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

In 1542 the manuscript of De revolutionibusarrived at Petreius’ printing office in Nürnberg followed by Rheticus who intended to see it through the press. I argued in Part VII that Johannes Petreius had in fact commissioned Rheticus to see if Copernicus had written anything substantial on his astronomical theories and if so to persuade him to allow Petreius to publish it. Petreius’ printing office was certainly the right address for the publication of a major new work on astronomy, as he was certainly the leading scientific publisher–astrology, astronomy, mathematics–in the Holy Roman Empire of German States and probably the whole of Europe but who was Johannes Petreius?


The Petreius printing office in Nürnberg Photo by the author

He was born Hans Peter, whereby Peter is the family name, into a family of wealthy farmers in the Lower Franconia village of Langendorf near Hammelburg in 1496 or 1497. He matriculated at the university of Basel in 1512, graduating BA in 1515 and MA in 1517. He next appears as a witness in a court case in Basel in 1519, where he is described, as working as a proofreader for the Basler printer publisher Adam Petri. This explains why he had chosen to study in Basel, as Adam Petri was his uncle. Petri is the Swizz German version of the name Peter. Presumably, having learnt the black art, as printing was known, from his uncle he moved to Nürnberg in 1523 and set up his own printing office. The was almost certainly an attempt by the Peter family to cash in on the gradual collapse of the Koberger printing office following the death of Aton Koberger in 1513. The Petri-Froben-Amerbach printing cooperative had been Koberger’s licensees in Basel, printing his titles on commission.


Source: Wikimedia Commons

Hans Peter now sporting the Latinised name, Johannes Petreius, succeeded in establishing himself against the local competition and by 1535 was the leading printer publisher in Nürnberg. Like most other printer publishers Petreius’ main stock in trade was printing religious volumes but in the 1530s he began to specialise in printing scientific texts. Exactly why he chose to follow this business path is not known but it was probably the ready availability of the large number of mathematical, astrological and astronomical manuscripts brought to Nürnberg by Regiomontanus when he set up his own printing office in 1471. This hypothesis is supported by the fact that several of Petreius’ earliest scientific publications were all of manuscripts from this collection, all of which were edited for publication by Johannes Schöner, who would later be the addressee of Rheticus’ Narratio  Prima.

This series of publications started with Schöner’s edition of Regiomontanus’ own De Triangulis in 1533, a very important work in the history of trigonometry. This was also one of the volumes that Rheticus took with him to Frombork, as a present for Copernicus.

Schöner followed this with Regiomontanus’ Tabulae astronomicaein 1536. Petreius’ activities in the area were not however restricted to Schöner’s output. Earlier he published the first Greek edition of Ptolemaeus’ Tetrabiblos, under the title Astrologica, edited by Joachim Camerarius (1500–1574), which included Camerarius’ translation into Latin of Books I & II and partial translations of Books III & IV together with his notes on Books I & II and the Greek text of the Centiloquium, a collection of one hundred astrological aphorism falsely attributed to Ptolemaeus, with a Latin translation by Giovanni Pontano (1426–1503).


Opening chapter of the first printed edition of Ptolemy’s Tetrabiblos, transcribed into Greek and Latin by Joachim Camerarius (Nuremberg, 1535). Source: Wikimedia Commons

A year earlier Petreius had published Johann Carion’s Practica new – auffs 1532 mit einer auslegung des gesehen cometen. Through these publications it is clear that the principle interest is in astrology and it is here that money was to be made. Over the next twenty plus years Petreius published more texts from Regiomontanus edited by Schöner, some of Schöner’s own works on astronomy and cartography, reckoning and algebra books from Christoph Rudolff  (c. 1500–before 1543) and Michael Stifel (1487–1567). Various scientific texts edited by Peter Apian including his and Georg Tannstetter’s edition of Witelo’s Perspectiva (1535), another of the volumes that Rheticus took with him to Frombork for Copernicus. Various Arabic astrological texts, the Tractatus astrologicae (1540) of Lucas Gauricus (1575–1558), who along with Schöner and Cardano was one of the most important astrologers of the first half of the sixteenth century. Petreius became the publisher of Gerolamo Cardano (1501–1576) north of the Alps, publishing his works on mathematics, astronomy, medicine, astrology and philosophy, all of which were highly successful.


Source: Wikimedia Commons

He also published alchemical works from Abū Muḥammad Jābir ibn Aflaḥ better known in the West as Geber. As well as all this, Petreius commissioned and published the first German translation of Vitruvius’ De architectura, a bible for Renaissance artist-engineers.

Petreius’ scientific catalogue was very wide but also had depth, including as it did various classics by Regiomontanus, Schöner, Stifel, Cardano and Witelo. If anybody could adequately present Copernicus’ masterpiece to the world then it was Johannes Petreius.

Rheticus had originally intended seeing Copernicus’ manuscript through the press but Philipp Melanchthon had other plans for his errant protégée. In the meantime Rheticus had, at the request of Joachim Camerarius, who was now rector of the University of Leipzig and had obviously been impressed by Rheticus during their meeting in Tübingen, been offered a chair in mathematics at Leipzig.


Joachim Camerarius, 18th-century engraving by Johann Jacob Haid. Source: Wikimedia Commons

In the autumn of 1542 Rheticus, under pressure from Melanchthon, left Nürnberg and preceded to Leipzig, where he was appointed professor of higher mathematics i.e. astronomy and music and his direct involvement in De revolutionibus came to an end. Petreius still needed an editor to see Copernicus’ weighty tome through the press and this duty was taken over, with serious consequences by Nürnberg’s Lutheran Protestant preacher, Andreas Osiander (1496 or 1498–1552).


Andreas Osiander portrait by Georg Pencz Source: Wikimedia Commons

Osiander was born in the small town of Gunzenhausen to the south of Nürnberg, the son of Endres Osiander a smith and Anna Herzog. His father was also a local councillor who later became mayor. He matriculated at the University of Ingolstadt in 1515 where he, amongst other things, studied Hebrew under the great humanist scholar and great uncle of Melanchthon, Johannes Reuchlin. In 1520 he was ordained a priest and called to Nürnberg to teach Hebrew at the Augustinian Cloister, a hot bed of reformatory debate, where he also became a reformer. In 1522 he as appointed preacher at the St Lorenz church and became a leading voice for religious reform. Osiander achieved much influence and power in Nürnberg when the city-state became the very first Lutheran Protestant state.

Osiander first became involved with Petreius when the latter started publishing his religious polemics. Petreius also published numerous religious works by both Luther and Melanchthon. Where or how Osiander developed his interest and facility in the mathematical sciences is simply not know but they are attested to by Cardano in the preface to one of his books published by Petreius. In fact it was Osiander, who was responsible for the correspondence between Cardano and the Petreius printing office and he edited Cardano’s books there. When or how Osiander became an editor for Petreius is also not known. In his capacity as editor of De revolutionibus Osiander committed what many have as one of the greatest intellectual crimes in the history of science, he added the infamous ad lectorum, an address to the reader with which the book opens.


Latin Wikisource

The ad lectorum is an essay that it pays to read in full but here we will just consider the salient points, Osiander writes:

There have already been widespread reports about the new novel hypothesis of this work, which declares that the earth moves whereas the sun is at rest in the centre of the universe.

Here Osiander lets us know that knowledge of Copernicus’ heliocentric hypothesis was already widespread–spread by the Commentariolus, the Narratio Prima and by rumour–indicating that there was going to be a high level of expectancy to learn the mathematical details of the system. He goes on:

Hence certain scholars, I have no doubt, are deeply offended and believe that the liberal arts, which were established long ago on a sound basis, should not be thrown in confusion.

Anticipating criticism from conservative circles Osiander goes into defensive mode:

But if these men are willing to examine the matter closely, they will find that the author has done nothing that is blameworthy. For it is the duty of an astronomer to compose the history of the celestial motions through careful and expert study. Then he must conceive and devise the causes of these motions or hypotheses about them. Since he cannot in any way attain to the true causes, he will adopt whatever suppositions enable the motions to be computed correctly from the principles of geometry for the future as well as the past.

Here we have the crux of Osiander’s defence. Astronomers are here to produce geometrical models in order to provide accurate predictions of celestial motions and not to determine the unobtainable true causes of those motions. This argument has been dubbed instrumentalist and some hail Osiander as the first instrumentalist philosopher of science. Instrumentalism is a metaphysical attitude to scientific theories that enjoyed a lot of popularity in modern physics in the twentieth century; it doesn’t matter if the models we use describe reality, all that matters in that they predict the correct numerical results. Osiander expands on this viewpoint:

For these hypotheses need not be true or even probable. On the contrary, if they provide a calculus consistent with the observations, that alone is enough.

Here we have the core of why the ad lectorum caused so much outrage over the centuries. Osiander is stating very clearly that the mathematical models of astronomers are useful for predictive purposes but not for describing reality. A view that was fairly commonplace over the centuries amongst those concerned with the subject. Copernicus, however, very clearly deviates from the norm in De revolutionibus in that he presents his heliocentric system as a real model of the cosmos. Osiander’s ad lectorum stands in clear contradiction to Copernicus’ intentions. Osiander then goes into more detail illustrating his standpoint before closing his argument as follows:

…the astronomer will take as his first choice that hypothesis which is easiest to grasp. The philosopher will perhaps rather seek the semblance of the truth. But neither of them will understand or state anything certain, unless it has been divinely revealed to him.

Here we have Osiander restating the standard scholastic division of responsibilities, astronomers provide mathematical models to deliver accurate predictions of celestial motions for use by others, philosophers attempt to provide explanatory models of those motions but truth can only be delivered by divine revelation. The modern astronomy, whose gradual emergence we are tracing had to break down this division of responsibilities in order to become accepted as we shall see in later episodes. Osiander closes with a friendly appeal to the reader to permit the new hypotheses but not to take them too seriously, and thereby make a fool of himself.

Therefore alongside the ancient hypotheses, which are no more probable, let us permit these new hypotheses also the become known, especially since they are admirable as well as simple and bring with them a huge treasure of very skilful observations. So far as hypotheses are concerned, let no one expect anything certain from astronomy, which cannot furnish it, lest he accept as the truth ideas conceived for another purpose, and depart from this study a greater fool than he entered it. Farewell.

There is a widespread belief that Osiander somehow smuggled his ad lectorum into De revolutionibus without the knowledge of either Copernicus or Petreius but the historical evidence speaks against this. There are surviving fragments of a correspondence between Osiander and Copernicus that make it clear that Osiander discussed the stratagem of presenting De revolutionibus as a hypothesis rather that fact with him; although we don’t know how or even if Copernicus reacted to this suggestion. More telling is the situation between Petreius and Osiander.

There is absolutely no way that Osiander could have added the ad lectorum without Petreius’ knowledge. This is supported by subsequent events. When the book appeared Tiedemann Giese was outraged by the presence of the ad lectorum and wrote a letter to the city council of Nürnberg demanding that it be removed and the book reissued without this blemish. The council consulted Petreius on the subject and he let them know in no uncertain terms that it was his book and what he put in it was his business and nobody else’s.

Petreius’ reaction illustrates an important point that modern commentators often overlook. Our concept of copyright didn’t exist in the sixteenth century, the rights to a publish work in general lay with the publisher and not the author. This is clearly demonstrated by the fact that when a publication provoked the ire of the authorities, civil or clerical, it was the printer publisher, who first landed before the court and then in goal rather than the author.

The ad lectorum was anonym but any reader, who was paying attention should have realised through the phrasing that Copernicus was not the author. The Nürnberger astronomer and instrument maker Johannes Pratorius (1537–1615), another Wittenberg graduate, wrote in his copy of De revolutionibus that Rheticus, when Pratorius visited him in 1569, had revealed to him that Osiander was the author of the ad lectorum.


Source: Wikimedia Commons

Michael Maestlin’s copy contains the same information also from Rheticus via Peter Apian. Kepler’s second hand copy had this information added by its original owner Hieronymus Schreiber (birth date unknown–1547), yet another Wittenberg graduate, who had received a gift copy signed by Petreius, because he had substituted for Rheticus in Wittenberg during the latter’s time in Frombork. All of this indicates that Osiander’s authorship of the ad lectorem was circulating on the astronomers’ grapevine by 1570 at the latest. It was first put into print, and thus made general public, by Kepler in his Astronomia Nova in 1609.

As with most books in the Early Modern Period there was no publication date for De revolutionibus but it seems to have been finished by 20thApril 1543, as Rheticus signed a finished copy on this date. According to a legend, put in the world by Tiedemann Giese, Copernicus received his copy, which was placed into his hands, on his dying day the 24thMay 1543. Owen Gingerich, who is the expert on the subject, estimates that the 1stedition probably had a print run of about 400 copies, which carried the mathematical details of Copernicus’ hypothesis out into the wide world.







Filed under Early Scientific Publishing, History of Astrology, History of Astronomy, Renaissance Science

12 responses to “The emergence of modern astronomy – a complex mosaic: Part IX

  1. having learnt the black art, as printing was known

    A handle with an obvious sardonic tone to modern ears. Did it share that at the time?

  2. Ray

    Hi Thony,

    Could you could you clarify how common were the instrumentalist views of astronomical models as presented in Osiander’s Ad Lectorem?

    On the one hand you say:

    Here we have the crux of Osiander’s defence. Astronomers are here to produce geometrical models in order to provide accurate predictions of celestial motions and not to determine the unobtainable true causes of those motions. This argument has been dubbed instrumentalist and some hail Osiander as the first instrumentalist philosopher of science.

    which I take to be suggesting that Osiander’s instrumentalism was not only rare, but unprecedented.

    But on the other hand you say:

    Osiander is stating very clearly that the mathematical models of astronomers are useful for predictive purposes but not for describing reality. A view that was fairly commonplace over the centuries amongst those concerned with the subject. Copernicus, however, very clearly deviates from the norm in De revolutionibus in that he presents his heliocentric system as a real model of the cosmos.

    which seems to suggest that Osiander’s instrumentalism was “commonplace,” even “the norm.”

    FWIW, my leaning at present is towards thinking that Osiander’s views as presented in the Ad Lectorem were rarely held, and even more rarely, sincerely believed among his contemporaries (although I could be convinced otherwise.) I read Ptolemy, for example, as presenting what he believes to be the reality of the cosmos, and not a convenient fiction. In fact he seems to suggest that mathematics, in which he includes astronomy, is more certain than physics or theology, which he gives as the other two branches of theoretical philosophy. (Makes sense if we’re judging by predictive accuracy at the time.) Did Peuerbach or Regiomontanus have a different take on these matters? Likewise The fact that several of Copernicus’s followers were offended by the Ad Lectorem seems to indicate, they at least did not share the views presented by Osiander. Do you have quotes from other 16th century authors suggesting they shared Osiander’s views?

    • Until modern times, at least in astronomy, the term of art was not “instrumentalism” but “save the phenomena”. I too would be interested to know who said that Osiander was the first instrumentalist.

      Of course, ripping these terms from all historical context is Not Good. Instrumentalism got a big boost in the early twentieth century from relativity and from quantum mechanics. The physicist David Mermin once memorably described the most popular philosphy of quantum mechanics (at least among working physicists) as “Shut up and calculate!”

      On the other hand, Ptolemy composed two separate works(*), the Almagest and the Planetary Hypotheses. The first delineates the geometrical models needed to predict planetary positions (and eclipses and so forth). The second added a bunch more cycles to give a physical mechanism for the planetary orbits. It would seem that Ptolemy did not regard the sole task of astronomy as “saving the phenomena”, but did believe in separating that part from more “realist” aspects.

      (*) Actually Ptolemy composed two other astronomical works: the Tetrabiblios, on astrology, and the Handy Tables.

      • Ray

        Point taken regarding anachronistic terminology. That said, what seems notable about Osiander’s Ad Lectorem is not just that it says astronomers should strive to “save the phenomena,” but that that should be their goal to the exclusion of all other goals. In particular having a model based on “true or even probable” hypotheses is not considered a reasonable goal for astronomers. This goes beyond the slogan of “saving the phenomena” in somewhat the same direction as that of 20th century Instrumentlists. The difference, I think, is that 20th century Instrumentalists typically denied that a coherent distinction could be made between seeking the truth and “saving the phenomena.” The Ad Lectorem on the other hand seems to believe in such a distinction but deems truth in astronomy to be unattainable without divine revelation. This seems like a very extreme position.

        Of course Osiander was right in at least one respect. Every astronomical model on offer, including that of Copernicus, was wrong in at least some important way.

      • Laurence Cox

        While in general I would agree with you that it is Not Good to use anachronistic terminology such as instrumentalist, here I think that it is applicable. Remember that the spheres of the Ptolemaic system were thought to be physical (made of the fifth element, quintessence); by avoiding the idea of physical spheres and only thinking in terms of the mathematics of spherical motion, Osiander’s approach made possible models like Tycho’s where the orbits of the Sun and Mars intersect.

        One can even consider Newton as an instrumentalist in this sense, as he declined to offer any hypothesis on the cause of gravitation.

      • @Lawrence Cox:
        I agree. Actually I was never an absolutist about anachronistic terminology, and certain forms of whiggism; it’s more a “handle with care”.

        I’ve become even more accepting after reading David Wootton’s The Invention of Science; he makes a strong case that all the huffing and puffing about “scientist” is overblown, for example.

        I have no problem calling Archimedes a mathematical physicist, so long as it’s clear that he’s not solving wave equations in a curved spacetime. After all, people say “King Agamemnon”, “King Edward I”, and “King Edward VIII”, without implying that they occupied the same political positions.

        I wanted to highlight that the senses in which Osiander and (say) Bohr were instrumentalists are as far apart as the kingships of Edward I and Edward VIII. Very different motivations, for one thing.

        By the way, Osiander was not broaching a new view of the task of the astronomer—at least that’s my understanding.

      • Ray, I’m neither your teacher nor your servant. You want to learn about Renaissance astronomy then go away and read the books on the subject!

    • Coming somewhat late to this discussion just a few comments. The view that Osiander’s position is instrumentalism is one applied by modern historians and one that I personally don’t accept. He is certainly a holder of the view first expounded by Plato that the role of the astronomer is to save the phenomena and attributed to all astronomers from Plato down to Newton by the 19th century French physicist Duhem (1861–1916). The task of explaining cosmological reality was the domain of philosophers not astronomers, strict demarcation. This concept, as Ray correctly says, was certainly not held by Ptolemaeus, who makes very clear at the beginning of his Syntaxis Mathematiké that he believes in the reality of his system. However, it is very clear in the Renaissance that astronomers are only interested in mathematical models, tables etc that deliver the most accurate predictions of celestial motions and not in any form of cosmological reality. The best example of this is that Maestlin chastises Kepler for suggesting a cosmological mechanism for his heliocentric model in his Mysterium Cosmographicum, which Maestlin edited for the press. Kepler is trespassing on the territory of the philosophers. As to the complaints of Copernicus’ friends about the Ad lectorum they are not concerned with the status of astronomers contra philosophers but the falsification of Copernicus’ intentions.

      • Ray

        Hi Thony. You say:

        However, it is very clear in the Renaissance that astronomers are only interested in mathematical models, tables etc that deliver the most accurate predictions of celestial motions and not in any form of cosmological reality. The best example of this is that Maestlin chastises Kepler for suggesting a cosmological mechanism for his heliocentric model in his Mysterium Cosmographicum, which Maestlin edited for the press.

        Is this demarcation of roles clear from before the time of Copernicus and Osiander or only 50 years later, when Kepler and Maestlin were moving Mysterium Cosmographicum to press? Do you have any earlier examples? Also, I should like to know more exactly what Maestlin said in criticizing Kepler. It is one thing to say that an astronomer should leave speculation about causes to philosophers, and another to say that an astronomer should freely speculate without regard to whether his speculations are true. The latter, which I take to be Osiander’s stated view seems much odder.

        That is to say. Are there good historical examples that distinguish between

        1) A scenario where Osiander is faithfully continuing a widely held tradition regarding the role of the astronomer.


        2) A scenario where the Ad Lectorem and similar views that followed are a reaction to Copernicus’s work, which concretely demonstrated that a view based on radically different assumptions about reality could “save the phenomena” as well as the long dominant view of Ptolemy.

      • Ray

        Thony, how responsive you choose to be to blog commenters is your own business I suppose, but if you wish to set yourself up as HistSci Hulk, enemy of bad history in your chosen niche, you really ought to make sure you aren’t promoting bad history yourself.

        I am quite capable of doing my own research, but thus far everything I’m finding is suggesting that the idea that 16th century astronomers didn’t care about the utility of their models is mostly a myth (possibly based on a few passages of Aquinas’s works having similar wording to Osiander’s preface, despite it being fairly clear from context that Aquinas’s intended message was quite different.) Certainly not only Ptolemy, but Copernicus, Tycho, and Fracastoro all cared about the truth of the models they originated. Ursus may be an exception among the major model builders (although I need to investigate further if he had strong opinions about whether celestial spheres should intersect.) Additionally, it seems many of the justifications for the claimed efficacy of astrology seem to have relied on the ordering of the celestial spheres, and the weak justification for that ordering in the Ptolemaic system was a bit of a scandal. This debate also makes no sense in a world where 16th century astronomers/astrologers have no interest in the reality of their models.

        I am also suspicious of your explanation of Copernicus’s friends’ objections to the Ad Lectorem. In the case of Rheticus, the annotation describing the incident from Maestlin’s copy of De Revolutionibus (as translated by Gingerich) suggests that Rheticus thought Osiander was “slandering astronomers” which is a bit of an odd phrasing if his concern was limited to the fact that Osiander was misrepresenting Copernicus in particular.

        As an amusing side note, on rereading Osiander’s preface, I noticed that his main argument against the reality of Ptolemy’s model was that it had Venus over 4 times closer to Earth at inferior conjunction than at superior conjunction. This is of course true not only in Ptolemy’s model, but also Copernicus’s,Tycho’s and reality. Nonetheless, he thought this had been refuted by experience. Not sure what to make of this. Osiander argues as if the absurdity of Venus varying so much in distance was common knowledge, but of course, even Tycho, who took naked eye “measurements” of star sizes seriously, didn’t find Osiander’s argument a sufficient reason to abandon his system.

  3. Ray

    Typo in my previous comment: should say “ the idea that 16th century astronomers didn’t care about the *reality* of their models is mostly a myth”

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