Mechanical Engineering

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 civilisation 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 AD 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 civilisations to satisfy the needs of the new society. These needs centred 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 centres 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 BC 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 barrel-like 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 labour. 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 horizontal gear wheel, which was installed above a sump that drained into the stream. The horizontal 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 centimetres 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 power”.

Watermills

The three main types of waterwheel had all been in existence since Classical times – the horizontal wheel and two variations of the vertical wheel. The horizontal wheel has vanes protuding 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.

Windmills

Where waterpower was scarce, the Muslims had recourse to the wind. Indeed it was in river-less 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 grist-milling.

Part II

Fine Technology

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.

Water Clocks

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. A pipe 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 trial-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.

Candle Clocks

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.

Miscellaneous

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 minimise 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.

Conclusions

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 travellers. 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 over emphasise 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.

THE END
References:

D.R. Hill (1991) Mechanical Engineering in the Medieval Near East. Scientific American, May: 64-69.
S.M.R. Musawi Lari (1977) Western Civilisation Throughout Muslim Eyes (Translated by: F.J. Goulding), Publisher: The Author, (Iran).
H.P. Rang & M.M. Dale (1993) Pharmacology (2nd ed.), Churchill Livingstone, Edinbburgh, p 3.

Source: al-shia.org

 


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