i. 109

Gravity, specific, of atoms, i. 100

Green dye, obtained from the buckthorn, i. 124

Griffithsia, structure, habitat, and organs of reproduction of, i. 233

Grimmiei, structure of the tribe, i. 329

Grinnelia americana, structure and mode of reproduction of, i. 230, 239

Gromia oviformis, structure of, ii. 26, 27

Gromiæ, structure of the genus, ii. 25-27

Guano, mauve dye obtained from, i. 125

Guernsey, richness of the iodine obtained from the sea-weeds of, i. 258

Guinea worm, structure and mode of reproduction of, ii. 147

Gums, formation of, i. 422

Gymnogramma rutæfolia, remarkable distribution of, i. 336

Gyrophora, structure of the genus, i. 308

H

Hairs of plants, structure of, i. 411

Halichondria panicea, mode of propagation of, ii. 60, 61

Haliomma, structure of, ii. 21

Haliotis splendens, or ear-shell, structure of, ii. 234

Haliseris, structure of, i. 247

Halogens, spectra of the, i. 146

Halurus, structure and mode of propagation of, i. 233

Hare’s-foot fern, i. 351

Hart’s-tongue fern, caudex of, i. 340 structure, habitat, and fructification of, i. 351, 352

Heart, and organs representing it in the lower animals, ii. 4

Heat generated by impetus, i. 27 quantity of heat which would be generated if it were arrested in its orbit, i. 27 probable cause of the heat of the sun, i. 28 effect of the absorption of heat on a body in expansion and contraction, i. 28 specific heat, i. 28 mechanical equivalent of heat, i. 29 causes of the heat which is the motive force of the steam-engine, i. 29 reciprocal action of heat and electricity, i. 31 intensity of the heat of the electric spark, i. 32 proof of the correlation of heat and electricity, i. 33 constancy in the amount and refrangibility of the light and heat absorbed and radiated, i. 34 property of some substances in the transmission of heat, i. 36 substances which transmit radiant heat freely but radiate badly, and vice versâ, i. 37 Tyndall’s experiments on the radiation and absorption 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 absorption of radiant heat by the vapours of volatile liquids, i. 40 Prof. Tyndall’s experiments showing the radiation to be equal to the absorption of radiant heat, i. 46 action of different thicknesses of the same gas or vapour on radiant heat, i. 47 dynamic absorption and radiation, i. 49 dynamical evolution of heat, i. 52 experiment illustrating the change of heat into light, i. 62 polarization of heat and light, i. 68, 69 by reflection and refraction, i. 69 effect of heat on the magnetism of iron, nickel, and cobalt, i. 77 extreme heat and light of electric discharges, i. 84 instances of the correlation of electricity and heat, i. 91 capacity of atoms for heat, i. 100 Mr. Croll’s experiments, i. 101 effects of heat on vegetation, i. 169 large amount of heat evolved by vegetables, i. 265 cause of animal heat, ii. 63

Helix, or snail, tentacles of, ii. 236

Helix aspersa, structure of the tongue of, ii. 237

Helix pomatia, teeth of, ii. 237

Hellebore, white, poisonous alkaloid of, i. 427

Helmet shell, structure of, ii. 234

Helminthosporium Hoffmanni, spores of, i. 285, 286

Helminthosporium nodosum, spores of, i. 286.

Helvella, structure and habitat of, i. 291

Hepaticæ, or liverworts, characters of the, i. 316

Hepialus virescens of New Zealand, Cordyceps Robertsii of the, i. 293

Herschel, Sir W., his discovery of invisible rays of light of high heating power, i. 36

Hewardia, structure of, i. 359

Himanthalia lorea, structure, fructification and habitat of, i. 256

Holly fern, structure of, i. 347

Holothuridæ, or sea-cucumbers, structure and mode of reproduction of,