Seerah Ibn al-Haytham — Abu 'Ali al-Hasan ibn al-Hasan ibn al-Haytham al-Basri (965-1040 CE): The Physicist, Mathematician, and Astronomer Who Wrote Kitab al-Manazir (The Book of Optics — the Most Influential Work in the History of Optics), Overturned the Ancient Greek Intromission/Extramission Debate, Discovered the Principles of the Camera Obscura, Pioneered the Modern Scientific Method of Hypothesis-Testing-Experiment, and Whose Work Influenced Roger Bacon, Leonardo da Vinci, and Johannes Kepler

Seerah Ibn al-Haytham (سِيرَةُ ابنِ الهَيثَم; full name: Abu 'Ali al-Hasan ibn al-Hasan ibn al-Haytham al-Basri; known in the Latin West as Alhazen; born 354 AH / 965 CE in Basra [Iraq]; died 430 AH / 1040 CE in Cairo; he worked under Fatimid Egypt; career: he served as a minister in Basra; moved to Egypt under the Fatimid Caliph al-Hakim [r. 996-1021 CE]; the canal project and the feigned madness story: Ibn al-Haytham is reported to have proposed to al-Hakim that he could regulate the Nile's flooding by constructing a dam — a project he then realized was beyond the engineering of his time; fearing al-Hakim's notoriously unpredictable anger, he feigned madness and was placed under house arrest; during these years of house arrest [approximately 1011-1021 CE, until al-Hakim's death], he wrote his most important works; the Kitab al-Manazir [كِتَابُ المَنَاظِر — The Book of Optics]: completed approximately 1027 CE; 7 books; the most comprehensive and mathematically rigorous treatment of optics produced in the ancient and medieval world; contents: [1] the theory of vision: Ibn al-Haytham definitively overturned the Greek 'extramission' theory [Plato: the eye emits rays that touch objects] in favor of the 'intromission' theory [Aristotle's direction: light from objects enters the eye]; his crucial innovation: he gave a rigorous mathematical account of how intromission works — light enters from each point on an object; only the ray that enters the eye perpendicularly passes through without being refracted; this one-to-one correspondence of points explains how the eye sees a coherent image; [2] the anatomy and psychology of vision: the eye as an optical instrument; processing from the eye through to the optic nerve and brain; [3] reflection and mirrors: curved mirrors; parabolic mirrors; the burning mirror problem; [4] refraction: bending of light between media; atmospheric refraction [explaining the apparent flattening of the sun near the horizon]; [5] the camera obscura: Ibn al-Haytham gave the first detailed description and mathematical treatment of the pinhole camera [camera obscura]; the image formed is inverted; the principle underlies all subsequent lens-based imaging; the scientific method: Ibn al-Haytham's Kitab al-Manazir exemplifies a method that historians of science now recognize as strikingly modern: [1] begin with observed phenomena; [2] formulate a hypothesis; [3] design an experiment to test it; [4] conduct the experiment; [5] draw conclusions; [6] revise the hypothesis if the experiment contradicts it; this hypothetico-deductive method, applied systematically, predates Francis Bacon [1620] by 600 years; other works: [1] Maqala fi al-Dawr [on periodic motion]; [2] various astronomical treatises; [3] works on geometry [including studies of parabolas and burning mirrors]; [4] works on number theory; influence: translated into Latin as 'De Aspectibus' by an unknown 12th-century translator; fundamental to the optical work of Roger Bacon [1214-1292], John Peckham, Witelo, and later Johannes Kepler [who explained the retinal image in 1604 using Ibn al-Haytham's theory]; Leonardo da Vinci's drawing of the camera obscura draws on his account; Kepler's Paralipomena ad Vitellionem [1604] — the work that established modern optical theory — builds directly on Ibn al-Haytham; the Fatimid connection: Ibn al-Haytham worked in Fatimid Cairo during the reign of al-Hakim; the Fatimid court's intellectual environment — which also produced Ismaili thinkers like al-Kirmani and supported the Dar al-'Ilm [House of Knowledge in Cairo] — was the context for his most productive years; he was not himself an Ismaili but he worked in the Fatimid intellectual ecosystem) revolutionized how humans understand sight.