Alhazen was an Arabic mathematician and physicist who wrote the first important book on optics since the time of Ptolemy. In it, he rejected the older notion that light was emitted by the eye in favor of the view accepted today. His Treasury of Optics (first published in Latin in 1572) discusses lenses, plane and curved mirrors, and colors. Prior to this work he made a near-disastrous expedition to southern Egypt, sponsored by the Caliph al-Hakim, to study possible ways of controlling the Nile. Realizing that the river could not be so easily tamed and that heads would (literally) roll when the bad news was relayed, Alhazen feigned madness upon his return and kept up the pretence until the Caliph died in 1021.