of the rarefied vapours of:— sodium, i. 141 iron, i. 142 calcium, i. 142 strontium, i. 142 lithium, i. 142 barium, i. 142 magnesium, i. 142 effect of high temperature on various spectra, i. 142, 143 effects of pressure on various spectra, i. 145 Gasteromycetes, characters of the family, i. 267 Gastropoda, structure of the shells of, ii. 234 structure of the animal, ii. 235 tongue of the, ii. 239 Gelidiaceæ, structure and mode of propagation of, i. 238 Gelidium corneum, structure and mode of propagation of, i. 238 form of, i. 243 Gems, crystals of, formed artificially by electricity, i. 74 Geranium, amount of radiant heat absorbed by the perfume of, i. 44 Glass, a non-conductor of electricity, i. 32 property of, in regard to the transmission of light, i. 36 impervious to chemical solar rays, i. 63 Gleichenineæ, sporangia of, i. 34 structure and habitat of, i. 344, 360 Globigerina bulloïdes, form of, ii. 28 Globigerina, structure of the genus, ii. 40, 41 Globigerinæ, abundance of at vast depths in the ocean, ii. 49-51 Globigerinidæ, characters of the family of, ii. 40 Glycerine, chemical combination forming, i. 97 Glyphidei, characters of the order, i. 309 Glucinum, i. 4 Gold, colour of, in reflected and in absorbed light, i. 35, 36 crystals of, formed artificially by electricity, i. 74 Gonidia, propagation of diatoms by, i. 202, 204 of lichens, i. 300 Goniometer, i. 38