The emergence of modern astronomy – a complex mosaic: Part VII

In his Commentariolus from around 1510 Copernicus tells us that his is planning to write a larger more technical work on his heliocentric hypothesis:

However I have thought it well, for the sake of brevity, to omit from this sketch mathematical demonstration, reserving these for my larger work

We don’t actually know when he started writing this work or when he finished it. As a canon of the cathedral of Frombork he was administrator in the prince-bishopric of Varmia, a position that he took seriously throughout his life, meaning that astronomy remained a part time occupation. It would be reasonable to assume that he started on the larger work, which would eventually become De revolutionibus, not long after completing the Commentariolus. Various experts have estimated that he finished the bulk of the book around 1530. However, he was very reluctant to publish, what would become his magnum opus. There is a standard myth that he feared religious censure and thus didn’t want to publish. There is, however, a well-founded theory that he was reluctant to publish because he couldn’t actually deliver what he had promised. In the Commentariolus he assured his readers that his heliocentric system would be simpler that the Ptolemaic geocentric one. In the end the system that he presented in De revolutionibus was more complex than the geocentric one in Peuerbach’s Theoricarum novarum planetarum, published by Regiomontanus in Nürnberg in 1473 from which Copernicus had learnt his astronomy. Also, although Copernicus’ system offered some advantages and simplifications over the geocentric system Copernicus could offer no real proof for his radical suggestion and the empirical physical evidence against a moving earth was still overwhelming. All of this raises the questions would Copernicus have ever submitted his manuscript for publication left to his own devices and what finally pushed him over the edge, so that he did publish? The answer is not what but who. Copernicus was convinced to publish by the young Wittenberger professor of mathematics, Georg Joachim Rheticus (1514–1574). (Note: there are no known portraits of Rheticus)

Rheticus was born Georg Joachim Iserin the son of Georg Iserin, a town physician, and Thomasina de Porris, a minor Italian aristocrat, in Feldkirch in what is now Austria. In 1528 Georg Iserin was found guilty of stealing from his patients, executed and the family name banned in perpetuity. Georg Joachim Rheticus became Georg Joachim de Porris. The family tragedy was alleviated somewhat for the young Georg Joachim, when Achilles Pirmin Gasser (1505–1577), another town physician, historian and astrologer, took over his upbringing and education.

Achilles_Pirminius_Gasser

Achilles Permin Gasser Source: Wikimedia Commons

In 1528 Gasser sent him to the Fraumünster collegiate church in Zurich, where he got to know and became friends with Conrad Gesner (1516–1565), who would go on to become an important sixteenth century polymath.

gesner001

Conrad Gesner Source: Wikimedia Commons

In 1532 Gasser sent him to his own alma mater, the Lutheran University of Wittenberg. Here Rheticus, with an obvious aptitude for the mathematical sciences, attracted the attention of Philipp Melanchthon (1497–1560), the rector of the university and founder of the Lutheran Protestant education system.

PhilippMelanchthon

Philipp Melanchthon portrait by Lucas Cranach the elder Source: Wikimedia Commons

Melanchthon, who had studied under Johannes Stöffler (1452–1531) and become an enthusiastic fan of astrology, was on the look out for talented mathematicians with whom to equip the new Protestant schools and university to further the growth of a new generation of astronomer/astrologers. It was in Wittenberg that Georg Joachim adopted the toponym Rheticus based in the Roman name for his home district Rhaetia In 1536 Rheticus graduated MA and Melanchthon appointed him professor for the lower mathematics, that is arithmetic and geometry, in Wittenberg.

In 1538 Rheticus took leave of absence from the university to go on an extended study tour of Southern Germany. Such tours were common practice on the mediaeval university and he went with the support of and a letter of introduction from Melanchthon. This letter was addressed to Johannes Schöner in Nürnberg, Philipp Apian in Ingolstadt and Philipp Imser in Tübingen.

The first station on his journey was Nürnberg where he studied astrology with Johannes Schöner (1477–1547) the professor of mathematics at the local gymnasium and a good friend of Melanchthon.

johannes_schoner_astronomer_01

Johannes Schöner Source: Wikimedia Commons

Here he got to know Nürnberg’s comparatively large mathematical community. He became friends with Georg Hartmann (1489–1564) a leading Renaissance instrument maker

ghartmann

Georg Hartmann Source: Astronomie in Nürnberg

and with mathematician later theologian Thomas Venatorius (1488­–1551). Rheticus also became acquainted with Johannes Petreius (1497–1550) the leading European printer/publisher of mathematical/astronomical/astrological texts.

johannes_petreius

Johannes Petreius Source: Wikimedia Commons

It was almost certainly in Nürnberg that Rheticus became aware of Copernicus, an astronomer in the distant north, who had an interesting new astronomical hypothesis.

I think Rheticus left Nürnberg with a commission from Petreius to go and visit Copernicus and ascertain if he had a book about his heliocentric hypothesis and if so to persuade him to allow Petreius to publish it. There is no known letter of commission and it is probable that none ever existed but there is strong circumstantial evidence to support this theory. When Rheticus left Nürnberg he carried with him six especially bound printed volumes, including three of Petreius’ best mathematical volumes, as a present for Copernicus.  Of course Rheticus’ Narratio Prima, the first ever printed account of Copernicus’ hypothesis, was in the form of an open letter addressed to Schöner in Nürnberg, who had close connections with Petreius. Rheticus received an answer to his Narratio Prima in the form of a letter from Andreas Osiander  (1498–1552), Nürnberg’s Lutheran preacher, who worked as an editor for Petreius and who would go on to edit De revolutionibus.

andreas-osiander

Andreas Osiander portrait by Georg Pencz Source: Wikimedia Commons

But if Rheticus was fulfilling a commission for Petreius, what did he get out of the deal. Consideration of the legal dispute over his mother’s will indicate that Rheticus was independently wealthy, so some sort of financial payment was probably not involved. However, in 1538 Rheticus was a young, unknown academic at the very beginning of his career and Petreius, as a leading European printer/publisher, was in a position to offer him career-advancing inducements. In 1542 Petreius published an edition of two speeches that Rheticus had held in Wittenberg, Orationes duae prima de astronomia & geographia altera de physica, habitae Vuittebergae / à Ioachimo Rhetico. Neither of these speeches is particularly significant and well below the level of academic text that Petreius usually published, certainly a step up for a novice academic. On 1 August 1540 Petreius went a step further dedicating to Rheticus his edition of the fourteenth-century physician Antonius de Motulmo’s De iudiciis nativitatum, one of the manuscripts brought to Nürnberg by Regiomontanus and edited by Schöner. In the sixteenth century book dedications were important and valuable instruments of credit, most often used to win the favour of important and wealthy patrons, to dedicate such a book to a mere mathematicus, and a novice at that, was a great honour indeed. The dedication is in the form of a fairly long letter, which praises Rheticus highly and urges him to bring Copernicus’ book to Petreius in Nürnberg for publication. Lastly in 1541 Petreius began to publish the annual prognostica of Achilles Gasser, Rheticus’ mentor. Rich rewards for Rheticus’ services.

There, of course, remains the question, would Petreius issue such a commission? The answer is a resounding yes. Having come across Girolamo Cardano’s Practica arithmetice et mensurandi singularis at the Frankfurt Book Fair he instructed Osiander to write to Cardano offering to become his Northern European publisher. Cardano quickly accepted the offer and the Cardano-Petreius partnership proved very profitable for both of them with Petreius publishing Cardano’s best selling volumes on mathematics, astrology, medicine and philosophy. Petreius also commissioned Walter Hermann Ryff (c. 1500–after 1551), a man perhaps best described as a sixteenth-century scientific hack, to produce the first German translation of Vitruvius’ De architectura, Vitruvius Teutsch: Nemlichen des aller namhafftigisten vn[d] hocherfarnesten, Römischen Architecti, und Kunstreichen Werck oder Bawmeisters, Marci Vitruuij Pollionis, Zehen Bücher von der Architectur vnd künstlichem BawendEin Schlüssel vnd einleytung aller Mathematische[n]. Lastly Petreius negotiated with Erasmus Reinhold (1511–1553), Rheticus’ fellow professor of mathematics in Wittenberg, to publish an edition of his extensive horoscope collection. Petreius had earlier published Cardano’s collection with great success. However this project together with Petreius’ planned publication of Reinhold’s Tabulae prutenticae collapsed with Petreius’ death in 1551.

It is often argued that Copernicus could not have know about the Archimedean manuscript The Sand Reckoner with its references to Aristarchus’ heliocentric hypothesis, as this was first published in Basel in 1544. However, Rheticus could have brought that knowledge with him from Nürnberg, as Venatorius was the editor of that Latin/Greek edition of the works of Archimedes published in Basel, based on a Greek manuscript brought to Nürnberg from Rome by Willibald Pirckheimer (1470-1530) and the Latin translation of Jacobus Cremonensis from the manuscript collection of Regiomontanus.

Leaving Nürnberg in 1539, Rheticus did not immediately head north to Frombork. There is no corroborative evidence that he visited Philipp Apian (1531–1589) the professor for mathematics in Ingolstadt but he did go to Tübingen. Melanchthon’s letter of introduction was addressed to Philipp Imser (1550–1570), Stöffler’s successor as professor of mathematics in Tübingen, however just at this time Imser was, following religious differences, suspended from his chair and Rheticus, instead, met up with Joachim Camerarius (1500-1574), humanist scholar, close friend of Melanchthon and his later biographer. Camerarius was another member of the Nürnberger group, who had been rector of the local gymnasium, appointed by Melanchthon, and had worked extensively as an editor for Petreius. Since 1535 he had been rector of the University of Tübingen and would later have a major influence on Rheticus’ career. From Tübingen Rheticus travelled home to Feldkirch, where he visited Achilles Gasser and whence he set out on his journey to Varmia and his fateful meeting with Copernicus.

14 Comments

Filed under History of Astrology, History of Astronomy, Renaissance Science

14 responses to “The emergence of modern astronomy – a complex mosaic: Part VII

  1. Ray

    Thony.

    I generally like your blog and have learned a lot from it, but you seem to have quite the tendency to let your contrarian streak get the better of you, as in the following passage, which contains a large number of statements that seem extremely tendentious to me:

    There is a standard myth that he feared religious censure and thus didn’t want to publish.

    I can only assume by this first sentence, you mean to say that it is a myth that Copernicus feared a formal charge of heresy as was later brought against Galileo? While I know of no good reason to suspect Copernicus feared a heresy charge, Copernicus did say himself that he was reluctant to publish for fear of ridicule, including ridicule based on scriptural arguments. The language Copernicus uses to describe this (at least in English translation) seems close enough to “religious censure” that you really should clarify if you mean that term in a more restricted sense.

    There is, however, a well-founded theory that he was reluctant to publish because he couldn’t actually deliver what he had promised. In the Commentariolus he assured his readers that his heliocentric system would be simpler that the Ptolemaic geocentric one. In the end the system that he presented in De revolutionibus was more complex than the geocentric one in Peuerbach’s Theoricarum novarum planetarum, published by Regiomontanus in Nürnberg in 1473 from which Copernicus had learnt his astronomy.

    Who promotes this theory? I can find a number of sources claiming that Copernicus’s model was more complex than Ptolemaic models (which generally means simply that it used more spheres) but none that claim that this increased complexity was a reason for delaying publication of De Revolutionibus. It seems unlikely to me that Copernicus would have had as an explicit goal, that his system must use fewer spheres than a Ptolemaic model, since he considered any number of spheres using an equant to be an unacceptable violation of the principle of uniform circular motion.

    In fact, as far as I can tell, the decision to use a sun centered arrangement, considered on its own, would have reduced both the conceptual complexity of the Ptolemaic system and the total number of spheres. That is to say, Copernicus’s system was only more complex than that of Ptolemy’s because he also insisted on replacing equants with multiple epicycles wherever they appeared. (I think Maestlin and Kepler explicitly considered heliocentric systems using equants.) To be fair, you seem to acknowledge that Copernicus’s system did provide some advantages and simplifications, but then you go on to say:

    Also, although Copernicus’ system offered some advantages and simplifications over the geocentric system Copernicus could offer no real proof for his radical suggestion and the empirical physical evidence against a moving earth was still overwhelming.

    What empirical physical evidence? All the claimed physical disproofs of Copernicus’s theory relied on Aristotelian mechanics, which as far as I can tell never was a viable source of useful empirical predictions, and which, insofar as it suggested a contradiction between observation and the motion of the Earth, was explicitly denied by Copernicus’s theory.

    • Kepler did work with equants for quite some time, and got pretty far with them. Without Tycho’s observations, Kepler’s equant-based models would have seemed entirely adequate and way simpler than anything previously proposed.

      Copernicus’s system used more spheres for a number of reasons; his refusal to use equants is probably the most important. But he also missed a simplification that Kepler achieved: making the planes of the planetary orbits all intersect in the true sun, rather than the mean sun. This screws up the the latitudes of the planets.

      In addition, Copernicus insisted on trying to fit some bad data from his predecessors. It has been suggested that this was a wise strategy for a new theory—discarding data that didn’t fit would have looked suspicious.

      What empirical physical evidence? All the claimed physical disproofs of Copernicus’s theory relied on Aristotelian mechanics, which as far as I can tell never was a viable source of useful empirical predictions…

      This remark is a classical example of presentism. While Aristotelian mechanics wasn’t unquestioned, there was certainly no fully formed alternative at the time, especially one that could serve as a foundation for a heliocentric model.

      It’s instructive to look at Kepler’s physics. Note that Kepler emphasized the role of physics in his Astronomia Nova. His physics though is at heart Aristotelian, with a steady “sweeping force” (called by a different name) required to keep each planet moving.

      • Ray

        This remark is a classical example of presentism. While Aristotelian mechanics wasn’t unquestioned, there was certainly no fully formed alternative at the time, especially one that could serve as a foundation for a heliocentric model.

        I disagree with the charge of presentism, but perhaps I worded my objection in a way that leaves me open to the charge. Let me rephrase: Copernicus’s model was explicitly constructed so that no physical experiment on Earth would distinguish it from an Aristotelian fixed Earth model. That is, he posited that all terrestrial objects shared in the motions of the earth. There was therefore no physical empirical evidence against a moving Earth, as it was posited by Copernicus. Rather there were theoretical arguments against it.

        I would also note that the theoretical model on which the arguments are based was itself lacking evidence at the time. As far as I can tell, Aristotelian mechanics was never put to practical use without substantial ad hoc additions (e.g. Ptolemy’s equant and Tartaglia’s circular arc joining the violent and natural parts of his trajectories for cannonballs.) Copernicus’s physics was itself broadly Aristotelian with some additions. So the question is whether there was empirical evidence favoring the versions of Aristotelian mechanics used by Copernicus’s critics over the version posited by Copernicus. I submit that there was not. In fact, Copernicus supports his particular modification to Aristotelian physics by the empirical example of a moving ship.

      • OK, maybe not classic presentism, as you explain it.

        Let me step back for a wider view. This whole topic is known in the history and philosophy of science as “theory choice”. Given a conflict between Theory A and Theory B, how should we choose?

        A classic presentist approach: using the latest modern knowledge, adjudicate which theory is more correct. This is now (and has been for decades) in bad odor among historians, Sometimes to an absurd degree. There’s been some pushback in recent years, and I think it’s often illuminating to turn a modern X-ray upon old theories. But you have to hedge your conclusions. Okay to say, “the equant is a first-order approximation to Kepler’s second law”. Not OK to say, “Boy was Aristotle stupid not to realize that his mechanics was crap.”

        The official “right way” to think about theory choice: try to inhabit the brains of the contemporaries who were fighting the battle of Theory A vs. Theory B. (By “official”, I mean that’s become the dominant view among historians ever since Butterfield coined the term “whiggism”.) Obviously I don’t think this is the only right way, but it has proved immensely valuable as a methodology in the history of science (and history more generally).

        I don’t really understand the point of your approach. You seem to be saying, Copernicus’s defenses were internally consistent. If his contemporaries had only accepted his premises, they would have realized that their objections were without merit. Maybe so. I don’t see how this helps us understand the intellectual history. When Thony says, “the empirical physical evidence against a moving earth was still overwhelming”, he is rightly emphasizing that Copernicus’s physics was deeply unconvincing to most readers of De revolutionibus. I think it’s fair to say that at the time, this was the major objection to heliocentricity.

        I do think you raise an important point with regard to simplicity. Thony wrote, “There is, however, a well-founded theory that he was reluctant to publish because he couldn’t actually deliver [a simpler system]”. Sounds to me that Thony has in mind one or more papers or books. Perhaps he’ll elaborate, or at least provide citations.

      • Ray

        I don’t really understand the point of your approach. You seem to be saying, Copernicus’s defenses were internally consistent. If his contemporaries had only accepted his premises, they would have realized that their objections were without merit. Maybe so. I don’t see how this helps us understand the intellectual history. When Thony says, “the empirical physical evidence against a moving earth was still overwhelming”, he is rightly emphasizing that Copernicus’s physics was deeply unconvincing to most readers of De revolutionibus.

        My problem with this line of reasoning is that to me “empirical” has a very specific meaning. That most (but by no means all) of Copernicus’s contemporaries found his physics unconvincing is neither necessary nor sufficient to establish the claim that they had “overwhelming empirical physical evidence” against it.

        For me, a classic example of a false belief at one time supported by empirical evidence is the claim that all swans are white. In the case of the moving Earth, however, I see in the history of the idea’s acceptance neither observations corresponding to the white swans nor to the black ones. I have already noted the lack of practical use for Aristotelian mechanics without ad hoc additions. As far as the black swans go, the first thing I would call physical empirical evidence of a moving Earth were Richer’s pendulum experiments of 1673, but this was well after the majority of astronomers had already come to accept a moving Earth. Unless Thony wants to claim that NOT seeing sunspots, or the moons of Jupiter, or astronomical data precise enough to distinguish between Keplerian orbits and equants constitutes overwhelming empirical physical evidence against the motion of the Earth, I just don’t think there’s any change in the available empirical evidence sufficient to explain the change in astronomical opinion.

        In sum, I could imagine Thony’s terminology perhaps describing the rise and fall of Horror Vacui (with Torricelli’s experiments playing the role of the black swan) but the timing’s all wrong for claiming that the impediment that delayed the acceptance of Copernican heliocentrism by 100 years was “overwhelming empirical physical evidence” against the motion of the Earth.

  2. In the end the system that he presented in De revolutionibus was more complex than the geocentric one in Peuerbach’s Theoricarum novarum planetarum, published by Regiomontanus in Nürnberg in 1473 from which Copernicus had learnt his astronomy.

    Are you using cycle-counting as the measure of complexity? I assume the context here is the historiography of this metric, from the myths of 80 cycle Ptolemaic systems, to the 19th & 20th century face-offs of that 80 against Copernicus’s supposed 34, culminating in Koestler’s famous debunking:

    It is amusing to note that even the most conscientious modern scholars, when writing about Copernicus, unwittingly betray that they have not read him. The give-away is the number of epicycles in the Copernican system. … In fact, Copernicus uses altogether forty-eight epicycles—–if I counted them correctly … Moreover, Copernicus had exaggerated the number of epicycles in the Ptolemaic system. Brought up to date by Peurbach in the fifteenth century, the number of circles required in the Ptolemaic system was not 80, as Copernicus said, but 40.

    Did any contemporaries of Copernicus, or of Tycho, or of Kepler or Galileo, explicitly use the total raw cycle count an argument for or against the heliocentric system? I use that phrasing to set aside a major argument that was used, namely that the earth’s orbit corresponds to a bunch of cycles in geocentric systems. That argument isn’t primarily about how many circles you have to use, but regularities (like periods) that the heliocentric system explains and the geocentric system doesn’t.

    (Parenthetically I note that Koestler perpetuated—or maybe originated, I don’t know—a new myth, that Peurbach simplified the Ptolemaic system. In fact, Peurbach increased the cycle count from the Almagest, and also from the system used, for example, to create the Alfonsine tables. This increase had absolutely nothing to do with predicting planetary positions; it was purely a matter of the mechanism for moving the planets (the physics, so the speak), and was, as we now know, taken from Ptolemy’s Planetary Hypotheses.)

    (You’ve pointed out that Peurbach was way easier to read than Ptolemy. Quite true, but that’s not the same as the complexity of the models.)

    • Ray

      Moreover, Copernicus had exaggerated the number of epicycles in the Ptolemaic system. Brought up to date by Peurbach in the fifteenth century, the number of circles required in the Ptolemaic system was not 80, as Copernicus said, but 40.

      Is it possible that Copernicus’s exaggerated circle count was referring to the number of circles that would be required after a standard construction was applied to replace the equant with epicycles?

      • Koestler’s circle count for Copernicus is based on a careful reading of De revolutionibus; he summarizes the tally in a table. Take a look at Koestler’s The Sleepwalkers, the table in note 9 to Chapter 2 of part 3. See also note 12 for the reasons Copernicus had to increase the number of cycles.

      • Ray

        I was actually asking about the claim that Copernicus exaggerated the number of epicycles in the Ptolemaic system. Might Copernicus have had in mind a version of Ptolemy’s system which was modified to remove the equant?

      • I don’t think Copernicus ever made the 80 cycle claim about the Ptolemaic system. (Koestler does say that, but I suspect he got that wrong. Wikipedia say, “The popular total of about 80 circles for the Ptolemaic system seems to have appeared in 1898. It may have been inspired by the non-Ptolemaic system of Girolamo Fracastoro, who used either 77 or 79 orbs in his system inspired by Eudoxus of Cnidus”, and they cite a book by Palter.)

        If anyone has more info, please chime in!

  3. Laurence Cox

    he finished the baulk of the book, I assume you meant bulk.

    Some years ago I attended a conference that included a talk by Owen Gingerich on Copernicus. At the end, in response to a question, he put a sheet on the overhead projector with a circle and the elliptical orbit of Mars marked on it. At that size they were virtually indistinguishable when aligned. It does illustrate that although mathematical concepts like the equant are normally represented as quite large in schematics of Ptolemaic astronomy, they would be difficult to see if drawn to scale for the planets.

    • Indeed, I did spreadsheet comparing the equant and area law for Mars, and the biggest difference amounts to less than 2 degrees per year. (It’s part of a document I wrote, “From Kepler to Ptolemy”; one of these days I’ll have to finish it and post it.)

      Kepler first produced models of the Martian and earthly orbits using equants and eccentric circles, and obtained agreement that would have been fine using pre-Tychonic levels of accuracy. As Curtis Wilson points out, the elliptical orbit was not Kepler’s most important innovation judged purely on the basis of predictive accuracy. The so-called “bisection of the eccentric” looms much larger. Heilbronn has a thorough discussion in The Sun in the Church, and there have been numerous technical papers on the topic.

  4. Ah, OK. I agree that “empirical” was a poor choice of words, and I’ll leave it up to Thony to defend it if he wants to.

    I also agree that the transition we’re discussing was driven at least equally by theory as by observation.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s