Chapter I: Preface (1)

We are all children of one Father, whose Works it should be our delight to study. As the intelligent child, standing by his parent's knee, asks explanations alike of the most simple phenomena, and of the most profound problems; so should man, turning to his Creator, continually ask for knowledge. Not because the profession of letters has, in these days, become a fashion, and that the man of general proficiency can best work out his success in worldly pursuits; but because knowledge is a treasure which gladdens the heart, dignifies the mind, and ennobles the soul.

The occupation of the mind, by the pursuit of knowledge, is of itself a good, since it diverts from evil, and by elevating and refining the mind, and strengthening the judgment, it fortifies us for the hour of temptation, and surrounds us with barriers which the powers of sin cannot successfully assail.

It is not contended that the mere acquisition of knowledge will either ensure a good moral nature, or convey religious truth. But both religion and morals will find in the diffusion of knowledge a ground work upon which their loftier temples may discover an acceptable foundation.

The man who comprehends the order of Nature, and the immutability of Divine law, must of necessity bring himself in some degree into accordance with that order, and under submission to the law: hence the _tendency_ of knowledge will always be found to harmonise the fragment with the mass, and to subvert the evil to the good.

The troubles of the world have arisen from the want of knowledge, not from the possession of it. And in proportion as man becomes an intelligent and reflective being, he will be a better creature in all the relations of life. If these benefits, vast and incalculable as they are, be the real tendency and result of knowledge, why is ignorance allowed to remain, and why is the world still distracted by error?

It is because the moral and intellectual qualities of man are, like all creations and gifts of God, the subjects of development, whose law is progression.

We can aid human improvement, but we cannot unduly hasten it. Whenever man has sprung too rapidly to a conclusion, he has alighted upon error, and has had to retrace his steps.

The greatest philosophers have been those who have clung to the demonstrative sciences, and have held that a simple truth well ascertained, is greater than the grandest theory founded upon questionable premises. Newton made more scientific revelations to mankind than any other philosopher; and his discoveries have borne the searching test of time, because he snatched at nothing, leaped over no chasm to establish a favourite dogma; but, by the slowest steps, and by regarding the merest trifles, as well as the highest phenomena, he learnt to read Nature correctly. He discovered that her atoms were letters, her blades of grass were words, her phenomena were sentences, and her complete volume a grand poem, teaching on every page the wisdom and the power of an Almighty Creator.

When he observed an apple fall to the ground, he asked the "Reason Why;" and in answer to that enquiry, there came one of the grandest discoveries that has ever been recorded upon the book of science. With that discovery a flood of light burst upon the human mind, illustrating in a far higher degree than had ever previously been conceived, the vastness of Almighty Power.

Why should not each of us enquire the "Reason Why" regarding everything that we observe? Why should we mentally _grope_ about, when we may _see_ our way? When addressed in a foreign tongue, we hear a number of articulated sounds, to which we can attach no meaning; they convey nothing to the mind, make no impression upon the in-dwelling soul. When those sounds are interpreted to us, in a language that we can understand, they impart impressions of joy, hope, surprise, or sorrow, because the words convey to us _a meaning_. In like manner, if we fail to understand Nature, its beauties, its teachings are lost. Everything speaks to us, but we do not understand the voices. They come murmuring from the brook, trilling from the bird, or pealing from the thunder; but though they reach the ear of the body, they do not impress the listening spirit.

Every flower, every ray of light, every drop of dew, each flake of snow, the curling smoke, the lowering cloud, the bright sun, the pale moon, the twinkling stars, speak to us in eloquent language of the great Hand that made them. But millions lose the grand lesson which Nature teaches, because they can attach no meaning to what they see or hear.

"THE REASON WHY" is offered as an interpreter of many of Nature's utterances. Great care has been taken that these interpretations may be consistent with the latest knowledge, obtained from the highest sources. If the author finds that his work if accepted for the good of those who seek not only to know, but to _understand_, he will make it his constant care to read the Book of Nature, and to add to the pages of this volume whatever interpretations the progress of enquiry and discovery may demand and supply.

INDEX, AND INDEX LESSONS.

[Pointing hand symbol] _The numbers refer to the Questions. The Index Lessons do not correspond with the Chapters, but are designed to bring together in their alphabetical connection, all the Questions and Answers upon each particular subject included in the work._

LESSON I.

Acids, vegetable, whence are they obtained, 1256

Actinism, what is it, 552

Actinism, what effect has it upon vegetation, 559

Actinism, at what season of the year is it most abundant, 560

ærial spectra, what is the cause of, 527

Affinity, what is the attraction of, 777

Air, why do we breathe it, 4

Air, what is the composition of it, 12

Air, what is its state after it has been breathed, 13

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,
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

Beetles, why have they hard horny wing-cases, 1320

Beetles, why have many of them hard horns, 1321

Bile, why does it separate nutritious from innutritious matter, 884

Birds, why have water-fowls feathers of a close and smooth
texture, 1033

Birds, why are they covered with feathers, 1030

Birds, why does black down grow under their feathers on the approach of
winter, 1036

Birds, why have they hard beaks, 1040

Birds, why are their beaks generally long and sharp, 1041

Birds, why are their bones hollow, 1050

Birds, why do they lay eggs, 1051

LESSON IX.

Birds, why have those with long legs short tails, 1052

Birds, why have aquatic web-feet, 1059

Birds, why have those that swim and dive short legs, 1060

Birds, why have some deep rough notches on the under surfaces of their
feet, 1061

Birds, why have they gizzards, 1072

Birds of prey, why have they no gizzards, 1084

Birds, why may wet and thunder be expected when they cease to sing, 1121

Birds of passage, why, if they arrive early, may severe weather be
expected, 1121

Birds, geological distribution of, 1326

Birds, tameness of in unfrequented countries, 1327

Birds, why are birds of song not also remarkable as birds of plumage,
1328

Birds, what are the velocities of their flights, 1329

Birds, what is the cause of their migrations, 1330

Black, why should parts of kettles and saucepans be allowed to remain,
204

Blood, in what proportions are the gases found in it, 39

LESSON X.

Blood, what is venous, 41

Blood, what is arterial, 42

Blood, what is the constitution of the, 899

Blood, what quantity does the human body contain, 920

Blood, how frequently does the whole quantity pass through the system,
922

Blowing upon tea, why does it cool it, 174

Bow, why does it propel the arrow, 847

Bow and arrow, what line does the arrow describe, 848

Bow and arrow, what forces tend to arrest the arrow, 849

Bow and arrow, why are there feathers at the ends of arrows, 850

Bones, how many are there in the human body, 923

Bones, of what substances are they composed, 924

Bones, what are the uses of the, 925

Bones, why are those of the back hollowed out, 927

Bones, why are those of the skull arched, 930

Bones, why are those of the skull divided by small sutures, 931

Bones, why are they hollow, 934

LESSON XII.

Bones, why are those of the arms and legs formed into long shafts, 935

Bones, why are those of the feet and hands numerous and small, 936

Botanical geography, 1208

Brain, why is it placed within the skull, 926

Bread-fruit trees, where are they natives of, 1223

Breathing, is it a kind of combustion, 17

Breaths, have people ever been poisoned by their own, 24

Breezes, why are summer said to be cool, 170

Breezes, what is the cause of sea and land, 235

Bubbles, why do they ascend in the air, 236

Bubbles, why do they fall, after having ascended, 237

Bubbles, why do they display rainbow colours, 499

Bubbles, why are they round, 825

Bubbles, why are they elongated when being blown, 826

Bubbles, why do they close, and become perfect spheres when shaken from
the pipe, 827

Bubbles, why do they change their colours in the sunshine, 828

Bubbles, why do they burst, 829

LESSON XI.

Burning or supporting combustion, what is the difference, 45

Burning-glasses, why do they appear to set fire to substances, 80

Butterflies, why do they lay their eggs upon cabbage-leaves, 1099

Butterflies' eggs, why do they lie dormant in the winter, 1288

Butterflies, why do they fly by day, 1296

Calms, why do they prevail at the equator, 671

Caloric, what is it, 72

Caloric, what is the source of it, 73

Caloric, what are the effects of it, 74

Caloric, why is it called a repulsive agent, 75

Caloric, how may it be excited to develope heat, 79

Caloric, is there any in ice, snow, water, marble, &c., 89

Caloric, how do we measure the quantity of in any substance, 329

Caloric, how does it travel, 332

Caloric, how do we know that it is caloric which fuses metals, 334

Calves and lambs, why have they no horns, 1069

Camel, why has its stomach a number of distinct bags, 1065

Candles, why do tallow require snuffing, 264

LESSON XIII.

Candles, why do composite and wax not require snuffing, 265

Candle, what becomes of it after it is burnt, 269

Capillary blood-vessels, why are they found in every part of the
system, 919

Capillary attraction, what is it, 780

Carbonic acid gas, how is it formed, 9

Carbonic acid gas, what becomes of it, 10

Carbonic acid gas, is it heavier or lighter than air, 11

Carbonic acid gas, what are the chief sources of, 16

Carbonic acid gas, what is its effect upon the human system, 21

Carbonic acid gas, what becomes of that formed by combustion, 59

Carbonic acid gas, what proportion is dangerous to life, 60

Carbonic acid, what is it, 798

Carbonic acid, where does it chiefly exist, 799

Carbonic acid, what are its pure states, 800

Carbon, what is it, 18

Carbon, will it produce flame when burnt in oxygen, 106

Carbon and hydrogen, what differences characterise the combustion of,
268

LESSON XIV.

Carbon, what is the purest form of it, 277

Card, why do the images on each side blend while a card is revolving,
846

Caterpillars, why do they appear in the spring, 1289

Caterpillars, why do they eat voraciously, 1290

Caterpillars, why do they pass into the state of the chrysalis, 1291

Caterpillars, why do they become torpid in the chrysalis, 1292

Caterpillars, why do they attach themselves to the leaves of plants
when in the chrysalis, 1294

Cats, &c., why do they see in the dark, 981

Cats' eyes, why are the pupils of nearly closed by day, 982

Cats, &c., why have they whiskers, 1096

Cattle, why if they run round in meadows may thunder be expected, 1122

Ceiling, how did Mr. Sands walk on the, 664

Champagne, why does it effervesce, 806

Champagne, why do bubbles rise from it in two or three columns, 807

Charcoal, why is it dangerous to burn it in rooms, 20

LESSON XV.

Charcoal fires, why do they not give flames, 107

Charcoal, what is it, 275

Charcoal, why does it act as a disinfectant, 809

Chicory, what is it, 1196

Chimney, why does it cease smoking after the fire has been lighted a
little while, 680

Chimney, why does a long one create a better draught than a short one,
681

Chimneys, why do some smoke when windows and doors are closed, 683

Chimneys that stand under elevated objects, why do they smoke, 685

Chimneys, why do sooty smoke, 687

Chimneys, why do they smoke in damp and gusty weather, 688

Chimney, why does it smoke when first lighted, 679

Chocolate, what is it, 1194

Circulation, why are the venous blood and chyle sent to the lungs, 887

Circulation, what is the course of the arterial blood, 888

Circulation, why does the blood impart vitality, 891

LESSON XVI.

Circulation, how do we know the blood is alive, 892

Circulation, why does the blood circulate, 893

Circulation, how is the body renewed by the blood, 894

Circulation, how does the blood return to the lungs after it has
reached the extremities, 895

Circulation, why are the veins more perceptible than the arteries, 897

Circulation, why when we prick the flesh does it bleed, 893

Circulation, what occurs during the, 899

Circulation, what becomes of the matter collected by the blood, 901

Circulation, how is the blood propelled through the arteries, 916

Circulation, why are the capillary vessels capable of receiving the
quantity of blood sent through larger vessels, 917

Cinnamon, where is it produced, 1239

Cleanliness, why does it promote health, 1015

Clothes on fire, why should persons throw themselves down, 252

Clothing, why do some articles feel cold, and others warm, 120

LESSON XVII.

Clothing, are conductors or non-conductors the warmer, 121

Clothing, why are white and light-coloured articles cool, 218

Clothing, why are dark-coloured dresses worn in winter, and light in
summer, 230

Clouds, what are they, 373

Clouds, why do we not see them ascend, 375

Clouds, why are they invisible when they rise, but become visible when
they have ascended, 376

Clouds, why do they not descend to the earth, 377

Clouds, at what altitudes do they fly, 378

Clouds, how many descriptions are there, 379

Clouds, what produces their various shapes, 380

Clouds, what are their dimensions, 381

Clouds, how are they affected by winds, 382

Clouds, what do Cirrus foretell, 389

Clouds, what do Cumulus foretell, 390

Clouds, what do Stratus foretell, 391

Clouds, what do Nimbus foretell, 392

Clouds, what do Cirro-cumulus foretell, 393

Clouds, what do Cirro-stratus foretell, 394

Clouds, what do Cumulo-stratus foretell, 395

LESSON XVIII.

Clouds, why are cloudy days colder than sunny days, 396

Clouds, why are cloudy nights warmer than clear nights, 397

Cloudy days and nights, why are they not always wet, 432

Clouds, why are they white, 531

Clouds, why are they sometimes yellow, 533

Clouds, what develops the electricity in the, 581

Clouds, why do they sometimes move towards each other from opposite
directions, 778

Clouds, why do they gather around mountain tops, 781

Cloves, where are they produced, 1231

Coal, what is it, 271

Coal, why do we know that it is of vegetable origin, 273

Coal, what are the chemical components of, 274

Coals, why do they produce yellow flame, 279

Cockles, why have they stiff muscular tongues, 1087

Cocoa, what is it, 1195

Cocoa, what tree produces it, 1221

Coffee-pot, why has it a wooden handle, 125

LESSON XIX.

Coffee, what is it, 1193

Coffee, where is it cultivated, 1224

Cohesion, what is the attraction of, 776

Coke-fires, why do they not give flames, 107

Coke, what is it, 278

Cold, when is a body said to be, 78

Cold, what is the cause of the sensation, 133

Cold, does it radiate, 207

Colour, why is a substance white, 466

Colour, why is a substance black, 467

Colour, why is a rose red, 468

Colour, why is a lily white, 469

Colour, why is a primrose yellow, 470

Colour, why are there so many varieties of colour and tint in nature,
471

Colours, remarks upon, 501

Combustion, what takes place during, 48

Combustion, how many kinds are there, 93

Conductors of heat, what substances are good, 110

Conductors of heat, why do bad conductors readily ignite, 295

Combustion, what is spontaneous, 311

Combustibles used for lighting, which vitiates the air most, 62

Conduction of heat, what is the, 113

Convection, what is the chief effect of the law of, 243

LESSON XX.

Cork, what is it, 1271

Cork-tree, why does it shed its own bark, 1272

Corns, why when they ache may rain be expected, 1115

Corn, why does the young ear come up enfolded in two leaves, 1167

Cotton, what is it, 1199

Cough, why do we, 1023

Crickets, why do they make a chirping noise, 1123

Cross-bills, why do their mandibles overlap each other, 1136

Cup in a pie, why does it become filled with juice, 631

Cup in a pie, does it prevent the juice from boiling over, 662

Dates, what are they produced by, 1221

Death-watch, why does it make a ticking noise, 1301

Dew, what is it, 345

Dew, what causes the decline of temperature which produces it, 347

Dew, why is there little or none, when the nights are cloudy, 348

Dew, why does it form most abundantly on cloudless nights, 349

Dew, why is there little under the branches of thick foliage, 351

LESSON XXI.

Dew, why is there none formed on windy nights, 352

Dew, why are valleys and low places chiefly subject to it, 353

Dew, what bodies receive little of it, 355

Dew, what bodies receive most of it, 354

Dew, at what period of the night is it chiefly formed, 356

Dew, why is it chiefly formed at that period, 357

Dew, in what parts of the world is the greatest quantity formed, 358

Dew, in what parts of the world is the least quantity formed, 359

Dew, why is it seldom formed at sea, 360

Dew, why is it, when heavy, regarded as a precursor of rain, 361

Dew, what is honey-dew, 364

Dew, why does it lie on the exposed sides of screens of plants, 401

Dew, why does it rest upon the upper surfaces of leaves, 402

Dews, why are cultivated lands more subject to them than those that are
uncultivated, 403

LESSON XXII.

Dew, why does the gravel-walk receive less dew than the grass, 404

Dew, why does little of it form at the base of hedges, walls, and
trees, 406

Dews, why do morning dews and mists usually come together, 407

Dew, what effect have winds upon its formation, 408

Dew, why does it form in round drops upon leaves, 794

Diamond, what causes the brilliant colours of the, 501

Digestion, why does food flow more freely to the stomach during, 879

Digestion, why does excess in eating impair, 880

Digestion, what changes occur to food in the stomach, 881

Digestion, what causes bilious attacks, 882

Digestion, how is the nutritious matter taken from that which is
innutritious, 885

Digestion, what becomes of the nutrition when it enters into the
circulation, 886

Dish-covers, why should they be plain in form, and have bright
surfaces, 203

Dogs, geographical distribution of, 1333

Dream, why do we, 1020

Drowsiness, why is it felt in crowded rooms, 22

LESSON XXIII.

Ducks and geese, why do they dash water over their backs on the
approach of rain, 1105

Ducks and geese, why have they square-pointed bills, 1044

Dyes, vegetable, what are they, 1259

Ear, why is it spread out externally, 984

Ears, why do hairs grow across them, 986

Ear-wig, why is it so called, 986

Ears, why is wax secreted in the, 987

Ears, why do singing noises occur in the, 988

Ears, why do people become deaf, 989

Ears, why do people accustomed to loud noises feel no inconvenience
from them, 990

Ears of animals of prey, why do they bend forward, 1063

Ears of animals of flight, why do they bend backward, 1064

Earth, why is it warmer than air during sunshine, 398

Earth, why is it colder than air after sunset, 399

LESSON XXIV.

Earth, how can man weigh the, 784

Earth, what is the weight of the, 788

Earth-worms, why have they no feet, 1085

Echoes, why do some occur immediately after the sounds, 742

Echoes, why do some occur at a considerable interval after the sound,
743

Echoes, why do some change the tone and quantity of sounds, 744

Echoes, why are there sometimes several to one sound, 745

Echoes, are they caused only by distant objects, 746

Echoes, what are they, 741

Electricity, what is it, 561

Electricity, why is it so called, 562

Electric fluid, why is it so called, 566

Electrics, what substances are, 567

Electricity, what is positive, 568

Electricity, what is negative, 569

Electricity, what is vitreous, 570

Electricity, what is resinous, 570

Electrical phenomena, what produces them, 571

Electricity, how does its equilibrium become disturbed, 572

Electricity, how does it seek to regain its equilibrium, 573

Electricity, what substances are conductors, 574

Electricity, what substances are non-conductors, 575

Electricity, what substances are insulators, 576

LESSON XXV.

Electricity, what is the effect when a current of electricity meets
with an insulator, 577

Electric sparks, what is the cause of, 578

Electricity, why does lightning attend it, 584

Electricity, why does it affect the shape of clouds, 613

Electric storms, why are they more frequent in hot than in cold
weather, 624

Electric storms, why do they frequently occur after dry weather, 625

Electric storms, why do they purify the air, 629

Electricity, what is Voltaic, 636

Electrical attraction, what is it, 778

Elementary body, what is meant by, 19

Element, what is the most abundant in nature, 756

Elephant, why has it a short unbending neck, 1076

Elephant, why has it a trunk, 1077

Elephants' hind legs, why do they bend forward, 1078

Etna, what are the botanical regions of Mount, 1240

Endogenous stems, what are they, 1280

LESSON XXVI.

Endogenous stems, why do they abound in tropical climates, 1281

Endogenous stems, why have they no bark, 1282

Endogenous stems, why do they grow to a great height, 1283

Exogenous stems, what are they, 1279

Exercise, why does it promote health, 1016

Exercise, why does it make us feel warm, 839

Explosions of gas, what is the best method of preventing, 65

Eye-balls, why are they white, 911

Eye-balls, why do they sometimes become blood-shot, 912

Eyes, why are they placed in the sockets of the skull, 929

Eyes, why are we able to move them, 965

Eye, why does the pupil look black, 968

Eye, why is the pupil larger sometimes than at others, 969

Eyes, why have we two, 970

Eyes, why having two, do we see singly, 971

Eyes, why are they provided with eyelids, 972

Eyelids, why are they fringed with eyelashes, 973

Eyes, whence are their humours derived, 976

LESSON XXVII.

Eyes, why do we feel inconvenienced by sudden light, 978

Eyes, why if we look upon a bright object and turn away, are we unable
to see, 979

Eyes, why are we able to see better after a little while, 980

Eyes, why do cats, bats, owls, &c., see in the dark, 981

Eels, why are their eyes covered with a transparent horny coat, 1130

Falling, what is the cause of bodies, 774

Fanning the face, why does it make us feel cooler, 172

Fata morgana, what is the cause of, 527

Fatigue, why do we feel, 1017

Feather, why does it fall to the earth more gradually than a shilling,
791

Features, why do we preserve the same through life, 903

Feel, why do we, 1004

Feeling, why is it impaired when the hands are cold, 1006

Feeling, why do the fingers prick and sting when they again become
warm, 1007

LESSON XXVIII.

Feeling, why do persons whose legs or arms have been amputated, for
some time continue to feel the part that has been removed, 1008

Fibrin, what is it, 899

Fingers, why can we raise them, 943

Fingers, why can we draw them back after they have been raised, 944

Fire, why does it burn more brightly when blown by a bellows, 27

Fire, what is it, 82

Fire, what are its properties, 83

Fire, what elements take part in its maintenance, 84

Fire, how does its combustion begin, 85

Fire-screens, how do they contribute to keep rooms cool, 217

Fire, why is it sometimes put out by blowing it when it is low, 262

Fire, why does poking it cause it to burn more brightly, 287

Fires, why do "blowers" improve the draft of air, 288

Fire, why does it sometimes appear red, and without flame, 283

Fire, what effect has it upon air, 284

Fires, why do charcoal and coke burn without flame, 292

Fires, why are charcoal and coke difficult to light, 293

Fires, a new plan of kindling, 293

LESSON XXIX.

Fires, why in lighting them do we first lay in paper, wood, and coal,
298

Fire, why does a poker laid across the top revive it when dull, 302

Fire-places, why should they be near the ground, 303

Fire, why does the blacksmith sprinkle water upon the coals of his
forge, 308

Fires, what is the best method of conveying air to, 684

Fish, why does putrifying look luminous, 95

Fishes, why have they fins, 1053

Fishes, why are their fins proportionately so much smaller than the
wings of birds, 1054

Fishes, why have they scales, 1055

Fishes, why do they float in streams, with their heads towards the
current, 1056

Fishes, why have they air-bladders, 1057

Fishes, why do not their eyes contract, 1129

Fishes, why have they no eyelids, 1132

Fishes, why have they the power of giving their eye-balls a sudden
motion, 1133

Fishes, why are their tails so much larger than their fins, 1137

Flame, what is it, 96

LESSON XXX.

Flame, what temperature is required to produce it, 101

Flame of a candle, why does the lower part of the flame appear blue, 246

Flame of a candle, why does the middle of the flame look dark, 217

Flame of a candle, why does the upper part produce a bright yellow
light, 248

Flame of a candle, why is there a fringe of pale light around the
flame, 249

Flame of a candle, why does it terminate in a point, 250

Flame of a candle, why does it lengthen when anything is held over it,
251

Flame or spark, why does pressing it put it out, 253

Flame of a candle, why does holding a candle upside down put it out, 257

Flame of a candle, why is it more difficult to blow out the flame of a
candle with a cotton wick than one with a rush wick, 258

Flame of a candle, why does blowing sharply on it put it out, 259

Flame of a candle, why will a gentle puff of air sometimes relight it,
260

LESSON XXXI.

Flame of a candle, why will not a similar puff rekindle a rushlight, 261

Flame of a candle, why will a piece of paper twisted to form an
extinguisher put it out, 263

Flame of a candle, why does it become dim when the wick is loaded with
carbon, 267

Flames of a fire, why do some appear much whiter than others, 280

Flames of a fire, why do some of them appear blue, 282

Flesh, why does it heal when we cut it, 902

Flesh-eaters, why do they satisfy themselves with a rapid meal, 1092

Flesh, why do the marks of deep cuts remain, 905

Flesh, why does that under the nails look red, 907

Flies, how can they walk on the ceiling, 663

Flies, why have they fine hairs growing on the extremities of their
legs, 1102

Flowers, what is the chief cause of the differences of their
temperatures, 227

Flowers, why may wet weather be expected when their perfume is strong,
1103

LESSON XXXII.

Flowers, why, if certain close, may rain be expected, 1116

Flying-top, why does it rise on the air, 843

Flying-top, why does it return to the earth, when its rotations are
expended, 844

Focus, what is a, 81

Fogs, what are they, 365

Fogs, why are certain coasts very liable to them, 366

Fogs, what are dry, 367

Fogs, why do they frequently rise in the morning and fall in the
evening, 371

Fogs, why do they sometimes rest upon a locality for days together, and
then disappear, 372

Food, why do we eat it, 869

Food, why do we eat animal and vegetable, 172

Food, why do we masticate it, 871

Food, how does it descend into the stomach, 875

Food, why do we not feel it being transmitted through the throat, 876

Food, why do we feel uneasy after eating to excess, 877

Food, why do we feel drowsy after eating heartily, 878

Food, why do some portions nourish us, while other portions are
useless, 883

LESSON XXXIII.

Fossil, vegetable, what is it, 272

Friction, why does it produce heat, 321

Friction, why does rubbing two surfaces together attract latent heat,
322

Frost, why is the air warmer during, 163

Frost, what is white, 412

Frost, what is black, 413

Frost, why are black frosts said to last, 414

Fruit, why do gooseberries, plums, &c., taste acid, 1184

Fruit, why do ripe taste sweet, and unripe sour, 1185

Fruits, why are succulent most abundant in tropical climates, 1207

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

Hearth-rug, and hearth-stone, their relative states of heat, 142

Heat, which are the better conductors, fluids or solids, 146

Heat, why are dense substances the best conductors, 147

Heat, why are fluids bad conductors, 148

Heat, why are woollen fabrics bad conductors, 149

Heat, is air a good or bad conductor, 150

LESSON XXXVII.

Heat, is water a good or a bad conductor, 151

Heat, how do we know that air is not a good conductor, 155

Heat, how do we know that water is not a good conductor, 156

Heat, why are bottles of hot water wrapped in flannel, 158

Heat, why are hot rolls wrapped in flannel, 159

Heat, what is the highest degree that man can bear, 176

Heat, why may man endure a high degree without injury, 178

Heat, why may we believe that the internal heat of the earth does not
arise from terrestrious combustion, 224

Heat, what is the radiation of, 181

Heat, what becomes of that which is radiated, 186

Heat, when does a body radiate it, 184

Heat, does the movement of the air affect the radiation of, 188

Heat, why will not the motion of air disturb the rays of, 190

Heat, what bodies are good radiators of, 192

Heat, what bodies are bad radiators of, 193

Heat, why does water keep hot longer in a bright metal jug, 195

LESSON XXXVIII.

Heat, may it be reflected, 210

Heat, are light or dark-coloured bodies the best reflectors, 211

Heat what bodies are the best reflectors of, 212

Heat, why is that which is reflected less intense than the primary, 214

Heat, can it be reflected in any great intensity, 215

Heat, are good reflectors also good absorbers, 216

Heat of the sun's rays, how is it diffused, 219

Heat, how do we know that it is absorbed by the earth, 222

Heat, do plants absorb it, 225

Heat, how is it diffused through the atmosphere, 232

Heat, how is it diffused through the ocean, 233

Heat, why is it developed during chemical changes, 312

Heat, what are the sources of, 323

Heat, what is the accepted theory of, 328

Heat, what is the point at which it becomes luminous, 545

Heat, what is the relative intensity of primary and reflected, 548

Heat to cold, why does a sudden change bring on illness, 1013

LESSON XXXIX.

Heat of the earth, Humboldt's opinion upon the internal, 1335

Heat of the earth, Hunt's opinion upon the internal, 1336

Hear, why do we, 983

Hiccough, why do we, 1027

Hoar-frost, what is it, 362

Hoar-frost, why does it foretell rain, 363

Hoar-frosts, why are they so frequent, and black-frost so unfrequent,
412

Hogs, why have Indian large tusks turning back towards their eyes, 1068

Hog, why is the under-jaw of the, shorter than the upper-jaw, 1039

Hoop, why does it roll without falling to the ground, 861

Hoop, why does it when falling make several side revolutions, 862

Horses, why have they smaller stomachs proportionately than other
animals, 1097

Horse, why has it no gall-bladder, 1098

Horses, why is the secretion of their eyes thick and glutinous, 1134

Horses and cattle, why do they stretch out their necks, and snuff the
air on the approach of rain, 1106

Horse-chestnut, why is it unfit for food, 1203

Hot, when is a body said to be, 77

LESSON XL.

Hot water, why does it feel hotter in a metal jug than in an
earthenware one, 126

Hot metal, why does it feel hotter than hot wool, 130

Hot metal and hot wool, which would become cold first, 131

Hot and cold bodies, why, when placed near each other, do their
temperatures approximate, 331

Humming-tops, why do we see the figures painted on them before they
spin, but not while they are spinning, 813

Humming-top, why does it make a noise, 810

Hydrogen, what is it, 49

Hydrogen, will it support animal life, 50

Hydrogen, will it support combustion, 51

Hydrogen, why will it explode, 52

Hydrogen, where does it chiefly exist, 54

Hydrogen, how is it obtained from coal, 57

Hydrogen-gas, is an escape of it dangerous to life, 63

Hydrogen-gas, what proportion mixed with air will explode, 64

Hydrogen-gas, does it rise or fall, 66

LESSON XLI.

Hydrogen-gas, what proportion is dangerous if inhaled, 67

Hydrogen-gas, what proportion may be recognised by its smell, 68

Hydrogen-gas, may the use of it be considered dangerous, 70

Hydrogen-gas, what sources of it are there in our dwellings, 69

Hydrogen, why will it burst into flame when coals become heated, 100

Hydrogen, why does hi-carburetted burn with a whiter flame than common
coal-gas, 281

Ice, why are blocks of it wrapped in flannel in summer time, 154

Ice, why does it melt, 325

Ice, why does it occupy more space than water, 752

Ignis fatuus, what is it, 318

Incidence, what is the line of, 519

Incidence, what is the angle of, 521

India-rubber, where is it obtained, 1254

Infants, why have they no teeth, 1070

Insects, why have they a large number of eyes, 1083

Insects, why have they long projections from their heads, 1100

Insects, why do they attach their eggs to leaves, 1295

Insects, why do they multiply so numerously, 1300

LESSON XLII.

Insects, what is a larva, 1302

Insects, what is a pupa, 1303

Insects, what is a chrysalis, 1304

Insects, what is a nymph, 1305

Insects, why do they abound in decaying substances and in putrid
waters, 1313

Insects, why do we see them in tanks of rain-water, 1314

Iron articles, why are they intensely cold in winter, 132

Iron articles, why do they usually feel cool, even when near a fire, 132

Ironing-box, why does the iron sometimes become too large for the box
to receive it, 335

Ironing-box, why does the iron enter it, when partially cooled, 336

Iron, why does it rust when wetted, 768

Jew's-harps, why do they give musical sounds, 851

Jew's-harps, why will they not produce loud sounds unless they are
applied to the mouth, 852

Jew's-harps, why does the alteration of the form of the mouth alter the
sounds, 853

Kangaroos and opossums, why have they pouches in which they carry their
young, 1139

LESSON XLIII.

Kettle-holders, of what use are they, 128

Kettles and saucepans, why should the lids and fronts of be kept
bright, 206

Kettles, why do they become encrusted with stony deposits, 762

Kite, why does it rise in the air, 840

Kite-string, why does it feel hot when running through the hand, 841

Kite, why does running with it cause it to ascend, 812

Knowledge, why should we seek it, 1

Knowledge, why does the possession of it give us power, 2

Knowledge, what are the benefits of, 3

Latent heat, will the abstraction of it reduce the bulk of bodies, 337

Latent heat, how do we know that it exists in air, 339

Laugh, why do we, 1026

Ligaments, what are they, 937

Ligaments, why are they wrapped around the joints, 938

Light, what is it, 451

Leaves, why are they green, 1181

Leaves, why do some turn yellow, 1186

Leaves, why do they fall off in the autumn, 1187

Leaves, how to make skeleton, 1159

LESSON XLIV.

Leaves, why do they turn brown in autumn, 1183

Legs crossed, why do we see the elevated leg move at regular intervals,
918

Light, at what velocity does it travel, 453

Light, how long does it take to travel from the sun to the earth, 454

Light what are the minor sources of, 457

Light, what is a ray of, 458

Light, what is a medium of, 459

Light, what is a beam of, 460

Light, what is a pencil of, 461

Light, what is the radiant point, 462

Light, what is the focus of, 463

Light, what is the constitution of a ray of, 464

Light, why are its rays white, 465

Light, what are the estimated vibrations of, 465

Light, what is the refraction of, 472

Light, is it refracted when it falls upon a surface in a straight line,
473

Light, is the direction in which its rays are best dependent on the
densities of the media, 474

Light, why does a spoon look bent when placed in a basin of water, 477

Light, why do we see the rays of the sun burst through the clouds in
different directions, 478

LESSON XLV.

Light, why is the apparent depth of water always deceptive, 479

Light, why are some substances opaque to it, 511

Light, how do we know that bodies reflect it in every direction, 517

Light, meditation on, 517

Light and heat, what are the differences between, 540

Light and heat, are they combined in the sun's rays, 541

Light and heat, how do we know that they are separate elements, 542

Light and heat, in what respects are they similar, 543

Light and heat, in what respects are they dissimilar, 544

Light, what is polarized, 549

Light, what is the velocity of artificial, 546

Light, at what rate does the light of the stars travel, 547

Light, why does it tarnish silver, 553

Light, why does it affect colours, 554

Light, why can pictures be taken by the sun's rays, 555

Light, when does it scorch plants, 558

Lightning, what is the cause of, 580

Lightning, why does it sometimes become zigzag, 586

Lightning, why is it sometimes forked, 587

LESSON XLVI.

Lightning, why is it sometimes like a lurid sheet, 588

Lightning, when is the flash straight, 587

Lightning, when does the flash appear blue, 591

Lightning, why is it sometimes red, at others blue, yellow, or white,
592

Lightning, does it ever pass from the earth to the clouds, 593

Lightning, does it pass from the clouds to the earth, 594

Lightning, what is the force of, 595

Lightning, why is it dangerous to stand near a tree during a storm, 596

Lightning, why is it dangerous to sit near a fire during a storm, 598

Lightning, why is it dangerous to be near water during a storm, 599

Lightning, are iron houses dangerous, 600

Lightning, why does it seize upon bell wires, &c., 601

Lightning, are umbrellas with steel frames dangerous, 603

Lightning, are iron bedsteads dangerous, 604

Lightning, what is the safest situation during a storm, 606

Lightning-conductors, do they attract electricity, 608

LESSON XLVII.

Lightning-conductors, which is the best metal for, 610

Lightning-conductors, why have they sometimes been found ineffective,
609

Lightning-conductors, why should large buildings have several, 611

Lightning-conductors, why should they have several branches penetrating
the earth, 612

Lightning, through what distance will its light penetrate, 622

Lightning, how may we calculate the distance of a storm, 623

Lightning, why is the flash generally succeeded by heavy rain, 626

Lightning, why is a flash generally followed by a gust of wind, 627

Lime-kilns, why do persons viewed through the hot air of, appear
distorted and tremulous, 483

Limpets, why is it difficult to strike them from rocks, 665

Lips, why are they red, 913

Liver, what effect has it upon the circulation, 901

Looking-glass, why, if you hold one at an angle towards the sun, will
light be thrown in an opposite direction, 208

Loss, is there any such thing in the operations of nature, 270

LESSON XLVIII.

Lungs, why are they placed in the chest of the body, 932

Magnetism, what is it, 633

Magnetic bodies, what are they, 634

Magpie, why is a single one said to foretell bad weather, 1118

Mahogany, what is it, 1190

Mahogany and other woods, why are there curious markings in, 1273

Man, why is he born without a covering, 1034

Man, why has he no external appendage to his mouth, 1037

Marbles, why do they revolve when propelled along the ground, 818

Marbles, why do striped appear to have more stripes when they are
rolling than when at rest, 819

Marbles, why do they rebound when dropped upon the pavement, 820

Marbles, why do they roll furthest upon smooth surfaces, 821

Marbles, how many forces contribute to stop their rolling, 882

Marbles, why do the stripes upon them disappear when they are spinning
rapidly, 823

Marbles, why are the rings upon them most perceptible at the "poles,"
while they are spinning, 824

LESSON XLIX.
Matches, do they ignite spontaneously, 313

Meat, why is it sooner cooked when a tin screen is placed before the
fire, 213

Metal, why does it run like a fluid when melted, 333

Mirrors, why do we see our features therein, 209

Mirrors, why do we see our faces in them, 512

Mirrors, what has the glass of to do with the reflection, 514

Mirrors, why do compound mirrors reflect many images of one object, 515

Mirrors, why do reflections appear as far behind a mirror as the object
reflected stands before it, 518

Mirage, what is the cause of the, 527

Mists, what are they, 368

Mists and fogs, what is the difference between them, 369

Mists end fogs, why do they disappear at sunrise, 370

Mistletoe, why have its berries a thick viscid juice, 1177

Mistletoe, how are its seeds conveyed to the bark of trees, 1178

Moles, why have they hard flat feet, 1074

Mole's fur, why is it glossy and smooth, 1075

LESSON L.

Moles, why are they permanent, 904

Moles, why may rain be expected when they throw up their hills, 1117

Monsoons, what are they, 672

Monsoons, what is the cause of, 673

Mornings, why are they usually clear when frosty, 410

Mother-of-pearl, what causes the rich tints displayed by, 500

Moths, why do they fly by night, 1297

Moths, why are their bodies generally covered with thick down, 1228

Moths, why do they fly against the candle-flame, 1299

Muscles, how many are there in the human body, 941

Muscle, what is the constitution of a, 942

Muscles, what degree of strength do they possess, 945

Muscles, what is the stimulus which sets them in action, 946

Mussels, why have they tendinous cords proceeding from their shells,
1086

Natural phenomena, a world of miniature, 690

Nails, why have we got them at the fingers' ends, 908

Nails, why is there a circular line of whitish colour at the root of
the, 909

LESSON LI.

Nails, why do white spots occur upon the, 916

Needle, why will it float if laid carefully upon water, 795

Nerves, what are they, 951

Nervous system, of what does it consist, 955

Nerve, what is the constitution of a, 956

Nervous fluid, what is the, 957

Nerves, how many kinds are there, 958

Nerves of motion, what are they, 959

Nerves of sensation, what are they, 960

Nerves of special sense, what are, 961

Nerves of sympathy, what are the, 962

Nights, why are they usually cold when clear, 411

Nitrogen, what is it, 33

Nitrogen, where is it found, 34

Nitrogen, could animals live in it, 37

Nitrogen, is it taken into the blood from the air, 40

Nitrogen, will it burn, 44

Nitrogen, what becomes of that which is inhaled, 46

Nitrogen, where does it find a fresh supply of oxygen, 47

Nitrous oxide, why does it excite the system, 38

Non-conductors of heat, what substances are, 111

Nostrils, why are they directed downwards, 994

LESSON LII.

Nose, why is it placed over the mouth, 995

Nutmegs, where are they produced, 1232

Ocean, how is it heated, 233

Oils and fats, what are vegetable, 1204

Oils and fats, animal, why are they found most abundantly in cold
climates, 1205

Oils and fats, vegetable, why are they found most abundantly in hot
countries, 1206

Opium, what is it, 1258

Ostriches, why have they small wings, 1031

Ostriches, why are their feathers soft and downy, 1032

Otters, seals, &c., why have they web-feet, 1062