Al-Haytham (Alhazen) on refraction.

The following rules were derived by al-Haytham:

When the angle of incidence i increases, the angles of refraction r and deviation d increase; but this variation is greater for angles of incidence i than it is for the angles of deviation d. The ratio of the angle of deviation to the angle of incidence d/i increases as the angle of incidence i increases. For a refraction from a less dense to a denser medium, d<0.5i; conversely, for a refraction from a denser to a less dense medium, d<0.5(i+d). A less dense medium deflects the light further away from the normal n. A more dense medium deflects the light nearer to the normal n.

(quoted from Authier, 1995)

Reference

Authier, M. (1995) Refraction and Cartesian 'Forgetfulness'. In: M. Serres (editor): A History of Scientific Thought, Elements of a History of Science. Blackwell, Oxford, 315 - 343. (Translation of Éléments d'Histoire des Sciences, Bordas, Paris, 1989)

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