EXHIBITS > The clocks of the ancient Greeks >
The ''anaphoric'' clock
A cam disc - on which a drawing represents the sky and the zodiac cycle – is rotated behind a bronze grid. The grid consists of 7 homocentric circles defining the month intervals and 24 curved rods defining the hours according to the "hour – month" diagram ("analemma"). The movement is achieved through a pulley and a flexible chain with a counterweight and a float weight which is lowered or lifted through the isochronous (=equal time) descent or ascent of the water level. This isochronous descent or ascent is assured because of the isochronous water outflow through a self-regulated controller of the constant level of the Ktesibios type.
Every day a pointer is located successively on the corresponding one of the 365 holes of the disc periphery, which define the days of the zodiac signs, and marks the 12 daily and 12 nocturnal non-isochronous hours according to the season.
SOURCES (about all clocks): "Vitrouvius, On arcgitecture, IX", "Ptolemy, About anallemma-Astronomica, Apotelesmatica", "Hipparchus, Των Αράτου και Ευδόξου φαινομένων εξήγησις", "Pap. Oxy. 470. 31-85", "Diodorus of Sicily, History", "Αthenaeus, Philosofers at dinner", "Diogenes Laertius, Lives of eminent Philosophers", "Strabon, Geography", "Apollonius, Conics", "Pliny the Elder, Natural history", "Sharon Gibbs, Greek and Roman sundials", "D. G. Price, Portable sundials in antiquity", "Herman Diels, Antike Technik", "Astronomic measuring instraments, Οικονόμου-Νικολαντωνάκης-Νίτσιου"