The House of Wisdom Page 16
As for the crusaders who preceded Adelard to Syria, the overwhelming majority were too blinded by ignorance and sectarian hatred, or by their own moral smugness, to recognize the accomplishments of the advanced civilization they now faced in battle. This tendency is reminiscent of the present day, when the West looks eastward and sees only barbarism. Adelard’s outlook proved a remarkable exception to the mood of his own times—which held that Islam was an evil faith with nothing to offer Christendom but the role of sacred enemy—and he came back to England very much a new man. Everything that was once familiar in his native land now appeared part of an alien and distasteful world.
Upon the insistence of friends and family, with whom he had just reunited, Adelard surveyed the state of English society. “I found,” he writes in Questions on Natural Science, shortly after his return home, “the princes barbarous, the bishops bibulous, judges bribable, patrons unreliable, clients sycophants, promisers liars, friends envious, and almost everybody full of ambition.”75 Ever the teacher, Adelard resolves that knowledge offers the best antidote to the “moral depravity” on display in his homeland. “I undertook the following treatise, which I know will be useful to its auditors, but whether it is pleasant, I do not know. For the present generation suffers from this ingrained fault, that it thinks that nothing should be accepted which is discovered by the ‘moderns.’ ”76
During his wanderings, Adelard tells us, he adopted his trademark flowing green cloak and began to sport a prominent signet ring, set with an obscure astrological symbol, in the same rich green, “less extensive but more efficacious” in its emerald hue. Adelard’s new intellectual outlook is no less startling. Gone is the young country gentleman who once dedicated earnest prose to the goddess of philosophy, in pale imitation of the bygone classical age; in his place stands the relentless seeker of knowledge and scientific truth. The new Adelard, now a citizen of the world, challenges the intellectual corruption, complacency, and rigidity that has dogged the West for centuries. Unlike the student from the cathedral schools who once branded the moderns “dumb,”the reborn Adelard is an ardent proponent of contemporary scholarship—only now his world is shaped by the new and dynamic Arab learning from the East.
Such knowledge, he says, can liberate the Western world from the burden of orthodoxy and give man permission to make his own way through the universe: “For I have learned one thing from my Arab masters, with reason as guide, but you another: you follow a halter, being enthralled by the picture of authority. For what else can authority be called other than a halter? As brute animals are led wherever one pleases by a halter, but do not know where or why they are led, and only follow the rope by which they are held, so the authority of written words leads not a few of you into danger, since you are enthralled and bound by brutish credulity.”77
Man should take refuge in God, he declares, only when his intellect proves incapable of understanding the world around him. Such a declaration connects Adelard of Bath directly to his spiritual and intellectual heir, the pioneering astronomer Galileo, whose public showdown with religious orthodoxy five centuries later would seal the end of the beginning of the Western scientific revolution. This wanderer in the flowing green robes issues the first explicit assertion in the Christian Middle Ages that the existence of God must not prevent man from exploring the laws of nature. “I will detract nothing from God, for whatever is, is from Him … We must listen to the very limits of human knowledge and only when this utterly breaks down should we refer things to God.”78
Chapter Six
“WHAT IS SAID OF THE SPHERE …”
ONE PALE DAWN, twenty-two years before the Antioch earthquake, a scholar-monk not far from Adelard’s West Country home quietly made scientific history. Pointing an astrolabe—one of the very few then in use in Europe—at an eclipse of the moon on October 18, 1092, Walcher, the prior of the monastery in Great Malvern, carried out the first known Western experiment to improve astronomical predictions. A year before, while traveling in Italy, the clergyman had witnessed a lunar eclipse but found he had no way to record the events overhead, other than to guess the approximate time. A brother monk who said he had witnessed the very same celestial phenomenon to the west in England gave a strikingly different estimate of the time.1 Walcher or his colleague was almost certainly in error, for any time difference between the two locales would have been perceptible but slim.2 Still, this was the same phenomenon once exploited by the early Abbasid astronomers to establish the difference in geographic coordinates between cities and other important places.
Confusion over the reported sightings stirred Walcher into action: “I still had no certainty about the time of the eclipse and I was distressed about this, because I was planning to draw up a lunar table and had no starting point.” He vowed not to be caught unprepared again. One year later, Walcher got his chance when an eclipse again darkened the nighttime sky, this time fifteen degrees above the western horizon. “I at once seized my astrolabe.” He used the device to note the position of the eclipse and to determine the time of day.3
Walcher was a leading figure in a small circle of local clerics with personal and intellectual roots back in Lotharingia, source of many of eleventh-century England’s most learned courtiers and churchmen. At the time, there was simply no secular education of note available, a circumstance that began to change, slowly at first and then picking up steam, with the Norman Conquest of 1066. The invaders brought the books and teaching masters of the European continent to England for the first time, although it would take until around 1130 before a serious scholastic community became established at Oxford.4 The late bishop of Bath and Wells, Giso, whose successor was Adelard’s own mentor, John de Villula, had been another member of this loose intellectual movement.5 So, too, was Robert, bishop of Hereford—like Walcher a native of Lotharingia and a keen astronomer and mathematician. At the time his friend and colleague was in Italy, Robert consulted the stars in preparation for a proposed journey to the dedication of Lincoln Cathedral; his reading of the stars correctly predicted that the ceremony would not take place as scheduled, allowing him to avoid a difficult and unnecessary journey.6
For a time, Prior Walcher worked closely with a converted Spanish Jew, Petrus Alfonsi, who arrived in the English Midlands with a basic knowledge of Arabic astronomy and mathematics. The pair collaborated on a failed attempt to present al-Khwarizmi’s zij to a Western audience, a project Adelard completed successfully.7 Petrus, born and educated in the Arabic cultural world of al-Andalus, was an effective polemicist. His diatribes against both the Jews, his former coreligionists, and the Muslims endeared him to many in positions of power. Little remembered today, the man known by Chaucer as Piers Alphonse was also the author of The Priestly Tales. This volume had a long-lasting influence on the development of Western literature, for it introduced European readers to the Arabic literary form of the framed tale—a story within a story—further popularized by the later translation of The Thousand and One Nights. Chaucer adopted Petrus’s novel approach in his own Canterbury Tales, as did Boccaccio in The Decameron.8 Petrus’s reports on the ways of the Muslims, including the spurious assertion that idol worship continued at the Kaaba in flagrant violation of Muhammad’s demand for absolute monotheism, helped shape some of the earliest anti-Muslim attitudes among the Christians.9
Many of these West Country monks were scholars at heart, and in their enthusiasm for the new learning they openly embraced such innovations as the astrolabe, the abacus, and the rudiments of the Arabic number system. Walcher’s determination to establish the correct time for his observation of the eclipse was typical of the new thinking—rational, precise, and grounded in experience—that slowly began to accompany these novelties. A basic text on the astrolabe, partially drawn from a very early Latin translation from Spain of the work of al-Khwarizmi, has been tentatively ascribed to Walcher or a member of his circle.10 At his death in 1125, the mathematician-cum-cleric was remembered as a “philosopher, astronomer, geom
eter and abacist.”11
Ignoring traditional religious questions that had preoccupied his predecessors, such as the annual dating of Easter, Walcher instead used his observational data to create a pair of new lunar tables. His new approach was in contravention of the teachings of the church fathers—and the authority of no less than the Venerable Bede.12 Walcher also adopted the modern system, already well established among the Arabs, of recording astronomical data in degrees, minutes, and seconds. This replaced the clumsy and less precise Roman fractions then in common use across Europe.13 Walcher’s tables were far more accurate than those that came before, which were based not on direct observation but on the traditional medieval computus. Nonetheless, they proved grossly inadequate. Walcher soon found that his prediction of a full moon for New Year’s Eve, 1107, for example, was off by as much as sixteen hours.14
Despite their new empirical basis, Walcher’s tables still suffered from the medieval convention of assigning an equal number of days to each of the twelve months. This made for tidy calculations, but it seriously undercounted the days of the year. An almost contemporaneous revision of the calendar in Persia by the savant Omar Khayyam—known in the East not for the poetry of The Rubaiyat but for his supremely elegant mathematics—calculated the length of the solar year to eleven decimal points. Lacking a theoretical understanding of the movement of the planets, Walcher and his colleagues were unable to exploit their newfound precision in scientific measurement. They needed help from the Arab astronomers.15
Adelard’s translation of the zij al-Sindhind provided one piece of the puzzle, giving the West its first real look at the inner workings of the Arabs’ mathematical astronomy. The geometry of Euclid supplied another, for it allowed the vast magnitudes involved in measuring the celestial bodies to be captured and expressed in terms of “angular distance” relative to the earth or to one another. It also allowed the accurate calculation and mapping of terrestrial and celestial positions, either on a sphere or “projected” onto a two-dimensional map or chart, or onto the faceplate of the astrolabe. With the publication of his original treatise On the Use of the Astrolabe, probably around 1149 or 1150, Adelard further revolutionized the way Western man understood the universe around him.16 He also made explicit the link between the new technology and the comprehensive Arab scientific edifice that stood behind it. From timekeeping to navigation, the secrets of the physical world could now be fully explored.
To Adelard, the astrolabe was more than just an instrument to aim at the sun or a prominent star and then use to take measurements or tell time; it was a polished bronze symbol for a fresh way to view the world, informed by classical philosophy and the innovations of the Arab scholars of the House of Wisdom. Armed with such a device, man could measure and begin to decipher the regular movements of the stars and the planets. He could explore the laws of nature and gain new insights into how things work. The universe was no longer an ineffable divine masterpiece; it was transformed into a giant laboratory, as well as an object of research to be studied and analyzed like any other. Attributes such as time and distance were no longer vague abstractions but took on real numerical values, opening the door to the rise of empirical science and the creation of organized, modern societies.
On the Use of the Astrolabe presented the Latin world, for the first time, with the beginnings of a coherent and comprehensive cosmology. Adelard laid to rest Isidore of Seville’s misguided teaching that the earth was flat and “shaped like a wheel” and other expressions of Western sacred geography. At the center of this new worldview sat the sphere—the “perfect solid” of the ancient Greeks and the only one that can rotate on its axis in absolute symmetry, always displacing the same space—and its two-dimensional representation, the circle. “Concerning the universe … and its different parts I will write in Latin what I have learned from the Arabs. You can take it for granted that the universe is not square, or rectangular, but a sphere. What is said of the sphere can be said of the universe,” Adelard informs the future King Henry II.17 Adelard dedicates the work to Henry, whom he may have earlier served as personal tutor.
Working in the tradition of al-Khwarizmi and other Arab scholars, who frequently introduce their scientific works as responses to entreaties that they share their learning with friends, students, or patrons, Adelard opens his astrolabe text with just such an appeal. Prince Henry, he tells us, turned to him for “the opinions of the Arabs about the sphere and circles and motions of the stars.” By this time a respected scholar and England’s foremost Arabist, Adelard forgoes the ritual humility of his Muslim mentors to lecture the teenage Henry on the vital importance of a scientific understanding of the natural world. “You say that whoever dwells in a house is not worthy of its shelter if he is ignorant of its material and makeup, quantity and quality, position and peculiarity. Thus if one who was born and raised in the palace of the world should forebear after the age of discretion to know the reason for so marvelous a beauty, he is unworthy of it and, were it possible, ought to be cast out.”18
Adelard first presents the basic tenets and concepts of spherical and theoretical astronomy, as well as key points of geography. He uses a globe as a model of the sphere of the earth, before introducing the computational powers of the astrolabe, the subject of the rest of the book.19 Available Latin sources offered some of the same material, but the powerful influence of at least two Arab scholars stands out. The first, of course, is al-Khwarizmi, whose zij al-Sindhind Adelard translated earlier. The author of On the Use of the Astrolabe assumes the reader is familiar with the zij, as well as with his own Latin version of Euclid, and the treatise relies heavily on the Arab star tables to complement the calculations carried out with the device itself. Adelard also makes an important change to some of the technical data from his edition of the zij al-Sindhind, converting the meridian from that of Cordoba to that of Bath.20
Using an approach similar to that in his Euclid text, Adelard provides both Arabic names and Latin equivalents for the various parts of the astrolabe. He also integrates its operation completely with al-Khwarizmi’s zij handbook, referring regularly to the data available in the star tables and thereby allowing the user to get the most out of the technology.21 The other central Arab voice is that of Maslama al-Majriti, who first transposed the zij al-Sindhind to the meridian of Cordoba and replaced its Persian calendar with the Islamic one. At one point, Adelard mentions an astrolabium doctoris Almirethi, a reference to an instrument that once belonged to al-Majriti or came from his school of mathematical astronomers.22
In laying out the “opinions of the Arabs,” Adelard devotes considerable space to the use of the circle to measure and depict the movements across the sphere of the universe, suggesting that this may still have been a novel idea among educated Western readers.23 Such an understanding was vital, for the circle and sphere provide the basic building blocks for the study of the heavens. Here, On the Use of the Astrolabe comes into its own, introducing and explicating the common models behind the perceived movement of the heavens. These include the central notion of a concentric universe, nested spheres controlling the general movements of the celestial bodies, as well as the so-called eccentric orbits of the planets—identified since classical times as the sun, the moon, Mercury, Venus, Mars, Jupiter, and Saturn. Each planet is assigned its own sphere, and all of them are grouped around the earth, at the center, Adelard explains, but their circular orbits within the sphere fluctuate between a high and a low point, carving an eccentric path in their regular rotations.24 And there are more spheres, including that of the fixed stars, as well as other refinements to keep the whole mechanism running like clockwork. On the Use of the Astrolabe is less a how-to on the astrolabe than a groundbreaking introduction to astronomy.
This complex theoretical apparatus reflects the heroic efforts by astronomers and philosophers over the centuries to address Plato’s dictum to “save the appearances”—that is, to account for the increasingly precise observations of the scientists without
violating the strict guidelines laid down by the Greeks and seemingly confirmed by common sense. In the fourth century B.C., Plato’s creation myth, Timaeus, spelled out some of the central requirements: The world as rendered by the Creator must be a perfect whole; it must be unique, allowing the creation of no other; and it must be immune to decay or corruption. “Wherefore, he made the world in the form of a globe, round as from a lathe, having its extremes in every direction equidistant from the center, the most perfect and most like itself of all figures; for he considered that the like is infinitely fairer than the unlike.”25 For the Greek philosophers, the perfection of the celestial world should also be reflected in the course of the planets, each tracing eternal, perfect circles across the heavens.
Similar arguments were also advanced for the spherical shape of the earth. Common sense and everyday experience seemed to support this: the round image cast on the moon during a lunar eclipse; the observation of a ship’s mast dropping below the horizon as it sailed from shore; or even the appearance or disappearance of the constellations as one moved north or south along the earth. The fact that a falling body, say an apple from a tree, appeared to plummet toward the center of the earth suggested that it must represent the center of the universe as well. There was no gravitational theory at the time to explain this phenomenon; besides, the notion that man inhabited the center of divine creation had obvious and long-lived religious and psychological appeal.26 Surely a loving, all-powerful God would not exile his supreme creation, man, to some cosmological backwater.