for the science, aiul a deep sense of duty, he now devoted the whole of his attention to tlie study of mathematics; and though lie had a decided preference for geometry, he did not confine himself to it, to the exclusion of the other branches of mathematical study, in most of which there is abundant evidence of his being well skilled. From 1711, he continued for nearly half a century to teach mathematics to two separate classes, at different hours, for five days in the week, during a continued session of seven months. His lectures were given with such perspicuity of method and language, and his demonstrations were so clear and successful, that among his scholars several rose to distinction as mathematicians; among whom may be mentioned the celebrated names of Colin Maclaurin, Dr Matthew Stewart, professor of mathematics at Edinburgh; the two reverend doctors Williamson, one of whom succeeded Dr Simson at Glasgow; the reverend Dr Trail, formerly professor of mathematics at Aberdeen; Dr James Moor, Greek professor at Glasgow; and professor Robison of Edinburgh, with many others of distinguished merit.
In 1758, Dr Simson having arrived at the advanced age of seventy-one years, found it expedient to employ an assistant in teaching; and in 1761, on his recommendation, the reverend Dr Williamson was made his assistant and successor. For the last remaining ten years of his life, he enjoyed a share of good health, and was chiefly occupied in correcting and arranging some of his mathematical papers; and sometimes, for amusement, in the solution of problems and demonstrations of theorems, which had occurred from his own studies, or from the suggestions of others. Though to those most familiar with him, his conversation on every subject seemed clear and accurate, yet he frequently complained of the decline of his memory, which no doubt protracted and eventually prevented him from undertaking the publication of many of his works, which were in an advanced state, and might with little exertion be made ready for the press. So that his only publication, after resigning his office, was a new and improved edition of Euclid's Data, which, in 1762, was annexed to the second edition of the Elements. From that period, he firmly resisted all solicitations to bring forward any of his other works on ancient geometry, though he was well aware how much it was desired from the universal curiosity excited respecting his discovery of Euclid's Porisms. It is a matter of regret, that out of the extensive correspondence which he carried on through life with many distinguished mathematicians, a very limited portion only is preserved. Through Dr Jurin, then secretary to the Royal Society, he had some intercourse with Dr Halley and other celebrated men; he had also frequent correspondence with Mr Maclaurin, with Mr James Stirling, Dr James Moor, Dr Matthew Stewart, Dr William Trail, and Mr Williamson of Lisbon. In the latter part of his life, his mathematical correspondence was chiefly with that eminent geometer, the earl of Stanhope, and with George Lewis Scott, esquire.
A life like Dr Simsori's, so uniform and regular, spent for the most part within the walls of a college, affords but little that is entertaining for the biographer. His mathematical researches and inventions form the important part of his history; and, with reference to these, there are abundant materials to be found in his printed works and MSS.; which latter, by the direction of his executor, are deposited in the college of Glasgow.
Dr Simson never was married; he devoted his life purely to scientific pursuits. His hours of study, of exercise, and amusement, were all regulated with the most unerring precision. "The very walks in the squares or gardens of the college were all measured by his steps; and he took his exercises by the hundred of paces, according to his time or inclination." His disposition was by no means of a saturnine cast: when in company with his friends his con-
