Thomas Young(1773–1829)

Thomas Young was born at the Quaker meeting-house community at Milverton in west Somerset on 13 June 1773, eldest of ten children of Thomas Young, a Milverton mercer and senior Quaker elder of the community, and Sarah Davis. The household was the standard rural-Quaker professional one: plain dress, plain speech, no music, no theatre, and a working assumption that the boys of the family would be put to working professions and not (as the post-Reformation Church of England would have preferred) to university and the clergy. The boy was kept at home with a private tutor through his earliest schooling because his reading-age was, on the assessment of his grandfather Robert Davis, more advanced than the local Milverton dame school could carry. By the standard family-biography sources he could read English at two, had read the Bible cover to cover at four, could read fluent Latin and Greek at six, and by fourteen had working competence in fourteen languages, English among them. The list ran to Hebrew, Aramaic, Persian, Arabic, Turkish, Amharic, Italian, French, Spanish, German, modern Greek, Coptic, and Samaritan.

The Quaker community pushed him into medicine in 1792. The standard professional gates for the Quaker tradition of the period were medicine (since neither the law nor the Anglican Church admitted dissenters) and the list of dissenting-Academy trades like printing and banking. He was nineteen and was sent to London to read medicine under the London-Quaker physician Sir Richard Brocklesby, who was his maternal great-uncle; he attended lectures at the Hunterian School at the Great Windmill Street anatomy theatre in 1792-93, moved on to Edinburgh in 1794 to take the medical-degree course there, and continued to Göttingen in 1795 to take the MD examinations under the German university system that was, in the 1790s, the establishment of European medical research. He took the MD at Göttingen in 1796, returned to Cambridge in 1797 to read at Emmanuel College for the additional working English MD requirements, and was admitted to the College of Physicians in 1803 at the age of thirty.

The double-slit experiment, the foundational evidence that light propagates as a wave (rather than as a stream of particles in the Newtonian corpuscular model the previous century had settled the question on), was first presented to the Royal Society on 24 November 1801. He had a lecture-theatre apparatus: a candle behind a aperture-screen, then a second screen with two narrow slits a fraction of an inch apart, and a viewing-screen behind on which the projected light fell. The corpuscular Newtonian theory predicted two bright lines on the viewing-screen, one behind each of the two slits. The wave theory, set out by Christiaan Huygens in the seventeenth century and never since experimentally demonstrated, predicted an interference pattern of alternating bright and dark fringes on the screen. The fringes appeared. The experiment was the foundational demonstration of the wave nature of light, was attacked by the Newtonian-corpuscular establishment of the period (his 1804 *On the Theory of Light and Colours* was savaged in the *Edinburgh Review* by the Newtonian Henry Brougham), and was vindicated when Augustin Fresnel's working mathematical wave theory came out in France in 1819. The wave theory of light is now the foundational underpinning of the optical sciences from quantum mechanics back through nineteenth-century classical optics; the double-slit experiment is the standard introductory demonstration in every undergraduate physics laboratory in the world.

The Egyptian work came at the same period. The Rosetta Stone, discovered by Captain Pierre-François Bouchard at Rosetta in the Nile Delta in July 1799 and taken by the British on the surrender of the French army of Egypt in 1801, was lodged in the British Museum in 1802. The stone carried a single text in three scripts: classical Greek (immediately legible), Egyptian demotic (the everyday-Egyptian script of the late-pharaonic and Ptolemaic period), and Egyptian hieroglyphic (the ceremonial script of the older period). Young, working from 1814 to 1818 on the British Museum's casts of the inscription, established the basic phonetic-and-determinative structure of the demotic script, identified the cartouche-name of Ptolemy in the hieroglyphic register, and worked out the first eighty or so working phonetic-and-determinative readings of individual hieroglyphic signs. The Frenchman Jean-François Champollion, working in parallel and with access to additional Egyptian inscriptions that Young did not have, completed the decipherment of the full hieroglyphic system in 1822. The relationship between Young's foundational working analysis and Champollion's completion has been a controversy of Egyptology for two hundred years; the modern professional-Egyptological view is that the decipherment was a two-stage achievement to which both men were essential.

He continued the medical practice through the whole period, was the Lecturer in Natural Philosophy at the Royal Institution in 1801-03, the Foreign Secretary of the Royal Society from 1804, the physician at St George's Hospital in Hyde Park Corner from 1811, the Secretary of the Board of Longitude from 1818, and a working contributor to twenty-three articles of the *Encyclopædia Britannica* on subjects from Hieroglyphics to Tides. He developed in his 1807 *Course of Lectures on Natural Philosophy* the concept of *Young's modulus*, the ratio of stress to strain in elastic deformation that is now the foundation of materials science. He married Eliza Maxwell, daughter of an Indian-civil-service judge, in 1804; the marriage was childless. He died at his London house at 28 Park Square on 10 May 1829, aged fifty-five, of complications from chronic respiratory illness. The Young name in the Scottish catalogue is the patronymic byname *young* (the younger or junior, marking the second of two same-named family members in the parish-register tradition); he carried the Quaker-Milverton variant of it from a west-Somerset mercer's household into the foundation of the wave theory of light, the first stage of Egyptian hieroglyphic decipherment, and the working principle of elastic strain on which modern engineering rests.