This two-volume set is a continuation of A. Mark Smith's pub. of Ibn al-Haytham's "De aspectibus," the most important treatise on optics of the Middle Ages, indeed, the most important treatise prior to the 17th century. This ed. of Alhacen's text will appeal to those who are interested in medieval scientific developments, but also to others for whom the study of optics, in particular, forms part of the cultural development of the later Middle Ages. The understanding of vision continues to gain importance in the historiography of intellectual life in this period, & Prof. Smith's work will be an important contribution to this scholarship. His translation of the Latin text accurately represents a challenging & technical original. Illustrations.