Charles Schmitt-Experimental Evidence for and Against Void
Transcript of Charles Schmitt-Experimental Evidence for and Against Void
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Experimental Evidence for
and against a Void: The
Sixteenth-Century Arguments
By Charles B. Schmitt*
I. INTRODUCTION
ONE OF THE CHIEF identifiable characteristics of the period which
we call the Renaissance is that philosophical thought gradually but
steadily rejected Aristotle as the dominant authority. The Stagirite's teach-
ings regarding logic, metaphysics, and psychology were all seriously and
fundamentally questioned during the fourteenth and fifteenth centuries. In
the course of the sixteenth century there emerged a strong critical tendency
which directed its attention more toward Aristotle's natural philosophy.
Among the thinkers of this century who criticized Aristotle from one or
another viewpoint concerning his doctrines of natural philosophy were
Gianfrancesco Pico, Julius Caesar Scaliger, Petrus Ramus, Bernardino Te-
lesio, Francesco Patrizi, Giambattista Benedetti, Giordano Bruno, and the
young Galileo Galilei. In all of these writers we find a deep-seated antipathy
to the Peripatetic world view.
Included in nearly all sixteenth-century critiques of Aristotle is some dis-
cussion of whether a void or empty space exists or could exist in nature with-
out supernatural intervention. Since the Aristotelian dictum nature abhors
a vacuum turned out to be one of his most questionable pronouncements
and one which seems to have been experimentally refuted in the seventeenth
century, it may be fruitful to once more consider the background of these
important experiments.1
In my opinion we can distinguish at least four different ways in which the
1 Of what has been written previously see
University of Leeds. A preliminary draft especially Pierre Duhem, Systeme du monde
of this paper was read before the History of (Paris: Hermann, 1913-1959), esp. Vol. VIII,
Science Society at San Francisco on 28 Dec. 1965. pp. 121-168; Cornelis de Waard, L'experience
The research necessary for the paper was car- barometrique: ses antecedents et ses explica-
ried out in part through the aid of Grant No. tions (Thouars: Imprimerie Nouvelle, 1936);
3809, Penrose Fund, American Philosophical W. E. K. Middleton, The History of the
Society. I would like to thank Professor Ernest Barometer (Baltimore: Johns Hopkins Press,
A. Moody for making a number of helpful sug- 1964); Middleton, Torricelli and the History
gestions in connection with its preparation. of the Barometer, Isis, 1963, 54:11-28.
3 52
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EVIDENCE FOR AND AGAINST A VOID
vacuum problem was discussed in the Middle Ages and Renaissance, namely
from theoretical, kinetic, theological, and experimental viewpoints.2 In this
paper I plan to deal with only the last of these and, even that one, only par-
tially. I shall discuss some of the experimental reasons which were com-
monly used in the course of the sixteenth century both for and against the
natural existence of a vacuum.
On the whole, we find that the Aristotelians showed greater interest in
vacuum experiments than did their opponents. This, of course, may seem
somewhat strange in view of the fact that the decisive blow against the vacuist
position was dealt in the middle of the seventeenth century largely through
experimental means. It is nevertheless the case that the most extensive dis-
cussions of experimental evidence for and against a vacuum in sixteenth-
century writings are to be found in the context of commentaries on Aristotle's
Physics and in the Quaestiones literature relating to the same work. It also
seems evident that the Aristotelian writers of the period are dependent in
large measure on the earlier commentaries and analyses of Aristotle's works.
Among the opponents of the Aristotelian position on the vacuum question
we find only two-Telesio and Patrizi-who discuss the experimental aspect
of the issue in a relatively detailed way. The fact that these two writers have
some rather unusual things to say on the subject gives them a particular
importance which should become apparent as we proceed.
Let us now compare the arguments advanced in favor of a vacuum by the
anti-Aristotelians with those used by the Aristotelians to show that a vacuum
cannot exist in nature. Among the questions which should be faced are the
following: (1) What relation, if any, is there between the sixteenth-century
discussions of vacuum experimentation and the experiments which played
such an important role in seventeenth-century discussions of the same sub-
ject? (2) Was the existence of a partial vacuum interpreted to mean that with
further evacuation a complete vacuum could be realized? (3) In what if any
way do the sixteenth-century discussions of vacuum experiments represent
an advance over like discussions of the thirteenth and fourteenth centuries?
II. THE COMPETING EXPERIMENTS
Duhem has pointed out that Aristotle and the Greek commentators did not
use experiment to demonstrate the impossibility of a void.3 This is not to
say that empirical and experimental arguments were not adduced in antiquity
2 1 plan to treat these viewpoints in greater even a vacuist like John Philoponus cites the
detail elsewhere. For further information see clepsydra argument only to show that air is not
Charles B. Schmitt, Changing Conceptions of weightless. See his In Aristotelis physicorum
Vacuum: 1500-1650, to appear in Proceedings libros commentaria, ed. H. Vitelli, Commen-
of the XI International Congress of the History taria in Aristotelem Graeca, Vol. XVII (Berlin:
of Science, Warsaw-Cracow, 24-31 August G. Reimeri, 1888), pp. 608, 612-613. I use the
1965. term experiment in a very general way in this
3 Duhem, op. cit., Vol. VIII, p. 123. Duhem paper to mean roughly an observation or an
admits (ibid., p. 125) that Aristotle and Simpli- experience of phenomena, either natural or
cius cited the clepsydra as showing that air has artificial and in no way do I mean to imply
weight. His assessment seems to be correct, for that the thinkers approached, other than in a
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CHARLES B. SCHMITT
in its favor, for we have the preface to Hero's Pneumatica4 to show that they
were. It remained, however, for the medievals to attempt systematically to
apply experiential evidence to resolve the questions raised by Aristotle in
the Physics. This they did (1) by developing various empirical arguments
against a vacuum actually existing in nature and (2) by refuting those argu-
ments which were meant to show that there are vacua in nature. Since the
thinkers of the Latin Middle Ages seem to have argued almost without excep-
tion that a vacuum cannot be produced in nature by anything less than a
supernatural power, the experimental evidence which they use ultimately
either supports the Aristotelian position or proves to be inadequate to demon-
strate the actuality of a vacuum ever existing secundum naturam. In other
words, all experimental evidence with regard to the vacuum problem either
acts as a positive support for the Aristotelian position or is inadequate to
refute it.5
In attempting to analyze the function which experiment played in six-
teenth-century discussions of the vacuum problem, we find that a new factor
enters the picture which had been absent in the medieval discussions. For
the first time since antiquity, it seems, there emerges a group of Western
thinkers who seriously entertain the possibility that either (1) there is a
naturally existing vacuum or (2) a void can be produced by purely natural
means. We can, therefore, study and directly compare the experimental evi-
dence adduced by the protagonists on both sides of the controversy. This
cannot be done in the case of the medieval discussions, for although many
experimental arguments were presented in favor of a vacuist position, they
seem always to have been refuted by counterarguments. Consequently, the
pro-vacuum arguments often appear to be merely the straw men later to be
demolished which fill out the contra section of a Scholastic question. In the
sixteenth century, however, we find flesh-and-blood defenders of a vacuist
position. These thinkers are quite willing to present, with all of the force
and vigor at their disposal, experimental evidence which they feel clearly
shows that the Aristotelian position is mistaken.
In general, the sixteenth-century discussions of vacuum experiments reveal
a rather confused situation which must be analyzed with great care. We find
very rudimentary way, the notion of experi-
ment which evolved in classical physics. The
precise meaning of experience and experi-
ment as they were used in the 16th century
is a matter of crucial importance for the entire
interpretation of Renaissance philosophy and
science. There has thus far been no detailed
and systematic investigation of this question
to the best of my knowledge. I plan to discuss
the matter further in a forthcoming paper to
be entitled Experiment and Experience: A
Comparison of Zabarella's View with that Ex-
pressed in Galileo's De motu.
4 Heronis Alexandrini opera quae supersunt
omnia, ed. Wilhelm Schmidt (Leipzig: Teub-
ner, 1899), Vol. I, pp. 2-28.
5 I do not preclude the possibility that there
may have been an isolated Latin who would
have argued that a vacuum could be naturally
produced or naturally exists. The only Latin
thinker, to the best of my knowledge, who held
such a position is Nicholas of Autrecourt. See
J. Reginald O'Donnell, Nicholas of Autre-
court, Mediaeval Studies, 1939, 1:216-222. In
the medieval Arabic and Hebrew traditions the
situation seems to have been different. See
Salomon Pines, Beitrdge zur islamischen Ato-
menlehre (Berlin: Heine, 1936); Franz Rosen-
thal, Das Fortleben der Antike im Islam (Zu-
rich/Stuttgart: Artemis Verlag, 1965), pp. 236-
242; and Harry A. Wolfson, Crescas' Critique of
Aristotle (Cambridge, Mass.: Harvard Univ.
Press, 1929), esp. pp. 54-62, 181-189, 398-422.
354
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EVIDENCE FOR AND AGAINST A VOID
the Aristotelians and anti-Aristotelians repeating the medieval arguments, but
more important than this, we often find them citing the same arguments,
ostensibly based on direct observation and experiment, to demonstrate the
validity of their two diametrically opposed theses. That is to say: the same
experiment is used to show that in nature there is a vacuum and that
there is not a vacuum. Let us now investigate several of these arguments in
some detail.
A. The Bellows
We first consider the case of the bellows and related phenomena. Argu-
ments based on the operation of this widely known device are among the
most common found in medieval and Renaissance discussions of the void. A
typical sixteenth-century statement of the argument to support the Scholastic
position is the following taken from the commentary on the Physics written
by the Jesuits at the University of Coimbra:
But experience as well as reason persuades the authority of philosophy that
a vacuum is not to be granted in the nature of things. Experience, because,
for example, the sides of the bellows, if they are drawn together, can be
separated by no force, unless the orifice, by which air might enter to fill the
interior space, is open.6
We find a more detailed description of the same phenomenon with certain
added embellishments in Franciscus Toletus' commentary on the Physics:
If the bellows are taken, completely folded up, and the bellows' orifice were
inserted into a jar, well closed on all sides, so that air could not enter, and
the sides of the bellows were raised, then certainly there would necessarily
be a vacuum within the bellows, for there would not be a place from which
the air might enter; since if the air in the jar would enter into the bellows,
it would be necessary that the jar be left void, for there would be no place
where air might enter into the jar.
. . It must be said that in this case the sides of the bellows would not
be raised, for if much force were applied, they would without doubt be
broken, because if they would not break they could not be separated.7
These are largely the traditional arguments which had been used during
the Middle Ages against the possibility of the natural occurrence of a void.
They were certainly known to all of the natural philosophers of the period we
are discussing. What, we might ask, was the reaction of the anti-Aristotelians
to these arguments? As we have said, the approach of these thinkers to the
vacuum question is not generally an experimental one. Nevertheless, they do
pay some attention to this type of experimental problem. Consequently,
Bernardino Telesio, one of the century's most incisive opponents of Peri-
6 Commentariorum Collegii Conimbricensis
Societatis Iesu in octo libros physicorum Aris- 7 Francisci Toleti . . . commentaria . . . in
totelis Stagiritae secunda pars (Lyon, 1602), col. octo libros Aristotelis de physica ausculta-
90. For a similar statement see Domingo de Soto, tione . . . (Lyon, 1580), pp. 451, 453. Cf. Giro-
Super octo libros physicorum Aristotelis quaes- lamo Cardano, De subtilitate, I, in Opera omnia
tiones (Salamanca, 1582) fol. 65vb. (Lyon, 1663), III, 359b.
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CHARLES B. SCHMITT
patetic philosophy, admits that it is true that if one attempts to open a bellows
with the orifice blocked, something will break, but only under the condition
that the material which joins the two sides is loose and thin. If it were
thick and heavy, it could not be broken.8 A similar experiment which does
not involve precisely a bellows, but illustrates the same thing, is considered
by Francesco Patrizi:
If a pouch full of water is squeezed, the water will flow out and the pouch will
remain compressed. Then let its mouth, through which the water has flowed,
be bound as tightly as possible. This done, let the pouch be stretched by
the hands; it will follow the hands, and thus the space inside will become
large, and since neither air, water, nor any other body entered it through the
bound mouth, who will henceforth doubt that that entire space is empty of
all body 9
We have here the rather puzzling situation in which the same type of
experiential evidence is used in defense of both of the opposing positions in
the controversy. The Aristotelians argue that a bellows with a restricted ori-
fice will break rather than allow an empty space to be opened up. Patrizi
seems to try to meet the argument head on by saying that a collapsible con-
tainer can indeed be made to house a space empty of all body. It is, however,
somewhat difficult to see precisely how he could accomplish this, if indeed
the container be completely empty and leak free. From Patrizi's description,
the device which he has in mind seems to be similar to the normal wineskin;
and to manually separate the sides of a collapsed wineskin whose opening
is blocked is certainly no easy task.
The arguments of the Aristotelians, on the other hand, seem to have
greater force (if we for a moment consider at face value the experimental
evidence in the arguments), for if one does apply force to separate the sides
of the normal bellows under the conditions stated, there will usually occur
a break at the weakest point or a leak. The realization of this fact probably
led Telesio to his rather ingenious solution. He argues that if we take ade-
quate precautions to make all parts of the bellows strong enough and if
we can apply a powerful enough force, the sides will actually be separated
and a void space created between them. Telesio seems to be arguing here, as
we shall see he does elsewhere, that in carrying out certain experiments special
apparatus must be designed or special conditions for the experiment must
be established. As he sees it, the Scholastic argument fails to become decisive
precisely because its adherents had not gone beyond a few very simple cases
in which the experiment is applicable. If the experiment is extended to take
in a variety of different conditions and provisions are made to construct a
8 Bernardini Telesii De rerum natura, ed. Igitur . . . in folle spatium vacuum fieri
V. Spampanato (Modena: Formiggini, 1910- fatendum est.
1923), Vol. I, p 88: 9 Francesco Patrizi, Nova de universis phi-
Follem itidem si comprimas et occludas, ut losophia libris quinquaginta comprehensa . . .
nullus illabenti aeri aditus pateat, tum ele- (Venice, 1593), Pt. II, fol. 63c. The English
vas expandasque, si pellis laxa gracilisque translation is taken from Benjamin Brickman,
sit, dirumpi earn videas; minime vero, si Francesco Patrizi on Physical Space, Journal
pellis crassa, densa et frangi inepta sit. of the History of Ideas, 1943, 4:234.
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EVIDENCE FOR AND AGAINST A VOID
bellows strong enough to withstand these conditions, the results obtained
will be different.
B. Freezing Water in a Closed Container
A second class of widely discussed experiments considers the result of
freezing a filled, closed container of water. Typical of the solutions offered
to this traditional problem is that of Toletus:
A very strong jar full of hot water is taken, and let it be well closed; then let
it be put in a very cold place. Either the water will freeze or it will not. If
not, it seems absurd since the natural agent should necessarily perform its
action. If it does freeze, then the water will occupy a small place because of
its condensation and the rest of the jar will remain void.
. I admit that the water should become cold and should freeze, never-
theless this could not be without the evaporation of subtle vapors, which
would fill the place left by the water.10
It will be noted here, as in what follows, that the assumption that water will
decrease in volume upon freezing seems to have been universally held among
the writers we are discussing.
Using a somewhat different line of reasoning to reach the same conclusion,
the Coimbra commentators argue: The water contained in the jar either
does not solidify because nature prevents the solidification, which it prefers
to the risk of a vacuum; or, if it does solidify, the jar itself is broken. 11
This mode of argument raises an additional problem, however. Certainly the
normal ceramic or glass jar might be expected to break under the circum-
stances, but what would happen were we to use a very strong (i.e., unbreak-
able ) container for the experiment? Are nature's laws invariable enough
that we might expect even a metal container to be broken in preference to
the law of fuga vacui? This question is faced squarely by the Spanish Domini-
can Domingo de Soto. After saying, as Toletus does, that there would have
to be an evaporation of some sort before the freezing would take place, the
Dominican continues:
But if you press the matter further. Let it be granted for example, that there
is a perfectly spherical iron container, completely uniform everywhere in
thickness and strength. This could be done either naturally or supernaturally.
Having no orifice, but nevertheless full of water and surrounded by the cold,
it could freeze. It is asked then, where it might break, lest a vacuum be
granted. It is answered that, in so far as I judge that water is heavy, it will
freeze in the lower part toward the earth; for this reason it will break at the
higher point, lest a vacuum be granted there.12
Thus, even if we have a strong iron container, it will break rather than
allow a vacuum. It seems as though by this time the Aristotelian horror
vacui had become one of the dominant laws of nature; it was held that all
l0 Toletus, op. cit., pp. 451, 453.
11 Collegium Conimbricense, op. cit., cols.
94-95.
12 De Soto, op. cit., fol. 66ra.
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CHARLES B. SCHMITT
sorts of rather unusual phenomena would take place rather than allow an
empty space to come about.
An opposing position was again taken by those two eminent anti-Aristo-
telians Telesio and Patrizi. Both argue that when the closed container is
put out into the cold the water will freeze, it will occupy less space, and
part of the container will become void of any body.13 Neither seems to be
particularly concerned about the problem of whether the container will break
or not, which apparently obsessed the Scholastics. It is to be supposed that
they could solve this problem in the same way as a similar problem was solved
in the bellows experiment, that is by using a container strong enough to
withstand any normal force which would be encountered. To the Scholastics'
contention that upon freezing, the water will give up vapors which will pre-
vent the formation of a void, Telesio argues that, on the contrary, when the
water contracts and freezes, you will find by experience that the vapors
and smoke will have become condensed into the water. 14 Telesio's argu-
ment is certainly more in accord with modern views regarding the reduction
of the vapor pressure of a liquid upon cooling and the significantly lower
vapor pressures of solid substances than of the corresponding liquid form.
One cannot help but think that it was also obvious to the observant indi-
vidual of the sixteenth century. In fact, such a thing is very definitely im-
plied, if not precisely spelled out, in Aristotle's theory of the transformation
of elements as found in the De generatione et corruptione. However, the
very fact that both sides in this controversy, which was ostensibly based on
firsthand experience, failed so miserably to recognize the fact that water
does not decrease in volume upon freezing, but increases, is itself of sig-
nificance. This seems to indicate that much of the apparent emphasis on
experience found in sixteenth-century writers consists in merely repeating
the experimenta of earlier treatises.
Consequently, what is in actuality a meaningful question and one which
gives us no a priori reason for not admitting an experimental approach turns
out to be a hopelessly confused mass of invalid arguments. The common
premise held by both sides (that water contracts upon freezing) proves to
be a false one and none of the participants in the debate seems to have made
any attempt either to validate or to invalidate this long-held assumption.
All of this tends to indicate that in large measure the evidence admitted into
the controversy was based upon thought experiments and the repetition
of traditional stories culled from a variety of sources, rather than upon
direct observation of the phenomena in question. Here we reach an aporia,
for we can find no good reason to choose, considering only the evidence
given, either the solution of the Aristotelians or that of their opponents.
13 Telesio, op. cit., Vol. I, pp. 87-88; Patrizi, dique occludas, ut aer nullus prorsus subire
op. cit., fol. 63va. id queat, tum vehementi id exponas frigori,
manifeste spatium vacuum in eo fieri intue-
14 Telesio, op. cit., Vol. I, pp. 87-88: bere; nam aquam in glaciem et minorem
Quin si ens quippiam crassioribus vaporibus contractam in molem, vapores fumumque
crassioreve fumo aut aqua repleas ac un- in aquam conspissatum experieris.
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EVIDENCE FOR AND AGAINST A VOID
Both are rendered ineffective by their common false premise that water con-
tracts upon freezing.
C. The Clepsydra
Discussions involving the operation of the clepsydra, or water clock, go
back to Aristotle himself, although he used the device to show that air has
weight rather than to demonstrate the impossibility of a void.15 Later the
clepsydra experiment was used in a more positive way to show that a vacuurr
cannot exist in nature.16 Throughout the sixteenth century this argument
remained one of the stock empirical weapons used by the Peripatetics to
substantiate their position. The Aristotelian argument is clearly summarized
by Domingo de Soto:
In the first place is the experiment of the clepsydra full of water, which lets
out no water from below while the upper orifice is blocked, lest a vacuum
should result; although when it is half full, it lets out some water, because
the air (since there might easily be rarefaction of it) rarefies in the upper
part 17
Philip Melanchthon frames it in very similar terms, emphasizing that the
water hangs, as it were, lest there be a discontinuity in nature:
There is an evident sign that there may not be a vacuum, nor may such a
thing be possible. A vacuum would produce discontinuous bodies. ... In
the clepsydra nothing trickles down if the upper opening is blocked, since
air does not enter from above. Consequently, the water hangs [pendet], lest, if
it were to leave [the clepsydra], a vacuum would result. However, the rule
of motion of heavy bodies is not changed without cause. But this cause is
evident: that nature avoids the discontinuity of bodies.18
Both of these writers, as well as many others we have not mentioned, repeat
the traditional Scholastic arguments. There is no great difference between
these sixteenth-century versions and those of the thirteenth-century theo-
logians and natural philosophers on this point, although it might be noted
that Melanchthon, immediately after the passage cited above, quotes directly
from Lucretius' De rerum natura to give an opposing position on the
vacuum question. This one rarely finds before the sixteenth century.19
15 Physics 213a25-213a27. For a more detailed
discussion of the clepsydra see pseudo-Aristotle,
Problemata XVI, 8, 914b9-915a25. See also
Hugh Last, Empedokles and His Klepsydra
Again, Classical Quarterly, 1924, 18:169-173,
and D. J. Furley, Empedocles and the Clep-
sydra, Journal of Hellenic Studies, 1957,
77:31-34.
16 See especially Duhem, op. cit., Vol. VIII,
pp. 130-168 passim.
17 Soto, op. cit. fol. 65vb. An alternative type
of demonstration, very common in the litera-
ture, is the following: If the upper orifice is
closed and the lower perforated portion of the
clepsydra is dipped into water, the water will
not enter, for there is no way for the air to get
out. See, for example, Hieronymus Borrius,
De motu gravium et levium (Florence, 1576),
pp. 226-227; Toletus, op. cit., p. 431; Julius
Pacius, Aristotelis . . . naturalis ascultation's
libri VIII (Frankfurt, 1596), pp. 600-601.
18 Philip Melanchthon, Initia doctrinae
physicae, in Corpus reformatorum, ed. C. G.
Bretschneider, Vol. XIII (Halle, 1846), col. 368.
19The extent to which sixteenth-century
Aristotelians were themselves influenced by
non-Aristotelian and non-Scholastic sources in
general, and by Lucretius in particular, re-
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CHARLES B. SCHMITT
We again find Telesio and Patrizi rejecting the Scholastic analysis of the
question. Once more Telesio suggests an interesting modification of the
original experiment, which would, according to him, demonstrate the oppo-
site of what it was originally meant to show:
Furthermore, it is permitted that space, which might in an absolute sense
be filled with no body and for that reason empty [inane] and void [vacuum],
may be granted or seen in the clepsydra itself. For these reasons the Peri-
patetics have argued that a vacuum cannot be granted: since if the clepsydra's
orifice is closed so no air can enter it and thus if the water within flowed
out of the lower openings, the place of the upper water might be rendered
void, by no means whatever will it flow out, but indeed the water stands
over the lower openings themselves and holds itself back. Moreover, this is
seen in all containers which are constructed in the same way and are every-
where closed so no air is allowed to enter them. Indeed, if you would make
only one opening of the clepsydra a little wider and you would somehow
open the lower part of it, you would see that the fluid within would im-
mediately flow down out of the [enlarged] opening and from the lower part.
Furthermore, honey and any other fluids which are a little heavier, as well
as very fine but dense and heavy powder, flow out of the openings of the
clepsydra.20
Telesio here argues to the effect that the Scholastics had not considered the
experiment in question carefully enough. He seems to agree with Melanch-
thon that water will hang in the clepsydra under the normal conditions
of the experiment. If the proper modifications are made, however, not only
quires further investigation. Julius Pacius cites
Lucretius often in reference to the vacuum
problem in op. cit., pp. 602-603, 605, 609-610,
633, 635. The De rerum natura was also used
in a striking way by Francesco Vimercato (Neal
W. Gilbert, Francesco Vimercato of Milan: A
Bio-bibliography, Studies in the Renaissance,
1965, 12:195) and Giulio Castellani (Charles B.
Schmitt, Giulio Castellani [1528-1586]: A Six-
teenth Century Opponent of Scepticism, Jour-
nal of the History of Philosophy, 1967, 5:15-39,
esp. pp. 36, 39). It is also interesting to note that
the avowedly anti-Aristotelian Gianfrancesco
Pico was cited as a source for arguments against
the Aristotelian view concerning the vacuum by
Collegium Conimbricense, op. cit., col. 90. See
Charles B. Schmitt, Who Read Gianfrancesco
Pico della Mirandola? Stud. Renaiss. 1964,
11:124-125.
20 Telesio, op. cit., Vol. I, p. 87:
Spatium porro, quod corpore nullo prorsus
repletum ac propterea inane vacuumque sit,
dari posse vel ipsis in clepsydris videre licet;
quae, quod si earum orificium ita occludatur,
ut aer nullus in eas subire queat, itaque si ex
infernis foraminibus inexistens aqua dela-
batur, superioris aquae locus vacuus fiat,
haudquaquam delabitur, sed vel quae fora-
minibus ipsis superstat, sustinet sese, vacu-
um dari non posse Peripateticis declarant.
In vasis praeterea omnibus, quae ita eaque
e re constructa et undique occlusa sunt, ut
nullus in ea ingressus aeri detur, hos spec-
tatur. Verum si unum tantum clepsydrarum
foramen paulo amplius effeceris et infernam
horum partem quidvis aperias, et ex illo
et ex hac inexsistentem fluorem statim deci-
dere videas. E clepsydrarum praeterea fora-
minibus, e quibus aqua non defluit, mel
fluoresque alii quivis paulo graviores et pul-
vis minutissimus at densus gravisque, decidit.
Patrizi's treatment of the issue is nearly the
same, op. cit., Pt. II, fols. 63rb-63va. A some-
what similar argument is the case of Cardano's
lamp, which became famous in the vacuum
discussions of the next centuries. This device,
consisting basically of an oil lamp, was said
to produce a vacuum when it begins to empty
because of the consumption of the oil. I plan
to write elsewhere on the long and interesting
history of this lamp as part of the vacuum con-
troversy. For Cardano's discussion of what he
calls the lucerna mirabilis, first treated in the
De subtilitate (first printing 1550), see his op.
cit., Vol. III, pp. 359-360. For an English trans-
lation and discussion of the relevant passage
see Leroy Thwing, Flickering Flames (Rutland,
Vt.: Tuttle, 1958), pp. 38-42.
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EVIDENCE FOR AND AGAINST A VOID
does the experiment fail to show the impossibility of a vacuum, but it seems
actually to indicate that there is more experimental evidence in favor of a
vacuum than against it.
D. Evacuation of a Vessel
One further bit of experimental evidence which was used in the sixteenth
century in favor of the vacuist position should now be discussed. Already
in antiquity Hero of Alexandria had argued that although not naturally
occurring, a continuous vacuum can be produced by drawing the air from
a container.21 This particular argument does not seem to have been dis-
cussed very extensively during the Middle Ages, although very similar ones-
for example, on the cupping glass-were quite common.22 One of the first
modern writers to make use of the ancient argument, as far as I have been
able to determine, was Adrian Turnebe in his De calore (completed before
1565). Here, though he touches on the vacuum problem only very briefly,
he argues, as Hero had, that there are inanitates quaedam interpositae in
nature. He then continues:
There is another certain emptiness, immense and extending widely, which
nature avoids, because of which it performs marvels, and propels heavy
body upward, which things it can nevertheless bring about. But, if you would
pierce through a glass ball and you would insert a small siphon through the
hole and you would carefully caulk around the hole, with your mouth you
could draw out the air which is inside and there would remain a great empti-
ness within. The proof of this would be the following: if before the air is let
in from the outside, you were to cover the siphon with your finger and you
were to turn it upside down in water, the liquid would enter when you
would remove your finger; and it would be drawn into the interior of the
ball.23
Francesco Patrizi cites essentially the same experiment, although in some-
what less detail. He does make one point which offers an important variation
of Turnebe's treatment. When describing the action of drawing out the air
from the sphere, he says: Let us draw out the air inside; we shall, without
doubt draw out a great deal; and thus there would necessarily remain much
of a vacuum. 24 Patrizi, therefore, realizes that only a partial vacuum can be
21 Hero, op. cit., Vol. I, pp. 8-10. For an Eng-
lish translation see The Pneumatics of Hero of
Alexandria, trans. J. G. Greenwood (London:
Taylor, Walton and Maberly, 1851), pp. 3-4.
22 See the texts of Duhem and De Waard
cited above in n. 1.
23 Adrianus Turnebus, De calore (Paris,
1600), fols. 15v-16r. The argument is repeated
in detail, including a direct quotation from
Turnebe, in Pierre Gassendi, Syntagma philoso-
phicumn, Sec. I, Bk. II, Ch. 4, in the Opera
omnia (Lyon, 1658), I, 198a.
24 Patrizi, op. cit., Pt. II, fol. 63rb: . . . in-
ternum aerem attrahamus, proculdubio mul-
tum extrahemus. Atque ita necessario vacui
multum relinquetur. Brickman (op. cit., p.
234) translates the last sentence as follows:
And so a large vacuum will necessarily be
left inside. This seems to me to be inaccurate.
The multum vacui seems to have the meaning
of a near vacuum or much of a vacuum
rather than a large vacuum. In the previous
sentence Patrizi has stated that a great deal
[multum] of air will be removed and not all
of the air. The distinction is, admittedly, a
rather minor one but in the present context
seems to be not unimportant. When Patrizi
speaks of large vacuum -as distinguished
from the small dispersed empty spaces we find
in the universe-he invariably seems to use the
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CHARLES B. SCHMITT
created by drawing the air out with the mouth. Turnebe, on the other hand,
gives every indication of actually believing that a complete vacuum can be
drawn. Regardless of this discrepancy between the two, both agree that the
experimental evidence is clearly in favor of a vacuist position.
III. ANALYSIS AND CONCLUSIONS
Let us now address ourselves to several questions of more general signifi-
cance. First, let us consider how the existence of a partial vacuum was in-
terpreted in the sixteenth century. Does the fact that we can draw a partial
vacuum (or, in more Scholastic language, produce a rarefied atmosphere)
indicate that a complete vacuum is possible or does it merely show that dif-
fering degrees of fullness are possible in a world which has no discon-
tinuity? The Scholastics generally held the position that the rarefaction and
condensation of matter can explain all of the phenomena which the positing
of a vacuum is meant to explain. However, with some Peripatetic thinkers
there appears to be a certain inconsistency. As we have seen, Toletus does
not seem to take the possibility of rarefaction into consideration in his
experiment of the bellows and the jar. This quite ingenious experiment,
which seems to offer a perfect instance for the rarefaction explanation, is
explained in rather disappointing and conventional terms. It stands in sharp
contrast with de Soto's contention regarding the clepsydra, where he argues
that when the device is only half full of water and the upper orifice is
blocked, some water will flow out, because the trapped air will increase in
volume to occupy the space left vacant by the outflowing water. There is,
consequently, some disagreement among the Aristotelians over just how the
rarefaction-condensation explanation will function. Patrizi, on the other
hand, who basically holds to a corpuscular theory very similar to Hero's (in
which there are naturally existing spatiola, void of all body, but no ingens
spatium vacuum), accepts this as evidence in behalf of the vacuum hypothe-
sis. There seems to be, therefore, a fundamental confusion-which goes back
to antiquity, we might add-as to what would constitute empirical evidence
for the actual existence of a vacuum. Ultimately, it seems to reduce to the
problem of whether rarefaction-condensation phenomena can adequately
be explained in terms of a full universe or whether a vacuum must be posited.
Thus, we find an Aristotelian (de Soto) citing the rarefaction of air as evidence
that there are no empty spaces in nature and an anti-Aristotelian (Patrizi)
citing it as evidence that there are.
From the Aristotelian point of view, although there is rarefaction and
condensation, the last bit of air, which marks the boundary between a rare-
fied but full space and an empty one, can never be extracted by natural
means. For the vacuist, the fact that some air can be extracted indicates that
term spatium inane. One should compare Gi- physicarum liber (Turin, 1585), p. 193. Here
ambattista Benedetti, Disputationes de quibus- Benedetti, one of the most distinguished 16th-
dam placitis Aristotelis, Ch. 34 in his Di- century defenders of the vacuist position, gives
versam speculationum mathematicarum et a rare allusion to experience.
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EVIDENCE FOR AND AGAINST A VOID
by the increased application of force more and more air can be removed
until finally the space will be empty. The disagreement arises over how the
same empirical data are to be interpreted and the crucial factor in the de-
cision seems to be the a priori theoretical construction which prompted the
experiment in the first place. Far from being decisive, the variously inter-
preted experiments merely reflect the already obvious position of their pro-
ponents. In a sense the results of the experiments have been determined
beforehand; given the conceptual framework in which they have been car-
ried out, they can give but a single result.
Secondly, how are the radically empirical arguments of Telesio and Patrizi
to be interpreted? As we have seen, both of these men present a series of
rather striking arguments which seem to go beyond the traditional empirical
discussions which we find among the Scholastics. Granted that the arguments
of these men show something of the inventiveness and ingenuity which must
be a stock resource of all good experimentalists, nevertheless there emerges
a further question to be considered. Do Telesio and Patrizi use the experi-
mental arguments in a positive way to establish the foundations of an em-
pirically based science or do they use them merely in a destructive way to
show that the Aristotelian arguments are not conclusive? Although both
make extensive use of empirical evidence in favor of their positions, their
general intent seems to have been to render the Aristotelian position inde-
terminate. As Patrizi at one place argues: Nothing is proved by them
[i.e., the ancients, who held that there is no vacuum] which the senses cannot
refute. 25 The implication is-and I think that a more careful examination
of Patrizi's general philosophical orientation will bear this out-that a sys-
tem of the physical world is basically a theoretical a priori construction, but
it must, at the same time, save the phenomena. There is always the phe-
nomenal world before us to act as a check for any system of natural philosophy,
and, for that reason, observation and experiment can reveal the weaknesses
of any system of natural philosophy. We can say, then, that experiment
does not appear to play a very important positive role in the formula-
tion of Patrizi's Neoplatonic philosophy. Experience and experiment are
more important in Telesio's philosophy of natura juxta propria principia,
but theoretical factors again generally seem to dominate.
Careful examination reveals that both Telesio and Patrizi adopt the stock
Aristotelian experiments meant to show that there cannot be a naturally
occurring vacuum in the physical world and they turn these against the
Peripatetics. The way in which the experimental arguments of Telesio and
Patrizi function bears a striking resemblance to the way in which the devel-
oping skeptical movement of the sixteenth century used arguments against
Aristotelian epistemology.26 The skeptic argued that the Aristotelian sense-
based theory of knowledge is valid only within a relatively narrow range
of boundary conditions and that further experiences drawn from outside
25 Patrizi, op. cit., Pt. II, fol. 63rb.
26 See my book, Gianfrancesco Pico (1469- phy (The Hague: Martinus Nijhoff, 1967), esp.
1533) and His Critique of Aristotelian Philoso- Ch. 4.
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CHARLES B. SCHMITT
this range render the Aristotelian theory unreliable at best. In general, both
Telesio and Patrizi say that the Scholastic experiments are valid as far as they
go, but when they are extended beyond the rather narrow limits envisioned
for them by their proponents, they not only fail to demonstrate what they
claim to, but indicate rather that the opposite is true. Once we have over-
come the technological problems of breaking bellows and cracking jars and
we have replaced the water of the clepsydra with heavier liquids, the vacuum-
less world picture is shattered. The Scholastic experimental arguments are
fine as far as they go, but to get a clearer and more accurate view of the world
we must extend them beyond their normal limits. It is only beyond the
realm of normal occurrence that we encounter the vacuum in a recog-
nizable form.27
Thirdly, let us consider what if any connection these experimental dis-
cussions have with the decisive experiments of the middle of the seventeenth
century. On the whole, it seems as though we do not find a great deal of
evidence to indicate that most of the writers we have been discussing were
really experimentalists themselves. There is a reliable tradition going back
to Telesio himself which attributes to him and to the followers of the phi-
losophia Telesiana an interest in experimentation.28 It seems clear, however,
that generally the writers who discuss the vacuum question do not really
go beyond the sum total of ancient and medieval knowledge on the subject.
In the writings which I have examined I have seen no discussion of the pos-
sible use of a suction pump to extract air from a vessel and thus create a
vacuum, although the suction pump was well known as a water-drawing
device in the sixteenth century.29 What seems evident, however, is that (1) cer-
tain ancient devices were reintroduced into the discussions, principally from
Hero's Pneumatica, (2) certain techniques known to the Arabs were either
reintroduced or rediscovered, and (3) some embellishments and modifica-
tions of the known experiments were suggested.
At any rate, almost all of the experiments which were utilized in the
vacuum discussions are rather primitive and by no stretch of the imagina-
27 A typically Aristotelian rejoinder to the
pro-vacuum arguments is that of the late 16th-
century Oxford professor John Case, who says:
Quintus locus [of the list of arguments he is
giving] est ab experientia, maxima, quod
omnia exempla quae ducuntur ad proban-
dum vacuum probe examinata inferant con-
trarium. Ut sunt illa de fistula explosa de
terrae motus causa, de clepsydra, de curcu-
bitula, de dolio cineribus pleno, non minus
tamen aquae recipiente quam si esset vacu-
um, de tabulis et follibus compressis et un-
dique obstructis. Sed haec omnia praetereo,
concludens nihil esse in rerum natura vac-
uum naturaliter: non negans tamen fieri
possit vi supernaturali et divina, quae nul-
lis mediis alligata potest in nihilum corpora
commutare efficere. (Ancilla philosophiae
seu epitome in octo libros physicorum Aris-
totelis [Oxford, 1599], p. 70; his italics.)
28 Antonio Persio, Liber novarum posi-
tionum (Venice, 1575), fol. 3v; Francis Bacon,
De principiis atque originibus secundum fabu-
las Cupidinis et coeli: sive Parmenidis et Tele-
sii et praecipue Democriti philosophia tractata
in fabula de Cupidine, in The Works of Fran-
cis Bacon, ed. James Spedding and Robert
Leslie Ellis (London: Longman, 1857-1874),
Vol. III, p. 115; Tommaso Cornelio, Progymnas-
mata physica (Venice, 1663), pp. 118-120; and
Raffaello Caverni, Storia del metodo sperimen-
tale in Italia (Florence: G. Civelli, 1891-1898),
Vol. I, pp. 435-436.
29 Sheldon Shapiro, The Origin of the Suc-
tion Pump, Technology and Culture, 1964,
5:566-574. I am indebted to Prof. Lynn T.
White for calling this paper to my attention.
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EVIDENCE FOR AND AGAINST A VOID
tion give anything like a definitive solution to the problem. In certain
ways they do point the way to the work of Torricelli, von Guericke, and
their followers, but we must categorically state that they in no way approxi-
mate them. We do find that the sixteenth-century discussions offer certain
hints which could lead to the seventeenth-century experiments. Telesio's
and Patrizi's suggestion that heavier liquids be used in experimental appa-
ratus to produce a vacuum bears some resemblance to the later use of mer-
cury in the barometric experiments.30 Again, the suggestion of Turnebe
and Patrizi regarding the evacuation of a sphere, joined to the widely dis-
cussed experiment of the impossibility of drawing apart two perfectly smooth
plates,31 points the way to von Guericke's experiment, but in no very defi-
nite way
Fourthly, the use of force and the attempt to extract from the physical
world that which it does not give up naturally (e.g., by extracting the air
from a sphere or by applying an extraordinary force to a specially prepared
bellows) indicates the road to more successful experimental procedures of
the succeeding centuries. It was progressively found that compelling na-
ture to do what it was not its nature to do, so to speak, often disclosed new
truths about the structure of the world. What the Scholastics interpreted to
be the puzzling and somewhat aberrant phenomena resulting from nature's
horror vacui, the more modern thinkers interpreted in a much more posi-
tive way. As Turnebe argued, the reluctance of nature to admit a void is
responsible for many marvels (miracula). The great popularity of the re-
introduced Pneumatica of Hero and the consequent development of the sci-
ence of pneumatics in the following centuries clearly indicate the fruits of
such an attitude.32
In conclusion to our rather limited investigation we can say that no major
experimental breakthrough was achieved in the sixteenth century. What is
significant is that Aristotelians and non-Aristotelians alike did confront tra-
ditional Scholastic arguments with newly discovered pro-vacuum sources
from antiquity such as Lucretius and Hero. Even if these ancients seemed
to make little impression on the Peripatetics (although they were known
30 It should be noted that certain medieval
Arabic thinkers had actually suggested the use
of mercury in such experiments. See Salomon
Pines, op. cit., esp. p. 80, n. 2.
31 The origin of this seems to be Lucretius,
De rerum natura I, lines 385-400. For its his-
tory see especially De Waard and Duhem as
cited in n. 1. Renaissance authors who discuss
it include de Soto, op. cit., fol. 66'a; Toletus,
op. cit., pp. 451, 453; and the Collegium Conim-
bricense, op. cit., cols. 89, 95. It is worth noting
that this seems to be the only experiential ar-
gument discussed by Galileo in the De motu
(1589-1590). See Le opere (Florence: G. Barbera,
1890-1909), Vol. I, pp. 394-395. This passage
is unfortunately not included in the recent
(partial) English translation by I. E. Drabkin
in Galileo Galilei on Motion and Mechanics
(Madison: Univ. Wisconsin Press, 1960). Per-
haps the most remarkable discussion of this,
especially with von Guericke's later experiment
in mind, is John Buridan, Subtilissime ques-
tiones super octo Physicorum libros (Paris,
1509), lib. IV, quaestio 7, fol. lxxiiiva, trans. into
French in Duhem, op. cit., Vol. VIII, pp. 126-
127
32 For Hero's influence in the Renaissance
see particularly Marie Boas, Hero's Pneumati-
ca: A Study of its Transmission and Influence,
Isis, 1949, 40:38-48, and Wilhelm Schmidt,
Heron von Alexandria im 17. Jahrhundert,
Abhandlungen zur Geschichte der Mathematik,
1898, 8:195-214.
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366 CHARLES B SCHMTT
and cited), they deeply influenced the new group of thinkers who were
openly hostile to the Aristotelian tradition. The experimental arguments in
favor of a vacuist position which were collected by the anti-Aristotelians
were a useful aid in the demolition of Aristotelian natural philosophy, but
they do not yet seem to have the importance which experiment will have in
the next century. The real development which took place within the group
of Renaissance pro-vacuum thinkers came from other roots. Most of the
evidence points to the fact that a vacuist position was considered to be ten-
able, not for reasons derived from experimental evidence, but for theoretical
reasons. The precise way in which the Renaissance scholars worked out a
coherent natural philosophy based on the vacuist presupposition must be
left for later study.