In the earliest period the names which come before us are chiefly those of compilers such as Augustin, a monk and an Irishman who wrote at Carthage, in Africa, in the seventh century, a Latin treatise on The Wonderful Things of the Sacred Scripture, still extant, in which, in connection with Joshua’s miracle, a very full account of the astronomical knowledge of the period, Ptolemaic, but in many ways remarkably accurate, is given.  There are, however, three distinguished names.  Virgil the Geometer, i.e., Fergil (O’Farrell), was Abbot of Aghaboe, went to the continent in 741, and was afterwards Bishop of Salzburg.  He died in 785.  He is remembered by his controversies with St. Boniface, one of which is concerned with the question of the Antipodes.  Virgil is supposed to have been the first to teach that the earth is spherical.  So celebrated was he that it has been thought that a part of the favor in which the author of the Aeneid was held by medieval churchmen was due to a confusion between his name and that of the geometer, sometimes spoken of as St. Virgil.

Dicuil, also an Irish monk, was the author of a remarkable work on geography, De Mensura Provinciarum Orbis Terrae, which was written in 825, and contains interesting references to Iceland and especially to the navigable canal which once connected the Nile with the Red Sea.  He wrote between 814 and 816 a work on astronomy which has never been published.  It is probable, but not certain, that he belonged to Clonmacnois.

Dungal, like the two others named above, was an astronomer.  He probably belonged to Bangor, and left his native land early in the ninth century.  In 811 he wrote a remarkable work, Dungali Reclusi Epistola de duplici solis eclipsi anno 810 ad Carolum Magnum.  This letter, which is still extant, was written at the request of Charlemagne, who considered its author to be the most learned astronomer in existence and most likely to clear up the problem submitted to him.

Before passing to the next period, a word should be said as to the medieval physicians, often if not usually belonging to families of medical men, such as the Leahys and O’Hickeys, and attached hereditarily to the greater clans.  These men were chiefly compilers, but such works of theirs as we have throw light upon the state of medical knowledge in their day.  Thus there is extant a treatise on Materia Medica (1459); written by Cormac MacDuinntsleibhe (Dunleavy), hereditary physician to the clan of O’Donnell in Ulster.  A more interesting work is the Cursus Medicus, consisting of six books on Physiology, three on Pathology, and four on Semeiotica, written in the reign of Charles I. of England by Nial O’Glacan, born in Donegal, and at one time physician to the king of France.