Born: about 1100 in possibly Seville, Spain
Died: about 1160

Jabir ibn Aflah is often known by the Latinised form of his name, namely Geber. Although not he was not in the first rank of Arabic mathematicians, he is important in the development of mathematics since his works were translated into Latin, and so became available to European mathematicians, whereas the work of some of the top rank Arabic mathematicians such as Abu'l-Wafa were not translated into Latin.

Very little information is available regarding Jabir ibn Aflah's life. That he came from Seville is known from two sources. Firstly he is described as "al-Ishbili" in manuscripts containing his treatises; this means "from Seville". The other source gives us not only the information that he came from Seville, but also a good estimate for the period in which he lived. The information comes from Maimonides.

Moses Maimonides, whose Arabic name was Abu 'Imran Musa ibn Maymun ibn 'Ubayd Allah, was a Jewish philosopher, jurist, and physician who was born in Córdoba in 1135. Among many important works he wrote The Guide of the Perplexed in Arabic in which he writes of:-

... ibn Aflah of Seville, whose son I have met ...

Jabir ibn Aflah invented an observational instrument known as the torquetum, a mechanical device to transform between spherical coordinate systems (see [3] for further details). He also gave his name to a theorem in spherical trigonometry, and his criticisms of Ptolemy's Almagest are well known. These criticisms appears in Jabir ibn Aflah's most famous work Islah al-Majisti (Correction of the Almagest). One sees that ibn Aflah even puts his argument regarding errors made by Ptolemy into the title of the work. In [4] Lorch explains Jabir ibn Aflah's most famous criticism, namely Ptolemy's placement of Venus and Mercury below the Sun. Ptolemy claimed that these planets could never be on a line between an observer on Earth and the sun., but ibn Aflah states that this is an error, and that Venus and Mercury are above the Sun.

It is a little difficult to establish the exact degree of originality of Correction of the Almagest. Certainly its general approach bears considerable similarity to the work of Abu'l-Wafa, but it may not be based on Abu'l-Wafa's work. Both may be based on the work of Thabit ibn Qurra, or the work of ibn Aflah, Abu'l-Wafa, and Thabit ibn Qurra may all be based on some still unknown source.

1. R P Lorch, Biography in Dictionary of Scientific Biography (New York 1970-1990). 
   http://www.encyclopedia.com/doc/1G2-2830902148.html

Books:

1. J Samsó, Las ciencias de los antiguos en al-Andalus (Madrid, 1992).

Articles:

1. R P Lorch, The astronomical instruments of Jabir ibn Aflah and the torquetum, Centaurus 20 (1) (1976), 11-34.
2. R P Lorch, The astronomy of Jabir ibn Aflah, Centaurus 19 (2) (1975), 85-107.
3. N M Swerdlow, Jabir ibn Aflah's interesting method for finding the eccentricities and direction of the apsidal line of a superior planet, in From deferent to equant (New York, 1987), 501-512.