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The oldest and simplest way of treating light is in terms of geometrical optics, and, over the centuries, it has sufficed to explain most practical applications. Perhaps the first systematic and intensive studies were conducted by the Arab mathematician and optician Abu Ali Al-Hasan Ibn Al-Haytham (b.c. 965 Basra, Iraq; d. 1039 Cairo, Egypt), whose work has been commemorated on the Pakistani stamp shown on the cover. In his treatise translated into Latin in 1270, Alhazen, as he became known to medieval Europe, theorized on various issues in optics: reflection, refraction, mirrors and lenses, aberrations, rainbows, and atmospheric refraction. Most notably, he correctly deduced that light from the object seen comes to the eye.