Snell’s law of refraction

Snell’s Law was discovered by various investigators over the centuries. In antiquity, optics began when Egyptians and Mesopotamians developed the first lenses with impressive mechanism based on reflection. Perhaps the first person to understand the basic relationship expressed by Snell’s Law was the Arabian mathematician Ibn Sahl in the year 984.

Abu Sa’d al-Ala Ibn Sahl 

Based on catoptrics and the study of burning mirrors and lenses, Abu Sa’d al-Ala Ibn Sahl (940-1000) devised a systemic elaboration of the fundamentals of dioptrics.

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.

Snellius Willebrord

In 1621, Snellius Willebrord discovered the law. It expresses the relationship between the path of a ray of light passing through the boundary of two adjacent substances and their respective refractive indices.  His unpublished notes on the subject were discovered by the Dutch scholar and manuscript collector Isaac Vossius around 1662.

Christiaan Huygens read unpublished equation by Snell and discussed the law in his Dioptrica, published in 1703.
Snell’s law of refraction

Ibn al-Haytham's Book of Optics

Book of Optics (Kitāb al-Manāẓir‎  in Arabic) was written in 1021 by Ibn al-Haytham in 1021. The book was first use of controlled experiments and reproducibility of its results.

The Book was translated into Latin around 1200. It was first printed in Latin in 1572 under the title Opticae Thesaurus Alhazeni Arabis Libri Septum by F. Risner.

Ibn al-Haytham was born in Basra in about 965 AD and died in Cairo in about 1040, In his autobiography he lists ninety-two of his own works, more than sixty of which have survive.

Ibn al-Haytham work reveals not only its revolutionary nature but also its comprehensiveness, touching all the known branches of optics.

The Optics of Ibn al-Haytham is the first authoritative work opposing the theory of Euclid, Ptolemy and other ancients that eye sends out rays of light and impinges on external things to view objects.

Ibn al-Haytham firmly rejected the emanation theory of vision and described how rays of light enters the eye from sources of light and from objects that reflects and refract light.

Ibn Haytham’s legacy in optics left a profound impression in the works of medieval scholars including Roger Bacon, John Pecham and Witelo and found conceptual prolongations an creative applications in the works of Renaissance artist and theorist such as Leon Battista Alberti, Lorenzo Ghiberti and Egnazio Danti.

Ibn-Haytham was aware of the structure of the eye form the view point of a physician as well as a physicist. Many anatomical names of the various parts of the eye that are used today are translations from the Arabic names given by Ibn al-Haytham in his Book of Optics.
Ibn al-Haytham's Book of Optics