Reproduction of a page of Ibn Sahl's manuscript showing his discovery of the law of refraction (from Rashed, 1990).

Interpretation of Ibn Sahl's construction. If the ratio of lengths L₁ / L₂ is kept equal to n₁ / n₂ then the rays satisfy the law of sines, or Snell's law.

For the physician, see Ali ibn Sahl Rabban al-Tabari. Abu al-Hasan Ali ibn Sahl Rabban al-Tabari ( (c 838&ndashc 870 CE) was a Muslim hakim, For the poet, see Ibn Sahl of Sevilla.

Ibn Sahl (Abu Sa`d al-`Ala' ibn Sahl) (c. 940-1000) was an Arabian mathematician and optics engineer associated with the court of Baghdad. The araB gene Promoter is a bacterial promoter activated by e L-arabinose binding A mathematician is a person whose primary area of study and research is the field of Mathematics. An engineer is a person professionally engaged in a field of Engineering. Baghdad (بغداد) is the Capital of Iraq and of Baghdad Governorate, with which it is also coterminous About 984 he wrote a treatise On Burning Mirrors and Lenses in which he set out his understanding of how curved mirrors and lenses bend and focus light. A curved mirror is a Mirror with a curved reflective surface which may be either convex (bulging outward or concave (bulging inward A lens is an optical device with perfect or approximate Axial symmetry which transmits and refracts Light, converging or diverging Ibn Sahl is credited with first discovering the law of refraction, usually called Snell's law. Refraction is the change in direction of a Wave due to a change in its Speed. In Optics and Physics, Snell's law (also known as Descartes' law or the law of refraction) is a formula used to describe the relationship ^[1][2] He used the law of refraction to work out the shapes of lenses that focus light with no geometric aberrations, known as anaclastic lenses. An aspheric lens or asphere is a lens whose surfaces have a profile that is neither a portion of a Sphere nor of a circular cylinder.

In the reproduction of the figure from Ibn Sahl's manuscript, the critical part is the right-angled triangle. A triangle is one of the basic Shapes of Geometry: a Polygon with three corners or vertices and three sides or edges which are Line 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. A hypotenuse is the longest side of a Right triangle, the side opposite of the Right angle. In Optics, a ray is an idealized narrow Beam of light. Rays are used to model the propagation of Light through an optical system by dividing the real light In Optics, a ray is an idealized narrow Beam of light. Rays are used to model the propagation of Light through an optical system by dividing the real light In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating ^[3] According to Rashed,^[2] the ratio of the length of the smaller hypotenuse to the larger is the reciprocal of the refractive index of the crystal. The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium

The lower part of the figure shows a representation of a plano-convex lens (at the right) and its 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 focal point on the axis at the left. Track listing Child – 516 All I Need – 355

In the remaining parts of the treatise, Ibn Sahl dealt with parabolic mirrors, ellipsoidal mirrors, biconvex lenses, and techniques for drawing hyperbolic arcs. A parabolic reflector (or dish or mirror) is a Parabola -shaped reflective device used to collect or distribute Energy such as A lens is an optical device with perfect or approximate Axial symmetry which transmits and refracts Light, converging or diverging

Ibn Sahl's treatise was used by Ibn al-Haitham (965–1039), one of the greatest Arabic scholars of optics. TemplateInfobox Muslim scholars --> ( Arabic: ابو علی، حسن بن حسن بن هيثم Latinized In modern times, Rashed found the manuscript to have been dispersed over two libraries. He reassembled it, translated it, and published it. ^[4]

See also

• History of optics
• Islamic science
• List of Arab scientists and scholars
• The Miracle of Light - a UNESCO article on the history of optics

References