The English physicist Thomas Young (1773-1829) is best known for his double-slit interference experiment which validated the wave theory of light and for the elastic modulus named for him.

Concerning Thomas Young, the noted physicist Sir Humphry Davy wrote: "He was a most amiable and good tempered man ... of universal erudition, and almost universal accomplishments. Had he limited himself to any one department of knowledge, he must have been the first in that department. But as a mathematician, a scholar, a hieroglyphist, he was eminent, and he knew so much it was difficult to say what he did not know."

Young was born in Milverton near Taunton on June 16, 1773, of Quaker parentage. A child prodigy, he had read through the Bible twice by the age of four and was reading and writing Latin at six. By the time he was 14 he had a knowledge of at least five languages, and eventually his repertoire grew to 12.

Young chose medicine as a career and trained at the universities of London, Edinburgh, Göttingen, and finally Cambridge (1797-1799). In 1808 he began practice in London, but because of his blunt truthfulness and his distrust of the practices of purging and bleeding then common he was not popular with his patients. In 1811 he joined the staff of St. George's Hospital. He died in his London home on May 10, 1829.

In 1793 Young explained the process of accommodation in the human eye. In 1801 he presented a paper on the nature of visual astigmatism and gave the constants of the eye; this paper is considered by ophthalmologists to be his most brilliant contribution. The following year he gave his theory of color vision, a notable advance in physiological optics.

In a lecture on the proper construction of arches Young casually pointed out that within wide limits the ratio of stress to strain was for most materials a constant. This characteristic constant for stretching is called Young's modulus of the substance. Turning to a completely different field, he "penetrated the obscurity that had veiled for ages the hieroglyphics of Egypt" through his deciphering of the Rosetta Stone.

Young's famous two-volume Lectures on Natural Philosophy (1807) contained the 60 lectures he gave at the Royal Institution while he was professor of natural philosophy there (1801-1803). The first volume contains the lectures and almost 600 drawings; the second volume includes several of his papers and about 20,000 references to the literature, many annotated.

Further Reading

• A particularly good book on Young is by Frank Oldham, Thomas Young: F.R.S. Philosopher and Physician (1933). See also Alexander Wood, Thomas Young: Natural Philosopher, 1773-1829 (1954). A good, brief discussion of him is in James Gerald Crowther, Scientific Types (1970).
• Kline, Daniel Louis, Thomas Young, forgotten genius: an annotated narrative biography, Cincinnati, Ohio: Vidan Press, 1993.