GREGORY, David, Savilian professor of astronomy at Oxford, whom Dr Smith has termed subtilissimi ingenii mathematicus, was the eldest son of Mr Gregory of Kinnairdy, brother of the above-mentioned Mr James Gregory. He was born at Aberdeen in 1661, and received the earlier parts of his education in that city. He completed his studies at Edinburgh; and, being possessed of the mathematical papers of his uncle, soon distinguished himself likewise as the heir of his genius. In the 23d year of his age, he was elected professor of mathematics in the university of Edinburgh; and published, in the same year, Exercitatio Geometrica de dimensione figurarum, five specimen methodi generalis dimetendi quasvis figuras, Edinburgh, 1684, 4to. He saw very early the excellence of the Newtonian philosophy; and had the merit of being the first who introduced it into the schools by his public lectures at Edinburgh. "He had (says Mr Whiston *) already caused several of his scholars to keep acts, as we call them, upon several branches of the Newtonian philosophy; while we at Cambridge, poor wretches, were ignomi-
nially studying the fictitious hypotheses of the Cartesianians."
In 1691, on the report of Dr Bernard's intention of resigning the Savilian professorship of astronomy at Oxford, David Gregory went to London; and being patronized by Sir Isaac Newton, and warmly befriended by Mr Flamstead the astronomer royal, he obtained the vacant professorship, for which Dr Halley was a competitor. This rivalry, however, instead of animosity, laid the foundation of friendship between these eminent men; and Halley soon after became the colleague of Gregory, by obtaining the professorship of geometry in the same university. Soon after his arrival in London, Mr Gregory had been elected a fellow of the royal society; and, previously to his election into the Savilian professorship, had the degree of doctor of physic conferred on him by the university of Oxford (A).
In 1693, he published in the Philosophical Transactions a resolution of the Florentine problem de Testudine veliformi quadrabili; and he continued to communicate to the public, from time to time, many ingenious mathematical papers by the same channel. In 1695, he printed at Oxford Catoptrica et Dioptrica Sphaerica Elementa; a work which, as he informs us in his preface, contains the substance of some of his public lectures read, eleven years before, at Edinburgh. This valuable treatise was republished first with additions by Dr William Brown, with the recommendation of Mr Jones and Dr Desaguliers; and afterwards by the latter of these gentlemen, with an appendix containing an account of the Gregorian and Newtonian telescopes, together with Mr Hadley's tables for the construction of both those instruments. It is not unworthy of remark, that, in the end of this treatise, there is an observation which shows, that what is generally believed to be a discovery of a much later date, the construction of achromatic telescopes, which has been carried to great perfection by Mr Dollond and Mr Ramsden, had suggested itself to the mind of David Gregory, from the reflection on the admirable contrivance of nature in combining the different humours of the eye. The passage is as follows: "Quod si ob difficultates physicas in speculis idoneis torno elaborandis et poliendis, etiamnum lentibus uti oporteat, fortassis media diversæ densitatis ad lentem objectivam componendam adhibere utile foret, ut à natura factum observeremus in oculi fabrica, ubi cristallinus humor (fere ejusdem cum vitro virtutis ad radios lucis refringendos) aequo et vitreo (aquæ quoad refractionem haud absimilibus) conjungitur, ad imaginem quam distincte fieri poterit, à natura nihil frustra moliente, in oculi fundo depingendam." Catopt. et Dioptr. Sphaer. Elem. Oxon. 1695, p. 98.
In 1702 our author published at Oxford, Astronomiæ Physicæ
* Memoirs of his own life, i. 32.
(A) On obtaining the above professorship, he was succeeded in the mathematical chair at Edinburgh by his brother James, likewise an eminent mathematician; who held that office for 33 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, which 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 32 years; and, resigning in 1739, was succeeded by his son, who eminently inherited the talents of his family, and died in 1763.
Gregory. Physice et Geometricæ Elementa; a work which is accounted his masterpiece. It is founded on the Newtonian doctrines, and was esteemed by Sir Isaac Newton himself as a most excellent explanation and defence of his philosophy. In the following year he gave to the world an edition in folio of the works of Euclid in Greek and Latin; in prosecution of a design of his predecessor Dr Bernard, of printing the works of all the ancient mathematicians. In this work, although it contains all the treatises attributed to Euclid, Dr Gregory has been careful to point out such as he found reason, from internal evidence, to believe to be the productions of some inferior geometer. In prosecution of Dr Bernard's plan, Dr Gregory engaged, soon after, with his colleague Halley, in the publication of the Conics of Apollonius; but he had proceeded but a little way in this undertaking when he died, in the 49th year of his age, at Maidenhead in Berkshire, A. D. 1710. To the genius and abilities of David Gregory, the most celebrated mathematicians of the age, Sir Isaac Newton, Dr Halley, and Dr Keill, have given ample testimonies. Indeed it appears that he enjoyed, in a high degree, the confidence and friendship of Sir Isaac Newton. This philosopher entrusted him with a manuscript copy of his Principia, for the purpose of making observations on that work. Of these observations there is a complete copy preserved in the library of the University of Edinburgh. They contain many valuable commentaries on the Principia, many interesting anecdotes, and various sublime mathematical discussions. Some of the paragraphs are in the hand-writing of Huygens, and they relate to the theory of light of this philosopher. The observations of Dr Gregory had come too late for the first edition of Newton's great work; but he availed himself of them in the second. Besides those works published in his lifetime, he left in manuscript, A Short Treatise of the Nature and Arithmetic of Logarithms, which is printed at the end of Dr Keill's translation of Commandine's Euclid; and a Treatise of Practical Geometry, which was afterwards translated, and published in 1745, by Mr Maclaurin.
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 appointed regius professor of modern history at Oxford by King George I. and died in 1767, in an advanced age, after enjoying for many years the dignity of dean of Christ-church in that university.