Training the Intelligent Eye: Understanding Illustrations in Early Modern Astronomy Texts

Abstract

Throughout the early modern period, the most widely read astronomical textbooks were Johannes de Sacrobosco's De sphaera and the Theorica planetarum, ultimately in the new form introduced by Georg Peurbach. This essay argues that the images in these texts were intended to develop an "intelligent eye." Students were trained to transform representations of specific heavenly phenomena into moving mental images of the structure of the cosmos. Only by learning the techniques of mental visualization and manipulation could the student "see" in the mind's eye the structure and motions of the cosmos. While anyone could look up at the heavens, only those who had acquired the intelligent eye could comprehend the divinely created order of the universe. Further, the essay demonstrates that the visual program of the Sphaera and Theorica texts played a significant and hitherto unrecognized role in later scientific work. Copernicus, Galileo, and Kepler all utilized the same types of images in their own texts to explicate their ideas about the cosmos.

Sacrobosco’s Sphaera in Spain and Portugal

“…In his commentary on Sacrobosco's first book, Chaves explains the difference between an orb and a sphere and includes a picture of an orb whose concavity has a different center than its outer surface. This material was certainly not necessary for navigation, but it was an important prelude to a discussion of the structure of celestial orbs in the more advanced astronomy text by Georg Peuerbach, the New Theorica (Crowther and Barker 2013). Chaves wrote this in a period when European astronomers, including Spanish astronomers like Jerónimo Muñoz, were debating whether celestial orbs existed or not, and if they did, what their internal structure was (Barker 2011) (Chap.…”

A Lathe and the Material Sphaera: Astronomical Technique at the Origins of the Cosmographical Handbook

“…A culminating proposition in Sacrobosco observes how "Euclid imagined that a sphere is caused by the revolution of a semicircle firmly set on a chord, returned around to the place it started from." 25 The geometrical rudiments added to fifteenth-century manuscript and printed editions of the Sphaera suggest the effort 20 For a more detailed overview of the developments described in this paragraph, see (Baldasso 2007), and especially (Crowther and Barker 2013). 21 This edition, and many others from Venice and Paris up to 1500 also included the Theorica of Georg Peuerbach and the Contra Cremonensem of Johannes Regiomontanus.…”

“…ex parte ad scindendum secandumque fiat aptus, exurget instrumentum tornandis spheris (haud secus quam circinus circulis) aptissimum." 3 The scholarly framework here includes(Johnson 1953; Gingerich 1988 Gingerich , 1999Hamel 2004Hamel , 2006Hamel , 2014Pantin 2001 Pantin , 2012Crowther and Barker 2013;Oosterhoff 2015;Valleriani 2017). 4 On Francesco Capuano de Manfredonia's work concerning Sacrobosco's Sphaera see (Chap.…”

Fashioning Cosmology: Franco Burgersdijk as the Author of the Dutch Tractatus de sphaera

“…The change did not reflect in his booklet on De sphaera. 66 On illustrations of De sphaera, see (Crowther and Barker 2013;Gingerich 1999;Hamel 2014, 23-49). 67 Moving parts were first introduced by Joseph Klug in the Wittenberg edition of 1538 (Gingerich 1999, 215).…”