Ioannis de Sacrobusto Libellus de anni ratione seu ut vocatur vulgo. Computus Ecclesiasticus. Cum praefatione Philippi Melanthonis. With woodcut title vignette and 6 astrological woodcut illustrations in the text.

[Anvers, Jean Richard, ca.1545?]. Sm-8vo. (14,7x9,4 cm.) (112 pp.) New leather spine, later boards (binding worn and chafed; name of Philip Melanchton on title page crossed out, contemporary doodle on last page; corner torn from one page without loss of text, one page slightly trimmed, chafing one woodcut; last flyleaf restored in the margin) � Stop-press variant of copy c:lvd:1141346 held by the Erfgoedbibliotheek Hendrik Conscience (the opening words of the dedication are reset). Adams (Holywood) 724. What Sacrobosco may be most famous for is his criticism of the Julian calendar. In his book on computus, entitled in Latin De Anni Ratione (English: On reckoning the years), dated circa 1235, he maintained that the Julian calendar had accumulated an error of ten days and that some correction was needed. The Julian calendar was instituted in the 1st century AD. and a calendar year contained 365.25 days, with the 0.25 day provided for by a Leap year every four years. However, the more precise length of a solar year is about 365.2425 days. The imprecise 365.25 days had resulted in an accumulated error of about 10 days by the 13th century. Sacrobosco made no proposal on how to get rid of the accumulated error. But looking to the future, he proposed to leave one day out of the calendar every 288 years to prevent continuing error. Sacrobosco's data were not quite as accurate as those of the Alfonsine tables which were produced a few decades later in the 1270s based on the Arabic Tables of Toledo. The astronomer Campanus of Novara in 1268 did similar work, again making use of Arabic astronomy sources. Sacrobosco too was influenced by Arabic astronomical sources, but not the same sources, and there is no indication in his writings that he could read Arabic. (Wikipedia). The preface by Melanchton is dated August 1538. He joined this text of 'De anni ratione' to his edition of 'De sphaera' on the instigation of Rheticus: "Valde probo consilium Georgii Ioachimi Rhetici, quod ad libellum de Sphaera adiunxit rationem Anni conscriptam ab eodem authore Ioanne de Sacro busto". (f.3.v.). Collation: A4,B-G8,H4. 16e eeuwse drukken