Ibn Sahl

Abu Sad al -Ala ibn Sahl, shortly Ibn Sahl (Arabic ابن سهل, أبو سعد العلاء, DMG Ibn Sahl, Abū Sa ʿ d al - ʿ Alā ʾ; * 940, † 1000 ), was a Persian mathematician and physicist, who in Baghdad had the time of flowering of Islam during the Abbasid Caliphate.

To 984 he wrote a treatise On Burning Mirrors and glasses, which contains the first known correct form of the law of refraction ( see right ). [ The date is derived from the dedication to the Buyids ruler Samsam -o- Dowleh, who reigned 983-987 in Baghdad. ]

Ibn Sahl's treatise was used by Ibn al - Haytham, but then fell into oblivion. The law was rediscovered in the 17th century by Thomas Harriot, Willibrord van Roijen Snell and Descartes and is now known as Snell's Law.

Only in 1990 succeeded the historian Roshdi Rashed to reconstruct the treatise of two custody in Damascus and Tehran fragments.