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Joannes de Sacrobosco
(John Holywood), a monk of English origin, lived in the first half of the thirteenth century as professor of astronomy at Paris; died in that city, 1256.
He owed his reputation as an astronomer chiefly to his astronomical textbook "De Sphaera," which was used at many universities for several centuries. There is much difference of opinion as to the place and time of his birth. As the Latinized name de Sacrobosco (de Sacrobusto or Sacrobuschus) seems to be a translation of the English name Holywood or Holybush, many say that Holywood (now Halifax), in Yorkshire, was his birthplace. Others give it as Holywood near Dublin; others again claim that he came from Nithsdale in Scotland. John made his studies at Oxford, but soon came to France, where, as a contemporary of St. Thomas Aquinas, he proved himself an efficient teacher of mathematics and astronomy. As many were deterred from undertaking the study of astronomy by such ponderous and to a great extent obscure works as those of Ptolemy, Alfraganus, and Albategnius, Holywood wisely resolved to write a compendium of spherical astronomy, which professors of this branch of knowledge could use as a textbook in their course of instruction. How well-timed his book was is shown by the numerous editions (amounting to almost one hundred) published before the middle of the seventeenth century, that is to say, before the new Copernican theory was generally adopted. The first printed copy dates from 1472, when it appeared at Ferrara, Italy, under the title: "Johannis de Sacrobusto seu Bosco anglici Sphaera mundi." Brevity and precision were the chief characteristics of the compendium. The lecturer was thus compelled to expound and amplify a great deal. Commentaries by various scholars were also published— e.g., by Ratdolt (1482), Cirvelli (1494), Cicchi, Capuani, Fabri (1495); Georgi, Boneti (1500), etc. Among the best known is the commentary of Father Christopher Clavius, S.J., which also saw many editions. In spite of the numerous revisions which Sacrobosco's book went through, indeed perhaps even owing to these corrections, it remains to this day a useful aid to the proper historical appreciation of the different questions which exercised men's minds from the thirteenth century onwards to the time of the reform of astronomy under Copernicus, Kepler, and Newton. Sacrobosco also wrote a treatise on the computation of feast days (Computus), a tract on arithmetic (Algorithmus), and a small work in the field of practical geometry (De Compositione quadrantis simplicis et compositi et utilitatibus utriusque). In the latter there is one of the oldest examples of the figures then found almost invariably on the reverse of the so-called astrolabe, a graduated quadrant with the help of which one could obtain the different hours of the day from the observation of the sun's height.