Trying Ursus: A Reappraisal of the Tycho-Ursus Priority Dispute

Abstract

1. INTRODUCTIONThe late sixteenth century is one of the most interesting and exciting periods in the history of astronomy. It is a period of both and transition, as Richard Jarrell has appropriately described it: consolidation of the mathematical techniques of Copernicus and transition from the purely mathematical account of planetary motions to a wider discussion of the actual nature of the universe.1 During the years following the publication of Copernicus's De revolutionibus in 1543, the most important developments in astronomy and cosmology took place in Northern Europe, particularly in Protestant Germany and Bohemia. Jarrell further classifies the serious practitioners of astronomy at the end of the century into three categories: loyal to the Ptolemaic order of the universe but willing to introduce Copernican mathematical techniques; those who had adopted some variation of the geo-heliocentric framework; and those who were confirmed Copernicans.2The humanistic educational reform initiated by Philip Melanchthon encouraged the study of mathematics and astronomy, and the University of Wittenberg became a sort of Mecca for the mathematical astronomers of the time. It was the place where Georg Rheticus, Copernicus's only direct disciple, had taught, and it became the place where Copernican astronomy was most seriously and thoroughly studied. Among those young astronomers who undertook the pilgrimage to Wittenberg was Tycho Brahe (1546-1601). But it was in Bohemia where the latter's encounter and subsequent brief period of collaboration with Johannes Kepler (1571-1630) took place. This was certainly one of the most significant events in the history of astronomy, for it involved an unprecedented fusion of theory and observation: Kepler was one of the ablest mathematicians in Europe and Tycho certainly the best observational astronomer.For our present purposes, what interests us is that both Tycho and Kepler came to work together under the patronage of Emperor Rudolph ? in Prague and, at the same time, both men worked under the shadow of a third character: Nicolaus Reimers Baer (1551-1600), also known by his Latin nickname of Ursus ('The Bear), who had been the former Imperial Mathematician, a post in which first Tycho and then Kepler were to succeed him. During the last decade of the sixteenth century, Tycho and Ursus became engaged in a fierce and bitter priority dispute over the invention of the geo-heliocentric system of the world, a compromise between Ptolemaic geocentrism and Copernican heliocentrism, and Kepler, who worked for Tycho, was also reluctantly drawn into it.Shortly after Tycho's first diagram of the geo-heliocentric system appeared in print, Ursus published a book of his own, containing a very similar cosmological arrangement. When Tycho learned about it, he accused Ursus of having stolen the system from him in a visit the latter made to Uraniborg, his observatory on the island of Hven. Tycho initially aired his accusation only in private correspondence, but when he decided to publish a selection of his letters, the matter went public. When Ursus in turn found himself labelled a plagiarist in print, he decided to respond, and he did so by publishing a second book attacking Tycho's claims to priority and originality in the discovery of the geo-hehocentric system, and also attacking him personally. As a result, Tycho decided to take legal action against Ursus, on the grounds of plagiarism and defamation. When arrangements were being made for the upcoming trial, and relevant circumstantial evidence was being gathered by Tycho, Ursus died, so the trial never took place. Nonetheless, Tycho persevered in his pursuit of Ursus beyond the grave. Now that the author was gone, the enemy was his book, so Tycho launched a campaign against Ursus's book and also planned to publish a volume of his own containing all the relevant documents, with the aim of settling matters forever: establishing his priority, restoring his honour and reputation, and refuting Ursus's claims. …