1. Galileo Galilei: Discorsi e Dimostrazioni Matematiche intorno a due nuoue Scienze, (Elsevier, Leiden 1638). Translated as: Galileo Galilei: Dialogues Concerning Two New Sciences, ed. by H. Crew, A. de Salvio (Northwestern University Press, Evanston, Ill. 1950)
2. J. A. von Segner: De raritate Luminis (Göttingen 1740)
3. C. de la Tour: Ann. Chim. Phys. 12, 167 (1819)
4. C. Wheatstone: Phil. Trans., 1834, 583
5. C. Wheatstone: Phil. Mag. 6, 61 (1835)