Science Projects And Inventions

Put a hand over an eye. Now stare at the centre of the smudge on the left. After a few seconds the smudge will mysteriously disappear.

Now repeat the same exercise with the smudge on the right. The circle prevents the smudge from vanishing. The reason is not understood.

HOW DOES IT WORK?

If you stare at anything long enough, the light sensing cells of the eyes become tired- They tend to "shut off" temporarily. If you move the eye slightly the cells are refreshed. Your stare wavers slightly between the smudge and the circle surrounding it and your eyes are refreshed and that is what keeps the smudge from disappearing.