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ID number:  BIRRC-P0009
Institution:  Research and Cultural Collections
Named collection:  Historic Physics Collection
Artist / Maker:  Bouron (as indicated on original record card)
Title / Object name:  Post Office Relay
Object type:  Electrical instrument
Materials:  Brass case with glass top (removed in photos) on wooden base
Measurements:  Diameter of base 13 cm, of brass case 7.5 cm, height 12 cm

Such relays were used at intervals along long-distance telegraph lines to boost signals that would otherwise not be strong enough to complete the distance. The incoming electrical pulse activates an electromagnet that operates a set of contacts, which then generate a new signal from a fresh battery. In this case the action, seen through the glass window, makes one contact just before breaking another.

Inscriptions / Translations:  On brass plate: GPO 45. Also engraved internally with a crown above 45

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