Arms and legs, why does it require the influence of the will to set them in motion, 917 Arms and legs, why are they made subject to the will, 919 Ascending, what is the cause of bodies, 775 Atmosphere, how is it heated, 232 Atmospheric humidity, why does it sometimes form clouds, at others form dews, fogs, mists, &c., 409 Atmospheric pressure, how high will it raise water, 652 Atmosphere, what is the, 639 Atmosphere, to what height does it extend, 639 Atmosphere, what is the amount of its pressure, 641 Atmosphere, what is the proportion of watery vapour in the, 642 Atmosphere, why are its upper regions intensely cold, 444 Atmosphere, what is the greatest height ever reached in the, 648 LESSON VI. Atmospheric pressure, what is the total amount on the earth's surface, 644 Atmosphere, what is the amount of its pressure upon the human body, 645 Atmosphere, why do we not feel its pressure, 646 Atmosphere, to what extent may its pressure vary, 702 Attractive agent, what is an, 76 Attraction, what is it, 772 Attraction, how many kinds are there, 773 Aurora Borealis, what is the cause of, 590 Bananas or plantains, where are they cultivated, 1220 Bark Peruvian, where is it produced, 1228 Barometer, what is a, 691 Barometer, why does it indicate the pressure of the atmosphere, 692 Barometer, why is it also called a "weather-glass", 693 Barometers, why are they constructed with circular dials, 694 Barometer, why does the hand change its position when the mercury rises or falls, 695 Barometer, why does tapping its face cause the hand to move, 696 Barometer, why does its fall denote the approach of rain, 699 LESSON VII. Barometer, why does its rise denote the approach of fine weather, 700 Barometer, how does it enable us to calculate the height of the mountains, 701 Barometer, when does it stand highest, 704 Barometer, when does it stand lowest, 705 Barometer, what effect has heat upon the, 707 Barometer, what effect has cold upon the, 708 Balloons, why do they ascend in air, 830 Balloons, why do air balloons become inflated, 831 Balloons, why do they sometimes burst when they reach a high altitude, 832 Bat and ball, what principles of natural philosophy are illustrated in the play, 867 Bats, why have they hooked claws in their wings, 1079 Bats, why do they fly by night, 1080 LESSON VIII. Bats, why do they sleep during winter, 1081 Beds, why should they be raised two feet from the ground, 15 Bed-room windows, why are they sometimes covered with ice crystals, 344 Beer, why will it not run out of a cask until a hole is made at the top, 660 Beer, why does it get flat, 805 Bees, why have they stings, 1101 Bees, why may we expect fine weather when bees wander far from their hives, 1114 Beetles, why are they called "coleoptera", 1319