Alhazen

Born in the city of Basra in what is now Iraq, Alhazen (al-HAHZ-un) achieved fame as a scholar and was invited to undertake a special project in Egypt. The caliph or leader of the Fatimids, an Islamic sect that controlled Egypt in his time, asked him to develop a means for controlling the flooding of the Nile River. Eager for advancement, Alhazen had insisted that he could do so. As he sailed southward on a barge toward the city of Aswan (AHS-wahn), however, he observed the magnificent structures built by the ancient Egyptians, and realized that if the river's flooding could be controlled at all, the people of that great civilization would have managed it

Thousands of years before. (Only in the 1960s was the Egyptian government, using modern technology, able to construct a dam to deal with this problem.) As for Alhazen, he got out of the job by pretending to be insane, then laid low until the caliph who had hired him died in 1021.

During the remaining eighteen years of his life, Al-hazen wrote about a wide array of subjects, most notably optics, or the science of vision. In his day, a number of beliefs about vision prevailed, all of them inherited from ancient times, and all extremely fanciful from the standpoint of modern knowledge. Some theorists promoted the idea of extramission, which maintained that the eye sent out rays that made it possible to see objects. Others claimed intromission, which took a variety of forms but basically came down to the idea that the object sent out rays to the eye. Alhazen was the first to realize that in fact light comes from self-luminous bodies such as the Sun or a lamp, then is reflected off of objects to the eye, which "catches" the reflected rays.

In addition to this and other theories put forth in his most famous work, Optics, Alhazen wrote about a number of related subjects such as rainbows, shadows, and the camera obscura, an early ancestor of the camera. He also wrote about astronomy, and like a number of Arab thinkers, helped chip away at mistaken beliefs inherited from the Greek astronomer Ptolemy (TAHL-uh-mee; c. a. d. 100-170)—including the idea that other planets revolve around Earth as part of imaginary circles. His greatest achievement, however, was the Optics, which influenced Roger Bacon and a number of scientists through Johannes Kepler (1571-1630), the first to add significantly to Alhazen's ideas.