The Oxford Electric Bell or Clarendon Dry Pile is located in the foyer of the Clarendon Laboratory at the University of Oxford. It was set up in 1840 and has rung almost continually after that. As of 2008^[update], it was still ringing, though nearly inaudibly due to muffling of the device.

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 4mm 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.

Probably the most interesting part of the bell is the pair of dry piles. Nobody is certain what they are composed of, 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.

Although devices of this sort can now be considered to be a novelty, at one point they 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.

[edit] See also

• Pitch drop experiment
• Beverly Clock

[edit] References

• Willem Hackmann, "The Enigma of Volta's "Contact Tension" and the Development of the "Dry Pile"", appearing in Nuova Voltiana: Studies on Volta and His Times Volume 3 (Fabio Bevilacqua; Lucio Frenonese (Editors)), (2000) pp. 103-119
• "Exhibit 1 - The Clarendon Dry Pile". Oxford Physics Teaching, History Archive. Retrieved on 2008-01-18.