NAT 
'them, without any change, till it be acted 
upon by something external. Law 2. The 
motion, or change of motion, is always pro- 
portional to the moving force by which it is 
produced, and in tlie direction of tlm right 
line in which that force is impressed. If a 
certain force produce a certain motion, a 
double force \Vill produce double tlie mo- 
tion, a triple force triple the motion, and so 
on. And this motion, since it is always di- 
rected to the same point with the generat- 
ing force, if the body were in motion before, 
is either to be added to it, as where the 
motions conspire j oi' subtracted from it, as 
when they are opposite; or combined 
obliquely, when oblique: being always 
compounded with it according to the de- 
naination of each. Law 3. Re-action is 
always contrary and equal to action ; or the 
actions of two bodies upon one anotlier are 
always mutually equal, and directed con- 
trary ways, and are to be estimated always 
in the same right line. Thus, whatever 
body presses or draws another is equally 
pressed or drawn by it. < So, if I press a 
stone with my finger, the finger is equally 
pressed by the stone: if a horse draw a 
weight forward by a rope, the horse is 
equally opposed or drawn back towards the 
w'eight; the equal tensioner stretch of the 
rope hindering the progress of the one as it 
promotes that of the other. Again, if any 
body, by striking on another, do in any 
manner change its motion, it will itself, by 
means of the otheP, undergo also an equal 
change in its own motion, by reason of the 
equality of the pressure. When two bodies 
meet, each endeavours to persevere in its 
state, and resists any change ; and because 
the change which is produced in either may 
be equally measured by the action which it 
excites upon the other, or by the resistance 
which it meets with from it, it follows that 
the changes produced in the motions of 
each are equal, but are made in contrary 
directions : the one acquires no new force 
but what the other loses in the same direc- 
tion ; nor does this last lose any force but 
what the other acquires ; and hence, though 
by their collisions motion passes from the 
one to the other, yet the sum of their 
motions, estimated in a given direction, is 
preserved the same, and is unalterable 
by their mutual actions upon each other. 
In these actions the changes are equal; 
not those, we mean, of the velocities, 
but those of the motions, or momenta; 
the bodies being supposed free from any 
other impedimenU. For tlie changes of 
NAT 
velocities, which are likewise made con-, 
trary ways, inasmuch as the motions are 
equally changed, aie reciprocally propor- 
tional to the bodies or masses. 
NATURALIST, a person well versed 
in tlie study of nature, and the knowledge 
of natural bodies, especially in what relates 
to animals, vegetables, metals, minerals, 
and stones. See Natural History. 
NATURE, according to Mr. Boyle, has 
eight dill’erent significations; it being used, 
1. For the author of nature, wliom the 
schoolmen call natura naturans, being the 
same with God. 2. By the nature of a 
thing, we sometimes mean its essence ; tiiat 
is, the attributes which make it what it is, 
whether the thing be corporeal or not ; as 
when we attempt to define the nature of a 
fluid, of a triangle, &c. 3. Sometimes we 
confound that which a man has by nature 
with what accrues to him by birth ; as when 
we lay, that such a man is noble by nature. 
4. Sometimes we take nature for an inter- 
nal principle of motion ; as when we say, 
that a stone by nature falls to tlie earth. 
5. Sometimes we understand by nature the 
established course of things. 6. Sometimes 
we take nature for an aggregate of powera 
belonging to a body, especially a living one ; 
in which sense physicians say, that nature is 
strong, weak, or spent; or tliat, in siich and 
such diseases, nature left to herself will 
perfonn the cure. 7. Sometimes we use 
the term nature for the universe, or whole 
system of the corporeal works of God ; as 
when it is said of a pheenix, or chimera, that 
there is no such thing in nature. 8. Some- 
times too, and tliat most commonly, w e ex- 
press by the word nature a kind of semi- 
deity, or other strange kind of being. 
If, says the same philosopher, I were to 
propose a notion of nature, less ambiguous 
than those already mentioned, and with 
regard to which many axioms, relating 
to that word, may be conveniently under- 
stood, T sliould first distinguish between the 
universal and the particular nature of things. 
Universal nature I would define to be Uie 
aggregate of the bodies that make up the 
world, in its present state, considered as a 
principle ; by virtue whereof they act and 
suffer, according to the laws of motion, pre- 
scribed by the author of all things. See the 
articles Body, Inertia, Motion, &c. 
And this makes way for the other subordi- 
nate notion ; since the particular nature of 
an individual consists in the general nature, 
applied to a distinct portion of the universe ; 
or, which is the same thing, it is a particular 
