At the invitation of the King of Egypt, Alhazen undertook the gigantic task of regulating the Nile. He was indeed a man of courage. Even back in those days the floods of that great river were a serious menace to lives and property, and control was attempted. But it was not until modern times that any successful regulation of the flood waters of the Nile was effected, and this was under the skill of British engineering; so Alhazen should not be blamed for his failure. Alhazen went to Egypt and made preliminary calculations. He saw that the task was impossible with available tools, men and knowledge, but to admit failure in those days usually meant losing a life--one’s own. Absolute rulers did not like to have agreements broken. Alhazen feigned madness and escaped. By pretending to lose his head he saved his life. Despite his failure with the Nile, Alhazen is regarded as the first great discoverer in optics after the time of Ptolemy. The Arabs were enthusiastic followers of Aristotle and also knew of the work of Archimedes, Ptolemy and other Greek scholars. Alhazen’s great work, _Opticae Thesaurus Alhazeni Arabis_, was first printed in 1572 but manuscript copies of the _De Aspectibus_ or _Perspectiva_ and the _De Crepusculis & Nubium Ascensionibus_ had found their way about the late 12th century into all the great libraries of the Middle Ages and his influence on all subsequent work in optics was great and widespread. The book is very curious, covering a multitude of subjects. Alhazen studied images, the various kinds of shadows and even attempted to calculate the size of the earth. He is credited with being the first to explain successfully the apparent increase of heavenly bodies near the horizon--the familiar phenomenon of the great sun at sunset and the huge harvest moon as it comes up in the East. Light also was extensively considered by Alhazen and he treated its use, setting down many rules on reflection and refraction. He recognized the element of time necessary to complete the act of vision; in other words, the persistence of vision or the time lag. He gave a description of the lens’ magnifying power as he was familiar with various lenses and mirrors. But, perhaps of most importance, Alhazen was the first to note in some detail the workings of the human eye. Alhazen discussed how we see but one picture even though we have two eyes, both functioning at the same time. He is also one of the authorities who made it possible for later scholars to know that the Greeks and Phoenicians knew and understood the simpler optical phenomena. It would be expecting too much to hope that Alhazen’s work would be unmixed with error. At his time and for centuries later, on account of the lack of suitable instruments and knowledge of what was being sought, the imagination was relied on more than it should have been in an exact science.