During the period of Islamic-Arabic extraordinary activity in Science and Technology (9th-13th century), there are some recorded contributions to the area of Automatic Control mainly in the development of water clocks using float valve regulators, different level controls using float valves or combination of syphons and the development of On-Off control. In this short survey, Professor Dr Mohamed Mansour, former Professor of Control Engineering At ETH Zürich surveys the subject by investigating the words of Banu Musa, Al-Muradi, Ridhwan al-Sa'ati and Al-Jazari.
Professor Dr. Mohamed Mansour*
During the period of Islamic-Arabic extraordinary activity in Science and Technology (9th-13th century), there are some recorded contributions to the area of Automatic Control mainly in the development of water clocks using float valve regulators, different level controls using float valves or combination of syphons and the development of On-Off control.
Figure 1: Professor Dr Mohamed Mansour.
The Islamic Arabic Automatic Control Technology had as a basis the Greek Technology of two scientists, namely Philon of Byzantium (Rhodes and Alexandria) of the second half of the third century BCE (his book, the Pneumatica was translated from Arabic into French and German in 1902 and 1899 respectively), and Heron of Alexandria of the first century CE (his book the Peumatica was translated into English and German in 1851 and 1899 respectively).
It is noted in Greek technology the language is Greek but the scientists need not be Greek as in the case with Islamic-Arabic technology.
It is known that there are hundreds of thousands of manuscripts dealing with Islamic Science and Technology to be edited and it is assumed that some of them deal with technology. This report is based on the following references [1-6].
Figure 2: Al-Biruni's Mechanical Calendar (British Library, MS OR 5593). (Source).
1. Automatic Control in Water Clocks
1.1. "The work of Archimedes on the Building of Clocks"
This is an Arabic book whose Arabic author is called pseudo-Archimedes with the earliest reference to it in the Fihrist of Al-Nadim (died 955 CE). From the literary style and the technique of its drawings, this clock book seems to be an Islamic work based on Greek-Roman technology as mentioned in . This clock used a float level regulator, which makes it a feedback device. A large float drove the whole apparatus. The description of the complicated clock is so thorough that it could be reconstructed almost completely. This book did have considerable influence on the two great chorological books of Al-Jazari and Ibn Al-Sa'ati and other Arabic authors like Ibn Al-Akfani.
Figure 3a-b: The Rear Perspective View.
1. 2. "Al-Jami bayna Al-Ilm wa 'l-'amal al-nafi' fi sina'at al-hiyal by Al-Jazari
This book  was written in 1206. Al-Jazari is from Al-Jazira, the area between Tigris and Euphrates. Sarton  mentions: "This treatise is the most elaborate of its kind and may be considered the climax of this line of Muslim achievement". "The distinctive feature of the book is its practical aspect. The book is rich in minute description of various kinds of devices. Hill maintains: "It is impossible to over-emphasize the importance of Al-Jazari`s work in the history of engineering. Until modern times, there is no other document from any cultural area that provides a comparable wealth of instructions for the design, manufacture and assembly of machines. Al-Jazari did not only assimilate the techniques of his non-Arab and Arab predecessors, he was also creative. He added several mechanical and hydraulic devices. The impact of these inventions can be seen in the later designing of steam engines and internal combustion engines, paving the way for automatic control and other modern machinery. The impact of Al-Jazari`s inventions is still felt in modern contemporary mechanical engineering ."
Hill  translated the book into English in 1974. A German translation was made in 1915. The chapter on water clocks describes 10 water clocks, the first two of them use float valve regulators. The various time-indicating mechanisms are propelled by a float. The other clocks are regulated differently. Al-Jazari mentions an old machine, which he inspected, in which a musical automaton was powered by a vertical water wheel. In his comments on this machine, he clearly implies that he knew how to control the speed of such a wheel by means of an escapement.
Figure 4: Miniature depicting an automat from a copy of al-Jazari's Kitab fi marifat al-hiyal al-handasiyya. MS copied in Syria or Egypt in 1315 CE. Leaf: 31.5 × 22 cm. Copied by Farrukh ibn Abd al-Latif. Opaque watercolor, ink and gold on paper, H: 30.2 W: 21.7 cm. (Source).
1.3. "Book on the Construction of Clocks and their Use" by Ridwan b.Muhammad Al-Saati Al-Khurasani (1203)
This book describes the monumental water clock built by Ridwan`s father at the Jayrun gate in Damascus. A German translation was made in 1915. A large float drives the clock, float valve regulator and the device for varying the length of the hours are incorporated.
1.4. "The Book of Secrets about the Results of Thoughts" by Al-Muradi of Andalusia (11th century)
This is the earliest description in Arabic of water clocks. This book deals with water clocks and other devices using automata. The treatise consists of 31 models of which 5 are essentially very large toys similar to clocks, in that automata are caused to move at intervals, but without precise timing. The prime movers are water wheels that can be overshot or undershot depending on the intensity of flow. There are nineteen clocks, all of which record the passage of the temporal hours by the movements of automata. The power came from large outflow clepsydras provided with concentric siphons. This power was transmitted to automata by very sophisticated mechanisms, which included segmental and epicyclic gears and the use of mercury. These are highly significant features; they provide the first known examples of complex gearing used to transmit high torque, while the adoption of mercury reappears in European clocks from the thirteenth century onwards.
Unfortunately, the only known manuscript of this work is badly defaced and it is not possible to understand exactly how the clocks worked. A weight driven clock with a mercury escapement appears in "Libros del Saber", a work written in Spanish at the court of Alfonsos of Castille about 1277 and consisting of translations and paraphrases of Arabic works. A novel feature in this treatise is the use of mercury in balances. Al-Zarquali built two large water clocks on the banks of the river Tagus at Toledo in 11th century .
Figure 5: The musical robot band designed by al-Jazari. (Source).
1.5. "Kitab Mizan Al-Hikma (The Book on the Balance of Wisdom)", Al-Khazini (1121-1122)
The eighth treatise of this work described two steelyard clepsydras. The main one, called the Universal Balance, was designed for 24-hour operation, and consisted of an iron beam divided into unequal arms by a fulcrum. An outflow clepsydra equipped with a syphon was suspended on the end of the short arm, and two movable weights, one large and one small, were suspended from the long arm, which was graduated into scales. As water discharged from the clepsydra, the weights were moved along the scale to keep the beam in balance. At any moment the hour of the day could be to minutes from the position of the small one.
Figure 6: Two pages from the manuscript of Al-Muradi Kitab al-asrar fi nata'ij al-afkar preserved at the Biblioteca Medicea-Laurentiana in Florence, Italy, MS Or 152. Note the damaged state of the manuscript. Source: Eduard Farré Olivé, La clepsidra de las Gacelas del manuscrito de relojes de Al-Muradi, Arte y Hora, March-April 1998, N°. 128-H11, pp. 10-18.
2. Automatic Control of Banu Musa
Kitab al-Hiyal (The Book of Ingenious Devices) is a mechanical writing by Banu Musa bin Shakir (9th century). The three sons of Musa organized translation and did original work in "Bayt Al-Hikma" (House of Wisdom) which was the science academy in Baghdad, the greatest scientific institution since the Museum and Library of Alexandria. Banu Musa were supporters of the translation movement which gathered momentum as that important epoch of the Islamic scientific awakening reached fruition in the 9th century. They extended their patronage to Thabit Ibn Qurra, to Hunayn Ibn Ishaq and to many other translators and scholars. They left more than 20 works which are known, including the seminal engineering book "Kitab Al-Hiyal" translated into English by Donald Hill in 1979 and parts of it into German by Wiedemann and Hauser in 1918 and Hauser in 1922. The book was edited in Arabic by Ahmad Al-Hassan in 1981.
Figure 7a-b: Reconstruction of the clock of Al-Muradi by Spanish scholars. A general view with its side opening revealing the working of the mechanism. Source: Eduard Farré Olivé , De Mensura Temporis. (1ª parte) "Arte y Hora" n. 123-H6, March-April 1997, pp. 8-16 (2ª parte) "Arte y Hora" n. 127-H10, January-February 1998, pp. 10-17; and Eduard Farré Olivé, La clepsidra de las Gacelas del manuscrito de relojes de Al-Muradi.
The written Arabic heritage in mechanical technology begins with the Banu Musa book. It is possible they knew Heron's Mechanics written in Alexandria in the first century and translated by Qusta Ibn Luqa at the time of Banu Musa. Hero‘s other books may have been known to the brothers, for he enjoyed great fame among Arabic scholars in the 10th century.
Banu Musa describe one hundred ingenious devices. Hill identified twenty five devices resembling the ones of Heron's and Philon's books. There exist also other parts of the Banu Musa machines which resemble certain elements in Hero and Philo work. There are Banu Musa machines which bear no resemblance to either Hero or Philo. These include the fountains and dredging machine designed to salvage submerged objects from the bottom of rivers and seas and so on. Banu Musa made use primarily of the principles of the science of hydrostatics and aerostatics. They used automatic valves, delayed-action systems and their application of the principles of automatic control testify of creative mentality. Hill notes the use of crankshafts for the first time in the history of technology.
In two models, they used a mechanism similar to the modern crankshaft, thus outstripping by 500 years the first description of the crankshaft in Europe. Mayr  mentions that they used syphons, float valves, Philon`s oil lamp, water wheels, etc. Some control systems work with nonmoving parts combining the principle of Philon`s oil lamp with some cleverly arranged syphons. They have contributions in technological refinements and new applications. They install throttling valves directly in the pipe requiring no constant force to keep them closed. These appear first in the book of Banu Musa. Also they introduce improvements on Philon`s oil lamp by ingenious combination of syphons added to the original system. Most important is the use of On-Off control with upper and lower limit for the controlled variable. Systems of this class are widely used in modern technology. The float valve used by Banu Musa, Al-Jazari and other Arabic engineers emerges again in the middle of the 18th century in Europe and in England.
Figure 8: Diagram of a selftrimming lamp from Kitab al-hiyal (Book of ingenious mechanical devices) by Banu Musa, preserved in the Granger Collection in New York. (Source).
 Otto Mayr, The Origins of Feedback Control. M.I.T. Press, 1970.
 Ahmad Y.Al-Hassan & Donald R.Hill, Islamic Technology. Cambridge University Press and Unesco, 1986.
 Donald R. Hill, Arabic Water Clocks. University of Aleppo, 1981.
 Banu Musa, The Book of Ingenious Devices. An Annotated Translation of the Treatise of Banu Musa by Donald R. Hill. Dordrecht: Reidel, 1979; reprinted in Islamabad, 1989. The Arabic text of this treatise was edited by Ahmad Y. Al-Hassan: Banu Musa, Kitab Al-Hiyal, Aleppo: Publications of the Institute for the History of Arabic Science, University of Aleppo, 1981.
 Al-Jazari, Al-Jami' bayna al-'ilm wa-'l-'amal al-nafi' fi sina'at al-hiyal (A Compendium on the Theory and Practice of the Mechanical Arts) by Ibn Al-Razzaz Al-Jazari (1206), edited by Ahmad Y.Al-Hassan, University of Aleppo,1979.
 George Sarton, Introduction to the History of Science, Philadelphia, 1931, vol. 2.
* Professor Dr. Mohamed Mansour was Emeritus Professor of Control Engineering at Swiss Federal Institute of Technology (ETH) in Zurich, Switzerland from September 1968 until September 1993. His fields of interest are control systems, especially stability theory and digital control, stability of power systems, and digital filters. He has published about 200 scientific papers, edited 6 books and supervised 47 Ph.D Students. See Prof. Dr.Mohamed Mansour: Publications and Curriculum Vitae; Mansour, Mohamed and Prof. Dr. Mohamed Mansour.