The American experimental physicist Percy Williams Bridgman (1882-1961) was a pioneer in investigating the effects of enormous pressures on the behavior of matter--solid, liquid, and gas.

Percy Bridgman was born in Cambridge, Mass., on April 21, 1882, the son of Raymond Landon and Mary Ann Maria Williams Bridgman. At high school in Newton, Mass., he was led into the field of science by the influence of one of his teachers.

Bridgman received his doctorate from Harvard University in 1908 and remained there as a research fellow in physics. He married Olive Ware in 1912, with whom he had a daughter and a son. By 1919 he rose to a full professorship, and 7 years later the university appointed him Hollis professor of mathematics and natural philosophy.

In 1946 Bridgman received the Nobel Prize in physics. He was a fellow of the American Academy of Arts and Sciences and at one time served as president of the American Physical Society. He continued to work at Harvard several years after his official retirement, until he died on Aug. 20, 1961.

Bridgman's major work dealt with the building of apparatus for the investigation of the effects of high pressures, apparatus that would not burst under pressures never reached before. Quite by accident he discovered that a packed plug automatically became tighter as more pressure was applied. This proved a key to his further experimentation. Using the steel alloy Carboloy and new methods of construction and immersing the vessel itself in a fluid maintained at a pressure of approximately 450,000 pounds per square inch (psi), which Bridgman later increased to more than 1,500,000 psi, he reached, inside the vessel, 6,000,000 psi by 1950. To measure such hitherto unattainable pressures, Bridgman invented new measuring methods.

The most striking effect of these enormous pressures was the change in the melting point of many substances. Bridgman also found different crystalline forms of matter which are stable under very high pressure but unstable under low pressure. Ordinary ice, for example, becomes unstable at pressures above about 29,000 psi and is replaced by stable forms. One of these forms is stable under a pressure of 290,000 psi at a temperature as high as 180°F. This "hot ice" is more dense than ordinary ice and sinks completely in water.

In 1955 the General Electric Company announced the production of synthetic diamonds, which their scientists, working on methods and information derived from Bridgman's work, had produced from ordinary carbon subjected to extremely high pressures and temperatures.

Further Reading

• Reflections of a Physicist (1950; 2d ed. 1955) is a collection of Bridgman's nontechnical writings on science. A detailed biography of Bridgman is in National Academy of Sciences, Biographical Memoirs, vol. 41 (1970). Niels H. de V. Heathcote, Nobel Prize Winners in Physics: 1901-1950 (1954), contains a chapter on Bridgman. He is included in Royal Society, Biographical Memoirs of Fellows of the Royal Society, vol. 8 (1962), and in National Academy of Sciences, Biographical Memoirs, vol. 12 (1970).
• Walter, Maila L., Science and cultural crisis: an intellectual biography of Percy Williams Bridgman (1882-1961), Stanford, Calif.: Stanford University Press, 1990.