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diff --git a/40652-0.txt b/40652-0.txt new file mode 100644 index 0000000..a7e7efb --- /dev/null +++ b/40652-0.txt @@ -0,0 +1,15539 @@ +*** START OF THE PROJECT GUTENBERG EBOOK 40652 *** + + A GUIDE TO THE SCIENTIFIC KNOWLEDGE OF THINGS FAMILIAR; + + BY + THE REV. DR. BREWER, + TRINITY HALL, CAMBRIDGE, + HEAD MASTER OF KING'S COLLEGE SCHOOL, + NORWICH, + IN UNION WITH KING'S COLLEGE, LONDON. + + LONDON: + JARROLD AND SONS, 47, ST. PAUL'S CHURCHYARD, + ALSO HAMILTON AND CO., SIMPKIN AND CO., + AND WHITTAKER AND CO. + + + + +PREFACE. + + +Of all science, none is more generally interesting than that which +explains the common phenomena of life. We see that salt and snow are +both white, a rose red, leaves green, and the violet a deep purple; but +how few persons ever ask the reason why! We know that a flute produces a +musical sound, and a cracked bell a discordant one--that fire is hot, +ice cold, and a candle luminous--that water boils when subjected to +heat, and freezes from cold; but when a child looks up into our face and +asks us "why,"--how many times is it silenced with a frown, or called +"very foolish for asking such silly questions!" The object of the +present book is to explain about 2000 of these "silly questions" (which +are often more easily asked than answered) in language so simple that a +child may understand it, yet not so childish as to offend the +scientific; and in order that the answers may be strictly correct, not +only the most approved modern authors have been consulted, but the +manuscript has been submitted sheet by sheet to the revision of two +gentlemen of acknowledged reputation for scientific attainments. To the +REV. A. BATH POWER, M. A. especially, great obligation is due, for a +careful revision of the whole manuscript, for many excellent hints, and +useful additions. In conclusion, so much diligence has been bestowed +upon this little work for nearly ten years, so much useful information +has been supplied by scientific friends, and so minute a revision has +been made of every answer, that it is no presumption to express a hope +that this "Guide to the Scientific Knowledge of Things Familiar" will +become generally useful and acceptable, not only to the young, but to +those advanced to maturer life. + +In this work some questions occur more than once, because they serve to +illustrate different principles; and whenever cognate questions occur, +the answers have been rendered as similar as possible, in order to +assist the memory of the learner. + + + + +SUBJECTS OF THE CHAPTERS. + + + PART I.--HEAT. + + + I.--The SUN a source of heat + + II.--ELECTRICITY a source of heat + Thunder and lightning + + III.--CHEMICAL ACTION a source of heat + III.--Combustion + IV.--Smoke and smoky chimneys + V.--Lamps and candles + VI.--Animal heat + + VII.--MECHANICAL ACTION a source of heat + VII.--Percussion + VIII.--Friction + VIII.--Compression + + IX.--EFFECTS OF HEAT + X.--Expansion + XI.--Liquefaction + XI.--Vaporization (clouds) + XII.--Evaporation + + XIII.--COMMUNICATION OF HEAT + XIII.--Conduction + XIV.--Absorption + XV.--Reflection + XVI.--Radiation (dew) + XVII.--Convection (boiling) + + + PART II.--AIR. + + XVIII.--AIR + Rust + Tarnish + + XIX.--CARBONIC ACID GAS + Froth + Effervescence + Fermentation, &c. + + XX.--CARBURETTED HYDROGEN GAS + Fire damp + Safety lamp + + XXI.--PHOSPHURETTED HYDROGEN GAS + Ignis fatuus + Ghosts + + XXII.--WIND + + XXIII.--BAROMETER + Ten special Rules + + XXIV.--SNOW. HAIL. RAIN + + XXV.--WATER + + XXVI.--ICE + Frost + Freezing mixtures + + XXVII.--LIGHT + Reflection + Telescopes + Refraction + Spectacles + Rainbows + Colour + + XXVIII.--SOUND + Ear trumpets + Echoes + + XXIX.--MISCELLANEOUS + Attraction + Anti-putrescents + Sleep + Dreams + Glossary + Index + + + + +PART I. + + + + +HEAT. + + +INTRODUCTION. + + +Q. _What is heat?_ + +A. The sensation of warmth. + + +Q. _How is this sensation produced?_ + +A. When we touch a substance of higher temperature than ourselves, the +warmer substance keeps parting with its heat, till both are of equal +temperature. + + +Q. _What is that "stream of heat" called, which flows thus, from one +body, to another?_ + +A. CALO'RIC. _Caloric_, therefore, is the _matter of heat_, which passes +from body to body; but HEAT is the _sensation, of warmth_, produced by +the influx of Calo'ric. + + +Q. _What are the four principal_ SOURCES _of heat_? + +A. 1.--The Sun. 2.--Electricity. 3.--Chemical Action: and 4.--Mechanical +Action. + + +Q. _What are the principal_ EFFECTS _of heat_? + +A. Expansion, Liquefaction, Vaporization, and Ignition. + + + + +CHAPTER I. + + +Q. _What is the_ PRINCIPAL _source of Heat_? + +A. The SUN. + + +Q. _Why do_ BURNING GLASSES _set fire to substances submitted to their +power_? + +A. The rays of the sun, collected by the Burning Glass, are all _bent to +one point_, called the "focus;" thus the heat and light, (which should +be diffused over the _whole_ glass,) being gathered together into one +point, are very greatly increased. + + +Q. _Why is there a_ DARK RIM _round this focus_? + +A. Because the rays of light, which should have fallen there, are _bent +into the focus_, and the space around, (being deprived of these rays) is +accordingly darkened. + + +Q. _Are_ ALL _the rays bent into one point_? + +A. No, not quite all: and, therefore, the rim round the focus is only +_slightly_ shadowed. + + + + +CHAPTER II. + + +Q. _What is the second chief source of heat?_ + +A. ELECTRICITY. + + +Q. _What is_ LIGHTNING? + +A. Lightning is only an _Electric Spark, taken from the clouds_. + + +Q. _What causes the discharge of an electric cloud?_ + +A. When a cloud, _overcharged_ with electric fluid, approaches another +which is _under-charged_, the fluid rushes from the former into the +latter, till both have the same quantity. + + +Q. _Is there any OTHER cause of lightning, besides the one just +mentioned?_ + +A. Yes; sometimes mountains, trees, and steeples, will discharge a +lightning cloud floating near; and sometimes electric fluid rushes out +of the _earth_, into the clouds. + + +Q. _What produces ELECTRICITY in the CLOUDS?_ + +A. 1st--The evaporation from the earth's surface. + +2ndly--The chemical changes perpetually going on: and + +3rdly--Currents of air of unequal temperature, excite electricity by +_friction_, as they pass by each other. + + +Q. _How HIGH are the LIGHTNING-CLOUDS from the earth?_ + +A. Electrical clouds are the _lowest of all clouds_; they are rarely +more than 700 yards above the ground; and sometimes, they actually +_touch the earth_ with one of their edges. + + +Q. _How high are the clouds generally?_ + +A. In a _fine_ day, the clouds are often 4 or 5 miles above our head; +but the average height of the clouds is from 1-1/2 to 2 miles. + + +Q. _Why is lightning sometimes_ FORKED? + +A. When the lightning-cloud is a long way off, the _resistance of the +air_ is so great, that the electrical current is diverted into a zig-zag +course. + + +Q. _Why does the resistance of the air make the lightning zig-zag?_ + +A. As the lightning _condenses_ the air, in the immediate advance of its +path; it keeps flying from side to side, in order to pass where there is +the _least resistance_. + + +Q. _How does lightning_ CONDENSE _the air in the immediate advance of +its path_? + +A. The air is condensed by the _rapidity_ of the lightning-flash. + + +Q. _Why is_ FORKED LIGHTNING _more_ DANGEROUS _than a straight flash_? + +A. Whatever _resists_ the flash, _diverts its course_; and when +_terrestrial_ objects offer resistance to the current, they are in great +danger of being destroyed. + + +Q. _Why are there sometimes_ TWO _flashes of forked lightning at the +same moment_? + +A. Sometimes (in very severe storms) a flash of lightning will divide +_into two or more parts_; and then each branch assumes the zig-zag +form. + + +Q. _Why is the FLASH sometimes quite STRAIGHT?_ + +A. When the lightning-cloud hovers _near the earth_, as the flash meets +with very little resistance, it is _not diverted_; or (in other words) +the flash is straight. + + +Q. _What is the cause of_ SHEET LIGHTNING? + +A. It is only the _reflection of distant flashes_, not distinctly +visible: and sometimes several flashes (from different clouds) +intermingle, and form one vast blaze or sheet of lightning. + + +Q. _Which_ FORM _of lightning is the most_ DANGEROUS? + +A. The _ball_ of fire is by far the most dangerous; and the _zig-zag_ +lightning is next in danger. _Sheet_ lightning is not often attended +with danger. + + +Q. _Why are_ BALLS OF FIRE _so very dangerous?_ + +A. Because (whenever they fall) much mischief is occasioned by their +_bursting_, which they always do, with an explosion like that of a +cannon. + + +Q. _Do these_ BALLS OF LIGHTNING _ever run along the ground?_ + +A. Yes; they often run a considerable way along the ground, then _stop_ +for a little time, and _burst in numberless pieces_: sometimes _each of +these pieces_ will explode; and at other times, the _whole ball_ will +burst at once, producing most mischievous consequences. + + +Q. _What mischief will these balls of fire produce?_ + +A. They will set houses and barns on fire; and kill all cattle and human +beings, which happen to be in their course. + + +Q. _Why does LIGHTNING sometimes KILL men and beasts?_ + +A. When the electric current passes through a man or beast, it produces +so _violent an action upon the nerves_, that it destroys life. + + +Q. _When is a person struck dead by lightning?_ + +A. Only when his body forms a part of the lightning's path: i. e. when +the electric fluid (in its way to the earth) actually passes _through +his body_. + + +Q. _Why are MEN sometimes MAIMED by lightning?_ + +A. Because lightning strikes with amazing force, whatever opposes it: +and if a man stand in the way, it strikes him such a blow, as to maim +him. + + +Q. _What is THUNDER?_ + +A. Lightning _parts the air_ through which it passes; and when the +parted air _closes_ again, the noise made by the concussion, is called +Thunder. + + +Q. _Why does lightning PART the air through which it passes? It does not +part a rod of iron._ + +A. Iron is a _conductor_, and therefore allows the fluid to go freely +through it: but air being a _non-conductor_, _resists_ the lightning; +which, therefore, rips it open, in order to pass through it. + + +Q. _Why is THUNDER sometimes ONE VAST CRASH?_ + +A. When the lightning-cloud is near the earth, as the flash is +_straight_,--the whole volume of air (through which it passes) +_collapses at once_; and produces one unbroken sudden _crash_. + + +Q. _What is meant by the air collapsing?_ + +A. When the rent air _closes again_, it is said to collapse. + + +Q. _Why is the PEAL sometimes an IRREGULAR mangling broken ROAR?_ + +A. When the lightning-cloud is a long way off, as the flash is zigzag, +the air does not collapse _all at once_; and as we hear the concussion +of one part after another, the peal is broken, protracted, and +irregular. + + +Q. _Which part of the collapsing air do we hear first?_ + +A. That part _nearest_ the _earth_; then the strata above; and last of +all, _that_ in the immediate vicinity of the cloud. + + +Q. _What is meant by_ "STRATA _of air?_" + +A. If a board were laid upon the earth, and several other boards were +piled upon it, this pile would represent strata of wood. + + +Q. _How does this illustration apply to the air?_ + +A. A layer of air covers the earth; another layer rests upon _it_; and +thus layer is piled upon layer, for 50 miles in height. Each layer is a +"stratum" of air; and the _plural_ of stratum is strata. + + +Q. _Why do we hear the collapsing of the air NEAREST the earth FIRST?_ + +A. Because sound takes a whole _second of time_ to travel 380 yards; but +the air is ripped from top to bottom instantaneously: if, therefore, the +cloud were 1000 yards off, we should hear the collapsing of the lowest +strata nearly _three seconds_, before we heard that in the immediate +vicinity of the cloud. + + +Q. _Why is the THUNDER sometimes like a deep GROWL?_ + +A. When the storm is _far distant_, the thunder sounds like a deep +growl. + + +Q. _Does not SCENERY affect the sound of thunder?_ + +A. Yes; the _flatter_ the country, the more unbroken the peal: +_Mountain_ scenery _breaks_ the peal, and makes it harsh and irregular. + + +Q. _What is the cause of ROLLING THUNDER?_ + +A. The rolling is produced by the _reverberation_ of the thunder along +the massive clouds. + + +Q. _What is meant by the reverberation?_ + +A. The echo. + + +Q. _Why is a flash of lightning generally followed by a POURING RAIN?_ + +A. The cloud _collapses_, as soon as the electric fluid has left it; and +the water it contained is squeezed out. + + +Q. _Why is a flash of lightning generally followed by a GUST of WIND?_ + +A. The flash _rent the air asunder_ through which it darted; and when +the two parts collapse, a rapid motion is produced, which we call +_wind_: the _vibration_ of the thunder contributes also to agitate the +air. + + +Q. _What is meant by the_ "VIBRATION _of the thunder_?" + +A. The quivering motion it gives to the air, by its loud sound. + + +Q. _Why is there NO THUNDER to what is called SUMMER LIGHTNING?_ + +A. Because the lightning-clouds are _so far off_, that the sound of the +thunder is _lost_, before it reaches the earth. + + +Q. _Do_ THUNDER-BOLTS _ever drop from the clouds?_ + +A. No; the notion of _thunder-bolts_ falling from the clouds, arises +from the _globular_ form, that is sometimes assumed by a flash of +lightning. + + +Q. _Why is the_ THUNDER _often several moments_ AFTER _the FLASH?_[1] + +A. The flash travels nearly _a million_ times faster than the thunder; +if, therefore, the thunder has _far to come_, it will not reach the +earth till a considerable time _after the flash_. + +[1] The speed of lightning is so great, that it would go 480 times round +the earth in one minute: whereas, thunder would go scarcely 13 miles in +the same space of time. + + +Q. _Can we not tell the DISTANCE of a thunder-cloud, by observing the +interval which elapses between the flash and the peal?_ + +A. Yes; the flash is _instantaneous_, but the thunder will take a whole +_second of time_ to travel 380 yards: hence, if the flash is 5 seconds +before the thunder, the cloud is 1900 yards off. + +(i. e. 380 × 5 = 1900 yards.) + + +Q. _What PLACES are most DANGEROUS to be in, during a STORM?_ + +A. It is very dangerous to be near a tree, or lofty building; it is +dangerous also, to be near a river, or any running water. + + +Q. _Why is it DANGEROUS to be NEAR a TREE, or lofty building, during a +thunder-storm?_ + +A. Because a tall pointed object, (like a tree or spire,) will +frequently _discharge_ a lightning-cloud; and then the electric fluid +_will pass down it_, in its way to the earth. + + +Q. _How can a TREE or SPIRE DISCHARGE a lightning-cloud?_ + +A. A lightning-cloud (floating over a _plain_) may be _too far off_ to +be discharged by it; but as a tree, or spire, would _shorten_ the +distance between the cloud and its conductor, it might no longer be too +far off a conductor to be discharged. + + +Q. _Is not air a CONDUCTOR of lightning?_ + +A. No; dry air is _not_ a conductor of lightning; and therefore, the +flash _rends it in twain_, to get to some conductor. + + +Q. _Why would it be dangerous to stand near a tree or spire, while +lightning is passing down it?_ + +A. Because the electric fluid (called lightning) always rushes down the +_outside_ of the tree or spire; and if any one were standing near, might +pass through _him_, and kill or maim him. + + +Q. _Does lightning go through the inside or outside of a tree?_ + +A. It rolls down the _outside_ of a _tree_; but passes through the +_inside_ of a _man_. + + +Q. _Why does lightning pass down the OUTSIDE of a tree?_ + +A. Lightning always makes choice of the best conductors; and the +_outside_ of a tree is a better conductor than the inside. + + +Q. _Why does lightning pass through the INSIDE of a man?_ + +A. As the _fluids_ of the human body make a better conductor than the +_skin_, therefore lightning passes _through_ a man, and not down the +skin. + + +Q. _Why is it DANGEROUS to be near a deep RIVER, or any other running +water, during a thunder-storm?_ + +A. Because running water is a good conductor; and lightning always takes +in its course the _best conductors_. + + +Q. _Why is it dangerous for a man to be near water, in a thunder-storm?_ + +A. Because the _height of a man_ may be sufficient to discharge a cloud: +and (if there were no _taller_ object nigh) the lightning might make the +_man_ its conductor to the water. + + +Q. _Why is it DANGEROUS to RING CHURCH-BELLS during a thunder-storm?_ + +A. For two reasons: 1st--Because the steeple may _discharge_ the +lightning-cloud, in consequence of its mere _height_. + +2ndly--The swinging of the bells causes _a current of air_, which +collects electric fluid. + + +Q. _Why is it unsafe to RUN or DRIVE FAST during a thunder-storm?_ + +A. The rapid motion of running causes a _current of air_, which collects +electric fluid, and is often fatal. + + +Q. _What PARTS of a DWELLING are most DANGEROUS during a thunder-storm?_ + +A. The fire-place, (especially if the fire be _lighted_); the attics and +cellar. It is also dangerous to sit close by the walls; to ring the +bell; or to bar the shutters, during a thunder-storm. + + +Q. _Why is it DANGEROUS to sit BEFORE a FIRE, during a thunder-storm?_ + +A. Because the heated air and soot are conductors of lightning; +especially when connected with such excellent conductors as the stove, +fender, and fire-irons. + + +Q. _Why are the ATTICS and CELLAR DANGEROUS, during a thunder-storm?_ + +A. Lightning sometimes passes _from the clouds_ to the earth, and +sometimes _from the earth_ to the clouds; and therefore, the _middle +story_ of a house is always the safest to be in, during a thunder-storm. + + +Q. _When does lightning pass FROM THE EARTH to the CLOUDS?_ + +A. When the clouds are in a "negative" state of electricity. + + +Q. _When does lightning pass FROM THE CLOUDS to the EARTH?_ + +A. When the clouds are in a "positive" state of electricity. + + +Q. _What is meant by the clouds being in a "positive state of +electricity?"_ + +A. When the clouds contain _more_ electric fluid than they _generally_ +do, they are said to be in a _positive_ state of electricity. + + +Q. _What is meant by the clouds being in a "negative state of +electricity?"_ + +A. When the clouds contain _less_ electric fluid than they _ought_ to +do, they are said to be in a _negative_ state of electricity. + + +Q. _Does the flash proceed from a negative or positive body?_ + +A. Always from a _positive_ body, or one over-burdened with electric +fluid. + + +Q. _When lightning flashes from the earth to the clouds, what is the +flash called?_ + +A. It is called the "returning stroke;" because the earth (being +over-burdened with electric fluid) _returns_ the surplus quantity to the +clouds. + + +Q. _Why is it DANGEROUS to lean BACK AGAINST A WALL during a +thunder-storm?_ + +A. Because the electric fluid sometimes runs down the _wall_ of a house +or room; and (as a man is a better conductor than a brick wall), would +make _him_ its path, and injure him. + + +Q. _Why is it dangerous to RING a BELL during a thunder-storm?_ + +A. Bell-wire is an _excellent conductor_; and (if a person were to touch +the bell-handle), the electric fluid, passing down the wire, might run +through his hand and injure it. + + +Q. _Why would the lightning run through a man touching a bell-handle?_ + +A. Because the human body is a better conductor than the _wall_ (between +the bell-handle and the floor); and as lightning always chooses the +_best_ conductors for its path, it would (in this case) pass through the +_man_, and injure him. + + +Q. _Why is it DANGEROUS to BAR a SHUTTER during a thunder-storm?_ + +A. The iron shutter-bar is an _excellent conductor_; and (if a person +were touching the bar), the electric fluid passing down it, might run +from the bar _through the person touching it_, and injure him. + + +Q. _Why is it dangerous to be in a CROWD during a thunder-storm?_ + +A. For two reasons. 1st--Because a _mass_ of people form a _better +conductor_ than an individual: and + +2ndly--The _vapour_ from a crowd _increases the danger_ of such a place. + + +Q. _Why is a MASS of bodies a better conductor than a single body?_ + +A. _Each_ living body is a _conductor of electricity_; and a connected +_mass_ of such conductors is more likely to be struck, than a _single +individual_. + + +Q. _Why is the danger increased by the_ VAPOUR _which rises from a +crowd?_ + +A. _Vapour_ is a conductor, and therefore, may determine the shock; +especially when connected with so many living bodies. + + +Q. _Why is a THEATRE dangerous, during a thunder-storm?_ + +A. Because the _crowd assembled_ there, and the _great vapour_ arising +from so many living bodies, render a theatre an _excellent conductor of +lightning_. + + +Q. _Why is a_ FLOCK _of sheep in greater danger than a smaller number?_ + +A. Because _each_ sheep is a _conductor_ of lightning, and the _greater +the number_, the _better its conducting power_; besides, the _vapour_ +arising from a flock of sheep _increases its conducting power_, and its +danger. + + +Q. _Why is a HERD of cattle in danger during a storm?_ + +A. 1st--The _number_ of living bodies increases the conducting power of +the _animal fluids_: and + +2ndly--The _vapour_ arising from a herd is also a good conductor. + + +Q. _If a person be ABROAD in a thunder-storm, what place is the SAFEST?_ + +A. Any spot about 20 or 30 feet from some tall tree or building; unless +that spot be near to running water. + + +Q. _Why would it be safe to stand 20 or 30 feet from some tall tree, in +a thunder-storm?_ + +A. Because the lightning would always choose the _tall tree_ as a +conductor, rather than the _shorter man_; and he would not be +sufficiently near the tree, to be injured by the electric current +passing down it. + + +Q. _If a person be in A CARRIAGE in a thunder-storm, in what way can he +travel most SAFELY?_ + +A. He should not lean _against_ the carriage; but sit upright, without +touching any of the four sides. + + +Q. _Why should not a person lean AGAINST the carriage in a storm?_ + +A. Because the electric fluid might run down the sides of the carriage; +and (if a person were leaning against the sides), would make choice of +_him_ for a conductor, and perhaps destroy life. + + +Q. _If a person be in A HOUSE during a thunder storm, what place is +SAFEST?_ + +A. Any room in the _middle story_. The _middle_ of the room is best; +especially if you place yourself on a mattrass, bed, or hearth-rug. + + +Q. _Why is the MIDDLE STORY of a house SAFEST in a thunder-storm?_ + +A. Because (even if the fluid _struck_ the house), its strength would be +exhausted before it reached the middle story. + + +Q. _Why is the MIDDLE of the ROOM more SAFE, than any other part of it, +in a thunder-storm?_ + +A. Because, if the lightning came into the room at all, it would come +down the _chimney_ or _walls_ of the room; and therefore, the further +distant from these, the better. + + +Q. _Why is a MATTRASS BED, or HEARTH-RUG a good security against injury +from lightning?_ + +A. Because they are all _non-conductors_; and, as lightning always takes +in its course the _best_ conductors, it would not select such things as +these. + + +Q. _Is it better to be WET or dry during a storm?_ + +A. To be _wet_: if a person be in the open field, the best thing he can +do, is to stand about 20 feet from some tree, and get _completely +drenched to the skin_. + + +Q. _Why is it better to be WET than dry?_ + +A. Because the _wet clothes_ would form a far _better conductor_ than +the _fluids of our body_; and, lightning would roll down the wet +clothes, _without touching our body at all_. + + +Q. _What is the SAFEST thing a person can do to avoid injury from +lightning?_ + +A. He should draw his bedstead into the middle of his room, commit +himself to the care of God, and go to bed; remembering that our Lord has +said, "The very hairs of your head are all numbered." + + +Q. _What is a LIGHTNING-CONDUCTOR?_ + +A. A metal rod fixed in the earth, running up the whole height of a +building, and rising in a point above it. + + +Q. _What metal is the best for this purpose?_ + +A. Stout copper wire. + + +Q. _Why is COPPER wire better than iron?_ + +A. 1st--Because copper is a better conductor than iron: + +2ndly--It is not so easily fused or melted: and + +3rdly--It is not so much injured by weather. + + +Q. _What is the GOOD of a lightning-conductor?_ + +A. Metal wire is a most excellent conductor; and as the lightning makes +choice of the _best conductors_, it would run down the _metal wire_, +rather than the _bricks_ of the building. + + +Q. _How far will the beneficial influence of a lightning-conductor +extend?_ + +A. It will protect a circumference all round, the diameter of which is +(at least) 4 times as long as that part of the rod, which _rises above +the building_. + + +Q. _Give me an example._ + +A. If the rod rise 2 feet above the house, it will protect the building +for (at least) 8 feet all round. + + +Q. _Why are not lightning-conductors more generally used?_ + +A. Because they are often productive of more harm than good. + + +Q. _How can lightning-conductors be productive of HARM?_ + +A. If the rod be _broken_ by weather or accident, the electric fluid +(being obstructed in its path) will rend the building into fragments. + + +Q. _Is there any OTHER evil to be apprehended from a lightning rod?_ + +A. Yes; if the rod be not big enough to conduct the _whole_ current to +the earth, the lightning will _fuse_ the metal, and greatly injure the +building. + + +Q. _How stout is it needful for the copper wire to be, that it may +conduct the fluid safely to the earth?_ + +A. It should be (at least) _one inch_ in diameter. + + +Q. _Why does LIGHTNING sometimes KNOCK DOWN HOUSES and churches?_ + +A. The steeple, or chimney is first struck; the lightning then darts to +the iron bars and cramps employed in the building; and (as it darts from +bar to bar) shatters to atoms the bricks and stones, which oppose its +progress. + + +Q. _Can you tell me how St. Bride's Church (London) was nearly destroyed +by lightning, about 100 years ago?_ + +A. The lightning first struck the metal vane, and ran down the rod; it +then darted to the iron cramps, employed to support the building; and +(as it flew from bar to bar) smashed the stones of the church, which lay +between. + + +Q. _Why did the lightning fly about from place to place, and not pass +down in a straight course?_ + +A. Because it always takes in its course the _best conductors_; and will +fly both right and left, in order to reach them. + + +Q. _Why does LIGHTNING turn MILK SOUR?_ + +A. Lightning causes the gases of the air (through which it passes) to +_combine_, and thus produces a poison, called _nitric acid_; some small +portion of which, mixing with the milk, turns it sour.[2] + +(N. B. Sometimes, the mere _heat_ of the air, during the storm, turns +milk sour.) + +[2] The air is composed of two gases, called oxygen and hydrogen, +_mixed_ together, but _not combined_. If oxygen is _combined_ with +nitrogen, it produces five deadly poisons, viz.--nitrous oxide, nitric +oxide, hyponitrous acid, nitrous acid, and nitric acid, according to the +proportion of each gas in the combination. + + +Q. _What is the difference between COMBINING and MIXING?_ + +A. When different ingredients mingle _without undergoing any chemical +change_, they are said to be _mixed_; but when the natural properties of +each are _altered by the union_, then those ingredients are said to be +_combined_. + + +Q. _Give me an example._ + +A. If different coloured sands be shaken together in a bottle, the +various grains will _mix_ together, but not combine: but if water be +poured on quick lime, the water will _combine_ with the lime, and not +mix with it. + + +Q. _Why are the different grains of sand said to be MIXED, when they are +shaken together?_ + +A. Because they are mingled together, but the property of each grain +remains the _same as it was before_. + + +Q. _Why is water poured on lime, said to COMBINE with it?_ + +A. Because the properties, both of the water and the lime, are _altered_ +by the mixture: the lime alters the character of the water, and the +water alters the character of the lime. + + +Q. _Do oxygen and nitrogen COMBINE, or only MIX together, in common +atmospheric air?_ + +A. They only _mix_ together, as grains of sand would do, when shaken in +a bottle. When oxygen and nitrogen _combine_, they do not constitute +_air_, but acid _poisons_. + + +Q. _Why does LIGHTNING turn BEER SOUR, although contained in a close +cask?_ + +A. If the beer be _new_, and the process of fermentation not complete, +lightning will so _accelerate_ the process, as to turn the liquor sour. + + +Q. _Why is NOT old beer and strong PORTER made SOUR by lightning?_ + +A. Because the _fermentation is complete_ already; and, therefore, is +not affected by electrical influence. + + +Q. _Why is METAL sometimes FUSED by lightning?_ + +A. Because the dimension of the metal is _too small_, to afford a path +for the electric current. + + +Q. _Why does LIGHTNING PURIFY the AIR?_ + +A. For two reasons: 1st--Because the oxygen and nitrogen of the air +_combine_,[3] and produce "nitric acid:" + +2ndly--Because the agitation of the storm _stirs up the air_. + +[3] The oxygen and hydrogen are not _combined_, but simply _mixed_ in +the ordinary air; but the lightning causes the mixed elements to +_combine_. + + +Q. _How does the production of nitric acid purify the air?_ + +A. Nitric acid acts very powerfully in _destroying exhalations_, arising +from putrid vegetable and animal matters. + + +Q. _Why is LIGHTNING more common in SUMMER and AUTUMN, than in spring +and winter?_ + +A. The heat of summer and autumn produces _great evaporation_; and the +conversion of _water to vapour_, always develops _electricity_. + + +Q. _Why does a THUNDER-STORM generally follow very DRY weather, and +rarely succeeds continued WET?_ + +A. The clouds are _always_ charged with electricity; but _dry air_ +(being a non-conductor), will not conduct the surplus fluid from the +clouds to the earth: so it violently _rends the dry air_ with a flash, +in order to relieve the cloud, and reach the earth. + + +Q. _What is the general DIRECTION of a THUNDER-STORM?_ + +A. Either from east to west; or else from north to south. + + +Q. _Why is ELECTRICITY excited by FRICTION?_ + +A. Electricity, like heat, exists in _all_ matter; but is often in a +_latent state_: friction _disturbs_ it, and brings it into active +operation. (see p. 31.) + + +Q. _Why is a TREE sometimes SCORCHED by lightning, as if it had been set +on fire?_ + +A. Lightning scorches it by its own _positive heat_, just the same as +fire would. + + +Q. _Why is the BARK of a TREE often ripped quite off by a flash of +lightning?_ + +A. As the lightning runs down the tree, it develops the latent heat so +_rapidly_, that it carries the bark of the tree along with it, while it +seeks to escape. + + +Q. _Why are BOUGHS of TREES broken off by lightning?_ + +A. The _mechanical force_ of lightning is very great; and when the flash +strikes a tree, it will often break off the boughs by the _force_ with +which it strikes against it. + + +Q. _Why is an electric shock felt MOST at the ELBOW JOINT?_ + +A. Because the path of the fluid is _obstructed by the joint_: and the +shock felt at the elbow is caused by the fluid _leaping from one bone to +another_. + + + + +CHAPTER III. + + +Q. _What is the third chief source of heat?_ + +A. CHEMICAL ACTION. + + +Q. _What is meant by chemical action being the source of heat?_ + +A. Many things, when their chemical constitution is changed, (either by +the abstraction of some of their gases, or by the combination of others +not before united,) evolve _heat_, while the change is going on. + + +Q. _Explain by illustration what you mean._ + +A. Water is cold, and sulphuric acid is cold; but if these two _cold_ +liquids be mixed together, they will produce _boiling heat_. + + +Q. _Why will COLD WATER, mixed with SULPHURIC ACID, produce heat?_ + +A. Because water (being _lighter_ than sulphuric acid), is _condensed_ +by the heavier liquid; and its heat is _squeezed out_, as water from a +sponge. + + +Q. _Why does COLD WATER, poured on LIME, make it intensely HOT?_ + +A. The heat is evolved by the chemical action, produced by the cold +water combining with the lime. + + +Q. _Where does the heat come from?_ + +A. It was in the water and lime before; but was in a _latent state_. + + +Q. _Was there heat in the cold water and lime, before they were mixed +together?_ + +A. Yes. _All_ bodies contain heat; the coldest ice, as well as the +hottest fire. + + +Q. _Is there HEAT even in ICE?_ + +A. Yes. But it is _latent_, (i. e. not perceptible to our senses).[4] + +[4] Latent, from the Latin word, Lateo, (to lie hid.) + + +Q. _How do you know there is heat, if you cannot perceive it?_ + +A. Thus:--Ice is 32° by the thermometer; but if ice be _melted_ over a +fire, (though 140° of heat are thus absorbed,) it will feel no _hotter_ +than it was before. (_i. e. it will be only 32°, and not 172°_)[5]. + +[5] 32°, i. e. 32 degrees; 140°, i. e. 140 degrees, &c. + + +Q. _What becomes of the 140°, which went into the ice to melt it?_ + +A. It is hidden in the water; or (to speak more scientifically) it is +stored up in a _latent state_. + + +Q. _How much heat may be thus secreted or made latent?_ + +A. _All_ things contain a vast quantity of latent heat; but, as much as +1140° of heat may remain latent in _water_. + + +Q. _How can 1140° of heat be added to water, without being perceptible +to our feelings?_ + +A. 1st--140° of heat are hidden in the water, when ice is melted by the +sun or fire. + +2ndly--1000° more of heat are secreted, when water is converted into +steam. Thus, before ice is converted into steam, 1140° of heat become +_latent_.[6] + +[6] Thus, one pint of boiling water, (212° according to the +thermometer,) will make 1800 pints of steam; but the steam is no hotter +to the touch than boiling water, both are 212°: therefore, when water is +converted into steam, 1000° of heat become latent. Hence, before ice is +converted to steam, it must contain 1140° of latent heat. + + +Q. _Can we be made to FEEL the heat of ICE or snow?_ + +A. Yes. Into a pint of snow put half as much salt; then plunge your hand +into the liquid; and it will feel so intensely cold, that the snow +itself will seem quite _warm_ in comparison to it. + + +Q. _Is SALT and SNOW really COLDER than snow?_ + +A. Yes, many degrees; and by dipping your hand into the mixture +_first_, and into snow _afterwards_, the mere snow will seem to be +comparatively warm. + + +Q. _What is FIRE?_ + +A. Combustion is another instance of heat, arising from chemical action. + + +Q. _What two things are essential to produce combustion?_ + +A. Fuel and air. + + +Q. _What are the elements of fuel?_ + +A. As bread is a compound of flour, yeast, and salt; so fuel is a +compound of hydrogen and carbon. + + +Q. _What are the ELEMENTS of atmospheric AIR?_ + +A. The air is a compound of oxygen and nitrogen _mixed_ together; in the +proportion of five gallons of nitrogen, to one of oxygen. + + +Q. _What is CARBON?_ + +A. The solid part of fuel. It abounds also in all animal bodies, earths, +and minerals. + + +Q. _Mention some different SPECIES of CARBON._ + +A. Common charcoal, lamp-black, coke, black lead, and the diamond, are +all varieties of carbon. + + +Q. _What is HYDROGEN?_ + +A. An inflammable gas. The gas used in our streets, is only the hydrogen +gas _driven out of coals by heat_. + + +Q. _What are the peculiar characteristics of hydrogen gas?_ + +A. Though this gas _itself_ will _burn_, yet a candle will _not_ burn +when immersed in it; nor can an animal live in it. Hydrogen gas is the +lightest of all known substances.[7] + +[7] Hydrogen gas may be made thus:--Put some pieces of zinc or iron +filings into a glass: pour over them a little sulphuric acid (vitriol), +diluted with twice the quantity of water; then cover the glass over for +a few minutes, and hydrogen gas will be given off. + +EXP. If a flame be put into the glass, an EXPLOSION will be made. + +If the experiment be tried in a phial, which has a piece of tobacco-pipe +run through the cork; and a light held a few moments to the top of the +pipe, a FLAME will be made. + +If a balloon be held over the phial, (so that the gas can inflate it,) +the balloon will ascend in a very few minutes. + + +Q. _What is OXYGEN?_ + +A. A gas, much heavier than hydrogen; which gives brilliancy to flame, +and is essential to animal life.[8] + +[8] Oxygen gas is much more troublesome to make than hydrogen. The +_cheapest_ plan is to put a few ounces of manganese (called the black +oxide of manganese) into an iron bottle, furnished with a bent tube; +set the bottle on a fire till it becomes red hot, and put the end of the +tube into a pan of water. In a few minutes, bubbles will rise through +the water; these bubbles are oxygen gas. + +These bubbles may be collected thus:--Fill a common bottle with water; +hold it topsy-turvy over the bubbles which rise through the pan, but be +sure the mouth of the bottle be held _in the water_. As the bubbles rise +into the bottle, the water will run out; and when all the water has run +out, the bottle is full of gas. Cork the bottle while the _mouth remains +under water_; set the bottle on its base; cover the cork with lard or +wax, and the gas will keep till it be wanted. + +N. B. The _quickest_ way of making oxygen gas, is to rub together in a +mortar half an ounce of oxide of copper, and half an ounce of chlorate +of potassa. Put the mixture into a common oil flask, furnished with a +cork which has a bent tube thrust through it. Heat the bottom of the +flask over a candle or lamp; and when the mixture is red hot, oxygen gas +will be given off. Note--the tube must be immersed in a pan of water, +and the gas collected as before. + +(Chlorate of potassa may be bought at any chemist's; and oxide of copper +may be procured by heating a sheet of copper red hot, and when cool, +striking it with a hammer: the scales that peel off, are oxide of +copper.) + +EXP. Put a piece of red hot charcoal, (fixed to a bit of wire,) into +your bottle of oxygen gas; and it will throw out most dazzling sparks of +light. + +Blow a candle out; and while the wick is still red, hold the candle (by +a piece of wire,) in the bottle of oxygen gas; the wick will instantly +ignite, and burn brilliantly. + +(Burning sulphur emits a _blue_ flame, when immersed in oxygen gas.) + + +Q. _What is NITROGEN?_ + +A. Nitrogen is another invisible gas. It _will not_ burn, like hydrogen; +and an animal cannot live in it: it abounds in animal and vegetable +substances, and is the chief ingredient of the common air.[9] + +[9] Nitrogen gas may easily be obtained thus:--Put a piece of burning +phosphorus on a little stand, in a plate of water; and cover a bell +glass over. (Be sure the edge of the glass stands _in the water_.) In a +few minutes the air will be decomposed, and nitrogen alone remain in the +bell glass. + +(N.B. The white fume which will arise and be absorbed by the water in +this experiment, is phosphoric acid; i. e. phosphorus combined with +oxygen of the air.) + + +Q. _Why is there so much nitrogen in the air?_ + +A. In order to _dilute_ the oxygen. If the oxygen were not thus diluted, +fires would burn out, and life would be exhausted too quickly. + + +Q. _What three elements are necessary to produce COMBUSTION?_ + +A. Hydrogen gas, carbon, and oxygen gas; the two former in the _fuel_, +and the last in the _air_ which surrounds the fuel. + + +Q. _What causes the combustion of the fuel?_ + +A. The hydrogen gas of the fuel being set free, and excited by a piece +of lighted paper, instantly _unites_ with the _oxygen of the air_, and +makes a yellow flame: this flame heats the _carbon of the fuel_, +which also unites with the oxygen of the air, and produces _carbonic +acid gas_. + + +Q. _What is carbonic acid gas?_ + +A. Only carbon (or charcoal) combined with oxygen gas. + + +Q. _Why does FIRE produce HEAT?_ + +A. 1st--By liberating _latent heat_ from the air and fuel: and + +2ndly--By throwing into _rapid motion_ the _atoms of matter_. + + +Q. _How is latent HEAT liberated by COMBUSTION?_ + +A. When the _oxygen_ of the air combines with the _hydrogen_ of the +fuel, the two gases _condense into water_; and latent heat is _squeezed +out_, as water from a sponge. + + +Q. _How are the ATOMS OF MATTER DISTURBED by COMBUSTION?_ + +A. 1st--When _hydrogen_ of fuel and _oxygen_ of air _condense into +water_, a _vacuum_ is made; and the air is disturbed, as a _pond_ would +be, if a pail of water were taken out of it: and + +2ndly--When the _carbon_ of fuel and _oxygen_ of air _expand into +carbonic acid gas_, the air is _again_ disturbed, as it would be by +the explosion of _gunpowder_. + + +Q. _How does fire condense HYDROGEN and OXYGEN into WATER?_ + +A. The _hydrogen of fuel_ and _oxygen of air_ (liberated by combustion) +combining together, _condense into water_. + + +Q. _How does fire expand CARBON into CARBONIC ACID GAS?_ + +A. The _carbon of fuel_ and _oxygen of air_ (combining together in +combustion) expand into a gas, called _carbonic acid_. + + +Q. _Why is a FIRE (after it has been long burning) RED HOT?_ + +A. When coals are heated _throughout_, the carbon is so completely mixed +with the oxygen of the air, that the _whole surface is in a state of +combustion_, and therefore _red hot_. + + +Q. _In a BLAZING fire, why is the UPPER surface of the COALS BLACK, and +the LOWER surface RED?_ + +A. Carbon (being very solid) requires a great degree of heat to make it +unite with the oxygen of the air. When fresh coals are put on, their +_under_ surface is heated before the upper surface; and one is _red_ (or +in a state of combustion), while the other is _black_. + + +Q. _Which burns the quicker, a BLAZING fire, or a RED HOT one?_ + +A. A _blazing_ fire burns out the fuel quickest. + + +Q. _Why do BLAZING COALS BURN QUICKER than red hot ones?_ + +A. In red hot coals, only the _mere surface_ is in a state of +combustion, because the carbon is _solid_; but in a _blazing_ fire, +(where the gases are escaping), the _whole volume of the coal +throughout_ is in a state of decomposition. + + +Q. _What is SMOKE?_ + +A. _Unconsumed_ parts of fuel (principally carbon), separated from the +solid mass, and carried up the chimney by the current of hot air. + + +Q. _Why is there MORE SMOKE when COALS are FRESH added, than when they +are red hot?_ + +A. Carbon (being solid), requires a great degree of heat to make it +unite with oxygen, (or, in other words, to bring it into a state of +perfect combustion): when coals are fresh laid on, _more carbon is +separated_ than can be _reduced to combustion_; and so it flies off in +smoke. + + +Q. _Why is there so LITTLE SMOKE with a RED HOT FIRE?_ + +A. When a fire is red hot, the _entire surface_ of the coals is in a +_state of combustion_; so a very little flies off unconsumed, as smoke. + + +Q. _Why are there DARK and BRIGHT SPOTS in a CLEAR cinder FIRE?_ + +A. Because the _intensity_ of the combustion is _greater in some parts_ +of the fire, than it is in _others_. + + +Q. _Why is the intensity of the combustion so unequal?_ + +A. Because the air flies to the fire in various and unequal currents. + + +Q. _Why do we see all sorts of GROTESQUE FIGURES in hot COALS?_ + +A. Because the _intensity_ of combustion is so _unequal_, (owing to the +gusty manner in which the air flies to the fuel; and the various shades +of red, yellow, and white heat mingling with the black of the unburnt +coal), produce strange and fanciful resemblances. + + +Q. _Why does PAPER BURN more readily than wood?_ + +A. Merely because it is of a _more fragile texture_; and, therefore, its +component parts are more easily heated. + + +Q. _Why does WOOD BURN more readily than coal?_ + +A. Because it is not so _solid_; and, therefore, its elemental parts are +more easily separated, and made hot. + + +Q. _When a FIRE is LIGHTED, why is PAPER laid at the BOTTOM, against the +grate?_ + +A. Because paper (in consequence of its fragile texture), so very +readily catches fire. + + +Q. _Why is WOOD laid on the top of the paper?_ + +A. Because wood, (being more _substantial_), _burns longer_ than +paper; and, therefore, affords a _longer contact of flame_ to heat the +coals. + + +Q. _Why would not paper do without wood?_ + +A. Because paper burns out so _rapidly_, that it would not afford +sufficient _contact of flame_ to heat the coals to combustion. + + +Q. _Why would not WOOD do WITHOUT shavings, straw, or paper?_ + +A. Because wood is too _substantial_ to be heated into combustion, by +the flame issuing from a mere _match_. + + +Q. _Why would not the paper do as well, if placed on the TOP of the +coals?_ + +A. As every blaze _tends upwards_, if the paper were placed on the _top_ +of the fire, its blaze would afford _no contact of flame_ to fuel lying +_below_. + + +Q. _Why should COAL be placed ABOVE the wood?_ + +A. As every flame tends _upwards_, if the wood were _above the coal_, +the _flame_ would not rise _through the coal_ to heat it. + + +Q. _Why is a FIRE KINDLED at the LOWEST BAR of a grate?_ + +A. As every flame tends _upwards_; when a flame is made at the _bottom_ +of a fire, it _ascends through the fuel_ and heats it: whereas, if the +fire were lighted from the _top_, the flame would _not come into +contact_ with the fuel piled below. + + +Q. _Why does COAL make such EXCELLENT FUEL?_ + +A. Because it is so very _hard_ and _compact_, that it burns away very +slowly. + + +Q. _Why will CINDERS become RED HOT, quicker than COALS?_ + +A. Because they are _more porous_ and _less solid_; and are, therefore, +sooner reduced to a state of combustion. + + +Q. _Why will not IRON CINDERS burn?_ + +A. Iron cinders are _cinders saturated with oxygen_; they are unfit for +fuel, because they can imbibe _no more oxygen_, being saturated already. + + +Q. _Why are CINDERS lighter than COALS?_ + +A. Because their vapour, gases, and volatile parts, have been driven off +by _previous combustion_. + + +Q. _Why will not STONES do for fuel, as well as COALS?_ + +A. Because they contain no _hydrogen_ (or inflammable gas) like coals. + + +Q. _Why will not WET KINDLING light a fire?_ + +A. 1st--Because the moisture of the wet kindling prevents the _oxygen of +the air from getting to the fuel_ to form it into carbonic acid gas: +and + +2ndly--The heat of the fire is perpetually _drawn off_, by the +conversion of _water_ into _steam_. + + +Q. _Why does DRY wood burn BETTER than GREEN?_ + +A. 1st--Because no heat is _carried away_, by the conversion of _water +into steam_: and + +2ndly--The pores of dry wood _are filled with air_, which supply the +fire with oxygen. + + +Q. _Why do TWO pieces of WOOD burn BETTER than ONE?_ + +A. 1st--Because they help to entangle the _heat of the passing smoke_, +and _throw it on the fuel_: and + +2ndly--They help to _entangle the air_ that passes over the fire, and +create a kind of _eddy_ or draught. + + +Q. _Why does SALT CRACKLE when thrown into a FIRE?_ + +A. Salt contains _water_; and the _cracking_ of the salt is owing to the +sudden _conversion of the water into steam_. + + +Q. _Why will not wood or paper burn, if they are steeped in a solution +of POTASH, phosphate of LIME, or AMMONIA (hartshorn)?_ + +A. Because any "al'kali" (such as potash) will _arrest the hydrogen_ (as +it escapes from the fuel), and prevent its _combination_ with the +_oxygen of air_. + + +Q. _What is an al'kali?_ + +A. The con'verse of an _acid_; as _bitter_ is the con'verse of _sweet_, +or _insipid_ the con'verse of _pungent_. + + +Q. _Why does a JET of FLAME sometimes burst into the room THROUGH THE +BARS OF A STOVE?_ + +A. The iron bars conduct heat to the _interior of some lump of coal:_ +and its volatile gas (bursting through the weakest part) is kindled by +the glowing coals over which it passes. + + +Q. _Why is this JET sometimes of a GREENISH YELLOW colour?_ + +A. When a lump of coals lies _over the hot bars_, or the coals below it +are not _red hot_, the gas which bursts from the lump _escapes unburnt_, +and is of a greenish colour. + + +Q. _Why does the gas escape UNBURNT?_ + +A. Because neither the _bars_ nor _coals_ (over which it passes) are +_red-hot_. + + +Q. _Why does a BLUISH FLAME sometimes flicker on the surface of hot +cinders?_ + +A. Gas from the hot coals _at the bottom of the grate_ mixing with the +_carbon of the coals above_, produces an inflammable gas (called +carbonic oxide), which burns with a blue flame. + + +Q. _Why is the FLAME of a good fire YELLOW?_ + +A. Because both the hydrogen and carbon of the fuel are in a state of +_perfect combustion_. It is the _white heat of the carbon_, which gives +the pale yellow tinge to the flaming hydrogen. + + +Q. _What is LIGHT?_ + +A. Rapid _undulations_ of a fluid called _ether_, striking on the eye. + + +Q. _How does COMBUSTION make these undulations of LIGHT?_ + +A. The atoms of matter (set in motion by heat) _striking against_ this +ether, produce _undulations_ in it; as a _stone_ thrown into a stream, +would produce undulations in the _water_. + + +Q. _How can UNDULATIONS of ether produce LIGHT?_ + +A. As _sound_ is produced by _undulations of air_ striking on the +_ear_; so _light_ is produced by undulations of _ether_ striking on the +_eye_. + + +Q. _What is ETHER?_ + +A. A very subtile fluid, which pervades and surrounds _every thing we +see_. + + +Q. _Mention a simple experiment to prove that LIGHT is produced by rapid +MOTION._ + +A. When a fiddle-string is _jerked_ suddenly, its rapid vibration +produces a grey _light_; and when a carriage wheel revolves very +quickly, it sends forth a similar light. + + +Q. _Does HEAT ALWAYS produce LIGHT?_ + +A. No: the heat of a stack of hay, or reeking dunghill, though very +_great_, is not sufficient to produce _light_. + + +Q. _Why is a YELLOW FLAME brighter than a RED HOT COAL?_ + +A. Because _yellow rays_ always produce the greatest amount of _light_; +though _red rays_ produce the greatest amount of _heat_. + + +Q. _Why is the LIGHT of a fire MORE INTENSE sometimes than at others?_ + +A. The _intensity_ of fire-light depends upon the _whiteness_ to which +the carbon is reduced, by combustion. If the carbon be _white hot_, its +_combustion is perfect_, and the light intense; if not, the light is +obscured by _smoke_. + + +Q. _Why will not CINDERS BLAZE, as well as FRESH coals?_ + +A. The _flame_ of coals is made chiefly by _hydrogen gas_. As soon as +this gas is consumed, the hot cinders produce only an _invisible_ gas, +called carbonic acid. + + +Q. _Where does the hydrogen gas of a fire come from?_ + +A. The _fuel is decomposed_ (by combustion) into its simple elements, +carbon and hydrogen gas. (see p. 33) + + +Q. _Why does not a FIRE BLAZE on a FROSTY NIGHT, so long as it does upon +another night?_ + +A. The air (being very cold) _rushes to the fire so rapidly_, that the +coals burn out _faster_, and the inflammable gas _is sooner consumed_. + + +Q. _Why does a FIRE burn CLEAREST on a FROSTY night?_ + +A. Because the volatile gases are quickly consumed; and the solid +carbon _plentifully supplied with air_, to make it burn bright and +intensely. + + +Q. _Why does a FIRE burn more intensely in WINTER than in SUMMER time?_ + +A. Because the air is _colder_ in winter, than in summer-time. + + +Q. _How does the COLDNESS of the air increase the HEAT of a fire?_ + +A. For two reasons: 1st--Because cold air being more _condensed_ than +hot air, contains a greater _body_: and + +2ndly--Cold air _rushes more quickly to the fire_, and supplies more +_oxygen_. + + +Q. _Why does the SUN, shining on a FIRE, make it DULL, and often put it +out?_ + +A. 1st--When the sun shines, the air is rarefied; and, therefore, _flows +more slowly to the fire_. + +2ndly--As the air is _rarefied_, even that which _reaches_ the fire, +_affords less nourishment_. + + +Q. _Why does the air flow to the fire more TARDILY for being RAREFIED?_ + +A. The greater the _contrast_ (between the _external air_, and that +_which has been heated by the fire_) the more _rapid_ will be the +current of air towards that fire. + + +Q. _Why does rarefied air afford LESS NOURISHMENT to fire, than cold +air?_ + +A. Because it is _spread out_, (like a piece of gold _beaten into +leaf_); and as a square inch of gold _leaf_ will not contain so much +gold as a square inch of _bullion_--so, a square inch of _rarefied_ air +has less _body_, than a square inch of _cold air_. + + +Q. _Why does a FIRE burn more fiercely in the OPEN AIR?_ + +A. 1st--Because the _air out-of-doors_ is more _dense_, than the air +in-doors: and + +2ndly--Because air is _more freely supplied_ to a fire out-of-doors. + + +Q. _Why is the air out-of-doors more DENSE than that in-doors?_ + +A. Because the circulation is more free; and as soon as any portion has +been _rarefied_, it instantly escapes, and is supplied by _colder +currents_. + + +Q. _Why does not a FIRE burn so freely in a THAW, as in a FROST?_ + +A. During a thaw, the air is filled with _vapour_; and, both _moves too +slowly_, and is _too much diluted_ to nourish the fire. + + +Q. _Why does a FIRE burn so fiercely in WINDY weather?_ + +A. In windy weather the _air is rapidly changed_, and affords plentiful +nourishment to the fire. + + +Q. _Why do a pair of BELLOWS get a fire up?_ + +A. A pair of bellows, (like the wind), _drives the air more rapidly to +the fire_; and the plentiful supply of oxygen soon makes the fire burn +intensely. + + +Q. _Why is a CANDLE BLOWN OUT by the breath, and not made more intense, +like a fire?_ + +A. As the flame of a candle is confined to a _very small wick_, it is +_severed_ from it by the breath; and (being unsupported) _must go out_. + + +Q. _Why is a SMOULDERING WICK sometimes REKINDLED by blowing it?_ + +A. The breath carries the air to it with _great rapidity_; and the +oxygen of the air kindles the _red hot wick_, as it kindles charred +wood. + + +Q. _Why is not the red hot wick kindled by the air AROUND it, without +BLOWING it?_ + +A. Because oxygen is not supplied with sufficient freedom, unless it be +_blown_ to the wick. + + +Q. _When is this experiment most likely to succeed?_ + +A. In _frosty_ weather; because the air contains more oxygen then, +_being condensed by the cold_. + + +Q. _Why does a POKER, LAID ACROSS a dull FIRE, revive it?_ + +A. For two reasons. 1st--Because the poker _concentrates the heat_, and +therefore increases it: and + +2ndly--Because the poker _arrests the air_ which passes over the fire, +and _produces a draught_. + + +Q. _Why do SEVERAL PIECES of WOOD or coal burn BETTER than ONE?_ + +A. When there are two or three pieces of wood on a fire, the air +_(circulating round them) produces an eddy_ or draught, which draws up +the fire. + + +Q. _Why are STOVES fixed on the FLOOR of a room?_ + +A. In order that the air, _on the lower part of the room_, may be heated +by the fire. + + +Q. _Would not the air of the lower part of a room be heated equally +well, if the stoves were fixed higher up?_ + +A. No; the heat of a fire has a very little effect upon the air _below +the level of the grate_; and, therefore, every grate should be as _near +to the floor_ as possible. + + +Q. _Why are our FEET so COLD when we sit close by a good fire?_ + +A. As the fire consumes the air which passes over it, _cold air_ rushes +through the crevices of the doors and windows _along the bottom of the +room_ to supply the deficiency; and these currents of cold air, _rushing +constantly over our feet_, deprive them of their warmth. + + +Q. _If a piece of PAPER be laid FLAT on a clear fire, it will NOT BLAZE, +but CHAR. Why so?_ + +A. The carbon of a clear fire, being sufficiently hot to unite with the +oxygen of the air, _produces carbonic acid gas_, which soon envelops +the paper laid flat upon the cinders: but carbonic acid gas will not +_blaze_. + + +Q. _If you BLOW the paper, it will BLAZE immediately. Why so?_ + +A. By blowing, or opening the door suddenly, _the carbonic acid is +dissipated_, and the paper is instantly fanned into flame. + + +Q. _Why does WATER EXTINGUISH a FIRE?_ + +1st--Because the water _forms a coating_ over the fuel, and keeps it +from the air: + +2ndly--The conversion of _water into steam_, draws off the _heat_ of the +burning fuel. + + +Q. _Why does a LITTLE WATER make a fire FIERCER, while a LARGER quantity +of water puts it OUT?_ + +A. Water is composed of _oxygen and hydrogen_; when, therefore, the fire +can decompose the water into its simple elements, it serves for _fuel_ +to the flame. + + +Q. _How can WATER serve for FUEL to fire?_ + +A. The _hydrogen_ of the water will burn with a _flame_; and the +_oxygen_ of the water will increase the _intensity_ of that flame. + + +Q. _If a house be on fire, is too LITTLE water worse than NO water at +all?_ + +A. Certainly. Unless the water be supplied so plentifully as _to quench +the fire_, it will increase the _intensity_, like fuel. + + +Q. _When will water EXTINGUISH FIRE?_ + +A. When the supply is so rapid and abundant, that the fire cannot +_convert it into steam_. + + +Q. _Does not a very LITTLE water SLACKEN the heat of fire?_ + +A. Yes, _till it is converted into steam_; but then it increases the +_intensity_ of fire, and acts like fuel. + + +Q. _Why does the WICK of a candle (when the flame has been blown out) +CATCH FIRE so readily?_ + +A. As the wick is already _very hot_, a little _extra_ heat will throw +it into flame. + + +Q. _Why does the EXTRA heat revive the flame?_ + +A. Because it again liberates the _hydrogen_ of the tallow, and ignites +it. + + +Q. _Cannot WOOD be made to BLAZE without actual contact with fire?_ + +A. Yes; if a piece of wood be held _near_ the fire for a little time it +will blaze, even though it does not _touch_ the fire. + + +Q. _Why will WOOD BLAZE, even if it does not touch the fire?_ + +A. The heat of the fire _drives out the hydrogen gas_ of the wood; which +is inflamed by contact with the red-hot coals. + + +Q. _Why will a NEIGHBOUR'S HOUSE sometimes CATCH FIRE, though no flame +of the burning house ever touches it?_ + +A. The heat of the burning house sets at liberty _the hydrogen gas_ of +the neighbouring wood-work, which is ignited by the flames or red-hot +bricks of the house on fire. + + +Q. _What is COKE?_ + +A. Coal freed from its volatile gases, by the action of artificial heat. + + +Q. _Why do ARNOTT'S STOVES sometimes SMELL so strong of SULPHUR?_ + +A. The fire is made of coke, which contains sulphur; and, whenever the +draught is not rapid enough _to drive the sulphur up the flue_, it is +emitted into the room. + + +Q. _What is meant by SPONTANEOUS COMBUSTION?_ + +A. Ignition produced by the action of _one uninflamed_ body on another. + + +Q. _Give an example of spontaneous combustion._ + +A. Goods packed in a warehouse will often catch fire of _themselves_; +especially such goods as cotton, flax, hemp, rags, &c. + + +Q. _Why do such GOODS sometimes CATCH FIRE of themselves?_ + +A. Because they are piled together in very _great masses_ in a _damp_ +state or place. + + +Q. _Why does this produce spontaneous combustion?_ + +A. The damp produces _decay_ or the decomposition of the goods, and the +great heat of the piled-up mass makes the decaying goods _ferment_. + + +Q. _How does this FERMENTATION produce COMBUSTION?_ + +A. During fermentation, _carbonic acid gas_ is given off by the +goods,--a slow combustion ensues,--till at length the _whole pile_ +bursts into _flame_. + + +Q. _Why is the HEAT of a LARGE MASS of goods GREATER than that of a +smaller quantity?_ + +A. Because compression _squeezes out_ heat, as water is squeezed from a +sponge; and as the goods of a large pile are greatly _compressed_, much +of their latent heat is _squeezed out_. + + +Q. _Why do HAY-STACKS sometimes CATCH FIRE of themselves?_ + +A. Either because the hay was got up _damp_, or because rain has +penetrated the stack. + + +Q. _Why will a HAY-STACK CATCH FIRE if the hay be damp?_ + +A. Damp hay soon _decays_, and undergoes a _state of fermentation_; +during which, _carbonic acid gas_ is given off, and the stack catches +_fire_. + + +Q. _Why does roasted COFFEE sometimes CATCH FIRE spontaneously?_ + +A. The _heat_ of coffee is greatly increased by being _roasted_; and the +_carbon of the coffee_ uniting with the _oxygen of the air_, produces +_carbonic acid gas_, and bursts into _flame_. + + +Q. _Why do old RAGS, used for CLEANING LAMPS and CANDLES, sometimes set +a HOUSE on FIRE?_ + +A. Because they very readily _ferment_, and (during fermentation) throw +off exceedingly inflammable gases. + + +(N.B. Lamp-black mixed with linseed oil is more liable to spontaneous +combustion, than anything that servants handle.) + + + + +CHAPTER IV. + +SMOKE. + + +Q. _Why does SMOKE ASCEND the chimney?_ + +A. As the air of the room passes over the fire, it becomes _heated_; and +(being thus made _lighter_,) ascends the chimney, carrying the smoke +with it. + + +Q. _What is SMOKE?_ + +A. Small particles of carbon, separated by combustion from the fuel, but +not _consumed_. + + +Q. _Why do SMOKE and steam CURL, as they ascend?_ + +A. Because they are moved in a _right line_, and then _pushed on all +sides_; and this forces them into a _circular_ motion. + + +Q. _What are BLACKS?_ + +A. When the hot air of the chimney has been cooled by the _external_ +air, it can no longer _buoy up_ the solid smoke; so it falls to the +earth in condensed flakes, called "blacks." + + +Q. _Why are there NO BLACKS in the smoke of a RAILWAY engine?_ + +A. The smoke of a railway engine consists chiefly of _watery vapour_, +which dissolves in air, as sugar does in water; but the smoke of a +common chimney consists of small fragments of _unburnt fuel_. + + +Q. _Why does a "COPPER HOLE" DRAW up more fiercely than an OPEN stove?_ + +A. As the air, which supplies the copper hole, must pass _through the +furnace_, it becomes exceedingly _heated_, and rushes up the chimney +with great violence. + + +Q. _What produces the ROARING noise made by a COPPER-HOLE fire?_ + +A. Air rushing rapidly through the crevices of the _iron door_, and up +the _chimney flue_. + + +Q. _Why is the ROAR LESS, if the copper-hole DOOR be thrown OPEN?_ + +A. Because _fresh_ air gets access to the fire _more easily_; and as the +air is not so intensely heated, its motion is not so _violent_. + + +Q. _Why do some CHIMNEYS SMOKE?_ + +A. If fresh air is not admitted into a room, _as fast as it is consumed +by the fire_, a current of air _will rush down the chimney_ to _supply +the deficiency_, and bring the smoke along with it. + + +Q. _What prevents air being supplied, as fast as it is consumed by the +fire?_ + +A. Leather and curtains round the doors; sand-bags at the threshhold and +on the window-frames; and other contrivances to keep out the draught. + + +Q. _Why is it needful for cold fresh air to be so constantly supplied?_ + +A. If water be taken with a pail out of a river, _other_ water will rush +towards the hole, as soon as the pail is lifted out; and if air be taken +from a room, (as it is, when some of it goes up the chimney) _other air_ +will rush towards the void to fill it up. + + +Q. _Why will it come down the chimney?_ + +A. Because if doors and windows are all made _air-tight_, it can get to +the room in no _other_ way. + + +Q. _What is the best REMEDY in such a case?_ + +A. The _speediest_ remedy is to open the door or window: but by far the +_best_ remedy is to carry a small tube from the hearth into the external +air. + + +Q. _Why is that the BEST remedy?_ + +A. Because the fire will be plentifully supplied with air by the tube; +the doors and windows may all remain air-tight; and we may enjoy a warm +fireside, without the inconvenience of draughts and cold feet. + + +Q. _Why is a CHIMNEY raised so high above the ROOF?_ + +A. If it were not so, it would smoke; as all funnels do which are too +short. + + +Q. _What is meant by the funnel, or flue of a chimney?_ + +A. That part of a chimney through which _the smoke passes_, is called +the funnel, or flue. + + +Q. _Why does a CHIMNEY SMOKE, if the funnel be very short?_ + +A. Because the _draught_ of a short flue _is too slack_ to carry the +smoke up the chimney. + + +Q. _Why is the DRAUGHT of a SHORT FLUE more SLACK that that of a long +one?_ + +A. For many reasons. 1st--_The fire is always dull and sluggish_ if the +chimney be too short. + +2ndly--The smoke rolls _out_ of the chimney, before it has acquired its +_full velocity_. + +3rdly--The wind, rain, and air, have more influence over a _short_ +funnel, than over a _long_ one. + + +Q. _Why is the FIRE always DULL and sluggish if the CHIMNEY-FLUE be very +SHORT?_ + +A. Because the draught is so bad: and as the rarefied air _passes up the +chimney very tardily_, _fresh air_ flows as tardily _towards the fire_, +to supply it with _oxygen_. + + +Q. _On what does the INTENSITY of fire depend?_ + +A. The _intensity_ of fire is always in proportion to the _quantity of +oxygen_ with which it is supplied. + + +Q. _Why does not SMOKE acquire its full VELOCITY in a SHORT funnel?_ + +A. Because the _higher_ smoke ascends in a flue, (provided it be clear +and hot) the _faster_ it goes; (as a stone falls faster and faster the +lower it descends): if, therefore, a _funnel be very short_, the smoke +never acquires its full velocity. + + +Q. _Does the DRAUGHT of a chimney depend on the SPEED of the SMOKE +through the flue?_ + +A. Yes. The more quickly _hot_ air flies _up the chimney_, the more +quickly _cold_ air will rush _towards the fire_ to supply the place; +and, therefore, the _longer the flue_, the _greater the draught_. + + +Q. _Why is the DRAUGHT of a LONG FLUE greater than that of a short one?_ + +A. Because the _higher_ smoke ascends, the _faster_ it goes; (as a stone +falls faster and faster, the nearer it approaches to the earth): if, +therefore, a funnel be _long_, the smoke acquires great _velocity_, and +the _draught_ is great. + + +Q. _If a CHIMNEY be TOO SHORT, and cannot be lengthened, what is the +best REMEDY to prevent smoking?_ + +A. To _contract the opening of the chimney_ contiguous to the stove. + + +Q. _Why will a_ SMALLER OPENING _against the stove_ PREVENT _the_ +SMOKING? + +A. As all the air (which enters the chimney) _must pass near the fire_, +it will become _greatly heated_, and _rise rapidly_ through the funnel; +and this _increase of heat_ will compensate for the _shortness of the +flue_. + + +Q. _Why will a_ ROOM SMOKE, _if there be_ TWO FIRES _in it?_ + +A. Because the _fiercer_ fire will exhaust the most air; and draw from +the _smaller_ one, to supply its demand. + + +Q. _Why will a chimney_ SMOKE _if there be a_ FIRE _in_ TWO ROOMS +_communicating with each other?_ + +A. Whenever the _door_ between the two rooms _is opened_, air will rush +from the chimney of the _inferior_ fire, to supply the _other_; and +_both_ rooms will be filled with smoke. + + +Q. _What is the_ REMEDY _in this case?_ + +A. Let a tube be carried from the hearth of each stove, into the +external air; and then _each_ fire will be so _well_ supplied, that +neither will need to borrow from the other. + + +Q. _Why do VESTRY CHIMNEYS so often SMOKE?_ + +A. Because the wind (striking against the steeple) _is reflected back_; +and tumbles down the vestry chimney, forcing the smoke _into the room_. + + +Q. _WHAT WINDS make vestry chimneys smoke?_ + +A. Those from the north-east or south-east; according to the position of +the vestry. + + +Q. _Why will the EASTERN winds make VESTRIES SMOKE, more than those from +the west?_ + +A. Because they _strike against the steeple_, and _bound back_ to the +vestry chimney: but _western_ winds cannot rebound over the roof of a +church. + + +(N. B. The _steeple_ of a church is always due _west_, and the _other_ +end of the church due _east_; if, therefore, a _western_ wind rebound, +it would rebound to the _west_, or _away from the church_, and not +towards it.) + + +Q. _Why does a HOUSE in a VALLEY very often SMOKE?_ + +A. Because the wind (striking against the surrounding hills) _rebounds +back again upon the chimney_, and destroys its draught. + + +Q. _What is the common REMEDY in both these cases?_ + +A. To fix a _cowl_ on the chimney top, to turn like a weather-cock, and +present its back to the wind. + + +Q. _Why will not a COWL always PREVENT a chimney SMOKING?_ + +A. If the wind be _strong_, it will keep the _opening_ of the cowl +_towards the steeple or hill_; and then the reflected wind will _blow +into the cowl_, and _down the chimney_. + + +Q. _As a cowl is such a poor remedy, can any OTHER be devised?_ + +A. If the chimney flue can be carried _higher_ than the steeple or +hills, no wind can enter the flue. + + +Q. _Why cannot the wind enter a chimney flue, if it be carried up HIGHER +than the steeple or hills?_ + +A. Because the reflected wind would strike against the _sides_ of the +chimney-flue, and not pass over the _opening_ at all. + + +Q. _In what OTHER cases will a CHIMNEY SMOKE?_ + +A. If both door and chimney be placed on _the same side of a room_, the +chimney will often smoke. + + +Q. _Why will a CHIMNEY SMOKE, if the DOOR and STOVE are both on the SAME +SIDE?_ + +A. Because when the door is opened, a current of air will _blow into the +chimney-place_, and drive the smoke into the room. + + +Q. _What REMEDY can be applied to this evil?_ + +A. The door must be set _opposite_ to the chimney, or nearly so; and +then the draught from the door _will blow the smoke up the chimney_, and +not into the room. + + +Q. _Why will a CHIMNEY SMOKE if it NEEDS SWEEPING?_ + +A. Because the obstruction in the chimney (presented by the loose soot, +to the free passage of the smoke) _delays its current_, and prevents the +draught. + + +Q. _Why will a CHIMNEY SMOKE, if OUT OF REPAIR?_ + +A. 1st--Because the _loose mortar and bricks_ obstruct the smoke: and + +2ndly--The _cold air_ (oozing through the chinks) _chills the air in the +chimney_, and prevents its ascent. + + +Q. _Why will an ARNOTT'S STOVE SMOKE, if the joints of the flue do not +fit air-tight?_ + +A. Because the _cold air_ (which gets through the joints) _chills the +air in the flue_, and prevents its ascent. + + +Q. _Why does an old fashioned FARM CHIMNEY-PLACE so often smoke?_ + +A. Because the opening is so _very large_, that much of the air which +goes up the chimney, _has never passed near the fire_; and this cold air +mixing with the other, so _reduces its temperature_, that it ascends +very slowly, and the draught is destroyed. + + +Q. _Why does a chimney smoke, if the DRAUGHT be SLACK?_ + +A. Because, unless the current of air up the chimney be very powerful, +it cannot _buoy the smoke up_ through the flue. + + +Q. _If the opening of a chimney be TOO LARGE, what REMEDY can be +applied?_ + +A. The chimney-place must be contracted. + + +Q. _Why will CONTRACTING the chimney-place PREVENT its SMOKING?_ + +A. As the air will then pass _nearer the fire_, it will be _more +heated_, and fly up the chimney _much faster_. + + +Q. _Why do almost all CHIMNEYS SMOKE in GUSTY weather?_ + +A. The gust (blowing the air _away_ from the top of the chimney) +_removes_ (for a time) _all resistance to the smoke_: but when the wind +_lulls_ again, the _resistance of the air suddenly returns_--the +_draught_ is _checked_--and a puff of smoke rushes into the room. + + +Q. _What is the use of a CHIMNEY-POT?_ + +A. When the opening of a chimney is _large_, the top must be contracted +by a chimney-pot, in order to increase the draught. + + +Q. _How does a CHIMNEY-POT INCREASE the DRAUGHT of a chimney?_ + +A. As the _same quantity_ of hot air has to escape _through a much +smaller opening_, it must pass through more quickly. + + +Q. _Why do tin BLOWERS help to get a fire up?_ + +A. Because they compel the air to go _through_ the fire, and not _over_ +it; therefore the fire is well supplied with oxygen, and the draught +greatly increased. + + +Q. _Why does a tin BLOWER INCREASE the DRAUGHT?_ + +A. As all the air which enters the chimney has to pass _through_ the +fire, it is much hotter, and ascends the chimney very fast; and the +faster the air _flies up the chimney_, the faster it rushes _towards the +fire_ also. + + +Q. _Why does a parlour often SMELL disagreeably of SOOT in SUMMER-TIME?_ + +A. The air in the _chimney_ (being _colder_ than the air in the +_parlour_) _descends into the room_, and leaves a disagreeable smell of +soot behind. + + +Q. _Why are the CEILINGS of PUBLIC OFFICES so BLACK and filthy?_ + +A. The heated air ascending, carries the dust and fine soot to the +ceiling; where the hot _air_ escapes through the plaster, and _leaves +the soot and dust_ behind. + + +Q. _Why are SOME parts of the ceiling BLACKER and more filthy than +others?_ + +A. As the air cannot penetrate the thick _joists_ of the ceiling, _it +passes by those parts_, and deposits its soot and dust on those which +are more penetrable. + + +Q. _What is CHARCOAL?_ + +A. Wood which has been exposed to a red heat, till it has been deprived +of all its gases and volatile parts. + + +Q. _Why is a CHARCOAL FIRE hotter than a wood fire?_ + +A. Because so large a quantity of _water_ has been abstracted from the +fuel, by the red heat to which it has been already exposed. + + +Q. _Why does charcoal REMOVE the TAINT of meat?_ + +A. Because it absorbs all odoriferous effluvia, whether they arise from +putrefying animal or vegetable matter. + + +Q. _Why is WATER PURIFIED by being filtered through charcoal?_ + +A. Charcoal absorbs the _impurities_ of the water, and removes all +disagreeable tastes and smells, whether they arise from animal or +vegetable matter. + + +Q. _Why are water and wine CASKS CHARRED inside?_ + +A. _Charring_ the inside of the cask reduces it to a _kind of charcoal_; +and charcoal (by absorbing animal and vegetable impurities) keeps the +liquor sweet and good. + + +Q. _Why does a piece of BURNT BREAD, steeped in impure WATER, make it +fit to drink?_ + +A. The surface of the bread is reduced to _charcoal_ by being burnt; and +the charcoal surface of the bread _abstracts all the impurities of the +water_, and makes it palatable. + + +Q. _Why should the TOAST and WATER, placed by the side of the sick, be +made of BURNT BREAD?_ + +A. The surface of the bread being _reduced to charcoal_ by being burnt, +prevents the water from being affected by the impurities of the sick +room. + + +Q. _Why are TIMBERS, which are to be exposed to damp, CHARRED?_ + +A. _Charcoal undergoes no change_ by exposure to air and water; +therefore timber will resist weather _much longer_, after it has been +charred. + + + + +CHAPTER V. + +LAMPS AND CANDLES. + + +Q. _Of what are OIL, TALLOW, and WAX composed?_ + +A. Principally of carbon and hydrogen gas. The _solid_ part is carbon, +the _volatile_ part is gas. + + +Q. _What is CARBON?_ + +A. A solid substance, generally of a black colour; well known under the +forms of charcoal, lamp-black, coke, black-lead, &c. + + +Q. _What is HYDROGEN GAS?_ + +A. The principal ingredient of water. It is well known in the form of +common _coal gas_: it burns so readily that it used to be called +"inflammable air."[10] + +[10] To make hydrogen gas, see p. 34. + + +Q. _Why does a CANDLE BURN when lighted?_ + +A. The heat of the lighted wick _decomposes the tallow_ into its +elementary parts of carbon and hydrogen; and the _hydrogen of the +tallow_, combining with the _oxygen of the air_, produces _flame_. + + +Q. _Why is the FLAME of a candle HOT?_ + +A. 1st--Because the flame liberates _latent heat_ from the air and +tallow: and + +2ndly--It throws into _rapid motion_ the _atoms of matter_. + + +Q. _How is LATENT HEAT liberated by the flame of a CANDLE?_ + +A. When the _hydrogen_ of the tallow and _oxygen_ of the air _combine_, +they _condense into water_; and much of their latent heat is _squeezed +out_. + + +Q. _How are the ATOMS of MATTER disturbed by the flame of a candle?_ + +A. 1st--When the _hydrogen_ of the tallow and _oxygen_ of the air +_condense into water_, a _vacuum_ is made; and the air is disturbed, as +a _pond_ would be, if a pail of _water_ were taken out. + +2ndly--When the _carbon_ of tallow and _oxygen_ of the air expand into +_carbonic acid gas_, the air is _again_ disturbed; in a similar way as +by the explosion of _gunpowder_. + + +Q. _Why does the flame of a CANDLE produce LIGHT?_ + +A. The chemical changes made by combustion, excite _undulations of +ether_, which (striking the eye) produce light. (see p. 46.) + + +Q. _Why is the FLAME of a CANDLE YELLOW?_ + +A. Only the _outer_ coat of the flame is yellow; the _lower_ part of the +flame is _violet_; and the _inside_ of the flame is _hollow_. + + +Q. _Why is the outside of the flame YELLOW?_ + +A. Because the _carbon of the tallow_ (being in a state of _perfect +combustion_) is made white-hot. + + +Q. _Why is the BOTTOM part PURPLE of the flame of a candle?_ + +A. The _bottom part_ of the flame is _overladen with hydrogen_, raised +from the tallow by the burning wick; and this _half-burnt gas_ gives a +_purple_ tinge to the flame. + + +Q. _Why is the INSIDE of the flame of a candle HOLLOW?_ + +A. Because it is _filled with vapour_, raised from the candle by the +_heat of the wick_. + + +Q. _Describe the different parts of the FLAME of a common CANDLE._ + +A. The flame consists of _three cones_. The innermost cone is hollow; +the intermediate cone of a dingy purple hue; and the outside cone is +yellow. + + +Q. _Why is the intermediate cone of a flame PURPLE, as well as the +BOTTOM of the flame._ + +A. Because the gases are not in a state of _perfect combustion_; but +contain an _excess of hydrogen_, which gives this cone a purple tinge. + + +Q. _Why is not the MIDDLE cone in a state of perfect combustion, as well +as the OUTER cone?_ + +A. Because the outer cone _prevents the oxygen of the air_ from getting +freely to the _middle of the cone_; and without the free access of +oxygen gas, there is no such thing as complete combustion. + + +Q. _Why does the FLAME of a candle point UPWARDS?_ + +A. The flame _heats the surrounding air_, which (being hot) _rapidly +ascends_, and drives the flame upwards at the same time. + + +Q. _Why is the FLAME of a candle POINTED at the top, like a cone?_ + +A. The _upper_ part of a flame is more _volatile_ than the lower parts; +and as it affords _less resistance to the air_, is reduced to a mere +point. + + +Q. _Why is the UPPER part of a flame more VOLATILE than the lower +parts?_ + +A. The _lower_ parts of the flame are laden with unconsumed gas and +watery vapour; which present considerable resistance to the air. + + +Q. _Why is the FLAME of a candle BLOWN OUT by a puff of breath?_ + +A. As the flame of a candle is attached to a _very small wick_, a puff +of breath _severs the flame from the wick_; and it goes out for want of +support. + + +Q. _Why does the FLAME of a candle make a GLASS DAMP, which is held over +it?_ + +A. The _hydrogen of the tallow_ combining with the _oxygen of the air_, +produce a "watery vapour," which is condensed by the _cold glass_ held +above the flame. + + +Q. _Why does our hand, held ABOVE a candle, suffer from the heat of the +flame so much more, than when it is placed BELOW the flame, or on ONE +SIDE of it?_ + +A. Because the hot gases and air (in their ascent) _come in contact_ +with the hand placed _above_ the flame: but when the hand is placed +_below_ the flame, or on _one side_, it only feels heat from +_radiation_. + + +Q. _Why is a RUSH LIGHT extinguished so much more quickly than a +cotton-wicked candle?_ + +A. As the _rush_ wick is _smooth_ and _hard_, the _mere motion of the +air_ (produced by carrying the candle from one place to another,) is +sufficient to sever the flame from the rush. + + +Q. _Why is it more difficult to blow out a COTTON wick?_ + +A. The _cotton_ wick is _quite full of small threads_ or filaments, +which help to _hold the flame on the wick_, like the roots of a tree. + + +Q. _Why does an EXTINGUISHER put a candle out?_ + +A. Because the air in the extinguisher _is soon exhausted of its oxygen_ +by the flame: and when there is no _oxygen to support it_, the flame +goes out. + + +Q. _Why does not a candle set fire to a PIECE OF PAPER twisted into an +extinguisher, and used as such?_ + +A. 1st--Because the flame very soon _exhausts the little oxygen_ +contained in the paper extinguisher: and + +2ndly--The flame invests the _inside of the paper extinguisher_ with +_carbonic acid gas_, which prevents it from blazing. + + +Q. _Why is a LONG WICK never upright?_ + +A. Because it is bent by its own weight. + + +Q. _Why is a LONG WICK covered with an EFFLORESCENCE at the top?_ + +A. The knotty or flowery appearance of the top of a wick arises _from an +accumulation of particles partly separated_, but still loosely hanging +to the wick. + + +Q. _Why is not the END of a long wick BURNT OFF, as it hangs over the +flames?_ + +A. Because the length of the wick so diminishes _the heat of the flame_, +that it is not _hot_ enough to burn it off. + + +Q. _Why do PALMER'S METALLIC WICKS never need SNUFFING?_ + +A. The wick is divided into two parts, each of which _bends outward_ to +the outside of the flame; where the _end is intensely heated_, and +_separated_ from the wick by the current of air up the candle. + + +Q. _Why do common CANDLES require to be SNUFFED?_ + +A. Because the heat of the flame is _not sufficient to consume the +wick_; and the _longer_ the wick grows, the _less heat_ the flame +produces. + + +Q. _Why do WAX CANDLES NEVER need SNUFFING?_ + +A. The wick of _wax_ candles is made _of very fine thread_, which the +heat of the flame is sufficient to consume: but the wick of _tallow_ +candles is made _of coarse cotton_, which is too substantial to be +consumed by the heat of the flame, and must be cut off by _snuffers_. + + +Q. _Why does a PIN, stuck in a RUSH-LIGHT, EXTINGUISH it?_ + +A. Because a _pin_ (being a good conductor), _carries away the heat of +the flame from the wick_, and prevents the combustion of the tallow. + + +Q. _What is the SMOKE of a CANDLE?_ + +A. Solid particles of carbon separated from the wick and tallow, but not +consumed. + + +Q. _Why are SOME particles consumed and not OTHERS?_ + +A. The _combustion of the carbon_ depends upon its _combining with the +oxygen of the air_: but as the outer surface of the flame _prevents the +access of air to the interior parts_, therefore much of the carbon of +those parts passes off in smoke. + + +Q. _Why do LAMPS SMOKE?_ + +A. Either because the _wick is cut unevenly_, or else because _it is +turned up too high_. + + +Q. _Why does a LAMP SMOKE when the WICK is cut UNEVENLY?_ + +A. 1st--Because the _points of the jagged edge_ (being very easily +separated from the wick,) _load the flame with more carbon than it can +consume_: and + +2ndly--As the heat of the flame is _greatly diminished by these bits of +wick_, it is unable to consume _even the usual quantity of smoke_. + + +Q. _Why does a LAMP SMOKE when the WICK is turned up too HIGH?_ + +A. Because more carbon is separated from the wick _than can be consumed +by the flame_. + + +Q. _Why do not "Argand burners" smoke?_ + +A. Because a current of air passes through the _middle of the flame_; +and therefore the carbon of the _interior_ is consumed, as well as that +_in the outer coating of the flame_. + + +Q. _Why does a LAMP-GLASS DIMINISH the SMOKE of a lamp?_ + +A. Because it both _concentrates and reflects the heat of the flame_; in +consequence of which, the heat is so greatly increased, _that very +little carbon escapes unconsumed_. + + + + +CHAPTER VI. + +ANIMAL HEAT. + + +Q. _What is the cause of ANIMAL HEAT?_ + +A. Animal heat is produced _by the combustion of hydrogen and carbon_ in +the capillary veins. + + +Q. _What are CAPILLARY VEINS?_ + +A. Veins _as small as hairs_ running _all over the body_; so called from +the Latin word "capilla'ris" (_like a hair_). + + +Q. _Do these CAPILLARY VEINS run all over the human body?_ + +A. Yes. Whenever blood _flows from a wound_, some _vein_ must be +divided; and as you cannot insert a needle into _any part of the body +without bringing blood_, therefore these little veins must run _through +every part_ of the human frame. + + +Q. _How do HYDROGEN gas and CARBON get into these very little veins?_ + +A. The food we eat is _converted into blood_, and blood contains both +_hydrogen_ and _carbon_. + + +Q. _How does COMBUSTION take place in the veins?_ + +A. The _carbon of the blood_ combines with the _oxygen of the air we +breathe_, and forms into _carbonic acid gas_. + + +Q. _What BECOMES of this CARBONIC ACID GAS formed in the human blood?_ + +A. Some of it is _thrown off by the breath_; and the rest of it is +_absorbed by the blood_, to keep up the animal heat. + + +Q. _What is the cause of the COMBUSTION of FIRE?_ + +A. The _carbon of fuel_ unites with the _oxygen of the air_, and forms +_carbonic acid gas_. + + +Q. _What is the cause of the COMBUSTION of a CANDLE or LAMP?_ + +A. The _carbon of the oil or tallow_ unites with the _oxygen of the +air_, and forms _carbonic acid gas_. + + +Q. _What is the cause of SPONTANEOUS COMBUSTION?_ + +A. The piled-up goods _ferment from heat and damp_; and (during +fermentation) _carbonic acid gas is formed_, as in the two former cases. + + +Q. _Does the HEAT of the HUMAN BODY arise from the SAME CAUSE as the +heat of FIRE?_ + +A. Yes, precisely. The _carbon of the blood_, combining with the _oxygen +of air inhaled_, produces _carbonic acid gas_, which is attended with +combustion. + + +Q. _If animal heat is produced by COMBUSTION, why does not the human +body BURN UP like a coal or candle?_ + +A. It actually does so. Every muscle, nerve, and organ of the body, +actually _wastes away like a burning candle_; and (being reduced to air +and ashes) is rejected from the system as useless. + + +Q. _If every bone, muscle, nerve, and organ, is thus consumed by +combustion, why is not the BODY entirely CONSUMED?_ + +A. It would be so, unless the parts destroyed _were perpetually +renewed_: but as a lamp will not go out, _so long as it is supplied with +fresh oil_; neither will the _body_ be consumed, _so long as it is +supplied with sufficient food_. + + +Q. _When a man is STARVED, what parts of the body go first?_ + +A. First the _fat_, because it is the most combustible; then the +_muscles_; last of all the _brain_; and then the man dies, like a +_candle which is burnt out_. + + +Q. _Why does WANT of sufficient NOURISHMENT often produce MADNESS?_ + +A. After the _fat and muscles_ of the body have been consumed by animal +combustion, the _brain_ is next attacked; and (unless the patient dies) +_madness must ensue from starvation_. + + +Q. _Why does a man SHRINK when STARVED?_ + +A. A starved man shrinks _just as a fire does_, unless it be supplied +with sufficient fuel. + + +Q. _What is the FUEL of the BODY?_ + +A. _Food is the fuel of the body_; and the _carbon of the food_ mixing +with the _oxygen of the air_, evolves heat in the same way that a fire +or candle does. + + +Q. _Why is EVERY part of the BODY WARM?_ + +A. As the capillary veins run through every part of the human body, and +the combustion of blood _takes place in the capillary veins_, therefore +_every part of the body is warm_. + + +Q. _Why does RUNNING make us WARM?_ + +A. When we run, _we inhale air more rapidly_; and the rapidity with +which we inhale air _fans the combustion of our body_, as a pair of +_bellows_ quickens the flame of a common fire. + + +Q. _How does INHALING AIR RAPIDLY make the body feel WARM?_ + +A. As the combustion of the blood is _more rapid_, (in consequence of +the introduction _of more oxygen from the air_), therefore _the blood is +more heated_, and every part of the body is warmer also. + + +Q. _Why does HARD WORK produce HUNGER?_ + +A. Because it produces _quicker respiration_; by which means a _larger +amount of oxygen is introduced into the lungs_, and the _capillary +combustion increased_. Hunger _is the notice_ (given by our body) to +remind us, _that our food-fuel must be replenished_. + + +Q. _Why does SINGING make us HUNGRY?_ + +A. Singing _increases respiration_; and as _more oxygen_ is introduced +into the lungs, _our food-fuel is more rapidly consumed_. + + +Q. _Why does READING ALOUD make us feel HUNGRY?_ + +A. Reading aloud _increases respiration_; and as _more oxygen_ is +introduced into the lungs, _our food-fuel is more rapidly consumed_. + + +Q. _Why do we feel MORE HUNGRY in the DAY-TIME than in the NIGHT-TIME?_ + +A. As we _breathe more slowly during sleep_, therefore, less _oxygen_ is +introduced into the lungs _to consume our food-fuel_. + + +Q. _Why do we need WARMER CLOTHING by NIGHT than by DAY?_ + +A. 1st--Because the _night is generally colder_ than the day. + +2ndly--As our _respiration is slower_, our _animal combustion is slower +also_; in consequence of which, _our bodies are more cold_. + + +Q. _Why do we PERSPIRE when very HOT?_ + +A. The pores of the body are _like the safety valves of a steam-engine_; +when the heat of the body is too great, the combustible gas and grease +_flow out in perspiration_, instead of _burning in the blood_. + + +Q. _Why do persons feel LAZY and averse to exercise, when they are +HALF-STARVED or ILL-FED?_ + +A. _Animal food_ contains great nourishment, and produces a desire for +_active occupations_; but when the body is not supplied with strong +food, this desire for muscular action _ceases_, and the person grows +slothful. + + +Q. _Why have persons, who follow HARD OUT-OF-DOORS OCCUPATIONS, more +APPETITE than those who are engaged in SEDENTARY pursuits?_ + +A. Hard bodily labour in the open air _causes much oxygen to be conveyed +into the lungs by inspiration_; the combustion of the food is carried on +quickly; _animal heat increased_; and need for nutritious food more +quickly indicated _by craving hunger_. + + +Q. _Why have persons who follow SEDENTARY PURSUITS less APPETITE than +ploughmen and masons?_ + +A. 1st--The air they inhale _is not so pure_, because its oxygen is +partly exhausted: and + +2ndly--Their respiration is neither _so quick nor strong_, and therefore +the combustion of their food is carried on more slowly. + + +Q. _Why do we like strong MEAT and GREASY food when the WEATHER is very +COLD?_ + +A. Strong meat and grease contain large portions of _hydrogen_, which +(when burned in the blood) produce a larger amount of heat than any +other kind of food. + + +Q. _Why do persons EAT MORE food in COLD weather, than in hot?_ + +A. In _cold_ weather the body requires more fuel _to keep up the same +amount of animal heat_; and as we _put more coals on a fire on a cold +day_ to keep our _room warm_, so we _eat more food on a cold day_ to +keep our _body warm_. + + +Q. _Why does COLD produce HUNGER?_ + +A. 1st--The air contains more _oxygen_ in cold weather; and as _fires +burn fiercer_, so _animal combustion is more rapid_: and + +2ndly--We are more _active_ in cold weather; and increased respiration +acts _like a pair of bellows_ on the capillary combustion. + + +Q. _Why does rapid DIGESTION produce a craving APPETITE?_ + +A. This is a wise providence to _keep our bodies in health_; in order +that the _body itself_ may not be consumed, it gives notice (by hunger) +that the _capillary fires need replenishing_. + + +Q. _Why do we feel a desire for ACTIVITY in cold weather?_ + +A. 1st--Because activity increases the warmth of the body, _by fanning +the combustion of the blood_: and + +2ndly--The _strong food_ we eat creates a desire for muscular exertion. + + +Q. _Why are the Esquimeaux so passionately fond of TRAIN OIL and WHALE +BLUBBER?_ + +A. Oil and blubber contain a very _large amount of hydrogen_, which is +exceedingly combustible; and as these people live in climates of intense +cold, the heat of their bodies is increased by the _greasy nature of +their food_. + + +Q. _Why do we feel a dislike to strong meat and greasy foods in very hot +weather?_ + +A. Strong meat and grease contain so much _hydrogen_, that they would +make us _intensely hot_; and therefore we refuse them in hot weather. + + +Q. _Why do we like fruits and vegetables so very much in hot weather?_ + +A. Fruits and vegetables contain _less carbon_ than meat, and therefore +produce _less blood_: instead of blood, _they combine into water_ as +they are digested, and keep the body cool. + + +Q. _Why do people say that FRUITS and VEGETABLES COOL the BLOOD?_ + +A. 1st--Because they _deprive the blood of carbon_, which is the chief +cause of animal heat: and + +2ndly--These gases coalesce into _water_, which greatly tempers the +animal heat. + + +Q. _Why do we feel LAZY and averse to activity in very HOT WEATHER?_ + +A. 1st--Because muscular activity would increase the heat of the body, +by _quickening the respiration_: and + +2ndly--The food we eat in hot weather, _not being greasy_, naturally +abates our desire for bodily activity. + + +Q. _Why do the inhabitants of tropical countries live chiefly upon rice +and fruit?_ + +A. Rice and fruit by digestion _are mainly converted into water_, and +(by cooling the blood) prevent the tropical heat from feeling so +oppressive. + + +Q. _Why are POOR PEOPLE generally AVERSE to CLEANLINESS?_ + +A. 1st--_Cleanliness increases hunger_; and as poor people are generally +_ill-fed_, they are averse to cleanliness. + +2ndly--_Dirt is warm_, (thus pigs who love _warmth_, are fond of +_dirt_); and as poor people are generally _ill-clad_, they like the +_warmth of dirt_. + + +Q. _Why are POOR PEOPLE generally AVERSE to VENTILATION?_ + +A. 1st--Because ventilation _increases the oxygen of the air_,--the +_combustion of food_,--and the _cravings of appetite_: and + +2ndly--Ventilation _cools the air of our rooms_: poor people, therefore, +(who are generally ill-clad) love the _warmth_ of an ill-ventilated +apartment. + + +Q. _Why does FLANNEL, &c. make us WARM?_ + +A. Flannel and warm clothing do not _make_ us warm, but merely _prevent +the body from becoming cold_. + + +Q. _How does flannel, &c. prevent the body from becoming cold?_ + +A. Flannel (being a bad conductor) will _neither carry off the heat of +the body into the cold air_, nor suffer the cold of the air _to come +into contact with our warm bodies_; and thus it is that flannel clothing +keeps us warm. + + +Q. _Why are FROGS and FISHES COLD-BLOODED animals?_ + +A. Because they consume _so little air_; and without a plentiful supply +of air, combustion is so slow, that very little animal heat is evolved. + + +Q. _Why is a DEAD BODY COLD?_ + +A. Air is no longer conveyed to the lungs after respiration has ceased; +and, therefore, animal heat _is no longer evolved by combustion_. + + + + +CHAPTER VII. + +MECHANICAL ACTION. + +1.--PERCUSSION. + + +Q. _How is heat produced by MECHANICAL ACTION?_ + +A. 1.--By Percussion. 2.--By Friction. 3.--By Condensation. + + +Q. _What is meant by PERCUSSION?_ + +A. _The act of striking_; as when a blacksmith strikes a piece of iron +on his anvil with his hammer. + + +Q. _Why does BEATING IRON make it RED-HOT?_ + +A. _Beating_ the iron _condenses the particles_ of the metal; and +squeezes out its latent heat, as water from a sponge. + + +Q. _Does COLD iron contain HEAT?_ + +A. Yes; _every thing_ contains heat; but when a thing _feels cold_, its +heat is LATENT. + + +Q. _What is meant by LATENT HEAT?_ + +A. Heat _not perceptible to our feeling_. When anything contains _heat_ +without _feeling_ the hotter for it, that heat is called "_latent_." +(See p. 31.) + + +Q. _Does COLD iron contain latent HEAT?_ + +A. Yes; and when a blacksmith _compresses the particles_ of the iron by +his hammer, he _squeezes out_ this latent heat, and makes the iron +red-hot. + + +Q. _How did blacksmiths use to LIGHT THEIR MATCHES before the general +use of lucifers?_ + +A. They used to place a soft iron nail upon their anvil; strike it two +or three times with a hammer; and the point became _sufficiently hot to +light a brimstone match_. + + +Q. _How can a NAIL (beaten by a hammer) IGNITE a brimstone MATCH?_ + +A. As the particles of the nail are _compressed by the hammer_, it +cannot contain _so much heat as it did before_; so some of it _flies +out_ (as water flows from a sponge when it is squeezed). + + +Q. _Why does STRIKING a FLINT against a piece of STEEL produce a SPARK?_ + +A. The blow _condenses_ those parts of the flint and steel which strike +_together_, and squeezes out their latent heat. + + +Q. _How does this development of HEAT produce a SPARK?_ + +A. A very small fragment (either of the steel or flint) _is knocked off +red-hot_, and sets fire to the tinder on which it falls. + + +Q. _Why is it needful to keep BLOWING the TINDER with the breath?_ + +A. Because _blowing_ the tinder, drives the _oxygen of the air_ towards +it. + + +Q. _Where does the OXYGEN of the air COME FROM, which is blown to the +lighted tinder?_ + +A. The air itself is composed of two gases (_nitrogen and oxygen_) mixed +together. + + +(Every 5 lbs. of common air contain 4 lbs. of nitrogen, and 1 lb. of +oxygen.) + + +Q. _What is the good of BLOWING OXYGEN GAS to lighted tinder?_ + +A. Oxygen gas _supports combustion_; and lighted tinder is _quickened by +the breath_, in the same way as a dull fire is revived by a _pair of +bellows_. + + +Q. _Why do HORSES sometimes STRIKE FIRE with their FEET?_ + +A. When iron horse-shoes strike against the flint-stones of the road, +_very small fragments_ (either of the shoe or stones) are _knocked off +red-hot_, and look like sparks. + + +Q. _What makes these fragments RED-HOT?_ + +A. The percussion _condenses_ the part struck, _and squeezes out its +latent heat_. + + + + +CHAPTER VIII. + +2.--FRICTION. + +3.--CONDENSATION. + + +Q. _What is meant by FRICTION?_ + +A. The act of _rubbing two things together_; as the Indians rub two +pieces of _wood_ together to produce fire. + + +Q. _How do the Indians produce FIRE, by merely RUBBING TWO PIECES of dry +WOOD TOGETHER?_ + +A. They take a piece of dry wood (sharpened to a point), which they rub +quickly up and down a _flat piece_, till a _groove_ is made; and the +_saw-dust_ (collected in this groove) soon _catches fire_. + + +Q. _Why does the saw-dust of the WOOD CATCH FIRE by RUBBING?_ + +A. The _latent heat_ of the wood is _developed by friction_; because the +particles of the wood are _squeezed closer together_, and the heat pours +out, as water from a sponge. + + +(The best woods for this purpose are _box-wood_ against _mulberry_, or +_laurel_ against _poplar_ or _ivy_.) + + +Q. _Do not CARRIAGE WHEELS sometimes CATCH FIRE?_ + +A. Yes; if the wheels be _dry_,--or _fit too tightly_,--or _revolve very +rapidly_,--they often catch fire. + + +Q. _Why do wheels catch fire in such cases?_ + +A. The _friction_ of the wheels against _the axle-tree_ is so great, +that their _latent heat is disturbed_, and produces ignition. + + +Q. _What is the use of GREASING CART WHEELS?_ + +A. The grease _lessens the friction_; and (by diminishing the +_friction_) the latent heat is less disturbed. + + +Q. _Why is the TOP of a MOUNTAIN COLDER than the VALLEY beneath, +although it be two or three miles nearer to the sun?_ + +A. 1st--Because the air on a mountain is _less compressed_, than the air +in a valley. + +2ndly--It is _more rarefied_: and + +3rdly--It is _less heated by reflection_. + + +Q. _Why is air COLDER on a mountain "because it is LESS COMPRESSED?"_ + +A. As the air in a _valley_ is more compressed (by the mass of air +above) than that on the top of a _mountain_, therefore _more heat runs +out_; just as more water runs from a sponge, the closer it is _squeezed +together_. + + +Q. _Why is a mountain-top COLDER than a valley, "because the AIR there +is MORE RAREFIED?"_ + +A. As the air is _more rarefied_, its heat is _diffused over a larger +space_ and is _less_ intense; just as a candle would _show less light_ +in a _large_ room, than in a _small_ one. + + +Q. _Why is a mountain-top COLDER than a valley, "because the AIR there +is LESS HEATED by REFLECTION?"_ + +A. Air is _not_ heated by the _sun_, but by _reflection from the surface +of the earth_; and as there is _no earth_ round a _mountain-top_ to +reflect heat, therefore the air there is intensely cold. + + +Q. _Why does RUBBING our HANDS and FACES make them feel WARM?_ + +A. Chiefly because the friction _excites the latent heat_ of our hands +and faces, and makes it sensible to our feeling. + + +Q. _When a man has been almost DROWNED, why is suspended animation +RESTORED by RUBBING?_ + +A. The vital heat of the body (which had become _latent_ by the action +of the water) is _again developed by friction_: and, as soon as this +animal heat can be excited, the vital powers of the body are restored. + + +Q. _Why do two pieces of ICE (rubbed together) MELT?_ + +A. Ice contains 140 _degrees of latent heat_, and (when two pieces are +_rubbed together)_ their _particles are compressed_, and this _latent +heat_ rolls out and _melts the ice_. + + +Q. _Are not FORESTS sometimes SET on FIRE by friction?_ + +A. Yes; when two branches or trunks of trees (blown about by the wind) +_rub violently against each other_, their _latent heat is developed_, +and sets fire to the forest. + + +Q. _What is meant by COMPRESSION?_ + +A. The act of _bringing parts nearer together_; as a sponge is +_compressed_ by being _squeezed in the hand_. + + +Q. _Cannot HEAT be evolved from common air merely by COMPRESSION?_ + +A. Yes; if a piece of _German tinder_ be placed at the _bottom of a +glass tube_, and the air in the tube _compressed by a piston_,[11] the +tinder will catch fire. + +[11] In a common syringe or squirt, the _handle_ part which _contains +the sucker_ (and is forced up and down), is called "The Piston." + + +Q. _Why will the tinder catch fire?_ + +A. Because the _air is compressed_; and its _latent heat being squeezed +out_, sets fire to the tinder at the bottom of the tube. + + + + +CHAPTER IX. + +EFFECTS OF HEAT. + + +1.--EXPANSION. + + +Q. _What are the principal EFFECTS of HEAT?_ + +A. 1.--Expansion. 2.--Liquefaction. 3.--Vaporization. 4.--Evaporation; +and 5.--Ignition. + + +Q. _Does HEAT EXPAND the AIR?_ + +A. Yes; if a bladder (partially filled with air) be tied up at the neck, +and _laid before the fire_, the air will _swell_ till the bladder +_bursts_. + + +Q. _Why will the AIR SWELL, if the bladder be laid before the fire?_ + +A. Because the heat of the fire _gets between the particles of air_, and +drives them _further apart from each other_; which causes the bladder to +expand. + + +Q. _Why do unslit CHESTNUTS CRACK with a loud noise, when ROASTED?_ + +A. Chestnuts contain a great deal of air, which is expanded by the heat +of the fire; and, as the thick rind prevents the air from escaping, it +violently _bursts through, slitting the rind_, and making a great noise. + + +Q. _What occasions the loud CRACK or report which we hear?_ + +A. 1st--The _sudden bursting of the rind_ makes a report, in the same +way as a piece of _wood_ or _glass_ would do, if _snapped in two_: and + +2ndly--The _escape of hot air_ from the chestnut makes a report also, in +the same way as _gunpowder_, when it escapes from a _gun_. + + +Q. _Why does the sudden BURSTING of the rind, or SNAPPING of a piece of +wood, make a REPORT?_ + +A. As the attraction of the parts is suddenly overcome, _a violent jerk_ +is given to the air; this jerk produces _rapid undulations_ in the air, +which (striking upon the ear) give the brain the sensation of _sound_. + + +Q. _Why does the ESCAPE OF AIR from the chestnut, or the EXPLOSION of +GUNPOWDER, produce a REPORT?_ + +A. Because a quantity of air (suddenly let loose) _pushes against the +air around_, in order to make _room for itself_; and as the _air of the +chestnut_ slaps against the _air of the room_, a _report_ is made, (as +when I _slap_ a book or table). + + +Q. _If a CHESTNUT be SLIT, it will NOT CRACK; why is this?_ + +A. Because the _heated air_ of the chestnut can _freely escape_ through +the _slit in the rind_. + + +Q. _Why does an APPLE spit and SPURT about, when roasted?_ + +A. An apple contains a vast quantity of _air_, which (being expanded by +the heat of the fire) _bursts through the peel_, carrying the juice of +the apple along with it. + + +Q. _Does an APPLE contain MORE AIR, in proportion, than a CHESTNUT?_ + +A. Yes, much more. There is as much condensed air in a common apple, as +would fill a space 48 _times as big as the apple itself_. + + +Q. _Where is all this quantity of AIR stowed in the APPLE?_ + +A. The _inside_ of an apple is _made up of little cells_ (like a +_honey-comb_), each of which contains a portion of the air. + + +Q. _When an APPLE is ROASTED, why is one part made SOFT, while all the +rest remains hard?_ + +A. When an apple is roasted, the air in the _cells next to the fire_ is +expanded and flies out; the _cells are broken_, and their juices _mixed +together_; so the apple _collapses_ (from loss of air and juice), and +feels _soft_ in those parts. + + +Q. _What is meant by the "apple COLLAPSING?"_ + +A. The _plumpness_ gives way, and the apple becomes _flabby_ and +_shrivelled_. + + +Q. _Why do SPARKS of fire start (with a crackling noise) from pieces of +WOOD laid upon a FIRE?_ + +A. The _air_ in the wood (expanded by the heat), _forces its way through +the pores of the log_; and carries along with it the _covering of the +pore_, which resisted its passage. + + +Q. _What is meant by the "PORES of the WOOD?"_ + +A. Very small _holes in the wood_, through which the _sap_ circulates. + + +Q. _What are the SPARKS OF FIRE, which burst from the WOOD?_ + +A. Very small pieces of wood _red hot_, separated from the log by the +_force of the air_, as it bursts from its confinement. + + +Q. _Why does DEAL make more snapping than any OTHER WOOD?_ + +A. The pores of deal are _very large_, and contain much _more air_ than +wood of a _closer grain_. + + +Q. _Why does DRY WOOD make more SNAPPING than GREEN WOOD?_ + +A. In _green wood_ the pores are filled with _sap_, and therefore +contain _very little air_; but in _dry_ wood the sap is _dried up_, and +the pores are filled with _air_ instead. + + +Q. _Why does DRY wood BURN more easily than GREEN or wet wood?_ + +A. Because the pores of dry wood are _filled with air_, which supports +combustion; but the pores of green or wet wood are filled with _vapour_, +which extinguishes flame. + + +Q. _Why does VAPOUR EXTINGUISH FLAME?_ + +1st--Because the coat of water (which wraps the fuel round) prevents +the _oxygen_ of the air from getting to the _fuel_, to form into +_carbonic acid gas_: and + +2ndly--Heat is perpetually carried off, by the formation of the sap or +water _into steam_. + + +(Carbonic acid gas is a compound of carbon and oxygen. The solid part of +the fuel is _carbon_, and one of the gases of the air is oxygen.) + + +Q. _What has CARBONIC ACID GAS to do with COMBUSTION?_ + +A. Combustion is produced by the _chemical action_ which takes place, +while the _carbon_ of fuel unites with the _oxygen_ of air, and forms +"_carbonic acid gas_." (See p. 36.) + + +Q. _Why do STONES SNAP and fly about, when heated in the FIRE?_ + +A. The air in the stones (expanded by the heat of the fire), _meets with +great resistance_ from the close texture of the stone; and, therefore, +_bursts forth with great violence_, tearing the stone to atoms, and +forcing the fragments into the room. + + +Q. _Must not AIR be very STRONG, to shatter into atoms a hard stone?_ + +A. Yes. All the dreadful effects of _gunpowder_ are merely the results +of the _sudden expansion of air_. + + +Q. _When bottled ALE and PORTER is set before a FIRE, why is the CORK +FORCED OUT sometimes?_ + +A. If the bottle be _not quite full_, there will be _air_ between the +liquor and the cork; this _air_ (expanded by the heat of the fire) +_forces out the cork_. + + +Q. _Why does ALE or PORTER FROTH more, after it has been set before the +fire?_ + +A. The _froth_ of ale or porter _depends upon the pressure_ to which it +is subjected; and as the air (between the liquor and the cork) is +_expanded_ by the heat, _it presses against the liquor_, and increases +the quantity of froth. + + +Q. _Why is the FROTH of ale and porter INCREASED by PRESSURE?_ + +A. Because the liquor absorbs _carbonic acid_ so long as it is under +_pressure_; and the moment that the pressure is _removed_, the carbonic +acid _escapes_ in foam or froth. + + +Q. _When a boy makes a BALLOON, and sets fire to the cotton or sponge +(which has been steeped in spirits of wine), why is the balloon +INFLATED, or blown out?_ + +A. The _air_ inside the balloon is _expanded by the flame_, till the +whole balloon is _blown out_ without a crumple. + + +Q. _Why does the BALLOON RISE, after it has been inflated by the +expanded air?_ + +A. The same quantity of air is expanded _to three or four times its +original volume_; and is made so much _lighter than common air_, that +even when all the paper, wire, and cotton are added, it is still lighter +bulk for bulk. + + +Q. _What is meant by being lighter "bulk for bulk?"_ + +A. If the balloon be 3 square feet in size, it is _lighter_ (when +inflated) than 3 square feet of _common air_, and therefore _floats +through it_; as a cork (at the bottom of a tub of water) would rise to +the surface. + + +Q. _Why does SMOKE RUSH UP a CHIMNEY?_ + +A. The heat of the fire _expands the air in the chimney_; and (being +thus made _lighter_ than the air around), it _rises up the chimney_, and +carries the smoke in its current. + + +Q. _Why has a LONG CHIMNEY a greater DRAUGHT than a short one?_ + +A. Because air rises faster and faster the _higher it ascends_ in a +chimney flue; the same as a stone falls faster and faster the _nearer +it approaches to the ground_. + + +Q. _Why will a LONG chimney SMOKE, unless the FIRE be pretty FIERCE?_ + +A. If the fire be not pretty fierce, its heat will not be sufficient to +_rarefy all the air in the chimney_; and then the chimney will _smoke_. + + +Q. _Why will the chimney smoke, if the fire be not BIG enough to heat +ALL the air in the CHIMNEY FLUE?_ + +A. Because the _cold air_ (condensed in the upper part of the flue), +_will sink from its own weight_, and sweep the ascending smoke _back +with it_ into the room. + + +Q. _What is the use of a COWL upon a chimney-pot?_ + +A. The cowl acts as a _screen against the wind_, to prevent it from +blowing into the chimney. + + +Q. _What HARM would the WIND do, if it were to BLOW into a CHIMNEY?_ + +A. 1st--It would prevent the smoke from getting out: and + +2ndly--The _cold air_ (introduced into the chimney by the wind) _would +fall down the flue_, and drive the smoke with it _back into the room_. + + +Q. _Why does a SMOKE-JACK turn round in a chimney?_ + +A. The current of hot air up the chimney, striking against the _oblique +vanes of the smoke-jack_, drives them round and round; in the same way +as the sails of a _wind-mill_ are driven round by the _wind_. + + +Q. _Why are some things SOLID, others LIQUID, and others GASEOUS?_ + +A. As _heat_ enters any substance, _it drives its particles further +asunder_; and a _solid_ (like _ice_) becomes a _liquid_; and a _liquid_ +(like _water_) becomes a _gas_. + + +Q. _Why does WATER SIMMER before it boils?_ + +A. The particles of water _near the bottom of the kettle_ (being formed +into _steam_ sooner than the rest) _shoot upwards_; but are _condensed_ +again (as they rise) _by the colder water_, and produce what is called +"simmering." + + +Q. _What is meant by SIMMERING?_ + +A. A gentle tremor or _undulation_ on the surface of the water. When +water _simmers_, the bubbles _collapse beneath the surface_, and the +steam is condensed to _water again_: but when water _boils_, the bubbles +_rise to the surface_, and _steam is thrown off_. + + +Q. _Why does a KETTLE SING when the water simmers?_ + +A. Because the _air_ (entangled in the water) escapes by _fits and +starts_ through the _spout of the kettle_; which makes a noise like a +wind instrument, when it is blown into. + + +Q. _Why does NOT a kettle SING, when the water BOILS?_ + +A. As _all_ the water is _boiling hot_, the steam meets with no +_impediment_, but freely escapes in a continuous stream. + + +Q. _When does a kettle sing most?_ + +A. When it is set on a _hob_ to boil. + + +Q. _Why does a kettle SING MORE when it is set on the SIDE of a fire, +than when it is set in the MIDST of the fire?_ + +A. When the kettle is set on the _hob_ to boil, the heat is applied very +_partially: one side is hotter than the other_, and therefore the steam +is more _entangled_. + + +Q. _Why does a KETTLE sing, when the boiling water begins to COOL +again?_ + +A. Because the _upper_ surface cools _first_; and the steam (still +rising from the lower parts of the kettle) is _again entangled_, and +escapes fitfully. + + +Q. _Why does BOILING WATER SWELL?_ + +A. Water (like air) _expands by heat_. The heat of the fire drives the +particles of water _further apart from each other_; and (as they are not +_packed so closely together_) they take up _more room_; or (in other +words) the water _swells_. + + +Q. _What is meant when it is said, "that HEAT drives the PARTICLES of +water further APART from each other."_ + +A. Water is composed of little globules, like very small grains of sand; +the heat _drives_ these particles _away from each other_; and (as they +then require more _room_) the water _swells_. + + +Q. _Why does BOILING WATER BUBBLE?_ + +A. Water contains _air_; and (as the water is heated) _the air is driven +out_, and raises a _bubble_ in that part of the water which resists its +escape. + + +Q. _Why does a KETTLE sometimes BOIL OVER?_ + +A. Liquids _expand very much by heat_; if, therefore, a kettle be +_filled with cold water_, some of it must _run over_ as soon as it is +_expanded by heat_. + + +Q. _But I have seen a KETTLE BOIL OVER, although it has not been filled +FULL of WATER; how do you account for THAT?_ + +A. If a fire be _very fierce_, the air is expelled so _rapidly_, that +the _bubbles are very numerous_; and (towering one above the other) +_reach the top of the kettle, and fall over_. + + +Q. _Why is a pot, which is full to OVERFLOWING (while the water is +boiling HOT), NOTHING LIKE FULL, when it has been taken off the fire for +a short time?_ + +A. When the water was _swelled by boiling heat_, it filled the pot even +to overflowing; but as soon as the water is _condensed by cold_, it +_contracts_ again, and occupies a much less space. + + +Q. _Why does the water of a KETTLE run out of the SPOUT when it BOILS?_ + +A. Because the steam cannot escape _so fast as it is formed_, and (being +_confined in the kettle_) _presses on the water with great power_, and +forces it out of the spout. + + +Q. _How can the PRESSURE of STEAM on the SURFACE of the water, FORCE the +water through the KETTLE-SPOUT?_ + +A. In the same manner as _the pressure of air_ on the _mercury of a +barometer_, forces the _quicksilver up the glass tube_. + + +Q. _What causes the RATTLING NOISE so often made by the LID of a +saucepan or boiler?_ + +A. The steam (seeking to escape) _forces up the lid_ of the boiler, and +the _weight_ of the lid causes it to _fall back again_: this being done +_frequently_, produces a rattling noise. + + +Q. _If the steam COULD NOT LIFT UP THE LID of the boiler, how would it +escape?_ + +A. If the lid fitted so tightly, that the steam could not raise it up, +the boiler would _burst into fragments_, and the consequences might be +fatal. + + +Q. _When steam pours out from the spout of a kettle, the STREAM begins +apparently HALF AN INCH off the SPOUT; why does it not begin CLOSE to +the spout?_ + +A. Steam is really _invisible_; and the half-inch (between the spout and +the "_stream of mist_") is the _real steam_, before it has been +condensed by air. + + +Q. _Why is not ALL the stream INVISIBLE, as well as that half-inch?_ + +A. As the steam _comes in contact with the colder air_, the invisible +particles (being _condensed_), roll one into another, and look like a +thick mist. + + +Q. _What BECOMES OF the STEAM? for it soon vanishes._ + +A. After it is condensed into mist, it is _dissolved by the air_, and +dispersed abroad as _invisible vapour_. + + +Q. _And what BECOMES of the INVISIBLE VAPOUR?_ + +A. Being _lighter than air_, it _ascends_ to the upper regions, where +(being again _condensed_) it contributes to form _clouds_. + + +Q. _Why does a METAL SPOON, left in a saucepan, RETARD the process of +BOILING?_ + +A. The metal spoon (being an excellent _conductor_) _carries off the +heat from the water_; and (as heat is carried off by the spoon) the +water takes a longer time to boil. + + +Q. _Why will a POT (filled with water) NEVER BOIL, when immersed in +ANOTHER vessel full of water also?_ + +A. Because water can _never be heated above the boiling point_: all the +heat absorbed by the water after it _boils_, is employed in _converting +the water into steam_. + + +Q. _How does the conversion of water into steam prevent the INNER POT +from BOILING?_ + +A. The moment the water in the larger pot is _boiling hot_ (or 212°), +_steam is formed_, and _carries off some of its heat_; therefore, 212 +_degs._ of heat can never _pass through it_, to raise the _inner_ +vessel to the _same heat_. + + +Q. _Why do SUGAR, SALT, &c. RETARD the process of BOILING?_ + +A. Because they have a tendency to _fix_ water by chemical attraction; +and therefore retard its _conversion into steam_. + + +Q. _If you want water to boil, without COMING IN CONTACT with the +SAUCEPAN, what plan must you adopt?_ + +A. _Immerse the pot_ (containing the water you want to boil) in a +saucepan containing _strong brine_, or sugar. + + +Q. _Why would the INNER vessel boil, if the OUTER vessel contained +strong BRINE?_ + +A. Though _water_ boils at 212 _degs._ of heat, yet _brine_ will not +boil till raised to 218 or 220 _degs._ Therefore, 212 _degs._ of +heat may easily pass through brine _to raise the vessel immersed in it +to boiling heat_, before any of it is _carried off by steam_. + + +Q. _Why will brine impart to another vessel MORE than 212°, and water +NOT SO MUCH?_ + +A. Because both liquids will _impart heat_ till they _boil_, and then +_they can impart heat no longer_. + + +Q. _Why can they impart no extra heat after they boil?_ + +A. Because all _extra_ heat is spent _in making steam_. Hence water will +_not_ boil a vessel of water immersed in it, because it cannot impart to +it 212 _degs._ of heat: but _brine_ will, because it can impart _more +than_ 212 _degs. of heat_, without being converted itself into steam. + + Ether boils at 104 _degs._ + Alcohol - - 173-1/2 " + Water - - 212 " + Water with one-fifth salt 219 " + Syrup boils at 221 " + Oil of turpentine, 304 " + Sulphuric acid 472 " + Linseed oil - 640 " + &c. &c. + + +Any liquid which boils at a _lower_ degree can be made to boil if +immersed in a liquid which boils at a higher degree. Thus a _cup of +ether_ can be made to boil in a saucepan of _water_. A _cup of water_ in +a saucepan of _brine or syrup_. But a _cup of water_ will _not_ boil if +immersed in _ether_; nor a _cup of syrup_ in _water_. + + +Q. _Why are CLOUDS HIGHER on a FINE DAY?_ + +A. 1st--Because the _air_ (expanded by heat) _drives them higher up_: +and + +2ndly--The _clouds themselves are lighter_, and therefore _more +buoyant_. + + +Q. _Why are the CLOUDS LIGHTER on a FINE DAY?_ + +A. Because their mists are either _absorbed by the dry air_, or +_vapourized_ by the hot sun. + + +Q. _Why is a CUP PUT topsy-turvy into a FRUIT-PIE?_ + +A. Its principal use is to _hold the crust up_, and _prevent it from +sinking_, when the cooked fruit gives away under it. + + +Q. _Does not the cup PREVENT the FRUIT of the pie from BOILING OVER?_ + +A. No, by no means; it would rather tend to _make it boil over_, than +otherwise. + + +Q. _Why would the cup tend rather to MAKE the FRUIT BOIL OVER?_ + +A. As soon as the pie is put into the oven, the _air_ in the cup will +_begin to expand_, and drive every particle of juice from under it; the +pie dish, therefore, will have a cup-full _less room_ to hold its fruit, +than if the cup were _taken out_. + + +Q. _If the juice is driven OUT of the cup, why is the CUP always FULL of +JUICE, when the pie is cut up?_ + +A. Immediately the pie is drawn, the _air_ in the cup begins to +_condense again_, and _occupy a smaller space_; in consequence of which, +there is no longer _enough air to fill the cup_, and so _juice_ rushes +in _to fill up the deficiency_. + + +Q. _Why does JUICE rush into the cup, because the cup is NOT FULL of +AIR?_ + +A. As the external air _presses upon the surface of the juice_, it +rushes into the cup _unobstructed_; as mercury rises through the tube of +a barometer through similar pressure. + + + + +CHAPTER X. + +EXPANSION FROM HEAT. + +_(Continued.)_ + + +Q. _Does heat expand every thing ELSE BESIDES air and water?_ + +A. Yes; _every_ thing (that man is acquainted with) is expanded by heat. + + +Q. _Why does a COOPER make his HOOPS RED-HOT, when he puts them on a +tub?_ + +A. 1st--As _iron expands by heat_, the hoops will be _larger_ when they +are red-hot; and will, therefore, _fit more easily on the tub_: and + +2ndly--As _iron contracts by cold_, the hoops will _shrink_ as they cool +down, and _girt the tub with a tighter grasp_. + + +Q. _Why does a WHEELWRIGHT make his hoops RED-HOT, which he fixes on the +NAVE of a WHEEL?_ + +A. 1st--That they may _fit on more easily_: and + +2ndly--That they may _girt the nave more tightly_. + + +Q. _Why will the wheelwright's HOOP FIT the nave MORE EASILY, because +they are made RED-HOT?_ + +A. As _iron expands by heat_, the hoops will be _larger_ when they are +hot; and (being larger) will go on the nave more _easily_. + + +Q. _Why will the HOOPS, which have been PUT ON HOT, girt the nave more +FIRMLY?_ + +A. As _iron contracts by cold_, the hoops will _shrink as they cool +down_; and, therefore, _girt the nave with a tighter grasp_. + + +Q. _Why does a farrier put the HORSE-SHOE on HOT?_ + +A. That it may _stick the closer_, when it has contracted by cold. + + +Q. _Why does a STOVE make a CRACKING NOISE, when a fire is very hot?_ + +A. The iron stove _expands by heat_, and (as it swells) the parts rub +both _against each other_, and _against the bricks around_, driving them +further off; and this produces a _cracking_ noise. + + +Q. _Why does a STOVE make a similar CRACKING NOISE, when a large FIRE is +TAKEN DOWN?_ + +A. The iron stove _contracts again_, as soon as the fire is removed; +and (as it shrinks into a smaller space) the parts _rub against each +other again_, and the _bricks are again disturbed_; and this produces a +cracking noise. + + +Q. _Why does the PLASTER round a STOVE CRACK and fall away?_ + +A. When the fire is lighted, _the iron-work_ (which expands more than +the brick-work and plaster) _pushes away the bricks and plaster_: but +when the fire is put out, the metal _shrinks_ again, and _leaves the +"setting" behind_. + + +Q. _Why does the PLASTER FALL AWAY?_ + +A. As a _chink_ is left (between the "setting" and the stove), the +plaster will frequently fall away _from its own weight_. + + +Q. _What OTHER cause contributes to BRING the PLASTER DOWN?_ + +A. As the _heat of the fire_ varies, the _size of the iron stove_ varies +also; and this swelling and perpetually contracting, keeps up such a +_constant disturbance about the plaster_, that it _cracks and falls +off_, leaving the fire-place very unsightly. + + +Q. _Why does the MERCURY of a THERMOMETER RISE in hot weather?_ + +A. Heat _expands the metal_; and as the metal is _increased in bulk_, it +occupies a _larger space_, (or, in other words, rises higher in the +tube.) + + +Q. _Why is a GLASS BROKEN, when HOT WATER is poured into it?_ + +A. Because the _inside of the glass_ is expanded by the hot water, and +_not the outside_; so the glass _snaps_ for want of _flexibility_. + + +Q. _Why is not the OUTSIDE of the GLASS expanded by the hot water, as +well as the INSIDE?_ + +A. Glass is a _non-conductor of heat_; and, therefore, _breaks_ before +the heat of the _inner surface_ is _conducted to the outside_. + + +Q. _Why does a GLASS snap, because the INNER surface is HOTTER than the +OUTER?_ + +A. _Glass is expanded by heat_; and as the inner surface expands, _it +stretches the outer surface till it snaps_. + + +Q. _Why is a CHINA CUP broken, if HOT WATER be poured over it, or into +it?_ + +A. China is a _non-conductor_; and, as the _inner surface expands by the +heat_, before the _outer one_, _it forms an arch_, and pulls the parts +of the cup asunder. + + +Q. _Why does the BOTTOM COME OFF, if a GLASS BEAKER be set on a warm +HOB?_ + +A. Glass is a _non-conductor_; and, as the _bottom of the glass_ (from +the warmth of the hot stove) _expands, before the sides are heated_, the +two parts _separate_ the one from the other. + + + + +CHAPTER XI. + +2.--LIQUEFACTION. + +3.--VAPORIZATION. + + +Q. _What is meant by LIQUEFACTION?_ + +A. The _state of being melted_; as ice is melted by the heat of the sun. + + +Q. _Why is ICE MELTED by the HEAT of the SUN?_ + +A. The _heat of the sun_ (entering the solid ice) _forces its particles +asunder_, till their attraction of cohesion is sufficiently overcome, to +_convert the solid ice into liquid_. (See p. 112.) + + +Q. _Why are METALS MELTED by the heat of FIRE?_ + +A. The _heat of the fire_ (entering the solid metal) _forces its +particles asunder_, till their attraction of cohesion is sufficiently +overcome, to _convert the solid metal to a liquid_. + + +Q. _Why is WATER converted to STEAM by the heat of FIRE?_ + +A. The _heat of the fire_ (entering the water) _divides its globules +into very minute bubbles_, which (being made lighter than air) fly off +from the surface _in the form of steam_. + + +Q. _Why does not WOOD MELT, like metal?_ + +A. Because the heat of the fire _decomposes_ the wood into _gas, smoke, +and ashes_; and the different parts _separate from each other_. + + +Q. _What is meant by VAPORIZATION?_ + +A. The _conversion of liquid into vapour_; as water is converted into +vapour by the heat of the sun. + + +Q. _What are CLOUDS?_ + +A. Moisture _evaporated from the earth_, and collected in the upper +regions of the air. + + +Q. _What is the difference between a FOG and a CLOUD?_ + +A. Clouds and fogs differ only in one respect. _Clouds are elevated +above our heads_: but _fogs come in contact with the surface of the +earth_. + + +Q. _If CLOUDS are WATER, why do they FLOAT on the air?_ + +A. 1st--The vapour of clouds is composed of _very minute bubbles_ +(called ves'cicles), which float like _soap bubbles_: and + +2ndly--Warm air (between the bubbles) _keeps them apart_, and makes the +mass _lighter_; and the currents of air (which constantly ascend from +the warm earth) _buoy them up_. + + +Q. _Why does VAPOUR sometimes form into CLOUDS, and sometimes rest upon +the earth as MIST or FOG?_ + +A. When the _surface of the earth_ is _warmer than the air_, the vapour +of the earth (being condensed by the chill air) becomes _mist or fog_. +But when the _air_ is _warmer than the earth_, the vapour _rises through +the air_, and becomes cloud. + + +Q. _Are ALL clouds ALIKE?_ + +A. No. They vary greatly in _density, height, and colour_. + + +Q. _What is the chief CAUSE of fog and CLOUDS?_ + +A. The changes of the wind. + + +Q. _How can the CHANGES of the WIND affect the CLOUDS?_ + +A. If a _cold current of wind_ blows suddenly over any region, it +_condenses_ the invisible vapour of the air into _cloud or rain_: but if +a _warm current of wind_, blows over any region, it _disperses_ the +clouds, by _absorbing their vapour_. + + +Q. _What_ COUNTRIES _are the_ MOST CLOUDY? + +A. Those where the winds are _most variable_, as Britain. + + +Q. _What COUNTRIES are the LEAST cloudy?_ + +A. Those where the winds are _not variable_, as Egypt. + + +Q. _What DISTANCE are the CLOUDS from the EARTH?_ + +A. Some _thin light clouds_ are elevated above the highest mountain-top; +some _heavy_ ones touch the steeples, trees, and even the earth: but +the _average_ height is between _one and two miles_. + + +(Streaky curling clouds, _like hair_, are often five or six miles high.) + + +Q. _What CLOUDS are the LOWEST?_ + +A. Those that are _most highly electrified_: lightning clouds are rarely +more than about 700 yards above the ground; and very often actually +_touch the earth with one of their edges_. + + +Q. _What is the THICKNESS of the CLOUDS?_ + +A. Some clouds are 20 _square miles in surface_, and above _a mile in +thickness_; while others are only a _few yards or inches_. + + +Q. _How can persons ascertain the thickness of a cloud?_ + +A. As the _tops of high mountains_ are generally _above the clouds_; +therefore, travellers (who climb the mountains) may _pass quite through +the clouds_, into a clear blue firmament, when they may see the clouds +_beneath their feet_. + + +Q. _Why are the CLOUDS so VARIABLE in SHAPE?_ + +A. The _shape_ of clouds depends upon two things:--Their state of +_electricity_, and _the wind_. + + +Q. _How can ELECTRICITY affect the SHAPE of CLOUDS?_ + +A. If one cloud be _full of electricity_, and another _not_, they will +be _attracted to each other_, and either coalesce,--diminish in +size,--or vanish altogether. + + +Q. _Which clouds assume the most FANTASTIC shapes?_ + +A. Those that are the most _highly electrified_. + + +Q. _What effect have WINDS on the SHAPE of CLOUDS?_ + +A. They sometimes _absorb them entirely_: sometimes _increase their +volume and density_; and sometimes _change the position of their parts_. + + +Q. _How can WINDS ABSORB CLOUDS altogether?_ + +A. _A warm dry wind_ will convert the substance of the clouds into +_invisible vapour_, and carry it in its own current. + + +Q. _How can WINDS INCREASE the bulk and density of CLOUDS?_ + +A. A _cold_ current of wind will _condense the invisible vapour of the +air_, and _add it to the clouds_ as it passes by. + + +Q. _How can WINDS CHANGE the SHAPE of CLOUDS by altering the position of +their parts?_ + +A. Because clouds are so voluble and light, that every breath of wind +changes the position of those ves'cicles or bubbles. + + +Q. _What are the general COLOURS of the CLOUDS?_ + +A. White and grey, _when the sun is above the horizon_: but red, orange, +and yellow, _at sun-rise and sun-set_. + + +The _blue sky_ cannot be considered as _clouds_ at all. + + +Q. _Why are the LAST CLOUDS of EVENING generally of a RED tinge?_ + +A. Because _red_ rays are the _least refrangible of all_; and, +therefore, _are the last to disappear_. + + +Q. _What is meant by being "LESS REFRANGIBLE"?_ + +A. Being _less able to be bent_. Blue and green rays being very easily +bent (_by the resistance of the air_) are thrown _off from the horizon_; +but red rays not being _bent back_ in the same way, give a tinge to the +evening clouds. + + +Q. _Why are MORNING CLOUDS generally of a RED tinge?_ + +A. Because red rays are the _least refrangible of all_, and not being +_bent back by the air_ (like blue and green), _strike upon the horizon_, +and give a tinge to the morning clouds. + + +Q. _Why is not the reflection of clouds always ALIKE?_ + +A. Because their _size, density, and situation in regard to the sun_, +vary perpetually; so that sometimes _one_ colour is reflected, and +sometimes _another_. + + +Q. _What regulates the MOTION of the CLOUDS?_ + +A. The _motion of the clouds_ is generally directed by the _winds_; but +sometimes _electricity_ will influence their motion also. + + +Q. _How do you know that CLOUDS move by OTHER influences besides WIND?_ + +A. Because we often see in calm weather _small clouds meeting each +other_ from opposite directions. + + +Q. _How do you know that ELECTRICITY affects the motion of the clouds?_ + +A. Because clouds often meet from _opposite directions_; and (after they +have discharged their opposite electricities into each other) _vanish +altogether_. + + +Q. _Into how many CLASSES are the different sorts of CLOUDS generally +divided?_ + +A. Into three classes:--viz. Simple, Intermediate, and Compound. + + +Q. _How are SIMPLE CLOUDS sub-divided?_ + +A. 1.--Cirrus. 2.--Cum'ulus; and 3.--Stra'tus. + + +Q. _What are CIRRUS CLOUDS?_ + +A. Clouds like _fibres_, _loose hair_, or _thin streaks_, are called +cirrus clouds. + + +Q. _Why are these clouds called CIRRUS?_ + +A. From the Latin word, _cirrus_ ("a lock of hair, or curl"): they are +the most _elevated of all clouds_. + + +Q. _What do CIRRUS clouds PORTEND?_ + +A. When the streamers point _upwards_, the clouds are _falling_, and +_rain is at hand_: but when the streamers point _downwards_, expect +easterly wind or drought. + + +Q. _What are CUM'ULUS CLOUDS?_ + +A. Cum'ulus clouds are lumps like great _sugar-loaves_,--_volumes of +smoke_,--or _mountain towering over mountain_. + + +Q. _Why are these monster masses called_ CUM'ULUS CLOUDS? + +A. From the Latin word, _cum'ulus_ (a mass or pile). + + +Q. _What do_ CUM'ULUS _clouds_ FORESHOW? + +A. When these piles of cloud are _fleecy_, and sail _against the wind_, +they indicate _rain_; but when their outline is very _hard_, and they +come up _with the wind_, they foretell _fine weather_. + + +Cumulus clouds should be _smaller_ towards evening than they are at +noon. If they _increase_ in size at sun-set, a thunder-storm may be +expected in the night. + + +Q. _What are_ STRA'TUS CLOUDS? + +A. Creeping mists, especially prevalent in a summer's evening: these +clouds rise at sun-set _in low damp places_, and are always _nearer the +earth_, than any _other_ sort of cloud. + + +Q. _Why are these mists called_ STRA'TUS _clouds?_ + +A. From the Latin word, _stra'tus_ ("laid low," or "that which lies +low"). + + +Q. _How are the_ INTERMEDIATE CLOUDS _sub-divided?_ + +A. Into two sorts. 1.--The Cirro-Cum'ulus; and 2.--The Cirro-Stra'tus. + + +Q. _What are CIRRO-CUM'ULUS CLOUDS?_ + +A. When _cirrus_ clouds spring from a _massy centre_; or when _heavy +masses of cloud_ terminate at their edges in _long streaks_, or what are +called "_mares' tails_." + + +A system of small round clouds may be called cirro-cum'ulus. + + +Q. _What do CIRRO-CUM'ULUS clouds generally FOREBODE?_ + +A. Continued drought, or hot dry weather. + + +Q. _What are CIRRO-STRA'TUS CLOUDS?_ + +A. They compose what is generally called a "_mackarel sky_." This class +of clouds always indicate _rain and wind_; hence the proverb-- + + "Mackarels' scales and mares' tails + Make lofty ships to carry low sails." + + +Q. _How are COMPOUND CLOUDS sub-divided?_ + +A. Compound clouds are also sub-divided into two sorts. 1.--The +Cum'ulo-stra'tus; and 2.--The Nimbus. + + +Q. _What is meant by CUM'ULO-STRA'TUS clouds?_ + +A. Those clouds which assume all sorts of _gigantic fancy forms_; such +as vast towers and rocks,--huge whales and dragons,--scenes of +battle,--and cloudy giants. This class of clouds is the most romantic +and strange of all. + + +Q. _What do the cumulo-stratus clouds foretell?_ + +A. _A change of weather_; either from fine to rain, or from rain to fine +weather. + + +Q. _What are NIMBUS CLOUDS?_ + +A. Nimbus is the Latin word for "clouds which bring a storm;" and all +clouds from which _rain falls_ are so named. + + +Q. _What APPEARANCE takes place in the CLOUDS at the approach of RAIN?_ + +A. The _cum'ulus_ cloud becomes _stationary_, and _cirrus streaks settle +upon it_, forming cumulo-stratus clouds; which are _black_ at first, but +afterwards of a _grey_ colour. + + +Q. _Why do CLOUDS gather ROUND MOUNTAIN-TOPS?_ + +A. Because (as they float along) _they dash against the mountains_; and +(being _arrested_ in their motion) collect round the top. + + +Q. _What is the USE of CLOUDS?_ + +A. 1st--They act as screens to arrest _the radiation of heat from the +earth_: + +2ndly--They temper the heat of the _sun's rays_: and + +3rdly--They are the great _store-houses of rain_. + + +Q. _Why is WIND said to BLOW UP the CLOUDS?_ + +A. When a _dry_ wind travels over sea, and accumulates _more_ vapour +than the air can _sustain_, it _relinquishes a part_ (as it flies along) +in the form of clouds. + + +Q. _Why does WIND sometimes DRIVE AWAY the CLOUDS?_ + +A. When wind travels over _dry climes_ or _thirsty deserts_, it becomes +_so dry itself_, that it absorbs vapour from the clouds, and _disperses_ +them. + + +Q. _What is the CAUSE of a RED SUN-SET?_ + +A. Because the vapour of the air is not _actually condensed into +clouds_, but only on the _point of being condensed_; in which state it +bends the _red rays of the sun towards the horizon_, where they are +reflected at sun-set. + + +Q. _Why is a RED SUN-SET an indication of a FINE DAY to-morrow?_ + +A. Because (notwithstanding the cold of sun-set) the vapours of the +earth are _not condensed into clouds_. Our Lord referred to this +prognostic in the following words: "When it is evening ye say, it will +be fair weather, for the sky is red." (Matt. xvi. 2.) + + +Q. _What is the cause of a coppery YELLOW SUN-SET?_ + +A. Because the vapour of the air is _actually condensed into clouds_; in +which case it "refracts" (or bends) the _yellow rays of the sun towards +the horizon_, where they are reflected at sun-set. + + +Q. _Why is a YELLOW SUNSET an indication of WET?_ + +A. Because the vapours of the air _are already condensed into clouds_; +rain, therefore, may be shortly expected. + + +Q. _What is the cause of a RED SUN-RISE?_ + +A. Vapour in the upper region of the air _just on the point of being +condensed_. + + +Q. _Why is a RED and LOWERING sky at SUNRISE an indication of a WET +DAY?_ + +A. Because the higher regions of the air are _laden with vapour_, on the +very _point of condensation_, which the rising sun cannot disperse. +Hence our Lord's observation, "In the morning (ye say) it will be foul +weather to-day, for the sky is red and lowering." (Matt. xvi. 3.) + + +Q. _Why is a GREY MORNING an indication of a FINE DAY?_ + +A. Because _that_ air alone _contiguous to the earth_ is damp and full +of vapour. There are no vapours in the _higher_ regions of the air _to +reflect red rays_; and hence the morning-light looks grey. + + +Q. _What difference (in the state of the air) is required, to make a +GREY and RED SUNRISE?_ + +A. In a _grey_ sunrise, only that portion of air _contiguous to the +earth is filled with vapour_; all the rest is clear and dry. But in a +_red_ sunrise the air in the _upper regions_ is so full of vapour that +the rising sun cannot disperse it. + + +Q. _Why is a GREY SUNSET an indication of WET?_ + +A. If the air on the _surface of the earth_ be very _damp at sunset_, it +is a proof that the air is _saturated with vapour_, and wet may be +expected: hence the proverb-- + + "Evening red and morning grey + Will set the traveller on his way; + But evening grey and morning red + Will bring down rain upon his head." + + +Q. _The proverb says, "A RAINBOW in the MORNING is the shepherd's +WARNING:" why is it so?_ + +A. A rainbow can only be formed _when the clouds_ (containing or +dropping rain) _are opposite the sun_: a _morning_ rainbow, therefore, +is _always in the west_, and indicates that bad weather is _on the road +to us_. + + +Q. _Why does a RAINBOW in the WEST indicate that BAD WEATHER is on the +road to us?_ + +A. Because our heavy rains are usually _brought by west or south-west +winds_; and, therefore, clouds which reflect the colour of the rainbow +_in the west_, are coming up _with the wind_, bringing rain with them. + + +Q. _The proverb says, "A RAINBOW at NIGHT, is the shepherd's DELIGHT;" +why is it so?_ + +A. As a rainbow is always _opposite to the sun_, therefore a rainbow at +_night_ is in the _east_, and indicates that bad weather is _leaving +us_. + + +Q. _Why does a RAINBOW in the EAST indicate that bad weather is LEAVING +us?_ + +A. As _west_ and _south-west_ winds bring _rain_, if the clouds have +been driven _from the west to the east_, they have passed _over us_, and +are going _away from us_. + + +Q. _What is meant by an AURORA BOREA'LIS, or northern light?_ + +A. A _luminous white cloud_ in the _north of the sky_ at night-time. +Sometimes streaks of blue, purple, and red,--and sometimes flashes of +light, are seen also. + + +In our island this phenomenon generally rises from a dark cloud (running +from the north to the east and west) elevated about 10 or 20 degrees +above the horizon: above this dark bed of clouds the luminous white +light appears. + + +Q. _What is the CAUSE of the AURORA BOREALIS, or northern light?_ + +A. _Electricity_ in the clouds. + + +Q. _Why is the AURORA BOREALIS generally a WHITE light?_ + +A. Because the electric fluid passes through air _extremely rarefied_: +and whenever electric fluid passes through _air much rarefied_, it +always produces a _white light_. + + +Q. _Why are there sometimes DIFFERENT COLOURS in the aurora borealis, +such as yellow, red, and purple?_ + +A. Because the electric fluid passes through _air of different +densities_. The most _rarefied air_ produces a _white light_; the most +_dry air, red_; and the most _damp_ produces _yellow_ streaks. + + +Q. _Does the AURORA BOREALIS forbode fine weather or WET?_ + +A. When its _corruscations are very bright_, it is generally followed by +stormy moist unsettled weather. + + +Q. _Why does a HAZE round the SUN indicate RAIN?_ + +A. Because the _haze_ is caused by _very fine rain falling in the upper +regions of the air_; when this is the case, a _rain_ of 5 _or_ 6 _hours +continuance_, may be expected. + + +Q. _Why is a HALO round the MOON a sure indication of RAIN?_ + +A. Because the halo is caused by _fine rain falling in the upper regions +of the air_. The _larger_ the halo the _nearer the rain-clouds_, and the +sooner may rain be expected. + + +Q. _Why does a BLACK MIST bring WET weather?_ + +A. The mist is _black_, because it is _overshadowed by dense clouds_ or +masses of vapour; and, therefore, it forebodes wet. + + +Q. _Why does a WHITE MIST indicate FINE weather?_ + +A. The mist is _white_, because _no clouds blacken it with their +shadow_; and (as the sky is cloudless) _fine weather_ may be expected. + + +Q. _Why do we FEEL almost SUFFOCATED in a hot cloudy night?_ + +A. Because the heat of the earth (being unable to escape into the upper +region of the air, in consequence of the clouds) _floats_, like a sea of +heat, _on the surface of the earth_. + + +Q. _Why do we feel more SPRIGHTLY in a clear bright night?_ + +A. Because the heat of the earth can readily escape into the upper +regions of the air, and is not confined and _pent-in by thick clouds_. + + +Q. _Why do we FEEL DEPRESSED in SPIRITS on a WET murky DAY?_ + +A. 1st--Because when the air is laden with vapour, _it has less oxygen_. + +2ndly--The air being lighter than usual, _does not balance the air in +our body_: and + +3rdly--Moist air has a tendency to relax the nervous system. + + +Q. _What is meant by the "air balancing the air" in our body?_ + +A. The human body is filled with air of the same density as that around: +if, therefore, we ascend into _purer air_, or descend into _denser air_, +the balance is destroyed, and _we feel oppressed and suffocated_. + + +Q. _Why do we feel OPPRESSED and SUFFOCATED if the air around is not of +the SAME DENSITY as that in our body?_ + +A. If the air around be more dense, it will _squeeze our body in_ by its +weight: if it be _less_ dense, the air in our body will _blow us out_. + + +Q. _Why do PERSONS who ASCEND in BALLOONS FEEL PAIN in their eyes, ears +and chest?_ + +A. Because the air in the upper regions is _more rare_ than the _air in +their bodies_; and (till the _equilibrium is restored_) great pain is +felt in all the more sensitive parts of the body. + + +Q. _Why do PERSONS who DESCEND in DIVING-BELLS FEEL PAIN in their eyes, +ears and chest?_ + +A. Because the air in the sea is _more dense_ than the air in their +bodies; and (till the _equilibrium is restored_) great pain is felt in +all the more sensitive parts of the body. + + +Q. _Why does the SEA HEAVE and SIGH just PREVIOUS to a STORM?_ + +A. The density of the air (just previous to a storm) is _very suddenly +diminished_, but the air in the sea is _not so quickly affected_; +therefore the sea heaves and sighs _in its effort to restore an +equilibrium_. + + +Q. _Why is the AIR so universally STILL just PREVIOUS to a TEMPEST?_ + +A. Because the air is _suddenly and very greatly rarefied_; and (as the +_density of the air is diminished_) its power _to transmit sound is +diminished also_. + + +Q. _How do you_ KNOW _that_ RAREFIED _air_ CANNOT TRANSMIT SOUND _so +well as dense air?_ + +A. Because the _sound of a bell_ (in the receiver of an air-pump) +_cannot be heard at all_, after the air has been partially exhausted; +and a pistol _fired on a high mountain_ would not sound louder than a +_common cracker_. + + +Q. _Why do we FEEL BRACED and LIGHT-HEARTED on a FINE spring or FROSTY +morning?_ + +A. 1st--Because there is _more oxygen_ in the air on a fine frosty +morning, than there is on a wet day: and + +2ndly--A brisk and frosty air has a tendency to _brace_ the nervous +system. + + +Q. _Why do DOGS and CATS (confined to a room) feel LAZY and DROWSY at +the approach of rain?_ + +A. 1st--Because the air does not contain _its full proportion of +oxygen_: and + +2ndly--Because the damp _relaxes their nervous system_, and makes them +drowsy. + + +Q. _Why do HORSES neigh, CATTLE low, SHEEP bleat, and ASSES bray, at the +approach of rain?_ + +A. 1st--As the air does not contain its full proportion of _oxygen_, +they feel a _difficulty in breathing_: and + +2ndly--As damp _relaxes their nerves_, they feel languid and uneasy. + + +Q. _Why do CANDLES and FIRES burn with a BLUER FLAME in WET weather?_ + +A. As the air contains _less oxygen_ in wet weather, the _heat of fire +is less intense_: and the flame is blue, _because the fuel is not +thoroughly consumed_. + + +Q. _Why do HILLS, &c. appear LARGER in WET weather?_ + +A. Because (when the air is _laden with vapour_) the rays of light are +_more dispersed_, and produce a larger reflection; objects, therefore, +seen at a distance, _appear larger_. + + +Q. _Why do TREES, &c. in WET weather appear FURTHER OFF than they really +are?_ + +A. Because the fog or mist _diminishes the light_ reflected from the +object; and as the object becomes _more dim_, it seems to be _further +off_. + + +Q. _Why does the SUN seem LARGER when he SETS and RISES, than he does at +noon?_ + +A. Because the rays pass through _more of the vapoury atmosphere_ which +surrounds the earth; and this vapoury atmosphere acts like a _magnifying +glass_. + +[Illustration: It is very manifest that the lines D C are shorter than +the lines E C: if, therefore, A be the earth, and D G E the boundary of +the atmosphere round the earth, then the rays M E C (at the _horizon_) +will pass through _more of the atmosphere_, than the rays S D C, which +are more elevated.] + + +Q. _Why does the MOON appear LARGER at her RISING and SETTING, than when +above our heads?_ + +A. Because the rays pass through _more of the vapoury atmosphere_ which +surrounds the earth; and this vapoury atmosphere _magnifies_ the moon, +just like a magnifying glass. + + +Q. _Why do CATS RUB their EARS when it is likely to rain?_ + +A. Either because the _air is full of vapour_, and its humidity +(piercing between the hair of the cat) _produces an itching sensation_; +or more probably, because the air is _overcharged with electricity._ + + +Q. _How can the ELECTRICITY of air produce a sensation of ITCHING?_ + +A. If the _air_ is overcharged with electricity, the _hair of the cat_ +is overcharged also; and this makes her feel _as if she were covered +with cobwebs_. + + +Q. _Why does the CAT keep RUBBING herself?_ + +A. Her _hair will not lie smooth_, but has a perpetual tendency to +become _turgid and ruffled_; so the cat keeps rubbing her coat and ears, +to _smooth the hair down_, and brush away the feeling of cobwebs. + + +Q. _Why do our HEADS and SKIN itch before rain?_ + +A. Probably because the _air is overcharged with electricity_; and, +therefore, a sensation (like that of cobwebs) _irritates the skin_, and +produces an itching. + + +Q. _Why do we HEAR distant CLOCKS more distinctly when rain is near at +hand?_ + +A. Because the _air is filled with vapour_, and water is a better +conductor of sound than dry air. + + +Q. _Why do we hear CHURCH-BELLS further, just previous to rain?_ + +A. Because the _air is filled with vapour_, and vapour is a better +conductor of sound than dry air. + + +Q. _Why do DOORS SWELL, when RAIN is at hand?_ + +A. Because the _air is filled with vapour_, which (penetrating into the +pores of the wood) _forces the parts further apart_, and swells the +door. + + +Q. _Why do DOORS SHRINK in DRY weather?_ + +A. Because the _moisture is absorbed from the wood_; and, as the +particles are _brought closer together_, the size of the door is +_lessened_, (or in other words, the _wood shrinks_). + + +Q. _Why is the AIR filled with offensive SMELLS previous to a coming +RAIN?_ + +A. Because the volatile parts, (which rise from dunghills, sewers, &c.), +being _laden with vapour_, are unable to rise so readily, as when they +are rarefied by a bright sun. + + +Q. _Why do FLOWERS smell SWEETER and STRONGER just previous to RAIN?_ + +A. Because the volatile parts (which constitute the _perfume_ of +flowers) are _laden with vapour_; and (being unable to rise) are +confined to the lower regions of the air. + + +Q. _Why do HORSES and other animals stretch out their necks, and SNUFF +up the AIR, just previous to a fall of RAIN?_ + +A. Because they _smell the odour of plants and hay_, and delight to +snuff in their fragrance. + + +Q. _Why does SMOKE FALL when RAIN is at hand?_ + +A. The air being less _dense_ in wet weather, _cannot buoy up smoke_ so +readily, as when _more dry and heavy_. + + +Q. _Why do SWALLOWS FLY LOW when RAIN is at hand?_ + +A. Because the _insects_ (of which they are in pursuit) _have fled from +the cold upper regions of the air_, to the _warm_ air near the earth: +and as their _food is low_, the swallows _fly low_. + + +Q. _Why do these INSECTS seek the lower regions of the air in WET +weather, more than in FINE weather?_ + +A. Because they are forced downward, by some current of cold air which +_drives them down_. + + +Q. _Why does a DOWNWARD current of COLD AIR bring RAIN?_ + +A. Because it _condenses the warm vapour_; which then descends in rain. + + +Q. _The proverb says, "A SINGLE MAGPIE in spring, FOUL WEATHER will +bring:" why is this the case?_ + +A. In cold stormy weather, _one magpie alone_ will leave its warm snug +nest _in search of food_, while the other stays with the _eggs or young +ones_; but in _fine mild_ weather (when their brood will not be injured +by cold) _both the magpies will fly out together_. + + +Q. _Why is it UNLUCKY for ANGLERS to see a SINGLE MAGPIE in spring?_ + +A. Because when _magpies fly abroad singly_, the weather is cold and +stormy; but when _both birds fly out together_, the weather is _warm and +mild_, which is _favourable for fishing_. + + +Q. _Why do SEA GULLS fly about the SEA in FINE weather?_ + +A. Because they _live upon fish_, which are found near the _surface of +the sea in fine weather_. + + +Q. _Why may we expect STORMY RAINS, when SEA GULLS assemble on the +land?_ + +A. Because the fish (on which they live) leave the _surface_ of the sea +in stormy weather, and _go down too deep for the gulls to get at them_; +they are obliged, therefore, to feed on the _worms and larvæ_ which are +driven out of the _ground_ at such times. + + +Q. _Why does the PETREL always fly to the SEA during a storm?_ + +A. Because the petrel _lives upon sea insects_, which are always to be +found in abundance _about the spray of swelling waves_. + + +(The Petrel is a bird of the duck-kind, which lives in the open sea. +They run on the top of the sea, and are called Petrels, or rather +Peter-els, from "St. Peter," in allusion to his walking on the sea, to +go to Jesus.) + + +Q. _Why do CANDLES and LAMPS SPIRT when RAIN is at hand?_ + +A. Because the _air is filled with vapour_, and the humidity _penetrates +the wick_; where (being formed into _steam_) it expands suddenly, and +produces a little explosion. + + +Q. _Why does a DROP of WATER sometimes ROLL along a piece of hot iron +without leaving the least trace?_ + +A. If the iron be _very hot indeed_, the _bottom_ of the drop is turned +into _vapour, before the drop can evaporate_; and the vapour thus formed +_buoys the drop up_, without allowing it to touch the iron at all. + + +Q. _Why does it ROLL?_ + +A. The _current of air_ (which is always passing over the heated +surface) _drives it along_. + + +Q. _Why does a LAUNDRESS put a little SALIVA on an IRONING-BOX to know +if it be hot enough?_ + +A. If the saliva _sticks to the box and is evaporated_, the box is +_not_ hot enough; but if the saliva _runs along the box_, it _is_. + + +Q. _Why is the BOX HOTTER if the saliva RUNS ALONG THE BOX, than if it +adheres to it till it is evaporated?_ + +A. If the saliva _runs along the box_, the iron is hot enough to +_convert the bottom of the drop_ of spittle into _vapour_; but if the +saliva _will not roll_, the box is _not_ hot enough to convert the +bottom of the drop of spittle into vapour. + + + + +CHAPTER XII. + +4.--EVAPORATION. + + +Q. _What is meant by EVAPORATION?_ + +A. The dissipation of liquid by its being _converted into vapour_. + + +Q. _What EFFECTS are produced by evaporation?_ + +A. The _liquid vaporized absorbs heat_ from the body whence it issues; +and the _body deprived of the liquid_ by evaporation, _loses heat_ +thereby. + + +Q. _If you WET your FINGER in your mouth, and hold it up in the air, why +does it FEEL COLD?_ + +A. The saliva quickly _evaporates_; and (as it evaporates) _absorbs heat +from the finger_, which makes it feel cold. + + +Q. _If you BATHE your TEMPLES with ether, why does it allay INFLAMMATION +and feverish heat?_ + +A. Ether very rapidly _evaporates_; and (as it evaporates) _absorbs heat +from the burning head_, producing a sensation of cold. + + +Q. _Why is ETHER better for this purpose than WATER?_ + +A. Because it requires _less heat to convert it into vapour_; and +therefore it evaporates much more _quickly_. + + +(Ether is converted into steam with 104 _degs._ of heat, but water +requires 212 _degs._ of heat to convert it into steam.) + + +Q. _Why does ETHER very greatly RELIEVE a SCALD or BURN?_ + +A. Because it _evaporates very rapidly_; and (while it is converted into +vapour) _carries off the heat of the burn_. + + +Q. _Why do we FEEL so COLD when we have WET FEET or CLOTHES?_ + +A. As the wet of our shoes or clothes _evaporates_, it _keeps absorbing +heat from the body_, which makes it feel cold. + + +Q. _Why do WET FEET or CLOTHES give us "COLD?"_ + +A. Because the evaporation _absorbs heat from the body so abundantly_, +that it is _lowered below its natural standard_; and therefore health is +injured. + + +Q. _Why is it DANGEROUS to SLEEP in a DAMP BED?_ + +A. Because the _heat of the body_ is continually absorbed _in converting +the damp of the sheets into vapour_; and as heat is abstracted from the +body, its temperature is reduced _below the healthy standard_. + + +Q. _Why do we not feel the same sensation of cold, if we throw a +MACINTOSH over our WET CLOTHES?_ + +A. The macintosh _prevents evaporation_, because the steam cannot escape +through the air-tight fabric; and (as the _wet cannot evaporate_ from +the clothes) no heat is absorbed from our bodies. + + +Q. _Why do NOT SAILORS get COLD, who are so often wet all day with +SEA-WATER?_ + +A. The _salt_ of the sea _retards evaporation_; and (as the heat of the +body is drawn off _very gradually_) the sensation of cold is prevented. + + +Q. _Why does SPRINKLING a HOT ROOM with water COOL IT?_ + +A. The heat of the room causes a _rapid evaporation of the sprinkled +water_; and as the water evaporates, _it absorbs heat from the room_, +and cools it. + + +Q. _Why does WATERING the STREETS and roads COOL THEM?_ + +A. The hot streets and roads part with their heat _to promote the +evaporation of the water sprinkled on them_. + + +Q. _Why does a SHOWER of RAIN seem to COOL the AIR in summer-time?_ + +A. The earth (being wet with the rain) _parts with its heat to promote +evaporation_; and as the _earth_ is cooled, it _cools the air_ also. + + +Q. _Why is LINEN DRIED by being exposed to the WIND?_ + +A. The air (blowing over the linen) _promotes evaporation_, by removing +the vapour from the _surface of the wet linen_, as soon as it is +formed. + + +Q. _Why is LINEN DRIED sooner in the open AIR, than in a confined room?_ + +A. Because the particles of vapour are more rapidly removed from the +surface of the linen by evaporation. + + +Q. _Why are WET SUMMERS generally SUCCEEDED by COLD WINTERS?_ + +A. Because the great evaporation (carried on through the wet summer) +_reduces the temperature of the earth lower than usual_, and produces +cold. + + +Q. _Why is ENGLAND WARMER than it used to be, when AGUES were so +common?_ + +A. Because it is _better drained_ and _better cultivated_. + + +Q. _Why does DRAINING land promote WARMTH?_ + +A. Because it _diminishes evaporation_; in consequence of which _less +heat_ is abstracted from the earth. + + +Q. _Why does CULTIVATION increase the WARMTH of a country?_ + +A. 1st--Because _hedges and belts of trees_ are multiplied; + +2ndly--Because the land is _better drained_; + +3rdly--Because the land is _dug and ploughed;_ and + +4thly--Because the vast _forests are cut down_. + + +Q. _Why do HEDGES and BELTS of TREES promote WARMTH?_ + +A. Because they _retard evaporation_, by keeping off the _wind_. + + +Q. _If belts of trees promote WARMTH, why do FORESTS produce COLD?_ + +A. 1st--Because they _detain and condense the passing clouds_: + +2ndly--They prevent the access of both _wind and sun_: + +3rdly--The soil of forests is always _covered with long damp grass, +rotting leaves, and thick brushwood_: and + +4thly--There are always many hollows in every forest _full of stagnant +water_. + + +Q. _Why do LONG GRASS and ROTTING LEAVES promote COLD?_ + +A. Because _they are always damp_; and the evaporation which they +promote, _is constantly absorbing heat_ from the earth beneath. + + +Q. _Why do DIGGING and PLOUGHING help to make a country WARM?_ + +A. Digging and ploughing help _to pulverize the soil_, by admitting +_air into it_, and this increases its mean temperature. + + +Q. _Why are FRANCE and GERMANY WARMER now, than when the vine would not +ripen there?_ + +A. Chiefly because _their vast forests have been cut down_; and the soil +is better _drained and cultivated_. + + +Q. _What becomes of the WATER of PONDS and TUBS in summer-time?_ + +A. Ponds and tubs in summer-time are often left dry, because their water +is _evaporated by the air_. + + +Q. _How is this EVAPORATION PRODUCED and carried on?_ + +A. The air contains heat, and changes the _surface of the water into +vapour_; this vapour (blending with the air) _is soon wafted away_; +while _fresh_ portions of air _blow over the water_, and produce a +_similar evaporation_; till the pond or tub is left quite dry. + + +Q. _Why are the WHEELS of some machines kept CONSTANTLY WET with WATER_? + +A. _To carry off the heat_ (arising from _the rapid motion_ of the +wheels) _by evaporation_, as soon as it is developed. + + +Q. _Why is MOULD HARDENED by the SUN?_ + +A. Because (when the moisture of the mould has been _evaporated by the +sun_) the earthy particles _come into closer contact_, and the mass +becomes more solid. + + +Q. _Show the WISDOM of GOD in this arrangement._ + +A. If the soil did not become _crusty and hard in dry weather_, the +_heat and drought would penetrate the soil_, and kill both seeds and +roots. + + +Q. _Why is TEA cooled FASTER in a SAUCER than in a cup?_ + +A. Because _evaporation is increased_ by _increasing the surface_; and +as tea in a saucer _presents a much larger surface to the air_, its heat +is more rapidly carried off by evaporation. + + +(The subject of "convection" will be treated of in a future chapter, and +would scarcely be understood in this place.) + + +Q. _Why is not the VAPOUR of the SEA SALT?_ + +A. Because the _salt_ is always _left behind_, by the process of +evaporation. + + +Q. _Why does a WHITE CRUST appear (in hot weather) upon CLOTHES wetted +by sea water?_ + +A. The white crust is the _salt of the water_ left on the clothes by +evaporation. + + +Q. _Why does this WHITE CRUST always DISAPPEAR in WET weather?_ + +A. In _wet_ weather the _moisture of the air dissolves the salt_; and, +therefore, it no longer remains visible. + + +Q. _Why should NOT persons, who take violent exercise, WEAR very THICK +CLOTHING?_ + +A. When the heat of the body is increased by exercise, _perspiration +reduces the heat_ (by evaporation) _to a healthy standard_: as thick +clothing _prevents this evaporation_, and confines the heat and +perspiration _to the body_, it is injurious to health. + + + + +CHAPTER XIII. + +COMMUNICATION OF HEAT. + + +1.--CONDUCTION. + + +Q. _How is HEAT COMMUNICATED from one body to another?_ + +A. 1. By Conduction. 2. By Absorption. 3. By Reflection. 4. By +Radiation: and 5. By Convection. + + +Q. _What is meant by CONDUCTION of heat?_ + +A. Heat communicated from one body to another, _by actual contact_. + + +Q. _Why does a PIECE of WOOD (blazing at ONE end) NOT FEEL HOT at the +OTHER end?_ + +A. _Wood is a bad conductor of heat_; and, therefore, heat does not +traverse freely through it: hence, though one end of a stick be +blazing-hot, the other end may be quite cold. + + +Q. _Why do SOME THINGS feel so much COLDER than others?_ + +A. Principally because _they are better conductors_; and, therefore, +draw off the heat from our body (which touches them) so much faster. + + +Q. _What are the BEST CONDUCTORS of HEAT?_ + +A. _Dense solid bodies_, such as metal and stone. + + +Q. _Which METALS are the most RAPID CONDUCTORS of HEAT?_ + +A. _Silver_ is the best conductor, then _copper_, then _gold_ or _tin_, +then _iron_, then _zinc_, and then _lead_. + + +Q. _What are the WORST CONDUCTORS of HEAT?_ + +A. All _light and porous bodies_, such as hair, fur, wool, charcoal, and +so on. + + +Q. _Why are COOKING VESSELS so often furnished with WOODEN HANDLES?_ + +A. Wood is _not a good conductor, like metal_; and, therefore, many +vessels (which are exposed to the heat of the fire) _have wooden +handles, lest they should burn our hands_ when we take hold of them. + + +Q. _Why is the HANDLE OF A METAL TEA-POT made of WOOD?_ + +A. As _wood is a bad conductor_, the heat of the boiling water is _not +so quickly conveyed to the wooden handle_, nor so quickly _poured into +the hand_ by it, as when the handle is made of metal. + + +Q. _Why would a METAL HANDLE BURN the HAND of the tea-maker?_ + +A. As metal is an _excellent conductor_, the heat of the boiling water +_rushes quickly into the metal handle_, and _into the hand that touches +it_. + + +Q. _How do you know that a METAL HANDLE would be HOTTER than a WOODEN +one?_ + +A. By _touching the metal collar_ into which the wooden handle is fixed: +though the _wooden handle is quite cold_, this _metal collar is +intensely hot_. + + +Q. _Why do persons use paper or WOOLLEN KETTLE-HOLDERS to take hold of a +kettle with?_ + +A. Paper and woollen are both very _bad conductors of heat_; and, +therefore, the heat of the kettle does _not readily pass through them to +the hand_. + + +Q. _Does the heat of the boiling kettle NEVER get through the woollen or +paper kettle-holder?_ + +A. Yes; but though the kettle-holder became as hot as the kettle itself, +it would never _feel_ so hot. + + +Q. _Why would not the kettle-holder FEEL so hot as the kettle, when it +really is of the same temperature?_ + +A. Because (being a very _bad_ conductor) _it disposes of its heat so +slowly_, that it is _scarcely perceptible_; but metal (being an +_excellent_ conductor) disposes of its heat so _quickly_, that the +sudden influx is painful. + + +Q. _Why then does HOT METAL feel so much MORE intensely WARM than HOT +WOOL?_ + +A. Because it gives out a much _greater quantity of heat in the same +space of time_; and the _influx_ of heat is, therefore, _more +perceptible_. + + +Q. _Why does MONEY in our pocket feel so HOT, when we stand BEFORE a +FIRE?_ + +A. Metal is an _excellent conductor_; and, therefore, becomes rapidly +heated. For the same reason it becomes _rapidly cold_, when it comes in +contact with a body _colder than itself_. + + +Q. _Why does a PUMP-HANDLE feel intensely COLD in WINTER?_ + +A. As metal is an _excellent conductor_, when the hot hand touches the +cold pump-handle, the heat passes rapidly _from the hand into the iron_; +and this rapid loss of heat produces a sensation of intense coldness. + + +Q. _Is the iron HANDLE of the pump really COLDER than the wooden PUMP +itself?_ + +A. No; every inanimate substance (exposed to the same temperature) +possesses the _same degree of heat_. + + +Q. _Why then does the IRON HANDLE seem so MUCH COLDER than the WOODEN +PUMP?_ + +A. Merely because the _iron is a better conductor_; and, therefore, +_draws off the heat from our hand_ much more rapidly than wood does. + + +Q. _Why does a STONE or marble HEARTH feel to the feet so much COLDER +than a CARPET or hearth-rug?_ + +A. Because _stone and marble are good conductors_, but _woollen carpets +and hearth-rugs_ are very _bad conductors_. + + +Q. _Why does the STONE HEARTH make our FEET COLD?_ + +A. As soon as the hearth-stone has absorbed a portion of heat from our +foot, it instantly disposes of it, and _calls for a fresh supply_; till +the hearth-stone has become of the _same temperature as the foot placed +upon it_. + + +Q. _Do not the woollen CARPET and HEARTH-RUG, also, conduct heat from +the human body?_ + +A. Yes; (but being very _bad conductors_) they convey _the heat away so +slowly_, that it is scarcely perceptible. + + +Q. _Is the COLD HEARTH-STONE and WARM CARPET then of the SAME +TEMPERATURE?_ + +A. Yes; everything in the room is _really of the same temperature_; but +some feel colder than others _because they are better conductors_. + + +Q. _How LONG will the hearth-stone feel cold to the feet resting on it?_ + +A. Till the _feet and the hearth-stone are both of the same +temperature_; and then the sensation of cold in the hearth-stone will go +off. + + +Q. _Why would not the HEARTH-STONE feel COLD, when it is of the SAME +temperature as our FEET?_ + +A. Because the heat would no longer _rush out of our feet into the +hearth-stone_, in order to produce an equilibrium. + + +Q. _Why does the HEARTH-STONE (when the fire is lighted) feel so much +HOTTER than the HEARTH-RUG?_ + +A. The hearth-stone is an _excellent conductor_; and, therefore, _parts +with its heat more readily_ than the woollen hearth-rug; which (being a +very _bad conductor_) parts with its heat reluctantly. + + +Q. _Why does PARTING with HEAT RAPIDLY make the HEARTH-STONE feel WARM?_ + +A. As the heat of the stone rushes _quickly into our foot_, it raises +its temperature _so suddenly_, that we cannot _help perceiving the +increase of heat_. + + +Q. _Why does the non-conducting power of the HEARTH-RUG prevent its +feeling so HOT as it really is?_ + +A. Because it parts with its heat _so slowly and gradually_, that we +scarcely _perceive its transmission_ into our feet. + + +Q. _When we plunge our HANDS into a basin of WATER, why does it produce +a sensation of COLD?_ + +A. Though the water (in which we wash) _is really warmer_ than the air +of our bed-room; yet because it is a _better conductor_, it _feels +colder_. + + +Q. _Why does the CONDUCTING power of water make it feel COLDER than the +air, though in reality it is WARMER?_ + +A. Because _it abstracts heat from our hands so rapidly_, that we feel +its loss; but the air abstracts heat _so very slowly_, that its _gradual +loss is hardly perceptible_. + + +Q. _Is water a GOOD CONDUCTOR of heat?_ + +A. No; _no liquid is a good conductor_ of heat; but yet water is a _much +better conductor than air_. + + +Q. _Why is WATER a BETTER CONDUCTOR of heat than AIR?_ + +A. Because _it is less subtile_; and the conducting power of any +substance depends upon _its solidity_, or the _closeness of its +particles_. + + +Q. _How do you know that WATER is NOT a GOOD CONDUCTOR of heat?_ + +A. Because water may be made to _boil at its surface_, without imparting +sufficient heat to _melt ice a quarter of an inch below the boiling +surface_. + + +Q. _Why are NOT LIQUIDS GOOD CONDUCTORS of heat?_ + +A. Because the heat (which should be transmitted) _produces +evaporation_, and _flies off in the vapour_. + + +Q. _Why does a POKER (resting on the fender) feel so much COLDER than +the HEARTH-RUG, which is further off the fire?_ + +A. The poker (being an excellent conductor) _draws heat from the hand +much more quickly than the rug_, which is a bad conductor: and, +therefore, (though both are _equally warm_) the poker seems to be much +colder. + + +Q. _Why are HOT BRICKS (wrapped in cloth) employed in cold weather to +KEEP the FEET WARM?_ + +A. Bricks are _bad conductors_ of heat, and cloth or flannel _still +worse_: therefore a hot brick (wrapped in flannel) will _retain its heat +a very long time_. + + +Q. _Why is a TIN PAN (filled with HOT WATER) employed as a FOOT WARMER?_ + +A. Because _polished tin_ (being a bad radiator of heat) _keeps hot a +very long time_; and warms the feet resting upon it. + + +Q. _What is meant by being a "bad RADIATOR of heat?"_ + +A. To radiate heat is to _throw off heat by rays_, as the sun; a +polished tin pan does _not throw off the heat of boiling water_ from its +surface, but _keeps it in_. + + +Q. _Why is the TIN FOOT-WARMER covered with FLANNEL?_ + +A. 1st--To prevent the perspiration of the foot from taking off the +_polish_ of the tin: + +2ndly--Flannel is a _very bad conductor_; and, therefore, helps to keep +the tin hot _longer_: and + +3rdly--If the feet were _not protected_, the conducting surface of the +tin _would feel painfully hot_. + + +Q. _What harm would it be if the POLISH of the tin were injured by the +perspiration of our feet?_ + +A. _Polished_ tin throws off its heat _very slowly_; but dull, +scratched, painted, or dirty tin, _throws off its heat very quickly_: +if, therefore, the tin foot-warmer were to _lose its polish_, it would +_get cold in a much shorter time_. + + +Q. _Why are FURNACES and stoves (where much HEAT is required) built of +porous BRICK?_ + +A. As bricks are bad conductors, they _prevent the escape of heat_: and +are, therefore, employed where great heat is required. + + +Q. _Why are FURNACE DOORS, &c. frequently COVERED with a paste of CLAY +and SAND?_ + +A. Because this paste is a _very bad conductor of heat_; and, therefore, +prevents the _escape of heat from the furnace_. + + +Q. _If a stove be placed in the MIDDLE of a room, should it be made of +bricks or IRON?_ + +A. A stove in the _middle of a room_ should be made of _iron_; because +iron is an _excellent conductor_, and rapidly communicates its heat to +the air around. + + +Q. _Why does the Bible say, that God "giveth SNOW like WOOL?"_ + +A. As _snow is a very bad conductor of heat_, it protects vegetables and +seeds from the frost and cold. + + +Q. _How does the non-conducting power of SNOW PROTECT VEGETABLES from +the FROST and cold?_ + +A. As snow is a bad conductor, it prevents the _heat_ of the earth _from +being drawn off_ by the cold air which rests upon it. + + +Q. _Why are WOOLLENS and FURS used in COLD weather for CLOTHING?_ + +A. Because they are _very bad conductors_ of heat; and, therefore, +_prevent the warmth of the body from being drawn off_ by the cold air. + + +Q. _Do not woollens and furs actually IMPART heat to the body?_ + +A. No; they merely _prevent the heat of the body from escaping_. + + +Q. _Where would the heat ESCAPE to, if the body were NOT wrapped in wool +or fur?_ + +A. The heat of the body would _fly off into the air_; for the cold air +(coming into contact with our body) _would gradually draw away its +heat_, till it was as cold as the air itself. + + +Q. _What then is the PRINCIPAL USE of CLOTHING in winter-time?_ + +A. _To keep the body air-tight_; and prevent the _external air_ (or +wind) from _coming into contact with it_, to absorb its heat. + + +Q. _Why are BEASTS COVERED with FUR, HAIR, or WOOL?_ + +A. Because fur, hair, and wool are very _slow conductors of heat_; and +(as dumb animals cannot be clad like human beings) God has given them a +_robe of hair_ or wool, to _keep them warm_. + + +Q. _Why are BIRDS covered with DOWN or FEATHERS?_ + +A. Because down and feathers are _very bad conductors of heat_; and (as +birds cannot be clad like human beings) God has given them a _robe of +feathers to keep them warm_. + + +Q. _Why are WOOL, FUR, HAIR, or FEATHERS such SLOW CONDUCTORS of heat?_ + + +A. Because a _great quantity of air_ lurks entangled between their +fibres; and _air is a very bad conductor of heat_. + + +Q. _If AIR be a BAD CONDUCTOR of heat, why should we not feel as warm +WITHOUT clothing, as when we are wrapped in wool and fur?_ + +A. Because the air (which is cooler than our body) _is never at rest_; +and, therefore, fresh particles (perpetually passing over our body) +_keep drawing off the heat little by little_. + + +Q. _Why does the ceaseless CHANGE of air tend to DECREASE the WARMTH of +a naked body?_ + +A. Thus:--the air which cases the body _absorbs as much heat from it as +it can, while it remains in contact_; it is then blown away, and makes +room for a _fresh coat of air_, which does the _same_. + + +Q. _Does the AIR (which encases a naked body) become by contact as WARM +as the BODY itself?_ + +A. It would do so, if it remained _motionless_; but as it remains only +_a very short time_, it absorbs as much heat as it _can in the time_, +and passes on. + + +Q. _Why do we feel COLDER in WINDY WEATHER, than in a CALM day?_ + +A. Because (in windy weather) the particles of air _pass over us more +rapidly_; and every _fresh_ particle takes from us _some_ portion of +heat. + + +Q. _Show the wisdom of God in making the AIR a BAD CONDUCTOR._ + +A. If air were a _good conductor_ (like iron and stone) the heat would +be drawn _so rapidly from our body_, that we must be _chilled to death_. +Similar evils would be felt also by all the animal and vegetable world. + + +Q. _Does not the bad conducting power of air enable persons to judge +whether an EGG be NEW or STALE?_ + +A. Yes; touch your tongue against the shell at the larger end; if it +_feels warm_ to the tongue, the _egg is stale_; if _not_, it is +new-laid. + + +Q. _Why will the SHELL of a STALE EGG feel WARM to the tongue?_ + +A. Between the shell and the "white of the egg" _there is a small +quantity of air_, which _expands in a stale egg_, from the _shrinking of +the white_. + + +Q. _Why does the expansion of air (at the end of an egg) make it feel +WARM to the tongue?_ + +A. As air is a very bad conductor, the _more air an egg contains_, the +_less heat will be drawn from the tongue_ when it touches the shell. + + +Q. _Why do ladies FAN themselves in summer, to make their FACES COOL?_ + +A. The fan _puts the air in motion_, and makes it pass more _rapidly +over their face_; and (as the temperature of the _air is always lower_ +than that of the human _face_) each puff of air _carries off some +portion of heat_ from the face. + + +Q. _Does FANNING the air make the AIR itself COOLER?_ + +A. No; fanning makes the _air hotter and hotter_. + + +Q. _Why does FANNING the air increase its HEAT?_ + +A. By causing the air continually to _absorb heat from the human body_ +which it passes over. + + +Q. _If fanning makes the AIR HOTTER, how can it make a PERSON feel +COOLER?_ + +A. Fanning makes the _air hotter_, but the _face cooler_; because it +keeps _taking the heat out of the face_, and _giving it to the air_. + + +Q. _Why is BROTH COOLED by BLOWING it?_ + +A. The breath causes a rapid _change of air_ to pass over the broth; and +(as the air is not so hot as the broth) _it keeps absorbing heat_, and +thus makes the broth cooler and cooler. + + +Q. _Would not the air absorb heat from the broth just as well WITHOUT +BLOWING?_ + +A. No; _air is a very bad conductor_; unless, therefore, _the change be +rapid_, the air nearest the surface of the broth _would soon become as +hot as the broth itself_. + + +Q. _But would not the hot air PART with its heat instantly to the +CIRCUMJACENT air?_ + +A. No; not instantly. Air is so bad a conductor, _that it parts with its +heat very slowly_: unless, therefore, the air be kept in _continual +motion_, it would _cool the broth very slowly indeed_. + + +Q. _Why does WIND generally feel COOL?_ + +A. Wind is only air in motion; and the more quickly the _air passes over +our body_, the more rapidly it _absorbs the heat_ therefrom. + + +Q. _Why does AIR ABSORB heat more QUICKLY by being set in MOTION?_ + +A. Because every fresh gust of air _absorbs a fresh portion of heat_; +and the more rapid the _succession of gusts_, the greater will be the +quantity of air absorbed. + + +Q. _If the AIR were HOTTER than our body, would the WIND feel COOL?_ + +A. No; if the air were _hotter than our body_, it would feel +_insufferably hot_. + + +Q. _Why would the AIR feel INTENSELY HOT, if it were WARMER than our +BLOOD?_ + +A. Because then the wind would _add to the heat of_ our body, instead of +_diminishing it_. + + +Q. _Is the AIR EVER as HOT as the human BODY?_ + +A. Not in _this_ country: in the hottest summer's day, the air is always +10 or 12 _degrees cooler than the human body_. + + +Q. _Is the EARTH a GOOD CONDUCTOR of heat?_ + +A. No; the power of _conducting_ heat depends upon the _continuity of +matter_; if the particles of which a thing is composed are not +_continuous_, they have very little power to _conduct heat_. + + +Q. _Why is the earth (BELOW the SURFACE) WARMER in WINTER than the +surface itself?_ + +A. Because the earth is a _bad conductor of heat_; and, therefore +(although the ground be frozen) the frost never penetrates _above an +inch or two below the surface_. + + +Q. _Why is the earth (BELOW the SURFACE) COOLER in SUMMER than the +surface itself?_ + +A. Because the earth is a _bad conductor of heat_; and, therefore, +(although the surface be scorched with the burning sun) the intense heat +cannot penetrate to _the roots_ of the plants and trees. + + +Q. _Shew the WISDOM of GOD in making the EARTH a BAD CONDUCTOR._ + +A. If the _heat and cold could penetrate the earth_ (as freely as the +heat of a fire penetrates iron), the springs would be dried up in summer +and frozen in winter, and all vegetation would perish. + + +Q. _Why is WATER from a SPRING so COOL in SUMMER?_ + +A. As the earth is a _bad conductor_, the burning rays of the sun can +penetrate only a few inches below the surface; in consequence of which, +the _springs of water are not affected_. + + +Q. _Why is it COOL under a SHADY tree in a hot summer's day?_ + +A. 1st--Because the overhanging foliage _screens off the rays of the +sun_: + +2ndly--As the rays of the sun are warded off, _the air_ (beneath the +tree) _is not heated by the reflection of the earth_: and + +3rdly--The leaves of trees, being _non-conductors_, allow no heat to +penetrate through them. + + +Q. _Why do the LAPLANDERS wear SKINS, with the FUR INWARDS?_ + +A. The _dry skin_ prevents the _wind from penetrating to their body_; +and as the _fur_ contains a _quantity of air_ between its hairs (which +soon _becomes heated by the body_) the Laplander is clad in _a case of +hot air, impervious to the cold and wind_. + + +Q. _Why does a LINEN SHIRT feel COLDER than a COTTON ONE?_ + +A. _Linen is a much better conductor_ than cotton; and, therefore, (as +soon as it touches the body) _it more rapidly draws away the heat_, and +produces a sensation of cold. + + +Q. _Why is the FACE COOLED by wiping the temples with a fine CAMBRIC +HANDKERCHIEF?_ + +A. The fine fibres of the cambric have a _strong capillary attraction +for moisture_; and are _excellent conductors of heat_: thus the moisture +and heat are _both abstracted from the face_, and a sensation of +coolness is produced. + +"Capillary attraction," i. e. _the attraction of a thread or hair_. The +wick of a candle is wet with grease, because the melted tallow runs up +the cotton from capillary attraction. + + +Q. _Why would not a COTTON handkerchief do as well?_ + +A. The coarse fibres of cotton have much less capillary attraction, and +are _nothing like such good conductors_ as linen: and, therefore, wiping +the face with a _cotton handkerchief_, increases the sensation of +warmth. + + + + +CHAPTER XIV. + +2.--ABSORPTION OF HEAT. + + +Q. _What is the difference between CONDUCTING heat, and ABSORBING heat?_ + +A. To _conduct_ heat, is to _transmit it from one body to another_ +through a conducting medium: to _absorb_ heat, is to _suck it up_, as a +sponge sucks up water. + + +Q. _Give me an example._ + +A. _Black cloth absorbs_, but does not _conduct heat_: thus, if black +cloth be laid in the sun, _it will absorb the rays_ very rapidly; but if +_one end of the black cloth_ be made hot, it would not _conduct the +heat_ to the _other_ end. + + +Q. _Are good CONDUCTORS of heat, good ABSORBERS also?_ + +A. No; every _good conductor of heat_ is a _bad absorber of it_; and _no +good absorber of heat_ can be a _good conductor_ also. + + +Q. _Is IRON a good ABSORBER of heat?_ + +A. No; _iron is a good conductor_, but a very _bad absorber_ of heat. + + +Q. _Why do the FENDER and FIRE-IRONS (which lie upon it) remain COLD, +although they are before a good fire?_ + +A. Because the metal fender and fire-irons have very _little capacity +for absorbing heat_; although they are soon made hot (by conduction), +when placed in _contact_ with the hot fire or stove. + + +Q. _Why does a KETTLE boil faster, when the bottom and back are COVERED +with SOOT?_ + +A. The _black soot absorbs heat_ very quickly from the fire, and the +metal _conducts it to the water_. + + +Q. _Why will not a NEW KETTLE boil so fast as an OLD one?_ + +A. Because the _bottom and sides_ of a new kettle are _clean and +bright_; but in an _old_ kettle _are covered with soot_. + + +Q. _Why would the KETTLE be SLOWER BOILING, if the BOTTOM and BACK were +CLEAN and bright?_ + +A. _Bright_ metal does _not absorb heat_, but _reflect it_ (i. e. throw +the heat _back_ again); and as the heat is _thrown off from the surface +of bright metal_, therefore, a new kettle is longer boiling. + + +Q. _Why do we wear WHITE LINEN and a BLACK outer DRESS, if we want to be +warm?_ + +A. The _black outer dress_ quickly _absorbs heat from the sun_, and +conveys it to the body; and the _white linen_ (being a _bad_ absorbent) +abstracts no heat from the warm body. + + +Q. _Why do persons WEAR WHITE dresses in SUMMER time?_ + +A. White _throws off the heat of the sun by reflection_, and is, +therefore, a very bad absorbent of heat; in consequence of which, it +never becomes _so hot from the scorching sun_ as dark colours do. + + +Q. _Why do NOT persons WEAR WHITE dresses in WINTER time?_ + +A. _White will not absorb heat_, like black and other dark colours; and, +therefore, _white_ dresses are _not so warm as dark ones_. + + +Q. _What COLOURS are WARMEST for dresses?_ + +A. For _outside_ garments _black is the warmest_, and then such colours +as _approach nearest to black_ (as dark blue and green). _White is the +coldest colour_ for external clothing. + + +Q. _Why are DARK COLOURS (for external wear) so much WARMER than LIGHT +ONES?_ + +A. Because _dark colours absorb heat from the sun_ more abundantly than +_light_ ones. + + +Q. _How can you prove that DARK colours are WARMER than LIGHT ones?_ + +A. If a piece of _black_ cloth and a piece of _white_ were laid upon +snow, in a few hours the _black cloth will have melted the snow +beneath_; whereas the _white_ cloth will have produced little or _no +effect upon it at all_. + + +N. B. The darker any colour is, the warmer it is, because it is a better +absorbent of heat. The order may be thus arranged:--1. Black (warmest of +all).--2. Violet.--3. Indigo.--4. Blue.--5. Green.--6. Red.--8. Yellow: +and 9. White (coldest of all). + + +Q. _Why are BLACK KID GLOVES so HOT in summer time?_ + +A. 1st--Because the _black absorbs the solar heat_: and + +2ndly--The _kid_ will not allow the heat of the hand _to escape through +the glove_. + + +Q. _Why are LISLE THREAD GLOVES so COOL in summer time?_ + +A. 1st--Because thread _absorbs the perspiration of the hands_: and + +2ndly--It _conducts away the heat_ of our hot hands. + + +Q. _Are Lisle thread gloves ABSORBENTS of heat?_ + +A. As Lisle thread gloves are generally of a _grey or lilac colour_, +they do _not absorb solar heat_. + + +Q. _Why is a PLATE-WARMER made of UN-PAINTED BRIGHT TIN?_ + +A. Bright tin reflects (or _throws back_) _the heat_, which issues from +the fire in rays; and (by reflecting the heat upon the meat) assists +greatly in roasting it. + + +Q. _Why would not the tin REFLECTOR do as well if it were PAINTED?_ + +A. If the tin reflector were _painted_, it would be utterly spoiled, +because it would then _absorb_ heat, and _not reflect it at all_. A +plate-warmer should be kept _very clean, bright, and free from all +scratches_. + + +Q. _Why should a REFLECTOR be kept so very CLEAN and free from +SCRATCHES?_ + +A. If a reflector be _spotted, dull, or scratched_, it will _absorb_ +heat, instead of _reflecting_ it; and, therefore, would be of no use +whatsoever as a _reflector_. + + +Q. _Why does HOAR-FROST remain on TOMBSTONES, long after it has melted +from the GRASS and GRAVEL-WALKS of a church-yard?_ + +A. Tomb-stones being _white_, will _not absorb heat_, like the darker +grass and gravel; and, therefore, _the white tombstones_ (being so much +colder) _retain the hoar-frost_ after it has melted from other things. + + +Q. _If black absorbs heat, why have those who live in HOT climates BLACK +SKINS, and not WHITE skins (which would not absorb heat at all)?_ + +A. Though the black skin of the negro _absorbs heat_ more plentifully +than the _white skin of a European_, yet the _blackness_ prevents the +sun from _blistering_ or _scorching it_. + + +Q. _How is it known that the BLACK colour prevents the sun from either +BLISTERING or SCORCHING the skin?_ + +A. If you put a _white glove_ on _one hand_, and a _black glove_ on _the +other_ (when the sun is burning hot), the hand with the _white_ glove +will be _scorched_, but _not the other_. + + +Q. _Which hand will FEEL the HOTTER?_ + +A. The hand with the _black glove_ will _feel_ the _hotter_, but it will +not be _scorched_ by the sun; whereas the hand with the _white glove_ +(though much _cooler_) will be _severely scorched_. + + +Q. _Why does the BLACK skin of a NEGRO NEVER SCORCH or BLISTER with the +hot sun?_ + +A. Because the _black colour absorbs_ the heat,--conveys it _below the +surface_ of the skin, and converts it to _sensible heat_ and +_perspiration._ + + +Q. _Why does the WHITE EUROPEAN SKIN BLISTER and SCORCH when exposed to +the hot sun?_ + +A. Because the _white will not absorb_ the heat; and, therefore, the hot +sun _rests on the surface of the skin_, and scorches it. + + +Q. _Why has a NEGRO BLACK EYES?_ + +A. The black colour of a negro's eyes defends them from the strong light +of the tropical sun. If a negro's eyes were not _black_, the sun would +_scorch them_, and every negro would be blind. + + +Q. _Why is WATER KEPT COOLER (in summer time) in a BRIGHT TIN POT, than +in an EARTHEN one?_ + +A. Because bright metal will _not absorb_ the heat of the summer sun, +like an _earthen_ vessel. + + +Q. _Why is BOILING water KEPT HOT in a BRIGHT TIN VESSEL longer, than in +an earthen one?_ + +A. Because bright tin will not suffer the heat of the boiling water _to +escape in rays_, as an earthen vessel does. + + + + +CHAPTER XV. + +3.--REFLECTION OF HEAT. + + +Q. _What is meant by REFLECTING HEAT?_ + +A. To reflect heat, is _to throw it back in rays_ from the surface of +the reflecting body, towards the place from whence it came. + + +Q. _What are the BEST REFLECTORS of heat?_ + +A. All _bright_ surfaces, and _light colours_. + + +Q. _Are GOOD ABSORBERS of heat GOOD REFLECTORS also?_ + +A. No; those things _which absorb heat best, reflect_ heat _worst_; and +those _which reflect heat worst, absorb_ it _best_. + + +Q. _Why are those things which ABSORB HEAT unable to REFLECT it?_ + +A. Because if any thing _sucks in heat_ like a sponge, it cannot _throw +it off_ from its surface; and if any thing _throws off heat_ from its +surface, it cannot _drink it in_. + + +Q. _Why are REFLECTORS always made of LIGHT-COLOURED and highly POLISHED +METAL?_ + +A. Because _light_ coloured and _highly polished metal_ makes the best +of all reflectors. + + +Q. _Why do not PLATE-WARMERS BLISTER and scorch the WOOD behind?_ + +A. Because the bright tin front _throws the heat of the fire back +again_, and will not allow it to penetrate to the wood behind. + + +Q. _If metal be such an excellent CONDUCTOR of heat, how can it REFLECT +heat, or throw it off?_ + +A. Polished metal is a _conductor of heat_, only when _that heat is +communicated by actual contact_; but whenever heat _falls upon bright +metal in rays_, it is _reflected back again_, and the metal remains +_quite cool_. + + +Q. _What is meant by "heat falling upon metal IN RAYS," and not "by +contact"?_ + +A. If a piece of tin were thrust _into_ a fire, it would be _in actual +contact with the fire_; but if it be _held before a fire_, the heat of +the fire _falls upon it in rays_. + + +Q. _What is the use of the TIN SCREEN or REFLECTOR used in ROASTING?_ + +A. The tin reflector _throws the heat of the fire back upon the meat_; +and, therefore, assists the _process of roasting_ and helps _to keep the +kitchen cool_. + + +Q. _How does a tin REFLECTOR tend to keep the KITCHEN COOL?_ + +A. Because it _confines the heat to the hearth_, and prevents it from +being dispersed throughout the kitchen. + + +Q. _Why does a LAMP GLASS DIMINISH the SMOKE of a LAMP?_ + +A. As _glass is a reflector_, it reflects the heat of the lamp _back +upon the flame_; in consequence of which, _less carbon escapes +unconsumed_ (as smoke). + + +Q. _Why are SHOES HOTTER for being DUSTY?_ + +A. 1st--Because dust absorbs heat: and + +2ndly--As it destroys the _blackness of our shoes_, it prevents them +from _throwing off the heat of our feet in rays_. + + +Q. _Why can we not SEE into the ROAD or STREET, when a CANDLE is lighted +in a room?_ + +A. _Glass is a reflector_; and, therefore, throws the rays of the candle +_back into the room_, and thus prevents our seeing into the road or +street. + + +Q. _Why can persons in the DARK STREET see into a ROOM (lighted by a +candle or lamp)?_ + +A. The pupil of the eye _expands greatly_, when persons are in the dark; +and, therefore, when any one in the dark street looks into a light room, +_his dilated pupil_ sees every thing distinctly. + + +Q. _Why does it always FREEZE on the TOP of a MOUNTAIN?_ + +A. Air is heated _by the reflection of the earth_, and not by the rays +of the sun; and, as there is no earth round a mountain-top _to reflect +heat_, therefore, it remains intensely cold. + + + + +CHAPTER XVI. + +4.--RADIATION. + + +Q. _What is meant by RADIATION?_ + +A. Radiation means _the emission of rays_: thus the sun radiates both +light and heat; that is, it emits _rays of light and heat_ in all +directions. + + +Q. _When is heat RADIATED from one body to another?_ + +A. When the two bodies are _separated by a non-conducting medium_: thus +the sun _radiates_ heat towards the earth, because the _air comes +between_ (which is a very bad conductor). + + +Q. _On WHAT does RADIATION DEPEND?_ + +A. On the _roughness_ of the radiating surface: thus if metal be +_scratched_, its radiating power is increased, because the _heat has +more points to escape from_. + + +Q. _Does a FIRE RADIATE heat?_ + +A. Yes; and because _burning fuel emits rays of heat_, therefore we +_feel warm_ when we stand before a fire. + + +Q. _Why does our FACE FEEL uncomfortably HOT, when we approach a FIRE?_ + +A. Because the fire radiates heat upon the face; which (not being +_covered_) feels the effect immediately. + + +Q. _Why does the fire catch the FACE more than the REST of the body?_ + +A. The _rest_ of the body is _covered with clothing_, which (being a +_bad conductor_ of heat) prevents the same sudden and rapid +transmission of heat to the skin. + + +Q. _Do those substances which RADIATE heat, ABSORB heat also?_ + +A. Yes. Those substances which _radiate most_, also _absorb most heat_: +and those which _radiate least_, also _absorb the least_ heat. + + +Q. _Does any thing ELSE radiate heat, BESIDES the SUN and FIRE?_ + +A. Yes; _all_ things radiate heat in _some_ measure, but _not equally +well_. + + +Q. _What things RADIATE heat the NEXT BEST to the sun and fire?_ + +A. All _dull_ and _dark substances_ are _good radiators_ of heat; but +all _light_ and _polished substances_ are _bad radiators_ of heat. + + +Q. _Why does a POLISHED METAL TEA-POT make BETTER TEA than a black +earthen one?_ + +A. As polished metal is a very _bad radiator_ of heat, it _keeps the +water hot much longer_; and the hotter the water is, the better it +"draws" the tea. + + +Q. _Why will not a DULL BLACK TEA-POT make good tea?_ + +A. Because the heat of the water _flies off so quickly_ through the dull +black surface of the tea-pot, that the _water is rapidly cooled_, and +will not "draw" the tea. + + +Q. _Do not pensioners, and most aged cottagers, prefer the little BLACK +EARTHEN TEA-POT to the bright METAL one?_ + +A. Yes; because they _set it on the hob "to draw;"_ in which case, the +little _black tea-pot_ will make the _best tea_. + + +Q. _Why will a BLACK TEA-POT make better tea than a bright metal one, if +it be set upon the HOB to DRAW?_ + +A. Because the black tea-pot will _absorb heat plentifully_ from the +fire, and keep the water _boiling hot_: whereas, a bright _metal_ +tea-pot (set upon the hob) would _throw off_ the heat by _reflection_. + + +Q. _Then sometimes a BLACK EARTHEN tea-pot is the best, and sometimes a +bright METAL one?_ + +A. Yes; when the tea-pot is _set on the hob "to draw,"_ the black +_earth_ is the _best_, because it _absorbs heat_: but when the tea-pot +is _not_ set on the hob, the bright _metal_ is the _best_, because it +_radiates heat very slowly_, and therefore _keeps the water hot_. + + +Q. _Why does a SAUCEPAN which has been USED, boil QUICKER than a NEW +ONE?_ + +A. Because the bottom and back are _covered with soot_; and the _black +soot_ rapidly _absorbs the heat_ of the glowing coals. + + +Q. _Why should the FRONT and LID of a SAUCEPAN be clean and BRIGHT?_ + +A. As they do not come in contact with the fire, they cannot _absorb +heat_; and (being bright) they will not suffer _the heat to escape_ by +radiation. + + +Q. _In what state should a SAUCEPAN be, in order that it may BOIL +QUICKLY?_ + +A. All those parts which _come in contact with the fire_ should be +covered with _soot_, to absorb heat; but all the _rest_ of the saucepan +should be as _bright as possible_, to prevent the _escape of heat_ by +radiation. + + +Q. _Why is it said that "SATURDAY'S KETTLE BOILS the FASTEST?"_ + +A. Because on Saturday the _front_ and _top_ of the kettle are generally +_cleaned_ and _polished;_ but the _bottom_ and _back_ of the kettle are +_never_ cleaned. + + +Q. _Why should NOT the BOTTOM and BACK of a kettle be CLEANED and +polished?_ + +A. Because they _come in contact with the fire_, and (while they are +covered with black soot) _absorb heat freely_ from the burning coals. + + +Q. _Why should the FRONT and TOP of a kettle be CLEAN and well +polished?_ + +A. Because polished metal _will not radiate heat_; and, therefore, +(while the front and top of the kettle are well polished) _the heat is +kept in_, and not suffered to escape by radiation. + + +Q. _Why is the INSIDE of a KETTLE and SAUCEPAN WHITE?_ + +A. _White will not radiate heat_: if, therefore, the inside of a boiler +be _white_, the liquor in it is _kept hot much longer_. + + +Q. _Why is the BOTTOM of a KETTLE nearly COLD, when the WATER is BOILING +HOT?_ + +A. Black soot is a very _bad conductor of heat_; and, therefore, the +heat of the boiling water is some considerable time, before it gets +_through the soot_ which adheres to the bottom of the kettle. + + +Q. _Why is the LID of a KETTLE so intensely HOT, when the water boils?_ + +A. The bright metal lid of the kettle _is an admirable conductor_ of +heat; and, therefore, _the heat from the boiling water pours into our +hand_ the moment we touch it. + + +Q. _Show the benefit of SMOKE in COOKING._ + +A. The carbon of the fuel (which flies off in smoke) naturally +_blackens_ all culinary vessels set upon the fire to boil, and thus +renders them fit for use. + + +("Culinary vessels" are vessels used in kitchens for cooking, as +saucepans, boilers, kettles, &c.) + + +Q. _How does SMOKE make culinary vessels FIT for USE?_ + +A. If it were not for the _smoke_, (which gathers round a kettle or +saucepan) _heat would not be absorbed_, and the process of boiling would +be greatly retarded. + + +Q. _Why is boiling water KEPT HOT best in a BRIGHT METAL pot?_ + +A. Because bright metal being a _bad radiator_ will not _throw off the +heat_ of the boiling water _from its surface_. + + +Q. _Why is WATER KEPT COLD in summer-time in a BRIGHT METAL pot, better +than in an EARTHEN vessel?_ + +A. Because bright metal _will not absorb heat_ from the hot air, like an +_earthen vessel_; in consequence of which, the water is kept cooler. + + +Q. _Why are DINNER-COVERS made of BRIGHT TIN or SILVER?_ + +A. Light-coloured and highly-polished metal _is a very bad radiator of +heat_; and, therefore, bright tin or silver will not allow the heat of +the cooked food _to escape through the cover by radiation_. + + +Q. _Why should a MEAT-COVER be very brightly POLISHED?_ + +A. If the cover be _dull or scratched_ it will _absorb heat from the hot +food beneath it_; and (instead of _keeping it hot_) will _make it cold_. + + +Q. _Why should a SILVER MEAT-COVER be PLAIN, and not CHASED?_ + +A. If the cover be _chased_, it will _absorb the heat of the food_ +covered by it; and instead of _keeping it hot_, will _make it cold by +absorption_. + + +Q. _What is DEW?_ + +A. Dew is the _vapour of the air condensed_, by coming in contact with +bodies _colder than itself_. + + +Q. _Why is the GROUND sometimes COVERED with DEW?_ + +A. The _earth is more heated_ by solar rays _than the air_, during the +_day_; but at _night_, the earth _parts with more heat_ than the _air_, +and becomes (in consequence) 5 or 10 degrees _colder_. + + +Q. _How does the EARTH being COLDER than the AIR account for the +deposition of DEW?_ + +A. As soon as the air _touches the cold earth_, its warm vapour is +_chilled_, and _condensed into dew_. + + +Q. _Why is the surface of the GROUND COLDER in a FINE clear NIGHT, than +in a CLOUDY one?_ + +A. On a fine clear star-light night, _heat radiates from the earth +freely_, and is lost in open space: but on a _cloudy_ night, the clouds +_arrest the process of radiation_. + + +Q. _Why is DEW deposited only on a FINE clear NIGHT?_ + +A. Because, when the night is _clear_ and _fine_, the _surface of the +ground radiates heat most freely_; and (being cooled down by this loss +of heat) _chills the vapour of the air into dew_. + + +Q. _Why is there NO DEW on a dull CLOUDY NIGHT?_ + +A. The clouds _arrest the radiation of heat from the earth_; and (as the +heat cannot freely escape) the surface is not sufficiently cooled down +_to chill the vapour of the air into dew_. + + +Q. _Why is a CLOUDY NIGHT WARMER than a FINE one?_ + +A. Because the clouds _prevent the radiation of heat from the earth_; +and, therefore, the surface of the earth remains _warmer_ on a dull +cloudy night. + + +Q. _Why is DEW most ABUNDANT in situations most EXPOSED?_ + +A. Because the radiation of heat _is not arrested_ by houses, trees, +hedges, or any other thing. + + +Q. _Why is there scarcely any DEW under a shady TREE?_ + +A. The shady head of the tree both _arrests the radiation of heat from +the earth_, and also radiates some of its own heat _towards the earth_; +and, therefore, the ground (underneath a tree) _is not sufficiently +cooled_ down to chill the vapour of the air into dew. + + +Q. _Why is there never much DEW at the foot of WALLS and HEDGES?_ + +A. 1st--Because the wall or hedge acts as a screen, _to arrest the +radiation of heat from the earth_: and + +2ndly--The wall or hedge also _radiates some portion of heat_ towards +the earth. + + +Q. _How do these things prevent the deposition of dew?_ + +A. As the ground (beneath a wall, tree, or hedge) is _not cooled by the +radiation of heat_, it remains of the _same temperature as the air_ +above it; in consequence of which, the vapours of the air are _not +chilled by it into dew_. + + +Q. _Why is there little or NO DEW beneath a FLOWER-AWNING, although that +awning be open on all four sides?_ + +A. 1st--Because the awning _arrests the radiation of heat from the +ground beneath_: and + +2ndly--It _radiates some of its own heat downwards_; in consequence of +which, the ground beneath an awning is _not sufficiently cooled down_ to +chill the vapour of air into dew. + + +Q. _How can a thin covering of BASS or even MUSLIN protect trees from +FROST?_ + +A. Because _any covering_ prevents the _radiation of heat from the +tree_; and if the tree be _not cooled down by radiation_, the vapour of +the air will _not be frozen_ as it comes in contact with it. + + +Q. _Why is the BASS or CANVASS itself (which covers the tree) always +DRENCHED with DEW?_ + +A. The bass or canvass covering _radiates heat_ both _upwards and +downwards_; and is, therefore, _so cooled down_, that it readily _chills +all the vapour of the air_ (which passes over it) _into dew_. + + +Q. _Why does SNOW at the foot of a HEDGE or WALL melt sooner, than in an +open field?_ + +A. Because the hedge or wall _radiates heat into the snow beneath_, +which melts it. + + +Q. _Why is there NO DEW after a WINDY NIGHT?_ + +A. 1st--Because the wind _evaporates the moisture_, as fast as it is +deposited; and + +2ndly--It _disturbs the radiation of heat_, and diminishes the +deposition of dew thereby. + + +Q. _Why are VALLEYS & HOLLOWS often thickly covered with DEW, although +they are sheltered?_ + +A. The surrounding hills prevent the _repose of air_ (in the valleys) +_from being disturbed_; but do not _overhang_ and _screen_ them, so as +to _arrest their radiation_. + + +Q. _Why does DEW FALL more ABUNDANTLY on SOME THINGS than upon OTHERS?_ + +A. Because some things _radiate heat more freely_ than others, and +therefore become _much cooler_ in the night. + + +Q. _Why are things which RADIATE HEAT MOST FREELY, always the most +THICKLY COVERED with DEW?_ + +A. Because the vapour of the air is _chilled into dew_, the moment it +comes in contact with them. + + +Q. _What kind of things RADIATE HEAT most FREELY?_ + +A. Grass, wood, and the leaves of plants, radiate heat _very freely_: +but polished metal, smooth stones, and woollen cloth, part with their +heat _very tardily_. + + +Q. _Do the leaves of ALL plants radiate heat EQUALLY WELL?_ + +A. No. Rough _woolly leaves_ (like those of a holly-hock) radiate heat +much _more freely_, than the _hard smooth polished leaves_ of a common +laurel. + + +Q. _Shew the WISDOM of GOD in making grass, the leaves of trees, and ALL +VEGETABLES, EXCELLENT RADIATORS of heat._ + +A. As vegetables _require much moisture_, and would often perish without +a plentiful deposit of dew, God wisely made them to _radiate heat +freely_, so as to _chill the vapour_ (which touches them) _into dew_. + + +Q. _Will polished METAL, smooth STONES, and woollen CLOTH, readily +collect DEW?_ + +A. No. While grass and the leaves of plants _are completely drenched +with dew_, a piece of _polished metal_, or of _woollen cloth_ (lying on +the same spot) will be _almost dry_. + + +Q. _Why would POLISHED METAL and WOOLLEN CLOTH be DRY, while grass and +leaves are drenched with DEW?_ + +A. Because the polished metal and woollen cloth _part with their heat so +slowly_, that the vapour of the air is _not chilled into dew_ as it +passes over them. + + +Q. _Why is a GRAVEL WALK almost DRY, when a grass plat is covered thick +with DEW?_ + +A. _Grass_, (_being a good radiator_) throws off its heat very _freely_; +but _gravel (being a very bad radiator)_ parts with its heat very +_reluctantly_. + + +Q. _Is that the reason why GRASS is SATURATED with DEW, and the GRAVEL +is NOT?_ + +A. Yes. When the vapour of warm air comes in contact with the _cold +grass_, it is instantly chilled into dew; but (as the gravel is _not so +cold as the grass_) the vapour of air is _not so freely condensed_ as it +passes over the gravel. + + +Q. _Why does DEW rarely fall upon hard ROCKS and BARREN lands?_ + +A. Rocks and barren lands are so _compact_ and _hard_, that they can +neither _absorb nor radiate much heat_; and (as their _temperature +varies but very little_) very little _dew_ distils upon them. + + +Q. _Why does DEW fall more abundantly on CULTIVATED soils, than on +BARREN lands?_ + +A. Because cultivated soils (being _loose and porous_) _absorb_ heat +freely during the day, and _radiate it_ by night; and (being _much +cooled by the rapid radiation of heat_) as the vapour of the air passes +over them, it is plentifully _condensed into dew_. + + +Q. _Shew the WISDOM of GOD in this arrangement._ + +A. Every plant and inch of land which _needs the moisture of dew_, is +adapted to _collect it_; but _not a single drop even of dew is wasted_, +where its refreshing moisture is _not required_. + + +Q. _Shew the WISDOM of GOD in making polished METAL and woollen CLOTH +BAD RADIATORS of heat._ + +A. If polished metal collected dew as easily as grass, it could _never +be kept dry_, and _free from rust_. Again, if woollen garments +collected dew as readily as the leaves of trees, we should be _often +soaking wet_, and subject to _constant colds_. + + +Q. _Shew how this affords a beautiful illustration of GIDEON'S MIRACLE, +recorded in the book of Judges, VI. 37, 38._ + +A. The _fleece of wool_ (which is a _very bad radiator_ of heat) was +_soaking wet_ with dew: when the _grass_ (which is a most _excellent +radiator_) was _quite dry_. + + +Q. _Was not this CONTRARY to the laws of NATURE?_ + +A. Yes; and was, therefore, a plain _demonstration of the power of God_, +who could change the very _nature of things_ at his will. + + +Q. _Why do our CLOTHES FEEL DAMP, after walking in a fine evening in +SPRING or AUTUMN?_ + +A. Because the vapour (_condensed by the cold earth_) lights upon them, +like dew. + + +Q. _Why are WINDOWS often covered with thick MIST, and the frames wet +with standing WATER?_ + +A. The temperature of the _external air_ always _falls at sun-set_, and +_chills the window-glass_, with which it comes in contact. + + +Q. _How does this account for the MIST and WATER on a WINDOW?_ + +A. As the warm vapour of the room _touches the cold glass_, it is +_chilled_ and _condensed into mist_; and the mist (collecting into +drops) _rolls down the window-frame_ in little streams of water. + + +Q. _Does the GLASS of a window COOL down more RAPIDLY than the AIR of +the room itself?_ + +A. Yes; because the air is _kept warm by fires_, and the _animal heat_ +of the people in the room; in consequence of which, the _air of a room +suffers very little diminution of heat_ from the setting of the sun. + + +Q. _Whence arises the VAPOUR of a ROOM?_ + +A. 1st--The very _air_ of the room _contains vapour_: + +2ndly--The _breath_ and _insensible perspiration_ of the inmates +_increase_ this vapour: and + +3rdly--_Hot dinners_, the _steam of tea_, &c. contribute to _increase it +still more_. + + +Q. _What is meant by "the INSENSIBLE PERSPIRATION?"_ + +A. From every part of the human body an _insensible and invisible +perspiration issues_ all night and day; not only in the hot weather of +_summer_, but also in the coldest day of _winter_. + + +Q. _If the perspiration be both INSENSIBLE and INVISIBLE, how is it +KNOWN that there IS any such perspiration?_ + +A. If you put your naked arm _into a clean dry glass cylinder_, the +_perspiration_ of your arm will soon _condense_ on the glass, like mist. + + +Q. _Why are CARRIAGE WINDOWS very SOON covered with thick MIST?_ + +A. The warm vapour of the carriage _is condensed the moment it touches +the cold glass_, and covers it over with a thick mist. + + +Q. _Why is the glass window COLD enough to condense the vapour of the +carriage?_ + +A. Because the _inside_ of the carriage is much _warmer_ than the +_outside_, and the glass window is made cold by contact with the +_external air_. + + +Q. _Where does the WARM vapour of the carriage come from?_ + +A. The warm _breath_ and _insensible perspiration_ of the persons riding +in the carriage, load the air of it with warm vapour. + + +Q. _What is the cause of the pretty FROST-WORK seen on bed-room WINDOWS +in winter-time?_ + +A. The _breath_ and _insensible perspiration_ of the sleeper (coming in +contact with the ice-cold window) is _frozen_ by the cold glass, and +forms those beautiful appearances seen in our bed-rooms in a winter +morning. + + +Q. _Why is the GLASS of a window colder than the WALLS of a room?_ + +A. Glass is a very _excellent radiator_; and, therefore, most _rapidly +parts with its heat_. + + +Q. _Why is a TUMBLER of cold WATER made quite DULL with mist, when +brought into a room FULL of PEOPLE?_ + +A. Because the _hot vapour of the room_ (coming in contact with the cold +tumbler) _is condensed upon it_; and changes its invisible and gaseous +form for that of a _thick mist_. + + +Q. _Why is a GLASS made quite DULL, by laying a HOT HAND upon it?_ + +A. The _insensible perspiration_ of the hot hand is _condensed_ upon the +cold glass, and thus made perceptible. + + +Q. _Why are WINE-GLASSES made quite DULL when they are brought into a +room FULL of COMPANY?_ + +A. The _hot vapour of the room_ (coming in contact with the cold +wine-glasses) _is condensed_ upon them, and covers them with vapour like +dew. + + +Q. _Why does this misty appearance GO OFF after a little time?_ + +A. Because the glass becomes of the _same temperature_ as the _air of +the room_, and will no longer _chill the vapour_ which touches it, and +_condense it into mist_. + + +Q. _Why is a WINE-GLASS (brought out of a CELLAR into the AIR) covered +with a thick MIST in summer-time?_ + +A. The vapour of the hot air is _condensed_ by the cold glass, and +covers it as a thick mist. + + +Q. _Why does BREATHING on a GLASS make it quite DULL?_ + +A. Because the hot breath is _condensed_ by the cold glass; and, +therefore, covers it with a thick mist. + + +Q. _Why do WALLS stand thick with WET in a sudden THAW?_ + +A. The walls (being thick) cannot _change their temperature so fast_ as +the thin air can; and, therefore, they _retain their cold_ after the +thaw has set in. + + +Q. _How does RETAINING their COLD account for their being so WET?_ + +A. As the vapour of the warm air _touches the cold wall_, it is +_chilled_ and _condensed into water_, which _sticks to the wall_, and +sometimes trickles down in little streams. + + +Q. _Why does a thick WELL-BUILT HOUSE contract more DAMP of this kind, +than an ORDINARY one?_ + +A. Because the walls are much _thicker_; and (if the frost has +penetrated _far into the bricks_) it takes a long time to reduce them to +the _same temperature as the air_. + + +Q. _Why are BANISTERS, &c. DAMP after a THAW?_ + +A. The wooden banister (being made of some very close-grained, varnished +wood) cannot _change its temperature so fast_ as the air; and, +therefore, _remains cold_ some time after the thaw has set in. + + +Q. _How does THIS account for the BANISTERS being DAMP?_ + +A. The vapour of the warm air (_coming in contact with the cold +banister_) is _chilled_, and condensed into _water upon it_. + + +Q. _Why is our BREATH VISIBLE in WINTER and NOT in SUMMER?_ + +A. In _winter_ the coldness of the air condenses our breath into +_visible vapour_; but in _summer_ the air is _not cold enough_ to +condense it into visible vapour. + + +Q. _Why are our HAIR and the BRIM of our HAT often covered with little +drops of pearly DEW in winter-time?_ + +A. The breath (issuing from our mouth and nose) _is condensed into +drops_, as it comes in contact with our cold hair or hat; and (being +condensed) hangs there in little dew-drops. + + +Q. _Why does the STEAM of a RAILWAY BOILER often pour down, like fine +rain, when the steam is "let off?"_ + +A. The steam from the steam-pipe (when the air is cold) _is condensed by +contact with the chill air_, and falls like fine rain. + + +Q. _Why is there LESS DEW when the WIND is EASTERLY, than when the wind +is WESTERLY?_ + +A. _Easterly_ winds cross the _continent of Europe_, and, (as they pass +over _land_) are _dry_ and _arid_; but _westerly_ winds cross the +_Atlantic Ocean_; and (as they pass over _water_) are _moist_ and _full +of vapour_. + + +Q. _How does the DRYNESS of an eastern wind PREVENT DEW-FALLS?_ + +A. As the easterly winds are _dry_, they _imbibe_ the moisture of the +air; and, therefore, there _is very little_ left to be condensed into +_dew_. + + +Q. _How does the MOISTNESS of a western wind PROMOTE dew-falls?_ + +A. As the westerly winds are _saturated with vapour_, they require a +_very little reduction of heat_ to cause a _copious deposition of dew_. + + +Q. _When is DEW most COPIOUSLY distilled?_ + +A. After a hot day in summer or autumn, with the _wind in the west_. + + +Q. _Why is DEW distilled most COPIOUSLY after a HOT day?_ + +A. Because the surface of the earth _radiates_ heat very freely at +sunset; and (becoming thus _much colder than the air_) _chills its +vapour_, and condenses it into dew. + + +Q. _Does not AIR radiate heat, as well as the EARTH and its various +plants?_ + +A. No. The air _never radiates heat_, nor is the air itself _made hot_ +by the _rays of the sun_. + + +Q. _How is the AIR made HOT or COLD?_ + +A. By _convection of hot or cold currents_. + + +Q. _What is meant by "CONVECTION of hot and cold currents?"_ + +A. The air (which is heated by the surface of the earth) _ascends, +warming the air_ through which it passes. _Other_ air (being warmed in a +similar way) _also ascends, carrying heat_; till _all the air_ is made +hot. + + +Q. _Is the AIR made COLD in a similar way?_ + +A. Yes. The air resting on the earth is _made cold by contact_: this +cold air makes the _air above it cold_; and cold currents or winds +_shake the whole together_, till all becomes of one temperature. + + +Q. _Why is MEAT very subject to TAINT on a MOON-LIGHT night?_ + +A. In a bright moon-light night, _meat radiates heat very freely_; and +is, therefore, soon _covered with dew_, which produces _rapid +decomposition_. + + +Q. _Why do PLANTS GROW RAPIDLY in MOON-LIGHT nights?_ + +A. In bright moon-light nights _rapid radiation is carried on_, and _dew +is plentifully deposited_ on young plants, which conduces much to their +growth and vigour. + + +Q. _Why is evening DEW INJURIOUS to HEALTH?_ + +A. Because the condensed vapours are always laden with _noxious +exhalations from the earth_: this is especially the case in _marshy_ +countries. + + +Q. _Is HONEY-DEW a similar thing to DEW?_ + +A. No. Honey-dew is a sweet liquid _shed by a very small insect_ (called +the aphis), and deposited in autumn _on the under surface_ of favourite +leaves. + + +Q. _Does HONEY-DEW INJURE leaves, or do them good?_ + +A. It injures them very much, because it _fills the pores_ of the leaf +with a _thick clammy liquid_; and, therefore, prevents the leaf from +_transpiring and absorbing_. + + +Q. _What EFFECT has honey-dew upon the APPEARANCE of a leaf?_ + +A. After a little time, the leaf (being _smothered_ and _starved_) +begins to turn a _dingy yellow_. + + +Q. _Are not ANTS very FOND of HONEY-DEW?_ + +A. Yes; and they crawl up the loftiest trees, in order to obtain it. + + +Q. _What is the cause of MIST (or earth-fog)?_ + +A. If the _night has been very calm_, a _rapid_ radiation of heat has +taken place in the earth; in consequence of which, the _air_ (resting on +the earth) _is made so cold_, that its vapour is _chilled_, and +condensed into a thick mist. + + +Q. _Why does not the MIST become DEW?_ + +A. Because the chill of the air _is so rapid_, that vapour is condensed +_faster than it can be deposited_; and (covering the earth in a mist) +_prevents any further radiation of heat_ from the earth. + + +Q. _When the earth can no longer RADIATE heat upwards, does it continue +to CONDENSE the vapour of the air?_ + +A. No; the air (in contact with the earth) becomes about _equal in +temperature_ with the surface of the earth itself; for which reason, the +mist is _not condensed into dew_, but remains _floating above the earth_ +as a thick cloud. + + +Q. _Why does this MIST seem to RISE HIGHER and HIGHER, and yet remain +quite as dense below as before?_ + +A. The air _resting on the earth_ is first chilled, and _chills the air_ +resting on _it_; the air which touches _this new layer of mist_ being +also _condensed_, layer is added to layer; and the mist seems to be +_rising_, when (in fact) it is only _deepening_. + + +Q. _Why does MIST and DEW VANISH as the SUN rises?_ + +A. Because the condensed vapour is _again rarefied by the heat of the +sun_, and separated into invisible particles. + + +Q. _Why is a DEW-DROP ROUND?_ + +A. Because every part of the drop _is equally balanced_; and, therefore, +there is no cause why _one part_ of the drop _should be further from the +centre_ than _another_. + + +Q. _Why is the DEW-DROP on a broad leaf sometimes FLATTENED?_ + +A. Whenever two or more drops of dew _roll together_, they make one +large _spheroid_ (or flattened drop). + + +Q. _Why will DEW-DROPS ROLL ABOUT CABBAGE-PLANTS, POPPIES, &c. without +wetting the surface?_ + +A. The leaves of cabbages and poppies are _covered with a very fine +powder_; and the dew-drop rolls over this fine powder, as a drop of rain +_over dust_, without wetting the surface. + + +Q. _Why does not the drop of RAIN WET the DUST over which it rolls?_ + +A. Because it is driven from grain to grain by _capillary repulsion_. + + +Q. _Why does not the DEW-DROP WET the POWDER of the CABBAGE-plant?_ + +A. Because it is driven from grain to grain by _capillary repulsion_. + + +Q. _Why will DEW-DROPS ROLL over ROSES, &c. without wetting their +petals?_ + +A. The leaves of a rose _contain an essential oil_, which prevents them +from absorbing the dew immediately. + + +Q. _Why can a SWAN or DUCK dive under water WITHOUT being WETTED?_ + +A. Because their feathers are covered _with an oily secretion_, which +repels the water. + + +Q. _What is the cause of MIST?_ + +A. When currents of air _from land_ mix with currents of air _from +water_, the currents _from the water are condensed into mist_ by the +colder currents _blowing from the land_. + + +Q. _Why are the currents of air from the LAND COLDER than those blowing +over WATER?_ + +A. Because the earth _radiates heat very freely_, and (being greatly +cooled down) _cools the air also_ which comes in contact with it. + + +Q. _Why is not the AIR, which passes over WATER, so COOL as that which +passes over LAND?_ + +A. Because _water does not cool down at sun-set_, so fast as the _land_ +does; and, therefore, the air in contact with it is _warmer_. + + +Q. _Why does not WATER cool down so fast as LAND?_ + +A. 1st--Because the _surface_ of water is _perpetually changing_, and as +fast as _one_ surface is made cold, _another_ is presented: and + +2ndly--The moment water is made cold _it sinks_, and _warmer portions of +water rise to occupy its place_: therefore, before the _surface of water +is cooled_, the _whole volume_ must be made cold; which is not the case +with land. + + +Q. _What is the cause of a "pea-soup" LONDON FOG?_ + +A. These fogs (which occur generally in the winter time) are occasioned +thus:--Some current of air (being suddenly _cooled_) _descends into the +warm streets_, preventing the rise of the smoke, and _forcing it back in +a mass_ towards the earth. + + +Q. _Why are there not ALWAYS FOGS every night?_ + +A. Because the air will always hold in solution a certain quantity of +vapour, (which varies according to its temperature): and when the air is +_not saturated with vapour_, it may be condensed without parting with +it. + + +Q. _Why are there EVER FOGS at night?_ + +A. If the air be _pretty well saturated with vapour_ during the day, as +soon as its capacity for holding vapour _is lessened by the cold night_, +it deposits some of the superabundant vapour in the form of dew or fog. + + +Q. _Why is there very OFTEN a fog over MARSHES and RIVERS at +night-time?_ + +A. The air of marshes is almost _always near saturation_; and, +therefore, the _least depression of temperature_, will compel it to +relinquish some part of its moisture in dew or fog. + + +Q. _What is the DIFFERENCE between DEW and RAIN?_ + +A. In _dew_, the condensation is made _near the earth's surface_: + +In _rain_, the drops fall _from a considerable height_; but the cause of +both is the same, viz.--COLD _condensing the vapour of the air_, when +it is near the point of _saturation_. + + +Q. _Why does MIST and FOG VANISH at sunrise?_ + +A. Because the condensed particles are again _changed into invisible +vapour_, by the heat of the sun. + + +Q. _What is the difference between a MIST and FOG?_ + +A. MIST is generally applied to _vapours condensed on marshes, rivers_, +and _lakes_. + +FOG is generally applied to _vapours condensed on land_, especially if +those vapours are _laden with smoke_. + + +Q. _What is the reason why condensed vapour sometimes forms into CLOUDS, +and sometimes into FOG?_ + +A. If the surface of the EARTH be _hotter than the air_, then the vapour +of the earth (_being chilled by the cold air_) becomes FOG: but if the +AIR be _hotter than the earth_, the vapour _rises through the air_, and +becomes CLOUD. + + +Q. _If cold air produces FOG, why is it not foggy on a FROSTY MORNING?_ + + +A. 1st--Because _less vapour is formed on a frosty day_; and + +2ndly--The vapour _is frozen upon the ground_ before it can rise from +the earth, and becomes HOAR-FROST. + + +Q. _Why are FOGS more general in AUTUMN than in spring?_ + +A. In spring _the earth is not so hot_ as it is in autumn. In AUTUMN the +_earth_ is generally _warmer than the air_; and, therefore, the vapour +(issuing from the earth) _is condensed into fog_ by the chill air. + + +Q. _Why are FOGS more common in VALLEYS than on HILLS?_ + +A. 1st--Because valleys _contain more moisture than hills_: and + +2ndly--They are _not exposed to so much wind_, (which dissipates the +vapour). + + +Q. _How does WIND dissipate FOGS?_ + +A. Either by _blowing them away_; or else by _dissolving them into +vapour again_. + + +Q. _What is HOAR-FROST?_ + +A. There are two sorts of hoar-frost: 1.--FROZEN DEW: and 2.--FROZEN +FOG. + + +Q. _What is the cause of the GROUND hoar-FROST, or frozen DEW?_ + +A. Very _rapid radiation of heat from the earth_; in consequence of +which, the _surface is so cooled down_, that it _freezes the dew_ +condensed upon it. + + +Q. _Why is HOAR-FROST seen only after a very CLEAR NIGHT?_ + +A. Unless the night has been very clear indeed, the earth will not have +thrown off heat enough by radiation, to _freeze_ the vapour condensed +upon its surface. + + +Q. _Why does HOAR-FROST very often COVER the GROUND and TREES, when the +water of rivers is not frozen?_ + +A. Hoar-frost is not the effect of cold in the _air_, but the cold of +the _earth_ (produced by excessive radiation); in consequence of which, +_the dew_ (condensed upon it) _is frozen_. + + +Q. _Why is the HOAR-FROST upon GRASS and VEGETABLES much thicker than +that upon lofty TREES?_ + +A. Because the air (resting on the _surface of the ground_) is much +colder after sun-set, than the _air higher up_; in consequence of +which, more vapour is condensed and frozen there. + + +Q. _Why is the AIR (resting on the surface of the EARTH) colder than +that in the HIGHER regions?_ + +A. Because the _earth radiates more heat_ than the _leaves of lofty +trees_; and, therefore, _condenses and freezes_ the vapour of the air +_more rapidly_. + + +Q. _Why are EVERGREENS often FROST-BITTEN, when lofty trees are NOT?_ + +A. Evergreens do not _rise far above the surface of the earth_; and (as +the air _contiguous to the earth_ is much _colder than that in the +higher regions_) therefore, the _low evergreen is often frost-bitten_, +when the lofty tree is uninjured. + + +Q. _Why are TOMB-STONES covered with HOAR-FROST, long after it has +melted from every object around?_ + +A. _White is a very bad absorbent of solar heat_; and, therefore, the +_white tomb-stone_ remains _too cold_ to thaw the frost congealed upon +its surface. + + +Q. _Why is there little or NO HOAR-FROST under SHRUBS and shadowy +TREES?_ + +A. 1st--Because the leafy shrubs and trees _arrest the process of +radiation_ from the earth: and + +2ndly--Shrubs and trees _radiate a little heat_ towards the earth; and, +therefore, the _ground beneath_ is never _cold enough to congeal the +little dew_ which rests upon it. + + +Q. _What is the cause of that HOAR-FROST which arises from FROZEN FOG?_ + +A. The thick fog (which invested the earth during the night) is +condensed _by the cold frost_ of early morning, and _congealed upon +every object_ with which it comes in contact. + + + + +CHAPTER XVII. + +5.--CONVECTION. + + +Q. _What is meant by the CONVECTION of HEAT?_ + +A. Heat communicated _by being carried_ to another thing or place; as +the hot water resting on the _bottom_ of a kettle, carries heat to the +water _through which it passes_. (_see p._ 246). + + +Q. _Are LIQUIDS good CONDUCTORS of heat?_ + +A. No; liquids are _bad conductors_; and are, therefore, made hot by +_convection_. + + +Q. _Why are LIQUIDS BAD CONDUCTORS of heat?_ + +A. Because heat _converts a liquid into steam_, and flies off with the +vapour, instead of being _conducted through the liquid_. + + +Q. _Explain how WATER is made HOT?_ + +A. The water _nearest the fire is first heated_, and (being heated) +_rises to the top;_ other cold water succeeds, is _also_ heated, and +rises in turn; and this interchange keeps going on, _till all the water +boils_. + + +Q. _Why is WATER in such continual FERMENT, when it is BOILING?_ + +A. This commotion is mainly produced by the _ascending and descending +currents_ of hot and cold water. + + +The escape of _air_ from the water contributes also to increase this +agitation. + + +Q. _How do these two currents PASS each other?_ + +A. The _hot ascending current_ passes close by the _metal sides_ of the +kettle; while the _cold descending current_ passes _down the centre_. + + +Q. _Why does BOILING WATER BUBBLE?_ + +A. The bubbles are _portions of steam_ (formed at the bottom of the +vessel) which _rise to the surface_, and escape into the air. + + +Q. _Why does a KETTLE RUN OVER, when the water BOILS?_ + +A. As the heat insinuates itself between the particles of water, _it +drives them asunder_; and (as the particles of water are _driven apart +from each other_) the _same_ vessel will no longer hold the expanded +water, and some runs over. + + +Q. _Why does a KETTLE SING, when it is ABOUT to BOIL?_ + +A. Water contains _a great deal of air_, which (being expanded by the +heat of the fire) escapes by fits _through the spout of the kettle_; +which sings in the same way as a trumpet does, when a person blows in +it. + + +Q. _Why does WATER BOIL?_ + +A. Boiling is the effect of a _more violent escape of air_ from the +heated water; when, therefore, the air is _not permitted to escape_, +water will _never boil_. + + +Q. _Why is HEAT applied to the BOTTOM, and not to the top of a KETTLE?_ + +A. Because the heated water _always ascends to the surface_, heating the +water through which it passes: if, therefore, heat were applied to the +_top of a vessel_, the water _below the surface_ would _never be +heated_. + + +Q. _As the lower part of a GRATE is made RED-HOT by the fire ABOVE, why +would not the WATER boil, if fire were applied to the TOP?_ + +A. The _iron_ of a grate is an _excellent conductor_; and, therefore, if +_one_ part be heated, the heat is conducted to _every other part_: but +_water_ is a _very bad conductor_, and will not diffuse heat in a +similar way. + + +Q. _How do you know that WATER is a BAD CONDUCTOR of heat?_ + +A. When a blacksmith immerses his red-hot iron in a tank of water, the +water which _surrounds_ the red-hot iron is made _boiling hot_, but the +water _below_ the surface remains quite cold. + + +Q. _If you wish to COOL LIQUIDS, where should the cold be applied?_ + +A. To the _top of the liquid_; because the _cold_ portion will always +_descend_, and allow the warmer parts to come in contact with the +cooling substance. + + +Q. _Does BOILING water get hotter by being KEPT on the FIRE?_ + +A. No; not if the steam be suffered to escape. + + +Q. _Why does not boiling water get HOTTER, if the steam be suffered to +ESCAPE?_ + +A. Because _as fast as the water boils_, it is converted into _steam_; +and the steam _carries away_ the additional heat, as fast as it is +communicated. + + +Q. _Is STEAM visible or INVISIBLE?_ + +A. Steam is _invisible_; but when it comes in contact with the air +(being _condensed into small drops_) it instantly becomes visible. + + +Q. _How do you know that STEAM is INVISIBLE?_ + +A. If you look at the spout of a boiling kettle, you will find that the +steam (which issues from the spout) is always invisible _for about half +an inch_; after which, _it becomes visible_. + + +Q. _Why is the steam INVISIBLE for only HALF AN INCH, and not either all +INVISIBLE or all VISIBLE?_ + +A. The air is not able to condense the steam as it first issues from the +spout, but when it _spreads_ and comes in contact with a larger volume +of air, the _invisible steam_ is readily condensed into _visible drops_. + + +Q. _Why is our BREATH VISIBLE in winter-time?_ + +A. Because _it is condensed by the cold air_ into small drops, which are +visible to the eye. + + +Q. _Why do STEAM-ENGINES sometimes BURST?_ + +A. Steam is very _elastic_; and this elasticity increases in a greater +proportion than the heat which produces it; unless, therefore, some +_vent_ be freely allowed, the steam heaves and swells, till it bursts +the vessel which confined it. + + +Q. _What BECOMES of the steam, after it has been condensed?_ + +A. It is _dissolved by the air_, and forms a part of its invisible +vapour. + + +Q. _Is AIR a good CONDUCTOR?_ + +A. No; _air is a very bad conductor_, and is heated (like water) _by +convection_. + + +Q. _How is a ROOM WARMED by a STOVE?_ + +A. The air _nearest the fire_ is made hot _first_; _the cold air +descends_, is heated also, and rises in turn; and this goes on, _till +all the air of the room is warmed_. + + +Q. _Why are FIRES placed on the FLOOR of a room, and not towards the +CEILING?_ + +A. As heated air always _ascends_, if the fire were not _near the +floor_, the lower part of the air (which we want to be the warmest) +would never be benefited by the fire at all. + + +Q. _If you take a POKER out of the fire, and hold the HOT END DOWNWARDS, +why is the HANDLE so intensely HOT?_ + +A. Because the hot end of the poker _heats the air around it_, and this +hot air (in its ascent) _scorches the poker_, and the _hand which holds +it_. + + +Q. _How should a RED-HOT POKER be carried so as not to BURN our +fingers?_ + +A. With the hot end _upwards_; because then the air (heated by the +poker) _would not pass over our hand_ to scorch it. + + +Q. _Why is a POKER (resting on the FENDER) COLD; but if it leans against +the STOVE, intensely warm?_ + +A. The poker is an _excellent conductor_; while, therefore, it rests +against the hot stove, the heat of the stove is _conducted into the +poker_; but when it _rests on the fender_, it does not come in _contact +with the hot stove_. + + +Q. _Why does it feel so COLD, when it rests on the FENDER?_ + +A. Not being so warm as our hand, it _imbibes the heat from it_ with +such _rapidity_, that our loss of heat is _palpable_, and produces the +sensation of coldness. + + +Q. _Why are FLUES (which are carried through a church or room) always +BLACKENED with BLACK LEAD?_ + +A. In order that the heat of the flue _may be more readily diffused_ +throughout the room. Black lead radiates heat more freely than any other +known substance. + + +Q. _Why do country people touch the thick end of an EGG with their +TONGUE, to know if it be STALE or not?_ + +A. The thick end of an egg always contains _a little air_ (between the +shell and the white); but, when the egg is stale, _the white shrinks_, +and the air expands. + + +Q. _How can the TONGUE tell from this, whether the egg be STALE or FRESH +laid?_ + +A. As air is a _very bad conductor_, if the egg be _stale_, it will feel +much _warmer to the tongue_, than if it be new-laid. + + +Q. _Why will the big end of an egg feel WARMER to the tongue, because it +contains more AIR?_ + +A. As air is a _bad conductor_, it will draw off the heat of the tongue +_very slowly_, and, therefore, _appear warm_; but when there is only a +_very little air in the egg_ (as the _white_ is a pretty good +conductor), the heat of the tongue will be _more rapidly_ drawn off, and +the egg _appear colder_. + + +Q. _Why is the large END of an EGG CRACKED, when put into a saucepan to +boil?_ + +A. _To let the air out_; if the large end were _not cracked_, the air +(expanded by the heat) _would enter the white of the egg_, and give it +an _offensive taste_. + + + + +PART II. + + + + +AIR. + + + + +CHAPTER XVIII. + + +Q. _Of what is atmospheric AIR composed?_ + +A. Principally of two gases, _oxygen_ and _nitrogen_; mixed together in +the following proportion: viz. 1 part of oxygen, to 4 parts of nitrogen. + + +Q. _What are the uses of the OXYGEN of the air?_ + +A. It is the _oxygen_ of the air which _supports combustion_, and +_sustains life_. + + +Q. _What is meant when it is said, that the OXYGEN of the air "SUPPORTS +COMBUSTION?"_ + +A. It means this; that it is the _oxygen of the air_ which makes _fuel +burn_. + + +Q. _How does the OXYGEN of the air make FUEL BURN?_ + +A. The fuel being decomposed (by heat) into _hydrogen_ and _carbon_; the +_carbon combines with the oxygen of the air_, and produces _combustion_. + + +Q. _What does the combination of carbon and oxygen produce?_ + +A. The _carbon of the fuel_ combining with the _oxygen of the air_ makes +CARBONIC ACID GAS. (_see pp. 36, 37_). + + +Q. _What becomes of the HYDROGEN of the FUEL?_ + +A. Hydrogen (being very inflammable) _burns with a blaze_, and is the +cause of the _flame_ which is produced by combustion. (_see p. 34_). + + +Q. _What becomes of the NITROGEN of the air, amidst all these changes +and combinations?_ + +A. The _nitrogen of the air escapes_, and is _absorbed by the leaves_ of +grass, trees, and various other vegetables. + + +Q. _What is meant when it is said, that OXYGEN "SUSTAINS LIFE?"_ + +A. It means this: if a person _could not inhale oxygen_, he would _die_. + + +Q. _What GOOD does this inspiration of OXYGEN do?_ + +A. 1st--It gives _vitality to the blood_: and + +2ndly--It is the _cause of animal heat_. + + +Q. _How is FOOD converted into BLOOD?_ + +A. After it is swallowed, it is dissolved in the stomach into a _grey +pulp_; it then passes into the intestines, and is converted by the +"bile" _into a milky substance_ (called _chyle_). + + +Q. _What BECOMES of the milky substance, called CHYLE?_ + +A. It is absorbed by the vessels called "_lacteals_," and poured into +the veins _on the left side of the neck_. + + +Q. _What becomes of the chyle AFTER it is POURED into the VEINS?_ + +A. It then _mingles with the blood_, and is itself _converted into +blood_. + + +Q. _How does the OXYGEN we inhale MINGLE with the BLOOD?_ + +A. The oxygen of the air mingles with the blood _in the lungs_, and +converts it into a _bright red colour_. + + +Q. _What colour is the blood BEFORE it is oxydized in the lungs?_ + +A. _A dark purple._ The oxygen turns it to _a bright red_. + + +Q. _Why are PERSONS so PALE who live in CLOSE ROOMS and CITIES?_ + +A. The blood derives its redness from the _oxygen_ of the air inhaled; +but, as the air in close rooms and cities _is not fresh_, it is +_deficient in oxygen_, and cannot turn the blood to a beautiful bright +red. + + +Q. _Why are PERSONS who live in the OPEN AIR and in the country, of a +RUDDY complexion?_ + +A. As the blood derives its bright red colour from the _oxygen_ of the +air inhaled, therefore, country-people (who inhale _fresh air_) are more +ruddy than citizens. + + +Q. _Why is not the air in CITIES so FRESH as that in the COUNTRY?_ + +A. Because it is impregnated with the _breath of its numerous +inhabitants_, the _odour of its sewers_, the _smoke of its fires_, and +many other impurities. + + +Q. _How does the COMBINATION of OXYGEN with the BLOOD produce animal +HEAT?_ + +A. The principal element of the blood is _carbon_, which (combining with +the oxygen of the air inhaled) produces _carbonic acid gas_, (in the +same way as burning fuel.) (_see pp._ 33, 36). + + +Q. _What becomes of the NITROGEN of the air, after the oxygen enters the +blood?_ + +A. The nitrogen is _exhaled_, and taken up by the leaves of trees and +other vegetables. (_see p._ 35). + + +Q. _Why does the vitiated air (after the oxygen has been absorbed) COME +OUT of the MOUTH, and not sink into the stomach?_ + +A. The vitiated air (being _heated by the heat of the body_) _ascends +naturally_, and passes by the _heavier fresh air_ (which we inhale) +without obstruction or injury. + + +Q. _If (both in combustion and in respiration) the OXYGEN of the air is +CONSUMED, and the NITROGEN REJECTED--Why are not the PROPORTIONS of the +AIR DESTROYED?_ + +A. Because the _upper surface of vegetable leaves_ (during the day) +_gives out oxygen_ and _absorbs nitrogen_, and thus the proper balance +is perpetually restored. + + +Q. _Show how God has made ANIMAL and VEGETABLE life DEPENDENT on each +other?_ + +A. _Animals_ require _oxygen_ to keep them alive, and _draw it from the +air_ by inspiration; the upper surface of _leaves_ (all day long) _gives +out oxygen_, and thus supplies the air with the _very gas_ required by +man and other animals. + + +Q. _Do not animals EXHALE the VERY GAS needed by VEGETABLES?_ + +A. Yes; animals reject the _nitrogen of the air_ (as not suited to the +use of animal life), but _vegetables absorb it_, as it is the food they +live on; and thus the vegetable world restores the equilibrium of the +air, disturbed by man and other animals. + + +Q. _Is AIR a good CONDUCTOR?_ + +A. No; air is a very _bad conductor_. + + +Q. _How is AIR HEATED?_ + +A. By "convective currents." + + +Q. _What are meant by "CONVECTIVE CURRENTS?"_ + +A. When a portion of air is heated, _it rises upward in a current_, +carrying the heat with it: other _colder air succeeds_, and (being +_heated_ in a similar way) _ascends also_; and these are called +convective currents. + + +("Convective currents;" so called from the Latin words, cum-vectus +(_carried with_) because the _heat_ is "carried with" the current.) + + +Q. _Is AIR HEATED by the RAYS of the SUN?_ + +A. No; air is _not heated_ (in any sensible degree) _by the action of +the sun's rays_ passing through it. + + +Q. _Why then is the AIR HOTTER on a SUNNY DAY, than on a CLOUDY one?_ + +A. On a fine day, the sun _heats the surface of the earth_, and the air +(resting on the earth) _is heated by contact_; as soon as it is heated +_it ascends_, and _other_ air succeeding is _heated in a similar way_, +till all is heated by convection. + + +Q. _If AIR be a BAD CONDUCTOR, why does hot IRON get COLD, by being +EXPOSED to the AIR?_ + +A. A piece of hot iron exposed to the air, is made cold--1st--By +"convection;" and + +2ndly--By "radiation." + + +Q. _How is hot iron (exposed to the air) made cold by CONVECTION?_ + +A. The air around the iron (being intensely heated by contact) rapidly +ascends, _carrying some of its heat with it_: other air succeeds, +_absorbs more heat_, ascends, and gives place to that which is _colder_; +till the hot iron _is cooled completely down_. + + +Q. _How is hot iron cooled by RADIATION?_ + +A. While the heat of the iron is being carried off by "convection," it +is _throwing off heat_ (on all sides) _by radiation_. + + +Q. _What is meant by RADIATION?_ + +A. Heat emitted (in all directions) from any surface, by _innumerable +rays_. + + +Q. _Why is BROTH COOLED by being left exposed to the AIR?_ + +A. Hot broth throws off _some_ heat by _radiation_; but it is _mainly_ +cooled down _by convection_. + + +Q. _How is hot BROTH cooled down by CONVECTION?_ + +A. The air _resting on the hot broth_ (being heated) _ascends_; _colder_ +air succeeding _absorbs more heat_, and _ascends also_; and this process +is repeated, till the broth is _made cool_. + + +Q. _Why is hot TEA and BROTH COOLED faster, for being STIRRED about?_ + +A. 1st--The agitation assists the liquor in _bringing its hottest +particles to the surface_: + +2ndly--The action of stirring _agitates the air_, and brings it +_quicker_ to the broth or tea: and + +3rdly--As the hottest particles are more rapidly brought into contact +with the air, therefore _convection is more rapid_. + + +Q. _Why is HOT TEA, &c. cooled more rapidly by BLOWING it?_ + +A. Because the heated air is _blown more rapidly away_; in consequence +of which, _cold air more rapidly succeeds_ to _absorb heat_ from the +surface of the tea or broth. + + +Q. _If a shutter be closed in the day-time, the stream of light +(piercing through the crevice) seems in CONSTANT AGITATION. WHY is +this?_ + +A. The air (in the sun-beam piercing through the shutter-crevice) is +_more heated_, than _that in its neighbourhood_; the convective current, +therefore, is _distinctly seen_, where little motes and particles of +dust are _thrown into agitation_ by the _violence_ of the current. + + +Q. _Why is the GALLERY of a CHURCH or theatre HOTTER than the AISLE or +pit?_ + +A. The hot air ascends from the _bottom_ to the _top of the room_, and +cold air (from the doors and windows) flies to the _bottom_ to supply +its place. + + +Q. _Why does a CROWDED ROOM produce HEAD-ACHE?_ + +A. Because we breathe air _vitiated by the crowd_. + + +Q. _How does a CROWD VITIATE the AIR of a ROOM?_ + +A. Whenever we breathe, the elements of the air are _separated_ in the +lungs, _some of the oxygen is absorbed by the blood_, and some of it is +converted into _carbonic acid gas_, and exhaled with the nitrogen. + + +Q. _Is ALL the NITROGEN REJECTED by the lungs?_ + +A. Yes; all the nitrogen of the air is always exhaled. + + +Q. _What is CARBONIC ACID GAS?_ + +A. As carbon has a very great affinity for oxygen, therefore, whenever +they are exposed to heat, they _combine_, and form carbonic acid gas +(or what is vulgarly called fixed air). + + +Q. _Is CARBONIC ACID GAS wholesome?_ + +A. No; it is quite _fatal to animal life_; and whenever it is inhaled, +it acts like a narcotic poison, (producing drowsiness which ends in +death). + + +Q. _Why is a CROWDED ROOM UNWHOLESOME?_ + +A. Because the oxygen of the air is either _absorbed by the lungs_, or +substituted for _carbonic acid gas_, which is a noxious poison. + + +Q. _Mention the historical circumstances, so well known in connection +with the "BLACK HOLE of CALCUTTA."_ + +A. In the reign of George II, the Raja (or Prince) of Bengal[12] marched +suddenly to Calcutta to drive the English from the country; as the +attack was unexpected, the English were obliged to submit, and 146 +persons were taken prisoners. + +[12] The Sur Raja, at Dowlat; a young man of violent passions, who had +but just succeeded to the throne. A. D. 1756. + + +Q. _What became of these prisoners?_ + +A. They were driven into a place about 18 feet square, and 15 or 16 feet +in height, with only two small grated windows. 123 of the prisoners died +in one night; and (of the 23 who survived) the larger portion died of +putrid fevers, after they were liberated in the morning. + + +Q. _Why were 123 persons SUFFOCATED in a few hours, from confinement in +this close hot PRISON-hole?_ + +A. Because the _oxygen of the air_ was soon consumed by so many lungs, +and its place supplied by _carbonic acid_ exhaled by the hot breath. + + +Q. _Why do persons in a crowded CHURCH feel DROWSY?_ + +A. 1st--Because the crowded congregation _inhale a large portion of the +oxygen of the air_, which alone can sustain vitality and healthy action: +and + +2ndly--The air of the church is impregnated with carbonic acid gas, +which (being a strong narcotic) produces drowsiness in those who inhale +it. + + +Q. _Why did the captives in the BLACK HOLE die SLEEPING?_ + +A. 1st--Because the _absence of oxygen_ quickly affects the vital +functions, depresses the nervous energies, and produces a lassitude +which ends in death: and + +2ndly--The _carbonic acid gas_ inhaled by the captives (being a narcotic +poison) would also produce _drowsiness and death_. + + +Q. _Why do PERSONS, who are so much in the OPEN AIR, enjoy the best +HEALTH?_ + +A. Because the air they inhale is _much more pure_. + + +Q. _Why is COUNTRY AIR more PURE than the air in CITIES?_ + +A. 1st--Because there are fewer inhabitants to vitiate the air: + +2ndly--There are more trees to restore the equilibrium of the vitiated +air: and + +3rdly--The free circulation of air keeps it pure and wholesome (in the +same way as running streams are pure and wholesome, while stagnant +waters are the contrary). + + +Q. _Why does the SCANTINESS of a country POPULATION render the COUNTRY +AIR more PURE?_ + +A. Because the fewer the inhabitants, _the less carbonic acid will be +exhaled_; and thus country people will inhale _pure oxygen_, instead of +air _impregnated with the narcotic poison_, called carbonic acid gas. + + +Q. _Why do TREES and FLOWERS help to make country AIR WHOLESOME?_ + +A. Because trees and flowers _absorb the carbonic acid_ generated by the +lungs of animals, putrid substances, and other noxious exhalations. + + +Q. _Why is the AIR of CITIES LESS wholesome than COUNTRY air?_ + +A. 1st--Because there are _more inhabitants_ to vitiate the air: + +2ndly--The _sewers_, _drains_, _bins_, and _filth of a city_, very +greatly vitiate the air: + +3rdly--The streets and alleys prevent a free circulation: and + +4thly--Besides all this, there are fewer trees to absorb the excess of +carbonic acid gas, and _restore the equilibrium_. + + +Q. _Why are PERSONS who live in CLOSE ROOMS and crowded CITIES, +generally SICKLY?_ + +A. Because the air they breathe is not pure, but is both _defective in +oxygen_, and impregnated with _carbonic acid gas_. + + +Q. _Where does the CARBONIC ACID of close ROOMS and CITIES COME from?_ + +A. From the lungs of the inhabitants, the sewers, drains, and so on: +besides, trees and gardens are not numerous enough _to absorb the +noxious gas_ as fast as it is generated. + + +Q. _What BECOMES of the CARBONIC ACID of crowded cities?_ + +A. Some of it is _absorbed by vegetables_, and the rest is _blown away +by the wind_, and diffused through the whole volume of the air. + + +Q. _Does not this constant diffusion of carbonic acid affect the PURITY +of the WHOLE AIR?_ + +A. No; because after it is thus diffused, _it is carried to various +lands_, and _absorbed_ in its passage by the _vegetable world_. + + +Q. _Why do persons who ascend in balloons feel intense pain in their +eyes and ears?_ + +A. Because the air of the upper regions is _more rarefied than the air +on the earth_; and the air inside their bodies (seeking to become of the +same rarity) _bursts through their eyes and ears_, producing an intense +pain. + + +Q. _Why is it often PAINFUL, and difficult to BREATHE, on a MOUNTAIN +top?_ + +A. Because the pressure of air on the mountain top is _not so great as +on the plain_; and the air inside our bodies (seeking to become of the +same rarity) _bursts through the pores of the body_, and produces great +pain. + + +Q. _Why do we feel OPPRESSED just PREVIOUS to a STORM?_ + +A. Because the air is _greatly rarefied by heat and vapour_; and the air +inside us (seeking to become of the same rarity) produces an oppressive +and suffocating feeling. + + +Q. _Why do DIVERS suffer great pain in their eyes and ears under water?_ + +A. Because the air at the bottom of the sea _is more dense_ than the air +_on the surface_; and while the air inside the diver's body is settling +into the same density, he feels oppressed with pain, especially in the +ears. + + +Q. _Why is this PAIN felt especially about the EARS of a DIVER?_ + +A. The ear is fitted with a small membrane called _the drum_ (or +tympanum), through which the dense air bursts, and the rupture very +often _produces incurable deafness_. + + +Q. _Why do our CORNS ache just previous to RAIN?_ + +A. Previous to rain, the density of air is greatly lowered (as every one +knows from the fall of the barometer); in consequence of an unequal +pressure, _our feet swell_; but the hard corn, _not being elastic_, is +painfully stretched and pressed. + + +(Some of this pain is due to electricity.) + + +Q. _Why do CELLARS feel WARM in WINTER?_ + +A. As the external air has not free access into cellars, they remain at +a _pretty even temperature_, which (in winter time) is about 10 degrees +_warmer_ than the external air. + + +Q. _Why do CELLARS feel COLD in SUMMER time?_ + +A. As the external air has not free access into cellars, they remain at +a _pretty even temperature_, which (in summer time) is about 10 degrees +_colder_ than the external air. + + +Q. _Why does lightning strike the OAK-tree more frequently than any +OTHER tree?_ + +A. 1st--Because the _grain of the oak, being closer_ than that of any +other tree, renders it a better conductor: and + +2ndly--The _sap_ of the oak contains a _large quantity of iron_ in +solution, which is a most admirable conductor of lightning. + + +Q. _Why does AIR rust IRON?_ + +A. The _oxygen of the air_ combines with the _surface of the iron_, and +produces _oxide of iron_, which is generally called rust. + + +This rust is a species of combustion. + + +Q. _Why does hot iron SCALE and PEEL off, when struck with a HAMMER?_ + +A. The _oxygen of the air_ very readily unites with _the surface of the +hot iron_, and forms a metallic oxide (or rust) which scales off when +struck with a hammer. + + +Q. _Does iron RUST in DRY air?_ + +A. No; iron undergoes no change in dry air. + + +Q. _Why do STOVES and FIRE-IRONS become RUSTY, in rooms which are not +OCCUPIED?_ + +A. Because the air is damp; and moist air _oxidizes_ (or rusts) iron and +steel. + + +Q. _In what part of the year is it most difficult to keep STOVES and +FIRE-IRONS BRIGHT?_ + +A. In _autumn and winter_; because the capacity of the air for holding +water _being on the decrease_, its vapour is deposited on every-thing +with which it comes in contact. + + +Q. _Why does GREASING iron prevent its becoming RUSTY?_ + +A. Because _grease_ prevents the humidity of air from coming in contact +with the _surface of the iron_. + + +Q. _Why do not STOVES rust so frequently as POKERS and TONGS?_ + +A. Because stoves are generally _covered with plumbago_, or black lead. + + +Q. _What is plumbago, or black lead?_ + +A. A mixture of charcoal and iron filings. + + +A most excellent varnish to prevent rust is made of 1 pint of fat oil +varnish, mixed with 5 pints of highly rectified spirits of turpentine, +rubbed on the iron or steel with a piece of sponge. This varnish may be +applied to bright stoves and even mathematical instruments, without +injuring their delicate polish. + + +Q. _Why does ornamental STEEL (of a purple or LILAC colour) rust more +readily than polished WHITE steel?_ + +A. Because the lilac tinge is produced by _partial oxidation_; and the +process which forms rust has, therefore, _already_ commenced. + + +Q. _How can lilac STEEL be kept FREE from RUST?_ + +A. By keeping it in a very _dry place_; for then no additional oxygen +will come in contact with it, to increase its amount of rust. + + +Q. _Do any OTHER metals (besides iron) combine rapidly with oxygen?_ + +A. Yes; copper, lead, mercury, and even silver to some extent. + + +Q. _Why does COPPER TARNISH?_ + +A. The tarnish of copper is caused by its _oxidation_; that is, the +oxygen of the air combines with the surface of the copper, and instead +of _rusting it_, covers it with a _dark tarnish_. + + +Q. _Why does LEAD lose its BRIGHTNESS, and become DULL and of a DARKER +hue, by being exposed to the air?_ + +A. The vapour of the air combines with the lead, and _oxidizes its +surface_; but instead of becoming _rusty_, the surface becomes _dull_, +and of a _darker colour_. + + +Q. _Why is it difficult to keep SILVER BRIGHT?_ + +A. Because the vapour of the air oxidizes its surface, and _tarnishes_ +it. + + +Q. _Why do silver TEA-POTS and SPOONS tarnish more quickly than silver +ore or bullion?_ + +A. Because alloy (of some _baser_ metal) is used to make it more _hard +and lasting_; and this _alloy_ oxidizes more quickly than silver itself. + + +Q. _Why does GERMAN silver turn a dingy yellow in a few hours?_ + +A. German silver has a great affinity for oxygen, and shows its +oxidation by a _sickly yellow tarnish_, instead of rust. + + +Q. _If quicksilver (or mercury) is tarnished like copper and lead,--Why +does it preserve its BRILLIANCY in BAROMETERS and THERMOMETERS?_ + +A. Because _air_ is excluded from it, and no moisture comes in contact +with it to _oxidize_ (or _tarnish_ it). + + +Q. _Is GOLD affected by the atmosphere?_ + +A. Not readily: gold will never combine with oxygen of itself, (or +without aid). + + +Q. _Which of the METALS is capable of resisting oxidation altogether?_ + +A. Plat'inum; in consequence of which, the graduated arcs of delicate +instruments for observation are made of plat'inum instead of any _other_ +metal. + + +Q. _Why is PLAT'INUM used for the graduated arcs of delicate +mathematical instruments, instead of any other metal?_ + +A. Because it will never oxidize; but retain its _bright surface_ in all +weathers free from both _rust and tarnish_. + + +Q. _Before plat'inum was discovered, which of the metals was employed +for the same purpose?_ + +A. Gold. + + +Platinum, (a white metal), so called from "plata," the Spanish word for +_silver_. It was first introduced into England by Mr. Wood, (A. D. 1749) +from South America. + + +Q. _For what other SCIENTIFIC purposes is PLAT'INUM now used?_ + +A. For crucibles in which _acids_ are employed, and for galvanic +batteries. + + +Q. _Why are CRUCIBLES (in which acids are employed) made of PLAT'INUM?_ + +A. Because the acid would act upon _other metals_, or upon _glass_, and +prevent the experimenter's success. + + +Q. _Which of the METALS have the GREATEST affinity to OXYGEN?_ + +A. Those called _potassium_ and _sodium_. + + +Potassium and sodium derive their names from potash and soda. Potassa is +the oxide of potassium; and soda is the oxide of sodium. + + +Q. _How is the affinity of potassium and sodium for oxygen shewn?_ + +A. They _decompose water_ the moment they are brought into contact with +it. + + +Q. _What effect has POTASSIUM on WATER?_ + +A. It _catches fire_ the moment it is thrown into water, and burns with +a vivid flame, which is still further increased by the combustion of +_hydrogen_ separated from the water. + + +(N.B. Water is composed of oxygen and hydrogen; and potassium separates +the two gases.) + + +Q. _What effect has SODIUM on WATER?_ + +A. It does _not take fire_ as potassium does, but undergoes very rapid +_oxidation_. + + +Q. _Is the FURR of KETTLES an oxide?_ + +A. No; the furr (or deposit of boiling water) is a precipitate of +_lime and mineral salt_, separated from the water by the process of +boiling. + + +Q. _Is not this FURR of boiling water often DANGEROUS?_ + +A. Yes; especially in _tubular boilers_, such as those employed in +railways. + + +Q. _Why is this FURR especially TROUBLESOME in RAILWAY engines?_ + +A. Because it is a _bad conductor of heat_; in consequence of which, it +hinders the evaporating effect of the fire, and prevents the economy of +fuel. + + +Q. _Why is this FURR especially DANGEROUS in RAILWAY engines?_ + +A. Because when it is deposited in the boilers, they are likely to +become _over-heated_; and then _explosion_ will take place from the +sudden generation of highly elastic steam. + + +Q. _Why cannot RAILWAY engines be fed with BRACKISH WATER?_ + +A. Because brackish water contains _mineral salt_, which makes a much +larger deposit of furr, than that which contains _only vegetable +matter_. + + + + +CHAPTER XIX. + +CARBONIC ACID GAS. + + +Q. _What is CHOKE DAMP?_ + +A. _Carbonic acid gas_ accumulated at the bottom of wells and pits, +which renders them noxious, and often fatal. + + +Q. _Why is not this carbonic acid TAKEN UP by the AIR, and DIFFUSED, as +it is in cities?_ + +A. Because (being _heavier than common air_) it cannot _rise from the +well or pit_; and no wind can get to it to blow it away. + + +Q. _Is CARBONIC ACID WHOLESOME?_ + +A. No; it is _fatal to animal life_, when inhaled through the mouth; +acting on the stomach, _as a narcotic poison_ (i. e. a poison which +produces death from drowsiness). + + +Q. _How can any one KNOW, if a place be infested with CARBONIC ACID +GAS?_ + +A. If a pit or well contain carbonic acid, _a candle_ (let down into it) +_will be instantly extinguished_. The rule, therefore, is this--Where a +_candle will burn, a man can live_; but _what will extinguish a candle_, +will _also destroy life_. + + +Q. _Why does a MINER lower a CANDLE into a mine, before he descends?_ + +A. Because the _candle will be extinguished_, if the mine contains +carbonic acid gas: but if the candle is _not extinguished_, the mine is +_safe_, and the man may fearlessly descend. + + +Q. _Why are PERSONS sometimes KILLED, by leaning over BEER VATS?_ + +A. Vats (where beer has been made) contain a _large quantity of carbonic +acid gas_, produced by the "vinous fermentation" of the beer; and when a +man incautiously _leans over a beer vat_, and inhales the carbonic acid, +he is immediately _killed_ thereby. + + +Q. _Why are PERSONS often KILLED, who enter BEER VATS to clean them?_ + +A. Carbonic acid (being _heavier than atmospheric air_) often rests upon +the _bottom of a vat_: when, therefore, a person enters the vat, and +_stoops to clean the bottom_, he inhales the pernicious gas, which +_kills_ him. + + +Q. _Why are the JUNGLES of Jarva and Hindostan so FATAL to life?_ + +A. Because vast quantities of _carbonic acid_ are thrown off by decaying +_vegetables_; and (as the wind cannot penetrate the thick brushwood to +blow it away) _it settles there_, and destroys animal life. + + +Q. _Why are PERSONS sometimes KILLED by having a CHARCOAL FIRE in their +bed-rooms?_ + +A. When charcoal is burned, the _carbon of the charcoal_ unites with the +_oxygen of the air_, and forms _carbonic acid gas_, which is a narcotic +poison. + + +Q. _Why does the carbonic acid gas of a CHARCOAL FIRE RISE and DISPERSE +itself about the room; whereas the carbonic acid gas of a BEER VAT +SETTLES near the FLOOR?_ + +A. The carbonic acid gas of a charcoal fire _is heated_ by the +_combustion of the fuel_, and rises; but the carbonic acid gas of a beer +vat is _not_ heated, and, therefore, rests on the _bottom of the vat_. + + +Q. _Why do persons throw LIME into BINS to PREVENT their offensive +SMELL, in summer time?_ + +A. Bins contain large quantities of _carbonic acid gas_, which readily +_combines with lime_, and produces "_carbonate of lime_," which is +entirely free from all offensive odour. + + +Q. _Why do persons throw LIME into SEWERS in summer time?_ + +A. Sewers (like bins) contain large quantities of _carbonic acid_, which +readily _combines with lime_, and produces _carbonate of lime_; and thus +the offensive gas of the sewer is neutralized. + + +Q. _Can carbonic acid be removed in any way BESIDES by LIME?_ + +A. Yes; _water_ thrown into a pit will disperse the carbonic acid. + + +Q. _What effect has WATER on CARBONIC ACID GAS?_ + +A. Water (under _pressure_) _absorbs_ carbonic acid gas; and _parts_ +with it (when the _pressure is removed_) in the form of EFFERVESCENCE. + + +Q. _Why does AERATED WATER effervesce, when the CORK is removed?_ + +A. While the _cork was fastened down_, the water _absorbed_ the carbonic +acid; but the moment _the pressure is removed_ (by taking out the cork) +the gas is given out with _effervescence_. + + +Q. _Why does SODA WATER effervesce?_ + +A. Soda water contains 8 times its own bulk of carbonic acid gas, which +makes its escape in _effervescence_, the moment that the _cork is +removed_. + + +Q. _Why does GINGER POP fly about in froth, when the string of the cork +is cut?_ + +A. All vinous fermentation produces carbonic acid gas. While the _cork +is fast_, the water of the liquor _absorbs_ the carbonic acid; but the +moment that the _pressure is removed_, the gas is given off in +_effervescence_. + + +Q. _Why does BOTTLED ALE froth, more than DRAUGHT ale?_ + +A. Because the _pressure_ is greater in a _bottle_ than in a tub which +is perpetually tapped: and effervescence is always produced _in +proportion to the pressure_. + + +Q. _Why does bottled ALE and PORTER become "LIVELY" and FROTHY by being +SET before the FIRE?_ + +A. The heat of the fire _expands the air_ (between the liquid and the +cork), and as this air expands, _it presses the liquid down_, which +causes effervescence. + + +Q. _What produces the FROTH of BOTTLED PORTER?_ + +A. The _carbonic acid gas_, produced by its _vinous fermentation_; which +is _absorbed by the liquor_ so long as the bottle is _well corked_, but +is _given off in froth_ as soon as the pressure of the cork is +_removed_. + + +Q. _What gives the pleasant ACID taste to soda water, ginger beer, +champagne, and cider?_ + +A. The presence of _carbonic acid_, generated by fermentation, and +liberated by effervescence when the pressure of the cork is removed. + + +Q. _Why does fresh SPRING WATER SPARKLE, when poured from one vessel to +another?_ + +A. Because fresh spring and pump water contain _carbonic acid_; and it +is the presence of this gas _which makes the water sparkle_. + + +Q. _What is the FERMENTATION of BEER and WINE?_ + +A. The production of carbonic acid gas and al'cohol. + + +Q. _How is CARBONIC ACID GAS produced by FERMENTATION?_ + +A. Malt and fruit _both contain sugar_; and sugar consists of carbon, +oxygen, and hydrogen. In fermentation, a part of the _carbon and oxygen_ +of the sugar escape, _in the form of carbonic acid gas_. + + +Carbonic acid gas is a compound of carbon and oxygen, in the following +proportions:--3 lbs. of carbon and 8 lbs. of oxygen will form 11 lbs. of +carbonic acid gas. Now, 100 lbs. of white sugar contains 43 lbs. of +carbon; 50 lbs. of oxygen; and 7 lbs. of hydrogen. + + +Q. _How is AL'COHOL produced by FERMENTATION?_ + +A. The _hydrogen of the sugar_ combines with the _residue of the oxygen +and carbon_ to form "AL'COHOL." + + +Q. _What is AL'COHOL?_ + +A. Al'cohol is the _spirit_ of wine or beer, obtained by _fermentation_. + + +(100 gallons of alcohol consist of 38 gallons of oxygen; 43-1/2 of +carbon; 15 of hydrogen; and 3-1/2 of nitrogen.) + + +Q. _Why is BARLEY MALTED?_ + +A. Because _germination_ is produced by the artificial heat; and in +germination the _starch of the grain_ is converted into _sugar_. + + +Q. _How is barley malted?_ + +A. The barley is _moistened with water_, and _heaped up_; by which +means, great _heat_ is produced, which makes the _barley sprout_. + + +Q. _Why is not the BARLEY suffered to GROW, as well as SPROUT?_ + +A. Plants in the _germ_ contain _more sugar_ than in any _other state_; +as soon as the germ _puts forth shoots_, the _sugar_ of the plant is +_consumed_, to _support the shoot_. + + +Q. _How is BARLEY PREVENTED from SHOOTING, in the process of MALTING?_ + +A. The barley is _put into a kiln_ as soon as it sprouts; and the _heat_ +of the kiln checks or _destroys the young shoot_. + + +Q. _Why is YEAST put into BEER to make it WORK?_ + +A. Yeast supplies the beer with _nitrogen_, which is one of the +ingredients of alcohol. + + +Alcohol consists of _oxygen_, _carbon_, and _hydrogen_, (obtained from +the sugar of malt), and _nitrogen_, (obtained from yeast). + + +Q. _Why is it NOT needful to put YEAST into WINE?_ + +A. Because fruit contains _carbon_, _hydrogen_, _oxygen_, and +_nitrogen_, in the form of "gluten;" and, therefore, ferments +_spontaneously_. + + +(Gluten is explained fully in the Appendix.--Turn to the word in the +Index.) + + +Q. _Does not MALT contain carbon, hydrogen, oxygen, and nitrogen, as +well as FRUIT?_ + +A. No; the sugar of malt contains _carbon_, _hydrogen_, and _oxygen_, +but _no nitrogen_; in consequence of which, _yeast_ (which contains +_nitrogen_) is _added to the wort_. + + +Q. _Why do NOT GRAPES ferment while they hang on the VINE?_ + +A. 1st--Because the skin lets out the _water of the pulp_, which causes +the grapes to shrivel and dry up: and + +2ndly--The skin _prevents_ the admission of _oxygen into the pulp_, from +the air without. + + +Q. _What is the FROTH or SCUM of fermented LIQUORS?_ + +A. _Carbonic acid gas_, which (being heavier than common air) _settles +on the top of the liquor_, in the form of scum. + + +Q. _Why does a small piece of raw MEAT, or a few RAISINS improve FLAT +BEER?_ + +A. 1st--Because they supply it with _nitrogen_ to form it into al'cohol. + +2ndly--As the raw meat, &c. _putrifies_, it gives off _carbonic acid +gas_ into the beer, which gives it "life." + + +Q. _Why is BEER FLAT, if the cask be open too long?_ + +A. Because _too much of the carbonic acid gas_ (produced by +fermentation) is suffered to _escape_. + + +Q. _How is the CARBONIC ACID GAS of BEER generated?_ + +A. The saccharine (or sugar) of the malt is converted by _fermentation_ +into carbonic acid gas and alcohol. + + +Q. _Why does BEER turn FLAT, if the VENT PEG be left OUT of the tub?_ + +A. Because the _carbonic acid gas escapes_ through the vent hole. + + +Q. _Why will NOT beer RUN OUT of the tub, till the VENT PEG is taken +out?_ + +A. When the tap is turned, _air rushes through the tap_ into the bottom +of the tub, and _holds the liquor in_. + + +The _upward_ pressure of air is illustrated by the + + +following simple experiment:--Fill a wine-glass with water; cover the +top of the glass with a piece of writing paper; turn the glass topsy +turvy, and the water will not run out. The paper is used merely to give +the air a medium sufficiently dense to act against. + + +Q. _Why does the BEER RUN FREELY, immediately the VENT PEG is taken +out?_ + +A. As soon as the vent peg is taken out, air rushes _through the vent +hole_ at the _top of the tub_,--presses the liquor _down_, and _forces +it through the tap_. + + +Q. _Why does liquor flow reluctantly out of a BOTTLE held upside down?_ + +A. Because the _upward pressure of the air_ prevents the liquor from +flowing out. + + +Q. _Why should a bottle be held OBLIQUELY, in order to be emptied of its +liquor?_ + +A. Because _air_ will then _flow into the bottle_, and help the liquor +out by _balancing the upward pressure_. + + +Q. _Why does wine (poured from a bottle QUICKLY) SPIRT about without +going into the decanter?_ + +A. The liquor fills the _top of the decanter_ (like a _cork_), and +leaves _no room_ for the air inside _to escape_; therefore, the decanter +(being _full of air_) refuses to admit the _wine_. + + +Q. _Why is BEER made STALE, by being exposed to the AIR?_ + +A. Because air _absorbs its carbonic acid_, which gave it "life." + + +Q. _Why is PORTER made STALE, by being exposed to the AIR?_ + +A. Because air _absorbs its carbonic acid_, which gave it "life." + + +Q. _Why does the EFFERVESCENCE of soda water and ginger beer so soon go +off?_ + +A. Because air _absorbs the carbonic acid_, which produced the +effervescence. + + +Q. _Why is BOILED WATER FLAT and insipid?_ + +A. Because the whole of the _carbonic acid is expelled_ by boiling, and +_absorbed by the air_. + + +Q. _Why does WATER become FLAT and insipid, after it has been DRAWN some +time?_ + +A. Because air _absorbs its carbonic acid_; and when its carbonic acid +is absorbed, the water is flat and insipid. + + +Q. _Why should spring WATER (used for WASHING) be exposed to the AIR?_ + +A. Spring water _contains carbonic acid_; but (by being exposed to the +_air_) this carbonic acid is _absorbed_, and the water becomes _more +soft_. + + +Q. _Why does YEAST make BREAD LIGHT?_ + +A. Flour contains a small portion of _saccharine matter_ (or sugar); and +the yeast (mixing with this) produces _fermentation_, as it does in +brewing. + + +Q. _How does FERMENTATION make the DOUGH RISE?_ + +A. During fermentation, _carbonic acid gas is evolved_; but the sticky +texture of the dough will not allow it to _escape_, so it _forces up +little bladders_ all over the dough. + + +Q. _Why is DOUGH placed BEFORE the FIRE?_ + +A. 1st--Because the heat of the fire _increases the fermentation_: and + +2ndly--It _expands the gas_ which is confined in the little bladders; in +consequence of which, the bladders are _blown up larger_, and the dough +becomes lighter and more porous. + + +Q. _Why is BREAD HEAVY, if the dough be removed from the fire?_ + +A. Because the dough _gets cold_, and then the air in the bladders +_condenses_,--the paste falls,--and the bread is close and heavy. + + +Q. _Whence does the HEAT of FIRE arise?_ + +A. The _carbon of fuel_ (when heated) _combines with the oxygen of the +air_, and produces _carbonic acid gas_: again, the _hydrogen of the +fuel_ combining with _other portions of oxygen_, condenses into _water_; +by which chemical actions _heat is evolved_. + + +Q. _Whence does the HEAT of our own BODY arise?_ + +A. The _carbon of the blood_ combines with the _oxygen of the air +inhaled_, and produces _carbonic acid gas_; which produces heat in a way +similar to burning fuel. + + +Q. _Whence does the HEAT of a DUNGHILL arise?_ + +A. The _straw, &c. of the dunghill_ undergoes _fermentation_ as it +decays: the fermentation produces _carbonic acid gas_, and heat is +evolved by a species of combustion (as in the two former cases). + + +Q. _What changes do VEGETABLES undergo from PUTREFACTION?_ + +A. The _hydrogen of the vegetables_ combines with the _oxygen of the +air_, and forms _water_: again, the _carbon of the vegetables_ combines +with _oxygen of the air_, and forms _carbonic acid gas_. Putrefaction, +therefore, is only another species of combustion. + + +Q. _What changes do ANIMAL bodies undergo from PUTREFACTION?_ + +A. The same as vegetables, with this addition--they give out _ammonia_, +_sulphur_, and _phosphorus_ also; which causes the _offensive smell_ of +putrefying animal bodies. + + +Q. _Why is LIME heated by a KILN?_ + +A. All marl and chalk abound _in carbonic acid_; and (when heated by a +fire) the carbonic acid _flies off in gas_, producing great heat. + + +Q. _What is MORTAR?_ + +A. Lime mixed with sand and water. + + +Q. _What is LIME?_ + +A. _Lime-stone burnt_ produces lime. + + +Q. _Why is the lime-stone BURNT, in order to make it into LIME?_ + +A. The fire _expels the carbonic acid_, and converts the hard lime-stone +into a _loose powder_. + + +Q. _Why does MORTAR become HARD, after a few days?_ + +A. Because the lime _re-imbibes_ the carbonic acid of the air, which was +_expelled by fire_; and the loose _powder_ again becomes as hard as the +original _lime-stone_. + + +Q. _Why is MORTAR adhesive?_ + +A. When the carbonic acid is expelled, the hard lime-stone is _converted +into a loose powder_, which (being mixed with sand and water) becomes a +_soft and sticky plaster_; but, as soon as it is placed between bricks, +it _imbibes carbonic acid again_, and hardens into _lime-stone_. + + + + +CHAPTER XX. + +CARBURETTED HYDROGEN GAS. + + +Q. _What is CHOKE-DAMP?_ + +A. _Carbonic acid gas_ accumulated at the bottom of wells and pits. It +is called CHOKE damp, because it _chokes_ (or suffocates) _every animal +that inhales it_. (_see p._ 264). + + +Q. _What is marsh-gas or FIRE-DAMP?_ + +A. _Carburetted hydrogen gas_ accumulated on marshes, in stagnant +waters, and coal pits; it is frequently called "inflammable air." + + +Q. _What is CARBURETTED HYDROGEN GAS?_ + +A. _Carbon_ combined with _hydrogen_. + + +Q. _How may CARBURETTED HYDROGEN GAS be PROCURED on marshes?_ + +A. By _stirring the mud_ at the bottom of any stagnant pool, and +collecting the gas (as it escapes upwards) in an inverted glass vessel. + + +Q. _What is COAL GAS?_ + +A. _Carburetted hydrogen_ extracted from coals, by the heat of _fire_. + + +Q. _Why is carburetted hydrogen gas called FIRE-DAMP, or inflammable +air?_ + +A. Because it very readily _catches fire and explodes_, when a light is +introduced to it. + + +Q. _Why is carburetted hydrogen gas frequently called MARSH GAS?_ + +A. Because it is generated in _meadows and marshes_ from putrefying +vegetable substances. (_See ignis fatuus_, _p._ 285). + + +Q. _What gas is evolved by the WICK of a burning CANDLE?_ + +A. _Carburetted hydrogen gas_: that is, the _carbon and hydrogen_ of the +tallow _combine into a gas_ from the heat of the flame; and this gas is +_carburetted hydrogen_, or inflammable air. + + +Q. _Why do COAL-MINES so frequently EXPLODE?_ + +A. Because the _carburetted hydrogen gas_ (which is generated in these +mines by the coals) explodes, when a light is incautiously introduced. + + +Q. _How can miners SEE in the coal-pits, if they may NEVER introduce a +LIGHT?_ + +A. Sir Humphrey Davy invented a lantern for the use of miners, called +"the Safety Lamp," which may be used without danger. + + +Q. _Who was SIR HUMPHREY DAVY?_ + +A. A very clever chemist, born in Cornwall. (1778--1829). + + +Q. _What kind of thing is the SAFETY LAMP?_ + +A. It is a kind of lantern _covered with a fine gauze wire_, instead of +glass or horn. + + +Q. _How does this fine GAUZE WIRE prevent an EXPLOSION in the coal +mine?_ + +A. 1st--Because flame will _never pass through fine gauze wire_: and + +2ndly--Though the wire get _red-hot_, it will not ignite the gas; for +carburetted hydrogen gas can be ignited only by _flame_. + + +(N. B. The interstices of the gauze wire must not exceed the 7th of an +inch in diameter.) + + +Q. _Why will not FLAME PASS THROUGH very fine wire-GAUZE?_ + +A. Because the metal wire is a very _rapid conductor of heat_; and when +the flame of burning gas in the lamp reaches the wire gauze, the heat +(which is needful to produce flame) is _conducted away by the wire_, and +the flame is _extinguished_. + + +Q. _Does the gas of the COAL-PIT get THROUGH the wire gauze INTO the +LANTERN?_ + +A. Yes; but the inflammable gas ignites and burns _inside the lamp_: as +soon, however, as this is the case, _the miner is in danger_, and should +withdraw. + + +Q. _Why is the miner in DANGER, if the gas ignites and burns in the +INSIDE of the safety-lamp?_ + +A. Because the heat of the burning gas will soon _destroy the wire +gauze_, and then the flame (being free) will set fire to the mine. + + + + +CHAPTER XXI. + +PHOSPHURETTED HYDROGEN GAS. + + +Q. _From what does the very OFFENSIVE EFFLUVIA of CHURCH-YARDS arise?_ + +A. From a gas called PHOSPHURETTED HYDROGEN; which is _phosphorus_ +combined with _hydrogen gas_. + + +Q. _What is PHOSPHORUS?_ + +A. A pale amber-coloured substance, resembling wax in appearance. The +word is derived from two Greek words, which mean "_to produce or carry +light_." ([Greek: phôs-pherein]). + + +Q. _How is PHOSPHORUS OBTAINED?_ + +A. By heating bones to a white heat; by which means the animal matter +and charcoal are _consumed_, and what is left is called "_phosphate of +lime_." + + +Q. _How is PHOSPHATE OF LIME converted into PHOSPHORUS?_ + +A. It is reduced to _powder_, and mixed with _sulphuric acid_; which +(being heated and filtered) is converted into _phosphorus_. + + +Q. _Of what are LUCIFER MATCHES made?_ + +A. Of phosphorus; and above 250 thousand lbs. of phosphorus are used +every year in London alone, merely for the manufacture of lucifer +matches. + + +Q. _Why does a PUTREFYING dead BODY SMELL so offensively?_ + +A. From the _phosphuretted hydrogen gas_, which always arises from +putrefying animal substances. + + +The escape of _ammonia_ and _sulphur_ contributes also to this offensive +effluvia. + + +Q. _What is the cause of the IGNIS FATUUS, Jack o'Lantern, or Will o'the +Wisp?_ + +A. This luminous appearance (which haunts meadows, bogs, and marshes) +arises from the _gas of putrefying animal and vegetable substances_; +especially decaying fish. + + +Q. _What gases arise from these PUTREFYING substances?_ + +A. _Phosphuretted hydrogen gas_ from putrefying _animal_ substances: and + +_Carburetted hydrogen_, (or inflammable gas) from fermenting _vegetable_ +matters. + + +Some persons erroneously think that the AURORA BOREALIS, or Northern +Lights, may be attributed to the same gases, burning in the upper +regions of the air. + + +Q. _How are these gases IGNITED on bogs and meadows?_ + +A. By the electricity of the air, the rays of the sun, some accidental +spark, the lamp of some traveller, or in some similar way. + + +And sometimes from the spontaneous combustion of some dung-heaps, &c. in +the locality. + + +Q. _Why does an ignis fatuus or Will o'the Wisp FLY from us when we RUN +to MEET it?_ + +A. When we run _towards_ an ignis fatuus, we produce a current of air, +which drives the light gas _forwards_. + + +Q. _Why does an ignis fatuus run AFTER us, when we FLEE from it in +fright?_ + +A. When we run _away_ from the ignis fatuus, we produce a current in the +way we run, which _attracts_ the light inflammable gas in the _same +course_. + + +Q. _Is not a kind of Jack o'Lantern sometimes produced by an INSECT?_ + +A. Yes; a swarm of luminous insects sometimes passes over a meadow, and +produces an appearance exactly like that of the ignis fatuus. + + +Q. _May this meteoric appearance be attributed to any OTHER cause, +besides those mentioned?_ + +A. Yes; if many horses, sheep, pigs, or oxen, are pastured on a meadow, +the _animal vapour_ arising from them (strongly electrified by the air) +_will ignite_, and produce a luminous appearance. + + +Q. _May not many GHOST stories have risen from some ignis fatuus lurking +about church-yards?_ + +A. Perhaps _all_ the ghost stories (which deserve any credit at all) +have arisen from the ignited gas of church-yards lurking about the +tombs, to which _fear_ has added its own creations. + + + + +CHAPTER XXII. + +WIND. + + +Q. _What is WIND?_ + +A. Wind is _air in motion_. + + +Q. _What PUTS the air in motion, so as to produce WIND?_ + +A. The principal causes are the _variations of heat and cold_, produced +by the succession of _day and night_, and the _four seasons_. + + +Q. _What effect has HEAT upon the air?_ + +A. Heat _rarefies_ the air, and causes it to _expand_. + + +Q. _How do you KNOW that heat causes the air to EXPAND?_ + +A. If a bladder _half full of air_ (tied tight round the neck), were +laid before a _fire_, the heat of the fire would expand the air so +much, that the bladder would soon be _entirely inflated_; (in this case, +the air in the bladder is expanded to _twice its original bulk_, by the +heat of the fire). + + +Q. _What EFFECT is produced upon air by RAREFACTION?_ + +A. It causes the air to _ascend through colder strata_, as a cork (put +at the bottom of a basin of water) would ascend through the water. + + +Q. _How do you KNOW that rarefied air ASCENDS?_ + +A. When a boy sets fire to the cotton of his balloon, the flame _heats +the air_ inside the balloon; and the air becomes _so light_, that it +ascends, and _carries the balloon with it_. + + +Q. _What effect is produced upon AIR by COLD?_ + +A. Air is _condensed by cold_, or squeezed into a smaller compass; in +consequence of which, _it becomes heavier_, and descends towards the +ground. + + +Q. _How do you KNOW that air is CONDENSED by COLD?_ + +A. After the bladder is _fully inflated_, (by lying before the fire), if +it be taken _away from the fire_, the bladder will _collapse_, and show +that it is not half full. + + +Q. _What is meant by the bladder "COLLAPSING?"_ + +A. The skin will become _wrinkled, shrivelled, and flabby_, because +there is not sufficient air inside to _fill it out_. + + +Q. _How do you KNOW that CONDENSED air will DESCEND?_ + +A. As soon as the cotton of the balloon _is burnt out_, the air inside +becomes _cold again_, and the balloon _falls to the earth_. + + +Q. _Does the SUN HEAT the AIR as it does the EARTH?_ + +A. No; the air is _not heated by the rays of the sun_, because air (like +water) is a very _bad conductor_. + + +Q. _How is the AIR HEATED?_ + +A. By _convection_, thus:--The _sun_ heats the _earth_, and the _earth_ +heats the _air resting upon it_; the air thus heated _rises_, and is +succeeded by _other air_, which is heated in a similar way, till _all +is warmed_ by "convective currents." + + +Q. _What is meant by "CONVECTIVE CURRENTS of air?"_ + +A. Streams of air heated by the earth, which _rise upwards_ and _carry +heat with them_, are called "convective currents" of hot air. + + +Q. _Is the air in a ROOM in perpetual motion, as the air ABROAD is?_ + +A. Yes; there are always _two currents of air_ in the room we occupy, +one of _hot_ air flowing _out_ of the room, and another of _colder_ air +flowing _into_ the room. + + +Q. _How do you KNOW, that there are these TWO currents of air in every +occupied ROOM?_ + +A. If I hold a lighted candle near the crevice _at the top of the door_, +the flame will be blown _outward_ (towards the _hall_); but if I hold +the candle _at the bottom of the door_, the flame will be blown +_inwards_ (into the _room_). + + +Q. _Why would the flame be blown OUTWARDS (towards the HALL), if the +candle were held at the TOP of the door?_ + +A. Because as the air of the room is warmed by the fire, &c., _it +ascends_; and (floating about the upper part of the room) some of it +escapes _through the crevice_ at the _top of the door_, and thus +produces a current of air _outwards_ (into the _hall_). + + +Q. _Why would the flame be blown INWARDS (into the ROOM), if the candle +were held at the BOTTOM of the door?_ + +A. Because after the warm air of the room has ascended to the ceiling, +or made its escape into the hall, &c., a partial _vacuum_ is made at the +_bottom of the room_; and cold air (from the hall) _rushes under the +door_ to supply the void. + + +Q. _What is meant by a "partial VACUUM being made, at the BOTTOM of the +ROOM?"_ + +A. A vacuum means a place _from which the air has been taken_: and a +"_partial_ vacuum" means, a place from which a _part of its air_ has +been taken away. Thus when the air on the floor _ascends to the +ceiling_, a partial vacuum is made _on the floor_. + + +Q. _And how is the VACUUM filled UP again?_ + +A. It is filled up by _colder air_, which rushes (under the _door_, and +through the _window_ crevices) into the room. + + +Q. _Give me an ILLUSTRATION._ + +A. If I dip a pail into a pond and fill it with water, a hole (or +vacuum) is made in the pond _as big as the pail_; but the moment I _draw +the pail out_, the hole is _filled up_ by the water around. + + +Q. _Show how this illustration APPLIES._ + +A. The heated air which ascends from the bottom of a room, is as much +_taken away_, as the water in the pail; and (as the void was instantly +supplied by _other water in the pond_) so the _void of air is supplied_ +by a current from _without_. + + +Q. _What is the CAUSE of WIND?_ + +A. The _sun_ heats the _earth_, and the _earth_ heats the _air resting +upon it_; as the warm air ascends, the void is filled up by a _rush of +cold air_ to the place, and this _rush of air_ we call WIND. + + +Q. _Does the WIND ALWAYS blow?_ + +A. Yes; there is always _some_ motion in the air; but the _violence_ of +the motion is perpetually varying. + + +Q. _Why is there always SOME motion in the air?_ + +A. As the earth is _always turning round_, the vertical rays of the sun +are always _varying_. + + +Q. _What do you mean by "the VERTICAL RAYS of the SUN?"_ + +A. The rays made at _noon-day_: when the sun is in a _direct line_ above +any place, his rays are said to be "vertical" to that place. + + +Q. _How are the VERTICAL rays of the sun always VARYING?_ + +A. Suppose the brass meridian of a globe to represent the vertical rays +of the sun; as you turn the globe round, _different parts_ of it will +pass under the brass rim, in constant _succession_. + + +Q. _And is it NOON-DAY to the place over which the SUN is VERTICAL?_ + +A. Yes; as each place passes _under the brass meridian_, it is +_noon-day_ to _one_ half, and _mid-night_ to the _other_. + + +Q. _Show how this ROTATION of the earth affects the AIR._ + +A. If we suppose the brass meridian to be the vertical sun, the whole +column of air _beneath_ will be heated by the _noon-day rays_; that part +which the sun has _left_, will become gradually _colder and colder_; and +that part to which the sun is _approaching_, will grow constantly +_warmer and warmer_. + + +Q. _Then there are THREE qualities of air about this spot?_ + +A. Yes; the air over the place which _has passed the meridian_ is +_cooling_: the air under _the vertical sun_ is the _hottest_; and the +air which is over the place _about to pass under the meridian_, is +_increasing in heat_. + + +Q. _How does this VARIETY in the HEAT of AIR produce WIND?_ + +A. The air always seeks to _preserve an equilibrium_; so the _cold air_ +rushes to the _void_, made by the _upward current of the warmer air_. + + +Q. _Why does not the wind ALWAYS BLOW ONE way, following the direction +of the SUN?_ + +A. Because the direction of the wind is subject to perpetual +interruptions from _hills and valleys_, _deserts and seas_. + + +Q. _How can HILLS and MOUNTAINS ALTER the course of the WIND?_ + +A. Suppose a wind, blowing from the north, comes to a mountain, as it +cannot pass _through it_, it must either rush _back again_, or _fly off +at one side_ (as a _marble_ when it strikes against a _wall_). + + +Q. _Do MOUNTAINS affect the wind in any OTHER way?_ + +A. Yes; many mountains are _capped with snow_, and the _warm air_ is +_condensed_ as it comes in contact with them; but as soon as the +_temperature of the wind_ is changed, its _direction_ may be changed +also. + + +Suppose A B C to be _three columns of air_. A, the column of air which +is _cooling down_; B, the column to which the _sun is vertical_; and C, +the column which _is to be heated next_. In this case the _cold_ air of +A will rush towards B C, because the air of B and C is _hotter_ than A. +But suppose now C to be a _snow-capped mountain_. As the hot air of B +reaches C, it is _chilled_; and (being now _colder_ than the air +_behind_) it rushes _back again_ towards A, instead of following the +sun. + + +Q. _How can the OCEAN affect the direction of the WIND?_ + +A. When the ocean rolls beneath the _vertical sun_, the water is _not +made so hot_ as the _land_; and (as another _change of temperature_ is +produced) another obstacle is offered to the _uniform direction of the +wind_. + + +Q. _Why is not the WATER of the sea made so HOT by the vertical sun, as +the surface of the LAND?_ + +A. 1st--Because the _evaporation_ of the sea is greater than that of the +land: + +2ndly--The waters are _never still_: and + +3rdly--The rays of the sun strike _into_ the water, and are _not +reflected from its surface_, as they are by _land_. + + +Q. _Why does the EVAPORATION of the sea prevent its surface from being +HEATED by the vertical sun?_ + +A. As water _absorbs_ heat by being _converted into vapour_; the surface +of the sea is continually _losing heat by evaporation_. + + +Q. _How does the MOTION of the sea prevent its surface from being HEATED +by the vertical sun?_ + +A. As one portion is heated _it rolls away_, and is succeeded by +_another_; and this constant motion prevents _one_ part of the sea from +being heated _more than another_. + + +Q. _How is the WIND affected by the SEA?_ + +A. When air from the hot earth _reaches the sea_, it is often +_condensed_, and either rushes _back again_, or else its violence is +very greatly _abated_. + + +Q. _Do CLOUDS affect the WIND?_ + +A. Yes. As passing clouds screen the direct heat of the sun from the +earth, they diminish the _rarefication of the air also_: and this is +_another_ cause why neither the strength nor direction of the wind is +_uniform_. + + +Q. _Would the winds blow regularly from east to west, if these +OBSTRUCTIONS were REMOVED?_ + +A. Without doubt they would. If the whole earth were covered with +_water_, the winds would always _follow the sun_, and blow from east to +west. Their irregularity is owing to the interspersion of _sea and +land_, and the irregularities of the earth's surface. + + +Q. _Do winds NEVER blow REGULARLY?_ + +A. Yes; in those parts of the world, where these obstructions do not +exist; as on the Atlantic and Pacific Ocean, the winds are pretty +uniform. + + +Q. _What are the winds, which blow over the ATLANTIC and PACIFIC Ocean, +called?_ + +A. They are called "Trade Winds." + + +Q. _Why are they called TRADE WINDS?_ + +A. Because (as they blow uniformly in one direction) they are very +convenient to those who _carry on trade_ by means of these oceans. + + +Q. _In what DIRECTION do the TRADE WINDS blow?_ + +A. That in the _northern_ hemisphere blows from the _north-east_: that +in the _southern_ hemisphere from the _south-east_. + + +Q. _Why do they not blow from the FULL NORTH and SOUTH?_ + +A. Because the _polar current_, combining with the _equatorial current_, +give the wind a _new direction_. + + +Q. _What is the CAUSE of the EQUATORIAL current?_ + +A. The rotation of the earth upon its axis. + + +Q. _What is the cause of the POLAR CURRENT?_ + +A. As the heat in the _torrid zone_ is always _greatest_, and at the +_poles_ the _least_, therefore a constant current of air rushes _from +the poles_ towards the _equator_. + + +Q. _How does the COMBINATION of these two currents give a new direction +to them both?_ + +A. When these currents of air meet at the equator, they _clash +together_, and fly off in a new direction. + + +Q. _Do trade winds blow from the north-east and south-east ALL the YEAR +ROUND?_ + +A. Yes, _in the open sea_; that is, in the Atlantic and Pacific Oceans +for about 30 degs. each side of the equator. + + +Q. _Do the TRADE WINDS blow uniformly from north-east and south-east in +the INDIAN OCEAN?_ + +A. No; nor yet in those parts of the _Atlantic_ and _Pacific_ which +_verge on the land_. + + +Q. _Why do not the trade winds blow uniformly from north-east and +south-east in the INDIAN OCEAN?_ + +A. Because when Arabia, Persia, India, and China, are exposed to the +enormous heat of their summer sun, the _air is so rarefied_, that the +colder air from the south pole rushes _towards these nations_, and not +to the _equator_; in consequence of which, a SOUTH-WEST wind is produced +for _six months of the year_. + + +Q. _How does it blow for the OTHER 6 months?_ + +A. When the sun has left the _northern_ side of the equator for the +_southern_, then the _southern part of the torrid zone_ is most heated; +and the cold air from the north (rushing towards the southern tropic) is +diverted to the NORTH-EAST, where it continues for the _other_ six +months of the year. + + +Q. _What are the six-month trade winds called?_ + +A. They are called MONSOONS; and blow from the _north-east_ from +September to April, and from the _south-west_ for the _other_ six months +of the year. + + +Q. _Have WE any regular winds in ENGLAND?_ + +A. No; our island (having a _continent on one side_, and a _sea on the +other_) has a most _variable_ climate. + + +Q. _Have the winds in England NO general direction throughout the year?_ + +A. We generally find that _easterly_ winds prevail during the _spring_ +of the year, and _westerly_ winds are most common in the _summer_ and +_autumn_. + + +S-West winds are most frequent in July and August. N-East winds in +January, March, April, May, June; and most seldom in July, September, +and December. + + +Q. _When are the WINDS in ENGLAND generally the HIGHEST?_ + +A. The winds in December and January are generally the highest. Those in +February and November the next; and those in August and September the +least boisterous. + + +Q. _Why are the winds of Europe generally HIGHEST in DECEMBER and +JANUARY?_ + +A. Because the sun is _furthest south_ in those months; and (as the heat +in these northern regions rapidly _decreases_) the _contrast between our +temperature_ and that of the _torrid zone_ is greater in December and +January, than in any _other_ two months throughout the year. + + +Q. _Why does this CONTRAST of heat increase the VIOLENCE of the WINDS?_ + +A. As the air always seeks to _preserve an equilibrium_, therefore the +_greater the contrast_, the more violent will be the rush of air to +_equalize_ the two volumes. + + +Q. _Why are the winds in Europe generally the most PLACID during the +months of SEPTEMBER and AUGUST?_ + +A. August and September are our _warmest months_, when we approach +nearer to the heat of the torrid zone than in any _other two months_; +therefore, the air (to and from the equator) _moves with less velocity_ +in our northern hemisphere. + + +Q. _Show the GOODNESS and WISDOM of GOD in the constant tendency of air +to equilibrium._ + +A. If the cool air of the polar regions did not rush into the torrid +zone, _it would become so hot_, that no human being could endure it. If +(on the other hand) the hot air from the torrid zone did not modify the +polar regions, they would soon become _insufferably cold_. + + +Q. _Why are EAST WINDS in England generally DRY?_ + +A. Because, as they come over the _vast continents_ of Asia and Europe, +they absorb _very little water_. + + +Q. _Why does their imbibing so little water make them DRY winds?_ + +A. Being thirsty when they reach our island, they readily imbibe +moisture from the air and clouds; and, therefore, _bring dry weather_. + + +Q. _Why is the NORTH WIND in England generally COLD?_ + +A. The north wind comes from the _polar regions_, over mountains of +snow, and seas of ice; in consequence of which, it is very _cold_. + + +Q. _Why are NORTH WINDS in England generally DRY and biting?_ + +A. As they come from regions _colder than our own_, they are _warmed by +the heat of our island_; and (as their temperature is raised) _they +absorb moisture_ from every thing they touch; in consequence of which, +they are both _dry and parching_. + + +Q. _Why is the SOUTH WIND generally WARM in England?_ + +A. The south wind comes over the hot sandy deserts of Africa, and is +heated by the land it traverses. + + +Q. _Why does the SOUTH WIND often bring us RAIN?_ + +A. The south wind (being much _heated_ by the hot sands of Africa) +_imbibes water very plentifully_, as it passes over the Mediterranean +Sea and British Channel. + + +Q. _Why does the SATURATION of the south wind cause RAIN?_ + +A. As soon as it reaches our cold climate, _it is condensed_, and its +vapour is squeezed out (as water from a wet sponge). + + +Q. _Why are WEST WINDS in England generally RAINY?_ + +A. The west winds come over the _Atlantic Ocean_, and are laden with +_vapour_: if, therefore, they meet with the least _chill_, some of the +vapour is squeezed out. + + +Q. _Why is a fine CLEAR DAY sometimes OVERCAST in a few minutes?_ + +A. Because some _sudden change of temperature_ has condensed the vapour +of the air _into clouds_. + + +Q. _Why are CLOUDS sometimes DISSIPATED quite as suddenly?_ + +A. Because some _dry wind_ (blowing over the clouds) has _imbibed their +moisture_, and carried it off in invisible vapour. + + +Q. _Why does a SOUTH-WEST wind bring us RAIN?_ + +A. As it comes from the _torrid zone_, and _crosses the ocean_, the hot +wind is _laden with vapour_; and as some of the heat escapes (as soon +as it reaches our northern island) the _vapour is condensed_, and +precipitated as rain. + + +Q. _Why does a NORTH-EAST wind RARELY bring RAIN?_ + +A. As it comes from a climate _colder than our own_, its capacity for +imbibing vapour is _increased_ when it reaches our island; in +consequence of which, it _dries the air_, dispels the clouds, and +promotes evaporation. + + +Q. _Why does WIND sometimes bring RAIN, and sometimes FINE weather?_ + +A. If the wind be _colder than the clouds_, it will condense their +vapour into _rain_: if the wind be _warmer than the clouds_, it will +_dissolve_ them, and cause them to disappear. + + +Q. _Why are MARCH winds DRY?_ + +A. Because they generally blow from the east or north-east; and, +therefore, _sweep over the continent of Europe_. + + +Q. _What is the USE of MARCH winds?_ + +A. They _dry the soil_ (which is saturated with the floods of February), +_break up the heavy clods_, and fit the land for the _seeds_ which are +committed to it. + + +Q. _Why does "MARCH COME IN like a LION?"_ + +A. Because it comes in with _blustering east winds_, which are essential +to dry the soil, which would otherwise _rot the seed_ committed to it. + + +Q. _Why does "MARCH GO OUT like a LAMB?"_ + +A. Because the water (evaporated by the high winds) falls again in +_showers_ to fertilize the earth, and _breaks the violence of the +winds_. + + +Q. _Why is it said that "A bushel of MARCH DUST is worth the king's +ransom?"_ + +A. Because it indicates that there has been a continuance of _dry +weather_; and unless _March be dry_, the seed will rot in the wet soil. + + +Q. _Why is it said "A DRY cold MARCH never BEGS BREAD?"_ + +A. Because the _dry cold winds_ of March prepare the soil for _seeds_, +which germinate, and produce fruit in the autumn. + + +Q. _Why is it said that "A WET MARCH makes a SAD autumn?"_ + +A. Because, if _March be wet_, so much of the seed _rots in the ground_, +that the autumn crops are spoiled. + + +Q. _Why is it said that "MARCH FLOWERS make NO summer BOWERS?"_ + +A. Because, if the _spring be very mild_, vegetation gets too forward, +and is _pinched by the nightly frosts_, so as to produce neither fruits +nor flowers. + + +Q. _Why is it said "A LATE SPRING makes a FRUITFUL YEAR?"_ + +A. Because if the vegetation of spring be _backward_, the frosty nights +will _do no harm_; for the fruits and flowers will not put forth their +tender shoots, till the nights become _too warm to injure them_. + + +Q. _Why is it said that "APRIL SHOWERS bring MAY FLOWERS?"_ + +A. Before seeds can germinate, _three_ things are essential:--Darkness, +Heat, and Moisture. April showers supply the principal nourishment on +which seeds depend for existence. + + +Q. _Does RAIN-water possess any fertilizing properties BESIDES that of +mere MOISTURE?_ + +A. Yes; rain-water contains "AMMONIA," to which much of its fertilizing +power may be attributed. + + +(Ammonia is a compound of nitrogen and hydrogen. Common hartshorn is +only ammonia and water.) + + +Q. _Why has God made NOVEMBER a very RAINY month?_ + +A. Because the rain hastens the _putrefaction of the fallen leaves_, and +this makes the earth fertile. + + +Q. _Why is there MORE rain FROM SEPTEMBER to MARCH than from March to +September?_ + +A. From September to March, the temperature of the air is _constantly +decreasing_; on which account, its _capacity for holding vapour_ is on +the _decrease_, and the vapour is precipitated as rain. + + +Q. _Why is there LESS rain FROM MARCH to SEPTEMBER, than from September +to March?_ + +A. From March to September, the temperature of the air is _constantly +increasing_; on which account, _its capacity for holding vapour_ is on +the _increase_, and very little is precipitated as rain. + + +Q. _Why is the RISING SUN in summer accompanied with a BREEZE?_ + +A. Because the heat of the rising sun _stops the radiation of heat_ +from the earth, and _warms its surface_. + + +Q. _How does this WARMTH produce a BREEZE?_ + +A. The air (resting on the earth's surface) is _warmed by contact_, +ascends upwards, and _colder air rushes in_ to fill up the void, which +is the cause of the _morning_ breeze. + + +Q. _Why is there often an EVENING BREEZE during the summer months?_ + +A. The earth _radiates heat at sun-set_, and the air is cooled down +quickly by contact: this condensation causes a _motion in the air_, +which is the evening breeze. + + +Q. _Why are TROPICAL ISLANDS always subject to a SEA-breeze every +MORNING (i. e. a breeze blowing from the sea to the land)?_ + +A. The solar rays are unable to heat the surface of the _sea_ as they do +the _earth_; therefore, the _air resting on the earth_ is more _heated_ +than the _air resting on the sea_; and the colder sea air blows _inland_ +to restore the equilibrium. + + +Q. _Why is the LAND BREEZE UNHEALTHY?_ + +A. Because it is frequently loaded with exhalations from _putrefying +animal_ and _vegetable_ substances. + + +Q. _Why is the SEA BREEZE fresh and HEALTHY?_ + +A. Because it passes over the fresh sea, and is _not_ laden with noxious +exhalations. + + +It is _healthy_, therefore, to walk on the sea-beach before ten o'clock +in the morning; but _unhealthy_ after sun-set. + + +Q. _Why is there generally a fresh breeze from the SEA (in English +watering places) during the summer and autumn MORNINGS?_ + +A. As the _land_ is _more heated by the sun_ than the _sea_; therefore, +air resting on the _land_ is hotter than air resting on the _sea_; in +consequence of which, cooler sea air glides _inland_, to restore the +equilibrium. + + +Q. _Why does the SEA BREEZE feel COOL?_ + +A. As the sun cannot make the surface of the _sea_ so hot as the surface +of the _land_; therefore, the air which blows from the sea, feels +_cooler than the air of the land_. + + +Q. _Why are TROPICAL ISLANDS subject to a LAND BREEZE every EVENING +(i. e. a breeze blowing from the land towards the sea)?_ + +A. The _surface of land_ cools down _faster_ (after sun-set) than the +surface of the _sea_: in consequence of which, the air of the cold land +_is condensed, sinks down_, and spreads itself into the warmer _sea +air_, causing the LAND BREEZE. + + +Q. _Why is the LAND BREEZE COOL?_ + +A. As the surface of the land is cooled at sun-set _quicker than the +surface of the sea_; therefore, the seaman feels the air from the land +to be chill. + + +Q. _Why is the TEMPERATURE of ISLANDS more EQUABLE than that of +CONTINENTS?_ + +A. Because the _water_ around the island _absorbs_ the extreme heat of +summer, and _gives out_ heat to mitigate the extreme cold of winter. + + +Q. _Why does the sea round an island GIVE OUT heat in winter?_ + +A. Unless the _sea be frozen_ (which is rarely the case), it is _warmer_ +than the frozen land; and, therefore, the warmth of the sea air (mixing +with the cold land air) helps to mitigate the intense cold. + + +Q. _Why are there WAVES in the sea?_ + +A. The wind (acting on the surface of the sea) _piles up ridges of +water_, which leave behind an _indentation_: as the water on all sides +rushes to _fill up this indentation_, the disturbance spreads on all +sides, and billow rolls after billow. + + +Q. _Why does WIND in England generally feel COLD?_ + +A. Because a _constantly changing surface_ comes in contact with our +body, to draw off its heat. + + +Q. _Why is a ROOM (even without a fire) generally WARMER than the OPEN +AIR?_ + +A. As the air in a room is _not subject to much change_, it soon becomes +of the same temperature as our skin, and no longer feels cold. + + +Q. _Why do we generally feel COLDER out-of-doors?_ + +A. Because the air (which surrounds us) _is always changing_; and as +fast as _one_ portion of air has become warmer by contact with our body, +_another colder portion_ surrounds us to absorb more heat. + + +Q. _Why are HOT FOODS made COOL by BLOWING them?_ + +A. Blowing causes the air (which covers the hot food) _to change more +rapidly_; in consequence of which, the hot air is _quickly blown away_, +and gives place to fresh _cold air_. + + +Q. _Why do ladies FAN THEMSELVES in hot weather?_ + +A. By the action of the fan, _fresh particles of air_ are perpetually +brought in contact with the face, and every fresh particle of air +_absorbs some heat_ from the skin. + + +Q. _Does the fan COOL the AIR?_ + +A. No; it makes the _air hotter_, by imparting to it the heat _out of +our face_: but it cools the _face_ blown upon, by transferring its heat +to the _air_. + + +Q. _Is the AIR in SUMMER time ever so hot as our bodies?_ + +A. No, not in England. In the hottest day in summer, the air of England +is 15 or 20 degrees cooler than the human body. + + +Q. _How fast does wind travel?_ + +A. A gentle breeze goes at about the rate of 5 miles an hour. A high +wind from 20 to 60. A hurricane from 80 to 100 miles an hour. + + +Q. _How is the VELOCITY of WINDS ascertained?_ + +A. By observing the velocity of the clouds, and by an instrument for the +purpose. + + +This instrument is called an ANEMOMETER. + + +Q. _How is the VELOCITY of the CLOUDS ascertained?_ + +A. By observing the speed of their shadow along the ground; which is +found in a high wind to vary from 20 to 60 miles an hour. + + +Q. _Why is there always a strong DRAUGHT through the KEYHOLE of a door?_ + +A. As the air of the room we occupy is _warmer than the air in the +hall_, therefore the cold hall air _rushes through the keyhole_ into the +room, and causes a draught. + + +Q. _Why is there always a strong DRAUGHT UNDER the DOOR, and through the +crevice on each side?_ + +A. The cold air _rushes from the hall_ under the door, &c. into the +room, to supply the _void_ caused in the room (by the escape of warm +air up the chimney, &c.) + + +Q. _Why is there always a DRAUGHT through the WINDOW crevices?_ + +A. The external air (being colder than the air of the room we occupy) +rushes through the window crevices _to supply the deficiency_, caused by +the escape of air up the chimney, &c. + + +Q. _Why is there more DRAUGHT if you open the LOWER SASH of a window, +than if you open the UPPER sash?_ + +A. If the _lower_ sash be open, the _cold external air_ will rush more +freely _into the room_; but if the _upper_ sash be open the _heated air +of the room_ will _rush out_; and (of course) there will be less +draught. + + +Q. _By which means is the ROOM better VENTILATED, by opening the lower +or the upper sash?_ + +A. A room is better _ventilated_ by opening the _upper sash_; because +the hot vitiated air (which always ascends towards the ceiling) _can +better escape_. + + +Q. _By which means is a HOT ROOM more quickly COOLED--By opening the +upper or the lower sash?_ + +A. A hot room is _cooled more quickly_ by opening the _lower sash_; +because the cold air can enter more freely by an _under_ current, than +by one _higher up_. + + +Q. _Why does WIND DRY damp LINEN?_ + +A. Because dry wind (like a dry sponge) imbibes the particles of vapour +from the surface of the linen, as fast as they are formed. + + +Q. _Which is the HOTTEST PLACE in a church, chapel, or theatre?_ + +A. The gallery. + + +Q. _Why is the GALLERY of all public places HOTTER than the lower parts +of the building?_ + +A. Because the heated air of the room _ascends_, and all the _cold air_ +(which can enter through the doors and windows) _keeps to the floor_, +till it has become heated. + + +Q. _Why do PLANTS often grow out of WALLS and TOWERS?_ + +A. Because sometimes the _wind_ blows the seed there with the dust; and +sometimes _birds_ (flying over) drop the seed which they had formerly +eaten. + + + + +CHAPTER XXIII. + +BAROMETER. + + +Q. _What is a BAROMETER?_ + +A. A weather-glass, or instrument to show the changes of the weather, by +marking the _variations in the weight of air_. + + +Q. _What is a THERMOMETER?_ + +A. An instrument to show how _hot or cold_ anything is. + + +Q. _What is the DIFFERENCE between a THERMOMETER and a BAROMETER?_ + +A. In a THERMOMETER the mercury is _sealed up from the air_: + +In a BAROMETER the mercury is left _exposed_ (or open) to the air. + + +Q. _If the mercury of the thermometer be SEALED UP from the air, how can +the air AFFECT it?_ + +A. The heat of the air passing _through the glass tube_ into the +mercury, causes it to _expand more or less_, and rise in the tube +accordingly. + + +Q. _Why is the TUBE of a BAROMETER left OPEN?_ + +A. That the air may _press upon it_ freely; and as this pressure is +_more_ or _less_, the mercury _rises or falls_ in the tube. + + +Q. _How can weather be affected by the WEIGHT of the air?_ + +A. When air is warm or moist, it is _lighter_ than usual: + +When it is cold or dry, it is _heavier_: and as a barometer marks +whether the air be _light_ or _heavy_, it indicates these _changes_. + + +Q. _How can you tell (by looking at a BAROMETER) what KIND of WEATHER it +will be?_ + +A. Because the mercury in the tube _rises and falls_, as the air becomes +lighter or heavier: and we can generally tell by the _weight_ of the +air, what kind of weather to expect. + + +Q. _Does the WEIGHT of the air VARY MUCH?_ + +A. Yes; the atmosphere in England varies as much as _one-tenth part_ +more or less. + + +Q. _What is the chief USE of a BAROMETER?_ + +A. To warn _sailors_ how to _regulate their ships_, before squalls come +on. + + +Q. _How can a BAROMETER warn SAILORS to regulate their SHIPS?_ + +A. As the barometer will tell when _wind_, _rain_, or _storm_ is at +hand, the sailor can make his ship trim before it overtakes him. + + +Q. _Are there any RULES which can be depended on?_ + +A. Yes; there are _ten special rules_ to direct us how to know the +changes of weather, by marking the mercury of a barometer. + + +Q. _What is the 1ST SPECIAL RULE in regard to the barometer?_ + +A. The barometer is _highest of all_ during a _long frost_; and it +generally rises with a _north-east wind_. + + +Q. _Why is the barometer HIGHEST of all during a long FROST?_ + +A. Because long frost _condenses the air very greatly_; and the more air +is _condensed_, the greater is its _pressure_ on the mercury of the +barometer. + + +Q. _Why does the barometer generally RISE with a NORTH-EAST wind?_ + +A. Because NORTH-EAST winds make the air both _cold and dry_: the air, +therefore, is both _condensed_, and _without vapour_. + + +Q. _What is the 2ND SPECIAL RULE in regard to the barometer?_ + +A. The barometer is _lowest of all_ during a _thaw which follows a long +frost_: it generally falls with SOUTH and WESTERN winds. + + +Q. _Why does the barometer fall LOWEST of all at the BREAKING UP of a +long FROST?_ + +A. 1st--Because the air (which had been much _dried_ by the frost) +_absorbs the moisture_ of the fresh warm current of wind from the south +or south-west: and + +2ndly--The air (which had been much _condensed_ by the frost) is +suddenly _expanded_ by the warm wind which is introduced. + + +Q. _Why does the barometer fall very low with SOUTH and WEST winds?_ + +A. Because SOUTH and WEST winds come heavily _laden with vapour_; and +_vaporized_ air is lighter than _dry air_. + + +Q. _What effect has WIND on the mercury?_ + +A. _All_ winds make the barometer _drop_, except EASTERN winds: those +winds which blow from the SOUTH, and SOUTH-WEST make it _drop the +lowest_. + + +Q. _Why do WINDS generally make the mercury of a barometer DROP?_ + +A. Wind is caused by a _partial vacuum_ in some parts of the globe; and +as the air _rushes in_ to supply this deficiency, _its general pressure +is lessened_, and the barometer falls. + + +Q. _What is the 3RD SPECIAL RULE in regard to the barometer?_ + +A. While the barometer stands above 30°, the air must be very _dry_ or +very _cold_, or perhaps _both_, and _no rain_ may be expected. + + +Q. _Why will there be NO RAIN if the AIR be very DRY?_ + +A. If the air be very _dry_ it will _absorb moisture_, and not part with +what it has _in rain_. + + +Q. _Why will there be NO RAIN if the AIR be very COLD?_ + +A. If the air be very _cold_ it is _so much condensed_, that it has +already parted with as much moisture as it can spare. + + +Q. _What is the 4TH SPECIAL RULE in regard to the barometer?_ + +A. When the barometer stands _very low_ indeed, there is never _much_ +rain, although a _fine day_ will seldom occur at such times. + + +Q. _What kind of WEATHER will it be when the barometer is UNUSUALLY +LOW?_ + +A. There will be _short heavy showers_, with sudden _squalls of wind_ +from the _west_. + + +Q. _Why will there be VERY LITTLE RAIN if the barometer be UNUSUALLY +LOW?_ + +A. Because the air must be very _warm_, or very _moist_, or perhaps +_both_. + + +Q. _Why will there be little or no rain, if the_ AIR _be very_ WARM? + +A. If the air be very warm it will have a tendency to _imbibe more +moisture_, and not to part with what it has. + + +Q. _Why will there be little or no rain if the air be MOIST, and the +barometer remains very LOW?_ + +A. If the air be ever so moist, rain will never fall till _cold air_ has +been introduced to _condense the vapour_; and the moment that the _cold_ +air is introduced, the barometer will _rise_. + + +Q. _What is the 5TH SPECIAL RULE in regard to the barometer?_ + +A. In summer-time (after a long continuance of fair weather) the +barometer will _fall gradually_ for 2 or 3 days before _rain_ comes; but +if the fall of the mercury be very _sudden_, a _thunder-storm_ is at +hand. + + +Q. _What is the 6TH SPECIAL RULE in regard to the barometer?_ + +A. When the sky is cloudless, and seems to promise fair weather, if the +barometer be _low_, the face of the sky will soon be suddenly +_overcast_. + + +Q. _What is the 7TH SPECIAL RULE in regard to the barometer?_ + +A. Dark dense clouds will pass over _without rain_, when the barometer +is _high_; but if the barometer be low, it will often rain _without any +gathering of clouds_. + + +Q. _What is the 8TH SPECIAL RULE in regard to the barometer?_ + +A. The _higher_ the barometer, the greater is the probability of _fair +weather_. + + +Q. _Why is the barometer HIGH in FINE weather?_ + +A. Because the air contains but _very little vapour_. The _drier_ the +air, the _higher_ does the mercury of the barometer rise. + + +Q. _What is the 9TH SPECIAL RULE in regard to the barometer?_ + +A. When the mercury is in a _rising_ state, _fine_ weather is at hand; +but when the mercury is in a _sinking_ state, _foul_ weather is near. + + +Q. _Why does the mercury RISE at the approach of FINE weather?_ + +A. Because the air is becoming more _dry_, and therefore its _pressure_ +is greater. + + +Q. _Why does the mercury SINK at the approach of FOUL weather?_ + +A. Because the air is _laden with vapour_, or _disturbed by wind_. + + +Q. _Why does VAPOUR in the air make the mercury SINK?_ + +A. Because vaporized air is _lighter than dry air_, and therefore its +_pressure is less_ on the mercury of the barometer. + + +Q. _What is the 10TH SPECIAL RULE in regard to the barometer?_ + +A. If (in frosty weather) it _begins to snow_, the barometer generally +rises to 32°, where it remains as long as the snow continues to fall; +if, after this, the weather _clear up_, you may expect _very severe +cold_. + + +Q. _How can you know if the MERCURY of the barometer be RISING?_ + +A. If it be _convex_ (i. e. higher in the _middle_ than at the _sides_;) +it is in a _rising state_. + + +Q. _How can you tell if the MERCURY of the barometer be about to FALL?_ + +A. If it be _concave_ (i. e. _hollow_ in the _middle_) it is in a +_falling state_. + + +Q. _Why is the mercury CONVEX when it is RISING?_ + +A. The sides of the mercury _rub against the glass tube_, and are +_delayed_ by it, so that the _middle_ part _rises faster_ than the +_sides_. + + +Q. _Why is the mercury CONCAVE when it is FALLING?_ + +A. The sides of the mercury _rub against the glass tube_, and are +_delayed_ by it, so that the _middle_ part _sinks faster_ than the +_sides_. + + +Q. _What effect does a THUNDER-STORM produce on the weather?_ + +A. Thunder is generally _preceded by hot_ weather, and _followed by +cold_ and showery weather. + + +Q. _What effect does a SUDDEN CHANGE produce on the weather?_ + +A. A great and sudden change (either from hot to cold, or from cold to +hot) is generally followed _by rain within 24 hours_. + + +Q. _Why is a sudden CHANGE from HOT to COLD followed by RAIN?_ + +A. The cold _condenses the air_ and its vapour; which, being condensed +and squeezed out, _falls in rain_. + + +Q. _Why is a sudden CHANGE from COLD to HOT followed by RAIN?_ + +A. Because the air is _quickly saturated with moisture_; and as soon as +_night_ comes on, the temperature is _lowered again_, and some of the +abundant moisture falls in rain. + + +Q. _Why is the air quickly SATURATED with MOISTURE, when HEAT succeeds +rapidly from COLD?_ + +A. Because the evaporation (which was checked by the cold) is _carried +on very rapidly_, in consequence of the _diminished pressure_ of the +air. + + +(N. B. The _less the pressure_ of the air, the more _rapidly it +evaporates_ moisture.) + + +Q. _When does the barometer VARY MOST?_ + +A. In winter time. + + +Q. _Why does the barometer vary MORE in WINTER than in SUMMER time?_ + +A. Because the _difference of temperature_ between the torrid and +temperate zones is _so great_, that the state of the air is perpetually +_disturbed_ by their mixing together. + + +Q. _When does the barometer VARY LEAST?_ + +A. In summer time. + + +Q. _Why does the barometer vary LESS in SUMMER than in WINTER time?_ + +A. Because the temperature of our island is _so nearly equal_ to that of +the torrid zone, that its state is _not much disturbed_ by interchange +of currents. + + +Q. _What effect has WIND on the barometer?_ + +A. NORTH and EAST winds make the mercury _rise_; all _other_ winds make +it _sink_; but SOUTH and WEST winds make it _sink lower_ than any other +winds. + + +Q. _Have HEAT and COLD any effect on the barometer?_ + +A. No, not of _themselves_; but because _cold_ weather is generally +either _dry_, or _rough with north-east winds_, therefore the mercury +_rises_ in cold weather; and because warm weather is often _moist_ or +_fanned by south-west winds_, therefore, the mercury sinks. + + +Q. _Why is the mercury of a barometer LOWER in the TORRID than in the +FRIGID zones?_ + +A. Because the warm air of the torrid zone contains much more _vapour_ +than the condensed air of the frigid zone; and the _moister_ the air, +the _less is its pressure_. + + +Q. _In what MONTHS is the barometer HIGHEST?_ + +A. In May and August; next to these, in June, March, September, and +April. + + +Q. _In what MONTHS is the barometer LOWEST?_ + +A. In November and February; then in October, July, December, and +January. + + +Q. _What are the DRIEST months?_ + +A. March and June; then May and August; then April and November. + + +Q. _What are the WETTEST months?_ + +A. October and February; then July and September; then January and +December. + + +Q. _Why is there LESS wet from MARCH to AUGUST, than there is from +August to March?_ + +A. Because the _heat is constantly increasing_; and the capacity of the +air to absorb and retain moisture increases likewise. + + +Q. _Why is there MORE wet from AUGUST to MARCH, than there is from March +to August?_ + +A. Because the _heat is constantly decreasing_, and the capacity of the +air to retain moisture decreases also; so that (although it often rains) +yet the air is always on the point of saturation. + + +Q. _Why does the mercury of a barometer RISE in a FROST?_ + +A. Because frost _condenses the air_; and condensed air is heavier than +_rarefied_ air. + + +Q. _Why does the mercury of a barometer FALL in a THAW?_ + +A. Because the air is both _warmer_ (or more rarefied), and also filled +with _vapour_. + + +Q. _What does a SUDDEN rise or fall of the barometer indicate?_ + +A. If the _rise_ be sudden, fine weather will not continue long: + +If the _fall_ be sudden, foul weather will not continue long. + + +Q. _What sort of weather may we expect if the barometer be very +FLUCTUATING?_ + +A. If the mercury fluctuates much, the weather will be very _changeable +and unsettled_. + + +The FALL of the barometer. + +In very _hot_ weather, the fall of the mercury denotes _thunder_. + +Except in very hot weather, the sudden falling of the barometer denotes +high wind. + +In _frosty_ weather, the fall of the barometer denotes _thaw_. + +If _wet_ weather happens _soon_ after the fall of the barometer, expect +but _little_ of it. + +In _wet_ weather if the barometer falls, expect much wet. + +In _fair_ weather, if the barometer falls much and _remains_ low, expect +much wet in a few days, and probably _wind_. + +N. B. The barometer sinks lowest of all for wind and rain together, next +to that for wind (except it be an east or north-east wind). + + * * * * * + +The RISE of the barometer. + +In _winter_ the rise of the barometer presages _frost_. + +In _frosty_ weather, the rise of the barometer presages _snow_. + +If _fair_ weather happens _soon_ after the rise of the barometer, expect +but _little_ of it. + +In _wet_ weather, if the mercury rises high and _remains_ so, expect +continued _fine_ weather in a day or two. + + +In wet weather, if the mercury rises suddenly very high, fine weather +will not last long. + +N. B. The barometer rises highest of all for north and east winds; for +all _other_ winds it sinks. + + * * * * * + +If the barometer be UNSETTLED. + +If the motion of the mercury be _unsettled_, expect unsettled weather. + +If it stand at "MUCH RAIN" and rise to "CHANGEABLE," expects _fair +weather of short continuance_. + +If it stand at "FAIR" and fall to "CHANGEABLE," expect _foul_ weather. + +N. B. Its motion _upwards_ indicates the approach of fine weather: its +motion _downwards_ indicates the approach of foul weather. + + + + +CHAPTER XXIV. + +SNOW. HAIL. RAIN. + + +Q. _What is SNOW?_ + +A. The condensed vapour of the air _frozen_, and precipitated to the +earth. + + +Q. _What is the CAUSE of SNOW?_ + +A. When the air is nearly saturated with vapour, and condensed by a +current of air _below freezing point_, some of the vapour is squeezed +out, and frozen into snow. + + +A few years ago, some fishermen (who wintered at Nova-Zembla), after +they had been shut up in a hut for several days, _opened the window_, +and the cold external air rushing in, instantly condensed the air of the +hut, and the vapour (which was squeezed out) fell on the floor _in a +shower of snow_. + + +Q. _Why does SNOW fall in WINTER time?_ + +A. Because the sun's rays are too _oblique_ to heat the surface of the +earth; and (as the _earth has no heat_ to radiate into the air) the air +is very cold. + + +Q. _What is SLEET?_ + +A. When flakes of snow (in their descent) pass through a bed of air +_above freezing point_, they melt; and fall to the earth as half-melted +snow or sleet. + + +Q. _What is the USE of SNOW?_ + +A. To keep the _earth warm_, and to _nourish_ it. + + +Q. _How can snow keep the EARTH WARM?_ + +A. Because it is a very _bad conductor_; in consequence of which, the +earth which is covered with snow, very rarely descends _below freezing +point_, even when the air is 15 or 20 degrees colder. + + +Q. _Why is SNOW a BAD CONDUCTOR of heat and cold?_ + +A. Because _air_ is confined and entangled between the crystals, and +_air_ is a very _bad conductor_; when, therefore, the earth is covered +with snow, it cannot throw off its heat by radiation. + + +Q. _Tell me the words of the PSALMIST_ (cxlvii. 16.) _respecting snow, +and explain what he means._ + +A. The Psalmist says--"The Lord giveth snow like wool:" and he means not +only that snow is as _white as wool_, but that it is also as _warm as +wool_. + + +Q. _Why is WOOL WARM?_ + +A. Because _air_ is entangled between the fibres of the wool, and air is +a _bad conductor_. + + +Q. _Why is SNOW WARM?_ + +A. Because _air_ is entangled between the crystals of the snow, and air +is a _bad conductor_. + + +Q. _Why does SNOW NOURISH the earth?_ + +A. Because it supplies it with _moisture_ for a considerable time; which +penetrates slowly into the soil, and insinuates itself through every +clod, ridge, and furrow. + + +Q. _Why is there NO SNOW in SUMMER time?_ + +A. No snow reaches the general surface of the earth in summer time, +because the _heat of the earth_ melts it in its descent. + + +Q. _Why are some MOUNTAINS ALWAYS COVERED with SNOW?_ + +A. 1st--Because the _air is more rarefied_; and rarefied air _abstracts +heat_ which it holds in a _latent state_: + +2ndly--As the mountain top is _not surrounded by earth_ to radiate heat +into the air; therefore, the snow is _not melted_ in its descent, but +falls on the mountain, and lies there. + + +Q. _Why is SNOW WHITE?_ + +A. Snow is formed of an infinite number of very minute crystals and +prisms, which reflect all the colours of the rays of light; and these +colours _uniting_ before they meet the eye, cause snow to appear white. + + +Q. _What is HAIL?_ + +A. Rain, which has passed in its descent _through some cold bed of air_, +and has been frozen into drops of ice. + + +Q. _Why is ONE bed of air COLDER than another?_ + +A. This is frequently caused by _electricity_ in the air, _unequally +distributed_. + + +Q. _Why is HAIL frequently accompanied with THUNDER and LIGHTNING?_ + +A. 1st--Because the _congelation of water into hail_ disturbs the +electricity of the air: and + +2ndly--The _friction_ (produced by the fall of hail) excites it still +more. + + +Q. _Why does HAIL fall generally in SUMMER and AUTUMN?_ + +A. 1st--Because the _air is more highly electrified_ in summer and +autumn: and + +2ndly--The vapours (being rarefied) ascend to the more elevated regions, +where the _cold is greater_ than it is nearer the earth. + + +Q. _What TWO things are essential to cause HAIL?_ + +A. Two _strata of clouds_ having _opposite electricities_, and _two +currents of wind_. The _lower cloud_ (being negative) is the one +_precipitated_. + + +Q. _What is RAIN?_ + +A. The vapour of the clouds or air _condensed_, and precipitated to the +earth. + + +Q. _Why is the vapour of the air or clouds PRECIPITATED?_ + +A. When the air is _saturated with vapour_, if a cold current +_condenses_ it, it is no longer _able to hold all its vapour_ in +solution, and some of it is squeezed out, and falls as rain. + + +Q. _Why does RAIN fall in DROPS?_ + +A. The vapoury particles in their descent _attract each other_; and +those which are sufficiently near, _unite_ and form into a drop. + + +Q. _Why does not the COLD of NIGHT ALWAYS cause rain?_ + +A. When the air is not _near saturation_ (although condensed by the +chill of evening), it will still be able to hold its vapour in solution. + + +Q. _Why does a PASSING CLOUD often drop RAIN?_ + +A. Because the cloud (travelling about on the wind) comes into contact +with _something that chills it_; and its vapour being squeezed out, +_falls to the earth as rain_. + + +Q. _Why are RAIN-DROPS sometimes much LARGER than at OTHER times?_ + +A. When the rain-cloud is floating _near the earth_, the drops are +large, because such a cloud is _much more dense_ than one which is more +elevated. + + +The size of the rain-drop is increased according to the _rapidity_ with +which the vapours are condensed. + + +Q. _Does not WIND sometimes INCREASE the SIZE of rain-drops?_ + +A. Yes; by blowing two or more drops into one. + + +Q. _Why do CLOUDS FALL in RAINY weather?_ + +A. 1st--Because the _clouds are heavy_ with abundant vapour: and + +2ndly--As the density of the air is _diminished_, it is less able to +buoy the clouds up. + + +Q. _How do you KNOW that the DENSITY of the air is DIMINISHED in RAINY +weather?_ + +A. Because the _mercury of a barometer falls_. + + +Q. _Why is RAIN-water more FERTILIZING than PUMP-water?_ + +A. Because it contains a compound of hydrogen and nitrogen (called +_ammonia_), which is a very excellent food for young plants. + + +Q. _Why is NOVEMBER made by God to be a RAINY MONTH?_ + +A. Because rain _hastens the putrefaction of the fallen leaves_ by +causing fermentation. + + +Q. _Why does RAIN PURIFY the AIR?_ + +A. 1st--Because it _beats down the noxious exhalations_ collected in the +air, and _dissolves_ them: + +2ndly--It mixes the air of the _upper_ regions with that of the _lower +regions_: and + +3rdly--It _washes the earth_, and sets in motion the stagnant _sewers +and ditches_. + + +Q. _Why are MOUNTAINOUS countries more RAINY than flat ones?_ + +A. The air (striking against the side of the mountains) is _carried up +the inclined plane_, and brought in contact with the _cold air of the +higher regions_, by which it is _condensed_, and its _vapour squeezed +out_. + + +Q. _Why does a SPONGE SWELL when it is WETTED?_ + +A. Because the water _penetrates the pores_ of the sponge, and drives +the particles of the sponge _further from each other_; in consequence of +which, the _bulk_ of the sponge is greatly _increased_. + + +Q. _Why do FIDDLE-strings SNAP in WET weather?_ + +A. Because the moisture of the air (penetrating the string) _causes it +to swell_; and (as the cord _thickens_) its _tension is increased_, and +the string snaps. + + +Q. _Why does PAPER PUCKER when it is WETTED?_ + +A. Because the moisture (penetrating the paper) _drives its particles +further apart_; and (as the moisture is absorbed _unequally_ by the +paper) some parts are more enlarged than others; in consequence of +which, the paper _blisters_ or _puckers_. + + +Q. _Why do the weather toys called CAPU'CHINS lift the cowl over the +figures in wet weather, and remove it in dry?_ + +A. The cowl of the capu'chin is _fastened to a piece of cat-gut_. When +the weather is _wet_, the moisture _swells the cat-gut_ and it is +_shortened_, by which means the _cowl is pulled up_; but in _dry_ +weather, the _string is loosened_, and the cowl falls down. + + +Q. _In another weather toy, the MAN comes out in WET weather, and the +LADY in FINE:--Why is this?_ + +A. The two figures are attached to a piece of _cat-gut_ in such a +manner, that when the _cat-gut is shortened by moisture_, it pulls the +_man out_; but when it is _loose_, the woman _falls out by her own +weight_. + + +Q. _Why are WET STOCKINGS DIFFICULT to PULL ON?_ + +A. The moisture (by penetrating the threads of the stockings) causes +them to _shrink in size_. + + +Q. _What is the MOST RAINY spot in ENGLAND?_ + +A. Keswick (in Cumberland); and then Kendal (a market town in +Westmoreland). + + +(In Keswick, about 63 inches of rain fall in a year. In Kendal, 58; +Manchester, 38; Liverpool, 34; Dublin and Cambridge, 25; Lincoln, 24; +London, 21; and in Paris, only 18.) + + +Q. _In which PART of the DAY does the MOST RAIN fall?_ + +A. More rain falls by _night_ than by day; because the cold night +_condenses the air_, and diminishes its capacity for holding vapour in +solution. + + +Q. _Does more rain fall in SUMMER or in WINTER time?_ + +A. There are _more rainy days_ from September to March; but _heavier_ +rains between March and September. + + +Q. _Why are there MORE RAINY DAYS from September to March, than from +March to September?_ + +A. Because the temperature of the air is _constantly decreasing_, and +its capacity for vapour decreases also; in consequence of which, it is +perpetually obliged to _part with some of its vapour_ in rain. + + +Q. _In what PART of the WORLD does RAIN fall MOST ABUNDANTLY?_ + +A. Near the _equator_; and the quantity of rain _decreases_ as we +approach the _poles_. + + +Q. _Why does MORE RAIN fall at the EQUATOR than at the POLES?_ + +A. Because the _contrast_ between the _night and day_ is very great. The +hot air _absorbs moisture very abundantly_ during the day; and when the +cold night _condenses_ the air, it is unable to _retain the moisture +imbibed_, and some of it falls in rain. + + + + +CHAPTER XXV. + +WATER. + + +Q. _What is WATER?_ + +A. Water is composed of _two gases_, oxygen and hydrogen. + + +(In 9 lbs. of water, 8 are oxygen, and 1 is hydrogen.) + + +Q. _Why is WATER FLUID?_ + +A. Because its particles are kept separate by _latent heat_; but when a +certain quantity of this latent heat is driven out, _water becomes +solid_, and is called ice. + + +Q. _How can WATER be converted into a GAS?_ + +A. By increasing its _latent heat_, the particles, of water are again +_subdivided into invisible steam_. + + +Q. _Why is PUMP water called HARD water?_ + +A. Because it is laden with foreign matters, and will not readily +_dissolve substances_ immersed in it. + + +Q. _What makes PUMP-water HARD?_ + +A. Because when it filters through the earth, it becomes impregnated +with _sulphate of lime_, and many other impurities from the _earths and +minerals_ with which it comes in contact. + + +Q. _Why is it difficult to WASH our HANDS clean with HARD water?_ + +A. Because the _soda of the soap_ combines with the _sulphuric acid_ of +the hard water, and the _oil of the soap_ with the _lime_, and float in +flakes on the top of the water. + + +N.B. Sulphate of lime consists of sulphuric acid and lime. + + +Q. _Why is it difficult to wash in SALT WATER?_ + +A. Because salt water contains _muriatic acid_; and the _soda of soap_ +combines with the _muriatic acid of the salt water_, and produces a +cloudiness. + + +Q. _Why does a BLACK HAT turn RED at the SEA SIDE?_ + +A. The _muriatic acid of the sea-water_ disturbs the _gallic acid of the +black dye_, and turns it _red_. + + +Q. _Of what is SOAP made?_ + +A. Of kelp (or the ashes of sea-weed dried and burnt in a pit) mixed +with oil or fat. + + +YELLOW SOAP is made of whale-oil, soda, and resin. SOFT SOAP is made of +oil and potash. HARD SOAP of oil and soda. + + +Q. _Why does WATER CLEAN dirty LINEN?_ + +A. Because the _oxygen_ of the water attaches itself to the _stains of +the linen_, and _dissolves_ them; as oxalic acid dissolves ink spots. + + +Q. _Why does SOAP greatly INCREASE the cleansing power of water?_ + +A. 1st--Because soap _increases the oxygen_ of the water: and + +2ndly--It _neutralizes the grease_ of the things washed. + + +Q. _Why is RAIN WATER SOFT?_ + +A. Because it has _not come in contact with earths and minerals_. + + +Q. _Why is it MORE EASY to WASH with SOFT water than with HARD?_ + +A. Because it unites freely with the soap, _dissolving_ it instead of +_decomposing it_, as hard water does. + + +Q. _Why do WOOD ASHES make HARD water SOFT?_ + +A. 1st--Because the _carbonic acid of the wood ashes_ combines with the +_sulphate of lime in the hard water_, and converts it into _chalk_: and + +2ndly--The _sulphuric acid of the water_ combines with the _potash of +the wood ashes_, and prevents it from neutralizing the oily matter of +the soap. + + +Q. _Why has RAIN water such an UNPLEASANT SMELL, when it is collected in +a rain water tub or tank?_ + +A. Because it is impregnated with _decomposed organic matter_, washed +from roofs, trees, or the casks in which it is collected. + + +Q. _Why does WATER MELT SUGAR?_ + +A. Because very minute particles of water _insinuate themselves into +the pores_ of the sugar, and force the crystals _apart from each other_. + + +Q. _Why does WATER MELT SALT?_ + +A. Because very minute particles of water insinuate themselves into the +_pores of the salt_, and force the crystals _apart from each other_. + + +Q. _Why does melted SUGAR or SALT give a FLAVOUR to the WATER?_ + +A. Because the sugar or salt (being disunited into very minute pieces) +_floats about the water_, and mixes with _every part_. + + +Q. _Why does HOT water melt sugar and salt QUICKER than COLD water?_ + +A. 1st--Because the _heat_ of the water entering the pores of the sugar +or salt, _opens a passage for the water_: and + +2ndly--The _particles of hot water_ being _smaller_ than those of cold, +can _more readily penetrate_ the pores of salt or sugar. + + +Q. _Why is SEA-water SALT?_ + +A. 1st--Because it contains _mines of salt_ at the bottom of its bed: + +2ndly--It is impregnated with _bituminous matter_, which is brackish: +and + +3rdly--It contains many _putrid substances_, which increase its +brackishness. + + +Q. _Why is NOT RAIN-water SALT, although most of it is evaporated from +the SEA?_ + +A. Because _salt will not evaporate_; and, therefore, when sea-water is +turned to vapour, its _salt is left behind_. + + +Q. _Why does STAGNANT water PUTREFY?_ + +A. Because leaves, plants, insects, &c. are decomposed in it. + + +Q. _Why is STAGNANT water full of WORMS, EELS, &c.?_ + +A. Because numberless insects _lay their eggs_ in the leaves and plants +which float on the surface; these eggs are soon hatched, and produce +swarms of worms, eels, and insects. + + +Q. _Why are FLOWING waters FREE from these IMPURITIES?_ + +A. 1st--Because the motion of running water _prevents its fermentation:_ + +2ndly--It _dissolves the putrid substances_ which happen to fall into +it: and + +3rdly--It casts _on the bank_ (by its current) such substances as it +cannot _dissolve_. + + +Q. _Why does RUNNING water OSCILLATE and WHIRL in its current?_ + +A. 1st--Because it _impinges against its banks_, and is perpetually +diverted from its forward motion: and + +2ndly--Because the _centre_ of a river _flows faster_ than its _sides_. + + +Q. _Why do the SIDES of a river flow more TARDILY than its CENTRE?_ + +A. Because they _rub against the banks_, and are delayed in their +current thereby. + + +Q. _Why does SOAPY water BUBBLE?_ + +A. Because the soap _makes the water tenacious_, and prevents the +bubbles from _bursting_ as soon as they are formed. + + +Q. _Why will not water bubble WITHOUT SOAP?_ + +A. Because it is not tenacious enough _to hold together the bubbles_ +that are formed. + + +Q. _When SOAP BUBBLES are blown from a pipe, why do they ASCEND?_ + +A. Because they are _filled with warm breath_, which is lighter than +air. + + + + +CHAPTER XXVI. + +ICE. + + +Q. _What is ICE?_ + +A. FROZEN WATER. When the air is reduced to 32 degrees of heat, water +will no longer remain in a _fluid state_. + + +Q. _Why is SOLID ICE LIGHTER than WATER?_ + +A. Because water _expands by freezing_; and as the _bulk is increased_, +the _gravity_ must be _less_. + + +Nine cubic inches of water become ten when frozen. + + +Q. _Why do EWERS BREAK in a FROSTY NIGHT?_ + +A. Because the water in them _freezes_; and as the _water is expanded by +frost_, it bursts the ewers to make room for its increased volume. + + +Q. _Why does it not expand UPWARDS (like boiling water), and RUN OVER?_ + +A. Because the _surface_ is first frozen, and the frozen surface acts as +a _plug_, which is more difficult to burst than the earthen ewer +itself. + + +Q. _Why do TILES, STONES, and ROCKS often SPLIT in winter?_ + +A. Because the moisture (which they imbibed) _freezes_, and by its +expansion _splits the solid mass_. + + +Q. _In winter time, FOOT-MARKS and WHEEL-RUTS are often covered with an +icy NET-WORK, through the interstices of which the soil is clearly +seen,--WHY does the water freeze in NET-WORK?_ + +A. The water in these hollows froze first at the _sides_ of the +foot-prints: other crystals gradually shot across the water, and would +have _covered the whole surface_, had not the earth _absorbed_ the water +before it had time to freeze. + + +Q. _In winter time these FOOT-MARKS and WHEEL-RUTS are sometimes covered +with a perfect SHEET of ice, and not an icy net-work,--Why is THIS?_ + +A. The _air being colder_ and the _earth harder_ (than in the former +case), the _entire surface_ of the foot-print is frozen over, before the +earth can _draw the water in_. + + +Q. _Why is not the ice SOLID in these ruts?--WHY is there only a very +thin FILM or NET-WORK of ice?_ + +A. Because the earth _absorbs the water_, and leaves the icy _film +behind_. + + +Q. _Does not water expand by HEAT as well as COLD?_ + +A. Yes; it expands as soon as it is more than 42 degrees _till it +boils_, and then it flies off in steam. + +[Illustration: Here A B measures the bulk of a portion of water at 42 +degrees. + +It goes on increasing in bulk to C D, when it boils. It also goes on +increasing in bulk to E F, when it freezes.] + + +Q. _Why do WATER-PIPES frequently BURST in FROSTY weather?_ + +A. Because the water in them _freezes_; and as the water _expands by +frost_, it bursts the pipes to make room for its increased volume. + + +Q. _When does WATER begin to EXPAND from cold?_ + +A. Water (which is wisely ordained by God to be an _exception_ to a +very general rule) _contracts_ till it is reduced to 42 degrees, and +then it _expands till it freezes_. + + +(Water freezes at 32°.) + + +Q. _Why does water expand when it freezes?_ + +A. Because it is converted into _solid crystals_, which _do not fit +close_, like the particles of water. + + +Q. _Why is the water at the BOTTOM of a river NEVER FROZEN?_ + +A. Because when water is colder than 42 degrees, it instantly _ascends +to the surface_; and (if it freezes) _floats there_ till it is melted. + + +(When a river is frozen, the water below the surface is never less than +42°.) + + +Q. _Show the WISDOM of GOD in this wonderful exception to a general +law._ + +A. If ice were _heavier than water_, it would _sink_; and a river would +soon become a solid _block of ice_, which could never be dissolved. + + +Q. _Why does not the cold ICE on the SURFACE of a river CHILL the water +BENEATH, and make it freeze?_ + +A. 1st--Water is a _very bad conductor_, and is heated or chilled by +CONVECTION only: + +2ndly--If the ice on the surface were to communicate its _coldness_ to +the water beneath, the _water beneath_ must communicate its _heat to the +ice_, and the ice would instantly _melt_: and + +3rdly--The ice on the surface acts as a _shield_ to _prevent the cold +air from penetrating the river_ to freeze it below the mere crust. + + +Q. _Why does WATER FREEZE at the SURFACE first?_ + +A. Because the surface is in _contact with the air_, and the air +_carries away its heat_. + + +Q. _Why does the coat of ice grow THICKER and THICKER, if the frost +CONTINUES?_ + +A. Because the _heat of the water_ (immediately below the frozen +surface) _passes through the pores of the ice_ into the _cold air_. + + +Q. _Why then are not WHOLE RIVERS FROZEN (layer by layer) till they +become solid ice?_ + +A. Because water is _so slow a conductor_, that our frosts never +continue _long enough_ to convert a whole river into a solid mass of +ice. + + +Q. _Why does not RUNNING water freeze so fast as STILL water?_ + +A. 1st--Because the motion of the current _dissolves the crystals_ as +fast as they are formed; and + +2ndly--The heat of the _under_ surface is more freely distributed to the +_upper_ surface by the _rolling water_. + + +Q. _When RUNNING water is FROZEN, why is the ICE generally very ROUGH?_ + +A. Because little flakes of ice are first formed and _carried down the +stream_, till they meet some _obstacle_ to _stop_ them; _other_ flakes +of ice (_impinging against them_) are arrested in like manner; and the +_edges_ of the different flakes _overlapping_ each other, _make the +surface rough_. + + +Q. _Why do SOME parts of a RIVER FREEZE LESS than OTHERS?_ + +A. Because _springs_ issue from the bottom, and (as they bubble upwards) +_thaw the ice_, or make it thin. + + +Q. _When persons FALL into a RIVER in winter time, why does the WATER +feel remarkably WARM?_ + +A. Because the _frosty air_ is at least 10 or 12 degrees _colder_ than +the water. + + +(The water below the surface is at least 42°; but the air 32°, or even +less.) + + +Q. _Why is SHALLOW water FROZEN QUICKER than DEEP water?_ + +A. Because (as the _whole volume_ of water must be cooled to 42 degrees +before the _surface can be frozen_) it will take a longer time to cool +down a _deep_ bed of water than a _shallow_ one. + + +Q. _Why is SEA-WATER RARELY FROZEN?_ + +A. 1st--Because the _mass of water is so great_ that it requires a very +long time to cool the whole volume down to 42 degrees: + +2ndly--The _ebb and flow_ of the sea interfere with the cooling +influence of the air: and + +3rdly--_Salt_ never freezes till the surface is cooled down at least 25 +degrees _below the freezing point_. + + +Q. _Why do some LAKES RARELY if ever FREEZE?_ + +A. 1st--Because they are _very deep_: + +2ndly--Because their water is supplied by _springs_, which bubble from +the bottom. + + +Q. _Why does the DEPTH of the water RETARD its FREEZING?_ + +A. As the _whole volume of water_ must be reduced to 42 degrees before +the _surface will freeze_, the _deeper_ the water, the _longer_ it will +be before the whole volume is thus reduced. + + +Q. _Why do SPRINGS at the bottom of a lake PREVENT its FREEZING?_ + +A. Because they keep continually sending forth _fresh water_, which +prevents the lake from being reduced to the necessary degree of +coldness. + + +Q. _Why is it COLDER in a THAW than in a FROST?_ + +A. When frozen water is _thawed_, it absorbs _heat from the air and +objects around_ to melt its ice, in consequence of which the cold is +greatly increased. + + +Q. _Why is it WARMER in a FROST than in a THAW?_ + +A. When water freezes it _gives out its latent heat_, in order that it +may be converted into _solid ice_; and as much _heat is liberated_ from +the water into the air, we feel warmer. + + +Q. _Why does SALT DISSOLVE ICE?_ + +A. Water freezes at 32°, but salt and water will not freeze _till the +air is 25° colder_: if, therefore, salt be added to frozen water it +becomes _liquid_, unless the thermometer stands below 7°, (which it +never does in our island). + + +Q. _Will any thing do INSTEAD of SALT?_ + +A. Yes; any _acid_, such as sulphuric, nitric, &c. + + +Q. _Why are SALT and SNOW mixed together, colder than SNOW?_ + +A. When _salt_ is mixed with snow, it _dissolves the crystals_ into a +fluid; and whenever a solid is converted to a liquid, _heat is +absorbed_, and the cold made more intense. + + +Q. _Why does FROST make the EARTH CRACK?_ + +A. During the warm weather the earth _absorbed abundance of moisture_, +which the winter _freezes_: and (as water _expands_ by frost) the +expanding water _thrusts the particles of earth apart from each other_, +and leaves a chink or crack behind. + + +Q. _Show the WISDOM of GOD in this arrangement._ + +A. These _cracks_ in the earth let in the air, the dew and rain, and +many gases favourable to vegetation. + + +Q. _Why does the EARTH CRUMBLE in SPRING?_ + +A. In spring the _ice_ of the clods _dissolves_, and the particles of +earth (which had been held apart by the expanded ice) are left +_unsupported_, and tumble into minute parts (because their _cement is +dissolved_). + + +Q. _Why does MORTAR CRUMBLE away in FROST?_ + +A. If the mortar was not _dried in the warm weather_, its moisture +_freezes_, _expands_, and thrusts the particles of the mortar away from +each other; but (as soon as the frost goes) the _water condenses_ and +leaves the mortar full of cracks and chinks. + + +Q. _Why does STUCCO PEEL from a WALL in FROSTY weather?_ + +A. If the stucco was not _dried in the warm weather_, its moisture +_freezes_, _expands_, and thrusts its particles away from the wall; but +as soon as the water condenses again by the thaw, the stucco (being +unsupported) _falls by its own weight_. + + +Q. _Why cannot BRICKLAYERS and PLASTERERS work in FROSTY weather?_ + +A. Because the bricks and plaster would _start from their position_ as +soon as the _frost_ came and expanded the mortar. + + +Q. _Why do BRICKLAYERS COVER their work with STRAW in spring and +autumn?_ + +A. Because straw is a non-conductor, and prevents the mortar of their +new work from _freezing_ during the cold nights of spring and autumn. + + +Q. _Why are WATER-PIPES often covered with STALL-LITTER in winter time?_ + +A. Because straw (being a non-conductor) prevents the _water of the +pipes from freezing_, and the _pipes from bursting_. + + +Q. _Why are delicate TREES covered with STRAW in WINTER?_ + +A. Because straw (being a non-conductor) prevents the _sap of the tree_ +from being frozen. + + +Q. _Can WATER be FROZEN in any way BESIDES by frosty weather?_ + +A. Yes; in very many ways. For example--a bottle of water wrapped in +_cotton_, and frequently _wetted with ether_, will soon freeze. + + +Q. _Why would WATER FREEZE if the bottle were kept constantly wetted +with ETHER?_ + +A. Because _evaporation_ would carry off the heat of the water, and +reduce it to _freezing point_. + + +Q. _Why does ETHER freeze under the RECEIVER of an AIR-pump, when the +air is exhausted?_ + +A. Because _evaporation_ is very greatly increased by the _diminution of +atmospheric pressure_; and the ether freezes by evaporation. + + +FREEZING MIXTURES. + +1. If nitre be dissolved in water, the heat of the liquid will be +reduced 16 degrees. + +2. If 5 oz. of nitre, and 5 of sal-ammoniac (both finely powdered) be +dissolved in 19 oz. of water, the heat of the liquid will be reduced 40 +degrees. + +3. If 3 lbs. of snow be added to 1 lb. of salt, the mixture will fall to +0° (or 32 degrees below freezing point). + +The two following are the coldest mixtures yet known:-- + +1. Mix 3 lbs. of muriate of lime with 1 lb. of snow. + +2. Mix 5 lbs. of diluted sulphuric acid with 4 lbs. of snow. + + +Q. _Why is it more easy to SWIM in the SEA than in a RIVER?_ + +A. Because the _specific gravity_ of salt water is _greater than that of +fresh_, and therefore it _buoys_ up the swimmer better. + + +Q. _How do cooks ascertain if their BRINE be SALT ENOUGH for pickling?_ + +A. They put an _egg into their brine_. If the egg _sinks_ the brine is +_not strong enough_, if the egg _floats_ it _is_. + + +Q. _Why will the EGG SINK if the brine be NOT STRONG enough for +pickling?_ + +A. As an egg is _heavier than water_, it will _sink_ if immersed +therein; but if as much _salt_ be added as the water can dissolve, the +egg will _float_. + + +Q. _Why will the EGG FLOAT in strong BRINE?_ + +A. Because the specific gravity of _salt and water_ is greater than that +of water _only_. + + +Q. _Why do persons SINK in water when they are UNSKILFUL SWIMMERS?_ + +A. 1st--Because (in their floundering about) they _take in water_ at +their nose and mouth, which makes them _heavier_: + +2ndly--FEAR _contracts the body_; and as the body is compressed by fear +into a smaller compass, it becomes _heavier_: and + +3rdly--The water and fear _take away the breath_; and when the breath is +taken from the body, its _bulk is reduced_, and it becomes _heavier_. + + +Q. _Why can QUADRUPEDS swim MORE EASILY than MAN?_ + +A. 1st--Because the _trunk_ of a quadruped is _lighter than water_, and +this is the greatest part of them: + +2ndly--The _position_ of a beast in water is a _natural_ one. + + +Q. _Why is it MORE DIFFICULT for a MAN to swim than for a BEAST?_ + +A. Because the _head and limbs_ of a man (like those of a beast) are +_heavier_ than water, and these compose more than _half his body_: + +2ndly--The _position_ of a man in water is _unnatural_ to him. + + +Q. _Why can FAT men SWIM more EASILY than SPARE men?_ + +A. _Fat is lighter than water_; and the _fatter_ a man is, the more +_buoyant_ will he be. + + +Q. _How are FISHES able to ASCEND to the SURFACE of water?_ + +A. Fishes have an _air-bladder_ near their abdomen: when this bladder is +_filled with air_, the fish increases in size; and (being lighter) +ascends through the water to its surface. + + +Q. _How are fishes able to DIVE in a minute to the BOTTOM of a stream?_ + +A. They _expel the air_ from their air-bladder; in consequence of which, +their _size is diminished_, and they sink instantly. + + + + +CHAPTER XXVII. + +LIGHT. + + +Q. _What is LIGHT?_ + +A. Rapid undulations of a fluid called ether, striking on the optic +nerve of the eye. (_See p. 46._) + + +The _heat_ of fire or of the sun sets the atoms of _matter_ in motion; +and these atoms, striking against the fluid _ether_, cause it to +undulate. + + +Q. _How FAST does LIGHT TRAVEL?_ + +A. Light travels so fast, that it would go eight times round the earth, +while a person counts "ONE." + + +Q. _Does ALL light travel equally fast?_ + +A. Yes; the light of the sun, or the light of a candle, or the light +from houses, trees, and fields. + + +Q. _Where does the LIGHT of HOUSES, TREES, and FIELDS come from?_ + +A. The light of the _sun_ (or of some lamp or candle) is _reflected from +their surfaces_. + + +Q. _Why are SOME surfaces BRILLIANT like glass and steel, and OTHERS +DULL like lead?_ + +A. Those surfaces which _reflect the most light_, are the most +_brilliant_; and those which _absorb_ light are _dull_. + + +Q. _What is meant by REFLECTING LIGHT?_ + +A. Throwing the rays of light _back again_, from the surface on which +they light. + + +Q. _What is meant by ABSORBING LIGHT?_ + +A. Letting the rays of light _sink below the surface_ which they touch, +so as not to be seen. + + +Q. _Why can a THOUSAND persons SEE the SAME OBJECT at the same time?_ + +A. Because it throws off from its surface _an infinite number of rays in +all directions_; and one person sees _one_ portion of these rays, and +another person _another_. + + +Q. _Why is the EYE PAINED by a SUDDEN light?_ + +A. Because the pupil of the eye is _burdened with rays_, before it has +had time to contract. + + +Q. _Why does it give us PAIN, if a CANDLE be brought suddenly towards +our BED at night time?_ + +A. In the dark _the pupils of the eyes dilate_ very much, in order to +_admit more rays_. When a candle is brought before them, the enlarged +pupil is _overladen with rays_, and feels pained. + + +Q. _Why CAN we BEAR the candle-light after a few moments?_ + +A, Because the pupil _contracts again_ almost instantly, and adjusts +itself to the quantity of light which falls upon it. + + +Q. _Why can we SEE NOTHING, when we leave a WELL-LIGHTED room, and go +into the DARK ROAD or street?_ + +A. Because the pupil (which _contracted_ in the bright room) does not +_dilate instantaneously_; and the contracted pupil is not able to +_collect rays enough_ (from the dark road or street) to enable us to see +before us. + + +Q. _Why do we SEE BETTER, when we get USED to the dark?_ + +A. Because the pupil _dilates_ again, and is able to gather together +more rays; in consequence of which, we see more distinctly. + + +Q. _If we look at the SUN for a few moments, why do all OTHER things +appear DARK?_ + +A. Because the pupil of the eye (which was _very much contracted_ by +looking at the sun) is _too small_ to collect sufficient rays from +_other objects_, to enable us to distinguish their colours. (_See_ +"accidental colours.") + + +Q. _If we watch a bright FIRE for a few moments, why does the ROOM seem +DARK?_ + +A. Because the pupil of the eye (which was very much _contracted_ by +looking at the fire) is _too small_ to collect sufficient rays from the +objects around, to enable us to distinguish their colours. + + +Q. _Why can we see the PROPER COLOUR of every object again, after a few +minutes?_ + +A. Because the pupil _dilates_ again, and accommodates itself to the +light around. + + +Q. _Why can TIGERS, CATS, and OWLS see in the DARK?_ + +A. Because they have the power of _enlarging the pupil of their eyes_, +so as to collect several scattered rays of light; in consequence of +which, they can _see distinctly_ when it is not light enough for us to +see _any thing at all_. + + +Q. _Why do CATS and OWLS SLEEP almost all DAY?_ + +A. As the pupil of their eyes is _very broad_, daylight _fatigues_ them; +so they close their eyes for relief. + + +Q. _Why do CATS keep WINKING, when they sit before a FIRE?_ + +A. As the pupil of their eyes is _very broad_, the light of the fire +_pains_ them; and they keep shutting their eyes to relieve the sensation +of too much light. + + +Q. _Why do TIGERS, CATS, OWLS, &c. PROWL by NIGHT for prey?_ + +A. As these animals cannot see distinctly in _strong daylight_, they +_sleep_ during the _day_: and as they can see clearly in the _dark_, +they prowl then for prey. + + +Q. _Why do GLOW-WORMS glisten by NIGHT only?_ + +A. Because the light of day is _so much stronger_, that it _eclipses_ +the feeble light of a glow-worm; in consequence of which, glow-worms are +_invisible by day_. + + +Q. _Why can we not see the STARS in the DAY-TIME?_ + +A. Because the light of day is so powerful, that it _eclipses the feeble +light of the stars_: in consequence of which, they are invisible by day. + + +Q. _Why can we see the STARS even at MID-DAY, from the bottom of a deep +WELL?_ + +A. As the rays of the sun never come _directly over a well_, but the +rays of the _stars_ do; therefore the light from those stars (in such a +situation) is more clear than the light of the _sun_. + + +Q. _What is the USE of TWO EYES, since they present only one image of +any object?_ + +A. The use of two eyes is to _increase the light_, or take in _more rays +of light_ from the object looked at, in order that it may appear _more +distinct_. + + +Q. _Why do we NOT see things DOUBLE, with TWO EYES?_ + +A. 1st--Because the _axis of both eyes is turned to one object_; and, +therefore, the _same impression_ is made on the ret´ina of _each eye_. + +2ndly--The nerves (which receive the impression) have _one point of +union_, before they reach the brain. + + +Q. _Why do we SEE OURSELVES in a GLASS?_ + +A. The rays of light from our face _strike against the surface of the +glass_, and (instead of being absorbed) _are reflected_, or sent back +again to our eye. + + +Q. _Why are the rays of light REFLECTED by a MIRROR?_ + +A. Because they cannot _pass through the impenetrable metal_ with which +the back of the glass is covered; so they _rebound back_, just as a +_marble_ would do if it struck against a wall. + + +Q. _When a marble is rolled towards a wall, what is that path THROUGH +WHICH IT RUNS called?_ + +A. The line of the _angle of incidence_. + + +Q. _When a marble REBOUNDS back again, what is the path it THEN +describes called?_ + +A. The line of the _angle of reflection_. + + +Q. _When the light of our face goes TO the GLASS, what is the path +through which it goes CALLED?_ + +A. The line of the _angle of incidence_. + + +Q. _When the light of our face is reflected BACK again from the mirror, +what is this RETURNING path called?_ + +A. The line of the _angle of reflection_. + + +Q. _Why does our reflection in a mirror seem to APPROACH us as we walk +TOWARDS it, and to RETIRE FROM us as WE retire?_ + +A. Because the line _of the angle of incidence_ is always _equal_ to the +_line and angle of reflection_. + +[Illustration: Here CA, EA and DB, FB are the lines of the angle of +incidence; and GA, KA and HB, LB are the lines of the angle of +reflection. When the arrow is at CD, its shadow will appear at GH, +because the line CA=GA and the angle CAB=angle GAB, &c.; and the same +may be said about the point D.] + + +Q. _Why can a man see his WHOLE PERSON reflected in a LITTLE MIRROR not +6 inches in length?_ + +A. Because the _line of the angle of incidence_ is always equal to the +_line and angle of reflection_. + + +Take the last figure--CD is much larger than the mirror AB; but the head +of the arrow C is reflected obliquely behind the mirror to G; and the +barb D appears at H.--Why? Because the line CA=AG and the angle +CAB=angle GAB, &c. The same may be said of the point D. + + +Q. _Why does a SHADOW in WATER always appear TOPSY-TURVY?_ + +A. Because the _line of the angle of incidence_ is always equal to the +_line and angle of reflection_. + +[Illustration: Here the arrow-head A strikes the water at F, and is +reflected to D; and the barb B strikes the water at E, and is reflected +to C. + +If a spectator stands at G, he will see the reflected lines CE and DF, +produced as far as G. + +It is very plain that the more elevated object A will strike the water, +and be projected from it more perpendicularly than the point B, and +therefore the shadow will seem inverted.] + + +Q. _When we see our SHADOW in WATER, why do we seem to STAND on our +HEAD?_ + +A. Because the _line of the angle of incidence_ is always equal to the +_line and angle of reflection_. + + +Suppose our head to be at A, and our feet at B; then the shadow of our +head will be seen at D, and the shadow of our feet at C. (_See last +figure._) + + +Q. _Why do WINDOWS seem to BLAZE at SUN-RISE and SUN-SET?_ + +A. Because glass is a good _reflector of light_; and the rays of the sun +(striking against the window glass) _are reflected_, or thrown back. + + +Q. _Why do NOT windows reflect the NOON-DAY rays also?_ + +A. They do, but the _reflection is not seen_. + + +Q. _Why is the reflection of the RISING and SETTING sun seen in the +window, and NOT that of the NOON-DAY sun?_ + +A. As the angle of _incidence_ always equals the _angle of reflection_, +therefore the rays of the noon-day sun enter the glass _too +perpendicularly_ for their reflection to be seen. + +[Illustration: Here AB represents a ray of the noon-day sun striking the +window at B; its reflection will be at C: + +But DB (a ray of the rising or setting sun) will be reflected to E (the +eye of the spectator).] + + +Q. _Why can we not see the REFLECTION of the SUN in a WELL, during the +day-time?_ + +A. Because the rays of the SUN _fall so obliquely_, that they _never +reach the surface of the water_ at all, but strike against the brick +sides. + +[Illustration: Let BDEC be the well, and DE the water. + +The ray AB strikes against the brick-work _inside_ the well; and + +The ray AC strikes against the brick-work _outside_ the well. + +None will ever touch the water DE.] + + +Q. _Why do we see the MOON reflected in a WELL very OFTEN?_ + +A. As the rays of the MOON are not so _oblique_ as those of the sun, +they will often reach the water. _(See next figure.)_ + + +Q. _Why are the STARS REFLECTED in a WELL, although the SUN is NOT?_ + +A. As the rays of the STARS are not so _oblique_ as those of the sun, +they will often reach the water. + +[Illustration: Here the moon's rays AB, AC, both strike the water DE, +and are reflected by it.] + + +Q. _In a sheet of water at noon, the sun appears to shine upon only ONE +spot, and all the REST of the water seems DARK,--WHY is this?_ + +A. Because the rays (which fall at various degrees of obliquity on the +water) are _reflected at similar angles_; but as only those which _meet +the eye of the spectator_ are visible, all the sea will appear dark but +_that one spot_. + +[Illustration: Here of the rays SA, SB, and SC, only the ray SC meets +the eye of the spectator D. + +The spot C, therefore, will appear luminous to the spectator D, but no +other spot of the water ABC.] + + +Q. _At night the MOON seems to be reflected from only ONE SPOT of a lake +of water, while all the REST seems DARK,--WHY is this?_ + +A. Because the rays (which fall at various degrees of obliquity on the +lake) _are reflected at similar angles_; but as only those which _enter +the eye of the spectator_ will be visible, all the water will appear +dark _but that one spot. (See last figure.)_ + + +Q. _Why are MORE STARS visible from a MOUNTAIN, than from a PLAIN?_ + +A. As the air _absorbs and diminishes light_, the _higher we ascend_, +the _less light will be absorbed_. + + +Q. _Why does the SUN seem LARGER at his RISE and SET, than it does at +NOON?_ + +A. Because the earth is surrounded by air, which acts like a _magnifying +glass_; and when the sun is near the horizon (as its rays _pass through +more of this air_), it is more magnified. + +[Illustration: Here SC represents a ray of the sun at noon, and MC a ray +of the sun near the horizon. DEG represents the air or atmosphere around +the earth. + +Because EC is longer than DC, therefore the rays of the sun at M pass +through _more air_ than the rays of the sun at S, and the sun is more +magnified.] + + +Q. _Why does the RISING and SETTING MOON appear so much LARGER, than +after it is risen higher above our heads?_ + +A. Because the earth is surrounded by air, which acts _like a magnifying +glass_; and when the moon is near the horizon (as its rays pass through +more of this air) it is more magnified. _(See last figure.)_ + + +Q. _When CANDLES are LIGHTED, we CANNOT SEE into the STREET or +road,--WHY is this?_ + +A. 1st--Because glass is a _reflector_, and throws the candle-light +_back into the room again_; and + +2ndly--The pupil of the eye (which has become _contracted_ by the light +of the room) is _too small_ to collect rays enough from the dark street, +to enable us to _see into it_. + + +Q. _Why can't persons in the street SEE into a WELL-LIGHTED ROOM?_ + +A. Because the pupil of their eyes is _much dilated by the dark_, and +cannot collect from the window sufficient rays to enable them to _see +into the room_. + + +Q. _Why do we often see the FIRE REFLECTED in our parlour WINDOW in +winter time?_ + +A. Because glass is a _good reflector_; and the rays of the fire +(striking against the window-glass) _are reflected back into the room +again_. + + +Q. _Why do we often see the shadow of our CANDLES in the window, while +we are sitting in our parlour?_ + +A. Because the rays of the candle (striking against the glass) are +_reflected back into the room_: and the _darker_ the night, the +_clearer_ the reflection. + + +Q. _Why is this reflection more clear, if the external AIR be DARK?_ + +A. Because the reflection is not then _eclipsed_ by the brighter rays of +the sun _striking on the other side of the window_. + + +Q. _Why is the SHADOW of an object (thrown on the wall) LARGER and +larger, the CLOSER any object be held to the CANDLE?_ + +A. Because the rays of light _diverge_ (from the flame of a candle) _in +straight lines_, like lines drawn from the centre of a circle. + +[Illustration: Here the arrow A held close to the candle, will cast the +shadow BF on the wall: while the same arrow held at C, would cast only +the little shadow D E.] + + +Q. _When we enter a long AVENUE of TREES, WHY does the avenue seem to +get NARROWER and narrower till it appears to MEET?_ + +A. Because the _further the trees are off_, the more _acute will be the +angle_ that any two will make with our eye. + +[Illustration: Here the width between the trees A and B will seem to be +as great as the line AB: But the width between the trees C and D will +seem to be no more than EF.] + + +Q. _In a long straight STREET, WHY do the houses seem to APPROACH NEARER +and nearer as they are more DISTANT?_ + +A. Because the more _distant the houses_ are, the more _acute will be +the angle_ which any two make with our eye. + + +Thus in the last figure-- + +If A and B were two houses at the top of the street, the street would +seem to be as wide as the line A B: + +And if C and D were two houses at the bottom of the street, the street +at the bottom would seem to be no wider than E F. + + +Q. _In an AVENUE of TREES, WHY do they seem to be SMALLER as their +distance increases?_ + +A. Because the _further the trees are off_, the more _acute will be the +angle_ made by their perpendicular height with our eye. + +[Illustration: Here the first tree A B will appear the height of the +line A B; but the last tree C D will appear only as high as the line E +F.] + + +Q. _In a long straight STREET, WHY do the houses seem to be SMALLER and +smaller the FURTHER they are OFF?_ + +A. Because the _further any house is off_, the more _acute will be the +angle_ made by its perpendicular height with our eye. + + +Thus in the last figure-- + +If A B be a house at the top of the street, its perpendicular height +will be that of the line A B. + +If C D be a house at the bottom of the street, its perpendicular height +will appear to be that of E F. + + +Q. _Why does a man on the TOP of a MOUNTAIN or church spire seem to be +no BIGGER than a CROW?_ + +A. Because the angle made by the _perpendicular height of the man_ (at +that distance) _with our eye_, is no bigger than the perpendicular +height of a _crow close by_. + +[Illustration: Let AB be a man on a distant mountain or spire, and CD a +crow close by: + +The man will appear only as high as the line CD, which is the height of +the crow.] + + +Q. _Why does the MOON appear to us so much BIGGER than the STARS, though +in fact it is a great deal SMALLER?_ + +A. Because the moon is _very much nearer to us_ than any of the stars. + +[Illustration: Let AB represent a fixed star, and CD the moon. + +AB, though much the larger body, will appear no bigger than EF; whereas +the moon (CD) will appear as big as the line CD to the spectator G. + +The moon is 240,000 miles from the earth, not quite a quarter of a +_million_ of miles. The nearest fixed stars are 20,000,000,000,000. +(i. e. 20 billions.) + +If a ball went 500 miles an hour, it would reach the moon in twenty +days: but it would not reach the nearest fixed star in 4,500,000 years. +Had it begun, therefore, when Adam was created, it would be no further +on its journey than a coach (which has to go from the bottom of Cornwall +to the top of Scotland) after it has past about three-quarters of a +mile.] + + +Q. _Why does the MOON (which is a sphere) APPEAR to be a FLAT surface?_ + +A. It is _so far off_, that we cannot distinguish any difference between +the _length of the rays_ which issue from the _edge_, and those which +issue from the _centre_. + +[Illustration: The rays AD and CD appear to be no longer than the ray +BD; but if all the rays seem of the same length, the part B will not +seem to be nearer to us than A and C, and therefore ABC will look like a +flat or straight line. + +The rays AD and CD are 240,000 miles long. + +The ray BD is 238,910 miles long.] + + +Q. _Why do the SUN and STARS (which are spheres) appear to be FLAT +surfaces?_ + +A. Because they are such an _immense way off_, that we can discern _no +difference of length_ between the rays which issue from the _edge_, and +those which issue from the _centre_ of these bodies. + + +The rays AD and CD appear no longer than BD; and as B appears to be no +nearer than A or C, therefore ABC must all seem equally distant; and ABC +will seem a flat or straight line. (See last figure.) + + +Q. _Why does DISTANCE make an object INVISIBLE?_ + +A. Because the angle (made by the _perpendicular height_ of the distant +object _with our eye_) is so very _acute_, that _one_ line of the angle +_merges in the other_. + +[Illustration: Here the tree AD would not be visible to the spectator C, +even if he were to approach as far as B; because no visible +perpendicular can be inserted between the two lines AC, DC, till after +the point B is past; when the tree will appear like a very little +speck.] + + +Q. _Why do TELESCOPES enable us to SEE objects INVISIBLE to the naked +eye?_ + +A. Because they _concentrate several rays_ within the tube of the +telescope, and _bend them upon the mirror or lens_, which acts as a +_magnifying glass_. + + +Q. _When a SHIP (out at sea) is approaching the shore, why do we SEE the +small MASTS before we see the bulky HULL?_ + +A. Because the _earth is round_, and the _curve_ of the sea _hides the +hull_ from our eyes, after the tall _masts_ have become visible. + +[Illustration: Here only that part of the ship above the line AC can be +seen by the spectator A; the rest of the ship is hidden by the swell of +the curve DE.] + + +Q. _What is meant by REFRACTION?_ + +A. The _bending of a ray of light_, as it passes from one medium to +another. + + +Q. _How is a ray of light BENT, as it passes from one medium to +another?_ + +A. When a ray of light passes into a _denser_ medium, it is bent +_towards the perpendicular_. When it passes into a _rarer_ medium, it is +bent _from_ the perpendicular. + +[Illustration: Suppose DE to be a perpendicular line. + +If AB (a ray of light,) enters the water, it will be bent _towards_ the +perpendicular to C. + +If (on the other hand) CB (a ray of light) emerges _from_ the water, it +would be bent _away from_ the perpendicular towards A.] + + +Q. _Why does a SPOON (in a glass of water) always appear BENT?_ + +A. Because as the light of the spoon _emerges from the water_, it is +_refracted_. + + +And the spoon looks like ABC. (See the last figure.) + + +Q. _Why does a river always appear more shallow than it really is?_ + +A. Because the light of the bottom of the river is REFRACTED as it +emerges out of the water: and (as a stick is not so long when it is +_bent_, as it is when it is _straight_) so the river seems less deep +than it really is. + + +Q. _How much deeper is a river than it seems to be?_ + +A. One-third. If, therefore, a river seems only 4 feet deep, it is +really 6 feet deep. + + +N. B. Many boys get out of their depth in bathing, in consequence of +this deception. Remember, a river is always one-third deeper than it +appears to be:--thus, if a river seems to be 4 feet deep, it is in +reality 6 feet deep, and so on. + + +Q. _Why do fishes always seem to be nearer the surface of a river than +they really are?_ + +A. Because the rays of light from the fish are _refracted_ as they +emerge from the eye: and (as a bent stick is not so far from end to end +as a straight one) so the fishes appear nearer our eye than they really +are. + + +Q. _Why are some persons NEAR-SIGHTED?_ + +A. Because the COR´NEA of their eye is so _prominent_, that the image of +distant objects is reflected _before it reaches the_ RET'INA; and, +therefore, is not distinctly seen. + + +N.B. The cor´nea shields the CRYSTALLINE LENS, and is more or less +convex according to the lens which it covers. + + +Q. _What is meant by the "COR'NEA of the EYE?"_ + +A. All the _outside_ of the visible part of the _eye-ball_. + +[Illustration: The curve A B C is called the COR'NEA. + +If this curve be too prominent (or convex), the eye is near-sighted. + +If too flat (or concave), the eye is far-sighted.] + + +Q. _What is meant by the "RET'INA of the EYE?"_ + +A. The net-work which lines the _back of the eye_, is so called. + +[Illustration: The net-work ABC is called the ret'ina, and the +projecting part DEF is called the cor'nea.] + + +Q. _What sort of GLASSES do NEAR-SIGHTED persons wear?_ + +A. If the cor'nea be _too convex_ (or projecting), the person must wear +double _concave glasses_, to counteract it. + + +Q. _What is meant by "DOUBLE CONCAVE GLASSES?"_ + +A. Glasses hollowed in _on both sides_. + +[Illustration: The figure A is double concave, or concave on both +sides.] + + +Q. _What is meant by the "IMAGE of objects being reflected BEFORE it +reaches the RET'INA?"_ + +A. If the cor'nea be _too convex_, the image of a distant object is +reflected (on the vitreous humours of the eye) _before it reaches the +ret'ina_. + +[Illustration: Thus the image is reflected at DE, instead of on ABC (the +ret'ina).] + + +Q. _What is the use of DOUBLE CONCAVE SPECTACLE glasses?_ + +A. Near-sighted spectacles _cast the reflection further back;_ and the +image (being _thrown upon the ret'ina_) becomes visible. + + +Q. _Why are OLD people FAR-SIGHTED?_ + +A. Because the humours of their eyes _are dried up by age_, and the +COR'NEA _sinks in_, or becomes flattened. + + +Q. _Why does the FLATTENING of the COR'NEA prevent persons seeing +objects which are NEAR?_ + +A. As the cor'nea _is too flat_, the image of any near object is formed +_behind the RET'INA of the eye_, and is not seen at all. + +[Illustration: The reflection is made at DE, instead of at ABC (the +retina).] + + +Q. _What sort of GLASSES do OLD people WEAR?_ + +A. As their cor'nea is _not sufficiently convex_, they must use _double +convex glasses_, to enable them to see objects near at hand. + + +Q. _What sort of glasses are DOUBLE CONVEX SPECTACLE-GLASSES?_ + +A. Glasses which _curve outwards_ on both sides. + +[Illustration: The figure A is double convex, or convex on both sides.] + + +Q. _What is the USE of DOUBLE CONVEX spectacle-glasses?_ + +A. As the image of near objects is reflected _behind the RET'INA_, these +double convex glasses _shorten the focus of the eye_, and bring the +image _into the eye_ (upon the ret'ina). + + +Q. _Why do NEAR-SIGHTED persons bring objects CLOSE to the eye, in order +to SEE THEM?_ + +A. As the distance between the _front and back of their eye is too +great_, distant objects are reflected _before they reach the ret'ina_; +therefore, near-sighted persons bring the objects _closer_, in order +that the reflection _may be cast further back_, (to reach the ret'ina). + + +Q. _Why do OLD people HOLD objects FURTHER OFF, in order to see them +better?_ + +A. As the distance between the _front and back of their eye is not great +enough_, the reflection of near objects is thrown _beyond the ret'ina_; +therefore, they hold objects _a long way off_, in order to bring their +images _forward_ (so as to cast it on the ret'ina). + + +Q. _Why are HAWKS able to see such an IMMENSE way off?_ + +A. Because they have a muscle in the eye which enables them to _flatten +their cor'nea_, by drawing back the crystalline lens. + + +This muscle is called the "marsupium." + + +Q. _Why can HAWKS not only see such a long way off, but also objects +within half-an-inch of their eye?_ + +A. Because their eyes are furnished with a broad circular rim which +_confines the action of this muscle_, and throws the _cor'nea forward_. + + +Q. _Into how many PARTS may a RAY of LIGHT be DIVIDED?_ + +A. Into three parts: BLUE, YELLOW, and RED. + +N.B. These 3 colours, by combination, make seven. 1.--RED. 2.--Red and +yellow form ORANGE. 3.--YELLOW. 4.--Yellow and blue make GREEN. +5.--BLUE. 6 and 7.--Shades of blue called INDIGO and VIOLET. + + +Q. _How is it KNOWN, that a ray of light consists of several different +colours?_ + +A. Because, if a ray of light be cast upon a triangular piece of glass +(called a prism), it will be distinctly divided into seven colours: +1.--Red; 2.--Orange; 3.--Yellow; 4.--Green; 5.--Blue; 6.--Indigo; and +7.--Violet. + + +Q. _Why does a PRISM DIVIDE a ray of light into VARIOUS COLOURS?_ + +A. Because all these colours have _different refractive powers_. Red is +refracted _least_, and blue the _most_; therefore, the _blue_ colour of +the ray will be bent to the _top_ of the prism, and the _red_ will +remain at the _bottom_. + +[Illustration: Here the ray AB received on a prism, would have the blue +part bent up to C; the yellow part to D; and the red part no further +than E.] + + +Q. _What is meant by the REFRACTION of a ray?_ + +A. _Bending it_ from its straight line. + + +Thus the ray AB of the last figure is refracted at B into three courses, +C, D, and E. + + +Q. _What is the cause of a RAINBOW?_ + +A. When the clouds opposite the sun _are very dark_, and rain is _still +falling_ from them, the rays of the bright sun _are divided by the +rain-drops_, as they would be by a prism. + +[Illustration: Let A, B, and C be three drops of rain; SA, SB, and SC +three rays of the sun. SA is divided into the 3 colours; the blue and +yellow are bent _above_ the eye D, and the _red_ enters it. + +The ray SB is divided into the three colours; the blue is bent _above_ +the eye, and the red falls _below_ the eye D; but the _yellow_ enters +it. + +The ray SC is also divided into the three colours. The blue (which is +bent most) enters the eye; and the other two fall below it. Thus the eye +sees the blue of C, and all drops in the position of C; the yellow of B, +and of all drops in the position of B; and the red of A, &c.; and thus +it sees a rainbow.] + + +Q. _Does EVERY person see the SAME colours from the SAME DROPS?_ + +A. No; _no two persons_ see the _same rainbow_. + +To another spectator the rays from SB might be _red_ instead of yellow; +the ray from SC, yellow; and the blue might be reflected from some drop +below C. To a _third_ person the red may issue from a drop above A, and +then A would reflect the yellow, and B the blue, and so on. + + +Q. _Why are there often TWO RAINBOWS at one and the same time?_ + +A. In _one_ rainbow we see the rays of the sun _entering the rain-drops +at the top_, and reflected to the eye _from the bottom_. + +In the _other_ rainbow, we see the rays of the sun _entering the +rain-drops at the bottom_, and reflected to the top, whence they reach +the eye. + +[Illustration: Here the ray SA strikes the drop at A,--is refracted or +bent to B,--is then reflected to C, where it is refracted again, and +reaches the eye of the spectator.] + +[Illustration: Here the ray SB strikes the drop at B,--is refracted to +A,--is then reflected to C,--is again reflected to D, when it is again +refracted or bent till it reaches the eye of the spectator.] + + +Q. _Why are the COLOURS of the SECOND bow all REVERSED?_ + +A. Because in _one_ bow we see the rays which enter at the _top_ of the +raindrops, _refracted from the bottom_: + +But in the _other_ bow we see the rays which enter at the _bottom_ of +the raindrops (after two reflections), _refracted from the top_. + +[Illustration: Here A, B, C, represent three drops of rain in the +PRIMARY (or inner) RAINBOW. + +The _least_ refracted line is RED, and BLUE the _most_. + +So the RED (or _least_ refracted rays) of all the drops in the position +of A,--the YELLOW of those in the position of B,--and the BLUE (or the +_most_ refracted rays) of the lowest drops, all meet the eye D, and form +a rainbow to the spectator. + +The reason why the primary bow exhibits the stronger colours is +this--because the colours are seen after _one_ reflection and _two_ +refractions; but the colours of the secondary (or upper) rainbow undergo +_two_ reflections and _three_ refractions.] + +[Illustration: Here also the _least_ refracted ray is RED, and the +_most_ refracted BLUE (as in the former case); but the position of each +is reversed.] + + +Q. _Why does a SOAP BUBBLE exhibit such VARIETY of COLOURS?_ + +A. The changing colour of the bubble depends upon the changing +_thickness of the film_ through which the ray passes. + + +Q. _How does the THICKNESS of the FILM affect the COLOUR of the soap +bubble?_ + +A. Because different _degrees of thickness_ produce different _angles of +refraction_, and, therefore, different colours reach the eye. + + +Q. _Why is the SOAP BUBBLE so constantly CHANGING its THICKNESS?_ + +A. As the bubble is _suspended_, the water keeps _running down from the +top_ to the bottom of the bubble, till the crown becomes so _thin_ as to +burst. + + +Q. _Why are the late EVENING CLOUDS RED?_ + +A. Because RED rays (being the _least refrangible_) are the _last to +disappear_. + +[Illustration: Here it will be seen that the red ray PA, being reflected +on the horizon at A, will be visible to us; but the YELLOW and BLUE rays +will be hidden by the curve of the earth.] + + +Q. _Why are the early MORNING clouds RED?_ + +A. Because RED rays (being the _least refrangible_) are the _first to +appear_. + + +_See last figure._--It is evident that PA (the red rays) will be +reflected on the horizon before either the yellow or blue ones. + + +Q. _What becomes of the BLUE and YELLOW rays?_ + +A. They are refracted _below the horizon_, and are soon made invisible +by the _curve of the earth_. (_See last figure._) + + +Q. _Why are the EDGES of CLOUDS more LUMINOUS than their CENTRES?_ + +A. Because the _body of vapour is thinnest_ at the edges of the clouds. + + +Q. _What is the cause of morning and evening TWILIGHT?_ + +A. When the sun is below the horizon, the rays (which strike upon the +atmosphere or clouds) _are bent down towards the earth_, and produce a +little light called twilight. + + +_See figure on p. 399._--Here the rays of PA will give _some_ light. + + +Q. _Why is a ray of LIGHT composed of VARIOUS COLOURS?_ + +A. If solar light were of _one colour only_, all objects would appear of +_that one colour_ (or else black.) + + +Q. _Why are some things of ONE COLOUR, and some of ANOTHER?_ + +A. As every ray of light is composed of all the colours of the rainbow, +_some_ things reflect _one of these colours_, and some _another_. + + +Q. _Why do some things reflect ONE COLOUR, and some ANOTHER?_ + +A. Because the _surface_ of things is so _differently constructed_, both +physically and chemically; and, therefore, _some_ things reflect _one_ +ray; some _two rays_; some _all_ the rays; and some _none_. + + +Q. _What mainly determines the COLOUR of any object?_ + +A. The fluid or gas either _in_ the body, or on its _surface_. + + +N. B. Nitrogen gives green,--Oxygen gives red,--Hydrogen gives blue +colours. + + +Q. _Why does DYING a silk, &c. CHANGE its COLOUR?_ + +A. Because the materials used in dyeing _alter the chemical +construction_ of the substance dyed. + + +Q. _Why is a ROSE RED?_ + +A. Because the surface of a rose _absorbs the blue and yellow_ rays of +light, and _reflects_ only the _red_ ones. + + +Q. _Why does a rose absorb the yellow and blue rays, and reflect the +RED?_ + +A. Because the action of the sun's rays on the oxygen (accumulated in +the petals) produces an _acid_ which turns them _red_. + + +The leaves which compose a flower, are called PETALS. + + +Q. _Why is a VIOLET BLUE?_ + +A. Because the surface of the violet _absorbs the red and yellow_ rays +of the sun, and _reflects_ the _blue_ only. + + +Q. _Why do violets absorb the red and yellow rays, and reflect the +BLUE?_ + +A. Because the petals of the violet contain an _alkali_, which gives +them a _purple tinge_. + + +Q. _Why is a PRIMROSE YELLOW?_ + +A. Because the surface of the primrose _absorbs the blue and red_ rays +of solar light, and _reflects_ the _yellow_ ones. + + +All plants which have much alkali in their ash, have blue or yellow +flowers. + +Those which have acid in their ash, have orange, pink, or red flowers. + +N. B. Anti-acids (like soda) are called ALKALIS. + + +Q. _Why are some things BLACK?_ + +A. Because they _absorb all the rays of light_, and reflect _none_. + + +Q. _Why are some things WHITE?_ + +A. Because they _absorb none of the rays of light_, but reflect them +_all_. + + +Q. _Why are COALS BLACK?_ + +A. Because they _absorb all the rays of the sun_ which impinge upon +them, and stifle their reflection. + + +Q. _Why is SNOW WHITE?_ + +A. Snow consists of a vast number of crystals (or small prisms), which +separate the rays into their elemental colours; but as these crystals +are very numerous, the colours _unite again_ before they meet the eye, +and _appear white_. + + +N. B. The combination of _all_ colours makes WHITE. + + +Q. _Why is SUGAR WHITE?_ + +A. Sugar consists of a vast number of small crystals, which separate the +rays into their elemental colours; but as these crystals are very +numerous, the colours _unite again_ before they meet the eye, and appear +_white_. + + +Q. _Why is SALT WHITE?_ + +A. Salt consists of a vast number of small crystals, which reflect the +various rays of light from different points of the salt; and as these +colours _unite_ before they meet the eye, the salt appears to be +_white_. + + +N. B. The combination of _all_ colours makes WHITE. + + +Q. _Why are the LEAVES of plants GREEN?_ + +A. Because the _carbon_ of the leaves is a _bluish olive_, and the _sap_ +and _tissue of the cells_, YELLOW; when, therefore, the _yellow sap_ +flows into the _blue carbon_, it produces a _green leaf_. + + +Q. _Why are leaves a LIGHT green in SPRING?_ + +A. Because the young leaves of spring have _more sap_ than _carbon_; +and, therefore, the _yellow_ of the green prevails. + + +Q. _Why are leaves a YELLOWISH BROWN in AUTUMN?_ + +A. Because the _carbon_ of the leaves is _dying away_, and the yellow +tinge of the _tissue_ and _falling sap_ prevails over the blue. + + +Q. _Why are plants a PALE YELLOW when kept in the DARK?_ + +A. Solar light is essential for the production of _carbon_; and as +plants kept in the dark _lose their carbon_, they lose the _blue colour_ +which should convert their yellow sap to _green_. + + +Q. _Why are POTATOES YELLOW?_ + +A. Potatoes are grown _underground_, and, therefore, contain very little +_carbon_ (or blue colour); hence the _yellow sap_ of the potato is not +converted to green by carbon. + + +Q. _Why are potatoes (which grow EXPOSED to the air and light) GREEN?_ + +A. Because the sun-light _increases their carbon_; which (mingling with +the yellow sap) turns the potato _green_. + + +Q. _Why is it DANGEROUS to SLEEP in a room which contains LIVING +PLANTS?_ + +A. Because they _exhale carbon in the dark_ in the form of CARBONIC ACID +GAS, which is destructive to animal life. + + +Q. _Why are SOME things (like glass) TRANSPARENT?_ + +A. In transparent bodies (like glass) all the rays of light _emerge on +the opposite side_. + + +Q. _Why are SOME things SHINING and splendid?_ + +A. Those objects which _reflect the most rays_ are the most _splendid_; +and those which _absorb_ them most, are _dull_. + + +Q. _Why are DESERTS so DAZZLING in summer time?_ + +A. Because each separate grain of sand _reflects the rays of the sun_ +like a mirror. + + +Q. _If you move a stick (burnt at one end) ROUND pretty briskly, it +seems to make a CIRCLE OF FIRE,--WHY is this?_ + +A. Because the eye _retains the image_ of any bright object, _after the +object itself is withdrawn_; and as the spark of the stick returns +_before the image has faded_ from the eye, therefore, it seems to form a +_complete circle_. + + +Q. _If separate figures (as a man and a horse) be drawn on separate +sides of a card, and the card TWISTED quickly, the man seems to be +seated on the horse,--WHY is this?_ + +A. Because the image of the horse _remains upon the eye_ till the _man_ +appears. + + +The Thaumatrope is constructed on this principle. + + +Q. _Why do the STARS TWINKLE?_ + +A. Fixed stars are _so far off_, that their rays of light do not strike +upon the eye _in a continuous flow_, but at _intervals_: when their rays +_reach the eye_, the star becomes _visible_, and then is obscured _till +the next batch of rays arrive_; and this _perpetually_ occurring, makes +a kind of _twinkling_. + + +Q. _If we look at a RED-hot FIRE for a few minutes, WHY does every thing +seem TINGED with a BLUISH GREEN colour?_ + +A. Because bluish green is the "ACCIDENTAL COLOUR" of red: and if we fix +our eye upon _any colour whatsoever_, when we turn aside, we see every +object tinged with _its accidental colour_. + + +Q. _If we wear BLUE GLASSES, (when we take them off,) every thing +appears tinged with ORANGE,--WHY is this?_ + +A. Because _orange_ is the "_accidental colour_" of blue: and if we look +through _blue glasses_, we shall see its "_accidental colour_," when we +lay our glasses aside. + + +Q. _If we look at the SUN for a few moments, every thing seems tinged +with a VIOLET colour,--WHY is this?_ + +A. Because _violet_ is the "accidental colour" of _yellow_ light; and as +the sun is _yellow_, we shall see its "accidental colour" _blue_, when +we turn from gazing at it. + + +Q. _Does not the DARK SHADOW (which seems to hang over every thing after +we turn from looking at the sun) arise from our eyes being DAZZLED?_ + +A. Partly so: the pupil of the eye is _very much contracted_ by the +brilliant light of the sun, and does not adjust itself immediately to +the feebler light of terrestrial objects; but, independent of this, the +"ACCIDENTAL COLOUR" of the sun being _dark violet_, would tend to throw +a shadow upon all things. (_See p. 366._) + + +Q. _Why is BLACK glass for spectacles the BEST for wear?_ + +A. Because _white_ is the accidental colour of _black_; and if we wear +_black glasses_, every thing will appear _in white light_, when we take +them off. + + +Q. _Why does every thing seem shadowed with a BLACK MIST, when we take +off our common SPECTACLES?_ + +A. Because the glasses are _white_, and black being its "accidental +colour," every thing appears in a _black shade_, when we lay our glasses +down. + + The accidental colour of red is bluish green. + " " " of orange " blue. + " " " of violet " yellow. + " " " of black " white. + +And the converse of this is true:-- + + The accidental colour of bluish green is red. + " " " of blue " orange. + " " " of yellow " violet. + " " " of white " black. + + +(The law of an accidental colour is this--The accidental colour is +always half the spectrum. Thus, if we take half the length of the +spectrum by a pair of compasses, and fix one leg in any colour, the +other leg will hit upon its accidental colour.) + +N. B. The spectrum means the seven colours--Red, orange, yellow, green, +blue, indigo, and violet, divided into seven equal bands, and placed +side by side in the order just mentioned. + + + + +CHAPTER XXVIII. + +SOUND. + + +Q. _What is SOUND?_ + +A. The vibration of some sonorous substance produces motion in the air +called SOUND WAVES, which strike upon the _drum of the ear_, and give +the sensation of sound. + + +Q. _What are MUSICAL SOUNDS?_ + +A. Regular and uniform successions of vibrations, which are always +pleasing to the ear. + + +Q. _How FAST does SOUND TRAVEL?_ + +A. About 13 miles in a minute, or 1142 feet in a second of time. + + +Q. _How fast does LIGHT TRAVEL?_ + +A. Light would go 8 times round the whole earth, while sound is going +its 13 miles. + + +Q. _Why are SOME things SONOROUS, and others NOT?_ + +A. The sonorous quality of any substance depends upon its _hardness and +elasticity_. + + +Q. _Why are COPPER and IRON SONOROUS, and not LEAD?_ + +A. Copper and iron are _hard and elastic_; but as lead is neither hard +nor yet elastic, it is _not sonorous_. + + +Q. _Of what is BELL-METAL made?_ + +A. Of _copper and tin_ in the following proportions:--In every 5 pounds +of bell-metal, there should be 1 lb. of tin, and 4 lbs. of copper. + + +Q. _Why is this mixture of tin and copper used for BELL-METAL?_ + +A. Because it is much _harder_ and more _elastic_ than either of the +pure metals. + + +Q. _Why is the SOUND of a bell STOPPED by TOUCHING the bell with our +finger?_ + +A. The weight of the finger _stops the vibrations_ of the bell; and as +soon as the bell _ceases to vibrate_, it ceases to make sound-waves in +the air. + + +Q. _Why does a SPLIT BELL make a HOARSE disagreeable sound?_ + +A. The _split_ of the bell causes a _double vibration_; and as the +sound-waves _clash and jar_, they impede each other's motion, and +produce discordant sounds. + + +Q. _Why does a FIDDLE-STRING give a musical sound?_ + +A. The bow drawn across the string _causes it to vibrate_, and this +vibration of the string _sets in motion the sound-waves of the air_, and +produces musical notes. + + +Q. _Why does a DRUM sound?_ + +A. The parchment head of the drum _vibrates_ from the blow of the +drum-stick, and sets in motion the sound-waves of the air. + + +Q. _Why do MUSICAL GLASSES give sounds?_ + +A. Because the glasses _vibrate_ as soon as they are struck, and set in +motion the sound-waves of the air. + + +Q. _Why do FLUTES, &c. produce musical sounds?_ + +A. The breath of the performer causes the _air in the flute to vibrate_, +and sets in motion the sound-waves of the air. + + +Q. _Why do PIANO-FORTES produce musical sounds?_ + +A. The _keys of the piano_ (being struck with the finger) lift up a +little hammer which _knocks against a string_; and the vibration thus +produced, sets in motion the sound-waves of the air. + + +Q. _Why are SOME notes BASS and some TREBLE?_ + +A. _Slow_ vibrations produce _bass or deep sounds_; whereas, _quick_ +vibrations produce _shrill or treble sounds_. + + +Q. _Why is an instrument FLAT when the STRINGS are UNSTRUNG?_ + +A. Because the vibrations are _too slow_; in consequence of which, the +sounds produced are not _shrill_ or _sharp_ enough. + + +Q. _Why can persons living a mile or two from_ + + +_a town HEAR the BELLS of the town-church SOME TIMES, and not at +OTHERS?_ + +A. Fogs, rain, and snow, obstruct the passage of sound; but when the air +is _cold and clear_, sound is propagated more easily. + + +Q. _Why can we NOT hear sounds (as distant church bells) in RAINY +weather, so well as in FINE weather?_ + +A. Because the falling rain _interferes with the undulations of the +sound-waves_, and breaks them up. + + +Q. _Why can we not hear sounds (as distant church bells) in SNOWY +weather, so well as in FINE weather?_ + +A. Because the falling snow _interferes with the undulations of the +sound-waves_, and stops their progress. + + +Q. _Why can we HEAR distant clocks MOST distinctly in CLEAR COLD +weather?_ + +A. Because the air is most _uniform_ then: there are not _two currents +of air_ (one up and one down) to interrupt the sound-waves. + + +Q. _Why can persons hear the VOICES of men in conversation for a MILE +distant, near the POLES, in winter time?_ + +A. Because the air is very _cold and very clear_; in consequence of +which, there are not _two currents of air_ (one up and one down) to +interrupt the sound-waves. + + +Captain Ross heard the voices of his men in conversation, a mile and a +half from the spot where they stood. + + +Q. _Why are not SOUNDS (such as distant church bells) heard so +distinctly on a HOT DAY as in FROSTY weather?_ + +A. Because there are _two currents of air_; the current of _hot_ air +_ascending from the earth_, and the current of _colder_ air _falling +towards_ the earth; and these two currents _break up the sound-waves_. + + +Q. _Why can we not hear SOUNDS (such as distant clocks) so distinctly in +a thick MIST or HAZE, as in a CLEAR night?_ + +A. Because the mist _diminishes the velocity_ of the sound-waves, and +(by overburdening them with vapour) _limits their length_. + + +Q. _Why do we hear SOUNDS better by NIGHT than by DAY?_ + +A. 1st--Night air is _more uniform_, because the ascending currents of +air (raised by the action of the sun's rays) _cease_ as the evening +advances; and + +2ndly--Night is more _still_ from the suspension of business, and the +cessation of the hum of men. + + +Q. _How should PARTITION WALLS be made to PREVENT the voices in +adjoining rooms from being HEARD?_ + +A. The space between the laths (or canvass) should be filled with +_shavings or saw-dust_; and then no sound would ever pass from one room +to another. + + +Q. _Why would SHAVINGS or saw-dust PREVENT the transmission of sound +from room to room?_ + +A. Because there would be _several different media_ for the sound to +pass through: 1st--the air; + +2ndly--the laths and paper; + +3rdly--the saw-dust or shavings; + +4thly--the air again: and every _variety_ diminishes the _strength of +the sound-waves_. + + +Q. _Why can DEAF people hear through an EAR TRUMPET?_ + +A. The ear trumpet restrains _the spread of the voice_, and limits the +_diameter of the sound-waves_; in consequence of which, their +_strength_ is increased. + + +Q. _Why are MOUNTAINS so NOISELESS and quiet?_ + +A. Because the air of mountains is _very rarefied_; and as the air +becomes _rarefied_, sound becomes less _intense_. + + +Q. _How do you know that the RARETY of air DIMINISHES the intensity of +SOUND?_ + +A. If a bell be rung in the receiver of an air-pump, the sound becomes +_fainter and fainter_ as the air is exhausted, till at last it is quite +_inaudible_. + + +Q. _What is the cause of ECHO?_ + +A. Whenever a sound-wave strikes against any _obstacle_ (such as a wall +or hill), _it is reflected_ (or thrown back); and this _reflected sound_ +is called an ECHO. + + +The same laws govern echo as light. (_See p. 370._) + + +Q. _What places are most FAMOUS for ECHOES?_ + +A. Caverns, grottoes, and ruined abbeys; the areas of antique halls; the +windings of long passages; the aisles of cathedral churches; mountains, +and ice-bergs. + + +Q. _Why are caverns, grottoes, and ruined abbeys FAMOUS for ECHOES?_ + +A. 1st--Because the sound-waves cannot pass _beyond_ the cavern or +grotto, and _must flow back_: + +2ndly--The _return waves_ (being entangled by the cavern) are _detained_ +for a short time, and come _deliberately_ to the ear. + + +Q. _Why are antique halls, winding passages, and cathedral aisles FAMOUS +for ECHOES?_ + +A. Because the sound-waves _cannot flow freely forward_, but strike +against the winding walls perpetually, and are beaten _back_. + + +Q. _Why are MOUNTAINS and ice-bergs FAMOUS for ECHOES?_ + +A. Because they present a _barrier_ to the sound-waves _which they +cannot pass_; and are sufficiently elastic to _throw them back_. + + +Q. _Why do not the walls of a ROOM or church produce ECHO?_ + +A. Because sound travels with such _velocity_, that the echo is _blended +with the original sound_, and produce but _one impression_ on the ear. + + +Sound travels 13 miles in a minute. + + +Q. _Why do very LARGE buildings (as cathedrals), often REVERBERATE the +voice of the speaker?_ + +A. Because the walls are _so far off from the speaker_, that the echo +does not _get back in time_ to blend with the original sound; and, +therefore, _each_ is heard separately. + + +Q. _Why do SOME echoes repeat only ONE syllable?_ + +A. The _further_ the echoing body is _distant_, the _more sound_ it will +_reflect_. If, therefore, the echoing body be _near_, it will repeat but +one syllable. + + +Q. _Why does an ECHO sometimes repeat TWO or more syllables?_ + +A. Because the echoing body is _far off_; and, therefore, there is time +for one reflection _to pass away_ before _another_ reaches the ear. + + +Q. _Why do WINDOWS RATTLE when CARTS pass by a house?_ + +A. 1st--Glass is _sonorous_; and the air communicates its vibrations to +the glass, which echoes the same sound: and + +2ndly--The _window-frame is shaken_ by the sound-waves _impinging +against the window_, and contributes to the noise. + + + + +CHAPTER XXIX. + +MISCELLANEOUS. + + +Q. _Why do the BUBBLES in a CUP OF TEA range round the SIDES of the +CUP?_ + +A. Because the cup _attracts them_. + + +Q. _Why do all the LITTLE BUBBLES tend towards the LARGE ones?_ + +A. Because the large bubbles (being the superior masses) _attract them_. + + +Q. _Why do the BUBBLES of a CUP OF TEA FOLLOW a TEA-SPOON?_ + +A. Because the tea-spoon _attracts them_. + + +Q. _Why are the SIDES of a pond covered with LEAVES, while the MIDDLE of +the pond is quite CLEAR?_ + +A. Because the shore _attracts_ the leaves to itself. + + +Q. _Why do all fruits, &c. (when severed from the tree) FALL to the +EARTH?_ + +A. Because the earth _attracts them_. + + +Q. _Why do persons (who water PLANTS) very_ + + +_often pour the water into the SAUCER, and not OVER the PLANTS?_ + +A. Because the water in the saucer is _supped up_ by the mould (through +the hole at the bottom of the flower-pot), and is transferred to the +stem and leaves of the plant by CAPILLARY ATTRACTION, (_See p. 84_). + + +Q. _Why is vegetation on the MARGIN of a RIVER more LUXURIANT than in an +open FIELD?_ + +A. Because the porous earth on the bank _sups up water_ to the roots of +the plants by CAPILLARY ATTRACTION. + + +Q. _Why is a LUMP of SUGAR (left at the bottom of a cup) so LONG in +MELTING?_ + +A. Because _as it melts_, it makes the tea above it _heavier_; and (so +long as it remains at the bottom) is surrounded by tea fully _saturated_ +with sugar; in consequence of which, the _same_ portions of liquid will +hold _no more sugar in solution_. + + +Q. _Why does the LUMP of SUGAR MELT more QUICKLY when STIRRED ABOUT?_ + +A. Because _fresh portions of unsaturated tea_ keep coming in contact +with the lump, and soon dissolve it. + + +Q. _Why does a PIECE OF SUGAR (held in a spoon at the TOP of our tea) +melt very RAPIDLY?_ + +A. Because as the tea becomes _sweetened_, it _descends to the bottom of +the cup_ by its own gravity; and _fresh_ portions of unsweetened tea are +brought constantly into contact with the sugar, till the lump is +entirely dissolved. + + +Q. _How can a SICK ROOM be kept FREE from unhealthy EFFLUVIA?_ + +A. Vinegar boiled with myrrh, or camphor, sprinkled in a sick room, will +_entirely correct putridity_. + + +Q. _Why does LIME destroy the offensive smells of BINS, SEWERS, &c.?_ + +A. Because it combines with the _carbonic acid_ of these places, and +converts it into CARBONATE OF LIME, which is entirely _free from smell_. + + +Q. _Why does CHLORIDE of LIME fumigate a sick room?_ + +A. Because the chlorine absorbs the _hydrogen of the stale air_; and by +this means removes both the _offensive smell_ and the _infection_ of a +sick room. + + +Q. _How can the TAINT of MEAT be removed?_ + +A. Either by washing with PYROLIGNEOUS ACID,--covering it for a few +hours with common CHARCOAL,--or by putting a _few lumps of charcoal_ +into the _water in which it is boiled_. + + +Q. _Why do these things DESTROY the TAINT of meat?_ + +A. Because they _combine_ with the _putrescent particles_, and +neutralize their offensive taste and smell. + + +Q. _Why should BED-ROOMS, COTTAGES, HOSPITALS, and STABLES, be washed +occasionally with LIME-WHITE?_ + +A. Because the lime _is very caustic_, and removes all organic matters +adhering to the walls. + + +Q. _How can MOULDINESS be prevented?_ + +A. The perfume of _any essential oil_ will prevent mouldiness from ink, +paste, preserves, &c. + + +Alum, salt of amber, borax, nitre, salt, camphor, charcoal, and +pyroligneous acid, are all excellent antiseptics. + +Salt, corrosive sublimates, copperas, and alum, all arrest the decay of +timber. (_See p. 426._) + + +Q. _Why will strong SOUCHONG TEA POISON FLIES?_ + +A. Because it produces _prussic acid_, which destroys their _nervous +system_. + + +Q. _Why is strong GREEN TEA UNWHOLESOME?_ + +A. Because it contains _prussic acid_, which destroys the _nervous +system_. + + +Q. _Why is a DEAD man TALLER than a living man?_ + +A. Because at death the CARTILAGES are _relaxed_. So, also, after a +night's rest, a man is _taller_ than when he went to bed. + + +Q. _What is SLEEP?_ + +A. Sleep is the _rest of the brain_ and _nervous system_. + + +Q. _Why can we not SEE, when we are asleep with our EYES OPEN?_ + +A. Because the "RET´INA of the eye" is _inactive_ and at rest. + + +Q. _Why can we not HEAR in sleep?_ + +A. Because the drum or "TYMPANUM of the ear" is placid and at rest. + + +Q. _Why can we not TASTE when we are asleep?_ + +A. Because the nerves _at the end of the tongue_ (called papillæ) are +inactive and at rest. + + +Q. _Why can we not FEEL when we are asleep?_ + +A. Because the _ends of the nerves_ (called papillæ), situated in the +skin, are inactive and at rest. + + +Q. _Why have persons in sleep no WILL of their own, but may be moved at +the will of ANY one?_ + +A. Because the "CEREBELLUM" (or _posterior_ part of the brain) is +inactive and at rest. + + +Q. _Why have DREAMERS no power of JUDGMENT or REASON?_ + +A. Because the "CEREBRUM" (or _front_ of the brain) is inactive and at +rest. + + +Q. _Why are DREAMS such FOOLISH and INCONSISTENT things?_ + +A. Because the "PINEAL GLAND" is acting _without the brain_; and the +_faculty of thinking_ exists in the "PINEAL GLAND," but the _faculty of +judgment_ in the "CEREBRUM of the brain." + + +The cerebrum of the brain occupies the top and front of the skull. The +PINEAL GLAND is a small conical gland (about the size of a pea) _in the +brain_. + + +Q. _Why do some persons LOSE all POWER of SENSATION?_ + +A. Because the "CEREBRUM" (or _front_ of their brain) _has been +injured_. + + +Q. _Why are many persons IDIOTS?_ + +A. Because the "CEREBELLUM of the brain" _has been removed_ by some +accident, or _injured by some disease_. + + +The cerebellum is all the posterior part of the brain. + + +Q. _Why does a person FEEL when he is TOUCHED?_ + +A. The ends of certain nerves (called PAPILLÆ) situated in the skin +_erect themselves_ when touched, and produce a nervous sensation called +FEELING. + + +Q. _Why are persons able to TASTE DIFFERENT FLAVOURS?_ + +A. Because the "PAPILLÆ" of the tongue and palate _erect themselves_ +when food touches them, and produce a nervous sensation called TASTE. + + +Q. _Why do very OLD people LOSE the power of VOLITION, SENSATION, and +THOUGHT?_ + +A. Because their _brain ossifies_; and as the "_cerebrum_" (or _front_ +of the brain) goes, they lose the power of _sensation and reason_; and +as the "_cerebellum_" (or _posterior_ part of the brain) goes, they lose +the power of _volition_. + + +Q. _Why are OLD people UNABLE to WALK?_ + +A. Because their _muscles become rigid_. + + + + +GLOSSARY. + + + ACETIC ACID, commonly called Distilled Vinegar. + CITRIC " " Juice of Lemons. + NITRIC " " Aqua Fortis. + OXALIC " " Salt of Lemons. + SULPHURIC " " Oil of Vitriol. + SULPHATE OF LIME " Plaster of Paris. + " MAGNESIA " Epsom Salts. + " SODA " Glauber Salts. + " ZINC " White Vitriol. + NITRATE OF SILVER " Lunar Caustic. + ACETATE OF COPPER " Verdigris. + MURIATE OF SODA " Table Salt. + TARTRATE OF POTASH " Tartar Emetic. + CARBONATE OF AMMONIA " Smelling Salts. + " LIME " Chalk, Marble, &c. + SUPER-ACETATE OF LEAD " Sugar of Lead. + OXIDE OF LEAD " Goulard. + + +SUBLIMATES are chemical preparations, the basis of +which is quicksilver. In CORROSIVE SUBLIMATES, the +quicksilver is _extinguished_, either by vitriol, potter's clay, or +some other ingredient. + +SUBLIMATION is a similar process to distillation; only +_solids_(such as metals) are employed, instead of _liquids_. + +Thus the fine _blue_ used by painters is a sublimate, and +made thus:--Take 2 parts of quicksilver, 3 flower of +brimstone, 8 sal ammoniac; and (having ground them) +put them with the quicksilver into a glass retort, luted at +the bottom; place the retort in a sand-heat; and (when the +moisture is given off) you will have a splendid blue +sublimate for painting. + + + + +INDEX. + + + ABSORBERS, best, 192 + not conductors, 185 + not reflectors, 192 + radiators, 197 + + ABSORPTION of HEAT, 184 + not conduction, 184 + of light, 364 + + ACCIDENTAL COLORS, 407, 408 + + Acetate of lead, 426 + + Acetic acid, 426 + + Acid of drinks, 269 + of fermentation, 269 + + Activity affected by cold, 91 + " by heat, 93 + + Aerated water, 267 + + Aeronauts feel pain, 254 + + Age affects the sensation, thought, judgment, 425 + power of walking, 425 + + AIR, 240 + always in motion, 293 + bad conductor, 13, 177, 178 + bad radiator, 219, 237 + cold, 177 + colder than blood, 181 + composed of two gases, 27, 240 + cooled by convection, 220 + " by rain, 159 + cools hot iron, 246 + density diminished by rain, 337 + descends when cold, 289 + double current in a room, 290 + dries linen, 160 + elements of, 33 + expanded by heat, 103 + full of smells, 152 + gets fire up, 50 + healthful, 252 + heated, 219, 245, 246, 289 + " not by sun, 290 + in a room, 252 + inflammable, _see hydrogen_ + in summer, 313 + of cities unhealthy, 243, 253 + of the country healthy, 243, 252 + on land colder than on water, 224 + on land cold at night, 230 + preserved normal, 244 + purified by lightning, 27 + rusts iron, 257 + still before a tempest, 146 + strong, 108 + varies in temperature, 335 + + Aisles famous for echoes, 417 + + Alcohol, 109, 270, 271 + + ALE, 109 + bottled, 268 + froth of, 109 + froth increased by heat, 268 + + Alkali, 45 + + Anenometer, 314 + + Anglers hate a magpie, 153 + + Angle of incidence, 370 + of reflection, 370 + + Animal heat, 83, 85, 243, 277 + + Animals and vegetables co-dependent, 244 + + Ants love honey-dew, 221 + + Appetite, 89, 90, 91 + (_See hunger._) + + Apples full of air, 105 + roasted, 105 + soft, 106 + + April showers, 307 + + Aqua fortis, 426 + + Argand lamps, 83 + + Arnott's stoves smell of sulphur, 56 + smoke, 69 + + Ascent in balloons painful, 145 + + Ashes soften water, 345 + + Asses bray in wet weather, 148 + + Aurora borealis, 142, 285 + coloured, 143 + white, 142 + a prognostic, 143 + + Avenues, 380 + + Azote, _see nitrogen_ + + + Bales catch fire spontaneously, 57 + + Balloons, 146 + inflated, 109 + rise, 110 + + Balls of fire, 6 + + Banisters wet, 216 + + Barley malted, 270 + + BAROMETER, 317 + affected by cold, 328 + " frost, 329 + " heat, 328 + " thaw, 329 + " wind, 327 + rules for its rise and fall, 330 + sudden change in, 330 + use of, 319 + varies most in winter, 327 + " least in summer, 327 + when highest, 328 + " lowest, 328 + + Barren land collects no dew, 209 + + Bass notes in music, 412 + + Bass preserves flowers from frost, 206 + + Bathing, danger of, 387 + with ether for inflammation, 157 + + Beakers broken by hot water, 126 + + Beasts covered with hair, 176 + + Beds damp, 157 + + BEER, fermentation of, 269 + flat, 273 + froth increased by bottling, 268 + froth increased by heat, 268 + raisins and raw meat improve it, 273 + stale, 275 + soured by lightning, 27 + not _old_ beer, 27 + spoiled, if the vent-peg be left out, 273 + yeast added to make it work, 271 + + Beer-vats dangerous, 265 + + Bells heard at a distance, 412 + cracked, sound harsh, 411 + silenced by a touch, 411 + + Bell-metal, 410 + + Bellows, 51 + + Bins purified, 266 + + Birds covered with feathers, 176 + + BLACK, 402 + cloth warm, 186 + eyes, 191 + glass for spectacles, 408 + hat turns red at the sea-side, 344 + Hole of Calcutta, 250 + kid gloves, 188 + lead, 258 + " prevents rust, 258 + mist, 144 + skin, 190 + tea-pot, 197 + " used by cotters, 198 + " set on a hob to draw, 198 + will never blister, 190 + + Blacks, 60 + none to railway engines, 60 + + Blacksmiths strike fire by nails, 96 + + Bladders inflated by heat, 103 + + BLAZE, blue, 46 + green, 45 + yellow, 46 + between the bars of a grate, 45 + + Blazing coals burn quickly, 39 + + Blood red, 242 + purple, 242 + + Blowers, 70 + + Blowing cools broth, 180, 247, 312 + tea, 248 + + Blue, 401 + glasses, 407 + sky, 132 + sublimate, 426 + + Body warm, 87 + + BOILING, 234 + WATER bubbles, 114, 283 + makes it flat, 275 + is in a ferment, 232 + rattles, 116 + runs over, 115, 233 + swells, 114 + one pot will not boil in another, 118 + retarded by a spoon, 117 + " by salt, sugar, 118 + + Bottled ale, &c., 268 + + Brackish water unfit for railway engines, 263 + + Bread heavy, 276 + made with yeast, 276 + + Breath exhaled, 244 + visible in winter, 217 + + Breathing difficult on a mountain, 255 + previous to a storm, 255 + + BREEZE at watering places, 310 + evening, 309 + morning, 308 + of islands, 309 + speed of, 313 + (_See wind._) + + Bricks for cold feet, 173 + + Brick stoves, 174 + + Bricklayers cannot work in a frost, 359 + cover new work with straw, 359 + + Brilliancy, 364 + + Brine retards boiling, 119 + tested, 361 + + Broth cooled by breath, 247, 312 + by convection, 247 + by stirring, 247 + + Bubbles in tea, 419 + of boiling water, 114 + + Bulk for bulk, 110 + + Burns cured, 157 + + Burning glasses, 2 + + + Caloric, 1 + + Cambric handkerchiefs cool, 184 + + Cambridge, rain of, 340 + + CANDLES, 74 + burn, 74 + " blue, 148 + cotton, not easily blown out, 79 + easily blown out, 51, 78 + and rekindled, 51, 55 + extinguished, 79 + flame hot, 75 + " hollow, 76 + " pointed, 77 + " purple below, 76 + " tends upwards, 77 + " yellow, 76 + gas of, 281 + held at a door, 290 + hottest _above_ the flame, 79 + give light, 76 + make glass damp, 78 + need snuffing, 81 + Palmer's, 80 + prevent our seeing abroad, 378 + reflected in a window, 379 + rush, easily go out, 79 + smoke, 81 + spirt, 155 + suddenly introduced give pain, 365 + wax, need no snuffing, 81 + + Candlestick rags catch fire spontaneously, 58 + + Capillary veins, 84 + + Captain Ross, 414 + + Carbon, 33, 74 + + Carbonate of lime, 426 + of soda, 426 + + CARBONIC ACID GAS, 37, 108, 249, 264 + deleterious, 250, 264 + in human bodies, 84 + its presence detected, 264 + + CARBURETTED HYDROGEN GAS, 279, 280 + + Carpets warm, 169 + + Carriage wheels catch fire, 99 + + Carriage windows misty, 213 + + Casks charred, 73 + + Cart grease, 100 + + Cathedral aisles famous for echoes, 417 + + CATS in wet weather, 147 + prowl by night, 367 + rub their ears, 150 + see in the dark, 367 + wink before a fire, 367 + + Cattle uneasy in wet weather, 148 + + Caverns famed for echoes, 416 + + Ceilings sooty, 71 + + Cellars cold in summer, 256 + warm in winter, 256 + + Cerebellum, 424 + + Cerebrum, 424 + + Chalk, 426 + + CHARCOAL, 72 + bad conductor, 166 + fire, 72 + " deleterious, 265 + purifies water, 72 + removes the taint of meat, 72 + + Charring bread, 73 + casks, 73 + wood, 73 + + CHEMICAL ACTION, 30 + + Chestnuts crack when roasted, 104 + not if slit, 105 + + Chimney pots, 71 + + CHIMNEYS SMOKE, if a room be too close, 61 + remedy, 62 + in vestries, valleys, 66 + remedy, 67 + in wind, 66, 111 + if too long, 62, 116 + " short, 62 + " large, 69 + remedy, 70 + when the draught is slack, 63, 69 + when the door is on the same side, 68 + remedy, 68 + when it needs repairing, 68 + sweeping, 68 + when two fires are in one room, 65 + remedy, 65 + + China broken by hot water, 125 + + Choke damp, 264, 279 + + Church bells heard at a distance, 151 + + Churchyards smell offensively, 283 + + Chyle, 242 + + Cider, 269 + + Cinders, 43 + iron, 43 + will not blaze, 48 + + Cirro-cumulus clouds, 136 + + Cirro-stratus clouds, 134 + + Cirrus clouds, 134 + + Citizens pale, 243 + + Citric acid, 426 + + City air unhealthy, 253 + + Clean kettles, 186 + + Cleanliness connected with the dietary, 93 + + Clear day overcast, 304 + + Clear nights exhilarating, 144 + + Clocks heard, at a distance, 151, 413 + + Close rooms unhealthy, 253 + + Cloth collects but little dew, 208 + + Clothes gather damp in summer, 211 + wet, 157 + + Clothing for workmen, 164 + promotes warmth, 176 + + CLOUDS, 127 + cause of, 129 + classes of, 134 + colour of, 132 + compound, 136 + " simple, 134 + differ from fog, 128, 227 + dissipated, 304 + distance from the earth, 129 + edges most luminous, 399 + electrical, 131 + fall in rainy weather, 337 + float, 128 + height of, 4, 120 + highest and lowest, 130 + intermediate, 135 + light, 120 + motion of, 133 + red, 132, 399 + round mountain tops, 137 + thickness of, 130 + " how ascertained, 130 + vary in shape, 129, 130 + " in colour, 133 + where most abundant, 129 + where least, 129 + use of, 137 + velocity of, 314 + wind affects them, 129, 131 + + Coal gas, 280 + mines explode, 281 + + Coals black, 403 + + COLD WEATHER affects the barometer, 328 + makes us love fat, 90 + " activity, 91 + out of doors, 312 + promotes hunger, 91 + + Collapsing, 289 + + Colour of clouds, 132, 133 + + Colours vary, 400 + some warm, some cold, 187 + + Combining not mixing, 25 + + COMBUSTION, _see fire_, 33, 85 + cause of, 36 + elements of, 36 + heat of, 37 + increased by wind, 58 + in the veins, 84 + + COMMUNICATION of HEAT, 164 + + Compound clouds, 136 + + Compression, 102 + + CONDENSATION, 98, 102 + + Condensed air, 289 + + CONDUCTION, 164 + not absorption, 184 + + CONDUCTORS, best, 165 + worst, 166 + not absorbers, 185 + of lightning, 22 + dangerous, 24 + + CONVECTION, 219, 231 + + Convective currents, 245 + cool broth, 247 + cool iron, 247 + + Cooking vessels with wooden handles, 166 + + Cooper applies hot hoops, 122 + + Copper sonorous, 410 + tarnishes, 259 + + COPPER-HOLE, 60 + roars, 60 + " not when the door is open, 60 + + Cornea, 388 + + Corns ache in wet weather, 256 + + Corpse cold, 95 + + Corrosive sublimates, 426 + + Cotton bales catch fire spontaneously, 57 + handkerchiefs hot, 184 + + Countrymen ruddy, 243 + + Cowls, 67, 111 + + Crowds produce drowsiness, 251 + head-ache, 249 + vitiate air, 249 + unhealthy, 250 + + Culinary vessels have wooden handles, 166 + should be sooty, 71, 201 + + Cultivation promotes dew, 210 + warmth, 160 + + Cumulo-stratus clouds, 136, 137 + + Cumulus clouds, 134, 135 + + Cup in a pie, 120 + why full of juice, 124 + + + Damp banisters, 217 + beds, 158 + house, 217 + + DANGER IN A STORM, 12 + in attics and cellars, 16 + a crowd, 18 + theatre, &c., 19 + before a fire, 15 + near a tree, 12 + river, 14 + flocks and herds are exposed to, 19 + those who bar shutters, 18 + lean against a wall, 17 + or carriage, 20 + who ring bells, 15, 17 + run, 15 + + Dark colours warm, 186 + radiate heat, 197 + + Davy, Sir H., 281 + + Day-light produces hunger, 88 + + Dead bodies cold, 95 + taller than living, 423 + + Deal snaps in fire, 107 + + Decanting liquor, 274 + spirting, 274 + + Depression of spirits, 145 + + Descent in a diving bell painful, 146 + + Deserts hot and dazzling, 405 + + DEW deleterious, 220 + differs from rain, 226 + distilled after a hot day, 219 + especially if the wind is westerly, 218 + unequally, 207 + in open places, 204 + in valleys and hollows, 207 + on clothes, 211 + cultivated lands, 210 + grass, 209 + leaves, &c., 208 + none beneath a tree, 204, 205 + a flower awning, 205 + hedge or wall, 205 + none in a cloudy night, 204 + in a windy night, 207 + especially if easterly, 218 + none on stones, cloth, 208 + deserts, gravel, metal, rocks, wool, 209 + + Dew-drops round, 223 + flattened, 223 + roll on cabbages, 223 + roses, 224 + + Digging promotes warmth, 161 + + Digestion, 91 + + Dinner covers, 202 + + Dirt warm, 93 + + Distant bells heard, 413 + clocks, 151 + objects appear small, 381, 382 + sight, 390 + spectacles for, 391 + + Distance makes things invisible, 384 + + Distilled vinegar, 426 + + Divers suffer pain, 255 + + Diving bell, 146 + + Doors swell and shrink, 151 + + Dogs uneasy in wet weather, 147 + + Dough, 274 + set before a fire to rise, 276 + + Double concave glasses, 389 + convex glasses, 391 + + Draining lands promote warmth, 160 + + DRAUGHT at a door, 314 + key-hole, 314 + window, 315 + slack, 63, 64, 69 + + Dreams, 424 + foolish things, 424 + + Drops of rain roll on dust, 155 + + Drowned men restored, 101 + + Drums, 411 + + DRY WOOD for kindling, 44 + burns best, 107 + snaps about, 107 + + Dryest months, 328 + + Dublin, rain of, 340 + + Duck dry in water, 224 + + Dunghills hot, 277 + + Dusty shoes hot, 194 + + Dyeing changes a colour, 401 + + + Ear-trumpets, 415 + + EARTH, bad conductor, 181 + cool in summer, 182 + cracks by frost, 357 + crumbles in spring, 358 + warm in whiter, 131 + + Earth-fog, 221 + + Earthen tea-pots, 197, 198 + set on a hob to draw, 198 + + East wind cold, 302 + dry, 303 + prevents dew, 218 + + Eat more in cold, 90 + less in warm weather, 91 + + Echo, 416 + + Echoes, two or more, 418 + + EFFERVESCENCE, 269 + soon subsides, 275 + + Egg cracked when boiled, 239 + tested, 178, 239 + + ELECTRICITY affects the clouds, 131, 133 + excited by friction, 29 + felt at the elbow joints, 27, 29 + hot, 3 + of clouds, 4 + positive & negative, 16 + + ENGLAND grows warmer and warmer, 160 + WINDS of, 300 + east dry, 302 + morning at watering places, 310 + most prevalent, 300 + north cold, 312 + north-east dry, 305 + south rainy, 303 + warm, 303 + south-west rainy, 304 + west rainy, 304 + when highest, 301 + lowest, 301 + _See March wind._ + + Epsom salts, 426 + + Esquimaux love blubber, 92 + + Equatorial current, 298 + + ETHER, 47 + boils, 119 + used for freezing, 360 + used for inflammation, scalds, burns, 157 + + European skin white, 191 + + EVAPORATION, 156 + freezes, 360 + + EVENING CLOUDS, 132 + grey, 140 + red, 138, 399 + + EVENING RAINBOW, 141 + + Evergreens frost-bitten, 230 + + Ewers broken by frost, 349 + + EXPANSION by HEAT, 103 + + Extinguishers, 79 + made of paper, 79 + + Eyes, two, 368 + see single, 369 + affected by blue glasses, 407 + fire-light, 407 + the sun, 407 + + + Face soon scorched, 196 + + Fanning, 179, 313 + + Far sight, 390 + spectacles for, 391 + + Farriers apply hot shoes, 123 + + Fat men swim best, 362 + + Feathers warm, 176 + + Feeling, 425 + + Feet cold before a fire, 53 + wet dangerous, 157 + + FERMENTATION, 269 + of dough, 276 + + Fender and fire-irons cold, 185 + + Fiddle-strings musical, 411 + snap from wet, 339 + + Fine weather braces, 147 + + Finger feels cold when wet, 157 + + FIRE black and red, 38, 40 + blazes, 39 + not in frost, 48 + burns blue, 148 + cause of, 36 + charcoal, 72 + damp, 280 + effect upon the eyes, 407 + extinguished, 54 + by water, 107 + fiercest in winter, 49 + out of doors, 50 + grotesque figures in, 40 + heat of, 280 + how increased, 63 + hot, 37 + kindled at the bottom, 42 + light dazzles, 366 + lighted with paper and wood, 41 + luminous, 46 + poker draws up, 52 + radiates heat, 196 + red hot, 38 + reflected on windows, 379 + sun dulls it, 49 + thaw dulls it, 50 + wind intenses it, 51 + _See combustion._ + + Fire-irons cold, 185 + rust, 257 + prevented, 258 + + Fishes ascend and dive, 363 + seem nearer than they are, 388 + cold, 94 + + FLAME of a CANDLE, 76 + described, 77 + blown out easily, 78 + damp, 78 + hollow, 76 + hottest above, 79 + pointed, 77 + purple and yellow, 76 + smokes, 81 + + Flame of a fire between the bars of a grate blue, 46 + green, 45 + yellow, 46, 47 + + Flannel warm, 94 + used for foot-warmers, 173 + + Flash, _see lightning_ + + Flat beer, 273 + improved, 273 + + Flavour discerned by the taste, 425 + + Flint and steel, 97 + + FLOWING WATER freezes slowly, 354 + makes rough ice, 354 + oscillates, 348 + pure, 347 + + Flower awnings arrest dew, 205 + purify air, 253 + + Flowers smell sweetest at night and before rain, 152 + + Flues blacked, 238 + _See chimney._ + + Flutes, 412 + + Fly-poison, 422 + + FOGS, 225, 226 + arrest sound, 413, 414 + cause of, 129 + differs from cloud, 128, 227 + mist, 227 + dispersed by wind, 228 + by sun, 227 + frozen, 231 + in autumn, 228 + in marshes, 226 + valleys, 228 + none in a frosty night, 227 + + Food converted to blood, 242 + cooled by the breath, 312 + + Foot-prints frozen, 350 + + Foot-warmers, 173 + + Forked lightning, 5 + dangerous, 5 + + Forests catch fire spontaneously, 102 + + France warmer than of yore, 162 + + FREEZING MIXTURES, 360 + + FRICTION (_see rubbing_), 98 + excites electricity, 29 + sets forests on fire, 102 + + Frogs cold, 94 + + FROST affects barometer, 329 + sound, 414 + braces, 147 + breaks ewers, 349 + tiles, stones, rocks, 350 + pipes, 351 + cracks earth, 357 + expands water, 352 + prevents fog, 227 + warm, 356 + + Froth of beer, 269, 350 + + Frozen ruts and footprints, 350 + + Fruits cool the blood, 92 + fall to the earth, 419 + pleasant in summer, 92 + + Fuel for the body, 87 + + Fumigation for sick rooms, 421 + + FUR, bad conductor, 166 + for clothing, 175 + warm, 171 + + Furnaces of brick, 174 + lined with clay, 174 + + Furr of kettles, 262 + steam engines dangerous, 263 + + + Gallery hot, 249, 316 + + Gas, 112 + of candles, 281 + + Gauze wire of safety lamps, 282 + prevents explosion, 282 + + German silver tarnishes, 260 + + German tinder, 102 + + Germany warmer than of yore, 162 + + Ghosts, 286 + + Gideon's miracle, 211 + + Ginger pop, 268 + acid, 269 + + GLASSES broken by hot water, 125 + covered with mist, 214 + which soon subsides, 215 + dulled by a hot hand, 215 + by breath, &c., 215 + _See spectacles._ + + Glass a reflector, 194 + soon cools, 212 + _See looking-glass._ + + Glauber salts, 426 + + Gloves, black kid, 188 + Lisle thread, 188 + + Glow-worms glisten by night, 368 + + GOD'S WISDOM 182, 208, 210, 302, 308, 352, 357 + + Gold never tarnishes, 260 + + Goulard, 426 + + Grapes never ferment, 272 + + Grass promotes warmth, 161 + collects dew, 209 + + Grate, _see stove_ + + Gravel collects no dew, 209 + + Gravity, 419 + + Gray morning, sign of a fine day, 140 + + GREASE liked in cold weather, 90 + loathed in hot, 92 + prevents rust, 258 + used for wheels, 100 + + Green colour, 401 + wood does not burn, 107 + + Grottoes famous for echoes, 416 + + Ground frost, 229 + + Growth promoted by moonlight, 220 + + Gulls fly to sea, 154 + to land, 154 + + Gusty weather makes a smoky house, 71 + + + HAIL, 331, 334 + cause of, 335 + accompanied with thunder, 335 + falls in summer, 335 + + Hair, bad conductor, 166 + covered with dew, 217 + + Halls famous for echoes, 417 + + Halo round the moon, 143 + + Hard work promotes hunger, 88 + + Hat covered with dew, 217 + turned red at the seaside, 344 + + Hawks see near and far, 392 + + Hay-stacks catch fire spontaneously, 58 + + Haze round the sun, 143 + moon, 143 + affects sound, 414 + + Head aches in a crowd, 249 + itches in wet weather, 150 + + Hearth-rug warm, 169 + + Hearth-stone cold, 169 + hot, 170 + + HEAT, 1 + and light, 47 + affects barometer, 328 + sound, 414 + animal, 83, 85, 277 + applied to the bottom of boilers, 234 + effects of, 2, 4, 103 + expands water, 352 + from beaten iron, 95 + LATENT, 31, 75, 96 + of candles, 75 + dunghills, 277 + fire, 37, 277 + lime, 278 + radiates, 196 + sources of, 2 + + Heavy bread, 160 + + Hills larger in a fog, 148 + + HOAR FROST, 228 + not found on trees, 230 + under shrubs, &c., 230 + of frozen fog, 231 + on clear nights only, 229 + on grass, 229 + tombstones, 189, 230 + very partial, 229 + + HONEY-DEW, 220 + ants fond of, 221 + effects of, 221 + injures plants, 221 + + Hot cloudy night oppressive, 144 + + Hot weather abates activity, 93 + appetite, 90 + love for grease, 92 + + Hottest place at church, 316 + + Hoops used red hot, 122, 123 + + Horse shoes fitted hot, 123 + + Horses strike fire, 98 + snuff up air, 152 + uneasy in dull weather, 148 + + Houses catch fire spontaneously, 56 + smoke in valleys, 66 + + Hunger, 88 + promoted by cold, 90 + day-light, 88 + singing, speaking, work, 88 + _See appetite._ + + Hydrogen gas, 34, 74 + + + ICE, 349 + lighter than water, 349 + grows thicker, 353 + dissolved by snow, 357 + melted by sun, 126 + + Ice-bergs famous for echoes, 417 + + Idiots, 424 + + IGNIS FATUUS, 285 + cause of, 286 + + Impure water purified, 72 + + Indian mode of striking fire, 99 + + Inflammable air, 34, 74 + + Insensible perspiration, 213 + + Intermediate clouds, 135 + + IRON, bad conductor, 185 + cinders, 43 + contains latent heat, 96 + cooled by air, 246 + convection, 246 + radiation, 246 + matches, 96 + rust, 257 + when most common, 258 + prevented, 258 + sonorous, 410 + stoves, 174 + + Ironing-box, 155 + + Islands equable in temperature, 311 + subject to wind, 309, 311 + + Itching in wet weather, 150 + + + Jack o'lanthorn, _see ignis fatuus_ + + Jet of flame through bars, 45 + + Juice of lemons, 426 + + Jungle of Hindostan fatal, 266 + + + Kendal rainy, 340 + + Keswick rainy, 340 + + KETTLE boils over, 115 + quickly when covered with soot, 186 + slowly when clean, 186 + when new, 186 + bottom should be sooty, 200 + cold when water boils, 200 + inside white, 200 + lid hot, 201 + furr, 262 + holder, 167 + not full after boiling, 115 + runs over, 233 + through the spout, 115 + sings, 113, 233 + top bright, 200 + + Kindling wet, 43 + + + Lakes which never freeze, 355 + + Lamps, 74 + Argand, 83 + smoke, 82, 83 + spirit, 155 + _See candle._ + + Lamp-glasses, 83 + + Land air cold, 224, 311 + breeze unhealthy, 309 + + Laplanders clad in skin, 183 + + LATENT HEAT, 31, 75, 96 + + Laziness promoted by want of food, 89 + by heat, 93 + + Lead tarnished, 259 + + LEAVES collect dew unequally, 208 + green, 404 + light green in spring, 404 + in a pond, 419 + pale in dark places, 403 + promote cold, 161 + yellow in autumn, 408 + + Lid of kettles, &c. hot, 201 + + Light bread, 276 + + LIGHT, 363 + composed of various colours, 400 + divided by a prism, 393 + from a flint, 97 + of candles, 76 + fire, 46 + sun, 363 + reflected, 364 + speed of, 364 + sudden painful, 365 + + LIGHTNING, 3 + balls, 6 + barks and snaps trees, 27 + comes from clouds, 16 + from earth, 16 + conductors, 22 + dangerous, 24 + follows dry weather, not wet, 28 + forked, 5 + fuses metal, 27 + kills animals, 7 + knocks down churches, 24 + maims, 8 + passes down the outside of a tree, 14 + passes through the inside of animals, 14 + purifies air, 27 + rare in winter, 28 + sheet, 6 + summer, 11 + common, 28 + straight, 6 + turns beer sour, 27 + not old beer, 27 + milk sour, 25 + _See danger, safety._ + + Lilac steel rusts, 259 + prevented, 259 + + LIME and water, 26, 30 + burned, 278 + hot, 277 + purifies bins, 266, 421 + sewers, 267, 421 + + Lime-wash for rooms, 422 + + Lincoln, rain of, 340 + + Linen cool wear, 183 + dried, 160, 316 + + Linseed oil boils, 119 + + LIQUEFACTION, 126 + + LIQUIDS, 112 + bad conductors, 172, 232 + cooled, 235 + + Lisle thread gloves, 188 + + Liverpool, rain of, 340 + + LONDON FOG, 225 + rain of, 340 + + Long flues, 110 + grass promotes cold, 161 + + Log of wood, 2 + two burn better than one, 44, 52 + + Looking-glass, 369 + + Lucifer matches, 284 + + Lunar caustic, 426 + + + Mackarel scales, &c., 136 + + Macintosh prevents cold, 158 + + Madness from starvation, 86 + + Malt, 270, 272 + + Man a swimmer, 362 + no bigger than a crow, 382 + + Manchester, rain of, 340 + + Magpies indicate weather, 153 + + Marble, 426 + + MARCH comes in like a lion, 306 + goes out like a lamb, 306 + dry good, wet bad, 306 + flowers undesirable, 307 + wind dry, 305 + + Marsh damp, 280 + + Marsupium, 392 + + Meat-covers, 202 + + MEAT liked in cold weather, 90 + loathed in hot, 92 + taint removed, 422 + tainted by moonlight, 220 + + MECHANICAL ACTION, 95 + + Mercury of barometer bright, 260 + concave, 325 + convex, 325 + its rise and fall, 325 + + METAL collects no dew, 209 + feels colder than wood, 168 + hotter than wood, 167 + fused by fire, 127 + by lightning, 27 + good conductor, 165 + handles burn, 166 + reflectors, 193 + tea-pots, 197 + + Milk soured by lightning, 25 + + Miners' danger, 283 + prevented, 265 + + Mirror, 369 + + MIST arrests sound, 414 + black, 144 + cause of, 224 + differs from cloud, 128 + dew, 222 + fog, 227 + seems to rise, 222 + vanishes at sunrise, 227 + white, 144 + + Mixing not combining, 25 + + Money hot in a pocket, 168 + + Monsoon, 300 + + Months, driest, 328 + wettest, 329 + + MOON, distance and size, 383 + largest at horizon, 149, 378 + reflected in water, 376 + in a well, 374 + seems flat, 383 + larger than stars, 383 + + Moonlight makes plants grow, 220 + taints meat, 220 + + MORNING breeze, 308 + gray, 140 + rainbow, 141 + red, 139, 399 + streaks, 132 + + MORTAR, 278 + adhesive, 279 + crumbles, 358 + + Motes in a sun-beam, 248 + + Mould hardened by sun, 163 + + Mouldiness prevented, 422 + + Mountains cold, 100, 195 + collect rain, 338 + famous for echoes, 417 + impede respiration, 255 + noiseless, 416 + + Muriate of soda, 426 + + Musical instruments, 411 + flat, 412 + + + Nails for matches, 96 + + Naves fitted on hot, 122 + + Near-sight, 388, 391 + spectacles for, 389 + + Negative electricity, 66 + + Negroes, why black, 190 + with black eyes, 190 + + New kettles boil slowly, 186 + + Night allays hunger, 88 + exhilarating, 144 + oppressive, 144 + produces cold, 89 + rainbow at, 141 + + Nimbus clouds, 137 + + Nitrate of silver, 426 + + Nitric acid, 28, 426 + + Nitrogen, 36 + + North wind cold, 302 + dry, 303 + + North-east wind dry, 305, 320 + + November rainy, 308, 338 + + + Oak attracts lightning, 257 + + Old people far-sighted, 390 + hold objects at a distance, 392 + lose their sensation, thought, volition, 425 + lose their power of walking, 425 + spectacles for, 391 + + Oil, 74 + linseed, 119 + of turpentine, 119 + of vitriol, 426 + + One pot will not boil in another, 118 + how to make it boil, 118 + + Oxalic acid, 426 + copper, 259 + iron, 257 + + OXIDE of lead, 259, 426 + platinum, 261 + potassium, 262 + silver, 260 + sodium, 262 + + Oxygen, 34 + of air, 97 + its use, 240 + supports combustion, 240 + sustains life, 240 + + Out-of-door work produces hunger, 89 + + Owls prowl at night, 367 + see in the dark, 367 + sleep all day, 367 + + + Paleness, 243 + + Palmer's candles, 80 + + Paper burns, 41 + not always, 44, 53 + extinguishers, 79 + puckers from wet, 339 + used for kindling, 41 + + Papillæ, 425 + + Paris, plaster of, 426 + rain of, 340 + + Parlours smell of smoke in summer, 71 + + Partition walls to arrest sound, 415 + + Pea-soup fog, 225 + + PERCUSSION, 95 + + Perspiration, 89 + + Petals, 402 + + Petrels, 154 + + Phosphate of lime, 284 + + Phosphorus, 283, 284 + + PHOSPHURETTED HYDROGEN GAS, 283 + + Piano-forte, 412 + + Pickle tested, 361 + + Pie with a cup, 120 + full of juice, 121 + + Pin puts a candle out, 81 + + Pineal gland, 424 + + Pipes broken by frost, 351 + + Piston, 102 + + PLANTS collect dew, 208 + deleterious in bedrooms, 405 + grow out of walls, 316 + + Plaster of Paris, 426 + of stoves falls away, 124 + + Plasterers cannot work in frost, 359 + + Platinum, 261 + its use, 261 + never tarnishes, 261 + + Plate warmer, 188, 193 + + Ploughing, promotes warmth, 161 + + Plumbago, 258 + prevents rust, 258 + + Poison for flies, 422 + + Poker draws up fire, 52 + cold, 172, 238 + how to carry it when hot, 237, 238 + rusts, 258 + prevented, 258 + + Polar current, 298 + + Poor averse to cleanliness, 93 + ventilation, 94 + lazy, 89 + + Pores of wood, 106 + + Porter, froth of, 109 + set before a fire, 109 + stale, 275 + + Positive electricity, 16 + + Potatoes, green, 405 + yellow, 404 + + Potassium, 262 + burns in water, 262 + + Primrose, 402 + + Prisms divide light, 393 + + Pump handle cold, 168 + water hard, 363 + + Purple steel rusts, 259 + its rust prevented, 259 + + PUTREFACTION, 277, 278 + + Putrefying bodies smell, 284, 285 + + + Quadrupeds swim, 362 + + + RADIATION, 195 + cools iron, 247 + + Radiators are absorbers, 197 + + Rags catch fire spontaneously, 58 + + Railway steamers, 218 + + RAIN, 331, 336 + affected by wind, 337 + after lightning, 11 + arrests sound, 413 + cause of, 326, 336 + cools air, 159 + differs from dew, 226 + falls in drops, 336 + fertilizing, 307, 337 + from passing clouds, 336 + heaviest in summer, 341 + least at the poles, 342 + melts salt, 346 + sugar, 345 + most in mountainous places, 338 + most in winter, 341 + near the equator, 341 + not salt, 347 + on dust, 223 + prognostics of, 137 + purifies air, 338 + sudden change, 326 + + RAINBOW, 394, 397 + colours reversed, 396 + morning, 141 + night, 141 + two, 395 + + Rain drops, 336 + vary in size, 337 + + Rain-water smells offensively, 345 + soft, 344 + stagnant, 347 + + Rainy months, 308 + parts of England, 340 + + Rattling of kettle-lid, 116 + + Ray of light divided, 393, 400 + + Reading aloud produces hunger, 88 + + RED colour, 401 + rose, 401 + sky, 132, 399 + sun-rise, 139 + sun-set, 139 + + Reflected light, 364 + + REFLECTION of HEAT, 192, 370 + + REFLECTORS, 192 + help the roast, 194 + keep kitchen cool, 194 + not absorbers, 192 + should be clean and bright, 189, 192 + should not be painted, 189 + + REFRACTION, 386, 394 + + Refrangible, 132 + + Retina, 388 + + Reverberation, 417 + + Rice for food, 93 + + RIVERS flow slowest at sides, 348 + freeze unequally, 354 + never frozen at bottom, 352 + not wholly frozen, 353 + shallow freeze fastest, 354 + seem shallower than they are, 387 + warm when frozen, 354 + + Roast apples, 105 + soft, 106 + chestnuts, 104 + + Road dark from a light room, 194 + + Rocks collect no dew, 209 + broken by frost, 350 + + Room cooled, 159, 315 + ventilated, 375 + warmed by fire, 237 + + Rose red, 401 + + Ross Captain, 414 + + Rotting leaves promote cold, 161 + + Rubbing, 99 + hands to warm them, 101 + melts ice, 101 + restores suspended animation, 101 + _See friction._ + + Ruddiness, 243 + + Ruins famed for echoes, 416 + + Running, promotes warmth, 87 + + Running water freezes slowly, 354 + makes rough ice, 354 + oscillates, 348 + promotes warmth, 87 + pure, 347 + + Rush lights easily blown out, 79 + extinguished by a pin, 81 + + RUST, 257 + prevented, 258 + when most troublesome, 258 + + + SAFETY IN A STORM abroad, 20 + at a slight distance from a tree, 20 + best to be wet, 22 + in a carriage, 20 + in bed, 22 + in-doors, 21 + + Safety lamp, 281, 282 + + Sailors rarely catch cold, 158 + + St. Bride's church destroyed by lightning, 24 + + SALT, 426 + and snow cold, 357 + and water, 31 + bad for washing, 343 + crackles in a fire, 44 + dissolves ice, 357 + by water, 346 + especially hot water, 346 + retards boiling, 118 + white, 403 + of lemons, 426 + smelling, 426 + water unfit for railway engines, 263 + + Sand dazzling, 405 + + Saturday's kettle boils fastest, 199 + + Saucepan boils best when black, 199 + slowly when new, 199 + lids should be clean and bright, 199 + + Scald cured, 157 + + Scum of fermentation, 272 + + Sea-beach healthy in the morning, 310 + not healthy at night, 310 + + Sea before storm, 146 + heaves and sighs, 146 + not much heated by sun, 296 + + Sea-gulls, 154 + + Sea water easier to swim in than fresh, 360 + rarely frozen, 355 + gives cold, 158 + salt, 346 + + Sea-waves, 312 + + Sedentary pursuits abate hunger, 90 + + SEEING in a glass, 369 + into a dark street, 366 + light room, 378 + ourselves in a small mirror, 371 + the same object, 365 + when used to darkness, 366 + + Sensation destroyed, 424 + of feeling, 425 + of taste, 425 + + Sewers purified, 267 + + Shade cool, 183 + + Shadow in water, 371, 372 + + Shadow larger as the object approaches a light, 379 + + Sheen, 405 + + Sheep bleat, 148 + + Sheet lightning, 6 + + Sheets wet, 157 + + Ships out at sea, 385 + + Shirts of linen, 183 + + Shoes hot when dusty, 194 + + Sick rooms purified, 421 + + Sides of a pond covered with leaves, 419 + + Swimming, 112 + + SILVER meat-covers, 202 + should not be chased, 202 + tarnishes, 260 + + Simple clouds, 134 + + Singing of a kettle, 113 + of boiling water, 233 + produces hunger, 88 + + Single magpie unlucky, 153 + + Skin, black does not scorch, 191 + white does, 191 + itches, 150 + + Sleep elongates the body, 423 + body feels not in, 425 + dreams in, 424 + ears hear not in, 423 + eyes see not in, 423 + mind wills not in, 424 + tongue tastes not in, 423 + + Sleet, 332 + + Slit chestnuts, 105 + + Smelling salts, 426 + + SMELLS in wet weather, 152 + of church-yards, 283 + of putrefying bodies, 284 + + SMOKE, 39, 59 + curls, 59 + falls, 152 + of fresh coals, 39 + lamps diminished, 83 + by a glass, 83 + rises, 110 + useful in cooking, 201 + + Smoky chimneys, 59 + _See chimney._ + + Smoke-jacks, 112 + + SNOW, 331 + arrests sound, 413 + bad conductor, 333 + cause of, 331 + falls in winter, 332 + not in summer, 334 + like wool, 175 + nourishes the earth, 333 + on mountains, 334 + soon melts beneath a hedge or wall, 206 + use of, 332 + warm, 332, 333 + white, 334, 402 + + Snow and salt cold, 31, 357 + + Soap, 344 + cleansing, 344 + hard, soft, 344 + yellow, 344 + + Soap-bubbles, 348, 398 + change colour, 399 + + Soapy water bubbles, 348 + + Soda water, 268, 269 + + Sodium, 262 + decomposes water, 262 + + Soft soap, 344 + + Solids, 112 + + Soot in summer, 71 + on ceilings, 71 + + Sooty kettles, 186 + + SOUND, 409 + affected by frost, 414 + heat, 414 + arrested by wet, 413 + velocity of, 410 + diminished by rarity of air, 416 + heard best by night, 414 + inaudible on mountains, 147 + + South wind rainy, 303, 320 + warm, 303 + + South-west wind rainy, 304 + + Sparks from a fire, 106 + a flint, 97 + a horse-shoe, 98 + + Spectacles, 389 + black, 408 + blue, 407 + for aged, 390 + near sights, 389 + + Split bells, 411 + + Sponge swells when wet, 339 + + SPONTANEOUS COMBUSTION, 56, 57, 58, 85 + + Spoons become dull, 26 + in water, 387 + retard boiling, 117 + + Speaking promotes hunger, 88 + + Spring best late, 307 + water cool, 182 + sparkles, 269 + + Springs prevent freezing, 356 + + Sprinkling to cool rooms, 159 + + Stagnant water, 347 + full of worms, 347 + + Stale beer, &c., _see beer_, 275 + + Stars distance and size of, 383 + invisible by day, 368 + seem flat, 384 + seen in a well, 368, 374 + seen on mountains, 376 + twinkle, 406 + + Starvation, 86 + produces madness, 86 + + STEAM, 127 + engines burst, 236 + invisible, 116, 235 + of a kettle, 236 + why visible, 117 + what becomes of it, 117 + + STEEL and flint, 97 + rusts, 259 + prevented, 259 + + Stillness before a storm, 146 + + Stirring cools broth, &c., 247 + + Stockings difficult to draw on when wet, 340 + + STONES broken by frost, 350 + cold, 169 + collect no dew, 208 + snap in fire, 108 + unfit for fuel, 43 + + STORMS, 146 + direction of, 28 + places of danger in, 12 + safety in, 20 + + Straw covered over brickwork, 359 + over trees, 359 + water-pipes, 359 + + Street dark from a light room, 194 + + STOVES crack, when lighted, 123 + when cooling, 123 + of bricks, 174 + on a floor, 52, 237 + rust, 257 + not often, 258 + prevented, 258 + settings fall away, 124 + warm a room, 237 + + Strata of air, 9 + + Stratus clouds, 135 + + Streets seem to meet at bottom, 381 + watered, 159 + + Stucco peels off in frost, 358 + + Sublimates, 426 + + Sublimation, 426 + + Sudden light painful, 365 + + SUGAR at top of tea melts quickly, 421 + left at the bottom of a cup melts slowly, 420 + melted by water, 345 + especially by hot water, 346 + retards boiling, 118 + stirred melts quickly, 420 + white, 402 + of lead, 426 + + Sulphate of lime, 426 + magnesia, 426 + soda, 426 + zinc, 426 + + Sulphuric acid, 426 + and water, 30 + boils, 110 + + Summer allays hunger, 90 + clothes for, 187 + creates dislike of grease, 92 + love of fruit, 92 + lightning, 11 + + Sun-beams full of mites, 248 + + SUN affects eyes, 407 + dazzles, 364 + dulls fire, 40 + largest at horizon, 149, 377 + not seen in a well, 373 + seems flat, 384 + source of heat, 2 + reflected in water, 375 + + Sun-rise red, 139 + + Sun-set gray, 140 + red, 138 + yellow, 139 + + Super-acetate of lead, 426 + + Swallows fly low, 152 + + Swan dry in water, 224 + + Swimmers sink, 361 + + Swimming, 262 + + Syrup boils, 119 + + + Table salt, 426 + + Tainted meat cured, 72, 422 + water, 72 + + Tallow, 74 + + Tarnish, 259 + + Tartar emetic, 426 + + Tartrate of potash, 426 + + Tarts have a cup inside, 120 + full of juice, 121 + + TEA cooled by blowing, 248 + by stirring, 247 + in a saucer, 163 + green deleterious, 423 + poison for flies, 423 + + TEA-POT, bright metal, 197 + tarnishes, 260 + black earth, 197 + preferred by some, 198 + set on a hob, 198 + + Telescopes, 385 + + Tempest, 146 + affects weather, 326 + _See storms._ + + Thaumatrope, 406 + + THAW affects barometer, 329 + cold, 320, 356 + dulls fire, 50 + + Thermometer, 307 + + Thick clothing unhealthy, 164 + + THUNDER, 8 + after lightning, 12 + bolts, 11 + deep growl, 10 + irregular roar, 9 + one crash, 8 + rolling, 10 + _See danger, safety, storm._ + + Tigers prowl by night, 367 + sleep all day, 367 + see in the dark, 367 + + Tiles broken by frost, 350 + + Timber charred, 73 + + Tin blowers, 70 + foot-warmers, 173 + reflectors, 193 + _See reflectors._ + + Tinder blown, 97 + + Toast and water, 73 + for the sick, 73 + + Tomb-stones frosted, 230 + + Tongs rust, 258 + prevented, 258 + + Trade-winds, 198 + + Transparency, 405 + + Treble, 412 + + TREES barked by lightning, 29 + collect dew, 208 + covered with bass, &c., 359 + look more distant in a fog, 148 + promote warmth, 161 + purify air, 253 + shade of, cool, 183 + + Tumblers, _see glasses_ + + Twilight, 399 + + Two eyes, 368 + see single, 369 + + + Unslit chestnuts, 104 + + Use of barometers, 317 + clouds, 137 + smoke in cooking, 201 + snow, 332 + + + Valley chimneys smoke, 66 + + VAPORIZATION, 126, 127 + + Vapour of a carriage, 214 + of a room, 212 + of sea not salt, 163 + + Vats fatal, 265 + + Vegetable and animal life co-dependent, 244 + + Vegetables collect dew, 208 + cool the blood, 92 + + Velocity of clouds, 314 + light, 364 + sound, 410 + wind, 313 + + Vent peg, 273, 274 + + VENTILATION, 315 + sought by the well-fed, 94 + not by the ill-fed, 94 + + Verdigris, 426 + + Vertical sun, 293 + + Vestry chimneys smoke, 66 + + Violets blue, 402 + + + Walls wet in winter, 216 + + Want connected with dirt, 93 + + Warm clothes, 187 + some things more than others, 165 + + Wash-hand-basin, 171 + + Washing, water for, 275 + should not be hard, 343 + + WATER, 38, 342 + and lime, 30 + and sulphuric acid, 30 + ashes soften, 345 + bad conductor, 171, 234 + boiling, 119, 232, 234 + bubbles, 114, 233 + rattles, 116 + runs over, 115, 233 + sings, 233 + cleans dirty linen, 344 + cold, 177 + converted to steam, 127, 343 + cools slowly, 225 + deep, freezes slowly, 356 + dried up in summer, 162 + expands by frost, 351 + by heat, 351 + extinguishes fire, 54, 107 + flat when boiled, 275 + fluid, 342 + flowing, pure, 347 + for washing, 275 + freezes at the surface, 253 + hard, 343 + unfit for washing, 343 + how preserved cool, 191, 202 + hot, 191 + heated, 232 + intenses fire, 54 + mixed with salt, boils slower, 119 + not heated above boiling, 235 + of a spring cool, 182 + purified, 72 + purifies bins, &c., 267 + salt, bad for washing, 343 + shallow, freezes fastest, 355 + slackens flame, 55 + soft, 344 + best for washing, 345 + sparkles, 269 + stagnant, 347 + full of worms, 347 + stale, 275 + swells with boiling, 114 + will not bubble without soap, 348 + warm when frozen, 354 + + Water pipes broken by frost, 351 + covered with litter, 359 + + Watering plants by the saucer, 420 + streets, 159 + + Waves, 312 + + Wax, 74 + + Wax candles need no snuffing, 81 + + Weather affected by tempests, 326 + prognostics of, 137 + told by barometer, 318 + rules, 319 + + Weather toys, 339, 340 + + Well, moon seen in, 374 + stars seen in, 368 + sun not seen in, 373 + + West Wind promotes dew, 218 + rainy, 304, 320 + + Wet clothes cold, 157 + feet dangerous, 157 + finger cold, 157 + kindling, 43, 44 + sheets, 158 + summer, cold winter, 160 + weather offensive, 145, 148 + + Wettest months, 329 + + Wheels catch fire, 99 + greased, 100 + kept cool by water, 162 + + Wheel-ruts frozen, 350 + + Wheelwright, 122 + + WHITE, 402 + blisters, 190 + body linen, 186 + crust on clothes, 163 + dresses for summer, 186 + not fit for winter, 187 + mist, 144 + vitriol, 426 + + WICKS cotton, need snuffing, 81 + have a knob when long, 80 + not upright when long, 80 + Palmer's wicks need no snuffing, 80 + smoke, 82 + _See candles._ + + Will o' the wisp, _see ignis fatuus_. + + WIND, 287 + affects barometer, 327 + clouds, 129, 131 + after lightning, 11 + altered by clouds, 295 + by seas, 295, 296 + brings dry, 305 + rain, 305 + cause of, 287, 292 + changes the shape of clouds, 132 + cold, 117, 180, 312 + dispels clouds, 131, 138 + fog, 228 + draws up fire, 51 + dries linen, 316 + feels hot sometimes, 181 + in England, 300 + increases clouds, 131, 138 + makes barometer fall, 320 + chimneys smoke, 66 + of a morning, 308 + of an evening, 309 + prevents dew, 206 + rate of travelling, 313 + regular, 297 + _See England, monsoon, north, south, west &c., trade-winds &c._ + + Winding passages famed for echoes, 417 + + Windows blazing with the sun, 372 + not at noon, 372 + covered with frost, 214 + mist, 211 + carriage, dull, 213 + rattle, 418 + + Wine glasses, _see glasses_ + + Wine made without yeast, 271 + + Winter clothing, 187 + promotes hunger, 90 + + WISDOM of GOD, 182, 208 210, 352, 357 + + WOOD burns, 41 + spontaneously, 55 + charred, 73 + hot at one end, cold at the other, 165 + ignited by friction, 99 + kindling, 41 + dry, 44 + wet, 107 + two logs burn best, 44, 52 + sends forth sparks, 106 + will not melt, 127 + + Wooden handles, 166 + + WOOL bad conductor, 166 + collects no dew, 209 + warm, 176, 333 + + Woollen clothing, 175 + + Work produces hunger, 88 + + + Yeast, 271 + makes light bread, 276 + not used in wine, 271 + + Yellow flame gives best light, 47 + soap, 344 + sun-set sign of wet, 139 + + +FINIS + + +JARROLD AND SONS, PRINTERS, NORWICH. + + + + +Transcriber's Notes: + +Archaic and inconsistent punctuation and spelling retained. + +Inconsistent question formats were regularized. + + + + + +End of the Project Gutenberg EBook of A Guide to the Scientific Knowledge of +Things Familiar, by Ebenezer Cobham Brewer + +*** END OF THE PROJECT GUTENBERG EBOOK 40652 *** |