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Two Kinds Of Properties
In accordance with the promise which I made to Your Excellency, I shall
certainly state my ideas concerning the proposition "Motion is the
cause of heat," explaining in what way it appears to me to be true.
But first it will be necessary for me to say a few words concerning that
which we call "heat," for I strongly suspect that the commonly
held conception of the matter is very far from the truth, inasmuch as heat
is generally believed to be a true accident, affection, or quality which
actually resides in the material which we feel to be heated. Now, whenever
I conceive of any material or corporeal substance, I am necessarily
constrained to conceive of that substance as bounded and as possessing this
or that shape, as large or small in relationship to some other body, as in
this or that place during this or that time, as in motion or at rest, as in
contact or not in contact with some other body, as being one, many, or
few--and by no stretch of imagination can I conceive of any corporeal body
apart from these conditions. But I do not at all feel myself compelled to
conceive of bodies as necessarily conjoined with such further conditions as
being red or white, bitter or sweet, having sound or being mute, or
possessing a pleasant or unpleasant fragrance. On the contrary, were they
not escorted by our physical senses, perhaps neither reason nor
understanding would ever, by themselves, arrive at such notions. I think,
therefore, that these tastes, odors, colors, etc., so far as their
objective existence is concerned, are nothing but mere names for something
which resides exclusively in our sensitive body (corpo
sensitivo), so that if the perceiving creatures
were removed, all of these qualities would be annihilated and abolished
from existence. But just because we have given special names to these
qualities, different from the names we have given to the primary and real
properties, we are tempted into believing that the former really and truly
exist as well as the latter.
An example, I believe, will clearly explain my concept. Suppose I pass my
hand, first over a marble statue, then over a living man. So far as the
hand, considered in itself, is concerned, it will act in an identical way
upon each of these objects; that is, the primary qualities of motion and
contact will similarly affect the two objects, and we would use identical
language to describe this in each case. But the living body, which I
subject to this experiment, will feel itself affected in various ways,
depending upon the part of the body I happen to touch; for example, should
it be touched on the sole of the foot or the kneecap, or under the armpit,
it will feel, in addition to simple contact, a further affection to which
we have given a special name: we call it "tickling." This latter
affection is altogether our own, and is not at all a property of the hand
itself. And it seems to me that he would be gravely in error who would
assert that the hand, in addition to movement and contact, intrinsically
possesses another and different faculty which we might call the
"tickling faculty," as though tickling were a resident property
of the hand per se. Again, a piece of paper or a feather, when gently
rubbed over any part of our body whatsoever, will in itself act everywhere
in an identical way; it will, namely, move and contact. But we, should we
be touched between the eyes, on the tip of the nose, or under the nostrils,
will feel an almost intolerable titillation--while if touched in other
places, we will scarcely feel anything at all. Now this titillation is
completely ours and not the feather's, so that if
the living, sensing body were removed, nothing would remain of the titillation
but an empty name. And I believe that many other qualities, such as taste,
odor, color, and so on, often predicated of natural bodies, have a similar
and no greater existence than this.
A solid body and, so to speak, one that is sufficiently heavy, when moved
and applied against any part of my body whatsoever, will produce in me the
sensation which we call "touch." Although this sense is to be
found in every part of the body, it appears principally to reside in the
palm of the hand, and even more so in the fingertips, with which, we can
feel the minutest differences of roughness, texture, and softness and
hardness--differences which the other parts of the body are less capable of
distinguishing. Some amongst these tactile sensations are more pleasing
than others, depending upon the differences of configuration of tangible
bodies; that is to say, in accordance with whether they are smooth or
irregular, sharp or dull, flexible or rigid. And the sense of touch, being
more material than the other senses and being produced by the mass of the
material itself, seems to correspond to the element of earth.
Since certain material bodies are continually resolving themselves into
tiny particles, some of the particles, because they are heavier than air,
will descend; and some of them, because they are lighter than air, will
ascend. From this, perhaps, two further senses are born,
for certain of the particles penetrate two parts of our body which are
effectively more sensitive than the skin, which is incapable of feeling the
incursion of materials which are too fine, subtle, or flexible. The
descending particles are received by the upper surface of the tongue, and
penetrating, they blend with its substance and moisture. Thus our tastes
are caused, pleasant or harsh in accordance with variations in the contact
of diversely shaped particles, and depending upon whether they are few or
many, and whether they have high or low velocity. Other particles ascend,
and entering the nostrils they penetrate the various nodes (mammilule) which are the instruments of smell; and
these particles, in like manner through contact and motion, produce savoriness or unsavoriness--again
depending upon whether the particles have this or that shape, high or low
velocity, and whether they are many or few. It is remarkable how
providently the tongue and nasal passages are situated and disposed, the
former stretched beneath to receive the ingression of descending particles,
and the latter so arranged as to receive those which ascend. The arrangement
whereby the sense of taste is excited in us is perhaps analogous to the way
in which fluids descend through the air, and the stimulation of the sense
of smell may be compared to the manner in which flames ascend in it.
There remains the element of air, which corresponds to the sense of sound.
Sounds come to us indiscriminately, from above and below and from either
side, since we are so constituted as to be equally disposed to every
direction of the air's movements; and the ear is so situated as to accommodate
itself in the highest possible degree to any position in space. Sounds,
then, are produced in us and felt when (without any special quality of
harmoniousness or dissonance) there is a rapid vibration of air, forming
minutely small waves, which move certain cartilages of a certain drum which
is in our ear. The various external ways in which this wave-motion of the
air is produced are manifold, but can in large part be reduced to the
vibrating of bodies which strike the air and form the waves which spread
out with great velocity. High frequencies give rise to high tones; low
frequencies give rise to low tones. But I cannot believe that there exists
in external bodies anything, other than their size, shape, or motion (slow
or rapid), which could excite in us our tastes, sounds, and odors. And
indeed I should judge that, if ears, tongues, and noses be taken away, the
number, shape, and motion of bodies would remain, but not their tastes,
sounds, and odors. The latter, external to the living creature, I believe
to be nothing but mere names, just as (a few lines back) I asserted
tickling and titillation to be, if the armpit or the sensitive skin inside
the nose were removed. As to the comparison between the four senses which
we have mentioned and the four elements, I believe that the sense of sight,
most excellent and noble of all the senses, is like light itself. It stands
to the others in the same measure of comparative excellence as the finite
stands to the infinite, the gradual to the instantaneous, the divisible to
the indivisible, the darkness to the light. Of
this sense, and all that pertains to it, I can pretend to understand but
little; yet a great deal of time would not suffice for me to set forth even
this little bit that I know, or (to put it more exactly) for me to sketch
it out on paper. Therefore I shall ponder it in silence.
I return to my first proposition, having now shown how some affections, often reputed to be indwelling properties of
some external body, have really no existence save in us, and apart from us
are mere names. I confess myself to be very much inclined to believe that
heat, too, is of this sort, and that those materials which produce and make
felt in us the sense of heat and to which we give the general name
"fire" consist of a multitude of tiny particles of such and such
a shape, and having such and such a velocity. These, when they encounter
our body, penetrate it by means of their extreme subtlety; and it is their
contact, felt by us in their passage through our substance, which is the
affection we call "heat." It will be pleasantly warm or
unpleasantly hot depending upon the number and the velocity (greater or
lesser) of these pricking, penetrating particles--pleasant if by their
penetration our necessary perspiring is facilitated, unpleasant if their
penetrating effects too great a division and dissolution of our substance.
In sum, the operation of fire, considered in itself, is nothing but
movement, or the penetration of bodies by its extreme subtlety, quickly or
slowly, depending upon the number and velocity of tiny corpuscles of flame
(ignicoli) and upon the greater or lesser density
of the bodies concerned. Many bodies dissolve in such a manner that the
major part of them becomes transformed into further corpuscles of flame;
and this dissolution continues as further dissolvable material is
encountered. But that there exists in fire, apart from shape, number,
movement, penetration, and contact, some further quality which we call
"heat," I cannot believe. And I again judge that heat is
altogether subjective, so that if the living, sensitive body be removed,
what we call heat would be nothing but a simple word. Since it is the case
that this affection is produced in us by passage of tiny corpuscles of
flame through our substance and their contact with it, it is obvious that
once this motion ceases, their operation upon us will be null. It is thus
that we perceive that a quantity of fire, retained in the pores and pits of
a piece of calcified stone, does not heat--even if we hold it in the palm
of our hand--because the flame remains stationary in the stone. But should
we swish the stone in water where, because of its weight, it has greater
propensity for movement and where the pits of the stone open somewhat, the
corpuscles of flame will escape and, encountering our hand, will penetrate
it, so that we will feel heat. Since, in order for heat to be stimulated in
us, the mere presence of corpuscles of flame is not by itself sufficient,
and since movement is required in addition, it is with considerable reason
that I declare motion to be the cause of heat.
This or that movement by which a scantling or other piece of wood is burned
up or by which lead and other metals are melted will continue so long as
the corpuscles of flame, moved either by their own velocity or (if this be
insufficient) aided by a strong blast from a bellows, continue to penetrate
the body in question; the former will resolve itself into further
corpuscles of flame or into ash; the latter will liquify
and be rendered fluid like water. From a common-sense point of view, to
assert that that which moves a stone, piece of iron, or a stick, is what
heats it, seems like an extreme vanity. But the friction produced when two
hard bodies are rubbed together, which either reduces them to fine flying
particles or permits the corpuscles of flame contained in them to escape,
can finally be analyzed as motion. and the particles, when they encounter
our body and penetrate and tear through it, are felt, in their motion and
contact, by the living creature, who thus feels those pleasant or
unpleasant affections which we call "heat," "burning,"
or "scorching."
Perhaps while this pulverizing and attrition continue, and remain confined
to the particles themselves, their motion will be temporary and their
operation will be merely that of heating. But once we arrive at the point
of ultimate and maximum dissolution into truly indivisible atoms, light
itself may be created, with an instantaneous motion or (I should rather
say) an instantaneous diffusion and expansion, capable--I do not know if by
the atoms' subtlety, rarity, immateriality, or by different and as yet unspecifiable conditions--capable, I say, of filling
vast spaces.
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