Nancassus, a learned Irish prelate, was born at Hannington, in Wiltshire, in 1638. He was made principal of St Albans's Hall, Oxford, in the year 1673, but removed to the provostship of Dublin College in 1678; was promoted to the bishopric of Leighlin and Ferns in 1682, translated to the archbishopric of Cashel in 1690, to that of Dublin in 1694, and raised to the primacy in 1703. Whilst he held the see of Dublin, he built a noble library for the use of the public, stocked it with choice books, and settled a provision for two librarians. He repaired, at his own expense, several decayed churches, besides buying up and restoring many impropriations, and presenting a great number of oriental manuscripts to the Bodleian Library. He was a learned and accomplished man, well versed in sacred and profane literature, in mathematics, natural philosophy, the learned languages, especially the oriental, and in both the theory and practice of music. He published, 1. Institutiones Logicae; 2. Manuductio ad Logicam, written by Philip de Trieu, to which he added the Greek text of Aristotle, and some tables and schemes; 3. An Introductory Essay on the Doctrine of Sounds. He died in 1713.