Steel Yard Clepsydra

Li Lan, Northern Wei dynasty, ca. 450 AD (replica)
Ancient Observatory Museum, Beijing

This is a closeup of the powering mechanism of a lever-arm water clock (clepsydra). Its operation depends on maintaining a drip siphon from the reservoir into the working bucket, whose descent raises a lever arm to tell the time. A float inside the reservoir allows the water to be taken from a constant level as it drains; this evens out the rate of the clock. See Chinese Astronomy for photos of the whole instrument.