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English: A replica of an ancient Chinese Siesmograph from Eastern Han Dynasty (25-220 CE)
This picture was taken in July 2004 from an exhibition at Chabot Space & Science Centre in Oakland California.
The plaque of the exhibit said:

Detecting a Quake

In 132 CE, after several serious earthquakes in China, astronomer Zhang Heng invented this instrument to warn people of the next one. When the ground shook, it moved a pendulum inside the jug. The pendulum pushed a lever that opened one dragon's mouth. A ball rolled out and into the toad's mouth below, sounding an alarm. The open dragon mouth pointed in the direction of the earthquake, notifying the Emperor.
Français : Réplique d'un ancienne Sismographe (chine orientale, Dynastie des Han (25-220 après JC) ; Photo prise en Juillet 2004, lors d'une exposition au Chabot Space & Science Centre à Oakland en Californie. Selon la légende affichée près de l'oeuvre, :
Sismographe ; En 132 Après JC,, après plusieurs graves tremblements de terre en Chine, l'astronome Zhang Heng a inventé cet instrument pour avertir les gens qu'un séisme était en cours ou en préparation. Quand la terre tremblait, même faiblement, un pendule suspendu au couvercle bougeait à l'intérieur du vase. Le pendule poussait un des levier ouvrant la bouche d'un des dragons. Une bille placée dans la bouche du dragon tombait alors dans celle du crapaud ci-dessous, donnant l'alarme. La seule bouche ouverte dragon donnait la direction du tremblement de terre, qui était notifié à l'empereur


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