|He was professor of natural philosophy from
1801 to 1803 at the Royal Institution. It was there that he presented the
modern physical concept of energy, and was elected in 1811 to a staff position
of St. George's Hospital, London.
In 1807 he developed a theory of color vision known as the Young-Helmholtz theory and described the vision defect called Astigmatism.
In 1802 Young demonstrated a simple proof of the wave theory of light. He forced light to pass through a narrow slit and then through two more narrow slits placed within a fraction of an inch of each other. The light from the two slits shined on a screen. Young found at the light beams spread apart and overlapped, and, in the area of overlap, bands of bright light alternated with bands of darkness. With this Young established the wave nature of light which he used to explain the colors on thin films, such as soap bubbles. He related color to wavelength, he calculated the approximate wavelengths of the seven colors recognized by Newton.
In 1817 he proposed that light waves were transverse (perpendicular to the direction of travel), rather than longitudinal (in the direction of travel). This explained polarization, the alignment of light waves to vibrate in the same plane.
With his discovery, however, Young came into conflict with the theories of Sir Isaac Newton, who tried to explain optical phenomena such as refraction and reflection in terms of gravitation like effects. As it turned out later, in a way, Newton's theory was given partial confirmation by the Quantum Theory. In the early 19th century, however, any opposition to a theory of Newton's was unthinkable by most English scientists. Ridiculed in England, Young’s theory was championed in France by Augustin Jean Fresnel (1788-1827) and Dominique-François-Jean Arago (1785-1853), and finally achieved acceptance in Europe. A savage anonymous review of his work in 1803 in the Edinburgh Review cast Young into scientific limbo for ten years. This review was by Lord Henry Peter Brougham (1778-1868), a proponent of the corpuscular theory.
Aside from being a physicist, he was a physician and an Egyptologist. He also established a coefficient of elasticity and helped to decipher the Rosetta Stone.