|Abu Sa’d al-Ala Ibn Sahl|
It is believed that Ibn Sahl established a principle akin to the so-called ‘Snell’s Law’ of refraction. Ibn Sahl shows that every transparent medium, including the ‘celestial sphere’ has a certain degree of opacity.
Ibn Sahl described a law of refraction in his treatise ‘On burning mirrors and lenses.’
In 1602, English astronomer and mathematician Thomas Harriot discovered the law but he did not publish his work.
Christiaan Huygens read unpublished equation by Snell and discussed the law in his Dioptrica, published in 1703.
Snell’s law of refraction