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Ibn al-Haytham - First ScientistChapter Five - Page 2
Ibn al-Haytham left no record of what he did for the years that al-Qifti says he was under house arrest. If, as al-Qifti says, al-Hakim took away Ibn al-Haytham’s possessions, the Iraqi scholar would not have had any of the books he brought to Egypt. As a result, he would not have been able to write his long-deferred commentary on the Almagest or commentaries on any other books. If he was not allowed to go outside, he would not have been able to observe enough of the night sky to write about astronomy. He would, however, have been able to watch the sky lighten at dawn, observe shafts of sunlight cut through his room in the afternoon, and ponder the light given off by an oil lamp in the evening. It is possible that Ibn al-Haytham realized how to conduct “true demonstrations relating to all objects of vision,” as he describes his task in The Book of Optics, during his long imprisonment. If his guards allowed him to have writing materials, he may have written some or all of The Book of Optics during his confinement in Cairo. Ibn al-Haytham begins The Book of Optics by discussing the two theories of vision that had been circulating since the time of the ancient Greeks. The first theory, advanced by Aristotle and his followers, whom Ibn al-Haytham calls “the physicists”—states that “vision is effected by a form which comes from the visible object to the eye.” The second theory, primarily advanced by Ptolemy and Euclid, whom Ibn al-Haytham calls “the mathematicians,” states that “vision is effected by a ray which issues from the eye to the visible object.” “These two notions,” Ibn al-Haytham wrote, “appear to diverge and contradict one another if taken at face value.” He continues:
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