Paul Christoph Mangelsdorf Jr., 90, formerly of Swarthmore, a retired physics professor, died Friday, March 6, of dementia at White Horse Village in Newtown Square.

He was the Morris L. Clothier Professor Emeritus of Physics at Swarthmore College, where he taught for 29 years.

"The college has lost not just a devoted teacher and generous mentor to countless students but also one of its most active and dedicated members," wrote Constance Hungerford, interim president, in an e-mail sent to Swarthmore College faculty and staff.

He also was a former researcher at the Woods Hole Oceanographic Institution in Woods Hole, Mass. He worked there during many summers, vacations, and sabbaticals.

Before moving to White Horse Village in 2004, Dr. Mangelsdorf was a longtime resident of both Swarthmore and West Falmouth, Mass. At Woods Hole, he did research about the chemical composition of the oceans; his research took him as far away as the Indian Ocean and to South America's Amazon River.

Born in New Haven, Conn., he was the son of Helen Parker and Paul C. Mangelsdorf, a world-renowned botanist who traced the origins of modern corn to the primitive maize grown by American Indians, according to his New York Times obituary.

The younger Dr. Mangelsdorf was raised in College Station, Texas, where his father was a professor at Texas A&M University.

When the son was in high school, the family moved to Newton, Mass. He earned a bachelor's degree in mathematics with high honors from Swarthmore College in 1949 and a doctorate in chemical physics from Harvard University in 1954.

Dr. Mangelsdorf enlisted in the Army in 1943 and served as an encryption analyst stationed in England. Later, he was sent to Germany to participate in the U.S. Strategic Bombing Survey, which assessed the results of Allied bombing in World War II.

After the war, he returned to his studies at Swarthmore. He met and married Mary Burnside in 1949.

Raised in a secular household, Dr. Mangelsdorf became interested in Quakerism as a young man; it was a religious experience that he could share with his wife and that did not conflict with his study of science.

The two became members of the Religious Society of Friends in the 1950s.

In the 1960s, they helped reopened a then-dormant Quaker meeting in West Falmouth, where Dr. Mangelsdorf remained a member for the rest of his life.

He also was active in the New England regional Quaker body - the New England Yearly Meeting - and attended Swarthmore Friends Meeting for decades.

Besides his wife, he is survived by daughters Helen, Sarah, and Martha; son Paul Mangelsdorf III; five grandchildren; and nieces and nephews.

A memorial service in the Quaker way will be held at 3 p.m. Saturday, April 18, at Swarthmore Friends Meeting, 12 Whittier Place, Swarthmore. Burial is private.

Donations may be made to the New England Yearly Meeting of the Religious Society of Friends, 901 Pleasant St., Worcester, Mass. 01602, or via