Ibn al-Haytham (Alhazen)

Ibn al-Haytham established that vision works by light entering the eye, and insisted that claims be tested by experiment. Born in Basra around 965, he was educated there and in Baghdad and worked as a civil servant. The Fatimid caliph al-Hakim invited him to Egypt around 1010 to regulate the flooding of the Nile. He travelled south, examined the terrain around Aswan, concluded that the engineering available could not do it, and reportedly feigned madness to escape the consequences of failure. He spent about a decade under house arrest, which is when he did his best work. The Book of Optics, in seven volumes, overturned the Greek consensus. Euclid and Ptolemy held that vision works by rays issuing from the eye; Ibn al-Haytham demonstrated that light travels from objects to the eye in straight lines, using the camera obscura, the observation that bright light causes pain and afterimages, and geometric argument. He gave the first clear account of the camera obscura, studied refraction, reflection from curved mirrors, the rainbow, atmospheric refraction and the apparent enlargement of the moon at the horizon, which he correctly attributed to perception rather than optics. His method is what distinguishes him. He wrote that the seeker after truth should attack from every side what he reads, suspect himself, and follow evidence rather than authority — and he tested his propositions with controlled apparatus rather than argument alone. He is frequently described as the first person to work in a recognisably scientific way. The Latin translation shaped Roger Bacon, Kepler and Descartes. He died around 1040.

MyHistorian
A causal knowledge graph of history