Diagram of a fancy clepsydra, this type being an automaton or self-adjusting machine. Water enters and raises the figure, which points at the current hour for the day. Spillover water operates a series of gears that rotates a cylinder so that hour lengths are appropriate for today's date. The ancient greeks and romans had twelve hours from sunrise to sunset; since summer days are longer than winter days, summer hours were longer than winter hours. Date: 1819.
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