Written by Richard Covington

Thorne Anderson ART ARCHIVE /UNIVERSITY LIBRARY ISTANBUL /DAGLI ORTI An astronomer calculates the position of a star with an armillary sphere and a quadrant in this illustration from a 16th-century Ottoman manuscript. Below: The 10th-century astronomer Abu Sa’id al-Sizji held the contemporary view that the Earth was the center of the universe, but he modeled the solar system on the concept that the Earth rotated on its axis—as shown in this display at the Institute for the History of Arab–Islamic Science in Frankfurt. THORNE ANDERSON

ou have to hand it to Ahmed Djebbar: The science historian certainly knows how to draw a crowd. As we circulate among the astrolabes, maps and hydraulic models of an eye-opening Paris exhibition on medieval Arabic science, curious museum-goers gather around us.

“Did you know that the Egyptian doctor Ibn al-Nafis recognized that the lungs purify blood in the 13th century, nearly 350 years before the Europeans?” he asks, standing in front of an anatomical drawing of the human body. “Or that the Arabs treated the mentally ill with music therapy as early as the ninth century?”

Examining a case of rare manuscripts, the dapper Lille University professor launches into a mini-lecture before the rapt group. The 13th-century Persian astronomer Nasir al-Din al-Tusi, the author of one of the yellowing Arabic-language texts, upended the geocentric Greek view of the universe, Djebbar explains, by declaring Ptolemy’s model of planetary motion flawed and creating his own more accurate, but still Earth-centered, version. Three centuries later, the Polish astronomer Nicholas Copernicus borrowed al-Tusi’s model to make the shocking proposition that the Earth revolves around the sun. “Al-Tusi made his observations without ctelescopes or even glasses,” says Djebbar, removing his own spectacles and waving them theatrically in the air. “Even though the Arabs possessed the knowledge to make lenses, they probably thought it was an idiotic idea. God made us like this; why hang something on our noses to see better?” he jokes, placing his glasses back on his nose with a flourish. His audience erupts into laughter as Djebbar, who was curator of “The Golden Age of Arabic Sciences”—the Paris exhibition, which ran from October 2005 through March 2006 at the Arab World Institute—tries to quiet them down.

For most westerners, and indeed for many Arabs, the spectacular achievements of Arabic-language science from the eighth through the 16th centuries come as a startling discovery, as if an unknown continent had suddenly appeared on the horizon. In mathematics, astronomy, medicine, optics, cartography, evolutionary theory, physics and chemistry, medieval Arab and Muslim scientists, scholars, doctors and mapmakers were centuries ahead of Europe. Centers for scientific research and experimentation emerged across Muslim lands—in Baghdad, Cairo, Damascus, Samarkand, Shiraz, Bukhara, Isfahan, Toledo, Córdoba, Granada and Istanbul.

Generations of science historians once rejected Islamic accomplishments. One critic, the French physicist Pierre Duhem, even accused Muslims of trying to destroy classical science in his 1914–1916 historic survey Le Système du Monde (The System of the World). Others asserted that the Arabic language itself was not suited for science, contends Roshdi Rashed, the dean of Islamic science in France. “Otherwise well-respected scholars like Ernest Renan and Paul Tannery excluded even the possibility of an Arabic contribution to science,” says Rashed, a former fellow at the Institute for Advanced Studies in Princeton, professor emeritus at the University of Paris and editor of the three-volume Encyclopedia of the History of Arabic Science.

The earliest known medical description of the eye, from a ninth-century work by Hunayn ibn Ishaq, is shown in this copy of a 12th-century manuscript at the Institute. Below: Kamal al-Din al-Farisi’s 13th-century demonstration of the separation of the visible spectrum of light by double refraction, reproduced in this display at the Institute for the History of Arab–Islamic Science in Frankfurt, helped advance the science of optics. THORNE ANDERSON (2)



Although an alternative spectrum of science historians, beginning with the 19th-century European Orientalists Jean-Jacques Sédillot and Eilhard Wiedemann and including the 20th-century Harvard professor George Sarton, staunchly promoted the pivotal Arab/Muslim role in science, the general public has remained largely unaware of Arab discoveries. The 1300-year period between the Greek golden age of science (from the fifth century BC to the second century of our era) and the 15th-century Italian Renaissance was perceived as a scientific desert. If Arab scholars were acknowledged at all outside academia, they were seen merely as useful messengers, conduits who preserved the classical Greek knowledge of Euclid, Aristotle, Hippocrates, Galen, Ptolemy, Archimedes and others through Arabic texts.

True enough, much of ancient science came back to Europe via Arabic translations, which were subsequently translated into Latin and other languages. (See “Lines of Transmission”). Some key texts, like Ptolemy’s Planisphere, Galen’s commentary on Hippocrates’ treatise Airs, Waters, Places and the final chapters of the third-century BC mathematician Apollonius’ book on conic sections exist only thanks to the Arabic translations, since the original Greek manuscripts have all disappeared.

But according to astrophysicist Jean Audouze, director of the French National Center for Scientific Research in Paris, the Arabs were not simply transmitters of Greek concepts; they were creators in their own right. Like Djebbar and Rashed, Audouze is one of a small number of dedicated scholars —fewer than 150 in France, Germany and Britain, but also scattered through the US , Arab countries, Asia and Latin America—who are struggling to give Arabic science the long overdue respect it deserves.

INTERFOTO PRESSEBILDAGENTUR / ALAMY Arab astronomers study the heavens in this print from a commentary on Cicero’s Somnium Scipionis, whose central character ranges through the celestial spheres that surround the Earth, and carry the planets and the stars. Below: The Canon of Medicine by Ibn Sina (known as Avicenna in the West) was first translated from Arabic into Latin in the 12th century and into Hebrew in 1279. It served as the chief guide to medical science in Europe and was used in medical schools there until the mid-17th century. BIBLIOTECA UNIVERSITARIA DI BOLOGNA / NATIONAL LIBRARY OF MEDICINE

“One of the more drastic consequences of the dismissal of the vast Islamic contribution is that you cannot understand classical science without it,” argues Rashed. “If you reduce the distance between Greek science and 17th century science, you are going to say, for example, that Apollonius first conceived algebraic geometry. But he has nothing of the kind in his writings. ”

“Either you push Apollonius to invent ideas he did not have or you pull back 17th-century scholars closer to Greek levels of understanding. This results in very serious errors of perspective. But if you take into account Arabic science, you are better able to understand what is truly new in the 17th-century outlook and the steps that led from Greek classical science.”

Tunisian geologist Mustafa El-Tayeb, director of science policy and sustainable development for the United Nations Education, Scientific and Cultural Organization in Paris, is another impassioned advocate for Islamic science. He believes that reclaiming a proper place for medieval Arab achievements is vital for encouraging future generations of Arab and Muslim researchers.

“When I hear reactionaries preaching to young Muslims that science is not good for Islam, I want these students to realize that it’s a crucial part of their heritage and not something to be rejected, or seen as alien,” says El-Tayeb. “As it is, the history of Islamic science is barely taught at all in universities across the Middle East.”

In fact, the discipline is everywhere in a deepening crisis, warns George Saliba, professor of Arabic and Islamic science at Columbia University. “The most urgent need now for the study of Islamic science is to train people who can edit and publish the hundreds of scientific texts that are still lingering in world libraries with almost no one aware of their existence, let alone their contents,” he says. “But despite this need, Islamic science historians are becoming an endangered species.” To make his point, Saliba cites the 200 to 300 Muslim treatises on planetary theories that he“s tracked down. Only two have been translated into European languages—one into Latin centuries ago and the other, in modern times, into English.

THE PRINT COLLETOR / ALAMY thousand years before English emerged as the international language of science in the latter half of the 20th century, the Arabic language unified scholars across the Muslim world, generating a lively market of ideas from Samarkand to Córdoba. “A book published in Central Asia could be read in southern Spain less than a year later,” explains Roshdi Rashed, an eminent Egyptian-born historian of science, in his office near Paris. “Islamic learning was not like Greek science, which was limited principally to the eastern Mediterranean, but was spread across most of the known world.” One celebrated example is the Kitab al-Istikmal, a treatise on geometry by Yusuf al-Mu’taman, the 11th-century king of Sarakusta (today’s Zaragosa in northern Spain). The Jewish philosopher Maimonides brought it from Córdoba to Cairo and copies were soon circulating in Baghdad. The work was eventually republished in the 13th century in Central Asia. Among the babel of scientists and scholars who crisscrossed the polyglot Muslim empire, the common language was Arabic. “Besides Maimonides, you have the great mathematician and physicist Alhazen (Ibn al-Haitham) moving from Basra to Cairo,” says Rashed, “and the astronomer Nasir al-Din al-Tusi journeying every year from Khorasan in northern Iran through Iraq and on to Aleppo to teach.” Even if scholars spoke Persian or another language at home, they wrote their papers in Arabic so that their colleagues in Baghdad, Toledo and elsewhere could understand them, he adds. Omar Khayyam may have penned his quatrains in Persian, but he explicated his mathematical concepts in Arabic. Correspondence among scientists—typically carried by cara- van messenger or carrier pigeon—was nearly as far-reaching in the 11th and 12th centuries as it was in the 17th, Rashed maintains. But despite its ultimate ascendancy, scholarly Arabic had a slow start. “Before the advent of science, Arabic was the language of poetry; it soon became the language of the new religion of Islam, but paradoxically, it did not become the language of power right away,” explains French science historian Ahmed Djebbar. Although the Umayyad caliph ‘Abd al-Malik decreed at the beginning of the eighth century that government institutions, schools, courts and communications conduct their business in Arabic, it took another 50 to 100 years before the translation of scientific texts from Greek, Syriac, Persian and Indian languages into Arabic got under way in earnest, with some 100 translators at work over the course of the ninth and 10th centuries, according to the 10th-century bibliographer Ibn al-Nadim of Baghdad. Baghdad’s Bayt al-Hikmah (“House of Wisdom”) became a vibrant center of translation. Works like Ptolemy’s Almagest and Dioscorides’ De Materia Medica were translated numerous times as scholars perfected Arabic terminology. The Greek word parabola was initially Arabicized phonetically as barabula, then subsequently refined to qat za’id, which literally means “thick section.” Diabetes was first rendered as diyabita then transformed to da as-sukkar (“sugar sickness”). Over time, Arabic scientific terms and star names were adopted into other languages, a list that includes alkali, alcohol, algebra, algorithm, alembic, alchemy, azimuth, elixir, nadir, zenith, Betelgeuse, Aldebaran, Rigel and Mizar. After some seven centuries in which Arabic dominated scientific discourse, it began to be eclipsed in the 15th century by Turkish as Ottoman rule expanded. Ghiyath al-Kashi’s 1427 mathematical treatise Risala al-Muhitiya (Treatise on the Circumference), in which he calculated the value of pi to 17 decimal places, was one of the last significant scientific texts in Arabic. By the time Taqi al-Din, the director of the Istanbul observatory, wrote his books in Arabic on light and marvelous machines in the second half of the 16th century, Latin had largely supplanted Arabic as the universal language of science. Unlike Arabic, however, which was understood by all classes and gave ordinary Muslims access to scholarly knowledge, Latin was used principally by academics and clergy, fencing science in as the preserve of an educated elite.

Yet the duty to promote the Arab intellectual legacy has never been greater, argues Rashed, underscoring the philosophical alliance between science, which strives for unity in the natural world, and religion, which seeks a similar balance in the realm of the spirit. “Muslim science demonstrates that there has always been a profoundly rational base to Islamic civilization,” he explains.

Drawing principally from Greek texts, but also Persian and Indian sources, medieval Islamic scientists made a staggering number of breakthroughs. The brilliant ninth-century Baghdad mathematician Muhammad ibn Musa al-Khwarizmi invented algebra, initially to resolve property disputes (even though countless generations of high school students wish he hadn’t bothered). He also solved linear and quadratic equations using algorithms, the basis of computer programming; the term itself is derived from his surname, testimony to al-Khwarizmi’s enduring gift to mathematics.

BETTMANN / CORBIS The Persian polymath-physician Avicenna appeared with his Greek forebears Galen and Hippocrates in this woodcut from an early 15th-century Latin medical book. Below: Avicenna remains a hero today. His portrait decks a wall in Bukhara, Uzbekistan. CHARLES & JOSETTE LENARS / CORBIS

Reversing the false Greek notion that light is emitted from the eye, the 11th-century physicist Alhasan ibn al-Haitham, known in the West by his Latinized first name as Alhazen, correctly asserted in Cairo that light rays travel in the opposite direction, reflecting off the surface of objects to enter the eye. Devising the first rudimentary pinhole camera, or camera obscura, Alhazen demonstrated that light emanates from an object in straight lines, establishing the principle of linear perspective essential to the art of Leonardo da Vinci and other Renaissance masters. (Alas, the Basra-born scientist did not invent film for his primitive camera; civilization would wait until the 19th century for the first photograph.) By putting his concepts to various tests, using the camera obscura and other tools, Alhazen also introduced the experimental method of proof, insisting that theories had to be verified in practice, a key element to modern science that was missing from the less empirical Greek tradition.

“Arab science succeeded as much in pragmatic applications as it did in theoretical concepts,” Audouze maintains. “Islamic scholars distinguished themselves from their Greek predecessors, who were more inventive in ideas than in practical matters.” Arab scholars also introduced the practice of peer review and citations to confirm their source material.

Although the Babylonians, Indians and Egyptians had astronomical observatories, those founded under Islamic rulers in Maragha (in present-day Iran), Samarkand and Istanbul were far more sophisticated, equipped with an impressive array of astrolabes, sundials, sextants, celestial globes and armillary spheres to track the movements of the planets and constellations.

Skilled at determining the precise location of Makkah from anywhere in the Muslim empire, Islamic astronomers were unsurpassed in their calculations and predictions. Many mosques engaged a full-time astronomer, called a muqqawit, to determine the hours of prayer and consult lunar calendars to fix the dates for Ramadan and other religious events.

Persian astronomer Muhammad ibn Ahmad al-Biruni (973–1048), a protean intellectual figure who wrote in Persian, Arabic, Greek, Hebrew and Sanskrit, and lived in Kath (in present-day Uzbekistan), corresponded with Abu al-Wafa, another astronomer 2000 kilometers (1242 mi) west in Baghdad, to coordinate the simultaneous observation of a lunar eclipse. On May 24, 997, according to al-Biruni’s book Al-athar al-baqiyah an al-qurun al-khaliyah (Vestiges of Bygone Days, usually shortened to The Chronology), they got their eclipse, measuring its duration and the moon’s angle in the sky to calculate the longitude of Kath with unprecedented exactitude.

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Arab astronomers and cartographers strove for—and frequently achieved— uncanny accuracy. To ascertain the distance separating degrees of latitude for a projected global map, the ninth-century Baghdad caliph al-Ma’mun dispatched 70 scientists into the Syrian desert. Using astrolabes, measuring rods and stretched lengths of cord, the teams walked until they observed a change of one degree in the elevation of the polestar, the equivalent to a degree of latitude. Reckoning the distance traveled at 562 2/ 3 Arab miles (64.5 statute miles or 103.8 km), they computed the Earth’s circumference, which is 360 degrees, as 23,220 statute miles, or around 37,380 kilometers, a respectable error only about seven percent less than the true figure of 24,800 miles (40,000 km). (However, around 200 BC the Alexandrian geographer Eratosthenes handily beat their estimate, calculating the Earth’s circumference at 39,690 km.)

Arabic/Muslim achievements in medicine were also impressive. The ninth-century Persian doctor Muhammad ibn Zakariya al-Razi, known in Latin as Rhazes, penned the first treatise on smallpox in his Kitab al-tajarib (Book of Experience), which probed some 900 cases of various maladies. Another Persian doctor, Abu Ali ibn Sina, or Avicenna (980–1037), compiled Qanun fi ’l-tib (Canon of Medicine), a five-volume compendium of Greek and Islamic healing that became one of the principal textbooks in European universities centuries later.

Abu al-Qasim al-Zahrawi (Abulcasis in Latin), a 10th-century surgeon in Córdoba, composed Al-Tasrif, a 30-chapter medical encyclopedia describing dozens of operations, complete with graphic illustrations of surgical instruments, including scalpels, cauterizing tools, feeding tubes and cupping glasses. (A 15th-century Turkish edition added instructively terrifying depictions of doctors treating patients.) Some 300 years after al-Zahrawi, another Andalusian doctor, Ibn al-Baitar, published Al-jami li mufradat al-adwiyya wa l-aghdhiyya (Book of Simple Medications and Alimentations), adding more than 400 medicines and curative plants to the 1,000 catalogued by the first-century doctor Dioscorides and other Greek botanists.

Arab scholars even theorized about evolution, arriving at conclusions that anticipated Darwin. In 1377, nearly half a millennium before the 1859 publication of On the Origin of Species, the Tunisian-born historiographer Ibn Khaldun, renowned as one of the founders of sociology, asserted in Al-Muqaddimah (Prolegomena), “The animal kingdom was developed, its species multiplied, and in the gradual process of Creation, it ended in man & arising from the world of the monkeys.”

The period from the ninth through the 16th centuries was also a golden age for hydraulic technology, with Muslim engineers devising underground canals, dams, waterwheels and water-lifting machines to modernize agriculture and provide fresh water to rapidly growing cities from Córdoba to Samarkand. Intricate water clocks, pumps and piston-driven machines were the forerunners of mechanisms that would not appear in Europe until the Italian Renaissance and later with the development of steam and internal-combustion engines in the 18th and 19th centuries.

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The importance of all branches of learning, including science, is emphasized in the Qur’an itself, which reads, in Chapter 58, Verse 11, “God will raise up in rank those of you who have been given knowledge.” The value placed on scholarship by Muslims at large is underscored by two sayings popularly linked to the Prophet Muhammad: “Search for learning even if it be in China,” and “The quest for learning is a duty for every Muslim.” Although these sayings cannot be traced to authentic hadiths (traditions) of the Prophet, they reflect the general feeling of esteem in which the Muslim community holds learning, based on the Qur’an’s emphasis on the importance of knowledge and reason, and respect for learned persons.

To Djebbar, early theological debates over the meaning of the words in the Qur’an, interpretations of hadith and etymological arguments on the Arabic language itself all nurtured the questioning spirit of rationalism necessary for scientific development. “These [religious and linguistic] critiques are the true departure point for the Arabic scientific tradition,” he asserts in his 2001 book, Une histoire de la science arabe (A History of Arabic Science).

Although Umayyad princes filled libraries in Damascus with Greek scientific texts from Spain, beginning in the early eighth century, and commissioned Arabic translations, the main push for scientific inquiry arose in Baghdad around the time of the city’s founding in 762.

Beginning with the first Abbasid caliph, al-Mansur, the victorious dynasty promoted science for ideological and political reasons. “The new rulers needed capable astronomers and geographers to measure the recently conquered empire under their control and to demonstrate to their subjects that Abbasid power was a force for good,” Djebbar explains. As rural populations migrated to the cities, creating a highly diverse, socially volatile mix of peoples, the demand for competent doctors, engineers and scientists exploded. Baghdad had a population of more than 800,000 inhabitants by the 10th century, and was, after Constantinople, the largest city on Earth.

At the end of the eighth century, Harun al-Rashid, the grandson of al-Mansur and the caliph whose court inspired The Thousand and One Nights, erected Baghdad’s first paper mill, the second in the empire. (The first mill had been constructed in Samarkand by Chinese engineers captured in the Battle of Talas in Central Asia around 750, according to Djebbar. The Chinese, who had been making paper since at least the second century BC , had kept the process a jealously guarded secret.) Shortly after the Baghdad plant opened, paper mills cropped up in virtually all the major Muslim cities. By the end of the 12th century, the Moroccan capital Fez sustained some 400 paper-making workshops.

The introduction of paper into the Middle East was a key technological breakthrough and a critical innovation for the spread of science. Paper gradually supplanted parchment and papyrus, making publication of manuscripts far cheaper and providing access to ideas for a much broader range of the educated public. Feather-light but sturdy paper was developed for use in correspondence by carrier pigeon. Since al-Biruni’s Chronology mentions an exchange of letters with Abu al-Wafa to measure an eclipse, Djebbar suggests that the two astronomers used carrier pigeon “air mail” to speed up their 2000-kilometer correspondence between Kath and Baghdad.

BIBLIOTHÈQUE NATIONALE / ARCHIVES CHARMET / BRIDGEMAN ART LIBRARY The 10th-century Andalusian surgeon Abu al-Qasim Khalaf ibn al-Abbas al-Zahrawi (known as Abulcasis in the West) wrote many medical books, including The Properties of Various Products. This page discusses the use and preparation of absinthe. Below: Two types of thyme are depicted on these pages of De Materia Medica, a guide to remedies by the Greek physician Dioscorides that was translated into Arabic in Baghdad in 1240. ART ARCHIVE / BODLEIAN LIBRARY

Around the same time that Harun al-Rashid ushered in the paper mill, he also founded Baghdad’s first hospital and a separate scientific academy known as Bayt al-Hikmah (“House of Wisdom”). Initially little more than the caliph’s private library, the House of Wisdom became a full-blown research and translation center and astronomical observatory under al-Rashid’s son, Caliph al-Ma’mun, who ruled from 813 to 833. It was here that the versatile al-Khwarizmi developed algebra and, turning his hand to cartography, drafted an elaborate map tracing the meanders of the Nile River.

According to Ibn al-Nadim, a local 10th-century bibliographer, al-Ma’mun had a prophetic dream of the white-bearded Aristotle seated on a throne in which the Greek philosopher advised the caliph on the path to wisdom through reason, law and faith. Al-Ma’mun took this vision as a sign to amass knowledge and shortly afterward sent a cohort of academics to Byzantium to bring back reams of scientific and philosophical texts to be translated into Arabic. Gradually, scholars acquired manuscripts from state archives and private collections in Alexandria, Damascus, Antioch, Harran and other cities. Although most of the books were in the original Greek, many volumes had already been translated between the fifth and seventh centuries into Syriac, the western Aramaic tongue used in ancient Syria. This massively ambitious initiative to translate Greek, Syriac, Persian and Indian treatises into Arabic lasted more than 200 years, from the middle of the 700’s until the end of the 10th century, according to Djebbar. (See “The Language”, above).

Al-Ma’mun’s patronage set an example, prompting princes, merchants, doctors and well-to-do scholars to finance research with charitable endowments, known as awqaf (waqf in the singular). “Scientists were always close to the courts; there was no such thing as independent science,” explains Rashed. “One had to eat and for that the scholars needed a patron, either the caliph, a wealthy merchant or a nobleman.”

The support of powerful benefactors became a vital element for the development of science across the Muslim empire. In Córdoba, the 10th-century caliph al-Hakam II sponsored extensive scholarly missions to scour manuscript collections in the eastern capitals to stock a library that soon rivaled the best in the world. In the early 11th century, the Fatimid ruler al-Hakim invited the renowned mathematician and physicist Alhazen to teach in his court, greeting him in person at the gates of Cairo, an extraordinary honor that gave a tremendous boost to the prestige of science in Egypt. That honeymoon ended abruptly, however, when Alhazen failed to realize the caliph’s scheme to regulate Nile flooding. Feigning madness to avoid execution, the scholar was placed under house arrest, taking advantage of the solitude to churn out a flood of treatises, biding his time until al-Hakim’s death in 1021.

Generally, scientists worked without religious constraints, Djebbar maintains, with Nestorian Christians, Jews and Muslims collaborating in relative harmony. The sort of persecution that inflamed the Spanish Inquisition in the 15th century and later fired the 1633 heresy trial of Galileo in Rome did not occur in Islamic countries at the time, he says.

“It was not because Muslims were nicer people than Christians,” the professor explains. “It was a matter of timing. In Christian countries, there was a scientific renaissance at a period when religion had already locked the doors of experimentation and speculation. In Arab countries, science arose shortly after Islam was established, creating its own secular space without reference to religion.”

There were, however, isolated instances of repression. Shortly after al-Hakam II’s death in Córdoba in 976, the prime minister Abu Amir al-Kahtani, who assumed power as regent for the underage prince Hisham, burned many of the manuscripts the caliph had acquired at such great cost, claiming that the teachings of the Greeks, particularly in astronomy and philosophy, contradicted the Qur’an. Only works of medicine and arithmetic were spared. Some 150 years later, in the 12th century, the Baghdad theologian and mystic Muhammad al-Ghazali branded theoretical mathematics and physics as dangerous, claiming that they bred a rationalistic philosophy that led to atheism, according to Djebbar.

Astrology also provoked a heated polemical debate that lasted for centuries. “Critics argued that astrology lied to people by claiming to predict the future when only God can see the future,” says Djebbar, “but no Muslim astrologer—and there were many at the various courts—was ever put to death because of his predictions.”

Although the first astronomical tables for calculating the positions of stars and planets arrived in Baghdad from Persia and India in the eighth century, the chief reference for Islamic astronomy was Ptolemy’s Almagest, or The Great Book, initially translated into Arabic by al-Hajjaj around 828. Contrary to a common misperception, the second-century scholar from Alexandria did not believe the Earth was flat. Like his Arab successors, however, he was convinced that the sun, moon and planets revolved in celestial spheres around the Earth. In an attempt to match this geocentric theory with the actual movement of heavenly bodies, Ptolemy posited an eccentric model that depended on off-center orbits that were “physically impossible,” according to Saliba of Columbia University. Struggling to reconcile the Greek universe with their own observations led a number of Islamic astronomers to challenge Ptolemy’s faulty concepts of celestial motion.

ong before Dan Brown’s Da Vinci Code popularized the Fibonacci sequence as an early clue to his murder mystery, the 13th-century Italian mathematician who gave his name to that number series was learning the principles of advanced arithmetic from Arab teachers in Bejaia, in present-day Algeria. In the Fibonacci sequence, every number after 0 and 1 is the sum of the previous two numbers, BIBLIOTHÈQUE DE LA FACULTÉ DE MÉDECINE / ARCHIVES CHARMET / BRIDGEMAN ART LIBRARY so that the sequence runs: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765, 10,946 and so on. The series appears in nature in many forms, including the spiral arrangements of sunflower seeds, pineapple fruitlets and pinecone scales; it appears in geometry, where, starting with the number 5, every other Fibonacci number is the length of the hypotenuse of a Pythagorean right triangle with integral sides; it recurs in mathematics, where the ratio between successive Fibonacci numbers approaches the classical “golden ratio” of 1:1.618033…. Like the Polish astronomer Copernicus and the Spanish physician Michael Servetus in the 16th century, Fibonacci, who was one of the founders of western mathematics, constructed a substantial portion of his pioneering scientific research on the foundations laid by his Arabic-speaking predecessors. Using Latin translations of Muhammad ibn Musa al-Khwarizmi’s treatises on algebra and algorithms, Fibonacci, also known as Leonard of Pisa, wrote the Liber abaci, the first widely available book on Arabic numerals and arithmetical problems, expanding Indian-based concepts that had arrived in Spain starting in the 10th century. On an expedition to Catalonia around 967 in search of unknown manuscripts, Gerbert, a Benedictine monk from Aurillac in Provence who later became Pope Sylvester II, came across Latin texts explaining Arabic numerals. He later taught about them, in Rheims and Rome, using a rudimentary abacus. From these modest beginnings, ancient Greek knowledge preserved in Arabic texts, as well as original Muslim science, was translated principally into Latin, Hebrew and Castilian Spanish to blossom gradually across Europe. In the courts of Toledo, Palermo and London, and the universities of Salerno, Padua, Paris and Oxford, a network of intellectual cross-pollination arose that spanned more than half a millennium, ushering in a European scientific renaissance. Translators such as Gerard of Cremona from Italy, Adelard of Bath from England, Constantine the African, who brought an entire library of Muslim medicine to Salerno, and Michael Scot, a Scotsman who studied in Spain and Sicily, crisscrossed Europe. These itinerant scholars disseminated critical Arab revisions of Greek learning and popularized the revolutionary innovations made by generations of Islamic astronomers, physicians, mathematicians and physicists. Roger Bacon, the 13th-century proponent of the experimental method, astronomers Tycho Brahe in the 16th century and Galileo in the 17th, English physician William Harvey, who formulated his theory of blood circulation on Arab models in the 17th century, and many others owe a direct debt to Muslim knowledge brought to the West in this period. Occasionally, there was a distinctly personal link between East and West. Journeying to Aleppo and elsewhere around the Middle East, the 17th-century Dutch Orientalist Jacobus Golius, who spoke and read Arabic, brought back the tracts of Alhazen. Since his son was secretary to Descartes in the Dutch city of Leiden, Golius excitedly showed his acquisitions to the exiled French mathematician, who incorporated the Muslim physicist’s findings on optics and geometry into his own writings, according to French science historian Roshdi Rashed. The transmission of Islamic science to Europe was not a fixed event like the delivery of a package whose contents launched the Renaissance. It was an ongoing, fluid exchange over time, a transfer that traveled in both directions, although it flowed mostly from East to West. Once Christian armies began to retake Spain in the 11th century and Crusaders returned from the Middle East over the course of the 12th and 13th centuries, western scholars began a dogged search for Arabic texts. Some key Arab and Persian documents, such as Alhazen’s Kitab al-Manazir (Book on Optics) and al-Khwarizmi’s Book on Indian Calculation, lost in their Arabic editions, have survived thanks only to Latin translations. “The translators were very important, but there was also a great deal of direct contact among the scientists themselves,” points out Rashed. “This explains why you find the same information in Arabic and Latin texts even though they are not exact translations; there was also verbal transmission of the knowledge.” The Castilian city of Toledo, which was reconquered by King Alfonso vi in 1085 after nearly four centuries of Arab rule, became a magnet for scholars intent on harvesting Arab and Greek science. According to science historian Ahmed Djebbar of the University of Lille, more than 100 major scientific and philosophical essays were translated in Toledo from Arabic into Latin and Hebrew between 1116 and 1187. In a typical example illustrating the cosmopolitan nature of this mountaintop city, the English philosopher Daniel of Morley recounts meeting the Italian linguist Gerard of Cremona near the banks of the Tagus River. The two foreigners were awestruck by the vestiges of several monumental water clocks built by Ibrahim ibn Yahya al-Zarqali (Azarchel in Latin) shortly before the city fell to Alfonso. By far the most prolific translator of the era, Gerard had left Italy chiefly in quest of Ptolemy’s Almagest, which existed only in Arabic and Syriac, a pre-Islamic language of ancient Syria. Uncovering an Arabic transcription in Toledo, he stayed there 30 years, making Latin translations of Ptolemy, Ibn Sina’s Canon, astronomical coordinates by al-Zarqali that became known as the “Toledan tables,” and al-Zahrawi’s manual on surgery, featuring a tonsillectomy technique as gruesome as it was efficacious. stiftung maximilianeum, munich / neue pinakothek Around the same time, Adelard of Bath, who had spent seven years traveling as far as Antioch seeking learning based on “reason rather than authority,” as he wrote in Quaestiones Naturales, returned to the court of English king Henry i. There he introduced Muslim research on trigonometry, botany, falconry and other subjects. Soaking up Muslim mathematics and astronomy in Córdoba and Toledo, his compatriot Daniel of Morley later lectured his Oxford students that they should “not despise the simple and clear opinions of the Arabs, but should note that Latin philosophers make heavy weather of these subjects quite unnecessarily.” Although Daniel of Morley’s books from Spain were destroyed in English religious wars, Oxford’s Bodleian Library later built up one of the most important collections of medieval Arabic manuscripts and 12th- and 13th-century Latin texts translated from Arabic sources. Landing in southern Italy around 1060 from Qayrawan, in today’s Tunisia, Constantine the African became a Benedictine monk at the abbey of Montecassino, 130 kilometers (80 miles) south of Rome. He transcribed numerous Arabic books, including Hunayn ibn Ishaq’s versions of discourses by Galen and Aristotle, Ibn Ishaq’s manual on ophthalmology and the physicians’ encyclopedia of Ali ibn Abbas al-Majusi. Rapidly adopted by doctors at Salerno’s medical school, Constantine’s translations eventually filtered into France, England and Germany. Even the Crusades failed to slow the pace of intellectual discourse—quite the contrary, argues Roshdi Rashed. “The Crusaders brought back a great deal of science, medicine, foods and so forth from the Middle East,” he explains. In the first half of the 13th century, in fact, the Arabic-speaking Holy Roman Emperor Frederick II maintained a thriving correspondence with Muslim philosophers and scientists from his court in Palermo, Sicily, and even during his occupation of Jerusalem. “When you consider the two sides were in the middle of fighting one another, this is fairly astonishing,” marvels Rashed. Frederick enthusiastically encouraged Muslim scientists, an enlightened policy of Arab–Christian cooperation begun by his grandfather, Roger II, who had sponsored the geographer Muhammad al-Idrisi. (See “The Third Dimension”.) In addition, Frederick financed translations of Arabic works, enlisting the services of Michael Scot, the astronomer-alchemist-wizard who later earned a place in Dante’s Inferno. Scot had achieved renown in Toledo for transcribing Nur al-Din ibn Ishaq al-Bitruji’s astronomical treatises on planetary motion and Averroes’ commentaries on Aristotle into Latin, according to French science historian Danielle Jacquart. Both texts represented heretical challenges to Catholic doctrine, and hiring such a subversive character no doubt contributed to the emperor’s ongoing problems with the church, which ultimately excommunicated Frederick II not once, but twice. Around 1277, Toledo again became the focus of Muslim science, as King Alfonso X commissioned the first renditions of Arabic texts into Castilian Spanish instead of Latin. Apart from sponsoring the Libros del saber de astronomía (The Books of Astronomical Knowledge), which incorporated Thabit ibn Qurra’s revision of the Almagest and translations of Abd al-Rahman al-Sufi’s Suwar al-kawakib al-thabit (Treatise on the Fixed Stars), Muhammad ibn Ahmad al-Biruni’s text on the spherical astrolabe and other Muslim texts, the king also promoted research into astrology, magic and philosophy.

The Syrian astronomer Muhammad ibn Jabir al-Battani, who worked in Raqqa from the late 10th century through the early 11th century, amended Ptolemy’s figures for the inclination of the Earth’s axis and was later praised by Copernicus as a source for his own heliocentric theory of the solar system. Around the same time, al-Biruni, who had been captured by Sultan Mahmud and hauled away to his court in Ghazni, in present-day Afghanistan, observed that the sun’s apogee, its highest point in the heavens, was mobile, not fixed, as Ptolemy had maintained. In his comprehensive encyclopedia of astronomy, Kitab al-qanun al-Mas’udi, or the Canon Mas’udicus, dedicated in 1031 to Mahmud’s son and successor, Mas’ud, al-Biruni also observed that the planets revolved in apparent elliptical orbits, instead of the circular orbits of the Greeks, although he failed to explain how they functioned. It was not until the 13th century that al-Tusi conceived a plausible model for elliptical orbits.

While parts of the Almagest underwent extensive revision by Arab and Persian scholars, much of this fundamental text was adopted intact. Commissioned by the Buwayid sultan Adud al-Dawla in Isfahan, the 10th-century astronomer Abd al-Rahman al-Sufi created a magnificently illustrated catalogue of the 1017 stars in 48 constellations enumerated by Ptolemy. It was a measure of the great value that medieval Muslim society placed on astronomy that this work was the first Islamic manuscript to contain figurative drawings. Al-Sufi’s elegant sketches in his Suwar al-kawakib al-thabit (Treatise on the Fixed Stars) are filled with whimsical lions, fanciful serpents and mythological characters representing constellations and zodiacal signs. Tracing the outline of Perseus (also called Farsawus, or Hamil Ra’s al-Ghul in Arabic) in red-painted stars, one dramatic scene depicts nearly identical facing images of the Greek hero, with Oriental features and flowing black hair, each brandishing a sword aloft and holding the head of a grimacing Medusa.

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While some astronomers devoted themselves to illustrating or improving Ptolemy’s science, others ventured forth on new tacks, designing more exact calendars, measuring eclipses and refining astronomical tables. In Cairo, the 10th-century scholar Ibn Yunus perfected tables used to calculate planetary motion to a number-crunching nine figures after the decimal point.

Three centuries later in Baghdad, the Persian polymath Zakariya al-Qazwini, a doctor, jurist, geographer and amateur astronomer, issued the first cosmography in the Muslim realm. This “layman’s guide to the universe” covered everything celestial—solar cycles, weather forecasting and ruminations on the comportment of angels—and terrestrial, with fanciful illustrations depicting animal, vegetal and mineral kingdoms. Some editions of his 1270 Kitab aja’ib al-makhluqat wa ghara’ib al-mawjudat (Book of Marvelous Creatures and Rare Things) contain movable paper levers with the sun at one end and the moon at the other, pivoting on the Earth in the center to demonstrate how the Earth casts a shadow on the moon during a lunar eclipse—“the first interactive book,” writes Parisian historian Danielle Jacquart.

One of the most forward-thinking scientific geniuses of the age was the astronomer-mathematician-theologian-physician al-Tusi. He was a Benjamin Franklin figure who persuaded the 13th-century Mongol conqueror Hulagu Khan to finance a boldly experimental observatory in the northwest Persian city of Maragha. Staffed by the most experienced astronomers in the empire, the new observatory set about educating a rising generation of stargazers. It was here that the scholar from Khorasan, who wrote more than 100 works of science, philosophy and poetry, contrived an ingenious model of heavenly motion that came tantalizingly close to explaining away the inconsistencies in Ptolemy’s theories.

“Al-Tusi’s couple” consists of one large circle representing the orbit of the moon and, inside it, a smaller circle, half the radius of the larger circle, that represents the orbit of a planet. Both circles, the “couple,” revolve in tandem around the Earth. As the couple orbits the Earth, the moon rotates in the same direction on its own orbit and the planet spins twice as fast on its inside orbit in the opposite direction. Using this model, both the moon and the planet appear to revolve around the Earth in elliptical orbits with oscillating centers. In this mind-bending way, al-Tusi tried to reconcile the irregular movements of the sun, moon and planets, yet preserve Ptolemy’s geocentric circular orbits.

Although Maragha, with its library and copper foundry for manufacturing astronomical tools, constituted one of the first astronomy schools in Islamic civilization, the observatory at Samarkand, inaugurated a century and a half later in 1420 by the ruler Ulugh Beg, the grandson of Timur (Tamerlane), was positively palatial. With its three-story tower 48 meters (156') in diameter, encircled by dozens of lofty arched niches decorated with blue, gold and green faience tiles, the observatory prided itself on its giant sextant—two stone circles dug 20 meters (66') into the ground that were used to gauge the height of the sun and the stars.

Here, more was definitely more, and size mattered enormously. “[The astronomers] considered that the instruments of grand dimension were the best adapted [for their work] for the simple reason that they allowed them to obtain more precise measurements,” writes Saliba in the catalog for the Arab science exhibition at the Arab World Institute. The celebrated Persian scholar Ghiyath al-Kashi (1380–1429), reputed for calculating the value of pi to 17 decimal points, was so impressed by their scale that he penned a letter to his father describing the techniques and materials employed to produce bigger—and presumably more exact—astronomical equipment.

After Maragha and Samarkand, another major observatory was built near the present-day site of Taksim Square in Istanbul around 1576, supplanting an earlier installation in the Galata Tower financed by Süleyman the Magnificent in 1557. Coming from Cairo, Taqi al-Din persuaded Sultan Murad III to found the best-equipped facility in the Muslim world. Some of the observatory’s exceptional instruments are depicted in a vivid painting from the manuscript Sama’ilnama in the library of Istanbul University. Here, 16 astronomers sporting flamboyant white turbans engage in animated discussion as they demonstrate astronomical clocks, updated globes and newfangled compasses (one shaped like a stick tripod as big as a man) to enhance star readings.

Unfortunately, Taqi al-Din’s success goaded jealous rivals to convince the sultan that the observatory was intended for un-Islamic astrology, not astronomy, according to Turkish-born Fuat Sezgin, director of the Institute for the History of Arabic-Islamic Sciences at the Goethe University in Frankfurt. Other scholars maintain that Taqi al-Din incurred the sultan’s wrath when the man of science tried to play fortuneteller, interpreting a comet’s passage as an omen of Ottoman victory over the Persians. (The Turks won the battle, but suffered a devastating plague and other setbacks that were blamed on the comet.) In any event, Murad ordered the magnificent edifice destroyed in 1580, dealing a significant blow to Islamic astronomy and helping to usher in a period of stagnation across all the sciences, says Sezgin. (See “The Third Dimension”).

Like astronomy, which evolved from the practical necessities of finding the directions and hours for prayers, Islamic mathematics was very much a hands-on affair at the beginning, a product of the marketplace and of the need for pragmatic legal precedents. Both algebra and the use of zero had the same end in mind—streamlining computations for business deals. Al-Khwarizmi had a hand in the development of both.

In his Kitab al-jabr (Book of Algebra)— the word comes from the Arabic word jabara, “to restore”—the Baghdad mathematician spells out his no-nonsense intent: “It’s a summary encompassing the finest and most noble operations for calculations which men may require for inheritances and donations, for shares and judgments, for commerce and all sorts of transactions that they have among them such as surveying tracts of land, digging canals and other aspects and techniques.”

In another treatise, the Book on Indian Calculation, which was lost in the Arabic original and only survived due to its Latin translation, al-Khwarizmi introduces the nine integers borrowed from the Indian system (1 through 9) and explains how zeroes are used to create multiples of ten, a hundred, a thousand and so on. Unlike archaic numerical systems, which were based on multiples of five, 12 or even 60, or cumbersome Roman numerals, the Indian–Arabic decimal system made arithmetic vastly simpler and more rapid.

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Using the geometry of Euclid and Apollonius as starting points, Muslim mathematicians went much farther than their Greek predecessors. While al-Biruni promulgated the first book on trigonometry in the 10th century, it was not until the 13th century that the Maragha astronomer al-Tusi developed trigonometry into a separate discipline. After absorbing Apollonius’ book on conic sections such as circles, parabolas, ellipses and hyperbolas, and deliberating over what was contained in the lost eighth chapter, Alhazen, the inventor of the camera obscura, proposed his own version of the book’s ending, adding solutions for computing the volume of a three-dimensional parabolic shape.

In 10th-century Baghdad, the mathematician-astronomer Abu Sahl al-Quhi formulated a life-saving use of trigonometry by employing it to determine the height and position of lighthouses and to gauge distances of ships at sea from hidden shoals. The resourceful scholar also invented the so-called “perfect compass,” a hand-held mechanical tool with an adjustable arm pivoting around a fixed arm, to trace ellipses and other conic sections.

Enlarging on Indian notions of the sine (the ratio of the length of the side of a right triangle opposite an acute angle to the length of the hypotenuse), the ninth-century mathematician Habash al-Hasin developed the concept of tangents (straight lines and planes touching arcs, circles and conic sections) to facilitate geometrical calculations.

When the multi-talented 11th-century Persian poet Omar Khayyam was not rhapsodizing in The Rubaiyat and other verse, he kept busy revising solar calendars for the Seljuk sultan Jalal al-Din and drafting geometrical proofs for cubic equations by intersecting parabolas with circles. The mathematical bard also circulated a visionary critique of Euclid’s theories on parallel lines that prefigured non-Euclidean geometry, to come some 800 years later.

In several other areas, Arab mathematicians were centuries ahead of European theorists. The 13th-century scholar Ibn Munim from Marrakech used Khayyam’s earlier studies to plot a triangular numerical grid that allowed him to figure permutations and combinations. This exercise yields, for example, the maximum number of words that can be created with the 28 letters of the Arabic alphabet. Four hundred years later, the 17th-century French mathematician Blaise Pascal reinvented Ibn Munim’s numerical grid.

The famous last theorem by Pascal’s colleague, Pierre de Fermat, offers another example of Muslim scholars presaging European discoveries. Some 600 years before Fermat posited his mathematical riddle—that there are no non-zero integers x, y and z such that xn + yn = zn where n is an integer greater than 2—Muslim scientists Alhazen, al-Sizji, al-Khazin and others were grappling with a similar conundrum. Fermat’s enigma would remain unsolved until 1994, when British mathematician Andrew Wiles at last provided a definitive proof.

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While Islamic mathematicians outstripped their Greek and Indian predecessors, Muslim doctors used Hippocrates and Galen as springboards for their own expanded findings about medicine and anatomy. In his seminal Canon, Ibn Sina expanded on Hippocrates’ influential fifth-century BC work, Airs, Waters, Places, by enumerating the effects that clean air and water and salubrious mountain and coastal environments have on health. Some Arab critiques of Greek physicians were pointedly specific. Writing about a famine in Egypt around 1200, Abd al-Latif al-Baghdadi recounts his observations of the skeletons of starvation victims, noting that the lower jaw consisted of a single bone, instead of two articulated bones, as Galen had wrongly concluded. Neither Galen nor al-Baghdadi was able to dissect human bodies, due to religious taboos that lasted until the 17th century.

Even before the consolidation of the Islamic empire, the Arabs sought to raise the abysmal standards of public health, with the first Muslim hospital opening in Damascus in 706. “One of the great successes of Arabic medicine was the organization of hospitals at a level that far surpassed Greek, Roman or Persian models,” says Djebbar.

Beginning in the late eighth century when Caliph Harun al-Rashid established a Baghdad hospital, doctors made daily rounds with their students, setting a precedent used in medical schools ever since. Typically, there was one courtyard wing for physically ill patients, another for those with moderate mental health problems and a third for those suffering from more severe psychological disorders. “In addition to music therapy, the courtyards all had fountains, trees and warbling birds so that the sounds of nature were part of the healing process,” notes the Lille professor.

A handful of institutions boasted incredibly luxurious circumstances. According to Ahmed Issa Bey in his 1928 book The History of Hospitals in Islam, the 12th-century Almohad ruler Abu Yusuf Ya’qub al-Mansur provided the fortunate patients of his Marrakech facility with running water in every room, wool blankets, silk sheets, free medicines and 30 dinars a day for food and other necessities. When indigent patients got well enough to leave, they received a small sum of money to ease their reentry into working society.

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A few of these medieval hospital buildings still exist intact, even though they now serve different purposes. Aleppo’s 14th-century Argun Maristan is a dramatic backdrop for folk dance, and a 12th-century stone hospital in Damascus houses the National Museum of Arabic Medicine and Science. Cairo’s Qalawun hospital, which treated some 4000 patients a day when it was constructed in the 13th century and accommodated lecture halls, a mosque and doctors’ residences, is currently one of the top ophthalmology clinics in Egypt.

Although physicians had to be certified, scores of uncertified barbers and itinerant surgeons practiced bloodletting, tooth extraction and more dangerous operations with few anesthetics or antiseptics. Surgery was so chancy in the 10th century that even the adventurous doctor Rhazes refused to allow ophthalmologists to remove his cataracts. But by the 14th century, the situation had improved dramatically. Persian surgeon Mansur ibn Ilyas produced sophisticated anatomical drawings tracing nerves, veins, arteries, muscles and complex organs like the heart and brain that aided him immensely in conducting effective operations.

Al-Zahrawi and other healers sang the praises of herbal cures, recommending the duhn, or oil, of laurel, wheat, sweet and bitter almonds, mustard and other plants. Wild mint purportedly relieved fatigue when used as a compress and drove out colds if taken as nose drops. “It will also cure the sting of a scorpion,” the 10th-century Córdoban doctor promised patients. One look at the fearsome arsenal of surgical tools in al-Zahrawi’s Al-Tasrif made quick converts to less intrusive herbal nostrums.

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Chemistry, a word derived from the Arabic al-kimya, was vigorously promoted, fostering a rigorous routine of trial-and-error experimentation that did not become widespread in Europe until the 18th century with Joseph Priestley, Antoine Lavoisier and other empirical researchers. According to the 10th-century bibliographer Ibn al-Nadim, Arab chemists manufactured waterproof fabrics, invisible inks and mosquito repellents. Around the same time, the Fatimid caliph al-Mu’izz designed a primitive pen with a self-contained ink cartridge nearly nine centuries before the Romanian student Petrache Poenaru invented the fountain pen in Paris in 1827.

The distillation of rosewater and other perfumes evolved into a Muslim specialty, with scents used medicinally to treat migraines, epilepsy and melancholy. In Kitab kimya al-’utoor w’ al-tas’idat (Book of the Chemistry of Perfumes and Distillations), the ninth-century scientist Abu Yusuf al-Kindi lists formulas for preparing some 107 perfumes.

In his survey of optics, the 10th-century Baghdad scholar Ibn Sahl observed that light passing through crystals, water and other translucent substances slows down and is bent at different angles according to the density of the material—the basic principle of refraction. According to Rashed, this was reformulated in the 17th century by Dutch scholar Willebrord van Roijen Snell and French mathematician René Descartes as the Snell-Descartes law, or the law of sines. In the early 14th century, more than 300 years after Ibn Sahl, Maragha astronomer-mathematician Kamal al-Din al-Farisi experimented with a glass sphere filled with water to analyze the way sunlight breaks into the spectrum colors of a rainbow.

The 12th-century Persian physicist Abdur Rahman al-Hazini incorporated Archimedes’ findings on the density, buoyancy and specific gravity of objects to perfect “the balance of wisdom,” an ingenious scale that resembled a miniature Calder mobile. Originally invented by Abu Hatim al-Isfizari, the device consisted of five hanging trays, one of which was immersed in water to verify precise amounts of gold, silver and other precious metals in coins, jewelry and other materials.

Even as gold and silver mining expanded, the fabrication of artificial rubies, sapphires and other gems grew into a lucrative industry. Poring over the works of Egyptian and Greek alchemists, a handful of Muslim scientists employed their expertise in minerals to dabble in the elusive quest for an elixir, a magical “philosopher’s stone,” capable of transforming lead to gold. All failed, of course. The eighth-century Persian scientist Jabir ibn Hayyan (Geber in the West), however, turned these experimental dead ends to advantage, concocting an array of previously unknown compounds, including sulfuric acid, caustic soda and nitric oxide, Djebbar explains.

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Far more useful than the alchemists’ hunt for gold were al-Biruni’s pioneering treatises on mineralogy and geology. In one work, the Persian scholar, who spent much of his career in Ghazni in Afghanistan, asserted that the desert was once covered by the sea. He supported this controversial thesis with detailed descriptions of perfectly preserved fossils of fish and other aquatic creatures, paving the way for paleontology.

Despite centuries of innovation, Islamic science ultimately went into an irreversible decline with the eclipse of Arab political and economic power, marked in the West by the fall of Granada in 1492 to the Castilian monarchs Ferdinand and Isabella, and in the East by the muscular expansion of the Ottoman Empire in the 16th century under Süleyman the Magnificent. But this slide into decadence was a slow process.

Surprisingly, perhaps, the Crusades in the 12th and 13th centuries did more to energize Muslim science than retard it, according to Rashed. (See “Lines of Transmission”). “The Crusades encouraged Muslims & to find out the secrets of their enemies’ forces,” he contends.

The first crippling blow to Islamic science occurred with the Mongol invasions, culminating in the devastating sack of Baghdad in 1258, when two million Muslims were massacred, libraries, laboratories, hospitals and the landmark House of Wisdom were destroyed, and the Tigris ran red with the blood of scholars and black with the ink of their books. “Even after the Mongol invasions, there was still a substantial amount of scientific investigation,” Rashed observes, “but scholars had to spend more time and energy preserving knowledge instead of pushing ahead with new explorations.”

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Another long-term reversal began in the 15th century, as Portuguese and Spanish navigators in heavily armed vessels exploited sea-trade routes between East and West. The slow-moving caravans of the Silk Road were gradually abandoned, breaking the Arab monopoly on commerce with the Orient and further undermining scientific progress, according to Rashed.

“Arabic science had arrived at a critical turning point where a cognitive revolution was needed in order to continue,” the French science historian explains. In mathematics, for example, complex equations became so cumbersome they required 50 pages to articulate. “Creating new symbols to condense these equations required a conceptual leap that’s possible in a society in expansion, but not in a society in decline,” says Rashed.

With the rise of Ottoman hegemony, the heyday of Islamic science drew to a close, he argues, since Turkish rulers were far more interested in pursuing military goals and piling up layers of bureaucracy than in encouraging research.

But the lessons of Islamic science have yet to be fully appreciated, even in the Arab world, Audouze maintains, where the unprecedented accomplishments of generations of medieval scholars should inspire contemporary Muslims to rebuild the foundations for a new round of discoveries.

“Science only develops in cultivated societies where the economy and commerce are in good health,” says the French astrophysicist. “And it creates a virtuous circle where the economy favors science which in turn generates profits and wealth of all kinds, spiritual as well as material.”