The following article by Abdel Aziz al-Jaraki, a scholar from Damascus, describes the context of the investigation carried on since several decades on a famous clock built by Fakhr al-Din Ridhwan al-Sa'ati at the beginning of the 6th centuty of Hijra (1202 CE) in his work `Amal al-Sa'at wa 'l-`Amal biha (The Operation of clocks and working with them). The author surveys also his ongoing endeavours to reconstruct this instrument and make it live again.
A number of attempts were made to explain a device that existed in the past near the Umayyad mosque in Damascus and had functioned for many centuries without much success. Of these are the famous scholarly works of Wiederman  and Hill . These considerations drove this author to try to shed some light upon this subject using personal interest, deep understanding of the original manuscripts and hands on experience in reconstructing such clocks.
The device in question is a water clock that alerted hourly beats with loud sound, six centuries before the construction of London's Big Ben in1859.
The clock was placed at the eastern entrance of the Umayyad mosque on the right side of the mosque exit, near the palace of government (Qasr al-Khadhra). The eastern door was named Bab al-sa'at (The Hours Gate). There are other names given to it (e.g., Bab Jayrun and Bab El-Labbadin). The clock was described by one of its early operators, Ridhwan, in a manuscript dated in 600 H/1202 CE. The device was named after him: the clock of Ridhwan al-Sa'ati. It is probably one of the most important mechanical devices in Muslim heritage that used relatively advanced practical technology.
|Figure 1. The Umayyad mosque in Damascus. This image has been released into the public domain by its author 'Isaam Bayazidi (at the Arabic Wikipedia project).|
This clock demonstrated a great importance of time estimation and consequently earned a prominent location between the government palace and the Umayyad mosque.
Some of its unique features included:
(a) Ability to connect the Hijra calendar for seasons change to the weather,
(b) Define the angle of the sun's rays,
(c) Divide the daytime into 12 equal hours, no matter how much it gets longer or shorter around the whole year,
(d) Alerts the hour by giving a loud sound.
Because of all these features, Ridhwan (as operator of the clock) was awarded a high status as a minister in the government and a special budget was devoted to the device by the government of the time.
Ridhwan's clock belongs to the group of hydraulic timing devices which were well known in the past such as Clepsydra  and Ghati . It demonstrates the development that had occurred in clock construction from the time when a water-wooden clock was gifted by Caliph Harun al-Rashid in 170 H/786 CE to Charlemagne I (reigned 768-814 CE). It is believed that different forms of such devices were spread in the Muslim world.
From the manuscript of Ridhwan al-Sa'ati, we find that Abu 'Abdullah Muhammad b. Naser b. Saghir b. Khalid al-Kaysarani, a scholar well versed in poetry, observational astronomy, engineering and mathematics, had started managing and operating the clock before the Sultan Nur Ed-Din Mahmud b. Zanki took over Damascus in the year 549 H/ 1154 CE.
After al-Kaysarani, the father of Ridhwan al-Sa'ati, Muhammad b. 'Ali al-Khurasani, had reconstructed the clock after it had got burned in 562 H/ 1166 CE. Then Ridhwan al-Sa'ati mentions three other people that had operated the clock after his father's death. These were: al-Muhadhab b. al-Naqqash, al-Muhadhab b. al-Hajib and Abu al-Fadhl al-Najjar.
Subsequently, the management of the device was transferred to Ridhwan al-Sa'ati himself. Ridhwan was known as Fakhr al-Din Ridhwan al-Sa'ati al-Khurasani al-Dimashqi. He held a ministerial post in the time of King 'Isa b. al-Malik al-'?del Muhammad who had assigned a special budget to this device.
The clock of Ridhwan  is a mechanical device – relatively advanced for its period– that works on water evacuation. It was constructed before it was described in 600 H/1202 CE.
The device was described in three manuscripts. The original (which was dictated by Ridhwan himself) is located now in the the library Forschungsbibliothek in Gotha in Germany. The other one is a copy that was scribed fifty-six years after the original by Baylak 'Abdullah al-Qabagaqi , an Egyptian engineer; it is kept in Istanbul. A third manuscript, a copy of that of al-Qabagaqi; it is preserved in Cairo (National Egyptian Library, Taymur Pasha collection, MS 24 Sina'a).
The clock device was described by different travelers. The first of whom was Rabbi Benjamin of Tudela who visited Damascus between 554 and 570 H (159-1174 CE) . His description is as follows:
"Damascus has a Mohammedan synagogue [sic] that is called the synagogue of Damascus; it is unequalled in the world. This must be the palace of Ibn Haddad. One of the walls was built by a magical power and it contains as many openings as the number of days of the solar year. The sun throws its rays in succession in the openings. These are divided into twelve degrees to match the hours of the daytime, from this arrangement one can figure the time ."
This description, of a sun clock assumed to be located near the Umayyad mosque, does not match by any means any description of the clock such as those made by Ridhwan himself and by two subsequent travelers, Ibn Jubayr and Ibn Battuta. It is likely that the description made by Rabbi Benjamin was mistakenly taken by Donald R. Hill in his book Arabic Water clocks as that of Ridhwan al-Sa'ati's clock.
Ibn Jubayr had described this water clock in the account he made of his journey and stay in Damascus in the year 580 H/1184 CE. His description is very close to that of Ridhwan al-Sa'ati's manuscript. The account by Ibn Battuta in 726 H/1326 CE is close to Ibn Jubayr's but much more concise.
The survey and the analysis of all the available literature about Ridhwan's clock revealed that the Egyptian engineer 'Abdullah Baylak al-Qabagaqi remains the person who had best understood this water clock because of his direct acquaintance with the device, and also because of a pertinent note which he inserted in his copy of Ridhwan's original manuscript:
"The author of this manuscript (himself) was aware of and an expert in the work of the clock except for al-siniyya [the tray]".
By this pertinent note, he revealed one of the weak points of Ridhwan's work related to the lack of understanding of a special part of the clock called al-siniyya, which is designed for the water exit.
Figure 3. Narrative of the description of the clock by Ibn Jubayr. In: Rihlat Ibn Jubayr, Beirut, 1986, vol. 2, pp. 218-219.
Figure 4. Narrative of Ibn Battuta. In: Rihlat Ibn Battuta. Quoted from the website al-Waaraq
In the early twentieth century, the German physicist and historian Eilard Wiedemann and Fritz Hauser studied the clock device and reached a high level of understanding of its workings. They published the results of their research in 1915 in several articles. Whilst their work was pioneering, unfortunately they produced an incomplete conception of the device and their explanations contained some errors.
Donald R. Hill discussed the subject of Ridhwan's clock. He relied on the studies of Wiedemann and Hauser on various water clocks, using much of their engineering drawings, albeit without acknowledging them. He then concluded his study by affirming: "All the descriptions written about this instrument aren't sufficient to reconstruct it". It appears that he confused the description of this same clock with that made by Isma'il ibn al-Razaz al-Jazari in his original Arabic manuscript which Hill had edited in the book A Compendium on the Theory and Practice of the Mechanical Arts (completed by al-Jazari in 602 H/1206 CE).
In the year 1926 an educational curriculum, named al-Qira'a al-Rashideh, was adopted in Syria and Egypt. Its first set of lessons was a text of the famous Muslim scholar Imam al-Ghazali (died on 505 H/1111 CE) about the beating water clock which carries the main concept of the clock of Ridhwan al-Sa'ati. An original copy of that educational book is kept in al-Zahiryeh library in Damascus. The present author was fortunate to have had access to it and scrutinized it carefully.
Figure 5. Diagram of Ridhwan al-Sa'ati's clock as depicted in the original manuscript of his book 'Amal al-Sa'at wa 'l-'Amal biha as edited by M. A. Dahman (Damascus, 1981). Reproduced from Jalal Shawqi, Al-'ulum wa 'l-ma'arif al-handasiyya fi al-hadhira al-islimiya (Mechanical Knowledge in Islamic Civlisation), Kuwait: KFAS, 1995, p. 297.
Furthermore, Sheikh Muhammad Ahmad Dahman edited the manuscript of Ridhwan and presented it with an important and learned introduction. He assumed that the manuscript rendered the original text sufficiently clear to assist in the reconstruction of the clock and consequently, did not add any comments to explain its operation and construction .
One has to warn, at this juncture, that there are claims that some parties actually reconstructed the clock of Ridhwan al-Sa'ati (the Umayyad mosque clock) and have even placed its pictures on the internet. Such claims have to be challenged through scientific scrutiny and due diligence by returning to the original manuscript and the works and drawings of Wiederman and Hauser, and Donald Hill.
To know this instrument with all its details and to try to reconstruct it, one should possess a detailed knowledge of Arabic mechanical works, including the book of Banu Musa (Baghdad, 3rd century H/9th century CE) Kitab al-hiyal (Book of machines), al-Jazari's long encyclopedia al-Jami' bayn 'l-'ilm wa 'l-'amal fi sina'at al-hiyal (Compendium of the theory and practice of the mechanical arts), the works of Taqi al-Din ibn Ma'ruf and the state of Arab mechanical engineering up till 10th century H/16th century CE.
The present author, with the encouragement of the Foundation for Science, Technology and Civilisation (FSTC, UK), has been able to reconstruct this fascinating and unique clock.
To have such a clock nowadays working, beating and ringing is a gratifying pleasure and a call from the past that fills us with pride and adds magic to the reality. Let us now describe this extraordinary device which was once considered one of the wonders of the Muslim world.
The original device was located on two levels on the right side of the one who leaves the eastern door of Umayyad mosque. The lower level contains the copper water vessel and float device that generates the movement, the upper level contains the mechanical parts that cause and control the activities of the clock.
The upper external part is a large wood and copper board of approximate dimensions (240 x 240 cm) containing the following:
1. Twelve brass doors, each one rotates on the hour to show its back face with the number of the hour that has passed;
2. Below the doors there is an indicator with a meniscus that slides – to show the parts of an hour – beside a ruler scaled into five minute parts;
3. Above each door there is a copper dome, each dome rises after an hour has passed;
4. At the sides of the copper doors two falcons (bazan) throw copper balls into a large copper cup to generate the ringing sound;
5. It has a circular copper plate with the signs of the zodiac inscribed on the circumference to connect the Hijri calendar (lunar calendar) with the solar calendar and also to forecast the annual weather and the change of seasons;
6. An arrow indicates the angle of the sun with respect to the earth during the daytime;
7. There is a semi-circular disc called the night circle that contains 12 circular openings that are lit when the clock turns to show the time at night;
8. The most important function of this clock is that it is called the temporal clock. This is because it divides each daytime whatever its length (a summer day or a winter day) into twelve equal hours and the same for the night hours. Thus, the daytime always remains 12 hours from sunrise to sunset which fixes the times of prayers (the noon prayer is always at 6 o'clock).
The ordinary 24-hour is called the flat clock and resembles our daily clocks (always dividing the day and night together into 24 hours). The Ridhwan temporal clock has the capability of working as flat clock as well. Obviously both clocks would be identical in timing during the spring equinox (21-22 March) and the autumn equinox (21-22 September) when the lengths of the day and the night are equal.
It is perhaps worth commenting that the correct title of the original manuscript of Ridhwan al-Sa'ati is `Amal al-Sa'at wa 'l-`Amal biha not 'Ilm al-Sa'at wa 'l-`Amal biha. The first means "The making of al-sa'at (the clock) and working with it". The second, which is used by all western researchers, means "The science of al-sa'at (the clocks) and working with it". This error unfortunately hides the fact that Ridhwan's manuscript was actually for instructing the operator and not on the science of clocks. Not knowing Arabic and not having hands on experience with water clocks can easily cause misinterpretation. For example, if one analyses the text carefully, one would find that Ridhwan divided the water regulator into 72 parts and not to 360 parts (like in Hill's explanation). One can even identify some other mistakes actually made by Ridhwan himself.
Ridhwan had explained in his manuscript that he wrote the description of al-sa'at to instruct a midi-clever worker on how to make the water clock.
 Eilhard Weidermann and Fritz Hauser, Uber die Uhren im Bereich der islamischen Kultur. Halle: Karras, 1915.
 Donald R. Hill, Arabic Water clocks, Aleppo: Aleppo University, Institute for the History of Arabic Science, 1981.
 In the clepsydra, timing is measured by the movement of the water surface as it leaks from a containing vessel that has an orifice at its base.
 Timing is measured in this waterclock by the level of an empty open vessel as it sinks due to water leaking into it through an orifice at its base. The device existed mainly in India in the past.
 It should be noted that the term sa'at is the plural of hour in Arabic. Nowadays, the Arabic term al-sa'ati refers to "watchmaker". The world famous advertising firm "Saachi and Saachi" derives its name from the Iraqi origin of the family named as-Sa'ati. The old Arabic term for clock was minjana or binkam.
 This author flourished around 681 H/1282 CE, for amongst his writings Kanz al-Tijjar fi Ma'rifati 'l- Ahjar is dated in this year (681 H/1282 CE). An autograph of this text is kept in the French National Library in Paris (MS arabe 2779). In it he describes the use of magnetic compass by Arab navigators.
 D.R. Hill, op. cit.
 The Itinerary of Rabbi Benjamin of Tudela, translated by A. von Asher (London, 1841), vol. 1, p.84; quoted in D.R. Hill, Arabic Water Clocks.
 Ridhwan b. Muhammad al-Sa'ati, 'Ilm al-Sa'at wa 'l-'Amal biha, edited by Muhammad Ahmad Dahman. Damascus: Maktab al-dirasat al-islamiyya, 1981.
* Abdel Aziz al-Jaraki is an architect in Damascus, and a consultant for Foundation for Science, Technology and Civilisation (FSTC), UK.