GREGORY. 
, the'method of infinites may ‘be conveniently applied to 
- Dr Gregory seems to have been one of the earliest 
Se. peel the Newtonian philosophy in Britain ; and 
the doctrines of Descartes were in the highest 
‘esteem at Cambridge, the true system of the universe 
‘was publicly taught in the university of Edinburgh. - 
In uence of a report that Dr Bernard pro- 
to resign the Savilian professorship of astronomy 
at Oxford, ry went to London in 1691, and, in 
spite of the brilliant talents of his competitor Dr Hal- 
ley, he was appointed to succeed Dr Bernard, through 
the friendship and influence of Sir Isaac Newton and 
Mr Flamstes Halley, who lost this appointment 
in ce of his attachment to infidelity, became 
afterw. the coll e of Dr , when, in 1703, 
he succeeded to Dr Wallis as Savilian professor of geo- 
metry. During Mr *s residence in London, he 
was elected a w of the Royal Society, and before 
his ap a ete the os Uy me univer- 
i Oxford conferred -u im the degree of 
elt of physic. ner 
In the year 1692, Viviani, one of the disciples of 
Galileo, had ae to mathematicians the Florentine 
lem of the quadrable dome. Leibnitz. and Ber- 
noulli had resolved this problem on the very day on 
which they had received it, and the Marquis L’ Hospi- 
tal had also given a solution, Dr Wallis and Dr Gre- 
were equally successful, and the latter:published 
solution in the Philosophical Transactions for 1693, 
under the title of Solution of the Florentine Problem, 
concerning the Testudo veliformis Quadrabilis. In 1694, 
he published another paper in the Transactions, con- 
taining a vindication of Mis uncle from a charge pre- 
ferred by the Abbot Galloise, * that James Gregory and 
‘Dr Barrow had stolen from Roberval their general pro- 
4 ions concerning ‘the transformation of curves. 
Galloise oa in the Memoirs of the Academy ‘for 
1783 ; and Dr Gregory put an end to the controversy 
by avery sharp answer, which appeared in the Philo- 
; ical Transactions for 1716, and which was the last 
‘of his communications to that learned body. 
In 1695, Mr Gregory published at Oxford his Catop 
tri- 
cee et Dioptrice Spherica@ Elementa, a Work which formed 
the substance of lectures which he delivered in 1684, 
in the university of Edinburgh, and which require no 
higher mathematical knowl than the elements of 
Euclid. This work was republished and translated by 
Dr William Browne, with several important additions; 
and a third edition of it by Dr Desaguliers, appeared in 
1735. In this work it is stated, that in the construction 
of telescopes, “it would perhaps be of service to make 
the = lens of a different medium, as we see done in 
the ic of the eye, where the crystalline humour 
(whose dona 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 on the bottom of the 
eye.” We cannot with the biographers of Dr 
Gregory, in considering this su ion as any thing 
like an anticipation of the principle of the achromatic 
telescope ; for it was impossible to form an idea of the 
“construction of that instrument, till it was discovered 
*® See Hist. Acad. Par. 1693. 
509 
that bodies possess different ‘dispersive powers. This 
remarkable of light, even the penetrating mind 
of Blowton failed wo'diesbers ahda¥@ tease tot bllons 
ourselves to diminish the well-earned reputation of 
Dollond, by giving to another any porti the praise 
which is so exclusively due to ‘himself. In the year 
1747, more than 50 years after this conjecture of Dr 
David or was published, the celebrated Euler 
suggested the human eye. as the model of an achroma- 
tic telescope, and several ignorant foreigners have ven« 
tured to claim a share of Dollond’s merit for this illus- 
trious mathematician. Whatever credit therefore may 
be given to Euler, must now be claimed for our coun 
tryman David Gregory. 
— the year ms our author published, in the Phil. 
ansactions, a long paper On the properties of the ca- 
Cotten curve “iteel ormed by a heavy he frexible 
chain, hangin eely from two points of suspension. 
The ieedbie - rd feet on is oscholion. 
tion, had been previously discovered and published by 
Huygens, Leibnitz, and Bernoulli, but without de- 
monstrations ; and Mr G proposed to himself to 
demonstrate these properties. An. anonymous writer 
in the Leipsic Acts for February 1691, attacked this 
paper as destitute of originality. Dr Gregory replied 
to this attack in the Phil Trans. for 1699, seat stioed 
as his own discovery the property of the catenaria as 
being the true geometrical of an equilibrated 
arch. This discovery, however, had been previously 
made by Dr Hooke. + 
The greatest of Dr Gregory’s works, and that on 
which his fame must rest, appeared at Oxford in 1702, 
entitled Astronomia Physice et Geometrie Elementa, 
Fol. In this valuable work, all the physical explana- 
tions are founded on the principles of the Newtonian 
hilosophy ; and the geometrical parts are either proved 
i reference to the writings of standard authors, or de- 
monstrated by lemmas inserted in their proper places. 
A very admirable analysis of this work was given, ap- 
roe by Dr ‘Halley, in.the Phil. Trans. for 1703. 
ewton himself considered these elements as an excel- 
lent defence and ition of his philosophy, 
This work was followed, in 1703, with an edition of 
Euclid, entitled Euclidis que ‘supersunt omnia, Gr. et 
Lat. ex recensione Davidis Gregorti, M.D. &c. ‘It was 
published in prosecution of a plan of Sir Henry Sa- 
ville to print the works of the ancient mathemati- 
cians. It contaihs the Elements; the Data; two mu- 
sical tracts ; the Optics and Catoptrics ; the tract De 
Divisionibus ; and a fragment, Levi et Pondero« 
$0. 
In the year 1704, Dr Gregory published, in the 
Philosophical Transactions, a paper on Cassini’s Orbit 
of the Planets, in which he shewed that the hypothe- 
‘tical curve p by that astronomer, is not consist- 
ent with the received doctrines of astronomy. : 
After Dr Halley had been appointed to the Savilian 
rofessorship of Geometry in 1703, he embarked with 
Dr Gregory in the prosecution of Sir Henry Saville’s 
plan, aad had begun the publication of the Conics of 
Apollonius ; but after having proceeded a short way in 
this undertaking, he was seized with an illness of which 
he died, at Maidenhead in Berkshire, on the 10th of Oc- 
tober 1710, in the'49th year of his age. 
He left behind him four sons by his wife Elizabeth, 
++ See Robison’s System of Mechanical Philosophy, Vol. I. 
& 
Gregory, 
David. 
—_—— 
