OF VACUUM.
_A._ It is hard to suppose, and harder to believe, that the infinite and
omnipotent Creator of all things should make a work so vast as is the
world we see, and not leave a few little spaces with nothing at all in
them; which put altogether in respect of the whole creation, would be
insensible.
_B._ Why say you that? Do you think any argument can be drawn from it to
prove there is vacuum?
_A._ Why not? For in so great an agitation of natural bodies, may not
some small parts of them be cast out, and leave the places empty from
whence they were thrown?
_B._ Because He that created them is not a fancy, but the most real
substance that is; who being infinite, there can be no place empty where
He is, nor full where He is not.
_A._ It is hard to answer this argument, because I do not remember that
there is any argument for the maintenance of vacuum in the writings of
divines: therefore I will quit that argument, and come to another. If
you take a glass vial with a narrow neck, and having sucked it, dip it
presently at the neck into a basin of water, you shall manifestly see
the water rise into the vial. Is not this a certain sign that you had
sucked out some of the air, and consequently that some part of the vial
was left empty?
_B._ No; for when I am about to suck, and have air in my mouth,
contracting my checks I drive the same against the air in the glass, and
thereby against every part of the sides of the hard glass. And this
gives to the air within an endeavour outward, by which, if it be
presently dipped into the water, it will penetrate and enter into it.
For air if it be pressed will enter into any fluid, much more into
water. Therefore there shall rise into the vial so much water as there
was air forced into the basin.
_A._ This I confess is possible, and not improbable.
_B._ If sucking would make vacuum, what would become of those women that
are nurses? Should they not be in a very few days exhausted, were it not
that either the air which is in the child’s mouth penetrateth the milk
as it descends, and passeth through it, or the breast is contracted?
_A._ From what experiment can you evidently infer that there is no
vacuum?
_B._ From many, and such as to almost all men are known and familiar. If
two hard bodies, flat and smooth, be joined together in a common
superficies parallel to the horizontal plane, you cannot without great
force pull them asunder, if you apply your force perpendicularly to the
common superficies: but if you place that common superficies erect to
the horizon, they will fall asunder with their own weight. From whence I
argue thus: since their contiguity, in what posture soever, is the same,
and that they cannot be pulled asunder by a perpendicular force without
letting in the ambient air in an instant, which is impossible; or almost
in an instant, which is difficult: and on the other side, when the
common superficies is erect, the weight of the same hard bodies is able
to break the contiguity, and let in the air successively; it is manifest
that the difficulty of separation proceeds from this, that neither air
nor any other body can be moved to any, how small soever, distance in an
instant; but may easily be moved (the hardness at the sides once
mastered) successively. So that the cause of this difficulty of
separation is this, that they cannot be parted except the air or other
matter can enter and fill the space made by their diremption. And if
they were infinitely hard, not at all. And hence also you may understand
the cause why any hard body, when it is suddenly broken, is heard to
crack; which is the swift motion of the air to fill the space between.
Another experiment, and commonly known, is of a barrel of liquor, whose
tap-hole is very little, and the bung so stopped as to admit no air; for
then the liquor will not run: but if the tap-hole be large it will,
because the air pressed by a heavier body will pierce through it into
the barrel. The like reason holds of a gardener’s watering-pot, when the
holes in the bottom are not too great. A third experiment is this: turn
a thin brass kettle the bottom upwards, and lay it flat upon the water.
It will sink till the water rise within to a certain height, but no
higher: yet let the bottom be perforated, and the kettle will be full
and sink, and the air rise again through the water without. But if a
bell were so laid on, it would be filled and sink, though it were not
perforated, because the weight is greater than the weight of the same
bulk of water.
_A._ By these experiments, without any more, I am convinced, that there
is not actually in nature any vacuum; but I am not sure but that there
may be made some little place empty, and this from two experiments, one
whereof is Toricellius’ experiment, which is this: take a cylinder of
glass, hollow throughout, but close at the end, in form of a sack.
_B._ How long?
_A._ As long as you will, so it be more than twenty-nine inches.
_B._ And how broad?
_A._ As broad as you will, so it be broad enough to pour into it
quicksilver. And fill it with quicksilver, and stop up the entrance with
your finger, so as to unstop it again at your pleasure. Then set down a
basin, or, if you will, a sea of quicksilver, and inverting the cylinder
full as it is, dip the end into the quicksilver, and remove your finger,
that the cylinder may empt itself. Do you conceive me? For there is so
many passing by, that I cannot paint it.
_B._ Yes, I conceive you well enough. What follows?
_A._ The quicksilver will descend in the cylinder, not till it be level
with that in the basin, according to the nature of heavy fluids, but
stay and stand above it, at the height of twenty-nine inches or very
near it, the bottom being now uppermost, that no air can get in.
_B._ What do you infer from this?
_A._ That all the cavity above twenty-nine inches is filled with vacuum.
_B._ It is very strange that I, from this same experiment, should infer,
and I think evidently, that it is filled with air. I pray, tell me, when
you had inverted the cylinder, full as it was, and stopped with your
finger, dipped into the basin, if you had then removed your finger,
whether you think the quicksilver would not all have fallen out?
_A._ No sure. The air would have been pressed upward through the
quicksilver itself: for a man with his hand can easily thrust a bladder
of air to the bottom of a basin of quicksilver.
_B._ It is therefore manifest that quicksilver can press the air through
the same quicksilver.
_A._ It is manifest; and also itself rise into the air.
_B._ What cause then can there be, why it should stand still at twenty
nine inches above the level of the basin, rather than any place else?
_A._ It is not hard to assign the cause of that. For so much quicksilver
as was above the twenty-nine inches, will rise the first level of that
in the basin, as much as if you had poured it on; and thereby bring it
to an equilibrium. So that I see plainly now, that there is no necessity
of vacuum from this experiment. For I considered only that naturally
quicksilver cannot ascend in air, nor air descend in quicksilver, though
by force it may.
_B._ Nor do I think that Torricellius or any other vacuist thought of it
more than you. But what is the second experiment?
_A._ There is a sphere of glass, which they call a recipient, of the
capacity of three or four gallons. And there is inserted into it the end
of a hollow cylinder of brass above a foot long; so that the whole is
one vessel, and the bore of the cylinder three inches diameter. Into
which is thrust by force a solid cylinder of wood, covered with leather
so just, as it may in every point exactly touch the concave superficies
of the brass. There is also, to let out the air which the wooden
cylinder as it enters (called the sucker) drives before it, a flap to
keep out the external air while they are pulling the sucker. Besides, at
the top of the recipient there is a hole to put into it anything for
experiment. The sucker being now forced up into the cylinder, what do
you think must follow?
_B._ I think it will require as much strength to pull it back, as it did
to force it in.
_A._ That is not it I ask, but what would happen to the recipient?
_B._ I think so much air as would fill the place the sucker leaves,
would descend into it out of the recipient; and also that just so much
from the external air would enter into the recipient, between the brass
and the wood, at first very swiftly, but, as the place increased, more
leisurely.
_A._ Why may not so much air rather descend into the place forsaken, and
leave as much vacuum as that comes to in the recipient? For otherwise no
air will be pumped out, nor can that wooden pestle be called a sucker.
_B._ That is it I say. There is no air either pumped or sucked out.
_A._ How can the air pass between the leather and the brass, or between
the leather and the wood, being so exactly contiguous, or through the
leather itself?
_B._ I conceive no such exact contiguity, nor such fastness of the
leather: for I never yet had any that in a storm would keep out either
air or water.
_A._ But how then could there be made in the recipient such strange
alteration both on animate and inanimate bodies?
_B._ I will tell you how. The air descends out of the recipient, because
the air which the sucker removeth from behind itself, as it is pulling
out, has no place to retire into without, and therefore is driven into
the engine between the wood of the sucker and the brass of the cylinder,
and causes as much air to come into the place forsaken by the retiring
sucker; which causeth, by oft repetition of the force, a violent
circulation of the air within the recipient, which is able quickly to
kill anything that lives by respiration, and make all the alterations
that have appeared in the engine.
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