The “anaphoric” clock

Kostas Kotsanas

It was a brilliant hydraulic clock which indicated, with accuracy, the 365 different hours of the year. A cam disc – on which a drawing represented
the sky and the zodiac cycle – rotated behind a bronze grid. The grid consisted of 7 homocentric circles defining the month intervals and 24 curved rods defining the hours according to the “hour – month” diagram (“analemma”). The rotation of the disc was achieved through a pulley and a flexible chain
with a counterweight and a weight-float which was lowered or lifted through the isochronous (=equal time) descent or ascent of the water level. This isochronous descent or ascent was ensured by the isochronous water outflow
through a self-regulated controller of the constant level of the Ktesibios type.
Every day a pointer was placed successively on the corresponding one of the 365 holes of the disc periphery, which defined the days of the zodiac year, and marked the 12-day and 12-night non-isochronous hours according to the season.