Ibn Khallikān (1)—and, before him, Muḥammad ibn Isḥāq al-Nadīm—records that the brothers were men of means whose lofty ambition drove them to master this science and to seek out ancient books. They spared no effort in acquiring such works and even brought specialists to translate them into Arabic.

They produced a Book of Ingenious Devices that contains remarkable and rare contrivances, and they likewise composed treatises on music. The caliph al-Maʾmūn relied upon them for astronomical observations and for determining the dimensions of the earth.

It is said that the Book of Ingenious Devices was by Aḥmad; the Book of the Part by Muḥammad; the Book on the World’s Beginnings by Muḥammad, as well as his Book on Celestial Motions; the Book of the Circular Rectangle by al-Ḥasan; and the Book of the Geometric Figure by Muḥammad.

They were the ones who calculated the circuit of the globe to be 24,000 miles, which they expressed as a total of 360 degrees. Muḥammad died in 259 AH.

137 – Ibn Yazdād, Abū Ṣāliḥ ʿAbd Allāh ibn Muḥammad*

The consummate vizier, Abū Ṣāliḥ ʿAbd Allāh ibn Muḥammad ibn Yazdād the secretary, served al-Mustaʿīn for several months after Aḥmad ibn al-Khaṣīb. He placed some of Bughā’s fiefs under sequestration, whereupon they threatened to kill him, so he went into hiding (2).

He was appointed vizier for al-Mustaʿīn a second time after Shujāʿ, but Bughā once more incited people against him—