Wikimedia
Kamal al-Din Hasan ibn Ali ibn Hasan al-Farisi, کمال الدین فارسی, was born in 1267 in Iran. The exact location of his birth is uncertain with Tabriz, Shiraz, and Isfahan listed as possible locations. It is known that he traveled to these cities and studied with a number of scholars of the time. The exact details of his ancestry, however, are also unknown. At the time, Tabriz was a center for scientific discovery, and Farsi studied at the school of Tabriz with the famous astronomer Qutb al-Din al-Shirazi, قطب الدین شیرازی, who in turn was a student of Nasir al-Din al-Tusi. Farsi died in Tabriz in 1319 [1].
12.1 Farisi and Color
Al-Farisi felt “perplexity” when he found several inconsistencies and errors in the classical works about optics [1]. His teacher then managed to obtain a manuscript copy of the Kitab al-Manazir from Ibn al-Haytham, which was brought in “from a very distant land (probably Egypt).” Farisi was greatly impressed by this work and decided to write a detailed commentary on it. He discussed it in great detail and completed it by adding appendices with other optical writings. Al-Farisi also included corrections to these texts, aptly calling the resulting work Tanqih al-Manazir, تنقیح المناظر, (Revision of the [Kitab] al-Manazir) [2].
In one of al-Farisi’s comments in the Tanqih, he described how an object is seen in a certain color under sunlight, but in a different color under moonlight, and yet in another color in the light of fire. From this, al-Farisi concluded that colors are not really present in objects, but depend on illumination [3]. The role of incident light had therefore been changed from being a mere catalyst for color vision as in the ancient Greek theories, to being as prominent as in modern color theory [4].
Together with his teacher Qutb al-Din al-Shirazi, al-Farisi tried to find explanations why the famous experiment of Ptolemy, with a spinning top (or mill stone) having sectors painted in different colors, led to new colors [5].
Regarding the colors of the rainbow, Ibn al-Haytham had supported the Aristotelian idea that these were due to a mixture of light and darkness. Al-Farisi rejected this concept. He argued that if it was true, then the colors of the rainbow would be ordered from bright to dark. In addition, the secondary rainbow would then have the same color order. Neither is supported by observation [6].
Double refraction and single reflection in a raindrop. Simultaneously with Theodoric of Freiberg, al-Farisi was the first to give the correct explanation of the rainbow in his Tanqih al-Manazir (©Library of the Masjid Sepahsalar, Tehran)
It was recently discovered that in his Tanqih, Farsi included the text of Tusi on color ordering, in which five paths were proposed to go from white to black [7]. In this way, this text would become available to many later generations. Farisi also sought for an explanation of the different orderings of the colors in the primary and secondary rainbow. His darkroom experiments let him conclude that various colors of the rainbow were produced by a superposition of different images as projected after reflections and refraction in the sphere [8]. Thereby, the colors became a function of the positions and luminous intensities of the composing images [9, 10].
The Tanqih al-Manazir would become widely spread in the Muslim world, where it was used in academic classrooms and would be commented upon until the sixteenth century. Therefore, in the Muslim world, this would be the main textbook on optics for more than three centuries. Since it was never translated into any Western language, its influence on European science is marginal at best.