Ageometer and theologian who also contributed to the field of optics, Isaac Barrow is best known for the influence he exerted over the career of the young Isaac Newton (1642-1727). Among his most important published works were Euclidis elementorum libri XV and Lectiones geometricae, in which he interpreted and synthesized the ideas of more well-known geometers for a popular audience.
Barrow's father, Thomas, was a merchant and linen draper for King Charles I, and his mother Anne died shortly after her son's birth in London in 1630. The boy proved an unruly student, and after a stint at the Charterhouse school, he was sent to Felsted School in Essex, where schoolmaster Martin Holbeach had a reputation as a stern disciplinarian. Barrow thrived in this environment, and became immersed in subjects that included Latin, Greek, Hebrew, French, logic, and the classics.
In the unrest leading up to the English Civil War (1642-48), Barrow's father suffered financial losses, and the son was forced to take a job as a tutor. In 1646, however, he obtained a scholarship to Trinity College, Cambridge, from whence he graduated two years later. In 1649, he was elected as a college fellow, and in 1652 earned his M.A., whereupon he went to work as a college lecturer and university examiner. He published his first work, Euclidis elementorum libri XV, in 1654. A translation of writings by Euclid (c. 325-c. 250 b.c.), the book became highly popular, and eventually appeared in a pocketsized edition.
With his rising fortunes, Barrow seemed a natural choice to take a highly respected Regius professorship in Greek, but again political tensions intervened. The university chancellor responsible for choosing among the candidates was none other than Oliver Cromwell, leader of the Puritans who overthrew Charles in the Civil War; and given Barrow's ties to the monarchy, he had no chance of obtaining the position. Embittered, Barrow spent nearly five years away from England, travelling through France, Italy, and Turkey on a Trinity College fellowship.
By 1660, when Barrow returned to his homeland, the political tides were turning again, and with the restoration of King Charles II to the throne, Barrow was ordained in the Anglican Church and appointed to the Regius professorship. He had become increasingly interested in mathematics while abroad, and now began supplementing his income by teaching geometry and astronomy at Gresham College. This led to his 1663 appointment as Lucasian professor of mathematics at Cambridge, a position that carried with it enough funds that he could give up his other teaching jobs.
As a further hallmark of his restored fortunes, Barrow was appointed as the first fellow of the recently founded Royal Society of London in 1663. In the six years that followed, he developed a series of lectures on geometry, or Lectiones geometricae, in which he brought together ideas from René Descartes (1596-1650), John Wallis (1616-1703), and James Gregory (1638-1675) in a format comprehensible to the rising generation of scholars.
Among the latter was Isaac Newton, for whom Barrow served as scholarship examiner in 1664. Biographers have generally credited Barrow with providing the initial spark of inspiration that, under considerable development by Newton, would lead to the latter's epochal work in physics. Particularly notable was Barrow's work in optics, which has long been overshadowed by Newton's considerably more impressive achievements in that field. As the student became greater, the teacher's impact receded: in 1669, Barrow stepped down as Lucasian professor in favor of Newton.
Barrow went on to serve as royal chaplain, and in 1673 returned to Trinity College at the king's request. He became vice chancellor in 1675, but died two years later at age 47. Barrow had never married, and the evidence indicates that he died of a drug overdose.