( 5' ) 
Omni a enim motus qut a duabus aut pluribus 
caufis pendet, eft compojitus : fo a ball out of a 
canon defcribes a curve towards the Earth, 
becaufe its direct progrefs is impeded by the 
air, and becaufe heavy bodies defcend flow- 
eft at firft. 
Such were the philofophical opinions of 
the celebrated Des Cartes: opinions which, 
as they were built on the bajelefs fabric of a 
vifiony would in time have melted into thin 
air; but the fudden oriental blaze of our 
great philofophical luminary, difpelied them, 
like a morning mift before the fun. The 
fimple power of gravitation appeared at firft 
an hypothefisj but it was an hypothefis 
confirmed by experiment, and demonftra- 
tively explanatory of the motions of the 
planets that conftitute our folar fyftem. 
This fyftem, and the Newtonian philofophy 
in general, I may probably delineate more 
at large in fome future letters. I (hall 
finifh the prefent biographically. 
Mr. Newton's celebrated Pbilofopfate Na- 
titralh Principia^ Mathematica^ was firft pub- 
liflied in 1687, by the Royal Society, under 
the infpection of Dr. Halley. In the fol- 
lowing year, he was elected member of Par- 
liament for the Univerfity of Cambridge; 
D 2 in 
