How can this be? Surely the whole point of Copernicus’ great advance was that his heliocentric model broke away from the ‘fixes’ to the Ptolemaic model, however mathematically clever they may have been. None of the Marāgha astronomers, including Ibn al-Shātir, had taken that revolutionary step away from geocentrism (although, in the case of Ibn al-Shātir’s lunar model, the distinction between heliocentricity and geocentricity is irrelevant since the moon does indeed orbit the earth). The point here is a subtle one, for what is crucial is not only that Copernicus was using the mathematical tricks developed by the Marāgha School, but that without them he would simply not have been able to arrive at his final heliocentric model. Like the Marāgha astronomers, Copernicus was initially far more concerned with the lack of uniform motion in the Ptolemaic system, with its reliance on equants and deferents. Indeed, so close was Copernicus’ approach to those of the Marāgha astronomers that he is now often regarded by historians as the last and most notable champion of the Marāgha School, rather than the first of the modern era. The Marāgha School is thus the link between Ptolemy and Copernicus, without which it is hard to understand how the Copernican revolution could have taken place.
Most historians now believe that the planetary models developed by al-Tūsi and Ibn al-Shātir found their way to Europe (perhaps via Constantinople) and provided Copernicus with the inspiration for his astronomical models. The idea of the Tūsi-couple may have arrived in Europe without the translation of any Arabic text into Latin, and an exact chain of transmission has not yet been identified. Certainly, several manuscripts containing the Tūsi-couple are still extant in Italy, where Copernicus studied between 1496 and 1503 and where he could have encountered the Marāgha theories.
But is all this fair? Are we somehow belittling Copernicus’ great achievement by tagging him onto the end of a long line of ‘geocentrics’? Certainly, his reintroduction of the heliocentric hypothesis was an act of great intellectual daring. In the preface of the De revolutionibus, Copernicus tells Pope Paul III, to whom he dedicates the book, of his great reluctance to publish his theory of the motion of the earth around the sun for fear of ridicule. He goes on to say that he was almost driven to give up on the work altogether and it was only the persistent entreaties of his close friends that convinced him to go ahead.13
As far as the idea of heliocentricity is concerned, it is now clear that sixteenth- and seventeenth-century Europeans, including Copernicus himself, were well aware of Aristarchus and his early heliocentric model, and that Copernicus was somewhat disappointed that the Greek had got there first. He even withheld Aristarchus’ name in his writing, apart from a footnote in an early version of his De revolutionibus which he later deleted.14
So not only was the mathematics that Copernicus used in developing his planetary model borrowed from the Islamic world, the heliocentric system to which he applied it had been known (but largely ignored) for nearly two millennia also. Despite all this, I quote from one of the world’s leading authorities on Islamic astronomy, George Saliba, who puts it thus:
There is no question of doubting the originality or genius of Copernicus by implying that he was less brilliant because he used fundamental theorems already discovered and used in Arabic astronomy some two or three centuries earlier. Nor is there any doubt that anyone else could lay claim to the theory of heliocentricity with which Copernicus has become so firmly associated. In fact, if the Copernican revolution is understood to mean the abandonment of geocentricity and the adoption of heliocentricity, which was the masterpiece of Copernicus’ work, then it is clear that he remains the unchallenged master of that revolution, and there is no precedent within Arabic astronomy that is in any way similar to heliocentricity.15
There is a nice comparison to make here with Einstein’s development of his Special Theory of Relativity at the beginning of the twentieth century. I shall therefore make a brief detour to describe his ideas in order to shed light on the analogy I wish to make.
The theory of relativity states that different observers moving relative to each other would disagree about distances and time intervals between two events. But since no one can claim to be in a privileged frame of reference, the notion of absolute lengths and times disappears. This could only be understood by unifying the concepts of space and time, which are intertwined mathematically through a set of equations known as Lorentz transformations (after the Dutchman Hendrik Lorentz, who first wrote them down a year before Einstein published his work). Indeed, much of the groundwork for relativity theory had already been carried out before Einstein, and an early form of the equations had been independently proposed by Lorentz and the Irish physicist George Fitzgerald in the 1890s to explain a famous experiment on the propagation of light.
The trouble was that Lorentz and Fitzgerald had the right equations, and got the right answer, but for the wrong reason. They misinterpreted what was going on by sticking to the widespread notion of the all-pervading ‘aether’ that was believed to carry light waves through space. Einstein’s great achievement was to propose a simple postulate with which he was able to give the correct interpretation of the physics. The notion that light needs some kind of medium to carry it along – in the same way that a water wave needs water – was shown by Einstein to be unnecessary. Everything slotted into place when he made the bold suggestion not only that a beam of light can travel through empty space but that it would be measured by us to have the same speed, no matter how fast we are moving relative to it.
This crucial concept and the ideas that followed, in which space and time are unified, give us a far deeper understanding of our world. While Lorentz and Fitzgerald’s equations turned out to be correct mathematically, it was Einstein who gave them the correct interpretation. We see that the value of a good interpretation of a scientific theory brings us closer to the truth, for without a valid interpretation we would still be groping in the dark, no matter how well our theory agreed with experiment.
The same can be said of Copernicus. The Marāgha astronomers may have devised the correct mathematics, but it was Copernicus who applied it with the right interpretation. Those before him had either proposed the right heliocentric cosmology without the underpinning mathematical theory, or they had come up with the mathematical theory applied to the wrong physical system. With a combination of insight and courage, Copernicus brought the two together. In a nutshell, he turned the philosophical idea of heliocentrism into a fully predictive mathematical theory.
There is one final parting comment to make before we leave this story. Copernicus did not of course give us a proper scientific theory. His was a mathematical model based on a hypothetical picture of the physical universe, for he had no knowledge of the law of gravitation. In fact, while he improved on Ptolemy’s cosmology by removing the earth from the centre of the universe and replacing it with the sun, we now know that even this was not quite right. To Copernicus, the outer sphere of the fixed and distant stars was also centred on the sun. But we have learnt that our sun sits on an outer arm of an average spiral galaxy in a nondescript part of the universe, and certainly not at the universe’s centre. How could poor Copernicus know this before the invention of the telescope? Indeed, modern cosmology based on Einstein’s theory and centuries of ever more comprehensive and accurate astronomical data have convinced us that the universe has no centre at all, much as the surface of the earth has no centre. What Copernicus described correctly (apart from the elliptical orbits that had to await the work of Kepler) was only our sun-centred solar system. So despite his undoubted genius, I stand by my belief that Copernicus was the last astronomer of the Marāgha School. As for the father of modern astronomy, that title should go to Galileo, for the real revolution only took place with his use of the telescope that was finally to prove Copernicus, and Aristarchus, right.
15
Decline and Renaissance
The history of science, like the history of all civilization, has gone through cycles.
Abdus Sala
m, Nobel Laureate
Several parallels immediately strike us when we compare the first great translation movement from Greek to Arabic with the second one from Arabic to Latin, jumping three hundred years from ninth-century Islamic Baghdad to twelfth-century Toledo in Christian Spain. Just as classics of Greek science such as Euclid’s Elements and Ptolemy’s Almagest were translated and refined several times by different people, so too were Arabic classics like Al-Khwārizmi’s al-Jebr and Ibn al-Haytham’s Optics. One can even reel off the list of the most prominent members of this second translation movement who carried out much of the work. The Englishmen Adelard of Bath and Robert of Chester and the Italian Gerard of Cremona are probably the best known; all three worked on translating al-Khwārizmi’s texts on mathematics. Other prominent names include Daniel of Morley, John of Seville, Herman the Dalmatian and Plato of Tivoli. The activity reached its peak around the middle of the twelfth century when a translation centre was set up by a bishop named Raymond of Toledo. Some of the translators, like their earlier counterparts in Baghdad, were very able scientists in their own right, although it is fair to say that there were no truly original thinkers among them of the stature of al-Khwārizmi, al-Kindi, Hunayn ibn Ishāq or Thābit ibn Qurra; nor was the Toledo school anywhere near as prolific as the House of Wisdom in Baghdad.
Among the most important Arabic texts to be studied early on was al-Khwārizmi’s al-Jebr, which was first translated into Latin in 1145 by Robert of Chester (a few years before Gerard of Cremona’s version).1 Robert was thus the first person to introduce the word ‘algebra’ into Europe. He also gave us the word ‘sine’, for the trigonometric quantity defined as the ratio of two sides of a right-angled triangle.2 But the way we arrived at this word from its Hindu origins also deserves mention, not least because most historians have got it slightly wrong.
Etymologically, we must begin with the Sanskrit word jya-ardha, which means ‘half the bowstring’ (or, geometrically, half the chord of a circle – see diagram opposite). The word jya-ardha was abbreviated by Hindu mathematicians to jiva, and this was transliterated in Arabic as jiba (since there is no ‘v’-sounding letter in the Arabic alphabet). This was in turn written with just the two letters j (jīm) and b (bā’). It is not clear to me whether this was a deliberate abbreviation or because the two vowels in the word were short sounds, and are therefore not written in Arabic. When Robert of Chester came to translate this word, he misread it as jayb, which in Arabic means ‘pocket’ (and not, as so many scholars have claimed ‘fold’, ‘bosom’, ‘bundle’ or ‘bay’). So he simply used the Latin word for pocket: sinus. Finally, English usage converted this word to ‘sine’. The first published use of the abbreviation ‘sin’, along with ‘cos’, and ‘tan’, was by the sixteenth-century French mathematician Albert Girard. Interestingly, in Arabic today the word for sine is in fact pronounced jayb.
So Arabic science began its osmosis into Europe. While, in comparison with the Islamic Empire, Western Europe was well and truly mired in its Dark Ages, we do occasionally find more-enlightened rulers encouraging a limited form of scholarship. For instance, the Viking King Cnut (Canute) of England, Norway and Denmark (r. 1016–35) attracted a number of scholars from northern France over to England. Later, the Norman King William (the Conqueror) also encouraged learning, and we witness the arrival in England of a mathematician, Robert of Lorraine, and an astronomer, Walcher of Malvern, towards the end of the eleventh century. Walcher is regarded as the very first English astronomer and is noted for using an astrolabe to measure the time of several solar and lunar eclipses and computing a set of tables giving the time of the new moons. He was also the very first English scholar of Arabic and one of the first translators of Arabic treatises into Latin.
The origin of the trigonometric sine of an angle as described by Hindu mathematicians.
We have seen how the very earliest transmission of Arabic science into Europe was thanks to men like Gerbert d’Aurillac in the tenth century. The process very gradually picked up pace over the next few centuries as the Reconquista brought more of the Andalusian centres under Christian control. But Spain was not the only avenue of transmission. Two other vital cities were Venice, which traded with many of the dynasties in the Muslim world, and Palermo, the capital of Sicily.
In 1061 a Norman mercenary by the name of Roger Guiscard arrived at the shores of Sicily with his army. Over a period of thirty years, he gradually wrested control of the island from its Muslim rulers. He reigned under the title of Grand Count Roger I and was pragmatic enough to make use of much of the Arabs’ machinery of government. In fact, like the Muslim rulers before them, the Normans were initially very tolerant of other religions and Sicily remained a land of religious freedom, with Muslims and Jews living peacefully alongside Catholic and Orthodox Christians, while Hebrew, Arabic, Latin and Greek were recognized as official languages. His son, Roger II, reigned for forty-two years (1112–54), mostly now as king; under his rule Sicily became a powerful and wealthy kingdom that included the whole of the southern half of Italy, with its capital, Palermo, as one of the most important cultural centres of Europe. We encountered him earlier as the ruler for whom the great Andalusian geographer al-Idrīsi wrote his famous Book of Roger.
But to what extent did Europe really remain in the shadow of the Islamic Empire? It would be wrong to dismiss completely any form of original scientific scholarship in Europe during the Islamic golden age, for there are always isolated pockets of intellectual activity and excellence wherever and whenever one looks in world history. Two notable lights and original thinkers who shone in the medieval darkness were the Italian Thomas Aquinas (c. 1225–74), and the Englishman William of Occam (c. 1288–1347). However, there were very few other Christian scholars whose achievements could rival their Muslim counterparts until the end of the fifteenth century and the arrival of Renaissance geniuses such as Leonardo da Vinci. By that time, European universities would have contained the Latin translations of the works of all the giants of Islam, such as Ibn Sīna, Ibn al-Haytham, Ibn Rushd, al-Rāzi, al-Khwārizmi and many others. In medicine in particular, translations of Arabic books continued to be studied and printed well into the eighteenth century.
Among the European scholars influenced by their Islamic counterparts before them were Roger Bacon, whose work on lenses relied heavily on his study of Ibn al-Haytham’s Optics, and Leonardo of Pisa (Fibonacci), who introduced algebra and the Arabic numeral characters after being strongly influenced by the work of al-Khwārizmi. Some historians have even argued that the great German astronomer Johannes Kepler may have been inspired to develop his groundbreaking work on elliptical orbits after studying the work of the twelfth-century Andalusian astronomer al-Bitrūji (Alpetragius), who had tried and failed to modify the Ptolemaic model. While far from the most important of Islamic astronomers, al-Bitrūji’s Principles of Astronomy (Kitab al-Hay’a) became very popular in Europe.3
Of course, the influence of Arabic scientists on the rest of the world, and Western Europe in the Middle Ages in particular, extended far beyond their achievements in the pure sciences. For example, I have not gone into detail about their contribution to what is described as the Islamic agricultural revolution and with it new methods of irrigation, or their creation of whole new chemical industries such as glassmaking and ceramics, or the sugar-refining industry. Their engineering feats in building dams, canals, waterwheels and pumps and their technological advances in clockmaking – all these advances in many ways changed the lives of millions of ordinary people directly and immediately.
Rather than turn this into a dry and lengthy list, I shall mention in passing just one example of a gift from the Arabs that I for one am rather grateful for: coffee – especially as it was originally banned in Europe as a ‘Muslim drink’. Its use can be traced back to ninth-century Ethiopia where, according to legend, an Arab goatherd named Khalid observed that his goats became livelier after eating the berries of the coffee plant. Intrigued, he boiled the berrie
s in water to produce the first cup of coffee. From Ethiopia, the drink spread to Egypt and Yemen, but it was in Arabia that coffee beans were first roasted and brewed as is done today. By the fifteenth century coffee had reached the rest of the Middle East, Persia, Turkey and North Africa.
In 1583, Leonhard Rauwolf, a German physician, gave this description of coffee after returning from a ten-year trip to the Near East:
A beverage as black as ink, useful against numerous illnesses, particularly those of the stomach. Its consumers take it in the morning, quite frankly, in a porcelain cup that is passed around and from which each one drinks a cupful. It is composed of water and the fruit from a bush called bunnu.
From the Muslim world, coffee first spread to Italy via Venice and quickly to the rest of Europe. The first European coffee house opened in Italy in the mid-seventeenth century. The colonial Dutch then began to grow it in Indonesia and, by the early eighteenth century, thanks to the efforts of the British East India Company, coffee finally became popular in England.
The story of coffee finally comes full-circle when, in 2007, an agreement was reached after a high-profile court battle between the government of Ethiopia, the home of coffee, and the coffee giants Starbucks over copyright of trademark names of certain Ethiopian coffee beans.
When it comes to feats of engineering in the Islamic Empire, I can do no better than to mention its most famous engineer, Ibn Isma’il al-Jazari (1136–1206), and describe his best-known invention. Originally from al-Jazīra, a region of northern Mesopotamia, he became one of the greatest clockmakers in history. His six-foot-high water-powered ‘Elephant Clock’ is one of the engineering wonders of the medieval world; an object of artistic beauty as well as engineering brilliance (see Plates 27 and 28). It used Archimedes’ water principles combined with Indian water-timing devices and was made up of a hollow model of an Indian elephant ridden by two Arabian figures, on a Persian carpet, with Chinese dragons and an Egyptian phoenix. The clock is based on what is called a perforated float, which acts as the actuator and timekeeper for all parts of the clock. Inside the belly of the hollow elephant is a tank of water in which is floating a bowl with a tiny hole in its bottom. The hole has been carefully drilled to allow in water at a precise rate, such that the bowl completely fills and sinks in exactly half an hour. A small chain that can only flex up and down keeps the bowl close to the side of the tank thus allowing it to only move vertically.
Pathfinders Page 28
