Thomas Young (1773-1829).

Thomas Young was an English physician and physicist, with a brilliant mind and eclectic interests. By the age of fourteen it is said that he was acquainted with Latin, Greek, French, Italian, Hebrew, Arabic and Persian. So great was his knowledge that he was called called Phenomena Young by his fellow students at Cambridge. He studied medicine in London, Edinburgh, and Göttingen and set up medical practice in London. His initial interest was in sense perception, and he was the first to realize that the eye focusses by changing the shape of the lens. He discovered the cause of astigmatism, and was the initiator, with Helmoltz, of the three colour theory of perception, believing that the eye constructed its sense of colour using only three receptors, for red, green and blue. In 1801 he was appointed Professor of Physics at Cambridge university. His famous double-slit experiment established that light was a wave motion, although this conclusion was strongly opposed by contemporary scientists who believed that Newton, who had proposed that light was corpuscular in nature, could not possibly be wrong. However Young's work was soon confirmed by the French scientists Fresnel and Arago. He proposed that light was a transverse wave motion (as opposed to longitudinal) whose wavelenght determined the colour. Since it was thought that all wave motions had to be supported in a material medium, light waves were presumed to travel through a so-called aether, which was supposed to fill the entire universe. He became very interested in Egyptology, and his studies of the Rosetta stone, discovered on one of Napoleon's expeditions in 1814, contributed greatly to the subsequent deciphering of the ancient Egyptian hieroglyphic writing. He did work in surface tension, elasticity (Young's modulus, a measure of the rigidity of materials, is named after him), and gave one of the earliest scientific definitions of energy.