Thomas Young (13.06.1773-10.05.1829) was an English scientist, one of the founders of wave optics, a Fellow of the Royal Society (1794) and its secretary in 1802-29. He was born in Milverton. From an early age he showed extraordinary abilities and a phenomenal memory. At 2 he learned to read fluently, at 4 he knew by heart many works of the English poets, at 8 — 9 he mastered the lathe and made various physical instruments, and by 14 he had become acquainted with the differential calculus (from Newton). He studied many languages (Greek, Latin, French, Italian, Arabic and others). He studied at the Universities of London, Edinburgh and Göttingen, where he first studied medicine but then became absorbed in physics, in particular optics and acoustics. In 1801 — 03 he was professor at the Royal Institution; from 1811 he was a physician at St George's Hospital (London), and at the same time from 1818 secretary of the Board of Longitude, in which post he directed the publication of the “Nautical Almanac”. In the last years of his life he worked on compiling an Egyptian dictionary.
His research was in optics, acoustics, heat, mechanics, mathematics, astronomy, geophysics, philology and zoology. In the history of science, however, he is best known as a physicist. He explained (1793) the accommodation of the eye by a change in the curvature of the lens. In his treatise “An Outline of Experiments and Inquiries respecting Sound and Light” (1800) he came out in defence of the wave theory of light and criticised Newton's corpuscular theory; in it he was also the first to point out the reinforcement and weakening of sound when sound waves are superposed (the interference of sound), and proposed the principle of the superposition of waves. In 1801 he was the first to explain the interference of light, and he introduced (1803) the term “interference”; in particular, starting from his principle of interference (1801), he explained Newton's rings. He also performed the first demonstration experiment on the interference of light, obtaining two coherent sources of light (1802). This experiment became a classic, like Fresnel's well-known experiment. In 1803 he attempted to explain the diffraction of light from a thin thread by relating it to interference, discovered the interference of ultraviolet rays, and showed that a half-wave is lost when a ray of light is reflected from a denser medium. He worked on a theory of colour vision. He measured the wavelengths of different colours, obtaining for the wavelength of red light a value of 0.7 micron and for violet 0.42 micron (1803). He expressed (1807) the idea that light and radiant heat differ from each other only in wavelength, and put forward (1817) the idea that light waves are transverse.
In the theory of elasticity Young studied shear deformation, and in 1807 he introduced a measure of elasticity, the tensile modulus (Young's modulus).
A member of the Paris Academy of Sciences.