Читать книгу Servants of Nature: A History of Scientific Institutions, Enterprises and Sensibilities - Lewis Pyenson - Страница 12

On a clear summer night walk as far as you can beyond the electric colours of urban life. Leave the shimmering rivers of hot air, as they snake above pavement and monument, causing the stars to twinkle. Go to where you can smell no exhaust, hear no human noise. Go at dusk and look up as the stars come out.

What may be seen? First there is the spectrum of the sky, yellow to red to faint-green and on to indigo. There may be birds, insects, and bats. There are condensation trails from high-flying jet aircraft, rapid transits of orbiting satellites, and shooting stars. Depending on one’s eyesight and location on the globe, the night sky reveals between one thousand and two thousand points of light. Located in a narrow band among these fixed stars there are seven objects that trace cyclical patterns. Until quite recently, the accidental trajectories of these seven objects – the sun, the moon, Mercury, Venus, Mars, Jupiter, and Saturn – found a central place in many civilizations. The stars have never reliably predicted the outcome of commercial, military, or personal initiatives, but their regular movements have nevertheless had an impact on our lives.

One among the seven moving stars is of critical importance. Biological cycles of growth and renewal reflect the apparent periodical motion of the sun – the solar year. We reckon age by solar cycles, not lunar ones, even in societies where the calendar is closely tied to the moon. This is so because the moon’s periodicity will not in itself predict spring inundations or winter rains, the return of migratory birds or fishes, or the best time to plant or harvest. Periodical changes in the moon’s aspect, linked with the slower, uneven velocity of the sun’s changing position in the sky, can be made to establish a yearly calendar of twelve months (each beginning with new moons) and a rather large fraction of leftover days. Astronomical science has traditionally focused on how to take care of the fraction. Once a calendar (months with a fixed number of days each) was in place, astronomical observations could be kept reliably. Records made possible the identification of cycles for the five remaining planets, the precession of the equinoxes, and predictions of such things as solar eclipses (or the possibility of them).

The existence of a calendar must not imply that we have direct access to events noted by it. Establishing a reliable chronology of antiquity – a goal sought by Europeans since medieval times – was possibly the greatest achievement of the broader historical discipline in the nineteenth century, and this occurred following a meticulous analysis of planetary records on Babylonian clay tablets. All calendars require intercalation of some sort (ours today supplies the odd day or second to round out the apparent solar year). The corrections may follow a formula or, more empirically, a celestial observation. The advantages of a determination of days and years by first principles is apparent to any head of state. Indeed, the state has generally supported astronomical observation – perhaps even (as some interpreters of Stonehenge contend) from paleolithic times.

Until Galileo Galilei pointed his telescope skyward, the seven stars that change their relative positions in a cyclical pattern were the givens of scientific endeavour. Predicting the movement of these jewels and orbs provided an arena for mathematical virtuosity, a justification for maintaining libraries, a reason for establishing schools of advanced learning, and an excuse for international collaboration. Because the patrons of this apparatus demanded practical results in the way of reliable calendars, astronomers devoted effort toward studying persistent empirical trends, such as the precession of the vernal equinox, the change in the stars behind the sun on the first day of spring.

Patrons demanded a great deal of their star gazers. Astronomers were called upon to pronounce on occasional spectacular events, such as eclipses. Through the twentieth century, astronomers have addressed meteorology – the corruptible, sublunar domain of Aristotelian physics named after the blazing objects in the sky, meteors, that were apparently as ephemeral as the rain. Astronomers were charged with telegraphical signals and radio broadcasts. They measured fundamental physical quantities in gravimetry (the gravitational constant identified by Isaac Newton) and optics (the speed of light, first calculated by Ole Christensen Römer [1644–1710]). Occasionally they chronicled the flight of migratory birds and assembled demographical statistics. They addressed whatever depended on a sharp eye and a head for figures. Until the twentieth century, astronomers were the practical masters of the realm of numbers.

The Islamic observatory

Astronomers differed from casual stargazers in that they required a special place for making observations. Observing in a grand observatory required a team of people. They had to be ready for the right moment and hope that a cloud did not intervene. In practice, this implied a support staff of servants and some form of lodging for the observers. Understanding the data required a library and calculating devices – whether pen and paper, abacus, clay tablet, or sand table. Apprentice observers had to be trained. Instruments had to be maintained. Regular reports about celestial omens and calendars had to be produced. Four thousand years of astronomical practice are continued at today’s enormous, mountain-top research installations.

We have seen that the endowed, residential college, or madrasa, was an innovation of medieval Islam. It is also to Islamic civilization that we owe the invention of the astronomical observatory. This occurred under al-Mamûn, early in the ninth century. A great patron of learning, al-Mamûn financed major astronomical complexes at Damascus and Baghdad. These possessed modifications of the instruments mentioned by Ptolemy, including an armillary sphere of concentric circles for tracking the stars, a marble mural quadrant (a graded quarter-circle mounted on a wall) for observing the height of stars above the horizon, and a five-metre gnomon or stile. The observatories assembled a group of perhaps as many as a dozen talented astronomers, one of whom was Ptolemy’s commentator al-Farghânî (Alfraganus, fl. 850), who constructed tables, or zijes, based on observations. Astrological interest, especially as it related to solar eclipses (for which Ptolemaïc data had to be corrected), was undoubtedly the motor of al-Mamûn’s astronomical patronage.

Knowledge may naturally tend to disaggregate, pooling here and there, channelling along one or another stream, evaporating into the air. The disaggregation is present in Islamic astronomy. During the Abbasid golden age, al-Mamûn’s observatories were distinct from the learned academy at Baghdad, the Dar al-Hikmah or House of Wisdom, which had been founded by Caliph Harun al-Rashid. The academy functioned as a collector and filter of learning from all sources, east and west. Greek and Indian texts, and possibly also Hebrew ones, were recovered and translated into Arabic. Among the most notable academicians was Abu Jafar Muhammad ibn Musa al-Khwarizmi (fl. 830), author of the first Arabic text on algebra (based on both Greek and Indian sources) as well as a work on Indian numerals. Al-Khwarizmi also composed a treatise on Hindu astronomy, recalculated much of Ptolemy’s data for the seven planets, and provided tables for calculating eclipses as well as trigonometrical functions. He certainly knew about the work conducted at al-Mamûn’s observatories, especially on establishing the obliquity of the ecliptic, but he chose not to incorporate the new results.

Al-Mamûn’s observatories did not survive his reign (he died in 833), but they established a precedent for observing nature. Over the next centuries, Islamic observatories extended their programmes to all the planets. The institutions became characterized by grand instruments (sometimes surpassing in size those at European locations up to the eighteenth century) and the staff (more numerous than European staff) to manoeuvre them. Observatories acquired legal status and operated under the eye of a director. The astronomical work and instrumental innovations of the polymath Ibn Sînâ (Avicenna, 980–1037), based on observations taken early in the eleventh century at an observatory financed by the amir of Isfahan at Hamadân, followed the earlier pattern. But the institutional evolution occurred unevenly. Distinguished observers, such as al-Battânî (Albategnius, fl. 880) and Ibn Yûnus (late tenth century), seem not to have availed themselves of a permanent observing facility, even though they were much concerned with astronomical innovation. Ibn Yûnus, for example, invented something akin to the method of transversals.

European commentators have traditionally celebrated Islamic savants as transmitters of Hellenistic learning; less time has been spent detailing Islamic scientific innovation. But there is no doubt that in astronomy, Islamic observations expanded and became more sophisticated. The crucial tasks of an Islamic observatory related only to the sun and the moon. One needed to establish dates of religious observances (for the Muslim lunar calendar) and times of daily prayers, keyed to sunrise and sunset. With the accessibility of Hellenistic texts, precise measurements of the sun led to interest in anomalous motions, such as precession of the equinoxes, and eventually to concern with the five remaining planets. Indeed, programmes to observe the five smaller bodies provided a justification for the permanent endowment of an observatory. It takes about thirty years of watching the sky to document all planetary regularities, and this is the working lifetime of an astronomer. Among observatories with a long-term programme was the one founded by the late eleventh-century Seljuq sultan Jalal al-Dîn Malikshâh at Isfahan; its staff of as many as eight men included al-Khayyami, the mathematician and astronomer known for his poetry as Omar Khayyam (ca.1048–ca.1131). The astronomers at the Malikshâh Observatory were the first to emphasize to their patron that it would take thirty years to record changes in the sky; from their time forward the generational argument became an astronomical watchword.

The slow pace of institutional development reflected uncertainties about using large measuring devices. One principle has dominated astronomy since antiquity: the larger the measuring device, the more accurate the observations. During the Islamic period large azimuthal rings installed on the ground to measure points on the compass were cast in copper (notably one five metres in diameter at the early twelfth-century al-Afdal al-Bataihî Observatory in Cairo), and large mural quadrants were cut into the ground and faced in marble. The moving parts of these instruments were usually made from wood – indeed, wood was preferred to brass for mural quadrants and even sextants up to the eighteenth century. But the wood warped with time and weather, especially as the large instruments were normally open to the elements. Heavy moving parts – the arm on one of Ptolemy’s rulers, for example – had to be suspended in such a way as to minimize creep. One reason for the slow growth of early observatories is that many astronomers, among them Ibn Yûnus, actually favoured small devices – even portable ones – that could be manipulated by one observer.

The peak of Islamic observatory-building took place during the thirteenth century, and its exemplar was the one founded at the city of Marâgha, south of Tabriz in present-day Iran, by Mangû, brother of the Muslim conqueror Hulâgû. Mangû, by all accounts a convinced patron of learning, seems to have first thought about inviting the most distinguished astronomer among his new Islamic subjects, Nasîr al-Dîn al-Tusî (1201–1274), to found an observatory at Beijing or possibly the Mongol capital of Qaraqurum. Indeed, during the Mongol period there was renewed intellectual interchange between East Asia and Central Asia. Several accounts refer to an Islamic astronomer, with his instruments, visiting China at just this time, and Chinese astronomers certainly travelled west. Nasîr al-Tusî may have gone east, but he certainly supervised the construction of the Marâgha Observatory, beginning in 1259. The inspiration for the Marâgha observatory, it is reasonable to assume, was Mangû’s familiarity with the Chinese tradition of constructing a new calendar for a new sovereign. To keep his hand in traditional, Chinese star-reckoning, Mangû brought Fao Mun-Ji to Marâgha at the onset of the enterprise.

To insure the life of the observatory beyond his own reign, Mangû provided it with a waqf endowment – the first known application of applying to astronomy the mechanism for endowing madrasa and hospital. The resulting revenues financed the observatory during the reigns of subsequent rulers until the dissolution of the Mongol state about 1316. Nasir al-Tusî’s sons succeeded him in directing the observatory, and it may be that he and they were the waqf administrators. The charitable endowment allowed the observatory to become an institution for instruction in the secular, or ancient sciences – the natural sciences excluded from the madrasas. In this, too, the observatory followed the pattern of Islamic teaching hospitals.

The Marâgha Observatory had a main building surmounted by a dome, through a hole in which the sun could be observed. It included an enormous library (by one account more than 400,000 volumes) and housed terrestrial and celestial globes. Many of the observatory’s rooms were excavated caves. (Astronomical observations are often made when a star passes overhead at the zenith, and for these altitude measurements, an excavated trench with a mural quadrant is fine.) Among its instruments were a fixed armillary sphere with five rings, a mural quadrant, a solar armilla, an equinoctial ring, and a parallactic ruler. The instruments went to produce a set of zijes, the so-called Ilkhâni Tables which provided data for all seven moving stars.

Marâgha formed a precedent for Mongol astronomical patronage. In the fifteenth century, Ulugh Beg (grandson of Timûr, feared in Europe as Tamerlane) erected the most magnificent of Islamic observatories at Samarqand. He became an expert astronomer, apparently constructing his observatory around an existing madrasa. He initiated astronomical instruction at the madrasa and drew talented astronomers, notably Ghiyâth al-Dîn al-Kashî (d. 1429), to the observatory, which he endowed with a waqf. The observatory apparently survived Ulugh Beg’s reign (he was murdered by his son), settling into a slow decline over the succeeding century. The Islamic tradition of grand astronomical institutions continued into the sixteenth century, with the construction of an observatory at Istanbul under the direction of Takiyüddin al-Rasid (1526–1585). It functioned for several years before being dismantled in 1580, at the request of the sultan who founded it. The last of the great Islamic observatories came in South Asia early in the eighteenth century, courtesy of Maharaja Swai Jai Singh II.

The Islamic tradition may be placed in perspective by introducing the late sixteenth-century astronomical fiefdom of Tycho Brahe (1546–1601), granted by King Frederick II of Denmark and financed by Tycho’s inherited fortune supplemented by Frederick’s largesse. Tycho had workshops for his instrument-makers, a mill for producing paper, and a printing press. The main house of Tycho’s Uraniborg functioned as a chateau, complete with running water, kitchen, chemical laboratories, workrooms, library (housing a five-foot-in-diameter celestial globe) and bedrooms. Tycho had large instruments mounted on the top of the house. A separate observatory building had more instruments set in subterranean rooms equipped with plinths. With its generous royal endowment and its massive, innovative instruments, Uraniborg was nothing other than the European counterpart of the Istanbul Observatory. Tycho’s observatory was an inspiration for Francis Bacon’s invocation of the notion of a House of Salomon, which in turn became a model for the Royal Society of London. In a sense, we may trace modern scientific institutions to medieval Islam.

It is doubtful that Tycho had first-hand information about the observatories of his Islamic predecessors. His instruments followed Ptolemy’s instructions, which he adapted and added to on the basis of European tradition – just as medieval Islamic astronomers began with Ptolemy and constructed innovative measuring arms, armillary spheres, and scales. Medieval Islamic observatories, located as they were between Western Europe and Eastern Asia, nevertheless suggest questions about interchanges between West and East.

When we look west, we find little direct Islamic inspiration for the organization of astronomical activity. The area of closest contact between Islam and Christianity, Andalusia, was insulated against the urge to construct grand state observatories. The insularity derived from the effective independence of Western Islam and especially the diverse Spanish emirates and kingdoms. This is not to say that intellectuals in Spain were less interested in the stars than were people in Central Asia. Certainly the eleventh-century group of astronomers around al-Zarqâli (d. 1100) who compiled zijes that became known in Europe as the Toledan Tables undertook significant observations, but the work was apparently accomplished without a permanent observing facility.

Chinese astronomy

What about the East? Can it be that the inspiration for Islamic observatories came from China? There is no doubt that various Chinese governments maintained astronomical offices, and with them the means of making sophisticated astronomical observations, for at least seven centuries before a similar spirit infected Islamic authorities.

Knowledge of the sky was an imperial prerogative from the time of the Han. The heavens were held to have conferred a mandate on the imperial house, and reading the stars was a way of learning whether terrestrial policies found divine favour. Portent astrology (where one sought divine instruction from the sky by reading celestial signs) rather than individual fate astrology (the notion of a preordained future that suffused western Eurasia) dominated the court institutions of Chinese astronomy. New rulers and new regimes, in fact, promulgated new calendars as a practical sign of their celestial mandate. In the Han, astronomy went under the Office of the Grand Historian, for it combined the functions of archivist and omen reader. About 90 BC, the head of this office, Ssu-ma Chhien, compiled the dynastic history known as the Shih Chi, which had chapters devoted to calendar construction and astrology. This tradition continued (with the same kind of ups and downs that characterize institutions of higher learning in the Mediterranean basin) for two millennia.

The Chinese dynasty at the time of the rise of Islam, the Thang, received ambassadors and merchants from Byzantium, Persia, and elsewhere. Among the foreigners living in China under the Thang were Indian astronomers. In the seventh century there are indications of Brahmin astronomy being translated into Chinese. Beginning around 650, three families of Indian astronomers held positions in the imperial astronomical bureau. Of these, astronomers of the Gautama family found their calendrical work officially adopted. Chhüthan Shi-Ta or Gautama Siddhartha (fl. 718), the greatest of the clan, became director of Thang astronomy and wrote a major mathematical work in 729 which featured the zero symbol, division of the circle into 360 degrees (the Chinese circle traditionally contained 364.25 degrees), and sexagesimal minutes and seconds. No doubt the resident Indian astronomer families made use of trigonometry, then unknown in China. Despite internecine disputes about astronomical secrets (the Chinese Buddhist monk and brilliant mathematician I-hsing became involved in some of these disputes), the Indian families produced an officially accepted calendar, calculated solar eclipses, and wrote an astrological treatise.

The observatory where the Indian astronomers lived and worked was large, even by modern standards. Two grand astrologers supervised the Astronomical Bureau in Thang China, an institution that combined features of observatory and college. They operated one of the largest astronomical schools of any time. In the bureau’s astrological department, 2 professors supervised 5 observers and 150 students; one professor of calendar-making oversaw 2 technicians and 41 students; 6 professors of time-keeping had 37 technicians, 440 clerks to handle various bells and drums that signalled the hours, and 360 students. Separate from the Astronomical Bureau was the Divination Bureau. Divination concerned foreseeing the future on the basis of traditions ranging from the I-Ching (Book of Changes) to geomancy (the favourable attributes and aspects of land that still inspire architectural design in Asia), and it followed the art of Yin and Yang (the qualitative masculine and feminine spirit that resided in all things). The director of divination had 2 vice-directors, 2 professors, 2 assistant professors, 37 technicians, and 45 students. On the twelve-rung scale of the civil service, the astrological directors held posts fifth from the top; experts in calendar-making ranked ninth, and experts in timekeeping apparently had no rating at all.

The apprentice system in Thang astronomy led into middle-management positions. The enterprise departed from a strict technical meritocracy, because directors were parachuted in from outside the bureau. And as foreigners came to carry out many of the calculations, there was little interest at the top or at the bottom in accuracy, fidelity, or innovation. With the exception of the foreign calculators, this institutional structure, modified and diminished in size, also took root in eighth-century Japan, where astronomical knowledge became the domain of a few families and where the dominant Chinese focus on calendar-making ceded to portent astrology.

The structure of astronomy at Chinese observatories separated calendrical mathematics from practical problems of terrestrial mensuration. Chinese maps followed a grid, for example, but unlike Ptolemy’s geography the grid was not keyed to astronomical measurements. There was a small mathematics school founded during the Thang period. Its professors did not rank high in the civil service, and the students were not destined for administrative posts. Sons of minor officials and commoners, the students did not have access to other schools; with their ‘Master of Mathematics’ diploma, they anticipated a career as land surveyor. To an extent even greater than in medieval Europe, Chinese society separated mathematical scholars and mathematical craftsmen.

In both Chinese and Islamic civilizations, the motivation for observing the skies related to legitimizing state authority, which promoted (or at least guaranteed) a faith. Both Chinese and Islamic rulers had heavenly mandates, and it was only natural to read heaven’s signs in the stars. The reign of a Chinese potentate often began with a new, star-informed calendar. The prayers of an Islamic caliph were regulated by the sun and moon, and his life was foretold by the remaining planets. Notwithstanding a divergent interpretation of celestial signs, observatories provided essential information both East and West.

We may identify a progressive evolution of techniques at both Islamic and Chinese observatories. There was in fact persistent interchange of techniques between the two civilizations: al-Khayyami reinterpreted what he thought were Chinese mathematical techniques, and Nasîr al-Tusî received an invitation to Beijing or Qaraqurum. Nevertheless, foreign knowledge (such as the Persian, Manichaean, and Nestorian texts that were translated into Chinese during the eighth century) eventually disappeared. One finds, for example, no trace of Ptolemaïc notions in Chinese texts. Chinese astronomers may have been instrumental in setting up one or another Islamic observatory, but we see nothing of Chinese norms in Central Asian astronomy.

Why? Because astronomy was a state secret and a clan monopoly, foreign astronomers found an ephemeral place in China. The astronomical sciences – astrology, navigation, cartography – could be prosecuted for the most part only under imperial authority; data, methods, and calculations were not available in the public sphere.

In the record of those times when astronomical innovations came to Asia and the Islamic world, however, we see another part of the answer. Innovation in the sciences of observation occurs in the context of aggressive expansion. When a civilization is actively assimilating foreign peoples and exotic cultures, traditional notions of all kinds are subject to modification. The scientific fruit of this expansive vision appears in Hellenistic Alexandria, tenth-century Salerno, thirteenth-century France, Renaissance Italy, Restoration England, eighteenth-century Scotland, and twentieth-century America.

Innovation in instruments

What were the innovations in astronomical instruments between the ancient observers of Stonehenge and the comparably majestic observatory on Hven where Tycho Brahe brought classical, Ptolemaïc astronomy to its apogee? Among the innovations of the Istanbul Observatory was a mechanical clock based on a European design. (Tycho, it may be noted, did not consider mechanical clocks reliable for astronomical work.) Clocks of all kinds flooded the Ottoman world during the sixteenth century, even though they were ill-suited for indicating prayer times, just as they streamed into East Asia as goodwill offerings of European ambassadors and missionaries. Only with Christiaan Huygens’s pendulum clock and the precise chronometers of the eighteenth century did regular, mechanical timepieces enter the observatory.

The astrolabe, perfected in medieval Islam, became a useful navigational device, and its precise scales – stamped and engraved on brass – could be employed for determining planetary positions, as could various wooden cross-staffs of European origin. Brass was also worked into armillary spheres, which allowed for a simultaneous measurement of celestial latitude and longitude. The sphere itself, more cumbersome than useful, could be reduced to a two-dimensional circle or part of a circle. When of large proportions, like the six-foot-radius quarter circle used by Tycho, the instrument could be fixed to a wall and adapted for taking altitude and meridian transits simultaneously. The gradual evolution of instruments, pioneered by professional astronomers, led directly to heliocentric, celestial mechanics: Johannes Kepler (1571–1630) began his reformation of astronomy because he focused on an 8-minute-of-arc discrepancy between Tycho’s observations and traditional calculations.

Observational practice, in particular the use of meridian transit instruments, guaranteed that Tycho’s notion of an observatory would continue to the end of the nineteenth century. The Paris Observatory, for example, took shape in the late seventeenth century as a residential mansion where quadrants, octants, and the new telescopes perambulated to an outdoor terrace. Telescopes went on the roof from the beginning, and wings were added for additional telescopes. In the nineteenth century, advances in metalworking made possible lightweight movable domes, which could enclose permanently mounted telescopic leviathans.

Small instruments evolved slowly and continually at least since the time of Ptolemy, but the large ones changed hardly at all. Innovations derived from star-watchers who needed to determine time and place. The astrolabe, invented in the Mediterranean around the fourth century, responded to the requirements of sailors and astrologers and especially to the men of affluence who underwrote the voyages and horoscopes. With its plates for various latitudes, the astrolabe provided a picture of the fixed stars in stereoscopic projection, and its obverse served to sight the altitude of celestial objects. A serious student of the stars, realizing the limitation by latitude of such a calculating device, would seek to generalize it; the universal astrolabe appeared by the eleventh century in Toledo. It would be obvious to a frequent user, furthermore, that one needed only a quarter-circle for determining time and place; as we have seen, quadrants of this kind enjoyed popularity by the fourteenth century.

The utility of devices like the astrolabe depended on the precision of their lines and scales and the regularity of their moving parts. Precision related to the rise of a craft tradition that eventually led to the emergence of professional instrument-makers. With the Renaissance, precision replaced figurative allusion as a rhapsody for people in the workaday world, and the prime measure of precise movement, the stars, attracted increasing attention. The growth of commerce and banking brought number – and its various transformations from one to another currency or system of weight and measure – to wider circles. Marine commerce with Asia and the New World generated demand for maps and navigational instruments. Calendrical reform assumed crisis proportions as feasts and anniversaries no longer corresponded with the seasons. Astrology became important in daily affairs as religious heterodoxy conveyed doubt and uncertainty about humanity’s place in the cosmos.