You can learn a great deal through your ears, but think how much more
you can learn through your eyes. Just count over all the things that
you have had to get your eyes to tell you to-day, and then shut your
eyes for a minute and think what it would mean never to be able to
see. Don't you think you ought to take very good care of your eyes?
You are going to keep them very busy all your life, and they deserve
the very best care you can give them.
[Illustration: THE LIGHT ON THE PAGE, NOT IN THE EYES]
Just as soon as lessons begin, you get out your books; and a good
share of the day in school you have a book before you, reading it or
studying it or copying from it. It makes a great difference to your
eyes how you hold the book and how the light falls. In reading, you
should always hold your book so that the light falls upon the page
from behind you, or from over one of your shoulders. In this way, the
brightest light that comes into your eyes is not from the window, but
from the page of your book.
If the light comes from a window in front of you, or if you sit in the
evening with your face toward the lamp when you read, the light coming
straight from the lamp or the window, as well as the light coming up
from the pages of the book, pours into your eyes; and this dazzles and
confuses your eyes, so that you can't see plainly and comfortably and
are very likely after a while to find that your head aches. At home,
of course, you can seat yourself with your back to the light when you
read; and usually at school your seats are so arranged that the light
falls from behind you or from one side. If not, by turning a little in
your seat, you can get the light from over your shoulder.
Notice how the light falls upon the blackboard. When the light comes
from the windows behind you, or from one side, you can see what is
written there quite plainly. But if the blackboard happens to be
between two windows, and especially if this is the lightest side of
the room, you will find that the light dazzles you so that you cannot
see the writing clearly.
You must have noticed, too, that if, after you have been reading from
the blackboard you look down again suddenly to the page of your book,
for an instant you will not see the letters plainly. Then, almost
before you have time to notice it, you feel a little change take place
inside your eyes, and the print upon the page of your book becomes
quite plain. This is because your eye has to change the shape of one
of the parts inside it, called the _lens_, before you can see clearly
the things that are near you. This change, which is called
_accommodation_, is made by a little muscle of the eye; and if you
keep your eyes working at close work, like reading or writing or
fancy-work, too long at a time, or if your eyes need glasses to make
them see clearly, and you haven't them on, this little muscle becomes
tired. Then the print of your book, or your writing, or the stitches
you have taken begin to blur before your eyes. Your eyes begin to feel
tired, and your head begins to ache. This is what we call _eye
strain_.
Sometimes this eye strain upsets your appetite or your digestion and
makes you sleepless and worried. The trouble may be caused by your own
carelessness: you may have been reading too long, or in a poor light,
or with the light shining right in your face instead of coming over
your shoulder. But sometimes it is caused by the fact that your eyes
are not just the right shape; and then the only way to relieve it is
to have proper glasses, or spectacles, fitted, which will make up for
this too flat or too round shape, or too large or too small size, of
your eyes.
If you cannot see clearly what is written on the blackboard when the
light falls upon it from behind you, or above; or if, in a good light,
you cannot read the words in your book quite easily, without straining
at all, when you hold the book either at arm's length or a foot from
your face; or if your head aches or your eyes begin to feel tired or
uncomfortable, or the letters begin to blur, after you have read
steadily--say, for half an hour,--it is a pretty sure sign that there
is some trouble with your eyes. Then you had better have them examined
at once by your family doctor or by the school doctor. In many schools
now there are doctors to test the children's eyes, and ears, too, so
that each child may have a chance to see and hear everything that the
other children can see and hear.
Not very many years ago people thought that glasses were only for old
people, but now we know that many children's eyes need glasses, too. I
knew a little girl whose sight was so poor that when she was standing
and looked down at the grass, she couldn't see the green blades. She
thought that the grass looked like a green blur to everyone, just as
it did to her; and so she never said anything about it. She was twelve
or thirteen years old before she found out that she couldn't see
clearly. Of course, trying hard to see things gave her a headache and
made her tired and cross. So some one took her to a doctor, and he saw
at once what was the matter and fitted her with glasses. Soon she was
quite well and strong; and how glad she was to see the leaves and a
hundred other things she had not seen before!
[Illustration: THE EYEBALL IN ITS SOCKET
The muscle from M to M, which helps to turn the eyeball, has
been cut away to show the optic nerve.]
Here we have a picture of the _eyeball_, as we call it. The little
bands fastened to it are the bands of muscle; and as soon as I say
_muscle_ you know what they are for--to move the eyeball about, up and
down and from side to side. There are muscles outside the eye as well
as inside. Coming out from the back of the eyeball is a pearly white
cord quite different from the muscle bands. This is what we call a
_nerve_. This nerve in your eye carries to your _brain_, or thinking
machine, picture-messages of whatever you look at.
The nerve in your eye gets messages of light much as the nerve deep in
your ear gets its messages of sound--from tiny waves in the air. The
light waves are smaller and faster even than the sound waves, and the
eye nerve is the only nerve that can get pictures of them. You know
that, for wireless messages, the receiving machines are not all alike
and cannot all take the same messages, if the messages are sent with
different sorts of electric waves; and neither can our receiving
machines. Some get messages of sight, and some of sound, and some of
touch, or taste, or smell.
Now shut your eyes as quickly as you can. How long did it take you? A
minute? No, not a quarter of a second. It is about the quickest thing
you can think of--"the twinkling of an eye." You shut your eyes "quick
as a wink" whenever anything seems likely to fly or splash into them,
and this is what the eyelids are for. If anything gets into the eye
before the lids can shut, the eye "waters," and _tears_ pour out of
it. These are made by a gland-sponge up under the upper lid, so as to
wash any dust or sand or other harmful speck out of the eye before it
can hurt the sensitive eyeball.
Now look at some one's eyeball. It is like the picture, isn't
it?--bright white around the edge and then a ring of color, brown or
blue or gray; and inside the color-ring, or _iris_, a little round
black hole that we call the _pupil_. Watch the little hole change as
you turn the face toward the window. It becomes ever so much smaller.
Now turn the face away from the window, back again into the shadow.
How did the pupil change this time?
[Illustration: EYES PROTECT THEMSELVES AGAINST THE LIGHT]
The iris, or color-ring, acts like a curtain, like the ring-shutter of
a camera, and closes up the hole, or pupil, when the light is too
bright and would dazzle or burn the inside of the eye; but when the
light is dim, the iris opens again, so as to let in light enough with
which to see. Look at the little window in your kitten's eyes. It is
not the same shape as yours; but when you carry her to the light, you
see how the iris closes in and leaves just a little black slit or
line.
You remember the blind children? Isn't it wonderful how they can play
games and study, too, even though they are blind! They have to make
their senses of touch and hearing tell them many things that you learn
through your sense of sight. Many of these children _need not have
been blind_, if the nurse who first took care of them when they were
born had known enough to wash their eyes properly, not with soap and
water, of course, but with just one or two drops of a kind of
medicine--an _antiseptic_, as we call it--that makes the eye perfectly
clean.
But you children who have good eyes that can see, do you really see
things when you look at them? You can train your eyes just as you can
train your ears. You can teach them to read quickly down a page, and
to find things in pictures, and, better still, to see things out of
doors, in the garden and the woods and on the seashore. We hear a
great deal about "sharp eyes," but most of us see very little of all
we might see. Our eyes are on the lookout, too, to protect us from
dangers that may come; with our skin and nose and ears, they are
constantly on the watch; so the better we see the safer we are.
Even if your eyes are perfect now, you will need to take good care of
them to keep them strong. Don't let any story, no matter how
interesting it is, tempt you to read in a dim light or a light that is
too strong. And if you can't see the blackboard easily, or can't read
big print, like the school calendar, across the room, tell your mother
or your teacher, so that she can ask the doctor to find out what the
matter is.