In books 4 and 5 of the De aspectibus Alhacen undertakes an analysis of the principles of reflection that culminates with his approach to ‘Alhazen’s Problem’ in book 5:  to find the point or points of reflection in a convex or concave spherical mirror for any randomly posed point of radiation and center of sight.  In the process, Alhacen attempts to establish the basic principles of reflection—e.g., that reflection occurs at equal angles within a single plane perpendicular to the reflecting surface, etc.—on the basis of various controlled experiments.

Original publication: Smith, A. Mark. Alhacen on the Principles of Reflection: A Critical Edition, with English Translation and Commentary, of Books 4 and 5 of Alhacen’s De aspectibus. Interpretatio Series B. 2020. URI: https://ircps.org/interpretatio-b/b004/. This material has been re-published in an unmodified form on the Canadian HSS Commons with the permission of Iter Canada. Copyright © the author(s). Their work is distributed by Interpretatio under a Creative Commons Attribution-NonCommercial 4.0 International License. For details, see https://creativecommons.org/licenses/.