Q.Why doesmortar crumbleaway infrost?A. If the mortar was notdried in the warm weather, its moisturefreezes,expands, and thrusts the particles of the mortar away from each other; but (as soon as the frost goes) thewater condensesand leaves the mortar full of cracks and chinks.
Q.Why doesmortar crumbleaway infrost?
Q.Why doesmortar crumbleaway infrost?
A. If the mortar was notdried in the warm weather, its moisturefreezes,expands, and thrusts the particles of the mortar away from each other; but (as soon as the frost goes) thewater condensesand leaves the mortar full of cracks and chinks.
A. If the mortar was notdried in the warm weather, its moisturefreezes,expands, and thrusts the particles of the mortar away from each other; but (as soon as the frost goes) thewater condensesand leaves the mortar full of cracks and chinks.
Q.Why doesstucco peelfrom awallinfrostyweather?A. If the stucco was notdried in the warm weather, its moisturefreezes,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 doesstucco peelfrom awallinfrostyweather?
Q.Why doesstucco peelfrom awallinfrostyweather?
A. If the stucco was notdried in the warm weather, its moisturefreezes,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.
A. If the stucco was notdried in the warm weather, its moisturefreezes,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 cannotbricklayersandplastererswork infrostyweather?A. Because the bricks and plaster wouldstart from their positionas soon as thefrostcame and expanded the mortar.
Q.Why cannotbricklayersandplastererswork infrostyweather?
Q.Why cannotbricklayersandplastererswork infrostyweather?
A. Because the bricks and plaster wouldstart from their positionas soon as thefrostcame and expanded the mortar.
A. Because the bricks and plaster wouldstart from their positionas soon as thefrostcame and expanded the mortar.
Q.Why dobricklayers covertheir work withstrawin spring and autumn?A. Because straw is a non-conductor, and prevents the mortar of their new work fromfreezingduring the cold nights of spring and autumn.
Q.Why dobricklayers covertheir work withstrawin spring and autumn?
Q.Why dobricklayers covertheir work withstrawin spring and autumn?
A. Because straw is a non-conductor, and prevents the mortar of their new work fromfreezingduring the cold nights of spring and autumn.
A. Because straw is a non-conductor, and prevents the mortar of their new work fromfreezingduring the cold nights of spring and autumn.
Q.Why arewater-pipesoften covered withstall-litterin winter time?A. Because straw (being a non-conductor) prevents thewater of the pipes from freezing, and thepipes from bursting.
Q.Why arewater-pipesoften covered withstall-litterin winter time?
Q.Why arewater-pipesoften covered withstall-litterin winter time?
A. Because straw (being a non-conductor) prevents thewater of the pipes from freezing, and thepipes from bursting.
A. Because straw (being a non-conductor) prevents thewater of the pipes from freezing, and thepipes from bursting.
Q.Why are delicatetreescovered withstrawin WINTER?A. Because straw (being a non-conductor) prevents thesap of the treefrom being frozen.
Q.Why are delicatetreescovered withstrawin WINTER?
Q.Why are delicatetreescovered withstrawin WINTER?
A. Because straw (being a non-conductor) prevents thesap of the treefrom being frozen.
A. Because straw (being a non-conductor) prevents thesap of the treefrom being frozen.
Q.Canwaterbefrozenin any waybesidesby frosty weather?A. Yes; in very many ways. For example—a bottle of water wrapped incotton, and frequentlywetted with ether, will soon freeze.
Q.Canwaterbefrozenin any waybesidesby frosty weather?
Q.Canwaterbefrozenin any waybesidesby frosty weather?
A. Yes; in very many ways. For example—a bottle of water wrapped incotton, and frequentlywetted with ether, will soon freeze.
A. Yes; in very many ways. For example—a bottle of water wrapped incotton, and frequentlywetted with ether, will soon freeze.
Q.Why wouldwater freezeif the bottle were kept constantly wetted withether?A. Becauseevaporationwould carry off the heat of the water, and reduce it tofreezing point.
Q.Why wouldwater freezeif the bottle were kept constantly wetted withether?
Q.Why wouldwater freezeif the bottle were kept constantly wetted withether?
A. Becauseevaporationwould carry off the heat of the water, and reduce it tofreezing point.
A. Becauseevaporationwould carry off the heat of the water, and reduce it tofreezing point.
Q.Why doesetherfreeze under thereceiverof anair-pump, when the air is exhausted?A. Becauseevaporationis very greatly increased by thediminution of atmospheric pressure; and the ether freezes by evaporation.FREEZING MIXTURES.1. If nitre be dissolved in water, the heat of the liquid will be reduced 16 degrees.2. If 5 oz. of nitre, and 5 of sal-ammoniac (both finely powdered) be dissolved in 19 oz. of water, the heat of the liquid will be reduced 40 degrees.3. If 3 lbs. of snow be added to 1 lb. of salt, the mixture will fall to 0° (or 32 degrees below freezing point).The two following are the coldest mixtures yet known:—1. Mix 3 lbs. of muriate of lime with 1 lb. of snow.2. Mix 5 lbs. of diluted sulphuric acid with 4 lbs. of snow.
Q.Why doesetherfreeze under thereceiverof anair-pump, when the air is exhausted?
Q.Why doesetherfreeze under thereceiverof anair-pump, when the air is exhausted?
A. Becauseevaporationis very greatly increased by thediminution of atmospheric pressure; and the ether freezes by evaporation.FREEZING MIXTURES.1. If nitre be dissolved in water, the heat of the liquid will be reduced 16 degrees.2. If 5 oz. of nitre, and 5 of sal-ammoniac (both finely powdered) be dissolved in 19 oz. of water, the heat of the liquid will be reduced 40 degrees.3. If 3 lbs. of snow be added to 1 lb. of salt, the mixture will fall to 0° (or 32 degrees below freezing point).The two following are the coldest mixtures yet known:—1. Mix 3 lbs. of muriate of lime with 1 lb. of snow.2. Mix 5 lbs. of diluted sulphuric acid with 4 lbs. of snow.
A. Becauseevaporationis very greatly increased by thediminution of atmospheric pressure; and the ether freezes by evaporation.
FREEZING MIXTURES.
1. If nitre be dissolved in water, the heat of the liquid will be reduced 16 degrees.
2. If 5 oz. of nitre, and 5 of sal-ammoniac (both finely powdered) be dissolved in 19 oz. of water, the heat of the liquid will be reduced 40 degrees.
3. If 3 lbs. of snow be added to 1 lb. of salt, the mixture will fall to 0° (or 32 degrees below freezing point).
The two following are the coldest mixtures yet known:—
1. Mix 3 lbs. of muriate of lime with 1 lb. of snow.
2. Mix 5 lbs. of diluted sulphuric acid with 4 lbs. of snow.
Q.Why is it more easy toswimin theseathan in ariver?A. Because thespecific gravityof salt water isgreater than that of fresh, and therefore itbuoysup the swimmer better.
Q.Why is it more easy toswimin theseathan in ariver?
Q.Why is it more easy toswimin theseathan in ariver?
A. Because thespecific gravityof salt water isgreater than that of fresh, and therefore itbuoysup the swimmer better.
A. Because thespecific gravityof salt water isgreater than that of fresh, and therefore itbuoysup the swimmer better.
Q.How do cooks ascertain if theirbrinebesalt enoughfor pickling?A. They put anegg into their brine. If the eggsinksthe brine isnot strong enough, if the eggfloatsitis.
Q.How do cooks ascertain if theirbrinebesalt enoughfor pickling?
Q.How do cooks ascertain if theirbrinebesalt enoughfor pickling?
A. They put anegg into their brine. If the eggsinksthe brine isnot strong enough, if the eggfloatsitis.
A. They put anegg into their brine. If the eggsinksthe brine isnot strong enough, if the eggfloatsitis.
Q.Why will theegg sinkif the brine benot strongenough for pickling?A. As an egg isheavier than water, it willsinkif immersed therein; but if as muchsaltbe added as the water can dissolve, the egg willfloat.
Q.Why will theegg sinkif the brine benot strongenough for pickling?
Q.Why will theegg sinkif the brine benot strongenough for pickling?
A. As an egg isheavier than water, it willsinkif immersed therein; but if as muchsaltbe added as the water can dissolve, the egg willfloat.
A. As an egg isheavier than water, it willsinkif immersed therein; but if as muchsaltbe added as the water can dissolve, the egg willfloat.
Q.Why will theegg floatin strongbrine?A. Because the specific gravity ofsalt and wateris greater than that of wateronly.
Q.Why will theegg floatin strongbrine?
Q.Why will theegg floatin strongbrine?
A. Because the specific gravity ofsalt and wateris greater than that of wateronly.
A. Because the specific gravity ofsalt and wateris greater than that of wateronly.
Q.Why do personssinkin water when they areunskilful swimmers?A. 1st—Because (in their floundering about) theytake in waterat their nose and mouth, which makes themheavier:2ndly—Fearcontracts the body; andas the body is compressed by fear into a smaller compass, it becomesheavier: and3rdly—The water and feartake away the breath; and when the breath is taken from the body, itsbulk is reduced, and it becomesheavier.
Q.Why do personssinkin water when they areunskilful swimmers?
Q.Why do personssinkin water when they areunskilful swimmers?
A. 1st—Because (in their floundering about) theytake in waterat their nose and mouth, which makes themheavier:2ndly—Fearcontracts the body; andas the body is compressed by fear into a smaller compass, it becomesheavier: and3rdly—The water and feartake away the breath; and when the breath is taken from the body, itsbulk is reduced, and it becomesheavier.
A. 1st—Because (in their floundering about) theytake in waterat their nose and mouth, which makes themheavier:
2ndly—Fearcontracts the body; andas the body is compressed by fear into a smaller compass, it becomesheavier: and
3rdly—The water and feartake away the breath; and when the breath is taken from the body, itsbulk is reduced, and it becomesheavier.
Q.Why canquadrupedsswimmore easilythanman?A. 1st—Because thetrunkof a quadruped islighter than water, and this is the greatest part of them:2ndly—Thepositionof a beast in water is anaturalone.
Q.Why canquadrupedsswimmore easilythanman?
Q.Why canquadrupedsswimmore easilythanman?
A. 1st—Because thetrunkof a quadruped islighter than water, and this is the greatest part of them:2ndly—Thepositionof a beast in water is anaturalone.
A. 1st—Because thetrunkof a quadruped islighter than water, and this is the greatest part of them:
2ndly—Thepositionof a beast in water is anaturalone.
Q.Why is itmore difficultfor amanto swim than for abeast?A. Because thehead and limbsof a man (like those of a beast) areheavierthan water, and these compose more thanhalf his body:2ndly—Thepositionof a man in water isunnaturalto him.
Q.Why is itmore difficultfor amanto swim than for abeast?
Q.Why is itmore difficultfor amanto swim than for abeast?
A. Because thehead and limbsof a man (like those of a beast) areheavierthan water, and these compose more thanhalf his body:2ndly—Thepositionof a man in water isunnaturalto him.
A. Because thehead and limbsof a man (like those of a beast) areheavierthan water, and these compose more thanhalf his body:
2ndly—Thepositionof a man in water isunnaturalto him.
Q.Why canfatmenswimmoreeasilythansparemen?A.Fat is lighter than water; and thefattera man is, the morebuoyantwill he be.
Q.Why canfatmenswimmoreeasilythansparemen?
Q.Why canfatmenswimmoreeasilythansparemen?
A.Fat is lighter than water; and thefattera man is, the morebuoyantwill he be.
A.Fat is lighter than water; and thefattera man is, the morebuoyantwill he be.
Q.How arefishesable toascendto thesurfaceof water?A. Fishes have anair-bladdernear their abdomen: when this bladder isfilled with air, the fish increases in size; and (being lighter) ascends through the water to its surface.
Q.How arefishesable toascendto thesurfaceof water?
Q.How arefishesable toascendto thesurfaceof water?
A. Fishes have anair-bladdernear their abdomen: when this bladder isfilled with air, the fish increases in size; and (being lighter) ascends through the water to its surface.
A. Fishes have anair-bladdernear their abdomen: when this bladder isfilled with air, the fish increases in size; and (being lighter) ascends through the water to its surface.
Q.How are fishes able todivein a minute to thebottomof a stream?A. Theyexpel the airfrom their air-bladder; in consequence of which, theirsize is diminished, and they sink instantly.
Q.How are fishes able todivein a minute to thebottomof a stream?
Q.How are fishes able todivein a minute to thebottomof a stream?
A. Theyexpel the airfrom their air-bladder; in consequence of which, theirsize is diminished, and they sink instantly.
A. Theyexpel the airfrom their air-bladder; in consequence of which, theirsize is diminished, and they sink instantly.
Q.What islight?A. Rapid undulations of a fluid called ether, striking on the optic nerve of the eye. (See p.46.)Theheatof fire or of the sun sets the atoms ofmatterin motion; and these atoms, striking against the fluidether, cause it to undulate.
Q.What islight?
Q.What islight?
A. Rapid undulations of a fluid called ether, striking on the optic nerve of the eye. (See p.46.)Theheatof fire or of the sun sets the atoms ofmatterin motion; and these atoms, striking against the fluidether, cause it to undulate.
A. Rapid undulations of a fluid called ether, striking on the optic nerve of the eye. (See p.46.)
Theheatof fire or of the sun sets the atoms ofmatterin motion; and these atoms, striking against the fluidether, cause it to undulate.
Q.Howfastdoeslight travel?A. Light travels so fast, that it would go eight times round the earth, while a person counts “one.”
Q.Howfastdoeslight travel?
Q.Howfastdoeslight travel?
A. Light travels so fast, that it would go eight times round the earth, while a person counts “one.”
A. Light travels so fast, that it would go eight times round the earth, while a person counts “one.”
Q.Doesalllight 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.Doesalllight travel equally fast?
Q.Doesalllight travel equally fast?
A. Yes; the light of the sun, or the light of a candle, or the light from houses, trees, and fields.
A. Yes; the light of the sun, or the light of a candle, or the light from houses, trees, and fields.
Q.Where does thelightofhouses,trees, andfieldscome from?A. The light of thesun(or of some lamp or candle) isreflected from their surfaces.
Q.Where does thelightofhouses,trees, andfieldscome from?
Q.Where does thelightofhouses,trees, andfieldscome from?
A. The light of thesun(or of some lamp or candle) isreflected from their surfaces.
A. The light of thesun(or of some lamp or candle) isreflected from their surfaces.
Q.Why aresomesurfacesbrilliantlike glass and steel, andothers dulllike lead?A. Those surfaces whichreflect the most light, are the mostbrilliant; and those whichabsorblight aredull.
Q.Why aresomesurfacesbrilliantlike glass and steel, andothers dulllike lead?
Q.Why aresomesurfacesbrilliantlike glass and steel, andothers dulllike lead?
A. Those surfaces whichreflect the most light, are the mostbrilliant; and those whichabsorblight aredull.
A. Those surfaces whichreflect the most light, are the mostbrilliant; and those whichabsorblight aredull.
Q.What is meant byreflecting light?A. Throwing the rays of lightback again, from the surface on which they light.
Q.What is meant byreflecting light?
Q.What is meant byreflecting light?
A. Throwing the rays of lightback again, from the surface on which they light.
A. Throwing the rays of lightback again, from the surface on which they light.
Q.What is meant byabsorbing light?A. Letting the rays of lightsink below the surfacewhich they touch, so as not to be seen.
Q.What is meant byabsorbing light?
Q.What is meant byabsorbing light?
A. Letting the rays of lightsink below the surfacewhich they touch, so as not to be seen.
A. Letting the rays of lightsink below the surfacewhich they touch, so as not to be seen.
Q.Why can athousandpersonsseethesame objectat the same time?A. Because it throws off from its surfacean infinite number of rays in all directions; and one person seesoneportion of these rays, and another personanother.
Q.Why can athousandpersonsseethesame objectat the same time?
Q.Why can athousandpersonsseethesame objectat the same time?
A. Because it throws off from its surfacean infinite number of rays in all directions; and one person seesoneportion of these rays, and another personanother.
A. Because it throws off from its surfacean infinite number of rays in all directions; and one person seesoneportion of these rays, and another personanother.
Q.Why is theeye painedby asuddenlight?A. Because the pupil of the eye isburdened with rays, before it has had time to contract.
Q.Why is theeye painedby asuddenlight?
Q.Why is theeye painedby asuddenlight?
A. Because the pupil of the eye isburdened with rays, before it has had time to contract.
A. Because the pupil of the eye isburdened with rays, before it has had time to contract.
Q.Why does it give uspain, if acandlebe brought suddenly towards ourbedat night time?A. In the darkthe pupils of the eyes dilatevery much, in order toadmit more rays. When a candle is brought before them, the enlarged pupil isoverladen with rays, and feels pained.
Q.Why does it give uspain, if acandlebe brought suddenly towards ourbedat night time?
Q.Why does it give uspain, if acandlebe brought suddenly towards ourbedat night time?
A. In the darkthe pupils of the eyes dilatevery much, in order toadmit more rays. When a candle is brought before them, the enlarged pupil isoverladen with rays, and feels pained.
A. In the darkthe pupils of the eyes dilatevery much, in order toadmit more rays. When a candle is brought before them, the enlarged pupil isoverladen with rays, and feels pained.
Q.Whycanwebearthe candle-light after a few moments?A, Because the pupilcontracts againalmost instantly, and adjusts itself to the quantity of light which falls upon it.
Q.Whycanwebearthe candle-light after a few moments?
Q.Whycanwebearthe candle-light after a few moments?
A, Because the pupilcontracts againalmost instantly, and adjusts itself to the quantity of light which falls upon it.
A, Because the pupilcontracts againalmost instantly, and adjusts itself to the quantity of light which falls upon it.
Q.Why can wesee nothing, when we leave awell-lightedroom, and go into thedark roador street?A. Because the pupil (whichcontractedin the bright room) does notdilate instantaneously; and the contracted pupil is not able tocollect rays enough(from the dark road or street) to enable us to see before us.
Q.Why can wesee nothing, when we leave awell-lightedroom, and go into thedark roador street?
Q.Why can wesee nothing, when we leave awell-lightedroom, and go into thedark roador street?
A. Because the pupil (whichcontractedin the bright room) does notdilate instantaneously; and the contracted pupil is not able tocollect rays enough(from the dark road or street) to enable us to see before us.
A. Because the pupil (whichcontractedin the bright room) does notdilate instantaneously; and the contracted pupil is not able tocollect rays enough(from the dark road or street) to enable us to see before us.
Q.Why do wesee better, when we getusedto the dark?A. Because the pupildilatesagain, and is able to gather together more rays; in consequence of which, we see more distinctly.
Q.Why do wesee better, when we getusedto the dark?
Q.Why do wesee better, when we getusedto the dark?
A. Because the pupildilatesagain, and is able to gather together more rays; in consequence of which, we see more distinctly.
A. Because the pupildilatesagain, and is able to gather together more rays; in consequence of which, we see more distinctly.
Q.If we look at thesunfor a few moments, why do allotherthings appeardark?A. Because the pupil of the eye (which wasvery much contractedby looking at the sun) istoo smallto collect sufficient rays fromother objects, to enable us to distinguish their colours. (See“accidental colours.”)
Q.If we look at thesunfor a few moments, why do allotherthings appeardark?
Q.If we look at thesunfor a few moments, why do allotherthings appeardark?
A. Because the pupil of the eye (which wasvery much contractedby looking at the sun) istoo smallto collect sufficient rays fromother objects, to enable us to distinguish their colours. (See“accidental colours.”)
A. Because the pupil of the eye (which wasvery much contractedby looking at the sun) istoo smallto collect sufficient rays fromother objects, to enable us to distinguish their colours. (See“accidental colours.”)
Q.If we watch a brightfirefor a few moments, why does theroomseemdark?A. Because the pupil of the eye (which was very muchcontractedby looking at the fire) istoo smallto collect sufficient rays from the objects around, to enable us to distinguish their colours.
Q.If we watch a brightfirefor a few moments, why does theroomseemdark?
Q.If we watch a brightfirefor a few moments, why does theroomseemdark?
A. Because the pupil of the eye (which was very muchcontractedby looking at the fire) istoo smallto collect sufficient rays from the objects around, to enable us to distinguish their colours.
A. Because the pupil of the eye (which was very muchcontractedby looking at the fire) istoo smallto collect sufficient rays from the objects around, to enable us to distinguish their colours.
Q.Why can we see theproper colourof every object again, after a few minutes?A. Because the pupildilatesagain, and accommodates itself to the light around.
Q.Why can we see theproper colourof every object again, after a few minutes?
Q.Why can we see theproper colourof every object again, after a few minutes?
A. Because the pupildilatesagain, and accommodates itself to the light around.
A. Because the pupildilatesagain, and accommodates itself to the light around.
Q.Why cantigers,cats, andowlssee in thedark?A. Because they have the power ofenlarging the pupil of their eyes, so as to collect several scattered rays of light; in consequence of which, they cansee distinctlywhen it is not light enough for us to seeany thing at all.
Q.Why cantigers,cats, andowlssee in thedark?
Q.Why cantigers,cats, andowlssee in thedark?
A. Because they have the power ofenlarging the pupil of their eyes, so as to collect several scattered rays of light; in consequence of which, they cansee distinctlywhen it is not light enough for us to seeany thing at all.
A. Because they have the power ofenlarging the pupil of their eyes, so as to collect several scattered rays of light; in consequence of which, they cansee distinctlywhen it is not light enough for us to seeany thing at all.
Q.Why docatsandowls sleepalmost allday?A. As the pupil of their eyes isvery broad, daylightfatiguesthem; so they close their eyes for relief.
Q.Why docatsandowls sleepalmost allday?
Q.Why docatsandowls sleepalmost allday?
A. As the pupil of their eyes isvery broad, daylightfatiguesthem; so they close their eyes for relief.
A. As the pupil of their eyes isvery broad, daylightfatiguesthem; so they close their eyes for relief.
Q.Why docatskeepwinking, when they sit before afire?A. As the pupil of their eyes isvery broad, the light of the firepainsthem; and they keep shutting their eyes to relieve the sensation of too much light.
Q.Why docatskeepwinking, when they sit before afire?
Q.Why docatskeepwinking, when they sit before afire?
A. As the pupil of their eyes isvery broad, the light of the firepainsthem; and they keep shutting their eyes to relieve the sensation of too much light.
A. As the pupil of their eyes isvery broad, the light of the firepainsthem; and they keep shutting their eyes to relieve the sensation of too much light.
Q.Why dotigers,cats,owls, &c.prowlbynightfor prey?A. As these animals cannot see distinctly instrong daylight, theysleepduring theday: and as they can see clearly in thedark, they prowl then for prey.
Q.Why dotigers,cats,owls, &c.prowlbynightfor prey?
Q.Why dotigers,cats,owls, &c.prowlbynightfor prey?
A. As these animals cannot see distinctly instrong daylight, theysleepduring theday: and as they can see clearly in thedark, they prowl then for prey.
A. As these animals cannot see distinctly instrong daylight, theysleepduring theday: and as they can see clearly in thedark, they prowl then for prey.
Q.Why doglow-wormsglisten bynightonly?A. Because the light of day isso much stronger, that iteclipsesthe feeble light of a glow-worm; in consequence of which, glow-worms areinvisible by day.
Q.Why doglow-wormsglisten bynightonly?
Q.Why doglow-wormsglisten bynightonly?
A. Because the light of day isso much stronger, that iteclipsesthe feeble light of a glow-worm; in consequence of which, glow-worms areinvisible by day.
A. Because the light of day isso much stronger, that iteclipsesthe feeble light of a glow-worm; in consequence of which, glow-worms areinvisible by day.
Q.Why can we not see thestarsin theday-time?A. Because the light of day is so powerful, that iteclipses the feeble light of the stars: in consequence of which, they are invisible by day.
Q.Why can we not see thestarsin theday-time?
Q.Why can we not see thestarsin theday-time?
A. Because the light of day is so powerful, that iteclipses the feeble light of the stars: in consequence of which, they are invisible by day.
A. Because the light of day is so powerful, that iteclipses the feeble light of the stars: in consequence of which, they are invisible by day.
Q.Why can we see thestarseven atmid-day, from the bottom of a deepwell?A. As the rays of the sun never comedirectly over a well, but the rays of thestarsdo; therefore the light from those stars (in such a situation) is more clear than the light of thesun.
Q.Why can we see thestarseven atmid-day, from the bottom of a deepwell?
Q.Why can we see thestarseven atmid-day, from the bottom of a deepwell?
A. As the rays of the sun never comedirectly over a well, but the rays of thestarsdo; therefore the light from those stars (in such a situation) is more clear than the light of thesun.
A. As the rays of the sun never comedirectly over a well, but the rays of thestarsdo; therefore the light from those stars (in such a situation) is more clear than the light of thesun.
Q.What is theuseoftwo eyes, since they present only one image of any object?A. The use of two eyes is toincrease the light, or take inmore rays of lightfrom the object looked at, in order that it may appearmore distinct.
Q.What is theuseoftwo eyes, since they present only one image of any object?
Q.What is theuseoftwo eyes, since they present only one image of any object?
A. The use of two eyes is toincrease the light, or take inmore rays of lightfrom the object looked at, in order that it may appearmore distinct.
A. The use of two eyes is toincrease the light, or take inmore rays of lightfrom the object looked at, in order that it may appearmore distinct.
Q.Why do wenotsee thingsdouble, withtwo eyes?A. 1st—Because theaxis of both eyes is turned to one object; and, therefore, thesame impressionis made on the ret´ina ofeach eye.2ndly—The nerves (which receive the impression) haveone point of union, before they reach the brain.
Q.Why do wenotsee thingsdouble, withtwo eyes?
Q.Why do wenotsee thingsdouble, withtwo eyes?
A. 1st—Because theaxis of both eyes is turned to one object; and, therefore, thesame impressionis made on the ret´ina ofeach eye.2ndly—The nerves (which receive the impression) haveone point of union, before they reach the brain.
A. 1st—Because theaxis of both eyes is turned to one object; and, therefore, thesame impressionis made on the ret´ina ofeach eye.
2ndly—The nerves (which receive the impression) haveone point of union, before they reach the brain.
Q.Why do wesee ourselvesin aglass?A. The rays of light from our facestrike against the surface of the glass, and (instead of being absorbed)are reflected, or sent back again to our eye.
Q.Why do wesee ourselvesin aglass?
Q.Why do wesee ourselvesin aglass?
A. The rays of light from our facestrike against the surface of the glass, and (instead of being absorbed)are reflected, or sent back again to our eye.
A. The rays of light from our facestrike 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 lightreflectedby amirror?A. Because they cannotpass through the impenetrable metalwith which the back of the glass is covered; so theyrebound back, just as amarblewould do if it struck against a wall.
Q.Why are the rays of lightreflectedby amirror?
Q.Why are the rays of lightreflectedby amirror?
A. Because they cannotpass through the impenetrable metalwith which the back of the glass is covered; so theyrebound back, just as amarblewould do if it struck against a wall.
A. Because they cannotpass through the impenetrable metalwith which the back of the glass is covered; so theyrebound back, just as amarblewould do if it struck against a wall.
Q.When a marble is rolled towards a wall, what is that paththrough which it runscalled?A. The line of theangle of incidence.
Q.When a marble is rolled towards a wall, what is that paththrough which it runscalled?
Q.When a marble is rolled towards a wall, what is that paththrough which it runscalled?
A. The line of theangle of incidence.
A. The line of theangle of incidence.
Q.When a marblereboundsback again, what is the path itthendescribes called?A. The line of theangle of reflection.
Q.When a marblereboundsback again, what is the path itthendescribes called?
Q.When a marblereboundsback again, what is the path itthendescribes called?
A. The line of theangle of reflection.
A. The line of theangle of reflection.
Q.When the light of our face goestotheglass, what is the path through which it goescalled?A. The line of theangle of incidence.
Q.When the light of our face goestotheglass, what is the path through which it goescalled?
Q.When the light of our face goestotheglass, what is the path through which it goescalled?
A. The line of theangle of incidence.
A. The line of theangle of incidence.
Q.When the light of our face is reflectedbackagain from the mirror, what is thisreturningpath called?A. The line of theangle of reflection.
Q.When the light of our face is reflectedbackagain from the mirror, what is thisreturningpath called?
Q.When the light of our face is reflectedbackagain from the mirror, what is thisreturningpath called?
A. The line of theangle of reflection.
A. The line of theangle of reflection.
Q.Why does our reflection in a mirror seem toapproachus as we walktowardsit, and toretire fromus asweretire?A. Because the lineof the angle of incidenceis alwaysequalto theline and angle of reflection.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 does our reflection in a mirror seem toapproachus as we walktowardsit, and toretire fromus asweretire?
Q.Why does our reflection in a mirror seem toapproachus as we walktowardsit, and toretire fromus asweretire?
A. Because the lineof the angle of incidenceis alwaysequalto theline and angle of reflection.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.
A. Because the lineof the angle of incidenceis alwaysequalto theline and angle of reflection.
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.
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 hiswhole personreflected in alittle mirrornot 6 inches in length?A. Because theline of the angle of incidenceis always equal to theline 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 can a man see hiswhole personreflected in alittle mirrornot 6 inches in length?
Q.Why can a man see hiswhole personreflected in alittle mirrornot 6 inches in length?
A. Because theline of the angle of incidenceis always equal to theline 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.
A. Because theline of the angle of incidenceis always equal to theline 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 ashadowinwateralways appeartopsy-turvy?A. Because theline of the angle of incidenceis always equal to theline and angle of reflection.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.Why does ashadowinwateralways appeartopsy-turvy?
Q.Why does ashadowinwateralways appeartopsy-turvy?
A. Because theline of the angle of incidenceis always equal to theline and angle of reflection.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.
A. Because theline of the angle of incidenceis always equal to theline and angle of reflection.
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.
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 ourshadowinwater, why do we seem tostandon ourhead?A. Because theline of the angle of incidenceis always equal to theline 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.When we see ourshadowinwater, why do we seem tostandon ourhead?
Q.When we see ourshadowinwater, why do we seem tostandon ourhead?
A. Because theline of the angle of incidenceis always equal to theline 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.)
A. Because theline of the angle of incidenceis always equal to theline 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 dowindowsseem toblazeatsun-riseandsun-set?A. Because glass is a goodreflector of light; and the rays of the sun (striking against the window glass)are reflected, or thrown back.
Q.Why dowindowsseem toblazeatsun-riseandsun-set?
Q.Why dowindowsseem toblazeatsun-riseandsun-set?
A. Because glass is a goodreflector of light; and the rays of the sun (striking against the window glass)are reflected, or thrown back.
A. Because glass is a goodreflector of light; and the rays of the sun (striking against the window glass)are reflected, or thrown back.
Q.Why donotwindows reflect thenoon-dayrays also?A. They do, but thereflection is not seen.
Q.Why donotwindows reflect thenoon-dayrays also?
Q.Why donotwindows reflect thenoon-dayrays also?
A. They do, but thereflection is not seen.
A. They do, but thereflection is not seen.
Q.Why is the reflection of therisingandsettingsun seen in the window, andnotthat of thenoon-daysun?A. As the angle ofincidencealwaysequals theangle of reflection, therefore the rays of the noon-day sun enter the glasstoo perpendicularlyfor their reflection to be seen.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 is the reflection of therisingandsettingsun seen in the window, andnotthat of thenoon-daysun?
Q.Why is the reflection of therisingandsettingsun seen in the window, andnotthat of thenoon-daysun?
A. As the angle ofincidencealwaysequals theangle of reflection, therefore the rays of the noon-day sun enter the glasstoo perpendicularlyfor their reflection to be seen.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).
A. As the angle ofincidencealwaysequals theangle of reflection, therefore the rays of the noon-day sun enter the glasstoo perpendicularlyfor their reflection to be seen.
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).
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 thereflectionof thesunin awell, during the day-time?A. Because the rays of thesunfall so obliquely, that theynever reach the surface of the waterat all, but strike against the brick sides.Let BDEC be the well, and DE the water.The ray AB strikes against the brick-workinsidethe well; andThe ray AC strikes against the brick-workoutsidethe well.None will ever touch the water DE.
Q.Why can we not see thereflectionof thesunin awell, during the day-time?
Q.Why can we not see thereflectionof thesunin awell, during the day-time?
A. Because the rays of thesunfall so obliquely, that theynever reach the surface of the waterat all, but strike against the brick sides.Let BDEC be the well, and DE the water.The ray AB strikes against the brick-workinsidethe well; andThe ray AC strikes against the brick-workoutsidethe well.None will ever touch the water DE.
A. Because the rays of thesunfall so obliquely, that theynever reach the surface of the waterat all, but strike against the brick sides.
Let BDEC be the well, and DE the water.The ray AB strikes against the brick-workinsidethe well; andThe ray AC strikes against the brick-workoutsidethe well.None will ever touch the water DE.
Let BDEC be the well, and DE the water.The ray AB strikes against the brick-workinsidethe well; andThe ray AC strikes against the brick-workoutsidethe well.None will ever touch the water DE.
Q.Why do we see themoonreflected in awellveryoften?A. As the rays of themoonare not soobliqueas those of the sun, they will often reach the water.(See next figure.)
Q.Why do we see themoonreflected in awellveryoften?
Q.Why do we see themoonreflected in awellveryoften?
A. As the rays of themoonare not soobliqueas those of the sun, they will often reach the water.(See next figure.)
A. As the rays of themoonare not soobliqueas those of the sun, they will often reach the water.(See next figure.)
Q.Why are thestars reflectedin awell, although thesunisnot?A. As the rays of thestarsare notsoobliqueas those of the sun, they will often reach the water.Here the moon's rays AB, AC, both strike the water DE, and are reflected by it.
Q.Why are thestars reflectedin awell, although thesunisnot?
Q.Why are thestars reflectedin awell, although thesunisnot?
A. As the rays of thestarsare notsoobliqueas those of the sun, they will often reach the water.Here the moon's rays AB, AC, both strike the water DE, and are reflected by it.
A. As the rays of thestarsare notsoobliqueas those of the sun, they will often reach the water.
Here the moon's rays AB, AC, both strike the water DE, and are reflected by it.
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 onlyonespot, and all therestof the water seemsdark,—Whyis this?A. Because the rays (which fall at various degrees of obliquity on the water) arereflected at similar angles; but as only those whichmeet the eye of the spectatorare visible, all the sea will appear dark butthat one spot.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.In a sheet of water at noon, the sun appears to shine upon onlyonespot, and all therestof the water seemsdark,—Whyis this?
Q.In a sheet of water at noon, the sun appears to shine upon onlyonespot, and all therestof the water seemsdark,—Whyis this?
A. Because the rays (which fall at various degrees of obliquity on the water) arereflected at similar angles; but as only those whichmeet the eye of the spectatorare visible, all the sea will appear dark butthat one spot.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.
A. Because the rays (which fall at various degrees of obliquity on the water) arereflected at similar angles; but as only those whichmeet the eye of the spectatorare visible, all the sea will appear dark butthat one spot.
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.
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 themoonseems to be reflected from onlyone spotof a lake of water, while all therestseemsdark,—Whyis this?A. Because the rays (which fall at various degrees of obliquity on the lake)are reflected at similar angles; but as only those whichenter the eye of the spectatorwill be visible, all the water will appear darkbut that one spot. (See last figure.)
Q.At night themoonseems to be reflected from onlyone spotof a lake of water, while all therestseemsdark,—Whyis this?
Q.At night themoonseems to be reflected from onlyone spotof a lake of water, while all therestseemsdark,—Whyis this?
A. Because the rays (which fall at various degrees of obliquity on the lake)are reflected at similar angles; but as only those whichenter the eye of the spectatorwill be visible, all the water will appear darkbut that one spot. (See last figure.)
A. Because the rays (which fall at various degrees of obliquity on the lake)are reflected at similar angles; but as only those whichenter the eye of the spectatorwill be visible, all the water will appear darkbut that one spot. (See last figure.)
Q.Why aremore starsvisible from amountain, than from aplain?A. As the airabsorbs and diminishes light, thehigher we ascend, theless light will be absorbed.
Q.Why aremore starsvisible from amountain, than from aplain?
Q.Why aremore starsvisible from amountain, than from aplain?
A. As the airabsorbs and diminishes light, thehigher we ascend, theless light will be absorbed.
A. As the airabsorbs and diminishes light, thehigher we ascend, theless light will be absorbed.
Q.Why does thesunseemlargerat hisriseandset, than it does atnoon?A. Because the earth is surrounded by air, which acts like amagnifying glass; and when the sun is near the horizon (as its rayspass through more of this air), it is more magnified.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 throughmore airthan the rays of the sun at S, and the sun is more magnified.
Q.Why does thesunseemlargerat hisriseandset, than it does atnoon?
Q.Why does thesunseemlargerat hisriseandset, than it does atnoon?
A. Because the earth is surrounded by air, which acts like amagnifying glass; and when the sun is near the horizon (as its rayspass through more of this air), it is more magnified.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 throughmore airthan the rays of the sun at S, and the sun is more magnified.
A. Because the earth is surrounded by air, which acts like amagnifying glass; and when the sun is near the horizon (as its rayspass through more of this air), it is more magnified.
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 throughmore airthan the rays of the sun at S, and the sun is more magnified.
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 throughmore airthan the rays of the sun at S, and the sun is more magnified.
Q.Why does therisingandsetting moonappear so muchlarger, than after it is risen higher above our heads?A. Because the earth is surrounded by air, which actslike 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.Why does therisingandsetting moonappear so muchlarger, than after it is risen higher above our heads?
Q.Why does therisingandsetting moonappear so muchlarger, than after it is risen higher above our heads?
A. Because the earth is surrounded by air, which actslike 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.)
A. Because the earth is surrounded by air, which actslike 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.Whencandlesarelighted, wecannot seeinto thestreetor road,—Whyis this?A. 1st—Because glass is areflector, and throws the candle-lightback into the room again; and2ndly—The pupil of the eye (which has becomecontractedby the light of the room) istoo smallto collect rays enough from the dark street, to enable us tosee into it.
Q.Whencandlesarelighted, wecannot seeinto thestreetor road,—Whyis this?
Q.Whencandlesarelighted, wecannot seeinto thestreetor road,—Whyis this?
A. 1st—Because glass is areflector, and throws the candle-lightback into the room again; and2ndly—The pupil of the eye (which has becomecontractedby the light of the room) istoo smallto collect rays enough from the dark street, to enable us tosee into it.
A. 1st—Because glass is areflector, and throws the candle-lightback into the room again; and
2ndly—The pupil of the eye (which has becomecontractedby the light of the room) istoo smallto collect rays enough from the dark street, to enable us tosee into it.
Q.Why can’t persons in the streetseeinto awell-lighted room?A. Because the pupil of their eyes ismuch dilated by the dark, and cannotcollect from the window sufficient rays to enable them tosee into the room.
Q.Why can’t persons in the streetseeinto awell-lighted room?
Q.Why can’t persons in the streetseeinto awell-lighted room?
A. Because the pupil of their eyes ismuch dilated by the dark, and cannotcollect from the window sufficient rays to enable them tosee into the room.
A. Because the pupil of their eyes ismuch dilated by the dark, and cannotcollect from the window sufficient rays to enable them tosee into the room.
Q.Why do we often see thefire reflectedin our parlourwindowin winter time?A. Because glass is agood 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 thefire reflectedin our parlourwindowin winter time?
Q.Why do we often see thefire reflectedin our parlourwindowin winter time?
A. Because glass is agood reflector; and the rays of the fire (striking against the window-glass)are reflected back into the room again.
A. Because glass is agood 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 ourcandlesin the window, while we are sitting in our parlour?A. Because the rays of the candle (striking against the glass) arereflected back into the room: and thedarkerthe night, theclearerthe reflection.
Q.Why do we often see the shadow of ourcandlesin the window, while we are sitting in our parlour?
Q.Why do we often see the shadow of ourcandlesin the window, while we are sitting in our parlour?
A. Because the rays of the candle (striking against the glass) arereflected back into the room: and thedarkerthe night, theclearerthe reflection.
A. Because the rays of the candle (striking against the glass) arereflected back into the room: and thedarkerthe night, theclearerthe reflection.
Q.Why is this reflection more clear, if the externalairbedark?A. Because the reflection is not theneclipsedby the brighter rays of the sunstriking on the other side of the window.
Q.Why is this reflection more clear, if the externalairbedark?
Q.Why is this reflection more clear, if the externalairbedark?
A. Because the reflection is not theneclipsedby the brighter rays of the sunstriking on the other side of the window.
A. Because the reflection is not theneclipsedby the brighter rays of the sunstriking on the other side of the window.
Q.Why is theshadowof an object (thrown on the wall)largerand larger, thecloserany object be held to thecandle?A. Because the rays of lightdiverge(from the flame of a candle)in straight lines, like lines drawn from the centre of a circle.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.Why is theshadowof an object (thrown on the wall)largerand larger, thecloserany object be held to thecandle?
Q.Why is theshadowof an object (thrown on the wall)largerand larger, thecloserany object be held to thecandle?
A. Because the rays of lightdiverge(from the flame of a candle)in straight lines, like lines drawn from the centre of a circle.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.
A. Because the rays of lightdiverge(from the flame of a candle)in straight lines, like lines drawn from the centre of a circle.
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.
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 longavenueoftrees,whydoes the avenue seem to getnarrowerand narrower till it appears tomeet?A. Because thefurther the trees are off, the moreacute will be the anglethat any two will make with our eye.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.When we enter a longavenueoftrees,whydoes the avenue seem to getnarrowerand narrower till it appears tomeet?
Q.When we enter a longavenueoftrees,whydoes the avenue seem to getnarrowerand narrower till it appears tomeet?
A. Because thefurther the trees are off, the moreacute will be the anglethat any two will make with our eye.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.
A. Because thefurther the trees are off, the moreacute will be the anglethat any two will make with our eye.
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.
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 straightstreet,whydo the houses seem toapproach nearerand nearer as they are moredistant?A. Because the moredistant the housesare, the moreacute will be the anglewhich 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 a long straightstreet,whydo the houses seem toapproach nearerand nearer as they are moredistant?
Q.In a long straightstreet,whydo the houses seem toapproach nearerand nearer as they are moredistant?
A. Because the moredistant the housesare, the moreacute will be the anglewhich 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:
A. Because the moredistant the housesare, the moreacute will be the anglewhich 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.
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 anavenueoftrees,whydo they seem to besmalleras their distance increases?A. Because thefurther the trees are off, the moreacute will be the anglemade by their perpendicular height with our eye.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 anavenueoftrees,whydo they seem to besmalleras their distance increases?
Q.In anavenueoftrees,whydo they seem to besmalleras their distance increases?
A. Because thefurther the trees are off, the moreacute will be the anglemade by their perpendicular height with our eye.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.
A. Because thefurther the trees are off, the moreacute will be the anglemade by their perpendicular height with our eye.
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.
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 straightstreet,whydo the houses seem to besmallerand smaller thefurtherthey areoff?A. Because thefurther any house is off, the moreacute will be the anglemade 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.In a long straightstreet,whydo the houses seem to besmallerand smaller thefurtherthey areoff?
Q.In a long straightstreet,whydo the houses seem to besmallerand smaller thefurtherthey areoff?
A. Because thefurther any house is off, the moreacute will be the anglemade 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.
A. Because thefurther any house is off, the moreacute will be the anglemade 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 thetopof amountainor church spire seem to be nobiggerthan acrow?A. Because the angle made by theperpendicular height of the man(at that distance)with our eye, is no bigger than the perpendicular height of acrow close by.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 a man on thetopof amountainor church spire seem to be nobiggerthan acrow?
Q.Why does a man on thetopof amountainor church spire seem to be nobiggerthan acrow?
A. Because the angle made by theperpendicular height of the man(at that distance)with our eye, is no bigger than the perpendicular height of acrow close by.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.
A. Because the angle made by theperpendicular height of the man(at that distance)with our eye, is no bigger than the perpendicular height of acrow close by.
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.
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 themoonappear to us so muchbiggerthan thestars, though in fact it is a great dealsmaller?A. Because the moon isvery much nearer to usthan any of the stars.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 amillionof 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 themoonappear to us so muchbiggerthan thestars, though in fact it is a great dealsmaller?
Q.Why does themoonappear to us so muchbiggerthan thestars, though in fact it is a great dealsmaller?
A. Because the moon isvery much nearer to usthan any of the stars.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 amillionof 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.
A. Because the moon isvery much nearer to usthan any of the stars.
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 amillionof 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.
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 amillionof 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 themoon(which is a sphere)appearto be aflatsurface?A. It isso far off, that we cannot distinguish any difference between thelength of the rayswhich issue from theedge, and those which issue from thecentre.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 does themoon(which is a sphere)appearto be aflatsurface?
Q.Why does themoon(which is a sphere)appearto be aflatsurface?
A. It isso far off, that we cannot distinguish any difference between thelength of the rayswhich issue from theedge, and those which issue from thecentre.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.
A. It isso far off, that we cannot distinguish any difference between thelength of the rayswhich issue from theedge, and those which issue from thecentre.
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.
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 thesunandstars(which are spheres) appear to beflatsurfaces?A. Because they are such animmense way off, that we can discernno difference of lengthbetween the rays which issue from theedge, and those which issue from thecentreof 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 do thesunandstars(which are spheres) appear to beflatsurfaces?
Q.Why do thesunandstars(which are spheres) appear to beflatsurfaces?
A. Because they are such animmense way off, that we can discernno difference of lengthbetween the rays which issue from theedge, and those which issue from thecentreof 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.)
A. Because they are such animmense way off, that we can discernno difference of lengthbetween the rays which issue from theedge, and those which issue from thecentreof 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 doesdistancemake an objectinvisible?A. Because the angle (made by theperpendicular heightof the distant objectwith our eye) is so veryacute, thatoneline of the anglemerges in the other.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 doesdistancemake an objectinvisible?
Q.Why doesdistancemake an objectinvisible?
A. Because the angle (made by theperpendicular heightof the distant objectwith our eye) is so veryacute, thatoneline of the anglemerges in the other.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.
A. Because the angle (made by theperpendicular heightof the distant objectwith our eye) is so veryacute, thatoneline of the anglemerges in the other.
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.
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 dotelescopesenable us toseeobjectsinvisibleto the naked eye?A. Because theyconcentrate several rayswithin the tube of the telescope, andbend them upon the mirror or lens, which acts as amagnifying glass.
Q.Why dotelescopesenable us toseeobjectsinvisibleto the naked eye?
Q.Why dotelescopesenable us toseeobjectsinvisibleto the naked eye?
A. Because theyconcentrate several rayswithin the tube of the telescope, andbend them upon the mirror or lens, which acts as amagnifying glass.
A. Because theyconcentrate several rayswithin the tube of the telescope, andbend them upon the mirror or lens, which acts as amagnifying glass.
Q.When aship(out at sea) is approaching the shore, why do weseethe smallmastsbefore we see the bulkyhull?A. Because theearth is round, and thecurveof the seahides the hullfrom our eyes, after the tallmastshave become visible.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.When aship(out at sea) is approaching the shore, why do weseethe smallmastsbefore we see the bulkyhull?
Q.When aship(out at sea) is approaching the shore, why do weseethe smallmastsbefore we see the bulkyhull?
A. Because theearth is round, and thecurveof the seahides the hullfrom our eyes, after the tallmastshave become visible.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.
A. Because theearth is round, and thecurveof the seahides the hullfrom our eyes, after the tallmastshave become visible.
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.
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 byrefraction?A. Thebending of a ray of light, as it passes from one medium to another.
Q.What is meant byrefraction?
Q.What is meant byrefraction?
A. Thebending of a ray of light, as it passes from one medium to another.
A. Thebending of a ray of light, as it passes from one medium to another.
Q.How is a ray of lightbent, as it passes from one medium to another?A. When a ray of light passes into adensermedium, it is benttowards the perpendicular. When it passes into ararermedium, it is bentfromthe perpendicular.Suppose DE to be a perpendicular line.If AB (a ray of light,) enters the water, it will be benttowardsthe perpendicular to C.If (on the other hand) CB (a ray of light) emergesfromthe water, it would be bentaway fromthe perpendicular towards A.
Q.How is a ray of lightbent, as it passes from one medium to another?
Q.How is a ray of lightbent, as it passes from one medium to another?
A. When a ray of light passes into adensermedium, it is benttowards the perpendicular. When it passes into ararermedium, it is bentfromthe perpendicular.Suppose DE to be a perpendicular line.If AB (a ray of light,) enters the water, it will be benttowardsthe perpendicular to C.If (on the other hand) CB (a ray of light) emergesfromthe water, it would be bentaway fromthe perpendicular towards A.
A. When a ray of light passes into adensermedium, it is benttowards the perpendicular. When it passes into ararermedium, it is bentfromthe perpendicular.
Suppose DE to be a perpendicular line.If AB (a ray of light,) enters the water, it will be benttowardsthe perpendicular to C.If (on the other hand) CB (a ray of light) emergesfromthe water, it would be bentaway fromthe perpendicular towards A.
Suppose DE to be a perpendicular line.If AB (a ray of light,) enters the water, it will be benttowardsthe perpendicular to C.If (on the other hand) CB (a ray of light) emergesfromthe water, it would be bentaway fromthe perpendicular towards A.
Q.Why does aspoon(in a glass of water) always appearbent?A. Because as the light of the spoonemerges from the water, it isrefracted.And the spoon looks like ABC. (See the last figure.)
Q.Why does aspoon(in a glass of water) always appearbent?
Q.Why does aspoon(in a glass of water) always appearbent?
A. Because as the light of the spoonemerges from the water, it isrefracted.
A. Because as the light of the spoonemerges from the water, it isrefracted.
And the spoon looks like ABC. (See the last figure.)
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 isrefractedas it emerges out of the water: and (as a stick is not so long when it isbent, as it is when it isstraight) so the river seems less deep than it really is.
Q.Why does a river always appear more shallow than it really is?
Q.Why does a river always appear more shallow than it really is?
A. Because the light of the bottom of the river isrefractedas it emerges out of the water: and (as a stick is not so long when it isbent, as it is when it isstraight) so the river seems less deep than it really is.
A. Because the light of the bottom of the river isrefractedas it emerges out of the water: and (as a stick is not so long when it isbent, as it is when it isstraight) 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.How much deeper is a river than it seems to be?
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.
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.