OF THE PRINCIPLES AND METHOD OF NATURAL
PHILOSOPHY.
_A._ This history of the old philosophers has not put me out of love,
but out of hope of philosophy from any of their writings. I would
therefore try if I could attain any knowledge therein by my own
meditation: but I know neither where to begin, nor which way to proceed.
_B._ Your desire, you say, is to know the causes of the effects or
phenomena of nature; and you confess they are fancies, and,
consequently, that they are in yourself; so that the causes you seek for
only are without you, and now you would know how those external bodies
work upon you to produce those phenomena. The beginning therefore of
your enquiry ought to be at; _What it is you call a cause?_ I mean an
efficient cause: for the philosophers make four kinds of causes, whereof
the efficient is one. Another they call the formal cause, or simply the
form or essence of the thing caused; as when they say, four equal angles
and four equal sides are the cause of a square figure; or that heaviness
is the cause that makes heavy bodies to descend; but that is not the
cause you seek for, nor any thing but this: _It descends because it
descends_. The third is the material cause, as when they say, the walls
and roof, &c. of a house are the cause of a house. The fourth is the
final cause, and hath place only in moral philosophy.
_A._ We will think of final causes upon some other occasion; of formal
and material not at all: I seek only the efficient, and how it acteth
from the beginning to the production of the effect.
_B._ I say then, that in the first place you are to enquire diligently
into the nature of motion. For the variations of fancies, or (which is
the same thing) of the phenomena of nature, have all of them one
universal efficient cause, namely the variety of motion. For if all
things in the world were absolutely at rest, there could be no variety
of fancy; but living creatures would be without sense of all objects,
which is little less than to be dead.
_A._ What if a child new taken from the womb should with open eyes be
exposed to the azure sky, do not you think it would have some sense of
the light, but that all would seem unto him darkness?
_B._ Truly, if he had no memory of any thing formerly seen, or by any
other sense perceived, (which is my supposition), I think he would be in
the dark. For darkness is darkness, whether it be black or blue, to him
that cannot distinguish.
_A._ Howsoever that be, it is evident enough that whatsoever worketh is
moved: for action is motion.
_B._ Having well considered the nature of motion, you must thence take
your principles for the foundation and beginning of your enquiry.
_A._ As how?
_B._ Explain as fully and as briefly as you can what you constantly mean
by motion; which will save yourself as well as others from being seduced
by equivocation.
_A._ Then I say, motion is nothing but change of place for all the
effect of a body upon the organs of our senses is nothing but fancy.
Therefore we can fancy nothing from seeing it moved, but change of
place.
_B._ It is right. But you must then tell me also what you understand by
place: for all men are not yet agreed on that.
_A._ Well then; seeing we fancy a body, we cannot but fancy it
somewhere. And therefore I think place is the fancy of here or there.
_B._ That is not enough. Here and there are not understood by any but
yourself, except you point towards it. But pointing is no part of a
definition. Besides, though it help him to find the place, it will never
bring him to it.
_A._ But seeing sense is fancy, when we fancy a body, we fancy also the
figure of it, and the space it fills up. And then I may define place to
be the precise space within which the body is contained. For space is
also part of the image we have of the object seen.
_B._ And how define you time?
_A._ As place is to a body, so, I think, is time to the motion of it;
and consequently I take time to be our fancy or image of the motion. But
is there any necessity of so much niceness?
_B._ Yes. The want of it is the greatest, if not the only, cause of all
the discord amongst philosophers, as may easily be perceived by their
abusing and confounding the names of things that differ in their nature;
as you shall see when there is occasion to recite some of the tenets of
divers philosophers.
_A._ I will avoid equivocation as much as I can. And for the nature of
motion, I suppose I understand it by the definition. What is next to be
done?
_B._ You are to draw from these definitions, and from whatsoever truth
else you know by the light of nature, such general consequences as may
serve for axioms, or principles of your ratiocination.
_A._ That is hard to do.
_B._ I will draw them myself, as many as for our present discourse of
natural causes we shall have need of; so that your part will be no more
than to take heed I do not deceive you.
_A._ I will look to that.
_B._ My first axiom then shall be this: Two bodies, at the same time,
cannot be in one place.
_A._ That is true: for we number bodies as we fancy them distinct, and
distinguish them by their places. You may therefore add: nor one body at
the same time in two places. And philosophers mean the same, when they
say: there is no penetration of bodies.
_B._ But they understand not their own words: for penetration signifies
it not. My second axiom is, that nothing can begin, change, or put an
end to, its own motion. For supposing it begin just now, or being now in
motion, change its way or stop; I require the cause why now rather than
before or after, having all that is necessary to such motion, change, or
rest, alike at all times?
_A._ I do not doubt but the argument is good in bodies inanimate; but
perhaps in voluntary agents it does not hold.
_B._ How it holds in voluntary agents we will then consider when our
method hath brought us to the powers and passions of the mind. A third
axiom shall be this: whatsoever body being at rest is afterwards moved,
hath for its immediate movement some other body which is in motion and
toucheth it. For, since nothing can move itself, the movent must be
external. And because motion is change of place, the movent must put it
from its place, which it cannot do till it touch it.
_A._ That is manifest, and that it must more than touch it; it must also
follow it. And if more parts of the body are moved than are by the
movent touched, the movent is not immediate. And by this reason, a
continued body, though never so great, if the first superficies be
pressed never so little back, the motion will proceed through it.
_B._ Do you think that to be impossible? I will prove it from your own
words: for you say that the movent does then touch the body which it
moveth. Therefore it puts it back; but that which is put back, puts back
the next behind, and that again the next; and so onward to any distance,
the body being continued. The same is also manifest by experience,
seeing one that walks with a staff can distinguish, though blind,
between stone and glass; which were impossible, if the parts of his
staff between the ground and his hand made no resistance. So also he
that in the silence of the night lays his ear to the ground, shall hear
the treading of men’s feet farther than if he stood upright.
_A._ This is certainly true of a staff or other hard body, because it
keeps the motion in a straight line from diffusion. But in such a fluid
body as the air, which being put back must fill an orb, and the farther
it is put back, the greater orb, the motion will decrease, and in time,
by the resistance of air to air, come to an end.
_B._ That any body in the world is absolutely at rest, I think not true:
but I grant, that in a space filled everywhere with body, though never
so fluid, if you give motion to any part thereof, that motion will by
resistance of the parts moved, grow less and less, and at last cease;
but if you suppose the space utterly void, and nothing in it, then
whatsoever is once moved shall go on eternally: or else that which you
have granted is not true, viz., that nothing can put an end to its own
motion.
_A._ But what mean you by resistance?
_B._ Resistance is the motion of a body in a way wholly or partly
contrary to the way of its movent, and thereby repelling or retarding
it. As when a man runs swiftly, he shall feel the motion of the air in
his face. But when two hard bodies meet, much more may you see how they
abate each other’s motion, and rebound from one another. For in a space
already full, the motion cannot, in an instant, be communicated through
the whole depth of the body that is to be moved.
_A._ What other definitions have I need of?
_B._ In all motion, as in all quantity, you must take the beginning of
your reckoning from the least supposed motion. And this I call the first
endeavour of the movent; which endeavour, how weak soever, is also
motion. For if it have no effect at all, neither will it do anything
though doubled, trebled, or by what number soever multiplied: for
nothing, though multiplied, is still nothing. Other axioms and
definitions we will take in, as we need them, by the way.
_A._ Is this all the preparation I am to make?
_B._ No, you are to consider also the several kinds and properties of
motion, viz., when a body being moved by one or more movents at once, in
what way it is carried, straight, circular, or otherwise crooked; and
what degree of swiftness; as also the action of the movent, whether
trusion, vection, percussion, reflection, or refraction; and farther you
must furnish yourself with as many experiments (which they call
phenomenon) as you can. And supposing some motion for the cause of your
phenomenon, try, if by evident consequence, without contradiction to any
other manifest truth or experiment, you can derive the cause you seek
for from your supposition. If you can, it is all that is expected, as to
that one question, from philosophy. For there is no effect in nature
which the Author of nature cannot bring to pass by more ways than one.
_A._ What I want of experiments you may supply out of your own store, or
such natural history as you know to be true; though I can be well
content with the knowledge of the causes of those things which everybody
sees commonly produced. Let us therefore now enquire the cause of some
effect particular.
_B._ We will begin with that which is the most universal, the universe;
and enquire in the first place, if any place be absolutely empty, that
is to say in the language of philosophers, whether there be any vacuum
in nature?
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