The Banū Mūsā
brothers ("Sons of Moses"), namely 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), were
three 9th-century Persian scholars who lived and worked in Baghdad. They are
known for their Book of Ingenious Devices on automata (automatic machines) and
mechanical devices.
Another important work
of theirs is the Book on the Measurement of Plane and Spherical Figures, a
foundational work on geometry that was frequently quoted by both Islamic and
European mathematicians.
The Banu Musa worked in astronomical observatories established in Baghdad
by the Abbasid Caliph al-Ma'mun as well as doing research in the House of
Wisdom. They also participated in a 9th-century expedition to make geodesic
measurements to determine the length of a degree.
Life
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 Marw,
Musa was employed as an astrologer and astronomer. After his death, his young
sons were looked after by the court of al-Maʾmūn. Al-Maʾmūn recognized the
abilities of the three brothers and enrolled them in the famous House of
Wisdom, a library and a translation center in Baghdad.
Studying in the House of Wisdom under Yahya ibn Abi Mansur, they
participated in the efforts to translate ancient Greek works into Arabic by
sending for Greek texts from the Byzantines, paying large sums for their
translation, and learning Greek themselves. On such trips, Muhammad met and
recruited the famous mathematician and translator Thābit ibn Qurra. At some
point Hunayn ibn Ishaq was also part of their team. The brothers sponsored many
scientists and translators, who were paid about 500 dīnārs a month. Had it not
been for the brothers' efforts, many of the Greek texts that they translated
would have been lost and forgotten.
After the death of al-Ma'mun, the Banu Musa continued to work 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 in
the House of Wisdom. At some point the Banu Musa became enemies of al-Kindi and
contributed to his persecution by al-Mutawakkil. They were later employed by
al-Mutawakkil to construct a canal for the new city of al-Jafariyya.
Mathematics and mechanics
The Banu Musa had a different view on area and circumference from the
Greeks. In the research they translated, the Greeks looked at volume and area
more in terms of ratios, rather than giving them an actual numerical value.
Most of them based such measurements relatively on another object's size. In
one of their surviving publications, the Kitab Marifat Masahat Al-Ashkal (The
Book of the Measurement of Plane and Spherical Figures) Banu Musa gave volume
and area number values. This is evidence that they were not just translating
and reproducing the Greek sources. They were actually building on concepts and
coming up with some of their own original works.
The most popular of their publications was the Kitāb al-Ḥiyal (The Tricks
Book), which was mostly the work of Aḥmad, the middle brother, was a book
filled with one hundred mechanical devices. There were some real practical
inventions in the book including a lamp that would mechanically dim,
alternating fountains, and a clamshell grab. Eighty of these devices were
described as "trick vessels" that showed a real mastery of mechanics,
with a real focus on the use of light pressure. Some of the devices seem to be
replications of earlier Greek works, but the rest were much more advanced than
what the Greeks had done.
Astronomy
They 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. Al-Ma’mun had them go to a desert in
Mesopotamia to measure the length of a degree. They also measured the length of
a year to be 365 days and 6 hours.
Politics
Although they were not made famous by their politics, they did have
interests outside the world of science, mainly the oldest brother Muhammad.
They were employed by the caliphs for many different projects, including the
canal mentioned above, and they were also a part of a team of 20 hired to build
the town of al-D̲j̲aʿfariyya for al-Mutawakkil. Taking on these types of civil
projects naturally got them involved in the political scene in Baghdad.
However, the height of Muhammad's political activity in the palace came towards
the end of his life, during a time when Turkish commanders were starting to take
control of the state. After al-Mutawakkil died, Muhammad helped al-Mustaʿīn get
the nomination instead of the caliph's brother. When the caliph's brother
besieged the city of Baghdad, Muhammad was sent to estimate the size of the
army, and when the siege was over he was sent to get the terms of how
al-Mustaʿīn would renounce the throne. This evidence shows where Muhammad ranks
at that time. He was trusted and respected by the highest levels of authority
at that time.
Automata
Most notable among
their achievements is their work in the field of automation, which they
utilized in toys and other entertaining creations. They have shown important
advances over those of their Greek predecessors.
· The Book of
Ingenious Devices describes 100 inventions; the ones which have been
reconstructed work as designed. While designed primarily for amusement
purposes, they employ innovative engineering technologies such as one-way and
two-way valves able to open and close by themselves, mechanical memories,
devices to respond to feedback, and delays. Most of these devices were operated
by water pressure.
· Qarasṭūn, a treatise on weight
balance.
· On Mechanical Devices, a work
on pneumatic devices, written by Ahmad.
· A Book on the Description
of the Instrument Which Sounds by Itself, about musical
theory.
Astronomy
· Book on the First
Motion of the Celestial Sphere (Kitāb Ḥarakāt
al‐falak al‐ūlā), 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
Mathematical Proof by Geometry That There Is Not a Ninth Sphere Outside the
Sphere of the Fixed Stars, by Ahmad.
· Book on The
Construction of the Astrolabe, quoted
by al-Biruni.
· Book on the Solar Year, was traditionally
attributed to Thābit ibn Qurra, but recent research has shown that it was
actually by the Bani Musa.
· On the Visibility of
the Crescent, by Muhammad.
· Book on the Beginning
of the World, by Muhammad.
· Book on the Motion of
Celestial Spheres (Kitāb Ḥarakāt al‐aflāk), by Muhammad.
· Book of Astronomy (Kitāb
al‐Hayʾa), by Muhammad.
· A book of zij, by
Ahmad
· Another book of zij,
listed under the Banu Musa, mentioned by Ibn Yunus.
Astrology
Cover of Kitāb
al-Daraj (The book of degrees), by Ahmad, as found in
the Saladin library, from before 1193 AD.
·
A translation of a
Chinese work called A Book of Degrees on the Nature of Zodiacal Signs.
·
Kitāb al-Daraj (The book of
degrees), by Ahmad.
Mathematics
· 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 Gerard of Cremona appeared the 12th century under the titles Liber
trium fratrum de geometria and Verba filiorum Moysi filii
Sekir. This treatise on geometry was used extensively in the Middle Ages,
quoted by authors such as Thābit ibn Qurra, Ibn
al‐Haytham, Leonardo Fibonacci (in his Practica geometriae), Jordanus
de Nemore, and Roger Bacon. Some theorems included in this
book are not found in any work of the Greek mathematicians.
· Conic Sections
of Apollonius of Perga, a recension of the Greek work, which was first
translated to Arabic by Hilāl al-ḥimṣī and Thābit ibn Qurra.
· Book on an Oblong Round
Figure, which contains a description of procedure used to draw
an ellipse using a string, now called the gardener's construction.
· Reasoning on
the Trisection of an Angle, by Aḥmad.
· A treatise containing a
discussion between Ahmad and Sanad ibn ʿAli.
· Book on a Geometric
Proposition Proved by Galen.
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