Fig. 19.—A WATER SPOUT.
Fig. 19.—A WATER SPOUT.
679.Why does the chimney smoke when the fire is first lighted?
Because the air in the chimney is of the same temperature as that in the room, and thereforewill not ascend.
680.Why does the smoking (into the room) cease, after the fire has been lighted a little while?
Because the air in the chimney, being warmed by the fire beneath, becomes lighter and ascends rapidly.
681.Why does a long chimney create a greater draught than a short one?
Because the short chimney containsless airthan the long one; there is, consequently, less difference of weight between the warmair of the short chimney and the external air; it therefore has not so great anascensive power.
"And, lo, the smoke of the country went up as the smoke of a furnace."—Gen. xix.
682.Why does smoke issue in folds and curls?
Because it ispressed uponby thecold airwhich alwaysrushes towards a rarer atmosphere. It thus illustrates the development ofstorms.
683.Why do some chimneys smoke when the doors and windows are closed?
Because the draught of air is not sufficient to supply the wants of the fire, and enable it to create anupward current.
684.What is the best method of conveying air to fires?
Tubes built in the walls, communicating with the outer air, and terminatingunderneath the grates.
685.Why is this the best method of ventilation?
Because doors and windows may then be made air-tight, anddraughts across rooms be prevented.
686.Why do chimneys that stand under elevated objects, such as hills, trees, and high buildings, smoke?
Because the wind, striking against the elevated object,flies back, and a part of itrushes downward.
687.Why do sooty chimneys smoke?
Because the accumulation of the sootdiminishes the size of the flue, and lessens the ascensive power of the draught, by reducing the quantity ofwarm air. It also obstructs the motion of the air, by theroughness of its surface.
688.Why do chimneys smoke in damp and gusty weather?
Because the ascending air issuddenly chilledby gusts of damp and cold air, and driven down the chimney.
"Remember that thou magnify his work, which men behold. Every man may see it; man may behold it afar off."—Job xxxvi.
689.Why does smoke ascend in a straight line in mild and fine weather?
Because the air is still, and being dry and warm itdoes not chill the smoke, nor drive it out of its course.
690.Why do the wings of wind-mills turn round?
Because the wind, strikingat an angleupon the wings, forces them aside; and as there are four wings all upon the same angle, and fixed upon the same centre, theoblique pressureof the wind causes the centre to rotate.
There is a world ofminiature phenomenawhich has never been fully recognised, in which we may see the mightier works of nature pleasingly and truthfully illustrated.
When the wind blows into the corner of a street, and whirling around, catches straw, dust, and feathers in its arms, and then wheels away, flinging the troubled atoms in all directions,—it is a miniature of the mightierwhirlwind, which wrecks ships, uproots trees, and levels houses with the earth.
When a cloud of dust, on a hot summer's day, rises and flies along the thirsty road, making the passenger close his eyelids, and dusting the leaves of wayside vegetation,—it is a miniature of the terriblesimoom, which blows from the desert sands, scattering death and devastation in its track.
When steam issues from the tea-urn, and becomes condensed in minute drops upon the window-pane,—the miniature is of theearth's heat, evaporating the waters, and the cold air of night condensing the vapours intodew.
When grass and corn bend before the wind, and are beaten down by its force; when the pond forgets its calm, and rises in troubled waves, casting the flotilla of natural boats that move upon its surface, in rude disorder upon its windward shore,—the little storm is but a miniature of those greathurricaneswhich wrecked a fleet in the Black Sea, and levelled the encampments of a mighty army.
When the snow that has gathered upon the house-top, warming beneath the smiles of the sun, slips from its bed, and drops in accumulated heaps from the roof,—it is a miniature of those terribleavalancheswhich in the Pyrenees bury villages in their icy pall, and doom man and beast to death.
When the rivulet hurries on its course, and meeting with obstructions, leaps over them in mimic wrath, overturning some little raft upon which, perchance, a weary fly has alighted,—it is a miniature of thoserapidson whose banks the hippopotamus and the alligator yet live; and where, though rarely, man may be seen directing his raft over the troubled current, amid the rush ofdebrisfrom forests unexplored.
And when, in a basin of the rivulet, two opposing currents meet, and form a little vortex into which insect life and vegetable fragments coming within thesphere of its influence are drawn,—it is a miniature of the roaringwhirlpool, or the wildermaelstromof the Norwegian seas.
Nature rehearses all her parts in mild whispers; and for every picture that she paints, she places a first study upon the canvas. Man need not go into the heart of her terrors to understand their laws. Many an unknown Humboldt, sitting by the river's side, may rejoice in the "aspects of nature," and share the bliss of knowledge with the great philosopher.
"Can any understand the spreadings of the clouds, or the noise of his tabernacle?"—Job xxxvi.
691.What is a barometer?
A barometer is an instrument whichindicates the pressure of the atmosphere, and which takes its name from two Greek words signifyingmeasurer of weight.
692.Why does a barometer indicate the pressure of the atmosphere?
Because it consists of a tube containingquicksilver, closed at one end and open at the other, so that the pressure of the air upon the open end balances the weight of the column of mercury (quicksilver), and when the pressure of the air upon the open surface of the mercury increases or decreases, the mercuryrises or fallsin response thereto.
693.Why is a barometer called also a "weather-glass"?
Because changes in the weather are generally preceded byalterations in the atmospheric pressure. But we cannot perceive those changes as they gradually occur; the alteration in the height of the column of mercury, therefore, enables us to know that atmospheric changes are taking place, and, by observation, we are enabled to determine certain rules by whichthe state of the weather may be foretoldwith considerable probability.
694.Why are barometers constructed with circular dials, and an index to denote changes?
Because that is a convenient mechanical arrangement, by whichthe alterations of the relative pressures of the air and the mercury aremore clearly denoted than by an inspection of the mercury itself.
"Fair weather cometh out of the north: with God is terrible majesty."—Job xxxvii.
Fig. 20.—BAROMETER.Fig. 21.—TUBE OF BAROMETER, WHEEL, AND PULLEY.
Fig. 20.—BAROMETER.
Fig. 20.—BAROMETER.
Fig. 21.—TUBE OF BAROMETER, WHEEL, AND PULLEY.
Fig. 21.—TUBE OF BAROMETER, WHEEL, AND PULLEY.
695.Why does the hand of the weather dial change its position when the column of mercury rises or falls?
Because a weight, whichfloats upon the open surface of the mercury, is attached to a string, having a nearly equal weight at the other extremity; the string is laid over a revolving pivot to which the hand is fixed, andthe friction of the string turns the hand, as the mercury rises or falls.
"Thou visitest the earth, and waterest it: thou greatly enrichest it with the river of God, which is full of water: thou preparest them corn, when thou hast so provided for it."—Psalm lxv.
696.Why does tapping the face of the barometer sometimes cause the hand to move?
Because the weight on the surface of the mercury frequentlyleans against the sides of the tube, and does not move freely. And, also, the mercury clings to the sides of the tube bycapillary attraction; therefore, tapping on the face of the barometersets the weight free, and overcomes the attraction whichimpedes the rise or fall of the mercury.
Fig. 21illustrates the mechanism at the back of the barometer. A is a glass tube; between A and E there exists avacuum, caused by the weight of the mercury pressing downwards. This space being a vacuum, makes the barometrical column more sensitive, as there is no internal force to resist or modify the effects of the external pressure. E represents the height of the column of mercury; C the open end of the tube; F the weight resting on the surface of the mercury; P the pivot over which the string passes, and upon which the hand turns; W the weight which forms the pulley with the weight F.
697.Which is the heavier, dry or vaporised air?
Dry air isheavierthan air impregnated with vapours.
698.Why is dry air heavier than moist air?
Because of theextreme tenuity of watery vapours, the density of which isless than that of atmospheric air.
699.Why does the fall of the barometer denote the approach of rain?
Because it shows that as the aircannot support the full weight of the column of mercury, the atmosphere must be thin with watery vapours.
The fall of the mercury in the long arm of the tube would cause the weight F to be pressed upwards. This would release the string to which the weight W is attached; it would, therefore, fall, and turn the hand down to Rain or Much Rain.
700.Why does the rise of the barometer denote the approach of fine weather?
Because the external air becoming dense, and free from highly elastic vapours, presses with increased force upon the mercury upon which the weight F floats; that weight, therefore, sinks in the short tube as the mercury rises in the long one, and in sinking turns the hand to Change, Fair, &c.
"He caused an east wind to blow in the heaven; and by his power he brought in the south wind."—Psalm lxxviii.
701.Why does the barometer enable us to calculate the height of mountains?
Because, as the barometer is carried up a mountain,there is a less depth of atmosphere above to press upon the mercury; it therefore falls, and by comparing various observations, it has been found practicable tocalculate the height of mountains by the fall of the mercury in a barometer.
702.To what extent of variation is the weight of the atmosphere liable?
It may vary as much asa pound and a half to the square inchat the level of the sea.
703.When does the barometer stand highest?
When there is aduration of frost, or whennorth-easterly windsprevail.
704.Why does the barometer stand highest at these times?
Because the atmosphere is exceedinglydry and dense, and fully balances theweight of the column of mercury.
705.When does the barometer stand lowest?
Whena thaw follows a long frost; or whensouth-west windsprevail.
706.Why does the barometer stand lowest at those times?
Becausemuch moisture exists in the air, by which it is rendered less dense and heavy.
707.What effect has heat upon the barometer?
It causes the mercury to fall,by evaporating moisture into the air.
708.What effect has cold upon the barometer?
It causes the mercury to rise, bychecking evaporation, andincreasing the density of the air.
"For so the Lord said unto me, I will take my rest, and I will consider in my dwelling place like a clear heat upon herbs, and like a cloud of dew in the heat of harvest."—Isaiah xviii.
In noting barometrical indications, more attention should be paid to thetendencyof the mercury at the time of the observation, than to theactual state of the column, whether it standshighorlow. The following rules of barometric reading are given as generally accurate, but liable to exceptions:—
Fair weatherindicated by theriseof the mercury.
Foulweather by thefallof the mercury.
Thunder, indicated by thefallof the mercury insultry weather.
Cold, indicated by theriseof the mercury in spring, autumn, and winter.
Heat, by thefallof the mercury in summer and autumn.
Frost, indicated by theriseof the mercury in winter.
Thaw, by thefallof the mercury during a frost.
Continued bad weather, when thefallof the mercury has beengradualthrough several fine days.
Continued fine weather, when theriseof the mercury has beengradualthrough several foul days.
Bad weather of short duration, when it sets in quickly.
Fine weather of short duration, when it sets in quickly.
Changeable weather, when anextremechange hassuddenlyset in.
Wind, indicated by a rapidriseorfall unattended by a change of temperature.
The mercuryrising, and the air becomingcooler, promisesfine weather; but the mercuryrising, and the air becomingwarmer, the weather willbe changeable.
If the top of the column of mercury appearsconvex, or curved upwards, it is an additional proof that the mercury isrising. Expectfineweather.
If the top of the column isconcave, or curved downwards, it is an additional proof that the mercury isfalling. Expectbadweather.
709.What is the thermometer?
The thermometer is an instrument in whichmercuryis employed to indicatedegrees of heat. Its name is derived from two Greek words, meaningheat measurer.
710.Why does mercury indicate degrees of heat?
Because itexpandsreadily withheat, andcontractswithcold; and as it passes freely through small tubes, it is the most convenient medium for indicatingchanges of temperature.
"When ye see a cloud rise out of the west straightway ye say, There cometh a shower; and so it is. And when ye see the south wind blow, ye say there will be heat; and it cometh to pass."—Luke xiii.
711.Why are there Reaumur's Thermometers and Fahrenheit's Thermometers?
Because their inventors, after whom they are named, adopted a different system ofnotation, orthermometrical marks; and as their thermometers have been adopted by various countries and authors, it is now difficult to dispense with either of them.
Fig. 22.—THE THERMOMETERS OF REAUMUR AND FAHRENHEIT COMPARED.
Fig. 22.—THE THERMOMETERS OF REAUMUR AND FAHRENHEIT COMPARED.
We have combined the two (seefig. 22.) The diagram will, we have no doubt, prove exceedingly useful to scientific readers and experimentalists. There is also another system of notation, adopted by the French, called thecentigrade, but it is not much referred to in Great Britain. In the centigrade thermometer 0 zero is the freezing point, and 100 the boiling point. Fahrenheit's scale is generally preferred. Reaumur's is mostly used in Germany. Of Fahrenheit's scale 32 is the freezing point, 55 is moderate heat, 76 summer heat in Great Britain, 98 is blood heat, and 212 is the boiling point. Mr. Wedgwood has invented a thermometer for testinghigh temperatures, each degree of which answers to l30 degrees of Fahrenheit. According to his scale cast iron melts at 2,786 deg.; fine gold at 2,016 deg.; fine silver 1,873 deg.; brass melts at 1,869 deg.; red heat is visible by day at 980 deg.; lead melts 612 deg.; bismuth melts 476 deg.; tin melts 412 deg.; and there is a curious fact with regard to the three metals, lead, bismuth, and tin, that if they are mixed in the proportions of 5, 8, and 3 parts respectively, the mixture (after previous fusion) will melt at a heat below that of boiling water.
712.What is the difference between the thermometer and the barometer?
In the thermometer the column of mercury is much smaller than in the barometer, and is sealed from the air; while in the barometer the column of mercury is open at one end to atmospheric influence.
713.Why does the mercury in the thermometer, being sealed up, indicate the external temperature?
Because the heat passes through the glass, in which the mercury is enclosed, andexpanding or contracting the metal within the bulb, causes the small column above it toriseorfall.
"Blessed is the people that know the joyful sound: they shall walk, O Lord, in the light of thy countenance."—Psalm lxxxix.
714.When does the thermometer vary most in its indication of natural temperature?
It varies more in thewinterthan in thesummerseason.
715.Why does it vary more in the winter than in the summer?
Because the temperature of our climatediffers more from the temperature of the torrid zones in the winterthan it does in thesummer, and theinequalities of temperaturecause frequent changes in the degree of prevailing heat.
The same remarks (714, 715,) apply to the barometer.
716.What is sound?
Sound is animpression produced upon the earbyvibrationsofthe air.
717.What causes the air to vibrate and produce sounds?
The atoms ofelastic bodiesbeing caused tovibrateby the application of some kind of force,the vibrations of those atoms are imparted to the air, and sound is produced.
718.How do we know that sounds are produced by the vibrations of the air, induced by the vibrations of the atoms of bodies?
If we take a tuning fork, and hold it to the ear, we hearno sound. If we move it rapidly through the air, or if we blow upon it, it producesno sound; but if westrike it,a sound immediately occurs; the vibration of the fork may be seen, and felt by the hand that holds it; andas those vibrations cease, the sounddies away.
719.How do we know that without air there would be no sound?
Because if a tuning fork were to be struck in avacuum(as under the receiver of an air pump)no soundwould be heard, although thevibrationsof the fork could bedistinctly seen.
"And even things without life giving sound, whether pipe or harp, except they give a distinction in the sounds, how shall it be known what is piped or harped."—Corinth. xiv.
720.How are the vibrations of sonorous bodies imparted to the air?
When a bell is struck, the force of the blow gives an instant agitation to all its particles. The air around the bell is driven back by the impulse of the force, and thus avibration of compressionis imparted to the air; but the air returns to the bell, by its own natural elasticity, thus producing avibration of expansion—when it is again struck, and thussuccessive vibrationsof compression and expansion aretransmitted through the air.
721.How rapidly are these vibrations transmitted through the air?
They travel at a rate of rather more thana quarter of a mile in a second, ortwelve miles and three-fourths in a minute.
722.Do all sounds travel at the same rate?
All sounds, whether strong or weak, high or low, musical or discordant,travel with the same velocity.
723.Why are bells and glasses stopped from ringing by touching them with the finger?
Because the contact of the fingerstops the vibrationof the atoms of the metal and glass, which thereforecease to impart vibrations to the air.
724.Why does a cracked bell give discordant sounds?
Because theconnectionbetween the atoms of the bell beingbroken,their vibrations are not uniform: some of the atoms vibratemore intenselythan the others; the vibrations imparted to the air are thereforejarringanddiscordant.
725.Why, when we see a gun fired at a distance, do we see the flash and smoke, before we hear the report?
Becauselight,which enables us tosee, travels at the velocity of192,000 miles in asecond; whilesound, by which wehear, travels only at the rate of a quarter of a mile in asecond.
"My heart maketh a noise in me: I cannot hold my peace, because thou hast heard, O my soul, the sound of the trumpet, the alarm of war."—Jer. iv.
726.Why does the tread of soldiers, when marching in long ranks, appear to be irregular?
Because the sounds proceeding fromdifferent distances, reach our ears invarying periods of time.
727.What are the numbers of vibrations in a second that produce the various musical sounds?
C or Do, 480 vibrations in a second; B or Si, 450 vibrations; A or La, 400 vibrations; G or Sol, 360 vibrations; F or Fa, 320 vibrations; E or Mi, 300 vibrations; D or Re, 270 vibrations; C or Do, 240 vibrations. It is thus seen that themore rapidthe vibrations, thehigherthe note, andvice versa.
728.Why does the length of a wire or string determine the sound that it produces?
Because theshorter the stringthemore rapidare its vibrations when struck.
729.Why does the tension of a wire or string affect its vibrations?
Because when the string or wire is tight, a touch communicates vibrations toall its particles; but when it is loose the vibrations areimperfectly communicated.
730.Why are some notes low and solemn, and others high and quick?
Because the vibrations of musical strings vary from 32 vibrations in a second, which produces a soft and deep bass, to 15,000 vibrations in a second, which produces the sharpest treble note.
731.Why can our voices be heard at a greater distance when we speak through tubes?
Because the vibrations areconfined to the air within the tube, and are not interfered with byother vibrationsor movements in the air; the tube itself is also agood conductor of sound.
"And I will cause the noise of thy songs to cease; and the sound of thy harps shall no more be heard."—Ezekiel xxvi.
732.Is air a good conductor of sound?
Air is agood conductor, but water is abetter conductor than air; wood, metals, the earth, &c., are alsogood conductors.
733.Why can we hear sounds at a greater distance on water than on land?
For various reasons: because the smooth surface of water is a good conductor; because there are fewer noises, or counter vibrations, to interfere with the transmission of sound; and because there are no elevated objects to impede the progress of the vibrations.
734.Why do sea-shells give a murmuring noise when held to the ear?
Because what may be calledexpended vibrationsalways exist in air where various sounds are occurring. Thesetremblingsof the air are received upon the thin covering of the shell, and thus beingcollected into a focus, aretransmitted to the ear.
735.Why can people in the arctic regions converse when more than a mile apart?
Because there the air, beingcold and dense, is a very good conductor; and thesmooth surface of the icealso favours thetransmission of sound.
736.Why do savages lay their heads upon the earth to hear the sounds of wild beasts, &c.?
Because the earth is a good conductor of sound. For this reason, also, personsworking under ground in minescan hear each other digging at considerable distances.
737.Why can church clocks be heard striking much more clearly at some times than at others?
Because the density of dry air improves thesound-conducting powerof the atmosphere. The transmission of sounds is also assisted by the direction of the winds.
"The morning is come unto thee, O thou that dwellest in the land: the time is come, the day of trouble is near, and not the sounding again of the mountains."—Ezekiel vii.
738.Why may the scratching of a pin at one extremity ofa long pole be heard by applying the ear to the opposite extremity?
Because wood is a good conductor of sound, and its atoms aresusceptible of considerable vibration. It is, therefore, chosen in numerous instances for the construction ofmusical instruments.
Deaf persons have been known to derive pleasure from music by placing their hands upon the wood-work of musical instruments while being played upon.
739.Why is the hearing of deaf persons assisted by ear-trumpets?
Because ear-trumpetscollect the vibrations of the airinto a focus, and make the sounds produced thereby more intense.
740.Why are sounding-hoards used to improve the hearing of congregations?
Because, being suspended over, and a little behind, the speaker, theycollect the vibrationsof the air, andreflectthem towards the congregation.
741.What are echoes?
Echoes are soundsreflectedby the objects on which they strike.
742.Why do some echoes occur immediately after a sound?
Because the reflecting surface isvery near; therefore the sound returns immediately.
743.Why do some echoes occur a considerable time after a sound?
Because they are at a considerable distance, and the sound takes time to travel to it, and an equal time to return.
744.Why do some echoes change the tone and quality of sound?
Because the reflecting surface, having vibratory qualities of its own,mingles its own vibrations with that of the sound.
745.Why are there sometimes several echoes to one sound?
Because there are variousreflecting surfaces, at different distances, each of which returns an echo.
"And God said, Let the waters under the heaven be gathered together onto one place, and let the dry land appear: and it was so."—Gen. i.
746.Are sounds reflected only by distant objects?
Sounds are doubtless reflected bywalls and ceilingsaround us. But we do not perceive the echoes, because they are so near that they occur at the same moment with the sound. In lofty buildings, however, there is frequently adouble sound, making the utterance of a speaker indistinct. This arises from the echo following very closely upon the sound.
747.Why, when we are walking under an arch-way or a tunnel, do our voices appear louder?
Because the sounds of our voices areimmediately reflected. And as agas reflector increases the intensity of light, soa sound reflectorwillincrease the apparent strength of our voices.
There are many places where remarkable echoes occur. On the banks of the Rhine, at Lurley, if the weather be favourable, the report of a rifle, or the sound of a trumpet, will be repeated at different periods, and with various degrees of strength, from crag to crag, on opposite sides of the river alternately. A similar effect is heard in the neighbourhood of some of the Lochs in Scotland. There is a place at Woodstock, in Gloucestershire, which is said to echo a sound fifty times. Near Rosneath, a few miles from Glasgow, there is a spot where, if a person plays a bar of music upon a bugle, the notes will be repeated by an echo, but a third lower; after a short pause, another echo is heard, again in a lower tone; then follows another pause, and a third repetition follows in a still lower key. The effect is very enchanting. The whispering galleries of St. Paul's, of the cathedral church of Gloucester, and of the Observatory of Paris, owe their curious effects to those laws of the reflection of sound, by which echoes are produced; but in these cases the effect is assisted by the elliptical form of the edifice, each person being in the focus of an ellipse.
748.What is water?
Water is a fluid composed oftwovolumes ofhydrogentooneofoxygen, oreightparts by weight ofoxygentooneofhydrogen. It is nearly colourless and transparent.
749.Why, if a saucer of water be exposed to the air, will it gradually disappear?
Because water is highly expansive, andrises in thin vapour, when in contact with warm and dry air.
"Behold there ariseth a little cloud from the sea, of the bigness of a man's hand. And it came to pass in the meantime, that the heaven was black with clouds and wind, and there was a great rain."—1 Kings xviii.
750.Why does steam issue from the spout of a kettle?
Because the heat of the fire passes into the water, anddrivesits atoms apart, making those of them that rise quickly to the surfacelighter than the air, upon which they consequently rise.
751.Why does water become solid when it freezes?
Because thelatent heat of the waterpasses away from between its atoms into the air; the atoms, therefore, draw closer together.
752.Why, if the atoms of water draw closer together when freezing, does ice expand, and occupy greater space than water?
Because,when the atoms of water are congealing, they do not form acompact mass, but arrange themselvesin groups of crystal points, which occupy greater space. Watercontractswhen freezing until it sinks to 40 deg., and then itexpandsas ice is formed.
32 deg. is said to be thefreezingpoint, but it should be called thefrozenpoint.
753.Why does water boil?
Because heat,entering into the lower portionsof the water,expandsit; the heated portions are thenspecifically lighterthan those that are cooler; the hot water thereforerises upward, and forces the cooler water down.
754.What proportion of the earth's surface is covered with water?
There are about one hundred and forty seven millions of square miles ofwater, to forty-nine and a half millions of square miles ofland.
755.What is the amount of water pressure?
The pressure of the sea, at the depth of 1,100 yards, is equal to 15,000 lbs.to the square inch.
"But the land, whither ye go to possess it, is a land of hills and valleys, and drinketh water of the rain of heaven."—Deut. xi.
756.What element is the most abundant in nature?
Oxygen, which forms so large a part ofwater. Of animal substances,oxygenformsthree-fourths; ofvegetable substancesit formsfour-fifths; ofmineral substancesit formsone-half; it formseight-ninthsof thewatersandone-fifthof theatmosphere; and aggregating the whole creation, fromone-half to two-thirdsconsists ofoxygen.
757.In what ways does man use oxygen?
Maneats,drinks,breathes, andburnsit, in various proportions and combinations. It is estimated thatthe human raceconsume in those various ways 1,000,000,000 lbs. daily; that thelower animalsconsume double that amount; and that, in the varied works of nature, no less than 8,000,000,000 lbs. ofoxygenare useddaily.
758.Why does water dissolve various substances?
Because theatoms of waterare very minute; they thereforepermeate the pores, or spaces, between the atoms of those bodies, andovercoming their attraction for each other, cause them to separate.
759.Why does hot water dissolve substances more readily than cold?
Because theheat assists to repel the particlesof the substance undergoing solution, andgives the water a freer passagebetween the atoms.
760.Why is pump water sometimes hard?
Because, in passing through the earth, it has become impregnated with mineral matters, usually thesulphateandcarbonate of lime.
761.Why is rain water soft?
Because it is derived from vapours which, in ascending to the clouds,could not bear up the mineral waters with them. It therefore became purified or distilled.
762.Why do kettles become encrusted with stony deposits?
Because that portion of the water which is driven off in steamleaves the mineral matters behind; they therefore form a crust around the sides of the kettle.
It is said that if a child's marble be placed in a kettle, it will attract the earthy particles, and prevent the encrusting of the sides of the vessel.
"He gathereth the waters of the sea together as an heap; he layeth up the depth in storehouses."—Psalm xxxiii.
763.Why is it difficult to wash in hard water?
Because the soap unites with the mineral matters in the water, and beingneutralisedthereby, cannotdissolve the dirtwhich we desire to cleanse away.
764.Why is the sea salt?
Because salt is a mineral which prevails largely in the earth, and which,being very soluble in water, is taken up by the ocean.
Lakes and rivers, also, even those that are considered fresh, hold in solutionsome degree of saline matters, which they contribute to the ocean.
As, in the evaporations from the sea, the salt remains in it, while the vapours fall as rain, and again wash the earth and carry some of its mineral properties to the ocean, thegreater saltness of the sea, as compared with rivers, is accounted for.
By some persons the opinion is entertained that the sea has beengradually getting salterever since the creation of the world. This, they say, arises from the evaporation of water free from salt, and the returns of the water to the sea, taking with it salt from the land.
765.What is the estimated amount of salt in the sea?
The amount of common salt in the various oceans is estimated at 3,051,342cubic geographical miles, or about five times more than the mass of the mountains of the Alps.
766.What is the depth of the sea?
The extreme depth has not, probably, been ascertained. But Sir James Ross took soundings about 900 miles west of St. Helena, whence he found the sea to be nearlysix miles in depth. Now, if we take the height of the highest mountain to be five miles, the distance from that extreme rise of the earth, to the known depth of the sea, will be no less thaneleven miles.
767.Why are the waters of some springs impregnated with mineral matters?
Because the water passes through beds of soda, lime, magnesia, carbonic acid, oxides of iron, sulphate of iron, &c., &c., andtakes up in some slight degree the particles of those minerals, according to the proportions in which they abound.
"Who hath measured the waters in the hollow of his hand, and meted out heaven with the span, and comprehended the dust of the earth in a measure and weighed the mountains in scales, and the hills in a balance?"—Isaiah xl.
768.Why does iron rust rapidly when wetted?
Because the water contains a large proportion of oxygen, some of which combines with the iron and formsan oxide of iron, which isrust.
769.Why does stagnant water become putrid?
Because thelarge amount of oxygenwhich it contains accelerates the decomposition of deadanimal and vegetable substancesthat accumulate in it.
770.Is there danger in drinking water on account of the living animalcules which it contains?
No danger arises from theliving creaturesin water; butputrefactivematters may produce serious diseases.
771.What is the best method of guarding against impurities?
By obtaining water from the purest sources, and by filtering it before drinking, by which nearly all extraneous matters would beseparated from it.
772.What is attraction?
Attraction is the tendency of bodies todraw near to each other. It is calledattraction, from two Latin words signifyingdrawing towards.
773.How many kinds of attraction are there?
There are five principal kinds ofattraction:—
1. The attraction ofgravitation.2. The attraction ofcohesion.3. The attraction ofchemical affinity.4. The attraction ofelectricity.5. Andcapillary attraction.
"Behold, the nations are as a drop of a bucket, and are counted as the small dust of the balance: behold, he taketh up the isles as a very little thing."—Isaiah xl.
774.Why do all bodies heavier than the air fall to the earth?
Because they are influenced by theattraction of gravitation, by which all bodies are drawn towardsthe centre of the earth.
775.Why do bodies lighter than the air ascend?
Because the air, being a denser body,obeys the law of attraction, and in doing sodisplaces lighter bodiesthat interfere with its gravitation.
776.Why do fragments of tea, and bubbles floating upon the surface of tea, draw towards each other, and attach themselves to the sides of the cup?
Because they are influenced by theattraction of cohesion.
Cohesion.—The act of sticking together.
777.Why will a drop of water upon the blade of a knife leave a dark spot?
Because theiron of the knife attracts the oxygen of the water, bychemical affinity; and the two substances form a thin coating ofoxide of iron.
Affinity.—Attraction between dissimilar particles through which they form new compounds.
778.Why do clouds sometimes move towards each other from opposite directions? and
779.Why do light particles of matter attach themselves to sealing wax, excited by friction?
Because they are moved by theattraction of electricity.
780.Why will a towel, the corner of which is dipped in water, become wet far above the water?
Because the water is conveyed up through the towel, bycapillary attraction. The atoms of the water are attracted by thethreads of the towel, and drawn up into thesmall spaces between the threads.
Capillary.—Resembling a hair, small in diameter.
"He stretcheth out the north over the empty place, and hangeth the earth upon nothing."—Job xxvi.
781.Why do small bodies floating upon water move towards larger ones?
Because the attractive power of alarge bodyis greater than that ofa small one. As each atom of matter has inherent power of attraction, it follows that alarge aggregation of particlesmust attract in proportion to the number of those particles.
782.Why do clouds gather around mountain tops?
Because they areattracted by the mountains.
783.Why would a piece of lead tied to a string, and let down from a church steeple, incline a little from the perpendicular towards the church?
Because themasses of stoneof which the church is built wouldattract the lead.
784.How can man weigh the earth?
By observing what is called thedeflectionof small bodieswhen brought within given distances of larger bodies, the degree of attractionexercised by the large body upon the smaller onebecomes known. This attraction of thelarge bodyexercised over thesmaller bodyis an opposing influence,acting against the earth's attraction of the small body, which is drawn out of its course: it constitutes anatural balance between the influence of the earth and another body, acting in opposition to it. Founded upon these, and some other data, man can weigh the earth, and give a morally certain result!
Deflection.—The act of turning aside.
785.How can man weigh the planets?
The planets exercise as certain an influence upon each otheras do two pieces of wood floating upon a basin of water. As the planetary bodies fly through their prescribed orbits,and approach nearer to, or travel further from, each other, they are observed todeviatefrom that course which they must have pursuedbut for the increase or the decrease of some influence of attraction. By making observationsat various times, and by comparinga number of results, it is possibleto weigh any planetary body, however vast, or however distant.
"Is not God in the height of the heaven? and behold the height of the stars, how high they are?"—Job xii.
786.How can man measure the distances of the planets?
By making observations atdifferent seasons of the year, when the earth is inopposite positions in her orbit; and by recording, byinstruments constructed with the greatest nicety, theangle of sight, at which the planetary body is viewed; by noticing, also,the various eclipses, and estimatinghow long the first light after an eclipse has ceasedreaches the earth, it is possible to estimate thedistancesof heavenly bodies,no matter how far in the depths of the universe those orbs may be.
787.What are the opinions founded upon estimates respecting the magnitude of the sun?
Thediameterof thesunis 770,800 geographical miles, or 112 times greater than the diameter of the earth; itsvolumeis 1,407,124 times that of the earth, and 600 times greater thanall the planets together; itsmassis 359,551 times greater than the earth; and 738 times greater than that ofall the planets. Asingle spotseen upon its surface has been estimated to extend over 77,000 miles in diameter, and acluster of spotshave been estimated to include an area of 3,780,000 miles.
788.What is the weight of the earth?
The earth has acircumferenceof 25,000 miles, and is estimated toweigh1,256,195,670,000,000,000,000,000 tons.
789.What is the specific gravity of a body?
It is its weight estimatedrelatively to the weights of other bodies.
790.What determines the force with which bodies fall to the earth?
Generally speaking, theirspecific gravity, which is proportionate to the density, orcompactness of the atomsof which they are composed.
791.Why does a feather fall to the earth more gradually than a shilling?
Because thespecific gravityof the feather and of the shilling isrelative to that of the air, the medium through which the feather and the shilling pass. If there wereno air, a shilling and a feather dropped at the same time from a height of forty miles,would reach the earth at the same moment.
"Where wast thou when I laid the foundations of the earth? declare, if thou hast understanding."
792.What is repulsion?
Repulsion is that property in matter by which itrepelsorrecedes from, those bodies for which it hasno attraction or affinity.
793.Why does dew form into round drops upon the leaves of plants?
Because itrepels the air, and thesubstances of the leavesupon which it rests. Because, also, its own particlescohere.
794.Why do drops of water roll over dusty surfaces?
Because theyrepelthe particles of dust; and also because their own particles havea stronger attraction for each otherthan for the particles of dust.
795.Why does a needle float when carefully laid upon the surface of water?
Because the needle and the watermutually repel each other.
796.Why does water, when dropped upon hot iron, move about in agitated globules?
Because thecaloricrepels the particles of the water.
797.Why does oil float upon the surface of water?
Because, besides being specially lighter than water, the particles of the oil and the watermutually repel each other.
798.What is carbonic acid?
Carbonic acid is a mixture ofcarbonandoxygen, in the proportion of 3 lbs. of carbon to 8 lbs. of oxygen.
"Who hath laid the measures thereof, if thou knowest? or who hath stretched the line upon it?"
799.Where does carbonic acid chiefly exist?
It exists in various natural bodies in which carbon and oxygen are combined; it is evolved by the decomposition of numerous bodies called carbonates, in which carbon is united with a particular base, such as the carbonate of lime, the carbonate of iron, the carbonate of copper, &c. It is also evolved by the processes offermentation, by thebreathing of animals, thecombustion of fuel, and thefunctions of plants. Carbonic acid alsoexists in various waters.
Carbonic acid isfound most largely in solid combinations with other bodies: it forms 44-100ths of all limestones and marbles, and it exists in smaller quantity, combined with other earths, and with metallic oxides.
800.What are the states in which pure carbonic acid exists?
Pure carbonic acid may exist in thesolid, theliquid, or theæriformstate. In thesolid stateit is produced only by artificial means, and it is then a white crystallised body, in appearancelike snow; in theliquid stateit is aheavy colourless fluid; in theæriform stateit is apungent,heavy,colourless gas, and is known ascarbonic acid gas.
801.Why does bottled porter produce large volumes of froth, much more than the bottle could contain?
Because, by the fermentive process,carbonic acidhas been developed in the porter, and is held inliquid solution; but it always has astrong tendency to escape, and directly the pressure is removed, itevolves into gas, by which it occupies much greater space, and forces the porter in millions of small bubbles out of the bottle.
802.Why does soda-water effervesce?
Becausecarbonic acid gasis forced into the waterby pressure. Pressurealters the gas into a liquid, and directly the pressure ceases, the liquid againevolves into gas.
803.Why does spring water taste fresh and invigorating?
Because it containscarbonic acid.
"Whereupon are the foundations thereof fastened? or who laid the cornerstone thereof."—Job xxxviii.
804.Why does boiled water taste flat and insipid?
Because thecarbonic acidhas beendriven offby boiling.
805.Why does beer which has been standing in a glass taste flat?
Because itscarbonic acidhas escaped ascarbonic acid gas.
806.Why, when we look into a glass of champagne, do we see bubbles spontaneously appear at the bottom, and then rise to the top?
Because, in the places where the bubbles are formed, theliquid carbonic acidis evolving intocarbonic acid gas.
807.Why do the bubbles arise from two or three points in columns, rapidly succeeding each other?
Because, when the formation of gas once begins, and bubbles ascend, there isless pressurein the line of thecolumn of bubbles; the carbonic acid, therefore, draws towards those points as theeasiest channel of escape.
These explanations equally apply to the "working" of beer, by which yeast is produced; to the effervescence of various waters, acidulated drinks, ginger beer, &c., and also to the "sponging" of bread, &c.
808.Why does gunpowder explode?
Gunpowder is made of a very intimatemechanical mixtureofnitrate of potash,charcoal, andsulphur. When these substances are heated to a certain degree, the nitrate of potash is decomposed, and itsoxygencombines with thecharcoalandsulphur, instantaneously forminglarge volumes of carbonic acid gasandnitrogen, which, seeking an escape, produce an explosion.
"Thus saith the Lord, Let not the wise man glory in his wisdom, neither let the mighty man glory in his might, let not the rich man glory in his riches."—Jeremiah ix.
809.Why does charcoal act as a powerful disinfectant?
Because thecarbonreadily absorbs, and combines withvarious gases, neutralising theiroffensive odours, and destroying theirunhealthy properties.
Let us now pause for a few moments to consider the importance of those two great divisions of nature, Air and Water, and to reflect upon the wisdom of some of those laws which are connected with the phenomena thereof, and which have not yet been sufficiently explained.
We have seen that the air is a thin elastic body surrounding the globe; thatit consists of certain gases essential to the life of animals, and to the growth of plants; and that it takes part in most of those chemical changes, which mark the transformations of the inorganic creation. Whether it be the burning of a piece of wood, the evaporation of a drop of water, the breathing of an animal, the respiration of a plant, or the fermentation of bodies, the air in almost every instance gives or receives—and in most of the operations in which it engages, it does both.
But there is one point of view, which we must add to those which have already been considered: the order of nature consists of generation, life, and death. Every beat of the watch signals the birth of millions of living things, and the same beat proclaims that as many living organisms have yielded up their vital spark, and that forthwith the elements of which they are composed must be dissolved, and restored to the great laboratory of nature.
The air is the vast receptacle of those organic matters which are undergoing dissolution. The body of the shipwrecked mariner, cast upon the shore of a desolate island, blackens in the sun, and the full round form gradually dwindles to skin and bone, until at last the few atoms that remain crumble into dust, and are scattered to the wind. The same process occurs, with some modifications, whether bodies are buried in the earth, or dissolve upon its surface. The leaves of forests fall and accumulate in heaps, where they ferment and dissolve, leaving only their more earthy particles behind.
The amount of matter which day by day passes from the state of the living to that of the dead, must be enormous; but from the difficulties of acquiring data, beyond the possibility of calculation. Such statistics as we have, however, enable us to form conclusions as to the mighty agencies in which the air is constantly engaged. There are on the earth 1,000,000,000 inhabitants of whom nearly 35,000,000 die every year, 91,824 every day, 3,730 every hour, and 60 every minute. Buteven the living die daily, and undergo an invisible change of substance, as we shall hereafter explain.
The bodies of those many millions are dissolved in the air, in vapours and gases which, before the dissolution of each corporeal organism is complete, begin to live again in the various forms of vegetable and animal life.
Of the number of animals living and dying upon the face of the earth, we can form no adequate estimate. Of mammals there are about 2,000 ascertained species; of birds 8,000 species; of reptiles 2,000 species; of fishes some 8,000 or 10,000 species; of molluscs some 15,000 species; of shell fish 8,000 species; of insects 70,000 species. And, including others not specified here, the total number ofspeciesof animals probably amounts to no less than 250,000,—each species consisting ofmany millionsof living creatures.
In the area of London alone, no less than 200,000 tons of fuel are annually cast into the air in the form of smoke. And if we take into account the vast operations of nature in evaporation, fermentation, and putrefactive decomposition, we may be enabled to form a conception of the mighty part which thatthin air, of which we think so little, plays in the grand alchemy of nature.
"I will praise thee; for I am fearfully and wonderfully made; marvellous are thy works; and that my soul knoweth right well."—Psalm cxxxix.
In addition, also, to the facts already communicated, respecting the sound-bearing and light-refracting properties of air, it must be remarked, that but for the atmosphere, and the general refraction of light by its particles—each atom as it were catching a fairy taper, and dancing with it before our view—the condition of vision would be widely opposite to that which exists, and totallyunsuited to our wants. The various objects upon which the illuminating rays of the sun fell, would be lighted up with an intense glare, but all around would be darkness, just as when a single ray of light is passed into a dark chamber, and directed upon a solitary object. The air, without becoming itself visible,diffuses luminous rays, in modified intensity, in every direction. If the air reflected so much light as to renderitself visible, it would appear like the glittering surface of the water reflecting the solar rays, and we should then be unable to see the various objects which surround us.
Of the importance of Water in the scheme of creation, man generally entertains an imperfect conception. It is simply supposed to afford moisture to plants, drink to animals, and to promote salubrity by its cleansing properties. Let us, however, contemplate man as he stands before us, noble in form, erect in position, full of strength, joy, ambition. How much of that noble form is composed of water? Suppose that it could all be instantaneously withdrawn—not the oxygen and the hydrogen, which might combine to form water—but the fluid that exists in his body aswater, unchanged—except by mechanical admixture with the secretions of the body—Why then that beautiful temple would collapse and become a mere shred, so thin, that it would seem but a shadow of the body as it existed before, and the beholder might doubt whether life ever inhabited a frame whose structure was so frail. It is said thatthree-fourthsby weight of the human body consist ofwater. Thus, if man weighs 120lbs., 90lbs. consist of water, and this subtracted, only 30lbs. of solid matter remain. This statement is rather under than over the fact.