ALHAZEN (Abu ’Ali al-Hasan ibn al-Hasan ibn al-Hajtam, Latin Alhacen)—a mathematician, physicist, and astronomer, b. 965 in Basra, d. 1038 in Cairo.

Alhazen spend most of his life in Egypt. He was associated with the Bayt al-Hikmah Institute (the School of Wisdom) which focussed on the mathematical and natural sciences and on producing translations and commentaries on the writings of Greek authors. He belonged to a secret religious and philosophical society called Ikhwan al-Safa’ (Brothers of Purity) whose purpose was to seek the truth, to work toward uniting all religions, and to create a universal philosophical system on the basis of science as it existed at the time.

The activities of the Brothers of Purity greatly influenced Alhazen’s work. He wrote around 100 scholarly works in different areas of knowledge (mathematics, physics, astronomy, and music). His works include a collection of astronomical observations, commentaries on Ptolemy’s Almagest, Euclid’s Elements, and Aristotle’s writings. His greatest achievement was his experiments and studies in optics culminating the work Kitab-al-menazir (Book of perspective). As early as the twelfth century, it was translated in Latin by Gerard of Cremona as De aspectibus or Perspectiva. The work was translated a second time by F. Risner in the sixteenth century under the title Optica thesaurus. His thought focussed on our sensory perception of the world (especially visual perception), the projection, reflection, and refraction of light (and the geometrical foundations of these phenomena), the construction of the eye, optical illusions, and the nature of light. Alhazen thought that the most perfect form of light is divine light (which every man receives at the moment of birth). Visible (or physical) light is a sign of divine light. Physical light constitutes form for corporeal substances. This work was very popular in the thirteenth century in the west and its theory of light influenced the views of R. Grosseteste, Witelo (Vitellio in Latin), and R. Bacon.

H. Bauer, Die Psychologie Alhazens, Mr 1911; A. Mrozek, Średniowieczna filozofia arabska [Mediaeval Arab philosophy], Wwa 1967, 95–103; J. Bielawski, Mały słownik kultury świata arabskiego [Small lexicon of the culture of the Arab world], Wwa 1971, 199.

Anna Z. Zmorzanka

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