book reviews Early Science and Medicine 21 (2016) 375-377 375

A. Mark Smith From Sight to Light: The Passage from Ancient to Modern Optics (Chicago: University of Chicago Press, 2015), pp. 480, $45.00 (cloth), ISBN 978 02 261 7476 1.

A. Mark Smith’s lucidly written account of the history of optics, from the an- cient world to the late seventeenth century, is comprehensive in scope and presents a radical break from the traditional narrative of the role medieval per- spectiva played in Johannes Kepler’s visual theory. Smith argues in a convinc- ing manner that while Kepler was clearly aware of perspectival sources, several elements of his thinking, and particularly his decision to accept the inverted retinal image as the principal means of sight, indicates a revolutionary turn away from the medieval tradition. This “Keplerian turn” had both analytic and epistemological elements, which Smith details at great length in his penulti- mate chapter. Smith characterizes his work as a “revamping” of David Lind- berg’s equally grand historical narrative Theories of Vision from Al-Kindi to Kepler, first published in 1976 (p. 4). In many ways this is an accurate assess- ment, barring Smith’s significant argumentative departure from the idea that Kepler relied on a firm grounding in perspectiva. Smith shifts his focus away from solely technical descriptions of optical theories, which can be found in Lindberg, and provides a much more inclusive history that treats the im­ portance of psychological and theological texts in the development of perspec- tiva. Smith begins his narrative by exploring the earliest roots of perspectiva in the ancient sources, particularly Plato, Aristotle, Galen, Euclid, and Ptolemy. He argues that Aristotle’s emphasis on explaining the psychological stages of vision, Galen’s physiological and anatomical explanation of vision, and the geometrical visual ray analysis of Euclid formed a highly sophisticated under- standing of sight. However, differences in these approaches led to a somewhat fragmented theoretical framework by the second century AD, with the most prominent disagreement occurring between proponents of intromission or ­extramission, i.e., whether sight occurred from light entering or visual rays ­issuing from the eye. Smith identifies Ptolemy’s “conceptual and methodologi- cal model” (p. 129), which unifies dispersed elements from his predecessors, as forming the basis for all subsequent optical investigations, both in the medi- eval Islamic world and the Latin West in the later Middle Ages and the Renais- sance. Smith next takes on some of the late Classical and early Arabic visual theo- ries. He shows that Neoplatonism and its offshoots, along with the commen- taries on Aristotle’s De anima in late Antiquity and the Islamic world, formed the core of a psychological understanding of optics that informed medieval perspectiva in important and distinctive ways. Particularly salient here is his ISSN 1383-7427 (print version) ISSN 1573-3823 (online version) ESM 4

©Early koninklijke Science brill and nv,Medicine leiden, 2016 | doi21 (2016) 375-377 10.1163/15733823-00214p11 A Journal for the Study of Science, Technology and Medicine in the Pre-modern Period 376 book reviews treatment of both John Philoponus’s visual theory and Augustine’s psychologi- cal model. Coupled with Avicenna’s model of the internal senses, Smith pro- vides us with several strands of the psychological, epistemological, and theological components of visual theory that later became influential in the perspectiva tradition. After providing an overview of some of the develop- ments in geometrical optics in the Islamic world, Smith turns his attention to Alhacen and his synthesizing Great Book on Optics. Smith rejects the idea that Alhacen “laid the foundations of modern optics on the ruins of its ancient, visual ray forerunner” (p. 224). Instead, he argues that Alhacen’s optical theory and analytic approach were built squarely upon a Ptolemaic model, and were not a revolutionary break from it. As Smith is primarily focused on the reception of Alhacen in the West, he misses the chance to show how Alhacen’s optical work related to his larger intellectual project, which includes his important astronomical work Doubts on Ptolemy. He also mentions that Alhacen’s attempt to synthesize visual ray theory with intromissionist accounts was by no means unique (as Philoponus and Avicenna had also done this). Having dethroned Alhacen from what Smith sees as an unwarranted historiographical pedestal, Smith turns to the recep- tion of Alhacen and other Islamic texts in medieval Europe. In his treatment of the reception of optical texts in the Latin West in the twelfth and thirteenth centuries, Smith stakes out a provocative position. Rather than treat the influx of Arabic and Greek scientific and philosophical texts as presenting a new and challenging body of work that medieval Latin scholars struggled to assimilate, Smith claims that Latin scholars were primed and prepped to absorb this new material within an extant optical tradition based on Calcidius’s commentary on the Timaeus, Seneca’s Natural Questions, Macrobius’s Saturnalia, and Saint Augustine. These sources were reworked by early medieval scholars such as the ninth-century John Scotus Eriugena in his Periphyseon and the early twelfth-century scholars Bernard Silvestris and ­William of Conches. This leads Smith to conclude that “Latin thinkers were fully prepared to understand and appreciate” (p. 241) sources such as Avicenna and Alhacen because they had developed a similar model of visual perception and cognition. It is certainly true that many historians have given short shrift to the state of learning in the Latin West prior to the Arabic and Greek transla- tions, but to say that their thinking was comparable to what the Arabs were doing in the same period is misleading and inaccurate. Smith admits that the development of perspectiva by Bacon, Pecham, and Witelo did not result in any technical or theoretical advances. The real ben- efit of the process of assimilation of Arabic texts came from Bacon’s “fusion” (p. 275) of Avicenna’s psychological model and Alhacen’s model of visual per- ception. For Smith, the psychological component was key to the perspectivists

Early Science and Medicine 21 (2016) 375-377