IDEA OF SOLIDITY.
1. We receive this Idea from Touch.
The idea of SOLIDITY we receive by our touch: and it arises from the
resistance which we find in body to the entrance of any other body into
the place it possesses, till it has left it. There is no idea which we
receive more constantly from sensation than solidity. Whether we move
or rest, in what posture soever we are, we always feel something under
us that supports us, and hinders our further sinking downwards; and the
bodies which we daily handle make us perceive that, whilst they remain
between them, they do, by an insurmountable force, hinder the approach
of the parts of our hands that press them. THAT WHICH THUS HINDERS THE
APPROACH OF TWO BODIES, WHEN THEY ARE MOVED ONE TOWARDS ANOTHER, I CALL
SOLIDITY. I will not dispute whether this acceptation of the word solid
be nearer to its original signification than that which mathematicians
use it in. It suffices that I think the common notion of solidity will
allow, if not justify, this use of it; but if any one think it better
to call it IMPENETRABILITY, he has my consent. Only I have thought the
term solidity the more proper to express this idea, not only because of
its vulgar use in that sense, but also because it carries something
more of positive in it than impenetrability; which is negative, and is
perhaps more a consequence of solidity, than solidity itself. This, of
all other, seems the idea most intimately connected with, and essential
to body; so as nowhere else to be found or imagined, but only in
matter. And though our senses take no notice of it, but in masses of
matter, of a bulk sufficient to cause a sensation in us: yet the mind,
having once got this idea from such grosser sensible bodies, traces it
further, and considers it, as well as figure, in the minutest particle
of matter that can exist; and finds it inseparably inherent in body,
wherever or however modified.
2. Solidity fills Space.
This is the idea which belongs to body, whereby we conceive it to fill
space. The idea of which filling of space is,—that where we imagine any
space taken up by a solid substance, we conceive it so to possess it,
that it excludes all other solid substances; and will for ever hinder
any other two bodies, that move towards one another in a straight line,
from coming to touch one another, unless it removes from between them
in a line not parallel to that which they move in. This idea of it, the
bodies which we ordinarily handle sufficiently furnish us with.
3. Distinct from Space.
This resistance, whereby it keeps other bodies out of the space which
it possesses, is so great, that no force, how great soever, can
surmount it. All the bodies in the world, pressing a drop of water on
all sides, will never be able to overcome the resistance which it will
make, soft as it is, to their approaching one another, till it be
removed out of their way: whereby our idea of solidity is distinguished
both from pure space, which is capable neither of resistance nor
motion; and from the ordinary idea of hardness. For a man may conceive
two bodies at a distance, so as they may approach one another, without
touching or displacing any solid thing, till their superficies come to
meet; whereby, I think, we have the clear idea of space without
solidity. For (not to go so far as annihilation of any particular body)
I ask, whether a man cannot have the idea of the motion of one single
body alone, without any other succeeding immediately into its place? I
think it is evident he can: the idea of motion in one body no more
including the idea of motion in another, than the idea of a square
figure in one body includes the idea of a square figure in another. I
do not ask, whether bodies do so EXIST, that the motion of one body
cannot really be without the motion of another. To determine this
either way, is to beg the question for or against a VACUUM. But my
question is,—whether one cannot have the IDEA of one body moved, whilst
others are at rest? And I think this no one will deny. If so, then the
place it deserted gives us the idea of pure space without solidity;
whereinto any other body may enter, without either resistance or
protrusion of anything. When the sucker in a pump is drawn, the space
it filled in the tube is certainly the same whether any other body
follows the motion of the sucker or not: nor does it imply a
contradiction that, upon the motion of one body, another that is only
contiguous to it should not follow it. The necessity of such a motion
is built only on the supposition that the world is full; but not on the
distinct IDEAS of space and solidity, which are as different as
resistance and not resistance, protrusion and not protrusion. And that
men have ideas of space without a body, their very disputes about a
vacuum plainly demonstrate, as is shown in another place.
4. From Hardness.
Solidity is hereby also differenced from hardness, in that solidity
consists in repletion, and so an utter exclusion of other bodies out of
the space it possesses: but hardness, in a firm cohesion of the parts
of matter, making up masses of a sensible bulk, so that the whole does
not easily change its figure. And indeed, hard and soft are names that
we give to things only in relation to the constitutions of our own
bodies; that being generally called hard by us, which will put us to
pain sooner than change figure by the pressure of any part of our
bodies; and that, on the contrary, soft, which changes the situation of
its parts upon an easy and unpainful touch.
But this difficulty of changing the situation of the sensible parts
amongst themselves, or of the figure of the whole, gives no more
solidity to the hardest body in the world than to the softest; nor is
an adamant one jot more solid than water. For, though the two flat
sides of two pieces of marble will more easily approach each other,
between which there is nothing but water or air, than if there be a
diamond between them; yet it is not that the parts of the diamond are
more solid than those of water, or resist more; but because the parts
of water, being more easily separable from each other, they will, by a
side motion, be more easily removed, and give way to the approach of
the two pieces of marble. But if they could be kept from making place
by that side motion, they would eternally hinder the approach of these
two pieces of marble, as much as the diamond; and it would be as
impossible by any force to surmount their resistance, as to surmount
the resistance of the parts of a diamond. The softest body in the world
will as invincibly resist the coming together of any other two bodies,
if it be not put out of the way, but remain between them, as the
hardest that can be found or imagined. He that shall fill a yielding
soft body well with air or water, will quickly find its resistance. And
he that thinks that nothing but bodies that are hard can keep his hands
from approaching one another, may be pleased to make a trial, with the
air inclosed in a football. The experiment, I have been told, was made
at Florence, with a hollow globe of gold filled with water, and exactly
closed; which further shows the solidity of so soft a body as water.
For the golden globe thus filled, being put into a press, which was
driven by the extreme force of screws, the water made itself way
through the pores of that very close metal, and finding no room for a
nearer approach of its particles within, got to the outside, where it
rose like a dew, and so fell in drops, before the sides of the globe
could be made to yield to the violent compression of the engine that
squeezed it.
5. On Solidity depend Impulse, Resistance and Protrusion.
By this idea of solidity is the extension of body distinguished from
the extension of space:—the extension of body being nothing but the
cohesion or continuity of solid, separable, movable parts; and the
extension of space, the continuity of unsolid, inseparable, and
immovable parts. Upon the solidity of bodies also depend their mutual
impulse, resistance, and protrusion. Of pure space then, and solidity,
there are several (amongst which I confess myself one) who persuade
themselves they have clear and distinct ideas; and that they can think
on space, without anything in it that resists or is protruded by body.
This is the idea of pure space, which they think they have as clear as
any idea they can have of the extension of body: the idea of the
distance between the opposite parts of a concave superficies being
equally as clear without as with the idea of any solid parts between:
and on the other side, they persuade themselves that they have,
distinct from that of pure space, the idea of SOMETHING THAT FILLS
SPACE, that can be protruded by the impulse of other bodies, or resist
their motion. If there be others that have not these two ideas
distinct, but confound them, and make but one of them, I know not how
men, who have the same idea under different names, or different ideas
under the same name, can in that case talk with one another; any more
than a man who, not being blind or deaf, has distinct ideas of the
colour of scarlet and the sound of a trumpet, could discourse
concerning scarlet colour with the blind man I mentioned in another
place, who fancied that the idea of scarlet was like the sound of a
trumpet.
6. What Solidity is.
If any one asks me, WHAT THIS SOLIDITY IS, I send him to his senses to
inform him. Let him put a flint or a football between his hands, and
then endeavour to join them, and he will know. If he thinks this not a
sufficient explication of solidity, what it is, and wherein it
consists; I promise to tell him what it is, and wherein it consists,
when he tells me what thinking is, or wherein it consists; or explains
to me what extension or motion is, which perhaps seems much easier. The
simple ideas we have, are such as experience teaches them us; but if,
beyond that, we endeavour by words to make them clearer in the mind, we
shall succeed no better than if we went about to clear up the darkness
of a blind man’s mind by talking; and to discourse into him the ideas
of light and colours. The reason of this I shall show in another place.