By Ian Crossland at minds.com
At the University of Oxford in England, a bell contiues to ring (though inaudibly behind glass) after 175 years of activity. The bell, known as the Oxford Electric Bell, consists of two brass bells, each located beneath a dry pile (a type of battery). A metal ball, or clapper, sits between the bells. It bounces into one bell where it is electrostatically charged and repelled, bouncing into the other bell. This process repeats at an oscillating frequency of 2 Hertz.
The real mystery behind the bell is the battery; no one knows what they’re made of. They are coated with molten sulphur to prevent effects from atmospheric moisture, that much is known, but the inner workings are still a mystery. The most common guess is that they are Zamboni piles, made of thin zinc and silver discs with paper, stacked and compressed tightly.
http://en.wikipedia.org/wiki/Oxford_Electric_Bell
http://www.techworm.net/2015/01/battery-boosting-bell-last-175-years-yet-know-one-knows.html
Image credit: http://en.wikipedia.org/wiki/File:Oxford_Electric_Bell.jpg
What frequency is the bell ringing.. What tone does it make.
For how long does it vibrate?