Category Archives: History of Optics

STOMP. STOMP, STOMP … KEPLER DID WOT!

I really shouldn’t but the HISTSCI_HULK is twisting my arm and muttering dark threats, so here goes. A week ago, we took apart Vedang Sati’s post 10 Discoveries By Newton That Changed The World. When I copied it to my blog, I removed the links that Sati had built into his post. I then made the mistake of following his link to his post on Kepler, so here we go again. 

Johannes Kepler Source: Wikimedia Commons

7 Ways In Which Johannes Kepler Changed Astronomy

Johannes Kepler was a German astronomer who discovered the three laws of planetary motion. Apart from his contributions to astronomy, he is also known to have pioneered the field of optics. In this post, let’s read some amazing facts about Kepler and his work. 

He obviously doesn’t rate Kepler as highly as he rates Newton, so the introduction is less hagiographic this time. However, it does contain one quite extraordinary claim, when he writes, “he is also known to have pioneered the field of optics.” Optics as a scientific discipline was pioneered by Euclid, who lived in the fourth century BCE, so about two thousand years before Kepler. There were also quite a few people active in the field in the two millennia in between.

Early Affliction

He suffered from small pox at a very early age. The disease left him with weak eyesight. Isn’t  it wonderful then how he went on to invent eyeglasses for near-eye and far-eye sightedness.

Kepler did indeed suffer from smallpox sometime around the age of four, which almost cost him his life and did indeed leave him with damaged eyesight. However, Kepler did not invent spectacles of any type whatsoever. The first spectacles for presbyopia, far-sightedness occurring in old age, began to appear in the last decades of the thirteenth century CE. Spectacles for myopia, short-sightedness, were widely available by the early fifteenth century. What Kepler actually did was to publish the first scientific explanation of how lenses function to correct defects in eyesight in his Astronomiae Pars Optica (The Optical Part of Astronomy), in 1604. Francesco Maurolico (1494–1574) actually gave the correct explanation earlier than Kepler in his Photismi de lumine et umbra but this was only published posthumously in 1611, so the credit for priority goes to Kepler

Astronomiae Pars Optica Source: Wikimedia Commons

Introduction to Astronomy

Kepler’s childhood was worsened by his family’s financial troubles. At the age of 6, Johannes had to drop out of school so to earn money for the family. He worked as a waiter in an inn.

As Kepler first entered school at the age of seven, it would have been difficult for his schooling to have been interrupted when he was six. His primary schooling was in fact often interrupted both by illness and the financial fortunes of the family. 

In the same year, his mother took him out at night to show him the Great Comet of 1577 which aroused his life-long interest in science and astronomy. 

Yes, she did!

Copernican Supporter

At a time when everyone was against the heliocentric model of the universe, Kepler became its outspoken supporter. He was the first person to defend the Copernican theory from a scientific and a religious perspective.

Not everyone was opposed to the heliocentric model of the universe, just the majority. Poor old Georg Joachim Rheticus (1514–1574), as the professor of mathematics, who persuaded Copernicus to publish De revolutionibus, he would be deeply insulted by the claim that Kepler was the “first person to defend the Copernican theory from a scientific and a religious perspective.” Rheticus, of course, did both, long before Kepler was even born, although his religious defence remained unpublished and was only rediscovered in the twentieth century. Rheticus was not the only supporter of Copernicus, who preceded Kepler there were others, most notably, in this case, Michael Mästlin (1550–1631), who taught Kepler the Copernican heliocentrism. 

Contemporary of Galileo

Galileo was not a great supporter of Kepler’s work especially when Kepler had proposed that the Moon had an influence over the water (tides). It would take an understanding many decades later which would prove Kepler correct and Galileo wrong.

It is indeed very true that Galileo rejected Kepler’s theory of the tides, when promoting his own highly defective theory, but that is mild compared to his conscious ignoring of Kepler’s laws of planetary motion, which were at the time the most significant evidence for a heliocentric cosmos.

Pioneer of Optics

Kepler made ground-breaking contributions to optics including the formulation of inverse-square law governing the intensity of light; inventing an improved refracting telescope; and correctly explaining the function of the human eye.

Kepler’s contributions to the science of optics were indeed highly significant and represent a major turning point in the development of the discipline. His Astronomiae Pars Optica does indeed contain the inverse square law of light intensity and the first statement that the image is created in the eye on the retina and not in the crystal lens.

However, that he invented an improved telescope is more than a little problematic. When Galileo published his Sidereus Nuncius in 1610, the first published account of astronomical, telescopic discoveries, there was no explanation how a telescope actually functions, so people were justifiably sceptical. Having written the book on how lenses function with his Astronomiae Pars Optica in 1604, Kepler now delivered a scientific explanation how the telescope functioned with his Dioptrice in 1611. 

Kepler Dioptrice Source: Wikimedia Commons

This contained not just a theoretical explanation of the optics of a Dutch or Galilean telescope, with a convex objective and a concave eyepiece, but also of a telescope with convex objective and convex eyepiece, which produces an inverted image, now known as a Keplerian or astronomical telescope, also one with three convex lenses, the third lens to right the inverted image, now known as a field telescope, and lastly, difficult to believe, the telephoto lens. Kepler’s work remained strictly theoretical, and he never constructed any of these telescopes, so is he really the inventor? The first astronomical telescope was constructed by Christoph Grienberger (1561–1636) for Christoph Scheiner (c. 1573–1650) as his heliotropic telescope, for his sunspot studies. 

Heliotropic telescope on the left. On the right Scheiner’s acknowledgement that Grienberger was the inventor

Is the astronomical telescope an improved telescope, in comparison with the Dutch telescope? It is very much a question of horses for courses. If you go to the theatre or the opera then your opera glasses, actually a Dutch telescope, will be much more help in distinguishing the figure on the stage than an astronomical telescope. Naturally, the astronomical telescope, with its wider fields of vision, is, as its name implies, much better for astronomical observations than the Dutch telescope once you get past the problem of the inverted image. This problem was solved with the invention of the multiple lens eyepiece by Anton Maria Schyrleus de Rheita (1604–1660), announced in Oculus Enoch et Eliae published in 1645, although he had already been manufacturing them together with Johann Wiesel (1583–1662) since 1643.

Helped Newton

His planetary laws went on to help Sir Isaac Newton derive the inverse square law of gravity. Newton had famously acknowledged Kepler’s role, in a quote: “If I have seen further, it is by standing on the shoulders of giant(s).

Sati is not alone in failing to give credit to Kepler for his laws of planetary motion in their own right, but instead regarding them merely as a stepping-stone for Newton and the law of gravity. Kepler’s laws of planetary motion, in particular his third law, are the most significant evidence for a heliocentric model of the cosmos between the publication of De revolutionibus in 1543 and Principia in 1687 and deserve to be acknowledged and honoured in their own right! 

Newton’s famous quote, actually a much-used phrase in one form or another in the Early Modern period, originated with Bernard of Chartres (died after 1124) in the twelfth century. Newton used it in a letter to Robert Hooke on 5 February 1675, so twelve years before the publication of his Principia and definitively not referencing Kepler:

What Des-Cartes [sic] did was a good step. You have added much several ways, & especially in taking the colours of thin plates into philosophical consideration. If I have seen further it is by standing on the sholders [sic] of Giants.

Kepler’s Legacy

There is a mountain range in New Zealand named after the famous astronomer. A crater on the Moon is called Kepler’s crater. NASA paid tribute to the scientist by naming their exo-planet telescope, Kepler.

Given the vast number of things named after Kepler, particularly in Germany, Sati’s selection is rather bizarre, in particular because it is a mountain hiking trail in New Zealand that is named after Kepler and not the mountain range itself.

Once again, we are confronted with a collection of half facts and straight falsehoods on this website, whose author, as I stated last time has nearly 190,000 followers on Facebook. 

Me: I told you that we couldn’t stop the tide coming in

HS_H: You’re not trying hard enough. You’ve gotta really STOMP EM!

Me: #histsigh

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

The astronomical librarian 

I’m continuing my look at the French mathematician astronomers of the seventeenth century with some of those, who were both members of Nicolas-Claude Fabri de Peiresc’s group of telescopic, astronomical observers, as well as Marin Mersenne’s informal Academia Parisiensis, starting with Ismael Boulliau (1605–1694), who like Peiresc and Mersenne was also a prominent member of the Republic of Letters with about 5000 surviving letters. 

Ismael Boulliau Source: Wikimedia Commons

Boulliau was born in Loudun, France the second son of Ismael Boulliau a notary and amateur astronomer and Susanne Motet on 28 September 1605. The first son had been born a year earlier and was also named Ismael, but he died and so the name was transferred to their second son. Both of his parents were Calvinists. His father introduced him to astronomy and in his Astronomia philolaica (1645) Ismael junior tells us that his father observed both Halley’s comet in 1607 and the great comet of 1618. The later was when Boulliau was thirteen years old, and one can assume that he observed together with his father. 

Probably following in his father’s footsteps, he studied law but at the age of twenty-one he converted to Catholicism and in 1631, aged twenty-six, he was ordained a priest. In 1632 he moved to Paris and began to work for Pierre Dupuy (1582–1651) and his brother Jacques (1591–1656), who were keepers of the Bibliothèque du Roi, today the Bibliothèque nationale de France. Boulliau held this position until the death of the Dupuy brothers and during that time travelled widely in Europe collecting books and manuscripts for the library. 

Pierre Dupuy Source: Wikimedia Commons

Boulliau also enjoyed the patronage of the powerful and influential de Trou family, who were closely connected with the library and who financed his book collecting travels. Following the death of the Dupuy brothers he became employed by the French ambassador to the United Provinces, a member of the de Trou family, a secretary and librarian. In 1666, following a dispute with his employer, he became librarian at the Collège de Laon in Paris. For the last five years of his live he returned to the priesthood in the Abbey St Victor near Paris where he died aged 89. Although Boulliau was an active member of Mersenne’s Academia Parisiensis he never became a member of the Académie des sciences, but he was elected one of the first foreign associates of the Royal Society on 4 April 1667. 

Abbey of St. Victor, 1655 Source: Wikimedia Commons

 Like Peiresc, Boulliau was a polymath with extensive knowledge of a wide range of humanities topics, which was useful in his work as a librarian, but, as with Peiresc, it is scientific activities that are of interest here. He continued to make astronomical observations throughout his life, which were of a high level of accuracy. In his Principia, Newton puts him on a level with Kepler for his determination of the planetary orbits. In Book 3 Phenomenon 4 of Principia Newton writes: 

But of all astronomers, Kepler and Boulliau have determined the magnitude of the orbits from observations with the most diligence. 

Boulliau’s first significant scientific publication was, however, not in astronomy but in optics, his De natura lucis (On the Nature of Light) (1638) based on the discussions he was having with Gassendi on the topic. This work is not particular important in the history of optics but it does contain his discussion of Kepler’s inverse square law for the propagation of light.

Source: Wikimedia Commons

His first astronomical work Philolaus (1639), which places him firmly in the Copernican heliocentric camp but not, yet a Keplerian was next. 

He now changed tack once again with a historical mathematical work. In 1644, he translated and published the first printed edition of Theon of Smyrna’s Expositio rerum mathematicarum ad legendum Platonem utilium a general handbook for students of mathematics of no real significance. Continuing with his mathematical publications. In 1657, he published De lineis spiralibus (On Spirals) related to the work of Archimedes and Pappus on the topic.

Source: Wikimedia Commons

Much later in 1682, he published Opus novum ad arithmeticam infinitorum, which he claimed clarified the Arithmetica infinitorum(1656) of John Wallis (1616–1703).

Source: Wikimedia Commons

All of Boulliau’s work was old fashioned and geometrical. He rejected the new developments in analytical mathematics and never acknowledged Descartes’ analytical geometry. As we shall see, his astronomy was also strictly geometrical. He even criticised Kepler for being a bad geometer. 

Boulliau’s most important publication was his second astronomical text Astronomia philolaica (1645).

Source: Wikimedia Commons

In this highly influential work, he fully accepted Kepler’s elliptical orbits but rejects almost all of the rest of Kepler’s theories. As stated above his planetary hypothesis is strictly geometrical and centres round his conical hypothesis:

“The Planets, according to that astronomer [Boulliau], always revolve in circles; for that being the most perfect figure, it is impossible they should revolve in any other. No one of them, however, continues to move in any one circle, but is perpetually passing from one to another, through an infinite number of circles, in the course of each revolution; for an ellipse, said he, is an oblique section of a cone, and in a cone, betwixt the vertices of the ellipse there is an infinite number of circles, out of the infinitely small portions of which the elliptical line is compounded. The Planet, therefore, which moves in this line, is, in every point of it, moving in an infinitely small portion of a certain circle. The motion of each Planet, too, according to him, was necessarily, for the same reason, perfectly equable. An equable motion being the most perfect of all motions. It was not, however, in the elliptical line, that it was equable, but in any one of the circles that were parallel to the base of that cone, by whose section this elliptical line had been formed: for, if a ray was extended from the Planet to any one of those circles, and carried along by its periodical motion, it would cut off equal portions of that circle in equal times; another most fantastical equalizing circle, supported by no other foundation besides the frivolous connection betwixt a cone and an ellipse, and recommended by nothing but the natural passion for circular orbits and equable motions,” (Adam Smith, History of Astronomy, IV.55-57).

Boulliau’s Conical Hypothesis [RA Hatch] Source: Wikimedia Commons

Boulliau’s theory replaces Kepler’s second law, and this led to the Boulliau-Ward debate on the topic with the English astronomer Seth Ward (1617–1689), the Savilian Professor of astronomy at Oxford University.

Bishop Seth Ward, portrait by John Greenhill Source: Wikimedia Commons

Ward criticised Boulliau’s theory in his In Ismaelis Bullialdi astro-nomiae philolaicae fundamenta inquisitio brevis (1653), also pointing out mathematical errors in Boulliau’s work. 

Boulliau responded to Ward’s criticisms in 1657, acknowledging the errors and correcting but in turn criticising Ward’s model in his De lineis spiralibus. A year earlier Ward had published his own version of Keplerian astronomy in his Astronomia geometrica (1656).

Source: Wikimedia Commons

This exchange failed to find a resolution but this very public debate between two of Europe’s leading astronomers very much raised awareness of Kepler’s work and was factor in its eventual acceptance of Kepler’s elliptical heliocentric astronomy. 

It was in his Astronomia philolaica that Boulliau was the first to form an inverse squared theory of attraction between the sun and the planets. 

As for the power by which the Sun seizes or holds the planets, and which, being corporeal, functions in the manner of hands, it is emitted in straight lines throughout the whole extent of the world, and like the species of the Sun, it turns with the body of the Sun; now, seeing that it is corporeal, it becomes weaker and attenuated at a greater distance or interval, and the ratio of its decrease in strength is the same as in the case of light, namely, the duplicate proportion, but inversely, of the distances that is, 1/d2 ​.

Here we see the influence of Kepler’s theory of light propagation, which as noted Boulliau discussed in his De natura lucis. However, having set up this hypothesis Boulliau goes on to reject it. 

… I say that the Sun is moved by its own form around its axis, by which form it was ignited and made light, indeed I say that no kind of motion presses upon the remaining planets … indeed [I say] that the individual planets are driven round by individual forms with which they were provided …

Despite Boulliau’s rejection of his own hypothesis, during Newton’s dispute with Hooke over who should get credit for the theory of gravity, he gives Boulliau the credit in a letter to Edmond Halley.

…so Bullialdus [i.e., Boulliau] wrote that all force respecting ye Sun as its center & depending on matter must be reciprocally in a duplicate ratio of ye distance from ye center, & used that very argument for it by wch you, Sr, in the last Transactions have proved this ratio in gravity. Now if Mr Hook from this general Proposition in Bullialdus might learn ye proportion in gravity, why must this proportion here go for his invention?

In 1667, Boulliau published a final astronomy book, Ad astronomos monita duo in which he was the first to establish the periodicity of the variable star, Mira Ceti.

Source:

His estimate of the period 333 days was only out by a one day. Mira had first been recognised as a variable star by David Fabricius beginning 3 August 1596.

Apart from his publications Boulliau kept Mersenne’s correspondence network alive for another thirty years after Mersenne’s death, communicating with Leopoldo de’ Medici (1617–1675) in Italy, Johannes Hevelius (1611–1687) in Danzig and Christiaan Huygens (1629–1695). Huygens first imparted his discovery of the rings of Saturn to Boulliau and Boulliau distributed Huygens’ System sarturnium (1658) in Paris. Boulliau also distributed Pascal’s Letters D’Amos Dettonville (1658–1659) to English and Dutch mathematicians, his challenge on the mathematics of the cycloid, an important publication in the development of calculus.

Ismael Boulliau is a prime example of a scholar, who didn’t make any major discoveries or develop any major theories himself but still had a very significant influence on the development of science.

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Filed under History of Astronomy, History of Mathematics, History of Optics, History of science, The Paris Provencal Connection

Musical, mathematical Minim, Marin Mersenne 

In the seventeenth century, Marin Mersenne (1588–1648) was a very central and highly influential figure in the European intellectual and scientific communities; a man, who almost literally knew everybody and was known by everybody in those communities. Today, in the big names, big events, popular versions of the history of science he remains only known to specialist historian of science and also mathematicians, who have heard of Mersenne Primes, although most of those mathematicians probably have no idea, who this Mersenne guy actually was. So, who was Marin Mersenne and why does he deserve to be better known than he is?

Marin Mersenne Source: Wikimedia Commons

Mersenne was born 8 September 1588, the son of Julien Mersenne and his wife Jeanne, simple peasants, in Moulière near Oizé, a small commune in the Pays de la Loire in North-Western France. He was first educated at the at the nearby College du Mans and then from 1604 to 1609 at the newly founded Jesuit Collège Henri-IV de La Flèche. The latter is important as in La Flèche he would have received the mathematical programme created by Christoph Clavius for the Jesuit schools and colleges, the best mathematical education available in Europe at the time. A fellow student at La Flèche was René Descartes (1596–1650) with whom he would become later in life close friends.

René Descartes at work Source: Wikimedia Commons

However, it is unlikely that they became friends then as Mersenne was eight years older. Leaving La Flèche he continued his education in Greek, Hebrew, and theology at the Collège Royal and the Sorbonne in Paris. In 1611 he became a Minim friar and a year later was ordained as a priest. The Minims are a mendicant order founded in Italy in the fifteenth century. From 1614 to 1618 he taught philosophy and theology at Nevers but was recalled to Paris in 1619 to the newly established house on the Place Royal (now Place des Vosges), where he remained, apart from travels through France, to Holland, and to Italy, until his death. 

View map of an area of Paris near Place Royale, now Place des Vosges, showing the Minim convent where Mersenne lived and the Rue des Minimes, not far from the Bastille, undated, but before 1789 (paris-grad.com) Source: Linda Hall Library

In Paris he was introduced to the intellectual elite by Nicolas-Claude Fabri de Pereisc (1580–1637)–wealthy astronomer, antiquarian, and patron of science–whom he had got to know in 1616. 

Nicolas-Claude Fabri de Peiresc by Louis Finson Source: Wikimedia Commons

Settled in Paris, Mersenne began a career as a prolific author, both editing and publishing new editions of classical works and producing original volumes. In the 1620s his emphasis was on promoting and defending the Thomist, Aristotelian philosophy and theology in which he’d been educated. In his first book, Questiones celeberrimae in Genesim (1623), 

he attacked those he saw as opponents of the true Catholic religion, Platonist, cabbalistic and hermetic authors such as Telesio, Pomponazzi, Bruno and Robert Fludd. His second book, L’impiété des déistes, athées, et libertins de ce temps (1624), continued his attacks on the propagators of magic and the occult. His third book, La Vérité des sciences (1625), attacks alchemists and sceptics and includes a compendium of texts over ancient and recent achievements in the mathematical sciences that he saw as in conformity with his Christian belief. The latter drew the attention of Pierre Gassendi (1592–1655), who became his closest friend. I shall return to their joint activities in Paris later but now turn to Mersenne’s own direct scientific contributions, which began to replace the earlier concentration on theology and philosophy.

Pierre Gassendi Source: Wikimedia Commons

Mersenne’s scientific interests lay in mathematics and in particular what Aristotle, who was not a fan of mathematics, claiming it did not apply to the real world, called the mixed sciences or mixed mathematics i.e., astronomy, optics, statics, etc. Here he compiled to collections of treatises on mixed mathematics, his Synopsis Mathematica (1626) and Universae geometriae synopsis (1644). In his Traité de l’Harmonie Universelle (1627), to which we will return, Mersenne gives a general introduction to his concept of the mathematical disciplines:

Geometry looks at continuous quantity, pure and deprived from matter and from everything which falls upon the senses; arithmetic contemplates discrete quantities, i.e. numbers; music concerns har- monic numbers, i.e. those numbers which are useful to the sound; cosmography contemplates the continuous quantity of the whole world; optics looks at it jointly with light rays; chronology talks about successive continuous quantity, i.e. past time; and mechanics concerns that quantity which is useful to machines, to the making of instruments and to anything that belongs to our works. Some also adds judiciary astrology. However, proofs of this discipline are borrowed either from astronomy (that I have comprised under cosmology) or from other sciences. 

In optics he addressed the problem of spherical aberration in lenses and mirrors and suggested a series of twin mirror reflecting telescopes, which remained purely hypothetical and were never realised.

Source: Fred Watson, “Stargazer: The Life and Times of the Telescope”, Da Capo Press, 2004, p. 115

This is because they were heavily and falsely criticised by Descartes, who didn’t really understand them. It was Mersenne, who pushed Descartes to his solution of the refraction problem and the discovery of the sine law. He wrote three books on optics, De Natura lucis (1623); Opticae (1644); L’Optique et la catoptrique (1651). Although his theoretical reflecting telescopes were published in his Harmonie universelle (1636), see below.

Mersenne also wrote and published collections of essays on other areas of mixed mathematics, mechanics, pneumatics, hydro- statics, navigation, and weights and measures, Cogitata physico-mathematica (1644); Novarum observationum physico- mathematicarum tomus III (1647). 

Mersenne dabbled a bit in mathematics itself but unlike many of his friends did not contribute much to pure mathematics except from the Mersenne prime numbers those which can be written in the form Mn = 2n − 1 for some integer n. This was his contribution to a long search by mathematicians for some form of law that consistently generates prime numbers. Mersenne’s law whilst generating some primes doesn’t consistently generate primes but it has been developed into its own small branch of mathematics. 

It was, however, in the field of music, as the title quoted above would suggest, which had been considered as a branch of mathematics in the quadrivium since antiquity, and acoustics that Mersenne made his biggest contribution. This has led to him being labelled the “father of acoustics”, a label that long term readers of this blog will know that I reject, but one that does to some extent encapsulate his foundational contributions to the discipline. He wrote and published five books on the subject over a period of twenty years–Traité de l’harmonie universelle (1627); Questions harmoniques (1634); Les preludes de l’harmonie universelle (1634); Harmonie universelle (1636); Harmonicorum libri XII (1648)–of which his monumental (800 page) Harmonie universelle was the most important and most influential.

Title page of Harmonie universelle Source: Wikimedia Commons

In this work Mersenne covers the full spectrum including the nature of sounds, movements, consonance, dissonance, genres, modes of composition, voice, singing, and all kinds of harmonic instruments. Of note is the fact that he looks at the articulation of sound by the human voice and not just the tones produced by instruments. He also twice tried to determine the speed of sound. The first time directly by measuring the elapse of time between observing the muzzle flash of a cannon and hearing the sound of the shot being fired. The value he determined 448 m/s was higher than the actual value of 342 m/s. In the second attempt, recorded in the Harmonie universelle (1636), he measured the time for the sound to echo back off a wall at a predetermined distance and recorded the value of 316 m/s. So, despite the primitive form of his experiment his values were certainly in the right range. 

Mersenne also determined the correct formular for determining the frequency of a vibrating string, something that Galileo’s father Vincenzo (1520–1591) had worked on. This is now known as Mersenne’s Law and states that the frequency is inversely proportional to the length of the string, proportional to the square root of the stretching force, and inversely proportional to the square root of the mass per unit length.

The formula for the lowest frequency is f=\frac{1}{2L}\sqrt{\frac{F}{\mu}},

where f is the frequency [Hz], L is the length [m], F is the force [N] and μ is the mass per unit length [kg/m].

Source: Wikipedia

Vincenzo Galileo was also involved in a major debate about the correct size of the intervals on the musical scale, which was rumbling on in the late sixteenth and early seventeenth centuries. It was once again Mersenne, who produced the solution that we still use today.

Although Mersenne is certainly credited and honoured by acoustic researchers and music theorists for his discoveries in these areas, perhaps his most important contribution to the development of the sciences in the seventeenth century was as a networker and science communicator in a time when scientific journals didn’t exist yet. 

Together with Gassendi he began to hold weekly meetings in his humble cell with other natural philosophers, mathematicians, and other intellectuals in Paris. Sometime after 1633 these meetings became weekly and took place in rotation in the houses of the participants and acquired the name Academia Parisiensis. The list of participants reads like an intellectual who’s who of seventeenth century Europe and included René Descartes, Étienne Pascal and his son Blaise, Gilles de Roberville, Nicolas-Claude Fabri de Pereisc, Pierre de Fermat, Claude Mydorge, the English contigent, Thomas Hobbes, Kenhelm Digby, and the Cavendishes, and for those not living in or near Paris such as Isaac Beeckman, Jan Baptist van Helmont, Constantijn Huygens and his son Christiaan, and not least Galileo Galilei by correspondence. When he died approximately six hundred letters were found in his cell from seventy-nine different correspondents. In total 193 scholars and literati have been identified as participants. Here it should be noted that although he tended to reject the new emerging sciences in his earlier defence of Thomist philosophy, he now embraced it as compatible with his teology and began to promote it.

This academy filled a similar function to the Gresham College group and Hartlib Circle in England, as well as other groups in other lands, as precursors to the more formal scientific academies such as the Académie des sciences in Paris and the Royal Society in London. There is evidence that Jean-Baptist Colbert (1619–1683), the French Minister of State, modelled his Académie des sciences on the Academia Parisiensis. Like its formal successors the Academia Parisiensis served as a forum for scholars to exchange views and theories and discuss each other’s work. Mersenne’s aim in establishing this forum was to stimulate cooperation between the participants believing science to be best followed as a collective enterprise.

Mersenne’s role was not restricted to that of convener, but he functioned as a sort of agent provocateur deliberately stimulating participants to take up research programmes that he inaugurated. For example, he brought Torricelli’s primitive barometer to Paris and introduced it to the Pascals. It is thought that he initiated the idea to send Blaise Pascal’s brother-in-law up the Puy de Dôme to measure the decreasing atmospheric pressure.

Blaise Pascal, unknown; a copy of the painting of François II Quesnel, which was made for Gérard Edelinck in 1691. Source: Wikimedia Commons

Although they never met and only corresponded, he introduced Christiaan Huygens to the concept of using a pendulum to measure time, leading to Huygens’ invention of the pendulum clock.

Portrait of Christiaan Huygens (1629-1695) C.Netscher / 1671 Source: Wikimedia Commons

It was Mersenne, who brought the still very young Blaise Pascal together with René Descartes, with the hope that the brilliant mathematicians would cooperate, in this case he failed. In fact, the two later became opponents divided by their conflicting religious views. Mersenne also expended a lot of effort promoting the work of Galileo to others in his group, even offering to translate and publish Galileo’s work in French, an offer that the Tuscan mathematician declined. He did, however, publish an unpublished text by Galileo on mechanics, Les Mechaniques de Galilée.

Although not the author of a big theory or big idea, or the instigators of a big event, Mersenne actually contributed with his activities at least as much, if not more, to the development of science in the seventeenth century as any of the more famous big names. If we really want to understand how science develops then we need to pay more attention to figures like Mersenne and turn down the volume on the big names. 

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Filed under History of Mathematics, History of Optics, History of science, The Paris Provencal Connection

I do wish people wouldn’t post things like this

I stumbled across the following image on Facebook, being reposted by people who should know better, and it awoke my inner HISTSCI_HULK:

I shall only be commenting on the first three images, if anybody has any criticism of the other ones, they’re welcome to add them in the comments.

To what extent Galileo developed his own telescope is debateable. He made a Dutch, telescope a model that had first been made public by Hans Lipperhey in September 1608. By using lenses of different focal lengths, he managed to increase the magnification, but then so did several others both at the same time and even before him.

Galileo was not the first to point the telescope skywards! As I have pointed out on several occasions, during that first demonstration by Lipperhey in Den Hague, the telescope was definitely pointed skywards:

The said glasses are very useful at sieges & in similar affairs, because one can distinguish from a mile’s distance & beyond several objects very well, as if they are very near & even the stars which normally are not visible for us, because of the scanty proportion and feeble sight of our eyes, can be seen with this instrument[1]

Even amongst natural philosophers and astronomers, Galileo was not the first. We know that Thomas Harriot preceded him in making astronomical observations. It is not clear, but Simon Marius might have begun his telescopic astronomical observations before Galileo. Also, the astronomers of the Collegio Romano began telescopic observations before Galileo went public with his Sidereus Nuncius and who was earliest they or Galileo is not determinable.

I wrote a whole very detailed article about the fact that Newton definitively did not invent the reflecting telescope that you can read here.

By the standards of the day William Herschel’s 20-foot telescope, built in 1782 seven years before the 40-foot telescope, was already a gigantic telescope, so the 40-footer was not the first. Worse than this is the fact that the image if of one of his normal ‘small’ telescopes and not the 40-footer. 

Herschel’s 40-foot telescope Source: Wikimedia Commons

People spew out these supposedly informative/educational or whatever images/articles, which are sloppily researched or not at all and are full of avoidable error. To put it bluntly it really pisses me off!


[1] Embassies of the King of Siam Sent to His Excellency Prince Maurits Arrived in The Hague on 10 September 1608, Transcribed from the French original, translated into English and Dutch, introduced by Henk Zoomers and edited by Huib Zuidervaart after a copy in the Louwman Collection of Historic Telescopes, Wassenaar, 2008 pp. 48-49 (original pagination: 9-11)

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Christmas Trilogy 2020 Part 2: Charles brightens up the theatre

There is a strong tendency in the present to view Charles Babbage as a one trick pony i.e., Babbage the computer pioneer. In reality he was a true polymath whose intellectual activities covered a very wide spectrum.

Already as a student at Cambridge, he agitated for major curriculum reform in the mathematics taught and practiced in Britain. He also produced some first class cutting edge mathematics, much of which for some reason he never published. His interest in automation stretched way beyond his computing engines and after extensive research on automations in industry, both throughout Europe and in Britain, he wrote and published a book on the organisation of industrial production, On the Economy of Machinery and Manufactures (1832), which became a highly influential bestseller, influencing the work of both John Stuart Mill and Karl Marx. He was a leader in a campaign to improve the standard of science research in Britain, largely aimed at what he saw as the moribund Royal society, which resulted in his Reflections on the Decline of Science and some of its Causes (1830). As part of this campaign, he was a leading figure in the establishment of the British Association for the Advancement of Science (BAAS).

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Engraving of Charles Babbage dated 1833 Source: Wikimedia Commons 

His achievements were not confined to purely intellectual activities, he was also an assiduous inventor of mechanical devices and improvement, well outside of his proto computers. For example, he designed and had constructed a four wheeled light carriage for one of his extensive tours of Europe. It was so designed that he could sleep on board and had drawers large enough to stow frock coats and technical plans without folding, as well as a small on board kitchen. However, it is his activities in practical optics that interest me here, in particular his foray into early theatre lighting, which I found fascinating, having, for several years in my youth, been a lighting technician both in theatre and live music.  

An ophthalmoscope is a medical instrument designed to make it possible to observe the interior of the eye by means of a beam of light. The invention of the ophthalmoscope is traditionally attributed to Hermann von Helmholtz in 1851. However, it would appear that Babbage preceded him by four years.

Charles Babbage, the mathematic genius and inventor of what many consider to be the forerunner of today’s computer, his analytical machine, was the first to construct an instrument for looking into the eye. He did this in 1847 but when showing it to the eminent ophthalmologist Thomas Wharton Jones he was unable to obtain an image with it and, thus discouraged, did not proceed further. Little did he know that his instrument would have worked if a minus lens of about 4 or 5 dioptres had been inserted between the observer’s eye and the back of the plano mirror from which two or three holes had been scraped. Some seven years later it was his design and not that of Helmholtz which had been adopted.

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The image shows a reconstruction of Babbage’s ophthalmoscope, c. 1847. No actual example survives but this replica was made for the Science Museum in 2003, based upon Wharton Jones’ written description.

Dr. Helmholtz, of Konigsberg, has the merit of specially inventing the ophthalmoscope. It is but justice that I should here state, however, that seven years ago Mr. Babbage showed me the model of an instrument which he had contrived for the purpose of looking into the interior of the eye. It consisted of a bit of plain mirror, with the silvering scraped off at two or three small spots in the middle, fixed within a tube at such an angle that the rays of light falling on it through an opening in the side of the tube, were reflected into the eye to be observed, and to which the one end of the tube was directed. The observer looked through the clear spots of the mirror from the other end. This ophthalmoscope of Mr Babbage, we shall see, is in principle essentially the same as those of Epkens and Donders, of Coccius and of Meyerstein, which themselves are modifications of Helmhotlz’s.

         Wharton-Jones, T., 1854, ‘Report on the Ophthalmoscope’, Chronicle of Medical Science (October 1854).

Around the same time as he built his ophthalmoscope, Babbage designed and built a mechanical, clockwork, programmable, self-occulting, signalling lamp to aid ship to ship and ship to shore communications. He was disappointed that the British marine fleets showed no interest in his invention, but the Russian navy used it against the British during the Crimean War. During the Great Exhibition of 1851, in which Babbage played a central role, he set his signal lamp in the window of his house in the evenings and people passing by would drop in their visiting card with the signalled number written on them. Babbage’s occulting lights were later used in lighthouses in various parts of the world starting in the USA.

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Babbage’s mechanical, clockwork, programmable, self-occulting, signalling lamp mechanism

Babbage was a theatre goer and during his phase of light experiments and invention he undertook an interesting project in theatre lighting. During the Renaissance, theatres, such as Shakespeare’s Globe, were open air arenas and performances took place in daylight. Later closed theatre and opera house were lit with chandeliers with the cut glass or crystal prisms dispersing the candlelight in all directions. Of course, the large number of candles needed caused much smoke and the dripping wax was a real problem. By the early nineteenth century theatres were illuminated with gas lamps.

One day during a theatre visit, Babbage noticed that during a moonlit scene the white bonnet of his companion had a pink taint and wondered about the possibility of using coloured light in theatre. He began a serious of interesting experiments with the then comparatively new limelight.

Limelight is an intense illumination created when an oxyhydrogen flame is directed at a cylinder of quicklime (calcium oxide). Quicklime can be heated to 2,572°C before melting and the light is produced by a combination of incandescence (the emission of electromagnetic radiation such as visible light e.g., red hot steel) and candoluminescence a form of radiation first observed and investigated in the early nineteenth century.

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Diagram of a limelight burner Source: Wikimedia Commons

As with many inventions the oxyhydrogen blowpipe has many fathers and was first developed in the late eighteenth and early nineteenth centuries by Jean-Baptiste-Gaspard Bochart de Saron (1730–1794), Edward Daniel Clarke (1769–1822) and Robert Hare (1781–1858) all of whose work followed out of the pneumatic discoveries of Carl Wilhelm Scheele (1742–1786), Joseph Priestly (1733–1804), who both discovered oxygen, and Henry Cavendish (1731–1810), who discovered hydrogen.

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Nineteenth century bellows-operated oxy-hydrogen blowpipe, including two different types of flashback arrestor John Griffen – A Practical Treatise on the Use of the Blowpipe, 1827 Source: Wikimedia Commons

The first to discover and experiment with limelight was the English chemist Goldsworthy Gurney (1792–1875)

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Goldsworthy Gurney Source: Wikimedia Commons

but it was the Scottish engineer Thomas Drummond (1797–1840) who, having seen it demonstrated by Michael Faraday (1791–1867),  first exploited its potential as a light source. Drummond built a practical working light in 1826, which he then used as a signal lamp in trigonometrical surveying. The light was bright enough to be seen at a distance of 68 miles by sunlight. Drummond’s application was so successful that limelight was also known as Drummond light and he was falsely credited with its discovery, instead of Gurney.

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Thomas Drummond by Henry William Pickersgill. The original picture is in the National gallery of Ireland Source: Wikimedia Commons

The earliest know public performance illuminated with limelight was an outdoor juggling performance by the magician Ching Lau Lauro (real name unknown) Herne Bay Pier in Kent in 1836. It was first used in theatre lighting in Covent Garden Theatre in 1837. By the 1860s and 1870s limelight was used worldwide in theatres and operas, used to highlight solo performers in the same way as modern spotlights, hence the expression, standing in the limelight. By the end of the nineteenth century, it had been largely replaced by electrical, carbon arc lighting.

 Babbage wanted to take the process one step further and use limelight not just as a very bright white light, but to introduce colour into theatre lighting. Babbage began to experiment with glass cells constructed out of two parallel sheets of glass and filled with solutions of various metal salts, such as chrome and copper. His experiment proved very successful and he developed coloured, limelight spots. Babbage now developed a dance scenario to display his new invention. He proposed replacing the stage footlights with four limelight projectors in the colours red, blue, yellow and purple. His imagined piece had four groups of dancers dressed in white, each of which entered the stage dancing in one of the four pools of light. Dancers springing from one pool of light into another would change colour. Gradually the apertures would widen with the lights crossing each other producing a rainbow of colours through which the dancers would circle. Babbage went on to develop a dramaturgy with dioramas telling an allegorical story.

Babbage discussed his project with Benjamin Lumley, the manager of the Italian Opera House (now Her Majesty’s Theatre) and arranged a demonstration of his new lights. The demonstration took place in the theatre with a smaller group of dancers, and it was apparently a great success. However, because of the fire risk he had two fire engines and their crews on standby during his demonstration and although impressed, Lumley declined a real performance with an audience because of the fire risk. Babbage didn’t develop the idea further.

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Portrait of Benjamin Lumley by D’Orsay Source: Wikimedia Commons

As a onetime theatre lighting technician and a historian of science, I would would quite like the idea of staging a modern version of Babbage’s little dance fantasy. I would also like to draw this episode in his life to the attention of all the Ada Lovelace acolytes, who are firmly of the opinion that Babbage was only capable of thinking about mathematics and therefore the imaginative flights of fancy in the Analytical Engine memoir notes must be entirely the work of Lady King.

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

 

By the end of the eighteenth century, Newton’s version of the heliocentric theory was firmly established as the accepted model of the solar system. Whilst not yet totally accurate, a reasonable figure for the distance between the Earth and the Sun, the astronomical unit, had been measured and with it the absolute, rather than relative, sizes of the orbits of the known planets had been calculated. This also applied to Uranus, the then new planet discovered by the amateur astronomer, William Herschel (1738–1822), in 1781; the first planet discovered since antiquity. However, one major problem still existed, which needed to be solved to complete the knowledge of the then known cosmos. Astronomers and cosmologists still didn’t know the distance to the stars. It had long been accepted that the stars were spread out throughout deep space and not on a fixed sphere as believed by the early astronomer in ancient Greece. It was also accepted that because all attempts to measure any stellar parallax down the centuries had failed, the nearest stars must actually be at an unbelievably far distance from the Earth.

Here we meet a relatively common phenomenon in the history of science, almost simultaneous, independent, multiple discoveries of the same fact. After literally two millennia of failures to detect any signs of stellar parallax, three astronomers each succeeded in measuring the parallax of three different stars in the 1830s. This finally was confirmation of the Earth’s annual orbit around, independent of stellar aberration and gave a yardstick for the distance of the stars from the Earth.

The first of our three astronomers was the Scotsman, Thomas Henderson (1798–1844).

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Thomas Henderson Source: Wikimedia Commons

Henderson was born in Dundee where he also went to school. He trained as a lawyer but was a keen amateur astronomer. He came to the attention of Thomas Young (1773-1829), the superintendent of the HM Nautical Almanac Office, after he devised a new method for determining longitude using lunar occultation, that is when a star disappears behind the Moon. Young brought him into the world of astronomy and upon his death recommended Henderson as his successor.

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Copy of a portrait of Thomas Young by Henry Briggs Source: Wikimedia Commons

Henderson didn’t receive to post but was appointed director of the Royal Observatory at the Cape of Good Hope. The observatory had only opened in 1828 after several years delay in its construction. The first director Fearon Fallows (1788–1831), who had overseen the construction of the observatory had died of scarlet fever in 1831 and Henderson was appointed as his successor, arriving in 1832.

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The Royal Observatory Cape of Good Hope in 1857 Illustrated London News, 21 March 1857/Ian Glass Source: Wikimedia Commons

The Cape played a major role in British observational astronomy. In the eighteenth century, it was here that Charles Mason (1728–1786) and Jeremiah Dixon (1733–1779), having been delayed in their journey to their designated observational post in Sumatra, observed the transit of Venus of 1761. John Herschel (1792–1871), the son and nephew of the astronomers William and Caroline Herschel, arrived at the Cape in 1834 and carried extensive astronomical observation there with his own 21-foot reflecting telescope. cooperating with Henderson successor Thomas Maclear. In 1847, Herschel published his Results of Astronomical Observations made at the Cape of Good Hope, which earned him the Copley Medal of the Royal Society.

Manuel John Johnson (1805–1859), director of the observatory on St Helena, drew Henderson’s attention to the fact that Alpha Centauri displayed a high proper motion.

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Ladder Hill Observatory St Helena Source

Proper motion is the perceived motion of a star relative to the other stars. Although the position of the stars relative to each other appears not to change over long periods of time they do. There had been speculation about the possibility of this since antiquity, but it was first Edmund Halley, who in 1718 proved its existence by comparing the measured positions of prominent stars from the historical record with their current positions. A high proper motion is an indication that a star is closer to the Earth.

Aimed with this information Henderson began to try to determine the stellar parallax of Alpha Centauri. However, Henderson hated South Africa and he resigned his position at the observatory in 1833 and returned to Britain. In his luggage he had nineteen very accurate determinations of the position of Alpha Centauri. Back in Britain Henderson was appointed the first Astronomer Royal for Scotland in 1834 and professor for astronomy at the University of Edinburgh, position he held until his death.

Initially Henderson did not try to determine the parallax of Alpha Centauri from his observational data. He thought that he had too few observations and was worried that he would join the ranks of many of his predecessors, who had made false claims to having discovered stellar parallax; Henderson preferred to wait until he had received more observational data from his assistant William Meadows (?–?). This decision meant that Henderson, whose data did in fact demonstrate stellar parallax for Alpha Centauri, who had actually won the race to be the first to determine stellar parallax, by not calculating and publishing, lost the race to the German astronomer Friedrich Wilhelm Bessel (1784–1846).

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Portrait of the German mathematician Friedrich Wilhelm Bessel by the Danish portrait painter Christian Albrecht Jensen Source: Wikimedia Commons

Like Henderson, Bessel was a self-taught mathematician and astronomer. Born in Minden as the son of a minor civil servant, at the age of fourteen he started a seven-year apprenticeship as a clerk to an import-export company in Bremen. Bessel became interested in the navigation on which the company’s ships were dependent and began to teach himself navigation, and the mathematics and astronomy on which it depended. As an exercise he recalculated the orbit of Halley’s Comet, which he showed to the astronomer Heinrich Wilhelm Olbers (1758–1840), who also lived in Bremen.

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Portrait of the german astronomer Heinrich Wilhelm Matthias Olbers (lithography by Rudolf Suhrlandt Source: Wikimedia Commons

Impressed by the young man’s obvious abilities, Olbers became his mentor helping him to get his work on Halley’s Comet published and guiding his astronomical education. In 1806, Olbers obtained a position for Bessel, as assistant to Johann Hieronymus Schröter (1745–1816) in Lilienthal.

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Johann Hieronymus Schröter Source: Wikimedia Commons

Here Bessel served his apprenticeship as an observational astronomer and established an excellent reputation.

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Schröter’s telescope in Lilienthal on which Bessel served his apprenticeship as an observational astronomer

Part of that reputation was built up through his extensive correspondence with other astronomers throughout Europe, including Johann Carl Fried Gauss (1777–1855). It was probably through Gauss’ influence that in 1809 Bessel, at the age of 25, was appointed director of the planned state observatory in Königsberg, by Friedrich Wilhelm III, King of Prussia.

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Königsberg Observatory in 1830. It was destroyed by bombing in the Second World War. Source: Wikimedia Commons

Bessel oversaw the planning, building and equipping of the new observatory, which would be his home and his workplace for the rest of his life. From the beginning he planned to greatly increase the accuracy of astronomical observations and calculation. He started by recalculated the positions of the stars in John Flamsteed’s stellar catalogue, greatly increasing the accuracy of the stellar positions. Bessel also decided to try and solve the problem of determining stellar parallax, although it would be some time before he could undertake that task.

One of the astronomers with whom Bessel took up contact was Friedrich Georg Wilhelm von Struve (1793–1864), who became a good friend and his rival in the search for stellar parallax, although the rivalry was always good natured. Struve was born the son of Jacob Struve (1755–1841), a schoolteacher and mathematician, in Altona then in the Duchy of Holstein, then part of the Denmark–Norway Kingdom and a Danish citizen.

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Friedrich Georg Wilhelm von Struve Source: Wikimedia Commons

Whilst he was still a youth, his father sent him to live in Dorpat (nowadays Tartu) in Estonia with his elder brother, to avoid being drafted into the Napoleonic army. In Dorpat he registered as a student at the university to study, at the wish of his father, philosophy and philology but also registered for a course in astronomy. He financed his studies by working as a private tutor to the children of a wealthy family. He graduated with a degree in philology in 1811 and instead of becoming a history teacher, as his father wished, he took up the formal study of astronomy. The university’s only astronomer, Johann Sigismund Gottfried Huth (1763–1818), was a competent scholar but was an invalid, so Struve basically taught himself and had free run of the university’s observatory whilst still a student, installing the Dolland transit telescope that was still packed in the crates it was delivered in. In 1813 he graduated PhD and was, at the age of just twenty, appointed to the faculty of the university. He immediately began his life’s work, the systematic study of double stars.

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The old observatory building in Dorpat (Tartu) Source: Wikimedia Commons

Like Bessel, Struve was determined to increase the accuracy of observational astronomy. In 1820 whilst in München, to pick up another piece of observational equipment, he visited Europe’s then greatest optical instrument maker, Joseph Fraunhofer (1787–1826), who was putting the finishing touches to his greatest telescopic creation, a refractor with a 9.5-inch lens.

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Joseph Fraunhofer Source: Wikimedia Commons

Struve had found his telescope. He succeeded in persuading the university to purchase the telescope, known as the ‘Great Refractor’ and began his search for observational perfection.

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Frauenhofer’s Great Refractor Source: Wikimedia Commons

Like Struve, Bessel turned to Fraunhofer for the telescope of his dreams. However, unlike Struve, whose telescope was a general-purpose instrument, Bessel desired a special purpose-built heliometer, a telescope with a split objective lens, especially conceived to accurately measure the distance between two observed objects. The first  really practical heliometer was created by John Dolland (1706–1761) to measure the variations in the diameter of the Sun, hence the name. Bessel needed this instrument to fulfil his dream of becoming the first astronomer to accurately measure stellar parallax. Bessel got his Fraunhofer in 1829.

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Königsberger Heliometer Source: Wikimedia Commons

One can get a very strong impression of Bessel’s obsession with accuracy in that he devoted five years to erecting, testing, correcting and controlling his new telescope. In 1834 he was finally ready to take up the task he had set himself. However, other matters that he had to attend to prevented him from starting on his quest.

The Italian astronomer Giuseppe Piazzi (1746–1826), famous for discovering the first asteroid, Ceres, had previously determined that the star 61 Cygni had a very high proper motion, meaning it was probably relatively close to the Earth and this was Bessel’s intended target for his attempt to measure stellar parallax.

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Giuseppe Piazzi pointing at the asteroid Ceres Painting by Giuseppe Velasco (1750–1826). Source: Wikimedia Commons

It was also Struve’s favoured object for his attempt but, unfortunately, he was unable in Dorpat with his telescope to view both 61 Cygni and a reference star against which to measure any observable parallax, so he turned his attention to Vega instead. In 1837, Bessel was more than somewhat surprised when he received a letter from Struve containing seventeen preliminary parallax observations of Vega. Struve admitted that they were not yet adequate to actually determine Vega’s parallax, but it was obvious that he was on his way. Whether Struve’s letter triggered Bessel’s ambition is not known but he relatively soon began a year of very intensive observations of 61 Cygni. In 1838 having checked and rechecked his calculations, and dismantled and thoroughly examined his telescope for any possible malfunctions, he went public with the news that he had finally observed a measurable parallax of 61 Cygni. He sent a copy of his report to John Herschel, President of the Royal Astronomical Society in London. After Herschel had carefully studied the report and after Bessel had answered all of his queries to his satisfaction. Herschel announced to the world that stellar parallax had finally been observed. For his work Bessel was awarded the Gold Medal of the Royal Astronomical Society. Just two months later, Henderson, who had in the meantime done the necessary calculations, published his measurement of the stellar parallax of Alpha Centauri. In 1839 Struve announced his for Vega. Bessel did not rest on his laurels but reassembling his helioscope he spent another year remeasuring 61 Cygni’s parallax correcting his original figures. 

All three measurements were accepted by the astronomical community and both Henderson and Struve were happy to acknowledge Bessel’s priority. There was no sense of rivalry between them and the three men remained good friends. Modern measurements have shown that Bessel’s figures were within 90% of the correct value, Henderson’s with in 75%, but Struve’s were only within 50%. The last is not surprising as Vega is much further from the Earth than either Alpha Centauri or Cygni 61 making it parallax angle much, much smaller and thus considerably more difficult to measure.

In the sixteenth century Tycho Brahe rejected heliocentricity because the failure to detect stellar parallax combined with his fallacious big star argument meant that in a heliocentric system the stars were for him inconceivably far away. I wonder what he would think about the fact that Earth’s nearest stellar neighbour Proxima Centauri is 4.224 lightyears away, that is 3. 995904 x 1013 kilometres!

 

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Filed under History of Astronomy, History of Optics, History of science, History of Technology

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).

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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.

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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.

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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.

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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.

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Jakob Dircksz de Graeff Source: Wikimedia Commons

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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.

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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.

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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).

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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.

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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.

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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.

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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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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

A scientific Dutchman

For many decades the popular narrative version of the scientific revolution started in Poland/Germany with Copernicus moving on through Tycho in Denmark, Kepler in Germany/Austria, Galileo et al in Northern Italy, Descartes, Pascal, Mersenne etc., in France and then Newton and his supporters and opponents in London. The Netherlands simply didn’t get a look in except for Christiaan Huygens, who was treated as a sort of honorary Frenchman. As I’ve tried to show over the years the Netherlands and its scholars–Gemma Frisius, Simon Stephen, Isaac Beeckman, the Snels, and the cartographers–actually played a central role in the evolution of the sciences during the Early Modern Period. In more recent years efforts have been made to increase the historical coverage of the contributions made in the Netherlands, a prominent example being Harold J Cook’s Matters of Exchange: Commerce, Medicine and Science in the Dutch Golden Age.[1]

A very strange anomaly in the #histSTM coverage concerns Christiaan Huygens, who without doubt belongs to the seventeenth century scientific elite. Whereas my bookcase has an entire row of Newton biographies, and another row of Galileo biographies and in both cases there are others that I’ve read but don’t own. The Kepler collection is somewhat smaller but it is still a collection. I have no idea how many Descartes biographies exist but it is quite a large number. But for Christiaan Huygens there is almost nothing available in English. The only biography I’m aware of is the English translation of Cornelis Dirk Andriesse’s scientific biography of Christiaan Huygens, The Man Behind the Principle.[2] I read this several years ago and must admit I found it somewhat lacking. This being the case, great expectation have been raised by the announcement of a new Huygens biography by Hugh Aldersey-Williams, Dutch Light: Christiaan Huygens and the Making of Science in Europe.[3]

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So does Aldersey-Williams fulfil those expectations? Does he deliver the goods? Yes and no, on the whole he has researched and written what is mostly an excellent biography of the Netherland’s greatest scientist[4] of the Early Modern Period but it is in my opinion marred by sloppy history of science fact checking that probably won’t be noticed by the average reader but being the notorious #histSTM pedant that I am I simply can’t and won’t ignore.[5]

My regular readers will known that I describe myself as a narrative contextual historian of science and I personally believe that if we are to understand how science has evolved historical then we have to tell that story with its complete context. This being the case I’m very happy to report that Aldersey-Williams is very much a narrative contextual historian, who tells the complete story of Christiaan Huygens life within its wider context and not just offering up a list of his scientific achievements. In fact what the reader gets for his money is not just a biography of Christiaan but also a biography of his entire family with some members being given more space than other. In particular it is a full biography of Christiaan and his father Constantijn, who played a significant and central role in shaping Christiaan’s life.

The book opens by setting the scientific scene in the early seventeenth-century Netherlands. We get introduced to those scientists, who laid the scientific foundations on which Christiaan would later build. In particular we get introduced to Simon Steven, who shaped the very practice orientated science and technology of the Early Modern Netherlands. We also meet other important and influential figures such as Hans Lipperhey, Isaac Beeckman, Willebrord Snel, Cornelius Drebbel and others.

There now follows what might be termed a book within a book as Aldersey-Williams delivers up a very comprehensive biography of Constantijn Huygens diplomat, poet, composer, art lover and patron and all round lover of knowledge. Constantijn was interested in and fascinated by almost everything both scientific and technological. His interest was never superficial but was both theoretical and practical. For example he was not only interested in the newly invented instruments, the telescope and the microscope, but he also took instruction in how to grind lenses and that from the best in the business. Likewise his love for art extended beyond buying paintings and patronising artists, such as Rembrandt, but to developing his own skills in drawing and painting. Here Aldersey-Williams introduces us to the Dutch term ‘kenner’ (which is the same in German), which refers to someone such Constantijn Huygens, whose knowledge of a subject is both theoretical and practical. Constantijn Huygens married Suzanna von Baerle for love and they had five children over ten years, four sons and a daughter, Christiaan was the second oldest, and Suzanna died giving birth to their daughter, also named Suzanna.

Constantijn Huygens brought up his children himself educating them in his own polymathic diversity with the help of tutors. When older the boys spent brief periods at various universities but were largely home educated. We now follow the young Christiaan and his older brother, also Constantijn, through their formative young years. The two oldest boys remained close and much of Christiaan’s astronomical work was carried out in tandem with his older brother. We follow Christiaan’s early mathematical work and his introduction into the intellectual circles of Europe, especially France and England, through his father’s widespread network of acquaintances. From the beginning Christiaan was set up to become either a diplomat, like his father, grandfather and brothers, or a scientist and it is the latter course that he followed.

Aldersey-Williams devotes an entire chapter to Christiaan’s telescopic observations of Saturn, with a telescope that he and Constantijn the younger constructed and his reputation making discovery of Titan the largest of Saturn’s moons, and the first discovered, and his determination that the strange shapes first observed by Galileo around Saturn were in fact rings. These astronomical discoveries established him as one of Europe’s leading astronomers. The following chapter deals with Huygens’ invention of the pendulum clock and his excursions into the then comparatively new probability theory.

Saturn and the pendulum clock established the still comparatively young Huygens as a leading light in European science in the second half of the seventeenth century and Aldersey-Williams now takes us through ups and downs of the rest of Christiaan’s life. His contact with and election to the Royal Society in London, as its first foreign member. His appointment by Jean-Baptist Colbert, the French First Minister of State, as a founding member of the Académie des sciences with a fairy generous royal pension from Louis XIV. His sixteen years in Paris, until the death of Colbert, during which he was generally acknowledged as Europe’s leading natural philosopher. His initial dispute over light with the young and comparatively unknown Newton and his tutorship of the equally young and unknown Leibniz. His fall from grace following Colbert’s death and his reluctant return to the Netherlands. The last lonely decade of his life in the Netherlands and his desire for a return to the scientific bustle of London or Paris. His partial rapprochement with Newton following the publication of the Principia. Closing with the posthumous publication of his works on gravity and optics. This narrative is interwoven with episodes from the lives of Constantijn the father and Constantijn his elder brother, in particular the convoluted politics of the Netherlands and England created by William of Orange, whose secretary was Constantijn, the younger, taking the English throne together with his wife Mary Stewart. Christiaan’s other siblings also make occasional appearances in letters and in person.

Aldersey-Williams has written a monumental biography of two generations of the Huygens family, who played major roles in the culture, politics and science of seventeenth century Europe. With a light, excellent narrative style the book is a pleasure to read. It is illustrated with 37 small grey in grey prints and 35 colour plates, which I can’t comment on, as my review proof copy doesn’t contain them. There are informative footnotes scattered through out the text and the, by me hated, hanging endnotes referring to the sources of direct quotes in the text. Here I had the experience more than once of looking up what I took to be a direct quote only to discover that it was not listed. There is an extensive bibliography of both primary and secondary sources and I assume an extensive index given the number of blank pages in my proof copy. There were several times when I was reading when I had wished that the index were actually there.

On the whole I would be tempted to give this book a glowing recommendation were it not for a series of specific history of science errors that simple shouldn’t be there and some general tendencies that I will now detail.

Near the beginning Aldersey-Williams tells us that ‘Stevin’s recommendation to use decimals in arithmetical calculations in place of vulgar fractions which could have any denominator [was] surely the sand-yacht of accountancy … Thirty years later, the Scottish mathematician John Napier streamlined Stevin’s notation by introducing the familiar comma or point to separate off the fractional part…” As is all too often the case no mention is made of the fact that Chinese and Arabic mathematicians had been using decimal fractions literally centuries before Stevin came up with the concept. In my opinion we must get away from this Eurocentric presentation of the history of science. Also the Jesuit mathematician Christoph Clavius introduced the decimal point less than ten years after Stevin’s introduction of decimal fractions, well ahead of Napier, as was its use by Pitiscus in 1608, the probable source of Napier’s use.

We also get told when discussing the Dutch vocabulary that Stevin created for science that, “Chemistry becomes scheikunde, the art of separation, an acknowledgement of the beginnings of a shift towards an analytical science, and a useful alternative to chemie that severs the etymological connections with disreputable alchemy.” This displays a complete lack of knowledge of alchemy in which virtually all the analytical methods used in chemistry were developed. The art of separation is a perfectly good term from the alchemy that existed when Stevin was creating his Dutch scientific vocabulary. Throughout his book Aldersey-Williams makes disparaging remarks about both alchemy and astrology, neither of which was practiced by any of the Huygens family, which make very clear that he doesn’t actually know very much about either discipline or the role that they played in the evolution of western science, astrology right down to the time of Huygens and Newton and alchemy well into the eighteenth century. For example, the phlogiston theory one of the most productive chemical theories in the eighteenth century had deep roots in alchemy.

Aldersey-Williams account of the origins of the telescope is a bit mangled but acceptable except for the following: “By the following spring, spyglasses were on sale in Paris, from where one was taken to Galileo in Padua. He tweaked the design, claimed the invention as his own, and made dozens of prototypes, passing on his rejects so that very soon even more people were made aware of this instrument capable of bringing the distant close.”

Firstly Galileo claimed that he devised the principle of the telescope and constructed his own purely on verbal descriptions without having actually seen one but purely on his knowledge of optics. He never claimed the invention as his own and the following sentence is pure rubbish. Galileo and his instrument maker produced rather limited numbers of comparatively high quality telescopes that he then presented as gifts to prominent political and Church figures.

Next up we have Willebrord Snel’s use of triangulation. Aldersey-Williams tells us, “ This was the first practical survey of a significant area of land, and it soon inspired similar exercises in England, Italy and France.” It wasn’t. Mercator had previously surveyed the Duchy of Lorraine and Tycho Brahe his island of Hven before Snel began his surveying in the Netherlands. This is however not the worst, Aldersey-Williams tells us correctly that Snel’s survey stretched from Alkmaar to Bergen-op-Zoom “nearly 150 kilometres to the south along approximately the same meridian.” Then comes some incredible rubbish, “By comparing the apparent height of his survey poles observed at distance with their known height, he was able to estimate the size of the Earth!”

What Snel actually did, was having first accurately determined the length of a stretch of his meridian using triangulation, the purpose of his survey and not cartography, he determined astronomically the latitude of the end points. Having calculated the difference in latitudes it is then a fairly simple exercise to determine the length of one degree of latitude, although for a truly accurate determination one has to adjust for the curvature of the Earth.

Next up with have the obligatory Leonard reference. Why do pop history of science books always have a, usually erroneous, Leonardo reference? Here we are concerned with the camera obscura, Aldersey-Williams writes: “…Leonardo da Vinci gave one of the first accurate descriptions of such a design.” Ibn al-Haytham gave accurate descriptions of the camera obscura and its use as a scientific instrument about four hundred and fifty years before Leonardo was born in a book that was translated into Latin two hundred and fifty years before Leonardo’s birth. Add to this the fact that Leonardo’s description of the camera obscura was first published late in the eighteenth century and mentioning Leonardo in this context becomes a historical irrelevance. The first published European illustration of a camera obscura was Gemma Frisius in 1545.

When discussing Descartes, a friend of Constantijn senior and that principle natural philosophical influence on Christiaan we get a classic history of mathematics failure. Aldersey-Williams tells us, “His best known innovation, of what are now called Cartesian coordinates…” Whilst Descartes did indeed cofound, with Pierre Fermat, modern algebraic analytical geometry, Cartesian coordinates were first introduced by Frans van Schooten junior, who of course features strongly in the book as Christiaan’s mathematics teacher.

Along the same lines as the inaccurate camera obscura information we have the following gem, “When applied to a bisected circle (a special case of the ellipse), this yielded a new value, accurate to nine decimal places, of the mathematical constant π, which had not been improved since Archimedes” [my emphasis] There is a whole history of the improvements in the calculation of π between Archimedes and Huygens but there is one specific example that is, within the context of this book, extremely embarrassing.

Early on when dealing with Simon Stevin, Aldersey-Williams mentions that Stevin set up a school for engineering, at the request of Maurits of Nassau, at the University of Leiden in 1600. The first professor of mathematics at this institution was Ludolph van Ceulen (1540–1610), who also taught fencing, a fact that I find fascinating. Ludolph van Ceulen is famous in the history of mathematics for the fact that his greatest mathematical achievement, the Ludophine number, is inscribed on his tombstone, the accurate calculation of π to thirty-five decimal places, 3.14159265358979323846264338327950288…

Next up we have Christiaan’s correction of Descartes laws of collision. Here Aldersey-Williams writes something that is totally baffling, “The work [his new theory of collision] only appeared in a paper in the French Journal des Sçavans in 1669, a few years after Newton’s laws of motion [my emphasis]…” Newton’s laws of motion were first published in his Principia in 1687!

Having had the obligatory Leonardo reference we now have the obligatory erroneous Galileo mathematics and the laws of nature reference, “Galileo was the first to fully understand that mathematics could be used to describe certain laws of nature…” I’ve written so much on this that I’ll just say here, no he wasn’t! You can read about Robert Grosseteste’s statement of the role of mathematics in laws of nature already in the thirteenth century, here.

Writing about Christiaan’s solution of the puzzle of Saturn’s rings, Aldersey-Williams say, “Many theories had been advanced in the few years since telescopes had revealed the planet’s strange truth.” The almost five decades between Galileo’s first observation of the rings and Christiaan’s solution of the riddle is I think more than a few years.

Moving on Aldersey-Williams tells us that, “For many however, there remained powerful reasons to reject Huygens’ discovery. First of all, it challenged the accepted idea inherited from Greek philosophers that the solar system consisted exclusively of perfect spherical bodies occupying ideal circular orbits to one another.” You would have been hard put to it to find a serious astronomer ín 1660, who still ascribed to this Aristotelian cosmology.

The next historical glitch concerns, once again, Galileo. We read, “He dedicated the work [Systema Saturnium] to Prince Leopoldo de’ Medici, who was patron of the Accademia del Cimento in Florence, who had supported the work of Huygens’ most illustrious forebear, Galileo.” Ignoring the sycophantic description of Galileo, one should perhaps point out that the Accademia del Cimento was founded in 1657 that is fifteen years after Galileo’s death and so did not support his work. It was in fact founded by a group of Galileo’s disciples and was dedicated to continuing to work in his style, not quite the same thing.

Galileo crops up again, “the real power of Huygens’ interpretation was its ability to explain those times when Saturn’s ‘handles’ simply disappeared from view, as they had done in 1642, finally defeating the aged Galileo’s attempts to understand the planet…” In 1642, the year of his death, Galileo had been completely blind for four years and had actually given up his interest in astronomy several years earlier.

Moving on to Christiaan’s invention of the pendulum clock and the problem of determining longitude Aldersey-Williams tells us, “The Alkmaar surveyor Adriaan Metius, brother of the telescope pioneer Jacob, had proposed as long ago as 1614 that some sort of seagoing clock might provide the solution to this perennial problem of navigators…” I feel honour bound to point out that Adriaan Metius was slightly more than simply a surveyor, he was professor for mathematics at the University of Franeker. However the real problem here is that the clock solution to the problem of longitude was first proposed by Gemma Frisius in an appendix added in 1530, to his highly popular and widely read editions of Peter Apian’s Cosmographia. The book was the biggest selling and most widely read textbook on practical mathematics throughout the sixteenth and well into the seventeenth century so Huygens would probably have known of Frisius’ priority.

Having dealt with the factual #histSTM errors I will now turn to more general criticisms. On several occasions Aldersey-Williams, whilst acknowledging problems with using the concept in the seventeenth century, tries to present Huygens as the first ‘professional scientist’. Unfortunately, I personally can’t see that Huygens was in anyway more or less of a professional scientist than Tycho, Kepler or Galileo, for example, or quite a long list of others I could name. He also wants to sell him as the ‘first ever’ state’s scientist following his appointment to the Académie des sciences and the accompanying state pension from the king. Once again the term is equally applicable to Tycho first in Denmark and then, if you consider the Holy Roman Empire a state, again in Prague as Imperial Mathematicus, a post that Kepler inherited. Galileo was state ‘scientist’ under the de’ Medici in the Republic of Florence. One could even argue that Nicolas Kratzer was a state scientist when he was appointed to the English court under Henry VIII. There are other examples.

Aldersey-Williams’ next attempt to define Huygens’ status as a scientist left me somewhat speechless, “Yet it is surely enough that Huygens be remembered for what he was, a mere problem solver indeed: pragmatic, eclectic and synthetic and ready to settle for the most probable rather than hold out for the absolutely certain – in other words. What we expect a scientist to be today.” My ten years as a history and philosophy of science student want to scream, “Is that what we really expect?” I’m not even going to go there, as I would need a new blog post even longer than this one.

Aldersey-Williams also tries to present Huygens as some sort of new trans European savant of a type that had not previously existed. Signifying cooperation across borders, beliefs and politics. This is of course rubbish. The sort of trans European cooperation that Huygens was involved in was just as prevalent at the beginning of the seventeenth century in the era of Tycho, Kepler, Galileo, et al. Even then it was not new it was also very strong during the Renaissance with natural philosophers and mathematici corresponding, cooperating, visiting each other, and teaching at universities through out the whole of Europe. Even in the Renaissance, science in Europe knew no borders. It’s the origin of the concept, The Republic of Letters. I suspect my history of medieval science friend would say the same about their period.

In the partial rapprochement between Huygens and Newton following the Publication of the latter’s Principia leads Aldersey-Williams to claim that a new general level of reasonable discussion had entered scientific debate towards the end of the seventeenth century. Scientists, above all Newton, were still going at each other hammer and tongs in the eighteenth century, so it was all just a pipe dream.

Aldersey-Williams sees Huygens lack of public profile, as a result of being in Newton’s shadow like Hooke and others. He suggests that popular perception only allows for one scientific genius in a generation citing Galileo’s ascendance over Kepler, who he correctly sees as the more important, as another example. In this, I agree with him, however he tries too hard to put Huygens on the same level as Newton as a scientist, as if scientific achievement were a pissing contest. I think we should consider a much wider range of scientists when viewing the history of science but I also seriously think that no matter how great his contributions Huygens can’t really match up with Newton. Although his Horologium oscillatorium sive de motu pendularium was a very important contribution to the debate on force and motion, it can’t be compared to Newton’s Principia. Even if Huygens did propagate a wave theory of light his Traité de la lumière is not on a level with Newton’s Opticks. He does have his Systema saturniumbut as far as telescopes are concerned Newton’s reflector was a more important contribution than any of Huygens refractor telescopes. Most significant, Newton made massive contributions to the development of mathematics, Huygens almost nothing.

Talking of Newton, in his discussion of Huygens rather heterodox religious views Aldersey-Williams discussing unorthodox religious views of other leading scientists makes the following comment, “Newton was an antitrinitarian, for which he was considered a heretic in his lifetime, as well as being interested in occultism and alchemy.” Newton was not considered a heretic in his lifetime because he kept his antitrinitarian views to himself. Alchemy yes, but occultism, Newton?

I do have one final general criticism of Aldersey-Williams’ book. My impression was that the passages on fine art, poetry and music, all very important aspects of the life of the Huygens family, are dealt with in much greater depth and detail than the science, which I found more than somewhat peculiar in a book with the subtitle, The Making of Science in Europe. I’m not suggesting that the fine art, poetry and music coverage should be less but that the science content should have been brought up to the same level.

Despite the long list of negative comments in my review I think this is basically a very good book that could in fact have been an excellent book with some changes. Summa summarum it is a flawed masterpiece. It is an absolute must read for anybody interested in the life of Christiaan Huygens or his father Constantijn or the whole Huygens clan. It is also an important read for those interested in Dutch culture and politics in the seventeenth century and for all those interested in the history of European science in the same period. It would be desirable if more works with the wide-ranging scope and vision of Aldersey-Williams volume were written but please without the #histSTM errors.

[1] Harold J Cook, Matters of Exchange: Commerce, Medicine and Science in the Dutch Golden Age, Yale University Press, New Haven & London, 2007

[2] Cornelis Dirk Andriesse, The Man Behind the Principle, scientific biography of Christiaan Huygens, translated from Dutch by Sally Miedem, CUP, Cambridge, 2005

[3] Hugh Aldersey-Williams, Dutch Light: Christiaan Huygens and the Making of Science in Europe, Picador, London, 2020.

[4] Aldersey-Williams admits that the use of the term scientist is anachronistic but uses it for simplicity’s sake and I shall do likewise here.

[5] I have after all a reputation to uphold

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Filed under Book Reviews, History of Astronomy, History of Mathematics, History of Navigation, History of Optics, History of Physics, History of science, Newton

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.

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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:

Magiae_naturalis_sive_de_miraculis_rerum_naturalium_(Giovanni_Battista_Della_Porta,_1584)

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.

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

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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.

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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.

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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.

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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.

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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.

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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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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.

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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),

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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.

 

 

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