Sfere solide e cielo fluido: Momenti del dibattito cosmologico nella seconda meta del Cinquecento.
Milan: Guerini e Associati, 2002. Pbk. xiv + 312 pp. append. [euro]36.50. ISBN: 88-8335-344-7.
In 1588 astronomical and cosmological thought in Europe was still dominated by Aristotle and Ptolemy. Although Copernicus had provided a new heliocentric system of the world in 1543, the dominant interpretation of his work in Northern Europe was developed by the students and colleagues of Philipp Melanchthon at the University of Wittenberg. The most important Wittenberg astronomers, Erasmus Reinhold and his successor Caspar Peucer, adopted Copernicus's mathematical models but developed physical and theological arguments against heliocentrism.
The young Tycho Brahe became convinced that the received cosmology was defective after observing the nova of 1572 and the comet of 1577. The nova demonstrated that change occurred in Aristotle's supposedly changeless celestial realm. The comet moved in a way that would carry it through the supposedly impenetrable shells of aether that carried celestial objects. Unable to countenance the motion of the earth because of arguments like those developed by Reinhold and Peucer, Brahe developed an alternative cosmology in which the moon and sun traveled around a stationary, central earth, but the motions of the other planets were centered on the sun.
Brahe delayed public presentation of his new system for nearly ten years. He was using Copernican dimensions that required the orbs carrying the sun and the planet Mars to intersect, a physical impossibility while he remained committed to celestial spheres. The intervention of Christoph Rothmann, court astronomer to Wilhelm IV, the Landgrave of Hesse, seems to have been crucial in persuading Brahe to replace planetary spheres with a continuous celestial fluid. After reading Rothmann's arguments in a book about the another comet that appeared in 1585, Brahe publicly announced his new system in 1588. But by then several other people had similar ideas. The development of Brahe's system and the parallel work of Giordano Bruno, Helisaeus Roslin and Nicolai Reymers (better known as Ursus), formed the subject of Granada's last book El debate cosmologico en 1588 (Naples, 1996). In his new book he focuses more specifically on Christoph Rothmann.
In comparison to Brahe's achievements, astronomy at the court of Wilhelm IV in Kassel has received little attention. But Wilhelm had instituted a program of systematic observation well before Brahe, using instruments of similar design if less heroic scale. Indeed Brahe visited Kassel in 1575, just before founding his own observatory on the island of Hven, and may have derived the design of some of his own instruments from those he saw in use there. Toward the end of the decade, at the same time that Brahe was establishing Hven, the Landgrave recruited Christopher Rothmann from Wittenberg in the role of mathematicus.
In Kassel, Rothmann wrote several complete books on astronomy and related matters, but these remained in manuscript, with the sole exception of his book on the 1585 comet, which was published posthumously by Snel in 1619. In this book Rothmann borrowed arguments from Ioannes Pena, a mathematician from the Paris circle of Petrus Ramus active in the 1550s, to establish that the substance of the heavens was fluid, as the Stoics taught, and not solid, as Aristotelians believed. Granada examines Pena and Ramus in an opening chapter and goes on to consider other aspects of Rothmann's historical influence. The next chapter examines letters exchanged between the Landgrave and Rothmann prior to the publication of his book on the 1585 comet. Granada goes on to consider Rothmann's deployment of a standard sixteenth-century doctrine on the relationship between science and religion, the position known as accommodationism. Rothmann's views are of particular interest as one of the first serious defenders of Copernican cosmology. Although he began his career as an orthodox Wittenberg astronomer, Rothmann defended Copernican cosmology in an exchange of letters, subsequently published by Brahe in 1596. In a section of the unpublished Observationum stellarum fixarum, discussed here by Granada, Rothmann developed detailed replies to Brahe's scriptural objections to Copernicanism. The next chapter returns to Pena and Ramus, linking them to Rothmann. After a brief examination of Ursus and Roslin, Granada concludes with a discussion of Rothmann's visit to Brahe in 1590.
Granada provocatively suggests that the rivalry between Kassel and Hven made Rothmann's visit tantamount to espionage, although another factor may have been Rothmann's medical needs. Tycho was also a famous alchemical physician, and Rothmann sought treatment for a painful and highly personal affliction. The outcome of the visit was unexpected; Rothmann failed to return to Kassel and resume his place at court. Perhaps he believed Brahe had cured him and refused to resume a public position opposing Brahe, out of gratitude. A newly discovered letter from Wilhelm to Rothmann in 1591 sheds some new light on the situation. Here Wilhelm employs German verbs that are properly used only for animals to describe Rothmann's eating and drinking habits. This is a grave insult and makes it clear that, whatever Rothmann's purposes in visiting Hven, his reasons for failing to return to Kassel included the loss of his patron's confidence, no later than the following year.
Granada's book is an important contribution to understanding the cosmological debates surrounding the introduction of Tycho's system and the parallel reception of Copernicanism. Also of special value to scholars are the extensive appendices which reproduce, in German, the 1585 correspondence between Rothmann and the Landgrave, an extract from Roslin's 1597 Tractatus Meteorastrologiphysicus on the origin of his version of the geo-heliocentric system, a partial transcription of the insulting letter from Wilhelm to Rothmann in 1591, and Rothmann's plea to Wilhelm's successor in 1597, seeking reinstatement; and, in Latin, the 1588 imperial license granted to Rothmann covering his intended astronomical publications, the chapter of his Observationum stellarum fixarum which makes use of accommodationism, the fifth chapter of Ursus's Fundamentum Astronomicum (1588) which contains his alternative to Tycho's system, and a series of letters on comets from Roslin to Michael Maestlin.
University of Oklahoma