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Ibn al‐Samḥ: Abū al‐Qāsim Aṣbagh ibn Muḥammad ibn al‐Samḥ al‐Gharnāṭī

Born  Cordova, al‐Andalus, (Spain), 979

Died  Granada, al‐Andalus, (Spain), 29 May 1035

Ibn al‐Samḥ, known also as al‐Muhandis (the geometer), was a noted mathematician and astronomer in Andalusia and an important member of the school of Maslama al‐Majrīṭī centered in Cordova. Because of political unrest, Ibn al‐Samḥ fled to Granada where he lived out the rest of his life. There he worked in the service of the local chief, the Berber Ḥabbūs ibn Māksan (reigned: 1019–1038), whose Jewish Minister, Samuel ben Nagrella, was also interested in mathematics and astronomy.

Ibn al‐Samḥ worked in the fields of astronomy, mathematics, and, possibly, medicine. The 14th‐century historian Ibn al‐Khaṭīb states that Ibn al‐Samḥ wrote an essay on history, but there is no other evidence for this assertion. Ibn al‐Nāshī, one of Ibn al‐Samḥ's most important disciples, gives a list of nine books written by his teacher.

In astronomy, Ibn al‐Samḥ, like his teacher Maslama al‐Majrīṭī, composed a zīj (an astronomical handbook with tables) based on Khwārizmī's Sindhind, which had been composed in 9th‐century Baghdad. Ibn al‐Samḥ also composed a treatise on the construction of the astrolabe and another on its use (Kitāb al‐ʿAmal bi‐ʾl‐asṭurlāb). Although Ibn al‐Ṣaffār's treatise on the astrolabe gained more popularity, this long book (129 chapters on the use of the instrument) is the most complete tract written in the Iberian Peninsula during the Middle Ages. The text is especially interesting because it deals with questions not usually analyzed in works of this kind, such as the visibility of the Moon and its latitude and longitude. His Kitāb al‐ʿAmal is also important because in it he quotes an unknown work by Ḥabash al‐Ḥāsib, clear evidence that this eastern astronomer was known in Andalusia at the end of the 10th century. The text also shows that the school of Maslama knew and used the works of Battānī. The Kitāb al‐ʿAmal was the source of a treatise on the use of the spherical astrolabe composed at the court of Alfonso X. Since the king's astronomers did not have an Arabic text on the spherical astrolabe from which to make the Castilian translation, they took Ibn al‐Samḥ's treatise and made an adaptation of it. His treatise on the construction of the equatorium – an instrument originally conceived in Andalusia and later developed in Latin Europe – is another of Ibn al‐Samḥ's major contributions to astronomy. Indeed, this treatise is the first known work dealing with this instrument and was followed by works written by Zarqāli and Abū al‐Ṣalt of Denia. The instrument described by Ibn al‐Samḥ is a hybrid astrolabe/equatorium, and his treatise is preserved in the Alfonsine translation included in the Libros del Saber de Astronomia. Ibn al‐Samḥ gives the numerical parameters necessary for the construction of the instrument and uses Battānī's values for the longitudes of the apogees of the planets, Khwārizmī‐Maslama's values for the ascending nodes of the planets, and the eccentricities and radii of the epicycles of the planets from the Almagest. The equatorium has eight plates (one for the Sun, six for the deferents of the Moon and the five planets, and one for the planetary epicycles) carefully explained and placed within the mater of an astrolabe. This instrument helps to determine the longitude of a planet and saves astronomers a great deal of time, especially considering that one of their main aims in the Middle Ages was to cast a horoscope. The historian Ibn Khaldūn mentions that Ibn al‐Samḥ wrote an abstract of the Almagest.

Ibn al‐Samḥ is well known for his many compositions in mathematics. His range of subject matter includes calculation, numbers, commercial arithmetic, theory of proportions, arithmetical operations, and the solution of quadratic and cubic equations. His work in geometry includes a commentary on the book of Euclid, and a general treatise that includes an important study of straight, curved, and broken lines. The latter is partially extant in a Hebrew translation.

Selected References

Comes, Mercè (1991). Ecuatoriosandalusíes: Ibn al‐Samḥ, al‐Zarqālluh y Abū‐l‐Ṣalt. Barcelona, pp. 27–78.

Millás Vallicrosa, José María (1943–1950). Estudios sobre Azarquiel. Madrid–Granada.

——— (1955). “Los primeros tratados de astrolabio en la España árabe.” Revista del Instituto Egipcio de Estudios Islámicos 3: 55–76, esp. 35–49. (Reprinted in Nuevos estudios sobre historia de la ciencia española. Barcelona, 1960, pp. 61–78.)

Pingree, David (1971). “Ibn al‐Samḥ.” In Encyclopaedia of Islam. 2nd ed. Vol. 3, pp. 928–929. Leiden: E. J. Brill.

Rashed, Roshdi (1995). Les mathématiques infinitésimales du IXeau XIesiècle, Vol. 1, pp. 885–973. Fondateurs et commentateurs: Banū Mūsā, Ibn Qurra, Ibn Sinān, al‐Khāzin, al‐Qūhī, Ibn al‐Samḥ, Ibn Hūd. London.

Rosenfeld, B. A. and Ekmeleddin Ihsanoğlu (2003). Mathematicians, Astronomers, and Other Scholars of Islamic Civilization and Their Works (7th – 19th c.). Istanbul: IRCICA, pp. 120–121.

Ṣāʿid al‐Andalusī (1912). KitābṬabaqāt al‐umam, edited by P. Louis Cheikho. Beirut: Imprimerie Catholique, pp. 69–70. French translation with notes by Régis Blachère as Livre des catégories des nations. Paris: Larose, 1935, pp. 130–131.

Samsó, Julio (1992). Las ciencias de los antiguos en al‐Andalus. Madrid: Mapfre.

Sezgin, Fuat (1978). Geschichte des arabischen Schrifttums. Vol. 6, Astronomie, p. 249. Leiden: E. J. Brill.

Viladrich, Mercè (1986). “El Kitāb al‐ʿamal bi‐l‐asturlāb” (Llibre de l'ús de l'astrolabi) d'Ibn al‐Samḥ. Estudi i traducció. Barcelona.