Franklin's Armonica

One of Benjamin Franklin many curious inventions was a musical instruments he called an armonica. Foot pedals rotated a series of glass bowls of graduated sizes, all kept moist by a trough of water in which the lower parts of each bowl were submerged. When a finger was touched to a spinning bowl, a clear musical tone resulted. The principal of the armonica is easily demonstrated with a glass of water. Now to make the music you get a cup of water then you move your fingers around on the top of the cup and then you should here music.

The reason this works is because your finger goes around the rim and when it does it was these tiny jerks, when it does that the glass will vibrate and you should hear just a violin bow.