Al-Hassan Ibn Al- Haytham
Al-Hassan ibn al-Haytham
The Arabian physicist, starwatcher, and mathematician al-Hassan ibn al-Haytham or Alhazen, established the theory of vision that prevailed till the 17th century. He also defended a theory of the physical reality world models.
Al-Hassan was born at Basra in southern Iraq, where he must have received all his education. He gained enough fame for his knowledge of physics in his youth that he was called to Egypt by the Fatimid ruler al-Hakim to attempt to regulate the flow of the Nile. Failing in this effort, he was disgraced and established himself as a copyist of mathematical documents there still exists in Istanbul a ...view middle of the document...
This problem al-Hassan takes up again in on the light of the moon, in which he disproves the ancient model that the moon reflects the sun's light like a mirror. Rather he believes that the moon is a self-illuminating body because each point on its surface broadcasts light rays in all directions, whereas each point on the surface of a mirror reflects a light ray from a single source (here the sun) in only one direction. However, he further believes that the eye receives two primary impressions in the act of vision light and color. Therefore he concludes that only some physical effect of the sun's light rays on the moon renders the latter's color (and thereby it’s light) visible. This explanation opens the possibility of integration, for the element of which the heavenly bodies are constituted is now seen to be, though qualitatively unchangeable as Aristotle insisted, yet subject to some quantitative change which renders their light visible when they are struck by the sun's light.
Work in optics
Al-Hassan’s greatest scientific achievements were in the field of optics. In the discussion of the nature of vision at the beginning of optics, he argues that light physically affects the eye, citing the pain experienced by looking directly at the Sun and the after image experienced by staring at fire and then looking into a weakly illuminated place. From this he argues that the assumption of emission of visual rays from the eye utilized by mathematical opticians, though convenient for their geometric analysis, must be physically wrong. Light rays rather proceed from the visible object to the eye and are always accompanied by color.
These mixed rays of light and color issue in all directions from a visible object, whether it is self-illuminating or an illuminated nontransparent body. They are professed when the object lies in the visual field of the eye, each point on the surface of the visible object emitting a ray...