Early work on the River Nile
Abu Ali Hasan Ibn al-Haitham was one of the most eminent of all physicists, whose contributions to sciences, in particularly optics, were outstanding. Known in the West as Alhazen, he is considered the 'father of modern optics'.
Iranian by birth, Alhazen received his education in both Basra and Baghdad, before travelling to Egypt, where on commission to Caliph al-Hakim, then ruler of Egypt, he attempted to find a way of controlling the flooding of the Nile River.
He reasoned that constructing a dam would enable water to be stored for irrigation in the dry season, and would prevent flooding at other times.
However, upon arriving at the proposed site, Alhazen realised that he had insufficient money and materials to successfully complete the project. Wishing to escape the wrath of Caliph he feigned madness, a pretence he maintained until Caliph's death 12 years later.
By this time, Alhazen was living and pursuing science in Spain. There he conducted examinations of optics, mathematics, physics, medicine as well as doing much to develop scientific method. Of his many works, the most distinguished was Kitab-al-Manadhir.
Translated into Latin in 1270, Opticae Thesaurus was the first real contribution to the science of optics in the first millennium and had a great influence on both Bacon and Kepler.
Of particular note, the six-volume work contains the first serious study of lenses, a disproof of Ptolemy's law of refraction, research into reflections from spherical and parabolic mirrors and the first accurate description of the anatomy of the human eye. He also studied the phenomena of eclipses, shadows, and rainbows and the role of the dispersion light in the determination of colours.
Many experiments were conducted in a dark room lit through a solitary hole. Outside the room, adjacent to the wall with the hole, Alhazen hung five lamps. He observed that these produced five 'lights' on the wall inside his dark room and that by placing an obstruction between one of the lanterns and the hole one of the 'lights' on the wall disappears. His observation that the lantern, the obstruction and the hole were in a straight line demonstrated that light travels in straight lines.
The fact that there were five 'lights' on the wall inside the room revealed that, despite there being five light sources simultaneously travelling through the hole, they were not mixed up. From this Alhazen deduced that vision was the product of light being reflected into the eye rather than rays from the eye scanning objects. This overturned a thousand years of Aristotelian scientific thought.
Alhazen's experiment was the first scientific description of the 'camera obscura' (dark room), the principle behind the pinhole camera.
The IET Archives holds a copy of Opticae Thesaurus dated 1572, the first year in which it was published. This edition is of particular note as, prior to being owned by IET past president, Silvanus P Thompson, it was also in the possession of the celebrated Andre Marie Ampere.
His book, Mizan al-Hikmah, examines the density of the atmosphere, atmospheric refraction, and why twilight begins or ends only when the sun is 19 degrees below the horizon. Ultimately, his desire was to use all of these aspects to determine the height of the atmosphere.
Mathematics and physics
Alhazen also made significant contributions to both mathematics and physics. In mathematics, he established the link between algebra and geometry that led to his development of analytical geometry.
In physics, he devised one of the first laws of motion, stating that a body moves perpetually until stopped by an external force or it changes direction.