A new light for optics: Ibn al-Haytham’s revolutionary theory

Ibn al-Haytham was an Arab philosopher of formidable talent and creativity. He lived at the end of the X century between Iraq and Egypt and is one of the best examples of the Middle-Age Arab scientists’ great sophistication. His Kitab al-Manzir (Book of Optics, 1010-1021) is a comprehensive treatise on the theories of vision and light, combining all the previous knowledge on the subject with a novel approach. The first chapters of the book inquire many optical facts with a detailed analysis based on repetition of experiments and inductive reasoning. One of these facts is whether light travels in straight rays and, to verify this statement, Ibn al-Haytham used a dark chamber – apparatus later made famous by Kepler. Moreover, he vindicated for the intromission theory of light, entailing the presence of light rays as independent entities.

Ibn al-Haytham’s book was revolutionary, not only for his improvement of optics’ experiments, or only due to his introduction of a new concept of induction based on mechanical repetitions. The novelty of his approach was especially due to his peculiar way of doing science, and to his profound consciousness on the fallibility of a human scientific enterprise based on sense data, as science is. Scientists must not rely on self-evident axioms, but should put them under test, inquiring their empirical consequences.

The book had a deep impression in Europe in his Latin translation, known as De Aspectibus, which became one of the principal source for optical writing produced in the second half of the XIII century by Bacon, Pecham and Witelo. However, due to a common historical phenomenon well summarized by the idiom traduttore tradittore, the differences between the Latin translation and the Arabic text are striking; for example, De Aspectibus lacks the first three chapters of the book. In these three chapters, Ibn al-Haytham summarizes the previous views of mathematicians and natural philosophers concerning vision, he states his own view on the nature of optical inquire and explains in detail the aim and methods of the book. Moreover, in the third chapter, on the properties of light, we find the description of several experiments using a dark chamber. It is therefore a very important part of the book: the Latin translation should be considered just as a truncated version of the story.

About the Author

Federico Forneris
Federico Forneris, PhD in Biochemistry and Structural Biology, is Principal Investigator of the Armenise-Harvard Laboratory of Structural Biology at the University of Pavia, Italy

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