ALHAZEN (ABU ALI AL-HASAN IBN ALHASAN), Arabian mathematician
of the 11th century, was born at Basra and died at Cairo in
1038. He is to be distinguished from another Alhazen who
translated Ptolemy's Almagest in the 10th 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, nevertheless,
a diligent and successful student, being 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. He taught,
previous to the Polish physicist Witelo, that vision does
not result from the emission of rays from the eye, and wrote
also on the refraction of light, especially on atmospheric
refraction, showing, e.g. the cause of morning and evening
twilight. He solved the problem of finding the point in a
convex mirror at which a ray coming from one given point shall
be reflected to another given point. His treatise on optics
was translated into Latin by Witelo (1270), and afterwards
published by F. Risner in 1572, with the title
Oticae thesaurus
Alhazeni libri VII., cum ejusdem libro de crepusculis et
nubium ascensionibus. This work enjoyed a great reputation
during the middle ages. Works on geometrical 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 Leiden.
See
Casiri, Bibl. Arab. Hisp. Escur.
J. E. Montucla,
Histoire des mathemaltiques (1758)
E. A. Sedillot,
Materiaux pour l'histoire des sciences mathematiques.
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