Ahmad ibn Musa ibn Shakir

Abu al-Qasim Ahmad ibn Musa ibn Shakir was the middle brother of the Banu Musa of Baghdad and the family's engineer — the brother whose name attaches to the Book of Ingenious Devices, the most famous mechanical treatise of the medieval Islamic world. ^{1 2} He was educated with his brothers Muhammad and al-Hasan at the House of Wisdom after their father Musa ibn Shakir's death, under the patronage of the caliph al-Ma'mun. ¹ No birth or death year is attested for him in the scholarship the English article rests on: that article dates him only to the ninth century and states that of the three brothers only Muhammad's death year, 873, is known. ¹ The Arabic article prints the years 803–873 for him, and his Wikidata item gives 805 and 873; all are unsourced and of one modern tradition, and they are preserved here as a tradition, not built into this record as dates. ^{2 3}

The Kitab al-Hiyal — the Book of Ingenious Devices — is the only one of Ahmad's works to survive, and it describes a hundred inventions. ¹ About twenty-five had practical use: mechanical fountains, a hurricane lamp, lamps that trim and feed themselves, a form of gas mask for underground work, and a clamshell grab for recovering objects from underwater. ¹ The rest are ingenious pouring vessels built to puzzle party guests — unimportant as objects, but the means behind them matter: automatic one-way and two-way valves, mechanical memories, feedback responses and delay mechanisms, most of them driven by water pressure and by small variations in fluid pressure that the Greek sources he drew on, Philo of Byzantium and Hero of Alexandria, had not developed so far. ¹ The book's automatic flute player — a figure that plays by means of a programmed mechanism — has been counted among the earliest programmable machines. ^{1 4} Its manuscripts survive at the Vatican, in Berlin and Gotha, and at the Topkapi in Istanbul, the last being the oldest and most reliable copy. ¹

Ahmad's treatise on the trisection of the angle, the Qawl Ahmad ibn Shakir fi tathlith al-zawiyah, survives in two Bodleian manuscripts and in medieval Latin translation — an attempt on one of the classical unsolved problems. ¹ A Book on the Description of the Instrument Which Sounds by Itself, credited to the brothers, describes what has been called the first music sequencer. ¹ A zij of his, now lost, was still being cited by the Egyptian astronomer Ibn Yunus around 990, and a lost Book of Astronomy analysing Ptolemy's spheres — the Kitab al-Hay'a, or Book on the First Motion of the Celestial Sphere — is also reported under his name. ¹ With his brothers he shared in the joint works and in the geodesic and observational programmes of the House of Wisdom circle. ^{1 5}

Ahmad taught a son of the caliph al-Mu'tasim, and with Muhammad he was drawn into the Ja'fariyya canal affair under al-Mutawakkil, when the caliph's adviser proposed that the two brothers be made to contribute to a palace's cost. ¹ A short treatise preserves his discussion with the engineer Sanad ibn Ali, possibly over the canal's failure — the same Sanad whose timely certification saved the brothers from the caliph's threat of crucifixion beside the drained canal. ¹ The Fihrist adds a family note the articles do not: Ahmad had a son, Mutahhar, who entered the circle of the caliph al-Mu'tadid's boon companions. ⁶ No source consulted names a religion or legal school for Ahmad, and his faith is recorded as unattested. ^{1 3}