Thomas Young(1773–1829)

Thomas Young was born into the Quaker community at Milverton in west Somerset on 13 June 1773, eldest of ten children of a mercer and Quaker elder. He was a prodigy: he could read fluent Latin and Greek at six, and by fourteen had working competence in fourteen languages, Hebrew, Persian, Arabic, Coptic and Samaritan among them.

The Quaker tradition pointed its sons to medicine, since the law and the Anglican Church were closed to dissenters. He read medicine in London, Edinburgh and Göttingen, took the MD at Göttingen in 1796, read for the additional English requirements at Emmanuel College, Cambridge, and was admitted to the College of Physicians in 1803.

The double-slit experiment, his foundational evidence that light propagates as a wave rather than as a stream of Newtonian particles, was first presented to the Royal Society on 24 November 1801. Light from a single source passed through two narrow slits and fell on a screen; instead of two bright lines the wave theory's interference pattern of alternating fringes appeared. The wave theory of light is now the foundational underpinning of the optical sciences, and the double-slit experiment is the standard introductory demonstration in every undergraduate physics laboratory in the world.

The Egyptian work ran in parallel. Working from 1814 to 1818 on the British Museum's casts of the Rosetta Stone, Young established the basic structure of the demotic script, identified the cartouche-name of Ptolemy in the hieroglyphic register, and worked out the first phonetic readings of individual hieroglyphic signs. Jean-François Champollion completed the full hieroglyphic decipherment in 1822; the modern Egyptological view is that the decipherment was a two-stage achievement to which both men were essential, and Young's was the first stage.

He kept the medical practice throughout, was the Royal Institution's Lecturer in Natural Philosophy, Foreign Secretary of the Royal Society, physician at St George's Hospital, Secretary of the Board of Longitude, and a contributor of twenty-three articles to the Encyclopædia Britannica. In his 1807 Course of Lectures he set out the concept now called Young's modulus, the ratio of stress to strain that is the foundation of materials science. He died at his London house on 10 May 1829, fifty-five years old. The Young name, the patronymic byname of the younger, he carried from a west-Somerset Quaker household into the foundation of the wave theory of light, the first stage of Egyptian decipherment, and the working principle of elastic strain on which modern engineering rests.