John de Sacrobosco

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Astronomer, applied mathematician; b. Paris, late 12th century, d. mid-13th century (1244 or 1256). Also known as John of Hollywood. Extant historical documents from his own time do not mention the name of Sacrobosco; his fame began only as a result of the growing popularity of his works. He is recognized as an early promoter of the ongoing project to describe nature mathematically. Franciscan and Dominican theologians took interest in Sacrobosco and wrote numerous commentaries on his De Sphaera. A 1271 commentary on De Sphaera by Robertus Anglicus identifies the author of the work as "Johannes de Sacrobosco Anglicus" suggesting an English origin. Historians seeking Sacrobosco's place of birth etymologically variously suggest England, Scotland, and Ireland. Most follow the early English tradition, although lacking a satisfactory etymological explanation for Sacrobosco or Hollywood. The popular suggestion of Halifax has since proven incorrect as fax refers to hair, not wood. His grave, apparently destroyed in the French Revolution, lay in the monastery of Saint-Mathurin in Paris. The epitaph recognized Sacrobosco as a famous astronomer and a computista an expert in time calculations. A 1297 commentary on De Sphaera connects Sacrobosco to the University of Paris, where he was likely on faculty from about 1221.

Four extant treatises can be attributed to Sacrobosco with some degree of certainty. In the popular textbook, Algorismus, he demonstrates the use of what he terms "Arabic" numerals for arithmetic, ushering the use of Indo-Arabic numerals into the university curriculum. His most notable work, Tractatus de Sphaera, is divided into four chapters concerning (1) the structure of the universe, (2) the circles of the celestial sphere, (3) the observable implications of the foregoing for the rotation of the heavens, and (4) the motion of planets, theories of Sun and Moon, and the cause of eclipses. De Sphaera follows a Ptolemaic model, but innovates in its explanation for the phenomenon of procession. While Algorismus cannot be dated, de Sphaera seems to have been composed during Sacrobosco's career at the University of Paris and an early manuscript dates to 1240. De Sphaera remained in constant print for two centuries, the last edition being published in 1674 at Antwerp. It is significantly shorter than Sacrobosco's Compotus, a general treatise on ecclesiastical and civil time reckoning written between 1232 and 1235. In the Compotus, Sacrobosco proposes reforms to the Julian calendar that would eliminate the effects of accumulated errors and bring stability to the dates of the equinoxes. The Tractatus de quadrante is a brief work describing the Old Quadrant and its use. A number of spurious works exist, such as the Theorica planetarum and commentaries on Aristotle's De Caelo and De generatione et corruptione.

Bibliography: o. pedersen, "In Quest of Sacrobosco, " Journal for the History of Astronomy 16 (1985), 175221. w. r. knorr, "Sacrobosco's Quadrans : Date and Sources, " Journal for the History of Astronomy 28 (1997), 197222. j. moreton, "John of Sacrobosco and the Calendar, " Viator 25 (1994), 229244. l. thorndike, The Sphere of Sacrobosco and its Commentators (Chicago 1949).

[j. h. barlow]

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John de Sacrobosco

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