Johannes de Sacrobosco or Sacro Bosco (John of Holywood, c. 1195 – c. 1256 AD) was an English scholar and astronomer who taught at the University of Paris and wrote the authoritative mediaeval astronomy text Tractatus de Sphaera.

Contents 1 Origins 2 Life 3 Tractatus de Sphaera 4 Algorismus 5 On the calendar 6 Works 7 Notes 8 References 9 External links

[edit] Origins

Although described as English, his birthplace is unknown because Sacrobosco is an otherwise unknown town or region. The belief on his nationality is based on a 1271 statement by Robertus Anglicus.^[1] Traditional theories were based on suggestions of antiquarians, without documentary proof.

Sacrobosco is also called John of Holywood, by reverse etymology from the Latin sacro bosco. A traditional belief, that he was born in Halifax, is due to John Leland,^[2] and was discredited by William Camden: Halifax^[3] means 'holy hair', not 'holy wood'.^[2] Sacrobosco has been identified, by Thomas Dempster, with an Augustinian canon from Holywood Abbey, Nithsdale (in fact a Premonstratensian house); which would be a reason for presuming him a Scot.^[2][4] He is also claimed by Holywood, County Down, this being based on a suggestion of Richard Stanihurst.^[2][5]

[edit] Life

The story that he was educated at the University of Oxford is no more documented than the stories on his origin.^[2]

According to a seventeenth century account, he arrived at the University of Paris on June 5, 1221, but whether as an arts student or as a licentiate (one having a Master of Arts degree from another university and thus qualified to teach) is unclear.^[6] In due course, he began to teach the mathematical disciplines at the University of Paris.

The year of his death is uncertain, with evidence supporting the years 1234, 1236, 1244, and 1256.^[7] The inscription marking his burial place in the monastery of Saint-Mathurin in Paris described him as a computist, who was an expert on the reckoning of time.^[8]

M. Christi bis C. quarto deno quarter anno

De Sacro Bosco discrevit tempora ramus,

Gratia cui dederat nomen divina Johannes:

The lunar crater Sacrobosco is named after him.

[edit] Tractatus de Sphaera

About 1230, his best known work, Tractatus de Sphaera, was published. In this book, Sacrobosco discussed the Earth and its place in the Universe. It was required reading by students in all Western European universities for the next four centuries. Its description of the Earth as a sphere and its popularity exposes the nineteenth-century opinion that medieval scholars thought the Earth was flat as a fabrication (See: Flat Earth).

[edit] Algorismus

In his Algorismus, theorized to have been his first work, Sacrobosco showed himself to be a strong proponent of the Arab methods of numerical calculation, his Algorismus being the first text to introduce Hindu-Arabic numerals and procedures into the European university curriculum.^[9]

[edit] On the calendar

What Sacrobosco may be most famous for is his criticism of the Julian calendar. In his book on computus, De Anni Ratione (1235), he maintained that the Julian calendar was ten days off and that some correction was needed. He made no proposal to correct the accumulated error of ten days but looking to the future, he proposed to leave one day out of the calendar every 288 years.^[10] In this book, he invented the false notion that Caesar Augustus took a day from February to give to August (see Julian calendar).^{[citation needed]}

[edit] Works

• Tractatus de Sphæra
• Algorismus, or De Arte Numerandi, printed without date or place [1490?], and at Vienna, 1517, by Hieronymus Vietor; Cracow, 1521 or 1522; and Venice, 1523
• De Anni Ratione, or De Computo Ecclesiastico, printed, Paris [1538?], 1550, 1572, 8vo.

[edit] Notes

[edit] References

• Pedersen, Olaf. "In Quest of Sacrobosco." Journal for the History of Astronomy, 16 (1985): 175-221.
• Holywood or Halifax, John in Dictionary of National Biography, 1885-1900.

[edit] External links

• Johannes de Sacrobosco