Dicuilus (Gaelic: ; fl.814–825 A.D.) was an Irish monk, astronomer, geographer and author born during the second half of the 8th century, possibly in the Hebrides. He travelled the Frankia around the turn of the 9th century and was involved with the Carolingian Renaissance under Louis the Pious. He was the author of astronomical and cosmographical treatises during the early 9th century, an example of Hiberno-Latin culture.
Background
The exact dates of Dicuil's birth and death are unknown; indeed all details of his life are known only from his writings. Tierney suggests his birth to be sometime around c.760–770 A.D. Of his life nothing is known except that he probably belonged to one of the numerous Irish monasteries of the Frankish Kingdom, and became acquainted by personal observation with islands near England and Scotland. From 814 and 816 Dicuil taught in one of the schools of Louis the Pious, where he wrote an astronomical work, and in 825 a geographical work.
In book 7 chapter 6, Dicuil describes Ireland as "our own island" and how he had at times lived in the Hebrides:
<blockquote>We do not read of islands being found in the sea west or north of Spain. There are islands around our own island Hibernia, some small and some very small. Near the island Britannia are many islands, some large, some small, and some medium-sized. Some are in the sea to her south and some in the sea to her west, but they abound mostly to the north-west and north. Among these I have lived in some, and have visited others; some I have only glimpsed, while others I have read about.
Based on similarities of style, it has been suggested that Dicuil may be the same person as the anonymous Hiberno-Latin poet and grammarian known as Hibernicus exul.
Astronomical computus
The astronomical work is a sort of computus of five books, in prose and verse. Four books are preserved in a manuscript which belonged formerly to the monastery of Saint-Amand in northern France, and is now at Valenciennes. A second manuscript is from the abbey of Saint Martin at Tours, and contains two chapters added to the fourth book, and two more chapters constituting a fifth book
Book 1 contains material on calendars, on 19-year lunar cycles, and on versification. It also contains an account of the two methods of calculating triangular numbers: by summation of the natural numbers, or by the multiplication together of two consecutive numbers divided by two
Book 2 contains material on the distance between the Earth and the heavens, and between the seven planets; methods for counting the lunar months; the monthly age of the moon; rules for calculating Easter and Lent; intercalary days (extra days) and subtracted days; solar and lunar years; more on versification.
Book 3 contains material on cycles of the stars; 19 year lunar cycles; other large cycles of the Sun and Moon; the first day of the natural year (the spring equinox in March).
Book 4 contains material on solar intercalary days and lunar subtracted days; and on the relative speed of travel of the Moon, Sun and stars.
De mensura Orbis terrae
Better known is the De mensura Orbis terrae, completed in 825 A.D;
!Siglum
!Library
!Shelfmark
!Folios
!Date (century)
!Fate
!Souce
|-
|P
|BnF
|Lat. 4806
|25r–40r
|late 9th
|Extant
|
|-
|D
|Saxon State and University Library Dresden
|De 182
|50v–62v
|9th – 10th
|Destroyed during the Bombing of Dresden
|
|-
|σ
|Cathedral Library of Speyer
|Codex Spirensis
|
|early 10th
|Lost
|
|}
Later medieval manuscripts also exist such as Bodleian MS. Canon. Misc. 378 (copied in 1436).
Published editions
The geography manuscript was known to Marcus Welser, Isaac Vossius, Claudius Salmasius, Jean Hardouin, and Johann Daniel Schöpflin. The three complete editions published so far have been:
Tierney's 1967 edition is currently the only complete translation of the work into English.