Avicenna, Abū ʿAlī al-Ḥusayn ibn ʿAbd Allāh ibn Sīnā
Iran’s Abu ‘Ali al-Husayn ibn ‘Abd Allah ibn Sina (Latinized name: Avicenna) was a Persian polymath and probably the most influential natural philosopher in all of Islamic history . He He was born around 980 AD near Bukhara (present-day Uzbekistan) and died in Hamadan (Iran). Already at the age of 16, famous physicians worked under his direction, and at the age of 18, Ibn Sina mastered the contemporary knowledge of the various sciences . His massive Qanun fi-‘l-tibb (Canon of Medicine) would be the main medical text in the East and West until the seventeenth century.
The Kitab al-Shifa (The cure [of ignorance]) is an equally immense four-part encyclopedia on mathematics, physics, and metaphysics [3, 4]. For several centuries this would be the main text on Aristotelian natural philosophy. Here, Ibn Sina displayed his Aristotelian sympathies mainly by refuting alternative theories. For theories on light and color, this meant that Ibn Sina rejected the so-called extramission theories advocated by Ptolemy and Euclid. Ibn Sina gave good arguments why it is absurd to assume that vision occurs by visual rays emerging from the eye. Instead, Ibn Sina explained vision in terms of forms transmitted from the visible object to the eye (i.e., by intromission). In this respect, he followed Aristotle just like Ibn Rushd . It would be Ibn al-Haytham, a contemporary of Ibn Sina, who would formulate a successful fusion of the optical theories of Ptolemy, Euclid, Galen, and Aristotle. It would be an intromission theory.
… the fact that white gradually passes to black by three paths. The first is via pale […], at first it progresses to pale, from there to grey, and continuing in this manner until black is obtained […]. There is also another path proceeding [from whiteness] toward red, and from there to red brown, thereafter to black. The third path is the one going to green, from there to indigo, thereafter to blackness. [4, 7]
Thus, Ibn Sina introduced what in modern terms would be called a two-dimensional color order (cf. the illustration above) . It would become known in Christian Europe as well, for example, through its inclusion in the Speculum maius from Vincent de Beauvais (1244) . Ibn Sina’s texts on color were also widely discussed in the Islamic world. When more than two centuries after Ibn Sina’s death a student of the astronomer al-Tusi formulated questions about Ibn Sina’s color ordering, al-Tusi further elaborated on this theory .
In his commentary, Ibn Sina also criticized the Aristotelian ideas on color mixing. For example, he disagreed with the Aristotelian tradition that claimed that green is composed of red and purple. According to Ibn Sina, a composition of red and purple does not produce green because from mixing red with purple, a color is produced that is brighter than purple but more purple than bright red. Instead, according to Ibn Sina green is formed by a mixture of yellow, black, and indigo blue . Further, Ibn Sina made a clear distinction between the brightness of a light source (lux, in the Latin translation of Ibn Sina’s work) and the “splendor” shining from an object (lumen) .
Finally, Ibn Sina was highly critical about what was known about the cause of the rainbow. He wrote that he was “not satisfied with what our friends the Peripatetics [i.e., Aristotle and his followers] have to say about the rainbow.” He continued by reporting some of his observations that cannot be explained by that theory, only to conclude that he himself also had nothing to add, except by a suggestion that the cause of these colors might be inside the eye of the observer .
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