Abu'l-Abbas Ahmad ibn Muhammad ibn Kathir al-Farghani,born in Farghana, Transoxiana, was one of the most distinguished astronomers in the service of al-Mamun and his successors. He wrote"Elements of Astronomy" (Kitab fi al-Harakat al-Samawiya waJawami Ilm al-Nujum i.e. the book on celestial motion and thoroughscience of the stars), which was translated into Latin i n the 12thcentury and exerted great influence upon European astronomybefore Regiomontanus. He accepted Ptolemy's theory and valueof the precession, but thought that it affected not only the starsbut also the planets. He determined the diameter of the eart h tobe 6,500 miles, and. found the greatest distances and also thediameters of the planets.
Al-Farghani's activities extended to engineering. According toIbn Tughri Birdi, he supervised the construction of the GreatNilometer at al-Fustat (old Cairo) . It was completed in 861, the yearin which the Caliph al-Mutawakkil, who ordered the construction,died. But engineering was not al-Farghani's forte, as transpires fromthe following story narrated by Ibn Abi Usaybi'a.
Al-Mutawakkil had entrusted the two sons of Musa ibn Shakir,Muhammad and Ahmad, with supervising the digging of a canalnamed al-Ja'fari. They delegated the work to Al-Farghani, thusdeliberately ignoring a better engineer, Sind ibn Ali, whom, outof professional jealousy, they had caused to be sent to Baghdad,away from al-Mutawakkil's court in Samarra. The canal was to runthrough the new city, al-Ja'fariyya, which al-Mutawakkil had builtnear Samarra on the Tigris and named after himself. Al-Farghanicommitted a grave error, making the beg inning of the canal deeperthan the rest, so that not enough water would run through thelength of the canal except when the Tigris was high. News of thisangered the Caliph, and the two brothers were saved from severepunishment only by the gracious willingn ess of Sind ibn Ali to vouchfor the correctness of al-Farghani's calculations, thus risking hisown welfare and possibly his life. As had been correctly predictedby astrologers, however, al-Mutawakkil was murdered shortly beforethe error became apparent. T he explanation given for Al-Farghani'smistake is that being a theoretician rather than a practical engineer,he never successfully completed a construction.
The Fihrist of Ibn al-Nadim, written in 987, ascribes only twoworks to Al-Farghani: (1 ) "The Book of Chapters, a summary ofthe Almagest" (Kitab al-Fusul, Ikhtiyar al-Majisti) and (2) "Bookon the Construction of Sun-dials" (Kitab 'Amal al-Rukhamat).
The Jawami, or 'The Elements' as we shall call it, was Al-Farghan i's best-known and most influential work. Abd al-Azizal-Qabisi (d. 967) wrote a commentary on it, which is preserved inthe Istanbul manuscript, Aya Sofya 4832, fols. 97v-114v. TwoLatin translations followed in the 12th century. Jacob Anatoliproduced a Heb rew translation of the book that served as a basis fora third Latin version, appearing in 1590, whereas Jacob Goliuspublished a new Latin text together with the Arabic original in1669. The influence of 'The Elements' on mediaeval Europe isclearly vindicat ed by the presence of innumerable Latin manuscriptsin European libraries.
References to it in madiaeval writers are many, and there is nodoubt that it was greatly responsible for spreading knowledge ofPtolemaic astronomy, at least until this role wa s taken over bySacrobosco's Sphere. But even then, 'The Elements' of Al-Farghanicontinued to be used, and Sacrobosco's Sphere was evidentlyindebted to it. It was from 'The Elements' (in Gherard's translation)that Dante derived the astronomic al knowledge displayed in the 'Vitanuova' and in the 'Convivio'.