James R. Voelkel. The Composition of Kepler's Astronomia nova.

Princeton: Princeton University Press, 2001. xx + 308 pp. index. illus. bibl. $49.50. ISBN: 0-691-00738-1.

James Voelkel's main purpose in The Composition of Kepler's Astronomia nova is to show that argument of the Astronomia nova was constructed in response to the harsh reception Kepler knew his ideas would receive. Kepler faced two main challenges to the reception of his work. He needed to prevent Tycho Brahe's heirs from censoring his results, and he needed to convince contemporary astronomers that his revolutionary blending of physics and astronomy was not only methodologically sound but the only means of improving astronomy. As a result, the wandering rhetorical style of the Astronomia nova should not be taken as a confessional description of discovery. Rather, the Astronomia nova was carefully written to persuade his audience that all approaches other than Kepler's own lead to intractable problems. Voelkel accomplishes his goal admirably.

The Composition of Kepler's Astronomia nova is divided into two parts. The first part deals with the composition and reception of Kepler's first book, the Mysterium cosmographicum (first published in 1596). The primary thesis in the Mysterium cosmographicum is that God created the (Copernican) universe to express the five platonic solids (the cube, tetrahedron, octahedron, icosahedron, and dodecahedron). This thesis takes up the bulk of the Mysterium cosmographicum, with a few chapters near the end of the book devoted to an attempt to explain planetary motion physically. Voelkel provides considerable evidence from Kepler's correspondences that Kepler's physical arguments were of more interest to him than the structure of the Mysterium cosmographicum suggests. Not only did the authorities at Tubingen University constrain the content to make the work more mathematically than physically oriented, but Kepler's otherwise supportive teacher and mentor, Michael Maestlin, had little sympathy for Kepler's physical arguments.

After providing the reader with the necessary background astronomical theory (chap. 1), Voelkel opens his discussion of the Mysterium cosmographicum in chapter 2 with an examination of the remaining fragments of a disputation Kepler wrote while a student at Tubingen University. Kepler was not yet an accomplished astronomer at this time, but even then we see several important precursors to his mature astronomical theory. In particular, we see that Kepler made the then-unusual move of comparing celestial and terrestrial physics. In the third chapter Voelkel focuses on Kepler's physical arguments in the Mysterium cosmographicum. The fourth chapter examines the reception of the Mysterium cosmographicum, with a very interesting discussion of the warnings Kepler received against providing a physical/ realist interpretation of the Copernican system.

The second part of Voelkel's book is on the composition of the Astronomia nova. In the fifth and sixth chapters Voelkel shows that while Tycho Brahe disapproved of Kepler's physical approach to astronomy, Brahe's death gave Kepler considerably more freedom to pursue his physical arguments. Nonetheless, Kepler's work was still constrained. As Voelkel argues in chapter 7, "[t]he very existence of that work [the Astronomia nova] and its unusual rhetorical structure are artefacts of Kepler's bitter struggle with Tycho's heirs to exploit his legacy" (143). Kepler was accused of sloth by one of Tycho's heirs, Franz Gansneb Tengnagel van Kamp, and the state of Kepler's research allowed him to quickly produce the Astronomia nova and the Astronomia pars Optica as a response (two of the most important scientific works of the seventeenth century). To avoid censorship by Tengnagel, "Kepler had to plan to present himself as blameless for overthrowing Tycho's legacy. It is from this that the apparently aimless narrative of the Astronomia nova ultimately derived" (151-52).

Voelkel also explores the more amicable interactions between Kepler and David Fabricius, an astronomer with whom Kepler shared his discoveries. This correspondence explains part of the character of the Astronomia nova because Fabricius provided Kepler with an indication of the points of resistance to his arguments. Voelkel argues that many of the arguments Kepler gave in the Astronomia nova were direct responses to Fabricius' queries.

Overall Voelkers book is an exceptional and important contribution to history of science studies. In addition to supplying a framework for understanding an important and difficult astronomical work, he provides an extremely detailed study of Kepler's valuable correspondences.

RHONDA MARTENS 

University of Manitoba