en>RobertHannah89: /* See also */

2012-09-04T12:36:27Z

See also

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	~~Hello!~~ <br>~~My name~~ is ~~Leopoldo~~ and I'~~m a 18 years old girl from Cagno~~.<br><br>~~my website~~ - ~~Fifa 15 Coin Generator~~, [http://~~Beautyvalley~~.cc/?~~document_srl~~=~~933445 Beautyvalley~~.Cc],		[[File:Ibn Sahl manuscript.jpg\|thumbnail\|275px\|Reproduction of a page of Ibn Sahl's manuscript showing his discovery of the law of refraction (from Rashed, 1990).]]
			[[File:Ibn Sahl.svg\|right\|thumb\|275px\|Interpretation of Ibn Sahl's construction. If the ratio of lengths <math>L_1/L_2</math> is kept equal to <math>n_1/n_2</math> then the rays satisfy the law of sines, or Snell's law.]]

			{{about\|the physicist\|the physician\|Ali ibn Sahl Rabban al-Tabari\|the poet\|Ibn Sahl of Sevilla}}

			'''Ibn Sahl''' ({{lang-ar\|ابن سهل}}) ('''Abu Saʿd al-ʿAlaʾ ibn Sahl ''') ({{lang-ar\|أبو سعد العلاء ابن سهل}}) (c. 940–1000) was a [[Muslim]] [[Persia\|Persian]] [[Islamic mathematics\|mathematician]], [[Islamic physics\|physicist]] and [[optics]] [[Inventions in the Islamic world\|engineer]] of the [[Islamic Golden Age]] associated with the [[Abbasid]] court of [[Baghdad]]. Ibn Sahl's 984<ref>{{cite journal\|last=Zghal\|first=Mourad\|coauthors=''et al.''\|date=2007\|title=The first steps for learning optics: Ibn Sahl's, Al- Haytham's and Young's works on refraction as typical examples\|journal=The Education and Training in Optics and Photonics Conference\|publisher=International Commission for Optics\|pages=3\|url=http://spie.org/etop/2007/etop07fundamentalsII.pdf\|accessdate=20 June 2011}}</ref> treatise ''On Burning Mirrors and Lenses'' sets out his understanding of how [[curved mirror]]s and [[lens (optics)\|lenses]] bend and focus light. Ibn Sahl is credited with first discovering the law of [[refraction]], usually called [[Snell's law]].<ref>K. B. Wolf, "Geometry and dynamics in refracting systems", ''European Journal of Physics'' '''16''', p. 14-20, 1995.</ref><ref name=rashed90>R. Rashed, "A pioneer in anaclastics: Ibn Sahl on burning mirrors and lenses", ''[[Isis (journal)\|Isis]]'' '''81''', p. 464–491, 1990.</ref> He used the law of refraction to derive lens shapes that focus light with no geometric aberrations, known as [[anaclastic lens]]es.

			In the reproduction of the figure from Ibn Sahl's manuscript, the critical part is the right-angled [[triangle]]. The inner [[hypotenuse]] shows the path of an [[incident ray]] and the outer hypotenuse shows an extension of the path of the [[refracted ray]] if the incident ray met a [[crystal]] whose face is vertical at the point where the two hypotenuses intersect.<ref>Kurt Bernardo Wolf, ''Geometric Optics on Phase Space'', p. 9, Springer, 2004, ISBN 3-540-22039-9 [http://books.google.com/books?vid=ISBN3540220399&id=KmpCDg-D39gC&pg=PA8&lpg=PA8&ots=NJM71aAIlg&dq=%22ibn+sahl%22&sig=USHa-lMN4NCsoQrr5qNM0_4fr1A#PPA9,M1 online]</ref> According to Roshdi Rashed,<ref name=rashed90/> an author and historian of medieval science and mathematics, the ratio of the length of the smaller hypotenuse to the larger is the [[Multiplicative inverse\|reciprocal]] of the [[refractive index]] of the crystal.

			The lower part of the figure shows a representation of a [[plano-convex lens]] (at the right) and its [[Optical axis\|principal axis]] (the intersecting horizontal line). The curvature of the convex part of the lens brings all rays parallel to the horizontal axis (and approaching the lens from the right) to a [[Focus (optics)\|focal point]] on the axis at the left.

			In the remaining parts of the treatise, Ibn Sahl dealt with [[parabolic mirror]]s, [[ellipsoidal mirror]]s, [[biconvex lens]]es, and techniques for drawing [[hyperbolic arc]]s.

			Ibn Sahl's treatise was used by [[Ibn al-Haitham]] (965–1039), one of the greatest Arab scholars of optics. In modern times, Rashed found the text to have been dispersed in manuscripts in two different libraries, one in Teheran, and the other in Damascus. He reassembled the surviving portions, translated and published them.<ref>Rashed, R., ''Géométrie et dioptrique au Xe siècle: Ibn Sahl, al-Quhi et Ibn al-Haytham.'' Paris: Les Belles Lettres, 1993.</ref>

			==See also==
			*[[History of optics]]
			*[[Islamic science]]
			*[[List of Persian scientists and scholars]]

			==References==
			{{reflist}}

			==External links==
			*{{cite encyclopedia \| editor=Thomas Hockey et al \| last=Berggren \| first=Len \| title=Ibn Sahl: Abū Saʿd al‐ʿAlāʾ ibn Sahl \| encyclopedia=The Biographical Encyclopedia of Astronomers \| publisher=Springer \| year=2007 \| location=New York \| page=567 \| url=http://islamsci.mcgill.ca/RASI/BEA/Ibn_Sahl_BEA.htm \| isbn=978-0-387-31022-0}} ([http://islamsci.mcgill.ca/RASI/BEA/Ibn_Sahl_BEA.pdf PDF version])
			*[http://unesdoc.unesco.org/images/0014/001412/141236E.pdf The Miracle of Light – a UNESCO article on the history of optics]

			{{Islamic mathematics}}

			{{DEFAULTSORT:Sahl}}
			[[Category:Medieval Persian mathematicians]]
			[[Category:Medieval Iraqi mathematicians]]
			[[Category:10th-century mathematicians]]
			[[Category:Mathematicians of medieval Islam]]
			[[Category:Medieval physicists]]
			[[Category:10th-century Iranian people]]

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