NEWTONIAN PHILOSOPHY. 
with the mechanical and mathematical phi- 
losophy. Others again, by Newtonian phi- 
losophy, understand that part of physical 
knowledge which Sir Isaac Newton has 
handled, imprbved, and demonstrated in 
his Principia. And, lastly, some by New- 
tonian philosophy, mean the new principles 
which Sir Isaac has brought into philosophy, 
the new system founded thereon, and the 
new solutions of phenomena thence de- 
duced ; or that which characterizes and dis- 
tinguishes his philosophy from all others ; 
and this is the sense, in which we shall 
chiefly consider it. 
As to the history of this philosophy, we 
have but little to say : it was first made 
public in 1686, by the author, then a fellow 
of Trinity College, Cambridge ; and in the 
year 1713, republished with considerable 
improvements. Several other authors have 
since attempted to make it plainer, by set- 
ting aside many of the more sublime mathe- 
matical researches, and substituting either 
more obvious reasonings or experiments in 
lieu thereof ; particularly Mr. Whiston, in 
his Prelect. Phys. Mathem. ’s Gravesande, 
in his Elem. and Inst, and the learned Com- 
ment of Le Seur and Jacquier upon Sir 
Isaac’s Principia. 
The philosophy itself is laid down chiefly 
in the third book of the Principia; the 
two preceding books being taken up in 
preparing the way, and demonstrating such 
principles of mathematics as have the most 
relation to philosophy : such are the laws 
and conditions of powers; and these, to 
render them less dry and geometrical, the 
author illustrates by scholia in philosophy, 
relating chiefly to the density and resistance 
of bodies, the motion of light and sounds, 
a vacuum, &c. In the third book he pro- 
ceeds to the philosophy itself; and from 
the same principles deduces the structure 
of the universe, and the powers of gravity, 
whereby bodies tend towards the Sun and 
planets ; and, from these powers, the mo- 
tions of the planets and comets, the theory 
of the Moon and the tides. This book, 
which he calls De Mundi Systemate, he 
tells us, was first written in the popular way ; 
but considering, that such as are unac- 
quainted with the said principles, would 
not conceive the force of the consequences, 
nor be induced to lay aside their ancient 
prejudices ; for this reason, and to prevent 
the thing from being in continual dispute, 
he digested the sum of that book into pro- 
positions, in the mathematical manner, so 
as it might only eoine to be read by such 
as had first considered the principles ; not 
that it is necessary a man should master 
them all, many of them, even the first rate 
mathematicians, would find a difficulty in 
getting over. It is enough to have read 
the definitions, laws of motion, and the 
three first sections of the first book; after 
which, the author himself directs us to pass 
on to the book De Systemate Mundi. 
Tlie great principle on which the whole 
philosophy is founded, is the power of gra- 
vity : this principle is not new ; Kepler, 
long ago, hinted at it in his Introduct. ad 
Mot. Martis. He even discovered some of the 
properties thereof, and their effects in the 
motions of the primary planets ; but the 
glory of bringing it to a physical demon- 
stration, was reserved to the English 
philosopher. See Gravitation. His 
proof of this principle from phenomena, 
together with the application of the same 
principle to the various other appearances 
of nature, or the deducing those appear- 
ances from fliat principle, constitute the 
Newtonian system; which, drawn in minia- 
ture, will stand thus : 
I. The phenomena are, 1. That the sa- 
tellites of Jupiter do, by radii drawn to 
the centre of the planet, describe areas pro- 
portional to the times ; and that their peri- 
odical times are in a sesqiiiplicate ratio of 
their distances from its centre; in which 
the observations of all astronomers agree. 
2. The same phenomenon holds of the 
satellites of Saturn, with regard to Sa- 
turn ; and of the Moon, with regard to the 
Earth. 3. The periodical times of the pri- 
mary planets about the Sun, are in a sesqui- 
plicate ratio of their mean distances from 
the Sun. But, 4. The primary planets do 
not describe areas any way proportional to 
their periodical times about the Earth ; 
as being sometimes seen stationary, and 
sometimes retrograde, with regard thereto. 
II. The powers whereby the satellites 
of Jupiter are constantly drawn out of 
their rectilinear course, and retained in 
their orbits, respect the centre of Jupiter, 
and are reciprocally as the squares of their 
distances from the same centre. The same 
holds of the satellites of Saturn, with re- 
gard to Saturn ; of the Moon, with regard 
to the Earth ; and of the primary planets, 
with regard to the Sun. See Centrai. 
FORCES. 
III. The Moon gravitates towards the 
Earth, and by the power of that gravity is 
retained in her orbit: and tlie same holds of 
the other satellites with respect to their 
