Isaac Barrow, an English divine and mathematician, born in London in October, 1630, died there, May 4, 1(577. He was the nephew of Isaac Barrow, bishop of Sodor and Man, and the son of Thomas Harrow, who, though of an ancient Norfolk family, was linendraper to Charles I., whom he followed to Oxford, subsequently attending Charles II. till the restoration. Young Isaac was admitted in 1643 as a pensioner in Peterhouse, Cambridge, and in 1645 entered Trinity college, obtaining the degree of M. A. in 1652 both in Cambridge and Oxford. In 1655 he set out for the continent and the Bast, and during his journey had a successful contest with an Alge'rine corsair, of which he wrote a poetical narrative; and in Constantinople he devoted himself to the study of Chrysostom. After his return he became professor of Greek at Cambridge (1660), and of geometry at Gresham college (1662), and fellow of the newly established royal society (1663). In conformity with the will of Lucas, he was the first Lucasian professor of mathematics at Cambridge from 1663 to 1669, when he resigned this post to his pupil and friend Isaac Newton, and devoted himself to theology, his uncle giving him a small sinecure in Wales, and the bishop of Salisbury making him a prebendary.

In 1670 he received the degree of D. D.; in 1672 he became master of Trinity college, the king, whose chaplain he was, regarding him as the best scholar of England; and in 1675 he was made vice chancellor of the university of Cambridge. In mathematics, and especially geometry, he had no superior except Newton, whom he was the first to encourage. In geometry he originated the idea of the incremental triangle, and paved the way for the fluxional and differential calculus of Newton and Leibnitz. His posthumous Lectiones Mathematical (1783) are regarded as a model of sound principles. His principal mathematical works have been translated into English by Kirby and Stone, and by others, and were edited by the late William Whewell for the use of Trinity college, Cambridge (1861). In the latter part of his life he devoted himself exclusively to the church, and his pulpit discourses acquired great celebrity. His sermons were excessively long, but effective and logical, and he was honored as a prodigy of learning, wit, virtue, and piety. In his moments of leisure he composed Greek and Latin verses. He was buried in Westminster abbey, where a monument perpetuates his memory.

The first edition of his theological and ethical writings, by Dr. Tillotson and Abraham Hall, appeared in 1685. An edition by the Rev. James Hamilton was published in Edinburgh in 1842, and in New York in 1845 (3 vols. 8vo).