1. V. Ronchi: The Nature of Light: An Historical Survey (Heinemann, London 1970)
2. Plato: Timaeus (Bobbs-Merrill, Indianapolis 1959) p. 117
3. D. C. Lindberg: The Beginnings of Western Science: The European Scientific Tradition in Philosphical, Religious, and Institutional Context, 600 B.C. to A.D. 1450 (Univ. Chicago Press, Chicago 1992) p. 455
4. D. Park: The Fire Within the Eye: A Historical Essay on the Nature and Meaning of Light (Princeton Univ. Press, Princeton 1997)
5. D. C. Lindberg: Studies in the History of Medieval Optics (Variorum Reprints, London 1983)