This Week's Experiment - #239 Reversing Flag

a computer paint program
or some paper and crayons

First you need a picture of an American flag. Not just any picture of a flag, but a very special one. We want a picture that has all of the wrong colors. Instead of red, white and blue, we want a flag that is green, black and yellow!

There are several ways to get this strange flag image. You can change a flag picture that you already have on your computer or draw your own, either with a computer drawing program, or with crayons or colored markers. You want the blue part of the flag to be yellow, the red part of the flag to be green and the white parts of the flag to be black.

Once you have this image, you are ready for the experiment. Stare at the center of the flag and try to keep your eyes from wandering. Keep staring at the flag for at least 20 seconds. The longer you stare, the better this will work. After staring for a while, then look at a blank piece of paper or a blank, white surface. You should see a glowing image of the American flag, in its proper colors.

How does this work? When you look at something that is blue, the blue light hitting the back of your eye releases a chemical that tells the nerves that you are seeing something blue. As you stare at the blue for a long time, these chemicals build up. Your eye gets "tired" of seeing blue and starts to ignore it. Once your eye starts to ignore some of the blue light, then you stare at a white sheet of paper. White light reflects from the paper and enters your eye. Your eye ignores the blue part, and sees a yellow afterimage instead. For each color that you stare at, you will see a different, reverse afterimage color.

You can do this with other images too. If you live outside the United States, try making a reverse image of your flag. An easy way to find out which colors to use for your reverse image is to stare at a normal picture of your flag. When you look at a blank, white surface, you will see a reverse color image. Now, make a picture of the flag with those colors and you will have a picture that will give you an afterimage in the true colors. If your flag has small details or if you try this with some other image, be prepared for the fact that small details do not work well. Your eye moves around too much as you are staring, and the details get blurred. You will get the best results with simple images, such as flags, rainbows (can you get all the colors?), etc.

I have even found that sometimes the same thing happens with food. After staring for a while at a plate containing a piece of chocolate cake, the image suddenly shifts to that of an empty plate, accompanied by a wonderful sensation in my mouth. This is an experiment that I highly recommend. In fact, I think I will go try it right now.

From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com

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