Banū Mūsā brothers | |
|---|---|
بنوموسی | |
 A blueprint left by theBanu Musa brothers of anoil-lamp that mechanically trims itself without human intervention—a significant innovation for the time | |
| Born | 9th century |
| Relatives | Nuʿaym ibn Muḥammad ibn Mūsā, the son of Abu Ja'far Muhammad |
| Academic work | |
| Era | Islamic Golden Age |
| Institutions | House of Wisdom |
| Main interests | Astronomy,geometry,mathematics, technology |
| Notable works | Kitab al-Hiyal al-Naficah ("The Book of Ingenious Devices"); Kitāb Maʿrifah masāḥat al-ashkāl al-basīṭah wa-al-kuriyyah ("Book on the Measurement of Plane and Spherical Figures") |
TheBanū Mūsā,[a] literallyThe Sons of Moses, refers to aPersian family ofpolymaths,astronomers,mathematicians, andengineers active in 9th centuryBaghdad. Both their own contributions and their direct connections to other prominent scholars of theHouse of Wisdom mark them as one of the most preeminent figures of theIslamic Golden Age.
The termBanū Mūsā is derived from the name ofMūsā ibn Shākir, and most commonly refers to his three sons;Muḥammad ibn Mūsā (before 803 – February 873);Aḥmad ibn Mūsā (d. 9th century); andAl-Ḥasan ibn Mūsā (d. 9th century).
Mūsā ibn Shākir was a renownedastronomer serving directly under theAbbasid caliphal-Ma'mun. After his death, his three sons received an education under al-Ma'mun’s direct orders, and were enrolled at theHouse of Wisdom in Baghdad. There they undertook the translation ofancient Greek works acquired fromByzantium, which they used to develop their own technological,mathematical andastronomical ideas. They were some of the earliest scholars to adoptGreek mathematics, but innovative in their approach to the concepts ofarea andcircumference by expressing them using numerical values instead ofratios. Theymade geodesic measurements to determine the length of a degree oflatitude, and so obtained a relatively accurate value for thecircumference of the Earth.
The Banū Mūsā wrote almost 20 books, all but three of which are now lost. The most important of all their works was atreatise ongeometry,Kitāb Maʿrifah masāḥat al-ashkāl al-basīṭah wa-al-kuriyyah ("Book on the Measurement of Plane and Spherical Figures"), which was used extensively by medieval mathematicians. Their most famous extant work (of which the oldest and most reliable copy is in theTopkapi Sarayi inIstanbul) isKitab al-Hiyal al-Naficah ("Book of Ingenious Devices"). It describes 100 inventions, many of which were pouring vessels, intended to entertain party guests. Some of their innovations, such as those that involvedfluid pressure variations andvalves, remained unsurpassed until the modern period. One of those inventions includes an automatic flute player that may have been the first programmable machine or computer.
The Banu Musa were the three sons ofMūsā ibn Shākir, who earlier in life had been ahighwayman and astronomer inKhorasan of unknown pedigree.[1] After befriendingal-Ma'mun, who was then a governor of Khorasan and staying inMerv, Musa was employed as anastrologer andastronomer.[2]
After Musa's death, the three orphaned children were cared for at the court of al-Maʾmūn, who made the senior Baghdad officialIshaq ibn Ibrahim al-Mus'abi their guardian.[3][4] Al-Ma’mun recognized their abilities, and enrolled them in theHouse of Wisdom, an institution created by him as a centre for collecting, translating and studying books from other lands.[5][6] In Baghdad, where they apparently lived for the rest of their lives, the three brothers studiedgeometry,mechanics, music,mathematics andastronomy, trained by a senior courtastrologer,Yaḥyā bin Abī Manṣūr.[2][7]
The three brothers, Moḥammad, Aḥmad, and Ḥasan, are often listed in what is assumed to be their order of seniority.[8][note 1]
The Banū Mūsā assisted al-Ma'mun's in his obsession to obtain and translate works from Greek intoArabic. They sent forGreek texts from theByzantines, or travelled themselves toByzantium to acquire them.[9] During their working lives they used their wealth and energy towards the translation of these works.[8] On his way home to Baghdad from Byzantium, Muhammad met and recruitedThābit ibn Qurra,[9] amoney changer fromHarran. Thābit went on to make important discoveries in algebra, geometry, and astronomy.[2][10]
Under the direction of al-Ma'mun, the Banū Mūsā worked with the most talented men available, includingal-Khwarizmi,al-Kindi,Al-Ḥajjāj ibn Yūsuf ibn Maṭar, and the mathematician and translatorHunayn ibn Ishaq, who became a close friend of one of the brothers, Muhammad.[7] Of the translators, three were paid about 500dinars a month.[1] None of the brothers were medically trained, and relied upon Ishaq bin Hunayn and Thabit bin Qurra to translate Greek medical works.[11] They exchanged ideas with other experts, including the astrologerAbu Ma'shar al-Balkhi, with whom Muhammed was in continuous contact.[12]
The brothers are likely to have used portable instruments such asarmillary spheres or dials when making their observations, which were recorded from around 847 to 869. From their Baghdad home, they observed stars in theconstellationUrsa Major In 847–848, and measured the maximum and minimumaltitudes of the Sun in 868–869. They also observed theSeptember equinox in the city ofSamarra. To calculate the difference inlatitude between Samarra andNishapur, they organized simultaneous observations of alunar eclipse.[13]
Whilst working for al-Ma’mun, the Banū Mūsā travelled to a desert nearSanjar, in northernMesopotamia, with the aim of measuring the length of a degree of latitude along ameridian, and from that verifying a value of 25,000 miles (40,000 km) obtained by the Greeks for theEarth's circumference.[2][9][14] They first measured the altitude of thePole Star, and then, using pegs and a rope as they moved north, stopped again when the altitude of the star changed by one degree. They repeated the same measurement, this time travelling southwards. The process was repeated at al-Kufa. From their measurements, the brothers obtained a value for the circumference of the Earth of 24,000 miles (39,000 km).[14]
Under the patronage of the caliphs that followed al Ma’mun—al-Mu'tasim,al-Wathiq, andal-Mutawakkil—the brothers continued to acquire great wealth and become influential in court. They used much of their wealth to collect the works of ancient writers, a practise that was later copied by other scholars at the House of Wisdom.[7][3] The brothers were very active during the reign of al-Mutawakkil, who was interested in mechanics, and asked the Banū Mūsā to write on this subject.[15] A son of al-Mu'tasim was educated by Ahmad, but the brothers' relations with the caliph are otherwise unknown. When close to death, al-Mu'tasim's successor al-Wathiq called together his astrologers, including Muhammed, who erroneously pronounced that the caliph would live for another 50 years.[15]
The Banū Mūsā's employment by the caliphs for differentcivil engineering projects, including their involvement in the building of the city of al-D̲j̲aʿfariyya for al-Mutawakki, led to them becoming involved in court politics. In 860, the Banū Mūsā and Mutawakkil’s architects were involved in obtaining land for a new city. The caliph’s advisor suggested that Muhammed and Ahmad bin Musa should be forced to contribute towards the expense of a new palace nearby.[16]
The peak of Muhammad's political activity came towards the end of his life, when Turkish commanders were starting to take control of the state. After the death of al-Mutawakkil, Muhammad helped al-Mustaʿīn to become nominated as caliph. Denied the throne, Al-Mustaʿīn's brother besieged Baghdad, and Muhammad was sent to estimate the size of the attacking army. After the siege, he was sent to find out the terms for al-Mustaʿīn to abdicate.[15]
It was during the reigns of al-Wathiq and al-Mutawakkil that internal rivalries arose between the scholars there. The Banū Mūsā became enemies of al-Kindi, and assisted in his persecution by al-Mutawakkil.[7] They criticized and ridiculed his treatise on theastrolabe, and caused al-Mutawakkil to have him beaten, removed from court, and his library confiscated. The library was returned back to him at a later date with the help of the Persian Jewish scholarSanad ibn Ali, who insisted the library was returned as a condition to him assisting the Banū Mūsā over his judgement concerning the construction of a canal for the city of al-Ja’fariyya.[12][17]
Shortly before his death, Mutawakkil gave the Banū Mūsā overall responsibility for building the al-Ja’fariyya canal; they in turn delegated the work to Fargftani. The caliph discovered that, due to an engineering error, once built, the water in the canal would drain away. He decreed that the brothers would becrucified beside the canal if this happened. Sanad bin Ah', who was the caliph's consultantengineer, agreed to proclaim—four months before the truth was to be revealed, and knowing that astrologers had predicted that the caliph was close to death—that no error had been made. The brothers were saved from execution when the caliph wasassassinated shortly afterwards.[15]
Of the three brothers, only the year that Mohammed died—January 873—is known.[8]
The Banū Mūsā wrote almost 20 books.[9] Moḥammad was the most productive of the brothers; of his many works, one still exists.[2] They worked together as well as separately: Jafar Muhammad was an expert on mathematics and astronomy, Ahmad excelled in technology, and al-Hasan in mathematics.[7] Muhammed knew the works of both Euclid and Ptolemy, and was considered by contemporaries to be an expert mathematician, astronomer, andphilosopher.[3]
All but three of the books attributed by scholars to the Banū Mūsā are now lost.[18] Many of the lost works are named in theBook of Ingenious Devices, their most famous work.[19]
The Banū Mūsā are known to have made many astronomical observations in Baghdad.[9]Kitāb bayyana fīhī bi-ṭarīq taʿlīmī wa-madhhab handasī annahū laysa fī khārij kurat al-kawākib al-thābitah kurah tāsiʿah[20] ("Book on the Mathematical Proof by Geometry that there Is not a Ninth Sphere Outside the Sphere of the Fixed Stars") is a lost book, reportedly written by Ahmed.[9] Also referred to as theKitāb al-Hay’a ("Book of Astronomy"), or theKitāb Ḥarakāt al-falak al-ūlā ("Book on the First Motion of the Celestial Sphere"), the work analysed thePtolemy'sgeocentric model of the cosmos, in which a ninth sphere is responsible for the motion of the heavens, and instead considered that the Sun, the Moon, the planets, and the stars all moved of their own volition.[9]
The other astronomical or astrological works by the Banū Mūsā are:
The calculation by Moḥammad and Aḥmad of the Sun’s mean motion in a year agreed with the result obtained by al-Bīrūnī—that a solar year was 365 days and less than 6 hours long. Aḥmad independently reached a similar conclusion in 851–852. They observed the longitude ofRegulus from their house on a bridge in Baghdad in 840–841, 847–848, and 850–851, and made observations ofSirius, Al-Bīrūnī used data about the Moon obtained by the Banū Mūsā in his astrological calculations.[2]
The Banū Mūsā were some of the earliest scholars to adoptGreek mathematics. They differed from the Greeks in their approaches to the concepts ofarea andcircumference, giving them numerical values rather than considering them in terms ofratios.[7]
The most important of the works produced by the Banū Mūsā was theKitāb maʻrifat masāḥat al-ashkāl al-basīṭah wa-al-kurīyah ("Book on the Measurement of Plane and Spherical Figures"), of which a commentary was made by the persian polymathNaṣīr al-Dīn al-Ṭūsī in the 13th century.[5][26] ALatin translation by the 12th century ItalianastrologerGerard of Cremona appeared entitledLiber trium fratrum de geometria andVerba filiorum Moysi filii Sekir.[9] This treatise on geometry, which is similar to Archimedes'sOn the measurement of the circle and On the sphere and the cylinder.[7] was used extensively in the Middle Ages, and was quoted by authors such as Thābit ibn Qurra,Ibn al-Haytham,Leonardo Fibonacci (in hisPractica geometriae),Jordanus de Nemore, andRoger Bacon.[9] It includestheorems not known to the Greeks.[27] The book was re-published in Latin with an English translation by the American historianMarshall Clagett, who has also summarized how the work influenced mathematicians during theMiddle Ages.[2]
The other known mathematical works by the Banū Mūsā were:
Kitab al-Hiyal al-Naficah ("The Book of Ingenious Devices"), the only surviving work by Aḥmad,[2] describes 100 inventions, 25 of which had a practical use.[32] These include mechanical fountains, ahurricane lamp, self-trimming and self-feeding lamps, a form ofgas mask for use underground, and agrabbing tool, constructed in the same way as a modern clamshell grab, for recovering underwater objects.[33] The book's other inventions are ingeniously built pouring vessels, designed to puzzle guests at parties. It is thought that some of these models were never constructed.[34][32][33]
The inventions employ innovative engineering ideas, such as automatic one-way and two-wayvalves, mechanical memories, devices capable of responding tofeedback, and delay mechanisms. Most of them were operated by waterpressure.[34] The trick vessels are unimportant in themselves; their significance forhistorians of engineering is the means by which they were developed.[33] Many of Ahmad's ideas were obtained from Greek texts such asPhilo of Byzantium'sPneumatics (3rd century BCE) andHero of Alexandria'sPneumatics (written in the 1st century CE). However, some of the devices, particularly when involving small variations influid pressure, and automatic control components such as valves, were developed by the Banū Mūsā.[18]
The most important copies of theKitab al-Hiyal al-Naficah are:[32]
The other technology-based works by the Banū Mūsā were:
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