Where Death Rings in the Hour: The Amazing Medieval Astronomical Clock of Prague
The technical sophistication of the Middle Ages tends to be underestimated. Near the end of the High Middle Ages, mechanical technology such as clocks and water mills, for example, were becoming quite advanced. A particularly impressive example of this technical skill is the astronomical clock at the old town hall in Prague, the modern-day capital of the Czech Republic. The clock was constructed in 1410 and contains dials which track the motion of the sun and moon through the year in both Central European Time and Old Czech Time. It also contains elaborate moving sculptures of various allegorical figures and the Twelve Apostles.
The Legend and Truth of the Clock’s Creation
According to a now discredited legend, the clock was built in the 15th century by a clockmaker by the name of Hanus. Hanus apparently made the clock and refused to tell the City Council of Prague how he had constructed it. When the city magistrates discovered that he had designed and planned to construct an even better clock for someone else, they were filled with jealousy and blinded him so that he would be unable to repeat his work. In revenge, Hanus is said to have broken the clock so that it could not be used until a hundred years later when someone was finally able to repair it.
But the real story of the clock was uncovered in the 1960s. It showed that the clock was built in 1410 by the clockmaker Mikulas of Kadan in collaboration with the astronomer and professor of Charles University, Jan Sindel. Since then it has broken many times, the first time being in 16th century, when it was repaired and improved by Jan Taborsky. It was in fact almost scrapped in the 1780s because the maintenance was too expensive. In 1865, it was renovated and a calendar dial was added to track feast days. It was damaged in 1945, as the Nazis retreated from Prague. This prompted it to be repaired again. After this repair, the clock was also changed from Old Czech Time to Central European Time.
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The Prague Astronomical Clock, c. 1791. ( Public Domain )
The Clock’s Dials and Sculptures
The clock as it exists today consists of two main dials, an astronomical dial and a calendar dial beneath it. The astronomical dial has a zodiac circle, a circle with Roman numerals, and then an outermost circle with Schwabacher numerals, a script that was prevalent in the Middle Ages. There are also gears with symbols for the sun and moon. The background of the dial has an inner blue circle and an outer circle.
The clocks dials. (jay8085/ CC BY 2.0 )
The outer circle is blue at the top and black near the bottom. The background is a depiction of the geocentric view of the universe prevalent at the time. The blue circle at the center is the earth and the outer circle is the sky above the city of Prague. The upper blue part of the circle represents the sky above the horizon and the lower black part represents the sky below the horizon. The sun is above the horizon when it is over the blue part and beneath the horizon when it is over the black part. The innermost ring contains the signs of the zodiac. The middle ring with Roman Numerals represents Central European Time, and the outermost ring represents Old Czech Time.
In addition to the dials, there are also several small sculptures surrounding the clock. These are representations of allegorical figures which include personifications of vanity, usury, lust, and death. The figure Death announces the passing of the hour by ringing a bell. Over the top of the two dials is a window where the Twelve Apostles appear in a precession every time the hour strikes. There are also figures of a philosopher, a chronicler, an astronomer, and an angel.
Some of the figures on the clock: Top – representations of vanity and usury ( CC BY SA 3.0 ) death and lust. ( CC BY SA 3.0 ) Bottom – the calendar portion of the clock with a philosopher, a chronicler, an astronomer, and an angel. ( CC BY SA 3.0 )
A Geocentric View
The clock was constructed over 130 years before the publication of On the Revolution of the Heavenly Spheres by Nicholas Copernicus and thus it presents a geocentric view of the universe. The clock did however represent the cutting edge of science and technology of its day. The clock makes use of the precession of the sun - where the sun, from the perspective of Earth, slowly moves along the ecliptic plane through the year with respect to the background stars. This is represented by the zodiacal circle on which the figure of the sun slowly moves through the same process of precession. It will be over different signs of the zodiac at different times depending on the month and year. The clock also makes use of the daily rotation of the earth which was perceived at the time to be the daily rotation of the celestial sphere. This is represented in the motions on the clock.