The assertion is startling, but so true that it can be verified by simple experiment. A piece of lean flesh—say of beef—cut an inch thick, and placed in a slow oven, and allowed to remain until all its water was driven off in vapour, would become as thin as a wafer, and as light as a cork. With a more scientific arrangement, it would be possible to collect the water, and the weights of the condensed vapour, and of the solid residue, would together make up the weight of the beef: if the piece weighed sixteen ounces, the weight of the water would be about 14 ounces, and thesolid matterabouttwo ounces.
Water holds a similar proportion in the bodies of all animals, and of vegetables. It is evident, therefore, that it occupies a more important place in the scale of creation than is generally accorded to it by the unobservant mind. We are indebted to it for those atmospheric changes which constitute the peculiar feature of our varying climate. Rising in invisible vapours, it builds palaces of glory in the skies, and often presents to the view of man the imagery of heaven. Persons who have ascended above the altitude of the clouds, have described the scene upon looking down towards them as the most celestial that the mind can conceive. Fields of fleecy radiance, majestically rolling like a sea of gold, occupied the whole range of vision, and seemed to embellish an eternity of space. Those golden clouds that at one time are decked in the richest splendour, and occupy the upper chambers of the Court of Nature, become grave councillors when the earth grows thirsty, and the plant droops with languor. They roll their heavy brows together, as in consultation upon some grave necessity: down come the refreshing showers, the mighty tongue of thunder rocks the air, the earth is drenched, and becomes fresh with the salubrity of her toilette; obnoxious substances, with their offensive exhalations, are swept away: living things rejoice, and beautiful flowers throw their incense in thanksgiving into the air; the broad blue heavens for a time look down andsmile upon the blessed work; and then the clouds again gather in a golden train, and one by one fill the high arches of the atmosphere, until the earth once more grows thirsty, and the flower supplicates for drink.
"How mighty are his wonders! his kingdom is an everlasting kingdom, and his dominion is from generation to generation."—Daniel iv.
With reference to Light, its wonders, and the curious but imperfect theories respecting it, we have little to add, except with regard to its physiological action upon the eyes of man and of animals, which will be given in another place. But of its sister, Darkness—for it would not do now to call darkness the antagonist of light, since it will be seen that they work harmoniously for good—we have to say, that recent discoveries indicate that darkness is as necessary to the health of nature as light. Not only is it necessary to compose man and animals to sleep, to give rest to the over-wrought nerves of the industrious—but light is the quickening power of vegetation, and although plants grow by night, they grow, as man does, when stretched upon his bed—but some of their functions, which are actively excited in the presence of light, are at rest in darkness. Nor is this all: there is not an atom upon the face of the earth which is not affected by the rays of the sun, their light, their heat, their actinism. Colours change: some are bleached, others are darkened. All bodies are expanded. The hardest rock sustainsan effectfrom the sun's rays; and an unceasing sun, shining upon the hardest granite, would in time produce such a disturbance of its atomic condition, that adamant would crumble away to dust.
The going down of the sun, therefore, marks the period when not only does the bird fly to her resting-place, and man turn to his couch; but whenevery atom of a vast hemispheresubsides into a state of quietude, and when homogeneous particles of matter return to their mutual rest.
In a few succeeding lessons, we intend to point out some of the scientific truths that areillustrated in the use of toys. We think we shall be able to show to our young readers, that even the hours of play may be made the periods of delightful instruction; and that there isno"reason why" the acquirement of knowledge should not sweetly accord with the occasional pursuit of those pastimes by which health of body and vigour of mind are induced.
But before we commence the discharge of that pleasant duty, let us say a few words respecting Carbon, that important agent in the world's history. It is, doubtless, perplexing to the minds of many persons, to understand how thediamondcan bepure carbon; howcharcoalcan becarbonalittle less purethan the diamond; and howcoalandsugarcan also be carbon,less purethan the charcoal. The statement that in the diamond carbon exists in a different atomic condition, is almost as instructive to the inquiring mind, as to say, "It is so,because it is."
Diamonds are expensive things, and so difficult to experiment upon, even if they were not expensive, that the doors of inquiry seem locked. To turn diamonds into charcoal, or into carbonic acid gas, is a very costly formula of experiment. Charcoal fires, thus sustained, would soon burn a man out of his house; and soda water, impregnated with carbonic acid gas, produced from diamonds, would be a very expensive beverage. If we could only turn charcoal into diamonds, and carbonic acid gas into brilliants, that would be quite another affair. A new Eldorado would be discovered, and there would be so many experimenters that, when they all succeeded, they would find that diamonds had lost their value. However, as a fact for the encouragement of those who would like to be early in the race, we may state that the atoms ofcharcoal which are repulsed from the charcoal points, during the electric agitation which produces the electric light, acquire a hardness and a sharpness almost equal to that of the diamond—only there is still the awkward obstacle in the way, thatthey happen to be black.
"He delivereth and rescueth, and he worketh signs and wonders in heaven and in earth."—Daniel vii.
We must see, therefore, whether there is anything in nature that we can experiment upon, theoretically or practically, to give us a clearer conception of this difficult matter. There is a largedew-dropresting upon a luxuriant cabbage leaf—one of those great leaves that have flourished in defiance of the snail, and now spreads out like the gigantic frond of theVictoria Regina. That dew-drop is one of the beautiful diamonds which Nature sprinkles about on cloudless nights, as if to show the stars, in answer to their twinkling, that we have something that will glisten and twinkle too.
The dew-drop is a very good imitation of a diamond, and to the lover of God's works, quite as precious as the stone set in gold. It does not consist of carbon—it probably may have a mite of carbonic acid in its embrace—but that is not necessary to our purpose: all we want to know is,the different atomic conditionsof which bodies are susceptible, and the very dissimilar appearances they exhibit under the variations of atomic states. It doesn't glisten so much as the diamond,because it is round—if we could cut it into a number offacets, it would refract light almost as perfectly as the diamond. It is notsolid—but we can freeze it, and we shall at once exhibit two different atomic conditions, that will represent nearly enough the diamond, and the liquid carbonic acid. Then, if we evaporate the dew-drop, we shall produce a volume of vapour nearlytwo thousand times as large as the dew-drop. The steam will be white; but we have only to imagine it black, and then we get an analogy of the differences of the atomic conditions that prevail inthe diamond,carbonic acid, andcharcoal,tinder,lamp-black, or any light form of carbon. Of course we have been illustratingatomic conditions only, and not chemical composition.
There are a few other facts connected with carbon that merit consideration. Carbonic acid gas,entering the lungs, is adeadly poison; butentering the stomach, which lies close under the lungs, and is over-lapped by them, it is arefreshing beverage. Although charcoal, when burnt, gives off the most poisonous gas, it seems to be very jealous of other gaseous poisons; for if it be powdered, and set about in pans where there is a poisonous atmosphere, it will seize hold of poisonous gases, and, by absorbing, imprison them. Even in a drop of toast and water, the charred bread seizes hold of whatever impurities exist in the water; and water passed through beds of charcoal, becomes filtered, and made beautifully pure, being compelled to give up to the charcoal whatever is obnoxious. If a piece of meat that has already commenced putrifying, be sprinkled with charcoal, it will not only object to the meat putrifying any further, but it willsweeten that which has already undergone putrefaction. Although, in the form of gas, it will poison the blood, and cause speedy stupefaction and death; if it be powdered, and stitched into a piece of silk, and worn before the mouth as a respirator, it will say to all poisonous gases that come to the mouth with the air, "I have taken this post to defend the lungs, and I arrest you, on a charge of murderous intention." Such are the various facts connected with carbon; and they forcibly indicate that those who understand Nature's works, are likely to receive her best protection.
"The father of the righteous shall greatly rejoice; and he that begetteth a wise child shall have joy of him."—Proverbs xxiii.
810.Why does a humming-top make a humming noise?
Because the hollow wood of the top vibrates, and the edges of the hole in its sidesstrike against the air as it spins; the air is thereby set in vibration.
811.Why does a peg-top hum less than a humming-top?
Because,being a solid body of wood, and having nohole in its sides, its particles arenot so easily thrown into vibration; consequently it does not so readily impart vibrations to the air.
812.Why does a peg-top sometimes hum, and at other times not?
Because, if it is spun withgreat force, and its peg isstruck sharplyagainst the pavement,the wood is set in vibration, and the surface of the top, repelling the air by its rapid motion, causesvibratory waves. But if it be spun with insufficient force,the wood is not set in vibration.
Fig. 23.—HUMMING-TOP BEFORE SPINNING.Fig. 24.—HUMMING-TOP SPINNING.
Fig. 23.—HUMMING-TOP BEFORE SPINNING.
Fig. 23.—HUMMING-TOP BEFORE SPINNING.
Fig. 24.—HUMMING-TOP SPINNING.
Fig. 24.—HUMMING-TOP SPINNING.
813.Why do we see the figures painted upon the humming-top, before it spins, but not while it is spinning?
Because the rapid whirling of the top brings the images of its different parts so quickly in succession uponthe retina of the eye,that theydeface each other, andimpart an impression of coloured rings, instead of definite objects.
"Train up a child in the way he should go; and when he is old, he will not depart from it."—Proverbs xxii.
814.Why does a top stand erect when it spins, but fall when it stops?
Because the top is under the influence of, and is balanced betweenopposing forces. The rapid rotation of the top gives to all its particles a tendency tofly from the centre. If the atoms of the wood were not held together by theattraction of cohesion, they would fly away in a circle outward from the top,just as drops of water fly off from a mop, while it is being twirled. If you take a spoonful of sand, salt, or dust, and drop it upon the top, it will be scattered in a circle, just as the atoms of the top would be,if they were free to separate, but not with the same force, because the atoms of the salt, &c., not being in an active state of rotation, would only be influencedby momentary contact with the rotating body. This tendency of the particles of a rotating body to fly outward from the centre, is calledthe centrifugal force.
Centrifugal.—From two Latin words meaning receding from the centre.
The other force influencing the top isthe attraction of gravitation: the attraction which, were the top not spinning, would draw it towards the earth. The "spill" projecting from the bottom of the topstands in the line in which the top is drawn towards the earthand keeps it from obeying the law of gravitation. Therefore the rotatory motion given to the top, by the rapid unwinding of the string, and the tendency of its atoms to fly outward,balance the topupon the line in which it is drawn to the earth, and which is occupied by the spill, which prevents it falling to the ground.
815.Why does a top first reel around upon the spill, then become upright, and "sleep," and then reel again, and fall?
Fig. 25.—PEG-TOP "REELING."
Fig. 25.—PEG-TOP "REELING."
Because, in being thrown from the hand, the top is delivered a little out of the perpendicular, but the spillis rounded off at the point, and when the top is rotating rapidly, the gravitative force which attracts the top to the ground continually acting upon it,draws the weightof the top on to the extreme centre of the round point. When the rotation subsides, and the centrifugal force is weakened, then the topis no longer balanced upon the extreme point of the spill, but falls upon its sides, until the force of gravitation is exertedbeyond the line of the spill, upon the body of the top, and then it falls to the ground.
"Even a child is known by his doings, whether his work be pure, and whether it be right."—Proverbs xx.
816.Why does a top "sleep?"
Because at that period of its spinning, which is called "sleeping," thecentrifugaland thegravitative forcesacting upon the top, arenearly balanced; and the top, obeying chiefly therotatory force, appears to be in a state of comparative rest.
817.Why does the top cease to spin?
Becausethe friction of the air against its sides, and thefriction of the spill against the ground, act in opposition to therotatory force, which is a temporary impulse applied by external means—the hand of the person who spins it—and as soon as thisapplied forceis expended, the top yields to the law of gravitation, which isa permanent and ever-prevailing force.
818.Why does a marble revolve, as it is propelled along the ground?
Because, in propelling the marble,the thumb impels the upper surface forward, and the finger draws the under surface backward. This gives a tendency to the upper and lower hemispheres of the marbleto separate, which they would do, but for thecohesion of the atomsof the marble. The upper part of the marble, therefore, rolls forward,drawing after it the under part, which acquires a forward motion by the force with which it is drawn upward, and in this way the opposite portions of the marble act upon each other in the successive revolutions.
When the marble strikes upon the earth, a new influence is exerted upon it, which isthe friction of the earthupon the surface that comes in contact with it; but the upper part of the marble, being free,overcomes the friction acting upon the lower part, and thus the marble continues to progress, untilthe applied force which projected it is expended.
"Better is a poor and a wise child, than an old and foolish king who will no more be admonished."—Ecclesiastes iv.
819.Why does a striped marble appear to have a greater number of stripes when rolling, than when at rest?
Because the stripes are presented inrapid successionto the eye; and as the eye receivesfresh impressions of stripes before the previous impressions have passed away, the stripes appear multiplied.
Fig. 26.—MARBLE AT REST.Fig. 27.—MARBLE ROLLING.
Fig. 26.—MARBLE AT REST.
Fig. 26.—MARBLE AT REST.
Fig. 27.—MARBLE ROLLING.
Fig. 27.—MARBLE ROLLING.
820.Why does a marble rebound when dropped upon the pavement?
Because the force of its fall to the earthcompresses the atomsof which the marble is composed; and the atoms then exert the force ofelasticity to restore themselves to their former condition; and by the exercise of this force the marble isrepelled, orthrown upward from the pavement. Although a marble may be made of very hard stone, yet that stone may beelastic, and possess, though in a much less degree,the same kind of elasticity which causes the India-rubber ball to rebound from the earth.
821.Why does a marble, assuming it to be impelled with equal force, roll further on ice than on pavement, and further on pavement than on a pebble walk?
Because thefrictionis greater upon pavement than upon ice, and greater upon a pebble walk than upon pavement.
822.How many forces contribute to stay the progress of a rolling marble?
The friction of theair, the friction of theearth, and theattraction of gravitation, which tends to bring all bodies to a state of rest.
"He shall turn the heart of the fathers towards the children, and the heart of the children to their fathers."—Malachi iv.
823.Why do the stripes upon a marble disappear when it is spun with great velocity?
Fig. 28—MARBLE SPINNING RAPIDLY.
Fig. 28—MARBLE SPINNING RAPIDLY.
Because, as in the case of the humming-top, the different parts of the surface arebrought so rapidly in succession to the sight, that theydeface or confusethe impressions upon the retina.
824.Why are rings most perceptible at the opposite points, or poles, of the marble?
Because the point, or pole,upon which the marble spins, and that whichcorresponds to it, on the upper surface, travelless rapidlythan the central portions, which being of a larger circumference, pass through a greater amount of space, in the same period of time. The stripes at thepolesof the marble, are, therefore visible, while those at itsequatorare imperceptible. (See522.)
825.Why are soap-bubbles round?
Because they areequally pressed upon all parts of their surfaceby the atmosphere.
826.Why are bubbles elongated when being blown?
Because theunequal pressure of the current of breathby which they are being filled, alters therelative pressureupon the outer surfaces.
827.Why does the bubble close, and become a perfect sphere, when shaken from the pipe?
Because theattraction of cohesiondraws the particles of soap together, directly the bubble is set free from the bowl.
"Children's children are the crown of old men; and the glory of children are their fathers."—Proverbs xvii.
Fig. 29.—BLOWING SOAP BUBBLES.
Fig. 29.—BLOWING SOAP BUBBLES.
828.Why do bubbles, blown in the sunshine, change their colours?
Because the films of the bubbles constantly change in thickness, through the atoms from the upper part descending towards the bottom, and therefore the varying thickness of filmrefracts, in different degrees, the rays of light.
829.Why do bubbles burst?
Because the atoms that compose their filmsfall towards the earth by gravitation; the upper portion of the bubbles thenbecomes very thin, and as the denser air of the atmospherepresses towards the warm breath within the bubble, it bursts the film.
See236,237,etc.,501,etc.
830.Why do balloons ascend in air?
Because the air or gas which they contain isspecifically lighter than the atmosphere;the atmosphere, therefore, forces itself underneath the balloon, by its own tendency towards the earth, and the balloon is thereby raised upwards.A balloon is but a larger kind of bubble, made of stronger materials.
831.Why does an air-balloon become inflated when the spirit set upon the sponge is lit?
Because theheatof the flame, and theburning of the spirit, A, create a volume ofrarefied, orthin air, which inflates the balloon, and makes itspecifically lighterthan the surrounding medium.
"A wise son heareth his father's instruction."—Proverbs xiii.
832.Why do balloons sometimes burst when they ascend very high?
Because, as they get into thethinner air, which exists athigh altitudes, the gas within them expands, and the coating of the balloon is burst asunder.
Fig. 30.—AIR-BALLOON.Fig. 31.—PAPER PARACHUTE.
Fig. 30.—AIR-BALLOON.
Fig. 30.—AIR-BALLOON.
Fig. 31.—PAPER PARACHUTE.
Fig. 31.—PAPER PARACHUTE.
833.Why does the gas of balloons expand in thin air?
Because the air exerts aless amount of pressureupon the air or gas contained in the balloons.
834.Why do parachutes fall very gradually to the ground?
Because theair, coming in contact with theunder surfaceof the expanded head of the parachute resists its downward progress.
835.Why does a shuttlecock travel slowly through the air?
Because the air acts upon the feathers of the shuttlecock, in the same manner as it does upon the parachute—it strikes against their expanded surface, and resists their progress through the air.
836.Why does the shuttlecock spin in the air?
Because the surfaces of the feathers fall upon the airobliquely, or slantingly, and therefore, as the shuttlecock descends, it turns in the air.
"Come ye children, hearken unto me, I will teach you the fear of the Lord."—Psalm xxxv.
Fig. 32.—BATTLEDORE AND SHUTTLECOCK.
Fig. 32.—BATTLEDORE AND SHUTTLECOCK.
837.Why do we hear a noise when we strike the shuttlecock with the battledore?
Because thepercussionof the shuttlecock upon the parchment of the battledore causes it to vibrate, and the vibrations are imparted to the air.
838.Why is the sound a dull and short one?
Because the vibrations of the parchment arenot very rapid, therefore there islittle intensityin the vibrations of the air.
839.Why does the exercise, afforded by playing battledore and shuttlecock, make us feel warm?
Because it makes us breathemore freely, and causes theblood to flow faster; we, therefore, inhale moreoxygen, which produces heat by combining with thecarbonof ourblood.
840.Why does a kite rise in the air?
A kite rises in the air by the force of the wind, whichstrikes obliquelyupon itsunder surface. The string is attached to the "belly-band" in such a manner that it is nearer thetopthan thebottomof the band: this causes the bottom of the kite, when its surface is met by the wind, to recede in the direction of the wind:the top is accordinglythrown forward, and the kite is made tolie obliquelyupon the current of air moving against it. The kite then beingdrawn by the string in one direction, andpressed by the air in another direction, moves in a line whichdescribes a medium between the two forces acting upon it.
"Be ye therefore followers of God, as dear children; and walk in love, as Christ also hath loved us."—Ephesians v.
Fig. 33.—DIAGRAM EXPLAINING THE FLIGHT OF A KITE.
Fig. 33.—DIAGRAM EXPLAINING THE FLIGHT OF A KITE.
841.Why does the kite-string feel hot when running through the hand?
Because therapid frictionsets free thelatent heatof thestring, attracts the heat of thehandto the spot where the friction occurs, and sets free the latent heat of theair, which follows thestringthrough the hand, and is compressed by the friction.
842.Why does running with the kite cause it to rise higher?
Because itincreases the forcewith which the wind strikes upon the surface of the kite. If a person were torun with a kite at the rate of five miles an hour, through a still air, the effect would beequal to a wind flying at the rate of five miles an houragainst a kite held by astationary string.
843.Why does the flying-top rise in the air?
Because its wingsmeet the air obliquely, just as the surface of the kite does. And thetwirling of the top, causing the obliquesurfaces of its wings to strike the air, producesthe equivalent effect of a wind from the earth blowing the top upwards.
"Children obey your parents in the Lord: for this is right."
844.Why does the flying-top return to the earth when its rotations are expended?
Because thereactionproduced by its wings striking upon the air, is insufficient to counteract theattraction of gravitation.
Fig. 34.—FLYING-TOP.Fig. 35.—PEA AND PIPE.
Fig. 34.—FLYING-TOP.
Fig. 34.—FLYING-TOP.
Fig. 35.—PEA AND PIPE.
Fig. 35.—PEA AND PIPE.
845.Why does a pea, into which a pin has been stuck, dance in suspension upon a jet of air blown through a pipe?
Because the jet of air, beingslightly compressedunder theconvexform of the pea, by the weight of the pin, forms aconcave cup of air, in which the pea rests.
In the case put, it is supposed that the pin ispassed through the peauntil its head comes in contact with it. The pin is dropped into the hole of the pipe, and the breath is then applied, the pipe being held upright. The pea will rise in the air, and be suspended upon the jet, while the point of the pin will rotate around the stem of the pipe. There are other methods of fixing the pin which alter the result, and require a different explanation to that given above.
846.Why does a mouse, painted upon one side of a card, and a trap upon the other, represent to the eye amouse in a trap when the card is rapidly twirled upon a string?
Because the image of the mouse is brought to the retina of the eye before the image of the trap has passed away. The two impressions, therefore,unite upon the retina, and produce the image of a mouse in a trap.
"Honour thy father and thy mother * * That it may be well with thee, and thou mayest be long on the earth."—Ephesians vi.
Fig. 36.—CARD WITH MOUSE-TRAP.Fig. 37.—REVERSE OF CARD WITH MOUSE.
Fig. 36.—CARD WITH MOUSE-TRAP.
Fig. 36.—CARD WITH MOUSE-TRAP.
Fig. 37.—REVERSE OF CARD WITH MOUSE.
Fig. 37.—REVERSE OF CARD WITH MOUSE.
847.Why will a bow stretched out of its natural position, propel an arrow through the air?
Because its substance, beinghighly elastic, the particles thereof seek to restore themselves to their former state, as soon as the resisting power is withdrawn. Theforcederived from this elasticity, is communicated to the arrow by the string against which it is placed.
848.Why is the arrow propelled forward?
Because the elasticity of the bow,acting equally upon its two ends, to which the string is fastened, produce a line of force in adiagonal direction. It thus illustrates the law, thatwhen a body is acted upon by two forces at the same time, whose directions are inclined to each other, it will not follow either of them, but will describe a line between the two.
849.What forces tend to arrest the flight of the arrow?
Thefriction of the air, and theattraction of gravitation.
"My son, give, I pray thee, glory to the Lord God of Israel, and make confession unto him."—Joshua vii.
850.Why are feathers usually fastened to the ends of arrows?
Because thegreater frictionof air acting upon them, opposes the progress of that part of the arrow in a greater degree than it does the other portion. The effect is,to keep the point of the arrow forward, and in a straight line with its opposite extremity. If the arrow were shot the reverse way from the bow, it wouldturn round, in the course of its flight, in consequence of the friction of the air, offering greater resistance to the progress of the feathered end.
Fig. 38.—BOW AND ARROW.Fig. 39.—JEW'S HARP.
Fig. 38.—BOW AND ARROW.
Fig. 38.—BOW AND ARROW.
Fig. 39.—JEW'S HARP.
Fig. 39.—JEW'S HARP.
851.Why does a Jew's harp give musical sounds?
Because thevibrations of the metal tongueare communicated to the ear.
852.Why will not the Jew's harp produce loud sounds unless it is applied to the mouth?
Because the vibrations are not very intense, but when it is blown upon by the breath, the air is pressed upon it, and the vibrations are thereby rendered more powerful.
853.Why does the alteration of the arrangement of the mouth, affect the formation of the sounds?
Because it sends the air to the tongue of the harp ina greater or lesser degree of compression.
"Hear, ye children, the instruction of a father, and attend to know understanding."—Proverbs iv.
854.Why does the pressure applied to the handle of an air pistol propel the cork?
Because, between the cork A and the air-tight piston C, there is aclosed chamber of airb. When the handle D, which moves the piston C, is rapidly pushed in, itcompresses the airuntil it is so much condensed, that it forces out the cork A.
Fig. 40.—AIR PISTOL, OR "POP-GUN."
Fig. 40.—AIR PISTOL, OR "POP-GUN."
855.Why must the handle be drawn out, before the cork is placed in?
Because otherwise a partialvacuumwould be formed between A and C, and there would not be sufficient air to force out the cork by the return of the piston C D.
856.Why does water rise in a syringe when the handle is drawn out?
Because the pressure of the air on the water outside of the syringe, forces it into the space vacated by the drawing up of the handle, and where, otherwise, avacuumwould be formed.
Fig. 41.—SYRINGE, WITH JET OF WATER.
Fig. 41.—SYRINGE, WITH JET OF WATER.
857.Why does not the water run out when the syringe is raised?
Because the pressure of the air upon the small orifice resists the weight of the water.
858.Why does the water leak out, but not run?
Because water has a tendency always tomove to the lowest point,but as the air does not enter freely the water cannot escape. It thereforedrops, as small portions of the air enter.
"Remember now thy creator in the days of thy youth."—Ecclesiastes xi.
859.Why cannot the handle be pressed in, if the finger is applied to the orifice?
Because water is notcompressible, like air; it must therefore escape before the handle can be pressed in. Air may be forced into a much smaller compass than is natural to it; but it is impossible tocompress waterin any great degree.
Fig. 42.—"SUCKER."Fig. 43.—HOOP.
Fig. 42.—"SUCKER."
Fig. 42.—"SUCKER."
Fig. 43.—HOOP.
Fig. 43.—HOOP.
860.Why does a "sucker" raise a stone?
Because underneath the suckera vacuumis formed and the external air, pressing on all sidesagainst the vacuum, lifts the stone. The term "sucker" is founded upon the mistaken notion that the leather "sucks," or "draws" the stone. That such is not the case is evident: if, when the stone is suspended, a pin's point be passed under the leather, so as to open a small passage for the air, the stone willdrop instantly.
861.Why does a hoop roll, without falling to the ground?
Because thecentrifugal forcegives it a motion which is called thetangent to a circle—that is, a tendency in all its partsto fly off in a straight line. When a piece of clay adhering to the hoop flies off, it leaves the hoop in a line which is straight with the part ofthe surface from which it was propelled; this line isthe tangent to the circle of the hoop; and the tendency of all the parts of the hoop to fly off in this manner, counteracts the attraction of the earth, so long as the hoop is kept in motion.
"Children obey your parents in all things: for this is well-pleasing unto the Lord."—Colossians iii.
862.Why does the hoop, in falling, make several side revolutions?
Because its onward movement, not being quite expended, influences thecentre of gravity of the hoop, and changes its line of direction. The hoop is also elastic, and when its sides strike the earth, they spring up again, and continue turning until the opposing forces are overcome by theattraction of gravitation.
863.Why will a little boy balance a large boy on a see-saw?
Because the "see-saw" may be placed so that its ends are atunequal distances from the centre. This gives the little boy the power ofleverage, by which is meant the increase of power, or weight, bymechanical means.
Fig. 44.—BOYS AND "SEE-SAW."
Fig. 44.—BOYS AND "SEE-SAW."
864.Why does the little boy sink to the ground when the larger boy slightly kicks the earth?
Because the larger boy, by kicking against the earth, opposes by mechanical force theattraction of gravitationacting upon him, and he becomestemporarilyless attracted to the earth than the little boy.
"Little children, let no man deceive you: he that doeth righteousness is righteous, even as he is righteous."—1 John iii.
865.Why can the little boy, if he choose, keep the big boy up, when once he is up?
Because, as the big boy is then onan inclined planewith thefulcrum, or centre upon which the see-saw moves, the arm ofthe lever, upon which the big boy sits, isrelatively shortened, and he has thenless mechanical power. Also, a portion of the weight of the larger boy is transmitted along the leverto the arm upon which the little boy sits.