Smoke, what is it, 289 LESSON LXIV. Smoke, why do fresh coals increase the quantity of, 291 Smoke, why does it issue in folds and curls, 632 Smoke, why does it ascend in mild and fine weather, 689 Snails, why can they move in an inverted position, 666 Snails, where do they obtain their shells, 1306 Snails, why do their shells grow, 1307 Snails, why are their shells spiral, 1308 Snails, why have they four tentacula attached to their heads, 1309 Snails, why are they able to move without feet, 1310 Snails, why do we see none in the winter time, 1311 Snails, why can they live in sealed shells, 1312 Sneeze, why do we, 1024 Snipes and woodcocks, why have they long, tapering bills, 1042 Snore, why do we, 1028 Snow, why does it keep the earth warm, 160 Snow, why is it a good non-conductor of heat, 162 Snow, what is it, 440 Snow, why is it white, 441 LESSON LXV. Snow, why is it warm, though white garments are cool, 442 Snow, why is it always on the tops of high mountains, 443 Snow-line, what is meant by the, 445 Snow, what is red, 446 Soda-water, why does it effervesce, 802 Soils, why are clayey unfavourable to vegetation, 1160 Soils, why are sandy unfavourable to vegetation, 1162 Soils, why are chalk unfavourable to vegetation, 1162 Soils, why are mixed favourable to vegetation, 1163 Soils, why do farmers manure their land, 1165 Soot, why should it be prevented from accumulating at the bottom and sides of saucepans, 205 Soot, what is it, 290 Sound, what is it, 716 Sounds, what causes the air to produce, 717 Sounds, how do we know that they are produced by vibrations, 718 Sounds, how do we know that without air there would be none, 719 Sounds, how are the vibrations of sonorous bodies imparted to the air, 720 LESSON LXVI. Sounds, how rapidly do the vibrations of travel, 721 Sounds, do all sounds travel at the same rate, 722 Sounds, why are bells and glasses stopped from ringing by touching them with the finger, 723 Sounds, why does a cracked bell give discordant, 724 Sounds, why do we see the flash of a gun before we hear the report, 725 Sound, why does the marching of long ranks of soldiers appear to be irregular, 726 Sounds, what are the numbers of vibrations that produce various, 727 Sounds, why does the length of a wire or string influence the sounds it produces, 728 Sound, why does the tension of a wire or string affect its vibrations, 729 Sound, why are some notes low and solemn, and others high and quick, 730 Sound, why can our voices be heard at a greater distance when we speak through tubes, 731 Sound, is air a good conductor, 732 Sounds, why can we hear them at a greater distance on water than on land, 733 LESSON LXVII. Sound, why do sea-shells give a murmuring noise when held to the ear, 734