Wikimedia, http://upload.wikimedia.org/wikipedia/commons/b/b6/Al-Tusi_Nasir.jpeg
Muhammad ibn Muhammad ibn Hasan al-Tusi, نصیر الدین طوسی, usually known as Nasir al-Din al-Tusi, or Tusi, was born in Tus (today Iran) in 1201. During his life, he worked in Maragha (Iran) and Baghdad (Iraq). His influence reaches into many fields [1]. Tusi died in Baghdad (Iraq) in 1274.
He learned basic science and Arabic from his father, Wajih al-din ibn Hasan, وجیه الدین ابن حسن, who was a theologian and a scholar, and learned mathematics and logic from his uncle Noor al-din Shi’i, نورالدین شیعی. He then studied with Nasir al-din ibn Hamze, ابن حمزه, who was a well-known Shiite jurisprudent, and at his recommendation moved to Nishapur to study further. There, he studied Ibn Sina’s work under Fakhr Razi’s, فخر رازی, guidance. His work on reforming Ptolemaic theoretical astronomy would be crucial for later astronomers, including Copernicus. In mathematics, he published landmark editions of the works of Euclid and Archimedes and developed trigonometry as a discipline separate from astronomy. He wrote several works on optics [2]. Al-Tusi was born into a Twelver Shi’a family. For Shiite theology, al-Tusi wrote an important work on ethics and also authored the first systematic treatment of rationalist theology in twelve-Imam Shiism, a work still central in Shiite theological education.
Under patrons at Ismaili courts, he became a famous mathematician. When in 1256 under Mongol rule, Hulagu destroyed the Abbasid Empire; al-Tusi had taken refuge at the last Ismaili stronghold located on mount Alamut. After the Mongols destroyed also this mountain fortress, Hulagu personally saved al-Tusi’s life since the ruler’s interest in astrology made him respect al-Tusi’s astronomical knowledge. Al-Tusi persuaded Hulagu to support building the first full-scale astronomical observatory in the world at Maragha. With al-Tusi as director, it would collect a mass of observation data for about 50 years, and it would inspire later observatories in Samarkand, India, and possibly even Tycho Brahe’s observatory in Denmark.
11.1 Tusi’s Color Order System
Regarding the production of colors from black and white there are numerous paths, from which one gradually walks from white to black. The path through yellow belongs there: First by the mixing of dense and fire, both in small amount, the straw-yellow is produced, then the lemon-yellow, then the saffron-yellow, then the orange-yellow, then the grenade-yellow, then in it the tendency towards black increases, according to the increase in the number of dense particles and the decrease of fire, until it becomes black.
Another path goes through red. First, it becomes rosy, then like evening-red, then blood-colored, then purple, then violet, violet-colored. […]
This all occurs according to the differences of particles in transparency, opacity (density), light and darkness. Now and then one sees a color together with another, and a different color is produced, such as green from yellow and blue, verdigris from green and white. There are infinitely many of such arrangements, and some are often found in small particles of plants and animals. Anyone who observes them is surprised by their number [3, 4].
Thus, while Ibn Sina had specified three paths from white to black, al-Tusi described five of such paths (see Fig. 10.1). They go via yellow, red, green, blue, and gray, as illustrated in the Figure. Remarkably, Forsius in 1611 also described five different tint/shade scales from white to black, as described in Chap. IV. This may all be compared to the German monk Theophilus (ca. 1120), who described how to produce up to twelve grades in a tint/shade scale [5]. The text of al-Tusi shows that he must have considered color space to be two dimensional. Interestingly, at approximately the same time in Latin Europe Grosseteste had argued on theoretical grounds that color space is three dimensional [6, 7].
Color order system according to Tusi [3]
Although several scholars before Nishaburi and al-Tusi had mentioned that green can be produced by mixing blue and yellow, no earlier scholar had described that depending on the mixing ratios, different hues of green are produced [7].
if white color and black color are mixed with each other, an incense-grey color will result.
This had been stated only twice before in history, and in much less clear wordings. Clearly this statement, which was a starting point for Newton’s optical work, was not made for the first time by Scaliger in 1557, as is generally thought [9].
Stamps commemorating Tusi from Iran and Azerbaijan (Wikimedia, Commemorative stamp of Nasir al-Din al-Tusi from Azerbaijan.)