A FUNNY FINGER

Do you want to see an interesting optical illusion? If you do, put your two forefingers together and hold them 7 or 8 centimetres in front of your eyes, as shown in the picture. Look over the fingers and focus your eyes on something far away. Now hold your fingers a centimetre away from each other and look between them. You will see a funny finger in the air with a nail at each end! This is what happens. When you hold your two fingers in front of your eyes, the picture of your left finger in your left eye and the picture of your right finger in your right eye come together in part^* and you see a funny finger with a nail at each end.

^* come together In part — частично сливаются

CIRCLES ON THE CARD

Draw four thick lines on a piece of cardboard, as shown in the picture. Push a pin through the centre. Then hold the pin and spin the piece of cardboard. To your surprise, you will see two concentric circles. The trick works with two lines, but the illusion is stronger if there are four.

A MISSING PIECE OF CAKE

Where is the missing piece of cake? You will find it if you turn the picture upside-down.^*

AN OPTICAL ILLUSION WITH A MATCH

If you want to see this interesting optical illusion, you must take two matches and a small rubber band. The matches must have no heads. Put the rubber band on two of the fingers of your left hand, as shown in the picture.

Put one of the matches through the rubber band and turn it many times from end A to end B. Then you put the other match between the two fingers of your left hand and the first match will not turn back. With your right finger you move match end A to the right. This will bring end В against the other side of the second match. Now you are going to demonstrate the illusion. Tell your friends that you can make the first match go through the second match. You raise your right finger for a moment. During this moment end В comes back to your right finger. This movement will be so quick that your friends will not notice It. After some practice you will be able to do it so well that your friends will not notice the movement of your right finger too. The illusion will make them think^* that one match has gone through the other match.

^* The illusion will make them think — Вследствие иллюзии они будут думать

MOON ILLUSION

One of the most interesting of all natural illusions is the large size of a full moon when we see it low on the horizon.^* Six hours later, when the moon is high in the sky, we think that it has become much smaller. But photographs show that the diameter of the moon when it is high in the sky is the same as when it is low on the horizon. We shall see the same illusion if we go to a planetarium. Scientists do not agree on why this happens. Some of them think that the moon on the horizon looks larger because we can see it together with some trees or houses (which are on the horizon too). But this does not explain why the illusion is the same at sea, where there is nothing on the horizon. Now some scientists think that this illusion takes place because things look smaller when we must raise our eyes to see them.

^* low on the horizon [ha'raizn] — у самого горизонта

AN ILLUSION WITH A THREE-KOPEK COIN

Can you put a three-kopek coin on this picture of a table so that the coin does not touch the sides of the table? At first you will think it is possible, but when you try to do it, you will find that the coin is very large. You thought that it was smaller. It was an illusion. The angles of the picture help to cause the illusion.^*

^* The angles of the picture help to cause the illusion.— Углы картинки помогают создать иллюзию.

If you want to see through your hand, you must take a sheet of paper and make a tube. With your right hand you put one end of the tube to your right eye, as you do it with a telescope. Then you hold your left hand at the tube, as shown in the picture. You focus your eyes on the wall of the room. It will seem to you that you are looking through a hole in your left hand. If you move your hand, you can find a place where it will seem to you that the hole is in the centre of your hand. It is binocular vision^* that explains this illusion. The picture of the hand in your left eye runs over the picture which you see with your right eye. If you move one of your hands away from the other, you will see that the hole is moving away from the centre of your left hand. Then you move the hand back, and the hole moves back to the centre of the left hand.

^* binocular vision — бинокулярное зрение ( при котором создается объемное восприятие предметов)

THE THIRD COIN

It is easy to show an interesting optical illusion with two coins. Hold the coins between your forefingers as you see in the picture. Rub the coins against each other. A third coin will appear between and below the other two. This is because your eyes keep the images of the two coins in their lowest positions. But nobody can explain well enough why the third coin always appears below and never above the real coins.

A STRANGE SPIRAL

You are sure that this picture shows a spiral line that begins from the centre. But if you try to follow the line with a pencil, you will find that it is not a spiral. You have a number of concentric circles. You may show this optical illusion to your friends if you twist together, a black and a white piece of rope to make one rope and put it on a carpet which has different pictures on it. Scientists give different explanations of this optical illusion. They don't agree on one explanation.

PAPER FILMS

You may show how cinema films run with the help of this paper toy. Fold in half a piece of paper 7¹/_t by 20 centimetres (Picture 1). On the lower leaf draw the face shown in Picture 2. On the upper leaf draw 1he face in Picture 3. Turn the upper leaf into a tube^* (Picture). Your left finger holds the upper left corner and your right hand holds a pencil above the upper leaf, as shown. Move the pencil up and down quickly. The upper leaf will unroll and roll up again,^* and you will see a short but funny film.

^* Turn the upper leaf into a tube — Сверните верхний листок в трубочку

^* will unroll and roll up again — будет раскручиваться и снова закручиваться

A TURNING DEVICE ^*

This turning device will show you that your eye can keep a picture of a thing for half a second after you have put that thing away. You can make a turning device in the following way. Cut out a square piece of cardboard 4 by 4 centimetres. Make two holes and tie short pieces of string, as shown in Picture 1. Draw a large fishbowl on one side of the square and a small fish on the other side. Hold the pieces of string between your fingers. Now you can turn the square very quickly with your fingers. When it is turning, you will see only one picture of the fish inside the bowl (Picture).

^* A Turning Device — Вертушка

AN ILLUSION WITH A PENCIL

You can make an interesting illusion with the help of a pencil. Take a pencil and hold it with your fingers near one end, as shown in the picture. Then you move your hand up and down no more than five centimetres. You must try not to move the pencil a little with your fingers. You hold it in an easy way so that it moves as your hand goes up and down. If you do it the right way, it will seem to you that you are holding a rubber pencil which bends all the time.

A PENDULUM WHICH MOVES IN A CIRCLE ^*

You can demonstrate this interesting optical illusion if you get a pendulum and dark eye-glasses. It is easy to make и pendulum. You tie a small thing to one end of a rope 60 cen-timetres long and your pendulum is ready. Then you ask your friend to stand at the other end of the room and move the pendulum there and back in front of your eyes. You hold the glasses so that only your right eye is looking through a dark glass. But your left eye must be open too. Then it seems to you that the pendulum is moving in a circle! Now hold your eye-glasses so that only your left eye is looking through the dark glass. Your right eye is open too, It seems to you that the pendulum is moving in a circle again, but in a different direction. Scientists explain this optical illusion in different ways. Some time ago one of the scientists explained it in the following way: the images of the pendulum get to your brain through the eye with the dark glass and through the other eye, on which there is no glass. But the images which come through the eye with the dark glass get to the brain a moment later than the images which come through the other eye, on which there is no glass. But some scientists say that this does not explain why it seems to us that the pendulum moves in a circle.

^* A Pendulum ['pendjulem] Which Moves in a Circle — Маятник, который ходит по кругу

THE STAMP WHICH DISAPPEARS

Put a stamp on your table. Then put a glass of water on the stamp. Cover the glass with a saucer, as shown. The stamp disappears! Walk around the glass and look into it from different sides. You will not be able to see the stamp. The explanation lies in the phenomenon of refraction.^* The rays of light bend ^* when they pass at an angle from water to air. The lines show the refraction. There is no angle from which you can see the stamp.

^* the phenomenon of refraction — зд, явление, которое называется преломлением лучей

^* The rays of light bend — Лучи света преломляются

THE TWO SIDES OF YOUR FACE ARE DIFFERENT

Do you think that the right side and the left side of your friend's face look the same? If you think they look the same, get his photograph and take a small mirror. (It is better to take a mirror without a frame.) Then you put one side of the mirror on the centre of the face, as shown in the picture. You will see the whole face of two left sides of the photograph. If you want, you may turn the mirror the other way and then you will see the whole face of two right sides of the photo. Many years ago some people thought that the two sides of a face could be different. For example, one side of the face may look happy and the other side unhappy. Today we know it is not true, but still the experiment is very interesting because it proves that the two sides of a face are not the same. You may try it on your own picture. The experiment will surprise you. You will see how different your "two" faces are.

YOU HAVEN'T SEEN THE REAL IMAGE OF YOUR FACE IN THE MIRROR

You have often looked into a mirror, of course. But you haven't seen the real image of your face yet. And this is why you couldn't see it. When you look into a mirror, you don't see your face as other people see it. You see a reversed image. If you close your left eye, your image closes its right eye. If you touch your right ear with your right hand, your image touches its left ear with its left hand. If you have two small mirrors, you can see your face as your friends see it. You hold the two mirrors at right angles to each other^* and look into them, as shown in the picture. After some practice you will be able to see the real image of your face. Now close your left eye and your image closes its left eye too. Touch your right ear with your right hand and your image touches its right ear with its right hand! This happens because each mirror reflects the image in the other mirror. So you see a reversed image of a reversed image, which, of course, is the same as the real image.

COLOUR THAT ISN'T THERE

To show this interesting phenomenon which scientists call "subjective colour"^* copy the circle which you see in the picture and put it on cardboard. Push a pin through the centre and turn it quickly. You will see many circles of different colours! Now change the direction and the order of colours will also change. A few years ago a television operator turned a large wheel of this sort, and people who were watching his programme saw the colours quite clearly on their black-and-white television screens.^* Scientists haven't yet agreed on what makes these colours appear.

^*  "subjective colour" — субъективно воспринимаемый цвет

^*   black-and-white television screen — черно-белый телевизионный экран

YOU CAN READ A SECRET LETTER FROM YOUR FRIEND

If you want to understand this secret letter which you have received from your friend, you must use a cylindrical glass stick.^* You hold the stick over the words of the letter near the page and read the letter through the glass stick. The glass stick shows you a reversed image of each letter. At the same time it helps you to see each letter right side up when your friend wrote it upside-down. So your friend and you must use the reversed letters which you see in the picture.

^*  a cylindrical glass stick — цилиндрическая стеклянная палочка

YOU CAN MAKE A STROBOSCOPE ^*

A stroboscope is a device which cuts off light for a moment, then for another moment and so on^* many times. When you look through it at a thing which is moving, it seems to you that it is moving slower or that it stops. You can easily make a stroboscope if you cut eight long holes in a round piece of cardboard. Then you put a pin through the centre of your cardboard circle and push the pin into a small stick or pencil so that you can turn the cardboard in front of one eye, as shown in the picture.

Now look through the stroboscope at a thing when it is moving. The thing may be an electric fan or even your stroboscope when you see it in the mirror. You make the strobo-ьсоре turn faster and slower. It will seem to you that the thing at which you are looking has stopped moving, or that it is moving slowly in the same direction, or that it is moving slowly in the other direction. This is because you see the thing only from moment to moment. Between these moments you do not see how it moves. At the cinema you often see illusions of this sort. It happens because the camera takes pictures of things when they are moving in the same way, that is from moment to moment.

^*  a stroboscope — стробоскоп (Это оптический прибор, при помощи которого можно видеть предмет, совершающий какое-либо движение, неподвижным или движущимся замедленно.)

^*  and so on — и так далее

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