Lines of Influence in Thirteenth-Century Optics: Bacon, Witelo, and Pecham

Abstract

HISTORIANS of mediaeval optics have devoted a large measure of their effort to the work of three men who wrote on optics in the second half of the thirteenth centuryRoger Bacon, Witelo, and John Pecham. Such an emphasis is not without justification: not only were they the ones who, under the influence of Alhazen's Perspectiva, produced the great thirteenth-century synthesis of optical knowledge, but it was chiefly through the dissemination of their works in manuscripts and printed editions that this optical knowledge was transmitted to subsequent generations. Because Bacon, Witelo, and Pecham all composed their optical works within a period of two decades or less (a relatively short period of time by mediaeval standards of communication), the question of influence is unavoidably raised. Not only is this question pertinent to the history of mediaeval optics, but the alleged influence of o-ne upon another has been used as a basis for generalizations regarding the course of thirteenth-century science in general;1 it is therefore of considerable importance to examine all the available evidence and decide who really influenced whom. To many historians, it has appeared that the lines of influence linking Bacon, Witelo, and Pecham can be easily determined from elementary considerations. Since it has been generally agreed that Bacon wrote his principal optical works before Witelo and Pecham wrote theirs, it has seemed self-evident that Witelo and Pecham read and were influenced by Bacon's works. To complete the picture, Witelo is explicitly cited in printed editions of Pecham's Perspectiva communis.2 But unfortunately, the problem of influence cannot be so easily resolved. In the first place, Bacon's works on optics were composed in partial secrecy and forwarded to the Papal court with little immediate circulation, and it cannot be assumed, without a comparison of doctrines and a study of the mechanics of transmission, that they were read by anybody. Secondly, the citations to Witelo appearing in printed versions of Pecham's Perspectiva communis are spurious, having been inserted into the 1542 (Nuremberg) edition by its editor, Georg Hartmann, and reprinted in subsequent editions.3 It is thus apparent that the question of influence must be reopened.