PETER of Blois (better known under the Latin form of his name, Petrus Blesensis), a learned man of the twelfth century, was born about the year 1120, at the city of Blois in France, from which he derived his name. He studied first at the university of Paris, where he displayed a fondness for poetry and rhetoric. From Paris he proceeded to Bologna to study civil and canon law, a branch of knowledge in which he very much excelled. A long-lost work of Petrus Blesensis on canon law and process was discovered some years ago, and an account of it published in the Zeitschrift für Geschichtliche Rechtswissenschaft, vol. vii. From his writings it appears that he cultivated medicine, and several branches of the mathematics, with no little care and success. But the study of theology formed the chief delight and business of his life. Unfortunately, however, the theology he studied was of that scholastic kind which consisted in vain attempts to explain and prove by logic the many absurd opinions which then prevailed. In attempting to explain the doctrine of the real presence, as held by the Latin church, he was the first who employed the famous term transubstantiation, which was soon afterwards adopted by the church, and has ever since been retained. Being appointed preceptor to William II., King of Sicily, in 1167, he obtained the custody of the privy seal; and, next to the Archbishop of Palermo, who was the prime minister, he had the greatest influence in all affairs. His power, however, was not of long duration; for the archbishop being banished in 1168, Peter soon afterwards left the court of Sicily, and returned into France. But in a short time he found another royal patron, having been invited into England by Henry II., who employed him as his private secretary, made him archdeacon of Bath, and gave him some other benefices. Having spent a few years at court, however, he got tired of that way of life, of which in one of his letters he has drawn a very unpleasing picture, and retired into the family of Richard, Archbishop of Canterbury, who had made him his chancellor about the year 1176. In this station he continued until the death of the archbishop in 1183, enjoying the highest degree of favour with that prelate, though he used much freedom in reproofing him for his remissness in the government of the church. He continued in the same station in the family of Archbishop Baldwin, who succeeded Richard, acting both as his secretary and as his chancellor. In 1187 he was also sent by the latter prelate on an embassy to Rome, to plead his cause before Urban III. in the famous controversy between him and the monks of Canterbury respecting the church of Hackington. After the departure of his friend and patron Baldwin for the Holy Land in the year 1190, Peter was in his old age involved in various troubles, the causes of which are not distinctly known; and he died in England in 1200. He appears from his works, which may be justly reckoned amongst the most valuable monuments of the age in which he flourished, to have been a man of great integrity and sincere piety, as well as of a lively, inventive genius, and uncommon erudition. His printed works consist of a great number of letters, which he collected together at the desire of Henry II., and of sermons and tracts. The best edition of his works is that of Pierre de Goussainville, Paris, 1667, fol.