Incunabula and the Keio University Library Collection

The title of this book, 'Computus', means 'calculation' (especially of time) in Latin. From ancient times, astronomers and mathematicians used the periodical table of astronomy in order to generate an accurate calendar. This was a highly important undertaking. Easter, for example, is one of the most important events in the Church calendar, and works like the 'Computus' were invaluable in allowing people to establish an accurate date for it.

Just as the Japanese remember even-numbered months (i.e. months that have less than thirty-one days) using the mnemonic 'Ni (=2) shi (=4) mu (=6) ku (=9) samurai (11)', which means 'samurai facing west', there is an old saying in Western culture: 'Thirty days hath September, April, June, and November....' The origin of this rhyme is said to be this work of Anianus. However, there is little information about the author, other than that he was a Benedictine monk active in France in the second half of the 13th century.

The present work by Anianus was first printed by a Parisian printer, Guy Marchant, after which approximately forty editions were published, in cities such as Paris and Lyon, up until the end of the 15th century. Keio has a copy of the 1488 edition, printed by Johann Prüss in Strasbourg together with Sacrobosco's De algorithmus. After completing his education at Oxford, Sacrobosco entered an Augustine monastery, where he remained until he died, c. 1220. He taught mathematics and philosophy at the University of Paris, and also produced works such as the Sphaera mundi (cf. IKUL 017) and De algorithmus. Not only did he introduce Hindu-Arabian mathematics to scholars in Europe, he also had a great influence on the development of the history of science.

The paraph marks of the Keio copy are handwritten, and were added after printing; the folio numbers and headings are underlined in red by hand. There seem to be no particular handwritten marginalia or commentaries, but an early owner wrote his name, 'Nicholaus Ellenbog', and it may have been this man who had the other printed book (IKUL 023b) bound with this copy (see also IKUL 023, 023b). The online version of the ISTC has a link to a website of the incunabula housed in Wolfenbüttel Library.

[Bibliography]
  Duncan, David Ewing, The Calendar: The 5000-Year Struggle to Align the Clock and the Heavens, and What Happened to the Missing Ten Days (London: Fourth Estate, 1998)
  Dictionary of Scientific Biography, ed. by Charles Coulston Gillispie and others (New York: Charles Scribner's Sons, 1981), II

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