Egidius of Baisiu's theory of pinhole images (Q1203014)

The problem of pinhole images has intrigued many Medieval and Renaissance scientists. Among the first are Bacon, Witelo, and Pecham, and the latter are Kepler and Maurolicco. They all wished to know why does the sun produce circular image after passing through angular apertures? A partial solution was offered by Ibn al-Haytham (Latin Alhazen d.c. 1040), and was limited to the analysis of the image of a solar eclipse through a circular opening only. Ibn al-Haytham's analysis, however, was apparently unknown in the Latin sources. The article under consideration is a study of an important Latin text in which such a problem is raised. The text, preserved in an early fourteenth-century copy, in the Jagiellonian Library in Cracow, Ms. 569, is unfortunately incomplete. The medieval author of the text is Brother Egidius of Baisiu, who apparently lived towards the end of the thirteenth century early fourteenth. This article offers an edition of the text of Brother Egidius, an English translation, and a commentary, in which it is demonstrated that Brother Egidius knew at least of Ibn al-Haytham's Opus, al-Manāẓir (Optics), although he may not have known of the more specialized treatment of the pinhole problem by the same author. The author concludes by speculating that if the full text of Brother Egidius were even to be found, we would probably have a medieval solution of the problem of pinhole images much along the same lines later followed by Kepler and others. In light of the abundance of copies of Pecham's Perspectiva and its commentaries, in which false solutions of the same problem are offered, one wonders with the author as to why the more correct solution of Brother Egidius was relegated to obscurity. The reference to Bacon's river which carries puffed up things and passes them through time while the weighty and solid things sink is of rhetorical interest only, and not of much historical value.