Review of the Principia of Newton. 29 
existence is occult, and imagined not proved, but not those, 
whose real existence is cleariy demonstrated by-observations. 
objections might be made to the affinities, and fun- 
damental principles of Chemistry, as the operative agents 
a a, 1 occult qualities, their nature and essence being 
wholly unknown. 
Newton repeatedly discarded iar attempts to investigate 
the physical properties or nature of those forces, whose laws 
he has so'successfully ab a ae ; I do not,” says he, 
** enquire into the physical causes and seats of those forces ; 
I indifferently, and promiscuously use for each other, the 
words attraction, impulse, or any kind of propension towards 
the centre, by considering these forces not physically, = 
mathematically,” &c. Not to detain the reader longer 
apparently obsolete point, I would refer the curious, he 
wish for more-information, to the Principia itself, and the ve- 
ry excellent introduction to it, by that great Philosopher, and 
Analyst, Mr. Roger Cot 
The principal subject of the 2d and 3d sections of the 
Principia, was the investigation of the ratio of the central 
action of the centripetal force to_be in motion by virtne of its 
inertia only, which by the first law of motion would be uni- 
form, and rectilinear. This, it is well known, must be the 
effect of some force, which has ceased to act. Hence curvi- 
linear orbits are the eflects of a motion continued by inertia, 
and. such variations of centripetal force, as may be necessary 
> for movements i in any sang deres curve. Bienes are the phy- 
arisen rai albanien epcoaetet the Files Ova Soikeue 
force only, or this regulated, or modified by the action of 
some contiguous bodies, whether by virtue of a constant force, 
or one perpetually varied aceording to any law of distance. 
These subjects are with great sagacity treated of generally, 
by our author, in the subsequent parts of this work, as far as 
they related to his grand philosophical object. — Bat he had 
not leisure to pursue them to the extent, to which his suc- 
cesso! 
rs, disp 
ers\-of analysis, have carried them. ° In the general en- 
thusiasm, which prevailed among mathematicians n pe Emi 
plove of the 17th century, for propounding to one the, 
