43 RE 
tion of Mr. Jones and Dr. Desaguliers, and 
afterwards by the latter of these gentle- 
men ; with an appendix, containing an ac- 
count 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 conclusion of this treatise, 
there is an observation which shows that 
the construction of achromatic telescopes, 
which Mr. Holland has carried to such 
great perfection, had occurred to the mind 
of David Gregory, from reflecting on the 
admirable contrivance of nature in com- 
bining the different humours of the eye. 
The passage 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 Oxford, 
in folio, “ Astronpmiae Physic® et Geome- 
tricas Elementa,” a work which is account- 
ed hig master-piece. It founded on the 
Newtonian, doctrines, and was esteemed by 
Newton himself as a most excellent expla- 
nation 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 prosecu- 
tion of a design of his predecessor Dr. Ber- 
nard, of printing the works of all the an- 
cient' mathematicians. In this work, which 
contains all the treatises that have been 
attributed to Euclid, Dr. Gregory lias been 
careful to point out such as he found reason, 
from internal evidence, to believe to be the 
productions of some inferior geometrician. 
In prosecution of the same plan, Dr. Gre- 
gory engaged soon after, with his colleague 
Dr. Halley, in the publication of the conics 
pf Apollonius ; but' lie had proceeded only 
a little way in flie undertaking, 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, be 
had several papers inserted in the Philos. 
Trans, vol. xviii, xix, xxi, xxiv ; and xxv, 
particularly a paper on the Catenarian 
curve, first considered by our author. 
He left also, in manuscript, a short Trea- 
tise of the Nature and Arithmetic of Loga- 
GRE 
rithms, which is printed at the end of Keill’# 
translations ot 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 lie 
had four sons, of whom, the eldest, David, 
was appoined Regius Professor of modern 
history, at Oxford, by King George the 
First, and died at an advanced age in 1767, 
after enjoying, for many years, the dignity 
of Dean of Christ Church: in that Univer- 
sity. 
When David Gregory quitted Edinburgh, 
he was succeeded in the Professorship of 
that University by his brother James, like- 
wise an eminent mathematician, y ho 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 vic- 
tim of an unfortunate attachment, that fur- 
nished the subject of Mallet’s well-known 
ballad of Wjlliam and Margaret. 
Another brother, Charles, was created 
Professor of Mathematics at St. Andrew’s, 
by Quedn Anne, in 1707. This office he 
held with reputation and ability for thirty- 
two years ; and resigning in 1739, was suc- 
ceeded by his son, who eminently inherited 
the talents of liis family, and died in 
1763. 
GRENADE, or grenado, in military 
affairs, a kind of small bomb or shell, being 
furnished with a touch-hole and fuse, aud is 
thrown by hand from the tops, iience they 
are frequently styled hand-grenades. The 
best way to secure one’s-self from the ef- 
fects of a grenade, is to lie flat down on the 
ground before it bursts. 
The grenades are of much later inven- 
tion and use than the bomb. They are 
usually about three inches in diameter, and 
weigh near three pounds. The metal may 
be one quarter or three-eighths of ail inch 
thick, and the hole about one-sixth. 
GREWIA, in botany, so named in ho- 
nour of Nehemiah Grew, M. D. F. R. S. 
fhe famous author of the “ Anatomy of Ve- 
getables,” a genus of the Gynaudria Poly- 
andria class and order. Natpral order of 
Columniferae. Tiliacese, Jussieu. Essen- 
tial character : calyx five-leaved ; petals 
five, with a iiectareous scale at the base of 
each ; berry four-celled. There are thir- 
teen species. 
GRIAS, in botany, a genus of the Po, 
