Previously Unpublished Works, Fascicles VI-VII

means of the leap of the moon original: "saltus lune." A periodic one-day adjustment to the lunar calendar to keep it synchronized with the solar year.. Helpericus is quoted once by Vincent of Beauvais (book xv, chapter 11) as Hilbertus, but he is not the author of the Computus usually cited in the Mirror of Nature original: "Speculum Naturale," a massive 13th-century encyclopedia by Vincent of Beauvais., which has not been identified.

The Computus The mathematical science used to calculate the date of Easter and other movable feasts. remained part of education until the end of the Middle Ages. Oxford students, for example, had to spend eight whole days in lectures on Arithmetic original: "Algorism," specifically the study of calculating with Arabic numerals as introduced by Al-Khwarizmi., the Sphere original: "Sphera." Refers to Johannes de Sacrobosco’s "De sphaera mundi," the standard medieval textbook on astronomy., and the Computus, probably those written by Sacrobosco. Anstey, ii. 413; cf. 416.

THE BASIS OF THE CHRISTIAN ERA.

Bede in chapter 47 of On the Reckoning of Time original: "De Temporum Ratione." Bede's seminal 8th-century work on chronology. raised the question of the date of the Crucifixion, misled by the difficulties raised by the Irish forgeries. The question was taken up by Abbo of Tours (945-1004 A.D.), who proved in his preface to the Bedan Canon and Tables that the Dionysian tables then in official use did not agree with the accepted dates for the Passion or for the death of St. Benedict. Abbo was brought to England by St. Oswald to form a school at Ramsey Abbey in 985 A.D., leaving at the end of 987 A.D. to become Abbot of Fleury, and dying on 13 November, 1004 A.D. His criticism is contained in two letters, one printed in the works of Bede (i. 308; Migne, xc. 283) as a preface to the Dionysian tables for 1-1595 A.D. with corrected cycles of Cyril and Abbo, the second (1003 A.D.) printed by Varin in the Bulletin of the Historical Committee of Written Monuments original: "Bulletin du Comité Historique des Monuments écrits.", i. (1849) 117. In these tracts Abbo argues that the Nativity according to Dionysius is twenty-eight years in advance of the date fixed from Eusebius. An Ephemeris A table showing the daily positions of celestial bodies. of Abbo is found in the British Museum MS. Tib. C. i, f. 14^a^.

The next important writer on the subject is Marianus Scotus, who, in 1076 A.D., wrote a Chronicle of which a full text with tables is to be found in B.M. MS. Nero C. v, f. 27, which begins: "The inquiry begins as to where first Easter..." original: "Incipit inquisitio ubi primum Pasca...". His cycle for 532 years differs slightly from that printed in Bede. He puts the Nativity at 22 B.C. of the Dionysian Calendar and the Crucifixion at 13 A.D.; the battle of Hastings is thus dated as 1088 A.D. The indictions A 15-year cycle used in the Roman Empire to date documents, which continued to be used for administrative purposes in the Middle Ages. run in the usual order, so that when there is a discrepancy in a document of the period between the indictions and the Anno Domini year, this may be the cause. His authorities are the Gospels, Bede, Dionysius, and Theophilus. A similar theory appears in an anonymous Ten-year book in the manner original: "Liber decennalis in modum."