Sound, why can people in the arctic regions converse when more than a mile apart, 735 Sounds, why do savages lay their heads upon the earth to catch sounds, 736 Sounds, why can church clocks be heard striking more plainly at some times than at others, 737 Sound, why may the scratching of a pin at one end of a long pole be heard at the opposite extremity, 738 Sound, why is the hearing of deaf persons assisted by ear-trumpets, 739 Sounding-boards, why are they used to improve the hearing of congregations, 740 Sounds, why, when we are walking under arches or tunnels, do our voices appear louder, 747 Spark, what causes it when a horse's shoe strikes against a stone, 340 Specific gravity, what is it, 789 Spiders, why have they the power of spinning webs, 1082 Spiders, why may fine weather be expected when they build their webs, 1108 LESSON LXVIII. Spiders, why may wet weather be expected when they hide, 1109 Spiders, why may wet weather be expected when they break off their webs and remove them, 1113 Spider, why, if the webs of the gossamer fly about in autumn, may east winds be expected, 1124 Spiders, gossamer, why can they float through the air, 1125 Spinal cord, what is the, 952 Spinal cord, why is it placed in the back-bone, 953 Spinal-cord, how do the branches pass out from it, 954 Spontaneous combustion, what substances are liable to it, 317 Spontaneous combustion, has it ever occurred in living bodies, 319 Spontaneous combustion, why does it occur in the case of the drunkard, 320 Spoon-bill, why has it a long expanded bill, lined with sharp, muscular points, 1045 Spoon-bill, why has it long legs, 1046 Squint, why do some people, 967 Starch, what is it, 1202 Star-lit nights, why are they usually colder than cloudy nights, 350 Stars, why do they twinkle, 484 LESSON LXIX. Stars, why does their twinkling foretell bad weather, 485 Steam, why does it issue from the spout of a kettle, 750 Storms, what is the cause of, 676 Storms, why do the most violent occur in and near the tropics, 677 Straw, why is it frequently used for manure, 1264 "Sucker," why does it raise a stone, 860 Sugar, what is it, 1197 Sugar-cane, where is it cultivated, 1226 Sun, what is its distance from the earth, 452 Sun, what is the, 455 Sun, from what does its luminosity arise, 456 Sun and moon, why do they appear smaller when near the meridian, than when near the horizon, 525 Sun, why do we see it before sunrise, and after sunset, 482 Sun, what is the magnitude of the, 787 Suppers, why do they cause dreams, 1021 Swallows, why may wet weather be expected when they fly low, 1104 Syringe, why does pressing in the handle force out a jet of water, 856 Syringe, why will not the water run out, unless the handle is pressed in, 857 LESSON LXX.