Banū Mūsā Brothers

The three brothers Abū Jaʿfar, Muḥammad ibn Mūsā ibn Shākir (before 803 – February 873); Abū al‐Qāsim, Aḥmad ibn Mūsā ibn Shākir (d. 9th century) and Al-Ḥasan ibn Mūsā ibn Shākir (d. 9th century), known as the Banū Mūsā ( fa, بنوموسی, "Sons of or Moses"), were Persian scholars, who lived and worked in Baghdad.

The Banū Mūsā, who are often not individually distinguishable in historical sources, worked as researchers in the House of Wisdom, and in astronomical observatories established in Baghdad by the Abbasid Caliph al-Ma'mun. They participated in an expedition to make geodesic measurements to determine the length of a degree of latitude. Their most notable work is the ''Book of Ingenious Devices'' on automata (automatic machines) and mechanical devices. They also produced the ''Book on the Measurement of Plane and Spherical Figures'', a work on geometry that was frequently quoted by both Islamic and European mathematicians.

Biographical details

Early years

Moḥammad, Aḥmad, and Ḥasan were the three sons of Mūsā ibn Shākir, who earlier in life had been a highwayman and an astronomer in Khorasan. After befriending the future Abbasid caliph al-Ma'mun, who was then a governor of Khorasan and staying in Merv, Musa was employed as an astrologer and astronomer by al-Ma'mun, who became caliph in 813.

After Mūsā ibn Shākir's death, his young sons were cared for at the court of al-Maʾmūn, a younger son of Harun al-Rashid. Al-Maʾmūn recognized the abilities of the three boys, and enrolled them in the House of Wisdom, a library and a translation centre in Baghdad. In Baghdad, where they apparently lived for the rest of their lives, they studied geometry, mechanics, music, mathematics and astronomy, trained by Yaḥyā bin Abī Manṣūr.

Accomplishments under the Abbasid Caliphate

Studying in the House of Wisdom under Yahya ibn Abi Mansur, the brothers participated in the efforts to translate ancient Greek works into Arabic by sending for Greek texts from the Byzantines, or travelling to Byzantium to acquire manuscripts. They paid large sums for their translation, and learning Greek themselves. On his way home to Baghdad from Byzantium, Muhammad met and recruited Thābit ibn Qurra, a money changer from Harran, and taught him astronomy.

Under the direction of Al-Ma'mun, the three brothers 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 Muhammad.Scientists and translators sponsored by the brothers were paid about 500 dinars a month. Had it not been for the brothers' efforts in translating Greek texts, many would have been lost and forgotten. The Banū Mūsā wrote almost 20 books, the majority of which are now not extant. Moḥammad was the most productive of the brothers; of his many works, one is extant.

The brothers worked together, but did have their own areas of expertise; Jafar Muhammad on mathematics and astronomy, Ahmad on technology, and al-Hasan on mathematics.They 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 847-8, and measured the maximum and minimum altitudes of the Sun in 868-9. They also observed the September equinox in the Persian city of Samarra.To calculate the difference in latitude between Samarra and Nishapur, they organized simultaneous observations of a lunar eclipse.

Al-Ma’mun had them go to a desert near Sanjar, to measure the length of a degree of latitude along a meridian. This measurement enabled them to obtain a value for the Earth's circumference.

After the death of al-Ma'mun, the Banū Mūsā continued to acquire wealth and influence, as they worked under the Caliphs al-Mu'tasim, al-Wathiq, and al-Mutawakkil. However, during the reign of al-Wathiq and al-Mutawakkil internal rivalries arose between the scholars of the House of Wisdom. The Banū Mūsā became enemies of al-Kindi, and assisted in his persecution by al-Mutawakkil. They were later employed by al-Mutawakkil to construct a canal for the new city of al-Jaʻfariyya.

Politics

The Banū Mūsā's employment by the caliphs for different civil engineering projects, including their involvement as part of a team that built the city of al-D̲j̲aʿfariyya for al-Mutawakki, led to them becoming involved involved in the politics of Baghdad. 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.

Works

Astronomy and astrology

The Banū Mūsā made many observations and contributions to the field of astronomy, writing nearly a dozen publications over their astronomical research. They made many observations on the Sun and the Moon.

According to Ebn Yūnes, the calculation by Moḥammad and Aḥmad of the Sun’s mean motion in a Persian 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 851852. They observed the longitude of Regulus from their house on a bridge in Baghdad in 840841, 847848, and 850851, and made observations of Sirius, Al-Bīrūnī used data about the Moon obtained by the Banū Mūsā in his calculations of the nativities () of the years.

("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 by Ahmed. Also referred to as the ("Book of Astronomy"), or the ("Book on the First Motion of the Celestial Sphere"), 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.

The other astronomical or astrological works by the Banū Mūsā are:
* ''Kitāb al-Daraj'' ( ar, كتاب الدرج; "The Book of Degrees"), a work by Ahmad.
* ''Book on the First Motion of the Celestial Sphere'' (''Kitāb Ḥarakāt al‐falak al‐ūlā''), an extant work containing a critique of the Ptolemaic system. Muhammad in this book denied the existence of the Ptolemaic 9th sphere which Ptolemy thought was responsible for the motion;
* ("Book on the Construction of the Astrolabe"), a work quoted by the 11th century Persian scholar al-Biruni;
* ("Book on the Solar Year"), which was once attributed to Thābit ibn Qurra;
* ("On the Visibility of the Crescent"), 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'';

Mathematics

The Banū Mūsā were some of the earliest scholars to adopt mathematical ideas begun by the ancient Greeks. They differed in their approaches to the concepts of area and circumference, giving them numerical values rather than considering them in terms of ratios.

The most important of all the works produced by the Banū Mūsā was the ("''Book on the Measurement of Plane and Spherical Figures''"), later edited by Naṣīr al‐Dīn al‐Ṭūsī in the 13th century. A Latin translation by the 12th century Italian astrologer Gerard of Cremona appeared entitled and . This treatise on geometry, which is similar in topics to Archimedes', ''On the measurement of the circle'' and ''On the sphere and the cylinder''. was used extensively in the Middle Ages, and was quoted by authors such as Thābit ibn Qurra, Ibn al‐Haytham, Leonardo Fibonacci (in his ), Jordanus de Nemore, and Roger Bacon. Some theorems included in this book are not found in any work of the Greek mathematicians. It was published in Latin with an English translation by the American historian Marshall Clagett, who has also summarized how the work influenced mathematicians during the Middle Ages.

The other known mathematical works by the Banū Mūsā were:
* 3 works relating to ''Conic Sections'', by the astronomer Apollonius of Perga, including ("Conic Sections of Apollonius"), a recension of the work, which was first translated to Arabic by Hilāl al-ḥimṣī and Thābit ibn Qurra (a lost book written by Muhammed).
* ("The Book of the Elongated Circular Figure"), a mathematical treatise by al-Hasan—and the only one that is attributed to him— now lost. It contained a description of a procedure used to draw an ellipse using a length of string, a technique that is now known as the "gardener's construction";
* ("Reasoning on the Trisection of an Angle"), by Aḥmad; The treatise involved the use moving geometric objects as moving. using kinematic methods to attempt to solve the classical problem of trisecting an angle.The manuscript and medieval Latin translations are extant. The two known manuscripts containing the treatise, MS. Marsh 720 and MS. Thurston 3, are held in the Bodleian Library at Oxford University.
* ("Book on a Geometric Proposition Proved by Galen"). A lost book by Muhammed.

Technology

Most notable among their achievements is their work in the field of automation, which they utilized in toys and other devices made for entertainment, and which were in advance of similar inventions by their Greek predecessors. The brothers are credited with inventing the first music sequencer, the earliest type of programmable machine.

("''The Book of Ingenious Devices''"), the only surviving work by Aḥmad, is a work that describes 100 inventions, 80 of which are examples of trick vessels. The other inventions described in the book include mechanical fountains, a "hurricane" lamp, self-trimming and self-feeding lamps, a form of gas mask for use underground and a grabbing tool, constructed in the same way as a modern clamshell grab, for recovering underwater objects.

The inventions employ innovative engineering ideas, such as automatic one-way and two-way valves, mechanical memories, devices capable of responding to feedback, and delay mechanisms. Most of them were operated by water pressure.
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The trick vessels are unimportant in themselves; their significance is the means by which they were developed' the Banū Mūsā used small pressure variations and conical valves, their first known use as automatic controllers.

Other technological works by the Banū Mūsā were:
* ("A Book on the Qarasṭūn"), a treatise on the weight balance, or steelyard. There is a similar work on the same subject written by Thabit bin Qurra, who was a student of the brothers.
* ''On Mechanical Devices'', a work on pneumatic devices, written by Ahmad.
* ''A Book on the Description of the Instrument Which Sounds by Itself'', an extant work about musical theory. The manuscript is held in Beirut.
* , a lost treatise containing a discussion between Ahmad and the Persian Jewish scholar Sanad ibn Ali, possibly about the difficulties encountered by the Banū Mūsā due to the failure by their agent Al-Farghani to properly build the Jaʻfariyya canal.

See also

* Inventions in the Muslim world
* Science in the medieval Islamic world

Notes

References

Sources

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PDF version

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Further reading

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Digitized manuscripts and translations

Manuscript facsimile of the
held in the Princeton University Library (Islamic Manuscripts, Garrett no. 501H)

Manuscript facsimile of ''The Book of Ingenious Devices''
held in the Vatican Library (Manuscript Vaticani Arabi 317)

Manuscript facsimile of
kept at Columbia University, New York (via the Internet Archive). The treatise is located from pp. 253265 (f. 116 to 122).
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PDF
version)
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External links

A list of works by the Banū Mūsā
from the Islamic Scientific Manuscripts Initiative (ISMI) website
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Pioneers of Engineering: Al-Jazari and the Banu Musa
' TV episode from Al Jazeera (25 minutes)
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{{DEFAULTSORT:Musa, Banu
873 deaths
People from Baghdad
Astronomers from the Abbasid Caliphate
Astronomers of the medieval Islamic world
Mathematicians from the Abbasid Caliphate
9th-century Iranian mathematicians
Iranian engineers
Iranian scientists
Inventors of the medieval Islamic world
9th-century people from the Abbasid Caliphate
9th-century Iranian astronomers
9th-century inventors
Brothers