Category Archives: Uncategorized

Galileo, Foscarini, The Catholic Church, and heliocentricity in 1615 Part 1 – the occurrences: A Rough Guide.

I have been criticised for claiming, in a recent post, that given time the Catholic Church would have come to accept heliocentricity in the seventeenth-century and in fact because Galileo acted unadvisedly he drove the Church to reject and condemn heliocentricity and thus to substantially delaying its acceptance by that organisation. The criticism was that this claim is speculative and thus not history and one critic even said not scientific. Point one, history is not science and is considerably more speculative than science, although, contrary to popular opinion, science is by no means free of speculation. In this case I think a certain amount of speculation is justified and by looking at the available facts on the attitudes of Catholic astronomers, and in particular the Jesuits, during the seventeenth-century both before and after the events of 1615, which will be discussed, it is possible to argue for a Catholic acceptance of heliocentricity, if Galileo and Foscarini had not driven the theologians into a corner causing them to reject it.

In the first seven decades following the publication of Copernicus’ De revolutionibus there was almost no rejection of heliocentricity on religious grounds but also very little acceptance by astronomers because of the substantial scientific problems that the theory entailed; problems associated with the physics of a moving earth. In a notorious footnote Copernican expert, Robert Westman, pointed out that there were only ten Copernican in the whole world between the publication of De revolutionibus in 1543 and 1600 and not all of those were astronomers, although it did include both Kepler and Galileo. After an initial period of excitement following the books publication Copernicanism was slowly drifting into obscurity due to its failure to deliver the goods, accurate astronomical tables. This situation changed dramatically in 1609.

In 1609 Kepler published his Astronomia Nova containing his first two laws of planetary motion based on solid empirical evidence supplied by Tycho Brahe and providing the best evidence for a heliocentric system by that time. The same year also saw the advent of telescopic astronomy, the telescope having been invented in the previous year, and the beginning of a series of astronomical discoveries by Thomas Harriot, Simon Marius, Galileo Galilei, and the Jesuit astronomers Odo van Maelcote, Giovanni Paolo Lembo and Christoph Grienberger that brought about the biggest changes in astronomy since human being first turned their gaze to the heavens; most notably Galileo published his initial discoveries in his Sidereus Nuncius in 1610. None of these discoveries proved heliocentricity but they did refute significant aspects of the accepted Aristotelian cosmology and the Ptolemaic geocentric astronomy forcing a serious and deep re-alignment of both disciplines. It was the Church’s own astronomers from the Jesuit Collegio Romano, who had quietly been making their own observations and discoveries before the publication of Sidereus Nuncius, who provided the much needed scientific confirmation of Galileo’s discoveries; passing this information on to the Church’s theologians. The Jesuit astronomers fully aware that Ptolemaic geocentricity was no longer tenable, following the discovery of the phases of Venus, like most other European astronomers, adopted the Tychonic helio-geocentric system; an intermediate solution that combined the best technical aspects of heliocentricity, for example the explanation of retrograde motion, without moving the earth. This was an important step down the road to heliocentricity, especially if, as it often was, combined with diurnal rotation. However Galileo could not accept this rational compromise, his ambition drove him on, because he wanted to go down in history as the man who established heliocentricity, ignoring in his egotism the work of Kepler who was much more advanced in his heliocentric astronomy than Galileo himself. To understand what happened next we need to briefly examine the position of the Church in this situation.

Religions are by their very nature conservative and opposed to sudden or significant change. They claim to be purveyors not just of truth but ‘the’ truth. This being the case all change is in one way or another an admission of failure; we got it wrong! This does not mean that religions are never changing, frozen in time, but it does mean that all change should be gradual, controlled and fully explainable within the religion’s own model of reality. A religion cannot allow itself to be seen to be forced to change by outside forces, otherwise believers might begin to question their monopoly on the truth. Since the thirteenth-century the Catholic Church had integrated an uneasy synthesis of Aristotelian cosmology and Ptolemaic astronomy, largely created by Albertus Magnus and his pupil Thomas Aquinas, into their model of reality, one that seemed to fit the known empirical facts. Now at the end of the first decade of the seventeenth-century this synthesis was crumbling away very fast and the Church was in a very dodgy situation, over which they had very little control, a potential nightmare for the theologians, the official purveyors of the truth. The central problem in this situation was that various passages in the Bible, supposedly the indisputable word of God, contradicted a heliocentric model with a stationary sun and a mobile earth, most notably Joshua 10:12 “…and he said in the sight of Israel, Sun, stand thou still upon Gibeon; and, Moon, in the valley of Ajalon”. If the sun wasn’t moving how could the Lord command it to stand still? The Church’s theologians were not stupid and it was very clear to them that if they accepted heliocentricity then they would have to abandon a literal interpretation of this and some other passages in the Bible; a change that they were only prepared to make if there was solid empirical evidence available to make it inevitable, as we will see.

By 1613 Galileo was chomping at the bit and was very egger eager to persuade the whole world, including the Church, to accept Copernican heliocentricity. His influential friends within the Church, who included Cardinal Maffeo Barberini the future Pope Urban VIII, were very much aware of the situation sketched above and warned Galileo that he should proceed with caution and not stir up trouble with the Church’s theologians. Galileo ignored this very sensible advice. The matter first came to a head with the so-called Letter to Castelli that in a modified form is better known as the Letter to Christina. How this came about we need to look at Galileo’s official function at the Medici Court in Florence.

Galileo had used the Sidereus Nuncius to acquire a position at the Medici Court dedicating the pamphlet to Cosimo II, his former mathematics pupil, and naming the Moons of Jupiter, his greatest discovery, the Medicean Stars in his honour. This followed lengthy correspondence with court officials as to which name would be most acceptable to the Grand Duke. Galileo’s efforts were rewarded with a position as court philosophicus and mathematicus and an appointment as professor of mathematics at the University of Pisa without teaching obligations, all for a very generous salary. What exactly was Galileo’s role as court philosophicus? The position sounds very impressive but in reality, within the structure of a Renaissance absolutist court, Galileo was a sort of intellectual court jester. In an age without Internet, radio, television or any of the other modern invention with which we waste our time, after dinner entertainment at a Renaissance court took various forms; one of these took the form of intellectual debates. Galileo was expected to entertain the dinner guests by disputing given philosophical or scientific themes with others, especially invited for the purpose. Cosimo and his guest were not particularly concerned who won a given debate or who was right, they were more interested in being entertained by clever and witty repartee, Galileo a brilliant polemicist was naturally a master at this game and more than earned his keep. The situation that led to Galileo writing the Letter to Christina actually took place in Galileo’s absence.

Late in 1613 the newly appointed professor of mathematics at the University of Pisa, Benedetto Castelli, a pupil of Galileo’s, attended a lunch hosted by the Grand Duchess Christina, Galileo’s earlier patron who had employed him to teach mathematics to Cosimo. Also present on this occasion was the Pisan professor for philosophy, Cosimo Boscaglia. Christina expressed doubts about the existence of the Moons of Jupiter and about their possible connection with the, in her eyes, heretical Copernican astronomy. Boscaglia assured her that the moons were indeed real and expressed similar doubts about their astronomical implications. After the meal Christina summoned Castelli to her chamber and in the presence of Boscaglia and other guests challenged him on the mobility of the earth. Castelli was in the hot spot, but according to his own account, in a letter to Galileo, he acquitted himself skilfully. Galileo now set in motion a chain of events that probably constitute the biggest error in his life. He wrote a long letter to Castelli supplying him with arguments to use against those quoting Bible passages against heliocentricity. He set about playing the theologian, reinterpreting those passages to make them conform to Copernican thought. He suggested for example that when the Lord commanded the sun to stand still he stopped its rotation about its axis, a rotation that Galileo had recently proved with his study of sunspots. The whole letter was, to put it mildly, a blunder.

Some of Galileo’s enemies, disgruntled Aristotelians who had been subjected publically to the scorn of Galileo’s sharp tongue, got hold of a copy of the letter and presented it to the Church authorities. Surprisingly the Church found most of the letter unobjectionable except for a handful of passages. Galileo tried to bluff his way out of the matter by claiming that those passages were not in the original but had been added to the copy by his enemies, whether you believe him or not is left entirely up to you. The Church demanded the original. In the meantime Galileo instead of backing down was working on an expanded version of the letter, which would go down in history as the Letter to Christina, to whom it was directly addressed. Galileo really did not know when to leave things alone. Why one might ask was it so terrible for Galileo to suggest new interpretations of the Bible?

The Catholic Church was founded on the premise that they, and they alone, were privileged to interpret the word of God. In the early sixteenth century various thinkers, who became known collectively as the Protestants, challenged the Church on this very issue, claiming that every individual had the right to read and interpret the word of God for himself. A universal claim that was later modified as the various branches of this protest movement solidified into established churches themselves. But I digress. This led to the greatest schism in Church history now known as the Reformation. From the middle of the century following the Council of Trent the Catholic Church hit back with its own movement, which became known as the Counter-Reformation, leading storm-troopers being the Jesuits, although they were not initially founded for this purpose. Galileo, a mere mathematicus and thus the lowest of the low in the intellectual hierarchy, was claiming the right to re-interpret the Bible just five years before the outbreak of the Thirty Years War the devastating and extremely bloody highpoint of this struggle between the forces of Reformation and Counter-Reformation. Not a clever move from a man who many regard as a genius.

To pour even more oil into the fire, as if Galileo’s own efforts were not enough, a Carmelite theologian, Paolo Antonio Foscarini, submitted a book he had written to the Church censors in 1615, which contained very similar reinterpretations of the Bible to bring it into line with the Copernican heliocentric hypothesis. Not surprisingly the anonymous censor thought the book to “excessively favour the rash opinion” of Copernicus. Like Galileo, Foscarini was not prepared to let matter lie and submitted both the text of his book and the censor’s judgement to the Jesuit Cardinal Roberto Bellarmino, who was considered one of the greatest living theologians. Bellarmino considered Foscarini’s book and Galileo’s letter and came to a famous conclusion that he sent to Foscarini in the form of a letter the relevant passages of which I have reproduced below.

My Very Reverend Father,

It has been a pleasure for me to read the Italian letter and the Latin paper you sent me. I thank you for both the one and the other, and I may tell you that I found them replete with skill and learning. As you ask for m y opinion, I will give it as briefly as possible because, at the moment I have very little time for writing.

First, I say it seems to me that your Reverence and Signor Galileo act prudently when you content yourselves with speaking hypothetically and no absolutely, as I have always understood that Copernicus spoke. For to say that the assumptions that the Earth moves and the Sun stands still saves all the celestial appearances better than do eccentrics and epicycles is to speak with excellent good sense and to run the risk whatever. Such a manner of speaking suffices for a mathematician. But to want to affirm that the Sun, in very truth, is at the centre of the universe and only rotates on its axis without traveling from east to west, and that the Earth is situated in the third sphere and revolves very swiftly around the Sun, is a very dangerous attitude and one calculated not only to arouse all Scholastic philosophers and theologians but also to injure our hold faith by contradicting the Scriptures….

Second, I say that, as you know, the Council of Trent forbids the interpretation of the Scriptures in a way contrary to the common agreement of the holy Fathers. Now if your Reverence will read, not merely the Fathers, but modern commentators on Genesis, the Psalms, Ecclesiastes, and Joshua, you will discover that all agree in interpreting them literally as teaching that the Sun is in the heavens and revolves round the Earth with immense speed and that the Earth is very distant from the heavens, at the centre of the universe, and motionless. Consider, then in your prudence, whether the Church can support that the Scriptures should be interpreted in a manner contrary to that of the holy Fathers and of all modern commentators, both Latin and Greek….

Third, I say that, if there were a real proof that the Sun is in the centre of the universe, that the Earth is in the third sphere, and that the Sun does not go round the Earth but the Earth round the Sun, then we should have to proceed with great circumspection in explaining passages of Scripture which appear to teach the contrary, and we should rather have to say that we did not understand them than declare an opinion to be false which is proved to be true. But I do not think there is any such proof since none has been shown to me. To demonstrate that the appearances are saved by assuming the sun at the centre and the earth in the heavens is not the same thing as to demonstrate that in fact the sun is in the centre and the earth is in the heavens. I believe that the first demonstration may exist, but I have very grave doubts about the second; and in case of doubt one may not abandon the Holy Scriptures as expounded by the hold Fathers…

Having very firmly pointed out that neither Galileo nor Foscarini had the right to interpret or reinterpret Holy Scripture, Bellarmino adds a very important comment in the final paragraph. He states very clearly that if there were proof of the heliocentric system then the Church would have to very carefully reinterpret the Bible, but he says, quite correctly, such proof does not exist at the moment so no deal. He then goes on the say that he personally doesn’t think that such proof would ever be found, proving that even Saint Roberto Bellarmino S. J. was not infallible. This final passage clearly illustrates something that the modern Galileo fan club love to ignore; in 1615 there was no empirical proof for the heliocentric hypothesis. It has been suggested that some Jesuit astronomers interpreted Bellarmino’s concession that if such a proof were to be found, as an instruction to go out and find one, but more of that in Part 2 – the consequences.

Things were now approaching the denouement. It was very clear to Galileo and all the other interested parties that the whole episode had been submitted to the Roman Inquisition. Instead of doing the sensible thing and keeping his head below the parapet, as advised by all of his influential friends including Cesi the head of the Academia dei LIncei and Cardinal Barberini, Galileo decided to go on the offensive. Obtaining permission from his employer, Cosimo, Galileo set off to Rome to canvas for the acceptance of heliocentricity. Knowing full well that he lacked empirical proof of heliocentricity, Galileo wrote up for the first time his infamous theory of the tides, thought out by him and Paolo Sarpi in the 1590s and which would go on to become Day Four, the crowning glory as he saw it, of his Dialogo. This theory posited that the tides were the result of the oceans swapping about like water in a moving bowl, as a result of the motion of the earth. It suffered from one major failure, and lots of minor ones, it only allowed for one tide a day, whereas there are in reality two.

Galileo arrived in Rome and began badgering anybody and everybody of influence that he could get hold off pressing copies of his theory of the tides into their hands and trying to persuade them to support his cause. He might as well have stayed at home, nobody in Rome, least of all influential public figures, was going to stick his neck out and help a mere mathematicus who was under investigation by the Inquisition.

It came as it had to come, the eleven members of the commission set up to adjudicate on the affair found that the idea that the Sun is stationary is “foolish and absurd in philosophy, and formally heretical since it explicitly contradicts in many places the sense of Holy Scripture…”; while the Earth’s movement “receives the same judgement in philosophy and … in regard to theological truth it is at least erroneous in faith.” Put into simple terms heliocentricity, as a theory of fact was both scientifically and theologically wrong. Galileo and Foscarini had forced the Church into making, what was to all intents and purposes, a disastrous judgement. As everybody knows the Pope instructed Bellarmino to inform Galileo of the commission’s judgement and to formally forbid him from holding or teaching the heliocentric theory. It is important to note that the theory, heliocentricity as a statement of fact, was forbidden and not the hypothesis, a distinction that was to play a very central role in the following decades.

Personally, this judgement had very little influence on Galileo life or status in Northern Italian society. Initially there were some rumours that he had been punished in some way by the Church, but at Galileo’s request Bellarmino wrote a letter stating that they had merely had a friendly chat and that Galileo was free of all suspicion. Unfortunately Galileo would later view this letter as a get out of gaol free card but that is the subject of another story. Galileo continued to be a highly feted figure in Northern Italian intellectual circles and to have easy access to the highest circles of the Church. He was not some sort of outcast battling the ignorant Curia, as he is often falsely depicted.

The direct consequences for the heliocentric hypothesis were that Foscarini’s book together with the books of the Protestant Copernicans, Michael Maestlin and Johannes Kepler were placed on the Index of Forbidden Books. Interestingly De revolutionibus was only placed on the Index until corrected. What this meant and the effect that all of this on the future development of heliocentricity will be dealt with in Part 2 – the consequences, which should, all thing being well appear here next week.

For those reading one of my The Transition to Heliocentricity: The Rough Guides posts for the first time you can find a list of links at the top of the website.


Filed under Uncategorized

Johannes Kepler’s Somnium and Katharina Kepler’s Trial for Witchcraft: The emergence of a myth.

At the beginning of the month physicist and popular science writer, Paul Halpern posted the following tweet:

Kepler’s remarkable Somnium, one of the 1st sci-fi stories, later used as evidence in his mother’s witchcraft trial:

Now knowing a thing or two about Kepler’s Johannes and his more than bizarre life, I’ve even written a post on the witchcraft trial, I tweeted back:

It wasn’t used as evidence in his mother’s trial

Now Paul is a conscientious historian of science who likes to check his facts and so he tweeted back, in turn:

Here’s my source:  ‪@APSphysics

The American Physical Society is an honourable organisation and one would expect them to get their facts right and here is what they have to say about Somnium:

Kepler also tried his hand at more fanciful writing, penning an allegory called Somnium (The Dream) in 1611 — arguably the earliest work of science fiction, since it centered on a trip to the moon and speculated about what astronomy would be like if conducted on another planet.

Many years later, Somnium would be used as evidence in his mother’s 14-month imprisonment and trial for witchcraft; it described a woman who summons a demon for help in mixing potions. (He revised the work after her acquittal to make the allegorical aspects crystal clear for the too-literal minded.)

The records of Katharina Kepler’s trial for witchcraft are still extant and I can state with confidence that Somnium was not only not used as evidence in the trial but was in fact never even mentioned, so it would appear that the APS is in the business of creating history of science myths. To make matters worse it would appear, at least superficially, that such a use would have been impossible as the trial took place in 1620-1621 and Somnium was first published in 1634!


To be fair to the APS the myth that they are peddling on their website wasn’t entirely their own creation and has its origins in a somewhat cryptic remark made by Kepler himself in the Somnium and first brought to notice by the historian of science, Marjorie Hope Nicolson.

Before we proceed to uncovering the story of this myth and few words about Somnium and how it relates to Frau Kepler and her alleged witchcraft. The origins of Somnium are somewhat convoluted. Whilst still a student in the 1590s Kepler wrote a disputation arguing in favour of Copernican heliocentricity based on the science-fiction device of viewing a heliocentric earth from the Moon. Vitus Müller, a professor of theology, refused to allow the theme to be disputed because of the subject matter. Kepler was, however, obviously pleased with his invention as he reworked the idea into a science-fiction short story in 1609, Somnium, which he mentions for the first time as “a geography of the moon” in his letter congratulating Galileo on the Sidereus Nuncius in 1610. The background story, which introduces the tale, concerns a youth called Duracotus who lives on the island of Iceland with his mother Fiolxhilde, a ‘wise woman’, who sold herbal charms to sailors. Out of curiosity the fourteen-year-old Duracotus opens and thereby destroys one of the charms that his mother has sold to a sea captain. Enraged his mother gives him to the captain as a servant to replace the, already paid for, charm. The youth ends up in Denmark on the island of Hven with Tycho Brahe where he stays for five years studying astronomy. Returning home he and his penitent mother are reunited and she reveals some of her magical powers to her son. Through her rapport with a daemon of the moon she is able to assist her son in travelling there, at which point this frame story is dropped. I won’t go into the main part of the story as everything we need in contained in this brief opening sequence. Aspects of the opening are very obviously autobiographical if only in a very loose way. Kepler did work together with Brahe but in Prague and not on Hven and as a mature mathematician and astronomer and not as a youthful apprentice. Katharina Kepler did in fact deal in charms and herbal cures and so can be identified with Fiolxhilde the mother in the story. It would appear that Kepler is accusing his own mother of being a witch in 1609. However, if Somnium was first published in 1634 how could this fictional accusation be involved in the real life accusations against Katharina Kepler, which started around 1615 and would play a major role in the lives of both mother and son. Somnium lay dormant amongst Kepler’s papers until the 1620s when over the entire decade Kepler added a total of 223 often very extensive explanatory footnotes to the text, in volume significantly greater than the story itself. Kepler uses the eighth of these footnotes to explain why he thinks that he and his story are to blame for his mother’s misfortune.

Somnium was published posthumously by Kepler’s son having been prepared for publication by his son in law in the hopes of generating some income for his family who had been left in a dire financial position by Kepler’s death and although it very obviously influenced other proto-science-fiction stories in the following centuries it was largely ignored both by scientists and by the historian of science who were apparently too busy analysing his real science publications to bother with this strange little tale. The first scholar to take a serious look at Somnium was the historian of science and literature Marjorie Nicolson in a paper from 1940, Kepler, The Somnium, and John Donne[1]. Nicolson draws our attention to Kepler’s footnote eight, which I will now quote in full

If I am not mistaken the author of that insolent satire called Ignatius, His Conclave [John Donne], got hold of a copy of this little work of mine, he stings me by name at the very beginning. As he goes along he brings poor Copernicus before the tribunal of Pluto, to which, if I am not mistaken, there is access through the abysses of Hekla. You, my friends, who have some knowledge of my affairs, and know the cause of my last trip to Swabia, especially those of you who have previously seen this manuscript, will judge that this writing and those affairs were ominous for me and mine. Nor do I disagree. Ominous indeed is the infliction of a deadly wound or the drinking of poison; and the spreading abroad of this writing seems to have been equally ominous for my domestic affairs. You would think a spark had fallen on dry wood; that is, that my words had been taken up by dark minds which suspect everything else of being dark. The first copy went from Prague to Leipzig, thence was taken to Tübingen in 1611 by Baron von Volckelsdorff and his tutor in morals and studies. Would you believe in the barbershops (as if the name Fiolxhilde is particularly ominous to people there by reason of their occupation) my little tale became the subject of conversation? Certainly in the years immediately following, from that city and that house, there issued slanderous talk about me, which, taken up by foolish minds, became blazing rumor, fanned by ignorance and superstition. Unless I am mistaken, you will agree that my home might have been without that plague of six years, and I without my recent year-long trip abroad, had I obeyed the instructions I dreamed Fiolxhilde had given. It has pleased me, therefore, to avenge the trouble my dream has caused me by publishing this work, which will be another punishment for my adversaries.[2]

Before considering the content of this fascinating footnote it pays to ask the question, “was Kepler a reliable witness”? In any court case where an accusation is carried by the unsubstantiated testimony of a single witness, as is often the case with rape for example, it is customary to question the general reliability of the witness, so how reliable should we consider Kepler to be in this case. Based on a survey of his voluminous autobiographical writings not very reliable at all. When writing about himself and his family Kepler displays clear evidence of paranoia and a very powerful persecution complex so all statements made by him concerning his personal circumstances should be treated with a healthy dose of scepticism; he has a strong tendency to pessimistic exaggerations.

This tendency can be very clearly seen in the opening sentences of the footnote. Because Donne’s Ignatius, His Conclave takes place in hell and mentions Kepler and because Kepler mentions the volcano Hekla on Iceland a supposed portal to hell in Somnium then it follows that Donne must have read Somnium, a rather thin justification, don’t you think? In fact if we look at Donne’s actually reference to Kepler then the accusation looks even stranger. In the opening paragraphs to Ignatius, His Conclave Donne writes the following:

“… [I] had liberty to wander through all places [… … …] the Planets, and of all those which are fixed in the firmament. Of which, I thinke it an honest part as yet to be silent, then to do Galileo wrong by speaking of it, who of late hath summoned the other worlds, the Stars, to come neerer to him, and give him account of themselves. Or to Keppler [sic], who (as himselfe testifies of himselfe) ever since Tycho Brahes death, hath received it into his care, that no new thing should be done in heaven without his knowledge” [3][emphases in original]

The reference to Galileo is, of course, to the Sidereus Nuncius and the quip about Kepler is a direct translation from Kepler’s De stella in Cygno, published in 1606, so there is no need to invoke an imaginary contact with the Somnium, although Nicolson erroneously tries just that. As Edward Rosen, in his authoritative translation of the Somnium[4], points out Donne’s Ignatius was written and published before Kepler claims to have misplaced a copy of the Somnium, so the facts don’t stack up. Rosen also points out that Donne deliberately leaves words out of his Kepler translation, making Kepler look more pompous than he is was in reality.

The rest of the footnote is more interesting and Kepler sketches a path of how a copy of his manuscript might have (did) arrived in Swabia and there have caused all of his mother’s subsequent troubles. There are however major problems with this thesis. Firstly the court records allow a very clear reconstruction of all the events leading up to and during Katharina Kepler’s witchcraft trial and it was very clearly the typical sort of dispute amongst neighbours and ex friends that characterise the majority of witchcraft trials in the period, no need to invoke a Somnium influence at all to explain what happened. More important if the Somnium had played a role, as Kepler suggests, wouldn’t it have been presented as evidence at the trial? “See, even her son thinks she’s a witch!” Nothing of the kind took place so I very much doubt that there is any truth what so ever to Kepler’s claims and insinuations. Not so Nicolson, who is convinced Kepler’s claims are correct. In her paper she writes:

Clearly, then, some work of Kepler’s, written about 1610, was circulated in manuscript, and carried into the “tonstrinae[barber’s shop, emphasis in original] – those early predecessors of the coffee-house – fanned a spark already burning, which then blazed up into a fire which almost consumed Kepler and his mother[5].

Even if we follow Nicolson in accepting Kepler’s footnote as gospel truth what we have here is the Somnium as a spark that started the rumours of witchcraft against Katharina Kepler and not a piece of evidence submitted at her trial.

It had taken more than three hundred years before somebody, Nicolson, took serious notice of Kepler’s footnote but it would only be twenty years before it was referenced again, also by Nicolson, in her monograph, Voyages to the Moon. In this book, which is justifiably regarded as a classic Nicolson very much features the Somnium devoting a substantial number of pages to it and its influence on later lunar voyage literature. In this account after a brief sketch of the witchcraft troubles of Katharina Nicolson write the following:

It was in 1615 – after the first version of the tale had circulated for some time in manuscript – that Kepler’s mother was charged with sorcery and came near to condemnation.

[ … … … ]

If Kepler had intended to publish the Somnium, any such idea was now out of the question. One of his most cryptic notes, in which long bitterness may be read into every line, implies the reason[6]. …

[There now follows the footnote quoted above interspersed with quote from her earlier paper]

Voyages to the Moon was, within academic circles, very widely read and so the claim that Somnium was responsible for Katharina’s troubles was now in the Keplerian public forum.

The next to pick up on this theme was the science writer John Lear who commissioned and annotated, what he thought was, the first English translation of the Somnium[7] in 1965. (As Lear himself admits, during the writing of his book he discovered there had been two earlier English translations one published and one unpublished) Unlike Nicolson, Lear rejects the possibility of Donne having read the Somnium, however he also accepts Kepler’s paranoid suspicions that his little tale was responsible for his mother’s woes devoting several pages of his introduction to the theme adding a great deal of detail of his own invention to the story in a way that makes it difficult to separate the known facts from his speculations. Lear even goes as far as accusing Max Casper, whose biography of Kepler he uses extensively in his book, of failing to correctly join up the dots and nail the lost manuscript of the Somnium as the tinder that started the flames that consumed Katharina.

In his definitive scholarly translation of the Somnium historian of science Edward Rosen, as stated above, demolishes the accusations against Donne but accepts the other accusation without a great deal of comment.

In 1976 popular science writer, Gale E. Christianson, repeated the story in a paper published in the journal Science Fiction Studies, Kepler’s Somnium: Science Fiction and the Renaissance Scientist.

The lunar geography was probably read privately in manuscript form for the last time in 1610. Through a rather complicated and unfortunate series of events, Kepler lost control of a copy in 1611 and a number of individuals—many of them unknown to Kepler personally—gained access to it, including some that the author would not have approved of. The Somnium was written for scientists and was little understood, except on the most superficial level, by those lacking a scientific background. Kepler suggests that it became the subject of gossip in the tonstrinae, the forerunner to the modern coffeehouse.19 Some of those who knew Kepler and his family, or at least thought they did, discovered sufficient autobiographical material in the manuscript to feed the fires of ignorance and superstition then engulfing Germany. They equated Johannes with Duracotus and made particular note of the similarities between Katherine Kepler, the astronomer’s mother, and Fiolxhilde, the fictional peddler of magic charms and herbs. Especially damning was the description of Fiolxhilde as a “wise woman” in league with celestial spirits, nor did Kepler’s joke about the Daemon’s preference for old witches as traveling companions help. To make matters worse, Katherine Kepler was well known for her vile temper and generally cantankerous disposition, not to mention the fact that the aunt who had cared for her as a child was burned at the stake as a witch. The stage was set, charges were leveled, and in 1615 Katherine Kepler was arrested on suspicion of practicing witchcraft. In his attempt to evade the scorn of the Aristotelians by concealing his pro-Copernican work in the guise of classical mythology, Kepler had inadvertently set a trap for himself and his mother, for they had become the unwitting victims of the seventeenth-century European witch-craze.

Johannes Kepler’s reputation as a noted mathematician-astronomer by no means served as a guarantee that Katherine Kepler would escape the fate of thousands of others who had already died at the stake for their alleged complicity in what authorities envisioned as a mass satanic conspiracy. Kepler was well aware of the seriousness of the charges and he put all else aside to work for Katherine’s exoneration. A long, tedious, and taxing legal battle resulted: only after five years, part of which his mother spent in prison, was the old woman released; but the damage had been done. Katherine Kepler died in April of 1622 from causes directly attributable to the rigors of her imprisonment; her son had been able to do little significant work while trying to obtain his mother’s release; and the publication of the Somnium, at least for the present, was out of the question. Historical circumstances, as during his student days at Tübingen in 1593, had again deprived Kepler of the opportunity to publicly air his views. Under these conditions, could it have truly mattered to Kepler whether or not his desire to speak out had been thwarted by a narrow-minded faculty senate impervious to all scientific inquiry deemed anti-Aristotelian, or a group of superstitious and half-crazed witch-hunters who had mistaken fantasy for reality?

Here, although according to her own footnotes her account is based on Nicolson’s Voyages to the Moon, there are no ifs, buts or maybes, Christianson lays the blame for Katharina’s troubles clearly on the “lost” Somnium manuscript.

Kepler’s original footnote is clearly highly speculative and although she hardens it up Nicolson still only sees it, to quote Kepler, as “a spark” that started the rumours against his mother and not an item of evidence at the trial. Although both Lear and Christianson add layers of speculative detail to Nicolson’s account neither of them takes the step of introducing the Somnium into the actual court proceedings. This leaves the question open as to whether the anonymous author of the APS piece consulted another text, as yet unknown to me, which took the fatal misstep from the Somnium as a spark that started rumours to the Somnium as substantive evidence at Katharina Kepler’s trial for witchcraft or whether this anonymous author consulting one or more of the texts that I have quoted put two and two together and made five and in the process set another myth of science free to muddy the waters of science history.


The Somnium is by the way an interesting document in the history of science of the Early Modern Period and well worth reading.

[1] Nicolson, Marjorie Hope, Kepler, the Somnium and John Donne, Journal of the History of Ideas, 1940, Vol. 1 pp. 259-80. Reprinted in Roots of Scientific Thought, eds. Philip P. Wiener and Aaron Noland, New York, Basic Books 1957, pp. 306-27.

[2] Lear, pp. 90-91

[3] John Donne, Ignatius His Conclave, An edition of the Latin and English texts with introduction and commentary by T. S. Healy S.J., Oxford at the Clarendon Press, 1969, p. 7

[4] Kepler’s Somnium: The Dream or Posthumous Work on Lunar Astronomy, Translated with a commentary, by Edward Rosen, University of Wisconsin Press, Madison, Milwaukee, and London, 1967, Appendix E, Kepler and Donne, pp. 212-13

[5] Nicolson 1957 pp. 312-13

[6] Marjorie Hope Nicolson, Voyages to the Moon, The Macmillan Company, New York, 1960, p. 44

[7] John Lear, Kepler’s Dream: With the full text and notes of Somnium, Sive Astronomia Lunaris, Joannis Kepleri Translated by Patricia Frueh Kirkwood, University of California Press, Berkeley ans Los Angeles, 1965.


Filed under Uncategorized

Whewell’s Gazette


Your weekly digest of all the best of

Internet history of science, technology and medicine

Editor in Chief: The Ghost of William Whewell

Volume #1                Monday 23 June 2014


Appearing weekly on Whewell’s Ghost

1 Comment

Filed under Uncategorized

Luca, Leonardo, Albrecht and the search for the third dimension.

Many of my more recent readers will not be aware that I lost a good Internet friend last year with the unexpected demise of the history of art blogger, Hasan Niyazi. If you want to know more about my relationship with Hasan then read the elegy I wrote for him when I first heard the news. Hasan was passionate about Renaissance art and his true love was reserved for the painter Raffaello Sanzio da Urbino, better known as Raphael. Today, 6th April is Raphael’s birthday and Hasan’s partner Shazza (Sharon) Bishop has asked Hasan’s friends in the Internet blogging community to write and post something today to celebrate his life, this is my post for Hasan.


I’m not an art historian but there were a couple of themes that Hasan and I had in common, one of these was, for example, the problem of historical dating given differing calendars. Another shared interest was the history of linear perspective, which is of course absolutely central to the history of Renaissance art but was also at the same time an important theme in Renaissance mathematics and optics. I have decided therefore to write a post for Hasan about the Renaissance mathematicus Luca Pacioli who played an important role in the history of linear perspective.


Luca Pacioli artist unknown

Luca Pacioli
artist unknown

Luca Pacioli was born in Sansepolcro in the Duchy of Urbino in 1445.

Duchy of Urbino  Henricus Hondius 1635

Duchy of Urbino
Henricus Hondius 1635

Almost nothing is known of his background or upbringing but it can be assumed that he received at least part of his education in the studio of painter and mathematician Piero della Francesca (1415 – 1492), who like Pacioli was born in Sansepolcro.

Piero della Francesca Self Portrait

Piero della Francesca
Self Portrait

Pacioli and della Francesca were members of what is now known as the Urbino school of mathematics, as was Galileo’s patron Guidobaldo del Monte (1545 – 1607). These three Urbino mathematicians together with, Renaissance polymath, Leone Battista Alberti (1404 – 1472) all played an important role in the history of linear perspective.


Leon Battista Alberti  Artist unknown

Leon Battista Alberti
Artist unknown

Whilst still young Pacioli left Sansepolcro for Venice where he work as a mathematics tutor. Here he wrote his first book, an arithmetic textbook, around 1470. Around this time he left Venice for Rome where he lived for several months in the house of Alberti, from whom he not only learnt mathematics but also gained good connections within the Catholic hierarchy. Alberti was a Papal secretary.

In Rome Pacioli studied theology and became a Franciscan friar. From 1477 Pacioli became a peripatetic mathematics teacher moving around the courts and universities of Northern Italy, writing two more arithmetic textbooks, which like his first one were never published.

Ludovico Sforza became the most powerful man in Milan in 1476, at first as regent for his nephew Gian Galeazzo, and then, after his death in 1494, Duke of Milan.

Ludovico Sforza Zanetto Bugatto

Ludovico Sforza
Zanetto Bugatto

Ludovico was a great patron of the arts and he enticed Leonardo to come and serve him in Milan in 1482. In 1496 Pacioli became Ludivico’s court mathematicus. Leonardo and Pacioli became colleges and close friends stimulating each other over a wide range of topics.


Leonardo Francesco Melzi

Francesco Melzi

Before he went to Milan Pacioli wrote his most famous and influential book his Summa de arithmetica, geometria, proportioni et proportionalità, which he published in Venice in 1494. The Summa, as it is generally known, is a six hundred-page textbook that covers the whole range of practical mathematics, as it was known in the fifteenth-century. Pacioli was not an original mathematician and the Summa is a collection of other peoples work, however it became the most influential mathematics textbook in Europe and remained so for almost the whole of the sixteenth-century. As well as the basics of arithmetic and geometry the Summa contains the first printed accounts of double entry bookkeeping and probability, although Pacioli’s account of determining odds is wrong. From our point of view the most important aspect of the Summa is that it also contains the first extensive printed account of the mathematics of linear perspective.


Pacioli Summa Title Page

Pacioli Summa
Title Page

According to legend linear perspective in painting was first demonstrated by Fillipo Brunelleschi (1377 – 1446) in Florence early in the fifteenth-century. Brunelleschi never published an account of his discovery and this task was taken up by Alberti, who first described the construction of linear perspective in his book De pictura in 1435. Piero della Francesca wrote three mathematical treatises one on arithmetic, one on linear perspective and one on the five regular Euclidian solids. However della Francesca never published his books, which seem to have been written as textbooks for the Court of Urbino where they existed in the court library only in manuscript. Della Francesca treatment of perspective was much more comprehensive than Alberti’s.

During his time in Milan, Pacioli wrote his second major work his Divina proportione, which contains an extensive study of the regular geometrical solids with the illustrations famously drawn by his friend Leonardo.


Leonardo Polyhedra


These two books earned Pacioli a certain amount of notoriety as the Summa contains della Francesca’s book on linear perspective and the Divina proportione his book on the five regular solids both without proper attribution. In his Lives of the Most Excellent Italian Painters, Sculptors, and Architects, from Cimabue to Our Timesthe Italianartist and art historian, Giorgio Vasari (1511 – 1574)


Giorgio Vasari Self Portrait

Giorgio Vasari
Self Portrait

accused Pacioli of having plagiarised della Francesca, a not entirely fair accusation, as Pacioli does acknowledge that the entire contents of his works are taken from other authors. However whether he should have given della Francesca more credit or not Pacioli’s two works laid the foundations for all future mathematical works on linear perspective, which remained an important topic in practical mathematics throughout the sixteenth and seventeenth centuries and even into the eighteenth with many of the leading European mathematicians contributing to the genre.

With the fall of Ludovico in 1499 Pacioli fled Milan together with Leonardo travelling to Florence, by way of Mantua and Venice, where they shared a house. Although both undertook journeys to work in other cities they remained together in Florence until 1506. From 1506 until his death in his hometown in 1517 Pacioli went back to his peripatetic life as a teacher of mathematics. At his death he left behind the unfinished manuscript of a book on recreational mathematics, De viribus quantitatis, which he had compiled together with Leonardo.

Before his death Pacioli possibly played a last bit part in the history of linear perspective. This mathematical technique for providing a third dimensional to two dimensional paintings was discovered and developed by the Renaissance painters of Northern Italy in the fifteenth century, one of the artists who played a very central role in bringing this revolution in fine art to Northern art was Albrecht Dürer, who coincidentally died 6 April 1528, and who undertook two journeys to Northern Italy explicitly to learn the new methods of his Italian colleagues.

Albrecht Dürer Self Portrait

Albrecht Dürer
Self Portrait

On the second of these journey’s in 1506-7, legend has it, that Dürer met a man in Bologna who taught him the secrets of linear perspective.  It has been much speculated as to who this mysterious teacher might have been and one of the favoured candidates is Luca Pacioli but this is highly unlikely. Dürer was however well acquainted with the work of his Italian colleagues including Leonardo and he became friends with and exchanged gifts with Hasan’s favourite painter Raphael.


Filed under History of Mathematics, History of Optics, Renaissance Science, Uncategorized


The title is supposed to make you think of a typical article in the Daily Fail, Britain’s most obnoxious representative of the gutter press. It represents one of the dominant reactions by members of the Gnu Model ArmyTM to the Cosmos Bruno AffairTM. According to people such as Jason Rosenhouse and P Z Myer the persecution of such notable scientists as Giordano Bruno and Galileo Galilei by the Catholic Church has definitely hindered the progress of science and for good measure they or their supporters quote the words of wisdom of Über-Guru Neil deGasse Tyson that without religion science would be a thousand years more advanced. What an outrage, truly horrific the Church it seems has a lot to answer for, although I find it rather strange that they can’t dish up more examples than poor old Giordano and that universal symbol of Church oppression Galileo. I’m sure if they re-read their Draper-White they could manage to find some new names to beat the ignorant historians around the head with. I say ignorant historians because it was the historians complaining about the Bruno cartoon on the first episode of Cosmos that has brought out this charge by these stalwart defenders of scientific integrity.

Let us assume for a moment that Rosenhouse-Myer are correct and that the Catholic Church did in fact persecute Bruno and Galileo to block scientific progress does this necessarily mean that they were successful in their dastardly deeds? Did they truly manage to interrupt, slow down, or hinder the adoption, acceptance or acknowledgement of the heliocentric hypothesis or the belief in an infinite universe or the perception that the sun is a star or vice versa? No doubt about it, this is a serious charge and one that should definitely be explicated.

Now Myer and Tyson are both practicing scientists whilst Rosenhouse is a mathematician, all of them work in disciplines that require one, if one makes a substantial claim, to provide the appropriate evidence or proof to support that claim. What is with their claim that religion has blocked the advance of science in general or in the case of Bruno and Galileo the acceptance of modern astronomy and cosmology in particular? Have our scientific practitioners provided the necessary evidence to back up their claims? Do they provide a tightly argued historical thesis based on solid documentary evidence to prove their assertions? Can they demonstrate that if the Church had not intervened modern astronomy would have become accepted much earlier than it was? Given their outspoken support of the ‘scientific method’, whatever that might be, you would expect them to do so, wouldn’t you? Do they hell! They don’t waste one single word on the topic. No evidence, no proofs, no academic arguments just plain straightforward unsubstantiated claims in the style of the gutter press. A pretty poor showing for the defenders of scientific faith.

But could they still be right? Even if they don’t take the trouble to provide the historical discourse necessary to substantiate their claims, could it be true that the Church’s actions against Bruno and Galileo did in fact have a negative influence on the acceptance of heliocentricity and other aspects of modern astronomy and cosmology? Let us examine the historical facts and answer the questions that Rosenhouse-Myer and Tyson are apparently above answering, the truth being apparently so obviously clear that they don’t require answering.

To start with the poor Giordano, Bruno was one of those who advocated Copernicus’ heliocentric astronomy already in the sixteenth-century. He however went beyond Copernicus in a series of cosmological speculations and it is these that Cosmos thought to be so important that they devoted eleven minutes of a forty-five minute broadcast to them. I shall deal with the acceptance of heliocentricity separately later and only address Bruno’s cosmology now. Copernicus himself expressly left the question as to whether the cosmos is finite or infinite, as he said, to the philosophers, with good reason. This question was purely speculative and could not, with the evidence and possibilities available to the Renaissance astronomer, be addressed in anything approaching a scientific manner. To all intents and purposes the cosmos appeared finite and Renaissance scholars had no means available to prove otherwise. Bruno’s speculation was of course not new.

In his own times Nicolas Cusanus had already considered the question and earlier, in the first-century BCE, the Epicurean philosopher poet Lucretius, Bruno’s inspiration, had included it in his scientific poem De rerum natura. Lucretius of course did not invent the concept but was merely repeating the beliefs of the fifth-century BCE Greek atomists. All of this demonstrates that the idea of an infinite cosmos was fairly common at the beginning of the seventeenth century and nothing the Church said or did was likely to stop anybody speculating about it. The thing that prevented anybody from going further than speculation was the lack of the necessary scientific apparatus to investigate the question, a similar situation to that of the string-theorists and multiverse advocates of today.

This does not mean that astronomers did not address the problem of the size of the cosmos and the distance to the stars. Amongst others Galileo, Jeremiah Horrocks, Christiaan Huygens and Isaac Newton all tried to estimate/calculate the distances within the solar system and outward towards the stars. First in the middle of the eighteenth century with the transit of Venus measurements were these efforts rewarded with a minimum of success. It wasn’t until the early nineteenth century that the first stellar distance measurements, through stellar parallax, were achieved. All of these delays were not caused by anything the Church had done but by the necessity of first developing the required scientific theories and apparatus.

Bruno’s next cosmological speculation was that the sun and the stars were one and the same. Once again there was nothing new in this. Anaxagoras had already had the same idea in the fifth-century BCE and John Philoponus in the fifth-century CE. Once again the problem with this speculation was not any form of religious objection but a lack of scientific theory and expertise to test it. This first became available in the nineteenth century with development of spectroscopy. This of course first required the development of the new matter theory throughout the seventeenth and eighteenth centuries, a process that involved an awful lot of science.

Bruno’s last speculation and the one that bothered the Church was the existence of inhabited planets other than the Earth. Again this was nothing new and whatever the Church might have thought about it that speculation generated a lively debate in the seventeenth century that is still going on. We still don’t actually know whether we are alone or not.

Given my knowledge of the history of science I can’t see anywhere, where the Church hindered or even slowed down scientific progress on those things that Bruno speculated about in his cosmological fantasy. But what about heliocentricity, here surely the Church’s persecution of both Bruno and Galileo hindered science bay the hounds of anti-religious rationalism.

What follows is a brief sketch of the acceptance of the heliocentric astronomy hypothesis in the sixteenth and seventeenth centuries. This is a subject I’ve dealt with before in various posts but it doesn’t hurt to repeat the process as there are several important lessons to be learnt here. To begin with there is a common myth that acceptance of ‘correct’ new scientific theories is almost instantaneous. To exaggerate slightly, Einstein published his General Theory of Relativity in 1915 and the world changed overnight or at the latest when Eddington confirmed the bending of light rays conform with general relativity in 1919. In reality the acceptance of the general theory of relativity was still a topic of discussion when I was being educated fifty years later and that despite numerous confirmatory tests. Before it is accepted a major new scientific theory must be examined, questioned, tested, reformed, modified and shown to be superior to all serious alternatives. In the Early Modern Period with communication considerably slower this process was even slower.

Copernicus published his De revolutionibus in 1543 and there were only ten people in the entire world, including Bruno but much more importantly both Kepler and Galileo, who accepted it lock, stock and barrel by 1600. This system had only one real scientific advantage over the geocentric one; it could explain the retrograde movement of the planets. However this was not considered to be very important at the time. There were some relatively low-key religious objection but these did not play any significant role in the very slow initial acceptance of the theory. The problematic objections were observationally empirical and had already been discussed by Ptolemaeus in his Syntaxis Mathematiké in the second-century CE. Put very simple if the world is spinning very fast and hurtling through space at an alarming speed why don’t we get blown away? Copernicus had the correct answer to this problem when he suggested that the atmosphere was carried round with the earth in the form of a bubble so to speak. Unfortunately he lacked the physics to explain and justify such a claim. It would take most of the seventeenth century and the combined scientific efforts of Kepler, Galileo, Stevin, Borelli, Descartes, Pascal, Huygens, Newton and a whole boatload of lesser lights to create the necessary physics to explain how gravity holds the atmosphere in place whilst the earth is moving.  This process was not hindered by the Church in anyway whatsoever.

There was a second level of acceptance of Copernicus theory, an instrumental one, as a mathematical model to deliver astronomical data for various applications, astrology, cartography, navigations etc. Here the system based on the same inaccurate data as the Ptolemaic one did not fair particularly well. Disgusted by the inaccuracy of both systems Tycho Brahe started a new long-term observational programme to obtain new accurate data. Whilst doing so he developed a third model, the so-called geo-heliocentric model, in which the planets orbited the sun, which in turn orbited the stationary earth. This model had the advantage of explaining retrograde motion without setting the earth in motions, a win-win situation.

The first major development came with the invention of the telescope in 1608 and its application to astronomical observation from 1609 onwards. The first telescopic discoveries did not provide any proofs for either the Copernican or the Tychonic models but did refute both the Aristotelian homocentric model and the Ptolemaic model. Around the same time a new candidate, the Keplerian elliptical astronomy, entered the ring with the publications of Kepler’s Astronomia nova in 1609. For a full list of the plethora of possible astronomical models at the beginning of the seventeenth century see this earlier post.

By 1620 the leading candidate was a Tychonic model with diurnal rotation. It should be pointed out that due to the attempts of Galileo and Foscarini to reinterpret Holy Scripture in favour of heliocentricity the Catholic Church had entered the action in 1615 and forbidden the heliocentric theory but not the heliocentric hypothesis. The distinction is important. The theory says heliocentricity is a scientific fact the hypothesis says it’s a possibility. At this time heliocentricity was in fact an unproved hypothesis and not a theory. This is the point where Rosenhouse-Myers step in and claim that the Church hindered scientific progress but did they. The straightforward answer is no. The astronomers and physicist carried on looking for answers to the open questions and solutions to the existing problems. There is no evidence whatsoever of a slowing down or interruption in their research efforts.

Between 1618 and 1621 Kepler published his Epitome astronomiae Copernicanae explaining his elliptical astronomy and his three laws of planetary motion in simple terms and in 1627 the Tabulae Rudolphinae the astronomical tables based on his system and Tycho’s new accurate data. It was these two publications that would lead to the general acceptance of heliocentricity by those able to judge by around 1660. Kepler’s publications delivered the desired accurate prognoses of planetary positions, eclipses etc. required by astrologers, cartographers, navigators etc.

At no point in the 120 years between the initial publication of Copernicus’ De revolutionibus and the general acceptance of heliocentricity in the form of Kepler’s elliptical astronomy is there any evidence of the Church having slowed or hindered progress in this historical process. To close it should be pointed out that it would be another seventy years before any solid scientific evidence for the heliocentric hypothesis was found by Bradley, in the form of stellar aberration.






Filed under History of Astronomy, History of science, Myths of Science, Uncategorized

A double heliocentrism anniversary?

Georg Joachim Rheticus was born 500 years ago today in Feldkirch, now in Austria, on 16th February 1514, as Dennis Danielson put it in the title of his excellent Rheticus biography, he was the first Copernican. [1] It was Rheticus who travelled to Frauenburg in 1539 and over many months persuaded Copernicus to publish his De revolutionibus, publishing his own Narratio prima, to test the water for the heliocentric hypothesis in 1540.

Rheticus' Horoscope taken from Danielson The First Copernican p. 16

Rheticus’ Horoscope taken from Danielson The First Copernican p. 16

Rheticus’ name will always be associated with that of Copernicus and heliocentrism.  Another who is inseparably bound up with Copernicus and heliocentrism is Galileo Galilei who celebrated his 450th birthday yesterday, or did he? All over the Internet people were celebrating Galileo’s 450th birthday yesterday, the 15th February, Both the MacTutor History of Mathematics article and the English Wikipedia give his birthdate as 15th February 1564, the latter citing Galileo at Work by Stillman Drake, the Grand Seignior of Galileo studies, but was it? Already on Thursday last week as people were gearing up for the great day Lorenzo Smerillo of Montclair State University pointed out on the History of Astronomy Mailing List that Galileo was actually born on the 16th February and not the 15th.  Somewhat confused, I turned to the two most recent   scholarly biographies of Galileo, David Wootton’s Galileo Watcher of the Skies[2] and John Heilbron’s Galileo[3]; the former says the 15th, the latter the 16th. Interestingly both refer to Galileo’s horoscope, which he cast himself. Another Galileo expert William Shea gives the birthdate in his Galileo Selected Writings, as the 16th and in a footnote explains the reason for the confusion, the same one that Smerillo had already given and which I will now explain.

Galileo's Horoscope

Galileo’s Horoscope

As you can see Galileo’s horoscope gives the date and time of birth twice:

1564. 15. febr. h. 22.30. lat. 42. 30

16. febr. h. 4. pm


The first set of figures are given in Italian hours, which follow the Islamic and Jewish custom of numbering the hours of the day from sunset. Sunset on the 15th February in Northern Italy was at 5:30 pm so the 22.30 hour on the 15th would be 4 pm on the 16th. This is of course the second set of figures giving the date and time of birth in French hours. This shows clearly that Galileo was born on the 16th not the 15th.  The 3.30 is probably an error estimate based on uncertainty as to the time of sunset.

Confusingly Wootton argues against this interpretation insisting on the 15th in a complex discussion of the subject.[4]

Our double anniversary is however somewhat confused by another piece of calendrical confusion. Both of our heliocentric astronomers were born before the calendar reform so their birthdates are given according to the Julian Calendar, this of course means that our double anniversary is not actually today but first on the 26th February.

Just to throw another spanner into the works, both of the birthdates are taken from Renaissance horoscopes making them instantly suspect, why? It was a common practice in the Renaissance for astrologers to rectify horoscopes. This was the practice of adjusting times of birth by hours and even sometimes a whole day to make the resulting horoscope more harmonious with the real life of the horoscope’s subject. Rheticus for example was known to be an adherent of this practice.

[1] Dennis Danielson, The First Copernican, Georg Joachim Rheticus and the Rise of the Copernican Revolution, Walker and co., New York, 2006

[2] David Wootton, Galileo Watcher of the Skies, Yale University Press, New Haven and London, 2010

[3] J. L. Heilbron, Galileo, Oxford University Press, Oxford, 2010

[4] David Wootton, Accuracy and Galileo: A Case Study in Quantification and the Scientific Revolution, The Journal of the Historical Society, Vol.10, 2010 pp. 43-55


Filed under History of Astronomy, Uncategorized

Alas, poor Wallace


I have never reblogged somebody else’s post from another blog but this superb post on the current public misrepresentation of Alfred Russel Wallace by his fan club, posted by John van Wyhe on Rebekah “Becky” Higgitt’s teleskopos blog, is so in tune with the ethos of the Renaissance Mathematicus that I have decided to reblog it here. Read and enjoy!

Originally posted on teleskopos:

This guest post by John van Wyhe is the result of my asking him to expand on a point raised on Facebook…

This year is the centenary of the death of Victorian naturalist Alfred Russel Wallace. This has sparked an unprecedented amount of media attention. (Compare with the 2009 Darwin bicentenary) The Wallace “experts” most often interviewed, however, are usually not historians of science, but scientists or enthusiasts. This would be unacceptable for physics, economics or even sports. So why is it so routinely the case for history of science? It is a small field, but there are many departments and scholars in our universities who conduct sophisticated research on science past. If we want to tell the public about Victorian science, surely historians of science should be in the conversation?

In the hands of admiring amateurs, Wallace has evolved into a heroic but forgotten genius – wrongfully obscured…

View original 687 more words

1 Comment

Filed under Uncategorized