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March 10, 1997

Dr. E.M. Purcell, 84, Shared Nobel for Work on Hydrogen

Dr. Edward M. Purcell, who made it possible to "listen" to the whisperings of hydrogen throughout the universe, died Friday in Cambridge, Mass. He was 84.

The cause was respiratory failure, a son said.

Purcell had been associated with Harvard University since 1936, retiring from there in 1977 as the Gerhard Gade University Professor.

In 1952, he shared the Nobel Prize in Physics for discovering a way to detect the extremely weak magnetism of the atomic nucleus. The method, measuring nuclear magnetic resonance, is widely used to study the structure of molecules and to measure magnetic fields.

The previous year, he and a graduate student, Harold I. Ewen, used an antenna on a Harvard roof for the first detection of radio emissions from clouds of hydrogen in space. As had been predicted, the emissions were at a wavelength of 21 centimeters, or 8.3 inches.

Because hydrogen is the dominant material of the universe, such observations became a prime astronomical tool. As the most prominent landmark in radio astronomy, that wavelength has also been the focus of efforts to detect signals from any civilizations on other worlds.

Purcell was a tall, thin man who retained his boyish appearance and diffidence into middle age. On scientific matters, however, he was outspoken, serving as a science adviser to Presidents Dwight D. Eisenhower, John F. Kennedy and Lyndon B. Johnson.

He was a past president of the American Physical Society and a member of the National Academy of Sciences, American Philosophical Society and American Academy of Arts and Sciences. In 1967, he won the Oersted Medal of the American Association of Physics Teachers, and in 1979, he received the National Medal of Science.

Edward Mills Purcell was born in Taylorville, Ill., on Aug. 30, 1912. His father was general manager of a regional telephone company and young Edward Purcell, after reading Bell System technical magazines, decided to become an electrical engineer.

His interest shifted to science and, after graduating from Purdue University in 1933, he spent a year as an exchange student at the Technische Hochschule in Karlsruhe, Germany. He got his master's and doctoral degrees in physics at Harvard and became a full professor in 1949.

On a leave of absence from Harvard during World War II, he worked at the Radiation Laboratory of the Massachusetts Institute of Technology, where radar was being perfected. There he also associated with I.I. Rabi and others who had made discoveries concerning the atomic nucleus.

When certain atomic nuclei, including those of hydrogen, are spinning, they generate magnetism, but so weakly that its detection had seemed hopeless. Purcell, armed with the latest information on energy states in nuclear particles and on microwave energy, surmised that with a strong magnetic field, he could bring the spinning nuclear particles of a specimen into alignment, then use microwaves to find their resonant frequency and magnetism.

For this, he shared the Nobel Prize with Dr. Felix Bloch of Stanford University, who had devised a similar method.

Dutch astronomers had predicted that in the near vacuum of space, lonely hydrogen atoms, after being moved to a slightly higher energy level by radiation or collision, would emit a radio wave with a 21-centimeter wavelength as they dropped back to the lowest energy level.

Working at night with borrowed equipment, help from a university carpenter and an investment of $400, Purcell and Ewen built a horn antenna atop Harvard's Lyman Laboratory, and the elusive radiation was detected. The same observation was then made by the Dutch scientists, who, by observing cloud motions, were able to map the otherwise invisible far side of the rotating Milky Way Galaxy.

Suggestions that others might try to communicate with Earth on that frequency led to extensive speculation about interstellar travel. Exotic propulsion schemes, like the use of antimatter as fuel, were proposed to drive vehicles across the vast distances between planetary systems. In a 1960 lecture at Brookhaven National Laboratory, where Purcell was a research collaborator, he threw cold water on such schemes.

Purcell conceded that the effects of relativity would bring time almost to a halt for high-speed space travelers. Such effects are real, he said, or the atom-smashing devices at Brookhaven would be useless.

"Some expensive machines around here would be in very deep trouble," he said. "All this stuff about traveling around the universe in spacesuits -- except for local exploration, which I have not discussed -- belongs back where it came from, on the cereal box."

In 1952, he and his colleagues described a way to send the microwaves of telephone or television over the horizon, bouncing them off irregularities in the ionosphere, the electrified upper layer of the atmosphere. That led to speculation about transoceanic signaling, but relays using orbiting satellites have proved more practical.

Purcell lived in Cambridge. In 1937, he married Beth C. Busser, who survives him, as do their sons, Dennis, of Medford, Mass., and Frank, of Arlington, Mass. A brother, Robert W., of Houston, also survives.

Of the work for which he shared a Nobel Prize, Purcell said, "We are dealing not merely with a new tool but with a new subject, a subject I have called simply nuclear magnetism." The private reward of many a discoverer, he said in accepting the prize, is suddenly "to see the world as something rich and strange."

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