Edward M. Purcell, Gerhard Gade University Professor Emeritus and co-winner of the 1952 Nobel Prize in Physics, died March 7 in Cambridge. He was 84.

He shared the Nobel Prize for discovering a way to detect the extremely weak magnetism of atomic nuclei. The method, measuring nuclear magnetic resonance, is widely used to study the structure of molecules and in medical imaging (MRI).

Born in Taylorville, Ill., on Aug. 30, 1912, Purcell graduated from Purdue University in 1933 and spent a year an as exchange student at the Technische Hochschule in Karlsruhe, Germany. He received 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 M.I.T.'s Radiation Laboratory, where radar was being perfected. He headed a group that developed advanced microwave radar.

When certain atomic nuclei, including those of hydrogen, are spinning, they produce magnetism, but so weakly that its detection is very difficult. 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 work, he shared the Nobel Prize in Physics with Felix Bloch of Stanford University, who had developed a similar method.

Purcell served as a science adviser to Presidents Dwight D. Eisenhower, John F. Kennedy, and Lyndon B. Johnson.

In 1985, Purcell was smong those scientists who took a stand against the development of "Star Wars," a space-based defense system, saying it wouldn't work and would only escalate the arms race.

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

Purcell leaves his wife, Beth Busser; his sons, Dennis of Medford and Frank of Arlington; and a brother, Robert of Houston, Texas.

Donations may be made in Purcell's memory to the Christ Church, 0 Garden St., Cambridge, MA 02138.

A memorial service is being planned for a later date.