A Disappearing Coin
If you look at an object which has been placed in water, owing to the phenomenon of refraction, the article appears in a different position from that in which it really is.
It is due to this phenomenon, therefore, that a stick, when half plunged into water, seems to be bent or broken.
A very interesting experiment based on this principle is the following:—
Take a bowl full of water, and at the bottom place a coin. Next request one of your friends to lower his head until his eye, the edge of the bowl, and the near edge of the cent, appear to be in the same line.
As a matter of fact, it is not the coin itself that your friend can see, but only the image created by refraction.
Now, keeping your friend in the same position, inform him that you intend to make the coin disappear from his view.
To do this, remove some of the water from the bowl, which may be accomplished by means of a small syringe ([Fig. 9]).
Fig. 9.—The disappearing coin.