skilled in geometry, ingenious devices (!lival), music and astronomy. According to Ibn al-Nad!m and Ibn Khallikän their weakest subject was astronamy, but this seems to conflict with the opinions of Ibn Yunus and al-BIrun!, hoth good judges, who spoke highly of the accuracy of the Banu Musa's astronomical observations. Mul)ammad, who was the most influential of the brothers, specialised in gcomctry and astronomy, and excellcd Al)mad in all the sciences except in the construction of ingenious devices. AI-l:Iasan was a brilliant geometrician with aretenlive memoryand great powers of deduction. A rival onee tried to discredit him in front of al-Ma'mun hy saying that al l:Iasan had read only six of the thirteen books of Euclid's Elements. AI-l:Iasan replied by saying that it was unnecessary for him to read the remainder because he could arrive at the answers to any of Euclid's problem s by deduction. AI-Ma'mun acknowledged al-l:Iasan 's skill, but did not excuse him, saying: "laziness has prevented you from 2 reading the whole ofit-it is to geometry as the Ictters a, b, t, 111 are to speech and writing. " (H. 264). AI-l:Iasan is rarely mentioned by name elsewhere in the sources and may have preferred to devote his time to scholarship, whereas his brothers were involved in a variety of undertakings. At the time of their entry into the House of Wisdom the Banu Musil were paar and needy (H.