Witelo
NAME: Witelo, but also spelled "Vitellio" or "Vitello".
ACHIEVEMENT: Medieval thinker who worked in the theory of optics.
NICKNAME/ALIAS: None
DATE & PLACE OF BIRTH: c. 1230/1235, in the duchy of Silesia, then a fief of
Poland - probably near or in Breslau (Wroclaw).
DATE & PLACE OF DEATH, AGE AT DEATH: Probably in the Premonstratensian monastery of Witow, near Piotrkow, Poland, at an unknown date - but after c. 1275.
Age at death unknown.
DISCIPLINE: Priest
FIELD: Physics/philosophy/religion
LANGUAGE: Latin
PARENTS: Is probable that one of his parents was Thuringian, as he called
himself Thuringo-polonus, also 'filius Polonorum et Thuringorum'
SIBLINGS: Unknown
SPOUSE: None
CHILDREN: None
EDUCATION: As an undergraduate at the University of Paris in the early
1250s; and then in Padua c. 1262-68, where he studied canon law.
MAJOR WORKS:
Perspectiva (optics)
De primaria cause penitentie (theology)
Datura demonum (theology)
LIFE & TIMES:
Very little is known of Witelo's life, but from a reference to time spent in Paris and a description of a nocturnal brawl that occurred there in 1253, it is probable that he received his undergraduate education at the University of Paris in the early 1250’s, so he must have been born in the early or middle 1230’s.
In the 1260’s Witelo was studying canon law at Padua, and late in 1268 or early 1269, he seems to have been in the Central Italian city of Viterbo, where he met William of Moerbeke, papal confessor and translator, to whom W. later dedicated his major work: “Perspectiva.”
He may have been the person of that name who served as chaplain to King Ottocar II of Bohemia and who was sent to Rome on a mission to Pope Gregory X in 1274. The Bern manuscript of Witelo's Perspectiva refers to the author as "Magister Witelo de Viconia", indicating that Witelo retired to the Premonstratensian abbey of Vicogne towards the end of his life.
“Perspectiva” (written during the 1270s) is an immense work, and no detailed analysis of its contents has ever been made. Most significant features include:-
Book I - mathematical principles required for optical demonstrations.
Book II – the nature of radiation, propagation of light and
colour in straight or refracted lines, shadows and pinhole images;
Book III - the physiology, psychology, and geometry of monocular and
binocular vision by means of rectilinear radiation;
Book IV - the perception of the twenty visible elements, other than light and
colour, including size, shape, remoteness, etc. and errors that occur in the perception of these - eg. errors in judging distance, shape, and relative size.
Book V - vision by reflected rays, beginning with the nature of, and geometrical laws of reflection, and going on to a detailed analysis of plane mirrors.
Books VI-IX - image formation in curved mirrors (convex spherical, convex
cylindrical, concave cylindrical, conical and parabolic mirrors)
Book X - vision by rays refracted at plane or spherical interfaces, and a discussion of the rainbow and other meteorological phenomena.
In the second half of the thirteenth century optics was not an experimental science. The main task of people like Witelo was to master the earlier literature on the subject. Chief of these was the work by <influenced by> Al Hazen* (“Optics”) which had been only recently translated into Latin. The similarity between Witelo’s and Al Hazen’s treatment (often, the use of the same terminology) suggests strongly that Witelo used Al Hazen as a source. Above all, Witelo agreed with Al Hazen that the act of vision did not involve light rays passing from the eye to the object, but the other way round.
Witelo was also influenced by <influenced by> Ptolemy’s* “Optica”, <influenced by> Euclid,* by <influenced by> Grosseteste,* <influenced by> Roger Bacon* and Hero of Alexandria (“Catoptrica”) who argued that reflection must happen in a straight line since nature “always acts along the shortest lines.”
Witelo also repeated Hero’s argument that the shortest lines connecting two points and a reflecting surface are those that make equal angles with the surface, and that the plane formed by the incoming and reflected rays is perpendicular to the reflecting surface (or, in the case of curved mirrors, its tangent), and that an object seen by reflection appears to be located where the backward extension of the ray falling on the eye intersects the perpendicular dropped from the visible object to the reflecting surface.
Witelo’s writing on this subject was not developed further in the West until the seventeenth century.
In particular, Witelo’s studies on refraction are valuable because the phenomenon was so little understood at the time. Following the description of Al Hazen, Witelo gave detailed instructions for making an instrument for measuring angles of refraction. Where Ptolemy and Al Hazen had given tables of refraction from air to water or glass, Witelo added tables in the other direction - from water or glass to air - as well as for refractions between water and glass.
The principle that the path of a refracted ray between a point A in one medium and a point B in another is independent of the sense in which the path is traversed, whether from A to B or from B to A, may have been first used by Witelo.
Witelo tried, unsuccessfully, to find general mathematical relations between the angles of incidence and refraction; and he applied his ideas on refraction to the study of lenses.
ASSESSMENT: Witelo was a vital link in the transmission of Greco-Arabic optics to the West. His work formed an integral part of optical theory in standard textbooks until the seventeenth century
EXTRA CONNECTIONS: Witelo’s influence was felt in the work of <influenced> Oresme* in the fourteenth century; <influenced> Ghiberti*, <influenced> Regiomontanus* and <influenced> Da Vinci* in the fifteenth century; <influenced> Benedetti*, <influenced> Brahe*, <influenced> William Gilbert*, and <influenced> Stevin* in the sixteenth century, <influenced> Kepler*, <influenced> Galileo*, <influenced> Snell*, and <influenced> Descartes* in the seventeenth century.
ONELINER: Witelo, influential medieval optics expert
BIBLIOGRAPHY:
Boyer, Carl B., The Rainbow: From Myth to Mathematics, London: Macmillan,
1987
Sarton, George, Introduction to the History of Science, 2 vols, Baltimore: Carnegie Institution of Washington, 1931