Thomas Young

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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 RosettaRosetta
, former name of Rashid
, city (1986 pop. 51,789), N Egypt, in the Nile River delta. The city once dominated the region's rice market; rice milling and fish processing are the main industries of modern Rashid. Founded in the 9th cent.
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), 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 modulusYoung'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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See biographies by H. B. Williams (1930) and A. Wood (1954).

Young, Thomas


Born June 13, 1773, in Milverton, in the county of Somerset; died May 10, 1829, in London. British physicist, physician, and astronomer; a founder of the wave theory of light. Fellow of the Royal Society of London (1794); foreign secretary of the Royal Society from 1802 to 1829.

Young had a variety of abilities and interests. At the age of eight, he studied geodesy and mathematics. When he was nine, he took up the study of history, botany, and languages, including Latin, Greek, Hebrew, and Arabic. Young studied medicine in London and Edinburgh and continued his studies at the University of Göttingen, where he attended the lectures of G. C. Lichtenberg. From 1801 to 1803, he was a professor at the Royal Institution in London. In 1811 he became a physician at St. George’s Hospital in London, a position he retained until his death. In 1818 he was appointed secretary to the Board of Longitude and superintendent of the Nautical Almanac.

Young’s scientific interests were extremely varied, the most important being optics, mechanics, the physiology of vision, and philology. In 1793, in a paper entitled “Observations on the Process of Vision,” Young showed that the accommodation of the eye is due to a change of curvature of the crystalline lens.

Young’s studies in optics led him to the idea that the corpuscular theory of light, which was the prevailing theory of light in his day, was incorrect. Hence he supported the wave theory. His ideas aroused the objections of British scientists; under their influence, he renounced his opinion. However, in 1800, in a treatise on optics and acoustics entitled “Experiments on Sound and Light,” Young again embraced the wave theory of light and, for the first time, considered the problem of the superposition of waves. His consideration of the problem led to his discovery of the principle of interference. Young introduced the term “interference” in 1802.

In a paper entitled “On the Theory of Light and Colors,” which he read to the Royal Society in 1801 and which was published in 1802, Young explained Newton’s rings on the basis of interference and described the first experiments on the determination of wavelengths of light. In 1803, in a paper entitled “Experiments and Calculations Pertaining to Physical Optics,” which was published in 1804, he considered the phenomenon of diffraction. Following A. Fresnel’s classical studies in the interference of polarized light, Young proposed that the vibrations of light are transverse. He also developed a theory of color vision based on the hypothesis that three kinds of sensitive fibers that react to the three primary colors exist in the retina.

In 1807, in his two-volume work A Course of Lectures on Natural Philosophy and the Mechanical Arts, Young summarized the results of his theoretical and experimental research in physical optics (he introduced the term “physical optics”). In the same work, he reported on his research in shear strain and introduced a numerical characteristic of elasticity in tension or compression. The characteristic is known as Young’s modulus. Young was the first to regard mechanical work as a quantity proportional to energy, which he defined as a quantity proportional to the mass of a body and the square of the body’s velocity. He introduced the term “energy.”

Young wrote approximately 60 articles for a supplement to the Encyclopaedia Britannica. He deciphered Egyptian hieroglyphs and determined the values of some of the signs inscribed on the Rosetta Stone. Young was a good musician and an expert on painting.


Miscellaneous Works, vols. 1–3. London, 1855.


Arago, F. Biografti znamenitykh astronomov, fizikov i geomelrov, vol. 2. St. Petersburg, 1860. (Translated from French.)
Wood, A. Thomas Young, Natural Philosopher, 1773–1829. Cambridge, 1954. (Contains a bibliography.)
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