Oxford Electric Bell

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The Oxford Electric Bell or Clarendon Dry Pile is located in the foyer of the Clarendon Laboratory at the University of Oxford. It was purchased by Robert Walker, who was Professor of Physics at Oxford from 1839 to 1865. The bell bears a label in his handwriting stating "Set up in 1840", though a later note indicates that it may have been constructed some 15 years earlier. As of 2006, it was still ringing, although inaudibly as it is muffled by its glass case.

The experiment consists of two brass bells, one each underneath a dry pile battery, the pair of batteries connected in series. A metal sphere about 4mm in diameter is suspended in between the batteries, and rings the bells by the action of electrostatic force. As the clapper touches one bell, it is charged by one battery, 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 batteries, or cells, have been able to last since the apparatus was set up. The frequency of its oscillation is about 2 Hz. As of 2006 the bells have been rung on the order of 10 billion times.

Probably the most interesting part of the bell is the set of batteries. Nobody is certain what they are made of, but it is known that they are coated with sulphur to prevent effects from atmospheric moisture. Records of similar popular curiosities of the period such as Zamboni piles indicate that they are probably of alternate layers of metal foil and paper coated with manganese dioxide.

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.

The Guinness Book of Records records it as the "world's most durable battery" delivering "ceaseless tintinnabulation".