The Reason Why. Robert Kemp Philp

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       Air, is that sent from the lungs light or heavy, 14

       Air, is it a good or bad conductor of heat, 150

       Air, why is a still summer said to be sultry, 171

       Air, why does it feel cooler when in motion, than when still, 175

       LESSON II.

       Air, when is it hot enough to destroy life, 179

       Air, why is it often excessively hot in chalk districts, 219

       Air, is it heated directly by the sun's rays, 221

       Air, why does it ascend the chimney, 240

       Air, why does it fly through the doors and windows towards the fire-place, 241

       Air, what does the motion of it in our rooms illustrate, 242

       Air, why does it become charged with watery vapour, 346

       Air, when is it said to be saturated with vapour, 430

       Air, what proportion of water is air capable of holding in the form of vapour, 431

       Air, what is its weight relative to that of water, 647

       LESSON III.

       Air, which is heavier, dry or vaporised, 697

       Air-pistol (or pop-gun), why does pressure applied to the handle propel the cork, 854

       Air-pistol, why must the handle be drawn out before the cork is placed in, 855

       Air, why does fresh impart a healthy appearance, 915

       Albumen, what is it, 899

       Alkalies, what are they, 36

       Amber, or electrum, what is it, 564

       Animals, how is their greater warmth in winter provided for, 168

       Animal forms, why are there so many, 1029

       Animal furs, why do they become thicker in the winter, 1035

       Animals, why have carnivorous, long pointed teeth, 1038

       LESSON IV.

       Animals with long necks, why have they large throats, 1049

       Animals, why cannot flesh-eaters live upon vegetables, 1071

       Animals, why can ruminating recover the food from their paunches, 1089

       Animals, why can ruminating keep the chewed from the unchewed food in their stomachs, 1090

       Animals, why do the smaller animals breed more abundantly than the larger ones, 1094

       Animals, domestic, why may change of weather be expected when they are restless, 1107

       Animals, plants, and minerals, what are the differences between them, 1140

       Animals that graze, why do they crop the tender blades, but leave the tall grass, 1287

       LESSON V.

       Animals, distribution of, 1326

       Arms and hands, why do we see blue marks upon them, 896

       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,