al-Jazari's "Book of Knowledge of Ingenious Mechanical Devices": The Castle Water Clock

This painting illustrates an elaborate clock that works by a series of reservoirs, floats, and pulleys that a servant must adjust every twelve hours. The clock is charmingly redundant, indicating the passage of time in numerous ways. Every hour of the day, a figure emerges from one of the twelve doorways in the arcade below the zodiacal signs, and the two falcons on the sides come out and drop balls from their beaks. Hourly during the night, one of the twelve roundels of the lower arch lights up. At the sixth, ninth, and twelfth hours, the musicians play their instruments. In addition, the disk at the top rotates so that, every two hours, one sign of the zodiac appears and another disappears.