a conspicuous figure in the republic of letters, being all professors of mathematics at the same time in three of the British universities, viz. David at Oxford, James at Edinburgh, and Charles at St. Andrew's.

Mr. Gregory, the subject of this memoir, while he lived at Kinardie, was a jest among the neighbouring gentlemen for his ignorance of what was doing about his own farm, but an oracle in matters of learning and philosophy, and particularly in medicine, which he had studied for his amusement, and began to practise among his poor neighbours. He acquired such a reputation in that science, that he was employed by the nobility and gentlemen of that county, but took no fees. His hours of study were singular, Being much occupied through the day with those who applied to him as a physician, he went early to bed, rose about two or three in the morning, and, after applying to his studies for some hours, went to bed again, and slept an hour or two before breakfast. He was the first man in that country who had a barometer; and hav ing paid great attention to the changes in it, and the corresponding changes in the weather, he was once in danger of being tried by the presbytery for witchcraft or conjuration. A deputation of that body waited upon him to inquire into the ground of certain reports that had come to their ears; but, affording them ample satisfaction, a prosecution was prevented.

About the beginning of the last century, he removed with his family to Aberdeen, and in the time of queen Anne's wars employed his thoughts upon an improvement in artillery, in order to make the shot of great guns more destructive to the enemy, and executed a model of the engine he had contrived. The late Dr. Reid, in his additions to the lives of the Gregorys, published in Hutton's Dictionary, informs us that he conversed with a clockmaker at Aberdeen, who had been employed in making this model; but having made many different pieces by direction without knowing their intention, or how they were to be put together, he could give no account of the whole. After making some experiments with this model, which satisfied him, Mr. Gregory was so sanguine in the hope of being useful to the allies in the war against France, that he set about preparing a field equipage with a view to make a campaign in Flanders, and in the mean time sent his model to his son the Saviliau professor, the subject of our next

Sir

article, that he might have his, and sir Isaac Newton's opinion of it. His son shewed it to Newton without letting him know that his own father was the inventor of it. Isaac was much displeased with it, saying, that if it had tended as much to the preservation of mankind, as to their destruction, the inventor would have deserved a great reward but, as it was contrived solely for destruction, and would soon be known by the enemy, he rather deserved to be punished, and urged the professor very strongly to destroy it, and if possible, to suppress the invention. It is probable the professor followed this advice, as he died soon after, and the model was never found. Sir Isaac's objection, however, appears rather to be fastidious, and might apply with equal force to any improvement in muskets, &c. or to gunpowder itself. When the rebellion. broke out in 1715, Mr. Gregory went a second time to Holland, and returned when it was over to Aberdeen, where he died about 1720, aged ninety-three, leaving behind him a history of his own time and country, which was never published. One of his daughters was mother to the late celebrated Dr. Thomas Reid of Glasgow, by whom the above particulars were first communicated.'

GREGORY (DAVID), son of the preceding, and nephew to the inventor of the reflecting telescope, was born June 24, 1661, at Aberdeen; where he also received the first grounds of his learning, but was afterwards removed to Edinburgh, and took his degree of M. A. in that university. The great advantage of his uncle's papers induced his friends to recommend the mathematics to him; and he had a natural subtilty of genius particularly fitted for that study, to which he applied with indefatigable industry, and succeeded so well that he was advanced to the mathematical chair, at Edinburgh, at the age of twenty-three. The same year he published a treatise, entitled "Exercitatio Geometrica de dimensione figurarum," Edinb. 1684, 4to, in which assuming the doctrine of indivisibility, and the arithmetic of infinites, as already known, he explained a method which not only suited his uncle's examples, left by him without any way of finding them, but discovered others, by which an infinite number of curve-lines, and the areas contained between them and right lines (such as no other method then known extended to) might be measured. He

' Hutton's Dict.—Gleig's Supplement to the Encycl. Britannica.

had already seen some hints in his uncle's papers concern. ing sir Isaac Newton's method, of which he made the best use he could*; and the advantage he found thereby raised an ardent desire in him to see that method published. Under this impatient expectation, the "Principia" was no sooner out in 1687, but our author took it in hand, and presently made himself so much master of it as to be able to read his professorial lectures upon the philosophy contained in it, and, causing his scholars to perform their exercises for their degrees upon several branches of it, be came its first introducer into the schools.

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He continued at Edinburgh till 1691, when, hearing of Dr. Bernard's intention to resign the Savilian professorship of astronomy at Oxford, he left Scotland, and, coming to London, was admitted a member of the royal society and paid his addresses to sir Isaac Newton, who took the first opportunity of recommending him to Mr. Flamstead (master of the mathematical school in Christ's-hospital, London), with a letter, recommending his mathematical merit above all exception in these terms: "Sir, it is almost a fortnight since I intended, with Mr. Paget and another friend or two, to have given you a visit at Greenwich; but sending to the Temple coffee-house, I understood you had not been in London for two or three weeks before, which made me think you were retired to your living for a time. The bearer hereof, Mr. Gregory, mathematic professor of Edinburgh college, in Scotland, intended to have given you a visit with us. You will find him a very ingenious person, and a good mathematician, worth your acquaintance." In proceeding, he mentions our author as a fit person, in case of Mr. Flamstead's death, to carry on his astronomical views. Thus recommended, the royal astronomer used his best interest to procure him success at Oxford, where he was elected astronomy-professor this year, having been first admitted of Baliol college, and incorporated M. A. February 8, and he was created M. D. on the

* In his Latin "Treatise of Practieal Geometry," there is a series of his uncle's, which he recommends for squaring the circle, though it converges so slow, as to be utterly of no use in practice, without some farther artifice. This is observed by Mr. Maclaurin, who published an English translation of it in 1745, 8vo, with additions, and the second edition was printed at Edin

burgh, 1751, 8vo. However, Mr. Maclaurin's remark shews our author's skill in infinite series to be very imperfect, at the time of reading those lectures, from which the tract was compiled after his death; and Mr. Cotes, of Cambridge, spoke slightly of his abilities în that doctrine. Gen. Dict. vol. IV. p. 144.

18th of the same month, but he had no relish for the technical part of his profession, and was seldom seen in the observatory. His genius lay more to geometry, and in that way he succeeded very well, both in his elements of optics, and of physical and geometrical astronomy. This last is reckoned his master-piece; and, having finished it in 1702, folio, he immediately engaged in carrying on the noble design of his predecessor, Dr. Bernard, to print all the works of the ancient mathematicians, the first-fruits of which appeared in an edition of Euclid's works in Greek and Latin, folio, the following year. In the same design he afterwards joined with his colleague, Dr. Halley, in preparing an edition of "Apollonius's Conics:" Dr. Bernard had left materials for the four first books, which our author undertook to complete, but was prevented by his death, which happened October 10, 1708. He died at the Greyhound-inn, at Maidenhead, in Berkshire, in his way from London to Bath. His disorder was a consumption. He was interred at Maidenhead, but there is a handsome marble monument erected to his memory in St. Mary's church at Oxford, by his wife.

Our professor's genius lay chiefly in inventing new and elegant demonstrations of the discoveries made by others. He gave the first demonstration of that curve, which is well known since by the name of catenaria, or the curve that is formed by a chain fastened at each end; and first discovered, that this curve inverted gave the form of a true and legitimate arch, all the parts supporting each othert. There are several other papers of his in the "Philosophical Transactions," vols. XVIII. XIX. XXI. XXIV. and XXV. He left also in MS. "A short treatise of the nature and arithmetic of Logarithms," which is printed at the end of Keill's translation of Commandine's Euclid; and the "Treatise of Practical Geometry" mentioned in the note, as published by Mr. Maclaurin. His explication of sir Isaac Newton's

*It was published in 1695, in Latin, entitled "Catoptricæ & Dioptrica Sphericæ Elementa, Oxon." 8vo, and was compiled from his lectures, read at Edinburgh in 1684. In it he gives the preference to sir Isaac Newton's reflecting telescope, above that of his uncle James Gregory. It was much esteemed for the neatness and easiness of the demonstrations; and a second edition in English came out in 1705,

by Dr. Browne; and a third in 1735, by Dr. Desaguliers, who added an appendix, containing the history of the two reflecting telescopes, with their several improvements at that time.

This is printed in the Phil. Trans. No. 231. He observes, that arches of all other forms, in stone, brick, and the like, are only supported by including some catenary curve, within the breadth of their ferming stones.

method, to construct the orbit of a comet by three accurate observations, is commended by Dr. Halley. Our author was a most intimate and confidential friend of sir Isaac, and was intrusted with a manuscript copy of the " Principia," for the purpose of making observations on it. Of these Newton availed himself in the second edition, they having come too late for his first publication, which was exceedingly hurried by Dr. Halley, lest Newton's backwardness might not let it appear at all. There is a complete copy of these observations preserved in the library of the university of Edinburgh, presented to it by Dr. James Gregory, the present professor of the practice of medicine. These contain many sublime mathematical discussions, many valuable commentaries on the "Principia," and many interesting anecdotes. There are in it some paragraphs in the hand-writing of Huygens relative to his theory of light.

Dr. David Gregory married, in 1695, Elizabeth, the daughter of Mr. Oliphant of Langtown in Scotland. By this lady he had four sons, of whom, the eldest, DAVID, was elected, from Westminster school in 1714, student of Christ church, Oxford; became rector of Semly in Wiltshire; was installed canon of Christ church, June 8, 1736, and dean, May 18, 1756. He was appointed the first professor of modern history and languages on the foundation of that professorship by George I. prolocutor of the lower house of convocation, and master of Sherburn hospital, near Durham. He died and was interred in Christ church cathedral, 1767, in the seventy-first year of his age, in the same grave with his wife Mary (Grey), who died in 1762.

When Dr. David Gregory, the Savilian professor, quitted Edinburgh, he was succeeded in the professorship at that university by his brother JAMES, likewise an eminent mathematician; who held that office for thirty-three years, and, retiring in 1725, was succeeded by the celebrated Maclaurin. A daughter of this professor James Gregory, a young lady of great beauty and accomplishments, was the victim of an unfortunate attachment, that furnished the subject of Mallet's well-known ballad of "William and Margaret." Another brother, CHARLES, was created professor of mathematics at St. Andrew's by queen Anne, in 1707. This office he held with reputation and ability for thirty-two years; and, resigning in 1739, was succeeded.