Category Archives: Mediaeval Science

The Astrolabe – an object of desire

Without doubt the astrolabes is one of the most fascinating of all historical astronomical instruments.

Astrolabe Renners Arsenius 1569 Source: Wikimedia Commons

Astrolabe Renners Arsenius 1569
Source: Wikimedia Commons

To begin with it is not simply one object, it is many objects in one:

 

  • An astronomical measuring device
  • A timepiece
  • An analogue computer
  • A two dimensional representation of the three dimensional celestial sphere
  • A work of art and a status symbol

 

This Medieval-Renaissance Swiss Army penknife of an astronomical instrument had according to one medieval Islamic commentator, al-Sufi writing in the tenth century, more than one thousand different functions. Even Chaucer in what is considered to be the first English language description of the astrolabe and its function, a pamphlet written for a child, describes at least forty different functions.

The astrolabe was according to legend invented by Hipparchus of Nicaea, the second century BCE Greek astronomer but there is no direct evidence that he did so. The oldest surviving description of the planisphere, that two-dimensional representation of the three-dimensional celestial sphere, comes from Ptolemaeus in the second century CE.

Modern Planisphere Star Chart c. 1900 Source: Wikimedia Commons

Modern Planisphere Star Chart c. 1900
Source: Wikimedia Commons

Theon of Alexandria wrote a thesis on the astrolabe, in the fourth century CE, which did not survive and there are dubious second-hand reports that Hypatia, his daughter invented the instrument. The oldest surviving account of the astrolabe was written in the sixth century CE by John Philoponus. However it was first the Islamic astronomers who created the instrument, as it is known today, it is said for religious purposes, to determine the direction of Mecca and the time of prayer. The earliest surviving dated instrument is dated 315 AH, which is 927/28 CE.

The Earliest  Dated Astrolabe Source: See Link

The Earliest Dated Astrolabe
Source: See Link

It is from the Islamic Empire that knowledge of the instrument found its way into medieval Europe. Chaucer’s account of it is based on that of the eight-century CE Persian Jewish astrologer, Masha’allah ibn Atharī, one of whom claim to fame is writing the horoscope to determine the most auspicious date to found the city of Baghdad.

So-called Chaucer Astrolabe dated 1326, similar to the one Chaucer describes, British Museum Source: Wikimedia Commons

So-called Chaucer Astrolabe dated 1326, similar to the one Chaucer describes, British Museum
Source: Wikimedia Commons

However this brief post is not about the astrolabe as a scientific instrument in itself but rather the last point in my brief list above the astrolabe as a work of art and a status symbol. One of the reasons for people’s interest in astrolabes is the fact that they are simply beautiful to look at. This is not a cold, functional scientific instrument but an object to admire, to cherish and desire. A not uncommon reaction of people being introduced to astrolabes for the first time is, oh that is beautiful; I would love to own one of those. And so you can there are people who make replica astrolabes but buying one will set you back a very pretty penny.

That astrolabes are expensive is not, however, a modern phenomenon. Hand crafted brass, aesthetically beautiful, precision instruments, they were always very expensive and the principal market would always have been the rich, often the patrons of the instrument makers. The costs of astrolabes were probably even beyond the means of most of the astronomers who would have used them professionally and it is significant that most of the well know astrolabe makers were themselves significant practicing astronomers; according to the principle, if you need it and can’t afford it then make it yourself. Other astronomers would probably have relied on their employers/patrons to supply the readies. With these thoughts in mind it is worth considering the claim made by David King, one of the world’s greatest experts on the astrolabe, that the vast majority of the surviving astrolabes, made between the tenth nineteenth centuries – about nine hundred – were almost certainly never actually used as scientific instruments but were merely owned as status symbols. This claim is based on, amongst other things, the fact that they display none of the signs of the wear and tear, which one would expect from regular usage.

Does this mean that the procession of astrolabes was restricted to a rich elite and their employees? Yes and no. When European sailors began to slowly extend their journeys away from coastal waters into the deep sea, in the High Middle Ages they also began to determine latitude as an element of their navigation. For this purpose they needed an instrument like the astrolabe to measure the elevation of the sun or of chosen stars. The astrolabe was too complex and too expensive for this task and so the so-called mariners astrolabe was developed, a stripped down, simplified, cheaper and more robust version of the astrolabe. When and where the first mariner’s astrolabe was used in not known but probably not earlier than the thirteenth century CE. Although certainly not cheap, the mariner’s astrolabe was without doubt to be had for considerably less money than its nobler cousin.

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Mariner’s Astrolabe Francisco de Goes 1608 Source: Istituto e Museo di Storia della Scienza, Firenze

Another development came with the advent of printing in the fifteenth century, the paper astrolabe. At first glance this statement might seem absurd, how could one possibly make a high precision scientific measuring instrument out of something, as flexible, unstable and weak as paper? The various parts of the astrolabe, the planisphere, the scales, the rete star-map, etc. are printed onto sheets of paper. These are then sold to the customer who cuts them out and pastes them onto wooden forms out of which he then constructs his astrolabe, a cheap but serviceable instrument. One well-known instrument maker who made and sold printed-paper astrolabes and other paper instruments was the Nürnberger mathematician and astronomer Georg Hartmann. The survival rate of such cheap instruments is naturally very low but we do actually have one of Hartmann’s wood and paper astrolabes.

Hartmann Paper Astrolabe Source: Oxford Museum of History of Science

Hartmann Paper Astrolabe
Source: Oxford Museum of History of Science

In this context it is interesting to note that, as far as can be determined, Hartmann was the first instrument maker to develop the serial production of astrolabes. Before Hartmann each astrolabe was an unicum, i.e. a one off instrument. Hartmann standardised the parts of his brass astrolabes and produced them, or had them produced, in batches, assembling the finished product out of these standardised parts. To what extent this might have reduced the cost of the finished article is not known but Hartmann was obviously a very successful astrolabe maker as nine of those nine hundred surviving astrolabes are from his workshop, probably more than from any other single manufacturer.

Hartmann Serial Production Astrolabe Source: Museum Boerhaave

Hartmann Serial Production Astrolabe
Source: Museum Boerhaave

 

If this post has awoken your own desire to admire the beauty of the astrolabe then the biggest online collection of Medieval and Renaissance scientific instruments in general and astrolabes in particular is the Epact website, a collaboration between the Museum of the History of Science in Oxford, the British Museum, the Museum of the History of Science in Florence and the Museum Boerhaave in Leiden.

This blog post was partially inspired by science writer Philip Ball with whom I had a brief exchange on Twitter a few days ago, which he initiated, on our mutual desire to possess a brass astrolabe.

 

 

 

 

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

The unfortunate backlash in the historiography of Islamic science

Anybody with a basic knowledge of the history of Western science will know that there is a standard narrative of its development that goes something like this. Its roots are firmly planted in the cultures of ancient Egypt and Babylon and it bloomed for the first time in ancient Greece, reaching a peak in the work of Ptolemaeus in astronomy and Galen in medicine in the second-century CE. It then goes into decline along with the Roman Empire effectively disappearing from Europe by the fifth-century CE. It began to re-emerge in the Islamic Empire[1] in the eight-century CE from whence it was brought back into Europe beginning in the twelfth-century CE. In Europe it began to bloom again in the Renaissance transforming into modern science in the so-called Scientific Revolution in the seventeenth-century. There is much that is questionable in this broad narrative but that is not the subject of this post.

In earlier versions of this narrative, its European propagators claimed that the Islamic scholars who appropriated Greek knowledge in the eighth-century and then passed it back to their European successors, beginning in the twelfth-century, only conserved that knowledge, effectively doing nothing with it and not increasing it. For these narrators their heroes of science were either ancient Greeks or Early Modern Europeans; Islamic scholars definitely did not belong to the pantheon. However, a later generation of historians of science began to research the work of those Islamic scholars, reading, transcribing, translating and analysing their work and showing that they had in fact made substantial contributions to many areas of science and mathematics, contributions that had flowed into modern European science along with the earlier Greek, Babylonian and Egyptian contributions. Also Islamic scholars such as al-Biruni, al-Kindi, al-Haytham, Ibn Sina, al-Khwarizmi and many others were on a level with such heroes of science as Archimedes, Ptolemaeus, Galen or Kepler, Galileo and Newton. Although this work redressed the balance there is still much work to be done on the breadth and deep of Islamic science.

Unfortunately the hagiographic, amateur, wannabe pop historians of science now entered the field keen to atone for the sins of the earlier Eurocentric historical narrative and began to exaggerate the achievements of the Islamic scholars to show how superior they were to the puny Europeans who stole their ideas, like the colonial bullies who stole their lands. There came into being a type of hagiographical popular history of Islamic science that owes more to the Thousand and One Nights than it does to any form of serious historical scholarship. I came across an example of this last week during the Gravity Fields Festival, an annual shindig put on in Grantham to celebrate the life and work of one Isaac Newton, late of that parish.

On Twitter Ammār ibn Aziz Ahmed (@Ammar_Ibn_AA) tweeted the following:

I’m sorry to let you know that Isaac Newton learned about gravity from the books of Ibn al-Haytham

I naturally responded in my usual graceless style that this statement was total rubbish to which Ammār ibn Aziz Ahmed responded with a link to his ‘source

I answered this time somewhat more moderately that a very large part of that article is quite simply wrong. One of my Internet friends, a maths librarian (@MathsBooks) told me I was being unfair and that I should explain what was wrong with his source, so here I am.

The article in question is one of many potted biographies of al-Haytham that you can find dotted all other the Internet and which are mostly virtual clones of each other. They all contain the same collection of legends, half-truths, myths and straightforward lies usually without sources, or, as in this case, quoting bad popular books written by a non-historian as their source. It is fairly obvious that they all plagiarise each other without bothering to consult original sources or the work done by real historian of science on the life and work of al-Haytham.

The biography of al-Haytham is, like that of most medieval Islamic scholars, badly documented and very patchy at best. Like most popular accounts this article starts with the legend of al-Haytham’s feigned madness and ten-year incarceration. This legend is not mentioned in all the biographical sources and should be viewed with extreme scepticism by anybody seriously interested in the man and his work. The article then moves on to the most pernicious modern myth concerning al-Haytham that he was the ‘first real scientist’.

This claim is based on a misrepresentation of what al-Haytham did. He did not as the article claims introduce the scientific method, whatever that might be. For a limited part of his work al-Haytham used experiments to prove points, for the majority of it he reasoned in exactly the same way as the Greek philosophers whose heir he was. Even where he used the experimental method he was doing nothing that could not be found in the work of Archimedes or Ptolemaeus. There is also an interesting discussion outlined in Peter Dear’s Discipline and Experience (1995) as to whether al-Haytham used or understood experiments in the same ways as researchers in the seventeenth-century; Dear concludes that he doesn’t. (pp. 51-53) It is, however, interesting to sketch how this ‘misunderstanding’ came about.

The original narrative of the development of Western science not only denied the contribution of the Islamic Empire but also claimed that the Middle Ages totally rejected science, modern science only emerging after the Renaissance had reclaimed the Greek scientific inheritance. The nineteenth-century French physicist and historian of science, Pierre Duhem, was the first to challenge this fairy tale claiming instead, based on his own researches, that the Scientific Revolution didn’t take place in the seventeenth–century but in the High Middle Ages, “the mechanics and physics of which modern times are justifiably proud to proceed, by an uninterrupted series of scarcely perceptible improvements, from doctrines professed in the heart of the medieval schools.” After the Second World War Duhem’s thesis was modernised by the Australian historian of science, Alistair C. Crombie, whose studies on medieval science in general and Robert Grosseteste in particular set a new high water mark in the history of science. Crombie attributed the origins of modern science and the scientific method to Grosseteste and Roger Bacon in the twelfth and thirteenth-centuries. A view that has been somewhat modified and watered down by more recent historians, such as David Lindberg. Enter Matthias Schramm.

Matthias Schramm was a German historian of science who wrote his doctoral thesis on al-Haytham. A fan of Crombie’s work Schramm argued that the principle scientific work of Grosseteste and Bacon in physical optics was based on the work of al-Haytham, correct for Bacon not so for Grosseteste, and so he should be viewed as the originator of the scientific method and not they. He makes this claim in the introduction to his Ibn al-Haythams Weg zur Physik (1964), but doesn’t really substantiate it in the book itself. (And yes, I have read it!) Al-Haytham’s use of experiment is very limited and to credit him with being the inventor of the scientific method is a step too far. However since Schramm made his claims they have been expanded, exaggerated and repeated ad nauseam by the al-Haytham hagiographers.

We now move on to what is without doubt al-Haytham’s greatest achievement his Book of Optics, the most important work on physical optics written between Ptolemaeus in the second-century CE and Kepler in the seventeenth-century. Our author writes:

In his book, The Book of Optics, he was the first to disprove the ancient Greek idea that light comes out of the eye, bounces off objects, and comes back to the eye. He delved further into the way the eye itself works. Using dissections and the knowledge of previous scholars, he was able to begin to explain how light enters the eye, is focused, and is projected to the back of the eye.

Here our author demonstrates very clearly that he really has no idea what he is talking about. It should be very easy to write a clear and correct synopsis of al-Haytham’s achievements, as there is a considerable amount of very good literature on his Book of Optics, but our author gets it wrong[2].

Al-Haytham didn’t prove or disprove anything he rationally argued for a plausible hypothesis concerning light and vision, which was later proved to be, to a large extent, correct by others. The idea that vision consists of rays (not light) coming out of the eyes (extramission) is only one of several ideas used to explain vision by Greek thinkers. That vision is the product of light entering the eyes (intromission) also originates with the Greeks. The idea that light bounces off every point of an object in every direction comes from al-Haytham’s Islamic predecessor al-Kindi. Al-Haytham’s great achievement was to combine an intromission theory of vision with the geometrical optics of Euclid, Heron and Ptolemaeus (who had supported an extramission theory) integrating al-Kindi’s punctiform theory of light reflection. In its essence, this theory is fundamentally correct. The second part of the paragraph quoted above, on the structure and function of the eye, is pure fantasy and bears no relation to al-Haytham’s work. His views on the subject were largely borrowed from Galen and were substantially wrong.

Next up we have the pinhole camera or better camera obscura, although al-Haytham was probably the first to systematically investigate the camera obscura its basic principle was already known to the Chinese philosopher Mo-Ti in the fifth-century BCE and Aristotle in the fourth-century BCE. The claims for al-Haytham’s studies of atmospheric refraction are also hopelessly exaggerated.

We the have an interesting statement on the impact of al-Haytham’s optics, the author writes:

The translation of The Book of Optics had a huge impact on Europe. From it, later European scholars were able to build the same devices as he did, and understand the way light works. From this, such important things as eyeglasses, magnifying glasses, telescopes, and cameras were developed.

The Book of Optics did indeed have a massive impact on European optics in Latin translation from the work of Bacon in the thirteenth-century up to Kepler in the seventeenth-century and this is the principle reason why he counts as one of the very important figures in the history of science, however I wonder what devices the author is referring to here, I know of none. Interesting in this context is that The Book of Optics appears to have had very little impact on the development of physical optics in the Islamic Empire. One of the anomalies in the history of science and technology is the fact that as far was we know the developments in optical physics made by al-Haytham, Bacon, Witelo, Kepler et al had no influence on the invention of optical instruments, glasses, magnifying glasses, the telescope, which were developed along a parallel but totally separate path.

Moving out of optics we get told about al-Haytham’s work in astronomy. It is true that he like many other Islamic astronomers criticised Ptolemaeus and suggested changes in his system but his influence was small in comparison to other Islamic astronomers. What follows is a collection of total rubbish.

He had a great influence on Isaac Newton, who was aware of Ibn al-Haytham’s works.

He was not an influence on Newton. Newton would have been aware of al-Haytham’s work in optics but by the time Newton did his own work in this field al-Haytham’s work had been superseded by that of Kepler, Scheiner, Descartes and Gregory amongst others.

He studied the basis of calculus, which would later lead to the engineering formulas and methods used today.

Al-Haytham did not study the basis of calculus!

He also wrote about the laws governing the movement of bodies (later known as Newton’s 3 laws of motion)

Like many others before and after him al-Haytham did discuss motion but he did not come anywhere near formulating Newton’s laws of motion, this claim is just pure bullshit.

and the attraction between two bodies – gravity. It was not, in fact, the apple that fell from the tree that told Newton about gravity, but the books of Ibn al-Haytham.

We’re back in bullshit territory again!

If anybody thinks I should give a more detailed refutation of these claims and not just dismiss them as bullshit, I can’t because al-Haytham never ever did the things being claimed. If you think he did then please show me where he did so then I will be prepared to discuss the matter, till then I’ll stick to my bullshit!

I shall examine one more claim from this ghastly piece of hagiography. Our author writes the following:

When his books were translated into Latin as the Spanish conquered Muslim lands in the Iberian Peninsula, he was not referred to by his name, but rather as “Alhazen”. The practice of changing the names of great Muslim scholars to more European sounding names was common in the European Renaissance, as a means to discredit Muslims and erase their contributions to Christian Europe.

Alhazen is merely the attempt by the unknown Latin translator of The Book of Optics to transliterate the Arabic name al-Haytham there was no discrimination intended or attempted.

Abū ʿAlī al-Ḥasan ibn al-Ḥasan ibn al-Haytham is without any doubt an important figure in the history of science whose contribution, particularly those in physical optics, should be known to anybody taking a serious interest in the subject, but he is not well served by inaccurate, factually false, hagiographic crap like that presented in the article I have briefly discussed here.

 

 

 

 

 

[1] Throughout this post I will refer to Islamic science an inadequate but conventional term. An alternative would be Arabic science, which is equally problematic. Both terms refer to the science produced within the Islamic Empire, which was mostly written in Arabic, as European science in the Middle Ages was mostly written in Latin. The terms do not intend to imply that all of the authors were Muslims, many of them were not, or Arabs, again many of them were not.

[2] For a good account of the history of optics including a detailed analysis of al-Haytham’s contributions read David C. Lindberg’s Theories of Vision: From al-Kindi to Kepler, University of Chicago Press, 1976.

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Filed under History of Optics, History of Physics, Mediaeval Science, Myths of Science, Renaissance Science

Counting the hours

My #histsci-soul-sisterTM, Rebekah “Becky” Higgitt, wrote a charming post on her H-Word Blog to mark the end of European summer time describing the mad scheme of a certain William Willett to introduce the time change in twenty minute increments over several weeks. This reminded me of a local time phenomenon that I’ve not yet blogged about, Der Große Nürnberger Uhr

The time taken for the earth to rotate once upon its axis or for the sun to appear to circle the earth (its irrelevant how you view it) is a given but how one then chooses to divide up this period into smaller, easier to handle units is purely arbitrary. We owe our twenty-four hour day to the ancient Egyptians. They marked the passing of time in the night by the raising of stars; twelve stars being allotted for any given night, thus dividing the night into twelve units. They being normally decimal in their thinking divided the day into ten units. Allotting one unit for twilight at each junction between day and night brought the total to twenty-four.

The ancient Greek astronomers took over the Egyptian solar calendar and their twenty-four hour day dividing the diurnal revolution into twenty-four equally long, or equinoctial, hours as we do now. However most cultures who adopted the twenty-four system before the early modern period divided the night and day each into twelve units producing hours that varied in length depending on the time of year. This variation got larger the further away from the equator the culture was. In the middle of summer daytime hours were very long and night-time ones very short and vice versa in the middle of winter.

Beginning in the fourteenth century the city state of Nürnberg introduced a system of dividing up the day that is a sort of halfway station between the unequal hours of the middle ages and equinoctial hours, the so called ‘Große Uhr’, in English ‘Large Clock’. In this system the number of hours allotted to the day and night changed approximately every three weeks, the number of daytime hours increasing from midwinter (8) to midsummer (16) and then decreasing from midsummer to midwinter. The number of night-time hours doing the opposite.

Date of change 1st half of year Daylight hours Night-time hours Date of change 2nd half of year

8

16

7 January

9

15

16 November

28 January

10

14

26 October

14 February

11

13

8 October

3 March

12

12

22 September

19 March

13

11

5 September

5 April

14

10

20 August

23 April

15

9

2 August

15 May

16

8

11 June

In 1506 the Nürnberger humanists created one of the most complicated sundials in the whole of Europe on the wall of the St Lorenz church in the city.

Sundial on the St Lorenz Church Nürnberg

Sundial on the St Lorenz Church Nürnberg

This sundial shows the time of day in various different variations of hours including of course the Large Nürnberg Clock

The definition on this picture is not good enough to say which lines are which.

The good citizens of Nürnberg continued to use their own unique way of counting the hours right down to the year 1811.

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

Nicolaus was not a priest.

Erik Kwakkei (@erik_kwakkei) drew my attention to a rather nice short video from Prager University by Anthony Esolen of Providence College explaining that the Middle Ages were anything but Dark and should actually be called the bright ages. This is a very well done little piece managing to correct a whole series of myths in a very short time span. However I can’t resist taking a pot shot at his completely inaccurate description of Nicolaus Copernicus.

Esolen says:

Nicolaus Copernicus was, “a priest astronomer at a Polish university”.

The only part of this brief statement that is correct is that Copernicus was an astronomer.  However, it is important to point out that he was only ever an amateur astronomer; astronomy was his hobby so to speak. He never taught it at a university.

Copernicus started his undergraduate studies at the University of Kraków in Poland but left without taking a degree. He continued his studies a various universities in Northern Italy, where he studied law and medicine, not astronomy, completing his studies in 1503 with a doctorate in canon law from the University of Ferrara.

Already as a teenager Copernicus had been appointed a cannon canon of the Chapter of Frauenburg Cathedral in Warmia, where his Uncle Lucas Watzenrode was Prince Bishop. The cannons canons of the cathedral were the administration or government of Warmia.

After graduation Copernicus became private physician and secretary to his Uncle. Later he served the chapter in numerous administrative positions until his death in 1543, this being his profession and not astronomy.

Although attached to the cathedral all of his life Copernicus never took holy orders and was thus never a priest. The false claim that he was appears to have been put into the world by Galileo.

As always I find it disappointing that in an otherwise good video disposing of myths about the Middle Ages the one sentence about Copernicus should consist of false facts. A little bit of research, about five minute, could have avoided this piece of stupidity.

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

Oh dear! More crap than you can shake a stick at.

One of the websites that I usually enjoy reading is Wonders & Marvels a collective of historians[1] who post mostly short reports on historical things, oft medical, that they have found fascinating. However, as I recently visited this delightful oasis of historical frivolity I groaned inwardly upon reading the post on Abū Alī al-Hasan ibn al-Hasan ibn al-Haytham (known simply as Ibn al Haytham or in mediaeval Europe as Alhacen or Alhazen) the mediaeval Islamic scholar by Pamela Toler that I found there. I hasten to add that Ms Toler is not solely to blame for the heap of excrement posing as history of science that she has posted there, as she was just regurgitating, probably inaccurately, what she had read in a popular book on Islamic science, about which more later.

After an opening paragraph that gives a somewhat mangled version of a part of Ibn al-Haytham’s biography Ms Toler presents us with the following paragraph:

While confined in his home, Alhazen revolutionized the study of optics and laid the foundation for the scientific method. (Move over, Sir Isaac Newton.) Before Alhazen, vision and light were questions of philosophy. Alhazen considered vision and light in terms of mathematics, physics, physiology, and even psychology. In his Book of Optics, he discussed the nature of light and color. He accurately described the mechanism of sight and the anatomy of the eye. He was concerned with reflection and refraction. He experimented with mirrors and lenses. He discovered that rainbows are caused by refraction and calculated the height of earth’s atmosphere. In his spare time, he built the first camera obscura.

Nearly every single claim in this brief paragraph is wrong and I shall now try, at least in outline, to correct some of the worst errors.

Whilst it is true that Ibn al-Haytham made a major advance in the study of optics I personally, as a gradualist, object strongly to any use of the word revolution in any of its forms when writing about the history of science. Ibn al-Haytham made an important step forward building on the work of others, his work in turn being pushed forward by others. He did not in anyway what so ever invent the scientific method. Put quite simply nobody did. (see next post!)

Before Alhazen, vision and light were questions of philosophy.

Here we start in on the real rubbish. The Islamic scholars inherited their knowledge of optics from the Greeks and to state simply that Greek optics consisted of questions of philosophy is to display a deep ignorance of the history of the subject. The Greek study of optics can be divided into three main areas: philosophical, medical and mathematical. The opinions on vision can be further categorised according to whether the rays that enable vision extrude from the eyes to the object viewed, extramission, from the object viewed to the eyes, intromission, or in both directions mixed.

Philosophical theories of vision were propagated by the Atomists, intromission, Plato, mixed, Aristotle, intromission mediumistic, and the Stoics also mixed. The mathematical theories laid the basis of geometrical optics, and were propagated by Euclid, Hero of Alexandria and Ptolemaeus, all three supporting an intromission extramission theory although it is not clear if this is purely instrumental in order to facilitate simpler calculations. The principle medical theory transmitted to the Islamic scientists was that of Galen who combined a surprisingly accurate physiological knowledge of the eye with a Stoic philosophy of vision. It is not necessary for our purposes to go into greater details. It should be pointed out that all the theories except that of the atomists involved the presence and active involvement of light although the visual rays were not simply light rays.

Ibn al-Haytham argued philosophically very strongly against extramission and for intromission whilst at the same time demonstrating that an intromission theory could successfully be combined with the geometric optics of Euclid. At the same time he integrated the theory of al-Kindi that light reflects in all directions from all points of a viewed object arguing that only light rays are involved in vision. His theory of vision was thus a clever synthesis of several different theories into a coherent whole and thus a major advance in the understanding of optics.

He accurately described the mechanism of sight and the anatomy of the eye.

Ibn al-Haytham adopted Galen’s description of the anatomy of the eye and added nothing to it. His theory of vision was defective in that he like Galen believed that vision takes place in the lens of the eye and not as Kepler correctly surmised on the retina. Because of this major defect in his theory Ibn al-Haytham was forced to develop an erroneous theory that only rays falling perpendicularly onto the lens of the eye were perceived. Otherwise the eye would perceive multiple images of the object. In reality the lens focusing all the rays no matter from which angle creates just one image on the retina.

He experimented with mirrors and lenses

Ibn al-Haytham describes a limited number of experiments to demonstrate that light in propgated in straight lines, something that nobody had doubted since Euclid at the latest. To what extent these were actual experiments or just thought experiments is disputed amongst the experts.

In his spare time, he built the first camera obscura.

The principle of the camera obscura was already known to Aristotle and even earlier to the Chinese scholar Mo-Ti in the fifth century BCE who referred to it as the locked treasure room.

Ms Toler discovered her enthusiasm for Ibn al-Haytham as she tells us through reading a popular book on Islamic science.

Modern physicist Jim al-Khalili, in his excellent The House of Wisdom: How Arabic Science Saved Ancient Knowledge and Gave Us the Renaissance, calls Alhazen the greatest physicist of the medieval world, and possibly the greatest in the 2000 years between Archimedes and Sir Isaac Newton. His Book of Optics was first translated into Latin in the late twelfth or early thirteen century. It had an enormous impact on the work of western scientists from Roger Bacon (c. 1214-1292) to Isaac Newton (1642-1727).

By pure chance I stumbled across a video of a public lecture that Jim al-Khalili gave earlier this year on the subject of his book. I’m not going to give a detailed analysis of this lecture as it contains enough errors to keep me in blog posts for at least a year. He seems to be of the opinion that because he is a physicist and was born in Baghdad that this qualifies him to write a book about the history of Islamic science. In the lecture he proudly tells us that he devoted all of eighteen months of his research time to researching this book. A. Mark Smith took fourteen years to research and write his annotated translation of the first three books of the Latin edition of Ibn al-Haytham’s Book of Optics but he is a mere historian and not a physicist. In his lecture al-Khahili gives a clear and explicit commitment to a Whig interpretation of the history of science and strong implied commitment to the great man theory; both of these have been rejected by real historians of science long ago.

A typical example of al-Khalili’s arrogant ignorance occurs in his lecture when he talks about the first use of place value decimal fractions in Arabic mathematics. First of all he apparently doesn’t know the difference between the decimal point and decimal fractions. He also doesn’t appear to know that the Babylonians were using place value fractions, albeit sexagesimal not decimal, a thousand years earlier. He then goes on to say that The Chinese developed decimal fractions about the same time as Arabic mathematicians “but we don’t know as much about them”! I hope he doesn’t make this statement within reach of the Needham Research Insitute. Al-Khalili appears to confuse his own ignorance of the history of science with the general state of the art.

Returning to the blog post we have the following statement:

Jim al-Khalili […] calls Alhazen the greatest physicist of the medieval world, and possibly the greatest in the 2000 years between Archimedes and Sir Isaac Newton.

None of the three scholars named above was a physicist in the modern sense of the word and as I’ve said in the past there is no such thing as “the greatest”.  Even if we ignore these criticisms al-Khalili’s statement would be a hopeless exaggeration. A much more sensible assessment of Ibn al-Haytham’s achievements is given by somebody who knows what he is talking about, historian of optics David C. Lindberg[2]:

Alhazen was undoubtedly the most significant figure in the history of optics between antiquity and the seventeenth century.

There is a substantial difference between the two claims most important, historically, Ibn al-Haytham’s influence stops with the new model of optics developed by Kepler.

As far as I can see without having read his book al-Khalili is a typical example of a scientist thinking because I’m an expert in my subject I can also write about its history without doing the groundwork. Writing history requires a different form of expertise to doing modern science and writing about the history of science requires a wide range of expertise that cannot be thrown together in ones spare time in eighteenth months if one is trying to write a survey of the scientific activity of a major culture over a period of something approaching a thousand years. To do so without first acquiring the necessary expertise results not in history but in a collection of anecdotes and clichés most of them inaccurate and many simply false.


[1] What is the collective noun for historians? A heap? A huddle? A hysteria? I somehow feel it should be alliterative.

[2] This quote is taken from David C. Lindberg, Theories of Vision from al-Kindi to Kepler, which is a good source for anybody wishing to fill in on the history of optics that I only sketch above.

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A mathematician who became Pope.

A standard question amongst historians of art and historians of science is Renaissance or renaissances? Was there just one large event in European history, The Renaissance, during which the whole of the lost knowledge of antiquity was recovered or were there a series of such periods throughout the Middle Ages in which this knowledge gradually trickled back into European culture bit by bit? The first version is the myth created by the scholars in the fifteenth century who first coined the terms Renaissance and Middle Ages. The second is much closer to what really happened in history.

One of these renaissances is the so-called first scientific or mathematical renaissance beginning in the twelfth century in which the so-called translators travelled to Spain and Sicily to translate both classical and Islamic scientific manuscripts from Arabic into Latin, reintroducing such classics as Euclid’s Elements or Ptolemaeus’ Syntaxis Mathematiké into Europe. However there had already been a steady trickle of Islamic scientific knowledge into Europe through Spain since the ninth century conveyed by individual scholars who had studied in Spain and then taught others in Northern Europe their freshly acquired treasures. One of the most well known of these was the French monk Gerbert d’Aurillac who died 12th May 1003.

800px-SylvestreII_aurilac

Statue of Pope Sylvester II in Aurillac, Auvergne, France Source: Wikimedia Commons

Gerbert, a peasant, was born about 945 and as a youth entered the Monastery of Aurillac as a menial but his intelligence was recognised and instead of being assigned kitchen duties he was given an education. From 967 to 970 he studied under Bishop Atto of Vich in Catalonia in the Spanish March, i.e. that part of Spain not under the rule of the Islamic Empire. In these three years Gerbert absorbed as much of the Islamic science and mathematics as he could. From Spain he went to Rome where he was introduced to the Pope and the German Emperor, Otto I, who was so impressed with the young scholar that he sent him to Rheims to complete his education.  He also served as tutor to Otto’s son the future Otto II. Under Otto II patronage he was appointed Abbott of Bobbio. He later succeeded to the Archbishopric of Rheims. After the death of Otto II he became tutor to the teenage Otto III and his cousin Pope Gregory V who appointed him Archbishop of Ravenna in 998. After Gregory’s death in 999 Gerbert was elevated to Pope with the support of Otto III, taking the name Sylvester II, although he only held the office for less than four years until his death in 1003.

Throughout his career at court and in the Church Gerbert was a passionate teacher of the mathematical sciences that he had learnt in his time in Spain. He wrote books on arithmetic, geometry and astronomy and was particularly interested in the astronomical methods of measuring time. He corresponded widely on mathematical topics and avidly collected manuscripts to extend his knowledge. He introduced the armillary sphere from Spain into Northern Europe and almost certainly played a roll in the introduction of the astrolabe. He might also have played a role in introducing the Hindu-Arabic numbers into Northern Europe.

Pope_Sylvester_II_(Gerbert_d'Aurillac)_-_De_geometria

12th century copy of Gerbert’s De geometria. Source: Wikimedia Commons

His achievements cannot be compared to some of the twelfth century translators such as Gerard of Cremona or Adelard of Bath but he was almost certainly the leading European scholar of the mathematical sciences outside of Muslim Spain in the tenth century and he and his student did much to make the Islamic knowledge of mathematics and astronomy known to a wider audience.

Next time a Gnu atheist tries to tell you that the Catholic Church was irreconcilably opposed to science in the Middle Ages tell them about Gerbert the mathematician who became Pope.

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It’s only been about 100 years!

There has been a lot of nonsense spouted in the last couple of days about the BBC’s decision to use the CE/BCE dating system instead of the AD/BC one, as usual the various commentators have trampled with both feet on the historical facts preferring brainless rhetoric to historical reality. So we have M. J. Robins on his Guardian blog claiming that the system has been in use for two thousand years in his tirade against the Daily Fail and Boris Johnson claiming 1500 years in his equally ridiculous tirade in the Daily Telegraph.

Let us look at the historical facts. The principle of counting years from the supposed birth of Christ was first introduced in 525 CE by Dionysius Exiguus in his efforts to determine the correct date for Easter. At the time it wasn’t used by anybody else. In the 8th century CE the English monk Bede used it in his work to determine the date of Easter. His pupil Alcuin of York introduced into the Court of Karl der Große (that’s Charlemagne for the English) From here its use spread slowly throughout Europe. Even the Vatican didn’t use it preferring to date years in terms of the reigns of popes. You will notice we are only talking about AD. The use of BC was first introduced in the 17th century as history within Europe started to become a real academic discipline. The use of the AD/BC dating system was first adopted by the Orthodox churches in the 18th century. The usage of this dating system was restricted to Europe and its colonies and was ignored by the majority of the world, until at the very earliest the late 19th century and in most cases the 20th century.

Through international trade and industry in the 20th century there was a need for a unified dating system and because of the economic dominance of the USA and Europe for such purposes the Gregorian calendar was adopted as the world’s norm. Why the rest of the world should also adopt a Christian system of referring to dates when less than 30% of the world’s population is Christian, even by the wildly inflated methods used by the churches to claim adherence, in this at best 100 year old universal dating system is something that those doing the screaming need to explain. As an explanation, to claim that the system has been in use for 2000 or 1500 years is a straight forward historical lie and wont wash.

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