Question VII
In What Sense Does Plato Say, That the Antiperistasis (or Reaction) of Motion -- By Reason There is no Vacuum-- Is the Cause of the Effects in Physicians' Cupping-Glasses, In Swallowing, In Throwing of Weights, In the Running of Water, In Thunder, In the Attraction of the Loadstone, And in the Harmony of Sounds (Timaeus 79-81).
1. For it seems unreasonable to ascribe the reason of such different
effects to the selfsame cause.
2. How respiration is made by the reaction of the air, he has
sufficiently shown. But the rest, he says, seem to be done miraculously, but really the
bodies thrust each other aside and change places with one another; while he has left for
us to determine how each is particularly done.
3. As to cupping-glasses, the case is thus: the air next to the flesh
being comprehended and inflamed by the heat, and being made more rare than the pores of
the brass, does not go into a vacuum (for there is no such thing), but into the air that
is without the cupping glass, and has an impulse upon it. This air drives that before it;
and each, as it gives away, strives to succeed into the place which was vacuated by the
cession of the first. And so the air approaching the flesh comprehended by the
cupping-glass, and exciting it, draws the humors into the cupping-glass.
4. Swallowing takes place in the same way. For the cavities about the
mouth and stomach are full of air; when therefore the meat is squeezed down by the tongue
and tonsils, the elided air follows what gives way, and also forces down the meat.
5. Weights also thrown cleave the air and dissipate it, as they fall
with force; the air recoiling back, according to its natural tendency to rush in and fill
the vacuity, follows the impulse, and accelerates the motion.
6. The fall also of thunderbolts is like to darting any thing. For by
the blow in the cloud, the fiery matter exploding breaks into the air; and it being broken
gives way, and again contracted above, by main force it presses the thunderbolt downward
contrary to Nature.
7. And neither amber nor the loadstone draws any thing to it which is
near, nor does any thing spontaneously approach them. But this stone emits strong
exhalations, by which the adjoining air being impelled forceth that which is before it;
and this being carried round in the circle, and returning into the vacuated place,
forcibly draws the iron in the same directions. In amber there is a flammeous and
spirituous nature, and this is by rubbing on the surface is emitted by recluse passages,
and does the same that the loadstone does. It also draws the lightest and driest of
adjacent bodies, by reason of their tenuity and weakness; for it is not so strong nor so
endured with weight and strength as to force much air and to act with violence and to have
power over great bodies, as the magnet has. But what is the reason the air never draws a
stone, nor wood, but iron only, to the loadstone? This is a common question both by them
who think the coition of these bodies is made by the attraction of the loadstone, and by
such as think it done by the incitement of the iron. Iron is neither so rare as wood, nor
altogether so solid as gold or a stone; but has certain pores and asperities, which in
regard of the inequality are proportionable to the air; and the air being received in
certain seats, and having (as it were) certain stays to cling to, does not slip away; but
when it is carried up to the stone and strikes against it, it draws the iron by force
along with it to the stone. Such then my by the reason of this.
8. But the manner of the waters running over the earth is not so
evident. But it is observable that the waters of lakes and ponds stand immovable, because
the air about them stagnates immovable and admits no vacuity. For the waters on the
surface of lakes and seas is trouble and fluctuates as the air is moved, it following the
motion of the air, and moving as it is moved. For the forces from below causes the
hollowness of the wave, and from above the swelling thereof; until the air ambient and
containing the water is still. Therefore the flux of such waters as follow the motion of
the retreating air, and are impelled by that which presses behind it, is continued without
end. And this is the reason that the stream increases with the waters, and is slow where
the water is weak, the air not giving way, and therefore suffering less reaction. So the
water of fountains must needs flow upwards, the extrinsic air succeeding into the vacuity
and throwing the water out. In a close house, that keeps in the air and wind, the floor
sprinkled with water causes an air or wind, because as the sprinkled water falls, the air
gives way. For it is so provided by Nature that air and water force one another and give
way to one another; because there is no vacuity in which one can be settled without
feeling the change and alteration in the other.
9. Concerning symphony, he shows how sounds harmonize. A quick sound is
acute, a slow is grave. Therefore acute sounds move the senses quicker; and these dying
and grave sounds supervening, what arises from the contemplation of one with the other
causes pleasure to the ear, which we call harmony. And by what has been said, it may
easily be understood that air is instrument of these things. For sound is the stroke upon
the sense of the hearer, caused by the air; and the air strikes as it is struck by the
thing moving, --- if violent, acutely,-- if languid, softly. The violent stroke comes
quick to the car; then the circumabient air receiving a slower, it affects and carries the
sense along with it.