GREGORY, David, Savilian professor of astronomy at Oxford, and termed by Dr Smith subtilissimi ingenii mathematicus, was the eldest son of Mr Gregory of Kinnardie, brother of the before-mentioned Mr James Gregory. He was born at Aberdeen in the year 1661, and received the earlier part 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 as the heir of his genius. In the twenty-third 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, sive specimen methodi generalis dimetiendi quavis Figuras, Edinburgh, 1684, 4to. He early perceived 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 already caused several of his scholars to keep acts, as we call them," says Whiston, "upon several branches of the Newtonian philosophy; while we at Cambridge, poor wretches, were ignominiously studying the fictitious hypotheses of the Cartesian."
In 1691, on the report of Dr Bernard's intention of resigning the Savilian professorship of astronomy at Oxford, David Gregory repaired to London; and being patronized by Sir Isaac Newton, and warmly befriended by Mr Flamsteed, 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 a lasting friendship between these eminent men; and Halley soon afterwards 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 as Savilian professor, he had the degree of doctor of physics conferred on him by the university of Oxford.1
In 1693 he published, in the Philosophical Transactions, a resolution of the Florentine problem De Testudine veli firmi quadrabili; and he continued to communicate to the public, from time to time, many ingenious mathematical papers, through the same channel. In 1695 he printed at Oxford Catoptrica et Dioptrica Spherica Elementa; a work which, as he informs us in the 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, and the recommendations of Mr Jones and Dr Desaguers; 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 instruments. It is not worthy of remark, that, at 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, namely, the construction of achromatic telescopes, which Mr Dollond and Mr Ramsden carried to a high degree of perfection, had suggested itself to the mind of David Gregory, from reflecting on the admirable contrivance in 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 diverse densitatis ad lentem objectivam componendam adhibere utile foret, ut a natura factum observamus in oculi fabrica, ubi cristallinus humor (fere ejusdem cum vitro virtutis ad radios lucis refringendos) aqueo et vitreo (aqueo quoad refractionem hanc absimilibus) conjungitur, ad imaginem quam distincte fieri poterit, a natura nihil frustra moliente, in oculi fundo depingendam."2
In 1702 our author published at Oxford, Astronomia Physica et Geometrica Elementa, a work which is accounted his masterpiece. It is founded on the Newtonian doctrines, and was esteemed by Sir Isaac Newton himself an 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, Greek and Latin, in prosecution of a design, formed by his predecessor Dr Bernard, of printing the works of all the ancient mathematicians. In this work, which contains all the treatises attributed to Euclid, Dr Gregory has been careful to point out such as he found reason to believe, from internal evidence, to be the productions of some inferior geometrician. In prosecution of Dr Bernard's scheme, Dr Gregory soon afterwards engaged with his colleague Halley in the publication of the Conics of Apollonius; but he had proceeded only a little way in this undertaking when, in 1710, he died at Maidenhead, in Berkshire, in the forty-ninth year of his age. To the genius and abilities of David Gregory, the most celebrated mathematicians of the age, Sir Isaac Newton, Dr Halley, and Dr Keill, have borne ample testimony. Indeed it appears that he enjoyed, in a high degree, the confidence and friendship of Sir Isaac Newton. This illustrious philosopher intrusted him with a manuscript copy of his Principia, for the purpose of making observations on that work. These observations came too late for the first edition of Newton's great work; but he availed himself of them in the second edition. Besides the works published in his lifetime, he left in manuscript a short Treatise on 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, and by her had four sons, the eldest of whom, David, was appointed regius professor of modern history at Oxford by King George I. and died in 1767, at an advanced age, after enjoying for many years the dignity of dean of Christ Church in that university.