ALHAZENS NEGLECTED DISCOVERIES OF VISUAL PHENOMENA

The first three books of the Book of Optics written by Alhazen in Cair o in the eleventh century were translated into English by A I Sabra in 1989. Book I deals with optics, the structure of the eye, image forma tion in the eye, and with the visual pathways. This book inspired all other books on optics from the thirteenth to the seventeenth century a nd formed the basis upon which Kepler solved the problem of image form ation. However, Alhazen's work contained in Books II and III has been almost totally ignored. These two books contain an account of hundreds of observations and experiments carried out by Alhazen on a broad ran ge of topics which are now studied under the heading of visual percept ion. He clearly enunciated many of the fundamental principles which ar e credited to scientists living in the last two hundred years, includi ng a theory of unconscious inference; the law of equal innervation of the eye muscles; the principles of binocular direction; constancy of s ize, shape, and colour; induced visual motion; the vertical horopter; the fusional range of binocular disparity; and many others.