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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',...
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