Although a distressingly big number of the works ascribed to Ibn al-Haytham and Al-Bīrūnī are lost without any hope of recovery, both men—and the destructive forces of the turbulent centuries that divide us from them—were good enough to leave us lists of their own writings and autobiographic reflections. Any study of their scientific works, and especially a comparative evaluation that tries to lay bare the roots and methodological orientations of their science, will therefore be able to start from their own explicit statements. Further details, however, will then have to be gathered from their other extant literary compositions; and only a careful reading of these works can show how far their scientific programs and methodological reflections have been carried out and where they have led.

To start with, the older one of the two men,⁴ Ibn al-Haytham is never satisfied to just state the...