Category Archives: Renaissance Science

Renaissance Science – I

To paraphrase what is possibly the most infamous opening sentence in a history of science book[1], there was no such thing as Renaissance science, and this is the is the start of a blog post series about it. Put another way there are all sorts of problems with the term or concept Renaissance Science, several of which should entail abandoning the use of the term and in a later post I will attempt to sketch the problems that exist with the term Renaissance itself and whether there is such a thing as Renaissance science? Nevertheless, I intend to write a blog post series about Renaissance science starting today.

We could and should of course start with the question, which Renaissance? When they hear the term Renaissance, most non-historians tend to think of what is often referred to as the Humanist Renaissance, but historians now use the term for a whole series of period in European history or even for historical periods in other cultures outside of Europe.

Renaissance means rebirth and is generally used to refer to the rediscovery or re-emergence of the predominantly Greek, intellectual culture of antiquity following a period when it didn’t entirely disappear in Europe but was definitely on the backburner for several centuries following the decline and collapse of the Western Roman Empire. The first point to note is that this predominantly Greek, intellectual culture didn’t disappear in the Eastern Roman Empire centred round its capitol Constantinople. An empire that later became known as the Byzantine Empire. The standard myth is that the Humanist Renaissance began with the fall of Byzantium to the Muslims in 1453 but it is just that, a myth.


Raphael’s ‘School of Athens’ (1509–1511) symbolises the recovery of Greek knowledge in the Renaissance Source: Wikimedia Commons

As soon as one mentions the Muslims, one is confronted with a much earlier rebirth of predominantly Greek, intellectual culture, when the, then comparatively young, Islamic Empire began to revive and adopt it in the eight century CE through a massive translation movement of original Greek works covering almost every subject. Writing in Arabic, Arab, Persian, Jewish and other scholars, actively translated the complete spectrum of Greek science into Arabic, analysed it, commented on it, and expanded and developed it, over a period of at least eight centuries.  It is also important to note that the Islamic scholars also collected and translated works from China and India, passing much of the last on to Europe together with the Greek works later during the European renaissances.


The city of Baghdad 150–300 AH (767 and 912 CE) centre of the Islamic recovery and revival of Greek scientific culture Source: Wikimedia Commons

Note the plural at the end of the sentence. Many historians recognise three renaissances during the European Middle Ages. The first of these is the Carolingian Renaissance, which dates to the eighth and ninth century CE and the reigns of Karl der Große (742–814) (known as Charlemagne in English) and Louis the Pious (778–840).


Charlemagne (left) and Pepin the Hunchback (10th-century copy of 9th-century original) Source: Wikimedia Commons

This largely consisted of the setting up of an education system for the clergy throughout Europe and increasing the spread of Latin as the language of learning. Basically, not scientific it had, however, an element of the mathematical sciences, some mathematics, computus (calendrical calculations to determine the date of Easter), astrology and simple astronomy due to the presence of Alcuin of York (c. 735–804) as the leading scholar at Karl’s court in Aachen.


Rabanus Maurus Magnentius (left) another important teacher in the Carolignian Renaissance with Alcuin (middle) presenting his work to Otgar Archbishop of Mainz a supporter of Louis the Pious Source: Wikimedia Commons

Through Alcuin the mathematical work of the Venerable Bede (c. 673–735), (who wrote extensively on mathematical topics and who was also the teacher of Alcuin’s teacher, Ecgbert, Archbishop of York) flowed onto the European continent and became widely disseminated.


The Venerable Bede writing the Ecclesiastical History of the English People, from a codex at Engelberg Abbey in Switzerland. Source: Wikimedia Commons

Karl’s Court had trade and diplomatic relations with the Islamic Empire and there was almost certainly some mathematical influence there in the astrology and astronomy practiced in the Carolingian Empire. It should also be noted that Alcuin and associates didn’t start from scratch as some knowledge of the scholars from late antiquity, such as Boethius (477–524), Macrobius (fl. c. 400), Martianus Capella (fl. c. 410–420) and Isidore of Seville (c. 560–636) had survived. For example, Bede quotes from Isidore’s encyclopaedia the Etymologiae.

The second medieval renaissance was the Ottonian Renaissance in the eleventh century CE during the reigns of Otto I (912–973), Otto II (955–983), and Otto III (980–1002). The start of the Ottonian Renaissance is usually dated to Otto I’s second marriage to Adelheid of Burgundy (931–999), the widowed Queen of Italy in 951, uniting the thrones of Germany (East Francia) and Italy, which led to Otto being crowned Holy Roman Emperor by the Pope in 962.


Statues of Otto I, right, and Adelaide in Meissen Cathedral. Otto and Adelaide were married after his annexation of Italy. Source: Wikimedia Commons

This renaissance was largely confined to the Imperial court and monasteries and cathedral schools. The major influences came from closer contacts with Byzantium with an emphasis on art and architecture.

There was, however, a strong mathematical influence brought about through Otto’s patronage of Gerbert of Aurillac (c. 946–1003). A patronage that would eventually lead to Gerbert becoming Pope Sylvester II.


Sylvester, in blue, as depicted in the Evangelistary of Otto III Source: Wikimedia Commons

A monk in the Monastery of St. Gerald of Aurillac, Gerbert was taken by Count Borrell II of Barcelona to Spain, where he came into direct contact with Islamic culture and studied and learnt some astronomy and mathematics from the available Arabic sources. In 969, Borrell II took Gerbert with him to Rome, where he met both Otto I and Pope John XIII, the latter persuaded Otto to employ Gerbert as tutor for his son the future Otto II. Later Gerbert would exercise the same function for Otto II’s son the future Otto III. The close connection with the Imperial family promoted Gerbert’s ecclesiastical career and led to him eventually being appointed pope but more importantly in our context it promoted his career as an educator.

Gerbert taught the whole of the seven liberal arts, as handed down by Boethius but placed special emphasis on teaching the quadrivium–arithmetic, geometry, music and astronomy–bringing in the knowledge that he had acquired from Arabic sources during his years in Spain. He was responsible for reintroducing the armillary sphere and the abacus into Europe and was one of the first to use Hindu-Arabic numerals, although his usage of them had little effect. He is also reported to have used sighting tubes to aid naked-eye astronomical observations.

Gerbert was not a practicing scientist but rather a teacher who wrote a series of textbook on the then mathematical sciences: Libellus de numerorum divisione, De geometria, Regula de abaco computi, Liber abaci, and Libellus de rationali et ratione uti.


12th century copy of De geometria Source: Wikimedia Commons

His own influence through his manuscripts and his letters was fairly substantial and this was extended by various of his colleagues and students. Abbo of Fleury (c. 945–1004), a colleague, wrote extensively on computus and astronomy, Fulbert of Chartres (c. 960–1028), a direct student, also introduced the use of the Hindu-Arabic numerals. Hermann of Reichenau (1013–1054 continued the tradition writing on the astrolabe, mathematics and astronomy.

Gerbert and his low level, partial reintroduction into Europe of the mathematical science from out of the Islamic cultural sphere can be viewed as a precursor to the third medieval renaissance the so-called Scientific Renaissance with began a century later at the beginning of the twelfth century. This was the mass translation of scientific works, across a wide spectrum, from Arabic into Latin by European scholars, who had become aware of their own relative ignorance compared to their Islamic neighbours and travelled to the border areas between Europe and the Islamic cultural sphere of influence in Southern Italy and Spain. Some of them even travelling in Islamic lands. This Scientific Renaissance took place over a couple of centuries and was concurrent with the founding of the European universities and played a major role in the later Humanist Renaissance to which it was viewed by the humanists as a counterpart. We shall look at it in some detail in the next post.

[1] For any readers, who might not already know, the original quote is, “There was no such thing as the Scientific Revolution, and this is a book about it”, which is the opening sentence of Stevin Shapin’s The Scientific Revolution, The University of Chicago Press, Chicago and London, 1996


Filed under History of science, Mediaeval Science, Renaissance Science, Uncategorized

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

This is a concluding summary to my The emergence of modern astronomy – a complex mosaic blog post series. It is an attempt to produce an outline sketch of the path that we have followed over the last two years. There are, at the appropriate points, links to the original posts for those, who wish to examine a given point in more detail. I thank all the readers, who have made the journey with me and in particular all those who have posted helpful comments and corrections. Constructive comments and especially corrections are always very welcome. For those who have developed a taste for a continuous history of science narrative served up in easily digestible slices at regular intervals, a new series will start today in two weeks if all goes according to plan!

There is a sort of standard popular description of the so-called astronomical revolution that took place in the Early Modern period that goes something liker this. The Ptolemaic geocentric model of the cosmos ruled unchallenged for 1400 years until Nicolas Copernicus published his trailblazing De revolutionibus in 1453, introducing the concept of the heliocentric cosmos. Following some initial resistance, Kepler with his three laws of planetary motion and Galileo with his revelatory telescopic discoveries proved the existence of heliocentricity. Isaac Newton with his law of gravity in his Principia in 1687 provided the physical mechanism for a heliocentric cosmos and astronomy became modern. What I have tried to do in this series is to show that this version of the story is almost totally mythical and that in fact the transition from a geocentric to a heliocentric model of the cosmos was a long drawn out, complex process that took many stages and involved many people and their ideas, some right, some only half right and some even totally false, but all of which contributed in some way to that transition.

The whole process started at least one hundred and fifty years before Copernicus published his magnum opus, when at the beginning of the fifteenth century it was generally acknowledged that astronomy needed to be improved, renewed and reformed. Copernicus’ heliocentric hypothesis was just one contribution, albeit a highly significant one, to that reform process. This reform process was largely triggered by the reintroduction of mathematical cartography into Europe with the translation into Latin of Ptolemaeus’ Geōgraphikḕ Hyphḗgēsis by Jacopo d’Angelo (c. 1360 – 1411) in 1406. A reliable and accurate astronomy was needed to determine longitude and latitude. Other driving forces behind the need for renewal and reform were astrology, principally in the form of astro-medicine, a widened interest in surveying driven by changes in land ownership and navigation as the Europeans began to widen and expand their trading routes and to explore the world outside of Europe.


The Ptolemaic Cosmos: Andreas Cellarius, Harmonia Macrocosmica 1660 Source: Wikimedia Commons

At the beginning of the fifteenth century the predominant system was an uneasy marriage of Aristotelian cosmology and Ptolemaic astronomy, uneasy because they contradicted each other to a large extent. Given the need for renewal and reform there were lively debates about almost all aspects of the cosmology and astronomy throughout the fifteenth and sixteenth centuries, many aspects of the discussions had their roots deep in the European and Islamic Middle Ages, which shows that the 1400 years of unchallenged Ptolemaic geocentricity is a myth, although an underlying general acceptance of geocentricity was the norm.

A major influence on this programme of renewal was the invention of moving type book printing in the middle of the fifteenth century, which made important texts in accurate editions more readily available to interested scholars. The programme for renewal also drove a change in the teaching of mathematics and astronomy on the fifteenth century European universities. 

One debate that was new was on the nature and status of comets, a debate that starts with Toscanelli in the early fifteenth century, was taken up by Peuerbach and Regiomontanus in the middle of the century, was revived in the early sixteenth century in a Europe wide debate between Apian, Schöner, Fine, Cardano, Fracastoro and Copernicus, leading to the decisive claims in the 1570s by Tycho Brahe, Michael Mästlin, and Thaddaeus Hagecius ab Hayek that comets were celestial object above the Moon’s orbit and thus Aristotle’s claim that they were a sub-lunar meteorological phenomenon was false. Supralunar comets also demolished the Aristotelian celestial, crystalline spheres. These claims were acknowledged and accepted by the leading European Ptolemaic astronomer, Christoph Clavius, as were the claims that the 1572 nova was supralunar. Both occurrences shredded the Aristotelian cosmological concept that the heaven were immutable and unchanging.

The comet debate continued with significant impact in 1618, the 1660s, the 1680s and especially in the combined efforts of Isaac Newton and Edmund Halley, reaching a culmination in the latter’s correct prediction that the comet of 1682 would return in 1758. A major confirmation of the law of gravity.

During those early debates it was not just single objects, such as comets, that were discussed but whole astronomical systems were touted as alternatives to the Ptolemaic model. There was an active revival of the Eudoxian-Aristotelian homocentric astronomy, already proposed in the Middle Ages, because the Ptolemaic system, of deferents, epicycles and equant points, was seen to violate the so-called Platonic axioms of circular orbits and uniform circular motion. Another much discussed proposal was the possibility of diurnal rotation, a discussion that had its roots in antiquity. Also, on the table as a possibility was the Capellan system with Mercury and Venus orbiting the Sun in a geocentric system rather than the Earth.


The Copernican Cosmos: Andreas Cellarius, Harmonia Macrocosmica 1660 Source: Wikimedia Commons

Early in the sixteenth century, Copernicus entered these debates, as one who questioned the Ptolemaic system because of its breaches of the Platonic axioms, in particular the equant point, which he wished to ban. Quite how he arrived at his radical solution, replace geocentricity with heliocentricity we don’t know but it certainly stirred up those debates, without actually dominating them. The reception of Copernicus’ heliocentric hypothesis was complex. Some simply rejected it, as he offered no real proof for it. A small number had embraced and accepted it by the turn of the century. A larger number treated it as an instrumentalist theory and hoped that his models would deliver more accurate planetary tables and ephemerides, which they duly created. Their hopes were dashed, as the Copernican tables, based on the same ancient and corrupt data, proved just as inaccurate as the already existing Ptolemaic ones. Of interests is the fact that it generated a serious competitor, as various astronomers produced geo-heliocentric systems, extensions of the Capellan model, in which the planets orbit the Sun, which together with the Moon orbits the Earth. Such so-called Tychonic or semi-Tychonic systems, named after their most well-known propagator, incorporated all the acknowledged advantages of the Copernican model, without the problem of a moving Earth, although some of the proposed models did have diurnal rotation.


The Tychonic Cosmos: Andreas Cellarius, Harmonia Macrocosmica 1660 Source: Wikimedia Commons

The problem of inaccurate planetary tables and ephemerides was already well known in the Middle Ages and regarded as a major problem. The production of such tables was seen as the primary function of astronomy since antiquity and they were essential to all the applied areas mentioned earlier that were the driving forces behind the need for renewal and reform. Already in the fifteenth century, Regiomontanus had set out an ambitious programme of astronomical observation to provide a new data base for such tables. Unfortunately, he died before he even really got started. In the second half of the sixteenth century both Wilhelm IV Landgrave of Hessen-Kassel and Tycho Brahe took up the challenge and set up ambitious observation programmes that would eventually deliver the desired new, more accurate astronomical data.

At the end of the first decade of the seventeenth century, Kepler’s Astronomia Nova, with his first two planetary laws (derived from Tycho’s new accurate data), and the invention of the telescope and Galileo’s Sidereus Nuncius with his telescopic discoveries are, in the standard mythology, presented as significant game changing events in favour of heliocentricity. They were indeed significant but did not have the impact on the system debate that is usually attributed them. Kepler’s initial publication fell largely on deaf ears and only later became relevant. On Galileo’s telescopic observations, firstly he was only one of a group of astronomers, who in the period 1610 to 1613 each independently made those discoveries, (Thomas Harriot and William Lower, Simon Marius, Johannes Fabricius, Odo van Maelcote and Giovanni Paolo Lembo, and Christoph Scheiner) but what did they show or prove? The lunar features were another nail in the coffin of the Aristotelian concept of celestial perfection, as were the sunspots. The moons of Jupiter disproved the homocentric hypothesis. Most significant discovery was the of the phases of Venus, which showed that a pure geocentric model was impossible, but they were conform with various geo-heliocentric models.

1613 did not show any clarity on the way to finding the true model of the cosmos but rather saw a plethora of models competing for attention. There were still convinced supporters of a Ptolemaic model, both with and without diurnal rotation, despite the phases of Venus. Various Tychonic and semi-Tychonic models, once again both with and without diurnal rotation. Copernicus’ heliocentric model with its Ptolemaic deferents and epicycles and lastly Kepler’s heliocentric system with its elliptical orbits, which was regarded as a competitor to Copernicus’ system. Over the next twenty years the fog cleared substantially and following Kepler’s publication of his third law, his Epitome Astronomiae Copernicanae, which despite its title is a textbook on his elliptical system and the Rudolphine Tables, again based on Tycho’s data, which delivered the much desired accurate tables for the astrologers, navigators, surveyors and cartographers, and also of Longomontanus’ Astronomia Danica (1622) with his own tables derived from Tycho’s data presenting an updated Tychonic system with diurnal rotation, there were only two systems left in contention.

Around 1630, we now have two major world systems but not the already refuted geocentric system of Ptolemaeus and the largely forgotten Copernican system as presented in Galileo’s Dialogo but Kepler’s elliptical heliocentricity and a Tychonic system, usually with diurnal rotation. It is interesting that diurnal rotation became accepted well before full heliocentricity, although there was no actually empirical evidence for it. In terms of acceptance the Tychonic system had its nose well ahead of Kepler because of the lack of any empirical evidence for movement of the Earth.

Although there was still not a general acceptance of the heliocentric hypothesis during the seventeenth century the widespread discussion of it in continued in the published astronomical literature, which helped to spread knowledge of it and to some extent popularise it. This discussion also spread into and even dominated the newly emerging field of proto-sciencefiction.

Galileo’s Dialogo was hopelessly outdated and contributed little to nothing to the real debate on the astronomical system. However, his Discorsi made a very significant and important contribution to a closely related topic that of the evolution of modern physics. The mainstream medieval Aristotelian-Ptolemaic cosmological- astronomical model came as a complete package together with Aristotle’s theories of celestial and terrestrial motion. His cosmological model also contained a sort of friction drive rotating the spheres from the outer celestial sphere, driven by the unmoved mover (for Christians their God), down to the lunar sphere. With the gradual demolition of Aristotelian cosmology, a new physics must be developed to replace the Aristotelian theories.

Once again challenges to the Aristotelian physics had already begun in the Middle Ages, in the sixth century CE with the work of John Philoponus and the impetus theory, was extended by Islamic astronomers and then European ones in the High Middle Ages. In the fourteenth century the so-called Oxford Calculatores derived the mean speed theorem, the core of the laws of fall and this work was developed and disseminated by the so-called Paris Physicists. In the sixteenth century various mathematicians, most notably Tartaglia and Benedetti developed the theories of motion and fall further. As did in the early seventeenth century the work of Simon Stevin and Isaac Beeckman. These developments reached a temporary high point in Galileo’s Discorsi. Not only was a new terrestrial physics necessary but also importantly for astronomy a new celestial physics had to be developed. The first person to attempt this was Kepler, who replaced the early concept of animation for the planets with the concept of a force, hypothesising some sort of magnetic force emanating from the Sun driving the planets around their orbits. Giovanni Alfonso Borelli also proposed a system of forces as the source of planetary motion.

Throughout the seventeenth century various natural philosophers worked on and made contributions to defining and clarifying the basic terms that make up the science of dynamics: force, speed, velocity, acceleration, etc. as well as developing other areas of physics, Amongst them were Simon Stevin, Isaac Beeckman, Borelli, Descartes, Pascal, Riccioli and Christiaan Huygens. Their efforts were brought together and synthesised by Isaac Newton in his Principia with its three laws of motion, the law of gravity and Kepler’s three laws of planetary motion, which laid the foundations of modern physics.

In astronomy telescopic observations continued to add new details to the knowledge of the solar system. It was discovered that the planets have diurnal rotation, and the periods of their diurnal rotations were determined. This was a strong indication the Earth would also have diurnal rotation. Huygens figured out the rings of Saturn and discovered Titan its largest moon. Cassini discovered four further moons of Saturn. It was already known that the four moons of Jupiter obeyed Kepler’s third law and it would later be determined that the then known five moons of Saturn also did so. Strong confirming evidence for a Keplerian model.

Cassini showed by use of a heliometer that either the orbit of the Sun around the Earth or the Earth around the Sun was definitively an ellipse but could not determine which orbited which. There was still no real empirical evidence to distinguish between Kepler’s elliptical heliocentric model and a Tychonic geo-heliocentric one, but a new proof of Kepler’s disputed second law and an Occam’s razor argument led to the general acceptance of the Keplerian model around 1660-1670, although there was still no empirical evidence for either the Earth’s orbit around the Sun or for diurnal rotation. Newton’s Principia, with its inverse square law of gravity provided the physical mechanism for what should now best be called the Keplerian-Newtonian heliocentric cosmos.

Even at this juncture with a very widespread general acceptance of this Keplerian-Newtonian heliocentric cosmos there were still a number of open questions that needed to be answered. There were challenges to Newton’s work, which, for example, couldn’t at that point fully explain the erratic orbit of the Moon around the Earth. This problem had been solved by the middle of the eighteenth century. The mechanical philosophers on the European continent were anything but happy with Newton’s gravity, an attractive force that operates at a distance. What exactly is it and how does it function? Questions that even Newton couldn’t really answer. Leibniz also questioned Newton’s insistence that time and space were absolute, that there exists a nil point in the system from which all measurement of these parameters are taken. Leibniz preferred a relative model.

There was of course also the very major problem of the lack of any form of empirical evidence for the Earth’s movement. Going back to Copernicus nobody had in the intervening one hundred and fifty years succeeded in detecting a stellar parallax that would confirm that the Earth does indeed orbit the Sun. This proof was finally delivered in 1725 by Samuel Molyneux and James Bradley, who first observed, not stellar parallax but stellar aberration. An indirect proof of diurnal rotation was provided in the middle of the eighteenth century, when the natural philosophers of the French Scientific Academy correctly determined the shape of the Earth, as an oblate spheroid, flattened at the pols and with an equatorial bulge, confirming the hypothetical model proposed by Newton and Huygens based on the assumption of a rotating Earth.

Another outstanding problem that had existed since antiquity was determining the dimensions of the known cosmos. The first obvious method to fulfil this task was the use of parallax, but whilst it was already possible in antiquity to determine the distance of the Moon reasonably accurately using parallax, down to the eighteenth century it proved totally impossible to detect the parallax of any other celestial body and thus its distance from the Earth. Ptolemaeus’ geocentric model had dimensions cobbled together from its data on the crystalline spheres. One of the advantages of the heliocentric model is that it gives automatically relative distances for the planets from the sun and each other. This means that one only needs to determine a single actually distance correctly and all the others are automatically given. Efforts concentrated on determining the distance between the Earth and the Sun, the astronomical unit, without any real success; most efforts producing figures that were much too small.

Developing a suggestion of James Gregory, Edmond Halley explained how a transit of Venus could be used to determine solar parallax and thus the true size of the astronomical unit. In the 1760s two transits of Venus gave the world the opportunity to put Halley’s theory into practice and whilst various problems reduced the accuracy of the measurements, a reasonable approximation for the Sun’s distance from the Earth was obtained for the very first time and with it the actually dimensions of the planetary part of the then known solar system. What still remained completely in the dark was the distance of the stars from the Earth. In the 1830s, three astronomers–Thomas Henderson, Friedrich Wilhelm Bessel and Friedrich Georg Wilhelm von Struve–all independently succeeded in detecting and measuring a stellar parallax thus completing the search for the dimensions of the known cosmos and supplying a second confirmation, after stellar aberration, for the Earth’s orbiting the Sun.

In 1851, Léon Foucault, exploiting the Coriolis effect first hypothesised by Riccioli in the seventeenth century, finally gave a direct empirical demonstration of diurnal rotation using a simple pendulum, three centuries after Copernicus published his heliocentric hypothesis. Ironically this demonstration was within the grasp of Galileo, who experiment with pendulums and who so desperately wanted to be the man who proved the reality of the heliocentric model, but he never realised the possibility. His last student, Vincenzo Viviani, actually recorded the Coriolis effect on a pendulum but didn’t realise what it was and dismissed it as an experimental error.

From the middle of the eighteenth century, at the latest, the Keplerian-Newtonian heliocentric model had become accepted as the real description of the known cosmos. Newton was thought not just to have produced a real description of the cosmos but the have uncovered the final scientific truth. This was confirmed on several occasions. Firstly, Herschel’s freshly discovered new planet Uranus in 1781 fitted Newton’s theories without problem, as did the series of asteroids discovered in the early nineteenth century. Even more spectacular was the discovery of Neptune in 1846 based on observed perturbations from the path of Uranus calculated with Newton’s theory, a clear confirmation of the theory of gravity. Philosophers, such as Immanuel Kant, no longer questioned whether Newton had discovered the true picture of the cosmos but how it had been possible for him to do so.


However, appearances were deceptive, and cracks were perceptible in the Keplerian-Newtonian heliocentric model. Firstly, Leibniz’s criticism of Newton’s insistence on absolute time and space rather than a relative model would turn out to have been very perceptive. Secondly, Newton’s theory of gravity couldn’t account for the observed perihelion precession of the planet Mercury. Thirdly in the 1860s, based on the experimental work of Michael Faraday, James Maxwell produced a theory of electromagnetism, which was not compatible with Newtonian physics. Throughout the rest of the century various scientists including Hendrik Lorentz, Georg Fitzgerald, Oliver Heaviside, Henri Poincaré, Albert Michelson and Edward Morley tried to find a resolution to the disparities between the Newton’s and Maxwell’s theories. Their efforts finally lead to Albert Einstein’s Special Theory of Relativity and then on to his General theory of Relativity, which could explain the perihelion precession of the planet Mercury. The completion of the one model, the Keplerian-Newtonian heliocentric one marked the beginnings of the route to a new system that would come to replace it.


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

Christmas Trilogy 2020 Part 3: The peregrinations of Johannes K

We know that human beings have been traversing vast distances on the surface of the globe since Homo sapiens first emerged from Africa. However, in medieval Europe it would not have been uncommon for somebody born into a poor family never in their life to have journeyed more than perhaps thirty kilometres from their place of birth. Maybe a journey into the next larger settlement on market day or perhaps once a year to an even larger town for a fair on a public holiday. This might well have been Johannes Kepler’s fate, born as he was into an impoverished family, had it not been for his extraordinary intellectual abilities. Although he never left the Southern German speaking area of Europe (today, Southern Germany, Austria and the Czech Republic), he managed to clock up a large number of journey kilometres over the fifty-eight years of his life. In those days there was, of course, no public transport and in general we don’t know how he travelled. We can assume that for some of his longer journeys that he joined trader caravans. Traders often travelled in large wagon trains with hired guards to protect them from thieves and marauding bands and travellers could, for a fee, join them for protection. We do know that as an adult Kepler travelled on horseback but was often forced to go by foot due to the pain caused by his piles.[1]

It is estimated that in the Middle ages someone travelling on foot with luggage would probably only manage 15 km per day going up to perhaps 22 km with minimal luggage. A horse rider without a spare mount maybe as much as 40 km per day, with a second horse up to 60 km per day. I leave it to the reader to work out how long each of Kepler’s journeys might have taken him.


Johannes Kepler Source: Wikimedia Commons

Johannes’ first journey from home took place, when he attended the convent-school in Adelberg at the age of thirteen, which lies about 70 km due west of his birthplace, Weil der Stadt, and about 90 km, also due west of Ellmendigen, where his family were living at the time.


Adelberg Convent Source: Wikimedia Commons

His next journey took place a couple of years later when he transferred to the Cistercian monastery in Maulbronn about 50 km north of Weil der Stadt and 30 west of Ellmendingen.


Maulbronn Monastery Source: Wikimedia Commons

Finished with the lower schools in 1589, he undertook the journey to the University of Tübingen, where he was enrolled in the Tübinger Stift, about 40 km south of Weil der Stadt.


The Evangelical Tübinger Stift on the banks of the Neckar Source: WIkimedia Commons

Johannes’ first really long journey took place in 1594, when on 11 April he set out for Graz the capital city of Styria in Austria to take up the posts of mathematics teacher in the Lutheran academy, as well as district mathematicus, a distance of about 650 km. The young scholar would have been on the road for quite a few days.


Graz, Mur und Schloßberg, Georg Matthäus Vischer (1670) Source: Wikimedia Commons

Although he only spent a few years in Graz, Kepler manged at first to stabilise his life even marrying, Barbara Müller, and starting a family. However, the religious conflicts of the period intervened and Kepler, a Lutheran Protestant living in a heavily Catholic area became a victim of those conflicts. First, the Protestants of the area were forced to convert or leave, which led to the closing of the school where Kepler was teaching and his losing his job. Because of his success as astrologer, part of his duties as district mathematicus, Kepler was granted an exception to the anti-Protestant order, but it was obvious that he would have to leave. He appealed to Tübingen to give him employment, but his request fell on deaf ears. The most promising alternative seemed to be to go and work for Tycho Brahe, the Imperial Mathematicus, currently ensconced in the imperial capital, Prague, a mere 450 km distant.


Prague in the Nuremberg Chronicle 1493 Source: Wikimedia Commons

At first Kepler didn’t know how he would manage the journey to Prague to negotiate about possible employment with Tycho. However, an aristocratic friend was undertaking the journey and took Johannes along as a favour. After, several weeks of fraught and at times downright nasty negotiations with the imperious Dane, Kepler was finally offered employment and with this promise in his pocket he returned to Graz to settle his affairs, pack up his household and move his family to Prague. He made the journey between Graz and Prague three times in less than a year.

Not long after his arrival in Prague, with his family, Tycho died and Kepler was appointed his successor, as Imperial Mathematicus, the start of a ten year relatively stable period in his life. That is, if you can call being an imperial servant at the court of Rudolf II, stable. Being on call 24/7 to answer the emperor’s astrological queries, battling permanently with the imperial treasury to get your promised salary paid, fighting with Tycho’s heirs over the rights to his data. Kepler’s life in Prague was not exactly stress free.

1608 saw Johannes back on the road. First to Heidelberg to see his first major and possibly most important contribution to modern astronomy, his Astronomia Nova (1609), through the press and then onto the book fair in Frankfurt to sell the finished work, that had cost him several years of his life. Finally, back home to Prague from Frankfurt. A total round-trip of 1100 km, plus he almost certainly took a detour to visit his mother somewhere along his route.

Back in Prague things began to look rather dodgy again for Kepler and his family, as Rudolf became more and more unstable and Johannes began to look for a new appointment and a new place to live. His appeals to Tübingen for a professorship, not an unreasonable request, as he was by now widely acknowledged as Europe’s leading theoretical astronomer, once again fell on deaf ears. His search for new employment eventually led him to Linz the capital city of Upper Austria and the post of district mathematicus. 1612, found Johannes and his children once again on the move, his wife, Barbara, had died shortly before, this time transferring their household over the comparatively short distance of 250 km.


Linz anno 1594 Source: Wikimedia Commons

Settled in Linz, Kepler married his second wife, Susanna Reuttinger, after having weighed up the odds on various potential marriage candidates and the beginning of a comparative settled fourteen-year period in his life. That is, if you can call becoming embroiled in the Thirty Years War and having your mother arrested and charged with witchcraft settled. His mother’s witchcraft trial saw Johannes undertaking the journey from Linz to Tübingen and home again, to organise and conduct her defence, from October to December in 1617 and again from September 1620 to November 1621, a round trip each time of about 1,000 km, not to forget the detours to Leonberg, his mother’s home, 50 km from Tübingen, from where he took his mother, a feeble woman of 70, back to Linz on the first journey.

In 1624, Johannes set out once again, this time to Vienna, now the imperial capital, to try and obtain the money necessary to print the Rudolphine Tables from Ferdinand II the ruling emperor, just 200 km in one direction. Ferdinand refused to give Kepler the money he required, although the production of the Rudolphine Tables had been an imperial assignment. Instead, he ordered the imperial treasury to issues Kepler promissory notes on debts owed to the emperor by the imperial cities of Kempten, Augsburg and Nürnberg, instructing him to go and collect on the debts himself. Kepler returned to Linz more than somewhat disgruntled and it is not an exaggeration that his life went downhill from here.

Kepler set out from Linz to Augsburg, approximately 300 km, but the Augsburg city council wasn’t playing ball and he left empty handed for Kempten, a relatively short 100 km. In Kempten the authorities agreed to purchase and pay for the paper that he needed to print the Rudolphine Tables. From Kempten he travelled on to Nürnberg, another 250 km, which he left again empty handed, returning the 300 km to Linz, completing a nearly 1,000 km frustrating round trip that took four months.

In 1626, the War forced him once again to pack up his home and to leave Linz forever with his family. He first travelled to Regensburg where he found accommodation for his family before travelling on to Ulm where he had had the paper from Kempten delivered so that he could begin printing, a combined journey of about 500 km. When the printing was completed in 1627, having paid the majority of the printing costs out of his own pocket, Kepler took the entire print run to the bookfair in Frankfurt and sold it in balk to a book dealer to recoup his money, another journey of 300 km. He first travelled back to Ulm and then home to his family in Regensburg, adding another 550 km to his life’s total. Regensburg was visited by the emperor and Wallenstein, commander in chief of the Catholic forces, and Kepler presented the Tables to the Emperor, who received them with much praise for the author.

In 1628, he entered the service of Wallenstein, as his astrologer, moving from Regensburg to Wallenstein’s estates in the Dutchy of Sagan, yet another 500 km. In 1630, the emperor called a Reichstag in Regensburg and on 8 October Kepler set out on the last journey of his life to attend. Why he chose to attend is not very clear, but he did. He journeyed from Zagan to Leipzig and from there to Nürnberg before going on to Regensburg a total of 700 km. He fell ill on his arrival in Regensburg and died 15 November 1630.


Regensburg Nuremberg Chronicle 1493 Source: Wikimedia Commons

The mathematical abilities of the young boy born to an impoverish family in Weil der Stadt fifty-eight-years earlier had taken him on a long intellectual journey but also as we have seen on a long physical one, down many a road.


[1] I almost certainly haven’t included all of the journeys that Kepler made in his lifetime, but I think I’ve got most of the important ones. The distances are rounded up or down and are based on the modern distances by road connecting the places travelled to and from. The roads might have run differently in Kepler’s day.

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

The solar year ends and starts with a great conjunction

Today is the winter solstice, which as I have explained on various occasions, in the past, is for me the natural New Year’s Eve/New Year’s Day rather than the arbitrary 31 December/1 January.


Obligatory Stonehenge winter solstice image

Today in also the occurrence of a so-called great conjunction in astronomy/astrology, which is when, viewed from the Earth, Jupiter and Saturn appear closest together in the night sky. Great conjunctions occur every twenty years but this one is one in which the two planets appear particularly close to each other.


Great conjunctions played a decisive role in the life of Johannes Kepler. As a youth Kepler received a state grant to study at the University of Tübingen. The course was a general-studies one to prepare the students to become Lutheran schoolteachers or village pastors in the newly converted Protestant state. Kepler, who was deeply religious, hoped to get an appointment as a pastor but when a vacancy came up for Protestant mathematics teacher in Graz, Michael Mästlin recommended Kepler and so his dream of becoming a pastor collapsed. He could have turned down the appointment but then he would have had to pay back his grant, which he was in no position to do so.

In 1594, Kepler thus began to teach the Protestant youths of Graz mathematics. He accepted his fate reluctantly, as he still yearned for the chance to serve his God as a pastor. Always interested in astronomy and converted to heliocentricity by Michael Mästlin, whilst still a student, he had long pondered the question as to why there were exactly six planets. Kepler’s God didn’t do anything by chance, so there had to be a rational reason for this. According to his own account, one day in class whilst explaining the cyclical nature of the great conjunctions in astronomy/astrology, which is when, viewed from the Earth, Jupiter and Saturn appear closest together in the night sky, he had a revelation.  Looking at the diagram that he had drawn on the board he asked himself, “What if his God’s cosmos was a geometrical construction and this was the determining factor in the number of planets?”


Kepler’s geometrical diagram of the cyclical nature of the great conjunctions in his Mysterium Cosmographicum Source: Linda Hall Library

Kepler determined from that point on in his life to serve his God as an astronomer by revealing the geometric structure of God’s cosmos. He first experimented with various regular polygons, inspired by the great conjunction diagram, but couldn’t find anything that fit, so he moved into three dimensions and polyhedra. Here he struck gold and decided that there were exactly six planets because their orbital spheres were separated by the five regular Platonic solids.


Source: Wikimedia Commons


He published this theory in his first academic book, Mysterium Cosmographicum (lit. The Cosmographic Mystery, alternately translated as Cosmic MysteryThe Secret of the World) 1597. The book also contains his account of the revelation inspired by the great conjunction diagram. This was the start of his whole life’s work as a theoretical astronomer, which basically consisted of trying to fine tune this model.

In the early seventeenth century, Kepler was still deeply religious, a brilliant mathematician and theoretical astronomer, and a practicing astrologer. As an astrologer Kepler rejected the standard Ptolemaic sun sign i.e., Aquarius, Virgo, Gemini, etc., astrology. Normal horoscope astrology. Sun signs, or as most people call them star signs, are 30° segments of the circular ecliptic, the apparent path of the Sun around the Earth and not the asterisms or stellar constellations with the same names. Kepler developed his own astrology based entirely on planetary aspects, that is the angles subtended by the planets with each other on the ecliptic. (see the Wikipedia article Astrological aspect). Of course, in Kepler’s own astrology conjunctions play a major role.

Turning to the so-called Star of Bethlehem, the men from the east (no number is mentioned), who according to Matthew 2:2, followed the star were, in the original Greek, Magoi (Latin/English Magi) and this means they were astrologers and not the sanitised wise men or kings of the modern story telling. Kepler would have been very well aware of this. This led Kepler to speculate that what the Magoi followed was an important astrological occurrence and not a star in the normal meaning of the word. One should note that in antiquity all visible celestial objects were stars. Stars simple Asteres, planets (asteres) planētai wandering (stars) and a comet (aster) komētēs, literally long-haired (star), so interpreting the Star of Bethlehem as an astrological occurrence was not a great sketch.

His revelation in 1603 was that this astrological occurrence was a great conjunction and in fact a very special one, a so-called fiery trigon, one that links the three fire signs, Aries, Leo, Sagittarius.


Calculating backwards, Kepler the astronomer, determined that one such had occurred in 7 BCE and this was the star that the Magoi followed.

Whether Kepler’s theory was historically correct or an accepted view in antiquity is completely impossible to determine, is the Bible story of Jesus’ birth even true? In Kepler’s own time, nobody accepted his deviant astrology, so I very much doubt that many people accepted his Star of Bethlehem story, which he published in his De Stella Nova in Pede Serpentarii (On the New Star in the Foot of the Serpent Handler) in 1606.

I’m sure that a great conjunction on the date of the winter solstice has a very deep astrological significance but whether astrologers will look back and say, “Ah, that triggered this or that historical occurrence” only the future will tell.

I thank all of those who have read, digested and even commented upon my outpourings over the last twelve months and fully intend to do my best to keep you entertained over the next twelve. No matter which days you choose to celebrate during the next couple of weeks, in which way whatsoever and for what reasons, I wish all of my readers all the best and brace yourselves for another Renaissance Mathematicus Christmas Trilogy starting on 25 December.



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

A master instrument maker from a small town in the Fränkischen Schweiz


Eggolsheim is a small market town about twenty kilometres almost due north of Erlangen in the Fränkischen Schweiz (Franconian Switzerland).


Eggolsheim Source: Wikimedia Commons

The Fränkischen Schweiz is a hilly area with many rock faces and caves in Middle Franconia, to the north of Nürnberg that is very popular with tourists, day trippers, wanderers, rock-climbers and potholers. It also has lots of old churches and castles.


Fränkische Schweiz Source Wikimedia Commons

When I first moved to Middle Franconia the Fränkischen Schweiz had the highest density of private breweries of anywhere in the world. It also has many bierkeller that during the summer months attract large crowds of visitors at the weekend. Eggolsheim is these days probably best known for its bierkeller, but in the late fifteenth century it was the birthplace of the Renaissance mathematicus, Georg Hartmann, who would become one of the leading instrument makers in Renaissance Nürnberg in the early sixteenth century.


Georg Hartmann Source: Astronomie in Nürnberg

Hartmann was born on 9 February 1489. Unfortunately, as with so many Renaissance figures, we know nothing about his background or childhood. He matriculated at the university of Ingolstadt in 1503, which is where people from Franconia often studied as there were no University in either Nürnberg or Bamberg. Johannes Werner and Johannes Stabius, two other members of Nürnberg’s Renaissance mathematical community were graduates of Ingolstadt. In 1506, Hartmann transferred to the University of Köln, where he studied mathematics and theology, graduating in 1510. As was quite common during this period he completed his studies on a journey through Italy between 1510 and 1518. He spent several years in Rome, where he was friends with Andreas Copernicus, the older brother of Nicolas, who died in Rome, possibly of leprosy or syphilis in 1518.

In 1518 Hartmann arrived in Nürnberg, where he was appointed a vicar of the St. Sebaldus Church, one of the two parish churches of the city. Unlike the modern Anglican Church, where the vicar is the principal priest of a church, in the sixteenth century Catholic Church a vicar was a deputy or replacement priest with a special function appointed either permanently or temporarily. He might, for example, be appointed to sing a daily mass in the name of a rich deceased member of the parish, who left a stipend in his will to pay for this service, as another of Nürnberg’s mathematical community, Johannes Schöner, was appointed to do in Kirchehrenbach, also in the Fränkischen Schweiz, in 1523. We don’t know what Hartmann’s specific duties in the St. Sebaldus Church were. In 1522 he was also granted the prebend of the St. Walburga Chapel in Nürnberg.

St. Sebald von Norden

St. Sebaldus in Nürnberg Source: Wikimedia Commons

This was a sinecure. It was not unusual for mathematici to receive sinecures from the Church to enable them to carry out their activities as mathematicians, instrument makers or cartographers in the service of the Church. This was certainly the case with Johannes Schöner, who was many years paid as a member of the St Joseph Beneficence in Bamberg but worked as mathematicus, printer and bookbinder for the Bishop. If this was actually so in Hartmann’s case is not known.

When he arrived in Nürnberg he became part of the, for the time, comparatively large community of mathematici, print makers, printer/publishers and instrument makers, which included both Werner and Stabius, the latter as a regular visitor, but both of whom died in 1522. I have written about this group before here and here. It also included Schöner, who only arrived in 1525, Erhard Etzlaub, Johann Neudörffer, Johannes Petreius and Albrecht Dürer.  Central to this group was Willibald Pirckheimer, who although not a mathematicus, was a powerful local figure–humanist scholar, merchant trader, soldier, politician, Dürer’s friend and patron–who had translated Ptolemaeus’ Geographia from Greek into Latin. Hartmann was friends with both Pirckheimer and Dürer, and acted as Schöner’s agent in Nürnberg, selling his globes in the city, during the time Schöner was still living in Kirchehrenbach. Like other members of this group Hartmann also stood in contact with and corresponded with many other scholars throughout Europe; the Nürnberger mathematici were integrated into the European network of mathematici.

Hartmann established himself as one of Nürnberg’s leading scientific instrument makers; he is known to have produced sundials, astrolabes, armillary spheres and globes. None of his armillary spheres or globes are known to have survived, although a few globe gores made by him are extant, an important factor when trying to assess the impact or range of an instrument maker, we can only work with that which endures the ravages of time. We know for example that Hartmann’s friend and colleague, Schöner, produced and sold large numbers of terrestrial and celestial globes but only a small handful of his globes are preserved.

A total of nine of Hartmann’s brass astrolabes are known to have survived and here Hartmann proved to be an innovator.


Hartmann astrolabe front



Hartmann astrolabe back

As far as is known, Hartmann was the earliest astrolabe maker to introduce serial production of this instrument. It is now assumed that he designed the instruments and then commissioned some of Nürnberg’s numerous metal workers to mass produce the separate parts of the astrolabe, which he them assembled and sold. Nine astrolabes might not seem a lot but compared to other known astrolabe makers, from whom often just one or two instruments are known, this is a comparatively large number. This survival rate suggests that Hartmann made and sold a large number of his mass-produced instruments.  

With his sundials the survival rate is much higher, there are seventy-five know Hartmann sundials in collection around the world. Hartmann made sundials of every type in brass, gold and ivory but is perhaps best known for his portable diptych sundials, a Nürnberg specialty. A diptych consists of two flat surfaces, usually made of ivory, connected by a hinge that fold flat to be put into a pocket. When opened the two surfaces are at the correct angle and joined by a thread, which functions as the dial’s gnomon. The lower surface contains a compass to help the user correctly orientate his dial during use.


Hartmann diptych sundial open


Hartmann diptych sundial closed


Open diptych sundial showing string gnomon and Hartmann’s name

Hartmann also made elaborate dials such as this ivory crucifix dial.


One thing that Hartmann is noted for is his paper instruments*. These are the elements for instrument printed on sheets of paper. These can be cut out and glued to thin wood backing to construct cheap but fully functioning instruments. Of course, the survival rates of such instruments are very low and in fact only one single paper astrolabe printed by Hartmann is known to have survived.


Hartmann paper astrolabe Source:History of Science Museum Oxford

However, we are lucky that several hundred sheets of Hartmann’s printed paper instruments have survived and are now deposited in various archives. There have been discussions, as to whether these were actually intended to be cut out and mounted onto wood to create real instruments or whether there are intended as sales archetypes, designed to demonstrate to customers the instruments that Hartmann would then construct out of ivory, brass or whatever.

Hartmann_Kruzifix_1529,_AGKnr4_2004,_s12 Hartmann paper crucifix


Printed paper instrument part



Apart from designing and constructing instruments Hartman was obviously engaged in writing a book on how to design and construct instrument. Several partial manuscripts of this intended work exist but the book was never finished in his lifetime. The book however does reveal his debt as an instrument designer to Johannes Stöffler’s Elucidatio fabricae usuque astrolabii.

As a manufacturer of portable sun dials with built in compasses Hartmann also developed a strong interest in the magnetic compass. Whilst living in Rome he determined the magnetic declination of the city, i.e., how much a compass needle varies from true north in that location. Hartmann also appears to have been the first to discover magnetic dip or inclination, which information he shared with Duke Albrecht of Prussia in a letter in 1544, but he never published his discovery, so it is usually credited to the English mariner Robert Norman, who published the discovery in his The Newe Attractive, shewing The Nature, Propertie, and manifold Vertues of the Loadstone; with the declination of the Needle, Touched therewith, under the Plaine of the Horizon in 1581.

The only book that Hartmann did publish in his lifetime was an edition of John Peckham’s Perspectiva communis, the most widely used medieval optic textbook, which was printed by Johannes Petreius in 1542.


Hartmann died in Nürnberg in 1564 and was buried in the St Johannes graveyard, outside the city walls, where the graves of his friend Pirckheimer, Dürer and Petreius can also be found amongst many other prominent citizens of the Renaissance city.  


Hartmann’s grave Source: Astronomie in Nürnberg


Hartmann’s epitaph Source: Astronomie in Nürnberg

  • For a detailed description of Hartmann’s printed paper instruments see: Suzanne Karr Schmidt, Interactive and Sculptural Printmaking in the Renaissance, Brill, 2017

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

Astrology in the age of Newton

My Annus Mythologicus blog post was recently retweeted on Twitter in response to an inane tweet from Richard Dawkins and somebody questioned the reference in it that Newton was inspired to take up mathematics upon reading a book on astrology. This was not a nasty attack but a genuine statement on interest from somebody who had difficulty believing a man, who has been called the greatest mathematician ever, should have had anything to do with an astrology book. There is a sort of naïve belief that it is impossible for the people in the age of Newton, which is touted as the birth of the age of modern science and rationalism, could have had anything to do with the so-called occult sciences. This belief led many people, who should have known better, to try and sweep Newton’s very active engagement with alchemy under the carpet. During Newton’s lifetime astrology lost its status as a university discipline but was still all pervasive and permeated all aspects and levels of society. In what follows I will sketch some of the details of the role of astrology in the age of Newton.


Newton – 1677 Source: Wikimedia Commons

The Renaissance/Early Modern Period could with justification be called the golden age of astrology in Europe. This period was actually coming to an end during Newton’s lifetime, but astrology had by no means totally disappeared. That golden age began roughly with the beginning of the fifteenth century. During the first half of the century the humanist universities of Northern Italy and Poland created the first regular, dedicated chairs for mathematics and astronomy, which were in fact chairs for astrology, created to teach astrology to medical students. Teaching astrology to medical students was one of the principle obligations of the professors for mathematics at these universities and continued to be so well down into the seventeenth century. This trend continued with the creation of the first such chair in Germany, at the University of Ingolstadt, in the early 1470s. Astrological medicine, or iatromathematics to it is formal name was just one branch of astrology that flourished in this period.

Medical astrology was along with astrological meteorology considered to be a form of natural astrology and even those, who rejected natal astrology, for example, accepted the validity of natural astrology. Opposed to natural astrology was judicial astrology collective term for a group of other forms of astrology. Natal astrology, or genethliacal astrology, is the classic birth horoscope astrology that everybody thinks of, when they first hear the term astrology.  Other forms of judicial horoscope astrology are mundane astrology concerns the fate of nations etc., horary astrology answers question by casting a horoscope when the question is presented, and electional astrology, which is used to determine the most appropriate or auspicious time to carry out a planned action.

All these forms of astrology were widespread and considered valid by the vast majority during the fifteenth and sixteenth centuries. Astrology was firmly established in the fabric of European society and almost all of the active astronomers were also active astrologers right down to those astronomers, who were responsible for the so-called astronomical revolution. Georg Peuerbach, Regiomontanus, Tycho Brahe, Johannes Kepler and Galileo Galilei were all practicing astrologers and in fact owed much of the patronage that they received to their role as astrologer rather to that of astronomer, although the terms were interchangeable in this period. The terms Astrologus, Astronomus and Mathematicus were all synonym and all had astrologer in the modern sense as their principle meaning. Following the invention of moving type printing in about 1450, by far and away, the largest number of printed articles were astrological ephemera, almanacs, prognostica, and writing and single sheet wall calendars. A trend that continued all the way down to the eighteenth century.

During the fifteenth and sixteenth century efforts to give astrology a solid empirical footing were central to the activities of the astronomer-astrologers. Starting with Regiomontanus several astronomers believed that the inaccuracies in astrological forecasting were due to inaccuracies in the astronomy on which it was based. The reform of astronomy, for exactly this reason, was a principle motivation for the research programmes of Regiomontanus, Tycho Brahe and Wilhelm IV, Landgrave of Hessen-Kassel. Another approach was through astro-meteorology, with astronomer keeping weather diaries in which they noted the horoscope for the day and the actual weather on that day. They were looking for correlations, which they failed to find, but the practice led to the beginnings of modern weather forecasting. Notable weather diarists were Tycho Brahe and Johannes Werner. There were also attempts to find genuine correlations between birth charts and biographies of prominent people. Such biographical horoscope collections existed in manuscript before the invention of movable type printing. One of the largest, still extant, such manuscript collections is that of Erasmus Reinhold, a professor of mathematics at Wittenberg. The first such printed collection was that of Gerolamo Cardano, Libelli duo: De Supplemento Almanach; De Restitutione temporum et motuum coelestium; Item Geniturae LXVII insignes casibus et fortuna, cum expositione, printed and published by Johannes Petreius, specialist for astrological literature, in Nürnberg in 1543; the same year as he published Copernicus’ De revolutionibus.


During the first half of the seventeenth century the failures to find empirical evidence for astrology, a change in the philosophy underpinning science, astrology was justified with Aristotelian metaphysics, and changes in the ruling methodologies of mainstream medicine led to a decline in the academic status of astrology. Although a few universities continued teaching astrology for medical students into the eighteenth century, astrology as a university discipline largely ceased to exist by 1660. However, astrology was still very much woven into the fabric of European society.

Newton was born in 1642, which meant he grew up during the Civil War and the Interregnum. Astrology was used by both sides as propaganda during Civil War. Most famously William Lilly (1602–1681) publishing powerful pamphlets on behalf of the parliamentary side.


Portrait of Lilly, aged 45, now housed in the Ashmolean Museum at Oxford Source: Wikimedia Commons

This caused him major problem following the restitution. Lilly’s Christian Astrology (1647) was a highly influential book in the genre. Lilly was friends with many important figures of the age including Elias Ashmole (1617–1692) an antiquary who gave his name to the Ashmolean Museum of Art and Archaeology in Oxford, which was founded on his collection of books, manuscripts many objects. Ashmole was a passionate astrologer and a founding member of the London Society of Astrologers, which included many prominent intellectuals and existed from 1649 to 1658 and was briefly revived in 1682 by the astronomer, astrologer, printer and globemaker Joseph Moxon (1627–1691).


Joseph Moxon. Line engraving by F. H. van Hove, 1692. Source: Wikimedia Commons

Moxon successfully sold Ptolemaic globes in the last quarter of the seventeenth century, which were intended for astrologers not astronomers. Moxon’s Ptolemaic globes reflect an actual fashion in astrological praxis that could be described as back to the roots. In the middle of the seventeenth century many astrologers decide that astrology wasn’t working, as it should, because the methodology used had drifted to far from that described by Ptolemaeus in his Tetrabiblos. This movement was led by the Italian P. Placido de Titis (1603 – 1668) whose Physiomathematica sive coelestis philosophia published in 1650 with an improved 2nd edition, 1675.



Alongside Moxon another English supporter of this back to the roots movement was John Partridge (1644–c. 1714), who published the first ever English translation of Ptolemaeus’ Tetrabiblos in 1704. Partridge was one of the most well-known astrologers of the age until he got skewered by Jonathan Swift in his infamous Isaac Bickerstaff letters beginning in 1708.

V0004503ER John Partridge. Line engraving by R. White, 1682, after hims

John Partridge. Line engraving by R. White, 1682 Credit: Wellcome Library, London. Wellcome Images Source: Wikimedia Commons John Partridge. Line engraving by R. White, 1682, after himself. 1682 By: Robert WhitePublished: – Copyrighted work available under Creative Commons Attribution only licence CC BY 4.0

We always talk about the big names in the histories of astronomy and mathematics, but it is often more insignificant practitioners, who teach the next generation. In this Newton’s education in astronomy followed the norm and he learnt his astronomy from the books of Vincent Wing (1619–1668) Astronomia Britannica (1669)


Author portrait of Vincent Wing engraved by T. Cross (Frontispiece to the “Astronomia Britannica” of 1669) Source: Wikimedia Commons

and Thomas Streete (1621–1689) Astronomia Carolina, a new theorie of Coelestial Motions (1661).


They were the two leading astronomers in England during Newton’s youth and were both practicing astrologers. The two men were rivals and wrote polemics criticising the errors in the others work. Streete was friends with several other astronomers such as Flamsteed, who also used the Astronomia Carolina as his textbook, or Halley together with whom Streete made observation. Streete was Keplerian and it’s Kepler’s astronomy that he presents in his Astronomia Carolina , although he rejected Kepler’s second law and presented the theories of Boulliau and Ward instead. It is very probable that reading Streete was Newton’s introduction to Kepler’s theories.

Flamsteed, as already said, like Newton, a student of Steete, actually cast an electional horoscope for the laying of the foundation stone of the Royal Observatory in 1675 although he didn’t actually believe in astrology but was maintaining a well-established tradition.


Another example of this sort of half belief can be found in the attitude of Newton and Halley to comets. The two of them did far more than anybody else to establish comets as real celestial bodies affected by the same physical laws as all other celestial bodies and not some sort of message from the heavens. However, whilst neither of them believed in the truth of astrology both retained a belief that comets were indeed harbingers of doom.

As I said at the beginning Newton grew up and lived all of his life in a culture permeated with a belief in astrology. At the end of the seventeenth century astrological ephemera–almanacs, prognostica, etc.–were still a mass market phenomenon.


Zodiac man in EPB/61971/A: Goldsmith, 1679. An almanack for the year of our Lord God, 1679 (London: Printed by Mary Clark, for the Company of Stationers, 1679), leaf B2 recto. Image credit: Elma Brenner. Source:

A large annual fair such as Sturbridge in 1663, the largest annual fair in Europe, would have had a large selection of astrological literature on offer for the visitors; a public many of whose yearly almanac was the only printed book that they bought and read.


It is perfectly reasonable that a twenty-one year old Newton, just entering his second year at Cambridge university, stumbled across an astrological publication that awakened his mathematical curiosity as reported separately by both John Conduitt and Abraham DeMoirvre, in their memoirs based on conversations with Newton.


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

Microscopes & Submarines

The development of #histSTM in the early decades of the Dutch Republic, or Republic of the Seven United Netherlands, to give it its correct name, was quite extraordinary. Alongside the development of cartography and globe making, the most advanced in the whole of Europe, there were important figures such as the engineer, mathematician and physicist, Simon Stevin, the inventors of the telescope Hans Lipperhey and Jacob Metius, the mathematical father and son Rudolph and Willebrord Snel van Royan and Isaac Beeckman one of the founders of the mechanical philosophy in physics amongst others. However, one of the most strange and wonderful figures in the Netherlands during this period was, without doubt, the engineer, inventor, (al)chemist, optician and showman Cornelis Jacobszoon Drebbel (1571–1631).


Source: Wikimedia Commons

Drebbel is one of those larger than life historical figures, where it becomes difficult to separate the legends and the myths from the known facts, but I will try to keep to the latter. He was born to Jacob Drebbel an Anabaptist in Alkmaar in the province of North Holland. He seems not to have received much formal education but in about 1587 he started attending the Academy of the printmaker, draftsman and painter Hendrick Goltzius (1558–1617) in Haarlem also in North Holland.


Hendrick Goltzius – Self-Portrait, c. 1593-1594 – Google Art Project Source: Wikimedia Commons

Goltzius was regarded as the leading engraver in the Netherlands during the period and he was also an active alchemist. Drebbel became a skilled engraver under Goltzius’ instruction and also acquired an interest in alchemy. In 1595 he married Sophia Jansdochter Goltzius, Hendrick’s younger sister. They had at least six children of which four survived into adulthood. The legend says that Sophia’s prodigal life style drove Drebbel’s continual need to find better sources for earning money.


Drebbel’s town plan of Alkmaar 1597 Source: Wikimedia Commons

Drebbel initially worked as an engraver, cartographer and painter but somewhere down the line he began to work as an inventor and engineer.


Astronomy [from the series The Seven Liberal Arts]. Engraving by Drebbel Source: Wikimedia Commons

Not surprisingly, for a Netherlander, he a turned to hydraulic engineering receiving a patent for a water supply system in 1598. In 1600 he built a fountain at the Noorderpoort in Middelburg and at the end of his life living in England he was involved in a plan to drain the Fens. At some point, possibly when he was living in Middelburg, he learnt the craft of lens grinding, which would play a central roll in his life.

Also in 1598 he acquired a patent for Perpetuum mobile but which he, however, had not invented. The so-called Perpetuum mobile was a sort of clock, which was in reality powered in changes by the air temperature and air pressure had actually been invented by Jakob Dircksz de Graeff (1571–1638), an influential politician and natural philosopher, who was a friend of both Constantijn Huygens and René Descartes, and Dr Pieter Jansz Hooft (1574/5–1636) a politician, physician and schoolteacher.


Jakob Dircksz de Graeff Source: Wikimedia Commons


Pieter Jansz Hooft (1619), Attributed to Michiel van Mierevelt Source: Wikimedia Commons

Drebbel not only patented the Perpetuum mobile but also claimed to have invented it. His increasing reputation driven by this wonder machine earned his an invitation to the court of King James VI &I in London as the guest of the crown prince Henry in 1604. When on the court in London the Queen accidentally broke the Perpetuum mobile, Drebbel was unable to repair it.


The barometric clock of Cornelis Drebbel patented in 1598 and then known as “perpetuum mobile”. Print by Hiesserle von Choda (1557-1665) Source: Wikimedia Commons

At the court in London he was responsible for staging masques, a type of play with poetry, music, dance, and songs that was popular in the sixteenth and seventeenth centuries. He designed and built the stage sets and wonderful machines to enchant the audiences. Drebbel was by no means the only scientist-engineer to be employed to stage such entertainments during the Early Modern Period but he appears to have been very good at it. It was almost certainly Drebbel, who through his contacts imported from the Netherlands the first ever telescope to be seen in England, which was presented to James at the high point of a masque in 1609. He also built a magic lantern and a camera obscura with which he also entertained the members of the court.

Drebbel’s reputation grew to the point where he received an invitation to the court of the Holly Roman Empire, Rudolf II, in Prague in October 1610. Rudolf liked to surround himself with what might be termed wonder workers. Amongst those who had served in this capacity in Prague were Tycho Brahe, John Dee, Edward Kelley, Johannes Kepler and Jost Bürgi. There are no reports of any interactions between Drebbel and either Kepler or Bürgi, who were all on the court of Rudolf at the same time. In Prague he once again functioned as a court entertainer or showman.


AACHEN, Hans von – Portrait of Emperor Rudolf II Source: Wikimedia Commons

Rudolf was deposed by his brother Archduke Mathias in 1611and Drebbel was imprisoned for about a year. Following the death of Rudolf in 1612, Drebbel was released from prison and returned to London. Here, however, his situation was not as good as previously because Henry, his patron, had died in 1612. He kept his head above water as a lens grinder and instrument maker.

As a chemist Drebbel published his best-known written work Een kort Tractaet van de Natuere der Elemente (A short treatise of the nature of the elements) (Haarlem, 1621).


He was supposedly involved in the invention of the explosive mercury fulminate, Hg(CNO)2, but this is disputed. He also developed other explosive mixtures. He invented a chicken incubator with a mercury thermostat to keep it at a constant, stable temperature. This is one of the earliest feedback controlled devices ever created. He also developed and demonstrated a functioning air conditioning system.


Error-controlled regulator using negative feedback, depicting Cornelius Drebbel’s thermostat-controlled incubator of circa 1600. Source: Wikimedia Commons

He didn’t himself exploit one of his most successful discoveries, one that he made purely by accident. He dropped a flask of aqua regia (a mixture of nitric and hydrochloric acid, normally used to dissolve gold) onto a tin windowsill and discovered that stannous chloride (SnCl2) makes the colour of carmine (the red dye obtained from the cochineal insect) much brighter and more durable. Although Drebbel didn’t exploit this discovery his daughters Anna and Catherina and their husbands the brothers, Abraham and Johannes Sibertus Kuffler (a German inventor and chemist) did, setting up dye works originally in Leiden and then later in Bow in London. The colour was known as Colour Kuffler of Bow Dye and was very successful. Kuffler later continued his father-in-law’s development of self-regulating ovens that he demonstrated to the Royal Society.

In the early 1620s Constantijn Huygens, the father of Christiaan, came to London on a diplomatic mission. He made the acquaintance of Drebbel, who demonstrated his magic lantern and his camera obscura for the Dutch diplomat. Huygens was much impressed by his landsman and for a time became his pupil learning how to grind lenses, a skill that he might have passed onto his sons.


Constantijn Huygens (1596-1687), by Michiel Jansz van Mierevelt. Source: Wikimedia Commons

It is not known, who actually invented the microscope and it’s more than likely that the principle of the microscope was discovered by several people, all around the same time, who like Galileo looked through their Galilean or Dutch telescope the wrong way round. What, however, seems to be certain is that Drebbel is the first person known to have constructed a Keplerian telescope, that is with two convex lenses rather than a concave and a convex lens. As with all of his other optical instruments, Drebbel put on microscope demonstration introducing people to the microscopic world, as always the inventor as showman.

Drebbel’s most famous invention was without doubt his submarine. This is claimed to be the first-ever navigable submarine but has become the stuff of legends, how much of story is fact is difficult to assess. His submarine consisted of a wooden frame covered in leather, and one assumes waterproofed in someway; it was powered by oar.


Artistic representation of Drebbel’s submarine, artist unknown Source: Wikimedia Commons

It had bladders inside that were filled with water to enable the submarine to submerge; the bladders were emptied when the vessel was required to surface. In total between 1620 and 1624 Drebbel built three different vessels increasing in size. The final submarine had six oars and could carry up to sixteen passengers. Drebbel gave public demonstrations with this vessel on the river Thames. According to reports the vessel dived to a depth of four to five metres and remained submerged for three hours traveling from Westminster and Greenwich and back again. Assuming the reports to be true, there has been much speculation as to how fresh air was supplied inside the closed vessel. These speculations include a mechanical solution with some form of snorkel as well as chemical solutions with some sort of chemical apparatus to generate oxygen. It is also reported that Drebbel took King James on a dive under the Thames. Despite all of this Drebbel failed to find anybody, who would be prepared to finance a serious use of his submarine.

In the later 1620s Drebbel served the Duke of Buckingham as a military advisor but his various suggestions for weapons proved impractical and failed, the British blaming  the inventor and Drebbel blaming the English soldiers, finally ruining whatever reputation he still had. As already stated above towards the end of his life he was supposedly involved in a scheme to drain the Fens but the exact nature of his involvement remains obscure. Drebbel died in financial straights in 1633 in London, where he was scraping a living running a tavern on the banks of the Thames.

















Filed under History of Alchemy, History of Cartography, History of Chemistry, History of Optics, History of Technology, Renaissance Science

Giambattista della Porta the most polymathic of all Renaissance polymaths?

Giambattista della Porta (1535(?)–1615) is well known to historians of Renaissance science but for the general public he remains a largely unknown figure. If he is known at all,  he is often written off as an occultist, because of the title of his most well known work Magia Naturalis. In fact in the late sixteenth and early seventeenth centuries he was a highly respected and influential member of the Italian Renaissance scientific community. Although he wrote and published profusely over a wide range of scientific and related topics he made no really major discoveries and produced no major inventions and unlike his contemporaries, Kepler and Galileo, who were both well acquainted with his work, he has been largely forgotten.


Giambattista della Porta Source: Wikimedia Commons

Giambattista Della Porta were born at Vico Equense, Near Naples, probably sometime in 1535 (he created the confusion about his birth date), the third of four sons of the nobleman Nardo Antonio dell Porta of whom three survived childhood.  His parental home resembled an intellectual salon where the boys were continually exposed to and educated by visiting philosophers, mathematicians, poets and musicians. Their education was completed by private tutors, who also taught the boys the attributes of a gentleman, dancing, riding, skilled performance in tournaments and games and how to dress well. Della Porta never attended university but enjoyed life as a well educated polymathic, gentleman of leisure. If he can be considered to have had a profession, then it is that of a dramatist, he wrote more than twenty theatrical works, but it is his extensive activities in the sciences that interest us here.

Already in 1558, at the age of 23, he published the fist version of his most well known work, the Magia Naturalis in four books, a sort of encyclopaedia of the Renaissance sciences. From the beginning it was a bestseller running to five editions in Latin within the first ten years with translations into Italian (1560), French (1565), Dutch (1566) and English (1658). A vastly expanded version in twenty books was published in 1589. This final version covers a wide range of topics:


Source: Wikimedia Commons

Book 1: Of the Causes of Wonderful Things Book 2: Of the Generation of Animals Book 3: Of the Production of New Plants Book 4: Of Increasing Household-Stuff Book 5: Of Changing Metals Book 6: Of Counterfeiting Glorious StonesBook 7: Of the Wonders of the Load-Stone Book 8: Of Physical Experiments Book 9: Of Beautifying Women Book 10: Of Distillation Book 11: Of Perfuming Book 12: Of Artificial Fires Book 13: Of Tempering Steel Book 14: Of CookeryBook 15: Of Fishing, Fowling, Hunting, etc. Book 16: Of Invisible Writing Book 17: Of Strange Glasses Book 18: Of Static Experiments Book 19: Of Pneumatic Experiment Book 20: Of the Chaos

The contents range from fairly banal parlour tricks, over engineering, experimental science, horticulture and husbandry to every day things. At the very beginning della Porta is very careful to explain what exactly he mean by the term natural magic:

There are two sorts of Magick; the one is infamous, and unhappy, because it has to do with foul Spirits and consists of incantations and wicked curiosity; and this is called Socery; an art which all learned and good men detest; neither is it able to yield an truth of reason or nature, but stands merely upon fancies and imaginations, such as vanish presently away, and leave nothing behind them; as Jamblicus writes in his book concerning the mysteries of the Egyptians. The other Magick is natural; which all excellent wise men do admit and embrace, and worship with great applause; neither is there any thing more highly esteemed, or better thought of, by men of learning. The most noble Philosophers that ever were, Pythagorus, Empedocles, Democritus, and Plato forsook their own countries, and lived abroad as exiles and banished men, rather than as strangers; and all to search out and to attain this knowledge; and when they came home again, this was the Science which they professed, and this they esteemed a profound mystery. They that have been most skillful in dark and hidden points of learning, do call this knowledge the very highest point, and the perfection’s of Natural Sciences; inasmuch that if they could find out or devise amongst all Natural Sciences, any one thing more excellent or more wonderful then another, that they would still call by the name of  Magick. Others have named it the practical part of natural Philosophy, which produces her effects by the mutual and fit application of one natural thing unto another.

The association of Magick with natural philosophy is continued in della Porta’s definition of the Magician:

This is what is required to instruct a Magician, both what he must know, and what he must observe; that being sufficiently instructed in every way, he may bring very strange and wonderful things to us. Seeing Magick, as we showed before, as a practical part of natural Philosophy, it behooves a Magician and one that aspires to the dignity of the profession, to be an exact and very perfect Philosopher.

Despite the very diverse nature of the Magia Naturalis it does contain elements of genuine experimental science. For example, it contains the first experimental disproof of the widely held medieval belief that garlic disables magnets. He also experimented with the cooling properties of dissolving nitre in water. As described here by Andrea Sella (@SellaTheChemist)

As well as the Magia Naturalis della Porta wrote and published a large number of monographs on a very wide range of topics. Cryptography was a popular topic in Renaissance Europe, the most famous book being Johannes Trithemius’ Poligraphia, della Porta published his De Furtivis Literarum Notis (1563), which contain innovative cryptographical ideas.


In 1586 he published a work on physiognomy De humana physiognomonia libri IIII,


From De humana physiognomonia, 1586 Source: Wikimedia Commons

which was still being referenced in the nineteenth century, two years later a book on phytonomy (the science of the origin and growth of plants), Phytognomonica, which contains the first observations on fungal spores.


Phytognomonica, 1588 Source: Wikimedia Commons

These two books confirm della Porta’s adherence to the Renaissance doctrine of signatures. This theory claimed that it was possible to determine the nature of things based on their external appearances.

This was by no means the limit to della Porta’s publishing activities. He also wrote an agricultural encyclopaedia, separate volumes on various fruit bearing trees, books on mathematics, astronomy, meteorology, military engineering, distillation and in 1589 a book on optics, his De refractione optics. We shall return to the latter.


This incredible literary outpouring was just part of his scientific activity, in about 1560 he founded an academic society, Accademia dei Segreti (Academia Secratorum Naturae), the Academy of the Secrets of Nature, which is considered to be the earliest scientific society. The academy met regularly in della Porta’s home and membership was open to all but to become a member one had to present a new secret of nature that one had discovered. We know what some of those new secrets were as della Porta included them in the twenty volume version of his Magia Naturalis. In 1578 della Porta was summoned to Rome and investigated by the Pope. We do not know the exact grounds for this summons but he was forced to shut down his academy on suspicion of sorcery. This is to a certain extent ironic because della Porta was very careful in all his writing to avoid controversial topics particularly religious ones.

Although it was shut down the Accademia dei Segreti, would later have a major influence on another, much more renowned, early scientific academy, Federico Cesi’s Accademia dei Lincei. Cesi was a huge admirer of della Porta and as a young man travelled to Naples to visit the older natural philosopher. On his return home he founded his own academy, whose name was inspired by a line from the preface of the Magia Naturalis:

… with lynx like eyes, examining those things which manifest themselves, so that having observed them, he may zealously use them.

In 1610 della Porta became the fifth member of the Accademia dei Lincei, one year before Galileo.

Another important aspect of Renaissance science was the establishment of private natural philosophical museums also known as Wunderkammer, or cabinets of curiosity. Della Porta had, as to be expected, a particular fine cabinet of curiosity that would influence others to create their own, the Jesuit Athanasius Kircher for example.


Fold-out engraving from Ferrante Imperato’s Dell’Historia Naturale (Naples 1599), the earliest illustration of a natural history cabinet Source: Wikimedia Commons

Della Porta made minor contribution to the advance of science and engineering over a wide range of disciplines but I first ran into della Porta in the context of the history of optics and it his association with this history that I want to look at in somewhat more detail. The early seventeenth century saw both a significant turn in the theory of optics and independently of that the invention of the telescope, an instrument that would go one to revolutionise astronomy, della Porta played a minor roll in both of these things.

The invention of the telescope, by Hans Lipperhey, first became public in September 1608 and the role it would play in the future of astronomy became explosively obvious when Galileo published his Sidereus Nuncius in March 1610. Already in August 1609 della Porta wrote a letter to Federico Cesi claiming to have invented the telescope, he wrote:

I have seen the secret use of the eyeglass and it’s a load of balls [coglionaria] in any case it is taken from book 9 of my De Refractione.[1]

Here della Porta’s memory is faulty, he is after all over seventy years old, what he is referring to is not in the De Refractione but rather in Chapter 10 of Book 17 of Magia Naturalis (1589). Here we find the following suggestive description:

Concave Lenticulars will make one see most clearly things that are afar off.  But Convexes, things near at hand.  So you may use them as your sight requires.  With a Concave Lenticulars you shall see small things afar off very clearly.  With a Convex Lenticular, things nearer to be greater, but more obscurely.  If you know how to fit them both together, you shall see both things afar off, and things near hand, both greater and clearly.  I have much helped some of my friends, who saw things afar off, weakly, and what was near, confusedly, that they might see all things clearly.  If you will, you may.

The lens combination that della Porta describes here is indeed that of the Dutch or Galilean telescope but as van Helden say, and I agree with him, he is here describing some form of spectacles but not a telescope. Kepler, however, who owned a copy of Magia Naturalis credits him with being the inventor of the telescope in his Dissertatio cum Nuncio Sidereo (Conversation with the Starry Messenger) (1610), where he wrote that a recent Dutch invention had been made public years earlier in Magia Naturalis. In 1641 Pierre Gassendi stated that the actual invention had been made by chance by Metius [Jacob Metius (after 1571–1628), who applied for a patent for a telescope two weeks later than Lipperhey] the idea for a similar one had been published years earlier by della Porta.

Later della Porta would graciously admit that his fellow Lynx, Galileo, had achieved much more with his telescope that he, della Porta, could have ever have hoped to do, whilst not abandoning his claim to having first conceived of the telescope.

Della Porta also played a small role in the history of the camera obscura, describing the improvement to the image obtained by placing convex lens into the pinhole, something probably first suggested by Gerolamo Cardano. He also suggested, this time as the first to do so, using a concave mirror to project the image onto a sheet of paper to facilitate drawing it. The popularity of the Magia Naturalis did much to spread knowledge of the camera obscura and its utility as a drawing instrument. Interestingly della Porta compared his camera obscura with the human eye but, unlike Kepler, failed to make the connection that the lens focuses the image on the retina. He continued to believe like everybody before him that the image in perceived in the lens itself.


First published picture of camera obscura in Gemma Frisius’ 1545 book De Radio Astronomica et Geometrica Source: Wikimedia Commons

Della Porta’s role in the turn in the theory of optics is less disputed but not so widely discussed.  Ancient Greek optics was almost exclusively about theories of vision and when taken up and developed in the Islamic Middle Ages this too remained the emphasis. Ibn al-Haytham in his work on optics showed that one could combine an intromission theory of vision with the geometric optics of Euclid, Hero and Ptolemaeus, who had all propagated an extramission theory of vision. This was a major development in the history of optics. In the thirteenth century Robert Grosseteste introduced optics as a central element in both his vision of science and his theology, which led to it being established as a mathematical discipline on the medieval university. Shortly after Roger Bacon, John Peckham and Witelo introduced al-Haytham’s theories on optics into the medieval European mainstream founding what became known as the perspectivist school of optics. Strangely there were no real further developments in the theory of optics down to the end of the sixteenth century when Johannes Kepler, almost singlehandedly, turned the study of optics from one of theories of vision to one of theories of light, thereby ending the reign of the perspectivists. I say almost singlehandedly but he did have two predecessors, who made minor contributions to this turn, Francesco Maurolico (1494–1575) and della Porta.

One major flaw in the perspectivist theory was its treatment of spherical convex lenses and spherical concave mirrors, which said that the images created by them appeared at a single focus point; this is a fallacy. This flaw was in the theory from its inception in the thirteenth century and remained unchecked and uncorrected all the way down to the end of the sixteenth century. The fact that the don’t create their images at a single focal point is, of course, the cause of spherical aberration, something that would plague the construction of telescopes and microscopes well into the eighteenth century. The man who corrected this error in optical theory was della Porta.  Using a mixture of experiments and analytical light ray tracing he came very close to the correct solution an important step towards Kepler’s light ray based theory of optics.


Della Porta’s ray tracing analysis of the reflection of a spherical concave mirror A. Mark Smith, “From Sight to Light: The Passage from Ancient to Modern Optics”, Chicago University Press, 2015 p. 349

Giambattista della Porta is an interesting example of a widespread phenomenon in the history of science. In his own times he was highly respected and regarded, throughout Europe, as a leading natural Philosopher. His books, translated into many languages, were bestsellers and that even long after his death. Johannes Kepler was a fan and Galileo disliked him because he saw him as a serious rival for the position of top dog natural philosopher, a position that Galileo very much desired for himself. However, today most people have never even heard of him and if then he is largely dismissed as a minor irrelevance or even, because of the title of his major work, as some sort of anti-science occultist. But if historians really want to understand what was going on in the scientific community of Europe in the Early Modern Period then they have to take figures like della Porta seriously and not just focus on the ‘big names’ such as Kepler and Galileo.













[1] Quoted from David Freedberg, The Eye of the Lynx: Galileo, His Friends and the Beginnings of Modern Natural History, University of Chicago Press, Chicago and London, 2002, ppb. p. 101 Albert van Helden in his The Invention of the Telescope, American Philosophical Society, Philadelphia, 1977, Reprint, 2008, translates the phrase with coglionaria as …”it’s a hoax” pp. 44-45

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

Oh really, might as well pack up and go home then.

The New Statesman recently had a review of Catherine Fletcher’s new book on the history of the Italian Renaissance, The Beauty and the Terror,[1] written by Rowan Williams under the title, Breaking the Renaissance myth.  For those, who might not know Rowan Williams is an ex Archbishop of Canterbury, who although ordained served as an academic rather than as a priest: However, he is/was a theologian and not a historian and very definitely not a historian of science.

Fletcher’s book is largely about what we might term the dark side of the Italian Renaissance and this is reflected in the title of Williams’ review.


I had no problems with the general tenor of what he had to say until I stumbled across the following two paragraphs in the middle of his review:

If we demythologise the Renaissance a little, we may learn to do more justice to what preceded it. Professor Fletcher has a brief discussion of scientific advances in the mid 16th century, especially in anatomy, navigational skills and botany – the latter two spurred on by the fresh stimulus of colonial travel and discovery. But the fact that this treatment is relatively brief and relates to a period rather later than the “high Renaissance” should give us pause if we are inclined to think of this as an epoch of spectacular scientific progress.

Many scholars have pointed out that the 15th and early 16th centuries are a rather stagnant period in many areas of natural science compared with some parts of the Middle Ages, when astronomy, mechanics and logic made substantial advances. The great 16th-century exception, Copernicus’s treatise of 1543 on the circulation of planets around the sun, was not a dramatic and total rejection of earlier astronomical method based on new scientific evidence, but a refinement designed to clear up the mathematics of charting the heavenly bodies. It was received with interest and some enthusiasm at the time, but was clearly not seen as a radical departure from the principles of Aristotle. Only with slightly later figures like Tycho Brahe (1546-1601) and Johannes Kepler (1571-1630) did actual observation of the heavens play a decisive part in the argument.

As somebody, who generally describes himself as a historian of Renaissance science I was, to say the least, more than somewhat discombobulated by the good Reverend Williams’ claims about my chosen discipline and I thought I might take a couple of minutes to examine them.

I’ll start with what Williams describes as Professor Fletcher’s brief discussion of scientific advances in the mid 16th century, especially in anatomy, navigational skills and botany. This is indeed extremely brief. The main text of the book is 350 pages long and there is a just-15-pages long chapter entitled, Art, Science and Reform of which only three pages deal with the scientific topics mentioned by Williams. This is principally a book of political history and the comment here have almost a throw away quality, something mentioned in passing. The anatomy mentioned is, of course, Vesalius’ De fabrica, which together with all the new developments in medicine, mainly in the North Italian universities, constitutes one of the largest revolutions in the entire history of medicine.  Fletcher does not discuss advances in the science of navigation, which were in fact very extensive in the 15th and 16th centuries, but the ‘navigations’ another term for the voyages of exploration and discovery undertaken in those centuries and their influence on developments back in Italy, as recorded by authors such as Giovanni Battista  Ramusio and Richard Hakluyt.

The botany refers to the establishment of botanical gardens at the universities of Padua and Pisa and the publications of herbaria (herbals) aimed at correcting such works as Pliny’s Natural History, as Vesalius had corrected Galen in medicine. What she doesn’t mention is that both the botanical gardens and the herbals were also part of the medical revolution, the scientific investigation of healing herbs being one of their central functions.

The last sentence of the first paragraph and the first of the second paragraph are a bit of a stunner. You know that I have a tendency to call myself a historian of Renaissance science and Williams is saying that I’m a historian of a bit of a damp squib. I’m used to people, who should know better, making rude and highly inaccurate statements about the history of medieval science, but to have somebody praise the vitality of medieval science, whilst at the same time putting the boot into Renaissance science is I think a first, at least as far as I’m concerned. This raises all sorts of problems, not least because the division between medieval science and Renaissance science is totally artificial and there is in reality continuity in European scientific activity that goes through from the translation movement in the twelfth century to at least the middle of the sixteenth century. Also I think to claim that medieval science made “substantial advances in astronomy, mechanics and logic” is a bit strong, as they were more involved in a game of catch up with antiquity and medieval Islam. On the other hand if you do try to identify a specifically Renaissance science, you first have to decide when it begins and when it ends. My own period definition of Renaissance science starts at the beginning of the fifteenth century and ends with the Thirty Years War. Kepler for all of his modernity is philosophically much more a Renaissance philosopher than a modern one, as is also Tycho. Galileo is more transitional but still has at least one foot in the Middle Ages.

Let us take stock and make an inventory of all the scientific activities that were developed and/or advanced in the period between 1400 and 1600. Regular readers will already have encountered much of what follows in various posts here over the years but it might prove of interest to see it laid out, if only in outline, all in one place.

We start with the first Latin translation of Ptolemaeus’ Geographia from the Greek by Jacobus Angelus in Florence in 1406. This is of course Renaissance culture in pure form, the translation from Greek into Latin of a major text from antiquity, above all because it was a text that had never been translated out of Arabic in the original translation movement. This text kicked off mathematical cartography in Renaissance Europe and with it revitalised astronomy, which was needed to determine latitude and longitude coordinates for this new form of cartography. The Ptolemaic world map, which very soon followed the translation both in manuscript and in print, was a totally new perception of the world in comparison to the medieval mappa mundi.

Harley 7182 ff.58v-59

A mid-15th century Florentine map of the world based on Jacobus Angelus’s 1406 Latin translation of Maximus Planudes’s late-13th century rediscovered Greek manuscripts of Ptolemy’s 2nd-century Geography. Ptolemy’s 1st (modified conic) projection. Credited to Francesco di Antonio del Chierico – Ptolemy’s Geography (Harleian MS 7182, ff 58–59) Source: Wikimedia Commons

The new cartography spread northwards throughout Europe helping to trigger the First Viennese School of Mathematics. Here Gmunden, Peuerbach and Regiomontanus modernised Ptolemaic astronomy, integrating the newly developing trigonometry and many Arabic developments into Peurbach’s Theoricae Novae Plaetarum (1473) and the Peuerbach & Regiomontanus Epitoma in Almagestum Ptolemae (1496), which became the new textbooks for astronomy for the next one hundred plus years and were also the books Copernicus used to learn his astronomy.


Title page Epitoma in Almagestum Ptolemae Source: Wikimedia Commons

The Second Viennese School of Mathematics with Johannes Stabius, Andreas Stiborius, Georg Tannstetter and Peter Apian pushed the advances in cartography and astronomy further.


Apian’s copy of the Waldseemüller world map, naming the new fourth continent America Source: Wikimedia Commons

The Viennese mathematici stood in close contact with their colleagues in Nürnberg, where Johannes Schöner and Johannes Werner also made substantial contributions to theses advances. Schöner in particular was heavily involved in the activities that led to the publication of Copernicus’ De revolutionibus in Nürnberg in 1543. It was Schöner, who also kicked off the production of printed terrestrial and celestial globe pairs,


Celestial globe by Johann Schöner, c.1534 Source: Museum of the History of Science, Oxford

which was picked up by Gemma Frisius, who taught astronomy, cartography and mathematics to Gerhard Mercator, who in turn would go on to revolutionise both cartography and globe making triggering the golden age of both disciplines in the Netherlands in the seventeenth century.


Abraham Ortelius, who produced and published the first modern atlas, was also a member of the Frisius-Mercator circle along with numerous other important cartographical innovators.


Frisius, of course, introduced triangulation an important new tool in cartography, surveying and geodesy. New surveying instruments, such as the plane table, were also developed to carry out surveying using triangulation.

The early modern cartographers were not just simple mapmakers, their publications also contained much geographical information, much of it new, as well as historical, anthropological and ethnographical information about the areas mapped.

Another member of this European wide group of mathematici, Pedro Nunes, in Portugal was the discovery of the fact that a course of constant compass bearing on the globe is not part of a great circle but a loxodrome, a spiral.


Image of Portuguese mathematician Pedro Nunes in Panorama magazine (1843); Lisbon, Portugal. Source: Wikimedia Commons

This knowledge lies at the centre of the so-called Mercator map projection. Turning to navigation, the Portuguese and later Spanish explorations out into the Atlantic led to major developments such as the determination of latitude and the development of new instruments for this purpose such as the backstaff and the marine astrolabe. At the end of our period in 1600 to be exact, William Gilbert published his De Magnete, as well as being the definitive text up to that time on magnets and magnetism, it was also an important text on empirical, experimental science. Although published at the end of our period it relied on earlier work on magnetism and the magnet by such researchers as Robert Norman.

Coming back to astronomy, Copernicus’ De revolutionibus didn’t, as often presented, appear out of thin air but was part of a general movement to modernise astronomy and above all to make it more accurate that begins with Peuerbach and Regiomontanus and gains a lot of momentum in the sixteenth century particularly in the Europa wide debate in the 1530s, in which Copernicus also took an active part. I will address here Williams’ mindboggling statement about De revolutionibus:

The great 16th-century exception, Copernicus’s treatise of 1543 on the circulation of planets around the sun, was not a dramatic and total rejection of earlier astronomical method based on new scientific evidence, but a refinement designed to clear up the mathematics of charting the heavenly bodies. It was received with interest and some enthusiasm at the time, but was clearly not seen as a radical departure from the principles of Aristotle. [my emphasis]

As almost always we are dealing with someone whose knowledge of Renaissance cosmology and astronomy is obviously very minimal. The Peuerbachian geocentric system of the cosmos with which Copernicus was working was not Aristotelian astronomy but an uneasy mash up of Aristotelian cosmology and Ptolemaic astronomy. In fact there was a major attempt to return to Aristotelian homocentric astronomy, launched by Fracastoro amongst other, during those debates in the 1530s. Whilst, in a mathematical sense, Copernicus’ heliocentric astronomy didn’t stray far from Ptolemaic astronomy with its deferents and epicycles, but without its, for Copernicus, offensive equant points, it deviated radically from Aristotle’s cosmology and physics. Fundamental to Aristotelian cosmology is the fact that the Earth is immobile at the centre of the cosmos, to place the Sun there instead and the Earth in orbit around the Sun is a very a radical departure from the principles of Aristotle. Fundamental to Aristotelian physics is that the cosmos in divide into supralunar and sublunar areas. Above the Moon’s orbit natural motion is uniform and circular below it natural motion is perpendicular to the Earth’s surface. Upwards for fire and air, downwards for earth and water. Giving the Earth three additional motions–diurnal rotation, annual orbit around the Sun and a circulating of the poles– was a very radical departure from the principles of Aristotle.

Moving on from the mathematical sciences–astronomy, cartography, navigation, and surveying–to mathematics itself, the Renaissance saw a massive development in trigonometry and its applications. All four of the named mathematical sciences make extensive use of trigonometry. Regiomontanus wrote the first complete account of the six basic trigonometrical functions in Europe, this had been done much earlier in Arabic science, which also presented trigonometry as a separate mathematical discipline and not just a subsidiary of astronomy; this was published by Schöner in 1533.

Rheticus published an expanded version of the trigonometry section of De revolutionibus as a separate work before De revolutionibus itself was published. The historian of mathematics, Grattan-Guinness, calls the Renaissance the age of trigonometry. We also have the transition of algebra from being merely commercial arithmetic to becoming a central mathematical discipline during the sixteenth century. This new analytical mathematics lay at the core of the so-called scientific revolution in the seventeenth century.

The fifteenth and sixteenth centuries also saw a renaissance in the mathematics and physics of Archimedes, in which Regiomontanus, once again, played a significant role. This renaissance peaked in 1544 when Thomas Venatorius published a bilingual, Greek and Latin, edition of the Works of Archimedes in Basel.


Archimedes, Opera omnia, Basel, 1544,

Galileo, who is often (falsely) called the founder of modern physics, explicitly took the work of Archimedes rather than that of Aristotle as reference point for his own work.

In the so-called natural sciences the Middle Ages were dominated by the Naturalis Historia of Gaius Plinius Secundus, or Pliny as he is know in English. This work is an encyclopaedia of everything that Pliny considered related to nature, astronomy, meteorology, geography, ethnography, anthropology, physiology, zoology, botany including agriculture and horticulture, pharmacology, magic, water, mining and mineralogy.  The work lacks originality and depth and is a ragbag of other sources thrown together under one concept, natural history; a term that we still use today. The Renaissance, especially after the invention of moving type book printing in the middle of the fifteenth century, saw the separating out and development of the individual disciplines as we known them today.

Vannoccio Biringuccio in his De la pirotechnia (1540) and Georgius Agricola in his De re metalica (1556) modernised and established metallurgy as an independent discipline. Agricola’s work together with his De natura fossilium also contributed substantially to the founding of geology and mineralogy as separate disciplines.


Zoology found its independence in the works of Ulisse Aldrovandi, who also contributed substantially to the foundations of geology, a word that he coined, and Conrad Gesner, who also published a fossil book. Aldrovandi was one of those who established a botanical garden and wrote and published a herbal. In zoology, some of the anatomists, who followed in the wake of Vesalius in the second half of sixteenth century, also instituted comparative anatomy, dissecting animal as well as human corpses.


Albrecht Dürer’s Rhinoceros from Conrad Gesner’s History Animalium

Herbals had already existed in the Middle Ages but following the invention of the printed book they took on a whole new dimension. The sixteenth century became the age of the great herbals of Otto Brunfels, Leonhart Fuchs, Hieronymus Bock, Rembert Dodoens, Carolus Clusius, Pietro Andrea Mattioli, Propero Alpino and others. Botanical gardens and herbariums, collections of dried plant specimens, were also established all over Europe and not just in university towns. Both the herbals and the botanical gardens served two purposes, on the one hand the study of botany and on the other the study of pharmacology. The authors of the herbals and the keepers of the botanical gardens and herbariums exchanged seeds, plants and dried specimens with their colleagues throughout Europe and even further afield. Researchers in the newly discovered lands (newly discovered for Europeans that is) sending specimens home from all over the world.


Leonhart Fuch’s Herbal

Williams emphasises that the little bit of scientific activity that he acknowledges took place during the Renaissance did so outside of the “high Renaissance”:

But the fact that this treatment is relatively brief and relates to a period rather later than the “high Renaissance” should give us pause if we are inclined to think of this as an epoch of spectacular scientific progress.

The expression “high Renaissance” is a highly dubious and rather meaningless historical concept, as it just basically means the short period when Leonardo, Raphael and Michelangelo were active, but is William’s implied claim that this period invoked no scientific progress really true?

The books on zoology and botany listed above were spectacularly illustrated, large format volumes and can even be viewed as the first printed coffee table books. What is interesting here is that they reflected and contributed to the development in fine art now labelled Naturalism. Many of the illustrators of those early coffee table books trained in the studios of the high Renaissance artists. Similarly the illustrations in the anatomical, medical works. This development lies at the heart of the so-called high Renaissance and alongside the realistic depiction of the natural world this included as a central element the development and use of linear perspective. Linear perspective is in fact a branch of applied or practical mathematics that developed in the Renaissance out of the medieval theories of optics. It developed further in the seventeenth century into projective geometry. The high Renaissance was not quite as devoid of scientific progress as Williams would have us believe.

Medicine also saw many new developments alongside the Vesalian revolution in anatomy. Many new drugs both botanical and mineral were sent back to Europe and investigated for their efficacy by those at home. With Paracelsus a whole new direction is medicine was established which grew and expanded following his death in 1541.


Paracelsus Source: Wikimedia Commons

This was a medicine based on alchemy and mineral rather than plant based medicines. The Paracelsian alchemy played a significant role in the transition from alchemy to modern chemistry and helped to establish the modern science of pharmacology. The first university chairs for chemistry at the beginning of the seventeenth century were chairs for Paracelsian medicine.

The sixteenth century also saw a restructuring of the medical industry in general with the physicians gaining prominence over the apothecaries, midwives and herbalist, creating a medical hierarchy that persists, with modifications, to the present day.

The above is merely a sketch of the scientific activity during the Renaissance and is by no means exhaustive. There are certainly other activities that I haven’t listed and even ones that I’m not aware of yet. However, I think I have outlined enough to show that the 15th and early 16th centuries are anything but a rather stagnant period in many areas of natural science compared with some parts of the Middle Ages. In fact those two centuries were rich in scientific developments and advances more than equal to anything produced in the earlier part of the Middle Ages. I would, however, once again emphasise that I think dividing the period between the twelfth and seventeenth centuries into Middle Ages and Renaissance with relation to the history of science is artificial and unproductive and we should look more at the continuities and less at the divisions.


[1] Catherine Fletcher, The Beauty and the Terror, The Bodley Head, London, 2020, As it is a book largely about political history I probably won’t be reviewing it here.


Filed under Renaissance Science

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

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

One of the most often repeated false statements in the history of science is that Isaac Newton discovered gravity. Of course he didn’t discovery it, it’s all around us. You can observe gravity every time you drop something. Making the claim more precise, by saying Newton discovered the law of gravity, doesn’t really improve the situation much. What Newton did do was he proved the law of gravity and made the fairly rational assumption based on the available evidence that this law applies universally to all bodies in the cosmos. An assumption that is not written in stone and has been questioned in the present time for the general theory of relativity, the theory that replaced the Newtonian theory of universal gravity and of which the Newtonian theory of gravity is a very good approximation for local cases. However we don’t want to take the path to modern theories of cosmology and dark matter but want to stay firmly in the seventeenth century with Newton.

We can start with a brief survey of theories of gravity before Newton. Originally gravity was the Latin term applied to Aristotle’s explanation of why, when dropped, things fall to the ground. Aristotle thought that objects did so through a form of vital attraction, returning to their natural home, consisting predominantly of the elements earth and water. Fire and air rise up. This only applied to the Earth, as things beyond the Moon were made of a fifth element, aether, the quintessence, for which the natural form of motion was uniform circular motion.

This neat model wouldn’t work, however for Copernicus’ heliocentric model, which disrupted the division between the sublunar and supralunar worlds. To get around this problem Copernicus suggested that each planet had its own gravity, like the Earth. So we have terrestrial gravity, Saturnian gravity, Venusian gravity etc. This led Alexander von Humboldt, in the 19th century, to claim that Copernicus should be honoured as the true originator of the universal theory of gravity, although it is by no means clear that Copernicus thought that he planetary gravities were all one and the same phenomenon.

The whole concept became even more questionable when the early telescopic astronomers, above all Galileo, showed that the Moon was definitely Earth like and by analogy probably the other planets too. At the end of a long line of natural philosophers stretching back to John Philoponus in the sixth century CE, Galileo also showed that gravity, whatever it might actually be, was apparently not a vitalist attraction but a force subject to mathematical laws, even if he did get the value for the acceleration due to gravity ‘g’ wrong and although he didn’t possess a clear concept of force.. Throughout the seventeenth century other natural philosophers, took up the trail and experimented with pendulums and dropped objects. A pendulum is of course an object, whose fall is controlled. Most notable were the Jesuit, natural philosopher Giovanni Battista Riccioli (1598–1671) and the Dutch natural philosopher Christiaan Huygens (1629–1695). Riccioli conducted a whole series of experiments, dropping objects inside a high tower, making a direct confirmation of the laws of fall. Both Riccioli and Huygens, who independently of each other corrected Galileo’s false value for ‘g’, experimented extensively with pendulums in particular determining the length of the one-second pendulum, i.e. a pendulum whose swing in exactly one second. As we will see later, the second pendulum played a central roll in an indirect proof of diurnal rotation. Huygens, of course, built the first functioning pendulum clock.

Turning to England, it was not Isaac Newton, who in the 1670s and 80s turned his attention to gravity but Robert Hooke (1635–1703), who was Curator of Experiments for the newly founded Royal Society. Like Riccioli and Huygens Hooke experimented extensively with dropping objects and pendulums to try and determine the nature of gravity. However his experiments were not really as successful as his continental colleagues. However, he did develop the idea that it was the force of gravity that controlled the orbits of the planets and, having accepted that comets were real solid objects and not optical phenomena, also the flight paths of comets. Although largely speculative at this point Hooke presented a theory of universal gravity, whilst Newton was still largely confused on the subject. Hooke turned to Newton in a letter with his theory in order to ask his opinion, an act that was to lead to a very heated priority dispute.

Before we handle that correspondence we need to go back to the beginnings of the 1670s and an earlier bitter dispute between the two.  In 1672 Newton announced his arrival on the European natural philosophy scene with his first publication, a letter in the Philosophical Transactions of the Royal Society (1671/72), A New Theory of Light and Colours, which described the experimental programme that he had carried out to demonstrate that white light actually consisted of the colours of the spectrum.


Newton’s original letter. Source: Royal Society

This brilliant piece of experimental optics did not receive the universal praise that, reading it today, we might have expected, in fact it was heavily criticised and attacked. Some critics were unable to reproduce Newton’s experimental results, probably because their prisms were of too poor quality. However, others, Hooke to the fore, criticised the content. Hooke and Huygens, the two current leaders in the field of optics both criticised Newton for interpreting his results within the framework of a particle theory of light, because they both propagated a wave theory of light. Newton actually wrote a paper that showed that his conclusions were just as valid under a wave theory of light, which, however, he didn’t publish. The harshest criticism came from Hooke alone, who dismissed the whole paper stating that he had already discovered anything of worth that it might contain . This did not make Newton very happy, who following this barrage of criticism announced his intention to resign from the Royal Society, to which he had only recently been elected.  Henry Oldenburg (c. 1619–1677), secretary of the Royal Society, offered to waive Newton’s membership fees if he would stay. Newton stayed but had little or nothing more to do with the society till after Hooke’s death in 1703. Newton did, however, write a very extensive paper on all of his optical work, which remained unpublished until 1704, when it formed a major part of his Opticks.

By  1679 tempers had cooled and Robert Hooke, now secretary of the Royal Society, wrote to Isaac Newton to enquire if he would be interested in reopening his dialogue with the Royal Society. In the same letter he asked Newton’s opinion on his own hypothesis that planetary motions are compounded of a tangential motion and “an attractive motion towards the centrall body…” Hooke is here referencing his Attempt to Prove the Motion of the Earth from Observations (1674, republished 1679),


which contains the following fascinating paragraph:

This depends on three Suppositions. First, That all Coelestial Bodies whatsoever, have an attractive or gravitating power towards their own Centers, whereby they attract not only their own parts, and keep them from flying from the, as we observe the earth to do, [here Hooke is obviously channelling Copernicus] but that they do also attract all other Coelestial Bodies that are within the sphere of their activity … The second supposition is this, That all bodies whatsoever that are put into a direct and simple motion, will so continue to move forward in a streight line, till they are by some other effectual power deflected and bent into a Motion, describing a Circle, Ellipsis, or some other more compounded Curve Line. [the principle of inertia, as propounded by Descartes] The third supposition is, That these attractive powers are so much the more powerful in operating, by how much nearer the body wrought upon is to there own Centers. Now what these several degrees are I have not yet experimentally verified…

Whether or not this is truly a universal theory of gravity is a much-debated topic, but if not, it comes very close and was moving much more in that direction than anything Newton had produced at the time. As we shall see later this was to cause not a little trouble between the two rather prickly men.

Newton declined the offer of a regular exchange of ideas, claiming that he was moving away from (natural) philosophy to other areas of study. He also denied having read Hooke’s paper but referred to something else in it in a later letter to Flamsteed. However, in his reply he suggested an experiment to determine the existence of diurnal rotation involving the usually dropping of objects from high towers. Unfortunately for Newton, he made a fairly serious error in his descripting of the flight path of the falling object, which Hooke picked up on and pointed out to him, if unusually politely, in his reply. Newton of course took umbrage and ended the exchange but he did not forget it.

In our next episode we will deal with the events leading up to the writing and publication of Newton’s great masterpiece, Philosophiæ Naturalis Principia Mathematica (1687), which include the repercussions of this brief exchange between Hooke and its author.




Filed under History of Astronomy, History of Mathematics, History of Optics, History of Physics, Renaissance Science