Ibn Sahl (full name: ''Abū Saʿd al-ʿAlāʾ ibn Sahl'' ; c. 940–1000) was a

Persian Persian may refer to: * People and things from Iran, historically called ''Persia'' in the English language ** Persians, the majority ethnic group in Iran, not to be conflated with the Iranic peoples ** Persian language, an Iranian language of the ...

mathematician and

physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate cau ...

of the

Islamic Golden Age The Islamic Golden Age was a period of scientific, economic, and cultural flourishing in the history of Islam, traditionally dated from the 8th century to the 13th century. This period is traditionally understood to have begun during the reign o ...

, associated with the

Buyid The Buyid dynasty or Buyid Empire was a Zaydi and later Twelver Shi'a dynasty of Daylamite origin. Founded by Imad al-Dawla, they mainly ruled over central and southern Iran and Iraq from 934 to 1062. Coupled with the rise of other Iranian dyna ...

court of

Baghdad Baghdad ( or ; , ) is the capital and List of largest cities of Iraq, largest city of Iraq, located along the Tigris in the central part of the country. With a population exceeding 7 million, it ranks among the List of largest cities in the A ...

. Nothing in his name allows us to glimpse his country of origin. He is known to have written an optical treatise around 984. The text of this treatise was reconstructed by Roshdi Rashed from two manuscripts (edited 1993).: Damascus, al-Ẓāhirīya MS 4871, 3 fols., and Tehran, Millī MS 867, 51 fols. The Tehran manuscript is much longer, but it is badly damaged, and the Damascus manuscript contains a section missing entirely from the Tehran manuscript. The Damascus manuscript has the title ''Fī al-'āla al-muḥriqa'' "On the burning instruments", the Tehran manuscript has a title added in a later hand ''Kitāb al-harrāqāt'' "The book of burners". Ibn Sahl is the first Muslim scholar known to have studied

Ptolemy Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...

's ''Optics'', and as such an important precursor to the ''

Book of Optics The ''Book of Optics'' (; or ''Perspectiva''; ) is a seven-volume treatise on optics and other fields of study composed by the medieval Arab scholar Ibn al-Haytham, known in the West as Alhazen or Alhacen (965–c. 1040 AD). The ''Book ...

'' by

Ibn Al-Haytham Ḥasan Ibn al-Haytham (Latinization of names, Latinized as Alhazen; ; full name ; ) was a medieval Mathematics in medieval Islam, mathematician, Astronomy in the medieval Islamic world, astronomer, and Physics in the medieval Islamic world, p ...

(Alhazen), written some thirty years later. Ibn Sahl dealt with the optical properties of

curved mirror A curved mirror is a mirror with a curved reflecting surface. The surface may be either ''convex'' (bulging outward) or ''concave'' (recessed inward). Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are ...

s and

lenses A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...

and has been described as the discoverer of the law of

refraction In physics, refraction is the redirection of a wave as it passes from one transmission medium, medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commo ...

(

Snell's law Snell's law (also known as the Snell–Descartes law, the ibn-Sahl law, and the law of refraction) is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing th ...

). Ibn Sahl uses this law to derive lens shapes that focus light with no geometric aberrations, known as anaclastic lenses. In the remaining parts of the treatise, Ibn Sahl dealt with parabolic mirrors, ellipsoidal mirrors, biconvex lenses, and techniques for drawing hyperbolic arcs. Ibn Sahl designed convex lenses that focus light rays that are parallel, which can cause an object to burn at a specific distance.

References

Sources

*Rashed, R. "A pioneer in anaclastics: Ibn Sahl on burning mirrors and lenses", ''

Isis Isis was a major goddess in ancient Egyptian religion whose worship spread throughout the Greco-Roman world. Isis was first mentioned in the Old Kingdom () as one of the main characters of the Osiris myth, in which she resurrects her sla ...

'' 81, pp. 464–491, 1990. *Rashed, R., ''Géométrie et dioptrique au Xe siècle: Ibn Sahl, al-Quhi et Ibn al-Haytham.'' Paris: Les Belles Lettres, 1993 * *
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* * {{DEFAULTSORT:Sahl Mathematicians under the Buyid dynasty 10th-century Iranian mathematicians Medieval physicists 10th-century Iranian scientists History of optics 1000 deaths

See also

References

Sources