Ibn Sahl (full name: Abū Saʿd al-ʿAlāʾ ibn Sahl Persian: ابوسعدالعلاءِبن سعل (ابن سهل); c. 940–1000) was a Persian[2][3][4][5] mathematician and physicist of the Islamic Golden Age,[6] associated with the Buyid court of Baghdad.
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's Optics, and as such an important precursor to the Book of Optics by Ibn Al-Haytham (Alhazen), written some thirty years later.
[9][10][11] Ibn Sahl uses this law to derive lens shapes that focus light with no geometric aberrations, known as anaclastic lenses.
Ibn Sahl designed convex lenses that focus light rays that are parallel, which can cause an object to burn at a specific distance.
Reproduction of Millī MS 867 fol. 7r, showing his
discovery of the law of refraction
(from Rashed, 1990). 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.
Interpretation of Ibn Sahl's construction. If the ratio of lengths
is kept equal to
then the rays satisfy the law of sines, or Snell's law. The inner
hypotenuse
of the right-angled triangle 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 change of medium whose face is vertical at the point where the two hypotenuses intersect. The ratio of the length of the smaller hypotenuse to the larger is the ratio of the refractive indices of the media.
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