Kepler was wot, you don’t say?


The Guardian is making a serious bid for the year’s worst piece of #histsci reporting or as Adam Shapiro (@tryingbiology) once put it so expressively, #histsigh! The article in question has the shock, horror, sensation headline: Groundbreaking astronomer Kepler ‘may have practised alchemy’. Ignoring the fact for the moment that he probably didn’t, given the period and the milieu in which Kepler lived and worked saying that he may have been an alchemist is about as sensational as saying he may have been a human being.


Johannes Kepler Source: Wikimedia Commons

The period in which Kepler lived was one in which the interest in alchemy was very widespread, very strong and very open. For eleven years he was Imperial Mathematicus at the court in Prague of the German Emperor Rudolph II, which was a major centre for all of the so-called occult sciences and in particular alchemy. In Prague Kepler’s original employer Tycho Brahe had been for years a practitioner of Paracelsian alchemical medicine (a very widespread form of medicine at the time), which to be fair the article sort of says. What they say is that Tycho was an alchemist, without pointing out that his alchemy was restricted to medical alchemy.


Tycho Brahe Source: Wikimedia Commons

One of his colleagues was the Swiss clockmaker Jost Bürgi, who had come to Prague from Hesse-Kassel,


Jost Bürge Source: Wikimedia Commons

where the Landgrave Moritz was a major supporter of alchemy, who appointed Johannes Hartmann (1568–1631) to the first ever chair for chemistry, actually Paracelsian medicine, at the university of Marburg. The real surprise is not that Kepler was an alchemist or practiced alchemy but rather that given the time and milieu in which he lived and worked that he wasn’t and didn’t.


Johannes Hartmann Source: Wikimedia Commons

How can I be so sure that Kepler didn’t dabble in alchemy? Simply because if he had, he would have written about it. Kepler is a delight, or a nightmare, for the historian, there is almost no figure that I know of in #histSTM, who was as communicative as Kepler. He wrote and published eighty three books and pamphlets in his lifetime covering a very wide range of topics and in all his written work he was always keen to explain in great detail to his readers just what he was doing and his thoughts on what he was doing. He wrote extensively and very openly on his mathematics, his astronomy, his astrology, his family, his private affairs, his financial problems and all of his hopes and fears. If Kepler had in anyway been engaged with alchemy, he would have written about it. If anybody should chime in now with, yes but alchemists kept they activities secret, I would point out in Kepler’s time the people practicing alchemy, particularly the Paracelsians, were anything but secretive. And it was with the Paracelsians that Kepler had the closest contact.

There are a few letters exchanged between Kepler and his Paracelsian physician friends, which show quite clearly that although Kepler displayed the natural curiosity of a scientific researcher in their alchemistic activities he did not accept the basic principles of alchemy. In his notorious exchange with Robert Fludd, he is very dismissive of Fludd’s alchemical activities. Kepler was not an alchemist.

From a historical point of view particularly bad is the contrast deliberately set up in the article between good science, astronomy and mathematics, and ‘dirty’ pseudo- science’, alchemy. This starts with the title:

Groundbreaking astronomer Kepler ‘may have practised alchemy’

Continues with the whole of the first paragraph:

The pioneering astronomer Johannes Kepler may have had his eyes on the heavens, but chemical analysis of his manuscripts suggests he was “willing to get his hands dirty” and may have dabbled in alchemy.

“Kepler, who died in 1630, drew on Copernicus’s work to find laws of planetary motion that paved the way for Isaac Newton’s theory of gravity” is contrasted with “The authors speculate that Kepler could have learned the “pseudo-chemical science.” 

A ‘pioneering astronomer’ with ‘his eyes on the heavens’, serious scientific activity, but ‘dabbled in alchemy’. Whoever wrote these lines obviously knows nothing about Kepler’s astronomical writing nor about early 17thcentury alchemy.

The article through its choice of descriptive terms tries to set up a black/white dichotomy between the man who paved the way for modern astronomy, good, and the practitioners of alchemy in the early seventeenth century, bad. However if we actually look at the real history everything dissolves into shades of grey.

Kepler was not just an astronomer and mathematician but also a practicing astrologer. People might rush in here with lots of Kepler quotes condemning and ridiculing the nativity horoscope astrology of his age, all of them true. However, he famously said one shouldn’t throw the baby out with the bath water defending the basic idea of astrology and presenting his own unique system of astrology based entirely on aspects, that is the angular position of the planets relative to each other. The author of the piece has obviously never turned the pages of either Kepler’s Mysterium Cosmographicum or his Harmonice Mundi. As I commented on Twitter, during a discussion of this article, Kepler’s cosmological heuristic with which he generated all of his successful astronomy was, viewed from a modern rational standpoint, quite simply bat shit insane. Things are not looking good for our pioneering astronomer.


Kepler’s Platonic solid model of the solar system, from Mysterium Cosmographicum (1596) Kepler’s explanation as to why there are only five planets and their order around the sun! Source: Wikimedia Commons

On the other side, as I have noted on several occasions, alchemy included much that we now label applied and industrial chemistry.  For example, alchemists were responsible for the production of pigments for painters and gunpowder for fireworks and cannons, and were often glassmakers. Alchemists were historically responsible for developing the laboratory equipment and methodology for chemical analysis. In the period under discussion many alchemists, including Tycho, were Paracelsian physicians, who are credited with the founding of the modern pharmacological industry. Historians of alchemy tend to refer to the alchemy of the seventeenth century as chymistry because it represents the historical transition from alchemy to chemistry. Not so much a pseudo-science as a proto-science.

Let us now consider the so-called evidence for the articles principle claim. Throughout the article it is stated that the evidence was found on Kepler’s manuscripts, plural. But when the evidence is actually discussed it turns out to be a single manuscript about the moon. On this manuscript the researchers found:

“…very significant amounts of metals associated with the practice including gold, silver, mercury and lead on the pages of Kepler’s manuscript about the moon, catalogued as “Hipparchus” after the classical astronomer.”

Is alchemy the only possible/plausible explanation for the traces of metals found on this manuscript? Could one suggest another possibility? All of these metals could have been and would have been used by a clock and instrument maker such as Jost Bürgi, who was Kepler’s close colleague and friend throughout his eleven years in Prague. Bürgi also had a strong interest in astronomy and might well have borrowed an astronomical manuscript. Of course such a solution doesn’t make for a sensational article, although all the available evidence very strongly suggests that Kepler was not an alchemist.

One final point that very much worries me is the provenance of this document. It is four hundred years old, who has owned it in the meantime? Where has it been stored? Who has had access to it? Until all of these questions can be accurately answered attributing its contamination to Kepler is just unfounded speculation.










Filed under History of Alchemy, History of Astrology, History of Astronomy, History of science, Myths of Science, Renaissance Science

15 responses to “Kepler was wot, you don’t say?

  1. Pingback: Kepler was wot, you don’t say? — The Renaissance Mathematicus | O LADO ESCURO DA LUA

  2. I’m not a chemist. It’s not just the Guardian; they are referring to a paper in Talanta. What is the status of this journal? It is published by Elsevier, known mainly for being expensive. They have some good journals, but also some really bad ones (Chaos, Solitons, and Fractals, anyone? What about the authors? Leading lights in their field, well known, average specimens, non-entities, or fools? (Bonus points if you spot the source from which I paraphrased that.)

    • JBauer

      I’m not familiar with that particular journal myself. It seems to specialize in analytical chemistry methods. For whatever it’s worth, its IF is 4.9 which is pretty good as far as these things go (it’s higher than the ACS journal Analytical Chemistry). After skimming the article itself, it’s mostly focused on the use of a new, non-destructive technique for determining what metals are present on the surfaces of some historical objects. Actually, the part in the article where they discuss Kepler and Alchemy isn’t half bad considering that the authors are all analytical chemists. They say, at least twice, that there is no evidence that Kepler practiced alchemy, although this doesn’t stop them from speculating (they aren’t as bad as The Guardian however). They cite one paper by Karin Figala from 1975 (Vistas in Astronomy 18, 457-469) entitled “Kepler and Alchemy,” and several about Brahe’s laboratory, and that’s about it.

      According to the paper, the manuscript in question was part of a collection bought by Catherine II in 1766 and has been stored in the Archives of the Russian Academy of Sciences (St. Petersburg branch). They don’t say any more than that, however.

  3. Typo: “thoughts on what he as doing”
    Thanks for your lovely debunking.

  4. All due props for pushing back on the alchemy thing.

    Kepler’s cosmological heuristic with which he generated all of his successful astronomy was, viewed from a modern rational standpoint, quite simply bat shit insane. [Accompanied by the famous Platonic solid pix.]

    Now I’d like to push back, a liitle, on this quote. It would be hard to find a more rational rationalist than Steven Weinberg (whatever may be his deficiencies as a historian). He wrote:

    [Modern physicists have not] gotten over the old Platonic fascination with short lists of mathematically possible objects, like regular polyhedrons. There are other such short lists that continue to intrigue physicists. … What makes Kepler’s scheme so foreign to us today is not his attempt to find some fundamental physical significance for the regular polyhedrons, but that he did this in the context of planetary orbits, which are just historical accidents.

    In short, there was nothing insane about Kepler’s attempt to explain the architecture of the universe using the symmetrical Platonic solids. Not that different from, e.g., today’s use of symmetry groups in particle physics.(Kepler of course had no reason to believe that the orbits of the planets were historical accidents.)

    • Steven Weinberg is without doubt a brilliant physicist but like most scientists he is a lousy historian of science. His To Explain the World: The Discovery of Modern Science is pure self confessed presentism and as such fairly useless. Here he has the historical story arse backwards. Kepler was looking for a justification for why there are and can only be exactly five planets. Inspired by the diagram produced by the conjunctions of Jupiter and Saturn he tried to fill the spaces between the planetary orbits with regular polygons but couldn’t find any good fits and then concluded because there were an infinite number of regular polygons they couldn’t provide the answer. Instead he argued that the cosmos was three dimensional so one needs polyhedra not polygons. Sudden insight, there are only five regular polygons so therefore there can only be five planets. Interestingly he then went on to produce the first systematic analysis of the so-called Archimedean semi-regular polyhedra and also star shaped polyhedra.

      • I know all that, but more to the point, so does Weinberg. (He didn’t have the story arse-backwards—he recounts the well-worn tale first, as you just did. After that he explains why Kepler’s idea was not so crazy after all.)

        You wrote, “… viewed from a modern rational standpoint, quite simply bat shit insane.” You’re explicitly discussing how Kepler’s idea looks from the present day. You made a presentist judgement, explicitly labeled as such; I’m just continuing the discussion.

        So does a preeminent modern physicist regard Kepler’s construction as “bat shit insane”? And the answer is a clear no!

        Don’t you mean 6 planets? Earth was planet for Kepler. 6 orbits, 5 spaces between orbits.

  5. The use of mercury to form an amalgam with other metals (particularly gold and silver) is well known. Dental amalgam is silver/tin/copper/mercury and mercury is used in the extraction of gold from deposits where it oxccurs as small flakes (as in placer mining). The gold is then separated from the mercury by heating. The process of fire-gilding also used a gold/mercury amalgam spread over the surface of an object to be gilded and then heated to drive off the mercury.

    • Are you suggesting that the use of these metals might possibly not be alchemical?

      • Here’s the Wikipedia article on gilding which you may find helpful as a starting point:

        It doesn’t account for the lead, but someone like Bürgi would probably be gilding clock parts for decorative purposes. Even Kepler might have needed to re-gild instruments if the gilding had worn off in places through handling. Some of the pictures in your Bürgi article look as though the items are gilded, is this specified in information about them?

  6. DW

    I couldn’t help but chuckle at this one. I’m currently taking a grad History Of Science course and I just read about Kepler and the alchemy at the time. It’s not shocking at all. Curious people seek the truth in whatever ways they can – for better or worst.

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