The theory of Pinhole images in the fourteenth century

Abstract

Toward the end of the thirteenth century, pinhole images were elevated to the status of un probleme celebre by the work of Roger Bacon, Witelo, and John Pecham. Earlier authors had commented on the remarkable ability of noncircular apertures to produce circular images of the sun, but little had been made of the fact. Bacon, however, wrote a sizable treatise on burning mirrors, one fourth of which he devoted to pinhole images and their implications for theories of the propagation of light. Witelo considered the problem of pinhole images in six propositions of his Perspectiva. Pecham devoted the longest proposition of his Perspectiva communis and sections of his Tractatus de perspectiva and De sphera to the same problem.1 The theory of pinhole images continued to occupy a position of considerable importance in the fourteenth century. The two most significant optical treatises of the century, the Questiones super perspectivam by Henry of Langenstein and the work of the same title by Blasius of Parma, each devote a full question to pinhole images. Earlier in the century, Egidius of Baisiu and Levi ben Gerson also dealt with the problem.2 The problem of pinhole images attracted so much attention in the thirteenth century because it posed a fundamental optical problem. At least since Euclid, the principle of rectilinear propagation of light had served as the foundation for an elaborate superstructure of geometrical optics. Although physical, physiological, and even psychological matters frequently intrude, a glance at almost any optical treatise written before the fourteenth century3 immediately reveals that geometrical elements predominate. Yet the phenomena of pinhole images seemed to cast doubt on the rectilinear propagation of light and thereby on the entire optical