Editing Thomas Young (scientist)

{{Short description|English polymath (1773–1829)}}
{{Use British English|date=October 2013}}
{{Use dmy dates|date=May 2017}}
{{Infobox scientist
| name              = Thomas Young
| post-nominals     = {{postnominals|country=GBR|size=100%|FRS}}
| image             = File:Thomas Young by Briggs cropped.jpg
| image_size        = 240px
| caption           = Portrait by [[Henry Perronet Briggs]], 1822
| birth_date        = {{birth date|df=yes|1773|06|13}}
| birth_place       = [[Milverton, Somerset]], England
| death_date        = {{death date and age|df=yes|1829|05|10|1773|06|13}}
| death_place       = London, England
| residence         =
| citizenship       = 
| nationality       = 
| field             = [[Physics]]<br /> [[Physiology]]<br /> [[Egyptology]]
| work_institutions = 
| alma_mater        = [[University of Edinburgh Medical School]]<br />[[University of Göttingen]]<br />[[Emmanuel College, Cambridge]]
| doctoral_advisor  = 
| doctoral_students = 
| known_for         = [[Wave theory of light]]<br />[[Young's interference experiment|Double-slit experiment]]<br />[[Astigmatism (eye)|Astigmatism]]<br />[[Wetting#The Young–Dupré equation and spreading coefficient|Young–Dupré equation]]<br>[[Young–Helmholtz theory]]<br />[[Young–Laplace equation]]<br>[[Young temperament]]<br/>[[Young's modulus]]<br>[[Young's rule]]
| author_abbrev_bot = 
| author_abbrev_zoo = 
| prizes            = 
| footnotes         = 
| signature         = Young Thomas signature.jpg 
}}
'''Thomas Young''' [[Fellow of the Royal Society|FRS]] (13 June 1773{{snd}}10 May 1829) was a British [[polymath]] who made notable contributions to the fields of [[Visual perception|vision]], [[light]], [[solid mechanics]], [[energy]], [[physiology]], [[language]], [[harmony|musical harmony]], and [[Egyptology]]. He was instrumental in the [[decipherment of Egyptian hieroglyphs]], specifically the [[Rosetta Stone]].

Young has been described as "[[The Last Man Who Knew Everything]]".<ref name=":0" /> His 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]].<ref>{{cite book|last=Kipnis|first=Naum S.|title= History of the Principle of Interference of Light|date=1991|publisher=Springer|pages=65|isbn=9780817623166 |url=https://books.google.com/books?id=e7fvAAAAMAAJ}}</ref> Young's work was subsequently supported by the work of [[Augustin-Jean Fresnel]].<ref>{{Cite book|last=Nolte|first=David D.|date=2023|title=Interference: The History of Optical Interferometry and the Scientists Who Tamed Light (Oxford University Press, 2023)|publisher=Oxford University Press |url=https://global.oup.com/academic/product/interference-9780192869760  |isbn=978-0192869760}}pp. 45-84</ref>

==Personal life==
Young belonged to a [[Quaker]] family of [[Milverton, Somerset]], where he was born in 1773, the eldest of ten children.<ref>{{cite web|title=Thomas Young|url=http://www-history.mcs.st-andrews.ac.uk/Biographies/Young_Thomas.html|publisher=School of Mathematics and Statistics University of St Andrews, Scotland|access-date=30 August 2017}}</ref><ref name="EB1911">{{EB1911|wstitle=Young, Thomas|inline=1|volume=28|page=940}}</ref> By the age of fourteen, Young had learned [[Greek language|Greek]], [[Latin]], [[French language|French]], [[Italian language|Italian]], [[Syriac language|Syriac]], [[Samaritan Hebrew]], [[Arabic]], [[Biblical Aramaic]], [[Persian language|Persian]], [[Turkish language|Turkish]], and [[Geʽez|Ge'ez]].<ref name=EB1911/><ref>{{cite book |author=Singh |first=Simon |title=The Code Book: The Evolution of Secrecy from Mary, Queen of Scots to Quantum Cryptography |title-link=The Code Book |date=October 1999 |publisher=[[Doubleday (publisher)|Doubleday]] |isbn=978-0-385-49532-5 |edition=1st |location=New York |pages=207–208 |language=en |author-link=Simon Singh}}</ref>

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]].<ref>{{cite web|title=Thomas Young (1773–1829)|date=5 May 2016|url=https://www.andrewgasson.co.uk/thomas-young-1773-1829/|publisher=Andrew Gasson|access-date=30 August 2017|archive-date=31 August 2017|archive-url=https://web.archive.org/web/20170831002910/https://www.andrewgasson.co.uk/thomas-young-1773-1829/|url-status=dead}}</ref> In 1797 he entered [[Emmanuel College, Cambridge]].<ref>{{acad|id=YN797T|name=Young, Thomas}}</ref> 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<ref name=EB1911/> (now recorded with a [[blue plaque]]). Young published many of his first academic articles anonymously to protect his reputation as a physician.<ref>{{cite book| last=Robinson|first=Andrew| author-link=W. Andrew Robinson | title=The Last Man Who Knew Everything: Thomas Young, the Anonymous Polymath Who Proved Newton Wrong, Explained How We See, Cured the Sick and Deciphered the Rosetta Stone|date=2006|publisher=[[Oneworld Publications]]|isbn=978-1851684946|page=4|title-link=The Last Man Who Knew Everything}}</ref>

In 1801, Young was appointed professor of [[natural philosophy]] (mainly [[physics]]) at the [[Royal Institution]].<ref>{{cite web|title=Ri Professors|url=http://www.rigb.org/our-history/people/ri-professors|publisher=Royal Institution|access-date=30 August 2017}}</ref> In two years, he delivered 91 lectures. In 1802, he was appointed foreign secretary of the [[Royal Society]],<ref>{{cite web|title=THOMAS YOUNG (1773–1829)|url=https://www.emma.cam.ac.uk/about/history/famous//index.cfm?id=9|publisher=Emmanuel College|access-date=30 August 2017|archive-date=31 August 2017|archive-url=https://web.archive.org/web/20170831002017/https://www.emma.cam.ac.uk/about/history/famous//index.cfm?id=9|url-status=dead}}</ref> of which he had been elected a fellow in 1794.<ref>{{cite web|title=Portrait of Thomas Young|url=https://pictures.royalsociety.org/image-rs-11916|publisher=Royal Society|access-date=30 August 2017}}</ref> 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.<ref name=EB1911/><ref>{{cite journal|last1=Morgan|first1=Michael|title=Thomas Young's Lectures on Natural Philosophy and the Mechanical Arts|journal=Perception|date=2002|volume=31|issue=12|pages=1509–1511|doi=10.1068/p3112rvw|doi-access=free}}</ref>

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 lighting|gas]] for lighting into London.<ref>{{cite book|last1=Weld|first1=Charles Richard|title=A History of the Royal Society: With Memoirs of the Presidents|date=2011|publisher=Cambridge University Press|isbn=9781108028189|pages=235–237|url=https://books.google.com/books?id=fhoeyvuEJI4C&q=Thomas+Young+gas+lighting&pg=PA236}}</ref> 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 2 seconds), and in 1818 he became secretary to the [[Board of Longitude]] and superintendent of the [[HM Nautical Almanac Office]].<ref name=EB1911/><ref>{{cite book|last1=Wood|first1=Alexander|last2=Oldham|first2=Frank|title=Thomas Young: Natural Philosopher, 1773-1829|date=1954|publisher=CUP Archive|pages=304–308|url=https://books.google.com/books?id=hHc6AAAAIAAJ&q=Thomas+Young+HM+Nautical+Almanac+Office&pg=PA308}}</ref>

Young was elected a Foreign Honorary Member of the [[American Academy of Arts and Sciences]] in 1822.<ref name=AAAS>{{cite web|title=Book of Members, 1780–2010: Chapter Y|url=http://www.amacad.org/publications/BookofMembers/ChapterY.pdf|publisher=American Academy of Arts and Sciences|access-date=8 September 2016}}</ref> A few years before his death he became interested in [[life insurance]],<ref name="Peacock, George 1855">{{cite book | title = Life of Thomas Young: M.D., F.R.S., &c.; and One of the Eight Foreign Associates of the National Institute of France | author = Peacock, George | publisher = J. Murray | year = 1855 | url = https://archive.org/details/lifethomasyoung01peacgoog| page = [https://archive.org/details/lifethomasyoung01peacgoog/page/n417 403] }}</ref> and in 1827 he was chosen as one of the eight foreign associates of the [[French Academy of Sciences]].<ref name=EB1911/> In the same year he became a first class corresponding member, living abroad, of the [[Royal Netherlands Academy of Arts and Sciences|Royal Institute of the Netherlands]].<ref>{{cite web|url=https://www.dwc.knaw.nl/biografie/pmknaw/?pagetype=authorDetail&aId=PE00004005 |archive-url=https://web.archive.org/web/20200822173837/https://www.dwc.knaw.nl/biografie/pmknaw/?pagetype=authorDetail&aId=PE00004005 |title=Thomas Young (1773 - 1829) |publisher=Royal Netherlands Academy of Arts and Sciences |archive-date=22 August 2020}}</ref> In 1828, he was elected a foreign member of the [[Royal Swedish Academy of Sciences]].<ref>{{cite book|last=Cooper|first=David K.C.|title=Doctors of Another Calling: Physicians Who Are Known Best in Fields Other than Medicine|date=2013|publisher=Rowman & Littlefield|isbn=9781611494679|pages=98–101|url=https://books.google.com/books?id=b3NBAgAAQBAJ&q=Thomas+Young+Royal+Swedish+Academy+of+Sciences&pg=PA99}}</ref>

In 1804, Young married Eliza Maxwell. They had no children.<ref>{{cite web| url=http://mathshistory.st-andrews.ac.uk/Biographies/Young_Thomas.html| first1=J. J.|last1=O'Connor| first2=E. F. |last2=Robertson| title=Thomas Young|publisher=School of Mathematics and Statistics University of St Andrews, Scotland| year=2006}}</ref>

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.<ref>{{Citation|last1=Bruce Fye|first1=W.|title=Thomas Young|journal=Clinical Cardiology|volume=20|issue=1|pages=87–88|year=1997|doi=10.1002/clc.4960200119|pmc=6656136|pmid=8994746|last2=Willis Hurst|first2=J.}}</ref> His body was buried in the graveyard of St. Giles Church at [[Farnborough, London|Farnborough]], in the county of [[Kent]]. [[Westminster Abbey]] houses a white marble tablet in memory of Young,<ref>'The Abbey Scientists' Hall, A.R. p58: London; Roger & Robert Nicholson; 1966</ref> bearing an epitaph by [[Hudson Gurney]]:<ref>
{{cite book|author=Samuel Austin Allibone|url=https://books.google.com/books?id=j2MLAAAAYAAJ&pg=PA2904|title=A Critical Dictionary of English Literature: And British and American Authors, Living and Deceased, from the Earliest Accounts to the Middle of the Nineteenth Century. Containing Thirty Thousand Biographies and Literary Notices, with Forty Indexes of Subjects, Volume 3|publisher=J. B. Lippincott & Co.|year=1871|page=2904}}</ref><ref>{{cite book|last1=Wood|first1=Alexander|url=https://books.google.com/books?id=hHc6AAAAIAAJ&pg=PA331|title=Thomas Young Natural Philosopher 1773–1829|last2=Oldham|first2=Frank|publisher=Cambridge University Press|year=1954|page=331}}</ref>

{{blockquote |
Sacred to the memory of Thomas Young, M.D., Fellow and Foreign Secretary of the Royal Society Member of the National Institute of France; a man alike eminent in almost every department of human learning. Patient of unintermitted labour, endowed with the faculty of intuitive perception, who, bringing an equal mastery to the most abstruse investigations of letters and of science, first established the undulatory theory of light, and first penetrated the obscurity which had veiled for ages the hieroglyphs of Egypt. Endeared to his friends by his domestic virtues, honoured by the World for his unrivalled acquirements, he died in the hopes of the Resurrection of the just.&nbsp;—Born at Milverton, in Somersetshire, 13 June 1773. Died in Park Square, London, 10 May 1829, in the 56th year of his age.}}

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 in 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."<ref>"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.</ref>

=== 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.<ref>[[Alexander Wood (physicist)|Wood, Alexander]]. 2011. ''Thomas Young: Natural Philosopher 1773–1829''. Cambridge University Press.  p. 56</ref> On [[George Peacock (mathematician)|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."<ref>[[Alexander Wood (physicist)|Wood, Alexander]]. 2011. ''[https://books.google.com/books?id=Jw9nLFVjXdEC Thomas Young: Natural Philosopher 1773–1829]''. Cambridge University Press. p. 329</ref> Authoritative sources have described Young in terms of a cultural Christian Quaker.<ref>Peacock & Leitch., ''[[iarchive:miscellaneouswo00youngoog|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."</ref><ref>[[Alexander Wood (physicist)|Wood, Alexander]]. 2011. ''Thomas Young: Natural Philosopher 1773–1829''. Cambridge University Press.  p. XVI</ref>

[[Hudson Gurney]] informed that before his marriage, Young had to join the [[Church of England]], and was baptized later.<ref>[[Alexander Wood (physicist)|Wood, Alexander]]. 2011. ''[https://books.google.com/books?id=Jw9nLFVjXdEC Thomas Young: Natural Philosopher 1773–1829]''. Cambridge University Press. p. 56</ref> 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.<ref>[[Alexander Wood (physicist)|Wood, Alexander]]. 2011, p. 56</ref> Yet, the day before his death, Young participated in religious sacraments; as reported in [[David Brewster]]'s ''Edinburgh Journal of Science'': "After some information concerning his affairs, and some instructions concerning the hierographical papers in his hands, he said that, perfectly aware of his situation, he had taken the sacraments of the church on the day preceding. His religious sentiments were by himself stated to be liberal, though orthodox. He had extensively studied [[The Bible|the Scriptures]], of which the precepts were deeply impressed upon his mind from his earliest years; and he evidenced the faith which he professed; in an unbending course of usefulness and rectitude."<ref>Brewster, David. 1831. ''[https://books.google.com/books?id=P_hSAAAAcAAJ The Edinburgh Journal of Science]''. Vol. 8, Blackwood. pp. 204;207</ref>

==Research==
===Wave theory of light===
{{see also|Wave–particle duality}}
In Young's own judgment, 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).<ref>{{cite web|title=Thomas Young (1773–1829)|url=http://www.geog.ucsb.edu/~jeff/115a/history/young.html|publisher=UC Santa Barbara|access-date=5 September 2016}}</ref><ref>{{cite web|last=Haidar|first=Riad|title=Thomas Young and the wave theory of light|url=https://www.bibnum.education.fr/sites/default/files/71-young-analysis.pdf|publisher=Bibnum|access-date=5 September 2016|archive-date=15 September 2016|archive-url=https://web.archive.org/web/20160915001601/https://www.bibnum.education.fr/sites/default/files/71-young-analysis.pdf|url-status=dead}}</ref> To do so, he had to overcome the century-old view, expressed in the venerable Newton's ''[[Opticks]]'', that light is a particle. Nevertheless, 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 (wave propagation)|interference]] in the context of water waves. With [[Young's interference experiment]], the predecessor of the [[double-slit experiment]], he demonstrated interference in the context of light as a wave.

[[File:Young-Thomas-Lectures1807-Plate_XXX.jpg|thumb|Plate from "Lectures" of 1802 (RI), pub. 1807]]

Young, speaking on 24 November 1803, to the Royal Society of London, began his now-classic description of the historic experiment:<ref>{{cite book|last=Shamos|first=Morris|title=Great Experiments in Physics|year=1959|publisher=Holt Rinehart and Winston|location=New York|pages=96–101}}</ref>
{{blockquote|The experiments I am about to relate ... may be repeated with great ease, whenever the sun shines, and without any other apparatus than is at hand to every one.<ref>{{cite journal|last=Young|first=Thomas|title=Bakerian Lecture: Experiments and calculations relative to physical optics |journal=Philosophical Transactions of the Royal Society |year=1804 |volume=94 |pages=1–2 |url=https://books.google.com/books?id=7AZGAAAAMAAJ&pg=PA1|bibcode=1804RSPT...94....1Y|doi=10.1098/rstl.1804.0001|s2cid=110408369|doi-access=free}}</ref>}}

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 {{convert|0.85|mm|in}} 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.<ref>{{cite book|last=Magie|first=William Francis|title=A Source Book in Physics|url=https://archive.org/details/in.ernet.dli.2015.449479|publisher=Harvard University Press|year=1935}} p. 309</ref> This supported the contention that light is composed of [[wave]]s.<ref>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/ {{Webarchive|url=https://web.archive.org/web/20160309130103/https://www.single-molecule.nl/notes/light-waves-and-photons/ |date=9 March 2016 }}.</ref>

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 [[Francesco Maria Grimaldi|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===
{{main|Young's modulus}}
[[File:Young - Mathematical elements of natural philosophy, 2002 - 3933182 F.tif|thumb|Young's ''Mathematical Elements of Natural Philosophy'']]

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''.<ref>{{cite book | title = Course of Lectures on Natural Philosophy and the Mechanical Arts | author = Young, Thomas | url = https://archive.org/details/bub_gb_fGMSAAAAIAAJ | page = [https://archive.org/details/bub_gb_fGMSAAAAIAAJ/page/n141 106] | quote = modulus thomas young. | year = 1845 | publisher = London: Taylor and Walton}}</ref>
However, the first use of the concept of Young's modulus in experiments was by [[Giordano Riccati]] in 1782—predating Young by 25 years.<ref>{{cite book | author = Truesdell, Clifford A.| year = 1960 | title = The Rational Mechanics of Flexible or Elastic Bodies, 1638–1788: Introduction to Leonhardi Euleri Opera Omnia, vol. X and XI, Seriei Secundae | publisher = Orell Fussli}}</ref>
Furthermore, the idea can be traced to a paper by [[Leonhard Euler]] published in 1727, some 80 years before Thomas Young's 1807 paper.

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); that is, stress = ''E'' × strain, for a uniaxially loaded specimen. Young's modulus is independent of the component under investigation; that is, 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. 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."<ref>"Structures, or Why Things Don't Fall Down" by J. E. Gordon, Penguin Books, 1978.</ref>

===Vision and colour theory===
Young has also been called the founder of physiological optics. In 1793 he explained the mode in which the eye [[accommodation (eye)|accommodates]] itself to vision at different distances as depending on change of the curvature of the [[lens (vision)|crystalline lens]]; in 1801 he was the first to describe [[Astigmatism (eye)|astigmatism]];<ref>{{cite journal | url = https://books.google.com/books?id=3I9JAAAAYAAJ&pg=PA23-IA3 | title = On the mechanics of the eye | journal = Philosophical Transactions of the Royal Society | volume = 91 | year = 1801 | pages = 23–88 | first = Thomas | last = Young|bibcode = 1801RSPT...91...23Y | doi = 10.1098/rstl.1801.0004 | doi-access = free }}</ref> 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.<ref name="EB1911" /><ref>{{cite journal|author=Young, T.|year= 1802|title= Bakerian Lecture: On the Theory of Light and Colours|journal=Phil. Trans. R. Soc. Lond.|volume= 92|pages=12–48| doi= 10.1098/rstl.1802.0004|doi-access= free}}</ref> 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]].<ref>{{cite journal |title=An Essay on the Cohesion of Fluids|jstor=107159|author=Young, Thomas|journal=Phil. Trans. |volume=95|pages=65–87|year=1805 |doi=10.1098/rstl.1805.0005|s2cid=116124581|url=https://archive.org/details/philtrans01794383 |doi-access=free}}</ref> 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.

In 1830, [[Carl Friedrich Gauss]], the German mathematician, unified the work of these two scientists to derive the [[Young–Laplace equation]], the formula that describes the [[capillary pressure]] difference sustained across the interface between two static fluids.

Young was the first to define the term "energy" in the modern sense.<ref>{{cite book |last=Weber |first=Wilhelm |title=Abhandlungen der Mathematisch-Physischen Classe der königlich Sächsischen Gesellschaft der Wissenschaften |publisher=S. Hirzel |date=1878 |chapter=Elektrodynamische Massbestimmungen insbesondere über die Energie der Wechselwirkung |url=https://archive.org/details/ueberdenausgang00fechgoog |page=[https://archive.org/details/ueberdenausgang00fechgoog/page/n699 650] }}</ref>  He also did work on the theory of tides paralleling that of Laplace and anticipating more well-known work by [[George Biddell Airy|Airy]].

===Young's equation and Young–Dupré equation===
{{further|Wetting}}
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," where he derived a formula for the wave speed of the pulse<ref>{{cite book | title = Thomas Young's research on fluid transients: 200 years on | author = Tijsseling, A.S., Anderson, A. | journal = Proc. of the 10th Int. Conf. On Pressure Surges (Editor S. Hunt), Edinburgh, United Kingdom, Pp. 21–33. | year = 2008 | publisher = BHR Group | isbn = 978-1-85598-095-2 }}</ref> 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).<ref name="EB1911" />

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 an appendix to his 1796 Göttingen dissertation {{lang|la|De corporis humani viribus conservatricibus}} there are four pages added proposing a universal phonetic alphabet (so as "not to leave these pages blank"; "{{lang|la|Ne vacuae starent hae paginae, libuit e praelectione ante disputationem habenda tabellam literarum universalem raptim describere}}"). It includes 16 "pure" vowel symbols, nasal vowels, various consonants, and examples of these, drawn primarily from French and English.

In his ''Encyclopædia Britannica'' article "Languages", Young compared the grammar and vocabulary of 400 languages.<ref name=":0">{{cite book | author=Robinson, Andrew | title=The Last Man Who Knew Everything: Thomas Young, the Anonymous Genius who Proved Newton Wrong and Deciphered the Rosetta Stone, among Other Surprising Feats | publisher=Penguin | year=2007 | isbn=978-0-13-134304-7 | url=https://archive.org/details/lastmanwhoknewev00robi }}</ref> 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]] proposed the grouping to which this term refers in 1647.

===Egyptian hieroglyphs===
{{main|Decipherment of ancient Egyptian scripts}}
Young made significant contributions to the [[decipher]]ment of [[writing in ancient Egypt|ancient Egyptian writing systems]]. He started his Egyptology work rather late, in 1813, when the work was already in progress among other researchers. He began by using an [[Demotic (Egyptian)|Egyptian demotic]] alphabet of 29 letters built up by [[Johan David Åkerblad]] in 1802 (14 turned out to be incorrect). Åkerblad was correct in stressing the importance of the demotic text in trying to read the inscriptions, but he wrongly believed that demotic was entirely alphabetic.<ref>E.A.W. Budge, [1893], [http://www.sacred-texts.com/egy/trs/trs04.htm ''The Rosetta Stone.''] www.sacred-texts.com p132</ref>

By 1814 Young had completely translated the "enchorial" text of the [[Rosetta Stone]]<ref name="EB1911" /> (using a list with 86 demotic words), and then studied the [[Egyptian hieroglyph|hieroglyphic alphabet]] but initially failed to recognise that the demotic and hieroglyphic texts were paraphrases and not simple translations.<ref>Young's first publications are as follows: "Letter to the Rev. S. Weston respecting some Egyptian Antiquities". With four copper plates [published under the name of his friend William Rouse Boughton, but written by Young], ''Archeologia Britannica''. London, 1814. Vol. XVIII. P. 59-72; [Anonymous publication], Museum Criticum of Cambridge, Pt. VI., 1815 (this includes the correspondence which took place between Young, [[Silvestre de Sacy]] and Akerblad)</ref>

There was considerable rivalry between Young and [[Jean-François Champollion]] while both were working on hieroglyphic decipherment. At first they briefly cooperated in their work, but later, from around 1815, a chill arose between them. For many years they kept details of their work away from each other. When Champollion finally published a translation of the hieroglyphs and the key to the grammatical system in 1822, Young (and many others) praised his work. Nevertheless, a year later Young published an ''Account of the Recent Discoveries in Hieroglyphic Literature and Egyptian Antiquities'',<ref name="EB1911" /> with the aim of having his own work recognised as the basis for Champollion's system.

Some of Young's conclusions appeared in the famous article "Egypt" he wrote for the 1818 edition of the ''[[Encyclopædia Britannica]]''.<ref name="EB1911" />

Young had correctly found the sound value of six hieroglyphic signs, but had not deduced the grammar of the language. Young himself acknowledged that he was somewhat at a disadvantage because Champollion's knowledge of the relevant languages, such as Coptic, was much greater.<ref>{{cite web|last1=Singh|first1=Simon|title=The Decipherment of Hieroglyphs|url=https://www.bbc.co.uk/history/ancient/egyptians/decipherment_01.shtml|publisher=BBC|access-date=8 October 2015}}</ref>

Several scholars have suggested that Young's true contribution to Egyptology was his decipherment of the demotic script. He made the first major advances in this area; he also correctly identified demotic as being composed by both ideographic and phonetic signs.{{sfn|Adkins|Adkins|2000|p=277}}

Subsequently, Young felt that Champollion was unwilling to share the credit for the decipherment. In the ensuing controversy, strongly motivated by the political tensions of that time, the British tended to champion Young, while the French mostly championed Champollion. Champollion did acknowledge some of Young's contribution, but rather sparingly. However, after 1826, when Champollion was a curator in the [[Louvre]], he did offer Young access to demotic manuscripts.<ref>{{cite web|title=Jean-François Champollion|url=http://greathistorians.com/en/jean-francois-champollion|publisher=Great Historians|access-date=8 October 2015|archive-date=20 April 2020|archive-url=https://web.archive.org/web/20200420184428/https://www.greathistorians.com/en/jean-francois-champollion|url-status=dead}}</ref>

In England, while [[Sir George Cornewall Lewis, 2nd Baronet|Sir George Lewis]] still doubted Champollion's achievement as late as 1862, others were more accepting. For example, [[Reginald Stuart Poole|Reginald Poole]], and Sir [[Peter Le Page Renouf]] both defended Champollion.{{sfn|Thomasson|2013}}

===Music===
Young developed [[Young temperament]], a method of tuning musical instruments.

==Legacy==
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".<ref>{{cite book|last1=Buick|first1=Tony|url=https://books.google.com/books?id=TKja1yLMLyQC&q=Thomas+Young+Herschel+truly+original+genius&pg=PA81|title=The Rainbow Sky: An Exploration of Colors in the Solar System and Beyond|date=2010|publisher=Springer Science & Business Media|isbn=9781441910530|page=81}}</ref> [[Albert Einstein]] praised him in the 1931 foreword to an edition of [[Isaac Newton]]'s ''[[Opticks]]''. Other admirers include physicist [[Lord Rayleigh]] and Nobel Physics laureate [[Philip W. Anderson|Philip Anderson]].

Thomas Young's name has been adopted as the name of the London-based [[Thomas Young Centre]], an alliance of academic research groups engaged in the theory and simulation of materials.

[[Young Sound]] in eastern [[Greenland]] was named in his honour by [[William Scoresby]] (1789–1857).<ref name="cat">[https://data.geus.dk/geusmap/?mapname=stednavnedb#baslay=baseMapGl&optlay=&extent=549832.8357720698,8582739.868248867,622444.3190166993,8680765.370629115&layers=grl_geus_north_east_higgins_map,grl_ne_higgins_placenames,grl_ne_placenames&filter_1=txt_search.part%3D%26placename%3D&filter_2=txt_search.part%3D%26placename%3D Place names, NE Greenland]</ref>

==Selected writings==
* [https://archive.org/details/bub_gb_fGMSAAAAIAAJ ''A Course of Lectures on Natural Philosophy and the Mechanical Arts'' (1807, republished 2002 by Thoemmes Press).]
* [https://books.google.com/books?id=Pb-JvNOjDhEC&pg=PA1 ''Miscellaneous Works of the Late Thomas Young, M.D., F.R.S.'' (1855, 3 volumes, editor John Murray, republished 2003 by Thoemmes Press).]
<gallery>
File:Young-1.jpg|Volumes I and II of ''A Course of Lectures on Natural Philosophy and the Mechanical Arts'' (1807)
File:Young-3.jpg|Title page to volume I of ''A Course of Lectures on Natural Philosophy and the Mechanical Arts'' (1807)
File:Young-6.jpg|Contents to volume I of ''A Course of Lectures on Natural Philosophy and the Mechanical Arts'' (1807)
File:Young-7.jpg|Title page to volume I of ''A Course of Lectures on Natural Philosophy and the Mechanical Arts'' (1807)
</gallery>

==See also==
*[[Coandă effect]]
*[[Color space]]
*[[History of energy]]
*[[List of Egyptologists#Y|List of Egyptologists]]
*[[Refractive index]]
*[[Ultrahydrophobicity]]

==References==
{{Reflist|30em}}

'''Works cited'''
*{{cite book | last1 = Adkins | first1 = Lesley | last2 = Adkins | first2 = Roy | title = The Keys of Egypt: The Obsession to Decipher Egyptian Hieroglyphs | publisher = Harper Collins Publishers | year = 2000 | isbn = 978-0-06-019439-0 | url = https://archive.org/details/keysofegyptobses00adki }}
*{{cite book|title=The Life of J. D. Åkerblad: Egyptian Decipherment and Orientalism in Revolutionary Times|first=Fredrik|last=Thomasson|publisher=BRILL|year=2013}}

==Further reading==
{{refbegin}}
* {{cite journal | author = Barr, E. Scott | title = Men and Milestones in Optics. II. Thomas Young | journal = Applied Optics | year = 1963 | volume = 2 | pages = 639–647 | url = http://ao.osa.org/ViewMedia.cfm?id=13115&seq=0 | doi = 10.1364/AO.2.000639 | bibcode = 1963ApOpt...2..639B | issue = 6 }}- The link is to a pdf version of the paper.
* {{cite journal | author = Robinson, Andrew | title = A Polymath's Dilemma | journal = Nature | year = 2005 | volume = 438 | pages = 291 | doi = 10.1038/438291a | issue = 7066 | pmid = 16292291 |bibcode = 2005Natur.438..291R | s2cid = 4417924 | doi-access = free }}
* {{cite journal | author = Robinson, Andrew | title = Thomas Young: The Man Who Knew Everything | journal = History Today |date=April 2006 | volume = 56 | pages = 53–57}}
* {{cite book | author = Robinson, Andrew | title = The Last Man Who Knew Everything: Thomas Young, the Anonymous Polymath Who Proved Newton Wrong, Explained How We See, Cured the Sick and Deciphered the Rosetta Stone | year = 2006 | publisher = Pi Press | location = New York | isbn = 978-0-13-134304-7 | url = https://archive.org/details/lastmanwhoknewev00robi }}
** [https://www.telegraph.co.uk/arts/main.jhtml?xml=/arts/2006/09/24/borob16.xml Reviewed]{{dead link|date=January 2025|bot=medic}}{{cbignore|bot=medic}} by Nicholas Shakespeare in [https://web.archive.org/web/20001219165200/http://www.telegraph.co.uk/ ''The Telegraph''], 24 September 2006.
** [http://www.newstatesman.com/200611130051 Reviewed] {{Webarchive|url=https://web.archive.org/web/20120322082257/http://www.newstatesman.com/200611130051 |date=22 March 2012 }} by Michael Bywater in [http://www.newstatesman.com/ ''The New Statesman''], 13 November 2006.
** [https://web.archive.org/web/20061228224508/http://www.telegraph.co.uk/arts/main.jhtml?xml=%2Farts%2F2006%2F11%2F26%2Fborob19.xml Reviewed] by Simon Singh in [https://web.archive.org/web/20001219165200/http://www.telegraph.co.uk/ ''The Telegraph''], 26 November 2006.
** [https://web.archive.org/web/20081202174000/http://www.timesonline.co.uk/article/0,,2102-2487627,00.html Reviewed] by Rosemary Hill in [https://web.archive.org/web/20001027132124/http://www.timesonline.co.uk/ ''The Times''], 10 December 2006.
** [http://books.guardian.co.uk/review/story/0,,1993741,00.html Reviewed] by PD Smith in ''[[The Guardian]]'', 20 January 2007.
* {{cite book | author = Saslow, Wayne | title = Electricity, Magnetism, and Light | year = 2002 | publisher = Thomson Learning | location = Toronton | isbn = 978-0-12-619455-5}}- Discusses Young's theoretical and experimental work on interference
* {{cite book | last1 = Wood|first1= Alex | first2= Frank |last2=Oldham | title = Thomas Young | year = 1954 | publisher = Cambridge University Press | location = Cambridge }}
*{{cite book | author = Young, Thomas | title = An Account of Some Recent Discoveries in Hieroglyphical Literature and Egyptian Antiquities | url = https://archive.org/details/anaccountsomere00youngoog | year = 1823 | publisher = John Murray | location = London }} Young's account of his hieroglyphic research. (reissued by [[Cambridge University Press]], 2010. {{ISBN|978-1-108-01716-9}})
{{refend}}

== External links ==
*{{Commons category-inline}}
*{{Wikiquote-inline}}
*{{wikisource author-inline}}
*[https://naadal.com/thomas-young/ Thomas Young, the founder of  wave theory] {{Webarchive|url=https://web.archive.org/web/20220819084250/https://naadal.com/thomas-young/ |date=19 August 2022 }}
* {{BHL author}}
* {{OL author}}
* {{Internet Archive author|sopt=t}}

{{Acoustics|state=collapsed}}
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{{DEFAULTSORT:Young, Thomas}}
[[Category:19th-century British archaeologists]]
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