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Witelo of Silesia
(1230-1275)

In the thirteenth century, Witelo wrote an exhaustive ten-volume work on optics entitled Perspectiva that served as the standard text on the subject until the seventeenth century. Yet, very little information about the life of Witelo is known. He is generally believed to have lived from around 1230 to 1275 BC and is often referred to as Polish due to his association with Silesia, a region of central Europe located mainly in southwest Poland and the northern Czech Republic. In 1262, Witelo visited Padua as part of the retinue of Prince Wladislaw, who was Chancellor of the Czech Kingdom and would later become Archbishop of Salzburg. In Padua, Witelo reportedly formed a friendship with Theodoric of Prague, who was Chaplain of the Czech King and would be sent with Witelo on a diplomatic mission to Lyons, France. Thus, Witelo appears to have had important connections and spent a certain amount of his life traveling, but is also believed to have settled at some point in the Polish city Legnica to teach.

Witelo’s classic treatise on optics is thought to have been completed around 1270. Similar to other texts of the period, it was copied by hand and circulated in manuscript form. The original manuscript has not been preserved, but a version of the text edited by the astronomer Regiomontanus was printed as a book in the mid-sixteenth century. Many scholars argue that Perspectiva is based at least partly on the Greek translation of the works of the Arab scholar Alhazen (965-1040), but the point is a contentious one. Undoubtedly many of the ideas proposed by the two men were similar. For instance, both Witelo and Alhazen rejected the common conception at the time that light rays were emitted from the eyes, instead suggesting that the eyes were passive receivers of light reflected from other objects. However, such parallels do not necessarily indicate that one text was copied from the other, and the modern scholarly debate about the matter is ongoing.

Among other topics addressed in Perspectiva, Witelo carefully considered refraction and through his observations, noted that the angle of refraction (bending light) is not proportional to the angle of incidence (incoming light), though he was not aware of the phenomenon known today as total internal reflection. He also explained how plane mirrors could be used to see objects outside of an enclosed space and depicted a method of producing parabolic mirrors from iron. Witelo’s work on optics was so extensive that the first major addendum to it was not undertaken until several centuries later, when Johannes Kepler published Ad Vitellionem Paralipomena, Quibus Astronomiae Pars Optica Traditur (Supplement to Witelo, in Which Is Expounded the Optical Part of Astronomy) in 1604.

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