On a summer night in 1945, Harvard-trained chemist Donald F. Hornig went into the New Mexico desert to climb a 100-foot steel tower to a metal shack, where he quietly baby-sat the world’s first atomic bomb.
At 25, he was one of the youngest members of the Manhattan Project and had helped devise the complex trigger for the bomb. While guarding against sabotage in the final hours before the dawn of the nuclear age, he read a book of humorous essays by writers such as Dorothy Parker as a thunderstorm pelted the shack with rain and wind.
“It was a deeply philosophical experience,” he deadpanned in 2005 during a gathering of Manhattan Project scientists, drawing laughter from the audience.
Dr. Hornig, who later served as science adviser to President Lyndon B. Johnson and president of Brown University, died Jan. 21 in Providence. He was 92 and had been diagnosed with Alzheimer’s disease.
During that solitary night in 1945, a phone call finally granted him permission to descend and head for the bunker. The bomb was detonated just before 5:30 a.m. on July 16, 1945.
“We’ve really opened a can of worms, haven’t we?” an exhausted Dr. Hornig recalled thinking to himself as the sky filled with fire.
In a 1968 interview archived at the LBJ Presidential Library in Texas, Dr. Hornig described the moments after the bomb exploded. He was in the bunker manning the “chicken switch” that would abort the test if necessary.
“The minute the firing needle dropped off and I knew it had detonated, I dashed out the door in time to see the fireball rising into the sky,” he said. “I was awestruck, just literally awestruck. This thing was more fantastic than anything I had ever imagined.”
The oldest of four children born to Midwestern parents who never finished high school, Dr. Hornig grew up in Milwaukee. A public school teacher recognized his intelligence and arranged for him to receive a scholarship to a prep school. He went to Harvard College as part of the class of 1940.
In later years, he often thought of that teacher back in Milwaukee.
“He very much regretted not keeping track of her,” said his wife, Lilli. “He said, ‘She made my life.’ ”
Dr. Hornig met Lilli Schwenk at Harvard on her first day of graduate school. He was “very energetic, friendly, and interesting,” she said. The two scientists were married for 69 years.
After graduating from Harvard with a doctorate in 1943, Dr. Hornig was working on deep water explosives at the Woods Hole Oceanographic Institution when he was invited to join the Manhattan Project. He initially declined because he didn’t want to uproot his wife from the house they had just settled into.
Two calls changed his mind. James Conant, then the president of Harvard, appealed to Dr. Hornig’s patriotism. And George Kistiakowsky, who had also been enlisted for the Manhattan Project and was one of Dr. Hornig’s Harvard mentors, questioned his sanity for considering saying no.
In 2005, Dr. Hornig recalled that Kistiakowsky thundered on the phone: “What the hell has gotten into you, Hornig?”
The Hornigs sold their boat, packed up their home, and drove west in an old Ford coupe to Los Alamos, N.M., where Lilli, who had a doctorate in chemistry, also worked on the project.
Three weeks after Dr. Hornig climbed the tower that night in 1945, the United States dropped atomic bombs in Japan, first on Hiroshima, and then Nagasaki.
For his 2006 book “Shockwave: Countdown to Hiroshima,” British filmmaker Stephen Walker interviewed Dr. Hornig when he was in his 80s.
“Something of the young Donald — excited and passionate about his work — crept into his voice and his demeanour as he relayed tales of his Los Alamos years,” Walker wrote in an e-mail.
“I had the distinct impression that these were possibly the most intellectually (and socially) satisfying years of his life,” Walker wrote. “To be at the heart of one of the greatest scientific endeavours in history — the very cutting-edge of a new technology — surrounded by some of the greatest minds in nuclear science, was an experience like no other. Of course he understood that the end was to make a bomb — and Donald did not shy from the implications of that — but it was also an attempt to push back the frontiers of knowledge and journey into the unknown, and he felt privileged to be a part of that.”
After World War II, Dr. Hornig taught at Brown and became a full professor at age 31. He left in 1957 to teach at Princeton University, where he was chairman of the chemistry department and served on President Dwight Eisenhower’s scientific advisory committee.
President John F. Kennedy named Dr. Hornig to be his science and technology adviser on Nov. 7, 1963, 15 days before he was assassinated.
Faced with critics of massive government spending on the space race, Dr. Hornig pledged savings through judicious project choices. “The days of pie-in-the-sky research are over,” he told the Globe in 1963. “Miracles of the kind performed during the war are a little harder to find. Scientists are no longer concentrated nor are their efforts. They do come, of course, but over periods of years.”
After Kennedy was assassinated, Lyndon Johnson kept him in the post. Their relationship was cool, but Dr. Hornig served for almost five years.
“I was never on easy personal terms,” Dr. Hornig told Science Magazine in 1969. “He invited me down to the ranch a couple of times, but we were never on a chatty basis. There’s always been a certain gap in attitude between a Texas rancher and an Ivy League professor.”
Dr. Hornig was president of Brown from 1970 to 1976, taking over as the university was deep in debt and roiling with social unrest. He cut spending by 15 percent, imposing a three-year austerity plan, and when he stepped down the school’s debt had been whittled from more than $4 million to $636,000.
“As Brown’s president, he was able to make difficult fiscal decisions that put the university back on a firm footing,” Christina H. Paxson, Brown’s current president, said in a prepared statement. “Much of Brown University’s success over the last three decades had its roots in these decisions, for which we remain grateful.”
In addition to his wife, Dr. Hornig leaves two daughters, Joanna Hornig Fox of Washington, D.C., and Ellen of Shrewsbury; a son, Christopher, of Washington; a brother, Arthur, of Lexington; a sister, Arline Westhall of Medina, Ohio; nine grandchildren; and 10 great-grandchildren.
A memorial service will be held at 2 p.m. March 23 in Manning Chapel at Brown University. Burial will be private.
After leaving Brown, Dr. Hornig joined the Harvard School of Public Health and was founding director of its interdisciplinary programs in health.
“Don valued using the combined brain power of many disciplines in addressing emergent public health problems,” Douglas Dockery, who chairs the school’s environmental health department, said in a statement. “He instilled that approach in us through his wisdom, wit, and warmth.”
Dr. Hornig also worked on local issues in Cambridge. He served as president of the Water Board and spearheaded regulations requiring dog owners to leash their pets at Fresh Pond.
“He was a very powerful personality,” his son said. “He was very engaged in life. He was enormously inquisitive and he was entirely self-made.”