GREGORY (Dn. DAVID), Savilian profes sor of astronomy, at Oxford, was nephew of the above-mentioned Mr. James Gre gory, being the eldest son of his brother, Mr. David Gregory of Kinardie, a gen tleman who had the singular fortune to see three of his sons all professors of ma thematics, at the same time, in three of the British universities, viz. our author David at Oxford, the second son James at Edinburgh, and the third son Charles at St. Andrew's. Our author David, the eld est son, was born at Aberdeen, in 1661, where he received the early parts of his education, but 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 in the same year he published " Exercitatio Geometrica de Dimensione Figurarum, sive Specimen Methodi generalis dime tiendi quasvis Figuras," Edinb. 1684, 4to. He very soon perceived the excellence of the Newtonian philosophy, and had the merit of being the first that intro duced it into the schools, by his public lectures at Edinburgh "He had (says Mr. Whitson, in the Memoirs of his own life, i. 32.) 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 ignominiously stu dying the fictitious hypothesis of the Car tesian." • In 1691, on the report of Dr. Bernard's intention of resigning the Savilian pro fessorship of astronomy at Oxford, our author went to London ; and being pa tronised by Newton, and warmly be friended by Mr. Flamstead, the astrono mer royal, he obtained the vacant pro fessorship, though Dr. Halley was a com petitor. This rivalship, however, instead of animosity, laid the foundation of friend ship between these eminent men ; and Halley soon after became the colleague of Gregory, by obtaining the Professor ship 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 Professor ship, had the degree of Doctor of Physic conferred on him by the University of Oxford.
In 1693, he published in the Philos. Trans. a solution of the Florentine pro blem, " De Testudine veliformi quadra bili " and he continued to communicate to the public, from time to time, many in genious mathematical pap ers by the same channel.
1695, he printed at Oxford, " Catop trim et Dioptricx Sphxricx Elerneina, a work, which, we are informed, in the preface, contains the substance of some of his public,lectures read at Edinburgh eleven years before. This valuable trea tise was republished in English 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 appen dix, containing an account of the Grego rian and Newtonian telescopes, together with Mr. Hadley's tables for the construc tion of both those instruments. It is not unworthy of remark, that, in the conclu sion of this treatise, there is an observa tion, which shows that the construction of achromatic telescopes, which Mr Dol land has carried tosuch great perfection, had occurred to the mind of David Gre gory, from reflecting on the admirable contrivance of nature in combining the different humours of the eye. The pas
sage is as follows : " Perhaps it would be of service to make the object lens of a different medium, as we see done in the fabric of the eye ; where the crystalline humour (whose power of refracting the rays of light differs very little from that of glass) is by nature, who never does any thing in vain, joined with the aqueous and vitreous humours (not differing from water as to their power of refraction) in order that the image may be painted as distinct as possible upon the bottom of the eye." In 1702, our author published at Ox ford, in folio, " Astronomi2e Physic et Geometricx Elementa," a work which is accounted his master-piece. It is founded on the Newtonian doctrines, and was es teemed by Newton himself as a most ex cellent 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 ; being done in a prosecution of a design of his predecessor, Dr. Bernard, of printing the works of all the ancient mathemati cians. In this work, which contains all the treatises that have been 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 geometri cian. In prosecution of the same plan, Dr Gregory engaged soon after, with his colleague Dr. Halley, in the publication of the conics of Apollonius ; but he had proceeded only a little way in the under taking, when he died at Maidenhead in Berkshire, in 1710, being the 49th year of his age.
Besides those works published in our author's life-time, as mentioned above, he had several papers inserted in the Philos. Trans. vol. xviii, xix, xxi, xxiv, and xxv, .particularly a paper on the Ca tenarian curve, first considered by our author.
He left also, in manuscript, a short Treatise of the Nature and Arithmetic of Logarithms, which is printed at the end of Keill's translations of Commandine's Euclid ; and a treatise of Practical Ge Ometry, which was afterwards translat ed, and published in 1745, by Mr. Mac laurin.
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 the First, and died at an advan ced age in 1767, after enjoying, for many years, the dignity of Dean of Christ Church in that University.
When David Gregory quitted Edin burgh, he was succeeded in the Profes sorship of that University by his brother James, likewise an eminent mathemati cian, who held that office for thirty-three years, and retiring in 1725, was succeed ed by the celebrated Maclaurin. A daughter of this Professor James Gre. gory, 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. Andrews, by Queen Anne, in 1707. This office he held with reputation and ability for thi rty two years ; and resigning, in 1739, was succeeded by his son, eminently in herited the talents of his family, and died in 1763.