125
M. Dobre and T. Nyden (eds.), Cartesian Empiricisms, Studies in History
and Philosophy of Science 31, DOI 10.1007/978-94-007-7690-6_6,
© Springer Science+Business Media Dordrecht 2013
Abstract When Descartes touches upon objects and operations of chemistry in the
fourth part of Principia philosophiae (1644), he destroys any possibility of chemistry
becoming a specifi c science. He reduces all chemical operations to matters of size,
shape and motion of particles. In the frame of Cartesian natural philosophy,
chemistry vanishes into mechanics. In this chapter, I would like to examine how,
under these conditions, some philosophers or chemists who were sometimes regarded
as Cartesian thinkers introduce chemical discourse in their natural philosophy.
Some of them, such as Boyle, said that the mechanical structure underlies all chemical
operations. Therefore, chemistry can only exist as empirical knowledge. Others
however, such as Lémery (father and son) proposes new mechanical explanations
specifi c to chemistry, in a way which is opposite to the theories of Principia
philosophiae . Chemistry, which cannot be developed without laboratory work,
leads to an unusual empirical Cartesianism which I suggest we examine in the light
of the debate between some French chemists at the Académie royale des sciences at
the end of the seventeenth century and the beginning of the eighteenth century.
Descartes did not like chemists, whom he also called alchemists. Like most of his
contemporaries, he considered the two words to be synonymous. He often jested at
alchemists and their little secrets, their vain quest after the philosopher’s stone.
But he levelled at them more fundamental criticisms, concerning both the nature of
their knowledge, and the shortcomings of their theorizing. This led him, in the
fourth part of his Principia philosophiae , to operate a grand scale reduction of the
workings of chemistry to the principles of his mechanistic conception of matter,
Chapter 6
Could a Practicing Chemical Philosopher
Be a Cartesian?
Bernard Joly
B. Joly (*)
Université Lille 3 , UMR 8163 “Savoirs, textes, langage,” Lille , France
e-mail: [email protected]
126
such as had been expounded in previous sections of his work. Under such
conditions, one could have imagined that chemistry, in the eyes of Cartesian
philosophers, could have no future. Fully integrated into Cartesian physics, it
seemed doomed to extinction as a specifi c discipline.
1
This proved in no way to be
true. It will be examined here why and how chemists were in a position to claim
that they belonged to Cartesianism in the late seventeenth and early eighteenth
centuries, a claim that induced them to develop a conception of Cartesianism
which granted an important place to laboratory experimentation.
2
But eventually it
will have to be asked whether such a standpoint made these Cartesian chemists
genuine empiricists.
6.1 The Mechanistic Reduction of the Objects of Chemistry
Descartes’ attitude towards chemistry may appear paradoxical, since he criticized it
while indulging in its practice. On the one hand, he seemed to reject it. Everyone
remembers the famous passage from Discours de la méthode , in which he dismissed
alchemy, astrology and magic as belonging to the “false science,” claiming that
henceforward it would no longer be possible to be abused by “the promises of an
alchemist or the predictions of an astrologer, the tricks of a magician or the frauds
and boasts of those who profess to know more than they do.”
3
In the same period, he
wrote to Marin Mersenne (1588–1648): “I am of a mind with you to laugh at the
imaginings of this chemist of whom you write, and believe that such chimeras do
not deserve to engage for one single moment the thoughts of an honest man.”
4
As a
result of the spread of Paracelsian ideas, the doctrines of alchemists were very
infl uential at the beginning of the seventeenth century. They could be associated
with the vast movement of criticism of Aristotelian ideas and his philosophy of
nature. Descartes had met alchemists, fi rst during his journey to Germany, then at
the beginning of the 1620s in Paris, before he turned away from their doctrines.
5
His dismissal of a subject to which he had been attracted in his youth, at a period
when he was trying to get away from the patterns of Scholasticism, seems to have
1
One can notice that, in the tree of philosophy presented in the Lettre-Préface of 1647, mechanics,
but also medicine, which Descartes often associated with chemistry, keeps a distinct place from
physics, which is not the case for chemistry.
2
Our enquiry is limited to the evocation of some fi gures among those who dealt with chemistry in
a would-be spirit of Cartesianism and has no vocation to cover the whole fi eld of the interactions
between Cartesianism and chemistry (or alchemy) in the seventeenth and eighteenth centuries
throughout Europe. A whole book would be needed for such a study.
3
See Discours de la méthode I. AT VI 9, CSM I 115.
4
Letter to Mersenne, March 1637. AT I 351: “Je me moque avec vous des imaginations de ce chymiste
dont vous m’écrivez, et croie que semblables chimères ne méritent pas d’occuper un seul moment
les pensées d’un honnête homme.”
5
See Gouhier 1958 ; Maillard 1998 ; Mehl 2001 .
B. Joly
127
become a lifelong standpoint in his doctrine. Thus, in 1649, he criticized in parallel
terms “those who boast of possessing secrets, in chemistry or judicial astrology.”
6
At the same time as he criticized it, Descartes showed an interest in the chemistry
of his time.
7
On April 15, 1630, he announced to Mersenne that he now studied
“chemistry and anatomy simultaneous; everyday I learn something that I cannot
fi nd in any book.”
8
Two years later he explained to him that he undertook “various
experiments to discover the essential differences between oils, ardent spirits, ordinary
waters and acidic liquids, salts, etc.”
9
These experiments served as a preparatory
work for the writing of Le Monde , a book which was to remain unpublished during
his lifetime. However, he gave a summary of this work in part 5 of the Discours de
la méthode , referring to chemical developments which left no trace in the manuscript
found after his death, and which gave us partial access to his work. It is also in the
Meteorology , the second scientifi c essay introduced by Discours de la méthode , that
we may fi nd the result of his chemical research. Descartes describes water “carrying
towards the top of an alembic the small particles of these oils which Alchemists
were in a practice of extracting from dry plants,”
10
or “these spirits or ‘eaux de vie’
which always rise fi rst from the distilled bodies.”
11
It is mainly in the third discourse
of Meteorology , devoted to salt, that Descartes refers to the works of chemists,
notably when he mentions “this extremely strong and sour water which can dissolve
gold, and which is named salt spirit or oil by Alchemists.”
12
Later on, Descartes frequently broached chemical topics with correspondents
asking for his advice. In this respect, Mersenne, Constantin Huygens (1596–1687)
and William Cavendish (1593–1676) were his main interlocutors. He let Mersenne
know about his various experimental attempts, and the latter communicated to him
the letters of Christophe de Villiers (1585–1650), a physician from Sens who was
taking an interest in alchemy and whose theories about salt were criticized by
Descartes. Chemical questions crop up several times in his correspondence with
Huygens, to whom he gave his advice in August 1638 about the dissolution of
metals by aqua fortis which do not attack the other mineral substances, or on “quick
silver [which] resolves gold, tin, and lead, though it can hardly fi x itself on the
other metals, and even less on the bodies which are not metallic.”
13
At that point,
6
Letter to Chanut, March 31, 1649. AT V 327, CSMK 370.
7
I have developed this point in Joly 2011 , Chap. II: “Descartes et les ‘chymistes’ de son temps.”
8
AT I 137, CSMK 21.
9
Letter to Mersenne, April 5, 1632. AT I 243, CSMK 37.
10
AT VI 241: “emporte vers le haut d’un alambic les petites parties de ces huiles que les Alchimistes
ont coutume de tirer des plantes sèches.”
11
AT VI 247 : “ces esprits ou eaux de vie, qui s’élèvent toujours les premières des corps
qu’on distille.”
12
AT VI 263–264 : “cette eau extrêmement aigre et forte, qui peut soudre l’or, et que les Alchimistes
nomment l’esprit ou l’huile de sel.”
13
Letter to Huygens, August 1638. AT II 351: “le vif argent [qui] résout l’or, l’étain et le plomb,
bien qu’il ne se puisse presque pas attacher aux autres métaux, et encore moins aux corps qui ne
sont point métalliques.”
6 Could a Practicing Chemical Philosopher Be a Cartesian?
128
Huygens considered Descartes a genuine expert on chemical questions, for in 1645
he asked Descartes to send him a little treatise on chemical operations similar to the
treatise on mechanics that he sent him a few years earlier, entitled Traité des engins .
14
Descartes declined the invitation, saying that everything he knew about the question
had been expressed in the fourth part of Principia philosophiae .
15
This did not prevent
him from taking up the subject again in 1646 in a letter to Cavendish in which
chemical developments occupy several pages. After renewing his criticism of
“chemists” who “use words in an uncommon sense only in order to make it seem that
they know what in fact they do not know,”
16
he expounds his views on the principles
of chemists, on the generation of stones, and on the nature of quicksilver.
It would be wrong to believe that Descartes had set up an opposition between
alchemy, whose illusory nature he denounced, and chemistry, whose practices he
accepted. On the contrary, he used each of the two terms interchangeably to refer to
the theories he condemned or to the practices of which he gave a new interpretation:
in 1649, he calls “chymistry” the theory and practice of those whom he called “alchi-
mists” in 1637. Such a situation should not surprise us, since the historians of ancient
chemistry have shown in recent years that the distinction between chemistry and
alchemy did not really make sense in the seventeenth century.
17
More than that,
Descartes’ diffi dence concerning “chymistry” or alchemy does not mean that he was
opposed to the transmutation of metals. Like many of his contemporaries, he thought
that the question of the philosopher’s stone, like that of squaring of the circle, must
be “searched by human understanding.”
18
It is not the operation in itself that seems
unreasonable to him, but the doctrine one uses to justify its possibility.
We should thus wonder about the reasons for the Cartesian paradox about
chemistry, which must be distinguished from the ambivalence around that question
which was rather widespread in his time
19
: why did Descartes strenuously reject a
knowledge whose operations he approved of? The various reasons for Descartes’
diffi dence of alchemy have been documented elsewhere.
20
They could be gathered
around two main lines here: the rejection of the founding principles of the alche-
mists’ doctrine, but also a defi ance of laboratory work, whose practical interest was
recognized, but which could be of no use as a means of justifying theory. Thus, in
Descartes’ eyes, the chemical doctrine can claim neither doctrinal soundness, nor
experimental basis. Two historical supports of alchemy, the book and the alembic,
are thus put to question.
14
Letter from Huygens to Descartes, July 7, 1645; AT IV 244 and 779. The Traité des engins had
been sent by Descartes to Huygens on October 5, 1637; AT I 435–447.
15
Letter to Huygens, August 4, 1645; AT IV 260 and 780. More about this later.
16
Letter to the Marquess of Newcastle, November 23, 1646; AT IV 569, CSMK 302.
17
See Halleux 1979 ; Principe and Newman 1998 ; Principe and Newman 2001 ; Joly 2007a .
18
Notae in programma ; AT VIII 353: “la recherche du raisonnement humain.”
19
Contrary to Francis Bacon or Mersenne, Descartes had no wish to reform alchemy, or to sort out
the various doctrinal standpoints. What he wanted to do was deny all chemical practices the
possibility of any theoretical basis. On Bacon’s attitude, see Joly
2003 ; on Mersenne’s, see Joly 2001b .
20
Joly 2011 , Chap. IV: “Le refus cartésien d’une science chimique.”
B. Joly
129
Descartes rejects the theories of matter on which chemists founded their work.
Challenging the fact that what they called their principles (Mercury, Sulfur, and
Salt) really had the status of principles, he disrupts one essential aspect of the theory
of matter which was at the heart of the alchemical doctrine. As he briefl y, but very
clearly states in the Lettre-préface of the French edition of the Principes de la
philosophie , the Mercury-Sulphur-Salt triad no more deserves the status of principle
than void and atoms, or hot, cold, dry and wet, and “all other similar things which
some people have proposed as their fi rst principles.”
21
Neither Democritean
atomism, nor the Aristotelian theory of sensitive qualities, nor the tria prima of
Paracelsians are compatible with the Cartesian theory of matter, such as expounded
in the second part of the Principia philosophiae . He expatiates on the subject in
several passages of his correspondence. Already in 1631, even though he conceded
some sort of interest in the alchemical research of his friend Villebressieu, he insisted
that “there is only one material substance which receives from an external agent its
action or its ability to move from one place to another.”
22
Far from being founding
principles, the elements and principles of chemists are nothing but the result of these
movements of matter. He comes back to this argument 10 years later, when he explains
to Mersenne the reasons for his disagreement with the theses of de Villers, the physician
from Sens. Expatiating upon the whole of the alchemists’ doctrines, he writes:
These Principles are nothing less than a wrong fantasy, deriving from the fact that, in their
distillations, they extract waters which are all the most slippery and fl exible parts of the
bodies from which they extract them, and refer them to Mercury. They also extract from
them oils, whose parts are shaped like branches, loose and fl exible enough to detach
themselves, and these they refer to Sulphur; and they refer to Salt the loosest parts of what
remains, which can mix and merge, so to say, with water; last, the grossest parts which
remain are their Caput mortuum , or Terra damnata , which they only account for as a
useless thing. As a matter-of-fact, I cannot conceive of these parts as indivisible or different
from one another, but through the diversity of their fi gures.
23
This way of justifying the existence of principles by invoking experiences of
distillation supposed to extract as such, could be found at that time in numerous
“chymical” texts, for instance those by Joseph Du Chesne (1544–1609) or Etienne
De Clave.
24
What Descartes objected to was not so much the operation itself, and
the results it entailed, as the way it generally used to be interpreted. Far from being
21
AT IXb 8, CSM I 183.
22
Letter to Villebressieu, Summer 1631; AT I 216, CSMK 33.
23
Letter to Mersenne, July 30, 1640; AT III 130–131: “Ces Principes ne sont rien qu’une fausse
imagination, fondée sur ce qu’en leurs distillations, ils tirent des eaux qui sont toutes les parties
plus glissantes et pliantes des corps dont ils les tirent, et qu’ils les rapportent au Mercure. Ils en
tirent aussi des huiles, dont les parties sont en forme de branches, assez déliées et pliantes pour
pouvoir être séparées, et ils les rapportent au Soufre; et ils rapportent au Sel les parties les plus
déliées de ce qui reste, qui se peuvent mêler et comme incorporer avec l’eau; puis enfi n les parties
plus grossières, qui demeurent, sont leur Caput mortuum , ou Terra damnata , qu’ils ne comptent
que comme une chose inutile. Au reste, je ne conçois point ces parties indivisibles ni autrement
différentes entre elles, que par la diversité de leurs fi gures.”
24
See Joly 2002 .
6 Could a Practicing Chemical Philosopher Be a Cartesian?
130
ontologically distinct principles that institute an irreducible plurality in the heart of
matter, Mercury, Sulfur, and Salt are nothing but various parts of one similar matter
and differ through nothing but their respective confi guration. Thus Descartes’
concern here is not with substituting the “wrong fantasy” of alchemists with the
“right” one, but rather with contrasting two methods with each other. Whereas
alchemists aimed, through an inductive approach, to justify their would-be principles
by resorting to experience, Descartes, on the contrary, meant to justify the empirical
properties of chemical substances by resorting to principles, which he did not imagine
but conceived, that is to say, deduced from their metaphysical foundations.
The same idea is repeated in his letter to Cavendish dated November 23, 1646:
In my view, the chemists’ salt, sulphur and mercury are no more different from each other
than the four elements of the philosophers, and not much more different from each other
than water is from ice, foam and snow. I think that all these bodies are made of the same
matter, and that the only thing which makes a difference between them is that the tiny parts
of this matter which constitute some of them do not have the same shape or arrangement as
the parts which constitute the others.
25
This doctrine was central to the 88 articles (45–123) devoted to the objects and
operations of chemistry in the fourth part of Principia philosophiae .
26
Resuming the
topic of the identifi cation of the would-be principles of chemists with the “three
kinds of bodies” whose formation he accounted for by mechanical arguments,
Descartes carries out a process of reduction of chemistry to mechanics, which ought
to result in its disappearance as a scientifi c discipline.
Yet, we are under restraint of reaching such a conclusion straight away, because
of Descartes’ constant interest in chemical operations, and particularly in distillation.
As has just been shown, the latter keeps the status of a privileged experience. If it is
no longer destined to exhibit vain principles, it nevertheless remains an essential
practice, which fully brings into relief the existence of clearly distinct categories of
chemical bodies whose natural formation mechanical interpretation accounts for by
operations of hammering, tearing apart or rubbing against one another. Descartes
does not deny the importance of experimental practices, but he keeps repeating his
concern with a knowledge which rests on experience and laboratory work. Several
times he complains of his lack of the full technical competence for carrying out
chemical experiments under good conditions, and expresses his wish of working in
company with a chemist able to carry out the various laboratory experiments.
He says so to Mersenne in 1642, referring to his former friend Villebressieu:
I have a good opinion of him for that he has the skills to put into practice what he could be
ordered in that respect [the “little secrets of chemistry”], and I hold him to be good-natured
enough. He offered to come and stay here with me, which I cannot accept at this moment,
because I do not wish to stop for any experiment till my Philosophy is published.
27
25
AT IV 570, CSMK 302.
26
AT VIII 231–269 for the Latin edition, AT IXb 225–266 for the French edition.
27
Letter to Mersenne, December 7, 1642; AT III 598: “Ce que j’estime en lui est qu’il a des mains
pour mettre en pratique ce qu’on lui pourrait prescrire en cela [les ‘petits secrets de chymie’], et
que je le crois d’assez bon naturel. Il m’offre de venir ici, ce que je ne voudrais pas maintenant, à cause
que je ne veux point arrêter à faire aucunes expériences, que ma Philosophie ne soit imprimée.”
B. Joly
131
In so far as the fourth part of the Principia philosophiae rests partly on the
evocation of the experiences made by chemists about fi re or distillation, such words
could be surprising. At any rate they are an indication that, at that time, Descartes
deemed he had suffi cient knowledge of chemistry to be able to launch into his
mechanistic interpretation of the operations and objects of chemistry. No doubt
Descartes does not say everything: it is established that, at that time, he frequented
Cornelis van Hoghelande (1590–1646), who used to practice chemical medicine.
If one may believe the testimony of Daniel Georg Morhof (1639–1691), this Dutch
chemist had “made a lot of experimentation in company with Descartes.”
28
However,
in later days, Descartes kept invoking his lack of experience when invited by friends
to proceed with his chemical experimenting. He said so to Huygens in 1645 to
motivate his refusal to write out the “little treatise of chymistry” that the latter had
asked from him:
As I have already given out the little knowledge I have of this subject in the fourth part of
my principles, when dealing with the nature of minerals and fi re and with all the diverse
effects to which almost the whole of Chemistry can be related, it is impossible for me to
write anything more without incurring the risk of running into error, for lack of making
experiments necessary to acquire the particular knowledge of each thing; and as I have no
practical opportunity to make them, I henceforward decide to put an end to this study, and
to all similar studies, which could only be carried on to my satisfaction with the help of
other people; for I still have enough researches to make, for which I need no other resources
than those of my own mind, to be able to live pleasantly enough for the rest of my days.
29
No doubt Descartes was no longer the same since he had announced his labora-
tory experimenting in 1630. He had realized that his capacities as an experimenter
were limited, and wished to devote his time to more rewarding activities such as
would not impinge upon his solitude as a philosopher. Yet this lack of experience
did not prevent him from writing the fourth part of Principia philosophiae , which
confi rms the essentially deductive nature of his reasoning in that work. A point
which is further confi rmed, in the following year, by his answer to Cavendish, to
whom he acknowledged that he had not yet made “all the necessary experiments” to
establish the nature of quicksilver. But he thought he knew enough to account for all
its properties, whether it be its fl uidity, its faculty to shape into tiny balls on a table,
or not to stick to the hands (alchemists would say that it is a kind of water that does
not wet), or to mix easily with lead or gold.
30
More than ever, it seemed that
Descartes thought it enough to account for the chemical properties of observable
28
Morhof 1673 ; testimony mentioned in Matton 1998 , 112: “…multa cum Cartesio operatus est.”
29
Letter to Huygens, August 4, 1645; AT IV 260–261 and 780–778: “Ayant déjà écrit tout le peu
que je savais touchant cette matière, en la quatrième partie de mes principes, lorsque j’y ai traité de
la nature des minéraux et de celle du feu, et de tous les divers effets auxquels se peut quasi
rapporter toute la Chymie, il ne m’est pas possible d’en rien écrire davantage, sans me mettre en
hasard de me méprendre, à cause que je n’ai point fait les expériences qui m’auraient été néces-
saires pour venir à la connaissance particulière de chaque chose; et n’ayant point la commodité de
les faire, je renonce dorénavant à cette étude et à tous les autres semblables, touchant lesquels je ne
pourrais entièrement me satisfaire sans l’aide d’autrui; car il en reste encore assez d’autres, auxquels
je n’ai besoin que de moi seul, pour occuper agréablement le reste de ma vie.”
30
Letter to the Marquiss of Newcastle, November 23 1646; AT IV 572, CSMK 302.
6 Could a Practicing Chemical Philosopher Be a Cartesian?
132
bodies by means of his mechanical physics, without confronting himself with new
hypotheses that could be confi rmed by experience. Thus one may be struck by the
absence of any heuristic dimension in his discourse about chemistry, which reduces
chemistry to a number of empirical observations with no status as scientifi c knowledge,
since the principles which account for the observed phenomena remain exterior to
it: as a matter of fact, they belong to the mechanistic system and the geometrical
properties of matter, which have been expounded in the general part of his physics.
6.2 What Is a Cartesian Chemistry?
The Cartesian critique of chemistry could but fi nd an echo at that time. It meets
halfway the strong reserves that had been expressed for centuries toward a knowl-
edge whose legitimacy was constantly put to question. Introduced into Europe in
the twelfth century, at a time when the works of Arabian scientists were being
translated, alchemy could never manage to fi nd its place in the network of medieval
sciences. As it could not separate theory from practice, it needed the presence of
a laboratory, which would have been out of place in universities dedicated to
intellectual pursuits. Related to Artes Mechanicae, it could not boast the status of
a speculative science.
31
Such a point of view, shared by a wide proportion of
intellectuals until the seventeenth century, was of course strongly reproved by
alchemists’ intent to show that alchemy was a genuine form of natural philosophy.
Thus, from the Summa Perfectionis by pseudo-Geber in the thirteenth century, to the
Abrégé des secrets chimiques (1636) by Pierre Jean Fabre (1588–1658) or the Traité
de la chymie (1661) by Nicaise Le Febvre (1610–1669), a series of works were
published and their aim was to argue that alchemy was rooted in a theory of matter,
which would have conferred it the rank of a philosophy.
Alchemy, which had been able to resist the onslaught of Aristotelianism and
Galenism, was not more threatened by the growth of mechanistic theories. One
could even say that those who referred to Cartesian ideas and wished to develop a
science based on the principles of mechanics, were obliged to take the resistance of
chemistry into account, so that what took place eventually was as much an adapta-
tion of Cartesianism to the claims of chemistry, as a submission of the latter to the
constraints of mechanism. It is true that the fi rst Cartesians remained faithful to their
master’s spirit. As was shown, respectively, by Luc Peterschmitt and Mihnea Dobre,
there is no denying that authors like Géraud de Cordemoy (1626–1684), Jacques Du
Roure (fl . 1653–1683), Robert Desgabets (1610–1678), or Jacques Rohault (1618–1672)
were dealing with the objects of chemistry, yet they no way considered the latter
as a science.
32
In his Traité de physique Jacques Rohault, admittedly, granted much more
importance to laboratory work than Descartes did in the fourth part of his
31
See Mandosio 1990–1991 , 1998 .
32
Peterschmitt 2007 ; Dobre 2011 .
B. Joly
133
Principes de la philosophie . The latter, as we have seen, had confessed, in a letter
to Huygens, that he had given up experimenting to gain access to the “individual
knowledge of each thing,” thus acknowledging the fact that the singular knowledge
of the properties of the diverse objects of chemistry had been of no use to him to
operate the mechanical reduction of chemistry. On the contrary, Rohault insisted,
“every useful Science ought to descend immediately to Particulars.”
33
According to
him, the properties of chemical bodies had to be established through laboratory
experiment, and not, as with Descartes, by means of a deduction of their process of
formation in the earth. No doubt he wrote that “all that which is produced by art in
the Laboratories of Chymists, is done naturally in the Bowels of the Earth,”
34
but
this parallelism, frequent in the works of alchemists, resulted in nothing but a greater
importance given to laboratory work, thus considered as a natural process. Thus, it
became possible to transmute Salts into acid liquids, “which the Chymists call Oyl ,
or Spirit of Salt , or Aqua-Fortis which is used to dissolve Metals with.”
35
Rohault then
gave the recipe for this operation, which consisted in distilling salt mixed up with
piled up clay. A little further on, he saw “the Experiments of Chymists, who by the
Resolution of Metals, can draw Salt and Sulphur out of them,”
36
as a confi rmation of
his theses on the constitution of metals, which accounted for his former assertion that
the transmutation of metals was a “moral impossibility,” but not an “absolute one.”
37
In the fi rst part of his work, Rohault had fully recognized the importance of the
works of chemists, granting them praises such as could not be found in Descartes:
Without doubt the whole World, and the Philosophers particularly, are very much obliged
to them for the Pains they have taken, and which they continue to take, to make a great
Number of Experiments, whereby they come to the Knowledge of diverse Properties of
many different Things. This gives them opportunity to fi nd out and discover the Nature
of Things…
38
33
Rohault 1671 , unpaginated preface: “une science d’usage doit bientôt descendre dans le particulier.”
An English translation was made available in the early eighteenth century and reprinted as
Rohault
1987 . For Rohault and his Cartesian experimental physics, see Chap. 9 by Dobre.
34
Rohault 1671 , II, 177: “tout ce que l’artifi ce produit dans les laboratoires des Chymistes se fait
naturellement dans les entrailles de la Terre.” Rohault
1987 , II, 148.
35
Rohault 1987 , II, 148.
36
Rohault 1987 , II, 155. Clarke’s English translation misses the reference to mercury in the French
text. For the original French text, see Rohault
1671 , II, 188: “l’expérience des Chymistes, qui par
la résolution des métaux en peuvent tirer leur sel et leur soufre, et même, si l’on en croit quelques-
uns, leur Mercure.” The experiments usually put forward as evidence for validating their theses,
were aimed at distilling vegetals and particularly wood. It is noteworthy that Rohault took up, for
his own account, the distillation of a metal, which could hardly be effected, and which is one
example of the extrapolations of which alchemists were often guilty.
37
Rohault 1671 , II, 186. Quite strangely the expression “moralement impossible” is not present in
the English translation, Rohault
1987 , II, 154.
38
Rohault 1987 , I, 109. Rohault 1671 , I, 137: “Tout le monde sans doute, et les Philosophes en
particulier, leur sont fort obligés de la peine qu’ils se sont donnée, et qu’il se donnent encore tous
les jours, à faire un très grand nombre d’expériences, par le moyen desquelles ils leur font connaître
les diverses propriétés de plusieurs Êtres différents. Ce qui leur donne la commodité de rechercher
et découvrir la Nature des choses.”
6 Could a Practicing Chemical Philosopher Be a Cartesian?
134
But he accompanied this recognition of the importance of the chemists’
experimental research for natural philosophy with strong reservations about both
their method and their principles. They were wrong in their principles, whose
number it was impossible to establish, and even more in their method, because,
limiting themselves to the knowledge of the “sensible Parts of which a Body is
composed,”
39
they prevented themselves from understanding the deep structure of
matter, and notably the part played by subtle matter, also called matter of the fi rst
element. Far from promoting a Cartesian chemistry, Rohault situated his chemical
observations within the framework of physics, a species of physics which remained
perfectly compatible with the spirit of Cartesian thought, insofar as it accounted
for all the operations and properties of bodies by the form and movement of their
constituent particles. Ultimately, there is no doubt that it was Descartes’ theory of
matter, and not the chemists’, which allowed him to explain the multiple operations
of the laboratory.
Among all the Cartesian philosophers who showed an interest in chemistry at
that period, Pierre-Sylvain Régis (1632–1707) was perhaps the one who went the
farthest to take into consideration the specifi city of that science. In this respect, the
opposition between the fourth and the fi fth parts of Book 4 of his physics, which in
itself constitutes the second tome of his Système de la philosophie , is quite revealing.
40
In the fourth part, entitled “Of the properties which are common to the hard Bodies
and to the liquid Bodies,” Régis, in fact, dealt mainly with fi re, its nature and effects.
In terms close to Descartes’, he considered fi re, not as a specifi c matter, but only as
the situation in which are placed:
terrestrial bodies whose non-sensitive parts are almost separated from one another, and so
much surrounded with the Matter of the fi rst Element, that they receive from it as much of
their speed, as the link which still exists between them can allow.
41
In confi rmation of this theory of the nature and properties of fi re, he even pro-
duced a drawing which mirrored perfectly the one with which Descartes illustrated
his point in articles 95–99 of his fourth part of the Principes de la philosophie .
42
His framework of thought was undoubtedly Cartesian here, with the development of
a theory of fi re wholly deduced from the properties of matter, without any resorting
to experimentation.
The fi fth part, entitled “Of the properties which are discovered to be those of hard
Bodies as a result of their resolution by dissolving Liquids,” is quite a different trend.
It does abound in mechanistic explanations, but these seem to be superadded to the
39
Rohault 1987 , I, 110. Rohault 1671 , I, 138.
40
Régis 1690 .
41
Régis 1690 , II, 262: “…les corps terrestres dont les parties insensibles sont presque séparées les
unes des autres et tellement environnées de la Matière du premier Elément qu’elles en reçoivent
autant de sa vitesse que la liaison qui est encore entr’elles le leur peut permettre.”
42
Régis 1690 , II, 265; Principes de la philosophie . AT IXb 253–255. I here refer to the French edi-
tion of Descartes, much more developed than the Latin edition.
B. Joly
