Used with
permission of Maiken Naylor, University at Buffalo, Buffalo, NY, USA,
http://ublib.buffalo.edu/libraries/units/sel/exhibits/stamps
Abu Ali al'Hasan ibn al'Haitam is known in the West as Alhazen, born 965 in Persia and dying in 1039 in Egypt. He is called the Father of Optics for his writings on and experiments with lenses, mirrors, refraction and reflection. He correctly stated that vision results from light that is reflected into the eye by an object, not emitted by the eye itself and then reflected back, as Aristotle believed. He solved the problem of finding the locus of points on a spherical mirror from which light will be reflected to an observer. From his studies of refraction he determined that the atmosphere has a definite height, and that twilight is caused by refraction of solar radiation from beneath the horizon. The optical diagram on this Pakistani commemorative in blue, green and black is hard to decipher because of the lack of contrast.