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Ibn Sahl is credited with first discovering the law of refraction,

Abu Muhammad ibn Muhammad al-Ghazali (c. 1058–1111);  known as Al-Ghazali or Algazel to the Western medieval world, was a Muslim theologian, jurist, philosopher, and mystic of Persian descent.
Al-Ghazali has sometimes been referred to by historians as the single most influential Muslim after the Islamic prophet Muhammad. Others have cited his movement from science to faith as a detriment to Islamic scientific progress. Besides his work that successfully changed the course of Islamic philosophy—the early Islamic Neoplatonism developed on the grounds of Hellenistic philosophy, for example, was so successfully refuted by al-Ghazali that it never recovered—he also brought the orthodox Islam of his time in close contact with Sufism. The orthodox theologians still went their own way, and so did the mystics, but both developed a sense of mutual appreciation which ensured that no sweeping condemnation could be made by one for the practices of the other.
Ghazali was given the unique title of Hujjat al-Islam, meaning 'The Proof of Islam', a title given to no other scholar or personality in Islamic history, further displaying his status within the religion. Furthermore, he is known by some as being, "literally the man who saved Islam."

http://en.wikipedia.org/wiki/Al-Ghazali