Kepler boiler (measuring device)

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Kepler boiler (Ulmer Kessel) from 1627 in the Museum Ulm.

The Kepler kettle (Ulmer kettle) is a measurement of the Ulmer measures hundredweight ( measure of weight), bucket (measure of content, especially for wine), cubit (measure of length, especially for canvas), shoe (measure of length) and Ime (measure of content, especially for grain), which the astronomer Johannes Kepler designed during his stay in Ulm 1626–1627 for the printing of the Rudolfinische Tafeln on behalf of the city council. Until 1626 there was a problem in Ulm that different original dimensions were used for calibration and calibration , which led to considerable problems with accounting in the trade.

Kepler recommended the manufacture of a cylindrical vessel that combines the exact units of length, space and weight and relates them geometrically and arithmetically to one another. Although the simpler decimal system was already known at that time, Kepler did without it, because that would have meant too much interference in the conventional units. In general, the changes should be as small as possible, taking into account the many trade relationships in Ulm and the acceptance of ordinary citizens.

The vessel should be constructed in such a way that it combines all common Ulm dimensions and makes it legible. Its inside diameter of 1 cubit (= 0.6 m) and an inside depth of 2 shoes (1 shoe = 0.292 m) results in a content of 1 bucket (= 164.6 l), which is filled with water (specific weight = 1 , 0) corresponds to 3½ quintals (1 quintal = 47.03 kg). If you fill the calibration vessel 64 times, you get 90 Ime (1 Ime = 117.08 l). (All information is approximate within the scope of the manufacturing accuracy at the time.)

In the early summer of 1627, Hans Braun was commissioned with the difficult task of making the vessel. The vessel was cast in bronze according to Kepler's exact specifications and received as the only ornament four feet and handles with four birds of prey heads designed as griffin claws. Its empty weight corresponds to 3½ quintals the weight of a filling with water.

A circumferential inscription in verse provides information about the use of the vessel (beginning with a small rosette, colons in the inscription mark the end of the first and the continuation in the second line): 

zwen schuch mein tieffe ein eln mein quer • ein geeichter aimer macht mich lehr • dan sind mir vierthalb centner bliben • vol donauw wasser :
: wege ich siben • doch lieber mich mit kernen euch • und vierund sechzig mal abstreich • so bistu neinzig ime reich • gos mich hans braun 1627

(Note: "fourth half" earlier for 3½, see hammer) . Originally, Kepler's intention for the inscription was a seven-line line in the rhyme scheme aa - bb - ccc in four-part iambic meter ; this was changed when the cauldron was made, but the superscripts in the text of the inscription still refer to it.

The special thing about the vessel is that Kepler succeeded in embodying five dimensions in one object and thus creating a universal original dimension for calibration.

After completion, the vessel was moved to the still-preserved wheelhouse at the Weinhaus. It was used when it came to checking the smaller calibration vessels and dimensions used for everyday use. According to a reference by M. Dieterich (Description of the City of Ulm, 1825, p. 65f.), The “Kepler Kessel” was set up on the first floor of the town hall by the early 19th century at the latest. It is not known when exactly the boiler got there. Via the association for art and antiquity, founded in 1841, it finally came to the Ulm Museum, where it can be admired in the city history department as a unique cultural and historical testimony. A replica of the boiler is in the Kepler Museum in Weil der Stadt , the birthplace of Johannes Kepler.

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  • Franz Hammer: Johannes Kepler's Ulm Year. The Rudolphinische Tafeln and the Ulm Kessel. in: Ulm and Upper Swabia. History and Art Journal. Announcements from the Association for Art and Antiquity in Ulm and Oberschwaben, 34 (1955), pp. 76 - 86
  • Hans-Joachim Albinus, Detlef Suckrau: Reminiscences of Johannes Kepler's stay in Ulm 1626–1627. New, strange and unsolved puzzles. Ulm and Oberschwaben, Vol. 61 (2019), pp. 175-211 (Chapter 2 on the Ulmer Kessel)
  • Johannes Kepler: All the poems. Edited and commented by Friedrich Seck . Translated by Monika Balzert (Spudasmata 180). Olms, Hildesheim, 2018 (No. 60 on the Ulmer Kessel)
  • Archives of the city of Ulm
  • Ulm City Museum
  • Kepler Museum Because of the city
  • Major works from the Ulm Museum of the Keplerkessel on Ulm.de