We may divide our survey of the debt owed to Ireland by science into
three periods: the earliest, the intermediate, and the latest.

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.