Young, Thomas, 1773–1829, English physicist, physician, and Egyptologist. He established (1799) a medical practice in London and was elected (1811) to the staff of St. George's Hospital there. His lectures while professor of natural philosophy (1801–3) at the Royal Institution, London, published as A Course of Lectures on Natural Philosophy and the Mechanical Arts (1807), introduced the modern physical concept of energy. An authority on the mechanism of vision and on optics, he stated (1807) a theory of color vision now known as the Young-Helmholtz theory, studied the structure of the eye, and described the defect called astigmatism. He is especially noted for reviving the wave theory of light as opposed to the corpuscular theory, advancing as proof a demonstration based upon the principle of interference of light, which he first formulated in 1801. He applied (1809) the wave theory to refraction and dispersion phenomena. Young's versatility is evidenced by his contributions to the theory of tides, his participation in the deciphering of the Rosetta Stone (see under Rosetta Rosetta Stone is a granitoid slab inscribed in hieroglyphic, demotic, and Greek with identical texts of a decree by a council of priests during the reign of Ptolemy V . Part of a stele dating from 196 B.C.
..... Click the link for more information. ), which provided a key to understanding Egyptian hieroglyphic writings, his explanation (1804) of capillarity (independently set forth by Laplace in 1805), and his establishment of a coefficient of elasticity, Young's modulus Young's modulus [for Thomas Young ], number representing (in pounds per square inch or dynes per square centimeter) the ratio of stress to strain for a wire or bar of a given substance.
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Bibliography

See biographies by H. B. Williams (1930) and A. Wood (1954).

Young, Thomas

(born June 13, 1773, Milverton, Somerset, Eng.—died May 10, 1829, London) English physicist. Trained as a physician, he practiced medicine at St. George's Hospital (from 1811 until his death) but spent much of his time on scientific research. He was the first to describe and measure astigmatism (1800–01) and the first to explain colour sensation in terms of retinal structures corresponding to red, green, and violet (1801). He established the principle of interference of light, thus resurrecting the century-old wave theory of light (1801). He explained capillarity independently of Pierre-Simon Laplace. Investigating elasticity, he proposed Young's modulus, a numerical constant that describes the elastic properties of a solid undergoing tension or compression. His other work included measuring the size of molecules and surface tension in liquids. With J.-F. Champollion, he helped decipher the inscriptions on the Rosetta Stone (1813–14).