Banū Mūsā brothers
The Banū Mūsā, literally The Sons of Moses, refers to a Persian family of polymaths, astronomers, mathematicians, and engineers active in 9th century Baghdad. Both their own contributions and their direct connections to other prominent scholars of the House of Wisdom mark them as one of the most preeminent figures of the Islamic Golden Age.
The term Banū Mūsā is derived from the name of Mūsā ibn Shākir, and most commonly refers to his three sons; Muḥammad ibn Mūsā ; Aḥmad ibn Mūsā ; and Al-Ḥasan ibn Mūsā.
Mūsā ibn Shākir was a renowned astronomer serving directly under the Abbasid caliph al-Ma'mun. After his death, his three sons received an education under al-Ma'mun’s direct orders, and were enrolled at the House of Wisdom in Baghdad. There they undertook the translation of ancient Greek works acquired from Byzantium, which they used to develop their own technological, mathematical and astronomical ideas. They were some of the earliest scholars to adopt Greek mathematics, but innovative in their approach to the concepts of area and circumference by expressing them using numerical values instead of ratios. They made geodesic measurements to determine the length of a degree of latitude, and so obtained a relatively accurate value for the circumference 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 a treatise on geometry, , which was used extensively by medieval mathematicians. Their most famous extant work is . It describes 100 inventions, many of which were pouring vessels, intended to entertain party guests. Some of their innovations, such as those that involved
fluid pressure variations and valves, 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.
Biographical details
Early years
The Banu Musa were the three sons of Mūsā ibn Shākir, who earlier in life had been a highwayman and astronomer in Khorasan of unknown pedigree. After befriending al-Ma'mun, who was then a governor of Khorasan and staying in Merv, Musa was employed as an astrologer and astronomer.After Musa's death, the three orphaned children were cared for at the court of al-Maʾmūn, who made the senior Baghdad official Ishaq ibn Ibrahim al-Mus'abi their guardian. Al-Ma’mun recognized their abilities, and enrolled them in the House of Wisdom, an institution created by him as a centre for collecting, translating and studying books from other lands. In Baghdad, where they apparently lived for the rest of their lives, the three brothers studied geometry, mechanics, music, mathematics and astronomy, trained by a senior court astrologer, Yaḥyā bin Abī Manṣūr.
The three brothers, Moḥammad, Aḥmad, and Ḥasan, are often listed in what is assumed to be their order of seniority.
Accomplishments under the Abbasid Caliphate
The Banū Mūsā assisted al-Ma'mun's in his obsession to obtain and translate works from Greek into Arabic. They sent for Greek texts from the Byzantines, or travelled themselves to Byzantium to acquire them. During their working lives they used their wealth and energy towards the translation of these works. On his way home to Baghdad from Byzantium, Muhammad met and recruited Thābit ibn Qurra, a money changer from Harran. Thābit went on to make important discoveries in algebra, geometry, and astronomy.Under the direction of al-Ma'mun, the Banū Mūsā worked with the most talented men available, including al-Khwarizmi, al-Kindi, Al-Ḥajjāj ibn Yūsuf ibn Maṭar, and the mathematician and translator Hunayn ibn Ishaq, who became a close friend of one of the brothers, Muhammad. Of the translators, three were paid about 500 dinars a month. None of the brothers were medically trained, and relied upon Ishaq bin Hunayn and Thabit bin Qurra to translate Greek medical works. They exchanged ideas with other experts, including the astrologer Abu Ma'shar al-Balkhi, with whom Muhammed was in continuous contact.
The brothers are likely to have used portable instruments such as armillary spheres or dials when making their observations, which were recorded from around 847 to 869. From their Baghdad home, they observed stars in the constellation Ursa Major In 847–848, and measured the maximum and minimum altitudes of the Sun in 868–869. They also observed the September equinox in the city of Samarra. To calculate the difference in latitude between Samarra and Nishapur, they organized simultaneous observations of a lunar eclipse.
Whilst working for al-Ma’mun, the Banū Mūsā travelled to a desert near Sanjar, in northern Mesopotamia, with the aim of measuring the length of a degree of latitude along a meridian, and from that verifying a value of obtained by the Greeks for the Earth's circumference. They first measured the altitude of the Pole 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.
Under the patronage of the caliphs that followed al Ma’mun—al-Mu'tasim, al-Wathiq, and al-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. 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. 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.
Involvement in politics
The Banū Mūsā's employment by the caliphs for different civil 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.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.
Jaʻfariyya canal
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. They criticized and ridiculed his treatise on the astrolabe, 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 scholar Sanad 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.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 be crucified beside the canal if this happened. Sanad bin Ah', who was the caliph's consultant engineer, 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 was assassinated shortly afterwards.
Deaths
Of the three brothers, only the year that Mohammed died—January 873—is known.Works
The Banū Mūsā wrote almost 20 books. Moḥammad was the most productive of the brothers; of his many works, one still exists. 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. Muhammed knew the works of both Euclid and Ptolemy, and was considered by contemporaries to be an expert mathematician, astronomer, and philosopher.All but three of the books attributed by scholars to the Banū Mūsā are now lost. Many of the lost works are named in the Book of Ingenious Devices, their most famous work.
Astronomy and astrology
The Banū Mūsā are known to have made many astronomical observations in Baghdad. is a lost book, reportedly written by Ahmed. Also referred to as the , or the , the work analysed the Ptolemy's geocentric 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.File:Kitāb-al-Daraj-page0013.jpg|thumb|Cover of the digitized version of the
The other astronomical or astrological works by the Banū Mūsā are:
- ;
- , a work quoted by the 11th century Persian scholar al-Biruni;
- , which was once attributed to Thābit ibn Qurra;
- , by Muhammad;
- Book on the Beginning of the World, by Muhammad, now lost;
- A non-extant by Ahmad was mentioned by the Egyptian astronomer and mathematician Ibn Yunus in his, written in ;
- A separate non-extant by the Banū Mūsā was mentioned by Ibn Yunus.
- A translation of a Chinese work called A Book of Degrees on the Nature of Zodiacal Signs;