ORE 



GRE 



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 'stables for the construe- 

 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 to such 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, " Astronomiae Physicse et 

 Geometricae 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 conies 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, 

 hejhad 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 If45, 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 thirty- 

 two years ; and resigning, in 1739, was 

 succeeded by his son, who eminently in- 

 herited the talents of his family, and died 

 in 1763. 



GRENADE, or GHEKADO, in military 

 affairs, a kind of small bomb or shell, 

 being furnished with a touch-hole and 

 fuse, and is thrown by hand from the 

 tops, hence they are frequently styled 

 hand-grenades. The best way to secure 

 one's-self from the effects of a grenade 

 is to lie flat down on the ground before it 

 bursts. 



The grenades are of much later in- 

 vention and use than the bomb. They 

 are usually about three inches in diame- 

 ter, and weigh near three pounds. The 

 roetal may be one quarter or three-eighths 

 of an inch thick, and the hole about one- 

 sixth. 



GREWIA, in botany, so named in ho- 

 nour of Nehemiah Grew, M. D. F. R. S. 

 the famous author of the " Anatomy of 



