The following tricks depend on the viewer's eyes telling him lies. Our eyes and brains sometimes play tricks on us, and things are not always what they seem to be. We will describe a few of these effects so you can use them as tricks to show your friends.

You might tell your audience that you will hypnotize them into seeing strange things. Say a few nonsense words and wave your hands in front of you. Tell them that they are in your power!

The next few are called flip-flops. As you look at them they seem to change from one point of view to another.

TUNNEL FLIP-FLOP

Tell a story. When the Holland Tunnel was built under the Hudson River, teams of workmen started on both sides of the river. They built strong rings of steel, one next to the other. They did this until they met in the middle, under the river. Here is a picture of rings. Look at it. Are you looking through it from New York to New Jersey, or from New Jersey to New York?

THE LONG AND SHORT OF IT

Show this drawing to your audience, and ask them to pick out the shorter and the longer lines. Ask them if any two lines are equal in length.

Line AB and BC are the same length.

You can make a similar drawing very easily. Draw lines AB and BC exactly the same length. Then connect A to C, and draw the other lines in somewhat the same shape as shown, putting point D way off to the right, so that the right part of the drawing is much larger than the left part. Now BC looks even longer than AB. This is a good illusion.

MAGIC BOOMERANG

Following are two sets of curved pieces. A looks smaller than B and 1 looks smaller than 2, but actually A and B are the same size and so are 1 and 2. Copy these and cut them out carefully. Reverse their positions, putting B above A and 2 above 1. Now their sizes seem to have been reversed too. The upper one always looks smaller.

Illustration A

Illustration B

Illustration 1

Illustration 2

You might tell a story. Say that these are copies of Australian boomerangs which are now on display in natural history museums. When they are thrown into the air and picked up again, their sizes have been changed. Then lay them down in reversed positions so your audience can see that they have indeed changed size.

MAGIC HEXAGON

A regular hexagon is a six-sided figure where all the sides are of the same length. This is an illustration of a regular hexagon with straight lines connecting all the points. But is it? As you look at it, it flip-flops to an illustration of a cube, a transparent box. It becomes a box similar to the one in the illustration next to it.

MAGIC BOX

This is a magic box similar to the one which flip-flops from the magic hexagon. As you look at this transparent box it flip-flops into any of the six boxes shown on the page.

The Magic Box

There seems to be no good explanation why these things flip-flop. Possibly the brain can see all the possibilities. But it can focus on only one at a time.

CORINTH CANAL

Two bridges cross a canal at different points. One is high, at ground level, and the other is low, at water level.

Is the AB bridge shorter or longer than the CD bridge? Try to guess and then measure each bridge.

THE IMPOSSIBLE FORK

This is an impossible fork because you can't eat with it. Nobody can make one. In fact, you can hardly look at it without getting dizzy.

If you hide the tips of the prongs with your fingers, you will see two prongs. If you hold your fingers over the base of the prongs you will see three prongs.

Tell your audience that when they get dizzy looking at it, they should lie down and close their eyes.

MAGIC STAIRCASE

This is another flip-flop illusion. The staircase first seems to be normal, going up to the right. As you look at it, it seems to flop and turn upside down.

You might tell a story of people trying to build a stairway into the sky. But they were never successful. As they climbed up, the staircase would flip over and they would fall off.

MAGIC PILE OF BOXES

This is a famous illusion which is frequently used to illustrate flip-flops.

As you look at it you sometimes see eight blocks; and sometimes, as you stare, it changes to seven blocks. Apparently our brains can handle only one view at a time, just as in the tunnel and other flip-flops shown in this book.