The main Movement
Between 1527 and 1530 Casper Brunner built the monumentaland artistic mechanisms, which controls the whole installation: the astronomical dial, both the large dials on the East and West fa’des, the hourly chime and the automata. We dare say that it is one of the greatest clock mechanisms ever builtand it has basically survived until the present day. The clock frame consists of a wrought-iron, late Gothicsupported construction, measuring 2.50 m in length, 1.70 m in depth and approx. 2.20 m in height. The whole mechanism contains 5 different gears: The main train with a pendulum (originally foliot), the quarter chime, the hourchime and two automata gears.
The five gears are driven by stone weights with a power reserve of about 28 hours. Therefore the weights with a total weightiness of 450 kg have to be pulled up every day.
The Astronomical Clock
The astronomical clock was first mentioned in the city accounts of 1444 when it had to be repainted. It therefore dates from the early 15th century and presumably belonged to the first original movement (soon after 1405). In 1530 Brunner took over the astronomical clock without making any major changes. We have a good idea of what it looked like in those days thanks to a contemporary painting, which is still extant (cf. fig. 4). A astrolabe type of dial is well cognised.
The twelvesome what arbitrarily arranged signs of the Zodiac can beclearly seen. Sun and moon orbit the zodiac, while a handindicates the hours on the outer edge of the dial (numberedin reverse order from I-XII). The lines on the planisphere indicate a southern stereographic projection. In the corners of the paintedborder, symbolic faces indicate the four winds. Above thedial the Roman deities Venus, Mars and Jupiter are paintedon the wall together with their attributes. The musical oriel is depicted on the right side of the dia.