The Coin That Comes Into View
This very simple experiment open people’s eyes. Take a bowl that you cannot see through, i.e., it must not be made of glass. Place a coin inside it, on the bottom; but place it up against the side so that it is just out of view. Now, whatever you do, do not move the position of your eyes. While in this position, get some one to pour water into the bowl. They must pour gently, because the experiment is spoiled if the coin is moved.
Note carefully what happens. As the water rises in the bowl, the coin slowly comes into view; although it has not moved in the slightest. Why is this? It is due to the fact that the rays of light are bent when they pass from one medium to another-here the light passes from air to water. The reason is that the refraction of air and of water are not the same.