Science Projects And Inventions

YOU  NEED:

• A page and a pencil

Call your friends. Take the pencil and put it horizontally on the line that connects from X and Y as in the illustration.

Your friends will maintain that the part of the grey rectangle below the pencil is a little darker than the portion of the rectangle above the pencil.

Now remove the pencil to show them that the grey area looks exactly the same right through the rectangle.

HOW  DOES  IT  WORK?

The subtle variation in the shades of grey does not register with the eyes. The eyes can distinguish it only when a pencil marks a spot halfway between the two grades.