GREGORY, James (1638-1675), one of the greatest names in modern mathematical and optical science, was the son of the minister of Drumoak in Aberdeenshire. He was born and brought up in the city of Aberdeen, and at an early period manifested a strong inclination and capacity for scientific pursuits. Before completing his twenty-third year he had published his famous treatise Optica Promota,
in which is explained the principle of the reflecting telescope, which is still called by his name and widely used. After the publication of this work, Gregory lost some precious time in making experiments, and allowed Newton to share with him the glory of perfecting his great invention. In telescopes of moderate size, the original or Gregorian form is still in use; but in those vast instruments adopted by the Herschels the improvements of Newton have been found indispensable. About the year 1665 Gregory went abroad and studied for some years at Padua, where he published his Vera Circuli et Hyperbola Quadratura, in which he propounded his method of an infinitely converging series for the areas of the circle and hyperbola. When this treatise was republished in 1668, the author appended to it another, entitled Geometria pars Universalis, in which he laid down with great elegance and originality a series of rules for the transmutation of curves, and the measurements of their solids of revolution. These and his other works brought Gregory into correspondence with the leading mathematicians of that day. Newton, Wallis, Halley, and Huygens, with the last of whom he carried on a discussion on the subject of his treatise on the quadrature of the circle and hyperbola. On returning to England, Gregory was elected a member of the Royal Society, and finally became professor of mathematics at St Andrews in 1669. In that same year he married a daughter of the famous painter Jameson, whom Walpole pronounced the "Scottish Vandyke." In 1674 he was transferred to the chair of mathematics in Edinburgh, which, however, he only held for about a year, when in October 1675 he was suddenly struck with blindness, while showing the satellites of the planet Jupiter to some of his students through one of his telescopes, and died a few days after at the early age of 37. James Gregory, according to Dr Hutton in his Philosophical and Mathematical Dictionary, was a man of very acute and penetrating genius. His temper was in some degree an irritable one; and, conscious of his merits as a discoverer, he seems to have been jealous of losing any portion of his reputation by the improvements of others on his inventions. He possessed one of the most amiable characters of a true philosopher, that of being content with his position in life. But the most brilliant part of his character is that of his mathematical genius as an inventor, which was of the first order.
Among the other works of Gregory, besides those we have already mentioned, are his Exercitationes Geometricae, Lond. 1668; and, it is alleged, The Great and New Art of Weighing Vanity, written to ridicule Sinclair, the slanderer of Boyle and Saunders, and published under the name of "Patrick Mathers, Archdeacon of the University of St Andrews." This latter, if it be really Gregory's, which is almost certain, is quite unworthy of its author.