trusted Gregory with a copy of his Principia in manuscript, on which Gregory
wrote a commentary; of the benefit of which the great author availed himself
in the second edition. Dr John Gregory presented a manuscript copy of this
to the university of Edinburgh, in the library of which it is carefully preserved. Of his posthumous works, two deserve particularly to be noticed; one on practical geometry, published by Mr Colin Maclaurin, and a small treatise
on the nature and arithmetic of Logarithms, subjoined to Keil's Euclid, which contains a simple and' comprehensive view of the subject.
An anecdote is told of David Gregory of Kinnaifdie, Dr Gregory's father, which it would not perhaps, be altogether proper to omit. He had, as was remarked at the beginning, a turn for mathematical and mechanical subjects, and during queen Anne's wars had contrived a method to increase the effect of field ordnance. He sent it to the Savilian professor, his son, wishing his opinion, together with Sir I. Newton's. Gregory showed it to Newton, who advised him earnestly to destroy it, as said Newton, "Any invention of that kind, if it even were effectual, would soon become known to the enemy, so that it would only increase the horrors of war." There is every reason to think that the professor followed Newton's advice, as the machine was never afterwards to be found.
It is a more singular circumstance, and indeed without parallel in the scientific history of Scotland, that this old gentleman lived to see three of his sons professors at the same time, viz. David, the subject of the preceding sketch; James, who succeeded his brother in the chair of mathematics at Edinburgh; and Charles, professor of mathematics in the university of St Andrews.
GREGORY, James, whose valuable discoveries served so much to accelerate the progress of the mathematical and physical sciences in the seventeenth century, was born in 1638, at Drumoak in Aberdeenshire, where his father, the reverend John Gregory, was minister. Little is known of James Gregory's father, but from some slight notice of him in the Minutes of the General Assembly; and whatever part of the genius of the subject of this memoir was possessed by inheritance seems to have descended from the mother. It is an observation of a distinguished philosopher of the present day, Dr Thomson, that, "he never knew a man of talent whose mother was not a superior woman;" and a more happy instance of the truth of this remark could not be found than that of James Gregory. Mrs Gregory seems to have descended from a family of mathematicians. Her father was Mr David Anderson of Finghaugh, whose brother, Alexander Anderson, was professor of mathematics, (about the beginning of the seventeenth century,) in the university of Paris, and he himself was long noted for his application to mathematical and mechanical subjects. The reverend John Gregory died when the subject of this article was yet in his boyhood, and left the care of the education of James to David, an elder brother, and the surviving parent. The mother having observed the expanding powers of his mind, and their tendency to mathematical reasoning, gave these early indications of his genius all possible encouragement, by instructing him herself in the elements of geometry. Having received the rudiments of his classical education at the grammar school of Aberdeen, he completed the usual course of studies at Marischal college. For a considerable time after leaving the university, James Gregory devoted his attention to the science of optics. The celebrated French philosopher Descartes had published his work on Dioptrics the year before Gregory was born, nor had any advances been made in that science until James Gregory published the result of his labours in a work printed at London in 1663, entitled, "Optics Promoted, or the mysteries of reflected and refracted rays demonstrated by the elements of geometry; to which is added, an appendix, exhibiting a solution of some of the most diffi-
