Thomas Young (scientist)



Thomas Young (June 13, 1773-May 10, 1829) was an English polymath, contributing to the scientific understanding of vision, light, solid mechanics, energy, physiology, and Egyptology.

Biography
Young belonged to a Quaker family of Milverton, Somerset, where he was born in 1773, the eldest of ten children. At the age of fourteen Young had learned Greek and Latin and was acquainted with French, Italian, Hebrew, Chaldean, Syriac, Samaritan, Arabic, Persian, Turkish and Amharic.

Young began to study medicine in London in 1792, moved to Edinburgh in 1794, and a year later went to Göttingen, where he obtained the degree of doctor of physics in 1796. In 1797 he entered Emmanuel College, Cambridge. In the same year he inherited the estate of his grand-uncle, Richard Brocklesby, which made him financially independent, and in 1799 he established himself as a physician at 48 Welbeck Street, London (now recorded with a blue plaque). Young published many of his first academic articles anonymously to protect his reputation as a physician.

In 1801 Young was appointed professor of natural philosophy (mainly physics) at the Royal Institution. In two years he delivered 91 lectures. In 1802, he was appointed foreign secretary of the Royal Society, of which he had been elected a fellow in 1794. He resigned his professorship in 1803, fearing that its duties would interfere with his medical practice. His lectures were published in 1807 in the Course of Lectures on Natural Philosophy and contain a number of anticipations of later theories.

In 1811 Young became physician to St. George's Hospital, and in 1814 he served on a committee appointed to consider the dangers involved by the general introduction of gas into London. In 1816 he was secretary of a commission charged with ascertaining the length of the second's pendulum, and in 1818 he became secretary to the Board of Longitude and superintendent of the HM Nautical Almanac Office.

A few years before his death he became interested in life insurance, and in 1827 he was chosen one of the eight foreign associates of the French Academy of Sciences.

Thomas Young died in London on May 10, 1829.

Later scholars and scientists have praised Young's work although they may know him only through achievements he made in their fields. His contemporary Sir John Herschel called him a "truly original genius". Albert Einstein praised him in 1931 foreword to an edition of Newton's Opticks. Other admirers include physicist Lord Rayleigh and Nobel laureate Philip Anderson.

Double-slit experiment
In physics, Thomas Young is perhaps best known for his work in physical optics, as the author of series of research which did much to establish the wave theory of light, and as the discoverer of the interference of light. In Young's double-slit experiment, c. 1801, he passed a beam of light through two parallel slits in an opaque screen, forming a pattern of alternating light and dark bands on a white surface beyond. This led Young to reason that light was composed of waves. (Tony Rothman in Everything's Relative and Other Fables from Science and Technology argues that there is no clear evidence that Young actually did the experiment. See also Newton wave-particle duality.)

Young's modulus
Young described the characterization of elasticity that came to be known as Young's modulus, denoted as E, in 1807, and further described it in his subsequent works such as his 1845 Course of Lectures on Natural Philosophy and the Mechanical Arts. However, the idea can be traced back to a paper by Leonhard Euler published in 1727, eighty years before Thomas Young's 1807 paper. The first use of the concept of Young's modulus in experiments was by Giordano Riccati in 1782 – predating Young by 25 years.

The Young's modulus relates the stress (pressure) in a body to its associated strain (change in length as a ratio of the original length), i.e. stress = E &times; strain, for a uniaxially loaded specimen. Young's modulus is independent of the component under investigation, i.e. it is an inherent material property (the term modulus refers to an inherent material property). Young's Modulus allowed, for the first time, prediction of the strain in a component subject to a known stress (and vice versa). Prior to Young's contribution, engineers were required to apply Hooke's F = kx relationship to identify the deformation (x) of a body subject to a known load (F). Where the constant (k) is a function of both the geometry and material under consideration. This required physical testing for any new component as the F = kx relationship is a function of both geometry and material. Young's Modulus depends only on the material, not its geometry, thus allowing a revolution in engineering strategies.

Vision and colour theory
Young has also been called the founder of physiological optics. In 1793 he explained the mode in which the eye accommodates itself to vision at different distances as depending on change of the curvature of the crystalline lens; in 1801 he was the first to describe astigmatism; and in his Lectures he presented the hypothesis, afterwards developed by Hermann von Helmholtz, that colour perception depends on the presence in the retina of three kinds of nerve fibres which respond respectively to red, green and violet light. This theory was experimentally proven in 1959.

See also Young–Helmholtz theory

Young–Laplace equation
In 1804 Thomas Young (Essay on the " Cohesion of Fluids, " Phil. Trans., 1805, p. 65) founded the theory of capillary phenomena on the principle of surface tension. He also observed the constancy of the angle of contact of a liquid surface with a solid, and showed how from these two principles to deduce the phenomena of capillary action.

The Young–Laplace equation is the formula for capillary action independently discovered by Laplace in 1805.

Young was the first to define the term "energy" in the modern sense.

Young's equation and Young–Dupré equation
Young’s equation describes the contact angle of a liquid drop on a plane solid surface as a function of the surface free energy, the interfacial free energy and the surface tension of the liquid. Young’s equation was developed further some 60 years later by Dupré to account for thermodynamic effects, and this is known as the Young–Dupré equation.

Medicine
In physiology Young made an important contribution to haemodynamics in the Croonian lecture for 1808 on the "Functions of the Heart and Arteries," and his medical writings included An Introduction to Medical Literature, including a System of Practical Nosology (1813) and A Practical and Historical Treatise on Consumptive Diseases (1815).

Young devised a rule of thumb for determining a child’s drug dosage. Young’s Rule states that the child dosage is equal to the adult dosage multiplied by the child’s age in years, divided by the sum of 12 plus the child’s age.

Languages
In his Encyclopaedia Britannica article "Languages", Young compared the grammar and vocabulary of 400 languages. In a separate work in 1813, he introduced the term Indo-European languages, 165 years after the Dutch linguist and scholar Marcus Zuerius van Boxhorn made such a proposal in 1647.

Egyptian hieroglyphs
Young was also one of the first who tried to decipher Egyptian hieroglyphs, with Silvestre de Sacy and Johan David Åkerblad who built up a demotic alphabet of 29 letters which was largely used by Young. But Åkerblad believed that demotic was entirely phonetic or alphabetic and was wrong. By 1814 he had completely translated the "enchorial" (demotic, in modern terms) text of the Rosetta Stone (he had a list with 86 demotic words), and then studied the hieroglyphic alphabet but failed to recognise that the demotic and hieroglyphic texts were paraphrases and not simple translations. In 1823 he published an Account of the Recent Discoveries in Hieroglyphic Literature and Egyptian Antiquities. Some of Young's conclusions appeared in the famous article "Egypt" he wrote for the 1818 edition of the Encyclopædia Britannica.

When the French linguist Jean-François Champollion published his translation of the hieroglyphs, Young praised his work but also stated that Champollion had based his system on Young's articles and tried to have his part recognized. Champollion, however, was unwilling to share the credit. In the forthcoming schism, strongly motivated by the political tensions of that time, the British supported Young and the French Champollion. Champollion, whose complete understanding of the hieroglyphic grammar showed the mistakes made by Young, maintained that he alone had deciphered the hieroglyphs. However, after 1826, he did offer Young access to demotic manuscripts in the Louvre, when he was a curator there.

Music
He developed Young temperament, a method of tuning musical instruments.

Selected writings of Thomas Young

 * A Course of Lectures on Natural Philosophy and the Mechanical Arts (1807, republished 2002 by Thoemmes Press).
 * Miscellaneous Works of the Late Thomas Young, M.D., F.R.S. (1855, 3 volumes, editor John Murray, republished 2003 by Thoemmes Press).