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.




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

The history of “scientist”

Today is a red-letter day for readers of The Renaissance Mathematicus; I have succeeded in cajoling, seducing, bullying, bribing, inducing, tempting, luring, sweet-talking, coaxing, coercing, enticing, beguiling[1] Harvard University’s very own Dr Melinda Baldwin into writing a guest post on the history of the term scientist, in particular its very rocky path to acceptance by the scientific community. First coined by William Whewell at the third annual meeting of the British Association for the Advancement of Science in 1833 in response to Samuel Taylor Coleridge’s strongly expressed objection to men of science using the term philosopher to describe themselves, the term experienced a very turbulent existence before its final grudging acceptance almost one hundred years later. In her excellent post Melinda outlines that turbulent path to acceptance, read and enjoy.


J.T. Carrington, editor of the popular science magazine Science-Gossip, achieved a remarkable feat in December of 1894: he found a subject on which the Duke of Argyll (a combative anti-Darwinian) and Thomas Huxley (a.k.a. “Darwin’s bulldog”) held the same opinion.

Carrington had noticed the spread of a particular term related to scientific research. He himself felt the word was “not satisfactory,” and he wrote to eight prominent writers and men of science to ask if they considered it legitimate. Seven responded. Huxley and Argyll joined a five-to-two majority when they denounced the term. “I regard it with great dislike,” proclaimed Argyll. Huxley, exhibiting his usual gift for witty dismissals, said that the word in question “must be about as pleasing a word as ‘Electrocution.’”

The word? “Scientist.”

Duke of Argyll

Duke of Argyll

Thomas Huxley

Thomas Huxley

Today “scientist” is not only an accepted title—it is a coveted one. To be a “scientist” is to be someone with an acknowledged right to make knowledge claims about the natural world. However, as the 1894 debate suggests, the term has a fraught history among English-speaking scientific practitioners. In retrospect, Huxley and Argyll’s rejection of “scientist” might seem merely quaint, even petty. But the history of the word “scientist” is not just a linguistic curiosity. Debates over its acceptance or rejection were, in the end, not about the word itself: they were about what science was, and what place its practitioners held in their society.

William Whewell

William Whewell

The English academic William Whewell first put the word “scientist” into print in 1834 in a review of Mary Somerville’s On the Connexion of the Physical Sciences. Whewell’s review argued that science was becoming fragmented, that chemists and mathematicians and physicists had less and less to do with one another. “A curious illustration of this result,” he wrote, “may be observed in the want of any name by which we can designate the students of the knowledge of the material world collectively.” He then proposed “scientist,” an analogue to “artist,” as the term that could provide linguistic unity to those studying the various branches of the sciences.

Most nineteenth-century scientific researchers in Great Britain, however, preferred another term: “man of science.” The analogue for this term was not “artist,” but “man of letters”—a figure who attracted great intellectual respect in nineteenth-century Britain. “Man of science,” of course, also had the benefit of being gendered, clearly conveying that science was a respectable intellectual endeavor pursued only by the more serious and intelligent sex.

“Scientist” met with a friendlier reception across the Atlantic. By the 1870s, “scientist” had replaced “man of science” in the United States. Interestingly, the term was embraced partly in order to distinguish the American “scientist,” a figure devoted to “pure” research, from the “professional,” who used scientific knowledge to pursue commercial gains.

“Scientist” became so popular in America, in fact, that many British observers began to assume that it had originated there. When Alfred Russel Wallace responded to Carrington’s 1894 survey he described “scientist” as a “very useful American term.” For most British readers, however, the popularity of the word in America was, if anything, evidence that the term was illegitimate and barbarous.


Nature Masthead

Nature Masthead

Feelings against “scientist” in Britain endured well into the twentieth century. In 1924, “scientist” once again became the topic of discussion in a periodical, this time in the influential specialist weekly Nature. In November, the physicist Norman Campbell sent a Letter to the Editor of Nature asking him to reconsider the journal’s policy of avoiding “scientist.” He admitted that the word had once been problematic; it had been coined at a time “when scientists were in some trouble about their style” and “were accused, with some truth, of being slovenly.” Campbell argued, however, that such questions of “style” were no longer a concern—the scientist had now secured social respect. Furthermore, said Campbell, the alternatives were old-fashioned; indeed, “man of science” was outright offensive to the increasing number of women in science.

In response, Nature’s editor, Sir Richard Gregory, decided to follow in Carrington’s footsteps. He solicited opinions from linguists and scientific researchers about whether Nature should use “scientist.” The word received more support in 1924 than it had thirty years earlier. Many researchers wrote in to say that “scientist” was a normal and useful word that was now ensconced in the English lexicon, and that Nature should use it.

However, many researchers still rejected “scientist.” Sir D’Arcy Wentworth Thompson, a zoologist, argued that “scientist” was a tainted term used “by people who have no great respect either for science or the ‘scientist.’” The eminent naturalist E. Ray Lankester protested that any “Barney Bunkum” might be able to lay claim to such a vague title. “I think we must be content to be anatomists, zoologists, geologists, electricians, engineers, mathematicians, naturalists,” he argued. “‘Scientist’ has acquired—perhaps unjustly—the significance of a charlatan’s device.”

In the end, Gregory decided that Nature would not forbid authors from using “scientist,” but that the journal’s staff would continue to avoid the word. Gregory argued that “scientist” was “too comprehensive in its meaning … The fact is that, in these days of specialized scientific investigation, no one presumes to be ‘a cultivator of science in general.’” And Nature was far from alone in its stance: as Gregory observed, the Royal Society of London, the British Association for the Advancement of Science, the Royal Institution, and the Cambridge University Press all rejected “scientist” as of 1924. It was not until after the Second World War that Campbell would truly get his wish for “scientist” to become the accepted British term for a person who pursued scientific research.

Tracing the acceptance or rejection of “scientist” among researchers not only gives us a history of a word—it also provides insight into the self-image of scientific researchers in the English-speaking world in a time when the social and cultural status of “science” was undergoing tremendous changes. Interestingly, the history of “scientist” shows that the word’s adoption cannot be straightforwardly associated with the professionalization of the sciences. “Scientist” was used in America to separate scientific researchers from “professionals.” In Britain, many researchers viewed “scientist” as a term that threatened their social and intellectual identity, a term that would open science up to any “Barney Bunkum” rather than confirm it as a selective, expert endeavor. Perhaps those who denounced the word might have been reassured by a glimpse into the future of the “scientist”—or perhaps they would still think that “scientists” might be better off as zoologists, chemists, and physicists.

Further reading on the word “scientist”:

Melinda Baldwin, Making Nature: The History of a Scientific Journal (Chicago: University of Chicago Press, forthcoming 2015).

Paul Lucier, “The Professional and the Scientist in Nineteenth-Century America,” Isis 100 (2009): 699-732.

Sydney Ross, “Scientist: The Story of a Word,” Annals of Science 18 (1962): 65-85.

Laura J. Snyder, The Philosophical Breakfast Club: Four Remarkable Friends who Transformed Science and Changed the World (New York: Broadway Books, 2012).

[1] Actually I just asked her and she said, yes.


Filed under History of science

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.


Filed under Early Scientific Publishing, History of Astronomy, History of Physics, Myths of Science, Newton

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




Filed under History of Astrology, History of Astronomy, History of Cartography, History of Navigation, History of science, Renaissance Science

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.


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

Whewell’s Gazette


Your weekly digest of all the best of

Internet history of science, technology and medicine

Editor in Chief: The Ghost of William Whewell

Volume #1                Monday 23 June 2014


Appearing weekly on Whewell’s Ghost

1 Comment

Filed under Uncategorized

Niels & Me: Dysgraphia – A history of science footnote.

One of the symptoms that, I think most, sufferers from mental illness share is the feeling of being alone with their daemons. “I’m the only one who feels like this!” “Why have I alone been afflicted?” This feeling of isolation and of having been somehow singled out for punishment in itself causes mental distress and deepens the crisis. An important step along the road to recovery is the realisation that one is not alone, that there are others who suffer similarly, that one hasn’t been singled out. I can still remember very clearly the day when I became certain that I am an adult ADD sufferer and a lot of my symptoms, including several that I didn’t regard as part of my illness, fell into place, received a label and a possible path back to mental health. As I have already related in my previous post I had very similar feelings on discovering dysgraphia and realising that it was one of my central daemons. One of those revelations concerning dysgraphia actually has a close connection to my history of science obsession and as this is a history of science blog I would like to tell the story here.

As should be clear from the name of this blog my main interest as a historian of science lies with the mathematical sciences in the Early Modern Period, however I try not to be too narrow and get stuck in a historical cul-de-sac, only able to understand a very narrow field of science over a very short period of time. In order to maintain a broad overview of the history of science I buy and read general surveys of the histories of other disciplines in other periods. One such book that I own is Robert P. Crease and Charles C. Mann The Second Creation: Makers of the Revolution in Twentieth-Century Physics[1], which, if my memory serves me correctly, I bought on the recommendation of dog owner, physics blogger and popular science book author Chad Orzel; a recommendation that I would endorse. I vividly remember, shortly after I bought it, curling up in bed with the book for my half hour read before going to sleep and waking up rather than dosing off, as I read the revelatory words on the first pages of chapter two, The Man Who Talked. I’m now going quote some fairly large chunks of those pages:

Bohr’ working habits have become legendary among his successors, part of the lore of science along with Einstein’s flyaway hair and Rutherford’s remark that relativity was not meant to be understood by Anglo-Saxons. Bohr talked. [emphasis in original] He discovered his ideas in the act of enunciating them, shaping thoughts as they came out of his mouth. Friends, colleagues, graduate students, all had Bohr gently entice them into long walks in the countryside around Copenhagen, the heavy clouds scudding overhead as Bohr thrust his hands into his overcoat pockets and settled into an endless, hesitant, recondite, barely audible monologue. While he spoke, he watched his listeners’ reactions, eager to establish a bond in a shared effort to articulate. Whispered phrases would be pronounced, only to be adjusted as Bohr struggled to express exactly [emphasis in original] what he meant; words were puzzled over, repeated, then tossed aside, and he was always ready to add a qualification, to modify, a remark, to go back to the beginning, to start the explanation over again. Then flatteringly, he would abruptly thrust the subject on his listener – surely this cannot be all? what else is there? – his big, ponderous, heavy-lidded eyes intent on the response. Before it could come, however, Bohr would have started talking again, wrestling with the answer himself. He inspected the language with which an idea was expressed in the way a jeweller inspects an unfamiliar stone, slowly judging each facet by holding it before an intense light[2].

Now I would never be so presumptuous to compare myself to Niels Bohr but this paragraph resonated with me on so many levels that I almost felt sick with excitement when I read it. With slight differences that is how I think, discover, formulate my ideas and my theories. In more recent years I sometimes feel really sorry for my listeners and try to throttle back the waterfall of words that pour out of my mouth; in earlier years I was not aware of my, basically anti-social, behaviour lost in that stream of consciousness word flow. However it was a paragraph two thirds of the way down the following page that made me sit bolt upright in bed.

As a schoolboy, Bohr’s worst subject had been Danish composition, and for the rest of his life he passed up no opportunity to avoid putting pen to paper. He dictated his entire doctoral dissertation to his mother, causing family rows when his father insisted that the budding Ph. D. should be forced to learn to write for himself; Bohr’s mother remained firm in her belief that the task was hopeless. It apparently was – most of Bohr’s later work and correspondence were dictated to his wife and a succession of secretaries and collaborators. Even with this assistance, it took him months to put together articles. Reading of his struggles, it is hard not to wonder if he was dyslexic[3]. [my emphasis]

I’m not a big fan of historical diagnosis by hearsay of illnesses that one or other famous figure from the past might have suffered. You could write an entire medical dictionary containing all the complaints that researchers have decided that the artist Van Gough suffered, according to their interpretation of the available facts. However my own personal situation leads me to the conclusion that Messrs. Crease and Mann are wrong and that Niels Bohr was not dyslexic but dysgraphic.

If you suffer from a disability that has caused you years of mental stress, then to discover that a famous historical figure suffered from the same ailment and despite this handicap was successful can be an incredible boost. Knowing that Bohr needed assistance to write his papers takes away some of the shame that I feel in having to ask people to check and correct the things that I write, as I said at the beginning, it’s knowing that you’re not alone.




[1] Robert P. Crease and Charles C. Mann,The Second Creation: Makers of the Revolution in Twentieth-Century Physics, Rutgers University Press, New Brunswick, New Jersey, Revised ed., 1996.

[2]Crease & Mann p. 20

[3]Crease & Mann p. 21


Filed under Autobiographical, History of Physics, History of science