Cairo emerged as an Islamic cultural center soon after its founding in 969 as the new capital of the Fatimids, the dynasty that for the next two centuries ruled North Africa, Egypt, and Syria. Under the caliphs al-Mu'izz (r. 969-75), al-Aziz (r. 975-96), and al-Hakim (r. 996-1021), the Fatimid caliphate in Egypt became the most powerful Islamic state in the world, with Cairo rivaling Baghdad in its splendor.
The enduring symbol of the Fatimid dynasty is the great mosque of al-Azhar, completed in 972 by al-Mu'izz, which became the first Islamic university, still functioning today. The emergence of Cairo as a cultural center was due to al-Hakim, founder of the Dar al-‘Ilm, the House of Science, a library whose fame was surpassed only by Baghdad's Bayt al-Hikma, the House of Wisdom. According to the fifteenth-century Egyptian historian al-Maqrizi, the Cairo library had forty rooms. Its collection included eighteen thousand manuscripts dealing with the “Science of the Ancients.” Like the ancient Library of Alexandria, the Fatimid Dar al-‘Ilm was also a research center and institute of higher learning, its staff including mathematicians, astronomers, and physicians as well as librarians, grammarians, lexicographers, copyists, and readers of the Koran.
The first of the great Islamic scientists to emerge in Fatimid Cairo was the astronomer Abd al-Rahman ibn Yunus (d. 1009). Ibn Yunus was born in Fustat, the predecessor of Cairo, and he witnessed the Fatimid conquest of Egypt as well as the founding of the new capital. He began his astronomical observations in 977, two years after al-Aziz became caliph. When al-Hakim succeeded to the caliphate in 996, at the age of eleven, his keen interest in astrology led him to sponsor Ibn Yunus, who continued his observations until 1003. Ibn Yunus spent the remaining six years of his life completing the Hakimid Tables, dedicated to Caliph al-Hakim. These are generally considered to be the most accurate astronomical tables compiled in Islamic science, and their illustrated manuscripts have been compared to those of al-Sufi in their beauty.
Ibn Yunus was also a famous astrologer. The astrological predictions in his treatise On the Attainment of Desire are based on the heliacal risings of Sirius (i.e., just before the sun) when the moon is in each of the twelve signs of the zodiac, as well as on the day of the week the Coptic year begins.
A biography of Ibn Yunus by his contemporary al-Musabbihi has been preserved in the works of later writers. This biography reveals that Ibn Yunus was an eccentric who paid no attention to his personal appearance; he was considered a comic figure in Cairo. One day, while in apparent good health, he announced that he would die seven days later, whereupon he locked himself in his house and put his manuscripts in order. He then recited the Koran continuously until he died, passing away on the very day that he had predicted, after which his son sold his manuscripts by the pound in the Cairo soap market.
The most renowned of all the scientists who worked in Fatimid Cairo was Abu Ali al-Hasan ibn al-Haytham (ca. 965-ca. 1041), known in the West as Alhazen. Ibn al-Haytham was born in Basra, in Iraq, where he studied mathematics and science before going to Egypt.
Several of his biographers differ about the details of Ibn al-Haytham's life after his departure from Basra. Ibn al-Qifti (d. 1248) says that Ibn al-Haytham went from Iraq to Egypt during the reign of Caliph al-Hakim, to whom he had proposed a construction that would regulate the flow of the Nile. When Ibn al-Haytham arrived in Egypt he was deeply impressed by the many ancient structures along the Nile, and he realized that if a river-control project were at all possible the ancient Egyptians would have put it into effect long ago. He admitted this when he met with al-Hakim, who nevertheless offered him a position in some government office. Ibn al-Haytham accepted the post for fear of offending the caliph, a bloodthirsty tyrant who had executed many of his advisers and commanders. But he sought to avoid dealing with al-Hakim by pretending to be insane, whereupon he was confined to his house and remained there until 1021, when the caliph disappeared one day, riding off into the desert, never to be seen again. Ibn al-Haytham then put aside his pretense of madness and took up residence near the Al-Azhar Mosque, teaching and copying Euclid's Elements and Ptolemy's Almagest, which supported him while he worked on his researches.
According to another of his biographers, Ibn Abi Usaybi (d. 1227), Ibn al-Haytham in his later years decided to ignore the rest of humanity and devote himself to seeking the truth as the surest way of gaining favor with God, a decision he attributed to his “good fortune, or a divine inspiration, or a kind of madness.” His first studies were in theology, but he was so frustrated by this that he became convinced that truth was to be found only in “doctrines whose matter was sensible and whose form was rational.” He concluded that such doctrines were to be found in the writings of Aristotle and in works on mathematics, physics, and metaphysics. Ibn Abi Usaybi gives a list of Ibn al-Haytham's works up to 2 October 1038, about three years before his death, consisting of ninety-two titles, including all fifty-five of his extant works. But even that list may not be complete, since Ibn al-Qifti states that he owned a book on geometry in Ibn al-Haytham's own hand dated a.h. 432, or A.D. 1040-1041, probably completed not long before he died.
Ibn al-Haytham's works on logic, ethics, politics, poetry, music, and theology have not survived, nor have his summaries of the writings of Aristotle and Galen. His extant works are in the fields where he is generally agreed to have made his most significant and enduring contributions: astronomy, mathematics, and, particularly, optics.
Ibn al-Haytham's masterpiece is his Book of Optics, which is considered one of the most important and influential works ever produced in Islamic science, representing a definite advance beyond what had been achieved by the ancient Greeks in their study of light. The Optics was translated into Latin in the late twelfth or early thirteenth century, under the title Perspectiva The Perspectiva was the subject of studies and commentaries in Europe until the seventeenth century, stimulating the study of optics in the Latin West.
Book I of the Optics presents Ibn al-Haytham's general theory of light and vision. His theory involved “visual rays” projected in straight lines from each point on the surface of a luminous body to a corresponding point on the pupils of the eyes, which act as lenses, from where the optic nerves transmit the “distinct form” of the object to the brain so as to form an image. Book II contains his theory of cognition based on visual perception, which influenced Western philosophers in the fourteenth century. Book III is concerned with binocular vision and with aberrations such as diplopia, or double vision. The next three books deal with catoptrics, phenomena involving reflection, which had been studied by Ptolemy, though not in such exhaustive detail as by Ibn al-Haytham.
The seventh and final book of the Optics is devoted to dioptrics, phenomena involving refraction, which also had been studied by Ptolemy. Ibn al-Haytham gives a detailed description of his improved version of Ptolemy's instrument for measuring refraction, which he used to study the bending of light at plane and spherical surfaces with air-water, air-glass, and water-glass interfaces. He summarized the results of his experiments in a set of eight rules for the relation between the angles made by the incident and refracted rays with the normal, or perpendicular to the surface. The last two rules stated that a denser refractive medium bends the light more toward the normal, while a rarer medium bends it away. Ibn al-Haytham was aware, as Ptolemy had been, that these two rules arose from the fact that the velocity of light is greater in the rarer medium than in the denser one. Ibn al-Haytham's theory introduced a new method, that of resolving the velocity of light into two independent components, one along the normal and the other perpendicular to it, where the first component changed in the refraction while the second remained constant. This approach, called the “parallelogram method,” was used by a number of European physicists from the thirteenth century onward, in the study of both light and motion.
Ibn al-Haytham refers to the work of an older contemporary named Abu Sa'd al ‘Ala ibn Sahl, who is the author of a recently discovered treatise on optics dated 983-85. It is evident from this treatise, and from the reference to him by Ibn al-Haytham, that Ibn Sahl correctly stated the law of refraction, which was not discovered in Europe until the seventeenth century. Although Ibn al-Haytham was aware of Ibn Sahl's discovery, he did not use it in his own study of refraction.
Besides the Optics, the extant writings of Ibn al-Haytham include nine minor works on light: The Light of the Moon, The Halo and the Rainbow, On Spherical Burning Mirrors, The Formation of Shadows, The Light of the Stars, Discourse on Light, The Burning Sphere, The Solar Rays, and The Shape of the Eclipse The last work is of particular interest because it describes the camera obscura, or pinhole camera, the first appearance of the device that eventually led to the development of photography.
The extant writings of Ibn al-Haytham also include twenty works on astronomy. The most popular of these was the treatise On the Configuration of the World, which was translated into Spanish, Hebrew, and Latin. His aim in this work was to give a physical model of the Ptolemaic astronomical system rather than a mathematical theory, one that would be “more truly descriptive of the existing state of affairs and more obvious to the understanding.” The model that he chose was that of the homo-centric spheres of Eudoxus, which he described fully and clearly without going into unnecessary technical detail, which may be why this work was so popular.
Another of Ibn al-Haytham's extant astronomical writings, known in its Latin translation as Dubitationes in Ptolemaeum, is a critique of three of Ptolemy's works: the Almagest, the Planetary Hypotheses, and the Optics So far as the Almagest was concerned, Ibn al-Haytham's main objection was to the equant, which merely disguised the fact that the planets in Ptolemy's model did not move with uniform velocity around the earth as a center
Ibn al-Haytham's fame as a mathematician stems largely from his solution to the so-called Alhazen's problem in Book V of his Optics That is, from two points outside a circle and in its plane, to draw lines meeting at the circumference and making equal angles with the surface normal, or perpendicular, at that point. This leads to a fourth-degree equation, which Ibn al-Haytham solved by finding the intersection points of a circle and a hyperbola.
Aside from the mathematical analysis in the Optics, a score of Ibn al-Haytham's writings exclusively on mathematics have survived, most of them brief and varying considerably in importance. One of the longest and most important of these works is entitledSolution of the Difficulties in Euclid's Elements. Here he tried to prove Euclid's fifth postulate, defining parallel lines, one of several such attempts by Islamic mathematicians. Another of his longer mathematical works, On Analysis and Synthesis, was written to explain the methods necessary for finding and proving theorems and constructions by illustrating their applications in arithmetic, geometry, astronomy, and music; this work placed particular emphasis on the role of “scientific intuition.”
The Fatimid dynasty came to an end in 1171 when Cairo was conquered by the great Kurdish warrior Salah al-Din ibn Ayyub, known in the West as Saladin, founder of the Ayyubid dynasty. Saladin (r. 1171-93) refortified Cairo, building an imposing citadel that still stands, along with the defense walls that enclosed the inner city in his time. Using Egypt as his power base, Saladin went on to conquer Syria and Mesopotamia, defeating the Crusaders at the Battle of Hattin in 1187 and reconquering Jerusalem for Islam.
The leading intellectual figure in Cairo at the beginning of the Ayyubid period was the Jewish philosopher Rabbi Moses ben Maimon, better known in the West as Maimonides (1135-1204). He was born in Cordoba; his family then moved to the Moroccan city of Fez, where he received most of his secular education, studying philosophy, law, and medicine at the Muslim university. In 1166 he settled in Egypt, first in Alexandria and then at Fustat in Cairo, where he became judge and unofficial head of the Jewish community.
After the establishment of the Ayyubid dynasty in 1171, Maimonides became the personal physician to Saladin's vizier, Al-Fadr al-Baisami, and later to Saladin's son and successor, Sultan al Aziz (r. 1193-98). At the same time he also tended the sick in Cairo, both Muslims and Jews. Besides his judicial and medical duties, Maimonides spent all of his spare time studying and writing, as he had since his earliest youth.
Maimonides was only fifteen when he finished his first book, A Treatise on Logic This was done in Arabic, as were all of his other books except his Mishnah Torah, a codification of the Talmudic law in fourteen volumes written in Hebrew, which took him ten years and was completed in 1180. His earlier books include the astronomical work entitled Treatise on the Calendar (1158) and his Commentary on the Mishnah (1168). The latter work, besides its discussion of Talmudic law, also contains considerable material on scientific subjects such as zoology, botany, and natural history, as well as psychology.
Maimonides began work in 1185 on what proved to be his masterpiece, The Guide of the Perplexed, an explanation of the fundamental theology and philosophy of Judaism, which he finished about five years later. Here Maimonides notes that his purpose is to show that rational philosophy does not contradict Jewish beliefs but, rather, helps a man attain the ultimate state of happiness, which is the perfection of his intellect so that he can contemplate the divine.
His many letters reveal the admiration Maimonides had for both ancient Greek and medieval Islamic philosophers, particularly Aristotle, Plato, al-Farabi, Ibn Sina, and Ibn Bajja, an Andalusian scientist. He accepted Aristotelian physics for the terrestrial world, though not for the celestial realm, which he thought might be beyond human understanding. An even more difficult problem for him was the obvious contradiction between the Aristotelian astronomical model of the homocentric spheres and the mathematical Ptolemaic theory of epicycles, eccentrics, deferents, and equants, and in his own thinking he did not accept any of the attempts by Islamic philosophers and astronomers that sought to resolve these questions.
Two Hebrew translations of The Guide of the Perplexed were done shortly after it was written, one by Samuel ibn Tibbon and the other by al-Harizi. During the next three centuries the Guide played a central role in Jewish philosophical discussions, with the followers of Maimonides vigorously defending his ideas against his detractors, some of whom wanted his books banned.
The Guide of the Perplexed was translated into Latin in the thirteenth century and exerted a significant influence on the so-called Scholastic philosophy that was developing at that time, as is evident in the works of Saint Thomas Aquinas. The Guide was still influential in western Europe as late as the time of Spinoza (1632-1677), who, although he severely criticized Maimonides, agreed with his idea that perfect world peace could be achieved through reason, for this was how Spinoza thought the messianic age would emerge.
Maimonides also wrote extensively on medicine, particularly on diet, psychological treatment, and the use of drugs, and ten of his medical works have survived. He acknowledged his debt to Galen, as did all medieval physicians. Nevertheless, in one of his medical works, Moses’ Chapters on Medicine, he listed forty contradictions in the writings of Galen, whom he also criticized for being ignorant in philosophy and theology.
Arabic sources rank Maimonides as one of the greatest physicians of all time, particularly because of his skill in treating psychosomatic problems. As an Arabic verse said in his praise, “Galen's medicine is only for the body, but that of [Maimonides] is for both body and soul.”
Maimonides was not the only scholar to move across the Islamic world from west to east. The pharmacologist and botanist Ibn al-Baytar (ca. 1190-1248) was born in Malaga and studied in Seville, then moved to Cairo; he died in Damascus. While in Cairo Ibn al-Baytar served as chief herbalist under the Ayyubid sultan al-Kamil (r. 1218-38) and his son and successor al-Salih (r. 1240-49).
Ibn al-Baytar's work in pharmacology is based on the writings of Dioscorides and Galen as well as those of his Arabic predecessors. His two best-known works are Al-Mughni, which describes simple medicines used for various illnesses, and Al-Jami, an alphabetical list of some fourteen hundred medicines based on his own researches as well as those of his Greek and Arabic predecessors. Ibn al-Baytar's main contribution was his systemization of the researches of Arabic scientists, who added between three and four hundred medicines to the thousand or so known since antiquity. His Al-Jami had considerable influence in the East, among both Muslims and Christians, for it was translated from Arabic into Armenian; but it was little known in the West.
The Ayyubid dynasty lasted until 1250, when the last sultan of that line was overthrown by the Mamluks, Turkish slaves who had come to dominate the Egyptian army. Eight years later the Mamluk general Bay-bars routed the Mongols in a great battle in Syria, the first major defeat suffered by the central Asian nomads, who then retreated into Anatolia and never again directly threatened Egypt. On his return to Egypt Bay-bars murdered Sultan Qutuz and usurped the throne, beginning one of the longest and most illustrious reigns (1260-76) in the history of the Mamluk dynasty, which lasted until it was annihilated by the Ottoman Turks in 1517.
The court physician during the reign of Sultan Baybars was Ala al-Din ibn al-Nafis (ca. 1208-1288), who was born in Transoxiana and studied medicine in Damascus. Besides being a physician, Ibn al-Nafis also lectured on jurisprudence at the al-Masruriyya School in Cairo. His importance as a physician, which led Muslims to call him the “second Ibn Sina,” was not fully recognized by Western historians, for many of his medical writings were unknown until quite recent times. His Comprehensive Book on the Art of Medicine, in eighty volumes, which he wrote in his thirties, was thought to have been lost until 1952, when one fragmentary volume was found in the Cambridge University Library; three other volumes of this work were subsequently discovered in the medical library at Stanford University, one of them dated 1243-44. One of the interesting sections in these fragmentary remains concerns the surgical techniques used by Ibn al-Nafis, which he describes in minute detail, with examples of specific operations as well as discussions concerning the duties of surgeons and the relationships among doctors, nurses, and patients.
The fame of Ibn al-Nafis stems from his discovery of the so-called minor circulation of the blood—that between the heart and lungs. The fact that he had made this discovery was not known until 1924, when the Egyptian physician Dr. Muhyo al-Deen Altawi discovered a manuscript, The Epitome of the Canon, an introduction to the work of Ibn Sina in which Ibn al-Nafis first describes the minor circulation of the blood.
It is possible that European physicians first learned of the minor circulation through a translation of the work of Ibn al-Nafis by Andrea Alpago of Belluno (d. 1520). The first European to write about the minor circulation was Michael Servetus (ca. 1510-1553), an Aragonese physician and theologian, who was condemned by Calvin for his unorthodox religious opinions and burned at the stake in Geneva. The definitive theory of blood circulation was finally given by the English physician William Harvey (1578-1657) in hisExercitatio Anatomica de Motu Cortis et Sanguinis, published in 1628, which is generally considered to mark the beginning of modern medicine.
Ibn al-Nafis was followed by his student Ibn al-Quff, who won renown as a surgeon and medical writer, his best-known treatise being The Basic Work Concerning the Art of Surgery Ibn al-Quff is credited with being the first to suggest the existence of capillaries in blood circulation. The first European scientist to make this discovery was Marcello Malpighi of Bologna (1628-1694), who in 1661 used a microscope to detect capillaries and explain their role in circulating blood between the arteries and veins.
During the Mamluk period Damascus was the second city of the empire, and in the latter half of the fourteenth century it rivaled and even surpassed Cairo as a center of science, producing one of the most outstanding astronomers in the history of Islamic science, Ibn al-Shatir (ca. 1305-ca. 1375).
Ibn al-Shatir is believed to have been born in Damascus in around 1305. His father died when he was six and he was then brought up by his grandfather, who taught him the craft of inlaying ivory. When he was about ten he traveled to Cairo to study astronomy, in the course of which he was inspired by the work of Abu ‘Ali al-Marrakushi, who had, circa 1280, written a compendium of mathematical astronomy and mathematical instruments.
After the completion of his studies Ibn al-Shatir returned to Damascus, where he was appointed chief astronomer of the Umayyad Mosque. His principal duties were to determine the exact times for the five daily occasions of prayer, as well as the dates when the holy month of Ramadan began and ended; he also constructed astronomical instruments and made observations and calculations to compile astronomical tables.
Ibn al-Shatir's first set of tables, which have not survived, apparently used his observations together with the standard Ptolemaic model to compute the entries for the sun, moon, and planets. But in a later work, entitled The Final Quest Concerning the Rectification of Principles, he developed an original planetary model significantly different from that of Ptolemy, which he then used to produce a new set of tables in a work called al-Zij al-Jadid (The New Planetary Handbook). His preface tells of how he came to write this work after reading the books of earlier Islamic astronomers, who, while expressing doubts about the Ptolemaic planetary model, were unable to formulate an alternative theory.
I therefore asked Almighty God to give me inspiration and help me to invent models that would achieve what was required, and God—may He be praised and exalted, all praise and gratitude to Him—did enable me to devise universal models for the planetary models in longitude and latitude and all other observable features of their motions, models that were free—thank God—from the doubts surrounding previous models.
Ibn al-Shatir's new planetary model used secondary epicycles rather than the equants, eccentric deferents, and epicycles employed by Ptolemy, his motive being to have the planets moving in orbits composed of uniform circular motions rather than to improve the agreement of his theory with observation. His model had no advantage over the Ptolemaic theory so far as the sun was concerned, but in the case of the moon it was clearly superior.
There is no evidence that any Arabic astronomer after Ibn al-Shatir formulated a new astronomical theory differing from the Ptolemaic model. His al-Zij al-Jadid continued to be referred to in Damascus for several centuries, and it was the subject of commentaries and revisions, one of which adapted it for use in Cairo. The latter was so popular that a commentary on it was published in Cairo in the mid-nineteenth century. Studies by historians of science beginning in 1957 have shown that the lunar model used by Ibn al-Shatir was essentially the same as the one employed by Copernicus in 1543, although research has not revealed the details of how or if in the course of two centuries the new astronomical theory made its way from Damascus to Poland.