27 November 789 AD: Feast day of Saint Vergilius (Fergal) the Irish missionary and astronomer died of Salzburg, Austria on this day. He was said to have been a descendant of Niall of the Nine Hostages. His original Christian name was Fergal. In the "Annals of the Four Masters" and the "Annals of Ulster" he is mentioned as Abbot of Aghaboe, in County Laois.

He left Ireland, intending to visit the Holy land, but he made it no further than Paris where Pepin, then mayor of the Palace under Childeric III, received him with great favour. After spending two years at Cressy, near Compiegne, he went to Bavaria, at the invitation of Duke Otilo, and within a year or two was made Abbot of St. Peter's at Salzburg. Out of humility, he "concealed his orders", and had a bishop named Dobdagrecus, a fellow countryman, appointed to perform his episcopal functions for him.

It was while Abbot of St. Peter's that he came into collision with St. Boniface. A priest having, through ignorance, conferred the Sacrament of Baptism using, in place of the correct formula, the words Baptizo te in nomine patria et filia et spiritu sancta. Vergilius held that the sacrament had been validly conferred. Boniface complained to Pope Zachary. The latter, however, decided in favour of Vergilius.

Later on, St. Boniface accused Vergilius of teaching a doctrine in regard to the rotundity of the earth, which was: "Contrary to the Scriptures". Pope Zachary's decision in this case was that "if it be proved that he held the said doctrine, a council be held, and Vergilius expelled from the Church and deprived of his priestly dignity"

Unfortunately we no longer possess the treatise in which Vergilius expounded his doctrine. Two things, however, are certain: first, that there was involved the problem of original sin and the universality of redemption; secondly, that Vergilius succeeded in freeing himself from the charge of teaching a doctrine contrary to Scripture. It is likely that Boniface misunderstood him, taking it for granted, perhaps, that if there are antipodes*, the "other race of men" are not descendants of Adam and were not redeemed by Christ. Vergilius, no doubt, had little difficulty in showing that his doctrine did not involve consequences of that kind.
http://www.newadvent.org/cathen/15353d.htm

After the martyrdom of St. Boniface, Vergilius was made Bishop of Salzburg (766 or 767) and laboured successfully for the up building of his diocese as well as for the spread of the Faith in neighbouring heathen countries, especially in Carinthia.. In 1233 he was canonized by Gregory IX. His doctrine that the Earth is a sphere was derived from the teaching of ancient geographers, and his belief in the existence of the antipodes was probably influenced by the accounts, which the ancient Irish voyagers gave of their journeys.

* The antipodes of any place on the Earth is the point on the Earth's surface which is diametrically opposite to it. Two points that are antipodal to each other are connected by a straight line running through the centre of the Earth