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diff --git a/40652-8.txt b/40652-0.txt index cf348f1..a7e7efb 100644 --- a/40652-8.txt +++ b/40652-0.txt @@ -1,39 +1,4 @@ -The Project Gutenberg EBook of A Guide to the Scientific Knowledge of -Things Familiar, by Ebenezer Cobham Brewer - -This eBook is for the use of anyone anywhere at no cost and with -almost no restrictions whatsoever. You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org - - -Title: A Guide to the Scientific Knowledge of Things Familiar - -Author: Ebenezer Cobham Brewer - -Release Date: September 3, 2012 [EBook #40652] - -Language: English - -Character set encoding: ISO-8859-1 - -*** START OF THIS PROJECT GUTENBERG EBOOK SCIENTIFIC KNOWLEDGE--THINGS FAMILIAR *** - - - - -Produced by David Garcia, Marilynda Fraser-Cunliffe, Matthew -Wheaton and the Online Distributed Proofreading Team at -http://www.pgdp.net (This file was produced from images -generously made available by The Internet Archive) - - - - - - - - +*** START OF THE PROJECT GUTENBERG EBOOK 40652 *** A GUIDE TO THE SCIENTIFIC KNOWLEDGE OF THINGS FAMILIAR; @@ -540,7 +505,7 @@ 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.) +(i. e. 380 × 5 = 1900 yards.) Q. _What PLACES are most DANGEROUS to be in, during a STORM?_ @@ -1135,14 +1100,14 @@ A. Yes. But it is _latent_, (i. e. not perceptible to our senses).[4] 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]. +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. +[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?_ +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_. @@ -1151,24 +1116,24 @@ 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_. +1140° of heat may remain latent in _water_. -Q. _How can 1140° of heat be added to water, without being perceptible +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 +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 +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 +[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. +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?_ @@ -3777,7 +3742,7 @@ 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°), +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_. @@ -3805,7 +3770,7 @@ 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 +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 @@ -4865,7 +4830,7 @@ 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 +they are obliged, therefore, to feed on the _worms and larvæ_ which are driven out of the _ground_ at such times. @@ -8782,7 +8747,7 @@ 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]). +light_." ([Greek: phôs-pherein]). Q. _How is PHOSPHORUS OBTAINED?_ @@ -9902,7 +9867,7 @@ 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 +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. @@ -10012,7 +9977,7 @@ _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; +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_. @@ -10886,7 +10851,7 @@ very general rule) _contracts_ till it is reduced to 42 degrees, and then it _expands till it freezes_. -(Water freezes at 32°.) +(Water freezes at 32°.) Q. _Why does water expand when it freezes?_ @@ -10902,7 +10867,7 @@ 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°.) +42°.) Q. _Show the WISDOM of GOD in this wonderful exception to a general @@ -10978,7 +10943,7 @@ 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 +(The water below the surface is at least 42°; but the air 32°, or even less.) @@ -11039,9 +11004,9 @@ 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 +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). @@ -11150,7 +11115,7 @@ 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). +0° (or 32 degrees below freezing point). The two following are the coldest mixtures yet known:-- @@ -11413,7 +11378,7 @@ 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_. +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. @@ -11886,12 +11851,12 @@ are. Q. _Why are some persons NEAR-SIGHTED?_ -A. Because the COR´NEA of their eye is so _prominent_, that the image of +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 +N.B. The cor´nea shields the CRYSTALLINE LENS, and is more or less convex according to the lens which it covers. @@ -12936,7 +12901,7 @@ 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. +A. Because the "RET´INA of the eye" is _inactive_ and at rest. Q. _Why can we not HEAR in sleep?_ @@ -12946,13 +12911,13 @@ 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 +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 +A. Because the _ends of the nerves_ (called papillæ), situated in the skin, are inactive and at rest. @@ -12998,14 +12963,14 @@ 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 +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_ +A. Because the "PAPILLÆ" of the tongue and palate _erect themselves_ when food touches them, and produce a nervous sensation called TASTE. @@ -14614,7 +14579,7 @@ INDEX. puckers from wet, 339 used for kindling, 41 - Papillæ, 425 + Papillæ, 425 Paris, plaster of, 426 rain of, 340 @@ -15571,361 +15536,4 @@ Inconsistent question formats were regularized. 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You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org - - -Title: A Guide to the Scientific Knowledge of Things Familiar - -Author: Ebenezer Cobham Brewer - -Release Date: September 3, 2012 [EBook #40652] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK SCIENTIFIC KNOWLEDGE--THINGS FAMILIAR *** - - - - -Produced by David Garcia, Marilynda Fraser-Cunliffe, Matthew -Wheaton and the Online Distributed Proofreading Team at -http://www.pgdp.net (This file was produced from images -generously made available by The Internet Archive) - - - - - - -</pre> - +<div>*** START OF THE PROJECT GUTENBERG EBOOK 40652 ***</div> <div class="handheld-break"> <img id="coverpage" class="border2" src="images/titlepage.jpg" width="400" height="654" alt="" /></div> @@ -21184,383 +21145,6 @@ JARROLD AND SONS, PRINTERS, NORWICH.<br /> <p>Archaic and inconsistent punctuation and spelling retained.</p> <p>Inconsistent question formats were regularized.</p></div> - - - - - - - -<pre> - - - - - -End of the Project Gutenberg EBook of A Guide to the Scientific Knowledge of -Things Familiar, by Ebenezer Cobham Brewer - -*** END OF THIS PROJECT GUTENBERG EBOOK SCIENTIFIC KNOWLEDGE--THINGS FAMILIAR *** - -***** This file should be named 40652-h.htm or 40652-h.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/4/0/6/5/40652/ - -Produced by David Garcia, Marilynda Fraser-Cunliffe, Matthew -Wheaton and the Online Distributed Proofreading Team at -http://www.pgdp.net (This file was produced from images -generously made available by The Internet Archive) - - -Updated editions will replace the previous one--the old editions -will be renamed. - -Creating the works from public domain print editions means that no -one owns a United States copyright in these works, so the Foundation -(and you!) can copy and distribute it in the United States without -permission and without paying copyright royalties. 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You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org - - -Title: A Guide to the Scientific Knowledge of Things Familiar - -Author: Ebenezer Cobham Brewer - -Release Date: September 3, 2012 [EBook #40652] - -Language: English - -Character set encoding: ASCII - -*** START OF THIS PROJECT GUTENBERG EBOOK SCIENTIFIC KNOWLEDGE--THINGS FAMILIAR *** - - - - -Produced by David Garcia, Marilynda Fraser-Cunliffe, Matthew -Wheaton and the Online Distributed Proofreading Team at -http://www.pgdp.net (This file was produced from images -generously made available by The Internet Archive) - - - - - - - - - - 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 x 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 deg. by the thermometer; but if ice be _melted_ over a -fire, (though 140 deg. of heat are thus absorbed,) it will feel no _hotter_ -than it was before. (_i. e. it will be only 32 deg., and not 172 deg._)[5]. - -[5] 32 deg., i. e. 32 degrees; 140 deg., i. e. 140 degrees, &c. - - -Q. _What becomes of the 140 deg., 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 deg. of heat may remain latent in _water_. - - -Q. _How can 1140 deg. of heat be added to water, without being perceptible -to our feelings?_ - -A. 1st--140 deg. of heat are hidden in the water, when ice is melted by the -sun or fire. - -2ndly--1000 deg. more of heat are secreted, when water is converted into -steam. Thus, before ice is converted into steam, 1140 deg. of heat become -_latent_.[6] - -[6] Thus, one pint of boiling water, (212 deg. 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 deg.: therefore, when water is -converted into steam, 1000 deg. of heat become latent. Hence, before ice is -converted to steam, it must contain 1140 deg. 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 deg.), -_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 deg., 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 larvae_ 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: phos-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 deg., 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 deg., 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 deg.) - - -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 deg.) - - -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 deg.; but the air 32 deg., 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 deg., but salt and water will not freeze _till the -air is 25 deg. colder_: if, therefore, salt be added to frozen water it -becomes _liquid_, unless the thermometer stands below 7 deg., (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 deg. (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 papillae) are -inactive and at rest. - - -Q. _Why can we not FEEL when we are asleep?_ - -A. Because the _ends of the nerves_ (called papillae), 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 PAPILLAE) 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 "PAPILLAE" 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 - - Papillae, 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 THIS PROJECT GUTENBERG EBOOK SCIENTIFIC KNOWLEDGE--THINGS FAMILIAR *** - -***** This file should be named 40652.txt or 40652.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/4/0/6/5/40652/ - -Produced by David Garcia, Marilynda Fraser-Cunliffe, Matthew -Wheaton and the Online Distributed Proofreading Team at -http://www.pgdp.net (This file was produced from images -generously made available by The Internet Archive) - 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