Fruits and vegetables, why do they ripen in succession, 1284 Furs, why are they worn in winter, 166 Galvanism, what is it, 635 Gas, what kind lights our streets, 56 Gas, why does it expand in thin air, 833 Geology, what has been its influence upon botanical geography, 1249 Giraffes, why have they small heads, 1322 Giraffes, why have they long necks, 1323 Giraffes, why have they long and flexible tongues, 1324 LESSON XXXIV. Giraffes, why are their nostrils narrow and small, and studded with hairs, 1325 Glass upon a lamp, why does it increase the brilliancy of the light, 266 Glass, why is it transparent, 506 Glass, does transparent reflect any light, 507 Glow-worms, why have they brushes attached to their tails, 1127 Glow-worms, why do they emit light, 1128 Gnats, why are their larvæ and pupæ found in water, 1314 Gnats, why may fine weather be expected if they fly in large numbers, 1110 Grasses, why are they so widely diffused throughout nature, 1166 Grasshoppers, why are they comparatively active in their pupa stages, 1293 Gravitation, what is the attraction of, 774 Guano, why is it a good manure, 1262 Gum resins, what are they, 1255 Gums, vegetable, what are they, 1254 Gunpowder, why does it explode, 808 Gutta-percha, whence is it obtained, 1254 LESSON XXXV. Hail, what is it, 448 Hail, why is it supposed that the electrical state of the clouds affects the formation of hail, 449 Hail-storms, why do they usually occur by day, 450 Hairs, why do they grow across the passages of the nostrils, 993 Halo, what is a, 494 Halo, what is the cause of a, 495 Haloes, why are they sometimes large, and at other times small, 496 Haloes, why do they foretell wet weather, 497 Hands, why when we hold them against the candle do we perceive a crimson colour, 906 Hay-stacks, why do they sometimes take fire spontaneously, 316 Head, why is it set upon the neck, 928 Hearing, why do people engaged in battle frequently lose their, 991 Hearing, death of a dog through noise, 991 Heart, why does it beat without any effort of the will, 948 Heart, why is it placed in the chest of the body, 932 Heart and lungs, why are they enclosed by ribs, 933 Heart, why are its motions made independent of the will, 950 LESSON XXXVI. Heat, what is it, 71 Heat, what are the properties of, 86 Heat, what is animal, 87 Heat, what is latent, 88 Heat, what is a conductor of, 108 Heat, what is a non-conductor of, 109 Heat, how is it transmitted from one body to another, 119 Heat, what is the radiation of, 114 Heat, what is the reflection of, 115 Heat, what is the absorption of,116 Heat, what is the convection of, 117 Heat, what is the cause of the sensation, 134 Heat, what becomes of that which the hearth-stone receives, 136 Heat, how long does a substance feel hot or cold to the touch, 139