What objects are good reflectors of light?
Those having smooth and polished surfaces; such as tin, silver, gold, and quicksilver.
What objects are poor reflectors of light?
Those having dull, uneven surfaces; such as iron, wood, cloth, leather, and calico.
Of what is every ray of sunlight composed?
It is composed of the seven colors of the rainbow.
What does a looking-glass do with these colors?
A looking-glass throws them all back from its surface.
What does a glass window do with these colors?
A glass window permits all these colors to pass through it.
What do opaque substances do with these colors?
They throw back or reflect some of them.
Do they all reflect the same color?
No; some reflect one color, and some another color.
What color does the grass reflect?
It reflects the green color; therefore, the grass is green.
What does the grass do with the other colors?
It absorbs or hides them in itself.
How do we know the color of anything?
We know it by the color which it reflects.
Why is the rose red?
Because it reflects the red color, and absorbs or hides the other colors in itself.
When anythingabsorbsall the colors of a ray of light, what color is it?
It is black.
When itreflectsall the colors of light, what color is it?
It is white.
Why are the letters on this page black?
Because they absorb all the colors of light, and reflect none.
Why is the paper white?
Because it reflects all the colors of light, and absorbs none.
Why are all things black in the dark?
Because there are no rays of light falling on them; hence, there is no color for them to reflect.
Does an object reflect its color in every direction?
It does reflect its color in every direction.
How do we know this?
Because thousands of persons, in different directions from the same object, can see it at the same time.
How are the rays of color reflected from an object?
They are reflected in straight lines.
Where must a person be so as to see an object?
He must be in a position so that there is nothing to prevent the rays of light passing in a straight line from the object to his eyes.
What color does a red ribbon reflect?
It reflects a red color.
Why are some red ribbons of a brighter red than others?
When they reflect a great many red rays, they are of a bright red color; but when they reflect only a few red rays, they are of a dull red color.
Upon what does the brightness or dullness of a color depend?
It depends upon the number of rays of that color reflected.
What variety does this produce?
It produces a great variety in the shades and tints of color.
Where may many of these shades and tints be seen?
In the pretty flowers that grow in the woods, fields, and gardens; in the beautiful tints of the leaves in autumn; and in the plumage of the birds that visit us every spring, and cheer us with their songs.
What may these things teach us?
They may teach us the goodness of God, in giving us a world so full of beauty; and we should feel ever thankful to Him for the great pleasure that we have in seeing them.
Why cannot we see the light of a lamp or candle distinctly, in the day-time?
Because the strong rays from the sun hide the more feeble rays from the lamp.
Why cannot we see the stars in the day-time?
Because the bright light from the sun hides their more feeble light.
When can we see the glow-worms or fire-flies best?
At night, when it is dark; because, at other times, the light of the sun hides their feeble light.
Where may we see them at night?
Flying about in all directions, looking like bits of fire moving in the air.
Does a looking-glass reflect all the colors of light falling upon it?
It does; hence, the ray of light is not changed.
When the object is of a blue color, why is blue only reflected?
Because it is the only color falling upon the glass, and there is no other color to reflect.
Is the color of any object changed by falling upon a looking-glass?
No; the color of every object is reflected from a looking-glass without change.
Do other objects generally reflect the colors falling upon them?
They do not; they absorb or hide the color of all other objects, and reflect only their own color.
If every object was a good reflector of color, like a looking-glass, what would result?
Then every object would reflect the color of every other object around it, and there would be an endless confusion of colors.
What objects reflect the most light?
Those of a white or light color.
What objects reflect the least light?
Those of a darker color; and the nearer the color approaches to black, the less light it reflects.
Why is it darker when the sky is covered by dark-colored, than by light-colored, clouds?
Because the dark-colored clouds reflect less light, than the light-colored clouds do.
What advantage do we derive from the green color of the grass and the leaves?
They reflect a soft, pleasant light, which does not dazzle or hurt our eyes.
How would it be if those objects were white?
They would dazzle us by the amount of light reflected.
If we wish to make a room light, of what color should the walls be?
They should be white; and when papered, it should be with light-colored paper.
Why does dark-colored paper darken a room?
Because it absorbs some of the rays of light which come in at the windows; hence, there is less light in the room. Dark-colored carpets, or dark furniture, darken the room for the same reason.
Does the light from a burning body differ from sun-light?
Yes; it differs in intensity, in color, and in many other ways.
What effect does the lamp-light have upon the color of some substances?
It changes their color.
Where may we find an example of this?
In trying to match the colors of thread or silk at night.
Why is the color different by lamp-light from what it is by daylight?
Because the yellow color of the lamp’s rays acts upon the color of the silk, forming a third color. Blue silk becomes green by lamp-light, and red silk becomes orange.
Are all persons able to distinguish one color from another?
No; some are color-blind. To such persons all colors appear to be alike.
What curious instances of color-blindness may be mentioned?
Dr. Mitchell tells of an officer who bought a blue coat and a red waistcoat, thinking them to be of the same color. He also tells of a tailor who patched a black waistcoat with a piece of crimson; and of another, who put a red collar on a blue coat. Dr. Dalton lost a piece of red sealing-wax in the grass, and he could not find it because it and the grass seemed of the same color to him.
How do the rays of light from the sun come to us?
They come to us in straight lines.
When the rays of light pass from one substance to another more dense, what takes place?
They are bent or turned from a straight course.
What is said of these bent rays?
They are said to berefracted.
What is meant by refraction?
Bending a ray of light, as it passes from one substance to another of different density; as from air to water, or from water to air.
Where may we see an example of refraction?
In the rays of light from a rod which has one end in the water.
Fig. 7.
Fig. 7.
Why does the rod appear to be bent?
Because light coming from the part of the rod under the water, is refracted or bent at the surface of the water, while the light from the part above thesurface, comes in straight lines to the eye; hence, the rod appears to be bent at the surface, as is represented inFig. 7.
How does a pole appear when one end is placed in the water?
It appears to be bent where it meets the surface of the water.
How does the part of the rod under water appear?
The part under the water appears to be raised up, as may be seen inFig. 7.
How does the bottom of a pond or stream of water appear?
It appears to be raised up, and the water does not seem so deep as it really is.
Why is this the case?
Because the light from the bottom of the pond is refracted or bent at the surface of the water; hence, the bottom appears to be raised up.
How much does the bottom of a pond or stream of water seem to be raised up?
About one-third of the depth of the water.
If the water is really six feet deep, how deep does it appear?
It appears to be only four feet deep.
What has frequently happened from not knowing this fact?
People have been drowned from getting into water deeper than it appeared to be.
Do the fish and other things floating in the water appear to be raised up?
Yes; like the bottom of the stream, they also appear to be only two-thirds as far from the surface as they really are.
If we wish to spear the fish, what must we do?
We must aim below the place where they seem to be, or we must strike perpendicularly at them.
When a ball is thrown against a wall, what is the path through which it goes called?
The line of incidence.
When the ball bounds back, what is its path called?
The line of reflection.
What is the angle at which a ball strikes the wall called?
The angle of incidence.
What is the angle at which the ball rebounds called?
The angle of reflection.
When a ray of light falls upon a looking-glass, what is the path through which it goes called?
The line of incidence.
When the ray is reflected, what is its path called?
The line of reflection.
Theangle of incidenceis the angle between a perpendicular and the line of incidence; and theangle of reflectionis the angle between the perpendicular and the line of reflection. The two angles are always equal to each other, as is represented inFig. 8.
Fig. 8.
Fig. 8.
When a ray of light strikes a looking-glass obliquely or slantingly, what is done with it?
The ray is reflected as obliquely from the glass as it strikes or falls upon it.
Why is the reflection of the sun in a pond of water seen near the edge at noon?
Because the angle of reflection is equal to the angle of incidence; and the observer must be nearly over the place where the rays strike, so that, when reflected, they may meet his eye.
Where is the reflection seen in the morning or in the evening?
It is seen nearer the middle of the pond; because the sun’s rays then fell more obliquely on the pond, and are reflected more obliquely to the eye.
When an opaque object is placed between a candle and a wall, why will there be a shadow?
Because the opaque object prevents the rays of light from falling on the wall.
Why will the shadow be larger, the nearer the object is to the candle?
Because the rays of light diverge, in every direction from the candle, in straight lines, and the nearer the object, the more rays will it intercept, as is represented inFig. 9.
Fig. 9.
Fig. 9.
InFig. 9, let L represent the flame of a candle. When the object is placed at A, the shadow on the wall will extend from C to D; but when the object is moved nearer, as at B, the shadow will extend from E to F.
Why does an object seem to be smaller, the farther it is from us?
Because the angle at which the light from it strikes the eye, is less when at a distance, than when near to the eye.
Fig. 10.
Fig. 10.
InFig. 10, the diameter of the near circle is from A to B; but the diameter of the more distant circle, although just as large, seems only to be from C to D.
Why does an object grow more dim the farther it is from us?
Because the rays of light from it spread out in every direction; and fewer rays enter the eye when it is at a distance than when it is near by.
What is the use of the telescope?
It is used to view distant objects.
Why can we see a distant object more distinctly with a telescope, than without one?
Because the telescope enlarges the image of the object, and it also collects more light from that object than is collected by the unaided eye; thus, making the image distinctly visible.
What class of objects do we view with a telescope?
We view the heavenly bodies; the sun, moon, and stars.
What is a spy-glass?
It is a glass mostly used to view distant objects on the earth.
Is the spy-glass like the telescope?
The spy-glass is much like the telescope, only it is smaller.
When looking through a spy-glass, how do objects appear?
They seem to be brought nearer to us, and they appear larger.
By whom are spy-glasses much used?
Spy-glasses are much used by persons on board of vessels, while at sea.
What instruments have we for magnifying small objects?
We have magnifying glasses and microscopes.
What are magnifying glasses?
They are single glasses or lenses, used for magnifying small objects.
By whom are magnifying glasses used?
They are used by jewellers, watchmakers, engravers, and others who examine small objects.
What are microscopes?
They are instruments used for examining very small objects.
How does a drop of rain-water or vinegar appear under the microscope?
It appears to be full of strange-looking creatures, which are always in motion.
How do the smallest insects appear?
They appear to be as perfectly formed as the larger ones which are seen with the naked eye.
What may be seen with a microscope?
Thousands of things too small to be seen by us unless they are magnified.
What kind of spectacles do near-sighted people use?
Near-sighted people use glasses, thickest at the edge and thinnest at the centre.
What kind of spectacles do we use as we grow old?
As we grow old we use glasses, thinnest at the edge and thickest at the centre.
Of what use are spectacles?
When the vision is defective, spectacles enable us to see objects more clearly.
How should spectacles be made?
They should be so made as to render objects distinct, but neither to magnify nor diminish them.
As people grow old, how do their eyes change?
Their eyes change so that they see objects at a distance better than those which are nearer, hence, in reading they hold a book farther from the eye.
What is that part of the eye called, which is blue, gray, or brown, in different persons?
It is called theiris.
What is the pupil of the eye?
The pupil is the black spot or hole in the centre of the iris.
Fig. 11.
Fig. 11.
What is the use of the pupil?
The pupil is the window of the eye, and the rays of light which enter the eye must pass through it.
What power has the iris over the pupil?
The iris has the power of making the pupil larger or smaller, according to the amount of light which it receives.
How does a bright light affect the iris?
It causes the iris to contract, so that the pupil becomes smaller.
How does a faint light affect the iris?
It causes the iris to dilate, so that the pupil becomes larger.
Of what advantage is the iris to the eye?
The iris acts like a sentinel to protect the eye from any sudden light.
How does a sudden light affect the eye?
A sudden light causes pain to the eye.
Of what shape is the pupil of the eye?
In man, the pupil of the eye is circular.
What is the size of the pupil of the eye?
The pupil varies from the one-twentieth to the one-third of an inch in diameter, depending upon the brightness of the light entering the eye.
How else are our eyes protected from any sudden light?
By means of our eyelids, which may be closed, and thus shut out all the light.
When we pass from a well-lighted room into the open air, at night, why does it seem darker at first than it does afterwards?
Because the pupil is contracted at first; but it soon dilates, and allows more rays of light to pass into the eye, so that the night seems less dark.
Why does the pupil become larger in the twilight?
So that more rays of light may enter the eye, whereby objects may be more distinctly seen.
Why can an owl or a bat see at night?
Because the pupil of the eye in them is quite large, and admits much light.
Why do they stay in dark places through the day?
Because the bright light of day hurts their eyes.
May the image of an object be retained in the eye after the eyelids are closed?
It may for a very short time, as any one can prove by first looking at some bright object, and then closing the eyelids.
Why does a burning coal moved rapidly around, seem like a circle of fire?
Because the light from it is retained a short time by the eye, thus seeming to form a complete circle.
Why cannot we count the posts in a fence, when riding rapidly in a car?
Because the light from each post falls in such quick succession upon the eye, that it cannot distinguish one post from another.
Can objects be seen distinctly when placed near the eye?
No; when objects are within six inches of the eye they cannot be seen distinctly.
Can objects be seen when at a great distance from the eye?
Yes; objects may be seen even when millions of miles away from us; thus, the sun is seen although ninety-five millions of miles from the earth, and someof the stars which we behold in the heavens, are still farther away than the sun.
Of what use is the eye to us?
The eye gives us ideas of the size, the shape, the color, the place, the distance, and the movements of things around us, so that we can use them the better to promote our comfort and our happiness.
What may we remember about the light?
And God said, “Let there be light;” and there was light. Thus the day was separated from the night, and the sun was made to send forth his silvery rays upon hill and valley, field and forest, causing the rarest buds and most beautiful blossoms to come forth from the lifeless earth, although no eye, save the All-Seeing One, was there to behold them!
Locomotive.
Decoration.
Illustrated Capital W
What is heat?
Heat is that agent which causes the feeling of warmth.
Can heat be seen?
No; heat cannot be seen, it can only be felt.
When we touch a substance hotter than we are, what takes place?
A part of the heat from that substance comes to us and causes a feeling of warmth.
When we touch a substance colder than we are, what takes place?
A part of the heat from us goes to that substance, and we experience a feeling of cold.
Does the amount of heat in any substance vary?
Yes; water may be heated until it is scalding hot, or the heat may be taken from it until it is frozen into ice.
What causes a substance to become cold?
Taking away heat from a substance causes it to become cold.
Then what is cold?
Cold is only the absence or want of heat.
When we pass from a very hot room to one moderately warm, how do we feel?
We experience a feeling of cold.
When we pass from a very cold room to one moderately warm, how do we feel?
We have a feeling of warmth, although the room is no warmer than in the first instance.
How else can we prove that we judge of heat and cold by our feelings?
If one hand be held in quite warm water, and the other in quite cold water, for a few moments, and then both hands be plunged into tepid water, the tepid water will feel cold to the hand that was in the warm water, and warm to the hand that was in the cold water.
Is there anything without heat?
No; the coldest substance known still contains some heat.
How many kinds of heat are there?
There are two kinds of heat.
What are the two kinds of heat?
Heat accompanied by light, as the heat from the sun, or a lamp; and heat without light, as the heat from boiling water.
From what source does heat mostly come?
Heat mostly comes from the sun, which is also the source of light.
What is said of the heat and light from the sun?
Heat and light from the sun come together in the sunbeam.
From what other source is heat obtained?
Heat is obtained from the burning of any substance.
What else does the burning of any substance produce?
It often produces light.
Can the light and heat from the sun easily be separated?
They cannot easily be separated.
What does a glass window do with the light and heat of the sunbeam?
It permits both the light and the heat to pass into the room, so that we can see the one and feel the other.
Are the light and heat from a fire united, as they are in the sunbeam?
They are not; but they seem to be separated from each other.
What does a glass window do with the light and heat from a fire?
It permits the light to pass through; but it stops the heat.
How may this be proved?
When a pane of glass is held between the face and a fire, it will protect the face from the heat.
Is there any heat without light?
Yes; many substances contain heat, but do not emit light.
Does light change the amount of heat in a substance?
No; boiling water is as hot in the dark as it is in the light; and ice is as cold in the daytime as it is at night.
Is there any other source of heat?
Yes; heat is produced by rubbing or striking substances together.
What will result from rubbing two pieces of wood together?
They may be rubbed until they take fire.
How do Indians kindle fires?
By rubbing two pieces of wood together until they take fire.
How is heat produced by the brakes on railroad cars?
It is produced by the car-wheels rubbing against the brakes.
What may be seen when a horse strikes his shoes against a stone?
Small sparks of fire, which contain heat, may be seen.
If a piece of iron be hammered, will its heat be increased?
Its heat will be increased.
How can this be proved?
A person can, by hammering a piece of cold iron, make it red-hot.
Could we live without heat?
No; our bodies must be kept warm, and this can be done only by heat.
Is this true of other living things?
Yes; all the animals and all the plants would die if heat were taken away.
How should we feel in regard to these things?
We should feel thankful to an All-wise Creator, for having provided us with both heat and light from a never-failing source—the sun.
How does heat generally affect substances?
Heatexpandsthem or makes them larger.
Does heat expand all metals?
Yes; all metals are expanded by heat.
When a rod of iron is heated, is it longer or shorter than when cold?
It is longer than when it is cold.
How do we know this?
We know it by measuring the rod when it is cold, and again when it is heated.
Will the rod be larger, as well as longer?
The rod will be larger.
How can we prove this?
The rod, when red-hot, will not go through as small a hole as when it is cold.
How do heat and cold affect most substances?
Heat expands most substances, and cold contracts them.
Do all metals expand alike by heat?
No; some metals expand much more than others.
How does heat expand substances?
Heat pushes the parts or atoms of an object farther from each other, and thus its size is increased.
What does a blacksmith do with a tire before putting it on a wheel?
He heats the tire red-hot.
Why does he heat the tire red-hot?
So that it will be increased in size, and will go on the wheel more easily.
What takes place as the tire cools?
It becomes smaller, and thus binds the parts of the wheel tightly together.
When a fire is made in a room, why does the furniture often make a snapping noise?
Because heat expands the wood, and the particles make a snapping noise upon separating.
Why does a stove make a crackling noise as it grows hot?
The particles of the iron make the noise in expanding.
If a piece of glass be held in the hand, will the glass become warm?
The glass will become as warm as the hand.
What part of the glass will be warmed first?
The part touching the hand will be warmed first.
What part of the glass will be warmed last?
The part farthest from the hand will be warmed last.
Which part of the glass will be expanded first?
The part touching the hand, because it is first warmed.
Which part will be expanded last?
The part farthest from the hand, because it is the last part warmed.
If any other warm substance touch the glass, will the glass be heated in the same manner?
The glass will be heated in the same manner.
What often results from this unequal heating?
The glass is broken.
Why are glass plates or tumblers broken when placed in hot water?
They are broken because the part next to the hot water is expanded more than that farther away.
Why will a cloth dipped in hot water and wrapped around the neck of a bottle loosen its stopper?
Because the heat from the cloth expands the neck of the bottle before it does the stopper, so that the stopper is loosened.
Why do stove-plates often break?
Because they are fitted together in the stove so that they have not room to expand without breaking.
What effect has cold upon substances?
Cold causes them to contract or grow smaller.
Thingsexpandunequally; do they alsocontractunequally?
They do contract unequally, and in this way may be broken.
Why are lamp chimneys often broken while the lamp is burning?
Because the heat of the flame causes them to expand unequally.
In what other way are they broken?
By a draught of cold air, or a drop of cold water, touching them, thus causing them to contract unequally.
Why are they sometimes broken when the lamp is not burning?
Because a current of cold air from a window or a door, blows upon them.
Does quicksilver expand when heated?
Like other metals, quicksilver expands as it grows warmer, and contracts as it grows cooler.
Is quicksilver in the form of a solid or a fluid?
It is a fluid as we usually see it.
For what is quicksilver used?
It is used for filling the tubes of thermometers.
What is a Thermometer?
It is an instrument used for measuring the degree or quantity of heat in any substance.
How does heat affect the quicksilver?
Heat expands the quicksilver, and causes it to rise in the tube.
How does cold affect the quicksilver?
Cold contracts the quicksilver, and causes it to fall in the tube.
Does heat expand liquids more than solids?
Heat does expand liquids more than solids.
Why are liquids expanded more than solids?
Because the particles of which they are formed are more easily separated or pushed apart by the heat.
If we continue to apply heat to a liquid, what becomes of it?
The liquid is changed into a gas or vapor.
What common example have we of vapor?
Water, when heated, is turned into steam.
Mention some gas.
Theairwe breathe is a gas.
How does heat affect the air?
Heat warms the air and causes it to expand.
Do solids all expand equally when heated?
No; some solids expand more than others; thus, zinc expands more than iron, and iron more than glass.