Category Archives: History of Astronomy

“…realigning the heavens with a single stroke of the brush.“ – Really?

Recently on twitter I stumbled across a problematic discussion, as to which single image had most changed the course of science. Although the various participants made stimulating and interesting suggestions, Darwin’s tree diagram, Franklin’s photo of DNA etc. I found this discussion problematic because it suffers from the same difficulties as discussion in the history of science as “the first”, “the greatest”, “the father of” and all similar hyperbolic claims, just how do you measure and compare the numerous candidates that spring to mind?

This discussion didn’t just appear out of cyberspace on somebody’s whim but was provoked by Joe Hanson at It’s OK to be Smart and his post Message from the Moon, which in turn was provoked by the set of washes of the moon by Galileo that had been circulating on Twitter a couple of days before.

Galileo's washes of the moon.

The watercolour sketches that Galileo made of his initial telescopic observations of the moon in 1609/10 are iconic images in the history of science that did have a major impact on the way humanity viewed the cosmos but there are an awful lot of inaccuracies in Hanson’s description of that impact that I am going to analyse here.

Hanson’s first minor error is to claim that the images he has posted on his blog are included in the Sidereus Nuncius. Galileo’s legendary publication does indeed included woodcuts of five of his lunar watercolours but the sheet displayed by Hanson, and here above, was not included, a trivial but important point.

Hanson informs us:

But hiding in their shadows lies a greater significance. The squiggled edges of that bleeding ink bear an observation that altered the heavens themselves. Or at the very least, our view of them.

And then goes on to explain why:

In 1610, cosmology, not that it had much to show for itself as a science, was still based on the ideas of Aristotle, who by this time had been dead for 18 centuries. So current! Copernicus’ observation that the Earth orbited the sun, first published in 1543, had begun to challenge Aristotelian supremacy, it wasn’t exactly a popular idea. 

Aristotle’s cosmological beliefs were based on the idea that the heavens were made of a perfect substance called “aether”, and therefore the circular motions and spherical shapes of heavenly bodies were also perfect. Earth, he claimed, was inherently imperfect, as were all the things that existed upon it. Everything in the heavens was awesome, and Earthly matter was inherently “just okay”, even if its name was Aristotle. This was one of the reasons people found Copernicus’ claims so hard to swallow. The imperfect Earth among the perfect heavens? Heresy! [emphasis in original]

Somewhat sloppily expressed but so far so good, although placing the earth in the heavens didn’t really play that much of a role in the initial rejection of Copernican cosmology being insignificant in comparison to the physical problems engendered by a moving earth. Hanson’s argument is that because Galileo’s interpretations of what he saw through his telescope, and don’t forget that they are interpretations, clearly suggested that the moon was not smooth and perfect but had a landscape like the earth he had realigned “the heavens with a single stroke of the brush”; a nice literary figure of speech but unfortunately one that doesn’t fit the historical facts.

Already in antiquity people, had speculated that the differing shades of the moons surface were the result of a mountainous landscape. This viewpoint was expressed most notably by Plutarch in his On The Face Which Appears in the Orb of the Moon, one of his collection of essays, the Moralia. This was well known and widely read in the sixteenth-century and was even used by Kepler as a springboard for his own “lunar geography”, the Somnium, written but not published before Galileo made his telescopic discoveries. This widespread alternative concept of the lunar surface made it much easier to accept Galileo’s discovery and considerably weakened any impact that it might have had on Aristotelian cosmology. However this was not the only factor that gives the lie to Hanson’s “single stroke of the brush” postulate. Aristotle’s division of the cosmos into two spheres one superlunar, which was perfect, unchanging and eternal, everything below, and the other sublunar, which was imperfect, constantly changing and subject to decay had been under attack for most of the century preceding Galileo’s discoveries, as I have already outlined in my post on Comets and Heliocentricity.

In the 1530s observations of several comets had led many leading European astronomers to the conclusion that comets were superlunar phenomena and not sublunar ones as Aristotle’s cosmology required. Comets are of course anything but perfect, unchanging and eternal. In the 1570s another generation of European astronomers, Tycho Brahe and Michael Maestlin to the fore, confirmed this conclusion making life more than somewhat difficult for any cosmologist who wished to maintain a strict Aristotelian party line. To make matters worse the stellar novae of 1572 and 1604 observed once again by Europe’s finest watchers of the heavens and determined by them to be unquestionably superlunar really put the kibosh on Aristotle’s wonderful division of the cosmos. All in all by 1610 Aristotle’s cosmology was already looking distinctly unhealthy and Galileo’s discovery of the lunar landscape far from being an unexpected deadly bolt out of the blue was just another blow helping it on its way to its grave.

Hanson might be forgiven for his over emphasis of the impact of Galileo’s lunar watercolours based obviously on his ignorance of Renaissance astronomical and cosmological history but the content of his closing paragraph displays an ignorance that I, for one, find hard to forgive. Our intrepid non-historian writes:

Galileo’s Sidereus Nuncius [emphasis in original] also included newly detailed maps of the constellations and the mention of four moons of Jupiter (although detailed observations of those were still centuries away), [my emphasis] but it was his drawings of our moon that bore the most impact on future astronomical science, realigning the heavens with a single stroke of the brush.

Having over emphasised the significance of the impact of Galileo’s lunar watercolours Hanson dismisses his discovery of the moons of Jupiter in a throwaway comment. He couldn’t demonstrate his ignorance of the material more spectacularly.

It was of course Galileo’s discovery of the four largest moons of Jupiter that caused the sensation and also did the most damage to Aristotelian cosmology, when he published the Sidereus Nuncius in 1610. Central to Aristotelian cosmology was the principle of homo-centricity, i.e. the concept that all celestial bodies, the sphere of the fixed stars and the seven planets, revolve around a common centre, the earth. The discovery of the Galilean moons, as they came to be known, was a direct empirical proof that the principle of homo-centricity was wrong. It lent indirect support to heliocentricity, which required two centres of revolution the sun for the fixed stars and the six planets and the earth for the moon. It was Galileo’s discovery of the Medician Stars, as he called them, which led to his much desired appointment as court philosophicus and mathematicus in Florence and professor of mathematics at the University of Pisa without teaching duties. Catapulting him almost overnight from being an obscure, ageing professor of mathematics to being Europe’s most notorious astronomer. The four moons of Jupiter are not “mentioned” in Sidereus Nuncius they are the reason for its hurried and secretive, to prevent anybody else beating him to the punch, composition and publication.

The illustrations of the moon in the Sidereus Nuncius are the eye candy, which the reader can admire but the far less visually spectacular diagrams of the positions of the four moons relative to Jupiter are the explosive content that make this slim pamphlet one of the most important scientific publications of all time and elevated Galileo into the pantheon of scientific heroes.

Page from Galileo's observation log displaying position of the moons relative to Jupiter

Page from Galileo’s observation log displaying position of the moons relative to Jupiter

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

How much can you get wrong in an eight hundred word biographical sketch of a very famous sixteenth and seventeenth-century mathematicus and philosophicus? – One helluva lot it seems?

If someone is doing the Internet equivalent of being a big-mouthed braggart and posting an article with the screaming title, “10 Absurdly Famous People You Probably Don’t Know Enough About” you would expect them to at least get their historical facts right, wouldn’t you? Well you would be wrong at least as far as “absurdly famous” person number seven is concerned, Galileo Galilei. Tim Urban the author of this provocative article on the ‘Wait But Why’ blog appears to think that history of science is something that you make up as you go along based on personal prejudice mixed up with some myths you picked up some night whilst drunk in a bar. Having not had a real go at somebody else’s terrible history of science for sometime now and not having deflated my favourite punching bag, Galileo or rather the hagiographic imbeciles who write about him, for even longer I thought I would kill two birds with one stone and correct Mr Urban’s little piece as it were a high school term paper. The blue text is original Urban the black comments are mine.

Galileo-300x263

Lived: 1564 – 1642

He makes a promising start in that he at least got the years of birth and death right, although with the same amount of effort he could have given us the exact dates – 15 February 1564 – 8 January 1642

In 11 words: Rare giant of scientific advancement fighting against hopelessly-backward Catholic Church

After that reasonably good beginning we go rapidly down hill. As I have commented on a number of occasions Galileo was by no means as rare or as gigantic as he is usually painted. He also spent most of his life getting along very happily with the Catholic Church with whom he was on good terms and which was in a lot of things, including scientific one, anything but hopelessly-backward. Just to quote one example about which I’ve blogged in the past, it was the Jesuit astronomers at the Collegio Romano who delivered the very necessary scientific confirmations of Galileo’s telescopic astronomical discoveries and then invited Galileo to Rome to celebrate them.

His main thing: Einstein called Galileo “the father of modern science,” which sums things up pretty nicely.

Einstein, as a leading historian of Renaissance science is of course highly qualified to make such a judgement. Regular readers of this blog should by now know my opinion of such expressions as “the father of” and in particular their use to describe Galileo. For those that don’t I recommend my post, “Extracting the stopper”, as a good starting-point.

Galileo made major discoveries about the motion of planets and stars, the motion of uniformly accelerated objects (i.e. that two objects would fall at the same rate regardless of their masses), sound frequency, and the basic principle of relativity, among other things

I must admit to being somewhat perplexed by the claim that Galileo made “major discoveries about the motion of planets and stars”; I’m not aware of any achievements by the good man in this direction, perhaps somebody could enlighten me?

—and major advancements in technology, including inventing or improving upon the telescope, microscope, thermometer, pendulum, and the compass.

Galileo made an improved telescope and might have been one inventor of the microscope, although this is clouded in uncertainty. He experimented with a thermoscope, not a thermometer, but probably did not invent it. He neither invented nor improved the pendulum and I don’t think he or anybody else ever claimed that he did so. He did however investigate the properties of the pendulum, although the law he set out for the pendulum is actually wrong.

The last claim is quite funny and turns up time and time again quoted by people who literally don’t know what they are talking about. Galileo had nothing to do with the (magnetic) compass but manufactured and marketed an improved version of the sector, or proportional or military compass. This is a hinged ruler with numerous scales used for making mathematical calculations particularly by artillery officers. This instrument has several independent inventors; the one improved by Galileo was invented by his mentor, Guidobaldo del Monte.

Galileo's military compass

Galileo’s military compass

His work was central to most future developments in science, including those of Newton and Einstein, and most of what he discovered was in contradiction with conventional wisdom—his work was as shocking and revolutionary in the 1600s as Einstein proclaiming that “time is relative” was in the 1900s.

This is typical of the hagiographical hogwash dished up by people writing about Galileo. The only part of Galileo’s work ‘central’ to Newton was the parabolic flight path of projectiles, which was discovered independently by other including Thomas Harriot. His only connection to Einstein is the rejection of Galilean relativity in the theory of the latter. Very little of Galileo’s own work was shocking and the only parts that were in anyway revolutionary were the laws of fall, discovered independently and earlier by Benedetti, and heliocentricity, a field in which Galileo was not the discoverer or inventor but merely the polemicist, who probably did more damage than good through his advocacy.

But the most impressive part about Galileo, other than his ability to make such a cranky facial expression in the above painting, is that he did everything he did in the face of threats and repression by the Catholic Church and their inane loathing of ground breaking scientific advancements.

I begin to get the impression that our author has a personal problem with the Catholic Church, which did not have an “inane loathing of ground breaking scientific advancements”, and except in the one case Galileo did nothing in “the face of threats and repression by the Catholic Church” but actually received much support and encouragement from many leading figure in the Church hierarchy for the vast majority of his life and work.

The main thing the Church kept yelling at Galileo for was his backing and advancement of Copernicus’s heliocentric model of the universe, which puts the sun, instead of the Earth, in the center of the solar system and suggests that the Earth’s spinning is why the sun appears to revolve around the Earth. The Church declared heliocentrism to be “foolish and absurd in philosophy, and formally heretical since it explicitly contradicts in many places the sense of Holy Scripture”—in particular, the parts of scripture that said things like, “the world is firmly established, it cannot be moved” and “the Lord set the earth on its foundations; it can never be moved”—and ordered Galileo “to abstain completely from teaching or defending this doctrine and opinion or from discussing it… to abandon completely… the opinion that the sun stands still at the center of the world and the earth moves, and henceforth not to hold, teach, or defend it in any way whatever, either orally or in writing. “That would be like modern-day governments imprisoning geologists who studied ancient rocks because their findings conflicted with the Bible’s accounts of the Great Flood. Or like preventing gay people from getting married because of passages in the Bible about sexual orientation. Thankfully, those times are over.

The above paragraph contains the real reason that Mr Urban is frothing at the mouth about the Catholic Church, Galileo’s clash with the Church on heliocentricity. Once again I’m not going to go into great detail about the whole sad sorry affair but will for the umpteenth time repeat that the central problem had very little to do with science, astronomy, cosmology or whatever but with the fact that in 1615 Galileo tried to tell the Church how to interpret the Bible. If he had not done this and instead bided his time patiently, as suggested by his friends, including Cardinal Maffeo Barberini the later Pope Urban VIII, the Church would in its own time almost certainly have adopted heliocentricity. Instead of which through Galileo’s pig-headedness the acceptance of heliocentricity by the Catholic Church was delayed by about one hundred and fifty years.

So the Church repressed the greatest genius of the century,

There’s no such thing as the greatest!

… finding him “vehemently suspect of heresy,” and placed him under house arrest for the rest of his life. Luckily, Galileo just hung out on his couch and kept doing his thing, publishing some of his most important works while under house arrest.

I know Galileo fans and militant atheists don’t like to hear this but, for the ‘crime’ of which he was found guilty, Galileo was treated very, very gently and his sentence was very mild.

Other things:

  • Galileo never married, having all three of his children out of wedlock with the same woman.
  • We got something right!
  • One of the reasons Galileo started inventing things (like the telescope) in the first place was that he badly needed money to deal with all the money his starving artist little brother kept “borrowing” from him.
  • Like many Renaissance mathematicians Galileo supplemented his income by designing, manufacturing and selling scientific instruments. He didn’t invent the telescope! Galileo was notoriously always short of money not because he supported his little brother financially, which he did, but because he enjoyed the good life and tended to live beyond his means.
  • He was briefly a professor at the University of Pisa, but he was inappropriate with his students and the university didn’t renew his contract.
  • The second part of the above sentence is a pure fabrication. Galileo was professor of mathematics in Pisa from 1589 till 1592 when he applied for and received the more prestigious and better-paid professorship for mathematics in Padua where he remained until 1610.
  • Despite his conflicts with the Church, Galileo was a devout Catholic. He briefly became a priest before his father convinced him to go into medicine, and his two daughters were nuns. But he was critical of the Church’s repression of science, stating, “Holy Writ was intended to teach men how to go to Heaven, not how the heavens go.”
  • That Galileo was a devout Catholic is a standard claim in the history of science repeated, I think, to make the Church look worse for their persecution of the man. This claim has been strongly challenged by Renaissance historian; David Wootton in his biography “Galileo: Watcher of the Skies” (Yale University Press, 2010), which paints Galileo convincingly as a very lax Catholic and possibly an unbeliever. Galileo was never a priest but did spend a few months in a monastery as a teenage novice, although he never took holy orders. Galileo’s two daughters were placed in a monastery because, being illegitimate, he considered them unmarriageable and also to spare him the cost of their dowries, a standard procedure in that period.
  • One of Galileo’s worst offenses against the Church was creating a character called Simplico in his famous book Dialogue Concerning the Two Chief World Systems, who always presented the old, incorrect, geocentric view. Simplico suggests “simpleton” in Italian just like it does in English, and in the book, Simplico does not come off very well. The issue is that a lot of what Simplico says in the book were well known to be the direct views of the Pope (Urban VIII), indirectly insulting the Pope and hastening Galileo’s path toward house arrest.
  • The character in the Dialogo who presents the case for geocentricity is called Simplicio not Simplico. The insult of the Pope was much more direct than suggested here. When Urban VIII granted Galileo permission to write a book explaining both geocentricity and heliocentricity, in order to prove that Catholics were not ignorant of the latter theory, he specifically instructed Galileo to include his own theological argument against deciding for one system over the other because this would “limit and restrict the Devine power and wisdom to some particular fancy of my own”. A not unreasonable viewpoint given that there were no proofs for the heliocentric system at that time. Galileo did as instructed including exactly those words in the final speech of Simplicio, the simpleton, on the last page of the book, who had had seven kinds of intellectual shit kicked out of him in the preceding four hundred pages (in the edition I own) by the other two characters. This really reduced Urban’s argument to a joke! Not a smart move, Signore Galilei.
  • It wasn’t until 200 years later in 1835 that the Church finally stopped its prohibition of books advocating heliocentrism and not until 1992 that the Vatican officially cleared Galileo’s name of any wrongdoing.
  • The church allowed the publication of an edition of Galileo’s works, excluding the Dialogo, in 1718 just 76 years after his death. In 1741 a complete edition of his works was authorised by Pope Benedict XIV. The general ban on works advocating heliocentricity was lifted in 1758.
  • It should be noted that Galileo’s church difficulties occurred in the heart of the Renaissance. You can only imagine what it was like to be a scientist in the far more repressive Middle Ages (and how much potential scientific advancement was stifled).
  • We’re back in anti-Church bullshit city! Within the history of science Galileo’s difficulties with the Church, which he largely brought down on his own head, remain a largely isolated incident. The Middle Ages were by no means more repressive than the Renaissance and in fact much scientific progress was made during the Middle Ages, following the re-establishment of an urban culture around 1000 CE. Also it should be noted that the majority of that progress was made by members of the Catholic Church. Galileo was very much aware of the work of his medieval predecessors and built his own work on the foundations that they had constructed.
  • Some weirdo cut the middle finger off of Galileo’s corpse a century after his death, and it is currently on display at the Museo Galileo in Florence.
  • He got something right again!
  • Galileo’s dad begrudgingly allowed him to leave medicine in favor of mathematics and died a few years later when Galileo was an amateur math professor—he had no idea his son was anything special, let alone “the Father of Modern Science.”
  • It is true that Vincenzo Galilei was not particularly enthusiastic when his son abandoned his medical studies, however Galileo was never an “amateur math professor” but a fully paid professional. On the “Father of Modern Science”, see above.

2014 equivalent: Elon Musk

I find the concept of Elon Musk being the 2014 equivalent of Galileo Galilei quite simply mindboggling!

Mr Urban your term paper does not meet the required standards. Your research is to put it mildly very sloppy and personal prejudice is not a substitute for scholarly endeavour, therefore I cannot award you anything but an F!

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

Comets and Heliocentricity: A Rough Guide

In the standard mythologised history of astronomy of the Early Modern Period comets are only mentioned once. We get told, in classical hagiographical manner, how Tycho Brahe observed the great comet of 1577 and thus smashed the crystalline spheres of Aristotelian cosmology freeing the way for the modern astronomy. That’s it for comets, their bit part in the drama that is the unfolding of the astronomical revolution is over and done with, don’t call us we’ll call you. The problem with this mythological account is that it vastly over emphasises the role of both Tycho and the 1577 comet in changing the view of the heavens and vastly under rates the role played by comets and their observations in the evolution of the new astronomy in the Early Modern Period. I shall deal with the crystalline spheres and their dissolution in a separate post and for now will follow the trail of the comets as they weave their way through the fifteenth, sixteenth and seventeenth centuries changing our perceptions of the heavens and driving the evolution of the new astronomy. I have dealt with various aspects of this story in earlier posts but rather than simple linking I will outline the whole story here.

In antiquity comets were a phenomenon to be marvelled at and to be feared. Strange apparitions lighting up the skies unpredictably and unexplainably, bringing with them, in the view of the astrology priests of earlier cultures, doom and disaster. As with almost all things Aristotle had categorised comets, fitting them into his grand scheme of things. Aristotle’s cosmology was a cosmology of spheres. In the centre resided the spherical earth, on the outer reaches it was enclosed in the sphere of the fixed stars. Between theses two were the spheres of the planets centred on and spreading outwards from the earth, Moon, Mercury, Venus,  Sun, Mars, Jupiter Saturn. This onion of celestial spheres was split into two parts by the sphere of the moon. Everything above this, superlunar, was perfect, unchanging and eternal, everything below, sublunar, imperfect, constantly changing and subject to decay. For Aristotle comets were a sublunar phenomenon and were not part of astronomy, being dealt with in his Meteorology, his book on atmospheric phenomena, amongst other things.

However Aristotle’s was not the only theory of comets in ancient Greek philosophy, the Stoics, whose philosophy was far more important and influential than Aristotle’s in late antiquity had a very different theory. For the Stoics the cosmos was not divided into two by the sphere of the moon but was a single unity permeated throughout by pneuma (whatever that maybe!). For them comets were not an atmospheric phenomenon, as for Aristotle, but were astronomical objects of some sort or other.

In the High Middle Ages as higher learning began to flourish one more in Europe it was Aristotle’s scientific theories, made compatible with Christian theology by Albertus Magnus and his pupil Thomas Aquinas, that was taught in the newly founded universities and so comets were again treated as atmospheric phenomena up to the beginning of the fifteenth century.

The first person to view comets differently was the Florentine physician and mathematicus Paolo dal Pozzo Toscanelli (1397–1482), best known for his letter and map supplied to the Portuguese Crown confirming the viability of Columbus’ plan to sail westwards to reach the spice islands. In the 1430s Toscanelli observed comets as if they were astronomical object tracing their paths onto star-charts thereby initiating a new approach to cometary observation. Toscanelli didn’t publish his observations but he was part of a circle humanist astronomers and mathematicians in Northern Italy who communicated with each other over their work both in personal conversation and by letter. In the early 1440s Toscanelli was visited by a young Austrian mathematician called Georg Aunpekh (1423–1461), better known today by his humanist toponym, Peuerbach. We don’t know as a fact that Toscanelli taught his approach to comet observation to the young Peuerbach but we do know that Peuerbach taught the same approach to his most famous pupil, Johannes Müller aka Regiomontanus (1436–1476), at the University of Vienna in the 1450’s. Peuerbach and Regiomontanus observed several comets together, including Halley’s Comet in 1456. Regiomontanus wrote up their work in a book, which included his thoughts on how to calculate correctly the parallax of a comparatively fast moving object, such as a comet, in order to determine its distance from earth. The books of Peuerbach and Regiomontanus, Peuerbach’s cosmology, New Theory of the Planets, published by Regiomontanus in Nürnberg in 1473, and their jointly authored epitome of Ptolemaeus’ Almagest, first published in Venice in 1496, became the standard astronomy textbooks for the next generation of astronomers, including Copernicus. Regiomontanus’ work on the comets remained unpublished at the time of his death.

Whereas in the middle of the fifteenth century, as Peuerbach and Regiomontanus were active there were very few competent astronomers in Europe the situation had improved markedly by the 1530s when comets again played a central role in the history of the slowly developing new astronomy. The 1530s saw a series of spectacular comets that were observed with great interest by astronomers throughout Europe. These observations led to a series of important developments in the history of cometary observation. Johannes Schöner (1477–1547) the Nürnberger astrologer-astronomer published Regiomontanus’ book on comets including his thoughts on the mathematics of measuring parallax, which introduced the topic into the European astronomical discourse. Later in the century Tycho Brahe and John Dee would correspond on exactly this topic. A discussion developed between various leading astronomers, including Peter Apian (1495–1552) in Ingolstadt, Nicolaus Copernicus (1473–1543) in Frauenburg, Gemma Frisius (1508–1555) in Leuven and Jean Péna (1528 or 1530–1558 or 1568) in Paris, on the nature of comets. Frisius and Pena in Northern Europe as well as Gerolamo Cardano (1501–1576) and Girolamo Fracastoro (circa 1476–1553) in Italy propagated a theory that comets were superlunar bodies focusing sunlight like a lens to produce the tail. This theory developed in a period that saw a major revival in Stoic philosophy. Apian also published his observations of the comets including what would become known, incorrectly, as Apian’s Law that the tails of comets always point away from the sun. I say incorrectly because this fact had already been known to Chinese astronomers for several centuries.

These developments in the theory of comets meant that when the Great Comet of 1577 appeared over Europe Tycho Brahe (1546–1601) was by no means the only astronomer, who followed it’s course with interest and tried to measure its parallax in order to determine whether it was sub- or superlunar. Tycho was not doing anything revolutionary, as it is normally presented in the standard story of the evolution of modern astronomy, but was just taking part in in a debate on the nature of comets that had been rumbling on throughout the sixteenth century. The results of these mass observations were very mixed. Some observers failed to make a determination, some ‘proved’ that the comet was sublunar and some, including Tycho on Hven, Michael Maestlin (1550–1631), Kepler’s teacher, in Tübingen and Thaddaeus Hagecius (1525–1600) in Prague, all determined it to be superlunar. There were many accounts published throughout Europe on the comet the majority of which still favoured a traditional Aristotelian astrological viewpoint of which my favourite was by the painter Georg Busch of Nürnberg. Busch stated that comets were fumes that rose up from the earth into the atmosphere where they collected and ignited raining back down on the earth causing all sorts of evils and disasters including Frenchmen.

On a more serious note the parallax determinations of Tycho et al led to a gradual acceptance amongst astronomers that comets are indeed astronomical and not meteorological phenomena, whereby at the time Maestlin’s opinion probably carried more weight than Tycho’s. This conclusion was given more substance when it was accepted by Christoph Clavius (1538–1612), who although a promoter of Ptolemaic astronomy, was the most influential astronomer in Europe at the end of the sixteenth century.

By the beginning of the seventeenth century comets had advanced to being an important aspect of astronomical research; one of the central questions being the shape of the comets course through the heavens. In 1607 the English astronomer, Thomas Harriot (circa 1560–1621), and his friend and pupil, the MP, Sir William Lower (1570–1615), observed Halley’s Comet and determined that its course was curved. In 1609/10 Harriot and Lower became two of the first people to read and accept Kepler’s Astronomia Nova, and Lower suggested in a letter to Harriot that comets also follow elliptical orbits making him the first to recognise this fact, although his view did not become public at the time.

The comet of 1618 was the source of one of the most famous disputes in the history of science between Galileo Galilei (1564–1642) and the Jesuit astronomer Orazio Grassi (1583–1654). Grassi had observed the comet, measured its parallax and determined that it was superlunar. Galileo had, due to an infirmity, been unable to observe the comet but when urged by his sycophantic fan club to offer an opinion on the comet couldn’t resist. Strangely he attacked Grassi adopting an Aristotelian position and claiming that comets arose from the earth and were thus not superlunar. This bizarre dispute rumbled on, with Grassi remaining reasonable and polite in his contributions and Galileo becoming increasingly abusive, climaxing in Galileo’s famous Il Saggiatore. The 1618 comet also had a positive aspect in that Kepler (1571–1630) collected and collated all of the available historical observational reports on comets and published them in a book in 1619/20 in Augsburg. Unlike Lower, who thought that comets followed Keplerian ellipses, Kepler thought that the flight paths of comets were straight lines.

The 1660s again saw a series of comets and by now the discussion amongst astronomers was focused on the superlunar flight paths of these celestial objects with Kepler’s text central to their discussions. This played a significant role in the final acceptance of Keplerian elliptical heliocentric astronomy as the correct model for the cosmos, finally eliminating its Tychonic and semi-Tychonic competitors, although some Catholic astronomers formally continued paying lip service to a Tychonic model for religious reasons, whilst devoting their attentions to discussing a heliocentric cosmos hypothetically.

The 1680s was a fateful decade for comets and heliocentricity. John Flamsteed (1646–1719), who had been appointed as the first Astronomer Royal in Greenwich in 1675, observed two comets in 1680, one in November and the second in mid December. Flamsteed became convinced that they were one and the same comet, which had orbited the sun. He communicated his thoughts by letter to Isaac Newton (1642–1727) in Cambridge, the two hadn’t fallen out with each other yet, who initially rejected Flamsteed’s findings. However on consideration Newton came to the conclusion that Flamsteed was probably right and drawing also on the observations of Edmund Halley began to calculate possible orbits for the comet. He and Halley began to pay particular attention to observing comets, in particular the comet of 1682. By the time Newton published his Principia, his study of cometary orbits took up one third of the third volume, the volume that actually deals with the cosmos and the laws of motion and the law of gravity. By showing that not only the planets and their satellite systems obeyed the law of gravity but that also comets did so, Newton was able to demonstrate that his laws were truly universal.

After the publication of the Principia, which he not only edited and published but also paid for out of his own pocket, Halley devoted himself to an intense study of the historical observations of comets. He came to the conclusion that the comet he had observed in 1682, the one observed by Peuerbach and Regiomontanus in Vienna in 1456 and the one observed by Harriot and Lower in London in 1607 were in fact one and the same comet with an orbital period of approximately 76 years. Halley published the results of his investigations both in the Philosophical Transactions of the Royal Society and as a separate pamphlet under the title Synopsis of the Astronomy of Comets in 1705. Halley determined the orbit of the comet that history would come to name after him and announced that it would return in 1758. Although long lived Halley had no hope of witness this return and would never know if his was right or not. Somewhat later the French Newtonian astronomer and mathematician Alexis Clairaut (1713–1765) recalculated the return date, introducing factors not considered by Halley, to within a one-month error of the correct date. The comet was first observed on Newton’s birthday, 25 December 1758 and reached perihelion, its nearest approach to the sun, on 13 March 1759, Clairault had predicted 13 April. This was a spectacular empirical confirmation of Newton’s theory of universal gravity and with it of heliocentric astronomy. Comets had featured in the beginnings of the development of modern astronomy in the work of Toscanelli, Peuerbach and Regiomontanus and then in the final confirmation of that astronomy with the return of Halley’s Comet having weaved their way through they whole story over the preceding 350 years.

 

 

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Published on…

Today I have been mildly irritated by numerous tweets announcing the 5th July 1687, as the day on which Isaac Newton’s Principia was published, why? Partially because the claim is not strictly true and partially because it evokes a false set of images generated by the expression, published on, in the current age.

In the last couple of decades we have become used to images of hoards of teens dressed in fantasy costumes as witches queuing up in front of large bookstores before midnight to participate in the launch of the latest volume of a series of children’s books on a juvenile wizard and his adventures. These dates were the days on which the respective volumes were published and although the works of other authors do not enjoy quite the same level of turbulence, they do also have an official publication date, usually celebrated in some suitable way by author and publisher. Historically this has not always been the case.

In earlier times books, particularly ones of a scientific nature, tended to dribble out into public awareness over a vague period of time rather than to be published on a specific date. There were no organised launches, no publisher’s parties populated by the glitterati of the age and no official publication date. Such books were indeed published in the sense of being made available to the reading public but the process was much more of a slapdash affair than that which the term evokes today.

One reason for this drawn out process of release was the fact that in the early centuries of the printed book they were often not bound for sale by the publisher. Expensive works of science were sold as an unbound pile of printed sheets, allowing the purchaser to have his copy bound to match the other volumes in his library. This meant that there were not palettes of finished bound copies that could be shipped off to the booksellers. Rather a potential purchaser would order the book and its bindings and wait for it to be finished for delivery.

Naturally historians of science love to be able to nail the appearance of some game changing historical masterpiece to a specific date, however this is not always possible. In the case of Copernicus’ De revolutionibus, for example, we are fairly certain of the month in 1543 that Petreius started shipping finished copies of the work but there is no specific date of publication. With other equally famous works, such as Galileo’s Sidereus Nuncius, the historian uses the date of signing of the dedication as a substitute date of publication.

So what is with Newton’s Principia does it have an official date of publication and if not why are so many people announcing today to be the anniversary of its publication. Principia was originally printed written in manuscript in three separate volumes and Edmond Halley, who acted both as editor and publisher, had to struggle with the cantankerous author to get those volumes out of his rooms in Cambridge and into the printing shop. In fact due to the interference of Robert Hooke, demanding credit for the discovery of the law of gravity, Newton contemplated not delivering the third volume at all. Due to Halley’s skilful diplomacy this crisis was mastered and the final volume was delivered up by the author and put into print. July 5th 1687 is not the date of publication as it is understood today, but the date of a letter that Halley sent to Newton announcing that the task of putting his immortal masterpiece onto the printed page had finally been completed and that he was sending him twenty copies for his own disposition. I reproduce the text of Halley’s letter below.

 

Honoured Sr

I have at length brought you Book to an end, and hope it will please you. the last errata came just in time to be inserted. I will present from you the books you desire to the R. Society, Mr Boyle, Mr Pagit, Mr Flamsteed and if there be any elce in town that you design to gratifie that way; and I have sent you to bestow on your friends in the University 20 Copies, which I entreat you to accept.[1]

 

 

[1] Richard S. Westfall, Never at Rest: A Biography of Isaac Newton, Cambridge University Press, Cambridge etc., 1980, p. 468.

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Planetary Tables and Heliocentricity: A Rough Guide

Since it emerged sometime in the middle of the first millennium BCE the principal function of mathematical astronomy was to provide the most accurate possible predictions of the future positions of the main celestial bodies. This information was contained in the form of tables calculated with the help of the mathematical models, which had been derived by the astronomers from the observed behaviour of those bodies, the planets. The earliest Babylonian models were algebraic but were soon replaced by the Greeks with geometrical models based on spheres and circles. To a large extent it did not matter if those models were depictions of reality, what mattered was the accuracy of the prediction that they produced; that is the reliability of the associated tables. The models of mathematical astronomy were judge on the quality of the data they produced and not on whether they were a true reproduction of what was going on in the heavens. This data was used principally for astrology but also for cartography and navigation. Mathematical astronomy was a handmaiden to other disciplines.

Before I outline the history of such tables, a brief comment on terminology. Data on the movement of celestial bodies is published under the titles planetary tables and ephemerides (singular ephemeris). I know of no formal distinction between the two names but as far as I can determine planetary tables is generally used for tables calculated for quantitatively larger intervals, ten days for example, and these are normally calculated directly from the mathematical models for the planetary movement. Ephemeris is generally used for tables calculated for smaller interval, daily positions for example, and are often not calculated directly from the mathematical models but are interpolated from the values given in the planetary tables. Maybe one of my super intelligent and incredibly well read readers knows better and will correct me in the comments.

The Babylonians produced individual planetary tables, in particular of Venus, but we find the first extensive set in the work of Ptolemaeus. He included tables calculated from his geometrical models in his Syntaxis Mathematiké (The Almagest), published around 150 CE, and to make life easier for those who wished to use them he extracted the tables and published them separately, in extended form with directions of their use, in what is known as his Handy Tables. This publication provided both a source and an archetype for all future planetary tables.

The important role played by planetary tables in mathematical astronomy is illustrated by the fact that the first astronomical works produced by Islamic astronomers in Arabic in the eighth-century CE were planetary tables known in Arabic as zījes (singular zīj). These initial zījes were based on Indian sources and earlier Sassanid Persian models. These were quickly followed by those based on Ptolemaeus’ Handy Tables. Later sets of tables included material drawn from Islamic Arabic sources. Over 200 zījes are known from the period between the eighth and the fifteenth centuries. Because planetary tables are dependent on the observers geographical position most of these are only recalculation of existing tables for new locations. New zījes continued to be produced in India well into the eighteenth-century.

With the coming of the European translators in the twelfth and thirteenth centuries and the first mathematical Renaissance the pattern repeated itself with zījes being amongst the first astronomical documents translated from Arabic into Latin. Abū ʿAbdallāh Muḥammad ibn Mūsā al-Khwārizmī was originally better known in Europe for his zīj than for The Compendious Book on Calculation by Completion and Balancing” (al-Kitab al-mukhtasar fi hisab al-jabr wa’l-muqabala), the book that introduced algebra into the West. The Toledan Tables were created in Toledo in the eleventh-century partially based on the work of Abū Isḥāq Ibrāhīm ibn Yaḥyā al-Naqqāsh al-Zarqālī, known in Latin as Arzachel. In the twelfth-century they were translated in Latin by Gerard of Cremona, the most prolific of the translators, and became the benchmark for European planetary tables.

In the thirteenth- century the Toledan Tables were superseded by the Alfonsine Tables, which were produced by the so-called Toledo School of Translators from Islamic sources under the sponsorship of Alfonso X of Castile. The Alfonsine Tables remained the primary source of planetary tables and ephemerides in Europe down to the Renaissance where they were used by Peuerbach, Regiomontanus and Copernicus. Having set up the world’s first scientific press Regiomontanus produced the first ever printed ephemerides, which were distinguished by the accuracies of their calculations and low level of printing errors. Regiomontanus’ ephemerides were very popular and enjoyed many editions, many of them pirated. Columbus took a pirate edition of them on his first voyage to America and used them to impress some natives by accurately predicting an eclipse of the moon.

By the fifteenth-century astronomers and other users of astronomical data were very much aware of the numerous inaccuracies in that data, many of them having crept in over the centuries through frequent translation and copying errors. Regiomontanus was aware that the problem could only be solved by collecting new basic observational data from which to calculate the tables. He started on such an observational programme in Nürnberg in 1470 but his early death in 1475 put an end to his endeavours.

When Copernicus published his De revolutionibus in 1543 many astronomers hoped that his mathematical models for the planetary orbits would lead to more accurate planetary tables and this pragmatic attitude to his work was the principle positive reception that it received. Copernicus’ fellow professor of mathematic in Wittenberg Erasmus Reinhold calculated the first set of planetary tables based on De revolutionibus. The Prutenic Tables, sponsored by Duke Albrecht of Brandenburg Prussia (Prutenic is Latin for Prussian), were printed and published in 1551. Ephemerides based on Copernicus were produced by Johannes Stadius, a student of Gemma Frisius, in 1554 and by John Feild (sic), with a forward by John Dee, in 1557. Unfortunately they didn’t live up to expectations. The problem was that Copernicus’ work and the tables were based on the same corrupted data as the Alfonsine Tables. In his unpublished manuscript on navigation Thomas Harriot complained about the inaccuracies in the Alfonsine Tables and then goes on to say that the Prutenic Tables are not any better. However he follows this complaint up with the information that Wilhelm IV of Hessen-Kassel and Tycho Brahe on Hven are gathering new observational data that should improve the situation.

As a young astronomer the Danish aristocrat, Tycho Brahe, was indignant that the times given in both the Alfonsine and the Prutenic tables for a specific astronomical event that he wished to observe were highly inaccurate. Like Regiomontanus, a hundred years earlier, he realised that the problem lay in the inaccurate and corrupted data on which both sets of tables were based. Like Regiomontanus he started an extensive programme of astronomical observations to solve the problem, initially at his purpose built observatory financed by the Danish Crown on the island of Hven and then later, through force of circumstances, under the auspices of Rudolph II, the Holy Roman German Emperor, in Prague. Tycho devoted almost thirty years to accruing a vast collection of astronomical data. Although he was using the same observational instruments available to Ptolemaeus fifteen hundred years earlier, he devoted an incredible amount of time and effort to improving those instruments and the methods of using them, meaning that his observations were more accurate by several factors than those of his predecessors. What was now needed was somebody to turn this data into planetary tables, enter Johannes Kepler. Kepler joined Tycho in Prague in 1600 and was specifically appointed to the task of producing planetary tables from Tycho’s data. Contrary to popular belief he was not employed by Tycho but directly by Rudolph.

Following Tycho’s death, a short time later, a major problem ensued. Kepler was official appointed Imperial Mathematicus, as Tycho’s successor, and still had his original commission to produce the planetary tables for the Emperor, however, legally, he no longer had the data; this was Tycho’s private property and on his death passed into the possession of his heirs. Kepler was in physical possession of the data, however, and hung on to it during the protracted, complicated and at times vitriolic negotiations with Tycho’s son in law, Frans Gansneb Genaamd Tengnagel van de Camp, over their future use. In the end the heirs granted Kepler permission to use the data with the proviso that any publications based on them must carry Tengnagel’s name as co-author. Kepler then proceeded to calculate the tables.

Put like this, it sounds like a fairly straightforward task, however it was difficult and tedious work that Kepler loathed intensely. It was not made any easier by the personal and political circumstances surrounding Kepler over the years he took to complete the task. Wars, famine, usurpation of the Emperor’s throne (don’t forget the Emperor was his employer) and family disasters all served to make his life more difficult.

Finally in 1626, twenty-six years after he started Kepler had finally reduced Tycho’s thirty years of observations into planetary tables for general use, now he only had to get them printed. Drumming up the financial resources for the task was the first hurdle that Kepler successfully cleared. He then purchased the necessary paper and settled in Linz to complete the task of turning his calculations into a book. As the printing was progressing all the Protestants in Linz were ordered to leave the city, Kepler, being Imperial Mathematicus, and his printer were granted an exemption to finish printing the tables but then Wallenstein laid siege to the city to supress a peasants uprising. In the ensuing chaos the printing shop and the partially finished tables went up in flames.

Leaving Linz Kepler now moved to Ulm where, starting from the beginning again, he was finally able to complete the printing of the Rudophine Tables, named after the Emperor who had originally commissioned them but dedicated to the current Emperor, Ferdinand II. Although technically not his property, because he had paid the costs of having them printed Kepler took the finished volumes to the book fair in Frankfurt to sell in September 1627.

Due to the accuracy of Tycho’s observational data and the diligence of Kepler’s mathematical calculations the new tables were of a level of accuracy never seen before in the history of astronomy and fairly quickly became the benchmark for all astronomical work. Perceived to have been calculated on the basis of Kepler’s own elliptical heliocentric astronomy they became the most important artefact in the general acceptance of heliocentricity in the seventeenth century. As already stated above systems of mathematical astronomy were judged on the data that they produced for use by astrologers, cartographers, navigators et al. Using the Rudolphine Tables Gassendi was able to predict and observe a transit of Mercury in 1631, as Jeremiah Horrocks succeeded in predicting and observing a transit of Venus for the first time in human history based on his own calculations of an ephemeris for Venus using Kepler’s tables, it served as a confirming instance of the superiority of both the tables and Kepler’s elliptical astronomy, which was the system that came to be accepted by most working astronomers in Europe around 1660. The principle battle in the war of the astronomical systems had been won by a rather boring set of mathematical tables, Johannes Kepler’s Tabulae Rudolphinae.

Rudolphine Tables Frontispiece

Rudolphine Tables Frontispiece

 

 

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The Transition to Heliocentricity: The Rough Guides

Prompted by a question from Brian Cox, on Twitter, I wrote a post outlining the history of Galileo’s engagement with heliocentricity and the Catholic Church giving it the sub-title “A Rough Guide”. This post in turn provoked a series of question and answers on Twitter between myself and my #histsci soul-sister Dr Rebekah “Becky” Higgitt, which I developed into a post on the role played by the observations of the phases of Venus in the gradual acceptance of heliocentricity; a second post to which I added the sub-title “A Rough Guide”. I have now decided to go with the flow and produce a series of posts dealing one by one with the various things that contributed to the gradual transition from a geocentric to a heliocentric astronomy during the sixteenth and seventeenth centuries, each post bearing the sub-title “A Rough Guide”.

The aim is to demonstrate that this transition was not a simple question of the one is right and the other wrong, as it is unfortunately all too often presented today, particularly by those of a gnu atheist persuasion, but that within the context of the times the various factors involved often required subtle and careful interpretation and were not the clear cut evidence that hindsight seems to make them now. For example, I hope I have already achieved this in the post on the phases of Venus. To make it easier for readers to put the whole series together and to form, for themselves, the big picture, I have added a new separate page to the Renaissance Mathematicus, which will contain a list of all the posts, with links.

Suggestions, from readers, for topics to be dealt with in this series are welcome; I already have a list of eight, the first of which will be posted some time next week.

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The Phases of Venus and Heliocentricity: A Rough Guide

The word planet comes from the Greek word for wanderer. When people first started observing the heavens most of those points of light that we call stars appeared to remain fixed in place relative to each other, although the whole bowl of twinkling points appeared to revolve around the earth once every twenty-four hours, hence they became known as the sphere of fixed stars. With time however the early observers noticed that some of those points of lights behaved very differently to the vast majority, appearing to wander somewhat randomly around the heavens and these maverick stars became the planets. Further observations showed that the movement of the wanderers were in fact not random but followed a regularity that could, over suitably long periods of time, be recorded and then predicted in advance and planetary astronomy was born, however the behaviour of the various wanderers differed.

The Sun and Moon, which were both regarded as planets, have very special geocentric orbits and delivered the basics of timekeeping, the year and the day – the Sun – and the month and possible the seven day week (the phases of the moon) – the Moon. In the most common order of the planets, Moon, Mercury, Venus, Sun, Mars Jupiter and Saturn moving outwards from the Earth the remaining five planets were divided into the inner and outer planets with the Sun’s orbit providing the dividing line. The outer planets – Mars, Jupiter and Saturn – display a rather curious behaviour. They trundle along quite regularly in one directions then halt, reverse direction for a short period, halt again then reversing direction once again continue as before. This brief period of reversed motion is called retrograde motion and I’ll deal with its history and significance for heliocentricity in another post.

The two inner planets – Mercury and Venus – display a completely different orbital behaviour viewed from the Earth. Firstly they never stray very far from the Sun. They disappear for periods of time first being one side of the sun then reappearing on the other side and lastly their orbits around the Earth is exactly the same as the Sun’s i.e. one year. This combination of phenomena led some astronomers in antiquity to hypothesise that Venus and Mercury do not orbit the Earth but the Sun, being carried with it on its annual journey around the Earth. This model became know as the Egyptian or Heracleidian system. It was also presented in late antiquity by Martianus Capella in his De nuptiis Philologiae et Mercurii (“On the Marriage of Philology and Mercury”) a text that was very well known and popular in the Middle Ages and so the Heracleidian model was also well known in the Early Modern Period.

 

Capellan system - Valentin Naboth (1573)

Capellan system – Valentin Naboth (1573)

In the sixteenth-century the Danish astronomer Tycho Brahe seeing the advantages of Copernicus’ heliocentric astronomy but very unhappy about a moving Earth extended the Heracleidian system in that he let all five of the planets orbit the Sun, which in turn orbited the Earth.

 

Tychonic System

Tychonic System

The telescope made its public debut in Holland in September 1608. Within a year Thomas Harriot in London, Simon Marius in Ansbach, Galileo Galilei in Padua, and the Jesuits Odo van Maelcote and Giovanni Paolo Lembo in Rome were all using the new instrument to make astronomical observations and ushering in a new era in our understanding of the cosmos. Famously, Galileo was the first in print with his Sidereus Nuncius, the impact of which I’ve dealt with here. The earliest known reference to the possibility of Venus having phases occurs in a letter sent by the mathematician Benedetto Castelli to his old teacher Galileo in December 1610. Referencing thoughts of Copernicus from chapter ten of book I of De revolutionibus, Castelli enquired if the telescope would make it possible to observe phases of Venus. This enquiry makes two assumptions, firstly that Venus orbits the sun and secondly that it is lit by reflected light from the sun and is not a light source itself.

Galileo experts are divided as to whether Galileo had already been considering the question before he received Castelli’s letter or whether he appropriated the idea without giving his onetime student the credit he deserved. Whatever, shortly after receiving this letter Galileo wrote to Kepler in Prague enclosing the following anagram announcing a new sensational discovery:

Haec immatura a me iam frustra leguntur o.y.

This reads in translation, “I am now bringing these unripe things together in vain, Oy!” It was common practice for researchers in the Early Modern Period to announce their new discoveries in the form of anagrams to establish their priority in an age that knew no patents or copyright in the modern sense. Kepler was unable to decipher Galileo’s message and had to wait until the Tuscan astronomer revealed his sensation to the world. Deciphered the anagram read as follows, in Latin:

Cynthiae figuras aemulatur mater amorum

In English translation this reads as, “The mother of love [Venus] copies the forms of Cynthia [the Moon]”. In other words Galileo had discovered that Venus has phases like the Moon and therefore must orbit the Sun and not the Earth. Also in 1610 Galileo informed his friend and former patron Christoph Clavius in Rome of his discovery. He included his discovery in his first letter on sunspots written and distributed privately in 1611/12 but which wasn’t published until 1613.

 

Galileo's Sunspot Letters

Galileo’s Sunspot Letters

Actually having phases was not a sufficient proof of Venus’ heliocentricity; the matter is in reality somewhat more complicated. If Venus were to orbit the Earth in a geocentric system between the Earth and the Sun, as proposed by Ptolemaeus, then it would also display phases. However the phases of the two configurations differ substantially so the accurate observation of those phases is a true experimentum crucis, in Francis Bacon’s sense, between a geocentric and a heliocentric Venus. What Galileo had in fact observed were phases consistent with a heliocentric orbit for Venus.

 

The Phases of Venus in both systems

The Phases of Venus in both systems

Independently of Galileo, Harriot, Marius and the Collegio Romano astronomers also observed the phases of Venus so there was no doubt that Venus and, by analogy, probably Mercury, (the phases of Mercury were first observed by the Jesuit astronomer Giovanni Battista Zupi in 1639) orbited the Sun and not the Earth. Harriot as usual did not publish, Marius sent his discovery to Kepler who published it in the preface of his Dioptrice in 1611. Odo von Maelcote included the Jesuit confirmation of Galileo’s observations in his speech during the banquet to honour Galileo at the Collegio Romano in 1611.

This discovery put an end, once and for all, to a pure geocentric system à la Ptolemaeus but did not as Castelli thought, in his letter to Galileo, provide definitive proof of Copernicus’ heliocentric system. Both the ancient Heracleidian and Tycho’s helio-geocentric systems would display the same, newly discovered, phases of Venus. This situation is illustrated on the famous title page of Riccioli’s Almagestum Novum (1651), which shows Ptolemaeus lying on the ground with his system, feebly claiming, “I will rise again” whilst Urania weighs the merits of the Copernican heliocentric system against those of Riccioli’s own semi-Tychonic system. In Riccioli’s system Mercury, Venus and Mars orbit the Sun, which in turn, together with Jupiter and Saturn, orbits the Earth. As far as I know, nobody other than Riccioli ever propagated this strange beast.

 

Title page Riccioli’s Almagestum Novum (1651)

Title page Riccioli’s Almagestum Novum (1651)

Although the phases of Venus were not decisive in deciding the conflict between the supporters of geocentricity and those of heliocentricity they did provide an important step along the twisting road towards the eventual acceptance of a heliocentric model, Kepler’s, for the then known cosmos.

 

h/t to my #histsci soul sister Rebekah “Becky” Higgitt whose questions on this topic on Twitter inspired this post.

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Science grows on the fertilizer of disagreement

At the weekend German television presented me with all three episodes of Jim Al-Khalili’s documentary on the history of electricity, Shock and Awe: The Story of Electricity. On the whole I found it rather tedious largely because I don’t like my science or history of science served up by a star presenter who is the centre of the action rather than the science itself, a common situation with the documentaries of ‘he who shall not be named’-TPBoPS, and NdGT. It seems that we are supposed to learn whatever it is that the documentary nominally offers by zooming in on the thoughtful features of the presenter, viewing his skilfully lit profile or following him as he walks purposefully, thoughtfully, meaningfully or pensively through the landscape. What comes out is “The Brian/Neil/Jim Show” with added science on the side, which doesn’t really convince me, but maybe I’m just getting old.

However my criticism of the production style of modern television science programmes is not the real aim of this post, I’m much more interested in the core of the first episode of Al-Khalili’s documentary. The episode opened and closed with the story of Humphrey Davy constructing the, then, largest battery in the world in the cellars of the Royal Institution in order to make the first ever public demonstration of an arc lamp and thus to spark the developments that would eventually lead to electric lighting. Having started here the programme moved back in time to the electrical experiments of Francis Hauksbee at the Royal Society under the auspices of Isaac Newton. Al-Khalili then followed the development of electrical research through the eighteenth-century, presenting the work of the usual suspects, Steven Gray, Benjamin Franklin etc., until we arrived at the scientific dispute between the two great Italian physicists Luigi Galvani and Alessandro Volta that resulted in the invention of the Voltaic pile, the forerunner of the battery and the first producer of an consistent electrochemical current. All of this was OK and I have no real criticisms, although I was slightly irked by constant references to ‘Hauksbee’s’ generator when the instrument in question was an adaption suggested by Newton of an invention from Otto von Guericke, who didn’t get a single name check. What did irritate me and inspired this post was the framing of the Galvani-Volta dispute.

Al-Khalili, a gnu atheist of the milder variety, presented this as a conflict between irrational religious persuasion, Galvani, and rational scientific heuristic, Volta, culminating in a victory for science over religion. In choosing so to present this historical episode Al-Khalili, in my opinion, missed a much more important message in scientific methodology, which was in fact spelt out in the fairly detailed presentation of the successive stages of the dispute. Galvani made his famous discovery of twitching frog’s legs and after a series of further experiments published his theory of animal electricity. Volta was initially impressed by Galvani’s work and at first accepted his theory. Upon deeper thought he decided Galvani’s interpretation of the observed phenomena was wrong and conducted his own series of result to prove Galvani wrong and establish his own theory. Volta having published his refutation of Galvani’s theory, the latter not prepared to abandon his standpoint also carried out a series of new experiments to prove his opponent wrong and his own theory right. One of these experiments led Volta to the right explanation, within the knowledge framework of the period, and to the discovery of the Voltaic pile. What we see here is a very important part of scientific methodology, researchers holding conflicting theories spurring each other on to new discoveries and deeper knowledge of the field under examination. The heuristics of the two are almost irrelevant, what is important here is the disagreement as research motor. Also very nicely illustrated is discovery as an evolutionary process spread over time rather than the infamous eureka moment.

The inspiration produced from watching Al-Khalili’s story of the invention of the battery chimes in very nicely with another post I was planning on writing. In a recent blog post, Joe Hanson of “it’s OKAY to be SMART” wrote about Galileo and the first telescopic observations of sunspots at the beginning of the seventeenth-century. The post is OK as far as it goes, even managing to give credit to Thomas Harriot and Johannes Fabricius, however it contains one truly terrible sentence that caused my heckles to rise. Hanson wrote:

Although Galileo’s published sunspot work was the most important of its day, on account of the “that’s no moon” smackdown it delivered to the Jesuit scientific community, G-dub was not the first to observe the solar speckles.

Here we have another crass example of modern anti-religious sentiment of a science writer getting in the way of sensible history of science. What we are talking about here is not the Jesuit scientific community but the single Jesuit physicist and astronomer Christoph Scheiner, who famously became embroiled in a dispute on the nature of sunspots with Galileo. Once again we also have an excellent example of scientific disagreement driving the progress of scientific research. Scheiner and Galileo discovered sunspots with their telescopes independently of each other at about the same time and it was Scheiner who first published the results of his discoveries together with an erroneous theory as to the nature of sunspots. Galileo had at this point not written up his own observations, let alone developed a theory to explain them. Spurred on by Scheiner’s publication he now proceeded to do so, challenging Scheiner’s claim that the sunspots where orbiting the sun and stating instead that they were on the solar surface. An exchange of views developed with each of the adversaries making new observations and calculations to support their own theories. Galileo was not only able to demonstrate that sunspots were on the surface of the sun but also to prove that the sun was rotating on its axis, as already hypothesised by Johannes Kepler. Scheiner, an excellent astronomer and mathematician, accepted Galileo’s proofs and graciously acknowledge defeat. However whereas Galileo now effectively gave up his solar observations Scheiner developed new sophisticated observation equipment and carried out an extensive programme of solar research in which he discovered amongst other things that the sun’s axis is tilted with respect to the ecliptic. Here again we have two first class researchers propelling each other to new important discoveries because of conflicting views on how to interpret observed phenomena.

My third example of disagreement as a driving force in scientific discovery is not one that I’ve met recently but one whose misrepresentation has annoyed me for many years, it concerns Albert Einstein and quantum mechanics. I have lost count of the number of times that I’ve read some ignorant know-it-all mocking Einstein for having rejected quantum mechanics. That Einstein vehemently rejected the so-called Copenhagen interpretation of quantum mechanics is a matter of record but his motivation for doing so and the result of that rejection is often crassly misrepresented by those eager to score one over the great Albert. Quantum mechanics as initial presented by Niels Bohr, Erwin Schrödinger, Werner Heisenberg et. al. contradicted Einstein fundamental determinist metaphysical concept of physics. It was not that he didn’t understand it, after all he had made several significant contributions to its evolution, but he didn’t believe it was a correct interpretation of the real physical world. Einstein being Einstein he didn’t just sit in the corner and sulk but actively searched for weak points in the new theory trying to demonstrate its incorrectness. There developed a to and fro between Einstein and Bohr, with the former picking holes in the theory and the latter closing them up again. Bohr is on record as saying that Einstein through his informed criticism probably contributed more to the development of the new theory than any other single physicist. The high point of Einstein’s campaign against quantum mechanics was the so-called EPR (Einstein-Podolsky-Rosen) paradox, a thought experiment, which sought to show that quantum mechanics as it stood would lead to unacceptable or even impossible consequences. On the basis of EPR the Irish physicist John Bell developed a testable theorem, which when tested showed quantum mechanics to be basically correct and Einstein wrong, a major step forward in the establishment of quantum physics. Although proved wrong in the end Einstein’s criticism of and disagreement with quantum mechanics contributed immensely to the theories evolution.

The story time popular presentations of the history of science very often presents the progress of science as a series of eureka moments achieved by solitary geniuses, their results then being gratefully accepted by the worshiping scientific community. Critics who refuse to acknowledge the truth of the new discoveries are dismissed as pitiful fools who failed to understand. In reality new theories almost always come into being in an intellectual conflict and are tested, improved and advanced by that conflict, the end result being the product of several conflicting minds and opinions struggling with the phenomena to be explained over, often substantial, periods of time and are not the product of a flash of inspiration by one single genius. As the title says, science grows on the fertilizer of disagreement.

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Galileo, the Church and Heliocentricity: A Rough Guide.

A couple of days ago on Twitter, Brian Cox asked the Twitter historians, “Did Galileo know that he would annoy the Church when he published The Starry Messenger?” The very simple answer to this question is, no but a lengthy discussion of the situation developed on Twitter. It was suggested that somebody should produce a short temperate answer to the question as a reference source and after some hesitation I have acquiesced. This will be a relative short presentation of the various stages of this historical process with a minimum of explanation and justification, as Joe Friday used to say, “the facts ma’am, just the facts!” This is of course my interpretation but it is based on a fairly good knowledge of the most recent principal secondary literature on the subject and it is one that I think would find fairly general agreement amongst those who have seriously studied the subject. Those who disagree are welcome, as always, to air their views in the comments but I expect those who choose to do so to base those views on historical facts and not on prejudice.

The first thing to make clear is the situation in terms of astronomy, cosmology and the Church in the first decade of the seventeenth-century before Galileo, Marius, Harriot, Lembo and others changed our view of the cosmos forever with the recently invented telescope. Astronomy and cosmology were not very high up on the Church’s agenda between 1600 and 1610. The vast majority of people, including the experts, still believed in a geocentric cosmos in the form developed by Ptolemaeus, the most modern version being basically that of Peuerbach and Regiomontanus. A very small handful believed in the Copernican heliocentric model, and believed is the right word because it lacked any real form of empirical proof and was burdened by all the physical problems engendered by a moving earth. A probably equally small number favoured a Tychonic geo-heliocentric model with or without a rotating earth and another small number were finding favour with Gilbert’s geocentric model with a rotating earth. All of the discussions were very academic and nothing that could or would threaten the dominance of a solid Bible conform geocentricity, so nothing for the Church to get its knickers in a twist about.

The telescopic discoveries were brand new empirical evidence and the biggest shake up in astronomy since mankind first cast its little beady eyes on the heavens. When he started to make his discoveries, late in 1609, Galileo was very much aware of the fact that he was sitting on the Renaissance equivalent of a Nobel prize, a knighthood and the keys to the treasure chest all in one and also very aware that he almost certainly wasn’t the only person making or about to make these discoveries. In the last point he was of course completely right, Harriot was ahead of him and Marius was breathing down his neck. Galileo was fully aware that if his wished to cash in then he had to get his priority claim in tout suite.

To understand this one needs to look at Galileo’s situation. In 1610 he was a forty-six year old professor of mathematics, stuck in the same rather lowly position for the last eighteen years. He was on the down hill slope to ill health, death and anonymity. He had already done his ground-breaking work on dynamics but hadn’t published it. If he were to die tomorrow nobody would remember him beyond a few close friends and his family. Now he had hit the jackpot and needed to cash in fast. He bunged his principal discoveries together in book form, in what was more a press release than a scientific report, the Sidereus Nuncius, and had it printed and published as fast as possible.

The last thing the Galileo wanted to do at this point was to annoy anybody; he wanted fame and fortune not infamy. He spent as much effort on getting permission to dedicate his small book to Cosimo Medici, the ruler of the Duchy of Florence, his home province, and his sometime private pupil, as he did on his telescopic observations. He also made very sure that the Medici would approve of the name he gave to the newly discovered moons of Jupiter; he was after preferment, which he got as a result of his clever tactical manoeuvring. He would have been mortified if his publication had caused problems with the Church in Rome because that would almost certainly have cost him any chance of an appointment to the Medici court, his main aim at the time. The Medici did in fact drop him when he finally collided with the Church in the 1620s.

The telescopic discoveries, which Galileo was the first to publish, shook up the whole of Europe and not just the Catholic Church. However the contents of Sidereus Nuncius neither disproved Ptolemaeus/Peuerbach nor did they prove Copernicus, as I’ve already explained here. Of course at first they did nothing at all because like all new scientific discoveries they needed to be confirmed by other astronomers. This proved to be somewhat difficult, as the available telescopes were very poor quality and Galileo was an exceptional telescopic observer. In the end it was the Church’s own official astronomers, the members of Clavius’ mathematical research group at the Collegio Romano, who with the active assistance of Galileo delivered the necessary confirmation of all of Galileo’s discoveries.

Hailed now as the greatest astronomer in Europe Galileo travelled in triumph to Rome where he was feted by the mathematicians of the Collegio Romano, who threw a banquet in his honour, had an audience with the Pope and was appointed a member of the Accademia dei Lincei who also threw a banquet in his honour. No signs of annoyance here. Galileo was appointed philosophicus and mathematicus to the Medici court in Florence, as well as professor for mathematics without teaching obligations at the University in Pisa. The humble insignificant mathematician had become a renowned social figure, almost overnight, feted and praised throughout Europe. High Church officials flocked to make his acquaintance and win his friendship, one of these, the Cardinal Maffeo Barberini, became a close friend and the cause of Galileo’s downfall later in his life.

Although nothing in the Sidereus Nuncius disproved the geocentric model of Ptolemaeus the discovery of the phases of Venus a short time later, by Galileo, Lembo, Harriot and Marius, did. The basic geocentric model was dead in the water and the Church had a problem because Holy Scripture clearly implied a geocentric cosmos. Riding on the wave of his fame Galileo wanted to go for the big one. He wanted to go down in history as the man who proved that the cosmos was heliocentric. Unfortunately he lacked a genuine proof. He had evidence that the cosmos was not geocentric and not homocentric but all the available empirical evidence satisfied both a heliocentric cosmos and a geo-heliocentric Tychonic one and it was the latter that most astronomers, still worried about the physical problems of a moving earth, tended to favour.

Around 1613, despite his lack of genuine proof Galileo began to canvas his newly won influential friends in Rome in an attempt to convince them to give their support to a call for the acceptance of a heliocentric cosmos, a dangerous move. The Church was a vast structure set in its ways and like a large ocean liner getting it to stop in full motion and reverse its direction was something that required a lot of time and space, Galileo eager to make his mark in history lacked the necessary patience to wait for the Church to accept the inevitable and was trying to force the pace. Several of his friends including Maffeo Barbarini advised him to calm down and not to force the Church into a corner, but Galileo, his ego inflated by his recent successes failed to heed this sound advice.

In the next couple of years both Galileo and the Carmelite father Paolo Antonio Foscarini tried to tell the Church how to reinterpret those passages of the Bible that contradict a heliocentric interpretation of the cosmos. This was a fundamental failure and guaranteed to annoy the Church extremely, which it did. One should remember that all of this was taking place in the middle of the Counter Reformation and on the eve of the Thirty Years War, which would kill off between one third and two thirds of the entire population of Middle Europe in what was basically an argument about who had the right to interpret the Bible. The Church set up a commission to investigate Foscarini’s book on the subject and the commission came down very hard on heliocentricity, calling it both philosophically (read scientifically) absurd and heretical. The accusation of heresy was not confirmed by the Pope and so was never official Church doctrine, but the damage was done. Cardinal Roberto Bellarmino was instructed to inform Galileo of the commission’s judgement. In a friendly chat Bellarmino did just this, informing Galileo that he could neither hold nor teach the theory that the cosmos was heliocentric. It is important to note that the theory was banned not the hypothesis. One could continue to discuss a hypothetical heliocentric cosmos, one could not, however, claim it to be fact. As many people have pointed out over the centuries this restriction was actually in line with the known empirical facts. The books of Kepler and other Protestants claiming that the cosmos was heliocentric were placed on the Index and Copernicus’ De revolutionibus was placed on the Index until corrected. Interestingly the Inquisition did just that. They removed the handful of passages from De revolutionibus that claimed the heliocentric cosmos to be fact and then gave the book free to be read, already in 1621. We still have Galileo’s personal censored copy of the book. This censorship was only really effective in Italy the rest of Europe not taking much notice of the Church’s efforts to suppress heliocentricity.

This setback did very little to slow down Galileo’s rise to fame and he became a very favoured celebrity throughout Northern Italy. Symptomatic for this is his notorious dispute with the Jesuit astronomer Orazio Grassi over the nature of comets that peaked in the publication of Galileo’s Il Saggiatore, in 1623. A dispute in which Grassi was scientifically right and Galileo wrong, but in which Galileo carried the laurels thanks to his superior polemic and the sycophantic cheers of his high powered fan club, which included the newly elected Pope, Urban VIII, Galileo’s old friend Maffeo Barberini.

Barberini’s elevation to the Holy Throne gave Galileo the chance he had been waiting and longing for, the chance to go down in history as the man who established the heliocentric cosmos. Using his friendship with the new Pope, Galileo convinced Barberini that the German Protestants were laughing at the Catholic Church because it had rejected heliocentricity because according to those dastardly Protestants the Catholics were too stupid to understand it. Beguiled by his silver tongued friend Barberini gave Galileo permission to write and publish a book in which he would present both the Ptolemaic and Copernican systems to demonstrate the deep astronomical knowledge of the Catholics but by no means was he to favour one of the systems. Galileo wrote the book, his Dialogo, in which he was anything but impartial and unbiased, as instructed, but instead left nobody in any doubt just how superior the Copernican system was in his opinion, however he still lacked any real empirical proof. Through a series of tricks he managed to get his book past the censors and into print. Galileo had erred very badly, you don’t play the most powerful absolutist ruler of your time for a fool, particularly not when that ruler is already displaying strong signs of the paranoia that, sooner or later, effects all absolutist rulers.

I’m not going to go into all of the contributory factors that played a part in the sorry mess that was Galileo’s trial by the Inquisitions, I’ll deal with those one day in another post, but it is safe to say that he got stamped on for his hubris. By comparison with other cases he didn’t actually get stamped on very hard and got off relatively lightly. I can already hear the screams of protest at the last sentence but within the context of the times and place where Galileo lived and moved it is an accurate description of his fate.

One thing that should be made very clear when discussing this whole sorry mess is that Galileo was never the fearless defender of scientific truth or freedom of speech that his modern fan club like to present him as. He was an extremely egotistical social climber with an eye on the main chance, his own undying fame. Through his ill-considered actions he achieved his goal but not quite in the way he had intended.

It is ironic that many people today still believe erroneously that Galileo actually proved the reality of a heliocentric cosmos in his Sidereus Nuncius.

[The original opening paragraph of this post was modified at the request of those who wish it to be used as a short simple reference source]

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The Moons of Jupiter

As anyone interested in astronomy or its history should know Io, Europa, Ganymede and Calisto are not only the names of four of Zeus’ lovers (or rape victims!) but also the names suggested privately by Kepler and publicly by Simon Marius for the four largest of Jupiter’s moons discovered on 7th and 8th January 1610 respectively by Galileo Galilei and Simon Marius. It must have been an exhilarating experience when they were first observed by those two pioneers of Renaissance telescopic astronomy and it is still an exciting one for an amateur astronomer in the twenty-first-century as related by Clive Thompson in a blog post at The Message. Unfortunately Thompson then goes on to complete misinterpret what that original discovery, four hundred years ago, meant for the cosmology and astronomy of the times. This is a topic I’ve dealt with before but it seems to be one that needs to be addressed at regular intervals like a game of #histsci Whac-A-Mole. What exactly did Thompson say that needs to be banged on the head?

Siderius [sic] Nuncius was a powerful piece of evidence that Copernicus was right: The Earth wasn’t the center of our solar system. The sun was, and the planets revolved around it. Astronomers had been gradually warming up to the idea, and even some church authorities had accepted the Copernican system as a mathematical theory. But by showing that Jupiter had its own moonsthat a planet could be a mini-system of its ownGalileo offered something rather more: Electrifying proof [emphasis in original] of the Copernican idea. You could argue endlessly (and people did) about the geometry and math of various systems explaining how the stars moved through the sky. It was just conjecture.

But proofthat’s different. Once people put their eyes to the telescope and saw those moons circling Jupiter, they had the same whoa-dude reaction that I had on the sidewalks of Brooklyn. The solar system got real. So real, in fact, that the church began to panic; and since Galileo went on to use his telescope to amass even more evidence against geocentrism, including the phases of Venus, religious authorities eventually stepped in and demanded he recant, or else.

To explain what is wrong with the above we first need to know what the accepted view of the cosmos in the first decade of the seventeenth-century. The standard model of the age was an uneasy alliance between Aristotelian cosmology and Ptolemaic astronomy. I say uneasy because the two systems were not actually compatible, something that the scholars of the period knew but chose, mostly, to ignore. It was this geocentric mish-mash that the handful of Copernicans and Tychonians were trying to dethrone. So what exactly was the scientific significance of the Galilei-Marius discovery of the Jupiter moons?

The discovery of the four principal moons of Jupiter didn’t actually have any direct relevance, either positive or negative, for Copernican heliocentricity. What it did do was to refute a central tenet of Aristotelian cosmology that of homo-centricity. Aristotelian cosmology stated that all celestial bodies revolve around the same central point, the earth. The discovery of the moons of Jupiter of course showed this to be totally wrong. Surprisingly this did little or no damage to Ptolemaic astronomy, as this was viewed by strict Aristotelians to already contradict this fundamental principle. In Ptolemaic astronomy the seven planets revolve around the centres of their respective epicycles, which are in turn carried around the earth, actually centred on a point other than the earth, on their deferents. This in the opinion of some Aristotelians was definitely not homo-centricity. This contradiction between the two systems of thought led to various revivals of concentric or homo-centric astronomy over the centuries the most recent being in the sixteenth-century barely a decade earlier than Copernicus’ publication of De revolutionibus. In fact Christoph Clavius, the leading proponent of Ptolemaic astronomy in 1610, regarded the homocentric astronomy of Giovanni Battista Amico and Girolamo Fracastoro to be a greater threat that Copernican heliocentricity and was quite happy to have it shot down by Jupiter’s moons.

Put very bluntly the discovery of the moons of Jupiter by Galileo and Marius was in no way what so ever a proof of the Copernican idea, something of which Galileo was very much aware and he did not try to present it as being one. Marius didn’t even consider it as he was a proponent of the Tychonic system to which he remained true all of his life.

The situation is of course different with the discovery of the phases of Venus. This discovery made independently by Thomas Harriot, Simon Marius, Galileo Galilei and Giovanni Paolo Lembo, the latter a Jesuit astronomer in Rome who probably discovered the phases before Galileo, effectively killed of a pure Ptolemaic astronomy as it proved that Venus, and probably Mercury by analogy (it would be some decades before the phases of Mercury were observed), orbited the sun and not the earth. Once again this is not in anyway a proof of the Copernican system, as there were other competing systems, the Heracleidian, in which Mercury and Jupiter Venus orbit the sun, which, along with the other planets, orbits the earth and the Tychonic in which all the planets except the moon orbit the sun which then orbits the earth, that were conform with the new telescopic discovery. In fact due to the very real unsolved physical problems presented by the concept of a moving earth most astronomers now chose the Tychonic model and not the Copernican one.

Thompson’s final comment about the Church panicking and forcing Galileo to recant is just pure historical hogwash. Any new empirical evidence needs to be confirmed by independent observers. It’s all very well for Professor Galilei the little known mathematicus from Padua to come along and say that he has discovered all of these wonderful things in the heavens with this new fangled device from Holland, if nobody else can see them. What is required is that other independent observers confirm that they too can see all that Signor Galilei claims to have seen. Given the extremely poor quality of the available telescopes and the optical limits of the Dutch or Galilean telescope this was not an easy task. Popular histories criticise contemporaries who failed to see what Galileo had seen but such critics have obviously never tried to observe the moons of Jupiter with a modern Galilean telescope with state-of-the-art good quality lenses, let alone one with very shitty quality seventeenth-century lenses. It is bloody difficult to put it mildly. So who in the end did provide the scientific confirmation that Galileo so desperately needed for his telescopic claims? This confirmation was delivered by the Jesuit professors of the Collegio Romano, the Vatican’s own astronomers. Doesn’t quite fit the picture of a Church in panic, does it?

The true reasons for that oh so notorious trial are far too complex so that I’m not going to deal with them here but I will just say that they have more to do with politics and authority than science. That however is the subject for another blog post on another day.

 

 

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