Thomas Young (13 June 177310 May 1829) was a British polymath who made notable contributions to the fields of vision, light, solid mechanics, energy, physiology, language, musical harmony, and Egyptology. He was instrumental in the decipherment of Egyptian hieroglyphs, specifically the Rosetta Stone.
Young's work influenced that of William Herschel, Hermann von Helmholtz, James Clerk Maxwell, and Albert Einstein. Young is credited with establishing Christiaan Huygens' wave theory of light, in contrast to the corpuscular theory of Isaac Newton. Young's work was subsequently supported by the work of Augustin-Jean Fresnel.
Personal life Young belonged to a Quaker family of Milverton, Somerset, where he was born in 1773, the eldest of 10 children. By the age of 14, Young had learned Greek, Latin, French, Italian, Syriac, Samaritan Hebrew, Arabic, Biblical Aramaic, Persian, Turkish, and Ge'ez.
Young began to study medicine in London at St Bartholomew's Hospital in 1792, moved to the University of Edinburgh Medical School in 1794, and a year later went to Göttingen, Lower Saxony, Germany, where he obtained the degree of doctor of medicine in 1796 from the University of Göttingen. 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 in the general introduction of gas for lighting into London. In 1816, he was secretary of a commission charged with ascertaining the precise length of the seconds pendulum (the length of a pendulum whose period is exactly two seconds), and in 1818 he became secretary to the Board of Longitude and superintendent of the HM Nautical Almanac Office.
Young was elected a Foreign Honorary Member of the American Academy of Arts and Sciences in 1822. A few years before his death he became interested in life insurance, and in 1827 he was chosen as one of the eight foreign associates of the French Academy of Sciences. In the same year, he became a first class corresponding member, living abroad, of the Royal Institute of the Netherlands. In 1828, he was elected a foreign member of the Royal Swedish Academy of Sciences.
In 1804, Young married Eliza Maxwell. They had no children.
Young died in his 56th year in London on 10 May 1829, having suffered recurrent attacks of "asthma". His autopsy revealed atherosclerosis of the aorta. His body was buried in the graveyard of St Giles' Church at Farnborough, in the county of Kent. Westminster Abbey houses a white marble tablet in memory of Young, bearing an epitaph by Hudson Gurney:
Young tutored Hudson Gurney as a child, and they remained lifelong friends. Gurney commissioned a portrait of Young by Thomas Lawrence, and there have been many copies based on this original painting. Young was highly regarded by his friends and colleagues. He was said never to impose his knowledge, but if asked, was able to answer even the most difficult scientific question with ease. Although very learned, he had a reputation for sometimes having difficulty communicating his knowledge. It was said by one of his contemporaries that, "His words were not those in familiar use, and the arrangement of his ideas seldom the same as those he conversed with. He was therefore worse calculated than any man I ever knew for the communication of knowledge.""Peacock's Life of Dr Young" by George Peacock, D.D., F.R.S., etc. Dean of Ely, Lowndean Professor of Astronomy, University of Cambridge, etc., quoted in "The Living Age" by E. Littell, Second Series, Volume X, 1855, Littell, Son and Company, Boston.
Religious views Though he sometimes dealt with religious topics of history in Egypt and wrote about the history of Christianity in Nubia, not much is known about Young's personal religious views. In George Peacock's account, Young never spoke to him about morals, metaphysics, or religion, though according to Young's wife, his attitudes showed that "his Quaker upbringing had strongly influenced his religious practices." Authoritative sources have described Young in terms of a cultural Christian Quaker.Peacock & Leitch., Miscellaneous works of the late Thomas Young (1855), London, J. Murray, p. 516: "he was pre-eminently entitled to the high distinction of a Christian, patriot, and philosopher."
Hudson Gurney informed that before his marriage, Young had to join the Church of England, and was baptized later. Gurney stated that Young "retained a good deal of his old creed, and carried to his scriptural studies his habit of inquisition of languages and manners," rather than the habit of proselytism. Yet, the day before his death, Young participated in religious sacraments; as reported in David Brewster's Edinburgh Journal of Science:
Research Wave theory of light
In Young's own judgement, of his many achievements the most important was to establish the wave theory of light set out by Christiaan Huygens in his Treatise on Light (1690). To do so, he had to overcome the century-old view, expressed in the venerable Newton's Opticks, that light is a particle. In the early 19th century, Young put forth a number of theoretical reasons supporting the wave theory of light, and he developed two enduring demonstrations to support this viewpoint. With the ripple tank, he demonstrated the idea of interference in the context of water waves. With additional experiments, including the predecessor of the double-slit experiment, he demonstrated interference in the context of light as a wave. Young also used his data from this experiment to calculate the wavelengths of different colors of light, coming very close to modern values. I found that six of the brightest red fringes, nearly at equal distances, occupied the whole of that image. The breadth of the aperture was , and its distance from the hair of an inch; the diameter of the hair was less than of an inch; as nearly as I could ascertain, it was . Hence, we have for the deviation of the first red fringe at the distance of and, as :::: or for the difference of the routes of the red light where it was most intense.
Young, speaking on 24 November 1803, to the Royal Society of London, began his now-classic description of the historic experiment:
In his subsequent paper, titled Experiments and Calculations Relative to Physical Optics (1804), Young describes an experiment in which he placed a card measuring approximately in a beam of light from a single opening in a window and observed the fringes of colour in the shadow and to the sides of the card. He observed that placing another card in front or behind the narrow strip so as to prevent the light beam from striking one of its edges caused the fringes to disappear. p. 309 This supported the contention that light is composed of waves.Both Young and Newton were eventually shown to be partially correct, as neither wave nor particle explanations alone can explain the behaviour of light. See e.g. http://www.single-molecule.nl/notes/light-waves-and-photons/ .
Young performed and analysed a number of experiments, including interference of light from reflection off nearby pairs of micrometre grooves, from reflection off thin films of soap and oil, and from Newton's rings. He also performed two important diffraction experiments using fibres and long, narrow strips. In his Course of Lectures on Natural Philosophy and the Mechanical Arts (1807), he gives Grimaldi credit for first observing the fringes in the shadow of an object placed in a beam of light. Within ten years, much of Young's work was reproduced and then extended by Augustin-Jean Fresnel.
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 Course of Lectures on Natural Philosophy and the Mechanical Arts. However, the first use of the concept of Young's modulus in experiments was by Giordano Riccati in 1782—predating Young by 25 years. Furthermore, the idea can be traced to a paper by Leonhard Euler published in 1727, some 80 years before Thomas Young's 1807 paper.
Young's modulus relates the stress (compression or decompression) in a body to its associated strain (fractional change in length); that is, stress = E × strain, for a uniaxially loaded specimen. Young's modulus is independent of the quantity under investigation; that is, it is an intensive property of the material. Young's Modulus allowed, for the first time, the 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. Finding k 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.
Young's problems in sometimes not expressing himself clearly were shown by his own definition of the modulus: "The modulus of the elasticity of any substance is a column of the same substance, capable of producing a pressure on its base which is to the weight causing a certain degree of compression as the length of the substance is to the diminution of its length." When this explanation was put to the Lords of the Admiralty, their clerk wrote to Young saying, "Though science is much respected by their Lordships and your paper is much esteemed, it is too learned ... in short it is not understood.""Structures, or Why Things Don't Fall Down" by J. E. Gordon, Penguin Books, 1978.
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, (the Young–Helmholtz theory), that colour perception depends on the presence in the retina of three kinds of nerve fibres. This foreshadowed the modern understanding of colour vision, in particular the finding that the eye does indeed have three colour receptors which are sensitive to different wavelength ranges.
Young–Laplace equation In 1804, Young developed 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 to deduce from these two principles the phenomena of capillary action. In 1805, Pierre-Simon Laplace, the French philosopher, discovered the significance of meniscus radii with respect to capillary action.