https://en.wikipedia.org/wiki/Oxford_Electric_Bell
Oxford Electric Bell
From Wikipedia, the free encyclopedia
The Oxford Electric Bell or Clarendon Dry Pile is an experimental electric bell that was set up in 1840 and which has run almost

continuously ever since, apart from occasional short interruptions caused by high humidity. It was "one of the first pieces"

purchased for a collection of apparatus by clergyman and physicist Robert Walker. It is located in a corridor adjacent to the

foyer of the Clarendon Laboratory at the University of Oxford, England, and is still ringing, though inaudibly, because it is

behind two layers of glass.
Design
The experiment consists of two brass bells, each positioned beneath a dry pile (a form of battery), the pair of piles connected

in series. A metal sphere approximately 4 mm in diameter is suspended between the piles, and rings the bells by means of

electrostatic force. As the clapper touches one bell, it is charged by one pile, and then electrostatically repelled, being

attracted to the other bell. On hitting the other bell, the process repeats. The use of electrostatic forces means that while

high voltage is required to create motion, only a tiny amount of charge is carried from one bell to the other, which is why the

piles have been able to last since the apparatus was set up. Its oscillation frequency is 2 hertz.
The exact composition of the dry piles is unknown, but it is known that they have been coated with molten sulphur to prevent

effects from atmospheric moisture and it is thought that they may be Zamboni piles.
At one point this sort of device played an important role in distinguishing between two different theories of electrical action:

the theory of contact tension (an obsolete scientific theory based on then-prevailing electrostatic principles) and the theory of

chemical action.
The Oxford Electric Bell does not demonstrate perpetual motion. The bell will eventually stop when the dry piles are depleted of
charge if the clapper does not wear out first.
"Oxford Electric Bell" by LeoPanthera - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Oxford_Electric_Bell.jpg#mediaviewer/File:Oxford_Electric_Bell.jpg
"Oxford-electric-bell" by Nicolas1981 - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Oxford-electric-bell.svg#mediaviewer/File:Oxford-electric-bell.svg