The Sourhern Journol of Philosophy (1985) Vol. XXIII, Supplement

JEAN PENA (1528-58) A N D STOIC PHYSICS IN T H E SIXTEENTH CENTURY

Peter Barker Virginia Polytechnic Inst it ut e

Introduction

It has long been recognised that revivals of Stoic ideas affected ethics’ and literature2, beginning in the mid-sixteenth century and reaching their greatest influence during the first half of the seventeenth century. There are no sustained discussions of the influence of Stoic ideas on scientific debates during the same period, although Stoic influences have been noted by a number of modern authorities.3 Stoic physics was regarded by its originators as one of a triad of foundational subjects, the others being logic and ethics, and the student was expected to master physics before proceeding to the study of ethics. The neglect of Stoic influence in scientific matters is particularly curious in view of the widespread recognition of Stoic contributions to ethics in the early modern period.

In an earlier paper, written in collaboration with Bernard R. Goldstein, I argued that seventeenth century physics was visibly indebted to the Stoics.4 In this paper I attempt to locate a plausible point for the entry of Stoic ideas into scientific debates during the sixteenth century. As a candidate I suggest the work of Jean Pena,s a Royal Professor of Mathematics at Paris, who drew on Stoic sources and was regarded as introducing Stoic ideas by scientists at the turn of the seventeenth century. I will present an outline of Pena’s life and opinions, before discussing the evidence linking Pena to the Stoics, and conclude with an examinationn of his influence. I will begin, however, with a brief review of the relevant aspects of Stoic physics.

As the early modern period will be my point of attention I will confine myself to those aspects of Stoic physics available in contemporary texts, the most important of which are Cicero’s De Natura Deorum, the Naturales Quaestiones of Lucius Annaeus Seneca and the De Mixtione of Alexander of Aphrodisiasb. Although none of these authors qualifies as an original source of Stoic physical doctrine, the revival of Stoic physics based on their works was an important step in the overthrow of Aristotelian orthodoxy during the early modern period’.

Stoic physics recognises three categories of complex object. Objects made up of self-contained and non-interacting parts, like a beach composed of grains of sand, belong to the first category. Objects made up of ordered but non-interacting parts, such as a wall made out of bricks, belong to the second category. The third category consists of true unities made up of parts that interact to form an organic whole. The

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distinguishing characteristic of a true unity is that the state of any one of its parts depends upon the state of all of the others. Living creatures are the model for this sort of complex object. Although many inanimate objects fall into the first or second class the parts of such objects may be true unities. The universe as a whole forms a true unitys.

The parts of true unities are united by an all-pervasive substance, called in Greek ‘pneuma’and in Latin ‘aer’ or ‘spirirus’. Thepneuma is an intimate combination of the two elements fire and air, with their relative proportions determining the local properties of the universal medium. The pneuma is in a state of perpetual tension, which is variously interpreted as a gross motion of the substance towards the center and back to the periphery of a true unity, or as a potential motion of the parts of the substance in these directions. The tensional state of the pneuma they contain distinguishes men, animals and plants from inanimate objects9.

In the case of the universe as a whole, the tension of the pneuma is directed inward from the sphere of the fixed stars, which is the periphery of the universe, to the center of the earth, and radially outwards once more. The inward tension conveys the influence of the heavens to the region of the earth and forms the rational basis for astrology. The heavens themselves are completely filled with pneuma. The Stoics follow convention in calling the substance of the heavens ‘aether’. But they are quite explicit that this is not a new-substance differing in kind from terrestrial substances. The substance of the heavens is properly understood as beingpneuma or aer, differing from common air only in purity.

It should be clear from what has already been said that the Stoic elements fire and air are not those employed by Aristotle. Although the Stoics followed Greek orthodoxy in recognising four fundamental elements: earth, water, air and fire; the elements fire and air are privileged in the Stoic scheme, and there is no fifth element for the heavens. Their cosmological scheme is therefore inconsistent with Aristotle’s principle that the heavens and the earth are totally distinct in substance and in the laws governing bodies in the two realms. The Stoics not only reject Aristotle’s account of the substance of the heavens but offer a unified physical theory of both the heavens and the earth.

Life of Jean Pena

Jean Pena was probably born in 1528, and died in Paris on the23rd of August 1558. There is some uncertainty about the date of his birth, as Hooykaas quoting Pierre de la Ramtelo, gives his age at the time of his death as only 26, while Frisch” gives the date of his birth as 1518. Nicolas Nancel, a fellow student, in a work published in Paris in 1559, and Jacques-Auguste de Thou, in a work published in Latin in 1604 (and in French in 1734), concur that Pena died at the age of thirty.

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Nancel adds that he was “scarcely thirty” while de Thou is the only source I have located giving an exact date for his deathI2. As the only date on which all authorities agree is the year of his death, I suggest taking the contemporary accounts of Nancel and de Thou as canonical and deriving the date of Pena’s birth by subtracting the figure on which they agreel3.

Pena was born at Aix-en-Provence to a family “distinguished in the magistracy”l4. He came to Paris as a student and was introduced to Pierre de la RamCe by Nancel. De la Rambe became his employer and patron. Pena was employed first as a copyist (according to Nancel he had a particularly fine italic hand), and later as a translator. He lived with de la Ramte’s other students at the CollCge de Presles. Nancel describes him as15

. . . a lonely and solitary person, never imposing himself on anyone, always hiding himself away in the library, content with poor clothes and food, a small, thin, graceful man,and somewhat consumptive as the manner of hisdeath was to prove, but remarkably studious and diligent.

Nancel’s last remark on Pena’s studiousness echoes de la RamCe who also noted Pena’s enthusiasm to study “all the arts”and especially Latin and Greek philosophy and mathematicsl6. Nancel, in his biography of de la RamCe, continues:l7

. . . [Pena] used to go every day to hear all the Royal Professors in Paris. 1 never knew or heard of any student in the city at the time who was more learned, or more earnestly engaged in the study of every art, language or other subject.

For our purposes the most significant point in these descriptions of Pena’s education is the apparent exhaustiveness of his studies, especially of ancient authors. It is therefore highly likely that he was acquainted with Seneca’s Naturales Quaestiones and Alexander of Aphrodisias’ De Mixtione, together with the works of Cicero, which were a general interest of his mentor Pierre de la Ramie. During this period Pena, Nancel and Reisner prepared Latin translations of Greek authors, including Aristarchus, Theodosius, Proclus, Autolycus and Hero’*.

Pena spent a number of years in a collaborative study of mathematics under de la RamCe, finally surpassing his mentor in mathematical accomplishments. Before the arrival of Pena, de la RamCe himself had been studying mathematics under the Royal Professor at Paris, Oronce Fink. On Fink’s death Pena was appointed to replace himI9. Pena’s appointment to the vacant chair, in 1555, was obtained through the influence of de la RamCe, and his patron the Cardinal of Lorraine. The appointment followed a novel examination during which the Greek text of Euclid was opened at random, the candidate then being required to explicate the text and reply to questions in the presence of the Cardinal and the Royal Professors20.

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Almost immediately Pena published three books. First was his Latin translation Euclidis Optica et Catoptrica (Pena 1557b), containing a long Preface “On the use of Optics,” (Pena 1557a). Pena’s subsequent influence derives almost exclusively from this Preface, in which he sets out his own original ideas on astronomy and cosmology, supporting them by optical arguments*’. Also in 1557, Pena published a second Latin translation of a work by Euclid under the title Rudimenta Musices. Last, in 1558, and again at Paris, he published an edition of Theodosius’ Sphaerica22. In this third book Pena was completing a project left unfinished at his death by Regiomontanus, the most influential astronomer of the century preceding Pena. Regiomontanus was responsible for introducing techniques for measuring the parallax of celestial objects, providing the basis for some of the arguments in the Preface to Pena’s Euclidis Optica et Catoptrica.

Pena lived only another year, dying in August 1558. It is not clear whether his death was the result of a long decline or a sudden illness. According to Nancel he ‘ I . . . wore himself out by excessive study, a n d . . . was so exhausted by disease and consumption that he succumbed to an untimely fate.”23 According to de Thou, “. . . he was carried off by a violent fever,” and buried in Paris at the Cloitre des Carmes24.

Opinions of Jean Pena

Pena’s most important bequest to posterity was an argument that the matter of the heavens was not Aristotelian aether but air. 1 will suggest below that Pena’s air is the same substance believed by the Stoics to fill the heavens.

Pena reached his conclusion that air extended to the fixed stars by an argument based on the optical phenomenon of refraction. It is a familiar fact that a straight stick standing in water appears bent below the surface. Refraction is the phenomenon responsible for this effect. More generally refraction means that the apparent position of an object will not correspond to its true position, if the light from the object crosses the boundary between two media of different densities on its way to the observer. Pena applied this reasoning to light reaching an observer on the Earth from the fixed stars, which were assumed to be distributed over the surface ofa sphere at a verygreat distance from the Earth.

According to the conventional Aristotelian cosmology of his day light from the fixed stars would have to pass through (at least) three media of differing densities to reach an observer on the Earth. These would be: first, the aether composing the spheres of the heavens; second, the element fire composing the outermost terrestrial sphere; and, third, the sphere of air. As a consequence, the apparent distance between two fixed points, for example two fixed stars, should appear

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greater near the horizon than overhead. From theabsense ofany visible differences in these distances Pena concluded that no boundaries between media had intervened as the light travelled to the observer.25

But stellar phenomena are most certain, and no such thing has ever appeared in all the centuries, to all the eminent men who have continually observed the stars. From this accurate examination the art of optics concludes that all this intervening space between the Moon and the fixed stars (I do not speak about the upper heaven) is full of this airy spirit which in no way differs from air . . . Gemma . . . showed that the distances of stars situated at no matter what attitude, observed with an instrument, appear always the same. Thus the art of optics teaches us that what is between us and the sphere of the fixed stars is air.

The same argument that counted against the Aristotelian theory of the substance of the heavens also led to the conclusion that there was no sphere of fire above the sphere of air but below the Moon.26

Thus, since, if there is fire above the air one must always, and in all the parts of heaven, see the stars refracted, except at the zenith, but, as we have already shown, from Gemma’s observations, the stars admit no refraction; thus it is evident, following the conclusion from the oracles of optics, that there is no fiery region between the air and the sphere of the Moon.

This not only constituted a major revision in terrestrial physics but also undermined the Aristotelian theories of comets and the Milky Way, both of which required the existence of the sphere of fire.

In the mid-sixteenth century it was generally accepted, following Aristotle, that comets were slowly burning vapors, either made up of ‘exhalations’rising from the earth or created by the motion of heavenly bodies which decomposed the terrestrial element fire in the region below the Moon. In both versions of the theory comets were sublunary phenomena and the element fire was a key ingredient in the resulting comet. The argument that the substance of the heavens was air therefore undermined this theory.

Pena offers two additional arguments against the Aristotelian theory of comets. The first is a consequence of Pena’s own explanation of the antisolar direction of comets’ tails, which had recently been discovered by Appian.27

In effect, their tail, which is turned in a direction opposite to the Sun, is a brilliant pyramid formed by the meeting of solar rays deflected from the perpendicular by the obstacle of a transparent body denser than air. A comet is therefore a transparent body, clear like the purest glass, since optics teaches us that pyramids of refraction cannot be formed except by these bodies.

Pena adds that, from observations of terrestrial fires, it is clear that they do not affect light in this way or produce pyramidical refractions.

The second argument rests on the proposition, which Pena employs repeatedly, that as all heavenly bodies move with equal speed, those which appear to move most slowly are the farthest away.28

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But since the motion of comets is sometimes slower and sometimes faster than the motion of the Moon, one concludes that certain comets move in the great space above the Moon, on the grounds that among things which move with equal speed, those which appear to move more slowly are further away.

Superlunary comets could not, of course, be composed of the terrestrial element fire in an Aristotelian universe.

Pena also rejected the Aristotelian account of the Milky Way as a sublunary phenomenon. In doing so he drew on arguments from parallax, in addition to the arguments on the substance of the heavens already presented. More than a century earlier another Frenchman, Levi ben Gerson (1288-1344) had argued from the absence of parallax that the Milky Way was not a sublunary phen~menon*~, although the influence of his work remains a matter for further research. At the end of the fifteenth century Regiomontanus had established a widely adopted technique for measuring the parallax of heavenly bodies. Regiomontanus applied the technique to comets, yielding a value consistent with a sublunary position. In the intervening decades before Pena the technique was improved, to the extent that Pena was again able to cite the absence of parallax for the Milky Way as evidence against its sublunary position.30

What should we say of those [physicists] who make up the Milky Way from dry, fiery exhalations, ignited by the movement of many large stars situated within the Milky Way? . . . The art of optics, by virtue of parallaxes, condemns this opinion and judges it false. For if the Moon has a parallax, how much greater will be that of the Milky Way, if it is beneath the sphere of the Moon?

All the above opinions are consistent with, and indeed required by, the theory of Copernicus. But although Pena rejected large parts of Aristotelian physics and cosmology, he did not accept Copernicus' theory. He discussed Copernicus' ideas sympathetically, but in the end endorsed the view that the Earth was near the center of the cosmos. Pena rejected Copernicus' triple motion of the Earth for lack of observational evidence, but regarded the precession of the equinoxes and variations in the apparent size of the fixed stars since antiquity as evidence for motion of the Earth.31

In summary, Pena is remarkable for his rejection of four Aristotelian doctrines: celestial spheres, the sphere of fire, the nature of comets and of the Milky Way. On the positive side his work is notable for its sympathetic treatment of the Copernican theory and for Pena's own positive proposal that air extended all the way to the fixed stars. His arguments for all these positions were highly innovative. The optical principles used by Pena in several of his arguments are based on observations of terrestrial phenomena. Both in his account of the heavens, and in his application of terrestrial optical principles to support conclusions about the nature of the heavens, Pena clearly abandoned the Aristotelian dogma of the total separation between the

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heavens and the earth, in an age when it was still almost universally accepted. Why did Pena find it natural to employ physical principles that applied uniformly to both the heavens and the earth?

Pena’s Stoicism

Pena’s rejection of the fundamental principles of Aristotelian physics and cosmology becomes intelligible if he is identified as drawing upon the rival tradition of Stoicism. But what evidence is there for the Stoic derivation of Pena’s ideas?

First in order of importance is Pena’s employment of the Stoic theory that the substance of the heavens is air. Textual evidence of an unusual sort links the substance as described by Pena to the Stoics. In the passage in which Pena’s proposal is introduced he uses the Latin phrase animabilem spiriturn to describe the substance of the heavens. The adjective animabilis is a variant of the more common animalis. This latter is usually translated by ‘consisting of air’ or simply ‘aerial’, so an animabilem spiriturn is a spirit consisting of air. What is remarkable, however, is the rarity of the variant form anirnabilis employed by Pena. Classical Thesauri record only a single occurence of the form in Latin literature.32 It occurs in Cicero’s De Natura Deorurn, book 2, chapter 36, line 9 1, where it is employed by Cicero’s Stoic spokesman Lucilius Balbus who is also speaking about air in an exposition of Stoic cosmology.33 Nancel’s biography of de la Ramte places Pena in a circle of avid Ciceronians. It seems altogether likely that Pena acquired this technical vocabulary from Cicero.

The content of the first passage in which Pena introduces his proposal for the substance of the heavens provides additional support for the identification of Pena’s celestial substance with the Stoic pneuma. Following a review of the opinions of Empedocles, Anaxagoras and the Scholastics, Pena says94

Optics . . . declares this whole space through which the planets move, in their regular path, without ever straying, to be an aerial spirit which, throughout nature, moves towards the heavens; which we breathe, and which cannot be distinguished from air.

Pena’s celestial substance pervades the whole universe. Like the Stoic pneuma its characteristic motion is towards the heavens (animabilem spiriturn. . . sufrlsum). This same substance which moves upwards, without interruption, all the way to the sphere of the fixed stars, is also the basis of respiration (Rochas adds “it gives us life”), in addition to being identified with common air. All these are attributes of the pneuma.

Indirect evidence also tends to support the identification of Pena’s celestial substance with the universal medium of the Stoics. Brahe’s students Longomontanus and Kepler both adopted the view that the substance of the heavens was air, and linked the doctrine to both Pena and the Stoics.35 Further evidence is provided by the importance of

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Stoic authors to de la Ramie and his circle. Cicero’s name appears on every second page of Nancel’s biography of de la Ramie36. The Stoics form only a part of the ancient sources drawn on by the Ramist reform movement, but their importance lies in the systematic alternative they present to orthodox Aristotelianism. The extent to which de la Ramte and his circle assimilated the details of Stoic doctrine is suggested by Nancel’s employment of the distinctively Stoic division of knowledge into physics, logic and ethics, and there is some indication that de la Ramie organised his own research along similar lines37.

An objection should be considered at this point. From the time of Regiomontanus to the time of Newton, all pervading vital spirits were a prominent feature of another renaissance tradition: neoplatonism of the sort derived from the (supposed) works of Hermes Trismegistus. As to whether Pena derived his aerial spirits from neoplatonic sources, the strongest evidence is the final section of his Preface to E~c l id .3~ Here Pena argues that ghosts and spirits, the favorite creatures of the neoplatonists, are nothing but optical illusions. He argues for a non- supernatural explanation of all such phenomena in a manner quite out of sympathy with neoplatonic aspirations. As the substance of the heavens forms part of the basis of natural law which Pena uses to explain away one of the neoplatonists’ main concerns, I feel confident in identifying Pena’s ‘air’with the Stoic’spneumaand not with the ‘world- soul’ of the neoplatonists.

The history of the Copernican revolution has been the subject of extensive reappraisal as the importance of neoplatonism has been recognised.39 Although neoplatonism had not received the recognition it deserved until the work of Yates, the suggestion that neoplatonic preoccupations explain all or the greater part of the scientific changes making up the Copernican revolution goes much beyond the evidence.40 I should make it clear that I am not attempting to replace Hermes Trismegistus with the Stoics. Stoic influences are an additional factor which must be taken into account in any complete picture of the period, together with neoplatonic ideas and other more familiar influences. It would be wrong to emphasise any one of these themes to the exclusion of the others.

On present evidence it would be inappropriate to label Pena a neostoic in the manner of Justus Lipsius or those criticised by Jansen’s Augustinus. By the last decade of the sixteenth century Lipsius had publicly identified himself as an adherent of Stoicism and begun producing systematic works on Stoic themes, including Stoic physics41. Stoic ideas became so widespread in the next two decades that they were specifically attacked by Cornelius Jansen in his A u g u ~ t i n u s . ~ ~ The period from Lipsius on, when Stoicism again came to be regarded as an intellectual position of sufficient contemporary importance to merit systematic development or systematic attack, was preceded by a period in which writers drew on Stoic ideas piecemeal. Pena’s work falls into

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the latter category. The list of classical authors translated by Pena while he was a student shows that, he was in a position to draw on several classical traditions. However, Pena clearly employed Stoic ideas in his work; such ideas are common among his immediate circle, and his ideas are linked with the Stoic pneuma by successors like Longomontanus and Kepler. Taking these pieces of evidence together, I conclude that Pena’s employment of Stoic ideas was self-conscious, and may be used to approximate the date of entry of Stoic ideas into specifically scientific disputes.

Pena S Influence

The most important avenue of Pena’s influence can be traced through the work of Tycho Brahe to Johann Kepler. Brahe repeatedly attributes the theory that the heavens are filled by air to Pena43, although he does not seem to have read Pena’s work Perhaps Brahe first learned of Pena’s theories from Pierre de la RamCe, whom he met in Augsburg in 1570.45 Brahe did not accept Pena’s idea that air extended to the fixed stars but he followed Pena in abandoning solid celestial spheres46, although on different grounds. With his unusually large and accurate astronomical instruments Brahe was able to detect atmo- spheric refraction. The first modern measurement is generally credited to him47 although atmospheric refraction had been considered in antiquity by Ptolemy and Proclus. Late medieval discussions of the subject, include the work of Bernard Walter, a co-worker of Regio- montanus. Brahe’s observations of atmospheric refraction undermined the reasoning used by Pena in concluding that the substance of the heavens is air. But separate reasons convinced Brahe that the heavens could not be composed of solid spheres. In Brahe’s own cosmological scheme the orbit of Mars intersected the orbit of the Sun, which would be impossible if each planet were supported by a solid sphere. Tycho concluded that the heavens were filled by some fluid substance&.

Although Brahe did not accept Pena’s Stoic theory of the substance of the heavens a number of his contemporaries and students did. Other astronomers who shared Pena’s view include Henry Brucaeus and Christopher Rothmann49. Similarly, Longomontanus, in his Astro- nomia Danica published in Amsterdam in 1622, describes “a most subtle and tenuous extended substance” which penetrates all space, even to the depths of the earth and is the source of “that air which is fitting and salubrious for animals.” This substance, which is “com- paratively spiritual, and to be likened to Aristotle’s fifth essence” is identified with the air said by Pena to fill the ~niverse5~. But the most detailed appreciation of Pena’s ideas is given by Brache’s co-worker Johann Kepler.

Kepler endorsed the view that the substance of the heavens was air, understood as the Stoicpneuma, as early as 1596 and as late as 1621.

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These dates correspond to the first publication of Kepler’s Mysterium Cosmographicum, and the republication of the same work with extensive new notes by the author commenting on the original text in the light of twenty-five years’ progress in astronomy; years which saw Galileo’s telescopic discoveries and Kepler’s own work on what are now called his laws of planetary motion.

In the first edition of the Mysterium Cosmographicum Kepler describes the substance of the heavens as follows5’:

Or by what bars, what chains, what heavenly adamant, has this Earth, which with Copernicus we have completely established to be moving, been brought into its sphere? With that air, no doubt, which (fermented and mixed with vapors) all we mendrink in all around the surface of the Earth, which we penetrate with our hand, with our body, but d o not part or separate, though it conveys the heavenly influences right into our bodies. For this is the heaven in which we and all worldly bodies live, move and have our being.

The phrase “in which we . . . live, move and have our being,” is instantly recognisable in the Christian tradition. It appears in Acts 17 v. 28, where it is used by St. Paul in his attack on the Stoics and EpicureansS2. Kepler’s allusive use of the phrase links the substance of the heavens to the Stoics. The passage above also suggests that Kepler hardly shared St. Paul’s opinion of the schooP. Kepler’s familiarity with Stoic sources is shown by a number of quotations from Cicero elsewhere in the work, although he tells us in the notes added to the second edition that at the time he had not read Seneca’s Naturales Quaestioness4.

In a note added to the passage quoted above in the 1621 edition Kepler continuess5:

The meaning of these words, then, is as follows: just as bodies d o not impede the heavenly influences from penetrating into our inner parts, so also powers capable of producing motion d o not require intermediate bodies, by which to take hold of the bodies of planets which are to be moved as if by chains or bars. I chose to make rather too bold a play with the word “air.” What is a sphere or a heaven? What but air? And what is air? What but animmaterialemanation of the body, which imparts motion to the planets,as it turns in its gyration? But, laying aside the play o n words, let usconcede that our “air”is a material body, through which magnetic, moving, heat-producing, light-producing, and similar powers can pass, so that it is a vapor not totally different in kind from air, but rather distinguished by degrees of thickness from the expanses of air which surround it.

In this passage we find a second strong endorsement of the view that the substance of the heavens is air, understood as a special form of the everyday substance. The suggestion that the celestial substance differs from its everyday counterpart in ‘thickness’ or density also recalls Stoic tensional theories of thepneuma. What is offered here is a descendant of the Stoic pneuma, adapted to Kepler’s sixteenth century interests, as shown by the long list of ‘powers’ which can pass through the medium. It is also noteworthy that Cicero’s Stoic spokesman denies that the planets are moved by the celestial substance56, although Stoic physics generally employed thepneuma as the basis for its account of change.

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By suggesting that the air which makes up the heavens moves the planets Kepler provides an explanation in the spirit of the mechanical philosophy, which goes beyond Stoic antecedents.

Kepler’s familiarity with Pena is shown by the preface to his Dioptrics, published in 161 1. The first half ofthe preface is an extended examination of Pena’s Preface to Euclid’s Optics, in which Kepler considers ‘the use of optics in philosophy,’ or rather the place of Pena’s optical arguments in what would today be called natural science57. Although Kepler approves Pena’s conclusions that there are no solid spheres in the heavens and that the celestial substance is a form of air5* he is obliged to correct Pena on a number of matters. Foremost among these is the existence of atmospheric refraction, established by Brahe’s observations. Kepler also endorses Pena’s rejection of the sphere of fire, and the superlunar position for comets and the Milky Way that follows from it. But Kepler cannot accept Pena’s arguments, and offers stronger arguments of his 0~1159.

In the present paper I regret that I must leave open the question of when Kepler became acquainted with Pena’s ideas. I have so far been unable to determine whether he was familiar with Pena’s work before meeting Brahe in 1600. In a letter to Maestlin written in October 1597, Kepler claimed to have answered the challenge of Pena’s mentor de la RamCe to provide an astronomy based on natural causes rather than fictions60. It is clear from his later work that Kepler shortly became familiar with Pena’s opinion that the substance of the heavens was air, that he recognised the Stoic origin of the idea, and that he put the idea to good use in his own work. And in Kepler’s writings Pena’s ideas would have been available to Isaac Newton.

A separate line of influence may be conjectured, leading from Pena through the writings of Chassinus (1614) and Basso (1621) to Descartes. Chassinus, who studied at Paris, rejected celestial spheres and believed that the heavenly bodies were moved by an aerial fluid. Thorndike suggests him as the inspiration for Descartes’vortices. Basso is cited by Descartes. Among his ideas are a universal fluid plenum, which he compares to the Stoic pneuma, and which conveys astrological influences from the heavens to the earth. Descartes’ familiarity with these ideas did not, however, extend to endorsementb’.

Writing in 1616 Nicolaus Mulerius repeats, as Pena’s, the opinion that air fills the heaven@. Although Mulerius sides with the astronomers like Brahe whom he classifies as Peripatetics rather than with the Pythagoreans who follow Copernicus, he denies that there are solid spheres in the heavens and claims this to be a general opinion of the age. Modern research confirms Mulerius. By the 1620’s the supporters of solid heavens were a dwindling minority63. Descartes and Newton began their work with the question of solid heavenly spheres already settled.

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The overthrow of the Aristotelian-Ptolemaic view of the universe begins with the work of fifteenth and sixteenth century astronomers and ends with the work of Descartes and Newton. Pena’s ideas may have contributed little to the mathematical physics which emerged as the new orthodoxy after this extended period of change. But his revival of Stoic theories played an important role in undermining the Aristotelian division of the heavens from the earth, and more specifically in the abandonment of the Aristotelian theory of the constitution of the heavens.

The wider significance of Pena’s contribution is twofold. First, Pena’s work is additional evidence for the contribution Stoic physics made to the scientific revolution. This is a contribution which has yet to be widely recognised or adequately appraised. Second, there is a widespread contemporary view that planetary astronomy, and spe- cifically the debates over the mathematical details of planetary orbits, was the engine driving the scientific revolution. Pena’s work is evidence in favor of an alternative viewpoint which emphasises debates on the nature of matter. But this is another story, which must wait for another occasion64.

NOTES

I Bridoux (1966); Eymard d’Angers (1976). * Although this has recently been questioned by Miner (1970). See also the reply by

Dobbs (1982) 516-7; Westman (1980) 118; Schmitt (1978) 205; McGuire (1977) 132. Barker and Goldstein (1984). The present paper develops ideas suggested by Bernard

R. Goldstein, and 1 have benefitted from his advice and encouragement while writing the paper. He should not, of course, be held responsible for the formulations presented here.

Or Jean de la Pkne (Montucla), known in Latin as loannes Pena, or Paena (Brahe). Recent editions of these works are Rackham (1933), Corcoran (1971) and Todd

(1976). On the availability of these works see, respectively, Rackham (1933) xviii-xix; Hine( 1980) 2 17, whoshows that Seneca had beenavailable from the early twelfth century; and Siraisi (1984), whodocuments citations to Alexander of Aphrodisias throughout our period .

Williams (1974).

Barker and Goldstein (1984). 8‘Universe’here means everything from the sphere of the fixed stars inwards. A further

distinction between Aristotle and the Stoics is their doctrine that a n infinite void exists outside the sphere of the fixed stars.

l o Hooykaas (1958) 46 text to n.3. 1 1 Kepler (1859) 573n.21.

l 3 The Nufionul Union Curulogue, v.448, p.216, in its single entry for Pena offers “1588?” a s the date of his death, repeating a n error from the biographical data accompanying the Readex Microprint edition of Pena’s Theodosii Sphuericorurn. See Hunt (1707).

On Stoic ‘cosmobiology’see especially Hahm (1977).

de Thou (1734). 3:299; for Nancel see Sharratt (1975) 199.

de Thou (1734) 298. 15 Sharratt (1975) 199. I 6 Hooykaas (1958) 4611.2. The Latin of Hooykaas’note is obscure in a number of

l 7 Sharratt (1975) 199. respects.

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18 Sharratt (1975) 205. IP Hooykaas (1958) 45-6. 2o Sharratt (1975) 199. 2 1 The whole of the Paris 1557 edition is available in the Readex Microprint series

Landmarks of Science, Euclides (1973). It is regrettable that Pena's name appears nowhere in the bibliographical data, and his Preface is indicated merely as'Front Matter'. The Preface is also available in the French translation of Rochas (1912) 217-38.

z2 Here I follow the Catalogue G5nCral of the Bibliothkque Nationale (1935) t.132, rather than Thorndike (1929) v.5, p.356 and n.109, who gives Padua, 1557, for Pena's edition of Theodosius. This work is now readily available in the edition of Hunt (1707).

z3 Sharratt (1975) 199. 24 de Thou (1734) 3:299. 25 Pena (1557a) iii lines 11-17, 24-28; Rochas (1912) 220, Cf. Brahe (1913) 2:77-79. 26 Pena (1557a) viii lines 31-36; Rochas (1912) 227. 27 Pena (1557a) ix lines 18-24; Rochas (1912) 228. z8 Pena (1557a) x lines 6-10 Rochas (1912) 229. 2q Goldstein (1976) 223. 3O Pena (1557a) x lines 11-18; Rochas (1912) 230; c.f. Kepler (1937) 4:33940. 3 1 Rochas (1912) 2234. l2 Thesaurus Linguae h t inae v.2, pt.1, p.73, col.'a', 1 .SO. c.f. Lewis and Short(1907),

and Stickney (1901) p.265 n.107.5 who translates the note of Schoemann. Cicero De Narura Deorum 2.36.91: "Principio enim terra sita in media parte mundi

circumfusa undique est hac animabile et spirabileque natura cui nomen est aer." The variant form animabilis occursin only some of the editions of the work, and was expunged in favor of onimalis by the early twentieth century.

l4 Pena (1557a) ii lines 32-36; Rochas (1912) 219. For Longomontanus, see Donahue (1975) 270. For Kepler, see below and his (1937)

4:335; his(1621) pp.60-61 note 4, p. 167, p.171 note 7, and p.219 note 5. Seealso Barker and Goldstein (1984), notes 3840 and accompanying text.

l6 Sharratt (1975). 37 Sharratt (1975) 21 I , 223-5. 38 Rochas (1912) 234-8. Jp Yates (1964). 40 This is made clear in the studies of Westman and McGuire (1977). 4 1 Barker and Goldstein (1984) 154-5. 42 Bridoux (1966) 204-5; 220. 43 Brahe (1913) 2:77, 3:154,6:135,187,320, 7: 121,147,172,212,230,251. 8:460. 44 Brahe (1913) 3:155, 7:121,212,251. 45 Dreyer (1963) 33. 46 Donahue (1975) 254-5. 47 Montucla (1799) 664-5. 48 Donahue (1975) 255. 49 Thorndike (1929) 634.

Donahue (1975) 270. 5 ' Kepler (1621) 167: tr. Duncan. 5z This is, as a matter of fact, the only place where the word 'Stoic'appears in the New

53 The present author is indebted to Alain Segonds for drawing his attention to the

54 Kepler (1621) 61, note 4 tr. Duncan. 55 Kepler (1621) 171, note 7: tr. Duncan. 56 De Natura Deorum, 11, xxi:54-S. 5' Kepler (1937) 4: 33443. s8 Kepler (1937) 4:335. Jq Kepler (1937) 4:337-8. * Kepler (1621), Introduction, p.29; Kepler (1937) 13:141, Cf. 165.

Testament.

allusion.

105

61 Thorndike (1929) 6: 382-84. Barker and Goldstein (1984) 156-7. 6* Thorndike (1929) 7:Sl-2.

Donahue (1975) 273-75. 64 1 would like to thank Roger Ariew, Cecil Aviotti, Ronald Epp, Rachel Laudan and

Eleonore Stump for criticism and assistance.

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