Optics by Johannes Kepler

The Optics was a product of Kepler's most creative period. It began as an attempt to give astronomical optics a solid foundation, but soon transcended this narrow goal to become a complete reconstruction of the theory of light, the physiology of vision, and the mathematics of refraction. The result is a work of extraordinary breadth whose significance transcends most categories into which it might be placed. It gives us precious insight into Kepler's thought during this crucial period, an insight all the more valuable in that most of his working papers from that time have been lost. Second, it is the culmination of a long and rich tradition in the science of optics, in distinct contrast with the new optical thought represented by Descartes---though Descartes built on insights derived from Kepler's work. And third, it presents discoveries in the physiology of vision, photometry, and the geometry of conic sections which have become part of our intellectual heritage. Especially notable are Kepler's discovery of the inverted retinal image, his theoretical grounding of the inverse-square photometric law, and his insights into the relations between the various conic sections.

 Among the treasures the Optics contains are Kepler's theory of the metaphysics of light and other quasi-material powers, a substantial commentary on Aristotle's theory of light, a remarkable, though ultimately unsuccessful, theory of refraction, and a fascinating speculation about the half-hidden heliocentrism of Euclid's Optics. The sections on parallax and atmospheric refraction are ancillary to the New Astronomy, and are frequently referred to in that work.

 Unlike many other scientific works of the first rank, the Optics is for the most part sufficiently nontechnical to be accessible to nonspecialists. At the same time, it is interesting enough to attract the attention of the educated layman as well as scholars in a wide variety of fields.

 The translation is accompanied by extensive footnotes (not end notes). Nearly all the diagrams were drawn anew for this edition. The two exceptions are reproductions of Kepler's original illustrations, used where the sense of the text requires them. Kepler's original index has been retained, supplemented by a second index prepared by the translator.