by Olaf Pedersen
© Oxford University Press 2004 All rights reserved
Sacrobosco, John de [John of Holywood] (d. c.1236), mathematician, was probably of British extraction, but the tradition that he came from Halifax in Yorkshire is unsupported. Contemporary records are silent about him and various accounts of his life rest only upon the arbitrary surmises of Leland, Bale, and later antiquaries. The date of his birth is unknown, and the only certainty is that he worked in Paris. He is not mentioned in the records of the university which, however, provided his tomb in the church of St Mathurin, with a monument on which an astronomical instrument was engraved, together with four lines of verse commemorating his fame as a computista, or calendar expert. These were copied before the monument was destroyed at the time of the French Revolution. In this situation the only clue to his life and achievement lies in his writings. In the course of time many works have been wrongly ascribed to Sacrobosco, but the following four books are authentic.
The Algorismus (in some manuscripts called Algorismus vulgaris or Algorismus de integris) has the incipit 'Omnia quae a primaeva origine rerum', and is a brief introduction (same 5600 words) to the new 'Arabic' numerals and the positional system of numbers. It explains all the elementary procedures of calculation from addition and subtraction to the extraction of square and cube roots. It is written in a dry and precise style, and demonstrates clearly the superiority of the new methods over the ancient Roman system. It was widely used and gave rise to several revised versions and commentaries, among which the great commentary by Peter Nightingale from 1291 occupies the first place. There were several printed editions between 1488 (Strasbourg) and 1582 (Antwerp). More recent printings by Halliwell (1838) and Curtze (1897) are now superseded by the critical edition by F. Saaby Pedersen (in Corpus Philosophorum Danicorum Medii Aevi, 10/1, 1983).
The Tractatus de spera, with the incipit 'Tractatum de spera quattuor capitulis distinguimus' is a longer work (some 9000 words) on elementary cosmology and astronomy. It is well organized in four chapters, describing respectively the general structure of the universe, the circles of the celestial sphere, the phenomena caused by the diurnal rotation of the heavens, and planetary motions and eclipses. The style is elegant and pleasant and, in the manner of the twelfth century, there are many quotations from both literary and scientific classical sources. Although it appears that the author was not familiar with the Almagest itself, he clearly aimed at making his students familiar with the elements of Ptolemaic astronomy, breaking away from the earlier tradition derived from Macrobius and Martianus Capella. No scientific work from the middle ages has ever enjoyed a similar popularity. The Spera is still extant in hundreds of manuscripts spread over all the major libraries of Europe, and there were at least 160 printed versions, from the editio princeps of 1482 (Ferrara) until 1673 (Antwerp). The Latin text is now available with an English translation in 'The Sphere' of Sacrobosco and its Commentators by Lynn Thorndike (1949).
Twice as long (some 19,000 words) is the Compotus, also called De anni ratione. It has the incipit 'Compotus est scientia considerans tempora', and deals with all aspects of time reckoning and calendaric problems. It is written in the same style as the Spera, but with even more references to earlier writers, and is of the same scope and importance as Bede's De temporum ratione, written 500 years earlier. Of particular interest is the discussion of the errors of the Julian calendar and Sacrobosco's proposal for eliminating them by methods essentially similar to those employed in the Gregorian reform of 1582: that is, by dropping ten days once and for all, and then leaving out one day with regular intervals. The Compotus was printed at least thirty-five times from Melanchthon's edition at Wittenberg in 1531 to the last edition at Antwerp in 1673. A modern, critical version is still a desideratum.
A fourth, brief treatise (about 2000 words) is usually called De quadrante and has the incipit 'Omnis scientia per instrumentum operative'. It describes the construction of the so-called 'old Quadrant' and its application as a sundial, and was critically examined by J. B. J. Delambre in 1819 (Histoire de l'astronomie du moyen âge, 243 ff.). Comparatively few manuscripts are preserved and no printed version seems to exist. For no obvious reason it has sometimes been reckoned among Sacrobosco's spurious works.
The dating of these works presents a very difficult problem. There is no evidence of when the Algorismus and the quadrant treatise were written. The Spera and the Compotus must be earlier than 1240, when they were both included in the same codex which is now in the Kongelige Bibliotek in Copenhagen (GKS 277, 2°). Internal evidence seems to indicate that the Spera is earlier than the Compotus, which is self-described as written in 1235; but in several manuscripts this year is given as 1232. The latter also ends with some verses pointing to the year 1234. In consequence it is natural to conclude that Sacrobosco's activity came to an end about 1235, in agreement with a notice in Miraeus that Sacrobosco died in 1236.
Sacrobosco's three principal works were often copied or bound together. Supplemented by a work on planetary theory and a set of astronomical tables, they formed the kernel of a corpus astronomicum on which the elementary teaching of astronomy was based for more than 300 years. This shows their inherent qualities, as does the fact that they were the subject of numerous later commentaries. They were brief, to the point, and contained very little that a student could afford to forget when passing on to a more advanced stage. It is also worth noticing that they were completely free from explicit astrological association. Despite their narrative form they contributed more than most other works to preserving the notion of science as the study of mathematical relationships between natural phenomena, in contradistinction to the Aristotelian view of science as a metaphysical quest for causal explanations.
O. Pedersen, 'In quest of Sacrobosco', Journal for the History of Astronomy, 16 (1985), 175-221
O. Pedersen, The corpus astronomicum and the traditions of medieval Latin astronomy, 3 (1975), 57-96
Petri Philomenae de Dacia et Petri de S. Audomaro opera quadrivialia, ed. F. S. Pedersen (1983), 174-201
'The sphere' of Sacrobosco and its commentators, ed. L. Thorndike (1949)
J. B. J. Delambre, Histoire de l'astronomie du moyen âge (Paris, 1819)
A. Miraeus, Rerum toto orbe gestarum chronica a Christo nato ad nostra usque tempora (Antwerp, 1608)
G. Sarton, Introduction to the history of science, 2 (1931), 617-19
L. Thorndike and P. Kibre, A catalogue of incipits of mediaeval scientific writings in Latin, rev. edn (1963)
P. Duhem, Le système du monde: histoire des doctrines cosmologiques de Platon à Copernic, 10 vols. (Paris, 1913-59), vol. 3, pp. 238-40
Kongelige Bibliotek, Copenhagen, GKS 277, 2°
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