ALHAZEN (al-hah'zen) [Aim ALI AL-HASAN IBN ALHA SAN], Arabian mathematician of the th centur, was born at Basra and died at Cairo in o38. He is to be distinguished from another Alhazen who translated Ptolemy's Almagest in the loth century. Having boasted that he could construct a machine for regulating the inundations of the Nile, he was summoned to Egypt by the caliph Hakim; but, aware of the impracticability of his scheme, and fearing the caliph's anger, he feigned madness until Hakim's death in 1021.
Alhazen was the first great discoverer in optics after the time of Ptolemy. According to Giovanni Battista della Porta, he first explained the apparent increase of heavenly bodies near the horizon, although Bacon gives the credit of this discovery to Ptolemy. His treatise on optics was translated into Latin by Witelo (127o), and afterwards published by F. Risner in 1572, with the title Opticae thesaurus Alhazeni libri V II ., cum ejusdem libro de crepusculis et nubium ascensionibus. Works on geomet rical subjects were found in the Bibliotheque nationale de Paris in 1834 by E. A. Sedillot ; other manuscripts are preserved in the Bodleian Library at Oxford and in the library of Leyden.