INDEX, AND INDEX LESSONS.

☞ 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]
Owls, why does their screeching denote change of weather, [1111]
Owls, why does their moping foretell death, [1112]
Oxen, sheep, deer, &c., why do they ruminate, [1088]
Oxen, and other quadrupeds, why have they a tough elastic ligament in their necks, [1138]
Oxygen, why is it necessary to life, [5]
Oxygen, what is its union with carbon called, [7]
LESSON LIII.
Oxygen, what is it, [25]
Oxygen of the air, why does it not take fire, [28]
Oxygen, why do we know that it will not burn of itself, [29]
Oxygen, why do we know that it is necessary to our existence, [30]
Oxygen, where is it found, [31]
Oxygen, why is it mixed with nitrogen in the air, [32]
Oxygen of water, why does it not support fire, [307]
Oxygen, in what way does man use it, [757]
Ozone, what is it, [630]
Ozone, why do we know that electricity produces it, [631]
Ozone, what are the properties of, [632]
Paleness, what is the cause of, [914]
Palms, what are their characteristics, [1221]
Paper held over a candle-flame, why does it become scorched, [244]
Paper held below a candle-flame, why does it scarcely become warm, [245]
Paper, why does it more readily ignite than wood, [294]
Paper, why, if it is laid flat upon the fire, will it "char" before it ignites, [304]
LESSON LIV.
Paper on a fire, why will it ignite when you send a puff of air to it, [305]
Parachutes, why do they fall gradually to the ground, [834]
Parrots, &c., why have they crooked bills, [1047]
Parrots, why can they move their upper as well as their lower beak, [1048]
Particles of matter, why do they draw near each other, [776]
Particles of matter, why will they attach themselves to sealing-wax excited by friction, [779]
Pea and pin, why do they rotate upon a jet of air blown through a tobacco-pipe, [845]
Peg-top, why does it make less noise than a humming-top, [811]
Peg-top, why does it sometimes hum, and at other times not, [812]
Pelican, why has it a large pouch under its bill, [1093]
Pepper, where is it produced, [1229]
Perspiration, why does it cool the body, [173]
Perspire, why do we, [1009]
Perspiration, how is it formed, [1010]
Perspiration, what is insensible, [1011]
Perspiration, what is sensible, [1012]
LESSON LV.
Phosphorous, why does it look luminous, [94]
Phosphorous, does it ignite spontaneously when placed upon a hot surface, [314]
Phosphorous, why does it ignite when sprinkled with powdered charcoal, [315]
Photographic pictures, how does light produce them, [556]
Photographic rooms, why are they glazed with blue glass, [557]
Pith-tumblers, why do they always pitch on one end, [868]
Planets, how can man weigh them, [785]
Planets, how can man measure their distances, [786]
Plants, do they absorb heat, [225]
Plants, how do we know that they absorb heat, [226]
Plants, why do screens prevent frost from killing them, [400]
Plants, why, if we cut across their stems, do we see tubes arranged in parallel lines, [1159]
Plants, why do some droop and turn to the earth after sunset, [1167]
Plants, why are the seeds of many enclosed in rich juice or pulp, [1172]
Plants, why have some tough curly tendrils, [1173]
LESSON LVI.
Plants, why have peas tendrils, and beans none, [1174]
Plants, why have grasses, &c., joints or knots in their stalks, [1176]
Plants, what is the circulation of sap in, [1179]
Plants, why does their sap ascend and descend, [1180]
Plants, why do they suffer from the smoke of cities, [1188]
Plants, why is it understood that some of them feel, [1141]
Plants, why is it understood that some of them move, [1142]
Plants, of what elementary substances are they composed, [1143]
Plants, whence do they derive their elementary substances, [1144]
Plants, how do they obtain carbon, [1145]
Plants, how do they obtain oxygen, [1146]
Plants, their decomposition of gases by day and by night, [1147]
Plants, how do they obtain hydrogen, [1147]
Plants, how do they obtain nitrogen, [1148]
Plants, how do they apply their elements to the formation of their structures, [1149]
Plants, how is their nutritive sap applied to their growth and nourishment, [1150]
LESSON LVII.
Plants, why do they grow, [1154]
Plants, why if we break the stem of a hyacinth do we see a glutinous fluid exude, [1155]
Plants, why if we split the petal of a tulip do we see cells containing different colouring matters, [1156]
Plants, why if we break a pea-shell across do we find a transparent membrane, [1157]
Plants, why if we cut through a cabbage-stump do we find a tough coating enveloping a cellular substance, [1158]
Plants, why are their seeds formed within the corollas of flowers, [1168]
Plants, why does the flower of the poppy turn down during the early formation of seed, [1169]
Plants, why have those of the pea-tribe a folding blossom, [1170]
Plants, why are leaf-buds enclosed in scales which fall off as the leaves open, [1171]
Plants, what is meant by "species" of, [1209]
Plants, what is meant by "genus" of, [1210]
Plants, progressive discovery of new species, [1211]
Plants, what are the three great classes of, [1212]
LESSON LVIII.
Plants, what are the characteristics of exogenous, [1213]
Plants, what are the characteristics of cryptogamus, [1216]
Plants, what are the effects of diverse climates upon, [1242]
Plants, what are the effects of altitude upon mountains, [1243]
Plants, what agencies influence their geographical distribution, [1250]
Plants, what are the chief facts connected with the distribution of by man, [1251]
Plants, why are herbaceous less solid than woody, [1265]
Plants, why are the stalks of herbaceous generally cylindrical, [1266]
Plants, what are the stomata of, [1267]
Plants, why are their stomata generally on the underside of their leaves, [1268]
Plants, why have they pith in their centres, [1269]
Porter, why does bottled produce large volumes of froth, [801]
Pulse, why do we feel it beat, [900]
Quadrupeds, geographical distribution of, [1331]
Quicksilver, why does it reflect light from mirrors, [513]
LESSON LIX.
Radiation, why does scratching a bright metal surface increase its powers of, [199]
Radiation of heat, what benefits arise from it, [415]
Radiation of light, what is it, [503]
Radiation, do all bodies radiate light, [504]
Rain, what is it, [416]
Rain, does it ever occur without clouds, [417]
Rain-drops, why are they sometimes large, and at other times small, [418]
Rains, at what seasons are they most prevalent, [419]
Rainy days, in what months of the year are they most frequent, [420]
Rainy days, why are there more from September to March, [421]
Rain, in what part of the world does the greatest quantity fall, [422]
Rain, in what part of the world do the heaviest rains fall, [423]
Rain, in what part of the world does the least rain fall, [424]
Rainy days, how many are there in a year, [425]
Rain, in what part of England does the greatest quantity fall, [426]
Rains, why do the heaviest occur in hot countries, [427]
LESSON LX.
Rain, why does the greatest quantity fall at the equator, [428]
Rain, why are some parts of the earth without it, [429]
Rain, why does it purify the air, [433]
Rainy localities, why are mountainous countries more rainy than flat ones, [434]
Rain, why does more fall by night than by day, [435]
Rain, why do bunches of dried sea-weed indicate its coming, [436]
Rain, why do weather-toys foretell its coming, [437]
Rain, the Capuchin toy; mysterious walk of a wooden horse, [438]
Rain, why does ladies' hair drop out of curl as rain approaches, [438]
Rain, why is it said to be coming, when the mountains are "putting on their night-caps", [439]
Rainbow, what causes a, [486]
Rainbow, why does it exhibit colours, [487]
Rainbows, why are there sometimes two, [488]
Rainbows, why are the columns of the secondary bow, arranged in the reverse order of those of the primary, [489]
LESSON LXI.
Rainbow colours, why do glass lustres and chandeliers exhibit them, [498]
Rainbows, why are the colours of the secondary bow fainter than those of the primary, [491]
Rainbow, what is a lunar, [492]
Rainbow, why is a lunar bow fainter than the solar, [493]
Rainbow, why is one in the morning the shepherd's warning, [538]
Rainbow, why is one at night the shepherd's delight, [539]
Refraction of light, what is it, [472]
Refraction and reflection of light, what is the difference, [502]
Reflections, why are they reversed, [490]
Reflection, why do black bodies reflect any light, [505]
Reflection, why does a window-pane appear to reflect better by night than by day, [516]
Reflection, what is the line of, [520]
Reflection, what is the angle of, [522]
Repulsion, what is it, [792]
Respiration, why does the chest expand when we breathe, [889]
Respiration, how does blood communicate with the air in the lungs, [890]
Rest, why does it invigorate us, [1018]
Rice, where is it cultivated, [1219]
Rosewood, what is it, [1191]
LESSON LXII.
Saliva, why does saliva enter the mouth while we are eating, [872]
Sea, why is it salt, [764]
Sea, what is the estimated amount of salt in the, [765]
Sea, what is the depth of the, [766]
Sea-gulls, why are they numerous in fine weather, [1119]
Sea-gulls, why do they fly over the land on the approach of stormy weather, [1120]
Sea-crow, why is its lower bill longer than the upper, [1135]
Sealing-wax, why does rubbing it attract to it small particles of matter, [565]
See, why do we, [963]
Seeds, why are they generally enveloped in hard cases, [1152]
Seeds, why do they throw out roots before they form leaves, [1153]
Seeds, why does the leaf-germ come up to the light and the root-germ penetrate the earth, [1285]
Seeds, why are they indigestible, [1286]
See-saw, why may a little boy balance a larger boy, [863]
See-saw, why does the little boy sink to the earth, when the larger boy kicks the ground, [861]
LESSON LXIII.
See-saw, why may the little boy keep the larger one up, when once he is up, [864]
Shadows, what is the cause of, [508]
Shadows, why is there some light where shadows fall, [510]
Shadows, why do they lengthen as the sun goes down, [526]
Shuttle-cock, why does it travel slowly through the air, [836]
Shuttle-cock, why do we hear a noise when we strike it with the battledore, [837]
Sight, why are two persons able to see each other, [551]
Sight, why can we see so many upon the small retina, [966]
Sight, why are we able to see at long or short distances, [974]
Sigh, why do we, [1025]
Silica, what is it, [1260]
Silk, what is it, [1200]
Skin, why does a chill of the produce inflammatory action in the lungs, [1014]
Sky, what is it, [530]
Sky, why is it red at sunset, [532]
Sleet, what is it, [447]
Sleep, what is it, [1019]
Smell, why do we, [992]
Smoke, what is it, [102]
Smoke, why is there so little when the fire is red, [105]
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]
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.
Syringe, why will the water leak out, but not run, [858]
Syringe, why cannot the handle be pressed in, if a finger is kept on the orifice, [859]
Tannin, what is it, [1257]
Taste, why do we, [996]
Taste, why are some substances sweet, others sour, &c., [997]
Taste, why is it most powerful after substances have been a little while in the mouth, [998]
Taste, why if we put out the tongue and touch it with a nub of sugar, shall we perceive no taste, [999]
Taste, why when we draw in the tongue do we then perceive the taste of the sugar, [1000]
Taste, through what nerves are we made sensible of the contact of sugar with the tip of the tongue, [1001]
Taste, why do connoisseurs of wines hold wine in their mouths a few seconds when judging of it, [1002]
Taste, why do they also pass the fumes of the wine through their nostrils, [1003]
Tea-pot, why does a bright metal one produce better tea than a black earthenware, [200]
LESSON LXXI.
Tea-pot, if the earthenware one were set by the fire, why would it then make the best tea, [201]
Tea, what is it, [1192]
Tea, where is it cultivated, [1225]
Tears, what is the cause of, [977]
Temperature, why do some articles feel colder than others, [138]
Temperature, why does it feel warmer after a frost has set in, [163]
Tendons, what are they, [939]
Tendons, why are they used to attach the muscles to the bones, [940]
Teneriffe, what are the botanical regions of the Peak of, [1241]
Thaumatrope, why do the figures on appear to dance, [869]
Thaw, why is it colder when a thaw takes place, [164]
Thermometer, what is the, [709]
Thermometer, why does it indicate degrees of heat, [710]
Thermometer, why are there Reaumur's and Fahrenheit's, [711]
Thermometer and barometer, what is the difference, [712]
Thermometer, in what season of the year does it vary most, [715]
Thunder, what is it, [614]
Thunder-peal, why is it sometimes loud and continuous, [616]
LESSON LXXII.
Thunder-peal, why is it sometimes broken and unequal, [617]
Thunder-peal, why is it sometimes a low, grumbling noise, [618]
Thunder-peal, why does it sometimes follow immediately after the flash of lightning, [620]
Thunder, through what distance will the sound travel, [621]
Thunderbolt, what is a, [628]
Tinder-box, the history of a, [340]
Toasting-fork, why has it a wooden handle, [124]
Tops, why do they stand erect while they spin, but fall when they stop, [814]
Tops, why do they "sleep", [816]
Tops, why do they cease to spin, [817]
Touch, in what part of the body is the sense of most perfect, [1005]
Toxicologists, what are they, [61]
Trap and ball, why is the ball propelled upward, when the trigger is struck, [866]
Trees, what are the estimated ages of, [1214]
Trees, what are the northern limits of, [1237]
Trees, why are they covered with bark, [1270]
LESSON LXXIII.
Trees, why have those with large trunks a great number of leafy branches, [1274]
Trees, why have poplars comparatively few leaves, [1275]
Trees, why had the mammoth comparatively few leaves, [1276]
Trees, why have oaks an abundance of leaves, [1277]
Trees, why are their trunks generally round, [1278]
Twilight, what is the cause of, [482]
Vacuum, what is a, [649]
Vacuum, is it possible to obtain a perfect, [650]
Vegetables, have they any heat, [90]
Vegetable structures, of what do they consist, [1151]
Vegetables, why do farmers sow different crops in rotation, [1164]
Vegetables, why are the hearts of cabbages, &c., pale yellow, [1182]
Vegetable productions, why are they so widely diffused, [1189]
Vegetable eaters, why do they feed so continually, [1091]
Vegetation, geographical distribution of, [1208]
Vegetation, what are the characteristics of tropical, [1218]
Vegetation, what are the changes in on quitting the tropics, [1232]
LESSON LXXIV.
Vegetation, what are the characteristics of, upon approaching the polar zones, [1234]
Vegetation, what are the characteristics of mountain, [1238]
Vines, where are their favourable climates, [1233]
Walking, why does it make us warmer, [26]
Water, what becomes of that formed by combustion, [58]
Water, is it a good or bad conductor of heat, [151]
Water, why does it extinguish fire, [306]
Water, why, when a blacksmith thrusts a hot iron into a tank, do we perceive a peculiar smell, [309]
Water, why does it freeze, [324]
Water, why does it become steam, [326]
Water, how many degrees of latent heat are hidden in its several states, [327]
Water, why does it expand when freezing, while bodies generally contract with cold and expand with heat, [341]
Water, why does it never freeze to a great depth, [342]
Water, how much deeper is it than it appears to be, [480]
LESSON LXXV.
Water, why has the exceptional law, by which it expands when freezing, been ordained, [343]
Water, why can we seldom succeed in the first attempt to touch anything lying at the bottom of, [481]
Water, what causes it to flow from a pump, [651]
Water, why does it run through a syphon, [655]
Water, what is it, [748]
Water, why does it become solid when it freezes, [751]
Water, why does it boil, [753]
Water, what proportion of the earth's surface is covered by it, [554]
Water, why does it dissolve substances, [758]
Water, why does hot dissolve more readily than cold, [759]
Water, why is it sometimes hard, [760]
Water, why is rain-water soft, [761]
Water, why is it difficult to wash in hard, [763]
Waters, why are some impregnated with mineral matters, [767]
Water, why does stagnant become putrid, [769]
Water, is there danger attending drinking it on account of animalculæ, [770]
Water, what are the means by which it may be purified, [771]
LESSON LXXVI.
Water, what is the pressure of, [775]
Water, why will a drop upon the blade of a knife leave a dark spot, [777]
Water, why does it roll in agitated globules when dropped upon hot iron, [796]
Water, why does oil float upon it, [797]
Water, why is spring fresh and invigorating, [803]
Water, why is boiled flat and insipid, [804]
Weather, why does a yellow sunset foretell wet, [534]
Weather, why does a red sunset foretell fine, [535]
Weather, why does a red sunrise foretell wet, [536]
Weather, why does a grey sunrise foretell dry, [537]
Weather, barometrical indications of, [708]
Whales, why have they a large development of oily matter about their heads, [1068]
Whale, why has it feathery bones extending from its jaws, [1095]
Whales, why are, their eyes provided with very thick coats, [1131]
Wheat, why do the ears stand up by day and turn down by night, [1175]
Wheat, what is it, [1199]
LESSON LXXVII.
Wheat, what is the northern limit of, [1235]
Wheat, why is silica diffused over its stem, [1261]
Wheat-crops, why do they greatly exhaust the soil, [1263]
Whirlwinds, what are they, [678]
Why do we see, [963]
Why do we wink, [975]
Why do we weep, [977]
Why do we hear, [983]
Why do we taste, [986]
Why do we smell, [992]
Why do we feel, [1004]
Why do we sleep, [1019]
Why do we dream, [1020]
Why do suppers produce dreaming, [1021]
Why do we yawn, [1022]
Why do we cough, [1023]
Why do we sneeze, [1024]
Why do we sigh, [1025]
Why do we laugh, [1026]
Why do we hiccough, [1027]
Why do we snore, [1028]
Why do we feel hungry, [1337]
Why do we feel thirsty, [1338]
Wick of a candle, why does it turn black as it burns, [225]
Wick of a candle, why is there a spark generally at the end of it, [256]
Will-o'-the-wisp, what is it, [318]
Winds, what is the cause of, [234]
Winds, why are east usually dry, [384]
Winds, why are west usually wet, [385]
Winds, why are north usually cold and dry, [386]
LESSON LXXVIII.
Winds, why are south warm and rainy, [387]
Wind, what is it, [666]
Winds, what are the velocities of, [667]
Winds, what are trade, [668]
Winds, what is the cause of trade, [669]
Winds, why do trade winds blow from east to west, [670]
Winds, what determines the character of, [674]
Wind-mills, why do their wings turn round, [690]
Windows, why do they reflect the sun's rays in the evening, [523]
Windows, why do they not reflect the sun's rays at noon, [524]
Wood, why does decayed look luminous, [95]
Wood, burning at one end, why does it not feel hot at the other, [118]
Wood, why is it a bad conductor of heat, [119]
Wood that is green, why does it hiss and steam when burning, [285]
Wood, why does it ignite less readily than paper, [297]
Woodcocks and snipes, why have they nerves running down to the tip of their bills, [1043]
Woodpeckers, why do they "tap" at old trees, [1066]
Woollens, why are they worn in winter, [166]
Wool, what is it, [1201]
Yawn, why do we, [1026]
Zoological geography, [1326]

"God looked down from heaven upon the children of men, to see if there were any that did understand that did see God."—Psalm liii.