Adjustable spark gap, early 19th century.


Adjustable spark gap, early 19th century. This instrument consists essentially of two brass balls. The lower one is supported on an insulated blue glass pillar; the upper one can be held at the required height above it by a catch. The catch can be released to let the upper ball make contact with the lower one. Either ball could be earthed while the other was charged.

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King George III
Object Number:
brass, glass and mahogany
spark gaps
King's College, London

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