ON WITELOS DIFFRACTION OF SUNLIGHT IN A CRYSTAL

Around the year 1270, Witelo, a son of 'Thuringians and Poles' who originated from Poland, diffracted beams of sunlight into colours in a transparent hexagonal crystal. The main goal of the current paper is to show the way in which Witelo systematically came closer to making his discovery, which took place at Viterbo, through proofs contained in Books Two and Ten of his major work entitled 'Perspectiva', written in 1271. The original Latin text of Witelo's optical discovery from the manuscript held at Cambridge, Emmanuel College Library 20, has been published in the journal 'Organon', 33 (2004), in the notes on pp. 76-80.