In 1801, Young was appointed professor ofnatural philosophy (mainlyphysics) at theRoyal Institution.[10] In two years, he delivered 91 lectures. In 1802, he was appointed foreign secretary of theRoyal Society,[11] of which he had been elected a fellow in 1794.[12] He resigned his professorship in 1803, fearing that its duties would interfere with his medical practice. His lectures were published in 1807 in theCourse of Lectures on Natural Philosophy and contain a number of anticipations of later theories.[5][13]
In 1811, Young became physician toSt George's Hospital, and in 1814 he served on a committee appointed to consider the dangers involved in the general introduction ofgas for lighting into London.[14] In 1816 he was secretary of a commission charged with ascertaining the precise length of theseconds pendulum (the length of a pendulum whose period is exactly 2 seconds), and in 1818 he became secretary to theBoard of Longitude and superintendent of theHM Nautical Almanac Office.[5][15]
In 1804, Young married Eliza Maxwell. They had no children.[20]
Young died in his 56th year in London on 10 May 1829, having suffered recurrent attacks of "asthma". His autopsy revealedatherosclerosis of the aorta.[21] His body was buried in the graveyard of St Giles’ Church atFarnborough, in the county ofKent.Westminster Abbey houses a white marble tablet in memory of Young,[22] bearing an epitaph byHudson Gurney:[23][24]
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. —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."[25]
Though he sometimes dealt with religious topics of history in Egypt and wrote about the history of Christianity inNubia, not much is known about Young's personal religious views.[26] OnGeorge Peacock's account, Young never spoke to him about morals, metaphysics or religion, though according to Young's wife, his attitudes showed that "hisQuaker upbringing had strongly influenced his religious practices."[27] Authoritative sources have described Young in terms of a cultural Christian Quaker.[28][29]
Hudson Gurney informed that before his marriage, Young had to join theChurch of England, and was baptized later.[30] 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.[31] Yet, the day before his death, Young participated in religious sacraments; as reported inDavid Brewster'sEdinburgh 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 studiedthe 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."[32]
In Young's own judgment, of his many achievements the most important was to establish thewave theory of light set out by Christiaan Huygens in hisTreatise on Light (1690).[33][34] To do so, he had to overcome the century-old view, expressed in the venerable Newton'sOpticks, 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 theripple tank he demonstrated the idea ofinterference in the context of water waves. Withadditional experiments, including the predecessor of thedouble-slit experiment, he demonstrated interference in the context of light as a wave.
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:[35]
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.[36]
In his subsequent paper, titledExperiments and Calculations Relative to Physical Optics (1804), Young describes an experiment in which he placed a card measuring approximately 0.85 millimetres (0.033 in) in abeam 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.[37] This supported the contention that light is composed ofwaves.[38]
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 fromNewton's rings. He also performed two important diffraction experiments using fibres and long narrow strips. In hisCourse of Lectures on Natural Philosophy and the Mechanical Arts (1807) he givesGrimaldi 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 byAugustin-Jean Fresnel.
Young'sMathematical Elements of Natural Philosophy
Young described the characterization of elasticity that came to be known as Young's modulus, denoted asE, in 1807, and further described it in hisCourse of Lectures on Natural Philosophy and the Mechanical Arts.[39]However, the first use of the concept of Young's modulus in experiments was byGiordano Riccati in 1782—predating Young by 25 years.[40]Furthermore, the idea can be traced to a paper byLeonhard Euler published in 1727, some 80 years before Thomas Young's 1807 paper.
Young's modulus relates thestress (compression or decompression) in a body to its associatedstrain (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 anintensive property of the material. 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."[41]
Young has also been called the founder of physiological optics. In 1793 he explained the mode in which the eyeaccommodates itself to vision at different distances as depending on change of the curvature of thecrystalline lens; in 1801 he was the first to describeastigmatism;[42] and in his lectures he presented the hypothesis, afterwards developed byHermann von Helmholtz, (theYoung–Helmholtz theory), that colour perception depends on the presence in the retina of three kinds of nerve fibres.[5][43] This foreshadowed the modern understanding ofcolour vision, in particular the finding that the eye does indeed have three colour receptors which are sensitive to different wavelength ranges.
In 1804, Young developed the theory of capillary phenomena on the principle ofsurface tension.[44] 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 theYoung–Laplace equation, the formula that describes thecapillary pressure difference sustained across the interface between two static fluids.
Young was the first to define the term "energy" in the modern sense.[45] He also did work on the theory of tides paralleling that of Laplace and anticipating more well-known work byAiry.
Young's equation describes thecontact 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.
In physiology Young made an important contribution tohaemodynamics 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.[46] His medical writings includedAn Introduction to Medical Literature, including aSystem of Practical Nosology (1813) andA Practical and Historical Treatise on Consumptive Diseases (1815).[5]
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.
In an appendix to his 1796 Göttingen dissertationDe corporis humani viribus conservatricibus there are four pages added proposing a universal phonetic alphabet (so as "not to leave these pages blank"; "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 hisEncyclopædia Britannica article "Languages", Young compared the grammar and vocabulary of 400 languages.[1] In a separate work in 1813, he introduced the termIndo-European languages, 165 years after the Dutch linguist and scholarMarcus Zuerius van Boxhorn proposed the grouping to which this term refers in 1647.
Young made significant contributions to thedecipherment ofancient 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 anEgyptian demotic alphabet of 29 letters built up byJohan 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.[47]
By 1814 Young had completely translated the "enchorial" text of theRosetta Stone[5] (using a list with 86 demotic words), and then studied thehieroglyphic alphabet but initially failed to recognise that the demotic and hieroglyphic texts were paraphrases and not simple translations.[48]
There was considerable rivalry between Young andJean-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 anAccount of the Recent Discoveries in Hieroglyphic Literature and Egyptian Antiquities,[5] 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 theEncyclopædia Britannica.[5]
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.[49]
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.[50]
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 theLouvre, he did offer Young access to demotic manuscripts.[51]
Later scholars and scientists have praised Young's work although they may know him only through achievements he made in their fields. His contemporary SirJohn Herschel called him a "truly original genius".[53]Albert Einstein praised him in the 1931 foreword to an edition ofIsaac Newton'sOpticks. Other admirers include physicistLord Rayleigh and Nobel Physics laureatePhilip Anderson.
Thomas Young's name has been adopted as the name of the London-basedThomas Young Centre, an alliance of academic research groups engaged in the theory and simulation of materials.
^"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.
^Wood, Alexander. 2011.Thomas Young: Natural Philosopher 1773–1829. Cambridge University Press. p. 56
^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."
^Wood, Alexander. 2011.Thomas Young: Natural Philosopher 1773–1829. Cambridge University Press. p. XVI
^Truesdell, Clifford A. (1960).The Rational Mechanics of Flexible or Elastic Bodies, 1638–1788: Introduction to Leonhardi Euleri Opera Omnia, vol. X and XI, Seriei Secundae. Orell Fussli.
^"Structures, or Why Things Don't Fall Down" by J. E. Gordon, Penguin Books, 1978.
^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)
Saslow, Wayne (2002).Electricity, Magnetism, and Light. Toronton: Thomson Learning.ISBN978-0-12-619455-5.- Discusses Young's theoretical and experimental work on interference
Wood, Alex; Oldham, Frank (1954).Thomas Young. Cambridge: Cambridge University Press.
