There are two striking aspects of Measuring Shadows by Raz Chen-Morris. Although this is a book about optics and light, why are we considering shadows? And why do we need a new book about Kepler? The first question is answered explicitly by Chen-Morris as he directs our attention to Kepler’s new technique for bringing scientific rigor—measurement—to light, which is a phenomenon inherently not measureable directly by observation. As Chen-Morris describes the unfolding of a new optics for the Copernican world, he shows how a startling new notion is spread throughout Ad Vitellionem Paralipomena, Quibus Astronomiae Pars Optica Traditur: you can only account for physical motions through artificially produced shadows and reflections. Chen-Morris examines how this plays out both in practical observational terms and epistemologically. The context for Kepler’s innovation in redefining requirements for measuring and supplying a new context for the study of light and vision, astronomy, and optics answers the second question of why another book about Kepler: this is a new reading of Kepler’s innovation.
Chen-Morris begins with a historiographical consideration of Kepler’s particular role in the development of the science of optics. The modern reader sees a shifting and increasingly diverse and multilayered tapestry of historical studies that lead to a deeper understanding of not just Kepler’s publication (in this case Ad Vitellionem Paralipomena) but indeed of Kepler’s thought processes—the emotional, philosophical, and social context for his work. Chen-Morris calls on the humanist literature, art, religion, and politics of Kepler’s world to fill out this picture, and his book takes its place among those richly delineated examinations of this period.
The key terms that emerge throughout this book are motion, measurement, and artificial. With the important shift that came with Copernicus, sensory experience failed to account for inherently invisible motions. Ad Vitellionem Paralipomena itself is a mix of tradition and innovation, and Chen-Morris sees Kepler as examining the different traditional interpretations and concepts, and then turning them “on their head” (5). In a traditional reading of Kepler, his innovation is seen as describing planetary orbits as ellipses and the eye as an instrument (a camera obscura) where an inverted image is traced on the retina. However, Chen-Morris sees Kepler’s innovation as a radical break with tradition, as Kepler develops a new language and new basis for optics. Measuring Shadows frames the fundamental problem of how to measure or investigate phenomena not immediately accessible by sense. Kepler breaks with earlier traditions that posit a direct connection between the object of sense and sense itself and takes on the question of how we examine what we cannot see. Kepler began his study by following up on Tycho’s instrument program, but ended up with the need to redefine the language of observation and the ontological status of geometry itself. Kepler’s solution to the problem he encountered involved redefining geometry in terms of possible paths of motion, and concluding that geometry is innate—originating with God’s creation of mind.
Chen-Morris provides a dynamic analysis of Kepler’s internal struggles with traditional optical solutions. Kepler’s thought processes seen in the context of a new conception of reading requires a new thinking about early modern natural philosophy, especially a reexamination of the exact definition of a reenvisioned mathematics and its role in the new science. Kepler was acknowledged as a mentor and inspiration by early modern natural philosophers, but Chen-Morris shows modern readers that we need to reexamine what those scientists actually read in Kepler’s work.
In Measuring Shadows Chen-Morris expands on his earlier research and deepens the understanding of Kepler’s whole program with his multilayered presentation. By filling out these descriptions of Kepler’s innovation he develops a rich and nuanced image of Kepler’s late Renaissance world—full of the interconnections of art, philosophy, mathematics, and politics. The story holds together in general, but sometimes it is difficult to understand the underlying thread, which itself is multilayered and complex—much like Kepler and Ad Vitellionem Paralipomena itself. The picture Chen-Morris paints is important because it fills out the world within which the later Scientific Revolution could emerge, and presents new questions to ask about later developments in optics and natural philosophy.
