The reason why
by Robert Kemp Philp · English · Gutenberg #47748 · 835,578 chars · public domain (US)
The Project Gutenberg eBook of The reason why
This eBook is for the use of anyone anywhere in the United States and
most other parts of the world at no cost and with almost no restrictions
whatsoever. You may copy it, give it away or re-use it under the terms
of the Project Gutenberg License included with this eBook or online
at www.gutenberg.org. If you are not located in the United States,
you will have to check the laws of the country where you are located
before using this eBook.
Title: The reason why
a careful collection of many hundreds of reasons for things which, though generally believed, are imperfectly understood. A book of condensed scientific knowledge for the million
Author: Robert Kemp Philp
Release date: December 23, 2014 [eBook #47748]
Most recently updated: October 24, 2024
Language: English
Other information and formats: www.gutenberg.org/ebooks/47748
Credits: Produced by Jonathan Ingram, Christian Boissonnas and the
Online Distributed Proofreading Team at http://www.pgdp.net
(This file was produced from images generously made
available by The Internet Archive/American Libraries.)
*** START OF THE PROJECT GUTENBERG EBOOK THE REASON WHY ***
THE
REASON WHY:
A CAREFUL
COLLECTION OF MANY HUNDREDS OF REASONS FOR THINGS WHICH, THOUGH
GENERALLY BELIEVED, ARE IMPERFECTLY UNDERSTOOD.
A BOOK OF CONDENSED SCIENTIFIC KNOWLEDGE FOR THE MILLION.
By THE AUTHOR OF "INQUIRE WITHIN."
This collection of useful information on "Common Things" is put in
the interesting form of "Why and Because," and comprehends a familiar
explanation of many subjects which occupy a large space in the
philosophy of Nature, relating to air, animals, atmosphere, caloric,
chemistry, ventilation, materia medica, meteorology, acoustics,
electricity, light, zoölogy, etc.
NEW YORK:
DICK & FITZGERALD, PUBLISHERS,
No. 18 ANN STREET.
PREFACE.
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
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
[Verse: "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.]
THE REASON WHY.
CHAPTER I.
1. _Why should we seek knowledge?_
Because it assists us to comprehend the _goodness and power of God_.
And it gives us power over the circumstances and associations by which
we are surrounded: the proper exercise of this power will greatly
promote our happiness.
2. _Why does the possession of knowledge enable us to exercise power
over surrounding circumstances?_
Knowledge enables us to understand that, in order to live healthily, we
require to breathe fresh and pure air. It also tells us that animal and
vegetable substances, undergoing decay, poison the air, though we may
not be able to see, or to smell, or otherwise discover the existence
of such poison. Knowing this, we become careful to remove from our
presence all such matters as would tend to corrupt the atmosphere. This
is only one of the countless instances in which knowledge gives us
power over surrounding circumstances.
3. _Name some other instances in which knowledge gives us power._
Knowledge of _Geography_ and of _Navigation_ enables the mariner to
guide his ship across the trackless deep, and to reach the sought-for
port, though he had never before been on its shores.
Knowledge of _Chemistry_ enables us to separate or to combine the
various substances found in nature. Thus we obtain useful and precious
metals from what at first appeared to be useless stones; transparent
glass from pebbles, through which no light could pass; soap from oily
substances; and gas from solid bodies.
[Verse: "Give instruction to a wise man, and he will be yet wiser;
teach a just man, and he will increase in learning."--PROVERBS IX.]
Knowledge of _Medicine_ enables the physician to overcome the ravages
of disease, and to save suffering patients from sinking prematurely to
the grave.
Knowledge of _Anatomy_ and of _Surgery_ enables the surgeon to bind up
dangerous fractures and wounds, and to remove, even from the internal
parts of bodies, ulcers and diseased formations that would otherwise be
fatal to life.
Knowledge of _Mechanics_ enables man to increase his power by the
construction of machines. The steam-ship crossing the ocean in
opposition to wind and tide, the railway locomotive travelling at
60 miles an hour, and the steam-hammer beating blocks of iron into
useful shapes, are evidences of the power which man acquires through a
knowledge of mechanics.
Knowledge of _Electricity_ enables man to stand in comparative safety
amid the awful war of the elements. Lightning, the offspring of
electricity, has a tendency to strike upon lofty objects by which
it may be attracted. By its mighty powers churches or houses may be
instantly levelled with the dust. But man, knowing that electricity
is strongly attracted by particular substances, raises over lofty
buildings rods of steel communicating with bars that descend into the
ground. The lightning, rushing with indescribable force toward the
steeple, is attracted by the bar of steel, and conducted harmlessly to
the earth. Man may thus be said to take even lightning by the hand,
and to divert its destroying force by the aid of Knowledge. And in
countless other instances "Knowledge is Power."
CHAPTER II.
4. _Why do we breathe air?_
Because the air contains _oxygen_, which is necessary to life.
5. _Why is oxygen necessary to life?_
Because it combines with the _carbon_ of the blood, and forms _carbonic
acid gas_.
[Verse: "Be not as the horse, or as the mule, which have
no understanding: whose mouth must be held with the bit and
bridle."--PSALM XXXII.]
6. _Why is this combination necessary?_
Because we are so created that the substances of our bodies are
constantly undergoing change, and this resolving of solid matter into a
gaseous form, is the plan appointed by our Creator to remove the matter
called _carbon_ from our systems.
7. _Why do our bodies feel warm?_
Because, in the union of _oxygen_ and _carbon_, heat is developed.
8. _What is this union of oxygen and carbon called?_
It is called _combustion_, which, in chemistry, means the decomposition
of substances, and the formation of new combinations, accompanied by
heat; and sometimes by light, as well as heat.
9. _What is formed by the union of oxygen and carbon?_
Carbonic acid gas.
10. _What becomes of this carbonic acid gas?_
It is sent out of our bodies by the compressure of the lungs, and
mingles with the air that surrounds us.
11. _Is this carbonic acid gas heavier or lighter than the air?_
Pure carbonic acid gas is the heaviest of all the gases. That which is
sent out of the lungs is not pure, because the whole of the air taken
into the lungs at the previous inspiration has not been deprived of its
_oxygen_, and the nitrogen is returned. Therefore the breath sent out
of the lungs may be said to consist of _air_, with a large proportion
of _carbonic acid gas_.
12. _What is the composition of air in its natural state?_
It consists of _oxygen_, _nitrogen_, and _carbonic acid gas_, in the
proportions of oxygen 20 volumes, nitrogen 79 volumes, and carbonic
acid gas 1 volume. It also contains a slight trace of watery vapour.
13. _What is the state of the air after it has once been breathed?_
It has parted with about one-sixth of its oxygen, and taken up an
equivalent of carbonic acid. And were the same air to be breathed six
times successively, it would have parted with _all_ its oxygen, and
could no longer sustain life.
[Verse: "A prudent man forseeth the evil, and hideth himself; but
the simple pass on, and are punished."--PROVERBS XXVII.]
14. _Is the impure air sent out of the lungs lighter or heavier than
common air?_
At first, being rarefied by warmth, it is _lighter_. But, if
undisturbed, it would become _heavier_ as it cooled, and would descend.
15. _Why is it proper to have beds raised about two feet from the
ground?_
Because at night, the bed-room being closed, the breath of the sleeper
impregnates the air of the room with carbonic acid gas, which,
descending, lies in its greatest density near to the floor.
16. _What are the chief sources of carbonic acid gas?_
The vegetable kingdom (as will be hereafter explained), the combustion
of substances composed chiefly of carbon, the breathing of animals, and
the decomposition of carbonic compounds.
17. _Is breathing a kind of combustion?_
It is. In the breathing of animals, the burning of coals, or of wood,
or candles, &c., similar changes occur. The _oxygen_ of the air
combines with the _carbon_ of the substance said to be burnt, and forms
_carbonic acid gas_, which unfits the air for the purposes of either
breathing or of burning, until it has been renewed by admixture with
the air.
18. _What is carbon?_
It is one of the elementary bodies, and is very abundant throughout
nature. It abounds mostly in vegetable substances, but is also
contained in animal bodies, and in minerals. The form in which it is
most familiar to us is that of _charcoal_, which is carbon almost pure.
19. _What is meant by an elementary body?_
An elementary body is one of those substances in which chemistry is
unable to discover more than one constituent. For instance, the chemist
finds that water is composed of _oxygen_ and _hydrogen_. Water is
therefore a _compound_ body. But _carbon_ consists of _carbon only_,
and therefore it is called a simple, or elementary body.
[Verse: "Where no wood is, there the fire goeth out: so where there
is no tale-bearer, the strife ceaseth."--PROVERBS XXVI.]
20. _Why is it dangerous to burn charcoal in rooms?_
Because, being composed of _carbon_ that is nearly pure, its combustion
gives off a large amount of _carbonic acid gas_.
21. _What is the effect of carbonic acid gas upon the human system?_
It induces drowsiness and stupor, which, if not relieved by
ventilation, would speedily cause death.
22. _What is the reason that people feel drowsy in crowded rooms?_
Because the large amount of carbonic acid gas given off with the
breaths of the people, makes the air poisonous and oppressive.
23. _What other causes of drowsiness are there?_
The candles, gas, or fires that may be burning in the rooms where
people are assembled. Three candles produce as much carbonic acid gas
as one human being; and it is probable that one gas-light produces as
much carbonic acid gas as two persons.
24. _Have people ever been poisoned by their own breaths?_
In the reign of George the Second, the Rajah of Bengal took some
English prisoners in Calcutta, and put 146 of them into a place which
was called the "Black Hole." This place was only 18 feet square by 16
feet high, and ventilation was provided for only by two small grated
windows. _One hundred and twenty-three of the prisoners died in the
night_, and most of the survivors were afterwards carried off by putrid
fevers. Many other instances have occurred, but this one is the most
remarkable.
CHAPTER III.
25. _What is oxygen?_
Oxygen is one of the most widely diffused of the elementary substances.
It is a gaseous body.
[Verse: "Stand in awe and sin not: commune with your own heart upon
your bed and be still"--PSALM IV.]
26. _Why do persons who are walking, or riding upon horseback feel
warmer than when they are sitting still?_
Because as they breathe more rapidly, the combustion of the _carbon_
in the blood is increased by the _oxygen_ inhaled, and greater heat is
developed.
27. _Why does the fire burn more brightly when blown by a bellows?_
Because it receives, with every current of air, a fresh supply of
_oxygen_, which unites with the _carbon_ and _hydrogen_ of the coals,
causing more rapid combustion and increased heat.
28. _Why does not the oxygen of the air sometimes take fire?_
Because oxygen, _by itself_, is incombustible. The wick of a candle,
which retains the slightest spark, being immersed in oxygen, will
instantly burst into a brilliant flame; and even a piece of iron wire
made red-hot, and dipped in oxygen, will burn rapidly and brilliantly.
Oxygen, though non-combustible of itself, is the most powerful
_supporter of combustion_.
29. _Why do we know that oxygen will not burn of itself?_
Because when we immerse a burning substance into a jar of oxygen, it
immediately burns with intense brilliancy; but directly it is withdrawn
from the oxygen, the intensity of the flame diminishes, and the oxygen
which remains is _unaffected_.
30. _Why do we know that oxygen is necessary to our existence?_
Because animals placed in any kind of gas, or in any combination of
gases, where oxygen _does not exist_, die in a very short time.
31. _Where is oxygen found?_
It is found in the air, mixed with _nitrogen_; in water combined with
_hydrogen_; in the tissues of vegetables and animals; in our blood; and
in various compounds called, from the presence of oxygen, _oxides_.
32. _Why is the oxygen of the air mixed so largely with nitrogen?_
Because _oxygen_ in any greater proportion than that in which it is
found in the atmosphere, would be too exciting to the animal system.
Animals placed in _pure oxygen_ die in great agony from fever and
excitement, amounting to madness.
[Verse: "As vinegar is to the teeth, and as smoke to the eyes, so is
the sluggard to him that sent him."--PROVERBS X.]
33. _What is nitrogen?_
Nitrogen is an elementary body in the form of gas.
34. _Where is nitrogen found?_
It is chiefly found in the air, of which it constitutes 79 out of 100
volumes. It may be mixed with oxygen in various proportions; but in the
atmosphere it is uniformly diffused. It is found in most animal matter,
_except fat and bone_. It is not a constituent of the _vegetable
acids_, but it is found in most of the _vegetable alkalies_.
35. _What are acids?_
Acids are a numerous class of chemical bodies. They are generally sour.
Usually (though there are exceptions) they have a great affinity for
water, and are easily soluble therein; they unite readily with most
_alkalies_, and with the various _oxides_. All acids are compounds of
two or more substances. Acids are found in all the kingdoms of nature.
36. _What are alkalies?_
Alkalies are a numerous class of substances that have a great affinity
for, and readily combine with, _acids_, forming _salts_. They exercise
peculiar influence upon vegetable colours, turning blues green, and
yellows reddish brown. But they will restore the colours of vegetable
blues which have been reddened by _acids_; and, on the other hand,
the _acids_ restore vegetable colours that have been altered by the
_alkalies_. Alkalies are found in all the kingdoms of nature.
37. _Could animals live in nitrogen?_
No; they would immediately die. But a mixture of _oxygen_ and
_nitrogen_, in equal volumes, constitutes _nitrous oxide_, which gives
a pleasurable excitement to those who inhale it, causing them to be
merry, almost to insanity; it has, therefore, been called _laughing
gas_.
38. _Why does nitrous oxide produce this effect?_
Because it introduces into the body more _oxygen_ than can be consumed.
It, therefore, deranges the nervous system, and being a powerful
stimulant, gives an unnatural activity to the nervous centres and the
brain.
[Verse: "Lord, make me know mine end, and the measure of my days,
that I may know how frail I am."--PSALM XXXIX.]
39. _In what proportions are the atmospheric gases found in the blood?_
The mean quantity of the gases contained in the human blood has been
found to be equal to 1-10th of its whole volume. In _venous_ blood, the
average quantity of _carbonic acid_ is about 1-18th, that of _oxygen_
about 1-85th, and that of _nitrogen_ about 1-100th of the volume of
the blood. In _arterial_ blood their quantities have been found to be
_carbonic acid_ about 1-14th, _oxygen_ about 1-38th, and _nitrogen_
about 1-72nd.
40. _Then is nitrogen taken into the blood from the air?_
Such a supposition is highly improbable. It is probably derived
from _nitrogenised food_, just as _carbonic acid_ is derived from
_carbonised food_.
41. _What is venous blood?_
Venous blood is that which is returning through the _veins_ of the body
from the organs to which it has been circulated.
42. _What is arterial blood?_
Arterial blood is that which is flowing from the heart through the
_arteries_ to nourish the parts where those arteries are distributed.
43. _What is the difference between venous and arterial blood?_
Venous blood contains _more_ carbonic acid, and _less_ oxygen and
nitrogen than arterial blood.
44. _Will nitrogen burn?_
It will not burn, nor will it support combustion.
45. _What is the difference between "burning" and "supporting
combustion?"_
Oxygen gas will not burn of itself, but it aids the decomposition
by fire of bodies that are combustible. It is therefore called a
_supporter of combustion_. But hydrogen gas, _though it burns of
itself_ will extinguish a flame immersed in it. It is therefore said
to be a body which will _burn_, but _will not support combustion_.
[Verse: "As coals are to burning coals, and wood to fire; so is a
contentious man to kindle strife."--PROVERBS XXVI.]
46. _What becomes of the nitrogen that is inhaled with the air?_
It is thrown off with the breath, mixed with _carbonic acid gas_, and
flies away to be renewed by a fresh supply of oxygen.
47. _Where does nitrogen find a fresh supply of oxygen?_
In the atmosphere. Nitrogen is said to possess a remarkable tendency to
_mix_ with oxygen, without having a positive chemical _affinity_ for
it. That is to say, neither the _oxygen_ nor the _nitrogen_ undergoes
any change by the union, except that of _admixture_. The oxygen and
the nitrogen still possess their own peculiar properties. Oxygen and
nitrogen are found in nearly the same proportions in all climates, and
at all altitudes.
48. _In combustion does any other result take place besides the union
of oxygen and carbon forming carbonic acid gas?_
Yes. Usually _hydrogen_ is present, which in burning unites with
_oxygen_, and forms _water_.
CHAPTER IV.
49. _What is hydrogen?_
Hydrogen is an elementary gas, and is the lightest of all known bodies.
50. _Will hydrogen support animal life?_
It will not. It proves speedily fatal to animals.
51. _Will hydrogen support combustion?_
Although it will burn, yielding a feeble bluish light, it will, if
pure, extinguish a flame that may be immersed in it. Hydrogen will
therefore _burn_, but will not _support combustion_.
52. _Why will hydrogen explode, if it will not support combustion?_
When hydrogen explodes it is always in combination with _oxygen_,
or with the common air, which contains _oxygen_. _Two_ measures of
hydrogen and _one_ of oxygen form a most explosive compound.
[Verse: "As smoke is driven away, so drive them away: as wax
melteth before the fire, so let the wicked perish at the presence of
God."--PSALM XLVI.]
53. _Why does hydrogen explode, when mixed with oxygen, upon being
brought in contact with fire?_
Because of its strong affinity for _oxygen_, with which, upon the
application of heat, it unites to form water.
54. _Where does hydrogen chiefly exist?_
In the form of _water_, where it exists in combination with _oxygen_.
_Eleven_ parts of hydrogen, and _eighty-nine_ of oxygen, form water.
55. _Is hydrogen found elsewhere?_
It is never found but in a state of combination; united with oxygen,
it exists in _water_; with nitrogen, in _ammonia_; with chlorine, in
_hydro-chloric acid_; with fluorine, in _hydro-fluoric acid_; and in
numerous other combinations.
56. _Is the gas used to illuminate our streets, hydrogen gas?_
It is; but it is combined with carbon, derived from the coals from
which it is made. It is therefore called _carburetted hydrogen_, which
means _hydrogen_ with _carbon_.
57. _How is hydrogen gas obtained from coals?_
It is driven out of the coals by heat, in closed vessels, which prevent
its union with _oxygen_.
58. _What becomes of the water which is formed by the burning of
hydrogen in oxygen?_
It passes into the air in the form of watery vapour. Frequently it
condenses, and may be seen upon the walls and windows of rooms where
many lights or fires are burning. Sometimes, also, portions of it
become condensed in the globes of the glasses that are suspended over
the jets of gas. _A large volume of these gases forms only a very small
volume of water._
59. _What becomes of the carbonic acid gas which is produced by
combustion?_
It is diffused in the air, which should be removed by adequate
ventilation.
[Verse: "I will both lay me down in peace and sleep: for thou, Lord,
only, makest me dwell in safety."--PSALM IV.]
60. _What proportion of carbonic acid gas is dangerous to life?_
Any proportion over the natural one of 1 per cent. may be regarded as
_injurious_. But toxicologists state that _five per cent._ of carbonic
acid gas in the atmosphere is _dangerous_ to life.
61. _What are toxicologists?_
Persons who study the nature and effects of poisons and their antidotes.
62. _Which kind of combustible used for lighting tends most to vitiate
the air?_
Assuming all the lights to be of the same intensity, the degree in
which the substances burnt would vitiate the atmosphere may be gathered
from the number of minutes each would take to exhaust a given quantity
of air. This has been found to be: rape oil, 71 minutes; olive oil, 72;
Russian tallow, 75; town tallow, 76; sperm oil, 76; stearic acid, 77;
wax candles, 79; spermaceti candles, 83; common coal gas, 98; canal
coal gas, 152. Thus it is shown that rape oil is _most destructive_ of
the atmosphere, and that coal gas is the _least destructive_.
63. _Is an escape of hydrogen gas from a gas-pipe dangerous to life?_
It is dangerous, first, by _inhalation_. There are no less than six
deaths upon record of persons who were killed by sleeping in rooms near
to which there was a leakage of gas.
It is dangerous, secondly, by _explosion_.
In 1848, an explosion of gas occurred in Albany-street,
Regent's-park, London. The gas accumulated in a shop for a very
short time only. It had been escaping from a crack in the meter
for about one hour and twenty minutes. The area of the room was
about 1,620 cubic feet. When the gas exploded, it blew out the
entire front of the premises, carried two persons through a window
into an adjoining yard, and forced another person on to the
pavement on the opposite side of the street, where she was killed.
The effect of the explosion was felt for more than a quarter of
a mile on each side of the house, and most of the windows in the
neighbourhood were shattered. The iron railings over the area of
the house directly opposite were snapped asunder; and a part of
the roof, and the back windows of another house, were carried to
a distance of from 200 to 300 yards. The pavement was torn up
for a considerable length, and the damage done to 103 houses
was afterwards reported to amount to £20,000. Other serious
explosions have taken place. The explosions of "_coal damp_,"
which frequently occur in mines, are of a similar character.
[Verse: "O Lord, our Lord, how excellent is thy name in all the
earth! who hast set thy glory above the heavens."--PSALM VIII.]
64. _What proportion of hydrogen gas with atmospheric air will explode?_
According to the researches of Sir Humphrey Davy, _seven_ or _eight_
parts of _air_, to _one_ of _gas_, produce the greatest explosive
effect; while _larger_ proportions of gas are less dangerous. A mixture
of _equal parts_ of gas and air will burn, but it will not explode.
The same is the case with a mixture of _two_ of _air_, or _three_ of
_air_, and _one_ of _gas_; but _four_ of _air_ and _one_ of _gas_ begin
to be explosive, and the explosive tendency increases up to _seven_
or _eight_ of _air_ and _one_ of _gas_, after which the increased
proportion of gas diminishes the force of the explosion.
65. _What is the best method of preventing the explosion of gas?_
Observe the rule, _never to approach a supposed leakage with a light_.
Fortunately the gas, which threatens our lives, warns us of the danger
by its pungent smell. The first thing to be done is to open windows
and doors, and to ventilate the apartment. Then turn the gas off at
the main, and wait a short time until the accumulated gas has been
dispersed.
66. _Does hydrogen gas rise or fall when it escapes?_
Being _twelve times lighter than common air_ it _rises_, and therefore
it would be better for ventilation to open the window at the _top_ than
at the _bottom_. But all gases exhibit a strong tendency to _diffuse
themselves_, and therefore they do not rise or fall in the degree that
might be anticipated.
67. _What proportion of hydrogen in the air is dangerous to life, if
inhaled?_
One-fiftieth part has been found to have a _serious effect_ upon
animals. The effects it produces upon the human system are those of
depression, headache, sickness, and general prostration of the vital
powers. It is therefore advisable to observe precautions in the use of
gas.
[Verse: "From the place of his habitation he looketh upon all the
inhabitants of the earth."--PSALM XXXIII.]
68. _What proportion of gas in the air may be recognised by the smell?_
By persons of acute powers of smelling it may be recognised when there
is _one_ part of _gas_ in _five hundred parts of atmospheric air_; but
it becomes very perceptible when it forms _one_ part in _a hundred and
fifty_. Warning is, therefore, given to us long before the point of
danger arrives.
69. _What other sources of hydrogen are there in our dwellings?_
It arises from the decomposition of animal and vegetable substances,
containing _sulphur_ and _hydrogen_. These give off a gas called
_sulphuretted hydrogen_, from which the fætid effluviam of drains
and water-closets chiefly arise. We should, therefore, take every
precaution to secure effective drainage, and to keep drain-traps in
proper order.
70. _May the use of gas for purposes of illumination be considered
highly dangerous?_
Not if it is intelligently managed. The appliances for the regulation
of gas are so very simple and perfect, that accidents seldom arise
except from neglect. In England 6,000,000 tons of coal are usually
consumed in the manufacture of gas, producing 60,000,000,000 cubic feet
of gas. And yet accidents are of very uncommon occurrence.
CHAPTER V.
71. _What is heat?_
Heat is a principle in nature which, like light and electricity, is
best understood by its _effects_. We popularly call that heat, which
raises the temperature of bodies submitted to its influence.
72. _What is caloric?_
Caloric is another term for heat. It is advisable, however, to use the
term _caloric_ when speaking of the _cause_ of heat, and of _heat_ as
the _effect_ of the presence of _caloric_.
[Verse: "While the earth remaineth, seed-time and harvest, and
cold and heat, and summer and winter, and day and night, shall not
cease."--GEN. VIII.]
73. _What is the source of caloric?_
The sun is its chief source. But caloric, in some degree, exists _in
every known substance_.
74. _What are the effects of caloric?_
Heat which, in proportion to its intensity, acts variously upon all
bodies, causing _expansion_, _fusion_, _evaporation_, _decomposition_,
_&c._
75. _Why is caloric called a repulsive agent?_
Because its chief effects are to _expand_, _fuse_, _evaporate_, or
_decompose_ the substances upon which it acts.
76. _What is an attractive agent, in contradistinction to a repulsive
agent?_
Chemical attraction, or affinity, is an attractive agent--as when
bodies seek of their own natures to unite and form some new body.
77. _When is a body said to be hot?_
When it holds so much _caloric_ that it diffuses heat to surrounding
objects.
78. _When is a body said to be cold?_
When it holds less _caloric_ than surrounding objects, and absorbs heat
from them.
79. _How may caloric be excited to develop heat?_
By any means which cause agitation, or produce an active change in the
condition of bodies. Thus friction, percussion, sudden condensation
or expansion, chemical combination, and electrical discharges, all
develope _heat_.
80. _Why do "burning glasses" appear to set fire to combustible
substances?_
Because they gather into one point, or _focus_, several rays of
_caloric_ as they are travelling from the sun, and the accumulation of
caloric developes that intensity of _heat_ which constitutes _fire_.
81. _What is a focus?_
In optics, it is the point or centre at which, or around which,
divergent rays are brought into the closest possible union.
[Verse: "Yet man is born to trouble, as the sparks fly upward.--I
would seek unto God, and unto God would I commit my cause."--JOB V.]
82. _What is fire?_
It is a violent chemical action attending the combustion of the
ingredients of _fuel_ with the _oxygen_ of the air.
83. _What are the properties of fire?_
It imparts heat, which has the effect of expanding both fluids and
solids.
It cannot exist without the presence of combustible materials.
It has a tendency to diffuse itself in every direction.
It cannot exist without oxygen or atmospheric air.
84. _What elements take part in the maintenance of a fire?_
Hydrogen, carbon, and oxygen. Hydrogen and carbon exist in the _fuel_,
and oxygen is supplied by the _air_.
85. _How does the combustion of a fire begin?_
A match made of phosphorous and sulphur (highly inflammable substances)
is drawn over a piece of sand-paper; the _friction_ of the match
induces the presence of _caloric_, which developes _heat_, and ignites
the match, the burning of which is sustained by the _oxygen_ of the
air. The flame is then applied to paper or wood, and the heat of the
flame is sufficient to drive out _hydrogen gas_, which unites with the
_oxygen_ of the air, and burns, imparting greater heat to the _carbon_
of the coals, which assumes the form of carbonic acid gas by union with
_oxygen_, and in a little while all the conditions of _combustion_ are
established.
86. _What are the properties of heat?_
It may exist without _fire_ or _light_.
It is not sensible to _vision_.
It makes an impression upon our _feelings_.
It acts powerfully upon _all bodies_.
It has no _weight_.
It attends, or is connected with, _all the operations of nature_.
It radiates from _all bodies_ in straight lines, and in all
_directions_.
It strikes most powerfully in _direct lines_.
Its rays may be collected into a _focus_, just as the rays of the sun.
It may be _reflected_ from a polished surface.
It is more easily _conducted_ by some substances than by others.
[Verse: "For my days are consumed like smoke, and my bones are
burned as an hearth."--PSALM CII.]
87. _What is animal heat?_
Animal heat is derived from the slow combustion of _carbon_ in the
blood of animals with the _oxygen_ of the air which the animals breathe.
88. _What is latent heat?_
Latent heat (or more properly _latent caloric_) is that which exists,
in some degree, in all _bodies_, though it may be imperceptible to the
_senses_.
89. _Is there latent caloric in ice, snow, water, marble, &c?_
Yes; there is some amount of _caloric_ in all substances.
A blacksmith may hammer a small piece of iron until it becomes
_red hot_. With this he may light a match, and _kindle the fire
of his forge_. The iron has become more dense by the hammering,
and it cannot again be heated to the same degree by similar
means, until it has been exposed _in fire_, to _a red heat_. Is
it not possible that, by hammering, the particles of iron have
been driven closer together, and _the latent heat_ driven out?
No further hammering will force the atoms nearer, and therefore
no further heat can be developed. But when the iron has _again
absorbed caloric_, by being plunged in a fire, it is again charged
with latent heat. Indians produce _sparks_ by rubbing together
_two pieces of wood_. Two pieces of ice may be rubbed together
until sufficient warmth is developed to _melt them both_. The
axles of railway carriages frequently become _red hot_ from
_friction_.
90. _Have vegetables heat?_
Yes; whenever oxygen combines with carbon to form carbonic acid gas,
an extrication of heat takes place, however minute the amount. Such
a combination occurs much more extensively during the germination of
seeds and the impregnation of flowers, than at any other time. In the
germination of barley heaped in rooms, previous to being converted
into malt, it is well known that a _considerable amount of heat is
developed_.
91. _Has any investigation of this subject ever been carefully made?_
Yes. Lamarck, Senebier, and De Candolle, found the flowers of the
_Arum Maculatum_, between three and seven o'clock in the afternoon, as
much as 7 deg. Reaum. warmer than the external air. Schultz found a
difference of 4 deg. to 5 deg. between the heat of the spathe of the
_Canadian pinnatifolium_ and the surrounding air, at six to seven
o'clock p.m. Other observations have established differences of as
much as 30 deg. between the temperature of the spathe of the _Arum
cordifolium_, and that of the surrounding atmosphere.
[Verse: "And there are diversities of operations, but it is the
same God which worketh in all."--CORINTHIANS XII.] 92. _Have plants
sometimes a temperature lower than that of the surrounding air?_
Yes. It has not only been found that under particular circumstances
the heat of certain parts of plants is elevated to a very remarkable
degree, but that, under nearly all circumstances, they have a
temperature different from that of the external air, being _warmer in
winter, and cooler in summer_.
CHAPTER VI.
93. _How many kinds of combustion are there?_
There are _three_, viz., slow oxydation, _when little or no light is
evolved_; a more rapid combination, _when the heat is so great as to
become luminous_; and a still more energetic action, _when it bursts
into flame_.
94. _Why does phosphorous look luminous?_
Because it is undergoing slow _combustion_.
95. _Why do decayed wood, and putrifying fish, look luminous?_
Because they are undergoing slow _combustion_. In these cases the heat
and light evolved are at no one time very considerable. But the _total
amount of heat_, and probably of _light_, generated through the lengthy
period of this slow oxydation, _amounts to exactly the same as would be
evolved during the most rapid combustion of the same substances_.
96. _What is flame?_
It is gaseous matter burning at a _very high temperature_.
97. _Why, when we put fresh coals upon a fire, do we hear the gas
escaping from the coals without taking fire?_
Because, the fire being slow, the temperature is not high enough to
ignite the gas.
[Verse: "I will praise thee, O Lord, with my whole heart; I will
show forth thy marvellous work."--PSALM IX.]
98. _What is the gas which escapes from the coals?_
Carburetted hydrogen.
99. _Why, if we light a piece of paper, and lay it where the gas is
escaping from the coals, will it burst into flame?_
Because the lighted paper gives a _heat sufficient_ to ignite the gas;
and because also hydrogen requires the contact of _flame_ to ignite it.
100. _Why, when the coals have become heated, will the hydrogen burst
into flame?_
Because the _carbon_ of the coals, and the _oxygen_ of the air, have
begun to combine, and have greatly increased the _heat_, and have
produced a rapid combustion, _so nearly allied to flame_, that it
_ignites the hydrogen_.
101. _What temperature is required to produce flame?_
That depends upon the nature of the combustible you desire to burn.
Finely divided phosphorous and phosphorated hydrogen will take fire at
a temperature of 60 deg. or 70 deg.; solid phosphorous at 140 deg.;
sulphur at 500 deg.; hydrogen and carbonic oxide at 1,000 deg. (red
heat); coal gas, ether, turpentine, alcohol, tallow, and wood, at
about 2,000 deg. (incipient white heat). When once inflamed they will
_continue to burn_, and will maintain a very high temperature.
102. _What is smoke?_
Smoke consists of small particles of _carbon_ of _hydrogen gas_, and
_other volatile matters_, which are driven off by heat and carried up
the chimney.
103. _Is it not a waste of fuel to allow this matter to escape?_
It is, as it might all be burnt up by better management.
104. _How may the waste be avoided?_
By putting on only a little coals at a time, so that the heat of the
fire shall be sufficient to consume these volatile matters as they
escape.
[Verse: "And the strong shall be as tow, and the maker of it as
a spark, and they shall both burn together, and none shall quench
them."--ISAIAH I.]
105. _Why is there so little smoke when the fire is red?_
Because the _hydrogen_ and the _volatile_ parts of the _coal_ have
already been driven off and consumed, and the combustion that continues
is principally caused by the _carbon_ of the coals, and the oxygen of
the air.
106. _Will carbon, burnt in oxygen, produce flame and smoke?_
It burns brightly, but it produces neither flame nor smoke.
107. _Why do not charcoal and coke fires give flame?_
Because the _hydrogen_ has been driven off by the processes by which
charcoal and coke are made.
108. _What is a conductor of heat?_
A conductor of heat is any substance through which heat is _readily
transmitted_.
109. _What is a non-conductor of heat?_
A non-conductor is any substance through which heat will _not_ pass
readily.
110. _Name a few good conductors._
Gold, silver, copper, platinum, iron, zinc, tin, stone, _and all dense
solid bodies_.
111. _Name a few non-conductors._
Fur, wool, down, wood, cotton, paper, and _all substances of a spongy
or porous texture_.
112. _How is heat transmitted from one body to another?_
By Conduction, Radiation, Reflection, Absorption and Convection.
113. _What is the Conduction of heat?_
It is the communication of heat from one body to another _by contact_.
If I lay a penny piece upon the hob, it becomes hot by _conduction_.
114. _What is the Radiation of heat?_
The transmission of heat by a _series of rays_. If I hold my hand
before the fire, the rays of heat fall upon it, and _my hand receives
the heat through radiation_.
[Verse: "Sing praises to the Lord, which dwelleth in Zion, declare
among the people his doings."--PSALM IX.]
115. _What is the Reflection of heat?_
The reflection of heat is the _throwing back_ of its rays towards the
direction whence they came. In a Dutch oven the rays of heat pass from
the fire to the oven, and are _reflected_ back again by _the bright
surface of the tin_. There is, therefore, considerable economy of heat
in ovens, and other cooking utensils constructed upon this plan.
116. _What is the Absorption of heat?_
The absorption of heat is the taking of it up by the body to which
it is transmitted or conducted. Heat was conveyed to my hand by
_radiation_, and _taken up_ by my hand by _absorption_.
117. _What is the Convection of heat?_
The convection of heat is the transmission of it _through_ a body or
a number of bodies, or particles of bodies, by those substances which
_first received it_; as when hot water rises from the bottom of a
kettle and imparts heat to the cold water lying above it.
CHAPTER VII.
118. _Why does not a piece of wood which is turning at one end, feel
hot at the other end?_
Because wood is _a bad conductor of heat_.
119. _Why is wood a bad conductor of heat?_
Because the arrangement of the particles of which it is composed does
not favour the transmission of _caloric_.
120. _Why do some articles of clothing feel cold, and others warm?_
Because some are bad conductors of heat, _and do not draw off much of
the warmth of our bodies_; while others are _better conductors_, and
_take up a larger portion of our warmth_.
[Verse: "The fining pot is for silver, and the furnace for gold: but
the Lord trieth the hearts."--PROVERBS XVII.]
121. _Which feels the warmer, the conductor or non-conductor?_
The non-conductor, as it does not readily _absorb_ the warmth of our
bodies.
122. _What substances are the best conductors of heat?_
Gold, silver, copper, and most substances of close and hard formation,
&c.
123. _What substances are the worst conductors of heat?_
Fur, eider down, feathers, raw silk, wood, lamp-black, cotton, soot,
charcoal, &c.
124. _Why has the toasting-fork a wooden handle?_
Because wood is not _so good a conductor_ as metal, therefore the wood
prevents the heat from being transmitted _by conduction_ to our hands.
125. _Why has the coffee-pot a wooden handle?_
Because the metal of the coffee-pot would otherwise _conduct the heat
to the hand_; but wood, _being a bad conductor_, prevents it.
126. _Why does hot water in a metal jug feel hotter than in an
earthenware one?_
Because metal, being a good conductor, _readily delivers heat to the
hand_; but _earthenware, being an indifferent conductor_, parts with
the heat slowly.
127. _How can we ascertain that wood prevents the conduction of heat to
the hand?_
By passing the top of the finger along the wooden handle of the
coffee-pot, until it reaches the point where the wood meets the metal.
The wooden handle will be found to be _cool_, but the metal will feel
_very hot_.
128. _Of what use are kettle-holders?_
Being made of _bad conductors_, such as wood, paper, or woollen cloth,
they will not readily _conduct_ the heat from the kettle to the hand.
[Verse: "Wisdom is the principal thing; therefore get wisdom: and
with all thy getting get understanding."--PROVERBS IV.]
129. _Will a kettle-holder, being a bad conductor, sometimes conduct
heat to the hand?_
Yes. But so slowly that the hand will not _feel the inconvenience of
too much heat_.
130. _Why does hot metal feel hotter than heated wool, though they may
both be of the same degree of temperature?_
Because metal gives out heat _more rapidly than wool_, by which it is
made _more perceptible to our feelings_.
131. _Which would become cold first--the metal or the wool?_
The _wool_, because, although the metal conducts heat more rapidly, to
a substance in contact with it, it does not _radiate heat_ as well as a
_black and rough substance_.
132. _Why do iron articles feel intensely cold in winter?_
Because iron is one of the best conductors, and draws off heat from the
hand very rapidly.
133. _What is the cause of the sensation called cold?_
When we feel cold, heat is being _drawn off from our bodies_.
134. _What is the cause of the sensation called heat?_
When we feel hot, our bodies are _absorbing heat_ from external causes.
The condition here implied is that of health, and of ordinary
circumstances. A person in a condition of fever, suffering from
intense heat arising from a diseased state of the blood, could not
be said to be _absorbing heat_. Nor could such a description apply
to a person who, by a very rapid walk, has raised the temperature
of his body considerably above its natural state, by the _internal
combustion_ which has already been described. A person feeling hot
in bed, from excessive clothes, feels hot from the _development of
heat internally_, which is not _conducted away_ with sufficient
rapidity to maintain the natural temperature of the body.
135. _If a person, sitting before a fire-place, without a fire, were
to set one foot upon a rug, and the other upon the stone hearth, which
would feel the colder?_
The foot on the stone, because stone is a good conductor, and would
_conduct the warmth of the foot away from it_.
[Verse: "The earth is the Lord's, and the fulness thereof; the
world, and they that dwell therein."--PSALM XXIV.]
136. _What does the hearth-stone do with the heat that it receives?_
It delivers it to the surrounding air, and to any other bodies with
which it may be _in contact_--and as it parts with heat, _it takes up
more from any body hotter than itself_.
137. _When there is no fire in a room, what is the relative temperature
of the various things in the room?_
They are all of the same temperature.
138. _If all the articles in the room are of the same temperature, why
do some feel colder than others?_
Because they differ in their relative powers of _conduction_. Those
that are the best conductors feel coldest, as they convey away the heat
of the hand most rapidly.
If you lay your hand upon the _woollen table cover_, or upon the
_sleeve of your coat_ or mantle, it will feel _neither warm nor
cold_, under ordinary circumstances. But if you raise your hand
from the table cover, or coat, and lay it on the marble mantel
piece, the mantel-piece will feel _cold_. If now you return
your hand from the mantel-piece to the table cover or coat, _a
sensation of warmth will become distinctly perceptible_. This will
afford a good conception of the relative _powers of conduction of
wool and marble_.
139. _How long does a substance feel cold or hot to the touch?_
Until it has brought the part touching it to the same temperature as
itself.
140. _When do substances feel neither hot nor cold?_
When they are of the same temperature as our bodies.
141. _Why, under these circumstances, do they feel neither hot nor
cold?_
Because they neither take heat from, nor supply it to, the body.
142. _Which would feel the warmer, when the fire was lighted, the
hearth-rug or the hearth-stone?_
The hearth-stone, because it is a _good conductor_, and would not
only _receive heat_ readily, but would _part with it as freely_
(thereby making its heat _perceptible_). But the hearth-rug, _being
a bad conductor_, would part with its heat very slowly, and it would
therefore be _less perceptible_.
[Verse: "Fire and hail; snow and vapour; stormy wind fulfilling his
word."--PSALM CXLVIII.]
143. _Would the hearth-stone feel hotter than the hearth-rug though
both were of the same temperature?_
It would feel _hotter than the hearth-rug_, because it would part with
its heat so rapidly that it would be the _more perceptible_.
144. _But if the hearth-stone and the hearth-rug were both colder than
the hand, which would feel the colder of the two?_
Then the hearth-stone would feel the colder, because, _being a good
conductor_, it would _take heat_ from the hand more freely than the
hearth-rug, which is a _bad conductor_.
145. _Why would the hearth-stone feel comparatively hotter in the one
case, and colder in the other?_
Because, _being a good conductor_, it would conduct heat rapidly _to_
the hand when hot, and take heat rapidly _from_ the hand when cold.
CHAPTER VIII.
146. _Which are the better conductors of heat, fluids or solids?_
Generally speaking, _solids_, especially those of them that are dense
in their substance.
147. _Why are dense substances the best conductors of heat?_
Because the heat more readily travels from particle to particle until
it pervades the mass.
148. _Why are fluids bad conductors of heat?_
Because of the want of _density_ in their bodies; and because a portion
of the imbibed heat always passes off from fluids by _evaporation_.
[Verse: "He casteth forth his ice like morsels: who can stand before
his word,"--PSALM CXLVII.]
149. _Why are woollen fabrics bad conductors of heat?_
Because there is a considerable amount of _air_ occupying the spaces of
the texture.
150. _Is air a good or a bad conductor?_
Air is a _bad conductor_, and it chiefly transmits heat, as water does,
by _convection_.
151. _Is water a good or a bad conductor?_
Water is an indifferent conductor, but it is a _better conductor than
air_.
152. _Why, when we place our hands in water, which may be of the same
temperature as the air, does the water feel some degrees colder?_
Because water, _being a better conductor than air_, takes up the warmth
of the hand _more rapidly_.
153. _Why, when we take our hands out of water do they feel warmer?_
Because the air does not abstract the heat of the hand so rapidly as
the water did, and the change in the degree of rapidity with which the
heat is abstracted _produces a sensation of increased warmth_.
154. _Why do we see blocks of ice wrapped in thick flannel in summer
time?_
Because the flannel, being a non-conductor, prevents the _external
heat_ from _dissolving the ice_.
Flannel wrapped around a _warm_ body _keeps in its heat_; and
wrapped around a _cold_ body, prevents heat from _passing into it_.
155. _How do we know that air is not a good conductor of heat?_
Because, _in still air_, heat would travel to a given point much more
rapidly, and in greater intensity, through even an indifferent _solid
conductor_, than it would through the _air_.
156. _How do we know that water is not a good conductor of heat?_
Because in a deep vessel containing _ice_, and with heat applied at the
top, some portion of the water may be made to boil _before the ice,
which lies a little under the surface, is melted_.
[Verse: "As snow in summer, and as rain in harvest; so honour is not
seemly for a fool."--PROV. XXVI.]
157. _Why would you apply the heat at the top, in this experiment?_
Because in heating water it _expands and rises_. The boiling of water
is caused by the heated water _ascending from the bottom_, and the
colder water descending to occupy its place. If the heat were not
applied at the top, it would be distributed quickly by _convection_,
but not by _conduction_.
158. _Why are bottles of hot water, used as feet-warmers, wrapped in
flannel?_
Because the flannel, _being a bad conductor_, allows the heat to _pass
only gently_ from the bottle, and preserves the warmth for a _much
longer time_.
159. _Why are hot rolls sent out by the bakers, wrapped up in flannel?_
Because the flannel, _being a bad conductor_, does not _carry off
rapidly the heat of the rolls_.
160. _Why is it said that snow keeps the earth warm?_
Because snow is a _bad conductor_, and prevents the frosty air from
_depriving the earth of its warmth_.
161. _Why are snow huts which the Esquimaux build found to be warm?_
Because snow, _being a bad conductor_, keeps in _the internal heat of
the dwelling_, and prevents the _cold outer air from taking away its
warmth_.
162. _Why is snow, being composed of congealed water (and water being a
better conductor than air), so good a non-conductor?_
Because in the process of congealation it is frozen into crystalline
forms, which, being collected into a mass, form a woolly body, thus
proving the truthfulness of the Bible simile, which says, God "giveth
snow like wool."
[Verse: "He giveth snow like wool: he scattereth the hoar frost like
ashes."--PSALM CXLVII.]
[Illustration: CRYSTALS OF SNOW, AS SEEN THROUGH A MICROSCOPE. FIG. 1.]
163. _Why does it frequently feel warmer after a frost has set in?_
Because, in the act of congealation a great deal of heat is given out,
and _taken up by the air_, and thus _the severity of the cold is in
some degree moderated_.
164. _Why is it frequently colder when a thaw takes place?_
Because, in the process of thawing, a certain amount of heat is
_withdrawn from the air_, and enters the thawed ice.
165. _What benefit results from these provisions of Nature?_
They moderate both the _severity of frosts_, and _the rapidity of
thaws_, which, in changeable climates, would be seriously detrimental
to _life_, and to _vegetation_.
166. _Why are furs and woollens worn in the winter?_
Because, being non-conductors, they prevent the warmth of the body from
being _taken up by the cold air_.
167. _Why are the skins of animals usually covered with fur, hair,
wool, or feathers?_
Because their coverings, being _non-conductors of heat_, preserve the
warmth of the bodies of the animals.
[Verse: "He sendeth out his word, and melteth them: he causeth his
wind to blow, and the waters to flow."--PSALM CXLVII.]
168. _How is the greater warmth of animals provided for in the winter?_
It is observed that, as winter approaches, there comes a short woolly
or downy growth, which, _adding to the non-conducting property of their
coats_, confines their animal warmth.
In small birds during winter, let the external colour of the
feathers be what it may, there will be found a kind of _black_
down next their bodies. Black is the _warmest colour_, and
the purpose here is to _keep in the heat_, arising from the
respiration of the animal.
169. _How is warmth provided for in animals that have no such coats?_
They are furnished with a layer of _fat_, which lies underneath the
skin. Fat consists chiefly of _carbon_, and is a _non-conductor_.
170. _Why are summer breezes said to be cool?_
Because, as they pass over the heated surface of the body, they bear
away a part of its heat.
171. _Why is a still summer air said to be sultry?_
Because, being heated by the sun's rays, _and being a bad conductor_,
it does not relieve the body by _carrying off its heat_.
172. _Why does fanning the face make it feel cooler?_
Because, by inducing currents of air to pass over the face, a part of
the excessive heat is taken up _and carried away_.
173. _Why does perspiration cool the body?_
Because it takes up a part of the heat, and, evaporating, _carries it
into the air_.
174. _Why does blowing upon hot tea cool it?_
Because it directs currents of air over the surface of the tea, and
these currents take up a part of the heat _and bear it away_.
175. _Why does air in motion feel cooler than air that is still?_
Because each wave of air _carries away a certain portion of heat_ and
being followed by another portion of air, _a further amount of heat is
borne away_.
[Verse: "Though I walk in the valley of the shadow of death I will
fear no evil, for thou art with me."--PSALM XXIII.]
176. _Is the atmosphere ever as hot as the human body?_
Not in this country. On the hottest day it is 10 or 12 deg. _cooler
than the temperature of our bodies_.
177. _What is the highest degree of artificial heat which man has been
known to bear?_
A man may be surrounded with air raised to the temperature of 300 deg.
(the boiling point being 212), and yet not have the heat of his body
raised more than two or three degrees above its natural temperature of
from 97 deg. to 100 deg.
178. _Why may man endure this degree of heat for a short time without
injury?_
Because the skin, and the vessels of fat that lie underneath it, are
bad conductors of heat.
And because perspiration passing from the skin and evaporating, would
_bear the heat away_ as fast as it was received.
Because, also, the vital principle (life) exercises a mysterious
influence in the preservation of living bodies from physical influences.
179. _Is the air ever hot enough, in any part of the world, to destroy
life?_
Yes. The hot winds of the Arabian deserts, which are called _simooms_,
scatter death and desolation in their track, withering trees and
shrubs, and burying them under waves of hot sand. When camels see the
approach of a simoom they rush to the nearest tree or bush, or to some
projecting rock, where they place their heads in an opposite direction
to that from which the wind blows, and endeavour to escape its terrible
violence. The traveller throws himself on the ground on the lee side of
the camel, and screens his head from the fiery blast within the folds
of his robe. But frequently both man and beast _fall a prey to the
terrible simoom_.
180. _Why are these hot winds so terrible in their effects?_
Because, being in motion, they search their way to every part of the
body, and passing over it _leave some portion of their heat behind_,
which is again followed by _additional heat from every fresh blast of
wind_.
[Verse: "The fear of the Lord is the beginning of knowledge: but
fools despise wisdom and instruction."--PROVERBS I.]
CHAPTER IX.
181. _What is Radiation?_
The radiation of heat is a _motion of the particles_, in a series of
rays, diverging in every direction from a heated body.
182. _What is this phenomena of Radiation understood to arise from?_
From a strongly repulsive power, possessed by particles of heat, by
which they are excited to recede from each other with great velocity.
183. _What is the greatest source of Radiation?_
The sun, which sends forth rays of _both light and heat_ in all
directions.
184. _When does a body radiate heat?_
When it is surrounded by a medium which is _a bad conductor_.
185. _When we stand before a fire, does the heat reach us by conduction
or by radiation?_
By radiation.
186. _What becomes of the heat that is radiated from one body to
another?_
It is either _absorbed_ by those bodies, or transmitted through
them and passed to other bodies by _conduction_, or diffused by
_convection_, or returned by _reflection_.
187. _How do we know that heat is diffused by radiation?_
If we set a metal plate (or any other body, though metal is best for
the experiment) before the fire, _rays of heat will fall upon it_. If
we turn the plate at a slight angle, and place another object in a
line with it, we shall find that the plate will _reflect the rays it
has received by radiation_, on to the object so placed; but if we place
an object _between the fire and the plate_, we shall find that the
rays of heat _will be intercepted_, and that the latter can no longer
_reflect heat_.
[Verse: "The fear of the Lord is the beginning of wisdom: a good
understanding have all they that do his commandments."--PSALM CXI.]
188. _Does the agitation of the air interfere with the direction of
rays of heat?_
It has been found that the agitation of the air does _not_ affect the
direction of rays of heat.
189. _Why, then, if a current of air passes through a space across
which heat is radiating, does the air become warmer?_
Because it takes up _some portion of the heat_, but it does not alter
the direction of the rays.
This is clearly illustrated by reference to _rays of light_ which
are seen under many circumstances. But they are never bent, moved,
nor in any way affected by the wind.
190. _Why will not a current of air disturb the rays of heat, just as
it would a spider's web, or threads of silk?_
Because heat is an _imponderable_ agent, that is, something which
cannot be acted upon by the ordinary physical agencies. It has _no
weight_, presents no _substantial body_, and is, in these latter
respects, similar to _light and electricity_.
191. _What other sources of radiation of heat are there besides the sun
and the fire?_
The _earth_, and all _minor bodies_, are, in some degree, _radiators of
heat_.
192. _What substances are the best radiators?_
All _rough_ and _dark_ coloured substances and surfaces are the _best
radiators of heat_.
193. _What substances are the worst radiators of heat?_
All _smooth_, _bright_, and _light coloured_ surfaces are _bad
radiators of heat_.
Dr. Stark, of Edinburgh, has proved, by a series of experiments,
the influence which the _colours_ of bodies have upon the
_velocity of radiation_. He surrounded the bulb of a thermometer
successively with equal weights of _black_, _red_, and _white_
wool, and placed it in a glass tube, which was heated to the
temperature of 180 deg. by immersion in hot water. The tube was
then cooled down to 50 deg. by immersion in cold water; the
_black_ cooled in 21 minutes, the _red_ in 26 minutes, and the
_white_ in 27 minutes.
[Verse: "Say unto wisdom, Thou art my sister; and call understanding
thy kinswoman."--PROVERBS VII.]
194. _If you wished to keep water hot for a long time, should you put
it into a bright metal jug, or into a dark earthenware one?_
You should put it into a _bright metal_ jug, because, _being a bad
radiator,_ it would not part readily with the heat of the water.
195. _Why would not the dark earthenware jug keep the water hot as long
as the bright metal one?_
Because the particles of earthenware being rough, and of dark colour,
_they radiate heat freely_, and the water would thereby be quickly
cooled.
CHAPTER X.
196. _But if (as stated in the Lessons upon Conduction) metal is a
better conductor of heat than stone or earthenware, why does not
the metal jug conduct away the heat of the water sooner than the
earthenware jug?_
It would do so, _if it were in contact with another conductor_; but,
being surrounded by air, _which is a bad conductor_, the heat must pass
off _by radiation_, and as bright metal surfaces are bad radiators,
the metal jug would retain the heat of the water _longer than the
earthenware one_.
197. _Supposing a red-hot cannon ball to be suspended by a chain from
the ceiling of a room, how would its heat escape?_
Almost entirely by _radiation_. But if you were to rest upon the
ball a cold bar of iron, a part of the heat would be drawn off by
_conduction_. Warm air would rise from around the ball, and, moving
upwards, would distribute some of the heat by _convection_. And some
of its rays, falling upon a mirror, or any other bright surface, might
be diffused by _reflection_.
[Verse: "I will teach you by the hand of God; that which is with the
Almighty will I not conceal."--JOB XXVII.]
198. _Do some substances absorb heat?_
Yes; those substances which are _the best radiators_ are also _the best
absorbers_ of heat.
199. _Why does scratching a bright metal surface increase its power of
radiation?_
Because every irregularity of the surface acts as a point of radiation,
or _an outlet_ by which the heat escapes.
200. _Why does a bright metal tea-pot produce better tea than a brown
or black earthenware one?_
Because bright metal _radiates but little heat_, therefore the water is
kept hot much longer, _and the strength of the tea is extracted by the
heat_.
201. _But if the earthenware tea-pot were set by the fire, why would it
then make the best tea?_
Because the dark earthenware tea-pot is a good _absorber of heat_, and
the heat it would _absorb_ from the fire would more than counterbalance
the loss by _radiation_.
202. _How would the bright metal tea-pot answer if set upon the hob by
the fire?_
The bright metal tea-pot would probably _absorb less heat_ than it
would radiate. Therefore it would not answer so well, _being set upon
the hob_, as the earthenware tea-pot.
203. _Why should dish covers be plain in form, and have bright
surfaces?_
Because, being bright and smooth, they will not allow heat to escape
_by radiation_.
204. _Why should the bottoms and back parts of kettles and saucepans be
allowed to remain black?_
Because a _thin_ coating of soot acts as a _good absorber of heat_, and
overcomes the _non-absorbing_ quality of the _bright surface_.
[Verse: "And the foolish said unto the wise, Give us of your oil,
for our lamps are gone out."]
205. _But why should soot be prevented from accumulating in flakes at
the bottom and sides of kettles and saucepans?_
Because, although soot is a _good absorber_ of heat, it is a _very bad
conductor_; an accumulation of it, therefore, would cause a waste of
fuel, by _retarding the effects of heat_.
206. _Why should the lids and fronts of kettles and saucepans be kept
bright?_
Because bright metal _will not radiate heat_; therefore, the heat
which is taken up readily through the _absorbing_ and _conducting_
power of the bottom of the vessel, is kept in and economised by the
_non-radiating_ property of the bright top and front.
207. _Does cold radiate as well as heat?_
It was once thought that _cold radiated_ as well as _heat_. But a mass
of ice can only be said to radiate cold, _by its radiating heat in less
abundance than that which is emitted from other bodies surrounding it_.
It is, therefore, _incorrect_ to speak of the _radiation of cold_.
CHAPTER XI.
208. _Why, if you hold a piece of looking-glass at an angle towards the
sum, will light fall upon an object opposite to the looking-glass?_
Because the rays of the sun are _reflected_ by the looking-glass.
209. _Why, when we stand before a mirror, do we see our features
therein?_
Because the rays of light that fall upon us are _reflected_ upon the
bright surface of the mirror.
210. _Why, if a plate of bright metal were held sideways before a fire,
would heat fall upon an object opposite to the plate?_
Because rays of heat may be _reflected_ in the same manner as the rays
of light.
[Verse: "But the wise answered saying, Not so; lest there be not
enough for us and you: but go ye rather to them that sell, and buy for
yourselves."--MATT. XXV.]
211. _Why would not the same effect arise if the plate were of a black
or dark substance?_
Because black and dark substances are not _good reflectors of heat_.
212. _What are the best reflectors of heat?_
Smooth, light-coloured, and highly polished surfaces, especially those
of _metal_.
213. _Why does meat become cooked more thoroughly and quickly when a
tin screen is placed before the fire?_
Because the bright tin reflects the rays of heat back again to the meat.
214. _Why is reflected heat less intense than the primary heat?_
Because it is impossible to collect all the rays, and also because a
portion of the caloric, imparting heat to the rays, is absorbed by
the air, and by the various other bodies with which the rays come in
contact.
215. _Can heat be reflected in any great degree of intensity?_
Yes; to such a degree that inflammable matters may be ignited by it.
If a cannon ball be made red hot, and then be placed in an iron stand
between two bright reflectors, inflammable materials, placed in a
proper position to catch the reflected rays, _will ignite from the
heat_.
There is a curious and an exceptional fact with reference to
_reflected_ heat, for which we confess that we are unable to
give "_The Reason Why_." It is found that snow, which lies near
the trunks of trees or the base of upright stones, melts before
that which is at a distance from them, though the sun may shine
equally upon both. If a blackened card is placed upon ice or snow
under the sun's rays, the frozen body underneath it will be thawed
before that which surrounds it. But if we _reflect_ the sun's
rays from a metal surface, the result is _directly contrary_--the
exposed snow is the first to melt, leaving the card standing as
upon a pyramid. Snow _melts_ under heat which is _reflected_ from
the trees or stones while it withstands the effect of the _direct
solar rays_. In passing through a cemetery this winter (1857),
when the snow lay deep, we were struck with the circumstance that
the snow in front of the head-stones facing the sun was completely
dissolved, and, in nearly every instance, the space on which the
snow had melted assumed a coffin-like shape. This forced itself so
much upon our attention that we remained some time to endeavour
to analyse the phenomena; and it was not until we remembered the
curious effect of _reflected heat_ that we could account for it.
It is obvious that the rays falling from the upper part of the
head-stone on to the _foot_ of the grave would be less powerful
than those that radiated from the _centre_ of the stone to the
centre of the grave. Hence it was that the heat dissolved at the
foot of the grave only a narrow piece of snow, which widened
towards the centre, and narrowed again as it approached the foot
of the head-stone, where the lines of radiation would naturally
decrease. Such a phenomena would prove sufficient to raise
superstition in untutored minds.
[Verse: "The light of the righteous rejoiceth, but the lamp of the
wicked shall be put out."--PROVERBS XIII.]
216. _Are good reflectors of heat also good absorbers?_
No; for reflectors at once _send back_ the heat which they receive,
while absorbers _retain it_. It is obvious, therefore, that
_reflectors_ cannot be good _absorbers_.
217. _How do fire-screens contribute to keep rooms cool?_
Because they turn away from the persons in the room rays of heat which
would otherwise make the warmth excessive.
218. _Why are white and light articles of clothing cool?_
Because they _reflect_ the rays of heat.
White, as a _colour_, is also a bad _absorber_ and _conductor_.
219. _Why is the air often found excessively hot in chalk districts?_
Because the soil _reflects_ upon objects near to it the heat of the
solar rays.
220. _How does the heat of the sun's rays ultimately become diffused?_
It is first _absorbed_ by the earth. Generally speaking, the earth
_absorbs_ heat by day, and _radiates_ it by night. In this way an
equilibrium of temperature is maintained, which we should not otherwise
have the advantage of.
221. _Does not the air derive its heat directly from the sun's rays?_
Only partially. It is estimated that the air absorbs only _one-third_
of the caloric of the sun's rays--that is to say, that a ray of solar
heat, entering our atmosphere at its most attenuated limit (a height
supposed to be about _fifty miles_), would, in passing through the
atmosphere to the earth, part with only one-third of its calorific
element.
[Verse: "As for the earth, out of it cometh bread; and under it is
turned up as it were fire."--JOB XXVIII.]
222. _What becomes of the remaining two-thirds of the solar heat?_
They are _absorbed_ chiefly by the _earth_, the great medium of
calorific _absorption_; but some portions are taken up by _living
things_, both animal and vegetable. When the _rays of heat_ strike upon
the earth's surface, they are passed from particle to particle into the
interior of the earth's crust. Other portions are distributed through
the air and water by _convection_, and a third portion is thrown
back into space by _radiation_. These latter phenomena will be duly
explained as we proceed.
223. _How do we know that heat is absorbed, and conducted into the
internal earth?_
It is found that there is a given depth beneath the surface of the
globe at which an equal temperature prevails. The depth increases as we
travel south or north from the equator, and corresponds with the shape
of the earth's surface, _sinking under the valleys, and rising under
the hills_.
224. _Why may we not understand that this internal heat of the earth
arises, as has been supposed by many philosophers, from internal
combustion?_
Because recent investigations have thrown considerable and satisfactory
light upon the subject. It has been ascertained that the internal
temperature of the earth _increases_ to a certain depth, _one degree in
every fifty feet_. But that below that depth the temperature _begins to
decline_, and continues to do so with every increase of depth.
225. _Do plants absorb heat?_
Yes. They both _absorb_ and _radiate_ heat, under varying
circumstances. The majestic tree, the meek flower, the unpretending
grass, all perform a part in the grand alchemy of nature.
[Verse: "Consider the lilies of the field, how they grow; they toil
not, neither do they spin."]
When we gaze upon a rose it is not its beauty alone that should
impress us: every moment of that flower's life is devoted to
the fulfilment of its part in the grand scheme of the universe.
It decomposes the rays of solar light, and sends the red rays
only to our eyes. It absorbs or radiates heat, according to the
temperature of the ærial mantle that wraps alike the flower and
the man. It distills the gaseous vapours, and restores to man the
vital air on which he lives. It takes into its own substance, and
incorporates with its own frame, the carbon and the hydrogen of
which man has no immediate need. It drinks the dew-drop or the
rain-drop, and gives forth its sweet odour as a thanksgiving. And
when it dies, it preaches eloquently to beauty, pointing to the
end that is to come!
CHAPTER XII.
226. _How do we know that plants operate upon the solar and atmospheric
heat?_
A delicate thermometer, placed among the leaves and petals of flowers,
will at once establish the fact, not only that flowers and plants have
a temperature differing from that of the external air, but that the
temperature varies in different plants according to the hypothetical,
or supposed requirements, of their existences and conditions.
227. _What is the chief cause of variation in the temperature of
flowers?_
It is generally supposed that their temperature is affected by their
_colours_.
228. _Why is it supposed that the colour of a flower influences its
temperature?_
Because it is found by experiment that the _colours_ of bodies bear an
important relation to their properties respecting _heat_, and hold some
analogy to the relation of _colours_ to _light_.
If when the ground is covered with snow, pieces of woollen cloth,
of equal size and thickness, and differing only in colour, are
laid upon the surface of the snow, near to each other, it will
be found that the relation of _colour_ to temperature will be as
follows:--In a few hours the _black_ cloth will have dissolved so
much of the snow beneath it, as to sink deep below the surface;
the _blue_ will have proved nearly as warm as the black; the
_brown_ will have dissolved less of the snow; the _red_ less than
the brown; and the white the _least_, or none at all. Similar
experiments may be tried with reference to the _condensation
of dew_, &c. And it will be uniformly found that the _colour_
of a body materially affects its powers of _absorption_ and of
_radiation_.
[Verse: "And yet I say unto you, that even Solomon, in all his
glory, was not arrayed like one of these."--MATT. VI.]
229. _Why do we know that these effects are not the result of light?_
Because they would occur, in just the same order, in the absence of
light.
230. _Why are dark coloured dresses usually worn in winter, and light
in summer?_
Because black _absorbs_ heat, and therefore becomes warm; while _light
colours_ do _not_ absorb heat in the same degree, and therefore they
remain cool.
231. _Why do iron articles, even when near fire, usually feel cool?_
Because they are bad absorbers, and do not take up heat freely, unless
they are _in contact_ with a hot body.
232. _How is heat diffused through the atmosphere?_
By _convection_. The warmth radiating from the surface of the earth
warms the air in contact with it; the air expands, and becoming
lighter, flies upwards, bearing with it the caloric which it holds, and
diffusing it in its course.
233. _How do the waters of the ocean become heated?_
Chiefly by _convection_. Nearly all the heat which the sun sheds
upon the ocean is borne away from its surface by evaporation, or is
radiated back into the atmosphere. But the ocean gathers its heat by
_convection_ from the earth. It girdles the shores of tropical lands
where, being warmed to a high degree of temperature, it sets across the
Atlantic from the Gulf of Mexico, and exercises an important influence
upon the temperature of our latitude.
234. _What is the cause of winds?_
Currents of air, and winds, are the result of _convection_. The air,
heated by the high temperature of the tropics, _ascends_, while the
colder air of the temperate and the frigid zones _blows towards the
equator_ to supply its place.
[Verse: "Give unto the Lord the glory due unto his name; worship the
Lord in the beauty of holiness."--PSALM XXIX.]
235. _What is the cause of sea breezes?_
Sea breezes are also the result of _convection_. The land, under the
heat of the day's sunshine, becomes of a high temperature, and the
expanded air on its surface _flies away towards the ocean_. As the sun
goes down, the earth cools again, and the air _flies back_ to find its
equilibrium.
Many countries by the sea are subjected to these periodical
breezes, known as either "land" or "sea breezes," according to
their direction. About eight o'clock in the morning an ærial
current begins to flow from the sea towards the land, and
continues until about three o'clock in the day; then the current
takes a reverse direction, flowing from the land to the sea.
This it continues to do throughout the night, until the time of
sunrise, when a temporary calm ensues.
236. _Why does a soap bubble ascend in the air?_
Because, being filled with _warm_ air, it is _lighter_ than the
surrounding medium, and therefore ascends.
237. _Why does the bubble fall after it has been in the air some time?_
Because the air contained in it has become cool, and, as it contains
carbonic acid gas, it is _heavier_ than the air.
238. _What became of the warmth at first contained in the bubble?_
It has been _distributed in the air_ through which the bubble passed.
239. _What does this simple illustration of the distribution of warmth
explain?_
It explains the law of _convection_, or _heat distribution_, over the
surface of the globe.
240. _Why does air ascend the chimney?_
Because, being heated, it becomes _lighter_ than the surrounding
medium, and therefore flies upwards, through the outlet provided for it.
241. _Why does air fly from the doors and windows towards the
fire-place?_
Because, as the warm air flies away, cold air rushes in to occupy its
place.
[Verse: "How much better is it to get wisdom than gold? and to get
understanding rather to be chosen than silver."--PROVERBS XVI.]
242. _What does this example of the motion of the air in our rooms
explain?_
It explains the movement of volumes of air by _convection_, and
illustrates the origin of _breezes_ and _winds_.
243. _What is the chief effect of this law of convection?_
Under its influence air and water are the great _equalisers of solar
heat_, rendering the earth agreeable to living things, and suited to
the laws of their existence.
Owing, also, to this law of _convection_, the constituents of the air
are equalised. The breath of life, supplied by the purer oxygen of the
"sunny south," is diffused in salubrious gales over the wintry climes
of the north. And the waters, evaporated from the bosom of the central
Atlantic Ocean and the Pacific, are borne across vast continents, and
poured down in fertilising showers upon distant lands.
To the educated mind, nothing is too simple to merit attention.
To the ignorant, few things are sufficiently attractive to excite
curiosity. Knowledge enables us to estimate the varied phenomena
that are hourly arising around us, and to see, even in the
most trifling effects, illustrations of those great causes and
consequences that govern with mighty power the material world.
Man, sitting by his fire-side, is enabled to witness the operation
of some of nature's grandest laws: _light_ and _heat_ are around
him; _conduction_, _radiation_, _reflection_, _absorption_,
and _convection_ of heat are all going on before him; little
winds are sweeping by his footstool, and warm currents, with
miniature clouds folded in their arms, are passing upward before
his view. Chemical changes are going on; the solid rock of coal
disappears, flying away as an invisible gas. The little "hills are
melted," and hard stones have been converted into "fervent heat."
Although some of these changes are imperceptible to the _eye_,
they are manifest to the educated _mind_; and the pleasures of
philosophical observation are as sweet as a poet's dreams.
CHAPTER XIII.
244. _Why will a piece of paper, held three or four inches over the
flame of a candle, become scorched?_
[Verse: "Neither do men light a candle, and put it under a bushel,
but on a candlestick; and it giveth light unto all that are in the
house."--MATT. V.]
Because the hot air and gas produced by the burning of the candle
_ascends_ rapidly.
245. _Why will a piece of paper held about an inch below the flame of a
candle scarcely become warmed?_
Because the heat _ascends_; and only a little of it falls upon the
paper, and that by _radiation_.
[Illustration: Fig. 2.--DIAGRAM SHOWING THE COMBUSTION OF A CANDLE.]
246. _Why does the lower part of the flame of a candle_ (D) _burn of a
blue colour?_
Because the _hydrogen_ of the tallow, having a stronger affinity for
the _oxygen_ of the air than _carbon_ has, ignites first. Pure hydrogen
burns with a bluish flame.
247. _Why does the middle of the flame_ (C) _look dark?_
Because it is occupied with gaseous vapours, derived from the tallow,
which have not yet _ignited_.
248. _Why does the upper part of the flame_ (B) _produce a bright
yellow light?_
Because it is in this part of the flame that the _hydrogen_ of
the candle, and the _oxygen_ of the air, combine, and there is
just sufficient _carbon_ mixed with the _hydrogen_ to improve its
_illuminating power_.
249. _Why is there a fringe of pale light_ (A) _around the upper part
of the flame?_
Because some of the _carbon_ escapes in a state of _incandesence_, and
as soon as it reaches the air it combines with _oxygen_, and so forms
_carbonic acid gas_.
If any dark body, such as the blade of a knife, be held between
the eye and the flame of the candle, so as to shut off the light
of the more luminous part, the pale fringe around the flame will
be found distinctly perceptible. _Incandesence_ means _heated to
whiteness_.
[Verse: "How oft is the candle of the wicked put out? and how oft
cometh their destruction upon them?"--JOB XXI.]
250. _Why does the flame terminate in a point?_
Because cold air rushes towards the flame in every direction, and
is carried upward. At the point where the flame terminates the cold
currents have so _reduced the temperature_ that combustion can no
longer be sustained.
251. _Why, if you hold anything immediately over the flame, will the
flame lengthen?_
Because, by preventing the rapid escape of the heated air, you maintain
a temperature which _increases the combustion_ at the point of the
flame.
252. _Why should persons whose clothes take fire, throw themselves
down?_
Because flame spreads most rapidly in an _upward_ direction.
253. _Why should persons whose clothes are on fire roll slowly about
when they are down?_
Because they thereby _press out_ the fire.
254. _Why does pressing a flame or a spark put it out?_
Because it prevents the contact of the flame or spark with the _oxygen_
of the air.
Extinguishers put out the flame of candles in the same manner. A
person dies from "suffocation" through the absence of oxygen; and
it is literally practicable to _"suffocate" a fire_.
255. _Why does the wick turn black as it burns?_
Because it consists principally of _carbon_.
256. _Why, when the point of the wick turns out and meets the air, does
it exhibit a bright spark?_
Because the _carbon_ of the wick comes into immediate contact with the
_oxygen_ of the air.
257. _Why does holding a candle "upside down" put it out?_
Because the melted grease runs down too rapidly, and at too low a
temperature to undergo combustion. It therefore _reduces the heat_, and
extinguishes the flame.
[Verse: "Lord, what is man that thou takest knowledge of him! or the
son of man, that thou makest account of him."--PSALMS CXLIV.]
258. _Why is it more difficult to blow out the flame of a candle with a
cotton wick than one with a rush wick?_
Because the cotton wick imbibes more of the combustible materials, and
holds in its loose texture the inflammable gases in a state ready for
combustion.
259. _Why does blowing sharply at a candle flame put it out?_
Because the breath drives away the vapour of the grease which, becoming
gaseous, supports the flame.
And because too rapid a flow of cold air reduces the temperature below
the point at which combustion can be maintained.
260. _Why will a gentle puff of breath, if given speedily after the
flame is extinguished, rekindle it?_
Because the _oxygen_ of the air combines with the _carbon_ and
_hydrogen_ that are still escaping from the _heated wick_, and
re-lights it.
261. _Why will not a similar puff rekindle the flame of a rushlight?_
Because its wick retains but _little heat_, and holds a comparatively
small amount of combustible matter in a _volatile state_.
262. _Why is a fire, when it is very low, sometimes put out by blowing
it?_
Because the too rapid flow of cold air _reduces the temperature_ of the
burning mass.
263. _Why will a piece of paper twisted like an extinguisher put out a
candle?_
Because, before the flame of the candle can ignite the paper, _the
oxygen contained within it is consumed_, and the flame is suffocated.
[Verse: "When his candle shined upon my head, and when by his light
I walked through darkness."--JOB XXIX.]
264. _Why do tallow candles require snuffing?_
Because the _oxygen_ of the air cannot reach the wick through the body
of flame--therefore the _unconsumed carbon_ accumulates upon the wick.
265. _Why do composite and wax candles not require snuffing?_
Because their wicks are made by a series of plaits, by which they are
bent to meet the _oxygen_ of the air, and consumed.
266. _Why does setting a glass upon a lamp increase its brilliancy,
though it shortens the flame?_
Because it conducts an increase of air to the flame, and the greater
supply of _oxygen_ causes the escaping vapour of oil to be all rapidly
consumed.
267. _Why does a candle burn dimly when the wick has become loaded with
carbon?_
Because the carbon _radiates_ the heat, and disperses it, and reduces
the heat of the flame below that temperature which is essential to its
_luminosity_.
268. _What differences characterise the combustion of carbon and of
hydrogen?_
The combustion of _carbon_ takes place without the production of flame.
The charcoal (or carbon in any other form) being heated to redness,
enters directly into combination with the _oxygen_ of the surrounding
air, and the carbonic acid gas, being invisible, passes away unobserved.
But in the combustion of _hydrogen_ the heat developed is so intense as
to render _the gas itself luminous_, just as iron may be heated to a
red or white heat.
269. _What has become of the candle when it has been burnt?_
It has been resolved partly into _carbonic acid gas_ which, though
unperceived, has diffused itself through the surrounding air; and
partly into _water_, which escaped in the form of thin vapour.
270. _Has any part of the candle been consumed or lost?_
No; there is no such thing as "loss" in the operations of nature. Every
particle of the candle, now invisible, exists either in the form of
_gas_, _vapour_, or _water_, with, perhaps, a few solid particles that
may be called _ashes_, but which are too minute to excite attention.
[Verse: "I know that whatsoever God doeth, it shall be for ever:
nothing can be put to it, nor anything taken from it; and God doeth it
that men should fear before him."--ECCLES. III.]
The economy of nature should teach us a very impressive
lesson--_nothing is suffered to be wasted_, not even the slightest
atom. As soon as any body has fulfilled its purpose in one state
of being, it is passed on to another. The candle, existing no
longer as a candle, is flying upon the wings of the air as
_carbonic acid gas_, and as _water_. These probably find their
way to the garden or the field, where the carbonic acid gas forms
the _food of the plant_, and the water affords it a refreshing
_drink_. And can it be supposed that the Almighty Being, who has
thus economised the existence of the _material_ creation, should
be less mindful of the immaterial _soul_ of man? There _is_ an
eternity before us, the certainty of which is evidenced even by
the laws of the material creation.
CHAPTER XIV.
271. _What is coal?_
Coal is a "_vegetable fossil_."
272. _What is meant by a vegetable fossil?_
It is a substance _originally vegetable_, which, by pressure and other
agencies within the earth, has been brought to a condition approaching
that of _mineral_ or earthy matter.
273. _Why do we know that coal is of vegetable origin?_
By the _chemical components_ of its substance; and also by the
_vegetable forms_ that are found abundantly in coal beds.
Professor Buckland, in his _Bridgewater Treatise_, speaking of
the impressions of plants found in the coal mines, says; "The
finest example I have ever witnessed is that of the coal mines
of Bohemia. The most elaborate imitations of living foliage upon
the painted ceilings of Italian palaces bear no comparison with
the beauteous profusion of extinct vegetable forms with which
the galleries of these instructive coal mines are overhung.
The roof is covered as with a canopy of gorgeous tapestry,
enriched with festoons of most graceful foliage, flung in wild
irregular profusion over every part of its surface. The effect
is heightened by the contrast of the coal-black colour of these
vegetables with the light ground-work of the rock to which they
are attached. The spectator feels himself transported, as if by
enchantment, into the forests of another world; he beholds trees,
of forms and characters now unknown upon the surface of the
earth, presented to his senses almost in the beauty and vigour of
their primeval life; their scaly stems and bending branches, with
their delicate apparatus of foliage, are all spread forth before
him, little impaired by the lapse of countless ages, and bearing
faithful records of extinct systems of vegetation which began
and terminated in times of which these relics are the infallible
historians."
[Verse: "Surely every man walketh in a vain show; surely they are
disquieted in vain: he heapeth up riches, and knoweth not who shall
gather them."--PS. XXXIX.]
274. _What are the chemical components of coal?_
They consist of _carbon_, _hydrogen_, _oxygen_, and _nitrogen_. The
proportions of these elements vary in different kinds of coal. Carbon
is the chief component; and the proportions may be stated to be,
generally, _carbon_, 90 per cent.; _hydrogen_, from 3 to 6 per cent.;
the other elements enter into the compound in such small proportions,
that, for all ordinary purposes, it is sufficient to say that coal
consists of _carbon_ and _hydrogen_, but chiefly of _carbon_.
275. _What is charcoal?_
Charcoal consists almost entirely of _carbon_. It is made from _wood_
by the application of heat, without the admission of air. The hydrogen
and oxygen of the wood are expelled, and that which remains is
charcoal, or _carbon_ in one of its purest states.
276. _What is animal charcoal?_
Animal charcoal, like vegetable charcoal, consists of _carbon_ in a
state approaching purity. It is made from the _bones of animals_,
heated in iron cylinders. It is commonly called _ivory black_.
277. _What is the purest form of carbon known?_
The purest form of _carbon_ is the _diamond_, which may be said to be
absolutely pure.
Hence we derive another of the beautiful lessons of science--a
lesson which teaches us to _despise nothing that God has given_.
The soot which blackens the face of a chimney-sweep, and the
diamond that glistens in the crown of the monarch, consist of the
same element in merely a different atomic condition. What a lesson
of humility this teaches to Pride! The haughty beauty as she walks
the ball-room, inwardly proud of the radiance of her gems as they
rise and fall upon her breast, little thinks or knows that _every
breath that is expired around her wafts away the like element of
which her treasures are composed_. That even in our own flesh and
bones the same abounding substance lies hid; and that the buried
tree of the primitive world, and the little flower of to-day, are
both the instruments of giving this singular element to man!
278. _What is coke?_
Coke is coal, divested of its hydrogen and other volatile parts, by
a similar process to that by which charcoal is produced. It forms the
residue after hydrogen gas has been made from coals. It consists almost
entirely of _carbon_.
[Verse: "Oh that men would praise the Lord for his goodness, and for
his wonderful works to the children of men."--PSALM CVII.]
279. _Why do burning coals produce yellow flame?_
Because the _hydrogen_ which they contain is combined with some
proportion of _carbon_, which imparts a bright yellow colour to the
flames.
280. _Why do some of the flames of a fire appear much whiter than
others?_
Because the quality of coals, and the conditions under which they are
burnt, are liable to variation. Some coals yield a _heavy_ hydrogen,
called _bi-carburetted hydrogen_, which burns with a much brighter
flame than _carburetted hydrogen_.
281. _Why does bi-carburetted hydrogen burn with a whiter flame than
the common coal gas?_
Because it is combined with a larger proportion of _carbon_, to which
it owes its increased luminosity.
282. _Why do some of the flames of a fire appear blue?_
Because the hydrogen which is escaping where those flames occur is
_pure hydrogen_, destitute of carbon.
283. _Why does the fire sometimes appear red, and without flame?_
Because the volatile gases have been driven off and consumed, and
combustion is continued by the _carbon_ of the coals and the _oxygen_
of the air.
284. _What effect has the burning of a fire upon the composition of the
air?_
It is found that in burning 10lb. of coal the oxygen contained in 1,551
cubic feet of air is altogether absorbed. It is therefore necessary to
keep the atmosphere of a room, in which a coal fire is burning, fresh
and pure, to supply 155 cubic feet of fresh air for every pound of coal
that is consumed.
[Verse: "O Lord how manifold are thy works, in wisdom hast thou made
them all: the earth is full of thy riches."--PSALM CIV.]
285. _Why does wood which is "green" hiss and steam when it is burnt?_
Because it contains a large amount of water, which must be evaporated
before combustion can proceed.
286. _What is the effect of this evaporation?_
A great deal of heat is unprofitably expended in driving off the water
of the fuel.
287. _Why does poking a fire cause it to burn more brightly?_
Because it opens avenues through which the air may enter to supply
_oxygen_.
288. _Why do "blowers" improve the draft of air through a fire?_
Because, by obstructing the passage of the current of air _over_ the
fire, they cause additional air to pass _through_ it, and therefore a
greater amount of _oxygen_ is carried to the coals.
289. _What is smoke?_
Unconsumed particles of _coal_, rendered volatile by heat, and driven
off.
290. _What is soot?_
_Carbon_ in minute particles, driven off with other volatile matters
and deposited on the walls of chimneys.
291. _Why do fresh coals increase the quantity of smoke?_
Because they contain volatile matters which are easily driven off; and
because, also, they reduce momentarily the heat, so that those matters
that first escape cannot be consumed.
292. _Why do charcoal and coke fires burn clearly and without flame?_
Because the _hydrogen_ has been previously driven off from those
substances.
293. _Why is it difficult to light charcoal and coke fires?_
Because they contain no _hydrogen_ to produce _flame_, and assist
combustion.
[Verse: "He hath made his wonderful works to be remembered: the Lord
is precious and full of compassion."--PSALM CXL.]
A new plan of kindling fires has lately been recommended. Coals
are to be laid in the _bottom_ of the fire-place to a considerable
depth, then the paper and wood are to be laid on, and then a
little coals and cinders over them. This plan of "laying in" the
fire is precisely the _reverse_ of that which has been pursued
for many years. The theory is, that when the coals in the bottom
are ignited, a more even combustion is kept up, whilst the smoke
and gas which would otherwise escape, and become as so much waste
fuel, is burnt up, and produces heat. We have heard the plan
strongly recommended by persons who have tried it, and who testify
to the great economy of fuel to which it conduces.
CHAPTER XV.
294. _Why does paper ignite more readily than wood?_
Because its texture is less _dense_ than that of wood; its particles
are therefore more _readily heated_ and decomposed.
295. _But if articles of loose texture are bad conductors of heat, why
do they so easily ignite?_
The fact that they are _bad conductors_ assists their ignition. The
heat which would pass from particle to particle of the dense substance
of iron, and be _conducted away_, accumulates in the interspaces of
paper, and ignites it.
296. _Why does wood ignite less readily than paper?_
Because its substance is _denser_ than that of paper; it therefore
requires a higher degree of heat to inflame its substance.
297. _Why does wood, when ignited, burn longer than paper?_
Because, being a denser substance, it submits a _larger number of
particles_, within a given space, to the action of the heat, and the
formation of gases.
298. _Why do we, in lighting a fire, first lay in paper, then wood, and
lastly coals?_
Because the paper is more easily ignited than wood, and wood than
coals; therefore the _paper_ assists the ignition of the _wood_, and
the _wood_ assists the ignition of the _coals_.
[Verse: "It is a good thing to give thanks unto the Lord, and to
sing praises unto thy name, O Most High."--PSALM XCII.]
299. _Why will not wood ignite by the flame of a match?_
It will do so, unless there is a great disproportion between the size
of the wood and the flame of a match. A _thin_ piece of wood will
ignite, but a square block will not, because the heat of the flame is
insufficient to raise the temperature of a _large surface_ to the point
that will drive out its gases.
300. _Why do we place the paper under the wood, and the wood under the
coals?_
Because heat and flame, when surrounded by air, have a strong tendency
to spread themselves _upwards_.
301. _Would it be possible to light the coals by putting the paper and
the wood upon the top?_
It would be possible; but the loss of heat would be so great, that a
_much larger quantity_ of paper and wood would be required.
302. _Why does a poker laid across the top of a dull fire revive it?_
Because the poker _radiates_ the heat it receives from the fire
downward upon the fuel.
Because, also, it divides the ascending air, and thereby _creates
currents_.
The amount of good which the poker does to the fire is very slight
indeed. Generally, the housewife stirs the fire first, and blows
or brushes away the ashes that prevent the influx of air. She then
places the poker upon the top, and the popular mind supposes that
the poker "draws" the fire. The custom of placing a poker over
the fire is of very remote antiquity. It was once believed that
forming _a cross_, by placing the poker over the bars, protected
the fire from the hostility of malignant _witches_!
303. _Why should fire-places be fixed as low as possible in rooms?_
Because heat _ascends_, and when the fire-places are high the lower
parts of the room are _inadequately warmed_.
Also, as currents of air fly towards the fire, elevated fire-places
_cause drafts_ about the persons of the inmates to a much greater
extent than they would if they were lower down.
[Verse: "Unto thee, O God, do we give thanks: for that thy name is
near thy wondrous works declare."--PSALM LXXV.]
304. _Why, if a piece of paper be laid with its flat surface upon the
fire, will it "char," but not ignite?_
Because, as in the case of the proper candle-extinguisher, the
_carbonic acid gas_ accumulating beneath it prevents its igniting.
305. _Why, if you direct a current of air towards the paper, will it
burst into a blaze?_
Because the carbonic acid gas is displaced by a current of air
containing _oxygen_.
306. _Why does water extinguish fire?_
Because it _saturates the fuel_, and prevents the gases thereof from
combining with the oxygen of the air.
307. _As water contains oxygen, why does not the oxygen of the water
support the fire?_
Because the affinity between the _hydrogen_ and _oxygen_ of the water
is so strong that fire cannot separate them.
Water may be decomposed by _heat_, as will be hereafter explained.
But the heat of an ordinary fire is insufficient. There is,
however, some reason for believing that, in cases of very large
fires, such as the accidental burning of houses, &c., when the
supply of water thrown upon the fire is very deficient, the water
_does_ become _decomposed_, and add to the fury of the flames.
308. _Why does the blacksmith sprinkle water upon the coals of his
forge?_
The blacksmith uses _small coals_ because the small pieces thereof are
more easily ignited than large lumps would be, and they convey heat
better by completely surrounding the articles put into the fire. He
sprinkles water on the coal dust _to hold its particles together by
cohesion_, until the heat forms it into a cake. A strong blast of hot
hair drives the vapour of the water away, and leaves a porous mass to
the action of the fire.
309. _Why, when the blacksmith thrusts a heated iron into a tankard of
water, do we recognise a peculiar smell?_
Because the intense heat disengages a small volume of the gases of
which water is formed.
[Verse: "Oh the depth of the riches both of the wisdom and knowledge
of God! how unsearchable are his judgments, and his ways past finding
out."--ROM. XI.]
310. _Which gas do we (in this instance) recognise by the smell?_
The _hydrogen_ gas. Oxygen gas possesses no odour.
311. _What is Spontaneous Combustion?_
Spontaneous combustion is that which occurs in various bodies when they
become highly heated by _chemical changes_.
312. _Why is heat developed during chemical changes?_
Because, as all bodies contain _latent caloric_, the disturbance of the
atoms of which those bodies are composed, during the new combinations
that constitute _chemical changes_, frequently sets the caloric free,
and an _accumulation of caloric_ produces spontaneous combustion.
313. _Does a match ignite spontaneously when drawn over a rough
surface?_
No. Because in this case the combustion arises from heat _applied by
friction_.
314. _Does phosphorous ignite spontaneously when held in a warm hand?_
Phosphorous will ignite when held in a warm hand, but it does not then
produce spontaneous combustion, because it ignites through the agency
of _applied heat_.
315. _But if a piece of dry phosphorous be sprinkled with powdered
charcoal it will ignite, without the application of heat. Why is this?_
Because the _carbon_ (charcoal) absorbs _oxygen_ from the air, and
conveys it to the _phosphorous_. Here are _chemical changes_ which
develope heat, and produce _spontaneous combustion_.
316. _Why do hay-stacks sometimes take fire?_
Because the hay, having become damp, decays, and passes on to a state
of _fermentation_, in which _chemical changes occur_, during which
heat is evolved. Hay, taking fire under these circumstances, would
exhibit _spontaneous combustion_.
[Verse: "Who hath woe? who hath sorrow? who hath contentions? who
hath babbling? who hath words without cause? who hath redness of the
eyes? * * * They that tarry long at the wine."--PROV. XXIII.]
317. _What substances are liable to produce spontaneous combustion?_
All substances which contain sugar, starch, and other components
liable to _fermentation_. All bodies that evolve, under low degrees of
temperature, _inflammable gases_. And all organic bodies undergoing
decay.
Grain, cotton, hemp, flax, coals, oily and greasy substances.
318. _What is the Ignis Fatuus (sometimes called "Will-o'-the-Wisp",
"Corpse Candles," and "Jack-o'-Lantern")?_
It is a flame produced by spontaneous combustion, caused by the decay
of animal or vegetable bodies, which evolve _phosphoretted hydrogen_
gas, under circumstances attended by a low degree of heat, sufficient
to ignite the gases. It is mostly seen over marshy places, and
burial-grounds.
Many a "Ghost Story" has owed its origin to these singular but
harmless appearances. People, ignorant of the cause, have been
terrified at the effect. To the fancy of an affrighted mortal,
the simple flame of the _Ignis Fatuus_ has assumed the form of
a departed friend, and even found a supernatural voice. If,
excited by a momentary daring, the beholder moved towards the
light upon which he gazed, it fled from him. If he turned from
it and walked away, it followed him, step by step. The darkness
of a lonely road, or the sacred solitude of a burial-place, have
been sufficient accessories to authenticate the appearance of a
spirit. And yet how simple the phenomenon? Matters so volatile as
those which produce the _Ignis Fatuus_ would naturally be driven
back by the motion in the air caused by an advancing body; and, on
the other hand, a body moving from them would create a current in
which the _Ignis Fatuus_ would follow. Poisonous gases, escaping
from decaying bodies, pass into the air and take fire. They are
thereby converted into harmless compounds. Thus we see that the
"ghost" which terrifies the mind of the ignorant, becomes a
"guardian angel" to the educated.
319. _Has spontaneous combustion ever occurred in living bodies?_
It has occurred in numerous instances to persons habituated to the
excessive use of spirits.
320. _Why should spontaneous combustion occur in the case of the
drunkard?_
Because spirituous drinks contain a large proportion of ALCOHOL, one
of the constituents of which is _hydrogen_. The vital energies of
the drunkard, being destroyed by excess, chemical agencies obtain an
ascendancy, and it is supposed that the _hydrogen_ of the alcohol
combines with the _phosphorous_ of the body to form _phosphoretted
hydrogen_, which ignites spontaneously, and literally consumes the
living temple.
[Verse: "Drought and heat consume the snow waters; so doth the grave
those which have sinned."--JOB XXIV.]
Cases of spontaneous combustion are of rare occurrence. But they
are sufficiently well authenticated by high medical authority,
in many parts of the world, to present an awful warning to
the inveterate drunkard. The cases of which we have read the
particulars present details of the most appalling description. How
signally the Almighty displeasure at intemperance is expressed,
when the very drink which imparts the mad pleasure of intoxication
is made the _direct_ instrument by which the drunkard is destroyed!
CHAPTER XVI.
321. _Why does friction produce heat?_
Because all bodies contain _latent heat_, that is, heat that lies hid
in their substance, and the rubbings of two bodies against each other
_draws the latent heat to the excited surfaces_.
322. _Why does the rubbing of two surfaces together attract latent heat
to those surfaces?_
Because it is a law of nature that _heat_ shall always attend _motion_;
and it is generally found that the _intensity of heat_ bears a specific
relation to the _velocity of motion_.
323. _What are the sources of heat?_
The _rays_ of the _sun_, the _currents_ of _electricity_, the _action_
of _chemicals_, and the _motion_ of _substances_.
324. _Why does water freeze?_
Because its latent heat is partly _drawn off_ by the surrounding air.
325. _Why does ice melt?_
Because the heat, once latent in the water, but drawn off by the air,
_has returned_ to it, and restored the water to its former condition.
[Verse: "So teach us to number our days, that we may apply our
hearts unto wisdom." PSALM XC.]
326. _Why does water become steam?_
Because a larger amount of heat has entered into it than can remain
latent in water. The water therefore expands and rises in the form of
vapour, or _water attenuated by heat_.
327. _How many degrees of heat are latent, or hidden, in the different
states of water?_
In thawing _ice_, 140 deg. of caloric become latent; and in converting
the water into steam, 1,000 deg. more of caloric are be taken up.
Therefore, _ice_ requires to take up 1,140 deg. of latent caloric
before it becomes steam.
328. _What is the most modern theory of heat?_
It is this--that caloric, which produces heat, is an extremely _subtile
fluid_, of so refined a nature that it possesses no weight, yet is
capable of diffusing itself among the particles of the most solid
bodies.
It is also believed that--all bodies are subject to the action of two
opposing forces: one, the _mutual attraction_ of their _particles_; the
other, the _repulsive force_ of _caloric_--and that bodies exist in the
_æriform_, _fluid_, or _solid state_, _according to the predominance of
either the one or the other of these opposing forces_.
329. _How do we measure the quantity of caloric in any substance?_
It is impossible to determine the amount of caloric which any body
contains. Our _sensations_ would obviously be deceptive, since, if we
dipped the right hand in snow, and held the left hand before the fire,
and then immersed both hands in cold water, the water would feel _warm_
to the _right hand_ and _cold_ to the _left hand_.
But, as _caloric_ uniformly expands substances that are under its
influence, one of the bodies most sensitive to _calorific_ effects
has been selected to be the _indicator_ of the amount of _caloric_.
This substance is _quicksilver_; and the scale of measurement, and
the apparatus for exhibiting the rise or fall of the quicksilver,
constitute the _thermometer_.
330. _If it is impossible to measure the amount of caloric in any
substance, how can it be said that ice absorbs_ 140 _deg. in becoming
water?_
Those figures simply record the amount of calorie indicated by the
_thermometer_. The instrument will show with sufficient accuracy
the _relative amount_ of caloric in various bodies, or in the same
bodies _under different circumstances_, but it can never determine the
_precise amount of caloric_ in any one body.
[Verse: "Great is the Lord, and greatly to be praised in the city of
our God, in the mountain of his holiness."--PSALM XLVIII.]
331. _Why, if a hot and a cold body were placed near to each other,
would the cold one become warmer, and the hot one cooler?_
Because _free caloric_ (that is, caloric that is not latent,) always
exhibits a tendency to establish an _equilibrium_. If twenty bodies, of
different temperatures, were placed in the same atmosphere, they would
_all soon arrive at the same temperature_. The caloric would leave the
bodies of those of the _highest_, and find its way to those of the
_lowest_ temperature.
332. _How does caloric travel?_
It travels in _parallel rays_ in all directions with a velocity
approximating to that of light; and it passes through various bodies
with a rapidity proportionate to their power of _conduction_.
333. _Why does melted metal run like a stream of fluid?_
Because _caloric_ has passed into its substance, and, repelling its
particles, has separated them to that degree which produces fluidity.
334. _How do we know that it is caloric passing into the substance of
the metal which produces this effect?_
Because, as soon as a bar of metal begins to be heated, it _expands_
and _lengthens_. It continues to do so, until the heat arrives at that
point which _causes the metal to melt_.
335. _Why does the iron of an ironing-box sometimes become too large
for the box to receive it?_
Because _caloric_ has passed into the substance of the iron, and
_repelled its particles_, by which it has become expanded.
336. _Why does the iron enter the box when it has become partially
cooled?_
Because a portion of the caloric has left the iron, the particles of
which have _drawn closer together_, and contracted the mass.
[Verse: "Cast thy burden upon the Lord, and he shall sustain thee;
he shall never suffer the righteous to be moved."--PSALM LV.]
This effect is frequently observed by females in domestic life,
who, when they are ironing, or using the Italian irons, find that
the heated metal has been too much expanded to enter the box or
tube. They find it necessary to wait until the cooling of the iron
has had the effect of reducing its dimensions. The expansion of
bodies by heat is one of the grandest and most important laws of
nature. We are indebted to it for some of the most beautiful, as
well as the most awful, phenomena. And science has gained some of
its mightiest conquests through its aid. Yet frequently, though
quite unthought of, in the hands of the humble laundress, will
be found a most striking illustration of this wonderful force of
caloric.
337. _Are there any instances in which the abstraction of latent heat
will reduce the hulk of bodies?_
Yes, there are several. But the most familiar one is that which is
exhibited by mixing a _pint_ of the _oil of vitriol_ with a _pint_ of
_water_. _A considerable amount of heat will be evolved_; and it will
be found that the two pints of fluid _will not afterwards fill a quart
measure_.
338. _Is there any latent heat in air?_
Yes: a considerable amount. In a pint measure of air, though in no way
evident to our perceptions, there lurks sufficient caloric to raise a
piece of metal several inches square to glowing redness.
339. _How do we know that caloric exists in the air?_
It has been positively demonstrated by the invention of a small
condensing syringe, by which, through the rapid compression of a small
volume of air, a spark is emitted which ignites a piece of prepared
tinder.
340. _What is the cause of the spark when a horse's shoe strikes
against a stone?_
The _latent heat_ of the iron or the stone is set free by the _violent
percussion_. The same effect takes place when _flint_ strikes against
_steel_, as in the old method of obtaining a light with the aid of the
tinder-box.
[Verse: "The waters are laid as with a stone, and the face of the
deep is frozen."--JOB XXXVIII.]
What an eloquent lecture might be delivered upon the old-fashioned
tinder-box, illustrated by the one experiment of "striking a
light." In that box lie, cold and motionless, the Flint and Steel,
rude in form and crude in substance. And yet, within the breast of
each, there lies a spark of that grand element which influences
every atom of the universe; a spark which could invoke the fierce
agents of destruction to wrap their blasting flames around a
stately forest, or a crowded city, and sweep it from the face of
the world; or which might kindle the genial blaze upon the homely
hearth, and shed a radiant glow upon a group of smiling faces; a
spark such as that which rises with the curling smoke from the
village blackmith's forge--or that which leaps with terrific wrath
from the troubled breast of a Vesuvius. And then the tinder--the
cotton--the carbon: What a tale might be told of the cotton-field
where it grew, of the black slave who plucked it, of the white
toiler who spun it into a garment, and of the village beauty who
wore it--until, faded and despised, it was cast amongst a heap of
old rags, and finally found its way to the tinder-box. Then the
Tinder might tell of its hopes; how, though now a blackened mass,
soiling everything that touched it, it would soon be wedded to
one of the great ministers of nature, and fly away on transparent
wings, until, resting upon some Alpine tree, it would make its
home among the green leaves, and for a while live in freshness
and beauty, looking down upon the peaceful vale. Then the Steel
might tell its story, how for centuries it lay in the deep caverns
of the earth, until man, with his unquiet spirit, dug down to
the dark depths and dragged it forth, saying, "No longer be at
peace." Then would come tales of the fiery furnace, what Fire had
done for Steel, and what Steel had done for Fire. And then the
Flint might tell of the time when the weather-bound mariners,
lighting their fires upon the Syrian shore, melted silicious
stones into gems of glass, and thus led the way to the discovery
of the transparent pane that gives a crystal inlet to the light
of our homes; of the mirror in whose face the lady contemplates
her charms; of the microscope and the telescope by which the
invisible are brought to sight, and the distant drawn near; of
the prism by which Newton analysed the rays of light; and of the
photographic camera in which the sun prints with his own rays the
pictures of his own adorning. And then both Flint and Steel might
relate their adventures in the battle-field, whither they had gone
together; and of fights they had seen in which man struck down his
fellow-man, and like a fiend had revelled in his brother's blood.
Thus, even from the cold hearts of flint and steel, man might
learn a lesson which should make him blush at the "glory of war;"
and the proud, who despise the teachings of small things, might
learn to appreciate the truths that are linked to the story of a
"tinder-box."
CHAPTER XVII.
341. _Since all bodies expand by heat and contract by cold, why does
water, when it reaches the freezing point, expand?_
Because, in freezing, water undergoes crystallization, in which its
particles assume a new arrangement occupying _greater space_.
342. _Why does water never freeze to a great depth?_
Because the covering of ice which is formed upon the surface of the
water prevents the cold air from continuing to draw off the _caloric_
of the water.
[Verse: "For he saith to the snow, Be thou on the earth; likewise to
the small rain, and to the great rain of his strength."--JOB XXXVII.]
343. _Why has this exceptional law of the expansion of water, when
freezing, been ordained?_
Because, but for this, deep waters might be frozen through their whole
depth. This would destroy the myriads of fish and other living things
that inhabit the water. Parts of the earth, now clad in verdure, would
be lost in eternal winter; and even in the most temperate zones it
would take months to effect a thaw; and thawing would be attended with
such floods and subterranean commotion as are terrible to contemplate.
344. _Why are bed-room windows sometimes covered with crystalline forms
on winter mornings?_
Because the vapour of the breaths of the inmates has condensed upon the
window-panes, and formed water. The water has frozen with the cold, and
exhibits the beautiful crystalline forms into which its particles are
arranged.
Here we have another domestic illustration of the great laws of
nature. It is the same law which locks the arctic regions in ice
and decorates our window-panes. This beautiful phenomenon is
usually witnessed by us on frosty mornings when we rise from our
beds. It has a story which the observer of nature may read in its
sparkling eyes. It tells that, although without the air is biting
cold, God has wrapped a mantle around the face of nature to keep
it from injury; and that the earth and the waters, though looking
chilled and dead, have still the warmth of life preserved in their
bosoms.
345. _What is dew?_
Dew is _watery vapour_ diffused in the air, _condensed_ by coming in
contact with bodies _colder than the atmosphere_.
346. _Why does the air become charged with watery vapour?_
Because, during the day, under the influence of the sun's rays, vapours
are _exhaled_ from all the moist and watery surfaces of the earth.
These vapours are _held in suspension_ in the atmosphere until, by a
change in the temperature of the earth, and of bodies on the surface of
the earth, they are _condensed_, and deposited in translucid drops.
347. _What causes the decline of temperature that favours the
deposition of dew?_
The earth, which during the day _received heat_ from the solar rays,
_radiates the heat_ back into the air, and therefore becomes itself
colder. All the various objects upon the face of the earth also
_radiate heat_ in a greater or lesser degree. And dew will be found to
be deposited upon the surfaces of such bodies in propo
Showing first 200,000 characters. Full text: gutenberg.org/ebooks/47748