On page 116 of the same work he writes that after Rhazes` death the works of Avicenna (AD 980-1037) were taken up. His influence on thought and philosophy and general science was profound, and his medical works (based on the works of Galen which he had found in the Samarqand library in Arabic translation) had a sensational outrech.
Other scientists followed – Abu`l-Qais of Andalusia; Ibn-Zahr of Andalusia; Abbas the Irani; Ali ibn-Rezvan of Egypt; Ibn Butlan of Baghdad; Abu Mansur Muwaffaq of Herat; Ibbn Wafeed of Spain; Masooya o Baghdad; Ali-ibn-Esau of Baghdad; Ammar of Mosul; Ibn-Rushd (Averroes) of Andalusia; whose works were translated into Latin were used in European universities. Europe knew nothing of the cholera bacterium when Islam entered Spain, and the people there regarded the disease as a punishment sent from heaven to exact the penalty of the sins: but Muslim physicians had already proved that even the public plague was a contagious disease and nothing else.
Dr. Meyerhof writes of Avicenna`s book “The Canon” that it is a masterpiece of medical science which proved its vworth by being printed in a series of 16 editions in the closing years of the 15th century AD, 15 Latin and one Arabic. In the 16th century more than a score of further editions were published, because of its value as a scientific work. Its use continued throughout the 17th and 18th centuries, so that it became the most widely known of all medical treatises. It is still consulted in medical schools.
Will Durant writes that Mohammad ibn Zachariah Razi (Rhazes) was one of Islam`s most progress physicians, author of 200 treatises and books well worth studying today: in particular his
1. “Smallpox and Measles” (published in Latin and other European tounges in 40 editions between 1497 and 1866), and
2. “The Great Encyclopedia” 20 volumes mostly unobtainable nowadays: five volumes were devoted to optics; translated into Latin AD 1279; printed in five editions in 1542 alone; known as the most authoritative work on the eye and its ailments and treatment for centuries; one of the nine basic works on which Paris University composed its medical course in 1394 AD.
Surgery made similar progress in the hands of Islamic practitioners, who even used anaesthetics, though theses are assumed to be of modern origin. They employed a henbane base.
Among Rhazes` innovations was the use of cold water to treat persistent fever, of dry-cupping for apoplexy, of mercury ointment and animal gut for wound sutures, and many others.
Further information on Islamic medicine can be sought from the many books on the subject. The diagnosis of tuberculosis from the fingernails, the cure of jundice, the use of cold water to prevent haemorrage, the crushing of stones in bladder and kidney to facilitate their removal, and surgery for hernia are among advances too numerous to mention in detail. The greatest of the Islamic surgeons was Abu`l Qasem of Andalusia, affectionately called Abu`l-Qays, and sometimes Abu`l-Qasees, flourit 11th century AD, inventor of very many surgical instruments and author of books to describe them and their uses -books translated and printed in innumerable editions in Latin and used all over Europe, the last such edition being in 1816.
Georgi Zeidan writes: “Within two centuries of the death of the Prophet, Mecca, Medina and and other great Muslim cities all had hospitals, while the Abbasid governors and their ministers competed each for his own region to have the best such institution for the care of the sick. Baghdad alone had four important hospitals. By three centuries after the hijra the governor Adhud-ud-Dowleh Deylamy had founded the Adhudi Hospital with 24 specialists, each master of his own particular field, a hospital which soon earned the reputation of excelling all hospitals throughout Islam, though in the course of time it too was surpassed.
The order and arrangement of Islamic hospitals was such that no distinctions of race, religion or occupation were recognised, but cure was administered with meticulous care to any patient. Separate wards were allotted for patients of specific diseases. These were teaching hospitals where the students learned theory and observed practice. In addition, There were travelling hospitals which carried doctors and their gear by camel or mule to every district. Sultan Mahmoud the Seljuk travelled with a hospital which required 40 camels for its transport.”
Dr. Gustave le Bon writes: “Muslim hospitals went in for preventive medicine and the preservation of health as much as if not more than for the cure of the already diseased. They were well-aired and had plenty of running water. Muhammad bin Zachariah Razi (Razes) was ordered by the Sultan to seek out the healthiest place in the Baghdad neighbourhood for the construction of a new hospital. He visited every section of the town and its environs, and hung up a piece of meat which he left while he looked into infectious diseases in the neighbourhood and studied climatic conditions, particularly the state of the water. He balanced all these various experimental tests and finally found them all to indicate that the place where the portion of meat was the last to putrefy and develop infectious bacteria was the spot on which to build. These hospitals had large common wards and also private wards for individuals. Pupils were trained in diagnosis and brought obserrvation and experience to the perfecting of their studies. There were also special mental hospitals, and pharmacies which dispensed prescriptions gratis.”
Marc Kapp writes: “Cairo had a huge hospital with playing fountains and flower-decked gardens and 40 large courtyards. Every unfortunate patient was kindly received, and after his cure sent home with five gold coins. While Cordoba, besides its 600 mosques and 900 hammams, had 50 hospitals.”
[Pharmacology, as many other branches of sciences, is considered by Europeans to be an entirely new scientific field. In this respect, they feel, like ancient tribes, that the world is limited to the horisons of their territory. One must realize that this knowledge has mainly originated from the Middle East as well as from China].
[In Europe, until recently,] there was a surprising reluctance to apply anything resembling scientific principles to therapeutics. Even Robert Boyle, who laid the scientific foundations of chemistry in the middle of the seventeenth century, was content, when dealing with therapeutics (A Collection of Choice Remedies, 1692), to describe and recommend a hotch-potch of messes consisting of worms, dung, urine and the moss from a dead man`s skull.
Gustave le Bon writes: “Besides the use of cold water to treat typhoid cases – a treatment later abandoned, though Europe is taking this Muslim invention up again in modern times after a lapse of centuries – Muslims invented the art of mixing chemical medicaments in pills and solutions, many of which are in use to this day, though some of them are claimed as wholly new inventions of our present century by chemists unaware of their distinguished history. Islam had dispensaries which filled prescriptions for patients gratis, and in part of countries where no hospitals were reachable, physicians paid regular visits with all the tools of their trade to look after public health.”
Georgi Zeidan writes: “Modern European pharmacologists who have studied the history of their profession find that Muslim doctors launched many of the modern beneficial specifics centuries ago, made a science of pharmacology and compound cures, and set up the first pharmacies on the modern model. So that Baghdad alone had 60 chemists shops dispencing prescriptions regularly at the charges of Caliph. Evidence of these facts can be seen in the names given in Europe to quite a number of medicines and herbs which betray their Arabic, Indian or Persian origin.” Such are `alcohol`, `alkaner`, `apricot`, `arsenic`, to quote some `a`s alone.
The Abbasid Caliph Haroun-al-Rashid sent Charlemagne in Aix from Baghdad a present of a clock made by his horologists which struck a bell on the hour very hour, to the great wonder and delight of the whole court of the newly crowned Holy Roman Emperor.
The massacre and expulsion of the Muslims of Andalusia by the Christians carried with it the clousure of many of the great factories that has existed under Islamic rule, and the standstill of progress that had been made in science, crafts, arts, agriculture, and other products of civilization. Towns began to fall into ruin because of the lack of skilled masons. Madrid dropped from 400,000 to 200,000 inhabitants: Seville, which had possessed 1,600 factories under the Muslims, lost all but 300, and the 130,000 workers formerly employed had no more jobs, while the census of Philip IV showed a fall of 75% in population figures.
It was the Muslims also who brought about the substitution of cotton-wove paper for the old parchments; and it was this invention which formed the basis for Europe`s later invention of printing, using an old Chinese technique, and so for the vast uprush of learning which came with the Renaissance. More, since monks were starved for parchment on which to write their religious works, they were tending more and more to scrape off priceless ancient scientific texts from old parchments and to use them again as palimpsets. The introduction of paper put a stop to this disastrous practice in time to save quite a number of texts which would have otherwise been lost for ever, as, alas, too many were.
A paper manuscript of the year AD 1009 was found in the Escorial library, and claims to be the oldest hand-written book on paper still in existence. Silk-wove paper, of course, was a Chinese invention, since silk was native to China though rare in Europe; and the Musulman genius lay in seeing the possibility of substituting cotton for silk, and so giving Europe a plentiful supply of a practicable material for the reproduction of books by the monkish scribes.
Philip Hitti writes in his “History of the Arabs” that the art of road-making was so well developed in Islamic lands that Cordova had miles of paved road lit from the houses on each side at night so that people walked in safety; while in London or Paris anyone who ventured out on a rainy night sank up to his ankles in mud – and did so for seven centuries after Cordova was paved! Oxford men then held that bathing was an idolatrous practice; while Cordovan students revelled in luxurious public hammams!
The Arabian Nights` tales of Sindbad the Sailor, and of his voyages to China, Japan, and the Spice Islands of Indonesia, give quite enough evidence of the brilliance of Arabic commercial shipping and the knowledge of meteorology and geography which was at their disposal. Small wonder that the Faith spread through them from Morocco to Mindanao.
But, besides the SE Asian seas, arabic sailors penetrated far down the East coast of Africa, and also up the rivers which are channels from the Black Sea into the distant interior of Russia. The Safarname (Travel journal) of Suleiman, a sea-captain of Seraf, the port on the Persian Gulf recently excavated by Dr. David Stronach of the British Institute of Persian Studies, was published at the end of the 9th century AD with accounts of his voyages to India and China. It was translated into Latin, as giving some of the earliest first-hand knowledge of China which ever reached Europe.
The geographer Ibn Hauqal (floruit circa AD 975) wrote in his preface: “I have written the latitude and longitude of the places of this earth, of all its countries, with their boundaries, and the dominions of Islam, with acareful map of each section on which I have marked numerous places, e.g. the cities, the kasbahs, the rivers, the lakes, the crops, the types of agriculture, the roads, the distances between place and place, the goods for commerce and everything else in the science of geography which can be useful to sovereigns and their ministers and interesting to all people in general.
Abu-Reihan al-Biruni, Ibn Batuta and Abu`l-Haussan are amongst other names in the history of the science of geography whose worldwide travels were accompanied by meticulous observation and painstaking notes, which are amongst the proudest achievements of science in our world to this day.
Jaber ibn Haiyan, disciple of the sixth Imam Ja`afar-i-Sadeq, became known world-wide as “the Father of Chemistry” and of Arab alchemy. His influence on western chemistry and alchemy was profound and long-lasting. Some hundred of his works survive. Of him the late Sayyid Hebbat-ud-Din Shahristani of Kadhemain, once Iraq`s Minister of Education, writes: “I have seen some 50 ancient MSS of works of Jaber all dedicated to his master Imam Ja`afar. More than 500 of his works have been put into print and are for the most part to be found among the treasures of the National libraries of Paris and Berlin, while the savants of Europe nickname him affectionately `Wisdom`s Professor` and attribute to him the discovery of 19 of the elements with their specific weights, etc. Jaber says all can be traced back to simple basic particle composed of a charge of lightning (electricity) and fire, the atom, or smallest indivisible unit of matter, very close to modern atomic science.
The blending of colouring matters, dyeing, extraction of minerals and metals, steelmaking, tanning, were amongst industrial techniques of which the Muslims were early masters. They produced Nitric Acid, Sulphoric acid, Nitro-glycerin, Hydrochloric Acid, Potassium, Aqua Ammonia, Sal Ammoniac, Silver Nitrate, Sulphoric Chloride, Potassium Nitrate, Alcohol, Alkali (both still known by their Arabic names), Orpiment (yellow tri-sulphide of arsenic; arsenic is derived from the Persian zar = gold, adjective zarnee = golden, Arabised with article “al” to “al-zernee” pronounced “azzernee” and so taken into Greek where was turned to the recognizable word “arsenikon” which means “masculine” since the gold colour was supposed to link it with the sun, a musculine diety!): and finally – though this does not close the list we might cite – Borax, also an Arabic word – Booraq. Further, the arts of distilling, evaporation, sublimation, and the use of Sodium, Carbon, Potassium Carbonate, Chloride, and Ammonium were common under the Abbasid Caliphate.
Baron Carra de Vaux, author of the chapter on “Astronomy and Mathematics” in “The Legacy of Islam” (OUP 1931 pp. 376-398), points out that the word “algebra” is a Latinisation of the Arabic term Al-jabr (= “i.e. of complicated numbers to a simpler language of symbols)., thereby revealing the debt the world owes to the Arabs for this invention. Furthermore the numerals that are used are “Arabic numerals” not merely in name but also in fact. Above all Arabs` realisation of the value of the Hindu symbol for zero laid the foundation of all our modern computerised technology. The word “zero”, like its cousin “cipher” are both attempts at transliterating the Arabic “sefr”, in order to convoy into Europethe reality and the meaning of that word in Arabic.
De Vaux writes: “By using ciphers the Arabs became the founders of the arithmetic of everyday life; they mada algebra an exact science and developed it considerably; they laid the foundations of analytical geometry; they were indisputably the founders of plane and spherical trigonometry. The astrolabe (safeeha) was invented by the Arab Al-Zarqali (Arzachel) who lived in Spain AD 1029-1087. The word “algorism” is a latinisation of the name of his home province Al-Khwarizmi. The Arabs kept alive the higher intellectual life and the study of science in a period when the Christian West was fighting desperately with barbarism”.
This is not the place to go further into Muslim achievements in mathimatics and astronomy. Suffice it to refer once again to the Jalali calendar of Omar Khayyam, with its formulae for exact calculation of the timing of the earth`s orbits round the sun, to which reference has been made earlier.
Cordova Mosque is one of the finest monuments of Muslim art in Europe. Its architect and masons were local talent, who introduced a number of novelties. The Muslims excelled at mosaic, inlay, fretwork and applique work of all types. Marvellous doors, pulpits, and ceilings are decorated in many of the ancient mosques all over the Muslim world with a lacelike design of mosaic, carved invory and wood and plaster, and fitted pieces of carved wood interlocking with each other with consummate artistry. Chased and engraved wood and ivory are everywhere. Thus the Altar of the Church of Saint Isidore Hispalensis (archbishop of Seville in the first years of the 7th century AD) like the carved ivory jewel-case made for Queen Isabella in the 11th century and the carved ivory box now in the Church at Bayeux of the 12th century (obviously some Crusader`s loot from the East) inlaid with silver in chased gold, are examples of that art which was the glory of Eastern lands. All this delicate and minute handiwork was carried out with the crudest and roughest of tools, itself a further tribute to the skill and artistry of the makers.
Jewel-studded boxes and cases and caskets are to be seen in many places, though the best are on view in the museums of Damascus and Cairo. Well said Sa`adi: “An Eastern artist may take 40 years to make one porcelain vase: the West turns out 100 a day, all like: the comparative worth of the two products can be easily reckoned!”
The Muslims were also past masters of the art of carved and coloured plaster work, in a style which still subsists though modern technologies are, alas, rendering the skill rarer all the time. Tenth century examples, some with enamelled work also, are to be found in Andalusia. The Alhambra has 13th century masterpieces of this work. The glitter like the later Italian Majolica. The famous Alhambra flower-vase, 1.5 metres high, is unique in this line.
IX. Mechanical Engineering
About the author
Donald R. Hill, a retired engineer, became interested in Arabic while serving with Britain`s Eighth Army in North africa during World War II. After the war, he worked for the Iraq Pertoleum Company, returning to England to join Imperyal Chemical Industries. He later moved to senior positions in the subsidiaries of two U.S. petrochemical corporations, from which he retired in 1984. He now devotes his time to Arabic studies, in which he has earned a master`s degree from Durham University and a Ph.D. from the University of London`s School of Oriental and African studies. His translation of al-Jazari`s book of mechines won for him a share of the 1974 Dexter Prize, awarded by the American Society for the History of Technology.
The West is accustomed to seeing its own intellectual development as having been shaped, in the main, by internal factors. This view of history traces our heritage back from the Industrial Revolution to the Enlightenment and Renaissance and, thence, via the monkish scribes of the Middle Ages, to the fountainhead: Greece, Rome and the ancient empires of the Fertile Crescent.
But the picture is incomplete because it ignores the intermediation of the civilization of Greek Christendom (or Byzantium), Hindu India, Confucian China and Islam. Our subject here is the technology of medieval Islam – the knowledge it preserved, the new ideas it contributed to the medieval world and the inventions by which it anticipated later developments.
When the prophet Muhammad died in A.D. 632, he left behind a new religion with its administrative centre at Medina and its spiritual heart at Mecca. Within about a year of his death the rest of Arabia had joined the Muslim fold; by 750 the Arab Empire stretched from the Pyrenees to central Asia.
Although the advent of Islam brought immense political, religious and cultural changes, the technological traditions were largely unaffected. In mechanical engineering the Muslims adapted the techniques of earlier civilizations to satisfy the needs of the new society. These needs centered on a city life more extensive than any seen since Roman times.
Baghdad`s population is estimated to have reached about 1.5 million in the 10th century, and cities such as Cordoba, Cairo and Samarkand, although smaller, were still of considerable magnitude. Paris, by contrast, would not number 100,000 souls for another 400 years. Feeding and clothing the inhabitants of the Islamic world`s vast urban centers placed great demands on agriculture and distribution. These, in turn, depended on technology for supplying irrigation water to the fields and for processing the crops into foodstuffs.
Water and water power, therefore, will constitute our first concern. Then we shall describe water mills. Finally, we shall turn to descriptions, most of them in a handful of treatises that have come down to us, of water clocks, fountains and various automata, some of which might seem trivial to modern eyes. Yet they exploit concepts, components and techniques that did not enter the armamentarium of European engineering until the time of the Renaissance.
The most ancient water-raising machine is the shaduf, a counterweighted lever from which a bucket is suspended into a well or stream. It appears in illustrations from as early as 2500 B.C. in Akkadin reliefs and is still in use today in parts of the Middle East. Other traditional water-raising machines, introduced between the third and first centuries B.C., include the screw, or water snail, whose invention is attributed to the great mathematician Archemides. It consists of a helical wooden blade rotating within a barrellike wooden cylinder, a design that could not push water up inclines greater than about 30 degrees, although 20 degrees was more common.
Higher lift was achieved by the noria, a large wheel driven by the velocity of the current. On the outer rim a series of compartments are fitted in between a series of paddles that dip into the water and provide the propulsive power. The water is scooped up by the compartments, or pots, and is discharged into a head tank or an aqueduct at the top of the wheel. Norias could be made quite large. The well-known whells at Hama on the river Orontes in Syria have a diameter of about 20 meters. The noria is self-acting, and its operation thus requires the presence of neither man nor beast. It is, however, expensive to build and maintain.
The “saqiya” is probably the most widespread and useful of all the water-raising machines that medieval Islam inherited and improved. It is a chain of pots driven by one or two animals by means of a pair of gears. The animals push a drawbar through a circle, turning an axle whose pinion meshes with a vertical gear. The gear carries a bearing for the chain of pots, or pot garland – two ropes between which earthenware pots are suspended. The chain of pots is optimal for raising comparatively small amounts of water from comparatively deep wells.
Other mechanisms, however, were required to raise large quantities of water relatively small distances. The problem can be solved by using a spiral scoop wheel, which raises water to the ground level with a high degree of efficiency. The machine is very popular in Egypt nowadays, and engineers at a research laboratory near Cairo have been trying to improve the shape of the scoop in order to achieve the maximal output. Although it appears very modern in design, this is not the case; a 12th-century miniature from Baghdad shows a spiral scoop wheel driven by two oxen.
These machines are still in use in many oil-poor middle eastern countries, because for many purposes they are at least as efficient as diesel-driven pumps. Moreover, they do not require imported fuels, spare parts or labor. Vital time can therefore be saved, when the loss of even a single day`s operation of a machine can kill a crop, making reliable performance literally a matter of life and death.
Given the importance of water-raising devices to the economy of many Islamic societies, it is hardly surprising that attempts were made to introduce new designs or modify existing ones. Some of the most interesting innovations are found in one section of Ibn al-Razzaz al-Jazari`s great book, The book of knowledge of Ingenious Mechanical Devices, which was completed in Diyar Bakr in Upper Mesopotamia in 1206 AD.
From our point of view, the most significant aspect of these machines is the ideas and components that they embody. For example, one of them is explicitly designed to eliminate out-of-balance loading and so produce a smoother operation. Another incorporates a crank, the first known example of the non-manual use of this important component. Some of these devices functioned as curiosities.
The invention containing the most features of relevance for the development of mechanical design, however, was intended as a practical machine for high-lift duties: a twin cylinder, water-driven pump. A stream turned a paddle wheel meshing with a horisontal gear wheel, which was installed above a sump that drained into the stream. The horisontal wheel contained a slot into which a vertical pin fitted near the perimeter of the wheel.
The turning wheel moved two connecting rods back and forth, thus driving opposing pistons made of copper disks spaced about six centimeters apart, the gap being packed with hemp. The pistons entered copper cylinders, each one having a suction and delivery pipe. One piston began its suction stroke while the other began its delivery stroke. This machine is remarkable for three reasons: it incorporates an effective means of converting rotary into reciprocating motion, it makes use of the double-acting principle and it is the first pump known to have had true suction pipes.
Waterpower was clearly a prominent concern of medieval Islamic planners. Whenever they mentioned a stream or river, for example, they often included an estimate of how many mills it would operate. One might say that they assessed streams for “mill powe”
The three main types of waterwheel had all been in existence since Classical times – the horisontal wheel and two variations of the vertical wheel. The horisontal wheel has vanes protruding from a wooden rotor, onto which a jet of water is directed. In modern Europe the design was altered to use water moving axially, like air flowing through a pinwheel, creating the water turbine. Interestingly, wheels with curved blades onto which the flow was directed axially are described in an Arabic treatise of the ninth century.
The more powerful vertical wheels came in two designs: undershot and overshot. The former is a paddle wheel that turns under the impulse of the current. The overshot wheel receives water from above, often from specially constructed channels; it thus adds the impetus of gravity to that of the current.
When the levels of rivers fall in the dry season, and their flow diminishes, undershot wheels lose some of their power. Indeed, if they are fixed to the banks of rivers, their paddles may cease to be immersed. One way this problem was avoided by mounting the waterwheels on the piers of bridges and taking advantage of the increased flow there. Another common solution was provided by the shipmill, powered by undershot wheels mounted on the sides of ships moored in midstream. On the rivers Tigris and Euphrates in the 10th century, in Upper Mesopotamia, which was the granary for Baghdad, enormous shipmills made of teak and iron could produce 10 tons of flour from corn in every 24-hour period.
Gristmilling – the grinding of corn and other seeds to produce meal – was always the most important function of mills. Mills were, however, put to many other industrial uses. Among these applications were the fulling of cloth, the crushing of mettalic ores prior to the extraction process, rice husking, paper making and the pulping of sugarcane. The usual method of adapting waterwheels for such purposes was to extend the axle and fit cams to it. The cams caused trip-hammers to be raised and then released to fall on the material.
Where waterpower was scarce, the Muslims had recourse to the wind. Indeed it was in riverless Seistan, now in the western part of Afghanistan, that windmills were invented, probably early in the seventh century A.D. The mills were supported on substructures built for the purpose or on the towers of castles or the tops of hills. They consisted of an upper chamber for the millstones and a lower one for the rotor. A vertical axle carried either 12 or six rotor blades, each covered with a double skin of fabric. Funnel-shaped ducts pierced the walls of the lower chamber, their narrower ends facing toward the interior in order to increase the speed of the wind when it flowed against the sails.
This type of windmill spread throughout the Islamic world and thence China and India. In medieval Egypt it was used in the sugarcane industry, but its main application was to gristmilling.
Now we turn to a type of engineering that is quite different from the utilitarian technology described so far. We may perhaps call it fine technology, since its distinguishing features derive from the use of delicate mechanisms and controls.
Some of these devices had obvious practical uses: water clocks were used in astronomical observations and were also erected in public places; astronomical instruments aided both observation and computation. Other gave amusement and aesthetic pleasure to the members of courtly circles. Still others undoubtedly had didactic purposes, for example, to demonstrate the principles of pneumatics as understood at the time. Apart from astronomical instruments and the remains of two large water clocks in Fez, Morocco, none of theses machines has survived. Our knowledge of them comes almost entirely from two of Arabic treatises that have come down to us.
The first is by the Bano (Arabic for sons of) Musa, three brothers who lived in Baghdad in the ninth century. They were patrons of scholars and translators as well as eminent scientists and engineers in their own right. They undertook public works and geodetic surveys and wrote a number of books on mathematical and scientific subjects, only three of which have survived.
The one that concerns us here is “The Book of Ingenious Devices”. It contains descriptions, each with an illustration, of 100 devices, some 80 of which are trick vessels of various kinds. There are also fountains that change shape at intervals, a “hurricane” lamp, self-trimming and self-feeding lamps, a gas mask for use in polluted wells and a grab for recovering objects from the beds of streams. This last is of exactly the same construction as a modern clamshell grab.
The trick vessels have a variety of different effects. For example, a single outlet pipe in a vessel might pour out first wine, then water and finally a mixture of the two. Although it cannot be claimed that the results are important, the means by which they were obtained are of great significance for the history of engineering. The Banu Musa were masters in the exploitation of small variations in aerostatic and hydrostatic pressures and in using conical valves as “in-line” components in flow systems, the first known use of conical valves as automatic controllers.
In several of these vessels, one can withdraw small quantities of liquid repeatedly, but if one withdraws a large quantity, no further extractions are possible. In modern terms, one would call the method used to achieve this result a fail-safe system.
The second major treatise to have come down to modern times was written by al-Jazari at the close of the 12th century. He was a servant of the Artuqid princes, vasals of Saladin (who vanquished Richard the Lion Heart during the Third Crusade). His work places him in the front rank of mechanical engineers from any cultural region in pre-Renaissance times.
Several of al-Jazary`s machines have been reconstructed by modern craftsmen working from his specifications, which provided far more detail than was customary in the days before patent law was invented. Such openness has rarely been encountered until recent times.
Al-Jazari`s clocks all employed automata to mark the passage of the hours. These included birds that discharged pellets from their beaks onto cymblas , doors that opened to reveal the figures of humans, rotating Zodiac circles, the figures of musicians who struck drums or played trumpets and so on. Generally speaking, the prime movers transmitted power to these automata by means of pulley systems and tripping mechanisms. In the largest of the water clocks, which had a working face of about 11 feet high by 4.5 feet wide, the drive came from the steady descent of a heavy float in a circular reservoir.
Clearly, some means of maintaining a constant outflow from the reservoir was needed and was indeed achieved in a most remarkable way. Apipe made of cast bronze led out from the bottom of the tap, and its end was bent down at right angles and formed into the seat of a conical valve. Directly below this outlet sat a small cylindrical vessel in which there bobbed a float with the valve plug on its upper surface.
When the tap opened, water ran into the float chamber, the float rose and caused a plug to enter the valve`s seat. Water was thus discharged from a pipe at the bottom of the float chamber, and the valve opened momentarily, whereupon water entered from the reservoir, the valve closed momentarily and so on. An almost constant head was therefore maintained in the float chamber by feedback control, and the large float in the reservoir descended at constant speed. Al-Jazari said he got the idea for his invention from a simpler version which he attributed to Archimedes.
This clock did not record equal hours of 60 minutes each, but temporal hours, that is to say, the hours of daylight or darkness were divided by 12 to give hours that varied with the seasons. This measurement required another piece of equipment: the pipe from the float chamber leading into a flow regulator, a device that allowed the orifice to be turned through a complete circle and thus to vary the static head below the surface of the water in the reservoir. Previous flow regulators had all been inaccurate , but al-Jazari describes how he calibrated the instrument accurately by painstaking tial-and-error methods. Another type of clock, which may have been al-Jazari`s own invention, incorporates a closed-loop system: the clock worked as long as it was kept loaded with metal balls with which to strike a gong.
Al-Jazari also describes candle clocks, which all worked on a similar principle. Each design specified a large candle of uniform cross section and known weight (they even laid down the weight of the wick). The candle was installed inside a metal sheath, to which a cap was fitted. The cap was made absolutely flat by turning it on a lathe; it had a hole in the centre, around which, on the upper side, was an indentation.
The candle, whose rate of burning was known, bore against the underside of the cap, and its wick passed through the hole. Wax collected in the indentation and could be removed periodically so that it did not interfere with steady burning. The bottom of the candle rested in a shallow dish that had a ring on its side connected through pulleys to a counterweight. As the candle burned away, the weight pushed it upward at a constant speed. The automata were operated from the dish at the bottom of the candle. No other candle clocks of this sophistication are known.
Other chapters of al-Jazari`s work describe fountains and musical automata, which are of interest mainly because in them the flow of water alternated from one large tank to another at hourly or half-hourly intervals. Several ingenious devices for hydraulic switching were used to achieve this operation. Mechanical controls are also described in chapters dealing with a potpourri of devices, including a large metal door, a combination lock and a lock with four bolts.
We see for the first time in al-Jazari`s work several concepts important for both design and construction: the lamination of timber to minimize warping, the static balancing of wheels, the use of wooden templates (a kind of pattern), the use of paper models to establish designs, the calibration of orifices, the grinding of the seats and plugs of valves together with emery powder to obtain a watertight fit, and the casting of metals in closed mold boxes with sand.
Previously how Islamic mechanical technology entered Europe is unknown. Indeed, there may be instances of ideas being inherited directly from the Greco-Roman tradition into medieval Europe. Nor can we rule out cases of reinvention. When allowances have been made, however, it seems probable that some elements of the rich vein of Islamic mechanical engineering were transmitted to Europe.
Any such technological borrowing would probably have been mediated by contacts between craftsmen, by the inspection of existing machines working or in disrepair and by the reports of travelers. The most likely location for the transfer of information was Iberia during the long years in which Christians and Muslims coexisted.
The diffusion of the elements of machine technology from lands of Islam to Europe may always remain partly conjectural. This should not in any way be allowed to devalue the achievements of the Muslim engineers, known and anonymous. Nor should we overemphasize the relevance of the Islamic inventions to modern machinery. Of equal or great importance is the contribution they made to the material wealth, and hence the cultural riches, of the medieval Near East.